JP2016177063A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of making the reduction of a back curl occurring due to fixation and the stabilization of conveyance compatible and capable of reducing a damage toward a recording paper toner image.SOLUTION: An image forming apparatus includes: an auxiliary nip part formed between a fixing device and a branch member by a drive roller and a follower roller; a guide member for guiding a recording paper in the downstream; and guide member movement means for moving the guide member to a first position and a second position. In a first position of the guide member, an intersection angle θ1 of the recording paper conveyance direction in the auxiliary nip part and the direction connecting the point at which the recording paper is separated from the auxiliary nip part to the downstream side is 20° or more and 50° or less, and a distance L from the center position of the auxiliary nip part to the guide member toward the recording paper conveyance direction in the auxiliary nip part is 15 mm or less, and an intersection angle θ of the recording paper conveyance direction in the auxiliary nip part and the guide direction of the guide member is 120°or more.SELECTED DRAWING: Figure 13

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a facsimile machine, or a printer.

  In an image forming apparatus using an electrophotographic system, an electrostatic latent image is formed in an image forming unit, and then developed with toner, which is a developer, to be visualized as a toner image, and then developed by a transfer device. The toner image is transferred onto a recording sheet, and then the image is fixed on the recording sheet with 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. Therefore, conventionally, inventions that eliminate back curl have been proposed (see Patent Documents 1, 2, and 3).

  The image forming apparatus disclosed in Patent Document 1 passes through the fixing nip portion on a conveyance path between a first conveyance roller and a second conveyance roller that are sequentially arranged at different positions on the downstream side of the fixing unit. Accordingly, a guide member is provided for guiding the recording paper while curving the recording paper in a direction opposite to the direction of the back curl generated on the recording paper. In this image forming apparatus, the recording paper transport speed by the second transport roller is set to a value larger than that of the first transport roller, so that the recording paper is curved in the direction opposite to the back curl direction. The paper is conveyed while being pressed against the member, and the curling of the recording paper is corrected.

  The transfer paper curl correction device of the image forming apparatus disclosed in Patent Document 2 has a pair of roller members on a conveyance path on the downstream side of the fixing device as a back curl correction means, and recording while passing through the pair of roller members. A guide member is provided that guides the paper while curving the paper in the opposite direction to the direction of the back curl. In this image forming apparatus, the curling of the recording paper is corrected by bending in the direction opposite to the back curl generated on the recording paper as it passes through the fixing nip portion.

  In the discharge device disclosed in Patent Document 3, a guide member is movably disposed in contact with the back side of the paper between a fixing nip portion and a discharge nip provided on the downstream side of the fixing nip portion, and the back generated by fixing. The curling of the recording paper is corrected by bending in the direction opposite to the curl and changing the contact force according to the stiffness of the paper.

  However, the conventional back curl correction method described above has the following problems.

  First, in the techniques disclosed in Patent Documents 1 and 2, the recording paper is always forcibly pressed by the guide member to curl in the opposite direction to the back curl. For this reason, for example, in the case of thick paper passing, there is no back curl in which the recording paper curls on the back surface in the fixing device. Therefore, when the guide plate is always in the first position, the guide plate is reversed, and the face curl is reversed. become. In addition, since the contact force between the guide plate and the recording paper is strong, the guide member causes damage (scratches) / guide member wear on the back side of the paper. Further, since the paper rigidity is high, when the tip comes out of the roller pair and the tip comes into contact with the guide member, the tip is bent, and it becomes difficult to stabilize the conveyance.

  Next, the technique disclosed in Patent Document 3 is configured such that the guide member that correctively deforms the recording paper can be moved in the retracting direction by the stiffness of the recording paper. There is no change in the conveyance while contacting the recording paper. Therefore, when double-sided paper is passed, there is an image on the first side on the back side of the recording paper that comes into contact with the guide member, and the toner image is damaged because this image side comes into contact with the guide member. There is also a problem.

  However, even if the guide member is moved to the final retracted position, the guide member position is determined by the stiffness of the recording paper, so that the guide member and the recording paper are conveyed while being in contact with each other. For this reason, when double-sided paper is passed, there is an image of the first surface on the back side of the recording paper that comes into contact with the guide member, and the image surface comes into contact with the guide member. Immediately after fixing on the second side, the image on the back side is not at a temperature at which the toner completely melts, but the toner image that has been heated comes into contact with the guide member. In this case, even with light contact, gloss unevenness (difference in gloss from the portion that is not in contact with the guide member) is likely to occur, and the contact pressure between the guide member and the recording paper can be controlled only with the stiffness of the recording paper. It is not possible to completely prevent and avoid uneven glossiness. In addition, there is a problem that the positional relationship between the fixing nip portion and the exit nip portion with respect to the guide plate is restricted, and the degree of freedom in layout is small.

  The present invention has been made to solve the above-described problems, and can achieve both reduction of back curl caused by fixing and stabilization of conveyance and reduction of damage to recording paper and toner images. It is an object of the present invention to provide an image forming apparatus that can be used.

