Sponge roller

Abstract

To provide a sponge roller having a small amount of change in outer diameter under high temperature conditions.SOLUTION: The sponge roller 1 includes a shaft body 2 and a foamed elastic layer 3 provided on the outer periphery of the shaft body 2, wherein the foamed elastic layer 3 is formed of a resin composition for the foamed elastic layer containing a base rubber, a foaming agent and a heat resistance improver, and the heat resistance improver contains at least iron oxide.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a sponge roller. [Background technology]

[0002] Various image forming devices using electrophotography are employed in printers such as laser printers and video printers, copiers, facsimiles, and multifunction machines thereof. Electrophotographic image forming devices are equipped with various printing rollers, each having a shaft body and an elastic layer formed on the outer circumferential surface thereof, such as a cleaning roller, a charging roller, a developing roller, a transfer roller, a secondary transfer roller, a pressure roller, a paper feed roller, and a fixing roller.

[0003] Among the above, sponge rollers such as pressure rollers and fixing rollers equipped with a foamed elastic layer are compressed in a fixing device at high temperatures for a long period of time in order to ensure a sufficient nip width with the corresponding roller, and therefore are required to have small changes in rubber hardness, outer diameter, etc. Various studies have been conducted to solve this problem. For example, Patent Document 1 proposes a method for manufacturing a low-hardness fixing roll in which a nip width can be ensured and the rubber hardness of the silicone rubber layer hardly changes even when exposed to high temperatures in the coating process, by using a silicone rubber layer containing a heat resistance improver such as carbon black. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-179047 Summary of the Invention [Problem to be solved by the invention]

[0005] Sponge rollers such as fuser rollers and pressure rollers have a problem in that their outer diameters shrink significantly under high temperature conditions, especially at the non-paper passing portions at the ends of the rollers. Therefore, in addition to the technology described in the above patent document, further measures are required to reduce the amount of change in outer diameter. The present invention has been made in view of the above circumstances, and has as its object to provide a sponge roller that has a small amount of change in outer diameter under high temperature conditions. [Means for solving the problem]

[0006] The present inventors have found that the above problems can be solved by incorporating a specific compound as a heat resistance improver into the foamed elastic layer, and have arrived at the present invention. The present invention provides the following solutions. [1] The present invention is a sponge roller having a shaft body and a foamed elastic layer provided on the outer periphery of the shaft body, wherein the foamed elastic layer is formed from a resin composition for a foamed elastic layer containing a base rubber, a foaming agent, and a heat resistance improver, and the heat resistance improver contains at least iron oxide, and the content of iron oxide is greater than 0.25 parts by mass per 100 parts by mass of the base rubber. [2] The sponge roller according to the above item [1], wherein the heat resistance improver contains iron oxide, cerium oxide, and carbon black. [3] The sponge roller according to the above item [1], wherein the foaming agent contains at least one of a chemical foaming agent and resin microballoons. [4] The sponge roller according to [1] above, which has a coating layer on the outer periphery of the foamed elastic layer, and the change in outer diameter after heating in a hot air dryer at 230°C for 72 hours is within ±0.2 mm. [5] The sponge roller according to the above item [1], wherein the content of the heat resistance improver in the resin composition for the foamed elastic layer is 0.5% by mass or more and 15% by mass or less. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a sponge roller that exhibits a small change in outer diameter under high temperature conditions. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a perspective view showing an embodiment of a sponge roller of the present invention. [Figure 2] FIG. 1 is a perspective view showing an embodiment of a sponge roller with a coating layer. [Figure 3] 1 is a graph showing the amount of change in outer diameter in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. [Sponge roller] As shown in Figure 1, the sponge roller 1 of the present invention comprises at least a shaft 2 and a foamed elastic layer 3 provided on the outer periphery of the shaft 2, and the foamed elastic layer 3 is formed from a resin composition for foamed elastic layers containing a base rubber, a foaming agent, and a heat resistance improver, and the heat resistance improver contains at least iron oxide, and the content of iron oxide is greater than 0.25 parts by mass per 100 parts by mass of the base rubber. Each component will be described in detail below.

[0010] <Shaft> The shaft 2 may preferably be a conductive shaft used in conventional sponge rollers. The shaft 2 is preferably made of at least one metal selected from the group consisting of iron, aluminum, stainless steel, and brass. Such a shaft 2 is also generally known as a "core metal."

[0011] The shaft 2 may contain an insulating resin. The insulating resin may be, for example, a thermoplastic resin or a thermosetting resin. The shaft 2 may include, for example, a core made of an insulating resin and a plating layer provided on the core. Such a shaft 2 can be obtained, for example, by plating the core made of an insulating resin to make it conductive. The shaft 2 is preferably a cored bar in order to obtain good electrical conductivity.

[0012] The shape of the shaft 2 is preferably, for example, rod-like or tubular. The cross-sectional shape of the shaft 2 may be, for example, circular or elliptical, or may be non-circular such as polygonal. The outer peripheral surface of the shaft 2 may be subjected to treatment such as cleaning, degreasing, or primer treatment.

[0013] The axial length of the shaft 2 is not particularly limited and may be adjusted appropriately depending on the type of the image forming apparatus in which it is installed. The diameter of the shaft 2 (diameter of the circumscribing circle) is also not particularly limited and may be adjusted appropriately depending on the type of the image forming apparatus in which it is installed.

[0014] <Foamed elastic layer> The foamed elastic layer 3 is formed by vulcanizing a resin composition for a foamed elastic layer, which contains (A) a base rubber, (B) a foaming agent, and (C) a heat resistance improver. The components of the resin composition for a foamed elastic layer are described below.

[0015] (A) Base rubber Examples of the base rubber include silicone rubber, acrylonitrile-butadiene rubber (NBR), styrene-butadiene rubber (SBR), epichlorohydrin rubber, and urethane rubber. In the case of silicone rubber, millable silicone rubber can be used as the base rubber. The millable silicone rubber is preferably an addition-curing millable silicone rubber. The addition-curing millable silicone rubber preferably contains, for example, at least (a) an organopolysiloxane, (b) a filler, and (c) a conductivity-imparting agent.

[0016] (a) Organopolysiloxane (a) Organopolysiloxane is represented by the following average composition formula (1): R 1 n SiO (4-n) / 2 …(1) In formula (1), n ​​is a positive number between 1.95 and 2.05. 1represents a substituted or unsubstituted monovalent hydrocarbon group, which may be the same or different. The hydrocarbon group preferably has 1 or more and 12 or less carbon atoms, more preferably 1 or more and 8 or less carbon atoms.

[0017] R 1 Examples of the R include alkyl groups such as methyl, ethyl, propyl, butyl, hexyl, and dodecyl groups, cycloalkyl groups such as cyclohexyl groups, alkenyl groups such as vinyl, allyl, butenyl, and hexenyl groups, aryl groups such as phenyl and tolyl groups, and aralkyl groups such as β-phenylpropyl groups. 1 may be groups in which some or all of the hydrogen atoms of these hydrocarbon groups have been substituted with a substituent. The substituent may be, for example, a halogen atom, a cyano group, etc. Examples of hydrocarbon groups having a substituent include a chloromethyl group, a trifluoropropyl group, and a cyanoethyl group.

[0018] The (a) organopolysiloxane is preferably one whose molecular chain terminals are blocked with a trialkylsilyl group such as a trimethylsilyl group, a dialkylaralkylsilyl group such as a dimethylvinylsilyl group, a dialkylhydroxysilyl group such as a dimethylhydroxysilyl group, or a trialalkylsilyl group such as a trivinylsilyl group.

[0019] (a) Organopolysiloxane preferably has two or more alkenyl groups in the molecule. (a) Organopolysiloxane preferably has two or more alkenyl groups in the molecule. 1 Of these, it is preferable that the alkenyl group account for 0.001 mol % or more and 5 mol % or less (more preferably 0.01 mol % or more and 0.5 mol % or less).Vinyl groups are particularly preferable as the alkenyl groups contained in (a) organopolysiloxane.

[0020] (a) Organopolysiloxane can be obtained, for example, by cohydrolytic condensation of one or more organohalosilanes, or by ring-opening polymerization of a cyclic polysiloxane such as a siloxane trimer or tetramer. (a) Organopolysiloxane may be essentially a linear diorganopolysiloxane, or may be partially branched. (a) Organopolysiloxane may also be a mixture of two or more types with different molecular structures.

