JPH0370725B2 - - 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 diameter of 0.05 μm or less and having a three-dimensional network structure within the particles.

The appearance of the ultrafine particle pre-crosslinked polymer latex produced by the present invention differs from ordinary polymer latex in that it has a slightly transparent appearance that is bluish-white to reflected light and yellow-red to transmitted light. It is viscous and can be 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-hydroxyethyl acrylate, acrylic acid, and acrylic acid amide can be produced by adding a crosslinking agent such as hexakismethoxymethylolmelamine. Inter-particle crosslinking is possible by this method, and performance can be further improved by baking hardening. In recent years, air pollution,
With the growing awareness of pollution problems in the work environment, 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 particularly important due to their economic efficiency and safety. It is seen as promising.

There are two types of water-based paints: aqueous solution type and water dispersion type.
Water-dispersed polymer latex is said to be the most promising and has the most expectations. However, in the industrial field, the insufficient performance of existing polymer latexes is an obstacle to their widespread use, and in the future, higher-performance polymer latexes are expected to replace organic solvent-based paints and adhesives. development 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, the particle size of the polymer latex must be adjusted as much as possible. It is desirable to make the particles extremely fine, and by making them ultrafine, it is possible to improve the degree of fusion, the smoothness and gloss of the film, the adhesion to finely uneven surfaces such as metal surfaces, and the 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, Because a film is formed by fusion, 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 a portion of high cross-linking density is embedded in a polymer 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 have been known in which reactive functional groups are added to the surface of polymer latex particles for cross-linking between particles, and functional groups such as carboxyl groups, hydroxyl groups, amino groups, amide groups, glycidyl groups, etc. A coating is created by crosslinking particles between particles using a crosslinking agent such as an aminoplast resin such as hexamethoxymethylmelamine or self-crosslinking between functional groups on a polymer latex made by copolymerizing a small amount of monomers having groups. Improvements have been made in terms of 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, and a film with excellent durability, thermal stability, and impact strength can be obtained. However, it is extremely difficult to introduce a three-dimensional network structure into the inside 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, and crosslinking using tetrafunctional or higher functional crosslinkable monomers such as divinylbenzene, diallyl phthalate, ethylene glycol dimethacrylate, and triacrylic ester. However, when using these multifunctional (crosslinking) monomers, it is necessary to use ultra-high-strength polymerization methods that do not use excessive amounts of surfactants such as sodium dodecyl sulfate as emulsifiers. It not only cannot produce a fine particle polymer latex, but also has the disadvantage of extremely poor polymerization stability despite the presence of a large amount of surfactant. This is because pendant vinyl groups remain due to the use of polyfunctional monomers, making the surface of the polymer latex particles highly reactive, resulting in agglomerization during the polymerization process, resulting in gelation of the entire system and a large amount of The drawback is that polymerization must be stopped at a low polymer concentration of 8 to 16% solids due to the formation of agglomerates, but it produces pre-crosslinked polymer latex with a high concentration of 30% or more, which is necessary for practical use. It was extremely difficult to do so.
In addition, the polymerization rate was extremely slow, and since a large amount of emulsifier was used, side effects of the emulsifier were a serious problem, and there were serious problems in practical application for industrial use.
The present inventors discovered that because the conventional method involves polymerizing or copolymerizing a polyfunctional monomer such as divinylbenzene, the highly reactive pendant vinyl groups cause aggregation of polymer latex particles. As a result of intensive research into whether there is a way to introduce a crosslinked structure into polymer latex particles without using a monomer, we found that a specific surfactant creates a three-dimensional network within polymer latex particles during the polymerization process. It was discovered that a structure was generated.

The present invention is based on this knowledge, and produces transparent ultrafine particles with a particle diameter of 0.05 μm or less without agglomeration even at a high polymer solid content concentration of 30 to 50%, and has a three-dimensional network inside the particles. To provide a method for practically producing a novel high-performance polymer latex having a structure.

That is, the present invention provides a monomer consisting of a monomer selected from lower alkyl esters of acrylic acid or methacrylic acid, or a mixture of these monomers and other polymerizable monomers copolymerizable with them. In carrying out emulsion polymerization in an aqueous medium, a polymerization initiator prepared by adding a trace amount of transition metal ions as a promoter to a known redox polymerization catalyst consisting of a persulfate and a reducing sulfoxy compound was used, and a commercially available emulsifier was used. By carrying out polymerization while stirring in the presence of a mixed system of bleached ceramic resin (white rack, transparent rack) and anionic surfactant commonly used in emulsion polymerization, the particle size is substantially reduced to 0.01~
This is a method for producing a polymer latex, which is characterized by forming an ultrafine crosslinked polymer latex having a uniform particle diameter of 0.05 μm, transparency and good dispersion stability.

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 × 10 ^-2 mol/are used, but for the production of transparent ultrafine polymer latexes. It is essential to add transition metal ions such as divalent copper ions in an amount of 2.5 ^-7 × 5.0 × 10 ^-4 mol/, preferably 2.5 × 10 ^-6 to 2.5 × 10 ^-4 mol/, as a polymerization accelerator. . The polymerization temperature can be used in a temperature range that activates the polymerization initiator, but a range of 50 to 60°C is effective; if the temperature exceeds 80°C, the stability of the resulting polymer latex will deteriorate, and the polymerization will be activated. Since deactivation of the agent occurs, it is necessary to carry out the polymerization while continuously dropping the monomer in small amounts in order to control the polymerization temperature.

