JP6094084B2 - Rubber composition for tire - Google Patents

Description

  The present invention relates to a rubber composition for tires that contains natural rubber and / or isoprene rubber and suppresses reversion during high-temperature vulcanization and improves processability.

  Generally, a rubber composition containing natural rubber or isoprene rubber is used for a structural member of a pneumatic tire. When natural rubber and isoprene rubber are vulcanized at a high temperature, reversion (reversion to vulcanization) occurs, such as thiophene, mercaptan, etc., which changes to bonds not involved in crosslinking. For this reason, there has been a problem that mechanical properties such as modulus, strength and hardness of a rubber composition containing natural rubber and isoprene rubber are lowered.

  As a countermeasure, Patent Document 1 proposes adding a bismaleimide compound as a vulcanization reversion inhibitor. However, when a bismaleimide compound is added, there is a problem that the viscosity of the rubber composition increases and the processability deteriorates.

JP 2005-42076 A

  An object of the present invention is to provide a rubber composition for tires that contains natural rubber and / or isoprene rubber and suppresses reversion during high temperature vulcanization and improves processability.

The rubber composition for tires of the present invention that achieves the above-mentioned object comprises 0.5 to 5 parts by weight of bismaleimide or acrylate and 15 parts by weight of zinc with respect to 100 parts by weight of diene rubber containing natural rubber and / or isoprene rubber. 1 to 5 parts by weight of a carboxylic acid zinc salt containing at least% aromatic carboxylic acid zinc salt is characterized.

The rubber composition for tires of the present invention is prepared by blending 0.5 to 5 parts by weight of bismaleimide or acrylate with respect to 100 parts by weight of diene rubber containing natural rubber and / or isoprene rubber. While suppressing 1-5 weight part of carboxylic acid zinc salt containing the aromatic carboxylic acid zinc salt of 15 weight% or more of zinc amount, the viscosity of a rubber composition can be made small and workability can be improved.

  The content of the natural rubber and / or isoprene rubber is preferably 50% by weight or more in 100% by weight of the diene rubber, and the mechanical properties such as the modulus, strength, and hardness of the tire rubber composition are made higher. Can do.

  A pneumatic tire using this tire rubber composition as at least one member selected from a run-flat liner, a belt layer, a bead filler, and a side rubber has excellent productivity and excellent tire durability.

  The rubber composition for tires of the present invention uses a diene rubber containing natural rubber and / or isoprene rubber as a rubber component. Preferably, natural rubber and / or isoprene rubber is the main component, and mechanical properties such as modulus, strength and hardness of the rubber composition can be enhanced.

  The content of the natural rubber and / or isoprene rubber is preferably 50% by weight or more, more preferably 90 to 100% by weight in 100% by weight of the diene rubber. If the content of natural rubber and isoprene rubber is less than 50% by weight, the mechanical properties such as modulus, strength, and hardness of the rubber composition may not be sufficiently increased.

  Examples of diene rubbers other than natural rubber and isoprene rubber include butadiene rubber, styrene butadiene rubber, acrylonitrile butadiene rubber, and butyl rubber. Of these, butadiene rubber and styrene butadiene rubber are preferable. These diene rubbers other than natural rubber and isoprene rubber can be used alone or in combination of two or more.

The rubber composition for tires of the present invention suppresses reversion when natural rubber and isoprene rubber are vulcanized at high temperature by blending bismaleimide or acrylate. The effect of suppressing reversion during high-temperature vulcanization is that the modulus when the rubber composition is vulcanized at a high temperature (for example, 170 ° C. or higher) relative to the modulus when the rubber composition is vulcanized at a low temperature (for example, 150 ° C. or lower). This can be confirmed by reducing the decrease rate.

  In the present invention, as the bismaleimide, those usually used in tire rubber compositions can be used. Suitable bismaleimides include, for example, N, N′-1,2-phenylene bismaleimide, N, N′-1,3-phenylene bismaleimide, N, N′-1,4-phenylene bismaleimide, N, N '-(4,4'-diphenylmethane) bismaleimide, 2,2-bis [4- (4-maleimidophenoxy) phenyl] propane, bis (3-ethyl-5-methyl-4-maleimidophenyl] methane, 1, Examples thereof include 3-bis (citraconimidomethyl) benzene, etc. Among them, 1,3-bis (citraconimidomethyl) benzene is preferable.

