JP2017021143A - Fixation device and image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixation device and image formation apparatus which can reduce a back curl that occurs following fixation of a toner image with respect to a recording sheet such as a transverse recording sheet in which the back curl relatively easily occurs.SOLUTION: A fixation device 20 comprises: a conveyance auxiliary roller pair 210 which includes a conveyance auxiliary driven roller 203 arranged on the toner fixation surface side of a recording sheet P on the downstream side in the recording sheet conveyance direction of a fixing nip part N and a conveyance auxiliary drive roller 204 arranged on the opposite side thereof, and is formed with an auxiliary nip part M holding the fixed recording sheet P between the rollers; and a guide member 205 which guides the fixed recording sheet P delivered from the auxiliary nip part M so that the toner fixation surface bends in a recessed shape on the downstream side of the auxiliary nip part M. The conveyance auxiliary driven roller 203 is formed into such a crown shape that the roller diameter on the central side is larger than the roller diameter on both end sides in the axial direction.SELECTED DRAWING: Figure 9

Description

  The present invention relates to a fixing device used in an electrophotographic image forming apparatus such as a copying machine, a printer, and a facsimile, and an image forming apparatus equipped with the fixing device.

  An image forming apparatus using an electrophotographic system develops an electrostatic latent image formed on the surface of a photosensitive drum with a toner as a developer to make a visible image as a toner image, and develops the developed toner image. Is transferred to the recording paper by a transfer device, and the toner image is fixed on the recording paper by a fixing device.

  The fixing device includes a heating member and a pressure roller that are pressed against each other to form a fixing nip portion. When the recording paper carrying an unfixed toner image is passed through the fixing nip portion, and when the paper is passed therethrough, The toner image is fixed on the recording paper by applying pressure and heating.

  In this type of thermal fixing, since there is a temperature difference between the heating member and the pressure roller, when the recording paper passes through the fixing nip portion, the front and back of the recording paper (the surface on the heating member side and the pressure roller) A temperature difference occurs on the back surface of the side. Specifically, the temperature of the surface of the recording paper in contact with the heating member is higher than the temperature of the back surface of the recording paper in contact with the pressure roller.

  As a result, after passing through the fixing nip part, the moisture contained in the recording paper evaporates more from the front side, and the amount of moisture movement from the back side to the front side increases, so the front side is the back side. As a result, the amount of moisture on the front side becomes larger than that on the back side, and the recording paper curls to the back side (hereinafter referred to as “back curl”).

  In particular, recently, from the viewpoint of energy saving / warming up, a fixing device has been developed which has a heating member with a low heat capacity and a high temperature rise. In such a fixing device, since the paper can be passed before the pressure roller side is warmed, the temperature difference between the heating member and the pressure roller becomes larger, and the temperature difference between the front and back of the recording paper at the time of fixing is increased. Easy to grow. For this reason, the back curl generated at the fixing nip portion is increasing. In such a fixing device, there is a problem that when the paper is discharged in a state where the back curl is large, the specified number of sheets cannot be discharged onto the discharge tray, or the stack on the discharge tray itself is disturbed. To do. In view of this, an invention for eliminating back curl has been proposed (see Patent Documents 1 and 2).

  The fixing device disclosed in Patent Document 1 includes a curl correction mechanism including a pair of conveying rollers and a guide on the downstream side of a fixing nip portion formed by a heat roller and a belt. This guide corrects curling of the recording material by urging the recording material delivered from the pair of conveying rollers toward the heat roller. The biasing angle of the guide is adjusted according to the thickness and weight of the recording paper.

  In the fixing device disclosed in Patent Document 2, a pair of conveying rollers including a hard roller and a soft roller is provided as a decurler on the downstream side of a fixing portion nip portion formed by a heating roller and an endless belt. The decurler nip portion formed by the hard roller and the soft roller is regulated by the hard roller and has a convex shape. As a result, the recording material bent at the fixing nip portion is bent in the direction opposite to the fixing portion nip portion at the decurler nip portion to correct the curl.

  However, the curl correction mechanism disclosed in Patent Document 1 corrects the curl of the recording paper by forcibly bending the recording material transported from the pair of transport rollers by a guide. It sticks to bend along the transport direction. For this reason, in the so-called horizontal recording paper in which the direction of the fibers (cellulose) constituting the recording paper is perpendicular to the transport direction, fibers are not included along the transport direction. There is a problem that it is difficult to bend to bend, and the back curl cannot be sufficiently corrected. In addition, since the horizontal recording paper does not have the fiber direction in the transport direction, the back curl curved along the transport direction in the fixing unit is larger than that of the vertical recording paper. In this case, the back curl cannot be corrected sufficiently.

  Next, in the fixing device disclosed in Patent Document 2, the recording material conveyed from the fixing nip portion is curled by the curling of the recording material by being passed through a decurler nip portion that is regulated by a hard roll and configured in a convex shape. Similar to Patent Document 1, the recording paper is stiffened so as to bend along the transport direction. For this reason, Patent Document 2 also has a problem that the back curl cannot be sufficiently corrected with respect to the horizontal recording paper as described above.

  The present invention has been made in order to solve the above-described problems, and occurs with fixing of a toner image even on a recording paper such as a horizontal recording paper on which back curl tends to appear relatively remarkably. An object of the present invention is to provide a fixing device and an image forming apparatus capable of reducing back curl.

  In order to solve the above-described problem, a fixing device according to the present invention includes a rotatable fixing member heated by a heating unit, and a rotatable pressure member that comes into contact with the outer peripheral surface of the fixing member. In a fixing device that melts and fixes toner on a recording sheet at a fixing nip portion formed between the outer peripheral surface of the fixing member and the outer peripheral surface of the pressure member, the fixing nip portion is disposed downstream of the fixing nip portion in the recording paper conveyance direction. A conveyance auxiliary driven roller disposed on the toner fixing surface side of the recording paper for assisting the conveyance of the recording paper and a conveyance auxiliary driving roller disposed on the back side of the toner fixing surface of the recording paper, the conveyance auxiliary driven A pair of auxiliary conveyance rollers in which an auxiliary nip portion is formed between the outer peripheral surface of the roller and the outer peripheral surface of the auxiliary conveyance drive roller, and an auxiliary nip portion that sandwiches the recording sheet with toner fixed sent from the fixing nip portion; A guide member for guiding the toner-fixed recording paper fed from the auxiliary nip portion downstream of the auxiliary nip portion in the recording paper conveyance direction so that a toner fixing surface is bent in a concave shape, The conveyance auxiliary driven roller is configured to have a crown shape in which the diameter of the roller on the center side is larger than the diameter of the rollers on both ends in the axial direction.

