JP2765473B2 - Method for producing acrylic emulsion - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a novel acrylic emulsion, and more particularly to a method for producing an acrylic emulsion having a high solid content of 65% or more and a low viscosity. It is used in the chemical industry for producing emulsions, the paint industry using acrylic emulsions, the adhesive industry, and the like.

[0002]

2. Description of the Related Art In recent years, with the expansion of applications of acrylic emulsions, it has been desired to impart various properties to acrylic emulsions. One of its properties is high solid differentiation, for example, in the adhesive industry, regardless of the adhesive label, adhesive tape, high solid differentiation of the acrylic emulsion used in its production, the drying time during coating It is strongly desired from the viewpoint of shortening and hence improvement of productivity. However, simply increasing the solid content leads to an increase in the viscosity of the acrylic emulsion, and the production thereof causes a great problem in terms of heat removal and contamination of the polymerization reactor. It is well known that in order to solve this problem, the particle size of the particles in the emulsion should be increased and the width of the particle size distribution should be widened, and various methods have been proposed. For example, U.S. Pat. No. 4,130,523 proposes a method in which a part of an emulsion is taken out of a polymerization reactor in the course of polymerization and is continuously charged again in the final stage to carry out polymerization. However, in this method, the equipment becomes complicated, and it is necessary to perform an operation involving the danger of taking out the emulsion during the polymerization reaction. Further, in the case of an emulsion lacking mechanical stability, a grid ( Lump). Also, Japanese Patent Application Laid-Open No. 56-157401 proposes a method of performing emulsion polymerization in the presence of a large amount of a polymerization inhibitor. This method is based on the presence of a large amount of unreacted monomer in an emulsion. Therefore, there is a problem that it is difficult to sufficiently exert the function of the emulsion. Furthermore, Japanese Patent Publication No. 61-47848 proposes a method in which a seed polymer is previously present in water charged in a polymerization reactor. This is a method in which it is difficult to accurately grasp the amount of the body and to obtain a uniform emulsion. On the other hand, during emulsion polymerization, it is also known that the sequential addition method of emulsion enables the production of an emulsion having a wide particle size distribution, which means that micelles in the emulsion supplied in the latter half of the polymerization cannot be sufficiently grown. It is a thing that utilizes that. However, since this method inevitably produces particles having a small particle size, the viscosity of the emulsion is often increased, and further, in the process of growing from small particles to large particles, the surface area of the particles increases. , The shortage of the emulsifier, the stability of the emulsion is impaired, the fusion of the particles is caused, or a water-soluble polymer is generated in the continuous phase, and as a result, the viscosity is increased. . In order to solve the problem of this method and supply a stable emulsion with low viscosity, a pre-emulsion was prepared by emulsifying the monomer using a slightly excessive emulsifier in advance, and the pre-emulsion was carried out continuously or intermittently. A method has been proposed in which emulsion polymerization is carried out by adding the mixture to a vessel, but an excessive emulsifier is used because it has a large effect on the properties of the emulsion, for example, when used in a pressure-sensitive adhesive, it causes a reduction in pressure-sensitive adhesive properties / adhesive strength. This is a difficult method.

[0003]

SUMMARY OF THE INVENTION The present inventors have sought to avoid the above-mentioned problems of the prior art and to provide a method for easily and efficiently producing an acrylic emulsion having a high solid content and good stability. Various studies were conducted.

[0004]

Means for Solving the Problems The inventors of the present invention have proposed an operation in which an amount of an emulsifier accompanying the growth (increase in surface area) of particles during polymerization is continuously or intermittently added to a polymerization reactor during emulsion polymerization. The present inventors have found that an excellent acrylic emulsion having a high solid content can be easily produced, and have completed the present invention.

That is, the present invention comprises the following two inventions. After starting polymerization while charging a monomer or monomer mixture mainly composed of a (meth) acrylate ester which is a pre-emulsion using an emulsifier, the emulsifier is added stepwise or A method for producing an acrylic emulsion, characterized in that the monomer or monomer mixture is emulsion-polymerized by continuously or intermittently adding the amount thereof in a linear manner. The method according to claim 1, wherein the total amount of the emulsifier added after the initiation of the polymerization is 0.01 to 5% by weight based on the finally obtained emulsion.

Hereinafter, the present invention will be described in more detail. ○ Monomer or monomer mixture The monomer or monomer mixture used in the present invention is (meth)
The main component is an acrylate ester, and specific examples of the (meth) acrylate ester include the following. Alkyl acrylates such as methyl acrylate, ethyl acrylate, butyl acrylate, propyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, lauryl acrylate, methyl methacrylate, methacrylic acid Alkyl methacrylates such as butyl, hydroxyalkyl acrylates, hydroxyalkyl methacrylates; Further, in the present invention, a monomer copolymerizable with the (meth) acrylic acid ester can be used in combination, and specific examples thereof are as follows. Acrylic acid, methacrylic acid, fumaric acid, itaconic acid, maleic acid, styrene,
Acrylonitrile, vinyl acetate, vinyl propionate,
Vinylidene chloride. When the amount of the monomer copolymerizable with the (meth) acrylic acid ester exceeds 50% by weight of the total monomer, the obtained emulsion becomes difficult to exhibit the properties as an acrylic emulsion. It is preferred to use it without.

○ Emulsifier The emulsifier used in the present invention is an emulsifier usually used for producing an emulsion, ie, an anionic or nonionic or a mixture thereof. Specifically, the anionic is a fatty acid soap. , An alkyl sulfonate, an alkyl aryl sulfonate, an alkyl sulfosuccinate, a polyoxyethylene alkyl sulfate, a polyoxyethylene aryl sulfate, etc., and a nonionic polyoxyethylene alkyl ether, a polyoxyethylene alkyl aryl ether, Polyoxyethylene sorbitan fatty acid esters, oxyethylene oxypropylene block polymers and the like can be mentioned. The amount of the emulsifier used is 0.1 to 10.0% by weight at the start of polymerization.
(The same applies hereinafter based on the finally obtained emulsion), and more preferably 0.1 to 4.0% by weight, and the amount added during the polymerization is 0.01.
To 5.0% by weight, more preferably 0.01 to 3.0% by weight.
% By weight. Therefore, the total amount of emulsifier used
It is preferably from 0.1 to 15.0% by weight, more preferably from 0.1 to 15.0% by weight.
1 to 7.0% by weight.

In the present invention, a polymerization initiator, a pH buffer, a neutralizing agent, an antifoaming agent, a stabilizer and the like usually used in emulsion polymerization are used in the same manner. There is no particular polymerization initiator, and it is a compound that generates a radical by heat or a reducing substance that is generally used in emulsion polymerization.For example, a water-soluble or oil-soluble persulfate or an azobis compound is used. . The amount of the polymerization initiator to be used is usually 0.1 to 2% by weight based on the monomer. When accelerating the polymerization rate or attempting polymerization at a low temperature, sodium sulfite, sodium bisulfite, and ferrous chloride are used. , Ascorbic acid, sodium aldehyde sulfoxylate and the like.

One example of the emulsion polymerization step in the present invention is as follows. First, as a first step, a pre-emulsion is prepared using as little emulsifier as possible to stably emulsify the monomer or monomer mixture in an appropriate amount of water. Next, the water charged into the polymerization reactor is heated to a predetermined polymerization temperature, and a pre-emulsion (monomer emulsion) and a polymerization initiator are added with stirring to start polymerization, and as the polymerization proceeds, the emulsifier is added. It is added separately continuously or intermittently to complete the polymerization. The emulsifier is added continuously or intermittently according to the progress of polymerization, that is, stepwise or linearly while increasing the amount of addition. When to add the emulsifier,
It is determined on the basis of the polymer conversion rate estimated from the polymerization time. Usually, the addition starts when the polymer conversion rate reaches 5% and ends when the polymer addition rate reaches 95%. Start adding at 10%, 90%
Is to end it. Addition outside of this range, especially when the end time is missed, may reduce the contribution to lowering the viscosity of the emulsion.

[0010]

[Function] By adding an emulsifier continuously or intermittently during emulsion polymerization, the surface area of micelles or particles which increase due to the growth of particles accompanying the progress of polymerization can be covered with the emulsifier, and the formation of micelles can be promoted uniformly. However, it is presumed that the acrylic emulsion having a high solid content obtained by the method of the present invention has stable particles, low viscosity and excellent mechanical stability.

[0011]

The present invention will be further described below with reference to examples. In the present invention, the solid content is determined according to JIS K 5407 (paint component test method). It is shown by the nonvolatile content% of the emulsion measured based on the heating residue.

Example 1 23.5 parts by weight of water (hereinafter simply referred to as "parts") was placed in a pressure-resistant reactor.
And heated to 80 ° C. After adding 0.5 part of ammonium persulfate while controlling the temperature at 80 ° C., a pre-emulsion having the following composition is introduced at a constant rate over 5 hours. 15.0 parts of water 25% aqueous solution of sodium polyoxyethylene alkylphenyl ether sulfate 2.8 Methyl methacrylate 14.0 2-ethylhexyl acrylate 85.0 Acrylic acid 1.0 1.0 part of the same emulsifier as above was added over 5 hours at a flow rate per unit time as follows. 0-1Hr: 0.000 parts / Hr 1-2Hr: 0.10 parts /
Hr 2-3Hr: 0.20 parts / Hr 3-4Hr: 0.30 parts /
Hr 4-5Hr: 0.40 parts / Hr The obtained emulsion has a solid content of 71.6% and a viscosity of 7
It was a stable emulsion with a median particle size of 1.455 μm at 10 cps.

Example 2 23.5 parts of water was charged into a pressure-resistant reactor and heated to 80 ° C. After adding 0.4 parts of ammonium persulfate while controlling the temperature to 80 ° C., a pre-emulsion having the following composition is introduced at a constant rate over 5 hours. Water 15.0 parts Polyoxyethylene alkyl aryl ether 1.6 Na ・ alkyl persulfate 0.6 Methacrylic acid 1.0 Phthyl acrylate 30.0 2-Ethylhexyl acrylate 60.0 Styrene 9.0 Further polymerization From a separate port, a total amount of 0.8 part of the same emulsifier mixture as above was added to the reactor over 5 hours at a flow rate per unit time as follows. 0-1Hr: 0.000 parts / Hr 1-2Hr: 0.08 parts /
Hr 2-3Hr: 0.16 parts / Hr 3-4Hr: 0.24 parts /
Hr 4-5Hr: 0.32 parts / Hr The obtained emulsion has a solid content of 65.0% and a viscosity of 6
It was a stable emulsion with a median particle diameter of 0.531 μm at 25 cps.

Comparative Example 1 Polymerization was carried out in the same manner as in Example 1 except that the emulsifier to be added from another mouth was added to the pre-emulsion in advance. The resulting emulsion had a solids concentration of 70.7.
7%, viscosity 2,960 cps, median particle size 0.751μ
m emulsion.

[0015]

According to the present invention, when an acrylic emulsion is prepared by emulsion polymerization, an emulsifier is continuously or intermittently added to the polymerization system during the emulsion polymerization to easily produce an acrylic emulsion having a high solid content and a low viscosity. It has become possible to manufacture.

Claims (2)

(57) [Claims] Claims: 1. A polymerization reaction is started while charging a monomer or a monomer mixture mainly composed of a (meth) acrylic acid ester, which is pre-emulsified with an emulsifier, into a polymerization reactor charged with water. A method for producing an acrylic emulsion, wherein the monomer or monomer mixture is emulsion-polymerized by continuously or intermittently adding an emulsifier in an increasing amount stepwise or linearly. 2. The total amount of the emulsifier added after the initiation of the polymerization is 0. 0, based on the finally obtained emulsion.
2. The method according to claim 1, wherein the amount is from 0.01 to 5% by weight.