JPH0931248A - Diene rubber composition - Google Patents

Abstract

(57) Abstract: [PROBLEMS] To provide a diene rubber composition having accelerated crystallization, improved mechanical properties, and excellent processability. A diene rubber containing a diene rubber, at least one selected from paraffins and higher saturated fatty acids, and at least one selected from a low molecular weight diene polymer, a higher unsaturated fatty acid and an ester of the higher unsaturated fatty acid. It is a rubber composition.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a diene rubber composition which has improved mechanical properties and processability and can be used as a substitute material for natural rubber.

[0002]

2. Description of the Related Art Synthetic diene rubbers such as polyisoprene have properties similar to natural rubber, and since they are synthetic products, their quality is stable, so they are used in various applications. Widely used. But,
Synthetic diene rubbers have a drawback that crystallization at a low temperature is slower than that of natural rubber, and therefore stretch crystallization does not occur even when stretched, and the rubber is cut without increasing stress. In other words, the synthetic diene rubber does not have high green strength (raw rubber strength) like natural rubber.

Therefore, the diene rubber is inferior in molding processability to natural rubber, and is required for manufacturing large tires and thread rubbers, which are required to have high processing characteristics (such as mechanical strength during processing) in product manufacturing. Could not be used as a substitute for natural rubber. On the other hand, natural rubber has a much better green strength than synthetic rubber and is excellent in processability, but in recent years, immediate allergies due to proteins contained in natural rubber are becoming a social problem, The measures are required.

On the other hand, the above-mentioned diene rubber, which is a synthetic product, does not contain any protein, and therefore there is no possibility of causing immediate allergy. Therefore, if the above-mentioned processability can be improved, the diene rubber can be a powerful substitute material for natural rubber. In particular, for rubber threads used in products such as underwear and paper diapers that come into direct or indirect contact with the human body, in recent years, due to their good fit, the return from polyurethane elastic threads to natural rubber has become remarkable. It is desired to develop a rubber material that does not cause the above-mentioned immediate allergy and has processability and mechanical properties equal to or close to those of natural rubber.

An object of the present invention is to solve the above-mentioned technical problems and to provide a diene rubber composition which has no possibility of causing immediate allergy, has improved mechanical properties and is excellent in processability. Is.

[0006]

The diene rubber composition of the present invention comprises a diene rubber, at least one selected from paraffins and higher saturated fatty acids, a low molecular weight diene polymer, a higher unsaturated fatty acid and the higher unsaturated fatty acid. It is characterized by containing at least one kind selected from esters of unsaturated fatty acids.

The inventors of the present invention conducted extensive research to find out the reason why natural rubber exhibits excellent mechanical properties. As a result, the fatty acid bound to the main chain of the natural rubber together with the protein promotes crystallization of the natural rubber. It was confirmed that it has contributed greatly to.
Therefore, the present inventors have repeatedly studied whether or not the crystallization characteristics of the diene rubber can be improved by applying the above findings to the diene rubber having a chemical structure similar to that of natural rubber. As a result, they have found that crystallization is promoted by introducing a hydroxyl group into polyisoprene having the same basic structure as natural rubber and then reacting it with stearyl chloride to introduce a stearoyl group into the main chain.

[0008] However, in the course of the research, it was discovered that the crystals were promoted by accident by simply adding a specific fatty acid to a diene rubber such as polyisoprene. As a result of further research, at least one of paraffins and higher saturated fatty acids and at least one selected from low molecular weight diene polymers, higher unsaturated fatty acids and esters of these higher unsaturated fatty acids were added to the diene rubber. By mixing the former, the former acts as a crystal nucleating agent and the latter acts as a plasticizer, promoting the crystallization of the diene rubber and obtaining new knowledge that the green strength is improved, and the present invention is completed. It came to do. That is, the improvement in green strength is a phenomenon in which the molecule is crystallized when the molecule is stretched and the drag force is increased. Therefore, it is considered that a composition that is more likely to be crystallized is improved in green strength.

Here, it is considered that the latter plasticizer has a function of facilitating the movement of the rubber molecules, facilitating the orientation of the rubber molecules in a predetermined coordination, and promoting crystallization. The diene rubber composition of the present invention preferably contains at least one selected from the paraffins and higher saturated fatty acids in an amount of 0.05 to 100 parts by weight of the diene rubber.
At least 5 parts by weight of the low molecular weight diene polymer, higher unsaturated fatty acid and its ester are contained in an amount of 0.05 to 5 parts by weight.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Examples of the diene rubber in the present invention include polymers or copolymers obtained by diene polymerization, and specific examples thereof include polybutadiene, polyisoprene, polychloroprene, butadiene-styrene copolymer. , Butadiene-acrylonitrile copolymer, isobutylene-isoprene copolymer and the like. Among them, polyisoprene having a molecular structure similar to that of natural rubber, particularly cis-1,4-polyisoprene, has a remarkable crystallization promoting effect.

The weight average molecular weight of the diene rubber used is preferably about 100,000 to 4,000,000. The paraffins and higher saturated fatty acids serve as a crystal nucleating agent which shows good dispersibility in the diene rubber and promotes crystallization. Examples of the paraffins include synthetic or natural paraffins having 6 or more carbon atoms, low molecular weight polyolefin having a number average molecular weight of 100 to 1000 (for example, low molecular weight polyethylene), and the like.

As the higher saturated fatty acid, for example, lauric acid, myristic acid, palmitic acid, stearic acid and the like have 10 or more carbon atoms, preferably 12 carbon atoms.
Approximately 18 can be mentioned. The low molecular weight diene polymer and the higher unsaturated fatty acid serve as a good plasticizer for the diene rubber and contribute to the promotion of crystallization. The low molecular weight diene polymer has a weight average molecular weight of 1,000 or less, preferably 500 to 100,000,
More preferably, it is 1,000 to 50,000 polyisoprene and the like.

The higher unsaturated fatty acid has, for example, 10 carbon atoms such as oleic acid, linoleic acid and linolenic acid.
As described above, those having about 12 to 18 carbon atoms are preferable. When using esters of these higher unsaturated fatty acids, there may be mentioned, for example, esters of linear or branched alkyl groups having 1 to 6 carbon atoms such as methyl groups and ethyl groups.

The diene rubber is mixed with the crystal nucleating agent and the plasticizer by an ordinary rubber mixing method using a roll, a Banbury mixer or the like. Alternatively, for example, these components are dissolved in an appropriate solvent and then the mixture is added. A method such as freeze-drying can also be used and is not particularly limited. The diene rubber composition of the present invention thus obtained has a vulcanizing agent (sulfur, sulfur-containing compound, etc.), a vulcanization accelerator, a reinforcing agent,
A known rubber compound such as a filler, a colorant, and a foaming agent is added and blended in a necessary amount according to the purpose, and ordinary molding and vulcanization are performed to obtain a desired rubber product. it can. At that time, the obtained diene rubber has a high degree of crystallinity and an excellent green strength, and is therefore excellent in processability in kneading, sheeting and various molding processes. Therefore, the diene rubber composition of the present invention is suitable as a raw material for general rubber products such as tires and thread rubbers.

[0015]

EXAMPLES The diene rubber composition of the present invention will be described in detail below based on examples. Examples 1-2 and Comparative Examples 1-2 With the compounding amounts shown in Table 1, cis-1,4-polyisoprene (Kuraprene IR10 manufactured by Kuraray Co., Ltd., weight average molecular weight: 1,
550,000 of a mixture of 450,000) with stearic acid and methyl linolenate was added to 50 ml of benzene, and then a freeze-dried diene rubber composition was obtained.

[0016]

[Table 1]

With respect to these diene rubber compositions, the crystallization rate at -25 ° C was measured by the following method. (Measurement Method of Crystallization Rate) The crystallization rate was measured using a dilatometer. That is, after putting 3 g of rubber into a 12 ml sample part, a capillary part was attached to this sample part, the inside of the system was evacuated, and mercury was filled inside, and the temperature was -25 ° C.
By immersing it in a liquid tank maintained at 1, to perform low temperature crystallization, and observing the displacement of mercury in the capillary part, the volume change of rubber due to crystallization was investigated over time.

The measurement results are shown in FIG. The crystallization rate of cis-1,4-polyisoprene itself as a blank is also shown in FIG. In FIG. 1, CPI means polyisoprene, SA means stearic acid, and ML means methyl linolenate. From FIG. 1, compared to the case where stearic acid and methyl linolenate were added to polyisoprene alone (Comparative Examples 1 and 2), crystallization was promoted in the case where both components were added (Examples 1 and 2). You can see that it is done. It is also found that the crystallization rate is equivalent to that of natural rubber. Example 3 The crystallization rate at −25 ° C. was measured in the same manner as in Example 2 except that linoleic acid was used instead of methyl linoleate. The results are shown in FIG. 2 together with the results of Example 2.

From FIG. 2, almost the same high crystallization-promoting action is observed even when unsaturated fatty acid which is a free acid is used instead of ester. Example 4 cis-1,4-polyisoprene (Kuraprene IR1
0) stearic acid and liquid polyisoprene (Kuraprene LIR 30, manufactured by Kuraray Co., Ltd., cis-1,4 structure: 68.7%,
Weight average molecular weight: 36,000) and the weight ratio is 99 /
Diene rubber compositions were obtained in the same manner as in Examples 1 and 2 except that the mixture was used in the proportion of 0.25 / 0.75 (IR10 / stearic acid / LIR30). Comparative Example 3 Same as Examples 1 and 2 except that a mixture of cis-1,4-polyisoprene and liquid polyisoprene alone in a weight ratio of 99/1 (IR10 // LIR30) was used. To obtain a diene rubber composition.

The crystallization rate of each rubber composition obtained in Example 4 and Comparative Example 3 was measured in the same manner as in Examples 1 and 2. The result is shown in FIG. FIG. 3 also shows the results of Example 2 and the blank. From Figure 3, liquid polyisoprene (Kuraprene, a low molecular weight diene polymer)
The crystallization rate is almost the same as the case of cis-1,4-polyisoprene alone (blank) only by adding 1% by weight of LIR30), but by adding stearic acid and the liquid polyisoprene, the crystal It can be seen that the conversion rate is improved to almost the same level as in Example 2.

[0021]

As described above, according to the present invention, the crystallization of the diene rubber is promoted, the mechanical properties are improved, and the diene rubber excellent in processability is obtained. Moreover,
Unlike the natural rubber, the diene rubber does not cause an immediate allergy, and thus has an effect of being suitable as a substitute material for the natural rubber.

[Brief description of drawings]

FIG. 1 is a graph showing the crystallization rate at −25 ° C. of the diene rubber compositions obtained in Examples 1 and 2 and Comparative Examples 1 and 2.

2] -25 ° C. of the diene rubber composition obtained in Example 3
2 is a graph showing the crystallization rate in FIG.

FIG. 3 is a graph showing the crystallization rate at −25 ° C. of the diene rubber compositions obtained in Example 4 and Comparative Example 3.

Claims (2)

[Claims] 1. A diene containing a diene rubber, at least one selected from paraffins and higher saturated fatty acids, and at least one selected from a low molecular weight diene polymer, higher unsaturated fatty acids and esters of these higher unsaturated fatty acids. Rubber composition. 2. With respect to 100 parts by weight of the diene rubber,
At least one selected from the paraffins and higher saturated fatty acids is contained in an amount of 0.05 to 5 parts by weight, and at least one selected from the low molecular weight diene polymer, the higher unsaturated fatty acid and the ester of the higher unsaturated fatty acid is 0. The diene rubber composition according to claim 1, wherein the diene rubber composition is contained in a proportion of 0.05 to 5 parts by weight, respectively.