  In order to solve the above-described problems, an image forming apparatus according to the present invention passes a recording sheet onto which an image has been transferred by an image forming unit to a fixing nip unit, and fixes the image to the recording sheet at the fixing nip unit. And an image forming apparatus having a recording paper conveyance path branching unit for switching between an out-of-machine discharge path for discharging the recording paper conveyed to the downstream side of the fixing apparatus and a reverse path for duplex printing. A back curl correction mechanism is provided on a conveyance path between the fixing device and the recording paper conveyance path branching unit, and the back curl correction mechanism is provided on a side where the back curl is generated on the recording paper in the fixing nip portion. Formed by a driving roller and a driven roller provided on the side for heating the recording paper, and provided on the same side as the driving roller, and an auxiliary nip portion for auxiliary conveyance of the recording paper A guide member that guides the recording paper, a first position where the guide member is required to press the front side in the conveyance direction of the recording paper passing through the auxiliary nip portion, and a second position away from the recording paper And a guide member moving means for moving the recording member to a recording paper transport direction in the auxiliary nip portion and a point at which the recording paper moves downstream from the auxiliary nip portion. A paper bending angle θ1 corresponding to an intersection angle with a direction connecting the point where the guide member contacts the recording paper is 20 ° or more and 50 ° or less, and from the center position of the auxiliary nip portion to the auxiliary nip portion. The distance L to the guide member in the recording paper conveyance direction is 15 mm or less, and the initial contact corresponds to the intersection angle between the recording paper conveyance direction and the guide direction of the guide member in the auxiliary nip portion. Degree θ is 120 ° or more.

  According to the present invention, it is possible to provide an image forming apparatus capable of reducing both back curl generated during fixing and stabilizing conveyance and reducing damage to a recording paper / toner image.

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 during back curl correction. 1 is a schematic configuration diagram of a fixing device according to an embodiment of the present invention when back curl is not corrected. FIG. In FIG. 3, it is the figure which looked at the arrow IV direction about the pressurization side separation conveyance member, the drive roll, and the guide member. FIG. 6 is a perspective view of a part of the fixing device as viewed from the conveyance path side when the outlet guide member is in the first position according to the embodiment of the present invention. FIG. 6 is an enlarged perspective view of a part of the fixing device as viewed from the conveyance path side when the outlet guide member is in a second position according to the embodiment of the present invention. FIG. 10 is a view of a part of the fixing device as viewed from the conveyance path side when the outlet guide member moving unit is operated and the outlet guide member is in the second position according to the embodiment of the present invention. FIG. 6 is a front view of a part of the fixing device as viewed from the conveyance path side when the outlet guide member is in the first position according to the embodiment of the present invention. FIG. 6 is a front view of a part of the fixing device as viewed from the conveyance path side when the outlet guide member is in a second position according to the embodiment of the present invention. It is a perspective view which shows the arrangement | sequence of a branch member and an exit guide member concerning one embodiment of this invention. FIG. 6 is a diagram illustrating a plurality of sheet conveyance paths by combining the position of the branching member and the position of the outlet guide member according to the embodiment of the present invention. FIG. 10 is a diagram for explaining the influence of the crossing angle between the recording paper conveyance direction and the exit guide member in the correction nip portion on back curl correction according to the embodiment of the present invention. It is explanatory drawing of the measurement conditions for measuring the effect of curl correction by a guide member, and conveyance property in one embodiment of this invention. It is explanatory drawing which measures the curl amount for evaluating the effect of curl correction concerning one embodiment of this invention. It is explanatory drawing of the measurement conditions for measuring the effect of curl correction at the time of changing the shape of a guide member, and conveyance property in one embodiment of this invention.

  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 illustrated 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 a pair of reversals. A roller 16 and a duplex unit 17 are provided.

  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 contains 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 has 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 that supplies toner and a cleaning device 8 that cleans the surface of the photoreceptor 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.

  Under the image forming units 4Y, 4M, 4C, and 4K, an exposure device 9 that exposes 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 at the upper part of the main body of the image forming apparatus, and four toner bottles 2Y, 2M, 2C, and 2K that store replenishing toner are detachably attached to the bottle container 2. ing. Toner is supplied from each toner bottle 2Y, 2M, 2C, 2K to each developing device 7 through a supply 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.

Note that recording paper as a recording medium includes, in addition to plain paper, thick paper, postcard, envelope, 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.

  Further, on the downstream side in the recording paper conveyance direction from the position of the secondary transfer roller 36, the fixing device 20 that pressurizes and heats the recording paper P carrying an unfixed toner image and fixes the toner image on the recording paper P. 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.

  A branch member 15 is provided between the paper discharge roller 13 and the fixing device 20. The branching member 15 is in the first state shown in FIG. 1 in the single-sided sheet passing mode, and is in the second state closed in the arrow direction from the first state shown in FIG. 1 in the double-sided sheet passing mode. It is fixed to the main body so as to be rotatable.

  In other words, the branching member 15 reverses the two-sided printing with the outside discharge path (path passing through the discharge roller 13) for discharging the recording paper P conveyed downstream of the fixing device 20 to the discharge tray 14 outside the apparatus. Since the route (a route passing through the duplex unit 17 described later) is switched, the recording paper transport route branching means of the present invention is configured. Further, a back curl correction mechanism C described later is provided between the branching member 15 and the fixing device 20.

  The double-side reversing path 40 includes a reversing roller 16 for switching back the recording paper P provided on the downstream side of the branching member 15, and a double-sided unit 17 between the reversing roller 16 and the registration roller 12. The duplex unit 17 includes conveyance rollers 42 to 44 to form a reversal path for duplex printing, and the recording paper P after fixing the first surface is switched back by the reversal roller 16 and passes through the conveyance rollers 42 to 44. Then, it is conveyed to the registration roller 12.

  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 rotationally driven clockwise in the drawing, and the surface of each photoconductor 5 is predetermined by the 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.

  Thus, 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 printer, 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 guided in the discharging direction and the refeeding direction via the branching member 15 for switching the path for discharging the recording paper P to the outside of the apparatus and the double-side reversing path. .

  In the single-sided sheet passing mode, the branching member 15 is opened, conveyed to the outside of the apparatus by a pair of discharge rollers 13 for discharging, and discharged to the outside of the apparatus provided on the upper surface of the image forming apparatus main body. It is discharged to a paper discharge tray 14 for stocking P.

  In the double-sided paper passing mode, the branching member 15 is closed in the direction of the arrow, so that the recording paper P after the first side fixing is guided to the double-sided reverse path 40. The recording sheet P guided to the duplex reversing path 40 is switched back by the pair of reversing rollers 16, conveyed to the duplex unit 17, conveyed again to the pair of registration rollers 12, and fed again. Similar to the first side, the second side image is printed on the back side of the recording paper P. Then, the recording paper P is discharged out of the apparatus by the paper discharge roller 13 and stocked on the paper discharge tray 14.

  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 fixing device 20 having the back curl correction mechanism C of the image forming apparatus 1 according to the embodiment of the present disclosure will be described in detail.
FIG. 2 is a cross-sectional view of a fixing device having a back curl correction mechanism according to the present embodiment.

  As shown in FIG. 2, the fixing device 20 is used to fix the toner image T after being transferred, which is carried on the recording paper P, by melting and infiltrating it with heat and pressure. A fixing belt 21 having a possible flexibility is provided.

  The fixing device 20 passes the recording paper P onto which the toner image has been transferred by the image forming unit A through the fixing nip N, and applies heat and pressure at the fixing nip N to fix the toner image on the recording paper P.

  In addition to an endless fixing belt (fixing member) 21, the fixing device 20 is opposed to form a fixing nip portion N by applying pressure to the fixing belt 21 in contact with the fixing belt 21. A pressure roller (pressure member) 22 that is a rotating body is provided. Inside the fixing belt 21, a heater (heat source) 23 including a plurality of halogen lamps 23 a and 23 b for heating the inner surface side of the fixing belt 21 at a place other than the fixing nip portion N is provided.

  Inside the fixing belt 21, a nip forming member 24 that is a base member for forming a nip disposed inside the fixing belt 21, a stay 25 that supports the nip forming member 24, and light emitted from the heater 23. Is provided on the fixing belt 21.

  Although not shown in detail, the nip forming member 24 that is a base member for forming a nip has a sliding sheet (low friction sheet) wound with a base pad.

  In the nip forming member 24 shown in FIG. 2, the shape of the fixing nip portion N is flat, but is not limited to this shape. For example, when the fixing nip portion N is formed in a concave shape along the circumferential surface of the pressure roller 22, the leading edge of the recording paper P passing through the fixing nip portion N is close to the pressure roller 22, and thus the fixing belt 21. There is an advantage that the separability from the is improved.

  The temperature of the fixing belt 21 is detected by a temperature sensor 27 provided on the side where the recording paper P enters the fixing nip portion, and used for feedback processing of the heater 23. In FIG. 2, an arrow F indicates the conveyance direction of the recording paper P.

  The fixing belt 21 is an endless belt formed in a thin and flexible sleeve shape, and is composed of a base material and a release layer located on the surface thereof. For the base material, a metal material such as nickel or A-SUS or a resin material such as polyimide is used. For the release layer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polytetrafluoroethylene (PTFE), or the like having releasability with respect to the toner is used.

  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 peripheral surface of the cored bar 22a, and a PFA provided on the surface of the elastic layer 22b. Or it is comprised by the mold release layer which consists of PTFE etc.

  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 as a base member in contact with the fixing belt 21.

  At the place where the pressure roller 22 and the fixing belt 21 contact each other, the elastic layer 22b of the pressure roller 22 is crushed so that pressure is applied to the fixing belt 21 and the nip forming member 24 has a predetermined width. The fixing nip portion N is secured.

  The pressure roller 22 is configured to be rotationally driven by a drive source such as a motor (not shown) provided in the printer 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 using radiant heat may be disposed inside the pressure roller 22. In addition, when the elastic layer 22b is not provided, the heat capacity is reduced and the fixability is improved. However, when the unfixed toner is crushed and fixed, minute irregularities on the belt surface are transferred to the image and the solid portion of the image is glossy. Unevenness may occur. In order to prevent this, it is desirable to provide an elastic layer having a thickness of 100 μm or more.

  Aluminum, iron, stainless steel, or the like can be selected as the pipe-shaped metal used for the hollow roller. When providing a heat source in the pressure roller 22, in order to prevent the support from being heated by radiant heat from the heat source, a heat insulating layer is provided on the support surface or a heat ray reflecting surface is provided by mirror treatment. Is desirable. The heat source in this case is not limited to the halogen heater described above, and an IH heater, a resistance heating element, or a carbon heater can also be used.

  In the case of the fixing device 20 described above, since the heating member having a low heat capacity is directly heated, the fixing device 20 has a very fast temperature rise, so that there is an advantage that the first print can be accelerated. However, from the viewpoint of the occurrence of the back curl on the recording paper P, the fixing is performed before the pressure roller is sufficiently warmed. Therefore, the back curl (for example, the curve of the solid line P ′ shown in FIG. (Shape) becomes very large.

  On the recording paper exit side of the fixing device 20, a separation transport mechanism is provided that separates the recording paper P that has passed through the fixing nip portion N in the vicinity of the fixing nip portion and guides the recording paper P toward the paper discharge portion in the discharge direction.

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

  The belt-side separation 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.

  A resin molded product is used for the pressure side separating member 202, and a support rod 202 </ b> A provided in a part thereof is rotatably supported on the housing side (not shown) so as to face the pressure roller 22. The swing end 202a can swing so as to be able to come into contact with and separate from the pressure roller 22.

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

  The back curl correction mechanism C provided between the branching member 15 and the fixing device 20 includes a driving roller 204, a driven roller 203, a guide member 205, and a guide member moving unit D.

  The driving roller 204 and the driven roller 203 are disposed on the downstream side of the separating members 201 and 202.

  The driving roller 204 is provided on the side where the back curl is generated on the recording paper P in the fixing nip portion (pressure roller 22 side) with respect to the conveyance path between the fixing device 20 and the branching member 15.

  The driven roller 203 is provided on the side where the recording paper P is heated (the fixing belt 21 side) in the fixing nip portion with respect to the conveyance path between the fixing device 20 and the branching member 15.

  The driving roller 204 and the driven roller 203 form an auxiliary nip portion and rotate and rotate to assist the conveyance of the recording paper P. The distance between the fixing nip portion and the auxiliary nip portion is set to be shorter than the length of the recording paper P.

  In order to prevent the occurrence of jamming, it is configured as follows. First, the diameter of the driving roller 204 is set to be larger than the diameter of the driven roller 203. The recording paper conveyance speed in the auxiliary nip portion is set slightly lower than the recording paper conveyance speed in the fixing nip portion. The nip pressure at the auxiliary nip portion is set to be smaller than the nip pressure at the fixing nip portion. With this configuration, the recording paper P is not jammed between the fixing nip portion and the auxiliary nip portion.

  The driving roller 204 may be formed of rubber at least on the roller peripheral surface, and the driven roller 203 may be formed such that at least the roller peripheral surface is harder than the roller peripheral surface of the driving roller 204 and has releasability.

  In this embodiment, the driving roller 204 includes a core metal 204a (hereinafter referred to as a roller shaft 204a), and a high coefficient of friction made of silicon, EPDM, urethane, fluororubber, or the like provided on the surface of the core metal 204a. The solid rubber material 204b is used to obtain a recording paper conveying force.

  The driven roller 203 has a structure in which a hollow pipe-shaped metal surface is covered with a low μ tube (thickness 30 to 300 μm) such as PFA, ETFA, FEP or the like.

  The reason for using a hollow pipe-shaped metal is to reduce the heat capacity and prevent the water vapor generated from the paper evaporated during fixing from adhering to the driven roller side, so that the heat from the fixing heats up quickly. is there.

  The reason why the low μ tube is arranged on the surface is that a small amount of toner that has not melted after fixing is difficult to adhere and does not accumulate even if it adheres. That is, the driven roller 203 side is conveyed while always in contact with the image surface side, and thus has the above-described configuration. The driven roller 203 is held on the image forming apparatus main body by a spring member (not shown) through a holder, and by pressing the holder with the spring, the driving roller 204 and the driven roller 203 come into contact with each other to form an auxiliary nip portion. The formed recording paper P can be auxiliary conveyed.

  The guide member 205 is provided from the fixing unit so that the center of rotation is coaxial with the roller axis of the driving roller 204. The guide member 205 is driven by a guide member moving means D, which will be described later, driven based on a control signal from the main body control unit, and a first position shown in FIG. 2 (advanced position for pressing the recording paper P) and FIG. To the second position (retracted position away from the recording paper P (not in contact)).

  When the guide member 205 is positioned at the first position shown in FIG. 2, the guide member 205 is in sliding contact so as to press the front side of the recording paper P passing through the auxiliary nip portion on the same side as the drive roller 204. The recording paper P functions to bend in a concave shape on the opposite side to the back curl.

  That is, when the guide member 205 is held at the first position, the drive roller is opposite to the direction of the recording paper P passing through the auxiliary nip portion (perpendicular to the line connecting the centers of the roller pairs). It is arranged at a position that closes the route from the same side as 204.

  For this reason, the leading edge of the recording paper P comes into contact with the guide member 205, and then the recording paper P is auxiliary conveyed by the nip conveying force between the driving roller 204 and the driven roller 203 while being pressed by the guide member 205. Become.

  Then, the guide member 205 is curved with respect to the recording paper P so as to form a concave curved surface on the opposite side to the back curl, and the back curl can be corrected. By using such a conveyance path, the recording paper P passing through the guide member 205 can improve the back curl generated by the fixing and can be discharged to the paper discharge tray 14.

  Next, the configuration of the guide member 205 and the guide member moving means D will be described with reference to FIGS.

  As shown in FIG. 4, the driving roller 204 is fitted and fixed to the pressure side separation member 202 with a roller shaft 204a supported at both ends rotatably via a sliding bearing 208, and the roller shaft 204a with a predetermined interval. It comprises a plurality of short cylindrical portions 204b made of an elastic material such as rubber.

  The driving roller 204 is rotatable by transmitting the rotational driving force from the guide member moving means D shown in FIG. 6 to the driving gear 210 fixed to the end of the roller shaft 204a via the idler gear 211.

  As shown in FIGS. 4 to 7, the guide member 205 is fixed to a support shaft 205 a that is supported at both ends so as to be rotatable at the upper ends of a pair of bracket arms 206. The pair of bracket arms 206 are fitted on the outer diameter portion of the sliding bearing 208 and are rotatable. A plurality of guide members 205 are respectively provided on a plurality of bosses 205b fitted and fixed to the support shaft 205a.

  The guide member 205 extends so that the base end is fixed to the boss 205 b and the projecting end covers the drive roller 204. The guide member 205 is configured to stop at a position where the stopper portion 206b of the bracket arm 206 contacts a part of the pressure-side separation member 202. The posture position of the guide member 205 corresponding to this position is the first position for changing the angle of the recording paper discharged from the auxiliary nip portion.

  As shown in FIGS. 5 to 7, the guide member moving means D includes a solenoid 220 as a drive source, a link mechanism 207 that swings when the solenoid 220 is actuated, and a tension spring 209. The solenoid 220 has a casing fixed to the image forming apparatus main body.

  One end of the tension spring 209 is locked to the side surface portion of the pressure-side separation member 202, and the other end is locked in the middle of the arm portion 206a of the bracket arm 206. The guide member 205 has the first position shown in FIG. The tension force of the spring is applied so that the bracket arm 206 is rotated in the direction as described above.

  As shown in FIG. 7, in the link mechanism 207, one end 207a in the horizontal direction is supported by the fixed pin shaft 207A, and the operating end 207b which is the other end is surrounded from the lower end of the arm portion 206a of the bracket arm 206. A long hole 207d provided at the upper end of the upward extension 207c that extends above the middle part in the horizontal direction is connected to the extension rod 220a of the solenoid 220 by a pin.

  As shown in FIG. 7, the extension rod 220a of the solenoid 220 is extended (position indicated by a dotted line), and the operating end 207b of the link mechanism 207 is the tip of the arm portion 206a of the bracket arm 206 as shown in FIG. It is in the state which is separated below.

  From the state shown in FIG. 6, when a current flows through the internal coil of the solenoid 220 based on the control signal of the control device, the extension rod 220a of the solenoid 220 is retracted. Thereby, the link mechanism 207 is rotated against the tensile force of the tension spring 209, and the operating end 207b lifts the tip of the arm portion 206a of the bracket arm 206 (state shown in FIG. 7). As a result, the guide member 205 is retracted from the first position shown in FIGS. 2 and 8 to the second position shown in FIGS.

  On the other hand, when the current to the internal coil of the solenoid 220 is cut off from the state shown in FIG. 7 based on the control signal of the control device, the bracket arm 206 is rotated by the tensile force of the tension spring 209, and the guide member 205 is 2 and the extension rod 220a of the solenoid 220 is retracted by the tensile force of the tension spring 209, resulting in the state shown in FIGS.

  With the above-described configuration, the gap between the drive roller 204 and the guide member 205 can have a configuration in which the dimensional tolerance of the component is least accumulated (only the radial distance tolerance from the axis center of each component). The guide member 205 can be moved in a state where the gap between the drive roller 204 and the guide member 205 is kept constant with high accuracy.

  As shown in FIG. 10, the branch member 15 is arranged in a plurality of claw shapes corresponding to the width direction orthogonal to the recording paper conveyance direction, and the guide member 205 is also orthogonal to the recording paper conveyance direction. Are arranged in a plurality of claw shapes corresponding to the width direction. In addition, the branch members 15 and the guide members 205 are alternately arranged.

  As a result, even if the swinging area of the branch member 15 and the swinging area of the guide member 205 overlap on the recording paper conveyance line, they are swung independently of each other to guide the recording paper. ing.

  11A to 11D show four conveyance paths for the recording paper formed by the combination of the first and second positions of the branching member 15 and the first and second positions of the guide member 205. FIG. Indicates. A one-dot chain line in the drawing indicates a conveyance path of the recording paper that passes through the auxiliary nip formed by the driving roller 204 and the driven roller 203.

  FIG. 11A shows a recording paper conveyance path in the thin paper single-sided printing mode, where the branch member 15 is in the second position and the guide member 205 is in the first position. The guide member 205 is brought into contact with the back surface (the back curl side surface) of the recording paper that is passing through the auxiliary nip portion so as to be curved so as to have a concave surface opposite to the back curl and to be guided to the paper discharge roller 13. It has become.

  FIG. 11B shows a recording paper conveyance path in the thick paper single-sided printing mode, and the branch member 15 and the guide member 205 are both in the second position. The guide member 205 is not in contact with the back surface of the recording paper that does not generate back curl while passing through the auxiliary nip portion, and the branch member 15 softly curves the recording paper and guides it to the paper discharge roller 13. Yes.

  FIG. 11C shows a recording sheet conveyance path for the first sheet passing in the thin sheet duplex printing mode, where the branch member 15 is in the first position and the guide member 205 is in the second position. The guide member 205 makes slight contact with the back surface (second surface) of the recording paper passing through the auxiliary nip portion where the back curl has been slightly corrected at the auxiliary nip portion, and the branching member 15 causes the recording paper to contact the reverse roller 16. It comes to lead.

  FIG. 11 (d) shows the conveyance path of the recording paper for passing the second surface in the thin paper duplex printing mode, and both the branching member 15 and the guide member 205 are in the second position. The guide member 205 is not in contact with the back surface (first surface) of the recording paper that does not cause back curl while passing through the auxiliary nip portion, and the branching member 15 softly curves the recording paper to the discharge roller 13. It comes to lead.

  As shown in FIG. 4, the guide member 205 has a plurality of rib shapes over the length, and the rib-shaped branch member 15 enters between the guide members 205.

  In order to obtain the curl correction effect, it is necessary to bring the tip of the guide member 205 close to the auxiliary nip portion. Therefore, a plurality of rubber portions of the driving roller 204 are provided so as to be spaced apart from each other. The guide member 205 is configured to enter between the rubber portion and the rubber portion.

  FIG. 12 shows a case where the rotation center of the guide member 205 is provided in alignment with the rotation center of the drive roller 204 (position indicated by a solid line in the drawing), and the rotation center of the guide member 205 is the rotation center of the drive roller 204. Is a comparative view in a case where is arranged away from the rotation center of the drive roller 204 by a certain gap (a dotted line position indicated by reference numeral 205 ′ in the figure).

  As can be seen in FIG. 12, the curl correction effect when the guide member 205 is at the solid line position is the same as the curl correction effect when the guide member 205 is at the dotted line position.

  The recording paper passing through the auxiliary nip portion is discharged in a direction perpendicular to a line connecting the centers of the driving roller 204 and the driven roller 203. For this reason, the contact angle θ ′ between the front end of the paper near the auxiliary nip portion when the guide member 205 is in the dotted line position and the guide member 205 is equal to the paper near the auxiliary nip portion when the guide member 205 is in the solid line position. It becomes smaller than the contact angle θ between the tip and the guide member 205.

  When this contact angle is small, the leading edge of the paper is buckled and bent and conveyed, and in the worst case, the risk of jamming increases. Conversely, when the guide member 205 is arranged such that the extension line of the surface that contacts the recording paper is displaced from the rotation center of the drive roller 204 and the contact angle is larger than the contact angle θ, the guide member 205 The curl correction effect of bending the paper is reduced.

  However, since the first position is a position where the guide member 205 is positively brought into contact with the back surface of the recording paper P, the conveyance resistance between the back surface of the recording paper P and the guide member 205 is large, and stress is applied to the paper itself. It will be.

  Therefore, the present inventor can set the first position of the guide member 205 to a position where the conveyance resistance between the back surface of the recording paper P and the guide member 205 is small and the stress applied to the paper itself can be reduced. A paper passing test was conducted. In this paper passing test, the edge of the guide member 205 is linear with the prototype of the fixing device according to the present embodiment, and the first crossing angle θ, the second θ1, and the distance shown in FIG. This was carried out by changing the value of L in various ways. This paper-passing test is an evaluation test for two points of whether the curl correction effect is obtained or the situation where the transportability is hindered. The results shown in Table 1 were obtained.

  The initial contact angle θ in FIG. 13 is an angle corresponding to the intersection angle between the recording paper conveyance direction and the guide direction of the guide member 205 in the auxiliary nip portion. The paper bending angle θ1 in FIG. 13 intersects the recording paper conveyance direction in the auxiliary nip portion and the direction connecting the point where the recording paper is separated from the auxiliary nip portion and the point where the guide member contacts the recording paper. An angle corresponding to a corner. A distance L in FIG. 13 is a distance from the center position of the auxiliary nip portion to the guide member 205 in the recording sheet conveyance direction in the auxiliary nip portion.

  In Table 1, curl correction is represented by ◎, ◯, and × grades. This is a prototype of the fixing device according to the present embodiment. First, as shown in FIG. 14, the test paper P on which the guide member 205 is not subjected to curl correction is used as the test paper P on which the image is fixed and discharged. The distance from the flat plate Q at the edge of the test paper P placed on the flat plate Q is measured as the curl amount. Next, the test paper P subjected to curl correction by the guide member 205 is placed on the flat plate Q and measured as the curl amount.

