JPH044335B2 - - 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 [e.g.
Transaction of IRI, Volume 40, Pages 239-256
1964]. To reduce the rolling resistance of a tire, the tread rubber material must have a high anti-flange modulus, and considering the driving conditions of the car, this anti-flange 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. vice versa,
In order to obtain high wet skid resistance, styrene-butadiene copolymer rubber with a relatively large amount of bound styrene (e.g., 30% by weight or more of bound styrene) or a styrene-butadiene copolymer rubber with a relatively high content of 1,2-bonds (e.g., 1, 2-It was necessary to increase the blending ratio of rubber with excellent wet skid resistance such as polybutadiene rubber (with a bond content of 60% or more), or to increase the amount of filler such as carbon black or process oil. 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 most harmonious range within a practically acceptable range. . 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 composition using the same styrene-butadiene copolymer rubber in which the compound is not introduced, the composition significantly improves the 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 something. That is, the object of the present invention is to provide a rubber composition for tire treads that has reduced rolling resistance without impairing mechanical properties and wet skid resistance. As a result of introducing at least 0.1 mole of benzophenones or thiobenzophenones having an amino group, alkylamino group or dialkylamino group per mole of the rubber molecule chain, the styrene content is 3 to 20% by weight, and 1 of the butadiene moiety is , 2- 20-95% by weight of styrene-butadiene copolymer rubber () with a bond content of more than 50% and less than 80% and a Mooney viscosity (ML ₁₊₄ , 100°C) of 20-150, natural rubber and / or polyisoprene rubber () with a cis-1,4-bond content of at least 90% and a 1,2-bond content of 60 to 5% by weight
Mooney viscosity (ML ₁₊₄ , 100℃) of 20% or less
~100 polybutadiene rubber ()50~0% by weight
This can be achieved by using a rubber composition for tire tread comprising as a rubber component. When the rubber composition for tires of the present invention is used, it is possible to obtain an excellent 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. is not particularly required, and the composition of the present invention can also be used for manufacturing tires that require a high rebound modulus. The high 1,2-
The styrene-butadiene copolymer rubber with a bond content is a styrene-butadiene copolymer rubber in which an alkali metal is bonded to the end of the molecular chain, or a styrene-butadiene copolymer rubber polymerized using an alkali metal-based catalyst commonly used in solution polymerization. Terminals or terminals of styrene-butadiene copolymer rubber molecular chains obtained by reacting the rubber obtained by adding an alkali metal in a post-reaction with the benzophenones or thiobenzophenones, and other than this. The compound has a carbon-carbon bond in the molecular chain, and has the general formula

Styrene-butadiene copolymer rubber introduced as an atomic group represented by [Formula] (wherein R ₁ and R ₂ represent hydrogen or the above-mentioned substituent, M represents O or S, and m and n represent integers, respectively) It is. Particularly desirable is a styrene-butadiene copolymer rubber in which the compound 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,
Examples include 4'-diaminobenzophenone, 4-dimethylaminobenzophenone, etc., and their corresponding thiobenzophenones, which have at least one amino group, alkylamino group or dialkylamino group on one or both benzene rings benzophenone and thiobenzophenone. Benzophenones and thiobenzophenones have 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 the sum of m and n. (each represents an integer from 1 to 10). The styrene-butadiene copolymer rubber into which the benzophenones and thiobenzophenones have been introduced into the molecular chain is obtained by, for example, polymerizing the styrene-butadiene copolymer rubber using an alkali metal-based catalyst and completing the polymerization reaction. Examples include a method in which the (thio)benzophenones are added to a rubber solution, and a method in which an alkali metal is added to the rubber in a solution of styrene-butadiene copolymer rubber and then the (thio)benzophenones are added. The alkali metal-based catalysts used in polymerization 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 (e.g., n- butyl lithium,
2-naphthyllithium, potassium-tetrahydrofuran complex, potassium-diethoxyethane complex, etc.). The (thio)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. Preferably
The amount is 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 bound styrene content in which the benzophenone or thiobenzophenone is introduced into the polymer chain is 3 to 20.
Weight%, 1,2-bond content of butadiene moiety is
The styrene-butadiene copolymer rubber () exceeding 50% and not exceeding 80% must be contained in an amount of at least 20% by weight or more in the rubber component of the rubber composition. 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. Moreover, if it exceeds 95% 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%
50% polybutadiene rubber () with a rubber component of 60 to 5% by weight and a 1,2-bond content of 20% or less
By containing up to 0% by weight, 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%
Blending of polyisoprene rubber () into () can improve strength properties without reducing impact modulus. However, if it exceeds 60% by weight, the wet skid resistance will drop significantly, which is not preferable. On the other hand, use polybutadiene rubber () with a 1,2-bond content of 20% or less as necessary () and ().
Although abrasion resistance can be improved by mixing with 50% by weight, it is not preferable because the strength properties and wet skid resistance will decrease significantly. Therefore, in order to maintain the strength properties, abrasion resistance, and wet skid resistance, which are important properties for a tire tread material, at a certain level or higher, and to improve the rebound modulus, the rubber composition of the present invention is most preferable. I discovered that. 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 can be prepared using various compounding agents commonly used in the rubber industry, such as sulfur, stearic acid, zinc white, various vulcanization accelerators (thiazole type, thiuram type, sulfenamide type, etc.), depending on the purpose and use.
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 target tire is manufactured through a molding and vulcanization process. 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. 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 to be used in the following examples. After cleaning and drying a stainless steel polymerization reactor with an internal volume of 2, and purging it with dry nitrogen,
1,3-butadiene 185~160g, styrene 15~
40g, n-hexane 600g, distyrene glycol dimethyl ether (diglyme) 1.2 and
1.6 mmol level, n-butyllithium 1.2 ml
(1.55 mol/, n-hexane solution) was added,
While stirring the contents, a polymerization reaction was carried out at 45° C. for 30 to 60 minutes. When the polymerization conversion rate reached approximately 80%, 1.5 mol of 4,4-bis(diethylamino)benzophenone was added to the polymerization catalyst amount, and after stirring for 5 minutes, the polymer solution in the polymerization reactor was converted into 2,6- The resulting polymer was taken out into a methanol solution containing 1.5% by weight of di-t-butyl-P-cresol (BHT), and the resulting polymer was coagulated. This at 60℃ for 24
The rubber was dried under reduced pressure for a period of time, and the Mooney viscosity of the obtained rubber was measured. [SBR(2), (4)]. In the same manner, the benzophenone was changed to the corresponding thiophenone.
SBR was also prepared [SBR (2'), (4')]. In addition, after the completion of the polymerization reaction, 4,4′bis(diethylamino)
The polymer solution was taken out into BHT-containing methanol without adding (thio)benzophenone, the resulting polymer was coagulated, and then dried rubber polymers were obtained in the same manner as above [SBR (1), (3)] . (2) In the same manner as in (1), 1,3-butadiene and styrene were copolymerized using 1.2 mmol 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 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)]. 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)benzophenone introduced. The styrene content and the 1,2-bond content of the butadiene moiety were measured by conventional infrared spectroscopy. 4,4'-bis(diethylamino)
The amount of (thio)benzophenone introduced was determined using ¹³ C-NMR.

【table】

[Table] Examples Rubber samples were kneaded and mixed with various compounding ingredients shown in Table 2 as a basic compound for tire tread in a Brabender type mixer having a capacity of 250 ml to obtain various rubber compound compositions. Sulfur and vulcanization accelerator were used in amounts that would achieve the optimum state when vulcanizing each rubber compound composition. These rubber compound compositions were heated to 160°C.
A test piece was prepared by press vulcanization 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】

[Table] From the results in Table 3, it can be seen that the reaction modulus of the present invention examples corresponding to Comparative Example Experiment Nos. 2 to 4 did not impair wet skid resistance or pico abrasion resistance.
An improvement effect of 3 to 4 points was observed. moreover
By appropriately combining SBR(2) with natural rubber and Cis-BR, as shown in Experiment No. 8, the impact modulus and wet skid resistance were balanced without impairing pico abrasion resistance and tensile strength. It has been shown that a rubber composition with good properties can be obtained. Example 2 Addition of carbon black to SBR(5) and SBR(6)
Table 4 shows the effects of increasing the dose from 50 _PHR to 55 _PHR . Generally, increasing the amount of carbon black improves abrasion resistance, but reduces rebound resilience. However, in the present invention, the reduction in rebound elasticity is smaller than in conventional rubber compositions. That is, a comparison between Experiment No. 6 and 6' of the comparative example and a comparison of Experiment No. 11 and 11' of the invention example shows that the decrease in recoil elasticity in the example of the invention is small. Therefore, in the present invention, it is expected that the wear resistance will be improved by increasing the amount of carbon black.

【table】

【table】

Claims (1)

[Claims] 1 In the styrene-butadiene copolymer rubber molecular chain,
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, and the bound styrene content is 3 to 20% by weight. , styrene-butadiene copolymer rubber (20-95% by weight) with a 1,2-bond content of more than 50% but less than 80% in the butadiene moiety and a Mooney viscosity (ML ₁₊₄ , 100℃) of 20-150 % and natural rubber and/or cis-1,4-
Polyisoprene rubber () with a bond content of at least 90% from 60 to 5% by weight and a 1,2-bond content of not more than 20%, Mooney viscosity (ML ₁₊₄ , 100 °C)
1. A rubber composition for a tire tread, comprising 50 to 0% by weight of polybutadiene rubber () having a polybutadiene rubber of 20 to 100 as a rubber component.