JP4924227B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an FBNF type fixing device having a fixing belt and an image forming apparatus including the fixing device.

  In an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multifunction machine having these functions, a latent image corresponding to an original is formed on a photosensitive drum, and toner is applied to the latent image. Thus, the visualized toner image is transferred onto a recording material, and then the toner image on the recording material is fixed and discharged.

  When a color image is formed, Y, M, C, and K latent images corresponding to the original color are formed on four photosensitive drums, and the visualized four color toner images are endless. After the primary transfer onto the intermediate transfer belt, the toner image transferred onto the recording material is fixed on the recording material, and the toner image transferred onto the recording material is fixed and discharged.

  As a fixing device for fixing a toner image in this way, a recording material on which the toner image is transferred at a nip formed by a fixing roller incorporating a heating means such as a halogen lamp and a pressure roller for pressing the fixing roller. There is a heat roller fixing type fixing device that heats and pressurizes while sandwiching and conveying the sheet, and such a fixing device is widely used because of its simple configuration.

  By the way, in such a fixing device, in order to increase the speed, it is necessary to supply a sufficient amount of heat to the toner and the recording material. For this purpose, it is necessary to widen the nip width. In order to increase the nip width, it is possible to increase the load by which the pressure roller presses the fixing roller, the thickness of the elastic layer formed of silicone rubber or the like in the pressure roller, the diameter of the two rollers, and the like. Conceivable.

  However, when the load of the pressure roller and the thickness of the elastic layer are increased, the nip width in the axial direction may become non-uniform, which may cause uneven fixing and wrinkling of the recording material. Further, when the diameter of the roller is increased, there is a problem that not only the fixing device is increased in size but also the warm-up time is increased.

  In order to solve this problem, a fixing roller having an elastic layer formed of silicone rubber on the outer peripheral surface and rotating with a heating means such as a halogen lamp in the center, and an endless shape rotating by being driven by the fixing roller The fixing belt, a pressure pad that presses the fixing roller from the inside of the fixing belt via the fixing belt, and a low-friction sliding sheet disposed between the fixing belt and the pressure pad, and a fixing roller; A so-called FBNF (Free Belt Nip Fuser) type fixing device that heats and pressurizes a recording material onto which a toner image has been transferred is sandwiched and conveyed at a nip formed by a fixing belt is disclosed in a patent publication. (See Patent Documents 1 and 2).

  According to this fixing device, the fixing belt pressed against the fixing roller by the pressure pad is elastically deformed, and a wide nip portion is formed between the fixing roller and the fixing belt. Therefore, it is possible to cope with high speed and the fixing device is not enlarged. Furthermore, since the heat capacity of the fixing belt is small, the warm-up time is shortened and energy is saved.

  In Patent Document 1, in order to further reduce the frictional resistance force when the fixing belt rotates and improve the slidability, a lubricant containing a modified fluorine oil between the fixing belt and the sliding sheet. The composition is interposed.

In Patent Document 2, since the sliding sheet is rubbed against the fixing belt while being pressed by the pressure pad, the surface of the sliding sheet on the fixing belt side is easily worn. In addition, the friction sheet is reduced and the wear is suppressed by making the sliding sheet have an elongation ratio with respect to the tensile load at 200 ° C. not more than a specific value.
JP 2005-84225 A JP 2005-321462 A

  As described in Patent Documents 1 and 2, in the FBNF type fixing device, a sliding sheet is disposed between the fixing belt and the pressure pad, thereby sliding the fixing belt and the pressure pad. The resistance is reduced. This suppresses problems such as an increase in power consumption of the driving motor of the fixing device, breakage of the reduction gear of the driving motor, occurrence of image misalignment due to hindered smooth rotation of the fixing belt, and acceleration of fixing belt wear. .

  In the fixing device, the recording material that has passed through the nip portion may stick to the fixing roller due to the adhesive force of the molten toner. In order to prevent this, the fixing belt is pressed toward the fixing roller from the inner peripheral surface side to the downstream side in the conveyance direction of the recording material with respect to the pressure pad to press the fixing belt against the fixing roller. There is a fixing device in which a separating member for forming a curl having a large curvature on a recording material by elastically deforming an elastic layer is provided. As a result, it is possible to separate the recording material from the fixing roller without providing a special separating member such as a separation claw.

