JPS6345702B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to anti-aging agents for rubber. It is well known that natural rubber or synthetic rubber products generally suffer from aging due to heat and aging due to repeated bending. Conventionally, various methods have been proposed to prevent such aging, and many of them involve the use of various anti-aging agents, such as phenyl-β-naphthylamine,
2,2,4-trimethyl-1,2-dihydroquinoline polymer or the like is used. However, even with these anti-aging agents, satisfactory performance in preventing aging due to heat and repeated bending has not yet been achieved.Especially in recent years, as rubber products have changed to radial tires and belt conveyors have increased in speed, There is a strong desire to maintain a long lifespan under conditions that are more prone to aging. For this reason, the present inventors particularly focused on heat resistance,
As a result of intensive studies on anti-aging agents that have excellent resistance to flex cracking, we have found that an anti-aging agent containing diphenylamine and the substituted diphenyl amine specified in the present invention in a specific ratio has extremely excellent heat resistance and flex resistance. Not only has performance,
It was discovered that the performance can be maintained even after long-term use, leading to the present invention. That is, the present invention uses 10 to 50% diphenylamine.
(wt%, the same applies hereinafter), preferably 20 to 40% and the following general formula () [In the formula, R ₁ and R ₂ represent a hydrogen atom, a C _3-12 alkyl group, or a C _7-9 aralkyl group. However, R ₁
and R ₂ are never both hydrogen atoms. ] The present invention provides an anti-aging agent for rubber which has excellent heat resistance and bending resistance and is composed of 90 to 50%, preferably 80 to 60%, of the substituted diphenylamine represented by the formula. Diphenylamine itself, which is a component of the anti-aging agent of the present invention, has no effect on the heat resistance of rubber;
In addition, although it has relatively excellent performance in terms of flex cracking resistance, it has high volatility, so the performance in flex cracking resistance deteriorates significantly after heat treatment, so it has not been used in practice as an anti-aging agent at all. It is. In addition, substituted diphenylamine, which is another component, has a problem in that although its volatility is suppressed compared to diphenylamine, it does not essentially improve heat resistance and also reduces flex cracking resistance. However, the present inventors have found that diphenylamine and substituted diphenylamine, which have the above-mentioned problems when used alone, are used together as anti-aging agents in the proportions specified in the present invention. They have discovered that it exhibits excellent heat resistance and flex cracking resistance. Examples of the compound represented by the general formula () used in the present invention include p-isopropyldiphenylamine, p,p'-di-isopropyldiphenylamine, p-butyldiphenylamine,
p,p'-di-butyldiphenylamine, p-amyldiphenylamine, p,p'-di-amyldiphenylamine, p-hexyldiphenylamine,
p,p'-di-hexyldiphenylamine, p-octyldiphenylamine, p,p'-di-octyldiphenylamine, p-nonyldiphenylamine, p,p'-di-nonyldiphenylamine, p-
Examples include dodecyldiphenylamine, p,p'-di-dodecyldiphenylamine, p,α-methylbenzyldiphenylamine, p,p'-di(α-methylbenzyl)diphenylamine, and these may be used alone or in combination. It is used as a mixture of two or more types. The anti-aging agent for rubber of the present invention is applicable not only to natural rubber but also to synthetic rubbers such as styrene-butadiene copolymer rubber, acrylonitrile-butadiene copolymer rubber, polybutadiene rubber, and polyisoprene rubber, and the amount added is 100 parts by weight of rubber. Usually 0.1 for
~7 parts by weight, preferably 0.5 to 4 parts by weight. The anti-aging agent of the present invention may be produced by appropriately selecting the degree of alkylation when alkylating diphenylamine, so that diphenylamine and substituted diphenylamine are in a predetermined ratio, or alternatively, each may be produced individually. The prepared diphenylamine and substituted diphenylamine may be mixed as appropriate, and the method is not limited and can be prepared arbitrarily. The anti-aging agent of the present invention has very excellent effects when used alone, but depending on the conditions and purpose of use, other additives, anti-aging agents such as N-phenyl-N'-alkyl-p-phenyl Nylenediamine, N-N'-diaryl-p-phenylenediamine, 2,2,4-trimethyl-1,2-
Dihydroquinoline polymers and the like may also be used. Next, the present invention will be specifically explained with reference to Examples. In addition, "Example middle part" indicates parts by weight. Example 1 100 parts of natural rubber, 45 parts of HAF carbon, 5 parts of zinc white
2.5 parts of sulfur, 1 part of stearic acid, 5 parts of process oil, 0.5 part of N-cyclohexylbenzothiazyl sulfenamide (vulcanization accelerator) and 2 parts of the anti-aging agent shown in Table 1 were added to a 6-inch mold by a conventional method. The mixture was mixed using a φ open roll and vulcanized at 140°C for 40 minutes to prepare a sample. Heat aging and flex cracking tests were conducted using this sample. The heat aging test was conducted in accordance with JIS K-6301, and the retention rate (%) of breaking strength was measured after heat aging at 100° C. for 48 hours using a test tube heat aging machine. The bending crack test was conducted in accordance with JIS K-6301, and a scratch with an original length of 2 mm was made on the sample, and the length of the scratch was measured after being bent 10,000 times. In addition, a similar test was conducted on a sample that had been heat aged in a gear oven at 100°C for 24 hours. The results are shown in Table 2.

【table】

[Table] Example 2 100 parts of styrene-butadiene rubber, HAF carbon
50 parts, process oil 5 parts, zinc white 5 parts, stearic acid 3 parts, sulfur 2.5 parts, N-cyclohexylbenzothiazyl sulfenamide (vulcanization accelerator) 1 part, and anti-aging agent shown in Table 1 2 parts were mixed using a 6-inch φ open roll in a conventional manner and heated to 145℃.
The heat resistance and flex crack resistance tests were conducted in the same manner as in Example 1 for the 30 minute vulcanized product. The heat aging condition was 110° C. for 24 hours, and the bending crack test measured the length after 5,000 times bending. The results are summarized in Table 2.

【table】

【table】

Claims (1)

[Scope of Claims] 1. An anti-aging agent for rubber characterized by comprising 10 to 50% by weight of diphenylamine and 90 to 50% by weight of a substituted diphenylamine represented by the following general formula. [In the formula, R ₁ and R ₂ represent a hydrogen atom, a C _3-12 alkyl group, or a C _7-9 aralkyl group. However, R ₁ and R ₂ are not both hydrogen atoms. ]