Rubber foam, insulation for flexible tubes or hoses of industrial robots

Abstract

To provide a rubber foam having good durability and high heat insulation property.SOLUTION: A rubber foam 1 includes acrylonitrile / butadiene rubber and polyvinyl chloride. The amount of acrylonitrile / butadiene rubber is 50 pts.mass to 90 pts.mass in the case when the total amount of acrylonitrile / butadiene rubber and polyvinyl chloride is 100 pts.mass and the rubber foam has a specific gravity of 0.05 to 0.15.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a rubber foam and a method for producing a rubber foam. [Background technology]

[0002] As cylindrical rubber molded articles, for example, hoses are disclosed in Patent Documents 1 and 2. Patent Document 1 discloses a hose using the following rubber composition: The rubber composition contains a rubber component and a chlorine-based flame retardant, and contains less than 70 parts by mass of chloroprene rubber per 100 parts by mass of the rubber component, with 5 parts by mass or more of the chlorine-based flame retardant blended per 100 parts by mass of the rubber component. Patent Document 2 discloses a hose using the following rubber composition: The rubber composition contains chloroprene rubber, butadiene rubber, and styrene-butadiene rubber as rubber components, with 60 to 80 parts by mass of chloroprene rubber per 100 parts by mass of the rubber component, and 5 to 25 parts by mass of silica blended with 100 parts by mass of the rubber component. Meanwhile, a cylindrical rubber foam is often used to surround a hose and provide thermal insulation. For example, a rubber foam is used as a so-called hose heater around a hose used in an industrial robot or the like. For example, Patent Document 3 discloses a heat insulating foam made of CR (chloroprene rubber) and PVC (polyvinyl chloride). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-2173 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-129684 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-74883 Summary of the Invention [Problem to be solved by the invention]

[0004] However, conventional heat insulating foams do not necessarily have sufficient durability or heat insulating properties, and improvements in these physical properties have been desired. The present disclosure has been made in view of the above-described circumstances, and has an object to provide a rubber foam having good durability and high thermal insulation properties. The present disclosure can be realized in the following aspects. [Means for solving the problem]

[0005] [1] A rubber foam containing acrylonitrile-butadiene rubber and polyvinyl chloride, When the total amount of the acrylonitrile-butadiene rubber and the polyvinyl chloride is 100 parts by mass, the amount of the acrylonitrile-butadiene rubber is 50 parts by mass or more and 90 parts by mass or less, A rubber foam having a specific gravity of 0.05 or more and 0.15 or less. [Effects of the Invention]

[0006] The rubber foam of the present disclosure has good durability and high thermal insulation properties. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a perspective view schematically illustrating an example of a rubber foam. [Figure 2] 1 is a photograph showing a rubber foam after an abrasion resistance test. DETAILED DESCRIPTION OF THE INVENTION

[0008] Here, a preferred example of the present disclosure will be described. [2] The rubber foam according to [1], which contains at least one selected from the group consisting of halogen-based flame retardants and antimony-based flame retardants. This configuration improves the flame retardancy of the rubber foam.

[0009] [3] The rubber foam according to [1] or [2], which is cylindrical. The cylindrical shape makes it useful as a hose heater.

[0010] [4] A method for producing a rubber foam using a mixture containing acrylonitrile-butadiene rubber, polyvinyl chloride, and azodicarboxylic acid amide particles as a raw material, comprising: As the azodicarboxylic acid amide particles, two or more types of particles having different median diameters are used, the median diameters of the two or more types of particles differ from one another by 1 μm or more and 15 μm or less, The method for producing a rubber foam, wherein the median diameter of any of the two or more types of particles is 5 μm or more and 40 μm or less. This manufacturing method provides a rubber foam having good durability and high thermal insulation properties.

[0011] The present disclosure will be described in detail below. Note that when a range is indicated as "x to y," it is assumed that x and y are included in the range unless otherwise specified.

