Low heat generation type rubber compositions

Abstract: A low heat generation type rubber composition comprises at least one rubber selected from natural rubber and synthetic diene rubbers, a reinforcing filler, and a thiadiazole compound expressed by the following general formula: in which R₁ and R₂, which may be the same as or different from each other, denote a mercapto group, an amino group, or a trifluoromethyl group. The reinforcing filler and the thiadiazole compound are contained in amounts of 20 to 150 parts by weight and 0.1 to 10 parts by weight, respectively.

Description: The present invention relates to low heat generation type rubber compositions. In order to respond to social requirements for natural resource saving and energy saving, considerable development of low fuel consumption tires has taken place for several years in the rubber industries, particularly in the tire industry. The development of such low fuel consumption tires requires low heat generation type rubber compositions. For instance, Japanese patent application Laid-open Nos. JP-A-57-51,503, 57-55,204, and 58-36,705 describes techniques for using styrene-butadiene rubber (SBR) in which the contents of bound styrene and vinyl bonds are controlled. However, those techniques could not be applied to rubbers other than SBR. Particularly, they could not be applied at all to natural rubber, which is most widely used in heavy duty pneumatic tires. On the other hand, Japanese Patent publication No. JP-A-50-38,131, GB-A-1,185,896, and US-A-2,315,856 describe that the heat generation characteristic of rubber compositions is improved by adding nitrosoquinolines or nitrosoanilines, thereto. However, while such nitroso compounds do indeed improve the heat generation characteristic, there is a problem in that when they are applied in case of polyisoprene rubber, wear resistance of the rubber compositions is greatly deteriorated due to notable peptizing action. Further, when the above nitroso compounds are applied in case of polyisoprene rubber, the heat generation characteristic is conspicuously improved; on the other hand, when they are applied to synthetic rubbers such as styrene-butadiene copolymer rubber or polybutadiene rubber, great heat generation characteristic-improving effect cannot be expected. The present invention aims to overcome the above problems i.e. that the nitroso compounds cannot be applied to natural rubber, that if they are applied to polyisoprene rubber, peptizing action is great, and that when the nitroso compounds are applied to styrene-butadiene copolymer rubber or polybutadiene rubber, great heat generation characteristic-improving effect cannot be expected, and to provide low heat generation type rubber compositions free from the above problems. The present inventors have accordingly made considerable examinations of heat generation improvers other than nitroso compounds, and as a result the present invention has been accomplished. The present invention provides a low heat generation type rubber composition comprising at least one rubber selected from natural rubber and a synthetic diene rubber, a reinforcing filler, and a thiadiazole compound expressed by the following general formula: in which R₁ and R₂, which may be the same as or different from each other, denote a mercapto group (-SH), an amino group (-NH₂), and a trifluoromethyl group (-CF₃), said reinforcing filler and said thiadiazole compound being in amounts of 20 to 150 parts by weight and 0.1 and 10 parts by weight with respect to 100 parts by weight of said at least one rubber. The rubbers used in the present invention may be suitably natural rubber, synthetic polyisoprene rubber, styrene-butadiene copolymer rubber, polybutadiene rubber, butyl rubber, etc. These rubbers may be used singly or two or more kinds of them may be used in combination. Thiadiazole compounds used in the present invention are mixed into the rubber compositions as heat generation improvers. As specific examples, mention may be made of 2,5-dimercapto-1,3,4-thiadiazole, 2-amino-5-mercapto-1,3,4-thiadiazole, 2-amino-5-trifluoromethyl-1,3,4-thiadiazole. These thiadiazole compounds may be used singly or two or more kinds of them may be used in combination. The mixing amount of the thiadiazole compound is from 0.1 to 10 weight parts, preferably 0.25 to 2 parts by weight, with respect to 100 parts by weight of the rubber component. If the mixing amount is less than 0.1 part by weight, almost no heat generation-improving effect can be expected for the rubber composition. If the mixing amount is more than 10 parts by weight, not only does the heat generation-improving effect disappear, but also the mechanical properties of the rubber composition are adversely affected. The reinforcing filler used in the present invention may be suitably carbon black. The mixing amount thereof is 20 to 150 parts by weight with respect to 100 parts by weight of the rubber component. If the mixing amount is less than 20 parts by weight, the reinforced degree of the rubber composition lowers. On the contrary, if the mixing amount is more than 150 parts by weight, not only is the heat generation characteristic adversely affected, but also physical properties such as wear resistance are remarkably deteriorated. In the present invention, besides the above reinforcing filler and heat generation improvers, compounding additives conventionally used in the rubber industry, such as a softener, an antioxidant, a vulcanization accelerator, a vulcanization acceleration aid a vulcanizer and the like may be blended, if necessary. The rubber compositions according to the present invention may be applied to all sorts of rubber articles such as tires, conveyor belts, hoses, etc. The invention will be further described with reference to the following illustrative Examples and Comparative Examples. Examples 1 to 3 and Comparative Examples 1 to 3 Various rubber compositions were each prepared by mixing 5.75x10⁻³ mole of a thiadiazole compound shown in Table 1, 100 parts by weight of natural rubber, 50 parts by weight of ISAF carbon black, 3 parts by weight of stearic acid, 1 part by weight of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylene diamine, 5 parts by weight of zinc oxide, 0.5 part by weight of N-oxydiethylene-2-benzothiazole sulfene amide, and 2.5 parts by weight of sulfur by using a Banbury mixer. With respect to the thus obtained rubber compositions, rebound resilience and sol molecular weight were evaluated. For comparison purpose, that which was added with no heat generation improver or those added with a nitroso compound were evaluated in the same manner as above. Results are shown in Table 1. Evaluation ways are as follows: Repulsion resilience Repulsion resilience was measured according to JIS K 6301. Sol molecular weight: After an unvulcanized rubber composition was immersed in tetrahydrofuran for 48 hours, carbon gel was removed. With respect to the remaining liquid, the molecular weight (Mw) of sol was measured by using "High Speed Liquid Chromatograph HLC-802 A" manufactured by Toyo Soda Co., Ltd. Example Comparative Eample 1 2 3 1 2 3 Heat generation improver 2,5-dimercapto-1,3,4-thiadiazole 2-amino-5-mercapto-1,3,4-thiadiazole 2-amino-5-trifluoromethyl-1,3,4-thiadiazole - 5-nitroso-8-hydroxyquinoline N-phenyl-p-nitrosoaniline Rebound resilience (%) 65.4 62.7 63.1 59.0 63.7 63.8 Sol molecular weight Mwx10⁵ 5.56 5.52 5.49 5.51 3.97 2.50 From Table 1, it is clear that the rubber compositions according to the present invention have no peptizing action for the polymer, and have remarkably improved heat generation characteristic. Examples 4 to 6 and Comparative Examples 4 to 6 Various rubber compositions were each prepared by mixing 5.75×10⁻³ mole of a thiadiazole compound shown in Table 1 into 137.5 parts by weight of styrene-butadiene copolymer rubber (SBR1712), 65 parts by weight of ISAF carbon black, 1 part by weight of stearic acid, 3 parts by weight of zinc oxide, 0.5 part by weight of 1,3-diphenyl guanidine, 1.0 part by weight of dibenzothiazyl disulfide and 1.5 parts by weight of sulfur by using a Banbury mixer. For comparison purpose, that which was added with no heat generation characteristic improver or those added with a nitroso compound were evaluated in the same manner as above. Results are shown in Table 2. Example Comparative Eample 4 5 6 4 5 6 Heat generation improver 2,5-dimercapto-1,3,4-thiadiazole 2-amino-5-mercapto-1,3,4-thiadiazole 2-amino-5-trifluoromethyl-1,3,4-thiadiazole - 5-nitroso-8-hydroxyquinoline N-phenyl-p-nitrosoaniline Rebound resilience (%) 45.1 43.8 44.6 40.3 41.9 41.5 As is clear from Table 2, the styrene-butadiene copolymer rubber compositions according to the present invention have excellent heat generation-improving effect as compared with Comparative Examples added with the nitroso compound. As explained above, and as is clear from the results in Examples, the rubber compositions of the present invention in which the reinforcing filler and the specific thiadizole compound are added to the rubber compound in respectively specified amounts have better heat generation-improving effect and improved polymer peptizing effects as compared with Comparative Examples added with the nitroso compounds. Thus, the rubber compositions according to the present invention have extremely great use values in a wide field as low heat generation type rubber compositions.

Claims: A rubber composition comprising at least one rubber selected from natural rubber and synthetic diene rubbers, a reinforcing filler, and a thiadiazole compound of the following general formula: in which R₁ and R₂, which may be the same as or different from each other, are a mercapto group, an amino group, or a trifluoromethyl group, said reinforcing filler and said thiadiazole compound being in amounts of 20 to 150 parts by weight and 0.1 to 10 parts by weight with respect to 100 parts by weight of said at least one rubber, respectively. A rubber composition as claimed in claim 1, characterized in that said at least one rubber is selected from natural rubber, synthetic polyisoprene rubber, styrene-butadiene copolymer rubber, polybutadiene rubber, and butyl rubber. A rubber composition as claimed in claim 1 or 2, characterized in that said thiadiazole compound is at least one compound selected from 2,5-dimercapto-1,3,4-thiadiazole, 2-amino-5-mercapto-1,3,4-thiadiazole, and 2-amino-5-trifluoromethyl-1,3,4-thiadiazole. A rubber composition as claimed in any of claims 1 to 3, characterized by comprising 0.25 to 2 parts by weight of said thiadiazole compound. A rubber composition as claimed in any of claims 1 to 4, characterized in that the reinforcing filler is carbon black.

Inventors: HATAKEYAMA KAZUYA, HIRATA YASUSHI, NAKAJIMA ICHIRO, HATAKEYAMA, KAZUYA, HIRATA, YASUSHI, NAKAJIMA, ICHIRO
Applicants: BRIDGESTONE CORP, BRIDGESTONE CORPORATION
Application year: 1989
Main classification: C08K5
IPC codes: C08K5, C08L7, C08K3, C08L21, C08L9