JP2005300864A - Image forming apparatus and image forming method - Google Patents

Abstract

[PROBLEMS] To suppress the occurrence of defective fixing and hot offset caused by a change in the required amount of fixing heat at every printout or by changing a transfer speed in accordance with the resolution of an image. (2) Avoiding an increase in cost by setting the heat resistance of the fixing device 56 on the assumption that the required fixing heat amount becomes considerably large. (3) The disturbance due to the rubbing of the unfixed image on the transfer paper P is suppressed.
A conveyor belt unit 60 is provided between a double-sided transfer device and a fixing device 56. Further, a speed changing means for changing the paper transport speed by the fixing device 56 and the paper transport speed by the transport belt 61 is provided. In addition, a charge imparting charger 63 that imparts charges to the surface of the transport belt 61 before receiving the transfer paper P is provided. Further, the length L1 of the post-fixing conveyance path from the transfer separation position P1 to the fixing receiving position P2 is subtracted from the vertical dimension of the A3-size paper by the dimension in the recording medium conveyance direction of the trailing edge side margin area. It was bigger than the value.
[Selection] Figure 2

Description

  The present invention relates to an image forming apparatus and an image forming method for forming images on both surfaces of a recording medium such as transfer paper by a so-called one-pass method.

  Conventionally, a so-called switchback method and a one-pass method are known as methods for forming images on both sides of a recording medium. In the switchback method, after a recording body having an image formed on one side thereof after passing through the transfer unit and the fixing unit is reversed, the recording unit is switched back to the transfer unit and the fixing unit, and then on the other side. Is a method of forming an image. On the other hand, in the one-pass method, an image is formed on both sides of the recording body without switching back the recording body by passing the recording body on which the visible image is transferred on both sides by the double-side transfer means, through the fixing means. The one-pass method is superior to the switchback method in the following points. That is, it is possible to avoid the cost increase by providing a complicated mechanism for switchback, the prolonged image formation time by switchback, and jamming by switching back the recording medium curled by heating by the fixing means. Is a point. As an image forming apparatus for forming a color image on both sides of a recording medium by such a one-pass method, those described in Patent Document 1, Patent Document 2, Patent Document 3, and the like are known.

  On the other hand, an image forming apparatus that changes the transfer speed in accordance with the resolution of an image is also known. In the low image quality mode for forming an image with a relatively low resolution, the image forming speed can be increased by increasing the transfer speed as compared with the high image quality mode for forming an image with a relatively high resolution. .

JP 2003-271026 A JP-A-11-38687 JP 2000-352889 A

  In the one-pass type image forming apparatus, the required amount of fixing heat per unit time is likely to change for each printout as compared with a single-sided type that forms an image on only one side of a recording medium or a switchback type. The necessary fixing heat amount is a heating amount per unit time necessary for fixing an unfixed visible image on a recording medium. In the single-side method or the switchback method, the recording body enters the fixing device in a state where an unfixed visible image is held on only one side. On the other hand, in the one-pass method, the recording medium enters the fixing device while holding an unfixed visible image on only one side, or enters the fixing device while holding an unfixed visible image on each side. Or enter. The amount of unfixed developer held differs greatly between a recording medium that holds an unfixed visible image on only one side and a recording body that holds the unfixed visible image on both sides. For this reason, in the one-pass method, the required amount of fixing heat easily changes every printout.

  In particular, in a one-pass color image forming apparatus that forms a multicolor image on both sides of a recording medium by superimposing a plurality of single-color images, in addition to the difference between single-sided and double-sided, the difference in the number of single-color image overlays However, the amount of heat required for fixing changes. For example, the amount of unfixed developer held on the recording body differs greatly between the case of forming a single color image and the case of forming a multicolor image by superimposing a plurality of single color images. For this reason, the required amount of fixing heat for each printout is more likely to change.

  In the one-pass type image forming apparatus, the necessary fixing heat amount for each printout is likely to change as described above. Therefore, hot offset and fixing failure are likely to occur compared to the single-sided type or the switchback type. This hot offset is a phenomenon in which the toner image is transferred to a heating member that presses the recording medium while heating it in the fixing device, causing white spots in the image on the recording medium. It occurs when heated. In addition, the fixing failure is caused by an insufficient heating amount for the recording medium.

  For the purpose of suppressing such hot offset and fixing failure, the present inventors have changed the temperature of the heating member of the fixing device according to the difference between the single-sided mode and the double-sided mode, the difference in the number of overlays, etc. A forming device was prototyped. However, in this way, the fixing device of the fixing device can be heated sufficiently within a limited fixing time even for a recording body in which the required amount of fixing heat is considerably large, such as a recording body in which a solid color image is formed on both sides. It is necessary to increase the heating capacity considerably. For this reason, as the heating member of the fixing device and the peripheral member thereof, a member that exhibits considerable heat resistance must be used, resulting in an increase in cost.

  On the other hand, in an image forming apparatus that changes the transfer speed in accordance with the resolution of the image, the fixing speed is set to the same speed as the transfer speed regardless of the amount of heat required for fixing. For this reason, the amount of heat per unit time (hereinafter referred to as fixing heat amount) given to the recording medium for fixing is increased in the low image quality mode in which the transfer speed is relatively fast and the high image quality mode in which the transfer speed is relatively slow. It will be different. Then, it becomes easy to cause a fixing failure in the low image quality mode, or to cause hot offset in the high image quality mode.

  Therefore, the present inventors provide a conveyance belt between the double-sided transfer means and the fixing device, and change the recording medium conveyance speed by the fixing device or the conveyance belt according to the required amount of fixing heat regardless of the transfer speed. A new image forming apparatus is under development. In this image forming apparatus, the distance between the double-side transfer unit and the fixing unit is sufficiently large so that the recording medium discharged from the double-side transfer unit can be conveyed toward the fixing device while being supported only by the conveyance belt. Accordingly, it is possible to arbitrarily change the conveyance speed regardless of the conveyance speed (transfer speed) of the recording medium by the double-side transfer unit while conveying the single recording medium toward the fixing device by the conveyance belt alone. Yes. And the conveyance speed by a fixing device is also changed according to the conveyance speed change of a conveyance belt. Then, the amount of fixing heat per unit time for the recording medium can be changed without changing the temperature of the heating member of the fixing device. For this reason, even when the required fixing heat amount becomes considerably large, the fixing process is performed with a sufficient heating amount without significantly increasing the heating temperature by the fixing device. Even when the required fixing heat amount is considerably small, the fixing process is performed with an appropriate heating amount without excessively heating the recording medium. Therefore, assuming that the required fixing heat amount is considerably increased, avoiding the increase in cost by setting the heat resistance of the fixing means, and fixing defects and hot offsets due to the change in the required fixing heat amount for each printout. Occurrence can be suppressed. In addition, since it is possible to provide a speed difference between the transfer speed and the fixing speed, it is possible to suppress the occurrence of fixing failure and hot offset caused by changing the transfer speed according to the resolution of the image.

  However, in this image forming apparatus, the unfixed image on the recording medium may be slightly rubbed against the belt surface and disturbed by the slight vibration of the conveying belt.

The present invention has been made in view of the above background, and an object of the present invention is to provide an image forming apparatus and an image forming method capable of realizing any of the items (1) to (3) listed below. Is to provide.
(1) Suppressing the occurrence of fixing failure and hot offset caused by the required amount of fixing heat changing at every printout or changing the transfer speed according to the image resolution.
(2) Avoiding an increase in cost by setting the heat resistance of the fixing means assuming that the required amount of fixing heat becomes considerably large.
(3) Suppressing disturbance due to rubbing of the unfixed image on the recording medium.

In order to achieve the above object, the invention of claim 1 is a latent image developing unit having a latent image bearing member for carrying a latent image, and developing means for developing the latent image carried on the surface of the latent image to a visible image. And latent image forming means for forming a latent image on the surface of the latent image carrier based on the image information, and transferring the first visible image developed on the latent image carrier to the first surface of the recording medium. On the other hand, while transferring the second visible image developed on the latent image carrier to the second surface of the recording medium and the recording medium after passing through the double-side transfer means An image forming apparatus comprising: a fixing unit that fixes the first visible image and the second visible image on the recording body; and a recording body storage unit that stores a recording body to be supplied to the double-sided transfer unit. A conveyance base that allows the recording medium discharged from the transfer means to be moved endlessly while being stretched by a plurality of stretching members. A conveying belt unit that is held on the surface of the toner cartridge and conveyed toward the fixing unit, a recording medium conveying speed by the fixing unit, a speed changing unit that changes a recording medium conveying speed by the conveying belt, and the recording medium accommodating unit. Latent image formation prohibiting means for prohibiting latent image formation by the latent image forming means on the latent image carrier area corresponding to the rear end side margin area of the maximum size recording medium that can be accommodated in the recording medium; Charge applying means for applying a charge to the surface of the conveying belt before receiving from the means, and the recording medium is transferred from the transfer separation position in the double-side transfer means when the recording medium is transferred to the conveying belt. The length of the post-transfer pre-fixing conveyance path, which is the recording medium conveyance path from the fixing device to the fixing reception position at the time of reception, is the dimension in the conveyance direction of the maximum size recording medium. Luo is characterized in that it has greater than a value obtained by subtracting the size of the recording material conveyance direction of the rear side margin area.
According to a second aspect of the present invention, there is provided a latent image carrying unit carrying a latent image, a latent image developing unit having developing means for developing the latent image carried on the surface thereof into a visible image, and the latent image carrying unit. The first visible image developed on the body is transferred to the first surface of the recording body, while the second visible image developed on the latent image carrier is transferred to the second surface of the recording body. A double-sided transfer unit; a fixing unit that fixes the first visible image and the second visible image on the recording body while conveying the recording body after passing through the double-sided transfer unit; An image forming apparatus including a recording body storage unit that stores a recording body to be held is held on a surface of a conveyance belt that is endlessly moved while being stretched by a plurality of stretching members. A conveying belt unit that conveys the toner to the fixing unit and the fixing unit. A speed changing means for changing the recording material transport speed and the recording material transport speed by the transport belt; and a charge applying means for applying a charge to the surface of the transport belt before receiving the recording body from the double-side transfer means; After transfer, which is a recording medium conveyance path from a transfer separation position in the double-side transfer means when the recording medium is transferred to the conveyance belt to a fixing reception position in the fixing device when the recording medium is received from the conveyance belt The length of the conveyance path before fixing is made larger than the dimension in the conveyance direction of the maximum size recording medium that can be accommodated in the recording medium accommodation means.
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, there is provided a static eliminating unit that neutralizes the conveyance belt region before the recording medium held on the surface is transferred to the fixing unit. It is characterized by.
According to a fourth aspect of the present invention, in the image forming apparatus according to the first, second, or third aspect, the recording medium conveyance speed by the fixing unit and the recording medium conveyance speed by the conveyance belt are set to the same speed. The speed changing means is configured as described above.
According to a fifth aspect of the present invention, in the image forming apparatus of the fourth aspect, the rear end of the recording body in the transport direction or the boundary between the rear end side blank area and the non-margin area of the recording body is Before passing through the transfer separation position, the recording medium conveyance speed by the fixing means and the conveyance belt is set to the same speed as the recording medium conveyance speed by the double-side transfer means, and after the trailing edge or boundary passes through the transfer separation position. The speed changing means is configured so that the recording medium conveyance speed by the fixing means and the conveyance belt is different from the recording medium conveyance speed by the double-side transfer means.
According to a sixth aspect of the present invention, there is provided the image forming apparatus according to the fifth aspect, wherein in the image forming apparatus according to the fifth aspect, depending on the size of the recording material supplied to the double-side transfer means, the paper is continuously discharged from the double-side transfer means. The speed changing unit is configured so that a plurality of recording bodies to be transferred are collectively transferred to the transport belt, and then a recording body transport speed by the fixing unit and the transport belt is different from a recording body transport speed by the double-side transfer unit. It is characterized by that.
According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, the charge is based on a timing at which the leading end of the recording material discharged from the double-side transfer means starts to contact the conveying belt. The charge application start timing by the application unit is determined.
The invention according to claim 8 is the image forming apparatus according to any one of claims 1 to 7, further comprising a belt base material made of polyimide or polyamide, and having a surface resistance value of 10 ⁸ to 10 ¹³ [Ω / □]. What was adjusted and whose volume specific resistance was adjusted to 10 < ⁶ > -10 < ¹² > [ohm * cm] was used as the said conveyance belt.
According to a ninth aspect of the present invention, in the image forming apparatus according to any one of the first to eighth aspects, the transfer separation position of the double-sided transfer means among a plurality of support rollers that support the conveying belt on the inner circumferential surface of the loop. A support roller having a diameter of 20 to 40 [mm] is used as the closest support roller, and a diameter of 20 to 30 [mm] is used as the support roller disposed closest to the fixing receiving position of the fixing unit. It is characterized by using a certain thing.
According to a tenth aspect of the present invention, in the image forming apparatus according to any one of the first to ninth aspects, as the fixing unit, the recording members sandwiched between the fixing nips while abutting each other to form a fixing nip are respectively opposite sides. The distance between the transfer separation position of the double-side transfer means and the conveyance receiving position which is the recording material reception position in the belt circumferential direction of the conveyance belt is 30 to 60 [mm]. And a distance between the pre-fixing conveyance completion position, which is the recording material delivery position in the belt circumferential direction of the conveyance belt, and the fixing nip entrance, which is the fixing reception position of the fixing unit, is 40 to 60 [mm]. It is characterized by being set to.
According to an eleventh aspect of the present invention, in the image forming apparatus according to any one of the first to ninth aspects, as the fixing unit, the recording members sandwiched between the fixing nips while abutting each other to form a fixing nip are respectively opposite sides. A pair of a fixing roller and a fixing belt that are heated from each other, and a transfer separation position of the double-sided transfer unit and the recording in the circumferential direction of the conveying belt when receiving the recording medium discharged from the double-sided transfer unit The distance from the belt surface recording body receiving position, which is the front end contact position of the body, is set to 30 to 60 [mm], and the pre-fixing conveyance completion position, which is the recording body delivery position in the belt circumferential direction of the conveyance belt, The distance from the fixing nip entrance of the fixing unit is set to 60 to 180 [mm].
According to a twelfth aspect of the present invention, in the image forming apparatus according to any one of the first to eleventh aspects, as the latent image developing unit, a first unit group including a plurality of first latent image developing units, and a plurality of second image forming units. A second group of units composed of latent image developing units, and the first visible image developed on the latent image carrier of each first latent image developing unit as the double-side transfer means, respectively, as a first intermediate transfer belt. The second visible image developed on the latent image carrier of each second latent image developing unit is superimposed on the second intermediate transfer belt, while being transferred onto the first surface in a batch. In addition, it is characterized in that what is collectively transferred and then transferred onto the second surface is used.
The invention according to claim 13 is the image forming apparatus according to claim 12, wherein the first intermediate transfer belt and the second intermediate transfer belt are brought into contact with each other to form a transfer nip, and the recording medium is transferred to the transfer nip. The double-side transfer means is configured to transfer a visible image onto both sides of the recording medium while being sandwiched and conveyed.
According to a fourteenth aspect of the present invention, in the image forming apparatus according to the thirteenth aspect, the length of the recording medium conveying path from the exit of the transfer nip to the fixing receiving position of the fixing unit is set to the maximum size recording. It is characterized in that it is larger than the body conveyance direction dimension.
According to a fifteenth aspect of the present invention, in the image forming apparatus according to the thirteenth or fourteenth aspect, a contact pressure adjusting means for adjusting a contact pressure between the first intermediate transfer belt and the second intermediate transfer belt in the transfer nip. Is provided.
According to a sixteenth aspect of the present invention, in the image forming apparatus according to the fifteenth aspect, the first intermediate transfer belt and the second intermediate transfer belt are sandwiched between each other and the intermediate transfer belt is pressurized while forming the transfer nip. A pair of pressure rollers, an eccentric roller rotatably fixed to the shaft of one of the rollers of the pressure roller pair, and an abutting roller abutted against the eccentric roller while being fixed to the shaft of the other roller And a rotating means for rotating the eccentric roller, and the contact pressure adjusting unit is configured to adjust the contact pressure according to a change in the distance between the shafts of the both support rollers accompanying the rotation of the eccentric roller. It is characterized by that.
According to a seventeenth aspect of the present invention, in the image forming apparatus according to any one of the thirteenth to sixteenth aspects, the first intermediate transfer belt and the second intermediate transfer belt are sandwiched between each other while forming the transfer nip. A pair of pressure rollers for pressing the transfer belt is provided, and the first intermediate transfer belt and the second intermediate transfer belt each have a belt detent projection on the belt inner peripheral surface at both ends in the width direction or in the vicinity thereof. And at least two of the supporting rollers that support the first intermediate transfer belt on the inner circumferential surface of the loop at a location different from the transfer nip, more than the pressure rollers constituting the pressure roller pair. At least two supporting rollers that use a long axial length and support the second intermediate transfer belt on the loop inner peripheral surface at a location different from the transfer nip. To, it is characterized in that used as a large axial length of the roller portion than either of the pressing roller which constitutes the pressure roller pair.
The invention according to claim 18 is the image forming apparatus according to any one of claims 13 to 17, wherein any one of the intermediate transfer belts is provided in a region where the first intermediate transfer belt and the second intermediate transfer belt are opposed to each other. There is provided a pressing member that presses from the front surface and curves its endless moving track toward the inside of the belt loop, and the conveying belt is positioned so that at least a part of the conveying belt is positioned within the intermediate transfer belt bending region by the pressing member. A belt is provided.
According to a nineteenth aspect of the present invention, in the image forming apparatus according to the eighteenth aspect, the charge applying means is disposed inside a loop of the conveying belt.
According to a twentieth aspect of the present invention, in the image forming apparatus according to the eighteenth aspect, the charge applying unit is disposed in the curved area of the intermediate transfer belt.
According to a twenty-first aspect of the invention, in the image forming apparatus of the twentieth aspect, the pressing member is also used as the charge applying unit.
According to a twenty-second aspect of the present invention, in the image forming apparatus according to any one of the eighteenth to twenty-first aspects, the first intermediate transfer belt or the second intermediate transfer belt pressed by the pressing member is supported by a loop inner peripheral surface. Among the plurality of support rollers, a support roller having a diameter of 20 to 30 [mm] is used as a support roller disposed adjacent to the pressing member on the upstream side in the belt movement direction from the pressing member, and The belt winding angle with respect to the support roller is set to 90 to 120 [°].
In the image forming apparatus according to any one of claims 18 to 22, the first intermediate transfer belt and the second intermediate transfer belt may take a space in the horizontal direction rather than the vertical direction. A horizontally stretched one is used, and the conveyor belt unit is one in which the conveyor belt is stretched in a horizontally long shape, and at least three of the projected images in the vertical direction of these three belts are used. It is characterized by being arranged in the vertical direction so that some of them overlap each other.
According to a twenty-fourth aspect of the present invention, in the image forming apparatus of the twenty-third aspect, the first unit group is disposed above the first intermediate transfer belt in the vertical direction, and the second unit group is disposed in the second intermediate transfer. The first unit group is disposed on the lower side of the first intermediate transfer belt and the second unit group is disposed on the upper side of the second intermediate transfer belt. It is characterized by being arranged on the lower side.
According to a twenty-fifth aspect of the present invention, in the image forming apparatus of the twenty-fourth aspect, as the pressing member, a first pressing member that presses the first intermediate transfer belt and a second pressing that presses the second intermediate transfer belt. A first intermediate transfer belt curved region by the first pressing member and a second intermediate transfer belt curved region by the second pressing member, and at least one of the conveyance belts in the curved region. The conveyor belt is disposed so that a part thereof is positioned, and the first unit group or the second unit group is positioned so that at least a part of the first unit group or the second unit group is positioned in the other curved region. A unit group is provided.
According to a twenty-sixth aspect of the present invention, in the image forming apparatus according to any one of the eighteenth to twenty-second aspects, the first intermediate transfer belt and the second intermediate transfer belt take a space in the vertical direction rather than in the horizontal direction. A vertically stretched one is used, and the conveyer belt unit is one in which the conveyer belt is stretched in a vertically long shape, and these three belts are at least a projected image in each horizontal direction. It is characterized by being arranged in a horizontal direction so that a part thereof overlaps each other.
According to a twenty-seventh aspect of the present invention, in the image forming apparatus of the twenty-sixth aspect, the first unit group is disposed so that the surface movement in the vertical direction faces the first intermediate transfer belt portion from the lower side to the upper side. In addition, the second unit group is disposed so as to face the second intermediate transfer belt portion where the surface movement in the vertical direction is from the lower side to the upper side, or the surface movement in the vertical direction is from the upper side to the lower side. The first unit group is disposed so as to face the first intermediate transfer belt portion, and the surface movement in the vertical direction is faced to the second intermediate transfer belt portion which is from the upper side to the lower side. The second unit group is arranged.
The invention according to claim 28 is the image forming apparatus according to claim 24, 25 or 27, wherein each first latent image developing unit and each second latent image developing unit are based on an imaginary line extending in the vertical direction. They are respectively arranged so as to have a line-symmetric posture.
The invention according to claim 29 provides a latent image forming step for forming a latent image on the surface of the latent image carrier based on image information, and a developing step for developing the latent image on the latent image carrier to a visible image. And transferring the first visible image developed on the latent image carrier to the first surface of the recording medium, while transferring the second visible image developed on the latent image carrier to the recording medium. A double-sided transfer step of transferring to the second surface, and a fixing step of fixing the first visible image and the second visible image to the recording body while conveying the recording body after passing through the double-sided transfer step; In the image forming method of forming an image on both sides of the recording body by carrying out the housing step of housing the recording body supplied to the double-sided transfer step in the recording body housing means, the recording body discharged from the double-sided transfer step The belt is held on the surface of the conveyor belt which is endlessly moved while being stretched by a plurality of stretch members, and is directed to the fixing process. A transporting step for transporting, a speed changing step for changing the recording member transporting speed by the fixing unit and the recording member transporting speed by the transporting belt, and charging the surface of the transporting belt before receiving the recording member from the double-sided transfer step. A latent image forming prohibition for prohibiting the formation of a latent image on a latent image carrier area corresponding to the trailing edge side blank area of the maximum size recording medium that can be accommodated in the recording medium accommodating means. Steps are provided in the latent image forming step, and from the transfer separation position when the recording body is transferred to the conveying belt by the double-sided transfer unit that performs the double-sided transfer step, the recording body by the fixing unit that performs the fixing step The length of the post-transfer pre-fixing conveyance path, which is the recording medium conveyance path to the fixing receiving position when receiving the toner from the conveyance belt, is determined from the conveyance direction dimension of the maximum size recording medium on the trailing edge side. It is characterized in that larger than the value obtained by subtracting the size of the recording material conveyance direction of a region.
According to a thirty-third aspect of the present invention, there is provided a developing step for developing a latent image on a latent image carrier into a visible image, and a first visible image developed on the latent image carrier on a first surface of a recording member. A double-sided transfer step of transferring the second visible image developed on the latent image carrier to the second surface of the recording body, and transporting the recording body after passing through the double-sided transfer step However, a fixing process for fixing the first visible image and the second visible image on the recording medium and a storing process for storing the recording medium supplied to the double-sided transfer process in the recording medium storing means are performed. In the image forming method of forming an image on both sides of the recording body, the recording body discharged from the double-sided transfer step is held on the surface of a conveying belt that is endlessly moved while being stretched on a plurality of stretching members. A transport process for transporting toward the fixing process, a recording medium transport speed by the fixing unit, and the transport base; A speed changing step for changing the recording medium conveyance speed by the toner and a charge applying step for applying a charge to the surface of the conveyance belt before receiving the recording medium from the double-side transfer step, and performing the double-side transfer step. The recording medium from the transfer separation position when the recording medium is transferred to the conveyance belt by the double-side transfer means to the fixing reception position when the recording medium is received from the conveyance belt by the fixing means for performing the fixing step. The length of the post-fixing pre-fixing conveyance path, which is a conveyance path, is made larger than the dimension in the conveyance direction of the maximum-size recording medium that can be accommodated in the recording medium accommodating means.

In these inventions, in the image forming apparatus having the configuration of claim 1 and the image forming method of claim 19, the heating temperature by the fixing unit is not changed by changing the conveyance speed of the recording medium in the fixing unit. The amount of fixing heat per unit time for the recording medium is changed. For this reason, even when the required fixing heat amount becomes considerably large, the fixing process is performed with a sufficient heating amount without significantly increasing the heating temperature by the fixing means. Even when the required fixing heat amount is considerably small, the fixing process is performed with an appropriate heating amount without excessively heating the recording medium. Therefore, it is assumed that the required fixing heat amount becomes considerably large, avoiding the cost increase by setting the heat resistance of the fixing means, and fixing defects and hot offset due to the change of the required fixing heat amount for each printout. Occurrence can be suppressed.
However, if the distance between the transfer separation position of the double-sided transfer means for discharging the transferred recording medium and the fixing receiving position of the fixing means for receiving the recording medium is too short, the front end side of the recording medium is conveyed by the fixing means. In this case, the rear end side is conveyed by the double-sided transfer means. Then, when the recording medium conveyance speed by the fixing means is slower than the recording medium conveyance speed (transfer speed) by the double-side transfer means, the conveyance of the recording medium is delayed between the fixing means and the double-side transfer means, and the recording medium Will be greatly bent or jammed. In addition, when the recording medium conveyance speed by the fixing unit is made higher than the recording medium conveyance speed by the double-side transfer unit, the rear end side of the recording medium may slip in the transfer unit and the image may be disturbed.
Therefore, a conveyance belt is provided between the transfer separation position of the double-sided transfer unit and the fixing receiving position of the fixing unit, and the length between both is set to the dimension in the conveyance direction of the maximum size recording unit that can be accommodated in the recording unit accommodation unit. Is larger than the value obtained by subtracting the size of the rear end side margin area. Then, at the timing immediately before the leading end of the recording body reaches the fixing receiving position of the fixing unit, the trailing end of the image area of the recording body can be advanced beyond the transfer separation position of the double-side transfer unit. At this time, most of the entire area of the recording medium has passed through the double-sided transfer means, and only a slight trailing edge margin area of at most several cm remains in the double-sided transfer means. For this reason, even if there is a difference in speed between the recording medium conveyance speed by the fixing means and the conveyance belt and the recording medium conveyance speed by the double-side transfer means, the recording medium may be greatly curved between the double-side transfer means and the fixing means. , It does not cause a situation such as generating a jam. Further, even if the trailing edge side margin area of the recording medium is slipped in the double-sided transfer means, no image is present in the trailing edge side margin area, so that the image is not disturbed by the slip. Therefore, it is not necessary to match the recording medium conveyance speed by the fixing unit or the conveyance belt with the recording medium conveyance speed of the double-side transfer unit, and it can be uniquely changed to meet the required fixing heat amount. As a result, it is possible to suppress the occurrence of fixing failure and hot offset caused by changing the transfer speed in accordance with the resolution of the image.
In addition, the recording medium discharged from the double-side transfer means is electrostatically adsorbed to the surface of the conveyance belt by applying a charge to the surface of the conveyance belt before receiving the recording medium from the double-side transfer means. And by this electrostatic attraction, the close contact between the recording medium and the conveyor belt is enhanced, thereby suppressing subtle friction between the recording medium and the belt surface due to slight vibration of the conveyor belt. Therefore, it is possible to suppress disturbance due to rubbing of the unfixed image on the recording medium.

In the image forming apparatus having the configuration according to claim 2 and the image forming method according to claim 20, as in the image forming apparatus according to claim 1, the necessary heat of fixing is considerably obtained by changing the conveyance speed of the recording medium by the fixing unit. To prevent the occurrence of fixing defects and hot offsets due to changes in the required amount of fixing heat for each printout, while avoiding cost increases by setting the heat resistance of the fixing means. Can do.
Further, a conveying belt is provided between the transfer separation position of the double-sided transfer means and the fixing receiving position of the fixing means, whereby the length between the two is set to the conveying direction of the maximum size recording medium that can be accommodated in the recording medium accommodating means. It is larger than the dimensions. Then, before the leading end of the recording body reaches the fixing receiving position of the fixing unit, the trailing end of the recording body is discharged from the double-sided transfer unit, and the transfer of the recording body from the double-sided transfer unit to the conveyance belt is completed. Become. After the delivery is completed, even if a linear speed difference is provided between the recording medium conveyance speed by the fixing means and the conveyance belt and the recording medium conveyance speed by the double-side transfer means, the recording medium is moved between the fixing means and the double-side transfer means. There is no occurrence of a large curvature. In addition, the rear end side of the recording medium does not slip in the double-side transfer means. Therefore, it is not necessary to match the recording medium conveyance speed by the fixing unit or the conveyance belt with the recording medium conveyance speed of the double-side transfer unit, and it can be uniquely changed to meet the required fixing heat amount. As a result, it is possible to suppress the occurrence of fixing failure and hot offset caused by changing the transfer speed in accordance with the resolution of the image.
Similarly to the image forming apparatus according to the first aspect, by causing the recording body to be electrostatically attracted to the conveyance belt, it is possible to suppress disturbance due to rubbing of the unfixed image on the recording body.

Hereinafter, a first embodiment of an electrophotographic printer (hereinafter simply referred to as a printer) will be described as an image forming apparatus to which the present invention is applied.
First, the basic configuration of the printer will be described. FIG. 1 is a schematic configuration diagram of the printer, showing the printer from the front direction. In the figure, this printer includes four first process units for individually generating four color first toner images of yellow, magenta, cyan, and black (hereinafter referred to as Y, M, C, and K). A first unit group including 7Y, M, C, and K is provided. In addition, a second unit group including four second process units 40Y, 40M, 40C, and 40K for individually generating four color second toner images Y, M, C, and K is also provided. These process units, which are latent image developing units, use Y, M, C, and K toners of different colors as image forming materials, but have the same configuration except that they are replaced when the lifetime is reached. Taking the first process unit 7Y for generating a first Y toner image, which is a first toner image, as an example, a drum-shaped photosensitive member 1Y as a latent image carrier, a drum cleaning device 2Y, a charge eliminating device 3Y, a charging device 4Y, A developing device 5Y, an exposure device 6Y, and the like are provided.

  In the photoreceptor 1Y, an aluminum cylinder having a diameter of 30 to 120 [mm] is covered with a surface layer of an organic semiconductor that is a photoconductive substance. An amorphous silicon surface layer may be coated. Further, it may be a belt shape instead of a drum shape.

  The charging device 4Y uniformly charges the surface of the photoreceptor 1Y that is rotated clockwise in the drawing by a driving unit (not shown). The uniformly charged surface of the photoreceptor 1Y is exposed and scanned by an exposure device 6Y that emits light from an LED array or the like, and carries an electrostatic latent image for Y. The electrostatic latent image for Y is developed into a first Y toner image by the developing device 5Y using Y toner. Then, primary transfer is performed on a first intermediate transfer belt 9 described later. The drum cleaning device 2Y removes the toner remaining on the surface of the photoreceptor 1Y after the intermediate transfer process. Further, the charge removal device 3Y removes the residual charge of the photoreceptor 1Y after cleaning. By this charge removal, the surface of the photoreceptor 1Y is initialized and prepared for the next image formation. Similarly, in the other first process units 7M, 7C, and 7K, first M, C, and K toner images, which are first toner images, are formed on the photoreceptors 1M, 1C, and 1K, and the first intermediate transfer belt 9 is formed. The toner image is primary-transferred superposedly on the upper Y toner image. The developing device may use a two-component developer containing toner and a magnetic carrier, or may use only toner powder. Further, the toner may be a pulverized toner manufactured by a pulverization method or a toner formed in a spherical shape, and a toner having a volume average particle size of 20 [μm] or less is preferable. More preferably, the thickness is 4 [μm] or more and 10 [μm] or less. A magnetic carrier having a volume average particle diameter of about 25 to 60 [μm] is preferable when a two-component developer is used.

  The second process units 40Y, 40M, 40C, and 40K have substantially the same configuration as the first process units 7Y, 7M, 7C, and 7K. Then, second Y, M, C, and K toner images, which are second toner images, are formed on the surfaces of the photoreceptors 41Y, 41M, 41C, and 41K, respectively. These second Y, M, C, and K toner images are primarily transferred while being superimposed on a second intermediate transfer belt 31 described later.

  An image data processing device E1 is disposed in the lower part of the printer housing. The image data processing device E1 generates an exposure scanning control signal based on an image information signal sent from a personal computer (not shown) or the like. Then, it is sent to the exposure devices 6Y, M, C, K of the first process units 7Y, M, C, K and the exposure devices 46Y, M, C, K of the second process units 40Y, M, C, K. . Each of the exposure devices 6Y, M, C, K, 46Y, M, C, and K serving as a latent image forming unit emits light based on the exposure scanning control signal. , M, C, K are irradiated. An electrostatic latent image is formed on the photoreceptors 1Y, 1M, 1C, 1K, 41Y, 1M, 1C, and 1K exposed by the irradiation. The four photoconductors 1Y, 1M, 1C, and 1K are arranged at equal intervals, and contact with a first intermediate transfer belt 9 described later at least during image formation. The four photoconductors 41Y, 41M, 41C, and 41K are also arranged at equal intervals, and contact with a second intermediate transfer belt 31 described later at least during image formation.

  A paper feed cassette 50 having a first paper feed roller 50a is disposed on the right side of the image data processing device E1 in the drawing, and a state of a transfer paper bundle in which a plurality of transfer papers P as recording media are stacked inside. Is housed in. The paper feed roller 50 a is in contact with the first transfer paper P in the bundle of transfer paper accommodated in the paper feed cassette 50. Then, by being driven to rotate by a driving means (not shown), the uppermost transfer paper P is sent out toward the first paper feed path 51 disposed on the right side of the paper feed cassette 50 in the drawing. As the paper feed cassette 50, in addition to the illustrated paper feed cassette 50, an air paper feed system composed of a vacuum mechanism can be used to reliably feed and separate the transfer paper P having various characteristics such as thick paper and thin paper. A thing may be adopted.

  A first paper feed path 51 extending in the vertical direction in the drawing on the right side of the paper cassette 50 in the drawing includes a first conveyance roller pair 52, a second conveyance roller pair 53, a registration roller pair 54, and the like. Then, the transfer paper P sent out from the paper feed cassette 50 is conveyed in the path from the lower side to the upper side in the figure while being sequentially held by the first conveying roller pair 52 and the second roller pair 53. The roller 54 is reached. The registration roller pair 54 rotates both rollers in the forward direction so as to hold the transfer paper P, but once the transfer body is sandwiched between the rollers, the rotation of both rollers is temporarily stopped. Then, the rotation is resumed at an appropriate timing, and the transfer paper P is sent out to a double-side transfer device described later. That is, the registration roller pair 54 functions as a timing roller pair. A paper feeding device 300 different from the paper feeding cassette 50 can be disposed on the right side of the printer in the drawing.

  In the present printer, a temperature / humidity sensor (not shown) is provided for the purpose of preventing the transfer paper P in the paper feed cassette 50 from absorbing moisture and deteriorating due to environmental changes. Then, the humidity in the cassette is kept constant by turning on / off the cooling fan F based on the detection result of the temperature / humidity sensor.

  A first transfer unit 8 is disposed in the vicinity of the first unit group. A second transfer unit 30 is disposed above the second unit group in the drawing. In this printer, a combination of the first transfer unit 8 and the second transfer unit 30 constitutes a double-sided transfer device as double-sided transfer means.

  The electrostatic latent images for Y, M, C, and K formed on the photoreceptors 1Y, M, C, and K of the first process units 7Y, M, C, and K are subjected to primary transfer by the first transfer unit 8. Go through the process. The first transfer unit 8 includes a first intermediate transfer belt 9, four primary transfer rollers 10Y, 10M, 10C, and 10K, a first cleaning device 11, a first pressing roller 12 serving as a pressing member, and the like. Further, eight stretching rollers 13 are provided for stretching the first intermediate transfer belt 9 while supporting the first intermediate transfer belt 9 on the inner circumferential surface of the loop. These six stretching rollers 13 include a nip inlet first roller 13a, a nip outlet first roller 13b, a first cleaning backup roller 13c, a primary transfer nip upstream roller 13d, a primary transfer nip downstream roller 13e, a tension roller 13f, The driving roller 13g is composed of a secondary transfer nip upstream roller 13h. While being supported by these, the first intermediate transfer belt 9 is endlessly moved clockwise in the drawing by the rotational drive of the drive roller 13g. The four primary transfer rollers 10Y, 10M, 10C, and 10K, which are transfer bias members, sandwich the first intermediate transfer belt 9 that is moved endlessly in this manner between the photoreceptors 1Y, 1M, 1C, and 1K. , M, C, and K primary transfer nips are formed. Then, in response to voltage supply from a power source (not shown), a primary transfer bias having a reverse polarity (for example, plus) to the toner is applied to the back surface (loop inner peripheral surface) of the first intermediate transfer belt 9.

  The first intermediate transfer belt 9 sequentially passes through the primary transfer nips for Y, M, C, and K along with the endless movement thereof. In each primary transfer nip, the first Y, M, C, and K toner images on the photoconductors 1Y, 1M, 1C, and 1K are primarily transferred by being superimposed by the action of the nip pressure and the primary transfer bias. As a result, a four-color superimposed toner image (hereinafter referred to as a four-color toner image) is formed on the first intermediate transfer belt 9. Instead of the four primary transfer rollers 10Y, 10M, 10C, and 10K of the bias application method, a charger method that discharges from the electrodes may be used.

  The second transfer unit 30 of the double-sided transfer device includes a second intermediate transfer belt 31, a second cleaning device 32, four primary transfer rollers 33Y, 33M, 33C, 33K, a second pressing roller 34 as a pressing member, and the like. ing. Also, six tension rollers 35 are provided. These six stretching rollers 35 are constituted by a nip inlet second roller 35a, a nip outlet second roller 35b, a separation roller 35c, a second cleaning backup roller 35d, a tension roller 35e, and a driving roller 35f. The second intermediate transfer belt 31 is endlessly moved counterclockwise in the figure by the rotational drive of the driving roller 35f while being stretched around these.

  The extended portion of the first intermediate transfer belt 9 from the first roller 12 at the nip entrance of the first transfer unit 8 to the first roller 13 at the nip exit comes into wide contact with the second intermediate transfer belt 31 of the second transfer unit 30 and is secondary. A transfer nip is formed. In the secondary transfer nip, the first intermediate transfer belt 9 and the second intermediate transfer belt 31 move their surfaces in the same direction.

  The transfer paper P sent out from the registration roller pair 54 toward the double-side transfer device is nipped in the secondary transfer nip, and then conveyed in the nip from the right side to the left side in the figure as the surface of the two intermediate transfer belts moves. Is done. In this process, the four-color toner images on the first intermediate transfer belt 9 are secondarily transferred to the first surface (the surface facing downward in the paper feed cassette 50) for the reason described later. Further, the four-color toner images on the second intermediate transfer belt 31 are secondarily transferred collectively onto the second surface opposite to the first surface. The four-color toner images transferred respectively to the first surface and the second surface are combined with the white color of the transfer paper P to form a full-color image.

  The transfer residual toner that has not been secondarily transferred to the transfer paper P adheres to the surface of the first intermediate transfer belt 9 after passing through the secondary transfer nip. This is cleaned by the first cleaning device 11. Specifically, the first intermediate transfer belt 9 includes a first cleaning device 11 disposed so as to contact the outer surface (front surface) of the loop, and a first cleaning device 11 disposed on the inner surface of the loop. It is sandwiched between the cleaning backup roller 13c. Then, the transfer residual toner on the front surface is mechanically or electrostatically collected by the first cleaning device 11 and cleaned. Similarly, the surface of the second intermediate transfer belt 31 after passing through the secondary transfer nip is also cleaned of the transfer residual toner on the front surface by the second cleaning device 32.

As the first intermediate transfer belt 9 and the second intermediate transfer belt 31, for example, those having a belt base made of a resin film or rubber and having a thickness of 50 to 600 [μm] can be used. A multilayer structure in which the front surface side of such a belt substrate is coated with a surface layer made of a material having excellent toner releasability may be used. In any case, it must exhibit electrical resistance that enables electrostatic primary transfer and secondary transfer. An example of such a belt is one in which carbon is dispersed in polyamide as a belt base material and the volume resistance value is adjusted to 10 ⁶ to 10 ¹² [Ωcm]. On the inner peripheral surfaces of both the intermediate transfer belts, in order to stabilize the belt running, a detent protrusion is provided in the vicinity of both ends in the width direction so as to extend over the entire belt circumference. The offset protrusions at both ends are abutted against the end of the stretching roller, thereby preventing the belt from being offset.

The eight primary transfer rollers 10Y, M, C, K, 33Y, M, C, and K are obtained by coating the surface of a roller metal core to which a primary transfer bias is applied with a conductive rubber material, and are specific to the volume. An example in which the resistance is adjusted to about 10 ⁵ Ωcm can be exemplified. Examples of the conductive rubber material include those obtained by dispersing carbon in urethane rubber and adjusting the volume specific resistance to about 10 ⁷ Ωcm.

  The transfer paper P that has been subjected to double-sided transfer processing by the double-sided transfer device is sent to a fixing device 56 that is a fixing means via a conveyance belt unit 60 described later. The fixing device 56 has two fixing rollers 56a and 56b that contact each other while rotating in the forward direction to form a fixing nip. Each of the fixing rollers 56a and 56b has heating means such as a halogen lamp (not shown), and heats the transfer paper P sandwiched between the fixing nips from both sides. By this heating, the full color images respectively formed on both sides of the transfer paper P are fixed on the transfer paper P. The fixed transfer paper P is discharged out of the apparatus through a cooling roller pair 57 and a paper discharge roller pair 58.

  The surface temperatures of the two fixing rollers 56a and 56b are respectively detected by temperature detection means (not shown). This temperature detection means transmits to the control part E2 arrange | positioned in the figure lower left in the inside of the housing of a printer main body. Based on the detection result of the surface temperature sent from the temperature detection means, the control unit E2 performs ON / OFF control of the power supply to the heat generating means of the fixing rollers 56a, b, and the surface temperature of the fixing rollers 56a, b. Is maintained within a certain range (target range).

  Since the fixing device 56 generates heat by the two fixing rollers 56a and 56b, there is a risk of damaging a member disposed in the vicinity thereof. Therefore, in this printer, a cooling device using a heat insulating member or an airflow is disposed in the vicinity of the fixing device 56. In the example shown in the figure, a heat shield frame 59 made of a heat insulating member is used as a cooling device to cover the periphery of the fixing device 56 so that heat is not transmitted to members disposed around the fixing device 56. The two fixing rollers 56a and 56b are made of the same material, hardness and surface property for the purpose of making the color and gloss of the images on both sides of the transfer paper P the same.

  In this printer, the above-described cooling roller pair 57 is disposed in the vicinity of the fixing device 56 for the purpose of quickly cooling the transfer paper P after the fixing process and stabilizing the unstable toner state at an early stage. ing. As the cooling roller pair 57, a heat pipe structure roller having a heat radiating portion can be adopted.

  In this printer, the stack tray is moved up and down according to the stack level by an elevator mechanism (not shown) for the purpose of stocking a large amount of the transfer paper P discharged to the outside by the paper discharge roller pair 58. The mechanism is adopted. In addition, after passing the paper discharge roller pair 58, the transfer paper P can be transported to another post-processing apparatus. As another post-processing apparatus, an apparatus for bookbinding such as punching, cutting, folding, and binding can be exemplified.

  A bottle container 55 is disposed above the first transfer unit 8 in the drawing. In the bottle container 55, there are first toner bottles BY1, BM1, BC1, BK1 and second toner bottles BY2, BM2, BC2, BK2, which individually contain toner to be supplied to the developing devices in each process unit. It is housed. The toner contained in these bottles is conveyed by a toner replenishing device (not shown) and replenished as appropriate to the developing devices in each process unit. As a toner transport mechanism in the toner replenishing device, a known MONO pump can be used. According to the method using the MONO pump, there are few restrictions on the installation location of each toner bottle, which is advantageous for space allocation in the printer. Further, since the toner can be replenished in a timely manner, it is not necessary to provide a large toner storage space in the developing device, and the developing device can be downsized.

  In this printer, a dedicated toner bottle is provided for each of the first process unit and the second process unit in the first unit group and the second unit group that are arranged in the vertical direction. However, for the same color toner, it is possible to use the same toner bottle in the first process unit and the second process unit. In addition, as the K toner bottle, which consumes more than other colors, one having a larger capacity than the other color toner bottles can be used.

  An operation display unit 90 such as a touch panel is fixed on the upper surface of the printer body. The operation display unit 90 can input predetermined information to the control unit E2 by an operator's key operation, and can display various information on a display screen based on a signal from the control unit E2.

  A waste toner container 91 is disposed on the right side of the sheet feeding cassette 50 in the drawing. The toner cleaned from the surface of each photoconductor and each intermediate transfer belt is collected in the waste toner container 91 by a collecting unit (not shown). In such a configuration, it is not necessary to provide a large capacity toner container in each cleaning device that cleans the photosensitive member and the belt, so that each cleaning device can be miniaturized. In addition, since waste toner can be discarded at a time, maintainability can be improved. For the purpose of preventing overflow of toner from the waste toner storage unit 91, it is desirable to configure the control unit E2 to provide a toner full sensor and to execute a control to issue a full alarm based on the detection result thereby. .

  Although the temperature inside the printer casing rises due to heat radiation from the fixing device 56 and the control unit E2, in this printer, excessive cooling can be prevented by operating the cooling fan F. The cooling fan F is coupled to the heat radiating part of the cooling roller pair 57 to ensure the cooling effect of the cooling roller pair 57.

[Single-sided print mode]
This printer can operate in a single-sided print mode for forming an image on only one side of the transfer paper P. There are two types of operation modes in the single-sided print mode, which can be switched by an operator's key operation. One of the two types is a system in which the four-color toner images superimposed on the first intermediate transfer belt 9 are collectively transferred onto the first surface of the transfer paper P. The other method is a method in which the four-color toner images superimposed on the second intermediate transfer belt 31 are secondarily transferred onto the second surface of the transfer paper P at once.

  In a case where images over a plurality of pages are continuously printed out on a plurality of transfer papers P, it is advantageous to control the image forming order so that the pages are aligned on the stack portion. This is because the page order can be naturally aligned by printing out the images from the last page. Therefore, in one of the two types of operation methods in the single-sided print mode, when a printout command is generated, first, the first intermediate transfer belt 9 and each of the photoreceptors 1Y, 1M, 1C, and 1K in the first unit group are used. Start driving. At the same time, the second intermediate transfer belt 31 starts to be driven. However, the photosensitive members 41Y, 41M, 41C, and 41K in the second unit group are separated from the second intermediate transfer belt 31 by a contact / separation mechanism (not shown). It is stopped without starting. Then, the first Y, M, C, and K toner images formed on the respective photoreceptors 1Y, 1M, 1C, and 1K of the first unit group are superimposed and transferred onto the first intermediate transfer belt 9 by the electrophotographic process 4. It becomes a color toner image. The four-color toner image is secondarily transferred onto the first surface of the transfer paper P at the secondary transfer nip, and becomes a full-color image. Thereafter, the same electrophotographic process and transfer are performed for the transfer paper P for the next page, and the transfer paper P with the image surface facing upward is sequentially stacked on the stack portion in descending order of the page number.

  In the other one of the two types of operation methods in the single-sided printing mode, an image is not formed by the first unit group in place of the second unit group, and image data is printed out in order from the young page image data for page alignment. This is different from the method described above. Since the other points are the same as the above-described method, detailed description is omitted.

[Duplex printing mode]
In the double-sided print mode in which images are formed on both sides of the transfer paper P, when a print command is issued, the formation of the four-color toner image by the first unit group and the formation of the four-color toner image by the second unit group are substantially parallel. Done. In the secondary transfer nip, the four-color toner image batch secondary transfer from the first intermediate transfer belt 9 to the first surface of the transfer paper P and the second intermediate transfer belt 31 to the second surface of the transfer paper P are performed. Four-color toner image batch secondary transfer is performed. In this way, full-color images are formed on both sides of the transfer paper P by the one-pass method.

  In the case where images over a plurality of pages are formed on both surfaces of a plurality of transfer papers P, an image corresponding to a lower numbered page is formed on the second surface of the transfer paper P on one transfer paper P, and a larger number An image corresponding to this page is formed on the first surface of the transfer paper P. By such image formation, transfer sheets P with a small number facing downward and a large number facing upward are sequentially stacked on the stack portion. Therefore, if the top and bottom of the final bundle of printed out papers are reversed, the first transfer sheet P with the front page being 1 page and the back side being 2 pages, the second page having the front side being 3 pages and the back side being 4 pages It is possible to obtain a bundle of printout sheets with the same page order, such as the transfer sheet P.

[Black monochrome mode]
This printer can also form a monochrome image using only K toner. In this case, three unused process units are generated in each of the first unit group and the second unit group. There are six first process units 7Y, M, and C for Y, M, and C, and second process units 40Y, 40, and 40 for Y, M, and C. In the case of the black monochrome mode, not only the process units are not operated but also they can be separated from the intermediate transfer belt. Specifically, the first intermediate transfer belt 9 and the second intermediate transfer belt 31 are supported on individual frames, and these frames are moved as necessary. As a result, the other three first process units 7Y, 7M, 7C are moved to the first intermediate transfer belt 9 while the photosensitive member 1K of the first process unit 7K is in contact with the first intermediate transfer belt 9. Make contact and separation. Further, the other three second process units 40Y, 40M, 40C are brought into contact with and separated from the second intermediate transfer belt 31 while the photosensitive member 41K of the second process unit 40K is in contact with the second intermediate transfer belt 31. . In the black monochromatic mode, the six process units other than those for K are separated from the intermediate transfer belt to form an image, thereby suppressing the wear of the photosensitive layer on the photosensitive members other than K, and the photoconductor Long life can be achieved.

Next, a characteristic configuration of the printer will be described.
In this printer, the maximum size transfer paper P that can be stored in the paper feed cassette 50 serving as a recording medium storage means is A3 size. And this printer can form an image on both sides, conveying this A3 size to the vertical direction which is a longitudinal direction.

  A conveyance belt unit 60 is disposed on the left side of the secondary transfer nip where the first intermediate transfer belt 9 and the second intermediate transfer belt 31 are in contact with each other in the drawing. The transport belt unit 60 includes a transport belt 61, a transport belt cleaning device 62, a charge applying charger 63 serving as a charge applying unit, a charge removing charger 64 serving as a charge removing unit, and the like. Moreover, it has the six support rollers 65 which support the conveyance belt 61 with a loop inner peripheral surface. Among these, the reference numerals 65a, 65b, 65c, and 65d denote a conveyance drive roller, a separation roller, a cleaning backup roller, and a charge application backup roller. The conveyor belt unit 60 moves the conveyor belt 61 endlessly in the counterclockwise direction in the figure by the rotational drive of the conveyor drive roller 65 a while stretching the conveyor belt 61 by these four tension rollers 65. Then, the transfer paper P discharged from the double-side transfer device including the first transfer unit 8 and the second transfer unit 30 is held on the surface of the transport belt 61 and transported toward the fixing device 56.

  FIG. 2 is a configuration diagram showing a paper conveyance path from the double-side transfer device to the fixing device 56 and the surrounding configuration. In the drawing, the first roller 13b at the nip outlet of the first transfer unit 8 changes the moving direction of the first intermediate transfer belt 9 immediately after passing through the secondary transfer nip so as to change abruptly. Is wound around the roller circumference. On the other hand, the second roller 35b at the nip exit of the second transfer unit 30 moves the second intermediate transfer belt 31 so that the moving direction of the second intermediate transfer belt 31 after passing through the secondary transfer nip is hardly changed. It is made to contact | abut only to the slight area | region of a roller surrounding surface. For this reason, the transfer paper P that has passed through the secondary transfer nip moves away from the first intermediate transfer belt 9 that rapidly changes the moving direction, and is held on the surface of the second intermediate transfer belt 31 that hardly changes the moving direction. Then, the sheet is conveyed toward the second intermediate transfer belt stretched position by the separation roller 35c disposed adjacent to the second roller 35b at the nip exit on the downstream side in the belt moving direction. The separation roller 35c wraps the second intermediate transfer belt 31 around the roller circumferential surface so that the moving direction of the second intermediate transfer belt 31 that moves substantially horizontally after passing through the secondary transfer nip is suddenly changed. ing. The transfer paper P that has reached the second intermediate transfer belt stretched portion by the separation roller 35c cannot follow the sudden change of direction of the second intermediate transfer belt 31, and the second intermediate transfer is performed depending on the strength of its own waist. Separate from belt 31. Then, the belt reaches the conveyor belt 61 while moving in a substantially horizontal direction just after passing through the nip.

  In such a configuration, the position indicated by P <b> 1 in the drawing is a transfer separation position in the double-sided transfer device when the transfer paper P is transferred to the transport belt 61. Specifically, the extension line in the moving direction of the second intermediate transfer belt 31 from the secondary transfer nip toward the separation roller 35c and the contact point with the separation roller 35c become the transfer separation position P1 in the double-sided transfer device.

  The transfer paper P delivered to the transport belt 61 is transported in a substantially horizontal direction along the upper stretched surface of the transport belt 61 as before. Of the six support rollers 65 that support the conveyance belt 61, when the conveyance belt is stretched by the separation roller 65 b disposed closest to the fixing device 56, the conveyance belt 61 is separated. The leading edge of the separated transfer paper P enters the fixing nip of the fixing device 56. In such a configuration, the position indicated by P <b> 2 in the drawing is a fixing receiving position in the fixing device 56 when the transfer paper P is received from the conveyance belt 61. Specifically, an extension line in the belt movement direction between the separation roller 35c and the support roller 65 that supports the conveyance belt 61 while adjoining on the upstream side in the belt movement direction starts contact with the fixing device 56. It becomes the position to do. This fixing receiving position P2 is the fixing nip entrance in this printer.

  A post-transfer pre-fixing conveyance path, which is a paper conveyance path from the transfer separation position P1 of the double-side transfer means to the fixing receiving position P2 of the fixing device 56, extends in a substantially straight line in the horizontal direction as shown in the figure. It is formed as follows.

  FIG. 3 is a block diagram showing a part of the electric circuit of the printer. In the figure, the speed control unit 100 has an arithmetic circuit made up of a CPU and the like (not shown), an information storage circuit made up of a RAM and the like. The first transfer drive motor 101 is a rotational drive source of a drive roller (13g) that moves the first intermediate transfer belt (9) (not shown) endlessly, and the rotational speed thereof is controlled by the speed controller 100. . The second transfer drive motor 102 is a rotational drive source of a drive roller (35f) that moves the second intermediate transfer belt (31) (not shown) endlessly, and its rotational speed is controlled by the speed controller 100. . The conveyance drive motor 103 is a rotational drive source of a conveyance drive roller (65a) that moves the conveyance belt (61) (not shown) endlessly, and the rotation speed is controlled by the speed controller 100. The fixing drive motor 104 is a rotational driving source for fixing rollers (56a, b) of a fixing device (56) (not shown), and the rotational speed thereof is controlled by the speed control unit 100. The speed control unit 100 can change the paper conveyance speed by the fixing device (56) and the paper conveyance speed by the conveyance belt (61) by changing the rotation speed of the conveyance drive motor 103 and the fixing drive motor 104. Therefore, in this printer, a speed changing unit that changes the recording medium conveyance speed by the fixing unit and the recording medium conveyance speed by the conveyance belt is configured by a combination of the speed control unit 100, the conveyance driving motor 103, the fixing driving motor 104, and the like. Yes.

  In addition to the various drive motors described above, an image information processing circuit 105, an image area ratio R calculation circuit 106, a paper size sensor 106, a registration sensor 107, an operation display unit 90, and the like are connected to the speed control unit 100.

  The image information processing circuit 105 generates a signal for causing each exposure unit of each process unit (not shown) to perform optical scanning based on image information sent from a personal computer (not shown) or the like. Further, the image area ratio R is calculated based on the printout paper size information and the output pixel number information included in the image information, and the result is sent to the speed control unit 100. The image area ratio R is the ratio of the area of the image area where the toner adheres to the total area of the transfer paper P. Therefore, in this printer, the image information processing circuit 105 performs the first Y, M, C, and K toner images that are the first visible image and the second Y, M, C, and K toner images that are the second visible image. It functions as an image area ratio R calculating means for calculating the area ratio on the transfer paper P.

  Further, the image information processing circuit 105 stores predetermined rear end margin information corresponding to A3 size paper that is the maximum size transfer paper P that can be accommodated in the paper feed cassette 50. The printout paper size information included in the image information sent from the personal computer or the like is A3 size, and the image information outputs an image to the margin area on the rear end side of the A3 size paper. When the image information is the content, the following processing is performed. That is, a process for prohibiting optical scanning on the photosensitive region corresponding to the trailing edge margin area so that an image is formed only in the leading edge area without forming an image in the trailing edge margin area. It is. Therefore, in this printer, the image information processing circuit 105 forms the latent image by the latent image forming unit on the latent image carrier region corresponding to the trailing edge side blank region of the maximum size recording member that can be stored in the recording member storage unit. It also functions as a latent image formation prohibiting means for prohibiting the above.

  The paper size sensor 106 detects the size of the transfer paper P accommodated in a paper feed cassette (50) (not shown) by a known technique and outputs a detection signal to the speed control unit 100. The registration sensor 107 detects the leading edge of the transfer paper P sent out from the registration roller pair (54) and outputs a detection signal to the speed control unit 100.

  In this printer, when the user operates the operation display unit 90, the thickness D, which is the characteristic of the transfer paper P stored in the paper feed cassette (50), is divided into three levels: a thin paper value, a plain paper value, and a thick paper value. And input to the speed control unit 100. In this configuration, the operation display unit 90 functions as a characteristic acquisition unit that acquires the characteristics of the recording medium accommodated in the recording medium accommodation unit.

  In FIG. 2 described above, the length L1 of the post-transfer pre-fixing conveyance path from the transfer separation position P1 to the fixing receiving position P2 is as follows. That is, the value is larger than the value obtained by subtracting the trailing edge margin, which is the dimension in the paper conveyance direction of the trailing edge side margin area, from the longitudinal dimension which is the dimension in the conveyance direction of A3 size paper. In such a configuration, at the timing immediately before the leading edge of the A3 size paper reaches the fixing receiving position P2 of the fixing device 56, the rear end of the image area of the A3 size paper is advanced ahead of the transfer separation position P1 of the double-sided transfer device. Can do. At this time, most of the entire area of the A3 size paper has passed through the double-sided transfer device, and only a slight trailing edge margin area of at most several centimeters remains in the double-sided transfer device. Even if a speed difference is provided between the post-transfer conveyance speed V2 which is the paper conveyance speed by the fixing rollers 56a and 56b and the conveyance belt 61 and the transfer speed V1 which is equal to the paper conveyance speed by the double-side transfer device at this timing, the paper conveyance performance is provided. Does not have a major impact on For example, even if the post-transfer conveyance speed V2 is slower than the transfer speed V1, a situation in which A3 size paper is greatly curved or jammed between the double-side transfer device and the fixing device 56 does not occur. For example, even if the post-transfer conveyance speed V2 is made faster than the transfer speed V1 and the trailing edge side margin area of A3 size paper is slipped on the second intermediate transfer belt 31, the trailing edge side margin area has no image. Does not exist. For this reason, the image of the unfixed image is not disturbed by the slip.

  When printing out is performed on a transfer sheet P smaller than A3 size paper, the rear end of the transfer sheet P is transferred on both sides before the leading end of the transfer sheet P reaches the fixing receiving position P2 of the fixing device 56. This is advanced before the transfer separation position P1 of the apparatus. Then, the transfer paper P is not supported by the fixing device 56 or the double-sided transfer device, but is transported only by the paper transport belt 61. For this reason, even if the post-transfer conveyance speed V2 is higher than the transfer speed V1, no slip of the transfer paper P on the second intermediate transfer belt 31 occurs.

  Therefore, the speed control unit (100) of the printer sets the linear speed of the fixing rollers 56a and 56b and the conveyance belt 61 to the same speed as the transfer speed until the predetermined timing comes from the start of image formation. Is supposed to change. Specifically, first, a post-transfer discharge timing based on the paper feed start timing by the registration roller pair (54), the transfer speed, the printout paper size information, and the distance from the registration position to the transfer separation position P1. t1 is calculated. The post-transfer discharge timing t1 is the timing at which the trailing edge of the transfer paper P reaches the transfer separation position P1 of the double-side transfer device. However, when the printout paper size information is A3 size, the post-transfer discharge timing is the timing at which the boundary between the trailing edge margin area and the non-margin area reaches the transfer separation position P1 instead of the trailing edge of the A3 size paper. Calculate as t1. Immediately after the post-transfer discharge timing t1, the linear speeds of the fixing rollers 56a and 56b and the conveying belt 61 are changed as necessary. However, the linear velocity of the fixing rollers 56a and 56b and the linear velocity of the conveying belt 61 are the same.

  By such a linear speed control, the amount of fixing heat per unit time for the transfer paper P is changed by changing the paper conveyance speed in the fixing device 56 as necessary. Then, the amount of heat for fixing the transfer paper P can be changed without changing the heating temperature by the fixing device 56. For this reason, even when the required fixing heat amount becomes considerably large, the fixing process is performed on the transfer paper P with a sufficient heating amount without significantly increasing the heating temperature by the fixing device 56. Even when the required fixing heat amount is considerably small, the fixing process is performed with an appropriate heating amount without excessively heating the transfer paper P. Therefore, it is possible to avoid an increase in cost due to setting the heat resistance of the fixing device 56 on the assumption that the necessary fixing heat amount is considerably increased. In addition, it is possible to suppress the occurrence of fixing failure and hot offset due to the required amount of fixing heat changing for each printout. Furthermore, since the transfer speed V1 and the post-transfer conveyance speed V2 can be made different, it is possible to suppress the occurrence of fixing failure and hot offset caused by setting the fixing speed to the same speed as the transfer speed regardless of the required fixing heat amount. You can also.

The speed control unit (100) is configured to change the post-transfer conveyance speed V2 based on the following four parameters listed.
(A) Image area ratio R of output image
(B) Thickness D of transfer paper P
(C) Output surface mode information M indicating which mode is single-sided or double-sided
(D) Number of image colors (number of overlays) C on each side of transfer paper P

  Specifically, in this printer, when the fixing speed is the same as the transfer speed V1, the following transfer paper P can be heated with a heating amount corresponding to the necessary fixing heat amount. That is, it is plain paper (output surface mode information = M, thickness D = plain paper value) on which a full-color image (color number C = 4) having an image area ratio R of 50% is transferred on both sides. Hereinafter, the transfer paper P is referred to as a heating amount standard paper.

  In addition, the speed control unit (100) of the printer stores an algorithm that can determine an appropriate post-transfer conveyance speed V2 corresponding to the required amount of fixing heat based on the four parameters described above. This algorithm includes, for example, a relational expression “V2 = V1 × speed change coefficient K” and a formula for obtaining the speed change coefficient K in this relational expression. According to the latter equation, output surface mode information = M, average value of image area ratio R on both sides = 50 [%], number of colors C = 4 (both sides), thickness D = plain paper value Further, the speed change coefficient K is obtained as “1”. In this case, even after the post-transfer discharge timing t1, the post-transfer conveyance speed V2 does not change, and the fixing process is performed at the same speed as the transfer speed V1. Further, when the necessary fixing heat amount of the transfer paper P after the transfer processing is larger than the necessary heating amount of the heating amount standard paper, the speed change coefficient is obtained as a value smaller than “1”. Accordingly, in this case, the post-transfer conveyance speed V2 becomes slower than the transfer speed V1 immediately after the post-transfer discharge timing t1 arrives. Further, when the necessary fixing heat amount of the transfer paper P after the transfer process is smaller than the necessary heating amount of the heating amount standard paper, the speed change coefficient is obtained as a value larger than “1”. Therefore, in this case, immediately after the post-transfer discharge timing t1 arrives, the post-transfer conveyance speed V2 becomes faster than the transfer speed V1.

  The conveyance speed control unit (100) calculates a pre-fixing conveyance completion timing t2 immediately after calculating the post-transfer discharge timing t1. This pre-fixing conveyance completion timing t <b> 2 is a time point when the trailing edge of the transfer sheet P conveyed toward the fixing device 56 while being held on the surface of the conveyance belt 61 is separated from the conveyance belt 61. It is calculated based on the post-transfer discharge timing t1, the post-transfer conveyance speed V2, the distance from the transfer separation position P1 to the transfer paper separation position of the conveyance belt 61, and the like.

  In the continuous print mode in which images over a plurality of pages are continuously printed out on a plurality of transfer sheets P, it is necessary to determine the subsequent image formation start timing based on the post-transfer conveyance speed V2 of the preceding image formation process. . This is for the reason explained below. That is, when the post-transfer conveyance speed V2 is always the same as the transfer speed V1 during the continuous printing operation, each image forming process is performed at equal time intervals so as to provide a predetermined inter-paper area between the transfer sheets. You can start with. However, in the case where the post-transfer conveyance speed V2 and the transfer speed V1 are different from each other, such a case causes a problem in a case where “V2 <V1” is set. Subsequent transfer paper P conveyed at the transfer speed V1 faster than the post-transfer conveyance speed V2 at the secondary transfer nip gradually catches up with the transfer paper P on the preceding conveyance belt 61 and rubs on it. It will be done. Therefore, the subsequent image formation start timing is determined based on the post-transfer conveyance speed V2 of the preceding image forming process. Specifically, when the post-transfer conveyance speed V2 is made different from the transfer speed V1 in the preceding image forming process, V1 and V2 are made different at least from the post-transfer discharge timing t1 to the pre-fixing conveyance completion timing t2. It will be. For this reason, if the subsequent image formation is started at a timing at which the leading end side of the succeeding transfer paper P reaches the transport belt 31 prior to the pre-transfer transport completion timing t2, the succeeding transfer paper P is removed. The rubbing is caused by the difference in linear velocity between the conveyance belt 61 and the second intermediate transfer belt 31. Accordingly, the pre-transfer conveyance completion timing t2 is obtained based on the post-transfer conveyance speed V2 of the preceding image forming process, and the subsequent transfer paper P is subsequently transferred so that the leading end side of the subsequent transfer paper P reaches the conveyance belt 31. The image formation start timing is determined.

  Depending on the size of the transfer paper P, a plurality of transfer papers P continuously sent out from the double-side transfer device are collectively delivered onto the transport belt 61, and then the post-transfer transport speed V2 is controlled to be different from the transfer speed V1. The speed control unit (100) is configured so that For example, in the case of B5 size transfer paper P, when transporting the inside of the apparatus with the short direction of the transfer paper P aligned with the moving direction of the transport belt 61, the B5 size transfer paper P is transferred onto the transport belt 61 by 2. Can be placed side by side (B5 size horizontal dimension = 148 mm, A3 size vertical dimension = 420 mm). Therefore, in such a case, when printing is continuously performed on three or more transfer sheets P, the following operation is executed. That is, first, an image forming process for the first transfer sheet and a second transfer sheet are performed at a timing such that the preceding two transfer sheets P can be conveyed between predetermined relatively short sheets. The image forming process for the image processing is executed continuously. Then, after the two transfer sheets P are continuously discharged from the double-side transfer device, strictly speaking, after passing the transfer separation position P1 to the rear end of the image of at least the second transfer sheet P, The post-transfer conveyance speed V2 is made different from the transfer speed V1. The timing at which the leading edge of the third transfer sheet P can be transferred to the conveyance belt 61 immediately after the trailing edge of the second transfer sheet P being transferred to the fixing device 56 is separated from the conveyance belt 61. Then, the image forming process for the third transfer sheet is started. In this way, in the continuous printing operation, it is possible to efficiently close the gap between sheets and shorten the image forming time.

  The conveying belt unit 60 is a charge applying unit that applies a charge having the same polarity (for example, negative polarity) as the toner of the first toner image or the second toner image to the surface of the conveying belt 61 before receiving the transfer paper P from the double-side transfer device. A charge-providing charger 63 is provided. The surface of the conveyance belt 61 to which the charge is applied by the charge applying charger 63 causes the transfer paper P received from the double-side transfer device to be electrostatically attracted to the front surface by the charge. The conveyance belt unit 60 enhances the adhesion between the transfer paper P and the conveyance belt 61 by this electrostatic adsorption, thereby suppressing subtle friction between the transfer paper P and the belt surface due to slight vibration of the conveyance belt 61. Thus, it is possible to suppress disturbance due to rubbing of the unfixed image on the transfer paper P.

  P3 in the drawing indicates a pre-fixing conveyance completion position which is a transfer separation position in the circumferential direction of the conveyance belt 61 before the transfer paper P is transferred to the fixing device 56. The conveyance belt unit 60 has a charge removal charger 64 that is a charge removal means for discharging the area of the conveyance belt 61 immediately before entering the conveyance completion position P3 before fixing. Prior to entering the pre-fixing conveyance completion position P <b> 3, the surface of the conveyance belt 61 to which the charge is applied by the charge application charger 63 and electrostatically attracts the transfer paper P is discharged by the charge removal charger 64. Thereby, the electrostatic adsorption force between the transport belt 61 and the transfer paper P is lost, and the transfer paper P is easily separated from the surface of the transport belt 61. Then, the transfer paper P is gradually separated from the belt from the leading end to the trailing end with the movement of the conveying belt 61 at the pre-fixing conveyance completion position P3, and is transferred to the fixing device 56. By neutralizing the transport belt 61 on which the transfer paper P is electrostatically attracted by the static elimination charger 64, the transfer paper P cannot be satisfactorily separated from the belt at the pre-fixing transport completion position P3, causing a jam. It is possible to suppress such a situation.

  The operation start timing of the charge applying charger 63 is determined based on the timing at which the leading edge of the transfer paper P discharged from the double-side transfer device starts to contact the transport belt 61. Specifically, after the print command is issued and the driving of the transport belt 61 is started, the transport belt region that is to come into contact with the leading edge of the transfer paper P discharged from the double-side transfer unit is opposed to the charge applying charger 63. Immediately before entering the position, the operation of the charge applying charger 63 is started. By determining the operation start timing as described above, it is necessary to start the operation of the charge applying charger 63 immediately after the printing command operation is issued, and to apply the charge belt region that does not contact the transfer paper P, that is, to apply the charge. It is possible to suppress wasteful energy consumption due to the application of electric charges to the conveyance belt region where there is no ink.

The conveyance belt 61 has a belt base material made of polyimide or polyamide, the surface resistance value is adjusted to 10 ⁸ to 10 ¹³ [Ω / □], and the volume resistivity is 10 ⁶ to 10 ¹² [Ω · cm. ] Adjusted to be used. Since polyimide and polyamide are resins having excellent heat resistance, it is possible to suppress deterioration of the conveyance belt 61 due to heat conduction from the fixing device 56. Further, by adjusting the electrical resistance value as described above, the transfer belt P can be reliably electrostatically adsorbed by reliably holding the charge applied by the charge applying charger 63 to the transport belt 61. it can.

  FIG. 4 is an enlarged configuration diagram illustrating an opposing region between the double-side transfer device and the conveyance belt unit 60 in an enlarged manner. P4 in the drawing indicates a conveyance receiving position which is a transfer paper leading edge contact start position in the belt circumferential direction of the conveyance belt 61 when the transfer paper P is received from the double-side transfer device. In this printer, the distance between the transfer separation position P1 of the double-side transfer device and the conveyance receiving position P4 of the conveyance belt unit 60 is set to 30 to 60 [mm]. This is for the reason explained below. That is, among the six support rollers 65 that support the conveyor belt 61 on the inner circumferential surface of the loop, the drive roller 65a shown in the drawing is disposed closest to the transfer separation position P1 of the double-side transfer device. . The transport belt unit 60 has a transport receiving position P4 at a belt-wrapped portion by the drive roller 65a. As the distance between the transfer separation position P1 and the conveyance receiving position P4 is decreased, the transfer paper delivery from the double-sided transfer device to the conveyance belt 61 can be improved. However, if it is set to less than 30 [mm], it is necessary to use a driving roller 65a having a very small diameter and being easily bent, and it becomes difficult to support the transport belt 61 satisfactorily. According to the experiments by the present inventors, unless the supporting roller supporting the conveying belt 61 is at least 20 [mm] or more in diameter, the conveying belt 61 is favorably moved endlessly by the axial roller deflection. I find it impossible to do that. Therefore, in this printer, the distance between the transfer separation position P1 and the conveyance receiving position P4 is set to 30 [mm] or more, and the conveyance belt 61 is used by using a drive roller 65a having a diameter of 20 [mm] or more. The endless movement is good. On the other hand, when the distance between the transfer separation position P1 and the transport receiving position P4 is greater than 60 [mm], when a thin paper is used as the transfer paper P, the leading edge of the transfer paper protruded from the transfer separation position P1 of the double-side transfer device. The leading edge of the transfer paper abuts on the conveyance belt region on the upstream side of the conveyance receiving position P4 due to the side deflection. Then, the transfer paper P is vibrated delicately due to the impact at the end of the contact, which may disturb the unfixed toner image on the transfer paper P. Therefore, in this printer, the distance between the transfer separation position P1 and the conveyance receiving position P4 is set to 60 [mm] or less, thereby suppressing the disturbance of the unfixed toner image due to the bump. On the other hand, if the driving roller 65a of the conveying belt unit 61 has a diameter larger than 40 [mm], it is difficult to set the distance between the transfer separation position P1 and the conveying receiving position P4 to 60 [mm] or less. become. Therefore, in the present printer, a driving roller 65a having a diameter of 40 [mm] or less is used.

  Of the two intermediate transfer belts of the double-sided transfer device, the second intermediate transfer belt 31 plays a role of transferring the transfer paper P to the transport belt 61. Of the plurality of support rollers for supporting the second intermediate transfer belt 31 on the back surface of the loop, the separation roller 35c in the drawing is disposed closest to the transport receiving position P4 of the transport belt unit 60. If the separation roller 35c having a diameter of less than 20 [mm] is used, it becomes difficult to move the second intermediate transfer belt 31 endlessly due to the bending. If a diameter larger than 40 [mm] is used, it becomes difficult to set the distance between the transfer separation position P1 and the transport receiving position P4 to 60 [mm] or less. Therefore, in this printer, the separation roller 35c also has a diameter of 20 to 40 [mm].

  FIG. 5 is an enlarged configuration diagram illustrating an enlarged area where the conveyance belt unit 60 and the fixing device 56 face each other. As the fixing rollers 56a and 56b of the fixing device 56, it is necessary to use a heat source such as a halogen lamp, which has a diameter larger than that of a general roller. If the diameter is equal to that of a general roller, a special heat source needs to be provided, resulting in an increase in cost. Therefore, in this printer, the distance between the pre-fixing conveyance completion position P3 and the fixing receiving position P2 is set to 40 [mm] or more. In this way, as the fixing rollers 56a and 56b, a relatively large diameter using an inexpensive one provided with a general heat source is used to avoid an increase in cost.

  On the other hand, when the distance between the pre-fixing conveyance completion position P3 and the fixing receiving position P2 is larger than 60 [mm], as in the case between the double-sided transfer device and the conveyance belt, when the thin paper is used as the transfer paper P, before fixing. The leading edge of the transfer paper projected from the conveyance completion position P3 is abutted against the fixing roller area upstream of the fixing nip entrance. However, even with such abutting, the transfer paper P is strongly electrostatically attracted to the transport belt 61, so that the unfixed toner image is hardly disturbed by the vibration of the transfer paper P. Therefore, the distance between the pre-fixing conveyance completion position P3 and the fixing receiving position P2 can be made larger than 60 [mm]. If this distance is too close, the conveying belt 61 is likely to be deteriorated by heat from the fixing rollers 56a and 56b. Therefore, it is advantageous for the life of the conveying belt 61 to be larger than 60 [mm]. However, if it is too large, jamming is likely to occur due to deterioration in paper delivery from the conveyor belt 61 to the fixing device 56. According to the experiments by the present inventors, when the thickness is larger than 100 [mm], when thin paper is used as the transfer paper P, it becomes easy to generate a jam suddenly. Therefore, in this printer, the distance between the pre-fixing conveyance completion position P3 and the fixing receiving position P2 is set to 100 [mm] or less to suppress jamming between the conveyance belt 61 and the fixing device 56.

  As previously shown in FIGS. 2 and 4, in this printer, the first intermediate transfer belt 9 and the second intermediate transfer belt 31 are brought into contact with each other to form a secondary transfer nip. The double-side transfer means is configured to transfer the toner image onto both sides of the transfer paper P while the transfer paper P is sandwiched and conveyed by the secondary transfer nip. In such a configuration, the transfer paper P can be more reliably fed from the double-side transfer device to the transport belt 61 as compared with the case where the transfer paper P is transported without being pinched at the nip.

  FIG. 6 is an enlarged configuration diagram showing the secondary transfer nip and the surrounding configuration. In the secondary transfer nip, the first intermediate transfer belt 9 and the second intermediate transfer belt 31 are sandwiched between the nip entrance first roller 13a and the nip entrance second roller 35a. The nip entrance first roller 13a includes a roller portion A having at least a surface made of an elastic material, and a shaft member B protruding from both ends in the axial direction thereof. Both ends of the shaft member B of the nip entrance first roller 13a are rotatably supported by bearings 150, and the shaft member B rotatably supports the eccentric roller 151 in the vicinity of each of the bearings 150. The two bearings 150 that support the shaft member B of the nip entrance first roller 13a are each urged toward the nip entrance second roller 35a by the coil spring 152. On the other hand, the nip entrance second roller 35a also includes a roller portion C having at least a surface made of an elastic material, and a shaft member D protruding from both ends in the axial direction thereof. Both ends of the shaft member D of the nip entrance second roller 35a are rotatably supported by bearings 153, and the shaft member D rotatably supports a disc-shaped abutting roller 154 in the vicinity of each of the bearings 153. doing. The cam surface of the eccentric roller 151 that is rotatably supported by the shaft member B of the nip entrance first roller 13a and the abutment roller 154 that is rotatably supported by the shaft member D of the nip entrance second roller are in contact with each other. The distance between the axes of both rollers is kept constant.

  FIG. 7 is a side view showing the eccentric roller 151 and the abutting roller 154. An eccentric roller 151 that is rotatably supported by a shaft member of a nip entrance first roller (not shown) has a gear portion at a part of its outer periphery. This gear portion meshes with a driving gear 155 that is rotated by a drive system (not shown). Further, the cam surface of the eccentric roller 151 is not provided with gear irregularities, and abuts against an abutment roller 154 that is rotatably supported by a shaft member of a nip entrance second roller (not shown). When the eccentric roller 151 is rotated clockwise by a predetermined angle in the drawing by the rotation of the driving gear 155, the contact force between the cam surface of the eccentric roller 151 and the abutting roller 154 increases. Then, the shaft member B of the nip entrance first roller moves upward in the figure, and the distance between the shafts of both rollers increases. Then, the contact pressure between the two entrance rollers in the secondary transfer nip is weakened. On the other hand, when the eccentric roller 151 is slightly rotated counterclockwise in the drawing from this state, the shaft member B of the first roller at the nip entrance moves downward in the drawing to increase the contact pressure between the two rollers. It is done. As described above, the printer is provided with the contact pressure adjusting means for adjusting the contact pressure between the first intermediate transfer belt and the second intermediate transfer belt in the secondary transfer nip. Then, by adjusting the contact pressure in this way, it is possible to adjust the transfer conditions by changing the transfer pressure at the secondary transfer nip as necessary.

  Although the contact pressure adjusting means for adjusting the contact pressure on the inlet side of the secondary transfer nip has been described, the contact pressure on the outlet side is also the same as that of the first nip outlet roller (13B9 and the second nip outlet). It can be adjusted by changing the distance between the shaft and the roller (35b), and the combination of the first roller (13a) at the nip entrance and the second roller (35a) at the nip entrance sandwiches both intermediate transfer belts. It functions as a pair of pressure rollers that pressurize both intermediate transfer belts while forming a secondary transfer nip.The combination of the nip outlet first roller (13b) and the nip outlet second roller (35b) is also in the middle. It functions as a pair of pressure rollers that pressurize both intermediate transfer belts while sandwiching the transfer belt to form a secondary transfer nip.

  FIG. 8 is a partial perspective view showing the first intermediate transfer belt 9 and the second intermediate transfer belt 31. In the figure, a first intermediate transfer belt 9 and a second intermediate transfer belt 31 are endless belt-like belt portions 9a and 9b, respectively, and belt inner peripheral surfaces over the entire belt circumference in the vicinity of both ends in the width direction. Belt protrusions 9b and 31b protruding from the belt. The end face of a support roller (not shown) that supports the belt abuts against the belt detent protrusions 9b and 31b, thereby preventing the wheel from being removed from the support roller due to the belt deviating running.

  FIG. 9 is a schematic diagram illustrating a configuration around the secondary transfer nip of the first transfer unit. In the figure, a nip inlet first roller 13a and a nip outlet first roller 13b are support rollers for supporting the first intermediate transfer belt 9 on the inner circumferential surface of the loop at the location of the secondary transfer nip. The first cleaning backup roller 13c is disposed adjacent to the nip outlet first roller 13b on the downstream side in the belt moving direction, and loops the first intermediate transfer belt 9 at a location different from the secondary transfer nip. It is a support roller supported by an inner peripheral surface. The secondary transfer nip upstream roller 13h is disposed adjacent to the nip entrance first roller 13a on the upstream side in the belt moving direction, and the first intermediate transfer belt 9 is disposed at a location different from the secondary transfer nip. It is a support roller supported by the loop inner peripheral surface. Each of the first cleaning backup roller 13c and the secondary transfer nip upstream roller 13h is longer than the nip inlet first roller 13a and the nip outlet first roller 13b by the dimension of 2 × L2 in the axial direction of the roller portion. It has become. Then, one end of the roller portion is disposed so as to be positioned outward in the axial direction by L2 from one end of the roller portion of the nip inlet first roller 13a and the nip outlet first roller 13b.

  An inner dimension L4 between two belt detent protrusions 9b provided near both ends of the first intermediate transfer belt 9 is slightly larger than the length L3 of the first cleaning backup roller 13c and the secondary transfer nip upstream roller 13h. It has become. Thus, the first intermediate transfer belt 9 meanders left and right within the range of “(length L4−length L3) / 2”. As long as the first intermediate transfer belt 9 meanders in this range, the belt detent protrusion 9b does not hit the roller portion of the nip inlet first roller 13a or the nip outlet first roller 13b having a short roller portion.

  In the secondary transfer nip, the first intermediate transfer belt 9 is pressed by the pair of pressure rollers, and the belt is compressed and deformed. If the belt detent protrusion 9b and the roller portion are brought into contact with each other in the vicinity of the portion that is compressed and deformed in this way, an excessive force may be applied to the portion that is compressed and deformed, and the belt may be damaged. . However, in this printer, the roller portions arranged on the upstream side and the downstream side of the nip are made longer than the pair of pressure rollers that pressurize the first intermediate transfer belt 9, and the belts are offset by the roller portions. This prevents the belt detent protrusion 9b from hitting the roller portion in the vicinity of the belt portion that is compressively deformed. Therefore, it is possible to avoid damage to the belt due to such abutment.

  In the second transfer unit 30 as well, the separation roller 35c and the driving roller 35f are such that the length of the roller portion is larger than the length of the roller portion of the nip inlet second roller 35a or the nip outlet second roller 35b. Similarly, the second intermediate transfer belt is prevented from being damaged. In addition, as in this printer, it is desirable that the length of the roller portion disposed adjacent to the pressure roller upstream or downstream of the secondary transfer nip is longer than that of the pressure roller pair. What is necessary is just to make the roller part length of at least 2 roller other than a roller longer than a pressure roller pair.

  In FIG. 1 described above, the second transfer unit 30 is pressed against the second intermediate transfer belt 31 from the front surface in a region where the first intermediate transfer belt 9 and the second intermediate transfer belt 31 face each other. A second pressing roller 34 is provided as a pressing member that curves the endless moving track toward the inner side of the belt loop. And the conveyance belt unit 60 is arrange | positioned so that most conveyance belt 61 may be located in the belt curve area | region by this 2nd press member. By doing so, as shown in the figure, while securing necessary spaces between the first intermediate transfer belt 9 and the conveyance belt 61 and between the conveyance belt 61 and the second intermediate transfer belt 31, respectively. These three belts can be compactly arranged in parallel to prevent the apparatus from becoming large.

  In FIG. 4 described above, of the plurality of support rollers that support the second intermediate transfer belt 31 pressed by the second pressing roller 34 on the inner circumferential surface of the loop, the belt moving direction upstream side of the second pressing roller 34. The support roller disposed adjacent to the pressing member is a separation roller 35c. In this printer, the separation roller 35c has a diameter of 20 to 30 [mm]. The reason for using such a diameter is because of the same reason as the conveyance driving roller 65a of the conveyance belt unit 60.

  The belt winding angle θ of the second intermediate transfer belt 31 with respect to the separation roller 35c of the second transfer unit 30 is set to 90 to 120 [°]. This is for the following reason. That is, in FIG. 4, in order to make the belt winding angle θ smaller than 90 [°], it is necessary to dispose the second pressing roller 34 inside the belt loop from the state shown in the drawing. If arranged in this way, the stretched shape of the second intermediate transfer belt 31 is bent into a wedge shape, and the addition to the second intermediate transfer belt 31 is rapidly increased to shorten its life. Further, when the belt winding angle θ is larger than 120 [°], it is difficult to make the distance between the transfer separation position P1 of the double-sided transfer device and the transport receiving position P4 of the transport belt unit 60 equal to or less than 60 [mm]. Become. By setting the belt winding angle θ in the range of 90 to 120 [°], the distance between the transfer separation position P1 and the conveyance receiving position P4 can be easily set to 60 without applying excessive stress to the second intermediate transfer belt 31. [Mm] or less.

  As shown in FIG. 1, in the second transfer unit 30, the second intermediate transfer belt 31 is stretched in a horizontally long flat shape so as to take a space in the horizontal direction rather than the vertical direction. On the other hand, in the first transfer unit 8, the first intermediate transfer belt 9 is stretched in a horizontally long shape so as to take a space in the horizontal direction rather than the vertical direction. The first intermediate transfer belt 9 and the second intermediate transfer belt 31 are arranged side by side in the vertical direction so that at least some of the projected images in the vertical direction overlap each other. That is, in this printer, the horizontally long first intermediate transfer belt 9 and the horizontally long second intermediate transfer belt 31 are arranged side by side in the vertical direction. In this configuration, the horizontally long first intermediate transfer belt 9 and the horizontally long second intermediate transfer belt 31 are arranged side by side in a horizontal direction, and the vertical direction and the horizontal direction are balanced. Can be an internal layout.

  The example in which the first intermediate transfer belt 9 and the second intermediate transfer belt 31 are stretched in a horizontally long shape has been described. However, the first intermediate transfer belt 9 and the second intermediate transfer belt 31 are each stretched in a vertically long shape so as to take a space in the vertical direction rather than in the horizontal direction. May be. In this case, as the conveyor belt unit 61, a conveyor belt 61 that is stretched in a vertically long shape is used, and these three belts are arranged in the horizontal direction so that at least some of the projected images in the horizontal direction overlap each other. It may be arranged side by side. By doing in this way, it is possible to make the internal layout balanced in the vertical direction and the horizontal direction, similarly to the printer according to the first embodiment.

  In this printer, as shown in the figure, a first unit group composed of four first process units 7Y, 7M, 7C, and 7K, and a second unit group composed of four second process units 40Y, 40M, 40M, 40C, and 40K. Both are arranged as follows. In other words, each of the corresponding intermediate transfer belts is disposed on the lower side in the vertical direction. By doing so, the first process unit 7Y, M, C, K and the second process unit 40Y, M, C, K can use the same specifications.

  The reason that the common specification can be used is as follows. 10 shows an example in which the first unit group is disposed above the first intermediate transfer belt 9 and the second unit group is disposed below the second intermediate transfer belt 31. FIG. In FIG. 11, FIG. 11 is an enlarged configuration diagram showing the first process unit 7Y in this example. The first process unit 7Y disposed on the upper side of the first intermediate transfer belt 9 is in the vicinity of the primary transfer nip for Y where the photoreceptor 1Y and the first intermediate transfer belt 9 are in contact with each other, and upstream of this. The developing device 5Y is disposed on the side. A drum cleaning device 2Y is disposed near the primary transfer nip and downstream of the primary transfer nip. Assume that the same specifications as those of the first process unit 7Y are used as the second process unit. Then, as shown in FIG. 12, the second process unit 40Y disposed below the second intermediate transfer belt 31 must be disposed in a posture in which the top and bottom are reversed with respect to the first process unit. This is because the photosensitive member 41Y is exposed only in the region from the developing device 45Y to the drum cleaning device 42Y, and the photosensitive member 41Y is brought into contact with the second intermediate transfer belt 31 above it in this region. Because there is no other way but to reverse the heaven and earth. When the top and bottom are reversed, the developing device 45Y is also reversed and the toner in the developing device is deposited on the ceiling instead of the original bottom surface. As a result, the toner cannot be normally conveyed in the developing device 45Y. In addition, as shown in the figure, if the photosensitive member 41Y is moved in the same direction as the surface movement direction of the second intermediate transfer belt 31 at the primary transfer nip, the photosensitive member 41Y must be rotated clockwise in the drawing. I must. In this case, the surface of the photoconductor must be processed in the order of development process → primary transfer process → cleaning process, but the reverse process is followed. Therefore, the same specification as that of the first process unit cannot be used as the second process unit, and the second process unit needs to have an internal layout suitable for being disposed below the intermediate transfer belt. There is.

  On the other hand, as shown in FIG. 1, when the first unit group and the second unit group are arranged on the lower side in the vertical direction of the corresponding intermediate transfer belt, those of common specifications can be used. FIG. 13 is an enlarged configuration diagram showing the second process unit of the printer. The process units for each color have substantially the same configuration except that the color of the toner to be used is different, so the subscripts Y, M, C, and K are omitted in FIG. In the figure, a photoconductor 41 that contacts the second intermediate transfer belt 31 moving from the left side to the right side in the figure rotates clockwise in the figure. A developing device 45 is disposed in the vicinity of the primary transfer nip and upstream of the primary transfer nip. A drum cleaning device 42 is disposed in the vicinity of the primary transfer nip and on the downstream side of the primary transfer nip. It is assumed that the second process unit 40 having such a configuration is reversed in the horizontal direction so as to have a line-symmetric posture with respect to the virtual line y extending in the vertical direction. Then, it is assumed that the one with the posture is disposed below the first intermediate transfer belt and used as the first process unit. Then, as shown in FIG. 14, the developing device 5 is not turned upside down, and the photosensitive member 1 is not rotated backward so as to perform the reverse process to the surface of the photosensitive member 1. The first process unit 7 can be disposed in a normal state. This is because the first process unit 7 and the second process unit 40 are both disposed below the corresponding intermediate transfer belt.

  Note that the first process unit 7 and the second process unit do not necessarily have to be arranged in a line-symmetric posture with respect to the virtual line y. Either one of them may be disposed at a slight angle from the line-symmetric posture so as not to hinder the toner conveyance in the developing device. In this printer, as shown in FIG. 1, the first process unit 7 is disposed in such a manner as being slightly inclined. By tilting in this way, it is possible to satisfactorily mesh the unevenness of the layout around the photosensitive member between the first process units that are adjacent to each other (hereinafter referred to as the adjacent relationship). Specifically, in the example shown in the figure, a convex portion formed by the developing device 5 on the other side is formed in the concave portion between the drum cleaning device 2 and the charging device 4 in one of the two first process units adjacent to each other. I'm biting. That is, each first process unit is disposed between two first process units that are adjacent to each other in such a posture that parts of the projected images in the vertical direction overlap each other. In such an arrangement, as shown in the figure, the unit interval of the first unit group can be narrower than that of the second unit group. The horizontal dimension of one unit group can be shortened. As a result, the circumferential length of the bracket-shaped first intermediate transfer belt 9 is shortened to be the same as the flat second intermediate transfer belt 31. With such a configuration, it is possible to manufacture each intermediate transfer belt with the same mold, thereby reducing the cost of each. It is also possible to use exactly the same intermediate transfer belts.

  If the process units in one unit group and the process units in the other unit group are arranged in a non-axisymmetric posture with respect to the virtual line y as in this printer, the unit Instead of being able to close the interval, the following disadvantages occur. In other words, in such a configuration, one process unit is disposed in an inclined posture with respect to the other process unit. In such an arrangement, the photosensitive member exposed area is larger than the case where the photosensitive member in the inclined posture is arranged in a line-symmetrical posture so that the photosensitive member in the inclined posture is sufficiently brought into contact with the intermediate transfer belt. A large area from the developing device to the drum cleaning device must be secured. As a result, the degree of freedom of layout around the photosensitive member in the process unit is deteriorated.

  In order to dispose both the first process unit 7 and the second process unit 40 vertically below the first intermediate transfer belt 9 and the second intermediate transfer belt 31, the first intermediate transfer belt 9 and the second process unit 40 are arranged. The first unit group needs to be positioned between the intermediate transfer belt 31. Therefore, in the printer, the first intermediate transfer belt 9 is bent toward the inner side of the loop by the pressing by the first pressing roller 12, and the first unit so that most of the first unit group is positioned in the belt bending region. A group is arranged. In this way, both the first process unit 7 and the second process unit 40 can be easily arranged vertically below the first intermediate transfer belt 9 and the second intermediate transfer belt 31. it can.

  A secondary transfer nip in which both intermediate transfer belts move while abutting each other is formed as follows. That is, the stretched portion between the nip inlet first roller 13a and the nip outlet second roller 13b in the first intermediate transfer belt 9 is the nip inlet second roller 35a and nip outlet second roller 35b in the second intermediate transfer belt 31. It is formed in contact with the extended portion between the two. The secondary transfer nip includes a belt first nip and a belt second nip. The range of the belt first nip includes an area where both intermediate transfer belts are sandwiched between the nip entrance first roller 13a of the first transfer unit 8 and the nip entrance second roller 35a of the second transfer unit 30, and the front and rear sides thereof. It is an area. Further, the range of the belt second nip includes an area where both intermediate transfer belts are sandwiched between the nip outlet first roller 13b of the first transfer unit 8 and the nip outlet second roller 35b of the second transfer unit 30, and This is an area ahead.

  At the above-described belt first nip, either the four-color toner image on the first intermediate transfer belt 9 or the four-color toner image on the second intermediate transfer belt 31 is batch-transferred onto the transfer paper P at a time. Is done. Further, at the belt second nip following the belt first nip, the other four-color toner image is secondarily transferred onto the transfer paper P all at once. In such a transfer, both four-color toner images are transferred from the belt to the transfer paper P while being in close contact with the transfer paper P. Therefore, compared with the case of transferring without close contact, the toner at the time of transfer is transferred. Scattering (hereinafter referred to as transfer dust) can be suppressed.

  FIG. 15 is a schematic diagram showing an example of the secondary transfer nip and the surrounding configuration. In the figure, the transfer paper P fed into the secondary transfer nip first passes through the belt first nip. Around the belt first nip, a secondary transfer bias having a polarity opposite to that of the toner is applied to the nip entrance second roller 35a. The nip entrance first roller 13a is electrically grounded. Then, in the belt first nip, the four-color toner images on the first intermediate transfer belt 9 are transferred from the nip entrance first roller 13a functioning as a ground roller to the nip entrance second roller 35a functioning as a transfer bias roller. Under the action of electrostatic force toward Then, the toner image is secondarily transferred from the first intermediate transfer belt 9 to the first surface of the transfer paper P. At this time, since the four-color toner image on the second intermediate transfer belt 31 receives an electrostatic force from the second surface side of the transfer paper P toward the second intermediate transfer belt 31 side, it is not secondarily transferred to the second surface. Continue to be restrained by the belt surface. Hereinafter, a method of electrostatically attracting and transferring a toner image from the ground roller side to the transfer bias roller side, such as transfer of a four-color toner image in the illustrated belt first nip, is referred to as an electrostatic attracting transfer method. That's it.

  On the other hand, a secondary transfer bias having the same polarity as the toner is applied to the nip outlet second roller 35b around the belt second nip where the transfer process is performed after the belt first nip. Further, the nip outlet first roller 13b is electrically grounded. Then, in the belt second nip, the four-color toner image on the second intermediate transfer belt 31 is moved from the nip outlet second roller 35b functioning as a transfer bias roller to the nip outlet first roller 13b functioning as a grounding roller. It receives the action of electrostatic force toward Then, the toner image is secondarily transferred from the second intermediate transfer belt 31 to the second surface of the transfer paper P. Hereinafter, such a method of electrostatically extruding and transferring a toner image from the transfer bias side to the ground roller side is referred to as an electrostatic extrusion transfer method.

  The present inventors have confirmed through experiments that the following reverse transfer is not caused when two consecutive secondary transfers as shown in the figure are performed. That is, a phenomenon in which the four-color toner image transferred onto the first surface of the transfer paper P at the belt first nip is reversely transferred from the first surface toward the first intermediate transfer belt 9 at the belt second nip. It is.

  As the secondary transfer nip and its peripheral configuration, the one shown in FIG. 16 may be adopted. In this configuration, the positional relationship between the transfer bias roller and the ground roller is opposite to that shown in FIG. Specifically, in the configuration shown in FIG. 15, the nip inlet second roller 35a and the nip outlet second roller 35b function as a transfer bias roller, while the nip inlet first roller 13a and the nip outlet first roller 13b. Was functioning as a grounding roller. On the other hand, in the configuration shown in FIG. 16, the nip inlet first roller 13a and the nip outlet first roller 13b function as a transfer bias roller, while the nip inlet second roller 35a and the nip outlet second roller 35b are grounded. It functions as a roller. A secondary transfer bias having a polarity opposite to that of the toner is applied to the nip entrance first roller 13a. Then, in the belt first nip, the four-color toner image on the second intermediate transfer belt 31 is electrostatically attracted toward the nip entrance first roller 13a functioning as a transfer bias roller, and the transfer paper P Secondary transfer is performed on the second surface. An electrostatic attraction transfer is performed. On the other hand, a secondary transfer bias having the same polarity as the toner is applied to the nip outlet first roller 13b. Then, in the belt second nip, the four-color toner image on the first intermediate transfer belt 9 is electrostatically pushed out from the side of the nip outlet first roller 13b functioning as a transfer bias roller, and the transfer paper P is transferred to the second nip. Secondary transfer is performed on one surface. Electrostatic extrusion transfer is performed. The present inventors have confirmed through experiments that such reverse transcription does not cause the following reverse transcription. That is, a phenomenon in which the four-color toner image transferred onto the second surface of the transfer paper P at the belt first nip is reversely transferred from the second surface toward the second intermediate transfer belt 31 at the belt second nip. It is.

  Further, the secondary transfer nip and its surrounding configuration shown in FIG. 17 may be adopted. In the drawing, a secondary transfer bias having the same polarity as that of toner is applied to a nip entrance second roller 35a that functions as a transfer bias roller around the belt first nip. Further, a secondary transfer bias having the same polarity as the toner is applied to the nip exit first roller 13b functioning as a transfer bias roller around the belt second nip. Then, the four-color toner image on the second intermediate transfer belt 31 is secondarily transferred to the second surface of the transfer paper P by the electrostatic extrusion method in the belt first nip, and then in the belt second nip. 1 A four-color toner image on the intermediate transfer belt 9 is secondarily transferred to the first surface by an electrostatic extrusion method. The present inventors have confirmed through experiments that such reverse transcription does not cause the following reverse transcription. That is, a phenomenon in which the four-color toner image transferred onto the second surface of the transfer paper P at the belt first nip is reversely transferred from the second surface toward the second intermediate transfer belt 31 at the belt second nip. It is.

  Further, the secondary transfer nip and its surrounding configuration shown in FIG. 18 may be adopted. In the figure, a secondary transfer bias having the same polarity as the toner is applied to the nip entrance first roller 13a that functions as a transfer bias roller around the belt first nip. Further, a secondary transfer bias having the same polarity as the toner is applied to the nip exit second roller 35b functioning as a transfer bias roller around the belt second nip. Then, after the four-color toner image on the first intermediate transfer belt 9 is secondarily transferred to the first surface of the transfer paper P by the electrostatic extrusion method in the belt first nip, The four-color toner image on the two intermediate transfer belt 31 is secondarily transferred to the second surface by the electrostatic extrusion method. The present inventors have confirmed through experiments that such reverse transcription does not cause the following reverse transcription. That is, a phenomenon in which the four-color toner image transferred onto the first surface of the transfer paper P at the belt first nip is reversely transferred from the first surface toward the first intermediate transfer belt 9 at the belt second nip. It is.

  Although the example in which the entrance roller and the exit roller are used as the transfer bias member has been described with reference to FIGS. 15 to 18, a transfer bias member may be provided separately from these rollers. Further, although the example in which the entrance roller and the exit roller are used as the grounding member facing the transfer bias member has been described, a grounding member may be provided separately from these rollers. FIG. 19 shows an example in which the transfer bias member and the grounding member are provided separately from the entrance roller and the exit roller. In the figure, a first transfer bias member 88 that is in contact with the back surface of the first intermediate transfer belt 9 between the first roller 13a at the nip entrance and the first roller 13b at the nip exit is disposed inside the loop of the first intermediate transfer belt 9. Is arranged. This is made of a conductive rubber material and is supported by a support member (not shown) so as to maintain a contact state with the back surface of the belt. In addition, a ground electrode plate 89 that is in contact with the back surface of the second intermediate transfer belt 31 between the nip inlet second roller 35a and the nip outlet second roller 35b is disposed inside the loop of the second intermediate transfer belt 31. ing. The ground electrode plate 89 is a metal plate, a conductive resin plate, a plate with a conductive resin sheet coated on the surface of a non-conductive substrate, or the like, and maintains a contact state with the back surface of the belt by a support member (not shown). So that it is supported. Then, both the first transfer bias member 88 and the nip outlet first roller 13b are opposed to each other through both intermediate transfer belts. A secondary transfer bias having a polarity opposite to that of the toner is applied to the first transfer bias member 88. Further, a secondary transfer bias having the same polarity as the toner is applied to the nip outlet first roller 13b. Then, the four-color toner image on the second intermediate transfer belt 31 is secondarily transferred to the second surface of the transfer paper P by the electrostatic attraction method at the belt first nip, and then at the belt second nip. 1 The four-color toner image on the intermediate transfer belt 9 is secondarily transferred onto the first surface of the transfer paper P by electrostatic extrusion. The present inventors have confirmed through experiments that such transfer does not cause reverse transfer in the belt second nip. Since the ground electrode plate 89 is used both facing the first transfer bias member 88 and the first nip outlet roller 13b, the configuration can be simplified and the component cost can be reduced.

  On the other hand, it is assumed that the secondary transfer nip and its peripheral configuration shown in FIG. 20 are adopted. In the drawing, the arrangement positions of the rollers around the secondary transfer nip are the same as those shown in FIG. However, the polarity of the secondary transfer bias applied to the first roller at the nip outlet is different from that shown in FIG. In this configuration, the four-color toner image on the second intermediate transfer belt 31 is secondarily transferred onto the second surface of the transfer paper P by the electrostatic attraction method at the belt second nip. At the same time, the four-color toner image transferred to the first surface of the transfer paper P at the belt first nip is also electrostatically attracted and reversely transferred from the first surface to the first intermediate transfer belt 9. The present inventors confirmed this by experiment.

When the four-color toner images are sequentially transferred to the opposite surface of the transfer paper P at the belt first nip and the belt second nip, the following two transfer orders are established. That is, the order in which the transfer from the second intermediate transfer belt 31 to the second surface of the transfer paper P is performed after the transfer from the first intermediate transfer belt 9 to the first surface of the transfer paper P is reversed. There are two kinds of order. Further, in consideration of whether the electrostatic attraction abandonment or the electrostatic extrusion method is performed on the upstream side or the downstream side, eight transfer methods are established in total. The present inventors tested all of these eight transfer systems and examined the presence or absence of reverse transfer in the belt second nip. Table 1 below shows the relationship between these eight transfer methods and the presence or absence of reverse transfer in the belt second nip.

  As shown in Table 1, in the eight types of transfer systems, reverse transfer did not occur in the belt second nip on the downstream side only in the four types of experiment numbers 3, 4, 7, and 8. When attention is paid to these, it is understood that secondary transfer of the electrostatic extrusion method is performed in the belt second nip. On the other hand, when attention is paid to the experiment numbers 1, 2, 5, and 6 in which the reverse transfer occurred, it can be seen that the electrostatic attraction type secondary transfer is performed at the belt second nip. Therefore, in the transfer system in which toner images having the same polarity are sequentially transferred to the opposite surface of the transfer paper P at the belt first nip and the belt second nip, electrostatic extrusion is performed at the belt second nip on the downstream side. It has been found that if the method is not adopted, reverse transcription is caused. Therefore, in this printer, secondary transfer of the electrostatic electrostatic extrusion method is performed at the belt second nip. In addition, although the example in which the secondary transfer nip formed by the belt first nip and the belt second nip that are connected to each other has been described, a secondary transfer nip that is not connected to each other may be formed.

  In this printer, each of the first process units 7Y, 7M, 7C, and 7K is provided with exposure devices 6Y, 6M, 6C, and 6K as first latent image forming means. Further, each of the second process units 40Y, 40M, 40C, 40K is provided with exposure devices 46Y, 46M, 46C, and 46K as second latent image forming means. In such a configuration, unlike the case where a laser optical system that needs to be installed separately from the first unit group or the second unit group is used as the exposure apparatus, the optical path from the exposure apparatus to the photoconductor may be blocked by the intermediate transfer belt. There is no. Therefore, the positional relationship between each unit group and each intermediate transfer belt can be designed without worrying about the optical path of the exposure apparatus, and the degree of layout freedom is improved.

  For the sake of layout, in this printer, as shown in FIG. 1, the second cleaning device 32 that cleans the second intermediate transfer belt 31 and the transport belt cleaning device 62 that cleans the transport belt 61 are mutually connected. Close positional relationship. If the second cleaning device 32 and the conveyance belt cleaning device 62 are arranged so that the projected images in the vertical direction overlap with each other, any one between the conveyance belt 61 and the second intermediate transfer belt 31 is provided. It is necessary to secure a space for interposing one cleaning device. Therefore, as shown in the drawing, it is desirable to devise the tension shape of both belts so that they can be arranged in a positional relationship such that the projected images in the vertical direction do not overlap each other.

  In this printer, the charge applying charger 63 of the transport belt unit 60 is disposed in the belt bending area of the second intermediate transfer belt 31 pressed by the second pressing roller 34. The transfer paper P can be electrostatically attracted to the transport belt 31 by effectively using the space inside.

  FIG. 21 is a main part configuration diagram showing a main part of the first modified example device. In the first modified apparatus, the first unit group and the second unit group are both arranged on the upper side rather than the lower side of the corresponding intermediate transfer belt. Even in this case, as shown in the figure, the first process unit 7 and the second process unit 40 can use common specifications. In the first modified apparatus, as shown in the drawing, each first process unit 7 and each second process unit are arranged in line-symmetric positions with respect to a virtual line extending in the vertical direction. It is arranged.

  As described above, when the first intermediate transfer belt 9 and the second intermediate transfer belt 31 are stretched in a horizontally long shape, the first unit group and the second unit group are respectively placed under the corresponding intermediate transfer belt. By arranging them side by side or on the upper side, common specifications of the process units can be achieved. On the other hand, when both the intermediate transfer belts are stretched in a vertically long shape, common specifications of the process units can be achieved by performing the following. The first unit group is disposed so that the surface movement in the vertical direction faces the first intermediate transfer belt portion from the lower side to the upper side, and the second intermediate transfer belt has the surface movement in the vertical direction from the lower side to the upper side. The second unit group is disposed so as to face the place. Alternatively, the first unit group is disposed so as to face the first intermediate transfer belt portion where the surface movement in the vertical direction is from the upper side to the lower side, and the second intermediate is performed from the upper side to the lower side. A second unit group is disposed so as to face the transfer belt portion. By doing in this way, both the 1st process unit and the 2nd process unit are made to face the belt location from which the surface movement in the perpendicular direction becomes the same direction. Then, the surface movement direction of the photosensitive member at the portion facing the belt can be made the same in each process unit without being reversed upside down. For this reason, common specification can be achieved.

  FIG. 22 is a main part configuration diagram showing the main part of the second modified example device. In the second modified apparatus, the fixing device 56 includes a pair of a fixing roller 56a and a fixing belt 56c that heats the recording medium sandwiched between the fixing nips while abutting each other to form the fixing nip from the opposite side. Is used. In such a fixing device 56, the fixing receiving position P2 is the surface of the fixing belt 56c upstream of the fixing nip entrance. In such a configuration, if the distance between the pre-fixing conveyance completion position P3 of the conveyance belt 61 and the fixing receiving position P2 of the fixing device 56 is set to 100 [mm] or less for the reason described above, the conveyance completion position before fixing is set. The distance D2 between P3 and the fixing nip entrance can be extended to 180 [mm] or less. As a result, compared to the case where the fixing belt 56c is not used, it is possible to reduce the thermal influence on the conveying belt 61 by the fixing rollers 56a and 56b. The fixing device 56 is provided with a driving roller 56d for moving the fixing belt 56c endlessly on the upstream side of the fixing roller 56b.

  FIG. 23 is a main part configuration diagram showing the main part of the third modified example device. In the third modified apparatus, the charge applying charger 63 of the transport belt unit 60 is arranged inside the loop of the transport belt 61 so that the charge for electrostatic adsorption is applied from the inside of the loop toward the transport belt 61. I have to. In such a configuration, the transfer paper P is electrostatically adsorbed to the transport belt 61 while effectively using the empty space inside the loop, and the disturbance of the unfixed image due to the rubbing of the transfer paper P on the transport belt 61 is suppressed. Can do.

  FIG. 24 is a main part configuration diagram showing the main part of the fourth modified example device. In the fourth modified apparatus, the second belt roller 34 that presses the second intermediate transfer belt 31 is brought into contact with not only the second intermediate transfer belt but also the conveyance belt 61 so that the second conveyor belt 61 is in contact with the second intermediate transfer belt 31. It is arranged close to the intermediate transfer belt 31. A voltage having the same polarity as the toner is applied to the second pressing roller 34. Then, the second pressing roller 34 can also be used as a charge applying unit that applies a charge for electrostatic attraction to the transport belt 61. Note that the second pressing roller 34 may be brought into contact via the conductive member 37 as shown in FIG. 25 instead of being brought into direct contact with the front surface of the conveyor belt 61. The function as the charge imparting means can be exhibited.

  FIG. 26 is a schematic configuration diagram showing a fifth modification device. In the fifth modified apparatus, the first unit group for forming the first toner image is not provided. Both the first toner image and the second toner image are formed in the second unit group disposed below the second transfer unit 30. The image forming process in such a configuration is as follows. That is, first, Y, M, C, K first toner images formed by the second unit group are superposed on the second intermediate transfer belt 31 and primarily transferred to obtain a first four-color toner image. Then, this is secondarily transferred collectively onto the first intermediate transfer belt 9 at the secondary transfer nip. Next, the Y, M, C, K second toner images formed by the second unit group are superimposed on the second intermediate transfer belt 31 and primarily transferred to obtain a second four-color toner image. The first four-color toner image on the first intermediate transfer belt 9 is thirdarily transferred to the first surface of the transfer paper P, while the second intermediate is transferred to the second surface of the transfer paper P. The second four-color toner image on the transfer belt 31 is secondarily transferred. In this configuration, since both the first toner image and the second toner image are formed by one second unit group, both the first unit group and the second unit group are provided, and the first toner image and the second toner group are provided. Compared with the case of forming a toner image, the configuration can be simplified and the cost increase can be suppressed. However, since the second four-color toner image must be formed after the first four-color toner image is secondarily transferred from the second intermediate transfer belt 31 to the first intermediate transfer belt 9, the first unit group. And the second unit group are provided, and there is a demerit that the image forming time is lengthened as compared with the case where both toner images are formed almost in parallel.

  The secondary transfer nip in the fifth modified apparatus is not formed by the contact of the extended portions of both intermediate transfer belts as in the printer according to the first embodiment. It is formed by the contact between the portion where the first intermediate transfer belt 9 is wound around the first nip roller 13i and the portion where the second intermediate transfer belt 31 is wound around the second nip roller 35i. In such a secondary transfer nip, two electric fields acting in opposite directions between the intermediate transfer belts cannot be formed side by side along the belt moving direction, and only one electric field can be formed. Therefore, in the secondary transfer nip, if the four-color toner image on the first intermediate transfer belt 9 and the four-color toner image on the second intermediate transfer belt 31 have the same polarity, the transfer paper P In contrast, only one of them is secondarily transferred.

  Therefore, in the fifth modified apparatus, as shown in an enlarged view in FIG. 27, a predetermined gap is provided between the front surface side of the first intermediate transfer belt 9 near the entrance of the secondary transfer nip. Opposite polarity reversing chargers 14 are provided. The polarity reversing charger 14 reverses the polarity of the four-color toner image on the first intermediate transfer belt 9 immediately before entering the secondary transfer nip by applying a positive charge. When the polarities of the four-color toner images on the first intermediate transfer belt 9 are reversed in this way, two four-color toner images having opposite polarities in the secondary transfer nip are transferred via the transfer paper P. It will be opposed. Then, one four-color toner image is electrostatically moved from the first intermediate transfer belt 9 side to the first surface side of the transfer paper P by one electric field formed in the secondary transfer nip, and the other 4 The color toner image is electrostatically moved from the second intermediate transfer belt 31 side to the second surface side of the transfer paper P. As a result, even if the secondary transfer nip has a considerably short dimension in the belt moving direction, the four-color toner images can be transferred almost simultaneously to both surfaces of the transfer paper P inside. Further, by reducing the dimension of the secondary transfer nip in the belt moving direction, it is possible to perform the jam processing operation more easily.

  In FIG. 27, among the first nip roller 13i disposed inside the loop of the first intermediate transfer belt 9 and the second nip roller 35i disposed inside the loop of the second intermediate transfer belt 31, the latter is transferred. An example of functioning as a bias roller is shown. Conversely, the former may function as a transfer bias roller. Further, the example in which the polarity of the four-color toner image on the first intermediate transfer belt 9 is reversed by the polarity reversal charger 14 has been described. However, the polarity of the four-color toner image on the second intermediate transfer belt 31 is reversed. Also good. Further, instead of reversing the polarity of any one of the four color toner images by the polarity reversing charger 14, the first unit group and the second unit group are configured to form toner images with toners having different polarities. The same effect can be obtained.

  FIG. 28 is a main part configuration diagram showing the main part of the sixth modified example device. This sixth modified apparatus is the same as the fifth modified apparatus except that a transfer charger 15 is provided instead of the polarity reversing charger. The two four-color toner images immediately before entering the secondary transfer nip are not reversed in polarity, and the two four-color toner images having the same polarity are entered into the secondary transfer nip. Only one of the four-color toner images can be transferred in the nip. For example, when the second nip roller 35i disposed inside the loop of the second intermediate transfer belt 31 is caused to function as a transfer bias roller and a secondary transfer bias having a polarity opposite to that of the toner is applied thereto, the first intermediate roller Only the four color toner images on the transfer belt 9 can be transferred to the transfer paper P by secondary transfer. However, a transfer charger 15 is provided to face the front surface of the second intermediate transfer belt 31 that has passed through the secondary transfer nip with a predetermined gap. Therefore, as shown in FIG. 28, the transfer charger 15 applies a charge to the first surface of the transfer paper P to transfer the four-color toner image on the second intermediate transfer belt 31 outside the secondary transfer nip to the transfer paper. Secondary transfer can be performed on the second surface of P. Even in this configuration, the size of the secondary transfer nip in the belt moving direction can be shortened, and the jam processing operation can be performed more easily.

  Next, a printer according to a second embodiment to which the invention is applied will be described. The basic configuration of the printer is almost the same as that of the printer according to the first embodiment, and a description thereof will be omitted. In this printer, the distance P1 to P2 shown in FIG. 2, that is, the length L1 of the post-fixing pre-fixing conveyance path is made larger than the vertical dimension of the A3 size paper which is the maximum size transfer paper P. ing. Then, before the leading edge of the A3 size paper reaches the fixing receiving position P2, the trailing edge of the A3 size paper is discharged from the double-side transfer device, and the paper delivery to the transport belt 61 is completed. After completing the delivery, even if a linear speed difference is provided between the paper conveyance speed by the fixing device 56 and the conveyance belt 61 and the paper conveyance speed by the double-side transfer device, the A3-size paper is between the fixing device and the double-side transfer device. Will not be bent greatly. In addition, a situation in which the rear end side of the A3 size paper is slipped in the double-sided transfer device does not occur. Therefore, it is not necessary to adjust the post-transfer conveyance speed V2 to the transfer speed V1, and it is possible to change the transfer speed V2 independently to meet the required fixing heat amount. As a result, it is possible to suppress the occurrence of fixing failure and hot offset caused by changing the transfer speed in accordance with the resolution of the image. The timing for making the post-transfer conveyance speed V2 different from the transfer speed V1 is the same as that in the first embodiment, and thus the description thereof is omitted.

  Further, in this printer, similarly to the printer according to the first embodiment, a belt linear movement region in which the conveyance belt 61 is linearly moved without being bent in a direction orthogonal to the surface direction is a conveyance path before fixing after transfer. Formed inside. Unlike the printer according to the first embodiment, this belt linear movement region is made larger than the vertical dimension of A3 size paper. In such a configuration, in this way, the transfer paper P is supported by only the transport belt 61 between the double-sided transfer device and the fixing device 56, and the entire region is held planarly on the surface of the transport belt 61. Create. Then, by transferring the transfer paper P to the fixing device 56 after having a flat posture without bending, the paper delivery property from the conveying belt 61 to the fixing device 56 can be improved.

  In the present printer, a transfer distance L1 between transfer and fixing, which is a recording medium transfer distance from the secondary transfer nip outlet to the fixing nip inlet that is the inlet of the fixing device 56, is set as follows. That is, it is set to be equal to or larger than the dimension in the longitudinal direction of the maximum size transfer paper P that can be stored in the paper feed cassette 50 that is a recording medium storage means. More specifically, the vertical dimension of the A3 size is 420 mm or more. In such a configuration, regardless of the size of the transfer sheet P, the maximum size of the A3 size is used as the upper limit, the leading end side is sandwiched in the secondary transfer nip and the leading end side is fixed to the fixing nip. It does not cause a situation of being caught in. This avoids a situation in which the transfer paper P is slightly rubbed against the surface of the second intermediate transfer belt 31 due to a slight difference in linear velocity between the secondary transfer nip and the fixing nip. Therefore, it is possible to avoid the disturbance of the unfixed toner image on the second surface due to the rubbing.

  As described above, in the printers according to the first embodiment and the second embodiment, since the transfer sheet P held on the surface is provided with the charge removal unit as the charge removal unit for discharging the transfer belt area before the transfer sheet P is transferred to the fixing unit 56. For the reasons described above, it is possible to suppress a situation in which the transfer paper P cannot be satisfactorily separated from the belt at the pre-fixing conveyance completion position P3 and a jam occurs.

  Further, the speed changing unit is configured so that the paper transport speed by the fixing device 56 and the paper transport speed by the transport belt 61 are the same. Accordingly, when the rear end side of the transfer paper P is transported toward the fixing device 56 by the transport belt 61 while fixing the front end side of the transfer paper P that has entered the fixing device 56, both transports are performed. It is possible to avoid the curvature of the transfer paper P, jamming, and unfixed image disturbance due to the difference in speed.

  Also, before the trailing edge of the transfer sheet P or the boundary between the trailing edge side blank area and the non-blank area on the transfer sheet P passes through the transfer separation position P1 of the double-side transfer device, the fixing device 56 and the transport belt 61 are used. Is set to the same speed as the paper conveyance speed (transfer speed V1) by the double-side transfer device, and after the trailing edge or boundary passes the transfer separation position P1, the paper conveyance speed by the fixing device 56 or the conveyance belt 61 is changed. The speed changing means is configured to be different from the paper conveyance speed by the double-side transfer device. Then, for the reasons described above, the rear end side of the transfer paper P is slipped on the second intermediate transfer belt 31, or the transfer paper P is greatly curved or jammed between the double-side transfer device and the conveyance belt 61. Such a situation can be avoided.

  Further, depending on the size of the transfer paper P supplied to the double-side transfer device, a plurality of transfer papers P continuously discharged from the double-side transfer device are collectively delivered to the transport belt 61 and then the paper by the fixing device 56 or the transport belt 61. The speed changing means is configured so that the conveyance speed is different from the paper conveyance speed by the double-side transfer device. Therefore, as described above, in continuous printout in which a plurality of transfer papers P can be held side by side on the conveyance belt 61, the space between the papers can be efficiently packed and the image forming time can be shortened.

  Further, the charge application start timing t4 by the charge application charger 63 is determined based on the transport reception start timing t3 which is the timing at which the leading edge of the transfer paper P discharged from the double-side transfer device starts to contact the transport belt 61. Therefore, it is possible to suppress wasteful energy consumption due to the application of charges to the conveyance belt region where it is not necessary to apply charges.

Further, it has a belt base material made of polyimide or polyamide, the surface resistance value is adjusted to 10 ⁸ to 10 ¹³ [Ω / □], and the volume resistivity is adjusted to 10 ⁶ to 10 ¹² [Ω · cm]. Therefore, the transfer paper P can be reliably electrostatically adsorbed to the transport belt 61 while suppressing deterioration of the transport belt 61 due to heat conduction from the fixing device 56.

  Among the plurality of support rollers that support the conveyance belt 61 on the inner circumferential surface of the loop, a support roller having a diameter of 20 to 40 [mm] as a support roller disposed closest to the transfer separation position P1 of the double-side transfer device. In addition, a support roller having a diameter of 20 to 30 [mm] is used as the support roller disposed closest to the fixing receiving position P <b> 2 of the fixing device 56. Then, for the reason described above, various problems due to the bending of the support roller while reliably transferring the transfer paper P between the second intermediate transfer belt 31 and the transport belt 61 or between the transport belt 61 and the fixing device 56. Can be suppressed.

  The fixing device 56 includes a pair of fixing rollers that heats the transfer paper P sandwiched between the fixing nips from the opposite surfaces while abutting each other to form a fixing nip. A transfer separation position P1 of the double-side transfer device and a belt surface paper receiving position P4 that is a fixing receiving position of the transfer paper P in the circumferential direction of the transport belt 61 when receiving the transfer paper P discharged from the double-side transfer device. The distance is set to 30 to 60 [mm]. Further, the distance between the pre-fixing conveyance completion position P3, which is the rear end separation position of the transfer paper P in the circumferential direction of the conveyance belt 61 when the transfer paper P is transferred to the fixing device, and the fixing nip entrance is set to 40 to 100 [ mm]. By doing so, as described above, the fixing roller 56a is reliably transferred while transferring the transfer paper P between the second intermediate transfer belt 31 and the transport belt 61 or between the transport belt 61 and the fixing device 56. , B can be suppressed from being excessively weakened.

  Further, in the second modified apparatus, as the fixing device 56, a pair of a fixing roller 56a and a fixing belt 56c that respectively heats the recording medium sandwiched between the fixing nips while abutting each other to form the fixing nip from the opposite surface side. Use what you have. The distance between the transfer separation position P1 of the double-side transfer device and the conveyance receiving position P4 of the conveyance belt 61 is set to 30 to 60 [mm]. Further, the distance between the conveyance completion position P3 before fixing of the conveyance belt 61 and the fixing nip entrance of the fixing device 56 is set to 60 to 180 [mm]. By doing so, as described above, it is possible to reduce the thermal influence on the conveyance belt 61 by the fixing rollers 56a and 56b as compared with the case where the fixing belt 56c is not used.

  In the printer of the first embodiment or the second embodiment, as a process unit that is a latent image developing unit, a first unit group including four first process units 7Y, 7M, 7C, and 7K and four second units are provided. The second unit group consisting of process units 40Y, M, C, and K is used. Further, as a double-sided transfer device, the first toner image developed on the photoreceptor of each first process unit is transferred onto the first intermediate transfer belt 9 while being transferred to the first surface of the transfer paper P. On the other hand, the second toner image developed on the photosensitive member of each second process unit is transferred onto the second intermediate transfer belt 31 so as to be transferred onto the second surface of the transfer paper P in a lump. Used. By doing so, as described above, only one unit group including a plurality of process units is provided, and a superimposed image obtained by superimposing the first toner image and a superimposed image obtained by superimposing the second toner image. As compared with the case where both are formed by one unit group, the image forming time can be greatly shortened.

  Further, the first intermediate transfer belt 9 and the second intermediate transfer belt 31 are brought into contact with each other to form a secondary transfer nip as a transfer nip, and the transfer sheet P is transferred while being sandwiched and conveyed by the secondary transfer nip. Since the double-sided transfer device is configured to transfer the toner image onto both sides of the paper P, the transfer is performed as compared with the case where the double-sided transfer device is configured to transport the transfer paper P without using the grip by the transfer nip. The transportability of the paper P can be improved.

  In the printer of the second embodiment, the length of the paper conveyance path from the outlet of the secondary transfer nip to the fixing receiving position P2 of the fixing device 56 is the maximum size that can be accommodated in the paper feeding cassette 50. It is larger than the dimension in the conveyance direction of the transfer paper P. In this way, as described above, the secondary transfer nip sandwiching the rear end side of the transfer paper P with the transfer speed V1 and the pre-fixing transport speed V2 being different is the transfer paper at the transfer speed V1. Disturbances in the unfixed image due to forcibly sending P toward the conveyance belt 61 can be suppressed.

  In the printers of the first and second embodiments, contact pressure adjusting means for adjusting the contact pressure between the first intermediate transfer belt 9 and the second intermediate transfer belt 31 in the secondary transfer transfer nip is provided. Therefore, the transfer conditions can be adjusted by changing the transfer pressure at the secondary transfer nip as required.

  Further, a pair of pressure rollers that pressurize both intermediate transfer belts while sandwiching the first intermediate transfer belt 9 and the second intermediate transfer belt 31 between each other to form a secondary transfer nip, and a shaft of one of the rollers. An eccentric roller 151 that is rotatably fixed to the shaft, an abutment roller 154 that is abutted against the eccentric roller 151 while being fixed to the shaft of the other roller, and a driving gear 155 that is a rotating means for rotating the eccentric roller. Yes. Then, the contact pressure adjusting means is configured to adjust the contact pressure of both intermediate transfer belts by the change in the distance between the shafts of both rollers accompanying the rotation of the eccentric roller 151. In this way, the secondary transfer pressure can be easily adjusted using the driving force of a rotational driving source such as a motor.

  Further, as the first intermediate transfer belt 9 and the second intermediate transfer belt 31, those having belt detent protrusions 9b and 31b on the belt inner peripheral surfaces at or near both ends in the width direction are used. The first cleaning backup roller 13c, which is at least two of the support rollers that support the first intermediate transfer belt 9 and the second intermediate transfer belt 31 on the inner circumferential surface of the loop at a location different from the secondary transfer nip, and the secondary transfer. As the nip upstream roller 13h, the nip inlet first roller 13a, the nip inlet second roller 35a, the nip outlet first roller 13b, and the nip outlet second roller 35, which are pressure rollers constituting a pressure roller pair, A roller portion having a large axial length is used. Further, a pressure roller pair is configured as a separation roller 35c and a driving roller 35f, which are at least two of the support rollers for supporting the second intermediate transfer belt 31 on the inner circumferential surface of the loop at a location different from the secondary transfer nip. Using a roller having a larger length in the axial direction than the first nip inlet roller 13a, nip inlet second roller 35a, nip outlet first roller 13b, and nip outlet second roller 35, which is a pressure roller. Yes. By doing so, it is possible to avoid damage to the intermediate transfer belt caused by pressing the belt detent projections 9b and 31b against the end face of the pressure roller in the vicinity of the belt portion to be compressed due to the influence of the nip pressure. it can.

  Further, in the opposite area between the first intermediate transfer belt 9 and the second intermediate transfer belt 31, either one of the intermediate transfer belts is pressed from the front surface, and the endless moving track is curved toward the inner side of the belt loop. A pressing roller as a member is provided, and the conveying belt 61 is disposed so that at least a part of the conveying belt 61 is positioned within the curved area of the intermediate transfer belt. By doing so, these three belts are secured while securing necessary spaces between the first intermediate transfer belt 9 and the conveyance belt 61 and between the conveyance belt 61 and the second intermediate transfer belt 31. Compact arrangement in parallel can suppress the increase in size of the apparatus.

  Further, in the third modified apparatus, since the charge applying charger 63 is disposed inside the loop of the transport belt 61, the transfer paper P on the transport belt 61 is used while effectively utilizing the empty space inside the loop. It is possible to suppress the disturbance of the unfixed image due to the rubbing.

  In the printers of the first and second embodiments, the charge imparting charger 63 is disposed in the second intermediate transfer belt curved area, so that the empty space between the belts can be effectively used and the conveyor belt can be used. It is possible to suppress the disturbance of the unfixed image due to rubbing of the transfer paper P on 61.

  Further, in the fourth modified apparatus, the second pressing roller 34 that curves the second intermediate transfer belt 31 toward the inner side of the loop is also used as a charge applying unit that applies a charge to the transport belt 61. Costs can be reduced by reducing the number of points.

  Further, in the printer of the first embodiment or the second embodiment, the second intermediate transfer belt 31 that is pressed and curved by the second pressing roller 34 is supported by the first support roller among the plurality of support rollers that support the inner circumferential surface of the loop. As the separation roller 35c, which is a support roller disposed adjacent to the pressing roller 34 on the upstream side in the belt movement direction with respect to the two pressing rollers 34, a separation roller 35c having a diameter of 20 to 30 [mm] is used. The belt winding angle θ with respect to the separation roller 35 is set to 90 to 120 [°]. By doing so, as described above, the distance between the transfer separation position P1 and the conveyance receiving position P4 can be easily reduced to 60 [mm] or less without applying excessive stress to the second intermediate transfer belt 31. Can do.

  Further, as the first intermediate transfer belt 9 and the second intermediate transfer belt 31, those stretched in a horizontally long shape so as to take a space in the horizontal direction rather than the vertical direction are used, and the conveyance belt unit 60 is conveyed. A belt 61 that is stretched in a horizontally long shape is used, and these three belts are arranged side by side in the vertical direction so that at least some of the projected images in the vertical direction overlap each other. By doing in this way, as above-mentioned, it can be set as the internal layout balanced in the perpendicular direction and the horizontal direction.

  In addition, the first unit group is disposed below the first intermediate transfer belt 9 in the vertical direction and the second unit group is disposed below the second intermediate transfer belt 31 in the vertical direction. Thus, the first process units 7Y, M, C, and K corresponding to the first intermediate transfer belt 9 and the second process units 40Y, 40M, 40C, and 40K corresponding to the second intermediate transfer belt 31 have a common specification. Cost can be reduced by using an object.

  In the first modified apparatus, the first unit group is disposed on the upper side in the vertical direction of the first intermediate transfer belt 9, and the second unit group is disposed on the upper side in the vertical direction of the second intermediate transfer belt 31. Therefore, for the reasons described above, the first process units 7Y, M, C, K corresponding to the first intermediate transfer belt 9 and the second process units 40Y, M, C, corresponding to the second intermediate transfer belt 31 are provided. With K, the cost can be reduced by using a common specification.

  In the printers of the first and second embodiments, the first pressing roller 12 that presses the first intermediate transfer belt 9 and the second pressing roller 34 that presses the second intermediate transfer belt are used as pressing rollers. The conveyor belt is disposed in the latter region, which is one of the first intermediate transfer belt curved region by the first pressing roller 12 and the second intermediate transfer belt curved region by the second pressing roller 34. The conveyor belt 61 is disposed so that at least a part of 61 is positioned, and the first unit group is disposed so that at least a part of the first unit group is positioned in the former area, which is the other curved area. doing. In this way, as described above, either the first unit group or the second unit group is added between the first intermediate transfer belt 9 and the second intermediate transfer belt 31 in addition to the conveyance belt 61. It is possible to easily realize that both unit groups are disposed below or on the corresponding intermediate transfer belt. Therefore, it is possible to easily realize the use of process units having common specifications for the first unit group and the second unit group.

  Even in the following manner, an internal layout in which the vertical direction and the horizontal direction are balanced can be achieved as in the printers of the first and second embodiments. That is, as the first intermediate transfer belt 9 and the second intermediate transfer belt 31, those that are stretched in a vertically long shape so as to take a space in the vertical direction rather than the horizontal direction are used, and the conveyance belt unit 60 is conveyed. A belt 61 that is stretched in a vertically long shape is used, and these three belts are arranged side by side in the horizontal direction so that at least some of the projected images in the horizontal direction overlap each other.

  Further, when arranged in this way, common specifications of the process units can be achieved as in the printers of the first and second embodiments by the following. That is, the first unit group is arranged so as to face the first intermediate transfer belt portion where the surface movement in the vertical direction is from the upper side to the lower side, and the second intermediate is made from the upper side to the lower side. The second unit group is disposed so as to face the transfer belt portion. Alternatively, the first unit group is disposed so as to face the first intermediate transfer belt portion where the surface movement in the vertical direction is from the lower side to the upper side, and the second middle is the surface movement in the vertical direction from the lower side to the upper side. The second unit group is disposed so as to face the transfer belt portion.

