JPS6295336A - Rubber composition - Google Patents

Abstract

PURPOSE:A rubber composition suitable for ink tubes, etc., having improved processing properties, long scorching time, stability, shorted vulcanization time and improved physical properties of vulcanized material obtained by blending raw material rubber with a scorch preventing agent and calcium stearate. CONSTITUTION:(A) 100pts.wt. raw material rubber comprising isobutylene- isoprene rubber having 350,000-450,000 viscosity-average molecular weight or obtained by blending the isobutylene-isoprene rubber with ethylene propylene rubber having 25,000-100,000 number-average molecular weight is blended with (B) a vulcanizing agent and a vulcanizing accelerator and (C) 0.2-5pts., preferably 0.2-3pts.wt. calcium stearate.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rubber composition containing calcium stearate as a scorch inhibitor.

Vulcanization accelerators, known as compounding agents for rubber compositions, exhibit an accelerating effect above a certain temperature. However, in general, the temperature at which the promoting effect is exerted is unclear, and when compounded into rubber, it becomes active even below the critical temperature, resulting in a phenomenon called scorch. The scorch phenomenon has become a serious problem in general rubber compounding, and in recent years, the scorch problem has become even more prominent as kneading equipment has become larger and rationalized by shortening cross-mixing time, and its prevention has become an extremely important issue. It has become.

Traditionally, to prevent scorch, it is necessary to store the fabric in a cool place to minimize heat history during the processing process, adjust the amount of vulcanizing agents and vulcanization accelerators, or add IJ [
Acids, amines, etc. are used. However, these compounding agents tend to improve the scorch time and at the same time lengthen the vulcanization time, so they are not a complete solution.

On the other hand, stearic acid is often used as an internal mold release agent in the rubber industry, but stearic acid tends to shorten the scorch.

The inventors of the present invention have conducted extensive research to solve these problems, and have found that by blending calcium stearate into a rubber composition based on butyl rubber or butyl rubber and EP rubber, the scorch time can be made extremely long. In addition, they have discovered that the vulcanization time can be shortened, productivity can be improved, and the release effect from the mold can be enhanced, and the present invention has been completed.

The raw rubber used in the present invention is butyl rubber or a mixture of butyl rubber and EP rubber. This raw R1 rubber can be one that is normally commercially available and is not particularly limited, but in practice, the viscosity average molecular weight of butyl rubber is about 3.
50,000 to 450.000, and the number average molecular weight of the EP rubber is preferably about 25,000 to 100.000. In addition, in the case of a mixture of butyl rubber and EP rubber,
It is desirable that the mixing ratio of EP rubber is 5 parts by weight to 30 parts by weight.

The present invention incorporates calcium stearate as an anti-scorch agent. The blending ratio is 0.0% per 100 parts of raw rubber.
It is 2 to 5 parts by weight, preferably 0.2 to 3 parts by weight. 0
．． If the amount is less than 2 parts by weight, the effect of incorporating calcium stearate cannot be increased by 1q. Further, from the viewpoint of economy and blooming of the rubber surface after vulcanization, 3 parts by weight is the practical upper limit.

Any known vulcanizing agent and vulcanization accelerator can be used. Vulcanizing agents include sulfur and MI yellow gold compound resin vulcanizing agents, and vulcanizing accelerators include 2-mercaptobenzothiacyl, tetramethylduram disulfide, N
-Cyclo=1sil-2-benzothiazyl, sulfuramide, etc.

A reinforcing agent, a filler, a softening agent, an awning prevention agent, a dispersing agent, etc. can be used as appropriate.

The rubber composition of the present invention has good processability, a long scorch time, is stable, and can shorten the vulcanization time, and the physical properties of the vulcanized product are better than those without calcium stearate or those with stearic acid. It's dripping with spots. Therefore, when inner tubes, waterproof sheets, etc. are made using this rubber composition, products with low air permeability, water permeability, and permanent elongation can be made without causing the problem of scorch.

Next, the present invention will be specifically explained using examples and comparative examples. In addition, parts in Examples and Comparative Examples mean parts by weight.

Examples and Comparative Examples Raw rubber: Isobutylene-isoprene copolymer rubber [Exxon Butyl 268 (trade name) manufactured by Exxon Chemical Co., Ltd.], ethylene propylene rubber (Vistalon 2200 (trade name) manufactured by Exxon Chemical Co., Ltd.) Compounding agent: Carbon black [Geast 1 manufactured by Tokai Carbon Co., Ltd., paraffin oil [Samper 1 manufactured by Sun Oil Co., Ltd.]
15), zinc oxide [manufactured by Sakai Kagaku Co., Ltd.], stearic acid [manufactured by Shin Nippon Rika Co., Ltd.], sulfur (manufactured by II+ Kagaku Co., Ltd.), calcium stearate [manufactured by Sankyoki Gosei Co., Ltd.], 2-mercaptobenzothiacyl [ Vulcanization accelerator M], tetramethylthuram disulfide (vulcanization accelerator TMT) For rubber composition evaluation, raw rubber was prepared using the raw material rubber and compounding agents listed above in the formulations shown in Tables 1 and 2. and the ingredients were mixed in a small Banbury type mixer (4L).

For mixing, first add the raw rubber at a Banbury side wall temperature of 80°C and a rotor rotation speed of 40 to 50 rpm, then add zinc oxide and half of the carbon black after 30 seconds, and then add the remaining carbon black and softener after 2 minutes and 30 seconds. This was done by adding . Then, the temperature of the jacket was adjusted so that mixing was completed in 6 minutes and the temperature of the mixture was 160°C.

The mixture prepared in this way was heated to 40°C.
The vulcanization accelerator, sulfur, calcium stearate or stearic acid were thoroughly mixed on a roll for 8 minutes, and then formed into a 2.5 mm thick rubber sheet.

Samples for measuring the physical properties of vulcanized rubber were vulcanized at the temperatures and vulcanization times shown in Tables 1 and 2, and then vulcanized with J+S K 630.
The 300% modulus, tensile strength, elongation at break, tear strength, and permanent elongation were measured using the test method No. 1.

The scorch time is the time required to increase by 5 points at 125°C and 1 to 3 points at 135°C using a Mooney viscometer.
Measurements were carried out under two measurement conditions: the time taken to reach the upper bound.

)+II curing speed is measured using a vibratory vulcanization tester (manufactured by Monnanto)
The measurements were carried out using a temperature of 170°C and a vibration angle of 5 degrees.

Figure 1 shows the relationship between the scorch times at 125°C and 135°C for the examples and comparative examples made of butyl rubber in Table 1, and Table 2 shows the examples and comparative examples of butyl rubber/EP rubber mixtures. At the same time, the relationship between scorch times is shown in Figure 2.

These results show that by using calcium stearate, a rubber composition with very excellent properties such as a long scorch time, a short vulcanization time, and little blooming phenomenon can be obtained.

[Brief explanation of drawings]

FIGS. 1 and 2 are graphs of the scorch time versus the blending ratio of stearic acid or calcium stearate in Examples and Comparative Examples. Patent Application Agent Patent Attorney Yuki Yamazaki Zo No. 1 Figure Weight Department

Claims (1)

[Claims] 100 weight of raw rubber is added to a rubber composition obtained by blending raw rubber with isobutylene-isoprene rubber (hereinafter referred to as butyl rubber) or ethylene propylene rubber (hereinafter referred to as EP rubber) and butyl rubber, and a vulcanizing agent and a vulcanization accelerator. A rubber composition containing 0.2 to 5 parts by weight of calcium stearate as a scorch inhibitor.