JP5978195B2 - Fixing device, separating member, and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device that fixes a toner image on a sheet, a separating member provided in the fixing device, and an image forming apparatus including the fixing device and the separating member.

  2. Description of the Related Art Conventionally, electrophotographic image forming apparatuses such as copying machines and printers include a fixing device that fixes a toner image on a sheet. The fixing device includes a fixing member (for example, a fixing roller or a fixing belt) and a pressure member (for example, a pressure roller or a pressure belt) that comes into pressure contact with the fixing member. The paper and toner image are heated and pressed in a fixing nip formed between the fixing member and the pressure member, so that the toner image is fixed on the paper.

  The fixing device having such a configuration usually includes a separation member (for example, a separation plate or a separation claw) that separates the sheet that has passed through the fixing nip from the fixing member. For example, Patent Document 1 discloses a separation plate (see “Separation Member 30” in Patent Document 1). In this prior art, a fluororesin coating region (see “Fluororesin layer 32” in Patent Document 1) is provided on the front and back surfaces of the separator plate, respectively. In this way, by providing a coating region not only on the front surface of the separation plate but also on the back surface, it becomes difficult for toner to adhere to the back surface of the separation plate, and toner deposited on the back surface of the separation plate is prevented from damaging the fixing member. It is possible to prevent image defects (for example, gloss streaks).

JP 2006-317492 A

  In the fixing device configured as described above, when the fixing member and the pressure member are rotated, the charge distribution in the direction of the rotation axis of the fixing member may be non-uniform. In such a case, when the sheet passes through the fixing nip, unfixed toner on the sheet is scattered, or the unfixed toner on the sheet is electrically adsorbed on the surface of the fixing member and is re-applied to the sheet after the rotation of the fixing member. There is a risk of adhesion, leading to image defects.

  In view of the above, an object of the present invention is to make the charge distribution in the direction of the rotation axis of the fixing member uniform and prevent the occurrence of image defects.

  The fixing device of the present invention separates a fixing member that rotates about a rotation shaft, a pressure member that presses against the fixing member to form a fixing nip, and a recording medium that has passed through the fixing nip from the fixing member. A separation member, and the fixing member includes a sheet passing area through which a recording medium passes, and a non-sheet passing area provided outside the sheet passing area. The sheet passing area includes a first sheet passing portion. And a second sheet passing portion having a charge amount larger than that of the first sheet passing portion, and the separation member includes a separation plate having a leading end opposed to the sheet passing region, and the separation plate is a recording plate A front surface portion facing the medium conveyance path, and a back surface portion provided on the back side of the front surface portion, the back surface portion including a coating region to which an insulating coating is applied, and the coating region includes The first paper passing portion overlaps the position in the rotation axis direction. A computing unit, wherein the position of the rotation axis direction overlaps the second copies feeding unit, characterized in that the width than the first coating portion is provided with a narrow second coating unit.

  Thus, by making the width of the second coating portion narrower than the width of the first coating portion, it is possible to promote discharge from the second paper passing portion where the position in the rotation axis direction overlaps with the second coating portion. Accordingly, the charge amount of the second sheet passing portion can be reduced to reduce the difference in charge amount between the first sheet passing portion and the second sheet passing portion, and the charge distribution in the rotation axis direction of the fixing member can be reduced. It becomes possible to make uniform. For this reason, it is possible to prevent the unfixed toner on the paper from being scattered or the unfixed toner on the paper from being electrically adsorbed on the surface of the fixing member and reattaching to the paper after the fixing member circulates. Thus, it is possible to prevent the occurrence of image defects.

  The first coating portion is provided at a central portion in the rotation axis direction of the coating region, and the second coating portion is provided at both end portions in the rotation axis direction of the coating region, and the tip side of the coating region. The edge portion of the coating region may extend linearly along the rotational axis direction, and the edge portion of the coating region on the side away from the tip portion may be curved toward the side away from the tip portion.

  By adopting such a configuration, when the first sheet passing portion is provided at the center portion in the rotation axis direction of the sheet passing region and the second sheet passing portion is provided at both ends in the rotation axis direction of the sheet passing region, It is possible to make the charge distribution of the fixing member uniform.

  The first coating portion is provided at one end of the coating region in the rotation axis direction, and the second coating portion is provided at the other end of the coating region in the rotation axis direction, and the tip portion of the coating region The edge on the side extends linearly along the rotational axis direction, and the edge on the side away from the tip of the coating region extends linearly so as to incline with respect to the rotational axis direction. May be.

  By adopting such a configuration, the first sheet passing portion is provided at one end portion in the rotation axis direction of the sheet passing region, and the second sheet passing portion is provided at the other end portion in the rotation axis direction of the sheet passing region. In this case, the charge distribution of the fixing member can be made uniform.

  The surface portion may include another coating region to which an insulating coating is applied, and the width of the other coating region may be wider than the width of the coating region.

  By adopting such a configuration, it is possible to reliably prevent toner from adhering to the surface portion.

  The separation member may further include a support plate that supports the separation plate, and a contact piece that is fixed to the support plate and contacts the non-sheet passing region.

  By adopting such a configuration, it is possible to maintain a constant interval between the sheet passing area and the tip of the separation plate without damaging the sheet passing area.

  The separation member of the present invention is provided in a fixing device that includes a fixing member that rotates about a rotation shaft and a pressure member that presses the fixing member to form a fixing nip, and passes through the fixing nip. A separation member that separates a sheet from the fixing member, wherein the fixing member includes a sheet passing area through which the sheet passes and a non-sheet passing area provided outside the sheet passing area; A first sheet passing portion and a second sheet passing portion having a charge amount larger than that of the first sheet passing portion, and the separation member includes a separation plate that opposes the leading end portion to the sheet passing region. The separation plate includes a surface portion facing a paper conveyance path, and a back surface portion provided on the back side of the surface portion, and the back surface portion includes a coating region to which an insulating coating is applied, The coating area is a position in the first paper passing portion and the rotation axis direction. A first coating portion that overlaps the second copies feed unit and the overlapping position of the rotation axis direction, wherein the width than the first coating portion is provided with a narrow second coating unit.

  Thus, by making the width of the second coating portion narrower than the width of the first coating portion, it is possible to promote discharge from the second paper passing portion where the position in the rotation axis direction overlaps with the second coating portion. Accordingly, the charge amount of the second sheet passing portion can be reduced to reduce the difference in charge amount between the first sheet passing portion and the second sheet passing portion, and the charge distribution in the rotation axis direction of the fixing member can be reduced. It becomes possible to make uniform. For this reason, it is possible to prevent the unfixed toner on the paper from being scattered or the unfixed toner on the paper from being electrically adsorbed on the surface of the fixing member and reattaching to the paper after the fixing member circulates. Thus, it is possible to prevent the occurrence of image defects.

  The image forming apparatus of the present invention includes any one of the fixing devices or the separating members described above.

  According to the present invention, the charge distribution in the direction of the rotation axis of the fixing member can be made uniform, and the occurrence of image defects can be prevented.

1 is a schematic diagram illustrating an outline of a color printer according to a first embodiment of the present invention. 1 is a cross-sectional view illustrating a fixing device of a color printer according to a first embodiment of the present invention. FIG. 2 is a perspective view illustrating an internal configuration of a housing in the fixing device of the color printer according to the first embodiment of the present invention. FIG. 2A is a plan view showing a fixing nip and its peripheral portion in the fixing device of the color printer according to the first embodiment of the present invention. (B) is AA sectional drawing of (a). (C) is BB sectional drawing of (a). FIG. 2 is a perspective view showing a fixing belt and a separating member in the fixing device of the color printer according to the first embodiment of the present invention. FIG. 3 is a cross-sectional view illustrating a separation member and its peripheral portion in the fixing device of the color printer according to the first embodiment of the present invention. (A) is a perspective view from the surface side which shows the separation member except the contact piece in the fixing device of the color printer which concerns on the 1st Embodiment of this invention. FIG. 5B is a perspective view from the back side showing the separating member excluding the contact piece in the fixing device of the color printer according to the first embodiment of the present invention. In the fixing device of the color printer which concerns on the 2nd Embodiment of this invention, it is a perspective view from the back surface side which shows the separation member except the contact piece.

<First Embodiment>
Hereinafter, a first embodiment of the present invention will be described.

  First, the overall configuration of the color printer 1 (image forming apparatus) will be described with reference to FIG. The color printer 1 includes a box-shaped printer main body 2, a paper feed cassette 3 that stores paper (not shown) is provided at the bottom of the printer main body 2, and paper is discharged at the top of the printer main body 2. A tray 4 is provided.

  An intermediate transfer belt 6 is installed between a plurality of rollers in the center of the printer main body 2, and an exposure device 7 composed of a laser scanning unit (LSU) is disposed below the intermediate transfer belt 6. Yes. Below the intermediate transfer belt 6, four image forming units 8 are provided for each toner color (for example, four colors of magenta, cyan, yellow, and black). Each image forming unit 8 is rotatably provided with a photosensitive drum 9, and around the photosensitive drum 9, a charger 10, a developing unit 11, a primary transfer unit 12, and a cleaning device 13 are provided. The static eliminator 14 is arranged in the order of the primary transfer process. Above the developing unit 11, a toner container 15 corresponding to each image forming unit 8 is provided for each toner color (for example, four colors of magenta, cyan, yellow, and black).

  On one side of the printer main body 2 (on the right side in the drawing), a paper conveyance path 16 is provided in the vertical direction. That is, the color printer 1 of the present embodiment is so-called vertical conveyance. A paper feed unit 17 is provided at the upstream end of the conveyance path 16, and a secondary transfer roller 18 is provided at one end (right end in the drawing) of the intermediate transfer belt 6 at a middle portion of the conveyance path 16, and downstream of the conveyance path 16. A fixing device 19 is provided in the section, and a paper discharge port 20 is provided at the downstream end of the conveyance path 16.

  Next, an image forming operation of the color printer 1 having such a configuration will be described. When the color printer 1 is turned on, various parameters are initialized, and initial settings such as temperature setting of the fixing device 19 are executed. When image data is input from a computer or the like connected to the color printer 1 and an instruction to start printing is given, an image forming operation is executed as follows.

  First, after the surface of the photosensitive drum 9 is charged by the charger 10, an electrostatic latent image is formed on the surface of the photosensitive drum 9 by laser light (see arrow P) from the exposure device 7. Next, the electrostatic latent image is developed into a toner image of a corresponding color by the developing device 11 with the toner supplied from the toner container 15. This toner image is primarily transferred to the surface of the intermediate transfer belt 6 in the primary transfer portion 12. Each image forming unit 8 sequentially repeats the above operation, whereby a full-color toner image is formed on the intermediate transfer belt 6. Note that the toner and charge remaining on the photosensitive drum 9 are removed by the cleaning device 13 and the static eliminator 14.

  On the other hand, the sheet taken out from the sheet feeding cassette 3 by the sheet feeding unit 17 is conveyed to the downstream side of the conveying path 16 in synchronism with the above-described image forming operation, and is transferred onto the intermediate transfer belt 6 by the secondary transfer roller 18. The full-color toner image is secondarily transferred to the paper. The sheet on which the toner image is secondarily transferred is conveyed downstream in the conveyance path 16 and enters the fixing device 19 where the toner image is fixed on the sheet. The sheet on which the toner image is fixed is discharged from the discharge port 20 onto the discharge tray 4.

  Next, the fixing device 19 will be described. Hereinafter, for convenience of explanation, the front side of the sheet in FIG. 2 is defined as the front side (front side) of the fixing device 19. An arrow Fr appropriately attached to each drawing indicates the front side (front side) of the fixing device 19.

  As shown in FIG. 2, the fixing device 19 includes a fixing unit 21 and an IH unit 22 provided on the left side of the fixing unit 21.

  First, the fixing unit 21 of the fixing device 19 will be described. The fixing unit 21 is detachable from the printer main body 2. As shown in FIG. 2, the fixing unit 21 includes a housing 23, a fixing roller 24 accommodated in a left side portion of the housing 23, a fixing belt 25 (fixing member) provided around the fixing roller 24, A pressure roller 26 (pressure member) housed in the right side of the housing 23, a thermistor 27 provided on the lower left side of the fixing belt 25, and a separation member 28 provided on the upper right side of the fixing belt 25. I have.

  As shown in FIG. 3, the housing 23 includes a first support part 30 and a second support part 31 provided on the right side of the first support part 30. A fulcrum portion 33 protrudes inward in the front-rear direction on the inner surface of the front and rear end walls 32 of the first support portion 30. The first support portion 30 supports the second support portion 31 so as to be swingable around the lower end side. The second support portion 31 is connected to a nip pressure switching mechanism 34 provided on the front end side and the rear end side of the housing 23, and the second support portion 31 can be swung by the nip pressure switching mechanism 34. It is like that.

  The fixing roller 24 (see FIG. 2 and the like) has a long cylindrical shape in the front-rear direction. The fixing roller 24 is supported by the first support portion 30 so as to be rotatable about a rotation axis X extending in the front-rear direction.

  The fixing roller 24 is constituted by, for example, a cylindrical base material layer and a cylindrical elastic layer provided around the base material layer. The base material layer of the fixing roller 24 is made of, for example, a metal such as stainless steel or aluminum. The elastic layer of the fixing roller 24 is made of, for example, silicon rubber or silicon sponge. As shown in FIG. 4A, the fixing roller 24 has a shape (so-called “crown shape”) in which the outer diameter gradually decreases from both front and rear end portions toward the front and rear center portion.

  The fixing belt 25 (see FIG. 2 and the like) is fixed to the outer periphery of the fixing roller 24, and rotates together with the fixing roller 24 about a rotation axis X extending in the front-rear direction. That is, in the present embodiment, the front-rear direction is the rotation axis direction of the fixing belt 25.

