Roller used in a fixing device, fixing device including the roller, and imaging apparatus

Abstract

A roller used in a fixing device, a fixing device including the roller, and an imaging apparatus, the roller including a rubber layer, the rubber layer including a plurality of void portions, pore channel portions connecting the void portions, and a filler, wherein an aspect ratio RA of the filler is 2.5 ≤ RA ≤ 215, and a linear expansion coefficient of the rubber layer is less than or equal to 400×10<supgt;‑6< / supgt> / K.

Description

Technical Field

[0001] The present disclosure relates to a roller used in a fixing device, a fixing device including the roller, and an imaging apparatus. The fixing device is included in an imaging apparatus (such as a copying machine or a printer) using an electrophotographic method or an electrostatic recording method. Background Art

[0002] As a fixing unit (fixing device) included in an imaging apparatus, there is a type of fixing unit in which a fixing nip portion is formed by a heating unit having a heat source and a pressure roller (roller) not having a heat source. A recording material having a toner image formed thereon is heated when being nipped in the fixing nip portion and conveyed, and thereby the toner image is fixed to the recording material.

[0003] In such a fixing unit, a pressure roller having the following layer structure is also used for the purpose of effectively transferring heat energy from the heating unit to the recording material and the toner. For example, in the pressure roller, a rubber layer is provided in which many void portions are dispersed, and thereby low heat conduction in the rubber layer is achieved. If such a pressure roller is used, the fixing unit reaches a temperature at which the toner image can be fixed within a short time after the fixing unit starts heating. Therefore, the quick start characteristic can be improved.

[0004] However, in a fixing unit including a pressure roller in which low heat conduction is achieved in the rubber layer, in the case of performing a fixing process on a small-sized recording material, a temperature rise is likely to occur in the non-sheet passing portion, which is an excessive temperature rise phenomenon in a region where the recording material does not pass.

[0005] Japanese Patent Application Laid-Open No. 2014-142406 discusses a pressure roller in which a heat conduction filler is added to a rubber layer including many void portions to achieve both maintaining the quick start characteristic and reducing the temperature rise in the non-sheet passing portion.

[0006] Incidentally, there are more demands than before for reducing the size of the imaging apparatus and reducing costs. To meet these demands, it is desired to shorten the length of the conveyance path of the recording material or simplify the conveyance mechanism. As a method for this purpose, the following configuration is possible.

[0007] First, the conveyance path of the recording material is designed to be as short as possible to shorten the conveyance distance of the recording material. The distance from the transfer unit that transfers the unfixed toner image to the recording material to the fixing unit that fixes the toner image to the recording material also becomes as short as possible (about several tens of millimeters). To simplify the conveyance mechanism for the recording material, the conveyance of the recording material in the transfer unit and the fixing unit is performed by the same motor, thereby reducing the number of motors.

[0008] In order to achieve the above-described configuration that satisfies size reduction and simplification, there are the following problems. The same motor is used to convey the recording material in the transfer unit and the fixing unit, and thus it is impossible to individually adjust the conveyance speed of the recording material in each unit. Therefore, it is difficult to adjust both the change in the conveyance speed of the recording material in the fixing unit and the change in the conveyance speed of the recording material in the transfer unit caused by the difference in the toner image.

[0009] In a fixing unit using a film heating method, the fixing unit has a configuration in which a plate-shaped heater is placed in the internal space of a cylindrical fixing film, and a fixing nip portion is formed by the heater and a pressure roller with the fixing film intervening therebetween, and the pressure roller is rotatably driven by a motor. The fixing film is rotated by the rotation drive of the pressure roller, and the recording material is introduced between the fixing film and the pressure roller to convey the recording material.

[0010] In the pressure roller, a rubber layer is provided. The rubber layer thermally expands when heated during printing. The above-described pressure roller in which a heat conduction filler is added to the rubber layer including many void portions also thermally expands. The heating degree varies depending on various printing conditions, and therefore, the amount of expansion of the rubber layer also changes in various ways. When the amount of expansion of the rubber layer changes, the diameter of the pressure roller also changes. Therefore, the conveyance speed of the recording material in the fixing unit changes.

[0011] If the conveyance speed in the fixing unit is much faster than that in the transfer unit and the recording material is excessively pulled, image elongation will occur, in which the toner image transferred to the recording material by the transfer unit elongates in the conveyance direction. In addition, the following problems occur. When the rear end of the recording material comes out of the sheet feeding unit upstream of the transfer unit in the conveyance direction, a large vibration occurs, and this vibration is transmitted to the transfer unit and the vibration interferes with the toner image.

[0012] Disclosure

[0013] The present disclosure relates to providing a pressure roller that reduces thermal expansion while achieving both maintaining a fast start-up characteristic and reducing the temperature rise in a non-sheet passing portion, and also provides a fixing unit including the pressure roller and an imaging apparatus including the fixing unit.

[0014] According to an aspect of the present disclosure, a roller used in a fixing device includes a rubber layer, the rubber layer including a plurality of void portions, a pore channel portion connecting the void portions, and a filler. The aspect ratio RA of the filler is 2.5 ≤ RA ≤ 215, and the linear expansion coefficient of the rubber layer is less than or equal to 400×10 -6 / K.

[0015] In the following description of exemplary embodiments with reference to the accompanying drawings, other features of the present disclosure will become apparent. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a cross-sectional view of an imaging device according to an embodiment of the present disclosure.

[0017] Figure 2A is a cross-sectional view of a fixing unit according to an embodiment of the present disclosure. Figure 2B is a perspective view of a pressure roller.

[0018] Figure 3 is a schematic cross-sectional view of a rubber layer of a pressure roller according to an embodiment of the present disclosure.

[0019] Figure 4 is a schematic perspective view of a mold for molding a pressure roller according to an embodiment of the present disclosure.

[0020] Figure 5 is a schematic cross-sectional view of a mold for molding a pressure roller according to an embodiment of the present disclosure.

[0021] Figure 6 is an example of a distorted image according to an embodiment of the present disclosure.

[0022] Figure 7A is an enlarged view of a normal portion of an image on a recording material according to an embodiment of the present disclosure. Figure 7B is an enlarged view of a distorted portion of an image on a recording material according to an embodiment of the present disclosure.

[0023] Figure 8 is a list of configurations in Examples 1 to 8 and Comparative Examples 1 and 2 according to an embodiment of the present disclosure.

[0024] Figure 9 is a list of measured values and evaluation results of configurations according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0025] (Imaging Device)

[0026] Figure 1 is a cross-sectional view of an imaging device 100. The imaging device 100 is a laser printer using an electrophotographic method.

[0027] The imaging device 100 includes a photosensitive drum (image bearing member) 1, which is an electrophotographic photosensitive member. The photosensitive drum 1 is formed by providing a photosensitive material such as an organic photoconductor (OPC), amorphous selenium, and amorphous silicon on a cylindrical main body of a drum formed of aluminum alloy or nickel. The photosensitive drum 1 is rotated by a motor M1 at Figure 1It is rotatably driven in the direction of the arrow R1 shown at a predetermined processing speed (circumferential speed). The surface of the photosensitive drum 1 is uniformly subjected to the charging process of the charging roller 2. The surface of the photosensitive drum 1 that has undergone the charging process is scanned by the laser scanner 3 according to the image information. Thus, an electrostatic latent image is formed on the photosensitive drum 1. The electrostatic latent image formed on the photosensitive drum 1 is developed and visualized using the toner supplied from the developing unit 4. The developing unit 4 includes a developing roller 41 that conveys the toner to the photosensitive drum 1.

[0028] In the imaging device 100, the transfer roller 5 is placed in contact with the photosensitive drum 1. The transfer roller 5 is biased toward the photosensitive drum 1. Between the photosensitive drum 1 and the transfer roller 5, a transfer portion T is formed. At the position of the transfer portion T, the toner image is transferred from the photosensitive drum 1 to the recording material P.

[0029] The recording material P is held in the holding tray 101 and fed one by one by the feeding roller 102. Each recording material P then passes through the conveying portion F formed by the conveying rollers 103 and 108, the transfer portion T formed by the photosensitive drum 1 and the transfer roller 5, and the fixing nip portion N in this order.

[0030] The conveyance of the recording material P in the conveying portion F, the transfer portion T, and the fixing nip portion N is all performed by the driving force of the motor M1. The conveyance speed of the recording material P in each portion is set to approximately 270 mm / second.

[0031] The leading end of the recording material P is detected by the top sensor 104. Based on the positional relationship between the top sensor 104 and the transfer portion T and the conveyance speed of the recording material P, the moment when the leading end of the recording material P reaches the transfer portion T is detected. The detection of this moment enables the toner image to be transferred to the correct position on the recording material P.

[0032] The recording material P onto which the toner image has been transferred is conveyed to the fixing unit (fixing device) 6. The fixing unit 6 heats and presses the recording material P carrying the toner image in the fixing nip portion N, thereby fixing the toner image to the recording material P. The recording material P on which the toner image is fixed is discharged to the discharge tray 107 through the discharge roller 106, and the discharge tray is formed on the upper surface of the device main body 110 of the imaging device 100. At the same time, the discharge sensor 105 detects the moments when the leading end and the trailing end of the recording material P pass through, thereby monitoring whether a jam occurs.

[0033] On the contrary, the toner remaining on the photosensitive drum 1 without being transferred to the recording material P when transferring the toner image is removed and collected from the photosensitive drum 1 by the cleaner 7. The cleaner 7 causes the cleaning blade 71 to scrape the surface of the rotating photosensitive drum 1 and remove the toner from the surface.

[0034] (Fixing Unit)

[0035] Figure 2A It is a cross-sectional view of a fixing unit (fixing device) 6. The fixing unit 6 uses a film heating method. The fixing unit 6 includes a heating unit 10 and a pressure roller 20. The heating unit 10 includes a cylindrical fixing film 13, a heater 11 placed in the internal space of the fixing film 13, a heater holder 12 that holds the heater 11, and a reinforcing bracket 15 that reinforces the heater holder 12. The heater holder 12 also serves as a guide that restricts the rotation locus of the fixing film 13.

[0036] The reinforcing bracket 15 is biased toward the pressure roller 20 by a spring (not shown). The heater 11, the holder 12, and the pressure roller 20 thus clamp the fixing film 13, and thus a fixing clamping portion N is formed between the fixing film 13 and the pressure roller 20. As described above, the pressure roller 20 is driven in the direction of arrow R2 by a motor M1, and the fixing film 13 rotates in the direction of arrow R3 by being driven by the pressure roller 20.

[0037] The recording material P onto which the toner image t is transferred is heated while being clamped in the fixing clamping portion N and conveyed. Thus, the toner image t is melted by the heat of the heater 11 and fixed to the recording material P.

[0038] On the surface of the heater 11 that is opposite to the surface that slidably contacts the fixing film 13, a thermistor 14, which is a temperature detection element, is placed. A signal indicating the detection result of the thermistor 14 is input to the engine control unit 302. Based on the signal from the thermistor 14, the engine control unit 302 controls the power supplied to the heater 11 so that the temperature of the heater 11 is maintained at a predetermined target temperature.

[0039] The heater 11 is a plate-shaped heater, which includes a long and narrow plate-shaped substrate 113 formed of ceramic (aluminum or aluminum nitride), a heating resistor 112 printed on the substrate 113, and an insulating layer 111 that covers the heating resistor 112. The insulating layer 111 is provided to ensure electrical insulation characteristics and wear resistance. The material of the insulating layer 111 according to this exemplary embodiment is glass. The heater 11 is placed such that the insulating layer 111 contacts the inner surface of the fixing film 13.

[0040] (Fixing film)

[0041] The fixing film 13 includes a base layer formed of a metal such as stainless steel or a heat-resistant resin such as polyimide, and a release layer formed on the base layer. The release layer is formed of a fluororesin, such as tetrafluoroethylene-ethylene vinyl fluoride copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), or polytetrafluoroethylene (PTFE). The release layer can be formed by coating the fluororesin directly on the surface of the base layer or via a primer layer, or by placing a fluororesin tube on the base layer. The fixing film 13 according to the present exemplary embodiment is a film in which the release layer is formed by coating a polyimide base layer with PFA. The total thickness of the fixing film 13 according to the present exemplary embodiment is 70 μm, and the outer circumferential length of the fixing film 13 is 56.7 mm.

[0042] Since the fixing film 13 rotates in sliding contact with the heater 11 and the heater holder 12, it is desirable to reduce the frictional resistance between the heater 11 and the heater holder 12 and the fixing film 13. Therefore, an appropriate amount of lubricant such as heat-resistant grease is placed between the surfaces of the heater 11 and the holder 12 and the inner circumferential surface of the fixing film 13. This enables the fixing film 13 to rotate smoothly.

[0043] (Pressure roller)

[0044] Figure 2B is a perspective view of the pressure roller 20. The pressure roller 20 includes a metal core 21 having a main body portion 21a and a shaft portion 21b, a rubber layer 22 disposed around the metal core 21, and a release layer 23 disposed around the rubber layer 22. The rubber layer 22 of the pressure roller 20 according to the present exemplary embodiment is formed of silicone rubber, and the release layer 23 is formed of a fluororesin. The diameter of the pressure roller 20 is 20 mm, and the thickness of the rubber layer 22 is 2.5 mm. The diameter of the main body portion 21a of the metal core 21 is 15 mm. The length in the axial direction of the pressure roller 20 (including the entire length of the shaft portion 21b) is 289 mm. The length of the portion where the rubber layer 22 is provided (the length of the main body portion 21a of the metal core 21) is 250 mm.

[0045] As will be described in detail below, the rubber layer 22 formed of silicone rubber includes void portions, pore channel portions connecting the void portions, and needle-shaped fillers (high heat conduction fillers).

[0046] (Metal core)

[0047] As the metal core of the pressure roller, a solid metal core or a hollow tubular metal core is known. In the case of the hollow tubular metal core, a heating element can also be placed inside the hollow tubular metal core. As the metal core 21 of the pressure roller 20 according to the present exemplary embodiment, both a solid metal core and a hollow tubular metal core can be used. However, it is not desirable to place a heating element inside the metal core 21. This is to achieve a configuration for promoting heat dissipation from the rubber layer 22 via the metal core 21 to prevent a temperature rise in the non-sheet passing portion.

[0048] The metal core 21 can be made of a metal material such as aluminum, aluminum alloy, steel, or stainless steel alloy. The metal core 21 of the pressure roller 20 according to the present exemplary embodiment is solid and made of steel, and the metal core 21 includes shaft rod portions 21b in both end portions in its axial direction.

[0049] (Rubber layer)

[0050] Figure 3 is a cross-sectional view showing the microstructure of the rubber layer 22. The main component of the rubber layer 22 is heat-resistant silicone rubber 22a. The rubber layer 22 includes a plurality of dispersed void portions 22b, pore channel portions 22c connecting the void portions 22b, and dispersed needle-like fillers 22d within the silicone rubber 22a. That is, the void portions 22b of the rubber layer 22 have the following structure: where adjacent void portions 22b among the plurality of void portions 22b are connected to each other through the pore channel portions 22c (communication pores). The silicone rubber 22a of the rubber layer 22 contains a silane coupling agent or an adhesive. This integrates the rubber layer 22 with the metal core 21. The rubber layer 22 will be described in more detail below.

[0051] (Release layer)

[0052] The main component of the release layer 23 is a fluororesin. As the fluororesin, PFA, FEP, PTFE, a mixture of these, or a product obtained by dispersing these polymers in a heat-resistant resin or rubber can be applied. As the release layer 23 of the pressure roller 20 according to the present exemplary embodiment, a resin tube formed of PFA is used.

[0053] Examples of the method for molding the release layer 23 composed of a resin tube include a method for molding the rubber layer 22 and then fixing the resin tube to the outer circumference of the rubber layer 22 with an adhesive, and a method for placing the resin tube inside a cylindrical outer mold and bonding the resin tube to the rubber layer 22 while molding the rubber layer 22. In the present exemplary embodiment, the following method is used. As Figure 4As shown, the resin tube 75 is placed inside the cylindrical outer mold 71, and the resin tube 75 is fixed in the opening portions at both ends in the longitudinal direction of the outer mold 71. Then, while molding the rubber layer 22, the resin tube 75 (which will eventually become the release layer 23) and the rubber layer 22 are integrated together. Figure 4 The state in which the resin tube 75 placed inside the cylindrical outer mold 71 is fixed in the opening portion of the outer mold 71 in a folded-back manner is shown. A method for manufacturing the pressure roller 20 will be described in detail below.

[0054] The thickness of the release layer 23 is 100 μm or less. It is desirable that the thickness of the release layer 23 be 10 μm or more and 50 μm or less. If the thickness of the release layer 23 is too large, the hardness of the pressure roller 20 may be high, and the fixing clamping portion N may not be able to form a desired width. The thickness of the release layer 23 of the pressure roller 20 according to the present exemplary embodiment is 30 μm.

[0055] (Detailed description of the rubber layer)

[0056] The configuration of the rubber layer 22 will now be described in detail. The rubber layer 22 has a microstructure such that the change in the conveyance speed of the recording material in the fixing unit 6 can be reduced.

[0057] (Silicone rubber)

[0058] It is desirable that the silicone rubber 22a be formed from a silicone rubber raw material that is cured by heat and has rubber elasticity. However, the type of the silicone rubber raw material is not particularly limited. Examples of the silicone rubber raw material include:

[0059] (1) An addition reaction-curing type liquid silicone rubber component, which is composed of an alkenyl-containing diorganopolysiloxane, an organohydrogenpolysiloxane containing a hydrogen atom bonded to a silicon atom, and a reinforcing filler, and is cured with a platinum catalyst to become a silicone rubber.

[0060] (2) An organic peroxide-curing type silicone rubber component, which is composed of an alkenyl-containing diorganopolysiloxane and a reinforcing filler, and is cured with an organic peroxide to become a silicone rubber, and

[0061] (3) A condensation reaction-curing type liquid silicone rubber component, which is composed of a hydroxy group-containing diorganopolysiloxane, an organohydrogenpolysiloxane containing a hydrogen atom bonded to a silicon atom, and a reinforcing filler, and is cured with a condensation reaction accelerating catalyst (such as an organotin compound, an organotitanium compound, or a platinum catalyst) to become a silicone rubber.

[0062] Among these, with respect to process moldability, addition reaction curable liquid silicone rubber components are ideal. For example, if the viscosity of the liquid material, which is a diorganopolysiloxane as a starting material, of the main component is 0.1 Pa·S or greater at 25°C, a rubber molded product can be easily obtained using a processing method such as a known metal mold casting method. As such liquid silicone rubber, commercially available liquid silicone rubber can be employed. A thickening agent or a reinforcing agent, as well as materials to be blended as described below, can be added as needed.

[0063] (Void portion)

[0064] Most of the void portions 22b of the rubber layer 22 are so-called communication holes that communicate with the outside of the pressure roller 20 via the hole passage portion 22c. In the pressure roller 20 according to the present exemplary embodiment, the outer circumference of the rubber layer 22 is covered with the release layer 23, but the rubber layer 22 is exposed to the outside at both end portions in the axial direction of the pressure roller 20. In a porous rubber layer having a communication hole structure, compared with a porous rubber layer having no communication hole structure (i.e., having an independent hole structure), the air present in the void portion is more likely to flow out of the void portion. For example, if the pressure roller 20 is heated, the air thermally expanded in the void portion 22b of the rubber layer 22 is discharged to the outside via the hole passage portion 22c, thereby preventing the diameter of the pressure roller 20 from changing.

[0065] Examples of the method for forming the void portion 22b having such a communication hole structure include a method of using a thermally degradable organic foaming agent while crosslinking the rubber component by heating, and a method of using an emulsified product obtained by mixing an uncrosslinked material of liquid silicone rubber and water with a thickening agent, an emulsifier, or the like. In the present exemplary embodiment, resin microspheres, which are hollow particles dispersed in liquid silicone rubber, are used to form the void portion 22b of the rubber layer 22. That is, the void portion 22b is a void portion generated by the resin microspheres. A resin microsphere flocculant having a high affinity for the resin microspheres and a low affinity for the silicone rubber material is added, whereby the hole passage portion 22c can be formed simultaneously with the thermal molding.

[0066] As the resin microspheres, various types of resin microspheres are available. In the present exemplary embodiment, in view of the dispersibility in liquid silicone rubber, the dimensional stability in molding, and the ease of handling, pre-expanded resin microspheres (product name: F80-DE, manufactured by MASTUMOTO YUSHI-SEIYAKU Co., Ltd.) including an acrylonitrile shell layer and having an average particle diameter of 10 μm to 200 μm are used.

[0067] In view of the specific gravity of the molded article, the blending amount of the resin microspheres and the liquid silicone rubber can be appropriately selected. The blending amount of the resin microspheres is typically 0.5 to 8 parts by weight relative to 100 parts by weight of the liquid silicone rubber. It is desirable that the blending amount of the resin microspheres be 1 to 5 parts by weight. If the blending amount of the resin microspheres is less than 1 part by weight, the specific gravity of the molded article may be high and the molded article may be hard. In addition, depending on the addition of the flocculant, the formation of the pore channel portion 22c may be unstable. If the blending amount of the resin microspheres is greater than 5 parts by weight, the volume of the resin microspheres may be large, and special consideration may be required for blending with the liquid silicone rubber.

[0068] As the flocculant, tetraethylene glycol is used in the present exemplary embodiment. The amount of the flocculant added to the liquid silicone rubber is about 3 to 15 parts by weight relative to 100 parts by weight of the liquid silicone rubber, but specifically depends on the blending amount of the resin microspheres relative to the liquid silicone rubber. If the addition amount of the flocculant is less than 3 parts by weight, there may be many isolated void portions 22b that are not connected to each other. If the addition amount of the flocculant is greater than 15 parts by weight, the thermomoldability may be low.

[0069] It is desirable that the volume ratio of the connected void portions 22b (connected pores) be 35% by volume or more and 65% by volume or less relative to the volume of the entire rubber layer 22. If the volume ratio of the void portion 22b is less than 35% by volume, the rubber layer 22 may be too hard to form the fixing clamping portion N. If the volume ratio of the void portion 22b is 65% by volume or more, the durability of the rubber may be low. All the void portions 22b of the rubber layer 22 do not have to be connected pores, and the rubber layer 22 may include independent pores.

[0070] (Needle-shaped filler)

[0071] The needle-shaped filler 22d is dispersed in the silicone rubber 22a in a substantially random state. As will be described in detail below, the rubber layer 22 is molded by injecting a liquid material including the needle-shaped filler 22d into a mold and causing the liquid material to flow. At this time, the needle-shaped filler 22d having a high aspect ratio is generally oriented according to the flow. In the case where hollow particles (hollow fillers) are used as the material for forming the void portion 22b, the orientation of the needle-shaped filler 22d in the flow direction can be prevented. It is considered that this is because the hollow particles act as so-called interfering particles. Therefore, when there are hollow particles during the molding of the rubber layer 22, compared with the case where there are no hollow particles, relatively more connection paths are formed due to the contact between the fibers of the needle-shaped filler 22d in the thickness direction of the rubber layer 22. That is, the thermal conductivity in the thickness direction of the rubber layer 22 is improved.

[0072] Examples of the acicular filler 22d include pitch carbon fibers, polyacrylonitrile (PAN) carbon fibers, glass fibers, and inorganic whiskers. When carbon fibers with high thermal conductivity are used as the acicular filler 22d, the above-described connection path serves as a heat conduction path, and the thermal conductivity in the thickness direction of the rubber layer 22 is increased compared to the case where hollow particles are not present. Then, the rubber layer 22 is laminated on the metal core portion 21 made of metal as described above, and thus heat accumulated in the non-sheet passing portion of the pressure roller 20 can be effectively transferred to the metal core portion 21 via the heat conduction path.

[0073] An acicular filler (or fibrous filler) refers to a filler having an acicular (or fibrous) shape that is long in a single direction.

[0074] In the present exemplary embodiment, the aspect ratio (length / diameter) RA of the filler used is 2.5 ≤ RA ≤ 215.

[0075] The reason for this limitation is that using an acicular filler with a high aspect ratio can reduce the thermal expansion of the silicone rubber 22a. However, the higher the aspect ratio (the longer the length), the more difficult it is to form a uniform rubber layer during manufacturing. In view of these circumstances, it is desirable that the fiber length of the filler be 25 μm or more and 1500 μm or less, and the fiber diameter of the filler be 7 μm or more and 10 μm or less. As described above, it is desirable that the aspect ratio RA of the filler be 2.5 ≤ RA ≤ 215. More desirably, the fiber length should be about 200 μm or more and 1100 μm or less.

[0076] In the present exemplary embodiment, as the acicular filler 22d, pitch carbon fibers having high thermal conductivity are used (product name: GRANOC Milled Fiber XN-100-25M (manufactured by NIPPON GRAPHITE FIBER CORPORATION), fiber diameter is 9 μm, average fiber length is 250 μm, aspect ratio is 28, density is 2.2 g / cm 3 ). As a measurement result, the thermal conductivity λ of the pressure roller 20 is approximately 0.8 to 2.0 W / m·K. Within this range, the blending amount of the acicular filler 22d can be reduced while achieving the effect of preventing the temperature rise in the non-sheet passing portion. Therefore, molding the pressure roller 20 is not difficult.

[0077] The thermal conductivity λ of the pressure roller 20 is measured by bringing a surface thermal conductivity meter (product name: QTM-500, manufactured by KYOTO ELECTRONICS MANUFACTURING CO., LTD.) into contact with the surface of the pressure roller 20. The sensor probe of the surface thermal conductivity meter (model: PD-11, manufactured by KYOTO ELECTRONICS INDUSTRY CO., LTD.) is brought into contact with the pressure roller 20 substantially parallel to the axial direction of the pressure roller 20. During the measurement, the sensor probe is used after calibrating it with a cylindrical body made of quartz and having the same diameter as the pressure roller 20.

[0078] (Method for manufacturing a pressure roller)

[0079] Now, a method for manufacturing the pressure roller 20 will be described. Figure 4 is an external perspective view of a casting mold for manufacturing the pressure roller 20. Figure 5 is a cross-sectional view along the axial direction of the pressure roller 20. The pressure roller 20 can be manufactured by other manufacturing methods. In the experimental examples described below, a plurality of pressure rollers 20 are formed and used for evaluation.

[0080] (Step of preparing a liquid component for a rubber layer (first step))

[0081] Needle-like fillers and resin microspheres are weighed and blended with an uncrosslinked addition reaction curable liquid silicone rubber. The needle-like fillers, resin microspheres, and the uncrosslinked addition reaction curable liquid silicone rubber are mixed together using a known mixture stirring method such as a rotary multi-functional mixture stirrer. Next, tetraethylene glycol is added as a flocculant for the resin microspheres, and mixing is continued for a certain period of time to prepare a liquid component for the rubber layer.

[0082] (Step of molding a rubber layer (second step))

[0083] As Figure 4 shown, a fluororesin tube 75 is firmly fixed inside a cylindrical outer mold 71 made of metal and having a length of 250 mm, a diameter of 28 mm, and an inner diameter of 20 mm in the longitudinal direction (axial direction of the pressure roller 20) of the mold for casting molding. The above dimensions correspond to the dimensions of the main body portion 21a of the metal core portion 21, the rubber layer 22, and the release layer 23 in the pressure roller 20.

[0084] As Figure 5As shown, a cavity 72 of a mold for casting molding is formed by a fluororesin tube 75 having a primer treatment performed on its inner circumferential surface and a metal core 74 having a primer treatment performed on its surface and having a diameter of 15 mm. The metal core 74 is supported by an outer mold 71 using bearings 76-1 and 76-2. The cavity 72 communicates with the outside of the outer mold 71 through communication paths 73-1 and 73-2. Then, a liquid component for a rubber layer prepared in the first step is injected from the communication path 73-1 (which is a flow path), thereby filling the inside of the cavity 72 with the liquid component. Then, the cavity 72 filled with the liquid component for the rubber layer is sealed by a sealing method (not shown). The metal core 74 corresponds to the metal core 21 of the pressure roller 20.

[0085] (Step of crosslinking the silicone rubber component (third step))

[0086] The mold for casting molding in which the cavity 72 is sealed is heated at 130 °C for 60 minutes, thereby curing the silicone rubber component of the rubber layer.

[0087] (Demolding step (fourth step))

[0088] After appropriately cooling the mold for casting molding by water cooling or air cooling, the pressure roller 20 is taken out from the mold for casting molding, in which the metal core 21, the rubber layer 22, and the release layer 23 are integrated.

[0089] (Secondary crosslinking step (fifth step))

[0090] The pressure roller 20 taken out from the mold for casting molding is placed in a hot air circulation furnace and maintained at a temperature of 230 °C for four hours, thereby performing secondary crosslinking.

[0091] (Evaluation method)

[0092] Now, an evaluation method for evaluating the pressure roller 20 will be described.

[0093] (Method for evaluating the change in the conveyance speed of the recording material in the fixing unit)

[0094] By using the following method, the effect of reducing the change in the conveyance speed of the recording material by using the pressure roller 20 was confirmed.

[0095] In order to evaluate only the conveyance speed of the recording material P in the fixing unit 6, a test is performed in the following state: The fixing unit 6 is removed from the image forming apparatus 100 and set in a so-called idling apparatus that can be rotationally driven, temperature-adjusted, and allows the recording material to pass through.

[0096] The test procedure is as follows.

[0097] Process 1: Cool the fixing unit 6 to the same temperature as the external air temperature (in this exemplary embodiment, the entire fixing unit 6 reaches a state of 25°C).

[0098] Process 2: Start the rotational drive of the pressure roller 20 so that the peripheral speed of the pressure roller 20 reaches 270 mm / sec, and at the same time start the heating control, where the target temperature for the temperature control of the heater 11 is 200°C.

[0099] Process 3: Three seconds after starting the rotational drive and heating control, pass a single A4-sized sheet of CANON RedLabel 80 g / cm 2 as the recording material P, and measure the paper speed of this sheet (the paper speed in Process 3 is VP1). Although the paper speed can be measured by various methods, in this exemplary embodiment, a laser Doppler measuring device is used to measure the paper speed.

[0100] Process 4: After passing the recording material P as described in Process 3, maintain the state where the peripheral speed of the pressure roller 20 is 270 mm / sec and the temperature is adjusted to 200°C for 120 seconds (idle for 120 seconds).

[0101] Process 5: Similar to Process 3, pass a single A4-sized sheet of CANON Red Label 80 g / cm 2 as the recording material P, and measure the paper speed of this sheet (the paper speed in Process 5 is VP2).

[0102] By performing the above tests, in the case where the imaging device 100 actually performs printing, the conveyance speed of the recording material P in the fixing unit 6 can be measured in the state where the temperature of the pressure roller 20 is the lowest and in the state where the temperature of the pressure roller 20 is the highest. The content of the above process is determined based on the state of the fixing unit 6 when the imaging device 100 performs printing.

[0103] In the case where the imaging device 100 performs printing, the temperature of the pressure roller 20 is the lowest when printing the first sheet because printing starts in the state where the fixing unit 6 is completely cooled. Therefore, the speed of the recording material P at this time is the lowest. In the imaging device 100 according to this exemplary embodiment, the moment when the first recording material P reaches the fixing unit 6 at the start of printing is 3 seconds after starting the rotational drive of the fixing unit 6 and the heating operation of the heater 11 simultaneously. Adjust the conditions of Process 3 to the actual conditions of the imaging device 100 when fixing the first sheet. The surface temperature of the pressure roller 20 when the sheet passes through is 130°C.

[0104] In contrast, when the imaging device 100 performs printing, the temperature of the pressure roller 20 is the highest when intermittently repeating the printing of sheet materials one by one. In the imaging device 100 according to the present exemplary embodiment, the temperature of the pressure roller 20 continues to rise until 100 sheets are intermittently printed one by one. For example, when printing a sheet of CANON Red Label 80 g / cm 2 under the condition of the sheet, the surface temperature of the pressure roller 20 saturates at 180 °C when printing the one-hundredth sheet and subsequent sheets. Therefore, the speed of the recording material P is the highest at this time.

[0105] Adjust the conditions of process 5 to the actual conditions of the imaging device 100 when fixing the one-hundredth sheet and subsequent sheets. The surface temperature of the pressure roller 20 is 180 °C when the sheet passes through.

[0106] Perform processes 1 to 5 in this way, measure the paper speed VP1 in process 3 and the paper speed VP2 in process 5, and thereby measure the maximum change rate VP2 / VP1 (= RV) of the conveying speed of the recording material in the fixing unit 6 of the imaging device 100.

[0107] (Method for evaluating an image)

[0108] A method for evaluating image defects caused by changes in the conveying speed of the recording material in the fixing unit 6 will now be described.

[0109] In the imaging device 100, as Figure 1 shown, the rotational driving of the conveying portion F, the transfer portion T, and the fixing clamping portion N is all performed by a motor (common motor) M1, and the conveying speed of the recording material P in each portion is configured to be approximately 270 mm / second. However, if the temperature of the pressure roller 20 becomes high, the conveying speed of the recording material P in the fixing clamping portion N is greater than 270 mm / second. In the case where the temperature of the pressure roller 20 is high, and if a single recording material P is simultaneously clamped by the conveying portion F, the transfer portion T, and the fixing clamping portion N, the recording material P is conveyed while being pulled together between the fixing clamping portion N and the conveying portion F and the transfer portion T.

[0110] If the conveyance of the recording material P continues, the rear end of the recording material P leaves the conveying portion F. However, at this moment, the balance between the pulling forces for pulling the recording material P together as described above is lost. Therefore, in the transfer portion T, the relative speed of the recording material P with respect to the peripheral speed of the photosensitive drum 1 fluctuates temporarily and greatly. This temporary fluctuation in the relative speed causes the toner image being transferred from the photosensitive drum 1 to the recording material P to be disturbed (blurred) (hereinafter referred to as a "distorted image").

[0111] Figure 6An example of a distorted image is shown. Figure 6 In FIG. 1 , a horizontal line image PTN1 (a line width of one dot and a pitch of two dots) is printed on the entire surface of the recording material P. A distorted portion is a portion where disturbance occurs in the toner image being transferred. The distorted portion appears darker than a normal portion.

[0112] Figure 7A and Figure 7B Shows Figure 6 Magnified views of the normal and distorted parts are shown. Figure 7A is an enlarged view of the normal part, and Figure 7B This is an enlarged view of the distorted part. Figure 7A and Figure 7B Both show an image formed by horizontal lines having a width of one dot in the conveying direction (the line is longer in the direction orthogonal to the conveying direction) and a spacing of two dots. Figure 7B In the distorted portion, the line width is larger than that in the normal portion, and the lines spread densely.

[0113] In this case, the image forming apparatus 100 intermittently prints on 100 sheets one by one. Figure 6 The image PTN1 in the image is taken, and the occurrence state of the distorted image on the 100th sheet is evaluated. If there is no distorted portion at all, the occurrence state is evaluated as "○". If there is a distorted portion but the distortion is slight (the distorted portion can be discerned by close observation), the occurrence state is evaluated as "Δ". If the distortion is worse than slight distortion (it can be understood at a glance that there is a distorted portion), the occurrence state is evaluated as "×".

[0114] In the image forming apparatus 100 according to the present exemplary embodiment, if the aforementioned maximum change rate RV of the conveyance speed of the recording material exceeds 1.0%, a distorted image corresponding to the level “Δ” starts to appear.

[0115] (Configuration of pressure roller)

[0116] An example of the pressure roller 20 will now be described by comparing the example with a comparative example. Figure 8 The configuration of the pressure roller used in Examples 1 to 8 and Comparative Examples 1 and 2 is shown. The items include the diameter of the pressure roller 20; the thickness of the rubber layer 22; the type, size (diameter×length), aspect ratio RA and addition amount of the filler; and the size, addition amount and connectivity ratio of the resin microspheres.

[0117] The interconnectivity of the resin microballoons indicates the ratio of the volume of the interconnected voids to the void volume calculated based on the size of the resin microballoons and the amount of the resin microballoons added. If the amount of the resin microballoons added is the same, the greater the value of the interconnectivity, the less likely the rubber layer 22 is to thermally expand.

[0118] In these comparisons, for ease of description, the connectivity rate is fixed at 75% in all configurations. The type of filler is asphalt carbon fiber (hereinafter referred to as "CF") in all configurations. As the filler, needle-like fillers with high thermal conductivity, such as glass fiber, can be used instead of CF.

[0119] Figure 9 The linear expansion coefficient and specific gravity of the rubber layer 22, the thermal conductivity λ of the pressure roller 20, the change rate RV of the conveyance speed of the recording material P, and the confirmation results of the occurrence of a distorted image are shown in Figure 8 the configuration shown. The content of the configuration and the evaluation results will be described with reference to Figure 8 and Figure 9 the following.

[0120] In Example 1, the diameter of the pressure roller 20 is 25 mm, and the thickness of the rubber layer 22 is 2.5 mm. The rubber layer 22 is formed by including carbon fiber (CF) as a filler and resin microspheres for forming void portions in liquid silicone rubber. The size of the carbon fiber (CF) in Example 1 is a fiber diameter of 9 μm, an average length of 250 μm, and an aspect ratio RA of 27.8. These carbon fibers (CF) are added such that the carbon fibers (CF) are 3.5 volume percent of the rubber layer 22.

[0121] Resin microspheres with a size (diameter) of 100 μm are added such that the resin microspheres are 50 volume percent of the rubber layer 22. Similar to the above method, tetraethylene glycol is used as a flocculant to connect the void portions to each other, and thus a connectivity rate of 75% is obtained. With the above configuration, the following effects are obtained.

[0122] The aspect ratio RA of the carbon fiber (CF) used is 27.8, and thus the carbon fiber (CF) has a high aspect ratio. Therefore, the effect of reducing the thermal expansion of the silicone rubber due to heating during printing is obtained. It is considered that this is because the linear expansion coefficient of the carbon fiber (CF) is only about 1 / 100 of that of the silicone resin, and thus the carbon fiber (CF) with a high aspect ratio reduces the expansion of the silicone resin near the carbon fiber (CF).

[0123] In addition, since the connected voids are formed by the resin microspheres, the rubber layer 22 is less likely to thermally expand.

[0124] That is, in the configuration of Example 1, the carbon fiber (CF) with a high aspect ratio reduces the actual expansion of the structure other than the void portion, and in addition, provides connected voids, thereby further reducing the thermal expansion of the entire rubber layer 22. According to the consideration of the present author, it should be understood that the above effects can be obtained when the fiber length of the filler is about 25 μm or more.

[0125] Since the fiber diameter of the filler is about 7 to 10 μm, it is desirable that the aspect ratio RA should be 2.5 or more. It should be understood that in order to stably manufacture the rubber layer 22 having a uniform structure as described above, the aspect ratio RA is desirably 215 or less. Therefore, in Examples 1 to 8, the value of the aspect ratio RA of the filler is 2.5 ≤ RA ≤ 215.

[0126] Conversely, the amount of the connected voids can be represented by the specific gravity of the rubber layer 22. In order to obtain the above effect of reducing thermal expansion, it is desirable that the specific gravity of the rubber layer 22 should be 0.70 or less. As Figure 9 shown, in Examples 1 to 8, the specific gravity of the rubber layer 22 is 0.70 or less.

[0127] In Examples 1 to 8, in the case where the aspect ratio RA of the filler and the specific gravity of the rubber layer 22 are within the above ranges, it should also be understood that the linear expansion coefficient of the rubber layer 22 is 400 (×10 -6 / K) or less.

[0128] As Figure 9 shown, in Example 1, with the above configuration, the maximum change rate RV of the conveying speed of the recording material is reduced to 0.70%, which is less than 1.0%. Therefore, the occurrence of a distorted image can be prevented.

[0129] The thermal conductivity λ of the pressure roller 20 is 1.2 W / m·K, which is within the above range of 0.8 [W / m·K] ≤ λ ≤ 2.0 [W / m·K]. Therefore, a temperature rise exceeding the heat-resistant temperature and a delay in the first print output time (FPOT) do not occur in the non-sheet passing portion.

[0130] Now, the features and evaluation results of Examples 2 to 8 will be described in order.

[0131] Example 2 has a configuration in which the average length of the carbon fiber (CF) becomes 1000 μm, whereby the aspect ratio RA is 111.1. Figure 8 The other items in are similar to those in Example 1.

[0132] The addition amount of the filler is the same as that in Example 1, but as Figure 9 shown, the thermal conductivity λ of the pressure roller 20 is 1.8 W / m·K, which is higher than the thermal conductivity in Example 1. The linear expansion coefficient of the rubber layer 22 is 300 (×10 -6 / K), which is lower than the linear expansion coefficient in Example 1. These two results are due to the following effects obtained by making the fiber length of the carbon fiber (CF) longer than the fiber length in Example 1.

[0133] The chance of heat conduction being inhibited by silicone rubber between carbon fibers (CF) is reduced, and thus, the thermal conductivity λ can be increased. The longer the length of a single carbon fiber (CF) (the higher the aspect ratio RA), the stronger the effect of reducing thermal expansion.

[0134] Therefore, in Example 2, the temperature rise margin with respect to the heat-resistant temperature in the non-sheet passing portion can be greater than the temperature rise margin in Example 1 (and there is no delay in FPOT either). In addition, the rate of change RV of the conveyance speed is 0.57%, which is lower compared to Example 1. Therefore, the margin with respect to the distorted image can also be greater than the margin in Example 1.

[0135] Example 3 is a formulation in which resin microspheres with a size (diameter) of 200 μm are added such that the resin microspheres are 60 volume percent of the rubber layer 22. The diameter of the resin microspheres is larger than that of the resin microspheres in Example 1, and the addition amount of the resin microspheres is also increased.

[0136] Since the void portion of the rubber layer 22 increases, the thermal conductivity λ of the pressure roller 20 is 1.1 W / m·K, which is lower than the thermal conductivity in Example 1, as Figure 9 shown. However, the thermal conductivity λ is in the range of 0.8 [W / m·K] ≤ λ ≤ 2.0 [W / m·K]. Therefore, there will be no temperature rise exceeding the heat-resistant temperature and no FPOT delay in the non-sheet passing portion.

[0137] Due to the increase in the void portion, the specific gravity of the rubber layer 22 drops to 0.43, which is lower than the specific gravity of the rubber layer 22 in Example 1, and the linear expansion coefficient of the rubber layer 22 is 300 (×10 -6 / K), which is lower than the linear expansion coefficient of the rubber layer 22 in Example 1. Therefore, the rate of change RV of the conveyance speed also decreases to 0.55%, which is low. This rate of change RV of the conveyance speed is a value lower than the rate of change of the speed in Example 2, where the linear expansion coefficient of the rubber layer 22 is the same, i.e., 300 (×10 -6 / K). This is because in Example 3, when providing more void portions than in Example 2 and the rubber layer 22 has a lower specific gravity than in Example 2, the diameter change caused by heating in the fixing nip portion N can be further reduced.

[0138] The conveyance speed of the recording material P in the fixing nip portion N is determined based on the diameter of the pressure roller 20 in the fixing nip portion N, and thus, compared to Example 2, the rate of change RV of the conveyance speed in Example 3 decreases. Therefore, the margin with respect to the distorted image can even be greater than the margin in Example 2.

[0139] In Example 4, the diameter of the pressure roller 20 is 5 mm larger than that in Example 1, while the formulation and thickness of the rubber layer 22 remain the same as those in Example 1. Due to the larger diameter, the rate of change RV of the conveying speed can be reduced to 0.60%, which is 0.1% lower than that in Example 1, even though the linear expansion coefficient of the rubber layer 22 is the same as that in Example 1. As described above, without changing the rubber layer 22, the margin with respect to the distorted image can also be larger than that in Example 1.

[0140] In Example 5, the thickness of the rubber layer 22 is 1.5 mm, which is 1 mm smaller than that in Example 1. Other items are the same as those in Example 1. Due to the thinner rubber layer 22, the rate of change RV of the conveying speed can be reduced to 0.46%, which is 0.24% lower than that in Example 1, even though the linear expansion coefficient of the rubber layer 22 is the same as that in Example 1. As described above, without changing the rubber layer 22, the margin with respect to the distorted image can also be larger than that in Example 1.

[0141] Example 6 has a configuration in which the average length of the carbon fiber (CF) becomes 1500 μm and the wire diameter becomes 7 μm, whereby the aspect ratio RA is 214.3. In addition, compared with Example 1, the amount of filler added is reduced, whereby the filler is added such that the filler is 2.8 volume percent of the rubber layer 22. Figure 8 Other items in are similar to those in Example 1.

[0142] Although the amount of filler added is reduced compared with Example 1, due to the increase in the aspect ratio RA of the filler, the thermal conductivity λ of the pressure roller 20 is 1.2 W / m·K, which is the same as that in Example 1 as shown Figure 9 The linear expansion coefficient of the rubber layer 22 is 240 (×10 -6 / K), which is lower than that of the rubber layer in Example 1. Thus, the rate of change RV of the conveying speed is 0.53%, which is reduced compared with Example 1. Therefore, the margin with respect to the distorted image can also be larger than that in Example 1.

[0143] Example 7 has a configuration in which the average length of the carbon fiber (CF) becomes 25 μm and the wire diameter becomes 10 μm, whereby the aspect ratio RA is 2.5. Compared with Example 1, the amount of filler added is increased, whereby the filler is added such that the filler is 4.2 volume percent of the rubber layer 22. Resin microspheres are also increased and added such that the resin microspheres are 54 volume percent of the rubber layer 22. Figure 8 Other items in are similar to those in Example 1.

[0144] In Example 7, a filler with a relatively low aspect ratio is used, and the thermal conductivity λ of the pressure roller 20 is 1.2 W / m·K, which is the same as that in Example 1. Example 7 is a formulation in which resin microspheres are increased to reduce the increase in specific gravity caused by the increase in the amount of filler and the increase in the linear expansion coefficient of the rubber layer 22.

[0145] The specific gravity reaches 0.51, which is lower than that in Example 1, and the linear expansion coefficient of the rubber layer 22 reaches 370 (×10 -6 / K), which is almost equal to the linear expansion coefficient of the rubber layer in Example 1. Thus, the rate of change RV of the conveying speed becomes 0.70%, which is the same as that in Example 1. Therefore, the margin with respect to the distorted image is also ensured to be equal to that in Example 1.

[0146] Example 8 is the following formulation, in which the same carbon fibers (CF) as those in Example 7 are used and the addition amount of the carbon fibers (CF) is increased such that the carbon fibers (CF) are 5.7 volume percentages of the rubber layer 22, and at the same time the addition amount of the resin microspheres is significantly reduced, and the resin microspheres are added such that the resin microspheres are 38 volume percentages of the rubber layer 22. This formulation aims to achieve significantly high heat conduction in this way. The linear expansion coefficient of the rubber layer 22 is 396 (×10 -6 / K), which is increased compared to the linear expansion coefficient of the rubber layer in Example 7. The specific gravity is 0.69, which is also higher than that in Example 7.

[0147] However, the thickness of the rubber layer 22 is 1.5 mm at the same time, which is 1 mm smaller than that in Example 7, and thus the rate of change RV of the conveying speed is 0.65%, which is lower than the rate of change of the conveying speed in Example 7. Therefore, the margin with respect to the distorted image increases compared to the margin in Example 7.

[0148] (Comparative Example 1)

[0149] Comparative Example 1 has a configuration in which carbon fibers (CF) with an average length of 18 μm, a wire diameter of 9 μm, and an aspect ratio RA of 2.0 are used. Figure 8 Other items in are similar to those in Example 1.

[0150] A filler with a low aspect ratio is used, and the addition amount is not increased. Therefore, the linear expansion coefficient of the rubber layer 22 is 405 (×10 -6 / K), which exceeds the linear expansion coefficient of the rubber layer in Example 1, and the rate of change RV of the conveying speed is 1.00%, which exceeds Example 1. Therefore, a slightly distorted image appears. In addition, the thermal conductivity λ of the pressure roller is 0.7 W / m·K, which is lower than the thermal conductivity of the pressure roller in Example 1. Therefore, a temperature rise exceeding the heat-resistant temperature may occur in the non-sheet-passing part.

[0151] (Comparative Example 2)

[0152] Comparative Example 2 is the following formulation, in which the same filler as in Example 1 is used, and the addition amount of the filler is significantly increased compared to Example 1, and at the same time the addition amount of the resin microspheres is significantly reduced compared to Example 1, and the resin microspheres are added such that the resin microspheres are 32 volume percent of the rubber layer 22. This formulation is intended to achieve a significantly high heat conduction in this way.

[0153] As Figure 9 shown, the thermal conductivity λ of the pressure roller 20 is 1.4 W / m·K, which is higher than the thermal conductivity of the pressure roller in Example 1, and the margin of the temperature rise with respect to the heat-resistant temperature in the non-sheet passing portion increases.

[0154] However, in this formulation, the resin microspheres are reduced, and thus the diameter change caused by heating in the fixing clamping portion N may be large. At the same time, the amount of silicone rubber increases, and thus the coefficient of thermal expansion of the rubber layer 22 is 430 (×10 -6 / K), which greatly exceeds the coefficient of thermal expansion of the rubber layer in Example 1. Therefore, the change rate RV of the conveyance speed is 1.30%, which greatly exceeds the change rate of the conveyance speed in Example 1. As a result, low-quality distorted images appear.

[0155] As described above, the rubber layer 22 includes a plurality of void portions 22b, pore channel portions 22c connecting the void portions 22b, and a filler 22d. Then, the aspect ratio RA of the filler 22d is 2.5 ≤ RA ≤ 215, and the linear expansion coefficient of the rubber layer 22 is 400×10 -6 / K or less. Thereby, a pressure roller can be provided that reduces thermal expansion while maintaining both quick start characteristics and reducing the temperature rise in the non-sheet passing portion.

[0156] Although the present disclosure has been described above based on specific exemplary embodiments, the present disclosure is not limited to the above exemplary embodiments.

[0157] In the pressure roller 20 in Examples 1 to 8, the rubber layer 22 is a single layer. Alternatively, another rubber layer (second rubber layer) may be provided around the rubber layer 22 (first rubber layer). As the second rubber layer, for example, a thermal insulation microsphere layer obtained by removing carbon fiber (CF) from the rubber layer 22 in Example 1 may be used so that the voids derived from the resin microspheres do not communicate with each other, or an existing solid rubber layer may be used.

[0158] With this double-layer structure, the balance between the rate of temperature rise in the fixing unit 6 and the temperature rise in the non-sheet passing portion can be adjusted. It is desirable that the thickness of the second rubber layer be 150 μm or more and less than 500 μm. More desirably, the thickness should be 200 μm or more and less than 400 μm. If the thickness is less than 150 μm, heat is transferred even on a short time scale. Therefore, it is difficult to exhibit sufficient quick start characteristics. If the thickness of the second rubber layer is 500 μm or more, it takes too much time to transfer heat to the inner layer 22 of the rubber layer, and thus heat is accumulated. Therefore, it is difficult to sufficiently reduce the temperature rise in the non-sheet passing portion.

[0159] Regarding the rate of change RV of the conveyance speed, if the thickness of the second rubber layer is set to be up to about 20% of the thickness of the rubber layer 22, then the adjustment of the parameters described in Figure 8 can achieve the rate of change RV of the conveyance speed that prevents the occurrence of a distorted image.

[0160] Although the above exemplary embodiments have been described using the fixing unit 6 in which the plate heater 11 is disposed in the internal space of the fixing film 13, the roller according to the present disclosure can be used in a fixing unit that applies current to the fixing film and heats itself.

[0161] Although the present disclosure has been described with reference to the exemplary embodiments, it should be understood that the present disclosure is not limited to the disclosed exemplary embodiments. The scope of the appended claims should be given the broadest interpretation so as to cover all such modifications and equivalent structures and functions.

Claims

1. A roller used in a fixing device, the roller comprising: A metal core; A rubber layer, the rubber layer including a plurality of void portions, pore channel portions connecting the void portions, and a filler; And A release layer provided around the rubber layer as a surface layer of the roller, wherein the aspect ratio RA of the filler is 2.5 ≤ RA ≤ 215, and the linear expansion coefficient of the rubber layer is less than or equal to 400 × 10 -6 / K, Wherein the specific gravity of the rubber layer is less than or equal to 0.70, Wherein the rubber layer between the metal core and the release layer is only one layer, and Wherein the void portions of the rubber layer are void portions derived from resin microspheres.

2. The roller according to claim 1, wherein the filler is carbon fiber or glass fiber.

3. The roller according to claim 1, wherein the average fiber length of the filler is greater than or equal to 25 μm and less than or equal to 1500 μm.

4. A fixing device that fixes an image formed on a recording material to the recording material, the fixing device comprising: A heating unit; And A pressure roller that forms a fixing nip portion with the heating unit, Wherein the pressure roller is the roller according to claim 1.

5. The fixing device according to claim 4, Wherein the heating unit includes a cylindrical film that contacts the surface of the pressure roller, and Wherein the fixing nip portion is formed between the film and the pressure roller.

6. The fixing device according to claim 5, wherein the heating unit includes a heater placed in an inner space of the film, and the fixing nip portion is formed by the heater and the pressure roller with the film intervening therebetween.

7. The fixing device according to claim 6, wherein the heater is a plate-shaped heater.

8. An imaging device that forms an image on a recording material, the imaging device comprising: An image bearing member; A transfer unit configured to transfer an image formed on the image bearing member to a recording material; And A fixing unit configured to fix an image formed on the recording material to the recording material, Wherein the fixing unit is the fixing device according to claim 4.

Images