Fixing apparatus and image forming apparatus

Abstract

The present invention provides a fixing device capable of suppressing the displacement of a sliding member that comes into contact with a rotating fixing belt at the fixing nip section. [Solution] The fixing device 8 comprises a fixing belt 81, a sliding member 85, a nip forming member 84, and a pressure roller 82. The sliding member 85 is sheet-shaped and is positioned adjacent to the radially inner side of the fixing belt 81, with the inner circumferential surface of the rotating fixing belt 81 sliding into contact with it. The nip forming member 84 is positioned radially inner of the fixing belt 81, with the sliding member 85 sandwiched between it and the inner circumferential surface of the fixing belt 81. The nip forming member 84 has an uneven surface 842 formed on its contact surface with the sliding member 85. The height Rpk of the protruding peaks of the uneven surface 842 is 2.5 [μm] or more and less than 500 [μm].

Description

Technical Field

[0001] The present invention relates to a fixing device and an image forming apparatus.

Background Art

[0002] In electrophotographic image forming apparatuses such as copiers and printers, a fixing device that employs a heat fixing method is widely used to fix an unfixed toner image formed on a sheet-like recording medium to the recording medium. The recording medium passes through a fixing nip portion formed by the contact of a heating member and a pressure member, and is heated and pressurized to fix the unfixed toner image.

[0003] For example, a conventional fixing device disclosed in Patent Document 1 includes a fixing belt, a pressure roller, a fixing member, and a sheet-like member. The fixing member is disposed on the inner peripheral side (radial inner side) of the fixing belt, and forms a nip portion by pressing against the pressure roller via the fixing belt. The sheet-like member is provided so as to cover the periphery of the fixing member, and is disposed opposite to the pressure roller with the fixing belt interposed therebetween. The sheet-like member reduces the sliding resistance between the fixing member and the fixing belt.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the conventional technology described above, the sheet-like member (sliding member) is provided so as to cover the periphery of the fixing member by overlapping and fitting holes formed on the upstream and downstream sides in the transport direction during deployment onto the protrusions of the fixing member. Because the fixing belt and the sheet-like member are pressed together by the fixing member, when the fixing belt rotates, the sheet-like member is pulled downstream of the fixing nip as the fixing belt rotates, and there is a risk that it will stretch and displace (deform). This raised concerns that damage to the sheet-like member and malfunction of the fixing belt may occur.

[0006] The present invention has been made in view of the above points, and aims to provide a fixing device and an image forming device that can suppress the displacement of a sliding member that comes into contact with a rotating fixing belt in the fixing nip section. [Means for solving the problem]

[0007] To solve the above problems, the fixing device of the present invention comprises a fixing belt, a sliding member, a nip forming member, a support member, and a pressurizing member, and fixes a toner image formed on the recording medium to the recording medium by inserting a recording medium into the fixing nip portion and heating and pressurizing it. The fixing belt is endless, heated by a heating unit, and rotates along the recording medium transport direction. The sliding member is sheet-shaped, arranged adjacent to the radially inner side of the fixing belt, and the inner circumferential surface of the rotating fixing belt slides into contact with the sliding member. The nip forming member is arranged radially inner of the fixing belt, with the sliding member sandwiched between it and the inner circumferential surface of the fixing belt. The support member is arranged radially inner of the fixing belt and supports the nip forming member. The pressurizing member contacts the nip forming member with a predetermined pressure, sandwiching the sliding member and the fixing belt, and forms a fixing nip portion between itself and the fixing belt. The nip forming member has an uneven portion formed on the contact surface with the sliding member. The height Rpk of the protruding peaks of the aforementioned uneven surface is 2.5 [μm] or more and less than 500 [μm]. [Effects of the Invention]

[0008] According to the configuration of the present invention, the frictional resistance between the sliding member and the nip-forming member can be increased, and the relative displacement of the sliding member with respect to the nip-forming member can be suppressed. In other words, the sliding member can be fixed in the fixing nip portion. This makes it possible to suppress the displacement (deformation) of the sliding member as the fixing belt rotates. Therefore, it is possible to prevent the occurrence of problems such as damage to the sliding member and poor rotation of the fixing belt. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic cross-sectional front view of an image forming apparatus according to one embodiment of the present invention. [Figure 2] Figure 1 is a cross-sectional front view of the fixing device of the image forming apparatus. [Figure 3] Figure 1 is a side view of the end face of the cutting section of the fixing device of the image forming apparatus. [Figure 4] Figure 2 is a top view of the nip-forming member of the fixing device. [Figure 5] Figure 2 is a plan view of the sliding member (in a flat state) of the fixing device. [Figure 6] Figure 3 is a magnified view of a portion of the fixing device. [Figure 7] This graph shows the relationship between the height difference of the uneven surface (height of the protrusions) and the number of sheets that can pass through the fixing nip section. [Modes for carrying out the invention]

[0010] Embodiments of the present invention will be described below with reference to the drawings. However, the present invention is not limited to the following.

[0011] Figure 1 is a schematic cross-sectional front view of an image forming apparatus 1 according to an embodiment. An example of the image forming apparatus 1 in this embodiment is a tandem-type color printer that transfers a toner image onto a sheet (recording medium) S using an intermediate transfer belt 71. The image forming apparatus 1 may be a so-called multifunction device equipped with functions such as printing, scanning (image reading), and facsimile transmission.

[0012] As shown in Figure 1, the image forming apparatus 1 comprises a sheet supply unit 3, a sheet transport unit 4, an exposure unit 5, an image forming unit 6, a transfer unit 7, a fixing device 8, a sheet discharge unit 9, and a control unit 10, all of which are located on the apparatus body 2.

[0013] The sheet supply unit 3 is located at the bottom of the main body 2 of the device. The sheet supply unit 3 holds multiple sheets (recording media) S before printing and separates and feeds out the sheets S one by one during printing. The sheet transport unit 4 extends vertically along the side wall of the main body 2 of the device. The sheet transport unit 4 transports the sheets S fed out from the sheet supply unit 3 to the secondary transfer unit 73 and the fixing device 8, and then discharges the fixed sheets S from the sheet discharge port 4a to the sheet discharge unit 9.

[0014] The exposure unit 5 is positioned above the sheet supply unit 3. The exposure unit 5 irradiates laser light, controlled based on image data, toward the image forming unit 6.

[0015] The image forming unit 6 is positioned above the exposure unit 5 and below the intermediate transfer belt 71. The image forming unit 6 includes an image forming unit 6Y for yellow, an image forming unit 6C for cyan, an image forming unit 6M for magenta, and an image forming unit 6B for black. These four image forming units 6 have the same basic configuration. Therefore, in the following description, the identification symbols "Y," "C," "M," and "B" representing each color may be omitted unless specifically required.

[0016] The image forming unit 6 includes a photosensitive drum that is supported to be rotatable in a predetermined direction (clockwise in Figure 1). The image forming unit 6 further includes a charging unit, a developing unit, and a drum cleaning unit arranged around the photosensitive drum along its rotational direction. A primary transfer unit 72 is positioned between the developing unit and the drum cleaning unit.

[0017] The photosensitive drum has a photosensitive layer formed on its outer peripheral surface. The charging unit charges the outer peripheral surface of the photosensitive drum to a predetermined surface potential. The exposure unit 5 exposes the outer peripheral surface of the photosensitive drum charged by the charging unit, and forms an electrostatic latent image of the original image with attenuated charge on the outer peripheral surface of the photosensitive drum. The developing unit supplies toner to the electrostatic latent image on the outer peripheral surface of the photosensitive drum for development, and forms a toner image. Each of the four image forming units 6 forms a toner image of a different color. The drum cleaning unit removes and cleans toner and the like remaining on the outer peripheral surface of the photosensitive drum after the toner image is primarily transferred to the outer peripheral surface of the intermediate transfer belt 71. In this way, the image forming unit 6 forms an image (toner image) that will be later transferred to the sheet S.

[0018] The transfer unit 7 includes an intermediate transfer belt 71, primary transfer units 72Y, 72C, 72M, 72B, a secondary transfer unit 73, and a belt cleaning unit 74. The intermediate transfer belt 71 is disposed above the four image forming units 6. The intermediate transfer belt 71 is rotatably supported in a predetermined direction (counterclockwise in FIG. 1), and is an endless intermediate transfer member on which the toner images formed by each of the four image forming units 6 are sequentially superimposed and primarily transferred. The four image forming units 6 are arranged in a so-called tandem manner in a row from the upstream side to the downstream side in the rotation direction of the intermediate transfer belt 71.

