JPH04104B2 - - 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. 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 proportion 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 add additives such as sulfur. I had to increase the amount of sulfurizing agent. However, this method has disadvantages such as reduced wet skid resistance and reduced mechanical properties. 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 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 is not introduced, the rubber composition significantly improves 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. The amount of bound styrene is 10 to 20% by weight, and the 1,2-bond content of the butadiene unit is 30 to 50%.
The Mooney viscosity (ML ₁₊₄ , 100℃) is 20 to 150.
The styrene-butadiene copolymer rubber (20 to 95% by weight), (a) the amount of bound styrene is 10 to 40% by weight, and the content of 1,2-bonds in the butadiene unit portion is
Styrene-butadiene copolymer rubber of 10 or more and less than 40% and/or (b) The amount of bound styrene is more than 20% by weight and less than 40% by weight, and the butadiene unit portion is 1,2-
Styrene-butadiene copolymer rubber () with a bond content of 40 to 50% and 60 to 5% by weight, a 1,2-bond content of 20% or less, and a Mooney viscosity (ML ₁₊₄ ,
Polybutadiene rubber (100℃) of 20 to 100
The object of the present invention is to provide a rubber composition for tire tread, which contains 40 to 0% by weight as a rubber component and has reduced 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. Styrene in which the benzophenones or thiobenzophenones have been introduced into the molecular chain used in the present invention.
Butadiene copolymer rubber is a styrene compound with an alkali metal bonded to the end of the molecular chain obtained using an alkali metal-based catalyst commonly used in solution polymerization.
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. The benzophenones and 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; and thiobenzophenone. The benzophenones and thiobenzophenones have the general formula

[Formula] (wherein R ₁ and R ₂ are hydrogen, an alkyl group, a cycloalkyl group,
a substituent selected from an alkenyl group, an alkoxy group, an amino group, an alkylamino group, a dialkylamino group, and a halogen, M is O or S, m and n
is a compound represented by m and n, each of which represents an integer from 1 to 10 in total. The styrene-butadiene copolymer rubber into which benzophenones or thiobenzophenones have been introduced into the molecular chain is obtained by polymerizing styrene-butadiene copolymer rubber using an alkali metal-based catalyst and completing the polymerization reaction. A method of adding the benzophenones or thiobenzophenones to a rubber solution,
Examples include a method in which an alkali metal is added to the rubber using an alkali metal-based catalyst in a solution of styrene-butadiene copolymer rubber, and then the benzophenones or thiobenzophenones are added. 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 benzophenone or thiobenzophenone introduced into the styrene-butadiene copolymer rubber is on average 0.1 mole or more per mole of rubber molecular chain. 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. The styrene-butadiene copolymer rubber () in which benzophenones or thiobenzophenones are introduced into the rubber molecular chain has a bound styrene content of 10 to 20% by weight and a 1,2-bond content of the butadiene unit portion.
30 to 50%, Mooney viscosity (ML ₁₊₄ , 100℃)
is 20 to 150. In the styrene-butadiene copolymer rubber (), if the amount of bound styrene and the content of 1,2-bonds in the butadiene unit portion are out of the above range, the abrasion resistance, rebound modulus, wet skid resistance, etc. will decrease. Undesirable. Further, if the Mooney viscosity (ML ₁₊₄ , 100°C) is less than 20, the repulsion elasticity will be lowered, and if it exceeds 150, the kneading processability will be poor and the mechanical properties such as tensile strength will be lowered, which is not preferable. More preferably, it is 30 to 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 the rebound elasticity is small and the purpose of the present invention cannot be achieved;
If it exceeds (2), the properties will be almost the same as those obtained using () alone, and the wet skid resistance or abrasion resistance will be poor, which is not preferable. In (a) of the styrene-butadiene copolymer rubber () which does not contain the (thio)benzophenones in the chain and is used in combination with (), the amount of bound styrene is 10
The content of 1,2-bonds in the butadiene unit is preferably 10% or more and less than 40% by weight. In (b), the amount of bound styrene is preferably more than 20% by weight and not more than 40% by weight, and the content of 1,2-bonds in the butadiene unit portion is preferably 40 to 50%.
In (a) and (b), if the amount of bound styrene is out of the above range, the wet skid resistance and rebound elasticity will drop significantly, which is not preferable. Furthermore, if the 1,2-bond content of the butadiene unit exceeds the above range, wet skid resistance and abrasion resistance will decrease, which is undesirable. Mooney viscosity is 20 to
150 is preferable; if it is less than 20, the rebound elasticity decreases,
If it exceeds 150, kneading processability will be poor and mechanical properties will deteriorate, which is not preferable. More preferably 30 to
It is 130. The content of () in the total rubber component is preferably 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 wet skid resistance or abrasion resistance will be poor. 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%, this purpose cannot be achieved. I don't like it because there isn't. The Mooney viscosity is preferably from 20 to 100. If it is less than 20, the rebound elasticity will be significantly lowered and the object of the present invention cannot be achieved, and if it exceeds 100, the kneading processability will be poor and the mechanical properties will be deteriorated, which is not preferred. More preferably, it is 30 to 80. () is preferably 40% by weight or less in the total rubber component. If it exceeds 40% by weight, the wet skid resistance will drop significantly, which is not preferable. More preferably, it is 30% by weight or less. 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, A rubber compound, which can be appropriately selected from process oils and the like, is kneaded and mixed using a mixer such as a roll or a Banbury 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) 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. After washing and drying a stainless steel reactor with an internal volume of 2 and purging it with dry nitrogen, styrene 40~
80g, 1,3-butadiene 120-160g, n-hexane 600g, n-butyllithium 1.2mmol,
0.24 mmol of diethylene glycol dimethyl ether (diglyme) was added, and polymerization was carried out at a temperature of 45 to 60°C for 60 to 120 minutes while stirring the contents. After the completion of the polymerization reaction, 1.5 times the catalytic amount of 4,4'-bis(diethylamino)benzophenone was added, and after stirring for 5 minutes, the polymer solution in the polymerization reactor was diluted with 2,6-di-t-butyl-P- The resulting polymer was taken out into a methanol solution containing 1.5% by weight of cresol (BHT) and coagulated. It was dried under reduced pressure at 60°C for 24 hours and its Mooney viscosity was measured [SBR(2)]. In the same manner, SBR was also prepared in which the benzophenone was replaced with the corresponding thiobenzophenone [SBR(2')]. After completion of the polymerization, the polymer solution was taken out into a BHT-containing methanol solution without adding the (thio)benzophenone, and the resulting polymer was coagulated, and then a dried polymer was obtained in the same manner as above [SBR(1 ), (3), (4)]. (2) Dissolve SBR (1) prepared in (1) in benzene,
SBR was solidified using the same procedure as above. This operation was repeated three times to remove the catalyst residue in the SBR.
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 (5)]. Table 1 shows the microstructure, Mooney viscosity, and amount of (thio)benzophenones introduced for the rubber prepared by the above method. The microstructure was measured by conventional infrared spectroscopy.The amount of (thio)benzophenones introduced was ^13C-
It was determined using 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
Test pieces were 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-benzothiazylsulfenamide) Variable (see Table 3) Regarding the vulcanizate of each rubber compound composition,
The strength properties were determined according to JIS K-6301, and the rebound elasticity was measured at a temperature of 55% using a Danlopt tripsomer.
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/
It was calculated by multiplying the wet skid resistance value of the blended vulcanizate of E-SBR-1502 by 100 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 above results are shown in Table 3.

【table】

[Table] From the results shown in Table 3, the rebound elastic modulus of Invention Examples 5, 6, and 10 to 12, which correspond to Comparative Examples 2 to 4, are all without impairing wet skid resistance or pico abrasion resistance. It can be seen that it is 4 to 6 points higher.

Claims (1)

[Claims] 1 In the styrene-butadiene copolymer rubber molecular chain,
Butadiene containing 10 to 20% by weight of bound styrene into which benzophenones or thiobenzophenones having at least one amino group, alkylamino group or dialkylamino group have been introduced in an amount of at least 0.1 mole per mole of the rubber molecular chain; Styrene with a 1,2-bond content of 30 to 50% in the unit part and a Mooney viscosity (ML ₁₊₄ , 100°C) of 20 to 150.
Butadiene copolymer rubber () 20 to 95% by weight,
(a) The amount of bound styrene is 10 to 40% by weight, and the content of 1,2-bonds in the butadiene unit is 10% or more, 40%
and/or (b) styrene-butadiene in which the amount of bound styrene is more than 20% by weight and not more than 40% by weight, and the 1,2-bond content of the butadiene unit portion is 40 to 50%. Copolymer rubber () 60 to 5% by weight, 1,2-bond content less than 20%, Mooney viscosity (ML ₁₊₄ , 100℃)
1. A rubber composition for a tire tread, comprising 40 to 0% by weight of polybutadiene (20 to 100) as a rubber component.