JP5294070B2 - Fixing apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device configured to improve separability of a recording medium, and prevent image distortion, wrinkle of recording medium, etc. <P>SOLUTION: The fixing device 8 is formed by a fixing roller 21 and a pressure roller 22 in contact with each other to curve a fixing nip N. The fixing device 8 has a guide member 23 for guiding a recording medium P to the fixing nip N. At least a downstream end edge 23b (in a recording medium conveyance direction A) of the surface 23a facing the recording medium conveyance path of the guide member 23 is disposed closer to the pressure roller 22 side than a curved reference surface Z that passes through the middle line o of the fixing nip N in the recording medium conveyance direction A, and is orthogonal to a plane Y passing through the middle line o and the axial line X of the fixing roller 21. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a fixing device that heats and pressurizes a recording medium to fix an image on the recording medium, and an image forming apparatus including the fixing device.

  2. Description of the Related Art Image forming apparatuses such as copiers, printers, facsimiles, and multi-function machines thereof often use a fixing device that fixes a toner image transferred onto a recording sheet as a recording medium by heat and pressure. Examples of the fixing device include a type in which a pressure roller is pressed against a fixing roller having a heating source such as a heater therein, and a type in which an endless pressure belt is pressed into contact with the fixing roller by a pressing member. . These fixing devices pass the recording paper on which the toner image is transferred through a fixing nip formed at a pressure contact portion between the fixing roller and the pressure roller or a pressure contact portion between the fixing roller and the pressure belt. The recording paper is heated and pressurized to fix the toner image on the recording paper.

  FIG. 23 is a simplified diagram of a fixing device having the fixing roller 100 and the pressure roller 200. As shown in FIG. 23, the recording paper P onto which the toner image T has been transferred passes through the fixing nip N between the fixing roller 100 and the pressure roller 200, and is then carried out in the direction of the dashed line a in the figure. It has become. However, since the heat fixing type fixing device as described above melts the toner T on the recording paper P by heat at the time of fixing, the conveyance direction of the recording paper P is caused by the adhesion of the melted toner T to the fixing roller 100. The direction may be changed from the direction of the alternate long and short dash line a toward the fixing roller 100. When the recording paper P is transported to the fixing roller 100 side beyond the boundary indicated by the alternate long and short dash line b due to the adhesive force of the melted toner T, the recording paper P is wound around the fixing roller 100.

  Here, the adhesion force of the melted toner to the fixing roller is F1, and the bending force required to wind the recording paper (the force required to bend the recording paper from the one-dot chain line a to the one-dot chain line b by an angle θ) is F2. Then, when the relationship of F1 <F2 is satisfied, the recording paper can be separated from the fixing roller and carried out.

  Conventionally, in order to easily separate the recording paper from the fixing roller, the toner adhesion force F1 is reduced by adding a release agent such as wax to the toner (Patent Document 1 below). reference). Further, in order to easily separate the recording paper from the fixing roller, as shown by a two-dot chain line in FIG. 23, by reducing the diameter of the fixing roller, the boundary line where the winding occurs is changed from the one-dot chain line b to the one-dot chain line b. There is also a method of increasing the bending force F2 required for winding the recording paper by changing to the position '.

  However, even if the adhesion force of the toner is reduced or the diameter of the fixing roller is reduced as described above, if the recording paper having a small bending rigidity (stiffness) such as a thin paper is used, the recording paper is wound. Since the bending force F2 required for this is reduced, winding around the fixing roller may occur.

  Therefore, in view of such circumstances, the present invention improves a separation property of a recording medium and can prevent image distortion and wrinkling of the recording medium, and an image forming apparatus including the fixing device. The device is to be provided.

  The invention of claim 1 comprises a fixing roller heated by a heating source and a pressure roller disposed in contact with the fixing roller, wherein the fixing roller and the pressure roller are formed in contact with each other. In the fixing device for fixing the unfixed image on the recording medium to the recording medium by passing the recording medium through the fixing nip, the fixing roller and the pressure roller are crowns whose outer peripheral surfaces are formed in a crown shape. And at least one reverse crown portion formed in a reverse crown shape, and the crown portion of the fixing roller and the reverse crown portion of the pressure roller are arranged in correspondence with each other, and By arranging the reverse crown portion of the fixing roller and the crown portion of the pressure roller so as to correspond to each other, the fixing roller and the pressure roller are brought into contact with each other. A fixing device formed by curving a fixing nip, comprising a guide member for guiding a recording medium to the fixing nip, and at least a downstream edge in a recording medium conveyance direction of a surface of the guide member facing the recording medium conveyance path Is disposed closer to the pressure roller than a curved reference plane passing through the center line of the fixing nip in the recording medium conveyance direction and perpendicular to the plane passing through the center line and the axis of the fixing roller. .

  When the recording medium enters the curved fixing nip, the recording medium is curved along the fixing nip. In this way, the apparent rigidity of the recording medium can be improved by curving the recording medium. This makes it possible to suppress the recording medium from being wound around the fixing roller when the recording medium is carried out of the fixing nip. Further, by bringing the fixing roller and the pressure roller into contact with each other in a state where the crown portion and the reverse crown portion correspond to each other, it is possible to suppress variation in contact pressure at the fixing nip. As a result, it is possible to suppress problems such as occurrence of uneven glossiness in a fixed image, and to realize good image formation.

  In addition, by disposing the guide member closer to the pressure roller than the curved reference surface, it is possible to prevent the recording medium curved by the fixing nip from coming into contact with the guide member. As a result, the conveyance path is not changed by the recording medium coming into contact with the guide member or the good conveyance performance is not impaired. In addition, it is possible to prevent the recording medium from being wrinkled or damaged.

  According to a second aspect of the present invention, in the fixing device according to the first aspect, the surface of the guide member facing the recording medium conveyance path is curved corresponding to the shape of the curved fixing nip, and the curved surface is curved. At least the downstream edge in the recording medium conveyance direction is disposed closer to the pressure roller than the curved reference surface.

  In the present invention, since the fixing nip is curved, for example, when the surface of the guide member facing the recording medium conveyance path is a plane, the distance from the downstream edge of the surface to the fixing nip is the conveyance of the recording medium. Different across the width. In particular, in the fixing nip, the distance becomes longer at a position where the reverse crown portion of the fixing roller and the crown portion of the pressure roller correspond to each other. As described above, if the distance between the surface of the guide member facing the recording medium conveyance path and the fixing nip varies, it may be difficult to guide the recording medium to the fixing nip. Therefore, as described above, the surface of the guide member facing the recording medium conveyance path is curved in accordance with the shape of the fixing nip, so that the curved edge of the surface of the guide member reaches the fixing nip. It is possible to easily guide the recording medium to the fixing nip by reducing the variation in distance.

  Further, by arranging at least the downstream edge of the curved surface of the guide member on the pressure roller side of the curved reference surface, it is possible to prevent the recording medium curved by the fixing nip from coming into contact with the guide member. can do. As a result, the conveyance path is not changed by the recording medium coming into contact with the guide member or the good conveyance performance is not impaired. In addition, it is possible to prevent the recording medium from being wrinkled or damaged.

  According to a third aspect of the present invention, in the fixing device according to the first aspect, a plurality of protrusions extending in the recording medium conveyance direction are arranged in parallel on a surface of the guide member facing the recording medium conveyance path, The height of each of the tops is set so that the surface passing through each top of the projections is curved corresponding to the shape of the curved fixing nip, and at least the downstream edge of the plurality of projections in the recording medium conveyance direction Is disposed closer to the pressure roller than the curved reference surface.

  In this case, by setting the height of each top so that the surface passing through each top of the plurality of protrusions is curved corresponding to the shape of the fixing nip, the distance from the downstream edge of each protrusion to the fixing nip is set. It is possible to reduce the variation in distance. Thus, the recording medium can be easily guided to the fixing nip as in the second aspect.

  In addition, by disposing at least the downstream edge of the plurality of protrusions closer to the pressure roller than the curved reference surface, the recording medium curved by the fixing nip is prevented from contacting the guide member (protrusion). can do. As a result, the conveyance path is not changed by the recording medium coming into contact with the guide member or the good conveyance performance is not impaired. In addition, it is possible to prevent the recording medium from being wrinkled or damaged.

  Further, in this case, by guiding the recording medium in contact with the protrusion, the contact area between the recording medium and the guide member is reduced between the recording medium and the guide member, compared with the case where the recording medium is guided in contact with the surface. Thus, the friction can be reduced, so that the transportability is improved. In addition, if foreign matter has adhered to the recording medium, foreign matter can be prevented from entering the fixing nip by causing the foreign matter to fall between the protruding portions when the recording medium comes into contact with the protruding portions. Can be prevented.

  According to a fourth aspect of the present invention, in the fixing device according to any one of the first to third aspects, the downstream end edge of the guide member is made to correspond to the shape of the outer peripheral surface of the pressure roller. It is formed in an uneven shape on the roller side.

  As a result, the downstream edge of the guide member can be disposed close to the outer peripheral surface of the pressure roller, so that the impact when the recording medium comes into contact with the surface of the pressure roller can be reduced. It is possible to suppress image disturbance on the medium and wrinkles / damage of the recording medium.

  According to a fifth aspect of the present invention, in the fixing device according to the fourth aspect, the distance between the downstream end edge of the guide member formed in the uneven shape and the outer peripheral surface of the pressure roller is constant. It is.

  As a result, the downstream edge of the guide member can be further brought closer to the pressure roller, so that the impact when the recording medium comes into contact with the surface of the pressure roller can be further reduced. It is possible to more effectively suppress image disturbance and wrinkling of the recording medium.

  According to a sixth aspect of the present invention, in the fixing device according to any one of the first to fifth aspects, the cross-sectional shape of the downstream end edge of the guide member is formed in a convex arc shape or a convex arc shape.

  Thus, when the pressure roller is shaken during driving, even if the pressure roller contacts the downstream edge of the guide member, it is possible to prevent the pressure roller from being damaged. Further, since the downstream end edge of the guide member is formed as described above, it is possible to suppress the adhesion of foreign matters such as toner to the downstream end edge, and it is possible to prevent the recording medium from being contaminated by the foreign matter. It is.

  According to a seventh aspect of the present invention, in the fixing device according to any one of the first to sixth aspects, a part of the downstream edge of the guide member in the recording medium conveyance direction is brought into contact with the surface of the pressure roller. It is a thing.

  As a result, even if the pressure roller shakes, the downstream edge of the guide member can be displaced by following the pressure roller, and the distance between the downstream edge of the guide member and the pressure roller is kept constant. Is possible. Thereby, it is possible to prevent variation in impact when the recording medium comes into contact with the surface of the pressure roller, and to stably exhibit the effect of suppressing image disturbance and wrinkles.

  According to an eighth aspect of the present invention, in the fixing device according to any one of the first to seventh aspects, at least a part of the downstream end edge of the guide member is covered with a thin film material for preventing foreign matter adhesion. is there.

  This makes it difficult for foreign matter such as toner to adhere to the portion of the guide member that is covered with the thin film material, so that the recording medium can be prevented from being contaminated by the foreign matter.

  According to a ninth aspect of the present invention, in the fixing device according to any one of the first to eighth aspects, the guide member has an electrical resistance that prevents leakage of a transfer current for transferring an image to a recording medium. It is.

  As a result, even when the recording medium comes into contact with the guide member during image transfer, the transfer current can be prevented from leaking from the guide member via the recording medium, and the image can be transferred stably and satisfactorily. it can.

  According to a tenth aspect of the present invention, there is provided a fixing roller that is heated by a heating source, an endless pressure belt, and a pressing member that presses an inner peripheral surface of the pressure belt to bring the pressure belt into contact with the fixing roller. A fixing device for fixing an unfixed image on the recording medium to the recording medium by passing the recording medium through a fixing nip formed by contact between the fixing roller and the pressure belt. Each has at least one crown portion whose outer peripheral surface is formed in a crown shape and one reverse crown portion whose outer peripheral surface is formed in a reverse crown shape, and the pressing member presses the pressure belt. The pressing surface has at least one convex surface portion formed in a convex shape and a concave surface portion formed in a concave shape, and corresponds to the crown portion of the fixing roller and the concave surface portion of the pressing member. In addition, the reverse crown portion of the fixing roller and the convex portion of the pressing member are arranged to correspond to each other, and the pressure belt is brought into contact with the fixing roller, whereby the fixing nip is formed. A fixing device that is curved and includes a guide member that guides a recording medium to the fixing nip, and at least a downstream end edge of the surface of the guide member that faces the recording medium conveyance path in the recording medium conveyance direction, The fixing nip is disposed closer to the pressure belt than the curved reference plane passing through the center line in the recording medium conveyance direction and perpendicular to the plane passing through the center line and the axis of the fixing roller.

  In this case, similarly to the first aspect of the invention, the recording medium enters the curved fixing nip, and the recording medium is also curved, so that the apparent rigidity of the recording medium is improved and the fixing is performed. It can be carried out from the nip, and the recording medium can be prevented from being wound around the fixing roller. In addition, the variation of the contact pressure in the fixing nip can be suppressed by bringing the fixing roller and the pressure belt into contact with each other in a state where the crown portion and the concave surface portion correspond to each other and the reverse crown portion and the convex surface portion correspond to each other. it can. As a result, it is possible to suppress problems such as occurrence of uneven glossiness in a fixed image, and to realize good image formation.

  Further, by arranging the guide member closer to the pressure belt than the curved reference surface, the recording medium curved at the fixing nip is prevented from coming into contact with the guide member as in the first aspect of the invention. Can do. As a result, the conveyance path is not changed by the recording medium coming into contact with the guide member or the good conveyance performance is not impaired. In addition, it is possible to prevent the recording medium from being wrinkled or damaged.

  An eleventh aspect of the invention is an image forming apparatus including the fixing device according to any one of the first to tenth aspects.

  The fixing device according to the present invention can be applied to an image forming apparatus.

  According to the present invention, when the recording medium is carried out of the fixing device, the apparent rigidity of the recording medium can be improved and the recording medium can be prevented from being wound around the fixing roller. Accordingly, it is possible to suppress the occurrence of problems such as jamming of the recording medium, and to provide a highly reliable fixing device and image forming apparatus. Further, the present invention can suppress variations in contact pressure at the fixing nip. Thereby, it is possible to suppress occurrence of uneven glossiness and the like in the fixed image, and it is possible to maintain good image formation. Furthermore, the present invention can prevent the recording medium curved at the fixing nip from coming into contact with the guide member, so that it is possible to prevent image disturbance, wrinkling and damage of the recording medium, and the like.

1 is a schematic diagram illustrating an overall configuration of a color image forming apparatus of the present invention. 1 is a perspective view of a fixing device according to Embodiment 1 of the present invention. FIG. 2 is a cross-sectional view of the fixing device. It is sectional drawing of a fixing roller and a pressure roller. FIG. 6 is a perspective view of a fixing device according to Embodiment 2 of the present invention. FIG. 2 is a cross-sectional view of the fixing device. It is sectional drawing of a fixing roller and a pressure roller. FIG. 9 is a perspective view of a fixing device according to Embodiment 3 of the present invention. FIG. 2 is a cross-sectional view of the fixing device. It is sectional drawing of a fixing roller and a pressure roller. FIG. 9 is a perspective view of a fixing device according to Embodiment 4 of the present invention. FIG. 2 is a cross-sectional view of the fixing device. It is sectional drawing of a fixing roller and a pressure roller. (A) is a top view of a pressure roller and a guide member, (B) is a principal part expanded sectional view of a guide member. FIG. 10 is a perspective view of a fixing device according to Embodiment 5 of the present invention. FIG. 2 is a cross-sectional view of the fixing device. It is sectional drawing of a fixing roller and a pressure roller. It is sectional drawing of the fixing device which concerns on Example 6 of this invention. It is sectional drawing of a fixing roller, a pressure belt, and a press member. It is a figure for demonstrating the measuring method of the apparent rigidity of a recording paper. 6 is a graph showing the relationship between the number of curvatures of the fixing nip and the apparent rigidity of the recording paper. It is a graph which shows the test result which compares the separation property of a recording paper, Comprising: (A) shows a test result in case only one crown part and a reverse crown part are shown, (B) shows a crown part and a reverse crown. The test result in the case of having one part each is shown. FIG. 6 is a diagram for explaining an operation in which a recording sheet is wound around a fixing roller.

