JPS60170605A - Preparation of ultrafine particulate already crosslinked polymer latex - Google Patents

Abstract

PURPOSE:To obtain an ultrafine particulate polymer having three-dimensional network structure in the particles, stable even in a high concentration, and suitable to a vehicle or binder for coating materials, by polymerizing a monomer containing ethylenically unsaturated bond in the presence of a polymerization initiator and an emulsifying agent. CONSTITUTION:A monomer selected from lower alkyl esters of (meth)acrylic acid or a mixture thereof with another polymerizable monomer copolymerizable with the above-mentioned monomer is polymerized in an aqueous medium. In the process, a polymerization initiator prepared by adding a very small amount of a transition metal ion, e.g. Cu<2+> in 2.5X10<-6>-2.5X10<-4>mol/l concentration, as an accelerator to a redox polymerization catalyst consisting of a persulfate and a reducing sulfoxy compound is used to carry out polymerization under stirring in the presence of a mixed system of a bleached shellac resin in combination with an anionic surfactant as an emulsifying agent to give the aimed polymer latex having uniform 0.01-0.05mum particle diameter and transparency and improved dispersion stability.

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

The ultrafine particle pre-crosslinked polymer latex produced by the present invention differs in appearance from ordinary polymer latex in that it has a transparent, slightly viscous appearance that appears bluish-white to reflected light and yellow-red to transmitted light. It can be used as a high-performance paint vehicle and as a penetrating agent in its own right. In addition, reactive type ultrafine particle low-crosslinked polymer latex copolymerized with functional monomers such as 2-hydroxyethyl acrylate, 7" lyric acid, and acrylic acid amide can be used with crosslinking agents such as hexakismethoxymethylolmelamine. By adding cross-linking between particles, it is possible to further improve the performance by curing the baking process.In recent years, with the increasing recognition of pollution problems such as air pollution and work environment, there has been a shift from organic solvent-based paints to water-based paints.
...The transition to isolid paints, powder paints, etc. is a major issue, but water-based paints are particularly promising due to their economic efficiency and safety.

There are two types of water-based paints: aqueous-solution and water-dispersible, but water-dispersible polymer latex is considered to be the most promising and has the most expectations. However, in the industrial field, the insufficient performance of existing polymer latex is an obstacle to its widespread use, and the development of higher-performance polymer latex as a substitute for organic solvent-based paints and adhesives is expected in the future. One of the new technological methods expected to improve the performance of polymer latex, which is indispensable, is to make polymer latex into ultrafine particles. In the case of polymer latex, the film is essentially formed by filling and fusing particles, so in order to maintain the same performance as organic solvent-based coatings, the particle size of polymer latex must be made as small as possible. It is desirable to make the particles ultrafine, and it is possible to improve the fusion bond, the smoothness and gloss of the film, and the adhesion and permeability to finely uneven surfaces such as metal surfaces. 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, particles are filled and fused. 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 into ultrafine particles.

A second method for improving the performance of polymer latex is to improve performance by introducing a three-dimensional network structure inside and between polymer latex particles. According to recent theories, durable coatings, 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. Therefore, the ultrafine polymer latex particles described above are crosslinked to form a three-dimensional network structure, and reactive functional groups are added to the particle surface. Therefore, it is thought that it is effective to form a three-dimensional network structure by forming crosslinks between particles or between particles and a continuous phase.

Conventionally, so-called reactive polymer latex, in which all reactive functional groups are added to the surface of polymer latex particles, has been known for crosslinking between particles. Polymer latex is made by copolymerizing a small amount of monomers with a small amount, and is crosslinked between particles using a crosslinking agent such as an aminoplast resin such as hexamethoxymethylmelamine, or self-crosslinking between functional groups to improve the strength and water resistance of the film. Improvements have been made. However, if it is possible to introduce a three-dimensional network structure not only between particles of polymer latex but also inside the particles of polymer latex, when it becomes a coating film, it will have a non-uniform network with a ring structure such as a lacquer film. This results 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 inside of microscopic polymer latex particles without gelling the entire polymer latex during the polymer latex synthesis process, and ultrafine particles of pre-crosslinked polymer latex have not been put into practical use. Not yet. Conventionally, known methods for producing crosslinked polymer latex include crosslinking by radiation irradiation, and crosslinking using tetrafunctional or higher functional crosslinking monomers such as divinylbenzene, diallyl phthalate, ethylene glycol dimethacrylate, and triacrylate. Polymerization or copolymerization methods are known, but when these multifunctional (crosslinking) monomers are used, they cannot be used without extremely large amounts of surfactants such as sodium dodecyl sulfate as emulsifiers. It not only cannot produce fine particle polymer latex, but also has the disadvantage of extremely poor polymerization stability despite the presence of a large amount of surfactant. Since kneading uses a polyfunctional polymer, pendant vinyl groups remain and the surface of the polymer latex particles is highly reactive, resulting in agglomerization during the polymerization process, causing the entire system to gel or forming a large amount of aggregates. The polymer concentration is 8 to 16 in terms of solid content.
It has the disadvantage that polymerization must be stopped at a concentration as low as 30% or more, and it has been extremely difficult to produce a crosslinked polymer latex with a high coagulation level of 30% or more, which is necessary for practical use. In addition, the polymerization rate is extremely slow, and since a large amount of emulsifier is used, side effects of the emulsifier are a serious problem, and there are major problems in practical application for industrial purposes. The present inventors believe that because the conventional method 5 involves polymerization or copolymerization of a polyfunctional monomer such as divinylbenzene, highly reactive pendant vinyl groups may cause aggregation of polymer latex particles. After conducting extensive research to find a way to introduce a crosslinked structure into polymer latex particles without using a polyfunctional monomer, we discovered that a specific surfactant can create a three-dimensional structure within polymer latex particles during the polymerization process. It was discovered that a network structure was formed.

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 μm, and the inside of the particle is three-dimensional. A method for practically producing a novel high-performance polymer latex having a network structure is provided.

That is, the present invention provides 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. When emulsion polymerizing the body in an aqueous medium, polymerization is carried out with stirring in the presence of a mixed system of a known persulfate and an anionic surfactant commonly used in emulsion polymerization. Particle size is 0.01~
This is a method for producing a polymer latex, which is characterized by forming an ultrafine particle decrosslinked polymer latex with transparency of 5 μm, good dispersion stability, and uniform particle diameter.

The polymerization initiator used in the present invention is 1.0×10
-3~1. Known redox catalysts such as potassium persulfate and sodium thiosulfate in equimolar concentrations of OXlo-2 mol/II are used, but in order to produce a transparent ultrafine polymer latex, 2. ! 5 X 10-7~5. OX I Q-'mol
/, d, preferably 2.5 x 10-g ~, 2.5X
It is essential to add transition metal ions such as divalent copper ions at 10'O1 l/l. The polymerization temperature can be used within a temperature range that activates the polymerization initiator;
℃ range is effective; if the temperature exceeds 80℃, the stability of the resulting polymer latex will deteriorate and the initiator will be deactivated, so in order to control the polymerization temperature, the monomer should be added continuously in small amounts. It is necessary to carry out the polymerization while adding the solution dropwise.

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(methacdi-alkyl ester) phosphoric acid. On the other hand, a commercially available bleached shellac resin can be used. The composition ratio of bleached shellac resin and anionic surfactant is preferably 1=3 to 3:1 by weight.

The bleached shellac resin used in the present invention is prepared by heating, e.g.
It is best to use it by dissolving it in aqueous ammonia heated to about ℃ 1. By adding an anionic surfactant to this, the emulsion used in the present invention can be obtained.

The concentration of this mixed emulsifier is in the range of 1 to 15% by weight, preferably 2 to 5% by weight, based on the aqueous medium. 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 degree of swelling 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 esters having polymerizable ethylene bonds such as ethyl acrylate, methyl methacrylate, 2-ethylhexyl acrylate butyl methacrylate, acrylonitrile, Wl vinyl, and styrene. , vinyl chloride, vinylidene chloride, etc. Functional monomers that can be copolymerized with the above-mentioned monomers include 2- and doroquinethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, polyethylene glycol (meth)acrylate, Examples include N-methylolacrylamide, glycidyl (meth)acrylate, acrylic acid, maleic anhydride, itaconic acid, acrylamide, and dimethylamine ethyl (meth)acrylate.

When the ultrafine particle low crosslinked polymer latex produced by the present invention has a low crosslinking degree and crosslinking density, it fuses with each other to form a continuous film, forming a highly elastic and tough film with a large initial modulus value. . In addition, if the degree of crosslinking is high and the crosslinking density is not low, the latex particles will not fuse with each other, so it is useful to add them to powder coatings to improve blocking properties and physical properties of the coating film. 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 amine groups on the surface of the latex particles, they cannot be reconstituted with polymerizable monomers or organic solvents. When dispersed, it is useful as a so-called high solid paint material that requires a small amount of solvent. Other existing powder coatings, solvent-based coatings, high solids coatings,
It can be used to improve the performance of water-based paints by mixing with them.

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

Example 1 A gas inlet pipe, a reflux condenser, and 5 g of composite glass for pH measurement were placed in an aqueous medium with 4 rnl of 28% ammonia water added to 60 g.
℃ and dissolve 1.0 g of Ew Frontier A-229E) H in di(methacrylic acid alkylene ester) phosphoric acid, which is an anionic copolymerizable emulsifier. In the polymerization, 10% of the monomer mixture of ethyl acrylate and methyl methacrylate (composition ratio 7:3) was first added.
A redox initiator consisting of equimolar amounts of potassium persulfate and sodium thiosulfate with copper sulfate (concentration in the system: 2.5 x 10 moil/l) as an accelerator. (Concentration in the system 3.0X10
, mOA'/l) T, 50-60'c, pH 4-7, and then the remaining 290 m4 of the ethyl acrylate-methyl methacrylate mixed monomer was gradually added to prevent a significant temperature rise due to the heat of polymerization. 60℃ while dropping
Polymerization was carried out as follows. The viscosity of the system increases as the polymerization progresses, making it difficult to disperse and stir the monomers, but before the viscosity of the polymerization system begins to increase, 2 to 4 ml of 28
% ammonia water is added dropwise or in advance before the start of polymerization to prevent an increase in the total viscosity of about 0.5% ammonium phosphate. Polymerization i1″1: Completed in about 35 minutes, and a transparent polymer latex that appeared yellow-red in transmitted light was obtained.Spectrophotometer so o
The light transmission jM rate of nm (using a 1 m glass cell) is 40.
5%, and the particle size measured using a Seiko microscope was 330A.

The obtained ultrafine particle polymer latex was air-dried on a glass plate, and the resulting film had very good transparency and was rated according to JIS standards.
The haze value (haze value) of the film measured using a K671'4 integrating sphere light transmittance measuring device was 1.3. Also JI
The 20° specular gloss by S Z8741 was 95% or more. Furthermore, this air-dried film is insoluble in benzene and acetone and swells while retaining its shape. The f-lumi wetness with respect to benzene was calculated from the area ratio of the film before and 48 hours after immersion in benzene, and was 7.4.

Example 2 When using the same method as in Example 1 and using 2 g of bleached shellac (white lac), which is less than in Example 1, ultrafine particles with very good transparency reaching a light transmittance of 63 cm were obtained. of polymer latex was produced, and the particle size was 308^. The transparency of the film obtained by air drying on a glass plate was very good (the haze value of the film by the JIS K6714 method was 13 inches, it was completely transparent, and the gloss was also extremely good. Although it was insoluble, it swelled, and the degree of swelling calculated from the area ratio was about 73.5.

Claims (1)

[Claims] (),) Consists of 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 emulsion polymerization of monomers in an aqueous medium, a polymerization initiator consisting of a redox polymerization catalyst consisting of a persulfate and a reducing sulfoxy compound, a trace amount of displaced metal ions added as a promoter, and an emulsifier. By polymerizing while stirring in the presence of a mixed system of bleached shellac resin and anionic surfactant, a transparent and highly stable dispersion with a particle size of 0.01 to 0.05 μm is obtained. A method for producing high-performance polymer latex characterized by forming ultrafine low-crosslinked polymer latex with uniform particle size.