JPH04102B2 - - 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 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 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 in that wet skid resistance and mechanical properties deteriorate. Conversely, when trying to obtain high wet skid resistance, the amount of bound styrene is relatively large (e.g., 30% by weight of bound styrene).
(above) styrene-butadiene copolymer rubber,
1,2-bond content is relatively high (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. These methods have a disadvantage in that the rebound resilience 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 has not been 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, an 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. benzophenones or thiobenzophenones having at least one amino group, alkylamino group or dialkylamino group per mole of the rubber molecular chain;
The mole-introduced bound styrene content is 10 to 40% by weight, and the 1,2-bond content of the butadiene unit is
10-50%, Mooney viscosity (ML ₁₊₄ , 100℃)
20~150 styrene-butadiene copolymer rubber ()
20-95% by weight and natural rubber and/or cis-
Polyisoprene rubber () 60-5% by weight with a 1,4 bond content of at least 90% and a Mooney viscosity (ML ₁₊₄ , 100°C) with a 1,2 bond content of not more than 20%
is achieved by using a tire tread rubber composition comprising 50 to 0% by weight of polybutadiene rubber (20 to 100) 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. 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-butadiene copolymer rubber in which an alkali metal is bonded to the end of the molecular chain, which is polymerized using an alkali metal-based catalyst commonly used in solution polymerization, or a styrene-butadiene copolymer rubber obtained using the catalyst. The ends or ends of the rubber molecular chain obtained by reacting the styrene-butadiene copolymer rubber obtained by adding an alkali metal to the styrene-butadiene copolymer rubber by post-reaction with the benzophenones or thiobenzophenones, and the ends thereof. The compound has a carbon-carbon bond in the molecular chain other than the general formula

[Formula] (In the formula, R ₁ and R ₂ are hydrogen or a substituent, M is O or the above S, m and n
is a styrene-butadiene copolymer rubber introduced as an atomic group represented by (representing an integer). Particularly preferred 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( diptylamino)-benzophenone, 4,
At least one amino group, alkylamino group or dialkylamino group is present in one or both benzene rings, such as 4'-diaminobenzophenone, 4-dimethylaminobenzophenone, etc., and their corresponding thiobenzophenones. benzophenone and thiobenzophenone. The benzophenones and thiobenzophenones have the general formula

[Formula] (In the formula, M is O or S as R ₁ , R ₂ is hydrogen or a substituent selected from an amino group, an alkylamino group, and a dialkylamino group, and m and n are the sum of m and n of 1 to (each representing an integer equal to 10). The styrene-butadiene copolymer rubber in which the (thio)benzophenones are introduced into the molecular chain is, for example,
A method of polymerizing styrene-butadiene copolymer rubber using an alkali metal-based catalyst and adding the (thio)benzophenones to the rubber solution after the polymerization reaction has been completed, in a solution of styrene-butadiene copolymer rubber, etc. Examples include a method in which an alkali metal is added to the rubber and then the (thio)benzophenones 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 -butyllithium, 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 benzophenones or thiobenzophenones have been introduced into the polymer chain, and the bound styrene content is 20
The styrene-butadiene copolymer rubber () having a content of ~40% by weight and a 1,2-bond content of the butadiene unit portion of 10% to 50% is contained at least 20% by weight of the total rubber components in the rubber composition. It is necessary to be present. If it is less than 20% by weight, the effect of improving the rebound modulus will be small and the object of the present invention will not be achieved. Also 95% by weight
Exceeding this is not preferable because the wear resistance decreases. Natural rubber and/or polyisoprene rubber () with a cis-1,4-bond content of at least 90% from 60 to 5% by weight of the total rubber component and 1,2
- By containing 50 to 0% by weight of polybutadiene rubber () with a bond content of 20% or less, it is possible to harmonize impact modulus (55℃) and wet skid resistance without impairing strength properties or abrasion resistance. A more excellent rubber composition for tire tread can be obtained. i.e. natural rubber and/or cis 1,
4- The combined use of polyisoprene rubber () with a bond content of at least 90% and () can improve strength properties without reducing impact modulus. However, if () exceeds 60% by weight, the wet skid resistance will decrease significantly, which is not preferable. On the other hand, blending polybutadiene rubber () with () and () with a 1,2-bond content of less than 20% can improve the wear resistance, but when it exceeds 50% by weight, the strength properties and wet skid resistance This is not preferable because it causes a significant decrease in performance. Therefore, in order to maintain the strength, abrasion resistance and wet skid resistance, which are important properties for a tire tread material, above a certain level, and to significantly improve the impact modulus, the rubber composition of the present invention is most preferable. This is what we discovered. 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 target tire is manufactured through a molding and vulcanization process. 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 Styrene-butadiene copolymer rubber (hereinafter referred to as
The method for preparing SBR (abbreviated as SBR) is shown below. (1) After cleaning and drying a stainless steel polymerization reactor with an internal volume of 2, and purging it with dry nitrogen,
Butadiene 110-145g, styrene 55-90g, n
-Hexane 600g, diethylene glycol dimethyl ether (diglyme) 0.24 and 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%,
4.4′-Bis(diethylamino)benzophenone was added to 1.5 mol of the polymerization catalyst amount, and after stirring for 5 minutes, the polymer solution in the polymerization reactor was reduced to 2.6 mol.
-di-t-butyl-p-cresol (BHT)
The resulting polymer was taken out into a 1.5% by weight methanol solution 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)] SBRs in which the benzophenone was replaced with the corresponding thiobenzophenone were also prepared [SBR(2'), (4'), (6')]. In addition, after the polymerization reaction, 4.4′-bis(diethylamino)(thio)
Polymer solution without adding benzophenone
The resulting polymer was taken out into BTR-containing methanol and coagulated, and dried rubber polymers were obtained in the same manner as above (SBR(1), (3), (5)). (2) 1,3-butadiene and styrene were copolymerized in the same manner as in (1) except that 0.24 mmol of diglyme was used. After the polymerization reaction was completed, the polymer solution in the polymerization reactor was poured into a BHT-containing methanol solution to solidify the produced SBR. Dissolve the separated crumb in benzene and perform SBR using the same procedure as above.
was solidified. Repeat this operation three times,
Catalyst residue in SBR was removed. Drying was performed under the same conditions as in (1) to obtain purified and dried SBR. 100 g of the above SBR was dissolved in 1000 g of dry benzene, 3.5 mmol of n-butyllithium and 3.5 mmol of tetramethylethylenediamine were added, and the mixture was reacted at 70° C. for 1 hour. Next, 2.7 mmol of 4,4'-bis(diethylamino)benzophenone was added, reacted for 5 minutes, and then coagulated and dried in the same manner as above [SBR(7)]. The styrene content of the styrene-butadiene copolymer rubber purified by the above method, the 1,2-bond content of the butadiene moiety, the Mooney viscosity, and the 4,4'-
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】

[Table] Example 1 A rubber sample was mixed with various compounding ingredients shown in Table 2 as a basic compound for tire tread, and a capacity of 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 give the optimum state when vulcanizing each rubber compound composition. 160 of these rubber compound compositions
A test piece was prepared by press vulcanization at 15 to 30 minutes at ℃.

[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-E-303-
Measured on 74 road surfaces (3M outdoor tile B, black Safety Walk), 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 Gutdrich Pico abrasion tester and calculated and expressed as Pico abrasion degree of E-SBR-1502 compound vulcanizate/Pico abrasion amount of each rubber compound vulcanizate x 100. The results are shown in Table 3. From Table 3, it can be seen that the rebound modulus of the invention examples and experiment numbers 7 to 15, which correspond to the comparative example experiment numbers 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 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 () with a 1,2-bond content of 10-50% in the butadiene unit moiety and a Mooney viscosity (ML ₁₊₄ , 100°C) of 20-150 and 20-95% by weight of natural Rubber and/or polyisoprene rubber with a cis-1,4-bond content of at least 90% ()60~
5% by weight and 1,2-bond content not more than 20% by weight, and Mooney viscosity (ML ₁₊₄ , 100℃) of 20-100
A rubber composition for a tire tread, comprising 50 to 0% by weight of polybutadiene rubber () as a rubber component.