JPS6225175B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention uses ethylene-propylene-diene ternary copolymer rubber (hereinafter referred to as EPDM) as a base material,
This invention relates to obtaining a rubber composition (hereinafter referred to as a compound) that can be used to produce various rubber products for food use that pass the Ministry of Health and Welfare No. 434 by an ordinary pressure continuous extrusion vulcanization method. EPDM has excellent weather resistance, heat resistance, water resistance, and chemical resistance, so it is suitable for food-use rubber products that require these properties.
It is applied to rubber for coffee siphons, pressure pads, mochi maker pads, hoses for solar water heaters, etc. Press vulcanization, in-die extension vulcanization, and extrusion can vulcanization are generally used to produce such products. However, when long products that require extrusion molding, such as hoses for solar water heaters, are not only difficult to handle using the conventional can vulcanization method, but also normal pressure is not suitable for productivity. It has the problem of being significantly inferior to continuous vulcanization, that is, salt bath vulcanization (LCM), hot air vulcanization (HAV), high frequency vulcanization (UHF), and fluid bed vulcanization (PCM). As a result of intensive research, the present inventors have discovered a compound that can be used to make rubber products that pass the Ministry of Health and Welfare Notification No. 434 using a normal pressure continuous vulcanization method (hereinafter referred to as the "CV method") in order to compensate for these drawbacks. The main difference between the compounds used in the CV method and the can vulcanization method is that the CV method requires quicklime (CaO) as an antifoaming agent, but the can vulcanization method does not require it. The can vulcanization method uses external pressure to suppress the evaporation of water in the compound during the vulcanization process, preventing foaming of the rubber product, whereas the CV method contains CaO. A common method is to convert the water in the compound into stable Ca(OH) ₂ and prevent foaming. Points to consider when selecting a compounding agent for rubber in order to obtain a product that passes the Ministry of Health and Welfare Notification No. 434 are that compounding agents or reaction products from vulcanization are specified in the evaporation residue section of the Ministry of Health and Welfare Notification No. 434. The question is whether or not it is soluble in the extract, that is, a 4% acetic acid aqueous solution. That is, as a matter of course, if it is soluble, it becomes a factor that significantly increases the amount of evaporation residue. Since Ca(OH) ₂ produced by blending CaO is soluble in a 4% acetic acid aqueous solution, rubber products obtained from compounds containing CaO are subject to evaporation residue (hereinafter referred to as evaporation residue) according to Ministry of Health and Welfare Notification No. 434. It can be predicted that the amount will exceed the regulation value considerably. Zinc white (ZnO) is a vulcanization activator essential for the vulcanization reaction of rubber, but it also has the same drawback because it is soluble in a 4% acetic acid aqueous solution. As mentioned above, the compound used in the can vulcanization method does not need to contain CaO, and the additives that increase the amount of evaporation residue include zinc white, carbon black, talc, clay, etc., but they have a particularly significant effect. is ZnO. The amount of ZnO used in ordinary rubber products is 3 to 6 parts by weight (hereinafter referred to as
PHR), but past research has demonstrated that it is possible to pass the evaporation residue level with this blending amount. The present inventors applied for Japanese Patent Application Publication No. 54-78745.
See issue. However, it goes without saying that when using a compound that requires the combination of multiple types of compounding agents (ZnO and CaO) that produce a particularly large amount of evaporation residue, such as the CV method, it becomes difficult to pass the evaporation residue test. Nor. As a result of various studies on ways to overcome the drawbacks of the compound used in the CV method as described above, the inventor of the present invention found that the amount of ZnO can be reduced by using ZnO together with a fatty acid zinc salt having a relatively small number of carbon atoms. As a result, we have developed a compound that can keep the evaporation residue below the regulated value in Ministry of Health and Welfare Notification No. 434 even if CaO is added, and prevent foaming of products in the CV method. discovered. In general, to obtain a compound for CV method that passes Ministry of Health and Welfare Notification No. 434, reinforcing agent limited to EPDM,
Fillers and limited vulcanization accelerators, plus ZnO,
The minimum requirement is to incorporate an appropriate amount of CaO, etc. The limited reinforcing agents, fillers, and vulcanization systems here refer to JP-A No. 54-117, for which the present inventor previously applied for a patent.
78745. That is, although the reinforcing agent is carbon black (furnace black) and the filler is clay or talc, a blending system containing carbon black alone is most preferable. The present invention is based on the idea of minimizing the amount of ZnO and CaO necessary to obtain rubber products using the CV method, but as a result of intensive study, it was found that there were some disadvantages. . In other words, as the blending amount of ZnO decreases, the evaporation residue decreases, leading to good results, but there is a tendency for the degree of vulcanization to decrease significantly, and compression set, tensile strength,
Rubber physical properties such as permanent elongation deteriorate. In addition, as the vulcanization rate becomes slower, the foaming phenomenon in the rubber products obtained by the CV method becomes more pronounced, which results in the need to increase the amount of CaO blended to prevent foaming, and the purpose is to reduce evaporation residue. cannot be fulfilled. These relationships are shown in FIGS. 1 and 2. FIG. 1 shows the relationship between the blending amount of Zinc White No. 1 and the compression set and evaporation residue amount of the vulcanizate in a vulcanized rubber composition having the basic formulation shown in Table 1. FIG. 2 shows the relationship between the blending amounts of Zinc White No. 1 and CaO and the amount of evaporation residue of the vulcanizate in a vulcanized rubber composition having the basic formulation shown in Table 1. The vulcanization conditions were press vulcanization at 160° C. for 30 minutes.

