Fixing device and image forming apparatus

Abstract

To provide a fixing device that prevents an extreme reduction in the temperature of a portion in an axial direction on a surface of a pressure member.SOLUTION: A fixing device 7 comprises: a fixing belt 20 that heats toner on a sheet; a pressure roller 21 that forms a pressure area N with the fixing belt 20 and applies pressure to the toner on the sheet passing through the pressure area; a heater 23 that is in contact with an inner face of the fixing belt 20 facing the pressure area N, and heats the fixing belt 20; and a separation member 35 that is in contact with the surface of the pressure roller 21 and peels off the sheet passing through the pressure area N from the surface of the pressure roller 21. The heater 23 has: a substrate 30 that is formed of an insulating body and extends in an axial direction corresponding to the fixing belt 20; and a plurality of resistance heating elements 32A-32C that are arranged side by side with gaps G therebetween in the axial direction on one face of the substrate 30 that is on an inner face side of the fixing belt 20, and generate heat upon being energized. The separation member 35 has separation pawls 36 that are in contact with the surface of the pressure roller 21 at positions shifted in the axial direction relative to the gaps G.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a fixing device that fixes a toner image on a medium and an image forming apparatus. [Background technology]

[0002] An electrophotographic image forming apparatus is equipped with a fixing device that thermally fixes toner on paper (medium). For example, the fixing device includes a rotating endless belt, a pressure roller that forms a nip (pressure area) between the endless belt and the pressure roller and presses the paper (toner) that passes through the nip while rotating, and a heating element that contacts the inner surface of the endless belt and heats the endless belt. The heating element includes multiple heat-generating elements arranged at intervals (creepage distances) in the axial direction (perpendicular to) of the endless belt. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-45247 Summary of the Invention [Problem to be solved by the invention]

[0004] In the fixing device described above, the surface temperatures of the endless belt and pressure roller are lower at positions facing the gap where there is no heat-generating member than at positions facing the heat-generating member. Furthermore, in fixing devices such as those described above, a separating member may be provided to contact the surface of the pressure roller because paper that passes through the nip may stick to the surface of the pressure roller. If the separating member were to contact the surface of the pressure roller at a position corresponding to the gap, the separating member would absorb heat from the surface of the pressure roller, further lowering the surface temperature of the pressure roller at the contact position of the separating member. This would result in uneven temperature at the nip along the axial direction, which could prevent proper toner fixation to the paper.

[0005] In consideration of the above circumstances, the present invention provides a fixing device and an image forming apparatus that prevent a portion of the surface of a pressure member in the axial direction from becoming extremely cold. [Means for solving the problem]

[0006] The fixing device of the present invention comprises a fixing belt formed in a cylindrical shape and rotating around its axis to heat toner on a medium; a pressure member forming a pressure area between the fixing belt and the pressure member, and pressing the toner on the medium as it passes through the pressure area while rotating around its axis; a heater extending in the axial direction of the fixing belt and contacting the inner surface of the fixing belt facing the pressure area to heat the fixing belt; and a separation member contacting the surface of the pressure member and peeling the medium that has passed through the pressure area from the surface of the pressure member. The heater is formed of an insulating material and has a substrate extending in the axial direction corresponding to the fixing belt, and a plurality of resistance heating elements arranged on one side of the substrate that is on the inner side of the fixing belt with a gap in the axial direction and that generate heat when electricity is passed through them. The separation member has at least one separation claw that contacts the surface of the pressure member at a position offset in the axial direction from the gap.

[0007] In this case, the separation claws may be formed in a spatula shape with a thinned tip, and the tip may be brought into contact with the surface of the pressure member in the vicinity of the pressure application area.

[0008] An image forming apparatus according to the present invention includes the fixing device described above. [Effects of the Invention]

[0009] According to the present invention, it is possible to prevent a portion of the surface of the pressure member in the axial direction from becoming extremely cold. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram (side view) showing the internal structure of an image forming apparatus according to one embodiment of the present invention. [Figure 2]FIG. 1 is a perspective view showing a fixing device according to an embodiment of the present invention. [Figure 3] FIG. 3 is a cross-sectional view taken along the line III-III in FIG. 2. [Figure 4] FIG. 2 is a bottom view schematically illustrating a heater of a fixing device according to an embodiment of the present invention. [Figure 5] FIG. 5 is a cross-sectional view of FIG. 4 . [Figure 6] 4A and 4B are rear views and other views showing a fixing device according to an embodiment of the present invention, illustrating the positional relationship between a heater and a separating member. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. In the drawings, Fr, Rr, L, R, U, and D indicate front, rear, left, right, top, and bottom. The front-to-back direction, left-to-right direction (axial direction), and top-to-bottom direction are perpendicular to one another. Terms indicating directions and positions are used in this specification, but these terms are used for convenience of explanation and do not limit the technical scope of the present invention. Furthermore, the terms "upstream," "downstream," and similar terms refer to "upstream" and "downstream" in the transport direction of paper P (medium) and similar concepts. In each drawing, the dimensions and angles of components are not accurate and are shown schematically for the purpose of explanation.

[0012] An image forming apparatus 1 according to an embodiment will be described with reference to Fig. 1. Fig. 1 is a schematic diagram (side view) showing the image forming apparatus 1.

[0013] The image forming apparatus 1 is an electrophotographic printer. The image forming apparatus 1 has an apparatus main body 2 that has a substantially rectangular parallelepiped appearance. A paper feed cassette 3 that stores, for example, paper P (medium) is detachably provided at the bottom of the apparatus main body 2. A paper output tray 4 is provided on the top surface of the apparatus main body 2. Note that the paper P, which is an example of a medium, is not limited to being made of paper, and may be a resin sheet or the like.

[0014] The image forming apparatus 1 includes a paper feeder 5, an imaging device 6, and a fixing device 7. The paper feeder 5 is provided at the upstream end of a transport path 9A that extends from the paper feed cassette 3 to the paper output tray 4, and sends out paper P stored in the paper feed cassette 3 one sheet at a time to the transport path 9A. The imaging device 6 is provided in the middle of the transport path 9A, and forms a toner image on the transported paper P. The fixing device 7 is provided downstream of the transport path 9A, and thermally fixes the toner image to the paper P.

[0015] The conveying path 9A is provided with a pair of registration rollers 10A that temporarily block the conveyed paper P to correct (skew correct) the inclination of the paper P. Below the conveying path 9A, a reversing conveying path 9B is provided that branches off on the downstream side of the conveying path 9A and merges with the upstream side of the conveying path 9A. The reversing conveying path 9B is provided with a plurality of pairs of conveying rollers 10B that convey the paper P.

[0016] The image forming device 6 includes a toner container 11, a drum unit 12, and an optical scanning device 13. The toner container 11 is located at the upper front of the device main body 2 and contains, for example, black toner (developer). The drum unit 12 includes a photosensitive drum 14, a charging device 15, a developing device 16, and a transfer roller 17. The photosensitive drum 14 is formed in a substantially cylindrical shape and is driven to rotate about its axis by a motor (not shown). The charging device 15, the developing device 16, and the transfer roller 17 are arranged around the photosensitive drum 14 in the order of the image formation process. The transfer roller 17 contacts the photosensitive drum 14 from below to form a transfer nip. The optical scanning device 13 is located above the photosensitive drum 14 and emits scanning light toward the surface of the photosensitive drum 14.

[0017] The image forming apparatus 1 is provided with a control device 8 that controls the entire apparatus. The control device 8 may be configured with a processor, or may be configured with a logic circuit (hardware) formed on an integrated circuit or the like. When configured with a processor, the processor reads and executes programs stored in memory to perform various processes. For example, a CPU (Central Processing Unit) is used as the processor. The memory is configured with one or more storage devices such as ROM (Read Only Memory) and RAM (Random Access Memory) depending on the application.

[0018] [Image formation processing] The following describes the operation of the image forming apparatus 1. The control device 8, which controls the image forming apparatus 1, executes the image forming process as follows based on image data input from an external terminal.

[0019] The charging device 15 charges the surface of the photosensitive drum 14, and the optical scanning device 13 emits scanning light based on image data to form an electrostatic latent image on the photosensitive drum 14. The developing device 16 develops a toner image on the photosensitive drum 14 using toner supplied from the toner container 11. The paper feeder 5 feeds paper P one sheet at a time from the paper feed cassette 3 to the transport path 9A. The paper P is transported along the transport path 9A, skew-corrected by a pair of registration rollers 10A, and enters the transfer nip. The transfer roller 17 transfers the toner image on the photosensitive drum 14 to the surface of the paper P as it passes through the transfer nip. The fixing device 7 thermally fixes the toner image to the paper P. In the case of single-sided printing, the paper P that has passed through the fixing device 7 is discharged to the paper output tray 4.

[0020] In the case of double-sided printing, the paper P that has passed through the fixing device 7 switches back at the downstream end of the conveying path 9A and is sent to the reverse conveying path 9B. The paper P is conveyed by the conveying roller pair 10B, returned from the reverse conveying path 9B to the conveying path 9A again, and after skew correction by the registration roller pair 10A, is sent to the transfer nip. Thereafter, the toner image is transferred onto the paper P and thermally fixed, and the double-sided printed paper P is discharged onto the paper output tray 4.

[0021] [Fusing device] Next, the fixing device 7 will be described with reference to Figures 2 to 6. Figure 2 is a perspective view showing the fixing device 7. Figure 3 is a cross-sectional view taken along line III-III in Figure 2. Figure 4 is a bottom view schematically showing the heater 23. Figure 5 is a cross-sectional view taken along line VV in Figure 4. Figure 6 is a rear view and the like showing the fixing device 7.

[0022] The fixing device 7 includes a fixing belt 20, a pressure roller 21, a heater 23, a heat equalizing member 26, and a separation member 35. The fixing belt 20 and the pressure roller 21 are supported by a frame (not shown), and the frame is fixed to the device body 2.

[0023] <Fixing belt> As shown in Figures 2 and 3, the fixing belt 20 is an endless belt formed in a generally cylindrical shape that is long in the left-right direction (axial direction). The fixing belt 20 is made of a heat-resistant and flexible material (polymer resin, metal, or a combination of polymer resin and metal). A pair of holding members 24 (see Figure 2) is inserted into both left and right ends of the fixing belt 20. The pair of holding members 24 guide the fixing belt 20 to rotate around its axis while maintaining its generally cylindrical shape. The fixing belt 20 is supported by a frame (not shown) via the pair of holding members 24.

[0024] As shown in FIG. 3, a support member 25 and a heater holder 22 are provided in the space surrounded by the fixing belt 20. The support member 25 is formed, for example, from a metal material such as stainless steel into a generally rectangular cylindrical shape that is elongated in the left-right direction (axial direction), and is installed between a pair of holding members 24. The heater holder 22 is fixed to the lower part of the support member 25. The heater holder 22 is formed, for example, from a heat-resistant and abrasion-resistant synthetic resin into a generally semi-cylindrical shape that is elongated in the left-right direction. The heater holder 22 curves along the inner surface of the fixing belt 20 and contacts the lower side of the inner surface of the fixing belt 20 (the side of the pressure region N). A fitting portion 22A into which the heater 23 is fitted is recessed in the lower part of the heater holder 22.

[0025] <Pressure roller> As shown in FIGS. 2 and 3, pressure roller 21, an example of a pressure member, is formed in a generally cylindrical shape that is long in the left-right direction. Pressure roller 21 has a metal core 21A and an elastic layer 21B, such as a silicone sponge, laminated on the outer circumferential surface of the metal core 21A (see FIG. 3). A drive motor M is connected to the left end of core 21A via a gear train (not shown) (see FIG. 2). Pressure roller 21 contacts fixing belt 20 from below, forming a pressure region N between itself and fixing belt 20. A toner image is fixed onto paper P as it passes through pressure region N. Note that pressure region N refers to the region extending from an upstream position where the pressure is 0 Pa, through a position where pressure is applied, to a downstream position where the pressure returns to 0 Pa.

[0026] The paper sheet P is transported with the center of its width in the left-right direction roughly aligned with the center of the pressure area N in the left-right direction (axial direction). For this reason, the fixing belt 20 (or the pressure area N) has a passing area A1 in the axial center that contacts the paper sheet P, and non-passing areas A2 on both sides in the axial direction that do not contact the paper sheet P (see FIG. 4). The transported paper sheet P always contacts the passing area A1 near the axial center, regardless of the size (left-right dimension) of the paper sheet P. In contrast, normal-sized paper sheets P (e.g., A4 size) contact both sides of the passing area A1 in the axial direction, but small-sized paper sheets P (e.g., A5, B5 size, etc.) do not contact the passing area A1.

