Fixing device and image forming apparatus

Abstract

To provide a fixing device capable of improving the thermal uniformity of a uniform temperature member in a sheet width direction, ensuring productivity (throughput) when continuously fixing small-size sheets, and maintaining low sliding resistance between the uniform temperature member and a fixing member.SOLUTION: A fixing device of the present invention comprises: a rotating fixing member; a uniform temperature member that contacts an inner circumferential surface of the fixing member and equalizes temperature in a rotation axis direction of the fixing member; a pressing member that contacts the uniform temperature member via the fixing member to form a nip portion and presses a recording material passing through the nip portion; and a heat source disposed inside the fixing member. The uniform temperature member is provided with a concave step portion in a region at least partially overlapping the nip portion, and the step portion has a sliding plate. The sliding plate is made of a material having lower sliding resistance and higher durability than the uniform temperature member. Accordingly, the thermal uniformity of the uniform temperature member in a sheet width direction is improved, thereby maintaining low sliding resistance between the uniform temperature member and the fixing member.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Fixing film type fixing devices, which have a fast heating temperature rise, are widely used in electrophotographic image forming devices such as copiers and printers. In this type of fixing device, a thin fixing film is directly heated by a halogen heater or the like, and a pressure roller is brought into contact with a nip forming member through the fixing film to form a fixing nip.

[0003] For example, Patent Document 1 discloses a fixing device that uses a copper heat equalizing member in the area that rubs against the fixing film to dissipate heat from the fixing film in the paper width direction when fixing small-sized paper continuously, in order to prevent both ends of the fixing film from becoming too hot.

[0004] Furthermore, Patent Document 2 discloses a fixing device that uses an aluminum heat equalizing member with an alumite coating on the part that rubs against the fixing film, thereby maintaining reliability and heat equalization and keeping the sliding resistance with the fixing member low. Summary of the Invention [Problem to be solved by the invention]

[0005] However, aluminum heat spreaders have a lower thermal conductivity than copper heat spreaders, making them unsuitable for use in high-speed machines with a thermal conductivity of 70 ppm or more, resulting in a decrease in throughput. On the other hand, applying a sliding coating to copper heat spreaders to improve their sliding properties increases costs.

[0006] Therefore, an object of the present invention is to provide a fixing device that improves the temperature uniformity of the heat equalizing member in the paper width direction, ensures productivity (throughput) when continuously fixing small-sized paper, and can maintain low sliding resistance between the heat equalizing member and the fixing member. [Means for solving the problem]

[0007] The above-mentioned problem is solved by a fixing device including: a rotating fixing member; a heat equalizing member that contacts the inner peripheral surface of the fixing member and equalizes the temperature of the fixing member in the direction of the rotation axis; a pressure member that contacts the heat equalizing member via the fixing member to form a nip portion and applies pressure to a recording material passing through the nip portion; and a heat source that is arranged inside the fixing member, wherein the heat equalizing member is provided in an area where a concave step portion at least partially overlaps with the nip portion, the step portion has a sliding plate, and the sliding plate is made of a material that has lower sliding resistance and higher durability than the heat equalizing member. [Effects of the Invention]

[0008] The fixing device of the present invention can ensure productivity (throughput) when continuously fixing small size paper, and can also maintain low sliding resistance between the heat equalizing member and the fixing member. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram illustrating the configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2] 1 is a schematic diagram illustrating the configuration of a fixing device according to an embodiment of the present invention. [Figure 3] FIG. 2 is a perspective view showing a heat spreader and a sliding plate according to an embodiment of the present invention. [Figure 4] FIG. 4 is an enlarged cross-sectional view of the sliding plate shown in FIG. [Figure 5] 4 is a detailed view (part 1) showing an enlarged view of a heat spreader and a sliding plate according to one embodiment of the present invention. FIG. [Figure 6] 4 is a detailed view (part 2) showing an enlarged view of the temperature equalizing member and the sliding plate according to one embodiment of the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] 1 is a schematic diagram of an image forming apparatus according to one embodiment of the present invention. Hereinafter, an embodiment in which the present invention is applied to a laser printer (hereinafter referred to as "printer"), which is an electrophotographic image forming apparatus, will be described.

[0011] This image forming apparatus 1 includes an image forming unit 100 that forms an image on a recording material, namely, paper P. The image forming unit 100 is a tandem-type image forming apparatus in which imaging units 10Y, 10M, 10C, and 10K for the colors yellow (Y), magenta (M), cyan (C), and black (K) are arranged along the rotation direction of an intermediate transfer belt 20 that serves as an intermediate transfer body. The imaging units 10Y, 10M, 10C, and 10K each include a photosensitive element 11Y, 11M, 11C, and 11K that serves as a latent image carrier, respectively.

[0012] Each of the image forming units 10Y, 10M, 10C, and 10K includes a charging device as a charging means, an optical writing device 9 as an electrostatic latent image forming means, and a developing device as a developing means around the photoreceptor 11Y, 11M, 11C, and 11K. Furthermore, each of the image forming units 10Y, 10M, 10C, and 10K includes a primary transfer device as a primary transfer means and a cleaning device as a cleaning means around the photoreceptor 11Y, 11M, 11C, and 11K.

[0013] The charging device charges the surface of the photoconductor uniformly to a predetermined potential, and the optical writing device 9 writes an electrostatic latent image onto the surface of the photoconductor uniformly charged by the charging device by exposing it to light in accordance with image information. The developing device creates a toner image by a development process in which toner of each color (Y, M, C, K) adheres to the electrostatic latent image on the photoconductor. The primary transfer device transfers the toner image on the photoconductor onto the intermediate transfer belt 20, and the cleaning device removes residual toner from the photoconductor.

[0014] The color toner images formed on the photoconductors 11Y, 11M, 11C, and 11K are primarily transferred onto the intermediate transfer belt 20 by the primary transfer device so as to be superimposed on each other, forming color toner images on the intermediate transfer belt 20. The color toner images on the intermediate transfer belt 20 are transported to an opposing area (secondary transfer area) to the secondary transfer device 30 as the intermediate transfer belt 20 rotates.

[0015] Meanwhile, a paper feed cassette 60 is disposed below the image forming unit 100 as a feeding unit that feeds the held paper P. A pickup roller 61 feeds paper P one sheet at a time from the paper feed cassette 60. Then, a pair of registration rollers 62 transports the paper P along a transport path to a secondary transfer area.

[0016] The color toner image on the intermediate transfer belt 20 is secondarily transferred by the secondary transfer device 30 onto a sheet of paper P, which is conveyed by a pair of registration rollers 62 at a predetermined timing in the secondary transfer region. The sheet of paper P on which the color toner image has been formed is then conveyed to the fixing device 40, which serves as a fixing means, where the color toner image is fixed onto the sheet of paper P by the action of heat and pressure. After the fixing, the sheet of paper P is conveyed along a conveyance path and discharged onto a sheet discharge tray 50 by a sheet discharge roller 63.

[0017] 2 is a schematic diagram of a fixing device according to one embodiment of the present invention. Fixing device 40 includes fixing belt 42, which is a rotating fixing member, pressure roller 41, which is a pressure member, and heat source 43 (a halogen heater in the illustrated example) disposed inside fixing belt 42, and performs fixing by applying heat and pressure.

[0018] A nip forming member 45 held by a fixing stay 44, which is a stay member, is disposed within the fixing belt 42. The nip forming member 45 forms a nip portion with the pressure roller 41, with the fixing belt 42 sandwiched therebetween.

[0019] (Pressure roller) Pressure roller 41 contacts the outer peripheral surface of fixing belt 42 to form a nip portion, and applies pressure to the recording material passing through the nip portion. Pressure roller 41 is a metal roller with a silicone rubber layer on the outer periphery, and a release layer (PFA or PTFE layer) is provided on the surface of the silicone rubber layer to provide releasability.

[0020] Furthermore, pressure roller 41 is pressed against the fixing belt by a spring or the like, and the rubber layer is crushed and deformed to provide a predetermined nip width. In Fig. 2, the unpressurized state of pressure roller 41 is shown by a solid line, and the pressed state is shown by a dashed line.

[0021] Pressure roller 41 rotates by receiving a driving force via gears from a driving source such as a motor provided in image forming apparatus 1. Fixing belt 42 rotates together with pressure roller 41 by receiving a driving force from pressure roller 41 at the nip portion.

[0022] The pressure roller 41 may be a solid roller, but a hollow roller is preferable because it has a smaller heat capacity. The pressure roller 41 may also have a heat source such as a halogen heater. The silicone rubber layer may be solid rubber, but if there is no heater inside the pressure roller, sponge rubber may be used. Sponge rubber is more preferable because it has better heat insulation properties and is less likely to lose heat from the fixing belt 42.

[0023] (fixing belt) The fixing belt 42 is an endless belt (or film) made of a metal belt such as nickel or SUS, or a resin material such as polyimide. The surface layer of the fixing belt 42 has a release layer such as a PFA or PTFE layer, which provides release properties to prevent toner from adhering to it.

[0024] An elastic layer formed of a silicone rubber layer or the like may be present between the base material and the release layer of the fixing belt 42. Without the silicone rubber layer, the heat capacity is reduced and fixing performance is improved, but when the unfixed image is crushed and fixed, the slight irregularities on the belt surface are transferred to the image, leaving a citrus peel-like mark on the solid part of the image. To improve this, a silicone rubber layer of 100 μm or more is required. The deformation of the silicone rubber layer absorbs the slight irregularities, improving the citrus peel image.

[0025] (Nip forming member) Nip forming member 45 is composed of heat equalizing member 45a, a sliding member and heat transfer member placed on the nip surface, and resin pad 45b that supports it. One of the roles of resin pad 45b is to provide insulation, suppressing heat absorption from fixing belt 42 to fixing stay 44 via nip forming member 45, thereby suppressing increases in warm-up time and TEC value.

[0026] Heat equalizing member 45a extends in the width direction of fixing belt 42 and has, for example, a pad shape. This heat equalizing member 45a is arranged to equalize the temperature in the rotational axis direction of fixing belt 42. In other words, it absorbs heat from high-temperature parts of fixing belt 42 and transfers the absorbed heat to low-temperature parts of fixing belt 42, thereby equalizing the temperature in the axial direction of fixing belt 42.

[0027] The heat-equalizing member 45a is made of a material with high thermal conductivity, such as copper (thermal conductivity: 398 W / mk), which allows heat to be transferred in a short time. The surface of the heat-equalizing member 45a is coated with a coating that provides excellent sliding properties. Examples of coating materials include resin-based materials such as polyimide resin, fluororesin, polyphenylene sulfide resin, and saturated polyester resin. Alternatively, such resin-based coating materials may be mixed with glass fiber, carbon, graphite, graphite fluoride, carbon fiber, molybdenum disulfide, or fluororesin.

[0028] Metal-based coating materials can also be used. Examples of metal-based coating materials include molybdenum disulfide, nickel, and composite plating of nickel and fluororesin. Examples of metal-based coating materials include anodized aluminum and anodized aluminum impregnated with resin or metal. Ceramics can also be used as coating materials. Examples of ceramics used as coating materials include silicon carbide ceramics, silicon carbide ceramics, alumina ceramics, and mixtures of these with molybdenum disulfide, fluororesin, etc.

[0029] The high thermal conductivity heat spreader 45a in this embodiment is made of a material with high thermal conductivity that allows heat to be transferred in a short time, and is processed as described above, thereby producing the high thermal conductivity heat spreader 45a.

[0030] (Fixed stay) Fixing stay 44 is a hollow metal pipe made of aluminum, iron, stainless steel, or another metal. In this embodiment, fixing stay 44 is rectangular, but may have any other cross-sectional shape. This prevents bending of nip forming member 45, which receives pressure from pressure roller 41, and ensures a uniform nip width in the axial direction.

[0031] (heat source) Two heat sources 43 for raising the temperature of the fixing belt 42 are provided inside the fixing belt 42. In this embodiment, the heat sources 43 are halogen heaters, and the fixing belt 42 is directly heated from the inner circumferential side by radiant heat from the heat sources 43. Here, the heat source 43 only needs to be able to heat the fixing belt 42, and may be an IH coil, a resistance heating element, a carbon heater, or the like.

[0032] (reflector) Furthermore, a reflector 48 is disposed within fixing belt 42 as a reflective member that reflects heat toward the fixing belt in order to minimize loss of radiant heat from heat source 43. Reflector 48 is made of a high-purity aluminum metal material as a base, and is made of high-brightness aluminum with multiple reflection-enhancing films and protective films formed on the surface to achieve high reflectivity, for example, 95% or higher. Depending on the configuration, an aluminum plate may be coated with silver to further improve reflectivity.

[0033] (Light blocking material) The light-shielding member 49 has a stepped shape with a light-shielding area that matches the width of the recording medium (paper width). It is arranged so that it rotates without contact along the inside of the fixing belt 42, and rotates to a position corresponding to each paper width to shield areas that do not need to be heated. This makes it possible to prevent the non-paper-passing areas from becoming overheated, even when narrow recording media are continuously passed through.

[0034] Next, the characteristic features of the present invention will be described.

[0035] Referring particularly to the central portion of Figure 2, the heat equalizing member 45a has a concave step portion in its central region across the paper width direction (i.e., the region that at least partially overlaps with the nip portion), and has a sliding plate 46 that fits into this step portion.

[0036] The sliding plate 46 is preferably made of a highly durable material because it is rubbed against the fixing belt 42 at high pressure by the pressure roller 41. In this embodiment, an alumite-coated aluminum plate (thermal conductivity: 236 W / mk) is used.

[0037] The anodized aluminum coating (anodized aluminum layer) is very hard and has excellent wear resistance, particularly against abrasive wear. Therefore, the sliding plate 46 of this embodiment serves as a sliding member that is wear-resistant against the inner circumferential surface of the fixing belt 42.

[0038] The temperature equalizing member 45a is made by forming a concave step in a copper plate by half-blanking, and fitting the sliding plate 46 into the step. "Half-blanking" is a type of processing method for plate material, in which a predetermined part of the plate material is made to protrude in a convex shape by about half the thickness of the plate material. "Half-blanking" has the advantage of being able to be manufactured quickly and inexpensively.

[0039] The temperature equalizing member 45a and the sliding plate 46 are fixedly connected to each other by adhesive, double-sided tape, or fastening means (screws, etc.) provided outside the paper passage area so that they do not shift from each other.

[0040] The concave step of the temperature equalizing member 45a is not limited to half-blanking, but may be formed by drawing or cutting. The step may also be formed by bending across the entire width of the paper. This allows for a larger concave depth and greater freedom in selecting the sliding plate thickness.

[0041] The convex portion of the heat equalizing member 45a is in partial contact (over the minimum area that can be held) with the resin pad 45b, which has a low thermal conductivity. This prevents the heat from the heat equalizing member 45a from escaping to the fixing stay 44, allowing for efficient use of the heat from the fixing belt 42. Furthermore, the resin pad 45b fits into the convex portion of the heat equalizing member 45a, preventing misalignment between the two.

[0042] When small-sized sheets of paper are successively fixed, the fixing device 40 of this embodiment can transfer heat from both ends of the sliding plate 46 to the center via the heat equalizing member 45a. This prevents the sliding plate 46 (and the heat equalizing member 45a) at both ends of the paper from becoming too hot when small-sized sheets of paper are successively fixed, ensuring productivity (throughput).

[0043] Next, advantageous configurations will be described.

[0044] Fig. 3 is a perspective view showing a heat spreader and a sliding plate according to one embodiment of the present invention, and Fig. 4 is an enlarged cross-sectional view of the sliding plate shown in Fig. 3. An advantageous configuration of the sliding plate 46 will be described using these figures.

