JP2008158019A - Fixing device and image forming apparatus equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of shortening a starting time and reducing power consumption, while securing high fixability and image quality. <P>SOLUTION: The fixing device 50 includes: a first fixing means 20 for fixing an unfixed toner image T carried on a paper (recording material) P; and a second fixing means 30 for re-fixing the toner image fixed on the paper P by the first fixing means 20, wherein a first fixing roller 21 located on the toner image side of the first fixing means 20 is constituted by disposing a release layer 24 on a core bar (metallic base material) 23, and a second fixing roller 31 located on the toner image side of the second fixing means 30 is constituted, by forming an elastic layer 34 on a core bar (metallic base material) 33 and forming a release layer 35 on the elastic layer 34. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fixing device for fixing an unfixed toner image transferred to a recording material such as paper, and an image forming apparatus including the fixing device.

  2. Description of the Related Art Image forming apparatuses such as copying machines, printers, and facsimiles that employ an electrophotographic system are provided with a fixing device for fixing an unfixed toner image transferred onto a recording material such as paper. Known fixing devices include a heat roller system including a fixing roller and a pressure roller that rotate while contacting each other, and a belt system that uses an endless fixing belt as a heating member.

  Here, a conventional fixing device employing a heat roller system will be described with reference to FIG.

  FIG. 4 is a cross-sectional view showing the basic structure of a conventional fixing device. The fixing device 150 shown in FIG. 4 carries an unfixed toner image T on the nip portion between the fixing roller 120 and the pressure roller 130 that rotate in pressure contact with each other. By introducing the paper P and nipping and conveying it, the unfixed toner image T is heated and pressurized to be fixed on the surface of the paper P.

  Here, in the fixing roller 120, an elastic layer 123 such as silicon rubber is provided on the outer periphery of a cylindrical cored bar 122 such as aluminum, and a release layer 124 of fluororesin such as PFA or PTFE is further provided on the surface of the elastic layer 123. It is configured by providing a heater 121 as a heat source inside the cored bar 122.

  Similarly to the fixing roller 120, the pressure roller 130 has a heater 131 therein, and is composed of a core metal 132, an elastic layer 133, and a release layer 134. The pressure roller 130 is pressed against the fixing roller 120 by a pressing means (not shown). Then, it rotates while forming a nip portion with the fixing roller 120.

  The thermistors 125 and 135 as temperature detecting means are brought into contact with the surfaces of the fixing roller 120 and the pressure roller 130, respectively, and the surfaces of the fixing roller 120 and the pressure roller 130 detected by the thermistors 125 and 135 are contacted. The heaters 121 and 131 are driven and controlled by a heater drive circuit (not shown) based on the temperature, and the temperature of the fixing roller 120 and the pressure roller 130 is controlled so as to reach the target temperatures.

  By the way, the fixing roller of the fixing device provided in the color image forming apparatus is provided with an elastic layer. This fixing roller does not have an elastic layer (that is, has a hard surface). This is because the surface comes into contact with a point, resulting in uneven gloss due to a partial fixing property difference, and this point is particularly noticeable in a color image. By providing an elastic layer on the fixing roller, the surface hardness of the fixing roller is lowered, and the unevenness of the toner image is surrounded by the surface of the fixing roller, thereby preventing uneven gloss.

  However, if heat is transferred from the inside of the fixing roller and the pressure roller by a heater provided inside the fixing roller and the pressure roller, the thermal conductivity of the elastic layer is small, so that the core metal temperature is higher than the roller surface temperature. Increases by several tens of degrees Celsius. In general, this temperature difference depends on the thickness of the elastic layer. The thicker the elastic layer, the larger the temperature difference. Therefore, if the temperature control temperature on the roller surface is increased as the speed increases, the core metal temperature also rises, and the rubber at the interface between the elastic layer and the core metal undergoes thermal degradation, causing the rubber to peel off. The performance is significantly reduced. For this reason, it is necessary to reduce the thickness of the elastic layer in order to lower the interface temperature between the elastic layer and the metal core to a temperature at which the rubber does not thermally deteriorate.

  However, when the thickness of the elastic layer is reduced, the nip width of the nip portion is reduced, and the roller diameter must be increased in order to ensure a predetermined nip width.

  In addition, since the thermal conductivity of the elastic layer is small, heat is transferred from the surface of the fixing roller to the sheet at the nip portion between the fixing roller and the pressure roller. Since the heat conduction is slow, the fixability is deteriorated even if the same nip width is provided as compared with the case where there is no elastic layer. Therefore, it is necessary to increase the roller diameter to increase the nip width. As a result, the time (warm-up time) required to raise the roller surface temperature to the temperature required for fixing becomes longer.

In view of this, Japanese Patent Application Laid-Open No. H10-228867 provides first and second fixing means for the purpose of increasing the printing speed and shortening the warm-up time (start-up time). The first heating unit is disposed on the image surface side, the first pressure member is disposed on the side opposite to the toner image surface, and the second pressure member is disposed on the toner image surface side in the second fixing unit. However, a configuration in which a second heating unit is disposed on the side opposite to the toner image surface has been proposed.
JP 2002-049258 A

  However, in the configuration proposed in Patent Document 1, the pressure member is disposed on the toner image surface side in the second fixing unit and the heating unit is disposed on the side opposite to the toner image surface. In order to raise the temperature to a fixing possible temperature (a temperature at which the toner surface can be melted and made uniform), the temperature must be raised by the heating means in contact with the pressure member. It is necessary to set the temperature higher than the required temperature of the member. In addition, since the pressure member is also heated from the outside, the surface temperature of the pressure member is the highest, the temperature decreases toward the inside, and the conventional internal heating method is used to obtain a desired fixing property. In comparison with this, it is necessary to increase the set temperature, which causes a problem that efficiency is deteriorated.

  In addition, the pressure member is composed of a fixed heating element and a slidable film with the inner surface facing and opposed to the heating element. In the pressure member thus configured, the film generates heat. Since the body always rotates while rubbing, the film is scraped and damaged, or the film does not rotate well, causing problems in conveying the sheet.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and a purpose of the present invention is to provide a fixing device capable of reducing start-up time and power consumption while ensuring high fixability and image quality. An image forming apparatus is provided.

  In order to achieve the above object, according to the first aspect of the present invention, there is provided a first fixing means for fixing an unfixed toner image carried on a recording material, and the first fixing means fixed on the recording material. In a fixing device including a second fixing unit for re-fixing a toner image on a recording material, a first fixing roller on the toner image side of the first fixing unit is provided with a release layer on a metal substrate. The second fixing roller on the toner image side of the second fixing unit is configured by providing an elastic layer on a metal substrate and providing a release layer on the elastic layer. .

  According to a second aspect of the present invention, in the first aspect of the present invention, when the color image is fixed on the recording material, the first and second heating sources for heating the first and second fixing rollers, respectively. After adjusting the temperature of each fixing roller to the target temperature, the recording material is passed through the first and second fixing means, and when fixing the monochrome image, only the first fixing roller is used as the first heating source. After the temperature is adjusted to the target temperature, the recording material is passed through the first and second fixing means regardless of the temperature of the second fixing roller.

  According to a third aspect of the present invention, in fixing the monochrome image in the second aspect of the invention, energization of the second heating source is stopped while the recording material passes through the first fixing unit. It is characterized by doing.

  According to a fourth aspect of the present invention, in the second or third aspect of the invention, at the time of warm-up, the temperature of the first fixing roller is adjusted to a target temperature and then the first heating source is not energized. The second heat source is energized to adjust the temperature of the second fixing roller to a target temperature.

  According to a fifth aspect of the present invention, in the invention of the fourth aspect, when fixing the monochrome image immediately after the warm-up, the first and second fixing rollers are adjusted to the target temperature, and then the recording material is moved to the first and second recording materials. When it is necessary to control the temperature of the second fixing roller to a target temperature at this time, the first heating source is energized while passing the recording material through the first fixing unit. When the second heat source is energized to adjust the temperature of the second fixing roller to the target temperature and the color image is fixed immediately after warming up, the first fixing roller is set to the target temperature. After the temperature is adjusted to the first temperature, the second heating source is energized when the first heating source is not energized, and the temperature of the second fixing roller is adjusted to the target temperature. It is characterized by passing through fixing means.

  According to a sixth aspect of the present invention, there is provided an image carrier that forms a latent image, developing means that develops the latent image formed on the image carrier and visualizes it as a toner image, and converts the toner image into the image. 6. The image forming apparatus comprising: a transfer unit that transfers the toner image transferred onto the recording material; and a fixing unit that fixes the toner image transferred onto the recording material. It is characterized by comprising a fixing device.

  According to the first aspect of the present invention, since the first fixing roller on the toner image side of the first fixing unit that fixes the unfixed toner image on the recording material does not have an elastic layer having a low thermal conductivity, The heat conduction to the surface of the first fixing roller at the nip portion is good, and the fixing property to the recording material is improved even at the same nip time and fixing temperature as compared with the fixing roller provided with the elastic layer. Therefore, the diameter of the fixing roller can be reduced as compared with the case where there is an elastic layer, the fixing temperature can be set low, and the warm-up time (start-up time) can be shortened.