  According to the present invention, a fixing device and an image forming apparatus that can reduce back curl that accompanies fixing of a toner image even on recording paper such as horizontal recording paper, on which back curl tends to appear relatively remarkably. Can be provided.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. 1 is a schematic configuration diagram of a fixing device according to an embodiment of the present invention. FIG. 3 is a schematic configuration diagram illustrating a separation conveyance mechanism and a back curl correction mechanism of the fixing device according to the embodiment of the present invention. FIG. 4 is a schematic configuration diagram of a back curl correction mechanism and a paper discharge unit shown in FIG. 3. FIG. 4 is a perspective view of a conveyance auxiliary drive roller shown in FIG. 3. It is a schematic perspective view which shows the structure of the guide member of the back curl correction mechanism shown in FIG. It is a schematic block diagram of the back curl correction mechanism shown in FIG. It is a top view of the conveyance auxiliary drive roller shown in FIG. FIG. 4 is a plan view of a conveyance auxiliary roller pair shown in FIG. 3. It is explanatory drawing explaining the function of the back curl correction mechanism with which the fixing device which concerns on embodiment of this invention is provided.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings.

First, the overall configuration of an image forming apparatus according to an embodiment of the present invention will be described.
An image forming apparatus 1 shown in FIG. 1 is a color laser printer, and includes an image forming unit A, a paper feeding unit B, a fixing device 20, a pair of paper discharge rollers 13, a paper discharge tray 14, and the like. Yes.

  The image forming unit A includes four image forming units 4Y, 4M, 4C, and 4K, an exposure device 9, a transfer device 3, and the like, which will be described later. The image forming apparatus 1 includes a back curl correction mechanism C in the fixing device 20 as a characteristic configuration. This will be described in detail below.

  In the center of the image forming apparatus main body of the image forming apparatus 1, four image forming units 4Y, 4M, 4C, and 4K are provided. Each of the image forming units 4Y, 4M, 4C, and 4K stores developers of different colors of yellow (Y), magenta (M), cyan (C), and black (K) corresponding to the color separation components of the color image. The configuration is the same except that.

  Specifically, each of the image forming units 4Y, 4M, 4C, and 4K includes a drum-shaped photoconductor 5 as a latent image carrier, a charging device 6 that charges the surface of the photoconductor 5, and a surface of the photoconductor 5. A developing device 7 for supplying toner and a cleaning device 8 for cleaning the surface of the photosensitive member 5 are included. In FIG. 1, only the photoconductor 5, the charging device 6, the developing device 7, and the cleaning device 8 included in the black image forming unit 4 </ b> K are denoted by reference numerals, and the other image forming units 4 </ b> Y, 4 </ b> M, and 4 </ b> C are illustrated. Since the configuration is the same as that of the black image forming unit 4K, the reference numerals thereof are omitted.

  Below each image forming unit 4Y, 4M, 4C, 4K, an exposure device 9 for exposing the surface of the photoreceptor 5 is disposed. The exposure device 9 includes a laser light source, a polygon mirror 51a, an f-θ lens 51b, a plurality of reflection mirrors 51c, and the like (not shown), and irradiates the surface of each photoconductor 5 with laser light based on image data. An electrostatic latent image is formed on the surface 5.

  A transfer device 3 is disposed above the image forming units 4Y, 4M, 4C, and 4K. The transfer device 3 includes an intermediate transfer belt 30 as an intermediate transfer member, four primary transfer rollers 31 as primary transfer means, a secondary transfer roller 36 as secondary transfer means, a secondary transfer backup roller 32, A cleaning backup roller 33, a tension roller 34, and a belt cleaning device 35 are provided.

  The intermediate transfer belt 30 is an endless belt and is stretched by a secondary transfer backup roller 32, a cleaning backup roller 33, and a tension roller 34. Here, by rotating the secondary transfer backup roller 32, the intermediate transfer belt 30 runs (rotates) in the direction indicated by the arrow in the figure.

  Each of the four primary transfer rollers 31 sandwiches the intermediate transfer belt 30 with each photoconductor 5 to form a primary transfer nip. Further, a power source is connected to each primary transfer roller 31 so that a predetermined DC voltage (DC) or a predetermined AC voltage (AC) is applied to each primary transfer roller 31.

  The secondary transfer roller 36 sandwiches the intermediate transfer belt 30 with the secondary transfer backup roller 32 to form a secondary transfer nip. Similarly to the primary transfer roller 31, a power source is also connected to the secondary transfer roller 36 so that a predetermined DC voltage (DC) or AC voltage (AC) is applied to the secondary transfer roller 36. It has become.

  The belt cleaning device 35 includes a cleaning brush and a cleaning blade disposed so as to contact the intermediate transfer belt 30. The waste toner collected by the belt cleaning device 35 is accommodated in a waste toner container via a waste toner transfer hose.

  A bottle container 2 is provided in the upper part of the image forming apparatus main body, and four toner bottles 2Y, 2M, 2C, and 2K that store replenishing toner are detachably attached to the bottle container 2. ing. Toner is replenished from each toner bottle 2Y, 2M, 2C, 2K to each developing device 7 via a replenishment path (not shown) provided between each toner bottle 2Y, 2M, 2C, 2K and each developing device 7. The

  On the other hand, a sheet feeding unit B is provided at the lower part of the image forming apparatus main body. The paper supply unit B includes a paper supply tray 10 that stores recording paper P as a recording medium, a paper supply roller 11 that carries the recording paper P out of the paper supply tray 10, and the like.

In addition to plain paper, the recording paper P includes thick paper, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheet, and the like. Further, a manual paper feed mechanism may be provided. In the present embodiment, cardboard refers to paper having a basis weight of 160 g / m ² or more.

  In the image forming apparatus main body, a conveyance path R is provided for discharging the recording paper P from the paper feed tray 10 through the secondary transfer nip to the outside of the apparatus. In the transport path R, a pair of registration rollers 12 serving as timing rollers for transporting the recording paper P to the secondary transfer nip at the transport timing is arranged upstream of the position of the secondary transfer roller 36 in the recording paper transport direction. It is installed.

  A fixing device that presses and heats the recording paper P carrying an unfixed toner image on the downstream side in the recording paper conveyance direction from the position of the secondary transfer roller 36 to melt and fix the toner image on the recording paper P. 20 is arranged. Further, a pair of paper discharge rollers 13 for discharging the recording paper P to the outside of the apparatus is provided on the downstream side of the conveyance path R in the recording paper conveyance direction from the fixing device 20. Further, a paper discharge tray 14 for stocking the recording paper P discharged outside the apparatus is provided on the upper surface of the image forming apparatus main body.

  Further, the fixing device 20 includes a back curl correction mechanism C described later on the downstream side of the fixing device 20 in the recording paper conveyance direction.

  Next, a basic operation of the image forming apparatus 1 according to the embodiment of the present invention will be described.

  First, when an image forming operation is started, each photoconductor 5 in each of the image forming units 4Y, 4M, 4C, and 4K is driven to rotate clockwise in the drawing, and the surface of each photoconductor 5 is predetermined by a charging device 6. Uniformly charged to polarity. The surface of each charged photoconductor 5 is irradiated with laser light from the exposure device 9 to form an electrostatic latent image on the surface of each photoconductor 5.

  At this time, the image information to be exposed on each photoconductor 5 is monochromatic image information obtained by separating a desired full-color image into color information of yellow, magenta, cyan, and black. The toner is supplied to the electrostatic latent images formed on the respective photoreceptors 5 by the developing devices 7 in this way, whereby the electrostatic latent images are visualized (visualized) as images.

  When the image forming operation is started, the secondary transfer backup roller 32 is driven to rotate counterclockwise in the figure, and the intermediate transfer belt 30 is caused to run in the direction indicated by the arrow in the figure.

  Further, by applying a constant voltage having a polarity opposite to the toner charging polarity or a voltage controlled by a constant current to each primary transfer roller 31, the primary transfer nip between each primary transfer roller 31 and each photoreceptor 5 is applied. A transfer electric field is formed.

  Thereafter, when each color image on the photoconductor 5 reaches the primary transfer nip as each photoconductor 5 rotates, the image on each photoconductor 5 is intermediated by the transfer electric field formed in the primary transfer nip. The images are sequentially superimposed and transferred onto the transfer belt 30.

  In this way, a full color image is carried on the surface of the intermediate transfer belt 30. Further, the toner on each photoconductor 5 that could not be transferred to the intermediate transfer belt 30 is removed by the cleaning device 8. Then, the surface of each photoconductor 5 is neutralized by the neutralization device, and the surface potential is initialized.

  In the lower part of the image forming apparatus main body, the paper feed roller 11 starts to rotate, and the recording paper P is sent out from the paper feed tray 10 to the transport path R. The recording paper P delivered to the transport path R is temporarily stopped by the registration rollers 12.

  Thereafter, rotation of the registration roller 12 is started at a predetermined timing, and the recording paper P is conveyed to the secondary transfer nip in accordance with the timing when the image on the intermediate transfer belt 30 reaches the secondary transfer nip. At this time, a transfer voltage having a polarity opposite to the toner charging polarity of the image on the intermediate transfer belt 30 is applied to the secondary transfer roller 36, thereby forming a transfer electric field in the secondary transfer nip. Then, the image on the intermediate transfer belt 30 is collectively transferred onto the recording paper P by this transfer electric field. At this time, the residual toner on the intermediate transfer belt 30 that could not be transferred onto the recording paper P is removed by the belt cleaning device 35 and conveyed to a waste toner container.

  Thereafter, the recording paper P is conveyed to the fixing device 20, and the image on the recording paper P is fixed to the recording paper P by the fixing device 20. The recording paper P conveyed from the fixing device 20 is conveyed to a back curl correction mechanism C described later, and the back curl of the recording paper P is corrected.

  Thereafter, the recording paper P is conveyed to the outside of the apparatus by a pair of discharge rollers 13 for discharge and discharged to the discharge tray 14 for stocking the recording paper P discharged outside the apparatus provided on the upper surface portion of the image forming apparatus main body. Is done.

  The above description is an image forming operation when a full color image is formed on the recording paper P. A single color image is formed using any one of the four image forming units 4Y, 4M, 4C, and 4K. It is also possible to form a two-color or three-color image using two or three image forming units.

  Next, the configuration of the fixing device 20 according to the embodiment of the present invention will be described in detail.

  As shown in FIG. 2, the fixing device 20 includes a fixing belt 21 as a rotatable fixing rotator, and an additional rotating body that is opposed to the fixing belt 21 and abuts on the outer peripheral surface thereof and is rotatably provided. A pressure roller 22, a halogen heater 23 as a heat source for heating the fixing belt 21, a nip forming member 24 disposed inside the fixing belt 21, and a stay 25 as a support member for supporting the nip forming member 24 The reflection member 26 that reflects the light emitted from the halogen heater 23 to the fixing belt 21, the temperature sensor 27 as temperature detecting means for detecting the temperature of the fixing belt 21, and the pressure roller 22 pressurize the fixing belt 21. A pressing means (not shown) is provided.

  The fixing belt 21 constitutes a fixing member according to the present invention, and the pressure roller 22 constitutes a pressure member according to the present invention.

  The fixing belt 21 is composed of an endless belt member (including a film) that is thin and flexible. Specifically, the fixing belt 21 includes a base material on the inner peripheral side formed of a metal material such as nickel or SUS or a resin material such as polyimide (PI), and a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA). Or the outer peripheral side release layer formed of polytetrafluoroethylene (PTFE) or the like. Further, an elastic layer formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluorine rubber may be interposed between the base material and the release layer.

  The pressure roller 22 includes a cored bar 22a, an elastic layer 22b made of foamable silicone rubber, silicone rubber, or fluororubber provided on the surface of the cored bar 22a, and PFA provided on the surface of the elastic layer 22b. And a release layer 22c made of PTFE or the like. The pressure roller 22 is pressed toward the fixing belt 21 by a pressure unit (not shown) and is in contact with the nip forming member 24 via the fixing belt 21. At the location where the pressure roller 22 and the fixing belt 21 are in pressure contact, the elastic layer 22b of the pressure roller 22 is crushed to form a fixing nip portion N having a predetermined width. The pressure roller 22 is configured to be rotationally driven by a driving source such as a motor provided in the image forming apparatus main body. When the pressure roller 22 is rotationally driven, the driving force is transmitted to the fixing belt 21 at the fixing nip portion N, and the fixing belt 21 is driven to rotate.

  In the fixing device 20 according to the present embodiment, the pressure roller 22 is a solid roller, but may be a hollow roller. In that case, a heating source such as a halogen heater 23 may be disposed inside the pressure roller 22. Further, when the elastic layer 22b is not provided, the heat capacity is reduced and the fixing property is improved. May occur. In order to prevent this, it is desirable to provide an elastic layer having a thickness of 100 μm or more. By providing an elastic layer having a thickness of 100 μm or more, minute unevenness can be absorbed by elastic deformation of the elastic layer, so that occurrence of uneven gloss can be avoided.

  The elastic layer 22b may be solid rubber, but if there is no heat source inside the pressure roller 22, sponge rubber may be used. Sponge rubber is more preferable because heat insulation is enhanced and heat of the fixing belt 21 is less likely to be taken away. Further, the fixing rotator and the counter rotator are not limited to being brought into pressure contact with each other, and may be configured to simply contact each other without applying pressure.

  Both end portions of each halogen heater 23 are fixed to the side plate of the fixing device 20. Each halogen heater 23 is configured to generate heat by being output controlled by a power supply unit provided in the main body of the image forming apparatus. The output control is based on the detection result of the surface temperature of the fixing belt 21 by the temperature sensor 27. Based on. By such output control of the halogen heater 23, the temperature of the fixing belt 21 (fixing temperature) can be set to a desired temperature. In addition to the halogen heater 23, an IH, a resistance heating element, a carbon heater or the like may be used as a heating source for heating the fixing belt 21.

  The nip forming member 24 is disposed in a longitudinal shape over the axial direction of the fixing belt 21 or the axial direction of the pressure roller 22, and is fixedly supported by a stay 25. Thus, the nip forming member 24 is prevented from being bent by the pressure of the pressure roller 22, and a uniform nip width is obtained in the axial direction of the pressure roller 22. The stay 25 is preferably formed of a metal material having high mechanical strength such as stainless steel or iron in order to satisfy the bending prevention function of the nip forming member 24. However, the stay 25 may be made of resin. It is.

  The nip forming member 24 is composed of a heat resistant member having a heat resistant temperature of 200 ° C. or higher. This prevents the nip forming member 24 from being deformed by heat in the toner fixing temperature region, and ensures a stable state of the fixing nip portion N, thereby stabilizing the output image quality. For the nip forming member 24, polyether sulfone (PES), polyphenylene sulfide (PPS), liquid crystal polymer (LCP), polyether nitrile (PEN), polyamide imide (PAI), polyether ether ketone (PEEK), etc. It is possible to use a typical heat resistant resin. In FIG. 2, the shape of the nip forming member 24 is such that the fixing belt 21 follows this when pressed, and the desired nip portion shape (first plane N1, arc N2, second plane N3) is obtained. However, it is good also as a flat shape from which N1, N2, and N3 become the same planar shape.

  The nip forming member 24 has a low friction sheet on the surface thereof. When the fixing belt 21 rotates, the fixing belt 21 slides with respect to the low friction sheet, so that the driving torque generated in the fixing belt 21 is reduced and the load due to the frictional force on the fixing belt 21 is reduced.

  The reflection member 26 is disposed between the stay 25 and the halogen heater 23. In the fixing device 20 according to the present embodiment, the reflecting member 26 is fixed to the stay 25. Further, since the reflecting member 26 is directly heated by the halogen heater 23, it is desirable that the reflecting member 26 be formed of a metal material having a high melting point. By arranging the reflection member 26 in this way, the light emitted from the halogen heater 23 toward the stay 25 is reflected to the fixing belt 21.

  As a result, the amount of light applied to the fixing belt 21 can be increased, and the fixing belt 21 can be efficiently heated. Further, since it is possible to suppress the radiant heat from the halogen heater 23 from being transmitted to the stay 25 and the like, energy saving can be achieved.

  In addition, without providing the reflecting member 26 in the fixing device 20 according to the present embodiment, the surface of the stay 25 on the side of the halogen heater 23 may be subjected to mirror processing such as polishing or painting to form a reflecting surface. The reflectance of the reflecting surface of the reflecting member 26 or the stay 25 is desirably 90% or more.

  However, in general, the shape and material of the stay 25 cannot be freely selected to ensure its strength. For this reason, when the reflecting member 26 is separately provided as in the fixing device 20 according to the present embodiment, the degree of freedom in selecting the shape and material is increased, and the reflecting member 26 and the stay 25 are specialized in their functions. Can do. Further, since the reflecting member 26 is provided between the halogen heater 23 and the stay 25, the position of the reflecting member 26 with respect to the halogen heater 23 is reduced, so that the fixing belt 21 can be efficiently heated.

  In addition, the fixing device 20 according to the present embodiment is devised in various configurations in order to further improve energy saving and first print time.

  Specifically, the fixing belt 21 can be directly heated by a halogen heater 23 at a place other than the fixing nip portion N (direct heating method). In the fixing device 20 according to the present embodiment, nothing is interposed between the halogen heater 23 and the fixing belt 21 (the left portion in FIG. 2), and the radiant heat from the halogen heater 23 is applied to the fixing belt 21 at that portion. I give it directly.

  Further, in order to reduce the heat capacity of the fixing belt 21, the fixing belt 21 is made thinner and smaller in diameter. Specifically, the thicknesses of the base material, the elastic layer, and the release layer constituting the fixing belt 21 are set in a range of 20 to 50 μm, 100 to 300 μm, and 10 to 50 μm, and the overall thickness is set. It is set to 1 mm or less. The diameter of the fixing belt 21 is set to 20 to 40 mm. In order to further reduce the heat capacity, the thickness of the entire fixing belt 21 is desirably 0.2 mm or less, and more desirably 0.16 mm or less. The diameter of the fixing belt 21 is desirably 30 mm or less.

  In the fixing device 20 according to the present embodiment, the diameter of the pressure roller 22 is set to 20 to 40 mm, and the diameter of the fixing belt 21 and the diameter of the pressure roller 22 are configured to be equal. Yes. However, it is not limited to this configuration. For example, the fixing belt 21 may be formed so that the diameter thereof is smaller than the diameter of the pressure roller 22. In that case, since the curvature of the fixing belt 21 at the fixing nip N is smaller than the curvature of the pressure roller 22, the recording paper P discharged from the fixing nip N is easily separated from the fixing belt 21.

  Although illustration is omitted, shielding members that shield heat from the halogen heater 23 are disposed between the fixing belt 21 and the halogen heater 23 at both ends in the axial direction of the fixing belt 21. Thereby, in particular, an excessive temperature rise in the non-sheet passing region of the fixing belt 21 during continuous sheet feeding can be suppressed, and deterioration or damage of the fixing belt 21 due to heat can be prevented.

  Next, the basic operation of the fixing device 20 according to the present embodiment will be described with reference to FIG.

  When the power switch of the image forming apparatus main body is turned on, power is supplied to the halogen heater 23 and the pressure roller 22 starts to rotate clockwise as indicated by an arrow A1 in FIG. As a result, the fixing belt 21 is driven to rotate counterclockwise in FIG. 2 by the frictional force with the pressure roller 22.

  Thereafter, the recording paper P carrying the unfixed toner image T in the image forming process described above is conveyed in the direction of the arrow A2 in FIG. 2 while being guided by a guide plate (not shown), and is in a pressure contact state. And is fed into the fixing nip N of the pressure roller 22. Then, the toner image T is fixed on the surface of the recording paper P by heat from the fixing belt 21 heated by the halogen heater 23 and pressure applied between the fixing belt 21 and the pressure roller 22.

  The recording paper P on which the toner image T has been fixed is carried out from the fixing nip N in the direction of arrow A3 in FIG. Next, the recording paper P on which the toner image T is fixed is corrected by the back curl correction mechanism C as will be described in detail later, and is then discharged out of the apparatus by the paper discharge roller 13 and is then discharged to the paper discharge tray. Stocked at 14.

  In the fixing device 20 according to the present embodiment, the nip forming member 24 is formed to be compact in order to dispose the stay 25 as large as possible in the fixing belt 21. Specifically, the width of the nip forming member 24 in the sheet conveyance direction is formed smaller than the width of the stay 25 in the sheet conveyance direction. As a result, the stay 25 can be disposed as large as possible in a limited space in the fixing belt 21, and the strength of the stay 25 can be ensured.

  In the fixing device 20 according to the present embodiment, the fixing belt 21 is configured to be guided only by the nip forming member 24 at a portion other than the end portion (at the end portion, the fixing belt 21 is the belt. It is also guided by a holding member (not shown)). That is, since no guide member other than the nip forming member 24 is provided between the fixing belt 21 and the stay 25, the stay 25 can be disposed closer to the fixing belt 21, and the strength of the stay 25 is improved. Can be achieved.

  In the fixing device 20 according to the present embodiment, the tip of the rising portion of the stay 25 is disposed so as to be close to the inner peripheral surface of the fixing belt 21 in the contact direction of the pressure roller 22. By doing so, the mechanical strength of the stay 25 can be improved, and the bending of the nip forming member 24 by the pressure roller 22 can be prevented. As a result, the nip width can be formed uniformly in the axial direction of the pressure roller 22, and a good image can be obtained.

  Further, as shown in FIG. 3, on the recording paper exit side of the fixing device 20, the recording paper P that has passed through the fixing nip N in the vicinity of the fixing nip is separated and guided to the paper discharge in the discharge direction. A transport mechanism is provided.

  The separation / conveying mechanism includes a belt-side separation / conveying member 201 having a front end 201a close to the fixing belt 21 side on the downstream side in the moving direction of the recording paper P moving from the fixing nip portion N, and a vibration close to the pressure roller 22 side. And a roller side separating and conveying member 202 having a moving end.

  The belt-side separating / conveying member 201 is provided to peel off the recording paper P that sticks and sticks to the fixing belt 21 from the fixing belt 21. For this reason, a metal sheet is used so as to obtain an accuracy capable of positioning the attached recording sheet P at a close position where the recording sheet P can be lifted from the surface of the fixing belt 21.

  The roller-side separation / conveyance member 202 is made of a resin molded product, and a support rod 202a provided in a part thereof is rotatably supported on the housing side (not shown) so as to face the pressure roller 22. The swinging end that swings can be swung so as to be able to come into contact with and separate from the pressure roller 22.

  The roller-side separating / conveying member 202 swings with respect to the pressure roller 22 so that, for example, when the jammed recording paper P is removed from the fixing nip N, the roller-side separation / conveyance member 202 swings greatly in a direction away from the pressure roller 22. Thus, a space for inserting the hand into the fixing nip portion N can be made. Thereby, the recording paper P can be pulled out.

  Next, the configuration of the back curl correction mechanism C provided in the fixing device 20 according to the embodiment of the present invention will be described.

  As shown in FIG. 3, the fixing device 20 according to the embodiment of the present invention includes a back curl correction mechanism C on the downstream side in the recording paper conveyance direction of the belt side separation conveyance member 201 and the roller side separation conveyance member 202. Yes. The back curl correction mechanism C includes a conveyance auxiliary roller pair 210 including a conveyance auxiliary driven roller 203 and a conveyance auxiliary driving roller 204 that assist the conveyance of the recording paper P, and a guide that assists the delivery of the recording paper P to the paper discharge roller 13. And a member 205.

  The conveyance auxiliary driven roller 203 assists the conveyance of the recording paper P on the downstream side of the fixing nip portion N in the recording paper conveyance direction, and is disposed on the toner fixing surface side of the recording paper P. The conveyance auxiliary drive roller 204 is disposed on the back side of the toner fixing surface of the recording paper P. Then, an auxiliary nip portion M is formed between the outer peripheral surface of the conveyance auxiliary driven roller 203 and the outer peripheral surface of the conveyance auxiliary drive roller 204 so as to sandwich the recording paper P with toner fixed sent from the fixing nip portion N. It has become.

  The guide member 205 guides the recording sheet P, which has been toner-fixed, delivered from the auxiliary nip portion M to the downstream side of the auxiliary nip portion M in the recording sheet conveyance direction so that the toner fixing surface is bent concavely.

  Therefore, the guide member 205 is arranged at an angle that positively bends the recording paper P. The recording paper P that has passed through the fixing nip N is guided by the conveyance auxiliary roller pair 210 and sent out on the extension line of the auxiliary nip M, but is bent toward the toner fixing surface by the angle of the guide member 205. That is, the recording paper P is bent in the opposite direction to the back curl. Thereby, the back curl of the recording paper P is corrected.

  As shown in FIG. 9, the conveyance auxiliary driven roller 203 is formed in a crown shape in which the roller diameter on the center side is larger than the roller diameters on both ends in the axial direction. The conveyance auxiliary driven roller 203 has an overall length of about 330 mm so that the recording paper P having the sheet size of “A3 Nobi” can be conveyed, and a radius difference between the center and the end is about 0.1 mm to 0.5 mm. Is formed.

  The conveyance auxiliary driven roller 203 extends parallel to the axial direction of the fixing belt 21, and is rotatably supported by a holder 207 provided on the belt side separation conveyance member 201. The holder 207 is urged toward the conveyance path side of the recording paper P by a spring (not shown).

  The conveyance auxiliary driven roller 203 includes a hollow cored bar and a release layer having a thickness of 30 to 300 μm formed on the surface of the cored bar. The conveyance auxiliary driven roller 203 uses a metal material such as aluminum, steel, or stainless steel for the core metal, and uses a resin material such as PFA or PTFE, which is a highly releasable material, for the release layer as the surface layer portion.

  The conveyance auxiliary drive roller 204 extends in parallel with the axial direction of the fixing belt 21, is rotatably supported by the roller side separation conveyance member 202, and is driven by a motor (not shown).

  As shown in FIG. 5, the conveyance auxiliary drive roller 204 includes a shaft 204a formed of a metal material such as aluminum, steel, and stainless steel, and a plurality of rollers 204b having the same outer diameter mounted on the shaft 204a at intervals in the axial direction. And is composed of. That is, the conveyance auxiliary drive roller 204 does not have a uniform outer diameter over its entire length, and a portion where the roller 204b is not mounted on the shaft 204a is a stepped portion 204c having a smaller outer diameter than other portions.

  The roller 204b includes a hollow cored bar and a grip layer formed on the surface of the cored bar. The roller 204b uses a metal material such as aluminum, steel, or stainless steel for the core metal, and a solid rubber material having a high coefficient of friction made of silicon, EPDM, urethane, fluoro rubber, or the like for the grip layer, thereby obtaining a recording paper conveyance force. I am trying to do it.

  The conveyance auxiliary drive roller 204 is configured such that the outer peripheral surface of the conveyance auxiliary driven roller 203 urged toward the conveyance path side of the recording paper P by a spring is brought into contact with the outer peripheral surface of each roller 204b.

  As a result, as shown in FIG. 7, the fixing device 20 forms an auxiliary nip portion M that holds the recording paper P on which the toner has been fixed at a position where the conveyance auxiliary driven roller 203 and the conveyance auxiliary driving roller 204 come into contact with each other. It has come to be. In the fixing device 20, when the conveyance auxiliary driving roller 204 is driven, the conveyance auxiliary driven roller 203 is rotated, and the recording paper P that has entered the auxiliary nip portion M is passed downstream in the recording paper conveyance direction. Yes.

  As shown in FIG. 8, the conveyance auxiliary drive roller 204 has a plurality of rollers 204b symmetrically in the axial direction of the shaft 204a with respect to the center of the recording paper conveyance path, and both edges of the recording paper P of various sizes. It arrange | positions so that the outer peripheral surface of either of the some rollers 204b may be contact | connected.

  As a result, the fixing device 20 sandwiches both edges of the recording paper P of various sizes in the auxiliary nip portion M between the conveyance auxiliary driven roller 203 and one of the rollers 204b of the conveyance auxiliary driving roller 204. ing.

  As shown in FIG. 6, the guide member 205 has a guide surface 205a facing the auxiliary nip portion M from the upper side, and is configured by a plurality of ribs 205b that enter the stepped portions 204c between the plurality of rollers 204b. It is attached to the conveying member 202. The plurality of ribs 205b fill the plurality of stepped portions 204c so as not to interfere with the rotation operation of the plurality of rollers 204b.

  The guide member 205 is configured such that the guide surface 205a is inclined toward the conveyance auxiliary driven roller 203 from the lower side toward the upper side. Further, the guide member 205 preferably has a vertical interval from the auxiliary nip portion M to the guide surface 205a of 10 mm or less.

  As a result, the fixing device 20 brings the leading end portion of the recording paper P delivered from the auxiliary nip portion M into contact with the guide surface 205a of the guide member 205 and guides it to the conveyance auxiliary driven roller 203 side. P is bent in the lateral direction. That is, the recording paper P on which toner has been fixed is guided such that the toner fixing surface is bent concavely.

  Further, the conveyance auxiliary drive roller 204 may be formed in a reverse crown shape (the drum shape) so as to correspond to the crown shape (see FIG. 9) of the conveyance auxiliary driven roller 203 (the reverse crown type conveyance auxiliary drive in FIG. 10). See roller 208). In this case, specifically, the conveyance auxiliary drive roller 204 is formed in an inverted crown shape in which the roller diameter on the center side is smaller than the roller diameters on both ends in the axial direction.

  Usually, the auxiliary clip part M which follows the shape of the conveyance auxiliary driven roller 203 is formed by pressing the conveyance auxiliary driven roller 203 having a metal core metal against the conveyance auxiliary driving roller 204 having an elastic layer. . Therefore, if the conveyance auxiliary drive roller 204 has a reverse crown shape such as the reverse crown type conveyance auxiliary drive roller 208 shown in FIG. 10, the pressing force required to form the auxiliary nip portion M can be reduced. As a result, it is possible to suppress conveyance problems such as linear speed fluctuations that occur when the conveyance auxiliary driven roller 203 and the conveyance auxiliary drive roller 204 are pressed against each other.

  Next, the function of the back curl correction mechanism C of the fixing device 20 according to the embodiment of the present invention will be described.

  As described above, when the recording paper P passes through the fixing nip portion N, a temperature difference occurs between the front and back of the recording paper P due to a temperature difference between the fixing belt 21 and the pressure roller 22. Therefore, as shown in FIG. 10, the recording paper P immediately after passing through the fixing nip N tends to be back curled in a convex shape on the toner fixing surface side as indicated by the curl direction B3. At this time, when the recording paper P is a horizontal sheet, the fiber arrangement direction B2 of the recording paper P is a direction orthogonal to the recording paper transport direction B1, so the curl in the curl direction B3 along the recording paper transport direction B1. In comparison with the longitudinal recording paper P, the back curl becomes large.

  Therefore, first, the recording paper P that has passed through the fixing nip N is passed through a crown-shaped auxiliary nip M formed in a conveyance auxiliary roller pair 210 including a conveyance auxiliary driven roller 203 and a reverse crown-shaped conveyance auxiliary driving roller 208. Is done. The crown-shaped auxiliary lip portion M functions to curve the toner fixing surface of the recording paper P passing through the auxiliary nip portion M in a concave shape in a direction perpendicular to the recording paper conveyance direction B1 (FIG. 10). B4). That is, the recording paper P is stiffened parallel to the recording paper transport direction B1 when passing through the auxiliary nip portion M. When the recording paper P is a horizontal line, the recording paper P is bent along the fiber arrangement direction B2, so that it can be effectively stiffened and is more effective in suppressing back curl.

  Next, the recording paper P that has been stiffened in parallel with the recording paper conveyance direction B1 by the auxiliary nip portion M is bent in a direction opposite to the back curl (B3 in FIG. 10) (B5 in FIG. 10) by the guide member 205. While being guided. Therefore, the recording paper P is guided by the paper discharge guide plate 206 with the back curl corrected as shown in FIG.

  In this way, the auxiliary nip portion M is first stiffened so as to bend along the direction perpendicular to the recording paper conveyance direction B1 (in the case of the horizontal recording paper P, the fiber arrangement direction B2). Then, the guide member 205 is further bent so as to bend along the recording sheet conveyance direction B1 (in the case of the horizontal recording sheet P, the direction orthogonal to the fiber arrangement direction B2). In this manner, the stiffness for correcting the back curl is performed in both the recording paper conveyance direction B1 and the direction orthogonal thereto. As a result, the back curl can be effectively corrected even with respect to the laterally recording paper P where the back curl is noticeable, and paper jams in the transport path R and the paper discharge port can be eliminated.

  In FIG. 10, the reverse crown type conveyance auxiliary drive roller 208 is used. However, even if the conveyance auxiliary drive roller 204 having the configuration shown in FIG. 5 is used, the crown-shaped auxiliary nip portion M is similarly formed. The same back curl correction function can be exhibited.

  In the fixing device 20 and the image forming apparatus 1 according to the present embodiment, the toner fixing surface of the recording paper P that has been toner-fixed delivered from the auxiliary nip portion M is concave on the downstream side of the auxiliary nip portion M in the recording sheet conveyance direction. A guide member 205 is arranged to guide it so as to be bent.

  For this reason, in the fixing device 20 and the image forming apparatus 1 according to the present embodiment, the toner fixing surface is convexly formed by the guide member 205 with respect to the recording paper P (FIG. 10) whose toner fixing surface is greatly curled convexly. On the contrary, it is corrected to bend in a concave shape. Thereby, a big back curl can be corrected.

  In the fixing device 20 and the image forming apparatus 1 according to the present embodiment, the conveyance auxiliary driven roller 203 is further formed in a crown shape in which the roller diameter on the center side is larger than the roller diameter on both ends in the axial direction.

  Therefore, the fixing device 20 and the image forming apparatus 1 according to the present embodiment are orthogonal to the recording paper conveyance direction B1 when the recording paper P passes through the crown-shaped auxiliary lip portion M of the conveyance auxiliary roller pair 210. The toner fixing surface is curved along the direction so as to be curved in a concave shape. In the case of the horizontal recording paper P, this is done so that the toner fixing surface is curved in a concave shape along the same direction as the paper fiber direction. As a result, it is possible to effectively correct the back curl even with the horizontal recording paper P.

  In the fixing device 20 and the image forming apparatus 1 according to the present embodiment, the conveyance auxiliary drive roller 204 is located on the center side with respect to the roller diameter on both ends in the axial direction so as to correspond to the crown shape of the conveyance auxiliary driven roller 203. Are formed in an inverted crown shape with a small roller diameter.

  For this reason, the fixing device 20 and the image forming apparatus 1 according to the present embodiment apply a load to the conveyance auxiliary roller pair 210 and positively form the auxiliary nip portion M that matches the crown shape of the conveyance auxiliary driven roller 203. There is no need. Therefore, it is possible to easily form the auxiliary nip portion M that matches the crown shape of the conveyance auxiliary driven roller 203. For this reason, the portion of the roller that is crushed when a load is applied is greatly reduced, so that problems caused by fluctuations in the conveying linear velocity are suppressed.

  In the fixing device 20 and the image forming apparatus 1 according to the present embodiment, both edges of the recording paper P sent out from the fixing nip portion N of the plurality of rollers 204b in the conveyance auxiliary drive roller 204 are any of the plurality of rollers 204b. It arrange | positions so that it may touch the outer peripheral surface.

  For this reason, in the fixing device 20 and the image forming apparatus 1 according to the present embodiment, both the edge portions of the recording paper P of various sizes in the auxiliary nip portion M are either the conveyance auxiliary driven roller 203 or the conveyance auxiliary driving roller 204. It can be held by the roller 204b. Therefore, the fixing device 20 and the image forming apparatus 1 according to the present embodiment can effectively reduce the curling of the recording paper P by the guide member 205 without loosening the shape of both edges of the recording paper P. it can.

  In the fixing device 20 and the image forming apparatus 1 according to the present exemplary embodiment, a plurality of ribs 205 b constituting the guide member 205 are inserted into a plurality of step portions 204 c formed on the conveyance auxiliary driving roller 204.

  For this reason, the fixing device 20 and the image forming apparatus 1 according to the present embodiment have the auxiliary nip portion even when the bending rate of the recording paper P between the conveyance auxiliary roller pair 210 and the guide member 205 is set large. The recording paper P delivered from M is not caught by the rib 205b. As a result, paper jams in the fixing device 20 are less likely to occur.

  In the fixing device 20 and the image forming apparatus 1 according to the present embodiment, the release layer that is the surface layer portion of the conveyance auxiliary driven roller 203 is formed of a resin material such as PFA or PTFE that is a high release material. .

  Therefore, in the fixing device 20 and the image forming apparatus 1 according to the present embodiment, the toner of the unmelted toner image T remaining on the recording paper P at the time of toner fixing is difficult to adhere to the conveyance auxiliary driven roller 203. Therefore, the fixing device 20 and the image forming apparatus 1 according to the present embodiment can prevent the recording paper P from being damaged due to the toner of the toner image T being accumulated on the conveyance auxiliary driven roller 203.

  Although the embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention. The fixing device according to the present invention is not limited to the image forming apparatus shown in FIG. 1, but is mounted on a monochrome image forming apparatus, a color laser printer, other printers, a copier, a facsimile, or a complex machine thereof. Is also possible.

  As described above, according to the present invention, it is possible to reduce the back curl caused by the fixing of the toner image even on the recording paper such as the horizontal recording paper on which the back curl tends to appear relatively remarkably. Therefore, the present invention is useful for fixing devices used in electrophotographic image forming apparatuses such as copying machines, printers, and facsimiles, and image forming apparatuses equipped with the fixing devices.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 20 Fixing apparatus 21 Fixing belt (fixing member)
22 Pressure roller (Pressure member)
23 Halogen heater (heating means)
24 nip forming member 203 conveyance auxiliary driven roller 204 conveyance auxiliary driving roller 204a shaft 204b roller 204c stepped portion 205 guide member 205a guide surface 205b rib 208 reverse crown type conveyance auxiliary driving roller 210 conveyance auxiliary roller pair A image forming unit C back curl correction Mechanism N Fixing nip part M Auxiliary nip part P Recording paper

JP 2006-23427 A (FIG. 1) Japanese Patent Laying-Open No. 2003-295657 (FIG. 2)

Claims (6)

A rotatable fixing member that is heated by a heating unit; and a rotatable pressure member that abuts on the outer peripheral surface of the fixing member; and an outer peripheral surface of the fixing member and an outer peripheral surface of the pressure member. In a fixing device that melts and fixes toner on a recording paper at a fixing nip portion formed therebetween,
A conveyance auxiliary driven roller disposed on the toner fixing surface side of the recording paper for assisting the conveyance of the recording paper on the downstream side of the fixing nip portion in the recording paper conveying direction and a back surface side of the toner fixing surface of the recording paper. An auxiliary nip that holds the toner-fixed recording sheet fed from the fixing nip portion between the outer peripheral surface of the auxiliary conveyance driven roller and the outer peripheral surface of the auxiliary conveyance drive roller. A pair of conveyance auxiliary rollers formed with a section;
A guide member for guiding the toner-fixed recording sheet fed from the auxiliary nip portion so that a toner fixing surface is bent concavely, on the downstream side of the auxiliary nip portion in the recording sheet conveyance direction. ,
The fixing auxiliary device is characterized in that the conveyance auxiliary driven roller is formed in a crown shape in which a roller diameter on the center side is larger than a roller diameter on both ends in the axial direction.   The conveyance auxiliary drive roller is formed in an inverted crown shape in which the roller diameter on the center side is smaller than the roller diameter on both end sides in the axial direction so as to correspond to the crown shape of the conveyance auxiliary driven roller. The fixing device according to claim 1. The conveyance auxiliary drive roller has a shaft and a plurality of rollers mounted on the shaft at intervals in the axial direction, and is outside of other portions of the shaft where the rollers are not mounted. A step with a small diameter is formed,
3. The fixing according to claim 1, wherein both edges of the recording paper fed from the fixing nip are disposed so as to contact one of the outer peripheral surfaces of the plurality of rollers. apparatus.   4. The fixing according to claim 3, wherein the guide member includes a plurality of ribs that have a guide surface facing the auxiliary nip portion and enter the plurality of stepped portions of the conveyance auxiliary driving roller. apparatus.   5. The fixing device according to claim 1, wherein a surface layer portion of the conveyance auxiliary driven roller is formed of a highly releasable material.   An image forming apparatus comprising the fixing device according to claim 1.

Images