JP6933042B2 - Rubber composition for side tread - Google Patents

Description

The present invention relates to a rubber composition for a side tread containing a natural rubber, an isoprene rubber, and / or a butadiene rubber.

When vulcanizing pneumatic tires, it is ideal to properly vulcanize all components. However, the heat history given at the time of vulcanization differs for each member depending on the tire size, the gauge of each component, the distance from the heat source, the vertical position in the mold, etc., so that the degree of vulcanization of each member is made uniform. It is difficult to set vulcanization conditions. In general, since the vulcanization conditions are adjusted to the part having the largest required heat history, some members are in a supervulcanized state. In particular, the rubber member constituting the side tread tends to be overvulcanized during vulcanization.

When a member formed of a rubber composition containing natural rubber, isoprene rubber, and / or butadiene rubber is in a supervulcanized state, its physical properties may deteriorate due to reversion (return to vulcanization), resulting in deterioration of tire characteristics. There is. The rubber composition containing these rubber components has a problem that the mechanical properties such as modulus, strength, and hardness are deteriorated because the crosslinked form is changed to a bond such as thiophene and mercaptan which is not involved in crosslinks by reversion. On the other hand, it is known that a rubber composition made of styrene-butadiene rubber is less likely to deteriorate in physical properties due to reversion because it forms a cross-linking point with styrene-butadiene rubber again even if the cross-linking point is cut by reversion. There is.

Patent Document 1 proposes the addition of a bismaleimide-based compound as a vulcanization reversion inhibitor. However, when a bismaleimide-based compound is added, there is a problem that the viscosity of the rubber composition increases and the processability deteriorates. Further, in the rubber composition preparation line, there is a problem that the production efficiency is lowered due to the new installation and improvement of the compounding agent measuring equipment and the deterioration of the measuring cycle.

Japanese Unexamined Patent Publication No. 2005-42076

An object of the present invention is to provide a rubber composition for a side tread containing natural rubber, isoprene rubber, and / or butadiene rubber while suppressing reversion.

The rubber composition for a side tread of the present invention that achieves the above object contains S part by mass of sulfur with respect to 100 parts by mass of a diene rubber containing at least 30% by mass or more of at least one selected from natural rubber, isoprene rubber and butadiene rubber. A rubber composition for side tread containing A parts by mass of a vulcanization accelerator, wherein the ratio (A / S) of the amount of the vulcanization accelerator to the amount of the sulfur is in the range of 6 to 12. It is characterized by being.

In the rubber composition for side tread of the present invention, the compounding amount ratio (A / S) of the vulcanization accelerator to sulfur was set in the range of 6 to 12, and therefore, a rubber component selected from natural rubber, isoprene rubber and butadiene rubber. Even if it contains, the reversal can be suppressed.

As the vulcanization accelerator, a sulfenamide-based vulcanization accelerator is preferable. Further, 30 to 60 parts by mass of carbon black can be blended with respect to 100 parts by mass of the diene rubber. Further, the ratio (A / S) of the blending amount of the vulcanization accelerator to the blending amount of sulfur is preferably in the range of 4 to 12.

The rubber composition for a side tread of the present invention contains at least one selected from natural rubber, isoprene rubber and butadiene rubber, and the content thereof is 50% by mass or more, preferably 70 to 100% by mass, based on 100% by mass of the diene rubber. It is mass%. The natural rubber, isoprene rubber, and butadiene rubber may each contain 30% by mass or more individually, or the total of two or more selected from these may be 30% by mass or more. When at least one selected from natural rubber, isoprene rubber, and butadiene rubber is 30% by mass or more, the rubber strength, abrasion resistance, bending fatigue resistance, and the like of the rubber composition can be improved.

The rubber composition for the side tread can include other diene-based rubbers other than natural rubber, isoprene rubber and butadiene rubber. Examples of other diene-based rubbers include styrene-butadiene rubber, styrene-isoprene rubber, styrene-isoprene-butadiene rubber, and acrylonitrile-butadiene rubber. Natural rubber, isoprene rubber, butadiene rubber and other diene rubbers have an epoxy group, a carboxy group, an amino group, a hydroxy group, an alkoxy group, a silyl group, an amide group, etc. at the end and / or side chain of the molecular chain. It may be a modified modified diene rubber.

The other diene-based rubber is 70% by mass or less, preferably 0 to 30% by mass, based on 100% by mass of the diene-based rubber. If the content of the other diene-based rubber exceeds 70% by mass, the rubber composition for side tread is less likely to be reversion, and the problem of the present invention does not exist. In particular, a rubber composition containing styrene-butadiene rubber as a main component (50% by mass or more in 100% by mass of diene-based rubber) is unlikely to undergo reversion.

The rubber composition for a side tread of the present invention comprises the above-mentioned diene-based rubber mixed with sulfur and a vulcanization accelerator. Here, when the blending amount of sulfur with respect to 100 parts by mass of the diene rubber is S by mass and the blending amount of the vulcanization accelerator is A by mass, the blending amount of the vulcanization accelerator with respect to the sulfur blending amount (S) ( The ratio (A / S) of A) is 1 or more, preferably 4 to 12, and more preferably 6 to 12. If the ratio (A / S) of the blending amounts of the vulcanization accelerator and sulfur is less than 1, the reversion cannot be sufficiently suppressed.

As the sulfur, sulfur that is usually blended in a rubber composition for a tire can be used. The vulcanization accelerator is not particularly limited, but is preferably a sulfenamide-based vulcanization accelerator, and reversion can be suppressed more efficiently. Examples of the sulfenamide-based vulcanization accelerator include N-cyclohexyl-2-benzothiazolyl sulfenamide, N-oxydiethylene-2-benzothiazolesulfenamide, and N- (tert-butyl) -2-benzothiazole. Sulfenamide and the like can be exemplified. Of these, N-cyclohexyl-2-benzothiazolesulfenamide is preferable.

The rubber composition for side tread of the present invention can contain carbon black. The blending amount of carbon black is preferably 20 to 60 parts by mass, more preferably 30 to 60 parts by mass, and further preferably 30 to 50 parts by mass with respect to 100 parts by mass of the diene rubber. The mechanical properties of the rubber composition can be improved by adding 20 parts by mass or more of carbon black and silica. Further, by setting the blending amount of carbon black and silica to 60 parts by mass or less, the heat generation property of the rubber composition can be reduced and the bending fatigue resistance can be improved. In addition, it is possible to suppress an increase in weight when the tire is used. Further, the rubber composition for side tread may contain an inorganic filler other than carbon black.

In the present invention, examples of carbon black include furnace carbon blacks such as SAF, ISAF, HAF, FEF, GPF, HMF, and SRF, and these may be used alone or in combination of two or more. Nitrogen adsorption specific surface area of carbon black is not particularly limited, preferably the 30 to 150 m ² / g, more preferably 30~95m ² / g, more preferably is 30 to 50 m ² / g .. By setting the nitrogen adsorption specific surface area of carbon black to 30 m ² / g or more, the mechanical properties of the rubber composition can be ensured. Further, by setting the nitrogen adsorption specific surface area of carbon black to 150 m ² / g or less, wear resistance and bending fatigue resistance can be improved. In the present specification, the nitrogen adsorption specific surface area of carbon black shall be measured in accordance with JIS K6217-2.

The rubber composition for side tread of the present invention can be used as a rubber composition for side tread such as a vulcanization or cross-linking agent, a vulcanization accelerator, an antiaging agent, a plasticizer, a processing aid, a terpene resin, or a thermosetting resin. Various commonly used additives can be blended within a range that does not impair the object of the present invention. Further, such an additive 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 side tread 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 side tread of the present invention is suitable for forming a side tread of a pneumatic tire. The pneumatic tire using the rubber composition for side tread of the present invention can be stably produced with excellent quality.
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.

Six types of rubber compositions for side tread (Examples 1 to 5, Comparative Example 1) having the common composition of the rubber compositions for side tread shown in Table 2 and blending the raw materials shown in Table 1 were prepared. The components excluding sulfur and the vulcanization accelerator were kneaded with a 1.7 L rubber tread mixer for 5 minutes, released when the temperature reached 145 ° C, and cooled to prepare 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 6 types of rubber compositions for side tread. In Table 1, the ratio (A / S) of the sulfur compounding amount (S mass part) to the vulcanization accelerator compounding amount (A mass part) was calculated and entered in the "blending ratio (A / S)" column. Described. The blending amount of each additive shown in Table 2 is expressed as a mass part with respect to 100 parts by mass of the diene rubber shown in Table 1.

The obtained rubber composition for side tread was vulcanized at 180 ° C. for 5 minutes (appropriate vulcanization) using a mold having a predetermined shape (inner dimensions; length 150 mm, width 150 mm, thickness 2 mm), and 10 Vulcanization molding was performed under two conditions of minute vulcanization (supervulcanization) to prepare a sample (vulcanized rubber test piece) of a rubber composition for side tread. Using the obtained vulcanized rubber test piece, 100% tensile stress and tan δ at 60 ° C. were measured by the test method shown below.

A dumbbell JIS No. 3 test piece was prepared in accordance with JIS K6251 using a vulcanized rubber test piece obtained by vulcanization at 100% tensile stress at 180 ° C. for 5 minutes and vulcanization for 10 minutes. Using the obtained test piece, a tensile test was conducted at room temperature (23 ° C.) at a tensile speed of 500 mm / min, and 100% tensile stress at 100% elongation was measured. The results obtained are for each test obtained by vulcanization (supervulcanization) at 180 ° C. for 10 minutes with respect to 100% tensile stress of each test piece obtained by vulcanization at 180 ° C. for 5 minutes (appropriate vulcanization). The ratio of 100% tensile stress of the piece was calculated as "retention rate of 100% tensile stress". This is because in the rubber compositions for side tread of Examples 1 to 5, vulcanization at 180 ° C. for 5 minutes is close to the proper vulcanization conditions. Vulcanization at 180 ° C. for 10 minutes is regarded as a supervulcanized state, and each vulcanization return is evaluated by the retention rate of 100% tensile stress. The closer the retention rate of 100% tensile stress is to 100%, the more the vulcanization reversion is suppressed.

60 ° C tan δ
Using a vulcanized rubber test piece obtained by vulcanization at 180 ° C. for 5 minutes and vulcanization for 10 minutes, an initial strain of 10 was used using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho Co., Ltd. in accordance with JIS K6394. The loss vulcanization tan δ at a temperature of 60 ° C. was measured under the conditions of%, amplitude ± 2%, and frequency 20 Hz. The smaller the value of tan δ (60 ° C.), the smaller the heat generation, which means that the tire has low rolling resistance. Further, when vulcanization returns, the value of tan δ (60 ° C.) increases and the heat generation property increases. Therefore, the result obtained was tan δ (60 ° C.) of each test piece obtained by vulcanization at 180 ° C. for 5 minutes, as opposed to tan δ (60 ° C.) of each test piece obtained by vulcanization at 180 ° C. for 10 minutes. The ratio of tan δ (60 ° C.) was calculated as “retention rate of tan δ (60 ° C.)”. This is because in the rubber compositions for side tread of Examples 1 to 5, vulcanization at 180 ° C. for 5 minutes is close to the proper vulcanization conditions. Vulcanization at 180 ° C. for 10 minutes is regarded as a supervulcanized state, and each vulcanization return is evaluated by the retention rate of tan δ (60 ° C.). The closer the retention rate of tan δ (60 ° C.) is to 100%, the more the vulcanization reversion is suppressed.

The types of raw materials used in Table 1 are shown below.
・ NR: Natural rubber, RSS # 3
-BR: Butadiene rubber, Nippon Zeon Co., Ltd. Nipol BR1220
-Carbon black: Soft grade carbon black, Tokai Carbon's Seast F, nitrogen adsorption specific surface area 42 cm ² / g
-Sulfur: Hosoi Chemical Industry Co., Ltd. Oil-treated sulfur, sulfur content is about 95% by mass
-Vulcanization accelerator: Noxeller CZ-G (CBS) manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.

The types of raw materials used in Table 2 are shown below.
・ Zinc oxide: Zinc oxide 3 types manufactured by Shodo Chemical Industry Co., Ltd. ・ Stearic acid: Bead stearic acid YR manufactured by NOF CORPORATION
-Anti-aging agent: DUTSCHLAND GMBH VULKANOX 4020 manufactured by LANXESS
-Wax: OZOACE-0015A manufactured by Nippon Seiro Co., Ltd.
・ Softener: Showa Shell Sekiyu Extract No. 4 S

As is clear from Table 1, it was confirmed that the rubber compositions for side treads of Examples 1 to 5 had a retention rate of 100 tensile stress and tan δ (60 ° C.) close to 100%, and reversion was suppressed. rice field.

In the rubber composition for side tread of Comparative Example 1, since the ratio (A / S) of the compounding amount (A) of the vulcanization accelerator to the compounding amount (S) of sulfur is less than 1, 100 tensile stress and tan δ ( 60 ° C.) is inferior.

Claims (4)

Rubber composition for side tread in which S part by mass of sulfur and A part by mass of vulcanization accelerator are mixed with 100 parts by mass of diene rubber containing at least 30% by mass or more of at least one selected from natural rubber, isoprene rubber and butadiene rubber. A rubber composition for a side tread, wherein the ratio (A / S) of the blending amount of the vulcanization accelerator to the blending amount of the sulfur is in the range of 6 to 12. The rubber composition for a side tread according to claim 1, wherein the ratio (A / S) of the blending amount of the vulcanization accelerator to the blending amount of sulfur is in the range of 8 to 12. The rubber composition for a side tread according to claim 1 or 2 , wherein the vulcanization accelerator is a sulfenamide-based vulcanization accelerator. The rubber composition for a side tread according to any one of claims 1 to 3, wherein 30 to 60 parts by mass of carbon black is blended with respect to 100 parts by mass of the diene rubber.