JP2001323004A - Method for producing aqueous polymer dispersion for coating, and its composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new method for producing an aqueous polymer dispersion for coating, suitable for a coating material having each of film-formability of a coating film, an antiblocking properties, water resistance, stain-proofuess and strength properties, or for a coating use. SOLUTION: This method for producing the aqueous polymer dispersion for the coating comprises a first step for carrying out an emulsion polymerization of 10-45 pts.wt. monomer mixture containing >=50 wt.% methyl methacrylate (the percentage of the monomer mixture in the first step is made 100 wt.%), and capable of providing a copolymer having 75-105 deg.C glass transition temperature in the presence of at least water, a surfactant and a polymerization initiator, and a following second step for carrying out an emulsion polymerization by adding 55-90 pts.wt. monomer mixture capable of providing a copolymer having -30 to 20 deg.C glass transition temperature (the amount of the whole monomer mixture is made 100 pts.wt.) dropwise to the resultant reacted composition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a water-based composite polymer having at least two kinds of glass transition temperatures and a composition thereof, and more particularly to a coating material having excellent film-forming properties, blocking resistance and water resistance. The present invention relates to a method for producing a coating aqueous polymer dispersion suitable for coating applications.

[0002]

2. Description of the Related Art Coatings composed of aqueous polymer dispersions, such as coatings on paints, papers and plastics, are used with superiority in terms of safety, environmental protection and economy. However, since film formation (film formation) from an aqueous polymer dispersion is performed by fusion of polymer particles, it is difficult to raise the glass transition temperature of the resin to a temperature higher than the film formation temperature in order to form a film at around normal temperature. It is. Therefore, a film formed from a low glass transition temperature remains tacky even after drying, has a contamination property due to adhesion of dust and dust, and has problems such as blocking when stacked on paper or film.

In order to improve these points, a method of adding a high-boiling organic solvent as a film-forming aid to an aqueous polymer dispersion to lower the film-forming temperature of a resin is generally performed. , When added in a relatively large amount, the water resistance of the film decreases, or the film forming aid volatilizes over a long period of time, changing the film properties,
There are problems such as embrittlement.

There is also a method of blending a hard polymer emulsion having a high glass transition temperature and a soft polymer emulsion having a glass transition temperature equal to or lower than room temperature to achieve both film forming properties and film hardness and blocking resistance. It is disclosed in JP-A-5-112758 and JP-A-9-111154. These methods have the disadvantages that, although the above problems are improved, the film strength is reduced, the bendability is reduced, and cracks are easily generated in the film.

Further, by designing the shell portion (surface layer) to have a higher glass transition temperature than the core portion (center layer) by a method generally called a core / shell type emulsion, the above-mentioned drawbacks of the blend type emulsion can be obtained. Improvements have been made. For example, JP-A-4-45169 discloses an emulsion coating composition having a specific particle size range in which the glass transition temperature of the center layer is -60 to 10C and the glass transition temperature of the surface layer is 0 to 100C. ing. JP-A-11-92708 discloses that the core / shell type emulsion obtained by multi-stage emulsion polymerization has a glass transition temperature of 0 to 80 ° C. for the shell portion (surface layer) and a glass transition temperature of the core portion (center layer). An emulsion for architectural exterior paints configured at -40 to 40 <0> C is disclosed. However, since it is extremely difficult to prove microscopically the emulsion particles having different glass transition temperatures of the central layer and the surface layer, in these patent specifications,
It discloses a production method assuming that a core layer (center layer) is formed from components charged in a first-stage reaction and a shell layer (surface layer) is formed from components charged in a second-stage reaction in a multistage polymerization.

[0006] Therefore, the conventional core / shell emulsion method for improving film forming properties, water resistance of a film, blocking resistance, strength properties of a film, etc., requires a low glass transition temperature for the pre-reaction of emulsion polymerization. It has been common practice to charge a monomer to be formed and then charge a monomer that forms a high glass transition temperature as a post-stage reaction to carry out emulsion polymerization.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide an aqueous coating film which is excellent in film-forming properties and has good blocking resistance, water resistance, stain resistance, and strength properties, and is suitable for applications such as paints and coatings. An object of the present invention is to provide a novel method for producing a combined dispersion.

