JPS6340202B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating unreacted components present in an ethylene-vinyl acetate copolymer emulsion (hereinafter abbreviated as EVA emulsion) after completion of emulsion polymerization.

EVA emulsions have a wide range of uses, including paint vehicles, adhesives, textile and paper processing, as well as cement and mortar admixtures.

However, when manufacturing EVA emulsion,
Even if the polymerization rate of vinyl acetate reaches nearly 100%, because ethylene is gaseous and the ethylene pressure must be increased to increase the reaction ratio with vinyl acetate, Excess ethylene is dissolved in the emulsion. On the other hand, after the completion of emulsion polymerization, ethylene in the gas phase is released to atmospheric pressure and recovered and reused, but unreacted vinyl acetate and dissolved ethylene in the EVA emulsion are not removed as they are.

If there is a large amount of unreacted vinyl acetate and dissolved ethylene in the EVA emulsion, it is a safety and health problem.In particular, if there is a large amount of dissolved ethylene, the solubility of ethylene decreases due to an increase in the environmental temperature, and the metal can filled with the emulsion is There is a risk of swelling and sometimes even bursting.

Methods to solve these problems include a method in which an antifoaming agent is injected after emulsion polymerization is completed, the ethylene is released to atmospheric pressure, and then the dissolved ethylene is removed by heating and stirring, and a method in which a polymerization catalyst is additionally added. A method is known in which the remaining components in the liquid phase are further copolymerized. However, these methods limit the amount of unreacted vinyl acetate to about 0.3% or less and the amount of dissolved ethylene.
It is difficult to reduce the amount to below about 100 ppm, and it also causes problems such as impairing the quality of the emulsion, which is not satisfactory.

As a result of intensive studies to solve the above problems, the present inventors first discharged excess ethylene (ethylene residual pressure) in the reaction system after the completion of emulsion polymerization, brought the inside of the reaction vessel to atmospheric pressure, and then applied an antifoaming agent. Furthermore, after adding the catalyst, an inert gas having a moisture content of 1 to 25 vol% is introduced into the gas phase inside the container at the same time as stirring, thereby reducing the amount of unreacted vinyl acetate without impairing the quality of the emulsion. We have found that it is possible to reduce the amount of dissolved ethylene to 0.3% or less and the amount of dissolved ethylene to 100 ppm or less, and have completed the present invention.

The EVA emulsion in the present invention is not obtained by any special method, but is intended to be an emulsion obtained according to a known method. For example, first, a surfactant, a protective colloid, a PH adjuster, water, a catalyst, and vinyl acetate (10 to 100% of a predetermined amount) are added and stirred to emulsify.

Next, nitrogen gas is pressurized to replace the inside of the autoclave, and then ethylene is pressurized. Polymerization is initiated by heating, and the remaining vinyl acetate (0 to 90% of the predetermined amount) and, if necessary, a further catalyst are added continuously, in portions, or all at once to continue polymerization. Pressure injection of ethylene may be carried out all at once, in batches, or continuously.

In the present invention, the catalyst used as an additional catalyst during emulsion polymerization or after the completion of emulsion polymerization is as follows:
Various free radical forming catalysts, such as peroxides,
Further, it is a redox catalyst consisting of a combination of a reducing agent and an oxidizing agent. Reducing agents (activators) include bisulfites, sulfoxylates, or other compounds with reducing properties such as ferrous salts and tertiary aromatic amines such as N.N-dimethylaniline. Oxidizing agents (initiators) include hydrogen peroxide, organic peroxides such as benzoyl peroxide, t-butyl hydroperoxide and the like. Specific combination catalysts or redox systems also include hydrogen peroxide and zinc formaldehyde sulfoxylate, hydrogen peroxide, ammonium persulfate or potassium persulfate and sodium metabisulfite, sodium bisulfite,
Included are ferrous sulfate, dimethylaniline, zinc formaldehyde sulfoxylate or sodium formaldehyde sulfoxylate.

The amount of the catalyst used during emulsion polymerization is suitably in the range of 0.05 to 2% based on the weight of vinyl acetate and other copolymerizable monomers introduced into the system. Alternatively, the activator is used in the form of an aqueous solution, and its amount is suitably in the range of 0.25 to 1 times the amount of the catalyst.

During emulsion polymerization, anionic surfactants, nonionic surfactants, and protective colloids are used as emulsifiers. As an anionic surfactant,
Examples include higher alcohol sulfate ester salts, alkylbenzene sulfonates, polyoxyethylene alkyl phenol sulfate salts, polyoxyethylene sulfate salts, dialkyl sulfosuccinates, etc. Nonionic surfactants include polyoxyethylene alkyl ether, polyoxyethylene alkyl phenol ether,
Examples include oxyethylene-oxypropylene block copolymer and polyoxyethylene sorbitan monolaurate.

Examples of protective colloids include polyvinyl alcohol, partially saponified polyvinyl alcohol, polyvinyl alcohol derivatives, modified polyvinyl alcohol, cellulose derivatives such as hydroxyethyl cellulose and hydroxypropyl cellulose, sodium polyacrylate, and polyacrylic acid amide.

The nonionic surfactant, anionic surfactant and protective colloid are 1 to 10% by weight and 1 to 10% by weight, respectively, based on the total weight of vinyl acetate and other polymerizable monomers introduced into the system. , a range of 0.2 to 10% by weight is suitable.

It is economically advantageous for the reaction temperature to be in the range of about 30 to 80°C, and the appropriate reaction pressure to be in the range of 5 to 100 atm.In order to obtain an emulsion with a high ethylene content, a high ethylene pressure is required. Needed.

The reaction time varies depending on the reaction temperature, amount of catalyst, type of catalyst, ethylene pressure, etc., but it is approximately 3 to 10 minutes with the aim of keeping the amount of unreacted vinyl acetate to 2% by weight or less.
However, other reaction times are possible.

The EVA emulsion of the present invention contains, as components other than ethylene and vinyl acetate, unsaturated vinyl monomers having a glycidyl group such as acrylic glycidyl and methacryl glycidyl, methylol compounds such as N-methylol acrylamide and N-methylol methacrylamide, and their like. methyl,
Unsaturated vinyl monomers having N-methylol groups or alkoxy groups such as alkyl ethers of ethyl and butyl ethers, acrylic acid, itaconic acid,
It also includes unsaturated vinyl monomers having a carboxyl group or carboxylic acid ester group such as maleic acid and their esters, vinyl esters of branched monocarboxylic acids such as versatectate vinyl ester, and those containing small amounts of vinyl chloride. It is something.

In the post-treatment method of the present invention, emulsion polymerization is carried out under the conditions described above, and after the reaction is completed, excess ethylene (residual pressure) is first discharged to bring the inside of the reaction vessel to atmospheric pressure. This reduces the amount of ethylene dissolved in the emulsion and at the same time facilitates the escape of ethylene from the emulsion. Then, an antifoaming agent is added in an amount of 0.01 to 0.5% by weight based on the emulsion. It is not appropriate to add the antifoaming agent to the reaction vessel under ethylene residual pressure because the antifoaming effect will be reduced. Next, after transferring the emulsion to another container (or leaving it in the reaction container), a polymerization catalyst is added in an amount of 0.01 to 0.5% by weight based on the emulsion. The catalyst is essential to further copolymerize unreacted vinyl acetate in the emulsion to below 0.3% by weight, which is within practical limits. Methods such as adding a catalyst during the emulsion polymerization reaction process or extending the reaction time to reduce the vinyl acetate unreacted component to 0.3% by weight or less require a large amount of catalyst, which reduces the quality of the emulsion.
Furthermore, it cannot be adopted because of problems such as a long reaction time.

Then, at the same time as stirring, an inert gas having a water content of 1 to 25 vol%, preferably 7 to 10 vol%, is passed through the gas phase in the container at a flow rate of 0.2 to 3 Nm ² /H per 1 m ² of the emulsion, and the mixture is heated at room temperature or slightly heated. Stir for approximately 2-15 hours.

Aeration of an inert gas having a water content of 1 to 25 vol% into the gas phase effectively drives out dissolved ethylene.
Gases other than inert gases are unsuitable because they inhibit the push-polymerization of residual vinyl acetate and ethylene.
Being a humid gas prevents the surface of the emulsion from drying and prevents the generation of coarse particles. In addition, if the moisture content is outside the range of 1 to 25 vol%,
The above effect cannot be obtained. In addition, blowing the inert gas into the emulsion is effective for expelling ethylene, but it is unsuitable because the emulsion foams violently.

EVA treated by the post-treatment method of the present invention
Since the emulsion has less than 0.3% residual vinyl acetate, there is no odor or quality change due to it, and since the dissolved ethylene content is less than 100 ppm, there is no risk of metal cans filled with the emulsion swelling or bursting. It can be stored and used safely without any concerns.

Next, the present invention will be specifically explained with reference to Examples. In the examples, "%" is based on weight unless otherwise specified.

Example 1 Vinyl acetate 4550Kg, water 5600Kg, PVA (saponification degree
88.0%, average degree of polymerization 1400) 230 kg and Rongarit 4.2 kg were placed in an autoclave, stirred to form an emulsion, replaced with _N2 gas, and then continuously heated and pressurized with ethylene to bring the internal temperature down. 60℃,
Maintain ethylene pressure 50Kg/cm ² G, vinyl acetate 1950Kg
9 while continuously adding a 1% aqueous solution of potassium persulfate (abbreviated as KPS) and dibasic sodium phosphate.
The reaction was carried out over a period of time. After exhausting excess ethylene and bringing it to atmospheric pressure, add antifoaming agent (Nopco 8034)
After adding 7.5Kg, the emulsion was transferred to another container. 0.1% aqueous solution of KPS as additional catalyst
100Kg was added, and at the same time, _N2 gas with a water content of about 9vol% was vented into the gas phase of the container at a flow rate of ^10Nm2 /H.
Stirred for hours. Then, it was neutralized with aqueous ammonia.

Unreacted vinyl acetate in the emulsion treated in this way is 0.25% and dissolved ethylene is 95ppm.
It was hot. The solid content of the emulsion is 55.6
%, average particle size is 600mμ, viscosity is 6300cps (25℃,
BH type, 4 rpm), and the vinyl acetate component of the copolymer was 83%.

Example 2 1200 kg of vinyl acetate, 4830 kg of water, 84 kg of sodium lauryl sulfate, 336 kg of polyoxyethylene nonyl phenyl ether, 20 kg of PVA (degree of saponification 88.0 mol%, average degree of polymerization 1400) and 45.6 kg of dibasic sodium phosphate were placed in an autoclave. After preparing and stirring to make an emulsified liquid and replacing it with _N2 gas, the temperature was raised continuously and the ethylene pressure was applied.The internal temperature was 60℃ and the ethylene pressure was
The reaction was carried out for 8 hours while maintaining a pressure of 55 kg/cm ² G and continuously adding 4800 kg of vinyl acetate, Rongalite, ammonium persulfate (abbreviated as APS), and a 1% aqueous solution of dibasic sodium phosphate. After exhausting the excess ethylene and bringing it to atmospheric pressure, apply an antifoaming agent (Nobuko).
8034) 7.5Kg was added and then the emulsion was transferred to another container. The emulsion was kept at 35℃, and 90Kg of 0.1% aqueous solution of APS was added as an additional catalyst.
At the same time, _N2 gas with a moisture content of 7 vol% is introduced into the gas phase of the container.
The mixture was stirred for 3 hours while being aerated at a flow rate of 15 Nm ² /H. Then, it was neutralized with aqueous ammonia. The emulsion treated in this way contained 0.27% unreacted vinyl acetate and dissolved ethylene.
It was 100ppm. The solid content of the emulsion is 55.2%, the average particle size is 270mμ, and the viscosity is 3100cps.
(25°C, BH type, 4 rpm), and the vinyl acetate component of the copolymer was 75%.

Control Example 1 An emulsion polymerization reaction was carried out for 9 hours in the same manner as in Example 1, and after continuing the emulsion polymerization reaction for an additional 3 hours under the same conditions, excess ethylene was discharged.
The unreacted vinyl acetate in the resulting emulsion is
0.41%, and dissolved ethylene was 400 ppm. While the emulsion was stored in 5-gallon cans, it was observed that the cans expanded due to the escape of dissolved ethylene from the liquid phase to the gas phase, causing the cans to collapse.

Control Example 2 An emulsion polymerization reaction was carried out for 9 hours in the same manner as in Example 1, excess ethylene was discharged, the pressure was brought to atmospheric pressure, 7.5 kg of antifoaming agent was added, and the emulsion was transferred to another container. The emulsion was heated to 45°C, 100 kg of 0.01% aqueous solution of KPS was added as an additional catalyst, and at the same time dry N ₂ gas (water content 0.1 vol%) was bubbled into the gas phase of the container at a flow rate of 10 Nm ² /H. When the emulsion was stirred for a long time, a large amount of coarse particles were generated due to drying of the surface of the emulsion.

Claims (1)

[Claims] 1. After emulsion polymerization of ethylene and vinyl acetate, and if necessary, other copolymerizable monomers, in an aqueous medium, excess ethylene in the reaction system is discharged to bring the inside of the reaction vessel to atmospheric pressure, and then an antifoaming agent is added. and a method for post-treatment of an ethylene-vinyl acetate copolymer emulsion, which comprises adding a catalyst and bubbling an inert gas having a water content of 1 to 25 vol% into the gas phase in the container while stirring.