  FIG. 1 is a schematic configuration diagram of a color image forming apparatus according to the present invention. As shown in FIG. 1, the color image forming apparatus includes four process units 1Y, 1C, 1M, and 1Bk configured to be detachable from the image forming apparatus main body 50. The process units 1Y, 1C, 1M, and 1Bk have the same configuration except that they contain toners of different colors of yellow, cyan, magenta, and black corresponding to the color separation components of the color image. Therefore, the configuration of one process unit 1Y will be described as an example.

  The process unit 1Y includes a photosensitive member 2 as an electrostatic latent image carrier, a charging device 3 as a charging unit that charges the surface of the photosensitive member 2, and a developing unit that forms a toner image on the surface of the photosensitive member 2. A developing device 4 and a cleaning blade 5 as a cleaning means for cleaning the surface of the photoreceptor 2 are provided.

  Above each of the process units 1Y, 1C, 1M, and 1Bk, an exposure device 7 is disposed as an exposure unit that exposes the surface of the photoreceptor 2. On the other hand, an intermediate transfer unit 6 is disposed below each process unit 1Y, 1C, 1M, 1Bk. The intermediate transfer unit 6 has an endless intermediate transfer belt 10. The intermediate transfer belt 10 is stretched around a plurality of rollers 17, 18, and 19, and is configured to be able to run around in the direction of the arrow in the figure. A belt cleaning device 16 is disposed at the left end of the intermediate transfer belt 10 in the figure.

  Four primary transfer rollers 11 as primary transfer means are disposed on the inner peripheral surface of the intermediate transfer belt 10. The photoconductor 2 included in each process unit 1Y, 1C, 1M, and 1Bk is pressed against the outer peripheral surface of the intermediate transfer belt 10 at a position facing the four primary transfer rollers 11 to form a primary transfer nip. A secondary transfer roller 12 as a secondary transfer unit is disposed at a position facing one roller 17 that stretches the intermediate transfer belt 10. The secondary transfer roller 12 is pressed against the outer peripheral surface of the intermediate transfer belt 10 to form a secondary transfer nip.

  A plurality of paper feed cassettes 13 that contain recording paper P as a recording medium are disposed below the image forming apparatus main body 50. Each paper feed cassette 13 is provided with a paper feed roller 14 and the like for carrying out the recording paper P. In the image forming apparatus main body 50, a recording medium conveyance path R (hereinafter referred to as a sheet conveyance path) for guiding the recording sheet P is disposed. In the paper transport path R, a pair of registration rollers 15 is disposed upstream of the secondary transfer roller 12 in the recording medium transport direction A (hereinafter referred to as the paper transport direction). Further, a fixing device 8 for fixing the image on the recording paper P is disposed downstream of the secondary transfer roller 12 in the paper transport direction A. A stock unit 9 for stocking the recording paper P discharged to the outside is provided on the left side of the image forming apparatus main body 50 in the drawing.

The basic operation of the image forming apparatus will be described below with reference to FIG.
When the image forming operation is started, the photosensitive members 2 of the process units 1Y, 1C, 1M, and 1Bk are driven to rotate counterclockwise by a driving device (not shown), and the surface of each photosensitive member 2 is charged by the charging device 3. It is uniformly charged to a predetermined polarity. The surface of each charged photoconductor 2 is irradiated with laser light from the exposure device 7, and an electrostatic latent image is formed on the surface of each photoconductor 2. At this time, the image information to be exposed on each photoconductor 2 is monochromatic image information obtained by separating a desired full-color image into color information of yellow, cyan, magenta, and black. The electrostatic latent image formed on the photoreceptor 2 in this way is supplied with toner by each developing device 4, whereby the electrostatic latent image is visualized as a toner image.

  Further, a constant voltage or a constant current controlled voltage having a polarity opposite to the toner charging polarity is applied to each primary transfer roller 11. As a result, a transfer electric field is formed at the primary transfer nip between each primary transfer roller 11 and each photoconductor 2. Then, the intermediate transfer belt 10 in which the toner images of the respective colors formed on the photoreceptors 2 of the process units 1Y, 1C, 1M, and 1Bk travel in the direction of the arrow in the drawing by the transfer electric field formed in the primary transfer nip. The images are superimposed and transferred sequentially. Thus, the intermediate transfer belt 10 carries a full-color toner image on its surface.

  Residual toner adhering to the surface of each photoconductor 2 after the toner image is transferred is removed from the surface of the photoconductor 2 by each cleaning blade 5, and then the surface is subjected to static elimination action by a static eliminator (not shown). Then, the surface potential is initialized to prepare for the next image formation.

  As the paper feed roller 14 rotates, the recording paper P is sent from one of the paper feed cassettes 13 to the paper transport path R. The recording paper P sent to the paper transport path R is timed by the registration roller 15 and sent to the secondary transfer nip between the secondary transfer roller 12 and the roller 17 facing it. At this time, a transfer voltage having a polarity opposite to the toner charging polarity of the toner image on the intermediate transfer belt 10 is applied to the secondary transfer roller 12, and a transfer electric field is formed in the secondary transfer nip. Then, the toner images on the intermediate transfer belt 10 are collectively transferred onto the recording paper P by the transfer electric field formed in the secondary transfer nip. The recording paper P to which the toner image has been transferred is conveyed to the fixing device 8, and the toner image is fixed by applying heat and pressure to the recording paper P. After the fixing process, the recording paper P is discharged from the fixing device 8 to the stock unit 9. Further, the toner remaining on the surface of the intermediate transfer belt 10 after image transfer is removed by the belt cleaning device 16.

  The above description is an image forming operation when a full-color image is formed on the recording medium S. A single color image can be formed using any one of the four process units 1Y, 1C, 1M, and 1Bk. Two or three process units may be used to form a two or three color image.

  Next, the configuration of the fixing device, which is a feature of the present invention, will be described with reference to FIGS. 2-19, the same code | symbol shows the same member or part.

FIG. 2 is a perspective view of the fixing device according to the first embodiment of the present invention.
As shown in FIG. 2, the fixing device 8 includes a fixing roller 21, a pressure roller 22, a guide member 23, and the like. The pressure roller 22 is in pressure contact with the fixing roller 21 at a predetermined pressure, and a fixing nip N is formed at a pressure contact portion where the pressure roller 22 is in pressure contact with each other. Each of the fixing roller 21 and the pressure roller 22 is formed to be curved so that the outer peripheral surface undulates in the axial direction. Specifically, the fixing roller 21 has alternately a crown portion C1 whose outer peripheral surface is formed in a crown shape and a reverse crown portion C2 whose outer peripheral surface is formed in a reverse crown shape in the axial direction. The pressure roller 22 also has a crown portion D1 whose outer peripheral surface is formed in a crown shape and a reverse crown portion D2 whose outer peripheral surface is formed in a reverse crown shape alternately in the axial direction. Here, the “crown shape” means a shape in which the roller diameter decreases toward both ends in the axial direction, and the “reverse crown shape” indicates that the roller diameter increases toward both ends in the axial direction. It refers to the shape.

FIG. 3 is a cross-sectional view of the fixing device taken along a plane perpendicular to the axial direction of the roller.
As shown in FIG. 3, a heater 24 as a heating source is disposed in the fixing roller 21 in the axial direction, and the fixing roller 21 is heated when the heater 24 generates heat. ing. A temperature detection device 25 that detects the surface temperature of the fixing roller 21 is disposed around the fixing roller 21. Based on the surface temperature of the fixing roller 21 detected by the temperature detecting device 25, a control device (not shown) controls the amount of heat generated by the heater 24 so that the surface temperature of the fixing roller 21 becomes a predetermined fixing temperature. It is configured.

  The fixing roller 21 includes a cylindrical metal core member 21a, an elastic layer 21b that covers the outer peripheral surface of the core member 21a, and a release layer 21c that covers the outer peripheral surface of the elastic layer 21b. Has been. In this embodiment, the crown portion C1 and the reverse crown portion C2 are formed by changing the thickness of the elastic layer 21b in the axial direction, but it is also possible to change the thickness of the core material 21a. The crown portion C1 and the reverse crown portion C2 can be formed.

  The pressure roller 22 includes a cylindrical metal core member 22a, an elastic layer 22b that covers the outer peripheral surface of the core member 22a, and a release layer 22c that covers the outer peripheral surface of the elastic layer 22b. It is configured. Similar to the fixing roller 21, the pressure roller 22 also forms the crown portion D1 and the reverse crown portion D2 by changing the thickness of the elastic layer 22b in the axial direction. The crown portion D1 and the inverted crown portion D2 can also be formed by changing the thickness of the first and second crowns.

  Further, the fixing roller 21 is driven to rotate clockwise in the drawing by a driving means (not shown). On the other hand, the pressure roller 22 is driven to rotate counterclockwise in the figure by the rotational driving of the fixing roller 21. The recording paper P carrying the unfixed image T is conveyed in the direction of the arrow A in the figure between the fixing roller 21 and the pressure roller 22 that rotate in this manner, so that the recording paper P is fixed in the fixing nip N. The unfixed image T is fixed on the recording paper P by being heated and pressurized.

  The guide member 23 is provided to guide the recording paper P to the fixing nip N. Therefore, the guide member 23 is disposed upstream of the fixing nip N in the paper transport direction A. Further, when the recording paper P is guided by the guide member 23, the guide member 23 is placed on the lower surface (image) of the recording paper P to be conveyed so that the guide member 23 does not contact the unfixed image T on the recording paper P. It is arrange | positioned so as to oppose the surface on the opposite side of a formation surface.

  The guide member 23 preferably has an electrical resistance that prevents leakage of a transfer current for transferring an image onto a recording sheet. As described above, when an image is transferred from the intermediate transfer belt to the recording paper, a transfer current (or transfer voltage) is applied to the secondary transfer nip, and the toner image is transferred onto the recording paper by the transfer electric field formed thereby. Is done. At this time, when the front end side of the recording paper comes into contact with the guide member 23 in a state where the rear end side of the recording paper is sandwiched between the secondary transfer nips, a transfer current forming a secondary transfer electric field is passed through the recording paper through the guide member 23. There is a risk of leakage. Therefore, if the guide member 23 has an electrical resistance that prevents the transfer current from leaking, the transfer current leaks from the guide member 23 through the recording paper even if the recording paper contacts the guide member 23 during image transfer. Image transfer can be performed stably and satisfactorily. In addition, in order for the guide member 23 to have an electrical resistance that prevents leakage of the transfer current, for example, the guide member 23 may be formed of an insulating member, or between the guide member 23 and the ground. A member having an insulating property may be interposed between the two.

FIG. 4 is a cross-sectional view of the fixing roller and the pressure roller cut along a plane parallel to the axial direction.
As shown in FIG. 4, the crown portion C1 of the fixing roller 21 and the reverse crown portion D2 of the pressure roller 22 are arranged to correspond to each other, and the reverse crown portion C2 of the fixing roller 21 and the crown portion D1 of the pressure roller 22 are arranged. The fixing roller 21 and the pressure roller 22 are in pressure contact with each other. As described above, in the present invention, the fixing roller 21 and the pressure roller 22 are disposed so that the concaves and the convexes correspond to each other, so that the fixing nip N is curved so as to wave in the axial direction.

In the present invention, the arrangement position of the guide member 23 is set as follows.
In FIG. 3, a plane Z passing through the center line O of the fixing nip N in the sheet conveyance direction A and passing through the center line O and the axis line X of the fixing roller 21 is called a curved reference plane. The member 23 is disposed on the pressure roller 22 side (downward in the drawing) from the curved reference plane Z. In general, the fixing nip N is formed with a predetermined width in the paper transport direction A in order to ensure good fixability. That is, the “center line O in the sheet conveyance direction A of the fixing nip N” is a line that connects the center positions of the fixing nip N in the sheet conveyance direction A in the axial direction of the roller. As shown in FIG. 4, since the fixing nip N is curved in the present invention, the center line O is also a curved line along the fixing nip N. Accordingly, the curved reference plane Z passing through the curved center line O is also a curved plane (see FIG. 4). In FIG. 4, the alternate long and short dash line located below the curved reference plane Z indicates the position of the surface 23 a of the guide member 23 that faces the sheet conveyance path.

5 to 7 show a fixing device according to a second embodiment of the present invention.
As shown in FIG. 5 or FIG. 7, in the second embodiment of the present invention, similarly to the first embodiment, the fixing roller 21 and the pressure roller 22 have crown portions C1, D1 and reverse crown portions C2, D2, respectively. It has alternately over the axial direction. Therefore, the fixing nip N formed when the rollers 21 and 22 are in pressure contact with each other is formed so as to be curved (see FIG. 7). On the other hand, in the second embodiment, the structure of the guide member 23 is different from that of the first embodiment. As shown in FIG. 5, the surface 23 a of the guide member 23 that faces the paper conveyance path is curved so as to be waved. Specifically, as shown in FIG. 7, the curved surface 23 a of the guide member 23 is formed to be uneven corresponding to the uneven shape of the curved fixing nip N.

  In FIG. 6, a surface Z passing through the center line O of the fixing nip N in the sheet conveying direction A and perpendicular to the plane Y passing through the center line O and the axis X of the fixing roller 21 is curved in the same manner as described above. When referred to as a reference surface, the surface 23a of the guide member 23 that faces the sheet conveyance path is disposed below the curved reference surface Z (see FIG. 7). Therefore, also in this case, the guide member 23 is disposed closer to the pressure roller 22 than the curved reference surface Z.

  The configuration of the second embodiment of the present invention has been described above. Since the structure other than the above-described structure is configured in the same manner as the first embodiment, detailed description thereof will be omitted.

8 to 10 show a fixing device according to Embodiment 3 of the present invention.
As shown in FIG. 8, the third embodiment of the present invention differs from the above embodiments in the structure of the guide member 23, and extends in the paper transport direction on the surface 23 a of the guide member 23 facing the paper transport path. A plurality of protrusions 26 are arranged side by side.

  In FIG. 10, when a virtual plane passing through the top of each protrusion 26 is represented by a dot-and-dash line S, this virtual line S is formed to be uneven corresponding to the uneven shape of the curved fixing nip N. ing. That is, the height of the top of each protrusion 26 is set so that the virtual line S is curved corresponding to the shape of the fixing nip N.

  In addition, in FIG. 9, the virtual surface S passing through the top of each protrusion 26 is arranged below the drawing with respect to the curved reference plane Z set in the same manner as described above. Therefore, also in this case, the guide member 23 is disposed closer to the pressure roller 22 than the curved reference surface Z.

  The configuration of the third embodiment of the present invention has been described above. Since the structure other than the above-described structure is configured in the same manner as the first embodiment, detailed description thereof will be omitted.

11 to 14 show a fixing device according to a fourth embodiment of the present invention.
As shown in FIG. 11, in the fourth embodiment of the present invention, the downstream end edge 23b of the guide member 23 is pressed in accordance with the outer peripheral surface shapes of the crown portion D1 and the reverse crown portion D2 of the pressure roller 22. An uneven shape is formed on the roller 22 side. Specifically, the downstream end edge 23b of the guide member 23 is formed with convex portions 23b ₁ projecting toward the pressure roller side 22 and recessed concave portions 23b ₂ alternately in the longitudinal direction. Then, as shown in FIG. 14A, the convex portion 23b ₁ is disposed corresponding to the recessed reverse crown portion D2 of the pressure roller 22, and the concave portion 23b ₂ is projected from the crown portion of the pressure roller 22. It arrange | positions corresponding to D1. In this way, by forming the downstream end edge 23b of the guide member 23 in an uneven shape, the downstream end edge 23b is pressurized as compared with the case where the downstream end edge 23b is formed in a straight shape (two-dot chain line in the figure). The roller 22 can be disposed close to the outer peripheral surface.

  Further, by setting the protruding amount and the recessed amount of the downstream end edge 23b of the guide member 23 to be the same as the protruding amount or the recessed amount of the outer peripheral surface of the corresponding pressure roller 22, the downstream end edge 23b and the pressing roller 22 are set. And the distance d (see FIG. 14A) can be made constant in the axial direction, and the downstream edge 23b can be further brought closer to the pressure roller 22.

  Further, as shown in FIG. 14B, the cross-sectional shape of the downstream end edge 23b is a convex arc shape in a cross section obtained by cutting the guide member 23 along a plane intersecting the axis of the fixing roller 21 or the pressure roller 22 (not shown). Alternatively, it is formed in a convex arc shape. Thereby, even if the pressure roller 22 comes into contact with the downstream end edge 23b of the guide member 23 when the pressure roller 22 is shaken during driving, the pressure roller 22 can be prevented from being damaged. . Further, if the cross-sectional shape of the downstream edge 23b is formed in a convex arc shape or a convex arc shape, foreign matters such as toner and paper dust are less likely to adhere to the downstream end edge 23b. It is also possible to suppress contamination. Alternatively, at least a part of the downstream end edge 23b of the guide member 23 may be covered with a thin film material for preventing foreign matter adhesion such as a fluororesin in order to suppress the adhesion of the foreign matter to the guide member 23.

  In addition, in the said Example 4, since another structure is comprised similarly to the said Example 1, detailed description is abbreviate | omitted.

15 to 17 show a fixing device according to Embodiment 5 of the present invention.
As shown in FIG. 15, in the fifth embodiment of the present invention, the downstream edge 23 b of the guide member 23 is made to correspond to the outer peripheral surface shape of the pressure roller 22, as in the fourth embodiment shown in FIG. 11 and the like. An uneven shape is formed on the pressure roller 22 side. Therefore, this embodiment also has a convex portion 23b ₁ and a concave portion 23b ₂ on the downstream end edge 23b, and the convex portion 23b ₁ is disposed corresponding to the inverted crown portion D2 in which the pressure roller 22 is concave. 23b ₂ is arranged corresponding to the crown D1 from which the pressure roller 22 protrudes.

Further, as shown in FIG. 16, in this embodiment, the convex portion 23 b ₁ of the downstream end edge 23 b is brought into contact with the corresponding reverse crown portion D 2 of the pressure roller 22. Therefore, even if the pressure roller 22 is shaken, the downstream end edge 23b of the guide member 23 can be displaced by following the pressure roller 22, and the distance between the downstream end edge 23b and the pressure roller 22 can be changed. Can be kept constant. Further, the abut and the pressure roller 22, so may be a part of the downstream edge 23b, may be brought into contact with the concave portion 23b ₂ of the downstream edge 23b to the crown portion D1 of the pressing roller 22 .

  Further, in order to prevent the outer peripheral surface of the pressure roller 22 from being damaged, a cross-sectional shape of a portion of the downstream end edge 23b that contacts the pressure roller 22 (specifically, a cross section in the same direction as FIG. 14B). May be formed in a convex arc shape or a convex arc shape.

  In the fifth embodiment of the present invention, the other structures are configured in the same manner as in the first embodiment, and detailed description thereof is omitted.

18 and 19 show a fixing device according to Embodiment 6 of the present invention.
As shown in FIGS. 18 and 19, the fixing device 8 according to the sixth embodiment of the present invention does not have the pressure roller 22. Instead, the fixing device 8 includes a pressure belt 27 and a pressing member 28. The fixing roller 21 has a cylindrical metal core material 21a, an elastic layer 21b covering the outer peripheral surface of the core material 21a, and an outer peripheral surface of the elastic layer 21b, as in the above embodiments. It is comprised by the mold release layer 21c to coat | cover. In addition, a heater 24 as a heating element is disposed in the fixing roller 21, and a temperature detection device 25 that detects the surface temperature of the fixing roller 21 is disposed around the fixing roller 21. The pressure belt 27 is constituted by an endless belt member made of a polyimide film or the like. The pressing member 28 includes an elastic layer 28a made of silicon rubber or the like and a holder 28b that holds the elastic layer 28a. The elastic layer 28a of the pressing member 28 is disposed so as to contact the inner peripheral surface of the pressure belt 27. In this state, the pressing member 28 is urged toward the fixing roller 21 by an urging means (not shown). . As a result, the pressing member 28 presses the inner peripheral surface of the pressure belt 27 to press the pressure belt 27 against the fixing roller 21, and the fixing nip N is brought into contact with the pressure contact portion where the pressure belt 27 and the fixing roller 21 press against each other. Is forming.

  When image fixing processing is performed in this fixing device, the fixing roller 21 is rotated in the clockwise direction in the drawing by a driving unit (not shown), and the pressure belt 27 is driven to rotate counterclockwise in the drawing. Then, the recording paper P carrying the unfixed image T is conveyed in the direction of the arrow A in the figure between the fixing roller 21 and the pressure belt 27 rotated in this manner, so that the recording paper P is fixed. The unfixed image T is fixed on the recording paper P by being heated and pressurized in the nip N.

Hereinafter, the configuration of the fixing roller 21 and the pressing member 28 will be described in detail.
As shown in FIG. 19, the fixing roller 21 alternately has crown portions C <b> 1 and reverse crown portions C <b> 2 in the axial direction as in the above embodiments. On the other hand, the pressing member 28 has convex surface portions E1 formed in a convex shape and concave surface portions E2 formed in a concave shape alternately on the pressing surface that presses the pressure belt 27 in the longitudinal direction. In this embodiment, the convex surface portion E1 and the concave surface portion E2 are formed by changing the thickness of the elastic layer 28a of the pressing member 28 in the longitudinal direction. Alternatively, the convex surface portion E1 and the concave surface portion E2 may be formed by changing the thickness of the holder 28b of the pressing member 28 in the longitudinal direction.

  The crown portion C1 of the fixing roller 21 and the concave surface portion E2 of the pressing member 28 are arranged in correspondence with each other, and the reverse crown portion C2 of the fixing roller 21 and the convex surface portion E1 of the pressing member 28 are arranged in correspondence with each other. Thus, the fixing roller 21 and the pressure belt 27 are brought into pressure contact with each other, so that the fixing nip N is curved so as to wave in the axial direction.

  As shown in FIG. 18, the fixing device 8 also includes a guide member 23 for guiding the recording paper P to the fixing nip N. In FIG. 18, a plane Z passing through the center line O of the fixing nip N in the sheet conveying direction A and perpendicular to the plane Y passing through the center line O and the axis line X of the fixing roller 21 is a curved reference plane in the same manner as described above. In other words, the surface 23a of the guide member 23 that faces the sheet conveyance path is disposed below the curved reference plane Z in the drawing. Therefore, also in this case, the guide member 23 is disposed closer to the pressure roller 22 than the curved reference surface Z.

