JPH0748537A - Water-based coating composition - Google Patents

Abstract

PURPOSE:To obtain the composition which can form a tough water-resistant coating film by neutralizing a vinyl polymer made from methyl methacrylate, an acid-group-containing vinyl compound, etc., dissolving the neutralized polymer in water and mixing the obtained solution with a specified aqueous polymer dispersion. CONSTITUTION:A mixture comprising 30-90wt.% methyl methacrylate, 0-30wt.% aromatic vinyl compound especially styrene, 4-20wt.% acid-group-containing vinyl compound especially (meth)acrylic acid and 0-66 wt. % other vinyl monomers [e.g. alkyl (meth)acrylate] is suspension-polymerized to obtain a vinyl polymer having a Tg of 30-110 deg.C, a weight-average molecular weight of 6X10<3> to 3X10<4> and an acid value of 35 to 130mgKOH/g, this polymer is neutralized, the neutralized polymer is dissolved in water to obtain an aqueous solution (A). This solution A is mixed with an aqueous dispersion (B) of a urethane polymer having a Tg of 30-120 deg.C and a weight-average molecular weight of 2X10<4> to 1X10<6> in an A/B weight ratio of 5/95 to 60/40 (in terms of the solid content) to obtain the composition. This composition is based on a solvent entirely consisting of water and can form a cracking-free water- resistant tough coating film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aqueous coating composition which is excellent in water resistance, stain resistance and blocking resistance and can form a tough coating film.

[0002]

2. Description of the Related Art In recent years, the needs for water-based paints and inks have increased, and various products have been developed. However, many of them do not use only water as a solvent,
Most of them required the combined use of organic solvents in order to satisfy various required performances.

However, due to recent severe environmental problems, a coating composition using only water as a solvent is desired. To date, various water-based paints and water-based ink compositions using only water as a solvent have been developed, but a tough coating film without cracks can be formed without using an organic solvent,
An aqueous coating composition capable of forming a coating film having excellent dryness, Tg higher than room temperature, excellent stain resistance and blocking resistance, and excellent water resistance has not been provided.

This is an aqueous polymer dispersion (emulsion,
In the (dispersion) system, a tough coating film cannot be formed because the coating film is easily cracked unless Tg is lower than room temperature, and conversely, when Tg is lower than room temperature, stain resistance and blocking resistance are deteriorated. This is also because when a drying aid is used in combination, environmental problems occur and the drying property is insufficient. On the other hand, in an aqueous polymer system, water resistance tends to be insufficient, and a tough coating film is difficult to form. Met.

Therefore, as an attempt to solve the above problems by combining the advantages of both the polymer aqueous dispersion system and the polymer aqueous solution system, emulsion polymerization is carried out in the polymer aqueous system to obtain a polymer aqueous solution. Hybridization with an aqueous polymer dispersion was investigated.

For example, in JP-A-60-37135, an acrylic polymer having a carboxyl group is reacted with 0.5 to 0.05 equivalent of glycidyl (meth) acrylate to 1 equivalent of the carboxyl group. Also disclosed is an aqueous coating composition obtained by emulsion-polymerizing a vinyl-based monomer in a water-alcohol mixed solvent using an ammonium or amine salt of an acrylic polymer as a dispersion stabilizer. Also,
In JP-A-63-221105, polymerization is performed while adding a mixture of a vinyl-based polymer, a vinyl-based monomer, and a polymerization initiator to a hydrophilic organic solvent, and then an aqueous alkali solution is added and dispersed. A method of making an aqueous dispersion is disclosed.

However, these all require the use of a different polymerization method for each type of composition, which is inconvenient for developing a wide variety of products in a wide variety of compositions, and it is a simple matter of polymer aqueous solution and polymer aqueous dispersion. It has been desired to develop a blend that can solve the above problems.

For this reason, various polymer aqueous solutions and polymer aqueous dispersions have been studied for blending, but few conventional polymer aqueous solutions are widely compatible with various polymer aqueous dispersions. In many cases, there was a problem that the water resistance of the polymer aqueous dispersion was remarkably impaired, and practical application was hindered.

[0009]

An object of the present invention is to provide an aqueous coating composition which can use a wide variety of aqueous polymer dispersions.

Another object of the present invention is to provide an aqueous coating composition capable of forming a tough coating film without cracks without using an organic solvent and having good drying property.

Still another object of the present invention is to provide an aqueous coating composition capable of forming a coating film having Tg higher than room temperature, excellent stain resistance and blocking resistance, and excellent water resistance. To do.

[0012]

That is, the present invention is
(A) Methyl methacrylate 30 to 90% by weight, (b)
It comprises 0 to 30% by weight of an aromatic vinyl compound, (c) 4 to 20% by weight of an acid group-containing vinyl compound, and (d) 0 to 66% by weight of another copolymerizable vinyl monomer, and has a second-order transition temperature. Is 30 to 110 ° C. and the weight average molecular weight is 6,000 to 3
A vinyl polymer aqueous solution obtained by neutralizing a vinyl polymer (I) having an acid value of 35 to 130 mgKOH / g with a base and dissolving it in water, and a second-order transition temperature of 30 to
120 ° C, weight average molecular weight of 200,000 to 2,000
And an aqueous dispersion of the polymer (II) of which the polymer solid content ratio is polymer (I) / polymer (II) = 5/95.
It is an aqueous coating composition obtained by mixing so as to be about 60/40.

[0013]

The vinyl polymer (I) used in the present invention is
(A) Methyl methacrylate 30 to 90% by weight, (b)
It is composed of 0 to 30% by weight of an aromatic vinyl compound, 4 to 20% by weight of (c) an acid group-containing vinyl compound, and (d) 0 to 66% by weight of another copolymerizable vinyl monomer.

Methyl methacrylate (a) is an essential component for imparting hardness to the vinyl polymer, and is 30 to 30%.
Used in a proportion of 90% by weight. If it is less than 30% by weight, the hardness is lowered, while if it exceeds 90% by weight, the water solubility is lowered. Further, if it is out of the above range, compatibility with the aqueous dispersion of the polymer (II) is lacking.

The aromatic vinyl compound (b) has the effect of imparting water resistance to the coating film, is copolymerized in the range of up to 30% by weight, and is preferably used in the range of 0 to 25% by weight. However, if it exceeds 30% by weight, the water solubility is lowered and the compatibility with the aqueous dispersion of the polymer (II) is lacking, which is not suitable. Specific examples of the aromatic vinyl compound include styrene, α-methylstyrene, p-methylstyrene, benzyl (meth) acrylate, and the like, of which styrene is particularly preferable.

The acid group-containing vinyl compound (c) imparts an acid group to the vinyl polymer, and is a vinyl compound having an acidic group such as carboxylic acid or sulfonic acid.
The acid group-containing vinyl compound has an acid value of 35 to 130 mgK of the vinyl polymer (I) obtained in the range of 4 to 20% by weight.
Used to be OH / g. Specific examples of the acid group-containing vinyl compound include monobasic acids such as acrylic acid, methacrylic acid and crotonic acid; dibasic acids such as fumaric acid, maleic acid and itaconic acid; and partial esters thereof. It is also possible to use a mixture of two or more of these. In particular, when a vinyl compound having a carboxylic acid is copolymerized, a compound having good water solubility and compatibility with the aqueous dispersion of the polymer (II) can be obtained. Also,
Particularly, when it is copolymerized with methacrylic acid or acrylic acid, it has a very good water solubility and compatibility.

