JPH0473458B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a rubber composition, and is characterized in that an imidazole dithiocarboxylic acid compound is blended into a raw material rubber, and when forming a composite of rubber and a metal material, particularly brass, it is possible to The present invention relates to a rubber composition with good adhesive properties. [Prior art] Composite materials that combine metal materials with high strength and rigidity and elastic and flexible rubber have been used in many industrial products, and it is difficult to bond the metal and rubber that make up the composite materials. Since force has a large effect on the performance of the product, after various studies, the adhesion between metal and rubber has been considerably improved, but the workability of the rubber used, such as short scorch time, etc.
Various problems currently exist. When adhering rubber and brass, mixing 6-R-2,4-dimercapto-1,3,5-triazine, which is a triazine derivative, into the raw rubber can improve the adhesion between the brass and the rubber. Are known. However, a representative example of this triazine derivative, 2,4,6-trimercapto-1,
Rubber compositions containing 3,5-triazine have an extremely short scorch time, and no suitable vulcanization retarder has been found, resulting in burnt development of the rubber composition during the manufacturing process, especially during kneading, and compound storage problems. Because the scorch time is quickly shortened by scratching, burning occurs and processing stability deteriorates, resulting in lower work efficiency and the production of defective products. [Problems to be solved by the invention] In view of the current situation, the present inventor has researched ways to improve workability and improve adhesion in adhesion between brass and rubber. In the rubber composition used to form the composite, by blending the imidazole dithiocarboxylic acid compound with the raw material rubber, the processability, especially the scorch time is increased compared to conventional methods, and the burning phenomenon during kneading work is prevented. We have achieved the present invention by being able to obtain a rubber composition that can be bonded directly to brass without decreasing its adhesive properties even when subjected to moist heat deterioration, and which can be directly bonded to brass. [Means for Solving the Problems] That is, the present invention provides a rubber composition used for forming a composite consisting of rubber and a metal material, which contains at least one rubber selected from natural rubber and sulfur-vulcanizable synthetic rubber. For 100 parts by weight of seed raw rubber,
general formula (In the formula, R is an alkyl group having 10 or less carbon atoms,
This rubber composition has good adhesion to brass and is characterized by containing 0.8 to 10 parts by weight of an imidazole dithiocarboxylic acid compound represented by R' (representing a hydrogen atom or an alkyl group having 10 or less carbon atoms). As the raw material rubber used in the present invention, any rubber that can be vulcanized by sulfur can be used, and natural rubber, synthetic rubber, or a mixture thereof can be used, but natural rubber, styrene, and butadiene copolymerized rubber can be used. Rubber (SBR), butadiene rubber (BR), acrylonitrile-butadiene copolymer rubber (NBR), or a mixture thereof are particularly preferably used. R in the imidazole dithiocarboxylic acid compound represented by the general formula () used in the present invention is an alkyl group having 10 or less carbon atoms, which may be linear or branched, such as methyl, ethyl, propyl , isopropyl, n-butyl, t
-butyl, hexyl, octyl, etc., and among these, methyl group and ethyl group are preferred. Further, R' is a hydrogen atom or an alkyl group having 10 or less carbon atoms. Alkyl groups may be linear or branched, such as methyl, propyl, isopropyl, n-butyl, t-butyl, hexyl, octyl, etc. Among these, hydrogen atoms, methyl groups, and ethyl groups preferable. The amount of imidazole dithiocarboxylic acid compound in the rubber composition according to the present invention is based on the raw material rubber.
0.8 to 10 parts by weight per 100 parts by weight, preferably
1.0 to 5 parts by weight is suitable. In the rubber composition of the present invention, sulfur is used as the vulcanizing agent, while a thiuram-based, thiazole-based, or sulfenamide-based vulcanization accelerator or a mixture thereof can be used as the vulcanization accelerator. Tetramethylthiuram monosulfide (TS), tetramethylthiuram disulfide (TT), dipentamethylenethiuram tetrasulfide, etc. are used as thiuram-based vulcanization accelerators, and as thiazole-based vulcanization accelerators, Dibenzothiazyl disulfide (DM), 2-mercaptobenzothiazole, 2-(N-N'-diethylthiocarbamoylthio)benzothiazole, 2-(4'-morpholinodithio)benzothiazole, etc. are used. Examples of sulfenamide vulcanization accelerators include N-cyclohexyl-2-benzothiazyl sulfenamide (CZ), N-oxydiethylene-2-benzothiazole sulfenamide, etc. The blending amount is 0.2 per 100 parts by weight of raw rubber.
~2.5 parts by weight is preferred. In addition to the above-mentioned compounds, commonly used rubber compounding agents such as zinc white, carbon black, and anti-aging agents can be appropriately blended into the raw rubber. The metal material used in the present invention is one commonly used in the rubber industry, and the surface for adhesion to the rubber composition is treated with brass, such as so-called brass plating wire or brass itself. The rubber composition of the present invention can be easily obtained by blending predetermined amounts of each of the above-mentioned components such as raw rubber and kneading with a mixing roll, Banbury mixer, etc., and then molding the rubber composition and brass with a press molding machine. A strongly bonded composite can be obtained by contacting the two materials using a method such as the following. [Function] The imidazole dithiocarboxylic acid compound used in the present invention acts as an adhesion promoter in the rubber composition. In the rubber composition according to the present invention, raw rubber
0.8 to 10 parts by weight, preferably 1.0 to 5 parts by weight of imidazole dithiocarboxylic acid compound per 100 parts by weight
By blending within a limited range of parts by weight, good effects such as extending the scorch time and adhesion to brass can be obtained, and if it is less than 0.8 parts by weight, the physical performance of the resulting rubber composition (low modulus) can be obtained. , low tensile strength, etc.) are not suitable for practical use, and the object of the present invention cannot be achieved in terms of adhesion, and if the amount exceeds 10 parts by weight, the adhesiveness of the rubber composition is sufficient, but the rubber The heat aging resistance is extremely poor and it cannot be put to practical use. In the present invention, by blending the imidazole dithiocarboxylic acid compound and the vulcanization accelerator in combination, it is possible to obtain a rubber composition with further excellent processing stability and good adhesiveness. Furthermore, the rubber composition of the present invention may be mixed with toluene, methyl,
It is also possible to dissolve it in an organic solvent such as ethyl ketone to form a rubber cement, and to bond the non-adhesive compound to brass. [Example] Next, the present invention will be explained in more detail by showing Examples and Comparative Examples. However, the blending amount (parts) is expressed on a weight basis unless otherwise specified. In addition, various tests were conducted using the following methods. ○ Mooney scorch test The sample is a sheet approximately 3.0 mm thick, and JIS K-
After preparing a Mooney scorch test sample based on JIS K-6300, 5. Mooney scorch test, the Mooney scorch time (time required for the 5-point torque value to rise from the lowest viscosity) at a test temperature of 125°C was increased according to JIS K-6300, 5. Measured using a rotor. ○ Adhesion test with brass After molding the sample into a sheet approximately 2.5 mm thick, the sheet was placed on a 3 mm thick brass plate that had been sufficiently immersed in toluene to degrease it and dried, and the surface was molded using a press molding machine. pressure
Pressure molding was performed at 30 kg/cm ² and 148° C. for 45 minutes.
Next, the 180° peeling force was measured at 50 on an autograph with a width of 25 mm.
Measurement was performed at a peeling rate of mm/sec. The peel force was measured by leaving the sample at room temperature for one day after creating the peel sample (initial adhesive strength), and by keeping the adhesive sample at a constant temperature of 50℃ and 95% relative humidity to examine the change in peel force due to moisture permeation in the raw rubber. The peeling force was measured for the sample that was left in a constant humidity room for two weeks. Examples 1 to 3 and Comparative Examples 1 to 2 Each sample was prepared by mixing the compositions shown in Table 1 for 15 minutes on a 70°C mixing roll, and a Mooney scorch test was conducted. The results are also listed in Table 1.

【table】

[Table] In Comparative Example 2, when 2,4,6-trimercapto-1,3,5-triazine was blended, the scorch time was extremely short compared to 27'00'' in Comparative Example 1, and 20℃×60%RH×1 month or 40℃
It can be seen that the scorch time is greatly reduced when left for 1 month x 95% RH. On the other hand, 2-methylimidazole-4-dithiocarboxylic acid, 2-ethylimidazole-4-dithiocarboxylic acid, and 2-ethyl-4-methylimidazole-5-dithiocarboxylic acid are 2,4,6-trimethylcapto-1, It can be seen that the reduction in scorch time is smaller than with 3,5-triazine, and the stock stability is also greatly improved. In addition, in Examples 1, 2, and 3, the scorch time of imidazoledithiocarboxylic acid also varied depending on the structure of its substituent; It can be seen that -ethyl-4-methylimidazole-5-dithiocarboxylic acid has the greatest effect of shortening the scorch time.
However, 2,4,6-trimercapto-1,3,5
-Compared to triazine, the reduction is smaller and the rate of decrease in scorch time due to stocking is also lower. Examples 4 to 6 and Comparative Examples 3 to 7 Samples made of the compositions shown in Table 2 were prepared in the same manner as in Example 1, and subjected to the Mooney scorch test and the adhesion test to brass. The results are also listed in Table 2.

【table】

【table】

[Table] In this example, various imidazole dithiocarboxylic acid compounds with different structures were blended in an amount of about 1/100 mol each, and comparative evaluation was performed. From this evaluation result, in relation to Example 1, the imidazole dithiocarboxylic acid compound of each structure is 2,
It was found that the scorch time was less shortened than 4,6-trimercapto-1,3,5-triazine, and the strength of adhesion to brass was determined by the structure of the substituents of imidazole dithiocarboxylic acid. It turns out that there is a dependence. That is, in this evaluation, 2-methylimidazole-4-dithiocarboxylic acid, 2-ethylimidazole-4-dithiocarboxylic acid, 2-
Ethyl-4-methylimidazole-5-dithiocarboxylic acid shows good adhesive strength, whereas 2-phenylimidazole-4-dithiocarboxylic acid has a phenyl group or undecyl group at the 2-position of imidazoledithiocarboxylic acid. acid, 2-phenyl-4-
Methylimidazole-5-dithiocarboxylic acid and 2-undecylimidazole-4-dithiocarboxylic acid do not have adhesion to brass, and imidazole-4-dithiocarboxylic acid, which does not have a substituent, also has no adhesion to brass. It can be seen that it has no gender. Examples 7 to 18 and Comparative Examples 8 to 10 Samples made of each composition shown in Table 3 were prepared in the same manner as in Example 1, and subjected to the Mooney scorch test and the adhesion test to brass. The results are also listed in Table 3.

【table】

[Table] In this evaluation, 2-methylimidazole-4-dithiocarboxylic acid, 2-ethylimidazole-4-dithiocarboxylic acid, and 2-ethylimidazole-4 showed good adhesion in Examples 4 to 6. -dithiocarboxylic acid and 2-ethyl-4-methylimidazole-5-dithiocarboxylic acid, the relationship between the amount added to the NBR rubber composition and the resulting adhesive strength was investigated. As a result, sufficient adhesive strength was observed at approximately 1/200 mole (0.8 to 0.9 parts by weight) of each of the above three types of imidazole dithiocarboxylic acids, and the adhesive strength reached saturation at 1/100 mole. It can be seen that the adhesive strength remains constant even if the amount is increased. On the other hand, the scorch time gradually decreases as the amount of imidazole dithiocarboxylic acid is increased, but a sufficiently long scorch time is maintained even at 1/200 mol or more, which is sufficient for bonding. Moreover, in Examples 16, 17, and 18
It can be seen that the addition of SBR does not reduce the adhesive strength. Examples 19-27 Samples made of each composition shown in Table 4 were prepared in the same manner as in Example 1, and subjected to a Mooney scorch test and an adhesion test to brass. The results are also listed in Table 4.

【table】

[Table] The development of adhesive strength with brass is thought to be due to the primary bonding force between sulfur and brass, and the formation of this bond is influenced by the crosslinking speed and form of rubber, so in this evaluation, 3 that showed effects in Examples 20 to 27
Regarding methylimidazole dithiocarboxylic acid, we conducted an evaluation to confirm the ability to develop adhesive strength when the vulcanization system was changed. As vulcanization systems, we selected representative sulfeinamide-based CZ, thiuram-based TS, and thiazole-based DM. As a result of this evaluation, 2-methylimidazole-4-
Dithiocarboxylic acid, 2-ethylimidazole-4
It can be seen that there is no dependence of the above-mentioned three types of vulcanization systems on the adhesion properties of either -dithiocarboxylic acid or 2-ethyl-4-methylimidazole-5-dithiocarboxylic acid. [Effects] Based on the structure explained above, the rubber composition of the present invention has a longer scorch time than conventional rubber compositions containing triazine derivatives such as trimercaptotriazine, can prevent burns during kneading work, and can prevent burning caused by leaving the compound unattended. There is almost no progress of burn,
Processing stability can be imparted, and there is no need to use cement as in the past for adhesion to brass, improving productivity. Furthermore, since the rubber composition of the present invention has good adhesion to brass, it can be used for composites of rubber and brass or metal materials plated with brass, and is particularly suitable for hoses,
It is useful for molds, belts, tires, etc.

Claims (1)

[Scope of Claims] 1. A rubber composition used for forming a composite consisting of rubber and a metal material, at least one selected from natural rubber and sulfur-vulcanizable synthetic rubber.
For 100 parts by weight of seed raw rubber, the general formula (In the formula, R is an alkyl group having 10 or less carbon atoms,
A rubber composition having good adhesion to brass, characterized in that it contains 0.8 to 10 parts by weight of an imidazole dithiocarboxylic acid compound represented by R' (representing a hydrogen atom or an alkyl group having 10 or less carbon atoms).