Plasticizers for rubber, rubber compositions, and rubber molded products

Abstract

To provide a plasticizer that exhibits excellent compatibility with rubber and sufficiently produces a plasticizing effect even in small amounts, a rubber composition containing the plasticizer that suppresses bleed-out and is less prone to deterioration over time, and a molded article thereof. [Solution] A styrene group-containing plasticizer for rubber comprising a cyclic polyarylene sulfide represented by the following general formula (1), a rubber composition containing the plasticizer, and a rubber molded article. [Formula 1] TIFF2026056109000006.tif2980 (In general formula (1), Ar represents an arylene group, Z represents S, SO, or SO2, and n is between 4 and 21.)

Description

Technical Field

[0001] The present invention relates to a plasticizer for rubber, a rubber composition, and a rubber molded product.

Background Art

[0002] Styrene group-containing rubbers typified by styrene-butadiene rubber are widely used in various applications such as automobile tires. Such rubber materials are usually used with a plasticizer in order to adjust rubber hardness, improve processability, improve cold resistance, etc. For example, in Patent Document 1, an ester-based plasticizer is used for a rubber component containing styrene-butadiene rubber. Further, in Patent Document 2, a plasticizer containing at least one selected from the group consisting of a resin and a liquid polymer is used for a rubber component containing butadiene rubber and styrene-butadiene rubber.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Generally, plasticizers and rubbers have poor compatibility, and it was necessary to blend a large amount of plasticizer in order to sufficiently plasticize the rubber. However, when a large amount of plasticizer is blended, bleeding out is promoted, and there is a problem that the amount of plasticizer in the rubber changes, so the properties of the composition and the molded product are likely to change over time.

[0005] Therefore, the problem to be solved by the present invention is to provide a plasticizer having excellent compatibility with rubber and exhibiting a sufficient plasticizing effect with a small amount, a rubber composition containing the plasticizer and having suppressed bleeding out and being less likely to change over time, and a molded product thereof. [Means for solving the problem]

[0006] In other words, the present invention encompasses the following aspects. [1] A styrene group-containing plasticizer for rubber comprising a cyclic polyarylene sulfide represented by the following general formula (1).

[0007] [ka] (In general formula (1), Ar represents an arylene group, Z represents S, SO, or SO2, and n is between 4 and 21.) [2] A styrene group-containing rubber composition containing 0.1 to 10 parts by mass of the rubber plasticizer described in claim [1] per 100 parts by mass of styrene group-containing rubber. [3] The styrene group-containing rubber composition according to claim [1], characterized in that at least a portion of the styrene group-containing rubber and the plasticizer for rubber according to claim [1] form a pseudo-rotaxane structure. [4] A molded article obtained by molding the rubber composition according to claim [3]. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a plasticizer that has excellent compatibility with rubber and exhibits a sufficient plasticizing effect even in small amounts, a rubber composition containing the plasticizer that suppresses bleed-out and is less prone to deterioration over time, and a molded article thereof. [Modes for carrying out the invention]

[0009] The embodiments of the present invention will be described in detail below, but the scope of the present invention is not limited to the embodiments described herein, and various modifications can be made without departing from the spirit of the invention. Furthermore, if multiple upper and lower limits are given for a particular parameter, any combination of these upper and lower limits can be used to create a suitable numerical range.

[0010] <Rubber plasticizer> The rubber plasticizer according to this embodiment consists of a cyclic polyarylene sulfide represented by the following general formula (1). It will be described below.

[0011] [ka] (In equation (1), Ar represents an arylene group, and Z represents S, SO, or SO2. n is a natural number between 4 and 21.)

[0012] The plasticizer according to this embodiment consists of a cyclic PAS in which repeating units are linked in a ring and have an opening inside the ring. The ring in which the repeating units are linked may have side chains. The cyclic PAS may be of one type or multiple types may be used in combination. In this specification, a single constituent unit derived from a single monomer component that constitutes the PAS may be referred to as a "repeating unit". The above repeating unit is not limited to consecutive constituent units, but may be a single constituent unit.

[0013] The above cyclic PAS includes repeating units represented by the following general formula (1). The above cyclic PAS may be a homoPAS consisting only of repeating units represented by the following general formula (1), or it may be a heteroPAS further including other repeating units copolymerizable with the above repeating units.

[0014] [ka] (In equation (1), Ar represents an arylene group, and Z represents S, SO, or SO2. n is a natural number between 4 and 21.)

[0015] Examples of the arylene group include divalent aromatic residues containing at least one benzene ring such as o-phenylene, m-phenylene, p-phenylene, phenylene substituted with an alkyl group having 1 to 6 carbon atoms, phenyl-substituted phenylene, halogen-substituted phenylene, amino-substituted phenylene, amide-substituted phenylene, etc. Among them, from the viewpoint of being able to control the fast decomposition rate of the biodegradable polymer and being more excellent in toughness, o-phenylene, m-phenylene, and p-phenylene are preferable, and p-phenylene is more preferable. Further, the above Z is preferably S (that is, a sulfur atom). The repeating unit represented by the general formula (1) in the above cyclic PAS may be one kind or a plurality of kinds.

[0016] From the viewpoint of being more excellent in plasticity, the ratio of the repeating unit represented by the general formula (1) to 100 mol of all the repeating units contained in the above cyclic PAS is preferably 80 mol% or more, more preferably 90 mol% or more, still more preferably 95 mol% or more, and particularly preferably 100 mol%.

[0017] The above other repeating units are preferably repeating units that do not contain an aromatic ring. The ratio of the above other repeating units to 100 mol of all the repeating units contained in the above cyclic PAS is preferably 10 mol% or less, more preferably 5 mol% or less.

[0018] From the viewpoint of being more excellent in compatibility, the ratio of the repeating unit having an aromatic ring to 100 mol of all the repeating units contained in the above cyclic PAS is preferably 80 mol% or more, more preferably 90 mol% or more, still more preferably 95 mol% or more, and particularly preferably 100 mol%. The repeating unit having an aromatic ring is preferably only the repeating unit represented by the above formula (1).

[0019] From the viewpoint of compatibility, the repeating number of the above cyclic PAS is 4 to 21. A larger repeating number is preferable because the opening is larger and the rubber component is more likely to penetrate.

[0020] (Method for producing cyclic PAS) The above-mentioned cyclic PAS can be produced, for example, by a method comprising the steps of: (1) reacting a polyhalo-aromatic compound with (i) an alkali metal sulfide or (ii) an alkali metal hydroxide and an alkali metal hydroxide in an organic polar solvent to obtain a crude reaction mixture containing at least PAS resin, cyclic PAS, an alkali metal halide and an organic polar solvent; (2) removing the solid phase component from the crude reaction mixture by solid-liquid separation to obtain a liquid phase component (A) containing at least cyclic PAS; and (3) obtaining cyclic PAS from the liquid phase component (A).

[0021] -Process (1)- Step (1) is a step in which a polyhalo-aromatic compound is reacted with (i) an alkali metal sulfide or (ii) an alkali metal hydroxide and an alkali metal hydroxide in an organic polar solvent to obtain a crude reaction mixture containing at least a PAS resin, a cyclic PAS, an alkali metal halide and an organic polar solvent.

[0022] Examples of the above polyhalo-aromatic compounds include halogenated aromatic compounds having two or more halogen atoms directly bonded to an aromatic ring, specifically dihalo-aromatic compounds such as p-dichlorobenzene, o-dichlorobenzene, m-dichlorobenzene, trichlorobenzene, tetrachlorobenzene, dibrombenzene, diiodobenzene, tribrombenzene, dibromnaphthalene, triiodobenzene, dichlorodiphenylbenzene, dibromdiphenylbenzene, dichlorobenzophenone, dibrombenzophenone, dichlorodiphenyl ether, dibromdiphenyl ether, dichlorodiphenyl sulfide, dibromdiphenyl sulfide, dichlorobiphenyl, and dibrombiphenyl, as well as mixtures thereof. These compounds may be block copolymerized. Among these, dihalogenated benzenes are preferred, and those containing 80 mol% or more of p-dichlorobenzene are particularly preferred.

[0023] Examples of polyhaloaromatic compounds having a nitro group include mono- or dihalonitrobenzenes such as 2,4-dinitrochlorobenzene and 2,5-dichloronitrobenzene; dihalonitrodiphenyl ethers such as 2-nitro-4,4'-dichlorodiphenyl ether; dihalonitrodiphenyl sulfones such as 3,3'-dinitro-4,4'-dichlorodiphenyl sulfone; mono- or dihalonitropyridines such as 2,5-dichloro-3-nitropyridine and 2-chlor-3,5-dinitropyridine; or various dihalonitronaphthalenes.

[0024] Furthermore, in the above manufacturing method, alkali metal sulfides or alkali metal hydroxides and alkali metal hydroxides (hereinafter sometimes referred to as sulfidating agents) are used as raw materials.

[0025] The alkali metal sulfides mentioned above include lithium sulfide, sodium sulfide, rubidium sulfide, cesium sulfide, and mixtures thereof. These alkali metal sulfides can be used as hydrates, aqueous mixtures, or anhydrous forms. Alkali metal sulfides can also be produced by the reaction of alkali metal hydroxides with alkali metal hydroxides. In addition, small amounts of alkali metal hydroxide may be added to react with the alkali metal hydroxides and alkali metal thiosulfates that are usually present in trace amounts in the alkali metal sulfides.

[0026] The alkali metal hydrosulfides mentioned above include lithium hydrogen sulfide, sodium hydrogen sulfide, rubidium hydrogen sulfide, cesium hydrogen sulfide, and mixtures thereof. Such alkali metal hydrosulfides can be used as hydrates, aqueous mixtures, or anhydrous forms.

[0027] The alkali metal hydroxides mentioned above are used together with the alkali metal hydroxides. Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, and cesium hydroxide, which may be used individually or in combination of two or more. Among these, lithium hydroxide, sodium hydroxide, and potassium hydroxide are preferred due to their availability, with sodium hydroxide being particularly preferred.

[0028] The above manufacturing method may also use a hydrated sulfidating agent as a raw material. In this case, it is preferable to dehydrate the hydrated sulfidating agent in the presence of at least an aprotic polar solvent before subjecting it to the polymerization reaction of the PAS resin. Furthermore, if the amount of aprotic polar solvent charged is small, for example, less than 1 mole per mole of sulfur atoms in the sulfidating agent, it is preferable to dehydrate the hydrated sulfidating agent and the aprotic polar solvent in the presence of a polyhalo-aromatic compound.

[0029] The dehydration step of the hydrated sulfidating agent is carried out by charging at least an aprotic polar solvent and a hydrated alkali metal sulfide or hydrated alkaline aqueous sulfide and alkali metal hydroxide as the hydrated sulfidating agent into a reaction vessel equipped with a distillation apparatus, heating to a temperature at which water is removed by azeotropy, specifically in the range of 300°C or less, preferably in the range of 80 to 220°C, more preferably in the range of 100 to 200°C, and then discharging the water from the system by distillation. In the dehydration step, it is preferable to dehydrate until the amount of water in the system carrying out the polymerization reaction is 5 moles or less, more preferably in the range of 0.01 to 2.0 moles, per mole of sulfur atoms of the sulfidating agent.

[0030] Examples of the above organic polar solvents include amides, ureas and lactams such as formamide, acetamide, N-methylformamide, N,N-dimethylacetamide, tetramethylurea, N-methyl-2-pyrrolidone, 2-pyrrolidone, N-methyl-ε-caprolactam, ε-caprolactam, hexamethylphosphoramide, N-dimethylpropyleneurea, and 1,3-dimethyl-2-imidazolidinonic acid; sulfolanes such as sulfolane and dimethylsulfolane; nitriles such as benzonitrile; ketones such as methylphenyl ketone and mixtures thereof. Among these, amides having an aliphatic cyclic structure such as N-methyl-2-pyrrolidone, 2-pyrrolidone, N-methyl-ε-caprolactam, ε-caprolactam, hexamethylphosphoramide, N-dimethylpropyleneurea, and 1,3-dimethyl-2-imidazolidinonic acid are preferred, and N-methyl-2-pyrrolidone is even more preferred.

[0031] In the PAS polymerization process, the polymerization reaction involves reacting the alkali metal sulfide as a sulfidating agent with a polyhalo-aromatic compound in the presence of these organic polar solvents. Alternatively, the polymerization reaction involves reacting the alkali metal hydroxide and alkali metal hydroxide as sulfidating agents with a polyhalo-aromatic compound in the presence of these organic polar solvents. The polymerization conditions are generally in the temperature range of 200 to 330°C, and the pressure should be in a range that substantially maintains the polymerization solvent and the polyhalo-aromatic compound, which is the polymerization monomer, in the liquid phase, and is generally selected from the range of 0.1 to 20 MPa, preferably from 0.1 to 2 MPa. The amount of polyhalo-aromatic compound charged is adjusted to be in the range of 0.2 moles to 5.0 moles, preferably from 0.8 to 1.3 moles, and more preferably from 0.9 to 1.1 moles, per mole of sulfur atoms of the sulfidating agent. Furthermore, the amount of aprotic polar solvent charged is adjusted to be in the range of 1.0 to 6.0 moles, preferably 2.5 to 4.5 moles, per mole of sulfur atoms of the sulfidating agent. The polymerization reaction is preferably carried out in the presence of a small amount of water, and the proportion is preferably adjusted as appropriate in consideration of the polymerization method, the molecular weight of the obtained polymer, and productivity. Specifically, the dehydration operation is carried out so that the amount of water is in the range of 2.0 moles or less, preferably 1.6 moles or less, per mole of sulfur atoms of the sulfidating agent. However, if the dehydration operation is carried out in the presence of a polyhalo-aromatic compound (for example, the method in "5)" in the specific embodiment below), the amount of water should be in the range of 0.9 moles or less, preferably 0.05 to 0.3 moles, more preferably 0.01 to 0.02 moles or less.

[0032] Specific embodiments of polymerizing a sulfidating agent and a polyhalo-aromatic compound in the presence of the aforementioned aprotic polar solvent include, for example, 1) A method using polymerization aids such as alkali metal carboxylates or lithium halides. 2) A method using branching agents such as aromatic polyhalogen compounds, 3) A method in which polymerization is carried out in the presence of a small amount of water, and then water is added to further polymerize the molecule. 4) A method in which, during the reaction of an alkali metal sulfide with an aromatic dihalogen compound, the gas phase portion of the reaction vessel is cooled to condense a portion of the gas phase inside the reaction vessel and reflux it into the liquid phase. 5) A manufacturing method is provided, which includes the essential steps of: producing a slurry containing solid alkali metal sulfide by reacting an alkali metal sulfide, or a hydrated alkali metal hydroxide and alkali metal hydroxide, with an amide, urea, or lactam having an aliphatic cyclic structure while dehydrating it in the presence of a polyhalo-aromatic compound; further dehydrating the slurry by adding a polar organic solvent such as NMP and distilling off the water; and then polymerizing the slurry obtained after the dehydration step by reacting a polyhalo-aromatic compound, alkali metal hydroxide, and an alkali metal salt of the hydrolysis product of the amide, urea, or lactam having an aliphatic cyclic structure, at a rate of 0.02 moles or less of water present in the reaction system per mole of a polar organic solvent such as NMP.

[0033] Thus, by polymerizing a dihalo-aromatic compound with (i) an alkali metal sulfide or (ii) an alkali metal hydroxide and alkali metal hydroxide in an organic polar solvent, a mixture of PAS resin, cyclic PAS, etc., can be obtained as a product. Other substances contained after the reaction may include by-products such as alkali metal-containing inorganic salts, carboxyalkylamino group-containing compounds, terminal SH group-containing compounds, unreacted raw materials, and water.

[0034] -Process (2)- Step (2) is a step of removing the solid phase component from the crude reaction mixture by solid-liquid separation to obtain a liquid phase component (A) containing at least cyclic PAS.

[0035] The above solid-liquid separation can be broadly divided into two types: the flash method and the quench method, which will be described later, and the quench method is preferred.

[0036] The Quench process is a method for separating particulate cyclic PAS by slowly cooling a crude reaction mixture. Generally, it involves gradually cooling the crude reaction mixture from a high-temperature, high-pressure state to crystallize the PAS resin in the reaction system, and then separating the solid component containing the PAS resin as granules by filtration or other means, while recovering the liquid. Generally, as the molecular weight of polymers increases, the interactions between polymers become stronger, resulting in decreased solubility in the solvent. Therefore, in this process, the PAS resin precipitates and becomes a solid, while the cyclic PAS and other components remain dissolved in the solvent. There are no particular restrictions on the cooling time in the Quench process, but a range of 0.1°C / min to 3°C / min is usually preferred. Furthermore, it is not necessary to cool at the same rate throughout the entire slow cooling process; a method of cooling at a rate of 0.1°C / min to 1°C / min until the granular PAS resin crystallizes, and then at a rate of 1°C / min or higher, is also preferred. Finally, it is preferable to cool the mixture to 70°C or higher, preferably 100°C or higher and 200°C or lower, and then remove the solid components containing the PAS resin by solid-liquid separation. Examples of solid-liquid separation in the Quench method include separating the material using filtration or a centrifuge such as a screw decanter, then adding water directly to the resulting filtration residue to form a slurry, and repeating the solid-liquid separation; or heating the resulting filtration residue in a non-oxidizing atmosphere to remove any remaining solvent.

[0037] In this process, if necessary, a step may be taken to remove some or most of the organic polar solvent in the crude reaction mixture by distillation, and after this step, the crude reaction mixture may be separated into solid and liquid components by filtration to remove the solid phase components. Furthermore, a step may be taken to wash the crude reaction mixture, or preferably the solid content (slurry) obtained after solid-liquid separation, by contacting it with water or an organic polar solvent.

[0038] -Process (3)- Step (3) is a step of obtaining a cyclic PAS oligomer from the liquid phase component (A). The method for obtaining a cyclic PAS oligomer from the liquid phase component (A) is not particularly limited, and known methods can be used as long as they do not impair the effects of the present invention. For example, one method is to remove the organic polar solvent by heating, wash the residue with an organic solvent or water, and then extract and purify the cyclic PAS oligomer using an organic solvent (see Japanese Patent Application Publication No. 2020-007490), or to remove the organic polar solvent using a membrane, wash the residue with an organic solvent or water, and then extract and purify the cyclic PAS oligomer using an organic solvent.

[0039] When removing organic polar solvents, it is desirable to remove the solvent so that the proportion of non-volatile matter is in the range of 20 to 100% by mass, preferably 20 to 99.99% by mass, and more preferably 30 to 90% by mass. The temperature at which solvent removal is performed by heating cannot be uniquely limited as it depends on the properties of the solvent used, but it is usually in the range of 20 to 150°C, preferably 40 to 120°C. Furthermore, the pressure at which solvent removal is performed is preferably below atmospheric pressure, which makes it possible to remove the solvent at a lower temperature.

[0040] The purity of the cyclic PAS obtained in this way is preferably in the range of 90% by mass or more, more preferably 95% by mass or more, even more preferably 98% by mass or more, preferably 100% by mass or less, and more preferably 99.99% by mass or less. Within this range, it is possible to exhibit excellent mechanical properties while reducing the gas generated when the composite structure is melt-molded.

[0041] In this disclosure, the term "styrene group-containing rubber plasticizer consisting of cyclic PAS" does not mean that the plasticizer does not contain any components other than cyclic PAS. For example, it may contain by-products, solvents, and other optional components produced by the above method. From the viewpoint of plasticity, it is preferable that the cyclic PAS is 90 parts by mass or more, more preferably 95 parts by mass or more, and even more preferably 98 parts by mass or more, per 100 parts by mass of plasticizer.

[0042] <Rubber composition> The rubber composition of this disclosure contains the above-mentioned plasticizer and rubber component. The rubber component used in this embodiment is a styrene-containing rubber containing styrene groups. The presence of styrene groups in the rubber component provides excellent compatibility with the plasticizer, and the rubber composition exhibits excellent toughness, ductility, flexibility, and processability.

[0043] The styrene group-containing rubber applicable to this embodiment is preferably a triblock copolymer, diblock copolymer, or mixture thereof having at least polystyrene units and polyolefin units. Examples of monomers constituting the polystyrene units include styrene; various styrene derivatives such as α-methylstyrene, m-methylstyrene, p-methylstyrene, ethylstyrene, isobutylstyrene, and tert-butylstyrene, with styrene being particularly preferred. Examples of polyolefin units include polyisoprene units, polybutadiene units, and poly(butadiene-ethylene) units, with polyisoprene units being a prime example. Specific examples of styrene group-containing rubber having such polystyrene units and polyolefin units include styrene-isoprene block copolymers, styrene-butadiene block copolymers, and styrene-ethylene-butylene block copolymers. Materials with a modified structure can also be used.

[0044] In this embodiment, the amount of plasticizer added is 0.1 to 10 parts by mass of the styrene group-containing rubber, preferably 1 to 10, and more preferably 3 to 10. Within this range, the rubber composition exhibits excellent toughness, ductility, flexibility, and processability.

[0045] In the rubber composition of this disclosure, it is preferable that at least a portion of the styrene group-containing rubber and the rubber plasticizer form a pseudo-rotaxane structure. A pseudo-rotaxane structure refers to a structure in which the chain-like styrene group-containing rubber penetrates the openings of the plasticizer, and the ends are not sealed by chelating groups. It is thought that the aromatic hydrocarbons of the plasticizer and the styrene moieties of the rubber component interact via ππ interactions, making it easier to form and maintain a rotaxane structure during kneading, and that it is fixed as a rotaxane structure after vulcanization. Having such a structure in the composition or molded article makes it difficult for the plasticizer to bleed out, and changes over time can be suppressed. However, the above mechanism is merely speculative, and even if the effects of the present invention are achieved for other reasons, they are still within the technical scope of the present invention.

[0046] The rubber composition disclosed herein may contain, as long as it does not impair the effects of the present invention, rubber components other than styrene group-containing rubber, as well as fillers, reinforcing agents, softeners, silane coupling agents, vulcanizing agents, vulcanization accelerators, vulcanization aids, activators, anti-aging agents, lubricants, pigments, antioxidants, light stabilizers, antistatic agents, flame retardants, mold release agents, ultraviolet absorbers, matting agents, fragrances, etc., as appropriate depending on the purpose.

[0047] The rubber composition of this disclosure can be formulated by conventional methods to incorporate essential components. For example, one method involves mixing the plasticizer and the styrene-containing rubber of this disclosure in a solvent that dissolves both, and then removing the solvent, or kneading the plasticizer and the styrene-containing rubber of this disclosure using conventional kneading equipment (such as a mill roll, Banbury mixer, or kneader blender). Alternatively, during the polymerization of the rubber component, the method may include a step of mixing the monomer components constituting the styrene-containing rubber, the plasticizer of this disclosure, and optionally a polymerization initiator in a polymerization solvent, and then polymerizing the mixture. When incorporating optional components, a more uniform composition can be obtained by incorporating and kneading them into a mixture of the plasticizer and styrene-containing rubber that has been thoroughly mixed beforehand.

[0048] The molded articles of this disclosure can be obtained by vulcanizing the above-mentioned rubber composition. The rubber composition can be molded by conventional molding methods, such as extrusion molding, injection molding, blow molding, injection blow molding, compression molding, and rotational molding. These molding methods can be appropriately selected depending on the type, size, and characteristics of the molded article. Injection molding and compression molding are preferred. In this case, the rubber composition may be pre-molded and then vulcanized, or it may be vulcanized simultaneously with the molding of the rubber composition. Alternatively, the rubber composition may be vulcanized simultaneously with the molding and then further secondary vulcanized. The vulcanization temperature and vulcanization time can be appropriately selected according to conventional methods. The heating method for vulcanization is not particularly limited, and general methods used for rubber vulcanization, such as heater heating, steam heating, oven heating, and hot air heating, can be used.

[0049] The method for vulcanizing molded articles is not particularly limited, and known methods can be used. Examples include sulfur vulcanization, polyol vulcanization, peroxide vulcanization, amine vulcanization, triazine vulcanization, and crosslinking with epoxy groups. When using polyol vulcanization, bisphenol compounds are used as vulcanizing agents. When using sulfur vulcanization, sulfur or sulfur-containing compounds are used as vulcanizing agents. When using peroxide vulcanization, organic peroxides are used as vulcanizing agents.

[0050] Applications of the molded articles disclosed herein include, for example, vehicle parts such as tires, sidewalls, and carcasses; building materials such as vibration-damping rubber; general industrial products such as belts, hoses, rubber blocks, tubes, and O-rings; daily necessities such as footwear, packings, and balls; and medical components such as rubber stoppers, tubes, gaskets, and packings. [Examples]

[0051] The present invention will be described below using examples and comparative examples, but it is not limited to these examples. Unless otherwise specified, "%" and "parts" refer to mass.

[0052] <Examples 1-3, Reference Example 1, and Comparative Examples 1-4> First, the plasticizer and rubber components were mixed according to the proportions listed in Table 1. Specifically, an arbitrary amount of plasticizer was added to 1 L of toluene, and the plasticizer was completely dissolved by heating under reflux. Then, the styrene-containing rubber was added and completely dissolved. The solution was vacuum-dried to completely remove the toluene and obtain a mixture. Subsequently, the mixture and the arbitrary components were kneaded for 5 minutes at 90°C and 500 rpm in a Lab Plast Mill Banbury type mixer "B-250" manufactured by Toyo Seiki Seisakusho Co., Ltd., according to the proportions listed in Table 1. After that, sulfur was added while kneading at room temperature for 5 minutes using a test roll manufactured by Kansai Roll Co., Ltd., and kneaded until uniform to obtain a rubber composition. Each of the obtained rubber compositions was placed in a 150 mm square mold and vulcanized at 160°C for 25 minutes to obtain rubber molded products with thicknesses of 2 mm and 6 mm.

[0053] <Rating>

[0054] (1) Measurement of weight loss Four g of each rubber composition was taken and heated at 100°C for 72 hours, and the weight loss rate before and after heating was measured. The results are shown in Table 1.

[0055] (2) Measurement of tensile elongation at break Tensile elongation at break was measured in accordance with K 6251 (2017). A dumbbell-shaped specimen (Type 3) was punched out from the obtained 2 mm thick rubber molded product, and measurements were taken at 200 mm / min and 2000 mm / min at 0°C and room temperature (23°C), respectively. The results are shown in Table 1.

[0056] (3) Measurement of wear resistance index Cylindrical test specimens with a diameter of 16 mm were punched out from the obtained 6 mm thick rubber molded product, and a DIN abrasion test was performed in accordance with JIS K6264-2 (2005). The test was performed using Method B under conditions of a load of 10 N and a length of 40 m, and the abrasion resistance index was calculated. The results are shown in Table 1.

[0057] (4) Measurement of durometer hardness The obtained 6 mm thick rubber molded product was measured using a Type A durometer in accordance with JIS K6253-3 (2012) "Vulcanized rubber and thermoplastic rubber - Method for determining hardness - Part 3: Durometer hardness". The results are shown in Table 1.

[0058] [Table 1]

[0059] The following ingredient ratios were used for the ingredients listed in Table 1. • Plasticizer A-1: A plasticizer consisting of cyclic PAS manufactured by the following method. a-2: Bis(2-ethylhexyl) adipate a-3: Bis(2-ethylhexyl) phthalate a-4: Bis[2-(2-butoxyethoxy)ethyl] adipate • Styrene-containing rubber B-1: "ESBR1500" manufactured by ENEOS Material Co., Ltd. • Additives C-1: Zinc Oxide "Type 2 Zinc Oxide" manufactured by Sakai Chemical Industry Co., Ltd. C-2: NOF Corporation Powdered Stearic Acid "Sakura" C-3: Mitsubishi Chemical Corporation's carbon black "Dia Black H" C-4: Finely powdered sulfur "Sulfur #325" manufactured by Hosoi Chemical Industry Co., Ltd. C-5: SANSELLER NS vulcanization accelerator manufactured by Sanshin Chemical Industry Co., Ltd.

[0060] <Manufacturing method for circular PAS> A 150-liter autoclave equipped with a stirring blade and bottom valve, connected to a pressure gauge, thermometer, and condenser, was charged with 19.413 kg (150 moles) of flake sodium sulfide (60.3 wt% Na2S) and 45.0 kg (454 moles) of N-methyl-2-pyrrolidone (NMP). The mixture was heated to 209°C while stirring under a nitrogen stream, and 4.644 kg of water was distilled off (the remaining water content was 1.13 moles per mole of sodium sulfide). The autoclave was then sealed and cooled to 180°C, and 21.631 kg (147 moles) of p-dichlorobenzene and 18.0 kg (182 moles) of NMP were charged. At a liquid temperature of 150°C, the mixture was pressurized to 0.1 MPa using nitrogen gas and the heating process was started. The mixture was heated to 240°C over 135 minutes and held for 30 minutes. The reaction was then completed by raising the liquid temperature to 250°C over 40 minutes and holding it for 73 minutes. After that, the autoclave was cooled. The bottom valve of the autoclave was opened at 100°C, and the reaction slurry was transferred to a 150-liter plate filter and pressure filtered at 120°C. 48.0 kg of NMP was added, and the mixture was pressure washed and filtered again. The weight of the recovered NMP filtrate was 80.0 kg. Water was added to the obtained NMP filtrate to form an aqueous slurry. Solid-liquid separation and water washing were repeated twice, and then the mixture was dried in a 120°C hot air dryer for 4 hours to obtain a powder. Chloroform was added to the obtained powder and stirred at 65°C for 1 hour. After cooling to room temperature, the mixture was filtered, and the residue after filtration was washed with chloroform at 25°C. The solids remaining after filtrate removal were dried in a 120°C hot air dryer for 4 hours to obtain 0.763 kg of cyclic PPS. FD-MS analysis revealed a mixture with 5 to 21 repeats. This was used as a plasticizer.

[0061] Table 1 shows that, comparing the examples with the comparative examples, Examples 1-3, which incorporated the plasticizer of this disclosure, exhibited comparable durometer hardness with smaller amounts of plasticizer added than Comparative Examples 2-4, while also demonstrating superior elongation and plasticity. Furthermore, the examples showed less weight loss and less bleed-out compared to the comparative examples.

Claims

1. A plasticizer for styrene group-containing rubber comprising a cyclic polyarylene sulfide represented by the following general formula (1). 【Chemistry 1】 (In general formula (1), Ar is an arylene group, and Z is S, SO, SO ２ (This shows that n is between 4 and 21.)

2. A styrene group-containing rubber composition comprising 0.1 to 10 parts by mass of the rubber plasticizer described in claim 1, per 100 parts by mass of styrene group-containing rubber.

3. The styrene group-containing rubber composition according to claim 2, characterized in that at least a portion of the styrene group-containing rubber and the rubber plasticizer according to claim 1 form a pseudo-rotaxane structure.

4. A molded article obtained by molding the rubber composition described in claim 3.

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