[0027] <Heater> 3 and 4, heater 23 extends in the left-right direction (axial direction) of fixing belt 20 and is fitted into fitting portion 22A of heater holder 22. Heater 23 comes into contact with the inner surface of fixing belt 20 facing pressure region N, and heats fixing belt 20. As shown in FIGS. 4 and 5, heater 23 has a substrate 30 and a heat generating portion 31.

[0028] (substrate) The substrate 30 is made of an insulator (electrically insulating material) such as ceramic. The substrate 30 is formed in a generally rectangular plate shape that extends in the left-right direction (axial direction) to correspond to the fixing belt 20. The substrate 30 is formed slightly shorter in the axial direction than the fixing belt 20, and is disposed inside the fixing belt 20 (in the space surrounded by the fixing belt 20) (see FIG. 6).

[0029] (heat generating part) The heat generating section 31 is provided on the lower surface (one surface) of the substrate 30, which faces the inner surface of the fixing belt 20 (see FIG. 5). As shown in FIG. 4, the heat generating section 31 is composed of three resistance heating elements 32A to 32C arranged in a row in the left-right direction (axial direction) with a gap G therebetween. In this specification, in descriptions common to the three resistance heating elements 32A to 32C, only Arabic numerals are used for the reference numerals. The gap G is set to an insulation distance (creepage distance) that can prevent creepage discharge between adjacent resistance heating elements 32.

[0030] The resistance heating element 32 is formed in a substantially rectangular shape from a metal material with high electrical resistance. The entire heat generating section 31 is shorter than the overall length of the fixing belt 20 in the left-right direction (axial direction) and is longer in the axial direction than the passing area A1 of the fixing belt 20 (see FIG. 4). In other words, both axial sides of the resistance heating elements 32B and 32C located on both outer sides in the axial direction face the non-passing area A2 of the fixing belt 20 (see FIG. 4). The resistance heating element 32A located in the center in the axial direction corresponds to the left-right width of a small-size paper P, and all of the resistance heating elements 32A to 32C correspond to the left-right width of a normal-size paper P.

[0031] Three individual electrodes 33A to 33C and a common electrode 33D are formed on the lower surface of the substrate 30. The three individual electrodes 33A to 33C and the common electrode 33D are formed, for example, from a metal material having a lower electrical resistance value than the resistance heating element 32. In this specification, when describing the three individual electrodes 33A to 33C and the common electrode 33D in common, they will be simply referred to as "electrode portion 33" and will be indicated by Arabic numerals only.

[0032] As shown in FIG. 4, the individual electrode 33A is connected to the downstream end (rear end) of the resistance heating element 32A located in the center in the axial direction. The other individual electrodes 33B and 33C are connected to the downstream ends of the resistance heating elements 32B and 32C, respectively. The common electrode 33D is connected to the upstream ends (front ends) of all of the resistance heating elements 32A to 32C. Each of the multiple electrode portions 33 extends from a portion connected to the heat generating element 31 to both outer sides of the heat generating element 31 in the axial direction. The multiple electrode portions 33 are electrically connected to devices (not shown) such as a power supply on both sides of the substrate 30 in the axial direction.

[0033] The heat generating portion 31 and the electrode portion 33 are covered with a coating layer 34 (see FIG. 5). The coating layer 34 is made of a material, such as ceramic, that has electrical insulation properties and exhibits low sliding friction against the inner surface of the fixing belt 20. The coating layer 34, the heat generating portion 31, and the electrode portion 33 can be formed with high precision on the substrate 30 by, for example, a film formation technique such as sputtering, a printed circuit board manufacturing technique, a screen printing technique, or a combination of these techniques.

[0034] The heater 23 is fitted into the fitting portion 22A of the heater holder 22 with the heat generating portion 31 (coating layer 34) facing the pressure roller 21, and the coating layer 34 is in contact with the inner surface of the fixing belt 20 (see FIG. 5). The heater 23 receives the fixing belt 20 pressed against the pressure roller 21, thereby forming a pressure region N at the contact portion between the fixing belt 20 and the pressure roller 21.

[0035] <Heat-equalizing member> Incidentally, since the fixing belt 20 has a smaller heat capacity than a roller or the like, the fixing device 7 that employs the fixing belt 20 has the advantage of requiring less time to warm up. However, for example, when small-sized sheets of paper P are continuously fixed, the paper P (toner image) absorbs heat in most of the passing area A1 of the fixing belt 20, preventing excessive temperature rise. However, the axial ends of the passing area A1 where the paper P does not pass and the non-passing area A2 may experience excessive temperature rise. Therefore, in the fixing device 7 according to this embodiment, a heat equalizing member 26 is provided in the heater 23 to prevent excessive temperature rise in the non-passing area A2 of the fixing belt 20 and the like.

[0036] The temperature equalizing member 26 is formed of a metal material such as an aluminum alloy. The temperature equalizing member 26 is formed in a substantially rectangular plate shape with approximately the same axial length as the substrate 30 of the heater 23. As shown in FIGS. 3 and 5 , the temperature equalizing member 26 is disposed inside the fixing belt 20 and is provided on (in contact with) the upper surface (one surface) of the heater 23 (substrate 30) opposite the fixing belt 20 (pressure region N). A lubricant (not shown), such as silicone grease, is applied between the temperature equalizing member 26 and the substrate 30. The lubricant not only brings the temperature equalizing member 26 and the substrate 30 into close contact with each other but also facilitates the transfer of heat from the heater 23 to the temperature equalizing member 26. The temperature equalizing member 26 absorbs heat generated by the heater 23 and transfers it in the axial direction. In other words, the temperature equalizing member 26 uniforms the temperature of the heater 23 along the axial direction. As a result, the temperature of the fixing belt 20 is also uniform along the axial direction, suppressing excessive temperature rise in the non-passage region A2. In this specification, the term "uniform" does not refer only to a completely constant state, but also to a state that allows for some degree of error.

[0037] The fixing device 7 is provided with a temperature detector 27 that detects the temperature of the heater 23 and cuts off power supply to the heater 23 if the detected temperature is abnormal. The temperature detector 27 is, for example, a thermo-cut or other heat-sensitive element and is provided in contact with the heater 23. Specifically, the temperature detector 27 is attached to the top surface of the fitting portion 22A of the heater holder 22, with the lower portion of the temperature detector 27 in contact with the top surface of the heat-equalizing member 26 (see FIG. 3). The temperature detector 27 is in contact with approximately the center of the heat-equalizing member 26 in the axial direction (not shown). The heater 23, the temperature detector 27, the drive motor M, and the like are electrically connected to the control device 8 and a power source (not shown). The control device 8 appropriately controls the power source, the heater 23, and the like. The temperature detector 27 is not limited to a thermo-cut, and may be, for example, a contact-type temperature sensor such as a thermocouple, a platinum resistance thermometer, a thermistor, or a bimetal thermometer.

[0038] [Function of the fixing device] Here, the operation (fixing process) of the fixing device 7 will be described. The control device 8 controls the drive motor M to rotate the pressure roller 21 around its axis. The fixing belt 20 rotates following the rotation of the pressure roller 21 (see the arrow in FIG. 2). The control device 8 also receives a detection signal from the temperature detection unit 27 and controls the heater 23 (or power supply) to maintain a preset target temperature. The heater 23 (heat generating unit 31) generates heat when energized, and heats the fixing belt 20 (pressure region N).

[0039] At this time, the control device 8 changes which of the three resistance heating elements 32A to 32C is heated (energized) depending on the size of the paper P. For example, when a normal-sized paper P passes through the pressure region N, the control device 8 executes control to cause all three resistance heating elements 32A to 32C to generate heat. On the other hand, when a small-sized paper P passes through the pressure region N, the control device 8 executes control to cause only one resistance heating element 32A to generate heat. This makes it possible to heat only the necessary portion of the fixing belt 20 (pressure region N) in accordance with the size of the paper P. As a result, it is possible to minimize the amount of power used. It is also possible to prevent excessive temperature rise at both ends of the fixing belt 20 in the axial direction.

[0040] When the fixing belt 20 (heater 23) reaches the target temperature, the control device 8 starts the image formation process already described. The paper P onto which the toner image has been transferred enters the pressure area N. The fixing belt 20 heats the toner (toner image) on the paper P as it passes through the pressure area N while rotating around its axis. The pressure roller 21 pressurizes the toner on the paper P as it passes through the pressure area N while rotating around its axis. The toner image is then fixed to the paper P, forming a fixed image on the paper P. The paper P with the fixed image is then discharged to the paper output tray 4.

[0041] <Separation member> In the fixing device 7, the paper P that has passed through the pressure region N may stick to the surface of the pressure roller 21. Therefore, as shown in FIGS. 3 and 6 , the fixing device 7 according to this embodiment is provided with a separating member 35 that contacts the surface of the pressure roller 21 and separates the paper P that has passed through the pressure region N from the surface of the pressure roller 21. The separating member 35 has a plurality of (e.g., four) separation claws 36 (see FIG. 6 ). The four separation claws 36 are supported, for example, on a support shaft 37 that extends substantially parallel to the pressure roller 21 downstream of the pressure region N. The four separation claws 36 are arranged at substantially equal intervals in the axial direction within the passing region A1 of the pressure region N (see FIG. 6 ). While the four separation claws 36 are arranged at substantially equal intervals in the axial direction in the illustrated embodiment, the arrangement is not limited thereto and may be arranged at unequal intervals. The support shaft 37 is supported by a frame (not shown) of the fixing device 7.

[0042] Specifically, each separation claw 36 has a base end 36A fixed to a support shaft 37, extends from the support shaft 37 toward the pressure roller 21, and has a tip end 36B in contact with the surface of the pressure roller 21. Each separation claw 36 is provided in an inclined position from the downstream side toward the upstream side in the rotation direction of the pressure roller 21. Each separation claw 36 is formed into a generally triangular prism shape that gradually becomes thinner from the base end 36A toward the tip end 36B. Each separation claw 36 is also formed into a spatula shape with a thinner tip end 36B, and the tip end 36B is in contact with the surface of the pressure roller 21 near the pressure region N. Note that the vicinity of the pressure region N refers to, for example, a position approximately 1 to 10 mm away from the downstream end of the pressure region N along the circumferential surface of the pressure roller 21.

[0043] In the fixing device 7, the heater 23 heats the fixing belt 20, but the pressure roller 21 is also heated through the fixing belt 20. To ensure proper toner fixation on the paper P, it is important to maintain the surface temperatures of not only the fixing belt 20 but also the pressure roller 21 at a predetermined temperature. In the heater 23 described above, the three resistance heating elements 32A-32C and the two gaps G are alternately arranged in the axial direction. Therefore, the surface temperatures of the fixing belt 20 and the pressure roller 21 are slightly lower in the area corresponding to the gaps G than in the area corresponding to the resistance heating elements 32. If the separating member 35 (separating claw 36) were to contact the surface of the pressure roller 21 at a position corresponding to the gap G, the separating member 35 would absorb heat from the surface of the pressure roller 21, further lowering the surface temperature of the pressure roller 21 at the contact position of the separating member 35. This would result in uneven temperature distribution in the pressure region N along the axial direction, potentially preventing proper toner fixation on the paper P.

[0044] Therefore, in the fixing device 7 according to this embodiment, as shown in FIG. 6 , each separation claw 36 of the separation member 35 contacts the surface of the pressure roller 21 at a position offset in the axial direction from the gap G. In other words, each separation claw 36 is positioned to avoid the gap G between the resistance heating elements 32 and contacts the surface of the pressure roller 21 at a position corresponding to the resistance heating element 32. Specifically, the two separation claws 36 positioned in the axial center region contact the pressure roller 21 at positions corresponding to both axial sides of the resistance heating element 32A and are provided to peel small-sized paper P from the surface of the pressure roller 21. The two separation claws 36 positioned on both axial sides contact the pressure roller 21 at positions slightly outside the axial centers of the resistance heating elements 32B and 32C. The four separation claws 36 are provided to peel regular-sized paper P from the surface of the pressure roller 21.

[0045] In the fixing device 7 according to the present embodiment described above, the three resistance heating elements 32A-32C are arranged on the underside of the substrate 30 with a gap G in the axial direction therebetween, and the separation claws 36 of the separating member 35 are in contact with the surface of the pressure roller 21 at positions offset in the axial direction from the gap G. This configuration allows the positions on the pressure roller 21 that become colder due to the gap G between the resistance heating elements 32 to be offset in the axial direction from the positions that become colder due to the heat absorption by the separating member 35 (separation claws 36). This prevents the surface of the pressure roller 21 (and the fixing belt 20) from becoming extremely cold in one portion in the axial direction. As a result, the temperature in the pressure region N is uniformed in the axial direction, allowing the toner to be properly fixed to the paper P.

[0046] Furthermore, in the fixing device 7 according to this embodiment, the tip 36B of the separation claw 36, which is formed in a spatula shape, comes into contact with the surface of the pressure roller 21 near the downstream side of the pressure application region N. This configuration makes it possible to efficiently peel off the paper P stuck to the surface of the pressure roller 21. Furthermore, because the tip 36B of the separation claw 36 is thin, the heat capacity of the separation claw 36 can be reduced, and a decrease in the temperature of the surface of the pressure roller 21 at the contact point of the separation claw 36 can be suppressed.

[0047] In the fixing device 7 according to the present embodiment, the separating member 35 has four separating claws 36, but the number is not limited to this and may be one to three separating claws 36, or may be five or more separating claws 36 (not shown). In other words, the separating member 35 only needs to have at least one separating claw 36. In addition, one separating claw 36 is preferably provided approximately in the center of the axial direction of the pressure roller 21 so as to be able to separate paper P of all sizes.

[0048] Furthermore, in the fixing device 7 according to this embodiment, the separation claw 36 is formed in a roughly triangular prism shape, and the tip 36B of the separation claw 36 is formed in a spatula shape, but this is not limited thereto, and for example, the separation claw 36 may be formed in a flat plate shape (not shown).

[0049] Furthermore, in the fixing device 7 according to this embodiment, the heat generating section 31 is divided into three resistance heating elements 32A to 32C, but this is not limiting and the heat generating section 31 may be divided into two, four or more, or may not be divided at all (all of which are not shown). Additionally, the heat generating section 31 may be a single resistance heating element extending from one side to the other in the axial direction, or a U-shaped resistance heating element extending from one side to the other in the axial direction and then folding back to extend from the other side to one side in the axial direction (all of which are not shown).

[0050] Furthermore, in the fixing device 7 according to this embodiment, the paper P passes through the center of the pressure region N in the axial direction, but this is not limiting and the paper P may pass through a position closer to one side of the pressure region N in the axial direction (not shown). In this case, the non-passing region A2 is set only on one side of the fixing belt 20 (or the pressure region N) in the axial direction. It is also advisable to change the arrangement of the separating member 35 (separating claw 36) to match the passing region A1.

[0051] Furthermore, in the fixing device 7 according to this embodiment, the pressure roller 21 is driven to rotate, and the fixing belt 20 is driven to rotate, but this is not limited to this, and the fixing belt 20 may be driven to rotate, and the pressure roller 21 may be driven to rotate.

[0052] Furthermore, in the description of the above embodiment, the present invention has been applied to a monochrome image forming device 1 as an example, but this is not limiting and the present invention may also be applied to, for example, a color printer, a copier, a facsimile, or a multifunction device.

[0053] The above-described embodiment shows one aspect of the fixing device and image forming apparatus according to the present invention, and the technical scope of the present invention is not limited to the above-described embodiment. The present invention may be variously changed, substituted, or modified without departing from the spirit of the technical concept, and the claims include all embodiments that may fall within the scope of the technical concept. [Explanation of symbols]

[0054] 1. Image forming device 7 Fixing device 20 Fixing belt 21 Pressure roller (pressure member) 23 Heater 30 boards 32A~32C Resistance heating element 35 Separation member 36 separation claw G Gap N pressure area P Paper (media)

Claims

1. a fixing belt formed in a cylindrical shape and rotating around its axis to heat the toner on the medium; a pressure member that forms a pressure region between itself and the fixing belt and that pressurizes the toner on the medium that passes through the pressure region while rotating around its axis; a heater extending in the axial direction of the fixing belt, contacting the inner surface of the fixing belt facing the pressure region, and heating the fixing belt; a separating member that comes into contact with a surface of the pressure member and separates the medium that has passed through the pressure region from the surface of the pressure member; The heater is a substrate formed of an insulating material and extending in the axial direction in correspondence with the fixing belt; a plurality of resistance heating elements that are arranged with gaps between them in the axial direction on one surface of the substrate that is the inner surface side of the fixing belt, and generate heat when energized; The fixing device, wherein the separating member has at least one separating claw that contacts the surface of the pressure member at a position offset in the axial direction from the gap.

2. 2. The fixing device according to claim 1, wherein the separation claw is formed in a spatula shape with a thinned tip, and the tip is brought into contact with the surface of the pressure member in the vicinity of the pressure region.

3. 3. An image forming apparatus comprising the fixing device according to claim 1.

Images