JP5474334B2 - Rubber composition and pneumatic tire - Google Patents

Description

  The present invention relates to a rubber composition capable of improving heat build-up, and a pneumatic tire using the rubber composition.

  In recent years, the demand for lower fuel consumption of automobiles has been increasing, and there is a strong demand for reducing the rolling resistance of tires. It is known that the rolling resistance is related to the exothermic property of the rubber composition. Therefore, reducing the hysteresis loss of the rubber composition, that is, suppressing the loss factor (tan δ) to be low is effective in reducing fuel consumption.

  In order to meet such a requirement, it is known that a modified polymer is prepared by adding a modifying group to a diene synthetic rubber such as styrene-butadiene rubber at the time of polymer production. The modified diene rubber can improve the affinity with an unmodified diene rubber with a filler such as carbon black or silica, and can increase the reactivity. Therefore, heat generation can be suppressed and fuel efficiency can be improved. However, this technique can generally only be carried out under anionic polymerization, so that the polymer species are limited to styrene-butadiene rubber and butadiene rubber with a low cis content. Therefore, although the fuel efficiency can be improved, there is a demerit that the reinforcing property is lowered.

  In Patent Documents 1 and 2 below, in order to improve the dispersibility of the filler in the natural rubber composition, a modified natural rubber obtained by graft polymerization of a polar group-containing monomer on a natural rubber latex, and a styrene-butadiene rubber or It is disclosed that a butadiene rubber is blended with a modified diene-based synthetic rubber obtained by modifying a tertiary amino group. In these documents, various types of polar groups are listed, but the actual amino acids used in the examples are tertiary amino groups. Therefore, modified natural rubbers and tertiary amino groups modified with tertiary amino groups are used. Only a combination with a modified diene-based synthetic rubber modified with a group is disclosed.

  Patent Document 3 below discloses that a diene rubber having an amino group introduced therein is blended with a diene rubber having a hydroxyl group and / or an epoxy group introduced therein. However, this document is directed to styrene-butadiene rubber or butadiene rubber as a modified diene rubber and does not disclose a combination with an epoxidized natural rubber.

  In addition, all of the above documents 1 to 3 use a blend of a modified diene rubber in which a functional group that interacts with a filler is introduced in order to improve the dispersibility of a filler such as silica or carbon black. It is only disclosed.

On the other hand, Patent Document 4 below discloses blending epoxidized natural rubber and chlorosulfonated polyethylene as a rubber composition having self-crosslinkability, but is not a combination of diene rubber polymers, Also, it is silent about the point of achieving both low heat generation and reinforcement.
JP 2006-15211 A JP 2006-152212 A JP 2006-036822 A JP 2001-329119 A

  In view of the above points, the present invention provides a rubber composition comprising a diene rubber polymer capable of improving low heat buildup without impairing reinforcing properties, and a pneumatic tire using the rubber composition. With the goal.

The pneumatic tire according to the present invention includes an epoxidized natural rubber (A) having an epoxidation rate of 20 to 60 mol%, and a diene rubber in which at least one functional group selected from a carboxyl group, a hydroxyl group, and an amino group is introduced. A rubber composition containing a polymer (B) is used for at least a part of a tire .

  According to the present invention, by using the epoxidized natural rubber (A) and the diene rubber polymer (B) having the specific functional group as a rubber component in combination, low exothermicity is obtained without impairing the reinforcing property. Can be improved. This is because the epoxy group of the epoxidized natural rubber (A) reacts with the carboxyl group, hydroxyl group or amino group of the diene rubber polymer (B) together with the effect of improving the dispersibility of the filler due to each functional group of each polymer. By doing so, it is considered that both the polymers are cross-linked and the above-described decrease in the conventional reinforcing property due to the use of the modified polymer can be compensated. Thus, since low exothermic property can be improved without impairing the reinforcing property, when used in a tire, the rolling resistance can be reduced and the fuel efficiency can be improved while maintaining the reinforcing property.

  Hereinafter, matters related to the implementation of the present invention will be described in detail.

  In the rubber composition according to the present invention, an epoxidized natural rubber (A) having an epoxidation rate of 20 to 60 mol% and at least one functional group selected from a carboxyl group, a hydroxyl group and an amino group are introduced as a rubber component. The diene rubber polymer (B) is used in combination.

