JPH04103B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to rubber compositions having improved rebound modulus. Specifically, the present invention relates to a rubber composition for tire treads containing, as a rubber component, a styrene-butadiene copolymer rubber in which specific benzophenones have been introduced into the molecular chain. Recently, from the viewpoints of both low fuel consumption and safety of automobiles, there has been a strong demand for a reduction in the rolling resistance of tires and an improvement in braking performance on wet road surfaces, that is, improvement in wet skid resistance. In general, these tire properties are considered to correspond to the dynamic viscoelastic properties of the tread rubber material, and are known to be contradictory properties [for example, Transaction of IRI, Vol. 40, Nos. 239-256]
1964]. In order to reduce the rolling resistance of a tire, the tread rubber material must have a high rebound elastic modulus, and considering the driving conditions of the car, this rebound elastic modulus is 50
It is necessary to evaluate at temperatures from ℃ to around 70℃. On the other hand, pretension brakes can be used to improve braking performance on wet roads, which is an important performance in terms of vehicle safety.
It is necessary that the wet skid resistance measured by a portable skid tester is high, and the tread rubber material must have a high energy loss as frictional resistance that occurs when the tire is braked and slides on the road surface. . Conventionally, in order to satisfy these two contradictory properties, emulsion polymerized styrene has been used as raw rubber.
Butadiene copolymer rubber, high cis polybutadiene rubber, low cis polybutadiene rubber, styrene-butadiene rubber obtained using an organolithium compound catalyst, natural rubber, high cis isoprene rubber, etc. are used singly or in combination. However,
It wasn't completely satisfying. In other words, in order to obtain high rebound elasticity, one must increase the blending ratio of rubber with poor wet skid resistance such as low cis-polybutadiene rubber or natural rubber, reduce the amount of filler such as carbon black, or increase the amount of filler such as sulfur. I had to increase the amount of vulcanizing agent.
However, this method has disadvantages such as reduced wet skid resistance and reduced mechanical properties. On the other hand, when trying to obtain high wet skid resistance, styrene-butadiene copolymer rubber with a relatively large amount of bound styrene (for example, 30% by weight or more of bound styrene) or 1,2
- Increase the proportion of rubber with excellent wet skid resistance such as polybutadiene rubber with a relatively high bond content (e.g. 1,2-bond content of 60% or more), fillers such as carbon black, or process oil. I had to increase the amount. This method has the disadvantage that the rebound elasticity is reduced. Therefore, the actual situation is that the composition of the raw rubber is determined so that the mechanical properties are within a practically acceptable range and the wet skid resistance and rebound elasticity are in the best balance within a practically acceptable range. Ta. For this reason, it was thought that the ability to achieve a balance between wet skid resistance and rebound elasticity by combining conventional rubbers had been reached. As a result of intensive research to solve the above-mentioned drawbacks, the present inventors surprisingly found that the rubber component contains a styrene-butadiene copolymer rubber in which specific benzophenones or thiobenzophenones have been introduced into the rubber molecular chain. Compared to a rubber composition containing the same styrene-butadiene copolymer rubber in which the compound has not been introduced, the rubber composition has significantly improved rebound resilience without reducing wet skid resistance, and has high rebound resilience. We have discovered that by taking advantage of these characteristics and increasing the amount of filler such as carbon black, if necessary, it is possible to improve mechanical properties such as abrasion resistance and achieve a balance between rebound elasticity and wet skid resistance, and have arrived at the present invention. It is ivy. That is, the present invention introduces at least 0.1 mole of benzophenones or thiobenzophenones having at least one amino group, alkylamino group, or dialkylamino group into the styrene-butadiene copolymer rubber molecular chain per mole of the rubber molecular chain. A styrene-butadiene copolymer rubber,
(a) Bound styrene content is 3% by weight or more, 10% by weight
Mooney viscosity (ML ₁₊₄ , 100℃) is less than 1,2-bond content of butadiene unit is 30~80%.
20 to 150 of the styrene-butadiene copolymer rubber and/or (b) a bound styrene content of 10 to 20% by weight,
1,2-bond content of butadiene unit is 50%
80% or less and a Mooney viscosity of 20 to 150 (20 to 90)
% by weight of natural rubber and/or polyisoprene rubber () with a cis-1,4-bond content of at least 90% and 60-5% by weight and a bound styrene content of 10-40% by weight with a butadiene unit fraction of 1, 2-
Contains 60 to 5% by weight of styrene-butadiene copolymer rubber () with a bond content of 10 to 50% as a component rubber, and the ratio of () to () is between 1:3 and 3:1. The present invention provides a rubber composition for tire tread that has reduced rolling resistance without impairing its characteristic wet skid resistance. By using the rubber composition for tire tread of the present invention, it is possible to obtain a tire that has a high level of balance between rolling resistance, which is important for tire performance, and braking performance on wet road surfaces, that is, wet skid resistance. It is possible to manufacture a tire that does not require a particular resistance value and only requires a high rebound modulus. The styrene-butadiene copolymer rubber in which benzophenones or thiobenzophenones are introduced into the rubber molecular chain used in the present invention is obtained by using an alkali metal-based catalyst commonly used in solution polymerization. Styrene with alkali metal bonded
Styrene-butadiene copolymer rubber molecules obtained by reacting butadiene copolymer rubber or rubber obtained using the catalyst with an alkali metal added in a post-reaction with the benzophenones or thiobenzophenones. The compound has a general formula with a carbon-carbon bond at the end of the chain or at the end and other molecular chains.

[Formula] (wherein R ₁ and R ₂ represent hydrogen or the above-mentioned substituents, M represents O or S, and m and n represent integers, respectively). It is polymerized rubber. Particularly desirable is a styrene-butadiene copolymer rubber in which the atomic group is introduced at the end of the molecular chain. Particularly preferred is a styrene-butadiene copolymer rubber in which the compound is introduced at the end of the molecular chain. The benzophenones or thiobenzophenones used in the present invention are, for example, 4,4'-bis(dimethylamino)-benzophenone, 4,4'-bis(diethylamino)-benzophenone, 4,4'-bis(diptylamino)-benzophenone, and 4,4'-bis(dimethylamino)-benzophenone. )-benzophenone, 4,4'-
Benzophenones having at least one amino group, alkylamino group, or dialkylamino group on one or both benzene rings, such as diaminobenzophenone, 4-dimethylaminobenzophenone, etc., and their corresponding thiobenzophenones. The benzophenones and thiobenzophenones have the general formula

[Formula] (wherein R ₁ and R ₂ are hydrogen, amino group, alkylamino group,
a substituent selected from dialkylamino groups, M
represents O or S, and m and n represent the sum of m and n from 1 to 10.
These are benzophenones represented by (each representing an integer). The styrene-butadiene copolymer rubber into which the benzophenones or thiobenzophenones have been introduced into the molecular chain is, for example, the rubber obtained by polymerizing the styrene-butadiene copolymer rubber using an alkali metal-based catalyst and completing the polymerization reaction. A method of adding the benzophenones to a solution, a method of adding an alkali metal to the rubber using the catalyst in a solution of styrene-butadiene copolymer rubber, etc., and then adding the benzophenones or thiobenzophenones. etc. can be exemplified. The alkali metal-based catalysts used in polymerization reactions and addition reactions are metal elements such as lithium, sodium, rubidium, and cesium used in ordinary solution polymerization, or their complexes with hydrocarbon compounds or polar compounds (for example, n- butyl lithium,
2-naphthyllithium, potassium-tetrahydrofuran complex, potassium-diethoxyethane complex, etc.). The benzophenones introduced into the styrene-butadiene rubber are on average per mole of rubber molecules.
It is 0.1 mole or more. If the amount is less than 0.1 mol, no improvement in rebound elasticity can be obtained. Preferably 0.3 mol or more,
More preferably 0.5 mol or more, particularly preferably
The amount is 0.7 mol or more, but if it is 5 mol or more, rubber elasticity is lost, which is not preferable. The styrene-butadiene copolymer rubber () in which the benzophenone or thiobenzophenone is introduced into the rubber molecular chain has (a) a bound styrene content of 3% by weight or more and less than 10% by weight, 1 of the butadiene unit portion, 2- The styrene-butadiene copolymer rubber having a bond content of 30 to 80% and a Mooney viscosity (ML ₁₊₄ , 100°C) of 20 to 150 and/or (b) a bond content of 10 to 20% by weight %, 1,2 of butadiene unit portion
- said styrene-butadiene copolymer rubber having a bond content of more than 50% and less than 80% and a Mooney viscosity of 20 to 150, wherein () is at least 20% by weight in the total rubber component of the rubber composition; It is necessary to include. If it is less than 20% by weight, the effect of improving rebound elasticity will be small, which is not preferable. Moreover, if it exceeds 90% by weight, wear resistance decreases, which is not preferable. Natural rubber and/or polyisoprene rubber () with a cis-1,4-bond content of at least 90%, 60-5% by weight of the total rubber component, a bound styrene content of 10-40% by weight, 1,0% of the butadiene moiety, 2 bond content 10-50
% styrene-butadiene copolymer rubber ()60~
By using a 5% by weight blend, a rubber composition with better balance between rebound modulus (55°C) and wet skid resistance can be obtained without impairing strength properties or abrasion resistance. i.e. natural rubber and/or
or has a cis 1,4-bond content of at least 90
% of polyisoprene rubber () to () can improve strength properties without reducing impact resilience. However, if it exceeds 60% by weight, the wet skid resistance will decrease significantly, so on the other hand, the bound styrene content is 10 to 40% by weight, and the 1,2-bond content of the butadiene unit is 10 to 50%.
Blending the high vinyl styrene-butadiene rubber () into a mixture of () and () has the effect of improving wet skid resistance without significantly lowering the impact modulus. If it exceeds 60% by weight of the total rubber component, the abrasion resistance will drop significantly, which is not preferable. Furthermore, if the amount is less than 5% by weight, the strength properties will not be improved. The weight ratio of () and () used is 1:3
~3:1 range, where () is 1 to ()
If it exceeds 3, the tensile strength decreases and becomes impractical. Furthermore, if () is less than 1 compared to () of 3, the wet skid resistance decreases and the object of the present invention cannot be achieved. Therefore, without impairing the strength properties and wear resistance, which are important properties for tire tread materials,
It has been discovered that the rubber composition of the present invention is most preferable in order to maintain wet skid resistance at a high level and to significantly improve impact resilience. All or part of the rubber components used in the present invention can be used as oil-extended rubber. The rubber composition for tire tread of the present invention has the following objectives:
Various compounding agents commonly used in the rubber industry depending on the application.
For example, sulfur, stearic acid, zinc white, various vulcanization accelerators (thiazole type, thiuram type, sulfenamide type, etc.), various grades of carbon black such as HAF and ISAF, reinforcing agents such as silica, calcium carbonate, fillers, Process oils can be selected as appropriate, and are kneaded and mixed using a Troll, Banbury, etc. mixer to form a rubber compound, which is then subjected to molding and vulcanization steps to produce the desired tire. Since the rubber composition of the present invention is able to balance recoil modulus and wet skid resistance at a high level, it is particularly suitable as a rubber material for automobile tire treads with improved safety and fuel consumption, but also for bicycle tires. It can also be used for Hereinafter, the present invention will be specifically explained with reference to Examples. Production Example (1) A method for preparing styrene-butadiene copolymer rubber (hereinafter sometimes abbreviated as SBR) into which benzophenones and thiobenzophenones are introduced will be shown to be used in the following examples. A stainless steel polymerization reactor with an internal volume of 2 was washed, dried, and replaced with dry nitrogen.
-butadiene 110-185g, styrene 15-90g,
n-hexane 600g, diethylene glycol dimethyl ether (diglyme) 0.24-1.60m
mol n-butyllithium 1.2ml (1.55mol/,
n-hexane solution) was added, and the contents were subjected to a polymerization reaction at 45 to 60°C for 30 to 120 minutes while stirring. When the polymerization conversion rate reached approximately 80%, 4.
After adding 1.5 times mol of 4'-bis(diethylamino)benzophenone to the amount of polymerization catalyst and stirring for 5 minutes, the polymer solution in the polymerization reactor was
-di-t-butyl-P-cresol (BHT)
Take out in 1.5% by weight methanol solution,
The resulting polymer was coagulated. This was dried under reduced pressure at 60°C for 24 hours, and the Mooney viscosity of the obtained rubber was measured [SBR (2), (4)]. In the same manner, the benzophenone was changed to the corresponding thiobenzophenone.
SBR was also prepared [SBR (2'), (4')]. After the polymerization reaction was completed, the polymer solution was taken out into BHT-containing methanol without adding 4,4'-bis(diethylamino)(thio)benzophenone, the resulting polymer was coagulated, and then dried in the same manner as above. Rubber polymers were obtained [SBR(1), (3),
(5), (6), (7)]. (2) The SBR (3) obtained in (1) was dissolved in benzene, and the SBR was solidified using the same procedure as in (1). Perform this operation 3
The catalyst residue in the SBR was removed several times.
Dry under the same conditions as (1), purify and dry
Got SBR. 3.5 mmol of n-butyllithium and 3.5 mmol of tetramethylethylenediamine were added to a solution of 100 g of this SBR dissolved in 1000 g of dry benzene, and the mixture was reacted at 70° C. for 1 hour. Next, the benzophenone compound used in (1) was
After adding 2.7 mmol and reacting for 5 minutes, it was coagulated and dried in the same manner as above [SBR(8)]. The styrene content, 1,2-bond content of the butadiene moiety, Mooney viscosity, and 4,4' of the styrene-butadiene copolymer rubber prepared by the above method
Table 1 shows the amount of -bis(diethylamino)(thio)benzophenone introduced. The styrene content and the 1,2-bond content of the butadiene moiety were measured by conventional infrared spectroscopy. The amount of 4,4'-bis(diethylamino)(thio)benzophenone introduced is ¹³ C-
It was determined using NMR.

[Table] Example Rubber samples were used as a base compound for tire tread, and various compounding agents with compounding prescriptions shown in Table 2 and a capacity of 250 ml were used.
Each rubber compound composition was obtained by kneading and mixing in a Brabender type mixer. Sulfur and vulcanization accelerator were used in amounts that would achieve the optimum state when vulcanizing each rubber compound composition. These rubber compound compositions
A test piece was prepared by press vulcanization at 160°C for 15 to 30 minutes. Table 2 Compounding method Raw material rubber (see Table 3) 100 parts by weight HAF carbon black 50 Aromatic process oil 5 ZnO, No. 3 3 Stearic acid 2 Sulfur Vulcanization accelerator (N-cyclohexyl -2-benzothiazyl sulfene acid) Variables (see Table 3) For the vulcanized rubber of each rubber compound composition, the strength properties were determined according to JIS-K-6301, and the rebound modulus was determined according to Danlop Lipso. Measurement was performed using a meter at a temperature of 55°C. Wet skid resistance was measured using a portable skid tester (manufactured by Stanley, UK) at 23°C, according to ASTM-E303-74.
Wet skid resistance value of each rubber compound vulcanizate / Wet skid resistance value of E-SBR compound vulcanizate x 100
It was calculated and displayed as an index. Pico wear index is according to ASTM-D-2228,
It was measured using a Gutdoritsu type pico abrasion tester and was calculated and displayed as: Pico abrasion of E-SBR-1502 compound vulcanizate/Pico abrasion of each rubber compound vulcanizate x 100. The above results are shown in Table 3. As shown in Table 3, the impact resilience modulus of Invention Examples 7 to 14 corresponding to Comparative Examples 2 to 6 was 3 to 5 without impairing wet skid resistance or pico abrasion resistance. The effect of improving points is recognized.

【table】

【table】

Claims (1)

[Claims] 1 In the styrene-butadiene copolymer rubber molecular chain,
A styrene-butadiene copolymer rubber into which at least 0.1 mole of benzophenones or thiobenzophenones having at least one amino group, alkylamino group, or dialkylamino group is introduced per mole of the rubber molecule chain, b) The bound styrene content is 3% by weight or more and less than 10% by weight, and the 1,2-bond content of the butadiene unit is 30 to 80%.
and the styrene-butadiene copolymer rubber and/or (B) having a Mooney viscosity (ML ₁₊₄ , 100°C) of 20 to 150.
The bound styrene content is 10 to 20% by weight, the 1,2-bond content of the butadiene unit exceeds 50%, and the 80
% or less, with a Mooney viscosity of 20 to 150.
20-90% by weight of butadiene copolymer rubber () and 60-5% by weight of natural rubber and/or polyisoprene rubber () with a content of at least 90% cis-1,4-bonds and 10-5% by weight of bound styrene content. 40% by weight, the 1,2-bond content of the butadiene unit portion is
10-50% styrene-butadiene copolymer rubber () 60-5% by weight as a rubber component, and the weight ratio of () and () is 1:3-3:1 for tire treads. Rubber composition.