  In the present invention, as the acrylate, those usually used in rubber compositions for tires can be used. As a suitable acrylate, the number of acroyl groups in one molecule is preferably 2 or more, more preferably 3 or more. If the number of acryloyl groups in one acrylate molecule is less than 2, the effect of suppressing reversion during high-temperature vulcanization may not be sufficiently obtained. Examples of the acrylate include 1,3-butylene glycol diacrylate, 1,5-pentanediol diacrylate, neopentyl glycol diacrylate, 1,6-hexanediol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, and tetraethylene. Glycol diacrylate Polyethylene glycol diacrylate, polypropylene glycol diacrylate, bis (4-acryloxy) polyethoxyphenylpropane oligoester diacrylate, pentaerythritol triacrylate, trimethylolpropane triacrylate, tetramethylolmethane tetraacrylate, dipentaerythritol hexaacrylate Dipentaerythritol pentaacrylate, It can be exemplified soybean ester polyacrylate. Of these, trimethylolpropane triacrylate is preferable.

The amount of bismaleimide or acrylate is 0.5 to 5 parts by weight, preferably 1.0 to 4.0 parts by weight, per 100 parts by weight of the diene rubber. If the blending amount of bismaleimide and acrylate is less than 0.5 parts by weight, the effect of suppressing reversion cannot be sufficiently obtained. Also, the modulus during high temperature vulcanization is inferior. If the amount of acrylate exceeds 5 parts by weight, the viscosity of the rubber composition increases and the processability deteriorates.

  The rubber composition for tires of the present invention is blended with an aromatic carboxylic acid zinc salt to reduce the viscosity of the rubber composition and improve processability. Further, the exothermic property (tan δ at 60 ° C.) of the vulcanized product obtained by vulcanizing the rubber composition at a high temperature can be reduced. Furthermore, the mechanical properties of the rubber composition such as modulus, strength, and hardness can be improved by blending zinc aromatic carboxylate. The compounding amount of the aromatic carboxylic acid zinc salt is 1 to 5 parts by weight, preferably 1.5 to 4.0 parts by weight, per 100 parts by weight of the diene rubber. If the amount of the aromatic carboxylic acid zinc salt is less than 1 part by weight, the effect of reducing the viscosity of the rubber composition cannot be obtained. On the other hand, when the blending amount of the aromatic carboxylic acid zinc salt exceeds 5 parts by weight, the exothermic property (tan δ at 60 ° C.) of the vulcanized product vulcanized at high temperature deteriorates.

  In the present invention, the aromatic carboxylic acid zinc salt is a zinc salt of an aromatic carboxylic acid which may have COOH in the benzene ring and may have any other substituent, and the zinc content is 15% by weight or more. It shall be. By making the zinc content of the aromatic carboxylic acid zinc salt 15% by weight or more, processability can be improved. Further, the exothermic property can be reduced.

  Examples of the aromatic carboxylic acid zinc salt having a zinc amount of 15% by weight or more include Activator 73A manufactured by Stractol.

  As the carboxylic acid zinc salt other than the aromatic carboxylic acid zinc, an aliphatic carboxylic acid zinc can be exemplified. By blending the aliphatic carboxylic acid zinc together with the aromatic carboxylic acid zinc salt, the workability can be improved and the exothermic property of the vulcanized product vulcanized at high temperature can be reduced.

  As the aliphatic carboxylic acid zinc, a zinc salt of a carboxylic acid having 10 to 40 carbon atoms (fatty acid zinc) is preferable. -G etc. are mentioned.

In the present invention, the weight ratio (A / B) between the blend amount (A) of bismaleimide or acrylate and the blend amount (B) of the carboxylic acid zinc salt containing the aromatic carboxylic acid zinc salt is preferably A / B. = 0.1 to 2.0, more preferably A / B = 0.3 to 1.2. By making the weight ratio (A / B) within such a range, workability can be improved and heat generation can be reduced.

  In the present invention, a reinforcing filler can be blended. Examples of the reinforcing filler include carbon black, silica, clay, talc, alumina, titanium dioxide, silicate, and the like. Of these, carbon black, silica, and clay are preferable. By blending these reinforcing fillers, the reinforcing properties of the rubber composition can be increased.

Carbon black and silica that are usually blended in a rubber composition for tires can be used. For example, the DBP absorption amount measured based on JIS K6217-4 of carbon fine rack is preferably 80 to 110 cm 3/100 g, the CTAB specific surface area measured based on JIS K6217-3 is preferably ^{30 to} 100 m ² / g, and JIS K6217. The nitrogen absorption specific surface area measured on the basis of -2 is preferably 30 to 110 m ² / g. Examples of the silica include wet method silica, dry method silica, and surface-treated silica. Among them, the CTAB adsorption specific surface area measured based on JIS K6217-3 is preferably 80 to 250 m ² / g, and JIS K6217-2. The nitrogen specific absorption specific surface area measured based on the above is preferably in the range of 100 to 280 m ² / g.

  The tire rubber composition may contain various additives generally used in tire rubber compositions such as vulcanization or crosslinking agents, vulcanization accelerators, various oils, anti-aging agents, and plasticizers. Such an additive can be kneaded by a general method to form a rubber composition, 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 normal rubber kneading machine such as a Banbury mixer, a kneader, or a roll.

  The rubber composition for tires of the present invention includes cords such as a cap tread portion, an under tread portion, a side rubber (side wall portion), a bead portion, a bead filler, a rim cushion, a carcass layer, a belt layer, and a belt cover layer of a pneumatic tire. It can be suitably used as a tire casing material such as a coated rubber for rubber, tie rubber, garnish, and a side-reinforced rubber layer having a crescent-shaped cross section in a run-flat tire (sometimes referred to as “run-flat liner” in this specification). In particular, bead fillers, rim cushions, run flat liners, belt layer cord covering rubbers, and side rubbers can be preferably used. When the tire rubber composition of the present invention is used for these tire casing materials, the characteristics of natural rubber and isoprene rubber can be maximized and the tire durability can be improved. The pneumatic tire using the rubber composition of the present invention for these members is excellent in productivity and can stably produce high quality products. At the same time, fatigue resistance, wear resistance and tire durability are excellent.

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

  18 kinds of rubber compositions (Examples 1 to 5 and Comparative Examples 1 to 18) composed of the compositions shown in Tables 2 to 4 including the additives shown in Table 1 as a common composition, except for sulfur and a vulcanization accelerator, respectively. The ingredients were weighed and kneaded for 5 minutes with a 1.5 liter closed Banbury mixer to release the masterbatch and cooled to room temperature. This master batch was mixed with a 1.5-liter closed Banbury mixer to which sulfur and a vulcanization accelerator were added and a tire rubber composition was prepared. In addition, the common mixing | blending shown in Table 1 means the compounding quantity (weight part) with respect to 100 weight part of diene rubbers described in Tables 2-4.

  The 18 types of rubber compositions obtained were evaluated for processability (Mooney viscosity), reversion-inhibiting effect (modulus at high temperature vulcanization, modulus retention) and heat build-up (tan δ at 60 ° C.) by the following methods.

Processability (Mooney viscosity)
In accordance with JIS K6300, the obtained rubber composition was subjected to a Mooney viscometer using an L-shaped rotor (38.1 mm diameter, 5.5 mm thickness), preheating time 1 minute, rotor rotation time 4 minutes, 100 The measurement was performed under the conditions of 2 ° C. and ° C. The obtained results are represented by an index with the value of Comparative Example 1 as 100, except for Examples 4 and 5 and Comparative Examples 12 and 13, and are shown in the column of “Workability” in Tables 2 and 3. Example 4 and Comparative Example 12 are shown in the column of “Workability” in Table 4 with an index that sets the value of Comparative Example 12 to 100. Example 5 and Comparative Example 13 are shown in the “workability” column of Table 4 with an index that sets the value of Comparative Example 13 to 100. A smaller index means a smaller Mooney viscosity and better workability.

Reversion suppression effect (modulus at high temperature vulcanization, modulus retention)
A high temperature vulcanized rubber test piece obtained by press vulcanizing the obtained 18 kinds of rubber compositions at 170 ° C. for 10 minutes using a mold having a predetermined shape, and a low temperature vulcanized rubber obtained by press vulcanizing for 20 minutes at 148 ° C. A test piece was prepared and punched into a dumbbell shape No. 3 (thickness 2 mm). The modulus of this high-temperature vulcanized rubber test piece and low-temperature vulcanized rubber test piece is based on JIS K6251 and using a fully automatic tensile tester with a thermostatic chamber made by Toyo Seiki Seisakusho, Strograph AR-T, pulling speed 500 mm / min. The 100% modulus at high temperature vulcanization and the 100% modulus at low temperature vulcanization were measured at a temperature of 23 ° C., respectively. The obtained 100% modulus at the time of high temperature vulcanization, except for Examples 4 and 5 and Comparative Examples 12 and 13, is an index that sets the value of Comparative Example 1 to 100 in the column of “Modulus” in Tables 2 and 3. Indicated. Example 4 and Comparative Example 12 are shown in the “Modulus” column of Table 4 with an index that sets the value of Comparative Example 12 to 100. The values of Example 5 and Comparative Example 13 are shown in the “Modulus” column of Table 4 with an index that sets the value of Comparative Example 13 to 100. A larger index means a higher 100% modulus at high temperature vulcanization.

  Further, the ratio of 100% modulus at high temperature vulcanization to 100% modulus at low temperature vulcanization was calculated for each of the 18 rubber compositions obtained, and the modulus retention at high temperature vulcanization was determined. The obtained modulus retention at the time of high temperature vulcanization is shown in the column of “modulus retention” in Tables 2 and 3, using the value of Comparative Example 1 as 100. The larger the index, the higher the modulus retention during high temperature vulcanization, which means that reversion is suppressed. The rubber composition of Comparative Example 1 had a 100% modulus at high temperature vulcanization of 1.9 MPa and a 100% modulus at low temperature vulcanization of 2.4 MPa.

Exothermic (tan δ at 60 ° C)
The obtained 18 kinds of rubber compositions were press vulcanized at 170 ° C. for 10 minutes using a mold having a predetermined shape to prepare test pieces. The dynamic viscoelasticity of the obtained test piece was measured for tan δ at an initial strain of 10%, an amplitude of ± 2%, a frequency of 20 Hz and a temperature of 60 ° C. using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho. The obtained results are represented by an index with the value of Comparative Example 1 as 100, except for Examples 4 and 5, and Comparative Examples 12 and 13, and are shown in the column of “Exothermic Properties” in Tables 2 and 3. Example 4 and Comparative Example 12 are shown in the “Exothermic” column of Table 4 with an index that sets the value of Comparative Example 12 to 100. Example 5 and Comparative Example 13 are shown in the “Exothermic Properties” column of Table 4 with an index that sets the value of Comparative Example 13 to 100. The smaller this index is, the smaller tan δ (60 ° C.) is, and the smaller the exothermic property, the better.

The raw materials used in Table 1 are shown below.
-Zinc oxide: 3 types of zinc oxide manufactured by Shodo Chemical Industry Co., Ltd.-Stearic acid: Beads stearic acid NY manufactured by NOF Corporation
Aroma oil: Showa Shell Sekiyu Extract No. 4 S
・ Sulfur: Fine powder sulfur with Jinhua seal oil manufactured by Tsurumi Chemical Industry Co., Ltd.

The raw materials used in Tables 2 to 4 are shown below.
・ NR: Natural rubber, RSS # 3
BR: Butadiene rubber, Nippon Zeon BR1220
・ CB: Carbon Black, N550, Toast Carbon Co., Ltd. Seest F
Bismaleimide: 1,3-bis (citraconimidomethyl) benzene, perkalink 900 manufactured by Flexis
Acrylate: trimethylolpropane triacrylate, number of acroyl groups in one molecule n = 4, SR354 manufactured by Sartomer
-Fatty acid zinc: Struktol A50P manufactured by Straktor
Aromatic carboxylate zinc-1: zinc amount 20% by weight, Activator 73A manufactured by Straktor
-Aromatic carboxylate zinc-2: zinc amount 12% by weight, Activator 73LM manufactured by Straktor

  As is clear from the results of Tables 3 and 4, the tire rubber compositions of Examples 1 to 5 improved the 100% modulus and modulus retention during high-temperature vulcanization to a level higher than the conventional level, and the Mooney viscosity was low. It was observed that processability was improved. Further, it was confirmed that the heat resistance is low and the rolling resistance when the tire is made is small and the fuel efficiency is improved.

  In Comparative Example 2 of Table 2, 100% modulus and modulus retention during high-temperature vulcanization are increased by adding bismaleimide to Comparative Example 1, but Mooney viscosity is increased and workability is deteriorated. Since Comparative Example 3 does not contain bismaleimide, acrylate and zinc aromatic carboxylate, the modulus retention cannot be sufficiently increased. Since Comparative Example 4 does not contain bismaleimide and acrylate, the exothermic property deteriorates.

  In Comparative Example 5, since the aliphatic zinc carboxylate was blended without blending the aromatic carboxylate zinc, the effect of reducing the heat generation cannot be obtained.

  In Comparative Example 6, since the zinc amount of the aromatic carboxylate is less than 15% by weight and bismaleimide and acrylate are not blended, the effect of improving processability cannot be obtained. In Comparative Example 7, since the zinc amount of the aromatic zinc carboxylate is less than 15% by weight, the effect of improving processability cannot be obtained.

  In Comparative Example 8 in Table 3, since the blending amount of bismaleimide is less than 0.5 parts by weight, the effect of increasing the 100% modulus and the modulus retention during high temperature vulcanization cannot be sufficiently obtained. Moreover, the effect which improves workability and exothermic property is not acquired. In Comparative Example 9, since the blending amount of bismaleimide exceeds 5 parts by weight, processability and heat generation are deteriorated.

  Since the compounding quantity of the zinc carboxylate containing the aromatic carboxylate zinc is less than 1 weight part in the comparative example 10, workability deteriorates. Since the compounding quantity of the zinc carboxylate containing the aromatic carboxylate of Comparative Example 11 exceeds 5 weight part, exothermic property deteriorates.

  In Table 4, since the compounding quantity of the zinc carboxylate containing aromatic zinc zinc exceeds 5 weight part and the bismaleimide and the acrylate are not mix | blended, the modulus retention rate deteriorates in the comparative example 12. Moreover, the effect which improves workability and exothermic property is not acquired. Since the compounding quantity of the zinc carboxylate containing the aromatic carboxylate zinc exceeds 5 weight part in the comparative example 12, a modulus retention rate deteriorates. Moreover, the effect which improves workability and exothermic property is not acquired.

Claims (4)

Carboxylic acid zinc salt containing aromatic carboxylic acid zinc salt of 0.5 to 5 parts by weight of bismaleimide or acrylate and zinc amount of 15% by weight or more with respect to 100 parts by weight of diene rubber containing natural rubber and / or isoprene rubber 1 to 5 parts by weight of a rubber composition for tires.   2. The tire rubber composition according to claim 1, wherein the natural rubber and / or isoprene rubber is contained in an amount of 50 wt% or more in 100 wt% of the diene rubber. The weight ratio (A / B) of the blend amount (A) of the bismaleimide or acrylate and the blend amount (B) of the carboxylic acid zinc salt containing the aromatic carboxylic acid zinc salt is A / B = 0.3. It is -1.2, The rubber composition for tires of Claim 1 or 2 characterized by the above-mentioned.   A pneumatic tire in which at least one member selected from a run flat liner, a belt layer, a bead filler, and a side rubber is formed from the rubber composition for a tire according to claim 1, 2 or 3.