Fixing device and image forming system

Abstract

To obtain a fixing device capable of widening the width in the transport direction of a recording medium, of a nip portion, compared to the case where the recording medium is transported to a nip portion which is formed by a heating member and two block-shaped pressure members held by a holding member and arranged separately in the circumferential direction, and the contact face of which is flat.SOLUTION: A fixing device 10 comprises: a rotatable heating roller 66; an endless belt 72 for transporting a recording medium P nipped between itself and the heating roller 66; a holding member 110 including a first pressure portion 112 for pressing the endless belt 72 against the heating roller 66; a notch portion 114 which is provided upstream of a transport direction of the first pressure portion 112 in the holding member 110, and which retreats from the first pressure portion 112 to a side opposite the heating roller 66 and has a curved face 114B of a shape formed along a circumferential surface of the heating roller 66; and a second pressure portion 130 which is attached to the notch part 114, presses the endless belt 72 against the heating roller 66 with a weaker force than that of the first pressure portion 112.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a fixing device and an image forming system. [Background technology]

[0002] The following Patent Document 1 discloses a fixing device having a rotatable heating member, an endless belt that runs in response to the rotation of the heating member, a holding member provided on the opposite side of the heating member and inside the endless belt, a first pressure member provided on the outlet side of the holding member from which a recording medium is discharged, and a second pressure member provided on the inlet side of the holding member from which a recording medium is inserted, and arranged at an angle to the first pressure member along the heating member and shaped to match the heating member.

[0003] The following Patent Document 2 discloses a belt fixing device that includes a heated endless sheet-like fixing belt, a nip forming member fixedly arranged inside the fixing belt so as not to rotate, and a rotatable pressure roller that is pressed against the nip forming member with the fixing belt sandwiched therebetween and whose contact portion with the fixing belt forms a fixing nip, the fixing belt rotating while sliding on the nip forming member as the pressure roller is rotated, and the fixing belt has an elastic layer provided on a base material. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-057528 A [Patent Document 2] JP 2004-286931 A Summary of the Invention [Problem to be solved by the invention]

[0005] The present disclosure provides a fixing device and an image forming system that can increase the width of the recording medium in the transport direction at the nip portion, compared to when the recording medium is transported to a nip portion formed by a heating member and two block-shaped pressure members held by a holding member and arranged circumferentially spaced apart, and having a flat contact surface. [Means for solving the problem]

[0006] The fixing device described in the first aspect has a rotatable heating member, a transport member that transports a recording medium sandwiched between the heating member and the holding member, a first pressure section that presses the transport member against the heating member, a notch portion that is provided on the holding member upstream of the first pressure section in the transport direction, retreating from the first pressure section to the opposite side of the heating member and having a curved surface shaped along the peripheral surface of the heating member, and a second pressure section that is attached to the notch portion and presses the transport member against the heating member with a pressing force weaker than that of the first pressure section.

[0007] A fixing device according to a second aspect is the fixing device according to the first aspect, wherein the first pressure section is made of a resin harder than the second pressure section.

[0008] A fixing device according to a third aspect is the fixing device according to the second aspect, wherein the second pressure applying portion is made of a foamed resin.

[0009] The fixing device according to a fourth aspect is the fixing device according to the first aspect, wherein the second pressure section is attached to the curved surface in the cutout portion, and the axial central portion is curved more convexly toward the heating member than both axial ends.

[0010] The fixing device according to the fifth aspect is the fixing device according to the fourth aspect, wherein the thickness of the second pressure section in a direction intersecting the curved surface is equal along the axial direction, and the curved surface is curved more convexly toward the heating member at the central portion in the axial direction than at both ends in the axial direction.

[0011] The fixing device according to the sixth aspect is the fixing device according to the fourth aspect, wherein the first pressure section has a shape such that a central portion in the transport direction of the recording medium protrudes toward the heating member further than the downstream and upstream sides in the transport direction of the recording medium, and a central portion in the axial direction protrudes toward the heating member further than both ends in the axial direction.

[0012] The fixing device according to the seventh aspect is the fixing device according to the first aspect, wherein the length of the second pressure section along the transport direction of the recording medium is longer than the length of the first pressure section along the transport direction of the recording medium.

[0013] The fixing device according to the eighth aspect is the fixing device according to the seventh aspect, wherein the length of the second pressure section along the transport direction of the recording medium is between two and eight times the length of the first pressure section along the transport direction of the recording medium.

[0014] The fixing device according to a ninth aspect is the fixing device according to the first aspect, further comprising a metal pressing member that presses the first pressure portion of the holding member against the heating member via the conveying member.

[0015] The fixing device according to a tenth aspect is the fixing device according to the first aspect, wherein the cutout portion has a wall portion that retreats in a direction intersecting with the first pressure portion, and the second pressure portion is attached to the cutout portion in a state where the second pressure portion is in contact with the wall portion.

[0016] An image forming system according to an eleventh aspect of the present invention includes an image forming unit that forms a toner image on a recording medium; and a fixing device according to any one of the first to tenth aspects that fixes the toner image on the recording medium. Effect of the Invention

[0017] According to the fixing device described in the first aspect, the width of the nip portion in the transport direction of the recording medium can be increased compared to when the recording medium is transported to a nip portion formed by a heating member and two block-shaped pressure members held by a holding member and arranged circumferentially spaced apart and having a flat contact surface.

[0018] According to the fixing device described in the second aspect, compared to a case in which the first pressure section and the second pressure section are formed from resins of the same hardness, the second pressure section can press the conveying member against the heating member with a pressing force weaker than that of the first pressure section, with a simpler configuration.

[0019] According to the fixing device described in the third aspect, compared to when the second pressure section is formed from a non-foamed resin, the second pressure section can press the conveying member against the heating member with a pressing force weaker than that of the first pressure section, with a simpler configuration.

