JP2004085880A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which has a belt fixing device capable of maintaining the long lives of a belt member and an auxiliary pressure member. <P>SOLUTION: In the image forming apparatus, the belt fixing device 17 has an endless belt member stretched between at least a support pressure roller 17a and a support heat roller 17c, and also an external pressure roller 17b. The external pressure roller 17b faces the support pressure roller 17a via the belt member and forms a fixing nip Nb. Further, before the fixing nip Nb, the belt member and the external pressure roller face each other to form an auxiliary nip Na. The auxiliary pressure member pressed to the auxiliary nip Na is provided. The belt fixing device is capable of altering glossiness. In order to alter glossiness, a control part exerts control so as to alter the temperature of the belt member and also alter the load of the auxiliary pressure member on the external pressure roller. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus including a belt fixing device used for image forming such as a copier, a printer, and a facsimile.
[0002]
[Prior art]
Conventionally, as a fixing device used in an electrophotographic image forming apparatus such as a copying machine, a printer, and a facsimile, a fixing rubber roller having an elastic layer and maintained at a predetermined temperature, and being pressed against a fixing rubber roller, 2. Description of the Related Art A heat roller fixing system in which a transfer material having an unfixed toner image formed thereon is heated while being nipped and conveyed by a pressure rubber roller having an elastic layer is often used.
[0003]
However, in this type of apparatus, the heat resistance and heat capacity of the fixing rubber roller are large, so that the warm-up time is long, the temperature inside the elastic layer is high, and the life of the fixing rubber roller is shortened.
[0004]
In addition, many color images have a large solid area, and many of the solid images are other than black. When a hard roller is used in place of the fixing rubber roller, there is a problem that image quality is deteriorated because uneven gloss is generated in accordance with unevenness of a transfer material (recording paper) or a toner layer.
[0005]
In order to solve these problems, an endless belt member (fixing belt) is used, and the fixing belt is supported and stretched by a plurality of roller members. A pressure roller (external pressure roller) opposed to the support pressure roller with the fixing belt interposed therebetween, and a heating roller (supporting heat roller) having a heating member for heating the fixing belt therein, and rotating the fixing belt. A winding portion (auxiliary nip portion) provided on the upstream side of the support pressure roller and around which the fixing belt is wound around the external pressure roller, and a support pressure roller and an external pressure roller ( A belt fixing device for fixing a toner image on a recording sheet with a fixing nip portion provided between the belt and a pressure roller is disclosed in Japanese Patent Application Laid-Open No. 10-307496.
[0006]
[Problems to be solved by the invention]
However, in a belt fixing device using a belt member disclosed in Japanese Patent Application Laid-Open No. H10-307496, a member such as a roller or a pad is generally used as an auxiliary pressing member for pressing and pressing an auxiliary nip portion. By using these auxiliary pressing members, pressure is applied from the inside of the fixing belt in the area of the winding portion (auxiliary nip portion) of the fixing belt (belt member), and the auxiliary pressing member is pressed against the auxiliary nip portion ( Pressure) to obtain a high glossiness of the image (toner image) at the time of fixing, this pressure increases the driving torque, increases the power consumption and shortens the life of the fixing belt. Invite. If the temperature of the fixing belt is lowered in order to obtain a low gloss, there is a problem that an image shift occurs in the auxiliary nip portion. In addition, when the auxiliary pressing member slides on the fixing belt during the glossiness control, and the auxiliary pressing member is repeatedly compressed by pressing, the auxiliary pressing member is worn or "set", so that the auxiliary pressing member is not pressed. There is also a problem that the life is shortened.
[0007]
SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus having a belt fixing device that reduces the above-mentioned problem, with respect to an image forming apparatus in which glossiness can be changed.
[0008]
[Means for Solving the Problems]
The object is to transfer an unfixed toner image onto a transfer material, and then pressurize and heat the unfixed toner image with a belt fixing device, and fix the image on the transfer material by fixing. The belt fixing device includes at least an endless belt member stretched between a supporting pressing roller and a supporting heating roller, and an external pressing roller, and the external pressing roller is provided with a belt member. Forming a fixing nip portion opposed to the supporting pressure roller, and prior to the fixing nip portion, forming an auxiliary nip portion by facing the belt member and the external pressure roller; The belt fixing device has a variable glossiness, and the control unit changes the temperature of the belt member when the glossiness is changed, and the auxiliary fixing member. It is achieved by an image forming apparatus and performs control to change the load on the external pressure roller members.
[0009]
By adopting the above configuration, the present invention performs gloss control while preventing image misalignment, and also performs fixing at the time of fixing, even when performing image formation with low gloss by lowering the temperature of the auxiliary nip portion. In addition to increasing the load on the auxiliary pressurizing member as the temperature of the belt member is reduced during gloss control, the excessive power consumption is suppressed, and the auxiliary pressurizing member at the belt member and the auxiliary nip portion is increased. It is possible to provide an image forming apparatus provided with a belt fixing device that prevents wear of the belt member and maintains the life of the belt member and the auxiliary pressing member for a long time.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described. Note that the description in this column does not limit the technical scope of the claims and the meaning of terms. Also, the following assertive description in the embodiment of the present invention indicates the best mode, and does not limit the meaning of the terms of the present invention or the technical scope.
[0011]
An image forming process and each mechanism of an embodiment of an image forming apparatus using a belt fixing device according to the present invention will be described with reference to FIGS. FIG. 1 is a sectional view of a color image forming apparatus showing an embodiment of an image forming apparatus using a belt fixing device according to the present invention, and FIG. 2 is a belt fixing device using a sliding pressure member according to the present invention. FIG. 3 is a diagram showing another example of the sliding pressure member of FIG. 2, and FIG. 4 is a switching control block diagram of high gloss and low gloss. In each example of the sliding pressure member, members having the same functional structure are denoted by the same reference numerals.
[0012]
In FIG. 1, the image forming apparatus GS includes an image forming apparatus main body GH and an image reading apparatus YS.
[0013]
An image reading device YS including an automatic document feeder 201 and a document image scanning exposure device 202 is provided above the image forming apparatus main body GH. A document D placed on a document table of the automatic document feeder 201 is conveyed by a conveying means, and one side or both sides of the document is scanned and exposed by an optical system of a document image scanning and exposing device 202, and is sent to a line image sensor CCD. Is read. At this time, the original D conveyed from the original platen is determined by the gloss level detection sensor PKa used as a gloss level selecting means to determine the gloss of the original image, the monochrome / color of the original image, and the double-sided image. Done.
[0014]
The analog signal photoelectrically converted by the line image sensor CCD is subjected to analog processing, A / D conversion, shading correction, image compression processing, and the like in an image processing section, and then to an image writing section (exposure means) 3Y, 3M, 3C. Send a signal to 3K.
[0015]
The automatic document feeder 201 has an automatic double-sided document conveying means. Since the automatic document feeder 201 can continuously read the contents of a large number of documents D conveyed from the document mounting table at once and accumulate it in the storage means (electronic RDH function), the copying function This is conveniently used when copying the contents of many originals, or when transmitting many originals D by facsimile function.
[0016]
The image forming apparatus main body GH is called a tandem-type color image forming apparatus, and includes a plurality of sets of image forming units 10Y, 10M, 10C, and 10K and an intermediate transfer as a belt-shaped intermediate transfer body. The belt 6 includes a sheet feeding / conveying unit including a re-feeding mechanism (ADU mechanism), and a belt fixing device 17 as a fixing unit.