[0021] (a) The organopolysiloxane has a kinematic viscosity of 1 x 10 at 25°C. -4 m 2 / s or more is preferable, and 1×10 -1 m 2 / s or more 1×10 1 m 2 / s or less is more preferable. The degree of polymerization of (a) organopolysiloxane is preferably, for example, 100 or more, and more preferably 3,000 or more and 10,000 or less.

[0022] (b) Filling material (b) Examples of fillers include silica-based fillers, such as fumed silica and precipitated silica.

[0023] Silica-based fillers include R 2 Si(OR 3 A surface-treated silica-based filler that has been surface-treated with a silane coupling agent represented by formula (R) 3 can be preferably used. 2 may be a group having a vinyl group or an amino group, such as a glycidyl group, a vinyl group, an aminopropyl group, a methacryloxy group, an N-phenylaminopropyl group, or a mercapto group. 3may be an alkyl group, such as a methyl group or an ethyl group. Silane coupling agents are readily available, for example, under the trade names "KBM1003" and "KBE402" manufactured by Shin-Etsu Chemical Co., Ltd. The surface-treated silica-based filler can be obtained by treating the surface of a silica-based filler with a silane coupling agent according to a standard method. Commercially available surface-treated silica-based fillers may be used, such as "Zeothix 95" manufactured by JMHUBER Corporation.

[0024] The amount of silica-based filler blended is preferably 11 to 39 parts by mass, and more preferably 15 to 35 parts by mass, per 100 parts by mass of (a) organopolysiloxane. The average particle size of the silica-based filler is preferably 1 to 80 μm, and more preferably 2 to 40 μm. The average particle size of the silica-based filler can be measured as the median size using a particle size distribution analyzer based on laser diffraction.

[0025] (c) Conductive agent (c) Examples of the conductivity-imparting agent include conductive powders containing conductive carbon, rubber carbons, metals, conductive polymers, etc. Carbon black is preferably used as the conductive powder, and examples of the carbon black include furnace black such as Ketjenblack (registered trademark), acetylene black, channel black, and thermal black. The resistance value of the foamed elastic layer 3 is preferably adjusted to the range of 4 to 9 (log Ω).

[0026] The Millable type silicone rubber used in the present invention may be, for example, KE-571-U, KE-1571-U, KE-951-U, KE-541-U, KE-551-U, KE-561-U, KE-961T-U, KE-1541-U, KE-1551-U, KE-941-U, or KE-971T-U manufactured by Shin-Etsu Chemical Co., Ltd. Furthermore, (c) as the millable type silicone rubber containing a conductivity imparting agent, KE-87C-40PU or the like can be used.

[0027] (B) Foaming agent The resin composition for a foamed elastic layer in the present invention contains at least one of a chemical foaming agent and resin microballoons as a foaming agent. As the chemical blowing agent, both inorganic and organic blowing agents can be used. Examples of inorganic blowing agents include sodium bicarbonate and ammonium carbonate. Examples of organic blowing agents include organic azo compounds such as diazoamino derivatives, azonitrile derivatives, and azodicarboxylic acid derivatives. Among organic azo compounds, azodicarboxylic acid amide and azobis-isobutyronitrile are preferably used. In particular, azobis-isobutyronitrile is preferably used.

[0028] Examples of resin microballoons include thermally expandable resin microballoons and pre-expanded microballoons. As the thermally expandable resin microballoons, microcapsules in which a liquid low-boiling hydrocarbon is encapsulated in a plastic polymer shell are preferably used. Examples of thermoplastic resins that make up the shell include vinylidene chloride / acrylonitrile copolymer, methyl methacrylate / acrylonitrile copolymer, and methacrylonitrile / acrylonitrile copolymer. It is preferable to use resin microballoons whose shell resin softening temperature is within an appropriate range to match the curing temperature of the silicone rubber. Examples of evaporative substances that can be encapsulated include hydrocarbons such as butane and isobutane.

[0029] Thermally expandable resin microballoons are commercially available as "Matsumoto Microsphere F Series" (manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.), "Expancel Series" (manufactured by Expancel Co., Ltd.), and the like.

[0030] Examples of pre-expanded microballoons include expanded bodies (plastic microballoons) made by expanding heat-expandable resin microballoons, and pre-expanded resin microballoons called composite type, in which calcium carbonate powder is wrapped around the shell of the expanded body. Pre-expanded microballoons are commercially available as "Matsumoto Microsphere (registered trademark, the same applies hereinafter) FE series," "Matsumoto Microsphere F-DE series," and "Matsumoto Microsphere MFL series" (manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.).

[0031] The particle size of the resin microballoons is preferably 30 μm or less, and more preferably 5 μm or more and 30 μm or less.

[0032] The content of the chemical foaming agent in the resin composition for the foamed elastic layer is preferably 0.1% by mass or more and 5% by mass or less. The blending amount of resin microballoons is preferably 0.5% by mass or more and 6% by mass or less in the resin composition for foamed elastic layer, from the viewpoint of obtaining cells with a uniform size while having a low specific gravity.

[0033] (C) Heat resistance improver The inventors' investigations have revealed that when the heat resistance improver contains at least iron oxide and the content of iron oxide is greater than 0.25 parts by mass per 100 parts by mass of base rubber, the change in outer diameter at high temperatures can be suppressed. On the other hand, when cerium oxide is used alone as the heat resistance improver, the change in outer diameter of the roller at high temperatures is aggravated. Therefore, in the present invention, the heat resistance improver contains at least iron oxide in an amount greater than 0.25 parts by mass per 100 parts by mass of the base rubber. The heat resistance improver may contain a combination of iron oxide and cerium oxide, or iron oxide and carbon black. The heat resistance improver may also contain iron oxide, cerium oxide, and carbon black, which can further reduce the change in outer diameter of the roller at high temperatures.

[0034] The content of the heat resistance improver in the resin composition for the foamed elastic layer is preferably 0.5% by mass or more and 15% by mass or less, and more preferably 1% by mass or more and 10% by mass or less. When iron oxide, cerium oxide, and carbon black are contained as the heat resistance improver, the content of iron oxide is preferably 20% by mass to 50% by mass, more preferably 20% by mass to 45% by mass, and even more preferably 30% by mass to 40% by mass, based on the total amount of the heat resistance improver. The content of cerium oxide is preferably 5% by mass to 25% by mass, and even more preferably 10% by mass to 20% by mass, based on the total amount of the heat resistance improver. The content of carbon black is preferably 1% by mass to 15% by mass, more preferably 2% by mass to 15% by mass, and even more preferably 3% by mass to 10% by mass, based on the total amount of the heat resistance improver. When iron oxide and cerium oxide are contained as the heat resistance improver, the mass ratio of cerium oxide to iron oxide is preferably 1:4 or more and 2:3 or less.

[0035] (D) Vulcanizing agent The resin composition for the foamed elastic layer may contain a vulcanizing agent, such as an addition reaction vulcanizing agent or an organic peroxide vulcanizing agent. Suitable examples of the addition reaction vulcanizing agent include organohydrogenpolysiloxanes, which are known as addition reaction vulcanizing agents having two or more SiH groups (SiH bonds) in one molecule. These addition reaction vulcanizing agents can be used alone or in combination. The amount of the addition reaction vulcanizing agent added is usually 0.1% by mass or more and 7% by mass or less in the resin composition for the foamed elastic layer.

[0036] When an addition reaction vulcanizing agent is used, the organic peroxide vulcanizing agent can crosslink the millable silicone rubber by itself, but when used in combination as a co-vulcanizing agent for the addition reaction vulcanizing agent, the physical properties of the resulting toner supply roller, such as strength and distortion, can be further improved. Examples of organic peroxide vulcanizing agents include benzoyl peroxide, bis-2,4-dichlorobenzoyl peroxide, dicumyl peroxide, di-t-butyl peroxide, and 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane. The amount of the organic peroxide vulcanizing agent blended is usually 0.1% by mass or more and 7% by mass or less in the resin composition for the foamed elastic layer. The organic peroxide vulcanizing agents can be used alone or in combination of two or more.

[0037] The addition reaction vulcanizing agent is preferably used in combination with an addition reaction catalyst. Examples of the addition reaction catalyst include platinum black, platinic chloride, chloroplatinic acid, reaction products of chloroplatinic acid with monohydric alcohols, complexes of chloroplatinic acid with olefins, platinum bisacetoacetate, palladium catalysts, and rhodium catalysts. The amount of the addition reaction catalyst to be added can be a catalytic amount.

[0038] The resin composition for a foamed elastic layer may further contain various additives. Examples of the various additives include auxiliary agents such as chain extenders, catalysts, dispersants, antioxidants, antioxidants, and non-silica fillers such as glass beads, pigments, colorants, processing aids, softeners, plasticizers, emulsifiers, flame retardancy improvers, acid acceptors, thermal conductivity improvers, mold release agents, and solvents. These various additives may be commonly used additives or may be specially used additives depending on the application.

[0039] The foamed elastic layer 3 can be formed by vulcanizing the resin composition for the foamed elastic layer on the outer periphery of the shaft 2. The vulcanization preferably includes a primary vulcanization step and a secondary vulcanization step. The primary vulcanization step and the secondary vulcanization step are each preferably performed at a temperature of 180°C or higher and 250°C or lower, and more preferably 200°C or higher and 230°C or lower. The vulcanization is preferably performed for 20 minutes or higher and 420 minutes or lower, and more preferably 30 minutes or higher and 240 minutes or lower. The method for forming the foamed elastic layer 3 is not particularly limited and may be continuous vulcanization by extrusion molding, pressing, injection molding, etc. For example, extrusion molding may be selected.

[0040] (Hardness of foamed elastic layer) The Asker C hardness of the foamed elastic layer 3 is preferably 20 Hs or more and 70 Hs or less, and more preferably 25 Hs or more and 50 Hs or less. When the Asker C hardness of the foamed elastic layer 3 is within the above range, when the sponge roller 1 is installed in an image forming apparatus as a pressure roller, transfer roller, or secondary transfer roller, a sufficient nip width can be ensured between the sponge roller 1 and a member that abuts or presses against it. The Asker C hardness of the foamed elastic layer 3 can be measured using an Asker C hardness tester in accordance with JIS K7312.

[0041] <Coating layer> As shown in FIG. 2, the sponge roller 1 of the present invention may have a covering layer 4 on the outer periphery of the foamed elastic layer 3. The covering layer 4 is preferably a resin tube. Materials that can be used for the resin tube include polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, FEP (tetrafluoroethylene-hexafluoropropylene copolymer), PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), ETFE (tetrafluoroethylene-ethylene copolymer), PVDF (polyvinylidene fluoride), polyethylene terephthalate, polyamide, polyimide, polycarbonate, polystyrene, ABS, and polyurethane. Of these, PFA is preferred. The resin tube can be produced by melt extrusion of a resin composition, etc. The resin tube can be attached to the foamed elastic layer 3 provided with the adhesive layer by a known pressure insertion method or vacuum insertion method.

[0042] <Change in outer diameter> As shown in Figure 2, when a sponge roller on which coating layer 4 has been formed is heated in a hot air dryer at 230°C for 72 hours, the change in outer diameter after heating can be improved to 5% to 50% of the change in outer diameter after heating of a sponge roller produced under similar conditions that does not contain a heat resistance improving agent. [Example]

[0043] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the examples shown below.

[0044] [Examples 1 and 2, and Comparative Examples 1 and 2] The sponge rollers of the examples and comparative examples were produced by the following procedure. (Formation of primer layer) An electroless nickel-plated shaft (solid, made of SUM23, diameter 18 mm, length 274.2 mm) was washed with ethanol, and its surface was coated with a silicone primer (product name "Primer No. 16", manufactured by Shin-Etsu Chemical Co., Ltd.). The primer-treated shaft was baked in a gear oven at 150°C for 10 minutes and then cooled at room temperature for at least 30 minutes, forming a primer layer on the outer surface of the shaft.

[0045] (Formation of foamed elastic layer) A resin composition for a foamed elastic layer was prepared using the raw materials and blending ratios shown in Table 1. Details of the raw materials in Table 1 are as follows.

[0046] -Resin composition for foamed elastic layer- (A) Base rubber (1) Silicone rubber (product name "KE-951-U", manufactured by Shin-Etsu Chemical Co., Ltd.) (2) Silicone rubber (product name "KE-77VBS", manufactured by Shin-Etsu Chemical Co., Ltd.) (B) Foaming agent (1) Chemical foaming agent (product name "SP-13", manufactured by Shin-Etsu Chemical Co., Ltd.) (2) Unexpanded microballoons (product name "Matsumoto Microspheres", manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.) (C) Heat resistance improver (1) Iron oxide, cerium oxide, carbon black (admixture) (2) Cerium oxide (3) Iron oxide (D) Vulcanizing agent (product name "C-3", manufactured by Shin-Etsu Chemical Co., Ltd.) (E) Colorant (1) Bengala (2) Product name: "KE-Color-CB", manufactured by Shin-Etsu Silicone Co., Ltd.

[0047] The resin composition for the foamed elastic layer was extruded to form a foamed elastic layer on the outer circumferential surface of the shaft. In the extrusion molding, the composition was heated in an infrared heating furnace (IR furnace) at 230°C for 30 minutes for primary vulcanization, and then heated in a gear oven at 225°C for 7 hours for secondary vulcanization. Next, polishing was carried out to make the foamed elastic layer 6.0 mm thick.

[0048] (Formation of coating layer) A resin tube (conductive PFA, thickness 50 μm) was attached as a covering layer to the outer periphery of the foamed elastic layer, so that the product diameter was 30 mm.

[0049] [Table 1]

[0050] [evaluation] The sponge rollers of the examples and comparative examples prepared as described above were evaluated as follows.

[0051] (Measurement of change in outer diameter) The outer diameters of the sponge rollers of the above examples and comparative examples were measured by the following method, and the measurement results are shown in FIG. (1)Measurement method The outer diameter of the roller at the same location before and after the heating test was measured using a laser length measuring device, trade name "Laser Scan Micrometer" (MITUTOYO Lsm-600), while the roller was rotated around the central axis of the shaft at a rotation speed of 30 rpm, and the amount of change in the outer diameter at each measurement point before and after the test was recorded as the amount of change in outer diameter. (2) Heating conditions: 230°C, 72 hours The roller was heated in a hot air dryer (ETAC HISPEC HIGH TEMPERATURE CHAMBER HT350KP). The journal was placed on a magazine and the roller was measured in a floating state.

[0052] 3, it was found that Example 2, which contained iron oxide as a heat resistance improver, had a smaller amount of change in outer diameter at high temperatures than Comparative Example 1, which contained no heat resistance improver. It was found that Example 1, which contained iron oxide, cerium oxide, and carbon black as heat resistance improvers, had an even smaller amount of change in outer diameter than Example 2. On the other hand, it was found that Comparative Example 2, which contained only cerium oxide as a heat resistance improver, had a larger amount of change in outer diameter than Comparative Example 1, which did not contain a heat resistance improver. [Explanation of symbols]

[0053] 1 sponge roller 2-axis body 3. Foam elastic layer 4 Covering layer

Claims

1. A sponge roller having a shaft body and a foamed elastic layer provided on the outer periphery of the shaft body, the foamed elastic layer is formed from a resin composition for a foamed elastic layer, the resin composition including a base rubber, a foaming agent, and a heat resistance improver; the heat resistance improver contains at least iron oxide, The sponge roller has an iron oxide content of more than 0.25 parts by mass per 100 parts by mass of the base rubber.

2. 2. The sponge roller according to claim 1, wherein the heat resistance improver contains iron oxide, cerium oxide, and carbon black.

3. 2. The sponge roller according to claim 1, wherein the foaming agent contains at least one of a chemical foaming agent and a resin microballoon.

4. 2. The sponge roller according to claim 1, wherein the foamed elastic layer has a coating layer on its outer periphery, and the change in outer diameter after heating in a hot air dryer at 230° C. for 72 hours is within ±0.15 mm.

5. 2. The sponge roller according to claim 1, wherein the content of the heat resistance improver in the resin composition for the foamed elastic layer is 0.5% by mass or more and 15% by mass or less.

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