JPH04101B2 - - 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, 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 isoprene rubber, etc. are used alone 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 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 a relatively high content of 1,2-bonds ( For example, it is necessary to increase the blending ratio of rubber with excellent wet skid resistance such as polybutadiene rubber (with a 1,2-bond content of 60% or more), or to increase the amount of filler such as carbon black or process oil. Ta. 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 a rubber containing as a rubber component a styrene-butadiene copolymer rubber into which specific benzophenones or thiobenzophenones have been introduced into the 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 characteristic of high rebound resilience. The inventors 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. It is ivy. That is, an object of the present invention is to provide a rubber composition for tire treads which has reduced rolling resistance without impairing mechanical properties and wet skid resistance, and in which at least one At least 0.1 mole of benzophenones or thiobenzophenones having amino, alkylamino, or dialkylamino groups are introduced per mole of the rubber molecular chain, the bound styrene content is 10 to 40% by weight, and the butadiene moiety is 20-90% by weight of styrene-butadiene copolymer rubber () having a 1,2-bond content of 10-50% and a Mooney viscosity (ML ₁₊₄ , 100°C) of 20-150, natural rubber and/or , polyisoprene rubber ()60 with a cis-1,4-bond content of at least 90%
~5% by weight, bound styrene content from 3 to 20% by weight, and 1,2-bond content in the butadiene moiety from 30 to 20% by weight.
80% styrene-butadiene copolymer rubber ()60
This is achieved by using a tire tread rubber composition containing ~5% by weight as a rubber component and in which the weight ratio of () to () is between 1:3 and 3:1. By using the rubber composition of the present invention, it is possible to manufacture tires that have 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. No particular resistance value is required;
The rubber composition of the present invention can also be used in the production of tires that only require 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 polymer with an alkali metal attached to the end of the molecular chain, which is polymerized 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.

Styrene- _butadiene copolymer introduced as an atomic group represented _by the formula It's 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,
4'-diaminobenzophenone, 4-dimethylaminobenzophenone, etc., and their corresponding thiobenzophenones, benzophenones having at least one amino group, alkylamino group, or dialkylamino group in one or both benzene rings. and thiobenzophenone. The benzophenones and thiobenzophenones are represented by the general formula:

[Formula] (In the formula, R ₁ and R ₂ are hydrogen or a substituent selected from an amino group, an alkylamino group, and a dialkylamino group, M is O or S, and m and n are such that the sum of m and n is 1. (each represents an integer from 10 to 10). The styrene-butadiene copolymer rubber with benzophenones introduced into the molecular chain is obtained by polymerizing the styrene-butadiene copolymer rubber using an alkali metal-based catalyst, and adding the (thio) into the rubber solution after the polymerization reaction is completed. Examples include a method of adding benzophenones, and a method of adding an alkali metal to a styrene-butadiene copolymer rubber in a solution and then adding the (thio)benzophenones. The alkali metal-based catalysts used in the polymerization and addition reactions are metal elements such as lithium, sodium, rubidium, and cesium, which are commonly used as solution polymerization catalysts, or their complexes with hydrocarbon compounds or polar compounds (for example, n- butyllithium, 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 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 preferred. The styrene-butadiene copolymer rubber () with a bound styrene content of 10 to 40% by weight and a 1,2-bond content of the butadiene moiety of 10 to 50% in which the benzophenone is introduced into the polymer chain is the present rubber composition. It is necessary that the rubber component contains at least 20% by weight of the rubber component. If it is less than 20% by weight, the effect of improving impact resilience will be small and the object of the present invention will not be achieved. 90 again
If it exceeds % by weight, the wear resistance decreases, which is not preferable. natural rubber and/or cis-1,
4 - 60-5% by weight of polyisoprene rubber () with a bond content of at least 90%, a bound styrene content of 3-20% by weight, butadiene moiety 1,2- styrene-butadiene with a bond content of 30-80% By using a blend of 60 to 5% by weight of copolymer rubber (), it is possible to create a rubber composition with a better balance between impact modulus (55°C) and wet skid resistance without impairing strength properties or abrasion resistance. can. That is, blending natural rubber and/or polyisoprene rubber () with a cis-1,4-bond content of at least 90% () can improve strength properties without reducing impact resilience. However, if it exceeds 60% by weight, the wet skid resistance will drop significantly, which is not preferable. On the other hand, the bound styrene content is 3 to 20% by weight, and the butadiene part is 1,
2- Blends of high vinyl, styrene-butadiene rubber () with a bond content of 30 to 80% () to () and () are effective in improving wet skid resistance without significantly reducing impact modulus. 60
Exceeding this percentage by weight is undesirable because the abrasion resistance will be markedly reduced. Usage rate (weight) of () and ()
is 1:3 to 3:1, and if () of the sum of () and () is less than 1/4, there will be little improvement in local characteristics;
When the value exceeds 4, the wet skid resistance decreases.
Therefore, in order to maintain wet skid resistance at a high level and significantly improve the impact modulus without impairing the strength properties and abrasion resistance, which are important properties for tire tread materials, the rubber composition of the present invention must be used. is most preferred. All or part of the rubber components used in the present invention can be used as oil-extended rubber. The rubber composition of the present invention is prepared with various compounding agents commonly used in the rubber industry depending on the purpose and use, such as 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, process oils, etc. can be selected as appropriate, and are kneaded and mixed using a mixer such as a roll or Banbury mixer. The rubber compound is made into a rubber compound, and the desired rubber product is manufactured through molding and vulcanization processes. 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) A method for preparing styrene-butadiene copolymer rubber (hereinafter sometimes abbreviated as SBR) into which the benzophenones are introduced will be described for use in the following examples. A stainless steel polymerization reactor with an internal volume of 2 was washed, dried, and replaced with dry nitrogen.
3-butadiene 110-185g, styrene 15-90g
g, n-hexane 600g, diethylene glycol dimethyl ether (diglyme) 0.24-1.60
mmol (3 levels between), n-butyllithium
1.2 ml (1.55 mol/n-hexane solution) was added, and the contents were polymerized at 45 to 60°C for 30 to 120 minutes while stirring. When the polymerization conversion rate reached approximately 80%, 4,4'-bis(diethylamino)benzophenone was added to 1.5 mnl of the polymerization catalyst amount.
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. 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), (6)]. Similarly, SBR in which the benzophenone was replaced with the corresponding thiobenzophenone was also prepared [SBR (2'), (4'), (6')]. 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 into rubber in the same manner as above. Polymers were obtained [SBR(1), (3),
(5), (7), (8)]. (2) In the same manner as in (1), 1,3-butadiene and styrene were copolymerized using 1.0 mmo of diglyme. After polymerization is complete, pour the polymer solution in the polymerization reactor into a methanol solution containing BHT to generate
Solidified SBR. The separated crumb was dissolved in benzene, and SBR was coagulated by the same operation as above. This operation was repeated three times to remove the catalyst residue in the SBR. Drying was performed under the same conditions as in (1) to obtain purified and dried SBR. 3.5 mmo of n-butyllithium and 3.5 mmo 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 (9)]. The styrene content of the styrene-butadiene copolymer rubber prepared by the above method, the 1,2-bond content of the butadiene moiety, the Mooney viscosity, and
Table 1 shows the amount of 4'-bis(diethylamino)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
Determined using ¹³ C-NMR.

[Table] Example A rubber sample was used as a base compound for tire tread,
Various formulations shown in Table 2 and capacity 250
Each rubber compound composition was obtained by kneading and mixing in a ml 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] Regarding the vulcanized rubber of each rubber compound composition, the strength characteristics were measured according to JIS-K-6301, and the rebound modulus was measured at a temperature of 55° C. using a Danlop lipometer. 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 / E-SBR
The wet skid resistance of the blended vulcanizate was calculated by multiplying by 100 and expressed 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 amount of E-SBR-1502 compound vulcanizate/Pico abrasion amount of each rubber compound vulcanizate x 100. The above results are shown in Table 3.

[Table] From the results in Table 3, it can be seen that the rebound modulus of experiments Nos. 6 to 12 of the present invention examples, which correspond to Experiments Nos. 2 to 5 of the comparative examples, was 3 without impairing wet skid resistance or pico abrasion resistance. An improvement effect of ~5 points was observed.

Claims (1)

[Claims] 1 In the styrene-butadiene copolymer rubber molecular chain,
The bound styrene content is 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 molecule chain. , 20-90% by weight of styrene-butadiene copolymer rubber () with a 1,2-bond content of the butadiene moiety of 10-50% and a Mooney viscosity (ML ₁₊₄ , 100°C) of 20-150; Rubber and/or polyisoprene rubber ()60-5 with a cis-1,4-bond content of at least 90%
Contains as a rubber component a styrene-butadiene copolymer rubber () with a combined styrene content of 3 to 20% by weight and a 1,2-bond content of the butadiene moiety of 30 to 80%, and ()and()
A rubber composition for tire tread, characterized in that the weight ratio of