[0017]
The image forming unit 10Y that forms a yellow (Y) color image includes a photosensitive drum 1Y as an image forming body, a charging unit 2Y as a Y toner image forming unit disposed around the photosensitive drum 1Y, and an exposure. There is a unit 3Y, a developing device 4Y and an image forming body cleaning unit 8Y. The image forming unit 10M that forms an image of magenta (M) color includes a photosensitive drum 1M as an image forming body, a charging unit 2M as a M toner image forming unit, an exposing unit 3M, a developing device 4M, and an image forming unit. It has a cleaning unit 8M. The image forming section 10C for forming a cyan (C) color image includes a photosensitive drum 1C as an image forming body, a charging section 2C as a C toner image forming section, an exposing section 3C, a developing device 4C, and an image forming section. It has a cleaning unit 8C. An image forming unit 10K for forming a black (K) color image includes a photosensitive drum 1K as an image forming body, a charging unit 2K as a K toner image forming unit, an exposing unit 3K, a developing device 4K, and an image forming unit. It has a cleaning unit 8K. The charging unit 2Y and the exposure unit 3Y, the charging unit 2M and the exposure unit 3M, the charging unit 2C and the exposure unit 3C, and the charging unit 2K and the exposure unit 3K constitute a latent image forming unit. The development by the developing devices 4Y, 4M, 4C, and 4K is performed by reversal development in which a development bias in which an AC voltage is superimposed on a DC voltage having the same polarity (negative polarity in the present embodiment) as the polarity of the toner to be used is applied. .
[0018]
The intermediate transfer belt 6 is wound around a plurality of rollers and is rotatably supported.
[0019]
The outline of the image forming process will be described below.
An image of each color formed by the image forming units 10Y, 10M, 10C and 10K is applied with a primary transfer transfer bias by a power source (not shown) having a polarity opposite to that of the toner to be used (positive in this embodiment). By the primary transfer rollers 7Y, 7M, 7C and 7K as the secondary transfer means, the color images (color toner images) are sequentially transferred onto the rotating intermediate transfer belt 6 (primary transfer) and synthesized. You. The recording paper P stored in the paper feed cassettes 20A, 20B, and 20C is fed by a feed roller 21 and a paper feed roller 22A provided in the paper feed cassettes 20A, 20B, and 20C, respectively, and is fed by transport rollers 22B, 22C, and 22D. Then, the sheet is conveyed to a secondary transfer roller 7A as a secondary transfer means via a registration roller 23 and the like, and a color image is collectively transferred onto one surface (front surface) of the recording paper P (secondary transfer).
[0020]
The recording paper P to which the color image has been transferred is subjected to a fixing process by the belt fixing device 17, is sandwiched by the discharge rollers 24, and is placed on a discharge tray 25 outside the apparatus.
[0021]
The untransferred toner remaining on the peripheral surfaces of the photosensitive drums 1Y, 1M, 1C, and 1K after the transfer is cleaned by the image forming body cleaning means 8Y, 8M, 8C, and 8K and enters the next image forming cycle.
[0022]
On the other hand, after the color image is transferred onto the recording paper P by the secondary transfer roller 7A, the residual toner is removed from the intermediate transfer belt 6 from which the recording paper P is separated by the curvature by the intermediate transfer body cleaning means 8A.
[0023]
Although the above image forming process has been described with reference to color image formation, it goes without saying that not only color image formation but also monochrome image formation and double-sided image formation are performed.
[0024]
The belt fixing device 17 according to the present invention has a configuration shown in FIG. 2, and supports and stretches the fixing belt 27 on one of the inner peripheral surfaces of the fixing belt 27 as an endless belt member. A supporting pressure roller 17a, a supporting heating roller 17c having a halogen heater HLa as a heating member therein and supporting and stretching the fixing belt 27 on the other inner peripheral surface of the fixing belt 27; The fixing belt 27 is stretched with an external pressure roller 17b which comes into contact with the pressure roller 17a and presses (presses) the support pressure roller 17a.