  However, in the fixing device provided with both the sliding sheet and the separating member, the sliding sheet is deformed with a large curvature along with the fixing belt by being pressed by the separating member. The pressing force is particularly higher than the portion pressed by the pressure pad, and the surface of the sliding sheet on the fixing belt side is easily worn by friction. Further, since the fixing belt is rotating, only a specific surface is not worn, but the same surface is partially worn because the sliding sheet is fixed. When the sliding sheet wears, the sliding resistance with the fixing belt increases, the smooth rotation of the fixing belt is hindered, the conveyance of the recording material becomes abnormal, the recording material is wrinkled, and the image is defective. There is a risk of doing.

  The present invention has been made in view of such problems, and in the FBNF type fixing device, even if the sliding sheet is partially worn by the pressing of the separating member, the simple configuration is achieved without replacing the sliding sheet. An object of the present invention is to propose a fixing device configured to automatically move a worn portion of a sliding sheet to replace a portion with less wear, and an image forming apparatus including the fixing device.

  In addition, the countermeasures regarding the wear of the portion pressed by the separating member in the sliding sheet are not described in Patent Documents 1 and 2, and the improvement of the lubricant described in Patent Documents 1 and 2 and the elongation rate against the tensile load Therefore, it is not sufficient to take measures such as setting the value to a specific value or less, and the life of the sliding sheet cannot be made sufficiently long.

The object is achieved by the invention described below.
1. A fixing roller having an elastic layer and rotating with a built-in heating means;
An endless fixing belt driven and rotated by the fixing roller;
A pressure unit that pressurizes the fixing belt from the inner peripheral surface side and presses the fixing belt against the fixing roller;
Located on the downstream side in the recording material conveyance direction with respect to the pressure unit, the fixing belt is pressed from the inner peripheral surface side to press the fixing belt against the fixing roller, and the elastic layer of the fixing roller is elastically deformed. Separating means for causing
Holding means for holding the pressurizing means and the separating means;
A sliding sheet disposed between the fixing belt and the pressure unit and the separation unit;
With
In a fixing device for fixing a toner image on a recording material at a nip portion formed between the fixing roller and the fixing belt,
The sliding sheet has a plurality of long holes that are long in the rotation direction of the fixing belt, and the plurality of long holes are provided at a plurality of protrusions provided at positions upstream of the nip portion of the holding unit in the rotation direction. The fixing device is characterized in that a portion of the elongated hole located downstream in the rotation direction is engaged with the protrusion at the initial stage of the use period.
2. 2. The fixing device according to 1, wherein the elongated hole is formed so that a width of a portion positioned on the upstream side is narrower than a width of a portion positioned on the downstream side.
3. 3. The fixing device according to 2, wherein the long hole is formed in a keyhole shape.
4). 3. The fixing device according to 2, wherein a portion of the long hole located on the upstream side is a cut formed in the rotation direction.
5. 3. The fixing device according to 2, wherein a portion of the elongated hole located on the upstream side is a perforation formed in the rotation direction.
6). The width of the portion located on the downstream side in the elongated hole is larger than the outer diameter of the protrusion, and the width of the portion located on the upstream side is smaller than the outer diameter of the protrusion. The fixing device according to any one of 2 to 5.
7). 2. The fixing device according to 1, wherein the elongated hole is formed by alternately connecting a portion having the same width as a portion located on the downstream side and a portion having a width narrower than the width. .
8). The width of the portion having the same width as the portion located on the downstream side in the long hole is larger than the outer diameter of the protrusion, and the width of the portion having a width narrower than the width is smaller than the outer diameter of the protrusion. 8. The fixing device according to 7, wherein
9. The long hole is formed so that the width of the portion located on the downstream side and the width of the portion located on the upstream side are substantially the same, and the periphery of the long hole is tightly attached with a rough surface inside the holding means. 2. The fixing device according to 1, wherein
An image forming apparatus comprising the fixing device according to any one of 10.1 to 9.

