JPH10182885A - Silica-loaded rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a rubber compsn. improved in processibility by incorporating an alkoxysilane, a sulfur-contg. silane coupling agent, and if necessary a silanol condensation catalyst into a silica-loaded rubber. SOLUTION: 100 pts.wt. rubber component comprising a natural and/or a synthetic rubber, 5-150 pts.wt. silica, an alkoxysilane represented by the formula (wherein R<1> is methyl, vinyl, or phenyl; R<2> is a 1-6C hydrocarbon group, etc.; and n is 1-6) in an amt. of 1-40wt.% of silica, a sulfur-contg. silane coupling agent e.g. bis-[3-(triethoxysilyl)propypl]tetrasulfide} in an amt. of 0.5-40wt.% of silica, if necessary a silanol condensation catalyst (e.g. dibutyltin dilaurate) in an amt. of up to 50wt.% of the silane coupling agent, and suitable amts. of a filler, a vulcanizing agent, an accelerator, oils, an antioxidant, etc., are compounded to give the objective compsn.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition containing silica, and more particularly, to a rubber composition having improved processability when unvulcanized.
The present invention relates to a vulcanizable silica-containing rubber composition.

[0002]

2. Description of the Related Art Fillers such as carbon black, calcium carbonate, alumina, aluminum sulfate, barium sulfate, calcium sulfate, silica, talc, clay, diatomaceous earth, and mica have been used in various rubbers. Since these fillers are inorganic substances or substances having a polar group on the surface thereof, there is a problem that mixing of the filler causes a reduction in cohesion with rubber.
Among these fillers, a rubber composition containing a silicon-containing filler, particularly silica, is used, for example, as a rubber composition for a tire tread having low heat generation and excellent abrasion resistance. However, tire treads containing silica have low rolling resistance and good grip on wet roads, but in the tire manufacturing process, phenomena such as increased viscosity of unvulcanized compounds, retardation of vulcanization, and reduced cohesion occur. However, there is a problem that the processability is poor. Various proposals have conventionally been made to solve such a problem, but none of them has been practically satisfactory.

[0003] As the above proposals, diethylene glycol and fatty acids are added (for example, see Rubber Industry Handbook <4th edition>, pp. 517-518, published in 1994), and metal carboxylate is added (for example, Tire). Techn
logic International 1995,
(See, for example, pages 107 to 108), and treatment of silica with a silicone oil in advance (see, for example, JP-A-6-248116). However, as mentioned above, all methods are practically sufficient. Absent.

[0004]

Accordingly, the present invention eliminates the above-mentioned problems of the prior art and improves the properties of the silica-containing vulcanizable rubber composition, for example, properties such as low heat build-up and abrasion resistance. An object of the present invention is to provide a silica-containing vulcanizable rubber composition in which the processability of an unvulcanized rubber composition is improved without substantially impairing it.

[0005]

According to the present invention, there is provided a rubber composition containing silica, comprising silica containing an alkoxysilane (I) represented by the formula (I) and a sulfur-containing silane coupling agent. A rubber composition is provided.

Embedded image (Wherein, R ¹ represents a methyl, vinyl or phenyl group;
R ² represents a hydrocarbon group having 1 to 6 carbon atoms or a hydrocarbon group containing an ether bond, and n is 1 to 6. )

According to a preferred embodiment of the present invention, there is provided a silica-containing rubber composition further comprising a silanol condensation catalyst containing 50% by weight or less of a silane coupling agent in the rubber composition.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the structure, operation and effect of the present invention will be described in detail. As described above, silica contributes to improving the physical properties of rubber, but since it is a substance having a polar group on its surface, the cohesion with rubber is reduced,
There was a problem that workability was poor. In particular, tire treads containing silica such as hydrated silica have good vulcanization properties, but have the disadvantage of poor processability when unvulcanized.
According to the findings of the present inventors, this is due to silanol groups (≡Si—OH) present on the silica surface, and a structure is formed in the silica-containing rubber composition due to the cohesive force of the silanol groups, and the viscosity is reduced. Due to the phenomenon that the vulcanization accelerator is adsorbed due to the polarity of the silanol group and the vulcanization is delayed, or the cohesion of the mixture is reduced due to insufficient compatibility with the non-polar rubber, The processability of the unvulcanized composition decreases. Further, a silane coupling agent is often used in combination with the silica-containing rubber composition to reinforce the rubber.However, a silanol group also exists in the inner cavity of the silica particles, and this is considered as a silane coupling agent. There is a problem that a large amount of the silane coupling agent must be blended because the reaction causes loss of the silane coupling agent and a reduction in the reinforcing effect. As in the prior art, when a polar substance such as diethylene glycol is added thereto, the phenomenon that a polar compounding agent such as a vulcanization accelerator is adsorbed can be prevented to some extent, but cannot be completely prevented, and a silane coupling agent or the like cannot be prevented. Neither was it possible to prevent substances that chemically bond with the silica particles from binding to the lumen.

However, according to the present invention, by mixing the alkoxysilane of the formula (I) into the rubber composition containing silica, the alkoxysilyl group reacts with the silanol group of the silica to cover the surface of the silica. Solves all the problems of the prior art, and increases the viscosity of unvulcanized products caused by the cohesive force and polarity of polar groups, and reduces wasteful consumption of polar additives such as vulcanization accelerators and silane coupling agents. Can be suppressed.

According to the present invention, the silica compounded in the rubber composition is not particularly limited, and silica generally used conventionally can be used. Specifically, wet-type and hydrophobic silica are used. Is exemplified.

The alkoxysilane (I) compounded in the silica-containing rubber composition according to the present invention has an alkoxysilyl group which reacts with a silanol group as described above, and has a lubricating effect by covering the surface of silica. It is believed that the alkoxy silane reacts with the surface of the silica while undergoing polymerization. Therefore, as an alkoxy group in one molecule, 2
One is preferred, and one does not polymerize and three or more gels. Further, n is preferably from 1 to 6, and if it exceeds 6, the bond with silica is weakened, which is not preferable. Such alkoxysilane is a known substance, and is commercially available or can be generally produced, for example, as follows.

The alkoxysilane (I) used in the present invention
Is a commercially available formula (II):

[0012]

Embedded image

(Wherein R ¹ and R ² are as defined above), which are synthesized by hydrolysis and condensation of the methoxy group, or represented by the formula (III):

[0014]

Embedded image

(Wherein R ¹ and n are as defined above) and an alcohol are reacted in the presence of a catalyst, or are synthesized by the formula (IV):

[0016]

Embedded image

(Wherein, R ¹ and R ² are as defined above), and can be synthesized by reacting a chloro group with an alcohol in the presence of water.

Examples of the alcohol include methanol, ethanol, propanol, butanol, pentanol and the like, and further include alcohols having an oxygen atom such as ethylene glycol monomethyl ether and diethylene glycol monomethyl ether.

Further, as the catalyst, chloroplatinic acid, platinum-ether complex, platinum-olefin complex, PdCl
₂ (PPh ₃ ) ₂ and RhCl ₂ (PPh ₃ ) ₂ .

The amount of the alkoxysilane used in the present invention is preferably 100% by weight or less, more preferably 1 to 40% by weight, based on the weight of silica in the rubber composition.
It is. If the blending amount of the alkoxysilane is too small, the desired effect cannot be obtained, while if it is too large, the alkoxysilane that does not bind to silica may exude from the vulcanized product, which is not preferable.

The amount of silica is not particularly limited, but is preferably 5 to 150 parts by weight, more preferably 20 to 120 parts by weight, per 100 parts by weight of rubber.
The rubber compounded as a main component in the silica compounded rubber composition according to the present invention may be any rubber conventionally compounded in various rubber compositions, for example, natural rubber (NR), polyisoprene rubber (IR), Various styrene-butadiene copolymer rubbers (SBR), various polybutadiene rubbers (B
R), acrylonitrile-butadiene copolymer rubber (N
Diene rubbers such as BR) and butyl rubber (IIR), and ethylene-propylene copolymer rubbers (EPR, EPDM)
Etc. can be used alone or as an arbitrary blend.

The sulfur-containing silane coupling agent used in the present invention can be any silane coupling agent conventionally used in combination with silica, and typical examples include those shown in Table I below. it can. Of these, bis- [3- (triethoxysilyl) -propyl]
Tetrasulfide is most preferred in terms of processability.

[0023]

[Table 1]

When a silane coupling agent is added to the vulcanizable rubber composition according to the present invention, the amount of the silane coupling agent used can be reduced and the wear resistance can be further improved as compared with the prior art. Can be. The preferred use amount of the silane coupling agent in the present invention is 40% by weight or less, more preferably 0.5 to 50% by weight, based on the amount of silica in the composition.
It is 40% by weight, particularly preferably 1 to 20% by weight. If the amount of the silane coupling agent is too small, it is difficult to obtain a desired effect, while if it is too large, scorch (scorch) may easily occur in the mixing or extrusion step, which is not preferable.

The rubber composition according to the present invention can further contain a silanol condensation catalyst. Examples of the silanol condensation catalyst used in the present invention include tin-based, titanium-based, and amine-based catalysts. Specific examples include dibutyltin dilaurate, dioctyltin, tetraisopropoxytitanium, titanium acetylacetonate, tributylamine, and stearyldimethylamine.

In the rubber composition according to the present invention, in addition to the above-mentioned essential components, a filler such as carbon black, a vulcanizing or crosslinking agent, a vulcanizing or crosslinking accelerator, various oils, an antioxidant, a plasticizer Various additives that are generally compounded for tires and other general rubbers can be compounded, and the compound is kneaded and vulcanized into a composition by a general method, and vulcanized or crosslinked. Can be used to
The compounding amounts of these additives can also be conventional general compounding amounts as long as they do not contradict the object of the present invention.

[0027]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but it goes without saying that the technical scope of the present invention is not limited to these Examples.

The following commercial products were used as the other components in the following standard examples, examples and comparative examples. Natural rubber: RSS # 1 SBR: Nipol NS116 (Nihon Zeon) Silica: Nipsil AQ (Nihon Silica) Silane coupling agent: Si69 (Dexa) (chemical name:
Bis- [3- (triethoxysilyl) -propyl] tetrasulfide) carbon black: Seast KH (Tokai Carbon)

Zinc oxide: Zinc flower No. 3 Stearic acid: Industrial stearic acid Antioxidant 6C: N-phenyl-N '-(1,3-dimethylbutyl) -p-phenylenediamine Powdered sulfur: 5% oil-treated Powdered sulfur Vulcanization accelerator CZ: N-cyclohexyl-2-benzothiazylsulfenamide

Preparation of Sample The vulcanization accelerator and components other than sulfur were kneaded in a 1.8 liter closed mixer for 3 to 5 minutes, and the vulcanization accelerator was added to the masterbatch released when the temperature reached 165 ± 5 ° C. And sulfur were kneaded with an 8-inch open roll to obtain a rubber composition. The unvulcanized physical properties of the obtained rubber composition were measured. The composition was then placed in a 15 × 15 × 0.2 cm mold at 160 ° C. for 20 minutes.
After press vulcanization for a minute, a target test piece (rubber sheet) was prepared, and vulcanization properties were evaluated.

The test methods for the unvulcanized properties and vulcanized properties of the compositions obtained in each example are as follows. Unvulcanized properties 1) Mooney viscosity: 10 based on JIS K 6300
It was measured at 0 ° C. 2) Vulcanization rate: 160 ° C based on JIS K 6300
The time (minutes) required to reach 95% degree of vulcanization was measured. 3) Scorch time: 12 based on JIS K 6300
The time (minute) at which the viscosity increased by 5 points at 5 ° C. was measured.

Vulcanization properties 1) 300% deformation stress, breaking strength, breaking elongation: JIS
Measured according to K6251 (Dumbbell-shaped No. 3 type)

The results obtained are shown in Table II.

[0034]

[Table 2]

[0035]

[Table 3]

[0036]

As shown in the results of Table II, in Examples 1 to 8 in which silica, alkoxysilane and sulfur-containing silane coupling agent were blended according to the present invention, as compared with Comparative Example 1 in which no alkoxysilane was blended. Low Mooney viscosity, short vulcanization time, long scorch time, and improved processability were observed.On the other hand, even with vulcanization properties, equivalent performance was obtained even if the silane coupling agent was reduced by half. Was. In addition, in the case where the silanol condensation catalyst was blended, it is considered that the reaction between the alkoxysilane and the silanol was promoted,
Vulcanization properties with high breaking strength were obtained.

Claims (2)

[Claims] 1. A rubber composition containing silica,
A silica-containing rubber composition comprising an alkoxysilane (I) represented by the formula (I): and a sulfur-containing silane coupling agent. Embedded image (Wherein, R ¹ represents a methyl, vinyl or phenyl group;
R ² represents a hydrocarbon group having 1 to 6 carbon atoms or a hydrocarbon group containing an ether bond, and n is 1 to 6. ) 2. The rubber composition according to claim 1, further comprising a silanol condensation catalyst in an amount of 50% by weight or less of the silane coupling agent.