[Table] As a result of trying to apply various zinc fatty acids and organic zinc compounds as vulcanization activators in place of ZnO, the inventor found that zinc salts of fatty acids with carbon atoms of 7 to 13, such as zinc octylate, It was discovered that it has a significant vulcanization activity effect. Other organic acid zinc salts are also effective in reducing evaporation residue, but fatty acid zinc with 14 or more carbon atoms, represented by zinc stearate, has a small vulcanization activity effect.
That is, the vulcanization rate is slow, the compression set is large, and fatty acids and other compounding agents precipitate on the surface of the rubber product, which causes bleeding, making it difficult to obtain a desirable product. Furthermore, zinc acetate, zinc acetylacetone, zinc naphthenate, etc. as zinc salts of fatty acids with carbon atoms of 6 or less and zinc salts of organic acids other than fatty acids are insoluble in compounds, have a significant odor, have little vulcanization activation effect, etc. All of them have problems and cannot be applied in terms of practicality. On the other hand, a compound containing zinc salt of a fatty acid having 7 to 13 carbon atoms instead of ZnO not only compensates for the drawbacks of compounds containing other similar compounds, but also improves initial performance compared to compounds containing ZnO alone. Since the vulcanization activity effect of ZnO is more pronounced, it is a favorable factor in terms of product shape retention and line speedup when produced by the CV method. The disadvantage is that it lacks sustainability. However, the present inventor succeeded in correcting this drawback by using ZnO in combination with a fatty acid zinc salt having 7 to 13 carbon atoms. That is, it is based on the idea that initial activity of the vulcanization reaction is provided by a fatty acid zinc salt having 7 or more and 13 or less carbon atoms, and sustainability is provided by ZnO. In particular, the effect of blending a fatty acid zinc salt with a carbon number of 7 or more and 13 or less is remarkable, and it not only has the effect of reducing the blended amount of ZnO, but also significantly accelerates the vulcanization rate, making it possible to reduce the blended amount of CaO. As a result, it has not only become very advantageous to keep the evaporation residue below the standard value according to Ministry of Health and Welfare Notification No. 434, but also
It has been found that the addition of CaO has the effect of improving compression set, which is significantly worse. As a result of further pursuing this point, the present inventor found that in order to balance the appearance, physical properties, and Ministry of Health and Welfare No. 434 of rubber products applied to food applications, the number of carbon atoms must be 7 or more.
It has been found that it is necessary to mix appropriate amounts of fatty acid zinc salts ZnO and CaO with a weight of 13 or less. In other words, fatty acid zinc salt with carbon number of 7 to 13 is 0.1 to 6 PHR, ZnO is 0.1 to 3 PHR, and CaO is 0.5 to 6 PHR.
It is desirable to use them together within the range of 3PHR, but in the CV method, if productivity is particularly important, zinc octylate should be used in the range of 1 to 3PHR, and ZnO should be used in the range of 1 to 3PHR.
~2PHR, and CaO is preferably blended in an amount of 1 to 2.5PHR. In a formulation example in which ZnO is not blended and the amount of fatty acid zinc salt having 7 or more and 13 or less carbon atoms is simply increased, the sustainability of vulcanization activity is slightly improved, but ZnO,
The improvement effect was not as great as in the case where a fatty acid zinc salt having 7 to 13 carbon atoms was used in combination. EPDM of the present invention is ethylene/propylene/dicyclopentadiene terpolymer rubber, ethylene/propylene/dicyclopentadiene ternary copolymer rubber,
These include propylene/2-ethylidenenorbornene ternary copolymer rubber, ethylene/propylene/1,4-hexadiene ternary copolymer rubber, and the like. Examples are shown below. However, the present invention is not limited to the examples. Examples Table 2 shows the formulation, vulcanization conditions, and physical properties of the obtained vulcanized rubber.

【table】

【table】 [Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between the blending amount of zinc white No. 1 in an EPDM vulcanized rubber composition and the compression set and evaporation residue amount of the vulcanizate. FIG. 2 is a diagram showing the relationship between the amount of vulcanizate and the amount of evaporation residue of the vulcanizate.

Claims (1)

[Claims] 1. For 100 parts by weight of ethylene-propylene-diene ternary copolymer rubber, add 0.1 to 5 parts by weight of Zinc White No. 1 and 0.1 to 5 parts by weight of fatty acid zinc salt having 7 to 13 carbon atoms.
6 parts by weight of calcium oxide, and 0.1 to 5 parts by weight of calcium oxide.