JPH0475253B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to rubber compositions having improved rebound modulus. More 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 or thiobenzophenones have been introduced into the molecular chain. Recently, from the viewpoints of both fuel efficiency 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. Generally, these tire properties are considered to correspond to the dynamic viscoelastic properties of the tread rubber material, and it is known that these properties are contradictory to each other [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, British technology is 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-cisoprene rubber, etc. have been used singly or in combination. but,
It wasn't completely satisfying. In other words, in order to obtain high rebound elasticity, one must increase the blending ratio of rubbers with poor efflux resistance such as low cis-polybutadiene rubber and natural rubber, reduce the amount of fillers such as carbon black, or add additives such as sulfur. I had to increase the sulfurizing agent. However, this method has disadvantages in that wet skid resistance and mechanical properties are reduced. Conversely, 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 blending ratio of rubber with excellent wet skid resistance such as polybutadiene rubber with a relatively high bond content (for example, 1,2-bond content of 60% or more), or increase the amount of filler such as carbon black or process oil. I had to let it happen. 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 inventors of the present invention surprisingly found that a rubber containing as a rubber component 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 is not introduced, the composition significantly improves rebound resilience without reducing wet skid resistance, and has the characteristics of high rebound resilience. We have discovered that it is possible to achieve a balance between rebound elasticity and wet skid resistance while improving mechanical properties such as abrasion resistance by increasing the amount of filler such as carbon black if necessary, and have arrived at the present invention. It is. That is, the present invention provides at least 0.1 mole of benzophenones or thiobenzophenones having at least one amino group, alkylamino group, or dialkylamino group in the styrene-butadiene copolymer rubber molecular chain per mole of the rubber molecular chain. Styrene-butadiene copolymerization with a bound styrene content of 10 to 40% by weight, a 1,2-bond content of the butadiene moiety of 10 to 50%, and a Mooney viscosity (ML ₁₊₄ , 100°C) of 20 to 150. Rubber (I) has a bound content of 3-20% by weight, a bound content of 20-95% and a bound styrene content of 40-95% by weight.
80% styrene-butadiene copolymer rubber ()60
5% by weight, and 40% to 0% by weight of polybutadiene rubber () with a 1,2-bond content of 20% or less and a Mooney viscosity (ML ₁₊₄ , 100°C) of 20 to 100. The object of the present invention is to provide a rubber composition for tire tread that reduces rolling resistance without impairing 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. The benzophenones or thiobenzophenones are reacted with a styrene-butadiene copolymer rubber to which an alkali metal is bonded, or a rubber obtained by using the catalyst and to which an alkali metal is added in a post-reaction. The compound has a general formula with a carbon-carbon bond at the end of the resulting styrene-butadiene copolymer rubber molecular chain or at the other end of the molecular chain.

