JP7263656B2 - Tire rubber composition and pneumatic tire - Google Patents

Description

TECHNICAL FIELD The present invention relates to a rubber composition for tires and a pneumatic tire using the same.

Pneumatic tires are required to improve fuel efficiency while imparting high grip performance on wet road surfaces (that is, wet grip performance). Therefore, there is a demand for a tire rubber composition that achieves both wet grip performance and low heat build-up performance. For example, in order to improve wet grip performance, there is a measure to blend a resin such as a petroleum resin into the rubber composition. Increasing the amount of general-purpose resins such as petroleum resins in order to meet the recent high demands for wet grip performance improves wet grip performance, but deteriorates low heat generation performance.

By the way, in Patent Document 1, in a rubber composition for tires, a hydrogenated copolymer obtained by hydrogenating a conjugated diene part of a copolymer obtained by copolymerizing an aromatic vinyl compound and a conjugated diene compound, and a softening Compounding a resin with a temperature of -20 to 45° C. and thereby improving rubber breaking strength, abrasion resistance, fuel efficiency and wet grip performance are described.

Patent Documents 2 and 3 disclose a high-molecular-weight aromatic vinyl compound-conjugated diene compound copolymer (styrene-butadiene copolymer) and a low-molecular-weight aromatic vinyl compound-conjugated diene compound copolymer (styrene - Blending a hydrogenated copolymer obtained by hydrogenating the conjugated diene compound portion (butadiene portion) of the butadiene copolymer) into the rubber composition for tires, and thereby achieving both grip performance and fracture resistance It is stated that

However, the hydrogenated polymers described in Patent Documents 1 to 3 are all copolymers of an aromatic vinyl compound and a conjugated diene compound, and the conjugated diene compound portion thereof is hydrogenated. There is no mention of partially hydrogenated polystyrene resin.

JP 2016-056351 A JP 2010-270314 A JP 2010-254922 A

An object of the present invention is to provide a rubber composition for tires capable of improving wet grip performance while suppressing deterioration of low heat build-up performance.

A rubber composition for a tire according to an embodiment of the present invention contains 1 to 50 parts by mass of a partially hydrogenated polystyrene resin with respect to 100 parts by mass of a diene rubber component containing styrene-butadiene rubber. A pneumatic tire according to an embodiment of the present invention is produced using the tire rubber composition.

According to the embodiment of the present invention, by adding a partially hydrogenated polystyrene resin to a diene rubber component containing styrene-butadiene rubber, wet grip performance can be improved while suppressing deterioration of low heat build-up performance.

The rubber composition according to the present embodiment comprises a diene rubber component containing styrene-butadiene rubber (SBR) and a partially hydrogenated polystyrene resin.

The diene-based rubber component may be styrene-butadiene rubber alone, or may be a combination of styrene-butadiene rubber and other diene-based rubbers. The styrene-butadiene rubber is not particularly limited, and may be emulsion-polymerized styrene-butadiene rubber (E-SBR) or solution-polymerized styrene-butadiene rubber (S-SBR). Also, unmodified styrene-butadiene rubber, modified styrene-butadiene rubber, or both may be used in combination.

Modified styrene-butadiene rubbers include, for example, styrene-butadiene rubbers into which functional groups containing oxygen atoms and/or nitrogen atoms have been introduced. When the styrene-butadiene rubber contains modified styrene-butadiene rubber, the balance between wet grip performance and low heat build-up performance can be further improved.

Examples of functional groups in the modified styrene-butadiene rubber include at least one selected from the group consisting of amino groups, alkoxy groups, hydroxy groups, epoxy groups, carboxy groups and carboxylic acid derivative groups. The amino group may be not only a primary amino group but also a secondary or tertiary amino group. In the case of a secondary or tertiary amino group, the total number of carbon atoms in the hydrocarbon group as a substituent is preferably 15 or less. Examples of alkoxy groups include methoxy, ethoxy, propoxy, and butoxy groups represented by —OA (where A is, for example, an alkyl group having 1 to 4 carbon atoms). It may be included as an alkoxysilyl group (at least one of the three hydrogens of a silyl group is substituted with an alkoxy group) such as a dialkoxysilyl group and a dialkylalkoxysilyl group. Examples of the carboxylic acid derivative group include an ester group derived from carboxylic acid (carboxylic acid ester group) and an acid anhydride group composed of an anhydride of dicarboxylic acid such as maleic acid or phthalic acid. Examples of the carboxylic acid ester group include an acrylate group (--O--CO--CH=CH ₂ ) and/or a methacrylate group (--O--CO--C(CH ₃ )=CH ₂ ) (hereinafter referred to as (meth)acrylate group ) are mentioned. As one embodiment, the functional group of the modified styrene-butadiene rubber may be at least one selected from the group consisting of amino groups, alkoxy groups and hydroxy groups. These functional groups may be introduced into at least one end of the styrene-butadiene rubber, or may be introduced into the molecular chain.

Other diene rubbers used in combination with styrene-butadiene rubber are not particularly limited, and examples include natural rubber (NR), synthetic isoprene rubber (IR), butadiene rubber (BR), styrene-isoprene copolymer rubber, butadiene- Examples include isoprene copolymer rubber, styrene-isoprene-butadiene copolymer rubber, and the like, and any one of them or a combination of two or more thereof may be used. Among these, it is preferable to use natural rubber and/or butadiene rubber.

The amount of styrene-butadiene rubber contained in the diene-based rubber component is not particularly limited. For example, 100 parts by mass of the diene rubber component may contain 30 parts by mass or more of styrene-butadiene rubber, may contain 50 parts by mass or more, may contain 60 parts by mass or more, or may contain 100 parts by mass of styrene-butadiene rubber. It may contain 90 parts by mass or less, or may contain 80 parts by mass or less.

In one embodiment, 100 parts by mass of the diene rubber component may contain 40 to 90 parts by mass of styrene-butadiene rubber and 10 to 60 parts by mass of natural rubber and/or butadiene rubber. In one embodiment, 100 parts by mass of the diene rubber component may contain 50 to 90 parts by mass of styrene-butadiene rubber and 10 to 50 parts by mass of butadiene rubber. In another embodiment, 100 parts by mass of the diene rubber component may contain 50 to 90 parts by mass of styrene-butadiene rubber and 10 to 50 parts by mass of natural rubber. In yet another embodiment, 100 parts by mass of the diene rubber component may include 50 to 80 parts by mass of styrene-butadiene rubber, 10 to 30 parts by mass of natural rubber, and 10 to 30 parts by mass of butadiene rubber.

In this embodiment, a partially hydrogenated polystyrene resin is added to the diene rubber component. Wet grip performance can be improved by adding such a resin. Moreover, the partially hydrogenated polystyrene resin has both a styrene unit highly compatible with the styrene-butadiene rubber, which is the matrix rubber, and a hydrogenated styrene unit having a low compatibility. Therefore, it is thought that a microphase structure different from that of non-hydrogenated polystyrene resin is formed in the matrix rubber, thereby preventing deterioration of low heat build-up performance.

A partially hydrogenated polystyrene resin is obtained by partially hydrogenating (that is, hydrogenating) a polystyrene resin. As the polystyrene resin, a polymer using substantially only styrene as a monomer is used, and a homopolymer of styrene is more preferably used. Here, examples of polymers using substantially only styrene include polymers in which 90% by mass or more of the monomers are styrene.

Partial hydrogenation does not hydrogenate all the styrene units of the polystyrene resin, but hydrogenates some of the styrene units while leaving unhydrogenated styrene units. Therefore, the partially hydrogenated polystyrene resin includes, as monomer units constituting the partially hydrogenated polystyrene resin, an unhydrogenated styrene unit having a benzene ring and a hydrogenated styrene unit having a hydrogenated benzene ring. . Here, the hydrogenated styrene unit may be a completely hydrogenated benzene ring to form a cyclohexyl ring, or a partially hydrogenated aromatic ring (for example, a cyclohexene ring). may be mixed.

Incidentally, the method of partially hydrogenating the polystyrene resin is not particularly limited. Partially hydrogenated polystyrene resins with different hydrogenation rates can be obtained by adjusting the temperature.

The hydrogenation rate of the partially hydrogenated polystyrene resin is preferably 10 to 90%. The hydrogenation rate is more preferably 20 to 90%, still more preferably 30 to 80%. The wet grip performance tends to improve as the hydrogenation rate increases.

The molecular weight of the partially hydrogenated polystyrene resin is not particularly limited. By using such a partially hydrogenated polystyrene resin with a small molecular weight, the effect of improving the wet grip performance can be further enhanced.

The amount of the partially hydrogenated polystyrene resin is preferably 1 to 50 parts by mass, more preferably 3 to 50 parts by mass, and still more preferably 5 to 45 parts by mass based on 100 parts by mass of the diene rubber component. and may be 10 to 40 parts by mass. As the amount of the partially hydrogenated polystyrene resin added increases, the effect of improving the wet grip performance can be enhanced. In addition, when the amount of the partially hydrogenated polystyrene resin to be blended is 50 parts by mass or less, it is possible to suppress the deterioration of the low heat build-up performance.

The rubber composition according to the present embodiment may contain silica as a reinforcing filler. By blending silica, the balance between wet grip performance and low heat generation performance can be further improved. Silica is not particularly limited, and for example, wet silica such as wet precipitation silica and wet gel silica may be used.

The amount of silica compounded is not particularly limited, and may be 10 to 150 parts by mass, 30 to 120 parts by mass, or 40 to 100 parts by mass with respect to 100 parts by mass of the diene rubber component.

In the rubber composition according to the present embodiment, as the reinforcing filler, silica may be used alone, or silica and carbon black may be used in combination. The carbon black is not particularly limited, and for example, various known varieties such as SAF grade (N100 series), ISAF grade (N200 series), HAF grade (N300 series), FEF grade (N500 series) (both ASTM grade). may be used either singly or in combination of two or more. The amount of carbon black compounded is not particularly limited, and may be 1 to 80 parts by mass, 1 to 50 parts by mass, or 2 to 15 parts by mass with respect to 100 parts by mass of the diene rubber component. In the present embodiment, it is preferable to use silica as the main reinforcing filler. For example, it is preferable that 50% by mass or more of the reinforcing filler is silica, and more preferably 70% by mass or more of the reinforcing filler is silica. is.

When silica is used as the reinforcing filler, it is preferable to add a silane coupling agent. Silane coupling agents include sulfide silane and mercapto silane. The amount of the silane coupling agent compounded is not particularly limited, and may be, for example, 2 to 20% by mass based on the amount of silica compounded.

In addition to the above components, the rubber composition according to the present embodiment includes oil, stearic acid, zinc oxide, anti-aging agents, waxes, processing aids, vulcanizing agents, vulcanization accelerators, and the like. Various additives generally used in can be blended.

Sulfur is preferably used as the vulcanizing agent. The amount of the vulcanizing agent to be compounded is not particularly limited, and may be, for example, 0.1 to 10 parts by mass or 0.5 to 5 parts by mass with respect to 100 parts by mass of the diene rubber component. Examples of vulcanization accelerators include various vulcanization accelerators such as sulfenamide-based, thiuram-based, thiazole-based, and guanidine-based vulcanization accelerators. can be done. The amount of the vulcanization accelerator compounded is not particularly limited, and may be, for example, 0.1 to 7 parts by mass or 0.5 to 5 parts by mass with respect to 100 parts by mass of the diene rubber component.

The rubber composition according to the present embodiment can be produced by kneading in accordance with a conventional method using a commonly used mixer such as a Banbury mixer, kneader, or roll. That is, for example, in the first mixing step (non-professional kneading step), additives other than the vulcanizing agent and the vulcanization accelerator are added and mixed together with the partially hydrogenated polystyrene resin to the diene rubber component, and then the obtained An unvulcanized rubber composition can be prepared by adding and mixing a vulcanizing agent and a vulcanization accelerator to the resulting mixture in the final mixing step (pro-kneading step).

The rubber composition according to the present embodiment can be used, for example, in tires for various applications such as passenger cars, trucks and buses for heavy loads, and is applied to various parts of tires such as the tread portion and sidewall portion of pneumatic tires. be able to. It is preferably used for the tread of pneumatic tires, that is, a rubber composition for tire treads.

In a pneumatic tire according to one embodiment, a tire member such as a tread rubber is produced using a rubber extruder or the like using the rubber composition, and combined with other tire members to produce an unvulcanized tire (green tire). After that, it can be produced by vulcanization molding at, for example, 140 to 180°C. For example, tread rubbers for pneumatic tires include those having a two-layer structure consisting of a cap rubber and a base rubber, and those having a single-layer structure in which the two are integrated. That is, in the case of a single-layer structure, the tread rubber is preferably made of the above rubber composition, and in the case of a two-layer structure, the cap rubber is preferably made of the above rubber composition.

Examples are shown below, but the present invention is not limited to these examples. Examples 1 to 4, 7 to 9, 10 to 11, 15 to 17, and 20 to 24 are reference examples.

Various chemicals used in Examples and Comparative Examples are as follows.
・SBR1: "JSR0122" manufactured by JSR Corporation (emulsion polymerization SBR, glass transition temperature: -40 ° C., oil-extended rubber: 34 parts by mass of oil content per 100 parts by mass of rubber solid content)
・ SBR2: JSR Corporation "HPR350" (alkoxy group (specifically, alkoxysilyl group) and amino group terminal modified solution polymerization SBR, glass transition temperature: -33 ° C.)
・SBR3: “JSR1723” manufactured by JSR Corporation (emulsion polymerization SBR, glass transition temperature: −53° C., oil-extended rubber: containing 37.5 parts by mass of oil per 100 parts by mass of rubber solids)
・ BR: “BR150B” manufactured by Ube Industries, Ltd.
・NR: RSS#3

・ Silica: “Nip Seal AQ” manufactured by Tosoh Silica Co., Ltd.
・ Silane coupling agent: “Si69” manufactured by Evonik Industries
・ Carbon black: Tokai Carbon Co., Ltd. “SEAST 3”
・ Oil: “Process NC140” manufactured by JXTG Energy Co., Ltd.
・Zinc oxide: “Zinchua No. 1” manufactured by Mitsui Mining & Smelting Co., Ltd.
・ Anti-aging agent: "Nocrac 6C" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
・ Stearic acid: “Lunac S20” manufactured by Kao Corporation
・Wax: "OZOACE0355" manufactured by Nippon Seiro Co., Ltd.
・Petroleum resin: “Petrotac 90” manufactured by Tosoh Corporation
- Non-hydrogenated styrene resin: "YS Resin SX100" manufactured by Yasuhara Chemical Co., Ltd.
・ Sulfur: “Powder Sulfur” manufactured by Tsurumi Chemical Industry Co., Ltd.
・ Vulcanization accelerator 1: "Sokushinol CZ" manufactured by Sumitomo Chemical Co., Ltd.
・ Vulcanization accelerator 2: "Noccellar D" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

Hydrogenated styrene resin 1: Partially hydrogenated polystyrene resin having a hydrogenation rate of 20% synthesized by the following method according to the method described in JP-A-63-43910. In a 5 L stainless steel autoclave with a stirring blade, 300 g of polystyrene (Yasuhara Chemical Co., Ltd. "YS Resin SX100", Mn = 1200), 2 L of cyclohexane, 5% ruthenium carbon (NE Chemcat Co., Ltd. "Ru / C, type B ( 100 g of Ru5%) (wet with water) and 150 g of isopropyl alcohol were added, and the mixture was purged with nitrogen. The temperature was raised to 140° C. while stirring, hydrogen gas was introduced at a pressure of 4.4 MPa, and a hydrogenation reaction was carried out for 10 hours. After completion of the hydrogenation reaction, the solution was cooled to room temperature, centrifuged and filtered, and the colorless and transparent solution was poured into methyl alcohol to precipitate, washed with methyl alcohol, dried under reduced pressure, and washed with water. Styrene-added resin 1 was obtained. The hydrogenation rate was 20%, the yield was 98% by mass, and Mn was 1,260.

Hydrogenated styrene resin 2: Partially hydrogenated polystyrene resin obtained by carrying out a hydrogenation reaction under the same conditions as in the method for synthesizing hydrogenated styrene resin 1, except that the reaction temperature was changed to 150°C. Hydrogenation rate: 45%, yield: 97% by mass, Mn: 1250.

Hydrogenated styrene resin 3: Partially hydrogenated polystyrene resin obtained by carrying out a hydrogenation reaction under the same conditions as in the method for synthesizing hydrogenated styrene resin 2, except that the reaction time was changed to 20 hours. Hydrogenation rate: 60%, yield: 95% by mass, Mn: 1250.

・Hydrogenated styrene resin 4: After the hydrogenation reaction is performed by the synthesis method of hydrogenated styrene resin 3, the temperature is raised to 160° C. and the hydrogenation reaction is further performed for 10 hours. Partially hydrogenated polystyrene resin obtained by Hydrogenation rate: 80%, yield: 92% by mass, Mn: 1260.

The method for measuring the hydrogenation rate and the number average molecular weight (Mn) of the partially hydrogenated polystyrene resin is as follows.
Hydrogenation rate: The same molar amount of polystyrene resin before and after the hydrogenation reaction is dissolved in tetrahydrofuran (THF), UV spectrum measurement is performed, and the degree of decrease in the integrated value of the absorption spectrum at 260 nm derived from the aromatic ring is calculated from the following formula. The addition ratio was calculated.
Hydrogenation rate (%) (molar ratio) = [(AB) / A] × 100
A = Integral value of absorption spectrum at 260 nm of polystyrene resin before reaction B = Integral value of absorption spectrum at 260 nm of hydrogenated polystyrene resin

· Number average molecular weight: Mn in terms of polystyrene was determined by gel permeation chromatography (GPC). Specifically, Shimadzu Corporation's "LC-10A" as a measuring device, Polymer Laboratories' "PLgel-MIXED-C" as a column, a differential refractive index detector (RI) as a detector, and THF as a solvent. The measurement temperature is 40° C., the flow rate is 1.0 mL/min, the concentration is 1.0 g/L, and the injection volume is 40 μL.

Evaluation methods in Examples and Comparative Examples are as follows.
・ Wet grip performance: Using a viscoelasticity tester manufactured by Toyo Seiki Co., Ltd., the loss factor tan δ was measured at a frequency of 10 Hz, static strain of 10%, dynamic strain of 1%, and temperature of 0 ° C. Table 1 shows Comparative Example 1. , the value of Comparative Example 4 in Table 2, the value of Comparative Example 6 in Table 3, and the value of Comparative Example 8 in Table 4 as 100, respectively. The larger the index, the better the wet grip performance.

・Low heat generation performance: Using a viscoelasticity tester manufactured by Toyo Seiki Co., Ltd., the loss factor tan δ is measured at a frequency of 10 Hz, static strain of 10%, dynamic strain of 1%, and temperature of 60 ° C. The reciprocal of the measured value is Table 1 shows the values of Comparative Example 1, Table 2 shows the values of Comparative Example 4, Table 3 shows the values of Comparative Example 6, and Table 4 shows the values of Comparative Example 8 as 100. A larger index indicates less heat generation and excellent low heat generation performance (low fuel consumption).

[First embodiment]
Using a Banbury mixer, according to the formulation (parts by mass) shown in Table 1 below, first, in the first mixing stage, compounding agents other than sulfur and a vulcanization accelerator were added to the diene rubber component and kneaded (exhaust temperature = 160°C), then sulfur and a vulcanization accelerator were added to the resulting kneaded product in the final mixing stage and kneaded (discharge temperature = 90°C) to prepare a rubber composition. Each obtained rubber composition was vulcanized at 160° C. for 30 minutes to prepare a test piece, and wet grip performance and low heat build-up performance were evaluated.

The results are shown in Table 1. In the case of petroleum resin, as shown in Comparative Examples 1 and 2, when the blending amount was increased, the wet grip performance was improved, but the low heat build-up performance was greatly deteriorated. Moreover, when a non-hydrogenated styrene resin is blended, as shown in Comparative Example 3, good grip on the wafer cannot be obtained. In contrast to Comparative Example 1 in which petroleum resin was blended, Examples 1 to 9 in which partially hydrogenated polystyrene resin was blended improved wet grip performance while suppressing significant deterioration in low heat generation performance as in the case of increasing the amount of petroleum resin. could be improved.

As shown in Examples 1 to 4, as the hydrogenation rate of the partially hydrogenated polystyrene resin increased, the effect of improving wet grip performance and low heat build-up performance increased. Further, as shown in Examples 3 and 7 to 9, when the amount of the partially hydrogenated polystyrene resin was increased, the wet grip performance could be significantly improved while suppressing the deterioration of the low heat build-up performance. As shown in Examples 4 to 6, by using modified styrene-butadiene rubber as the styrene-butadiene rubber, wet grip performance and low heat build-up performance could be further improved.

[Second embodiment]
A rubber composition was prepared in the same manner as in Example 1 according to the formulation (parts by mass) shown in Table 2 below, and each rubber composition obtained was vulcanized at 160°C for 30 minutes to prepare a test piece. , Wet grip performance and low heat generation performance were evaluated.

The results are shown in Table 2. As in the first example of the SBR/BR system, also in the second example of the SBR/NR system, by blending the partially hydrogenated polystyrene resin, the wet grip performance is improved while suppressing the deterioration of the low heat generation performance. (see Examples 10-14).

[Third embodiment]
According to the formulation (parts by mass) shown in Table 3 below, a rubber composition was prepared in the same manner as in Example 1, and each rubber composition obtained was vulcanized at 160°C for 30 minutes to prepare a test piece. , Wet grip performance and low heat generation performance were evaluated.

The results are shown in Table 3. As in the first example of the SBR/BR system and silica blending, in the third example of the SBR/NR/BR system and silica/carbon black blending in the same amount, the partially hydrogenated polystyrene resin was blended to achieve low heat generation. It was possible to improve wet grip performance while suppressing significant deterioration in performance (see Examples 15-19).

[Fourth embodiment]
According to the formulation (parts by mass) shown in Table 4 below, a rubber composition was prepared in the same manner as in Example 1, and each rubber composition obtained was vulcanized at 160°C for 30 minutes to prepare a test piece. , Wet grip performance and low heat generation performance were evaluated.

The results are shown in Table 4. As in the first example of the SBR/BR system, also in the fourth example of the SBR/NR system, by blending the partially hydrogenated polystyrene resin, the wet grip performance is improved while suppressing the deterioration of the low heat generation performance. (see Examples 20-24).

Although several embodiments of the invention have been described above, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments, their omissions, replacements, modifications, etc., are included in the invention described in the scope of claims and equivalents thereof, as well as being included in the scope and gist of the invention.

Claims (4)

100 parts by mass of a diene rubber component containing modified styrene-butadiene rubber into which functional groups containing oxygen atoms and/or nitrogen atoms have been introduced, and polystyrene resin , which is a homopolymer of styrene, is partially hydrogenated. A rubber composition for tires containing 1 to 50 parts by mass of a partially hydrogenated polystyrene resin. The rubber composition for tires according to claim 1, wherein the partially hydrogenated polystyrene resin has a hydrogenation rate of 10 to 90%. 3. The rubber composition for tires according to claim 1, further comprising 10 to 150 parts by mass of silica with respect to 100 parts by mass of said diene rubber component. A pneumatic tire produced using the tire rubber composition according to any one of claims 1 to 3.