JPH01118412A - Vulcanization process of ethylene-acrylate elastomer - Google Patents

Abstract

PURPOSE:To contrive to improve scorch resistance and kneading workability, etc., simultaneously with the acceleration of vulcanization speed by a method in which ethylene, a specified acrylate and the material containing a specified oxazoline ring are copolymerized in a specified ratio, and the contained acryl elastomer is vulcanized under a specified condition. CONSTITUTION:(a) 15-60wt.% of ethylene, (b) 80-30wt.% of at least one kind acrylate selected from the group composed of alkylacrylate inwhich alkyl radical has 1-4 of carbon atoms and alkylmethacrylate, and (c) 15-0.1wt.% of monomer containing the oxazoline ring containing unsaturated radical in second position, are copolymerized, and the ethylene-acrylate elastomer containing oxazoline radical is obtained. The vulcanization of the ethylene-acrylate elastomer containing oxazoline radical is easily carried out by heating it under the existence of polymercapto compound containing two or more of mercapto groups. This vulcanized object is excellent in mechanical property, heat again resistance, metallic corrosion resistance and water resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for vulcanizing acrylic elastomers. More specifically, the present invention relates to a method for vulcanizing a vulcanizable acrylic elastomer that can impart excellent properties in terms of cross-polishability, rapid vulcanization, metal corrosion resistance, water resistance, and the like.

[Conventional technology]

Acrylic elastomer is an elastomer that exhibits properties such as excellent heat resistance, weather resistance, and oil resistance due to the saturated structure of the main chain of the polymer and the polarity of the side chain groups. ), hoses, electrical parts, coating materials, etc.

Acrylic elastomers include acrylic copolymer elastomers obtained by copolymerizing acrylic esters as main monomers and ethylene-acrylate copolymer obtained by copolymerizing ethylene and acrylic esters or methacrylic esters as main monomers. Polymer elastomer 2
Seed-type products are currently being industrialized and put into practical use.

In the copolymer elastomers of Niku et al., a small amount of crosslinking site-donating monomer is copolymerized, and by selecting a vulcanization system according to the type of crosslinking site, the vulcanization reaction are being carried out efficiently. The following vulcanization systems are used depending on the type of crosslinking site.

-'' Tachibana Kore (1! ~ Added, active halogen group polyamine, polyamine derivative, alkaline soap - sulfur or sulfur donating compound, epoxy group polyamine, polyamine derivative, alkaline soap - sulfur or sulfur donating compound, dithiocarbamate, Organic carboxylic acid ammonium salt carboxyl group Polyepoxy compound - base, polyamine or polyamine derivative - base Among these crosslinking sites, active halogen groups are, for example, 2-chloroethyl vinyl ether, vinyl chloroacetate, vinylbenzyl chloride, vinylbenzyl chloroacetate , 2-chloroethyl acrylate, etc., and can be vulcanized using the above vulcanization system, but has poor metal corrosion resistance due to hydrogen halide or its salts generated during the vulcanization reaction. In addition to the drawbacks, when an alkali soap-sulfur or sulfur-donating compound is used as a vulcanization system, a decrease in water resistance and electrical properties is unavoidable due to the inclusion of the highly hydrophilic alkali soap.

In addition, when epoxy groups are introduced as crosslinking sites by copolymerizing glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, vinyl glycidyl ether, etc., metal corrosivity is not observed during vulcanization and in the vulcanized product. , the balance between vulcanization rate and fabric scorchability is not sufficient. That is, when a high vulcanization rate is obtained, the scorch property is significant, and the processing safety at the time of cross-wires and the storage stability of the fabric are not satisfactory. On the other hand, if the scorch property is in a satisfactory state, the vulcanization rate will be slow, which will hinder the efficiency of the vulcanization molding process. When an alkali soap monosulfur or a sulfur-donating compound is used as the vulcanization system, the water resistance of the vulcanizate decreases, as in the case of active halogen group crosslinking sites.

Furthermore, in the case of carboxyl group crosslinking sites introduced by copolymerizing acrylic acid, methacrylic acid, maleic acid monoester, itaconic acid, etc., vulcanizates with less metal corrosion and low compression set can be obtained. However, since the vulcanization rate is not necessarily high, similar to the case of the epoxy group crosslinking site, a decrease in scorch property is often a problem when trying to increase the vulcanization rate.

In addition to this, there is also a problem that during cross-wiring processing, there is a tendency to stick to the metal parts of cross-wire parts such as rolls, kneaders, Banbury mixers, etc., and extra labor is required.

[Problem to be solved by the invention]

The present invention solves the problems encountered with the conventional acrylic elastomers described above, that is, a sufficiently fast vulcanization rate can be obtained, and at the same time, it has excellent scorch resistance (processing safety, storage stability of fabrics), and The object of the present invention is to provide a method for vulcanizing a new vulcanizable acrylic elastomer that has excellent cross-wire processing properties (stickiness when cross-wired), metal corrosion resistance, water resistance, etc.

The purpose of the present invention is to copolymerize a specific oxazoline ring-containing monomer as a crosslinking site component into an ethylene-acrylate elastomer, and further utilize the reactivity of the oxazoline groups distributed in the side chains of the polymer to form a polyester. It has been found that this can be achieved by vulcanization in the presence of a mercapto group-containing compound.

[Means to solve the problem]

Accordingly, the present invention relates to a method of vulcanizing a novel vulcanizable ethylene-acrylate elastomer, the vulcanization of the ethylene-acrylate elastomer comprising: (a) ethylene 15
~60% by weight, (b) 80-30% by weight of at least one acrylate selected from the group consisting of alkyl acrylates and alkyl methacrylates in which the alkyl group has 1 to 4 carbon atoms, and (c) in the 2-position. This is carried out by vulcanizing an ethylene-acrylate elastomer containing 15 to 0.1% by weight of an oxazoline ring-containing monomer having an unsaturated group by copolymerization in the presence of a polymercapto group-containing compound.

Copolymerization reactions for obtaining ethylene-acrylate elastomers containing oxazoline groups are described, for example, in U.S. Pat.
99,123, the high pressure polymerization method described in US Pat. No. 3,350,372, and US Pat. No. 3,956,2.
This is carried out in accordance with the low-pressure alternating copolymerization method described in the specification of No. 48.

Comonomer component (b) used as the main monomer together with ethylene includes methyl acrylate, ethyl acrylate, n- or isopropyl acrylate, n-
Or an alkyl acrylate or alkyl methacrylate in which the alkyl group has 1 to 4 carbon atoms, such as imbutyl acrylate or the corresponding methacrylate. The reason why the number of carbon atoms in the alkyl group is limited to 1 to 4 is because if the number of carbon atoms increases more than this, the oil resistance becomes poor.

The copolymers obtained by copolymerizing ethylene with alkyl acrylates and/or alkyl methacrylates can have any desired composition of each, but for the purposes of the present invention, based on the total comonomer weight, 15-60% ethylene, also alkyl acrylate and/or
Alternatively, the alkyl methacrylate must be contained in a proportion of 80 to 30% without being copolymerized.

Examples of the oxazoline ring-containing monomer having an unsaturated group at the 2-position of the comonomer component (c) include 2-vinyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-iso Examples include propenyl-2-oxazoline, and 15 to 0.1% of the total monomer weight, preferably 1%
It is used in a proportion of 0 to 0.5%. If the usage ratio is less than this, a sufficient amount of crosslinking sites will not be introduced into the copolymer elastomer, while if it is used more than this, the crosslinking density of the vulcanizate will generally increase, the elongation rate will decrease, and the rubber-like elasticity will deteriorate. Along with this, physical properties such as heat aging resistance and compression set are also adversely affected.

During copolymerization, at least one type of polymerizable monomer that can be copolymerized with these monomers can be copolymerized.

Examples of such polymerizable monomers include vinyl chloride, vinylidene chloride, acrylonide-7-lyl, methacrylate tolyl, styrene, α-methylstyrene, vinyl acetate, ethyl vinyl ether, butyl vinyl ether, divinylbenzene, ethylene glycol diacrylate, and polyethylene. Glycol diacrylate, allyl methacrylate, triallyl isocyanurate, allyl alcohol, 2-hydroxyethyl acrylate, etc. are used, and in some cases, alkyl acrylates and alkoxyalkyl acrylates having 5 or more carbon atoms can also be used. When copolymerizing these polymerizable monomers, it is desirable to keep the proportion within the range of about 30% or less, preferably about 20% or less of the total comonomer weight.

Vulcanization of the oxazoline group-containing ethylene-acrylate elastomer can be easily carried out by heating in the presence of a polymercapto compound having two or more mercapto groups such as a thiol group, thiocarboxyl group, or thiophenol group.

Examples of polymercapto compounds include 1,6-dimercabutohexane, dimercabutodylether-8=, 1,5- or 2,7-dimercabutonaphthalene,
2゜2-dimercaptodiethyl sulfide, 2-dibutylamino-4,6-dithiol-S-triazine, 2-
Phenylamino-4,6-sithio-s-triazine, 1,4-dimercapto-2,3-butanediol, 2
,5-dimercapto-1,3,4-thiadiazole,3
, 4-dimercaptotoluene and the like in an amount of 0.2 to 10 parts by weight, preferably 0.5 to 5 parts by weight, per 100 parts by weight of the elastomer. This usage ratio depends on the vulcanization rate, scorch resistance, mechanical properties of the vulcanizate,
This range was selected from the viewpoint of various properties such as heat aging resistance and compression set. That is, if the usage ratio is lower than this, the vulcanization rate will drop and the general physical properties of the vulcanizate will not be satisfactory.
On the other hand, if it is used in excess of this, although the vulcanization rate generally increases, the scorch resistance (processing safety, storage stability), general properties of the vulcanizate, etc. are often impaired, and it is also inefficient. Therefore, both are undesirable.

