JPH0216338B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a method for producing vulcanized foams of 1,2 polybutadiene. For more details,
This invention consists of 40 to 100 parts by weight of 1,2 polybutadiene with a vinyl bond content of 70% or more and a crystallinity of 10 to 50%, and 60 to 0 parts by weight of one or more types of raw rubber selected from natural rubber and synthetic rubber. 1 to 20 parts by weight of a blowing agent having a mixing ratio of dinitrosopentamethylenetetramine and azodicarbonamide of 8/1 to 1/1, a vulcanizing agent, and a vulcanization accelerator. The foaming agent, foaming aid, filler, and other compounding agents are kneaded together, heated at a temperature above the decomposition temperature of the foaming agent, and then pressurized and then pressurized to achieve excellent dimensional stability and uniform, fine, independent foam with only primary vulcanization. The present invention relates to a method for producing a 1,2 polybutadiene vulcanized foam having a cellular structure. A method of producing a foam by heating a composition of 1,2 polybutadiene mixed with a vulcanizing agent, a blowing agent, and other additives and performing only primary vulcanization is known. The blowing agents conventionally used to produce 1,2 polybutadiene vulcanized foam include organic blowing agents such as nitroso-based, azo-based, and hydrazine-based blowing agents, and inorganic blowing agents such as sodium bicarbonate and ammonium bicarbonate. . However, with these foaming agents, slight changes in heating temperature and heating time during vulcanization and foaming result in unstable dimensions of the resulting foam, resulting in uneven foam structure. In order to produce fine and uniform foams, it is necessary to strictly control conditions such as heating temperature and heating time, resulting in a decrease in production efficiency. The inventors have been conducting intensive studies to solve these drawbacks for some time, and found that 1,2 polybutadiene is used as a mixture of one or more types of natural rubber and synthetic rubber, and it is used in an amount of 40 to 100% by weight of the entire mixture. By using two types of blowing agents, dinitrosopentamethylenetetramine (hereinafter referred to as DPT) and azodicarbonamide (hereinafter referred to as ADC) in a specific ratio, the vulcanization and foaming conditions are not controlled so strictly. In both cases, it was discovered that a foam consisting of fine closed cells with excellent dimensional stability and a uniform cell structure can be obtained. In order to obtain a foam with a uniform foam structure, the 1,2 polybutadiene used in the present invention must have a vinyl bond content of 70% or more and a crystallinity of 5 to 50%, and its intrinsic viscosity is 0.7. ~3.0 is preferred. The 1,2-polybutadiene of the present invention is mixed with one or more types of so-called raw rubber, such as natural rubber and synthetic rubber, depending on the properties of the target foam, and the proportion used is 40 to 40% of the total weight of the raw rubber. 100
Weight%. If it is less than 40% by weight, the foam will shrink significantly and it will be difficult to obtain a foam with good dimensional stability. The raw rubber to be mixed and used is not particularly limited, but typical examples include polyisoprene rubber, styrene-butadiene rubber, high styrene rubber, polybutadiene rubber, acrylonitrile-butadiene rubber, chloroprene rubber, and ethylene propylene rubber. The blowing agent must be used in combination with DPT and ADC, and the purpose of the present invention cannot be achieved if either one is used alone. Their blending ratio is DPT/
The weight ratio of ADC is 8/1 to 1/1, preferably 4/1 to 2/1. If the DPT exceeds this value, the foam tends to become non-uniform, resulting in color unevenness in the appearance of the foam. Furthermore, if the amount of ADC exceeds this range, the vulcanization rate will slow down and the foamability and dimensional stability will deteriorate. The amount of the blowing agent to be used is appropriately determined depending on the desired expansion ratio, and is 1 to 20 parts by weight based on a total of 100 parts by weight of 1,2 polybutadiene and raw rubber.
If the amount of the blowing agent used is less than the above range, only a foam with an extremely low expansion ratio will be obtained; if the amount of the blowing agent used is more than the above range, most of the gas generated by the decomposition of the blowing agent will be in the composition. They can escape to the outside without being incorporated into the interior, which can lead to cracks in the resulting foam. Vulcanization in the present invention is carried out by a general method, such as a sulfur-vulcanization accelerator system or an organic peroxide, but it is particularly preferable to use a sulfur-vulcanization accelerator system, which is inexpensive and has excellent storage stability. is preferred.
Further, in the composition of the present invention, other compounding agents that are blended in general rubber compositions, such as fillers, activators, anti-aging agents, processing aids, etc. may be added as appropriate. There are no particular limitations on the method of mixing the formulations in the present invention, such as a Banbury type mixer, a pressure kneader,
Any mixing method used for general rubber compounds such as oven rolls may be used, and mixing is preferably performed at a temperature in the range of 70 to 120°C. The mixture thus obtained is fed into a mold and heated to 130-180°C under pressure, preferably
The compound is vulcanized and the blowing agent is decomposed by heating in a temperature range of 140 to 170° C. and above the decomposition temperature of the blowing agent. The mold clamping pressure is required to substantially suppress the expansion of the gas generated by the decomposition of the blowing agent, and is usually carried out at a pressure of 80 kg/cm ² or more. The foam produced according to the present invention is used for footwear materials (outer soles, inner soles, midsoles, etc.), industrial products, cushioning materials, packaging materials, and the like. Next, the present invention will be specifically explained with reference to Examples and Comparative Examples. In Examples and Comparative Examples, 100% tensile stress (M100), breaking strength (TB), breaking elongation (EB), and tear strength (TR-B) are JISK6301.
The hardness was measured using a rubber tester type C (sponge hardness tester made by Kobunshi Keiki), the density was measured by the buoyancy method, and the foaming ratio was measured according to a conventional method. The foam structure was evaluated using a 40x magnifying glass according to the following criteria. ◎: Bubbles are fine and uniform. ○: Bubbles are fine and relatively uniform. Δ: Bubbles are small but non-uniform. ×: Bubbles are large and non-uniform. In addition, the appearance of the foam was evaluated by visually observing conditions such as surface roughness, blisters, and cracks, and using the following criteria. ◎: There are no cracks or blisters, and the surface texture is good. ○: There are no cracks or blisters, but the surface texture is poor. △: There are no cracks, but there are blisters and the surface texture is poor.
JSRRB820, vinyl bond content 92%, crystallinity 25
% [η] toluene at 30°C = 1.25) with polyisoprene rubber (JSRIR2200 manufactured by Japan Synthetic Rubber Co., Ltd.) and high styrene rubber (JSR0061 manufactured by Japan Synthetic Rubber Co., Ltd.) at 60:
The mixture was added at a weight ratio of 30:10 to 100 parts by weight, and DPT/ADC was used as a blowing agent at varying ratios, and the mixture was kneaded at the mixing ratio shown in Table 1.
A foam was obtained by vulcanization at 155°C for 12 minutes. The results are shown in Table 1. From these results, it is clear that Examples 1 to 4 provide foams with excellent physical properties, foam structure, and appearance. Comparative Examples 1 to 3 Using the same raw materials as Examples 1 to 4, a blowing agent was added.
When DPT and ADC are used alone
The method of Examples 1-4 was repeated with the DPT/ADC ratio reduced to 1/2. The results are also listed in Table 1. In Comparative Example 1, elongation at break and tear strength decreased. In addition, the foam structure was non-uniform, the appearance was blistered, and the surface texture was poor. In Comparative Examples 2 and 3, the vulcanization rate was slow and the vulcanization temperature was 155
A good foam could not be obtained at ℃. Although a foam was obtained by raising the vulcanization temperature and lengthening the vulcanization time, the foaming ratio was small and the tensile stress and breaking strength were lowered, which was not preferred for practical use.

[Table] Example 5, Comparative Example 4 Using the same raw materials as Examples 1 to 4, changing the amounts of 1,2 polybutadiene, crude rubber, and blowing agent as shown in Table 2, and changing the vulcanization temperature and vulcanization time. Except for this, the methods of Examples 1 to 4 were repeated to examine changes in expansion ratio. Figure 1 shows the relationship between vulcanization temperature and foaming ratio when the vulcanization time is constant for 12 minutes and the vulcanization temperature is varied.
Figure 2 shows the relationship between vulcanization time and expansion ratio when the vulcanization temperature was kept constant at 155°C and the vulcanization time was varied. From these results, it is clear that according to the present invention, even if the vulcanization temperature and vulcanization time are varied, the expansion ratio of the foam does not change much and the dimensional stability is excellent.

【table】

【table】 [Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between vulcanization temperature and expansion ratio of the compositions of Example 5 and Comparative Example 4, and FIG. 2 is a graph showing the relationship between vulcanization time and expansion ratio.

Claims (1)

[Claims] 1 Vinyl bond content is 70% or more and crystallinity is 5
A total of 100 parts by weight of 40 to 100 parts by weight of ~50% 1,2-polybutadiene and 60 to 0 parts by weight of one or more types of raw rubber selected from natural rubber and synthetic rubber,
Vulcanization and foaming in the presence of a vulcanizing agent and 1 to 20 parts by weight of a blowing agent containing dinitrosopentamethylenetetramine and azodicarbonamide in a ratio of 8/1 to 1/1 by weight to form a closed cell foam. A method for producing a vulcanized foam of 1,2 polybutadiene, characterized by: