JP7006039B2 - Rubber composition for tire tread - Google Patents

Description

The present invention relates to a rubber composition for a tire tread that improves the dispersibility of silica.

In order to improve the performance of pneumatic tires, it is important to achieve both wet grip performance and wear resistance. In recent years, in order to improve wet grip performance and low rolling resistance, a rubber composition containing silica having a fine particle size or a new silane coupling agent has been studied (see, for example, Patent Document 1).

However, although silica having a fine particle size is expected to improve wear resistance, it is difficult to disperse it well in diene rubber, and it is said that both wet grip performance and wear resistance are compatible. There is a problem that the effect of the period cannot be sufficiently obtained.

Japanese Unexamined Patent Publication No. 2013-224356

An object of the present invention is to provide a rubber composition for a tire tread in which the dispersibility of silica is improved to achieve both wet grip performance and wear resistance.

（式（１）において、Ｒは水素または炭素数４～２５のアシル基であり、水素およびアシル基がそれぞれ１つ以上である。ＡＯは炭素数２～６のアルキレンオキシド、ｎは２～１０の整数である。） A rubber for tire tread , which comprises 30 to 160 parts by mass of silica and 0.5 to 20 parts by mass of a sucrose alkylene oxide compound represented by the following formula (1) in 100 parts by mass of a diene rubber. Composition.

(In the formula (1), R is hydrogen or an acyl group having 4 to 25 carbon atoms , and each has one or more hydrogen and an acyl group. AO is an alkylene oxide having 2 to 6 carbon atoms, and n is 2 to 10 carbon atoms. It is an integer of.)

In the rubber composition for tire tread of the present invention, 30 to 160 parts by mass of silica and 0.5 to 20 parts by mass of a specific sucrose alkylene oxide compound are blended in 100 parts by mass of a diene rubber, so that the dispersibility of silica is dispersible. Wet grip performance and wear resistance can be improved more than the conventional level.

The silica has a fine particle diameter of 140 to 300 m ² / g with a CTAB adsorption specific surface area. Further, in the above formula (1), R is preferably an acyl group having 6 to 22 carbon atoms, and AO is preferably ethylene oxide or propylene oxide.

The diene rubber constituting the rubber composition for a tire of the present invention is not particularly limited, and for example, natural rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, butyl rubber, styrene-isoprene rubber, styrene-isoprene- Examples thereof include butadiene rubber and acrylonitrile-butadiene rubber. Of these, natural rubber, butadiene rubber, and styrene-butadiene rubber are preferable. These diene rubbers may be modified diene rubbers whose molecular chain ends and / or side chains are modified with an epoxy group, a carboxy group, an amino group, a hydroxy group, an alkoxy group, a silyl group, an amide group, or the like.

（式（１）において、Ｒは水素または炭素数４～２５のアシル基、ＡＯは炭素数２～６のアルキレンオキシド、ｎは２～１０の整数である。） The rubber composition for a tire of the present invention contains a sucrose alkylene oxide compound represented by the following formula (1).

(In the formula (1), R is hydrogen or an acyl group having 4 to 25 carbon atoms, AO is an alkylene oxide having 2 to 6 carbon atoms, and n is an integer of 2 to 10 carbon atoms.)

In formula (1), R is hydrogen or an acyl group having 4 to 25 carbon atoms. It is preferable that R in the formula (1) has one or more hydrogen and acyl groups, and each has a plurality of hydrogen and acyl groups. Since R is hydrogen, the affinity with silica can be improved. Further, since R is an acyl group having a relatively large number of carbon atoms, it secures an affinity for a diene-based rubber and suppresses bleeding out to the rubber surface when a sucrose alkylene oxide compound is blended. When R is an acyl group, the number of carbon atoms thereof is preferably 6 to 22, and more preferably 11 to 18 carbon atoms. If the acyl group has less than 4 carbon atoms, the sucrose alkylene oxide compound may easily bleed out to the rubber surface.

R as an acyl group can be described as an acyl group (R'CO-) derived from a carboxylic acid (R'COOH) having an alkyl group (R') having 3 to 24 carbon atoms. Alkyl groups (R') having 3 to 24 carbon atoms include, for example, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecylic, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecil, and icosyl. , Henikosil, Dokosen, Tridecylic, Tetricosyl, etc. can be mentioned. Preferred examples thereof include decyl, undecylic acid, heptadecyl, dodecyl, heptadecyl, octadecyl and the like.

In the formula (1), AO is an alkylene oxide having 2 to 6 carbon atoms, and the carbon number thereof is preferably 2 to 4, more preferably 2 to 3. AO is preferably ethylene oxide or propylene oxide, more preferably ethylene oxide. Further, n is an integer of 2 to 10, preferably 3 to 8, and more preferably an integer of 3 to 5. By setting AO and n in this way, it is possible to have both an affinity for silica and an affinity for diene-based rubber, and it is possible to improve the dispersibility of silica having a fine particle size. That is, by introducing hydrogen in which alkylene oxide is interposed in sucrose and an acyl group in which alkylene oxide is interposed, the dispersibility of silica in diene-based rubber can be improved more than ever.

Examples of the sucrose alkylene oxide compound represented by the formula (1) include sucrose ethylene oxide lauric acid ester, sucrose ethylene oxide stearic acid ester, and the like. These sucrose ethylene oxide fatty acid esters can improve the dispersibility of silica having a fine particle size in the rubber composition for tires, improve the wet grip performance, and improve the wear resistance. Moreover, since it has an appropriate affinity with diene-based rubber, it does not excessively bleed out to the rubber surface.

The sucrose alkylene oxide compound represented by the formula (1) is blended in an amount of 0.5 to 20 parts by mass, preferably 1 to 15 parts by mass, and more preferably 2 to 10 parts by mass with respect to 100 parts by mass of the diene rubber. .. If the blending amount of the sucrose alkylene oxide compound is less than 0.5 parts by mass, the effect of improving the dispersibility of silica cannot be sufficiently obtained. Further, when the blending amount of the sucrose alkylene oxide compound exceeds 20 parts by mass, bleed-out is likely to occur and the wet grip performance is deteriorated.

The rubber composition for a tire of the present invention contains silica having a fine particle size. Examples of silica include wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, and the like, and these may be used alone or in combination of two or more. The CTAB adsorption specific surface area of silica is 140 to 300 m ² / g, preferably 180 to 280 m ² / g, and more preferably 200 to 260 m ² / g. Silica having a CTAB adsorption specific surface area of less than 140 m ² / g can have good dispersibility in diene-based rubber by using a silane coupling agent or the like. The rubber composition for a tire of the present invention targets silica having a CTAB adsorption specific surface area of 140 m ² / g or more, which has been difficult to disperse well. The upper limit of the CTAB adsorption specific surface area is preferably about 300 m ² / g from the viewpoint of ease of manufacturing and handling of silica. In the present specification, the CTAB specific surface area of silica is a value measured by ISO 5794.

In the present invention, silica is blended in an amount of 30 to 160 parts by mass, preferably 50 to 160 parts by mass, and more preferably 70 to 155 parts by mass with respect to 100 parts by mass of the diene rubber. If the blending amount of silica is less than 30 parts by mass, the mechanical properties of the rubber composition are insufficient and the wear resistance cannot be improved. On the other hand, if it exceeds 160 parts by mass, the dispersibility of silica is lowered and the wear resistance is deteriorated. In addition, the weight increases when tires are used.

A silane coupling agent can be blended with silica. By blending a silane coupling agent, the dispersibility of silica with respect to diene rubber can be improved, and the balance between wear resistance and wet grip performance can be further improved.

The type of silane coupling agent is not particularly limited as long as it can be used in a rubber composition containing silica, and for example, bis- (3-triethoxysilylpropyl) tetrasulfide and bis (3-). Examples of sulfur-containing silane coupling agents such as triethoxysilylpropyl) disulfide, 3-trimethoxysilylpropylbenzothiazoletetrasulfide, γ-mercaptopropyltriethoxysilane, and 3-octanoylthiopropyltriethoxysilane can be exemplified. ..

The blending amount of the silane coupling agent is preferably 3 to 15% by mass, more preferably 5 to 10% by mass, based on the weight of silica. If the blending amount of the silane coupling agent is less than 3% by mass of the silica blending amount, the silica dispersion may not be sufficiently improved. If the blending amount of the silane coupling agent exceeds 15% by mass of the silica blending amount, the silane coupling agents are condensed with each other, and the desired hardness and strength in the rubber composition cannot be obtained.

The rubber composition for a tire of the present invention comprises a reinforcing filler other than silica, a vulcanization or cross-linking agent, a vulcanization accelerator, an antiaging agent, a plasticizer, a processing aid, a terpene resin, a thermosetting resin and the like. Various additives generally used in rubber compositions for tires can be blended within a range that does not impair the object of the present invention. Further, such additives can be kneaded by a general method to form a rubber composition, which can be used for vulcanization or cross-linking. The blending amount of these additives can be a conventional general blending amount as long as it does not contradict the object of the present invention. The rubber composition for a tire of the present invention can be produced by mixing each of the above components using a normal rubber kneading machine, for example, a Banbury mixer, a kneader, a roll, or the like.

The rubber composition for a tire of the present invention is suitable for forming a tread portion and a side portion of a pneumatic tire. The pneumatic tire having the tread portion and / or the side portion formed of the rubber composition for a tire of the present invention can improve wet grip performance and wear resistance more than the conventional level. In addition, rolling resistance can be reduced.

Hereinafter, the present invention will be further described with reference to Examples, but the scope of the present invention is not limited to these Examples.

Twenty kinds of rubber compositions for tires having the common composition shown in Table 4 and containing the compounds shown in Tables 1 to 3 (Examples 1 to 9, Standard Examples 1 to 3, Comparative Examples 1 to 8) are used. In preparation, the components excluding sulfur and the vulcanization accelerator were kneaded with a 1.7 L Banbury mixer for 5 minutes, released when the temperature reached 145 ° C, and cooled to obtain a masterbatch. Sulfur and a vulcanization accelerator were added to the obtained master batch and kneaded with an open roll at 70 ° C. to obtain 20 kinds of rubber compositions for tires. Since the styrene-butadiene rubber (SBR) shown in Tables 1 to 3 contains 37.5 parts by mass of an oil component with respect to 100 parts by mass of the rubber component, the blending amount of the net rubber component is shown in parentheses. The blending amount of each compound shown in Table 4 is represented as a mass portion with respect to 100 parts by mass of the diene-based rubber shown in Tables 1 to 3.

The obtained rubber composition for tires is vulcanized at 170 ° C. for 10 minutes using a mold having a predetermined shape (inner dimensions; length 150 mm, width 150 mm, thickness 2 mm), and a test comprising the rubber composition for tires. Pieces were made. The pain effect, wet grip performance and bleed-out property of the obtained test piece were evaluated by the following methods.

Pain effect Using a strain shear stress measuring machine (RPA2000 manufactured by α-Technology), the obtained test piece has a strain shear modulus [G'0.28] (MPa) of 0.28% strain and a strain of 30.0. % Strain-shear elastic modulus [G'30.0] (MPa) was measured, and the difference [G'0.28-G'30.0] (MPa) was calculated as the Pain effect. The obtained results are represented by an exponent in which the value of Standard Example 1 is 100 in Table 1, the value of Standard Example 2 is 100 in Table 2, and the value of Standard Example 3 is 100 in Table 3. Shown in the "Pain effect" column of. The smaller this index is, the smaller the Pain effect is and the better the dispersibility of silica is.

Wet grip performance (tanδ at 0 ° C)
Using the obtained test piece, in accordance with JIS K6394: 2007, using a viscoelastic spectrometer (manufactured by Iwamoto Seisakusho Co., Ltd.), a stretch deformation strain rate of 10% ± 2%, a frequency of 20 Hz, and a temperature of 0 ° C. Tan δ was measured under the conditions. The obtained results are represented by an exponent in which the value of Standard Example 1 is 100 in Table 1, the value of Standard Example 2 is 100 in Table 2, and the value of Standard Example 3 is 100 in Table 3. It is shown in the column of "wet performance" of. The larger this index is, the larger the tan δ at 0 ° C. is, which means that the wet grip performance is excellent when the tire is used.

Bleed-out property The obtained test piece was allowed to stand in an oven at 40 ° C. for 2 weeks to adjust the condition. Then, the surface of the test piece was visually observed, and the bleed-out state was evaluated on a 5-point scale based on the following criteria. The obtained results are shown in the column of "bleed-out property" in Table 1. The larger this index is, the better the bleed-out property is.
5: No dullness or bleed-out is observed on the surface of the test piece (unchanged).
4: About 30% of the surface area of the test piece is dull.
3: The surface of the test piece is dull as a whole.
2: Bleedout is observed in about 30% of the surface area of the test piece.
1: Bleed-out is observed on the entire surface of the test piece.

