JPS61166848A - Aqueous dispersion of film-forming resin - Google Patents

Abstract

PURPOSE:To provide an aqueous dispersion giving a paint, etc. exhibiting excellent water-resistance and adhesivity to the substrate, by centrifuging an aqueous dispersion produced by the emulsion polymerization of two kinds of ethylenic unsaturated monomers, and redispersing the precipitated particles in water. CONSTITUTION:(A) An ethylenic unsaturated monomer capable of forming a water-soluble polymer by homopolymerization and (B) another ethylenic unsaturated monomer copolymerizable with the component A and capable of giving a water-insoluble polymer by homopolymerization are subjected to emulsion polymerization in water. The aqueous dispersion of the copolymer is optionally diluted with water, and centrifuged to precipitate at least a part of the copolymer particles. The copolymer particles consisting of the precipitated particles are redispersed in water to obtain an aqueous dispersion essentially free from water-soluble polymer component. The component A is an alpha,beta-monoethylenic unsaturated carboxylic acid, its neutralized product or its N-alkylolamide, etc.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention provides a film-forming material suitable for paints, non-woven fabric binders, etc. that has excellent physical properties, particularly good water resistance, and excellent adhesion to substrates. This invention relates to a copolymerized aqueous dispersion.

[Prior art]

In general, copolymerized aqueous dispersions of ethylenically unsaturated monomers such as styrene and acrylic acid esters obtained by ordinary emulsion polymerization are superior in terms of resource saving, energy saving, and working environment, so they have been used in construction in recent years. It has come to be widely used as waterproofing materials, adhesives, etc. However, it has the drawback of being inferior in terms of water resistance, rust prevention, etc., compared to solvent-based unbonded polyester heavy fats and acrylic resin binders. That is, when a coating film formed from an ordinary aqueous copolymer dispersion is immersed in water, the coating film whitens and swells. In addition, when it is applied to metal and subjected to tests such as water resistance, salt water resistance, or sludge spray resistance, blisters and rust are observed to occur.

Therefore, in order to improve the water resistance of a coating film formed from an aqueous dispersion of a copolymer, the crosslinking group is enlarged or
In place of the emulsifier used when producing an aqueous dispersion through emulsion polymerization, it has been proposed to perform polymerization using a polymeric protective colloid such as CMC or polyvinylpyrrolidone, but none of these methods yielded satisfactory results. It didn't come.

In investigating ways to improve the water jetting properties of coating films formed from this type of copolymerized aqueous dispersion, the present inventors investigated water-soluble components present in the aqueous dispersion, particularly the three components listed below. I heard the sound.

(1) Hydrophilic group-containing water-soluble polymers Hydrophilic groups such as carboxyl groups improve the stability (mechanical stability, chemical stability, freeze stability, etc.) of the water dispersion, and also improve the stability of the water dispersion. Hydrophilic monomers are often introduced for the purpose of improving adhesive strength, cohesive strength, etc. However, conventionally, this type of emulsion has generally been produced by emulsion copolymerization of the main monomer and an unsaturated monomer having a hydrophilic group such as a carboxyl group in the molecule.
Generally, the latter monomer has high water solubility, so it polymerizes in the aqueous phase to produce a water-soluble polymer containing a hydrophilic group.

(2) Free emulsifier The emulsifier used during polymerization provides a place for particle generation during emulsion polymerization and stabilizes the dispersion of particles during and after polymerization. Although it is irreversibly adsorbed, some of it exists as an aqueous solution in an aqueous dispersion.

(3) @Acid salts Conventionally, persulfates are mainly used in this type of emulsion polymerization catalyst, but these produce sulfates through side reactions during polymerization.

[Specific means to resolve the issue]

The present inventors centrifuged the aqueous dispersion obtained by emulsion polymerization to precipitate the dispersed particles, and redispersed the precipitated particles in water to produce a copolymer that substantially does not contain the above-mentioned water-soluble components. The idea was to produce an aqueous dispersion. In fact, when we tested a film from this redispersion, we found that it was so good that it was hard to believe that it was a film made from an aqueous dispersion; in other words, it was similar to a film obtained from a solvent-based polymer. Heading This invention has been achieved.

In other words, the aqueous resin dispersion of the present invention that provides a film with improved water resistance contains at least one type of ethylenically unsaturated monowax (component a) that polymerizes independently to form a water-soluble polymer. , a copolymerized aqueous dispersion obtained by emulsion polymerization in an aqueous medium of at least one type of ethylenically unsaturated monomer (component b) that can be copolymerized with this and polymerizes alone to give a water-insoluble polymer. Either as is or after diluting with water, centrifugation is performed to precipitate all or a part of the copolymerized particles, and then a copolymer consisting only of these precipitated particles is redispersed in water. It is characterized by not containing a water-soluble polymer component.

The ethylenically unsaturated monomer used in the emulsion polymerization of the present invention, which can be polymerized alone to give a water-soluble polymer, is not particularly limited in type, but may be copolymerizable.

For example, α, β-monoethylenically unsaturated carboxylic acids include unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid, and 3-carbon acids such as maleic acid, fumaric acid, itaconic acid, and citraconic acid. ~5 unsaturated dicarboxylic acids or their alkali neutralized salts, ■α, βα and β-
Monoethylene amide or N-alkylolamide includes acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide; α,β-7noethylenoethylenically unsaturated alcoholamine includes hydroxyethyl acrylate; Examples include polyoxyethylene monomethacrylate and dimethylaminoethyl methacrylate, and two or more of them may be used in combination. The copolymerization ratio of component a is 0.5 to 15% by weight, preferably 1 to 6% by weight based on the total polymerizable monomer component. In addition, the ethylene kine saturated monomer that can be copolymerized with the above-mentioned component a and polymerizes alone to give a water-insoluble polymer is not particularly limited in type, and can be arbitrarily selected according to the desired characteristics. can. Specifically, vinyl aromatic compounds (for example, styrene, etc.), alkyl esters of acrylic acid or methacrylic acid having 1 to 16 carbon atoms, vinyl esters (for example, vinyl acetate, vinyl propionate, etc.), vinyl halides (for example, vinyl chloride, vinylidene chloride, etc.), acrylonitrile, methacrylonitrile, ethylene, glycidyl methacrylate, and 1,3-
Examples include dienes (for example, butadione, etc.), and two or more of them can be used in combination.

Emulsion polymerization itself is well known to those skilled in the art, and examples of emulsifiers used in emulsion polymerization include anionic surfactants such as alkyl sulfates, alkylbenzene sulfonates, polyoxyethylene alkyl sulfates, and polyoxyethylene alkylphenol ether sulfates; polyoxyethylene alkyl ether,
Examples include nonionic surfactants such as polyoxyethylene alkylphenol ether, ethylene oxide propylene oxide block copolymer, and sorbitan derivatives.

In addition, as a polymerization initiator in emulsion polymerization, for example, persulfates such as potassium persulfate and ammonium persulfate,
Examples include hydrogen peroxide, organic peroxides such as benzoyl peroxide, cumene hydroperoxide, and tertiary butyl hydroperoxide, and azobisin butyronitrile.

In order to produce the water-dispersed polymer emulsion of the present invention that does not substantially contain water-soluble components, firstly, the above-mentioned components a and b are emulsion polymerized in an aqueous medium, and the resulting copolymerized polymer is The aqueous dispersion is centrifuged as it is or after being diluted with water to precipitate all or part of the polymer particles. Although it is possible to centrifuge the copolymer aqueous dispersion obtained by emulsion polymerization as it is to precipitate the polymer particles, generally copolymer aqueous dispersion obtained by emulsion polymerization with a resin solid content of 40 to 60% by weight is used. The solution is preferably diluted with water to 3-30% and then centrifuged.

That is, if the solid content is 30% or more, the viscosity of the aqueous dispersion is high and the polymer particles will not easily settle during centrifugation, and if the solid content is 3% or less, the particles will settle easily.
The drawback is that the amount of sedimented particles is small, making it impractical.

The difficulty of sedimentation of particles during centrifugation is largely influenced by the copolymer composition of dispersed particles and particle diameter, in addition to the resin solid content (dispersion viscosity) mentioned above.

That is, copolymerized particles containing a large amount of monomers that give a copolymer with a high specific gravity, such as vinyl chloride, vinylidene chloride, methyl methacrylate, etc., are easier to settle, and the larger the diameter of the dispersed particles, the easier it is. be. The effects of the viscosity of the dispersion, the specific gravity of the copolymer, and the particle diameter on the sedimentation rate of particles during centrifugation can be summarized in general formula (1).

Here, W: Angular velocity j2 tt: Time for the particle to move from rl to r2.

S: Sedimentation coefficient, determined from the relational expression (2).

On the other hand, practically speaking, the time required for centrifugation should be about 5 hours or less, and the rotation speed must be set so that the dispersed particles settle within that time. Centrifuged at .000-35.00 Orpm. Furthermore, it is not preferable to centrifuge at a high rotational speed for too long. The precipitated particles are pressed together so strongly that some of them are fused together, making the subsequent step of redispersing the precipitated particles difficult.

The polymer particles precipitated by the above-mentioned centrifugation are isolated and collected, and then water is added and stirred so that the solid content becomes 30 to 50% by weight and redispersed in water. It is difficult to uniformly disperse the isolated and recovered polymer particles immediately after adding water, but if you let them stand for a while after adding water, you can easily disperse them uniformly by stirring with a stirring blade etc. A dispersion liquid can be obtained.

Hereinafter, emulsion polymerization examples of copolymerized aqueous dispersions and examples for obtaining a desired redispersion liquid from the aqueous dispersions obtained in these emulsion polymerization examples will be described in detail.

Emulsion polymerization example 1 Temperature controller, anchor stirrer, reflux condenser, supply volume 4,
The following materials were charged into a reaction vessel equipped with a thermometer and a nitrogen inlet tube.

water
200 parts 35% aqueous solution of sodium salt of sulfuric acid half ester of p-nonylphenol (anionic emulsifier) to which 20 moles of ethylene oxide have been added O,S parts p-nonylphenol to which 25 moles of ethylene oxide have been added (nonionic emulsifier) 20 parts of 20% water@liquid were prepared as the following mixture as feed (■).

water 200
Parts 35% aqueous solution of the above anionic emulsifier 12 parts 20% aqueous solution of the above nonionic emulsifier 10 parts Methyl methacrylate 275 parts Butyl acrylate
205 parts acrylic acid
20 parts Separately, a solution of 2.5 parts of potassium persulfate in 85 parts of water was prepared as feed (2).

After the interior of the reactor charged with the above-mentioned materials was purged with nitrogen gas, 10% of Feed I was added and heated to 90°C, and then 10% of Feed I was injected. While heating and stirring at 90°C, feed (1) and the remainder of feed (2) were uniformly fed into the reactor little by little over a period of 3 to 3.5 hours. After the supply was completed, the mixture was kept at 90° C. for another 1.5 hours and reacted with stirring, and then the inside of the reaction vessel was cooled to room temperature.

Table 1 shows the composition ratio of monomers and characteristics of the dispersion liquid in Emulsion Polymerization Example 1.

Emulsion Polymerization Examples 2 and 3 Emulsion polymerization was carried out in accordance with Emulsion Polymerization Example 1 except that the copolymerization ratio was changed as shown in Table 1 below.

Emulsion Polymerization Example 4 Water was placed in a reaction vessel equipped with a temperature controller, a stirrer, a supply container, a thermometer, and a nitrogen introduction tube.
0 parts lauryl sulfate 1 part potassium persulfate 1.5 parts were charged, the pressure was reduced after purging with nitrogen gas, and while the inside of the reaction container was kept at 45°C and stirred, the inside of the supply container was replaced with nitrogen gas. Vinylidene chloride 200 parts Ethyl acrylate 200 parts Butyl acrylate 85 parts Acrylic acid
15 parts water
A mixture consisting of 250 parts and 8 parts of sodium dodecylbenzenesulfonate was uniformly fed into the reactor over a period of 12 hours. After the supply ends, the reactor internal pressure becomes 0.
The reaction was carried out by stirring while maintaining the temperature of 45° C. until the temperature reached #/iG, and then the inside of the reaction vessel was cooled to room temperature.

Each monomer in the monomer composition in Table 1 is indicated using the following abbreviations.

MMA...Methyl methacrylate St
・−・・Styrene BA ・・・−・Butyl acrylate AA
...Acrylic acid MAA ...Methacrylic acid AAmide ... Acrylamide VDC ...
... Vinylidene chloride EA ... Ethyl acrylate HEA
...Hydroxyethyl acrylate Example 1 Polymer aqueous dispersion 1 obtained by emulsion polymerization in Emulsion Polymerization Example 1
An aqueous dispersion prepared by adding 150 parts of water to 0.00 parts was diluted to 20,000 parts using a Hitachi high-speed centrifuge (Model 5CH55).
Centrifugation was performed for 2 hours at rpm. 60 parts of the recovered monomer contained some water, and 60 parts of water was added to make 3.
After standing for a period of time, the mixture was stirred to obtain a homogeneous dispersion with a solid content of 40%. Table I lists the solid content and centrifugation conditions of the dispersion liquid to be centrifuged, as well as the characteristics of the obtained redispersion liquid.

As is clear from comparing the light transmittance of the aqueous dispersion obtained by emulsion polymerization with the light transmittance of the aqueous dispersion obtained by redispersing them after centrifugation, centrifugation causes aggregation of dispersed particles, It is assumed that almost no deformation has occurred.

Examples 2.3 & 4 The solid content of the dispersion liquid to be centrifuged and the centrifugation conditions were changed as shown in Table 2, and Examples 2 to 4 Fi were emulsion polymerization rows 2 to 4, respectively.
This was carried out using an aqueous dispersion polymerized in Redispersions having the characteristics shown in Table 1 were obtained.

(Space below) Table I Test Examples The aqueous dispersions obtained in each polymerization series and Examples were neutralized with aqueous ammonia, and dexanol/benzyl alcohol (1/1) was added as a film-forming agent at a simulated temperature. I added a side dish that has a temperature of 0°C. The film obtained from this formulation was tested according to the following test methods and evaluated according to the following evaluation methods. The results are summarized in Figure 2.

(11 Water Resistance Test The above formulation was formed into a film at 20°C for one week so that the film thickness after drying was SOOμ. This film was
A punched test piece was prepared with an m x 5 an angle.

This test piece was immersed in water at 20° C. for 7 days and then extracted, and the change in hue of the film (degree of whitening), water absorption rate, and edge expansion rate were measured.

(2) Moisture Permeability Test The above formulation was dried on a polyester film at 20° C. for one week so that the film thickness after drying was 200 to 220 μm. The moisture permeability of this film was measured according to JIS ZO208 "Moisture permeability test method for moisture-proof packaging materials".

Table 2 Effects> As is clear from the results in Table 2, the physical properties of the coatings in Examples were as follows:
The physical properties are significantly superior to those of films obtained from emulsion polymerization solutions.

Claims (1)

[Scope of Claims] 1) At least one type of ethylenically unsaturated monomer (component a) that polymerizes alone to give a water-soluble polymer, and which is copolymerizable with this monomer and polymerizes alone and is insoluble in water. A copolymerized aqueous dispersion obtained by emulsion polymerization of at least one type of ethylenically unsaturated monomer (component b) in an aqueous medium to give a polymer with the desired properties is used as it is, or after dilution with water, centrifugation is performed. A film obtained by precipitating all or part of copolymer particles and then redispersing copolymer particles consisting only of the precipitated particles in water, which is characterized in that it does not substantially contain a water-soluble polymer component. Resin aqueous dispersion for forming. 2) The aqueous resin dispersion according to claim 1, wherein component a is at least one of α,β-monoethylenically unsaturated carboxylic acids or neutralized products thereof. 3) The aqueous resin dispersion according to claim 1, wherein component a is at least one of α,β-monoethylenically unsaturated amide or N-alkylolamide. 4) The aqueous resin dispersion according to claim 1, wherein component a is at least one of α,β-monoethylenically unsaturated alcohol and/or amine.