Heater, image heating device, and image forming apparatus

Abstract

To reduce temperature unevenness and prevent deterioration of a heater.SOLUTION: In a heater (300) in which heating element patterns (302) are arranged side by side between two electric conductor patterns (303, 301) formed in a longitudinal direction of a heater substrate, the inclination of a tangent line of the shortest route (311) of current flowing in the heating element patterns (302) changes multiple times or continuously from a starting point (313) to an intermediate point (314) between the starting point and an end point (316).SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a heater used in a fixing device that fixes a toner image formed by an image forming unit onto a recording material. [Background technology]

[0002] There are known image forming apparatuses that form an unfixed toner image corresponding to image information on a recording material such as paper or glossy film by an image forming process such as electrophotography, electrostatic recording, magnetic recording, etc. In such image forming apparatuses, in order to fix the toner image on the surface of the recording material as a permanently fixed image, a heat treatment (fixing process) is performed in which the toner image is melted by an image heating device (fixing device) and brought into close contact with the recording material.

[0003] A commonly known fixing device is a film heating type shown in Patent Document 1. The fixing device of this type is mainly composed of a fixing film, a plate-shaped heater equipped with a heating element that is placed in the internal space of the fixing film and generates heat when electricity is applied, and a pressure roller that is in pressure contact with the heater via the fixing film to form a nip. The fixing device of the film heating type has a small thermal capacity, and is therefore characterized by quick start-up and excellent power saving.

[0004] The fixing device may continuously print recording materials that are narrow in the direction perpendicular to the recording material conveyance direction (longitudinal direction of the heater, fixing film, and other components). In this case, a phenomenon occurs in which the temperature of the heater, fixing film, and other components in the portion where the recording material does not pass (hereinafter, non-paper passing portion) rises (non-paper passing portion temperature rise). When non-paper passing portion temperature rise occurs, the print speed is reduced to make the temperature of the heated components below the heat resistance temperature.

[0005] For this reason, Patent Document 2 shows a configuration in which the heating element of the heater is divided into multiple heating regions in the longitudinal direction of the recording material, and the heat generation can be controlled independently. In this configuration, the heat generation in the heating regions corresponding to the non-paper passing portions is reduced, thereby suppressing the temperature rise in the non-paper passing portions and preventing a decrease in the printing speed.

[0006] Furthermore, in Patent Document 2, a heating element is arranged in parallel between two conductors arranged approximately parallel to the longitudinal direction on a heater substrate, and a current flows in the short direction of the heater (parallel to the conveying direction of the recording material). In this configuration, even if a temperature rise occurs partially in non-paper passing areas within the same heat generation area, the resistance value of the heating element increases in the heated area, and the current flows in a detour, so that the temperature rise in the non-paper passing areas can be suppressed due to the positive resistance-temperature characteristics of the heating element.

[0007] Furthermore, Patent Document 3 discloses a configuration in which each heating element is arranged in parallel between two conductors and angled with respect to the short direction of the heater, thereby reducing the longitudinal temperature unevenness that occurs between the heating element portion and the gap where there is no heating element. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 4-44075 [Patent Document 2] JP 2014-59508 A [Patent Document 3] Patent Publication No. 2022-142622 Summary of the Invention [Problem to be solved by the invention]

[0009] In a heater in which the heating element is formed at an angle between two conductors to reduce temperature unevenness as in Patent Document 3, there is a problem that when the heater drive voltage applied between the two conductors is high, the heater deteriorates faster and its lifespan is shortened.

[0010] The present invention has been made in consideration of the above problems, and an object of the present invention is to reduce temperature unevenness and suppress deterioration of the heater. [Means for solving the problem]

[0011] In order to achieve the above object, a heater in the present invention includes a heater substrate, a first conductor arranged on a surface of the heater substrate along a longitudinal direction, a second conductor arranged parallel to the first conductor in the longitudinal direction of the heater substrate with a gap therebetween, and a heating element arranged between the first conductor and the second conductor in the lateral direction of the heater substrate and electrically connecting the first conductor and the second conductor, In a heater in which current flows through the heating element and generates heat when electricity is passed between the first conductor and the second conductor, the shortest path of current flowing through the heating element from one of the first conductor and the second conductor to the other is not a straight line, the slope of the tangent to the shortest path changes multiple times or continuously in at least a portion of the region between the one conductor and the other conductor until it reaches a midpoint from the one conductor to the other conductor, and the shortest path runs from the one conductor to the other conductor without being folded back in the longitudinal direction. Effect of the Invention

[0012] According to the present invention, it is possible to reduce temperature unevenness and suppress deterioration of the heater. [Brief description of the drawings]

[0013] [Figure 1] 1 is a schematic diagram of an image forming apparatus according to a first embodiment of the present invention; [Diagram 2] 1 is a schematic cross-sectional view of a fixing device 200 according to a first embodiment of the present invention; [Diagram 3] Cross-sectional and plan views of a heater 300 according to a first embodiment [Figure 4] FIG. 1 is a diagram showing a heat generation pattern of a heater 300 according to a first embodiment; [Diagram 5] FIG. 1 is a diagram showing a heating pattern of a heater in Comparative Example 1. [Figure 6] FIG. 13 is a diagram showing a heating pattern of a heater in Comparative Example 2. [Figure 7] FIG. 13 is a diagram showing a heating pattern of a heater in Comparative Example 3. [Figure 8]FIG. 13 is a diagram showing a heating pattern of a heater in Comparative Example 4. [Figure 9] FIG. 1 is a diagram comparing the heat distribution of the heater heat pattern in the first embodiment with the heat distribution of the heater heat pattern in the comparative example. [Figure 10] FIG. 1 is a diagram comparing equipotential lines of the heating pattern of the heater in the first embodiment and the heating pattern of the comparative example. [Figure 11] FIG. 11 is a diagram showing a heating pattern of a heater in another embodiment of the first embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, the embodiment of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative positions of the components described in the embodiment may be changed as appropriate depending on the configuration of the device to which the invention is applied and various conditions. In other words, the scope of the present invention is not limited to the following embodiment. EXAMPLES

[0015] The image forming apparatus, the fixing device, and the heater of this embodiment will be described first, and finally, the shape of the heating element of the heater, which is a characteristic feature of the present invention, will be described in detail.

[0016] [General configuration of image forming device] FIG. 1 is a schematic diagram showing an example of an electrophotographic laser beam printer as an image forming apparatus. Here, an image forming operation in an image forming apparatus 10 will be described. Recording materials 30 (paper) are fed one by one from a paper feed tray 11 by a paper feed roller 12, and are conveyed to a process cartridge 14 at a predetermined timing by a conveying roller 13. The process cartridge 14 also incorporates a photosensitive drum 15, a charging means 16, and a developing means 17. The charging means 16 is disposed in pressure contact with the photosensitive drum 15, and the surface of the photosensitive drum 15 is uniformly charged by the charging means 16. Thereafter, exposure based on image information is performed by a scanner unit 19, which is an exposure means, and an electrostatic latent image is formed on the surface of the photosensitive drum 15. The developing means 17 is provided downstream of the exposure position in the rotation direction of the photosensitive drum 15. When the electrostatic latent image formed on the photoconductor drum 15 comes to a position facing the developing means 17, toner is supplied from the developing means 17 to the electrostatic latent image, and a toner image (visible image) is formed on the photoconductor drum 15.

[0017] On the other hand, the recording material 30 is transported at a timing synchronized with the moving speed of the toner image formed on the photosensitive drum 15. Then, when the recording material 30 reaches the photosensitive drum 15, the toner image on the photosensitive drum 15 is transferred to the recording material 30 at a transfer nip formed by the pressure contact portion between the photosensitive drum 15 and the transfer roller 20.

[0018] The recording material 30 onto which the toner image has been transferred is conveyed to a fixing device 200 having a heater 300 formed with a heating element that generates heat when supplied with power. The fixing device 200 is made up of two rotating members that rotate while facing each other and pressing against each other, and fixes the toner image on the recording material 30 by heat and pressure.

[0019] Thereafter, the recording material 30 is discharged to the outside of the apparatus by discharge rollers 22 and 23, and a series of printing operations is completed. Reference numeral 18 denotes a cleaning means for cleaning the photosensitive drum 15.

[0020] 1, the image forming apparatus may be, for example, a color image forming apparatus having a plurality of image forming units corresponding to the respective colors.Furthermore, the image forming apparatus may be an image forming apparatus having a primary transfer unit that transfers the toner image on the photosensitive drum 15 to the intermediate transfer belt, and a secondary transfer unit that transfers the toner image on the intermediate transfer belt to a sheet.

[0021] [Configuration of Fixing Device 200] 2 is a schematic cross-sectional view of the fixing device 200 in this embodiment. The fixing device 200 has a fixing film 202 as a belt member, and a heater 300 that is disposed in the internal space of the fixing film 202 and contacts the inner surface of the fixing film 202. The fixing device 200 also has a pressure roller 208 as a nip forming member that forms a fixing nip portion N together with the heater 300 via the fixing film 202, and a metal stay 204.

[0022] The fixing film 202 is a cylindrically formed multi-layer heat-resistant film, with a base layer made of a thin heat-resistant resin such as polyimide or a metal such as stainless steel. The surface of the fixing film 202 is coated with a heat-resistant resin with excellent releasability such as tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA) to form a release layer in order to prevent toner adhesion and ensure separability from the recording material P. Furthermore, to improve image quality, a heat-resistant rubber such as silicone rubber may be formed as an elastic layer between the base layer and the release layer.

[0023] The pressure roller 208 has a core metal 209 made of iron, aluminum or the like, and an elastic layer 210 made of silicone rubber or the like.

[0024] The heater 300 has a heating element, electrodes for power supply, and a protective layer formed on a ceramic heater substrate 305, and generates heat when electricity is applied to the heating element. The heater substrate 305 may be made of a metal plate other than ceramic material, and in that case, an insulating layer may be added between the electrodes or heating element and the metal plate. The protective layer formed on the heater 300 includes a surface protective layer 308 provided on the side of the fixing nip N and a surface protective layer 307 provided on the opposite side of the fixing nip N. A plurality of electrodes (electrode E3 described below is shown here as a representative) and electrical contacts (electrical contact C3 described here as a representative) are provided on the opposite side of the fixing nip N, and each electrical contact supplies power to each electrode. The heater 300 will be described in detail later.

[0025] A safety element 212 such as a thermoswitch or a thermal fuse that is activated when the heater 300 generates abnormal heat to cut off the power supplied to the heater 300 is in direct contact with the heater 300 or indirectly via the holding member 201 .

[0026] The heater 300 is held by a heater holding member 201 made of heat-resistant resin, and heats the fixing film 202. The heater holding member 201 has a guide function for guiding the rotation of the fixing film 202.

[0027] The metal stay 204 urges the heater holding member 201 holding the heater 300 toward the pressure roller 208 when subjected to a pressure force (not shown), thereby forming a fixing nip portion N between the fixing film 202 and the pressure roller 208 .

[0028] The pressure roller 208 receives power from a motor (not shown) and rotates in the direction of arrow R1. As the pressure roller 208 rotates, the fixing film 202 rotates in the direction of arrow R2. The unfixed toner image on the recording material P is fixed by applying heat from the fixing film 202 while nipping and conveying the recording material P in the fixing nip N. In order to ensure the sliding properties of the fixing film 202 and obtain a stable driven rotation state, a highly heat-resistant fluorine-based lubricating grease (not shown) is interposed between the heater 300 and the fixing film 202.

[0029] In addition to the grease, other members such as a sheet member may be interposed between the heater and the fixing film in order to ensure sliding properties and to smooth out temperature variations.

[0030] [Heater 300 Configuration] The configuration of heater 300 will be described with reference to Figure 3. Figure 3(A) is a cross-sectional view of heater 300, and Figure 3(B) is a plan view of each layer of heater 300. Figure 3(B) shows a transport reference position X of recording material P in image forming apparatus 1. The transport reference in this embodiment is the center reference, and recording material P is transported so that its center line in a direction perpendicular to the transport direction (longitudinal direction) is aligned with transport reference position X. Figure 3(A) is also a cross-sectional view of heater 300 at transport reference position X.

[0031] The heater 300 has a ceramic heater substrate 305 as a planar base material. A back surface layer 1 and a back surface layer 2 covering the back surface layer 1 are provided on the heater substrate 305. In addition, a sliding surface layer 1 and a sliding surface layer 2 covering the sliding surface layer 1 are provided on the surface of the heater substrate 305 opposite to the back surface layer 1.

[0032] Conductor patterns 301 and 303 are formed on the back surface layer 1 in the longitudinal direction of a heater substrate 305 in a substantially parallel manner. Conductor pattern 301 is divided into 301a on the upstream side and 301b on the downstream side in the transport direction (short side direction of the substrate), but are electrically connected and function as one conductor pattern. Heater pattern 302 is formed between conductor pattern 301 and conductor pattern 303. Heater pattern 302 is configured so that a heater generates heat when electricity is passed between conductor patterns 301 and 303 in the transport direction.

[0033] Like the conductive pattern 301, the heating elements are also arranged separately on the upstream side (302-1a, etc.) and downstream side (302-1b, etc.) in the transport direction.

[0034] The conductive pattern 303 is divided into five longitudinal regions (A1 to A5) (303-1 to A5), each of which is connected to an independent power supply circuit. Therefore, the heat generation amount of the heating elements (302-1 to A5) in each longitudinal region can be controlled independently, and as in Patent Document 2, the temperature rise in non-paper passing areas can be suppressed even when narrow recording materials are passed through.

[0035] In this embodiment, of the five divided longitudinal regions, the longitudinal width of the A3 region in the longitudinal center is 145 mm, which is close to the width of an A5 sized paper. The longitudinal width including the outer regions A2 and A4 is 185 mm, which is close to the width of a B5 sized paper. The width including the outer regions A1 and A5 is 220 mm, which is close to the width of a letter sized paper. In other words, the length of the entire heating element is 220 mm.

[0036] The number of divisions of the heat generating element is arbitrary, and the heat generating elements at symmetrical positions (eg, 302-2 and 302-4) which are independently driven in this embodiment may be driven as one heat generating element.

[0037] In the figure, E1 to E5 are electrical contacts for supplying power to the heating elements, and E6 is a common electrode contact. By configuring various patterns in this way, a current path is formed that flows from the power supply electrodes E1 to E5, which are independent for each heating element, via each of the conductor patterns 303-1 to 5, through each of the heating elements 302-1 to 5, and through the conductor pattern 301 to the common electrode E6.

[0038] The back surface layer 2 is composed of an insulating surface protective layer 307 (glass in this embodiment), and covers the conductors 301, 303, and heating element 302. The surface protective layer 307 is formed except for the location of the electrode E, and is configured so that an electrical contact C (not shown) can be connected to the electrode E from the back surface layer 2 side of the heater.

[0039] Thermistors TH (TH-1 to TH-7) serving as temperature detection means are formed on the sliding surface layer 1 located on the opposite side of the back surface layer 1 across the heater substrate 305 in order to detect the temperature of each longitudinal region in which the heating elements 302-1 to 5 are arranged. Also formed are conductors ET1 to ET7 functioning as independent wiring patterns for extracting temperature signals detected by each thermistor, and a conductor EG functioning as a wiring pattern for power supply common to each thermistor.

[0040] In this way, by providing a temperature detection means for each heating region heated by each heating element, it is possible to control the heating regions A1 to A5 of the heaters aligned in the longitudinal direction to different temperatures independently.

[0041] The sliding surface layer 2 is composed of a surface protection layer 308 (glass in this embodiment) having slidability and insulating properties, and covers the thermistor TH, the conductor ET, and the conductor EG while ensuring slidability with the inner surface of the fixing film 202. The surface protection layer 308 is formed except for both longitudinal ends of the heater 300 in order to provide electrical contacts with the conductors ET and EG.

[0042] The resistance of the heating elements is set to 1440 W in total when connected to a commercial 120 V AC power source. In other words, the combined resistance when each heating element is connected in parallel is 10 Ω.

[0043] [Heater heating element pattern shape] Fig. 4 is a detailed diagram showing the shape of heater heating element 302-3a in the portion surrounded by dotted line portion 309 in Fig. 3. Conductor pattern 303-3 and conductor pattern 301a are shown at the top and bottom of the figure, respectively, with heating element 312 formed in parallel between them. The portion between the conductor patterns where no heating element is formed is electrically insulated, so no current flows and no heat is generated.

[0044] In this embodiment, in order to reduce temperature unevenness in the longitudinal direction, each heating element is arranged at an angle to the short side direction (transport direction, vertical direction in FIG. 4) of the heater 300. In addition, the heating element 312 in this embodiment is not a straight rod shape, but is curved as shown below. The dashed line 310 in the figure indicates the middle line between the conductor patterns 303-3 and 303-3, and the dashed line 311 indicates the shortest path of the current flowing through the heating element 312 from the conductor pattern 303-3 to the conductor pattern 301a. Since the heater drive voltage applied between the conductor patterns generates an electric field in the vertical direction in the figure, the current flows most in the shortest path in the vertical direction in the heating element. As a result, the place where the amount of heat generated is large is also likely to be concentrated on the shortest path 311.

[0045] The shape of the heating element in this embodiment has the following features. The first is that the shortest path 311 of the current flowing through the heating element 312 is not a straight line, but at least a part of the shortest path 311 is curved. The second is that the heating element pattern is configured so that the inclination of the tangent of the shortest path 311 changes multiple times or continuously until it reaches the midpoint 314 between one conductor pattern side and the other conductor pattern side. The third is that the shortest path 311 is configured to go from one conductor pattern 303-3 to the other conductor pattern 301a without being folded back in the longitudinal direction of the heater substrate 305. In other words, the shortest path 311 is configured to go from one side to the other in the longitudinal direction (left and right direction in the figure) when going from one side to the other in the lateral direction (up and down direction in the figure), but not vice versa. It can also be said that the heating element shape does not overlap in the lateral direction.

[0046] 4, an example will be described of the locus on shortest path 311 from conductor pattern 303-3 to midpoint 314. First, starting from left end 313 of the boundary between conductor pattern 303-3 and heating element 312, the path forms a curve that follows the left contour of the curved heating element to a point indicated as midpoint 315, and the slope of the tangent to shortest path 311 changes continuously. From midpoint 315 to midpoint 314, the path forms a straight line that crosses the heating element.

[0047] In this embodiment, the distance from when the inclination of the tangent point first changes to when it last changes is called the "distance of the inclination change region." The ratio of the distance (inclination change distance) from the end point 313 to the midpoint 314 in the shortest path 311 to the point where the inclination of the tangent point first changes to when it last changes is called the "inclination change region ratio." In this embodiment, the point where the inclination of the tangent point first changes is the left end 313, and the point where the inclination of the tangent point last changes is the midpoint 315. In this embodiment, the inclination change region distance ratio is set to about 50%.

[0048] If the slope change area distance ratio is set small and the area where the slope of the tangent of the shortest current path 311 changes is concentrated within too short a distance, heat will be concentrated in a small area, and sufficient effect of suppressing deterioration of the heater 300 will not be obtained. The effect of suppressing deterioration of the heater can be obtained by ensuring that the slope change area distance ratio is at least 20% or more. Also, although the slope of the tangent of the shortest path 311 changes, it proceeds from right to left in the figure and does not overlap in the short direction.

[0049] Next, the positional relationship between heating element 312 and heating element 317, which are arranged side by side in the longitudinal direction in Fig. 4, will be described. F1 in the figure indicates the longitudinal distance from start point 313 to end point 316 of shortest current path 311, that is, the longitudinal width through which the shortest current path passes. Also, G1 in the figure indicates the distance from end point 316 of shortest current path 311 to the start point of shortest current path 318 of the adjacent heating element 317 (that is, the longitudinal width through which the shortest current path does not pass).

[0050] In this embodiment, the heating elements are arranged so that the relationship F1>G1 is satisfied. By arranging them in this way, the width of G1, which is the longitudinal region where the shortest current path does not pass and where the amount of heat generated is relatively small, is narrowed, and uneven heating and the associated uneven gloss of the image can be reduced.

[0051] [Effect of the Heating Element Pattern in this Example] Next, in order to demonstrate the effects of this embodiment, the heating element pattern of this embodiment in FIG. 4 is compared with a heating element pattern of a comparative example shown below in terms of heater durability and temperature unevenness in the longitudinal direction.

[0052] Fig. 5 is a diagram showing the heating element shape of Comparative Example 1. Similar to Patent Document 3, Comparative Example 1 has a diagonal rod-like heating element shape 322 that can reduce uneven heating. The shortest path 321 of current in Comparative Example 1 is a straight line as shown in Fig. 5. That is, in the heating element shape 322 in Comparative Example 1, the gradient of the tangent of the shortest path 321 from the left end 323 of the boundary between the heating element 322 and the conductor pattern 303-3 to the midpoint 324 never changes.

[0053] Fig. 6 is a diagram showing a heating element pattern of Comparative Example 2. As shown by heating element 332 in Fig. 6, in Comparative Example 2, the slope of the tangent line changes only once at midpoint 335 from the left end of the boundary with conductor pattern 303-3 to midpoint 334.

[0054] 7 is a diagram showing a heating element pattern of Comparative Example 3. In Comparative Example 3, similar to Comparative Example 2, the shortest current path 341 has a polygonal shape in which the slope of the line changes only once at midpoint 345 from left end 343 of the boundary with conductor pattern 303-3 to midpoint 344.

[0055] FIG. 8 is a diagram showing the heating element pattern of Comparative Example 4. In Comparative Example 4, as shown in 352 in FIG. 8, the heating element is folded back in the longitudinal direction. This configuration is known from JP 2021-33254 A. In Comparative Example 3, the inclination of the tangent of the shortest current path 351 changes multiple times (three times) up to the midpoint 354, and the shortest current path is folded back twice in the longitudinal direction to form a heating element shape.

[0056] To compare durability, a print endurance test was conducted with the heater drive voltage set to 140V, assuming a high voltage would be applied. Those in which deterioration of the heating element was observed before the planned number of prints (100%) was reached were marked with an X, those in which deterioration of the heating element was observed before reaching 1.5 times the lifespan were marked with a △, and those in which no deterioration was observed even after 1.5 times the lifespan were marked with an ◯. Regarding heater deterioration, those in which the resistance value of the heater (the resistance value between conductor patterns 303-3 and 301a) had increased by 3% or more from the initial value were deemed to have deteriorated.

[0057] The durability comparison results are shown in Table 1 below.

[0058] [Table 1]

[0059] In the heating element patterns of Comparative Examples 1, 2, and 3, deterioration of the heater (increase in resistance value) was observed before reaching 1.5 times the expected life. In contrast, the heating element pattern of this embodiment showed no deterioration, and improved durability was confirmed. In addition, no temperature unevenness occurred in this embodiment and Comparative Examples 1, 2, and 3.

[0060] The heating element pattern of Comparative Example 4 showed no problems with durability or temperature unevenness, but another problem arose because the heating element pattern was folded back. In other words, in order to prevent the folded heating elements from overlapping each other in the short-side direction and to electrically insulate them, in addition to the heating element width corresponding to the number of times it was folded back, a blank area 356 where no heating element was generated was required, and the short-side width of the heating element (the distance between the conductor patterns) was greatly expanded. As a result, the short-side width of the heater was expanded, and the fixing device became larger in size.

[0061] [Reasons why effects were achieved in the examples] Next, a description will be given of the presumed reason why the difference in durability occurred between the embodiment and comparative example 1. Fig. 9 is a diagram comparing the heat generation distribution (simulation results) of the heaters in this embodiment and comparative example 1.

[0062] 9(a) shows the heat generation distribution of the embodiment, and (b) shows the heat generation distribution of the comparative example 1. In the figure, parts with a large amount of heat generation are shown in dark colors, and parts with a small amount of heat generation are shown in light colors, and for comparison, the total amount of heat generation is set to the same value for both.

[0063] In both the example and comparative example 1, the portion where the shortest current path approaches the contour (boundary line) of the heating element is displayed darker, and the amount of heat generated is greater. Specifically, in the example, this is the portion indicated by the two-dot-and-one-chain line 353 in Fig. 9(a), and in the comparative example 1, this is the portion indicated by the two-dot-and-one-chain line 363 in Fig. 9(b).

[0064] Here, it can be seen that in Comparative Example 1, heat generation is excessively concentrated at the center of point 363. In contrast, in the Example, areas with high heat generation are distributed in a dispersed manner in area 353 near the outline of the heating element where the shortest current path is continuously curved.

[0065] The reason for this difference in the degree of concentration of heat generation is as follows. Figure 10 shows equipotential lines in a heating element when current is applied to the heating element. Figure 10(a) shows equipotential lines 359 in this embodiment, and Figure 10(b) shows equipotential lines 369 in Comparative Example 1. The equipotential lines 369 in Comparative Example 1 shown in Figure 10(b) are dense in the location indicated by 363 where the concentration of heat generation was observed, and a large potential difference occurs in a small area. Since the amount of heat generation is proportional to the square of the potential difference, this explains why heat generation is concentrated in such a location where the equipotential lines are dense.

[0066] 10(a) of the embodiment, the equipotential lines 359 are not as dense as those of the comparative example 1, and the concentration of heat generation is suppressed. The equipotential lines tend to be spaced closer together in the region 353 where the slope of the tangent to the shortest current path changes, and heat generation tends to concentrate therein. In this embodiment, the slope change region distance ratio is set to 20% or more (about 50% in this embodiment), as described above, so that the range of this region 353 can be secured wider, and the equipotential lines are evenly distributed within the region to prevent concentration, thereby suppressing the concentration of heat generation.

[0067] In the comparative example, the heating element deteriorates in the area where heat is excessively concentrated, causing an increase in heater resistance. On the other hand, in the example, heat is not excessively concentrated in a small area, so the heater does not deteriorate due to wear and tear, and durability is improved.

[0068] According to the results of the simulation of heat generation distribution shown in FIG. 9, the heat generation amount at the location with the greatest amount of heat generation (the darkest part) in the embodiment shown in FIG. 9(a) was reduced to half of the heat generation amount at the location with the greatest amount of heat generation (the center part of 363 in the figure) in Comparative Example 1 shown in FIG. 9(b).

[0069] In the cases of Comparative Examples 2 and 3, in which the shortest current path bends once before the midpoint, heat concentration was observed at point 335 in Fig. 6 and point 345 in Fig. 7, where the current path bends, as in Comparative Example 1. The decrease in durability shown in Table 1 occurs for the same reason as in Comparative Example 1.

[0070] In the case of Comparative Example 4, where the shortest current path bends multiple times before reaching the midpoint, the places where heat is likely to concentrate are dispersed into multiple locations, and the distance of the shortest current path is long, reducing the amount of heat generated per unit length, so no deterioration of the heating element was observed. Increasing the distance between the conductor patterns and lengthening the current path as in Comparative Example 4 can prevent heat concentration. However, this increases the width of the heater in the short direction, resulting in larger heaters and fixing devices.

[0071] [Other embodiments] Fig. 11 is a diagram showing the shape of a heating element in another embodiment. Compared to the shape of the heating element in Fig. 4, adjacent heating elements are arranged upside down and connected to each other on the conductive pattern side of the heating elements.

[0072] Similar to the heating element pattern in Fig. 4, the slope of the tangent of the shortest current path 361 changes continuously between position 363 and position 365, up to the midpoint 364 between the conductor patterns. Therefore, similar to the heating element shape in Fig. 4 of this embodiment, heat is not concentrated in a small area, and deterioration of the heater can be suppressed. Also, the width F2 through which the shortest current path passes is wider than the width G2 through which the shortest path does not pass, and the occurrence of temperature unevenness can be similarly suppressed.

[0073] In the case of the heating element in FIG. 4, in order to insulate adjacent heating elements from each other, the heating elements need to be spaced apart by a certain distance or more. However, in the case of the heating element in FIG. 11, the heating elements are connected to each other near the conductor pattern, so there is no need to separate them, and there is an advantage in that there is a high degree of freedom in arrangement. Also, in the case of the heating element in FIG. 11, in order to stabilize the electrical connection between the heating element and the conductor pattern, the heating element is often formed so that it partially invades (overlaps) the conductor pattern as shown by 369 in the figure. The configuration in FIG. 11 has fewer connections between the heating element and the conductor pattern than the configuration in FIG. 4, so the total area of ​​the heating element invading the conductor pattern can be reduced, and even in such a case, there is an advantage in that the amount of material used for the heating element can be reduced.

[0074] As described above, according to this embodiment, it is possible to reduce temperature unevenness and suppress deterioration of the heater even when the heater driving voltage is high. In addition, it is possible to prevent the width of the heater in the short direction from becoming excessively large. [Explanation of symbols]

[0075] 10 Image forming device 11 Paper feed tray 12 Paper feed roller 13 Conveyor roller 14 Process cartridge 15 Photosensitive drum 16 Charging means 17 Developing methods 18 Cleaning means 19 Scanner unit 20 Transfer roller 22 Paper ejection roller 23 Paper ejection roller 30 Recording materials 200 Fixing device 201 Retaining member 202 Fixing film 204 Metal Stay 208 Pressure roller 209 Core 210 Elastic layer 212 Safety element 300 Heater 301 Conductive Pattern 302 Heating element pattern 303 Conductive Pattern 305 Heater Board 307 Surface protective layer 308 Surface protective layer

Claims

1. A heater substrate; a first conductor disposed on a surface of the heater substrate along a longitudinal direction; a second conductor arranged parallel to the first conductor in the longitudinal direction of the heater substrate and spaced apart from the first conductor in the lateral direction of the heater substrate; a heating element disposed between the first conductor and the second conductor in the short-side direction of the heater substrate and electrically connecting the first conductor and the second conductor; a heater having a first conductor and a second conductor, the heater generating heat by passing a current through the heating element, the shortest path of a current flowing through the heating element from one of the first conductor and the second conductor to the other conductor is not a straight line; The gradient of the tangent of the shortest path changes multiple times or continuously in at least a part of a region between the one conductor and the other conductor until the midpoint is reached, and A heater, wherein the shortest path runs from the one conductor to the other conductor without being folded back in the longitudinal direction.

2. When the ratio of the distance from the first change to the last change in the slope of the tangent of the shortest path to the distance to the midpoint of the shortest path of the current from the one conductor to the other conductor is defined as the slope change range ratio, 2. The heater according to claim 1, wherein the ratio of the slope change area is 20% or more.

3. 3. The heater according to claim 1, wherein at least a part of the shortest path of the current is a curve.

4. The heating elements are arranged side by side in the longitudinal direction of the heater substrate, The distance in the longitudinal direction from the start point to the end point of the shortest path through the heating element is F1, When the distance in the longitudinal direction between the end point of the shortest path and the start point of the shortest path of the current flowing through the heating element disposed adjacent thereto in the longitudinal direction is G1, F1>G1 4. The heater according to claim 1, wherein the following relationship is satisfied:

5. 5. The heater according to claim 1, wherein patterns of the first conductor, the second conductor, and the heating element are formed on a back surface layer of the heater substrate, and a thermistor is provided on a sliding surface layer opposite the back surface layer of the heater substrate.

6. A cylindrical fixing film; The heater according to claim 1 , which is disposed in the internal space of the fixing film; a pressure roller that is in pressure contact with the heater via the fixing film to form a nip portion; having A fixing device heats the toner formed on the conveyed recording material in the nip portion, thereby fixing the toner to the recording material.

7. an image forming means for forming a toner image on a recording material; a fixing device as claimed in claim 2 for fixing a toner image formed on said recording material by said image forming means onto said recording material; An image forming apparatus comprising:

Images