  Epoxidized natural rubber (A) is obtained by introducing an epoxy group into the double bond of the main chain of natural rubber, and can be obtained, for example, by reacting natural rubber latex with peracetic acid.

  As the epoxidized natural rubber (A), those having an epoxidation rate of 20 to 60 mol% are used. When the epoxidation rate is less than 20 mol%, not only the affinity with a filler such as silica is insufficient, but also the reinforcing effect by reaction with the diene rubber polymer (B) and the improvement effect of low heat generation are insufficient. It becomes. When the epoxidation rate exceeds 60 mol%, workability deteriorates. The epoxidation rate is more preferably 20 to 30 mol%, whereby the effect of improving low heat buildup can be further enhanced. The epoxidation rate means a modification rate with respect to the full double bond of natural rubber before epoxidation.

  The diene rubber polymer (B) is a modified diene polymer having any of a carboxyl group, a hydroxyl group, and an amino group. By combining the diene rubber polymer (B) with a functional group reactive to the epoxy group with the epoxidized natural rubber (A), the low heat build-up is improved without impairing the reinforcement. can do. The diene rubber polymer (B) includes a diene polymer containing a carboxyl group alone, a diene polymer containing a hydroxyl group alone, a diene polymer containing an amino group alone, and two or more of these functional groups. A diene polymer contained alone, or two or more of these polymers may be used in combination.

  In the diene rubber polymer (B), the type of polymer serving as a base is not particularly limited as long as it is a diene polymer, and various diene synthetic polymers may be mentioned. Examples of the diene-based synthetic polymer include a polymer of a conjugated diene monomer or a copolymer of a conjugated diene monomer and an aromatic vinyl monomer. Examples of the conjugated diene monomer include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethylbutadiene, and 1,3-butadiene and isoprene are particularly preferable. Examples of the aromatic vinyl monomer include styrene, o-, m- or p-methylstyrene, p-tert-butylstyrene, vinylnaphthalene and the like, and styrene is particularly preferable. Specific examples of the polymer include styrene-butadiene rubber (SBR), polybutadiene rubber (BR), polyisoprene rubber (IR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, and the like. More preferred are SBR and BR.

  The diene polymer itself containing a carboxyl group, a hydroxyl group, or an amino group is known, and its production method is not limited. For example, a carboxyl group, an amino group, or a hydroxyl group may be introduced by modifying a polymer synthesized by anionic polymerization with a modifying agent, or a monomer having a carboxyl group, an amino group, or a hydroxyl group by emulsion polymerization. May be introduced into the polymer chain by copolymerizing with the monomer of the base polymer.

  A method for producing a carboxyl group-modified diene rubber polymer containing a carboxyl group (—COOH) is not particularly limited. For example, as disclosed in JP-A-5-255408, a hydrocarbon is used. In the solvent, a conjugated diene monomer is polymerized using an alkyl lithium catalyst as an initiator, and the active living end and carbon dioxide are reacted to introduce a carboxyl group into the polymer end. Further, a carboxyl group may be introduced into the polymer main chain by adding thioglycolic acid to polybutadiene having a 1,2-double bond.

  A method for producing a hydroxyl group-modified diene rubber polymer containing a hydroxyl group is not particularly limited, and examples thereof include a method disclosed in WO96 / 23027.

  The production method of the amino group-modified diene rubber polymer containing an amino group is not particularly limited, and examples thereof include methods disclosed in WO 03/029299 and JP-A-9-71687. The amino group may be not only a primary amino group but also a secondary or tertiary amino group.

  Among the above, the functional group of the diene rubber polymer (B) is preferably a carboxyl group and / or a hydroxyl group, more preferably a carboxyl group, from the viewpoint of an excellent effect of improving low heat build-up.

  The blending ratio of the epoxidized natural rubber (A) and the diene rubber polymer (B) is 20 to 80 parts by weight of the epoxidized natural rubber (A) and 100 parts by weight of the diene rubber polymer (B) 80 in 100 parts by weight of the rubber component. It is preferable that it is -20 weight part. When the blending amount of any one of the polymers is less than 20 parts by weight, the effect of improving the reinforcing property due to the reaction with the other polymer becomes small.

  In the rubber composition of the present invention, a diene rubber other than the epoxidized natural rubber (A) and the diene rubber polymer (B) is blended as a rubber component within a range not impairing the effects of the present invention. May be. Examples of such other diene rubbers include various unmodified diene rubbers such as natural rubber, polyisoprene rubber, styrene-butadiene rubber, polybutadiene rubber, styrene-isoprene copolymer rubber, butadiene-isoprene. Copolymer rubber and the like.

  You may mix | blend the filler which consists of a silica and / or carbon black with the rubber composition of this invention. Silica and carbon black may be used alone or in combination. Although the compounding quantity of a filler is not specifically limited, It is preferable that it is 20-200 weight part with respect to 100 weight part of rubber components, More preferably, it is 50-100 weight part.

The carbon black is not particularly limited, and for example, carbon black having colloidal characteristics having a nitrogen adsorption specific surface area (BET) of 25 to 160 m ² / g can be used. Here, the nitrogen adsorption specific surface area of carbon black is a value measured according to JIS K6217-2. Examples of such carbon black include various grades such as ASTM numbers N110, N220, N330, N550, and N660.

Examples of silica include wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, and the like. Among them, wet silica having both fracture characteristics and low rolling resistance is used. It is also preferable from the viewpoint of excellent productivity. Although it does not specifically limit as a colloidal characteristic, For example, it is preferable that nitrogen adsorption specific surface area (BET) is 100-300 m < ² > / g. The BET of silica is measured according to the method described in the BET method described in ISO 5794.

  When using silica, it is preferable to use 2-20 weight% of silane coupling agents with respect to the amount of silica, more preferably 5-15 weight%. The silane coupling agent is not particularly limited. For example, bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) tetra Examples include sulfide silanes such as sulfide, and protected mercaptosilanes such as 3-octanoylthio-1-propyltriethoxysilane and 3-propionylthiopropyltrimethoxysilane.

  In addition to the above components, the rubber composition of the present invention generally includes a process oil, zinc white, stearic acid, wax, anti-aging agent, vulcanizing agent, vulcanization accelerator, vulcanizing aid, resins and the like. Various additives used in the composition can be used without limitation as long as the effects of the present invention are not impaired. The rubber composition can be prepared by kneading using a commonly used Banbury mixer, a mixer such as a roll or a kneader.

  The use of the rubber composition is not particularly limited, and examples thereof include various uses such as treads and sidewalls, belts and ply topping rubbers, tires such as bead fillers and rim strips, conveyor belts, and vibration-proof rubbers. When the rubber composition is used for a tire, rubber portions (tread rubber and the like) of various pneumatic tires can be constituted by vulcanization molding at, for example, 140 to 200 ° C. according to a conventional method.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

  Using a closed banbury mixer with a capacity of 1.7 liters, rubber compositions for tire treads of Examples and Comparative Examples were prepared according to the formulations shown in Tables 1 to 4 below. The detail of each component in Tables 1-4 is as follows.

-ENR25: Epoxidized natural rubber having an epoxidation rate of 25 mol%, "ENR25" manufactured by Kungpu Langley
ENR50: epoxidized natural rubber having an epoxidation rate of 50 mol%, “ENR50” manufactured by Kunpu Langley
NR: unmodified natural rubber, RSS # 3,
Unmodified SBR1: Unmodified styrene-butadiene rubber synthesized by anionic polymerization, “VSL5025-2HM” manufactured by LANXESS (styrene content = 24 wt%, vinyl content = 63 wt%),
Modified SBR1: modified styrene-butadiene rubber having a carboxyl group synthesized by anionic polymerization, “PBR4003” manufactured by LANXESS (styrene content = 24 wt%, vinyl content = 63 wt%),
Unmodified SBR2: Unmodified styrene-butadiene rubber, “SBR1721” manufactured by Nippon Zeon Co., Ltd. (styrene content = 40 wt%, vinyl content = 18 wt%),
Modified SBR2: modified styrene-butadiene rubber having amino group, “# 9590” manufactured by Nippon Zeon Co., Ltd. (styrene content = 40 wt%, vinyl content = 18 wt%),
Unmodified BR1: Unmodified polybutadiene rubber synthesized by anionic polymerization, “Diene NF35R” (cis 1,4 content = 32 wt%) manufactured by Asahi Kasei Corporation,
Modified BR1: Modified polybutadiene rubber having a hydroxyl group synthesized by anionic polymerization, “Tuffden E40” (cis 1,4 content = 32 wt%) manufactured by Asahi Kasei Corporation.