[0025]
A fixing nip Nb is formed between the support pressure roller 17a and the external pressure roller 17b with the fixing belt 27 heated by the support heating roller 17c interposed therebetween, and a fixing nip Nb is formed upstream of the fixing nip Nb (fixing nip Nb The fixing belt 27 and the external pressure roller 17b are opposed to each other to form an auxiliary nip portion Na wound around the external pressure roller 17b between the fixing belt 27 and the external pressure roller 17b. By applying heat and pressure through the auxiliary nip Na and the fixing nip Nb, the toner image (or color toner image) on the recording paper P is fixed. By the auxiliary nip Na, the contact time between the fixing belt 27, which is a heat supply source for the recording paper P, and the recording paper P can be increased, and the fixability and glossiness can be increased.
[0026]
As the fixing belt 27, a nickel electroformed belt having an inner diameter of about 60 to 150 mm and a thickness of about 20 to 80 μm or a heat-resistant resin belt of polyimide or the like having a thickness of about 50 to 200 μm is used as a base. On the outside (outer peripheral surface) of the base, a silicon rubber having a thickness of about 100 to 500 μm is coated, and as a release layer, the surface is subjected to PFA (perfluoroalkoxy) or PTFE coating with a thickness of about 30 to 50 μm, Alternatively, a material coated with a PFA tube is used.
[0027]
The supporting pressure roller 17a is, for example, a cylindrical metal pipe 171a having a thickness of about 2 to 5 mm using a steel material such as STKM (carbon steel pipe for machine structure), and a thickness of 0 mm on the outer peripheral surface of the metal pipe 171a. As a soft roller having an outer diameter of about 25 to 70 mm, a silicon rubber layer 172a of about 0.5 to 5 mm is provided, and a PFA (perfluoroalkoxy) tube 173a having a thickness of about 30 to 70 μm is provided outside the silicon rubber layer 172a. Be composed.
[0028]
The external pressure roller 17b is, for example, a cylindrical metal pipe 171b having a thickness of about 2 to 5 mm using steel or aluminum such as STKM (carbon steel pipe for machine structure) and an outer peripheral surface of the metal pipe 171b. A silicone rubber layer 172b having a thickness of 1 to 3 mm, and a release layer 173b using a PFA (perfluoroalkoxy) tube having a thickness of about 20 to 50 μm outside the silicone rubber layer 172b; It is configured as a soft roller of about 80 mm. Further, a halogen heater HLa as a heating element may be provided inside the external pressure roller 17b as shown by a dotted line in the figure.
[0029]
The supporting and heating roller 17c in which a halogen heater HLa as a heating element for heating the fixing belt 27 is provided is a cylindrical metal pipe 171c having a thickness of about 1 to 2 mm using, for example, aluminum as a base, and A PFA (perfluoroalkoxy) coating 172c having a thickness of about 10 to 30 μm is formed on the outer peripheral surface of the pipe 171c, and is configured as a roller member having an outer diameter of about 30 to 70 mm. Further, as shown by a thick arrow in the drawing, the support heating roller 17c is urged in a direction away from the support pressure roller 17a, and the fixing belt 27 is stretched.
[0030]
The support pressure roller 17a is rotationally driven by a drive motor (not shown), and the fixing belt 27 is supported and conveyed by the rotation of the support pressure roller 17a to be driven to rotate. The external pressure roller 17b may be driven to rotate, the fixing belt 27 may be transported by the external pressure roller 17b, and the fixing belt 27 may be driven to rotate.
[0031]
An auxiliary guide nip Na formed between the fixing belt 27 and the external pressure roller 17b and a fixing nip Nb formed between the support pressure roller 17a and the external pressure roller 17b form an entrance guide plate 17s. Then, the toner image (or the color toner image) on the recording paper P which enters the fixing area through the fixing unit is pressurized and heated, and is fixed and fixed on the recording paper P.
[0032]
Further, a temperature sensor TS1 is provided as a temperature detecting means that comes into contact with the support heating roller 17c, and controls the temperature of the support heating roller 17c. Further, as indicated by a dashed line, the fixing belt 27 may be provided with a temperature sensor TS2 as a temperature detecting means to control the temperature of the fixing belt 27. Of course, the temperature detecting means can be provided not only on one side but on both sides.
[0033]
At the entrance of the auxiliary nip Na, an auxiliary pad HP which is a sliding pressure member that presses the fixing belt 27 from the inner peripheral surface (inside) of the fixing belt 27 and slides on the fixing belt 27 is provided. The auxiliary pad HP is provided in parallel with the center of the external pressure roller 17b. For example, a rectangular silicone rubber foam (150 to 250% foam) having a width of about 8 to 15 mm, solid rubber, or heat-resistant resin is used. As shown in the belt fixing device 17 of FIG. 2, the pressing spring SPa pressing the auxiliary pad HP by the rotation of the eccentric cam HC rotated about the eccentric shaft Ja by, for example, a drive motor (not shown). The pressing force is changed to change the load on the external pressure roller 17b at the auxiliary nip Na of the auxiliary pad HP. The pressing spring SPA is provided between the spring receiver SPA1 on the eccentric cam HC side and the spring receiver SPA2 on the auxiliary pad HP side. Further, as shown in the belt fixing device 17 in FIG. 3, the fixing belt 27 is pressurized from the inner peripheral surface (inside) of the fixing belt 27 to the entrance of the auxiliary nip Na, and a fixing belt pressing member (belt member pressing member) is used. An auxiliary roller HR used as a member) may be provided. The auxiliary roller HR is provided in parallel with the center of the external pressure roller 17b, for example, on the outer peripheral surface of a core metal having an outer diameter of about 5 to 20 mm. It is made of a member provided with a silicone rubber foam (150-250% foam) having a thickness of about 3 to 10 mm and an outer diameter of about 15 to 30 mm. As shown in FIG. By the rotation of the eccentric cam HC rotated about the eccentric shaft Ja, the pressing force of the pressing spring SPa pressing the rotation shaft Jb of the auxiliary roller HR is changed, and the pressing force of the auxiliary roller HR at the auxiliary nip portion Na is changed. It may be changed to load the parts pressure roller 17b. The pressing spring SPa is provided between the spring receiver SPB1 on the eccentric cam HC side and the spring receiver SPB2 on the rotation axis Jb side of the auxiliary roller HR.
[0034]
According to the present invention, in the belt fixing device 17 described with reference to FIGS. 2 and 3, the glossiness of the toner image (image) at the time of fixing is made variable. In this section, the temperature of the fixing belt 27 is changed and the load of the auxiliary pad HP applied to the external pressure roller 17b is changed as described above. Thus, the load of the auxiliary pad HP toward the auxiliary nip Na is increased.
[0035]
Specifically, as shown in FIG. 3, in forming a low gloss image, the halogen heater HLa as a heating member is turned on (lit) to heat the supporting heating roller 17 c to, for example, about 180 to 200 ° C. When the temperature of the fixing belt 27 is maintained at about 160 to 180 ° C. by TS1 and TS2, for example, when a start button is pressed from the operation unit, the image forming program P1 stored in the ROM of the storage unit is transmitted through the control unit. Then, the image forming unit described with reference to FIG. 1 forms a monochrome image or a color image. The glossiness in this case is about 40 °.
[0036]
When the high gloss mode is selected by the gloss switch button from the operation unit, the high gloss image forming program P2 stored in the ROM of the storage unit is executed through the control unit, and a high gloss monochrome image or Image formation of a color image is performed. At this time, the halogen heater HLa is turned on, and the temperature of the fixing belt 27 is maintained at about 200 ° C. and the glossiness of the image is made about 60 ° by detection of the temperature sensors TS1 and TS2. In the high gloss mode, the load of the auxiliary pressing member such as the auxiliary pad HP and the auxiliary roller HR is set to, for example, 50 to 100 N (A3 width).
