Heating device, fixing device, image forming apparatus

Abstract

To solve the problem in which: temperature unevenness occurs in a belt member in the arrangement direction of a plurality of resistance heating elements.SOLUTION: A fixing device 6 comprises: a fixing belt 20; a pressure roller 21 that is opposite to the fixing belt 20; a planar heater 22 that has a plurality of resistance heating elements 31; and a heater holder 23 that holds the heater 22. The plurality of resistance heating elements 31 are arranged side by side. The heater holder 23 is in contact with the heater 22 in a direction in which the pressure roller 21 applies pressure to the fixing belt 20. The heater holder 23 has relief parts 23b, 23c that reduce the contact area with the heater 22 in the pressure direction compared with the other portion at positions corresponding to division areas B of the resistance heating elements 31 in the arrangement direction of the plurality of resistance heating elements 31.SELECTED DRAWING: Figure 12

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 as a heating device is provided with a fixing belt as a belt member and a planar heating element for heating the fixing belt. As such a heating element, there is a type in which a plurality of resistance heating elements, which are the main heat generating parts, are arranged and electrically connected in parallel to each other.

[0003] In the above-mentioned heating element, the amount of heat generated by the heating element is smaller in the divided regions between the resistance heating elements than in other regions, which causes a problem that the temperatures of the heating element and the fixing belt become non-uniform in the arrangement direction of the multiple resistance heating elements.

[0004] The fixing device of Patent Document 1 (JP 2019-164328 A) is provided with a heater holder that holds the heater from its back side. This heater holder is provided with a plurality of guide parts that guide the fixing belt in the longitudinal direction of the heater. The heat capacity of the guide parts is made smaller at positions corresponding to the divided regions of the resistance heating element than at positions corresponding to the non-divided regions, thereby suppressing local temperature drops in the fixing belt. Summary of the Invention [Problem to be solved by the invention]

[0005] There was a problem that temperature unevenness occurred in the belt member in the arrangement direction of the multiple resistance heating elements. [Means for solving the problem]

[0006] In order to solve the above problems, the present invention provides a heating device comprising a belt member, an opposing member opposing the belt member, a planar heating element having a plurality of resistance heating elements, and a holding member for holding the heating element, wherein the resistance heating elements are arranged in a line, the holding member contacts the heating element in a direction opposite to a pressure direction of the opposing member against the belt member, and the holding member has a relief portion at a position corresponding to a divided region of the resistance heating elements in the arrangement direction of the plurality of resistance heating elements, which makes the contact area with the heating element in the pressure direction smaller than other portions, and the holding member is provided at least in a passage area through which a recording medium passes in the arrangement direction of the plurality of resistance heating elements, The recording medium conveying device has an upstream contact portion and a downstream contact portion that protrude toward the heating body and contact the heating body in a direction opposite to the pressure direction, the downstream contact portion is spaced from the upstream contact portion in the recording medium conveying direction and is provided at a position downstream of the upstream contact portion in the recording medium conveying direction, and has a gap portion where the downstream contact portion is not provided at a position corresponding to the downstream end of the heating body in the recording medium conveying direction at a position where the downstream contact portion is provided in the arrangement direction of the multiple resistance heating elements. The holding member is provided in a non-passing region in an arrangement direction of the plurality of resistance heating elements, which is a region where the recording medium does not pass through, from a position of the upstream contact portion in the recording medium conveying direction to a position corresponding to a position of the downstream contact portion, and has a non-passing region contact portion that protrudes toward the heating element and contacts the heating element in a direction opposite to the pressure direction. It is characterized by: Effect of the Invention

[0007] This makes it possible to suppress temperature unevenness in the belt member in the arrangement direction of the multiple resistance heating elements. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of an image forming apparatus. [Diagram 2] 1 is a cross-sectional view showing a schematic configuration of a fixing device according to an embodiment of the present invention. [Diagram 3] FIG. [Figure 4] FIG. 4 is a diagram showing a power supply circuit to a heater. [Diagram 5] FIG. 5 is a plan view showing a heater having a different configuration from that in FIG. [Figure 6] FIG. 5 is a plan view showing a heater having a different configuration from that in FIG. [Figure 7]6 is a diagram showing the positional relationship between the temperature distribution in the arrangement direction of the fixing belt and the arrangement of heaters. FIG. [Figure 8] FIG. 6 is a diagram showing divided regions of the heater in FIG. 5. [Figure 9] FIG. 13 is a diagram showing divided regions of a heater different from those described above. [Figure 10] FIG. 7 is a diagram showing divided regions of the heater in FIG. 6. [Figure 11] FIG. [Figure 12] FIG. 4 is a diagram showing the positional relationship between heaters and heater holders in the arrangement direction. [Figure 13] FIG. 13 is a perspective view showing a modified example of the recess portion. [Figure 14] FIG. 13 is a perspective view showing a modified example of the recess portion. [Figure 15] FIG. 4 is a plan view showing a state in which the heater holder holds a heater. [Figure 16] FIG. 13 is a diagram showing a heater in which the width of the resistive heating element in the divided region is increased. 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. In the following description, a fixing device that fixes a toner image onto a paper surface will be described as an example of a heating device.

[0010] A monochrome image forming apparatus 1 shown in FIG. 1 is provided with a photoconductor drum 10. The photoconductor drum 10 can carry toner as a developer on its surface. The photoconductor drum 10 is a drum-shaped rotating body that can rotate in the direction of the arrow in the figure. Around the photoconductor drum 10, there are a charging roller 11, a developing device 12 including a developing roller 19, and a cleaning blade 13. The charging roller 11 uniformly charges the surface of the photoconductor drum 10. The developing roller 19 supplies toner to the surface of the photoconductor drum 10. The cleaning blade 13 cleans the surface of the photoconductor drum 10.

[0011] An exposure unit 3 is disposed above the process unit 2. The exposure unit 3 emits a laser beam Lb based on image data. The laser beam Lb is irradiated onto the surface of the photoconductor drum 10 via a mirror 14.

[0012] Further, transfer means 15 is disposed at a position facing the photoconductor drum 10. The transfer means 15 includes a transfer charger, and transfers the image on the surface of the photoconductor drum 10 onto the paper P.

[0013] A paper feed unit 4 is located at the bottom of the image forming apparatus 1. The paper feed unit 4 is made up of a paper feed cassette 16, a paper feed roller 17, etc. A registration roller 18 is disposed downstream of the paper feed roller 17 in the transport direction. The paper feed cassette 16 stores paper P as a recording medium. The paper feed roller 17 conveys the paper P from the paper feed cassette 16 to the transport path 5.

[0014] The fixing device 6 includes a fixing belt 20 and a pressure roller 21. The fixing belt 20 is heated by a heater, which will be described later, serving as a heating element. The pressure roller 21 applies pressure to the fixing belt 20.

[0015] Hereinafter, the basic operation of the image forming apparatus 1 will be described with reference to FIG.

[0016] When the image forming operation is started, first, the charging roller 11 charges the surface of the photoconductor drum 10. Then, the exposure unit 3 irradiates the photoconductor drum 10 with a laser beam Lb based on image data. This reduces the potential of the irradiated portion of the photoconductor drum 10, and an electrostatic latent image is formed in that portion. Toner is supplied from the developing device 12 to the surface portion of the photoconductor drum 10 on which the electrostatic latent image has been formed, and the electrostatic latent image is visualized as a toner image (developer image). Then, the toner and the like remaining on the photoconductor drum 10 after transfer is removed from the surface of the photoconductor drum 10 by the cleaning blade 13.

[0017] On the other hand, when an image forming operation is started, at the bottom of the image forming apparatus 1, the paper P accommodated in the paper feed cassette 16 is sent to the conveying path 5 by the paper feed roller 17 of the paper feed unit 4 being driven to rotate.

[0018] The paper P sent to the transport path 5 is timed by the registration rollers 18 and transported to the transfer section at a timing that faces the toner image on the surface of the photosensitive drum 10. This transfer section is an opposing portion between the transfer means 15 and the photosensitive drum 10. The toner image is transferred onto the surface of the paper P transported to the transfer section by the application of a transfer bias by the transfer means 15.

[0019] The paper P onto which the toner image has been transferred is transported to the fixing device 6. The paper P is heated and pressurized by the heated fixing belt 20 and pressure roller 21, and the toner image is fixed onto the surface of the paper P. Then, the paper P onto which the toner image has been fixed is separated from the fixing belt 20, transported by a pair of transport rollers provided downstream of the fixing device 6, and discharged onto a paper output tray. The paper output tray is provided outside the device.

[0020] Next, the configuration of the fixing device will be described.

[0021] As shown in FIG. 2, the fixing device 6 according to the present embodiment includes an endless fixing belt 20 as a belt member (fixing member or rotating member), a pressure roller 21 as an opposing 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, and a thermistor as a temperature detection means. The pressure roller 21 contacts the outer peripheral surface of the fixing belt 20 to form a fixing nip N as a nip portion. The heater 22 heats the fixing belt 20. The heater holder 23 holds the heater 22. The stay 24 supports the heater holder 23 from its rear side. The thermistor detects the temperature of the fixing belt 20. The fixing belt 20, the pressure roller 21, the heater 22, the heater holder 23, and the stay 24 extend in a direction perpendicular to the paper surface of FIG. 2, and hereinafter, this direction is also referred to as the longitudinal direction of each member, or simply the longitudinal direction. This direction is the axial direction of the pressure roller 21 and also the width direction of the paper P passed through the fixing device 6 .

[0022] The fixing belt 20 has 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 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 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. The fixing belt 20 is a member to be heated by the heater 22.

[0023] The pressure roller 21 has an outer diameter of, for example, 25 mm. The pressure roller 21 is composed of a solid iron core 21a, an elastic layer 21b, and a release layer 21c. The elastic layer 21b is formed on the surface of the core 21a. The elastic layer 21b is made 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 increase the releasability of the pressure roller 21 surface, it is desirable for the release layer 21c to be a fluororesin layer having a thickness of, for example, about 40 μm.

[0024] 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. When the pressure roller 21 rotates in the direction of the arrow in FIG. 2, the fixing belt 20 is rotated accordingly.

[0025] The heater 22 is a planar heating element provided along the longitudinal direction.

[0026] The heater 22 is composed of a plate-shaped base material 30, a resistance heating element (heating portion) 31, an insulating layer 32, and the like. The resistance heating element 31 is provided on the base material 30. The insulating layer 32 covers conductors such as the resistance heating element 31. 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 via the insulating layer 32.

[0027] 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 6. The stay 24 supports the heater holder 23 and the heater 22 held thereby. As a result, when the pressure roller 21 is pressed against the fixing belt 20, the heater 22 reliably receives the pressing force of the pressure roller 21, and the fixing nip N is stably formed between the fixing belt 20 and the pressure roller 21.

[0028] 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, and the heater 22 can efficiently heat the fixing belt 20.

[0029] The heater holder 23 is provided with guide members (contact members) 26 that guide the fixing belt 20. The guide members 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 members 26 are arranged at intervals in the longitudinal direction of the heater 22 (see FIG. 11). Each guide member 26 is formed in a substantially fan shape and has a belt-facing surface 260. The belt-facing surface 260 faces the inner circumferential surface of the fixing belt 20 and is an arc-shaped or convex curved surface extending in the belt circumferential direction.

[0030] As shown in FIG. 2, when the fixing device 6 according to the present embodiment starts a printing operation, the pressure roller 21 is rotationally driven, and the fixing belt 20 starts to rotate. 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 member 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, when the temperature of the fixing belt 20 reaches a predetermined target temperature (fixing temperature), the paper P carrying the unfixed toner image is transported between the fixing belt 20 and the pressure roller 21 (fixing nip N). As a result, the unfixed toner image is heated and pressurized to be fixed to the paper P.

[0031] Next, the configuration of the heater 22 will be described in more detail.

[0032] 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. An insulating layer 32 is provided to cover the surface of the base material 30 and these conductive parts and to insulate them from each other.

[0033] As the material of the substrate 30, ceramics such as alumina and aluminum nitride, glass, mica, heat-resistant resin materials such as polyimide (PI) are preferable because they have excellent heat resistance and insulation. As another material of the substrate 30, the aforementioned insulating material may be laminated on a conductive material. For example, as the conductive material constituting the substrate 30, materials with high thermal conductivity such as aluminum, copper, silver, graphite, and graphene are more preferable. In other words, these materials can improve image quality by uniformizing the temperature of the entire heater by the action of thermal conduction.

[0034] Materials that can be used for the resistance heating element 31 and the power supply lines 33a and 33b include silver (Ag), palladium (Pd), platinum (Pt), ruthenium oxide (RuO2), etc. A conductive material paste made by mixing these materials is applied onto the substrate 30 by screen printing or the like, and then fired to form the resistance heating element 31 and the power supply lines 33a and 33b.

[0035] Here, the resistance heating element 31 is the main heat generating portion of the heater 22, and when a voltage of 40% of the rated voltage is applied to the fixing device 6 for 3 seconds, the temperature of the resistance heating element 31 rises by 100 degrees or more.

[0036] The insulating layer 32 can be formed from ceramics such as alumina and aluminum nitride, glass, mica, polyimide, and other heat-resistant resin materials, which are preferable because the insulating layer 32 has excellent heat resistance and insulation properties.

[0037] Each resistance heating element 31 is connected to a first electrode portion 34a via a power supply line 33a, and to a second electrode portion 34b via a power supply line 33b. Each resistance heating element 31 is electrically connected in parallel. In this embodiment, the multiple resistance heating elements 31 are arranged in the longitudinal direction X. Hereinafter, this longitudinal direction X is also referred to as the arrangement direction of the multiple resistance heating elements 31, or simply as the arrangement direction. In the following description, the vertical direction Y in FIG. 3, which is a direction intersecting the arrangement direction (perpendicular to the present embodiment) and different from the thickness direction of the substrate 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. The arrangement intersecting direction is also the short-side direction of the heater 22.

[0038] The resistance heating element 31 has a PTC characteristic. The PTC characteristic is a characteristic in which the resistance value increases as the temperature increases (when a constant voltage is applied, the heater output decreases). Since each resistance heating element 31 has a PTC characteristic, the output of the heater 22 increases at low temperatures, and the temperature of the fixing belt 20 can be increased quickly. In addition, since the output of the heater 22 decreases at high temperatures, excessive temperature increase of the fixing belt 20 in non-paper passing areas can be suppressed, for example, when small size paper is continuously printed.

[0039] 4, 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 control unit 220 is configured with a microcomputer including a CPU, ROM, RAM, an I / O interface, etc.

[0040] 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, a thermostat 27 is disposed as a power cut-off means at the other end side in the arrangement direction of the heaters 22. The thermostat 27 cuts off the power supply to the resistance heating element 31 when the temperature of the resistance heating element 31 reaches or exceeds a predetermined temperature. The thermistor 25 and thermostat 27 contact the back surface of the substrate 30 (the side opposite to the side where the resistance heating element 31 is disposed) to detect the temperature of the heater 22.

[0041] The control unit 220 controls the amount of power supplied to each resistance heating element 31 via the triac 210. The control unit 220 determines the amount of power supplied to each resistance heating element 31 based on the temperature detected by the thermistor 25, and determines the amount of power to be supplied taking into consideration the amount of heat absorbed by the paper P when the paper passes through the fixing device 6.

[0042] 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. 5, the resistance heating element 31 may be rectangular, or as shown in Fig. 6, the resistance heating element 31 may be made of a linear portion that is folded back to form a substantially parallelogram shape.

[0043] 7A and 7B are diagrams showing temperature distribution in the arrangement direction of fixing belt 20. FIG. 7A shows the arrangement of heaters 22. FIG. 7B shows the temperature T of fixing belt 20 on the vertical axis and each position in the arrangement direction of fixing belt 20 on the horizontal axis.

[0044] As shown in FIG. 7(a) and FIG. 7(b), in the divided region B between the resistance heating elements 31 in the arrangement direction (or the expanded divided region C including the periphery thereof), the area occupied by the resistance heating elements 31 is smaller than that of the other regions, and the amount of heat generated is smaller. As a result, the temperature of the fixing belt 20 in the divided region B is smaller than that of the other regions, causing temperature unevenness in the arrangement direction of the fixing belt 20. The temperature of the heater 22 is also lower in the divided region B or the expanded divided region C. Here, as shown in the enlarged view of FIG. 7(a), the divided region B means an arrangement direction region including the entire portion into which the resistance heating element 31, which is the main heat generating portion of the heater 22, is divided in the arrangement direction. In addition to the divided region B, an area including a range corresponding to the connection portion 311 of the resistance heating element 31 is defined as the expanded divided region C. The connection portion 311 refers to a portion of the resistance heating element 31 that extends in the arrangement crossing direction and is connected to each of the power supply lines 33a and 33b.

[0045] As shown in FIG. 8, the heater 22 having the rectangular resistance heating element 31 shown in FIG. 5 also has a lower temperature in the divided region B than in the other regions. Also, in the heater 22 having the resistance heating element 31 shaped as shown in FIG. 9, the temperature in the divided region B is lower than in the other regions. Furthermore, as shown in FIG. 10, the heater 22 having the resistance heating element 31 shaped as shown in FIG. 6 also has a lower temperature in the divided region B than in the other regions. However, by overlapping adjacent resistance heating elements 31 in the arrangement direction as in FIG. 7, FIG. 9, and FIG. 10, the temperature drop in the other regions of the divided region B can be suppressed. Note that, as in FIG. 8 to FIG. 10, when the resistance heating element 31 does not have the above-mentioned connection portion 311 (see FIG. 7) and the portion extending in the arrangement crossing direction is constituted by a power supply line, or when the connection portion extends in a direction perpendicular to the arrangement direction (up and down direction in FIG. 8, etc.), the expanded divided region C does not exist (the expanded divided region C is in the same range as the divided region B).

[0046] Next, the heater holder 23 that holds the heater 22 will be described in more detail, and then the structure of the heater holder 23 that suppresses a drop in temperature in the divided region B will be described.

[0047] As shown in FIG. 11, the heater holder 23 has abutment portion 23a that abuts against the back surface of the base material 30 of the heater 22 (see the hatched portion in FIG. 11). The abutment portion 23a is a portion that protrudes in the pressure direction of the pressure roller 21 against the fixing belt 20, and extends in the arrangement direction. This pressure direction is the left-right direction in FIG. 2, and hereinafter will also be simply referred to as the pressure direction. This pressure direction is also the thickness direction of the heater holder 23, or the approach direction of the pressure roller 21 to the heater holder 23. The abutment portion 23a abuts against the back surface of the base material 30 in the pressure direction across the arrangement direction. The heater holder 23 has a hole that penetrates in the pressure direction at a position corresponding to the above-mentioned thermistor or thermostat.

[0048] The contact portions 23a are provided on both sides of the heater holder 23 in the array crossing direction, and a non-contact portion where the contact portions 23a are not provided exists at the center of the heater holder 23 in the array crossing direction. By making the short side center of the heater holder 23 non-contact with the substrate 30, the area of ​​the heater holder 23 in contact with the substrate 30 is reduced, and heat transfer from the heater 22 to the heater holder 23 can be suppressed. Note that one side of the array direction (the left side in FIG. 11) is a portion where the heater 22 is not provided with the resistance heating element 31, is a non-paper passing region, and the amount of heat transfer from the heater 22 to the heater holder 23 is also small. Therefore, in this portion, the heater holder 23 is in contact with the substrate 30 even at the center of the array crossing direction.

[0049] The heater holder 23 also has relief portions at multiple locations in the arrangement direction that reduce the contact area with the heater 22 in the pressure direction. In this embodiment, the relief portion on the upstream side in the paper transport direction (the lower side in FIG. 11) is a notch portion 23b that reduces the width of the contact portion 23a in the arrangement crossing direction. The relief portion on the downstream side in the paper transport direction is a non-contact portion 23c that partially eliminates the contact portion 23a (making the width in the arrangement crossing direction zero) and does not contact the heater 22 at that position in the arrangement direction.

[0050] As shown in FIG. 12, the cutout portion 23b and the non-contact portion 23c as the relief portion are provided at a position corresponding to the divided region B (particularly, in this embodiment, the enlarged divided region C) in the arrangement direction. As a result, the contact area between the heater 22 and the heater holder 23 in the pressure direction is reduced at the position corresponding to the divided region B in the arrangement direction, and the amount of heat transferred from the heater 22 to the heater holder 23 is reduced compared to other portions. In particular, by providing the non-contact portion 23c, the contact portion 23a and the heater 22 do not come into contact with each other in the pressure direction at the position of the non-contact portion 23c in the arrangement direction, and the amount of heat transferred from the heater 22 to the heater holder 23 can be particularly reduced. In this way, the relief portion is a portion that makes the contact area between the heater holder 23 and the heater 22 smaller than the contact area of ​​the other portions outside the divided region in at least a part of the position corresponding to the divided region in the arrangement direction. However, the other portions outside the divided region do not need to be the entire range outside the divided region. In other words, the contact area of ​​the portion in which the recess is provided in the arrangement direction is smaller than that of at least a part of the other portion.

[0051] As a result, the heat loss due to heat transfer from the heater 22 to the heater holder 23 can be reduced at the position corresponding to the divided region B in the arrangement direction. Therefore, the temperature of the heater 22 and the fixing belt 20 in the divided region B becomes high, and the temperature drop in the divided region B shown in FIG. 7 can be suppressed. Therefore, the temperature unevenness in the arrangement direction of the fixing belt 20 can be suppressed. In particular, by providing the relief portion at the position corresponding to the enlarged divided region C in the arrangement direction as in this embodiment, the heat transfer from the heater 22 to the heater holder 23 can be suppressed even around the divided region, so that the temperature unevenness in the arrangement direction of the fixing belt 20 can be further suppressed. Note that the relief portion does not need to be provided in the entire divided region, and by providing it in at least a part of the divided region, the effect of suppressing the temperature unevenness in the arrangement direction of the fixing belt 20 can be obtained as described above.

[0052] As in this embodiment, by providing the notch 23b on the upstream side in the paper transport direction and the non-contact portion 23c on the downstream side, a certain amount of contact area between the heater 22 and the heater holder 23 can be secured at a position corresponding to the upstream divided region B. This allows the heater holder 23 to more appropriately receive the pressure force from the pressure roller 21 on the downstream side in the paper transport direction. This makes it possible to prevent the formation of abnormal images.

[0053] Conversely to the above embodiment, a non-contact portion may be provided on the upstream side of the heater holder 23, and a notch portion may be provided on the downstream side. By ensuring the contact area between the heater 22 and the heater holder 23 on the upstream side at a position corresponding to the divided region B in the arrangement direction, the pressure distribution on the inlet side of the fixing nip can be made uniform in the arrangement direction. This makes it possible to prevent the occurrence of wrinkles in the paper. Furthermore, it is also possible to provide notches on both the upstream side and the downstream side, and to make the width of each notch portion in the intersecting direction of the arrangement different.

[0054] In addition to changing the range of the relief portion between the upstream and downstream sides in the paper transport direction in the array crossing direction, the relief portion may also be changed in the array direction. For example, as shown in Fig. 13, the width in the array direction of the cutout portion 23b, which is the relief portion on the upstream side in the paper transport direction, can be made larger than the width in the array direction of the non-contact portion 23c, which is the relief portion on the downstream side.

[0055] The shape of the relief portion is not limited to the above. For example, as shown in FIG. 14, the contact portion 23a of the heater holder 23 is provided at the downstream side in the paper conveying direction as a relief portion with an interrupted portion 23d in which the contact portion is provided intermittently in the arrangement direction. In this embodiment, the interrupted portion 23d is provided with a substantially circular cross section. The interrupted portion 23d provides an intermittent non-contact portion of the heater holder 23 with respect to the heater 22, and prevents the non-contact portion from continuing over a wide range in the arrangement direction. Therefore, the configuration of this embodiment reduces the contact area between the heater 22 and the heater holder 23 in the divided region, and effectively suppresses the deflection of the heater 22 when the pressure roller 21 applies pressure.

[0056] In addition, the shape of the relief portion in each divided region provided in the arrangement direction, and the width in the arrangement direction and the arrangement cross direction do not need to be the same. For example, the width of the relief portion in the divided region on the end side of the arrangement direction may be set larger than that of the center side. When starting up the image forming apparatus, the end side in the arrangement direction of the fixing belt 20 and the heater 22 is more likely to lose heat than the center side due to heat transfer by contact with other members such as side plates and heat dissipation in the air, and the temperature is less likely to rise than the center side. Therefore, by increasing the width of the relief portion on the end side in the arrangement direction, the outflow of heat to the heater holder 23 on the end side can be further suppressed, and the temperature difference with the center side can be suppressed. As described above, the shape of each relief portion, the width in the arrangement direction and the arrangement cross direction can be optimally selected so that the temperature of the fixing belt 20 and the heater 22 can be uniformed in the arrangement direction, taking into consideration the configuration of the fixing device 6 and the usage environment. This makes it possible to effectively suppress temperature unevenness in the arrangement direction of the fixing belt 20 and the heater 22, and to suppress bending of the heater 22.

[0057] 12, when viewed in the pressure direction (viewed in a direction perpendicular to the paper surface of FIG. 12), in the range corresponding to divided region B in the arrangement direction, the range in the arrangement crossing direction (up and down direction in FIG. 12) in which the abutting portion 23a is provided is the range outside the region in which the resistance heating element 31 is provided (i.e., the range above dotted line L1 or below dotted line L2 in FIG. 12). As a result, in divided region B, the heater holder 23 does not contact the heater 22 at a position corresponding to the resistance heating element 31, which is the main heat generating portion of the heater 22. Therefore, in divided region B, heat transfer from the heater 22 to the heater holder 23 can be effectively suppressed, and temperature unevenness in the arrangement direction of the heater 22 and the fixing belt 20 can be suppressed.

[0058] As shown in Fig. 15, the heater 22 is held by the heater holder 23 by fitting the heater 22 into a recess (where the abutment portion 23a, etc. are arranged) of the heater holder 23. At this time, the protrusion 23e of the heater holder 23 fits into a recess 30a (not shown in Fig. 7, etc.) provided in the base material 30. This allows the heater 22 to be positioned relative to the heater holder 23 in the arrangement direction and the intersecting arrangement direction. Note that Fig. 15 omits the illustration of the resistance heating element 31, electrode portions, etc. formed on the surface of the base material 30.

[0059] 16, a width expansion portion 31a that increases the width of the resistance heating element 31 in the crossing direction of the arrangement may be provided in a range corresponding to the divided region B. This increases the amount of heat generated by the resistance heating element 31 in the divided region B, and suppresses a drop in temperature of the heater 22 and the fixing belt 20 in the divided region B. This makes it possible to suppress temperature unevenness in the arrangement direction of the heater 22 and the fixing belt 20.

[0060] Furthermore, when viewed in the pressure direction (viewed in a direction perpendicular to the paper surface of FIG. 16), it is preferable that the position corresponding to the width expansion portion 31a overlaps with the range of the fixing nip, so that heat generated by the width expansion portion 31a can be efficiently transmitted to the fixing nip.

[0061] The nip range can be measured by the following method. That is, any heat-resistant paint (e.g., fluorine-based paint or silicon-based paint) is applied to the surface of the heater facing the inner side of the fixing belt, and a fixing nip is formed between the pressure roller and the fixing belt. After that, the coated surface of the heater is observed to check the difference in the wear state of the paint. Specifically, the non-nipped area has a surface that remains in the coated state, while the nipped area has a surface where the coating is rough. This makes it possible to determine whether or not the area is nipped.

[0062] 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.

[0063] The image forming apparatus according to the present invention is not limited to the monochrome image forming apparatus shown in FIG. 1, but may be a color image forming apparatus, a copying machine, a printer, a facsimile, or a combination machine of these.

[0064] Examples of recording media 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.

