JP5463734B2 - Rubber composition for tire - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a tire rubber composition, and more specifically, in a rubber composition containing carbon black and silica, the tire rubber composition is improved in wear resistance without deteriorating extrusion processability. About.

  In recent years, pneumatic tires for passenger cars are required to have excellent driving stability at high speeds and grip performance on wet road surfaces, and to reduce rolling resistance in order to improve fuel efficiency. As a countermeasure, silica is added to the tire rubber composition as a reinforcing material in addition to carbon black. In this case, the proportion of carbon black is relatively reduced by the amount of silica added. However, since silica has a smaller reinforcing effect than carbon black, when silica is blended, there is a problem that wear resistance is lowered unless the amount of silica is increased.

  Conventionally, in order to make the wear resistance of a rubber composition containing silica equal to or better than that of a rubber composition containing carbon black alone, a carbon black with a small particle size is used, or the blending ratio of carbon black is increased. However, there is a problem that the extrudability of the rubber composition is deteriorated because the rubber viscosity is increased and the mixing property of the carbon black is deteriorated. Similarly, when the amount of silica is increased in order to improve the wear resistance, the rubber viscosity increases and the dispersibility of silica deteriorates and the workability deteriorates, so the desired effect cannot be obtained. .

  In the latter case, it is known to improve the dispersibility of silica and increase the wear resistance by blending a silane coupling agent with silica (see, for example, Patent Document 1). However, even if a silane coupling agent is blended, the effect of reducing the viscosity of the rubber composition cannot be obtained, so the extrusion processability of the rubber composition deteriorated by the blending of carbon black and silica cannot be improved. It was.

  Therefore, it has been a very difficult task to improve the wear resistance of a rubber composition containing carbon black and silica without deteriorating the extrusion processability.

JP 7-48476 A

  An object of the present invention is to provide a rubber composition for tires which is improved in wear resistance without deteriorating extrusion processability in a rubber composition containing carbon black and silica.

The rubber composition for a tire of the present invention that achieves the above object is at least 1 with respect to 100 parts by weight of a diene rubber containing 10% by weight or more of an aromatic vinyl conjugated diene copolymer having a glass transition temperature of −25 ° C. or lower. 1 to 10 parts by weight of a phenol compound having two alkylthiomethyl groups, 5 to 50 parts by weight of carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of 100 to 140 m ² / g, and 30 to 90 parts by weight of silica are blended. In addition, the total of the carbon black and silica is 40 to 120 parts by weight.

  The phenol compound may be one represented by the following formula (1), and is preferably 2,4-bis (octylthiomethyl) -6-methylphenol.

（式中、Ｒ^１、Ｒ^２はそれぞれ独立に炭素数６〜１２のアルキル基、Ｒ^３は水素原子又は炭素数１〜６のアルキル基である。）

(In the formula, R ¹ and R ² are each independently an alkyl group having 6 to 12 carbon atoms, and R ³ is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.)

  The tire rubber composition of the present invention is preferably used for a tread portion of a pneumatic tire, and the pneumatic tire thus made has excellent wear resistance while maintaining and improving the extrusion processability.

The rubber composition for tires of the present invention has at least one alkylthiomethyl group per 100 parts by weight of a diene rubber containing 10% by weight or more of an aromatic vinyl conjugated diene copolymer having a glass transition temperature of −25 ° C. or less. 1 to 10 parts by weight of a phenol compound, 5 to 50 parts by weight of carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of 100 to 140 m ² / g, and 30 to 90 parts by weight of silica, and the carbon black Since the total particle size of silica and silica is 40 to 120 parts by weight, the particle size reduction and blending amount of carbon black are limited, so that the wear resistance of the rubber composition is increased without deteriorating the extrusion processability. . In addition, by blending together 1 to 10 parts by weight of a phenolic compound having an alkylthiomethyl group, the dispersibility of silica is improved to further improve the wear resistance of the rubber composition, and the viscosity of the rubber composition is reduced. Therefore, it is possible to achieve extrudability higher than the conventional level.

  In the tire rubber composition of the present invention, a diene rubber is used as the rubber component. As the diene rubber, an aromatic vinyl conjugated diene copolymer having a glass transition temperature of −25 ° C. or lower is necessarily included. Wear resistance is increased by blending an aromatic vinyl conjugated diene copolymer having a glass transition temperature of −25 ° C. or lower. It also ensures the grip performance required for pneumatic tire treads. Examples of the aromatic vinyl conjugated diene copolymer include styrene butadiene rubber (SBR). As a kind of styrene butadiene rubber, any of solution polymerization styrene butadiene rubber and emulsion polymerization styrene butadiene rubber may be used as long as it has the glass transition temperature described above. The styrene-butadiene rubber may be an oil-extended product, but the glass transition temperature of the oil-extended SBR is the glass transition temperature of the styrene-butadiene rubber in a state that does not include an oil-extended component (oil).

  The glass transition temperature of the aromatic vinyl conjugated diene copolymer is −25 ° C. or lower, preferably −25 ° C. to −70 ° C., more preferably −25 ° C. to −65 ° C. If the glass transition temperature of the aromatic vinyl conjugated diene copolymer is too low, the wear resistance is excellent, but the tan δ in the low temperature region, particularly around −10 ° C., is too low and the wet grip performance is reduced. In the present invention, the glass transition temperature is a temperature at the midpoint of the transition region, as measured by a differential scanning calorimetry (DSC) under a temperature increase rate condition of 20 ° C./min.

  The blending amount of the aromatic vinyl conjugated diene copolymer having a glass transition temperature of −25 ° C. or less in the diene rubber is 10% by weight or more, preferably 40 to 100% by weight, more preferably 60 to 100% by weight. When the blending amount of the aromatic vinyl conjugated diene copolymer having a glass transition temperature of −25 ° C. or lower is less than 10% by weight, it is difficult to ensure wear resistance.

  In the present invention, natural rubber, isoprene rubber, butadiene rubber, acrylonitrile-butadiene rubber, butyl rubber, glass transition temperature is-as the diene rubber other than the aromatic vinyl conjugated diene copolymer having a glass transition temperature of -25 ° C or lower. Examples thereof include styrene-butadiene rubber having a temperature higher than 25 ° C. Of these, butadiene rubber, natural rubber, and isoprene rubber are preferable. These diene rubbers can be used alone or as any blend.

In the present invention, by adding a phenol compound having at least one alkylthiomethyl group (—CH ₂ —S—R, where R represents an alkyl group), the dispersibility of silica is improved, and the rubber composition The effect | action which reduces the viscosity of is performed. Thus, the abrasion resistance of a rubber composition is further improved by improving the dispersibility of silica. Moreover, extrusion processability improves by reducing the viscosity of a rubber composition. Furthermore, since the phenolic compound having an alkylthiomethyl group has an antioxidant action and a gelation-inhibiting effect, the heat aging resistance of the rubber composition is improved, so that the rubber characteristics can be prevented from decreasing over time. For this reason, for example, the flexible rubber characteristic as a tread rubber can be maintained over time, and the performance of the pneumatic tire can be maintained for a long period of time.

The phenol compound used in the present invention may have at least one alkylthiomethyl group (—CH ₂ —S—R), but preferably has two. The alkyl group constituting the alkylthiomethyl group preferably has 6 to 12 carbon atoms. It is presumed that the sulfur atom (S) in the alkylthiomethyl group increases the affinity with silica, thereby improving the dispersibility of the silica and reducing the rubber viscosity. Therefore, even if a phenolic compound not having an alkylthiomethyl group or a phenolic antioxidant not having an alkylthiomethyl group is blended, the effect of improving the dispersibility of silica and improving the wear resistance and the effect of reducing the rubber viscosity are I can't get it.

  In the present invention, the phenol compound having at least one alkylthiomethyl group is preferably represented by the following formula (1).

（式中、Ｒ^１、Ｒ^２はそれぞれ独立に炭素数６〜１２のアルキル基、Ｒ^３は水素原子又は炭素数１〜６のアルキル基である。）

(In the formula, R ¹ and R ² are each independently an alkyl group having 6 to 12 carbon atoms, and R ³ is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.)

R ¹ and R ² are independent of each other and may be the same as or different from each other. R ¹ and R ² are alkyl groups having 6 to 12 carbon atoms, preferably 7 to 11 carbon atoms, and may be either a linear alkyl group or a branched alkyl group. Examples of such an alkyl group include a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, and a dodecyl group, and among them, a heptyl group, an octyl group, a nonyl group, a decyl group, and an undecyl group are preferable. .

R ³ is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, preferably 1 to 3 carbon atoms, and may be either linear or branched. Examples of such an alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, and a hexyl group. Among these, R ³ is preferably a hydrogen atom, a methyl group, an ethyl group, or a propyl group.

In the formula (1), the position of the hydroxyl group (—OH) may be between two alkylthiomethyl groups (—CH ₂ —S—R ¹ (R ² )) or next to the alkyl group (—R ³ ). .

  As the phenol compound used in the present invention, 2,4-bis (octylthiomethyl) -6-methylphenol is particularly preferable. This phenol compound is commercially available, and examples thereof include Irganox 1520 manufactured by Ciba Specialty Chemicals and HP400 manufactured by Kawaguchi Chemical Industry.

In this invention, the compounding quantity of the phenolic compound which has an alkylthiomethyl group is 1-10 weight part with respect to 100 weight part of diene rubbers, Preferably it is 1-5 weight part. When the blending amount of the phenol compound is less than 1 part by weight, the viscosity cannot be reduced, the extrusion processability cannot be improved, and the wear resistance cannot be improved. Further, the heat aging resistance of the rubber composition is improved, and deterioration with time cannot be suppressed. Moreover, when the compounding quantity of a phenol compound exceeds 10 weight part, the reduction effect of a viscosity and the further improvement effect of heat aging resistance cannot be expected, and it exists in the tendency for abrasion resistance to fall.

  In the present invention, the wear resistance of the rubber composition is improved by blending carbon black. The compounding quantity of carbon black is 5-50 weight part with respect to 100 weight part of diene rubbers, Preferably it is 10-40 weight part. When the blending amount of carbon black is less than 5 parts by weight, the rubber composition has insufficient wear resistance and the rubber strength cannot be sufficiently increased. Moreover, when the compounding quantity of carbon black exceeds 50 weight part, the mixability with respect to rubber | gum will deteriorate, and rolling resistance and extrusion processability will deteriorate.

The carbon black used in the present invention has a nitrogen adsorption specific surface area (N ₂ SA) of 100 to 140 m ² / g, preferably 100 to 130 m ² / g. When the nitrogen adsorption specific surface area of the carbon black is less than 100 m ² / g, the particle size of the carbon black becomes excessive, so that the wear resistance and rubber strength of the rubber composition cannot be sufficiently increased. When the nitrogen adsorption specific surface area exceeds 140 m ² / g, the particle size of the carbon black becomes too small, so that the rubber viscosity increases and the extrusion processability deteriorates. Moreover, rolling resistance deteriorates. The nitrogen adsorption specific surface area (N ₂ SA) of carbon black was determined according to JIS K6217-2.

  In the present invention, by adding silica, the hysteresis loss (or tan δ) is reduced and the rolling resistance is reduced. The compounding quantity of a silica is 30-90 weight part with respect to 100 weight part of diene rubbers, Preferably it is 40-80 weight part. When the amount of silica is less than 30 parts by weight, the effect of reducing tan δ cannot be sufficiently obtained. On the other hand, when the amount of silica exceeds 90 parts by weight, the processability is deteriorated such as a long mixing time, which is not preferable.

Silica used in the present invention, CTAB adsorption specific surface area is preferably 80~250m ² / g, may more preferably at 100 to 200 m ² / g. When the CTAB adsorption specific surface area of silica is less than 80 m ² / g, the breaking strength decreases and the wear resistance performance deteriorates. When the CTAB adsorption specific surface area of silica exceeds 250 m ² / g, the rubber viscosity increases and the extrusion processability deteriorates. The CTAB adsorption specific surface area of silica was determined based on the standard of ASTM-D3765-80.

  The total amount of carbon black and silica is 40 to 120 parts by weight, preferably 50 to 110 parts by weight, based on 100 parts by weight of the diene rubber. When the total amount of carbon black and silica is less than 40 parts by weight, the wear resistance cannot be sufficiently increased. On the other hand, when the total amount of carbon black and silica exceeds 120 parts by weight, the viscosity of the rubber composition for tires increases and the extrusion processability deteriorates.

  In this invention, it is preferable to mix | blend a sulfur containing silane coupling agent, and the dispersibility of the silica with respect to a diene rubber is improved. By improving the dispersibility of silica, the low rolling resistance and wear resistance of the rubber composition can be improved. The compounding amount of the sulfur-containing silane coupling agent is 2 to 15% by weight, preferably 6 to 10% by weight of the silica compounding amount. When the sulfur-containing silane coupling agent is less than 2% by weight of the silica content, the dispersion of the silica is deteriorated, and it is impossible to achieve both low rolling resistance and wear resistance. When the sulfur-containing silane coupling agent exceeds 15% by weight, the scorch time of the rubber composition becomes too short and premature vulcanization tends to occur.