The emulsifier used in the present invention is a mixed system of bleached shellac resin and an anionic surfactant, and examples of the anionic surfactant include known anionic surfactants commonly used in emulsion polymerization, such as long-chain α-olefin sulfonic acid. Examples include sodium, polyoxyethylene alkyl allyl ether sulfate, disodium alkyl diphenyl oxide sulfonate, and preferably di(methacrylic acid alkyl ester) phosphoric acid. On the other hand, commercially available bleaching shellac resins can be used. The composition ratio of bleached shellac resin and anionic surfactant is preferably 1:3 to 3:1 by weight.

The bleached ceramic resin used in the present invention can be heated,
For example, it is preferable to use it by dissolving it in advance in aqueous ammonia heated to about 60°C, and by adding an anionic surfactant thereto, the emulsion used in the present invention can be obtained. The concentration of this mixed emulsifier is 1 to 15%, preferably 2 to 15%, based on the aqueous medium.
It is in the range of 5% by weight. When such a mixed emulsifier is used, the polymer latex particles form a three-dimensional network structure. As the amount of bleached shellac resin in the mixed emulsifier increases, the crosslinking density increases and particles become more difficult to coalesce and fuse with each other.

The resulting film is insoluble in benzene, and the swelling degree and gel content in benzene depend on the content of bleached shellac resin in the emulsifier mixture, and the degree of crosslinking can be freely controlled.

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

When the ultrafine particle pre-crosslinked polymer latex produced according to the present invention has a low crosslinking degree and crosslinking density, it fuses with each other to form a continuous film, and is a highly elastic and tough film with a large initial modulus value. form. 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 latexes but also have functional groups such as carboxyl groups, hydroxyl groups, and amino groups on the surface of the latex particles, it is necessary to use polymerizable monomers or organic solvents. When redispersed, it is useful as a so-called high solids paint material that requires a small amount of solvent. 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, the following was added to 400 ml of distilled water.
An emulsifier was prepared by dissolving 5 g of commercially available bleached ceramic resin (white rack) in an aqueous medium at 60°C by adding 4 ml of 28% ammonia water, and di(alkylene methacrylate), an anionic copolymerizable emulsifier. ester) phosphoric acid (New Frontier A-229E) Dissolve 10g. Polymerization was first carried out by dispersing 10 ml of a monomer mixture of ethyl acrylate and methyl methacrylate (composition ratio 7:3), and adding copper sulfate (a concentration of 2.5 x 10 ^-6 mol/in the system as an accelerator) while maintaining constant stirring. A redox initiator consisting of equimolar amounts of potassium persulfate and sodium thiosulfate (concentration in the system: 3.0
x 10 ^-3 mol/) at 50 to 60°C and pH 4 to 7, then the remaining 290 ml of ethyl acrylate-methyl methacrylate mixed monomer was gradually added to prevent a significant temperature rise due to polymerization heat. Polymerization was carried out at a temperature below 60°C while adding the solution dropwise. As the polymerization progresses, the viscosity of the system increases, making it difficult to disperse and stir the monomers, but before the viscosity of the polymerization system begins to rise, add 2 to 4 ml of 28% ammonia water dropwise. Before starting polymerization, approximately 0.5 g of ammonium phosphate is added in advance to prevent an increase in viscosity. Polymerization was completed in about 35 minutes, and a highly transparent polymer latex that appeared yellow-red under transmitted light was obtained. The light transmittance measured using a spectrophotometer at 800 nm (using a 1 cm glass cell) was 40.5%, and the particle size measured using an electron microscope was 330 Å.

The obtained ultrafine particle polymer latex was air-dried on a glass plate, and the film obtained had very good transparency. value) was 1.3. Also, the 20° specular gloss according to JIS Z8741 is 95
% or more. Furthermore, this air-dried film is insoluble in benzene and acetone and swells while retaining its shape. The degree of swelling in benzene was determined from the area ratio of the film before and 48 hours after immersion in benzene.
It was 7.4.

Example 2 When using the same method as in Example 1 but using 2 g of bleached shellac resin (white lacquer), which is less than in Example 1, a highly transparent ultrafine particle polymer with a light transmittance of 63% was obtained. latex produces,
The particle size was 308 Å. The transparency of the film obtained by air drying on a glass plate is very good and meets JIS standards.
The film obtained by the K6714 method had a haze value of 1.3%, was completely transparent, and had an extremely good gloss. Although the film was insoluble in benzene, it swelled and the degree of swelling determined from the area ratio was about 73.5.

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. For emulsion polymerization, a polymerization initiator consisting of a redox polymerization catalyst consisting of a persulfate and a reducing sulfoxy compound, a trace amount of transition metal ions added as an accelerator, and a bleached shellac resin and an anionic surfactant as emulsifiers are used. In the presence of a mixed system combining agents,
A high-grade polymer latex characterized by forming an ultrafine crosslinked polymer latex with a transparent particle size of 0.01 to 0.05 μm, uniform particle size, and good dispersion stability by polymerizing while stirring. Method of manufacturing performance polymer latex.