  The unmodified SBR1 and the modified SBR1, the unmodified SBR2 and the modified SBR2, and the unmodified BR1 and the modified BR1 are polymers that are substantially different only in the presence or absence of modification.

In each rubber composition, as a common formulation, 75 parts by weight of silica (“Ultrasil 7000GR” manufactured by Evonik, BET = 170 m ² / g) is added to 100 parts by weight of the rubber component, and a silane coupling agent (Evonik “ Si69 ") 5.6 parts by weight, mineral oil (aromatic oil," X-140 "manufactured by JOMO) 30 parts by weight, anti-aging agent (N-phenyl-N '-(1,3-dimethylbutyl) -p-phenylene Diamine, 2 parts by weight of “Nocrack 6C” manufactured by Ouchi Shinsei Chemical Co., Ltd., 2 parts by weight of stearic acid (“industrial stearic acid” manufactured by Kao Corporation), zinc oxide (“No. 1 zinc manufactured by Mitsui Kinzoku Mining Co., Ltd.) "Hana") 3 parts by weight, paraffin wax (Nippon Seiwa Co., Ltd. "Ozoace 0355") 2 parts by weight, vulcanization accelerator (N-tert-butyl-2-benzothiazolylsulfur) N'amido, Ouchi Shinko Chemical Industrial Co., Ltd. "NOCCELER NS-P"), 1.5 parts by weight of sulfur (Tsurumi Chemical Industry Co., Ltd. "5% oil treated powder sulfur") was blended 2 weight parts.

  Each rubber composition obtained was vulcanized at 160 ° C. for 30 minutes to prepare a test piece having a predetermined shape. Using the obtained test piece, tan δ as a low heat generation index and a reinforcing index The breaking strength was measured by the following method.

Tan δ: According to JIS K6394, tan δ was measured under the conditions of frequency 10 Hz, dynamic strain 2%, 70 ° C., Table 1 shows the values of Comparative Example 1, Table 2 shows the values of Comparative Example 5, and Table 3 shows the values. The values of Comparative Example 8 are shown in Table 4 as indices with the value of Comparative Example 11 as 100. The smaller the numerical value, the smaller the tan δ.

-Breaking strength: According to JIS K6251, a tensile test (dumbbell shape No. 3) was carried out to measure the tensile strength. Table 1 shows the values of Comparative Example 1, Table 2 shows the values of Comparative Example 5, In Table 3, the value of Comparative Example 8 is displayed as an index, and in Table 4, the value of Comparative Example 11 is expressed as an index of 100, respectively. The larger the value, the greater the breaking strength and the better the reinforcement.

The results are as shown in Tables 1 to 4. Comparative Examples 2, 6, 9, and 11 in which a diene rubber polymer modified with a carboxyl group, a hydroxyl group, or an amino group is combined with an unmodified natural rubber, compared with Comparative Examples 1, 5, 8, and 11 in which unmodified rubbers are combined. In No. 12, although the low exothermic property was improved, the reinforcing property was lowered. Further, in Comparative Examples 3, 4, 7, 10, and 13 in which epoxidized natural rubber was combined with an unmodified diene rubber polymer, both low heat buildup and reinforcement were reduced. On the other hand, when it is Examples 1-5 which combined the epoxidized natural rubber and the diene-type rubber polymer modified with the said specific functional group, with respect to Comparative Examples 1, 5, 8, and 11, the reinforcing property is improved. While maintaining, the low heat build-up was greatly improved.

Claims (4)

An epoxidized natural rubber (A) having an epoxidation rate of 20 to 60 mol%, and a diene rubber polymer (B) having at least one functional group selected from a carboxyl group, a hydroxyl group and an amino group introduced therein A pneumatic tire using a rubber composition as at least a part of a tire. 2. The rubber composition according to claim 1, wherein 100 parts by weight of a rubber component is composed of 20 to 80 parts by weight of the epoxidized natural rubber (A) and 80 to 20 parts by weight of the diene rubber polymer (B). Pneumatic tire . The pneumatic tire according to claim 1 , wherein the rubber composition contains a filler made of silica and / or carbon black. The pneumatic tire according to any one of claims 1 to 3, wherein the diene rubber polymer (B) is at least one selected from styrene-butadiene rubber and polybutadiene rubber.