Foamed rubber roller and method for manufacturing a foamed rubber roller

Abstract

This invention provides a foamed rubber roller with high durability and a method for manufacturing a foamed rubber roller. [Solution] The foamed rubber roller of the present invention comprises at least a core shaft and a foamed layer made of silicone rubber provided on the outer circumference of the core shaft, characterized in that the arithmetic mean roughness (Ra) of the outer surface of the core shaft, in accordance with JIS B 0601, satisfies 3.3 ≤ Ra ≤ 7.42. The method for manufacturing the foamed rubber roller of the present invention comprises a step of applying a surface treatment to the outer surface of the core shaft, characterized in that the arithmetic mean roughness (Ra) of the outer surface of the core shaft after surface treatment, in accordance with JIS B 0601, satisfies 3.3 ≤ Ra ≤ 7.42.

Description

[[Technical Field]]

[0001] The present invention relates to a foamed rubber roller and a method for manufacturing a foamed rubber roller, and particularly relates to a foamed rubber roller having high durability and a method for manufacturing the foamed rubber roller. [[Background Art]]

[0002] In electrophotographic reproducing apparatuses such as copying machines and laser beam printers, a heat fixing method is employed as a method for fixing an unfixed toner image transferred onto a sheet. In the heat fixing method, as a fixing roller that performs fixing and heating and a pressure roller that is in pressure contact with the fixing roller, foamed rubber rollers are widely used, in which a foam layer is formed of foamed rubber having open cells on the outer circumferential surface of a core shaft made of aluminum, iron or the like, and a release layer such as a fluororesin is provided on the surface of the foam layer (Patent Document 1). In recent years, the performance required for electrophotographic reproducing apparatuses has increased, and in particular, fixing rollers and pressure rollers are required to have improved durability along with higher speed operation. For this reason, manufacturers are aiming to improve the durability of foamed rubber rollers by changing materials to foamed rubber with good physical properties, primers with high adhesiveness, and the like. [[Prior Art Document]] [[Patent Document]]

[0003] [[Patent Document 1]] Japanese Unexamined Patent Publication No. 2016-8990 [[Summary of the Invention]] [[Problem to be Solved by the Invention]]

[0004] The method based on material change is more expensive than conventional methods, which directly leads to an increase in product cost and impairs the price competitiveness of products. In addition, since it becomes necessary to re-evaluate various performances along with the design change, it takes a long time and cost before the new material can be adopted. The present invention aims to overcome the above-mentioned problems of the prior art and to realize a technology for manufacturing foamed rubber rollers with high durability without changing the materials. [Means for solving the problem]

[0005] The foamed rubber roller of the present invention comprises at least a core shaft and a foamed layer made of silicone rubber provided on the outer circumference of the core shaft, and is characterized in that the arithmetic mean roughness (Ra) of the outer surface of the core shaft, in accordance with JIS B 0601, satisfies the following formula. 3.3 ≤ Ra ≤ 7.42

[0006] The present invention relates to a method for manufacturing a foamed rubber roller, comprising the step of applying a surface treatment to the outer surface of a core shaft, characterized in that the arithmetic mean roughness (Ra) of the outer surface of the core shaft after surface treatment, in accordance with JIS B 0601, satisfies the following formula. 3.3 ≤ Ra ≤ 7.42 [Effects of the Invention]

[0007] According to the foamed rubber roller and foamed rubber roller manufacturing method of the present invention, by numerically controlling the surface roughness of the outer surface of the core shaft, it is possible to manufacture a foamed rubber roller with high durability without changing the material. [Brief explanation of the drawing]

[0008] [Figure 1] Diagram explaining foamed rubber rollers [Figure 2] Diagram illustrating the relationship between arithmetic mean roughness (Ra) and the durability of foamed rubber rollers. [Figure 3] Explanation diagram for the heat resistance test [Figure 4] Graphs related to the analysis of measurement results [Modes for carrying out the invention]

[0009] The foamed rubber roller and the method for manufacturing the foamed rubber roller of the present invention will be described in detail below.

[0010] <1> Foamed rubber roller Foamed rubber rollers are rollers used in electrophotographic copiers, and are used as fixing rollers, pressure rollers, or transport rollers. Here, a "fixing roller" is a roller that applies heat to paper onto which toner has been transferred, fixing the toner to the paper. A "pressure roller" is a roller that works in conjunction with the fixing roller, pressing the paper against the fixing roller to ensure proper toner adhesion. A "transport roller" is a roller that moves the paper within the device. The foamed rubber roller comprises a core shaft, a foamed layer provided on the outer circumference of the core shaft, and a release layer covering the outer circumference of the foamed layer (Figure 1). The thickness of each layer varies depending on the application and specifications of the foamed rubber roller, but typically the foam layer is about 1 to 10 mm thick, and the release layer is about 10 to 100 μm thick. Furthermore, when foamed rubber rollers are used as conveyor rollers, the release layer is not an essential component.

[0011] <2> core shaft The core shaft is a cylindrical component that forms the central part of the foamed rubber roller. The core shaft comprises a cylindrical body and journals protruding from both ends of the body along the central axis of the body. In this invention, unless otherwise specified, "core shaft" refers to the body of the core shaft. The core shaft can be made of materials such as aluminum alloy, iron, stainless steel, or copper alloy. Furthermore, to ensure corrosion resistance and durability, the surface may be treated with rust-preventive or oxide coatings. To increase the bonding area with the foam layer and improve adhesion by utilizing the anchoring effect, the outer surface of the core shaft is surface-treated with abrasive paper or the like.

[0012] <2.1> Surface roughness This invention is characterized by its use of surface roughness based on JIS B 0601(:2013) for the outer surface of the core shaft in quality control of foamed rubber rollers. In other words, this invention has found a significant correlation between the surface roughness of the core shaft of a foamed rubber roller and its durability, and based on this finding, it has achieved improved durability of foamed rubber rollers without changing the material. In the present invention, the arithmetic average roughness (Ra) specified in JIS B 0601 is used for quality control of the core shaft. Ra is an index indicating the average unevenness of the outer circumferential surface of the core shaft, and correlates with the contact area between the core shaft and the foam layer. When the Ra of the outer circumferential surface of the core shaft is below a predetermined value, the adhesiveness between the core shaft and the foam layer is insufficient, and there is a risk that the foam layer peels off from the core shaft. Therefore, a lower limit value for Ra is set. The lower limit value of Ra is 3.3, which is a control value for mass production of products. When the Ra of the outer circumferential surface of the core shaft exceeds a predetermined value, voids are easily formed in the valley portions of the roughness curve (Figure 2). In addition, near the interface of the core shaft, the fluidity of the silicone rubber composition decreases, and the density of sugar powder and water-absorbent polymer in the silicone rubber composition becomes higher compared to that on the surface layer side. As a result, the cell porosity near the interface of the core shaft in the foam layer becomes excessively large, which may become a starting point of fracture. Therefore, an upper limit value for Ra is defined. The upper limit value of Ra is 7.42, which is obtained through analysis of the heat durability test described later. From the above, in the present invention, control is performed such that Ra of the outer circumferential surface of the core shaft of the foamed rubber roller falls within the following range. [Formula] 3.3≦Ra≦7.42

[0013] <3>Foam layer The foam layer is an elastic layer having a porous structure provided with countless fine cells inside. The foam layer can be produced by vulcanizing a silicone rubber composition composed of silicone rubber, water-soluble sugar powder, and an elution aid according to a predetermined procedure. As the silicone rubber, for example, addition reaction type liquid silicone rubber that cures via an addition reaction using a platinum-based catalyst, condensation reaction type liquid silicone rubber that cures via a condensation reaction, or organic peroxide type liquid silicone rubber that cures via a peroxidation reaction, etc., can be employed. Further, the silicone rubber may contain a reinforcing filler such as carbon black, silica, or calcium carbonate as a reinforcing material. As the sugar powder, for example, granulated sugar, glucose, lactose, sucrose, trehalose, fructose, granulated sugar, powdered sugar, or mixtures thereof, etc., can be employed. It is desirable that the particle diameter of the sugar powder is approximately 1 to 1000 μm. As the elution aid, for example, triethylene glycol, ethylene glycol, glycerin, propylene glycol, pentaerythritol, glycerin-α-monochlorohydrin, diethylene glycol, dipropylene glycol, or polyglycerin can be employed. Note that the present invention is not limited by the means for forming the foamed layer, and for example, regardless of an elution method using sugar powder, a method of mixing a water-absorbent polymer and water into a silicone rubber composition and volatilizing the moisture in the water-absorbent polymer by secondary vulcanization may also be used. In this case, the silicone rubber composition is composed of silicone rubber, water, a water-absorbent polymer, and a surfactant.

[0014] <4>Release Layer The release layer is a layer for improving releasability from toner. The release layer can be configured as a tube structure that covers the outer periphery of the foamed layer. As the release layer, for example, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), or polyvinylidene fluoride (PVdF) can be employed. Further, instead of a fluororesin, a polyimide resin, a polyamideimide resin, or the like may also be employed. It is desirable that the inner surface of the tube of the release layer is previously subjected to a roughening treatment by etching.

[0015] <5>Method for Producing Foamed Rubber Roller When the foamed rubber roller is a fixing roller, the foamed rubber roller is produced, for example, by the following method.

[0016] <5.1>Surface Treatment of Core Shaft A surface treatment is performed on the outer peripheral surface of the core shaft. The surface treatment can be appropriately selected from known methods such as polishing with abrasive paper, sandblasting, chemical etching, shotblasting, and plasma treatment. In surface treatment, the surface roughness of the outer surface of the core shaft is controlled to fall within the following range in terms of arithmetic mean roughness (Ra) in accordance with JIS B 0601. [Formula] 3.3≦Ra≦7.42

[0017] <5.2> Mold Set A cylindrical mold is erected with a bottom plate having an injection hole to seal the bottom. A fluororesin tube, which constitutes the release layer, is inserted into the mold, and a core shaft is erected in the center of the fluororesin tube and fixed coaxially. A primer is applied to the outer surface of the core shaft and the inner surface of the fluororesin tube.

[0018] <5.3> Preparation of Silicone Rubber Composition Granulated sugar is crushed and classified into a particle size range of 10 to 200 μm. 130 parts by mass of granulated sugar powder are mixed with 25 parts by mass of triethylene glycol, and 100 parts by mass of silicone rubber is added to the mixture. This mixture is then stirred with a stirrer for 30 minutes to prepare the silicone rubber composition.

[0019] <5.4> Primary vulcanization The silicone rubber composition is degassed under vacuum, filled into the mold through the injection hole in the bottom plate, and subjected to primary vulcanization at 120°C for 30 minutes. During primary vulcanization, the silicone rubber composition is heat-cured, forming a cured silicone rubber body with sugar powder dispersed inside between the core and the release layer.

[0020] <5.5>Immersion After curing, the cylindrical mold is opened, the cured silicone rubber body is removed along with the core shaft, and immersed in 80°C hot water for 2 hours. During immersion, water penetrates into the cured silicone rubber, dissolving the sugar powder and triethylene glycol dispersed inside the cured silicone rubber, and these are then discharged to the outside along with the water. This creates a foamed layer with a continuous network of fine bubbles inside the cured silicone rubber.

[0021] <5.6> Secondary vulcanization After immersion, the foam layer and core shaft are removed from the hot water and subjected to secondary vulcanization at 220°C for 4 hours. Through the above process, a foamed rubber roller with a three-layer structure is obtained, in which a foamed silicone rubber layer and a release layer made of fluororesin are sequentially laminated on a core shaft. If the foamed rubber roller is a conveyor roller that does not have a release layer, the same manufacturing process is carried out except for the fluororesin tube. [Examples]

[0022] <1> Heat resistance test A heat resistance test was conducted on the foamed rubber roller (Figure 3). The heat resistance test involves continuously rotating a foamed rubber roller while heating it to a constant temperature, and measuring the distance traveled before the foam layer ruptures. In detail, a heat roller is placed below the foamed rubber roller so as to be parallel to its axial direction, and the outer surface of the foamed rubber roller is compressed by pressing the heat roller against it. The compression amount of the foamed rubber roller is set to 1.65 mm. This means that the distance between the center of the foamed rubber roller and the center of the heat roller is reduced by 1.65 mm, with the state where the surfaces of the foamed rubber roller and the heat roller are in contact being defined as 0 mm. The heat roller is heated from the inside, raising its surface temperature to 220°C. Under the above conditions, the foamed rubber roller is continuously rotated at a roller speed of 300 mm / sec, and the rotation is stopped when the foam layer ruptures. Here, the rupture of the foam layer is recognized when the load on the foamed rubber roller due to compression from the heat roller changes by ±3% or more compared to the load one second earlier.

[0023] <2> Required performance of foamed rubber rollers The foamed rubber rollers used in electrophotographic copiers are required to have the capability to rotate continuously at speeds of 30 km or more. This distance is equivalent to the continuous printing of 100,000 sheets of A4 paper (297 mm in length).

[0024] <3> Measurement of surface roughness After the durability test, the rubber layer of the foamed rubber roller was removed from the core shaft, and the arithmetic mean roughness (Ra) of the outer surface was measured according to JIS B0601.

[0025] <4> Measurement results Table 1 shows the results of the durability test and the surface roughness measurement. The test specimen numbers are assigned in ascending order of Ra value.

[0026] [Table 1]

[0027] <5> Analysis of measurement results A significant correlation was observed between the Ra value of the outer surface of the core axis and the distance traveled (Figure 4). Test subjects 16-22 all had an Ra of over 7.42, and their continuous running distance was generally less than 20km, failing to reach the required performance of 30km. This is thought to be because the roughness of the outer surface of the core shaft makes it easy for voids to form at the bottom of the valleys, and furthermore, the fluidity of the silicone rubber composition decreases near the core shaft, increasing the bubble rate, which ultimately becomes the starting point for fracture. On the other hand, test specimens 1 to 15 all had an Ra of 7.42 or less, achieving the required continuous running distance of 30 km. This is thought to be because the roughness of the outer surface of the core shaft was not excessive, making it difficult for voids to form at the bottom of the valleys, and the reduced air bubble ratio near the core shaft of the silicone rubber composition made it difficult for fracture initiation points to occur.

Claims

1. A foamed rubber roller comprising at least a core shaft and a foamed layer made of silicone rubber provided on the outer circumference of the core shaft, The arithmetic mean roughness (Ra) of the outer surface of the aforementioned core shaft, in accordance with JIS B 0601, is characterized in that it satisfies the following formula (1): Foamed rubber roller. 3.3≦Ra≦7.42...Formula (1)

2. A method for manufacturing a foamed rubber roller comprising at least a core shaft and a foamed layer made of silicone rubber provided on the outer circumference of the core shaft, The step includes applying a surface treatment to the outer circumferential surface of the core shaft, The arithmetic mean roughness (Ra) of the outer surface of the core shaft after surface treatment, in accordance with JIS B 0601, is characterized in that it satisfies the following formula (1): A method for manufacturing foamed rubber rollers. 3.3≦Ra≦7.42...Formula (1)

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