JP2010059268A - Rubber composition for tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for a tire which prevents hardening due to ageing to suppress the secular change of on-ice frictional force, and further improves rolling resistance. <P>SOLUTION: The rubber composition is characterized by compounding 100 pts.wt. of a diene rubber with 10 to 120 pts.wt. of silica, 1 to 20 pts.wt. of heat-expandable microcapsules and 0.01 to 10 pts.wt. of a tea extract containing catechin, and by compounding a silane coupling agent by 1 to 12 wt.% with respect to the compounded amount of the silica. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a rubber composition for tires, and more specifically, a rubber composition for tires of a pneumatic tire which prevents hardening due to aging, suppresses secular change of frictional force on ice, and reduces rolling resistance. Related to things.

  There are various configurations that improve the frictional force on ice of pneumatic tires (studless tires) for ice and snowy roads. Of these, many bubbles are formed in the tread rubber, so that when the tread steps on the ice surface, There is one that absorbs and removes a water film and repeatedly disengages it by centrifugal force when it is separated from the ice surface, thereby increasing the frictional force on ice. Patent Document 1 proposes, as a means for forming such bubbles, that a thermally expandable microcapsule is blended with a rubber composition for a tire and expanded by heating in a vulcanization process to form resin-coated bubbles. ing. At the same time, in Patent Document 1, in order to further increase the frictional force on ice of the studless tire, by adding silica to the tire rubber composition, the hardness of the tread rubber is maintained flexibly even at a low temperature, and adhesion to the ice surface is achieved. It is proposed to increase. Further, by blending silica, the hysteresis loss (tan δ) is reduced, so that a merit that rolling resistance is reduced can be obtained.

However, even a studless tire using such a tread rubber has a problem that the friction force on ice decreases after the second season because the tread rubber is hardened with aging. Also, since studless tires generally have a tendency to increase rolling resistance, it is required to reduce rolling resistance in order to improve fuel efficiency.
JP 2003-105138 A

  An object of the present invention is to provide a rubber composition for tires that prevents aging due to aging, suppresses secular change of frictional force on ice, and further improves rolling resistance.

  The rubber composition for tires of the present invention that achieves the above object is a tea extract comprising 10 to 120 parts by weight of silica, 1 to 20 parts by weight of thermally expandable microcapsules, and catechin with respect to 100 parts by weight of diene rubber. 0.01 to 10 parts by weight, and 1 to 12% by weight of a silane coupling agent based on the silica content.

  The tea extract preferably contains 5% by weight or more of catechin. Moreover, the tea extract contains (+)-catechin, (−)-epicatechin, (+)-gallocatechin, (−)-epigallocatechin, (−)-epicatechin gallate and (−)-epigallocatechin gallate. It is good to contain at least 1 sort (s) chosen from the group which consists of.

  This rubber composition for tires can be suitably used as a constituent material of a tread portion of a pneumatic tire.

  According to the rubber composition for tires of the present invention, the tea extract containing 10 to 120 parts by weight of silica, 1 to 20 parts by weight of thermally expandable microcapsules, and 0.1 to 10 parts by weight of catechin is added to 100 parts by weight of diene rubber. When blended with 01 to 10 parts by weight and blending 1 to 12% by weight of the silane coupling agent with respect to the silica blending amount, the tea extract functions as an antioxidant and improves the anti-aging performance of the rubber composition. Therefore, it is possible to suppress the curing of the rubber composition accompanying aging and to reduce the secular change of the frictional force on ice. Moreover, since the effect | action which improves the dispersibility of a silica further is acquired by mix | blending the tea extract containing a catechin, the hysteresis loss of a rubber composition can be made small and low rolling resistance can be improved further.

  In the tire rubber composition of the present invention, a diene rubber is used as the rubber component. Examples of the diene rubber include natural rubber, isoprene rubber, butadiene rubber, styrene butadiene rubber, acrylonitrile-butadiene rubber, and butyl rubber, which are usually used in tire rubber compositions. In particular, when used for the tread portion of a studless tire, natural rubber, butadiene rubber, and styrene butadiene rubber are preferable. These diene rubbers may be used alone or in a plurality of types.

  By adding silica to the rubber composition for a tire, it is possible to maintain the flexibility of the rubber at a low temperature, increase the adhesion to the ice surface, and improve the frictional force on ice. At the same time, it acts to reduce the rolling resistance of the tire in order to reduce the hysteresis loss of the rubber composition.

  In the present invention, the amount of silica is 10 to 120 parts by weight, preferably 10 to 100 parts by weight, and more preferably 10 to 80 parts by weight with respect to 100 parts by weight of the diene rubber. When the amount of silica is less than 10 parts by weight, the flexibility of the rubber at low temperatures cannot be sufficiently maintained, and the effect of reducing the hysteresis loss (tan δ) cannot be sufficiently obtained. If the blending amount of silica exceeds 120 parts by weight, the processability of the rubber composition deteriorates such as poor dispersion and increased viscosity. The kind of silica is not particularly limited, and those usually blended in a rubber composition can be used. Examples thereof include wet method silica, dry method silica, and surface-treated silica.

  In the present invention, the silane coupling agent improves the dispersibility of silica and enhances the reinforcement with rubber, thereby improving the flexibility of the rubber at low temperatures and further increasing the frictional force on ice. Moreover, since the hysteresis loss of the rubber composition is further reduced by improving the dispersibility of silica, the low rolling resistance is further improved. The amount of the silane coupling agent is 1 to 12% by weight, preferably 2 to 10% by weight, based on the amount of silica. When the silane coupling agent is less than 1% by weight of the amount of silica, it is impossible to expect dispersion of silica to maintain flexibility of the rubber at low temperatures and reduction of rolling resistance. If the silane coupling agent exceeds 12% by weight, the silane coupling agents will aggregate and condense, making it impossible to obtain the desired effect. In addition, the reaction of the silane coupling agent with the silanol group on the silica surface results in elimination of lower alcohols such as methanol and ethanol, and this lower alcohol affects the expansibility of the thermally expandable microcapsules described later. The blending amount of is preferably as small as possible within the range of ensuring the dispersibility of silica.

  Any silane coupling agent may be used as long as it can be used in a rubber composition containing silica, and a sulfur-containing silane coupling agent is particularly preferable. Examples of the sulfur-containing silane coupling agent include bis- (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, and γ-mercaptopropyl. Examples thereof include triethoxysilane and 3-octanoylthiopropyltriethoxysilane.

  The thermally expandable microcapsule used in the present invention has a structure in which a thermally expandable substance is encapsulated in a shell material formed of a thermoplastic resin. For this reason, when the microcapsules in the rubber composition are heated during vulcanization of the unvulcanized tire, the thermally expansible material contained in the shell material expands to increase the particle size of the shell material, and in the tread rubber A large number of resin-coated bubbles are formed. As a result, the water film generated on the ice surface is efficiently absorbed and removed, and a micro edge effect is obtained, so that the frictional force on ice is increased. Examples of such thermally expandable microcapsules include trade name “EXPANCEL 091DU-80” or “EXPANCEL 092DU-120” manufactured by EXPANSEL, Sweden, or trade name “Microsphere” manufactured by Matsumoto Yushi Seiyaku Co., Ltd. F-85D "or" Microsphere F-100D "can be used.

  In this invention, the compounding quantity of a microcapsule is 1-20 weight part with respect to 100 weight part of diene rubbers, Preferably it is 1-16 weight part. When the blending amount of the microcapsules is less than 1 part by weight, the volume of the resin-coated bubbles in the tread rubber is insufficient, and the friction force on ice cannot be obtained sufficiently. On the other hand, when the blending amount exceeds 20 parts by weight, the wear resistance of the tread rubber is deteriorated.

  The rubber composition for tires of the present invention can improve anti-aging performance and improve silica dispersibility by blending a tea extract containing catechin. That is, the tea extract containing catechin functions as an antioxidant and can suppress the rubber composition from aging and curing over time. For this reason, in order to maintain the softness | flexibility of the tread rubber of a pneumatic tire, it can suppress that the friction force on ice falls after the 2nd season.

  Moreover, since the effect | action which improves the dispersibility of a silica further is acquired by mix | blending the tea extract containing a catechin, the hysteresis loss of a rubber composition can be made small and low rolling resistance can be improved further. Therefore, by blending tea extract containing catechins, the amount of silane coupling agent can be reduced, so methanol and ethanol that are eliminated by the reaction between the silane coupling agent and the silanol groups on the silica surface. The generation amount of lower alcohol such as can be reduced. For this reason, in order to suppress the expansion | swelling of the thermal expansion microcapsule at the time of vulcanization and to improve expansibility, the friction force on ice can be made more excellent.

  The amount of tea extract containing catechin is 0.01 to 10 parts by weight with respect to 100 parts by weight of diene rubber. The amount is preferably 0.01 to 7 parts by weight, more preferably 0.015 to 5 parts by weight, and still more preferably 0.02 to 4 parts by weight. When the blending amount of the tea extract is less than 0.01 parts by weight, the effect of suppressing aging of the rubber composition and the effect of improving silica dispersion cannot be obtained sufficiently. Moreover, when the compounding quantity of a tea extract exceeds 10 weight part, raw material cost will become high and it is not practical.

  The tea extract used in the present invention is a tea extract containing catechin, preferably (+)-catechin, (−)-epicatechin, (+)-gallocatechin, (−)-epigallocatechin, (− It contains at least one selected from the group consisting of) -epicatechin gallate and (-)-epigallocatechin gallate. The tea extract may contain free theaflavin, theaflavin monogallate A, theaflavin digallate and the like as components other than catechin. The content of catechin in the tea extract is preferably 5% by weight or more, more preferably 5 to 75% by weight. When the content of catechin is less than 5% by weight, sufficient anti-aging performance cannot be obtained.

  The tea extract used in the present invention is an extract from at least one selected from green tea, oolong tea, and black tea. From these tea leaves or ground tea leaves, water or hot water, an organic solvent is used as an extractant. Extraction may be performed at an extraction temperature of ˜60 ° C. Examples of the organic solvent include methanol, ethanol, isopropanol, and ethyl acetate. These extractants may be used alone or in combination of two or more.

  For the tea extract, the fraction extracted with the above extractant is used. When extracted with water or hot water, the extract may be used as it is as a tea extract, but from the viewpoint of handleability, the extract is removed from the extract by spray drying, freeze drying, etc. It is good to use it.

  As the tea extract used in the rubber composition for tires of the present invention, the tea extract described above may be used as it is, or as an antioxidant comprising a mixture to which other natural compounds and / or surfactants are added. May be used. Such antioxidants are commercially available, for example, Sun Chemical Co., Ltd. Sanphenon DK (catechin content 70 wt%), Sanflavone HG (catechin content 45 wt%), Sankatol No1 (catechin content 7 wt%) Etc. can be illustrated.

  The rubber composition for tires of the present invention can increase the strength of rubber and improve the wear resistance by blending carbon black. The compounding amount of carbon black is preferably 5 to 90 parts by weight, more preferably 10 to 80 parts by weight with respect to 100 parts by weight of the diene rubber. When the blending amount of carbon black is less than 5 parts by weight, the rubber strength cannot be sufficiently increased and the wear resistance cannot be improved. Moreover, when the compounding quantity of carbon black exceeds 90 weight part, the rolling resistance of the rubber composition for tires will deteriorate. Moreover, workability deteriorates, such as mixing time becoming long.

The carbon black suitably used in the present invention has a nitrogen adsorption specific surface area (N ₂ SA) of preferably 30 to 150 × 10 ³ m ² / kg, more preferably 60 to 130 × 10 ³ m ² / kg. Good. When the nitrogen adsorption specific surface area of carbon black is less than 30 × 10 3 ^{m 2} / ^kg can not be made sufficiently high rubber strength. When the nitrogen adsorption specific surface area exceeds 150 × 10 ³ m ² / kg, the mixing time becomes long and the workability deteriorates, and the hysteresis loss increases and the rolling resistance deteriorates. The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is determined according to JIS K6217-2.

  You may mix | blend inorganic fillers other than carbon black and a silica with the rubber composition for tires of this invention. Examples of the inorganic filler include clay, calcium carbonate, aluminum hydroxide, mica, talc and the like. In addition, various additives commonly used in rubber compositions for tires such as vulcanizing agents, vulcanization accelerators, anti-aging agents, plasticizers, coupling agents other than silane coupling agents, etc. These additives can be kneaded by a general method to obtain a rubber composition for tires, which can be used for vulcanization or crosslinking. 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 tire rubber composition of the present invention suppresses the curing of the rubber composition with aging, so that the secular change of frictional force on ice is reduced and the dispersibility of silica is further improved. Loss can be reduced and rolling resistance can be further improved. The tire rubber composition is preferably applied to a tread portion of a pneumatic tire, particularly a studless tire. The studless tire using the rubber composition has excellent on-ice frictional force and low rolling characteristics and is suitable for the second season. It can suppress that the friction force on ice falls after that.

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

  Eight types of tire rubber compositions (Examples 1 to 5 and Comparative Examples 1 to 3) having the composition shown in Table 1 were mixed with 1.7 liters of components excluding sulfur, a vulcanization accelerator, and a thermally expandable microcapsule. The mixture was kneaded with a closed Banbury mixer for 5 minutes, and when it reached 145 ± 10 ° C., it was discharged and cooled to room temperature. This was prepared by blending sulfur, a vulcanization accelerator and a thermally expandable microcapsule and mixing them with the same Banbury mixer.

  The obtained eight rubber compositions for tires (Examples 1 to 5 and Comparative Examples 1 to 3) were press vulcanized at 160 ° C. for 20 minutes in a predetermined mold to prepare rubber test pieces. The obtained vulcanized rubber specimens were evaluated for frictional force on ice, anti-aging performance, and tan δ by the following methods.

Friction force on ice A sheet obtained by vulcanizing the obtained rubber composition for tire was attached to a flat columnar base rubber, and measured using an inside drum type ice friction tester at a measurement temperature of -1.5 ° C and a load of 0. The friction coefficient on ice was measured under the conditions of 54 MPa and a drum rotation speed of 25 km / h. The obtained friction coefficient on ice is shown in Table 1 as the friction force on ice with the value of Comparative Example 1 as 100. The larger this index, the better the frictional force on ice.

Aging prevention performance Using the obtained tire rubber composition, a test piece vulcanized into a shape of a Rupke sample (a cylindrical shape having a thickness of 12.5 mm and a diameter of 29 mm) was prepared. 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 the test specimens before and after the aging treatment, the rubber hardness at a temperature of 20 ° C. was measured by a durometer type A in accordance with JIS K6253, and each (rubber hardness after aging treatment / rubber hardness before aging treatment × 100) Was used to calculate the rate of change in rubber hardness (%). The obtained results are shown in Table 1 as anti-aging performance with the value of Comparative Example 1 as 100. The smaller this index is, the better the anti-aging performance is, meaning that the curing of the rubber composition has been reduced.

tan δ (60 ° C)
With respect to the dynamic viscoelasticity of the obtained test piece, tan δ at a temperature of 60 ° C. was measured using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho Co., Ltd. under conditions of an initial strain of 10%, an amplitude of ± 2%, and a frequency of 20 Hz. The obtained results are shown in Table 1 as an index with the value of Comparative Example 1 as 100. It means that the smaller the index of tan δ (60 ° C.), the smaller the rolling resistance and the better.

In addition, the kind of raw material used in Table 1 is shown below.
NR: Natural rubber RSS # 3
BR: butadiene rubber, NIPOL BR1220 manufactured by Nippon Zeon Co., Ltd.
Carbon black: Seast 6 manufactured by Tokai Carbon Co., Ltd. (nitrogen adsorption specific surface area of 119 m ² / g)
Silica: Nippon Sil AQ manufactured by Nippon Silica Industry Co., Ltd.
Silane coupling agent: Si69 manufactured by Dexa
Zinc oxide: Zinc oxide, 3 types manufactured by Shodo Chemical Industry Co., Ltd. Stearic acid: Beads manufactured by NOF Co., Ltd.
Tea extract: Taiyo Kagaku Sankator No1 (catechin content: 7% by weight)
Aroma oil: Showa Shell Sekiyu Extract 4 S
Sulfur: Fine powder sulfur vulcanization accelerator with Jinhua seal oil manufactured by Tsurumi Chemical Co., Ltd .: Noxeller CZ-G manufactured by Ouchi Shinsei Chemical Co., Ltd.
Thermally expandable microcapsules: Microsphere F-100D manufactured by Matsumoto Yushi Seiyaku Co., Ltd.

Claims (4)

  With 100 parts by weight of diene rubber, 10 to 120 parts by weight of silica, 1 to 20 parts by weight of thermally expandable microcapsules, 0.01 to 10 parts by weight of tea extract containing catechin, and silane coupling A rubber composition for tires containing 1 to 12% by weight of an agent based on the amount of silica.   The tire rubber composition according to claim 1, wherein the tea extract contains 5% by weight or more of catechin.   The tea extract comprises (+)-catechin, (−)-epicatechin, (+)-gallocatechin, (−)-epigallocatechin, (−)-epicatechin gallate and (−)-epigallocatechin gallate. The tire rubber composition according to claim 1, comprising at least one selected from the group consisting of:   A pneumatic tire comprising a tread made of the rubber composition for a tire according to claim 1, 2 or 3.