[0045] The sliding plate 46 of this embodiment is made of aluminum or an aluminum alloy and has an alumite coating (alumite layer 54) on its surface (the surface facing the inner circumferential surface of the fixing belt 42) as shown in Fig. 3. In addition, as shown in Fig. 4, a plurality of regularly arranged micropores 54a in the alumite layer 54 (on the aluminum base material 52) are filled with molybdenum disulfide (MoS2) 56, which is a solid lubricant.

[0046] The anodized aluminum layer 54 is very hard and has excellent wear resistance, particularly against abrasive wear. On the other hand, the molybdenum disulfide 56 is a solid lubricant with a lower friction coefficient than the anodized aluminum layer 54. Therefore, the heat equalizing member 45a of this embodiment can be a sliding member that has both wear resistance and lubricity against the inner circumferential surface of the fixing belt 42.

[0047] (Variation) In the above embodiment, molybdenum disulfide is used as the solid lubricant, but this is not limiting. Alternatively, polytetrafluoroethylene (PTFE) or fluorine grease may be impregnated and filled into the micropores 54a of the anodized aluminum layer 54.

[0048] 5 is a detailed view (part 1) showing an enlarged view of a heat equalizing member and a sliding plate according to one embodiment of the present invention. As shown in FIG. 5, the length dimension (la) of the step portion of heat equalizing member 45a is greater than the length dimension (lb) of sliding plate 46 (la > lb), and a gap (g) of approximately 1 mm or less is formed between the step portion and sliding plate 46 on the upstream side in the recording material conveyance direction.

[0049] A lubricant is applied between the fixing belt 42, which is rotated at high pressure, and the sliding plate 46 to reduce friction. The lubricant present between the fixing belt 42 and the sliding plate 46 is temporarily held in the gap (g) while being circulated, so that the rate of deterioration of the lubricant is slowed by refreshing the lubricant, thereby achieving a long lifespan. Note that the gap (g) is not limited to being located upstream of the nip N (see FIG. 5), but may also be located downstream of the nip N.

[0050] 6 is a detailed view (part 2) showing an enlarged view of the heat equalizing member and sliding plate according to one embodiment of the present invention. As shown in FIG. 6, the depth dimension (ta) of the step portion is greater than the thickness dimension (tb) of sliding plate 46 (ta>tb), and the surface of sliding plate 46 facing the fixing belt 42 has a step with respect to the surface of heat equalizing member 45a facing the fixing belt 42. Pressure roller 41 is pressed so that nip portion N includes step portion A on the downstream side in the conveyance direction of the recording material.

[0051] By forming a nip portion with a step shape, the leading edge of the paper is discharged closer to pressure roller 41, improving the separation of the paper from fixing belt 42. Furthermore, the step creates a high load on the rear end of nip portion N, which presses the molten toner onto the paper, improving fixing performance.

[0052] The present invention has been described in detail above using the embodiments. This embodiment is merely an example, and various modifications can be made without departing from the spirit and scope of the present invention. For example, the embodiment and the modifications may be combined with each other.

[0053] Furthermore, the effects described in the embodiments of the present invention are merely a list of the most preferable effects resulting from the present invention, and the effects of the present invention are not limited to those described in the embodiments of the present invention.

[0054] For example, aspects of the present invention are as follows. (Aspect 1) a rotating fixing member; a temperature equalizing member that contacts an inner circumferential surface of the fixing member and equalizes the temperature of the fixing member in the axial direction of the rotation; a pressure member that contacts the heat equalizing member via the fixing member to form a nip portion and applies pressure to the recording material passing through the nip portion; a heat source disposed inside the fixing member, the temperature equalizing member has a recessed step portion provided in a region at least partially overlapping with the nip portion, the recessed step portion having a sliding plate thereon; The fixing device is characterized in that the sliding plate is made of a material having lower sliding resistance and higher durability than the heat equalizing member. (Aspect 2) 2. The fixing device according to claim 1, wherein the heat equalizing member has a thermal conductivity greater than that of the sliding plate. (Aspect 3) a length dimension of the step portion in the recording material conveyance direction is greater than a length dimension of the sliding plate in the recording material conveyance direction; 3. The fixing device according to aspect 1 or 2, wherein the step portion and the sliding plate form a gap of about 1 mm or less on the upstream side or downstream side in the conveyance direction of the recording material. (Aspect 4) The depth dimension of the step portion is greater than the thickness dimension of the sliding plate, a surface of the sliding plate facing the fixing member has a step with respect to a surface of the heat equalizing member facing the fixing member; and 4. The fixing device according to any one of aspects 1 to 3, wherein the pressure member applies pressure so that the nip portion includes the step on the downstream side in the conveyance direction of the recording material. (Aspect 5) 5. The fixing device according to claim 1, wherein the step portion of the temperature equalizing member is formed by half-punching. (Aspect 6) The fixing device according to any one of aspects 1 to 5, wherein the sliding plate is made of aluminum or an aluminum alloy, has an anodized aluminum layer on a surface facing the inner circumferential surface of the fixing member, and a plurality of micropores in the anodized aluminum layer are filled with a solid lubricant having a lower friction coefficient than the anodized aluminum layer. (Aspect 7) An image forming apparatus including the fixing device according to any one of the first to sixth aspects. [Explanation of symbols]

[0055] 1. Image forming device 9 Optical writing device 10C,10K,10M,10Y Image forming section 11C,11K,11M,11Y Photoreceptor 20 Intermediate transfer belt 30 Secondary transfer device 40 Fixing device 41 Pressure roller 42 Fixing belt 43 Heat source 44 Fixing stay 45 Nip forming member 45a Heat equalizing member 45b resin pad 46 Sliding plate 48 Reflector 49 Light blocking material 50 Output tray 52 Aluminum base material 54 Anodized aluminum layer 54a Micropore 56 Molybdenum disulfide 60 Paper cassette 61 Pickup roller 62 Registration roller pair 63 Paper ejection roller 100 Image forming unit A Step P paper [Prior art documents] [Patent documents]

[0056] [Patent Document 1] Japanese Patent Publication No. 2022-139858 [Patent Document 2] Patent Publication No. 2021-096348

Claims

1. a rotating fixing member; a temperature equalizing member that contacts an inner circumferential surface of the fixing member and equalizes the temperature of the fixing member in the axial direction of the rotation; a pressure member that contacts the heat equalizing member via the fixing member to form a nip portion and applies pressure to the recording material passing through the nip portion; a heat source disposed inside the fixing member, the temperature equalizing member has a recessed step portion provided in a region at least partially overlapping with the nip portion, the recessed step portion having a sliding plate thereon; The fixing device is characterized in that the sliding plate is made of a material having lower sliding resistance and higher durability than the heat equalizing member.

2. 2. The fixing device according to claim 1, wherein the heat equalizing member has a thermal conductivity greater than that of the sliding plate.

3. a length dimension of the step portion in the recording material conveyance direction is greater than a length dimension of the sliding plate in the recording material conveyance direction; 2. The fixing device according to claim 1, wherein a gap of about 1 mm or less is formed between the step portion and the sliding plate on the upstream side or downstream side in the conveying direction of the recording material.

4. The depth dimension of the step portion is greater than the thickness dimension of the sliding plate, a surface of the sliding plate facing the fixing member has a step with respect to a surface of the heat equalizing member facing the fixing member; and 2. The fixing device according to claim 1, wherein the pressure member applies pressure so that the nip portion includes the step on the downstream side in the conveying direction of the recording material.

5. 2. The fixing device according to claim 1, wherein the step portion of the temperature equalizing member is formed by half-blanking.

6. 2. The fixing device according to claim 1, wherein the sliding plate is made of aluminum or an aluminum alloy, has an anodized aluminum layer on a surface facing the inner circumferential surface of the fixing member, and a plurality of micropores in the anodized aluminum layer are filled with a solid lubricant having a lower friction coefficient than the anodized aluminum layer.

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

Images