JPS6223762B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a vulcanizable elastomer. More specifically, the present invention relates to a method for producing a vulcanizable elastomer that provides a vulcanizate with excellent heat aging resistance. Copolymerization of vinyl chloroacetate ClCH ₂ COOCH=CH ₂ as a crosslinking site component in an acrylate copolymer elastomer (abbreviated as acrylic elastomer in the present invention) containing alkyl acrylate or alkoxyalkyl acrylate and alkoxyalkyl acrylate as main components. This has already been introduced (Japanese Patent Publication No. 39-20515, Japanese Patent Publication No. 47-23421, Japanese Patent Publication No. 43-24200, etc.). These acrylic elastomers can be vulcanized using vulcanization systems such as fatty acid alkaline soap-sulfur or sulfur-donating compound systems, polyamine systems, or organic carboxylic acid ammonium salt systems, and have oil resistance, weather resistance, and compression permanent properties. Although it is very useful for providing a vulcanizate with excellent properties such as distortion, it is still at an insufficient level in terms of heat aging resistance and cannot be said to be satisfactory after all. For this reason, there has recently been a growing demand for acrylic elastomers to have improved heat aging resistance, especially for applications such as automatic parts. One solution to this problem is proposed in JP-A No. 50-45031, in which an ethylene-alkyl acrylate-maleic acid monoalkyl ester terpolymer elastomer is mixed with, for example, methylene dianiline-diphenylguanidine. It is described that a vulcanizate exhibiting high heat aging resistance can be obtained by vulcanization using a sulfur system. However, in this terpolymer, there is an ethylene polymerized moiety that is significantly inferior in terms of oil resistance, so the copolymer as a whole has an essential drawback that is unacceptable, and therefore it still cannot be used to produce the desired acrylic material. At present, elastomers are not available. As a result of various studies aimed at improving the heat aging resistance of acrylic elastomers without having any adverse effects on oil resistance or other vulcanized physical properties, the inventors of the present invention have developed an acrylic elastomer containing vinyl chloroacetate as a crosslinking site component. It has now been found that the above object can be effectively achieved by further copolymerizing hydroxyalkyl acrylate or hydroxyalkyl methacrylate. Accordingly, the present invention relates to a method for producing a vulcanizable acrylic elastomer, which comprises: (a) an alkyl acrylate in which the alkyl group has 1 to 8 carbon atoms; 55 to 98.9% by weight of at least one acrylate selected from the group consisting of alkoxyalkyl acrylates each having 1 to 4 carbon atoms, (b) 10 to 1% by weight of vinyl chloroacetate, (c) hydroxyalkyl acrylate or hydroxyalkyl methacrylate 5
0.1% by weight and (d) 30-0% by weight of at least one other monomer copolymerizable with these monomers. Each of these monomer components (a), (b) and (d) are the same as those used in conventional acrylic elastomers, as listed below. Further, examples of the hydroxyalkyl (meth)acrylate as the monomer component (c) include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 3-hydroxyethyl acrylate, and 2-hydroxyethyl acrylate.
Hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, etc. are used. These hydroxyalkyl (meth)acrylates are 1
The species or more collectively represent 5 to 50% of the total comonomer.
It is used in a proportion of 0.1% by weight, preferably 2-0.2% by weight. Examples of the alkyl acrylate of comonomer component (a) include methyl acrylate, ethyl acrylate, n- and iso-propyl acrylate,
n- and iso-butyl acrylate, n-amyl acrylate, n-hexyl acrylate, 2
-Ethylhexyl acrylate, n-octyl acrylate, and 2-cyanoethyl acrylate, which is a substituted product thereof, are used, and among these, ethyl acrylate and n-butyl acrylate are particularly preferred. As the alkoxyalkyl acrylate, methoxymethyl acrylate, ethoxymethyl acrylate, 2-methoxyethyl acrylate, 2-ethoxyethyl acrylate, 2-butoxyethyl acrylate, etc. are used, and among these, 2-methoxyethyl acrylate and 2-ethoxyethyl acrylate are particularly used. Ethyl acrylate is preferred. The number of carbon atoms in the alkyl group and alkoxyalkyl group of these acrylates is limited because if the number of carbon atoms increases beyond this limit, the resulting acrylic elastomer will no longer satisfy the balance between low-temperature properties and oil resistance. It is. One or more acrylate monomers to be subjected to the copolymerization reaction account for 55 to 98.9 of the total comonomers.
% by weight, preferably from 75 to 98.9% by weight, and especially when balanced low temperature properties and oil resistance are desired, alkoxyalkyl acrylates may be used in a proportion from 15 to 65% by weight. is preferred. The comonomer component (b), vinyl chloroacetate, accounts for 10 to 1% by weight, preferably 5 to 1% by weight of the total comonomer.
It is used in a proportion of 1.5% by weight. Other comonomers for comonomer component (d) include, for example, vinyl chloride, vinylidene chloride, acrylonitrile, styrene, vinyl acetate, ethyl vinyl ether, butyl vinyl ether, acrylic acid, methacrylic acid, itaconic acid, methyl methacrylate, Ethyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, divinylbenzene, allyl acrylate, vinyl acrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, polyethylene glycol diacrylate, propylene glycol diacrylate, butylene glycol diacrylate, and these Corresponding methacrylates and the like are used. One or more of these comonomers is subjected to the copolymerization reaction in a total amount of 30 to 0% by weight, preferably 20 to 0% by weight of the total comonomers. An acrylic elastomer copolymerized with 2 to 20% by weight of acrylonitrile provides a vulcanizate with superior high tensile strength, and a small amount (preferably 2% by weight or less) of a polyene monomer such as a divinyl compound is copolymerized. The processed acrylic elastomer has better rollability and extrusion properties.
Furthermore, in the case of an acrylic elastomer obtained by emulsion polymerization, a small amount (preferably 0.5 to 5
By copolymerizing styrene (% by weight),
It enables a copolymerization reaction with extremely few coagulated substances, that is, excellent polymerization stability. The copolymerization reaction may be carried out by any of the conventionally known polymerization methods, such as the method of emulsion polymerization without using an emulsifier, which has recently attracted attention (22nd Polymer Symposium Abstracts - 309) 314
Pages, -315-320 and Pigments Vol. 18, No. 2, 1359-
(see page 1363), but the preferred method is to form an emulsion aqueous solution in the presence of an emulsifier, a polymerization initiator, and a degree of polymerization regulator added as necessary, at about -10 to 100°C, preferably. is about 20
A method of polymerization at a temperature of ~80°C is used. As the polymerization initiator, commonly used free radical catalysts can be used, but redox catalysts are particularly preferred, specifically hydrogen peroxide and ferrous salts or ascorbic acid and persulfates. Combinations of hydrogen sulfite metal salts, thiosulfates or amines, kyumene hydroperoxide and ferrous salts are used. Mercaptans, preferably higher alkyl mercaptans such as dodecyl mercaptan, are used as polymerization degree regulators, which are particularly effective when relatively soft elastomers are to be obtained. As an emulsifier,
Anionic or nonionic surfactants may be used alone or in mixtures, as well as various dispersants. Specifically, for example, higher alkyl sulfates, alkylaryl sulfonates, polyoxyethylene alkyl ether sulfate salts, polyoxyethylene alkyl ether phosphate salts, polyoxyethylene alkyl ethers, polyoxyethylene alkyl ether phosphates, etc. Acid esters and corresponding alkylaryl ethers, naphthalene sulfonic acid-formalin condensates, cresol-Schefferic acid-formalin condensates, and the like are used. The acrylic elastomer obtained as a result of the copolymerization reaction is mixed with commonly used vulcanizing agents and other compounding ingredients (e.g. reinforcing agents, fillers, anti-aging agents, plasticizers, etc.) according to conventionally known mixing methods.
After mixing with a lubricant (such as a lubricant), it is generally vulcanized by heating to 120°C or higher. Vulcanized products have excellent properties such as heat resistance, oil resistance, weather resistance, ozone resistance, and compression set, so these properties can be used to make various sealing materials (gaskets, packing, O -rings, oil seals, etc.), various hoses, covering materials, etc.
It can be widely used for various belts and rolls, but compared to conventional acrylic elastomers, it has extremely superior heat aging resistance.
It can be used more effectively in applications that are exposed to high temperature conditions of 150°C or higher. The invention will now be described with reference to the following examples. Example 1 Comonomer mixture A with the following monomer composition (parts by weight)
-C were copolymerized to synthesize acrylic elastomers A to C (C is a comparative example), respectively.

[Table] The copolymerization reaction was carried out as follows. First, 2.5 parts by weight of vinyl chloroacetate (the same applies hereinafter), about 24.6 parts corresponding to 1/4 of the total comonomer mixture excluding vinyl chloroacetate, 0.005 parts of dodecyl mercaptan, 2 parts of polyoxyethylene dodecyl ether, 1 part of sodium dodecyl sulfate and 200 parts of water were charged into a reaction vessel, and the mixture was thoroughly purged with nitrogen while stirring while maintaining the liquid temperature at about 45°C. Then, when 0.04 parts of ammonium persulfate and 0.04 parts of sodium bisulfite are added, the polymerization reaction begins and the temperature begins to rise, so immediately about 72.9 parts of the remaining comonomer mixture (containing 0.015 parts of dodecyl mercaptan) is added to about It was continuously added dropwise little by little over 40 minutes. At this time, the temperature of the inner solution was maintained at approximately 60°C. Thereafter, the mixture was stirred for an additional hour to complete the copolymerization reaction, and the resulting copolymer latex was poured into 15% saline at about 85°C to coagulate the copolymer. When this is washed with water and dried, the Mooney viscosity (ML ₁₊₄ , 100℃) changes.
42 acrylic elastomers A, 43 acrylic elastomers B and 42 acrylic elastomers C were obtained. For each elastomer obtained, 100 parts of acrylic elastomer, 55 parts of HAF carbon black, 1 part of stearic acid, 4,4'-bis(4-
α,α-dimethylbenzyl)diphenylamine 2
A vulcanized compound was prepared with a formulation consisting of 3 parts of sodium stearate, 0.5 part of potassium stearate, and 0.3 part of sulfur. Corresponding formulations and (comparative examples) were prepared. Each formulation was cured at a vulcanization temperature of 170°C for 10 minutes or
Press vulcanization was carried out for 20 minutes, and the 10 minute vulcanizates were further post-vulcanized (in an oven) at 150° C. for 15 hours. Table 2 shows the physical property values of each vulcanizate. Note that the measurement was performed according to the method of JISK-6301.