  When the curl amount of the test paper P on which the curl correction is performed is reduced by 10 mm or more as compared with the curl amount when the guide member 205 does not perform the curl correction, ◎ is given and 5 mm or more and less than 10 mm. In the case of reduction, ◯ is given, and in the case of reduction of less than 5 mm, × is given. As a test result, Comparative Examples 1 and 4 were curl correction x.

In Table 1, the transportability is represented by a grade evaluation of ◯ and X. This was evaluated with respect to 11 types of transportability of Comparative Examples 1 to 5 and Examples 1 to 6 on a thin paper having a basis weight of 52 g / m ^{2 by} a prototype of the fixing device according to the present embodiment. In the evaluation of transportability, θ, θ1, and L in FIG. 13 are respectively set as the numerical values in the table, and 1000 sheets are passed for each type. Then, a cross was marked, and a circle was marked if none occurred. As test results, Comparative Examples 1 to 3 and 5 were transportability x.

  The comprehensive judgment in Table 1 was taken as comprehensive judgment x when both the curl correction test result and the transportability test result were x. In Table 1, the numerical region was specified for those having a comprehensive judgment of “O”. As a result, when the guide member 205 is set to the first position so that the crossing angle θ1 is 20 ° or more and 50 ° or less, the distance L is 15 mm or less, and the crossing angle θ is 120 ° or more, fixing is performed. It was found that it is possible to achieve both reduction of back curl that occurs and stabilization of conveyance.

  As shown in FIG. 15, even when the edge of the guide member 205 is curved, the first crossing angle θ, the second θ1, and the value of the distance L in FIG. If the crossing angle θ, the second θ1, and the distance L are the same, the result of Table 1 is obtained.

  On the other hand, when the second surface of the recording paper P that is not a thick paper is passed in the double-sided paper passing mode, the surface with the image (first surface) comes into contact with the guide member 205, and image blurring and gloss streaks occur. Cheap.

  In particular, when the second surface is passed, during the fixing of the second image surface in the fixing unit, the first surface image as the back surface is also reheated through the fixing nip. For this reason, when the heated first-surface image is rubbed strongly by the guide member 205, the toner is easily peeled off or the gloss is likely to change.

  Therefore, the guide member 205 is positioned at the second position shown in FIG. The guide member 205 located at the second position is in non-contact with the recording paper P passing through the auxiliary nip portion, and functions so as not to bend the recording paper P.

  When the guide member 205 is positioned at the second position, the guide member 205 is largely retracted in the conveyance direction of the recording paper P discharged from the auxiliary nip portion (perpendicular to the line connecting the centers of the roller pair). Therefore, it will be in a position where it does not actively contact the paper. In this case, the back curl at the time of paper conveyance cannot be corrected, but stress on the paper is not applied, so that the above-described back surface scratches, abrasion, image blurring, and gloss streaks do not occur.

  Unlike the fixing of the first-side image, when the second-side paper passing mode of the recording paper P, which is not a thick paper, is not backcurled, the guide member 205 is not retracted to the second position. , A favorable effect is obtained.

  It should be noted that the guide member 205 is not retracted to the second position when the second surface of the recording paper P that is not a thick paper is passed in the double-sided paper passing mode, but the guide member 205 is positioned between the single-sided printing and the double-sided printing. At least during single-sided printing, it is configured to come to the first position.

  On the other hand, when the recording paper P is a strong thick paper or the like, when the guide member 205 is positioned at the first position, the contact resistance with the guide member 205 is smaller than that of the recording paper P that is a thin paper with weak stiffness. Is big. For this reason, the stress applied to the paper itself is further increased, a trace of contact is easily generated on the back surface of the paper, and the guide member 205 itself is easily worn.

  However, when the recording paper P is a strong thick paper or the like, no back curl occurs. Therefore, when the recording paper P is a strong thick paper or the like, the guide member 205 is not shown in both the first-side paper passing mode in the single-sided paper passing mode and the second-side paper passing mode in the double-sided paper passing mode. The second position shown in FIG.

  As described above, by switching the guide member 205 between the first position and the second position, both the back curl correction and the avoidance of image blur are achieved.

  According to the image forming apparatus of the present embodiment, the driving roller 204 and the driven roller 203 are provided immediately after the downstream side of the fixing device 20, and the guide member 205 is positioned immediately after the downstream side of the auxiliary nip portion. It can be switched to the position. As a result, the back curl of the recording paper P is bent to the opposite side by the fixing device 20, so that the correction can be made only under the condition that the back curl needs to be corrected.

  For example, in the case of thick paper passing, since the back curl in which the recording paper P is curled on the back surface does not occur in the fixing device 20, when the guide member 205 is always in the first position, the guide plate is reversed and the face curl is reversed. become. Further, since the contact force between the guide member 205 and the recording paper is strong, the guide member 205 causes damage (scratches) on the back surface of the paper and wear of the guide member 205. Further, since the paper rigidity is high, the back curl is also corrected from the viewpoint that the tip is bent when the tip comes out from the auxiliary nip portion of the driving roller 204 and the driven roller 203 and the tip contacts the guide member 205. There is no need to be in position.

