JP2011052137A - Rubber composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition showing excellence in initial adhesion to a metallic reinforcing material such as a steel cord and the like and the adhesion after deterioration. <P>SOLUTION: The used rubber composition comprises 100 pts.wt. of diene-based rubber, 0.1 to 10.0 pts.wt. of 2-substituted dithiobenzothiazole compound represented by the chemical formula (I), 0.1 to 5.0 pts.wt. of N,N-dicyclohexyl-2-benzothiazolyl sulfenamide represented by chemical formula (II), and 1 to 10 pts.wt. of sulfur (wherein R is 1 to 10C linear, branched or cyclic alkyl group or alkenyl group). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a rubber composition excellent in initial adhesion to a steel cord and adhesion after aging.

  In recent years, steel reinforcing materials made of steel are used as needed for rubber products such as belts and hoses, as well as pneumatic tires that support the suspension of automobiles. In such a rubber product, the adhesion between the reinforcing material and the rubber is often a problem.

  In particular, automobile tires are manufactured by combining rubber and steel cords, but tires are used under conditions of high heat generation due to higher performance (higher speed, higher horsepower, larger size) of vehicles. Accordingly, a high level of improvement is required for the adhesion between the steel cord used as a reinforcing material and rubber.

Conventionally, N, N-dicyclohexyl-2-benzothiazolylsulfenamide (hereinafter abbreviated as DCBS) has been mainly used as a vulcanization accelerator to improve the adhesion between rubber and steel cord. However, since adhesion cannot be said to be sufficient only by vulcanization with DCBS, an organic acid cobalt salt or the like is blended as an adhesion promoter.
However, the conventional rubber composition containing an organic acid cobalt salt cannot sufficiently satisfy the recent required performance because of a large decrease in adhesiveness due to heat aging. For this reason, there is a demand for a rubber composition that is more excellent in initial adhesion to a steel cord and adhesion after heat aging.

JP 2008-308672 A JP 2009-138050 A

  An object of this invention is to provide the rubber composition excellent in the initial stage adhesiveness with respect to metal reinforcement materials, such as a steel cord, and the adhesiveness after aging.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have used DCBS together with a 2-substituted dithiobenzothiazole compound as a vulcanization accelerator when vulcanizing a diene rubber. As a result, it was found that the intended purpose was achieved, and the present invention was completed.
That is, the first invention is represented by the chemical formula (II) and 0.1 to 10.0 parts by weight of the 2-substituted dithiobenzothiazole compound represented by the chemical formula (I) with respect to 100 parts by weight of the diene rubber. A rubber composition comprising 0.1,5.0 parts by weight of N, N-dicyclohexyl-2-benzothiazolylsulfenamide and 1-10 parts by weight of sulfur.
A second invention is the rubber composition according to the first invention, wherein the sulfur is insoluble sulfur and / or soluble sulfur.
In a third invention, the 2-substituted dithiobenzothiazole compound is 2-propyldithiobenzothiazole, 2-butyldithiobenzothiazole, 2-pentyldithiobenzothiazole, 2-hexyldithiobenzothiazole, 2-heptyldithiobenzothiazole and The rubber composition according to the first invention or the second invention, wherein the rubber composition is at least one selected from 2-cyclohexyldithiobenzothiazole.

（式中、Ｒは炭素数１〜１０の直鎖状、分岐状または環状のアルキル基もしくはアルケニル基を表わす。）

(In the formula, R represents a linear, branched or cyclic alkyl group or alkenyl group having 1 to 10 carbon atoms.)

  The rubber composition of the present invention is more excellent in steel adhesion than a rubber composition containing only DCBS as a vulcanization accelerator.

Hereinafter, the present invention will be described in detail.
The 2-substituted dithiobenzothiazole compound used in the practice of the present invention can be synthesized by the method described in US Pat. No. 3,859,297. For example, by heating 2-mercaptobenzothiazole and N-cyclohexylthiophthalimide in a suitable solvent, the desired 2-cyclohexyldithiobenzothiazole is produced in high yield.

Examples of the 2-substituted dithiobenzothiazole compound include:
2-methyldithiobenzothiazole,
2-ethyldithiobenzothiazole,
2-propyldithiobenzothiazole,
2-butyldithiobenzothiazole,
2-pentyldithiobenzothiazole,
2-hexyldithiobenzothiazole,
2-heptyldithiobenzothiazole,
2-octyldithiobenzothiazole,
2-nonyldithiobenzothiazole,
2-decyldithiobenzothiazole,
2-isopropyldithiobenzothiazole,
2-neopentyldithiobenzothiazole,
2-cyclopentyldithiobenzothiazole,
2-cyclohexyldithiobenzothiazole,
2-allyldithiobenzothiazole,
2-isopropenyl dithiobenzothiazole,
2- (cyclohexenyl-2 ′) dithiobenzothiazole,
2- (thiazolyl-2 ′) dithiobenzothiazole,
2- (thiadiazole-2 ′) dithiobenzothiazole,
2- (pyrimidinyl-2 ') dithiobenzothiazole etc. are mentioned, These can be used preferably. Two or more selected from these 2-substituted dithiobenzothiazole compounds may be used in combination.

  DCBS used in the practice of the present invention is a vulcanization accelerator widely used in the rubber vulcanization field, and is commercially available, for example, under the trade name “Noxeller DZ” manufactured by Ouchi Shinsei.

  Sulfur used in the practice of the present invention is soluble sulfur or insoluble sulfur, and these may be used in combination.

  In the rubber composition of the present invention, the 2-substituted dithiobenzothiazole compound is preferably blended at a ratio of 0.1 to 10.0 parts by weight with respect to 100 parts by weight of the diene rubber, and more preferably 0.2 to It is more preferable to mix at a ratio of 2.0 parts by weight. When the blending ratio of the 2-substituted dithiobenzothiazole compound is less than 0.1 part by weight, the effect of improving the adhesion between the vulcanized rubber and the steel cord cannot be obtained. On the other hand, when the blending ratio of the 2-substituted dithiobenzothiazole compound exceeds 10.0 parts by weight, the vulcanization speed becomes slow and a long time is required for vulcanization.

  In the rubber composition of the present invention, it is preferable to blend DCBS at a ratio of 0.1 to 5.0 parts by weight with respect to 100 parts by weight of the diene rubber, and further 0.1 to 2.0 parts by weight. It is more preferable to mix | blend in a ratio. When the blending amount of DCBS is less than 0.1 parts by weight, the tensile strength and elastic modulus of the vulcanized rubber are lowered. Further, even if the blending amount of DCBS is more than 5.0 parts by weight, improvement in the properties of vulcanized rubber cannot be expected.

  In the rubber composition of the present invention, it is preferable to blend 1 to 10 parts by weight of soluble sulfur and / or insoluble sulfur as sulfur with respect to 100 parts by weight of diene rubber, and further 2 to 5 parts by weight. It is more preferable to mix | blend in a ratio. If the sulfur is less than 1 part by weight, the vulcanized rubber is not sufficiently crosslinked. Moreover, when sulfur exceeds 10 weight part, the breaking elongation (EB) of a vulcanized rubber will fall on the contrary.

  The rubber composition of the present invention is excellent in adhesion when vulcanizing and bonding a steel reinforcing material such as a steel cord and rubber. The diene rubber used in the rubber composition of the present invention comprises at least one selected from natural rubber and diene synthetic rubber. Examples of the diene-based synthetic rubber include styrene-butadiene copolymer rubber (SBR), polyisoprene rubber (IR), polybutadiene rubber (BR), acrylonitrile-butadiene rubber, chloroprene rubber, and butyl rubber.

  The rubber composition of the present invention may contain carbon black (including surface-treated materials), silica, clay, talc and the like that have been conventionally used for rubbers as reinforcing agents and fillers. it can. The mixing ratio of these reinforcing agents and fillers is not particularly limited, but is preferably 40 to 120 parts by weight with respect to 100 parts by weight of the diene rubber.

  Moreover, adhesion promoters, such as organic acid cobalt salt generally used conventionally, can be used for the rubber composition of this invention.

  Furthermore, the rubber composition of the present invention is used to improve the dispersibility of zinc oxide (zinc white) or magnesium oxide as a vulcanization acceleration aid, process oil (for example, naphthenic oil) as a processing stabilizer, and filler. Waxes (for example, stearic acid), antioxidants, ozone cracking inhibitors, peptizers, adhesive resins, vulcanization retarders and the like can be used as long as the effects of the present invention are not impaired.

  The rubber composition of the present invention can be obtained, for example, by kneading using a closed kneader such as a Banbury mixer or a kneader such as an open roll. And after shaping | molding, it can vulcanize | curing and can be set as rubber products, such as a tire and a belt.

  The rubber composition of the present invention has better adhesion to a steel cord after vulcanization than a rubber composition using only DCBS. Furthermore, after being subjected to environmental stress, for example, after being left for a long time under high temperature and high humidity conditions, the adhesiveness with the steel cord is sufficiently maintained.

  Hereinafter, although an example and a comparative example explain the present invention, the present invention is not limited to these.

[2-Substituted Dithiobenzothiazole Compound]
The 2-substituted dithiobenzothiazole compounds used in Examples 1 to 5 are as follows.
2-propyldithiobenzothiazole (sometimes referred to simply as propyl)
2-butyldithiobenzothiazole (sometimes referred to simply as butyl)
2-pentyldithiobenzothiazole (sometimes referred to simply as pentyl)
2-hexyldithiobenzothiazole (sometimes referred to simply as hexyl)
2-Heptyldithiobenzothiazole (sometimes referred to simply as heptyl)

  These 2-substituted dithiobenzothiazole compounds are prepared by previously reacting an N-chlorophthalimide and a disulfide compound to produce an N-substituted thiophthalimide compound as an intermediate, and then reacting the intermediate with 2-mercaptobenzothiazole. And synthesized. The obtained product was confirmed to be the desired 2-substituted dithiobenzothiazole by infrared absorption spectrum, NMR spectrum and mass spectrometry.

[2-cyclohexyldithiobenzothiazole (sometimes referred to simply as cyclohexyl)]
The 2-cyclohexyldithiobenzothiazole used in Examples 6 to 10 was synthesized by the method described in US Pat. No. 3,859,297. Specifically, commercially available N-cyclohexylthiophthalimide and 2-mercaptobenzothiazole were reacted in the presence of a toluene solvent, and phthalimide by-produced by the reaction was removed and purified according to a conventional method.

[DCBS]
The DCBS used in the examples is as follows.
・ DCBS: Trade name "Noxeller DZ" (manufactured by Ouchi Shinsei Chemical Industry)

Other raw materials used in Examples and Comparative Examples are as follows.
・ Natural rubber: Standard Malaysian rubber SMR-CV60
Carbon black: trade name “Seast G3” (manufactured by Tokai Carbon, nitrogen adsorption: 79 m ² / g, DBP oil absorption: 101 ml / 100 g)
・ Zinc flower: Trade name "Zinc oxide 2 types" (manufactured by Shodo Chemical Industry)
・ Naphthenic oil: Trade name “SNH-22” (manufactured by Sankyo Oil Chemical Co., Ltd., process oil)
・ Stearic acid: Trade name “MXST” (made by Miyoshi Oil & Fats)
Insoluble sulfur: Trade name “Muclon OT20” (manufactured by Shikoku Chemicals)

[Steel adhesion test]
In accordance with ASTM D2229, a 1 × 5 structure (element diameter 0.25 mm) brass-plated steel cord is embedded in an unvulcanized rubber sheet to a length of 12.5 mm and vulcanized at 160 ° C. for 10 minutes. Vulcanization adhesion was performed to prepare a test piece. The pulling strength of the steel cord and the rubber coverage were measured when the specimen was left at room temperature for 24 hours (initial) and when it was aged at 100 ° C. for 24 hours.
These data are all shown as relative values when the value of the comparative example before aging treatment is taken as 100. The larger the value, the better the adhesion.

[Examples 1 to 5]
Natural rubber, carbon black, zinc white, naphthenic oil and stearic acid were blended so as to have the blending ratios shown in Table 1, and kneaded using a Banbury mixer to prepare a master batch. Insoluble sulfur, 2-substituted dithiobenzothiazole compound and DCBS are blended in the masterbatch so as to have the blending ratios shown in Table 1, respectively, kneaded using a two-roll mixer with a surface temperature of 70 ° C., and an unvulcanized rubber sheet Was prepared. A steel adhesion test was conducted using this unvulcanized rubber sheet. The test results obtained were as shown in Table 1.

[Examples 6 to 10]
Insoluble sulfur, 2-cyclohexyldithiobenzothiazole, and DCBS are blended in the blending ratio shown in Table 1 to the master batch prepared in the same manner as in the above-described example, and an unvulcanized rubber sheet is prepared, and a steel adhesion test is performed. It was. The test results obtained were as shown in Table 1.

[Comparative Example 1]
In the same manner as in the examples, insoluble sulfur and DCBS were blended in the master batch at the blending ratio shown in Table 1, to prepare an unvulcanized rubber sheet, and a steel adhesion test was performed. The test results obtained were as shown in Table 1.

    According to the test results shown in Table 1, the rubber composition using both the 2-substituted dithiobenzothiazole compound and DCBS as the vulcanization accelerator is compared with the rubber composition using only DCBS as the vulcanization accelerator. Improved steel adhesion after initial and aging.

  ADVANTAGE OF THE INVENTION According to this invention, the rubber composition excellent in adhesiveness with steel metal reinforcements can be provided, and utilization to rubber products, such as a tire for motor vehicles, a belt, and a hose, is anticipated.

Claims (3)

0.1 to 10.0 parts by weight of a 2-substituted dithiobenzothiazole compound represented by the chemical formula (I) and N, N-dicyclohexyl-2-formyl represented by the chemical formula (II) with respect to 100 parts by weight of the diene rubber. A rubber composition comprising 0.1 to 5.0 parts by weight of benzothiazolylsulfenamide and 1 to 10 parts by weight of sulfur.

(In the formula, R represents a linear, branched or cyclic alkyl group or alkenyl group having 1 to 10 carbon atoms.)   The rubber composition according to claim 1, wherein the sulfur is insoluble sulfur and / or soluble sulfur.   2-substituted dithiobenzothiazole compounds are 2-propyldithiobenzothiazole, 2-butyldithiobenzothiazole, 2-pentyldithiobenzothiazole, 2-hexyldithiobenzothiazole, 2-heptyldithiobenzothiazole and 2-cyclohexyldithiobenzothiazole The rubber composition according to claim 1, wherein the rubber composition is at least one selected from the group consisting of: