JP2012189921A - Image forming apparatus - Google Patents

Abstract

An object of the present invention is to suppress the occurrence of curvature separation failure of a recording sheet from an intermediate transfer belt 16 without providing a separation claw or a separation bias electrode.
The intermediate transfer belt is moved endlessly while being wound around a plurality of support rollers disposed inside the loop, and the intermediate transfer belt is in contact with the secondary transfer counter roller in a whole area in the circumferential direction of the intermediate transfer belt. The secondary transfer roller 20 is brought into contact with the wound portion from the outside of the loop to form a secondary transfer nip, and Y, M, and so on due to the contact between the photoreceptors 2Y, M, C, and K and the intermediate transfer belt 16 are formed. In a configuration in which Y, M, C, and K toner images are superimposed and transferred from the photosensitive member to the belt at the primary transfer nip for C and K, and then transferred to the recording paper at the secondary transfer nip at a time for secondary transfer. Regarding the diameter D [mm] of the transfer counter roller 18 and the minimum recording paper basis weight W [g / m ² ], “D [mm] ≦ 0.23 W [g / m ² ] +5.1 The thing which has the relationship of "was used.
[Selection] Figure 1

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile, or a printer that transfers a toner image formed on the front surface of an endless belt member to a recording sheet sandwiched between transfer nips of the belt member and a nip forming roller. It is about.

  As this type of image forming apparatus, for example, the one described in Patent Document 1 is known. This image forming apparatus includes a process unit that forms a toner image on the surface of a photoreceptor by a known electrophotographic process, and a transfer unit that transfers the toner image on the photoreceptor to a recording sheet. The transfer unit forms a primary transfer nip by bringing an endless intermediate transfer belt stretched by a plurality of support rollers disposed inside the belt loop into contact with the photosensitive member. Then, the toner image on the photoreceptor is primarily transferred to the surface of the intermediate transfer belt in the primary transfer nip. A secondary transfer nip is formed by contacting the secondary transfer roller at a portion of the intermediate transfer belt in the circumferential direction where the intermediate transfer belt is wound around the support roller. When the toner image primarily transferred onto the surface of the intermediate transfer belt enters the secondary transfer nip, the toner image is brought into close contact with the recording paper fed into the secondary transfer nip at the same timing, and the influence of the secondary transfer electric field is applied. Is secondarily transferred onto the surface of the recording sheet. When the recording paper on which the toner image is transferred in this way passes through the secondary transfer nip, the recording paper is separated in curvature from the intermediate transfer belt traveling along the curved surface of the support roller, and sent to the fixing device.

  In the image forming apparatus having such a configuration, the recording paper that has passed through the secondary transfer nip may move along with the intermediate transfer belt without causing the curvature separation from the surface of the intermediate transfer belt, and may cause a jam. As countermeasures for avoiding such a jam, a separation claw for mechanically forcibly separating the recording paper is pressed against the belt surface near the outlet of the secondary transfer nip, or for electrostatic separation of the recording paper. A technique for bringing the separation bias electrode close to the belt surface is known.

  However, in recent years when the size of the apparatus has been reduced, it has become difficult to secure a space for disposing a separation claw and a separation bias electrode near the outlet of the secondary transfer nip.

  The present invention has been made in view of the above background, and an object of the present invention is to suppress the occurrence of curvature separation failure of a recording paper from a belt member without providing a separation claw or a separation bias electrode. An image forming apparatus is provided.

In order to achieve the above-mentioned object, the invention of claim 1 is directed to a belt driving device that moves an endless belt member endlessly while being wound around a plurality of support rollers disposed inside the loop, A toner image forming means for forming a toner image on the front surface, and a portion around the nip back support roller, which is one of the plurality of support rollers, in the circumferential direction of the belt member. A nip forming roller that abuts from the outside of the loop to form a transfer nip; and a feeding unit that feeds recording paper toward the transfer nip, and transfers the toner image on the front surface of the belt member to the transfer nip. After the recording paper is transferred to the recording paper, the recording paper that has passed through the transfer nip has a curvature of the belt member that is curved along the peripheral surface of the nip back support roller in the vicinity of the transfer nip. An image forming apparatus separates from the belt member I, as the nip back supporting roller, for its diameter D [mm], the recording paper minimum basis weight W of the design [g / m ^2] and "D [mm ] ≦ 0.23W [g / m ² ] +5.1 ”is used.
According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the bearings that rotatably support both ends of the nip back support roller in the rotation axis direction are held immovably by the holding members. It is characterized by.
According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the nip back support roller functions as a drive roller that moves the belt member endlessly by its own rotational drive. is there.

In these inventions, the present inventors will describe later by having a relationship of “support roller diameter D [mm] ≦ 0.23 × recording paper minimum basis weight W [g / m ² ] +5.1”. As clarified in the experiment, the recording paper after passing through the transfer nip is satisfactorily separated from the surface of the belt member by curvature. Therefore, it is possible to suppress the occurrence of the curvature separation defect of the recording paper from the belt member without providing the separation claw and the separation bias electrode.

1 is a schematic configuration diagram illustrating a printer according to an embodiment. FIG. 2 is an enlarged configuration diagram illustrating a process unit for K of the printer. FIG. 2 is a partially enlarged configuration diagram illustrating a partially enlarged transfer unit in the printer. FIG. 6 is a partially enlarged configuration diagram for explaining an effect of promoting the curvature separation of recording paper by electrostatic transfer of toner. The graph which shows the relationship between the diameter of a secondary transfer roller, the minimum paper basic weight, and curvature separability.

Hereinafter, as an image forming apparatus to which the present invention is applied, an embodiment of an electrophotographic printer (hereinafter simply referred to as a printer) will be described.
First, the basic configuration of the printer will be described. FIG. 1 is a schematic configuration diagram showing the printer. In the figure, this printer includes four process units 1Y, M, C, and K for forming toner images of Y (yellow), M (magenta), C (cyan), and K (black). . These use Y, M, C, and K toners of different colors as the image forming material, but the other configurations are the same and are replaced when the lifetime is reached. Taking a process unit 1K for forming a K toner image as an example, as shown in FIG. 2, a drum-shaped photosensitive member 2K as a latent image carrier, a drum cleaning device 3K, a charge eliminating device (not shown), and a charging device 4K. And a developing device 5K. These are integrally attached to and removed from the printer body while being supported by a common support.

  The charging device 4K uniformly charges the surface of the photoreceptor 2K that is rotated clockwise in the drawing by a driving unit (not shown). The uniformly charged surface of the photosensitive member 2K is exposed and scanned by the laser beam L to carry an electrostatic latent image for K. The electrostatic latent image for K is developed into a K toner image by a developing device 5K using K toner (not shown). Then, intermediate transfer is performed on an intermediate transfer belt 16 described later.

  The drum cleaning device 3K removes the transfer residual toner adhering to the surface of the photoreceptor 2K after the intermediate transfer process. Further, the static eliminator neutralizes residual charges on the photoreceptor 2K after cleaning. By this charge removal, the surface of the photoreceptor 2K is initialized and prepared for the next image formation. Similarly, in the process units (1Y, M, C) of other colors, (Y, M, C) toner images are formed on the photoconductors (2Y, M, C), and on the intermediate transfer belt 16 described later. Intermediate transfer.

  The developing device 5K includes a vertically long hopper 6K that stores K toner (not shown) and a developing unit 7K. In the hopper 6K, an agitator 8K that is rotationally driven by a driving means (not shown), an agitation paddle 9K that is rotationally driven by a driving means (not shown) vertically below, and rotated by a driving means (not shown) below the vertical direction. A toner supply roller 10K to be driven is disposed.

  The K toner in the hopper 6K moves toward the toner supply roller 10K by its own weight while being stirred by the rotational drive of the agitator 8K and the stirring paddle 9K. The toner supply roller 10K has a metal cored bar and a roller portion made of foamed resin or the like coated on the surface of the metal core. The toner supply roller 10K adheres the K toner in the hopper portion 6K to the surface of the roller portion. Rotate while.

  In the developing unit 7K of the developing device 5K, a developing roller 11K that rotates while contacting the photoreceptor 2K and the toner supply roller 10K, and a thinning blade 12K that contacts the tip of the developing roller 11K are disposed. Yes. The K toner adhered to the toner supply roller 10K in the hopper 6K is supplied to the surface of the development roller 11K at the contact portion between the development roller 11K and the toner supply roller 10K. When the supplied K toner passes through the contact position between the roller and the thinning blade 12K as the developing roller 11K rotates, the layer thickness on the roller surface is regulated. Then, the K toner after the layer thickness regulation adheres to the electrostatic latent image for K on the surface of the photosensitive member 2K in the developing region which is a contact portion between the developing roller 11K and the photosensitive member 2K. By this adhesion, the electrostatic latent image for K is developed into a K toner image.

  Although the process unit for K has been described with reference to FIG. 2, the process units 1Y, M, and C for Y, M, and C also perform Y, M, and C on the surfaces of the photoreceptors 2Y, M, and C by a similar process. A C toner image is formed.

  In FIG. 1 described above, an optical writing device 70 is disposed above the process units 1Y, M, C, and K in the vertical direction. The optical writing device 70, which is a latent image writing device, optically scans the photoreceptors 2Y, M, C, and K in the process units 1Y, M, C, and K with laser light L emitted from a laser diode based on image information. To do. By this optical scanning, electrostatic latent images for Y, M, C, and K are formed on the photoreceptors 2Y, M, C, and K. The optical writing device 70 uses a plurality of optical lenses and mirrors as a photoconductor while polarizing laser light (L) emitted from a light source in a main scanning direction with a polygon mirror that is rotationally driven by a polygon motor (not shown). Is irradiated. You may employ | adopt what performs optical writing by the LED light emitted from several LED of the LED array.

  Below the process units 1Y, 1M, 1C, and 1K, there is disposed a transfer unit 15 that moves the endless intermediate transfer belt 16 endlessly in the counterclockwise direction while stretching. In addition to the intermediate transfer belt 16, the transfer unit 15 serving as transfer means includes a tension roller 17, a secondary transfer counter roller 18, four primary transfer rollers 19Y, M, C, K, a secondary transfer roller 20, and a belt cleaning device. 21 and a cleaning backup roller 22.

  The intermediate transfer belt 16 is stretched by a tension roller 17, a secondary transfer counter roller 18, a cleaning backup roller 22, and four primary transfer rollers 19Y, 19M, 19C, and 19K disposed inside the loop. Then, it is moved endlessly in the same direction by the rotational force of the secondary transfer counter roller 18 that is driven to rotate counterclockwise in the figure by a driving means (not shown).

  The four primary transfer rollers 19Y, 19M, 19C, and 19K sandwich the intermediate transfer belt 16 that is moved endlessly in this manner between the photoreceptors 2Y, 2M, 2C, and 2K. By this sandwiching, primary transfer nips for Y, M, C, and K where the front surface of the intermediate transfer belt 16 and the photoreceptors 2Y, M, C, and K abut are formed.

  A primary transfer bias is applied to each of the primary transfer rollers 19Y, 19M, 19C, and 19K by a transfer bias power source (not shown), whereby the electrostatic latent images on the photoreceptors 2Y, 2M, 2C, and 2K, A primary transfer electric field is formed between the primary transfer rollers 19Y, 19M, 19C, and 19K. Instead of the primary transfer rollers 19Y, 19M, 19C, and 19K, a transfer charger, a transfer brush, or the like may be employed.

  When Y toner formed on the surface of the photoreceptor 2Y of the Y process unit 1Y enters the above-described primary transfer nip for Y as the photoreceptor 2Y rotates, the photosensitive member 2Y is exposed to light by the action of the transfer electric field and nip pressure. Primary transfer is performed on the intermediate transfer belt 16 from the body 2Y. The intermediate transfer belt 16 on which the Y toner image is primarily transferred in this way passes through the primary transfer nips for M, C, and K along with the endless movement thereof, and the photoreceptors 2M, C, and K. The upper M, C, and K toner images are sequentially superimposed on the Y toner image and primarily transferred. A four-color toner image is formed on the intermediate transfer belt 16 by the primary transfer of superposition.

  The secondary transfer roller 20 abuts from the outer side of the belt loop to form a secondary transfer nip at a portion of the intermediate transfer belt 16 in the circumferential direction around the secondary transfer counter roller 18. A secondary transfer bias is applied to the secondary transfer roller 20 by a transfer bias power source (not shown). By this application, a secondary transfer electric field is formed between the secondary transfer roller 20 and the secondary transfer counter roller 18 connected to the ground.

  Below the transfer unit 15, a paper feed cassette 30 that stores a plurality of recording sheets P in a bundle of sheets is slidably attached to the printer housing. In the paper feed cassette 30, a paper feed roller 30a is brought into contact with the top recording paper P of the paper bundle, and the recording paper is rotated by rotating it in a counterclockwise direction in the drawing at a predetermined timing. P is sent out toward the paper feed path 31.

  A registration roller pair 32 is disposed near the end of the paper feed path 31. The registration roller pair 32 stops the rotation of both rollers as soon as the recording paper P delivered from the paper feed cassette 30 is sandwiched between the rollers. Then, rotation driving is resumed at a timing at which the sandwiched recording paper P can be synchronized with the four-color toner image on the intermediate transfer belt 16 in the above-described secondary transfer nip, and the recording paper P is directed to the secondary transfer nip. Send it out.

  The four-color toner image on the intermediate transfer belt 16 brought into close contact with the recording paper P at the secondary transfer nip is secondarily transferred onto the recording paper P under the influence of the secondary transfer electric field and the nip pressure. Combined with the white color of P, a full color toner image is obtained. The recording paper P having the full-color toner image formed on the surface in this manner is separated from the secondary transfer roller 20 and the intermediate transfer belt 16 by the curvature when passing through the secondary transfer nip. Then, the toner is fed into a fixing device 34 described later via a post-transfer conveyance path 33.

  The transfer residual toner that has not been transferred to the recording paper P adheres to the intermediate transfer belt 16 after passing through the secondary transfer nip. This is cleaned from the belt surface by a belt cleaning device 21 in contact with the front surface of the intermediate transfer belt 16. The cleaning backup roller 22 disposed inside the loop of the intermediate transfer belt 16 backs up the cleaning of the belt by the belt cleaning device 21 from the inside of the loop. Hereinafter, the toner removed from the surface of the intermediate transfer belt 16 by the belt cleaning device 21 is referred to as belt waste toner.

  The fixing device 34 forms a fixing nip by a fixing roller 34a containing a heat source such as a halogen lamp (not shown) and a pressure roller 34b that rotates while contacting the fixing roller 34a with a predetermined pressure. The recording paper P fed into the fixing device 34 is sandwiched between the fixing nips such that the unfixed toner image carrying surface is brought into close contact with the fixing roller 34a. Then, the toner in the toner image is softened by the influence of heating and pressurization, and the full color image is fixed.

  The recording paper P discharged from the fixing device 34 passes through the post-fixing conveyance path 35 and then reaches the branch point between the paper discharge path 36 and the pre-reversal conveyance path 41. On the side of the post-fixing conveyance path 35, a switching claw 42 that is rotationally driven around a rotation shaft 42a is disposed. By the rotation, the vicinity of the end of the post-fixing conveyance path 35 is closed. Or open it. At the timing when the recording paper P is sent out from the fixing device 34, the switching claw 42 stops at the rotational position indicated by the solid line in the drawing, and the vicinity of the end of the post-fixing conveyance path 35 is opened. Therefore, the recording paper P enters the paper discharge path 36 from the conveyance path 35 after fixing, and is sandwiched between the rollers of the paper discharge roller pair 37.

  When the single-sided print mode is set by an input operation to an operation unit including a numeric keypad (not shown) or a control signal sent from a personal computer (not shown), the recording sandwiched between the paper discharge roller pair 37 is performed. The paper P is discharged out of the machine as it is. Then, it is stacked on the sheet placement portion which is the outer surface portion of the upper cover 50 of the housing.

  On the other hand, when the duplex printing mode is set, the trailing edge of the recording paper P conveyed through the paper discharge path 36 while the front end is sandwiched between the paper discharge roller pair 37 passes through the post-fixing conveyance path 35. The switching claw 42 is rotated to the position of the one-dot chain line in the drawing, and the vicinity of the end of the post-fixing conveyance path 35 is closed. At substantially the same time, the paper discharge roller pair 37 starts to rotate in the reverse direction. Then, the recording paper P is conveyed while the rear end side is directed to the top, and enters the pre-reversal conveyance path 41.

  In FIG. 1, one end of the printer is a reversing unit 40 that can be opened and closed with respect to the main body of the housing by swinging about a swing shaft 40a. When the paper discharge roller pair 37 rotates in the reverse direction, the recording paper P enters the pre-reversal conveyance path 41 of the reversing unit 40 and is conveyed from the upper side to the lower side in the vertical direction. Then, after passing between the rollers of the pair of reverse conveying rollers 43, it enters the reverse conveying path 44 that is curved in a semicircular shape. Furthermore, while the upper and lower surfaces are reversed as the sheet is conveyed along the curved shape, the traveling direction from the upper side in the vertical direction to the lower side is also reversed, and conveyed from the lower side in the vertical direction toward the upper side. Is done. Thereafter, the toner enters the secondary transfer nip again through the above-described paper feed path 31. Then, after the full color image is collectively transferred to the other surface, the post-transfer conveyance path 33, the fixing device 34, the post-fixation conveyance path 35, the paper discharge path 36, and the paper discharge roller pair 37 are sequentially passed. And discharged outside the machine.

  The reversing unit 40 includes an outer cover 45 that can swing with respect to the main body of the housing, and a second swinging body 46 that can swing further with respect to the outer cover 45. Specifically, the outer cover 45 of the reversing unit 40 is supported so as to swing around a swinging shaft 40a provided in the housing of the printer main body. By this swinging, the outer cover 45 opens and closes with respect to the housing together with the second swinging body 46 held therein. As shown by the dotted line in the figure, when the outer cover 45 is opened together with the second rocking body 46 therein, the paper feed path 31, the secondary transfer nip formed between the reversing unit 40 and the printer main body side, The post-transfer conveyance path 33, the fixing nip, the post-fixation conveyance path 35, and the paper discharge path 36 are vertically divided into two and exposed to the outside. Thereby, jammed paper in the paper feed path 31, the secondary transfer nip, the post-transfer conveyance path 33, the fixing nip, the post-fixation conveyance path 35, and the paper discharge path 36 can be easily removed.

  The second rocking body 46 is supported by the external cover 45 so as to rock around a rocking shaft (not shown) provided in the external cover 45 in a state where the external cover 45 is opened. When the second oscillating body 46 is opened with respect to the outer cover 45 by this swing, the pre-reverse transport path 41 and the reverse transport path 44 are vertically divided into two and exposed to the outside. As a result, the jammed paper in the pre-reversal conveyance path 41 and the reversal conveyance path 44 can be easily removed.

  The upper cover 50 of the printer casing is a door for the casing. As shown by the arrows in the figure, the shaft member 51 is supported so as to be swingable. By rotating a predetermined angle in the counterclockwise direction in the figure, the shaft member 51 is opened. And the maintenance inspection opening of a housing is opened.

A toner transport device 100 is disposed between the transfer unit 15 and the paper feed cassette 30 in the vertical direction inside the printer. The toner conveying device 100 conveys the toner collected from the process units 1Y, 1M, 1C, and 1K of each color and the intermediate transfer belt 21 to its own collected toner container.
In the printer having such a configuration, the recording paper P that has passed through the secondary transfer nip may move along with the intermediate transfer belt 16 without causing a curvature separation from the surface of the intermediate transfer belt 16, and may cause a jam. As a measure for avoiding the occurrence of such a jam, as shown in FIG. 3, a separation claw 23 for mechanically separating the recording paper P is pressed against the belt surface in the vicinity of the outlet of the secondary transfer nip. Conceivable. Further, the separation bias electrode 24 for electrostatically separating the recording paper P may be placed close to the belt surface.

  However, in recent years when the size of the apparatus is reduced, it has become difficult to secure a space for disposing the separation claw 23 and the separation bias electrode 24 near the outlet of the secondary transfer nip.

Next, experiments conducted by the present inventors will be described.
The inventors prepared a printer testing machine having the same configuration as the printer according to the embodiment. In this printer testing machine, the width of the intermediate transfer belt 16 and the length of each photoconductor in the axial direction are about 230 [mm]. Using this printer tester, a test was conducted in which A4 size recording paper was continuously passed. The continuous test paper passing is a test in which 10 recording papers are continuously passed through the secondary transfer nip while the secondary transfer bias is applied to the secondary transfer roller 20. In continuous test passing, since no toner image is formed on the intermediate transfer belt 16, the recording paper passes through the secondary transfer nip without the toner image being secondarily transferred. The reason why the toner image is not secondarily transferred to the recording paper but only passed through the secondary transfer nip is as follows. That is, when a toner image is formed on the intermediate transfer belt 16, the toner constituting the toner image is unfixed and powdery. Can be easily detached from the belt surface. As shown in FIG. 4, when the toner image is secondarily transferred from the belt surface to the recording paper P, the toner is electrostatically moved from the belt surface side to the secondary transfer roller 20 side. A force is applied to P in a direction away from the belt surface. As a result, when the toner image is present on the belt surface, the recording paper P is more easily separated from the belt surface than when the toner image is not present. Therefore, a condition that the recording paper P is simply passed through the secondary transfer nip without forming a toner image is a condition that is most likely to cause the curvature separation failure of the recording paper P. Therefore, continuous test paper passing without forming a toner image on the intermediate transfer belt 16 is performed.

As the recording paper P, A4 size paper was used, and it was passed through the secondary transfer nip in a horizontally long posture (a posture in which the short side direction was aligned with the conveying direction). Regarding the pressure of the secondary transfer nip, four types of 20, 30, 40, and 50 [N] were set, and continuous test paper passing was performed under each pressure condition. In addition, the process linear velocity was set to three types of 60, 120, and 180 [mm / sec], and continuous test paper was passed under each linear velocity condition. Further, as shown in the following Table 1, four types of intermediate transfer belts 16 having different materials and thicknesses were used, and a continuous test paper was passed through each belt.

As the A4 size recording paper P, copy printing paper 45 kY (54 g / m ² ) manufactured by NBS Ricoh, copy printing paper 55 kY (65 g / m ² ) manufactured by NBS Ricoh, and Mys made by NBS Ricoh Three types of paper EP (70 g / m ² ) were used. A continuous test was passed for each paper type.

  While sequentially changing the seven secondary transfer counter rollers 18 having different diameters, continuous test paper passing was performed with each of the secondary transfer counter rollers 18. The diameters of the secondary transfer counter roller 18 are seven types of 16, 18, 20, 21, 22, 23, and 24 [mm].

  Four secondary transfer nip pressures x three process linear velocities x four belt types x three paper types x seven roller diameters = 1008 conditions were used for continuous test paper passing. As described above, the amount of paper passed per continuous test pass is 10 sheets. When curvature separation failure occurred even in one of the 10 sheets, x (separation failure occurred) was evaluated as ◯ (no separation failure) when no curvature separation failure occurred.

  From the results of these 1008 continuous test paper passes, it was found that the curvature separation property of the recording paper from the belt is not affected by the process linear velocity, the secondary transfer nip pressure, and the belt type. Even if the process linear velocity was changed, the secondary transfer nip pressure was changed, or the belt type was changed, the curvature separation did not change. It should be noted that the process linear velocity did not affect the curvature separability in the range of 60 to 180 [mm / sec] when the recording paper passed through the secondary transfer nip for about 0.1 seconds. This is thought to be due to the electrostatic force acting on the paper.

  On the other hand, the diameter of the secondary transfer counter roller 20 serving as the nip back support roller and the type of the recording paper greatly affected the curvature separation. Specifically, the larger the diameter of the secondary transfer counter roller 20, the worse the curvature separability. Further, the smaller the basis weight of the recording paper, the worse the curvature separability. FIG. 5 shows the relationship among the diameter of the secondary transfer counter roller 20, the basis weight of the recording paper, and the curvature separation property. Of the plotted points in FIG. 5, when only the plotted points with the result of curvature separability being “◯” were extracted and the regression linear equation was calculated, a function of diameter D = 0.23 × basis weight + 5.1 was obtained. It was. If the condition is a straight line indicated by this function or a region below the straight line, curvature separation failure does not occur.

The recording paper is set in the paper feed cassette by the user, and what kind of recording paper is used is determined at the discretion of the user. However, it is possible to specify the minimum basis weight W [g / m ² ] of the recording paper to the user. For example, “Use a paper with a basis weight of OOg / m ² or more.”, “The minimum paper basis weight that this printer can handle is OOOOg / m ² ”. The minimum recording paper basis weight W, which is the minimum value of the recording paper basis weight, is designated to the user.

Therefore, in this printer, the recording paper minimum basis weight W [g / m ² ] is specified for the user by using the above-described notation in the instruction manual of the apparatus. The secondary transfer body roller 20 has a relationship of “diameter D [mm] of the secondary transfer counter roller 20 ≦ 0.23 × minimum basis weight of recording paper W [g / m ² ] +5.1”. It is equipped with.

  In such a configuration, the recording paper after passing through the secondary transfer nip is satisfactorily separated from the surface of the intermediate transfer belt 16 as clarified by the experiment of continuous test paper passing by the present inventors. Therefore, it is possible to suppress the occurrence of the curvature separation failure of the recording paper from the intermediate transfer belt 16 without providing a separation claw or a separation bias electrode.

  Since the stiffness of the recording paper P is not affected by the width of the recording paper P (the dimension in the direction orthogonal to the transport direction), the curvature separation property of the recording paper P from the intermediate transfer belt 16 is It is considered that the recording paper P is not affected by the difference in width.

  In this printer, bearings that rotatably support both ends of the secondary transfer counter roller 20 in the rotation axis direction are held immovably by side plates of the apparatus main body. That is, the secondary transfer counter roller 20 is configured to be immovable. Thus, by causing the secondary transfer nip to exist at a specific position regardless of the tension of the intermediate transfer belt 16, occurrence of fluctuations in the secondary transfer nip position due to fluctuations in tension is avoided. Therefore, it is possible to avoid the occurrence of the variation in curvature separation due to the change in the secondary transfer nip position due to the variation in the tension of the intermediate transfer belt 16.

  In this printer, the secondary transfer counter roller 20 functions as a drive roller that moves the intermediate transfer belt 16 endlessly by its own rotational drive. In such a configuration, by causing the intermediate transfer belt 16 to be pressed against the secondary transfer counter roller 20 at the secondary transfer nip under pressure, occurrence of belt slip on the surface of the secondary transfer counter roller 20 functioning as a driving roller is suppressed. Can do.

16: Intermediate transfer belt (belt member)
17: Tension roller (support roller)
18: Secondary transfer opposing roller (nip back support roller, drive roller)
20: Secondary transfer roller (nip forming roller)
32: Registration roller pair (feeding means)

JP 2007-140041 A

Claims (3)

A belt driving device that moves an endless belt member endlessly while being wound around a plurality of support rollers disposed inside the loop; and a toner image forming unit that forms a toner image on the front surface of the belt member; A nip forming roller that forms a transfer nip by abutting from the outside of the loop against a nip back support roller that is one of the plurality of support rollers among the entire circumferential direction of the belt member; , Feeding means for feeding recording paper toward the transfer nip,
And after the toner image on the front surface of the belt member is transferred to the recording paper in the transfer nip, the recording paper that has passed through the transfer nip is moved around the nip back support roller in the vicinity of the transfer nip. In the image forming apparatus that separates from the belt member by the curvature of the belt member that is curved along a surface,
As the nip back support roller, the diameter D [mm] and the designed minimum basis weight W [g / m ² ] of recording paper “D [mm] ≦ 0.23 W [g / m ² ] +5. An image forming apparatus using an apparatus having a relationship of “1”. The image forming apparatus according to claim 1.
An image forming apparatus, wherein bearings for rotatably supporting both ends of the nip back support roller in the rotational axis direction are held immovably by holding members, respectively. The image forming apparatus according to claim 2.
An image forming apparatus, wherein the nip back support roller functions as a drive roller that moves the belt member endlessly by its own rotational drive.

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