JP2006003695A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make it possible to obtain a fixing nip width optimum to the kind of transfer materials and eliminate jamming and image rubbing at the entrance of the fixing nip when the transfer material enters. <P>SOLUTION: This image forming device has an endless fixing belt 84 extended around the heater roller 83 having a heater and a push roller 81 facing the pressure roller 82, a transfer material guide 87 to guide the transfer material S carried to the fixing nip N, and a support arm member 89 which enables to change the pressing length at the fixing nip N in pressure contact with the pressure roller 82 by moving the heater roller 83 and changes the direction of the transfer material S toward the nip N by moving the guide 87 as the heater roller 83 moves. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus that forms an image by heating and fixing an unfixed toner image formed on a transfer material by a fixing device having a fixing belt.

  Conventionally, a fixing device used in an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multifunction machine having these functions has a fixing roller maintained at a predetermined temperature and an elastic layer. A heat roller fixing system in which a transfer material on which an unfixed toner image is formed is nipped and conveyed by a pressure roller in pressure contact with the fixing roller is heated, from a low speed machine to a high speed machine, from a monochrome machine to a color machine. Until widely adopted.

  The conventional heat roller fixing type fixing device is disadvantageous in terms of power saving because it is necessary to heat the fixing roller having a large heat capacity when heating the toner on the transfer material. There is a problem that it takes time to warm up, and the time until the printing starts (warming up time) becomes long.

  A fixing belt fixing system that solves this problem forms a fixing nip portion by pressing a fixing belt rotatably supported by a heating roller and a supporting roller against a pressure roller, and forms a toner image conveyed from a transfer unit. By sandwiching the transferred material at the fixing nip portion, the toner image on the transfer material is heated and pressurized to be fixed.

  With the diversification of consumer needs in recent years, the demand for copying not only ordinary transfer paper but also various types of transfer materials such as cardboard and OHP sheets has increased. Accordingly, the fixing device is required to have a function of setting optimum fixing conditions according to the thickness and paper quality of various transfer materials used.

  In particular, in a fixing device of a full-color copying machine, setting of finer fixing conditions is required than in a fixing device of a monochrome copying machine using only black toner because of the properties of each color toner used. A full-color copier requires a high-quality image, and when using coated glossy paper, setting of special fixing conditions is required.

  Here, the fixing conditions depend on the amount of heat applied and the pressure applied. The amount of heat applied is determined by the temperature of the heating member and the time of the heating member. Therefore, the adjustment of the fixing conditions means the adjustment of the temperature of the heating member, the adjustment of the heating time, or the adjustment of the pressing time.

  That is, transfer materials such as cardboard, OHP sheets, and coated glossy paper require a relatively large amount of heat, so the pressurizing force is increased compared to plain paper or the surface temperature of the heating member is increased. Increase the time or pressurize and heat the transfer material.

The fixing device described in Patent Document 1 has means for moving at least one of a plurality of support rollers of the fixing belt, and the contact width of the fixing belt while maintaining a constant contact pressure with the fixing roller by the moving means. Is something that changes.
JP-A-5-165357

  In order to fix the toner image formed on the transfer material at high speed, it is necessary to widen the nip width between the fixing roller and the pressure roller that sandwich the transfer material. In order to widen the nip width, the conventional roller fixing device cannot avoid increasing the diameter of the fixing roller and the pressure roller, and there is a problem that the warming up time is significantly increased due to an increase in heat capacity accompanying an increase in size. there were.

  To solve this problem, even if the heating time is extended by the contact area where the belt is wound around the pressure roller using the fixing belt, the heat capacity of the fixing belt is limited, so the contact time with the fixing belt is extended. The effect is limited, and since it depends on the heat supply from the external pressure roller, the transfer material is heated and the thermal efficiency is low.

  In particular, in a fixing device of a color image forming apparatus, since a four-color toner image is heated and fixed, it is necessary to increase a heat supply amount as compared with a single-color toner image. In addition, when a graphic image, a picture image, or the like is performed in a color image forming apparatus, the amount of toner adhering to the transfer material is large, and it is necessary to increase the heat supply amount during the heat fixing process. Further, in order to give gloss to a color image, it is necessary to increase the amount of heat supply during the heat fixing process.