  Further, in the first modified apparatus, the first process units 7 and the second process units 40 are respectively arranged so as to be in a line-symmetric posture with respect to a virtual line extending in the vertical direction. Yes. In this way, for the reasons described above, it becomes possible to narrow the photosensitive member exposed area of each process unit compared to the case where they are arranged in a non-symmetrical posture with respect to each other. The degree of freedom in layout can be improved.

1 is a schematic configuration diagram illustrating a printer according to a first embodiment. FIG. 3 is a configuration diagram showing a paper conveyance path from a double-side transfer device to a fixing device of the printer and its peripheral configuration. FIG. 2 is a block diagram showing a part of an electric circuit of the printer. FIG. 3 is an enlarged configuration diagram illustrating an enlarged facing area between the double-sided transfer device and the conveyance belt unit. The expanded block diagram which expands and shows the opposing area | region of the conveyance belt unit and an identification apparatus. FIG. 2 is an enlarged configuration diagram showing a secondary transfer nip of the printer and its surrounding configuration. The side view which shows the eccentric roller and the butting roller of the printer. FIG. 3 is a partial perspective view showing a first intermediate transfer belt and a second intermediate transfer belt of the printer. FIG. 3 is a schematic diagram illustrating a configuration around a secondary transfer nip of a first transfer unit of the printer. FIG. 3 is a configuration diagram illustrating an example in which a first unit group is disposed above the first intermediate transfer belt while a second unit group is disposed below the second intermediate transfer belt. FIG. 11 is an enlarged configuration diagram showing a first process unit in the example of FIG. 10. The expanded block diagram which shows the example which used the 1st process unit as a 2nd process unit. FIG. 3 is an enlarged configuration diagram illustrating a second process unit of the printer. The expanded block diagram which shows the example which reversed the 2nd process unit to the horizontal direction, and was used as a 1st process unit. The schematic diagram which shows the 1st example of the secondary transfer nip and its surrounding structure. The schematic diagram which shows the 2nd example of the secondary transfer nip and surrounding structure. The schematic diagram which shows the 3rd example of the secondary transfer nip and surrounding structure. The schematic diagram which shows the 4th example of the secondary transfer nip and surrounding structure. The schematic diagram which shows the 5th example of the secondary transfer nip and surrounding structure. The schematic diagram which shows the comparative example of the secondary transfer nip and surrounding structure. The principal part block diagram which shows the principal part of a 1st modification apparatus. The principal part block diagram which shows the principal part of a 2nd modification apparatus. The principal part block diagram which shows the principal part of a 3rd modification apparatus. The principal part block diagram which shows the principal part of a 4th modification apparatus. The principal part block diagram which shows the modification of the principal part. The schematic block diagram which shows a 5th modification apparatus. The expanded block diagram which shows the circumference | surroundings of the secondary transfer nip of the same 5th modification apparatus. The principal part block diagram which shows the principal part of a 6th modification apparatus.

Explanation of symbols

1Y, M, C, K photoconductor (first latent image carrier)
5Y, M, C, K Developing device (first developing means)
6Y, M, C, K Exposure device 7Y, M, C, K First process unit (first latent image developing unit)
8 First transfer unit (part of double-sided transfer means)
9 First intermediate transfer belt 19a Polarity reversing charger (polarity reversing means)
19b Transfer charger (charge imparting means)
30 Second transfer unit (part of double-sided transfer means)
31 Second intermediate transfer belt 40Y, M, C, K Second process unit (second latent image developing unit)
41Y, M, C, K photoconductor (second latent image carrier)
45Y, M, C, K Developing device (second developing means)
46Y, M, C, K Exposure device (part of latent image forming means)
50 Paper feed cassette (recording body accommodation means)
56 Fixing device (fixing means)
60 Conveying belt unit 61 Conveying belt 63 Charge applying charger (charge applying means)
64 Static elimination charger (static elimination means)
P Transfer paper (recording medium)
y Virtual line L1 Length of transfer path after transfer and before fixing

Claims (30)

A latent image carrier that carries a latent image, a latent image developing unit that has a developing unit that develops the latent image carried on the surface of the latent image into a visible image, and a surface of the latent image carrier based on image information. A latent image forming means for forming a latent image; and a first visible image developed on the latent image carrier, which is transferred to the first surface of the recording medium, while being developed on the latent image carrier. (2) a double-sided transfer means for transferring the visible image to the second surface of the recording medium, and the first visible image and the second possible image on the recording medium while conveying the recording medium after passing through the double-sided transfer means. In an image forming apparatus comprising: a fixing unit that fixes a visual image; and a recording body storage unit that stores a recording body to be supplied to the double-side transfer unit
A conveying belt unit that conveys the recording medium discharged from the double-sided transfer unit to the fixing unit while being held on the surface of the conveying belt that is endlessly moved while being stretched by a plurality of stretching members, and the fixing unit And a latent image carrier area corresponding to a margin area on the rear end side of the maximum size recording body that can be accommodated in the recording body accommodation means. A latent image formation prohibiting unit that prohibits latent image formation by the latent image forming unit, and a charge applying unit that applies a charge to the surface of the conveyance belt before receiving the recording medium from the double-sided transfer unit,
The length of the post-transfer pre-fixing conveyance path that is the recording medium conveyance path from the transfer separation position that is the recording medium separation position from the double-side transfer means to the fixing reception position that is the recording body reception position of the fixing means An image forming apparatus, wherein the size is larger than a value obtained by subtracting the size in the recording material conveyance direction of the trailing edge side blank area from the size in the conveyance direction of the maximum size recording material. A latent image carrying body carrying a latent image, a latent image developing unit having a developing means for developing the latent image carried on the surface of the latent image into a visible image, and a first image developed on the latent image carrying body. A double-side transfer means for transferring a visual image to the first surface of the recording body, and transferring a second visible image developed on the latent image carrier to the second surface of the recording body; A recording medium containing a fixing means for fixing the first visible image and the second visible image to the recording medium while conveying the recording medium after passing through the recording medium, and a recording medium supplied to the double-side transfer means An image forming apparatus comprising:
A conveying belt unit that conveys the recording medium discharged from the double-sided transfer unit to the fixing unit while being held on the surface of the conveying belt that is endlessly moved while being stretched by a plurality of stretching members, and the fixing unit And a speed changing means for changing the recording medium conveying speed by the conveying belt and the recording medium conveying speed by the conveying belt, and a charge applying means for applying an electric charge to the surface of the conveying belt before receiving the recording medium from the double-side transfer means. ,
The length of the post-transfer pre-fixing conveyance path that is the recording medium conveyance path from the transfer separation position that is the recording medium separation position from the double-side transfer means to the fixing reception position that is the recording body reception position of the fixing means An image forming apparatus characterized in that it is larger than the dimension in the conveyance direction of the maximum size recording body that can be accommodated in the recording body accommodation means. The image forming apparatus according to claim 1 or 2,
An image forming apparatus, comprising: a discharging unit that discharges the conveyance belt area before transferring the recording material held on the surface to the fixing unit. The image forming apparatus according to claim 1, 2 or 3.
An image forming apparatus, wherein the speed changing unit is configured so that a recording medium conveyance speed by the fixing unit and a recording medium conveyance speed by the conveyance belt are the same. The image forming apparatus according to claim 4.
Before the rear end of the recording body in the transport direction or the boundary between the trailing edge side blank area and the non-blank area of the recording body passes through the transfer separation position, the recording body by the fixing means or the transport belt is used. The conveyance speed is set to the same speed as the recording medium conveyance speed by the double-side transfer means, and after the trailing edge or boundary passes through the transfer separation position, the recording medium conveyance speed by the fixing means or the conveyance belt is changed to the double-side transfer means. An image forming apparatus characterized in that the speed changing means is configured so as to be different from the recording medium conveying speed by the above. The image forming apparatus according to claim 5.
Depending on the size of the recording medium supplied to the double-side transfer means, a plurality of recording bodies continuously discharged from the double-side transfer means are collectively delivered to the transport belt, and then the recording medium transport speed by the fixing means and the transport belt. An image forming apparatus characterized in that the speed changing means is configured so as to be different from a recording medium conveying speed by the double-side transfer means. The image forming apparatus according to claim 1,
An image forming apparatus, wherein the charge application start timing by the charge application unit is determined based on the timing at which the leading edge of the recording medium discharged from the double-side transfer unit starts to contact the conveyance belt. The image forming apparatus according to claim 1,
A belt base material made of polyimide or polyamide, having a surface resistance adjusted to 10 ⁸ to 10 ¹³ [Ω / □] and a volume resistivity adjusted to 10 ⁶ to 10 ¹² [Ω · cm] Is used as the conveying belt. The image forming apparatus according to claim 1,
Among a plurality of support rollers for supporting the conveyor belt on the inner circumferential surface of the loop, a support roller having a diameter of 20 to 40 [mm] is used as a support roller disposed closest to the transfer separation position of the double-side transfer means. An image forming apparatus using a support roller having a diameter of 20 to 30 [mm] as a support roller disposed closest to a fixing receiving position of the fixing unit. The image forming apparatus according to claim 1,
The fixing unit includes a fixing roller pair that heats the recording medium sandwiched between the fixing nips while abutting each other to form the fixing nip from the opposite surface side, the transfer separation position of the double-sided transfer unit, The distance between the conveyance belt and the conveyance receiving position, which is the recording body reception position in the belt circumferential direction, is set to 30 to 60 [mm], and the conveyance before conveyance is the recording medium delivery position in the belt circumferential direction of the conveyance belt. An image forming apparatus, wherein a distance between a completion position and a fixing nip entrance which is a fixing receiving position of the fixing unit is set to 40 to 100 [mm]. The image forming apparatus according to claim 1,
As the fixing unit, a unit having a pair of a fixing roller and a fixing belt for heating a recording medium sandwiched between the fixing nips while contacting each other to form a fixing nip from the opposite side is used. The distance between the separation position and the belt surface recording body receiving position which is the tip contact position of the recording body in the circumferential direction of the conveying belt when receiving the recording body discharged from the double-side transfer means is 30 to 60 mm. And the distance between the conveyance completion position before fixing, which is the recording material delivery position in the belt circumferential direction of the conveyance belt, and the fixing nip entrance of the fixing unit is set to 60 to 180 [mm]. An image forming apparatus. The image forming apparatus according to claim 1,
As the latent image developing unit, a first unit group consisting of a plurality of first latent image developing units and a second unit group consisting of a plurality of second latent image developing units are used.
As the double-sided transfer means, the first visible image developed on the latent image carrier of each first latent image developing unit is transferred onto the first intermediate transfer belt, and then transferred to the first surface at once. On the other hand, the second visible image developed on the latent image carrier of each second latent image developing unit is transferred onto the second intermediate transfer belt and then transferred onto the second surface at once. An image forming apparatus using the apparatus. The image forming apparatus according to claim 12.
The first intermediate transfer belt and the second intermediate transfer belt are brought into contact with each other to form a transfer nip, and a visible image is transferred onto both sides of the recording medium while the recording medium is sandwiched and conveyed by the transfer nip. Thus, an image forming apparatus comprising the double-sided transfer means. The image forming apparatus according to claim 13.
An image forming apparatus, wherein a length of a recording medium conveyance path from an exit of the transfer nip to a fixing receiving position of the fixing unit is larger than a conveyance direction dimension of the maximum size recording medium. The image forming apparatus according to claim 13 or 14,
An image forming apparatus comprising a contact pressure adjusting means for adjusting a contact pressure between the first intermediate transfer belt and the second intermediate transfer belt in the transfer nip. The image forming apparatus according to claim 15.
A pair of pressure rollers that pressurize both intermediate transfer belts while forming the transfer nip by sandwiching the first intermediate transfer belt and the second intermediate transfer belt between each other, and one of the rollers in the pressure roller pair. An eccentric roller that is rotatably fixed to the shaft, an abutment roller that is abutted against the eccentric roller while being fixed to the shaft of the other roller, and a rotating means that rotates the eccentric roller. An image forming apparatus characterized in that the contact pressure adjusting means is configured to adjust the contact pressure according to a change in the distance between the shafts of both support rollers accompanying rotation of the support roller. The image forming apparatus according to any one of claims 13 to 16,
A pressure roller pair for pressing the intermediate transfer belt while forming the transfer nip by sandwiching the first intermediate transfer belt and the second intermediate transfer belt between each other;
As the first intermediate transfer belt and the second intermediate transfer belt, belts each having a belt detent projection on the belt inner peripheral surface at or near both ends in the width direction are used.
As at least two of the support rollers for supporting the first intermediate transfer belt on the inner circumferential surface of the loop at a location different from the transfer nip, the axial direction of the roller portion is greater than any of the pressure rollers constituting the pressure roller pair. Use the one whose length is
In addition, as at least two of the support rollers for supporting the second intermediate transfer belt on the inner circumferential surface of the loop at a location different from the transfer nip, the roller portion is more than any of the pressure rollers constituting the pressure roller pair. An image forming apparatus having a length in the axial direction is large. The image forming apparatus according to claim 13.
A pressing member that presses one of the intermediate transfer belts from the front surface in a region where the first intermediate transfer belt and the second intermediate transfer belt face each other and curves its endless moving track toward the inside of the belt loop; An image forming apparatus, wherein the conveying belt is disposed so that at least a part of the conveying belt is positioned in a curved region of the intermediate transfer belt by the pressing member. The image forming apparatus according to claim 18.
An image forming apparatus, wherein the charge applying unit is disposed inside a loop of the conveying belt. The image forming apparatus according to claim 18.
An image forming apparatus, wherein the charge applying means is disposed in the curved area of the intermediate transfer belt. The image forming apparatus according to claim 20, wherein
An image forming apparatus, wherein the pressing member is also used as the charge applying unit. The image forming apparatus according to any one of claims 18 to 21,
Of a plurality of support rollers that support the first intermediate transfer belt or the second intermediate transfer belt pressed by the pressing member on the inner circumferential surface of the loop, adjacent to the pressing member upstream of the pressing member in the belt moving direction. An image having a diameter of 20 to 30 [mm] as a support roller disposed so as to be fitted, and a belt winding angle with respect to the support roller is set to 90 to 120 [°] Forming equipment. The image forming apparatus according to any one of claims 18 to 22,
As the first intermediate transfer belt and the second intermediate transfer belt, those stretched in a horizontally long shape so as to take a space in the horizontal direction rather than in the vertical direction are used, and the conveyor belt is used as the conveyor belt unit. An image forming apparatus characterized in that a belt that is stretched in a horizontally long shape is used, and these three belts are arranged in the vertical direction so that at least some of the projected images in the vertical direction overlap each other. 24. The image forming apparatus according to claim 23.
The first unit group is disposed above the first intermediate transfer belt in the vertical direction and the second unit group is disposed above the second intermediate transfer belt in the vertical direction, or the first unit group is disposed. Is arranged on the lower side in the vertical direction of the first intermediate transfer belt, and the second unit group is arranged on the lower side in the vertical direction of the second intermediate transfer belt. 25. The image forming apparatus according to claim 24.
As the pressing member, a first pressing member that presses the first intermediate transfer belt and a second pressing member that presses the second intermediate transfer belt are provided, and a first intermediate transfer belt bending region by the first pressing member is provided. And the second intermediate transfer belt curved region by the second pressing member, the conveying belt is disposed so that at least a part of the conveying belt is located in one of the curved regions, and the other An image forming apparatus, wherein the first unit group or the second unit group is disposed so that at least a part of the first unit group or the second unit group is positioned in the curved region. The image forming apparatus according to any one of claims 18 to 22,
As the first intermediate transfer belt and the second intermediate transfer belt, those stretched in a vertically long shape so as to take a space in the vertical direction rather than in the horizontal direction are used, and the transport belt is used as the transport belt unit. An image forming apparatus characterized in that a vertically long shape is used and these three belts are arranged in the horizontal direction so that at least a part of the projected images in the horizontal direction overlap each other. 27. The image forming apparatus according to claim 26.
The first unit group is disposed so as to face the first intermediate transfer belt portion where the surface movement in the vertical direction is from the lower side to the upper side, and the second surface movement in the vertical direction is from the lower side to the upper side. The second unit group is disposed so as to face the intermediate transfer belt portion, or the first unit so that the surface movement in the vertical direction faces the first intermediate transfer belt portion from the upper side to the lower side. An image forming apparatus comprising: a plurality of groups; and the second unit group is disposed so as to face the second intermediate transfer belt portion whose surface movement in the vertical direction is from the upper side to the lower side. . The image forming apparatus according to claim 24, 25 or 27.
An image forming apparatus, wherein each first latent image developing unit and each second latent image developing unit are arranged so as to have a line-symmetric posture with respect to a virtual line extending in a vertical direction. A latent image forming step for forming a latent image on the surface of the latent image carrier based on image information; a developing step for developing the latent image on the latent image carrier into a visible image; and A double-sided transfer step of transferring the developed first visible image to the first surface of the recording body while transferring the second visible image developed on the latent image carrier to the second surface of the recording body. A fixing process for fixing the first visible image and the second visible image on the recording medium while conveying the recording medium after passing through the double-sided transfer process, and a recording medium supplied to the double-sided transfer process In an image forming method of forming an image on both sides of the recording body, carrying out the housing step of housing the recording body in the recording body housing means,
A conveying step of conveying the recording medium discharged from the double-sided transfer step toward the fixing step while being held on the surface of a conveying belt that is endlessly moved while being stretched by a plurality of stretching members; A speed changing step for changing the recording body transport speed and the recording body transport speed by the transport belt, and a charge applying step for applying a charge to the surface of the transport belt before receiving the recording body from the double-side transfer step, A latent image formation prohibiting step is provided in the latent image forming step for prohibiting latent image formation on the latent image carrier region corresponding to the trailing edge side blank region of the maximum size recording member that can be accommodated in the recording member accommodating means,
In a recording medium conveyance path from a transfer separation position that is a recording body separation position from a double-sided transfer unit that performs the double-sided transfer process to a fixing reception position that is a recording body reception position of the fixing unit that performs the fixing process. The length of a certain post-transfer pre-fixing conveyance path is made larger than a value obtained by subtracting the size in the conveyance direction of the trailing edge side blank area from the dimension in the conveyance direction of the maximum size recording medium. Image forming method. A developing step of developing the latent image on the latent image carrier into a visible image; and transferring the first visible image developed on the latent image carrier to the first surface of the recording medium, A double-sided transfer step of transferring the second visible image developed on the carrier to the second surface of the recording body, and the recording body after passing through the double-sided transfer step while transporting the recording body to the recording body; A fixing process for fixing the first visible image and the second visible image and a storing process for storing the recording medium supplied to the double-sided transfer process in the recording medium storing means are performed to form images on both sides of the recording medium. In the image forming method to
A conveying step of conveying the recording medium discharged from the double-sided transfer step toward the fixing step while being held on the surface of a conveying belt that is endlessly moved while being stretched by a plurality of stretching members; A speed changing step for changing the recording body transport speed and the recording body transport speed by the transport belt, and a charge applying step for applying a charge to the surface of the transport belt before receiving the recording body from the double-side transfer step,
In a recording medium conveyance path from a transfer separation position that is a recording body separation position from a double-sided transfer unit that performs the double-sided transfer process to a fixing reception position that is a recording body reception position of the fixing unit that performs the fixing process. An image forming method, wherein a length of a certain post-transfer pre-fixing conveyance path is made larger than a dimension in a conveyance direction of a maximum-size recording medium that can be accommodated in the recording medium accommodating means.

Images