JPS58157842A - Rubber composition for use of food and hygiene - Google Patents

Abstract

PURPOSE:The titled composition capable of producing rubber products coming up to Notification No.434 of the Ministry of Public Welfare by normal continuous extrusion vulcanization process at normal pressure, obtained by blending ethylene.propylene.diene terpolymer rubber with zinc white, a zinc salt of a fatty acid and calcium oxide. CONSTITUTION:100pts.wt. ethylene.propylene.diene terpolymer rubber in blended with 0.1-5pts.wt. zinc white No.1, 0.1-6pts.wt. zinc salt of 7-13C fatty acid and 0.1-5pts.wt. calcium oxide. The composition comes up to the standard of evaporation residue, regulated by Notification No.434 of the Ministry of Public Welfare. The initial activity of valcanization reaction is maintained by the zinc salt of the fatty acid, and durability is kept by zinc white. In continuous extrusion vulcanization process at normal pressure, especially in case that productivity is a matter of great account, 1-3pts.wt. zinc octylate, 1-2pts.wt. zinc white and 1-2.5pts.wt. calcium oxide are preferably added to the rubber.

Description

Detailed Description of the Invention The present invention uses ethylene-propylene-diene three-light copolymer rubber (hereinafter referred to as EPQM) as a base material,
This invention relates to obtaining a rubber composition (hereinafter referred to as "comparado") that can be used to produce various rubber products for food use that meet the requirements of the No. EPDM has excellent weather resistance, heat resistance, water resistance, and chemical resistance, so it can be used in food-use rubber products that require these properties, such as rubber for coffee siphons, pressure vessel packing,
It is applied to mochi pounders, hoses for solar water heaters, etc.

Methods for producing such products include press vulcanization,
Generally, injector vulcanization and extrusion can vulcanization are used. 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. Continuous vulcanization, ie, salt bath vulcanization (LCM), hot air vulcanization (HAY), high frequency vulcanization (UHF), and fluidized bed vulcanization (PCM), suffer from the problem of being significantly inferior.

As a result of intensive research, the present inventor has developed a continuous vulcanization method (hereinafter referred to as the "CV method") in order to compensate for these shortcomings and comply with Ministry of Health, Labor and Welfare Notification 4.
We have discovered a compound that produces rubber products that pass No. 84.

The main difference between the compounds used in the CV method and the can vulcanization method is that quicklime (hereinafter referred to as C1O) is essential as an antifoaming agent in the CV method, but it is not necessary in the can vulcanization method. The can vulcanization method is characterized by using external pressure to suppress the evaporation of moisture in the compound during the vulcanization process, thereby preventing foaming of the rubber product, whereas the CV method uses CaO. A common method is to convert moisture in the compound into stable Cλ(oi-t) 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. 484 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. 484. 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. It can be predicted that rubber products obtained from compounds containing Ch(0f()*CaO produced by blending CaO) will considerably exceed the regulatory value of evaporation residue (hereinafter referred to as evaporation residue) of the Ministry of Health and Welfare Notification No. 484. .

Furthermore, zinc white (ZnU) 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% aqueous acetic acid solution.

Comparand used in the can vulcanization method does not require the addition of CaO as mentioned above, and additives that increase the amount of evaporation residue include zinc white, carbon black, talc, clay, etc. ZnO has a significant influence on ζ. The amount of ZnO used in ordinary rubber products is about 8 to 6 parts by weight (hereinafter referred to as PHR), but past research has demonstrated that it is possible to pass the evaporation residue test with this amount. ing.

See Japanese Patent Application No. 54-78745.

However, it goes without saying that when using a compound that requires the combination of multiple types of compounding agents (ZnO and C20) 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 eliminate the drawbacks of the compound used in the CV method as described above, the inventor of the present invention found that by using ZnO and a fatty acid salt having a relatively small number of carbon atoms together, the blending amount of ZnO can be reduced. As a result, even if CaO is added, the evaporation residue can be kept below the regulation value of Ministry of Health and Welfare Notification No. 484, and CV
We have discovered a compound that can prevent foaming of products using this method.

In general, in order to obtain a compound for the CV method that passes the Ministry of Health and Welfare Notification No. 484, it is necessary at least to mix limited reinforcing agents, fillers, and limited vulcanization accelerators with EPDM, as well as appropriate amounts of ZnO, CaO, etc. be.

The reinforcing agent, filler, and vulcanization system mentioned here are based on Japanese Patent Application Laid-Open No. 54-78746, for which the present inventor previously applied for a patent.

That is, it is most preferable that the reinforcing agent is carbon black (1-nes black) and the filler is clay or talc, or that the filler is a blend of carbon black alone.

The present invention uses Zn necessary to obtain rubber products by the CV method.
Although this method is based on the idea of reducing the amount of O1CaO mixed as much as possible, as a result of intensive study, it was found that there are some disadvantages.

In other words, as the amount of ZnO is reduced (1), the evaporation residue decreases, leading to good results, but there is a tendency for the degree of vulcanization to decrease significantly, and rubber physical properties such as compression set, tensile strength, and permanent elongation deteriorate. do.

In addition, as the vulcanization rate becomes slower, the foaming phenomenon in rubber products obtained by the CV method becomes more pronounced, so in order to prevent foaming, it is necessary to increase the amount of CaO blended, thereby reducing the amount of evaporation residue. L, N who cannot fulfill the purpose
.

These relationships are shown in FIGS. 1 and 2.

Diagram I41 shows the relationship between the amount of Zinc White No. 1 blended and the compression set and evaporation residue amount of the vulcanizate in the 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 m1.

The vulcanization conditions were press vulcanization at 160° C. for 80 minutes.

Table 1 Basic formulation *1 Kyodo Yakuhin R-800 4!2 Zinc-dimethyl-dithiocarbamate *8
Zinc-diethyl-dithiocarbamate *4 Zinc-di-n-butyl-dithiocarbamate *6 Dipentamethylene lentithurum hexasulfide pot 6 Pester PP made by Bengami Lime *7 Kanamekatoku No. 1 manufactured by Sakai Chemicals Here, the present invention As a result of trying to apply various zinc fatty acids and organic zinc compounds as vulcanization activators to replace ZnO, they found that zinc salts of fatty acids with 7 to 13 carbon atoms, such as zinc octylate, have a remarkable vulcanization activating effect. I discovered that.

Other organic acid zinc salts are also effective in reducing evaporation residue, but fatty acid zinc with 14 or more carbon atoms, such as zinc stearate, has a small vulcanization activation effect, that is, the vulcanization rate is slow and the compression resistance is low. Historically, fatty acids and other compounding agents precipitate on the surface of rubber products, which causes bleed, making it difficult to obtain desirable products.

Furthermore, zinc acetate, zinc acetylacetone,
Zinc naphthenate and the like are each insoluble in the compound, and they all have problems such as being extremely irritating and having little υ sulfuric acid activation effect, making them impossible to apply from a practical point of view.

On the other hand, a compound containing a fatty acid zinc salt having 7 to 18 carbon atoms instead of ZnO not only compensates for the drawbacks of compounds containing other similar compounds, but also improves ZnO.
Since the initial vulcanization activation effect is more pronounced than in compounds containing nO alone, it is a favorable factor in terms of product shape retention, line speedup, etc. when produced by the Cv method. However, on the other hand, it has the disadvantage of lacking in sustainability of vulcanization activity compared to Zn01ζ.

However, the present inventors succeeded in correcting these drawbacks by using ZnO in combination with a fatty acid zinc salt having 7 to 18 carbon atoms.

That is, it is based on the idea that the initial activity of the vulcanization reaction is provided by a monofatty acid zinc salt having 7 or more and 18 or less carbon atoms, and the durability is provided by ZnO.

In particular, the effect of blending a fatty acid zinc salt with a carbon number of 7 or more and 18 or less is significant, 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 amount of Coo blended. .

As a result, it has been found that not only is it extremely advantageous to maintain the evaporation residue below the standard value according to Ministry of Health and Welfare Notification No. 484, but it is also effective in improving compression set, which is significantly worsened by adding CaO.

As a result of further pursuing this point, the present inventor found that in order to balance the appearance, physical properties, Ministry of Health and Welfare No. 484, etc. of rubber products applied to food applications, fatty acid zinc salt ZnO having 7 or more and 18 or less carbon atoms.

It has been found that it is necessary to mix appropriate amounts of CaO.

That is, the fatty acid zinc salt having 7 or more and 18 or less carbon atoms has 0.
1~(5PHR%ZnO is 0.1~8PHR.

It is desirable to use CaO in combination within the range of 0.6 to 3 PHR, but in the Cv method, if productivity is particularly important, zinc octylate should be used in the range of 1 to 9 PHR, Zn.
O is 1-2 PHR.

It is preferable to blend 1 to 2.5 PHR of C@0. In a formulation example in which ZnO is not blended and the amount of fatty acid zinc salt having 7 to 18 carbon atoms is simply increased, the sustainability of vulcanization activity is slightly improved;
The improvement effect was not as great as in the case where a fatty acid zinc salt of 8 or less was used in combination.

The EPDM of the present invention is ethylene/propylene/dicyclopentadiene terpolymer rubber, ethylene/propylene/
These include 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.

Table 2 of Examples shows the formulation, vulcanization conditions, and physical properties of the obtained vulcanized rubber.

Footnotes to s2 table [1g1] F, PDM manufactured by Sumitomo Chemical Co., Ltd. (*2) FEF type carbon black C manufactured by Tokai Carbon *8) Paraffin-based process oil manufactured by Idemitsu Kosan (Book 4) Processing aid manufactured by Kyodo Yakuhin (Book 5) ) zinc-dimethyl-dithiocarbamate (ni6
) Zinc-diethyl-dithiocarbamate (*7) Zinc-n-butyl-dithiocarbamate (*8) Dipentamethylenethiourea hexasulfide (*9) The standard for evaporation residue according to Ministry of Health and Welfare Notification No. 484 is 80 ppm or less. The vulcanization conditions were 160°C x 16 minutes.

(4clO) The vulcanization conditions were continuous hot air vulcanization at 200°C for 6 minutes.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between the amount of zinc white No. 1 blended in an EPDM vulcanized rubber composition and the compression set $ and amount of evaporation residue of the vulcanizate. Ca
FIG. 3 is a diagram showing the relationship between the amount of O added and the amount of evaporation residue of the vulcanizate. Fig. 1 2845 Zinc white No. 1 blending amount (PHR) Fig. 2 12845 Zinc white No. 1 blending amount (PHR)

Claims (1)

[Claims] Zinc white No. 1 0.1 to 5 parts by weight, carbon number 7 per 100 parts by weight of ethylene-propylene-diene ternary copolymer rubber
A rubber composition that passes the evaporation residue standards of the Ministry of Health and Welfare Notification No. 484, which is characterized by blending 0.1 to 6 parts by weight of fatty acid submersal salts of 18 or less and 0.1 to 5 parts by weight of calcium oxide. thing.