JP2014026082A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve temperature detection accuracy of a planar heating element by using an excessive temperature rise preventing device which prevents an excessive temperature rise of the planar heating element within an operational temperature range.SOLUTION: A fixing device includes: a planar heating element 20 in a planar shape; a heat diffusing member 22 that comes into contact with one surface of the planar heating element 20 and diffuses the heat of the planar heating element 20; a belt member sliding on the heat diffusing member 22 to conduct the heat of the heat diffusing member 22; and a pressurizing member 21 that comes into contact with the other surface of the planar heating element 20 and pressurizes the planar heating element 20 in a direction toward the heat diffusing member 22. Grooves and ribs as a rugged shape are formed on a contact-pressing surface of the pressurizing member 21 with the planar heating element 20; and an excessive temperature rise preventing device 23 that prevents an excessive temperature rise of the planar heating element 20 is disposed on the back surface to the contact-pressing surface of the pressurizing member 21.

Description

  The present invention relates to a fixing device that fixes a toner image formed on a recording medium in an image forming apparatus such as an electrophotographic printer, a copying machine, and a facsimile, and an image forming apparatus including the fixing device.

  A fixing device in a conventional image forming apparatus has a structure in which heat from a planar heating element is transmitted to a stretched fixing belt via a heat diffusion member. Furthermore, it has a structure having a fixing roller and a pad, and a pressure roller opposed to the fixing roller and the pad. The recording medium on which the toner image is formed is conveyed to the nip formed by the fixing roller and the pressure roller, so that the toner image is fixed on the recording medium by heat and pressure to form an image. Has been.

  In Japanese Patent Application Laid-Open No. 2007-322888 (Patent Document 1), a fixing device having a fixing belt can reduce the heat capacity of the entire fixing device, so that the time required to reach a fixing temperature is short and the power required for fixing is also low. Although there is an advantage that it can be reduced, it is described that there is a problem that the temperature control is deteriorated due to a large temperature drop when the toner is fixed on the recording medium. Therefore, according to Patent Document 1, a heating member that heats the fixing belt by contacting the fixing belt on the upstream side in the belt traveling direction of the nip region is provided.

JP 2007-322888 A

  However, in the conventional fixing device, no investigation has been made on the use of an overheat prevention device for preventing an excessive increase in the temperature in the fixing device.

  An object of the present invention is to provide a fixing device capable of using an inexpensive overheat prevention device.

  In order to solve the above problem, a fixing device according to the present invention includes a planar sheet heating element, a heat diffusion member that contacts one surface of the sheet heating element and diffuses heat of the sheet heating element. The belt member that slides with the heat diffusing member, conducts heat of the heat diffusing member, contacts the other surface of the planar heating element, and pressurizes the planar heating element toward the thermal diffusing member. A pressurizing member, and forming a concavo-convex shape on a pressure contact surface of the pressure member with the planar heating element, and overheating the planar heating element on the back surface of the pressure contact surface of the pressure member. It is characterized by providing an overtemperature prevention device for preventing it.

  According to the present invention having the above-described configuration, the overheat protector is used within the operating temperature range by bringing the pressure member into pressure contact with the planar heating element and bringing the overheat protector into contact with the pressure member. And it becomes possible to raise the temperature detection precision of a planar heating element.

FIG. 3 is an exploded perspective view of main members of the fixing device according to the first embodiment. 1 is a schematic configuration diagram of an image forming apparatus to which a first embodiment is applied. FIG. 3 is an explanatory diagram illustrating a configuration of a fixing device according to the first embodiment. It is a disassembled perspective view of the planar heating element regarding 1st Embodiment. It is a perspective view of the heat-diffusion member regarding 1st Embodiment. It is a disassembled perspective view of the temperature rise prevention apparatus regarding 1st Embodiment. It is explanatory drawing regarding a pressurization member. It is explanatory drawing which shows the positional relationship of the longitudinal direction of the planar heating element and pressurization member regarding 1st Embodiment. It is explanatory drawing which shows the positional relationship of the medium heating direction of the planar heating element and pressurization member regarding 1st Embodiment. It is explanatory drawing which shows the flow of the heat from the planar heat generating body regarding 1st Embodiment. It is explanatory drawing which shows the specific example of the pressurization member to which 1st Embodiment is applied. It is explanatory drawing which compared the time until the temperature of a thermal-diffusion member reaches | attains a target value from the time of the electric power supply start to a planar heating element. It is explanatory drawing which shows the pressurization member regarding 2nd Embodiment. It is explanatory drawing which compared the temperature distribution of the longitudinal direction of each heat-diffusion member 22, when the pressurization member 21 of 1st Embodiment and the pressurization member 41 of 2nd Embodiment are used.

(First embodiment)
FIG. 2 is a schematic configuration diagram of an image forming apparatus to which the first embodiment is applied. The image forming apparatus 1 is a printer, a copier, a facsimile, or the like, and may be any image forming apparatus that can use the fixing device to which the present invention is applied. In this example, a color image forming apparatus will be described, but a monochrome image forming apparatus can be similarly applied.

  The image forming apparatus 1 includes a paper feed cassette 4 that accommodates a print medium 3, toner image forming units 12K, 12Y, 12M that form toner images 33 of each color on the print medium 3 in the order of black, yellow, magenta, and cyan. 12C, a fixing device 2 that fixes the toner image 33 formed on the print medium 3 to the print medium 3, and a paper feed mechanism that transports the print medium 3 from the paper feed cassette 4 to the toner image forming units 12K, 12Y, 12M, and 12C. And a discharge mechanism 16 that conveys the print medium 3 discharged from the fixing device 2 to the discharge unit 19.

  The toner image forming units 12K, 12Y, 12M, and 12C include photosensitive drums 13K, 13Y, 13M, and 13C, and a charging device, a developing device, and a photosensitive cleaning device (not shown). Exposure devices 15K, 15Y, 15M, and 15C that form electrostatic latent images on the surfaces of the photosensitive drums 13K, 13Y, 13M, and 13C are installed adjacent to the photosensitive drums 13K, 13Y, 13M, and 13C. The transfer rollers 14K, 14Y, 14M, and 14C are installed to face the photosensitive drums 13K, 13Y, 13M, and 13C with the transfer belt 10 interposed therebetween. The paper feed mechanism 5 includes paper feed rollers 6 a and 6 b, a separation piece 7, a transport roller 8, and a registration roller 9 that separate and feed the print media 3 contained in the paper feed cassette 4 one by one. Yes. Then, the paper feed mechanism unit 5 sends the print medium 3 from the paper feed cassette 4 installed at the bottom of the image forming apparatus 1 to the toner image forming units 12K, 12Y, 12M, and 12C. The discharge mechanism unit 16 includes a discharge roller 17 and a discharge conveyance roller 18. The discharge mechanism 16 conveys the print medium 3 discharged from the fixing device 2 installed downstream of the transfer belt 10 by the discharge roller 17 and discharges the print medium 3 to the discharge unit 19 by the discharge roller 18.

  FIG. 3 is an explanatory diagram showing the configuration of the fixing device according to the first embodiment. The fixing device 2 includes a planar heating element 20 formed in a planar shape for heating the stretched fixing belt 26, a heat diffusion member 22 that diffuses the heat of the planar heating element 20, and heat of the heat diffusion member 22. A load is applied to the fixing belt 26 as a belt member that conducts heat, the pressure member 21 that pressurizes the sheet heating element 20 in the direction of the heat diffusion member 22, the heat diffusion member 22, the sheet heating element 20, and the pressure member 21. An elastic member 24 that stretches the fixing belt 26, a support member 25 that supports the elastic member 24, a fixing roller 30 that forms a nip portion 32 with the pressure roller 31, a fixed pressing member 29, and a fixed pressing member 29. The pressure roller 31 forms a nip portion 32 by pressure contact.

  The fixing belt 26 is stretched between the heat diffusion member 22, the fixing roller 30, and the fixed pressing member 29. The fixing belt 26 is rotated according to the rotation of the fixing roller 30 and slides while being pressed against the heat diffusion member 22. Accordingly, the toner image 33 is fixed to the print medium 3 by heat and pressure by transporting the print medium 3 on which the toner image 33 is formed to the nip portion 32 from the arrow direction.

  FIG. 1 is an exploded perspective view of main members of the fixing device according to the first embodiment. The figure shows the positional relationship among the planar heating element 20, the pressure member 21, the heat diffusion member 22, the overtemperature prevention device 23, the elastic member 24, and the support member 25. That is, a heat diffusion member 22 that slides with a fixing belt 26 (not shown in FIG. 1) is disposed at the top, and a planar sheet heating element 20 is disposed below the heat diffusion member 22. Furthermore, a pressurizing member 21 that pressurizes the planar heating element 20 in the direction of the heat diffusing member 22 via an uneven press-contact surface, which will be described later, that is, upward is disposed below, and a plurality of elastic members are disposed below it. Reference numeral 24 is arranged to apply a load to the pressure member 21.

  Similarly, an overheat prevention device 23 as an overheat prevention device described later is disposed under the pressurizing member 21. That is, the overheat prevention device 23 is provided on the back surface of the concavo-convex pressure contact surface of the pressurizing member 21 to prevent the overheating of the planar heating element 20. The overtemperature preventing device 23 and the elastic member 24 are supported by a support member 25. Note that the bottom of the support member 25 is fixed to a fixed pressing member 29 via a second elastic member 28 as shown in FIG.

  FIG. 4 is an exploded perspective view of the sheet heating element according to the first embodiment. The sheet heating element 20 is formed by forming a thin insulating layer 203 such as a glass layer on a base material 200 such as stainless steel or ceramic, and a resistance heating using a material such as a nickel-chromium alloy or a silver-palladium alloy. It is a heater formed in a planar shape on which a body 201 and an electrode 202 are formed and further protected by a protective layer 204 made of a fluorine resin. Note that an electrical insulating layer 203 is formed under the substrate 200, and the protective layer 204 is protected under the electrical insulating layer 203. In the present embodiment, the resistance heating elements 201 are arranged in parallel in two rows in the longitudinal direction of the planar heating element 20. Here, the longitudinal direction of the planar heating element 20 indicates the + X direction, which is a direction perpendicular to the medium running direction (+ Y) on the medium surface. In addition, one surface 204a that is the protective layer 204 on the upper surface of the planar heating element 20 is in contact with a planar region 221 that is the lower surface of the heat diffusion member 22 described below. Then, the other surface 204b, which is the protective layer 204 on the lower surface of the planar heating element 20, is in contact with an uneven pressing surface 210 of the pressing member 21 described later.

  FIG. 5 is a perspective view of the heat diffusing member according to the first embodiment. FIG. 4A is a perspective view showing a curved surface area that is the upper surface of the heat diffusion member, and FIG. 4B is a perspective view showing a planar area that is the lower surface. The heat diffusion member 22 has a function of diffusing the heat of the planar heating element 20. The thermal diffusion member 22 is formed of a material having high thermal conductivity and workability such as aluminum and copper. As shown in FIG. 4A, the curved surface region 220 which is the upper surface of the heat diffusion member 22 is pressed against the inside of the fixing belt 26 by a load generated from the elastic member 24. Therefore, the fixing belt 26 slides while being pressed against the curved surface region 220 which is the upper surface of the heat diffusion member 22. Then, as shown in FIG. 2B, the planar region 221 that is the lower surface of the heat diffusing member 22 is in pressure contact with the heat generating surface of the planar heating element 20. The elastic members 24 arranged in the longitudinal direction press the heat generating surface of the planar heating element 20 against the flat region 221 of the heat diffusing member 22, thereby suppressing unevenness in shape such as warping and twisting in the longitudinal direction. Thereby, the dispersion | variation by a longitudinal direction position can be decreased about the heat transfer rate from the planar heat generating body 20 to the heat-diffusion member 22. FIG.

  FIG. 6 is an exploded perspective view of the overheat prevention device according to the first embodiment. The overheat prevention device 23 as an overheat prevention device detects the temperature, and when the temperature exceeds a certain temperature, the thermostat 230 is turned off, the fixing members 231a and 231b for fixing the thermostat 230, and the thermostat 230 are pressurized. The elastic member 232 is abutted against the member 21. The overheat prevention device 23 has a role to prevent overheating of the planar heating element 20. The upper limit of the operating temperature of the thermostat 230 is 270 ° C. The overheat prevention device 23 is provided on the back surface 211 of the pressure contact surface 210 of the pressure member 21.

  The pressurizing member 21 has a heat capacity of 12.5 J / K or more and 25.0 J / K or less so that the overheat prevention device 23 in contact can be used within the operating temperature range. The pressure member 21 is provided between the sheet heating element 20 and the elastic member 24, and is pressed against the sheet heating element 20 by the elastic member 24.

  FIG. 7 is an explanatory diagram relating to the pressure member. FIG. 4A shows a pressure member 34 having no grooves or ribs as a comparative example to be described later. The left side of the figure shows the upper surface of the pressure member 34, and the right side shows the lower surface of the pressure member 34. FIG. 2B shows the pressure member 21 according to the first embodiment, the left side of the figure shows the upper surface of the pressure member 21, and the right side shows the lower surface of the pressure member 21. As shown in FIG. 2B, the pressing member 21 has a plurality of groove portions 212 a and rib portions 212 b alternately formed on the pressing surface 210 that is the upper surface in contact with the planar heating element 20. The contact area between the planar heating element 20 and the pressure member 21 is smaller than the contact area with the pressure member 34 having no grooves or ribs shown in FIG. FIG. 2C shows the pressing member 21-1 relating to the first embodiment created by punching out a sheet metal. As shown in the figure, the object of the present invention can be achieved even if the concave and convex shape of the pressure member 21-1 is formed by providing a plurality of ribs by punching out a sheet metal.

  The uneven shape of the pressure member 21 in the first embodiment will be described as a shape constituted by the groove portion 212a and the rib portion 212b shown in FIG. In the present embodiment, the grooves 212a and the ribs 212b are formed continuously in parallel with the longitudinal direction of the planar heating element 20 (parallelism 0.2 with respect to the central axis in the longitudinal direction of the planar heating element). The rib portion 212b is pressed against the planar heating element 20, whereby the warpage in the longitudinal direction of the planar heating element 20 can be reduced.

  FIG. 8 is an explanatory diagram showing the positional relationship in the longitudinal direction between the planar heating element and the pressure member according to the first embodiment. The rib portion 212b of the pressing member 21 and the resistance heating element 201 arranged in parallel in two rows in the longitudinal direction of the planar heating element 20 have the following relationship. That is, as shown in the figure, the longitudinal range L212 of the rib portion 212b is provided so as to overlap 90% or more of the longitudinal range L201 of the resistance heating element 201.

  FIG. 9 is an explanatory diagram showing a positional relationship between the planar heating element and the pressure member in the medium traveling direction according to the first embodiment. As shown in the drawing, the medium traveling direction range B212 of the rib portion 212b is a range B ′ (the length is the medium of the resistance heating element 201) with the center line of the medium traveling direction range B201 of each resistance heating element 201 as a common center line. And 40% or more of the length in the traveling direction). Therefore, when the pressure member 21 is pressed against the planar heating element 20 by the elastic member 24, the load of the elastic member 24 is concentrated on the resistance heating element 201, so that the resistance heating element 201 of the planar heating element 20 is thermally diffused. The area that can contact the planar region 221 of the member 22 increases. As a result, it is possible to increase the temperature rise rate of the heat diffusion member 22 and to reduce variations in the temperature rise rate at the longitudinal position of the heat diffusion member 22. The pressing member 21 is formed of a material having high thermal conductivity and workability such as aluminum and copper.

  The operation of the image forming apparatus 1 to which the embodiment of the present invention is applied will be described. First, when the image forming apparatus 1 is turned on and the operator performs an image forming start operation, the print medium 3 stored in the paper feed cassette 4 is separated one by one by the paper feed rollers 6 a and 6 b and the separation piece 7. And sent out. Then, the print medium 3 is conveyed to the transfer belt 10 by the conveyance roller 8 and the registration roller 9. At this time, in the toner image forming units 12K, 12Y, 12M, and 12C, the photosensitive drums 13K, 13Y, 13M, and 13C are charged by a charging device (not shown), and an exposure device is formed on the surface of the charged photosensitive drums 13K, 13Y, 13M, and 13C. An electrostatic latent image is formed by 15K, 15Y, 15M, and 15C. The formed electrostatic latent image is developed by a developing device (not shown), and toner images as developer images are formed on the photosensitive drums 13K, 13Y, 13M, and 13C.

  Next, the printing medium 3 conveyed to the transfer belt 10 passes between the photosensitive drums 13K, 13Y, 13M, and 13C and the transfer rollers 14K, 14Y, 14M, and 14C as the transfer belt 10 travels by the conveyance rollers 11a and 11b. To do. At this time, the toner images formed on the photosensitive drums 13K, 13Y, 13M, and 13C are transferred to the printing medium 3. After the transfer, the toner remaining on the photosensitive drums 13K, 13Y, 13M, and 13C is collected by a photosensitive cleaning device (not shown). Then, the toner image 33 is conveyed from the transfer belt 10 to the fixing device 2, and the toner image 33 on the printing medium 3 is fixed to the printing medium 3 by heat and pressure. The fixed printing medium 3 is conveyed and discharged to the discharge unit 19 by the discharge roller 17 and the discharge conveyance roller 18.

  Next, the operation of the fixing device 2 to which the embodiment of the present invention is applied will be described. As the image forming apparatus 1 starts image formation, the fixing roller 30 rotates in the direction in which the print medium 3 is conveyed, and the fixing belt 26 rotates while the fixing belt 30 slides while being pressed against the heat diffusion member 22. As a result, it rotates following. The planar heating element 20 generates heat when electric power is supplied, and heat is conducted from the planar heating element 20 to the thermal diffusion member 22 through the planar region 221 of the thermal diffusion member 22. The heat conducted to the heat diffusing member 22 is conducted from the heat diffusing member 22 to the fixing belt 26 that slides through the curved surface region 220 of the heat diffusing member 22. The temperature detection means (not shown) detects the temperature of the fixing belt 26, and the control unit (not shown) controls the power supply to the planar heating element 20 so that the temperature of the fixing belt 26 is maintained at a predetermined fixing temperature. .

  Further, the heat of the planar heating element 20 is transmitted to the pressurizing member 21 through the press contact surface 210 of the pressurizing member 21 that is in press contact with the planar heating element 20. The pressure contact surface 210 of the pressure member 21 has a plurality of groove portions 212a and rib portions 212b parallel to the longitudinal direction of the sheet heating element 20 as described above. In this way, the temperature rise of the planar heating element 20 is prevented by bringing the overheat prevention device 23 into contact with the pressure member 21. In a state where the fixing belt 26 is heated to a predetermined fixing temperature, the toner image 33 is fixed to the print medium 3 by heat and pressure by transporting the print medium 3 on which the toner image 33 is formed to the nip portion 32. .

  FIG. 10 is an explanatory diagram showing the flow of heat from the planar heating element according to the first embodiment. FIG. 5A shows the flow of heat from the planar heating element 20 when the pressing member 21 in the first embodiment is used. When the sheet heating element 20 generates heat, heat is transferred between the contact areas 401 formed by the sheet heating element 20 and the heat diffusing member 22 as indicated by an arrow H1. Then, heat is transferred between the contact areas 402 formed by the planar heating element 20 and the pressure member 21 as indicated by an arrow H2. As described above, the pressure contact surface 210 of the pressure member 21 has a plurality of grooves 212a and ribs 212b.

  On the other hand, FIG. 5B shows the flow of heat from the planar heating element 20 when a pressure member 34 without ribs or grooves as a comparative example is used. When the sheet heating element 20 generates heat, heat is transferred between the contact areas 403 formed by the sheet heating element 20 and the heat diffusing member 22 as indicated by an arrow H3. Then, heat is transferred between the contact areas 404 formed by the planar heating element 20 and the pressure member 34 as indicated by an arrow H4.

  As shown in FIG. 5B, when the pressure member 34 of the comparative example is used, the contact area 403 between the sheet heating element 20 and the heat diffusion member 22, the sheet heating element 20 and the pressure member 34, The contact area 404 is substantially the same. Contact area 403≈contact area 404.

  On the other hand, as shown in FIG. 5A, when the pressure member 21 of the first embodiment is used, the pressure contact surface 210 in contact with the planar heating element 20 in the pressure member 21 has a longitudinal direction. Are provided with a plurality of groove portions 212a and rib portions 212b. Therefore, the contact area 402 between the planar heating element 20 and the pressure member 21 is smaller than the contact area 401 between the planar heating element 20 and the heat diffusing member 22. Therefore, contact area 401> contact area 402.

  Therefore, as shown in the figure, the heat transfer rate from the planar heating element 20 to the pressure member 21 is slower than that of the comparative example, and conversely, the heat transfer from the planar heating element 20 to the heat diffusion member 22 is performed. Since the speed is increased, the temperature rise time of the heat diffusion member 22 and the fixing belt 26 is shortened. Here, the temperature rise time is the time from the start of supplying power to the sheet heating element 20 until the surface temperature of the fixing belt 26 reaches the fixing temperature (160 ° C.) which is a target value. Further, the temperature rising speed indicates the temperature rising speed at this time.

  FIG. 11 is an explanatory view showing a specific example of a pressure member to which the first embodiment is applied. 4A is an explanatory view showing the longitudinal direction of the pressure member 21, and FIG. 2B is a cross-sectional view taken along the line AA. In this specific example, the thickness of the pressure member 21 is 2.0 mm, the number of the rib portions 212b is three, the depth of the rib portions 212b is 0.5 mm, the length of the rib portions 212b in the longitudinal direction is 320 mm, The width of the rib portion 212b was set to X = 1.0 or 2.0 mm. The output of the planar heating element 20 is 100 V, 1200 W, the length of each resistance heating element 201 in the longitudinal direction is 312.5 mm, and the width (length in the medium running direction) is 2.38 mm. The pressure was 44.1 N (4.9 N × 9).

  In the state where the surface heating element 20, the heat diffusing member 22, and the pressure member 21 of the first embodiment or the pressure member 34 of the comparative example shown in FIG. When power was supplied to the body 20 to generate heat, the time until the temperature of the curved surface region 220 of the heat diffusing member 22 reached the target value (160 ° C.) was as shown in FIG.

  FIG. 12 is an explanatory diagram comparing the time until the temperature of the heat diffusing member reaches the target value (160 ° C.) from the start of power supply to the planar heating element (room temperature 25 ° C.). The figure shows no ribs (pressure member 34 of a comparative example), a pressure member 21 (first embodiment) with a rib width of 2 mm, and a pressure member 21 (first embodiment) with a rib width of 1 mm. The form is used. According to the figure, it can be seen that if the contact area between the pressure member 21 and the planar heating element 20 is reduced by thinning the rib, the heat transfer speed to the heat diffusing member 22 is increased and the arrival time is shortened.

  As described above, according to the first embodiment, a concavo-convex shape is formed on the surface side of the pressure member 21 that is in pressure contact with the planar heating element 20, and the overtemperature prevention device 23 is Since the temperature is detected by the overheat prevention device 23 in contact with the opposite side of the surface on which the shape is formed, the detected temperature on the overheat prevention device 23 side is higher than the temperature on the planar heating element 20 side. Detected at low temperature. For this reason, the overheat prevention device 23 can be used for the fixing device 2. Further, the overheat prevention device 23 can be used even if an inexpensive one having a low operating temperature range is selected.

  Then, by providing a plurality of groove portions 212a and rib portions 212b parallel to the longitudinal direction of the planar heating element 20 on the pressure contact surface 210 of the pressing member 21 that contacts the planar heating element 20, the planar heating element 20 and The contact area 402 of the pressing member 21 is smaller than the contact area 401 of the planar heating element 20 and the heat diffusing member 22. As a result, the heat transfer speed from the sheet heating element 20 to the pressure member 21 is slow, and conversely, the heat transfer speed from the sheet heating element 20 to the heat diffusion member 22 is fast. The temperature rise time of the belt 26 can be shortened.

  Further, the rib portion 212 b of the pressure member 21 is formed continuously and parallel to the longitudinal direction of the planar heating element 20, and is pressed against the planar heating element 20, thereby extending the longitudinal direction of the planar heating element 20. Warpage can be suppressed, and the temperature increase rate of the heat diffusion member 22 can be increased, and variations in the temperature increase rate at the longitudinal position of the heat diffusion member 22 can be reduced.

  Further, the ribs 212b of the pressure member 21 are provided at positions overlapping the resistance heating elements 201 arranged in two rows of the planar heating elements 20 as shown in FIG. The area where the resistance heating element 201 of the planar heating element 20 can come into contact with the planar region 221 of the heat diffusing member 22 is increased, and the temperature rise rate of the heat diffusing member 22 is increased. Variations in the temperature rise rate at the longitudinal position can be reduced.

(Second Embodiment)
FIG. 13 is an explanatory view showing a pressure member according to the second embodiment. FIG. 4A is an explanatory view showing the longitudinal direction of the pressure member 41, and FIG. 4B is a cross-sectional view taken along the line BB. In the pressure member 41 according to the present embodiment, a groove portion 412 a and rib portions 412 b and 412 c are formed on the pressure contact surface 410 with the planar heating element 20 as an uneven shape. The rib portions 412b and 412c are different in the shapes of the rib portions 412b at both ends in the longitudinal direction and the rib portions 412c other than both ends. Compared with the pressure member 21 of the first embodiment, the pressure member 41 according to the present embodiment has a smaller area of the rib portions 412b at both ends in the longitudinal direction. That is, the width of the rib portion 412b at both ends is narrower than the width of the rib portion 412c other than both ends. Other configurations are the same as those in the first embodiment.

  As in the first embodiment, when the sheet heating element 20 generates heat, the heat of the sheet heating element 20 is transmitted to the heat diffusing member 22 and at the same time, the heat is transmitted to the pressure member 41. Here, in the case of the pressure member 34 of the comparative example and the pressure member 21 according to the first embodiment, the temperature of the end of the heat diffusion member 22 in the conduction of heat to the heat diffusion member 22 by the planar heating element 20. The rising speed is slower than the temperature rising speed except at the end. As shown in FIG. 13, the area of the rib portion 412 b at both ends of the pressure member 41 is smaller than the area of the rib portion 412 c other than both ends, so that the contact area of both ends with the planar heating element 20 is small. It becomes small and the heat transfer rate from the planar heating element 20 becomes slow compared with other than the end. That is, on the contrary, the heat transfer speed from the planar heating element 20 to the heat diffusion member 22 is increased.

  A specific example of the pressure member 41 when the second embodiment is applied is shown in FIG. In this specific example, rib portions 412b at both ends of the pressure member 21 (rib width X = 2.0 mm) to which the first embodiment of FIG. 11 is applied (length in the longitudinal direction from each end point 30 mm) The number of ribs was 2 and the rib width was 1.0 mm. The rib portion 412c other than both end portions has three ribs and a rib width of 2.0 mm. Other configurations are the same as those in the first embodiment.

  As shown in FIG. 10, the planar heating element 20, the thermal diffusion member 22, and the pressure member 41 of the second embodiment or the pressure member 21 of the first embodiment (rib width X = 2.0 mm). In a state where pressure was applied in combination with each other, when electric power was supplied to the sheet heating element 20 to generate heat, the temperature distribution in the longitudinal direction of the heat diffusing member 22 became as shown in FIG. FIG. 14 shows the longitudinal direction of each heat diffusion member 22 when the pressure member 21 (rib width X = 2.0 mm) of the first embodiment and the pressure member 41 of the second embodiment are used. It is explanatory drawing which compared these temperature distributions. The temperature distribution is shown when the medium traveling center position is 0 mm, the side where the electrode 202 of the sheet heating element 20 is on the + direction, and the temperature at the position of −25 mm reaches 160 ° C. when the temperature of the thermal diffusion member 22 rises. It is a thing. According to the figure, when the ribs 412b at both ends are processed (second embodiment), the temperature of the end is increased by about 10 ° C. compared to before processing (first embodiment). I understand.

  As described above, according to the second embodiment, the area of the rib part 412b at both ends is smaller than the area of the rib part 412c other than both ends as compared with the pressure member 21 of the first embodiment. Since the contact area with the planar heating element 20 at the rib portions 412b at both ends of the pressing member 41 is smaller than that at both ends, the heat from the planar heating element 20 can be obtained. Transmission speed becomes slow. That is, conversely, the heat transfer speed from the planar heating element 20 to the heat diffusing member 22 is increased. Therefore, when the sheet heating element 20 generates heat, the temperature rising speed at the end of the heat diffusing member 22 can be increased, and the difference from the temperature rising speed other than at the end can be reduced.

  In the first and second embodiments, a plurality of groove portions 212a, 412a and rib portions 212b, 412b, 412c are provided on the pressure contact surfaces 210, 410 of the pressure members 21, 41 with the planar heating element 20. Each may be singular. In the first and second embodiments, a plurality of groove portions 212a and 412a and rib portions 212b, 412b and 412c are formed on the pressure contact surfaces 210 and 410 of the pressure members 21 and 41 with the planar heat generating member 20 in the length of the sheet heating element length. Although formed in parallel and continuously to the hand direction, several grooves 212a and 412a may be added to the direction parallel to the medium running direction. In the first and second embodiments, the rib portions 212b, 412b, and 412c formed on the pressure members 21 and 41 are provided so as to overlap the resistance heating element 201 of the planar heating element 20, but the resistance heating element 201 is provided. The number of rib portions 212b, 412b, and 412c that are in pressure contact with each other may be singular or plural.

2 Fixing device 3 Print medium 20 Planar heating element 21 Pressure member 22 Thermal diffusion member 23 Overtemperature prevention device 24 Elastic member 25 Support member 26 Fixing belt 33 Toner image 210 Pressure contact surface 212a Groove portion 212b Rib portion

Claims (6)

A planar heating element,
A thermal diffusion member that contacts one surface of the planar heating element and diffuses the heat of the planar heating element;
A belt member that slides with the heat diffusion member and conducts heat of the heat diffusion member;
A pressure member that contacts the other surface of the planar heating element and pressurizes the planar heating element in the direction of the heat diffusing member;
An uneven temperature is formed on the pressure contact surface of the pressure member with the planar heating element, and an overtemperature prevention device is provided on the back surface of the pressure contact surface of the pressure member to prevent the temperature of the planar heating element from overheating. A fixing device characterized by that.   The fixing device according to claim 1, wherein the uneven shape includes a groove shape and a rib shape that are formed in parallel and continuously with a longitudinal direction of the planar heating element. The planar heating element has a resistance heating element arranged in the longitudinal direction,
The fixing device according to claim 2, wherein the rib shape is formed at a position overlapping the resistance heating element of the planar heating element.   The fixing device according to claim 3, wherein in the rib shape, the width of both end portions in the longitudinal direction of the pressure member is narrower than the width other than the both end portions.   The area of the contact surface between the planar heating element and the pressure member is smaller than the area of the contact surface between the planar heating element and the heat diffusing member. Fixing device. A planar heating element,
A thermal diffusion member that contacts one surface of the planar heating element and diffuses the heat of the planar heating element;
A belt member that slides with the heat diffusion member and conducts heat of the heat diffusion member;
A pressing member that contacts the other surface of the planar heating element and pressurizes the planar heating element toward the heat diffusion member;
An uneven temperature is formed on the pressure contact surface of the pressure member with the planar heating element, and an overtemperature preventer is provided on the back surface of the pressure contact surface of the pressure member to prevent the planar heating element from overheating. An image forming apparatus comprising a fixing device provided.

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