[0065] 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, it is possible to suppress temperature unevenness in the arrangement direction of the belt member (heated member). [Explanation of symbols]

[0066] 1. Image forming device 6 Fixing device (heating device) 20 Fixing belt (belt member or fixing member) 21 Pressure belt (opposing member or pressure member) 22 Heater (heating element) 23 Heater holder (holding member) 23a Contact part 23b Cutout (relief) 23c Non-contact portion (relief portion) 23d Intermittent section (relief section) 30 Base material 31 Resistance heating element 31a Width expansion section 311 Connection 32 Insulating layer 33a, 33b Power supply line (conductor) 34a, 34b electrode section B Split area C Expanded division area N Fixing nip (nip part) X arrangement direction (arrangement direction of multiple resistance heating elements) Y Array cross direction (direction crossing the array direction of multiple resistance heating elements) [Prior art documents] [Patent documents]

[0067] [Patent Document 1] JP 2019-164328 A

Claims

1. A belt member; an opposing member opposed to the belt member; A planar heating element having a plurality of resistance heating elements; A heating device comprising: a holding member for holding the heating body, A plurality of the resistance heating elements are arranged in a row, the holding member is in contact with the heating body in a direction opposite to a direction in which the opposing member applies pressure to the belt member, the holding member has a recess at a position corresponding to a divided region of the resistance heating elements in an arrangement direction of the plurality of resistance heating elements, the recess having a smaller contact area with the heating elements in the pressure direction than other portions; the holding member is provided at least in a passing region that is a region through which a recording medium passes in an arrangement direction of the plurality of resistance heating elements, protrudes toward the heating elements, and has an upstream contact portion and a downstream contact portion that contact the heating elements in a direction opposite to the pressure application direction, the downstream contact portion is spaced apart from the upstream contact portion in a recording medium transport direction and is provided at a position downstream of the upstream contact portion in the recording medium transport direction, a gap portion where the downstream contact portion is not provided at a position corresponding to a downstream end portion of the heating body in a recording medium conveyance direction in a position where the downstream contact portion is provided in an arrangement direction of the plurality of resistance heating bodies, The heating device is characterized in that the holding member is arranged in a non-passing area, which is an area in the arrangement direction of the multiple resistance heating elements where the recording medium does not pass through, from the position of the upstream abutment portion in the recording medium transport direction to a position corresponding to the position of the downstream abutment portion, and has a non-passing area abutment portion that protrudes toward the heating element and abuts against the heating element in the direction opposite to the pressure application direction.

2. The heating element has an electrode portion and a conductor connecting the electrode portion and the resistance heating element, the resistive heating element has a connection portion extending in a direction intersecting an arrangement direction of the plurality of resistive heating elements and connected to the conductor, The heating device according to claim 1 , wherein the recess is provided at a position corresponding to the connection portion in an arrangement direction of the plurality of resistance heating elements.

3. 3. A heating device as described in claim 1 or 2, wherein at a position corresponding to the divided area in the arrangement direction of the resistive heating element, the contact position of the holding member with the heating element in a direction intersecting the arrangement direction of the resistive heating element is outside the area in which the resistive heating element is arranged.

4. The heating device according to claim 1 , wherein at least a portion of the recess is a non-contact portion that keeps the holding member out of contact with the heating element at the position where the recess is provided in the arrangement direction of the multiple resistance heating elements.

5. The heating element has a plurality of divided regions in an arrangement direction of the resistance heating elements, The holding member has a plurality of the recesses, 5. The heating device according to claim 1, wherein at least one of a width in a direction in which the plurality of resistive heating elements are arranged and a width in a direction intersecting the direction in which the plurality of resistive heating elements are arranged is different for each of the recesses.

6. the holding member contacts the heating element at both ends in a direction intersecting an arrangement direction of the plurality of resistance heating elements, 6. The heating device according to claim 1, wherein the holding member has the recesses at both ends of the heating element in a direction intersecting the arrangement direction of the multiple resistance heating elements, and at least one of the widths of the recesses in the arrangement direction of the multiple resistance heating elements, the widths in the direction intersecting the arrangement direction of the multiple resistance heating elements, or the shapes of the recesses are different.

7. 7. The heating device according to claim 1, wherein the resistive heating elements have a width expansion portion at a position corresponding to the divided region in the arrangement direction of the resistive heating elements, the width of the resistive heating elements being larger in a direction intersecting the arrangement direction of the resistive heating elements than in other portions.

8. 8. The heating device according to claim 7, wherein the opposing member forms a nip portion with the belt member at a position corresponding to the width expansion portion.

9. A fixing device comprising the heating device according to claim 1 , for fixing an image on a recording medium.

10. An image forming apparatus comprising the fixing device according to claim 9.

Images