  The fixing belt 25 includes, for example, a base material layer, an elastic layer provided around the base material layer, and a release layer (surface layer) that covers the elastic layer. The base material layer of the fixing belt 25 is made of a metal such as nickel, for example. The elastic layer of the fixing belt 25 is made of, for example, silicon rubber or silicon sponge. The release layer of the fixing belt 25 is made of a fluorine resin such as PFA or PTFE.

  As shown in FIG. 4A, the fixing belt 25 has a shape (so-called “crown shape”) in which the outer diameter gradually decreases from both front and rear end portions toward the front and rear center portion. On the outer peripheral surface of the fixing belt 25, a sheet passing area 35 through which a sheet (for example, A3 size sheet) passes, and both front and rear sides of the sheet passing area 35 (outside the sheet passing area 35), the sheet does not pass. And a paper passing area 36 is provided. A first paper passing portion 37 is provided at the center in the front-rear direction of the paper passing region 35, and second paper passing portions 38 are provided at both ends in the front-rear direction of the paper passing region 35.

  The pressure roller 26 (see FIG. 2 and the like) has a long cylindrical shape in the front-rear direction. The pressure roller 26 is supported by the second support portion 31 so as to be rotatable about a rotation axis Y extending in the front-rear direction. That is, in the present embodiment, the front-rear direction is the rotation axis direction of the pressure roller 26. The pressure roller 26 includes a base material layer, an elastic layer provided around the base material layer, and a release layer (surface layer) that covers the elastic layer. The base material layer of the pressure roller 26 is made of a metal such as stainless steel or aluminum. The elastic layer of the pressure roller 26 is made of, for example, silicon rubber or silicon sponge. The release layer of the pressure roller 26 is made of, for example, a fluororesin such as PFA or PTFE.

  As shown in FIG. 4A and the like, the pressure roller 26 is in pressure contact with the fixing belt 25, and a fixing nip 40 is formed between the fixing belt 25 and the pressure roller 26. Hereinafter, the pressure of the fixing nip 40 is referred to as “nip pressure”, and the width of the fixing nip 40 is referred to as “nip width”. As described above, the fixing roller 24 and the fixing belt 25 have a shape (so-called “crown shape”) in which the outer diameter gradually decreases from both front and rear end portions toward the front and rear center portion. Accordingly, the nip width of the portion corresponding to the second paper passing portion 38 of the fixing belt 25 rather than the nip width W1 of the portion corresponding to the first paper passing portion 37 of the fixing belt 25 (see FIG. 7B). W2 (see FIG. 7C) is widened.

  The pressure roller 26 moves in the proximity / separation direction (substantially left-right direction in the present embodiment) with the fixing belt 25 as the nip pressure switching mechanism 34 (see FIG. 3) swings the second support portion 31. The nip pressure is switched as the pressure roller 26 moves.

  The thermistor 27 (see FIG. 2) is, for example, a non-contact type temperature detection unit. The thermistor 27 is configured to detect the temperature of the fixing belt 25 and output the detection result to a control unit (not shown).

  As shown in FIG. 2, the separation member 28 is disposed on the downstream side of the fixing belt 25 in the paper transport direction (see arrow Z in FIG. 2), and is provided close to the fixing belt 25.

  As shown in FIG. 5, the separation member 28 has a long shape in the front-rear direction. The separation member 28 includes a support plate 41, a separation plate 42 supported by the support plate 41, and contact pieces 43 fixed to both front and rear ends of the support plate 41.

  The support plate 41 of the separation member 28 has a shape that is long in the front-rear direction. The support plate 41 is made of sheet metal, for example. The support plate 41 includes a main body portion 44, a bent portion 45 bent toward the lower left side from the upper end of the main body portion 44, and an attachment portion 46 bent toward the lower left side from both front and rear ends of the main body portion 44. I have.

  A rectangular notch 47 is provided at each of the front lower corner and the rear lower corner of the main body 44 of the support plate 41. A first positioning hole 48 is provided above each notch 47 in the front end and the rear end of the main body 44 of the support plate 41. A first insertion hole 49 is provided on the front end portion and the rear end portion of the main body portion 44 of the support plate 41 on the upper side of each notch portion 47 and on the inner side in the front-rear direction of each first positioning hole 48. A plurality of groove portions 51 are recessed in the front edge portion (left lower edge portion) of the bent portion 45 of the support plate 41 at intervals in the front-rear direction.

  A mounting hole 52 is provided in the upper part of each mounting portion 46 of the support plate 41, and a fulcrum portion protruding from the inner surfaces of the front and rear end walls 32 of the first support portion 30 (see FIG. 3). 33 is inserted. Accordingly, the separation member 28 is supported by the first support portion 30 in a state where the separation member 28 can rotate around the fulcrum portion 33. An extending portion 53 that extends toward the upper right is provided at the lower end portion of each mounting portion 46, and an L-shaped hook portion 54 that protrudes inward in the front-rear direction at the upper right end portion of the extending portion 53. Is provided. A coil spring 80 (biasing member) is attached to the hook portion 54.

  The separation plate 42 of the separation member 28 has a flat plate shape that is long in the front-rear direction. The separation plate 42 is fixed to the support plate 41 by means such as welding. The separation plate 42 is made of a conductive material such as a sheet metal and is electrically grounded. A second positioning hole 55 is provided at a position corresponding to the first positioning hole 48 of the main body 44 of the support plate 41 at the front end portion and the rear end portion of the separation plate 42. A second insertion hole 56 is provided at a position corresponding to the first insertion hole 49 of the main body 44 of the support plate 41 on the inner side in the front-rear direction of each second positioning hole 55.

  As shown in FIG. 6, the front end portion 57 (lower end portion) of the separation plate 42 is opposed to the sheet passing area 35 of the fixing belt 25 with an interval. The separation plate 42 includes a front surface portion 58 facing the paper conveyance path 16 and a back surface portion 59 provided on the back side of the front surface portion 58.

  7A, the front side coating region 61 (another coating region) is formed on the surface portion 58 of the separation plate 42. The front side coating region 61 is coated with a fluororesin (insulating coating). The front side coating region 61 is formed by coating the surface portion 58 of the separation plate 42 without masking, and is formed over the entire surface portion 58 of the separation plate 42.

  The front side coating areas 61 are provided on the front and rear sides of the main coating part 62 and the main coating part 62 that overlaps with the paper passing area 35 of the fixing belt 25 and the front and rear sides of the fixing belt 25. And an auxiliary coating portion 63 that overlaps in the direction. A lead line C in FIG. 7A indicates the boundary between the main coating portion 62 and the auxiliary coating portion 63.

  The lower edge part (edge part on the tip part 57 side) and the upper edge part (edge part on the side away from the tip part 57) of the main coating part 62 and each auxiliary coating part 63 extend linearly along the front-rear direction. ing. Therefore, the vertical width (width in the direction orthogonal to the front-rear direction) of the main coating portion 62 and each auxiliary coating portion 63 is uniform. Since each auxiliary coating part 63 is provided above the notch 47 of the main body part 44 of the separation plate 42, the vertical width of each auxiliary coating part 63 is narrower than the vertical width of the main coating part 62. Yes.

  As shown in the spotted display in FIG. 7B, the back side coating region 70 (coating region) is located on the back surface portion 59 of the separation plate 42 at a portion where the sheet passing region 35 of the fixing belt 25 overlaps the position in the front-rear direction. Is provided. The back side coating region 70 is coated with a fluororesin (insulating coating). The back side coating region 70 is formed by masking and coating the back surface portion 59 of the separation plate 42, and is provided in a lower portion (portion on the front end portion 57 side) of the back surface portion 59 of the separation plate 42. . Therefore, the vertical width (width in the direction orthogonal to the front-rear direction) of the back side coating region 70 is narrower than the vertical width of the main coating portion 62 and the auxiliary coating portion 63 of the front side coating region 61 (the main coating portion of the front side coating region 61). 62 and the auxiliary coating portion 63 have a vertical width wider than the vertical width of the back side coating region 70). The coating of the separation plate 42 passes from the front surface portion 58 through the front end portion 57 to the back surface portion 59. Therefore, the back side coating area 70 is continuous with the front side coating area 61.

  A first coating portion 71 is provided at the center in the front-rear direction of the back side coating region 70. The first coating portion 71 overlaps with the first sheet passing portion 37 of the sheet passing region 35 of the fixing belt 25 in the front-rear direction. Note that the lead line D in FIG. 7B indicates the boundary between the first coating portion 71 and portions on both sides thereof.

  Second coating portions 72 are provided at both ends in the front-rear direction of the back side coating region 70. The second coating portion 72 overlaps with the second paper passing portion 38 of the paper passing region 35 of the fixing belt 25 in the front-rear direction. Note that a lead line E in FIG. 7B indicates the boundary between the second coating portion 72 and the inner portion in the front-rear direction.

  The lower edge portion (edge portion on the front end portion 57 side) of the back side coating region 70 extends along the front-rear direction, and the upper edge portion (edge portion on the side away from the front end portion 57) of the back side coating region 70 is on the upper side (edge portion). It is curved toward the side away from the distal end portion 57). Therefore, the vertical width of the second coating part 72 (the width in the direction orthogonal to the front-rear direction) is narrower than the vertical width of the first coating part 71. Thus, the vertical width of the back side coating area 70 is non-uniform.