  According to the image forming apparatus of the present embodiment, from the above viewpoint, the driving unit that switches the position of the guide member 205 is provided, and the position of the guide member 205 can be switched depending on conditions. As a result, it is possible to achieve both reduction of back curl generated during fixing and stabilization of conveyance, and reduction of damage to the recording paper P can be achieved.

  According to the image forming apparatus of the present embodiment, the recording paper conveyance speed in the auxiliary nip portion on the downstream side is set to be higher than the recording paper conveyance speed in the fixing nip portion. Thereby, the slack between the conveyance auxiliary roller and the guide member is reduced, the effect of bending the recording paper is further obtained, and the back curl can be corrected.

  In order to correct the curl using the roller pair and the guide member, the angle accuracy between the roller pair and the guide member (specifically, the angle of the recording paper discharged from the roller pair and the guide member) is important. is there. Further, in order to reliably convey the large curled paper leading edge generated by the fixing, it is necessary to set the positional relationship between the roller pair and the guide member leading edge severely.

  According to the image forming apparatus of the present embodiment, the rotation center of the guide member 205 is configured coaxially with the axis of the drive roller 204. Accordingly, the angle accuracy of the guide member 205 can be configured with high accuracy with minimal variation in order to correct the curl, and the positions of the roller pair and the guide member can be accurately maintained.

  According to the image forming apparatus of the present embodiment, during single-sided printing, the guide member 205 is disposed at the first position, and the fixing device fixes the recording paper P to be curled on the back side and discharges the paper in a corrected state. can do. Thereby, it is possible to prevent the specified number of sheets from being stacked on the paper discharge tray 14 from being disturbed and the stacking on the paper discharge tray 14 from being disturbed. Also, during double-sided printing, by arranging the guide member 205 at the second position, it is possible to prevent occurrence of image blurring, gloss flaws, and the like on the first surface.

  According to the image forming apparatus of the present embodiment, the back curl does not occur in the fixing device 20 in the case of the second-side paper passing in the double-sided printing mode of thin paper and in the case of the paper passing through the thick paper. On the other hand, the guide member 205 can avoid the problem of face curling. Further, it is possible to avoid the problem that damage (scratch) occurs on the back side of the paper and the guide member 205 is worn. Furthermore, since the paper rigidity is high, it is possible to avoid the problem that the front end is bent without buckling when the front end comes out of the auxiliary nip portion and is on the guide member 205.

  As described above, the image forming apparatus according to the present invention has an effect that it is possible to achieve both reduction of back curl caused by fixing and stabilization of conveyance and reduction of damage to the recording paper / toner image. It is useful for an image forming apparatus.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus A Image forming part P Recording paper N Fixing nip part 15 Branch member (Recording paper conveyance path branch means)
20 fixing device C back curl correction mechanism 203 driven roller 204 driving roller 204a roller shaft D guide member moving means

JP 2001-48399 A JP-A-9-188456 JP 2012-91891 A

Claims (5)

A fixing device for passing the recording paper onto which the image has been transferred in the image forming unit to the fixing nip and fixing the image on the recording paper at the fixing nip, and the recording paper conveyed downstream of the fixing device; In an image forming apparatus having a recording paper conveyance path branching means for switching between an out-of-machine discharge path and a reverse path of double-sided printing,
A back curl correction mechanism is provided in a transport path between the fixing device and the recording paper transport path branching unit;
The back curl correction mechanism is:
An auxiliary nip portion that is formed by a driving roller provided on a side where the back curl of the recording paper is generated in the fixing nip portion and a driven roller provided on a side that heats the recording paper, and auxiliary transports the recording paper;
A guide member provided on the same side as the drive roller for guiding the recording paper;
A guide member moving means for moving the guide member to a first position where the recording paper front direction portion passing through the auxiliary nip portion is pressed and a second position away from the recording paper; Have
The first position of the guide member is
Paper corresponding to the crossing angle of the recording paper conveyance direction in the auxiliary nip portion, and the direction connecting the point where the recording paper moves downstream from the auxiliary nip portion and the point where the guide member contacts the recording paper. The bending angle θ1 is 20 ° or more and 50 ° or less,
A distance L from the center position of the auxiliary nip portion to the guide member in the recording paper conveyance direction in the auxiliary nip portion is 15 mm or less,
An image forming apparatus, wherein an initial contact angle θ corresponding to an intersection angle between a recording paper conveyance direction and a guide direction of the guide member in the auxiliary nip portion is 120 ° or more.   The image forming apparatus according to claim 1, wherein a recording paper conveyance speed in the auxiliary nip portion is set to be higher than a recording paper conveyance speed in the fixing nip.   The guide member is provided so that a rotation center is coaxial with a roller shaft of the drive roller, and is configured to be movable to a plurality of positions by being rotated by the guide member moving means. Item 3. The image forming apparatus according to Item 1 or 2.   The image according to any one of claims 1 to 3, wherein the guide member is configured to come to the first position during at least one-side printing of single-side printing and double-side printing. Forming equipment.   The said guide member moving means is comprised so that the said guide member may be moved to the said 2nd position, when the said recording paper is a cardboard, The one of the Claims 1 thru | or 4 characterized by the above-mentioned. The image forming apparatus described.

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