  Further, in this embodiment, the surface 23a of the guide member 23 facing the sheet conveyance path is formed in a flat shape. However, as in the embodiment 2 shown in FIG. You may make it curve corresponding to. Alternatively, as in the third embodiment shown in FIG. 8, a plurality of protrusions 26 can be arranged side by side on the surface 23a facing the sheet conveyance path.

The operation and effect of each embodiment of the present invention will be described below.
As described above, in the fixing device of the present invention, the fixing nip N is curved so as to wave. Therefore, when the recording paper P enters the fixing nip N during the fixing process, the recording paper P is bent along the fixing nip N. In this way, the apparent rigidity of the recording paper P can be improved by curving the recording paper P. Therefore, according to the fixing device of the present invention, the apparent rigidity of the recording paper P can be improved and the recording paper P can be carried out from the fixing nip N, so that the winding of the recording paper P around the fixing roller 21 is suppressed. can do.

  By the way, when the recording paper P curved and deformed by the fixing nip N comes into contact with the guide member 23, the transport path of the recording paper P may be changed or good transportability may be impaired. As a result, the image forming surface of the recording paper P may come into contact with peripheral components and the like, and the unfixed image may be disturbed, or the recording paper P may be wrinkled or damaged. Therefore, in the present invention, the guide member 23 is disposed on the pressure roller 22 (or pressure belt 27) side of the curved reference surface Z so that the curved recording paper P does not contact the guide member 23. Yes. That is, the curved reference surface Z is a virtual curved surface that represents the movement path of the curved recording paper P, and the guide member 23 is disposed closer to the pressure roller 22 than the curved reference surface Z. 23 can be disposed so as not to overlap the moving path of the recording paper P. In the present invention, by providing the guide member 23 as described above, the contact with the recording paper P is prevented, and the occurrence of image disturbance, wrinkling or damage of the recording paper P is prevented.

  In the present invention, since the fixing nip is curved, when the surface 23a facing the sheet conveyance path is a flat surface like the guide member 23 of Embodiment 1 shown in FIG. 2 or 3, the downstream edge of the surface 23a. The distance from 23b to the fixing nip N varies across the sheet conveyance width direction. As shown in FIG. 4, the fixing nip N with respect to the guide member 23 (the above-described facing surface 23 a) particularly at a location where the reverse crown portion C 2 of the fixing roller 21 and the crown portion D 1 of the pressure roller 22 correspond to each other. Since the position is separated upward, the distance is increased. As described above, when the distance between the surface 23 a of the guide member 23 facing the sheet conveyance path and the fixing nip N varies, it may be difficult to guide the recording sheet P to the fixing nip N. For this reason, in the second embodiment shown in FIG. 5, the surface 23a of the guide member 23 that faces the sheet conveyance path is curved in accordance with the shape of the fixing nip N, so that the surface 23a of the curved guide member 23 is curved. It is possible to make it easier to guide the recording paper P to the fixing nip N by reducing the variation in the distance from the downstream edge 23b to the fixing nip N.

  Further, since the curved surface 23a of the guide member 23 is disposed closer to the pressure roller 22 than the curved reference surface Z, the recording paper P curved by the fixing nip N is guided by the guide member 23 (curved above). It is possible to prevent the contact surface 23a) from contacting. As a result, the recording path P does not change the transport path or impair good transportability when the recording sheet P contacts the guide member 23. Therefore, the image forming surface of the recording sheet contacts the peripheral components. It is possible to prevent the occurrence of turbulence, wrinkling or damage of the recording paper.

  In the case of Example 3 shown in FIG. 8, the heights of the plurality of protrusions 26 provided on the guide member 23 are set so as to correspond to the curved shape of the fixing nip N. It is possible to reduce the variation in the distance from the downstream end edge 26b to the fixing nip N. Accordingly, it is possible to easily guide the recording sheet to the fixing nip as in the second embodiment.

  In addition, since the plurality of protrusions 26 are arranged closer to the pressure roller 22 than the curved reference surface Z, the recording paper P curved by the fixing nip N comes into contact with the guide member 23 (protrusion 26). Can be prevented. As a result, the recording path P does not change the transport path or impair good transportability when the recording sheet P contacts the guide member 23. Therefore, the image forming surface of the recording sheet contacts the peripheral components. It is possible to prevent the occurrence of turbulence, wrinkling or damage of the recording paper.

  Furthermore, in this case, the recording paper P and the guide member 23 are compared with the first or second embodiment in which the recording paper P is brought into contact with the projection 26 and guided to guide the recording paper P in contact with the surface. Since the contact range can be reduced and the friction generated between them can be reduced, there is an advantage that the transportability is improved. In addition, when foreign matter adheres to the recording paper P, the foreign matter is dropped between the projections 26 when the recording paper P comes into contact with the projections 26, and it is difficult for foreign matter to enter the fixing nip N. It is also possible to prevent malfunctions.

  As shown in the fourth embodiment shown in FIG. 11, the downstream end edge 23 b of the guide member 23 is formed in an uneven shape toward the pressure roller 22, so that the downstream end edge 23 b approaches the outer peripheral surface of the pressure roller 22. Therefore, the impact when the recording paper P comes into contact with the surface of the pressure roller 22 can be reduced. As a result, it is possible to suppress image distortion and wrinkles. Further, when the distance d (see FIG. 14A) between the downstream end edge 23b and the pressure roller 22 is made constant, the downstream end edge 23b can be brought closer to the pressure roller 22. Thereby, the impact generated on the recording paper P can be further reduced, and image distortion and wrinkles can be effectively suppressed.

  Further, as in the fifth embodiment shown in FIG. 16, when a part of the downstream end edge 23b of the guide member 23 is brought into contact with the surface of the pressure roller 22, even if the pressure roller 22 is shaken, The downstream end edge 23b of the guide member 23 can be displaced by following the pressure roller 22, and the distance between the downstream end edge 23b and the pressure roller 22 can be maintained constant. As a result, it is possible to prevent variations in impact when the recording paper P abuts against the surface of the pressure roller 22 and to stably exhibit the effect of suppressing image disturbance and wrinkles.

  In addition, the present inventor conducted a test to examine the relationship between the number of curvatures of the fixing nip and the apparent rigidity of the recording paper conveyed from the fixing nip. Hereinafter, the test will be described in detail.

As the fixing device used for the test, the fixing device of the present invention including the fixing roller having the crown portion and the reverse crown portion and the pressure roller, and the fixing roller and the pressure roller not having the crown portion and the reverse crown portion were provided. A conventional fixing device was applied. In addition, the test apparatus of the present invention is prepared in two types, a type having three crown parts and three reverse crown parts, and a type having seven crown parts. The amplitude (height) of the crown portion was 0.2 mm. Further, in all the fixing devices used for the test, the thicknesses of the elastic layer of the fixing roller and the elastic layer of the pressure roller were set to 1.7 mm. Then, in each fixing device, the apparent rigidity of the various sheets when the various sheets having a basis weight (weight per unit area) of 64 g / m ² , 69 g / m ² , and 90 g / m ² were carried out was measured. .

  A method for measuring the apparent rigidity of the various sheets will be briefly described. First, as shown in FIG. 20, the recording paper P is passed through the fixing nip N between the fixing roller 61 and the pressure roller 62, and the laser light L from the displacement measuring device 70 is emitted to the front end of the recording paper P. When irradiated, the conveyance of the recording paper P is stopped. After the stopped recording paper P disappears, the laser beam L is irradiated from the displacement measuring device 70 to the bent recording paper P, and the displacement of the recording paper P is measured. Thereafter, the recording paper P is advanced by a predetermined distance, the recording paper P is again irradiated with the laser light L, and the displacement is measured. Then, the apparent rigidity of the recording paper P is calculated from the obtained displacement of the recording paper P.