In the vulcanization operation, this vulcanizing agent component is usually combined with other ingredients such as reinforcing agents, fillers, vulcanization accelerators that are added as necessary,
This is done by mixing with the elastomer along with antiaging agents, stabilizers, plasticizers, lubricants, processing aids, etc. by a commonly used mixing method such as roll mixing, Banbury mixing, kneader mixing, solution mixing, etc., and then heating. The vulcanization temperature is generally about 120°C or higher, preferably about 1
Temperatures of 50°C or higher are used.

〔Example〕

Next, the present invention will be explained with reference to examples.

(Example of ethylene-acrylate elastomer synthesis)
After the inside of the heat-resistant polymerization tube was sufficiently purged with nitrogen, 100 parts of methyl acrylate (weight, the same hereinafter), 8 parts of 2-vinyl-5-methyl-2-oxazoline, 300 parts of tertiary butanol, and 0.0 parts of azobisisobutyronitrile were added. Prepare 4 parts,
After that, the internal temperature was raised to about 70°C, and then ethylene was introduced under pressure until the internal pressure reached about 1000 kg/cy&. During the reaction, ethylene was intermittently fed for 10 hours at a temperature of about 75°C and about 900-1000 kg/a &
pressure was maintained. After the reaction is complete and the unreacted monomers are exhausted,
Ethylene-acrylate elastomer A was obtained by steam cleaning and drying.

The obtained copolymer elastomer contained 42.5% by weight of ethylene and 54% by weight of methyl acrylate based on the results of elemental analysis.
3 and 3.2% by weight of 2-vinyl-5-methyl-2-oxazoline, and its solution viscosity η
sp/c (85°C, 0.2% xylene solution) is 0.72
dl! /g.

(Comparative example of ethylene-acrylate elastomer synthesis)
In the above example, a copolymerization reaction was carried out in the same manner using 16 parts of ethylhydrodiene malate in place of 8 parts of 2-vinyl-5-methyl-2-oxazoline.
Acrylate elastomer B was obtained.

The obtained copolymer elastomer contained 41.3% by weight of ethylene and 54% by weight of methyl acrylate based on the results of elemental analysis.
It has a composition consisting of 2% by weight and 4.5% by weight of ethylhydrodiene malate, and its solution viscosity is 7+sp/c (
85℃, 0.2% xylene solution) is 0.68 dl! /g
(Vulcanization) -11= For each of the obtained elastomers, the compounding ingredients of compounding prescriptions I to (m) shown in Table 1 below were kneaded with a 4-inch open roll, and the vulcanizability of each was determined. A blended composition was prepared. Note that all numbers in parentheses are comparative examples.

Table 1 Mooney viscosity and scorch time (the time required for Mooney viscosity to reach the minimum value + 5, which is a measure of processing safety and storage stability) for each of the prepared vulcanizable compound compositions =12- was measured at 121°C. Further, the composition was press-cured at 180°C for 6 minutes, and then secondarily cured in an oven at 175°C for 4 hours. The physical property values of the obtained vulcanizate are determined by J
It was measured according to IS K-6301 and the results are shown in Table 2 below. In addition, the metal corrosion test was conducted on cold rolled steel plate (
A vulcanized rubber sheet (thickness: 2 mm) was placed on SPCC-3B), and after leaving it in an oven at 150°C for 72 hours, the vulcanized rubber sheet was removed, and the relative humidity of the steel plate was 60%.

The steel plate was left in a constant temperature and humidity chamber at a temperature of 25°C for 10 days, and the degree of corrosion was evaluated based on discoloration of the steel plate surface.

(The following is a blank space) From the results of 2, the ethylene-acrylate elastomer according to the present invention has an oxazoline group that serves as a crosslinking site in its copolymer side chain, so it can be effectively vulcanized by a polymercapto compound. It can be seen that the vulcanizate exhibits excellent mechanical properties, heat aging resistance, metal corrosion resistance, and water resistance, and is also excellent in terms of cross-mixing processability and the balance between vulcanization rate and scorch resistance.

Claims (1)

[Scope of Claims] 1. (a) 15 to 60% by weight of ethylene; (b) at least one member selected from the group consisting of alkyl acrylates and alkyl methacrylates in which the alkyl group has 1 to 4 carbon atoms; Acrylate 80-30
% by weight and (c) an acrylic elastomer containing 15 to 0.1% by weight of an oxazoline ring-containing monomer having an unsaturated group at the 2-position is vulcanized in the presence of a polymercapto group-containing compound. A method for vulcanizing ethylene-acrylate elastomer, characterized by: