Rubber composition for seals and seals using the rubber composition for seals

Abstract

The present invention provides a rubber composition for a seal, which comprises 100 parts by mass of a rubber component, 50 to 140 parts by mass of silica, 1 to 20 parts by mass of a silane coupling agent, and 15 to 35 parts by mass of carbon black. The rubber component is preferably an ethylene-propylene-diene rubber.

Description

Technical Field

[0001] The present invention relates to a rubber composition for a seal and a seal using the rubber composition for a seal. Background Art

[0002] There is a problem that rubber seals for equipment for storing high-pressure hydrogen are liable to blister. The blister phenomenon refers to the following phenomenon: gas that has penetrated into the interior of the rubber due to high pressure expands while remaining in the interior of the rubber under the influence of rapid decompression at high temperature, causing the rubber material to rupture.

[0003] In International Publication No. 2007 / 145313 (Patent Document 1) and International Publication No. 2008 / 001625 (Patent Document 2), a rubber composition in which silica is blended as a reinforcing material in silicone rubber is disclosed. Further, in Japanese Unexamined Patent Application Publication No. 2015-206002 (Patent Document 3), a rubber composition in which carbon black is blended in ethylene-propylene-diene rubber (EPDM) is disclosed. In Japanese Unexamined Patent Application Publication No. 2015-108104 (Patent Document 4), an EPDM O-ring blended with carbon black and silica is disclosed, and in International Publication No. 2003 / 104317 (Patent Document 5), an elastic compound blended with carbon black and microsilica is disclosed.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: International Publication No. 2007 / 145313

[0007] Patent Document 2: International Publication No. 2008 / 001625

[0008] Patent Document 3: Japanese Unexamined Patent Application Publication No. 2015-206002

[0009] Patent Document 4: Japanese Unexamined Patent Application Publication No. 2015-108104

[0010] Patent Document 5: International Publication No. 2003 / 104317 Summary of the Invention

[0011] Problems to be Solved by the Invention

[0012] In high-pressure hydrogen equipment, the pressure of hydrogen to be processed gradually increases, and seals with more excellent sealing performance at low and high temperatures are required. However, for a composition excellent in blister resistance at high temperature, its low-temperature property (recovery property at low temperature) is poor, and a seal that satisfies both properties has not been realized.

[0013] An object of the present invention is to provide a rubber composition for a seal that can improve the sealing performance of high-pressure gas at high and low temperatures, and a seal formed by crosslinking the rubber composition for a seal.

[0014] Means for Solving the Problem

[0015] The present invention includes the following rubber composition for a seal and a seal using the rubber composition for a seal.

[0016] [1] A rubber composition for a seal, which contains 100 parts by mass of a rubber component, 50 to 140 parts by mass of silica, 1 to 20 parts by mass of a silane coupling agent, and 15 to 35 parts by mass of carbon black.

[0017] [2] The rubber composition for a seal according to [1], wherein the rubber component is ethylene-propylene-diene rubber.

[0018] [3] The rubber composition for a seal according to [2], wherein the Mooney viscosity of the ethylene-propylene-diene rubber at 125 °C measured according to JIS K6300-1:2013 is 50 to 90, or the Mooney viscosity at 100 °C is 30 to 60, and the ethylene-propylene-diene rubber contains 45 to 55% by mass of structural units derived from ethylene.

[0019] [4] The rubber composition for a seal according to any one of [1] to [3], wherein the silica is spherical.

[0020] [5] The rubber composition for a seal according to any one of [1] to [4], wherein the average particle diameter of the silica is 5 nm to 5 μm.

[0021] [6] The rubber composition for a seal according to any one of [1] to [5], which does not contain a plasticizer.

[0022] [7] A seal formed by a crosslinked product of the rubber composition for a seal according to any one of [1] to [6].

[0023] Advantageous Effects of the Invention

[0024] According to the present invention, it is possible to provide a rubber composition for a seal that can improve the sealing performance of high-pressure gas at high and low temperatures, and a seal formed by crosslinking the rubber composition for a seal. Detailed Description of the Invention

[0025] The rubber composition for a seal contains [A] a rubber component, [B] silica, [C] a silane coupling agent, and [D] carbon black. Hereinafter, each component contained in the rubber composition for a seal and any optionally contained components will be described in detail.

