JP4583023B2 - Rubber composition for tire sidewall - Google Patents

Description

  The present invention relates to a rubber composition for a tire sidewall and a pneumatic tire using the same.

  Conventionally, rubber for tire sidewall has been composed of rubber (highly unsaturated rubber) having a high double bond content such as natural rubber, isoprene rubber, butadiene rubber and the like. However, since these highly unsaturated rubbers have a double bond in the main chain, they have low ozone resistance, heat resistance, etc., and cracks may occur due to long-term storage and use. For this reason, attempts have been made to improve crack resistance by adding amine-based anti-aging agents or waxes, but the decomposition products and waxes of the added amine-based anti-aging agents are deposited on the tire surface. There was a problem of changing the tire color to reddish brown or white.

  As means for solving the above problem, it has been proposed to use rubber having good weather resistance such as ethylene propylene diene rubber (EPDM) (see Patent Document 1). However, since EPDM has an ethylene segment, when it is cooled after the temperature rises to near 100 ° C. during use of the tire, the ethylene segment causes crystallization, and this crystal starts as a crack. There was a problem.

  Further, a method has been proposed in which a specific amount of bromobutyl rubber is blended and no antioxidant or wax is blended, but there is a problem that crack resistance and the like are not sufficient.

JP-A-8-231773

  An object of the present invention is to provide a rubber composition for a tire sidewall that greatly reduces energy loss and is excellent in weather resistance, discoloration resistance and crack resistance, and a pneumatic tire using the rubber composition.

The present invention includes polybutadiene rubber having —S— (S) _n — crosslinks (where n is an integer of 1 to 7), and further includes natural rubber, polyisoprene rubber, polybutadiene rubber, and styrene butadiene rubber. It relates to a rubber composition for a tire sidewall containing at least one diene rubber selected from the group consisting of

In addition, the present invention includes a polybutadiene rubber having a —S— (S) _n — crosslink (where n is an integer of 1 to 7), and further a bromobutyl rubber or a carbon number of 4 to 7 The present invention relates to a rubber composition for tire sidewalls containing a halide of a copolymer of isomonoolefin and paraalkylstyrene.

  Furthermore, the present invention relates to a pneumatic tire having a two-layer structure comprising an inner layer rubber adjacent to a carcass and an outer layer rubber outside the carcass, and the outer layer rubber comprising the rubber composition for a tire sidewall.

  ADVANTAGE OF THE INVENTION According to this invention, energy loss can be reduced significantly and the rubber composition for tire sidewalls which are excellent in a weather resistance, discoloration resistance, and crack resistance, and a pneumatic tire using the same can be provided.

The first rubber composition for a tire sidewall according to the present invention comprises a polybutadiene rubber (sulfur-containing BR) having a —S— (S) _n — crosslink (where n is an integer of 1 to 7). And at least one diene rubber selected from natural rubber (NR), polyisoprene rubber (IR), polybutadiene rubber (BR) and styrene butadiene rubber (SBR).

In the cross-linked bond —S— (S) _n — that BR has, n is an integer of 1 to 7. If n is less than 1, the C—S dissociation energy of the cross-linking bond is too large, and the reactivity of the sulfur-containing BR decreases. When n exceeds 7, it becomes easy to return to vulcanization, or during the vulcanization, the rubber composition is markedly cured over time.

The —S— (S) _n — crosslink of the sulfur-containing BR is introduced between the polymer chains by reacting a sulfurizing agent such as sulfur dichloride with polybutadiene. For example, a sulfurizing agent and BR can be reacted at the final stage of the BR polymerization reaction or by adding a sulfurizing agent after the polymerization reaction to introduce —S— (S) _n — crosslinks. -S- (S) _n- crosslinks are introduced, so that some vulcanization (self-dynamic vulcanization) occurs during kneading with other rubber components, and compatibility with other rubbers. And BR is finely dispersed. Here, the self-dynamic vulcanization refers to vulcanization that occurs without adding a vulcanizing agent separately. The fuel consumption of a tire using the rubber composition of the present invention as a sidewall is improved, and at the same time, the wear resistance is improved.

  The sulfur content of the sulfur-containing BR is preferably 0.001 to 5% by weight in the polybutadiene rubber. If it is less than 0.001% by weight, there is a tendency that the effect of improving fuel efficiency is not observed. On the other hand, if it exceeds 5% by weight, the tendency to burn rubber during kneading increases.

  The lower limit of the content of sulfur-containing BR in the first rubber composition for a tire sidewall of the present invention is preferably 10% by weight in the total rubber component comprising sulfur-containing BR and other rubber components, More preferably, it is% by weight. Moreover, about the upper limit of content, it is preferable that it is 80 weight%, and it is more preferable that it is 70 weight%. If it is less than 10% by weight, the amount of sulfur-containing BR tends to be too small, and the bending fatigue resistance tends to decrease. Moreover, when it exceeds 80 weight%, there exists a tendency for the amount of sulfur containing BR to increase too much and for workability to fall.

  The rubber composition for tire sidewall of the present invention is at least one selected from natural rubber (NR), polyisoprene rubber (IR), polybutadiene rubber (BR) and styrene butadiene rubber (SBR) together with sulfur-containing BR. Of diene rubber. Among them, it is preferable to contain NR, IR and BR because of high compatibility with sulfur-containing BR.

  The second rubber composition for a tire sidewall according to the present invention is a halogenated compound (halogenated PMS) of bromobutyl rubber or a copolymer of isomonoolefin having 4 to 7 carbon atoms and paraalkylstyrene together with sulfur-containing BR. Modified rubber).

  As the sulfur-containing BR, the same one as described in the first rubber composition for a tire sidewall is used.

  The lower limit of the content of sulfur-containing BR in the second tire sidewall rubber composition of the present invention is preferably 20% by weight in the total rubber component comprising sulfur-containing BR and other rubber components, 25 More preferably, it is% by weight. Moreover, about the upper limit of content, it is preferable that it is 60 weight%, and it is more preferable that it is 55 weight%. If it is less than 20% by weight, the amount of sulfur-containing BR tends to be too small, and the bending fatigue resistance tends to decrease. On the other hand, when the amount exceeds 60% by weight, the amount of sulfur-containing BR is excessively increased, and the content of bromobutyl rubber or halogenated PMS-modified rubber is relatively small, being 15% by weight or less, and the weather resistance tends to decrease. is there.

  In the halogenated PMS-modified rubber, for example, part or all of hydrogen may be substituted with the halogen by bromine, chlorine, or the like.

  The content of bromobutyl rubber or halogenated PMS-modified rubber is preferably 15 to 50% by weight in the rubber component. About the minimum of content, it is more preferable that it is 20 weight%. Further, the upper limit of the content is more preferably 40% by weight. If it is less than 15% by weight, the weather resistance tends to decrease unless an antioxidant is blended. On the other hand, when the amount exceeds 50% by weight, the adhesiveness to other tire members tends to decrease when the rubber composition is used for the sidewall.

  Moreover, the rubber composition for a tire sidewall of the present invention can contain a filler such as carbon black in addition to the rubber component. The compounding amount of carbon black is preferably 15 to 80 parts by weight with respect to 100 parts by weight of the rubber component. If it is less than 15 parts by weight, the rubber tends not to be sufficiently reinforced. Moreover, when it exceeds 80 weight part, there exists a tendency for the obtained rubber component to become hard too much.

  In addition to the rubber component and filler, the rubber composition of the present invention includes various rubber softeners, waxes, anti-aging agents, metal oxides, stearic acid, zinc oxide, vulcanizing agents, vulcanization accelerators, and the like. Various additives usually used in the rubber industry can be blended.

  A rubber composition containing a rubber component consisting only of sulfur-containing BR and a diene rubber is added to the kneaded product obtained in the first step and the first step in which the raw materials other than the vulcanizing agent and the vulcanization accelerator are kneaded. It is preferably obtained through a second step of adding and kneading the sulfurizing agent and a vulcanization accelerator and a third step of vulcanizing the obtained kneaded product, and zinc oxide is added in the first step. On the other hand, when bromobutyl rubber or halogenated PMS modified rubber is contained as a rubber component, zinc oxide is preferably blended in the second step, and may be blended in both the first step and the second step. More preferred. By blending in the second step, or both the first step and the second step, self-dynamic vulcanization occurs, the rubber is finely dispersed, and the fuel efficiency characteristics are improved.

  Further, when bromobutyl rubber or halogenated PMS modified rubber is contained as a rubber component, it is preferable not to add a wax, an antioxidant, and stearic acid to the rubber composition. The effect of preventing discoloration of rubber is obtained by not blending.

  The pneumatic tire of the present invention is a tire sidewall having a two-layer structure comprising an inner layer rubber adjacent to a carcass and an outer layer rubber outside the carcass, and the outer layer rubber is made of the rubber composition for a tire sidewall.

  It is preferable that the sidewall rubber 5 has a two-layer structure including an inner layer rubber 6 adjacent to the carcass 2 and an outer layer rubber 7 disposed on the outer side thereof (FIG. 1). By having a two-layer structure, the crack resistance is improved and the cost is reduced.

  The rubber composition of the present invention is used for tire sidewalls, and particularly preferably used as the outer layer rubber 7 of the pneumatic tire.

  Specific examples and comparative examples of the present invention are shown below, but the present invention is not limited thereto.

The materials used in the examples and comparative examples will be described together below.
NR: RSS # 3
BR1: UBEPOL BR150B manufactured by Ube Industries, Ltd.
BR2: Nipol 1220 manufactured by Nippon Zeon Co., Ltd.
Sulfur-containing BR: BUNA CB24 manufactured by Bayer (containing -S- (S) n- cross-linked bond (n = 1))
Halogenated PMS modified rubber: EXXPRO90-10 (halogenated rubber of copolymer of isomonoolefin having 4 to 7 carbon atoms and paraalkylstyrene) manufactured by Exxon Chemical Co., Ltd.
Bromobutyl rubber: PolyBB 2040 manufactured by Bayer
Carbon black: Seest SO manufactured by Tokai Carbon Co., Ltd.
Process oil: Dynaprocess oil PW32 made by Idemitsu Kosan Co., Ltd.
Wax: Sunnock anti-aging agent manufactured by Ouchi Shinsei Chemical Co., Ltd .: Nocrack 6C manufactured by Ouchi Shinsei Chemical Co., Ltd.
Stearic acid: Nippon Oil & Fats Co., Ltd. Zinc oxide: Mitsui Mining & Mining Co., Ltd. Zinc Hua 2 types sulfur: Tsurumi Chemical Co., Ltd. powder sulfur vulcanization accelerator 1: Ouchi Shinsei Chemical Industry Noxeller NS
Vulcanization accelerator 2: Noxeller DM manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

Test method (rolling resistance)
Using a spectrometer manufactured by Ueshima Seisakusho, tan δ was measured under the conditions of dynamic strain amplitude ± 2%, frequency 10 Hz, and temperature 70 ° C. The numerical value of the comparative example was set to 100, and the relative value was shown. It shows that rolling resistance is so low that a numerical value is small and it is favorable.

(Ozone resistance 1)
An exposure test was conducted at a temperature of 40 ° C., an ozone concentration of 50 pphm, an elongation rate of 20%, and a 48 hour period to determine the cracking state of the specimen. Determination of the crack state of the test piece was determined according to JIS K6259.

(Ozone resistance 2)
The crack state of the test piece was determined under the same conditions as ozone resistance 1 except that the elongation rate was 50% and the exposure test time was 96 hours.

(Bend fatigue resistance 1)
A sample for a dematcher bending crack growth test in which a 2 mm cut was made in the test piece was set in a testing machine, and the crack growth length (mm) after bending fatigue was repeated 500,000 times in accordance with JIS K6260. The ambient temperature was room temperature.

(Bending fatigue resistance 2)
The crack growth length was measured under the same conditions as in bending fatigue resistance 1, except that the ambient temperature was 80 ° C.

(Appearance discoloration)
The specimens were exposed outdoors to avoid rainwater. The color change state after 30 days of exposure was visually evaluated in five levels, and the color change was larger and the value closer to 1 was indicated.

Example 1 and Comparative Example 1
In accordance with the formulation shown in Table 1, in the first kneading step, other than sulfur and the vulcanization accelerator 1 are kneaded in a Banbury mixer, and then in the second kneading step, sulfur and the vulcanization accelerator 1 are used in a roll. Kneaded. In the first kneading step, the rubber temperature at the time of discharge was 150 ° C. The resulting kneaded product was vulcanized at 170 ° C. for 15 minutes to prepare rubber compositions of Example 1 and Comparative Example 1.

  The obtained rubber composition was used for tests of rolling resistance, ozone resistance 1 and bending fatigue resistance. The evaluation results are shown in Table 1.

  From Example 1 and Comparative Example 1, it can be seen that the rolling resistance can be significantly reduced by blending the sulfur-containing BR without lowering the bending fatigue resistance and ozone resistance.

Examples 2-4 and Comparative Examples 2-3
In accordance with the formulation shown in Table 2, in the first kneading step, other than sulfur, vulcanization accelerator 2 and zinc oxide are kneaded in a Banbury mixer, and then in the second kneading step, sulfur and vulcanized in a roll. The accelerator 2 and zinc oxide were kneaded (rubber temperature at the time of discharging the first kneading step: 142 ° C.), and the obtained kneaded product was prepared by vulcanization at 170 ° C. for 15 minutes. In Comparative Example 2, zinc oxide was kneaded only in the first kneading step (rubber temperature at the time of discharging the first kneading step: 155 ° C.). In Example 4, both the first and second kneading steps were used. Was kneaded with zinc oxide (rubber temperature at discharge of the first kneading step: 143 ° C.).

  The obtained rubber composition was used for tests of ozone resistance 2, bending fatigue resistance and appearance discoloration. The evaluation results are shown in Table 2.

Test results From comparison between Comparative Example 3 and Example 2, it was found that flex resistance was improved by blending sulfur-containing BR. In addition, it was confirmed that this effect can be obtained with both halogenated PMS-modified rubber and bromobutyl rubber. Furthermore, from Example 4 , it was found that the bending resistance was further improved by dividing and kneading zinc oxide twice.

It is a general | schematic fragmentary sectional view of the pneumatic tire of this invention.

Explanation of symbols

1 Bead core 2 Toroidal carcass 3 Belt layer 4 Tread 5 Side wall rubber 6 Inner layer rubber 7 Outer layer rubber 8 Crown

Claims (3)

-S- (S) _n - (wherein, n is an integer of 1 to 7) of the cross-linking include polybutadiene rubber having further containing natural rubber, carbon black, 100 parts by weight of the rubber component against it, a rubber composition for a tire sidewall you containing 15 to 80 parts by weight. Including polybutadiene rubber having a cross-linking of —S— (S) _n — (wherein n is an integer of 1 to 7), bromobutyl rubber, or isomonoolefin having 4 to 7 carbon atoms and paraalkyl A rubber composition for a tire sidewall, comprising a halide of a copolymer with styrene. 3. A tire sidewall having a two-layer structure comprising an inner layer rubber adjacent to a carcass and an outer layer rubber outside the carcass, wherein the outer layer rubber comprises the rubber composition for a tire sidewall according to claim 1 or 2.

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