JP2014098066A - Tire rubber composition and pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tire rubber composition that improves scorching performance of a rubber composition containing a protected mercapto-based silane coupling agent with silica.SOLUTION: A tire rubber composition includes diene rubber of 100 pts.mass, silica of 10-150 pts.mass, syndiotactic-1,2-polybutadiene of 3-25 pts.mass with a melting point of 110°C or less, and a protected mercapto-based silane coupling agent of 5-30 pts.mass based on silica of 100 pts.mass.

Description

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

  There is an increasing demand for lower fuel consumption in automobiles, and it is required to make the rubber composition constituting the tire difficult to generate heat, reduce rolling resistance, and improve fuel efficiency. As a technique for reducing rolling resistance, silica is used as a filler, and a silane coupling agent is used to improve the dispersibility.

  As the silane coupling agent, there are a sulfide type and a mercapto type, and the mercapto type silane coupling agent is advantageous in terms of reduction of rolling resistance. However, the mercapto-based silane coupling agent has a short scorch time, so that there is a problem in that it is likely to be burned during mixing of the rubber composition or during the extrusion process.

  In order to improve the scorch performance when such a mercapto-based silane coupling agent is blended, Patent Document 1 discloses that an isocyanate compound is used in combination. Patent Document 2 discloses that the scorch performance is improved by blending a large amount of zinc oxide or using a sulfide-based silane coupling agent together with a mercapto-based silane coupling agent. However, it is not disclosed that the scorch performance can be improved by blending syndiotactic-1,2-polybutadiene (hereinafter sometimes referred to as SPB).

  On the other hand, Patent Document 3 discloses improving the balance of wear resistance, fracture characteristics, low hysteresis loss, and wet skid characteristics by blending a modified conjugated diene rubber and SPB. However, the combination of SPB and a specific mercapto silane coupling agent is not disclosed, and it is not disclosed that the scorch performance can be improved by blending SPB.

JP 2006-089698 A JP 2007-217465 A JP 2009-235191 A

  In order to improve the low fuel consumption performance, the present inventor has excellent low fuel consumption performance by blending syndiotactic-1,2-polybutadiene in a system blended with a specific mercapto silane coupling agent together with silica. It was found that the scorch performance can be improved without impairing the performance. That is, an object of the present invention is to provide a rubber composition capable of improving the scorch performance in combination with a specific mercapto silane coupling agent.

  The rubber composition for tires according to the present invention includes 100 parts by mass of a diene rubber, 10 to 150 parts by mass of silica, 3 to 25 parts by mass of syndiotactic-1,2-polybutadiene having a melting point of 110 ° C. or less, and the following general It is at least one selected from the group consisting of a silane coupling agent represented by the formula (1) and a silane coupling agent having a group represented by the following general formula (2), and 100 parts by mass of the silica On the other hand, it contains 5 to 30 parts by mass of a mercapto silane coupling agent.

(R ¹ ) _m (R ² — (O—R ³ ) _k —O—) _n Si—R ⁴ —SH (1)
In formula (1), R ¹ is an alkoxy group having 1 to 3 carbon atoms, R ² is an alkyl group having 5 to 16 carbon atoms, R ³ is an alkylene group having 1 to ⁴ carbon atoms, and R ⁴ is 1 to 16 carbon atoms. An alkylene group, n = 1 or 2, m + n = 3, k = 2 to 20.

In formula (2), R ⁵ is an alkylene group having 1 to 9 carbon atoms, and R ⁶ is an alkyl group having 1 to 20 carbon atoms.

  The pneumatic tire according to the present invention is formed using the rubber composition.

  According to the present invention, the scorch performance can be improved by using a specific mercapto-based silane coupling agent and syndiotactic-1,2-polybutadiene in combination.

  Hereinafter, matters related to the implementation of the present invention will be described in detail.

  In the rubber composition according to the present embodiment, the diene rubber as the rubber component is not particularly limited. For example, natural rubber (NR), polyisoprene rubber (IR), polybutadiene rubber (BR), styrene butadiene rubber (SBR). ), Acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer, or a modified diene rubber obtained by modifying these with a functional group containing a hetero atom. Can be mentioned. These diene rubbers may be used alone or in combination of two or more. Preferably, it is at least one selected from NR, IR, SBR, BR, and their modified rubber, and particularly preferably at least one selected from NR, SBR, and their modified rubber.

  As the modified diene rubber, modified SBR or modified BR is preferably used, and modified SBR is particularly preferable. The functional group may be introduced at the molecular end or may be introduced into the molecular chain, but is preferably introduced at the terminal.

Examples of the functional group of the modified diene rubber include a hydroxyl group (—OH), an amino group, a carboxyl group (—COOH), a carboxylic acid derivative group, an alkoxy group, an epoxy group, a thiol group (—SH), and halogen. Can be mentioned. Each of these may be introduced alone or in combination of two or more. These functional groups interact with silanol groups (Si-OH) on the silica surface, that is, have reactivity such as reactivity or hydrogen bonding that can chemically bond with silanol groups. As such, it contributes to improving the dispersibility of silica. Here, the amino group may be not only a primary amino group but also a secondary or tertiary amino group. Examples of the carboxyl group include maleic acid, phthalic acid, acrylic acid, and methacrylic acid. Examples of the carboxylic acid derivative group include ester groups derived from these carboxylic acids (carboxylic acid ester groups) and acid anhydride groups composed of anhydrides of dicarboxylic acids such as maleic acid and phthalic acid. Examples of the carboxylic acid ester group include a (meth) acrylate group, that is, an acrylate group (—O—CO—CH═CH ₂ ) and / or a methacrylate group (—O—CO—C (CH ₃ ) ═CH ₂ ). Is a preferred example. Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, a butoxy group and the like expressed as -OR (where R is an alkyl group). For example, a trialkoxysilyl group, an alkyl dialkoxysilyl group, a dialkylalkoxysilyl group. It may be included as an alkoxysilyl group such as a group (in which at least one of the three hydrogens of the silyl group is substituted with an alkoxy group). Examples of the halogen include fluorine, chlorine, bromine and iodine. Among these functional groups, a functional group containing an oxygen atom such as a hydroxyl group, a carboxyl group, a carboxylic acid derivative group, or an alkoxy group is preferable from the viewpoint of enhancing the interaction with the silanol group of silica.

  Modified diene rubbers having such a functional group are known per se, and the production method thereof is not limited. For example, the functional group may be introduced by modifying solution-polymerized SBR or BR synthesized by anionic polymerization with a modifying agent, or the monomer having the functional group constitutes the base polymer. You may introduce | transduce into a molecular chain by copolymerizing with a monomer.

  As an embodiment, the diene rubber as the rubber component may be the above-described modified SBR alone or a blend of 50% by mass or more of the modified SBR and 50% by mass or less of the other diene rubber.

Silica is blended in the rubber composition according to this embodiment as a filler. The silica is not particularly limited, and examples thereof include wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, etc. Among them, wet silica is preferable. The colloidal characteristics of silica are not particularly limited, but those having a nitrogen adsorption specific surface area (BET) of 120 to 250 m ² / g by the BET method are preferably used, and more preferably 150 to 230 m ² / g. The BET of silica is measured according to the BET method described in ISO 5794.

  The compounding quantity of a silica can be 10-150 mass parts with respect to 100 mass parts of said diene rubbers, More preferably, it is 20-120 mass parts, More preferably, it is 40-100 mass parts.

  In the rubber composition according to the embodiment, the filler may be the above silica alone or a blend of silica and another filler. As other fillers, carbon black is preferable, but other inorganic fillers such as clay, talc, mica, etc. can also be used. The blending amount of the other filler containing carbon black is preferably 50% by mass or less, more preferably 30% by mass or less, with respect to the entire filler.

In the rubber composition according to this embodiment, a silane coupling agent is blended in order to improve the dispersibility of silica. In particular, in this embodiment, a mercapto silane coupling agent is blended because it is advantageous in terms of fuel efficiency. Specific examples include a silane coupling agent represented by the following general formula (1) and a silane coupling agent having a group represented by the following general formula (2). Or in combination of two or more. These silane coupling agents are those in which the mercapto group (SH) is protected directly or indirectly, so that the reactivity is suppressed as compared with general mercaptosilanes, and protected mercapto-based silane couplings. It can be called an agent. Specifically, the silane coupling agent represented by the formula (2) has a thiol ester structure in which a mercapto group is protected with an acyl group, and is directly protected. On the other hand, in the silane coupling agent represented by the formula (1), the mercapto group itself remains as it is, but the alkyl polyether group represented by R ² — (O—R ³ ) _k —O— is sterically hindered. It is indirectly protected by suppressing the reaction of the mercapto group.

(R ¹ ) _m (R ² — (O—R ³ ) _k —O—) _n Si—R ⁴ —SH (1)

In the above formula (1), R ¹ is an alkoxy group having 1 to 3 carbon atoms, more preferably a methoxy group or an ethoxy group. Further, ^{R 2} is an alkyl group having 5 to 16 carbon atoms, more preferably an alkyl group having 8 to 15 carbon atoms. R ³ is an alkylene group having 1 to 4 carbon atoms, and more preferably an alkylene group having 1 to 3 carbon atoms. R ⁴ is an alkylene group having 1 to 16 carbon atoms, more preferably an alkylene group having 1 to 10 carbon atoms, and still more preferably an alkylene group having 2 to 5 carbon atoms. n represents 1 or 2, and m + n = 3, more preferably n = 2 and m = 1. Moreover, k shows the number of 2-20, More preferably, it is k = 3-10. When there are a plurality of R ¹ , R ² and R ³ in one molecule, they may be the same or different.

As a silane coupling agent represented by Formula (1), what is represented by following formula (1-1) can be mentioned.

  In formula (1-1), k = 5 (average value) and j = 12 (average value). The silane coupling agent represented by the formula (1-2) is available as “VP Si363” manufactured by Evonik Degussa.

In the above formula (2), R ⁵ is an alkylene group having 1 to 9 carbon atoms, more preferably an alkylene group having 1 to 5 carbon atoms, still more preferably an alkylene group having 2 to 4 carbon atoms. R ⁶ is an alkyl group having 1 to 20 carbon atoms, more preferably an alkyl group having 1 to 18 carbon atoms, and still more preferably an alkyl group having 5 to 9 carbon atoms. As group represented by Formula (2), group represented by following formula (2-1) is more preferable.

As a silane coupling agent which has group represented by Formula (2), what is represented by following formula (2-2) can be mentioned.

In formula (2-2), R ⁷ is an alkoxy group having 1 to 3 carbon atoms, preferably a methoxy group or an ethoxy group. R ⁸ is an alkyl group or alkenyl group having 1 to 18 carbon atoms, preferably an alkyl group having 1 to 4 carbon atoms. p represents an integer of 1 to 3, and p + q = 3, and more preferably p = 3 and q = 0. When there are a plurality of R ⁷ and R ⁸ in each molecule, they may be the same or different. R ⁵ and R ⁶ are the same as those in the formula (2). Examples of the silane coupling agent represented by the formula (2-2) include 3-octanoylthio-1-propyltriethoxysilane represented by the following formula (2-2-1). It is available as “NXT” manufactured by Performance Materials. Other examples include 3-propionylthiopropyltrimethoxysilane.

Examples of the silane coupling agent having a group represented by the formula (2) include those represented by the following formula (2-3), formula (2-4), and formula (2-5). it can.

Wherein (2-5), ^{R 9} is independently an alkylene group or an alkenediyl group having 1 to 9 carbon atoms, x is the number of 1 to 20, y is a number of 0 to 20. The silane coupling agent represented by Formula (2-3) is “NXT Low-V Silane” manufactured by Momentive Performance Materials, and the silane coupling agent represented by Formula (2-4) is In addition, as “NXT Ultra Low-V Silane” manufactured by Momentive Performance Materials, the silane coupling agent represented by Formula (2-5) is “NXT-Z” manufactured by Momentive Performance Materials. As available.

  The blending amount of the protected mercapto-based silane coupling agent can be 5 to 30 parts by mass, more preferably 8 to 20 parts by mass with respect to 100 parts by mass of silica. In the rubber composition according to the present embodiment, the protected mercaptosilane is basically used alone as the silane coupling agent. However, as long as the effect thereof is not impaired, other sulfide-based silane coupling agents and the like are used. These silane coupling agents may be used in combination.

  Syndiotactic-1,2-polybutadiene (SPB) is blended in the rubber composition according to this embodiment. By using SPB together with the protected mercapto-based silane coupling agent in the rubber composition containing silica, the reactivity of the protected mercapto-based silane coupling agent can be suppressed, and the scorch performance can be improved. Specifically, the deterioration of the scorch performance due to the blending of the mercapto-based silane coupling agent can be remarkably improved by blending the SPB, and the scorch performance and the excellent low performance of the mercapto-based silane coupling agent can be improved. Both fuel efficiency and performance can be achieved.

  As SPB, one having a melting point of 110 ° C. or lower is used. By using SPB having such a low melting point, deterioration of wear resistance can be suppressed. The melting point of SPB is preferably 30 to 110 ° C, more preferably 60 to 110 ° C. Here, the melting point is a melting peak temperature of a DSC curve measured according to JIS K7121.

  SPB can be produced by 1,2-polymerizing 1,3-butadiene using a syndiotactic-1,2 polymerization catalyst, and the melting point can be adjusted by additives and polymerization conditions. . Syndiotactic-1,2 polymerization catalysts include soluble cobalt such as cobalt octoate, cobalt 1-naphthate, cobalt benzoate and the like, and organoaluminum compounds such as trimethylaluminum, triethylaluminum, tributylaluminum, triphenylaluminum and the like. Examples of the catalyst system include carbon disulfide, but are not particularly limited.

  The blending amount of SPB can be 3 to 25 parts by mass with respect to 100 parts by mass of the diene rubber. When the blending amount of SPB is 3 parts by mass or more, the effect of improving the scorch performance is excellent. Since SPB tends to improve the scorch performance improvement effect and low fuel consumption performance when the blending amount is large, the upper limit is not particularly limited from these points, but if the blending amount is too large, the wear resistance performance is improved. Since it tends to deteriorate, the amount is preferably 25 parts by mass or less. The blending amount of SPB is more preferably 5 to 20 parts by mass with respect to 100 parts by mass of the diene rubber. SPB is a thermoplastic resin and is not included in the blending amount of the diene rubber as a rubber component.

  In the rubber composition according to the present embodiment, in addition to the above components, oils such as process oil, zinc white, stearic acid, anti-aging agents, vulcanizing agents, vulcanization accelerators and the like are generally used in rubber compositions. Various additives used can be blended. Examples of the vulcanizing agent include sulfur and sulfur-containing compounds, and are not particularly limited. However, the blending amount is preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the diene rubber. More preferably, it is 0.5-5 mass parts. Moreover, as a compounding quantity of a vulcanization accelerator, it is preferable that it is 0.1-7 mass parts with respect to 100 mass parts of said diene rubbers, More preferably, it is 0.5-5 mass parts.

  The rubber composition can be prepared by kneading according to a conventional method using a commonly used Banbury mixer, kneader, roll, or other mixer. That is, in the first mixing stage, the rubber component is added and mixed with the silica, the protected mercapto-based silane coupling agent and the SPB, and other additives excluding the vulcanizing agent and the vulcanization accelerator, and then obtained. A rubber composition can be prepared by adding and mixing a vulcanizing agent and a vulcanization accelerator to the resulting mixture in the final mixing stage.

  The rubber composition according to this embodiment as described above is preferably used for a rubber composition for forming a rubber portion of a pneumatic tire, and various kinds of air can be obtained by vulcanization molding at 140 to 180 ° C., for example, according to a conventional method. The rubber part (tread rubber, sidewall rubber, etc.) of the entering tire can be configured. In particular, it is preferably used for a tread rubber of a pneumatic tire, and a tire having excellent fuel efficiency can be manufactured.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

  Using a Banbury mixer, according to the composition (parts by mass) shown in Table 1 below, first, in the first mixing stage, components other than sulfur and vulcanization accelerator are added and mixed (discharge temperature = 160 ° C.), and then obtained. In the final mixing stage, sulfur and a vulcanization accelerator were added to and mixed with the resulting mixture (discharge temperature = 90 ° C.) to prepare a tire tread rubber composition. The details of each component in Table 1 are as follows.

SBR1: amino group terminal modified solution polymerized styrene butadiene rubber, "# 9590" manufactured by Nippon Zeon Co., Ltd.
SBR2: unmodified styrene butadiene rubber, “SBR1502” manufactured by JSR Corporation
SPB-1: Syndiotactic-1,2-polybutadiene having a melting point of 95 ° C., “RB820” manufactured by JSR Corporation
SPB-2: Syndiotactic-1,2-polybutadiene having a melting point of 105 ° C., “RB830” manufactured by JSR Corporation
SPB-3: Syndiotactic-1,2-polybutadiene having a melting point = 126 ° C., “RB840” manufactured by JSR Corporation
・ Carbon black: “Seast KH” manufactured by Tokai Carbon Co., Ltd.
Silica: “Nip Seal AQ” manufactured by Tosoh Silica Co., Ltd. (BET specific surface area = 205 m ² / g)
・ Oil: “Process NC140” manufactured by JOMO Sun Energy Co., Ltd.
・ Sulphide-based silane coupling agent: “Si69” manufactured by Evonik Degussa
・ Mercapto-based silane coupling agent 1: Momentive Performance Materials “NXT”
Mercapto silane coupling agent 2: “VP Si363” manufactured by Evonik Degussa
・ Stearic acid: “Lunac S-20” manufactured by Kao Corporation
・ Zinc flower: “Zinc flower 1” manufactured by Mitsui Mining & Smelting Co., Ltd.
Anti-aging agent: “Antigen 6C” manufactured by Sumitomo Chemical Co., Ltd.
・ Wax: “Sunknock N” manufactured by Ouchi Shinsei Chemical Co., Ltd.
・ Vulcanization accelerator: “Soxinol CZ” manufactured by Sumitomo Chemical Co., Ltd.
・ Sulfur: “Sulfur Powder” manufactured by Tsurumi Chemical Co., Ltd.

  For each rubber composition, scorch performance was evaluated in an unvulcanized state, and wear resistance performance was evaluated using a test piece having a predetermined shape vulcanized at 150 ° C. for 30 minutes. Further, using each rubber composition as a tread rubber, a pneumatic radial tire of 215 / 45ZR17 was produced according to a conventional method, and the fuel efficiency was evaluated. Each evaluation method is as follows.

・ Scorch performance: Mooney scorch test in accordance with JIS K6300-1 was performed using a rheometer (L-shaped rotor), t5 value (minute) at the time of measurement at a preheating of 1 minute and a temperature of 125 ° C. was obtained. It was shown as an index with a value of 100. The larger the index, the longer the scorch time, that is, the less scorch is possible, and the better the scorch performance is.

-Wear resistance performance: In accordance with JIS K6264, using a Lambourne wear tester manufactured by Iwamoto Seisakusho Co., Ltd., the wear loss was measured under the conditions of a load of 40 N and a slip rate of 30%. It was shown as an index with the value of 100 as 100. The larger the index, the less wear loss and the better the wear resistance.

Low fuel consumption performance: The rolling resistance was measured when running at 80 km / h with a single-axis drum tester for measuring rolling resistance at a room temperature of 23 ° C. with an air pressure of 230 kPa and a load of 4.4 kPa. The result was shown by the index | exponent which set the value of the comparative example 1 to 100 about the reciprocal number of rolling resistance. The larger the index is, the smaller the rolling resistance is, and thus the better the fuel efficiency performance is.

  The results are as shown in Table 1, and in Comparative Examples 2 and 3 in which the silane coupling agent is simply replaced with a protected mercapto type, as compared to Comparative Example 1 which is a control using a sulfide silane coupling agent. Although the fuel economy performance was significantly improved, the scorch performance was greatly deteriorated.

  On the other hand, when it is Examples 1-5 which used the protected mercapto type | system | group silane coupling agent and SPB together, while showing the outstanding fuel-efficient performance equivalent to or more than Comparative Examples 2 and 3, scorch performance is notable. It was improved, and excellent workability comparable to that of Comparative Example 1 using a sulfide-based silane coupling agent was obtained. Moreover, the wear resistance was also ensured.

  In Comparative Example 4, the amount of SPB was too small, and the effect of improving the scorch performance was insufficient. In Comparative Example 5, the amount of SPB was too large, and the wear resistance was impaired. In Comparative Example 6, since SPB having a high melting point was used, the wear resistance was inferior.

Claims (2)

100 parts by weight of diene rubber,
10 to 150 parts by mass of silica;
3 to 25 parts by mass of syndiotactic-1,2-polybutadiene having a melting point of 110 ° C. or less;
It is at least one selected from the group consisting of a silane coupling agent represented by the following general formula (1) and a silane coupling agent having a group represented by the following general formula (2), and 100 masses of the silica 5 to 30 parts by mass of a mercapto-based silane coupling agent with respect to parts,
A tire rubber composition comprising:
(R ¹ ) _m (R ² — (O—R ³ ) _k —O—) _n Si—R ⁴ —SH (1)
(In the formula, R ¹ is an alkoxy group having 1 to 3 carbon atoms, R ² is an alkyl group having 5 to 16 carbon atoms, R ³ is an alkylene group having 1 to ⁴ carbon atoms, and R ⁴ is an alkylene group having 1 to 16 carbon atoms. Group n is 1 or 2, m + n = 3, k = 2-20.)

(In the formula, R ⁵ is an alkylene group having 1 to 9 carbon atoms, and R ⁶ is an alkyl group having 1 to 20 carbon atoms.)   A pneumatic tire using the rubber composition according to claim 1.