[0019] The primary transfer units 72Y, 72C, 72M, 72B are disposed above the image forming units 6Y, 6C, 6M, 6B of each color, sandwiching the intermediate transfer belt 71. The secondary transfer unit 73 is upstream of the fixing device 8 with respect to the sheet conveyance direction of the sheet conveyance unit 4, and is disposed downstream of the four image forming units 6Y, 6C, 6M, 6B with respect to the rotation direction of the intermediate transfer belt 71. The belt cleaning unit 74 is disposed downstream of the secondary transfer unit 73 with respect to the rotation direction of the intermediate transfer belt 71.

[0020] The primary transfer unit 72 transfers the toner image formed on the outer peripheral surface of the photosensitive drum to the intermediate transfer belt 71. In other words, the toner image is primarily transferred to the outer peripheral surface of the intermediate transfer belt 71 by the primary transfer units 72Y, 72C, 72M, and 72B for each color. Then, as the intermediate transfer belt 71 rotates, the toner images of the four image forming units 6 are continuously superimposed and transferred to the intermediate transfer belt 71 at a predetermined timing, whereby a color toner image in which toner images of four colors, yellow, cyan, magenta, and black, are superimposed is formed on the outer peripheral surface of the intermediate transfer belt 71.

[0021] The color toner image on the outer peripheral surface of the intermediate transfer belt 71 is transferred to the sheet S that has been sent in synchronization by the sheet conveyance unit 4 at the secondary transfer nip formed in the secondary transfer unit 73. The belt cleaning unit 74 removes and cleans the deposits such as toner remaining on the outer peripheral surface of the intermediate transfer belt 71 after secondary transfer. In this way, the transfer unit 7 transfers (records) the toner image formed on the outer peripheral surface of the photosensitive drum to the sheet S.

[0022] The fixing device 8 is disposed above the secondary transfer unit 73. The fixing device 8 heats and presses the sheet S to which the toner image has been transferred to fix the toner image to the sheet S.

[0023] The sheet discharge unit 9 is disposed above the transfer unit 7. The sheet S on which the toner image has been fixed and the printing is completed is conveyed to the sheet discharge unit 9. The sheet discharge unit 9 allows the printed sheet (printed matter) to be taken out from above.

[0024] The control unit 10 includes a CPU, an image processing unit, a memory unit, and other electronic circuits and electronic components (none of which are shown). The CPU controls the operation of each component provided in the image forming apparatus 1 based on control programs and data stored in the memory unit, and performs processing related to the functions of the image forming apparatus 1. The sheet supply unit 3, sheet transport unit 4, exposure unit 5, image forming unit 6, transfer unit 7, and fixing unit 8 each receive individual commands from the control unit 10 and perform printing on the sheet S in conjunction. The memory unit is composed of a combination of a non-volatile memory device (not shown), such as a program ROM (Read Only Memory) or data ROM, and a volatile memory device (not shown), such as a RAM (Random Access Memory).

[0025] Next, the configuration of the fixing device 8 of the embodiment will be described in detail. Figure 2 is a cross-sectional front view of the fixing device 8 of the image forming apparatus 1 of Figure 1. Figure 3 is a side view of the cut end of the fixing device 8 of the image forming apparatus 1 of Figure 1.

[0026] For the sake of explanation, Figures 2 and 3 depict a configuration in which the fixing belt 81 is positioned above the fixing nip section N and the pressure roller (pressure member) 82 is positioned below it. In Figure 2, the right side is the upstream side (transfer section 7 side) in the sheet transport direction relative to the fixing device 8, and the left side is the downstream side (sheet discharge section 9 side) in the sheet transport direction relative to the fixing device 8. Figure 2 is a cross-sectional view along line II-II in Figure 3, and Figure 3 is a cross-sectional end view along line III-III in Figure 2.

[0027] As shown in Figures 2 and 3, the fixing device 8 includes a fixing belt 81, a pressure roller 82, a heating unit 83, a nip forming member 84, a sliding member 85, a support member 86, and a belt guide 87.

[0028] The fixing belt 81 is supported in the housing of the fixing device 8 so as to be rotatable around a horizontal axis. The fixing belt 81 is endless and consists of a cylindrical shape with an outer diameter of, for example, 20 mm to 50 mm, and is longer than the pressure roller 82 in the direction of the rotation axis (the sheet width direction perpendicular to the sheet transport direction, the paper depth direction in Figure 2, and the left and right lateral directions in Figure 3). The fixing belt 81 is rotatable along the transport direction of the sheet S, which is the recording medium.

[0029] The fixing belt 81 has a laminated structure in which an elastic layer and a release layer are provided on the outer periphery of the heating layer, which is the base layer. The heating layer is composed of, for example, a metal film such as nickel with a thickness of 30 [μm] to 50 [μm], or a polyimide film with a thickness of 50 [μm] to 100 [μm] mixed with metal powder such as copper, silver, or aluminum. The elastic layer is composed of, for example, silicone rubber with a thickness of 100 [μm] to 500 [μm]. The release layer is composed of, for example, a fluororesin such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) with a thickness of 30 [μm] to 50 [μm]. The fixing belt 81 is heated by the heating section 83.

[0030] The pressure roller 82 is supported in the housing of the fixing device 8 so as to be rotatable around a horizontal axis. The pressure roller 82 is cylindrical in shape and is shorter than the fixing belt 81 in the direction of the rotation axis (sheet width direction, paper depth direction in Figure 2, left-right lateral direction in Figure 3).

[0031] A predetermined pressure is applied to the pressure roller 82 toward the fixing belt 81 by a pressure mechanism (not shown). As a result, the pressure roller 82 comes into contact with the outer surface of the fixing belt 81. In other words, it comes into contact with the nip-forming member 84 with a predetermined pressure, sandwiching the sliding member 85 and the fixing belt 81. A fixing nip portion N is formed between the pressure roller 82 and the fixing belt 81.

[0032] The pressure roller 82 is connected to a drive source (not shown), for example, a motor, and rotates counterclockwise in Figure 2, receiving power from the motor. The pressure roller 82 contacts the outer surface of the fixing belt 81, providing rotational driving force to the fixing belt 81. The fixing belt 81 rotates clockwise in Figure 2, following the rotation of the pressure roller 82. The operation of the fixing belt 81 is controlled by the control unit 10.

[0033] The pressure roller 82 has a laminated structure in which an elastic layer and a release layer are provided on the outer circumference of the core metal. The core metal is made of a metal such as iron or aluminum with a diameter of 20 to 25 mm. The elastic layer is made of a material such as silicone rubber with a thickness of 3 to 8 mm and an outer diameter of 30 to 35 mm. The release layer is made of a fluororesin such as PFA with a thickness of approximately 10 to 50 μm.

[0034] The heating unit 83 is positioned opposite the side of the fixing belt 81 where the pressure roller 82 is located, with a predetermined gap between it and the outer circumferential surface of the fixing belt 81. The heating unit 83 extends longer than the fixing belt 81 and the belt guide 87 along the rotation axis direction (sheet width direction) of the fixing belt 81.

[0035] The heating section 83 comprises an excitation coil 831 and a holding member, a core, etc., which are not shown. The excitation coil 831 and the core are held in a predetermined position relative to the fixing belt 81 by the holding member. The excitation coil 831 is made of Litz wire, which is made by bundling multiple conductors together, and is wound so as to extend along the rotation axis direction (sheet width direction) of the fixing belt 81. The excitation coil 831 is configured in an arc shape along the outer circumferential surface of the fixing belt 81 in the circumferential direction of the fixing belt 81.

[0036] The heating unit 83 heats the fixing belt 81 by electromagnetic induction. More specifically, the heating unit 83 heats the fixing belt 81 by inductive heating of the heating layer of the fixing belt 81. The heating unit 83 may also be composed of a halogen heater that extends over the entire area in the rotational axis direction of the fixing belt 81 and is positioned close to the inner circumferential surface of the fixing belt 81 at the fixing nip portion N.

[0037] The nip-forming member 84 is positioned radially inward of the fixing belt 81, with a sliding member 85 sandwiched between it and the inner circumferential surface of the fixing belt 81. The nip-forming member 84 is positioned opposite the pressure roller 82, separated by the sliding member 85 and the fixing belt 81. The nip-forming member 84 contacts the inner circumferential surface of the fixing belt 81 via the sliding member 85, forming a fixing nip portion N between the fixing belt 81 and the pressure roller 82.

[0038] The nip-forming member 84 has a substantially rectangular parallelepiped shape that extends along the rotational axis direction (sheet width direction) of the fixing belt 81 and is approximately the same length as the fixing belt 81. The nip-forming member 84 has a base material made of, for example, a metal such as aluminum or a heat-resistant resin such as a liquid crystal polymer. The nip-forming member 84 may have an elastic layer made of, for example, an elastomer or silicone rubber on the side of the base material facing the fixing belt 81.

[0039] The sliding member 85 is positioned adjacent to the radially inward side of the fixing belt 81 at the fixing nip portion N. The sliding member 85 is sandwiched between the inner circumferential surface of the fixing belt 81 and the nip forming member 84. The sliding member 85 comes into contact with the inner circumferential surface of the rotating fixing belt 81 as it slides. The sliding member 85 is a sheet-like member with a thickness of approximately 0.5 mm. The sliding member 85 aims to reduce the sliding load between the inner circumferential surface of the fixing belt 81 and the nip forming member 84.

[0040] The support member 86 is positioned radially inward of the fixing belt 81. The support member 86 extends longer than the fixing belt 81 along the rotational axis direction (sheet width direction) of the fixing belt 81. The support member 86 is held by side plates (not shown) provided on both outer sides in the rotational axis direction of the fixing belt 81, ensuring sufficient strength to apply pressure between the support member 86 and the pressure roller 82. The support member 86 is composed of, for example, a rectangular tubular member and supports the nip forming member 84 between itself and the inner surface of the fixing belt 81.

[0041] The belt guide 87 is positioned radially inward of the fixing belt 81, facing the heating section 83 with the fixing belt 81 in between. The belt guide 87 contacts the inner circumferential surface of the fixing belt 81, excluding the fixing nip section N, and supports the fixing belt 81 from the radially inward side. The belt guide 87 is made of sheet metal that extends along the rotation axis direction (sheet width direction) of the fixing belt 81 and has approximately the same length as the fixing belt 81.

[0042] The belt guide 87 is made of an elastic magnetic metal such as SUS430 with a thickness of 0.1 mm to 0.5 mm. The belt guide 87 plays a role in stabilizing the rotational trajectory of the anchor belt 81 and in improving the efficiency of heating the anchor belt 81 by absorbing the magnetic field that penetrates the anchor belt 81 and generating heat.

[0043] With the above configuration, the fixing device 8 inserts the sheet S into the fixing nip section N between the fixing belt 81 and the pressure roller 82, and fixes the toner image formed on the sheet S to the sheet S by heating and pressurizing it.

[0044] Next, the detailed configuration of the nip-forming member 84 and the sliding member 85 will be described. Figure 4 is a top view of the nip-forming member 84 of the fixing device 8 in Figure 2. Figure 5 is a plan view of the sliding member 85 (flat state) of the fixing device 8 in Figure 2. In Figures 3 and 4, the direction indicated by the arrow Dw is the rotation axis direction (sheet width direction) of the fixing belt 81, and the direction indicated by the arrow Dc is the rotation direction (sheet conveying direction) of the fixing belt 81. The rotation axis direction (sheet width direction) Dw of the fixing belt 81 and the rotation direction (sheet conveying direction) Dc of the fixing belt 81 are orthogonal to each other.

[0045] As shown in Figures 2 and 4, the nip-forming member 84 has a projection 841. The projection 841 is formed on the side of the nip-forming member 84 opposite to the fixing nip portion N. In other words, the projection 841 is formed on the surface of the nip-forming member 84 facing the support member 86.

[0046] Multiple projections 841 are formed on the surface facing the support member 86, arranged side by side in the rotational direction Dc and the rotational axis direction Dw of the fixing belt 81. In this embodiment, the nip forming member 84 has 12 projections 841, as shown in Figure 4. More specifically, the 12 projections 841 consist of 6 projections arranged side by side in the rotational axis direction Dw of the fixing belt 81, and 2 rows arranged side by side in the rotational direction Dc of the fixing belt 81. The projections 841 are oval-shaped (long elliptical) in plan view, extending in the rotational axis direction Dw of the fixing belt 81, and protruding toward the support member 86.

[0047] The support member 86 has connection holes 861 formed on the surface facing the nip-forming member 84. The connection holes 861 face the projections 841 of the nip-forming member 84 in the radial direction of the fixing belt 81. Twelve connection holes 861 are formed on the surface facing the nip-forming member 84, the same number as the twelve projections 841. The connection holes 861 have a shape, size, and arrangement (positional relationship) that allows the projections 841 to be inserted. The support member 86 supports the nip-forming member 84 by allowing each projection 841 to be individually inserted into each connection hole 861.

[0048] As shown in Figures 2 and 5, the sliding member 85 has a coupling hole 851. Figure 5 shows the sheet-like sliding member 85 unfolded into a flat state. In its flat state, the sliding member 85 has a rectangular shape in plan view, extending in the rotational direction Dc and the rotational axis direction Dw of the fixing belt 81.

[0049] The coupling holes 851 are formed at both ends of the sheet-like sliding member 85 in the rotational direction Dc of the fixing belt 81. As shown in Figure 5, in each region of the sliding member 85 at both ends in the rotational direction Dc of the fixing belt 81, there are 12 coupling holes 851, the same number as the 12 protrusions 841. The 12 coupling holes 851 are arranged side by side in the rotational direction Dc and the rotational axis direction Dw of the fixing belt 81. The coupling holes 851 are oval-shaped (long elliptical) in plan view, extending in the rotational axis direction Dw of the fixing belt 81, similar to the protrusions 841. The coupling holes 851 have a shape, size, and arrangement (positional relationship) that allows the protrusions 841 to be inserted. The coupling holes 851 penetrate the sheet-like sliding member 85 in the thickness direction.

[0050] The sheet-like sliding member 85 is substantially cylindrical in shape and extends in the rotational axis direction Dw of the fixing belt 81, and covers the periphery of the nip-forming member 84 by being wrapped around it (see Figure 2). At this time, the sheet-like sliding member 85 is wrapped around the nip-forming member 84, with one end and the other end of the fixing belt 81 overlapping in the opposing region between the support member 86 and the nip-forming member 84 in the rotational direction Dc.

[0051] When the sliding member 85 is wrapped around the nip forming member 84, the 12 coupling holes 851 formed at each end of the sliding member 85 in the rotation direction Dc of the fixing belt 81 overlap. The projections 841 are inserted into the coupling holes 851. More specifically, with respect to each of the 12 projections 841, the projection 841 is inserted continuously into the coupling hole 851 at one end of the sliding member 85 in the rotation direction Dc of the fixing belt 81 and into the coupling hole 851 at the other end.

[0052] With the above configuration, the sliding member 85 can be positioned so as to face the inner circumferential surface of the fixing belt 81, extending from the upstream region to the downstream region of the fixing nip portion N with respect to the rotational direction Dc of the fixing belt 81. This makes it possible to effectively reduce the sliding load between the inner circumferential surface of the fixing belt 81 and the nip forming member 84.

[0053] Next, the more detailed configuration of the nip-forming member 84 will be described. Figure 6 is a partially enlarged view of the fixing device 8 in Figure 3. Figure 6 is a partially enlarged view of the area of ​​circle A in Figure 3.

[0054] The nip-forming member 84 has a surface with irregularities 842. The surface with irregularities 842 is the surface of the nip-forming member 84 facing the sliding member 85, and is formed on the contact surface of the nip-forming member 84 with the sliding member 85. The surface with irregularities 842 is a region in which the convex and concave portions facing the sliding member 85 repeatedly extend in the radial direction of the fixing belt 81. The surface with irregularities 842 is formed, for example, by blasting or by molding.

[0055] According to the above configuration, the frictional resistance between the sliding member 85 and the nip-forming member 84 can be increased, and the relative displacement of the sliding member 85 with respect to the nip-forming member 84 can be suppressed. In other words, the sliding member 85 can be fixed in the fixing nip portion N. This suppresses the displacement (deformation) of the sliding member 85 as the fixing belt 81 rotates. Therefore, it is possible to prevent problems such as damage to the sliding member 85 and poor rotation of the fixing belt 81.

[0056] The unevenness of the uneven portion 842 should be such that the height difference (height of the protrusions) is necessary to fix the sliding member 85 at the fixing nip portion N. If the height difference (height of the protrusions) of the uneven portion 842 is less than a predetermined value, there is a risk that the sliding member 85 cannot be fixed at the fixing nip portion N. As a result, the sliding member 85 will be more likely to be displaced (deformed) as the fixing belt 81 rotates, which may lead to problems such as damage to the sliding member 85 or poor rotation of the fixing belt 81.

[0057] On the other hand, if the height difference of the unevenness of the uneven portion 842 (the height of the protrusions) is excessively large, there is a concern that the pressure on the protrusions of the uneven portion 842 may become too high, potentially damaging and breaking the fixing belt 81. In addition, there is a risk that the pressure between the pressure roller 82 and the fixing belt 81 in the fixing nip portion N may become too high, potentially adversely affecting the image (toner image) on the sheet S.

[0058] Therefore, it is necessary to appropriately set the height difference of the unevenness of the uneven portion 842 (height of the protrusions). Figure 7 is a graph showing the relationship between the height difference of the unevenness of the uneven portion 842 (height of the protrusions) and the number of sheets S that can pass through the fixing nip portion N.

[0059] More specifically, the horizontal axis of the graph in Figure 7 uses the "protruding peak height Rpk [μm]" which is a surface texture parameter specified in JIS B 0671-2:2002, to evaluate the height difference of the irregularities (height of the protrusions) of the irregularities 842. The vertical axis of the graph in Figure 7 shows the number of sheets S that can pass through the fixing nip section N before the sliding member 85 breaks (lifespan).

[0060] As shown in Figure 7, the dashed lines in the figure indicate the number of sheets S that can pass through the fixing nip section N corresponding to each value of the protruding peak height Rpk of the uneven section 842 (lifetime). The protruding peak height Rpk of the uneven section 842 must be such that, as a performance requirement for the fixing device 8, the number of sheets S that can pass through the fixing nip section N (lifetime) is at least 100,000. Furthermore, as mentioned above, the protruding peak height Rpk of the uneven section 842 should not be made unnecessarily large.

[0061] The surface texture parameter "Protruding peak height Rpk" mentioned above represents the height of the peak region, which has multiple wedge-shaped peaks that constitute the surface roughness of the object. In order for the irregularities of the uneven portion 842 of the nip-forming member 84 to bite sufficiently into the sliding member 85 and increase the frictional force, the protruding peak height Rpk of the uneven portion 842 must be at least 2.5 [μm]. Furthermore, in order for the irregularities of the uneven portion 842 to not damage the sliding member 85, the protruding peak height Rpk of the uneven portion 842 must be kept below 500 [μm].

[0062] Therefore, based on Figure 7, the height Rpk of the protruding peaks of the uneven portion 842 was configured to be 2.5 [μm] or more and less than 500 [μm]. This configuration makes it possible to increase the frictional resistance between the sliding member 85 and the nip forming member 84, and to suppress the relative displacement of the sliding member 85 with respect to the nip forming member 84. In other words, it is possible to fix the sliding member 85 at the fixing nip portion N. This makes it possible to suppress the displacement (deformation) of the sliding member 85 as the fixing belt 81 rotates. Therefore, it is possible to prevent the occurrence of problems such as damage to the sliding member 85 and poor rotation of the fixing belt 81.

[0063] Furthermore, based on Figure 7, it is preferable that the height Rpk of the protruding peaks of the uneven portion 842 is 5.0 [μm] or more and less than 500 [μm]. With this configuration, the frictional resistance between the sliding member 85 and the nip-forming member 84 can be significantly increased, and the effect of suppressing the relative displacement of the sliding member 85 with respect to the nip-forming member 84 can be enhanced. As a result, the number of sheets S that can pass through the fixed nip portion N before the sliding member 85 breaks (lifespan) exceeds 150,000 sheets, thereby improving safety against breakage of the sliding member 85.

[0064] Furthermore, it is preferable that the uneven portion 842 is formed over the entire contact area with the sliding member 85 on the contact surface of the nip forming member 84 with the sliding member 85. With this configuration, the sliding member 85 becomes less susceptible to displacement (deformation), and the effect of suppressing the relative displacement of the sliding member 85 with respect to the nip forming member 84 can be improved. This makes it possible to enhance the effect of suppressing the displacement (deformation) of the sliding member 85 as it rotates with the fixing belt 81.

[0065] Furthermore, the sliding member 85 is made of a fibrous material. Specifically, the sliding member 85 is made of, for example, heat-resistant fibers and a fluororesin such as PTFE (polytetrafluoroethylene). In addition, if the sliding surface of the sliding member 85 with the fixing belt 81 is made of a fluororesin, it may also be constructed by weaving in PPS (polyphenylene sulfide) fibers or the like for reinforcement.

[0066] While the fibrous member is effective in reducing the sliding load between the inner circumferential surface of the anchoring belt 81 and the nip-forming member 84, it can be prone to deformation as the anchoring belt 81 rotates. Therefore, with the above configuration, even if the sliding member 85 is made of a fibrous member and stretched by being pulled downstream as the anchoring belt 81 rotates, it is possible to suppress an increase in the contact area between the sliding member 85 and the anchoring belt 81.

[0067] Furthermore, if the sliding member 85 is made of fiber material, it may shrink due to heating of the fixing belt 81. As a result, in addition to the stretching force in the downstream direction mentioned above, an inward force due to shrinkage in the rotational axis direction (longitudinal direction) will also be generated at the outer ends of the parts of the sliding member 85 that engage with the coupling holes 851 at both ends. Consequently, the fibers constituting the sliding member 85 may fray from the coupling holes 851.

[0068] Therefore, as in the configuration of the above embodiment, by setting the height Rpk of the protruding peaks Rpk of the uneven portion 842 of the nip-forming member 84 to 2.5 [μm] or more and less than 500 [μm], it becomes possible to suppress the shrinkage of the sliding member 85 due to heating. This prevents fraying of the fibers constituting the sliding member 85 due to the shrinkage of the sliding member 85. Consequently, it is possible to prevent the occurrence of problems such as damage to the sliding member 85 and poor rotation of the fixing belt 81.

[0069] Although embodiments of the present invention have been described above, the scope of the present invention is not limited thereto, and various modifications can be made to implement the invention without departing from the spirit of the invention.

[0070] For example, in the above embodiment, the image forming apparatus 1 is a so-called tandem-type color printing image forming apparatus that sequentially superimposes images of multiple colors, but it is not limited to such a model. The image forming apparatus may be a color printing image forming apparatus that is not of the tandem type, or a monochrome printing image forming apparatus. [Industrial applicability]

[0071] The present invention can be used in fixing devices and image forming devices. [Explanation of Symbols]

[0072] 1. Image forming apparatus 2. Main unit of the device 6 Image forming unit 8. Fixing device 81 Fixing belt 82 Pressure roller (pressure component) 83 Heating section 84 Nip forming member 85 Sliding member 86 Support Member 87 Belt Guide 841 Protrusion 842 Uneven part 851 Joint hole Dc Rotation direction Dw Rotation axis direction N Fixing nip section S Seat

Claims

1. An endless fixing belt that is heated by a heating unit and rotates along the direction of recording medium transport, A sheet-like sliding member is positioned adjacent to the radially inward side of the fixing belt, and the inner circumferential surface of the rotating fixing belt comes into contact with it while sliding. A nip-forming member is positioned radially inward of the fixing belt, sandwiching the sliding member between it and the inner circumferential surface of the fixing belt, A support member is positioned radially inward of the fixing belt and supports the nip forming member, A pressing member that contacts the nip-forming member with a predetermined pressure, sandwiching the sliding member and the fixing belt, to form a fixing nip portion between itself and the fixing belt, A fixing apparatus comprising a fixing nip portion, wherein a recording medium is inserted into the fixing nip portion and heated and pressurized to fix a toner image formed on the recording medium to the recording medium, The nip-forming member has an uneven surface formed on the contact surface with the sliding member, The fixing device is characterized in that the height Rpk of the protruding peaks of the uneven portion is 2.5 [μm] or more and less than 500 [μm].

2. The fixing device according to claim 1, characterized in that the height Rpk of the protruding peaks of the uneven portion is 5.0 [μm] or more and less than 500 [μm].

3. The fixing device according to claim 1, characterized in that the uneven portion is formed over the entire area of ​​the contact region with the sliding member.

4. The nip-forming member has a projection formed on the side opposite to the fixing nip portion, The fixing device according to claim 1, characterized in that the sliding member is formed at both ends in the rotational direction of the fixing belt and has coupling holes into which the projection is inserted.

5. The recording medium includes an image forming unit that forms a toner image, A fixing apparatus according to any one of claims 1 to 4, wherein the recording medium on which the toner image has been formed by the image forming unit is heated and pressurized to fix the toner image to the recording medium, An image forming apparatus characterized by comprising:

Images