  According to the fixing device and the image forming apparatus of the present invention, in the FBNF type fixing device, even if the sliding sheet is partially worn by the pressing of the separating member, the sliding sheet is not replaced, and the structure is simple. The worn part of the sliding sheet is automatically moved to replace the less worn part. Therefore, the sliding sheet wear increases the sliding resistance with the fixing belt, the smooth rotation of the fixing belt is hindered, the recording material is not transported normally, the recording material is wrinkled, and the image is not defective. There is no possibility that it will occur, and the durability of the sliding sheet is increased.

  Embodiments relating to the fixing device of the present invention will be described below with reference to the drawings.

  First, an example of an image forming apparatus using the fixing device of the present invention will be described based on the configuration diagram of FIG.

  The image forming apparatus includes an image forming apparatus main body GH and an image reading apparatus YS.

  The image forming apparatus main body GH is called a tandem type color image forming apparatus, and a plurality of sets of image forming units 10Y, 10M, 10C, and 10K, a belt-like intermediate transfer member 6, a sheet feeding and conveying unit, a fixing device 9, and the like. Consists of.

  An image reading device YS including an automatic document feeder 201 and a document image scanning exposure device 202 is installed on the upper part of the image forming apparatus main body GH. The document d placed on the document table of the automatic document feeder 201 is transported by a transport unit, and an image on one or both sides of the document is scanned and exposed by the optical system of the document image scanning exposure device 202, and the line image sensor CCD is scanned. Is read.

  A signal formed by photoelectric conversion by the line image sensor CCD is subjected to analog processing, A / D conversion, shading correction, image compression processing, and the like in an image processing unit, and then exposure means 3Y, 3M, 3C, 3K. Sent to.

  In the image forming unit 10Y that forms a yellow (Y) image, a charging unit 2Y, an exposure unit 3Y, a developing unit 4Y, and a cleaning unit 8Y are arranged around the photosensitive drum 1Y. The image forming unit 10M that forms a magenta (M) color image includes a charging unit 2M, an exposure unit 3M, a developing unit 4M, and a cleaning unit 8M around the photosensitive drum 1M. In the image forming unit 10C that forms a cyan (C) color image, a charging unit 2C, an exposure unit 3C, a developing unit 4C, and a cleaning unit 8C are arranged around the photosensitive drum 1C. In the image forming unit 10K that forms a black (K) image, a charging unit 2K, an exposure unit 3K, a developing unit 4K, and a cleaning unit 8K are arranged around the photosensitive drum 1K. The charging unit 2Y and the exposure unit 3Y, the charging unit 2M and the exposure unit 3M, the charging unit 2C and the exposure device 3C, and the charging unit 2K and the exposure device 3K constitute a latent image forming unit.

  The developing units 4Y, 4M, 4C, and 4K include a two-component developer composed of a toner having a small particle size of yellow (Y), magenta (M), cyan (C), and black (K) and a carrier.

  The intermediate transfer body 6 is wound around a plurality of rollers and is rotatably supported.

  The fixing device 100 heats and pressurizes the toner image on the recording paper (recording material) P at a nip portion formed between the heated fixing roller 101 and the fixing belt 102 and fixes the toner image.

  Thus, each color image formed by the image forming units 10Y, 10M, 10C, and 10K is sequentially transferred onto the rotating intermediate transfer body 6 by the transfer means 7Y, 7M, 7C, and 7K (primary transfer). A toner image synthesized with a color image is formed. The recording paper P stored in the paper feeding cassette 20 is fed by the paper feeding means 21 and is conveyed to the transfer means 7A via the paper feeding rollers 22A, 22B, 22C, 22D, the registration rollers 23, etc. A color image is transferred onto P (secondary transfer). The recording paper P to which the color image has been transferred is heated and pressurized by the fixing device 100, and the color toner image on the recording paper P is fixed. Thereafter, the sheet is sandwiched between the sheet discharge rollers 24 and placed on the sheet discharge tray 25 outside the apparatus.

  On the other hand, after the color image is transferred to the recording paper P by the transfer means 7A, the residual toner is removed by the cleaning means 8A from the intermediate transfer body 6 from which the recording paper P is separated by curvature.

  The image forming apparatus for forming a color image has been described above. However, an image forming apparatus for forming a monochrome image may be used, or an intermediate transfer member may or may not be used.

  Next, an embodiment of the main configuration of the fixing device 100 of the present invention will be described with reference to FIG. FIG. 2 is a cross-sectional view orthogonal to the longitudinal direction of the fixing belt 102 and the like.

  The fixing roller 101 includes a halogen lamp (heating means) H in the center, and a cylindrical cored bar 101A formed of aluminum, iron, or the like, and an elastic made of silicone rubber that covers the cylindrical cored bar 101A and has high heat resistance. A layer 101B and a release layer 101C made of a fluororesin such as PFA (perfluoroalkoxy) or PTFE (polytetrafluoroethylene) which further covers the elastic layer 101B.

  The fixing belt 102 includes a base made of polyimide having a thickness of about 100 μm, and a release layer made of PFA or PTFE having a thickness of about 25 μm covering the outer surface of the base. Is formed. It should be noted that if the base and the release layer are drawn on the fixing belt 102 having a small thickness, the figure becomes unclear and is omitted.

  The pressure pad 103 is made of silicone rubber softer than the elastic layer 101B, and is held by a holder 108 made of heat resistant resin together with a base sheet metal 104 made of stainless steel and a base member 105 made of heat resistant resin. Yes. A compression spring 106 is disposed on the base member 105. The pressurizing means corresponds to the pressurizing pad 103, the base metal plate 104, the base member 105, and the compression spring 106.

  The separation member 107 is disposed on the downstream side in the conveyance direction of the recording paper P in order to improve the separation of the fixed recording paper P. The separation member 107 is made of a heat-resistant resin or a metal such as aluminum and has a tip formed in a circular arc having a large curvature, and is held by a holder 109 formed of a heat-resistant resin through a base metal plate 104 and a metal frame 110. ing. The separating means corresponds to the separating member 107.

  The holders 108 and 109 are held by a frame 110 disposed in the center. The holding means corresponds to the holders 108 and 109 and the frame 110.

  The sliding sheet 111 is formed of a glass fiber sheet or PTFE sheet coated with Teflon (registered trademark), and is between the inner peripheral surface of the fixing belt 102 and the pressure pad 103 and between the inner peripheral surface of the fixing belt 102 and the separation member. 107, and one end is fixed to the holder 109.

  The oil pad 112 is formed of a sponge or the like and contains a lubricant made of silicone oil or the like. The oil pad 112 is held by the holder 109 and pressed against the inner peripheral surface of the fixing belt 102.

  Note that the holder 109 also has a function as a guide member for guiding the fixing belt 102 when the fixing belt 102 rotates.

  In the fixing device 100 configured as described above, the fixing roller 101 heated by the halogen lamp H and driven by a driving unit (not shown) rotates in the clockwise direction. The pressure pad 103 is pressed by the compression spring 106 through the base metal plate 104 and the base member 105, and presses the fixing belt 102 from the inner peripheral surface side through the sliding sheet 111 to press-contact the fixing roller 101. .

  Accordingly, the fixing belt 102 rotates counterclockwise by the rotation of the fixing roller 101 and presses against the fixing roller 101 and elastically deforms in a concave shape together with the pressure pad 103. A wide nip portion N is formed. Then, the conveyed recording paper P is closely attached at the nip portion N, and the unfixed toner on the recording paper P is fixed by being heated and pressurized.

  Further, the inner peripheral surface of the fixing belt 102 slides on the sliding sheet 111 in the vicinity of the nip portion N. Since the sliding sheet 111 is formed of a material having a small friction coefficient, the sliding resistance between the both is fixed. Is small. In addition, since the silicone oil or the like as a lubricant is supplied from the oil pad 112 to the inner peripheral surface of the fixing belt 102, the sliding resistance is further reduced.

  Further, the separating member 107 presses the fixing belt 102 against the fixing roller 101 via the sliding sheet 111, and elastically deforms the elastic layer 101B and the release layer 101C of the fixing roller 101 into a concave shape having a large curvature. Accordingly, the recording paper P fixed at the nip portion N is reliably peeled off and separated from the fixing roller 101 without using a separation claw or the like.

  Here, the sliding sheet 111 is deformed with a large curvature by being pressed by the separating member 107 together with the fixing belt 102. The portion pressed by the separation member 107 in the sliding sheet 111 (hereinafter referred to as the separation portion B) has a particularly higher pressing force than the portion pressed by the pressure pad 103, and the surface of the sliding sheet 111 on the fixing belt 102 side. Is easy to wear due to friction. Further, since the fixing belt 102 is rotating, only a specific surface is not worn, but the same surface is partially worn because the sliding sheet 111 is fixed. When the sliding sheet 111 is worn, the sliding resistance with the fixing belt 102 increases, the smooth rotation of the fixing belt 102 is hindered, the conveyance of the recording material P becomes abnormal, and the recording material P is wrinkled. There is a risk of image defects. Note that the width of the separation portion B in the rotation direction of the fixing belt 102 is about 2 mm.

  A configuration for solving such a problem will be described with reference to FIG. FIG. 3A is a view of the sliding sheet 111 as viewed from the surface side, and FIG. 3B is a cross-sectional view of the sliding sheet 111, the protrusion 109A provided on the holder 109, and the like.

  As shown in FIG. 3A, a plurality of long holes 111A that are long in the rotational direction are provided on the sliding sheet 111 on the upstream side in the rotational direction of the fixing belt 102, and each long hole 111A is formed in a keyhole shape. Has been. The long hole 111A has a wide portion 111A1 having a wide width and a narrow portion 111A2 having a narrow width. The wide portion 111A1 is located on the downstream side in the rotation direction of the fixing belt 102, and the narrow portion 111A2 is located on the upstream side in the rotation direction. positioned. On the other hand, the holder 109 is provided with a plurality of protrusions 109A respectively corresponding to the plurality of long holes 111A, and in the initial period of use of the fixing device 100, the wide part 111A1 of the long hole 111A engages with the protrusions 109A. ing.

  Further, the width of the wide portion 111A1 in the long hole 111A is larger than the outer diameter of the protrusion 109A, and the width of the narrow portion 111A2 is smaller than the outer diameter of the protrusion 109A.

  Here, the initial period of use of the fixing device 100 means a time when a new image forming apparatus is purchased or leased and starts to be used. Also, it means a time when the old fixing device 100 is replaced with a new fixing device 100 due to maintenance and starts to be used even if it is not a new image forming apparatus.

  In the initial period of use of the fixing device 100, the wide portion 111A1 of the long hole 111A is engaged with the protrusion 109A as described above, but the sliding sheet 111 is rotated in the rotational direction of the fixing belt 102 by the rotation of the fixing belt 102. Therefore, the wide portion 111A1 and the protruding portion 109A are pulled and shifted. And this state is maintained for a while.

  As the fixing device 100 continues to be used, the separation portion B of the sliding sheet 111 is worn, and the sliding resistance with the fixing belt 102 increases. As a result, the torque with which the sliding sheet 111 rotates with the rotation of the fixing belt 102 increases. When the torque rises to a predetermined torque, the sliding sheet 111 is rotated and slightly pulled by the fixing belt 102, the protrusion 109A bites into the narrow part 111A2, and the worn part located at the separation part B is on the downstream side. Moving. As a result, the portion with less wear of the sliding sheet 111 is newly moved to the position of the separation portion B, and the torque is reduced.

  Eventually, wear also occurs in the new separation part B, the torque rises again, the same movement is performed, and this is repeated.

  In this way, the sliding sheet 111 is rotated by the fixing belt 102 by utilizing the fact that the surface of the sliding sheet 111 is worn and torque increases.

  When the initial torque of the sliding sheet 111 in the initial period of use is T1, the torque driven by the fixing belt 102 is T2, and the large wear limit torque that causes a failure is T3, the following conditional expression Set to satisfy.

T1 <T2 <T3
As a result, even if the sliding sheet 111 is worn, the sliding sheet is rotated around the fixing belt 102 before the torque causing the trouble, and the portion with less wear moves to the position of the separation portion B. Torque decreases. Also, the traveling is stopped.

  The torque T2 that is rotated by the fixing belt 102 is determined by the width and thickness of the narrow portion 111A2, the outer diameter of the protruding portion 109A, the frictional resistance between the sliding sheet 111 and the protruding portion 109A, and the like.

  Further, when the protrusion 109A bites into the narrow portion 111A2, the sliding sheet 111 is deformed in the surface direction. In this embodiment, the clearance between the surface 109B of the holder 109 and the surface 110A of the frame 110 is as follows. It is assumed that it is sufficiently larger than the thickness of the sliding sheet 111.

Next, a comparative experiment of torque transition between a sliding sheet having a long hole and a conventional sliding sheet will be described.
(1) Experimental conditions / fixing device: fixing device / sliding sheet having the structure shown in FIG. 2: FGF404-4 (trade name) manufactured by Chuko Kasei
The long hole has a keyhole shape, and its dimensions are shown in FIG.
・ Fixing belt: Polyimide substrate, inner diameter 35 mm
-Load for pressing the fixing belt and its internal parts in the direction of the fixing roller: 50 kgf
-Torque measurement: Measure the load torque with the rotating shaft of the fixing roller (2) Experimental results The graph of FIG.

  In FIG. 5, the vertical axis represents torque (kgf), the horizontal axis represents the number of copies, ○ represents a case where a sliding sheet having a long hole was used, and x represents a case where a conventional sliding sheet was used. .

The initial torque T1 was 3 kgf, and the wear limit torque T3 was 5 kgf.
(3) Consideration When a sliding sheet having a long hole is used, the sliding sheet moves along with the fixing belt before the increased torque reaches the wear limit torque T3, and the sliding sheet wears. Since a small part newly moves to the position of the separation part B, the torque decreases. Thereafter, the torque increased again, but the torque did not reach the wear limit torque T3 repeatedly in the same manner.

  On the other hand, when the conventional sliding sheet is used, the torque continues to increase, eventually reaching the wear limit torque T3, the conveyance of the recording material is not normal, the recording material is wrinkled, and the image is defective. did.

  By the way, the shape of the long hole provided in the sliding sheet is not limited to the keyhole shape as described above, and various shapes can be adopted.

  FIG. 6A shows an example in which the narrow portion 211A2 of the long hole 211A is cut with a thin cutter to form a cut, and the cut narrow portion 211A2 is in contact with each other from both sides without forming a long groove. In this case, the torque T2 that rotates with respect to the initial torque T1 is larger than that of the keyhole shape, so that it is used when the wear limit torque T3 is large.

  FIG. 6B shows an example in which the narrow portion 311A2 of the long hole 311A is formed as a perforation. In this case, since the accompanying torque T2 is further increased, it is used when the wear limit torque T3 is larger.

  Further, in the long holes 211A and 311A, the widths of the wide portions 211A1 and 311A1 are both larger than the outer diameters of the protrusions 209A and 309A, and the widths of the narrow portions 211A2 and 311A2 are smaller than the outer diameters of the protrusions 209A and 309A.

  FIGS. 7A and 7B are examples in which the wide portions 411A1 and 511A1 and the narrow portions 411A2 and 511A2 of the long holes 411A and 511A are alternately connected. In this case, when the sliding sheet moves, it acts like a click stop, so that the movement amount of the sliding sheet can be easily controlled.

  Further, in the long holes 411A and 511A, the widths of the wide portions 411A1 and 511A1 are both larger than the outer diameters of the protrusions 409A and 509A, and the widths of the narrow portions 411A2 and 511A2 are smaller than the outer diameters of the protrusions 409A and 509A.

  FIG. 8 shows an example in which the long hole 611A is formed with substantially the same width without a wide portion or a narrow portion. In this case, the clearance between the surface 109B of the holder 109 and the surface 110A of the frame 110 is configured to be equal to or slightly narrower than the thickness of the sliding sheet 111. It is narrowed by. Further, the surface 109B and the surface 110A are formed as rough surfaces having high frictional resistance. Accordingly, even if the width of the long hole 611A is the same, the sliding sheet 111 is gradually rotated around the fixing belt 102 against the frictional resistance of the rough surface. The torque in this case is not related to the dimensional relationship between the long hole 611A and the protrusion 609A or the frictional resistance between them, but the sliding sheet 111, the surface 109B of the holder 109 and the surface 110A of the frame 110 that tightly attach it. This is determined by the frictional resistance, and the management object is different from each of the aforementioned long holes.