[0012] 1. Rubber foam 1 The rubber foam 1 contains acrylonitrile-butadiene rubber (NBR) and polyvinyl chloride (PVC). When the total amount of the acrylonitrile-butadiene rubber and polyvinyl chloride is 100 parts by mass, the amount of the acrylonitrile-butadiene rubber is 50 parts by mass or more and 90 parts by mass or less, from the viewpoint of maintaining low thermal conductivity of the rubber foam 1 while exhibiting excellent abrasion resistance.

[0013] (1) Specific gravity The specific gravity of the rubber foam 1 is 0.05 or more and 0.15 or less, preferably 0.07 or more and 0.13 or less, and more preferably 0.08 or more and 0.10 or less, from the viewpoint of imparting high durability and high thermal insulation to the rubber foam 1. The specific gravity of the rubber foam 1 refers to a value measured at a temperature condition of 23°C by the "water displacement method" according to Method A of JIS K7112.

[0014] (2) Acrylonitrile-butadiene rubber The acrylonitrile-butadiene rubber (NBR) is not particularly limited as long as a known one is appropriately selected and used. The amount of acrylonitrile (AN content) contained in the acrylonitrile-butadiene rubber (NBR) is not particularly limited. The amount of acrylonitrile (AN content) is, for example, preferably 23% by mass or more and 43% by mass or less, and more preferably 28% by mass or more and 38% by mass or less. The Mooney viscosity ML(1+4) of acrylonitrile-butadiene rubber (NBR) at 100°C measured in accordance with JIS K6300 is not particularly limited. From the viewpoint of reducing the specific gravity and maintaining the shape of the sponge, this Mooney viscosity ML(1+4) is preferably 30 or more and 70 or less, and more preferably 40 or more and 60 or less.

[0015] (3) Flame retardants The rubber foam 1 preferably contains a flame retardant. Any flame retardant can be used as the flame retardant. The type of flame retardant is not particularly limited, but from the viewpoint of achieving a high flame retardant effect with a small blending amount without reducing the properties of the foam, such as the tensile modulus of elasticity, it is preferable to use a combination of a halogen-based flame retardant and an antimony-based flame retardant.

[0016] Examples of halogen-based flame retardants include chlorine compounds and bromine compounds, and two or more of these may be used in combination. Suitable examples of the chlorine compound include chlorinated paraffin and perchloropentacyclodecane. Suitable examples of the bromine compound include tetrabromobisphenol A, ethylenebistetrabromophthalimide, pentabromodiphenyl ether, octabromodiphenyl ether, decabromodiphenyl ether, hexabromocyclododecane, and brominated polystyrene.

[0017] Examples of antimony-based flame retardants include antimony trioxide, antimony pentoxide, antimony trichloride, and antimony pentachloride.

[0018] When a halogen-based flame retardant and an antimony-based flame retardant are used in combination, the content (addition amount) of the halogen-based flame retardant per 100 parts by mass of the rubber component (100 parts by mass of the total of the acrylonitrile-butadiene rubber and polyvinyl chloride) is preferably 30 parts by mass or more and 80 parts by mass or less, and more preferably 45 parts by mass or more and 65 parts by mass or less, from the viewpoint of imparting sufficient flame retardancy while maintaining high durability. The content (addition amount) of the antimony-based flame retardant is preferably 5 parts by mass or more and 30 parts by mass or less, and more preferably 10 parts by mass or more and 20 parts by mass or less, per 100 parts by mass of the rubber component (100 parts by mass of the total of the acrylonitrile-butadiene rubber and polyvinyl chloride), from the viewpoint of imparting sufficient flame retardancy while maintaining high durability.

[0019] (4) Filler The rubber foam 1 may contain a filler. Any filler can be used as the filler. Examples of the filler include inorganic fillers such as calcium carbonate, talc, magnesium hydroxide, mica, clay, aluminum hydroxide, magnesium hydroxide, barium sulfate, silicic acid, titanium oxide, bentonite, carbon black, mica, glass fiber, and wood flour. From the viewpoints of processability, dimensional stability of the product, and strength of the product, the amount of the filler is preferably 40 parts by mass or more and 140 parts by mass or less per 100 parts by mass of the rubber component.

[0020] (5) Other ingredients Other components include a softener, a crosslinking agent, a foaming agent, and the like. The softener may be any of vegetable oils such as lauric acid, ricinoleic acid, baltimic acid, cottonseed oil, soybean oil, castor oil, palm oil, etc., or mineral oils such as paraffinic, naphthenic, aromatic, etc. The amount of softener is preferably 30 to 110 parts by weight per 100 parts by weight of the rubber component from the viewpoints of kneadability, product strength, etc. The total amount of filler and softener added is preferably 70 to 250 parts by weight per 100 parts by weight of the rubber component. The compounding ratio of filler to softener is preferably 65:35 to 50:40. By setting the total amount and ratio of filler and softener to be added within the above ranges, compatibility is improved and moldability, such as rubber kneading, is excellent.

[0021] Sulfur and organic peroxides are used as crosslinking agents. Sulfur is used in the case of sulfur crosslinking, and organic peroxides are used in peroxide crosslinking. Examples of organic peroxides include dicumyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2,5-di-(t-butylperoxy)hexane, and t-butylcumyl peroxide. The amount of the crosslinking agent is preferably 0.1 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the rubber component. It is preferable to use a crosslinking accelerator or crosslinking aid together with the crosslinking agent.

[0022] Examples of the crosslinking accelerator include benzothiazyl disulfide, 2-mertocaptobenzothiazole, dipentamethylene thiuraum tetrasulfide, tetramethylthiuraum disulfide, and zinc oxide. Examples of the crosslinking aid include divinylbenzene, ethylene dimethacrylate, trimethylolpropane trimethacrylate, ethylene glycol dimethacrylate, triallyl cyanurate, and triallyl isocyanurate.

[0023] The foaming agent may be one or more selected from organic foaming agents and inorganic foaming agents. The organic blowing agent is not particularly limited, but azo compounds are preferred examples. The azo compounds are not particularly limited, but one or more of azodicarboxylic acid amide (ADCA), barium azodicarboxylate, azobisisobutyronitrile (AIBN), azocyclohexylnitrile, azodiaminobenzene, etc. are preferred examples. The inorganic foaming agent is not particularly limited, and examples of inorganic foaming agents that can be used include hydrogen carbonates such as sodium hydrogen carbonate (baking soda) and ammonium hydrogen carbonate, carbonates such as sodium carbonate and ammonium carbonate, nitrites such as sodium nitrite and ammonium nitrite, borohydrides such as sodium borohydride, azides, and other known inorganic foaming agents. The amount of the foaming agent is preferably 5 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the rubber component. It is also preferable to use a foaming assistant together with the foaming agent, and examples of the foaming assistant include urea compounds, organic compounds, and inorganic salts. Other ingredients may also be added, such as processing aids, colorants, antioxidants, etc. Examples of processing aids include stearic acid and palmitic acid.

[0024] (6) Shape of rubber foam 1 The shape of the rubber foam 1 is not particularly limited. The shape of the rubber foam 1 can be changed appropriately depending on the application. For example, a cylindrical shape can be suitably adopted as the shape of the rubber foam 1 (see FIG. 1). The cylindrical rubber foam 1 can be used as a heat insulating tube. The heat insulating tube is used to insulate flexible tubes and flexible hoses for industrial robots and the like.

[0025] (7) Effects of the rubber foam 1 according to the embodiment The rubber foam 1 has good durability because it contains acrylonitrile-butadiene rubber and polyvinyl chloride in a specified ratio. The surface of this rubber foam 1 is more slippery than that of EPDM sponge, so it has excellent abrasion resistance. The rubber foam 1 has high thermal insulation properties because it contains acrylonitrile-butadiene rubber, which has low thermal conductivity, and polyvinyl chloride, which also has low thermal conductivity. The thermal conductivity of the polymer alone is 0.25 W / m K for acrylonitrile-butadiene rubber, 0.13 W / m K for polyvinyl chloride, and 0.36 W / m K for EPDM. Moreover, the rubber foam 1 of this embodiment has a specific gravity of 0.05 or more and 0.15 or less, and has particularly low thermal conductivity.

[0026] 2. Method for producing rubber foam 1 (1) Method for producing rubber foam 1 In the method for producing the rubber foam 1, a mixture containing acrylonitrile-butadiene rubber, polyvinyl chloride, and azodicarboxylic acid amide particles is used as a raw material. Two or more types of azodicarboxylic acid amide particles with different median diameters are used. The median diameters of the two or more types of particles differ from each other by 1 μm or more and 15 μm or less. The median diameter of each of the two or more types of particles is 5 μm or more and 40 μm or less. The reason why it is believed that the use of two or more types of azodicarboxylic acid amide particles having different median diameters in this way allows the rubber foam 1 to have good durability and high heat insulating properties will be explained below. In this manufacturing method, it is believed that vulcanization first proceeds moderately while the particles with a small median diameter expand. During this process, the foam retains gas. Then, when the expansion of the particles with a small median diameter is nearly complete, the particles with a large median diameter expand, which is believed to lower the specific gravity of the rubber foam 1.

[0027] When the particles having the smallest median diameter among two or more types of particles having different median diameters are designated as first particles and the particles having the largest median diameter are designated as second particles, the mass ratio of the first particles to the second particles is preferably 95:5 to 20:80, more preferably 92:8 to 25:75, and even more preferably 60:40 to 25:75, from the viewpoint of slowing down the vulcanization of the rubber during foaming, thereby improving the balance between foaming and vulcanization, suppressing gas escape, and lowering the specific gravity of the rubber foam. When there are two types of particles with different median diameters, the particles with the smaller median diameter are the first particles, and the particles with the larger median diameter are the second particles.

[0028] From the viewpoint of achieving a good balance between foaming and vulcanization, suppressing gas escape, and reducing the specific gravity of the rubber foam, the total amount of azodicarboxylic acid amide particles is preferably 5 parts by mass or more and 100 parts by mass or less, and more preferably 10 parts by mass or more and 50 parts by mass or less, per 100 parts by mass of the rubber component (100 parts by mass of the total of acrylonitrile-butadiene rubber and polyvinyl chloride).

[0029] Here is an example of a suitable method for producing a rubber foam. First, the rubber component, compatibilizer, filler, etc. are primarily kneaded using a Banbury mixer, kneader, or the like. This does not include crosslinking agents, crosslinking accelerators, crosslinking aids, foaming agents, or foaming aids. The primary kneading conditions are preferably a temperature of 50°C to 180°C and a kneading time of 3 to 30 minutes. The resulting primary kneaded mixture is then added with the crosslinking agent, crosslinking accelerator, crosslinking aid, foaming agent, and foaming aid, and the secondary kneading is performed. The secondary kneading conditions are preferably a temperature of 20°C to 80°C and a kneading time of 3 to 30 minutes. The resulting secondary kneaded mixture is formed into the desired shape using a calendar molding machine, extrusion molding machine, or the like. The mixture is then placed in a crosslinking / foaming mold and subjected to primary crosslinking / foaming and secondary crosslinking / foaming, in that order, to obtain a rubber foam. The primary crosslinking / foaming is preferably performed at 100°C to 160°C for 3 to 20 minutes. The secondary crosslinking and foaming is preferably carried out at 160°C to 220°C for 5 to 20 minutes.

