JPS631979B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a vibration-proof rubber composition having a hardness (JIS-A) in the range of 55 to 80. More specifically, a composition comprising a diene rubber containing at least 40% by weight of natural rubber and/or polyisoprene rubber and a reactive low molecular weight styrene-butadiene terpolymer containing chloromethylstyrene, The present invention relates to a vibration-proof rubber composition that has excellent processability and is excellent in flex cracking resistance, vibration absorption properties, compression set, etc. required for vibration-proof rubber. In general, in order to prevent noise and vibration from transportation such as cars and motorcycles, as well as industrial machinery, etc.
So-called anti-vibration rubber is used. The characteristics required of this type of anti-vibration rubber are: (1) It must be hard enough to support large static loads. That is, a static spring constant of a certain value or more is required as necessary. (2) The transmission coefficient of external force when receiving a dynamic load of 100 to 200 Hz is small, that is, the dynamic spring constant is small. This means that the vibration absorption rate is high, but the static-dynamic ratio (dynamic spring constant/static spring constant at 100Hz) is generally used as a parameter to express both characteristics (1) and (2). It can be said that the smaller the value, the better the anti-vibration characteristics. (3) Good repeated fatigue resistance. Since anti-vibration rubber is repeatedly subjected to external forces over a long period of time, it generally tends to crack and eventually break. In particular, the higher the hardness of the material, the more likely it is that the flex cracking resistance and elongation cyclic fatigue properties will deteriorate.Therefore, a rubber material with high hardness and excellent cyclic fatigue properties is desired. In order to increase the hardness, it is usually possible to increase the amount of carbon black filled or increase the amount of vulcanizing agent, but in the former case, the processability during kneading and molding, and the heat generation properties of the vulcanizate decrease. , the static-dynamic ratio increases. Further, in the latter case, there is a problem in that the repeated fatigue resistance properties are significantly deteriorated, and the above properties cannot be fully satisfied simply by increasing the amount of carbon black or the amount of vulcanizing agent. In order to solve the above problems, there is a method of adding a reactive plasticizer to the rubber, which acts as a plasticizer during processing and increases the molecular weight after the crosslinking reaction or is incorporated into the crosslinked network. Currently, a general method that expects the effect of a reactive plasticizer is to use a liquid rubber with a molecular weight of about 1,000 to 10,000 that has a moderate plasticizing effect and a COOH group in the molecule or at both ends of the molecule.
Liquid rubber with functional groups such as OH groups and SH groups used in combination with a crosslinking agent, 2. Method using liquid rubber polysulfide, 3. No specific functional groups and number average molecular weight close to 10,000 to 100,000. There is a method of using materials (for example, low-molecular-weight polybutadiene, low-molecular-weight polyisoprene) that take into account the balance between plasticizing effect and crosslinking property. However, in method 1, there is no suitable crosslinking agent that satisfies processability and crosslinking reactivity at the same time, and in methods 2 and 3, low molecular weight polymers that do not participate in crosslinking remain, so a sufficient increase in hardness is expected. Can not. As a result of intensive research to solve the above problems, the present inventors have found that by using a specific reactive plasticizer, it is possible to use conventional high-hardness anti-vibration rubber and natural rubber filled with a reactive plasticizer. The inventors have discovered that a vibration-proof rubber composition with superior vibration-damping properties can be obtained, and have arrived at the present invention. That is, the present invention provides (A) diene rubber 100 containing at least 40% by weight of natural rubber and/or polyisoprene rubber.
Based on the weight part, (B) chloromethylstyrene with an intrinsic viscosity [η] of 0.1 to 1.3 d/g at 30°C in toluene and a chloromethylstyrene content of 2 to 10% by weight;
This is a vibration-proof rubber composition containing 5 to 50 parts by weight of a styrene-butadiene terpolymer. The diene rubber (A) constituting the rubber composition of the present invention is made of natural rubber and/or polyisoprene rubber, or contains at least 40% of them.
% by weight, with the remainder being a diene rubber such as polybutadiene rubber, styrene-butadiene rubber, or acrylonitrile-butadiene rubber. [η] of the chloromethylstyrene-containing styrene-butadiene terpolymer used in the present invention is from 0.1 to
It needs to be within the range of 1.3 d/g, preferably 0.3 to 1.0 d/g. When [η] is less than 0.1, it is not preferable because it does not participate sufficiently in crosslinking and vibration-proofing properties such as hardness, modulus, and compression set deteriorate. On the other hand, if it exceeds 1.3 d/g, no softening effect can be expected as a low molecular weight copolymer. The chloromethylstyrene content in the chloromethylstyrene-containing styrene-butadiene terpolymer is from 2 to 10% by weight. If the chloromethylstyrene content exceeds 10% by weight, the balance between hardness and flex cracking resistance will be poor, and if it is less than 2% by weight, sufficient crosslinking will not be formed. The total styrene content (total of chloromethylstyrene and styrene) in the terpolymer is determined from the viewpoint of processability and physical properties.
It is preferably 30% by weight or less. The anti-vibration rubber composition of the present invention comprises diene rubber (A) 100
Contains 5 to 50 parts by weight of the chloromethylstyrene-containing styrene-butadiene terpolymer (B), but if the amount of the terpolymer (B) added is less than 5 parts by weight does not improve workability, and if it exceeds 50 parts by weight, the hardness increases and the repeated elongation fatigue properties are impaired. The method for mixing the diene rubber (A) and the terpolymer (B) is not particularly limited, and any method can be adopted. The anti-vibration rubber composition of the present invention may contain crosslinking agents, crosslinking aids, reinforcing agents, fillers, processing aids, anti-aging agents, and other compounding agents that are usually blended into rubber. There is no particular restriction on the amount of these additions, and they can be determined as appropriate as necessary. Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples. Examples 1 and 2 and Comparative Examples 1 to 5 (1) Formulation The formulations of the Examples and Comparative Examples in Table 1 are shown below. The units of numbers in the table are parts by weight.

[Table] (2) Processability, physical properties Compound Mooney viscosity ML100℃1+4 was adopted as a guideline for processability. Hardness and compression set were measured in accordance with JIS K6301. The compression set conditions are 70°C for 22 hours. For the static-dynamic ratio and static spring constant, Young's modulus values measured by a viscoelastic spectrometer manufactured by Iwamoto Seisakusho were used. Bending crack resistance is determined by the number of bends N per 10 mm of crack growth in the Dematschier bending crack growth test.
It is evaluated by multiplying by 10 ^-4 . However, it is meaningless to directly compare samples with different hardnesses, so in the graph where the 300% modulus of each sample is plotted against N x 10 ^-4 , the 300% modulus is set to 100 Kgf/ ^cm2. The standard for flex cracking resistance is N×10 ^-4 when
Therefore, the larger the value, the better the characteristics. These results are shown in Table 2.

[Table] The compound Mooney viscosity of Examples 1 and 2 is
It is smaller than that of Comparative Example 2, and it can be seen that the workability of Examples 1 and 2 is better than that of Comparative Example 2.
Furthermore, it can be seen that the vibration damping properties of Examples 1 and 2 are also superior to that of Comparative Example 2, since the static-dynamic ratio is small and the static spring constant and flex crack resistance are large. It can be seen that the vibration damping properties of Examples 1 and 2 are better than those of Comparative Examples 1 to 5, and are particularly excellent in flex crack resistance. It is also clear that the composition of the present invention has a small compression set and excellent compression set. As mentioned above, the composition to which the low molecular weight styrene-butadiene terpolymer containing chloromethylstyrene according to the present invention is added has better anti-vibration properties than the compositions to which conventional liquid rubber or highly aromatic extender oil is added. It can be seen that it has excellent properties, flex cracking resistance, and compression set. Examples 3 to 5 and Comparative Examples 6 and 7 (1) Formulation The plasticizers of Examples 3 to 5 and Comparative Examples 6 and 7 were:
The chloromethylstyrene-containing styrene-butadiene terpolymer shown in Table 3 is used. Table 3 shows the chloromethylstyrene content, intrinsic viscosity in toluene at 30°C (abbreviated as [η]TL 30°C in the table), and total styrene content of the terpolymer.

[Table] The formulation is the same as in Example 2 in Table 1. (2) Processability and physical properties Processability and physical properties were evaluated in the same manner as in Examples 1 and 2, and the results are shown in Table 4. [η] In Comparative Example 6 where TL 30°C is smaller than 0.1, Example 3
-5, the hardness is smaller and the compression set is larger. Furthermore, compared to Examples 3 to 5,
So-called anti-vibration properties such as static spring constant are poor. In addition, when [η] TL 30°C is 1.5 d/g (Comparative Example 8), which is larger than the range of the present invention, the compound Mooney viscosity is extremely high compared to Examples 3 to 5, resulting in poor workability.
Furthermore, the flex cracking resistance is also poor. Thus, it can be seen that there is an appropriate range for [η]TL 30°C of the low molecular weight styrene-butadiene terpolymer containing chloromethylstyrene.

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Claims (1)

[Claims] 1. Diene rubber (A) 100 containing at least 40% by weight of natural rubber and/or polyisoprene rubber
Chlormethylstyrene with an intrinsic viscosity [η] of 0.1 to 1.3 d/g at 30°C in toluene and a chloromethylstyrene content of 2 to 10% by weight based on the weight part.
A vibration-proof rubber composition containing 5 to 50 parts by weight of a styrene-butadiene terpolymer (B).