[Formula] (wherein R ₁ and R ₂ are hydrogen or the above-mentioned substituents, M is O or S,
m and n each represent an integer. ) is a styrene-butadiene copolymer rubber introduced as an atomic group. 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 rubber 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(dibutyl amino)-benzophenone, 4,
Benzophenones having at least one amino group, alkylamino group or dialkylamino group in one or both benzene rings, such as 4'-diaminobenzophenone, 4-dimethylaminobenzophenone, etc., and their corresponding thiobenzophenones; It is. 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
is a benzophenone represented by O or S, m and n each represent an integer in which the sum of m and n is 1 to 10. A method of adding benzophenones or thiobenzophenones in which the benzophenones have been introduced into the molecular chain, and a method of adding an alkali metal to the rubber using the catalyst in a solution of styrene-butadiene copolymer rubber, and then adding the benzophenones. Alternatively, a method of adding thiobenzophenones can be exemplified. The alkali metal-based catalysts used in the polymerization reaction and addition reaction include the metal elements 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 benzophenone introduced into the styrene-butadiene copolymer rubber is on average 0.1 mole or more per mole of rubber molecules. If the amount is less than 0.1 mol, no improvement in rebound elasticity can be obtained. The amount is preferably 0.3 mol or more, more preferably 0.5 mol or more, particularly preferably 0.7 mol or more, but if it is 5 mol or more, rubber elasticity is lost, which is not preferable. Styrene-butadiene copolymer rubber () in which the benzophenones used in the present invention are introduced into the main chain
The bound styrene content of is preferably 10 to 40% by weight. If the bound styrene content is less than 10% by weight, the wet skid resistance will decrease, making it impossible to achieve the object of the present invention, which is undesirable, and if it exceeds 40% by weight, the rebound elasticity will be significantly decreased, which is undesirable. The 1,2-bond content of the butadiene moiety is 10~
50% is preferred. If the 1,2-bond content is less than 10%, the wet skid resistance will decrease, which is undesirable, and if it exceeds 50%, the wear resistance will decrease, which is undesirable. Mooney viscosity (ML ₁₊₄ , 100℃)
is preferably from 20 to 150; if it is less than 20, the rebound elasticity decreases, and if it exceeds 150, kneading processability is poor and mechanical properties such as tensile strength are decreased, which is not preferred. More preferably it is 30-130. () is preferably 20 to 95% by weight of the total rubber component. If it is less than 20% by weight, the effect of improving rebound elasticity is small and the object of the present invention cannot be achieved, and if it exceeds 95% by weight, the properties will be almost the same as those obtained by using () alone.
Wet skid resistance or abrasion resistance is poor and undesirable. The bound styrene content of the styrene-butadiene copolymer rubber () which does not contain benzophenones in the main chain and is used in combination with () is preferably 3 to 20% by weight. The bound styrene content in () is 3
If it is less than 20% by weight, the mechanical properties will deteriorate, which is undesirable, and if it exceeds 20% by weight, the rebound elasticity will decrease, which is not preferable. 1,2- of the butadiene moiety
The binding content is preferably 40-80%. If the 1,2-bond content is less than 40%, wet skid resistance decreases, which is undesirable, and if it exceeds 80%, wear resistance decreases, which is undesirable. Mooney viscosity is
The number is preferably from 20 to 150, and if it is less than 20, the rebound elasticity decreases, and if it exceeds 150, the kneading processability is poor and the mechanical properties are deteriorated, which is not preferred. More preferably it is 30-130. The content of () in the rubber component is preferably from 60 to 5% by weight; if it exceeds 60% by weight, the rebound elasticity will decrease, and if it is less than 5% by weight, the composition will have poor wet skid resistance or abrasion resistance, which is not preferable. In the present invention, polybutadiene rubber () with a 1,2-bond content of 20% or less is used as necessary to improve wear resistance in practice, but if the 1,2-bond content exceeds 20%, the This is not desirable because it cannot be achieved. Mooney viscosity is preferably 20 to 100,
If it is less than 20, the recoil elasticity will drop significantly and the object of the present invention cannot be achieved, and if it exceeds 100, kneading processability will be poor and mechanical properties will deteriorate, which is not preferable.
More preferably it is 30-80. () is preferably 40% by weight or less in the total rubber component, more preferably 30% by weight or less.
% by weight or less. If () exceeds 40% by weight, the wet skid resistance will drop significantly, which is not preferable. 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 and calcium carbonate, fillers, A rubber compound, which can be appropriately selected from process oils, rolls, Banbury, etc., is kneaded and mixed to form a rubber compound, which is then subjected to molding and vulcanization steps to produce the desired tire. The rubber composition of the present invention is capable of harmonizing recoil modulus and wet skid resistance at a high level, and is therefore particularly suitable as a rubber material for automobile tire treads with improved safety and fuel consumption. It can also be used for tires. Hereinafter, the present invention will be specifically explained with reference to Examples. Production Example (1) Styrene-butadiene copolymer rubber (hereinafter referred to as SBR) in which the benzophenones and thiobenzophenones used in the following examples are introduced into the main chain.
(sometimes abbreviated as ) is shown below. A stainless steel reactor with an internal volume of 2 was washed, dried, and replaced with dry nitrogen, then styrene 55~
90 g of 1,3-butadiene, 145-110 g of n-hexane, and 1.2 mm of n-butyllithium were added thereto, and the contents were polymerized at a temperature of 45-60°C for 1-2 hours while stirring. After the completion of the polymerization reaction 4,
After adding 1.5 times the catalytic amount of 4'-bis(diethylamino)benzophenone in moles and stirring for 5 minutes,
The polymer solution in the polymerization reactor was converted into 2,6-di-t-
The resulting polymer was taken out into a methanol solution containing 1.5% by weight of butyl-p-cresol (BHT), and the resulting polymer was coagulated. It was dried under reduced pressure at 60°C for 24 hours and its Mooney viscosity was measured [SBR2, 4, 6]. In addition, SBR in which the benzophenone was replaced with the corresponding thiobenzophenone was also prepared in the same manner [SBR2', 4',
6′]. After completion of the polymerization, the polymer solution was taken out into a BHT-containing methanol solution without adding the benzophenone or the thiobenzophenone, and the resulting polymer was coagulated, and then a dried polymer was obtained in the same manner as above [SBR1 , 3, 5]. (2) SBR3 obtained in (1) was dissolved in benzene, and SBR was coagulated 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 [SBR9]. (3) In the same manner as above, using a styrene polymerization reactor with an internal volume of 2, 15 to 40 g of styrene, 1,3
-butadiene 185-160g, n-hexane 600g,
1.2 mmol of n-butyllithium was added, and polymerization was carried out at a temperature of 45° C. for 30 to 60 minutes while stirring the contents. After the polymerization was completed, the polymer solution was taken out into a BHT-containing methanol solution to coagulate the resulting polymer, and then dried polymers were obtained in the same manner as above [SBR7, 8]. Table 1 shows the microstructure, Mooney viscosity, and amount of EAB introduced for the rubber prepared by the above method. The microstructure was measured by conventional infrared spectroscopy. The amounts of benzophenones and thiobenzophenones introduced were determined using ¹³ C-NMR.

[Table] Example: As a basic composition for tire tread, various compounding agents and raw rubber of the compounding prescription shown in Table 2 were mixed in a volume of 250 ml.
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 Raw rubber (see Table 3) 100 parts by weight HAF carbon black 50 Aromatic process oil 5 ZnONo.3 3 Stearic acid 2 Sulfur vulcanization accelerator (N-cyclohexyl-2-benzothiazyl Sulfenamide) Variable (see Table 3) Regarding the vulcanizate of each rubber compound composition,
The strength properties were determined according to JISK-6301, and the rebound elasticity was determined using a Dunlop tribometer at a temperature of 55%.
Measured at ℃. Wet skid resistance was measured using a portable skid tester (manufactured by Stanley, UK) at 23°C on an ASTME-303-74 road surface (outdoor type B, black safety walk manufactured by 3M). Wet skid resistance value/E
- Wet skid resistance value of compound vulcanizate of SBR-1502 x 1
00 and expressed as an index. The amount of pico wear was measured using a Gutdrich Pico abrasion tester in accordance with ASTMD-2228, and was calculated as: wear amount of SBR-1502 blended vulcanizate/wear amount of each blended vulcanizate x 100, and expressed as an index. The results are shown in Table 3. From the results shown in Table 3, the rebound elastic modulus of Inventive Examples 8 to 17, which correspond to Comparative Examples 2 to 7, is 3 to 5 points higher without impairing wet skid resistance or pico abrasion resistance. Recognize.

【table】

【table】

Claims (1)

[Claims] 1 In the styrene-butadiene copolymer rubber molecular chain,
A bound styrene content of 10 to 40% by weight, in 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 molecular chain; Styrene-butadiene copolymer rubber (20-95% by weight) with a 1,2-bond content of the butadiene moiety of 10-50% and a Mooney viscosity (ML ₁₊₄ , 100℃) of 20-150, and a bonded styrene content. styrene-butadiene copolymer rubber () having a content of 3 to 20% by weight and a 1,2-bond content of the butadiene moiety of 40 to 80%;
- A rubber for tire treads, characterized in that it comprises as a rubber component 40 to 0% by weight of polybutadiene rubber () having a bond content of 20% or less and a Mooney viscosity (ML ₁₊₄ , 100°C) of 20 to 100. Composition.