JPH0370724B2 - - Google Patents

Description

Detailed Description of the Invention The present invention involves emulsion polymerization or emulsion copolymerization of a monomer having an ethylenic double bond and various monomers including a functional monomer copolymerizable with the monomer in an aqueous medium. The present invention relates to a method for producing a high-concentration, stable, and high-performance polymer latex having ultrafine particles with a particle size of 0.05 μm or less and a three-dimensional steel structure within the particles.

The ultrafine particle pre-crosslinked polymer latex produced by the present invention has a transparent appearance that differs from ordinary polymer latex in that it appears bluish-white to reflected light and yellow-red to transmitted light. It is somewhat viscous and is used as a high-performance paint vehicle and as a highly permeable binder. In addition, reactive type ultrafine particle pre-crosslinked polymer latex copolymerized with functional monomers such as 2-hydroxy-ethyl acrylate, acrylic acid, and acrylic acid amide can be used with crosslinking agents such as hexaxementoxymethylolmelamine. By adding it, cross-linking between particles is possible, and performance can be further improved by baking hardening. In recent years, as awareness of pollution problems such as air pollution and work environments has increased, the transition from organic solvent-based paints to water-based paints, high-solids paints, powder paints, etc. has become a major issue, but water-based paints are especially economical. It is considered promising due to its safety.

There are two types of water-based paints: aqueous solution type and water dispersion type, but water dispersion type polymer latex is the most promising and has the most expectations.

However, in the industrial field, the insufficient performance of existing polymer latexes has hindered their widespread use, and in the future, higher performance polymers will be needed to replace organic solvent-based paints and adhesives. Development of latex is essential.

One of the new technological methods that is expected to improve the performance of polymer latex is the formation of ultrafine particles of polymer latex.

In the case of polymer latex, the film is essentially formed by filling and fusing particles, so in order to maintain the same level of performance as organic solvent-based coatings, it is necessary to
It is desirable to make the particle size of polymer latex as small as possible.
It is possible to improve the film's smoothness, gloss, adhesion to finely uneven surfaces such as metal surfaces, and permeability. In addition, in the case of organic solvent-based paints, the polymer and crosslinking agent (curing agent) are uniformly mixed to improve the performance of the coating film, such as baking crosslinking, whereas in the case of polymer latex-based paints, particle filling and fusion are required. Because a film is formed by adhesion, the polymer and curing agent are not mixed uniformly. Therefore, in order to minimize the non-uniformity of the film inherent in polymer latex systems, it is very important to make the latex particles ultrafine.

A second method for improving the performance of polymer latex is to improve performance by introducing a three-dimensional network structure inside the polymer latex particles and between the polymer latex particles. According to recent theories, durable paint films, such as lacquer films, unsaturated polyester resin films, and alkyd resin films, have a ring structure in which parts of high cross-linking density are embedded in polymers with low cross-linking density. It is believed that the ultrafine polymer latex particles have a non-uniform network structure.
It is effective to create a three-dimensional network structure and further add reactive functional groups to the particle surface to create cross-bonds between the particles or between the particles and the continuous phase to form a three-dimensional network structure. it is conceivable that.

Conventionally, so-called reactive polymer latexes, in which reactive functional groups are added to the surface of polymer latex particles, have been known for crosslinking between particles. A polymer latex made by copolymerizing a small amount of a monomer having groups is crosslinked between particles using a crosslinking agent such as an aminoplast resin such as hexamethoxymethylmelamine or self-crosslinking between functional groups to form a film. Improvements have been made in strength, water resistance, etc. However, if it is possible to introduce a three-dimensional network structure not only between particles of polymer latex but also inside the polymer latex particles, it is possible to create a non-uniform coating with a ring structure such as a lacquer film. It has a network structure, resulting in a film with excellent durability, thermal stability, and impact strength.
However, it is extremely difficult to introduce a three-dimensional network structure into the interior of microscopic polymer latex particles without gelling the entire polymer latex during the polymer latex synthesis process. Not put into practical use. Conventionally,
Known methods for producing crosslinked polymer latex include crosslinking by radiation irradiation, polymerization of tetrafunctional or higher crosslinkable monomers such as divinylbenzene, diallyl phthalate, ethylene glycol dimethacrylate, triacrylic ester, etc. Copolymerization methods are known, but when these multifunctional (crosslinkable) monomers are used, ultrafine particles cannot be formed unless a surfactant such as sodium dodecyl sulfate is used in a significantly large amount as an emulsifier. Not only is it not possible to produce a polymer latex of 100%, but also the polymerization stability is extremely poor despite the presence of a large amount of surfactant. This is because pendant vinyl groups remain due to the use of multifunctional monomers and the surface of the polymer latex particles is highly reactive, resulting in agglomerization during the polymerization process, resulting in gelation of the entire system or This is due to the fact that polymerization must be stopped at a low polymer concentration of about 8 to 16% solids, and pre-crosslinked polymer latex with a high concentration of 30% or more is required for practical purposes. It was very difficult to generate.

