Heating device, fixing device, and image forming apparatus

Abstract

To increase the soaking properties of a heater (high-temperature member) without changing the outer shape of a soaking member.SOLUTION: A heating device comprises: a rotating member (fixing belt 20) that has an axial direction; a high-temperature member (heater 22) that is in contact with the rotating member to heat the rotating member along the axial direction; and a soaking member 28 that is in contact with the high-temperature member to increase the soaking properties of the high-temperature member in the axial direction. The soaking member 28 is formed of a plurality of materials different in heat capacity per unit volume.SELECTED DRAWING: Figure 9

Description

[Technical Field]

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

[0002] The fixing device (heating device) has a fixing belt (rotating member), a planar heater (high-temperature member) provided inside the fixing belt, a heat equalizing plate (heat equalizing member) that promotes heat transfer in the heater's longitudinal direction and suppresses temperature unevenness in the longitudinal direction, and a thermistor (temperature detection member) that detects the temperature of the heater, etc.

[0003] The temperature of the fixing belt just before it reaches the fixing nip is prevented from varying in the longitudinal direction (axial direction) by promoting heat transfer using a heat equalizer plate. However, conventional fixing devices still face problems such as poor fixing due to temperature sagging at the edge of the paper passing area and damage to the fixing belt due to excessive temperature rise in non-paper passing areas.

[0004] Therefore, various inventions have been proposed that promote temperature uniformity in the axial direction of the fixing belt by changing the shape of the heat equalizer plate. For example, in the invention of Patent Document 1 (JP 2022-54951 A), openings 28a are formed at both longitudinal ends of the heat equalizer 28, as shown in Figure 16. This results in regions α, β, and γ with different heat capacities being formed in the longitudinal direction of the heat equalizer 28. The heat capacities of the heat equalizer 28 are arranged in descending order as regions α, γ, and β.

[0005] The temperature of the fixing belt tends to drop at the edges of the paper passing area, but this is suppressed by reducing the heat capacity of area β. Also, by ensuring a certain heat capacity in area γ, excessive temperature rise in non-paper passing areas is also suppressed. However, when openings 28a are formed in the heat equalizing member 28, unresolved issues remain, such as insufficient strength at the openings 28a and uneven temperature distribution in the paper passing direction.

[0006] In addition, in the inventions of Patent Document 2 (Japanese Patent No. 6614816) and Patent Document 3 (Japanese Patent No. 7013433), by forming bent portions or recesses in parts of the heat spreader plate, the heat capacity per unit area of the first region including the bent portions is made larger than the heat capacity per unit area of the second region including the recessed portions. This is intended to suppress temperature rise at the edges, but conversely, this can cause problems such as insufficient heating of the first region where the bent portions are located and excessive heating of the second region where the recessed portions are located, making it necessary to take measures such as adjusting the heat generation amount by partially narrowing or widening the width of the heater's heat-generating portion. This requires specialized combinations of heat spreader plate and heater shapes, which requires the heaters to be custom-made, increasing costs.

[0007] 17, in the case of a heater 2 in which the first electrode portion 34A and the second electrode portion 34B are disposed at one end, the base material 2a of the heater 2 becomes longer in the longitudinal direction on the side where the connector CN is located (increasing the heat capacity). As a result, the heat capacity of the base material 2a becomes asymmetrical across the center of the heat generating element, which tends to cause uneven temperature distribution of the fixing belt.

[0008] Therefore, it is conceivable to suppress uneven temperature of the fixing belt by forming extensions 28b, 28c of different lengths on both ends of the heat equalizing member 28. However, forming a long extension 28c makes it difficult to reduce the size of the fixing device (heating device). Summary of the Invention [Problem to be solved by the invention]

[0009] In recent years, miniaturization of fixing devices has become mainstream, and it is necessary to shorten the dimensions of fixing devices, especially in the longitudinal direction (the direction perpendicular to the paper feed direction), as much as possible. However, if the heat equalizing plate is made of the same material as in Patent Documents 1 to 3, there is a problem that the fixing device becomes large. Therefore, the problem that this invention aims to solve is to improve the heat uniformity of the heater (high-temperature member) without changing the external shape of the heat equalizing member. [Means for solving the problem]

[0010] In order to solve the above-mentioned problems, the heating device of the present invention is a heating device including a rotating member having an axial direction, a high-temperature member that comes into contact with the rotating member and heats the rotating member along the axial direction, and a heat-equalizing member that comes into contact with the high-temperature member and improves the heat uniformity of the high-temperature member in the axial direction, wherein the heat-equalizing member is made of a plurality of materials with different heat capacities per unit volume. [Effects of the Invention]

[0011] According to the present invention, the temperature uniformity of the heater (high-temperature member) can be improved without changing the outer shape of the temperature uniformity member. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram illustrating the configuration of an image forming apparatus. [Figure 2] 1 is a side cross-sectional view showing a schematic configuration of a fixing device according to an embodiment of the present invention. [Figure 3] FIG. [Figure 4] FIG. 4 is a plan view of a heater having a different resistive heating element shape from that of FIG. 3. [Figure 5] FIG. 5 is a plan view of a heater having a resistance heating element with a different shape from those in FIGS. 3 and 4. [Figure 6] FIG. 2 is a plan view showing a heater in which resistance heating elements are connected in series. [Figure 7A] FIG. 10 is a diagram illustrating power supply to a heater. [Figure 7B] 10 is a flowchart showing a control operation of a heater. [Figure 8A] FIG. 2 is a perspective view showing a heater holder, a heat equalizing member, a heater, and a thermistor. [Figure 8B] FIG. 10 is a cross-sectional view showing a recess of a heater holder to which a temperature equalizing member and a heater are attached. [Figure 8C] FIG. 1(a) is a plan view showing a thermistor, and FIG. 1(b) is a diagram showing the back side of the thermistor and the insulation distance between the thermistor and the heat equalizing member. [Figure 9] 2A to 2C are diagrams showing (a) a first embodiment, (b) a second embodiment, and (c) a third embodiment of a temperature equalizing member. [Figure 10] 10A to 10D are diagrams showing (a) fourth, (b) fifth, (c) sixth, and (d) seventh embodiments of the temperature equalizing member. [Figure 11] 10A, 10B, and 10C are diagrams showing the temperature equalizing member according to an eighth, ninth, and tenth embodiments, respectively; [Figure 12] 10A to 10D are diagrams showing (a) an eleventh embodiment, (b) a twelfth embodiment, (c) a thirteenth embodiment, and (d) a fourteenth embodiment of a temperature equalizing member. [Figure 13] FIG. 2 is a side cross-sectional view showing a schematic configuration of a fixing device different from the above. [Figure 14] FIG. 2 is a side cross-sectional view showing a schematic configuration of a fixing device different from the above. [Figure 15] FIG. 2 is a side cross-sectional view showing a schematic configuration of a fixing device different from the above. [Figure 16] FIG. 10 is a plan view showing a heat equalizing plate of a conventional fixing device. [Figure 17] FIG. 10 is a plan view showing a heat equalizing plate and a heater of a conventional fixing device. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In each drawing, the same or corresponding parts are designated by the same reference numerals, and duplicated explanations will be appropriately simplified or omitted. Hereinafter, a fixing device that fixes an image on paper as a recording medium will be described as an example of a heating device of the present invention.

[0014] ●Outline of image forming device Fig. 1 is a schematic diagram of an image forming apparatus according to one embodiment of the present invention. 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. Each imaging unit 1Y, 1M, 1C, and 1Bk has the same configuration except that it contains a developer of a different color: yellow, magenta, cyan, or black.

[0015] These color developers correspond to the color separation components of the color image. Each of the imaging units 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.

[0016] The developing device 4 forms a toner image by supplying toner as a developer to the surface of the photoreceptor 2. The cleaning device 5 cleans the surface of the photoreceptor 2.

[0017] For example, inorganic photoreceptors such as amorphous silicon and selenium, and organic photoreceptors such as titanyl phthalocyanine can be used as the photoreceptor 2. Examples of the organic photoreceptor include a laminated photoreceptor having a laminated structure in which a layer (charge generation layer) in which a charge generation material such as metal-free phthalocyanine or titanyl phthalocyanine is dispersed in a binder resin and a layer (charge transport layer) in which a charge transport material is dispersed in a binder resin are stacked on a support such as an aluminum drum, and a single-layer photoreceptor having a single-layer photosensitive layer on a support in which both a charge generation material and a charge transport material are dispersed in a binder resin.

[0018] In the case of a single-layer photoreceptor, a hole transport material and an electron transport material may be added to the photosensitive layer as charge transport materials. An undercoat layer may be provided between the support and the multilayer charge generating layer or the single-layer photosensitive layer.

[0019] The image forming apparatus 100 also includes an exposure device 6, a paper feed device 7 as a recording medium supply unit, a transfer device 8, a fixing device 9 as a heating device, and a paper discharge device 10. The exposure device 6 exposes the surface of each photoconductor 2 to light to form an electrostatic latent image on that surface. The paper feed device 7 includes a paper feed tray 16 and a paper feed roller 17.

[0020] A paper feeder 7 supplies paper P as a recording medium to a paper transport path 14 as a transport path for the recording medium. A transfer device 8 transfers the toner image formed on each photoreceptor 2 onto the paper P. A fixing device 9 fixes the toner image transferred onto the paper P onto the surface of the paper P.

[0021] A paper discharge device 10 discharges the paper P outside the apparatus. The image forming units 1, photosensitive member 2, charging device 3, exposure device 6, transfer device 8, etc. constitute an image forming means for forming an image on paper.

[0022] 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.

[0023] The primary transfer rollers 12 transfer the toner images on the photoconductors 2 onto the intermediate transfer belt 11. The secondary transfer rollers 13 transfer the toner images transferred onto the intermediate transfer belt 11 onto paper P. Each of the multiple primary transfer rollers 12 is in contact with the photoconductor 2 via the intermediate transfer belt 11.

[0024] As a result, the intermediate transfer belt 11 and each photoconductor 2 come into contact with each other, forming a primary transfer nip therebetween. Meanwhile, the secondary transfer roller 13 comes into contact with one of the rollers that stretch 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.

[0025] An elastic intermediate transfer belt can also be used as the intermediate transfer body. For example, an elastic intermediate transfer belt can be formed by laminating a flexible elastic layer on a rigid base layer that provides relatively good flexibility. A guide member for preventing deviation of the intermediate transfer belt 11 can be provided on the inner peripheral surface of the intermediate transfer belt 11 to prevent the intermediate transfer belt 11 from meandering.

[0026] 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). A pair of rollers such as the timing rollers 15 provided on the paper transport path 14 is a transport member for transporting the paper P on the paper transport path 14.

[0027] ●Printing operation of image forming device Next, the printing operation of the image forming apparatus will be described with reference to Fig. 1. When an instruction to start the 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.

[0028] Next, the exposure device 6 exposes the surface of each photoconductor 2 based on the image information of the original read by the original reader or the print information instructed to be printed from the terminal. This reduces the potential of the exposed area, forming an electrostatic latent image. Toner is then supplied from the developing device 4 to this electrostatic latent image, forming a toner image on each photoconductor 2.

[0029] The toner images formed on each photoconductor 2 rotate with the rotation of the photoconductor 2 and reach the primary transfer nip (the position of the primary transfer roller 12). The toner images are then transferred onto the intermediate transfer belt 11, which rotates counterclockwise in FIG. 1, so as to be superimposed one on top of the other.

[0030] The toner image transferred onto the intermediate transfer belt 11 is then transported to the secondary transfer nip (the position of the secondary transfer roller 13) as the intermediate transfer belt 11 rotates. The toner image is transferred to the paper P that has been transported through the secondary transfer nip.

[0031] This paper P is supplied from paper supply tray 16. After being supplied from paper supply device 7, paper P is temporarily stopped by timing roller 15 and then conveyed to the secondary transfer nip in accordance with the timing at which the toner image on intermediate transfer belt 11 reaches the secondary transfer nip.

[0032] In this way, a full-color toner image is carried on the paper P. After the toner image is transferred, the toner remaining on each photoreceptor 2 is removed by each cleaning device 5.

[0033] 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. The paper P is then discharged outside the apparatus by a paper discharge device 10, completing the series of printing operations.

[0034] ●Configuration of the fixing device Next, the configuration of the fixing device will be described with reference to Fig. 2. As shown in Fig. 2, the fixing device 9 according to this embodiment includes a fixing belt 20, a pressure roller 21 as a pressure member (opposing member), a heater 22 as a high-temperature member, a heater holder 23 as a holding member, a stay 24 as a support member, a thermistor 25 as a temperature detection member, a heat equalizing member 28 as a high-thermal conductive member, a thermostat, etc. The fixing belt 20 is an endless belt.

[0035] The pressure roller 21 faces and contacts the outer peripheral surface of the fixing belt 20, forming a fixing nip N as a nip portion between the pressure roller 21 and the fixing belt 20. The heater 22 heats the fixing belt 20.

[0036] The heater holder 23 holds the heater 22. The stay 24 supports the heater holder 23. The thermistor 25 abuts against the back surface of the substrate 30 and detects the temperature thereof.

[0037] The fixing member provided in the fixing device is one aspect of the rotating member provided in the heating device. The fixing device 9 of this embodiment is provided with a fixing belt 20 as a specific example of the fixing member.

[0038] The direction perpendicular to the plane of the paper in Fig. 2 (see direction X in Fig. 3) is the longitudinal direction of the fixing belt 20, pressure roller 21, heater 22, heater holder 23, stay 24, heat equalizing member 28, and fixing device 9, and hereinafter this direction will also be referred to simply as the longitudinal direction. Note that this longitudinal direction is also the belt width direction of the fixing belt 20 or the axial direction of the pressure roller 21, and is also the width direction of the paper being transported. The paper width direction is the direction perpendicular to the paper transport direction and thickness direction.

[0039] 2 is the widthwise direction of the heater 22 and the heat equalizing member 28, and is also the paper conveyance direction and the opposite direction. Also, the left-right direction Z in FIG. 2 is the thicknesswise direction of the substrate 30 and the heater 22, and is also the pressure direction of the pressure roller 21 against the fixing belt 20 and the opposite direction.

[0040] The heater 22, the heat equalizing member 28, and the thermistor 25 are arranged overlapping in the thickness direction of the substrate 30. "Arranged overlapping" here includes cases where the two members are directly overlapped and abutting in the thickness direction, as well as cases where another member or space is interposed between them. In this embodiment, the X, Y, and Z directions are perpendicular to each other.

[0041] The fixing belt 20 has a base layer made of a cylindrical substrate made of polyimide (PI) having an outer diameter of 25 mm and a thickness of 40 to 120 μm. A release layer made of a fluorine-based resin 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 to enhance 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 base and the release layer.

[0042] The fixing belt 20 of this embodiment is a rubberless belt that does not have an elastic 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.

[0043] The pressure roller 21 has an outer diameter of, for example, 25 mm and is composed of a solid iron core 21a, an elastic layer 21b formed on the surface of the core 21a, and a release layer 21c formed on the outside of the elastic layer 21b. The elastic layer 21b is made of silicone rubber and has a thickness of, for example, 3.5 mm. The release layer 21c is a conductive layer formed by adding a conductive filler such as carbon to PFA.

[0044] 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.

[0045] 2, the pressure roller 21 is rotated in the direction of arrow A1, which in turn causes the fixing belt 20 to rotate in the direction of arrow A2. The A1 and A2 directions are the rotation directions of the pressure roller 21 and fixing belt 20 during the image forming operation or fixing operation.

[0046] The heater 22 is disposed so as to be in contact with the inner peripheral surface of the fixing belt 20. The heater 22 in this embodiment is in contact with the pressure roller 21 via the fixing belt 20, and serves as a nip forming member that forms a fixing nip N between the heater 22 and the pressure roller 21.

[0047] The fixing belt 20 is a member to be heated by the heater 22. In other words, the heater 22 heats the paper P passing through the fixing nip N via the fixing belt 20.

[0048] The heater 22 is a planar heating element provided longitudinally 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.

[0049] Furthermore, the heater 22 is in contact with the inner circumferential surface of the fixing belt 20 on the insulating layer 32 side, and the heat generated from the resistance heating element 31 is transferred to the fixing belt 20 via 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 substrate 30, but conversely, the resistance heating element 31 and the insulating layer 32 may be provided on the heater holder 23 side of the substrate 30.

[0050] In this case, since the heat from the resistance heating element 31 is transferred to the fixing belt 20 via the base material 30, it is desirable that the base material 30 be made of a material with high thermal conductivity, such as aluminum nitride. Also, by making the base material 30 out of a material with high thermal conductivity, it is possible to sufficiently heat the fixing belt 20 even if the resistance heating element 31 is placed on the opposite side of the base material 30 from the fixing belt 20 side.

[0051] The heater holder 23 and the stay 24 are disposed on the inner peripheral side of the fixing belt 20. The stay 24 is made of a metal channel material, and both ends of the stay 24 in the longitudinal direction are supported by both side plates of the fixing device 9.

[0052] 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 while the pressure roller 21 is pressed against the fixing belt 20. This ensures that the fixing nip N is stably formed between the fixing belt 20 and the pressure roller 21. In this embodiment, the heater holder 23 has a lower thermal conductivity than the base material 30.

[0053] The heater holder 23 is desirably made of a heat-resistant material because it is prone to becoming hot due to the heat from the heater 22. For example, if the heater holder 23 is made of a heat-resistant resin with low thermal conductivity, such as LCP or PEEK, 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.

[0054] The heater holder 23 has a holding recess 23b for holding the heater 22. As shown in Fig. 2, the heater holder 23 is integrally provided with guide ribs 26 for guiding the fixing belt 20. A plurality of guide ribs 26 are provided in the longitudinal direction on both the upstream and downstream sides of the heater holder 23 in the paper transport direction.

[0055] The guide rib 26 is formed in a generally fan shape. The guide rib 26 is provided along the inner peripheral surface of the fixing belt 20 and has an arc-shaped or convex curved guide surface 260 extending in the circumferential direction of the belt.

[0056] The heater holder 23 has an insertion hole 23a penetrating through the heater holder 23 in the thickness direction within the recess 23b. A thermistor 25 is provided in the insertion hole 23a.

[0057] The heat spreader 28 is made of a material having a higher thermal conductivity than the substrate 30. In this embodiment, the heat spreader 28 can be made of an aluminum alloy, steel, a graphite sheet, or other conductor.

[0058] Making the heat equalizing member 28 plate-shaped improves the positional accuracy of the heater 22 relative to the heater holder 23 and the heat equalizing member 28. Arranging the heat equalizing member 28 promotes heat transfer in the longitudinal direction, making it possible to equalize the temperature of the heater 22 and, ultimately, the fixing belt 20 in the longitudinal direction. Making the heat equalizing member 28 from a metal material improves processability and improves its dimensional accuracy.

[0059] Next, we will explain how to calculate the thermal conductivity. When calculating the thermal conductivity, first, the thermal diffusivity of the object is measured, and then the thermal conductivity is calculated using this thermal diffusivity. The thermal diffusivity was measured using a thermal diffusivity and thermal conductivity measuring device (product name: ai-Phase Mobile 1u, ai-Phase Corporation).

[0060] In order to convert the thermal diffusivity into thermal conductivity, the values of density and specific heat capacity are required. The density was measured using a dry automatic densitometer (trade name: Accupyc 1330, manufactured by Shimadzu Corporation).

[0061] The specific heat capacity was measured using a differential scanning calorimeter (product name: DSC-60, manufactured by Shimadzu Corporation) with sapphire as a reference material with a known specific heat capacity. In this example, the specific heat capacity was measured five times, and the average value at 50°C was used. When the density and specific heat capacity are ρ and C, respectively, the thermal conductivity λ can be calculated from the thermal diffusivity α obtained from the thermal diffusivity measurement using the following formula (1): λ=ρ×C×α (1)

[0062] In the fixing device 9 according to this embodiment, when a printing operation is started, the pressure roller 21 is driven to rotate, and the fixing belt 20 starts to rotate accordingly. At this time, the inner circumferential surface of the fixing belt 20 comes into contact with and is guided by the guide surface 260 of the guide rib 26, so that the fixing belt 20 rotates stably and smoothly.

[0063] Furthermore, power is supplied to resistance heating element 31 of heater 22, thereby heating fixing belt 20. Then, when the temperature of fixing belt 20 reaches the fixing temperature, which is a predetermined target temperature, paper P carrying an unfixed toner image is transported in the direction of arrow A3 to fixing nip N between fixing belt 20 and pressure roller 21, as shown in FIG.

[0064] Next, a more detailed configuration of the heater 22 provided in the fixing device will be described with reference to Fig. 3. Fig. 3 is a plan view of the heater according to this embodiment.

[0065] 3, a plurality of (four) resistance heating elements 31, power supply lines 33A and 33B as conductors, and first and second electrode portions 34A and 34B are provided on the surface of a plate-shaped substrate 30. However, the number of resistance heating elements 31 is not limited to that in this embodiment. Hereinafter, the power supply lines 33A and 33B will also be referred to as power supply lines 33, and the first electrode portion 34A or the second electrode portion 34B will also be referred to as electrode portion 34.

[0066] 2, which is the longitudinal direction of the heater 22 etc., and which is the left-right direction X in FIG. 3, is also the arrangement direction of the plurality of resistance heating elements 31. Hereinafter, this direction will also be simply referred to as the arrangement direction.

[0067] 3, which is a direction intersecting the arrangement direction, particularly a perpendicular direction in this embodiment, and which is a direction 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 intersecting arrangement direction. The intersecting arrangement 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 widthwise direction of the heater 22 or the transport direction of paper passing through the fixing device 9.

[0068] A heating section 35 is divided into a plurality of sections in the arrangement direction by the plurality of resistance heating elements 31. Each resistance heating element 31 is electrically connected in parallel to a pair of electrode sections 34A, 34B via power supply lines 33A, 33B.

[0069] 3, which is one end of the substrate 30 in the arrangement direction. The power supply lines 33A and 33B are made of a conductor having a smaller resistance value than the resistance heating element 31.

[0070] Resistance heating element 31 is made of a material with PTC (positive temperature coefficient of resistance) characteristics, and is characterized in that as the temperature rises, the resistance value increases and the heater output decreases. Because resistance heating element 31 has PTC characteristics and the heating section 35 is configured so that it is divided in the arrangement direction, it is possible to prevent excessive temperature rise of fixing belt 20 when small-sized paper is passed through.

[0071] In other words, when a sheet of paper narrower than the overall width of the heat generating section 35 is passed through, the heat of the fixing belt 20 is not absorbed by the paper in the area outside the paper width, and the temperature of the resistance heating element 31 corresponding to that area rises. Because 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, its resistance value also rises.

[0072] This reduces the heater output, i.e., the amount of heat generated, relatively, and suppresses temperature rise at the edge. Furthermore, by electrically connecting multiple resistance heating elements 31 in parallel, it is possible to suppress temperature rise in non-paper passing areas while maintaining printing speed. The heating elements that make up the heating section 35 may be other than resistance heating elements having PTC characteristics. Furthermore, the resistance heating elements may be arranged in multiple rows in the direction crossing the arrangement of the heaters 22.

[0073] The resistance heating element 31 can be formed, for example, by applying a paste made of a mixture 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 value of the resistance heating element 31 is set to 80 Ω at room temperature.

[0074] In addition to the materials mentioned above, the resistance heating element 31 may be made of a resistance material such as a silver alloy (AgPt) or ruthenium oxide (RuO2). 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 with a lower resistance value than the resistance heating element 31.

[0075] The material of the substrate 30 is preferably a ceramic such as alumina or aluminum nitride, which has excellent heat resistance and insulation properties, or a non-metallic material such as glass or mica. In this embodiment, an alumina substrate is used, which is 8 mm wide in the cross-array direction, 270 mm wide in the array direction, and 1.0 mm thick.

[0076] Alternatively, the substrate 30 may be formed by laminating an insulating material onto a conductive material such as a metal. As the metal material for the substrate 30, aluminum, stainless steel, etc. are preferable because they are low in cost.

[0077] 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, insulating and protecting them and maintaining sliding properties with the fixing belt 20.

[0078] The region in which the resistance heating elements 31 are provided in the longitudinal direction is the main heat-generating region D of the heater 22, and the main heat-generating region D also includes the region between the resistance heating elements 31. In other words, the main heat-generating region D of the heater 22 extends from one longitudinal end of the resistance heating element 31 arranged on the most one longitudinal side to the other longitudinal end of the resistance heating element 31 arranged on the most other longitudinal side. The main heat-generating region D is the region where the heater 22 mainly generates heat, and the heater 22 also generates a small amount of heat in regions outside the main heat-generating region D.

[0079] 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 they 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. 4, the resistance heating element 31 may be rectangular.

[0080] 5, the resistance heating element 31 may be made of a linear portion that is folded back to form a substantially parallelogram shape. As shown in FIG. 4, the portion extending from the block-shaped resistance heating element 31 toward the power feeder 33 (the portion extending in the array crossing direction) may be part of the resistance heating element 31, or may be made of the same material as the power feeder 33.

[0081] 6, the heater 22 has two resistance heating elements 31 connected in series and extending in the longitudinal direction. The two resistance heating elements 31 are connected to electrodes 34A and 34B via power supply lines 33A and 33B, respectively, on the left side of FIG. 6. The two resistance heating elements 31 are also connected in series via power supply line 33C on the right side of FIG. 6.

[0082] 3 to 6, the length of the base material 30 is longer on the left side of each figure than on the right side with respect to the center position D1 of the main heat generation area D. This is because the left side of the figure is longer due to the arrangement of the electrode parts 34A and 34B.

[0083] Due to this asymmetry in the length of the base material 30, heat from the heater 22 tends to flow outward in the longitudinal direction in the left portion of the base material 30. Therefore, when looking at the heater 22 alone, the temperature tends to be lower in the left portion than in the right portion in Figures 3 to 6.

[0084] In addition, the thermistor 25 of this embodiment is disposed on the end side, opposite the electrode portions 34A and 34B, which are the side where the temperature in the longitudinal direction becomes higher (see FIG. 13). Thermistor 25 detects the side where the temperature is higher, thereby effectively suppressing the rise in the end temperature.

[0085] ●Power supply circuit Fig. 7A is a diagram showing a power supply circuit to the heater shown in Fig. 3. As shown in Fig. 7A, in this embodiment, the power supply circuit for supplying power to each resistance heating element 31 is configured by electrically connecting an AC power supply 200 and electrode portions 34A and 34B of the heater 22.

[0086] The power supply circuit is also provided with a triac 210 that controls the amount of power supplied. The amount of power supplied to each resistance heating element 31 is controlled by control unit 220 via triac 210 based on the temperatures detected by thermistors 25A and 25B.

[0087] The control unit 220 is configured by a microcomputer including a CPU, ROM, RAM, I / O interface, etc. The control unit 220 may be provided in the fixing device or in the main body of the image forming apparatus.

[0088] ●Flowchart Next, the heater control operation according to this embodiment will be described with reference to the flowchart of Fig. 7B. First, when a printing operation is started in the image forming apparatus (S1 in Fig. 7B), the control unit 220 starts supplying power from the AC power supply 200 to each resistance heating element 31 of the heater 22 (S2 in Fig. 7B).

[0089] As a result, each resistance heating element 31 starts to generate heat, heating the fixing belt 20. At this time, thermistor 25 (central thermistor) arranged in the longitudinal central region of heater 22 detects temperature T4 of resistance heating element 31 located in the central region of heater 22 (S3 in FIG. 7B). Then, based on temperature T4 obtained from central thermistor 25, control unit 220 controls the amount of power supplied to each resistance heating element 31 by triac 210 so that each resistance heating element 31 reaches a predetermined temperature (S4 in FIG. 7B).

[0090] At the same time, the temperature T8 of the resistance heating element 31 is also detected by the thermistor (end thermistor) 25 arranged on the longitudinal end side of the heater 22 (S5 in FIG. 7B). N or more (T8≧T N ) is determined (S6 in FIG. 6), and N If the temperature is less than this, it is determined that an abnormally low temperature (disconnection) has occurred, and the power supply to the heater 22 is cut off (S7 in FIG. 7B), and an error message is displayed on the operation panel of the image forming apparatus (S8 in FIG. 7B).

[0091] On the other hand, if the detected temperature T8 is equal to the predetermined temperature T N If this is the case, it is determined that no abnormally low temperature has occurred and printing operation is started (S9 in FIG. 7B). Furthermore, if temperature control based on detection by the central thermistor 25 becomes impossible due to damage or a disconnection of the resistance heating element 31, there is a risk that other resistance heating elements 31, including the resistance heating elements 31 at the longitudinal ends, will become abnormally hot. In this case, when the resistance heating element 31 reaches a predetermined temperature or higher, the thermostat 27 operates to cut off the power supply to the resistance heating element 31, thereby preventing the resistance heating element 31 from becoming abnormally hot.

[0092] Heater holder 8A is a perspective view showing each member such as a heater holder provided inside fixing belt 20. In the following figures, thermistor 25 will be described as thermistor 25A (see FIG. 7A) arranged on the longitudinal end side of main heat generation region D, and thermistor 25A will be simply referred to as thermistor 25.

[0093] The longitudinal end sides of the main heat generating region D refer to, for example, the regions at both ends when the main heat generating region D is divided into thirds in the longitudinal direction. Also, the thermistor 25B in Fig. 7A is omitted in Fig. 8A, and the same applies to the subsequent figures.

[0094] 8A, an insertion hole 23a and a temperature equalizing member holding hole 23c are provided in holding recess 23b of heater holder 23. An AC connector 29 is attached to the other longitudinal side of heater holder 23 (the right side in FIG. 8).

[0095] The AC connector 29 can electrically connect the heater 22 to the power source side by contacting the contact terminals in the terminal holder 291 with the first electrode portion 34A and the second electrode portion 34B. The heat equalizing member 28 also has bent portions 28a3 as protrusions on both ends in the longitudinal direction.

[0096] When assembling these components, first, the temperature equalizing member 28 is fitted into the holding recess 23b of the heater holder 23. At this time, the bent portion 28a3 of the temperature equalizing member 28 is inserted into the temperature equalizing member holding hole 23c, and the bent portion 28a3 is locked to the heater holder 23 (this will be described in detail later).

[0097] Thereafter, the heater 22 is fitted into the holding recess 23b so as to overlap the heat equalizing member 28. In this state, the substantially U-shaped terminal holder 291 of the AC connector 29 sandwiches the other longitudinal side of the heater holder 23, heat equalizing member 28, and heater 22, thereby fixing the heat equalizing member 28 and heater 22 to the heater holder 23. The thermistor 25 is inserted into the insertion hole 23a from the back side of the heater holder 23, i.e., the side opposite the heater 22 side.

[0098] Fig. 8B is a cross-sectional view showing the inside of holding recess 23b of heater holder 23 with heat equalizing member 28 and heater 22 attached to heater holder 23. The cross-sectional view of Fig. 8B is a cross-sectional view perpendicular to the short-side direction of heater 22. In reality, heater 22, heat equalizing member 28, heater holder 23, and thermistor 25 are stacked with almost no gaps in the thickness direction, but for convenience, gaps are shown in Fig. 8B.

[0099] As shown in Fig. 8B, bent portion 28a3 of heat equalizing member 28 is formed by bending one longitudinal side of the plate member in two stages. More specifically, a predetermined longitudinal portion of the plate member is bent 90 degrees to one side in the thickness direction, and then a portion closer to the longitudinal end than the bent portion is bent 90 degrees to the opposite surface. However, the bend does not necessarily have to be at a 90-degree angle.

[0100] Bent portion 28a3 is inserted into temperature equalizing member holding hole 23c of heater holder 23. At this time, as shown in Fig. 8A, protrusion 23c1 forming temperature equalizing member holding hole 23c is inserted into hole 28a2 provided in the center of bent portion 28a3.

[0101] 8B, when temperature equalizing member 28 moves in a direction that causes it to fall off heater holder 23, the upper surface of tip 28a1 of bent portion 28a3 in FIG. 8B comes into contact with back surface 23d of heater holder 23 (see the arrow in FIG. 8B). This allows bent portion 28a3 to be locked onto heater holder 23, preventing temperature equalizing member 28 from falling off heater holder 23.

[0102] The heat-sensing element 251, which is the temperature detection portion of the thermistor 25, is in contact with the temperature-equalizing member via the insulating sheet 252. This allows the heat-sensing element 251 to detect the temperature of the temperature-equalizing member .

[0103] As shown in Fig. 8C(a), the thermistor 25 has a heat-sensitive element 251 as a temperature detection unit, an insulating sheet 252 as an insulating unit, a holder 253, and a harness 254. As shown in Fig. 8C(b), the harness 254 is fixed to the holder 253 by a solder portion 255. The solder portion 255 is a conductor portion.

[0104] 8B, the thermal element 251 contacts the temperature equalizing member 28 via the insulating sheet 252. The bent portion 28a3 of the temperature equalizing member 28 is provided to protrude downward in FIG. 8B, which is the thermistor 25 side (particularly the solder portion 255 side) in the thickness direction of the base material 30 (the vertical direction in FIG. 8B), more than the other portions of the temperature equalizing member 28.

[0105] An insulation distance H1 in the longitudinal direction is provided between the solder portion 255 and the bent portion 28a3. That is, in this embodiment, the bent portion 28a3 protrudes downward in FIG. 8B toward the thermistor 25, thereby providing the insulation distance H1 in the longitudinal direction between the solder portion 255 and the bent portion 28a3. However, the bent portion 28a3 does not necessarily have to be the portion of the heat equalizing member 28 that protrudes furthest toward the thermistor 25 in the thickness direction.

[0106] Embodiment of the heat equalizing member 9A shows first, second, and third embodiments of the plate-shaped temperature equalizing member 28, with the upper diagram showing a plan view and the lower diagram showing a cross-sectional view. The first, second, and third embodiments of FIG. 9A, (b), and (c) can all be configured symmetrically. FIG. 9C1 shows a cross-sectional view taken along the line c1-c1 in FIG. 9C.

[0107] The heat equalizing member 28 is made of multiple materials with different heat capacities per unit volume. This allows the thermal characteristics of the heat equalizing member 28 to be finely adjusted without changing the outer shape of the heat equalizing member 28, making it easy to achieve a desired temperature distribution (temperature profile) for the heater 22 as a high-temperature member. Therefore, even if the base material 2a is long on the connector CN side as shown in Figure 17, the heat capacity can be balanced in the left-right direction to equalize the temperature of the fixing belt without extending the end of the heat equalizing member 28 on the side opposite the connector CN.

[0108] That is, in the first embodiment of the heat equalizing member 28 shown in Figure 9(a), the central portion (paper passing region) in the longitudinal direction (axial direction) that forms the first region is made of copper (Cu), and the two end portions (non-paper passing regions) in the longitudinal direction (axial direction) that form the second region are made of aluminum (Al). Of course, the metal materials with different heat capacities are not limited to the combination of copper (Cu) and aluminum (Al). This makes it possible to slow the temperature rise in the end portions (non-paper passing regions) compared to the central portion (paper passing region), suppress excessive temperature rise in the non-paper passing regions, and prevent damage to the fixing belt 20.

[0109] That is, the specific heat of copper (kJ / kg K) is 0.386, while that of aluminum (Al) is 0.905. Also, the thermal conductivity of copper (Cu) is 398, while that of aluminum (Al) is 237. Aluminum (Al) has a lower thermal conductivity than copper (Cu), but a higher specific heat.

[0110] At both longitudinal ends (non-paper passing areas), heat is not absorbed by paper passing, so heat from the heater 22 accumulates and the temperature tends to rise excessively, but by making these ends out of aluminum Al, which has a higher specific heat than copper Cu, it is possible for the aluminum Al to absorb some of the heat from the heater 22. This makes it possible to suppress excessive temperature rise at the ends and prevent damage to the fixing belt.

[0111] Copper (Cu) and aluminum (Al) can be used to form clad materials (edge lay structure). Clad materials are made by bonding two or more different metals together, making them highly functional metal materials that can have composite properties that cannot be achieved with a single material.

[0112] Clad materials have high peel strength because the boundary between dissimilar metals is diffusion bonded (alloyed by element diffusion) without the use of adhesives, etc., and are also excellent in terms of weight reduction, heat dissipation, corrosion resistance, and formability, so they are used in a variety of fields. Note that Patent Document 4 (JP 2016-9008 A) discloses that the heat equalizing plate and magnetic plate are made of clad material (column 0068, Figure 8), but does not disclose that the heat capacity of the clad material is made different in the longitudinal direction (axial direction).

[0113] The second embodiment of the heat spreader 28 shown in Fig. 9(b) is the same as that shown in Fig. 9(a), except that a copper-aluminum alloy layer (Cu+Al) is added as an overlay. That is, between the copper (Cu) in the longitudinal center and the aluminum (Al) at the longitudinal end (edge of the paper-passing area), the upper layer is a copper-aluminum alloy layer (Cu+Al), and the lower layer is a third region (edge of the paper-passing area) of copper layer Cu extending from the central copper (Cu). This third region can also be made of clad material.

[0114] The third area (the edge of the paper passing area) is prone to poor fixing due to temperature sagging, but by making the third area a two-layer structure consisting of an alloy layer (Cu+Al) and a copper Cu layer in the thickness direction and adjusting the thermal conductivity, poor fixing due to temperature sagging can be prevented.

[0115] In the third embodiment of the heat spreader 28 shown in Figure 9(c), the third region (edge of the paper passing region) is formed of an aluminum Al layer extending from the aluminum Al at the edge and an alloy layer (Cu+Al). The alloy layer (Cu+Al) is formed toward one widthwise side of the heat spreader 28, and the aluminum Al layer and the alloy layer (Cu+Al) are combined in the widthwise direction to form the third region. As shown in Figure 9(c1), an alloy layer (Cu+Al) is formed as an overlay on the underside of the aluminum Al layer on the opposite side in the widthwise direction.

[0116] 9(c) can be made of a clad material. Although poor fixing due to temperature sag is likely to occur in the third region (edge of the paper passing region), poor fixing due to temperature sag can be prevented by making the third region a composite region of an alloy layer (Cu+Al) and a copper (Cu) layer and adjusting the thermal conductivity.

[0117] 10 is a plan view showing (a) fourth, (b) fifth, (c) sixth, and (d) seventh embodiments of the plate-shaped heat equalizing member 28. Each heat equalizing member 28 can be made of a clad material (edge lay structure).

[0118] The heat equalizing member 28 in each diagram in Fig. 10 is configured asymmetrically so that the end on the connector CN side has a smaller heat capacity than the opposite end. The second region on the opposite side of the connector CN in each diagram in Fig. 10 is made entirely of aluminum Al. The reason for the asymmetrical configuration is to balance the heat capacity on the left and right (make it symmetrical) and equalize the temperature of the fixing belt when the base material 2a is long on the connector CN side as in Fig. 17.

[0119] That is, in the fourth embodiment of Fig. 10(a), the aluminum Al is shorter in the longitudinal direction in the second region on the connector CN side and longer on the opposite side, so compared to Fig. 9(a), Fig. 10(a) has a smaller heat capacity in the second region on the connector CN side.

[0120] In the fifth embodiment shown in Fig. 10(b), the second region on the connector CN side is formed as an extension of the aluminum Al in the first region in the center, so that the heat capacity of the second region on the connector CN side is smaller in Fig. 10(b) than in Fig. 9(a).

[0121] In the fifth embodiment shown in Fig. 10(b), the second region on the connector CN side is formed as an extension of the aluminum Al in the first region in the center, so that the heat capacity of the second region on the connector CN side is smaller in Fig. 10(b) than in Fig. 9(a).

[0122] In the sixth embodiment shown in Fig. 10(c), the second region on the connector CN side is made of an alloy of copper and aluminum (Cu+Al), so compared to Fig. 9(a), the heat capacity of the second region on the connector CN side in Fig. 10(c) is reduced.

[0123] 10(d), the first region in the center and the second region on the connector CN side are continuously formed of an alloy of copper and aluminum (Cu+Al). Therefore, the heat capacity of the second region on the connector CN side is smaller than that of the aluminum second region on the opposite side of the connector CN.