FIG. 21 is a graph showing the relationship between the number of curvatures of the fixing nip and the apparent rigidity of various sheets. In FIG. 21, the vertical axis represents the apparent rigidity of the recording paper, and the horizontal axis represents the number of curves of the fixing nip. Here, the number of curvatures of the fixing nip is represented by the number of crown portions and reverse crown portions. For example, when there are no crown part and reverse crown part, the number of curves of the fixing nip is 0, and when there are three crown parts and three reverse crown parts, the number of curves of the fixing nip is 3. Also, in the figure, the triangle plots the measured value of the recording paper with a basis weight of 90 g / m ² , plots the solid square with the measured value of the recording paper with a basis weight of 69 g / m ² , and plots with ●. Is a measured value of a recording paper having a basis weight of 64 g / m ² .

  Referring to the graph of FIG. 21, when the fixing device of the present invention in which the number of curves of the fixing nip is 3 or 7 as compared with the case of using the conventional fixing device in which the curvature of the fixing nip is 0, It can be seen that the apparent rigidity of various papers is increased. Further, since the apparent rigidity of the recording sheet is larger when the number of curvatures of the fixing nip is 7, the effect of increasing the apparent rigidity of various sheets as the number of curvatures of the fixing nip increases. It is assumed that there is. The test results shown in FIG. 21 show the effect of improving the apparent rigidity of the recording paper in one embodiment of the present invention, but the same effect can be obtained in other embodiments of the present invention. .

  Further, when there is no load in which the fixing roller 21 and the pressure roller 22 are not pressed against each other, the height of the crown portion and the reverse crown portion (or the convex surface portion and the concave surface portion) of the fixing roller 21 and the pressure roller 22 (or the pressing member 28) is high. It is desirable to set the length to be 0.1 mm or more and 0.5 mm or less. Alternatively, the height difference between the top portion of the crown portion (or the convex surface portion) and the bottom portion of the reverse crown portion (or the concave surface portion) is set to be 0.2 mm or more and 1 mm or less at the time of no load. It is preferable. It is preferable that these heights are 0.1 mm or more (the height difference is 0.2 mm or more). When the height is less than 0.1 mm (the height difference is 0.2 mm), the recording paper is This is because the amount of bending is reduced, and the apparent rigidity of the recording paper necessary for separating the recording paper satisfactorily cannot be obtained. The height is preferably 0.5 mm or less (the height difference is 1 mm or less). When the height exceeds 0.5 mm (the height difference is 1 mm), the crown portion and the reverse crown portion (or the convex surface portion). This is because there is a possibility that the difference in rotational speed between the recording surface and the concave surface portion becomes large and the recording paper is wrinkled. Therefore, by setting the height or height difference between the crown portion and the reverse crown portion within the above range, the apparent rigidity of the recording paper is sufficiently secured and the winding of the recording paper around the fixing roller is surely suppressed. In addition, it is possible to carry out the recording sheet without generating wrinkles, and it is possible to perform good image formation.

  Note that, when the fixing roller 21 and the pressure roller 22 are in pressure contact, the elastic layers of the rollers 21 and 22 are compressed, so that the difference in height also decreases with the compression. Generally, in the fixing roller 21 and the pressure roller 22, when the compressibility of the elastic layer exceeds 20%, the elastic layer is plastically deformed, which causes generation of image noise and abnormal noise. Usually, it is set to be 20% or less. In the embodiment of the present invention, since the compression rate of the elastic layer is set to 20%, the height difference in the state where the rollers 21 and 22 are pressed against each other is 80% of the height difference in the no-load state. Specifically, the height difference in the loaded state is 0.16 mm or more and 0.8 mm or less.

  Further, the present inventor has determined that the recording sheet is separated when the fixing roller and the pressure roller have only one crown portion and one reverse crown portion and one crown portion and one reverse crown portion. The test which compares sex was done. The result is shown in FIG.

  In FIG. 22, (A) shows the test result when only one crown part and one reverse crown part are provided, and (B) shows the test result when each has one crown part and one reverse crown part. . 22A and 22B, the vertical axis represents the apparent rigidity of the recording paper, and the horizontal axis represents the amplitude (height) of the crown portion and the reverse crown portion. Also, in (A) and (B) of the same figure, an alternate long and short dash line α represents a boundary line of apparent rigidity of the recording sheet that divides the case where the recording sheet can be satisfactorily separated from the fixing roller and the case where it cannot. In the figure, an alternate long and short dash line β indicates a boundary line between the amplitude of the crown portion and the reverse crown portion that separates the case where wrinkles may occur on the recording paper and the case where there is no possibility of such wrinkles. Specifically, when the apparent rigidity of the recording paper is larger than the boundary line α, the recording paper can be separated satisfactorily. Conversely, when the apparent rigidity is smaller than the boundary line α, the recording paper is separated well. Can not do it. Further, when the amplitude of the crown portion and the reverse crown portion is larger than the boundary line β, wrinkles are generated on the recording paper, and conversely, when the amplitude is smaller than the boundary line β, no wrinkles are generated on the recording paper.

  As shown in FIG. 22A, when only one of the crown portion and the reverse crown portion is provided, the apparent rigidity of the recording paper is made larger than the boundary line α so as to separate the recording paper satisfactorily. In this case, the amplitude of the crown portion or the like must be set larger than about 1 mm, and there is a concern that wrinkles may occur on the recording paper. On the other hand, when each of the crown portion and the reverse crown portion shown in FIG. 22B is provided, the apparent rigidity of the recording paper is greatly increased even with the same amplitude value as that in FIG. It can be seen that there is an improvement. Therefore, in the case of having one crown portion and one reverse crown portion, as shown in FIG. 22B, the apparent rigidity of the recording sheet is set larger than the boundary line α and is opposite to the crown portion. The amplitude of the crown portion can be set within a range of about 0.45 mm to about 0.5 mm where no wrinkle is generated on the recording paper. Therefore, in the case of having one crown portion and one reverse crown portion, both good separation of the recording paper and good image formation that does not cause wrinkles on the recording paper can be realized.

  As described above, when each of the crown portion and the reverse crown portion is provided, the effect of improving the apparent rigidity of the recording paper is improved as compared with the case where only one crown portion and the reverse crown portion are provided. Remarkably larger. Therefore, the present invention is characterized in that the fixing roller and the pressure roller each have at least one crown portion and one reverse crown portion. Further, as described above, by increasing the number of crown portions and reverse crown portions, the apparent rigidity of the recording paper can be further increased, and the separability can be further improved.

  The test results shown in FIG. 22 show the effect of improving the apparent rigidity of the recording paper in one embodiment of the present invention, but the same effect is achieved in other embodiments of the present invention. Is possible.

  By the way, the fixing roller and the pressure roller described in Japanese Patent Application Laid-Open No. 2005-352297, Japanese Patent Publication No. 7-104636, Japanese Patent No. 3119405, Japanese Patent No. 3267416, etc. already disclosed are either crown portions or It is composed of a roller having a reverse crown portion, and the other is composed of a straight roller. In this case, when the fixing roller and the pressure roller are pressed against each other, a curved surface having a crown shape or an inverted crown shape is pressed against the straight surface, so that a portion with a high contact pressure and a portion with a low contact pressure are generated in the fixing nip. The variation in contact pressure increases over time. As described above, when the contact pressure varies greatly in the fixing nip, when fixing an image, the image portion that has passed through the portion where the contact pressure is high has high glossiness, and the image portion that has passed through the portion where the contact pressure is low is glossy. Therefore, there is a problem that unevenness in glossiness of the image is caused and good image formation cannot be performed.

