JPH0343281B2 - - Google Patents

Description

[Detailed description of the invention]

This invention is a hydrosol, that is, a particle size of 0.01 to 0.1μ.
It relates to a method for producing a dispersion in which polymer particles of m are stably dispersed in water, and more specifically, the polymer particles are composed of a specific low molecular weight polymer to stabilize general aqueous dispersions, particularly emulsifier-free emulsions. The present invention relates to a method for producing hydrosols useful as additives for improving properties and physical properties. Aqueous dispersions of vinyl polymers are widely used in coating materials, pressure-sensitive adhesives, adhesives, etc., and many studies have been conducted on their production methods. A typical method is the so-called emulsion polymerization method in which vinyl monomers are polymerized in water in the presence of a surfactant. In the emulsion polymerization method, nonionic or anionic surfactants are usually used as surfactants, but in order to obtain stable polymer emulsions using these surfactants, it is generally necessary to It is necessary to increase the dosage. However, by increasing the amount of surfactant added, a polymer emulsion with excellent stability can be obtained, but on the other hand, the coating formed from the polymer emulsion thus obtained has low water resistance and poor adhesive properties. There are other problems. For this reason, many studies have been made on so-called emulsifier-free emulsion polymerization, in which polymerization is carried out using only a small amount of surfactant or no surfactant. However, the polymer emulsion obtained by emulsifier-free emulsion polymerization method is
Although it improves water-resistant adhesive properties, it has poor stability because it does not contain a surfactant, and there are problems with long-term storage.Furthermore, it may require modification of the polymer when used for various purposes. However, if a resin or the like is added as a modifier in such a case, there are problems such as agglomeration of emulsion particles immediately occurring. Therefore,
It is desirable to develop additives that can be added to such polymer emulsions, especially emulsifier-free polymer emulsions, in arbitrary proportions to supplement the stability of the emulsion and to favorably modify the properties of the emulsion polymer. It was rare. By the way, we have so far made polymers obtained by various polymerization methods into a substantially solid content, and then
Neutralize the acidic groups in the polymer with an alkali or alkaline aqueous solution, and then add water to reduce the particle size to 0.1~
We have proposed a method for producing 0.01 μm hydrosol. In this method, water dispersions with good stability were obtained, and the coatings formed from these polymerized dispersions had good water resistance because no emulsifier was used. While conducting extensive research on such new hydrosols, the inventors came up with the idea of applying the hydrosol obtained by the above method as an additive to the above-mentioned general polymer emulsions, especially emulsifier-free polymer emulsions. However, as a result of repeated many experimental studies based on this, the method for obtaining the polymer in hydrosolization was further specified, and the average molecular weight was made relatively small. This led to the completion of this invention. That is, in this invention, the ethylenically unsaturated monomer is added in an amount of 0.5 to 10 parts by weight per 100 parts by weight of the unsaturated monomer.
A weight average molecular weight of 1×10 ³ to 1×10 ⁴ having the above acidic group at one end of the molecule by radical polymerization in the presence of a chain transfer agent having an acidic group in the proportion of parts by weight.
A low molecular weight polymer is obtained, and an alkali or alkaline aqueous solution is added thereto in a state containing a lump or a small amount of an organic solvent to neutralize some or all of the acidic groups in the polymer molecule, and the above polymer is The present invention relates to a method for producing a hydrosol, which is characterized in that a hydrosol having an average particle diameter of 0.01 to 0.1 μm and stably dispersed in water is obtained. The hydrosol obtained by the method of this invention is
It can be blended in any proportion to a general aqueous dispersion, especially an aqueous dispersion obtained without using an emulsifier or a surfactant, or with a very small amount of emulsifier, and by this blending, the above water dispersion It can significantly improve the stability of the polymer, such as its mechanical stability and storage stability, and it can also improve the physical properties of the polymer before compounding, such as imparting adhesive properties and flexibility to the resulting coatings and other molded products. It can be greatly improved. In addition,
The aqueous dispersion to be modified is not limited to the above-mentioned emulsion, but also includes a slurry or a hydrosol as already proposed by the present inventors. As described above, the hydrosol obtained by the method of the present invention functions effectively as an additive for general aqueous dispersions, and since it itself does not contain an emulsifier and has excellent water resistance, it can be used in various aqueous dispersions mentioned above. In combination with dispersions, it can be widely applied to various fields such as paints and paper sizing agents, as well as pressure-sensitive adhesives, adhesives, overcoat materials, exterior materials, interior materials, packaging materials, and films. In this invention, first, an ethylenically unsaturated monomer is subjected to radical polymerization in the presence of a chain transfer agent having an acidic group to obtain a low molecular weight polymer. The above ethylenically unsaturated monomers include, for example, acrylic esters and methacrylic esters having an alkyl group having 1 to 15 carbon atoms, particularly preferably 3 to 10 carbon atoms, vinyl ethers, vinyl esters, acrylonitrile, acrylamide, hydroxylalkyl Examples include acrylate, styrene, vinyl chloride, ethylene, ethylenically unsaturated monomers having functional groups such as amino groups in the molecule, and one or more of them may be selected depending on the purpose of use. use. A chain transfer agent having an acidic group is useful for keeping the molecular weight of a polymer to a low level, and also has the function of introducing an acidic group at one end of the molecule of the resulting polymer through chain transfer. be. Examples of such chain transfer agents include those having a carboxyl group as an acidic group, such as mercaptoacetic acid, mercaptopropionic acid, mercaptosuccinic acid, and thiosalicylic acid. The amount of the chain transfer agent having the above acidic group used is:
0.5 to 100 parts by weight of ethylenically unsaturated monomer
It should be set within the range of 10 parts by weight, and this amount
When the amount is less than 0.5 parts by weight, it is difficult to form a hydrosol, and when it is more than 10 parts by weight, there is a problem that water resistance and adhesive properties are lacking when formed into a film. Examples of the polymerization initiator necessary for radical polymerization include organic peroxides such as benzoyl peroxide, perbutyl octate, and t-butyl hydroperoxide, and azo compounds such as azobisisobutyronitrile and azobiscyanovaleric acid. It will be done. Among these initiators, initiators having an acidic group in the molecule, such as azobiscyanovaleric acid, which are effective in introducing an acidic group to the terminal end of the polymer molecule, are desirable. Although the polymerization method is not particularly limited, from the viewpoint of obtaining a polymer with a relatively high molecular weight, it is preferable to employ a bulk polymerization method that does not use any medium such as an organic solvent or water. Further, a solution polymerization method using a hydrophilic solvent such as an organic solvent such as alcohols such as methanol, ethanol, propanol, and butanol in an amount of about 20% by weight or less is also desirable. The low molecular weight polymer obtained in this way must have an average molecular weight set in the range of 1 x 10 ³ to 1 x 10 ⁴ , and if it is outside the above range, it will be difficult to hydrosolize or it will not be possible to hydrosolize. However, it does not function effectively as an additive for an aqueous dispersion, making it difficult to improve the stability of the dispersion. In this invention, next, a low molecular weight polymer having the above-mentioned molecular weight and having an acidic group introduced at one end of the molecule is added to an alkali or alkaline aqueous solution in the form of a lump or in a state containing the above-mentioned small amount of solvent, while stirring. Add to neutralize. The treatment temperature at this time is kept at a constant temperature depending on the type and properties of the polymer, but is generally 40 to 95°C. The alkali or alkaline aqueous solution used for neutralization treatment includes ammonia, ammonia water, caustic soda, caustic alkali aqueous solution such as caustic potash, etc., and is usually used at a ratio of about 1/50 to 2 equivalents to the acidic group of the polymer. do it. After this neutralization treatment, if water is gradually added while stirring and mixing thoroughly, a so-called phase inversion phenomenon will occur at regular intervals.
An O/W type dispersion is produced in which water forms a continuous layer and polymer particles are dispersed therein. After this dispersion is produced, a necessary amount of water is gradually added to adjust the viscosity and solid content concentration of the dispersion. The viscosity is generally 30 to 1000 poise at 25°C, and the solids concentration is usually 10 to 60% by weight. The thus obtained dispersion is a hydrosol in which the average particle diameter of the low molecular weight polymer as the dispersed particles is 0.01 to 0.1 μm, and the polymer particles are uniformly and stably dispersed in water. This hydrosol,
Solids content compared to other water dispersions such as emulsions
The solid content is usually 0.5 to 30 parts by weight per 100 parts by weight, and if necessary, additives such as a crosslinking agent are added, and the mixture is cast on a carrier and dried as described above. Excellent effects can be obtained. Examples of this invention will be described below. In addition,
In the following, parts shall mean parts by weight. Example 1 60 parts of n-butyl methacrylate 40 parts of ethyl acrylate 0.1 part of azobiscyanovaleric acid 6 parts of thioglycolic acid 15 g of the above composition was placed in a four-necked flask (No. 1), and the mixture was purged with nitrogen for 40 minutes while stirring. did. While dripping the remaining amount from the dropping funnel,
Reacted at ℃ for 4 hours, weight average molecular weight 8×10 ³
A copolymer of (by GPC) was synthesized. Next, 1/16 equivalent of a caustic soda aqueous solution (80% by weight) was added to the carboxyl groups of this copolymer to neutralize the copolymer at a temperature of 86°C. 250 parts of water per 100 parts was gradually added dropwise over a period of about 2 hours. When 150 parts of water was added dropwise, a phase inversion phenomenon occurred in which the continuous layer became water. The hydrosol thus obtained had a viscosity (at 25° C.) of 125 poise, a solids concentration of 28.5% by weight, and an average particle diameter of 0.06 μm (according to Nanosizer). The hydrosol obtained in this way is added to the polymer emulsion (A) obtained by the method described below, and its solid content is
The solid content was 10 parts per 100 parts, and the mechanical stability was measured using a Maron tester. In addition, the above formulation was thickened with 25% by weight ammonia water to a viscosity of approximately 50 poise, and then coated on a 100μ polyester film to a dry thickness of 50μm and dried to obtain an adhesive tape. The water absorption rate, degree of whitening, and adhesive strength of the tape were measured. These results were as shown in the table below. <Polymer emulsion (A)> Ethyl acrylate 2 parts 2-ethylhexyl acrylate 3 parts Sodium lauryl sulfate 0.75 parts Ammonium persulfate 0.1 part Water Emulsion polymerization was carried out at 65°C for 1 hour using 160 parts, and then ammonium persulfate was added to this. Add 0.1 part of 2-ethylhexyl acrylate and 192.5 parts of acrylic acid.
A monomer mixture consisting of 2.5 parts was added dropwise over 2 hours, and the mixture was aged at 75°C for 1 hour. The obtained polymer emulsion (A) had a viscosity of 0.2 poise, a pH of 3, and a polymer particle size of 2000 Å. Example 2 2-Ethylhexyl acrylate 80 parts Methyl methacrylate 20 parts Azobisisobutyronitrile 0.15 parts Mercaptopropionic acid 8 parts Viscosity 115 Poise (25℃), solid content concentration
A hydrosol of 27.5% by weight and an average particle size of 0.08 μm was obtained. The properties of this hydrosol were measured in the same manner as in Example 1, and the results are also listed in the table below. Example 3 n-Butyl acrylate 70 parts Acrylonitrile 30 parts Benzoyl peroxide 0.15 parts Thiosalicylic acid 7 parts Viscosity 130 poise (25 ° C.) Solid concentration
A hydrosol of 28.0% by weight and an average particle size of 0.07 μm was obtained. The properties of this hydrosol were measured in the same manner as in Example 1, and the results are also listed in the table below.

【table】

[Table] As is clear from the above table, the hydrosol obtained by the method of the present invention has excellent water resistance without impairing the water resistance of the known polymer emulsion (the emulsion of Comparative Example 1 in which a small amount of emulsifier was used). The stability and adhesive strength of the emulsion can be significantly improved, and the water resistance can be greatly improved compared to the ordinary polymer emulsion according to Comparative Example 2, which uses a large amount of emulsifier. It can be seen that better results are obtained in terms of characteristics as well.

Claims (1)

[Claims] 1 The ethylenically unsaturated monomer is
Radical polymerization is carried out in the presence of a chain transfer agent having an acidic group at a ratio of 0.5 to 10 parts by weight per 100 parts by weight to obtain a weight average molecular weight of 1×10 ³ to 1× having the above acidic group at the end of a molecule. A low molecular weight polymer of 10 ⁴ is obtained, and an alkali or alkaline aqueous solution is added thereto in bulk or in a state containing a small amount of organic solvent to neutralize some or all of the acidic groups in the polymer molecule, and the above-mentioned Polymer has an average particle size of 0.01~0.1μ
A method for producing a hydrosol, characterized by obtaining a hydrosol stably dispersed in water within a range of m.