JP2023046737A - rubber composition - Google Patents

Abstract

To provide rubber compositions having excellent silica dispersibility and heat resistance, and to provide rubber molding having excellent silica dispersibility, heat resistance, and fuel consumption performance.SOLUTION: This invention relates to: [1] a rubber composition comprises a rubber component (A), silica (B), a silane coupling agent (C), a conjugated heterocyclic compound (D), and sulfur (E), wherein the conjugated heterocyclic compound (D) is a compound having at least one thiol group attached to one or more conjugated heterocyclic rings selected from a thiazole ring, an isothiazole ring, a thiadiazole ring, an imidazole ring, a pyrazole ring, a triazole ring, a pyridine ring, a pyrimidine ring, a pyrazine ring, and a triazine ring, a content of sulfur (E) is 1.2 pts.mass or less based on 100 pts.mass of the rubber component (A), and a mass ratio [(E)/(D)] of sulfur (E) to the conjugated heterocyclic compound (D) is 0.1 to 2; and [2] a rubber molding made by vulcanizing the rubber composition.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to rubber compositions and rubber moldings.

Rubber is an amorphous and soft polymer substance, and mainly composed of organic polymers such as natural rubber and synthetic rubber, and is a material (elastic rubber) with a high elastic limit and a low elastic modulus. Utilizing such properties of rubber, rubber compositions containing rubber are used in various fields such as tires, sealing materials, and vibration-isolating and vibration-isolating materials.
Rubber compositions for tires and the like usually contain silica as an inorganic filler in order to reduce energy loss associated with deformation. Since the surface of silica is highly hydrophilic and has a problem of low dispersibility in rubber, it has been proposed to use various additives and dispersants in rubber in order to take advantage of the characteristics of rubber and obtain more favorable performance. is done.

For example, Patent Document 1 describes a natural polymer containing a specific polysulfide polymer (vulcanizing agent) and one or more of specific sulfenamide, mercaptobenzothiazole, phenylsulfenamide, and triazine (vulcanization accelerator). A vulcanizable rubber composition comprising rubber and/or synthetic rubber is disclosed.
In Patent Document 2, a modified natural rubber latex obtained by adding a polar group-containing mercapto compound to natural rubber latex and adding the polar group-containing mercapto compound to natural rubber molecules in the natural rubber latex is coagulated and dried. A rubber composition using modified natural rubber is disclosed.
Patent Document 3 discloses a resin-rubber composite having excellent adhesiveness between a resin member and a rubber member that is in direct contact with the resin member. A composite is disclosed. In Examples, a filler having a silanol group, a polysulfide-based silane coupling agent, triazinedithiol, sulfur and other raw materials were mixed and stirred at 110° C. for 3 minutes to obtain a rubber sheet having a thickness of 2.5 mm. It is stated that

JP-A-58-167634 JP 2006-152045 A WO2019/208800

However, in Patent Document 1, sulfur is not used, and in Patent Documents 2 and 3, the content of sulfur is 1.5 parts by mass or more with respect to 100 parts by mass of the rubber component. The heat resistance and fuel consumption performance of the molded article are not sufficiently satisfactory.
In particular, in Patent Document 3, a rubber sheet prepared by mixing a composition is bonded to a resin member and vulcanized at 145 to 150° C. (1.7 to 3.4 parts by mass of sulfur per 100 parts by mass of rubber added). Through this vulcanization operation, the silica and rubber in the rubber sheet are bonded with the silane coupling agent and adhered to the resin member, but the dispersion of silica is insufficient.
An object of the present invention is to provide a rubber composition excellent in silica dispersibility and heat resistance, and a rubber molding excellent in silica dispersibility, heat resistance and fuel efficiency.

The present inventors have found that in a rubber composition containing a rubber component, silica, a silane coupling agent, a conjugated heterocyclic compound, and sulfur, a specific compound having a thiol group is used as the conjugated heterocyclic compound, and sulfur, a conjugated heterocyclic compound We have found that the above problems can be solved by adjusting the content of the ring compound to a specific range.

That is, the present invention provides the following [1] and [2].
[1] A rubber composition containing a rubber component (A), silica (B), a silane coupling agent (C), a conjugated heterocyclic compound (D), and sulfur (E),
The conjugated heterocyclic compound (D) is one or more conjugated heterocyclic rings selected from a thiazole ring, an isothiazole ring, a thiadiazole ring, an imidazole ring, a pyrazole ring, a triazole ring, a pyridine ring, a pyrimidine ring, a pyrazine ring, and a triazine ring. is a compound having a structure in which at least one thiol group is bonded to
The content of sulfur (E) is 1.2 parts by mass or less per 100 parts by mass of the rubber component (A),
A rubber composition in which the mass ratio [(E)/(D)] of sulfur (E) to the conjugated heterocyclic compound (D) is 0.1 or more and 2 or less.
[2] A rubber molded article obtained by vulcanizing the rubber composition of [1].

According to the present invention, it is possible to provide a rubber composition excellent in silica dispersibility and heat resistance, and a rubber molding excellent in silica dispersibility, heat resistance, and fuel efficiency.

[Rubber composition]
The rubber composition of the present invention is a rubber composition containing a rubber component (A), silica (B), a silane coupling agent (C), a conjugated heterocyclic compound (D), and sulfur (E),
The conjugated heterocyclic compound (D) is one or more conjugated heterocyclic rings selected from a thiazole ring, an isothiazole ring, a thiadiazole ring, an imidazole ring, a pyrazole ring, a triazole ring, a pyridine ring, a pyrimidine ring, a pyrazine ring, and a triazine ring. is a compound having a structure in which at least one thiol group is bonded to
The content of sulfur (E) is 1.2 parts by mass or less per 100 parts by mass of the rubber component (A),
The mass ratio [(E)/(D)] of sulfur (E) to the conjugated heterocyclic compound (D) is 0.1 or more and 2 or less.

According to the present invention, it is possible to obtain a rubber composition excellent in silica dispersibility and heat resistance, and a rubber molding excellent in silica dispersibility, heat resistance, and fuel efficiency. Although the reason is not necessarily clear, it is considered as follows.
The rubber composition of the present invention contains a small amount of sulfur (E) and a conjugated heterocyclic compound (D) having a thiol group in a specific ratio. This conjugated heterocyclic compound (D) generates a thiyl radical (RS.) when kneading the rubber composition, and this thiyl radical accelerates the scission of the S—S bond contained in the silane coupling agent. It is thought that dispersibility improves.
In addition, the conjugated heterocyclic compound (D) having a thiol group, like sulfur, crosslinks between rubber molecules, resulting in an improvement in the initial viscosity of the rubber composition and the heat resistance of the resulting rubber molding. expected to improve.
In the rubber composition of the present invention, since the silica (B) is uniformly dispersed in the rubber component (A), the affinity between the silica (B) and the rubber component (A) is increased, and the rubber composition is Vulcanized rubber moldings are considered to have improved mechanical strength and improved fuel efficiency (tan δ decreased).

<Rubber component (A)>
The rubber component (A) used in the present invention is not particularly limited, and natural rubber and synthetic rubber can be used. Among these, one or more selected from natural rubber and diene-based synthetic rubber is preferable from the viewpoint of abrasion resistance, availability, and the like.
Natural rubbers include SMR, SIR, STR, RSS, etc., and SMR20, STR20, RSS#3, RSS#4, etc. are preferred.
Natural rubber can be modified before use, and examples of modified natural rubber include epoxidized natural rubber and hydrogenated natural rubber.
Diene synthetic rubbers include polyisoprene rubber (IR), polybutadiene rubber (BR), styrene/butadiene copolymer rubber (SBR), acrylonitrile/butadiene copolymer rubber (NBR), chloroprene rubber, butyl rubber, and the like. .

Among these, from the same viewpoint as above, one or more selected from natural rubber, modified natural rubber, IR, BR, SBR, and NBR is preferable, and one or more selected from BR, SBR, and natural rubber is more preferable. preferable. BR or SBR and natural rubber can also be used together.
The copolymer rubber may be a block copolymer or a random copolymer, but a random copolymer is preferred from the viewpoint of silica dispersibility and heat resistance.
The rubber component (A) can be used alone or in combination of two or more.

<Silica (B)>
The rubber composition of the present invention contains silica (B) from the viewpoint of improving the heat resistance and improving the heat resistance, wear resistance and fuel efficiency of the resulting rubber molding.
The silica (B) used in the present invention is not particularly limited, and wet silica, dry silica and colloidal silica can be used. Among these, wet-process silica containing hydrous silicic acid as a main component is preferred. Wet-process silica includes precipitation-process silica, gel-process silica, and sol-gel-process silica, and precipitation-process silica is more preferable.
Silica (B) can be used individually or in combination of 2 or more types.
The BET specific surface area of silica (B) (measured in accordance with ISO 5794/1) is preferably 50 m ² /g or more, from the viewpoints of silica dispersibility and rubber reinforcing properties in rubber compositions and rubber moldings. It is more preferably 100 m ² /g or more, still more preferably 150 m ² /g or more, and preferably 350 m ² /g or less, more preferably 300 m ² /g or less, still more preferably 250 m ² /g or less.
The average secondary particle size of silica (B) is preferably 10 μm or more, more preferably 15 μm or more, and still more preferably 18 μm or more, from the viewpoint of dispersibility of silica in rubber compositions and rubber moldings and rubber reinforcing properties. Yes, and preferably 100 μm or less, more preferably 80 μm or less, and even more preferably 50 μm or less.

Commercially available examples of silica include trade names manufactured by Tosoh Silica Co., Ltd.: NipSeal AQ (BET specific surface area: 205 m ² /g), NipSeal KQ (BET specific surface area: 240 m ² /g), and products manufactured by Evonik. Name: Ultrasil VN3 (BET specific surface area: 175 m ² /g).

In the present invention, the rubber composition may optionally contain carbon black as an inorganic filler. By containing carbon black, the electrical resistance can be lowered and charging can be suppressed.
There is no particular limitation on the carbon black used, and in addition to grade carbon black such as high, medium or low structure SAF, ISAF, IISAF, N339, HAF, FEF, GPF, and SRF, silica is supported on the carbon black surface. A dual phase filler of carbon and silica or the like can be used. Among these, SAF, ISAF, IISAF, N339, HAF, and FEF grade carbon blacks are preferred.
The DBP absorption of carbon black (measured according to ASTM D2414-65T) is preferably 70 cm ³ /100 g or more, more preferably 80 cm ³ /100 g or more, still more preferably 90 cm ³ /100 g or more.
In addition, the nitrogen adsorption specific surface area of carbon black ( _N AS, measured according to JIS K 6217-2:2017) is preferably 60 m ² /g or more, more preferably 80 m ² /g or more, still more preferably 100 m ² /g or more.
In the present invention, as an inorganic filler, alumina, calcium carbonate, clay, talc, zeolite, diatomaceous earth, etc. can be contained as necessary.

<Silane coupling agent (C)>
The rubber composition of the present invention contains a silane coupling agent (C) from the viewpoint of improving the dispersibility and heat resistance of silica and improving the dispersibility, heat resistance, and fuel efficiency of the resulting rubber molded product. do.
The silane coupling agent (C) is not particularly limited, and those used in commercially available rubber compositions can be used. Examples of the silane coupling agent (C) include polysulfide, mercapto, vinyl, epoxy, styryl, methacrylic, acrylic, and amino silane coupling agents. Among these, polysulfide-based silane coupling agents are preferred from the same viewpoint as above.

As the polysulfide-based silane coupling agent (C), compounds represented by the following general formula (II) are preferred.
(R ³ —O) _3-p R ³ _p —Si—R ⁴ —S _n —R ⁴ —Si—R ³ _q (OR ³ ) _3-q (II)
In formula (II), R ³ is an alkyl group having 1 to 8 carbon atoms, R ⁴ is an alkanediyl group having 1 to 8 carbon atoms, and n is an integer of 2 or more and 6 or less. p and q are each independently an integer of 0 or more and 3 or less, but p and q cannot both be 3;
The number of carbon atoms in the alkyl group represented by ^R3 is 1 or more, preferably 6 or less, more preferably 4 or less, and still more preferably 3 or less. Preferred examples of the alkyl group include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group and tert-butyl group.
The number of carbon atoms in the alkanediyl group represented by R4 is ¹ or more, and preferably 6 or less, more preferably 4 or less, and still more preferably 3 or less.
n is an integer of 1 or more, preferably 2 or more, and preferably 5 or less, more preferably 4 or less.
p and q are preferably each independently 0 or 1;

Examples of the compound represented by formula (II) include bis(3-triethoxysilylpropyl) tetrasulfide, bis(3-triethoxysilylpropyl) trisulfide, bis(3-triethoxysilylpropyl) disulfide, bis( 2-triethoxysilylethyl) tetrasulfide, bis(3-trimethoxysilylpropyl) tetrasulfide, bis(3-triethoxysilylethyl) tetrasulfide, bis(3-methyldimethoxysilylpropyl) tetrasulfide, bis(2- trimethoxysilylethyl)tetrasulfide, bis(3-trimethoxysilylpropyl)disulfide and the like.
Among these, one or more selected from bis(3-triethoxysilylpropyl) tetrasulfide, bis(3-triethoxysilylpropyl) trisulfide, and bis(3-triethoxysilylpropyl) disulfide are preferred, and bis One or more selected from (3-triethoxysilylpropyl)tetrasulfide and bis(3-triethoxysilylpropyl)disulfide are more preferred.
The polysulfide-based silane coupling agents (C) can be used alone or in combination of two or more.

Examples of commercially available polysulfide-based silane coupling agents include Si75, Si69, etc. manufactured by Evonik, KBE-846, etc. manufactured by Shin-Etsu Chemical Co., Ltd., and Cabras 2A manufactured by Daiso. , Cabras 2B, Cabras 4, and the like.

<Conjugated heterocyclic compound (D)>
The rubber composition of the present invention contains a conjugated heterocyclic compound (D) from the viewpoint of improving the dispersibility and heat resistance of silica and improving the dispersibility, heat resistance, and fuel efficiency of the resulting rubber molded product. do.
A conjugated heterocyclic compound refers to a heterocyclic compound having a conjugated structure. A conjugated structure is a structure in which the electrons of two or more chemical bonds interact with each other and are delocalized. It refers to a structure that is delocalized by interacting with each other in a row.
The conjugated heterocyclic compound has a monocyclic conjugated ring (conjugated monocyclic) structure, has 1 to 3 nitrogen atoms and 0 or 1 sulfur atom in the monocyclic ring, and has 2 to 12 carbon atoms. is preferred.
Specifically, the conjugated heterocyclic compound (D) used in the present invention includes a thiazole ring, an isothiazole ring, a thiadiazole ring, an imidazole ring, a pyrazole ring, a triazole ring, a pyridine ring, a pyrimidine ring, a pyrazine ring, and a triazine ring. A compound having a structure in which at least one thiol group is bonded to one or more conjugated heterocycles selected from
From the same viewpoint as above, the conjugated heterocyclic compound (D) has a structure in which at least one thiol group is bonded to one or more conjugated heterocyclic rings selected from thiadiazole rings, pyridine rings, pyrimidine rings, and triazine rings. Preferred are compounds having

Compounds having a structure in which at least one thiol group is bound to a thiadiazole ring include 2,5-dimercapto-1,3,4-thiadiazole (MTD) and 2-amino-5-mercapto-1,3,4-thiadiazole. , 2-amino-5-trifluoromethyl-1,3,4-thiadiazole and the like. Among these, 2,5-dimercapto-1,3,4-thiadiazole is preferred from the viewpoint of reactivity.

As the compound having a structure in which at least one thiol group is bonded to one or more conjugated heterocyclic rings selected from pyridine ring, pyrimidine ring, and triazine ring, compounds represented by the following general formula (I) are preferred.

In formula (I), R ¹ represents a hydrogen atom, a hydrocarbon group having 1 to 8 carbon atoms, an SH group, or an amino group optionally substituted with a hydrocarbon group having 1 to 16 carbon atoms, R ² represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an SH group, and X ¹ and X ² represent a nitrogen atom or a CH group.
In formula (I), R ¹ is preferably a hydrogen atom, a hydrocarbon group having 1 to 6 carbon atoms, an SH group, or an amino group having a hydrocarbon group having 1 to 14 carbon atoms, more preferably A hydrogen atom, an alkyl or alkenyl group having 1 to 4 carbon atoms, an SH group, or an amino group having an alkyl or alkenyl group having 1 to 12 carbon atoms, more preferably a hydrogen atom, an SH group, or a carbon an alkyl group having 1 to 10 carbon atoms or an alkenyl group having 1 to 4 carbon atoms, more preferably a hydrogen atom, an SH group, or an alkylamino group having 1 to 8 carbon atoms is.
R ² is preferably a hydrogen atom or an SH group.

Specific examples of the compound represented by formula (I) include 2-mercaptopyridine, 3-mercaptopyridine, 4-mercaptopyridine, 1,3,5-triazine-2,4,6-trithiol, dimethylamino- 1,3,5-triazine-2,4-dithiol, 6-(dibutylamino)-1,3,5-triazine-2,4-dithiol, 6-diallylamino-1,3,5-triazine-2, 4-dithiol, 6-(diisopropylamino)-1,3,5-triazine-2,4-dithiol, 6-(diisobutylamino)-1,3,5-triazine-2,4-dithiol, 6-di( 2-ethylhexyl)amino-1,3,5-triazine-2,4-dithiol, 6-(allylamino)-1,3,5-triazine-2,4-dithiol, 6-(butylamino)-1,3 ,5-triazine-2,4-dithiol and the like.
Among these are 2-mercaptopyridine, 1,3,5-triazine-2,4,6-trithiol, 6-(dibutylamino)-1,3,5-triazine-2,4-dithiol, 6-( Diisopropylamino)-1,3,5-triazine-2,4-dithiol is preferably one or more selected from 2-mercaptopyridine and 6-(dibutylamino)-1,3,5-triazine-2,4 - One or more selected from dithiols are more preferred.
A conjugated heterocyclic compound (D) can be used individually or in combination of 2 or more types.

<Sulfur (E)>
The rubber composition of the present invention contains sulfur (E) in order to vulcanize it into a rubber molding.
Sulfur (E) includes powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, soluble sulfur and the like commonly used in the rubber industry.
Sulfur (E) can be used alone or in combination of two or more.

<Other ingredients>
In addition to the above components, the rubber composition of the present invention may optionally contain various additives commonly used in the rubber industry, such as anti-aging agents, anti-scorch agents, and softening agents, as long as they do not impair the object of the present invention. , stearic acid, process oil, zinc oxide, vulcanizing agents, vulcanization accelerators, and the like.

<Content of each component in the rubber composition>
The rubber composition of the present invention contains or contains a rubber component (A), silica (B), a silane coupling agent (C), a conjugated heterocyclic compound (D), and sulfur (E), and optionally It further contains or blends the above-mentioned additives according to need.
The content of each component in the rubber composition will be described below, but the content means both the content and the blending amount.
The rubber component (A) constitutes the main component of the rubber composition, and its content in the rubber composition is preferably 25% by mass or more, more preferably 30% by mass or more, and still more preferably 35% by mass or more. It is more preferably 40% by mass or more, and preferably 80% by mass or less, more preferably 70% by mass or less, still more preferably 60% by mass or less, and even more preferably 50% by mass or less.

The content of silica (B) is determined based on 100 parts by mass of the rubber component (A) from the viewpoint of improving the heat resistance, wear resistance, and fuel efficiency of the resulting rubber molded article and from the viewpoint of the processability of the rubber composition. , preferably 30 parts by mass or more, more preferably 40 parts by mass or more, still more preferably 50 parts by mass or more, and even more preferably 60 parts by mass or more, and dispersing silica uniformly in the rubber composition From the viewpoint, it is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, still more preferably 100 parts by mass or less, and even more preferably 80 parts by mass or less.
When the rubber composition and the rubber molded article further contain carbon black, the content of carbon black is set to , preferably 1 part by mass or more, more preferably 2 parts by mass or more, still more preferably 5 parts by mass or more, and from the viewpoint of reducing heat build-up of the resulting rubber molded article, preferably 35 parts by mass or less, more It is preferably 25 parts by mass or less, more preferably 20 parts by mass or less.

The content of the silane coupling agent (C), particularly the polysulfide-based silane coupling agent (C), improves the dispersibility of silica and improves the heat resistance and fuel efficiency of the resulting rubber molded product. (A) With respect to 100 parts by mass, it is preferably 1 part by mass or more, more preferably 2 parts by mass or more, still more preferably 3 parts by mass or more, and preferably 12 parts by mass or less, more preferably 10 parts by mass. It is not more than 8 parts by mass, more preferably not more than 8 parts by mass.
In addition, the content of the silane coupling agent (C), particularly the polysulfide-based silane coupling agent (C), is preferably 1 part by mass or more with respect to 100 parts by mass of the silica (B) from the same viewpoint as above. It is more preferably 2 parts by mass or more, still more preferably 4 parts by mass or more, and is preferably 20 parts by mass or less, more preferably 16 parts by mass or less, and still more preferably 12 parts by mass or less.

The content of the conjugated heterocyclic compound (D) is preferably based on 100 parts by mass of the rubber component (A) from the viewpoint of improving the dispersibility of silica and improving the heat resistance and fuel efficiency of the obtained rubber molding. is 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, still more preferably 0.3 parts by mass or more, and preferably 5 parts by mass or less, more preferably 4 parts by mass or less, still more preferably It is 3 parts by mass or less.

From the viewpoint of sufficiently vulcanizing the unvulcanized rubber composition, and from the viewpoint of improving the heat resistance and fuel efficiency of the resulting rubber molded product, the content of sulfur (E) is added to 100 parts by mass of the rubber component (A). 1.2 parts by mass or less, preferably 1.1 parts by mass or less, more preferably 1.0 parts by mass or less, and even more preferably 0.9 parts by mass or less.

The mass ratio [(C)/(D)] of the silane coupling agent (C) to the conjugated heterocyclic compound (D) improves the dispersibility of silica and improves the heat resistance and fuel efficiency of the rubber molding. Therefore, it is preferably 1 or more, more preferably 1.5 or more, still more preferably 2 or more, still more preferably 2.5 or more, and preferably 30 or less, more preferably 25 or less, still more preferably 20 or less , and more preferably 15 or less.
Ratio of the number of moles of the silane coupling agent (C) to the number of moles of thiol groups in the conjugated heterocyclic compound (D) [moles of the silane coupling agent (C)/thiol groups in the conjugated heterocyclic compound (D) Number of moles] is preferably 0.1 or more, more preferably 0.3 or more, and still more preferably 0.5 or more, from the viewpoint of improving the dispersibility of silica and improving the heat resistance and fuel efficiency of the rubber molding. , more preferably 0.7 or more, and preferably 3 or less, more preferably 2 or less, still more preferably 1.5 or less, still more preferably 1.2 or more.

The mass ratio [(B)/(D)] of the silica (B) to the conjugated heterocyclic compound (D) is preferable from the viewpoint of improving the dispersibility of silica and improving the heat resistance and fuel efficiency of the rubber molding. is 20 or more, more preferably 30 or more, still more preferably 40 or more, and is preferably 400 or less, more preferably 300 or less, still more preferably 200 or less, and even more preferably 160 or less.

The mass ratio of sulfur (E) to the conjugated heterocyclic compound (D) [(E)/(D]) is preferably 0.1 or more from the viewpoint of improving the heat resistance and fuel efficiency of the resulting rubber molding. is 0.2 or more, more preferably 0.3 or more, more preferably 0.4 or more, and is 2 or less, preferably 1.9 or less, more preferably 1.8 or less, further preferably 1 .7 or less.

<Manufacture of rubber composition>
The rubber composition of the present invention is prepared by kneading a rubber component (A) with a composition containing silica (B), a silane coupling agent (C), a conjugated heterocyclic compound (D), and sulfur. It can be produced by adding and mixing sulfur to the obtained rubber kneaded product after obtaining the kneaded product.
The preferred range of the content of each component (A) to (D) is as described above.

More specifically, for example, the rubber component (A) contains silica (B), a silane coupling agent (C), a conjugated heterocyclic compound (D), and optionally carbon black, an antioxidant, stearin Components such as acid and process oil are kneaded at, for example, 140° C. or higher using a kneader such as a Banbury mixer, a roll, an intensive mixer, etc., to mix the silane coupling agent (C) and the conjugated heterocyclic compound (D). The silica (B) is dispersed in the rubber composition while reacting to break the —S—S— bond of the silane coupling agent (C).
The above kneading temperature is such that the conjugated heterocyclic compound (D) cleaves the —S—S— bond contained in component (C), and the cleaved component (C) bonds the rubber component (A) and silica (B) together. is bonded to improve the dispersibility of silica in the rubber composition, and from the viewpoint of improving the heat resistance and fuel efficiency of the resulting rubber molding, preferably 143 ° C. or higher, more preferably 146 ° C. or higher, further preferably It is 148° C. or higher, and preferably 165° C. or lower, more preferably 160° C. or lower, and even more preferably 158° C. or lower.

After obtaining a rubber kneaded product in which the silica (B) is uniformly dispersed in the rubber composition, sulfur is added and mixed.
The temperature at which sulfur is added and mixed is preferably less than 140° C., more preferably 130° C. or less, even more preferably 125° C. or less, and even more preferably 120° C. or less from the viewpoint of preventing vulcanization reaction from occurring. In addition to sulfur, if necessary, zinc oxide, a vulcanization accelerator (sulfenamide type, guanidine type, etc.), etc. are added and mixed with the rubber kneaded product to obtain an unvulcanized rubber composition. can be done.

[Rubber molding]
The rubber molded article of the present invention is obtained by vulcanizing the unvulcanized rubber composition of the present invention.
The unvulcanized rubber composition is molded by a known method, preferably 140° C. or higher, more preferably 145° C. or higher, and preferably 200° C. or lower, more preferably 180° C. or lower, by heating or heating. It can be a pressurized and vulcanized rubber molding.
The contents of components (A) to (D) in the rubber molded article and their preferred ranges are the same as in the case of the rubber composition.
The resulting rubber molded product has excellent silica dispersibility, heat resistance, and fuel efficiency, so it can be used as tire components such as tires, tire inner liners, treads, tread bases, carcasses, sidewalls, and bead portions, as well as various rubber belts. , various sealing materials, vibration isolating materials, and rubber moldings such as shoe soles.

Examples 1-6 and Comparative Examples 1-7
The raw material components shown in Table 1 were prepared, and the ingredients excluding zinc oxide, sulfur, and vulcanization accelerator were kneaded according to the formulation shown in Table 1 at a maximum temperature of 150°C for 4 minutes using a Banbury mixer. Next, zinc oxide, sulfur and a vulcanization accelerator were added and kneaded for 2 minutes at a maximum temperature of 110°C to obtain an unvulcanized rubber composition.
The resulting unvulcanized rubber composition was heated at 160° C. for 30 minutes to obtain a sheet-like vulcanized rubber molding.

Details of each component shown in Table 1 are as follows.
[Rubber component (A)]
*1: Solution polymerization SBR manufactured by JSR Corporation, product name: HPR850, styrene content 27.5% by mass
*2: RSS#3
[Silica (B)]
*3: Manufactured by Tosoh Silica Corporation, trade name: Nip Seal AQ, BET specific surface area 205 m ² /g
〔Carbon black〕
*4: Beilum Carbon Chemical Company, Furnace Black, trade name: N234, DBP absorption: 125 cm ³ /100 g, N ₂ AS: 117 m ² /g
[Silane coupling agent (C)]
*5: Bis(triethoxysilylpropyl) disulfide, manufactured by Evonik, trade name: Si75 (S2)
[Conjugated heterocyclic compound (D)]
*6: 2-Mercaptopyridine, manufactured by Tokyo Chemical Industry Co., Ltd. *7: 6-(Dibutylamino)-1,3,5-triazine-2,4-dithiol, manufactured by Tokyo Chemical Industry Co., Ltd. *8: 2,5 -Dimercapto-1,3,4-thiadiazole, manufactured by Tokyo Chemical Industry Co., Ltd. *9: 2,4,6-trimethylpyridine, manufactured by Tokyo Chemical Industry Co., Ltd.

〔others〕
*10: N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., trade name: Nocrac 6C
*11: Manufactured by Kao Corporation, trade name: Lunax S-70V
*12: Naphthenic process oil, manufactured by Japan Sun Oil Co., Ltd., product name: SUNTHENE 410
*13: Zinc oxide (first grade) manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.
*14: Sulfur (powder, for chemical use) manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.
*15: Sulfenamide-based vulcanization accelerator, N-cyclohexyl-2-benzothiazolylsulfenamide, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., trade name: Noxcellar CZ-G
*16: Guanidine-based vulcanization accelerator, 1,3-diphenylguanidine, manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd., trade name: Noxeller D

Using the vulcanized rubber molded bodies obtained in Examples and Comparative Examples, evaluation of silica dispersibility and measurement of tensile stress and loss tangent (tan δ) were performed by the following methods. Table 1 shows the results.
(1) Evaluation of silica dispersibility Using a viscoelasticity measuring device (manufactured by TA Instruments Co., Ltd., ARES-G2), in torsion mode, 50 ° C., frequency 10 Hz, strain 0.1% to 10% The shear elastic modulus G' of the obtained sheet-like rubber molding was measured in the range of , and the shear elastic modulus G' when 0.1% strain was applied and the shear elastic modulus G' when 5% strain was applied were calculated according to the following formula (1). The difference ΔG' from the elastic modulus G' was calculated to evaluate silica dispersibility.
ΔG' (kPa) = G' (0.1%) - G' (5%) (1)
In formula (1), G' (0.1%) is the shear modulus when 0.1% strain is applied at 50°C, and G' (5%) is the shear elasticity when 10% strain is applied at 50°C. rate.
Table 1 shows the values relative to ΔG′ of the rubber molding of Comparative Example 1, which is 100.
If the relative value of ΔG' is less than 100, preferably 90 or less, it indicates that the silica (filler) in the rubber molding (rubber composition) is well dispersed.

(2) Measurement of tensile stress at 200% elongation A vulcanized rubber test piece obtained by vulcanizing the rubber composition at 160 ° C. for 30 minutes was processed into a JIS dumbbell-shaped No. 3 test piece, and JIS K 6251 A tensile test was performed according to , and the tensile stress (MPa) at 200% elongation at 25°C was measured.
Also, after the vulcanized rubber test piece was heat-aged at 100° C. for 72 hours, the tensile stress (MPa) at 200% elongation was measured in the same manner as described above.
In Table 1, the tensile stress at 200% elongation is shown as an index with the value of the tensile stress in Comparative Example 1 before the heat aging treatment set to 100. An index closer to 100 indicates less aging even after heat treatment, and an index of 130 or less indicates good grip.

(3) Measurement of loss tangent (tan δ) Using a viscoelasticity measuring device (manufactured by TA Instruments, ARES-G2), a sheet obtained under the conditions of a temperature of 50 ° C., a dynamic strain of 5%, and a frequency of 10 Hz The loss tangent (tan δ) of the rubber molding was measured. Table 1 shows relative values when tan δ of the rubber molding of Comparative Example 1 is 100.
If the relative value of tan δ is 95 or less, for example, the rolling resistance of the tire when used as a tire is low, the tire has low heat build-up, and when used as a vehicle tire, the fuel efficiency performance is improved.

From Table 1, the rubber molded bodies obtained in Examples 1 to 6 of the present invention have a difference in shear modulus (ΔG') of less than 100 compared to the rubber molded bodies obtained in Comparative Examples 1 to 7. It can be seen that it has excellent dispersibility of silica (filler), small change in tensile stress due to heating, excellent heat resistance, small loss tangent (tan δ), and excellent fuel efficiency.

The rubber composition of the present invention has excellent silica dispersibility and heat resistance, and the rubber molding of the present invention has excellent silica dispersibility, heat resistance, and fuel efficiency. Especially suitable for various tires for large vehicles (large trucks, buses, construction vehicles, etc.), tire members such as tire treads, various rubber belts, various sealing materials, vibration isolation materials, shoe soles, etc. available for

Claims (7)

A rubber composition containing a rubber component (A), silica (B), a silane coupling agent (C), a conjugated heterocyclic compound (D), and sulfur (E),
The conjugated heterocyclic compound (D) is one or more conjugated heterocyclic rings selected from a thiazole ring, an isothiazole ring, a thiadiazole ring, an imidazole ring, a pyrazole ring, a triazole ring, a pyridine ring, a pyrimidine ring, a pyrazine ring, and a triazine ring. is a compound having a structure in which at least one thiol group is bonded to
The content of sulfur (E) is 1.2 parts by mass or less per 100 parts by mass of the rubber component (A),
A rubber composition in which the mass ratio [(E)/(D)] of sulfur (E) to the conjugated heterocyclic compound (D) is 0.1 or more and 2 or less. Claim that the conjugated heterocyclic compound (D) is a compound having a structure in which at least one thiol group is bonded to one or more conjugated heterocyclic rings selected from a thiadiazole ring, a pyridine ring, a pyrimidine ring, and a triazine ring. 1. The rubber composition according to 1. A compound having a structure in which at least one thiol group is bonded to at least one conjugated heterocyclic ring selected from a pyridine ring, a pyrimidine ring, and a triazine ring is a compound represented by the following general formula (I). 3. The rubber composition according to Item 1 or 2.

(In the formula, R ¹ represents a hydrogen atom, a hydrocarbon group having 1 to 8 carbon atoms, an SH group, or an amino group optionally substituted with a hydrocarbon group having 1 to 16 carbon atoms, and R ² represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an SH group, and X ¹ and X ² represent a nitrogen atom or a CH group.) The rubber composition according to any one of claims 1 to 3, wherein the silane coupling agent (C) is a polysulfide silane coupling agent. The rubber composition according to any one of claims 1 to 4, wherein the content of the conjugated heterocyclic compound (D) is 0.1 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the rubber component (A). . Ratio of the number of moles of the silane coupling agent (C) to the number of moles of thiol groups in the conjugated heterocyclic compound (D) [moles of the silane coupling agent (C)/thiol groups in the conjugated heterocyclic compound (D) number of moles] is 0.1 or more and 3 or less, the rubber composition according to any one of claims 1 to 5. A rubber molded article obtained by vulcanizing the rubber composition according to any one of claims 1 to 6.