JP2020094149A - Rubber additive, rubber additive composition, tire rubber composition, tire crosslinked rubber composition, and tire rubber product, and tire - Google Patents

Abstract

To provide a tire rubber composition that makes it possible to obtain a crosslinked rubber composition having a high dynamic storage elastic modulus without sacrificing workability, provide a rubber additive added to the rubber composition and the rubber additive composition, and provide a tire rubber product and a tire including the rubber composition or crosslinked rubber composition.SOLUTION: A tire rubber composition contains a rubber component, a vulcanizer, and a compound represented by the following formula (I). (In formula (I), Ris a hydrogen atom, -C(=O)-OR, -OR, or -C(=O)-R, R-Rindependently represent a C1-22 hydrocarbon group, R-Rindependently represent a hydrogen atom or a hydroxy group, at least two of R-Rare hydroxy groups).SELECTED DRAWING: None

Description

The present invention relates to an additive for rubber, an additive composition for rubber, a rubber composition for tires, a crosslinked rubber composition for tires, a rubber product for tires, and a tire.

In recent years, in order to reduce fuel consumption of automobiles in response to social demands for energy saving, tires with low rolling resistance are required, and a rubber composition excellent in lower heat generation (lower loss) than ever before is desired. There is.
On the other hand, improvement in wear resistance of automobile tires is desired, and a rubber composition having a large storage elastic modulus, particularly a dynamic storage elastic modulus (E′) is desired.

In Patent Document 1, a specific resin composition and a thermoplastic resin are prescribed for natural rubber or synthetic isoprene rubber in order to provide a rubber composition having low heat generation and high elasticity. Rubber compositions compounded in proportions are described.

JP2012-92179A

In Patent Document 1, a rubber composition having low exothermicity and high elasticity for a specific rubber component was obtained, but the rubber component used was limited. Further, the amounts of the resin composition and the thermoplastic resin to be added were large, and the selectivity of the rubber composition formulation was limited.

An object of the present invention is to provide a rubber composition for a tire, which can obtain a crosslinked rubber composition having a high dynamic storage elastic modulus without deteriorating processability. Another object of the present invention is to provide a rubber additive and a rubber additive composition to be added to the rubber composition. Furthermore, it is to provide a rubber product for a tire and a tire using the rubber composition or the crosslinked rubber composition.

As a result of intensive studies, the present inventor has found that the above problems can be solved by blending a compound having a specific structure.
That is, the present invention relates to the following <1> to <11>.
<1> A rubber composition for a tire, which comprises a rubber component, a vulcanizing agent, and a compound represented by the following formula (I).

(In formula (I), R ¹ represents a hydrogen atom, —C(═O)—OR ^a , —OR ^b , or —C(═O)—R ^c , and R ^{a to} R ^c are each independently a carbon atom. And R ^{2 to} R ⁴ each independently represent a hydrogen atom or a hydroxyl group, and at least two of R ^{2 to} R ⁴ are hydroxyl groups.)

<2> The rubber composition for a tire according to <1>, wherein the compound represented by the formula (I) is a compound represented by the following formula (II).

(In Formula (II), R ¹ represents a hydrogen atom, —C(═O)—OR ^a , —OR ^b , or —C(═O)—R ^c , and R ^{a to} R ^c are each independently a carbon atom. Represents a hydrocarbon group of the formulas 1 to 22, and R ³ represents a hydrogen atom or a hydroxyl group.)

<3> The rubber composition for a tire according to <1> or <2>, wherein the compound represented by the formula (I) is a compound represented by the following formula (III).

(In Formula (III), R ¹ represents a hydrogen atom, —C(═O)—OR ^a , —OR ^b , or —C(═O)—R ^c , and R ^{a to} R ^c are each independently a carbon atom. It represents a hydrocarbon group of the number 1 to 22.)

<4> The tire according to any one of <1> to <3>, further containing a filler, and the content of the filler is 30 to 100 parts by mass with respect to 100 parts by mass of the rubber component. Rubber composition.
<5> Further, a mass ratio of the content of the vulcanization accelerator to the content of the compound represented by the formula (I) containing the vulcanization accelerator (represented by the vulcanization accelerator/formula (I) Compound) is 0.2-5.0, The rubber composition for tires in any one of <1>-<4>.
<6> The tire according to any one of <1> to <5>, in which the content of the compound represented by the formula (I) is 0.05 to 10 parts by mass with respect to 100 parts by mass of the rubber component. Rubber composition.
<7> A crosslinked rubber composition for tire obtained by crosslinking the rubber composition for tire according to any one of <1> to <6>.
<8> A rubber product for a tire, characterized by using the rubber composition for a tire according to any one of <1> to <6> or the crosslinked rubber composition for a tire according to <7>.
<9> A tire characterized by using the rubber composition for a tire according to any one of <1> to <6> or the crosslinked rubber composition for a tire according to <7>.
<10> A rubber additive comprising a compound represented by the following formula (I).

(In formula (I), R ¹ represents a hydrogen atom, —C(═O)—OR ^a , —OR ^b , or —C(═O)—R ^c , and R ^{a to} R ^c are each independently a carbon atom. And R ^{2 to} R ⁴ each independently represent a hydrogen atom or a hydroxyl group, and at least two of R ^{2 to} R ⁴ are hydroxyl groups.)

<11> An additive composition for rubber, containing the additive for rubber according to <10>.

ADVANTAGE OF THE INVENTION According to this invention, the rubber composition for tires which can obtain the crosslinked rubber composition which has a high dynamic storage elastic modulus can be provided, without making processability bad. Further, it is possible to provide a rubber additive to be added to the rubber composition and the rubber additive composition. Furthermore, a rubber product for tires and a tire using the rubber composition or the crosslinked rubber composition can be provided.

Hereinafter, the present invention will be described in detail based on its embodiments. In the following description, the description of “A to B” indicating a numerical range indicates a numerical range including A and B which are end points, and is “A or more and B or less” (when A<B), or “ “A or less and B or more” (when A>B).

[Rubber composition for tire, additive for rubber, and additive composition for rubber]
The tire rubber composition of the present invention (hereinafter, also simply referred to as “the rubber composition of the present invention”) is a rubber component, a vulcanizing agent, and a compound represented by the above formula (I) (hereinafter, “the present invention”). (Also referred to as "rubber additive").
Further, the rubber additive of the present invention comprises a compound represented by the above formula (I). Further, the rubber additive composition of the present invention contains the rubber additive of the present invention.
As a result of intensive studies by the present inventors, a crosslinked rubber composition obtained by crosslinking a compound represented by the above formula (I), that is, a rubber composition containing the rubber additive of the present invention, is obtained. It was found to have a high dynamic storage modulus (E'). Further, it has been found that the rubber composition does not have poor processability due to the addition of the rubber additive of the present invention. Although the detailed mechanism by which the above-mentioned effect is obtained is unknown, a part thereof is estimated as follows.
It is considered that in the course of vulcanization, the compound represented by the formula (I) (rubber additive of the present invention) and the rubber component form a pseudo crosslink. On the other hand, the compound represented by the formula (I) has a function as an antioxidant and is therefore considered to inhibit the formation of sulfur bridges. That is, although sulfur crosslinking is inhibited, pseudo crosslinking is formed between the compound represented by the formula (I) and the rubber component. In such a cross-linked system, it is considered that pseudo cross-linking disappears due to deformation, and it is presumed that a high dynamic storage elastic modulus (E′) was achieved. Furthermore, although the reason is unknown, it was found that the processability of the rubber composition does not deteriorate even if the compound represented by the formula (I) is added.
Hereinafter, each component constituting the rubber composition for tires of the present invention, the method for producing the rubber composition for tires, and the additive composition for rubber will be described in detail.

<Rubber component>
The rubber composition for tires of the present invention contains a rubber component.
The rubber component is a rubber component capable of forming crosslinks with a vulcanizing agent, and may be appropriately selected from rubber components used in the rubber industry. Suitable rubber components include natural rubber and diene-based synthetic rubber, and these can be used alone or in combination.
Examples of the diene synthetic rubber include styrene-butadiene copolymer (SBR), polybutadiene (BR), polyisoprene (IR), styrene-isoprene copolymer (SIR), butadiene-isoprene copolymer, butadiene-styrene- Examples thereof include isoprene copolymer, acrylonitrile-butadiene copolymer, chloroprene rubber, butyl rubber (IIR), halogenated butyl rubber and the like. Further, a part thereof may have a branched structure by using a polyfunctional modifier, for example, a modifier such as tin tetrachloride.
The rubber component preferably contains a styrene-butadiene copolymer or natural rubber. The rubber component may be used alone or in combination of two or more.

<Compound represented by formula (I)>
The tire rubber composition of the present invention contains a compound represented by the following formula (I). Further, the rubber additive of the present invention comprises a compound represented by the following formula (I).

(In formula (I), R ¹ represents a hydrogen atom, —C(═O)—OR ^a , —OR ^b , or —C(═O)—R ^c , and R ^{a to} R ^c are each independently a carbon atom. And R ^{2 to} R ⁴ each independently represent a hydrogen atom or a hydroxyl group, and at least two of R ^{2 to} R ⁴ are hydroxyl groups.)

In formula (I), R ¹ represents a hydrogen atom, -C(=O)-OR ^a , -OR ^b , or -C(=O)-R ^c , and R ^{a to} R ^c each independently have a carbon number. It represents a hydrocarbon group of 1 to 22.
The hydrocarbon group having 1 to 22 carbon atoms represented by R ^{a to} R ^c may be linear, branched or cyclic, and may have an unsaturated bond such as a double bond or a triple bond. Good. Among these, a linear or branched hydrocarbon group is preferable, and a linear hydrocarbon group is more preferable. R ^{a to} R ^c are preferably an alkyl group or an alkenyl group, and more preferably a linear alkyl group or a linear alkenyl group.
The carbon number of R ^{a to} R ^c is 1 or more, preferably 2 or more, more preferably 3 or more, further preferably 6 or more, from the viewpoint of obtaining a crosslinked rubber composition having a high dynamic storage elastic modulus, and , 22 or less, preferably 18 or less, more preferably 14 or less, still more preferably 10 or less.

Of these, R ¹ is preferably ^a hydrogen atom or —C(═O)—OR ^a , more preferably —C(═O)—OR ^a , and alkoxycarbonyl where R ^a is an alkyl group. More preferably, it is a group.
If R ¹ is a carboxy group (—COOH), the processability of the rubber composition will be poor. Further, the carbon number of R ^a to R ^c is greater than 22 can not be obtained a rubber composition having a high dynamic storage modulus.

In formula (I), R ^{2 to} R ⁴ each independently represent a hydrogen atom or a hydroxyl group, and at least two of R ^{2 to} R ⁴ are hydroxyl groups. Any two or more of R ^{2 to} R ⁴ may be hydroxyl groups.
When at least two of R ^{2 to} R ⁴ are hydroxyl groups, at least R ² (or R ⁴ ) and R ³ may be hydroxyl groups, or at least R ² and R ⁴ may be hydroxyl groups and are not particularly limited. However, from the viewpoint of obtaining an excellent effect, at least R ² and R ⁴ are preferably hydroxyl groups.
Therefore, the compound represented by the formula (I) is preferably a compound represented by the following formula (II).

(In Formula (II), R ¹ represents a hydrogen atom, —C(═O)—OR ^a , —OR ^b , or —C(═O)—R ^c , and R ^{a to} R ^c are each independently a carbon atom. Represents a hydrocarbon group of the formulas 1 to 22, and R ³ represents a hydrogen atom or a hydroxyl group.)

In formula (II), R ¹ , R ^{a to} R ^c and their preferred embodiments are the same as R ¹ , R ^{a to} R ^c in formula (I) and their preferred embodiments.
In the compound represented by the formula (I), it is more preferable that R ² , R ³ and R ⁴ are hydroxyl groups.
Therefore, the compound represented by the formula (I) is more preferably the compound represented by the following formula (III). The compound represented by formula (I) is more preferably pyrogallol or a gallic acid ester.

(In Formula (III), R ¹ represents a hydrogen atom, —C(═O)—OR ^a , —OR ^b , or —C(═O)—R ^c , and R ^{a to} R ^c are each independently a carbon atom. It represents a hydrocarbon group of the number 1 to 22.)

In formula (III), R ¹ , R ^{a to} R ^c and their preferred embodiments are the same as R ¹ , R ^{a to} R ^c in formula (I) and their preferred embodiments.

The compound represented by the formula (I) is commercially available, but can be produced by a usual esterification reaction, for example, using an acid such as gallic acid and a primary alcohol as raw materials. it can.

The content of the compound represented by the formula (I) in the rubber composition is preferably 100 parts by mass of the rubber component from the viewpoint of obtaining a crosslinked rubber composition having a low heat buildup property and a high dynamic storage elastic modulus. Is 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, further preferably 0.3 parts by mass or more, still more preferably 0.5 parts by mass or more, and preferably 10 parts by mass or less, It is more preferably 5 parts by mass or less, still more preferably 3 parts by mass or less, still more preferably 2.5 parts by mass or less.

<Vulcanizing agent>
The rubber composition for tires of the present invention contains a vulcanizing agent.
The vulcanizing agent is not particularly limited, and normally, sulfur is used, and examples thereof include powdered sulfur, precipitated sulfur, colloidal sulfur, surface-treated sulfur, insoluble sulfur and the like.
In the rubber composition of the present invention, the content of the vulcanizing agent is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass with respect to 100 parts by mass of the rubber component, from the viewpoint of sufficiently promoting vulcanization. By mass or more, more preferably 0.5 parts by mass or more, still more preferably 1 part by mass or more, and from the viewpoint of improving aging resistance, preferably 10 parts by mass or less, more preferably 5 parts by mass or less. , And more preferably 3 parts by mass or less.

<Vulcanization accelerator>
The rubber composition for a tire of the present invention preferably contains a vulcanization accelerator.
The vulcanization accelerator is not particularly limited and may be appropriately selected depending on the purpose. Specifically, CBS (N-cyclohexyl-2-benzothiazole sulfenamide), TBBS (Nt-butyl-2-benzothiazole sulfenamide), TBSI (Nt-butyl-2-benzothiazole sulfenamide) Sulfenamide-based vulcanization accelerators such as phenimide); guanidine-based vulcanization accelerators such as DPG (diphenylguanidine); thiuram-based vulcanization accelerators such as tetraoctylthiuram disulfide and tetrabenzylthiuram disulfide; MBT ( 2-mercaptobenzothiazole), MBTS (di-2-benzothiazolyl disulfide) and other thiazole vulcanization accelerators; vulcanization accelerators such as zinc dialkyldithiophosphate; and the like. These may be used alone or in combination of two or more.
Among these, it is preferable to contain at least a sulfenamide-based vulcanization accelerator as the vulcanization accelerator from the viewpoint of promoting appropriate vulcanization in the presence of the compound represented by the formula (I). More preferably, it contains at least CBS and TBBS.

The content of the vulcanization accelerator in the rubber composition for a tire is preferably 0.1 parts by mass or more with respect to 100 parts by mass of the rubber component, from the viewpoint of promoting an appropriate vulcanization at an appropriate vulcanization rate. , More preferably 0.3 parts by mass or more, still more preferably 0.5 parts by mass or more, even more preferably 1 part by mass or more, and preferably 10 parts by mass or less, more preferably 7.5 parts by mass or less. , And more preferably 5 parts by mass or less.
In the tire rubber composition, the mass ratio of the content of the vulcanization accelerator to the content of the compound represented by the formula (I) (vulcanization accelerator/compound represented by the formula (I)) is From the viewpoint of suppressing the vulcanization-inhibiting effect of the compound represented by the formula (I), advancing appropriate vulcanization, and obtaining a crosslinked rubber composition having low heat buildup, preferably 0.2 or more, more preferably It is 0.3 or more, more preferably 1.0 or more, and preferably 5.0 or less, more preferably 3.0 or less, and further preferably 2.5 or less.

<Filling material>
The rubber composition for a tire of the present invention preferably contains a filler if necessary.
As the filler, an organic filler such as carbon black, an inorganic filler such as silica, or a mixture of these two types of fillers may be used. Among these, one or more fillers selected from carbon black and silica are preferably used.
The carbon black is not particularly limited, and any carbon black conventionally used as a filler for rubber can be appropriately selected and used. For example, SRF, GPF, FEF, HAF, ISAF, SAF and the like are used, and particularly preferred are FEF, HAF, ISAF, SAF and the like which are excellent in bending resistance and fracture resistance.
From the viewpoint of reinforcement, carbon black has a nitrogen adsorption specific surface area N ₂ SA (based on JIS K 6217-2:2001) of preferably 30 m ² /g or more, more preferably 35 m ² /g or more. , And preferably 150 m ² /g or less, more preferably 130 m ² /g or less.
Carbon black may be used individually by 1 type, and may be used in combination of 2 or more type.

On the other hand, examples of the silica include wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), calcium silicate, and aluminum silicate. Among them, wet silica is preferable.
The BET specific surface area (measured according to ISO 5794/1) of this wet silica is preferably 40 m ² /g or more, more preferably 80 m ² /g or more, and preferably 350 m from the viewpoint of reinforcing property. ^{It is 2} /g or less, more preferably 300 m ² /g or less. As such silica, commercially available products such as "Nipsil AQ" and "Nipsil KQ" manufactured by Tosoh Silica Co., Ltd. and "Ultrasil VN3" manufactured by Degussa can be used.
One type of silica may be used alone, or two or more types may be used in combination.
Examples of the inorganic filler other than silica include aluminum hydroxide, clay, talc, calcium carbonate, zeolite and the like.

In the rubber composition for tires of the present invention, the total amount of the fillers is preferably 30 parts by mass or more, and more preferably 40 parts by mass with respect to 100 parts by mass of the rubber component, from the viewpoint of reinforcing properties and low heat buildup. As described above, the amount is more preferably 50 parts by mass or more, and preferably 100 parts by mass or less, more preferably 90 parts by mass or less, and further preferably 80 parts by mass or less.
In the present invention, it is preferable to use carbon black and silica in combination, and in this case, the content of carbon black in the rubber composition of the present invention is 100 parts by mass of the rubber component from the viewpoint of reinforcing property and low heat buildup. On the other hand, it is preferably 1 part by mass or more, more preferably 2 parts by mass or more, further preferably 3 parts by mass or more, and preferably 60 parts by mass or less, more preferably 50 parts by mass or less, and further preferably 40 parts by mass. It is below the mass part.
When carbon black and silica are used in combination, the content of silica in the rubber composition of the present invention is preferably 1 part by mass with respect to 100 parts by mass of the rubber composition from the viewpoint of reinforcing properties and low heat buildup. Or more, more preferably 3 parts by mass or more, further preferably 5 parts by mass or more, still more preferably 10 parts by mass or more, and preferably 99 parts by mass or less, more preferably 90 parts by mass or less, further preferably 80 parts by mass. It is below the mass part.

(Silane coupling agent)
When silica is used as a filler in the rubber composition for a tire of the present invention, it is preferable to add a silane coupling agent for the purpose of further improving its reinforcing property.
Examples of the silane coupling agent include bis(3-triethoxysilylpropyl) tetrasulfide, bis(3-triethoxysilylpropyl) trisulfide, bis(3-triethoxysilylpropyl) disulfide, bis(2-triethoxysilyl). Ethyl) tetrasulfide, bis(3-trimethoxysilylpropyl) tetrasulfide, bis(2-trimethoxysilylethyl) tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltri Methoxysilane, 2-mercaptoethyltriethoxysilane, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyltetrasulfide, 3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyltetrasulfide, 2-triethoxysilyl Ethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropyl benzothiazolyl tetrasulfide, 3-triethoxysilylpropyl benzolyl tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3-trimethoxy Silyl propyl methacrylate monosulfide, bis(3-diethoxymethylsilylpropyl) tetrasulfide, 3-mercaptopropyl dimethoxymethylsilane, dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, dimethoxymethylsilylpropyl benzothiazolyl Examples thereof include tetrasulfide, and among these, bis(3-triethoxysilylpropyl)polysulfide and 3-trimethoxysilylpropylbenzothiazyltetrasulfide are preferable from the viewpoint of reinforcing effect and the like.
These silane coupling agents may be used alone or in combination of two or more.

In the rubber composition for a tire of the present invention, the compounding amount of the preferable silane coupling agent varies depending on the type of the silane coupling agent and the like, but improves the dispersibility of silica and suppresses gelation of the rubber component. Therefore, with respect to 100 parts by mass of silica, it is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, further preferably 2 parts by mass or more, and preferably 20 parts by mass or less, more preferably 15 parts by mass. It is not more than 10 parts by mass, more preferably not more than 10 parts by mass.

<Other ingredients>
The rubber composition for tires of the present invention may contain other additives in addition to the components described above, within a range not impairing the object of the present invention. Other additives may be appropriately selected from various additives usually used in the rubber industry, and specifically, antiaging agent, softening agent, colorant, flame retardant, lubricant, foaming agent, plasticizer, Examples thereof include processing aids, antioxidants, anti-UV agents, antistatic agents, anti-coloring agents, and other compounding agents.
The rubber composition of the present invention may contain a vulcanization accelerating aid such as zinc white or fatty acid from the viewpoint of accelerating vulcanization. The fatty acid may be saturated or unsaturated, and may be linear or branched. The number of carbon atoms is not particularly limited, and for example, one having 1 to 30 carbon atoms, preferably 15 to 30 carbon atoms can be used.
Specific examples of the fatty acid include cyclohexanoic acid (cyclohexanecarboxylic acid), naphthenic acid such as alkylcyclopentane having a side chain, hexanoic acid, octanoic acid, decanoic acid (including branched carboxylic acid such as neodecanoic acid), dodecanoic acid. Saturated fatty acids such as tetradecanoic acid, hexadecanoic acid and octadecanoic acid (stearic acid), unsaturated fatty acids such as methacrylic acid, oleic acid, linoleic acid and linolenic acid, resin acids such as rosin, tall oil acid and abietic acid. And stearic acid is preferred. These may be used alone or in combination of two or more. In the present invention, stearic acid and zinc white can be preferably used, and it is particularly preferable to use zinc white and stearic acid together.
The total content of these vulcanization acceleration aids in the rubber composition is not particularly limited, but from the viewpoint of kneading workability and acceleration of vulcanization, it is preferably 0. It is 5 parts by mass or more, more preferably 1 part by mass or more, further preferably 3 parts by mass or more, and preferably 15 parts by mass or less, more preferably 10 parts by mass or less, and further preferably 7 parts by mass or less.

Examples of the antioxidant that can be used in the rubber composition of the present invention include 3C (N-isopropyl-N'-phenyl-p-phenylenediamine), 6C[N-(1,3-dimethylbutyl)-N'-phenyl. -P-phenylenediamine], TMDQ (2,2,4-trimethyl-1,2-dihydroquinoline polymer), AW (6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline), diphenylamine And a high-temperature condensate of acetone.
The antioxidants may be used alone or in combination of two or more.
The content of the antioxidant in the rubber composition is preferably 100 parts by mass with respect to 100 parts by mass of the rubber component, from the viewpoint of imparting sufficient weather resistance and ozone resistance, and suppressing discoloration and deterioration of crack resistance. 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, further preferably 1 part by mass or more, and preferably 6 parts by mass or less, more preferably 5 parts by mass or less, further preferably 3 parts by mass. It is below.

<Preparation of tire rubber composition>
The method for producing the rubber composition for a tire of the present invention is not particularly limited.
The rubber composition of the present invention can be produced by blending various compounding agents and kneading with a Banbury mixer, a roll, an intensive mixer, a twin-screw extruder or the like, heating and extruding.
From the viewpoint of suppressing the occurrence of vulcanization during the production of the rubber composition and improving the handling properties during the production, the components to be contained in the rubber composition, excluding the vulcanizing agent and the vulcanization accelerator, are pre-blended. It is preferable to prepare a rubber composition by mixing and mixing (1st kneading process), and then mixing and mixing a vulcanizing agent and a vulcanization accelerator (2nd kneading process).
By preparing the rubber composition by the above method, vulcanization does not occur even when the first kneading step is performed under high temperature conditions, and therefore the rubber composition can be manufactured with high productivity.
Regarding the kneading temperature in the first kneading step, the maximum temperature is preferably 250°C or lower, more preferably 200°C or lower, still more preferably 180°C or lower, from the viewpoint of suppressing thermal decomposition of each component. From the viewpoint of productivity, the kneading temperature in the first kneading step is preferably 100°C or higher, more preferably 120°C or higher, and even more preferably 140°C or higher.
The maximum temperature of the kneading temperature in the second kneading step is preferably 150° C. or lower, more preferably 130° C. or lower, from the viewpoint of suppressing the occurrence of vulcanization during kneading. From the viewpoint of productivity, the kneading temperature in the second kneading step is preferably 80°C or higher, more preferably 100°C or higher.

<Rubber additive composition>
The rubber additive composition of the present invention contains the rubber additive of the present invention. The rubber additive composition of the present invention includes, in addition to the rubber additive of the present invention (compound represented by the formula (I)), additives commonly used in the rubber industry, such as an antioxidant and a softening agent. Agents, silane coupling agents, fatty acids such as stearic acid, zinc oxide (zinc white), vulcanizing agents, vulcanization accelerators and the like.

[Crosslinked rubber composition]
The crosslinked rubber composition of the present invention is obtained by crosslinking the rubber composition of the present invention described above. The crosslinked rubber composition has at least crosslinks formed by vulcanization, and in addition to this, for example, pseudo crosslinks formed by the compound represented by the formula (I) may be formed.
The conditions for the cross-linking are not particularly limited and may be appropriately selected depending on the intended purpose, but it is preferable that the heating temperature is 120 to 200° C. and the heating time is 1 to 900 minutes.

[Rubber products for tires and tires]
The rubber composition for tires of the present invention is particularly preferably used for tires.
The rubber product for a tire of the present invention is not particularly limited except that the rubber composition or the crosslinked rubber composition of the present invention is used. When the crosslinked rubber composition of the present invention is used for a tire, the application site of the crosslinked rubber composition is not particularly limited and can be appropriately selected depending on the purpose, for example, tread portion, sidewall portion. It can be preferably used for at least one member of a bead portion, an inner liner, and other reinforcing rubber portions. Among these, it is preferable to use the rubber composition of the present invention for the cap tread rubber and the base tread rubber from the viewpoint of effectively improving the crack growth resistance and wettability of the tire.
Further, the tire of the present invention is not particularly limited except that the above rubber composition is used, and can be manufactured by a conventional method. That is, in the unvulcanized stage, the rubber composition of the present invention is extruded into, for example, a tread member, and is pasted and molded by a usual method on a tire molding machine to mold a green tire. A tire is manufactured by heating and pressing this raw tire in a vulcanizer. Further, as the gas to be filled in the tire, in addition to normal air or air whose oxygen partial pressure is adjusted, an inert gas such as nitrogen, argon or helium can be used.

The rubber additive and the rubber additive composition of the present invention are not limited to the tire rubber composition, and may be widely added to other rubber compositions, and the rubber additive or the rubber additive of the present invention. The rubber composition added with the agent composition or the crosslinked rubber composition obtained by crosslinking the composition can be used for various rubber products.
Examples of rubber products include, in addition to the tires described above, anti-vibration rubber, seismic isolation rubber, belts such as conveyor belts, rubber crawlers, and various hoses.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

The components used in Examples and Comparative Examples are as follows.
NR: RSS #1
SBR-1: JSR #1500 (non-oil-extended SBR, manufactured by JSR Corporation)
SBR-2: Nipol NS-210 (solution polymerization SBR, manufactured by Nippon Zeon Co., Ltd.)
CB: Seast 3 (carbon black (HAF, N ₂ SA=79 m ² /g), manufactured by Tokai Carbon Co., Ltd.)
Silica: Nipsil AQ (silica (BET specific surface area=205 m ² /g), manufactured by Tosoh Silica Co., Ltd.)
Silane coupling agent: Si69 (bis[(3-triethoxysilyl)propyl]tetrasulfide, manufactured by Evonik)
Aging 6C: Nocrac 6C (Antiaging agent, N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)
TBBS: Sansera NS-G (vulcanization accelerator, N-(t-butyl)-2-benzothiazole sulfenamide, manufactured by Sanshin Chemical Industry Co., Ltd.)
MBTS: dibenzodithiazyl disulfide (vulcanization accelerator, manufactured by Tokyo Chemical Industry Co., Ltd.)
DPG: 1,3-diphenylguanidine (vulcanization accelerator, manufactured by Wako Pure Chemical Industries, Ltd.)
Stearic acid: trade name "Lunack S-70V", manufactured by Kao Co., Ltd. ZnO: manufactured by Wako Pure Chemical Industries, Ltd. Sulfur: manufactured by Wako Pure Chemical Industries, Ltd.

Compound A: Stearyl gallate (octadecyl gallate, manufactured by Tokyo Chemical Industry Co., Ltd.)
Compound B: n-octyl gallate (manufactured by Tokyo Chemical Industry Co., Ltd.)
Compound C: Propyl gallate (manufactured by Wako Pure Chemical Industries, Ltd.)
Compound D: Pyrogallol (manufactured by Wako Pure Chemical Industries, Ltd.)
Compound E: gallic acid (manufactured by Wako Pure Chemical Industries, Ltd.)
The structures of Compound A to Compound E are shown below.

Examples 1-1 to 1-6 and Comparative examples 1-1 to 1-2, and Examples 2-1 to 2-6 and Comparative examples 2-1 to 2-2
Blends having the blending ratios shown in Tables 1 and 2 were kneaded using a Banbury mixer, and further vulcanized at 145° C. for 33 minutes using a pressure vulcanizer to obtain a crosslinked rubber composition.
Further, the blending proportions shown in Tables 1 and 2 were kneaded using a Banbury mixer, and the respective rubber compositions in an unvulcanized state were used for pneumatic radial tires for passenger cars (tire size 195/60R15). A pneumatic radial tire for passenger cars was manufactured according to a conventional method by arranging it on a tread (tread cap portion) and vulcanizing it.

[Evaluation]
The following evaluation was performed on the obtained crosslinked rubber composition (vulcanized rubber composition).
(1) Measurement of storage elastic modulus (E′ (30° C., 1%)) and loss tangent (tan δ (30° C., 1%)) With respect to the obtained crosslinked rubber composition (vulcanized rubber composition), Using a spectrometer manufactured by Ueshima Seisakusho Co., Ltd., under conditions of an initial load of 160 g, a strain of 1% and a frequency of 52 Hz, the dynamic storage elastic modulus at 30% strain at a strain of 1% (tensile dynamic storage elastic modulus, E′). (30° C., 1%)) and loss tangent (tan δ (30° C., 1%)) were measured.
Regarding the dynamic storage elastic modulus (E′), the dynamic storage elastic modulus (E′) of Comparative Example 1-1 or Comparative Example 2-1 was set as 100 and expressed as an index. It should be noted that the larger the value of E', the better the steering stability and wear resistance of the vehicle.
Further, the loss tangent (tan δ) was expressed as an index with the loss tangent (tan δ) of Comparative Example 1-1 or Comparative Example 2-1 being 100. It should be noted that the smaller the value of tan δ, the lower the heat buildup, and the lower the rolling resistance when used in a tire.

(2) Mooney viscosity (100°C)
Based on JIS K 6300, using MVR VR-1130 manufactured by Ueshima Seisakusho, the Mooney viscosity [ML ₁₊₄ ] of the obtained rubber composition (unvulcanized rubber composition) was measured at 100° C., The comparative example 1-1 or the comparative example 2-1 was set as 100 and displayed as an index. The smaller the Mooney viscosity value, the better the processability.

Examples 3-1 to 3-2 and Comparative examples 3-1 to 3-2
The components shown in Table 3 were mixed at the mixing ratio shown in Table 3 to prepare a rubber composition. For the preparation, a Banbury mixer (manufactured by Kobe Steel, Ltd.) and a roll mixer (manufactured by Kansai Roll Co., Ltd.) were used to knead in the order of the first kneading step and the second kneading step to prepare a rubber composition. did. The maximum temperature of the rubber composition in the first kneading step was 170°C, and the maximum temperature of the rubber composition in the second kneading step was 120°C. The vulcanization was performed at a temperature of 160° C., and the vulcanization time was defined by Curast T90 value (min)×1.5 times. The Curast T90 value (min) was measured by vulcanizing each rubber composition at a temperature shown in the table using a curast meter “FLAT DIE RHEOMETER MODEL VR-3110” manufactured by Kamijima Seisakusho Co., Ltd. It was determined by measuring the time (T90) until the value reached 90% of the maximum torque value. The obtained rubber composition was vulcanized at 160° C. for 20 minutes.
The obtained rubber composition was used and evaluated by the following methods.

[Evaluation]
(1) Measurement of storage elastic modulus and loss tangent Using the rubber composition after vulcanization obtained in each example, using a viscoelasticity measuring device “ARES-G2” (manufactured by TA Instruments), The storage modulus and loss tangent were measured.
The storage elastic modulus (shear dynamic storage elastic modulus) and loss tangent were measured at a temperature of 50° C., a dynamic strain of 0.1%, and a frequency of 10 Hz.
The comparative example 3-1 was set as 100 and displayed as an index. The larger the storage elastic modulus is, the better the rigidity is, and the steering stability and wear resistance of the vehicle when used as a tire are excellent. The smaller the loss tangent is, the smaller the rolling resistance of the tire when used in the tire and the better the fuel economy.

(2) Measurement of Mooney Viscosity The obtained rubber composition (unvulcanized rubber composition) was measured according to JIS K 6300 using MVR VR-1130 manufactured by Ueshima Seisakusho Co., Ltd. at 100° C. to obtain Mooney viscosity [ML ₁₊₄ ] was measured, and the comparative example 3-1 was set as 100 and displayed as an index. The smaller the value, the better the workability.

From the results of Tables 1 to 3, by adding a compound having a specific structure, a cross-linked rubber having a small amount of addition, low exothermicity, and a high dynamic storage elastic modulus (E′) It has been shown that a rubber composition can be provided from which the composition is obtained. Further, it was shown that the rubber composition had a low Mooney viscosity and was excellent in processability.

According to the present invention, a rubber composition for a tire is provided, which is capable of obtaining a crosslinked rubber composition for a tire having a high dynamic storage elastic modulus, without impairing processability, and also to the rubber composition for a tire. An additive for rubber to be added and an additive composition for the rubber are provided. The rubber composition and the crosslinked rubber composition are applicable to rubber products and are particularly useful for tire applications. A tire using the rubber composition or the crosslinked rubber composition is expected to have excellent wear resistance, low heat generation, and excellent energy saving.

Claims (11)

A rubber composition for a tire, comprising a rubber component, a vulcanizing agent, and a compound represented by the following formula (I).

(In formula (I), R ¹ represents a hydrogen atom, —C(═O)—OR ^a , —OR ^b , or —C(═O)—R ^c , and R ^{a to} R ^c are each independently a carbon atom. And R ^{2 to} R ⁴ each independently represent a hydrogen atom or a hydroxyl group, and at least two of R ^{2 to} R ⁴ are hydroxyl groups.) The rubber composition for a tire according to claim 1, wherein the compound represented by the formula (I) is a compound represented by the following formula (II).

(In Formula (II), R ¹ represents a hydrogen atom, —C(═O)—OR ^a , —OR ^b , or —C(═O)—R ^c , and R ^{a to} R ^c are each independently a carbon atom. Represents a hydrocarbon group of the formulas 1 to 22, and R ³ represents a hydrogen atom or a hydroxyl group.) The rubber composition for tires according to claim 1 or 2, wherein the compound represented by the formula (I) is a compound represented by the following formula (III).

(In formula (III), R ¹ represents a hydrogen atom, —C(═O)—OR ^a , —OR ^b , or —C(═O)—R ^c , and R ^{a to} R ^c are each independently a carbon atom. It represents a hydrocarbon group of the number 1 to 22.) The rubber composition for tires according to claim 1, further comprising a filler, and the content of the filler is 30 to 100 parts by mass with respect to 100 parts by mass of the rubber component. Furthermore, the mass ratio of the content of the vulcanization accelerator to the content of the compound represented by the formula (I) containing the vulcanization accelerator (vulcanization accelerator/compound represented by the formula (I)) is The rubber composition for tires according to any one of claims 1 to 4, which has a viscosity of 0.2 to 5.0. The rubber composition for tires according to claim 1, wherein the content of the compound represented by the formula (I) is 0.05 to 10 parts by mass with respect to 100 parts by mass of the rubber component. A crosslinked rubber composition for tire, which is obtained by crosslinking the rubber composition for tire according to any one of claims 1 to 6. A rubber product for tires, characterized by using the rubber composition for tires according to any one of claims 1 to 6 or the crosslinked rubber composition for tires according to claim 7. A tire comprising the tire rubber composition according to any one of claims 1 to 6 or the crosslinked rubber composition for a tire according to claim 7. A rubber additive comprising a compound represented by the following formula (I).

(In formula (I), R ¹ represents a hydrogen atom, —C(═O)—OR ^a , —OR ^b , or —C(═O)—R ^c , and R ^{a to} R ^c are each independently a carbon atom. And R ^{2 to} R ⁴ each independently represent a hydrogen atom or a hydroxyl group, and at least two of R ^{2 to} R ⁴ are hydroxyl groups.) An additive composition for rubber, comprising the additive for rubber according to claim 10.