【table】

[Table] From the above results, the vulcanizate using the acrylic elastomer having a hydroxyl group in the copolymer side chain according to the present invention has extremely high retention of physical properties in the heat aging test at 150°C or higher, and other It can be seen that there is almost no adverse effect on physical properties. Furthermore, the difference from the comparative vulcanizate becomes even more noticeable at higher temperatures and for longer periods of time, and the superiority of the acrylic elastomer of the present invention can be understood. In contrast, in the comparative vulcanizate, certain bonds at the crosslinking points or bonding side chain sites are likely to undergo cleavage;
As a result of the collapse-type thermal aging behavior, it is thought that typical softening deterioration occurs, such as a decrease in 100% modulus, an increase in elongation, and a decrease in tensile strength. Example 2 According to the polymerization method of Example 1, comonomer mixtures D to H having the following monomer compositions (parts by weight) were copolymerized to form acrylic elastomers D to H (H is a comparative example), respectively. Synthesized.

【table】

[Table] For each elastomer obtained, 100 parts of acrylic elastomer, 50 parts of HAF carbon black, 1 part of stearic acid, 4,4'-(bis-4
-α,α-dimethylbenzyl)diphenylamine 2 parts, sodium stearate 2.5 parts, potassium stearate 1 part and sulfur 0.3 parts, each of which was
Comparative examples were prepared from acrylic elastomers D, E, F, G, and H by kneading on a 10-inch open roll. Table 4 shows the physical property values of the vulcanizates obtained from each compound.

【table】

【table】

[Table] From the above results, in any case, in the vulcanizate ~ using the acrylic elastomer having a hydroxyl group in the copolymer side chain according to the present invention,
It can be seen that the degree of retention of various physical properties in heat aging tests of 150°C or higher is extremely high, and that it is also effective for the purpose of providing high-strength acrylic elastomers. The superiority of the present invention is even more pronounced under conditions of heat aging at higher temperatures and for longer periods of time, and therefore acrylic is optimal for use in various sealing materials and various hoses, which have been in increasing demand in recent years. It can be said to be an elastomer. Example 3 According to the polymerization method of Example 1, monomer mixtures I to K having the following comonomer compositions (parts by weight) were copolymerized to form acrylic elastomers I to K (J,
K is a comparative example) was synthesized.

[Table] The relative humidity of the obtained elastomer
It was left in a constant temperature and humidity chamber at 60°C for 7 days and then dried. Each of the dried elastomers was kneaded according to the formulation of Example 2 to prepare corresponding formulations from acrylic elastomers I, J and K, and XI (XI is a comparative example). Table 6 shows the physical property values of vulcanizates to XI obtained from each blend.

[Table] The acrylic elastomer of the present invention is characterized by copolymerizing vinyl chloroacetate as a crosslinking site component and a hydroxyl group-containing monomer as a component for improving heat aging resistance. In the elastomer, as in the above-mentioned elastomer K, a comonomer having a chloroacetyl group on the same side chain that plays the same role as vinyl chloroacetate, and also a hydroxyl group that plays the same role as the object of the present invention. It is expected that similar effects will be obtained when body components are copolymerized. However, in reality Table 6
As shown in Figure 2, the chloroacetate moiety that becomes the crosslinking site is hydrolyzed by humidification and heating treatment (if the chloroacetate group and hydroxyl group are on the same side chain, the catalytic action by the hydroxyl group chloroacetate groups are hydrolyzed in the presence of moisture), and its storage stability as an elastomer is poor, making it practically useless. On the other hand, in the acrylic elastomer of the present invention, no hydrolytic deactivation of the crosslinking sites occurs at all, and the elastomer is also found to have excellent storage stability.

Claims (1)

[Claims] 1 (a) At least one selected from the group consisting of alkyl acrylates in which the alkyl group has 1 to 8 carbon atoms, and alkoxyalkyl acrylates in which the alkyl group and the alkylene group each have 1 to 4 carbon atoms. Acrylate 55~
98.9% by weight, (b) vinyl chloroacetate 10-1
(c) 5-0.1% by weight of hydroxyalkyl acrylate or hydroxyalkyl methacrylate and (d) 30-0% by weight of at least one other monomer copolymerizable with these monomers. A method for producing a vulcanizable acrylic elastomer, the method comprising: