Heating device, fixing device, image forming apparatus

Abstract

To prevent the generation of wrinkles in a body to be heated.SOLUTION: A heating device comprises: a heater 22 that has a substrate 30 and a resistance heating element 31 arranged while being divided into plurality; a fixing belt 20; and a pressure roller 21 that applies pressure to the fixing belt 20. When the amount of increase in an outer diameter of the pressure roller 21 from a center position C0 toward ends of a heating area of the heater 22 in an arrangement direction X is an outer diameter increase amount of the pressure roller 21, the pressure roller 21 has, in the arrangement direction X, outer diameter increase amount large areas J2 that are areas closer to the center of the heating area of the heater 22 than a center position B0 of a division area between the resistance heating elements 31 and including a position corresponding to the division area between the resistance heating elements 31, and an outer diameter increase amount small area J1 that is an area closer to the center of the heating area of the heater 22 than the outer diameter increase amount large areas J2. The outer diameter increase amount large areas J2 have a larger amount of increase in outer diameter than that of the outer diameter increase amount small area J1.SELECTED DRAWING: Figure 15

Description

[Technical field]

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

[0002] A fixing device (heating device) that uses heat to fix a toner image on paper (heated object) is provided with a planar heating element having a resistive heating element on a substrate, a fixing belt as a rotating member, and a pressure roller as a pressure member that applies pressure to the fixing belt.

[0003] For example, in Patent Document 1 (JP 2020-86277 A), a heater (heating element) has a plurality of resistance heating elements arranged in a manner that divides the heater into several parts in the longitudinal direction. In such a fixing device, the amount of heat generated by the heater is small at positions corresponding to the divided areas of the resistance heating elements, and the temperatures of the fixing belt and pressure roller are also small.

[0004] In a fixing device, paper wrinkles occur when the paper (heated object) passes through the fixing nip formed between the fixing belt and the pressure roller. By increasing the outer diameter of the pressure roller from the center toward the end in the axial direction, a force is applied to the paper passing through the fixing nip toward the end in the width direction, thereby suppressing the occurrence of paper wrinkles. Summary of the Invention [Problem to be solved by the invention]

[0005] The objective is to suppress the occurrence of wrinkles in a heated object. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, the present invention provides a heating device including a base material, a heating body having a resistance heating element divided into a plurality of parts and arranged, a rotating member, and a pressing member that presses the rotating member, wherein, when an amount by which the outer diameter of the pressing member increases from a center position side of a heating area of ​​the heating body toward an end side in an arrangement direction of the plurality of resistance heating elements is defined as an outer diameter increase amount of the pressing member, the pressing member has a large outer diameter increase amount region including at least a part of a range of 10 mm to 30 mm toward the center of the heating area of ​​the heating body from the center position of the divided areas between the resistance heating elements in the arrangement direction of the plurality of resistance heating elements, and a small outer diameter increase amount region provided in a range of 20 mm from the center position of the heating area toward the end side of the heating area in the arrangement direction of the plurality of resistance heating elements, and the large outer diameter increase amount region has a larger outer diameter increase amount than the small outer diameter increase amount region. The resistance heating element is formed by folding back a linear portion, and the folding angle of the linear portion is an acute angle. It is characterized by: Effect of the Invention

[0007] The occurrence of wrinkles in the heated object can be suppressed. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of an image forming apparatus. [Diagram 2] FIG. 2 is a schematic diagram of a fixing device. [Diagram 3] FIG. [Figure 4] FIG. 4 is a diagram showing power supply to a heater. [Diagram 5] FIG. 4 is a plan view of a heater having a resistive heating element with a different shape from that of FIG. 3. [Figure 6] FIG. 6 is a plan view of a heater having a resistive heating element with a different shape from those in FIGS. 3 and 5. [Figure 7] FIG. 4 is a plan view showing divided regions between the resistive heating elements. [Figure 8] FIG. 4 is a diagram showing a temperature distribution in the arrangement direction of a fixing belt and a pressure roller. [Figure 9] FIG. 6 is a diagram showing divided regions of the heater in FIG. 5. [Figure 10]FIG. 9 is a diagram showing divided regions of resistance heating elements having a different shape from that in FIG. 8. [Figure 11] FIG. 7 is a diagram showing divided regions of the heater in FIG. 6. [Figure 12] FIG. 4 is a plan view of a pressure roller different from the embodiment. [Figure 13] 13 is a diagram showing an outer diameter profile in the arrangement direction of the pressure roller before and after thermal expansion. FIG. [Figure 14] FIG. 2 is a plan view of the pressure roller according to the first embodiment. [Figure 15] 15 is a diagram showing the outer diameter profile in the arrangement direction of the pressure roller in FIG. 14 before and after thermal expansion. [Figure 16] 13A and 13B are diagrams illustrating outer diameter profiles in the arrangement direction of a pressure roller according to a second embodiment before and after thermal expansion. [Figure 17] 13A and 13B are diagrams illustrating outer diameter profiles in the arrangement direction of a pressure roller according to a third embodiment before and after thermal expansion. [Figure 18] FIG. 13 is a diagram showing divided regions of a heater in which a plurality of resistive heating elements are arranged in the short side direction. [Figure 19] FIG. 7 is a diagram showing the folding angle of the heater in FIG. 6. [Figure 20] FIG. 13 is a diagram showing a heater holder having a protrusion. [Figure 21] FIG. 13 is a plan view showing a heater having a different configuration. [Figure 22] FIG. 4 is a side cross-sectional view showing a schematic configuration of a fixing device different from the above. [Diagram 23] FIG. 4 is a side cross-sectional view showing a schematic configuration of a fixing device different from the above. [Figure 24] FIG. 2 is a schematic diagram illustrating a configuration of an image forming apparatus different from that in FIG. [Diagram 25] 1 is a side cross-sectional view showing a schematic configuration of a fixing device according to an embodiment of the present invention. [Figure 26] 22 is a plan view of a heater in the fixing device of FIG. 21. [Figure 27] FIG. 2 is a perspective view of a heater and a heater holder. [Figure 28]FIG. 4 is a perspective view showing a state in which a connector is attached to a heater. [Figure 29] FIG. 2 is a diagram showing the arrangement of a thermistor and a thermostat. [Diagram 30] FIG. 4 is a diagram showing a groove portion of a flange. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and the duplicated description will be appropriately simplified or omitted. Hereinafter, a fixing device provided in an image forming apparatus will be described as a heating device according to one embodiment of the present invention.

[0010] FIG. 1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention.

[0011] The image forming apparatus 100 shown in FIG. 1 includes four imaging units 1Y, 1M, 1C, and 1Bk that are detachable from the image forming apparatus main body. The imaging units 1Y, 1M, 1C, and 1Bk have the same configuration except that they contain different color developers, namely, yellow, magenta, cyan, and black. These color developers correspond to the color separation components of a color image. Each imaging unit 1Y, 1M, 1C, and 1Bk includes a drum-shaped photoconductor 2 as an image carrier, a charging device 3, a developing device 4, and a cleaning device 5. The charging device 3 charges the surface of the photoconductor 2. The developing device 4 supplies toner as a developer to the surface of the photoconductor 2 to form a toner image. The cleaning device 5 cleans the surface of the photoconductor 2.

[0012] The image forming apparatus 100 also includes an exposure device 6, a paper feeder 7, a transfer device 8, a fixing device 9, and a paper discharge device 10. The exposure device 6 exposes the surface of each photoconductor 2 to light and forms an electrostatic latent image on the surface. The paper feeder 7 supplies paper P as a recording medium to a paper transport path 14. The transfer device 8 transfers the toner image formed on each photoconductor 2 to the paper P. The fixing device 9 fixes the toner image transferred to the paper P to the surface of the paper P. The paper discharge device 10 discharges the paper P to the outside of the apparatus. The imaging units 1, the photoconductor 2, the charging device 3, the exposure device 6, the transfer device 8, etc. constitute an image forming means for forming an image on paper.

[0013] The transfer device 8 has an endless intermediate transfer belt 11 as an intermediate transfer body, four primary transfer rollers 12 as primary transfer members, and a secondary transfer roller 13 as a secondary transfer member. The intermediate transfer belt 11 is stretched by a plurality of rollers. The primary transfer rollers 12 transfer the toner images on the photoconductors 2 to the intermediate transfer belt 11. The secondary transfer rollers 13 transfer the toner images transferred onto the intermediate transfer belt 11 to a sheet of paper P. Each of the primary transfer rollers 12 contacts the photoconductors 2 via the intermediate transfer belt 11. As a result, the intermediate transfer belt 11 and each photoconductor 2 come into contact with each other, and a primary transfer nip is formed between them. Meanwhile, the secondary transfer roller 13 contacts one of the rollers stretching the intermediate transfer belt 11 via the intermediate transfer belt 11. As a result, a secondary transfer nip is formed between the secondary transfer roller 13 and the intermediate transfer belt 11.

[0014] Further, a pair of timing rollers 15 is provided on the paper transport path 14 between the paper feeder 7 and the secondary transfer nip (secondary transfer roller 13).

[0015] Next, the printing operation of the image forming apparatus will be described with reference to FIG.

[0016] When an instruction to start a printing operation is given, in each of the imaging units 1Y, 1M, 1C, and 1Bk, the photoconductor 2 is rotated clockwise in FIG. 1, and the surface of the photoconductor 2 is charged to a uniform high potential by the charging device 3. Next, the exposure device 6 exposes the surface of each photoconductor 2 based on the image information of the original document read by the original reading device or the print information instructed to be printed from the terminal. This reduces the potential of the exposed portion, forming an electrostatic latent image. Then, toner is supplied from the developing device 4 to this electrostatic latent image, and a toner image is formed on each photoconductor 2.

[0017] The toner images formed on each photoconductor 2 rotate with the rotation of each photoconductor 2 and reach the primary transfer nip (the position of the primary transfer roller 12). The toner images are transferred to the intermediate transfer belt 11, which rotates counterclockwise in FIG. 1, so as to be superimposed one on the other. The toner images transferred onto the intermediate transfer belt 11 are transported to the secondary transfer nip (the position of the secondary transfer roller 13) with the rotation of the intermediate transfer belt 11. The toner images are transferred to the paper P transported at the secondary transfer nip. This paper P is supplied from the paper feeder 7. The paper P supplied from the paper feeder 7 is stopped once by the timing roller 15, and then transported to the secondary transfer nip in accordance with the timing at which the toner image on the intermediate transfer belt 11 reaches the secondary transfer nip. Thus, a full-color toner image is carried on the paper P. After the toner image is transferred, the toner remaining on each photoconductor 2 is removed by each cleaning device 5.

[0018] The paper P onto which the toner image has been transferred is transported to a fixing device 9, which fixes the toner image onto the paper P. Thereafter, the paper P is discharged outside the apparatus by a paper discharge device 10, completing a series of printing operations.

[0019] Next, the configuration of the fixing device will be described.

[0020] As shown in FIG. 2, the fixing device 9 according to the present embodiment includes a fixing belt 20 as a rotating member or fixing member, a pressure roller 21 as a counter rotating member or pressure member, a heater 22 as a heating body, a heater holder 23 as a holding member, a stay 24 as a supporting member, a thermistor 25 as a temperature detecting member, a thermostat, and the like. The fixing belt 20 is an endless belt. The pressure roller 21 contacts the outer peripheral surface of the fixing belt 20 to form a fixing nip N between the fixing belt 20 and the pressure roller 21. The heater 22 heats the fixing belt 20. The heater holder 23 holds the heater 22. The stay 24 supports the heater holder 23. The thermistor 25 detects the temperature of the back surface of the substrate 30. The direction perpendicular to the paper surface of FIG. 2 is the longitudinal direction of the fixing belt 20, the pressure roller 21, the heater 22, the heater holder 23, the stay 24, and the like, and hereinafter, this direction will be simply referred to as the longitudinal direction. This longitudinal direction corresponds to the width direction of the paper being transported, the width direction of the fixing belt 20, and the axial direction of the pressure roller 21.

[0021] The fixing belt 20 has a tubular substrate (base material) made of polyimide, for example, with an outer diameter of 25 mm and a thickness of 40 to 120 μm. A release layer made of fluororesin such as PFA or PTFE and having a thickness of 5 to 50 μm is formed on the outermost surface of the fixing belt 20 in order to increase durability and ensure releasability. An elastic layer made of rubber or the like and having a thickness of 50 to 500 μm may be provided between the substrate and the release layer. The substrate of the fixing belt 20 is not limited to polyimide, and may be a heat-resistant resin such as PEEK or a metal substrate such as nickel (Ni) or SUS. The inner peripheral surface of the fixing belt 20 may be coated with polyimide, PTFE, or the like as a sliding layer.

[0022] The pressure roller 21 is composed of a solid iron core 21a, an elastic layer 21b, and a release layer 21c. The iron core 21a is formed with an outer diameter of, for example, 25 mm. The elastic layer 21b is formed on the surface of the core 21a. The elastic layer 21b is formed of silicone rubber and has a thickness of, for example, 3.5 mm. The release layer 21c is formed on the outside of the elastic layer 21b. In order to improve the releasability of the pressure roller 21, it is desirable to form the release layer 21c from a fluororesin layer having a thickness of, for example, about 40 μm.

[0023] The pressure roller 21 is urged toward the fixing belt 20 by the urging means, so that the pressure roller 21 is pressed against the heater 22 via the fixing belt 20. As a result, a fixing nip N is formed between the fixing belt 20 and the pressure roller 21. The pressure roller 21 is configured to be rotationally driven by a driving means, and when the pressure roller 21 rotates in the direction of the arrow in FIG. 2, the fixing belt 20 is rotated accordingly.

[0024] The heater 22 is a planar heating element provided across the width direction of the fixing belt 20. The heater 22 is composed of a plate-shaped base material 30, a resistance heating element 31 provided on the base material 30, an insulating layer 32 covering the resistance heating element 31, and the like. The heater 22 is in contact with the inner circumferential surface of the fixing belt 20 on the insulating layer 32 side, and heat generated from the resistance heating element 31 is transferred to the fixing belt 20 through the insulating layer 32. In this embodiment, the resistance heating element 31 and the insulating layer 32 are provided on the fixing belt 20 side (fixing nip N side) of the base material 30, but conversely, the resistance heating element 31 and the insulating layer 32 may be provided on the heater holder 23 side of the base material 30. In that case, since the heat of the resistance heating element 31 is transferred to the fixing belt 20 through the base material 30, it is desirable that the base material 30 is made of a material with high thermal conductivity such as aluminum nitride. Furthermore, by forming the base material 30 from a material with high thermal conductivity, even if the resistance heating element 31 is disposed on the opposite side of the base material 30 from the fixing belt 20 side, it is possible to sufficiently heat the fixing belt 20.

[0025] The heater holder 23 and the stay 24 are disposed on the inner circumferential side of the fixing belt 20. The stay 24 is made of a metal channel material, and both ends thereof are supported by both side plates of the fixing device 9. The heater holder 23 and the heater 22 are supported by the stay 24, so that the heater 22 can reliably receive the pressing force of the pressure roller 21 in a state in which the pressure roller 21 is pressed against the fixing belt 20. As a result, the fixing nip N is stably formed between the fixing belt 20 and the pressure roller 21. In this embodiment, the thermal conductivity of the heater holder 23 is set to be smaller than that of the base material 30.

[0026] The heater holder 23 is desirably formed of a heat-resistant material because it is likely to become hot due to the heat of the heater 22. For example, when the heater holder 23 is formed of a heat-resistant resin with low thermal conductivity such as LCP, the heat transfer from the heater 22 to the heater holder 23 is suppressed. This allows the heater 22 to heat the fixing belt 20 efficiently.

[0027] The heater holder 23 is provided with guide portions 26 for guiding the fixing belt 20. The guide portions 26 are provided on the upstream side (below the heater 22 in FIG. 2) and downstream side (above the heater 22 in FIG. 2) of the belt rotation direction of the heater 22. The upstream and downstream guide portions 26 are arranged at intervals in the longitudinal direction of the heater 22. Each guide portion 26 is formed in a substantially fan shape and has a belt facing surface 260 in the shape of an arc or a convex curved surface extending in the belt circumferential direction so as to face the inner circumferential surface of the fixing belt 20.

[0028] The heater holder 23 has a plurality of openings 23a in the longitudinal direction. The openings 23a are openings that penetrate the heater holder 23 in the thickness direction. The thermistor 25 and a thermostat, which will be described later, are provided in the openings 23a. The thermistor 25 and the thermostat are pressed against the back surface of the substrate 30 by a spring 29.

[0029] In the fixing device 9 according to the present embodiment, when a printing operation is started, the pressure roller 21 is driven to rotate, and the fixing belt 20 starts to rotate by the pressure roller 21. At this time, the inner circumferential surface of the fixing belt 20 contacts and is guided by the belt facing surface 260 of the guide portion 26, so that the fixing belt 20 rotates stably and smoothly. In addition, the fixing belt 20 is heated by supplying power to the resistance heating element 31 of the heater 22. Then, in a state in which the temperature of the fixing belt 20 has reached a predetermined target temperature (fixing temperature), as shown in FIG. 2, a sheet P carrying an unfixed toner image is conveyed between the fixing belt 20 and the pressure roller 21 (fixing nip N), so that the unfixed toner image is heated and pressurized to be fixed to the sheet P. The fixing belt 20 is a member to be heated by the heater 22. In addition, the sheet P is a heated body to be heated in the fixing nip N.

[0030] FIG. 3 is a plan view of the heater according to the present embodiment.

[0031] 3, a plurality of (four) resistance heating elements 31, power supply lines 33A and 33B as conductors, a first electrode portion 34A and a second electrode portion 34B are provided on the surface of a plate-shaped base material 30. However, the number of resistance heating elements 31 is not limited to that in this embodiment.

[0032] In this embodiment, the resistance heating element 31 provided in the heater 22 is divided into multiple parts and arranged in the longitudinal direction. Each resistance heating element 31 is connected in parallel. In this manner, in this embodiment, the longitudinal direction of the heater 22, etc. (direction perpendicular to the paper surface of FIG. 2) is also the arrangement direction X of the multiple resistance heating elements 31. Hereinafter, the arrangement direction of the multiple resistance heating elements 31 is also simply referred to as the arrangement direction. In addition, the vertical direction Y in FIG. 3, which is a direction intersecting the arrangement direction (perpendicular in this embodiment) and different from the thickness direction of the base material 30, is also referred to as the direction intersecting the arrangement direction of the multiple resistance heating elements 31, or simply as the arrangement intersecting direction. In this embodiment, the arrangement direction is the same direction as the longitudinal direction, and the arrangement intersecting direction is also referred to as the longitudinal intersecting direction. The arrangement intersecting direction Y is a direction along the surface of the base material 30 on which the resistance heating elements 31 are provided, and is also the short-side direction of the heater 22, or the transport direction of the paper passed through the fixing device 9.

[0033] A heating section 35 divided into a plurality of parts in the arrangement direction is formed by a plurality of resistance heating elements 31. Each resistance heating element 31 is electrically connected in parallel to a pair of electrode parts 34A, 34B provided at one end of the substrate 30 in the arrangement direction (the left end in FIG. 3) via power supply lines 33A, 33B. The power supply lines 33A, 33B are made of a conductor having a smaller resistance value than the resistance heating element 31. From the viewpoint of ensuring insulation between the resistance heating elements 31, the gap between adjacent resistance heating elements 31 is preferably 0.2 mm or more, and more preferably 0.4 mm or more. Moreover, if the gap between adjacent resistance heating elements 31 is too large, a temperature drop is likely to occur in the gap. For this reason, from the viewpoint of suppressing temperature unevenness across the arrangement direction, the gap is preferably 5 mm or less, and more preferably 1 mm or less.

[0034] The region of the heater 22 where the resistance heating elements 31 are arranged in the arrangement direction is the region where the heater 22 mainly performs heating, and hereinafter this region is referred to as the heating region C of the heater 22. The heating region C is a region including the gaps between the resistance heating elements 31 (see FIG. 5). Also, the straight line C0 in FIG. 3 indicates the center position of the heating region C.

[0035] The resistance heating element 31 is made of a material having a PTC (positive temperature coefficient of resistance) characteristic, and is characterized in that the resistance value increases (heater output decreases) as the temperature increases.

[0036] The resistance heating element 31 has a PTC characteristic, and the heating section 35 is divided in the arrangement direction, so that the fixing belt 20 can be prevented from overheating when small-sized paper is passed through. In other words, when paper narrower than the entire width of the heating section 35 is passed through, the paper does not take heat from the fixing belt 20 in the area outside the paper width, so the temperature of the resistance heating element 31 corresponding to that part rises. Since the voltage applied to the resistance heating element 31 is constant, when the temperature of the resistance heating element 31 outside the paper width rises and its resistance value rises, the output (heat generation amount) decreases relatively, and the end temperature rise is suppressed. In addition, since the multiple resistance heating elements 31 are electrically connected in parallel, the temperature rise of the non-paper passing part can be suppressed while maintaining the printing speed. The heating element constituting the heating section 35 may be other than the resistance heating element having the PTC characteristic. In addition, the resistance heating elements may be arranged in multiple rows in the arrangement crossing direction of the heaters 22.

[0037] The resistance heating element 31 can be formed, for example, by applying a paste made of silver palladium (AgPd) and glass powder to the substrate 30 by screen printing or the like, and then firing the substrate 30. In this embodiment, the resistance heating element 31 has a resistance value of 80 Ω at room temperature. In addition to the above-mentioned materials, the resistance heating element 31 can be made of silver alloy (AgPt) or ruthenium oxide (RuO 2 The power supply line 33 and the electrode portion 34 may be made of silver (Ag) or silver-palladium (AgPd) by screen printing or the like. The power supply line 33 is made of a conductor having a smaller resistance value than the resistance heating element 31.

[0038] As the material of the substrate 30, ceramics such as alumina and aluminum nitride, which have excellent heat resistance and insulation, and non-metallic materials such as glass and mica are preferable. In this embodiment, an alumina substrate having a width of 8 mm in the cross direction of the array, a width of 270 mm in the array direction, and a thickness of 1.0 mm is used. Alternatively, the substrate 30 may be formed by laminating an insulating material onto a conductive material such as a metal. As the metal material of the substrate 30, aluminum and stainless steel are preferable because they are low cost. By forming the substrate 30 from a stainless steel plate, cracks due to thermal stress can be suppressed. In addition, the substrate 30 may be formed from a material with high thermal conductivity such as copper, graphite, and graphene in order to improve the thermal uniformity of the heater 22 and increase the image quality.

[0039] The insulating layer 32 is made of heat-resistant glass having a thickness of, for example, 75 μm. The insulating layer 32 covers the resistance heating element 31 and the power supply line 33, insulates and protects them, and maintains the sliding property with the fixing belt 20.

[0040] FIG. 4 is a diagram showing a power supply circuit to the heater according to the present embodiment.

[0041] 4, in this embodiment, a power supply circuit for supplying power to each resistance heating element 31 is configured by electrically connecting an AC power source 200 and the electrodes 34A, 34B of the heater 22. The power supply circuit is also provided with a triac 210 for controlling the amount of power supplied. The amount of power supplied to each resistance heating element 31 is controlled by a control unit 220 via the triac 210 based on the temperature detected by the thermistor 25. The control unit 220 is configured with a microcomputer including a CPU, a ROM, a RAM, an I / O interface, etc.

[0042] In this embodiment, the thermistors 25 are disposed in a central region in the arrangement direction of the heaters 22, which is within the minimum paper passing width, and at one end side in the arrangement direction of the heaters 22. Furthermore, at one end side in the arrangement direction of the heaters 22, a thermostat 27 is disposed as a power cut-off means for cutting off the power supply to the resistance heating element 31 when the temperature of the resistance heating element 31 becomes equal to or higher than a predetermined temperature. The thermistor 25 and thermostat 27 come into contact with the back surface of the substrate 30 to detect the temperature.

[0043] In this embodiment, the first electrode portion 34A and the second electrode portion 34B are provided on the same side in the arrangement direction, but may be provided on different sides. The shape of the resistance heating element 31 is not limited to that of this embodiment. For example, as shown in FIG. 5, the resistance heating element 31 may be rectangular, or as shown in FIG. 6, the resistance heating element 31 may be formed by folding back a linear portion. In FIG. 6, as an example, the resistance heating element 31 is formed into a substantially parallelogram shape by the linear portion. As shown in FIG. 5, a portion extending from the block-shaped resistance heating element 31 toward the power supply line 33 (a portion extending in the arrangement crossing direction) may be a part of the resistance heating element 31, or may be made of the same material as the power supply line 33.

[0044] Incidentally, by dividing the resistance heating element 31 into several parts and arranging them in the longitudinal direction as shown in Fig. 7, it is possible to suppress excessive temperature rise in the heater 22 and non-paper passing areas of the fixing belt 20 as described above. However, on the other hand, in the divided area B between the resistance heating elements 31 shown in the enlarged view of Fig. 7, it is smaller than the range occupied by the resistance heating element 31 and other heated areas, and the amount of heat generated by the heater 22 is small. Note that the divided area B of the resistance heating element 31 means the arrangement direction area including all the parts divided in the arrangement direction of the resistance heating element 31, which is the main heat generating part of the heater 22. Also, the straight line B0 in Fig. 7 indicates the center position of the divided area B.

[0045] 8 is a diagram showing the temperature distribution in the arrangement direction of the fixing belt 20 and the pressure roller 21 heated by the heater 22. The horizontal axis represents the arrangement direction X, and the vertical axis represents the temperature T. In the diagram, the solid line represents the temperature of the fixing belt 20, and the dashed line represents the temperature of the pressure roller 21.

[0046] As shown in FIG. 8, the temperatures of fixing belt 20 and pressure roller 21 are low at positions corresponding to divided region B in the arrangement direction and in the vicinity thereof, resulting in temperature unevenness in the arrangement direction.

[0047] 9, the temperature of divided region B is lower than the other portions in heater 22 having resistive heating element 31 of rectangular shape shown in FIG. 5. The temperature of divided region B is lower than the other portions in heater 22 having resistive heating element 31 of shape shown in FIG. 10. The temperature of divided region B is lower than the other portions in heater 22 having resistive heating element 31 of shape shown in FIG. 6. However, by overlapping adjacent resistive heating elements 31 in the arrangement direction as shown in FIG. 7, 10 and 11, the temperature drop in divided region B with respect to the other portions can be suppressed.

[0048] Next, a problem caused by temperature unevenness of the pressure roller 21 will be described using a pressure roller 21 having a different shape from that of this embodiment shown in FIG.

[0049] 12 has an inverted crown shape in which the outer diameter gradually increases toward the ends (both ends of the heating area relative to the center position C0) of the heating area, with the center position C0 as the boundary. Hereinafter, the difference L between the outer diameter of the end of the arrangement direction of the pressure roller 21 and the outer diameter at the center position C0 of the heating area of ​​the pressure roller 21 will be referred to as the crown amount L. In addition, the side of the center position C0 of the pressure roller 21 will be referred to as the "inside" of the pressure roller 21, and the end sides of the pressure roller 21 relative to the center position C0 will be referred to as the "outside" of the pressure roller 21.

[0050] By forming the pressure roller 21 in this shape, the outer diameter of the pressure roller 21 increases toward the outside in the width direction, and it is possible to increase the force applied to the paper P. This makes it possible to apply an outward force in the width direction (arrangement direction) to the paper P passing through the fixing nip, and it is possible to prevent wrinkles from occurring in the paper being transported through the fixing nip.

[0051] However, when temperature unevenness occurs in the arrangement direction of the pressure roller 21 as described above, the thermal expansion amount of the pressure roller 21 differs in the arrangement direction, and the effect of suppressing paper wrinkles described above cannot be adequately obtained. The relationship between the thermal expansion amount of the pressure roller 21 and the effect of suppressing paper wrinkles will be described below.

[0052] FIG. 13 is a diagram showing the outer diameter profile of the pressure roller 21 in the arrangement direction due to thermal expansion. The horizontal axis of the diagram indicates the arrangement direction, and the vertical axis of the diagram indicates the outer diameter of the pressure roller 21. The straight line D1 shown in the lower part of the diagram is the outer diameter profile of the pressure roller 21 in the arrangement direction before thermal expansion (cold state), in other words, a diagram in which the size of the outer diameter is plotted continuously in the arrangement direction. The curve D2 shown in the upper part of the diagram indicates the outer diameter profile of the pressure roller 21 after thermal expansion, and the dashed line D3 indicates the outer diameter profile of the pressure roller 21 in the case where it is thermally expanded by an equal amount at each position in the arrangement direction. This is the same for the pressure roller 21 in FIG. 15 described later. Note that in FIG. 13 and FIG. 15 described later, the increase in the outer diameter of the pressure roller 21 is exaggerated for convenience.

[0053] The amount of increase in the outer diameter of the pressure roller 21 is defined as the amount of increase in the outer diameter of the pressure roller 21 from the center position C0 of the heating area C (see FIG. 3) toward either end of the heating area C. The amount of increase in the outer diameter can be calculated as the difference in the outer diameter in a certain section in the arrangement direction. The inclination of each of the lines D1 to D3 at each position in the arrangement direction can also be regarded as the absolute value of the amount of increase in the outer diameter at that position.

[0054] As shown in Fig. 13, the temperature of the pressure roller 21 is low in the arrangement direction at the center position B0 of the divided region and its surrounding area (see Fig. 8), so the amount of thermal expansion of the pressure roller 21 is also small in this range. In other words, the difference in value between the solid line D2 and the dashed dotted line D3 in Fig. 13 becomes large. As a result, the outer diameter of the pressure roller 21 does not gradually increase outward as shown by the solid line D2, and the pressure roller 21 becomes concave near the center position B0 of the divided region.

[0055] The deviation in the amount of thermal expansion of the pressure roller 21 also causes a bias in the force that the pressure roller 21 applies to the paper P at each position in the arrangement direction. This bias causes paper wrinkles to occur in the paper P transported through the fixing nip N. In particular, the bias in the force applied to the paper P becomes large at the maximum point E shown in FIG. 13, making the paper wrinkles more likely to occur.

[0056] The maximum point E is the position where the slope of the solid line D2 in Fig. 13 is reversed (the position where the slope changes from the slope where the outer diameter increases toward the outside to the slope where the outer diameter decreases toward the outside). That is, in a configuration where the force applied to the paper P increases toward the outside, like the pressure roller 21 of the solid line D1 in Fig. 13, a force in the stretching direction (the direction toward the outside of the arrangement direction) can be uniformly applied to the paper P. In contrast, in the pressure roller 21 of the solid line D2 in Fig. 13, in the range inside the center position B0 of the outer divided area, the outer diameter of the pressure roller 21 becomes smaller toward the outside, in contrast to the other ranges. That is, the force applied to the paper P decreases toward the outside. Therefore, a force in the outward direction (the direction in which the paper P is stretched) is applied to the paper P inside the maximum point E, and a force in the inward direction (the direction in which the paper P is contracted) is applied to the paper P outside the maximum point E. Therefore, at the maximum point E, forces in two opposing directions (stretching and shrinking directions) are applied to the paper P, causing paper wrinkles.

[0057] Next, the pressure roller 21 of this embodiment will be described. As shown in Fig. 14, the pressure roller 21 of this embodiment has a small outer diameter increase region J1 on the inside in the arrangement direction and a large outer diameter increase region J2 on the outside in the arrangement direction. The small outer diameter increase region J1 has a relatively larger outer diameter increase than the large outer diameter increase region J2. The outer diameter increase of the small outer diameter increase region J1 and the large outer diameter increase region J2 is constant in the arrangement direction. That is, the pressure roller 21 has a larger outer diameter increase on the outside in the arrangement direction than on the inside in the arrangement direction, with an inflection point 21d provided midway in the arrangement direction as a boundary.

[0058] In this embodiment, the inflection point 21d is provided inside the position corresponding to the maximum point E. That is, in the case of the pressure roller 21 where the amount of increase in the outer diameter is constant as shown in FIG. 12, the inflection point 21d is provided inside the position corresponding to the position where the amount of increase in the outer diameter is reversed.

[0059] As described above, in the region inside the center position B0 of the divided region in the arrangement direction, the increase in the outer diameter of the pressure roller 21 is reversed to negative due to thermal expansion. In contrast, in this embodiment, as described above, the increase in the outer diameter of the region inside the center position B0 of the divided region (specifically, the region inside the center position B0 of the divided region and outside the region J1) is made larger relative to the increase in the outer diameter of the region inside it (specifically, the region J1). In this way, by setting the increase in the outer diameter in the region inside the center position B0 of the divided region to be large in advance in consideration of the deviation in the amount of thermal expansion of the pressure roller 21, it is possible to suppress the drop in the increase in the outer diameter inside the center position B0 of the divided region, and to suppress the occurrence of paper wrinkles. Specifically, as shown in FIG. 15, the difference between the curve D2 and the straight line D3 can be reduced in the range from the inflection point 21d to the center position B0 of the divided region. This reduces the force acting in the inward direction on the paper P, and suppresses the occurrence of paper wrinkles.

[0060] The occurrence of paper wrinkles can be suppressed by making the amount of increase in outer diameter of at least a part of the divided region inside the center position B0 of the divided region between the resistance heating elements in the pressure roller 21 larger relative to the amount of increase in outer diameter of the region inside this region. Note that the center position B0 of the divided region between the resistance heating elements referred to here is the center position B0 of the divided region provided in the heater 22 that is provided at a position different from the center position C0 of the heating region, and is the center position B0 of the two outer divided regions.

[0061] Alternatively, the occurrence of paper wrinkles can be suppressed by making the increase in outer diameter of at least a portion of the region in the range of 10 to 30 mm inside the central position B0 of the dividing region between the resistive heating elements relatively larger than the increase in outer diameter of a region 20 mm outside the central position C0 of the heating region.

[0062] Moreover, it is preferable that the inflection point 21d is located at a position outside the position 30 mm inside from the center position B0 of the division area between the resistance heating elements. If the inflection point 21d is located too far inside, the range of the large outer diameter increase amount area J2 will be wide and the crown amount L will be too large. Therefore, the force applied to the paper P will be too large and the behavior of the paper P will be unstable when passing through the fixing nip N. This will cause the toner image on the surface of the paper P to come into contact with other members, causing an abnormal image. However, by locating the inflection point 21d as described above, the force applied to the paper P can be suppressed.

[0063] The position of inflection point 21d is not limited to the arrangement in Fig. 15. However, inflection point 21d is preferably provided at a position corresponding to maximum point E or further inside. For example, in the embodiment shown in Fig. 16, inflection point 21d is provided at a position outside Fig. 15 and corresponding to maximum point E (see Fig. 12). This makes it possible to obtain the effect of suppressing paper wrinkles as described above, while also reducing the range of the large outer diameter increase region and reducing the amount of crowning.

[0064] 17 has a second small outer diameter increase region J3 outside the large outer diameter increase region J2. That is, the pressure roller 21 has another inflection point 21d2 in addition to the inner inflection point 21d1, and has a second small outer diameter increase region J3 outside the other inflection point 21d2. In the pressure roller 21 of this embodiment, the outer diameter increase increases once in the large outer diameter increase region J2 outside the innermost small outer diameter increase region J1, and then the outer diameter increase decreases again in the second small outer diameter increase region J3 outside the large outer diameter increase region J2.

[0065] As shown in Figures 15 and 16, if the entire region outside the inflection point 21d is set as the large outer diameter increase region J2, the occurrence of paper wrinkles can be suppressed, but the crown amount L becomes large. Therefore, in this embodiment, only the region where the outer diameter increase amount needs to be particularly large, that is, the region inside the center position B0 of the divided region, is set as the large outer diameter increase region J2, and the region outside that is set as the second small outer diameter increase region J3. This makes it possible to suppress the occurrence of paper wrinkles and minimize the crown amount L. However, by setting at least a part of the region outside the center position B0 of the divided region as the small outer diameter increase region J3, the crown amount L can be reduced.

[0066] Moreover, these configurations of the pressure roller 21 are suitable for application to a fixing device having a configuration in which the base of the fixing belt 20 is made of a resin material such as polyimide as in this embodiment. In other words, if the thermal conductivity of the fixing belt 20 is low, heat is less likely to be conducted in the arrangement direction. Therefore, temperature unevenness in the arrangement direction is likely to occur in the fixing belt 20 and the pressure roller 21 due to a drop in temperature in the divided area B between the resistance heating elements 31. Therefore, deviations in the amount of thermal expansion of the pressure roller 21 are also likely to occur, so it is suitable to apply the configuration of the pressure roller 21 of this embodiment.

[0067] Furthermore, these configurations of the pressure roller 21 are suitable for application to a fixing device in which the thermal conductivity of the base material 30 of the heater 22 is low. In other words, if the thermal conductivity of the base material 30 is low, heat conduction in the arrangement direction becomes difficult. Therefore, temperature unevenness in the arrangement direction of the pressure roller 21 is likely to occur due to temperature drops in the divided regions B between the resistance heating elements 31. Therefore, deviations in the amount of thermal expansion of the pressure roller 21 are likely to occur, so it is suitable to apply the configuration of the pressure roller 21 of this embodiment. Specifically, it is suitable to apply the configuration of the pressure roller 21 of this embodiment to a fixing device in which the thermal conductivity of the base material 30 is 100 W / m·K or less.

[0068] Next, a method for calculating the thermal conductivity will be described. When calculating the thermal conductivity, first, the thermal diffusivity of the object is measured, and then the thermal conductivity is calculated using the measured thermal diffusivity.

[0069] The thermal diffusivity was measured using a thermal diffusivity / thermal conductivity measuring device (product name: ai-Phase Mobile 1u, ai-Phase Corporation).

[0070] In order to convert the thermal diffusivity to thermal conductivity, the values ​​of density and specific heat capacity are necessary. A dry automatic density meter (product name: Accupyc 1330, manufactured by Shimadzu Corporation) was used to measure the density. A differential scanning calorimeter (product name: DSC-60, manufactured by Shimadzu Corporation) was used to measure the specific heat capacity, and sapphire was used as a reference material with a known specific heat capacity. In this embodiment, the specific heat capacity was measured five times, and the average value at 50°C was used. If the density and specific heat capacity are ρ and C, respectively, the thermal conductivity λ can be obtained from the thermal diffusivity α obtained by the thermal diffusivity measurement by the following formula 1.

[0071]

number

[0072] Even in a configuration in which a heat equalizing plate (high thermal conductive member) made of a member with high thermal conductivity such as a metal material is not provided as in the present embodiment, temperature unevenness is likely to occur in the arrangement direction of the pressure roller 21. Therefore, it is preferable to apply the configuration of the pressure roller 21 of the present embodiment to a fixing device with such a configuration. Furthermore, compared to a configuration in which the heater 22 contacts the inner surface of the fixing belt 20 via other members such as the heat equalizing plate or a sliding sheet, a configuration in which the heater 22 contacts the fixing belt 20 directly is more likely to cause temperature unevenness in the arrangement direction of the fixing belt 20 and the pressure roller 21. Therefore, it is preferable to apply the configuration of the pressure roller 21 of the present embodiment to a fixing device with such a configuration.

[0073] Moreover, the heater 22 of this embodiment is provided with a thickness of 1.0 mm. A heater 22 with a small thickness, specifically, a heater 22 with a thickness of 1.1 mm or less, has a small thermal capacity, and is prone to temperature unevenness in the arrangement direction of the heater 22. In other words, temperature unevenness in the arrangement direction is prone to occur in the fixing belt 20 and the pressure roller 21. Therefore, deviations in the amount of thermal expansion of the pressure roller 21 are also likely to occur, and therefore it is preferable to apply the configuration of the pressure roller 21 of this embodiment.

[0074] 18, a plurality of resistance heating elements 31 are provided in the short side direction. Specifically, the heater 22 has a first row in the short side direction, which is made up of a plurality of resistance heating elements 31A, and a second row in the short side direction, which is made up of a plurality of resistance heating elements 31B. The first row and the second row refer to rows in which a plurality of resistance heating elements 31 are provided in the longitudinal direction. In the case of the heater 22 of this embodiment, the arrangement direction of the heater 22 refers to the longitudinal direction of the heater 22, and the arrangement crossing direction refers to the short side direction of the heater 22.

[0075] The divided area B1 between the resistance heating elements 31A in the first row and the divided area B2 between the resistance heating elements 31B in the second row overlap in the longitudinal direction. In the heater 22 having such a configuration, the temperature of the pressure roller 21 is particularly likely to drop at the position corresponding to the divided area between the resistance heating elements. Therefore, it is preferable to apply the above-mentioned configuration of the pressure roller 21 to suppress paper wrinkles.

[0076] Furthermore, when the resistance heating element 31 is configured by folding back a linear portion, as in the heater 22 shown in Fig. 6, if the folding back angle of the folded back portion is an acute angle, the temperature drop in the divided region becomes large. In other words, as shown in Fig. 19, if the folding back angle α of a part of the folded back portion is an acute angle, the temperature drop is likely to occur in the acute angle portion. Therefore, it is preferable to apply the above-mentioned configuration of the pressure roller 21 to suppress paper wrinkles.

[0077] In the above-described configuration in which the outer diameter of the pressure roller 21 increases toward the outside, the crown amount L (see FIG. 12) increases, which may make it difficult for the pressure roller 21 to come into contact with the fixing belt 20 on the inside.

[0078] 20, in this embodiment, surface 23b of heater holder 23 on the heater 22 side (bottom surface of the recess that holds heater 22) protrudes toward pressure roller 21 further than the end sides at the center side in the arrangement direction. This allows fixing belt 20 to be made convex at the center side in the arrangement direction and to abut against the center part of pressure roller 21. Note that surface 23b has a convex shape at the center side in the assembly state when pressure roller 21 and fixing belt 20 are not in pressure contact with each other.

[0079] 21, in the heater 22 of this embodiment, three resistance heating elements 31 are provided across the arrangement direction of the substrate 30. One of the three resistance heating elements 31 constitutes a central heating section 35A as a first heating section arranged in the center of the arrangement direction of the substrate 30, and the remaining two constitute end heating sections 35B as second heating sections arranged on both sides of the central heating section 35A in the arrangement direction. The central heating section 35A and the end heating section 35B are configured so that heat generation can be controlled independently of each other.

[0080] In Fig. 21, assuming that the multiple electrode portions 34 are, from the left, a first electrode portion 34A, a second electrode portion 34B, a third electrode portion 34C, and a fourth electrode portion 34D, only the central heating portion 35A generates heat when a voltage is applied to the second electrode portion 34B and the fourth electrode portion 34D. Also, when a voltage is applied to the first electrode portion 34A and the second electrode portion 34B, only the end heating portion 35B on the left side of Fig. 21 generates heat, and when a voltage is applied to the second electrode portion 34B and the third electrode portion 34C, only the end heating portion 35B on the right side of Fig. 21 generates heat.

[0081] Furthermore, if the first electrode portion 34A and the third electrode portion 34C are connected in parallel externally so that a voltage can be applied simultaneously, it is possible to simultaneously heat both end heating portions 35B by applying a voltage to the electrodes 34A, 34C and the second electrode portion 34B. Note that the arrows in Fig. 21 indicate the direction of current flowing in the arrangement direction of the heating portions 35A, 35B.

[0082] When the width of the paper being passed is equal to or smaller than the width L1 of the central heating part 35A, only the central heating part 35A is heated, and when the width of the paper being passed is larger than the width L1 of the central heating part 35A, each end heating part 35B is heated in addition to the central heating part 35A, so that the size of the heating area can be changed according to the size of the paper passing area. Furthermore, by adjusting the width L1 of the central heating part 35A to the width of a small size paper (e.g., A4 paper width: 215 mm) and adjusting the width L2 of the heating area including one end heating part 35B to the other end heating part 35B to the width of a large size paper (e.g., A3 paper width: 301 mm), when these papers are passed, excessive temperature rise is unlikely to occur in the non-paper passing area (since there is almost no non-paper passing area on the heating parts 35A and 35B), so that printing productivity can be improved.

[0083] Even in the heater 22 described above, a drop in temperature occurs in the fixing belt 20 and the pressure roller 21 in the divided area B between the resistance heating elements 31. Therefore, by applying the configuration of the pressure roller 21 described above, the occurrence of paper wrinkles can be suppressed.

[0084] Although an embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

[0085] In addition to the fixing device described above, the present invention can also be applied to fixing devices as shown in Figures 22 and 23. The configuration of each fixing device shown in Figures 22 and 23 will be briefly described below.

[0086] First, in the fixing device 9 shown in FIG. 22, a pressure roller 44 is disposed on the opposite side of the fixing belt 20 from the pressure roller 21 side. The pressure roller 44 is a counter rotating member that rotates opposite the fixing belt 20 as a rotating member. The pressure roller 44 and the heater 22 are configured to sandwich and heat the fixing belt 20. On the other hand, on the pressure roller 21 side, a nip forming member 45 is disposed on the inner periphery of the fixing belt 20. The nip forming member 45 is supported by the stay 24. The nip forming member 45 and the pressure roller 21 sandwich the fixing belt 20 to form a fixing nip N.

[0087] 23, the above-mentioned pressure roller 44 is omitted, and in order to ensure the circumferential contact length between the fixing belt 20 and the heater 22, the heater 22 is formed in an arc shape in accordance with the curvature of the fixing belt 20. The rest of the configuration is the same as that of the fixing device 9 shown in FIG.

[0088] 22 and 23, the amount of heat generated by the heater 22 is small in the divided area B between the resistance heating elements 31 of the heater 22, and the amount of thermal expansion of the pressure roller 21 is small. Therefore, by providing the pressure roller 21 similar to the embodiment described above, the occurrence of paper wrinkles can be suppressed.

[0089] The image forming apparatus according to the present invention is not limited to the color image forming apparatus shown in FIG. 1, but may be a monochrome image forming apparatus, a copying machine, a printer, a facsimile, or a combination machine of these.

[0090] 24, for example, image forming apparatus 100 of this embodiment includes image forming means 50 including a photosensitive drum and the like, a paper transport section including a pair of timing rollers 15 and the like, paper feeder 7, fixing device 9, paper discharge device 10, and reading section 51. Paper feeder 7 includes multiple paper feed trays, each of which stores paper of a different size.

[0091] The reading unit 51 reads an image of the document Q. The reading unit 51 generates image data from the read image. The paper feeder 7 stores a plurality of sheets P and sends the sheets P to a conveying path. The timing rollers 15 convey the sheets P on the conveying path to the image forming means 50.

[0092] The image forming means 50 forms a toner image on the paper P. Specifically, the image forming means 50 includes a photosensitive drum, a charging roller, an exposure device, a developing device, a replenishing device, a transfer roller, a cleaning device, and a charge removing device. The toner image represents, for example, an image of an original Q. The fixing device 9 applies heat and pressure to the toner image to fix the toner image to the paper P. The paper P on which the toner image has been fixed is transported to the paper discharge device 10 by a transport roller or the like. The paper discharge device 10 discharges the paper P outside the image forming apparatus 100.

[0093] Next, a fixing device 9 of this embodiment will be described. Descriptions of configurations common to the fixing devices of the above-mentioned embodiments will be omitted as appropriate.

[0094] As shown in FIG. 25, the fixing device 9 includes a fixing belt 20, a pressure roller 21, a heater 22, a heater holder 23, a stay 24, a thermistor 25, and the like.

[0095] A fixing nip N is formed between the fixing belt 20 and the pressure roller 21. The nip width of the fixing nip N is 10 mm, and the linear speed of the fixing device 9 is 240 mm / s.

[0096] The fixing belt 20 has a polyimide base and a release layer, and does not have an elastic layer. The release layer is made of a heat-resistant film material such as fluororesin. The outer diameter of the fixing belt 20 is about 24 mm.

[0097] The pressure roller 21 includes a core metal 21a, an elastic layer 21b, and a release layer 21c. The pressure roller 21 has an outer diameter of 24 to 30 mm, and the elastic layer 21b has a thickness of 3 to 4 mm.

[0098] The heater 22 includes a base material, a heat insulating layer, a conductor layer including a resistance heating element, and an insulating layer, and is formed to have an overall thickness of 1 mm. The heater 22 has a width Y1 in the array cross direction of 13 mm.

[0099] As shown in FIG. 26, the conductor layer of the heater 22 includes a plurality of resistance heating elements 31, a power supply line 33, and electrode portions 34A to 34C. In this embodiment, as shown in the enlarged view of FIG. 26, the plurality of resistance heating elements 31 are divided in the arrangement direction to form divided regions B (however, in FIG. 26, only the divided regions B are illustrated in the enlarged view, but in reality, divided regions are provided between all of the resistance heating elements 31). The resistance heating elements 31 form three heat generating sections 35A, 35B1, and 35B2. By passing electricity through the electrode portions 34A and 34B, the heat generating sections 35B1 and 35B2 generate heat. By passing electricity through the electrode portions 34A and 34C, the heat generating section 35A generates heat. For example, when performing a fixing operation on a small size paper, the heat generating section 35A is made to generate heat, and when performing a fixing operation on a large size paper, all of the heat generating sections are made to generate heat.

[0100] As shown in Fig. 27, the heater holder 23 holds the heater 22 in its recess 23c. The recess 23c is provided on the heater 22 side of the heater holder 23. The recess 23c is composed of a surface 23c1 that is approximately parallel to the base material 30 and is recessed toward the stay 24 side more than the other surfaces of the heater 22, a wall portion 23c2 provided on the inside of the heater holder 23 on both sides in the arrangement direction of the heater holder 23 (or on one side), and a wall portion 23c3 provided on the inside of the heater holder 23 on both sides in the arrangement crossing direction. The heater holder 23 has a guide portion 26. The heater holder 23 is formed of LCP (liquid crystal polymer).

[0101] As shown in FIG. 28, a connector 70 includes a housing made of resin (for example, LCP), and a plurality of contact terminals provided inside the housing.

[0102] The connector 70 is attached so as to sandwich the heater 22 and the heater holder 23 from the front and back sides together. In this state, each contact terminal comes into contact (pressure-welded) with each electrode portion of the heater 22, electrically connecting the heat generating portion 35 and the power source provided in the image forming apparatus via the connector 70. This enables power to be supplied from the power source to the heat generating portion 35. Note that in order to ensure connection with the connector 70, at least a portion of each electrode portion 34 is not covered with an insulating layer and is exposed.

[0103] The flanges 53 are provided on both sides of the fixing belt 20 in the arrangement direction, and hold both ends of the fixing belt 20 from the inside of the belt. The flanges 53 are fixed to the housing of the fixing device 9. The flanges 53 are inserted into both ends of the stays 24 (see the arrow directions from the flanges 53 in FIG. 28).

[0104] The attachment direction of the connector 70 to the heater 22 and heater holder 23 is the direction that intersects the arrangement of the heaters (see the direction of the arrow from the connector 70 in FIG. 28). When the connector 70 is attached to the heater holder 23, a convex portion provided on one of the connector 70 and the heater holder 23 may be engaged with a concave portion provided on the other, and the convex portion may move relatively within the concave portion. The connector 70 is attached to the heater 22 and heater holder 23 on one side of the arrangement direction, opposite to the side on which the drive motor of the pressure roller 21 is provided.

[0105] 29, thermistors 25 are provided on the center side and end side of the arrangement direction of the fixing belt 20, facing the inner circumferential surface of the fixing belt 20. The heater 22 is controlled based on the temperatures on the center side and end side of the arrangement direction of the fixing belt 20 detected by the thermistor 25. Note that one of these thermistors 25 is provided at a position corresponding to a division area between the resistance heating elements of the heater 22, as in the above-mentioned embodiment.

[0106] Thermostats 27 are provided on the central side and end sides of the arrangement direction of fixing belt 20, facing the inner circumferential surface of fixing belt 20. When the temperature of fixing belt 20 detected by thermostat 27 exceeds a predetermined threshold value, power supply to heater 22 is stopped.

[0107] Flanges 53 are provided on both ends of the fixing belt 20 in the arrangement direction to hold the respective ends of the fixing belt 20. The flanges 53 are made of LCP (liquid crystal polymer).

[0108] 30, a slide groove 53a is provided in the flange 53. The slide groove 53a extends in the direction in which the fixing belt 20 approaches and separates from the pressure roller 21. An engagement portion of the housing of the fixing device 9 engages with the slide groove 53a. The engagement portion moves relatively within the slide groove 53a, so that the fixing belt 20 can move in the direction in which the fixing belt 20 approaches and separates from the pressure roller 21.

[0109] In the fixing device 9 described above, too, a drop in temperature occurs in the fixing belt 20 and the pressure roller 21 in the divided area B between the resistance heating elements 31. Therefore, by applying the configuration of the pressure roller 21 described above, the occurrence of paper wrinkles can be suppressed.

[0110] Examples of recording media or heated objects include paper P (plain paper), as well as cardboard, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheets, plastic film, prepreg, copper foil, and the like.

[0111] Furthermore, the present invention is not limited to the fixing device described in the above embodiment, but can also be applied to a drying device that dries ink applied to paper, and further to a heating device such as a laminator that thermocompresses a film as a covering member onto the surface of a sheet such as paper, or a heat sealer that thermocompresses the seal portion of a packaging material. By applying the present invention to such devices, the occurrence of wrinkles in the heated object can be suppressed. [Explanation of symbols]

[0112] 1. Image forming device 9 Fixing device (heating device) 20 Fixing belt (rotating member) 21 Pressure roller (pressure member) 21d Inflection point 22 Heater (heating element) 23 Heater holder (holding member) 30 Base material 31 Resistance heating element B Split area B0 Center position of the divided area C heating area C0 Center position of the heating area E local maximum point J1 Small outer diameter increase area J2 Large increase in outer diameter area P Paper (recording medium or heated object) X: Arrangement direction of multiple resistance heating elements Y array cross direction (longitudinal cross direction) [Prior art documents] [Patent documents]

[0113] [Patent Document 1] JP 2020-86277 A

Claims

1. A heating element having a base material and a plurality of divided and arranged resistive heating elements; A rotating member; A heating device including a pressure member that presses the rotating member, When the amount of increase in the outer diameter of the pressure member from the center position side to the end position side of the heating region of the heating element in the arrangement direction of the plurality of resistance heating elements is defined as an outer diameter increase amount of the pressure member, the pressure member has, in an arrangement direction of the plurality of resistance heating elements, a large outer diameter increase region including at least a part of a range of 10 mm to 30 mm toward the center of the heating region of the heating element from a center position of a dividing region between the resistance heating elements, and a small outer diameter increase region provided in a range of 20 mm from the center position of the heating region toward an end side of the heating region, the large outer diameter increase region has a larger outer diameter increase amount than the small outer diameter increase region, A heating device, wherein the resistance heating element is formed by folding back a linear portion, and the folding angle of the linear portion is an acute angle.

2. the pressure member has an inflection point at a position 10 mm or more away from a center position of a dividing region between the resistance heating elements toward a center position of a heating region of the heating element in an arrangement direction of the plurality of resistance heating elements, 2. The heating device according to claim 1, wherein, in an arrangement direction of the plurality of resistance heating elements, a region toward an end of the heating region of the heating elements from the inflection point is a region of large outer diameter increase, and a region toward a central position of the heating region of the heating elements is a region of small outer diameter increase, with the inflection point as a boundary.

3. 3. The heating device according to claim 2, wherein the inflection point is provided within a range of 10 mm to 30 mm from the center of the region separating the resistive heating elements toward the center of the heating region of the heating element.

4. A heating element having a base material and a plurality of divided and arranged resistive heating elements; A rotating member; A heating device including a pressure member that presses the rotating member, when an amount by which the outer diameter of the pressing member increases from the side of the center position of the heating region of the heating element toward the end side in the arrangement direction of the multiple resistance heating elements is defined as an outer diameter increase amount of the pressing member, the pressing member has a large outer diameter increase amount region which is a region that is closer to the center of the heating region of the heating element than the center position of the dividing region between the resistance heating elements in the arrangement direction of the multiple resistance heating elements and includes a position corresponding to the dividing region between the resistance heating elements, and a small outer diameter increase amount region which is a region closer to the center of the heating region of the heating element than the large outer diameter increase amount region, the large outer diameter increase region has a larger outer diameter increase amount than the small outer diameter increase region, A heating device, wherein the resistance heating element is formed by folding back a linear portion, and the folding angle of the linear portion is an acute angle.

5. In the arrangement direction of the plurality of resistance heating elements, another inflection point is provided closer to an end portion of the heating region of the heating element than a center position of a division region between the resistance heating elements, 5. The heating device according to claim 1, wherein in an arrangement direction of the plurality of resistance heating elements, an increase in outer diameter of an end region of the heating region of the heating element, which is separated from the other inflection point by another inflection point, is smaller than an increase in outer diameter of a central region of the heating region of the heating element.

6. A holding member for holding the heating body is provided, The heating device according to claim 1 , wherein a surface of the holding member facing the pressure member protrudes toward the pressure member at a center side in an arrangement direction of the plurality of resistance heating elements further toward the pressure member than at end sides.

7. 7. The heating device according to claim 1, wherein the heating element is made of a metal material and does not include a highly heat-conductive member in contact with the heating element.

8. The heating device according to claim 1 , wherein the base material of the rotating member is made of a resin material.

9. The arrangement direction of the plurality of resistance heating elements is the longitudinal direction of the heating element, If a direction along the surface of the base material on which the resistance heating element is provided and a direction intersecting the longitudinal direction is defined as a longitudinal intersecting direction, The heating element has a plurality of rows in a direction intersecting the longitudinal direction, in which a plurality of the resistance heating elements are arranged in the longitudinal direction, 9. The heating device according to claim 1, wherein a dividing region between the resistive heating elements in the longitudinal direction and a dividing region between the resistive heating elements in a different row in the direction crossing the longitudinal direction overlap in position in the longitudinal direction.

10. The heating device according to claim 1 , wherein the heating element is in direct contact with the rotating member.

11. 11. The heating device according to claim 1, wherein the heating element has a thickness of 1.1 mm or less.

12. 12. The heating device according to claim 1, wherein the base material has a thermal conductivity of 100 W / m·K or less.

13. 13. The heating device according to claim 1, which is a fixing device for fixing a toner image on a recording medium by heat.

14. An image forming apparatus comprising the heating device according to claim 1 .

Images