JP7745665B2 - Rubber composition, vulcanizate, and vulcanized molded article - Google Patents

Description

The present invention relates to a rubber composition, a vulcanizate, and a vulcanized molded article.

Chloroprene rubber has excellent mechanical strength, weather resistance, chemical resistance, heat resistance, cold resistance, and oil resistance, and is widely used as a material for general industrial transmission belts and conveyor belts, automotive air springs, vibration-damping rubber, hoses, wipers, immersion products, sealing parts, adhesives, boots, rubber-coated cloth, rubber rolls, and more.

For example, Patent Document 1 discloses a rubber composition containing 100 parts by mass of chloroprene rubber, 20 to 80 parts by mass of silica filler, 0.5 to 4 parts by mass of a maleimide compound, and 0.1 to 3 parts by mass of an organic peroxide.

Japanese Patent Application Laid-Open No. 2021-95493

However, conventional chloroprene-based rubber compositions have room for improvement in terms of heat resistance and compression set in vulcanized molded products of rubber compositions containing the chloroprene-based rubber. Specifically, it has been difficult to obtain a rubber composition that can produce vulcanized products and vulcanized molded products that are excellent in both elongation at break and compression set after heating.

The present invention was made in consideration of these circumstances and provides a rubber composition that can produce vulcanizates and vulcanized molded articles that are excellent in both elongation at break and compression set after heating.

According to the present invention, there is provided a rubber composition containing 100 parts by mass of chloroprene rubber, 2 to 100 parts by mass of silica having a BET specific surface area of 10 to 120 m ² /g, 0.1 to 8 parts by mass of a maleimide compound, 0.1 to 5 parts by mass of an organic peroxide, and 1 to 15 parts by mass of a silane coupling agent relative to 100 parts by mass of the silica.

The present inventors have conducted extensive research and have found that a rubber composition can be obtained that can give vulcanizates and vulcanized molded articles that are excellent in both elongation at break and compression set after heating, by blending 100 parts by mass of chloroprene rubber, 2 to 100 parts by mass of silica having a BET specific surface area of 10 to 120 m ² /g, 0.1 to 8 parts by mass of a maleimide compound, 0.1 to 5 parts by mass of an organic peroxide, and 1 to 15 parts by mass of a silane coupling agent per 100 parts by mass of the silica, and have thus completed the present invention.

According to another aspect of the present invention, there is provided a vulcanizate of the rubber composition described above.
According to another aspect of the present invention, there is provided a vulcanized molded article of the above-described rubber composition.
Various embodiments of the present invention will be described below as examples, and the embodiments shown below can be combined with each other.

[1] A rubber composition comprising 100 parts by mass of chloroprene rubber, 2 to 100 parts by mass of silica having a BET specific surface area of 10 to 120 m2/g, 0.1 to 8 parts by mass of a maleimide compound, 0.1 to 5 parts by mass of an organic peroxide, and 1 to 15 parts by mass of a silane coupling agent relative to 100 parts by mass of the silica.
[2] The rubber composition according to [1], wherein the chloroprene-based rubber comprises a homopolymer of 2-chloro-1,3-butadiene, or a copolymer of 2-chloro-1,3-butadiene and at least one monomer selected from 2,3-dichloro-1,3-butadiene and an unsaturated nitrile monomer.
[3] The rubber composition according to [1] or [2], wherein the silane coupling agent includes at least one selected from a silane coupling agent having a double bond in its structure, a silane coupling agent having an amino group, and a silane coupling agent having a double bond and an amino group.
[4] The rubber composition according to any one of [1] to [3], wherein the silane coupling agent is at least one silane coupling agent selected from vinyltrimethoxysilane, vinyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, 3-(meth)-acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropylmethyldiethoxysilane, 3-(meth)acryloxypropylmethyltriethoxysilane, and N-phenyl-3-aminopropyltrimethoxysilane.
[5] The rubber composition according to any one of [1] to [4], further comprising 0.1 to 20 parts by mass of a hydrotalcite compound per 100 parts by mass of the chloroprene rubber.
[6] The rubber composition according to any one of [1] to [5], wherein the maleimide compound is at least one maleimide compound selected from 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, N,N'-( 4-methyl-1,3-phenylene)bismaleimide, and 1,6-bismaleimide-(2,2,4-trimethyl)hexane.
[7] The rubber composition according to any one of [1] to [6], wherein the organic peroxide is at least one organic peroxide selected from dicumyl peroxide, 1,4-bis[(t-butylperoxy)isopropyl]benzene, tert-butyl-α-cumyl peroxide, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane, 2,5-bis(tert-butylperoxy)-2,5-dimethyl-3-hexyne, and 4,4-bis[(t-butyl)peroxy]butyl pentanoate.
[8] The rubber composition according to any one of [1] to [7], further comprising 1 to 30 parts by mass of a compound having a thioether structure per 100 parts by mass of the chloroprene rubber.
[9] A vulcanizate of the rubber composition according to any one of [1] to [8].
[10] A vulcanized molded article of the rubber composition according to any one of [1] to [8].

The rubber composition of the present invention can be used to produce vulcanizates and vulcanized molded articles that are excellent in both elongation at break and compression set after heating. Furthermore, the resulting vulcanizates and vulcanized molded articles can be used to their full potential as various components that require excellent heat resistance and/or excellent compression set, and are particularly suitable for use as sealing materials, gaskets, packing, etc.

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

1. Rubber Composition The rubber composition according to the present invention contains 100 parts by mass of chloroprene rubber, 2 to 100 parts by mass of silica having a BET specific surface area of 10 to 120 ^m2 /g, 0.1 to 8 parts by mass of a maleimide compound, 0.1 to 5 parts by mass of an organic peroxide, and 1 to 15 parts by mass of a silane coupling agent per 100 parts by mass of the silica. The rubber composition according to the present invention is a rubber composition from which a vulcanizate and a vulcanized molded article excellent in both elongation at break and compression set after heating can be obtained.

1.1 Chloroprene-Based Rubber The chloroprene-based rubber according to the present invention refers to a rubber containing a chloroprene-based polymer having chloroprene (2-chloro-1,3-butadiene) as a monomer unit (monomer unit = structural unit). Examples of the chloroprene-based 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-based polymer is not particularly limited.

Note that 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 in this embodiment.

A chloroprene-based rubber according to one embodiment of the present invention may contain a homopolymer of 2-chloro-1,3-butadiene (hereinafter referred to as chloroprene), or a copolymer of 2-chloro-1,3-butadiene and at least one monomer selected from 2,3-dichloro-1,3-butadiene and an unsaturated nitrile monomer. A chloroprene-based rubber according to one embodiment of the present invention may be made of a rubber containing a homopolymer of chloroprene and a copolymer of chloroprene and at least one monomer selected from 2,3-dichloro-1,3-butadiene and an unsaturated nitrile monomer, or may be made of a rubber containing a homopolymer of chloroprene, or may be made of a rubber containing a copolymer of chloroprene and at least one monomer selected from 2,3-dichloro-1,3-butadiene and an unsaturated nitrile monomer.

A chloroprene-based rubber according to one embodiment of the present invention may include a copolymer containing 2,3-dichloro-1,3-butadiene monomer units and monomer units derived from an unsaturated nitrile monomer. In the chloroprene-based rubber according to one embodiment of the present invention, when the rubber is taken as 100% by mass, the total content of the 2,3-dichloro-1,3-butadiene monomer units and the unsaturated nitrile monomer units may be less than 25% by mass, and is preferably 1% by mass or more and less than 25% by mass.
The content of 2,3-dichloro-1,3-butadiene monomer units and unsaturated nitrile monomer units in the chloroprene rubber according to one embodiment of the present invention is, for example, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24 mass%, less than 25 mass%, and may be within a range between any two of the numerical values exemplified here.

The chloroprene-based rubber according to one embodiment of the present invention preferably contains a copolymer containing monomer units derived from an unsaturated nitrile monomer. The content of unsaturated nitrile monomer units in the chloroprene-based rubber according to one embodiment of the present invention may be, for example, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, or 24% by mass, or less than 25% by mass, or may be within a range between any two of the values exemplified here. By making the content of unsaturated nitrile monomer units less than 25% by mass, the resulting rubber composition has sufficient cold resistance. Furthermore, in particular, by making the content of unsaturated nitrile monomer units 1% by mass or more, the resulting rubber composition has sufficient oil resistance, and a vulcanized molded article having an excellent balance of tensile strength and cold resistance can be obtained.

Examples of unsaturated nitriles include acrylonitrile, methacrylonitrile, ethacrylonitrile, and phenylacrylonitrile. These unsaturated nitriles can be used alone or in combination of two or more. It is preferable for the unsaturated nitrile to contain acrylonitrile, as this facilitates excellent moldability and allows the vulcanized molded article to have excellent breaking strength, breaking elongation, hardness, tear strength, and oil resistance.

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 can be 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.

The chloroprene-based rubber according to one embodiment of the present invention preferably contains 60 to 100% by mass of chloroprene monomer units, assuming the chloroprene-based rubber to be 100% by mass. The chloroprene monomer unit content in the rubber may be, for example, 60, 65, 70, 75, 80, 85, 90, 95, 99, or 100% by mass, and may be within a range between any two of the values exemplified here. By ensuring that the chloroprene monomer unit content falls within the above range, a rubber composition can be obtained that can produce molded articles with an excellent balance of hardness, tensile strength, and cold resistance.

The chloroprene-based rubber according to one embodiment of the present invention may also have monomer units other than chloroprene monomer, 2,3-dichloro-1,3-butadiene monomer, and unsaturated nitrile monomer. The monomer units other than chloroprene monomer, 2,3-dichloro-1,3-butadiene monomer, and unsaturated nitrile monomer are not particularly limited as long as they are copolymerizable with chloroprene monomer, 2,3-dichloro-1,3-butadiene monomer, and unsaturated nitrile monomer, and include, but are not limited to, esters of (meth)acrylic acid (methyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, etc.), hydroxyalkyl (meth)acrylates (2-hydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, etc.), 1-chloro-1,3-butadiene, butadiene, isoprene, ethylene, styrene, sulfur, etc.

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 and unsaturated nitrile monomer, when the rubber is taken as 100 mass%. The content of monomer units other than chloroprene monomer and unsaturated nitrile monomer in the 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 monomer and unsaturated nitrile monomer within this range, the effects of copolymerizing these monomers can be achieved without impairing the properties of the resulting rubber composition.
Furthermore, the chloroprene-based rubber according to one embodiment of the present invention may be composed only of chloroprene monomer units and unsaturated nitrile monomer units, or may be composed only of chloroprene monomer units.

In the rubber composition according to the present invention, the chloroprene rubber may be used alone or in combination of two or more kinds.
When the rubber composition according to one embodiment of the present invention contains two or more types of chloroprene-based rubbers, it is preferable that the total content of unsaturated nitrile monomer units and 2,3-dichloro-1,3-butadiene contained in the two or more types of chloroprene-based rubbers contained in the rubber composition is less than 25 mass%.

The chloroprene-based polymer (chloroprene homopolymer, chloroprene copolymer, etc.) contained in the chloroprene-based rubber of 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.

1.2 Manufacturing Method of Chloroprene-Based Rubber The manufacturing method of the chloroprene-based rubber according to the present invention is not particularly limited, but the rubber can be obtained by a manufacturing method including an emulsion polymerization step of emulsion-polymerizing raw material monomers including a chloroprene monomer.
In the emulsion polymerization step according to one embodiment of the present invention, a chloroprene monomer and, as necessary, monomers including 2,3-dichloro-1,3-butadiene and an unsaturated nitrile monomer are emulsion-polymerized using an emulsifier, a dispersant, a catalyst, a chain transfer agent, and the like, appropriately, and when a target final conversion rate is reached, a polymerization terminator is added to obtain a latex containing a chloroprene-based polymer containing chloroprene monomer units.
Next, unreacted monomers can be removed from the polymerization solution obtained by the emulsion polymerization step by any method, including, but not limited to, steam stripping.
Thereafter, the pH is adjusted, and the mixture is subjected to conventional steps such as freezing and coagulating, washing with water, and hot air drying, to obtain a chloroprene rubber containing a chloroprene polymer.

There are no particular restrictions on the polymerization initiator used in emulsion polymerization, and any known polymerization initiator commonly used in the emulsion polymerization of chloroprene can be used. Examples of polymerization initiators include potassium persulfate, ammonium persulfate, sodium persulfate, hydrogen peroxide, and organic peroxides such as t-butyl hydroperoxide.

There are no particular restrictions on the emulsifier used in emulsion polymerization, and any known emulsifier commonly used in the emulsion polymerization of chloroprene can be used. Examples of emulsifiers 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).

The molecular weight modifier used in emulsion polymerization is not particularly limited, and known molecular weight modifiers 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.

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

There are no particular restrictions on the polymerization terminator, and any known polymerization terminator commonly used in the emulsion polymerization of chloroprene can be used. Examples of polymerization terminators include phenothiazine (thiodiphenylamine), 4-t-butylcatechol, and 2,2-methylenebis-4-methyl-6-t-butylphenol.

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

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 used.

1.3 Silica The rubber composition according to the present invention contains 2 to 100 parts by mass of silica having a BET specific surface area of 10 to 120 m ² /g per 100 parts by mass of chloroprene rubber. Silica is generally added to rubber compositions as a filler. Silica forms a covalent bond with the chloroprene polymer via surface functional groups (e.g., OH groups) present on the silica surface and a silane coupling agent. This is thought to result in a stronger binding of the chloroprene polymer than with other fillers such as carbon, improving elasticity and compression set.

Although there are no particular limitations, examples of silica that can be used include wet silica filler (hydrated silicic acid), dry silica filler (anhydrous silicic acid), and colloidal silica filler, with wet silica filler being preferred. Surface-unmodified silica can also be used as silica. Surface-modified silica can also be used as silica.

The silica contained in the rubber composition according to the present invention has a BET specific surface area of 10 to 120 ^{m 2} /g. The BET specific surface area is, for example, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, or 120 ^{m 2} /g, and may be within a range between any two of the values exemplified herein. By setting the BET specific surface area of the silica within a specific range, the rubber composition according to the present invention becomes a rubber composition that can produce vulcanizates and vulcanized molded articles that are excellent in both elongation at break and compression set after heating. It is presumed that by setting the BET specific surface area of the silica to be equal to or less than the above upper limit, the number of surface functional groups present on the silica surface per unit mass is specified, and the specific surface functional groups (e.g., OH groups) present on the silica surface increase the reactivity with chloroprene-based rubber during heating, decrease the compatibility between silica and chloroprene-based rubber, and suppress aggregation of silica particles. Furthermore, by making the BET specific surface area of the silica equal to or less than the upper limit, the amount of surface functional groups per silica particle increases, the number of reaction sites with the silane coupling agent on each silica particle increases, and the chloroprene polymer near the silica can be firmly confined, which is thought to improve the compression set. Furthermore, by making the BET specific surface area of the silica equal to or more than the lower limit, the processability of the rubber composition can be maintained.

The specific surface area of silica can be measured using, for example, a rapid surface area measuring device SA-1000 manufactured by Shibata Chemical Instruments Co., Ltd., using the gas-phase adsorption method with nitrogen gas as the adsorbent gas.

The rubber composition of the present invention contains 2 to 80 parts by mass of silica per 100 parts by mass of chloroprene rubber. The silica content may be, for example, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 parts by mass, or may be within a range between any two of the values exemplified here. By adding silica in an amount equal to or greater than the above upper limit, reinforcing effects and abrasion resistance can be maintained. Furthermore, by adding silica in an amount equal to or less than the above upper limit, aggregation and scorch are suppressed, allowing vulcanization to proceed sufficiently.

Silica can be used alone or in combination of two or more types. When the rubber composition of the present invention contains two or more types of silica, it is sufficient that the specific surface area of the mixed silica contained in the rubber composition of the present invention satisfies the above numerical range.

1.4 Silane Coupling Agent The rubber composition according to the present invention contains 1 to 15 parts by mass of a silane coupling agent per 100 parts by mass of silica. The silane coupling agent is added to improve the dispersibility of silica in the rubber and the reinforcing effect between the rubber and the silica.

The silane coupling agent is not particularly limited, and those used in commercially available rubber compositions can be used, such as vinyl coupling agents, epoxy coupling agents, styryl coupling agents, methacrylic coupling agents, acrylic coupling agents, amino coupling agents, polysulfide coupling agents, and mercapto coupling agents.
The silane coupling agent according to one embodiment of the present invention preferably contains at least one selected from a silane coupling agent having a double bond in its structure, a silane coupling agent having an amino group, and a silane coupling agent having a double bond and an amino group.
The silane coupling agents can be used alone or in combination of two or more.

The silane coupling agent having a double bond in its structure is not particularly limited except that it has a double bond in its structure, and includes, for example, a vinyl coupling agent, a styryl coupling agent, a methacrylic coupling agent, and an acrylic coupling agent.In particular, from the viewpoint of processability and reinforcing effect, a vinyl coupling agent, a methacrylic coupling agent, and an acrylic coupling agent are preferred.The silane coupling agent having a double bond in its structure more preferably has a (meth)acrylic group in its structure, and even more preferably has a methacrylic group.
Specific examples of silane coupling agents having a double bond in their structure include vinyltrimethoxysilane, vinyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropylmethyldiethoxysilane, 3-(meth)acryloxypropylmethyltriethoxysilane, vinyltriacetoxysilane, and allyltrimethoxysilane.

There are no particular limitations on the silane coupling agent having an amino group, other than that it contains an amino group in its structure, and those used in commercially available rubber compositions can be used. The silane coupling agent having an amino group can be an amino-based coupling agent. The silane coupling agent having an amino group can be a silane coupling agent having a primary amino group and/or a secondary amino group, and a silane coupling agent having a secondary amino group is more preferable. Examples of silane coupling agents having an amino group include N-phenyl-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, and N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane hydrochloride.

A rubber composition according to one embodiment of the present invention may also contain a silane coupling agent that has neither a double bond nor an amino group in its structure. The content of the silane coupling agent that has neither a double bond nor an amino group in its structure is preferably less than the total content of the silane coupling agent that has a double bond in its structure, the silane coupling agent that has an amino group, and the silane coupling agent that has a double bond and an amino group. In a rubber composition according to one embodiment of the present invention, when the total amount of silane coupling agents contained in the rubber composition is taken as 100% by mass, the total content of the silane coupling agent that has a double bond in its structure, the silane coupling agent that has an amino group, and the silane coupling agent that has a double bond and an amino group is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more. A rubber composition according to one embodiment of the present invention may not contain a silane coupling agent that has neither a double bond nor an amino group in its structure.

The rubber composition of the present invention contains 1 to 15 parts by mass of silane coupling agent per 100 parts by mass of silica. The content of silane coupling agent can be, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 parts by mass, and may be within a range between any two of the values exemplified here. Using the silane coupling agent within this range provides the necessary and sufficient effects and suppresses the occurrence of scorch.

5. Maleimide Compound The chloroprene rubber composition according to one embodiment of the present invention contains 0.1 to 8 parts by mass of a maleimide compound per 100 parts by mass of the chloroprene rubber. The maleimide compounds can be used alone or in combination of two or more.

Maleimide compounds can contribute to the vulcanization of rubber compositions as co-crosslinking agents. 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, N,N'-( 4-methyl-1,3-phenylene ) bismaleimide, and 1,6-bismaleimide-(2,2,4-trimethyl)hexane. From the viewpoint of improving the heat resistance and compression set resistance of the resulting vulcanized molded article, it is particularly preferable to use N,N'-m-phenylenebismaleimide (also known as m-phenylenedimaleimide).

A rubber composition according to one embodiment of the present invention contains 0.1 to 8 parts by mass of a maleimide compound per 100 parts by mass of chloroprene-based rubber. The content of the maleimide compound is, for example, 0.1, 0.2, 0.3, 0.5, 1, 2, 3, 4, 5, 6, 7, or 8 parts by mass, and may be within a range between any two of the values exemplified herein. By setting the content of the maleimide compound at or above the above-mentioned lower limit, the vulcanization of the resulting rubber composition proceeds more sufficiently, resulting in a vulcanized molded product with excellent compression set resistance and elongation at break after heating. Furthermore, by setting the content of the maleimide compound at or below the above-mentioned upper limit, the rubber elasticity of the resulting vulcanized molded product can be sufficiently maintained, and a decrease in compression set resistance can be suppressed.

1.6 Organic Peroxide The rubber composition according to the present invention contains 0.1 to 5 parts by mass of an organic peroxide.
The organic peroxide can be used as a vulcanizing agent. The organic peroxide can be used alone or in combination of two or more.

Examples of organic peroxides include dicumyl peroxide, benzoyl peroxide, 1,1-bis(t-butylperoxy)-3,5,5-trimethylcyclohexane, diisobutyryl peroxide, cumyl peroxyneodecanoate, di-n-propyl peroxydicarbonate, diisopropyl peroxydicarbonate, di-sec-butyl peroxydicarbonate, 1,1,3,3-tetramethylbutyl peroxyneodecanoate, di(4-t-butylcyclohexyl)peroxydicarbonate, di(2-ethylhexyl)peroxydicarbonate, t-hexyl peroxyneodecanoate, t-butyl peroxyneodecanoate, t-butyl peroxyneoheptanoate, t-hexyl peroxypivalate, and t-butyl peroxyneodecanoate. Chilperoxypivalate, di(3,5,5-trimethylhexanoyl)peroxide, dilauroyl peroxide, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, disuccinic acid peroxide, 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane, t-hexylperoxy-2-ethylhexanoate, di(4-methylbenzoyl)peroxide, t-butylperoxy-2-ethylhexanoate, di(3-methylbenzoyl)peroxide, benzoyl(3-methylbenzoyl)peroxide, dibenzoyl peroxide, 1,1-di(t-butylperoxy)-2-methylcyclohexane, 1,1-di(t-hexylperoxy)-3,3,5-trimethylcyclohexa hexane, 1,1-di(t-hexylperoxy)cyclohexane, 1,1-di(t-butylperoxy)cyclohexane, 2,2-di(4,4-di-(t-butylperoxy)cyclohexyl)propane, t-hexylperoxyisopropyl monocarbonate, t-butylperoxymaleic acid, t-butylperoxy-3,5,5-trimethylhexanoate, t-butylperoxylaurate, t-butylperoxyisopropyl monocarbonate, t-butylperoxy-2-ethylhexyl monocarbonate, t-hexylperoxybenzoate, 2,5-di-methyl-2,5-di(benzoylperoxy)hexane, t-butylperoxyacetate, 2,2-di-(t-butylperoxy)butane, t-butylperoxybenzoate, n- Examples of suitable perfluorooctanoic acid peroxides include butyl 4,4-di(t-butylperoxy)valerate, 1,4-bis[(t-butylperoxy)isopropyl]benzene, di-t-hexyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, t-butylcumyl peroxide, di-t-butyl peroxide, p-menthane hydroperoxide, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexyne-3, diisopropylbenzene hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, cumene hydroperoxide, t-butyl hydroperoxide, 4,4-bis[(t-butyl)peroxy]butyl pentanoate, and 2,5-bis(tert-butylperoxy)-2,5-dimethyl-3-hexyne. Among these, at least one selected from dicumyl peroxide, 1,4-bis[(t-butylperoxy)isopropyl]benzene, tert-butyl-α-cumyl peroxide, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane, 2,5-bis(tert-butylperoxy)-2,5-dimethyl-3-hexyne, and 4,4-bis[(t-butyl)peroxy]butyl pentanoate is preferred, and 1,4-bis[(t-butylperoxy)isopropyl]benzene is particularly preferred.

The rubber composition of the present invention may contain 0.1 to 5 parts by mass of organic peroxide per 100 parts by mass of chloroprene-based rubber. The amount of organic peroxide added may be, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, or 5 parts by mass, and may be within a range between any two of the values exemplified here. By keeping the organic peroxide content within the above numerical range, processing safety is ensured and a good vulcanizate can be obtained.

1.7 Hydrotalcite Compound The rubber composition according to the present invention may contain 0.1 to 20 parts by mass of a hydrotalcite compound per 100 parts by mass of the chloroprene rubber. The hydrotalcite compound can function as an acid acceptor.
As the hydrotalcite compound, compounds represented by the following formula can be used.
[M ²⁺ _1-x M ³⁺ _x (OH) ₂ ] ^x+ [A _n-x/n・mH ₂ O] ^x-

In the above formula,
M ²⁺ : at least one divalent metal ion selected from Mg ²⁺ , Zn ²⁺ , etc. M ³⁺ : at least one trivalent metal ion selected from Al ³⁺ , Fe ³⁺ , etc. A ^n- : at least one n-type anion selected from CO ₃ ^2- , Cl ^- , NO ₃ ^{2- ,} etc. X: 0<X≦0.33 can be satisfied.

Examples of hydrotalcite compounds include Mg _4.3 Al ₂ (OH) _12.6 CO ₃ .3.5H ₂ O, Mg ₃ ZnAl ₂ (OH) ₁₂ CO ₃ .3H ₂ O, Mg _4.5 Al ₂ (OH) ₁₃ CO ₃ .3.5H ₂ O, Mg _4.5 Al ₂ (OH) ₁₃ CO ₃ , Mg ₄ Al ₂ (OH) ₁₂ CO ₃ .3.5H ₂ O, Mg ₆ Al ₂ (OH) ₁₆ CO ₃ .4H ₂ O, Mg ₅ Al ₂ (OH) ₁₄ CO ₃ .4H ₂ O, Mg ₃ Al ₂ (OH) ₁₀ CO ₃ .1.7H ₂ O, and Mg _0.7 Al _0.3O1.15 , and the like, _and particularly preferred _{are Mg4.3Al2} (OH) _{12.6CO3.3.5H2O , Mg3ZnAl2 ( OH ) 12CO3.3H2O , and Mg0.7Al0.3O1.15 .}

When a hydrotalcite compound is used, the amount of the hydrotalcite compound added can be 0.1 to 20 parts by mass per 100 parts by mass of chloroprene rubber. The amount of the hydrotalcite compound added can 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, 15, 16, 17, 18, 19, or 20 parts by mass, and may be within a range between any two of the values exemplified here. The hydrotalcite compounds can be used alone or in combination of two or more.

1.8 Compound Having a Thioether Structure The chloroprene rubber composition according to one embodiment of the present invention can contain 1 to 30 parts by mass of a compound having a thioether structure per 100 parts by mass of the chloroprene rubber. By using a compound having a thioether structure in combination with an organic peroxide, vulcanization can be sufficiently progressed within the specified vulcanization time, resulting in a rubber composition from which a vulcanizate having excellent compression set resistance and heat resistance can be obtained. In addition, the organic peroxide remaining after crosslinking and the hydroperoxide produced by thermal degradation are decomposed, further improving the heat resistance of the resulting vulcanized molded article.

A compound having a thioether structure according to one embodiment of the present invention can be represented by, for example, the following formula (1), or can have a structural unit represented by formula (2): wherein R ¹ , R ² , R ³ , and R ⁴ can be any organic group which may have a substituent.

When the compound having a thioether structure according to one embodiment of the present invention is represented by formula (1), it is preferable that at least one of R ¹ and R ² contains an ether structure. When the compound having one or more thioether structures according to one embodiment of the present invention contains a structural unit represented by formula (2), it is preferable that at least one of R ³ and R ⁴ contains an ether structure. Furthermore, in formula (2), n is any natural number of 1 or more. Furthermore, it is preferable that the compound having one or more thioether structures according to one embodiment of the present invention has two or more ether structures.

In one embodiment, R ¹ , R ² , R ³ , and R ⁴ each preferably have an alkylene group having 2 to 20 carbon atoms, more preferably an alkylene group having 2 to 11 carbon atoms. In another embodiment, R ¹ , R ² , R ³ , and R ⁴ may each have a carbonyl group.

The amount of the compound having a thioether structure added can be 1 to 30 parts by mass per 100 parts by mass of chloroprene rubber. The amount of the compound having a thioether structure added can be, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 20, 25, or 30 parts by mass, and may be within a range between any two of the values exemplified here. By adding an amount of the compound having a thioether structure equal to or greater than the above lower limit, organic peroxides remaining after crosslinking when an organic peroxide is added and hydroperoxides generated by thermal degradation are decomposed, resulting in a vulcanizate with superior heat resistance. Furthermore, by adding an amount of the compound having a thioether structure equal to or less than the above upper limit, vulcanization proceeds more thoroughly, resulting in a rubber composition with sufficient moldability and superior compression set resistance and heat resistance for a vulcanized molded product.

1.9 Vulcanizing Agent In addition to the above compounds, the rubber composition according to one embodiment of the present invention may contain a vulcanizing agent. Examples of the vulcanizing agent include metal oxides. Examples of metal oxides include zinc oxide, magnesium oxide, lead oxide, trimelead tetroxide, iron trioxide, titanium dioxide, and calcium oxide. The metal oxide preferably contains at least one of zinc oxide and magnesium oxide, and may contain both zinc oxide and magnesium oxide, and preferably contains at least zinc oxide.

The rubber composition of the present invention may contain 0.1 to 15 parts by mass of the above-mentioned vulcanizing agent per 100 parts by mass of chloroprene-based rubber. The content of the above-mentioned vulcanizing agent 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. The vulcanizing agents may be used alone or in combination of two or more.

1.10 Filler (reinforcement)
The rubber composition according to the present invention may also contain a filler (reinforcing material) other than silica.
Examples of fillers and reinforcing materials 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, clay, talc, and calcium carbonate. These may be used alone or in combination of two or more.

In a rubber composition according to one embodiment of the present invention, the total amount of silica and fillers (reinforcing materials) other than silica contained in the rubber composition is preferably 2 to 100 parts by mass when the chloroprene rubber is taken as 100 parts by mass. In a rubber composition according to one embodiment of the present invention, the content of fillers/reinforcing materials other than silica can be 50% by mass or less when the total amount of silica and fillers (reinforcing materials) other than silica contained in the rubber composition is taken as 100% by mass. The content of fillers/reinforcing materials other than silica can be, for example, 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, or 50% by mass, and may be within a range between any two of the values exemplified here. A rubber composition according to one embodiment of the present invention may not contain fillers (reinforcing materials) other than silica.
In the rubber composition according to one embodiment of the present invention, by setting the content of fillers other than silica within the above-mentioned numerical range, the hardness of the vulcanizate and vulcanized molded article can be improved while maintaining the effects of the present invention.

1.11 Lubricants and Processing Aids The rubber composition according to the present invention may further contain a lubricant or processing aid. The lubricant or processing aid is added primarily to improve processability, such as by making the rubber composition easier to release from rolls, molding dies, extruder screws, etc. Examples of lubricants and processing aids include fatty acids such as stearic acid, paraffin-based processing aids such as polyethylene, fatty acid amides, petrolatum, and factice. These may be used alone or in combination of two or more. The rubber composition according to the present invention may contain 15 parts by mass or less of the lubricant or processing aid, and may also contain 10 parts by mass or less, per 100 parts by mass of the chloroprene-based rubber contained in the rubber composition. The content of the lubricant or processing aid may be, for example, 0, 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. The rubber composition according to the present invention may not contain a lubricant or processing aid.

1.12 Sulfur/Vulcanization Accelerator The rubber composition according to the present invention may contain sulfur and a vulcanization accelerator. Alternatively, the rubber composition according to the present invention may contain neither sulfur nor a vulcanization accelerator. The rubber composition may contain 5.0 parts by mass or less of the sulfur/vulcanization accelerator per 100 parts by mass of the chloroprene-based rubber. The content of the sulfur/vulcanization accelerator may be, for example, 0, 0.1, 0.3, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, or 5.0 parts by mass, or may be within a range between any two of the values exemplified here.

The type of vulcanization accelerator is not particularly limited as long as it does not impair the effects of the present invention. The vulcanization accelerator is preferably a vulcanization accelerator that can be used for vulcanizing chloroprene-based rubber. One or more vulcanization accelerators can be freely selected and used.
Examples of the vulcanization accelerator include thiuram-based, dithiocarbamate-based, thiourea-based, guanidine-based, xanthogenate-based, and thiazole-based accelerators.

Examples of thiuram vulcanization accelerators include tetramethylthiuram disulfide (TMTD), tetraethylthiuram disulfide, tetrabutylthiuram disulfide, tetrakis(2-ethylhexyl)thiuram disulfide, tetramethylthiuram monosulfide, and dipentamethylenethiuram tetrasulfide.
Examples of dithiocarbamate vulcanization accelerators include sodium dibutyldithiocarbamate, zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc N-ethyl-N-phenyldithiocarbamate, zinc N-pentamethylenedithiocarbamate, copper dimethyldithiocarbamate, ferric dimethyldithiocarbamate, and tellurium diethyldithiocarbamate.
Examples of thiourea vulcanization accelerators include thiourea compounds such as ethylene thiourea, diethyl thiourea (N,N'-diethyl thiourea), trimethyl thiourea, diphenyl thiourea (N,N'-diphenyl thiourea), and 1,3-trimethylene-2-thiourea.
Examples of the guanidine vulcanization accelerator include 1,3-diphenylguanidine, 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, and di-o-tolylguanidine salts of dicatechol borate.
Examples of xanthogenate-based vulcanization accelerators include zinc butylxanthogenate and zinc isopropylxanthogenate.
Examples of the thiazole vulcanization accelerator include 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, 2-mercaptobenzothiazole zinc salt, cyclohexylamine salt of 2-mercaptobenzothiazole, 2-(4'-morpholinodithio)benzothiazole, and N-cyclohexylbenzothiazole-2-sulfenamide.
Examples of triazine-based vulcanization accelerators include 2,4,6-trimercapto-s-triazine.
These may be used alone or in combination of two or more.

1.13 Plasticizer/Softener The rubber composition according to the present invention may contain a plasticizer/softener. The plasticizer/softener is added to adjust the processability of the unvulcanized rubber composition and the flexibility of the vulcanized product and vulcanized molded article after vulcanization. There are no particular restrictions on the plasticizer/softener, as long as it is compatible with rubber. Examples of plasticizers and softeners include vegetable oils such as rapeseed oil, linseed oil, castor oil, and palm oil, phthalate plasticizers, ester plasticizers such as DUP (diundecyl phthalate), DOP (dioctyl phthalate), DINP (diisononyl phthalate), DOTP (dioctyl terephthalate), DOS (dioctyl sebacate), DBS (dibutyl sebacate), DOA (dioctyl adipate), DINCH (diisononyl 1,2-cyclohexanedicarboxylate), TOP (trioctyl phosphate), and TBP (tributyl phosphate), ether ester compounds, aromatic oils, naphthenic oils, lubricating oils, process oils, paraffin, liquid paraffin, Vaseline, and petroleum asphalt. These may be used alone or in combination of two or more.

A rubber composition according to one embodiment of the present invention may contain 50 parts by mass or less of a plasticizer/softener when the chloroprene-based rubber contained in the rubber composition is 100 parts by mass. The content of the plasticizer/softener may be, for example, 0, 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, or 50 parts by mass, and may be within a range between any two of the values exemplified here. A rubber composition according to one embodiment of the present invention may also contain no plasticizer.

1.14 Others In addition to the components described above, the rubber composition according to the present invention may further contain components such as antioxidants, antioxidants, stabilizers, flame retardants, and vulcanization retarders, as long as the effects of the present invention are not impaired.
Examples of the antioxidants and antioxidants include ozone antioxidants, phenolic antioxidants, amine antioxidants, acrylate antioxidants, imidazole antioxidants, metal carbamates, waxes, phosphorus antioxidants, sulfur antioxidants, etc. Examples of the imidazole antioxidants include 2-mercaptobenzimidazole, 2-mercaptomethylbenzimidazole, and zinc salt of 2-mercaptobenzimidazole.
The rubber composition according to the present invention may contain 0.1 to 10 parts by mass of an antioxidant and an antioxidant, based on 100 parts by mass of the chloroprene rubber contained in the rubber composition.

2. Method for Producing Rubber Composition A rubber composition according to one embodiment of the present invention can be obtained by kneading a chloroprene rubber, silica, a maleimide compound, an organic peroxide, a silane coupling agent, and other necessary components at a temperature equal to or lower than the vulcanization temperature. Examples of devices for kneading the raw material components include conventionally known kneading devices such as mixers, Banbury mixers, kneader mixers, and open rolls.

3. Characteristics of rubber composition (heat resistance of vulcanized molded product)
In a rubber composition according to one embodiment of the present invention, when the elongation at break EB of a vulcanized molded product molded in accordance with JIS K6299, as measured in accordance with JIS K6251, is ₀ , and the elongation at break EB of the vulcanized molded product heated at 150°C for 144 hours, as measured in accordance with JIS K6251, is _i , the change in elongation at break ΔEB calculated by the following formula is preferably −68 or more.
ΔEB=(EB _i -EB ₀ )÷EB ₀ ×100
The change in elongation at break ΔEB is, for example, −68, −67, −66, −65, −60, −55, −50, −45, or −40, and may be within a range between any two of the values exemplified here.

(Compression set of vulcanized molded product)
The rubber composition according to one embodiment of the present invention is preferably such that a vulcanized molded article obtained by press vulcanization molding at 180°C for 30 minutes has a compression set of 34 or less, measured under test conditions of 150°C and 72 hours in accordance with JIS K 6262:2013.
The compression set may be, for example, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, or within a range between any two of the values exemplified herein.

4. Unvulcanized molded body, vulcanized product, and vulcanized molded body The unvulcanized molded body according to this embodiment uses the rubber composition according to this embodiment, and is a molded body (molded article) of the rubber composition (unvulcanized state) according to this embodiment. The manufacturing method of the unvulcanized molded body according to this embodiment includes a step of molding the rubber composition (unvulcanized state) according to this embodiment. The unvulcanized molded body according to this embodiment is made of the rubber composition (unvulcanized state) according to this embodiment.

The vulcanizate of this embodiment is a vulcanizate of the rubber composition of this embodiment.The method for producing the vulcanizate of this embodiment includes a step of vulcanizing the rubber composition of this embodiment.

The vulcanized molded article of this embodiment is a vulcanized molded article of the rubber composition of this embodiment. The vulcanized molded article of this embodiment uses the vulcanizate of this embodiment and is a molded article (molded product) of the vulcanizate of this embodiment. The vulcanized molded article of this embodiment is made from the vulcanizate of this embodiment.

The vulcanized molded article of this embodiment can be obtained by molding a vulcanized product obtained by vulcanizing the rubber composition of this embodiment (unvulcanized state), and can also be obtained by vulcanizing a molded article obtained by molding the rubber composition of this embodiment (unvulcanized state). The vulcanized molded article of this embodiment can be obtained by vulcanizing the rubber composition of this embodiment after or during molding. The method for producing the vulcanized molded article of this embodiment includes a step of molding the vulcanized product of this embodiment, or a step of vulcanizing the unvulcanized molded article of this embodiment.

It is preferable that the change in elongation at break ΔEB and compression set of the vulcanizate and vulcanized molded body according to one embodiment of the present invention are within the above numerical ranges.

The unvulcanized molded articles, vulcanized articles, and vulcanized molded articles according to this embodiment can be used as rubber parts in various industrial fields, such as buildings, structures, ships, railways, coal mines, and automobiles. Because vulcanized articles made from the rubber composition according to this embodiment have excellent elongation at break and compression set after heating, they can be used in a variety of components where these properties are required. The rubber composition according to this embodiment can be used as rubber parts in various industrial fields, such as buildings, structures, ships, railways, coal mines, and automobiles, and can be used as rubber parts such as automotive rubber components (e.g., automotive seals), hose materials, rubber molds, gaskets, rubber rolls, industrial cables, industrial conveyor belts, and sponges. Taking advantage of its properties, the rubber composition according to this embodiment can be used in a variety of components where excellent heat resistance and/or excellent compression set are required, and is particularly suitable for use as seals, gaskets, packing, etc.

(rubber components for automobiles)
Automotive rubber components include gaskets, oil seals, and packings, which are used to prevent the leakage of liquids and gases and the intrusion of debris and foreign objects such as rainwater and dust into machinery and equipment. Specifically, there are gaskets used for fixed applications and oil seals and packings used for moving parts. Gaskets with sealed components 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. A vulcanizate made from a rubber composition according to one embodiment of the present invention exhibits no observed bleeding and excellent elongation at break and compression set after heating, making it possible to manufacture seals that utilize these properties, for example.

(hose material)
Hose materials are bendable pipes, and specific examples include high- and low-pressure hoses for water supply, oil supply, air supply, steam supply, hydraulic pressure, etc. Since the vulcanizate of the rubber composition according to one embodiment of the present invention is excellent in elongation at break and compression set after heating, it is possible to manufacture hose materials that utilize these properties, for example.

(Rubber mold)
Rubber molded products include vibration-isolating rubber, vibration-damping materials, boots, etc. Vibration-isolating rubber and vibration-damping materials are rubbers that prevent the transmission and spread of vibrations, and specific examples include torsional dampers, engine mounts, muffler hangers, etc. that absorb vibrations and prevent noise when the engine of an automobile or various vehicles is running. The rubber composition of the present invention can increase the tensile strength of vibration-isolating rubber and vibration-damping materials. This makes it possible to produce vibration-isolating rubber and vibration-damping materials that can be used in high-load applications, which was difficult with conventional rubber compositions.
Furthermore, a boot is a bellows-shaped member whose outer diameter gradually increases from one end to the other, and specific examples include boots for constant velocity joint covers, boots for ball joint covers (dust cover boots), boots for rack and pinion gears, etc., which are used to protect drive parts of automobile drive systems, etc. The vulcanizate of the rubber composition according to one embodiment of the present invention is excellent in elongation at break and compression set, and therefore, for example, it is possible to manufacture boots that are used by taking advantage of these properties.

(gaskets, etc.)
Gaskets, oil seals, and packings are components in machines and equipment that prevent the leakage of liquids and gases and the intrusion of debris and foreign objects such as rainwater and dust into the interior. Specifically, there are gaskets used for fixed applications and oil seals and packings used for moving parts. Gaskets in which the sealing part is fixed with bolts or the like 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. A vulcanizate made from a rubber composition according to one embodiment of the present invention has excellent elongation at break and compression set, making it possible to manufacture seals that utilize these properties, for example.

(rubber roll)
Rubber rolls are manufactured by adhesively coating a metal core such as an iron core with rubber, and are generally manufactured by spirally winding a rubber sheet around a metal iron core. Rubber materials such as NBR, EPDM, and CR are used for rubber rolls depending on the required characteristics for various applications such as papermaking, various metal manufacturing, film manufacturing, printing, general industrial use, agricultural equipment such as rice hullers, and food processing. CR has good mechanical strength that can withstand the friction of the objects being conveyed, and is therefore used in a wide range of rubber roll applications. The rubber composition of the present invention has excellent elongation at break and compression set, making it possible to manufacture rubber rolls that utilize these properties.

(industrial cables)
Industrial cables are linear components for transmitting electrical or optical signals. They are made by covering a good conductor such as copper or a copper alloy, or an optical fiber, with an insulating coating layer, and a wide variety of industrial cables are manufactured depending on their structure and installation location. A vulcanizate made from the rubber composition according to one embodiment of the present invention is excellent in elongation at break and compression set after heating, and therefore can be used to manufacture industrial cables that utilize these properties, for example.

(industrial conveyor belts)
Industrial conveyor belts are made of rubber, resin, and metal, and are selected to suit a wide variety of uses. Among these, rubber conveyor belts are inexpensive and widely used, but when used in environments where there is a lot of friction and collision with the conveyed goods, they have been prone to damage due to deterioration. A vulcanizate made from a rubber composition according to one embodiment of the present invention has excellent elongation at break and compression set after heating, and therefore can be used to produce industrial conveyor belts that take advantage of these properties.

(sponge)
Sponges are porous materials with countless fine pores inside, and are specifically used in vibration-damping materials, sponge sealing parts, wetsuits, shoes, etc. The rubber composition of the present invention can increase the tensile strength of the sponge. Furthermore, since a chlorine-based rubber is used, the flame retardancy of the sponge can also be increased. A vulcanizate made from the rubber composition according to one embodiment of the present invention has excellent elongation at break and compression set after heating, and therefore can be used to produce, for example, sponges that take advantage of these properties or sponges with excellent flame retardancy. Furthermore, the hardness of the resulting sponge can be appropriately adjusted by adjusting the content of the foaming agent, etc.

Methods for molding the rubber composition (unvulcanized state) and vulcanized product according to this embodiment include press molding, extrusion molding, calendar molding, etc. The temperature for vulcanizing the rubber composition may be set appropriately according to the composition of the rubber composition, and may be 140 to 220°C, or 160 to 190°C. The vulcanization time for vulcanizing the rubber composition may be set appropriately according to the composition of the rubber composition, the shape of the unvulcanized molded product, etc., and may be 10 to 60 minutes.

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

<Method of producing acrylonitrile-containing chloroprene rubber>
A 3-L polymerization vessel equipped with a heating/cooling jacket and a stirrer was charged with 24 parts by mass of chloroprene (monomer), 24 parts by mass of acrylonitrile (monomer), 0.5 parts by mass of diethylxanthogen disulfide, 200 parts by mass of purified water, 5.00 parts by mass of potassium rosinate (manufactured by Harima Chemicals Co., Ltd.), 0.40 parts by mass of sodium hydroxide, and 2.0 parts by mass of sodium salt of β-naphthalenesulfonic acid formalin condensate (manufactured by Kao Corporation). Next, 0.1 parts by mass of potassium persulfate was added as a polymerization initiator, and emulsion polymerization was carried out in a nitrogen stream at a polymerization temperature of 40°C. 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 quantity of the refrigerant over the first 10 seconds of polymerization, and the flow rate was 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 as a polymerization terminator was added to terminate the polymerization. Thereafter, unreacted monomers in the reaction solution were removed under reduced pressure to obtain an acrylonitrile-containing chloroprene-based latex containing a chloroprene-acrylonitrile copolymer.

The above-mentioned conversion [%] of the acrylonitrile-containing 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, "solid content concentration" refers to the concentration [% by mass] of the solid content 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 charged 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. "Charged amount of monomer" refers to the total amount [g] of the monomer initially charged into the polymerization vessel and the amount of monomer added in portions from the start of polymerization to a certain time. The "monomer" referred to here is the total amount of chloroprene and acrylonitrile.
Conversion rate = {[(total charge amount × solid content concentration / 100) - evaporation residue] / charge amount of monomer} × 100 (A)

The pH of the above-mentioned acrylonitrile-containing chloroprene latex was adjusted to 7.0 using acetic acid or sodium hydroxide, and the acrylonitrile-containing chloroprene latex was then freeze-coagulated on a metal plate cooled to -20°C to break the emulsion, yielding a sheet. This sheet was then washed with water and dried at 130°C for 15 minutes to obtain solid acrylonitrile-containing chloroprene rubber.

The content of acrylonitrile monomer units contained in the acrylonitrile-containing chloroprene rubber was calculated from the content of nitrogen atoms in the chloroprene-acrylonitrile copolymer rubber. Specifically, the content of nitrogen atoms in 100 mg of chloroprene-based rubber was measured using an elemental analyzer (Sumigraph 220F, manufactured by Sumika Chemical Analysis Center, Ltd.), and the content of acrylonitrile monomer units was calculated.

The above elemental analysis was carried out 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 prepared using aspartic acid (10.52%) with a known nitrogen content as the standard substance.
The acrylonitrile-containing chloroprene rubber obtained by the above production method had an acrylonitrile monomer unit content of 10.0% by mass.

<Preparation of Rubber Composition>
The components were mixed as shown in Tables 1 to 3 and kneaded with an 8-inch open roll to obtain rubber compositions of Examples and Comparative Examples.

The components used to obtain the rubber composition are as follows:
<Chloroprene rubber>
Acrylonitrile (AN)-containing chloroprene rubber: acrylonitrile-containing chloroprene rubber prepared by the above-mentioned production method Mercaptan-modified chloroprene rubber: mercaptan-modified chloroprene rubber, "S-40V" manufactured by Denka Co., Ltd.

Silica: "ULTRASIL360" manufactured by Evonik Industries AG BET specific surface area: 55 m ² /g
Silica: "Nipsil E-74P" manufactured by Tosoh Silica Corporation BET specific surface area: 50 m ² /g
Silica: "Nipsil ER-R" manufactured by Tosoh Silica Corporation BET specific surface area: 78 m ² /g

Silane coupling agent: 3-methacryloxypropylmethoxysilane, "KBM-503" manufactured by Shin-Etsu Chemical Co., Ltd. Silane coupling agent with a double bond

Silane coupling agent: N-phenyl-3-aminopropyltrimethoxysilane, "KBM-573" manufactured by Shin-Etsu Chemical Co., Ltd. Silane coupling agent having a secondary amine

Silane coupling agent: (3-mercaptopropyl)trimethoxysilane, Toray Dow Corning "Z-6062" mercapto type

Carbon black: FEF, manufactured by Asahi Carbon Co., Ltd., "Asahi #60"
Organic peroxide: 1,4-bis[(t-butylperoxy)isopropyl]benzene, NOF Corporation, "Perbutyl P-40"
Organic peroxide: 4,4-bis[(t-butyl)peroxy]butyl pentanoate, NOF Corporation, "Perhexa V-40"
Vulcanization accelerator: Trimethylthiourea, Ouchi Shinko Chemical Industry Co., Ltd., "Noccela TMU"
Maleimide compound (co-crosslinking agent): m-phenylenedimaleimide, Ouchi Shinko Chemical Industry Co., Ltd., "Balnoc PM"
Compound having a thioether structure: thioether-based plasticizer, "Vulcanol OT" manufactured by LANXESS (a mixture mainly composed of compound A containing one or more thioether structures and two or more ether structures, and compound B containing one or more thioether structures and three or more ether structures)
Vulcanizing agent: Zinc oxide, Sakai Chemical Industry Co., Ltd. "Zinc oxide type 2"
Hydrotalcite (acid acceptor): Mg _0.7 Al _0.3 O _1.15 , Kyowa Chemical Industry Co., Ltd. "KW-2100"
Antioxidant: 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, Ouchi Shinko Chemical Industry Co., Ltd., "Nocrac CD"
Lubricant/processing aid: Stearic acid: "Stearic acid 50S" manufactured by New Japan Chemical Co., Ltd.

<Evaluation of vulcanized molded products>
Vulcanized molded articles were prepared using the above rubber compositions and evaluated as follows. The results are shown in Tables 1 to 3.

(Heat resistance (change in elongation at break after heating))
The obtained rubber composition was press-vulcanized in accordance with JIS K6299 at 180°C for 20 minutes to prepare a sheet-like vulcanized molded product having a thickness of 2 mm.
The obtained sheet was molded into a dumbbell-shaped No. 3 test piece, and the elongation at break EB ₀ was measured in accordance with JIS K 6251. Next, the vulcanized molded article was heated at 150°C for 144 hours, and the elongation at break EB _i was measured again in accordance with JIS K 6251. The change in elongation at break ΔEB before and after the heat resistance test was calculated from the elongation at break EB ₀ before heating and the elongation at break EB _i after heating.
ΔEB=(EB _i -EB ₀ )÷EB ₀ ×100

(Compression set)
The rubber composition was press-vulcanized at 180°C for 30 minutes to produce a cylindrical vulcanized molded article having a diameter of 29 mm and a height of 12.5 mm. The compression set of the vulcanized molded article was measured at 150°C for 72 hours in accordance with JIS K 6262:2013.

Claims (11)

100 parts by mass of chloroprene rubber;
2 to 100 parts by mass of silica having a BET specific surface area of 10 to 120 m ² /g;
0.1 to 8 parts by mass of a maleimide compound;
0.1 to 5 parts by mass of an organic peroxide;
A rubber composition containing 1 to 15 parts by mass of a silane coupling agent per 100 parts by mass of the silica,
The rubber composition further contains 0.1 to 9 parts by mass of a hydrotalcite compound per 100 parts by mass of the chloroprene rubber. The rubber composition according to claim 1, wherein the chloroprene-based rubber contains a homopolymer of 2-chloro-1,3-butadiene or a copolymer of 2-chloro-1,3-butadiene and at least one monomer selected from 2,3-dichloro-1,3-butadiene and an unsaturated nitrile monomer. The rubber composition according to claim 1 or claim 2, wherein the silane coupling agent includes at least one selected from a silane coupling agent having a double bond in its structure, a silane coupling agent having an amino group, and a silane coupling agent having a double bond and an amino group. The rubber composition according to claim 1 or 2, wherein the silane coupling agent is at least one silane coupling agent selected from vinyltrimethoxysilane, vinyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropylmethyldiethoxysilane, 3-(meth)acryloxypropylmethyltriethoxysilane, and N-phenyl-3-aminopropyltrimethoxysilane. The rubber composition according to claim 1 or 2, wherein the maleimide compound is at least one maleimide compound selected from the group consisting of 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, N, N' -(4-methyl-1,3-phenylene)bismaleimide, and 1,6-bismaleimide-(2,2,4-trimethyl)hexane. The rubber composition according to claim 1 or 2, wherein the organic peroxide is at least one organic peroxide selected from dicumyl peroxide, 1,4-bis[(t-butylperoxy)isopropyl]benzene, tert-butyl-α-cumyl peroxide, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane, 2,5-bis(tert-butylperoxy)-2,5-dimethyl-3-hexyne, and 4,4-bis[(t-butyl)peroxy]butyl pentanoate. The rubber composition according to claim 1 or claim 2, further comprising 1 to 30 parts by mass of a compound having a thioether structure per 100 parts by mass of the chloroprene rubber. 100 parts by mass of chloroprene rubber;
2 to 100 parts by mass of silica having a BET specific surface area of 10 to 120 m ² /g;
0.1 to 8 parts by mass of a maleimide compound;
0.1 to 5 parts by mass of an organic peroxide;
A rubber composition containing 1 to 15 parts by mass of a silane coupling agent per 100 parts by mass of the silica,
The rubber composition, wherein the silane coupling agent comprises at least one selected from a silane coupling agent having a double bond in its structure, a silane coupling agent having an amino group, and a silane coupling agent having a double bond and an amino group. 100 parts by mass of chloroprene rubber;
2 to 100 parts by mass of silica having a BET specific surface area of 10 to 120 m ² /g;
0.1 to 8 parts by mass of a maleimide compound;
0.1 to 5 parts by mass of an organic peroxide;
A rubber composition containing 1 to 15 parts by mass of a silane coupling agent per 100 parts by mass of the silica,
The rubber composition further contains 1 to 30 parts by mass of a compound having a thioether structure relative to 100 parts by mass of the chloroprene rubber. A vulcanizate of the rubber composition described in claim 1, claim 2, claim 8, or claim 9. A vulcanized molded article of the rubber composition according to claim 1, claim 2, claim 8, or claim 9.