Rubber composition, vulcanized molded article, and diaphragm

Abstract

To provide a rubber composition by which a vulcanized molded article with superior nitrogen gas resistance and flex fatigue resistance can be obtained, a vulcanized molded article with superior nitrogen gas resistance and flex fatigue resistance, and a diaphragm including the vulcanized molded article.SOLUTION: The present invention provides a rubber composition comprising a chloroprene-based rubber, wherein the chloroprene-based rubber comprises a chloroprene-based rubber containing 5 to 20 mass% of an unsaturated nitrile monomer unit, and wherein the rubber composition is intended for use in a diaphragm.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a rubber composition, a vulcanizate, and a diaphragm.

[0002] Rubber compositions containing chloroprene rubber have excellent mechanical strength, weather resistance, chemical resistance, heat resistance, cold resistance, and oil resistance, and are therefore widely used as materials for general industrial transmission belts and conveyor belts, automotive air springs, vibration-proof rubber, hoses, wipers, immersion products, sealing parts, adhesives, boots, rubber-coated fabrics, rubber rolls, and other products.

[0003] For example, Patent Document 1 discloses an invention relating to a sulfur-modified chloroprene rubber composition comprising a sulfur-modified chloroprene rubber, a vulcanization accelerator, zinc oxide, and magnesium oxide, wherein the blending amount of the vulcanization accelerator is 0.1 to 5 parts by weight, and the blending amounts of zinc oxide and magnesium oxide are specified by a predetermined relational expression between each blending amount and the Mooney scorch time t. Furthermore, Patent Document 2 discloses an invention relating to a copolymer of a chloroprene monomer and an unsaturated nitrile compound, which has a Mooney viscosity ML(1+4)100°C of 20 to 80 and has a functional group with a specific structure. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-209522 [Patent Document 2] International Publication No. 2020 / 044899 Summary of the Invention [Problem to be solved by the invention]

[0005] However, conventional rubber compositions have room for improvement in the nitrogen gas resistance and flex fatigue resistance of vulcanized molded articles of the compositions.

[0006] The present invention has been made in consideration of the above circumstances, and provides a rubber composition that can give a vulcanized molded article having excellent nitrogen gas resistance and flexural fatigue resistance, a vulcanized molded article having excellent nitrogen gas resistance and flexural fatigue resistance, and a diaphragm comprising the vulcanized molded article. [Means for solving the problem]

[0007] According to the present invention, there is provided a rubber composition containing a chloroprene-based rubber, the chloroprene-based rubber containing 5 to 20 mass% of unsaturated nitrile monomer units, and the rubber composition is for use in a diaphragm.

[0008] As a result of extensive research, the present inventors have newly discovered that, in a rubber composition containing a chloroprene-based rubber, by adding a chloroprene-based rubber containing a specific amount of unsaturated nitrile monomer units to the rubber composition, a rubber composition can be obtained from which a vulcanized molded article having excellent nitrogen gas resistance and flexural fatigue resistance can be obtained, and in particular, a rubber composition from which a vulcanized molded article having properties suitable for diaphragm applications can be obtained, thereby completing the present invention.

[0009] Various embodiments of the present invention will be described below as examples, and the embodiments described below can be combined with each other. [1] A rubber composition containing a chloroprene-based rubber, the chloroprene-based rubber containing 5 to 20 mass% of unsaturated nitrile monomer units, and the rubber composition is for use in a diaphragm. [2] The rubber composition according to [1], further comprising a plate-like filler. [3] A rubber composition comprising a chloroprene-based rubber, the chloroprene-based rubber containing 5 to 20 mass% of unsaturated nitrile monomer units, and the rubber composition also containing a platy filler. [4] The rubber composition according to [2] or [3], comprising 10 to 130 parts by mass of the platy filler per 100 parts by mass of the chloroprene rubber. [5] The rubber composition according to any one of [1] to [4], comprising 1.0 to 15.0 parts by mass of a softener per 100 parts by mass of the chloroprene rubber. [6] The rubber composition according to any one of [1] to [5], further comprising 0.1 to 7.0 parts by mass of a processing aid per 100 parts by mass of the chloroprene rubber. [7] The rubber composition according to any one of [1] to [6], wherein the content of the vulcanization accelerator A relative to 100 parts by mass of the chloroprene rubber is 3.0 parts by mass or less, and the vulcanization accelerator A is at least one selected from the group consisting of thiuram compounds, sulfenamide compounds, and thiazole compounds. [8] The rubber composition according to any one of [1] to [7], wherein the content of antioxidant A per 100 parts by mass of the chloroprene rubber is 3.0 parts by mass or less, and the antioxidant A is at least one selected from the group consisting of imidazole antioxidants and bisphenol antioxidants. [9] The rubber composition according to any one of [1] to [8], wherein a volume change rate ΔV of a vulcanized molded product of the rubber composition when immersed in engine oil 10W-30 at 100°C for 72 hours is 10% or less.

[10] The rubber composition according to [1] or [3], wherein when a vulcanized molded product of the rubber composition is subjected to a De Mattia flexural fatigue test in accordance with JIS K6260 under conditions of a stroke of 58 mm, a speed of 300±10 rpm, and 23°C, the number of flexural fatigue tests at which cracks occur exceeds 1,000.

[11] A vulcanized molded article of the rubber composition according to [1] or [3].

[12] A diaphragm comprising the vulcanized molded article according to

[11] . [Effects of the Invention]

[0010] The rubber composition according to the present invention can provide a vulcanized molded article having excellent nitrogen gas resistance and flexural fatigue resistance. Furthermore, the vulcanized molded article according to the present invention has excellent nitrogen gas resistance and flexural fatigue resistance, making it particularly suitable for diaphragm applications. The diaphragm according to the present invention includes a vulcanized molded article having excellent nitrogen gas resistance and flexural fatigue resistance, and therefore suffers less wear when exposed to nitrogen gas than conventional diaphragms, and suffers less from defects such as cracks caused by repeated flexing, resulting in a longer life. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described in detail below by illustrating embodiments of the present invention. The present invention is not limited by these descriptions. The features of the embodiments of the present invention described below can be combined with each other. Furthermore, each feature can be an invention independently.

[0012] 1. First perspective 1.1 Rubber composition A rubber composition according to a first aspect of the present invention is a rubber composition containing a chloroprene-based rubber, the chloroprene-based rubber containing 5 to 20 mass % of unsaturated nitrile monomer units, and the rubber composition is for use in a diaphragm. A rubber composition according to one embodiment of the present invention is a rubber composition containing a chloroprene-based rubber, and by adding a chloroprene-based rubber containing a specific amount of unsaturated nitrile monomer units to the rubber composition, it is possible to obtain a vulcanized molded article having the properties required, particularly in diaphragm applications. A vulcanized molded article made from a rubber composition according to one embodiment of the present invention has excellent nitrogen gas resistance and flex fatigue resistance. Furthermore, a vulcanized molded article made from a rubber composition according to one embodiment of the present invention also has excellent oil resistance, particularly resistance to engine oil. Diaphragm vulcanized molded articles used in diaphragm pumps are used under harsh conditions, with one surface exposed to nitrogen gas and the other surface exposed to oil such as engine oil, and are repeatedly flexed. Because of this, defects can occur with repeated use, and the life of the vulcanized molded article constituting the diaphragm can sometimes be rate-limiting for the life of the product. The present invention has newly discovered the advantage that, when a vulcanized article made from a rubber composition containing a specific chloroprene-based rubber is used in a diaphragm used under such specific and harsh conditions, the occurrence of defects can be suppressed and the life can be extended. Furthermore, the rubber composition according to one embodiment of the present invention exhibits low roll adhesion in the preparation process of a vulcanized molded product, resulting in excellent moldability, and / or causes little mold contamination during molding, making it possible to efficiently produce vulcanized molded products, and is also advantageous in terms of cost and effort.

[0013] 1.1.1 Chloroprene rubber The chloroprene rubber according to the present invention refers to a rubber containing a chloroprene polymer having chloroprene (2-chloro-1,3-butadiene) as a monomer unit (monomer unit = structural unit). Examples of the chloroprene polymer include a chloroprene homopolymer and a chloroprene copolymer (a copolymer of chloroprene and a monomer copolymerizable with chloroprene). The polymer structure of the chloroprene polymer is not particularly limited.

[0014] Commercially available 2-chloro-1,3-butadiene may contain a small amount of 1-chloro-1,3-butadiene as an impurity. 2-chloro-1,3-butadiene containing such a small amount of 1-chloro-1,3-butadiene can also be used as the chloroprene monomer of this embodiment.

[0015] The chloroprene rubber according to the present invention contains a chloroprene rubber containing an unsaturated nitrile monomer unit. The chloroprene-based rubber according to the present invention may contain one or more chloroprene-based rubbers. The chloroprene-based rubber according to one embodiment of the present invention may contain a chloroprene-based rubber containing one or more unsaturated nitrile monomer units. The chloroprene-based rubber according to one embodiment of the present invention may further contain a chloroprene-based rubber that does not contain one or more unsaturated nitrile monomer units.

[0016] The chloroprene-based rubber (the chloroprene-based rubber containing unsaturated nitrile monomer units and the chloroprene-based rubber not containing unsaturated nitrile monomer units) according to one embodiment of the present invention may contain monomer units derived from a monomer other than the chloroprene monomer and the unsaturated nitrile monomer. The monomer other than the chloroprene monomer and the unsaturated nitrile monomer is not particularly limited as long as it is copolymerizable with the chloroprene monomer, and examples thereof include (meth)acrylic acid esters (e.g., methyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate), hydroxyalkyl (meth)acrylates (e.g., 2-hydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate), 2,3-dichloro-1,3-butadiene, 1-chloro-1,3-butadiene, butadiene, isoprene, ethylene, styrene, and sulfur. For example, the chloroprene-based rubber according to one embodiment of the present invention may include 2,3-dichloro-1,3-butadiene monomer units.

[0017] The chloroprene-based rubber containing unsaturated nitrile monomer units according to the present invention contains 5 to 20% by mass of unsaturated nitrile monomer units. The content of unsaturated nitrile monomer units in the chloroprene-based rubber containing unsaturated nitrile monomer units according to one embodiment of the present invention is, for example, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20% by mass, and may be within a range between any two of the values exemplified here. By setting the content of unsaturated nitrile monomer units in the rubber composition within the above-mentioned range, the nitrogen gas resistance and flex fatigue resistance of the vulcanized molded article can be improved. Furthermore, the oil resistance, particularly the resistance to engine oil, of the vulcanized molded article can be improved.

[0018] When the chloroprene-based rubber according to one embodiment of the present invention contains two or more chloroprene-based rubbers, the content of unsaturated nitrile monomer units contained in the two or more chloroprene-based rubbers based on the total amount of the two or more chloroprene-based rubbers contained in the rubber composition is preferably within the above-mentioned range, based on 100% by mass of the total of the two or more chloroprene-based rubbers contained in the rubber composition. That is, in the chloroprene-based rubber according to one embodiment of the present invention, the content of unsaturated nitrile monomer units in the chloroprene-based rubber contained in the rubber composition is preferably 5 to 20% by mass, based on 100% by mass of the chloroprene-based rubber contained in the rubber composition, and the content of the unsaturated nitrile monomer units may be within a range between any two of the above-mentioned numerical values. Furthermore, in the chloroprene-based rubber according to one embodiment of the present invention, the content of acrylonitrile monomer units in the chloroprene-based rubber contained in the rubber composition is preferably 5 to 20% by mass, based on 100% by mass of the chloroprene-based rubber contained in the rubber composition, and the content of the acrylonitrile monomer units may be within a range between any two of the above-mentioned numerical values.

[0019] Examples of unsaturated nitriles include acrylonitrile, methacrylonitrile, ethacrylonitrile, and phenylacrylonitrile. The unsaturated nitriles can be used alone or in combination of two or more. The unsaturated nitrile preferably contains acrylonitrile, from the viewpoint of easily obtaining excellent moldability and easily obtaining excellent breaking strength, breaking elongation, hardness, tear strength, and oil resistance in a vulcanized molded product.

[0020] The content of unsaturated nitrile monomer units in chloroprene-based rubber can be calculated from the nitrogen atom content in the chloroprene-based rubber. Specifically, the nitrogen atom content of 100 mg of chloroprene-based rubber is measured using an elemental analyzer (Sumigraph 220F, manufactured by Sumika Chemical Analysis Center, Ltd.), and the content of structural units derived from unsaturated nitrile monomers can be calculated. Elemental analysis can be performed under the following conditions. For example, the electric furnace temperatures are set to 900°C for the reactor, 600°C for the reduction furnace, 70°C for the column, and 100°C for the detector. Oxygen is used as the combustion gas at a flow rate of 0.2 mL / min, and helium is used as the carrier gas at a flow rate of 80 mL / min. A calibration curve can be created using aspartic acid (10.52%), which has a known nitrogen content, as a standard substance.

[0021] The chloroprene rubber according to one embodiment of the present invention preferably contains 80 to 95% by mass of chloroprene monomer units when the chloroprene rubber is taken as 100% by mass. The content of chloroprene monomer units in the chloroprene rubber is, for example, 80, 85, 90, or 95% by mass, and may be within a range between any two of the values exemplified here. By setting the content of chloroprene monomer units within the above range, a rubber composition can be obtained that can give a molded article with an excellent balance of hardness, tensile strength, and cold resistance.

[0022] A chloroprene-based rubber according to one embodiment of the present invention may contain 0 to 20 mass% of monomer units other than chloroprene monomer units and unsaturated nitrile monomer units, when the chloroprene-based rubber is taken as 100 mass%. The content of monomer units other than chloroprene monomer units and unsaturated nitrile monomer units in the chloroprene-based rubber may be, for example, 0, 2, 4, 6, 8, 10, 12, 14, 16, 18, or 20 mass%, and may be within a range between any two of the values exemplified here. By adjusting the copolymerization amount of monomers other than chloroprene monomers and unsaturated nitrile monomers to fall within the above range, the effects of copolymerizing these monomers can be achieved without impairing the properties of the resulting rubber composition.

[0023] When a rubber composition according to one embodiment of the present invention contains two or more types of chloroprene-based rubber, it is preferable that the content based on the total amount of each monomer unit contained in the two or more types of chloroprene-based rubber falls within the above-mentioned numerical range relative to 100% by mass of the total of the two or more types of chloroprene-based rubber contained in the rubber composition.

[0024] The chloroprene polymer (chloroprene homopolymer, chloroprene copolymer, etc.) contained in the chloroprene rubber according to the present invention may be a sulfur-modified chloroprene polymer, a mercaptan-modified chloroprene polymer, a xanthogen-modified chloroprene polymer, a dithiocarbonate-based chloroprene polymer, a trithiocarbonate-based chloroprene polymer, a carbamate-based chloroprene polymer, etc.

[0025] The weight average molecular weight (Mw), number average molecular weight (Mn), and molecular weight distribution (polydispersity of molecular weight, Mw / Mn) of the chloroprene rubber may be within the following ranges, from the viewpoint of easily obtaining well-balanced mechanical properties, etc.

[0026] The weight average molecular weight of the chloroprene rubber is, for example, 10 × 10 3 g / mol, 50 × 10 3 g / mol, 100 × 10 3 g / mol, 300 × 10 3 g / mol, 400 × 103 g / mol, 450 × 10 3 g / mol, 500 × 10 3 g / mol, 800 × 10 3 g / mol, 1000 × 10 3 g / mol, 2000 × 10 3 g / mol, 3000 × 10 3 g / mol, 5000 × 10 3 g / mol and may be within a range between any two of the values exemplified herein.

[0027] The number average molecular weight of chloroprene rubber is, for example, 1 × 10 3 g / mol, 5 × 10 3 g / mol, 10 × 10 3 g / mol, 50 × 10 3 g / mol, 100 × 10 3 g / mol, 130 × 10 3 g / mol, 200 × 10 3 g / mol, 300 × 10 3 g / mol, 500 × 10 3 g / mol, 800 × 10 3 g / mol, 1000 × 10 3 g / mol and may be within a range between any two of the values exemplified herein.

[0028] The molecular weight distribution of the chloroprene rubber is 1.0, 1.5, 2.0, 2.5, 3.0, 3.2, 3.4, 3.5, 3.8, 4.0, 5.0, 8.0, or 10, and may be within a range between any two of the numerical values exemplified here.

[0029] The weight average molecular weight (Mw) and number average molecular weight (Mn) of the chloroprene rubber can be measured by gel permeation chromatography (GPC) and converted into polystyrene equivalents, and specifically, can be measured by the method described in the examples.

[0030] 1.1.2 Chloroprene rubber manufacturing method The method for producing the chloroprene rubber according to the present invention is not particularly limited, but the rubber can be obtained by a production method including an emulsion polymerization step of emulsion polymerizing raw material monomers including a chloroprene monomer. In an emulsion polymerization process according to one embodiment of the present invention, raw material monomers containing a chloroprene monomer and, if necessary, an unsaturated nitrile monomer are emulsion-polymerized using appropriate emulsifiers, dispersants, catalysts, chain transfer agents, etc., and when the target final conversion rate is reached, a polymerization terminator is added to obtain a latex containing a chloroprene polymer containing chloroprene monomer units. Next, unreacted monomers can be removed from the polymerization solution obtained by the emulsion polymerization process. This method is not particularly limited, and examples include steam stripping. The pH is then adjusted, and the resulting mixture is subjected to conventional processes such as freeze coagulation, water washing, and hot air drying to obtain a chloroprene rubber containing a chloroprene polymer.

[0031] The polymerization initiator used in emulsion polymerization is not particularly limited, and any known polymerization initiator generally used in emulsion polymerization of chloroprene can be used. Examples of the polymerization initiator include potassium persulfate, ammonium persulfate, sodium persulfate, hydrogen peroxide, and organic peroxides such as t-butyl hydroperoxide.

[0032] The emulsifier used in emulsion polymerization is not particularly limited, and any known emulsifier generally used in emulsion polymerization of chloroprene can be used. Examples of the emulsifier include alkali metal salts of saturated or unsaturated fatty acids having 6 to 22 carbon atoms, alkali metal salts of rosin acid or disproportionated rosin acid (e.g., potassium rosinate), and alkali metal salts of formalin condensates of β-naphthalenesulfonic acid (e.g., sodium salt).

[0033] The molecular weight modifier used in emulsion polymerization is not particularly limited, and any known molecular weight modifier commonly used in emulsion polymerization of chloroprene can be used, such as mercaptan compounds, xanthogen compounds, dithiocarbonate compounds, trithiocarbonate compounds, and carbamate compounds. Xanthogen compounds, dithiocarbonate compounds, trithiocarbonate compounds, and carbamate compounds are preferably used as molecular weight modifiers for the chloroprene rubber according to one embodiment of the present invention.

[0034] The polymerization temperature and the final conversion rate of the monomer are not particularly limited, but the polymerization temperature may be, for example, 0 to 50°C or 10 to 50°C. The polymerization may be carried out so that the final conversion rate of the monomer falls within the range of 40 to 95% by mass. In order to adjust the final conversion rate, a polymerization terminator that terminates the polymerization reaction may be added to terminate the polymerization when the desired conversion rate is reached.

[0035] The polymerization terminator is not particularly limited, and any known polymerization terminator commonly used in emulsion polymerization of chloroprene can be used, such as phenothiazine (thiodiphenylamine), 4-t-butylcatechol, and 2,2-methylenebis-4-methyl-6-t-butylphenol.

[0036] The chloroprene rubber according to one embodiment of the present invention can be obtained, for example, by removing unreacted monomers by a steam stripping method, adjusting the pH of the latex, and then performing conventional steps such as freeze coagulation, water washing, and hot air drying.

[0037] Chloroprene rubbers are classified into mercaptan-modified, xanthogen-modified, sulfur-modified, dithiocarbonate-based, trithiocarbonate-based and carbamate-based types depending on the type of molecular weight modifier.

[0038] 1.1.3 Other rubbers The rubber composition according to one embodiment of the present invention may contain rubbers other than chloroprene-based rubber. Examples of other rubbers include natural rubber (NR), hydrogenated acrylonitrile butadiene rubber (H-NBR), acrylonitrile butadiene rubber (NBR), chlorosulfonated polyethylene (CSM), ethylene-propylene-diene rubber (EPDM), isoprene rubber (IR), styrene-butadiene rubber (SBR), epoxidized natural rubber (ENR), acrylonitrile butadiene rubber (NBR), styrene-isoprene-butadiene copolymer rubber (SIBR), epichlorohydrin rubber (CO), acrylic rubber (ACM), urethane rubber (U), silicone rubber (Q), fluororubber (FKM), and polysulfide rubber (T). The rubber according to one embodiment of the present invention may not contain polybutadiene rubber. The polybutadiene rubber may be a rubber composed of butadiene homopolymer.

[0039] A rubber composition according to one embodiment of the present invention preferably contains 50% by mass or more of chloroprene rubber when the rubber contained in the rubber composition is 100% by mass. The content of chloroprene rubber may be, for example, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100% by mass, or may be within a range between any two of the values exemplified here. A rubber composition according to one embodiment of the present invention preferably contains 50% by mass or more of a chloroprene rubber containing an unsaturated nitrile monomer unit, assuming that the rubber contained in the rubber composition is 100% by mass. The content of the chloroprene rubber may be, for example, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100% by mass, or may be within a range between any two of the values exemplified here. The rubber composition according to one embodiment of the present invention preferably contains 20% by mass or more of rubber when the rubber composition is taken as 100% by mass, for example, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100% by mass, and may be within a range between any two of the numerical values exemplified here. The rubber composition according to one embodiment of the present invention preferably contains 20% by mass or more of chloroprene rubber when the rubber composition is taken as 100% by mass, for example, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100% by mass, and may be within a range between any two of the numerical values exemplified here.

[0040] 1.1.4 Plate-like fillers The rubber composition according to one embodiment of the present invention may contain a plate-like filler. The plate-like filler refers to a filler that has a flat shape and extends in a plane. The rubber composition according to one embodiment of the present invention can further improve nitrogen gas resistance and oil resistance by including a platy filler. The rubber composition according to one embodiment of the present invention can include one or more types of platy fillers.

[0041] The plate-like filler preferably has a plate-like (layered) crystal structure. The plate-like filler preferably comprises one or more selected from inorganic fillers such as talc (magnesium silicate hydrate, for example, Imeflex T20), clay (aluminum silicate hydrate, for example, Dexy Clay), mica (mica), boron nitride, plate-like carbon, and organic fillers such as coal pulverization, and more preferably comprises one or more selected from talc (magnesium silicate hydrate, for example, Imeflex T20), clay (aluminum silicate hydrate, for example, Dexy Clay).

[0042] The plate-like filler can have an average particle size of 0.1 to 30 μm. The average particle size is, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30 μm, and may be within a range between any two of the values exemplified here. Here, the average particle size can be the average particle size on a mass basis calculated from the particle size distribution measured in accordance with JIS Z 8815-1994. The aspect ratio of the plate-like filler can be 2 or more, and can be 2 to 1000. The aspect ratio is, for example, 2, 3, 5, 10, 20, 30, 40, 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, or 1000, and may be within a range between any two of the numerical values exemplified here. The aspect ratio can be calculated by dividing the major axis of the particle by the thickness, and the major axis and thickness can be values measured using an electron microscope such as a SEM.

[0043] A rubber composition according to one embodiment of the present invention may contain 10 to 130 parts by mass, and preferably 20 to 100 parts by mass, of a platy filler relative to 100 parts by mass of the chloroprene rubber contained in the rubber composition. The amount of the platy filler is, for example, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, or 130 parts by mass, or may be within a range between any two of the numerical values exemplified here. The rubber composition according to one embodiment of the present invention can further improve the nitrogen gas resistance and oil resistance by containing the platy filler in an amount within the above range.

[0044] 1.1.5 Other fillers and reinforcing agents A rubber composition according to one embodiment of the present invention may contain a filler and / or a reinforcing agent other than the platy filler. The filler and reinforcing agent other than the platy filler may be a spherical or nearly spherical filler, and may have an aspect ratio of less than 2. Examples of fillers and reinforcing agents other than the platy filler include furnace carbon blacks such as SAF, ISAF, HAF, EPC, XCF, FEF, GPF, HMF, and SRF; modified carbon blacks such as hydrophilic carbon black; thermal carbons such as channel black, lamp black, FT, and MT; acetylene black; ketjen black; silica; and calcium carbonate. A rubber composition according to one embodiment of the present invention may contain one or more fillers and / or reinforcing agents other than the platy filler.

[0045] In a rubber composition according to one embodiment of the present invention, the content of the filler other than the platy filler and the reinforcing agent relative to 100 parts by mass of the chloroprene rubber can be 0 to 100 parts by mass. The content of the filler other than the platy filler and the reinforcing agent is, for example, 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 parts by mass, and may be within a range between any two of the numerical values exemplified here. In the rubber composition according to one embodiment of the present invention, the hardness of the vulcanized molded product can be adjusted by including the content of the filler other than the platy filler and the reinforcing agent within the above-mentioned numerical ranges.

[0046] A rubber composition according to one embodiment of the present invention may contain a total of 10 to 160 parts by mass, and preferably 20 to 140 parts by mass, of filler per 100 parts by mass of chloroprene-based rubber contained in the rubber composition. The total filler content is, for example, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, or 160 parts by mass, or may be within a range between any two of the numerical values exemplified here. The rubber composition according to one embodiment of the present invention contains a platy filler, and may also contain a platy filler and a filler and / or a reinforcing agent other than the platy filler. A rubber composition according to one embodiment of the present invention may contain 10% by mass or more of a platy filler relative to 100% by mass of the filler contained in the rubber composition. The content ratio of the platy filler may be, for example, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100% by mass, or may be within a range between any two of the values exemplified here.

[0047] 1.1.6 Softeners The rubber composition according to one embodiment of the present invention may contain a softener. Softeners are primarily used to impart plasticity to rubber and reduce the hardness of vulcanized products. It is preferable that the softener has a certain level of compatibility with the chloroprene-based rubber. However, if the compatibility is too high, roll adhesion may deteriorate, so it is preferable that the softener has an appropriate level of compatibility with the chloroprene-based rubber. Examples of softeners include vegetable oils such as castor oil, rapeseed oil, linseed oil, soybean oil, olive oil, and coconut oil. These may be used alone or in combination of two or more. From the viewpoint of having suitable compatibility with chloroprene-based rubber, the rubber composition according to one embodiment of the present invention preferably contains vegetable oil, more preferably rapeseed oil, linseed oil or soybean oil, and particularly preferably rapeseed oil.

[0048] A rubber composition according to one embodiment of the present invention may contain 15 parts by mass or less, and preferably 1.0 to 15.0 parts by mass, of a softener per 100 parts by mass of chloroprene rubber. The content of the softener may be, for example, 0, 0.1, 0.5, 1.0, 5.0, 10.0, or 15.0 parts by mass, or may be within a range between any two of the values exemplified here.

[0049] By containing a softener in the above-described manner, the rubber composition according to one embodiment of the present invention can more effectively achieve both reduced roll adhesion in the preparation process of a vulcanized molded body and reduced mold contamination during molding.

[0050] 1.1.7 Processing aids The rubber composition according to the present invention may contain a processing aid, which is added mainly to improve processability, such as by making the rubber composition easier to release from rolls, molding dies, extruder screws, etc.

[0051] The rubber composition according to one embodiment of the present invention may contain 15 parts by mass or less, and preferably 1.0 to 7.0 parts by mass, of a processing aid per 100 parts by mass of chloroprene rubber. The content of the processing aid is, for example, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5.0, 5, 5.5, 6.0, 6.5, or 7.0 parts by mass, and may be within a range between any two of the values exemplified here.

[0052] The processing aid preferably includes at least one selected from the group consisting of fatty acid ester lubricants such as stearic acid, stearic acid monoamide (e.g., Alflow S-10, manufactured by NOF Corporation), organosilicon compounds (e.g., WS-180, 280, 212, and 16, manufactured by Struktol Company of America, LLC), microcrystalline wax (e.g., Hi-Mic 1080, manufactured by Nippon Seiro Co., Ltd.), polyethylene wax (e.g., ACPE617A, manufactured by Allied Signal), paraffin wax (e.g., Sunnock N, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.), and wax-based processing aids such as petrolatum, and rubber-based processing aids such as polybutadiene rubber (e.g., JSR BR01, manufactured by JSR Corporation). The polybutadiene rubber is preferably composed of a butadiene homopolymer. Furthermore, from the viewpoint of achieving both the processability of the resulting rubber composition and the mechanical properties of the vulcanized molded product, it is preferable that the processing aid according to one embodiment of the present invention contains two or more types of processing aids, and it is preferable that it contains at least two types selected from the group consisting of the specific examples listed above. For example, a rubber composition according to an embodiment of the present invention preferably contains a wax-based processing aid (e.g., polyethylene wax) and a rubber-based processing aid (e.g., polybutadiene rubber). The rubber composition according to an embodiment of the present invention may contain, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, or 7.0 parts by mass of the paraffin-based processing aid (e.g., polyethylene wax) and the rubber-based processing aid (e.g., polybutadiene rubber), and may be within a range between any two of the numerical values exemplified here. A rubber composition according to one embodiment of the present invention may contain, for example, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 6.6, 6.7, 6.8, or 6.9 parts by mass of a paraffin-based processing aid (e.g., polyethylene wax), and may be within a range between any two of the values exemplified herein. A rubber composition according to one embodiment of the present invention may contain, for example, 0.1, 0.2, 0.3, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, or 6.5 parts by mass of a rubber-based processing aid (e.g., polybutadiene rubber), and may be within a range between any two of the values exemplified herein.

[0053] By containing the processing aid in the above-described manner, the rubber composition according to one embodiment of the present invention can more effectively achieve both reduced roll adhesion in the preparation process of a vulcanized molded product and reduced mold contamination during molding.

[0054] 1.1.8 Vulcanizing agents and vulcanization accelerators The rubber composition according to the present invention may contain a vulcanizing agent and / or a vulcanization accelerator. The types of vulcanizing agent and vulcanization accelerator are not particularly limited as long as they do not impair the effects of the present invention. The vulcanizing agent and vulcanization accelerator preferably contribute to the vulcanization of the chloroprene rubber.

[0055] One or more vulcanizing agents can be freely selected and used. Examples of the vulcanizing agent include sulfur, zinc oxide, and maleimide-based compounds. The vulcanizing agent preferably contains at least one of zinc oxide and maleimide-based compounds, and may also contain zinc oxide and maleimide-based compounds. Examples of maleimide compounds include N,N'-o-phenylene bismaleimide, N,N'-m-phenylene bismaleimide, N,N'-p-phenylene bismaleimide, N,N'-(4,4'-diphenylmethane) bismaleimide, 2,2-bis-[4-(4-maleimidophenoxy)phenyl]propane, bis(3-ethyl-5-methyl-4-maleimidophenyl)methane, bisphenol A diphenyl ether bismaleimide, 3,3'-dimethyl-5,5'-diethyl-4,4'-diphenylmethane bismaleimide, 4-methyl-1,3-phenylene bismaleimide, and 1,6'-bismaleimide-(2,2,4-trimethyl)hexane, and it is preferable to include N,N'-m-phenylene bismaleimide (also known as m-phenylene dimaleimide). In a rubber composition according to one embodiment of the present invention, the content of the vulcanizing agent per 100 parts by mass of the chloroprene rubber can be 15 parts by mass or less, and preferably 10.0 parts by mass or less. The content of the vulcanizing agent may be, for example, 0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, or 15.0 parts by mass, or may be within a range between any two of the values exemplified here. Note that the rubber composition according to the present invention may not contain a vulcanizing agent.

[0056] Examples of vulcanization accelerators include thiuram compounds, dithiocarbamate compounds, sulfenamide compounds, thiourea compounds, guanidine compounds, xanthogenate compounds, and thiazole compounds. These may be used alone or in combination of two or more types as needed. A rubber composition according to one embodiment of the present invention may contain 0 to 10.0 parts by mass of vulcanization accelerator per 100 parts by mass of chloroprene rubber. The content of the vulcanization accelerator may be, for example, 0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, or 10.0 parts by mass, or may be within a range between any two of the values exemplified here.

[0057] The rubber composition according to one embodiment of the present invention may contain a vulcanization accelerator A. Here, the vulcanization accelerator A may be at least one selected from thiuram compounds, sulfenamide compounds, and thiazole compounds. In a rubber composition according to one embodiment of the present invention, the content of vulcanization accelerator A relative to 100 parts by mass of chloroprene rubber can be 3.0 parts by mass or less. The content of vulcanization accelerator A is, for example, 0, 0.1, 0.2, 0.3, 0.4, 0.5, 1.0, 1.5, 2.0, 2.5, or 3.0 parts by mass, and may be within a range between any two of the values exemplified here. The rubber composition may contain one or more types of vulcanization accelerator A, and the content of vulcanization accelerator A refers to the total amount of vulcanization accelerator A contained in the rubber composition. The rubber composition may not contain vulcanization accelerator A.

[0058] Examples of thiuram compounds include tetramethylthiuram disulfide (TMTD), tetraethylthiuram disulfide, tetrabutylthiuram disulfide, tetrabenzylthiuram disulfide, tetrakis(2-ethylhexyl)thiuram disulfide, tetramethylthiuram monosulfide, and dipentamethylenethiuram tetrasulfide. Examples of sulfenamide compounds include compounds having a sulfenamide structure. Examples of sulfenamide compounds include N-cyclohexyl-2-benzothiazolyl sulfenamide and N-oxydiethylene-2-benzothiazolyl sulfenamide. The sulfenamide compounds may be compounds having a sulfenamide structure and a thiazole skeleton. Examples of thiazole compounds include 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, 2-mercaptobenzothiazole zinc salt, cyclohexylamine salt of 2-mercaptobenzothiazole, 2-(4'-morpholinodithio)benzothiazole, N-cyclohexylbenzothiazole-2-sulfenamide, N-cyclohexyl-2-benzothiazolyl sulfenamide, and N-oxydiethylene-2-benzothiazolyl sulfenamide.

[0059] When the content of the vulcanization accelerator A in the rubber composition according to one embodiment of the present invention is within the above numerical range, the rubber composition can produce a molded article with an even more suitable crosslink density and can further improve the nitrogen gas resistance.

[0060] The rubber composition according to one embodiment of the present invention may contain a vulcanization accelerator other than the vulcanization accelerator A. Examples of thiourea compounds include ethylene thiourea, diethyl thiourea (N,N'-diethyl thiourea), trimethyl thiourea, diphenyl thiourea (N,N'-diphenyl thiourea), and 1,3-trimethylene-2-thiourea. Examples of dithiocarbamate compounds include sodium dibutyldithiocarbamate, zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc N-ethyl-N-phenyldithiocarbamate, zinc N-pentamethylenedithiocarbamate, copper dimethyldithiocarbamate, ferric dimethyldithiocarbamate, and tellurium diethyldithiocarbamate. Examples of the guanidine compounds include 1,3-diphenylguanidine, 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, and di-o-tolylguanidine salts of dicatechol borate. Examples of xanthate compounds include zinc butylxanthate, zinc isopropylxanthate, etc. Examples of benzimidazole compounds include compounds having a benzimidazole skeleton.

[0061] In a rubber composition according to one embodiment of the present invention, the content of a vulcanization accelerator other than vulcanization accelerator A relative to 100 parts by mass of the chloroprene rubber can be 0 to 7.0 parts by mass. The content of vulcanization accelerator A is, for example, 0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, or 7.0 parts by mass, and may be within a range between any two of the numerical values exemplified here. The rubber composition can contain one or more types of vulcanization accelerators other than vulcanization accelerator A.

[0062] 1.1.9 Acid acceptor The rubber composition according to one embodiment of the present invention may contain an acid acceptor. The acid acceptor may include at least one selected from the group consisting of hydrotalcite compounds, magnesium and aluminum solid solutions, magnesium oxide, lead oxide, trimelead tetroxide, iron trioxide, titanium dioxide, and calcium oxide, and may include at least one selected from the group consisting of hydrotalcite compounds, magnesium and aluminum solid solutions, and magnesium oxide, and preferably includes magnesium oxide. The acid acceptors may be used alone or in combination of two or more.

[0063] As the hydrotalcite, one represented by the following formula can be used. [M 2+ 1-x M 3+ x (OH)2] x+ [A n-x / n mH2O] x-

[0064] In the above formula, M 2+ :Mg 2+ , Zn 2+ At least one divalent metal ion selected from M 3+ :Al 3+ , Fe 3+ At least one trivalent metal ion selected from A n- :CO3 2- , Cl ― , NO3 2- At least one n-type anion selected from X:0 <X≦0.33とすることができる。

[0065] As for hydrotalcite, Mg 4.3 Al2(OH) 12.6 CO3·3.5H2O, Mg3ZnAl2(OH) 12 CO3·3H2O, Mg 4.5 Al2(OH) 13 CO3·3.5H2O, Mg 4.5 Al2(OH) 13 CO3, Mg4Al2(OH) 12 CO3·3.5H2O, Mg6Al2(OH) 16 CO3·4H2O, Mg5Al2(OH) 14 CO3·4H2O, Mg3Al2(OH) 10 CO3·1.7H2O, etc., and particularly preferred is Mg 4.3 Al2(OH) 12.6 CO3·3.5H2O, Mg3ZnAl2(OH) 12 CO3·3H2O.

[0066] The amount of the acid acceptor added can be 0.1 to 15 parts by mass relative to 100 parts by mass of the chloroprene polymer contained in the rubber composition, and may be, for example, 0.1, 0.2, 0.3, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 parts by mass, or may be within a range between any two of the values exemplified here.

[0067] 1.1.10 Antioxidants The rubber composition according to one embodiment of the present invention may contain an antioxidant. The type of antioxidant is not particularly limited as long as it does not impair the effects of the present invention. The antioxidant can be used to suppress oxidation of the rubber composition and improve heat resistance. Examples of the antioxidant include phenol-based antioxidants, amine-based antioxidants, acrylate-based antioxidants, imidazole-based antioxidants, carbamic acid metal salts, phosphorus-based antioxidants, and sulfur-based antioxidants. One or more types of antioxidants can be used.

[0068] A rubber composition according to one embodiment of the present invention may contain 0 to 8.0 parts by mass of an antioxidant relative to 100 parts by mass of chloroprene rubber. The content of the antioxidant is, for example, 0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, or 8.0 parts by mass, and may be within a range between any two of the values exemplified here. Note that the rubber composition according to the present invention may not contain an antioxidant.

[0069] The rubber composition according to one embodiment of the present invention may contain an antioxidant A. Here, the antioxidant A may be at least one selected from imidazole-based antioxidants and bisphenol-based antioxidants. In a rubber composition according to one embodiment of the present invention, the content of antioxidant A relative to 100 parts by mass of chloroprene rubber can be 3.0 parts by mass or less. The content of antioxidant A is, for example, 0, 0.1, 0.2, 0.3, 0.4, 0.5, 1.0, 1.5, 2.0, 2.5, or 3.0 parts by mass, and may be within a range between any two of the values exemplified here. The rubber composition may contain one or more types of antioxidant A, and the content of antioxidant A refers to the total amount of antioxidant A contained in the rubber composition. The rubber composition does not necessarily need to contain antioxidant A.

[0070] Examples of imidazole-based antioxidants include 2-mercaptobenzimidazole, 2-mercaptomethylbenzimidazole, and zinc salts of 2-mercaptobenzimidazole. Examples of bisphenol-based antioxidants include 2,2'-methylenebis(4-ethyl-6-tert-butylphenol), 4,4'-butylidenebis(6-tert-butyl-m-cresol), 4,4'-thiobis(3-methyl-6-tert-butylphenol), and butylated reaction products of p-cresol and dicyclopentadiene.

[0071] Some antioxidants, such as antioxidant A, may affect the vulcanization of the rubber composition. In one embodiment of the present invention, when the content of antioxidant A is within the above-mentioned numerical range, a molded product with even more suitable crosslink density can be obtained, and nitrogen gas resistance can be further improved. The rubber composition according to one embodiment of the present invention may also contain an antioxidant other than the antioxidant A. For example, the rubber composition according to one embodiment of the present invention may contain an amine-based antioxidant. The amine-based antiaging agent preferably contains an aromatic secondary amine-based antiaging agent, and examples of the aromatic secondary amine-based antiaging agent include N-phenyl-1-naphthylamine, alkylated diphenylamine, octylated diphenylamine, 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, p-(p-toluenesulfonylamido)diphenylamine, N,N'-di-2-naphthyl-p-phenylenediamine, N-isopropyl-N'-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, and N-(3-methacryloyloxy-2-hydroxypropyl)-N'-phenyl-p-phenylenediamine.

[0072] A rubber composition according to one embodiment of the present invention may contain 0 to 5.0 parts by mass of an antioxidant other than antioxidant A relative to 100 parts by mass of chloroprene rubber. The content of the antioxidant other than antioxidant A is, for example, 0, 1.0, 2.0, 3.0, 4.0, or 5.0 parts by mass, and may be within a range between any two of the numerical values exemplified here. The rubber composition may contain one or more types of antioxidants other than antioxidant A.

[0073] 1.1.11 Other ingredients In addition to the above-described components, the rubber composition according to the present invention may further contain components such as organic peroxides, silane coupling agents, co-crosslinking agents, stabilizers, flame retardants, and vulcanization retarders, within ranges that do not impair the effects of the present invention.

[0074] 1.2.Method for producing rubber composition The rubber composition according to one embodiment of the present invention can be obtained by kneading rubber and other necessary components at a temperature equal to or lower than the vulcanization temperature. A method for producing the rubber composition according to one embodiment of the present invention can include a mixing step of mixing the chloroprene-based rubber and other necessary components at a temperature equal to or lower than the vulcanization temperature.

[0075] A manufacturing method according to one embodiment of the present invention may include a first mixing step and a second mixing step. In the first mixing step, a rubber component containing a chloroprene-based rubber and raw materials containing compounding ingredients for the first mixing step are mixed to obtain a rubber composition precursor, and in the second mixing step, compounding ingredients for the second mixing step are added to the rubber composition precursor and mixed to obtain a rubber composition.

[0076] In the first mixing step, raw materials including a rubber component and compounding ingredients for the first mixing step are mixed to obtain a rubber composition precursor. The compounding ingredients for the first mixing step may not contain a vulcanizing agent, a vulcanization accelerator, or antioxidant A. The compounding ingredients for the first mixing step preferably do not contain any components that affect vulcanization and crosslinking. The compounding ingredients for the first mixing step may contain at least one, two, three, four, five, or six of the following: an acid acceptor, a softener, a processing aid, a filler such as a platy filler, a reinforcing material, and an antioxidant other than antioxidant A, or may contain all of these.

[0077] In the second mixing step, the compounding ingredients for the second mixing step are added to the rubber composition precursor and mixed to obtain a rubber composition. The compounding ingredients for the second mixing step may include a vulcanizing agent, a vulcanization accelerator, and antioxidant A. The compounding ingredients for the second mixing step may also include an acid acceptor, a softener, a processing aid, a filler such as a platy filler, a reinforcing material, an antioxidant other than antioxidant A, and the like.

[0078] In each mixing step, examples of the apparatus for kneading the raw material components include conventionally known kneading apparatuses such as mixers, Banbury mixers, kneader mixers, open rolls, etc. Examples of the apparatus for kneading include conventionally known kneading apparatuses such as mixers, Banbury mixers, kneader mixers, open rolls, etc.

[0079] 1.3 Properties of rubber compositions (Moldability) When the rubber composition according to one embodiment of the present invention is heated to 50°C and kneaded using rolls with a gap of 2 mm, it is preferable that the rubber composition is not difficult to peel off from the rolls, and more preferably, no sticking is observed.

[0080] When the rubber composition according to one embodiment of the present invention is press-vulcanized to produce a vulcanized molded product, it is preferable that the mold surface is free of contamination, and more preferably free of contamination and haze. Note that "haze" refers to a state in which the mold surface is cloudy and a thin layer of volatile matter is attached, but the reflection of the mold surface is still visible. "Contamination" refers to a state in which solid matter is attached to the mold surface or volatile matter has accumulated, making it impossible to see the reflection of the mold surface. The above evaluation can be performed according to JIS K 6299:2012, when a 2 mm-thick sheet-like vulcanized molded product (test vulcanized molded product 1) is produced by press-vulcanizing the obtained rubber composition at 160°C for 20 minutes.

[0081] (nitrogen gas resistance) When a vulcanized molded product of the rubber composition according to one embodiment of the present invention is exposed to a nitrogen atmosphere of 5 to 6 MPa for 100 hours, it is preferable that no deformation is observed, more preferably that no deformation is observed and the area with roughness is less than 40% of the total area (100%), and even more preferably that no deformation is observed and no roughness is observed. The above evaluation can be performed using a test vulcanized molded product 1, and specifically, it can be performed by the method described in the examples.

[0082] (Oil resistance (engine oil 10W-30)) In a rubber composition according to one embodiment of the present invention, when a vulcanized molded product of the rubber composition is immersed in 10W-30 engine oil at 100°C for 72 hours, the volume change ΔV before and after immersion, based on JIS K 6258, is preferably 10% or less. The volume change ΔV may be, for example, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10%, and may be within a range between any two of the values exemplified here. The above evaluation can be performed using a test piece measuring 25 mm in length and 20 mm in width punched out from the test vulcanized molded product 1, and specifically, can be performed by the method described in the examples.

[0083] (Flexibility test) In a rubber composition according to one embodiment of the present invention, when a de Mattia flexural fatigue test is performed using a vulcanized molded article of the rubber composition according to JIS K 6260 under conditions of a stroke of 58 mm, a speed of 300±10 rpm, and 23°C, the number of flexural fatigue tests at which cracks appear is preferably more than 1,000. The number of flexural fatigue tests at which cracks appear may be, for example, 1,001, 2,000, 3,000, 4,000, 5,000, 10,000, 50,000, 100,000, 250,000, 500,000, 500,000, 750,000, or 1,000,000, or may be within a range between any two of the values exemplified herein. The evaluation can be performed using a vulcanized molded article for the de Mattia flexural fatigue test, which is prepared by press-vulcanizing the rubber composition at 160°C for 20 minutes. Specifically, the evaluation can be performed using the method described in the Examples.

[0084] 1.4 Unvulcanized moldings, vulcanized products and vulcanized moldings An unvulcanized molded article according to one embodiment of the present invention uses a rubber composition according to one embodiment of the present invention, and is a molded article (molded product) of the rubber composition (unvulcanized state) according to one embodiment of the present invention. A method for producing an unvulcanized molded article according to one embodiment of the present invention includes a step of molding the rubber composition (unvulcanized state) according to one embodiment of the present invention. The unvulcanized molded article according to one embodiment of the present invention is made of the rubber composition (unvulcanized state) according to one embodiment of the present invention.

[0085] A vulcanizate according to one embodiment of the present invention is a vulcanizate of the rubber composition according to one embodiment of the present invention. A method for producing a vulcanizate according to one embodiment of the present invention includes a step of vulcanizing the rubber composition according to one embodiment of the present invention.

[0086] A vulcanized molded article according to one embodiment of the present invention is a vulcanized molded article of a rubber composition according to one embodiment of the present invention. The vulcanized molded article according to one embodiment of the present invention uses a vulcanizate according to one embodiment of the present invention and is a molded article (molded product) of the vulcanizate according to one embodiment of the present invention. The vulcanized molded article according to one embodiment of the present invention is made of a vulcanizate according to one embodiment of the present invention.

[0087] The vulcanized molded article according to one embodiment of the present invention can be obtained by molding a vulcanizate obtained by vulcanizing the rubber composition (unvulcanized state) according to one embodiment of the present invention, and can also be obtained by vulcanizing a molded article obtained by molding the rubber composition (unvulcanized state) according to one embodiment of the present invention. The vulcanized molded article according to one embodiment of the present invention can be obtained by vulcanizing the rubber composition according to one embodiment of the present invention after molding or during molding. A method for producing a vulcanized molded article according to one embodiment of the present invention comprises a step of molding a vulcanized article according to one embodiment of the present invention, or a step of vulcanizing an unvulcanized molded article according to one embodiment of the present invention.

[0088] (nitrogen gas resistance) When the vulcanized molded article according to one embodiment of the present invention is exposed to a nitrogen atmosphere of 5 to 6 MPa for 100 hours, it is preferable that no deformation is observed, more preferably that no deformation is observed and the area with roughness is less than 40% of the total area (100%), and even more preferably that no deformation is observed and no roughness is observed.

[0089] (Oil resistance (engine oil 10W-30)) When the vulcanized molded article according to one embodiment of the present invention is immersed in 10W-30 engine oil at 100°C for 72 hours, the volume change ΔV before and after immersion is preferably 10% or less based on JIS K 6258. The volume change ΔV may be, for example, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10%, and may be within a range between any two of the values exemplified here.

[0090] (Flexibility test) When a vulcanized molded article according to one embodiment of the present invention is subjected to a de Mattia flexural fatigue test at 23°C under conditions of a stroke of 58 mm, a speed of 300±10 rpm, and a temperature of 23°C in accordance with JIS K 6260, the number of flexural fatigue tests at which cracks appear preferably exceeds 1,000. The number of flexural fatigue tests at which cracks appear may be, for example, 1,001, 2,000, 3,000, 4,000, 5,000, 10,000, 50,000, 100,000, 250,000, 500,000, 500,000, 750,000, or 1,000,000, or may be within a range between any two of the values exemplified here.

[0091] The vulcanized molded article according to one embodiment of the present invention can be used for a diaphragm. A diaphragm according to one embodiment of the present invention includes the above-described vulcanization molded article. Generally, the diaphragms used in diaphragm pumps are used under harsh conditions in which one surface is exposed to nitrogen gas and the other surface is exposed to oil such as engine oil, and the diaphragm is repeatedly flexed. As a result, defects can occur in certain areas of the diaphragm due to repeated use. However, the vulcanized molded article of the rubber composition according to the present invention has excellent resistance to nitrogen gas and flex fatigue, and can suppress the occurrence of defects in the diaphragm, thereby achieving a longer lifespan.

[0092] 2. Second perspective 2.1 Rubber composition A rubber composition according to a second aspect of the present invention is a rubber composition containing a chloroprene-based rubber, the chloroprene-based rubber containing 5 to 20 mass % of unsaturated nitrile monomer units, and a platy filler. A rubber composition according to one embodiment of the present invention is a rubber composition containing a chloroprene-based rubber, and by adding a platy filler to the rubber composition, it is possible to obtain a vulcanized molded article having excellent nitrogen gas resistance and flexural fatigue resistance. Furthermore, the vulcanized molded article of the rubber composition according to one embodiment of the present invention is also excellent in oil resistance, particularly resistance to engine oil. Furthermore, the rubber composition according to one embodiment of the present invention exhibits low roll adhesion in the preparation process of a vulcanized molded product, resulting in excellent moldability, and / or causes little mold contamination during molding, making it possible to efficiently produce vulcanized molded products, and is also advantageous in terms of cost and effort. The following will mainly explain the differences from the first viewpoint.

[0093] 2.1.1 Chloroprene rubber, manufacturing method of chloroprene rubber, other rubbers The chloroprene rubber, the method for producing the chloroprene rubber, and other rubbers are as described above in the first aspect.

[0094] 2.1.2 Plate-like fillers The rubber composition according to one embodiment of the present invention contains a platy filler. The preferred type and content of the platy filler are as described above in the first aspect.

[0095] 2.1.2 Other fillers and reinforcing agents, softeners, processing aids, vulcanizing agents and vulcanization accelerators, acid acceptors, antioxidants, and other ingredients Other fillers and reinforcing agents, softeners, processing aids, vulcanizing agents and vulcanization accelerators, acid acceptors, antioxidants, and other components are as described above in the first aspect.

[0096] 2.2 Manufacturing method and properties of rubber composition The production method and properties of the rubber composition are as described above in the first aspect.

[0097] 2.3 Unvulcanized moldings, vulcanized products and vulcanized moldings The methods for producing the unvulcanized molded article, the vulcanized product, and the vulcanized molded article, as well as the properties of the vulcanized molded article, are as described above in the first aspect.

[0098] The vulcanized molded article of the rubber composition according to the present invention has excellent nitrogen gas resistance and flexural fatigue resistance, and therefore can be used, in particular, as various components requiring these properties. Furthermore, the vulcanized molded article of the rubber composition according to one embodiment of the present invention also has excellent oil resistance, particularly engine oil resistance, and therefore can be used, in particular, as various components requiring nitrogen gas resistance, flexural fatigue resistance, and / or oil resistance (particularly engine oil resistance). The rubber composition, unvulcanized molded article, vulcanized product, and vulcanized molded article according to one embodiment of the present invention can be used as rubber parts in various industrial fields such as buildings, structures, ships, railways, coal mines, and automobiles. They can be used for rubber parts such as automotive rubber parts (e.g., automotive seals), hose materials, rubber molds, gaskets, rubber rolls, industrial cables, industrial conveyor belts, sponges, and diaphragms, and can be used, in particular, as components used in environments requiring excellent nitrogen gas resistance, flexural fatigue resistance, and / or oil resistance (particularly engine oil resistance). As an example, the vulcanizate and vulcanization molded article according to one embodiment of the present invention can be suitably used for sealing purposes such as diaphragms, hoses, gaskets, etc. Diaphragm applications are as described above in the first aspect.

[0099] (hose material) Hose materials are flexible pipes, and specific examples include high- and low-pressure hoses for water supply, oil supply, air supply, steam supply, hydraulic pressure, etc. The rubber composition according to one embodiment of the present invention can be used to produce hose materials for use in environments requiring excellent nitrogen gas resistance, flex fatigue resistance, and / or oil resistance (particularly resistance to engine oil).

[0100] (gaskets, etc.) Gaskets, oil seals, and packings are components used in machines and equipment to prevent the leakage of liquids and gases and the intrusion of debris and foreign objects such as rainwater and dust. Specifically, there are gaskets used for fixed applications and oil seals and packings used for moving parts. Gaskets whose sealing parts are fixed with bolts or other fasteners are made of various materials depending on the purpose, as opposed to soft gaskets such as O-rings and rubber sheets. Packings are also used for rotating parts such as pump and motor shafts, moving parts of valves, reciprocating parts such as pistons, coupler connections, and water stop parts of water faucets. The rubber composition according to one embodiment of the present invention makes it possible to manufacture seals for use in environments requiring excellent nitrogen gas resistance, flexural fatigue resistance, and / or oil resistance (especially resistance to engine oil). [Example]

[0101] The present invention will be described in more detail below based on examples, but the present invention should not be construed as being limited to these examples.

[0102] <Method for producing chloroprene rubber (chloroprene-acrylonitrile copolymer rubber AN 10% by mass)> A 3-L polymerization vessel equipped with a heating / cooling jacket and a stirrer was charged with 24 parts by weight of chloroprene (monomer), 24 parts by weight of acrylonitrile (monomer), 0.5 parts by weight of diethylxanthogen disulfide, 200 parts by weight of purified water, 5.00 parts by weight of potassium rosinate (Harima Chemicals Co., Ltd.), 0.40 parts by weight of sodium hydroxide, and 2.0 parts by weight of sodium salt of β-naphthalenesulfonic acid formalin condensate (Kao Corporation). Next, 0.1 parts by weight of potassium persulfate was added as a polymerization initiator, and emulsion polymerization was carried out at a polymerization temperature of 40°C under a nitrogen gas flow. The chloroprene was added in portions starting 20 seconds after the start of polymerization. The portion-by-portion addition flow rate was adjusted with a solenoid valve based on the change in the heat content of the refrigerant over the first 10 seconds of polymerization. The flow rate was then readjusted every 10 seconds thereafter for continuous polymerization. When the polymerization rate relative to the total amount of chloroprene and acrylonitrile reached 50%, 0.02 parts by mass of phenothiazine, a polymerization terminator, was added to terminate the polymerization. Thereafter, unreacted monomers in the reaction solution were removed under reduced pressure to obtain a chloroprene-based latex containing a chloroprene-acrylonitrile copolymer.

[0103] The above-mentioned conversion rate [%] of the chloroprene latex was calculated from the dry mass of the air-dried chloroprene latex. Specifically, it was calculated using the following formula (A). In the formula, "solids concentration" refers to the concentration [mass %] of the solids obtained by heating 2 g of a sample of chloroprene latex at 130°C and removing volatile components such as the solvent (water), volatile chemicals, and raw materials. "Total charge amount" refers to the total amount [g] of raw materials, reagents, and solvent (water) charged into the polymerization vessel from the start of polymerization to a certain time. "Evaporation residue" refers to the mass [g] of chemicals and raw materials charged from the start of polymerization to a certain time that do not volatilize under conditions of 130°C and remain as solids together with the polymer. "Monomer charge amount" refers to the sum [g] of the amount of monomer initially charged into the polymerization vessel and the amount of monomer added in portions from the start of polymerization to a certain time. Note that "monomer" here refers to the total amount of chloroprene and acrylonitrile. Conversion rate = {[(total charge amount × solid concentration / 100) - evaporation residue] / charge amount of monomer} × 100 (A)

[0104] The pH of the chloroprene latex was adjusted to 7.0 using acetic acid or sodium hydroxide, and then the chloroprene latex was demulsified by freezing and coagulating it on a metal plate cooled to -20°C to obtain a sheet. The sheet was washed with water and then dried at 130°C for 15 minutes to obtain a solid chloroprene rubber (chloroprene-acrylonitrile copolymer rubber AN 10% by mass).

[0105] The content of acrylonitrile monomer units contained in the chloroprene-based rubber (chloroprene-acrylonitrile copolymer AN 10% by mass) was calculated from the content of nitrogen atoms in the chloroprene-acrylonitrile copolymer rubber. Specifically, an elemental analyzer (Sumigraph 220F, manufactured by Sumika Chemical Analysis Center, Ltd.) was used to measure the content of nitrogen atoms in 100 mg of the chloroprene-based rubber (chloroprene-acrylonitrile copolymer rubber AN 10% by mass), and the content of acrylonitrile monomer units was calculated.

[0106] The above elemental analysis was performed as follows. The electric furnace temperatures were set to 900°C for the reactor, 600°C for the reduction furnace, 70°C for the column, and 100°C for the detector. Oxygen gas was flowed at 0.2 mL / min as the combustion gas, and helium gas was flowed at 80 mL / min as the carrier gas. A calibration curve was created using aspartic acid (10.52%), which has a known nitrogen content, as the standard substance. The chloroprene-acrylonitrile copolymer rubber AN10% by mass obtained by the above production method had an acrylonitrile monomer unit content of 10.0% by mass.

[0107] <Method for producing chloroprene rubber (chloroprene-acrylonitrile copolymer rubber AN5 mass%, AN20 mass%, AN3 mass%, AN25 mass%)> The amount of acrylonitrile monomer added in the polymerization process was changed to obtain chloroprene-based rubbers (chloroprene-acrylonitrile copolymers AN5 mass%, AN20 mass%, AN3 mass%, and AN25 mass%) containing acrylonitrile monomer units of 5, 20, 3, and 25 mass%.

[0108] (Examples 1 to 21, Comparative Examples 1 to 4) <Preparation of Rubber Composition> Among the components listed in Tables 1 to 3, the rubber component, processing aid, acid acceptor, filler, reinforcing material, softener, and Nocrac CD were mixed using an 8-inch open roll to obtain a rubber composition precursor that did not contain a vulcanizing agent, etc. (first mixing step). Then, the rubber composition precursor, the vulcanizing agent, the vulcanization accelerator, and the remaining antioxidant were kneaded using an 8-inch open roll (second mixing step) to obtain rubber compositions of Examples and Comparative Examples.

[0109] The components used to obtain the rubber composition are as follows: Chloroprene rubber: the above-mentioned chloroprene-acrylonitrile copolymer AN 10 mass%, AN 5 mass%, AN 20 mass%, AN 3 mass%, AN 25 mass% NBR (acrylonitrile butadiene rubber): N237H (medium-high nitrile acrylonitrile monomer unit content 34% by mass) manufactured by JSR Corporation Natural rubber: HB Chemical, SMR-CV60

[0110] (processing aids) Polybutadiene rubber (BR01): JSR Corporation, JSR BR01 Polyethylene wax (ACPE617A): Allied Signal, ACPE617A (acid acceptor) MgO (#150): Magnesium oxide, manufactured by Kyowa Chemical Industry Co., Ltd., Kyowa Mag 150 (Fillers and reinforcing agents) Carbon black (N330 (HAF)): Asahi Carbon Co., Ltd., Asahi #70 Imeflex T20 (main ingredient: magnesium silicate hydrate): manufactured by Nippon Mistron Co., Ltd. Dexyclay (main ingredient: aluminum silicate hydrate): manufactured by Vanderbilt Minerals, LLC. (softener) Rapeseed oil: Rapeseed oil manufactured by Showa Chemical Co., Ltd. (vulcanizing agent) ZnO: Zinc oxide, manufactured by Sakai Chemical Industry Co., Ltd., two types of zinc oxide Sulfur: Hosoi Chemical Industry Co., Ltd., finely powdered sulfur, 200 mesh (Vulcanization accelerator) Noccela TMU: Trimethylthiourea, thiourea-based compound, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., Noccela TMU Valnoc PM: N,N'-m-phenylenedimaleimide, a maleimide-based compound, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., Valnoc PM Noccela DM: Dibenzothiazole disulfide, a thiazole compound, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., Noccela DM Noccela TT: Tetramethylthiuram disulfide, a thiuram compound, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., Noccela TT Noccela CZ: N-cyclohexyl-2-benzothiazolylsulfenamide, a sulfenamide compound, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., Noccela CZ Noccela TBZTD: Tetrabenzyl thiuram disulfide, a thiuram compound, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., Noccela TBZTD (anti-aging agent) Nocrac CD: 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, aromatic secondary amine antioxidant, Ouchi Shinko Chemical Industry Co., Ltd., Nocrac CD Nocrac MB: 2-mercaptobenzimidazole, an imidazole-based antioxidant, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., Nocrac MB Nocrac 6C: N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., aromatic secondary amine antioxidant, Nocrac 6C Nocrac NS-5: 2,2'-methylenebis(4-ethyl-6-tert-butylphenol), bisphenol-based antioxidant, Nocrac NS-5

[0111] The rubber compositions were evaluated by the following methods. (Moldability) The rubber composition was heated to 50° C. and kneaded using rolls with a gap of 2 mm, and the adhesion to the rolls was evaluated according to the following evaluation criteria. A: No adhesive B: Slight stickiness was observed C: Adhesion was observed D: The adhesive was strong and it was difficult to peel off from the roll.

[0112] <Preparation of Test Vulcanized Molded Product 1> The obtained rubber composition was press-vulcanized in accordance with JIS K 6299:2012 at 160°C for 20 minutes to prepare a sheet-like vulcanized molded product having a thickness of 2 mm (test vulcanized molded product 1).

[0113] (mold contamination) The degree of contamination of the chrome-plated mold surface used in the above press vulcanization was evaluated according to the following evaluation criteria. "Hazy" means that the mold surface is hazy and has a thin layer of volatile matter attached, but the reflection of the mold surface is still visible. "Contaminated" means that solid matter has attached to the mold surface or volatile matter has accumulated, and the reflection of the mold surface cannot be confirmed. A: There was no clouding or contamination on the mold surface. B: The mold surface appeared cloudy C: Slight contamination D: Contamination was present on the entire surface

[0114] (nitrogen gas resistance) Test vulcanized molded article 1 was exposed to a nitrogen atmosphere of 5 to 6 MPa for 100 hours, and the appearance was observed and evaluated according to the following evaluation criteria. A: The surface is in good condition and no roughness is observed. B: The surface is rough and the rough area is more than 0% and less than 40% of the total area (100%). C: The surface is rough and the rough area is 40% or more of the total area (100%). D: Roughness is observed on the surface, and the rough area is 40% or more of the total area (100%), and deformation is also observed.

[0115] (Oil resistance (engine oil 10W-30)) A test specimen measuring 25 mm in length and 20 mm in width was punched out from the test vulcanized molded article 1. The test specimen was immersed in engine oil 10W-30 (manufactured by ENEOS Corporation) at 100°C for 72 hours. The volume change rate ΔV was calculated based on JIS K 6258. The obtained volume change rate ΔV was evaluated according to the following criteria. A: 3% or less B: More than 3%, less than 7% C: More than 7%, less than 10% D: More than 10%

[0116] <Preparation of Test Vulcanized Molded Article 2> The obtained rubber composition was press-vulcanized at 160°C for 20 minutes to prepare a vulcanized molded article for the De Mattia flexural fatigue test. (Flexibility test) Using the obtained vulcanized test molded article 2, a De Mattia flexural fatigue test was carried out in accordance with JIS K 6260. The number of flexural fatigue tests at which cracks occurred was measured under conditions of a stroke of 58 mm, a speed of 300±10 rpm, and room temperature (23°C). The flexural fatigue resistance was evaluated according to the following criteria. A: Over 250,000 times B: More than 10,000 times, less than 250,000 times C: More than 1,000 times, less than 10,000 times D: 1,000 times or less

[0117] [Table 1]

[0118]

Table 2

[0119]

Table 3

Claims

1. A rubber composition containing a chloroprene-based rubber, The chloroprene-based rubber includes a chloroprene-based rubber containing 5 to 20% by mass of unsaturated nitrile monomer units, The rubber composition is for use in a diaphragm.

2. The rubber composition according to claim 1 , comprising a platy filler.

3. A rubber composition containing a chloroprene-based rubber, The chloroprene-based rubber includes a chloroprene-based rubber containing 5 to 20% by mass of unsaturated nitrile monomer units, The rubber composition includes a platy filler.

4. 4. The rubber composition according to claim 2, wherein the platy filler is contained in an amount of 10 to 130 parts by mass per 100 parts by mass of the chloroprene rubber.

5. 4. The rubber composition according to claim 1, further comprising 1.0 to 15.0 parts by mass of a softener relative to 100 parts by mass of the chloroprene rubber.

6. 4. The rubber composition according to claim 1, further comprising 0.1 to 7.0 parts by mass of a processing aid relative to 100 parts by mass of the chloroprene rubber.

7. 4. The rubber composition according to claim 1, wherein the content of the vulcanization accelerator A relative to 100 parts by mass of the chloroprene rubber is 3.0 parts by mass or less, The rubber composition, wherein the vulcanization accelerator A is at least one selected from the group consisting of thiuram compounds, sulfenamide compounds, and thiazole compounds.

8. 4. The rubber composition according to claim 1, wherein the content of the antioxidant A relative to 100 parts by mass of the chloroprene rubber is 3.0 parts by mass or less, The rubber composition, wherein the antioxidant A is at least one selected from the group consisting of imidazole-based antioxidants and bisphenol-based antioxidants.

9. The rubber composition according to claim 1 or 3, wherein a volume change rate ΔV when a vulcanized molded product of the rubber composition is immersed in engine oil 10W-30 at 100°C for 72 hours is 10% or less.

10. 4. The rubber composition according to claim 1, wherein when a vulcanized molded product of the rubber composition is subjected to a De Mattia flexural fatigue test in accordance with JIS K 6260 under conditions of a stroke of 58 mm, a speed of 300±10 rpm, and 23°C, the number of flexural fatigue tests at the time when cracks occur exceeds 1,000.

11. A vulcanized molded article of the rubber composition according to claim 1 or 3.

12. A diaphragm comprising the vulcanized molded article according to claim 11.

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