Furthermore, since the polymerization rate is extremely slow and a large amount of emulsifier is used, side effects of the emulsifier are a major problem, which poses major problems in practical use in industrial applications.

The present inventors discovered that the conventional method involves polymerizing or copolymerizing a multifunctional monomer such as divinylbenzene, which causes aggregation of highly reactive pendant vinyl groups or polymer latex particles. After intensive research into whether there was a way to introduce a crosslinked structure into polymer latex particles without using a polyfunctional monomer, we found that a specific surfactant was introduced into polymer latex particles during the polymerization process. It was discovered that a dimensional network structure was generated. The present invention is based on this knowledge, and the polymer solids concentration is
Even at a high concentration of 50%, the particle size remains unchanged without agglomeration.
To provide a method for practically producing a novel high-performance polymer latex, which is transparent ultrafine particles of 0.05 μm or less and has a three-dimensional network structure inside the particles.

That is, the present invention uses a monomer selected from lower alkyl esters of acrylic acid or methacrylic acid, or a mixture of these monomers and other polymerizable monomers that can be copolymerized. For emulsion polymerization in an aqueous medium, a polymerization initiator is used, which is a redox polymerization catalyst consisting of a known persulfate and a reducing sulfoxy compound, to which a trace amount of transition metal ions, such as divalent copper ions, are added as a promoter. ,
In addition, as an emulsifier, N-(1,2-dicarboxyethyl)-N-alkylsulfosuccinic acid monoamide sodium salt, such as N-(1,2-dicarboxyethyl)-N-octadecylsulfosuccinic acid monoamide tetrasodium salt, etc. are generally used. Anionic surfactants used in emulsion polymerization, such as polyoxyethylene alkyl ether sulfate salts, preferably copolymerizable emulsifiers such as di(methacrylic acid long chain alkyl ester) phosphates, and mixtures of surfactants. By carrying out polymerization in the presence of a system with stirring, an ultrafine crosslinked polymer latex with a substantially transparent particle size of 0.01 to 0.05 μm, good dispersion stability, and uniform particle size is formed. This is a method for producing polymer latex characterized by the following.

The polymerization initiator used in the present invention is 1.0×
Known redox catalysts such as potassium persulfate and sodium thiosulfate in equimolar concentrations of 10 ^-3 to 1.0 x 10 ^-2 mol/are used, but for the production of transparent ultrafine polymer latexes. is 2.5×10 ^-7 to 7.5×10 ^-5 mol/2 as a polymerization accelerator.
Addition of transition metal ions such as valent copper ions is essential. The polymerization temperature can be used within a temperature range that activates the polymerization catalyst, but if it exceeds 80℃, the stability of the resulting polymer latex will deteriorate and the initiator will be deactivated, so it is necessary to control the polymerization temperature. It is necessary to carry out the polymerization while continuously dropping the monomer in small amounts.

The emulsifier used in the present invention is a known anionic surfactant normally used in emulsion polymerization, such as long-chain α-olefin sodium sulfonate, polyoxyethylene alkyl allyl ether sulfate salt, disodium alkyl diphenyl oxide sulfonate. , di(methacrylic acid alkyl ester) phosphoric acid, etc. and N-(1,2-dicarboxymethyl)-N-octadecylsulfosuccinic acid monoamide sodium salt such as N-(1,2-dicarboxyethyl)-N-octadecylsulfosuccinic acid. It is a combination of monoamide tetrasodium, N-octadecylsulfosuccinic acid monoamide disodium, etc., and the weight composition ratio is 1:3 to 1:3.
The ratio is preferably 3:1, and the concentration of this mixed emulsifier is preferably 1 to 10%, preferably 2 to 5% by weight, based on the aqueous medium. When such mixed emulsifiers are used, the polymer latex particles form a three-dimensional network structure. N-(1,2-dicarboxyethyl)-N in mixed emulsifier
- As the amount of sodium octadecyl sulfosuccinate increases, the crosslinking density increases, making it difficult for particles to coalesce and fuse with each other.

The resulting film is insoluble in benzene, and the gel content determined from 24-hour Soxhlet extraction depends on the content of sodium N-(1,2-dicarboxyethyl)-N-octadecylphosuccinic acid monoamide in the emulsifier mixture; The degree can be freely controlled.

Monomers used in the present invention include esters having polymerizable ethylene bonds such as ethyl acrylate, methyl methacrylate, 2-ethylhexyl acrylate, and butyl methacrylate, acrylonitrile, vinyl acetate, styrene, and chloride. Vinyl, vinylidene chloride, etc., and functional monomers that can be copolymerized with the above monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and polyethylene glycol (meth)acrylate. , N-methylolacrylamide, glycidyl (meth)acrylate, acrylic acid, maleic anhydride, itaconic acid,
Acrylamide, dimethylaminoethyl (meth)
Examples include acrylate.

When the degree of crosslinking and crosslinking density of the ultrafine particulate pre-crosslinked polymer textiles produced by the present invention is low, they fuse together to form a continuous film, resulting in a highly elastic and tough film with a large initial modulus value. Forms a film. Further, if the degree of crosslinking is high and the crosslinking density is not low, the latex particles will not fuse with each other, so that they are useful for improving blocking properties and physical properties of the coating film by adding them to powder coatings. In particular, in the case of reactive type polymer latexes that are not only ultrafine particles and crosslinked polymer latexes but also have functional groups such as carboxyl groups, hydroxyl groups, and amino groups on the surface of the latex particles, polymerizable monomers or organic When redispersed in a solvent, it is useful as a so-called high solids paint material with little volumetric agent. It can also be used to improve the performance of existing powder coatings, solvent-based coatings, high-solids coatings, and water-based coatings by mixing with them.

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Using a 1000 ml four-neck separable flask equipped with a gas inlet tube, a reflux condenser, a composite glass electrode for PH measurement, and a stirring device, in 400 ml of distilled water,
22.6 g of a 36% aqueous solution of monoamide tetrasodium N-(1,2-dicarboxyethyl)-N-octadecylsulfosuccinate as an emulsifier and di(methacrylic acid long chain alkyl ester) phosphoric acid (first industrial pharmaceutical
Melt 4g of NewfrontierA-229E) at 60-70℃.
Make it. For polymerization, a monomer mixture of ethyl acrylate and methyl methacrylate (composition ratio 7:3) was first used.
A redox initiator (in the system) consisting of equimolar amounts of potassium persulfate and sodium thiosulfate with copper sulfate (concentration in the system of ^2.5 concentration
3.0×10 ^-3 mol/) at 60 to 70°C and pH 4 to 7, then the remaining 250 ml of ethyl acrylate-methyl methacrylate mixed monomer was added while preventing a significant temperature rise due to polymerization heat. Polymerization was carried out by gradually dropping the mixture. As the viscosity of the polymerization system increases as the polymerization progresses, it becomes difficult to disperse and stir the monomers.
Add 4 ml of 28% ammonia water dropwise, or add about 0.5 g of ammonia phosphate in advance before starting polymerization. Polymerization was completed in about 30 to 40 minutes, and a transparent polymer latex was obtained that appeared blue-white in reflected light and yellow-red in transmitted light. The light transmittance measured by a spectrophotometer at 800 nm (using a 1 cm glass cell) was 26%, and the particle size measured by an electron microscope was 430 Å. The obtained ultrafine particle polymer latex was naturally dried on a glass plate, and the film obtained had very good transparency.
The haze value of the film was determined using a JIS K6714 integrating sphere light transmittance measuring device (the haze value was 3.5%).
In addition, the 20° specular gloss according to JIS Z8741 is over 95%, and the gloss is very good. The film formed by air drying only swells in benzene acetone and is almost insoluble, and the degree of swelling in benzene, calculated from the area ratio of the film before and 48 hours after immersion in benzene, is 8.1.
It was hot.

Example 2 The emulsifier N-(1,2
The amount of tetrasodium dicarboxyethyl)-N-octadecylsulfosuccinic acid monoamide used was larger than in Example 1, and 34 g of a commercially available 36% solution was used.
(3% based on aqueous medium), polymerization was similarly observed.
The process was completed within 35 minutes, and a translucent ultrafine particle polymer latex with a light transmittance of 21% at 800 nm was obtained.

The film obtained by air drying on a glass plate had good transparency and gloss. The film is insoluble in benzene and swells while retaining its shape. The degree of swelling determined from the area ratio before and after immersion in benzene was 5.2.

Claims (1)

[Claims] 1. A monomer selected from lower alkyl esters of acrylic acid or methacrylic acid, or a mixture of these monomers and other polymerizable monomers that can be copolymerized, in an aqueous medium. In emulsion polymerization, a polymerization initiator is used, in which a trace amount of transition metal ion is added as a promoter to a redox polymerization catalyst consisting of a persulfate and a reducing sulfoxy compound, and N-(1,2- The particle size can be substantially reduced by polymerizing with stirring in the presence of a mixed system of a combination of dicarboxyethyl)-N-octadecylsulfosuccinic acid monoamide sodium salt and an anionic surfactant.
A method for producing a high-performance polymer latex, which is characterized by forming an ultrafine particle pre-crosslinked polymer latex with transparency of 0.01 to 0.05 μm, good dispersion stability, and uniform particle size.