[0008]

SUMMARY OF THE INVENTION The present inventors have conducted intensive studies on a method of controlling the emulsion polymerization step in multiple steps, and as a result, surprisingly, a reverse procedure different from the conventional core-shell polymerization method has been found. It was found that the emulsion polymerized by this method provides a coating suitable for coating and coating applications that has excellent film forming properties, blocking resistance, water resistance, stain resistance, and strength physical properties compared to conventional methods. The invention has been reached.

That is, the present invention provides a method for preparing methyl methacrylate in the presence of at least water, a surfactant and a polymerization initiator.
0% by weight or more (100% by weight of the monomer mixture in the first step)
The copolymer has a glass transition temperature of 75 to
A first step of emulsion polymerization of 10 to 45 parts by weight of the monomer mixture giving 105 ° C. (the total monomer mixture is 100 parts by weight), and then the reaction product has a glass transition temperature of − A method for producing an aqueous polymer dispersion for coating and a coating aqueous polymer composition comprising a second step in which 55 to 90 parts by weight of a monomer mixture giving a temperature of 30 to 20 ° C are dropped and emulsion-polymerized. More preferably, after the polymerization rate of the monomer mixture in the first step reaches at least 90% by weight, the emulsion dispersion of the monomer mixture in the second step is dropped to carry out emulsion polymerization. This is a method for producing an aqueous polymer dispersion suitable for use.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below in detail. The aqueous polymer dispersion of the present invention has a glass transition temperature (hereinafter referred to as Tg) of 75 to 1 as the first step of emulsion polymerization.
A monomer mixture containing methyl methacrylate as a main component that gives a temperature of 05 ° C. is charged, and after the polymerization rate reaches 90% by weight or more, subsequently, as a second step, Tg is −30 to 20 ° C.
To complete the emulsion polymerization. The quantitative ratio of the monomer mixture used in the first step and the second step is such that the total monomer mixture is 10%.
As 0 parts by weight, the first step is 10 to 45 parts by weight, and the second step is 55 to 90 parts by weight. Tg of the polymer in the first step
Is less than 75 ° C., or when the quantitative ratio is less than 10% by weight, the blocking resistance and stain resistance of the film are impaired even though the film forming property is good, which is not preferable. On the other hand, when the Tg of the polymer in the first step exceeds 105 ° C., or
If the quantitative ratio is more than 45% by weight, the film-forming properties are reduced, and the film intended for the present invention cannot be obtained. When the polymerization rate of the monomer in the first step is lower than 90% by weight, the charged composition of the monomer in the second step is different from the actual resin composition, and the film forming property is undesirably reduced. .
Here, the Tg of the copolymer is determined by the method of indicating the film hardness of a synthetic resin emulsion (107
-1996) ”, using a Tg value of each homopolymer described in the above.

The monomer used in the first step is methyl methacrylate alone or a copolymer having a Tg of 75 to 105 ° C.
Is used as a mixture of methyl methacrylate and a copolymerizable monomer. When the amount of methyl methacrylate is less than 50% by weight, it is difficult to achieve both film forming properties and physical properties such as blocking resistance and stain resistance of the film, and the effect of the present invention is not exhibited. Examples of the copolymerizable monomer include the following monomers. (Meth) acrylate monomer: methyl acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, sec
-Butyl (meth) acrylate, t-butyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, n-nonyl (meth) acrylate, isononyl (meth) acrylate, decyl (Meth) acrylate, undecyl (meth) acrylate, dodecyl (meth) acrylate, n-amyl (meth) acrylate,
Aromatic such as isoamyl (meth) acrylate, benzyl (meth) acrylate, lauryl (meth) acrylate, cyclohexyl (meth) acrylate, tetradecyl (meth) acrylate, stearyl (meth) acrylate, 2-methoxyethyl acrylate, ethyl carbitol acrylate, etc. Vinyl monomers: styrene, α-methylstyrene, chlorostyrene, 4-hydroxystyrene, vinyltoluene, (meth) acrylonitrile, vinyl acetate, vinyl propionate, vinyl versate, and the like. One or more monomers selected from these can be used.

