JPS6144101B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention prevents the generation of bubbles in vulcanized rubber,
Moreover, the compression strain of vulcanized rubber is excellent.
Related to EPDM rubber compositions. Due to its excellent ozone resistance, weather resistance, and heat resistance, EPDM is widely used in automotive weather strips, water hoses, air hoses, packing materials, construction window frame rubber, electric wire covering rubber, etc. ing. By the way, in recent years, continuous extrusion vulcanization methods such as liquid bath vulcanization (LCM), fluidized bed vulcanization (PCM), high frequency (UHF) vulcanization, and hot air vulcanization (HAV) have become available as methods for producing EPDM vulcanized products. In these manufacturing methods, which are often used, almost no external pressure is applied during the vulcanization process, and the water contained in the rubber material turns into steam due to heating during the vulcanization process, which causes bubbles to form in the vulcanized rubber. This is a contributing factor. Therefore, in the prior art, in order to prevent the generation of bubbles due to this moisture, a method has been used in which quicklime is blended into rubber to trap the moisture with quicklime, and the quicklime is converted into slaked lime. However, by blending quicklime in this way, the generation of air bubbles can be prevented, but EPDM
The disadvantage was that the permanent compression strain of the vulcanized rubber increased. As a result of various studies on methods to eliminate such drawbacks, the present inventor found that when 2.5 to 10 parts by weight of higher fatty acids having 10 or more carbon atoms are blended with 1 to 20 parts by weight of quicklime per 100 parts by weight of EPDM, It has been found that a rubber composition can be obtained which has excellent compression set in vulcanized rubber as well as prevention of bubble generation. Normally, when fatty acids such as stearic acid are used as a rubber compounding agent, in the case of EPDM rubber, the amount of fatty acids blended is in the range of 0.5 to 2 PHR. However, the present inventor recommends that a large amount of fatty acids such as stearic acid be incorporated in EPDM formulations containing quicklime, although literature recommends incorporating as little amount as possible to prevent physical properties such as tensile stress from decreasing. We have found that compression set can be improved by The present invention is based on this knowledge. That is, the present invention provides a rubber composition characterized in that 1 to 20 parts by weight of quicklime and 2.5 to 10 parts by weight of a higher saturated fatty acid having 10 or more carbon atoms are blended per 100 parts by weight of EPDM. . The EPDM rubber composition of the present invention is characterized by the combination of quicklime and a specific amount of higher saturated fatty acids having 10 or more carbon atoms, as described above. Conventional rubber compounding agents, ie, carbon black, plasticizers, softeners, zinc white, white fillers, vulcanization accelerators, vulcanizing agents, and anti-aging agents can be used as appropriate. The quicklime used in the present invention is either limestone, calcium carbonate, slaked lime, or mixtures thereof, which are fired at temperatures above the decomposition temperature of substances that produce calcium oxide when fired, or quicklime produced from these materials. Other substances (for example, iron oxide, silica, alumina, etc. that produce calcium salts by calcination) are added to retard the hydration rate of It is. The finer the particle size of the powder particles and the fewer coarse particles, the better the results.
It is desirable that the thickness be 150μ or less. It is also possible to use this powdered quicklime treated with mineral oil. The suitable amount of quicklime in these powders is 1 to 20 parts by weight per 100 parts of rubber; less than 1 part by weight cannot be expected to be effective in preventing bubbles in the rubber due to water in the vulcanization method, which requires almost no external pressure; There is no need for more than 1 part. The fatty acids used in the composition of the present invention are higher saturated fatty acids having 10 or more carbon atoms. Lower fatty acids with a small number of carbon atoms cannot achieve the effects of the present invention. In addition, fatty acids with unsaturated bonds in their molecules, such as oleic acid and linoleic acid, inhibit vulcanization, reduce the tensile stress of vulcanized rubber, and cause deterioration due to oxidation by oxygen in the air. There's a problem. Therefore, the fatty acid used in the present invention needs to have a low content of unsaturated fatty acids. (See Table 6) The amount of fatty acid blended in the composition of the present invention is
The amount is 2.5 to 10 parts by weight per 100 parts by weight, and if it is about 1 to 2 parts by weight, it will not have a noticeable effect on improving the compression set of vulcanized rubber in which quicklime coexists. However, the effect of improving compression set is small, and in addition, there is an increased risk of a decrease in the tensile stress of the vulcanized rubber and a so-called bloom in which fatty acids, fatty acid salts, etc. precipitate on the surface. The blending ratio of fatty acids is preferably 4 to 6 parts by weight. Examples Samples according to Examples 1-10 were prepared as follows. Samples of Reference Examples 1 to 10 were prepared in the same manner. Sample preparation method EPDM polymers and various compounding agents listed in Table 1, Table 3, Table 4, Table 5, and Table 6 were blended in the proportions listed in each table, and the total weight was 1.2 ~1.4Kg, and create a masterbatch using a BR type 1.7 Banbury mixer (manufactured by Kobe Steel, Ltd.) under the following conditions, excluding the vulcanization accelerator and vulcanizing agent.

[Table] After cooling the obtained composition, knead the vulcanization accelerator and vulcanizing agent for about 7 minutes using an 8-inch roll mill, form a sheet, cool it, and use a 45-ton electric press to mix Tables 2, 4, and 6.
It was vulcanized under the conditions described in the footnotes and used as a sample.

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[Table] Products with coarse particles removed using a Tsushiyu sieve

[Table] The measurement results of the physical properties of the vulcanized rubber of each sample are shown in Tables 2, 4, and 6. From the results shown in these tables, it is clear that the effect of the present invention is that the compression set is greatly improved by incorporating a large amount of higher saturated fatty acids having 10 or more carbon atoms in the EPDM rubber composition containing quicklime. Ru. In particular, reference example 2
Comparison of and Examples 1 and 2, Reference Examples 5 and 6 and Example 3
By comparing Examples 7 to 6 and Reference Example 7 to Examples 7 to 10, the effects of the present invention become clear.

Claims (1)

[Claims] 1 For 100 parts by weight of EPDM, 1 to 20 parts by weight of quicklime and 2.5 to 10 parts by weight of higher saturated fatty acids having 10 or more carbon atoms.
An EPDM rubber composition characterized by blending parts by weight.