WO2024203824A1 - Rubber composition, vulcanization molded body, and rubber roll - Google Patents

Abstract

The present invention provides a rubber composition which makes it possible to achieve a vulcanization molded body that has excellent water resistance and alkali resistance. The present invention specifically provides a rubber composition which contains a rubber component, wherein if X is the hardness of a laminate, which is obtained by superposing vulcanization molded bodies 1 of the rubber composition for testing upon each other until the thickness of the laminate reaches 6.0 mm or more, as measured by a type A durometer in accordance with JIS K 6253-3 (2023) and Y is the heat generation as obtained by evaluating a vulcanization molded body 2 of the rubber composition for testing by a constant strain flexometer test in accordance with JIS K 6265 (2018) under the conditions of 40° C, a strain of 0.175 inch, a load of 55 pounds and a frequency of 1,800 times per minute, the hardness X and the heat generation Y satisfy the formula (1) below. Meanwhile, the vulcanization molded body 1 for testing is a sheet-like vulcanization molded body having a thickness of 2 mm, the sheet-like vulcanization molded body being obtained by press-vulcanizing the rubber composition in accordance with JIS K 6299 (2012) under the conditions of 170°C and 20 minutes, and the vulcanization molded body 2 for testing is a cylindrical vulcanization molded body having a diameter of 15 mm and a height of 25 mm, the cylindrical vulcanization molded body being obtained by press-vulcanizing the rubber composition under conditions of 170°C and 20 minutes.　(1): 1.4X - Y > 45.0

Description

Rubber composition, vulcanized molded product, and rubber roll

The present invention relates to a rubber composition, a vulcanized molded product, and a rubber roll.

Rubber products are 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, etc.

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, in which 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 previously determined 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 of a specific structure.

Japanese Patent Application Publication No. 11-209522 International Publication No. 2020/044899

However, conventional rubber compositions have room for improvement in terms of water resistance and alkali resistance in vulcanized molded products made from the composition.

The present invention was made in consideration of these circumstances, and provides a rubber composition that can produce vulcanized molded products with excellent water resistance and alkali resistance.

According to the present invention, there is provided a rubber composition containing a rubber component, wherein a laminate obtained by stacking test vulcanized molded articles 1 of the rubber composition to a thickness of 6.0 mm or more has a hardness measured by a type A durometer based on JIS K 6253-3:2023 of X, and a test vulcanized molded article 2 of the rubber composition is evaluated in a constant strain flexometer test based on JIS K 6265:2018 under conditions of 40°C, strain of 0.175 inches, load of 55 pounds, and vibration frequency of 1,800 times per minute, and the hardness X and heat generation Y satisfy the following formula (1), and the test vulcanized molded article 1 is obtained by stacking test vulcanized molded articles 1 of the rubber composition to a thickness of 6.0 mm or more, and the hardness X and heat generation Y satisfy the following formula (1), The test vulcanized molded body 1 is a cylindrical vulcanized molded body having a diameter of 15 mm and a height of 25 mm, obtained by press-vulcanizing the rubber composition at 170°C for 20 minutes based on Japanese Patent Laid-Open No. 6299:2012. The test vulcanized molded body 2 is a cylindrical vulcanized molded body having a diameter of 15 mm and a height of 25 mm, obtained by press-vulcanizing the rubber composition at 170°C for 20 minutes based on Japanese Patent Laid-Open No. 6299:2012.
1.4X-Y>45.0 (1)

The inventors conducted extensive research and discovered that by adjusting the rubber composition formulation so that the hardness X of a test vulcanized molded product 1 of the rubber composition and the heat generation Y of a test vulcanized molded product 2 of the rubber composition satisfy a specific relationship, a rubber composition can be obtained that can produce a vulcanized molded product with excellent water resistance and alkali resistance, which led to the completion of the present invention.

Below are examples of various embodiments of the present invention. The embodiments shown below can be combined with each other.

[1] A rubber composition containing a rubber component, wherein a laminate obtained by stacking test vulcanized molded products 1 of the rubber composition to a thickness of 6.0 mm or more has a hardness measured with a type A durometer based on JIS K 6253-3:2023 of X, and a test vulcanized molded product 2 of the rubber composition is evaluated in a constant strain flexometer test based on JIS K 6265:2018 under conditions of 40°C, strain of 0.175 inches, load of 55 pounds, and vibration frequency of 1,800 times per minute, and the hardness X and heat generation Y satisfy the following formula (1), and the test vulcanized molded product 1 is obtained by stacking test vulcanized molded products 1 of the rubber composition to a thickness of 6.0 mm or more. The test vulcanized molded body 1 is a cylindrical vulcanized molded body having a diameter of 15 mm and a height of 25 mm, obtained by press-vulcanizing the rubber composition at 170°C for 20 minutes based on MHI No. 6299:2012.
1.4X-Y>45.0 (1)
[2] The rubber composition according to [1], wherein the hardness X is 40 or more and 98 or less.
[3] The rubber composition according to [1] or [2], wherein the rubber component contains a chloroprene-based polymer.
[4] The rubber composition according to [3], wherein the chloroprene polymer contains 80 to 100 mass % of chloroprene monomer units relative to 100 mass % of the chloroprene polymer.
[5] A vulcanized molded article of the rubber composition according to any one of [1] to [4].
[6] A rubber roll comprising a core and a surface layer provided on the peripheral surface of the core, the surface layer including the vulcanized molded article according to [5], and used in at least one of an acid washing line and an alkali washing line.
[7] A vulcanized molded product containing a rubber component, wherein when the vulcanized molded product is made into a test vulcanized molded product 1' having a thickness of 6.0 mm or more, the hardness measured with a type A durometer based on JIS K 6253-3:2023 is X', and when the vulcanized molded product is made into a cylindrical test vulcanized molded product 2' having a diameter of 15 mm and a height of 25 mm, the heat generation determined by evaluation in a constant strain flexometer test based on JIS K 6265:2018 under conditions of 40°C, strain of 0.175 inches, load of 55 pounds, and vibration frequency of 1,800 times per minute is Y', the hardness X' and heat generation Y' satisfy the following formula (2).
1.4X'-Y'>45.0 (2)

The rubber composition according to the present invention makes it possible to obtain a vulcanized molded article having excellent water resistance and alkali resistance. Furthermore, since the vulcanized molded article according to the present invention has excellent water resistance and alkali resistance, these properties can be utilized to use it as various components that require water resistance and/or alkali resistance, such as rubber rolls. The rubber roll according to one embodiment of the present invention has excellent water resistance and alkali resistance, and can be used, for example, as at least one rubber roll in an acid washing line and an alkali washing line.

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 a rubber component.

1.1 Rubber Component The rubber component according to the present invention may contain at least one selected from chloroprene rubber, natural rubber (NR), hydrogenated acrylonitrile butadiene rubber (H-NBR), acrylonitrile butadiene rubber (NBR), and chlorosulfonated polyethylene (CSM). The rubber component preferably contains at least one selected from chloroprene rubber and natural rubber (NR), and the rubber composition according to one embodiment of the present invention preferably contains chloroprene rubber, i.e., it preferably contains a chloroprene polymer.

1.1.1 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.

The chloroprene-based polymer according to one embodiment of the present invention may have a monomer unit derived from a monomer other than the chloroprene monomer. The monomer other than the chloroprene monomer is not particularly limited as long as it is copolymerizable with the chloroprene monomer, and examples of the monomer other than the chloroprene monomer include unsaturated nitriles, 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.), 2,3-dichloro-1,3-butadiene, 1-chloro-1,3-butadiene, butadiene, isoprene, ethylene, styrene, sulfur, etc. The chloroprene-based polymer according to one embodiment of the present invention may contain at least one monomer unit selected from 2,3-dichloro-1,3-butadiene and an unsaturated nitrile monomer. The chloroprene polymer according to one embodiment of the present invention may contain unsaturated nitrile monomer units.

The chloroprene polymer according to one embodiment of the present invention can have an unsaturated nitrile monomer unit content of 25% by mass or less, preferably 20% by mass or less, and more preferably less than 20% by mass, when the chloroprene polymer is taken as 100% by mass. The unsaturated nitrile monomer unit content 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, or 25% by mass, and may be within a range between any two of the numerical values exemplified here. By making the content of the unsaturated nitrile monomer unit in the rubber composition equal to or less than the above upper limit, the water resistance and cold resistance of the vulcanized molded product of the rubber composition are further improved. In addition, by including the unsaturated nitrile monomer unit, the oil resistance of the vulcanized molded product of the rubber composition is improved.

Examples of unsaturated nitriles include acrylonitrile, methacrylonitrile, ethacrylonitrile, and phenylacrylonitrile. The unsaturated nitriles may be used alone or in combination of two or more. It is preferable that the unsaturated nitrile contains acrylonitrile, from the viewpoint of easily obtaining excellent moldability, and from the viewpoint of easily obtaining excellent breaking strength, breaking elongation, hardness, tear strength, and oil resistance in the vulcanized molded product.

The content of unsaturated nitrile monomer units contained in chloroprene rubber can be calculated from the content of nitrogen atoms in the chloroprene rubber. Specifically, the content of nitrogen atoms in 100 mg of chloroprene rubber can be measured using an elemental analyzer (Sumigraph 220F: manufactured by Sumika Chemical Analysis Center Co., 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, and oxygen is flowed at 0.2 mL/min as the combustion gas and 80 mL/min as the carrier gas. A calibration curve can be created using aspartic acid (10.52%), which has a known nitrogen content, as a standard substance.

The chloroprene polymer according to one embodiment of the present invention preferably contains 75 to 100 mass% of chloroprene monomer units, and more preferably 80 to 100 mass%, when the chloroprene polymer is taken as 100 mass%. The content of chloroprene monomer units in the chloroprene polymer may be, for example, 75, 80, 85, 90, 95, 99, or 100 mass%, and may be within a range between any two of the numerical values exemplified here. By setting the content of chloroprene monomer units within the above numerical range, a rubber composition can be obtained that can give a molded article with an excellent balance of hardness, tensile strength, and cold resistance.

The chloroprene polymer 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 polymer is taken as 100 mass%. The content of monomer units other than chloroprene monomer units and unsaturated nitrile monomer units in the chloroprene polymer 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 numerical values exemplified here. By adjusting the copolymerization amount of monomers other than chloroprene monomer and unsaturated nitrile monomer to the above range, it is possible to achieve the effect of copolymerizing these monomers without impairing the properties of the resulting rubber composition.

The chloroprene-based rubber according to one embodiment of the present invention can contain at least one polymer selected from a chloroprene homopolymer, a copolymer containing chloroprene monomer units and unsaturated nitrile monomer units, and a copolymer containing chloroprene monomer units and 2,3-dichloro-1,3-butadiene monomer units.

The rubber component according to the present invention may use one chloroprene rubber alone or two or more chloroprene rubbers in combination.
When the rubber composition according to one embodiment of the present invention contains two or more chloroprene-based rubbers, it is preferable that the content based on the total amount of each monomer unit contained in the two or more chloroprene-based polymers be within the above-mentioned numerical range relative to 100 mass% in total of the two or more chloroprene-based polymers contained in the rubber composition.

The chloroprene polymer (chloroprene homopolymer, chloroprene copolymer, etc.) contained in the chloroprene 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.

1.1.2 Method for Producing Chloroprene Rubber There is no particular limitation on the method for producing the chloroprene rubber of the present invention. The chloroprene rubber can be obtained by a production 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 or a raw material monomer containing a chloroprene monomer and other monomers is emulsion-polymerized using an appropriate amount of an emulsifier, a dispersant, a catalyst, a chain transfer agent, etc., and when the target final conversion rate is reached, a polymerization terminator is added to obtain a latex containing a chloroprene-based polymer containing a chloroprene monomer unit. Next, unreacted monomers can be removed from the polymerization liquid obtained by the emulsion polymerization step. The method is not particularly limited, and examples of the method include a steam stripping method. Thereafter, the pH is adjusted, and a chloroprene rubber containing a chloroprene-based polymer is obtained through conventional processes such as freeze coagulation, water washing, and hot air drying.

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

The emulsifier used in emulsion polymerization is not particularly limited, and any known emulsifier commonly used in 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 regulator used in emulsion polymerization is not particularly limited, and any known molecular weight regulator 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 can be suitably used as molecular weight regulators for the chloroprene rubber according to one embodiment of the present invention.

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 stops the polymerization reaction may be added to terminate the polymerization when the desired conversion rate is reached.

There are no particular limitations on the polymerization terminator, and any known polymerization terminator commonly used in 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 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 going through conventional processes such as freeze coagulation, water washing, and hot air drying.

Chloroprene rubber is classified into mercaptan-modified type, xanthogen-modified type, sulfur-modified type, dithiocarbonate-based type, trithiocarbonate-based type, and carbamate-based type depending on the type of molecular weight regulator.

1.2 Organic Peroxide The rubber composition according to the present invention may contain an organic peroxide. One or more organic peroxides may be freely selected and used.

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, t-butyl peroxypivalate, 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-trimethylcyclohexane, 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-butylperoxy2-ethylhexyl monocarbonate, t-hexylperoxybenzoate, 2,5-di-methyl-2,5-di(benzoylperoxy)hexane, t-butylperoxy butylperoxyacetate, 2,2-di-(t-butylperoxy)butane, t-butylperoxybenzoate, n-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, and t-butyl hydroperoxide. Among these, at least one selected from dicumyl peroxide, 1,4-bis[(t-butylperoxy)isopropyl]benzene, t-butyl-α-cumyl peroxide, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane, and 2,5-dimethyl-2,5-bis(t-butylperoxy)hexyne-3 is preferred, with 1,4-bis[(t-butylperoxy)isopropyl]benzene being particularly preferred.

The rubber composition according to the present invention preferably contains 0 to 5 parts by mass of organic peroxide relative to the rubber components contained in the rubber composition, from the viewpoint of ensuring processing safety and being able to obtain a good vulcanized molded product. The content of organic peroxide is, for example, 0, 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 numerical values exemplified here. In addition, the rubber composition according to one embodiment of the present invention does not contain an organic peroxide, and by adjusting the types and amounts of other components, it is also possible to adjust the hardness X, heat generation Y, and the relationship between hardness X and heat generation Y.

1.3 Vulcanizing agent The rubber composition according to the present invention may contain a vulcanizing agent. The type of vulcanizing agent is not particularly limited as long as it does not impair the effects of the present invention. The vulcanizing agent is preferably a vulcanizing agent that can be used for vulcanizing chloroprene-based rubber. One or more vulcanizing agents may be freely selected and used. An example of the vulcanizing agent is zinc oxide.

The rubber composition according to the present invention preferably contains 1 to 15 parts by mass of a vulcanizing agent relative to the rubber component contained in the rubber composition, from the viewpoint of ensuring processing safety and being able to obtain a sufficiently vulcanized molded product. The content of the vulcanizing agent is, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 parts by mass relative to 100 parts by mass of the rubber component contained in the rubber composition, and may be within a range between any two of the numerical values exemplified here.

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

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・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.

Examples of _hydrotalcite include _Mg4.3Al2 ( _OH ) _{12.6CO3.3.5H2O} , _Mg3ZnAl2 (OH) _{12CO3.3H2O , Mg4.5Al2 ( OH ) 13CO3.3.5H2O , Mg4.5Al2} ( _OH ) _13CO3 , _{Mg4Al2 ( OH} ) _{12CO3.3.5H2O , Mg6Al2 ( OH ) 16CO3.4H2O , Mg5Al2 ( OH} ) _14CO3.4H2O , _{and Mg3Al2} ( _OH ) _{10CO3.1.7H2O . Particularly preferred is Mg4.3 Al2 ( OH} ) _{12.6CO3.3.5H2O} , _{Mg3ZnAl2 ( OH ) 12CO3.3H2O} .

The amount of the acid acceptor added can be 0.1 to 15 parts by mass per 100 parts by mass of the rubber component contained in the rubber composition. The amount of the acid acceptor 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, or 15 parts by mass, and may be within a range between any two of the numerical values exemplified here.

1.5 Maleimide Compound The rubber composition according to one embodiment of the present invention may contain a maleimide compound. The maleimide compounds may 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, 4-methyl-1,3-phenylene bismaleimide, and 1,6'-bismaleimide-(2,2,4-trimethyl)hexane. From the viewpoint of improving the heat resistance of the resulting vulcanized product and vulcanized molded body, it is particularly preferable to use N,N'-m-phenylene bismaleimide (also known as m-phenylene dimaleimide).

The rubber composition according to one embodiment of the present invention may contain 0 to 10 parts by mass of a maleimide compound per 100 parts by mass of the rubber component. The content of the maleimide compound may be, for example, 0, 0.1, 0.2, 0.3, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 parts by mass, and may be within a range between any two of the numerical values exemplified here. By setting the content of the maleimide compound to the above lower limit or more, the vulcanization of the obtained rubber composition proceeds more sufficiently, and a vulcanized molded product having good mechanical properties and heat resistance can be obtained. In addition, by setting the content of the maleimide compound to the above upper limit or less, the rubber elasticity of the obtained vulcanized molded product can be sufficiently maintained. In addition, the rubber composition according to one embodiment of the present invention may not contain a maleimide compound, and instead, by adjusting the types and amounts of other components, the hardness X, heat generation Y, and the relationship between hardness X and heat generation Y can be adjusted.

1.6 Filler The rubber composition according to an embodiment of the present invention may contain a filler, and may contain carbon black. Examples of carbon black include furnace carbon black such as SAF, ISAF, HAF, EPC, XCF, FEF, GPF, HMF, and SRF, modified carbon black such as hydrophilic carbon black, channel black, lamp black, thermal carbon such as FT and MT, acetylene black, and ketjen black.

The rubber composition according to the present invention may contain 0 parts by mass or more and less than 100 parts by mass of carbon black per 100 parts by mass of the rubber component. The carbon black content may be, for example, 0, 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 99 parts by mass, or may be within a range between any two of the numerical values exemplified here.

The rubber composition according to the present invention may also contain fillers other than carbon black, provided that the effects of the present invention are not impaired. Examples of fillers other than carbon black include silica, such as wet silica filler (hydrated silica), dry silica filler (anhydrous silicic acid), and colloidal silica filler, clay, talc, and calcium carbonate. These may be used alone or in combination of two or more.

In the rubber composition according to one embodiment of the present invention, when the rubber component is taken as 100 parts by mass, the total amount of carbon black and fillers (reinforcing materials) other than carbon black contained in the rubber composition is preferably 0 to 100 parts by mass. In the rubber composition according to one embodiment of the present invention, when the total amount of carbon black and fillers (reinforcing materials) other than carbon black contained in the rubber composition is taken as 100 mass%, the content of fillers/reinforcing materials other than carbon black can be 50 mass% or less. The content of fillers/reinforcing materials other than carbon black can be, for example, 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, or 50 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 can also not contain fillers (reinforcing materials) other than carbon black. In addition, the rubber composition according to one embodiment of the present invention can adjust the hardness X and heat generation Y, and the relationship between hardness X and heat generation Y, by not blending carbon black and fillers other than carbon black, and adjusting the types and blending amounts of other components.

1.7 Silane coupling agent When the rubber composition according to one embodiment of the present invention contains silica as a filler, it may contain a silane coupling agent. There is no particular limitation on the silane coupling agent, 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. In particular, from the viewpoint of scorch resistance and reinforcing effect, vinyl coupling agents, methacrylic coupling agents, and acrylic coupling agents that start reacting under high temperature conditions during crosslinking are preferred.

The rubber composition according to one embodiment of the present invention may contain 0.5 to 10 parts by mass of a silane coupling agent per 100 parts by mass of silica contained in the rubber composition. The content of the silane coupling agent may be, for example, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 parts by mass per 100 parts by mass of silica, and may be within a range between any two of the numerical values exemplified here. Silica may be used alone or in combination of two or more types. By containing the above-mentioned silane coupling agent and setting the content of the silane coupling agent within the above numerical range, it is possible to improve the dispersibility of the silica filler in the rubber and the reinforcing effect between the rubber and the silica filler, and to suppress the occurrence of scorch.

1.8 Lubricant, Processing Aid The rubber composition according to the present invention may further contain a lubricant and/or a processing aid. The lubricant and processing aid are mainly added to improve processability, such as making the rubber composition easier to peel off from rolls, molding dies, extruder screws, etc. Examples of the lubricant and processing aid include fatty acids such as stearic acid, paraffin processing aids such as polyethylene, fatty acid amides, vaseline, factice, etc. These may be used alone or in combination of two or more. The rubber composition according to the present invention may contain 0.1 to 15 parts by mass of the lubricant and processing aid per 100 parts by mass of the rubber component, and may also be 1 to 10 parts by mass. The content of the lubricant and processing aid is, for example, 0.1, 0.2, 0.5, 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 numerical values exemplified here.

1.9 Vulcanization Accelerator The rubber composition according to the present invention may contain a vulcanization accelerator, and may contain 0 to 5.0 parts by mass of the vulcanization accelerator when the rubber composition contained in the composition is 100 parts by mass. The content of the vulcanization accelerator is, for example, 0, 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 parts by mass, and may be within a range between any two of the numerical values exemplified here. In addition, the rubber composition according to the present invention may not contain a vulcanization accelerator. The rubber composition according to one embodiment of the present invention does not contain a vulcanization accelerator, and by adjusting the type and amount of other components, it is also possible to adjust the hardness X and heat generation Y, and the relationship between the hardness X and heat generation Y.

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 vulcanization of chloroprene rubber. The vulcanization accelerator can be freely selected and used alone or in combination of two or more kinds.
Examples of the vulcanization accelerator include sulfur, thiuram-based vulcanization accelerators, dithiocarbamate-based vulcanization accelerators, thiourea-based vulcanization accelerators, guanidine-based vulcanization accelerators, xanthogenate-based vulcanization accelerators, and thiazole-based vulcanization accelerators.

Examples of the thiuram vulcanization accelerator include tetramethylthiuram disulfide (TMTD), tetraethylthiuram disulfide, tetrabutylthiuram disulfide, tetrakis(2-ethylhexyl)thiuram disulfide, tetramethylthiuram monosulfide, and dipentamethylenethiuram tetrasulfide.
Examples of the dithiocarbamate-based vulcanization accelerator 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 thiourea-based vulcanization accelerator 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 the xanthogenate-based vulcanization accelerator include zinc butylxanthogenate and zinc isopropylxanthogenate.
Examples of the thiazole-based vulcanization accelerator include 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, 2-mercaptobenzothiazole zinc salt, 2-mercaptobenzothiazole cyclohexylamine salt, 2-(4'-morpholinodithio)benzothiazole, and N-cyclohexylbenzothiazole-2-sulfenamide.
These may be used alone or in combination of two or more.

1.10 Others In addition to the above-mentioned components, the rubber composition according to the present invention may further contain components such as an antiaging agent, an antioxidant, a flame retardant, and a vulcanization retarder, as long as the effects of the present invention are not impaired. Examples of the antiaging agent and the antioxidant include ozone antiaging agents, phenolic antiaging agents, amine antiaging agents, acrylate antiaging agents, imidazole antiaging agents, carbamic acid metal salts, waxes, phosphorus antiaging agents, and sulfur antiaging agents. Examples of the imidazole antiaging agents include 2-mercaptobenzimidazole, 2-mercaptomethylbenzimidazole, and zinc salts of 2-mercaptobenzimidazole. The rubber composition according to the present invention may contain 0.1 to 10 parts by mass of the antiaging agent and the antioxidant in total, relative to 100 parts by mass of the rubber component contained in the rubber composition.

The rubber composition according to one embodiment of the present invention is such that, by setting the types and contents of the components in the rubber composition to the above-mentioned aspects, the hardness X of the test vulcanized molded product 1 of the rubber composition and the heat generation Y of the test vulcanized molded product 2 of the rubber composition tend to satisfy the relationship of formula (1).

2. Method for Producing Rubber Composition The rubber composition according to one embodiment of the present invention can be obtained by kneading the rubber component and other necessary components at a temperature equal to or lower than the vulcanization temperature. The method for producing the rubber composition according to one embodiment of the present invention can include a mixing step of mixing the rubber component and other necessary components at a temperature equal to or lower than the vulcanization temperature.

The production method according to one embodiment of the present invention may include a first mixing step, a standing step, and a second mixing step.
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, and in the standing step, the rubber composition precursor is stood at 23°C or less for 12 hours or more, and in the second mixing step, the compounding ingredients for the second mixing step are added to the rubber composition precursor after standing and mixed to obtain a rubber composition.

In the first mixing step, raw materials including a rubber component and compounding components for the first mixing step are mixed to obtain a rubber composition precursor. The compounding components for the first mixing step may not include a vulcanizing agent, a vulcanization accelerator, an organic peroxide, or a maleimide compound. It is preferable that the compounding components for the first mixing step do not include components that contribute to vulcanization and crosslinking. The compounding components for the first mixing step may include at least one, two, three, four, five, or six of carbon black, acid acceptors, lubricants, processing aids, plasticizers, and antioxidants, or may include all of these.

In the standing step, the rubber composition precursor is allowed to stand for 12 hours or more at 23° C. or lower. The standing temperature can be, for example, 5 to 23° C., and may be 5, 8, 11, 14, 17, 20, or 23° C., or may be within a range between any two of the numerical values exemplified here. The standing time can be, for example, 12 to 24 hours, and may be, for example, 12, 14, 16, 18, 20, 22, or 24 hours, or may be within a range between any two of the numerical values exemplified here.
In one embodiment of the present invention, the hardness X and heat generation Y can be adjusted by undergoing a standing process.

In the second mixing step, the compounding components for the second mixing step are added to the rubber composition precursor after standing and mixed to obtain a rubber composition. The compounding components for the second mixing step may include a vulcanizing agent, a vulcanization accelerator, an organic peroxide, and a maleimide compound. The compounding components for the second mixing step may also include carbon black, a lubricant, a processing aid, a plasticizer, an acid acceptor, an anti-aging agent, etc.

In each mixing step, the raw material components are kneaded using conventional kneading devices such as mixers, Banbury mixers, kneader mixers, and open rolls.

3. Characteristics of Rubber Composition In one embodiment of the rubber composition, when a laminate obtained by stacking test vulcanized molded products 1 of the rubber composition to a thickness of 6.0 mm or more is measured with a type A durometer based on JIS K 6253-3:2023 as X, and a test vulcanized molded product 2 of the rubber composition is evaluated in a constant strain flexometer test based on JIS K 6265:2018 under conditions of 40°C, strain of 0.175 inches, load of 55 pounds, and vibration frequency of 1,800 times per minute as Y,
The hardness X and the heat generation Y satisfy the following formula (1).
1.4X-Y>45.0 (1)

Here, the test vulcanized molded article 1 is a sheet-like vulcanized molded article having a thickness of 2 mm obtained by press-vulcanizing a rubber composition based on JIS K 6299:2012 under conditions of 170°C and 20 minutes.
The test vulcanized molded article 2 was a cylindrical vulcanized molded article having a diameter of 15 mm and a height of 25 mm, which was obtained by press-vulcanizing the rubber composition at 170° C. for 20 minutes.

The rubber composition according to the present invention is a rubber composition capable of obtaining a vulcanized molded article having excellent water resistance and alkali resistance by adjusting the hardness X and heat generation Y of the vulcanized molded article of the rubber composition so that the hardness X and heat generation Y satisfy the relationship of formula (1).
The hardness X can be controlled by adjusting the manufacturing conditions described later, for example, by the amount of the filler and the plasticizer. The heat generation Y can be controlled by adjusting the manufacturing conditions described later, for example, by the type and amount of the filler, the crosslink density of the obtained vulcanized molded body, and the type and amount of the plasticizer. It is considered that when the amount of the filler is increased, the heat generation Y increases, when the crosslink density becomes dense, the heat generation Y decreases, and when the amount of the plasticizer is increased, the heat generation Y increases. Here, it is presumed that when the relationship between the hardness X and the heat generation Y is adjusted to satisfy the formula (1), the amount of the filler, the amount of the plasticizer, the crosslink density, etc. at the hardness X are adjusted, and thus it is possible to obtain a rubber composition capable of obtaining a vulcanized molded body having excellent water resistance and alkali resistance.
The value of (1.4X-Y) can be greater than 45.0 and less than or equal to 100.0, for example, 45.5, 50.0, 55.0, 60.0, 65.0, 70.0, 75.0, 80.0, 85.0, 90.0, 95.0, 100.0, or within a range between any two of the numerical values exemplified here.

In the rubber composition according to one embodiment of the present invention, it is preferable that the hardness X of a laminate obtained by stacking test vulcanized molded bodies 1 of the rubber composition to a thickness of 6.0 mm or more, as measured with a type A durometer according to JIS K 6253-3:2023, is 40 to 98. The hardness X may be, for example, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 98, or may be within a range between any two of the numerical values exemplified here.

Hardness X can be controlled by adjusting the manufacturing method of the rubber composition, for example, the presence or absence, type and amount of each component blended into the rubber composition, particularly the type and amount of filler and plasticizer, as well as the manufacturing conditions of the rubber composition (particularly the presence or absence, temperature and time of a standing process).

In the rubber composition according to one embodiment of the present invention, the heat generation Y determined by evaluating a test vulcanized molded product 2 of the rubber composition in a constant strain flexometer test based on JIS K 6265:2018 under conditions of 40°C, strain of 0.175 inches, load of 55 pounds, and vibration frequency of 1,800 times per minute is preferably 85°C or less. Heat generation Y may be, for example, 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, or 85°C, or may be within a range between any two of the values exemplified here.

The heat generation Y can be controlled by adjusting the manufacturing method of the rubber composition, in particular the presence or absence, type and amount of each component blended into the rubber composition, such as the presence or absence, type and amount of fillers and components that contribute to vulcanization and crosslinking, as well as the manufacturing conditions of the rubber composition (in particular the presence or absence, temperature and time of a standing process).

Hardness X and heat generation Y can be specifically evaluated by the method described in the Examples.

In the rubber composition according to one embodiment of the present invention, when a test vulcanized molding 1 and/or a test vulcanized molding 2 of the rubber composition is immersed in water at 70°C for 144 hours, the volume change rate ΔV calculated based on JIS K 6258 is preferably less than 9%, and more preferably less than 6%. The volume change rate ΔV when immersed in water at 70°C for 144 hours is, for example, 0, 1, 2, 3, 4, 5, 6, 7, 8% or less than 9%, 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, when a test vulcanized molding 1 and/or a test vulcanized molding 2 of the rubber composition is immersed in 10% sodium hydroxide at 70°C for 144 hours, the volume change rate ΔV calculated based on JIS K 6258 is preferably less than 10%, and more preferably less than 7%. When immersed in water at 70°C for 144 hours, the volume change rate ΔV is, for example, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9%, or less than 10%, and may be within a range between any two of the numerical values exemplified here.

The water resistance and alkali resistance of the vulcanized molded product of the rubber composition can be measured specifically by the method described in the Examples.

6. Unvulcanized molded body, vulcanized product, and vulcanized molded body The unvulcanized molded body according to one embodiment of the present invention uses the rubber composition according to one embodiment of the present invention, and is a molded body (molded product) of the rubber composition (unvulcanized state) according to one embodiment of the present invention. The manufacturing method of the unvulcanized molded body 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 body according to one embodiment of the present invention is made of the rubber composition (unvulcanized state) according to one embodiment of the present invention.

The vulcanizate according to one embodiment of the present invention is a vulcanizate of the rubber composition according to one embodiment of the present invention. The method for producing the 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.

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

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

In one embodiment of the present invention, the vulcanized molded product has a hardness of X', measured with a type A durometer in accordance with JIS K 6253-3:2023 when the vulcanized molded product is made into a test vulcanized molded product 1' having a thickness of 6.0 mm or more, and Y', measured with a constant strain flexometer test under conditions of 40°C, strain of 0.175 inches, load of 55 pounds, and vibration frequency of 1,800 times per minute when the vulcanized molded product is made into a cylindrical test vulcanized molded product 2' having a diameter of 15 mm and a height of 25 mm, in accordance with JIS K 6265:2018,
It is preferable that the hardness X′ and the heat generation Y′ satisfy the following formula (2).
1.4X'-Y'>45.0 (2)
The test vulcanization molded article 1' having a thickness of 6.0 mm or more may be a laminate of a plurality of vulcanization molded articles having a thickness of less than 6.0 mm. The test vulcanization molded article 1' may have a thickness of 6.0 mm or more and 7.0 mm or less.

The value of (1.4X-Y) is greater than 45.0, for example, 45.5, 50.0, 55.0, 60.0, 65.0, 70.0, 75.0, 80.0, 85.0, 90.0, 95.0, 100.0, and may be within a range between any two of the values given here as examples.

The hardness X' of the test vulcanized molded body 1' according to one embodiment of the present invention may be, for example, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 98, and may be within a range between any two of the numerical values exemplified here.

The heat generation Y' of the test vulcanized molded body 2' according to one embodiment of the present invention may be, for example, 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, or 85°C, or may be within a range between any two of the values exemplified here.

The vulcanized molded product according to one embodiment of the present invention has a volume change rate ΔV calculated based on JIS K 6258 when immersed in water at 70°C for 144 hours of preferably less than 9%, more preferably less than 6%. The volume change rate ΔV when immersed in water at 70°C for 144 hours of may be, for example, 0, 1, 2, 3, 4, 5, 6, 7, 8% or less than 9%, and may be within a range between any two of the numerical values exemplified here.

The vulcanized molded product according to one embodiment of the present invention has a volume change rate ΔV calculated based on JIS K 6258 when immersed in 10% sodium hydroxide at 70°C for 144 hours, which is preferably less than 10%, and more preferably less than 7%. The volume change rate ΔV when immersed in water at 70°C for 144 hours may be, for example, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9% or less than 10%, and may be within a range between any two of the numerical values exemplified here.

The hardness, heat generation, water resistance, and alkali resistance of the vulcanized molded body can be specifically measured by the method described in the Examples. The hardness, heat generation, water resistance, and alkali resistance of the vulcanized molded body can also be controlled by adjusting the manufacturing method of the rubber composition, for example, the presence, type, and amount of each component blended into the rubber composition, particularly the presence, type, and amount of fillers and components that contribute to vulcanization and crosslinking, as well as the manufacturing conditions of the rubber composition (particularly the presence, temperature, and time of a standing process).

The unvulcanized molded product, vulcanized product, and vulcanized molded product 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. The rubber composition according to the present invention has excellent water resistance and alkali resistance, so it can be used as various components where these properties are required. The rubber composition, vulcanized product, and vulcanized molded product 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, and can be used for rubber parts such as automotive rubber parts (e.g., automotive seal materials), hose materials, rubber molded products, gaskets, rubber rolls, industrial cables, industrial conveyor belts, and sponges. In particular, it can be used as transmission belts, conveyor belts, hoses, wipers, immersion products, seal parts, adhesives, boots, rubber-coated cloth, rubber rolls, vibration-proof rubber, or sponge products.

(Rubber parts for automobiles)
Rubber components for automobiles include gaskets, oil seals, and packings, which are components that prevent leakage of liquids and gases and intrusion of garbage and foreign objects such as rainwater and dust into machines and devices. Specifically, there are gaskets used for fixed applications and oil seals and packings used for moving parts and movable parts. For gaskets in which the sealing part is fixed by bolts or the like, various materials are used according to the purpose, as opposed to soft gaskets such as O-rings and rubber sheets. In addition, packings are used for rotating parts such as the shafts of pumps and motors, moving parts of valves, reciprocating parts such as pistons, connecting parts of couplers, water stop parts of water faucets, etc. The rubber composition of the present invention can improve water resistance and alkali resistance. This makes it possible to manufacture automobile parts with excellent oil resistance, which was difficult to do with conventional rubber compositions.

(Hose material)
Hose materials are flexible pipes, and specific examples include high- and low-pressure hoses for water supply, oil supply, air supply, steam, and hydraulic use. The rubber composition of the present invention can enhance the water resistance and alkali resistance of the hose material while maintaining the processability of the unvulcanized product. This makes it possible to manufacture, for example, a hose material with excellent water resistance and alkali resistance, which was difficult to achieve with conventional rubber compositions.

(Rubber mold)
The rubber molded products include anti-vibration rubber, vibration-damping materials, boots, etc. Anti-vibration rubber and vibration-damping materials are rubbers that prevent the transmission and spread of vibrations, and specifically include torsional dampers, engine mounts, muffler hangers, etc. for automobiles and various vehicles that absorb vibrations during engine operation to prevent noise. The rubber composition of the present invention can improve the water resistance and alkali resistance of anti-vibration rubber and vibration-damping materials. This makes it possible to produce anti-vibration rubber and vibration-damping materials with excellent water resistance and alkali resistance, which was difficult to achieve with conventional rubber compositions.
A boot is a bellows-shaped member whose outer diameter gradually increases from one end to the other end, and specific examples include constant velocity joint cover boots for protecting drive parts such as automobile drive systems, ball joint cover boots (dust cover boots), rack and pinion gear boots, etc. The rubber composition of the present invention can improve water resistance and alkali resistance. This makes it possible to manufacture boots that can be used in harsher environments than conventional rubber compositions.

(Gaskets, etc.)
Gaskets, oil seals and packings are components that prevent leakage of liquids or gases and intrusion of garbage or foreign objects such as rainwater or dust into machines or equipment. Specifically, there are gaskets used for fixed applications and oil seals and packings used for moving parts. For gaskets where the sealing part is fixed with bolts or the like, various materials are used according to the purpose, as opposed to soft gaskets such as O-rings and rubber sheets. Packings are also used for rotating parts such as the shafts of pumps and motors, the movable parts of valves, reciprocating parts such as pistons, the connection parts of couplers, the water stop parts of water faucets, etc. The rubber composition of the present invention can improve the water resistance and alkali resistance of these members. This makes it possible to manufacture sealing members with excellent water resistance and alkali resistance, which was difficult to achieve with conventional rubber compositions.

(Rubber roll)
A rubber roll is manufactured by adhesively covering a metal core such as an iron core with rubber, and is generally manufactured by winding a rubber sheet around a metal iron core in a spiral shape. Rubber materials such as NBR, EPDM, and CR are used for rubber rolls according to the required characteristics of 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 object being conveyed, so it is used in a wide range of rubber roll applications. Furthermore, there is a problem that rubber rolls that convey heavy objects are deformed by load, and improvements are required. The rubber composition of the present invention can increase the water resistance and alkali resistance of the rubber roll. This makes it possible to manufacture an embossing rubber roll that is excellent in water resistance and alkali resistance, which was difficult to achieve with conventional rubber compositions. The rubber composition according to one embodiment of the present invention can be used as a rubber roll used in at least one of an acid washing line and an alkali washing line.

A rubber roll according to one embodiment of the present invention comprises a core and a surface layer provided on the peripheral surface of the core, the surface layer including the vulcanized molded body described above, and the rubber roll is used in at least one of an acid washing line and an alkali washing line.

(Industrial cables)
An industrial cable is a linear member for transmitting electrical or optical signals. It is made by covering a good conductor such as copper or a copper alloy, or an optical fiber, with an insulating covering layer, and a wide variety of industrial cables are manufactured depending on their structure and installation location. The rubber composition of the present invention can improve the water resistance and alkali resistance of industrial cables. This makes it possible to manufacture industrial cables with excellent water resistance and alkali resistance, which was difficult to achieve with conventional rubber compositions.

(Industrial conveyor belts)
Industrial conveyor belts are available in rubber, resin, and metal, and are selected according to a wide variety of usage methods. Among these, rubber conveyor belts are inexpensive and widely used, but when used in an environment where there is a lot of friction and collision with the transported goods, they tend to deteriorate and break. The rubber composition of the present invention can improve the water resistance and alkali resistance of industrial conveyor belts. This makes it possible to manufacture industrial conveyor belts with excellent water resistance and alkali resistance that can be used in harsh environments, which was difficult with conventional rubber compositions.

(sponge)
A sponge is a porous material with numerous fine holes inside, and is specifically used in vibration-proofing members, sponge seal parts, wet suits, shoes, etc. The rubber composition of the present invention can improve the acid resistance and water resistance of the sponge. In addition, since a chloroprene-unsaturated nitrile copolymer rubber is used, it is also possible to improve the flame retardancy of the sponge. This makes it possible to produce a sponge with excellent water resistance and alkali resistance that can be used in harsh environments, which was difficult with conventional rubber compositions, and a sponge 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 one embodiment of the present invention 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. The vulcanization temperature may be, for example, 140, 150, 160, 170, 180, 190, 200, 210, or 220°C, and may be within a range between any two of the numerical values exemplified here. 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 body, etc., and may be 10 to 300 minutes. For example, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300 minutes, or within a range between any two of the values exemplified here.

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

<Production method of chloroprene rubber (A-2)>
Into a polymerization vessel having an internal volume of 3 L equipped with a heating/cooling jacket and a stirrer, 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 pure 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) were added. Next, 0.1 parts by mass of potassium persulfate was added as a polymerization initiator, and emulsion polymerization was carried out under a nitrogen gas flow at a polymerization temperature of 40° C. The above-mentioned chloroprene was added in portions starting 20 seconds after the start of polymerization, and the portion-by-portion addition flow rate was adjusted with a solenoid valve based on the change in the heat quantity of the refrigerant for 10 seconds from the start of polymerization, and the flow rate was readjusted every 10 seconds thereafter, so that the polymerization was carried out continuously. 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.

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

The pH of the above-mentioned chloroprene-based latex (R-2) was adjusted to 7.0 using acetic acid or sodium hydroxide, and the chloroprene-based latex was frozen and coagulated on a metal plate cooled to -20°C to break the emulsion, yielding a sheet. The sheet was washed with water and then dried at 130°C for 15 minutes to obtain solid chloroprene-based rubber (A-2).

The content of acrylonitrile monomer units contained in the chloroprene rubber (A-2) 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 Co., Ltd.) was used to measure the content of nitrogen atoms in 100 mg of chloroprene rubber (A-2), and the content of acrylonitrile monomer units was calculated. The content of acrylonitrile monomer units was 10.0% by mass.

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. The calibration curve was created using aspartic acid (10.52%) with a known nitrogen content as the standard substance.
The chloroprene rubber (A-2) obtained by the above-mentioned production method had an acrylonitrile monomer unit content of 10.0 mass %.

<Production method of chloroprene rubber (A-1)>
The amount of acrylonitrile monomer added in the polymerization step was changed to obtain a chloroprene rubber (A-1) having an acrylonitrile monomer unit content of 5.0 mass % in the chloroprene rubber.

(Examples 1 to 19, Comparative Examples 1 to 13)
<Preparation of Rubber Composition>
Of the components shown in Tables 1 to 4, the components excluding the organic peroxide, vulcanization accelerator, maleimide compound, and vulcanizing agent were mixed on an 8-inch open roll to obtain a rubber composition precursor not containing a vulcanizing agent or the like (first mixing step). The obtained rubber composition precursor was then allowed to stand at 23°C for 12 hours. Thereafter, the rubber composition precursor, the organic peroxide, the vulcanization accelerator, the maleimide compound, and the vulcanizing agent were kneaded on an 8-inch open roll (second mixing step) to obtain rubber compositions of the examples and comparative examples.

(Comparative Examples 14 to 17)
<Preparation of Rubber Composition>
Of the components shown in Table 4, the components excluding the organic peroxide, vulcanization accelerator, maleimide compound, and vulcanizing agent were mixed with an 8-inch open roll to obtain a rubber composition precursor not containing a vulcanizing agent, etc. (first mixing step). Next, without a standing step, the rubber composition precursor, the organic peroxide, the vulcanization accelerator, the maleimide compound, and the vulcanizing agent were kneaded with an 8-inch open roll (second mixing step) to obtain a rubber composition of the comparative example.

The components used to obtain the composition are as follows:
Rubber component:
Chloroprene rubber A-1: Chloroprene-acrylonitrile copolymer AN (acrylonitrile monomer unit) content: 5% by mass
Chloroprene rubber A-2: Chloroprene-acrylonitrile copolymer AN (acrylonitrile monomer unit) content 10% by mass,
Chloroprene rubber A-5: mercaptan-modified chloroprene rubber (chloroprene homopolymer), manufactured by Denka Co., Ltd., S-40V
・Natural rubber: HB Chemical Company, SMR-CV60

Carbon black: Asahi #70, HAF, manufactured by Asahi Carbon Co., Ltd.
Organic peroxide: 1,4-bis[(t-butylperoxy)isopropyl]benzene, NOF Corporation, Perbutyl P-40

Vulcanization accelerator:
Noccela TMU: Trimethylthiourea, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., Noccela TMU
Sulfur: Sulfur, manufactured by Hosoi Chemical Industry Co., Ltd., fine sulfur 200 mesh Noccela TT: Tetramethylthiuram disulfide, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., Noccela TT
Noccela CZ: N-cyclohexyl-2-benzothiazolyl sulfenamide, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., Noccela CZ

Maleimide compound: m-phenylenedimaleimide, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., Valnoc PM
Plasticizer: Ether ester compound, manufactured by ADEKA Corporation, Adeka Cizer RS-700
Vulcanizing agent: zinc oxide, manufactured by Sakai Chemical Industry Co., Ltd., zinc oxide type 2 Acid acceptor: magnesium oxide, manufactured by Kyowa Chemical Industry Co., Ltd., Kyowamag 150
Anti-aging agents:
Nocrac CD: 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., Nocrac CD
Nocrac 6C: N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., Nocrac 6C
Processing aid: stearic acid, New Japan Chemical Co., Ltd., stearic acid 50S

<Preparation of test vulcanized molded body 1>
The obtained rubber composition was press-vulcanized at 170°C for 20 minutes in accordance with JIS K 6299:2012 to produce a sheet-like vulcanized molded product having a thickness of 2 mm (test vulcanized molded product 1).

(Hardness)
The test vulcanized molded articles 1 were stacked to a thickness of 6.0 mm or more to form a laminate. The hardness of the laminate was measured with a type A durometer in accordance with JIS K 6253-3:2023. The thickness of the laminate was 6.0 to 7.0 mm.

(Water resistance (volume change rate after immersion in 70°C water for 144 hours))
A test piece having a length of 25 mm and a width of 20 mm was punched out from the above-mentioned test vulcanized molded body 1. The test piece obtained was immersed in water at 70° C. for 144 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: Less than 3% B: 3% or more, less than 6% C: 6% or more, less than 9% D: 9% or more

(Alkaline resistance (volume change rate after immersion in 10% sodium hydroxide at 70°C for 144 hours))
A test piece measuring 25 mm in length and 20 mm in width was punched out from the above-mentioned test vulcanized molded body 1. The test piece obtained was immersed in 10% sodium hydroxide at 70° C. for 144 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: Less than 4% B: 4% or more, less than 7% C: 7% or more, less than 10% D: 10% or more

(Fever)
The rubber composition was press-vulcanized at 170°C for 20 minutes to obtain a cylindrical vulcanized molded body (test vulcanized molded body 2) having a diameter of 15 mm and a height of 25 mm. Based on JIS K 6265:2018, a Goodrich Flexometer was used to evaluate heat generation by a constant strain flexometer test. The constant strain flexometer test is a test method for evaluating fatigue characteristics due to heat generation inside a test piece by applying a dynamic repeated load to a test piece such as vulcanized rubber. In detail, a static initial load is applied to the test piece under a constant temperature condition, and a sine vibration of a constant amplitude is further applied to measure the heat generation and creep amount of the test piece that change over time. The test method was performed based on JIS K 6265:2018 under conditions of 40°C, strain of 0.175 inches, load of 55 pounds, and vibration frequency of 1,800 times per minute, and heat generation (°C) was measured.

Claims (7)

A rubber composition comprising a rubber component,
The vulcanized molded test pieces 1 of the rubber composition are stacked to a thickness of 6.0 mm or more to form a laminate, the hardness of which is measured with a type A durometer according to JIS K 6253-3:2023 and designated as X;
The test vulcanized molded product 2 of the rubber composition is evaluated in a constant strain flexometer test based on JIS K 6265:2018 under conditions of 40°C, strain of 0.175 inches, load of 55 pounds, and vibration frequency of 1,800 times per minute, where the heat generation is defined as Y.
The hardness X and heat generation Y satisfy the following formula (1),
The test vulcanized molded article 1 is a sheet-like vulcanized molded article having a thickness of 2 mm obtained by press-vulcanizing the rubber composition at 170° C. for 20 minutes in accordance with JIS K 6299:2012.
The test vulcanized molded body 2 is a cylindrical vulcanized molded body having a diameter of 15 mm and a height of 25 mm, obtained by press-vulcanizing the rubber composition at 170° C. for 20 minutes.
Rubber composition.
1.4X-Y>45.0 (1) The rubber composition according to claim 1, wherein the hardness X is 40 or more and 98 or less. The rubber composition according to claim 1 or 2, wherein the rubber component includes a chloroprene-based polymer. The rubber composition according to claim 3, wherein the chloroprene polymer contains 80 to 100 mass% of chloroprene monomer units relative to 100 mass% of the chloroprene polymer. A vulcanized molded article of the rubber composition according to claim 1 or claim 2. A rubber roll,
The present invention comprises a core bar and a surface layer provided on a peripheral surface of the core bar,
The surface layer comprises the vulcanized molded article according to claim 5,
The rubber roll is used in at least one of an acid washing line and an alkali washing line. A vulcanized molded article containing a rubber component,
When the vulcanized molded article is a test vulcanized molded article 1' having a thickness of 6.0 mm or more, the hardness measured with a type A durometer based on JIS K 6253-3:2023 is defined as X',
When the vulcanized molded body is a cylindrical test vulcanized molded body 2' having a diameter of 15 mm and a height of 25 mm, the heat generation determined by evaluation in a constant strain flexometer test based on JIS K 6265:2018 under conditions of 40°C, strain of 0.175 inches, load of 55 pounds, and vibration frequency of 1,800 times per minute is defined as Y'.
A vulcanized molded product, in which hardness X' and heat generation Y' satisfy the following formula (2).
1.4X'-Y'>45.0 (2)