  The recording material that has passed through the first fixing unit is passed through the second fixing unit. The second fixing roller on the toner image side of the second fixing unit has an elastic layer. The surface hardness decreases, and the second fixing roller comes into contact with the surface so as to wrap around the unevenness of the toner image, so that the heat is uniformly transmitted to the entire surface of the toner image, and the toner is crushed by the pressure so that the surface becomes smooth. Thus, uneven gloss that occurs after passing through the first fixing means can be eliminated.

  According to the second aspect of the present invention, in fixing the color image, the temperature of the first and second fixing rollers is adjusted to the target temperature, and then the recording material is passed through the first and second fixing means. In addition, it is possible to ensure high fixability and prevent occurrence of uneven gloss.

  According to the third aspect of the present invention, when fixing the monochrome image, the energization to the second heating source is stopped while the recording material passes through the first fixing means. Energy saving can be achieved by keeping it low.

  According to the fourth aspect of the present invention, when fixing a monochrome image capable of obtaining high fixability and image quality regardless of the temperature of the second fixing roller, the first fixing roller is heated to the target temperature immediately after the warm-up. After the adjustment, the recording material carrying the unfixed toner image may be immediately passed through the first and second fixing means, and in this way the warm-up time can be shortened. At this time, if only monochrome images are fixed continuously, it is not necessary to heat the second constant fixing roller, and therefore it is not necessary to energize the second heating source. Can be realized.

  When fixing a color image immediately after warm-up, it is necessary to adjust the temperature of the first and second fixing rollers to the target temperature. In this case, first, the temperature of the first fixing roller is first set to the target temperature. Then, when the first heating source is not energized, the second heating source is energized to adjust the temperature of the second fixing roller to the target temperature, and the recording material carrying the unfixed toner image is And the second fixing means. Thus, by alternately energizing the first heating source and the second heating source, the maximum power (rated power) of each heating source can be set large, so the warm-up startup time is shortened. This is particularly effective when fixing only monochrome images.

  According to the invention described in claim 5, when fixing a monochrome image immediately after warm-up, the recording material is passed through the first and second fixing means after the temperature of the first fixing roller is adjusted to the target temperature. At this time, if it is necessary to adjust the temperature of the second fixing roller to the target temperature, the second heating source can be used when the first heating source is not energized while passing the recording material through the first fixing means. Since the temperature of the second fixing roller is adjusted to the target temperature by energizing the printer, it is necessary to fix the color image in advance when a color image formation signal is input while fixing the monochrome image. When the first heating source is not energized while passing the recording material carrying the unfixed toner image at that time, the second heating source is energized to adjust the temperature of the second fixing roller to the target temperature. To prepare for subsequent fixing of color images It can be placed.

  According to the invention described in claim 6, in the image forming apparatus capable of forming both monochrome images and color images, the start-up time can be shortened while ensuring high fixability and image quality of monochrome images and color images. The power consumption can be reduced.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

[Image forming apparatus]
FIG. 1 is a front sectional view of an image forming apparatus according to the present invention. The illustrated image forming apparatus is a tandem type color image forming apparatus, and a black image forming unit 1BK, The yellow image forming unit 1Y, the cyan image forming unit 1C, and the magenta image forming unit 1M are arranged in a line at regular intervals.

  Each of the image forming units 1BK, 1Y, 1C, and 1M includes photosensitive drums 2a, 2b, 2c, and 2d as image carriers and developing devices 3a, 3b, 3c, and 3d, a primary charger (not shown), and cleaning. Equipment and the like.

  Here, the photosensitive trams 2a to 2d are drum-shaped photosensitive members, and are rotationally driven at a predetermined process speed in a direction indicated by an arrow (counterclockwise) by a driving device (not shown). Further, the developing devices 3a to 3d accommodate toners of black (BK), yellow (Y), cyan (C) and magenta (M), respectively, and are formed on the photosensitive drums 2a to 2d. Each color toner is attached to each electrostatic latent image to visualize each electrostatic latent image as a toner image of each color. The primary charger (not shown) uniformly charges the surfaces of the photosensitive drums 2a to 2d to a predetermined potential by a charging bias applied from a charging bias power source.

  Further, transfer rollers 4a to 4d as primary transfer means are arranged so as to be in contact with the respective photosensitive drums 2a to 2d via the endless intermediate transfer belt 5 at each primary transfer portion. Here, the intermediate transfer belt 5 is stretched between the driving roller 6, the driven roller 7 and the backup roller 8 so as to be able to run on the lower surface side of each of the photosensitive drums 2 a to 2 d. In the secondary transfer portion, the secondary transfer roller 9 is disposed so as to be in contact with the intermediate transfer belt 5. Further, an ID sensor 10 and a sensor backup roller 11 are disposed at opposing positions inside and outside the intermediate transfer belt 5. Although not shown, a belt cleaning device is provided in the vicinity of the driven roller 7.

  Furthermore, a paper feed cassette 12 is detachably installed at the bottom of the apparatus main body 100. A plurality of sheets of recording material P, which are recording materials, are stacked and stored in the paper feed cassette 12, and in the vicinity of the paper feed cassette 12, a pickup roller 13 for taking out the paper P one by one from the paper feed cassette 12, and A cassette paper feed roller 14 and a manual paper feed roller 15 are provided for feeding the taken paper P to the horizontal transport path L1.

  By the way, the sheet P is temporarily held on the upstream side (upstream side in the transport direction of the paper P) of the secondary transfer portion (the contact portion between the backup roller 8 and the secondary transfer roller 9) of the horizontal transport path L1. A registration roller 16 that is supplied to the secondary transfer unit at a predetermined timing later is provided.

  A fixing device 50 according to the present invention is provided on the downstream side of the secondary transfer portion of the transport path L1. The fixing device 50 includes a first fixing unit 20 and a second fixing unit 30 arranged along the conveyance direction of the paper P. Details of the configuration will be described later.

  The conveyance path L2 arranged in the vertical direction on one side in the apparatus main body 100 extends to the paper discharge tray 17 provided on the upper surface of the apparatus main body 100. A paper discharge roller 19 is provided.

  Next, an image forming operation by the color image forming apparatus having the above configuration will be described.

  When an unillustrated start button is pressed and an image formation start signal is issued, the photosensitive drums 2a to 2d in the image forming units 1BK, 1Y, 1C, and 1M are set in a predetermined direction in the arrow direction (counterclockwise direction) in FIG. The photosensitive drums 2a to 2d are rotationally driven at a process speed, and are uniformly charged by a primary charger (not shown). The surfaces of the photosensitive drums 2a to 2d are irradiated with laser light modulated by the color image signals for the respective colors, and electrostatic latent images corresponding to the color image signals of the respective colors are formed on the photosensitive drums 2a to 2d. Each is formed.

  First, black toner is attached to the electrostatic latent image formed on the photosensitive drum 2a of the black image forming unit BK by the developing device 3a to which a developing bias having the same polarity as the charged polarity of the photosensitive drum 2a is applied. The electrostatic latent image is visualized as a black toner image. This black toner image is transferred to the arrow shown in FIG. 1 by the action of the transfer roller 4a to which a primary transfer bias opposite in polarity to the toner is applied in the primary transfer portion (transfer nip portion) between the photosensitive drum 2a and the transfer roller 4a. Primary transfer is performed on the intermediate transfer belt 5 that is rotationally driven in the direction.

  The intermediate transfer belt 5 on which the black toner image is primarily transferred as described above moves to the next yellow image forming unit 1Y. In the yellow image forming unit 1Y, similarly to the above, the yellow toner image formed on the photosensitive drum 2b is transferred to the black toner image on the intermediate transfer belt 5 at the primary transfer portion.

  Similarly, cyan and magenta toners formed on the photosensitive drums 2c and 2d of the cyan and magenta image forming units 1C and 1M on the black and yellow toner images superimposed and transferred on the intermediate transfer belt 5, respectively. The images are sequentially superimposed on each primary transfer portion, and a full-color toner image is formed on the intermediate transfer belt 5. The transfer residual toner which is not transferred onto the intermediate transfer belt 5 and remains on the photosensitive drums 2a to 2d is removed by cleaning devices (not shown), and the photosensitive drums 2a to 2d are prepared for the next image formation. .

  Then, the paper feed cassette 12 to the pickup roller 13 are synchronized with the timing at which the front end of the full-color toner image on the intermediate transfer belt 5 reaches the secondary transfer portion (transfer nip portion) between the backup roller 8 and the secondary transfer roller 9. The paper P sent out to the transport path L1 by the cassette paper feed roller 14 is transported to the secondary transfer section by the registration roller 16. Then, a full-color toner image is secondarily transferred from the intermediate transfer belt 5 to the sheet P conveyed to the secondary transfer portion by the secondary transfer roller 9 to which a secondary transfer bias having a polarity opposite to that of the toner is applied. The

  Thus, the sheet P on which the full-color unfixed toner image has been transferred is conveyed to the fixing device 50, where the toner image is first fixed by the first fixing unit 20, and then the second fixing unit 30. The toner image is re-fixed. Then, the sheet P on which the toner image is fixed is transported upward along the transport path L2 by the transport roller 18 and is discharged onto the paper discharge tray 17 by the paper discharge roller 19 to complete a series of image forming operations. Incidentally, the transfer residual toner which is not transferred onto the paper P in the secondary transfer portion and remains on the intermediate transfer belt 5 is removed by the belt cleaning device (not shown), and the intermediate transfer belt 5 is prepared for the next image formation. .

  By the way, the color image forming apparatus according to the present embodiment can also form a monochrome image. When a monochrome image is formed, the black toner image formed on the photosensitive drum 2a by the black image forming unit 1BK. Only the toner image is primarily transferred onto the intermediate transfer belt 5, and thereafter, the black toner image is secondarily transferred and fixed from the intermediate transfer belt 5 onto the paper P in the same manner as described above to form a monochrome image.

Fixing device]
Next, an embodiment of the fixing device according to the present invention will be described.

<Embodiment 1>
FIG. 2 is a schematic cross-sectional view showing the basic configuration of the fixing device according to the first embodiment of the present invention.

  The fixing device 50 according to the present embodiment includes a first fixing unit 20 and a second fixing unit 30 disposed on the downstream side thereof.

  Here, the first fixing unit 20 includes a first fixing roller 21 having an outer diameter of φ25 mm and a pressure roller 22 having an outer diameter of φ25 mm that is pressed against the fixing roller 21 by a pressing unit (not shown). . The fixing roller 21 is provided with a release layer 24 made of fluororesin such as PFA or PTFE on the surface of a cylindrical cored bar 23 made of aluminum or the like having a thickness of 1.0 mm, and serves as a first heating source inside the cored bar 23. The heater 25 is provided.

  Further, the pressure roller 22 is provided with an elastic layer 27 such as silicon rubber having a thickness of 5.5 mm on the outer periphery of a core metal 26 such as aluminum or iron having an outer diameter of φ14 mm, and further, PFA, PTFE or the like is provided on the surface of the elastic layer 27. The fluororesin release layer 28 is formed, and is pressed against the fixing roller 21 by a pressing means (not shown) and rotates while forming a nip portion with the fixing roller 21.

  A thermistor 29 as temperature detecting means is brought into contact with the surface of the fixing roller 21, and the heater 29 is driven and controlled by a heater drive circuit (not shown) based on the surface temperature of the fixing roller 21 detected by the thermistor 29. Then, the temperature control is performed so that the surface temperature of the fixing roller 21 becomes the temperature control target temperature.

  A non-contact type separation plate 41 made of metal or resin is provided on the exit side of the sheet conveyance direction with respect to the nip portion of the fixing roller 21, and the surface of the separation plate 41 is PFA or PTFE. A release layer of fluororesin such as is formed. In this embodiment, the non-contact type separation plate 41 is used, but a contact type separation plate or a separation claw may be used.

  On the other hand, the second fixing unit 30 includes a second fixing roller 31 having an outer diameter of φ25 mm and a pressure roller 32 having an outer diameter of φ25 mm pressed against the fixing roller 31 by a pressing unit (not shown). The fixing roller 31 is provided with an elastic layer 34 such as silicon rubber having a thickness of 2.0 mm on the outer periphery of a cylindrical metal core 33 such as aluminum having a thickness of 1.0 mm, and further, PFA, PTFE or the like is provided on the surface of the elastic layer 34. A release layer 35 of fluororesin is provided, and a heater 36 as a second heating source is provided inside the cored bar 33.

The pressure roller 32 is provided with an elastic layer 38 such as silicon rubber having a thickness of 1.5 mm on the outer periphery of a core metal 37 such as aluminum or iron having a diameter of 22 mm, and the surface of the elastic layer 38 is made of PFA or PTFE. A fluororesin release layer 39 is formed, and is pressed against the fixing roller 31 by a pressing means (not shown) and rotates while forming a nip portion with the fixing roller 31.
The cored bar 37 of the pressure roller 32 may be solid or hollow.

  A thermistor 40 as temperature detecting means is brought into contact with the surface of the fixing roller 31, and the heater is driven and controlled by a heater drive circuit (not shown) based on the surface temperature of the fixing roller 31 detected by the thermistor 40. Thus, the temperature control is performed so that the surface temperature of the fixing roller 31 becomes the temperature control target temperature.

  Further, a non-contact type separation plate 42 made of metal or resin is provided on the exit side of the sheet conveyance direction with respect to the nip portion of the fixing roller 31. The surface of the separation plate 42 is PFA, PTFE, or the like. A release layer of fluororesin is formed. In this embodiment, the non-contact type separation plate 42 is used, but a contact type separation plate or a separation claw may be used. Further, as in the present embodiment, the elastic layer 38 of the pressure roller 32 is made thinner than the elastic layer 34 of the fixing roller 31, or the hardness of the elastic layer 34 of the fixing roller 31 is set to be lower than that of the elastic layer 38 of the pressure roller 32. By adopting a configuration in which the paper P is separated downward by increasing the hardness, the configuration may be such that the separation plate 422 is eliminated and the pickup is picked up by a guide instead.

  Thus, in the fixing device 50 including the first fixing unit 20 and the second fixing unit 30 as described above, the first fixing roller 21 on the toner image side of the first fixing unit 20 is made of metal. A release layer 24 is provided on a core metal 23 that is a base material, and the second fixing roller 31 on the toner image side of the second fixing unit 30 is provided with an elastic layer on a core metal 33 that is a metal base material. 34, and the release layer 35 is provided on the elastic layer 34, the following effects can be obtained.

  That is, the first fixing roller 21 on the toner image side of the first fixing unit 20 that fixes the unfixed toner image T on the paper P does not have an elastic layer having a low thermal conductivity. The heat conduction to the surface of one fixing roller 21 is good, and the fixing property to the paper P is improved even at the same nip time and fixing temperature as compared with the fixing roller provided with the elastic layer. Therefore, the diameter of the fixing roller 21 can be reduced as compared with the case where there is an elastic layer, the fixing temperature can be set low, and the warm-up time (start-up time) can be shortened.

  However, since the first fixing roller 21 does not have an elastic layer, the surface of the fixing roller 21 is in contact with the unevenness of the surface of the toner image at a point, resulting in uneven gloss due to a partial difference in fixability. This is particularly noticeable in color images.

  Therefore, in the present embodiment, the sheet P that has passed through the first fixing unit 20 is passed through the second fixing unit 30, and the second fixing roller 31 on the toner image side of the second fixing unit 30 is Since the elastic layer 34 is provided, the surface hardness of the toner image is lowered, and the second fixing roller 31 comes into contact with the surface so as to wrap up the unevenness of the toner image, so that heat is uniformly transmitted to the entire surface of the toner image, When the toner is crushed by the pressure, the surface becomes smooth, and gloss unevenness generated after passing through the first fixing unit 20 can be eliminated.

  The second fixing unit 30 is intended only to smooth the toner surface and eliminate gloss unevenness. In addition to smoothing the toner surface and eliminating gloss unevenness as in the conventional heat roller system, the second fixing unit 30 is not yet determined. The amount of heat supplied to the paper P can be reduced compared to the case where the contact toner image has to be fixed on the recording material. Therefore, similarly to the first fixing unit 20, the second fixing unit 30 can reduce the diameter of the fixing roller 31 and set the fixing temperature low, so that the start-up time can be shortened.

In this embodiment, fixing rollers 21 and 31 are used for the first and second fixing units 20 and 30, respectively, and these fixing rollers 21 and 31 are rotated at a linear velocity substantially equal to the conveying linear velocity of the paper P. By driving, the fixing film 50 having high durability can be realized without sliding the fixing film.
In the fixing device 50 according to the present embodiment, when the color image is fixed on the paper P, the first and second heaters 25 for heating the first and second fixing rollers 21 and 31, respectively. 36, after adjusting the fixing rollers 21 and 31 to the target temperature, the first fixing roller is used when the paper P is passed through the first and second fixing means 20 and 30 to fix the monochrome image. After adjusting the temperature of only 21 to the target temperature by the first heater 25, the paper P is passed through the first and second fixing means 20, 30 regardless of the temperature of the second fixing roller 31.

  As described above, in fixing a color image, the temperature of the first and second fixing rollers 21 and 31 is adjusted to a target temperature, and then the paper P is passed through the first and second fixing units 20 and 30. As a result, high fixability can be ensured and gloss unevenness can be prevented.

  On the other hand, in fixing a monochrome image in which gloss unevenness due to a difference in partial fixing properties is difficult to understand, the temperature of only the first fixing roller 21 is adjusted to the target temperature, and then the sheet is irrespective of the temperature of the second fixing roller 31. Since P is passed through the first and second fixing means 20 and 30, the warm-up time can be shortened.

  Further, in the present embodiment, when fixing a monochrome image, the energization of the second heater 36 is stopped while the paper P passes through the first fixing means 20, so that the power consumption is reduced. Energy saving can be achieved.

  Furthermore, in the present embodiment, at the time of warm-up, the first fixing roller 21 is adjusted to the target temperature, and then the second heater 36 is energized when the first heater 25 is not energized. The temperature of the fixing roller 31 was adjusted to the target temperature.

  Therefore, when fixing a monochrome image that provides high fixability and image quality regardless of the temperature of the second fixing roller 31, the first fixing roller 21 is adjusted to the target temperature immediately after warming up, and then unfixed. The paper P carrying the toner image T may be immediately passed through the first and second fixing means 20 and 30. By doing so, the warm-up time can be shortened. At this time, if only monochrome images are fixed continuously, the second fixing roller 31 does not need to be heated, and therefore the second heater 36 does not need to be energized. Can be realized.

  In this embodiment, when fixing a monochrome image immediately after warm-up, the sheet P is transferred to the first and second fixing units 20 and 30 after the temperature of the first fixing roller 21 is adjusted to the target temperature. At this time, if it is necessary to adjust the temperature of the second fixing roller 31 to the target temperature, the first heater 25 is not energized while the sheet P is passed through the first fixing unit 20. The second heater 36 is energized to adjust the temperature of the second fixing roller 31 to the target temperature. Therefore, when a color image formation signal is input during fixing of a monochrome image, it becomes clear that it is necessary to fix the color image in advance, while passing the paper P carrying the unfixed toner image T. When the first heater 25 is not energized, the second heater 36 is energized to adjust the temperature of the second fixing roller 31 to the target temperature, thereby preparing for the subsequent fixing of the color image.

<Embodiment 2>
Next, a fixing device according to Embodiment 2 of the present invention will be described with reference to FIG.

  FIG. 3 is a schematic cross-sectional view showing the basic configuration of the fixing device according to the embodiment of the present invention. In FIG. 3, the same elements as those shown in FIG.

  The fixing device 50 ′ according to the present embodiment is characterized in that the pressure roller 22 common to the first fixing unit 20 and the second fixing unit 30 is used.

  That is, the first fixing unit 20 includes a fixing roller 21 having an outer diameter of φ20 mm and a pressure roller 22 having an outer diameter of φ50 mm that is pressed against the fixing roller 21 by a pressing unit (not shown). The fixing roller 21 is provided with a release layer 24 of fluororesin such as PFA or PTFE provided on the surface of a cylindrical cored bar 23 made of aluminum or the like having a thickness of 1.0 mm, and the cored bar 23 is used as a first heating source. A heater 25 is provided.

  The pressure roller 22 is provided with an elastic layer 27 made of silicon rubber or the like having a thickness of 10 mm on the outer periphery of a shaft or hollow cored bar 26 made of aluminum or iron having an outer diameter of φ30 mm. A release layer 28 of fluororesin such as PTFE is formed, and is pressed against the fixing roller 21 by a pressing means (not shown) and rotates while forming a nip portion with the fixing roller 21.

  A thermistor 29 as temperature detecting means is brought into contact with the surface of the fixing roller 21, and the heater 29 is driven and controlled by a heater driving circuit (not shown) based on the surface temperature of the fixing roller 31 detected by the thermistor 29. Then, the temperature control is performed so that the surface temperature of the fixing roller 31 becomes the temperature control target temperature.

  Further, a non-contact type separation plate 41 made of metal or resin is provided on the exit side of the sheet conveyance direction with respect to the nip portion of the fixing roller 31. PFA, PTFE, or the like is provided on the surface of the separation plate 41. A release layer of fluororesin is formed. In this embodiment, the non-contact type separation plate 41 is used, but a contact type separation plate or a separation claw may be used.

  On the other hand, the second fixing unit 30 arranged immediately after the first fixing unit 20 includes a fixing roller 31 having an outer diameter of φ20 mm and an additional member having an outer diameter of φ50 mm pressed against the fixing roller 31 by a pressing unit (not shown). The pressure roller 22 is configured. Here, the pressure roller 22 is common to the first fixing unit.

  The fixing roller 31 is provided with an elastic layer 34 such as silicon rubber having a thickness of 1.0 mm on the outer periphery of a cylindrical metal core 33 such as aluminum having a thickness of 1.0 mm, and further, PFA, PTFE or the like is provided on the surface of the elastic layer 34. A release layer 35 of fluororesin is provided, and a heater 36 as a second heat source is provided inside the cored bar 33.

  Similar to the first fixing unit 20, the pressure roller 22 is pressed against the fixing roller 31 by a not-shown pressing unit and rotates while forming a nip portion with the fixing roller 31.

  A thermistor 40 as temperature detecting means is brought into contact with the surface of the fixing roller 31, and the heater 36 is driven and controlled by a heater driving circuit (not shown) based on the surface temperature of the fixing roller 31 detected by the thermistor 40. Then, the temperature control is performed so that the surface temperature of the fixing roller 31 becomes the temperature control target temperature.

  In addition, a non-contact type separation plate 42 made of metal or resin is provided on the exit side of the sheet conveyance direction with respect to the nip portion of the fixing roller 31, and the surface of the separation plate 42 is made of PFA, PTFE or the like. A release layer of fluororesin is formed. In this embodiment, the non-contact type separation plate 42 is used, but a contact type separation plate or a separation claw may be used.

  Thus, since the basic configuration of the fixing device 50 ′ according to the present embodiment is the same as that of the fixing device 50 according to the first embodiment, the same effects as in the first embodiment are obtained in this embodiment. Is obtained.

1 is a front sectional view of an image forming apparatus according to the present invention. 1 is a schematic cross-sectional view showing a basic configuration of a fixing device according to Embodiment 1 of the present invention. FIG. 6 is a schematic cross-sectional view showing a basic configuration of a fixing device according to Embodiment 2 of the present invention. FIG. 10 is a schematic cross-sectional view illustrating a basic configuration of a conventional fixing device.

Explanation of symbols

1BK Black image forming unit 1Y Yellow image forming unit 1C Cyan image forming unit 1M Magenta image forming unit 2a to 2d Photosensitive drum (image carrier)
3a to 3d Developing device (developing means)
4a to 4d Transfer roller (transfer means)
5 Intermediate Transfer Belt 6 Drive Roller 7 Follower Roller 8 Backup Roller 9 Secondary Transfer Roller 10 ID Sensor 11 Sensor Backup Roller 12 Paper Feed Cassette 13 Pickup Roller 14 Cassette Paper Feed Roller 15 Manual Feed Roller 16 Registration Roller 17 Ejection Paper tray 18 Transport roller 19 Paper discharge roller 20 First fixing means 21 First fixing roller 22 Pressure roller 23 Core metal (metal substrate)
24 release layer 25 heater (first heating source)
26 Core metal (metal base)
27 Elastic layer 28 Release layer 29 Thermistor 30 Second fixing means 31 Second fixing roller 32 Pressure roller 33 Core metal (metal base)
34 Elastic layer 35 Release layer 36 Heater (second heating source)
37 Core (metal base)
38 Elastic layer 39 Release layer 40 Thermistor 41, 42 Separating plate 50, 50 'Fixing device 100 Main body L1 Horizontal conveyance path L2 Vertical conveyance path P Paper (recording material)
T Unfixed toner image

Claims (6)

First fixing means for fixing an unfixed toner image carried on a recording material, and second fixing means for refixing the toner image fixed on the recording material by the first fixing means on the recording material In the fixing device provided with
The first fixing roller on the toner image side of the first fixing unit is configured by providing a release layer on a metal substrate, and the second fixing roller on the toner image side of the second fixing unit is A fixing device comprising an elastic layer provided on a metal substrate and a release layer provided on the elastic layer.   When fixing a color image on a recording material, the temperature of each fixing roller is adjusted to a target temperature by first and second heating sources that heat the first and second fixing rollers, respectively, and then the recording material is used. Is passed through the first and second fixing means to fix the monochrome image, the temperature of the second fixing roller is adjusted after the temperature of only the first fixing roller is adjusted to the target temperature by the first heating source. 2. The fixing device according to claim 1, wherein the recording material is passed through the first and second fixing means regardless of the above.   3. The fixing device according to claim 2, wherein when fixing the monochrome image, the energization to the second heating source is stopped while the recording material passes through the first fixing unit.   At the time of warm-up, the temperature of the first fixing roller is adjusted to a target temperature, and then the second heating roller is energized by energizing the second heating source when the first heating source is not energized. The fixing device according to claim 2, wherein the temperature is adjusted to a predetermined temperature.   When fixing a monochrome image immediately after warm-up, the recording material is passed through the first and second fixing means after the temperature of the first fixing roller is adjusted to a target temperature. At this time, the second fixing is performed. When it is necessary to control the temperature of the roller to the target temperature, the recording material is passed through the first fixing unit and the second heating source is energized when the first heating source is not energized. When the temperature of the fixing roller No. 2 is adjusted to the target temperature and the color image is fixed immediately after warming up, the temperature of the first fixing roller is adjusted to the target temperature, and then the first heating source is energized. 5. A fixing apparatus according to claim 4, wherein the recording material is passed through the first and second fixing means after the second heating source is energized to adjust the temperature of the second fixing roller to the target temperature when there is not. . An image carrier that forms a latent image, a developing unit that develops the latent image formed on the image carrier and visualizes it as a toner image, and transfers the toner image from the image carrier onto a recording material. In an image forming apparatus comprising a transfer unit for fixing and a fixing unit for fixing a toner image transferred onto a recording material,
An image forming apparatus comprising the fixing device according to any one of claims 1 to 5.

Images