  In addition, it is difficult to realize transfer materials having various thicknesses under the same fixing conditions. Under good fixing conditions for thin paper, fixing properties cannot be ensured for thick paper, and under good fixing conditions for thick paper, hot offset occurs with thin paper. Thus, there are the following methods for securing the fixing property corresponding to the thickness of the transfer material, but each has a problem.

  (1) When the fixing temperature is increased in order to obtain the fixing condition corresponding to the thick paper, the fixing temperature cannot be changed immediately, so that a waiting time occurs. In the case of thick paper, if the fixing temperature is raised in order to ensure the fixing property, the gloss tends to be excessively high.

  (2) When the fixing pressure is increased in order to obtain a fixing condition corresponding to thick paper, the influence of the pressure on the fixability is small, and securing the fixability with the pressure is impossible from the viewpoint of durability.

  (3) If the transfer material conveyance speed is lowered to extend the fixing nip time, the copy speed is also lowered.

  In order to solve the above problems, as disclosed in Patent Document 1, a technique for changing the fixing nip width and corresponding to the paper thickness of various transfer materials has been disclosed. The problem with this technology is the paper conveyance path. In the fixed transfer material path, the transfer material path does not change even if the fixing nip width changes. It became.

  The present invention achieves quick start by shortening the warm-up time by an image forming apparatus provided with a fixing belt type fixing device, and a roller that stretches a pressure contact member and a fixing belt that are moved when the fixing nip width is changed In addition, it is possible to prevent jamming and image rubbing around the entrance and exit of the fixing nip by moving the transport surface in conjunction with the transfer material transport guide.

  Each of the above objects can be achieved by the following solutions.

  The image forming apparatus according to claim 1, wherein a fixing device that heat-fixes an unfixed toner image formed on a transfer material at a fixing nip portion where a heated fixing belt and a pressure roller are pressed against each other, and a transfer material conveying unit And an endless fixing belt that is wound around a heating roller having a heating member and a pressure roller that faces the pressure roller, and is conveyed to the fixing nip portion. The transfer material conveyance guide member for guiding the transfer material, and the heating roller can be moved to change the pressure contact length in the fixing nip portion that is in pressure contact with the pressure roller, and in conjunction with the movement of the heating roller. And a support arm member that moves the transfer material conveyance guide member and makes the transfer material entry direction into the fixing nip portion variable.

  The image forming apparatus according to claim 2, wherein a fixing device and a transfer material conveying unit that heat-fix an unfixed toner image formed on a transfer material at a fixing nip portion where a heated fixing belt and a pressure roller are in pressure contact with each other. And an endless fixing belt wound around a heating roller having a heating member and a pressure roller facing the pressure roller, and moving the pressure roller to move the pressure roller. The pressure roller moving means that can change the pressure contact length in the fixing nip portion that is in pressure contact with the pressure roller, fixed to the pressure roller moving means, moved in conjunction with the movement of the pressure roller, and the fixing And a transfer material transport guide member that makes at least one of a transfer material entry direction and a transfer material discharge direction into the nip portion variable.

  4. The image forming apparatus according to claim 3, wherein the fixing device heats and fixes the unfixed toner image formed on the transfer material at a fixing nip portion where the heated fixing belt and the pressure roller are pressed against each other. And an endless fixing belt that is wound around a heating roller having a heating member and a pressure roller that faces the pressure roller, and is conveyed to the fixing nip portion. The transfer material conveying guide member for guiding the transfer material, and the pressure contact length in the fixing nip portion that is in pressure contact with the pressure roller by moving the pressure roller can be changed, and in conjunction with the movement of the pressure roller, And a support arm member that moves the transfer material conveyance guide member and makes the transfer material discharge direction to the fixing nip portion variable.

  The image forming apparatus of the present invention can obtain the following effects by the configuration described above.

  According to the first aspect of the present invention, the transfer material conveyance guide member is moved in conjunction with the movement of the support arm member that enables the pressure contact length in the fixing nip portion that is in pressure contact with the pressure roller by moving the heating roller. By moving the transfer material into the fixing nip portion in a moving direction, jamming and image rubbing around the fixing nip portion inlet portion can be prevented.

  According to the second aspect of the present invention, the transfer material conveyance guide member is moved in conjunction with the movement of the support arm member that enables the pressure contact length in the fixing nip portion that is in pressure contact with the pressure roller by moving the pressure roller. By moving at least one of the transfer material entering direction and the transfer material discharging direction to the fixing nip portion, it becomes possible to prevent jamming and image rubbing around the fixing nip portion entrance portion.