[0037]
In the low gloss mode, an appropriate load is applied to the auxiliary pressing members such as the auxiliary pad HP and the auxiliary roller HR, for example, a load of 100 to 150 N with an A-3 vertical feed size width (more than 300 mm) at the auxiliary nip Na. The toner (toner image) is temporarily fixed on the recording paper P by being applied to the external pressure roller 17b, and an image deviation caused by a deviation between the recording paper P and the fixing belt 27 in the auxiliary nip Na is avoided. Let it. To further obtain a low gloss level, the temperature of the fixing belt 27 is reduced to about 140 ° C. by detecting the temperature sensors TS1 and TS2 with the halogen heater HLa turned off, and the gloss level of the image is reduced to about 20 °. Let it. In this case, the load on the auxiliary pressing members such as the auxiliary pad HP and the auxiliary roller HR is, for example, A-3 vertical feed size width (more than 300 mm), and a load of 200 to 300 N is externally pressed by the auxiliary nip Na. It is applied toward the roller 17b, whereby the image shift can be avoided.
[0038]
In the above description, the power required to drive the driving system (not shown) of the belt fixing device 17 including the driving of the driving motor and its driver and the load of the deceleration / transmission system was 10 W, 14 W, and 19 W, respectively.
[0039]
The pressurization at the auxiliary nip portion Na causes an increase in the driving torque of the fixing belt 27 as described above, which not only increases the power consumption of the motor, but also increases the pulling and shearing load on the fixing belt 27 and increases the pressure member. Is a pad (auxiliary pad HP), wear of the fixing belt 27 and the auxiliary pad HP due to sliding, and if the pressing member is a roller (auxiliary roller HR), the life is shortened by repeated compression. As described above, the load of the pressing member such as the auxiliary pad HP or the auxiliary roller HR is changed according to the temperature of the fixing belt 27. When the temperature of the fixing belt 27 is high, it is desirable to reduce the load on the pressing members such as the auxiliary pads HP and the auxiliary rollers HR, and to increase the load on the sliding pressing members in accordance with the decrease in the temperature of the fixing belt 27. . When the auxiliary pad HP is used as the sliding pressure member, wear due to sliding and the influence of the abrasion powder are large, so that the use of the auxiliary roller HR has a greater effect of obtaining a longer life.
[0040]
Pressing the external pressure roller 17b (fixing belt 27) at the auxiliary nip Na by the sliding pressure member such as the auxiliary pad HP or the auxiliary roller HR also has the effect of increasing the glossiness. Even if the durability is somewhat shortened or the power is increased, the halogen heater HLa is turned on to obtain higher glossiness than when no pressure is applied to the fixing belt 27 by the sliding pressure member. The fixing belt 27 may be further heated and pressurized when the fixing belt 27 is set to a high temperature.
[0041]
Further, it is more preferable that the rotation of the eccentric cam HC described above can be selected as a continuous pressurization of the auxiliary nip Na. However, a simple pressurizing variable mechanism including a drive motor and an eccentric cam HC (not shown) can be used. For the purpose of realization, it may be configured to be variable in two or more stages. The above-described temperature of the fixing belt 27 by the heating member and the load on the auxiliary nip Na by the pressing member are merely examples, and are appropriate values depending on the toner used, the speed of the image forming apparatus, the paper (transfer material) used, and the like. Are different and are appropriately selected. For example, when the fixing belt 27 has a high linear temperature of 180 to 200 ° C. at a low linear velocity of 100 mm / s or less, the auxiliary pressure can be released.
[0042]
As described above, the fixing belt 27 is driven by the support pressure roller 17a or the external pressure roller 17b, and the recording paper holding the toner image (toner image) conveyed to the fixing area by the entry guide plate 17s or the like. P is pressed by an appropriate pressing force by an auxiliary nip portion Na provided at the entrance, and is pre-fixed, and is externally pressed by a supporting pressure roller 17a around which a fixing belt 27 is wound with the recording paper P interposed therebetween. The toner image (toner image) is fixed on the recording paper P by the heat of the fixing belt 27 and the pressure by the external pressure roller 17b in the fixing nip Nb where the pressure is applied by the fixing roller 17b. At this time, since the rubber of the fixing belt 27 is brought into contact with the toner layer (toner image) on the recording paper P via a rubber or a thin release layer, the rubber is deformed, and the recording paper P and the toner layer are deformed. The toner image (toner image) is maintained at an appropriate gloss because the toner image (toner image) is uniformly fixed without unevenness of gloss. It is separated from the fixing belt 27.