  On the other hand, in the fixing devices according to the first to fifth embodiments of the present invention, the fixing roller and the pressure roller are disposed so that the crown portion and the reverse crown portion correspond to each other. In the fixing device according to the sixth embodiment of the present invention, the fixing roller and the pressing member are disposed so that the crown portion and the concave portion correspond to each other and the reverse crown portion and the convex portion correspond to each other. Thus, in the present invention, the fixing nip is formed by pressing (contacting) the fixing roller and the pressure roller, or the fixing roller and the pressing member in correspondence with the convex and concave portions. It is possible to make the contact pressure uniform by suppressing variations in the contact pressure. Thereby, it is possible to realize good image formation by suppressing unevenness of glossiness of the image.

  Further, in the fixing device of the present invention, in order to ensure the separation of the recording paper without generating image noise, the fixing roller 21 and the pressure roller 22 are brought into pressure contact with each other in the axial direction without any gap. Preferably N is formed. If there is a gap between the fixing roller 21 and the pressure roller 22, pressure unevenness occurs in the fixing nip N in the axial direction, causing image noise.

  Further, in order to ensure the separation of the recording paper without generating wrinkles on the recording paper, the crown portion and the reverse crown portion of the fixing roller 21 and the pressure roller 22 are continuously formed in the axial direction. Is preferred. If the crown portion and the reverse crown portion are not formed continuously, such as when the crown portion and the reverse crown portion are disposed at positions separated from each other, wrinkles may occur when the recording paper is conveyed. .

  Further, it is desirable to set the sum of the thicknesses of the respective elastic layers at arbitrary positions in the axial direction in a state where the fixing roller 21 and the pressure roller 22 are arranged in correspondence with each other. If the sum of the thicknesses of these elastic layers is not constant, the pressure peak values in the rotation direction of the rollers 21 and 22 are different in the axial direction, causing pressure unevenness in the fixing nip and causing image noise. It is.

  As mentioned above, although each Example of this invention was described, this invention is not limited to the above-mentioned Example, Of course, a various change can be added in the range which does not deviate from the summary of this invention. In each of the embodiments of the present invention, a plurality of (two or more) crown portions C1 and D1 and reverse crown portions C2 and D2 or convex surface portions E1 and concave surface portions E2 are formed. As shown in the test results, if there is at least one of them, it is possible to increase the apparent rigidity of the recording paper and improve the separation.

  Further, in each of the above embodiments, the entire surface 23a of the guide member 23 that faces the sheet conveyance path is pressed from the curved reference surface Z so that the recording sheet curved by the fixing nip does not contact the guide member 23. However, if it is possible to prevent contact between the recording paper and the guide member 23, the guide member 23 includes at least the downstream edge 23b of the surface 23a facing the paper conveyance path. Part. Further, as in the embodiment shown in FIG. 8, in the case where a plurality of protrusions 26 are provided on the guide member 23, at least the downstream end edge 26 b of these protrusions 26 is positioned on the pressure roller 22 with respect to the curved reference plane Z. What is necessary is just to arrange | position to the side.

  The fixing device of the present invention can be mounted not only on the color image forming apparatus shown in FIG. 1 but also on a monochrome image forming apparatus, a copying machine, a printer, a facsimile, or a complex machine thereof.

8 Fixing Device 21 Fixing Roller 22 Pressure Roller 23 Guide Member 23a Surface Opposing the Paper Transport Path 23b Downstream Edge 24 Heater (Heating Source)
26 Protruding portion 27 Pressure belt 28 Press member A Paper transport direction (recording medium transport direction)
d Interval N Fixing nip O Fixing nip center line P Recording paper (recording medium)
R Paper transport path (recording medium transport path)
S The surface passing through the top of the protrusion T T Unfixed image X The axis of the fixing roller Y The plane passing through the center line and the axis of the fixing roller Z Curved reference surface

JP 2004-109697 A

Claims (11)

A fixing roller heated by a heating source; and a pressure roller disposed in contact with the fixing roller. The recording medium is placed in a fixing nip formed by the fixing roller and the pressure roller being in contact with each other. In a fixing device for fixing an unfixed image on the recording medium to the recording medium by passing it through,
The fixing roller and the pressure roller each have at least one crown portion whose outer peripheral surface is formed in a crown shape and one reverse crown portion formed in a reverse crown shape, and the crown portion of the fixing roller. And the reverse crown portion of the pressure roller are disposed in correspondence with each other, and the reverse crown portion of the fixing roller and the crown portion of the pressure roller are disposed in correspondence with each other, A fixing device in which the fixing nip is curved by bringing pressure rollers into contact with each other,
A guide member for guiding a recording medium to the fixing nip; and at least a downstream edge of the surface of the guide member facing the recording medium conveyance path in the recording medium conveyance direction, and a center line of the fixing nip in the recording medium conveyance direction. A fixing device, wherein the fixing device is disposed closer to the pressure roller than a curved reference plane orthogonal to a plane passing through the center line and the axis of the fixing roller.   The surface of the guide member that faces the recording medium conveyance path is curved corresponding to the shape of the curved fixing nip, and at least the downstream edge of the curved surface in the recording medium conveyance direction is from the curved reference surface. The fixing device according to claim 1, wherein the fixing device is also disposed on the pressure roller side.   A plurality of protrusions extending in the recording medium conveyance direction are arranged side by side on the surface of the guide member facing the recording medium conveyance path, and the surface passing through the tops of the plurality of protrusions has the shape of the curved fixing nip. The height of each of the tops is set so as to be curved correspondingly, and at least the downstream end edge of the plurality of protrusions in the recording medium conveyance direction is disposed closer to the pressure roller than the curved reference surface. The fixing device according to claim 1.   4. The fixing device according to claim 1, wherein the downstream end edge of the guide member is formed in a concavo-convex shape on the pressure roller side so as to correspond to a shape of an outer peripheral surface of the pressure roller.   The fixing device according to claim 4, wherein a distance between the downstream end edge of the guide member formed in the uneven shape and an outer peripheral surface of the pressure roller is constant.   The fixing device according to claim 1, wherein a cross-sectional shape of the downstream end edge of the guide member is formed in a convex arc shape or a convex arc shape.   The fixing device according to claim 1, wherein a part of a downstream edge of the guide member in a recording medium conveyance direction is in contact with a surface of the pressure roller.   The fixing device according to claim 1, wherein at least a part of the downstream end edge of the guide member is covered with a thin film material for preventing foreign matter adhesion.   The fixing device according to claim 1, wherein the guide member has an electrical resistance that prevents a transfer current from leaking to transfer an image to a recording medium. A fixing roller heated by a heat source; an endless pressure belt; and a pressing member that presses an inner peripheral surface of the pressure belt to bring the pressure belt into contact with the fixing roller. In a fixing device for fixing an unfixed image on the recording medium to the recording medium by passing the recording medium through a fixing nip formed by contacting the pressure belts with each other,
The fixing roller has at least one crown portion whose outer peripheral surface is formed in a crown shape and one reverse crown portion whose outer peripheral surface is formed in a reverse crown shape, and the pressing member includes the pressure belt. The pressing surface that presses at least one convex surface portion formed into a convex shape and at least one concave surface portion formed into a concave shape,
The crown portion of the fixing roller and the concave surface portion of the pressing member are arranged in correspondence with each other, the reverse crown portion of the fixing roller and the convex surface portion of the pressing member are arranged in correspondence with each other, and A fixing device in which the fixing nip is curved by bringing a pressure belt into contact with the fixing roller,
A guide member for guiding a recording medium to the fixing nip; and at least a downstream edge of the surface of the guide member facing the recording medium conveyance path in the recording medium conveyance direction, and a center line of the fixing nip in the recording medium conveyance direction. A fixing device, wherein the fixing device is disposed closer to the pressure belt than a curved reference plane perpendicular to a plane passing through the center line and the axis of the fixing roller.   An image forming apparatus comprising the fixing device according to claim 1.

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