  The sulfur-containing silane coupling agent is not particularly limited as long as it can be used in a rubber composition containing silica, and examples thereof include bis- (3-triethoxysilylpropyl) tetrasulfide and bis (3-triethoxysilylpropyl) disulfide. , 3-trimethoxysilylpropylbenzothiazole tetrasulfide, γ-mercaptopropyltriethoxysilane, 3-octanoylthiopropyltriethoxysilane, and the like.

  In the present invention, by adding a softening agent, grip performance based on a diene rubber containing an aromatic vinyl conjugated diene copolymer having a glass transition temperature of −25 ° C. or lower can be brought to a higher level. The blending amount of the softening agent is preferably 1 to 50 parts by weight, more preferably 3 to 40 parts by weight with respect to 100 parts by weight of the diene rubber. If the blending amount of the softening agent is less than 1 part by weight, the grip performance may not be sufficiently ensured. Moreover, when the compounding quantity of a softening agent exceeds 50 weight part, there exists a possibility that abrasion resistance and low rolling resistance may deteriorate. The softeners are all softeners contained in the tire rubber composition, and the blending amount of the softener is a softener component (process oil or extender oil) and rubber that are oil-extended on a diene rubber. The total amount with the softening agent mix | blended with the composition shall be said.

  Examples of the softener include petroleum-based softeners and vegetable oil-based softeners. Examples of petroleum-based softeners include paraffinic oil, aroma-based oil, and naphthenic oil. Of these, aroma oil is preferable.

  The tire rubber composition of the present invention is generally used in tire rubber compositions such as fillers, vulcanizing agents, crosslinking agents, vulcanization accelerators, anti-aging agents, and processing aids other than those described above. Various additives can be blended, and such additives can be kneaded by a general method to obtain a rubber composition for tires, which can be used for vulcanization or crosslinking. Examples of fillers other than carbon black and silica include clay, titanium oxide, talc, calcium carbonate, aluminum hydroxide, mica and the like. As long as the amount of these additives is not contrary to the object of the present invention, a conventional general amount can be used. The rubber composition for tires of the present invention can be produced by mixing the above components using a known rubber kneading machine such as a Banbury mixer, a kneader, or a roll.

  The rubber composition for tires of the present invention can improve wear resistance without deteriorating extrusion processability. This tire rubber composition can be suitably used for the tread portion. Moreover, it can be suitably used not only for racing tires but also for passenger car tires with improved grip performance. In these pneumatic tires, since the rubber composition as a raw material is excellent in extrusion processability, the shape stability of the processed extruded molded body is high, so that the quality stability is excellent and the wear resistance is further increased. can do.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, the scope of the present invention is not limited to these Examples.

  Nine kinds of rubber compositions for tires (Examples 1 to 4 and Comparative Examples 1 to 5) having the composition shown in Table 1 were weighed with the composition components except sulfur and a vulcanization accelerator, and a 1.7 L sealed type. The master batch kneaded at a temperature of 150 ° C. for 5 minutes with a Banbury mixer was discharged outside the apparatus and cooled at room temperature. This master batch was subjected to a 1.7 L hermetic Banbury mixer, and sulfur and a vulcanization accelerator were added and mixed to prepare a tire rubber composition.

  Mooney viscosity was evaluated by the following method using the obtained nine types of rubber compositions for tires (Examples 1 to 4, Comparative Examples 1 to 5). Moreover, nine types of rubber compositions were each vulcanized at 150 ° C. for 30 minutes in a mold having a predetermined shape to prepare test pieces, and the wear resistance and heat aging resistance were measured by the following methods.

Mooney Viscosity The Mooney viscosity (ML _{1 + 4} ) of the obtained rubber composition is based on JIS K6300, using a Mooney viscometer with an L-shaped rotor (38.1 mm diameter, 5.5 mm thickness), and a preheating time of 1 minute. The measurement was performed under the conditions of a rotor rotation time of 4 minutes, 100 ° C., and 2 rpm. The obtained results are shown in Table 1 as an index with the value of Comparative Example 1 as 100. A smaller index means a lower viscosity and better extrusion processability.