Further, in addition to these non-functional monomers,
A monomer having a functional group such as a carboxyl group, a hydroxyl group, or an amide group may be used in combination. Specific examples thereof include a carboxyl group-containing monomer: (meth) acrylic acid, maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, crotonic acid, and maleic acid, having 1 to 1 carbon atoms of itaconic acid.
Amide group-containing monomers such as half-esters with 2 straight-chain or branched-chain alcohols: (meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N, N-dimethyl ( Hydroxyl group-containing monomers such as (meth) acrylamide: 2-hydroxyethyl (meth) acrylate, 4-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth)
Examples include acrylate, caprolactone-modified (meth) acrylate, polyethylene glycol (meth) acrylate, and polypropylene glycol (meth) acrylate. The use of such a monomer having a carboxyl group, a hydroxyl group, or an amide group has the effect of improving the stability of emulsion polymerization. However, the monomer mixture used in the first step has an effect of 5% by weight or less, It is effective to keep the proportion of the functional monomer smaller than that of these functional monomers used in the two steps, preferably 0 to 2% by weight, in order to achieve both the film forming property and the film properties of the present invention. In addition, as long as the effects of the present invention are not impaired, a small amount of divinylbenzene, diallyl phthalate, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, or the like may be used. Of radical polymerizable monomer having two double bonds, glycidyl (meth) acrylate, 3,4-epoxycyclohexyl (meth) acrylate, N-methylolacrylamide, diacetoneacrylamide, acetoacetoxyethyl (meth) acrylate Anionic monomers can also be used.

Although the composition and quantitative ratio of the monomer used in the second step are not particularly limited, the Tg of the copolymer
Is required to be −30 to 20 ° C. Tg is-
When the temperature is lower than 30 ° C., the physical properties such as blocking resistance and stain resistance of the film are reduced. When the Tg is higher than 20 ° C., the film forming property is reduced. Even if it does, the water resistance is undesirably reduced. The quantitative ratio of the monomer mixture constituting the second step is 55 to 90 parts by weight based on 100 parts by weight of the whole monomer mixture. When the amount is less than 55 parts by weight, the film forming property of the aqueous polymer composition is reduced. When the amount is more than 90 parts by weight, it is difficult to achieve both the film forming property and the film properties of the present invention. Absent.

In the process for producing an aqueous polymer dispersion of the present invention, a monomer mixture forming a high Tg (75 to 105 ° C.) is charged in the first step of emulsion polymerization, and then a low Tg is added in the second step.
This is a method in which a monomer mixture forming (-30 to 20 ° C.) is charged and emulsion polymerization is performed. Emulsion polymerization of the monomer mixture of the first step in the presence of water, an emulsifier and a polymerization initiator, and after the polymerization rate reaches at least 90% by weight, emulsion polymerization of the monomer mixture of the second step. is necessary. Preferably, the monomer mixture of the first step is dropped in accordance with the progression rate of the polymerization, and the monomer mixture of the second step is continuously dropped at a stage where the polymerization reaction of the first step is almost completed. is there. When the polymerization rate of the emulsion polymerization in the first step did not reach at least 90% by weight and the monomer mixture in the second step was continuously reacted, the obtained polymer composition was formed in the second step. The Tg of the copolymer is higher than the Tg of the target polymer,
The compatibility between the film forming property and the film properties of the present invention is unfavorably reduced.

In the emulsion polymerization method of the first step, a method of dropping a monomer mixture into a reaction vessel charged with at least water, a surfactant and a polymerization initiator (monomer dropping method), There is a method (a pre-emulsion dropping method) of dropping an emulsified state of both water and a surfactant into a reaction vessel charged with water and, if necessary, a part of the surfactant and a polymerization initiator. The aqueous polymer dispersion of the invention is
It can be obtained using these two methods. In particular, in the case of the monomer dropping method, there is a feature that the effect of lowering the film-forming temperature is higher than that of an emulsion polymerization method in which the entire copolymer composition is the same and the process is usually performed in one step. In the emulsion polymerization method of the second step, a pre-emulsion dropping method in which a monomer mixture is emulsified in advance is preferable because of good reaction stability during polymerization.

The emulsifier used in the emulsion polymerization of the aqueous polymer composition of the present invention is not particularly limited, but an anionic emulsifier, a nonionic emulsifier and a reactive emulsifier can be used. At least one from the group shown below
More than one species can be used. Examples of anionic emulsifiers include potassium oleate, sodium lauryl sulfate, sodium dodecylbenzenesulfonate, sodium alkylnaphthalenesulfonate, sodium dialkylsulfosuccinate, sodium polyoxyethylene alkyl ether sulfate, sodium polyoxyethylene alkyl allyl ether sulfate, and polyoxyethylene sodium. Ethylene alkyl ether phosphate, polyoxyethylene alkyl allyl ether phosphate, and the like. As a nonionic emulsifier, polyoxyethylene alkyl ether,
Examples include polyoxyethylene alkyl allyl ether, polyoxyethylene oxypropylene block copolymer, polyethylene glycol fatty acid ester, and polyoxyethylene sorbitan fatty acid ester. Examples of the reactive emulsifier include polyethylene glycol mono (meth) acrylate, polyoxyethylene alkylphenol ether (meth) acrylate, ammonium 2- (meth) acryloyloxyethylsulfonate, and polyoxyethylene having various molecular weights (different EO addition moles). Monomaleic acid esters of ethylene glycol and derivatives thereof,
(Meth) acryloyl polyoxyalkylene alkyl ether phosphate esters and the like. Preferably, an anionic emulsifier, a reactive emulsifier and a combination thereof are used.

The amount of the emulsifier used is usually 10
It is sufficient to use about 0.2 to 10 parts by weight with respect to 0 parts by weight, and preferably 0.5 to 5% by weight. When the amount of the emulsifier is within this range, an emulsion having an appropriate particle size can be obtained without producing a coagulated product. If the amount of the emulsifier is too large, the water resistance of the aqueous polymer composition decreases.

The polymerization initiator used in the emulsion polymerization of the aqueous polymer composition of the present invention is a generally used radical polymerization initiator. Radical polymerization initiators are those that generate radicals by heat or reducing substances to cause addition polymerization of polymerizable monomers, and include water-soluble or oil-soluble persulfates, peroxides, azobis compounds and the like. is there. Specifically, potassium persulfate, sodium persulfate, ammonium persulfate, hydrogen peroxide, t-butyl hydroperoxide, t-butyl peroxybenzoate, 2,2-azobisisobutyronitrile, 2,2-azobis ( 2-diaminopropane) hydrochloride, 2,2-azobis (2,4-dimethylvaleronitrile), and the like, and are preferably water-soluble. When acceleration of the polymerization rate or low-temperature reaction is desired, a reducing agent such as sodium bisulfite, ferrous chloride, ascorbic acid, and formaldehyde sulfoxylate salt can be used in combination with a radical polymerization initiator.

The amount of the polymerization initiator used is 100
The amount is usually 0.02 to 3 parts by weight, preferably 0.05 to 1 part by weight based on parts by weight.

The emulsion polymerization for obtaining the aqueous polymer dispersion of the present invention can be carried out at a solid concentration of usually 30 to 75% by weight, preferably about 40 to 65% by weight in an aqueous medium. The polymerization reaction is usually carried out at 40 to 95 ° C, preferably 60 to 95 ° C.
At a reaction temperature of about 90 ° C. for 1 to 10 hours, preferably 3 hours
It may be performed for about 6 hours.

If necessary, a molecular weight modifier can be used in the emulsion polymerization. As the molecular weight modifier,
Specific examples include butyl mercaptan, dodecyl mercaptan, octyl thioglycolate, isopropyl alcohol, methanol, carbon tetrachloride and the like. The amount used is from 0.001 to 2.0% by weight, preferably from 0.05 to 1.0% by weight, based on the monomer component.

The aqueous polymer dispersion of the present invention may contain, if necessary, known additives such as a film forming aid, a plasticizer, a filler, a pigment, a viscosity modifier, an antifoaming agent, a preservative, a dispersant, An antioxidant, an ultraviolet absorber, an ultraviolet stabilizer, an antifreezing agent, a flame retardant, a flame retardant, and the like can be blended as long as the effects of the present invention are not impaired.

[0023]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. In addition,
Parts in Examples show parts by weight, and% shows% by weight.

Example 1 In a beaker, 30 parts of styrene, 35.8 parts of 2-ethylhexyl acrylate, 17.5 parts of methyl methacrylate, 1.7 parts of acrylic acid, and 1.7 parts of acrylic acid were previously used as the monomer mixture used in the second step. Water-soluble emulsifier Sodium alkyl allyl sulfosuccinate (trade name Elminol JS-2 manufactured by Sanyo Chemical Industries, Ltd.) 3.6 parts, sodium polyoxyethylene nonylphenyl ether sulfate (trade name Levenol WZ manufactured by Kao Corporation) 5.6 parts Then, take 31.2 parts of deionized water and emulsify by stirring. A reactor equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen inlet tube, and a dropping funnel was equipped with 57 parts of deionized water and a reactive emulsifier sodium alkyl allyl sulfosuccinate (trade name Eleminor JS-2 manufactured by Sanyo Chemical Industries, Ltd.). 0.26 parts and 0.4 parts of sodium polyoxyethylene nonylphenyl ether sulfate (trade name: Revenol WZ, manufactured by Kao Corporation) were charged, nitrogen was allowed to flow in, the internal temperature was raised to 80 ° C., and deionized water was added. At 10
% Of ammonium persulfate dissolved in%. Subsequently, a monomer mixture of 14.7 parts of methyl methacrylate and 0.3 part of acrylic acid in the first step is dropped over 1 hour. Emulsion polymerization is performed at an internal temperature of 80 to 85 ° C. Immediately after the completion of the dropping of the monomer mixture in the first step, the solid content was measured.
, It was 92% by weight in terms of conversion. Subsequently, the previously prepared emulsion of the monomer mixture of the second step was added dropwise over 3 hours, and in parallel, 1 part was added with deionized water.
2 parts of ammonium persulfate dissolved in 0% are added dropwise. After completion of the dropping in the second step, the mixture is aged at the same temperature for 3 hours and then cooled to room temperature. Adjusted with 1.6 parts of 25% aqueous ammonia and water, the solid content concentration was 49.7%, and the viscosity was 2,500 mPa.
An aqueous polymer dispersion having a pH of s and a pH of 8.8 was obtained. The aqueous polymer dispersion was observed at normal temperature for film formation, a film was formed at room temperature, and the film was tested for blocking resistance and water whitening resistance. The results were all very good as shown in Table 1.

Examples 2 to 4 Example 2 differs from Example 1 in that the amounts of methyl methacrylate and acrylic acid added dropwise in the first step of Example 1 were increased. The reaction was carried out in the same manner as in Example 1 except that the kind and amount of the monomer dropped in the first step were changed. Immediately after the completion of the dropping in the first step, the conversion of the polymerization rate by solid content measurement was 93% by weight. Obtain an aqueous polymer dispersion as shown in Table 1 below, observe the room-temperature film forming property of the aqueous polymer dispersion, form a film at room temperature,
The coating was tested for blocking resistance and water whitening resistance. The results were all very good, as shown in Table 1.

Comparative Example 1 and Comparative Example 2 Comparative Example 1 reacted in the same manner as in Example 1 except that the type of monomer was the same and the amount was changed. Comparative Example 2 reacted in the same manner as in Example 1 except that the first step of Example 2 was partially replaced with styrene for methyl methacrylate.
An aqueous polymer dispersion as shown in Table 1 was obtained, the room-temperature film forming property of the aqueous polymer dispersion was observed, and the coating was tested for blocking resistance and water whitening resistance. The result is
As shown in Table 1, Comparative Example 1 had good room-temperature film-forming properties and water-whitening resistance, but lacked blocking resistance. Comparative Example 2 was inferior in room-temperature film forming properties, and lacked blocking resistance and water whitening resistance.

Comparative Example 3 In Comparative Example 3, the monomer mixture obtained in the second step of Example 2 was used in the first step.
The reaction was carried out in the same manner as in Example 1 except that the emulsion polymerization was carried out in the step and the monomer in the first step was emulsion-polymerized in the second step. An aqueous polymer dispersion as shown in Table 1 was obtained, the room-temperature film forming property of the aqueous polymer dispersion was observed, and the coating was tested for blocking resistance and water whitening resistance. As a result, as shown in Table 1, there was no room temperature film forming property, and the blocking resistance and the water whitening resistance were insufficient.

Comparative Example 4 In Comparative Example 4, the type and amount of the monomer were the same as those in Example 1,
This is an aqueous polymer dispersion obtained by emulsion polymerization of the monomer mixture in one step without the reaction of the first step. The reaction was performed in the same manner as in Example 1. An aqueous polymer dispersion as shown in Table 1 was obtained,
The film forming property of the aqueous polymer dispersion at normal temperature was observed, and the film was tested for blocking resistance and water whitening resistance. As shown in Table 1, there was no room temperature film forming property, and the blocking resistance and the water whitening resistance were insufficient.

Comparative Example 5 In Comparative Example 5, an aqueous dispersion (A) obtained by emulsion polymerization of a monomer mixture in the same ratio as in the first step of Example 2 was used. The aqueous dispersion (B) obtained by emulsion polymerization of the monomer mixture at a ratio of (A) / (B) = 3
It is blended at a ratio of 0/70 (solid content ratio). The film forming properties of the blended liquid were observed at room temperature, a film was formed at room temperature, and the film was tested for blocking resistance and water whitening resistance. However, the blocking resistance and the water whitening resistance were insufficient.

[0030]

[Table 1]

[0031]

[Table 2]

The monomers used in Tables 1 and 2 are indicated by the following abbreviations. ST: styrene (Tg: 100 ° C) 2EHA: 2-ethylhexyl acrylate (Tg: -70 ° C) MMA: methyl methacrylate (Tg: 105 ° C) AAc: acrylic acid (Tg: 106 ° C)

In Tables 1 and 2, the minimum film-forming temperature was MF.
T. (° C.)

[Test Method] Minimum film forming temperature (MFT)
Is measured according to JIS K 6828 "minimum film forming temperature" test method.

The film forming property at room temperature is obtained by applying the aqueous polymer dispersion of the present invention to a glass plate at 100 g / m ² / wet and observing the film forming property at 20 ° C. and 65% RH. I do. ：: Film formation △: Film formation but fine cracks observed ×: No film formation

The blocking resistance is as follows: 100 g / m 2 of the aqueous polymer dispersion obtained by the production method of the present invention on a glass plate.
² / wet at room temperature, 20 ° C, 65% R
H was allowed to stand for 3 days to form a film, which was used as a test sample. This test sample was evaluated as "non-stick" according to JIS K5400.
In accordance with the test method, a load was applied to 80 g / cm ² , left in a thermostat at 45 ° C. for 16 hours, returned to room temperature, and judged by gauze adhesion. ：: no gauze adhesion Δ: slight gauze adhesion ×: gauze adhesion

As to the water whitening resistance, a test sample prepared in the same manner as the “blocking resistance” is left in warm water at 60 ° C. for 24 hours, and then immediately in water at room temperature for 24 hours. Remove from water and dry at room temperature to observe the whitening of the film. ：: no whitening Δ: slightly whitened ×: whitened

[0038]

According to the present invention, a high T is used in the first step of emulsion polymerization.
g (75-105 ° C.), followed by dropwise addition of a monomer mixture forming a low Tg (-30-20 ° C.) in the second step to form an aqueous polymer dispersion for emulsion polymerization. This is a method for producing a liquid. The resulting aqueous polymer dispersion is
Excellent film-forming properties at room temperature without using a film-forming aid, has moderate hardness, can provide a film having excellent blocking resistance and water-whitening resistance, and is useful as a coating material and a coating agent for various coatings. .

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Claims (3)

[Claims] 1. A glass of a copolymer containing at least 50% by weight of methyl methacrylate (100% by weight of a monomer mixture in the first step) in the presence of at least water, a surfactant and a polymerization initiator. A first step of emulsion-polymerizing 10 to 45 parts by weight of the monomer mixture giving a transition temperature of 75 to 105 ° C. (total monomer mixture is 100 parts by weight), followed by a copolymer to the reaction composition Has a glass transition temperature of -30 to
A method for producing an aqueous polymer dispersion for coating, comprising a second step in which 55 to 90 parts by weight of a monomer mixture giving 20 ° C. is added dropwise to carry out emulsion polymerization. 2. The aqueous weight for coating according to claim 1, wherein after the polymerization rate of the monomer mixture in the first step reaches at least 90% by weight, the emulsified dispersion of the monomer mixture in the second step is dropped. A method for producing a combined dispersion. 3. In the presence of 10 to 45 parts by weight of copolymer particles having a glass transition temperature of 75 to 105 ° C. (100 parts by weight of the whole polymer), the glass transition temperature of the copolymer is −
An aqueous polymer composition for coating obtained by emulsion-polymerizing 55 to 90 parts by weight of a monomer mixture giving 30 to 20 ° C.