JP7202110B2 - Rubber composition for sealing material and sealing material using the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a rubber composition for sealing materials and a sealing material using the same.

Carbon black has long been used as a reinforcing material for rubber. Non-Patent Document 1 (Shintaro Kunizawa, "New Usage of Carbon Black", Journal of the Japan Rubber Association, Vol. 31, No. 9, pp. 749-754, 1958) describes a combination of multiple carbon blacks having different particle sizes and surface properties. It is described that it is possible to improve the processability, reduce the cost, and impart the properties of carbon black by blending it into a rubber composition. However, specific studies on combinations of multiple carbon blacks have not been sufficiently conducted.

Shintaro Kunisawa, "New Usage of Carbon Black", Journal of the Japan Rubber Association, Vol. 31, No. 9, 1958, p. 749-754

Reinforcing agents such as carbon black and silica, which have a small particle size and a large specific surface area, have a high reinforcing effect and increase the mechanical strength (tensile strength) at room temperature and hardness. However, if a large amount of a reinforcing material having a large specific surface area is blended into the rubber composition in order to increase the strength, the hardness of the crosslinked sealing material tends to be too high. Therefore, in order to obtain a sealing material having appropriate hardness, it may be possible to fill only a small amount of reinforcing material having a large specific surface area. Since the tensile strength at high temperatures increases as the content of the reinforcing material increases, a sealing material in which only a small amount of the reinforcing material can be filled cannot obtain sufficient mechanical strength at high temperatures.

On the other hand, when a rubber composition is filled with a reinforcing material having a large particle size and a small specific surface area, the hardness is difficult to increase, so the filling amount can be increased, and the mechanical strength at high temperatures can be increased. However, a sealing material filled with a reinforcing material having a small specific surface area is inferior in mechanical strength at room temperature. In addition, when a large amount of reinforcing material is filled, the repulsive force (permanent compression strain) also decreases. Such a sealing material can be used in fixed parts, but is not suitable for use in driving parts (moving parts) under severe environments such as high temperature and high pressure.

An object of the present invention is to provide a rubber composition for a sealing material that achieves both mechanical strength at room temperature and mechanical strength at high temperature and retains good repulsive force, and a sealing material obtained by cross-linking this. It is to be.

The present invention includes the following.
[1] A rubber composition for a sealing material containing a rubber component and carbon black,
A rubber composition for a sealing material, wherein the particle size distribution of carbon black is multimodal.

[2] The rubber composition for a sealing material according to [1], which contains 25 parts by mass or more and 200 parts by mass or less of carbon black with respect to 100 parts by mass of the rubber component.

[3] The rubber composition for sealing material according to [1] or [2], wherein the carbon black is a mixture of at least two carbon blacks.

[4] The sealing material according to any one of [1] to [3], wherein the carbon black contains at least one kind of carbon black having an arithmetic mean particle size of 1/2 or less of the maximum arithmetic mean particle size. rubber composition.

[5] The rubber composition for sealing materials according to any one of [1] to [4], wherein the carbon black has a difference between the maximum arithmetic mean particle size and the minimum arithmetic mean particle size of 20 nm or more and 450 nm or less. .

[6] Carbon black includes small particle size carbon black having an arithmetic mean particle size of 5 nm or more and less than 100 nm and large particle size carbon black having an arithmetic mean particle size of 100 nm or more and 500 nm or less, [1] to [ 5] The rubber composition for a sealing material according to any one of 5].

[7] The rubber composition for sealing materials according to [6], wherein the mass ratio of the small particle size carbon black and the large particle size carbon black is 10:1 to 1:3.

[8] The rubber composition for sealing materials according to any one of [1] to [7], wherein the carbon black contains MT and at least one selected from the group consisting of MAF and HAF.

[9] The sealing material according to any one of [1] to [8], wherein the rubber component includes at least one selected from the group consisting of vinylidene fluoride rubber, tetrafluoroethylene-propylene rubber and perfluoroelastomer. Rubber composition for

[10] The rubber component contains tetrafluoroethylene-propylene rubber,
Carbon black includes MT, MAF and HAF,
5 parts by mass or more and 10 parts by mass or less of MT per 100 parts by mass of the rubber component, and the total amount of MAF and HAF is 20 parts by mass or more and 30 parts by mass or less, according to any one of [1] to [9] A rubber composition for sealing materials.

[11] A sealing material comprising a crosslinked product of the rubber composition according to any one of [1] to [10].

[12] The sealing material according to [11], which has a hardness of 95 or less as measured according to JIS K6253-3:2012.

[13] The sealing material according to [11] or [12], which is an O-ring.

According to the present invention, there is provided a rubber composition for a sealing material that achieves both mechanical strength at normal temperature and mechanical strength at high temperature and retains good repulsive force, and a sealing material obtained by cross-linking the rubber composition. can do.

The rubber composition for sealing materials of the present invention contains [A] a rubber component and [B] carbon black. Hereinafter, each component contained in the rubber composition for sealing materials of the present invention and optionally contained components will be described in detail.

[A] Rubber component Rubber components include, for example, fluorine rubber, 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), silicone rubber (Q) and the like can be used. From the viewpoint of heat resistance, fluororubber is preferable. Further, as the rubber component used in the present invention, a rubber component having a relatively high Mooney viscosity [ML(1+4) 100°C] at 100°C measured according to JIS K6300-1, for example, 50 or more and 100 or less. is suitable. For example, in the case of a rubber component with a high Mooney viscosity such as fluororubber, the problem of hardness tends to cause the problem that only a smaller amount of reinforcing material can be filled than a rubber component with a low Mooney viscosity. The rubber component may consist of only one type, or may contain two or more types.

Examples of the fluororubber include vinylidene fluoride fluororubber (FKM), tetrafluoroethylene-propylene rubber (FEPM), perfluoroelastomer (tetrafluoroethylene-perfluoromethyl vinyl ether rubber, FFKM), and the like. The rubber component preferably contains at least one selected from the group consisting of FKM, FEPM and FFKM, more preferably FEPM.

FKM is mainly composed of vinylidene fluoride, and includes, for example, vinylidene fluoride (VDF)-chlorotrifluoroethylene-based polymer, vinylidene fluoride (VDF)-hexafluoropropylene (HFP)-based polymer, vinylidene fluoride (VDF)- Hexafluoropropylene (HFP) - tetrafluoroethylene (TFE) polymer, vinylidene fluoride (VDF) - propylene (Pr) - tetrafluoroethylene (TFE) polymer, vinylidene fluoride (VDF) - tetrafluoroethylene ( TFE)-perfluoromethyl vinyl ether (PMVE) based polymer and vinylidene fluoride (VDF)-perfluoromethyl vinyl ether (PMVE) based polymer. Commercially available products of FKM include, for example, "Viton" manufactured by Chemours Co., Ltd. and "DAIEL G" manufactured by Daikin Industries, Ltd.

FEPM is a fluororubber based on alternating copolymers of tetrafluoroethylene (TFE) and propylene (Pr). Commercial products of FEPM include, for example, "AFLAS" manufactured by AGC Corporation.

FFKM is a fluororubber of a copolymer of tetrafluoroethylene (TFE) and perfluoromethyl vinyl ether (PMVE). Commercial products of FFKM include, for example, "Kalrez" manufactured by DuPont.

[B] Carbon Black The particle size distribution of the carbon black contained in the rubber composition for sealing materials according to the present invention is multimodal. When the particle size distribution of carbon black is multimodal, even carbon black having a large specific surface area can be highly filled in the rubber composition for sealing materials, and the mechanical strength can be increased not only at normal temperature but also at high temperature. can be done. The particle size distribution of carbon black is preferably bimodal or trimodal. Here, the particle size distribution can be grasped as follows. First, an electron microscope is used to photograph carbon black particles at an appropriate magnification. 100 or more (for example, 100 or more and 2000 or less) particles are randomly selected from the obtained image, and the primary particle diameter thereof is measured. The particle size distribution of carbon black can be represented by plotting the particle size on the horizontal axis and the number of particles on the vertical axis. Also, the particle size distribution can be determined by a general laser diffraction particle size distribution analyzer.

In the particle size distribution of carbon black, the ratio of the minimum maximum particle size to the maximum maximum particle size is preferably 1:20 to 1:2, more preferably 1:15 to 1:3. In the particle size distribution of carbon black, the difference between the maximum particle size and the minimum maximum particle size is preferably 20 nm or more and 450 nm or less, more preferably 50 nm or more and 400 nm or less. Carbon black preferably includes carbon black having a maximum value at 5 nm or more and less than 100 nm and carbon black having a maximum value at 100 nm or more and 500 nm or less in the particle size distribution of carbon black.

The rubber composition for sealing materials preferably contains carbon black in an amount of 25 to 200 parts by mass, more preferably 30 to 100 parts by mass based on 100 parts by mass of the rubber component. If the blending amount of carbon black is too small, the crosslinked product may not have sufficient mechanical strength, and if the blending amount is too large, the hardness of the crosslinked product may become too high.

Carbon black may be either conductive or non-conductive, and is classified into furnace black, channel black, acetylene black, ketjen black, thermal black, lamp black, etc. according to the manufacturing method. Carbon black preferably includes furnace black.

The iodine adsorption amount of carbon black is preferably 25 g/kg or more and 250 g/kg or less. The iodine adsorption amount of carbon black can be measured by the method described in K 6217-1:2008.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 20 m ² /g or more and 160 m ² /g or less. The nitrogen adsorption specific surface area can be measured by the method described in JIS K6217-2:2001.

Dibutyl phthalate (DBP) absorption of carbon black is preferably 70 ml/100 g or more and 160 ml/100 g or less. Dibutyl phthalate (DBP) absorption can be measured by the method described in JIS K6217-4:2008.

The carbon black is preferably a mixture of at least two carbon blacks, more preferably a mixture of two or three carbon blacks.

The carbon black preferably contains at least two carbon blacks with different arithmetic mean particle sizes. The carbon black contains at least one carbon black having an arithmetic mean particle size of preferably 1/2 or less, more preferably 1/20 or more and 1/3 or less of the maximum arithmetic mean particle size. Here, the arithmetic average particle size is taken by an electron microscope, the primary particle size of carbon black randomly selected from the obtained image is measured, and the arithmetic mean value is obtained.

In carbon black, the difference between the maximum arithmetic mean particle size and the minimum arithmetic mean particle size is preferably 20 nm or more and 450 nm or less, more preferably 50 nm or more and 400 nm or less. When carbon blacks with different arithmetic mean particle sizes are used together, the carbon blacks with small arithmetic mean particle sizes enter the gaps between the carbon blacks with large arithmetic mean particle sizes, and the carbon blacks are dispersed. Black can be highly filled. As a result, even if cracks occur in the sealing material, the cracks are stopped by the presence of the carbon black, and the tensile strength at room temperature and the tensile strength at high temperatures can be further improved.

Carbon black preferably includes small particle size carbon black having an arithmetic mean particle size of 5 nm or more and less than 100 nm, and large particle size carbon black having an arithmetic mean particle size of 100 nm or more and 500 nm or less. Small particle size carbon black has a large specific surface area, for example, an iodine adsorption amount higher than 40 mg/g, and a high reinforcing property. The arithmetic mean particle size of the small particle size carbon black may be 15 nm or more and 60 nm or less. Large particle size carbon black has a small specific surface area and low reinforcing properties. By using carbon blacks with different reinforcing properties together, it becomes possible to fill the carbon black with a higher amount, and the tensile strength can be increased not only at room temperature but also at high temperatures. At this time, the compression set, which is one of the indices of heat resistance, exhibits a good value, and the repulsive force required for the sealing material can be maintained. In addition, since the ratio of the rubber component in the rubber composition for sealing materials is reduced, manufacturing costs can be reduced and swelling of the sealing material can be suppressed when exposed to steam or when immersed in a chemical solution or oil. can. In addition, since the filling rate of carbon black is increased, roll workability is improved, and working efficiency can be improved.

Examples of carbon black include SAF (N110, average particle size: 19 nm, N ₂ SA: 139 m ² /g, DBP absorption: 113 ml/100 g), SAF-HS (average particle size Diameter: 19 nm, N ₂ SA: 142 m ² /g, DBP absorption: 130 ml/100 g), ISAF-LS (N219, average particle size: 23 nm, N ₂ SA: 106 m ² /g, DBP absorption: 75 ml/100 g ), ISAF (N220, average particle size: 23 nm, N ₂ SA: 115 m ² /g, DBP absorption: 113 ml/100 g), N234 (average particle size: 19 nm, N ₂ SA: 124 m ² /g, DBP absorption : 125 ml/100 g), IISAF-HS (N285, average particle size: 26 nm, N ₂ SA: 99 m ² /g, DBP absorption: 129 ml/100 g), HAF-LS (N326, average particle size: 28 nm, N ₂ SA: 84 m ² /g, DBP absorption: 75 ml/100 g), LI-HAF (average particle size: 29 nm, N ₂ SA: 74 m ² /g, DBP absorption: 103 ml/100 g), HAF (N330, average particle Diameter: 28 nm, N ₂ SA: 77 m ² /g, DBP absorption: 101 ml/100 g), N339 (average particle diameter: 26 nm, N ₂ SA: 83 m ² /g, DBP absorption: 128 ml/100 g), HAF- HS (N347, average particle size: 28 nm, N ₂ SA: 82 m ² /g, DBP absorption: 126 ml/100 g), N351 (average particle size: 29 nm, N ₂ SA: 74 m ² /g, DBP absorption: 127 ml /100 g), MAF (average particle size: 38 nm, N ₂ SA: 49 m ² /g, DBP absorption: 133 ml/100 g), FEF (N550, average particle size: 43 nm, N ₂ SA: 42 m ² /g, DBP absorption: 115 ml/100 g), GPF (N660, average particle size: 62 nm, N ₂ SA: 27 m ² /g, DBP absorption: 87 ml/100 g), SRF (N774, average particle size: 66 nm, N ₂ SA: 27 m ² /g, DBP absorption: 68 ml/100 g), FT (N880, average particle size: 122 nm, N ₂ SA: 19 m ² /g, DBP absorption: 42 ml/100 g), MT (N990, average particle size: 250 nm-480 nm, N ₂ SA: 12 m ² /g, DBP absorption: 41 ml/100 g).

Examples of the small particle size carbon black include SAF grade to SRF grade carbon black, and one of them or a combination of two or more of them may be used. Examples of large particle size carbon black include FT grade and MT grade carbon black, and one or two of them may be used in combination.

Carbon black preferably contains MT and at least one selected from the group consisting of MAF and HAF. Commercially available MT carbon products include "HTC #20" manufactured by Shin Nikka Carbon Co., Ltd., and "Thermax" manufactured by Cancarb Limited. Commercial products of MAF carbon include "SEAST 116" manufactured by Tokai Carbon Co., Ltd., and "Asahi 60H" manufactured by Asahi Carbon Co., Ltd., and the like. Commercially available products of HAF carbon include "Diablack H" manufactured by Mitsubishi Chemical Corporation, "SEAST 3" manufactured by Tokai Carbon Co., Ltd., and the like.

The ratio of the arithmetic mean particle size of the small particle size carbon black and the arithmetic mean particle size of the large particle size carbon black is preferably 1:20 to 1:2, more preferably 1:15 to 1:3. .

The mass ratio of small particle size carbon black and large particle size carbon black can be appropriately adjusted depending on the required hardness and mechanical strength, but is preferably 10:1 to 1:3, more preferably 6:1. ~1:1.

The rubber composition for sealing materials preferably contains 0 to 100 parts by mass of small particle size carbon black and 0 to 100 parts by mass of large particle size carbon black based on 100 parts by mass of the rubber component.

A preferred embodiment of the rubber composition for sealing materials according to the present invention is a rubber composition for sealing materials containing a rubber component and carbon black, wherein the rubber component contains a tetrafluoroethylene-propylene rubber, and the carbon black is A rubber composition for a sealing material containing MT, MAF and HAF, containing 5 parts by mass or more and 10 parts by mass or less of MT per 100 parts by mass of a rubber component, and a total amount of MAF and HAF of 20 parts by mass or more and 30 parts by mass or less is mentioned.

[Crosslinking agent]
The cross-linking system of the rubber component is not particularly limited. For example, in the case of FKM and FEPM, the peroxide cross-linking system, polyamine cross-linking system, and polyol cross-linking system may be ethylene-propylene rubber (EPM) or ethylene-propylene-diene rubber (EPDM). For example, peroxide cross-linking system, sulfur cross-linking system, quinoid cross-linking system, resin cross-linking system, if perfluoroelastomer (FFKM), peroxide cross-linking system, bisphenol cross-linking system, triazine cross-linking system, oxazole cross-linking system, imidazole cross-linking system, thiazole crosslinked systems. The rubber component may be crosslinked with any one type of crosslinking system, or may be crosslinked with two or more types of crosslinking systems.

The peroxide cross-linking agent (radical polymerization initiator) used in the peroxide cross-linking system is, for example, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane (commercially available product: NOF Corporation "Perhexa 25B"); dicumyl peroxide (commercially available example: NOF Corporation "Percumyl D"); 2,4-dichlorobenzoyl peroxide; di-t-butyl peroxide; t-butyl dicumyl peroxide; benzoyl Peroxide (Example of commercial product: NOF Corporation "Nyper B"); 2,5-dimethyl-2,5-(t-butylperoxy)hexyne-3 (Example of commercial product: NOF Corporation "Perhexin 25B"); 2,5-dimethyl-2,5-di(benzoylperoxy)hexane; α,α'-bis(t-butylperoxy-m-isopropyl)benzene (commercial examples: manufactured by NOF Corporation "Perbutyl P"); t-butyl peroxyisopropyl carbonate; parachlorobenzoyl peroxide; Only one peroxide crosslinking agent may be used, or two or more thereof may be used in combination.

The content of the cross-linking agent in the rubber composition for sealing material is usually 0.1 parts by mass or more and 10 parts by mass or less, preferably 0.5 parts by mass or more and 5.0 parts by mass with respect to 100 parts by mass of the rubber component. It is below. Within this range, the cross-linking reaction can proceed sufficiently, so that it is possible to obtain a sealing material excellent in hardness, mechanical strength and repulsive force.

[Co-crosslinking agent]
Examples of the co-crosslinking agent used in the peroxide cross-linking system include triallyl isocyanurate (example of commercially available product: “TAIC” manufactured by Nippon Kasei Co., Ltd.); triallyl cyanurate; triallyl formal; triallyl trimellitate; '-m-Phenylenebismaleimide; dipropargyl terephthalate; diallyl phthalate; Only one co-crosslinking agent may be used, or two or more co-crosslinking agents may be used in combination. Among the above, the co-crosslinking agent preferably contains triallyl isocyanurate from the viewpoint of reactivity and heat resistance of the obtained crosslinked rubber molding.

The content of the co-crosslinking agent in the rubber composition for sealing material is 1 part by mass or more and 20 parts by mass or less, more preferably 2 parts by mass or more and 10 parts by mass or less, relative to 100 parts by mass of the rubber component. If the content of the co-crosslinking agent is too small, the 100% tensile stress of the sealing material may decrease, and if it is too large, the elongation at break may decrease.

[Other ingredients]
The rubber composition for sealing materials of the present invention may contain other components than those mentioned above, if necessary. Other contained components include, for example, fillers other than carbon black (including extender pigments and coloring pigments), antioxidants, antioxidants, processing aids, stabilizers, tackifiers, polyhydric alcohols, plasticizers, Additives such as flame retardants, waxes and lubricants can be mentioned. Additives may be used alone or in combination of two or more.

When the rubber composition for sealing material contains the above additives, the content thereof may be an amount commonly used in the relevant field.

Specific examples of fillers are 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. are included.

Specific examples of anti-aging agents include phenol derivatives, aromatic amine derivatives, amine-ketone condensates, benzimidazole derivatives, dithiocarbamic acid derivatives, thiourea derivatives and the like.

Specific examples of vulcanization accelerators include thiuram-based, thiazole-based, sulfenamide-based, thiourea-based, guanidine-based, and dithiocarbamate-based compounds.

Examples of processing aids include thermoplastic resins, liquid rubbers, oils, plasticizers, softeners, internal mold release agents, tackifiers such as stearic acid and zinc oxide. When the rubber component contains FKM, FEPM or FFKM, it may contain a fluororesin or particles thereof as a filler and a liquid fluororubber as a processing aid. When the rubber component comprises EPM or EPDM, it may contain processing aids such as paraffinic oils.

Specific examples of internal release agents include higher fatty acids, fatty acid esters, fatty acid amides, fluororesins, silicone resins, hydrocarbon resins, and the like.

Specific examples of polyhydric alcohols include, for example, diethylene glycol.

Specific examples of plasticizers include narrowly defined plasticizers (phthalate-based, adipate-based, aliphatic dibasic ester-based, phosphate-based, citrate-based, trimellit-based plasticizers, etc.), Oils (naphthenic process oils, paraffinic process oils, aromatic process oils, vegetable oils, epoxidized vegetable oils, etc.) are also included.

The rubber composition of the present invention can be prepared by uniformly kneading the above ingredients. As the kneader, for example, a conventionally known one such as a mixing roll, a pressure kneader, an internal mixer (Banbury mixer) can be used. At this time, among the components to be mixed, the components excluding the components that contribute to the cross-linking reaction (cross-linking accelerator, cross-linking retarder, cross-linking agent, etc.) are first uniformly kneaded, and then the components that contribute to the cross-linking reaction are added. You may make it knead|mix. The kneading temperature is preferably around room temperature, for example.

<Seal material>
The sealing material of the present invention comprises a crosslinked product of the rubber composition for sealing materials according to the present invention. The sealing material can be produced by crosslinking (vulcanizing) and molding a rubber composition for sealing materials. As the cross-linking/molding method, conventionally known methods such as injection molding, compression molding, and transfer molding can be employed.

The heating temperature (crosslinking temperature) during molding is, for example, about 120 to 220° C., and the heating time (crosslinking time) is, for example, about 0.5 to 120 minutes. After vulcanization molding, secondary cross-linking may be performed at a temperature of about 120 to 280° C., if necessary. The secondary cross-linking time is, for example, about 0.5 to 24 hours.

The sealing material may be a packing, a gasket, or the like. The shape of the sealing material is appropriately selected according to its application, and a representative example thereof is an O-ring having an O-shaped cross section.

The sealing material according to the present invention preferably maintains appropriate hardness, and preferably has a hardness of 95 or less as measured according to JIS K6253-3:2012. If the hardness is too high, there is a risk that the sealing performance will deteriorate, especially in the drive section. INDUSTRIAL APPLICABILITY The sealing material according to the present invention has excellent mechanical strength at room temperature and high temperature, and also retains resilience, so that it can be suitably used for driving parts under high temperature and high pressure conditions.

EXAMPLES The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to these.

[Preparation of Rubber Composition for Seal Member and Fabrication of Seal Member]
<Example 1>
A rubber composition for sealing members was prepared according to the following procedure. According to the compounding composition shown in Table 1 (the unit of the compounding amount in Table 1 is parts by mass), predetermined amounts of the rubber component, three types of carbon black, processing aid, cross-linking agent and co-cross-linking agent were added using a 10 L kneader. Kneaded. The resulting kneaded product was thermally crosslinked at 170°C for 10 minutes (first crosslinking step), and then thermally crosslinked at 230°C for 16 hours (second crosslinking step) to obtain a molded product. .

<Example 2>
A sealing material was obtained in the same manner as in Example 1, except that the blending amounts of the three types of carbon black were changed according to Table 1.

<Example 3>
A sealing material was obtained in the same manner as in Example 1, except that two types of carbon black shown in Table 1 were used as the carbon black.

<Example 4>
A sealing material was obtained in the same manner as in Example 1, except that a different cross-linking agent from that in Example 1 was used, and the amount of the co-cross-linking agent and the amount of carbon black were changed according to Table 1.

<Comparative Examples 1 to 3>
A sealing material was obtained in the same manner as in Example 1, except that one type of carbon black shown in Table 1 was blended.

The details of the formulations in Table 1 are as follows.
[1] Rubber component: AFLAS600S (manufactured by AGC Co., Ltd., tetrafluoroethylene-propylene rubber)
[2] Processing aid: sodium stearate (Yoneyama Pharmaceutical Co., Ltd.)
[3] Carbon black 1: MT carbon (Thermax N990 ULTRA-PURE, arithmetic mean particle size 250-350 nm, N ₂ SA: 9 m ² /g, manufactured by Cancarb Limited)
[4] Carbon black 2: MAF carbon (Sheast 116, arithmetic mean particle size 38 nm, N ₂ SA: 49 m ² /g, DBP absorption: 133 ml/100 g, manufactured by Tokai Carbon Co., Ltd.)
[5] Carbon black 3: HAF carbon (Diablack H, average particle size 28-36 nm, N ₂ SA: 79 m ² /g, DBP oil absorption: 105 cm ³ /100 g, manufactured by Mitsubishi Chemical Corporation)
[6] Co-crosslinking agent: TAIC (triallyl isocyanurate, manufactured by Nippon Kasei Co., Ltd.)
[7] Cross-linking agent: Perbutyl P (1,3-bis(t-butylperoxy-isopropyl)benzene, manufactured by NOF Corporation)
[8] Cross-linking agent: Perhexa 25B (2,5-dimethyl-2,5-di-t-butyl-peroxyhexane, manufactured by NOF Corporation)

[Evaluation of physical properties of molded product]
According to JIS K6250:2006, a dumbbell-shaped No. 3 test piece was die-cut according to JIS K6251:2010 from a sheet-like molded product having a thickness of 2 mm. This test piece was pulled at 500 mm/min, and tensile strength, elongation at break, and 100% modulus were measured using a Schopper tensile tester. Further, according to JIS K6253-3:2012, the hardness of the sheet-shaped molding was measured with a type A durometer hardness tester. All these tests were performed at 25°C.

[Hot strength]
After leaving the dumbbell-shaped No. 3 test piece in an atmosphere of 200° C. for 20 minutes or longer, a tensile test was performed in the same manner as above in an atmosphere of 200° C. to measure the hot strength.

[Compression set rate]
The compression set rate was measured according to JIS K 6262:2013. A JIS large test piece (diameter: 29 mm, thickness: 12.7 mm) was sandwiched using spacers so that the compressibility was 25%, and held at 200°C for 72 hours. After releasing the compression of the specimen and allowing it to cool for 30 minutes at the standard temperature of the test room, the thickness of the specimen was measured. The compression set (Compression Set, CS) is expressed by the following formula:
Compression set rate (%) = {(h0-h1)/(h0-h2)} x 100
calculated based on h0 is the thickness (mm) of the test piece before the test, h1 is the thickness (mm) of the test piece after cooling for 30 minutes, and h2 is the thickness (height) (mm) of the spacer.

[Roll workability]
When the rubber composition for sealing material was kneaded using a kneader, the case where no adhesion to the roll was observed was evaluated as "◯", and the case where the adhesion to the roll was observed was evaluated as "Δ".

Table 1 shows the evaluation results. The molded articles of Examples 1 to 3 had high tensile strength at room temperature and high hot strength, indicating excellent mechanical strength at room temperature and high temperature. In addition, the permanent compression strain rate was small, and the repulsive force was maintained. Therefore, when at least two types of carbon black having different arithmetic mean particle sizes are mixed and a sealing material composition containing carbon black having a multimodal particle size distribution is crosslinked, mechanical strength at room temperature and mechanical strength at high temperature are improved. It has been found that a molded product can be obtained that is compatible with the physical strength and retains the repulsive force. Although the molded article of Example 4 used a different cross-linking agent, it had good tensile strength, hot strength and compression set. Moreover, all of Examples 1 to 4 had good roll workability.

In contrast, the molded articles of Comparative Examples 1 to 3 were inferior in at least one of tensile strength, hot strength and compression set. Moreover, in Comparative Examples 1 and 3, roll workability was not good.

Claims (11)

A rubber composition for a sealing material containing a rubber component and carbon black,
The particle size distribution of the carbon black is multimodal,
The rubber component is at least one selected from the group consisting of tetrafluoroethylene-propylene rubber, ethylene-propylene-diene rubber, ethylene-propylene rubber, nitrile rubber, hydrogenated nitrile rubber, butyl rubber and silicone rubber,
The carbon black includes small particle size carbon black having an arithmetic average particle size of 5 nm or more and less than 100 nm, and large particle size carbon black having an arithmetic average particle size of 100 nm or more and 500 nm or less,
The mass ratio of the small particle size carbon black and the large particle size carbon black is 10:1 or more and less than 1:1,
A rubber composition for sealing materials that does not contain talc and carbon nanofibers. 2. The rubber composition for a sealing material according to claim 1, comprising 25 parts by mass or more and 200 parts by mass or less of said carbon black with respect to 100 parts by mass of said rubber component. 3. The rubber composition for a sealing material according to claim 1, wherein said carbon black is a mixture of at least two carbon blacks. The rubber composition for a sealing material according to any one of claims 1 to 3, wherein the carbon black contains at least one kind of carbon black having an arithmetic mean particle size of 1/2 or less of the maximum arithmetic mean particle size. thing. The rubber composition for a sealing material according to any one of claims 1 to 4, wherein the carbon black has a difference between a maximum arithmetic mean particle size and a minimum arithmetic mean particle size of 20 nm or more and 450 nm or less. The rubber composition for sealing material according to any one of claims 1 to 5, wherein the carbon black contains MT and at least one selected from the group consisting of MAF and HAF. The rubber composition for sealing materials according to any one of claims 1 to 6, wherein the rubber component contains tetrafluoroethylene -propylene rubber . the rubber component comprises tetrafluoroethylene-propylene rubber;
the carbon black includes MT, MAF and HAF;
8. The rubber component according to any one of claims 1 to 7, comprising 5 parts by mass or more and 10 parts by mass or less of MT, and a total amount of 20 parts by mass or more and 30 parts by mass or less of MAF and HAF, based on 100 parts by mass of the rubber component. rubber composition for sealing materials. A sealing material comprising a crosslinked product of the rubber composition according to any one of claims 1 to 8. 10. The sealing material according to claim 9, which has a hardness of 95 or less as measured according to JIS K6253-3:2012. The sealing material according to claim 9 or 10, which is an O-ring.