JP5504549B2 - Rubber composition for tire tread - Google Patents

Description

  The present invention relates to a rubber composition for tire treads, and more particularly to a rubber composition for tire treads including a specific butadiene rubber composition and excellent in low temperature characteristics.

  As pneumatic tires used for running on icy and snowy roads, studless tires are often used instead of conventional spike tires, and further improvement in performance on ice has been required.

  In order to improve the performance on ice, it is important to increase the coefficient of friction with the road surface by increasing the flexibility of the rubber used for the tread portion at a low temperature (around −30 ° C.). At low temperatures, the elastic modulus of the rubber increases, making it impossible to follow the unevenness of the road surface. Also, the frozen road surface has less surface unevenness than the normal road surface, so the energy dissipation that occurs between the rubber and the road surface (tanδ) Contributes to the performance on ice. It is necessary to increase the real contact area between the rubber and the road surface at a low temperature, and it is more important to lower the storage elastic modulus E ′ around −30 ° C. (lower elastic modulus). For example, the use of butadiene rubber or natural rubber, which is a polymer having a low glass transition temperature, and a large amount of a softening agent are added to the rubber composition to improve flexibility at low temperatures. In particular, high-cis butadiene rubber having a high cis content that lowers the glass transition temperature is used for butadiene rubber. However, the high-cis butadiene rubber has the property of crystallizing in a low temperature region around -10 to 0 ° C because the microstructure is more uniform. This crystallization remains after vulcanization and raises the storage elastic modulus around -30 ° C.

  As a study on improving the performance on ice, for example, (A) the intrinsic viscosity [η] measured in toluene at 30 ° C. is 3.0 to 7.0 and the cis-1,4-structure content is 80% or more. High molecular weight polybutadiene containing polybutadiene as a main component 30 wt% or more and less than 70 wt%, (B) Intrinsic viscosity [η] measured in toluene at 30 ° C is 0.1 to 0.5, and cis-1,4- A low molecular weight polybutadiene having a structure content of 80% or more as a main component and having a low molecular weight polybutadiene of more than 30% by weight and 70% by weight or less, and specifying each weight average molecular weight (Mw), wear resistance, wet skid performance, A polybutadiene rubber composition for tires excellent in ice skid performance is disclosed (Patent Document 1).

Japanese Patent Laid-Open No. 11-60812

The present invention is a rubber composition for a tire tread comprising a rubber component not showing crystallization and a specific butadiene rubber composition composed of butadiene rubber showing crystallization, while maintaining general characteristics such as wear resistance, In particular, an object of the present invention is to provide a rubber composition for a tire tread capable of significantly improving the performance on ice by greatly reducing the elastic modulus at −30 ° C.

  The present invention focuses on a technology for effectively suppressing crystallization of butadiene rubber, and (A) butadiene rubber (a) exhibiting crystallization has at least one rubber component (b) not exhibiting crystallization. A specific butadiene rubber composition (a) + (b) containing 10 to 90 parts by weight and (B) 90 to 10 parts by weight of another diene rubber as a rubber component The present invention relates to a rubber composition.

  The rubber composition for a tire tread as described above, wherein the butadiene rubber (a) exhibiting crystallization has a cis-1,4 bond content of 90% or more.

  The rubber composition for tire tread is characterized in that the rubber component (b) not showing crystallization is butadiene rubber.

  The rubber component (b) which does not show crystallization is butadiene rubber, and its microstructure has a cis-1,4 bond content of 65 to 95% and a 1,2 bond content of 4 to 30%. The present invention relates to the above-described rubber composition for a tire tread.

The present invention relates to an automobile tire characterized by using the tire tread rubber composition as a base material.

As described above, in the rubber composition for tire tread according to the present invention, the specific butadiene rubber composition containing at least 1% by weight or more of the rubber component (b) not showing crystallization in the butadiene rubber (a) showing crystallization. (A) Since it is a rubber composition for a tire tread characterized by containing 10 to 90 parts by weight and another diene rubber 90 to 10 parts by weight as a rubber component, general characteristics such as wear resistance are maintained. However, the on-ice performance can be remarkably improved by greatly reducing the elastic modulus particularly at −30 ° C.

  The specific butadiene rubber composition, which is an important element of the present invention, is a butadiene rubber that exhibits crystallization, and a rubber component that does not exhibit crystallization is blended. The crystallization of butadiene rubber, which shows crystallization, is suppressed and the crystallinity is not exhibited after vulcanization. Accordingly, the elastic modulus in the vicinity of −30 ° C., which correlates with the performance on ice, can be greatly reduced, and desired flexibility can be obtained.

  In addition, butadiene rubber having a cis-1,4 bond content of 90% or more, particularly of butadiene rubber exhibiting crystallization, has an advantage that it has excellent properties such as wear resistance and heat generation characteristics.

  Further, the rubber component (b) which does not show crystallization is a butadiene rubber, and its microstructure has a cis-1,4 bond content of 65 to 95% and a 1,2 bond content of 4 to 30%. Certain butadiene rubbers have the advantage of greatly improving the heat generation characteristics while maintaining the excellent wear resistance of the butadiene rubber (a) exhibiting crystallization.

  The specific butadiene rubber composition (A) used for the tire tread rubber composition of the present invention contains at least 1% by weight or more of a rubber component (b) that does not show crystallization in the butadiene rubber (a) that shows crystallization. Specific butadiene rubber composition (a) + (b).

  The butadiene rubber (a) showing crystallization contained in the specific butadiene rubber composition has a cis-1,4 bond content of 90% or more in order to improve basic physical properties such as wear resistance and heat generation characteristics. The cis-1,4 bond content is more preferably 95% or more.

  The butadiene rubber showing crystallization and the rubber component not showing crystallization contained in the specific butadiene rubber composition cause co-vulcanization at the time of vulcanization and do not show crystallinity after vulcanization. The elastic modulus can be greatly reduced. If the ratio of the rubber component not showing crystallization is less than 1% by weight, the crystallization behavior of the rubber composition after vulcanization cannot be suppressed, and the effect of lowering the storage elastic modulus at around -30 ° C. is sufficiently manifested. Can not.

  Considering the balance between performance on ice and wear resistance, the preferred proportion of the rubber component not showing crystallization is 5 to 60% by weight, more preferably 10 to 60% by weight in the specific butadiene rubber composition.

Examples of rubber components that do not show crystallization include butadiene rubber, styrene butadiene rubber, polyisoprene, butyl rubber (IIR), ethylene propylene rubber (EPM, EPDM), acrylonitrile butadiene rubber (NBR), which do not have high cis content, Examples thereof include polysulfide rubber, polyvinyl chloride, and polystyrene. In addition, derivatives of these rubbers such as tin compounds, epoxy-modified, silane-modified, and maleic acid-modified rubbers described above can be used, and these rubbers may be used alone or in combination of two or more. Of these, butadiene rubber is preferred, more preferably its microstructure has a cis-1,4 bond content of 65-95% and a 1,2 bond content of 4-30%, more preferably cis-1. , 4 bond content is 70 to 95%, and 1,2 bond content is 5 to 25%, particularly preferably 7 to 15%. Further, the trans-1,4 bond content is preferably 5% or less, particularly preferably 0.5 to 4.0%. The Mooney viscosity (ML _{1 + 4} ) of this butadiene rubber is not particularly limited, but is preferably 10 to 200, particularly preferably 25 to 100. The butadiene rubber specified as described above has high compatibility with butadiene rubber exhibiting crystallization, and can suppress crystallization of the vulcanizate more effectively.

  Furthermore, the butadiene rubber having a specific microstructure that does not exhibit crystallization includes metallocene type complexes of vanadium metal compounds and non-coordinating anions and cations as disclosed in JP-A-9-291108. And a polymerization catalyst comprising an ionic compound and / or an aluminoxane.

  In addition, the polymerization method of the butadiene rubber which shows crystallization contained in the specific butadiene rubber composition of this invention is not specifically limited, The butadiene rubber polymerized by the solution polymerization method, the emulsion polymerization method, etc. can be used. Further, the polymerization catalyst is not particularly limited, and butadiene rubber polymerized with a cobalt catalyst, a neodymium catalyst, a nickel catalyst, a titanium catalyst or the like can be used. These butadiene rubbers can also be used as various derivatives, for example, butadiene rubber modified with a tin compound, epoxy-modified, silane-modified or maleic acid-modified.

  The amount of the specific butadiene rubber composition is 10 to 90 parts by weight, more preferably 15 to 80 parts by weight, per 100 parts by weight of the rubber component. If it is less than 10 parts by weight, the desired performance on ice cannot be obtained, and if it exceeds 90 parts by weight, the processability and cut resistance of the tire tread rubber composition are undesirably lowered.

  Other diene rubbers used in blends are high cis polybutadiene rubber, low cis polybutadiene rubber (BR), natural rubber, polyisoprene rubber, ethylene propylene diene rubber (EPDM), nitrile rubber (NBR), butyl rubber (IIR). And chloroprene rubber (CR). Derivatives of these rubbers such as polybutadiene rubber modified with tin compounds and the above-mentioned rubbers modified with epoxy, silane, and maleic acid can also be used. These rubbers can be used alone or in combination of two or more. May be.

  The rubber composition for tire treads includes reinforcing agents and fillers such as carbon black and silica, softeners, plasticizers, vulcanizing agents, vulcanization accelerators, anti-aging agents, etc., which are commonly used in the rubber industry. The compounding chemicals can be blended.

  In addition to various types of carbon black, reinforcing agents include inorganic reinforcing agents such as white carbon, activated calcium carbonate, and ultrafine magnesium silicate, syndiotactic 1.2 polybutadiene resin, polyethylene resin, polypropylene resin, high styrene resin, and phenol. There are organic reinforcing agents such as resin, lignin, modified melamine resin, coumarone indene resin and petroleum resin, particularly preferably carbon black having a particle size of 90 nm or less and dibutyl phthalate (DBP) oil absorption of 70 ml / 100 g or more, For example, FEF, FF, GPF, SAF, ISAF, SRF, HAF and the like can be mentioned.

  As the vulcanizing agent, known vulcanizing agents such as sulfur, organic peroxides, resin vulcanizing agents, and metal oxides such as magnesium oxide are used.

  As the vulcanization aid, known vulcanization aids such as aldehydes, ammonia, amines, guanidines, thioureas, thiazoles, thiurams, dithiocarbamates, xanthates and the like are used.

  Examples of the filler include inorganic fillers such as calcium carbonate, basic magnesium carbonate, clay, Lissajous and diatomaceous earth, and organic fillers such as recycled rubber and powder rubber.

  Examples of the anti-aging agent include amine / ketone series, imidazole series, amine series, phenol series, sulfur series and phosphorus series.

  The process oil may be any of aromatic, naphthenic, and paraffinic.

  The rubber composition for a tire tread can be obtained by kneading with a mixer such as an ordinary Banbury mixer or kneader.

  The rubber composition for tire treads of the present invention is particularly suitable for running on icy and snowy road surfaces, for example, used for passenger cars such as studless tires, all-season tires, snow tires, for light trucks, trucks / buses, industrial vehicles, etc. The The rubber composition for tire treads of the present invention can also be used for passenger cars, light trucks, trucks / buses, industrial vehicles, etc. suitable for general traveling. Further, the rubber composition for tire treads of the present invention is not only used for tire treads, but also tire members such as base treads, sidewalls, side reinforcing layers for run-flat tires, carcass, belts, beads, shoes, mats. It can be widely used for industrial purposes such as industrial products.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. The physical properties of the base rubber of the rubber component used in the examples and comparative examples, and the physical properties of the vulcanizates of the obtained rubber compositions for tire treads were measured as follows.
(1) Mooney viscosity ; a value measured at 100 ° C. according to JIS K6300.
(2) Microstructure : Performed by infrared absorption spectrum analysis. The microstructure was calculated from the absorption intensity ratio of cis 740 cm ⁻¹ , trans 967 cm ⁻¹ and vinyl 910 cm ⁻¹ .
(3) Crystallization ; using a differential scanning calorimeter (DSC),
1) Pretreatment (i) Temperature rise from room temperature to 100 ° C at 10 ° C / min (ii) Hold at 100 ° C for 10 minutes (iii) Temperature drop from 100 ° C to -70 ° C at -5 ° C / min (iV) -70 Hold at 10 ° C. for 10 minutes (V) Rapid cooling from −70 ° C. to −150 ° C. at −40 ° C./min (Vi) Hold at 10 ° C. for 10 minutes 2) Measurement of crystallinity −10 ° C./min from 150 ° C. to 100 ° C. The temperature was determined by observing the crystal peak of the endothermic curve obtained under the analysis conditions for temperature increase.
(4) Performance on ice : Using a viscoelasticity measuring device EPLEXOR manufactured by GABO, the storage elastic modulus E ′ was measured under the conditions of a temperature of −30 ° C., a dynamic strain of ± 0.3%, and a frequency of 10 HZ. The index was evaluated with an index of 100. The smaller the value, the higher the flexibility and the better the performance on ice.
(5) Abrasion resistance : measured according to JIS K6264 using a Lambourn abrasion tester at a slip rate of 60%, and Comparative Example 1 was evaluated as 100. The higher the index, the better the wear resistance.
(6) Heat generation characteristics : In accordance with JIS K6265, the test was performed at a test temperature of 100 ° C. for 25 minutes, and the difference between the test temperature and the start temperature was measured. The smaller the index, the smaller the heat generation and the better.
(Embodiments) The present invention will be described below based on embodiments.

  Table 1 shows the Mooney viscosity, microstructure, and crystallization characteristics of the rubber components (BR-1 to BR-3) used in the examples.

  BR-1 and BR-3 use commercially available butadiene rubber. BR-1 is UBEPOL-BR150L, a high-cis butadiene rubber made by Ube Industries, and BR-3 is a diene 55 made by Asahi Kasei Chemicals. Cis butadiene rubber.

BR-2 is a specific butadiene rubber that does not exhibit crystallization according to the present invention, and a reference example relating to its production method is shown below.
(Reference Example 1; production of BR-2)
A toluene solution (1.3-butadiene: 814 g) containing 30 wt% of 1.3-butadiene is charged into a 5 L autoclave equipped with a stirrer purged with nitrogen and stirred. Next, hydrogen gas was introduced to increase the pressure by 0.092 kgG / cm ² . Triethylaluminum (2.25 mmol) was added successively at 30 ° C. over 3 minutes, then trityltetra (perfluorophenyl) borate (0.039 mmol) and cyclopentadienyl vanadium trichloride (0.026 mmol) were added successively, and the polymerization temperature was 30 ° C. Polymerization was carried out for minutes.
















After the polymerization, an equivalent mixture of ethanol and heptane containing 2,6-di-t-butyl-p-cresol was injected to stop the reaction, and the solvent was evaporated and dried. The yield of the obtained polymer was 32%.

  BR-1 is a butadiene rubber having a cis-1,4 bond content of 95% or more and exhibits crystallization. On the other hand, BR-2 and BR-3 are butadiene rubbers which do not show crystallization. Among them, BR-2 is specified with a cis-1,4 bond content of 65 to 95% and a 1,2 bond content of 4 to 30%, and is closer to the microstructure of BR-1. It can be expected that the crystallization of the vulcanizate can be suppressed more effectively.

  Table 2 shows the butadiene rubber compositions used in Examples using the BRs shown in Table 1. This table shows the ratio of each BR contained in the butadiene rubber composition in weight%.

  Further, in the compounding system of the butadiene rubber composition and natural rubber shown in Table 2, the rubber compositions for tire treads of Examples and Comparative Examples in Table 3 were prepared in the respective compounding amounts shown in Table 3.

  In addition, each compounding agent and compounding amount which were commonly used for the rubber composition for tire treads of Table 3 are as follows, and a butadiene rubber composition and natural rubber (NR) were used using a 1.7 L test Banbury mixer. RSS # 1) and carbon black were kneaded and then the vulcanizing agent was mixed with an open roll. Next, press vulcanization was performed at a temperature of 150 ° C. for 30 minutes, and performance on ice, wear resistance and heat generation characteristics were evaluated using the obtained vulcanized test pieces. The results are shown in Table 2.

  Compounding ingredients other than rubber components and compounding amount (parts by weight) Carbon black (Tokai Carbon Co., Ltd. Seest 9 SAF): 50 parts by weight, aroma-based process oil: 3 parts by weight, No. 1 zinc white: 3 parts by weight, stearic acid : 2 parts by weight, anti-aging agent 6C (Ouchi Shinsei Chemical Co., Ltd. Nocrack 6C): 2 parts by weight, anti-aging agent NS (Ouchi Shinsei Chemical Co., Ltd. Noxeller NS): 1 part by weight, sulfur: 1 .5 parts by weight.

  As shown in Table 3, in each example of the present invention, the performance on ice is greatly improved while maintaining the wear resistance, and the heat generation characteristics are also improved. Comparing Example 1 and Example 2, since Example 1 includes BR-2 having a specific microstructure, the effect of improving on-ice performance and heat generation characteristics is increased.

  On the other hand, regarding the content of the butadiene rubber composition, Comparative Example 1 in which the proportion of BR-1 which is a butadiene rubber exhibiting crystallization is too large and Comparative Example 2 in which the proportion of the specific butadiene rubber composition (A) is too small In the former, the improvement in performance on ice cannot be obtained, and in the latter, the wear resistance is greatly reduced.

The rubber composition for a tire tread of the present invention is used in combination with other means for improving the performance on ice, for example, foamed rubber, addition of fine particles made of organic or inorganic substances, blending of a softening agent or a silica-based filler. be able to.

Claims (5)

(A) a butadiene rubber (a) showing a crystallization, microstructure, cis-1,4 bond content of not exhibit crystallization is 65 to 95% and 1,2-bond content of 4-15% specific butadiene rubber composition which butadiene rubber (b) is included through 603 wt% (a) + (b) 15 to 80 parts by weight, (B) a rubber component and other diene rubber 85 to 20 parts by weight A rubber composition for a tire tread, characterized by comprising:   The rubber composition for a tire tread according to claim 1, wherein the cis-1,4 bond content of the butadiene rubber (a) exhibiting crystallization is 90% or more. The rubber composition for a tire tread according to claim 1 or 2, wherein the butadiene rubber (b) not showing crystallization has a Mooney viscosity (ML _{1 + 4} ) of 25 to 100. The rubber composition for a tire tread according to any one of claims 1 to 3, wherein (B) the other diene rubber is natural rubber. An automotive tire comprising the rubber composition for a tire tread according to any one of claims 1 to 4 as a base material.