  Further, even in the case of the long holes shown in FIGS. 3, 6 and 7, the clearance between the surface 109B of the holder 109 and the surface 110A of the frame 110 is narrowed so that the surfaces 109B and 110A are formed into rough surfaces. The movement of the moving sheet 111 may be affected by surface friction.

1 is a configuration diagram of an image forming apparatus. FIG. 3 is a cross-sectional view in a direction orthogonal to the longitudinal direction of the fixing device. It is a figure, such as a sliding sheet. It is a figure which shows the dimension of a long hole of a keyhole shape. It is an experiment graph of a sliding sheet. It is a figure of the long hole of a different shape. It is a figure of the long hole of a different shape. It is a figure of the long hole of a different shape.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Fixing device 101 Fixing roller 102 Fixing belt 103 Pressure pad 107 Separating member 109 Holder 109A, 209A, 309A, 409A, 509A, 609A Projection 109B, 110A Surface 110 Frame 111 Sliding sheet 111A, 211A, 311A, 411A, 511A , 611A Long hole 111A1, 211A1, 311A1, 411A1, 511A1 Wide part 111A2, 211A2, 311A2, 411A2, 511A2 Narrow part H Halogen lamp P Recording material N Nip part B Separating part

Claims (10)

A fixing roller having an elastic layer and rotating with a built-in heating means;
An endless fixing belt driven and rotated by the fixing roller;
A pressure unit that pressurizes the fixing belt from the inner peripheral surface side and presses the fixing belt against the fixing roller;
Located on the downstream side in the recording material conveyance direction with respect to the pressure unit, the fixing belt is pressed from the inner peripheral surface side to press the fixing belt against the fixing roller, and the elastic layer of the fixing roller is elastically deformed. Separating means for causing
Holding means for holding the pressurizing means and the separating means;
A sliding sheet disposed between the fixing belt and the pressure unit and the separation unit;
With
In a fixing device for fixing a toner image on a recording material at a nip portion formed between the fixing roller and the fixing belt,
The sliding sheet has a plurality of long holes that are long in the rotation direction of the fixing belt, and the plurality of long holes are provided at a plurality of protrusions provided at positions upstream of the nip portion of the holding unit in the rotation direction. The fixing device is characterized in that a portion of the elongated hole located downstream in the rotation direction is engaged with the protrusion at the initial stage of the use period. The fixing device according to claim 1, wherein the elongated hole is formed so that a width of a portion positioned on the upstream side is narrower than a width of a portion positioned on the downstream side. The fixing device according to claim 2, wherein the elongated hole is formed in a keyhole shape. The fixing device according to claim 2, wherein a portion of the elongated hole located on the upstream side is a cut formed in the rotation direction. The fixing device according to claim 2, wherein a portion of the long hole located on the upstream side is a perforation formed in the rotation direction. The width of the portion located on the downstream side in the elongated hole is larger than the outer diameter of the protrusion, and the width of the portion located on the upstream side is smaller than the outer diameter of the protrusion. The fixing device according to claim 2. The long hole is formed by alternately connecting a portion having the same width as a portion located on the downstream side and a portion having a width narrower than the width. Fixing device. The width of the portion having the same width as the portion located on the downstream side in the long hole is larger than the outer diameter of the protrusion, and the width of the portion having a width narrower than the width is smaller than the outer diameter of the protrusion. The fixing device according to claim 7, wherein the fixing device is provided. The long hole is formed so that the width of the portion located on the downstream side and the width of the portion located on the upstream side are substantially the same, and the periphery of the long hole is tightly attached with a rough surface inside the holding means. The fixing device according to claim 1, wherein the fixing device is provided. An image forming apparatus comprising the fixing device according to claim 1.

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