JP6217815B1 - Heating device, fixing device, image forming device - Google Patents

Abstract

When a planar heating element is overheated, a current path in the planar heating element is easily interrupted. A heating device includes a planar heating element that generates heat when an electric current flows through the heating apparatus, and imparts tension to the planar heating element in a crossing direction that intersects a thickness direction of the planar heating element. A section. [Selection] Figure 4

Description

  The present invention relates to a heating device, a fixing device, and an image forming apparatus.

  Patent Document 1 discloses the following configuration. In the configuration of Patent Document 1, IR sensors are provided outside both ends of the fixing belt. This IR sensor is provided in a direction to look inside the fixing belt from the window portion at the end of the fixing belt, and measures the amount of radiant energy from a heating element provided inside the fixing belt. The control unit determines whether an abnormally high temperature has occurred in the heating element based on the output value from the IR sensor, and stops supplying power to the heating element when it is determined that an abnormality has occurred. Control.

Japanese Patent Laying-Open No. 2015-111182

  Here, when a planar heating element that generates heat due to current flowing through itself is overheated, the planar heating element blows off to interrupt the current path and stop the heating state of the planar heating element. Conceivable.

  An object of the present invention is to make it easier to interrupt a current path in a planar heating element when the planar heating element is overheated compared to a configuration in which no tension is applied to the planar heating element.

  The invention according to claim 1 is a planar heating element that generates heat when a current flows through itself, and an applying unit that applies tension to the planar heating element in a crossing direction that intersects the thickness direction of the planar heating element. And comprising.

In the invention of claim 1, the planar heating element is formed with a plurality of holes.

According to a second aspect of the present invention, in the planar heating element, the aperture ratio of the holes has a distribution in the intersecting direction.

In the invention of claim 3, the planar heating element has a plurality of rows in which the holes are arranged in the intersecting direction, each hole in one row, and each hole in another row adjacent to the row. Are arranged so as to be shifted in the crossing direction.

According to a fourth aspect of the present invention, the planar heating element is made of a material having a melting temperature of 700 ° C. or lower.

The invention of claim 5 includes a belt heated by the planar heating element, and a pressure member that pressurizes the recording medium with the recording medium sandwiched between the belt.

According to a sixth aspect of the present invention, both end portions in the axial direction of the belt are non-passing portions through which the recording medium does not pass, and the planar heating element is located in the center in the axial direction at both end portions in the axial direction. The aperture ratio is smaller than the part side.

A seventh aspect of the invention includes an image forming unit that forms an image on a recording medium, and a fixing device according to the fifth or sixth aspect that fixes the image formed on the recording medium to the recording medium.

  According to the configuration of the first aspect of the present invention, when the planar heating element is overheated, the current path in the planar heating element is likely to be interrupted as compared with the configuration in which no tension is applied to the planar heating element.

According to the configuration of the first aspect of the present invention, the current path in the planar heating element is easily interrupted by the tension applied to the planar heating element, as compared with the configuration including the planar heating element having no plurality of holes. .

According to the configuration of the second aspect of the present invention, compared to the configuration in which the aperture ratio of the holes is constant in the crossing direction, the ease of blocking the current path in the planar heating element can be adjusted in the crossing direction.

According to the configuration of the third aspect of the present invention, the width of the current path in the planar heating element compared to the configuration in which the holes in one row and the holes in the other row are arranged at the same position in the crossing direction. The variation of the can be reduced.

According to the configuration of claim 4 of the present invention, the current path in the planar heating element is more likely to be interrupted as compared with the configuration in which the planar heating element is formed of a material having a melting temperature exceeding 700 ° C.

According to the structure of Claim 5 of this invention, it can suppress that a belt is overheated compared with the structure by which tension | tensile_strength is not provided to a planar heating element.

According to the configuration of the sixth aspect of the present invention, it is possible to suppress variation in the axial direction of the ease of blocking the current path in the planar heating element, as compared with the configuration in which the aperture ratio is constant in the belt axial direction.

According to the configuration of the seventh aspect of the present invention, it is possible to suppress the component parts of the image forming apparatus including the fixing device from being overheated as compared with the configuration in which no tension is applied to the planar heating element.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an exemplary embodiment. 1 is a schematic diagram illustrating a configuration of a fixing device according to an exemplary embodiment. FIG. 3 is a perspective view illustrating a configuration of one end portion in a longitudinal direction of the fixing module according to the present embodiment. FIG. 3 is a perspective view illustrating a configuration of the other end portion in the longitudinal direction of the fixing module according to the embodiment. It is an expanded view which shows the structure of the planar heating element which concerns on this embodiment. It is sectional drawing which shows the structure of the planar heating element which concerns on this embodiment. It is the schematic which shows distribution of the emitted-heat amount of the planar heating element which concerns on this embodiment. It is sectional drawing which shows the state to which tension | tensile_strength was provided in the structure shown in FIG. It is the schematic which shows a mode that a current pathway is interrupted | blocked in the planar heating element which concerns on this embodiment. It is the schematic which shows the arrangement | positioning of the hole of the planar heating element which concerns on this embodiment, and the relationship of the emitted-heat amount. It is the schematic which shows the arrangement | positioning of the hole of the planar heating element which concerns on a comparative example, and the relationship of the emitted-heat amount. It is an expanded view which shows the modification which made the aperture ratio of the planar heating element constant in the longitudinal direction. It is the schematic which shows the modification which made the shape of the hole of a planar heating element into a regular hexagon.

  Below, an example of an embodiment concerning the present invention is described based on a drawing.

(Image forming apparatus 10)
First, the configuration of the image forming apparatus 10 will be described. FIG. 1 is a schematic diagram illustrating a configuration of the image forming apparatus 10.

  As shown in FIG. 1, the image forming apparatus 10 includes an image forming apparatus main body 11 in which each component is provided. Inside the image forming apparatus main body 11, a plurality of storage units 12 that store recording media P such as paper, an image forming unit 14 that forms images on the recording media P, and images formed on the recording media P are stored. And a fixing device 60 (an example of a heating device) that fixes the recording medium P. Further, inside the image forming apparatus main body 11, there are a transport section 16 that transports the recording medium P from each storage section 12 to the image forming section 14, and a control section 20 that controls the operation of each section of the image forming apparatus 10. Is provided. A discharge unit 18 for discharging the recording medium P is provided on the upper part of the image forming apparatus main body 11.

  The image forming unit 14 includes image forming units 22Y, 22M, 22C, and 22K (hereinafter referred to as “forming units”) that form toner images of colors of yellow (Y), magenta (M), cyan (C), and black (K). 22Y to 22K) and an intermediate transfer belt 24 (transfer body) to which the toner images formed by the image forming units 22Y to 22K are transferred. Further, the image forming unit 14 transfers a toner image formed by each of the image forming units 22Y to 22K to the intermediate transfer belt 24, and the toner image transferred to the intermediate transfer belt 24 to the intermediate transfer belt 24. And a secondary transfer roll 28 for transferring to the recording medium P. The image forming unit 14 is not limited to the above-described configuration, and may be another configuration as long as it forms an image on the recording medium P.

  Each of the image forming units 22Y to 22K includes a photoreceptor 32 that rotates in one direction (for example, counterclockwise in FIG. 1). Since the image forming units 22Y to 22K are configured in the same manner, the reference numerals of the respective portions in the image forming units 22Y, 22M, and 22C are omitted in FIG.

  Around each photoconductor 32, in order from the upstream side in the rotation direction of the photoconductor 32, the charging device 23 for charging the photoconductor 32 and the photoconductor 32 charged by the charging device 23 are exposed to electrostatically charge the photoconductor 32. An exposure device 36 that forms a latent image and a developing device 38 that develops the electrostatic latent image formed by the exposure device 36 to form a toner image are provided.

  The intermediate transfer belt 24 is formed in an annular shape and is disposed on the upper side of the image forming units 22Y to 22K. On the inner periphery of the intermediate transfer belt 24, winding rolls 42, 43, and 45 around which the intermediate transfer belt 24 is wound are provided. For example, the intermediate transfer belt 24 rotates (rotates) in one direction (for example, the clockwise direction in FIG. 1) while being in contact with each photoconductor 32 when the winding roll 45 is driven to rotate. . The winding roll 42 is an opposing roll that faces the secondary transfer roll 28.

  The primary transfer roll 26 faces the photoconductor 32 with the intermediate transfer belt 24 interposed therebetween. Between the primary transfer roll 26 and the photoconductor 32 is a primary transfer position T1 at which the toner image formed on the photoconductor 32 is transferred to the intermediate transfer belt 24.

  The secondary transfer roll 28 faces the winding roll 42 with the intermediate transfer belt 24 interposed therebetween. A space between the secondary transfer roll 28 and the winding roll 42 is a secondary transfer position T2 at which the toner image transferred to the intermediate transfer belt 24 is transferred to the recording medium P.

  The transport unit 16 includes a delivery roll 46 that feeds the recording medium P accommodated in the storage unit 12, a transport path 48 that transports the recording medium P sent to the delivery roll 46, and a recording medium sent by the delivery roll 46. And a plurality of transport rolls 50 that transport P to the downstream side.

(Fixing device 60)
Next, a specific configuration of the fixing device 60 will be described.

  As shown in FIG. 1, the fixing device 60 is disposed on the downstream side in the transport direction with respect to the secondary transfer position T2. A transport roll 52 that discharges the recording medium P on which the toner image is fixed to the discharge unit 18 is provided on the downstream side in the transport direction with respect to the fixing device 60.

  Specifically, as illustrated in FIG. 2, the fixing device 60 includes a fixing belt module 70 and a pressure roll 64 (an example of a pressure member). The fixing belt module 70 includes a fixing belt 72 (an example of a belt), a sheet heating element 80, a support member 74, a pair of holding members 76, and a pad 78. The sheet heating element 80, the support member 74, the pair of holding members 76, and the pad 78 are disposed on the inner peripheral side of the fixing belt 72.

  As shown in FIGS. 3 and 4, the support member 74 is formed in a rectangular tube shape and has a length along the axial direction of the fixing belt 72. The pad 78 shown in FIG. 2 has elasticity and has a length along the axial direction of the fixing belt 72. The pad 78 is attached to a side surface 74S of the support member 74 on the pressure roll 64 side. As a result, the pad 78 is supported by the support member 74.

  By pressing the pressure roll 64 against the pad 78 via the fixing belt 72, a contact region 60S (fixing nip) where the fixing belt 72 and the pressure roll 64 come into contact is formed.

  The pressure roll 64 is rotationally driven, and the fixing belt 72 is configured to rotate following the pressure roll 64. As a result, the pressure roll 64 conveys the recording medium P introduced into the contact area 60 </ b> S while being pressed between the fixing belt 72.

  Note that the fixing belt 72 and the pressure roll 64 have non-passing portions through which the recording medium P does not pass at both axial ends.

  The pair of holding members 76 are plate-shaped, have a length along the axial direction of the fixing belt 72, and have a substantially Z shape when the fixing belt 72 is viewed in the axial direction. Each of the pair of holding members 76 has one end attached to each of the upper and lower surfaces 74U and 74B of the support member 74 and the other end fixed to each of the one end and the other end of the sheet heating element 80. . As a result, the sheet heating element 80 is held in an arc shape when viewed in the axial direction of the fixing belt 72, and comes into contact with the inner periphery of the fixing belt 72.

  The planar heating element 80 generates heat and heats the fixing belt 72 as described later. In the fixing device 60, the pressure roller 64 conveys the recording medium P while being pressed between the fixing belt 72 in the contact area 60 </ b> S, and the toner image transferred to the recording medium P by the heat of the fixing belt 72 is transferred. It is fixed on the recording medium P.

(Surface heating element 80)
Next, a specific configuration of the planar heating element 80 will be described.

  The planar heating element 80 has a function of generating heat when a current flows through itself. As shown in FIG. 2, the planar heating element 80 is planar (plate-shaped) and has a length along the axial direction of the fixing belt 72 in a direction intersecting the thickness direction thereof. (See FIG. 5). As shown in FIG. 6, the planar heating element 80 includes a heating layer 82 and insulating layers 84 formed on the front and back surfaces of the heating layer 82.

  The heat generating layer 82 is made of a conductor such as metal. Specifically, the heat generation layer 82 is made of a material whose melting temperature is, for example, a temperature exceeding the fixing temperature (for example, 250 ° C.) or more and 700 ° C. or less. Examples of the material include aluminum (melting temperature: 660 ° C.), lead (melting temperature: 328 ° C.), magnesium (melting temperature: 651 ° C.) and zinc (melting temperature: 419 ° C.), and alloys thereof. It is done.

  Further, the thickness of the heat generation layer 82 is determined from an electric resistance value for obtaining a predetermined heat generation amount and ease of assembly and processing. Specifically, the thickness of the heat generation layer 82 is, for example, not less than 10 μm and not more than 50 μm, and is thicker than the insulating layer 84.

  The insulating layer 84 is made of a resin material such as polyimide. The insulating layer 84 may be formed by alumite treatment. In the planar heating element 80, specifically, when a current flows through the heating layer 82, Joule heat is generated due to the internal resistance of the heating layer 82, and the planar heating element 80 generates heat.

  Further, as shown in the development view of FIG. 5, the planar heating element 80 includes strips 91, 92, 93 having a length along the axial direction of the fixing belt 72, a common electrode 99, and individual electrodes 94. , 95, 96. The common electrode 99 is provided in common at one end in the longitudinal direction of the strips 91, 92, 93. The individual electrodes 94, 95, and 96 are individually provided on each of the other longitudinal ends of the strips 91, 92, and 93. In the sheet heating element 80, one or a plurality of belt bodies that generate heat are selected from the belt bodies 91, 92, and 93 by selecting an electrode through which a current flows from among the individual electrodes 94, 95, and 96.

  In FIG. 5, the longitudinal direction of the sheet heating element 80 (band bodies 91, 92, 93) and the axial direction of the fixing belt 72 are indicated by arrows X. In FIG. 5, the short side direction of the planar heating element 80 (band bodies 91, 92, 93) and the circumferential direction of the fixing belt 72 are indicated by an arrow Y.

  Each of the strips 91, 92, and 93 is formed with a plurality of circular holes 88 that pass through the heat generating layer 82 and the insulating layer 84. Specifically, the hole 88 includes a large-diameter hole 88A and a small-diameter hole 88B having a smaller diameter than the large-diameter hole 88A. The strips 91, 92, and 93 are formed in a mesh shape (net shape) by forming a plurality of holes 88. The hole 88 is formed by, for example, etching after determining a formation position by laser marking. Thus, the holes 88 are formed in a pattern in which the distance between the holes is a specified value.

  The opening diameter of the large-diameter hole 88A is larger than the opening diameter of the small-diameter hole 88B, and is set, for example, in the range of more than 10 μm and 50 μm or less. The opening diameter of the small-diameter hole 88B is smaller than the opening diameter of the large-diameter hole 88A, and is set, for example, in the range of 10 μm or more and less than 50 μm. The overall aperture ratio of each band 91, 92, 93 is, for example, not less than 1% and not more than 50%. The aperture ratio is the ratio of the area of all the holes 88 to the area of the strips 91, 92, 93. The area of all the holes 88 is calculated by (area per number of large diameter holes 88A × number) + (area per number of small diameter holes 88B × number).

  Furthermore, in each of the strips 91, 92, 93, the aperture ratio of the holes 88 has a distribution in the longitudinal direction (an example of the crossing direction). Specifically, in the belt body 91, the low aperture ratio portion 110 having a relatively low aperture ratio is formed in the central portion in the longitudinal direction, and the high aperture ratio portion 112 having a higher aperture ratio than the low aperture ratio portion 110 is in the longitudinal direction. It is formed on both end sides. In the band bodies 92 and 93, the high aperture ratio portion 112 is formed in the center portion in the longitudinal direction, and the low aperture ratio portions 110 are formed on both end portions in the longitudinal direction. In the low aperture ratio portion 110, since the aperture ratio is low, the electrical resistance value is small and the heat generation amount is small. Further, since the aperture ratio is high in the high aperture ratio portion 112, the electrical resistance value is large and the heat generation amount is increased.

  Therefore, as shown in FIG. 7, in the band body 91 (see the alternate long and short dash line), the amount of heat generation is relatively small in the low aperture ratio portion 110 at the center in the longitudinal direction, and the high aperture ratio portions 112 at both ends in the longitudinal direction. , The calorific value is larger than that in the central part in the longitudinal direction. In the band body 92 (see the solid line) and the band body 93 (see the broken line), the amount of heat generation is relatively large in the high aperture ratio portion 112 at the center in the longitudinal direction, and in the low aperture ratio portions 110 at both ends in the longitudinal direction, The calorific value is less than in the center of the direction.

  The high aperture ratio portion 112 at the center portion in the longitudinal direction of the band body 93 is longer in the longitudinal direction than the high aperture ratio portion 112 at the center portion in the longitudinal direction of the strip body 92. For this reason, the heating range of the fixing belt 72 by the belt body 93 is longer than the heating range of the fixing belt 72 by the belt body 92. Further, the high aperture ratio portions 112 on both ends in the longitudinal direction of the band 91 are arranged at positions overlapping the low aperture ratio portions 110 on both ends in the longitudinal direction of the strip 92 in the longitudinal direction of the sheet heating element 80. Has been. For this reason, the fixing belt 72 is heated by the bands 91 and 92 in a heating range longer than the heating range of the fixing belt 72 by the band 93.

  In the present embodiment, the heating range of the fixing belt 72 is changed by selecting the belts 91, 92, and 93 that supply electric power according to the width of the recording medium P. For example, the width of the recording medium P is classified into three stages of large, medium, and small. When the width is small, the band 92 is used, when the width is medium, the band 93 is used, and when the width is large, the bands 91 and 92 are divided. It is configured to be used.

  The recording medium P is conveyed by a center register with the center in the axial direction of the fixing belt 72 as a reference.

  Specifically, as shown in FIG. 5, the low aperture ratio portion 110 is configured, for example, by arranging three rows formed by arranging large-diameter holes 88 </ b> A in the longitudinal direction of the planar heating element 80. Has been. Further, each of the large-diameter holes 88A in each row along the longitudinal direction in the low aperture ratio portion 110 is shifted in the longitudinal direction with respect to each of the large-diameter holes 88A in the row adjacent in the short direction. (See FIG. 10).

  In the high aperture ratio portion 112, for example, five rows formed by arranging the small diameter holes 88B in the longitudinal direction of the planar heating element 80 are arranged, and the arrangement density of the small diameter holes 88B is increased. Yes. In addition, each of the small diameter holes 88B in each row along the longitudinal direction in the high aperture ratio portion 112 is arranged so as to be shifted in the longitudinal direction with respect to each of the small diameter holes 88B in the row adjacent in the short direction.

  Furthermore, in this embodiment, as shown in FIG. 4, tension coil springs 124, 125, and 126 (an example of an applying unit) that apply tension to the planar heating element 80 in the longitudinal direction thereof are the individual electrodes 94, 95, 96. In the planar heating element 80, as shown in FIG. 3, the common electrode 99 is fixed to the side surface 74T of the support member 74, and as shown in FIG. 4, each of the individual electrodes 94, 95, 96 is tensioned. Tension is applied by being pulled by the coil springs 124, 125, and 126. A power source (not shown) is connected to the tension coil springs 124, 125, and 126, and power can be supplied to the individual electrodes 94, 95, and 96 through the tension coil springs 124, 125, and 126.

  In the present embodiment, in the planar heating element 80, the thermal expansion coefficient of the insulating layer 84 is higher than the thermal expansion coefficient of the heat generation layer 82. For this reason, as indicated by an arrow in FIG. 8, the expansion amount of the insulating layer 84 is larger than the expansion amount of the heat generating layer 82, and when the heat generating layer 82 and the insulating layer 84 are thermally expanded, the heat generating layer 82 becomes the insulating layer. The tension is applied to the heat generating layer 82 by the tension 84.

(Operation according to this embodiment)
Next, the operation according to this embodiment will be described.

  In the present embodiment, Joule heat is generated due to the internal resistance of the heat generating layer 82 by causing a current to flow between the common electrode 99 of the sheet heating element 80 and the individual electrodes 94, 95, and 96. Fever.

  In the present embodiment, for example, when the recording medium P having a small width, which is classified into three levels of large, medium, and small, is transported, the belt 92 is heated and the fixing belt 72 is heated. . The recording medium P is sandwiched and conveyed by the fixing belt 72 and the pressure roll 64, whereby the toner image transferred to the recording medium P is fixed to the recording medium P.

  Then, as shown in FIG. 9A, when a part of the planar heating element 80 is locally overheated, the temperature of the part becomes the melting temperature as shown in FIG. 9B. Reach and blow. When the part is melted, the current path in this part is interrupted, and the current flowing to the part flows to another part. As a result, as shown in FIG. 9C, the current flowing through another portion increases and is overheated, and the other portion is melted and the current path is interrupted. In this way, by fusing in a chain manner, all current paths in the planar heating element 80 are blocked, and the supply of power is stopped.

  Further, in the present embodiment, the planar heating element 80 is tensioned in the longitudinal direction of the planar heating element 80 by the tension coil springs 124, 125, and 126. For this reason, compared with the structure (1st comparative example) to which the tension | tensile_strength is not provided to the planar heating element 80 in the longitudinal direction, the overheated part in the planar heating element 80 becomes easy to be blown out. Therefore, according to the configuration of the present embodiment, when the planar heating element 80 is overheated, the current path in the planar heating element 80 is easily interrupted as compared with the first comparative example.

  In the present embodiment, the planar heating element 80 has a plurality of holes 88. For this reason, compared with the configuration using the planar heating element having no plurality of holes (second comparative example), the overheated portion of the planar heating element 80 is melted by the tension applied to the planar heating element 80. It becomes easy. Therefore, according to the configuration of the present embodiment, when the planar heating element 80 is overheated, the current path in the planar heating element 80 is likely to be interrupted as compared with the second comparative example.

  Thus, in this embodiment, since the current path in the planar heating element 80 is easily interrupted, the supply of power to the planar heating element 80 is quickly stopped as compared to the first comparative example and the second comparative example. The state in which the planar heating element 80 is overheated is eliminated in a short time.

  Thus, since the state in which the sheet heating element 80 is overheated is eliminated in a short time, the fixing belt 72 that contacts the sheet heating element 80 is suppressed from being overheated. Furthermore, overheating of the pressure roll 64 that contacts the fixing belt 72, the recording medium P sandwiched between the contact areas 60S, and other components of the image forming apparatus 10 is suppressed.

  In particular, in the present embodiment, a material having a melting temperature of 700 ° C. or lower is used as the planar heating element 80, and therefore the planar heating element is formed of a material having a melting temperature exceeding 700 ° C. Compared with the third comparative example), the current path in the planar heating element 80 is easily interrupted. Therefore, according to the configuration of the present embodiment, compared to the third comparative example, the surface of the recording medium P sandwiched between the fixing belt 72, the pressure roll 64, and the contact region 60S and other components are overheated. The heat generation of the heating element 80 is stopped.

  Here, in the configuration (fourth comparative example) in which the temperature sensor detects the overheating state of the sheet heating element 80 and stops the power supply to the sheet heating element 80, a temperature sensor for detecting the overheating condition is necessary. become. Further, in the fourth comparative example, when an overheated state occurs in a portion where the temperature sensor is not disposed in the longitudinal direction of the planar heating element 80, the overheated state cannot be detected and the power supply cannot be stopped. There is.

  On the other hand, in the present embodiment, when the planar heating element 80 is locally overheated, the overheated portion is melted and the current path is interrupted. A sensor for detection becomes unnecessary. Further, in the present embodiment, since the portion where the overheated state in the planar heating element 80 is melted is melted, a blocking operation is performed in which the current path is blocked due to the difference in the position in the longitudinal direction of the portion where the overheated state has occurred. Or not executed.

  Moreover, in this embodiment, each strip 91, 92, 93 of the planar heating element 80 has the aperture ratio of the holes 88 distributed in the longitudinal direction. In the low aperture ratio portion 110, since the aperture ratio is low, the resistance is small and the heat generation amount is small. On the other hand, in the high aperture ratio portion 112, since the aperture ratio is high, the resistance is large and the heat generation amount is large. Therefore, in the high aperture ratio portion 112, the melting temperature is easily reached in relation to the aperture ratio, and the current path is easily interrupted. For this reason, compared with the structure (comparative example) in which the aperture ratio of the holes is constant in the longitudinal direction, the ease of interrupting the current path in the planar heating element 80 can be changed in the longitudinal direction.

  Further, in the band bodies 92 and 93, the central portion in the longitudinal direction, which is the high aperture ratio portion 112, corresponds to a passing portion through which the recording medium P passes and is a portion that absorbs heat by the recording medium P. On the other hand, both end portions in the longitudinal direction which are the low aperture ratio portions 110 are non-passing portions through which the recording medium P does not pass and are portions where heat is not absorbed by the recording medium P.

  Therefore, from the viewpoint of being a non-passing portion of the recording medium P, the longitudinal ends of the strips 92 and 93 are likely to reach the melting temperature and the current path is likely to be interrupted. However, both end portions in the longitudinal direction are low aperture ratio portions 110, and the low aperture ratio portions 110 have a small amount of heat generation, and are difficult to reach the melting temperature in relation to the aperture ratio, and the current path is interrupted. Hateful.

  Thus, from the viewpoint of being a non-passing portion of the recording medium P, the current path in the sheet heating element 80 can be easily blocked by disposing the low aperture ratio portion 110 in the portion where the current path is easily blocked. Variation in the longitudinal direction is suppressed.

  In the present embodiment, as shown in FIG. 10, each of the large-diameter holes 88 </ b> A in each row along the longitudinal direction in the low aperture ratio portion 110 corresponds to the large-diameter holes 88 </ b> A in the rows adjacent in the short direction. For each, they are offset in the longitudinal direction.

  Here, in the configuration in which each large-diameter hole 88A in each row is disposed at the same position in the longitudinal direction with respect to each large-diameter hole 88A in the row adjacent in the short direction (fifth comparative example). As shown in FIG. 11, the width of the current path formed between the large-diameter holes 88A varies in the longitudinal direction. For this reason, electric resistance values vary in the longitudinal direction, and the amount of heat generated varies in the longitudinal direction.

  On the other hand, in this embodiment, as shown in FIG. 10, each of the large-diameter holes 88A in each row is in the longitudinal direction with respect to each of the large-diameter holes 88A in the row adjacent in the short direction. Since they are shifted, the variation in the longitudinal direction of the width of the current path formed between the large-diameter holes 88A is reduced as compared with the fifth comparative example. Thereby, as compared with the fifth comparative example, the variation in the heat generation amount in the longitudinal direction is reduced, and it is suppressed that the current path is easily interrupted in the longitudinal direction.

  Further, in the present embodiment, each small-diameter hole 88B in each row along the longitudinal direction in the high aperture ratio portion 112 is shifted in the longitudinal direction with respect to each small-diameter hole 88B in the row adjacent in the short direction. Has been placed. Accordingly, in the high aperture ratio portion 112, similarly, each of the small diameter holes 88B in each row is arranged at the same position in the longitudinal direction with respect to each of the small diameter holes 88B in the row adjacent in the short direction. Compared with the configuration (comparative example), it is suppressed that the current path is easily blocked in the longitudinal direction.

<Modification>
In the present embodiment, the fixing device as the heating device has been described, but the present invention is not limited to this. As an example of the heating device, for example, a device in which the sheet heating element 80 is disposed for dehumidification of the recording medium P in the storage unit 12 that stores the recording medium P may be used. Any device that uses and heats it may be used.

  Moreover, in this embodiment, although the hole 88 was formed in the planar heating element 80, it is not restricted to this. As an example of the planar heating element, a planar heating element that does not have the hole 88 may be used. Examples of the planar heating element having no hole 88 include a carbon heater and a ceramic heater using a substrate such as alumina.

  In the present embodiment, in the sheet heating element 80, the aperture ratio of the holes 88 has a distribution in the longitudinal direction in each of the belt bodies 91, 92, and 93, but the present invention is not limited to this. For example, as shown in FIG. 12, a planar heating element 80 having a constant aperture ratio in the longitudinal direction may be used.

  Moreover, in this embodiment, although the hole 88 was circular shape, it is not restricted to this. For example, as shown in FIG. 13, the hole 88 may have a regular hexagonal shape. By making the hole 88 a regular hexagon, the width of the current path formed between the holes 88 is constant.

  Further, in the portion where the aperture ratio is the same in the planar heating element 80, a configuration in which a large number of small holes are formed and a large number of narrow current paths are formed has a smaller number of large holes than a small hole. It is considered that the current path is more likely to be blown than the configuration having a small number of wide current paths. Therefore, for example, the configuration may be such that the current path is changed by changing the width of the current path while the aperture ratio is the same in each part of the planar heating element 80.

  The present invention is not limited to the above-described embodiment, and various modifications, changes, and improvements can be made without departing from the spirit of the present invention. For example, the modification examples described above may be appropriately combined.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 14 Image forming part 60 Fixing apparatus (an example of a heating apparatus)
64 Pressure roll (an example of a pressure member)
72 Fusing belt (an example of a belt)
80 Planar heating element 88 Hole 124, 125, 126 Tensile coil spring (an example of application portion)

Claims (7)

A planar heating element in which a plurality of holes are formed and generates heat when current flows through itself,
An applying unit that applies tension to the planar heating element in a crossing direction intersecting a thickness direction of the planar heating element;
With
In the planar heating element, one end side in the cross direction is fixed to a support member, and the other end side in the cross direction is divided into a plurality of parts.
The applying unit is a heating device that applies tension to the planar heating element by pulling each of the other end sides of the planar heating element divided into a plurality . The planar heating element is:
The heating apparatus according to claim 1, wherein the aperture ratio of the holes has a distribution in the intersecting direction. The planar heating element has a plurality of rows in which the holes are arranged in the intersecting direction,
The holes in one row and the holes in another row adjacent to the row are arranged so as to be shifted in the intersecting direction so that the electric resistance value does not vary in the intersecting direction. The heating device according to 1. The heating device according to claim 1, wherein the planar heating element is formed of a material having a melting temperature of 700 ° C. or less.   A belt heated by the planar heating element;
  A pressurizing member that pressurizes the recording medium with the belt sandwiching the recording medium;
  A fixing device as a heating device according to any one of claims 1 to 4.   Both end portions in the axial direction of the belt are non-passing portions through which the recording medium does not pass,
  The planar heating element has a smaller opening ratio at both end sides in the axial direction than at the central portion side in the axial direction.
  The fixing device according to claim 5, which refers to claim 2.   An image forming unit for forming an image on a recording medium;
  The fixing device according to claim 5 or 6, wherein an image formed on the recording medium is fixed to the recording medium.
  An image forming apparatus comprising:

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