The types of raw materials used in Tables 1 to 3 are shown below.
-SBR: Styrene-butadiene rubber, E581 manufactured by Asahi Kasei Corporation, oil exhibit containing 37.5 parts by mass of oil component with respect to 100 parts by mass of rubber component-BR: butadiene rubber, polybutadiene rubber manufactured by Nippon Zeon Co., Ltd. Nipol BR1220
-Silica-1: Zeosil 200MP manufactured by Solvay, CTAB adsorption specific surface area is 144 m ² / g
-Silica-2: Tokuyama KS30-SC manufactured by Tokuyama Corporation, CTAB adsorption specific surface area is 300 m ² / g
-Silica-3: Hisil EZ200G manufactured by PPG Industries, CTAB adsorption specific surface area is 280 m ² / g.
-Silane coupling agent: Sulfur-containing silane coupling agent, Si69 manufactured by Dexa
-Sucrose alkylene oxide-1: sucrose ethylene oxylauric acid ester, R in the above formula (1) is an acyl group derived from hydrogen or lauric acid, AO is ethylene oxide, n is 3 to 5, NH1400 manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. -1
-Sucrose alkylene oxide-2: sucrose ethylene oxystearic acid ester, R in the above formula (1) is an acyl group derived from hydrogen or stearic acid, AO is ethylene oxide, n is 3 to 5, NH1400 manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. -2
-Sucrose fatty acid ester: manufactured by Mitsubishi Chemical Foods, Inc., where n is 0 in the above formula (1).

The types of raw materials used in Table 4 are shown below.
・ Stearic acid: NOF beads stearic acid ・ Zinc oxide: Zinc oxide 3 types manufactured by Shodo Chemical Industry Co., Ltd. ・ Anti-aging agent: 6PPD manufactured by Flexis Co., Ltd.
・ Oil: Aroma oil manufactured by Fujikosan Co., Ltd. ・ Sulfur: Sulfur powder containing Jinhua stamped oil manufactured by Tsurumi Chemical Industry Co., Ltd. ・ Vulcanization accelerator 1: Noxeller CZ-G (CBS) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
-Vulcanization accelerator 2: Soxinol DG (DPG) manufactured by Sumitomo Chemical Co., Ltd.

As is clear from Tables 1 to 3, it was confirmed that the rubber compositions for tires of Examples 1 to 9 improved the dispersibility of silica and improved the wet grip performance more than the conventional level. In addition, there is little bleed-out and it is good.

Since the rubber composition for a tire of Comparative Example 1 contains less than 0.5 parts by weight of the sucrose alkylene oxide compound, the dispersibility of silica and the wet grip performance cannot be improved.
In the rubber composition for a tire of Comparative Example 2, since the sucrose alkylene oxide compound exceeds 20 parts by mass, the bleed-out is inferior, and the wet grip performance is deteriorated accordingly.
Since the rubber compositions for tires of Comparative Examples 3 and 4 contain a sucrose fatty acid ester instead of the sucrose alkylene oxide compound, the effect of improving the dispersibility of silica and the wet grip performance cannot be sufficiently obtained.

Claims (4)

A rubber for tire tread , which comprises 30 to 160 parts by mass of silica and 0.5 to 20 parts by mass of a sucrose alkylene oxide compound represented by the following formula (1) in 100 parts by mass of a diene rubber. Composition.

(In the formula (1), R is hydrogen or an acyl group having 4 to 25 carbon atoms , and each has one or more hydrogen and an acyl group. AO is an alkylene oxide having 2 to 6 carbon atoms, and n is 2 to 10 carbon atoms. It is an integer of.) The rubber composition for a tire tread according to claim 1, wherein the silica has a CTAB adsorption specific surface area of 140 to 300 m ² / g. The rubber composition for a tire tread according to claim 1 or 2, wherein R in the formula (1) is hydrogen or an acyl group having 6 to 22 carbon atoms. The rubber composition for a tire tread according to claim 1, 2, or 3, wherein the AO in the formula (1) is ethylene oxide or propylene oxide.