JP5205876B2 - Rubber composition for tire tread - Google Patents

Description

  The present invention relates to a rubber composition for a tire tread, and more specifically, improved braking performance on wet road surfaces (hereinafter referred to as “wet braking performance”), rolling resistance (fuel efficiency), and wear resistance. The present invention relates to a rubber composition for a tire tread.

  Styrene-butadiene copolymer rubber (SBR) having a high glass transition temperature (Tg) as a rubber component and a technology for improving wet braking performance and reducing rolling resistance by adding silica to a rubber composition for a tire tread A technique for improving wet braking performance by using it is conventionally known. However, since silica has a problem of high cohesiveness and low affinity for SBR, a technique using a silane coupling agent in combination with silica. Has been developed (Patent Document 1). On the other hand, a system in which high Tg SBR is blended with natural rubber, for example, as a low Tg polymer is generally incompatible because of their different solubility parameters. In such a system, if the compounding amount of silica is increased as compared with the compounding amount of carbon black, the rolling resistance and wet braking performance are improved, but the compatibilization proceeds and Tg increases, resulting in high wear resistance. There was a problem of lowering.

JP 2004-59999 A

  Accordingly, an object of the present invention is to provide a rubber composition for a tire tread having improved rolling resistance, wet braking performance and wear resistance.

As a result of intensive studies to solve the above-mentioned problems, the present inventors mixed a high-Tg hydroxyl group-containing conjugated diene-aromatic vinyl copolymer, silica, an aromatic oil, and a silane coupling agent to form a mixture. Then, by adding natural rubber and / or polyisoprene rubber and carbon black to this mixture, the rolling resistance and wet braking performance are improved despite the fact that the amount of silica is considerably larger than that of carbon black. The inventors have found that the wear resistance is improved and have completed the present invention.

That is, according to the present invention, (A) (A1) 55 to 85 parts by weight of a hydroxyl group-containing conjugated diene-aromatic vinyl copolymer having a glass transition temperature of 35 to -20 ° C, and (A2) natural rubber and A rubber component comprising 15 to 45 parts by weight of a polyisoprene rubber;
(B) (B1) 75 to 110 parts by weight of silica having a nitrogen adsorption specific surface area (N ₂ SA) of 100 to 300 m ² / g, and (B2) a nitrogen adsorption specific surface area (N ₂ SA) of 50 to 200 m ² / g. a filler component containing 10 to 20 parts by weight of carbon black as g,
(C) 30 to 65 parts by weight of aroma oil,
(D) 6 to 8.5% by weight of the silane coupling agent based on the total weight of the silica (B1);
And a mixture obtained by blending the hydroxyl group-containing conjugated diene-aromatic vinyl copolymer (A1), silica (B1), aroma oil (C) and silane coupling agent (D) with natural rubber and / or Alternatively, a rubber composition for a tire tread characterized by comprising a polyisoprene rubber (A2) and carbon black (B2) is provided.

  The rubber component (A) of the rubber composition for a tire tread of the present invention comprises (A1) 55 to 85 parts by weight of a hydroxyl group-containing conjugated diene-aromatic vinyl copolymer having a glass transition temperature of 35 to -20 ° C. (A2) It comprises 15 to 45 parts by weight of natural rubber and / or polyisoprene rubber.

  The hydroxyl group-containing conjugated diene-aromatic vinyl copolymer (A1) is a conjugated diene rubber having at least one hydroxyl group in the molecule. As the hydroxyl group-containing conjugated diene-aromatic vinyl copolymer (A1), a known one can be used as long as it has a glass transition temperature of −35 to −20 ° C. The hydroxyl group-containing conjugated diene-aromatic vinyl copolymer (A1) includes, for example, an aromatic vinyl monomer having a primary, secondary, or tertiary hydroxyl group, a conjugated diene monomer, and Accordingly, it can be obtained by copolymerizing with other copolymerizable monomers. Alternatively, the hydroxyl group-containing conjugated diene-aromatic vinyl copolymer (A1) is a copolymer of an aromatic vinyl monomer, a conjugated diene monomer, and another copolymerizable monomer as required. To produce a diene polymer having an active metal in the molecule, and then reacting with a modifying agent such as ketones, esters, aldehydes and epoxies to produce primary, secondary or tertiary It is obtained by introducing a hydroxyl group into a diene polymer.

  As the component (A2) constituting the rubber component (A) of the rubber composition of the present invention, natural rubber (NR), polyisoprene rubber (IR), or a combination of any ratio thereof can be used.

  In blending the rubber composition of the present invention, the hydroxyl group-containing conjugated diene-aromatic vinyl copolymer (A1), silica (B1), aroma oil (C), and silane coupling agent described below in the first mixing step. After mixing (D) to form a mixture, in the next second mixing step, component (A2) is blended with the carbon black (B2) described below in this mixture. In the first step of mixing a hydroxyl group-containing conjugated diene-aromatic vinyl copolymer having excellent affinity with silica with silica in the presence of an aroma oil and a silane coupling agent, a large amount of silica is added due to the presence of the aroma oil. Even if it mix | blends with, dispersibility of a silica can be raised to a favorable level, without reducing mixing workability. Thus, by blending components (A1), (A2), (B1), (B2), (C) and (D) in a two-stage mixing process, a high Tg hydroxyl group-containing conjugated diene-aromatic vinyl is obtained. The copolymer phase and the low Tg natural rubber and / or polyisoprene rubber phase compounded in the second mixing step are kept in an incompatible state. As a result, the wet performance is improved by the high Tg of the hydroxyl group-containing conjugated diene-aromatic vinyl copolymer phase and the silica dispersed therein, and the rolling resistance is reduced by the low Tg rubber phase of natural rubber and / or polyisoprene rubber. In addition, the wear resistance is considered to be improved.

The filler component (B) used in the rubber composition of the present invention includes (B1) 75 to 110 parts by weight of silica having a nitrogen adsorption specific surface area (N ₂ SA) of 100 to 300 m ² / g, and (B2) nitrogen adsorption. And 10 to 20 parts by weight of carbon black having a specific surface area (N ₂ SA) of 50 to 200 m ² / g. The silica used (component (B1)) has only to have a nitrogen adsorption specific surface area (N ₂ SA) of 100 to 300 m ² / g, and is appropriately selected from those generally used in the rubber industry. can do. When the N ₂ SA of silica is less than 100 m ² / g, the contact area between the polymer and the filler becomes small, and a reduction in reinforcement is observed. Silica with N ₂ SA exceeding 300 m ² / g is difficult to disperse in the rubber component because of its high cohesiveness. In the description of the present specification, “nitrogen adsorption specific surface area (N ₂ SA)” means a specific surface area (unit m ² / g) measured according to ASTM D3037. The amount of silica is 100 parts by weight in total of the rubber component (A), that is, 100 weights in total of the hydroxyl group-containing conjugated diene-aromatic vinyl copolymer (A1) and natural rubber and / or polyisoprene rubber (A2). 75 to 110 parts by weight per part, preferably 80 to 105 parts by weight. When the blending amount of silica (B1) exceeds the above range with respect to 100 parts by weight of the rubber component (A), the mixing processability is lowered. Moreover, when the compounding quantity of a silica (B1) is less than the minimum of the said range with respect to 100 weight part of rubber components (A), the silica filling rate in a hydroxyl-containing conjugated diene-aromatic vinyl copolymer phase is set. Due to the low, the reinforcing property is lowered, and the desired physical properties cannot be obtained.

The carbon black (B2) used in the rubber composition of the present invention may have any nitrogen adsorption specific surface area (N ₂ SA) of 50 to ²⁰⁰ m ² / g, and is generally used in the rubber industry. However, SAF, ISAF, and HAF grades that are usually used in rubber compositions for tire treads can be used. When N ₂ SA is less than 50 m ² / g, the filling amount can be increased, but the reinforcing effect becomes insufficient and the wear resistance is lowered. Carbon black with N ₂ SA exceeding 200 m ² / g has high cohesiveness and is difficult to disperse in the rubber component. The compounding amount of the carbon black (B2) is 100 parts by weight of the rubber component (A), that is, the hydroxyl group-containing conjugated diene-aromatic vinyl copolymer (A1) and natural rubber and / or polyisoprene rubber (A2). And 10 to 20 parts by weight per 100 parts by weight in total. If the blending amount of the carbon black (B2) exceeds the above range, the ratio of the carbon black in the entire filler becomes excessive, and desired physical properties such as low fuel consumption and low heat generation cannot be obtained. If the blending amount of carbon black (B2) is too small, the reinforcing property is lowered.

In this specification, “aromatic oil” is a lubricant that acts as a lubricant when mixing rubber components, fillers, and other compounding agents, lowers the viscosity of the rubber composition during mixing, and improves the dispersion of the compounding agent. is there. The blending amount of the aroma oil in the rubber composition of the present invention is 30 to 65 parts by weight per 100 parts by weight of the rubber component (A). By blending the aroma oil in an amount within this range, the mixing processability can be improved, and the dispersibility of silica can be increased to a good level. The aromatic oil (C) used in the rubber composition of the present invention preferably has an aromatic hydrocarbon weight percentage of 15 to 70% by weight when determined in accordance with ASTM D2140, and has an IP346 / The percentage by weight of polycyclic aromatic (PCA) when calculated according to 92 is less than 3% by weight. More preferably, when the weight percentage of carbon constituting the aromatic hydrocarbon, paraffin hydrocarbon and naphthene hydrocarbon determined in accordance with ASTM D2140 is represented as C _A , C _P and C _N , respectively. C _A , C _P and C _N are within the ranges of 15 wt% ≦ C _A ≦ 30 wt%, 35 wt% ≦ C _P ≦ 60 wt%, and 20 wt% ≦ C _N ≦ 35 wt%, respectively. It is. By using oil having C _A , C _P and C _N values within the above ranges, desired physical properties can be obtained without reducing the activity of the modifying group of the hydroxyl group-containing conjugated diene-aromatic vinyl copolymer (A1). Can be further improved. As an aromatic oil (c) having a C _A , C _P and C _N value within the above range and a PCA weight percentage of less than 3% by weight, a heavy fraction obtained by distilling crude oil under reduced pressure is solvent extracted. Examples thereof include TDAE (Treated Distillate Aromatic Extract) oil obtained by hydrogenating the insoluble matter. Generally, a high-boiling petroleum fraction is used as a process oil for rubber. Depending on the chemical structure of the hydrocarbon, paraffinic hydrocarbons, which are chain saturated hydrocarbons, and naphthenic hydrocarbons, which are cyclic saturated hydrocarbons, are used. It is classified into hydrogen and aromatic hydrocarbons. These hydrocarbons are generally distinguished by a numerical value known as a viscosity specific gravity constant (hereinafter referred to as “VGC”). Aromatic hydrocarbons have a VGC of 0.900 or more, and are paraffinic. The hydrocarbon has a VGC of 0.790 to 0.849, and the naphthenic hydrocarbon has a VGC of 0.850 to 0.899. According to an analysis method known as a ring analysis method such as ASTM D2140, the value of the sample such as VGC and refractive index, specific gravity, kinematic viscosity, and the like is used to determine the paraffinic hydrocarbon, naphthenic hydrocarbon and aromatic carbonization of the sample. The proportion (% by weight) of carbon constituting hydrogen can be determined.

  The silane coupling agent (component (D)) used in the rubber composition of the present invention is used to promote dispersion of silica (B1) in the hydroxyl group-containing conjugated diene-aromatic vinyl copolymer (A1). The blending amount is 6 to 8.5% by weight based on the total weight of silica (B1). Conventional silane coupling agents (D) can be used. Specific examples of the silane coupling agent (D) include bis (3-triethoxysilylpropyl) tetrasulfide and bis (3-triethoxysilylpropyl). A disulfide etc. can be mentioned.

  In the rubber composition of the present invention, in addition to the above components, if necessary, any compounding agent generally used in the art, for example, a vulcanization accelerator, a vulcanizing agent, a processing aid, Anti-aging agents, fillers other than silica and carbon black, and the like can be appropriately added in general compounding amounts. Of these optional compounding agents, the compounding agents excluding the vulcanizing agent and the vulcanization accelerator are added in any step of the first mixing step and the second mixing step. A vulcanizing agent and a vulcanization accelerator are added in the third mixing step. As a mixing method used in compounding the rubber composition of the present invention, a general method can be used. Generally, a lump, pellet or powder compounding agent is mixed with a suitable mixer such as a kneader, It can mix using an internal mixer, a Banbury mixer, a roll, etc. After preparing a rubber composition by mixing various compounding agents, a tread of a pneumatic tire can be formed by a general pressure molding method.

  The present invention will be described in more detail with reference to the following examples and comparative examples, but it goes without saying that the technical scope of the present invention is not limited by these examples.

Preparation of Rubber Compositions of Comparative Examples 1 to 5 and Examples 1 to 3 In the first mixing step, a hydroxyl group-containing conjugated diene-aromatic vinyl using a 1.7 liter sealed Banbury mixer according to the formulation shown in Table 1 below. The copolymer (A1), silica (B1), aroma oil (C), silane coupling agent (D), and any compounding agent such as zinc oxide are mixed for about 6 minutes, and the temperature is 150. Released when it reached ° C. Next, using the same mixer as used in the first mixing step as the second mixing step, the mixture obtained in the first mixing step is mixed with natural rubber and / or polyisoprene rubber, carbon black, and oxidation. An optional compounding agent such as zinc was added and mixed for about 5 minutes, and the resulting mixture was cooled to room temperature. Next, a vulcanization accelerator and sulfur are added to the mixture obtained in the second mixing step and mixed with an open roll to obtain each unvulcanized rubber composition of Comparative Examples 1 to 5 and Examples 1 to 3. It was.

Preparation of hydroxyl group-containing conjugated diene-aromatic vinyl copolymer In an autoclave with a stirrer, 8000 g of cyclohexane, 460 g of styrene and 700 g of butadiene were added, and 3.5 mmol of tetramethylethylenediamine (TMEDA) and 11 mmol of n-butyllithium were added. Polymerization was carried out at 50 ° C. Ten minutes after the start of the polymerization, 840 g of butadiene was continuously added. After confirming that the polymerization conversion was 100%, equimolar methanol was added to the active terminal (Li) to terminate the polymerization. To the obtained solution, 60 mmol of sec-butyllithium and 60 mmol of TMEDA were added and reacted at 70 ° C. for 1 hour, 60 mmol of ethylene oxide was added, and the mixture was further stirred for 20 minutes. After stopping the reaction by adding 120 mmol of methanol, the polymer was recovered by a steam stripping method. The glass transition temperature (Tg) measured by a differential scanning calorimeter (DSC) under a nitrogen atmosphere under a temperature rising rate of 10 ° C./min was −30 ° C.

Test Method Each unvulcanized rubber composition of the above Examples and Comparative Examples was vulcanized in a predetermined mold at 160 ° C. for 20 minutes to produce a vulcanized rubber test piece. Tested by the test method. The test results are shown in Table 1 below.
(1) Wet braking performance (tan δ (0 ° C))
Based on JIS K6394, a loss tangent tan δ (tan δ (0 ° C.)) at 0 ° C. was determined using a viscoelastic spectrometer (manufactured by Toyo Seiki Seisakusho). The value of tan δ (0 ° C.) obtained in Comparative Examples 2 to 5 and Examples 1 to 3 was expressed as an index as a relative value when the value of tan δ (0 ° C.) of Comparative Example 1 was 100. tan δ (0 ° C.) indicates that the larger the relative value, the better the wet braking performance.

(2) Rolling resistance (tan δ (60 ° C))
Based on JIS K6394, a loss tangent tan δ (tan δ (60 ° C.)) at 60 ° C. was determined using a viscoelastic spectrometer (manufactured by Toyo Seiki Seisakusho). The value of tan δ (60 ° C.) obtained in Comparative Examples 2 to 5 and Examples 1 to 3 was expressed as an index as a relative value when the value of tan δ (60 ° C.) of Comparative Example 1 was 100. tan δ (60 ° C.) represents that the smaller the relative value, the smaller the rolling resistance and the better the fuel consumption.

(3) Abrasion resistance Based on JIS K6264, using a Lambourn Abrasion Tester (manufactured by Iwamoto Seisakusho Co., Ltd.), measured under the conditions of a load of 4.0 kg (39 Newtons) and a slip rate of 30% for comparison. The amount of wear determined in Comparative Examples 2 to 5 and Examples 1 to 3 was expressed as a relative value when the amount of wear in Example 1 was 100. It represents that it is excellent in abrasion resistance, so that a relative value is large.

Table 1 footnotes:
(1): SIR (Tg = about −60 ° C.)
(2): Nipol NS116R manufactured by Nippon Zeon Co., Ltd. (solution polymerization SBR, non-oil extended, Tg = −22 ° C.)
(3): Hydroxyl-containing conjugated diene-aromatic vinyl copolymer obtained by the above synthesis method
(4): Zeosil 1165MP made by Rhodia (N ₂ SA = 163 m ² / g)
(5): Three types of zinc oxide manufactured by Shodo Chemical Industry Co., Ltd.
(6): Bead stearic acid manufactured by NOF Corporation
(7): SANTOFLEX 6PPD (chemical name: N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine) manufactured by Flexis
(8): Sunnock manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
(9): Si69 made by Degussa (chemical name: bis (3-triethoxysilylpropyl) tetrasulfide)
(10): Process X-140 manufactured by Japan Energy Co., Ltd. (% C _A = 43,% C _P = 28,% C _N = 29, PCA = 45 wt%)
(11): NP-700 manufactured by Idemitsu Kosan Co., Ltd. (% C _A = 19,% C _P = 58,% C _N = 23, PCA = 2.9% by weight)
(12): Seast 7HM manufactured by Tokai Carbon Co., Ltd. (N ₂ SA = 126 m ² / g)
(13): Fine powder sulfur with Jinhua seal oil manufactured by Tsurumi Chemical Co., Ltd.
(14): Noxeller CZ-G (chemical name: N-cyclohexyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
(15): Nokutizer D (chemical name: 1,3-diphenylguanidine) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

  From the results of Table 1 above, it can be seen that the rubber compositions (Examples 1 to 3) of the present invention have improved wet braking performance, reduced rolling resistance, and improved wear resistance. Furthermore, it can be seen that wet braking performance, rolling resistance and wear resistance are further improved by using low aroma oil as the aroma oil.

Claims (3)

(A) (A1) 55 to 85 parts by weight of a hydroxyl group-containing conjugated diene-aromatic vinyl copolymer having a glass transition temperature of 35 to -20 ° C, and (A2) natural rubber and / or polyisoprene rubber 15 to 45 A rubber component consisting of parts by weight;
(B) (B1) 75 to 110 parts by weight of silica having a nitrogen adsorption specific surface area (N ₂ SA) of 100 to 300 m ² / g, and (B2) a nitrogen adsorption specific surface area (N ₂ SA) of 50 to 200 m ² / g. a filler component containing 10 to 20 parts by weight of carbon black as g,
(C) 30 to 65 parts by weight of aroma oil,
(D) 6 to 8.5% by weight of the silane coupling agent based on the total weight of the silica (B1);
And a mixture obtained by blending the hydroxyl group-containing conjugated diene-aromatic vinyl copolymer (A1), silica (B1), aroma oil (C) and silane coupling agent (D) with natural rubber and / or Or the rubber composition for tire treads which mix | blends polyisoprene rubber (A2) and carbon black (B2).   2. The tire tread rubber according to claim 1, wherein the aromatic oil (C) has an aromatic hydrocarbon content of 15 to 70% by weight and a polycyclic aromatic content of less than 3% by weight. Composition.   The aromatic oil (C) is a so-called TDAE oil obtained by hydrogenating an insoluble matter obtained by solvent extraction of a heavy fraction obtained by distilling crude oil under reduced pressure. Item 3. A tire tread rubber composition according to Item 2.