  As shown in FIG. 6 and the like, the contact piece 43 of the separation member 28 includes a fixed portion 75 and a contact portion 76 extending from the lower end portion of the fixed portion 75 toward the lower right. The fixing portion 75 is provided with a third insertion hole 77. The contact piece 43 is attached to the support plate 41 by a screw 78 that passes through the first insertion hole 49 of the main body 44 of the support plate 41, the second insertion hole 56 of the separation plate 42, and the third insertion hole 77 of the fixing portion 75. It is fixed. As shown in FIG. 5, the contact portion 76 is in contact with the non-sheet passing region 36 of the fixing belt 25. The contact portion 76 is pressed against the non-sheet passing region 36 of the fixing belt 25 by a coil spring 80 attached to the hook portion 54 of the support plate 41. As a result, the distance between the leading end 57 of the separation plate 42 and the sheet passing area 35 of the fixing belt 25 is kept constant.

  Next, the IH unit 22 (see FIG. 2) of the fixing device 19 will be described. The IH unit 22 is fixed to the printer body 2. The IH unit 22 is housed in the case member 81, the case member 81, an IH coil 82 (heat source) provided in an arc shape along the outer periphery of the fixing belt 25, and the case member 81. And an arch core 83 provided along the outer periphery.

  In the fixing device 19 configured as described above, when the toner image is fixed on the paper, the pressure roller 26 is rotated by a driving source (not shown). When the pressure roller 26 is thus rotated, the fixing belt 25 that is in pressure contact with the pressure roller 26 rotates in the direction opposite to the pressure roller 26 together with the fixing roller 24. Further, when the toner image is fixed on the sheet, the fixing belt 25 is induction-heated by the IH coil 82. In this state, when the sheet on which the unfixed toner image is transferred passes through the fixing nip 40, the sheet and the toner image are heated and pressurized to fix the toner image on the sheet. The paper that has passed through the fixing nip 40 is separated from the fixing belt 25 by the separation plate 42 of the separation member 28.

  Incidentally, in the present embodiment, as described above, the release layer (surface layer) of the fixing belt 25 and the pressure roller 26 is made of a fluororesin. In such a case, when the fixing belt 25 and the pressure roller 26 are rotated in a pressure contact state, the fixing belt 25 and the pressure roller 26 are frictionally charged negatively. Normally, the triboelectric charge amounts of the fixing belt 25 and the pressure roller 26 are proportional to the nip width. In this embodiment, the nip width W1 of the portion corresponding to the first paper passing portion 37 of the fixing belt 25 (FIG. 7 ( The nip width W2 (see FIG. 7C) of the portion corresponding to the second paper passing portion 38 of the fixing belt 25 is wider than that shown in b). For this reason, the charge amount of the second paper passing portion 38 is larger than that of the first paper passing portion 37 of the fixing belt 25, and the charge distribution in the front-rear direction of the fixing belt 25 becomes uneven. When the sheet passes through the fixing nip 40 in such a state, the unfixed toner on the sheet is scattered, or the unfixed toner on the sheet is electrically adsorbed on the surface of the fixing belt 25 and the fixing belt 25 rotates. There is a risk of re-adhering to the paper.

  However, in the present embodiment, the width of the second coating portion 72 is narrower than the width of the first coating portion 71 in the back side coating region 70 provided on the back surface portion 59 of the separation plate 42. By adopting such a configuration, it is possible to promote discharge from the second sheet passing portion 38 where the position in the front-rear direction overlaps with the second coating portion 72. Accordingly, the charge amount of the second sheet passing portion 38 can be reduced to reduce the difference in charge amount between the first sheet passing portion 37 and the second sheet passing portion 38, and the fixing belt 25 in the front-rear direction can be reduced. The charge distribution can be made uniform. Therefore, it is possible to prevent the unfixed toner on the paper from being scattered, or the unfixed toner on the paper from being electrically adsorbed on the surface of the fixing belt 25 and reattaching to the paper after the fixing belt 25 rotates. It is possible to prevent image defects from occurring.

  In the present embodiment, the first coating portion 71 is provided at the center in the front-rear direction of the back side coating region 70, and the second coating portions 72 are provided at both ends in the front-rear direction of the back side coating region 70. And the lower edge part (edge part on the front end part 57 side) of the back side coating area 70 extends linearly along the front-rear direction, and the upper edge part (the edge part on the side away from the front end part 57) of the back side coating area 70. Is curved toward the upper side (side away from the tip portion 57). By adopting such a configuration, the first sheet passing portion 37 is provided at the center portion in the front-rear direction of the sheet passing area 35 of the fixing belt 25, and the second end portions in the front-rear direction both ends of the sheet passing area 35 of the fixing belt 25. When the paper passing portion 38 (the portion having a larger charge amount than the first paper passing portion 37) is formed, the charge distribution of the fixing belt 25 can be made uniform.

  Further, the surface portion 58 of the separation plate 42 includes a front side coating region 61 to which a fluororesin coating (insulating coating) is applied. The vertical width of the front side coating region 61 is larger than the vertical width of the back side coating region 70. wide. By adopting such a configuration, it is possible to reliably prevent toner from adhering to the surface portion 58 of the separation plate 42.

  The separation member 28 includes a separation plate 42, a support plate 41 that supports the separation plate 42, and a contact piece 43 that is fixed to the support plate 41 and contacts the non-sheet passing region 36 of the fixing belt 25. ing. By adopting such a configuration, the distance between the sheet passing area 35 of the fixing belt 25 and the front end portion 57 of the separation plate 42 can be kept constant without damaging the sheet passing area 35 of the fixing belt 25. Become.

  If the vertical width of the back side coating region 70 is too wide, the discharge from the fixing belt 25 to the separation plate 42 is excessively restricted, and the charge is accumulated in the fixing belt 25 too much. Along with this, there is a possibility that electromagnetic noise is generated or an electrical component (for example, the thermistor 27) is damaged when the fixing belt 25 is discharged. On the other hand, if the vertical width of the back side coating region 70 is too narrow, the discharge from the fixing belt 25 to the separation plate 42 is excessively promoted, and the surface of the fixing belt 25 is not electrically conductive when the surface of the fixing belt 25 is not conductive. The potential rises or falls locally. Accordingly, the unfixed toner on the sheet is scattered due to the potential difference between the surface of the fixing belt 25 and the sheet, or the unfixed toner on the sheet is electrically adsorbed on the surface of the fixing belt 25 and the fixing belt 25 There is a risk of reattaching to the paper after the lap. As described above, if the vertical width of the back side coating region 70 is too wide or too narrow, there is a possibility that a problem may occur along with this.

  On the other hand, in this embodiment, the back side coating region 70 is formed by masking and coating the back surface portion 59 of the separation plate 42, and the lower portion (tip portion 57) of the back surface portion 59 of the separation plate 42. The back side coating region 70 is provided in the side portion. By adopting such a configuration, it is possible to set the vertical width of the back side coating region 70 to an appropriate value, and it is possible to appropriately discharge from the fixing belt 25 to the separation plate 42. Therefore, it is possible to prevent the above problems.

  In this embodiment, the case where the fixing belt 25 (fixing member) has a crown shape has been described. However, in another different embodiment, the pressure roller 26 (pressure member) may have a crown shape. When the curve drawn by the crown shape of the fixing belt 25 (fixing member) and the pressure roller 26 (pressure member) varies depending on the model and application of the color printer 1, the upper edge (tip portion) of the back side coating region 70 is used. It is preferable that the curve drawn by the edge portion on the side away from 57 is also changed depending on the model and application of the color printer 1.

  Although the case where the IH coil 82 is used as a heat source has been described in the present embodiment, a heater such as a halogen heater or a ceramic heater may be used as a heat source in other different embodiments.

  In this embodiment, the case where the fixing belt 25 is used as the fixing member has been described. However, in another different embodiment, a fixing roller may be used as the fixing member.

  In this embodiment, the case where the configuration of the present invention is applied to the color printer 1 has been described. However, in other different embodiments, the present invention is applied to other image forming apparatuses such as a monochrome printer, a copier, a facsimile machine, and a multifunction machine. A configuration may be applied.

<Second Embodiment>
Next, a second embodiment of the present invention will be described. Note that description of the same parts as those in the first embodiment is omitted.

  In the color printer 1 described in the first embodiment, when a bias for secondary transfer is applied to the secondary transfer roller 18, for example, the relationship between the direction of the current flowing through the secondary transfer roller 18 is The charge amount at the front end portion (the other end portion in the front-rear direction) may be larger than the rear end portion (one end portion in the front-rear direction) of the next transfer roller 18. In such a case, the charge amount of the front end portion of the paper on which the toner image is secondarily transferred by the secondary transfer roller 18 is larger than that of the rear end portion. Accordingly, as shown in FIG. 8, a first sheet passing portion 37 is formed at the rear end portion of the sheet passing area 35 of the fixing belt 25, and a second end portion is formed at the front end portion of the sheet passing area 35 of the fixing belt 25. A sheet passing portion 38 (a portion having a larger amount of charge than the first sheet passing portion 37) is formed.

  Therefore, in this embodiment, the first coating portion 71 is provided at the rear end portion (one end portion in the front-rear direction) of the back side coating region 70, and the second coating portion 72 is provided at the front end portion (the other end portion in the front-rear direction) of the back side coating region 70. (A portion whose vertical width is narrower than that of the first coating portion 71) is provided. Further, the lower edge portion (edge portion on the front end portion 57 side) of the back side coating region 70 extends linearly along the front-rear direction, and the upper edge portion (edge portion on the side away from the front end portion 57) of the back side coating region 70. ) Extends linearly so as to be inclined with respect to the front-rear direction. 8 indicates the boundary between the first coating portion 71 and its front portion, and the lead line G in FIG. 8 indicates the boundary between the second coating portion 72 and its rear portion.

  By adopting such a configuration, the first sheet passing portion 37 is formed at the rear end portion of the sheet passing region 35 of the fixing belt 25, and the second sheet passing portion is formed at the front end portion of the sheet passing region 35 of the fixing belt 25. When 38 (a portion having a larger amount of charge than the first sheet passing portion 37) is formed, the charge distribution of the fixing belt 25 can be made uniform.

  In the present embodiment, the first coating portion 71 is provided at the rear end portion of the back side coating region 70, and the second coating portion 72 is provided at the front end portion of the back side coating region 70. On the other hand, when the charge distribution of the fixing belt 25 in the other different embodiments is opposite to that of the present embodiment, the first coating portion 71 is provided at the front end portion of the back side coating region 70 and the rear end of the back side coating region 70 is provided. You may provide the 2nd coating part 72 in a part.

1 Color printer (image forming device)
16 Conveyance path 19 Fixing device 25 Fixing belt (fixing member)
26 Pressure roller (pressure member)
28 Separating member 35 Sheet passing area 36 Non-sheet passing area 37 First sheet passing section 38 Second sheet passing section 40 Fixing nip 41 Support plate 42 Separating plate 43 Abutting piece 57 (of separating plate) Front end 58 Front surface 59 Back Part 61 Front side coating area (other coating areas)
70 Back side coating area (coating area)
71 First coating portion 72 Second coating portion X Rotating shaft (of fixing belt)

Claims (7)

A fixing member that rotates about a rotation axis;
A pressure member that presses against the fixing member to form a fixing nip; and
A separation member that separates the paper that has passed through the fixing nip from the fixing member,
The fixing member is
A paper passing area through which the paper passes, and
A non-sheet passing area provided outside the sheet passing area,
The paper passing area is
A first paper passing section;
A second sheet passing portion having a charge amount larger than that of the first sheet passing portion,
The separation member includes a separation plate that opposes a leading end portion to the sheet passing region,
The separation plate is
A surface portion facing the paper conveyance path;
A back surface portion provided on the back side of the front surface portion,
The back surface portion includes a coating region to which an insulating coating is applied,
The coating area is
A first coating portion where the first paper passing portion and the position in the rotation axis direction overlap;
A fixing device comprising: the second sheet passing portion and a second coating portion whose position in the rotation axis direction overlaps and narrower than the first coating portion. The first coating portion is provided at a central portion in the rotation axis direction of the coating region,
The second coating portion is provided at both ends of the coating region in the rotation axis direction,
The edge on the tip side of the coating region extends linearly along the rotational axis direction,
The fixing device according to claim 1, wherein an edge portion of the coating region on a side away from the tip portion is curved toward a side away from the tip portion. The first coating portion is provided at one end of the coating region in the rotation axis direction,
The second coating portion is provided at the other end portion in the rotation axis direction of the coating region,
The edge on the tip side of the coating region extends linearly along the rotational axis direction,
2. The fixing device according to claim 1, wherein an edge portion of the coating region on a side away from the tip end portion extends linearly so as to incline with respect to the rotation axis direction. The surface portion includes another coating region provided with an insulating coating,
The fixing device according to claim 1, wherein a width of the other coating region is wider than a width of the coating region. The separating member is
A support plate for supporting the separation plate;
The fixing device according to claim 1, further comprising a contact piece fixed to the support plate and contacting the non-sheet passing region. A fixing device that includes a fixing member that rotates about a rotation shaft and a pressure member that presses against the fixing member to form a fixing nip, and separates the sheet that has passed through the fixing nip from the fixing member. A separating member,
The fixing member is
A paper passing area through which the paper passes, and
A non-sheet passing area provided outside the sheet passing area,
The paper passing area is
A first sheet passing portion that is charged to a predetermined polarity;
A second paper passing portion that is charged to the predetermined polarity and has a larger charge amount than the first paper passing portion;
The separation member includes a separation plate that opposes a leading end portion to the sheet passing region,
The separation plate is
A surface portion facing the paper conveyance path;
A back surface portion provided on the back side of the front surface portion,
The back surface portion includes a coating region to which an insulating coating is applied,
The coating area is
A first coating portion where the first paper passing portion and the position in the rotation axis direction overlap;
A separation member comprising: the second sheet passing portion and a second coating portion whose position in the rotation axis direction overlaps and narrower than the first coating portion.   An image forming apparatus comprising the fixing device according to claim 1 or the separating member according to claim 6.

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