[0043]
According to the present invention, by adopting the above-described configuration, even when the image of low glossiness is formed by lowering the temperature of the auxiliary nip portion Na at the time of fixing, the glossiness control is performed while preventing the image shift. Further, since the load of the auxiliary pressing member such as the auxiliary pad HP or the auxiliary roller HR is increased in accordance with the lowering of the temperature of the fixing belt 27 during the gloss control at the time of fixing, excessive power consumption is also suppressed. At the same time, the wear of the auxiliary pad HP on the fixing belt 27 and the auxiliary nip Na is suppressed, and the life of the fixing belt 27 and the auxiliary nip Na is maintained long.
[0044]
【The invention's effect】
According to the present invention, even when performing low-gloss image formation by lowering the temperature of the auxiliary nip during fixing, gloss control is performed while preventing image shift, and gloss control during fixing is performed. As the load on the auxiliary pressurizing member is increased as the temperature of the belt member is lowered, excessive power consumption is suppressed, and wear of the auxiliary pressurizing member at the belt member and the auxiliary nip is prevented. In addition, it is possible to provide an image forming apparatus including a belt fixing device that can maintain the life of the belt member and the auxiliary pressing member for a long time.
[Brief description of the drawings]
FIG. 1 is a cross-sectional configuration diagram of a color image forming apparatus showing an embodiment of an image forming apparatus using a belt fixing device according to the present invention.
FIG. 2 is a schematic sectional configuration diagram of an example of a belt fixing device using a sliding pressure member according to the present invention.
FIG. 3 is a view showing another example of the sliding pressure member of FIG. 2;
FIG. 4 is a switching control block diagram of high gloss and low gloss.
[Explanation of symbols]
1Y, 1M, 1C, 1K Photoconductor drums 2Y, 2M, 2C, 2K Charging means 3Y, 3M, 3C, 3K Exposure means 4Y, 4M, 4C, 4K Developing device 7A Secondary transfer rollers 7Y, 7M, 7C, 7K 1 Next transfer roller 8A Intermediate transfer body cleaning means 8Y, 8M, 8C, 8K Image forming body cleaning means 10Y, 10M, 10C, 10K Image forming unit 17 Belt fixing device 17a Support pressure roller 17b External pressure roller 17c Support heat roller 17s Entry guide plate 27 Fixing belt HLa Halogen heater HP Auxiliary pad HR Auxiliary roller Na Auxiliary nip Nb Fixing nip P Recording paper

Claims (3)

After transferring the unfixed toner image onto the transfer material, in the image forming apparatus that presses and heats the unfixed toner image with a belt fixing device and fixes the unfixed toner image on the transfer material to perform fixing.
The belt fixing device,
An endless belt member stretched between at least the supporting pressure roller and the supporting heating roller,
With an external pressure roller,
The external pressure roller forms a fixing nip portion facing the support pressure roller via a belt member,
Prior to the fixing nip portion, the belt member and the external pressure roller face each other to form an auxiliary nip portion,
An auxiliary pressing member that presses toward the auxiliary nip portion is provided,
The belt fixing device has a variable glossiness,
The control unit changes the temperature of the belt member when changing the glossiness,
An image forming apparatus, wherein control is performed to change a load applied to the external pressure roller by the auxiliary pressure member. 2. The image forming apparatus according to claim 1, wherein a load applied to an auxiliary nip portion of the auxiliary pressing member is increased in accordance with a decrease in the temperature of the belt member. The image forming apparatus according to claim 1, wherein the auxiliary pressing member slides on the belt member.

Images