  According to the third aspect of the present invention, the transfer material conveyance guide member for guiding the transfer material conveyed to the fixing nip portion, and the pressure contact length at the fixing nip portion where the pressure roller is moved and pressed against the pressure roller are changed. And a support arm member that moves the transfer material conveyance guide member in conjunction with the movement of the pressing roller to change the transfer material discharge direction to the fixing nip portion. It has become possible to prevent image rubbing.

  In particular, in a fixing device of a color image forming apparatus, when a toner image of four colors is heated and fixed to perform a graphic image, a picture image, etc., when giving gloss to a color image, or when using a transfer material having different paper quality It is effective for high-quality image formation.

  Hereinafter, a fixing device according to the present invention and an image forming apparatus equipped with the fixing device will be described with reference to the drawings.

[One Embodiment of Image Forming Apparatus]
FIG. 1 is a cross-sectional configuration diagram of a color image forming apparatus showing an embodiment of an image forming apparatus provided with a fixing device according to the present invention.

  This color image forming apparatus is called a tandem type color image forming apparatus, and a plurality of sets of image forming units 10Y, 10M, 10C, and 10K arranged in tandem, and a rotatable half-roller that winds a plurality of rollers. It comprises a conductive endless belt-like intermediate transfer member 7, a paper feeding / conveying means, and a fixing device 8.

  The image forming unit 10Y that forms a yellow image includes a charging unit 2Y, an exposure unit 3Y, a developing unit 4Y, a primary transfer unit 5Y, and a cleaning unit 6Y arranged around the image carrier 1Y. The image forming unit 10M that forms a magenta image includes an image carrier 1M, a charging unit 2M, an exposure unit 3M, a developing unit 4M, a primary transfer unit 5M, and a cleaning unit 6M. The image forming unit 10C that forms a cyan image includes an image carrier 1C, a charging unit 2C, an exposure unit 3C, a developing unit 4C, a primary transfer unit 5C, and a cleaning unit 6C. The image forming unit 10K that forms a black image includes an image carrier 1K, a charging unit 2K, an exposure unit 3K, a developing unit 4K, a primary transfer unit 5K, and a cleaning unit 6K.

  The color images formed by the image forming units 10Y, 10M, 10C, and 10K are sequentially transferred onto the rotating intermediate transfer body 7 by the primary transfer units 5Y, 5M, 5C, and 5K, and synthesized color images. Is formed. A transfer material (hereinafter referred to as “paper”) S accommodated in the paper feed cassette 20 is fed by a paper feed means 21, passes through a plurality of intermediate rollers 22 A, 22 B, 22 C, 22 D, and a registration roller 23, and then is secondary. The color image is transferred onto the paper S at a time by being conveyed to the transfer means 5A. The sheet S on which the color image has been transferred is fixed by the fixing device 8, sandwiched between the sheet discharge rollers 24, and placed on the sheet discharge tray 25 outside the apparatus.

  At the time of double-sided image formation, the sheet S on which the image is formed on the first surface discharged from the fixing device 8 is branched from the sheet discharge path by the branching unit 26 and passes through the lower reverse sheet passing paths 27A, 27B, 27C. Then, they merge at the intermediate roller 22D. The reversely conveyed sheet S is conveyed to the secondary transfer means 5A through the registration roller 23, and the color image is collectively transferred onto the second surface of the sheet S. The sheet S on which the color image has been transferred is fixed by the fixing device 8, sandwiched between the sheet discharge rollers 24, and placed on the sheet discharge tray 25 outside the apparatus.

  On the other hand, after the color image is transferred to the sheet S by the secondary transfer unit 5A, the residual toner is removed by the cleaning unit 6A from the intermediate transfer body 7 which has separated the curvature of the sheet S.

[First Embodiment of Fixing Device]
FIG. 2 is a sectional view showing the first embodiment of the fixing device 8 of the present invention. FIG. 3 is a perspective view of the fixing device 8.

  The belt-fixing type fixing device 8 has an internal pressure roller (pressure roller) 81, an external pressure roller (pressure roller) 82, and an external pressure roller 82, which are a pair of pressure members that rotate in pressure contact with each other. A heating member H1 such as a halogen lamp disposed, a rotatable heating roller 83, a heating member H2 such as a halogen lamp disposed inside the heating roller 83, and the outer peripheral surfaces of the heating roller 83 and the internal pressing roller 81 are wound. It comprises a rotating fixing belt 84 and the like.

  The internal pressing roller 81 is composed of a base, a foamed silicone rubber layer, and a heat-resistant release layer. For example, a cylindrical substrate having a thickness of 2 to 5 mm using a steel material such as STKM (carbon steel pipe for mechanical structure), a foamed silicone rubber layer having a thickness of 1 to 3 mm formed on the outer peripheral surface of the substrate, and foaming It is a roller having an outer diameter of 20 to 50 mm, comprising a heat-resistant release layer such as PFA (perfluoroalkoxy) or PTFE (polytetrafluoroethylene) having a thickness of 30 to 100 μm on the outside of the silicone rubber layer.

  The external pressure roller 82 includes a base, a heat resistant elastic layer, and a heat resistant release layer. The base is, for example, a metal pipe having a thickness of 2 to 5 mm using a steel material such as STKM or an aluminum alloy material. The heat-resistant elastic layer is obtained by providing a silicone rubber layer having a thickness of 2 to 4 mm on the outer peripheral surface of the substrate. The heat-resistant release layer is a tube such as PFA or PTFE having a thickness of 20 to 50 μm outside the heat-resistant elastic layer. Inside the external pressure roller 82, a heating member H1 for heating the external pressure roller 82 is disposed.

  The external pressure roller 82 is biased by a spring 85 and presses the internal pressure roller 81 via the fixing belt 84 to form a fixing nip portion N.

  The heating roller 83 is composed of a base and a heat-resistant release layer. The substrate is a pipe having a thickness of 1 to 3 mm made of steel or an aluminum alloy material. The heat-resistant release layer is obtained by forming a coating layer made of PFA having a thickness of 10 to 30 μm on the outer peripheral surface of the substrate. Inside the heating roller 83, a heating member H2 for heating the heating roller 83 is disposed.

  The fixing belt 84 is an endless belt that winds the outer peripheral surfaces of the internal pressing roller 81 and the heating roller 83.

  The fixing belt 84 includes a flexible substrate, a heat resistant elastic layer, and a heat resistant release layer. The flexible substrate (heat ray absorbing layer) is formed of any one of stainless steel, nickel alloy, and polyamideimide (PAI) having a thickness of 50 to 100 μm. The heat resistant elastic layer is obtained by coating the outer peripheral surface of a flexible substrate with a silicone rubber having a thickness of 100 to 300 μm. The heat-resistant release layer is obtained by coating the surface of the heat-resistant elastic layer with PFA or PTFE having a thickness of 25 to 50 μm.

  The surface temperature of the fixing belt 84 is detected by the temperature detection element TS1, and is maintained within a predetermined temperature range by a temperature control unit (not shown).

  The toner image t formed on the transfer material S is heated and melted by the fixing belt 84 at the fixing nip portion N and pressed by the external pressure roller 82 and the internal pressure roller 81 biased by the spring 85. Then, it is fixed on the transfer material S.

  The internal pressing roller 81 is rotated by power transmission means such as a motor M1 as a driving source and a gear train, and rotates the fixing belt 84.

  The spring 85 urges the external pressure roller 82 via a support member (not shown) and presses the internal pressure roller 81 of the fixing device 8 via the fixing belt 84.

  A temperature detection element TS1 is disposed on the outer peripheral surface of the heating roller 83, and a temperature detection element TS2 is disposed on the outer peripheral surface of the external pressure roller 82. The temperature detection element TS1 detects the surface temperature of the heating roller 83. A control means (not shown) controls the surface temperature of the heating roller 83 to a predetermined temperature based on the detection signal of the temperature detection element TS1. The temperature detection element TS2 detects the surface temperature of the external pressure roller 82. A control means (not shown) controls the surface temperature of the external pressure roller 82 to a predetermined temperature based on the detection signal of the temperature detection element TS2.

  A transfer material conveyance guide member including a first guide member 86 and a second guide member 87 is disposed between the fixing nip portion N where the fixing belt 84 and the external pressure roller 82 are in pressure contact with the secondary transfer unit 5A. did. The first guide member 86 on the side close to the secondary transfer means 5A is composed of a pair of upper and lower guide plates that allow the sheet S to pass through, and is supported so as to be swingable about the support shaft 86A.

  The first guide member 86 and the second guide member 87 are slidably connected by a joint shaft 86B. The other end of the second guide member 87 is connected to one end of the link 88 so as to be swingable. The sheet S on which the toner image t has been transferred by the secondary transfer unit 5A passes through the conveyance path of the first guide member 86 composed of a pair of upper and lower guide plates, and advances in sliding contact with the sheet conveyance surface of the second guide member 87. Then, the toner enters the fixing nip portion N between the rotating fixing belt 84 and the external pressure roller 82.

  The toner image t formed on the sheet S is heated and melted by the fixing belt 84 and the external pressure roller 82 in the fixing nip portion N, and is pressed by the internal pressure roller 81 and the external pressure roller 82. It is fixed on the paper S.

  The other end of the link 88 is connected to the support arm member 89 so as to be swingable. One end portion of the support arm member 89 is fitted to both shaft end portions of the rotation shaft 81 </ b> A of the internal pressing roller 81 so as to be swingable.

  Both end portions of the rotating shaft 83A of the heating roller 83 are engaged with a fork-shaped recess 89A formed at a substantially intermediate position of the support arm member 89 so as to be able to roll. The joint shaft 86B of the first guide member 86 is fitted and connected to the long groove portion 89B formed at the other end portion of the support arm member 89.

  At one end of the support arm member 89, a protrusion 89C is integrally formed. The drive rotation of the motor M2 causes the cam C to rotate and swing the projection 89C, thereby swinging the support arm member 89, swinging the rotating shaft 83A, and swinging the heating roller 83. Let By swinging the heating roller 83, the support arm member 89 is swung by the nip angle of the fixing nip portion N where the fixing belt 84 and the external pressure roller 82 are in pressure contact with each other, and the fixing belt 84 is swung. The angle θ1 can be changed.

  The transfer material S discharged from the secondary transfer means 5A passes through the conveyance path of the fixedly arranged first guide member 86, and the fixing nip N where the rotating fixing belt 84 and the external pressure roller 82 are in pressure contact with each other. The second guide member 87, which is held in a bent shape so as to have an angle at which it is easy to enter, is slidably contacted with the sheet conveyance surface and proceeds toward the fixing nip portion N.

  FIG. 4 is a cross-sectional view of the image forming apparatus including the fixing device 8 and the transfer material conveying unit, showing a state in which the fixing belt 84 is swung to change the nip angle.

  Due to the drive rotation of the motor M2, the support arm member 89 is swung, the fixing belt 84 is swung, and the nip angle θ1 changes to θ2 (see FIGS. 2 and 3).

  When the image forming apparatus main body is turned on, the fixing belt 84 and the heating roller 83 are controlled so as to be maintained at a position where the nip angle θ2 shown in FIG. 4 suitable for fixing plain paper is formed.

  When a mode for forming an image on a transfer material such as an OHP sheet, glossy paper, or thick paper is set in the operation unit 9 of the image forming apparatus main body, the driving rotation of the motor M2 starts, the heating roller 83 starts moving, and the cam C Rotates the protrusion 89C to swing the support arm member 89, and moves the heating roller 83 engaged with the recess 89A of the support arm member 89 in a direction away from the external pressure roller 82. By this movement, the fixing belt 84 is oscillated, and the nip angle θ2 in pressure contact with the external pressure roller 82 is reduced (θ1> θ2). Therefore, the nip width at which the fixing belt 84 and the external pressure roller 82 come into contact is suitable for fixing a transfer material such as an OHP sheet, glossy paper, or thick paper.

  In this state, the support arm member 89 swings the second guide member 87 about the joint shaft 86 </ b> B via the link 88 so as to be substantially the same plane as the first guide member 86. The transfer material S that has passed through the conveyance path of the first guide plate member 86 is held so as to have an angle at which it can easily enter the fixing nip N where the rotating fixing belt 84 and the external pressure roller 82 are in pressure contact. The second guide member 87 slidably contacts the sheet conveyance surface and proceeds toward the fixing nip portion N.

[Second Embodiment of Fixing Device]
5A and 5B are sectional views showing a second embodiment of the fixing device 8 of the present invention. In addition, about the code | symbol used in FIG. 5, the same code | symbol is attached | subjected to the part which has the same function as FIG. Further, differences from the first embodiment will be described.

  The internal pressing roller 81, the external pressure roller 82, and the heating roller 83 have the same configuration as in the first embodiment. The heating roller 83 is supported by a member having substantially the same shape as that of the support arm member 89 shown in FIGS.

  The external pressure roller 82 is rotatably supported by the support 91. A first guide member (transfer material conveyance guide member) 92A is fixed to the upstream side of the support 91 in the transfer material conveyance direction, and a second guide member (transfer material conveyance guide member) 92B is fixed to the downstream side.

  The support body 91 is slidably supported by the guide member 93. Driving means comprising a rack gear 94A and a pinion gear 94B is disposed below the support 91, and the support 91 is moved by the motor M3 and power transmission means (not shown).

  A paper discharge roller 95 is disposed downstream of the second guide member 92B in the transfer material conveyance direction.

  FIG. 5A is a cross-sectional view of the fixing device 8 in a mode for fixing the transfer material S such as an OHP sheet, glossy paper, and thick paper.

  When this mode is set, the pinion gear 94B at the fixed position is rotated by driving the motor M3, the rack gear 94A is linearly moved, and the support 91 is moved along the guide member 93 from the initial position to the right in the figure. As the support 91 moves, the external pressure roller 82 also moves together, and the nip width of the fixing nip portion N where the external pressure roller 82 and the fixing belt 84 are in pressure contact with each other increases.

  At the same time, due to the movement of the support 91, the first guide member 92A and the second guide member 92B fixed to the support 91 also move together, and the direction in which the transfer material S is introduced into the fixing nip N and the fixing. The discharge direction of the transfer material S from the nip portion N is made substantially constant.

  FIG. 5B is a cross-sectional view of the fixing device 8 in a mode for fixing the transfer material S such as plain paper.

  When this mode is set, the support 91 stops at the initial position, and the nip width of the fixing nip portion N where the external pressure roller 82 and the fixing belt 84 are in pressure contact with each other is reduced. The first guide member 92 </ b> A and the second guide member 92 </ b> B fixed to the support 91 make the introduction direction of the transfer material S to the fixing nip portion N and the discharge direction of the transfer material S from the fixing nip portion N substantially constant. To do.

[Third Embodiment of Fixing Device]
6A and 6B are sectional views showing a third embodiment of the fixing device 8 of the present invention. In addition, about the code | symbol used in FIG. 6, the same code | symbol is attached | subjected to the part which has the same function as FIG. Further, differences from the second embodiment will be described.

  The fixing device 8 includes a support roller 96, an external pressure roller 82, a heating member H <b> 1 disposed inside the external pressure roller 82, a rotatable heating roller 83, and a heating disposed inside the heating roller 83. The fixing belt 84 is wound around the outer peripheral surfaces of the member H2, the heating roller 83, and the support roller 96, and the heating roller 83 and the external pressure roller 82 are in pressure contact with each other via the fixing belt 84.

  A support arm member 97 is swingably supported on a swing shaft provided on the same axis as the rotation shaft of the heating roller 83 and connected to a driving means (not shown). A support shaft 96A of the support roller 96 is fitted in a long groove portion 97A formed at one end of the support arm member 97. A connecting pin 98 </ b> A of a paper discharge guide member (transfer material conveyance guide member) 98 is fitted in the long groove portion 97 </ b> B formed in the distal end portion of the support arm member 97. The paper discharge guide member 98 is supported so as to be swingable about the support shaft 98B.

  FIG. 6A is a cross-sectional view of the fixing device 8 in a mode for fixing the transfer material S such as an OHP sheet, glossy paper, and thick paper.

  When this mode is set, the support arm member 97 is swung by a drive source and power transmission means (not shown), and the support roller 96 is centered on a swing shaft provided coaxially with the heating roller 83. By swinging clockwise, the support roller 96 descends, approaches the outer peripheral surface of the external pressure roller 82, and the nip width of the fixing nip portion N where the fixing belt 84 and the external pressure roller 82 come into pressure contact increases. . As a result, the amount of heat transfer to the transfer material S passing through the fixing nip N can be increased.

  In conjunction with the swinging of the support arm member 97, the downstream side in the transfer material transport direction of the paper discharge guide member 98 connected to the support arm member 97 is lowered, so that the transfer material S can be easily discharged to the paper discharge roller 95. To do.

  FIG. 6B is a cross-sectional view of the fixing device 8 in a mode for fixing the transfer material S such as plain paper.

  When this mode is set, the support arm member 97 is swung in the clockwise direction shown in the figure, the support roller 96 is lifted, and is moved away from the outer peripheral surface of the external pressure roller 82, so that the fixing belt 84 and the external pressure roller 82 are moved. The nip width of the fixing nip portion N where they are in pressure contact with each other is reduced. Thereby, the amount of heat transfer to the transfer material S passing through the fixing nip N can be optimized.

  Further, in conjunction with the swinging of the support arm member 97, the downstream side in the transfer material transport direction of the paper discharge guide member 98 connected to the support arm member 97 rises, so that the transfer material S can be easily discharged to the paper discharge roller 95. To do.

1 is a cross-sectional configuration diagram of a color image forming apparatus showing an embodiment of an image forming apparatus including a fixing device according to the present invention. 1 is a cross-sectional view illustrating a first embodiment of a fixing device according to the present invention. The perspective view of a fixing device. FIG. 3 is a cross-sectional view of an image forming apparatus including a fixing device and a transfer material conveying unit that show a state in which the nip angle is changed by swinging the fixing belt. Sectional drawing which shows 2nd Embodiment of the fixing device of this invention. Sectional drawing which shows 3rd Embodiment of the fixing device of this invention.

Explanation of symbols

8 Fixing Device 81 Internal Pressure Roller (Pressing Roller)
82 External pressure roller (pressure roller)
83 Heating roller 84 Fixing belt 86 First guide member (transfer material conveyance guide member)
87 Second guide member (transfer material conveyance guide member)
88 link 89 support arm member 91 support 92A first guide member (transfer material conveyance guide member)
92A Second guide member (transfer material conveyance guide member)
93 Guide member 95 Paper discharge roller 96 Support roller 97 Support arm member 98 Paper discharge guide member (transfer material conveyance guide member)
M1, M2, M3 Motor N Fixing nip S Transfer material (paper)

Claims (3)

In an image forming apparatus comprising: a fixing device that heat-fixes an unfixed toner image formed on a transfer material at a fixing nip portion where a heated fixing belt and a pressure roller are pressed against each other; and a transfer material conveying unit.
An endless fixing belt wound around a heating roller having a heating member and a pressure roller facing the pressure roller;
A transfer material conveyance guide member for guiding the transfer material conveyed to the fixing nip portion;
It is possible to change the pressure contact length in the fixing nip portion that is in pressure contact with the pressure roller by moving the heating roller, and to move the transfer material conveyance guide member in conjunction with the movement of the heating roller to move the fixing nip. A support arm member that makes the transfer material entry direction into the part variable;
An image forming apparatus comprising: In an image forming apparatus comprising: a fixing device that heat-fixes an unfixed toner image formed on a transfer material at a fixing nip portion where a heated fixing belt and a pressure roller are pressed against each other; and a transfer material conveying unit.
An endless fixing belt wound around a heating roller having a heating member and a pressure roller facing the pressure roller;
A pressure roller moving means for changing the pressure contact length in the fixing nip portion that moves the pressure roller and presses against the pressure roller;
A transfer material conveyance guide member that is fixed to the pressure roller moving means, moves in conjunction with the movement of the pressure roller, and changes at least one of a transfer material entry direction and a transfer material discharge direction to the fixing nip portion. When,
An image forming apparatus comprising: In an image forming apparatus comprising: a fixing device that heat-fixes an unfixed toner image formed on a transfer material at a fixing nip portion where a heated fixing belt and a pressure roller are pressed against each other; and a transfer material conveying unit.
An endless fixing belt wound around a heating roller having a heating member and a pressure roller facing the pressure roller;
A transfer material conveyance guide member for guiding the transfer material conveyed to the fixing nip portion;
It is possible to change the pressure contact length in the fixing nip portion that is in pressure contact with the pressure roller by moving the pressure roller, and moves the transfer material conveyance guide member in conjunction with the movement of the pressure roller to move the fixing nip portion. A support arm member that makes the transfer material discharge direction to the variable,
An image forming apparatus comprising:

Images