[0124] 11A, 11B, and 11C are plan views showing (a) eighth, (b) ninth, and (c) tenth embodiments of the plate-shaped temperature equalizing member 28. Each temperature equalizing member 28 can be made of a clad material (edge lay structure). Each of the views in FIG. 11 shows the same structure as FIG. 9A except that a copper-aluminum alloy (Cu+Al) is added to the third region (edge of the paper passing region).

[0125] 11(a), the alloy (Cu+Al) is formed on one side in the width direction in the third region (edge of the paper passing region) of the heat equalizing member 28. The opposite side in the width direction of the third region (edge of the paper passing region) is formed of copper (Cu) extending from the first region in the center.

[0126] 11(b), an alloy (Cu+Al) is formed near the widthwise center in the third region (edge of the paper passing region) of the heat equalizing member 28. Both sides of the widthwise direction of the third region (edge of the paper passing region) are formed of copper (Cu) extending from the first region in the center.

[0127] 11(c), an alloy (Cu+Al) is formed on both sides in the width direction in the third region (edge of the paper passing region) of the heat equalizing member 28. The center in the width direction of the third region (edge of the paper passing region) is formed of copper (Cu) extending from the first region in the center.

[0128] In each embodiment of FIG. 11, the thermal conductivity of the third region (edge of the paper passing region) can be adjusted by arranging the alloy (Cu+Al), so that poor fixing due to temperature sagging can be suppressed.

[0129] 12 is a cross-sectional view showing (a) 11th, (b) 12th, (c) 13th, and (d) 14th embodiments of the plate-shaped heat equalizing member 28. Each heat equalizing member 28 can be made of a clad material (overlay structure).

[0130] The eleventh embodiment shown in Figure 12(a) and the thirteenth embodiment shown in Figure 12(c) are configured symmetrically. That is, the first region in the center is made of copper (Cu), and the second regions at both ends are made of aluminum (Al). The third region (end of the paper passing region) is formed with a two-layer structure of an upper layer of copper (Cu) and a lower layer of aluminum (Al).

[0131] Figure 12(a) shows a two-layer structure with a copper (Cu) and aluminum (Al) ratio of 1:2 in the thickness direction. Figure 12(c) shows a two-layer structure with a copper (Cu) and aluminum (Al) ratio of 1:1 in the thickness direction. The thickness ratio can be any other ratio.

[0132] The twelfth embodiment shown in Figure 12(b) and the fourteenth embodiment shown in Figure 12(d) are configured asymmetrically. That is, in Figure 12(b), the first region in the center is configured from copper (Cu), and the second regions at both ends are configured from aluminum (Al). Also, the third region (end of the paper passing region) on the opposite side of the connector CN in Figure 12(b) is formed by directly extending the aluminum (Al) of the second region.

[0133] The second region on the connector CN side is formed with a two-layer structure of an upper layer of copper (Cu) and a lower layer of aluminum (Al). The upper layer of copper (Cu) is formed by directly extending the copper (Cu) in the first region in the center, and the lower layer of aluminum (Al) is formed by directly extending the aluminum (Al) in the second region at the edge.

[0134] 12(d), the first region in the center (edge of the paper passing region), the second region on the connector CN side, and the third region on both sides are formed with a two-layer structure of copper (Cu) as an upper layer and aluminum (Al) as a lower layer. In other words, this two-layer structure is formed continuously from the second region on the right to the third region on the left. Because aluminum (Al) is cheaper than copper (Cu), it is possible to reduce the cost of the heat equalizing member 28 while finely adjusting the thermal characteristics.

[0135] Modified examples of fixing devices In addition to the fixing device described above, the present invention can also be applied to fixing devices such as those shown in Figures 13 to 15. The configuration of each fixing device shown in Figures 13 to 15 will be briefly described below.

[0136] 13, a pressure roller 39 is disposed on the opposite side of the pressure roller 21 with respect to the fixing belt 20. The pressure roller 39 is an opposing rotating member that rotates opposite the fixing belt 20 as a rotating member.

[0137] The pressure roller 39 and heater 22 are configured to sandwich and heat the fixing belt 20. Meanwhile, on the pressure roller 21 side, a nip forming member 41 is disposed on the inner periphery of the fixing belt 20. The nip forming member 41 is supported by a stay 24. The nip forming member 41 and the pressure roller 21 sandwich the fixing belt 20 to form a fixing nip N.

[0138] 14, the above-mentioned pressure roller 39 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 to match 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.

[0139] Finally, a description will be given of the fixing device 9 shown in Fig. 15. The fixing device 9 comprises a heating assembly 42, a fixing roller 43 which is a fixing member, and a pressure assembly 44 which is an opposing member.

[0140] The heating assembly 42 includes the heater 22, the heat equalizing member 28, the heater holder 23, the stay 24, and the heating belt 48 as a rotating member, which are described in the previous embodiment. The fixing roller 43 is an opposing rotating member that rotates opposite the heating belt 48 as a rotating member.

[0141] The fixing roller 43 is made up of a solid iron core 43a, an elastic layer 43b formed on the surface of the core 43a, and a release layer 43c formed on the outer surface of the elastic layer 43b. A pressure assembly 44 is provided on the side of the fixing roller 43 opposite to the heating assembly 42 side.

[0142] The pressure assembly 44 has a nip forming member 45 and a stay 46 arranged therein, and a pressure belt 47 as a pressure member rotatably arranged so as to enclose the nip forming member 45 and the stay 46. Then, the paper P is passed through the fixing nip N2 between the pressure belt 47 and the fixing roller 43, and heat and pressure are applied to fix the image.

[0143] 13 to 15, the configurations of the temperature equalizing member 28 and heater holder 23 of the above-described embodiment can also be adopted. This ensures an insulating distance between the temperature equalizing member 28 and thermistor 25, and also suppresses a temperature drop at the longitudinal end sides of the heater 22.

[0144] Furthermore, the heating device of the present invention is not limited to the fixing device described in the above embodiment. That is, it may be a drying device that dries ink applied to paper, or 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 a seal portion of a packaging material. By applying the present invention to such heating devices, the temperature uniformity of the heater (high-temperature member) can be improved.

[0145] The image forming apparatus according to the present invention is not limited to the color image forming apparatus shown in Fig. 1, but may also be a monochrome image forming apparatus, a copier, a printer, a facsimile, or a combination machine of these, etc. Furthermore, recording media include paper P (plain paper), as well as cardboard, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, overhead projector sheets, plastic film, prepreg, copper foil, etc.

[0146] The aspects of the present invention are as follows, for example. [First aspect] A heating device comprising a rotating member having an axial direction, a high-temperature member that contacts the rotating member and heats the rotating member along the axial direction, and a heat-equalizing member that contacts the high-temperature member and improves the heat uniformity of the high-temperature member in the axial direction, characterized in that the heat-equalizing member is made of multiple materials with different heat capacities per unit volume. [Second Aspect] The heating device of the first aspect, characterized in that the heat capacity per unit volume of the heat equalizing member is made to vary in the axial direction. [Third Aspect] The heating device of the first aspect, wherein the heat capacity per unit volume of the heat equalizing member is greater at the ends than at the center in the axial direction. [Fourth Aspect] The heating device of the first aspect, wherein the specific heat of the heat equalizing member is greater at the end portions than at the central portion in the axial direction. [Fifth Aspect] A heating device according to any one of the first and fourth aspects, characterized in that the temperature equalizing member is made of a clad material formed by bonding and integrating multiple metals. [Sixth Aspect] The heating device of the fifth aspect, characterized in that the heat-equalizing member has the same thickness in the axial direction, has a first region formed of copper in the center of the axial direction, and has a second region formed of aluminum at the end of the axial direction. [Seventh Aspect] The heating device of the sixth aspect, wherein the heat equalizing member has a third region formed of an alloy of copper and aluminum between the first region and the second region. [Eighth Aspect] The heating device of the seventh aspect, characterized in that the third region between the first region and the second region is two-layered in the thickness direction of the heat equalizing member, accepting the end of the first region or the second region. [Aspect 9] The heating device according to aspect 7 or 8, wherein a plurality of the third regions are formed in the axial direction. [10th Aspect] A heating device according to any one of the 7th to 9th aspects, characterized in that the third region between the first region and the second region is formed as a composite region by receiving an end of the first region or the second region in the width direction of the heat equalization member. [Eleventh Aspect] A fixing device having an opposing member that faces the outer peripheral surface of the rotating member, a sheet member holding a toner image is passed through a nip portion formed between the opposing member and the rotating member, and the toner image is fixed to the sheet member by a heating device of any one of the first to tenth aspects, characterized in that the high-temperature member of the heating device has a heater that generates heat when electricity is passed through it, the heater has a power supply connector at one end in the axial direction, and the heat capacity of the heat-equalizing member on both outer sides of the sheet member's paper passage area in the axial direction is larger on the side opposite the power supply connector than on the side of the power supply connector. [12th Aspect] An image forming apparatus comprising the fixing device of the 11th aspect. [Explanation of symbols]

[0147] 1: Imaging unit 1Y, 1M, 1C, 1Bk: Imaging unit 2: Heater 2: Photoreceptor 2a: Base material 3: Charging device 4: Developing device 5: Cleaning device 6: Exposure device 7: Paper feeder 8: Transfer device 9: Fixing unit 10: Paper ejection unit 11: Intermediate transfer belt 12: Primary transfer roller 13: Secondary transfer roller 14: Paper transport path 15: Timing roller 16: Paper feed tray 17: Paper feed roller 20: Fixing belt 21: Pressure roller 21a: Iron core 21a: Core metal 21b: Elastic layer 21c: Release layer 22: Heater (high temperature member) 23: Heater holder 23a: Insertion hole 23b: Retaining recess 23b: Recess 23c: Heat equalizing member holding hole 23c1: Convex portion 23d: Back side 24: Stay 25, 25A, 25B: Thermistor 26: Guide rib 27: Thermostat 28: Heat equalization component 28a: Opening 28a3: Bending portion 28a1: Tip 28a2: Hole 28b, 28c: Extension part 29: AC connector 30: Base material 31: Resistance heating element 32: Insulation layer 33: Power supply line 33A, 33B: Power supply line 33C: Power supply line 34: Electrode part 34A, 34B: Electrode part 35: Heat generating part 39: Pressure roller 41: Nip forming member 42: Heating assembly 43: Fixing roller 43a: Iron core 43a: Core metal 43b: Elastic layer 43c: Release layer 44: Pressure assembly 45: Nip forming member 46: Stay 47: Pressure belt 48: Heating belt 100: Image forming device 200: AC power supply 210: Triac 220: Control unit 251: Heat-sensitive element 252: Insulating sheet 253: Holder 254: Harness 255: Soldering part 260: Guide surface 291: Terminal holder CN: Connector D: Main heating area D1: Central position H1: Insulation distance N: Fixing nip (nip part) N2: Fixing nip P: Paper [Prior art documents] [Patent documents]

[0148] [Patent Document 1] Japanese Patent Publication No. 2022-54951 [Patent Document 2] Patent No. 6614816 [Patent Document 3] Patent No. 7013433 [Patent Document 4] Japanese Patent Application Laid-Open No. 2016-9008

Claims

1. A heating device including a rotating member having an axial direction, a high-temperature member that contacts the rotating member to heat the rotating member along the axial direction, and a heat-equalizing member that contacts the high-temperature member to improve heat uniformity of the high-temperature member in the axial direction, A heating device characterized in that the heat equalizing member is made of a plurality of materials having different heat capacities per unit volume.

2. 2. The heating device according to claim 1, wherein the heat capacity per unit volume of said heat equalizing member is varied in the axial direction.

3. 2. The heating device according to claim 1, wherein the heat capacity per unit volume of said heat equalizing member is greater at the end portions than at the central portion in the axial direction.

4. 2. The heating device according to claim 1, wherein the specific heat of said heat equalizing member is greater at the ends than at the center in the axial direction.

5. 2. The heating device according to claim 1, wherein the temperature equalizing member is made of a clad material in which a plurality of metals are bonded together to form an integrated unit.

6. 2. The heating device according to claim 1, wherein the heat equalizing member has a uniform thickness in the axial direction, a first region formed of copper in the central portion in the axial direction, and a second region formed of aluminum at each end in the axial direction.

7. 7. The heating device according to claim 6, wherein said heat equalizing member has a third region between said first region and said second region, said third region being made of an alloy of copper and aluminum.

8. 8. The heating device according to claim 7, wherein the third region between the first region and the second region is formed as a two-layer structure by receiving an end of the first region or the second region in the thickness direction of the heat equalization member.

9. 8. The heating device according to claim 7, wherein a plurality of the third regions are formed in the axial direction.

10. 8. The heating device according to claim 7, wherein the third region between the first region and the second region is formed as a composite region by receiving an end of the first region or the second region in the width direction of the heat equalization member.

11. 11. A fixing device having an opposing member facing an outer peripheral surface of the rotating member, wherein a sheet member carrying a toner image is passed through a nip portion formed between the opposing member and the rotating member, and the toner image is fixed to the sheet member by a heating device according to claim 1, a fixing device characterized in that the high-temperature member of the heating device has a heater that generates heat when current is applied, the heater has a power supply connector at one end in the axial direction, and the heat capacity of the heat equalizing member on both outer sides of the paper passage area of the sheet member in the axial direction is larger on the side opposite to the power supply connector than on the side of the power supply connector.

12. An image forming apparatus comprising the fixing device of claim 11.

Images