JP4606807B2 - Rubber composition for tire tread - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a rubber composition for a tire tread, and in particular, a tire having a high content ratio of non-petroleum resources that suppresses deterioration in rubber physical properties due to reversion and thermal aging, and further improves fuel efficiency and wear resistance. The present invention relates to a rubber composition for treads.

  In recent years, methods such as using styrene butadiene rubber as a rubber component have been performed in order to improve the fuel efficiency of vehicles and the wear resistance of tires.

  However, in recent years, environmental issues have become more important, regulations on carbon dioxide emission control have been strengthened to control global warming, and the supply of oil has been declining year by year due to the limited amount of petroleum raw materials. Oil prices are expected to rise in the future, and there are limits to the use of petroleum resources such as styrene butadiene rubber and carbon black for tires.

  Therefore, it is necessary to use non-oil resources such as natural rubber, modified natural rubber (epoxidized natural rubber, etc.), silica, etc., assuming the future time of oil depletion. However, in that case, performance that is equivalent to or better than that obtained by using petroleum resources that have been used in the past is required, so fuel efficiency and wear resistance are improved after using non-oil resources. It is being considered to do.

  For example, natural rubber may be used in place of styrene butadiene rubber, which is a petroleum resource, in order to demonstrate the grip of the tire, or natural rubber or isoprene rubber may be used to improve wear resistance. Has been made. However, natural rubber, natural rubber-derived rubber, and isoprene rubber are prone to reversion during vulcanization, and also have problems such as aging due to heat and deterioration of rubber properties. Performance could not be demonstrated.

  Patent Document 1 discloses a tire rubber composition using a specific styrene butadiene rubber, but there is no idea of substituting for resources other than petroleum, and since it does not have epoxidized natural rubber, There was a problem that rolling resistance could not be reduced while maintaining dry wet grip performance and wet grip performance.

JP 2000-143877 A

  An object of the present invention is to provide a rubber composition for a tire tread having a high content ratio of non-petroleum resources that suppresses deterioration of rubber physical properties due to reversion and heat aging, and further improves fuel efficiency and wear resistance. To do.

The present invention relates to natural rubber and / or isoprene rubber, epoxidized natural rubber, sulfur and general formula (1):
R ¹ -S ₂ -AS ₂ -R ² (1)
(In the formula, A represents an alkylene group having 1 to 12 carbon atoms, and R ¹ and R ² each independently represents a monovalent organic group containing a nitrogen atom.) The present invention relates to a rubber composition for treads.

  The ratio of the sulfur content to the anti-reversion agent is preferably 0.2-5.

  According to the present invention, by incorporating an epoxidized natural rubber and an anti-reversion agent, reversion can be prevented, and at the same time, deterioration of rubber physical properties due to heat aging is suppressed, and further fuel efficiency and wear resistance are improved. A tire rubber composition for tire tread can be provided.

  The rubber composition for a tire tread of the present invention contains natural rubber and / or isoprene rubber and epoxidized natural rubber as rubber components.

  The content of natural rubber and / or isoprene rubber in the rubber component is preferably 10% by weight or more, and more preferably 20% by weight or more. If the content is less than 10% by weight, rolling resistance tends to increase and wear resistance tends to decrease. The content of natural rubber and / or isoprene rubber is preferably 70% by weight or less, and more preferably 50% by weight or less. When the content exceeds 70% by weight, it tends to be difficult to obtain sufficient dry grip performance and wet grip performance.

  The epoxidation rate of the epoxidized natural rubber is preferably 5 to 70%. If it is less than 5%, the effect of increasing the glass transition temperature is hardly obtained, and there is a tendency that the effect of improving the dry grip performance and the wet grip performance is not obtained. If it exceeds 70%, the rubber hardness is increased and natural rubber is increased. / Because compatibility with isoprene rubber is remarkably lowered, wear resistance tends to be lowered.

  As the rubber component, for example, butadiene rubber, styrene butadiene rubber, butyl rubber and the like can be used in combination with natural rubber, isoprene rubber and epoxidized natural rubber.

  The rubber composition for tire treads of the present invention contains sulfur. Sulfur is used as a vulcanizing agent.

  The sulfur content is preferably 0.3 parts by weight or more and more preferably 0.5 parts by weight or more with respect to 100 parts by weight of the rubber component. When the sulfur content is less than 0.3 parts by weight, the wear resistance tends to decrease. Further, the sulfur content is preferably 3 parts by weight or less, and more preferably 2.5 parts by weight or less. When the sulfur content exceeds 3 parts by weight, the hardness increases, and there is a tendency that sufficient grip force cannot be obtained.

The rubber composition for tire treads of the present invention contains an anti-reversion agent. Examples of the reversion inhibitor include compounds represented by the following general formula (1).
R ¹ -S ₂ -AS ₂ -R ² (1)
(In the formula, A represents an alkylene group having 1 to 12 carbon atoms, and R ¹ and R ² each independently represents a monovalent organic group containing a nitrogen atom.)

Examples of the compound represented by the general formula (1) include those represented by the general formula (2) including ═N—C (═S) — in which the carbon atoms of R ¹ and R ² are bonded to a dithio group. It is done.

(Wherein R ^{3 to} R ⁶ each independently represents an alkyl group having 1 to 12 carbon atoms, an aryl group having 6 to 9 carbon atoms or an aralkyl group having 7 to 10 carbon atoms, and n Represents an integer of 1 to 12.)

In the general formula (1), R ^{3 to} R ⁶ in the formula are preferably an aralkyl group, particularly a benzyl group, and n is 1 to 12 because the reversion preventing effect is large. preferable. Of these, 1,6-bis (N, N-dibenzylthiocarbamoyldithio) hexane is most preferably used as the reversion inhibitor.

  The content of the anti-reversion agent is preferably 0.3 parts by weight or more with respect to 100 parts by weight of the rubber component, and more preferably 0.5 parts by weight or more. If the content is less than 0.3 parts by weight, the effect of preventing reversion tends to be hardly obtained. Further, the content of the anti-reversion agent is preferably 3 parts by weight or less, and more preferably 2.5 parts by weight or less. When the content exceeds 3 parts by weight, rolling resistance tends to remarkably increase.

  The ratio of the sulfur content to the anti-reversion agent is preferably 0.2 or more, and more preferably 0.4 or more. If the content ratio is less than 0.2, the amount of monosulfur in the vulcanizate tends to decrease, and the rolling resistance tends to increase. The content ratio is preferably 5 or less, more preferably 4 or less, and even more preferably 3 or less. If the content ratio exceeds 5, the amount of monosulfur in the vulcanized product tends to decrease, rolling resistance increases, and wear resistance tends to decrease.

  In the tire tread rubber composition of the present invention, in addition to the rubber component, sulfur and anti-reversion agent, compounding agents generally used in tire rubber compositions, for example, reinforcing fillers such as carbon black and silica , Silane coupling agents, softening agents such as oil, anti-aging agents, stearic acid, zinc oxide, vulcanization accelerators, and the like can be appropriately blended.

  As the carbon black, those commonly used in the tire industry, such as ISAF and HAF, can be used.

  The compounding amount of carbon black is preferably 120 parts by weight or less with respect to 100 parts by weight of the rubber component. When the amount exceeds 120 parts by weight, the hardness increases more than necessary, and the rubber physical properties tend to be impaired.

  As silica, those prepared by a wet method or a dry method generally used in the tire industry can be used.

  The compounding amount of silica is preferably 100 parts by weight or less with respect to 100 parts by weight of the rubber component. When the amount exceeds 100 parts by weight, the hardness increases more than necessary, and the rubber physical properties tend to be impaired.

  When silica is blended, a silane coupling agent can be used in combination.

  Examples of the silane coupling agent include bis (3-triethoxysilylpropyl) disulfide, bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, and bis (2-triethoxy). Silylpropyl) tetrasulfide, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, and the like, and these can be used alone or in any combination.

  It is preferable that the compounding quantity of a silane coupling agent is 4-15 weight part with respect to 100 weight part of silica. If the blending amount is less than 4 parts by weight, the coupling effect cannot be sufficiently obtained and the wear resistance tends to be reduced. If the amount exceeds 15 parts by weight, the effect of improving the physical properties by the coupling agent is lost, and the cost is further increased. Tend.

  Examples of the vulcanization accelerator include guanidines, thioureas, thiazoles, sulfenamides, thiurams, etc., but the physical properties of the rubber composition can be improved in a balanced manner, so that guanidines and / or sulfenamides are used. Is preferred. Of these, guanidines are preferably used in combination with silica when silica is added as a reinforcing agent in order to increase the vulcanization rate.

  The blending amount of the vulcanization accelerator is preferably 0.3 to 3 parts by weight with respect to 100 parts by weight of the rubber component. If the blending amount of the vulcanization accelerator is less than 0.3 parts by weight, vulcanization tends to be remarkably delayed. If the blending amount exceeds 3 parts by weight, not only the vulcanization speed is too high, but also reversion is prevented. There is a tendency to inhibit the function of the agent.

  The rubber composition for a tire tread of the present invention is obtained by kneading the rubber component, sulfur, an anti-reversion agent, and, if necessary, a vulcanization accelerator and other compounding agents, followed by vulcanization. Can do.

  The vulcanization temperature is preferably 145 ° C or higher, and more preferably 150 ° C or higher. When the added temperature is less than 145 ° C., the effect of preventing reversion cannot be obtained, and the rolling resistance tends not to be sufficiently reduced. The vulcanization temperature is preferably 190 ° C. or lower, and more preferably 185 ° C. or lower. When the vulcanization temperature exceeds 190 ° C., the rubber decomposition reaction tends to occur, the rolling resistance increases, and the wear resistance tends to decrease.

  The vulcanization time is preferably 4 minutes or more, and more preferably 6 minutes or more. When the vulcanization time is less than 4 minutes, the vulcanization does not proceed sufficiently and the rolling resistance tends to increase. The vulcanization time is preferably 60 minutes or less, more preferably 45 minutes or less. When the vulcanization time exceeds 60 minutes, not only the productivity is lowered, but also the effect of the anti-reversion agent is insufficient and the rolling resistance tends to increase.

  The rubber composition for a tire tread of the present invention is used for a tire tread among tire members because reversion and heat aging are suppressed, rolling resistance is sufficiently reduced and wear resistance is also improved. Is done.

  The rubber composition for a tire tread of the present invention is produced into a tire by a usual method. That is, if necessary, the rubber composition for a tire tread of the present invention blended with the above-mentioned compounding agent is extruded according to the shape of the tire tread of the tire at an unvulcanized stage, and is usually used on a tire molding machine. By molding by this method, an unvulcanized tire is formed. The unvulcanized tire is heated and pressurized in a vulcanizer to obtain a tire.

  EXAMPLES The present invention will be specifically described below based on examples, but the present invention is not limited to these.

Examples 1-4 and Comparative Examples 1-5
<Description of chemicals>
Styrene butadiene rubber: NS116 manufactured by Nippon Zeon Co., Ltd.
Natural rubber: RSS # 3
Isoprene rubber: IR2200 manufactured by JSR Corporation
Epoxidized natural rubber: ENR25 manufactured by Guthrie (epoxidation rate 25%)
Carbon Black ISAF: Diamond Black I manufactured by Mitsubishi Chemical Corporation
Silica: Ultrazil VN3 manufactured by Degussa
Silane coupling agent: Si266 (bis (3-triethoxysilylpropyl) disulfide) manufactured by Degussa
Anti-aging agent: NOCRACK 6C manufactured by Ouchi Shinsei Chemical Co., Ltd.
Stearic acid: Zinc oxide manufactured by Nippon Oil & Fats Co., Ltd .: Zinc Hua 2 types manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powder sulfur vulcanization accelerator manufactured by Tsurumi Chemical Industry Co., Ltd. Noxeller NS (Nt-butyl-2-benzothiazolylsulfenamide) manufactured by
Vulcanization accelerator 2: Noxeller D (diphenylguanidine) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Reversion inhibitor: KA9188 manufactured by Bayer (1,6-bis (N, N-dibenzylthiocarbamoyldithio) hexane)

<Method for producing unvulcanized rubber sheet>
Using a 1.7 L Banbury mixer, blends other than sulfur, a vulcanization accelerator, and a reversion inhibitor were kneaded in the blend amounts shown in Table 1 to obtain a kneaded product. And each unvulcanized rubber sheet was obtained by knead | mixing the kneaded material, the sulfur of a compounding quantity shown in Table 1, a vulcanization accelerator, and a reversion inhibitor with a roll.

(Reversion test)
Using a curast meter, the vulcanization curve of the unvulcanized rubber sheet at 170 ° C. was measured. Assuming that the maximum torque (MH) value was 100, the torque value 15 minutes after the time when MH was indicated was shown as a relative value, and the value obtained by subtracting the relative value from 100 was taken as the reversion rate. The smaller the reversion rate, the better the reversion is suppressed.

<Manufacture of vulcanized samples>
The unvulcanized rubber sheet obtained by the above production method was vulcanized at 170 ° C. for 10 minutes to prepare a vulcanized sample, which was used in the following tests.

(Heat aging test)
According to JIS K6251, the rupture strength (Tb) and elongation at break (Eb) of the vulcanized sample were measured. Next, Tb and Eb of the sample obtained by heat aging the sample for 72 hours at 100 ° C. were measured. And Tb change rate (%) and Eb change rate (%) were computed from the measured value of the sample after aging with respect to the measured value of the sample before aging, respectively. The larger the change rate, the smaller the rubber property change due to heat aging.

(Rolling resistance test)
Using a spectrometer manufactured by Ueshima Seisakusho, tan δ of the vulcanized sample was measured under the conditions of dynamic strain amplitude ± 2%, frequency 10 Hz, and temperature 70 ° C. Indicated by value. A smaller relative value indicates a lower rolling resistance and better fuel efficiency.

(Abrasion test)
Using a Lambourn abrasion tester, the abrasion weight was measured after wearing for 3 minutes at a load of 2.5 kgf and a slip rate of 40%. The wear weight was converted from the specific gravity into a wear volume (hereinafter referred to as wear amount). And the value of the comparative example 2 was set to 100, and each was displayed by the relative value. The larger the relative value, the smaller the amount of wear and the better the wear resistance.

  The results are shown in Table 1.

  From the results of Table 1, not only reversion is remarkably suppressed by blending epoxidized natural rubber and 1,6-bis (N, N-dibenzylthiocarbamoyldithio) hexane, but also physical properties of rubber due to heat aging. It is possible to suppress the deterioration of the fuel consumption and further improve the fuel efficiency and wear resistance.

Claims (2)

For rubber components consisting only of natural rubber and / or isoprene rubber and epoxidized natural rubber, sulfur and general formula (1):
R ¹ -S ₂ -AS ₂ -R ² (1)
(In the formula, A represents an alkylene group having 1 to 12 carbon atoms, and R ¹ and R ² each independently represents a monovalent organic group containing a nitrogen atom.)
Ri Do from anti-reversion agents expressed in,
A rubber composition for a tire tread , wherein the content of natural rubber and / or isoprene rubber in the rubber component is 10 to 50% by weight and the content of epoxidized natural rubber is 50 to 90% by weight . The rubber composition for a tire tread according to claim 1, wherein the ratio of the sulfur content to the anti-reversion agent is 0.2 to 5.