[0026] [A] Rubber component

[0027] As the rubber component, for example, ethylene-propylene-diene rubber (EPDM), ethylene-propylene rubber (EPM), nitrile rubber (NBR; acrylonitrile-butadiene rubber), hydrogenated nitrile rubber (HNBR; hydrogenated acrylonitrile-butadiene rubber), butyl rubber (IIR), fluororubber (FKM), silicone rubber (Q), etc. can be used. As the rubber for a seal, from the aspect of having good properties, EPDM, HNBR, FKM, etc. are preferred. The rubber component can be composed of only one kind or can contain two or more kinds.

[0028] The seal crosslinked from the rubber composition for a seal does not generate blisters and does not leak air in the high-temperature and high-pressure cycle test at a temperature of 100 °C and a pressure of 100 MPa described below. In addition, the seal crosslinked from the rubber composition for a seal does not leak air in the low-temperature and high-pressure cycle test at a temperature of -40 °C and a pressure of 100 MPa described below. Leakage of air in a low-temperature environment is usually caused by a decrease in the shape followability and recoverability of the seal. EPDM is a rubber excellent in low-temperature properties (recoverability at low temperatures), chemical resistance, and cleanliness. In addition, since it is cheaper than NBR, HNBR, FKM, Q, etc., it is one of the rubber components suitable for seal applications.

[0029] EPDM is a terpolymer containing structural units derived from ethylene, structural units derived from propylene, and structural units derived from a diene monomer. In EPDM, by adjusting the content ratio of the structural units derived from ethylene to the structural units derived from propylene, the rubber properties can be controlled. For example, when the ratio of the structural units derived from ethylene is increased, there is a tendency for the chemical resistance and crystallinity (and thus mechanical strength) of the rubber to increase. On the other hand, when the ratio of the structural units derived from ethylene is decreased, there is a tendency for the molding processability and fluidity of the rubber to decrease. In order to produce a molded product (seal) with better processability and high quality by injection molding, the fluidity of the rubber component used is preferably relatively low.

[0030] From such a viewpoint, the content of the structural units derived from ethylene in EPDM is usually 70% by mass or less, preferably 55% by mass or less, more preferably 51% by mass or less. If the content of the structural units derived from ethylene is within the above range, good fluidity can be imparted to EPDM, and good low-temperature properties can be imparted to the seal.

[0031] On the other hand, when the content of the structural unit derived from ethylene is too low, the tensile strength of the resulting seal is insufficient. Therefore, the content of the structural unit derived from ethylene in EPDM is usually 40% by mass or more, preferably 45% by mass or more, and more preferably 48% by mass or more.

[0032] Specific examples of the diene monomer constituting EPDM include: non-conjugated diene monomers such as 5-ethylidene-2-norbornene (ENB), dicyclopentadiene (DCPD), 1,4-hexadiene (1,4-HD), methyltetrahydroindene, 5-methylene-2-norbornene, cyclooctadiene, and dicyclooctadiene. Among them, from the aspect that EPDM shows good crosslinking speed (vulcanization speed) or the heat resistance of the resulting seal is also excellent, it is preferable to use ENB and 1,4-HD. In particular, from the aspect of excellent crosslinking speed, it is more preferable to use ENB. As the diene monomer, either one monomer can be used alone, or two or more monomers can be used in combination.

[0033] From the viewpoint of improving the crosslinking speed and the moldability of the rubber composition, the content of the structural unit derived from the diene monomer in EPDM is usually 1% by mass or more, preferably 2.5% by mass or more. In addition, considering the ease of deterioration of the seal due to a large amount of double bonds remaining after crosslinking, the content of the structural unit derived from the diene monomer in EPDM is usually 14% by mass or less, preferably 10% by mass or less, and more preferably 5.0% by mass or less.

[0034] The Mooney viscosity [ML(1+4)125°C] of the rubber component used in the rubber composition for seals measured according to JIS K6300-1:2013 is preferably 90 or less, and more preferably 85 or less. The Mooney viscosity [ML(1+4)125°C] of the rubber component is preferably 40 or more, more preferably 50 or more, and further preferably 75 or more. When the Mooney viscosity is too high, the processability may be poor.

[0035] The Mooney viscosity [ML(1+4)100°C] of the rubber component used in the rubber composition for seals measured according to JIS K6300-1:2013 is preferably 60 or less, and more preferably 50 or less. The Mooney viscosity [ML(1+4)100°C] of the rubber component is preferably 30 or more, more preferably 35 or more, and further preferably 40 or more.

[0036] Preferably, the Mooney viscosity of the EPDM at 125°C measured according to JIS K6300-1:2013 is 50 to 90, or the Mooney viscosity at 100°C is 30 to 60, and the EPDM contains 45 to 55% by mass of ethylene-derived structural units. If the above EPDM is used as a rubber component, a seal with excellent followability in a lower temperature environment can be obtained. Such a seal will not leak high-pressure gas even without using grease at a temperature of -40°C. The use environment of a seal without grease and with good sealing performance is not limited, so it has high versatility and the failure during maintenance (such as seal replacement) will be reduced. In addition, such a seal can seal high-pressure gas even at a temperature of -45°C.

[0037] If specific examples of commercially available EPDM are cited, for example, "EPT" manufactured by Mitsui Chemicals, Inc., "ESPRENE" manufactured by Sumitomo Chemical Co., Ltd., "EP" manufactured by JSR Corporation, "KELTAN" manufactured by LANXESS, etc., all of which are trade names. Preferably, "ESPRENE 5361", "ESPRENE 501A", etc. with excellent low-temperature recovery properties manufactured by Sumitomo Chemical Co., Ltd. can be used.

[0038] [B] Silica

[0039] Silica is highly filled in the sealant composition. By highly filling silica, hydrogen is difficult to penetrate into the interior of the seal, so the anti-foaming property of the seal can be improved. The hydrogen adsorption property of silica is lower than that of carbon black, so it is more useful to use silica for improving the anti-foaming property.

[0040] As the silica, the silica generally used as a filler for exerting a reinforcing effect in general-purpose rubbers can be used. The silica is not particularly limited, and examples include dry silica manufactured by thermal decomposition of halogenated silicic acid or organosilicon compounds, a method of oxidizing SiO vaporized by heating and reducing silica sand, etc.; wet silica manufactured by thermal decomposition of sodium, etc. As the silica, dry silica is preferably used. As the silica, only one kind of silica can be used, or two or more kinds of silica can be used in combination.

[0041] For the silica, it contains at least 70% by mass of silica component (SiO2). The specific surface area of the silica is preferably 10 to 120 m 2 / g, more preferably 15 to 40 m 2 / g.

[0042] Silica is preferably spherical. Conventionally, there has been an upper limit to the amount of silica that can be incorporated into a rubber composition for seals, and it has been difficult to highly fill the silica. However, in the case where the silica is spherical, compared with silica of other shapes (for example, chain-like), the friction between silicas is less and the dispersibility is improved, so that the silica can be highly filled in the rubber composition for seals. In addition, when a large amount of silica is contained, the low-temperature properties of the seal may be reduced, but if the silica is spherical, the reduction in low-temperature properties is less likely to occur. Therefore, it is easier to balance the anti-foaming property and the low-temperature property of the seal. It should be noted that "spherical" includes not only true spheres but also somewhat deformed spheres.

[0043] From the viewpoints of suppression of aggregation and smoothness, the average particle diameter of the silica is preferably 5 nm to 5 μm, more preferably 10 nm to 1 μm, and still more preferably 50 nm to 200 nm. When the average particle diameter of the silica is too large, the anti-foaming property and the low-temperature property of the seal may be reduced. The average particle diameter can be obtained, for example, by the following method: morphological observation is carried out using a microscope, the particle diameters of the silica in the observation field of view are measured by image analysis, and the average value of the measured values is calculated.

[0044] The content of silica in the rubber composition for seals is 50 to 140 parts by mass, preferably 80 to 140 parts by mass, relative to 100 parts by mass of the rubber component. When the content of silica is too large, the low-temperature property of the seal may be reduced.

[0045] 〔C〕Silane coupling agent

[0046] The rubber composition for seals contains a silane coupling agent for highly filling silica. The silane coupling agent has a reactive group that chemically bonds to an inorganic material and a reactive group that chemically bonds to an organic material in the molecule, and thus has the function of an adhesive that connects an organic material and an inorganic material that are usually difficult to bond. When the surface of the silica is coated with the silane coupling agent, the surface of the silica becomes hydrophobic, and the aggregation of the silica can be prevented. Thereby, the silica can be more dispersedly and highly filled in the rubber composition for seals, and the anti-foaming property of the seal can be improved. In addition, the silane coupling agent increases the bonding strength between the silica and the rubber component, and thereby also improves the anti-foaming property.

[0047] The silane coupling agent is not particularly limited, and examples thereof include vinyl-based, acrylic-based, epoxy-based, mercapto-based, and amino-based silane coupling agents.

[0048] Examples of vinyl-based silane coupling agents include vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, etc. Examples of acrylic-based silane coupling agents include 3-acryloxypropyltrimethoxysilane, etc. Examples of epoxy-based silane coupling agents include 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, etc. Examples of methacrylic-based silane coupling agents include 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, etc. These silane coupling agents can be used alone or in combination of two or more.

[0049] The content of the silane coupling agent in the rubber composition for seals is 1 to 20 parts by mass, preferably 1 to 10 parts by mass, relative to 100 parts by mass of the rubber component. By including a larger amount of the silane coupling agent than in the past, the anti-foaming property of the rubber composition for seals is improved. However, when the amount of the silane coupling agent is excessive, the elongation at break is extremely reduced, so there may be a risk of breakage or a decrease in low-temperature properties during use.

[0050] 〔D〕Carbon black

[0051] The rubber composition for seals contains carbon black. By containing carbon black, the strength and anti-foaming property of the seals can be improved.

[0052] The content of carbon black is 15 to 35 parts by mass relative to 100 parts by mass of the rubber component. From the viewpoint of maintaining the co-crosslinking agent, the content of carbon black is preferably 20 parts by mass or more relative to 100 parts by mass of the rubber component. However, since carbon black adsorbs hydrogen, when a large amount is compounded, the anti-foaming property may be reduced. The total content of silica and carbon black is preferably 95 to 140 parts by mass relative to 100 parts by mass of the rubber component. By highly filling fillers such as silica and carbon black, the anti-foaming property is improved, but when the compounding amount of the filler is excessive, the rigidity of the seals is too high, and the low-temperature properties may be reduced.

[0053] In addition, the carbon black is preferably spherical. When the carbon black is closer to a true sphere (smaller specific surface area), the carbon black is not easily aggregated, and the low-temperature properties of the rubber composition for seals are not easily reduced. From the viewpoint of reinforcement, it is preferable that the particle size of the carbon black is small.

[0054] The carbon black can be either conductive or non-conductive, and examples according to its production method include: furnace black, channel black, acetylene black, Ketjen black, thermal cracking carbon black, lamp black, etc. The carbon black can be used alone or in combination of two or more.

[0055] As the carbon black, for example, types such as SAF, ISAF, ISAF-HF, ISAF-LS, IISAF-HS, HAF, HAF-HS, HAF-LS, MAF, FEF, FEF-LS, GPF, GPF-HS, GPF-LS, SRF, SRF-HS, SRF-LM, FT, MT, etc. can be used. Two or more carbon blacks with different particle sizes can be used.

[0056] The average particle size of the carbon black sometimes varies depending on each manufacturing company. For example, SAF is 19 nm, ISAF is 23 nm, HAF is 28 nm, MAF is 38 nm, FEF is 43 nm, GPF is 62 nm, SRF is 66 nm, and FT is 122 nm.

[0057] [E] Co-crosslinking agent

[0058] The rubber composition for seals preferably further contains a co-crosslinking agent. Examples of the co-crosslinking agent include: quinone dioxime, ethylene glycol dimethacrylate, divinylbenzene, diallyl phthalate, triallyl isocyanurate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, 1,2-polybutadiene, metal salts of methacrylic acid, metal salts of acrylic acid, etc. As the co-crosslinking agent, either only one co-crosslinking agent can be used, or two or more co-crosslinking agents can be used in combination.

[0059] The content of the co-crosslinking agent in the rubber composition for seals is preferably 1 to 20 parts by mass, more preferably 1 to 10 parts by mass, relative to 100 parts by mass of the rubber component. Within this range, the fluidity and processability of the rubber composition for seals can be improved. Within this range, the foam resistance of the crosslinked seals can be further improved. When the content of the co-crosslinking agent is too small, the 100% tensile stress of the seals may be reduced. When the content of the co-crosslinking agent is too large, the elongation at break during cutting is less than 100%, and the low-temperature performance may be reduced.

[0060] [F] Other contained components

[0061] The rubber composition for seals can contain other components in addition to the above components as needed. Examples of other contained components include: fillers other than silica and carbon black (including extender pigments and coloring pigments), surfactants other than silane coupling agents, anti-aging agents, vulcanization accelerators, antioxidants, processing aids (such as stearic acid), vulcanization aids (such as zinc oxide), stabilizers, tackifiers, polyols, flame retardants, waxes, lubricants, etc. As the additives, either only one additive can be used, or two or more additives can be used in combination.

[0062] When the rubber composition for seals contains the above additives, their content can be the amount commonly used in the art.

[0063] Examples of the filler include: alumina, zinc oxide, titanium dioxide, clay, talc, diatomaceous earth, barium sulfate, calcium carbonate, magnesium carbonate, calcium oxide, mica, graphite, aluminum hydroxide, aluminum silicate, hydrotalcite, granular or powdered resin, metal powder, glass powder, ceramic powder, etc.

[0064] Examples of the anti-aging agent include: phenol derivatives, aromatic amine derivatives, amine-ketone condensates, benzimidazole derivatives, dithiocarbamate derivatives, thiourea derivatives, etc.

[0065] Examples of the vulcanization accelerator include: compounds of the thiuram type, thiazole type, sulfenamide type, thiourea type, guanidine type, dithiocarbamate type, etc.

[0066] Examples of the processing aid include: thermoplastic resin, liquid rubber, oil, softening agent, internal mold release agent, tackifier, etc. For example, when the rubber component is FKM or FFKM, a fluororesin or its particles may be contained as the filler, and a liquid fluororubber may be contained as the processing aid. For example, when the rubber component is EPM or EPDM, a paraffin-based oil may be contained as the processing aid. The content of the processing aid is preferably 0.5 to 5 parts by mass, more preferably 1.0 to 2.5 parts by mass, based on 100 parts by mass of the rubber composition for the seal.

[0067] Examples of the internal mold release agent include: higher fatty acids, fatty acid esters, fatty acid amides, fluororesins, silicone resins, hydrocarbon resins, etc. From the viewpoint of improving low-temperature properties, the content of the internal mold release agent is preferably 0.5 to 5 parts by mass, more preferably 1.0 to 2.5 parts by mass, based on 100 parts by mass of the rubber composition for the seal. When the content of the internal mold release agent is less than 0.5 part by mass, the mold release effect is small because there is a risk of rubber sticking to the mold and contaminating the mold. In addition, the rubber composition for the seal can improve the low-temperature properties without reducing the anti-foaming property by containing a high-viscosity internal mold release agent.

[0068] Examples of the surfactant other than the silane coupling agent include nonionic surfactants. Examples of the nonionic surfactants include higher alcohols and polyhydric alcohols. Specific examples of the polyhydric alcohol include diethylene glycol. When the polyhydric alcohol is contained, the hydroxyl groups of the silica are inhibited, and the dispersibility and strength of the silica are improved.

[0069] As the crosslinking agent, sulfur, organic sulfur compounds, disulfides, organic peroxides, etc. can be used. As the organic peroxides used in EPDM and H-NBR, for example, 2,5-dimethyl-2,5-di-tert-butyl-peroxyhexane-3, di-tert-butyl peroxide, 2,5-dimethyl-2,5-di-tert-butyl-peroxyhexane, tert-butyl cumyl peroxide, 1,3-bis(tert-butylperoxy-isopropyl)benzene, dicumyl peroxide, butyl 4,4-di-tert-butylperoxyvalerate, 2,2-di-tert-butylperoxybutane, 1,1-di-tert-butylperoxy-3,3,5-trimethylcyclohexane, benzoyl peroxide, di(o-methylbenzoyl)peroxide, di(p-methylbenzoyl)peroxide, tert-butyl peroxybenzoate, etc. can be exemplified.

[0070] The content of the crosslinking agent in the rubber composition for seals is usually 0.1 to 20 parts by mass, preferably 0.2 to 10 parts by mass, relative to 100 parts by mass of the rubber component. If within this range, the crosslinking reaction can proceed sufficiently, and thus a cushioning material with excellent hardness, mechanical strength, compression set resistance, etc., and excellent impact resistance can be obtained.

[0071] When the rubber composition for seals contains an excessive amount of filler to improve blister resistance, there is a tendency for the hardness to increase, the elongation at break to decrease, and the seals to become brittle. When a plasticizer is contained, these properties are improved and the low-temperature performance also becomes better. However, when a large amount of plasticizer is contained, the plasticizer component is likely to precipitate on the surface of the molded product, or the plasticizer component is likely to be extracted by lubricants such as grease. As a result, a reduction in volume, a decrease in low-temperature performance and heat resistance, and a decrease in sealing performance may be caused. From this point of view, the rubber composition for seals preferably does not contain a plasticizer.

[0072] [Method for manufacturing seals]

[0073] The rubber composition for seals can be prepared by uniformly kneading the above-mentioned components. As the kneading machine, for example, conventionally well-known kneading machines such as a mixing roll, a kneader, and a Banbury mixer can be used. At this time, the components other than the components contributing to the crosslinking reaction (crosslinking accelerator, crosslinking retarder, crosslinking agent, etc.) in each compounding component can be uniformly kneaded in advance, and then the components contributing to the crosslinking reaction are kneaded. The kneading temperature is, for example, around room temperature.

[0074] <Seals>

[0075] The seal is formed from a cross-linked product of the above-described rubber composition for seals. The seal can be produced by cross-linking (vulcanizing) / molding the rubber composition for seals. As the cross-linking / molding method, conventionally known methods such as injection molding, compression molding, and transfer molding can be employed.

[0076] The heating temperature (cross-linking temperature) during molding is, for example, about 100 to 200 °C, and the heating time (cross-linking time) is, for example, about 0.5 to 120 minutes. When using HNBR, EPDM, CR, FKM, or VMQ as the rubber component, post-curing is preferably performed.

[0077] The seal can be a packing, gasket, etc. The shape of the seal can be appropriately selected according to its use, and a representative example is an O-ring with an O-shaped cross-section. The seal is excellent in low-temperature properties and anti-blowing properties, and thus can be preferably used, for example, as a seal for a storage tank for storing high-pressure hydrogen at 80 MPa. In addition, as a storage of high-pressure gas, not only hydrogen, but also when using oxygen, nitrogen, helium, etc., the seal can be preferably used.

[0078] Examples

[0079] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

[0080] [Physical Property Evaluation of Molded Products]

[0081] From a physical property evaluation specimen in the form of a sheet with a thickness of 2 mm produced in accordance with JIS K6250:2006, dumbbell-shaped No. 3 test pieces were demolded in accordance with JIS K6251:2017. The test pieces were stretched at 500 mm / min, and the tensile strength, elongation at break, and 100% tensile stress were measured using a Shopper-type tensile testing machine. In addition, in accordance with JIS K6253:2012, the hardness of the sheet-shaped physical property evaluation specimen was measured using a Type A durometer hardness testing machine. All of these tests were performed at a temperature of 25 °C.

[0082] [High-Temperature and High-Pressure Cycle Test of Seals]

[0083] A seal test specimen molded into an O-ring was installed on a flange, and a cycle test was performed under the conditions shown in Table 1 to evaluate the anti-blowing properties. After the cycle test, the cross-section of the O-ring was observed, and the seal with observed damage was evaluated as "B", and the seal without observed cracks was evaluated as "A". In addition, under the conditions shown in Table 1, the presence or absence of air leakage was detected. The seal with detected air leakage was evaluated as "B", and the seal without detected air leakage was evaluated as "A".

[0084] [Table 1]

[0085] Pressure rising rate 2MPa / s Pressure dropping rate 100MPa / s Maximum pressure 100MPa Minimum pressure 0MPa Maximum pressure holding 1s Minimum pressure holding 1s Number of pressure cycles 50 times Temperature 100℃ Test fluid Helium

[0086] [Low-temperature and high-pressure cycling test of seals]

[0087] A seal test specimen formed into an O-ring was placed on the flange, and a cycling test was conducted under the conditions shown in Table 2. After the test, the cross-section of the O-ring was observed, and the seals with observed breakage were evaluated as "B", while the seals without observed cracks were evaluated as "A". In addition, under the conditions shown in Table 2, air leakage was detected. The test was carried out with or without applying a grease (silicone grease, KF-96H-100 million cSt, manufactured by Shin-Etsu Chemical Co., Ltd.) to the sealing part. The seals with detected air leakage were evaluated as "B", and the seals without observed air leakage were evaluated as "A".

[0088] [Table 2]

[0089] Pressure rising rate 100MPa / s Pressure dropping rate 100MPa / s Maximum pressure 100MPa Minimum pressure 0MPa Maximum pressure holding 1s Minimum pressure holding 1s Number of pressure cycles 50 times Temperature -40℃ Test fluid Helium

[0090] [Preparation of rubber composition for seals and production of molded articles]

[0091] Each component listed in Table 3 was kneaded in a 10L pressure kneader to prepare rubber compositions for seals of the examples and comparative examples. The obtained rubber compositions for seals were put into a mold heated to a temperature of 160 to 180°C and molded by pressure pressing. The molding time was 5 to 20 minutes. Further, secondary vulcanization was carried out at a temperature of 160 to 180°C for 0.5 to 2 hours to obtain specimens for physical property evaluation and seal test specimens.

[0092] The normal physical properties of the specimens for physical property evaluation were measured according to the above evaluation method. The above cycling test was conducted to evaluate the sealing performance of the seal test specimens at high and low temperatures. The results are shown in Table 3.

[0093] [Table 3]

[0094]

[0095] Details of the compounds in Table 3 are as described below. The unit of the compounding amount in the table is parts by mass.

[0096] [1] Rubber component A: ESPRENE 5361 (manufactured by Sumitomo Chemical Co., Ltd., EPDM: the content of structural units derived from ethylene is 49% by mass, the content of structural units derived from 5-ethylidene-2-norbornene (ENB) as a diene monomer is 3.5% by mass, and the Mooney viscosity [ML(1+4)125°C] measured according to JIS K6300-1 at 125°C is 83.)

[0097] 〔2〕 Rubber component B: ESPRENE 501A (manufactured by Sumitomo Chemical Co., Ltd., EPDM: the content of structural units derived from ethylene is 52% by mass, the content of structural units derived from 5-ethylidene-2-norbornene (ENB) as a diene monomer is 4.0% by mass, and the Mooney viscosity [ML(1+4)100°C] measured according to JIS K6300-1 at 100°C is 44.)

[0098] 〔3〕 Vulcanization accelerator: Two types of zinc oxide (manufactured by HAKUSUI TECH Co., Ltd.)

[0099] 〔4〕 Anti-aging agent: Nocrac 224S (manufactured by Ouchi Shinko Chemical Industrial Co., Ltd., 2,2,4-trimethyl-1,2-dihydroquinoline copolymer)

[0100] 〔5〕 Processing aid: LUNAC S50V (manufactured by Kao Corporation, stearic acid)

[0101] 〔6〕 Carbon black: Seast GSO (manufactured by TOKAI CARBON Co., Ltd., furnace black)

[0102] 〔7〕 Silicon dioxide: sidistar (manufactured by Elkem, spherical silicon dioxide, BET surface area 20m 2 / g, CTAB adsorption specific surface area 30m 2 / g, DBP absorption 85g / 100g, average particle size 150nm)

[0103] 〔8〕 Silane coupling agent: KBM1003 (manufactured by Shin-Etsu Chemical Co., Ltd., vinyltrimethoxysilane)

[0104] 〔9〕 Polyol: Diethylene glycol (manufactured by Nippon Catalyst Co., Ltd.)

[0105] 〔10〕 Co-crosslinking agent: HiCross M (manufactured by Seiko Chemical Co., Ltd., trimethylolpropane trimethacrylate)

[0106] 〔11〕 Crosslinking agent A: Sulfur (manufactured by Tsurumi Chemical Co., Ltd., colloidal sulfur)

[0107] 〔12〕 Crosslinking agent B: Perkadox 14-40 (manufactured by Kayaku Akzo Co., Ltd., 40% dilution of bis(tert-butylperoxyisopropyl)benzene, organic peroxide)

[0108] As shown in Table 3, for the seal test specimens of Examples 1 to 3 obtained by crosslinking a rubber composition for seals containing 50 to 140 parts by mass of silica, 1 to 20 parts by mass of a silane coupling agent, and 15 to 35 parts by mass of carbon black with respect to 100 parts by mass of a rubber component, even when exposed to a high-temperature and high-pressure environment, no cracks were observed in the specimen cross-section, and the anti-foaming property was excellent. In addition, air leakage under the high-temperature and high-pressure environment was not confirmed, so it can be known that the seal test specimens of Examples 1 to 3 have excellent sealing performance at high temperatures. When the seal test specimens of Examples 1 to 3 were tested by applying a lubricating grease under a low-temperature and high-pressure environment, no air leakage was confirmed, and the sealing performance at low temperatures was excellent. In addition, it can be known that: in the seal test specimen of Example 1 using EPDM with more excellent cold resistance, even when no lubricating grease was applied at a temperature of -40°C, no air leakage was confirmed, and a seal with more excellent low-temperature properties than those of Examples 2 and 3 was obtained.

[0109] On the other hand, compared with Example 1 or 2, the physical property evaluation specimens of Comparative Examples 1, 2, and 4 had a low 100% tensile stress, and their seal test specimens foamed during the high-temperature and high-pressure cycle test. The hardness of the physical property evaluation specimen of Comparative Example 3 increased, the tensile strength and elongation at break decreased, its seal test specimen foamed during the high-temperature and high-pressure cycle test, and the low-temperature property also decreased.

[0110] [Reference Example]

[0111] By the same method as in Example 1, rubber compositions for seals of Reference Examples 1 and 2 were prepared according to Table 4, and physical property evaluation specimens were obtained. The normal physical properties of the physical property evaluation specimens were measured according to the above evaluation method. The results are shown in Table 4.

[0112] [Table 4]

[0113]

[0114] The details of the compounds in Table 4 are as follows. The unit of the compounding amount in the table is parts by mass.

[0115] 〔1〕Rubber component B: ESPRENE 501A (manufactured by Sumitomo Chemical Co., Ltd., EPDM: the content of the structural unit derived from ethylene is 52% by mass, the content of the structural unit derived from 5-ethylidene-2-norbornene (ENB) as a diene monomer is 4.0% by mass, and the Mooney viscosity [ML(1+4)100°C] measured according to JIS K6300-1 at 100°C is 44.)

[0116] 〔2〕Vulcanization aid: Two types of zinc oxide (manufactured by HAKUSUI TECH Co., Ltd.)

[0117] 〔3〕Antioxidant: Nocrac 224S (manufactured by Ouchi Shinko Chemical Industrial Co., Ltd., 2,2,4 - trimethyl - 1,2 - dihydroquinoline copolymer)

[0118] 〔4〕Processing aid: LUNAC S50V (manufactured by Kao Corporation, stearic acid)

[0119] 〔5〕Carbon black: Seast GSO (manufactured by TOKAI CARBON Co., Ltd., furnace black)

[0120] 〔6〕Silica A: sidistar (manufactured by Elkem, spherical silica, BET surface area 20 m 2 / g, CTAB adsorption specific surface area 30 m 2 / g, DBP absorption 85 g / 100 g, average particle size 150 nm)

[0121] 〔7〕Silica B: AEROSIL 200 (manufactured by Nippon AEROSIL Co., Ltd., BET surface area 200 m 2 / g, hydrophilic fumed silica, average particle size 7 - 40 nm)

[0122] 〔8〕Silane coupling agent: KBM1003 (manufactured by Shin - Etsu Chemical Co., Ltd., vinyltrimethoxysilane)

[0123] 〔9〕Polyol: diethylene glycol (manufactured by Nippon Shokubai Co., Ltd.)

[0124] 〔10〕Co - crosslinking agent A: HiCross M (manufactured by Seiko Chemical Co., Ltd., trimethylolpropane trimethacrylate)

[0125] 〔11〕Co - crosslinking agent B: TAIC (manufactured by Nippon Kasei Co., Ltd., triallyl isocyanurate)

[0126] 〔12〕Crosslinking agent A: sulfur (manufactured by Tsurumi Chemical Co., Ltd., colloidal sulfur)

[0127] 〔13〕Crosslinking agent B: Perkadox 14 - 40 (manufactured by KAYAKU Akzo Co., Ltd., 40% dilution of bis(tert - butylperoxyisopropyl)benzene, organic peroxide)

[0128] It is expected that compared with Example 2, the hardness of the specimen for physical property evaluation of Reference Example 1 containing silica B instead of silica A increases, the tensile strength and elongation at break decrease, and the foam resistance is poor. In addition, it is expected that compared with Example 2, the 100% tensile stress of the specimen for physical property evaluation of Reference Example 2 containing co - crosslinking agent B instead of co - crosslinking agent A decreases, and the foam resistance and low - temperature performance are poor.

Claims

1. A rubber composition for a sealant, which comprises 100 parts by mass of a rubber component, 50 to 140 parts by mass of silica, 1 to 20 parts by mass of a silane coupling agent, 15 to 35 parts by mass of carbon black, 1 to 20 parts by mass of a co-crosslinking agent, and 0.1 to 20 parts by mass of a crosslinking agent. The rubber composition further comprises 0.5 to 5 parts by mass of a processing aid based on 100 parts by mass of the rubber composition. The average particle size of the silica is 50 nm to 200 nm. The rubber component is an ethylene-propylene-diene rubber, and the Mooney viscosity of the ethylene-propylene-diene rubber at 125 °C measured according to JIS K6300-1:2013 is 50 to 90. The ethylene-propylene-diene rubber contains 45 to 49 mass% of structural units derived from ethylene. The co-crosslinking agent is trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, or a combination thereof.

2. The rubber composition for a sealant according to claim 1, wherein the silica is spherical.

3. The rubber composition for a sealant according to claim 1 or 2, wherein no plasticizer is contained.

4. A sealant formed from a crosslinked product of the rubber composition for a sealant according to any one of claims 1 to 3.

Images