Further, the other vinyl-based monomer (d) copolymerizable with the above-mentioned monomers (a) to (c) is used in the range of 0 to 66% by weight, and at least one polymerization is possible. It can be arbitrarily selected from those having various vinyl groups according to the purpose. Specific examples of the vinyl-based monomer (d) include ethyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, t-butyl (meth) acrylate, cyclohexyl (meth) acrylate, (Meth) having an alkyl group having 1 to 18 carbon atoms such as 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate
Acrylic acid alkyl ester; 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate and other hydroxyalkyl (meth) acrylates; ethylene glycol di (meth) acrylate, butylene glycol (meth) acrylate and other glycol di ( (Meth) acrylate; alkylamino (meth) acrylates such as dimethylaminoethyl (meth) acrylate; and dimethylaminoethyl (meth) acrylate methyl chloride salt, cyclohexyl (meth) acrylate, allyl (meth) acrylate, trimethylolpropane tri (meth) ) Acrylate, glycidyl (meth) acrylate, vinyl acetate, vinyl propionate, (meth) acrylonitrile and the like.

The second-order transition temperature of the vinyl polymer (I) is
It is necessary to be 30 to 110 ° C., preferably 35 to 105 ° C., as measured by the DSC method. If it is lower than 30 ° C, the stain resistance becomes insufficient or the blocking resistance decreases. If it exceeds 110 ° C, the coating film becomes brittle. Regarding the molecular weight of the vinyl polymer, the weight average molecular weight measured by the GPC method needs to be 6,000 to 30,000, and preferably 8,000 to 25,000. 6,
If it is less than 000, the coating film tends to be brittle. Also 30,
If it exceeds 000, the water solubility tends to decrease and the polymer (I
It also lacks compatibility with the aqueous dispersion of I). The acid value is determined by dropping KOH dissolved in ethanol into an aqueous vinyl polymer solution based on the color change point of phenolphthalein and titrating the K to be necessary for neutralizing 1 g of the vinyl polymer.
When expressed in mg of OH, 35 to 130 mg KOH /
must be g, preferably 40-110 mg KO
H / g. If it is less than 35 mgKOH / g, the water solubility will decrease, and if it exceeds 130 mgKOH / g, the polymer (I
The compatibility with the aqueous dispersion I) is reduced and the water resistance is insufficient.

As a polymerization method for producing the vinyl polymer (I), a suspension polymerization method, a solution polymerization method, a bulk polymerization method or the like can be applied, but a suspension polymerization method is particularly preferable. Is. In particular, rather than a monomer produced by a method of dividing the monomer into several parts while advancing the polymerization and adding the monomer into the system while advancing the polymerization, the monomer is added to the system over several hours while the polymerization is advancing. What is produced by the batch charging method of monomers in which polymerization is started after being charged all at once into the system is excellent in water resistance and at the same time excellent in compatibility with the aqueous dispersion of the urethane polymer (II).
It is considered that these are mainly the effect of copolymerizability. As a dispersant in suspension polymerization, 70-100
A known water-soluble polymer such as polyvinyl alcohol or polymethacrylic acid soda salt having a saponification degree in the range of% can be used. The solvent in the solution polymerization is not particularly limited as long as it dissolves the monomers and polymers used in the present invention, but alcohols such as methanol, ethanol, isopropyl alcohol, n-butanol; ethyl cellosolve, cellosolve. Acetate, butyl carbitol; glycols such as propylene glycol methyl ether; acetic acid esters such as ethyl acetate and butyl acetate; ketones such as methyl ethyl ketone and methyl isobutyl ketone; As the polymerization catalyst, conventionally known initiators such as azo-based initiators such as azobisisobutyronitrile and peroxide-based initiators such as benzoyl peroxide can be arbitrarily used according to the purpose.

Further, for controlling the molecular weight of the vinyl polymer (I), a chain transfer agent such as n-dodecyl mercaptan or α-methylstyrene dimer is added to the above vinyl monomer mixture, if necessary. be able to.

The vinyl polymer (I) thus obtained imparts water solubility by neutralizing the acid groups in the vinyl polymer (I) with a base to form a salt. Then
Dissolved in water. It is not necessary that all the acid groups of the vinyl polymer (I) be neutralized, and normally 30% or more of the acid groups are neutralized.

Examples of bases used for neutralization include ammonia, triethylamine, propylamine, diethylamine, tripropylamine, dibutylamine, amylamine, 1-aminooctane, 2-dimethylaminoethanol, ethylaminoethanol, 2-diethylaminoethanol. , 1-amino-2-propanol, 2-amino-
1-propanol, 3-amino-1-propanol, 1
Volatile substances such as dimethylamino-2-propanol, 3-dimethylamino-1-propanol, 2-propylaminoethanol, ethoxypropylamine, aminobenzyl alcohol, and morpholine are mentioned.

On the other hand, the aqueous dispersion of the polymer (II) has a second-order transition temperature of 30 to 120 ° C. and a weight average molecular weight of 200,
The type of polymer is not particularly limited as long as it uses a polymer of 000 to 2,000,000, and for example, an acrylic resin, an alkyd resin, a urethane resin, an epoxy resin, a polyester resin, Examples thereof include vinyl resins such as polyvinyl chloride and polyvinyl acetate, and cellulose resins such as nitrocellulose and cellulose acetate butyrate.

If the second-order transition temperature of the polymer (II) is less than 30 ° C., the blocking resistance is insufficient, and if it exceeds 120 ° C., the coating film tends to be cracked. When the weight average molecular weight is less than 200,000, the toughness of the coating film tends to be insufficient, and when it exceeds 2,000,000, the coating film tends to be cracked.

The method for producing an aqueous dispersion of the polymer (II) includes emulsion polymerization, dissolving a polymer having an acid group such as carboxylic acid in a hydrophilic organic solvent, or in a hydrophilic organic solvent. A method of neutralizing a polymer organic solvent solution prepared by solution polymerization with a base and dispersing it in water, dissolving the polymer in a hydrophilic organic solvent, and then high shearing force in water containing a surfactant. Various methods can be adopted, such as a method of dispersing by applying. Among them, those produced by the emulsion polymerization method are particularly preferable because they have good water resistance.

The aqueous coating composition of the present invention comprises an aqueous solution of the vinyl polymer (I) and an aqueous dispersion of the polymer (II) in a polymer solid content ratio of polymer (I) / weight. Coalescence (II)
= 5 / 95-60 / 40. When the mixing ratio is less than 5/95, it becomes difficult to form a tough coating film without cracks without using a film-forming auxiliary. On the other hand, if the mixing ratio exceeds 60/40, the water resistance decreases. The method for mixing the aqueous solution of the vinyl polymer (I) and the aqueous dispersion of the polymer (II) is not particularly limited,
Both solutions may be mixed at room temperature, or both solutions may be mixed after heating. The aqueous solution of the vinyl polymer (I) is usually used in a concentration of 15 to 35% by weight. As the aqueous dispersion of the polymer (II), one having a concentration of the polymer (II) of 25 to 60% by weight is usually used.

The aqueous coating composition of the present invention thus obtained contains additives such as antifoaming agents, pigment dispersants and preservatives in order to exhibit high performance as paints and inks. It is also possible to use.

The coating method for forming a coating film on the surface of various materials using the aqueous coating composition of the present invention includes a spray coating method, a roller coating method, a bar coating method, an air knife coating method and a casting method. Examples of the method include, but are not limited to, a method, a brush coating method, and a dipping method.

When the aqueous coating composition of the present invention is used as a paint, it is usually used in the temperature range of room temperature to 60 ° C. for 10 seconds to
A coating film is formed by drying for 10 hours.

[0030]

EXAMPLES The present invention will be described in detail below with reference to examples. In addition, "part" and "%" in an Example show "weight part" and "weight%", respectively. (1) Production of vinyl-based polymer I-1 A polymerization apparatus equipped with a stirrer, a thermometer, and a reflux condenser, capable of both heating and cooling, was added with 200 parts of deionized water and polyvinyl alcohol (saponification degree). 80%, degree of polymerization 1,70
0) After adding 0.6 parts and stirring to completely dissolve polyvinyl alcohol, the stirring was stopped once, and 70 parts of methyl methacrylate (hereinafter abbreviated as MMA), 10 parts of styrene (hereinafter abbreviated as St), 10 parts of n-butyl acrylate (hereinafter abbreviated as n-BA), methacrylic acid (hereinafter, MA)
Add 10 parts of A and agitate again, add 0.5 parts of azobisisobutyronitrile (hereinafter abbreviated as AIBN) and 4 parts of n-dodecyl mercaptan (hereinafter abbreviated as n-DM), and add 75 The temperature was raised to 0 ° C., and the reaction was carried out for 3 hours so that the reaction temperature was maintained at 75 to 80 ° C. Then, the temperature was raised to 95 ° C. and maintained for 1 hour to complete the reaction. The obtained polymer had a molecular weight of 12,000, an acid value of 65 mgKOH / g, and a second-order transition temperature of 87 ° C. (2) Production of vinyl-based polymers I-2 to I-11 By the same operation as in the production method of vinyl-based polymer I-1, Table 1
The vinyl-based monomer composition shown in Table 1 was polymerized using the radical initiator and the chain transfer agent shown in Table 1, and the characteristic values of the obtained polymer are shown in Table 2.

[0031]

[Table 1] Explanation of symbols BPO: Benzoyl peroxide n-BMA: n-Butyl methacrylate EHA: Ethylhexyl acrylate MeSt: α-Methylstyrene dimer AA: Acrylic acid

[0032]

[Table 2] (3) Production of vinyl-based polymer I-12 Isopropyl alcohol (hereinafter abbreviated as i-PA) 100 in a polymerization apparatus equipped with a stirrer, thermometer, reflux condenser and capable of both heating and cooling. Part, MMA65 part, St
10 parts, 12 parts of n-BA, 13 parts of MAA, 2 parts of AIBN and 3 parts of n-DM were added and stirring was started, the temperature was raised to 80 ° C. to start polymerization, and 0.2 parts of AIBN was added at intervals of 1 hour. Polymerization was completed by maintaining temperature for 51 hours, solid content 51%,
An i-PA solution of a vinyl polymer having a viscosity of 10,000 cps was obtained. Then, this solution was put in a vat, and i-PA was evaporated in a dryer heated to 50 ° C. to obtain a solid content of 99.5.
% Vinyl polymer solids were obtained. The obtained polymer had a molecular weight of 13,000, an acid value of 85.5 mgKOH / g, and a second-order transition temperature of 84 ° C. (4) Production of vinyl-based polymer I-13 100 parts of i-PA was added to a polymerization apparatus equipped with a stirrer, a thermometer, and a reflux condenser, and both heating and cooling were possible, and stirring was started. The temperature was raised to ℃, MMA 65 parts, St10
Part, n-BA 12 parts, MAA 13 parts and AIBN 3 parts were added dropwise over a period of 4 hours, and then A was added every 1 hour.
Polymerization was terminated by adding 0.1 part of IBN while maintaining the temperature for 4 hours to obtain a vinyl polymer i-PA solution having a solid content of 50% and a viscosity of 2,000 cps. After that, this solution was put in a vat, and i-PA was placed in a dryer heated to 50 ° C.
Was evaporated to obtain a vinyl polymer solid having a solid content of 99.5%. The obtained polymer has a molecular weight of 11,000 and an acid value of 8.
It was 5.5 mgKOH / g and the second-order transition temperature was 84 ° C. (5) Dissolution of vinyl-based polymer in water 50 g of vinyl-based polymer I-1 and deionized in a 300 ml flask equipped with a stirrer, thermometer, reflux condenser and capable of both heating and cooling. Water (148 g) was added and stirring was started, 28% ammonia water (3.5 g) was gradually added, the temperature was then raised to 50 ° C., the temperature was maintained for 2 hours to complete the dissolution, and the vinyl-based polymer I-1 aqueous solution was added. A lysate was obtained. The resulting aqueous solution had a solid content of 25% and a viscosity of 500 cps. For vinyl polymers I-2 to I-13, the addition amount of 28% ammonia water and deionized water was calculated according to the following calculation method, and the dissolution operation was performed by the same method. However, the vinyl polymer I-6 could not be dissolved. Required ammonia water (g) = A / 56.1 / 1000 × 5
0 × 17 ÷ 0.28 (In the formula, A represents the acid value (mgKOH / g) of the polymer.) Necessary deionized water (g) = 150−Necessary ammonia water (g) × 0.72 (6) Production of Polymer Aqueous Dispersion II-1 A polymerization apparatus equipped with a stirrer, a thermometer, and a reflux condenser, capable of both heating and cooling, has 100 parts of deionized water and 35 polyoxyethylene units. Oxyethylene nonyl phenyl ether 2 parts, sodium lauryl sulfate 1
Parts and 0.5 parts of potassium persulfate are added, stirring is started, the temperature is raised to 70 ° C., and a mixture of 57 parts of MMA, 25 parts of n-butyl methacrylate, 15 parts of n-BA, and 3 parts of MAA is added over 4 hours. After dropping, the temperature was raised to 80 ° C. and the temperature was maintained for 2 hours to terminate the reaction to obtain a polymer aqueous dispersion. The resulting polymer had a second-order transition temperature of 52 ° C. and a weight average molecular weight of 1,000,000, and the aqueous dispersion had a solid content of 50% and a viscosity of 3,000 cps. (7) Production of Polymer Aqueous Dispersion II-2 By the same production method as in (6), a mixture of St-85 parts, ethylhexyl acrylate 14 parts and MAA 1 part of a vinyl-based monomer was polymerized. A polymer having a weight average molecular weight of 500,000 at 67 ° C. was obtained, and the aqueous dispersion had a solid content of 50% and a viscosity of 800 cps. (8) Production of Polymer Aqueous Dispersion Liquid II-3 In a polymerization apparatus equipped with a stirrer, a thermometer, and a reflux condenser, both heating and cooling are possible. I-PA 25 parts, MMA
42 parts, St 23 parts, n-BMA 28 parts, MAA acid 7 parts and AIBN 0.1 parts were charged, then the temperature was raised to 80 ° C., and the temperature was raised while adding AIBN 0.1 part each. Hold for 7 hours, then cool to 50 ° C, 28
% 3.1 Ammonia water and 150 parts of deionized water were gradually added, and the temperature was raised to 95 ° C. over 3 hours.
-PA was distilled off to about 1% of the initial charged amount to obtain an aqueous dispersion of the polymer. The second-order transition temperature of the obtained polymer was 76 ° C., the weight average molecular weight was 350,000, and this aqueous dispersion had a solid content of 40% and a viscosity of 200 cps. (9) Production of Polymer Aqueous Dispersion II-4 In a 1000 ml reaction vessel equipped with a thermometer, a stirrer, and a condenser, 13 parts of dimethylolpropionic acid, 80 parts of N-methyl-2-pyrrolidone, 100 parts of polytetramethylene glycol. , 5 parts of trimethylolpropane were added, and 90
It was heated to dissolve at 0 ° C. Next, after adding 48 parts of isophorone diisocyanate and stirring for 10 minutes, 0.1 part of dibutyltin dilaurate was added, and the temperature was raised to 95 ° C. and the reaction was carried out for 1 hour.

The hydrophilic group-containing oligomer thus obtained was neutralized with 5 parts of triethylamine, and then deionized water 3
00 parts was added and the mixture was stirred for 1 hour to obtain an aqueous dispersion. The polymer obtained had a second-order transition temperature of 40 ° C., a weight average molecular weight of 220,000, and the aqueous dispersion had a solid content of 29% and a viscosity of 8,000 cps.

Example 1 60 g of a 25% solid aqueous solution of vinyl polymer I-1 and 120 g of polymer aqueous dispersion II-1 were weighed in a beaker and lightly mixed with a stick to prepare blend liquid 1. . In this case, the vinyl polymer I-1 and the polymer aqueous dispersion II-
The polymer solids ratio of 1 is 20:80. No precipitate was observed 24 hours after blending, confirming compatibility as a solution. In addition, when Blend liquid 1 was applied to a glass plate to a solid film thickness of 80 μm and dried in an environment of 15 ° C. and 60% RH, it became tack-free in 2 minutes,
A transparent coating film without cracks was formed. Even when the coating film was rubbed with a nail, no damage such as scratches was found on the coating film. Further, two coated glass plates were prepared, and the coating films were stacked together and left to stand in an environment of 30 ° C. and 70% RH for 2 days, and no fusion of the coating film was observed. In addition, the coated glass plate was immersed in deionized water at 30 ° C for 2
No change was observed in the coating film when it was taken out after being kept for 0 hour and left for 1 hour in a room at 15 ° C. and 60% RH.

Examples 2 to 9 and Comparative Examples 1 to 8 Blend liquids were prepared in the same manner as in Example 1 and evaluated. The results are shown in Table 3 below. The symbols of the results of each evaluation test have the following meanings. [Compatibility] Solution S: No precipitate is observed.

IS: There is a precipitate. Coating film C: The coating film is transparent and has good compatibility.

VSH: The coating film is slightly opaque and the compatibility is slightly poor.

SH: The coating film is more opaque than the VSH stage, and the compatibility is lower than that in the VSH stage.

H: The coating film is opaque from the SH stage,
Compatibility is lower than that of SH (impractical level). [Film Formability] A solid film having a thickness of 80 μm is coated on a glass plate and dried under an environment of 15 ° C. and 60% RH. Good: A good coating film without cracks. Bad: The coating film is cracked. [Abrasion resistance (toughness of coating film)] A glass plate is coated so as to have a solid film thickness of 80 μm, dried under an environment of 15 ° C. and 60% RH, and then rubbed with a nail. Good: No damage such as scratches is found on the coating film. Poor: Damaged, cracked, etc. on the coating film. [Blocking resistance] Two glass plates are coated so as to have a solid film thickness of 80 μm, respectively, at 15 ° C. and 60% R
After drying in an environment of H, the coating films are laminated together and left in an environment of 30 ° C. and 70% RH for 2 days. Good: No fusion of the coating film is observed. Bad: The coating film is fused. [Water resistance] A glass plate having a solid film thickness of 80 μm was coated, dried under an environment of 15 ° C. and 60% RH, and then kept in 40 ° C. warm water for 2 days, taken out, and then removed at 15 ° C.
And it is left for 1 hour in a room of 60% RH. Good: No change is observed in the coating film. Poor: Some damage such as clouding of the coating film.

[0040]

[Table 3]

[0041]

According to the aqueous coating composition of the present invention, a tough coating film having no cracks can be formed without using an organic solvent, and the coating film has a Tg higher than room temperature and stain resistance, It has excellent blocking resistance, water resistance, and good dryness. Further, the aqueous solution of the vinyl polymer used in the present invention is widely compatible with various polymer aqueous dispersions, so that they can be hybridized by a simple blend thereof, and a wide variety of aqueous coating compositions can be obtained. Product development can be implemented easily.

Claims (2)

[Claims] 1. (a) Methyl methacrylate 30 to 90
% By weight, (b) 0 to 30% by weight of aromatic vinyl compound,
(C) 4 to 20 wt% of acid group-containing vinyl compound and (d) 0 to 66 wt% of other copolymerizable vinyl monomer.
And a second-order transition temperature of 30 to 110 ° C., a weight average molecular weight of 6,000 to 30,000, and an acid value of 35 to 1
An aqueous vinyl polymer solution obtained by neutralizing 30 mg KOH / g of the vinyl polymer (I) with a base and dissolving it in water.
The second-order transition temperature is 30 to 120 ° C. and the weight average molecular weight is 20.
With an aqueous dispersion of polymer (II) of 20,000 to 2,000,000, the polymer solid content ratio is polymer (I) / polymer (II) = 5/95 to 60/40. An aqueous coating composition obtained by mixing as described above. 2. The aqueous coating composition according to claim 1, wherein the vinyl polymer (I) is polymerized by a suspension polymerization method.