[0030] (2) Effects of the method for producing the rubber foam 1 according to the embodiment In a method for producing a rubber foam 1 according to an embodiment, particles of two or more types of azodicarboxylic acid amides having different median sizes are foamed in a rubber component containing acrylonitrile-butadiene rubber and polyvinyl chloride so as to reduce the density of the rubber foam 1. Therefore, this production method can produce a rubber foam 1 containing acrylonitrile-butadiene rubber, which has low thermal conductivity as an inherent material property, and polyvinyl chloride, which also has low thermal conductivity as an inherent material property, and which also has a low specific gravity, and as a result has particularly low thermal conductivity. Furthermore, this production method can produce a rubber foam 1 containing acrylonitrile-butadiene rubber and polyvinyl chloride, which has a slippery surface and excellent abrasion resistance. [Example]

[0031] The present invention will be explained in more detail below with reference to examples.

[0032] 1. Preparation of Rubber Foam (Examples 1 to 8 and Comparative Examples 1 to 3) Various rubber foams were produced according to the blending ratios shown in Table 1. In this case, the raw materials shown in Table 3 were blended in common for Examples 1 to 8 and Comparative Examples 1 to 3. Table 2 shows the names of the raw materials and manufacturers listed in Table 1. In Table 1, "DPT" means "N,N'-dinitrosopentamethylenetetramine."

[0033] [Table 1]

[0034] [Table 2]

[0035] [Table 3]

[0036] The primary kneading was carried out using a kneader at a temperature of 160°C for a kneading time of 5 minutes, and the secondary kneading was carried out using a roll at a temperature of 50°C for a kneading time of 10 minutes. Primary crosslinking and foaming: internal volume 57cm 3 70 g of the secondary kneaded product was placed in a mold, and the kneading was carried out at 130° C. for 10 minutes. Secondary crosslinking and foaming were carried out at 200°C for 5 minutes using the same mold as for primary crosslinking and foaming.

[0037] 2. Evaluation Method (1) Specific gravity Measurement was carried out at a temperature of 23°C using JIS K7112 Method A "Water Displacement Method".

[0038] (2) Thermal conductivity The thermal conductivity is a value measured in accordance with JIS-A1412-2. The thermal conductivity was measured by the probe method using a rapid thermal conductivity meter (QTM-500) manufactured by Kyoto Electronics Manufacturing Co., Ltd.

[0039] (3) Flame retardancy Flame retardancy was measured in accordance with the 20mm vertical flame test (IEC60695-11-10 Method B, ASTM D3801). Test specimens were attached vertically to a clamp and exposed to a 20mm flame for 10 seconds twice. The flame behavior was rated as V-0, V-1, V-2, or Not. If each of the criteria was met, the flammability classification was determined to be "V-0." Burning time of each test piece: 10 seconds or less Total burn time for 5 sticks: 50 seconds or less Burning and glowing time for each test piece: 30 seconds or less Burn to clamp: None Cotton ignition by dripping: No

[0040] (4) Abrasion resistance The abrasion resistance test method (abrasion test method) was carried out as follows: After 2000 rubs, if there was no abrasion on the surface, it was rated as "good", and if there was abrasion, it was rated as "poor". Testing equipment name: Gakushin type friction testing machine Test method: JIS K 6404-4 Test method for rubber-coated and plastic-coated fabrics Part 4: Durability test 8.3 Gakushin-type friction test Load (weight of friction element): 200g ·Friction speed: 30 times / min ·Friction distance: 100mm - Cotton cloth was wrapped around the friction element.

[0041] (5) Overall Judgment The judgment was as follows: "Good": Meets all three of the following criteria. "Fail": Does not meet one or more of the following three criteria. <Item> [1] Thermal conductivity: 0.043 W / m K or less [2] Flame retardant: V-0 equivalent [3] Wear resistance test results: Good

[0042] 3.Results The results are shown in Table 4.

[0043] [Table 4]

[0044] (1) Fulfillment status of each requirement in Examples 1 to 8 The rubber foams of Examples 1 to 8 satisfy all of the following requirements (a) to (d). Requirement (a): A rubber foam containing acrylonitrile-butadiene rubber and polyvinyl chloride. Requirement (b): When the total amount of the acrylonitrile-butadiene rubber and the polyvinyl chloride is 100 parts by mass, the amount of the acrylonitrile-butadiene rubber is 50 parts by mass or more and 90 parts by mass or less. Requirement (c): The specific gravity is between 0.05 and 0.15. Requirement (d): Two types of azodicarboxylic acid amide particles with different median diameters are used.

[0045] (2) Fulfillment status of each requirement in Comparative Examples 1 to 3 In contrast, the rubber foams of Comparative Examples 1 to 3 do not satisfy the following requirements. Comparative Example 1 does not satisfy the requirements (a), (b), (c), and (d). Comparative Example 2 does not satisfy the requirements (a), (b), and (d). Comparative Example 3 does not satisfy requirements (c) and (d).

[0046] (3) Results and Considerations of Examples 1 to 8 The rubber foams of Examples 1 to 8 received good results in the overall assessment. The rubber foams of Examples 1 to 8 had low thermal conductivity of 0.043 W / m K or less, flame retardancy equivalent to V-0, and excellent abrasion resistance. Fig. 2 shows the state of Example 2 and Comparative Example 1 after the abrasion resistance test. Example 2 on the right side of Fig. 2 showed no abrasion on the surface, while Comparative Example 1 on the left side showed abrasion on the surface.

[0047] (4) Results and Considerations of Comparative Examples 1 to 3 The rubber foam of Comparative Example 1 used EPDM as the rubber component and had a high specific gravity. The rubber foam of Comparative Example 1 had high thermal conductivity and poor abrasion resistance. The rubber foam of Comparative Example 2 uses only NBR as the rubber component. The rubber foam of Comparative Example 2 had poor abrasion resistance. The rubber foam of Comparative Example 3 uses NBR and PVC as rubber components. However, the rubber foam of Comparative Example 3 is not produced using two or more types of azodicarboxylic acid amide particles with different median diameters, and has a high specific gravity. The rubber foam of Comparative Example 3 has a high thermal conductivity of 0.059 W / m K. From the above results, it was confirmed that the specific gravity of the rubber foam was low when a rubber foam containing acrylonitrile-butadiene rubber and polyvinyl chloride, and containing 50 parts by mass or more and 90 parts by mass or less, was produced using two types of azodicarboxylic acid amide particles having different median sizes, as in Examples 1 to 8. It was confirmed that the rubber foams of Examples 1 to 8 had low thermal conductivity, high flame retardancy, and high abrasion resistance.

[0048] 4. Effects of the Example According to the above examples, it is possible to provide a rubber foam having low thermal conductivity, high flame retardancy, and high abrasion resistance.

[0049] The present invention is not limited to the above-described embodiments, and various modifications and variations are possible within the scope of the claims of the present invention. [Explanation of symbols]

[0050] 1...Rubber foam

Claims

1. A rubber foam comprising acrylonitrile-butadiene rubber, polyvinyl chloride, a halogen-based flame retardant, and an antimony-based flame retardant, When the total amount of the acrylonitrile-butadiene rubber and the polyvinyl chloride is 100 parts by mass, the amount of the acrylonitrile-butadiene rubber is 50 parts by mass or more and 90 parts by mass or less, the content of the halogen-based flame retardant is 45 parts by mass or more and 65 parts by mass or less, and the content of the antimony-based flame retardant is 10 parts by mass or more and 20 parts by mass or less, A rubber foam having a thermal conductivity of 0.032 W / m·K or more and 0.043 W / m·K or less.

2. An insulating material for flexible tubes or hoses of industrial robots, comprising the rubber foam described in claim 1.

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