JP2000344949A - Rubber composition for automotive tire tread - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject composition excellent in dispersibility of silica and carbon black and having satisfiable mechanical strength, processability, etc., by using a specific polymer coupling agent in a rubber composition comprising the silica and carbon black compounded therein. SOLUTION: This composition is obtained by including (A) a conjugated diene elastomer (cis-1,4-polyisoprene rubber), (B) a filler composed of silica and carbon black in an amount of 30-120 pts.wt. based on 100 pts.wt. of the conjugated diene elastomer (A) and (C) a polymer silane coupling agent prepared by adding 10-300 pts.wt. of a silane compound represented by formula I (R1 is a 1-6C bivalent alkylene; R2 to R4 are each methoxy, ethoxy, phenoxy or the like) [e.g. a compound represented by formula II (Me is methyl)] to 100 pts.wt. of a butadiene-based polymer (e.g. polybutadiene) having 500-10,000 number-average molecular weight in an amount: of 1-30 pts.wt. based on 100 pts.wt. of the conjugated diene elastomer (A).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition for an automobile tire tread which contains silica and carbon black as inorganic fillers in a good dispersion state and has excellent mechanical strength and fuel efficiency.

[0002]

2. Description of the Related Art Silica has long been used as a white filler for rubber. However, when silica is kneaded with rubber, it is extremely difficult to uniformly disperse the silica in the rubber because the viscosity increases significantly. there were. In order to solve this problem, a method of adding a low molecular weight silane coupling agent such as alkylsilane, vinylsilane, aminosilane or mercaptosilane at the time of kneading silica has been adopted.

However, mercaptosilane has problems such as odor generated during heating and kneading, insufficient mechanical strength of the obtained rubber composition, and undesired crosslinking reaction (deterioration of scorch characteristics) upon heating. However, the effect was not always enough.

On the other hand, in recent years, the use of rubber containing silica on the red surface of automobile tires can improve fuel economy during normal driving without deteriorating the grip performance of the tire during braking and on wet road surfaces. Was found. To balance these conflicting properties,
It is extremely difficult with a conventional automobile tire using only carbon black as an inorganic filler, and it can be said that this is an excellent feature of a silica-containing tire. In particular, carbon dioxide gas emitted from automobiles is a cause of global warming, and the excellent fuel economy of silica-containing tires can be said to be preferable from the viewpoint of today's environmental problems. Therefore, a technique for efficiently and uniformly dispersing silica in rubber has become a very important problem today.

[0005] The above silica-containing tires have already been put to practical use, but in the production thereof, a uniform dispersion of silica is achieved by using a certain bifunctional silane coupling agent in combination with silica. Bis (3-triethoxysilylpropyl) described in JP-A-8-176345, JP-A-9-302149, and JP-A-10-1565 as the above bifunctional silane coupling agent.
Tetrasulfite is generally widely used. In this silane coupling agent, the ethoxysilyl groups present at both ends of the molecule react with silanol groups on the silica surface, and the tetrasulfite portion at the center of the molecule reacts with the double bond of the rubber, thereby sharing with both silica and rubber. It can be said that the compound has an excellent molecular structure capable of forming a bond.

However, Journal of the Rubber Association of Japan, 71, 76
(1998) has the disadvantage that, in addition to the extremely high price of the above compound, an undesirable crosslinking reaction occurs due to liberation of a sulfur atom contained in the central portion of the molecule during heating and kneading (poor scorch characteristics). It is described.

Further, as a novel polymeric silane coupling agent for silica-containing automobile tires, Japanese Patent Application Laid-Open No. 9-1946.
No. 38, and polyorganosiloxanes described in JP-A-10-53707 or modified products thereof are known. However, these polymeric silane coupling agents do not contain any structural units capable of chemically bonding to rubber, or even if they do, the amount thereof is extremely small. It is impossible to obtain a rubber composition which can be used for a tread of an automobile tire having excellent mechanical strength. For this reason, there is a problem that the above-mentioned polymer silane coupling agent is used in combination with a low-molecular silane coupling agent.

[0008]

SUMMARY OF THE INVENTION It is a primary object of the present invention to provide a novel rubber composition for an automobile tire tread which solves the problems encountered in conventional rubber compositions for automobile tires containing silica. . The present inventors have conducted intensive studies to develop a rubber composition containing silica and carbon black suitable for this purpose. As a result, by using a specific polymer silane coupling agent, the dispersion of silica and carbon black was improved. Not only is it excellent,
The present inventors have found that a novel rubber composition for an automobile tire tread exhibiting satisfactory mechanical strength, workability, and fuel efficiency can be obtained at low cost, and have reached the present invention.

[0009]

The present invention contains 30 to 120 parts by weight of a filler comprising silica and carbon black and 1 to 30 parts by weight of a polymer silane coupling agent per 100 parts by weight of a conjugated diene elastomer. And the polymer silane coupling agent has a number average molecular weight of 5
A silane compound represented by the following general formula (1) is added to 100 parts by weight of a butadiene-based polymer having a molecular weight of 00 to 10,000.
A rubber composition for an automobile tire tread, which is a coupling agent obtained by adding 0 to 300 parts by weight.

[0010]

Embedded image

Wherein R ¹ is a divalent alkylene group having 1 to 6 carbon atoms, and R ² , R ³ and R ⁴ are each independently a methoxy group, an ethoxy group, a phenoxy group, a methyl group, an ethyl group Or a phenyl group, provided that R ² , R ³
And at least one of R ⁴ is a methoxy, ethoxy or phenoxy group. The silane coupling agent used in the present invention is hereinafter referred to as a coupling agent X.

Accordingly, the rubber composition for an automobile tire tread according to the present invention comprises (a) a conjugated diene-based elastomer,
(B) 30 to 120 parts by weight of an inorganic filler composed of silica and carbon black per 100 parts by weight of the conjugated diene elastomer, and (c) 1 to 30 parts by weight of a polymer silane also per 100 parts by weight of the conjugated diene elastomer It contains a coupling agent X, and its main performance characteristics are a low-cost rubber composition for automobile tire treads having good vulcanization characteristics and processability, and excellent fuel consumption characteristics and grip performance. It is possible.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The conjugated diene-based elastomer component used in the present invention is not particularly limited as long as it is a rubbery polymer mainly containing a conjugated diene. Specific examples thereof include cis 1,4-polyisoprene rubber, 3,4-polyisoprene rubber, emulsion-polymerized styrene / butadiene copolymer rubber, solution-polymerized styrene / butadiene copolymer rubber, isoprene / butadiene copolymer rubber, and styrene / isoprene copolymer rubber. Styrene / isoprene / butadiene turbomer rubber, cis 1,4-polybutadiene rubber, trans 1,4
-Polybutadiene rubber (70-95% trans), low vinyl polybutadiene rubber (10-30% vinyl), medium vinyl polybutadiene rubber (30-50% vinyl), high vinyl polybutadiene rubber (50-90% vinyl), emulsion polymerized styrene / Butadiene / acrylonitrile terpolymer rubber and butadiene / acrylonitrile copolymer rubber. These may be used alone or in combination of two or more.

The fillers used in the present invention, silica and carbon black, are not particularly limited. As the silica, one or more of dry method white carbon, wet method white carbon, colloidal silica, precipitated silica, and the like can be used. There is no particular restriction on the specific surface area of the silica, preferably 50 to 400 m ² / g, more preferably 100 to 250 m ² / g, particularly preferably 120 to
It is in the range of 200 m ² / g. The specific surface area here is A
It is a nitrogen adsorption specific surface area (BET method) by the measuring method according to STM D3037-81. There is no particular limitation on carbon black. One or more of all carbon blacks conventionally used in tires and especially in tire treads can be used.

The amount of the filler containing silica and carbon black is in the range of 30 to 120 parts by weight, preferably 50 to 100 parts by weight, per 100 parts by weight of the conjugated diene elastomer. It is not preferable that the ratio of the filler deviates from this range, because the resulting rubber composition has significantly reduced abrasion resistance and the like, and has poor processability. Further, the weight ratio of silica to carbon black used in the present invention is preferably silica / carbon black = 10/90 to 99 /
1, more preferably 30/70 to 95/5, particularly preferably 50/50 to 90/10.

The coupling agent X used in the present invention is an essential component for imparting the rubber composition of the present invention with viscoelastic properties excellent in processability, mechanical strength and fuel economy. The silane coupling agent X is a silane compound (mercaptosilane) represented by the above general formula (1) to a carbon-carbon unsaturated bond present in a butadiene-based polymer.
Is a compound obtained by a radical addition reaction of a mercapto group (HS-).

In the general formula (1), R ¹ has 1 to 6 carbon atoms.
Represents a divalent alkylene group, specifically, -CH
_{2 -, - (CH 2)} 2 -, - (CH 2) 3 -, - (CH
_{2) 4 -, - (CH} 2) 5 - or - (CH _{2) 6} - shows a. R ² , R ³ and R ⁴ may be the same or different and each represents a methoxy group, an ethoxy group, a phenoxy group, a methyl group, an ethyl group or a phenyl group.
However, at least one of R ² , R ³ and R ⁴ needs to be a methoxy group, an ethoxy group or a phenoxy group.
Preferred specific examples of the silane compound represented by the general formula (1) include the following compounds (in the formula, M
e represents a methyl group and Et represents an ethyl group).

[0018]

Embedded image

In synthesizing the coupling agent X, the amount of the mercaptosilane of the general formula added to the butadiene-based polymer is 10 to 10 parts by weight per 100 parts by weight of the butadiene-based polymer.
It is selected in the range of 300 parts by weight. When the amount of the silane compound is 1
If the amount is less than 0 parts by weight, the reactivity between the obtained polymer silane coupling and silica decreases, so that the rubber composition finally obtained can maintain satisfactory processability and mechanical strength. Can not. On the other hand, when the amount of the silane compound is more than 300 parts by weight, the crosslinking reactivity between the obtained polymer silane coupling agent and rubber is undesirably reduced. It is not economically preferable to use a large amount of the silane compound.

On the other hand, the butadiene-based polymer to which the silane compound represented by the general formula (1) is added has a number average molecular weight of 500 to 10,000, preferably 500 to 500.
Those in the range of 0 are selected. Number average molecular weight is 500
Even if the addition reaction product obtained by using a smaller polymer is incorporated into the composition, a rubber composition having sufficient mechanical strength cannot be obtained. Further, when a polymer having a number average molecular weight of more than 10,000 is used, the viscosity of the addition reaction system is significantly increased, which hinders the execution of the addition reaction. The butadiene-based polymer used in the addition reaction preferably has a vinyl group content of 50 mol% or more and 80 mol% or less, and 55 mol% or more and 75 mol% or less of all double bonds present in the polymer. It is more preferred that:

More specifically, the butadiene-based polymer used in the addition reaction has a number average molecular weight in the range of 500 to 5,000 and a vinyl group content of 50 to 80 moles of the total double bonds present in the polymer. % Polybutadiene is preferred. The vinyl group in the butadiene-based polymer has higher reactivity than the internal olefin. Therefore, when the vinyl group content is less than 50 mol% of the total double bonds present in the butadiene-based polymer, it takes a long time to add a predetermined amount of mercaptosilane, and side reactions such as a cross-linking reaction easily occur. . For this reason, the addition reaction product obtained using a butadiene polymer having a low vinyl group content is as follows:
The performance as a silane coupling agent decreases. Also,
The use of a butadiene-based polymer having a vinyl group content of more than 80 mol% significantly increases the viscosity of the addition reaction system.
It interferes with the progress of the reaction. Furthermore, in order to obtain a butadiene-based polymer having a vinyl group content exceeding 80 mol%, anionic polymerization at a low temperature is required, and as a result, the price of the butadiene-based polymer used as a raw material of the coupling agent X rises. Invite.

The addition reaction of the butadiene-based polymer and the silane compound (1) for obtaining the coupling agent X proceeds even by simple heating, but it is preferable to coexist with a radical generator in order to proceed more quickly. . By using a radical generator, the desired addition reaction can be completed in a short time under mild reaction conditions, and a reaction product with a high addition rate can be obtained. The radical generator used is not particularly limited, and commercially available organic peroxides, azo compounds, hydrogen peroxide and the like can be used.

Specific examples of the organic peroxide include methyl ethyl ketone peroxide, cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, methylcyclohexanone peroxide, acetylacetone peroxide, and 1,1-bis (tert-butylperoxide). Oxy) -3,3,5-trimethylcyclohexane 1,1-bis (tert-butylperoxy) -3,3,5-cyclohexane, 2,2-bis (tert-butylperoxy) butane, tert-butylhydro Peroxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, paramenthane hydroperoxide, 2,5
-Dimethylhexane 2,5-dihydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, di-tert-butyl peroxide, tert-butyl cumyl peroxide, dicumyl peroxide, bis (tert-butyl) Peroxyisopropyl) benzene, 2,5-dimethyl-2,5-di (tert-butylperoxy) hexane, 2.5-
Hexanoyl peroxide, lauroyl peroxide, succinic peroxide, benzoyl peroxide and its substituted product, 2,4-dichlorobenzoyl peroxide, metatoluoyl peroxide, diisopropylperoxydicarbonate, tert-butyl-2-ethyl Hexanoate, di-2-ethylhexyl peroxy dicarbonate, dimethoxy isopropyl peroxy carbonate, di (3-methyl-3-methoxybutyl) peroxy dicarbonate, tertiary butyl peroxy acetate, tertiary butyl peroxy pivalate , Tertiary butyl peroxy neodecanoate, tertiary butyl peroxy octanoate, tertiary butyl peroxy 3,3,5-trimethylhexanoate, tertiary Peroxy laurate, tertiary Rii butyl peroxycarbonate, tertiary Rii butyl peroxybenzoate, there are tertiary Rii-butylperoxy isobutyrate and the like.

Specific examples of the azo initiator include 2,2'-
Azobisisobutyronitrile, 1,1'-azobis (cyclohexane-1-carbonitrile), 2,2'-azobis (2-methylbutyronitrile), 2,2'-azobis (2,4-dimethylvalero Nitrile), 2,2'-azobis (2,4-dimethyl-4-methoxyvaleronitrile), 2,2'-azobis (2- (2-imidazoline-
2-yl) propane), 2,2'-azobis (2,4,
4-trimethylpentane), 2,2'-azobis (2-
Methylpropane), 2,2'-azobis (2-hydroxymethylpropionnitrile), 4,4'-azobis (4-cyanovaleric acid), dimethyl 2,2 '
-Azobis (2-methylpropionate), 2-cyano-2-propylazoformamide, 2-phenylazo-
4-methoxy-2,4-dimethylvaleronitrile and the like.

The desired addition reaction can be carried out under ultraviolet irradiation or visible light irradiation in the presence of a photoinitiator. The addition reaction can be performed without a solvent, but can be performed using a solvent inert to radicals for the purpose of suppressing a rise in the viscosity of the reaction system and removing the heat of reaction. As the solvent, aromatic hydrocarbon solvents such as benzene, toluene, xylene, and mixed xylene, and aliphatic hydrocarbon solvents such as hexane, heptane, and ligroin can be used.

In the composition of the present invention, the compounding amount of the coupling agent X is selected in the range of 1 to 30 parts by weight, preferably 2 to 15 parts by weight per 100 parts by weight of the conjugated diene elastomer. If the amount of the coupling agent X is less than 1 part by weight, the effect as a silane coupling agent cannot be exhibited. If the amount exceeds 30 parts by weight, the vulcanization characteristics of the obtained rubber composition will deteriorate.

The basic constituent components of the rubber composition for an automobile tire tread according to the present invention are a conjugated diene elastomer, a filler comprising silica and carbon black, and a coupling agent X. Agents, for example, zinc oxide, stearic acid, an antioxidant, a vulcanization accelerator, process oil, other silane coupling agents represented by bis (3-triethoxysilylpropyl) tetrasulfide (Si-69), and the like. Can be added. The addition amount of these is usually preferably 1 to 10 parts by weight per 100 parts by weight of the conjugated diene elastomer. Hereinafter, the present invention will be further described with reference to examples, but the present invention is not limited to these examples.

[0028]

EXAMPLES Synthesis Example 1 of Polymeric Silane Coupling Agent Polybutadiene having a number average molecular weight of 930 and a vinyl group content of 65% (manufactured by Nippon Petrochemical Co., Ltd.) was placed in a reactor equipped with a stirrer, a thermometer and a nitrogen inlet tube. Nisseki polybutadiene B-100
0) 100 parts by weight, 3-mercaptopropyltrimethoxysilane (KBM-803, manufactured by Shin-Etsu Chemical Co., Ltd.) 1
After adding 00 parts by weight and 1 part by weight of peroxytertiarybutyl-2-ethylhexanoate (Perbutyl O manufactured by NOF Corporation) as an initiator, the inside of the reactor was purged with nitrogen using a nitrogen introducing tube. . Then, under nitrogen atmosphere, 8
The reaction was performed at 5 ° C. for 6 hours. After completion of the reaction, volatile components in the reaction product were removed under reduced pressure while maintaining the temperature at 85 ° C.
The obtained pale yellow transparent liquid was used as a silane coupling agent A.

Synthesis Example 2 of Polymeric Silane Coupling Agent Except that the raw material polybutadiene was changed to polybutadiene having a number average molecular weight of 2000 and a vinyl group content of 65% (Nisseki polybutadiene B-2000 manufactured by Nippon Petrochemical Co., Ltd.) A silane coupling agent B was obtained in the same manner as in Synthesis Example 1. Synthesis Example 3 of Polymeric Silane Coupling Agent Polybutadiene as a raw material was polybutadiene having a number average molecular weight of 3000 and a vinyl group content of 65% (Nippon Petrochemical Co., Ltd.)
Silane coupling agent C by the same operation as in Example 1 except that the product was changed to Nisseki Polybutadiene B-3000).
I got Synthesis Example 4 Synthesis of Polymeric Silane Coupling Agent A raw material was prepared by using a number average molecular weight of 2000 and a vinyl group content of 65%.
100 parts by weight of polybutadiene (Nippon Petrochemical Co., Ltd. Nisseki San polybutadiene B-2000) and 250 parts by weight of 3-mercaptopropyl trimethoxysilane (KBM-803 manufactured by Shin-Etsu Chemical Co., Ltd.) Polymer silane coupling agent D was prepared in the same manner as in Synthesis Example 1.
I got

Examples 1 to 4 and Comparative Examples 1 to 2 Mixing / Kneading of Rubber Compositions Kneading was performed by the following method with the mixing shown in Table 1 to prepare rubber compositions. Kneading method Preparation of master batch (kneading other than vulcanization system) The master batch prepared in 2.1 was wound around an open roll at 100 ° C. for 4 minutes, then mixed with a vulcanization system and a silane coupling agent and kneaded in 4 minutes. . The components used in the compounding are as follows.

SBR1500 and SL-574 NR (RSS # 1) manufactured by JSR SBR (NS116) manufactured by Natural Rubber Co., Ltd. N234 manufactured by Zeon Corporation Nip Seal VN-3 manufactured by Tokai Carbon Co. Aromax 3 manufactured by Nippon Silica Co. Two types of zinc oxide manufactured by Katayama Chemical Co., Ltd. Stearic acid manufactured by Shodo Chemical Co., Ltd. Noxeller D and CZ manufactured by NOF Corporation Nocrack 6C manufactured by Ouchi Shinko Chemical Co., Ltd. Sulfur manufactured by Ouchi Shinko Chemical Co., Ltd. Sulfur manufactured by Hosoi Chemical Co., Ltd.

[0032]

[Table 1]

Various tests on the samples obtained in Examples 1 to 3 and Comparative Examples 1 and 2 were measured by the following methods. (Mooney viscosity measurement, Mooney scorch test, and vulcanization degree test) Test method JIS K 6300 Curastometer Amplitude ± 1 °, frequency 1.67 Hz (100 cpm) (Hardness test) Test method JIS K 6253 (Tensile test) ) Test method JIS K6251 Specimen shape: Dumbbell-shaped No. 3 (abrasion test) Test method According to JIS K6264 B method Weight: 4.50 kgf Angle: 10 degrees Preliminary test: 500 times Main test: 500 times (viscoelasticity test) ) Test method JIS K 7198 Method A Specimen shape: 1 mm × 5 mm × 30 mm Measurement mode: Tensile mode Measurement frequency: 10 Hz Heating rate: 2 ° C / min Measurement temperature: -10 to 70 ° C Dynamic strain: 0.1% Tester: Rheometrics viscoelasticity measuring device RSA-II (Test result) Each test of the rubber composition obtained in Formulation 1 The results are shown in Table 2.

[0034]

[Table 2]

As is clear from the results shown in Table 2, the Mooney viscosity of Comparative Example 1 in which no silane coupling agent was added was extremely high, and the workability was poor. Further, since there is no bond between silica and rubber, the tensile stress of the rubber composition is low and the abrasion resistance is poor. On the other hand, in Comparative Example 2 using a low molecular weight silane coupling agent, although the effect as a coupling agent was recognized in the tensile test, the value of the Mooney scorch test was short, and the workability was not sufficiently improved. In addition, there is a problem in abrasion resistance.

On the other hand, in the rubber composition for a tread of an automobile tire according to the present invention, not only good vulcanizing properties and good mechanical properties are improved, but also a dynamic index which is an index of the rolling friction of the tire. In the experimental viscoelasticity measurement, it shows a value equivalent to that of the system to which the low-molecular-weight silane coupling agent that has already been used is added.

[0037]

As described above, in the rubber composition for an automobile tire tread of the present invention, by using an inexpensive specific polymer silane coupling agent, the dynamic viscoelasticity which is an index of the rolling friction of the tire is obtained. The mechanical properties and workability can be improved without impairing the properties.

Claims (6)

[Claims] 1. A filler 3 comprising silica and carbon black per 100 parts by weight of a conjugated diene elastomer.
0 to 120 parts by weight and 1 part of the polymer silane coupling agent
To 30 parts by weight, and the polymer silane coupling agent has the following general formula (1) based on 100 parts by weight of a butadiene-based polymer having a number average molecular weight of 500 to 10,000.
A rubber composition for an automobile tire tread, which is a coupling agent obtained by adding 10 to 300 parts by weight of a silane compound represented by the formula: Embedded image (Wherein R ¹ is a divalent alkylene group having 1 to 6 carbon atoms, and R ² , R ³ and R ⁴ are each independently a methoxy, ethoxy, phenoxy, methyl, ethyl or phenyl group) Wherein at least one of R ² , R ³ and R ⁴ is a methoxy group, an ethoxy group or a phenoxy group.) 2. The conjugated diene elastomer is cis 1,4.
-Polyisoprene rubber, 3,4-polyisoprene rubber,
Styrene / butadiene copolymer rubber, isoprene / butadiene copolymer rubber, styrene / isoprene copolymer rubber, styrene / isoprene / butadiene terpolymer rubber, cis 1,4-polybutadiene rubber, trans 1,4-polybutadiene rubber (70-95% trans), Low vinyl polybutadiene rubber (10-30% vinyl), medium vinyl polybutadiene rubber (30-50% vinyl), high vinyl polybutadiene rubber (50-90% vinyl), emulsion polymerized styrene / butadiene / acrylonitrile terpolymer rubber and butadiene / acrylonitrile The rubber composition for an automobile tire tread according to claim 1, which is selected from the group consisting of a copolymer rubber. 3. A silane compound having the formula: The rubber composition for an automobile tire tread according to claim 1, wherein the rubber composition is a silane compound represented by the formula (wherein Me represents a methyl group). 4. A silane compound having the formula: The rubber composition for an automobile tire tread according to claim 1, wherein the rubber composition is a silane compound represented by the formula (Et represents an ethyl group). 5. The butadiene-based polymer forming the polymer silane coupling agent has a number average molecular weight of 500 to 5,000.
The rubber composition for an automobile tire tread according to claim 1, wherein the vinyl group content is in the range of 50 mol% to 80 mol% of the total double bonds. 6. The rubber composition for an automobile tire tread according to claim 1, wherein the butadiene-based polymer is polybutadiene.