[0020] According to the fixing device described in the fourth aspect, the pressing force of the second pressure section is prevented from decreasing in the central portion in the axial direction, compared to when the second pressure section is held on the curved surface in the cutout portion and has an even shape in the axial direction.

[0021] The fixing device according to the fifth aspect is easier to manufacture than a case in which the second pressure section is formed to be thicker at the axial center than at both axial ends.

[0022] According to the fixing device described in the sixth aspect, the pressing force of the first pressure section is prevented from decreasing in the central part in the axial direction, compared to when the first pressure section is shaped uniformly in the transport direction and axial direction of the recording medium.

[0023] According to the fixing device described in the seventh aspect, it is easier to ensure the length of the nip portion between the transport member and the heating member, compared to when the second pressure section and the first pressure section have the same length along the transport direction of the recording medium.

[0024] According to the fixing device of the eighth aspect, the length of the nip portion between the transport member and the heating member can be secured more easily than when the length of the second pressure unit in the transport direction of the recording medium is shorter than twice the length of the first pressure unit in the transport direction of the recording medium, and the fixing performance of the toner image on the recording medium can be maintained more easily than when the length of the second pressure unit in the transport direction of the recording medium is longer than eight times the length of the first pressure unit in the transport direction of the recording medium.

[0025] According to the fixing device of the ninth aspect, it is easier to configure the first pressure section to press the conveying member against the heating member with a stronger pressing force than the second pressure section, compared to the case where the cutout side of the holding member is pressed against the heating member via the conveying member.

[0026] According to the fixing device described in the tenth aspect, the width of the nip portion formed by the first and second pressure sections and the heating member in the recording medium transport direction can be increased compared to when the wall portion receding from the first pressure section and the second pressure section are positioned apart.

[0027] According to the image forming system described in the 11th aspect, the fixing temperature can be lowered compared to a case in which a recording medium is transported to a nip section formed by a heating member and two block-shaped pressure members held by a holding member and arranged circumferentially spaced apart, and having a flat contact surface. [Brief description of the drawings]

[0028] [Figure 1] 1 is a schematic diagram illustrating an image forming system including a fixing device according to a first embodiment. [Diagram 2] 1 is a cross-sectional view showing a fixing device according to a first embodiment. [Diagram 3] FIG. 2 is a partial enlarged view showing the fixing device according to the first embodiment. [Figure 4] FIG. 2 is a side view showing a part of the pressure unit of the fixing device according to the first embodiment, illustrating a holding member having a first pressure portion and a second pressure portion attached to a cutout portion of the holding member. [Diagram 5]FIG. 2 is a perspective view showing a part of the pressure unit of the fixing device according to the first embodiment, illustrating a holding member having a first pressure portion and a second pressure portion attached to a cutout portion of the holding member. [Figure 6] 6 is a cross-sectional view taken along line 6A-6A of the pressurizing unit shown in FIG. 4. [Figure 7] 7 is a cross-sectional view taken along line 7A-7A of the pressurizing unit shown in FIG. 4. [Figure 8] 5 is a graph showing a pressing force of the fixing device according to the first embodiment in a paper passing direction of a recording medium. [Figure 9] FIG. 4 is a cross-sectional view showing a fixing device according to a comparative example. [Figure 10] 6 is a graph showing a pressing force in a recording medium conveying direction of a fixing device according to a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] An example of an embodiment of the present invention will be described below with reference to the drawings. Note that the arrow H in each drawing indicates the vertical direction, the arrow W indicates the horizontal direction, which is the device width direction, and the arrow D indicates the device depth direction, which is perpendicular to the vertical and horizontal directions.

[0030] [First embodiment] The image forming system according to the first embodiment will be described below.

[0031] <Image forming system configuration> Fig. 1 is a schematic diagram showing the configuration of an image forming system 10 as viewed from the front side. As shown in Fig. 1, the image forming system 10 has an image forming device main body 12, and at least one paper feed unit 18, an image forming section 14, and a fixing device 36 are mounted inside this image forming device main body 12. The image forming system 10 also has an outlet 34 disposed at the top of the image forming device main body 12, and a transport path 32 that transports the recording medium P sent out from the paper feed unit 18 through the image forming section 14 and the fixing device 36 to the outlet 34. Each component will be described below.

[0032] (Feed unit) The paper feed unit 18 includes a paper feed unit body 20 and a paper feed cassette 22 in which the recording medium P is stored. The paper feed unit 18 also includes a pickup roll 24 that draws out the recording medium P loaded in the paper feed cassette 22, and a feed roll 28 and a retard roll 26 that feed the recording medium P while sorting it. The recording medium P loaded in the paper feed cassette 22 is transported along a transport path 32 to a registration roll 38 described later by the rotation of the pickup roll 24, the feed roll 28, and the retard roll 26. The paper feed cassette 22 is detachably attached to the paper feed unit body 20. The number of paper feed units may be one or more, but in the first embodiment, two paper feed units 18 are provided as shown in FIG. 1.

[0033] (Image forming section) The image forming section 14 is an example of an image forming section, and forms a toner image on a recording medium P by an electrophotographic method. As an example, the image forming section 14 includes an image carrier 44 made of a photoreceptor, a charging device (e.g., a charging roll) 56 that uniformly charges the image carrier 44, and an optical writing device 58 that writes a latent image on the image carrier 44 charged by the charging device 56 with light. The image forming section 14 also includes a developing device 60 having a developing roll that visualizes the latent image on the image carrier 44 formed by the optical writing device 58 with toner, and a transfer device (e.g., a transfer roll) 42 that transfers the toner image formed by the developing device 60 to a recording medium P. The image forming section 14 also includes a cleaning device 62 that performs cleaning to remove toner remaining on the image carrier 44.

[0034] The optical writing device 58 is, for example, a scanning type laser exposure device, and passes through a process cartridge 64 (described later) to form a latent image on the image carrier 44. Note that, as another embodiment of the optical writing device 58, an LED, a surface emitting laser, or the like can be used.

[0035] The process cartridge 64 integrates the image carrier 44, the charging device 56, the developing device 60, and the cleaning device 62, and can be replaced as a whole. The process cartridge 64 can be removed from the image forming apparatus main body 12 by opening the discharge portion 16.

[0036] The toner image transferred onto the recording medium P by the transfer device 42 is fixed onto the recording medium P by the fixing device 36. The configuration of the fixing device 36 will be described later.

[0037] (Transport path) The transport path 32 is a passage for the recording medium P that connects the pickup roll 24 of the lower paper feed unit 18 to the discharge outlet 34 at the top of the image forming apparatus main body 12. The transport path 32 is inside the image forming apparatus main body 12 and has a portion that is formed along the vertical direction from the pickup roll 24 of the lower paper feed unit 18 to the fixing device 36.

[0038] A transfer device 42 and an image carrier 44 are disposed upstream of the fixing device 36 in the transport direction of the recording medium P on the transport path 32, and a registration roll 38 is disposed upstream of the transfer device 42 and the image carrier 44. Furthermore, a discharge roll 40 is disposed near the discharge port 34 of the transport path 32.

[0039] <Operation of the image forming system> Here, the operation of the image forming system 10 will be described. The recording medium P sent out by the pickup roll 24 from the paper feed cassette 22 of the paper feed unit 18 is separated by the retard roll 26 and the feed roll 28 and guided to the conveying path 32, where it is temporarily stopped by the registration roll 38. Then, the recording medium P is conveyed between the transfer device 42 and the image carrier 44 in a timed manner by the registration roll 38, whereby the toner image is transferred from the image carrier 44 to the recording medium P, and the transferred toner image is fixed by the fixing device 36. Furthermore, the recording medium P with the fixed toner image is discharged from the discharge port 34 to the discharge section 16 by the discharge roll 40.

[0040] <Configuration of the fixing device> Next, the fixing device 36 according to the first embodiment provided in the image forming system 10 will be described.

[0041] As shown in FIG. 2, the fixing device 36 includes a heating roll 66 as an example of a heating member, an endless belt 72 formed in an endless belt shape, and a guide member 74 that guides the endless belt 72 so that it can rotate freely. The endless belt 72 is an example of a conveying member. The fixing device 36 also includes a pressure unit 76 that is disposed inside the endless belt 72 and presses the endless belt 72 against the heating roll 66. As will be described later, the fixing device 36 has a Free Belt Nip Fuser (FBNF) type configuration in which a first pressure section 112 and a second pressure section 130 having different hardness are provided in the pressure unit 76. The fixing device 36 may include an impregnated pad (not shown) that supplies a lubricant to the inside of the endless belt 72.

[0042] (Guide material) The guide members 74 are disposed on both ends of the endless belt 72 and the pressure unit 76, and the pressure unit 76 is supported by the guide members 74. Note that a sliding sheet (not shown) for reducing friction between the endless belt 72 and the pressure unit 76 may be provided between the endless belt 72 and the pressure unit 76.

[0043] (heat roll) The heating roll 66 has a cylindrical roll portion 84 and a heater 86 arranged in the roll portion 84. The roll portion 84 is rotatably supported by a heating roll bearing (not shown) and rotates in the direction of the arrow A. The roll portion 84 also has a core 88 made of a metal material such as iron, stainless steel, or aluminum, and a release layer 90 coated or applied to the core 88. As an example, the roll portion 84 is a so-called hard roll that does not have an elastic layer. The core 88 has an outer diameter of, for example, 25 mm and a thickness of, for example, 0.7 mm. The release layer 90 is made of a material that is insulating and has excellent release properties, such as a fluororesin such as PFA (perfluoroalkoxyalkane), and has a thickness of, for example, 20 μm.

[0044] As an example, a plurality of (e.g., five) peeling claws 92 are in contact with the roll portion 84. The heater 86 is composed of, for example, two lamps. In addition, as an example, a thermostat 94 is provided facing the heating roll 66 on the opposite side of the heating roll 66 from the endless belt 72.

[0045] (endless belt) The endless belt 72 is provided between the heating roll 66 and the pressure unit 76, and travels in the direction of the arrow C following the rotation of the heating roll 66. The endless belt 72 transports the recording medium P sandwiched between the heating roll 66 and the endless belt 72. The heating roll 66 and the endless belt 72 come into contact with each other while being pressurized by the pressure unit 76, forming a nip portion 102, and the toner image is fixed to the recording medium P by the nip portion 102. The endless belt 72 is formed in an endless belt shape having a thickness of, for example, 75 μm, using a synthetic resin such as polyimide. Although not shown in the figure, a release layer made of a fluororesin such as PFA (perfluoroalkoxyalkane) is provided on the surface of the endless belt 72.

[0046] An introduction side guide section 96 is provided upstream of the nip section 102. The recording medium P transported in the direction of arrow B is guided by this introduction side guide section 96, and the leading end of the recording medium P is led to the nip section 102. Although not shown, a discharge side guide section that guides the recording medium P is provided downstream of the nip section 102.

[0047] (Pressure unit) 2 and 3, the pressurizing unit 76 includes a holding member 110 having a first pressurizing section 112, a notch 114 provided on the holding member 110 on the upstream side of the first pressurizing section 112 in the conveying direction, and a second pressurizing section 130 attached to the notch 114. The pressurizing unit 76 also includes a pressing member 140 that presses the first pressurizing section 112 of the holding member 110 against the heating roll 66, and a housing 142 that supports the pressing member 140.

[0048] The pressing member 140 is supported so as to press the first pressing section 112 of the holding member 110 and the second pressing section 130 attached to the notch section 114 of the holding member 110 against the heating roll 66. As a result, the first pressing section 112 and the second pressing section 130 are pressed against the heating roll 66 via the endless belt 72, forming a nip section 102 where the endless belt 72 and the heating roll 66 come into contact with each other. Each component of the pressing unit 76 will be described below.

[0049] 3 and 4, as described above, the holding member 110 has the first pressure section 112 and the notch 114 which retreats from the first pressure section 112 to the opposite side of the heating roll 66 on the upstream side of the first pressure section 112 in the conveying direction. The notch 114 has a wall section 114A which retreats from the first pressure section 112 in the intersecting direction, and a curved surface 114B which is formed from the rear end of the wall section 114A into a shape that follows the circumferential surface of the heating roll 66.

[0050] As an example, the holding member 110 has a length equal to the axial length of the heating roll 66. The holding member 110 (i.e., the first pressure applying section 112) is formed of a heat-resistant resin such as glass-containing polyethylene terephthalate (PET). As an example, the first pressure applying section 112 is formed of a resin harder than the second pressure applying section 130. That is, the hardness of the first pressure applying section 112 is higher than the hardness of the second pressure applying section 130, and the second pressure applying section 130 is softer than the first pressure applying section 112.

[0051] As an example, the Asker C hardness of the first pressure applying portion 112 is equal to or greater than 70 degrees and equal to or less than 75 degrees, and the Asker C hardness of the second pressure applying portion 130 is equal to or greater than 30 degrees and equal to or less than 35 degrees. The Asker C hardness is determined as follows. Measurements are taken at 80 equally spaced points on the surface using a de facto standard Asker C hardness tester manufactured by Kobunshi Keiki Co., Ltd., and the average value is regarded as the Asker C hardness of the surface layer. The measurements are taken in an environment of a temperature of 23° C. and a humidity of 55% RH.

[0052] The second pressure unit 130 is attached to at least the curved surface 114B of the cutout portion 114 in a state of contacting the wall portion 114A of the cutout portion 114 (see FIG. 4). As an example, the second pressure unit 130 is attached to the curved surface 114B with an adhesive or the like. At that time, the second pressure unit 130 may be fixed to the wall portion 114A with an adhesive or the like. Since the second pressure unit 130 is attached to the cutout portion 114 in a state of contacting the wall portion 114A, the second pressure unit 130 and the first pressure unit 112 are continuously arranged along the conveying direction (arrow B direction) of the recording medium P. That is, no gap is formed between the second pressure unit 130 and the first pressure unit 112, and the second pressure unit 130 and the first pressure unit 112 are not arranged apart from each other.

[0053] The second pressure unit 130 presses the endless belt 72 against the heating roll 66 with a pressing force weaker than that of the first pressure unit 112. As an example, the second pressure unit 130 has a length equal to the length of the holding member 110 in the longitudinal direction. The second pressure unit 130 is formed of, for example, a heat-resistant foamed resin such as silicone sponge.

[0054] As shown in Fig. 6, when the second pressure applying unit 130 is attached to the curved surface 114B of the cutout portion 114, the axial center portion 130A of the second pressure applying unit 130 is curved in a convex shape toward the heating roll 66 more than the axial end portions 130B on both sides. In Fig. 6, in order to make the configuration easier to understand, the heating roll 66 before the second pressure applying unit 130 is pressed against the heating roll 66 in the direction of arrow D is shown by an imaginary line. Also, in Fig. 6, the second pressure applying unit 130 is shown in an exaggerated shape compared to the actual shape so that the convex curved shape can be seen.

[0055] As an example, the thickness t of the second pressurizing unit 130 in the direction intersecting the curved surface 114B is equal along the axial direction, and the curved surface 114B is shaped such that the central portion 121A in the axial direction is curved more convexly toward the heating roll 66 than the end portions 121B on both sides in the axial direction. It is preferable that the variation in the thickness t of the second pressurizing unit 130 in the direction intersecting the curved surface 114B is within 5%, for example. As a result, the second pressurizing unit 130 attached to the curved surface 114B is curved such that the central portion 130A in the axial direction is curved more convexly toward the heating roll 66 than the end portions 130B on both sides in the axial direction.

[0056] As shown in Fig. 7, the first pressure applying unit 112 has a shape in which a central portion 122A in the axial direction protrudes toward the heating roll 66 more than both end portions 122B in the axial direction. In Fig. 7, in order to make the configuration easier to understand, the heating roll 66 before the first pressure applying unit 112 is pressed against the heating roll 66 in the direction of arrow D is shown by an imaginary line. Also, in Fig. 7, the central portion of the first pressure applying unit 112 is shown in an exaggerated shape compared to the actual shape so that the protruding shape can be seen.

[0057] 3 and 4, the first pressure applying section 112 has a central portion 124A in the transport direction (arrow B direction) of the recording medium P that protrudes toward the heating roll 66 further than an upstream end portion 124B and a downstream end portion 124C in the transport direction of the recording medium P. That is, the first pressure applying section 112 has a shape in which the central portion 124A is curved in a convex shape along the transport direction of the recording medium P (arrow B direction).

[0058] The length L1 of the second pressure section 130 along the transport direction of the recording medium P is longer than the length L2 of the first pressure section 112 along the transport direction of the recording medium P (see FIG. 4). It is preferable that the length L1 of the second pressure section 130 along the transport direction of the recording medium P is two to eight times the length L2 of the first pressure section 112 along the transport direction of the recording medium P. For example, the length L1 of the second pressure section 130 along the transport direction of the recording medium P is set to about 3.5 times the length L2 of the first pressure section 112 along the transport direction of the recording medium P.

[0059] The pressing member 140 supports the holding member 110, and both ends of the pressing member 140 are supported by the guide members 74, so that the pressing member 140 presses the holding member 110 against the heating roll 66. At this time, the end of the pressing member 140 in the longitudinal direction (i.e., the device depth direction) penetrates the guide members 74, and the end of the pressing member 140 in the longitudinal direction is biased toward the heating roll 66 by a biasing means (not shown) such as a spring.

[0060] The pressing member 140 is made of, for example, metal. As an example, the pressing member 140 is an L-shaped member, and one end in the longitudinal direction is inserted into a recess 115 formed on the inside of the first pressure section 112 of the holding member 110 (see FIG. 3). The longitudinal direction of the pressing member 140 is disposed in a direction intersecting with the surface of the first pressure section 112.

[0061] The housing 142 is formed from a synthetic resin, for example, glass-filled polytetrafluoroethylene (PET), and supports the holding member 110, the pressing member 140, and the endless belt 72.

[0062] <Operation of the First Embodiment> Next, the operation of the first embodiment will be described.

[0063] In the fixing device 36 of the image forming system 10, the recording medium P onto which the toner image has been transferred by the image forming section 14 passes through the conveying path 32 and is sent to a nip section 102 where the endless belt 72 and the heating roll 66 are brought into pressurized contact with each other by a pressurizing unit 76. The pressurizing unit 76 includes a first pressurizing section 112 of a holding member 110 and a second pressurizing section 130 attached to a notched section 114 of the holding member 110. The first pressurizing section 112 and the second pressurizing section 130 press the endless belt 72 against the heating roll 66, thereby forming the nip section 102.

[0064] At this time, the heating roll 66 is driven to rotate, and the endless belt 72 also moves around the outer periphery of the pressure unit 76 in response to the heating roll 66, so that the recording medium P is sent into the nip portion 102. The leading end of the recording medium P sent in is sandwiched between the heating roll 66 and the endless belt 72, and is first pressed against the heating roll 66 and the second pressure unit 130, and then pressed against the heating roll 66 and the first pressure unit 112, so that the toner image is fixed to the recording medium P. The second pressure unit 130 presses the endless belt 72 against the heating roll 66 with a pressing force weaker than that of the first pressure unit 112.

[0065] 8 shows the pressing force (i.e., pressure distribution) of the nip portion 102 in the paper passing direction (i.e., transport direction) of the recording medium P between the endless belt 72 and the heating roll 66. As shown in FIG. 8, the nip portion 102 between the heating roll 66 and the endless belt 72 includes a pre-nip portion 102A formed by the second pressure unit 130 on the upstream side (i.e., the entrance side) of the transport direction of the recording medium P, and a main nip portion 102B formed by the first pressure unit 112 on the downstream side (i.e., the exit side) of the transport direction of the recording medium P (see FIG. 3). First, in the pre-nip portion 102A on the upstream side (i.e., the entrance side) of the transport direction of the recording medium P, the second pressure unit 130 presses the recording medium P against the heating roll 66 with a pressing force weaker than that of the first pressure unit 112. Thereafter, in the main nip portion 102B on the downstream side in the conveying direction of the recording medium P (ie, the outlet side), the first pressure section 112 presses the recording medium P against the heating roll 66 with a stronger pressing force than the second pressure section 130.

[0066] In addition, when using a heating roll 66 that does not have an elastic layer, it is necessary to make the width of the nip portion 102 in the conveying direction of the recording medium P wide in order to obtain a sufficient pressing force in the nip portion 102. In the first embodiment, the notch portion 114 of the holding member 110 is provided with a curved surface 114B that retreats from the first pressure unit 112 to the opposite side of the heating roll 66 and has a shape along the circumferential surface of the heating roll 66, and the second pressure unit 130 is attached to the curved surface 114B of the notch portion 114. Therefore, in the graph shown in FIG. 8, the width of the nip portion 102 (width in the conveying direction of the recording medium P) by the first pressure unit 112 and the second pressure unit 130 becomes wide. By widening the width of the nip portion 102 (width in the conveying direction of the recording medium P) by the first pressure unit 112 and the second pressure unit 130, the fixing temperature by the heating roll 66 can be reduced. As an example, the length of the nip portion 102 in the conveying direction of the recording medium P is about 14 mm. As an example, the fixing temperature at the nip portion 102 between the heating roll 66 and the endless belt 72 is 104°C.

[0067] As described above, in the fixing device 36, the second pressure section 130 is attached to the cutout portion 114 that is receded from the first pressure section 112 of the holding member 110 to the side opposite the heating roll 66 and has a curved surface 114B shaped along the circumferential surface of the heating roll 66. Therefore, in the fixing device 36, the width of the nip portion 102 in the conveying direction of the recording medium P can be increased compared to the case where the recording medium P is conveyed to a nip portion that is formed by the heating roll and two block-shaped pressure members that are held by the holding member and spaced apart in the circumferential direction and have flat contact surfaces.

[0068] Furthermore, since the second pressure unit 130 is attached to the cutout 114 having the curved surface 114B shaped along the circumferential surface of the heating roll 66 receding from the first pressure unit 112 of the holding member 110, the elastic forces of the first pressure unit 112 and the second pressure unit 130 are less likely to decrease, that is, to become worn out, even if the fixing device 36 is used over time. For this reason, in the graph shown in FIG. 8, a pressure valley where the pressing force between the first pressure unit 112 and the second pressure unit 130 becomes weaker is less likely to occur.

[0069] Fig. 9 shows a fixing device 200 of a comparative example. As shown in Fig. 9, the fixing device 200 of the comparative example includes an endless belt 202, a guide member 204, and a pressure unit 206 arranged inside the endless belt 202. In the fixing device 200, the recording medium P is transported in a transport direction (direction of arrow B) along the horizontal direction, and is sent into a nip portion 222 where the endless belt 202 and the heating roll 66 come into contact with each other.

[0070] The pressurizing unit 206 includes a holding member 210 having a first pressurizing section 212, a notch 214 provided on the holding member 210 on the upstream side of the first pressurizing section 212 in the conveying direction, and a second pressurizing section 230 attached to the notch 214 via a plate member 215. The pressurizing unit 206 also includes a pressing member 240 that presses the holding member 210 against the heating roll 66 via the endless belt 202, and a housing 242 that supports the pressing member 240. The notch 214 includes a planar contact surface 214A recessed on the opposite side of the heating roll 66, and the second pressurizing section 230 is attached via a planar plate member 215 arranged on the contact surface 214A. The contact surface 214A extends in a direction intersecting the axial direction of the heating roll 66 when viewed from the direction along the axial direction of the heating roll 66.

[0071] The holding member 210 including the first pressure member 212 is made of a resin (such as polytetrafluoroethylene) harder than the second pressure member 230. The second pressure member 230 is made of a foamed resin (such as silicone sponge).

[0072] 9 and 10, the nip portion 222 between the heating roll 66 and the endless belt 202 includes a prenip portion 222A by the second pressurizing portion 230 on the upstream side (i.e., the entrance side) in the conveying direction of the recording medium P, and a main nip portion 222B by the first pressurizing portion 212 on the downstream side (i.e., the exit side) in the conveying direction of the recording medium P. First, in the prenip portion 222A on the upstream side (i.e., the entrance side) in the conveying direction of the recording medium P, the second pressurizing portion 230 presses the recording medium P toward the heating roll 66 with a pressing force weaker than that of the first pressurizing portion 212. Then, in the main nip portion 222B on the downstream side (i.e., the exit side) in the conveying direction of the recording medium P, the first pressurizing portion 212 presses the recording medium P toward the heating roll 66 with a pressing force stronger than that of the second pressurizing portion 230.

[0073] In the fixing device 200 of the comparative example, the notch 214 of the holding member 210 has a flat contact surface 214A, and the second pressure unit 230 is attached via a flat plate material 215 arranged on the contact surface 214A. Therefore, the length of the prenip portion 222A by the second pressure unit 230 along the conveying direction of the recording medium P is shorter than the length of the prenip portion 102A by the second pressure unit 130 attached to the notch 114 of the holding member 110 as in the first embodiment along the conveying direction of the recording medium P (see FIGS. 9 and 10). As an example, the length of the nip portion 222 in the conveying direction of the recording medium P, which is the total of the prenip portion 102A and the main nip portion 222B, is about 6 mm. In addition, the fixing temperature for fixing the toner image on the recording medium P becomes higher by shortening the length of the nip portion 222 in the conveying direction of the recording medium P. As an example, the fixing temperature at the nip portion 222 between the heating roll 66 and the endless belt 202 is 125°C.

[0074] In contrast, in the fixing device 36 of the first embodiment, the notch 114 of the holding member 110 has a curved surface 114B shaped along the circumferential surface of the heating roll 66. Therefore, the length of the second pressure unit 130 attached to the notch 114 along the transport direction of the recording medium P can be made longer than the length of the second pressure unit 230 attached via a plate member 215 to the planar contact surface 214A of the notch 214 of the fixing device 200 of the comparative example along the transport direction of the recording medium P.

[0075] Furthermore, in the fixing device 36, the first pressure applying section 112 is formed of a resin harder than the second pressure applying section 130. Therefore, in the fixing device 36, the second pressure applying section 130 can press the endless belt 72 against the heating roll 66 with a pressing force weaker than that of the first pressure applying section 112 with a simpler configuration than when the first pressure applying section and the second pressure applying section are formed of resins of the same hardness.

[0076] Moreover, in the fixing device 36, the second pressure applying section 130 is formed of a foamed resin. Therefore, in the fixing device 36, the second pressure applying section 130 can press the endless belt 72 against the heating roll 66 with a pressing force weaker than that of the first pressure applying section 112 with a simpler configuration than when the second pressure applying section is formed of a non-foamed resin.

[0077] In the fixing device 36, the second pressure unit 130 is attached to the curved surface 114B of the cutout 114 such that the axial center portion 130A is curved more convexly toward the heating roll 66 than the end portions 130B at both ends in the axial direction (see FIG. 6). Therefore, in the fixing device 36, the pressing force of the second pressure unit 130 is prevented from decreasing in the axial center portion 130A, compared to when the second pressure unit is held on the curved surface of the cutout and has an even shape in the axial direction.

[0078] In the fixing device 36, the thickness of the second pressure section 130 in the direction intersecting the curved surface 114B is equal along the axial direction, and the curved surface 114B has a shape in which the central part 121A in the axial direction is curved more convexly toward the heating roll 66 than the end parts 121B on both sides in the axial direction (see FIG. 6). Therefore, the fixing device 36 is easier to manufacture than when the second pressure section is formed so that the central part in the axial direction is thicker than both ends in the axial direction.

[0079] In the fixing device 36, the first pressure section 112 has a shape in which a central portion 124A in the transport direction of the recording medium P protrudes toward the heating roll 66 more than an upstream end portion 124B and a downstream end portion 124C in the transport direction of the recording medium P (see FIG. 3). Furthermore, the first pressure section 112 has a shape in which a central portion 122A in the axial direction protrudes toward the heating roll 66 more than end portions 122B at both ends in the axial direction (see FIG. 7). Therefore, in the fixing device 36, the pressing force of the first pressure section 112 is suppressed from decreasing at the central portion 124A in the axial direction, compared to a case in which the first pressure section has a uniform shape in the transport direction and the axial direction of the recording medium.

[0080] In the fixing device 36, the length L1 of the second pressure section 130 along the transport direction of the recording medium P is longer than the length L2 of the first pressure section 112 along the transport direction of the recording medium P (see FIG. 4). Therefore, in the fixing device 36, it is easier to ensure the length of the nip portion 102 between the endless belt 72 and the heating roll 66, compared to a case in which the lengths of the second pressure section and the first pressure section along the transport direction of the recording medium are equal.

[0081] In the fixing device 36, the length L1 of the second pressure section 130 along the conveying direction of the recording medium P is two or more times and eight or less times the length L2 of the first pressure section 112 along the conveying direction of the recording medium P. For this reason, in the fixing device 36, it is easier to ensure the length of the nip portion 102 between the endless belt 72 and the heating roll 66, compared to a case where the length of the second pressure section along the conveying direction of the recording medium is shorter than twice the length of the first pressure section along the conveying direction of the recording medium. In addition, it is easier to maintain the fixing performance of the toner image on the recording medium P, compared to a case where the length of the second pressure section along the conveying direction of the recording medium is longer than eight times the length of the first pressure section along the conveying direction of the recording medium.

[0082] Furthermore, the fixing device 36 is provided with a metal pressing member 140 that presses the first pressure section 112 of the holding member 110 against the heating roll 66 via the endless belt 72. For this reason, the fixing device 36 is easily configured so that the first pressure section 112 presses the endless belt 72 against the heating roll 66 with a stronger pressing force than the second pressure section 130, compared to a case in which the side of the notched portion of the holding member is pressed against the heating roll via the endless belt.

[0083] Furthermore, in the fixing device 36, the notch 114 includes a wall 114A that recedes from the first pressure unit 112 in a direction intersecting the first pressure unit, and the second pressure unit 130 is attached to the notch 114 in a state of contacting the wall 114A. Therefore, in the fixing device 36, the width of the nip 102 formed by the first pressure unit 112, the second pressure unit 130, and the heating roll 66 in the conveying direction of the recording medium P can be increased compared to a case in which the wall receding from the first pressure unit and the second pressure unit are disposed apart.

[0084] Moreover, the image forming system 10 equipped with the fixing device 36 has the image forming section 14 that forms a toner image on the recording medium P, and the fixing device 36 that fixes the toner image on the recording medium P. The fixing device 36 makes it easier to ensure the width of the nip section 102 formed by the first pressure section 112, the second pressure section 130, and the heating roll 66 in the conveying direction of the recording medium P. For this reason, the image forming system 10 can lower the fixing temperature compared to the case where the recording medium is conveyed to the nip section formed by the heating roll and two block-shaped pressure members held by a holding member and spaced apart in the circumferential direction, and whose contact surface is flat.

[0085] 〔supplementary explanation〕 In the first embodiment, the endless belt 72 is provided, but the present disclosure is not limited to this configuration, and as long as the recording medium P can be transported, the configuration can be changed to another one.

[0086] In the first embodiment, the second pressure applying portion 130 is made of a foamed resin, but the present disclosure is not limited to this configuration. For example, the second pressure applying portion may be made of a resin other than a foamed resin, as long as the material is softer than the hardness of the first pressure applying portion.

[0087] In the first embodiment, it is possible to change the ratio between the length of the first pressure section 112 along the transport direction of the recording medium P and the length of the second pressure section 130 along the transport direction of the recording medium P. In addition, the members constituting the pressure unit 76 are not limited to those disclosed herein, and can be changed as appropriate.

[0088] Although the present invention has been described in detail with respect to a specific embodiment, it will be apparent to those skilled in the art that the present invention is not limited to such an embodiment, and that various other embodiments are possible within the scope of the present invention.

[0089] [Additional Notes] Preferred aspects of the present disclosure will be described below.

[0090] (((1))) a rotatable heating element; a conveying member for conveying a recording medium sandwiched between the conveying member and the heating member; a holding member including a first pressure section that presses the conveying member against the heating member; a notch provided on the upstream side of the first pressure section in the holding member in the conveying direction, receding from the first pressure section to the opposite side of the heating member, and having a curved surface shaped along a peripheral surface of the heating member; a second pressurizing unit attached to the notch and pressing the conveying member against the heating member with a pressing force weaker than that of the first pressurizing unit; A fixing device having the same.

[0091] (((2))) The fixing device according to (((1))), wherein the first pressure section is formed of a resin harder than the second pressure section.

[0092] (((3))) The fixing device according to (((1))) or (((2))), wherein the second pressure section is made of foamed resin.

[0093] (((4))) The fixing device described in any one of (((1))) to (((3))), wherein when the second pressure section is attached to the curved surface in the cutout portion, the central portion in the axial direction is curved more convexly toward the heating member than both end portions in the axial direction.

[0094] (((5))) The thickness of the second pressure section in a direction intersecting with the curved surface is equal along the axial direction, The fixing device according to (((4))), wherein the curved surface is shaped so that a central portion in the axial direction is curved more convexly toward the heating member than both end portions in the axial direction.

[0095] (((6))) The fixing device described in any one of (((1))) to (((5))), wherein the first pressure section has a shape in which a central portion in the transport direction of the recording medium protrudes toward the heating member further than the downstream and upstream sides in the transport direction of the recording medium, and a central portion in the axial direction protrudes toward the heating member further than both end portions in the axial direction.

[0096] (((7))) A fixing device described in any one of ((1)) to (((6))), wherein the length of the second pressure section along the transport direction of the recording medium is longer than the length of the first pressure section along the transport direction of the recording medium.

[0097] (((8))) The fixing device described in ((7))), wherein the length of the second pressure section along the transport direction of the recording medium is between two and eight times the length of the first pressure section along the transport direction of the recording medium.

[0098] (((9))) The fixing device described in any one of ((1))) to (((8))) is provided with a metal pressing member that presses the first pressure portion of the holding member against the heating member via the conveying member.

[0099] (((10))) The cutout portion includes a wall portion that is recessed in a direction intersecting with the first pressure portion, The fixing device according to any one of (((1))) to (((9))), wherein the second pressure section is attached to the cutout section in a state of contacting the wall section.

[0100] (((11))) an image forming unit that forms a toner image on a recording medium; A fixing device according to any one of ((1))) to (((10))) that fixes a toner image on the recording medium; An image forming system comprising:

[0101] According to the fixing device described in (((1))), the width of the nip portion in the transport direction of the recording medium can be increased compared to when the recording medium is transported to a nip portion formed by a heating member and two block-shaped pressure members held by a holding member and arranged circumferentially spaced apart, and having a flat contact surface.

[0102] According to the fixing device described in (((2))), compared to a case in which the first pressure section and the second pressure section are formed from resins of the same hardness, the second pressure section can press the conveying member against the heating member with a pressing force weaker than that of the first pressure section, with a simpler configuration.

[0103] According to the fixing device described in (((3))), compared to a case in which the second pressure section is formed from a non-foamed resin, the second pressure section can press the conveying member against the heating member with a pressing force weaker than that of the first pressure section, with a simpler configuration.

[0104] According to the fixing device described in (((4))), the pressing force of the second pressure section is prevented from decreasing in the central part in the axial direction, compared to when the second pressure section is held on the curved surface in the cutout portion and has an even shape in the axial direction.

[0105] The fixing device described in (((5))) is easier to manufacture than a case in which the second pressure section is made thicker at the axial center than at both axial ends.

[0106] According to the fixing device described in (((6))), the pressing force of the first pressure section is prevented from decreasing in the central part in the axial direction, compared to when the first pressure section is shaped uniformly in the transport direction and axial direction of the recording medium.

[0107] According to the fixing device described in (((7))), it is easier to ensure the length of the nip portion between the transport member and the heating member, compared to when the lengths of the second pressure section and the first pressure section along the transport direction of the recording medium are equal.

[0108] According to the fixing device described in (((8))), the length of the nip portion between the transport member and the heating member can be secured more easily than when the length of the second pressure unit in the transport direction of the recording medium is shorter than twice the length of the first pressure unit in the transport direction of the recording medium. The fixing performance of the toner image on the recording medium can be maintained more easily than when the length of the second pressure unit in the transport direction of the recording medium is longer than eight times the length of the first pressure unit in the transport direction of the recording medium.

[0109] According to the fixing device described in (((9))), it is easier to configure the first pressure section to press the conveying member against the heating member with a stronger pressing force than the second pressure section, compared to when the side of the cutout portion of the holding member is pressed against the heating member via the conveying member.

[0110] According to the fixing device described in (((10))), the width in the recording medium transport direction of the nip portion formed by the first and second pressure sections and the heating member can be increased compared to a case in which the wall portion receding from the first pressure section and the second pressure section are positioned apart.

[0111] According to the image forming system described in (((11))), the fixing temperature can be lowered compared to a case in which a recording medium is transported to a nip portion formed by a heating member and two block-shaped pressure members held by a holding member and spaced apart in the circumferential direction, and having a flat contact surface. [Explanation of symbols]

[0112] 10. Image forming system 14 Image forming section (an example of an image forming section) 36 Fixing device 66 Heating roll (an example of a heating member) 72 Endless belt (an example of a conveying member) 76 Pressurizing Unit 84 Roll section 110 Retaining member 112 First pressure section 114 Notch 114A Wall section 114B Curved Surface 121A Center part (an example of the center part in the axial direction of a curved surface) 121B End (an example of both ends of a curved surface in the axial direction) 122A Center section (example of center section in axial direction) 122B End (an example of both ends in the axial direction) 124A Center portion (an example of the center portion in the conveying direction of the recording medium) 124B upstream end (an example of the upstream side in the conveying direction of the recording medium) 124C downstream end (an example of the downstream side in the conveying direction of the recording medium) 130 Second pressure section 130A Center section (example of center section in axial direction) 130B End (an example of both ends in the axial direction) P Recording medium

Claims

1. a rotatable heating element; a conveying member for conveying a recording medium sandwiched between the conveying member and the heating member; a holding member including a first pressure section for pressing the conveying member against the heating member; a notch provided on the holding member upstream of the first pressure unit in the conveying direction, receding from the first pressure unit to an opposite side of the heating member, and having a curved surface that is shaped along a circumferential surface of the heating member; a second pressure unit attached to the notch and pressing the conveying member against the heating member with a pressing force weaker than that of the first pressure unit; A fixing device having the same.

2. The fixing device according to claim 1 , wherein the first pressure section is made of a resin harder than the second pressure section.

3. The fixing device according to claim 2 , wherein the second pressure section is made of a foamed resin.

4. The fixing device according to claim 1 , wherein the second pressure section has a shape such that, when attached to the curved surface in the cutout portion, the central portion in the axial direction is curved more convexly toward the heating member than both end portions in the axial direction.

5. The thickness of the second pressure portion in a direction intersecting with the curved surface is equal along the axial direction, 5. The fixing device according to claim 4, wherein the curved surface is curved so that a central portion in the axial direction is curved more convexly toward the heating member than both end portions in the axial direction.

6. The fixing device according to claim 4, wherein the first pressure section has a shape in which a central portion in the transport direction of the recording medium protrudes toward the heating member further than the downstream and upstream sides in the transport direction of the recording medium, and a central portion in the axial direction protrudes toward the heating member further than both ends in the axial direction.

7. The fixing device according to claim 1 , wherein a length of the second pressure section along the transport direction of the recording medium is longer than a length of the first pressure section along the transport direction of the recording medium.

8. The fixing device according to claim 7 , wherein the length of the second pressure section along the transport direction of the recording medium is between two and eight times the length of the first pressure section along the transport direction of the recording medium.

9. The fixing device according to claim 1 , further comprising a metal pressing member for pressing the first pressure portion of the holding member against the heating member via the conveying member.

10. The cutout portion includes a wall portion that is recessed in a direction intersecting with the first pressure portion, The fixing device according to claim 1 , wherein the second pressure portion is attached to the notch portion in a state where the second pressure portion is in contact with the wall portion.

11. an image forming unit that forms a toner image on a recording medium; The fixing device according to claim 1 , which fixes a toner image on the recording medium; An image forming system comprising:

Images