Abrasion resistance Abrasion amount of the obtained test piece in accordance with JIS K6264 using a Lambourn abrasion tester (manufactured by Iwamoto Seisakusho) under the conditions of load 49N, slip rate 25%, time 4 minutes, room temperature Was measured. The obtained results are shown in Table 1 as an index with the reciprocal of the wear amount of Comparative Example 1 as 100. Higher index means better wear resistance.

Heat aging resistance From the obtained test piece, a JIS No. 3 dumbbell-type test piece was cut out in accordance with JIS K6251. Each test piece was divided into two groups, and one of them was subjected to air heat aging treatment at 80 ° C. for 120 hours. Using this test piece with and without heat aging treatment, 100% deformation stress was measured in accordance with JIS K6251 and heat aging was performed for each (100% deformation stress after aging treatment / initial 100% deformation stress × 100). The increase rate (%) of 100% deformation stress accompanying processing was calculated. The obtained results are shown in Table 1 as “heat aging resistance” with the value of Comparative Example 1 as 100. It means that the smaller the index is, the more the vulcanized rubber specimen is cured (increase in 100% deformation stress) due to the heat aging treatment.

In addition, the kind of raw material used in Table 1 is shown below.
SBR1: emulsion polymerization styrene butadiene rubber, glass transition temperature -52 ° C. (NIPOL 1712 manufactured by Nippon Zeon Co., Ltd., oil-extended product with 37.5 parts by weight of aroma oil added to 100 parts by weight of SBR)
SBR2: emulsion polymerization styrene butadiene rubber, glass transition temperature -20 ° C (NIPOL 9529 manufactured by Nippon Zeon Co., Ltd., oil-extended product with 50 parts by weight of aroma oil added to 100 parts by weight of SBR)
BR: butadiene rubber, NIPOL BR1220 manufactured by Nippon Zeon Co., Ltd.
Carbon black 1: Nitrogen adsorption specific surface area 119 m ² / g (Tokai Carbon Co., Ltd. Seest 6)
Carbon black 2: Nitrogen adsorption specific surface area 142 m ² / g (Mitsubishi Chemical Corporation Dia Black A)
Silica: Ultrasil 7000GR manufactured by Evonik Degussa
Coupling agent: Silane coupling agent, Si69 manufactured by Evonik Degussa
Zinc oxide: 3 types of zinc oxide manufactured by Shodo Chemical Industry Co., Ltd. Stearic acid: Beads manufactured by NOF Co., Ltd. Bead stearic acid anti-aging agent: SANTOFLEX 6PPD manufactured by Flexis
Phenol compound 1: 2,4-bis (octylthiomethyl) -6-methylphenol, HP400 manufactured by Kawaguchi Chemical Industry Co., Ltd.
Phenol compound 2: Dibutylhydroxytoluene, BHT manufactured by Honshu Chemical Industry Co., Ltd.
Aroma oil: Showa Shell Sekiyu Extract 4 S
Vulcanization accelerator 1: Noxeller CZ-G manufactured by Ouchi Shinsei Chemical Co., Ltd.
Vulcanization accelerator 2: Noxeller DG made by Ouchi Shinsei Chemical Co., Ltd.
Sulfur: Fine powder sulfur with Jinhua seal oil manufactured by Tsurumi Chemical Co., Ltd.

Claims (5)

1 to 10 parts by weight of a phenol compound having at least one alkylthiomethyl group with respect to 100 parts by weight of a diene rubber containing 10% by weight or more of an aromatic vinyl conjugated diene copolymer having a glass transition temperature of −25 ° C. or less, 5 to 50 parts by weight of carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of 100 to 140 m ² / g and 30 to 90 parts by weight of silica are blended, and the total of the carbon black and silica is 40 to 120 parts by weight. A rubber composition for tires. The tire rubber composition according to claim 1, wherein the phenol compound is represented by the following formula (1).

(In the formula, R ¹ and R ² are each independently an alkyl group having 6 to 12 carbon atoms, and R ³ is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.)   The tire rubber composition according to claim 2, wherein the phenol compound is 2,4-bis (octylthiomethyl) -6-methylphenol.   The tire rubber composition according to claim 1, 2 or 3, which is used for a tread portion of a pneumatic tire.   A pneumatic tire using the tire rubber composition according to claim 1.