JPH04261443A - Rubber additive and rubber composition - Google Patents

Abstract

PURPOSE:To provide a rubber additive capable of giving a rubber composition excellent in freeze-resistance and frictional resistance and provide a rubber composition compounded with the rubber additive. CONSTITUTION:The objective rubber additive contains the ester of trimethylolpropane and a higher fatty acid containing 50-90wt.% of isostearic acid. A rubber composition is produced by compounding the rubber additive.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber additive capable of producing a rubber composition having excellent cold resistance and friction resistance, and a rubber composition containing the rubber additive.

0002

2. Description of the Related Art Rubber products generally harden and lose elasticity at temperatures below the freezing point. Rubber products that are used under dynamic conditions over a wide temperature range from below freezing to above room temperature, such as automobile tires, anti-vibration rubber, and diaphragms, lose their performance when their elasticity decreases at low temperatures. There is a tendency to decrease. Therefore, rubber compositions used in these rubber products are desired to have good cold resistance.

[0003] In order to improve the cold resistance of the rubber composition,
It is most preferable to use a rubber that is the main raw material with a low glass transition point, but lowering the glass transition point of the raw material rubber will affect other properties of the rubber composition, such as strength, skid resistance, and spring constant. Because of this, the type of raw material rubber used was often limited.

[0004] Therefore, a method has been proposed in which esters of higher fatty acids or higher alcohols are used in place of the petroleum softeners conventionally used in rubber compositions.

Examples of these synthetic plasticizers include straight chain fatty acids having 10 to 20 carbon atoms (such as myristic acid, palmitic acid, stearic acid,
oleic acid, etc.) and neopentyl type polyol (see JP-A No. 62-253641), the number of carbon atoms is 1.
Esters of 0 to 20 straight chain fatty acids and trimethylolpropane (see JP-A-1-113444), esters obtained by reacting polyhydric alcohols or higher alcohols, higher unsaturated fatty acids and glycols (JP-A-1-113444); 1
22532), etc.

These conventional synthetic plasticizers have a low coagulation temperature and a small amount of volatilization, so they can maintain the effect of improving the cold resistance of the rubber composition over a long period of time, while improving dynamic physical properties such as frictional resistance. There was a problem that the decrease in .

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a rubber additive that makes it possible to obtain a rubber composition that is excellent in both cold resistance and friction resistance, and a rubber composition containing the rubber additive. With the goal.

[0008]

[Means for Solving the Problems] That is, the present invention provides a rubber additive containing an ester of a higher fatty acid containing isostearic acid as a main component and a trihydric alcohol other than glycerin, and a rubber additive that can be applied to natural rubber. and/or a rubber composition characterized in that at least 5 parts by weight of one or more diene-based synthetic rubbers are blended based on a total of 100 parts by weight.

[0009] The higher fatty acid used in the present invention has isostearic acid as a main component.

[0010] In the present invention, the isostearic acid content in the higher fatty acid is 50 to 90% by weight, preferably 60 to 90% by weight.
It is preferably 70 to 85% by weight, more preferably 70 to 85% by weight. If the isostearic acid content is less than 50% by weight, there is no effect of improving the cold resistance of the resulting rubber composition.

[0011] Since the amount of isostearic acid obtained from hydrolysis of animal and vegetable oils is not large enough to be used on an industrial scale, the isostearic acid used in the present invention is usually oleic acid obtained by hydrolyzing natural oils and fats. A by-product is used when synthesizing dimer acid from higher fatty acids containing a large amount of . Since the dimer acid and the mixture produced by the side reaction contain various components with similar physicochemical properties, it is difficult and costly to extract isostearic acid from the product mixture and purify it to a high purity.
Further, even if the purity of isostearic acid is increased to more than 90% by weight, there is little increase in cold resistance, so it is not necessary to increase the purity to more than 90% by weight.

On the other hand, in general, compounds have a property that the freezing point is lower when similar compounds are mixed together than when the purity is close to 100%, and although we have not confirmed this with 100% purity, this study It is believed that the same applies to the inventive esters. Therefore, cold resistance is rather improved by using a mixture containing about 10% by weight of higher fatty acids other than isostearic acid.

Trihydric alcohols other than glycerin used in the present invention include trimethylolpropane, trimethylolethane, and the like.

Rubbers used in the present invention include natural rubber and diene-based synthetic rubbers having side chains in the molecular structure such as styrene-butadiene rubber, isoprene rubber, and isoprene-based rubber.
Mention may be made of butadiene rubber, isoprene-butadiene-styrene copolymer, nitrile rubber and chloroprene. Incidentally, these rubbers may be used alone or in a blend. Also, these rubbers may be blended with other diene-based synthetic rubbers that can be vulcanized with sulfur.

Like conventional plasticizers, the additive of the present invention acts as a lubricant by intervening between rubber molecules or between rubber and a reinforcing agent in a rubber composition. Therefore, if a large amount is added, strength properties such as abrasion resistance and tear resistance will deteriorate. Therefore, the proportion in the rubber composition should be 3.
The content is preferably 0% by weight or less, and if it exceeds 30% by weight, the practical strength will be insufficient. On the other hand, if the amount is small, the cold resistance improvement effect of the additive will be reduced, so at least 5 parts by weight are required per 100 parts by weight of rubber.

[0016]

[Action] When conventional higher fatty acid or higher alcohol esters are used as rubber additives, ester molecules are interposed between rubber molecules, separating adjacent rubber molecules, and the ester molecules also act as a lubricant. Therefore, it is presumed that the physical properties of the rubber composition deteriorate. The present invention enables higher fatty acids to have a branched structure with short side chains, so that the side chains of ester molecules and the side chains of rubber molecules, such as styrene residues in SBR and methyl groups in natural rubber, are intertwined. A weak bond is formed between the rubber molecules and the degree of deterioration of the physical properties of the rubber composition is weakened.In addition, if there is a short side chain, it becomes a steric hindrance and prevents the ester molecules from aligning at low temperatures. This invention was developed based on the hypothesis that the cold resistance of the rubber composition would be improved by lowering the freezing point of the rubber composition.

[0017]

[Example] 60 parts by weight of butadiene rubber (hereinafter "parts by weight" will be referred to as "parts"). To 100 parts of rubber consisting of 40 parts of styrene-butadiene rubber, 55 parts of the following rubber additives, 70 parts of carbon black, 3 parts of zinc white, 2 parts of stearic acid, 2 parts of sulfur, and cyclohexyl and benzothiazyl were added. A rubber composition was prepared by blending 1.5 parts of sulfenamide and 1 part of an anti-aging agent. Rubber additive TMIS-1: Ester TMI of higher fatty acid and trimethylolpropane containing 40% by weight of isostearic acid
S-2; Ester TMIS-3 of higher fatty acid and trimethylolpropane containing 50% by weight of isostearic acid
TMIS-4, an ester of higher fatty acid and trimethylolpropane containing 60% by weight of isostearic acid;
Ester of higher fatty acid containing 70% by weight of isostearic acid and trimethylolpropane TMIS-5; Ester of higher fatty acid and trimethylolpropane containing 80% by weight of isostearic acid TMIS-6; Higher fatty acid containing 90% by weight of isostearic acid and trimethylol Propane ester TMOL; Ester OIL of higher fatty acids mainly composed of oleic acid and trimethylolpropane; Naphthenic petroleum softener commonly used for rubber

The following tests were conducted on the above rubber composition. The results are shown in "Table 1". (1) 23° hardness: Hardness measured at a temperature of 23°C (23° hardness)
) -5° hardness: Hardness measured at a temperature of -5°C (3)
-15° hardness: Hardness measured at a temperature of -15°C (4)
-5°Hardness increase rate: After aging at a temperature of 70°C for 4 weeks, the change in hardness measured at a temperature of -5°C with respect to the hardness at a temperature of 23°C before aging.

[Equation 1] (5) -15°Hardness increase rate: After aging at a temperature of 70°C for 4 weeks, the change in hardness measured at a temperature of -15°C with respect to the hardness at a temperature of 23°C before aging.

[Equation 2] (6) Pico wear: Measured according to the American testing material standard ASTM (the higher the value, the better) (7) Tα (°C): When measured at different temperatures using a spectrometer manufactured by Iwamoto Seisakusho Loss tangent (ta
nδ) at its maximum value (here, Tα is the temperature at which the rubbery elastic region transitions to the glassy region under dynamic conditions, which is usually about 20°C higher than the statically measured glass transition point).

[0019]

[Table 1]

Blend A (comparative example 1) using a conventional petroleum softener has excellent hardness and pico wear at room temperature, but Tα
It can be seen that the temperature is high and the cold resistance is poor. On the other hand, B formulation (Comparative Example 2), which contains oleic acid ester, which is conventionally used as a cold-resistant plasticizer, has low Tα and excellent cold resistance, but is inferior in hardness and pico wear at room temperature. I understand.

[0021] In Examples 1 to 5, the rate of increase in hardness is smaller than that of Blend A, and Tα is also lower, indicating that they are excellent in cold resistance. Furthermore, F to H combinations (Examples 3 to 5)
It can be seen that Pico wear is higher than that of Blend A, and there is no deterioration in dynamic properties.

[0022] D to H formulations (Examples 1 to 5) all have a smaller hardness increase rate and hardness change rate over time than B formulation, are superior in cold resistance, and have higher purity of isostearic acid. It can be seen that the cold resistance improves as the temperature increases. Also, regarding pico friction, it is superior to B formulation, especially F, G, and H formulations.
It can be seen that it is superior to the combination.

[0023] E blend (Example 2) and F blend (Example 3)
The reason why there is a large difference in the effect between isostearic acid and ester is that the number of isostearic acid esters bonded in one molecule is two or more in all molecules in the F formulation, and the side chain of isostearic acid becomes a steric hindrance. It is assumed that this is because the linear chain portions of the fatty acids are close to each other and the molecules are arranged because not all two fatty acids are bonded in E formulation. Therefore, in order to improve cold resistance without reducing dynamic physical properties, it is preferable that at least two isostearic acids are combined, and the amount of isostearic acid contained in the raw material higher fatty acid is 50 to 90% by weight, Preferably 60 to 90% by weight, more preferably 7
It can be seen that the content is 0 to 85% by weight.

[0024]

[Effects of the Invention] By using the rubber additive of the present invention, it is possible to obtain a rubber composition that is excellent in both cold resistance and friction resistance.

Claims (6)

[Claims] 1. A rubber additive containing an ester of a higher fatty acid mainly composed of isostearic acid and a trihydric alcohol other than glycerin. 2. The rubber additive according to claim 1, wherein the trihydric alcohol is trimethylolpropane. [Claim 3] Higher fatty acids contain isostearic acid by 50%
The rubber additive according to claim 1, containing ~90% by weight. Claim 4: An ester of a higher fatty acid containing isostearic acid as a main component and a trihydric alcohol other than glycerin is mixed with one or two of natural rubber and/or diene-based synthetic rubber.
At least 5 parts per 100 parts by weight of rubber of
A rubber composition characterized in that it contains parts by weight. 5. The rubber composition according to claim 4, wherein the trihydric alcohol is trimethylolpropane. [Claim 6] The higher fatty acid contains isostearic acid by 50%.
5. The rubber composition according to claim 4, comprising ~90% by weight.