JPH11286655A - Aqueous coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an aq. coating compsn. which can form a coating film excellent in initial hardness, softness, and alkali resistance by compounding an aq. soln. of a specific vinyl polymer, an aq. dispersion of a specific polymer, and an org. hydrazine deriv. SOLUTION: This compsn. contains (A) an aq. soln. of a vinyl polymer which is formed from (a) 20-90 wt.% methyl methacrylate, (b) 0-40 wt.% styrene, (c) 0.5-10 wt.% vinyl monomer having at least one carbonyl and/or aldehyde group, (d) 3-40 wt.% vinyl monomer having an acid group, and (e) 10-70 wt.% other vinyl monomers and has a second-order transition temp. of 0-120 deg., a wt. average mol.wt. of 6,000-60,000, and an acid value of 30-200 mgKOH/g, (B) an aq. dispersion of a polymer having a wt. average mol.wt. of 100,000 or higher, and (C) an org. hydrazine deriv. having at least two hydrazine groups.

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 capable of satisfying three points of initial hardness, flexibility and alkali resistance.

[0002]

2. Description of the Related Art In recent years, from the environmental point of view, the needs for completely water-based water-based paints and inks have been greatly increased, and many varieties have been developed. However, at present, most of them are less capable of satisfying both initial hardness and flexibility than conventional solvent systems.

In the case of aqueous dispersions, many of them have excellent flexibility, but most of them lack initial hardness. The following two points can be cited as situations where the initial hardness is insufficient. (1) When the Tg of the polymer is low, a film-forming aid or the like is not required, but the hardness of the coating film itself is insufficient. (2) When the Tg of the polymer is high, it is necessary to add a plasticizer, a film-forming aid, and the like in order to obtain a good coating film, and high hardness is developed after complete drying, but the initial hardness is insufficient. . In the case of an aqueous solution, a good film-forming property can be obtained without using a plasticizer or a film-forming aid even at a high Tg, but in order to ensure solubility in water, it is necessary to reduce the molecular weight. Lack of flexibility.

[0004] As described above, the aqueous dispersion and the aqueous solution have a complementary relationship. Therefore, many studies have been made on blending the two.

For example, Japanese Patent Publication No. 7-1770 discloses that
It is described that a vinyl dispersion having a high acid value produced by an emulsion polymerization method is blended with a vinyl dispersion having a low acid value in order to achieve both physical properties and film forming properties. In Japanese Patent Application Laid-Open No. 7-48537, a vinyl polymer aqueous solution containing no organic solvent is blended with an aqueous dispersion of a specific polymer, whereby water resistance, stain resistance, blocking resistance, and toughness are improved. Aqueous coating compositions capable of forming various coating films have been proposed.

However, another major drawback of aqueous solutions is the lack of alkali resistance. this is,
In order to express the solubility of vinyl based aqueous solution in water,
This is due to the carboxylic acid being introduced into the polymer chain. By neutralizing this carboxylic acid with a base to form a salt, the solubility of the aqueous solution in water is developed. However, when a volatile base is used, the base is volatilized during drying, and the aqueous solution is dissolved. Will be insoluble in water. Therefore, when it comes into contact with the alkaline water again, the solubility in the water is expressed again, and the alkali resistance is largely insufficient.

[0007] As described above, at present, a technique capable of simultaneously providing flexibility, initial hardness, and alkali resistance has not been established.

Accordingly, an object of the present invention is to provide an aqueous coating composition capable of achieving three points of initial hardness, flexibility and alkali resistance.

[0009]

Means for Solving the Problems As a result of intensive studies to achieve the above object, an aqueous medium, an aqueous dispersion of a high molecular weight polymer, and a carbonyl group and / or an aldehyde group capable of reacting with a hydrazine residue were obtained. The aqueous solution introduced and 1
It has been found that the above object can be achieved by the presence of an organic hydrazine derivative having a hydrazine residue in the molecule.

That is, the present invention relates to (a) 20-90% by weight of a methyl methacrylate unit and (b) 0-90% of a styrene unit.
40% by weight, (c) 0.5 to 10% by weight of a vinyl monomer unit having at least one carbonyl group and / or aldehyde group in the molecule, (d) vinyl monomer unit having an acid group 3 to 40% by weight, (e) 10 to 70% by weight of other vinyl monomer units, a secondary transition temperature of 0 to 120 ° C, and a weight average molecular weight of 6,000 to 60,0
An aqueous solution [A] of a vinyl polymer obtained by neutralizing a vinyl polymer [I] having an acid value of 30 to 200 mgKOH / g with a base and dissolving it in water, having a weight average molecular weight of 100, And an organic hydrazine derivative [C] having two or more hydrazine residues, and a mixing ratio [I] / [II] of the polymer. ] Is 1/99 to 70/30, and the hydrazine residue of the organic hydrazine derivative is 0.1 to 2 mol per 1 mol of the carbonyl group and / or aldehyde group contained in the polymer [I]. The present invention relates to an aqueous coating composition characterized by being blended into a water-based coating composition.

In the above composition, when the vinyl polymer [I] is produced by a suspension polymerization method,
Better alkali resistance.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The vinyl polymer [I] of the present invention comprises (a) methyl methacrylate units of 20 to 90.
(B) 0 to 40% by weight of a styrene unit, (c) 0.5 to 10% by weight of a vinyl monomer unit having at least one carbonyl group and / or aldehyde group in a molecule, (d) Vinyl monomer unit having an acid group 3 to 40
%, And 10 to 70% by weight of (e) other copolymerizable vinyl monomer units.

When the amount of the methyl methacrylate unit of the component (a) is less than 20% by weight, the initial hardness is insufficient no matter how the aqueous dispersion [B] is selected. On the other hand, if it exceeds 90% by weight, the flexibility becomes insufficient, no matter how the aqueous dispersion [B] is selected. The content of this methyl methacrylate unit is
Preferably from 30 to 80% by weight, more preferably from 40 to 7% by weight.
The range is 0% by weight.

The styrene unit of the component (b) can be introduced as needed for the purpose of improving the solubility of the vinyl polymer [I] in water. It can be contained up to 40% by weight as a constituent. When the styrene unit of the component (b) exceeds 40% by weight, the compatibility with the aqueous dispersion [B] tends to be insufficient. The content of the styrene unit is preferably 3 to 30% by weight, more preferably 3 to 2% by weight.
It is in the range of 5% by weight.

Component (c), a vinyl monomer unit having at least one carbonyl group and / or aldehyde group in the molecule, undergoes a crosslinking reaction with an organic hydrazine derivative [C] having a hydrazine residue. It is indispensable as a part to be formed, and it is necessary to contain 0.5 to 10% by weight. If it is less than 0.5%, the alkali resistance becomes insufficient, and if it exceeds 10% by weight, the compatibility with the aqueous dispersion [B] becomes insufficient. The content of the vinyl monomer unit is preferably in the range of 1 to 5% by weight.

At least one component (c) is present in the molecule.
The vinyl monomer unit having one carbonyl group and / or aldehyde group is formed from a monomer having at least one keto group and / or aldehyde group in the molecule and a copolymerizable double bond. The "carbonyl group" does not include a carbonyl group contained in a carboxyl group, an ester group or an amide group. For example, acrolein, diacetone acrylamide, vinyl methyl ketone, (meth) acrylamide pivalinaldehyde, diacetone (meth) acrylate, acetonyl acrylate, 2-hydroxypropyl acrylate acetyl acetate, acetoacetoxyethyl (meth) acrylate, butanediol-1, Examples thereof include 4-acrylate-acetyl acetate and acrylamidomethylanisaldehyde, among which acrolein, diacetone acrylamide and vinyl methyl ketone are particularly preferred. These monomers can be used alone or in combination depending on the application.

The acid value is imparted to the vinyl polymer [I] by copolymerizing a vinyl monomer having an acid group such as a carboxylic acid group or a sulfonic acid group. The water solubility is good when a vinyl monomer having the copolymer is copolymerized, and particularly good when methacrylic acid or acrylic acid is copolymerized.

Specific examples of the monomer which forms the vinyl monomer unit having an acid group as the component (d) include monobasic acids such as acrylic acid, methacrylic acid, crotonic acid, and fumaric acid. Examples thereof include dibasic acids such as maleic acid and itaconic acid and partial esters thereof. These may be used alone or as a mixture. The content of the vinyl monomer unit having an acid group must be 3 to 40% by weight,
Preferably it is in the range of 6 to 25% by weight.

The acid value in the present invention is determined by titrating KOH dissolved in ethanol dropwise to an aqueous vinyl polymer solution based on the color change point of phenolphthalein. When the amount of KOH required to neutralize 1 g of the vinyl polymer [I] is shown in mg, the acid value is 30 to 20.
0 mgKOH / g, preferably 40 to
130 mgKOH / g. When the amount is less than 30 mgKOH / g, the solubility of the vinyl polymer [I] in water is insufficient. When the amount exceeds 200 mgKOH / g, the aqueous dispersion [B] is used.
Lacks compatibility with

The monomer forming the other vinyl monomer unit of the component (e) is not particularly limited, and may be any of those having at least one polymerizable vinyl group. It can be arbitrarily selected according to. For example, ethyl (meth) acrylate, n-butyl (meth)
Acrylate, i-butyl (meth) acrylate, t-
Butyl (meth) acrylate, cyclohexyl (meth)
(Meth) acrylic acid alkyl ester having an alkyl group having 1 to 18 carbon atoms such as acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, and stearyl (meth) acrylate, or alkyl methacrylate, α-methyl Aromatic vinyl compounds such as styrene and benzyl (meth) acrylate, and others, 2-hydroxyethyl (meth) acrylate,
Hydroxyalkyl (meth) acrylates such as hydroxypropyl (meth) acrylate, ethylene glycol di (meth) acrylate, butylene glycol (meth)
Glycol di (meth) acrylates such as acrylates,
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,
Known polymerizable vinyl monomers such as vinyl propionate, (meth) acrylonitrile, and paramethylstyrene are exemplified.

The secondary transition temperature of the vinyl polymer [I] is as follows:
Must be 0 to 120 ° C. as measured by the DSC method,
Preferably it is 35-105 degreeC. If the temperature is lower than 0 ° C., the initial hardness becomes insufficient. On the other hand, when the temperature exceeds 120 ° C., the flexibility is insufficient no matter how the aqueous dispersion [B] is selected.

The molecular weight of the vinyl polymer [I] is determined by GPC
Weight average molecular weight of 6,000 to 6
000, preferably from 8,000 to
30,000. If it is less than 6,000, flexibility will be insufficient no matter how the aqueous dispersion [B] is selected. On the other hand, when it exceeds 60,000, the aqueous dispersion [B]
And compatibility with

The method for polymerizing the monomer mixture containing the components (a) to (e) is not particularly limited, but a suspension polymerization method is preferred. The polymer obtained by the suspension polymerization method has better compatibility with the aqueous dispersion [B].

As the polymerization catalyst, a conventionally known initiator such as an azo initiator such as azobisisobutyronitrile and a peroxide initiator such as benzoyl peroxide may be used.
It can be used arbitrarily according to the purpose.

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

As the dispersant in the suspension polymerization, 70 to
Known water-soluble polymers such as polyvinyl alcohol and sodium poly (meth) acrylate having a saponification degree in the range of 100% can be used.

In the case of performing the solution polymerization, the solvent used is not particularly limited as long as it can dissolve the monomer and polymer used in the present invention.
Alcohols such as ethanol, isopropyl alcohol, n-butanol, ethyl cellosolve, cellosolve acetate, butyl carbitol, glycols such as propylene glycol methyl ether, acetates such as ethyl acetate and butyl acetate, methyl ethyl ketone, methyl isobutyl ketone And the like.

The method for dissolving the vinyl polymer [I] obtained as described above in water is such that 30 to 100% of the acid of the vinyl polymer is neutralized with a base to form a salt, It is performed by imparting properties.

Examples of the base include ammonia, triethylamine, propylamine, diethylamine, tripropylamine, dibutylamine, amylamine, 1-aminooctane, ethanolamine, dimethylaminoethanol, ethylaminoethanol, diethylaminoethanol, 1-amino- 2-propanol, 2-amino-1
-Propanol, 3-amino-1-propanol, 1-
Dimethylamino-2-propanol, 3-dimethylamino-1-propanol, 2-amino-1-butanol,
Volatile bases such as 2-propylaminoethanol, ethoxypropylamine, aminobenzyl alcohol, aminophenol, aminothiophenol, 3-diethylamino-1,2-propanediol, diethanolamine, triethanolamine, aminoacetophenone, morpholine and the like. .

Polymer [II] Constituting Aqueous Dispersion [B]
Is not particularly limited as long as the weight-average molecular weight is 100,000 or more, but may be acrylic, alkyd, urethane, epoxy, polyester, vinyl chloride, vinyl acetate and other vinyl-based, nitrocellulose, Cellulose-based resin materials such as cellulose acetate butyrate are exemplified. Weight average molecular weight of 100,00
If it is less than 0, the flexibility is insufficient. The method for producing the aqueous dispersion [B] of the polymer [II] is not particularly limited, but is a method based on emulsion polymerization, in which a polymer containing an acid such as a carboxylic acid is dissolved in a hydrophilic organic solvent. Or a method of neutralizing a polymer organic solvent solution prepared by solution polymerization in a hydrophilic organic solvent with a base, and dispersing the solution in water,
Various industrially used production methods such as a method in which a polymer is dissolved in a hydrophilic organic solvent and dispersed in water containing a surfactant by applying a high shear force can be used.

The blend ratio of the aqueous solution [A] of the vinyl polymer [I] and the aqueous dispersion [B] of the polymer [II] used in the present invention is the polymer ratio (weight ratio) [I ]
/ [II] needs to be 1/99 to 70/30, and it is particularly preferable that [I] / [II] is 5/95 to 40/60. If the polymer ratio [I] / [II] is less than 1/99, the initial hardness will be insufficient. Also, the polymer ratio [I]
If / [II] exceeds 70/30, the flexibility is insufficient.

The method of blending the aqueous solution [A] and the aqueous dispersion [B] is not particularly limited, and examples thereof include a method of blending both at room temperature and a method of blending both while heating.

The organic hydrazine derivative [C] having two or more hydrazine residues may be used in an amount of 0.1 to 2 mol per 1 mol of the carbonyl group and / or aldehyde group contained in the polymer [I]. Be blended. If it is less than 0.1 mol, the alkali resistance becomes insufficient, and if it exceeds 2 mol, the compatibility with the aqueous dispersion [B] becomes insufficient.

The organic hydrazine derivative [C] includes 2
Dicarboxylic acid dihydrazides having from 10 to 10, especially from 4 to 6, carbon atoms, such as oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, adipic acid dihydrazide, isophthalic acid dihydrazide, sebacic acid dihydrazide, maleic acid dihydrazide, maleic dihydrazide, Fumaric acid dihydrazide and itaconic acid dihydrazide. Aliphatic water-soluble dihydrazines having 2 to 4 carbon atoms include, for example, ethylene-1,2.
-Dihydrazine, propylene-1,3-dihydrazine,
There is butylene-1,4-dihydrazine. Among these, adipic dihydrazide, isophthalic dihydrazide, sebacic dihydrazide, and succinic dihydrazide are preferable from the viewpoint of alkali resistance.

Aqueous solution [A], aqueous dispersion [B] and 2
Various pigments can be dispersed after blending the organic hydrazine derivative [C] having two or more hydrazine residues.

Further, in order to exhibit high performance as a paint and an ink, additives such as an antifoaming agent, a pigment dispersant, and a preservative can be added. Further, an organic solvent may be appropriately added to enhance the drying property.

[0037]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments. In the examples, "parts" and "%" indicate "parts by weight" and "% by weight", respectively.

<Production of vinyl polymer> Production of vinyl polymer (1) Deionized water 200 was introduced into a polymerization apparatus equipped with a stirrer, a thermometer, a reflux condenser and capable of both heating and cooling. Parts and polyvinyl alcohol (80% saponification degree, 17 polymerization degree)
00) 0.6 parts was added and the mixture was stirred to completely dissolve the polyvinyl alcohol. Thereafter, the stirring was stopped once, and 66 parts of methyl methacrylate, 10 parts of styrene, 10 parts of n-butyl acrylate, 4 parts of diacetone acrylamide,
10 parts of methacrylic acid was added and stirring was started again. Then, 0.5 parts of azobisisobutyronitrile and 4 parts of n-dodecylmercaptan were added, and the temperature was raised to 75 ° C. The reaction was carried out for 3 hours so that the reaction temperature was maintained at 75 to 80 ° C, and then the temperature was raised to 95 ° C. The reaction was terminated by heating and maintaining for 1 hour. The obtained polymer had a molecular weight of 12,000 and an acid value of 65 mg KO.
H / g and the secondary transition temperature were 84 ° C.

Production of Vinyl Polymers (2) to (27) In the same manner as in the method for producing the vinyl polymer (1),
Vinyl monomers having the composition shown in Table 1 were polymerized using the radical initiator and the chain transfer agent shown in Table 1, respectively.
Table 2 shows the characteristic values of the obtained polymer. The units of the numerical values in Table 1 are parts by weight.

[0040]

[Table 1]

[0041]

[Table 2] Production of vinyl polymer (28) Isopropyl alcohol 1 was introduced into a polymerization apparatus equipped with a stirrer, thermometer, reflux condenser and capable of both heating and cooling.
00 parts, methyl methacrylate 64 parts, styrene 10
Parts, 11 parts of n-butyl acrylate, 2 parts of acetoacetoxyethyl methacrylate, 13 parts of methacrylic acid, 2 parts of azobisisobutyronitrile and 3 parts of n-dodecylmercaptan, and the mixture was stirred and heated to 80 ° C. The polymerization was started. Next, 0.2 parts of azobisisobutylnitrile was added every hour, and the temperature was maintained for 9 hours to terminate the polymerization. An isopropanol solution of a vinyl polymer having a solid content of 51% and a viscosity of 10,000 cps was obtained. Thereafter, the solution was put into a vat, and isopropanol was evaporated in a dryer heated to 50 ° C., and the solid content was 99.5%.
To obtain a vinyl polymer solid. The resulting polymer is
The molecular weight was 13,000, the acid value was 85.5 mgKOH / g, and the secondary transition temperature was 84 ° C.

Production of vinyl polymer (29) Isopropyl alcohol 1 was placed in a polymerization apparatus equipped with a stirrer, a thermometer and a reflux condenser and capable of both heating and cooling.
Then, stirring was started and the temperature was raised to 80 ° C., and 64 parts of methyl methacrylate, 9 parts of styrene, 11 parts of n-butyl acrylate, 3 parts of diacetone acrylamide, 13 parts of methacrylic acid, azobisisobutyronitrile were added. 3 parts of the mixture were added dropwise over 4 hours. Thereafter, 0.1 part of azobisisobutylnitrile was added every hour, and the temperature was maintained for 4 hours to terminate the polymerization. Thereafter, the solution was put into a vat, and isopropanol was evaporated in a drying machine heated to 50 ° C. to obtain a vinyl polymer solid having a solid content of 99.5%. The obtained polymer had a molecular weight of 11,00.
0, acid value 85.5mgKOH / g, secondary transition temperature 84 ° C
Met.

<Production of aqueous solution of vinyl polymer>
A vinyl polymer (1) into a 300 mL flask equipped with a thermometer and a reflux condenser and capable of both heating and cooling
50 g and 148 g of deionized water were added, stirring was started, and 3.5 g of 28% aqueous ammonia was gradually added. Thereafter, the temperature was raised to 50 ° C., and the temperature was maintained for 2 hours to complete the dissolution. A solution having a solid content of 25% and a viscosity of 500 cps was obtained.

For the vinyl polymers (2) to (29), the addition amounts of 28% ammonia water and deionized water were calculated according to the following calculation method, and the dissolution operation was performed in the same manner. However, the vinyl polymer (21) could not be dissolved.

Required ammonia water (g) = A {56.1}
1000 × 50 × 17 ÷ 0.28 A: Acid value of polymer (mgKOH / g) Required deionized water (g) = 150−aqueous ammonia (g) ×
0.72 <Production of Polymer Aqueous Dispersion> Production of Polymer Aqueous Dispersion (a) Deionization into a polymerization apparatus equipped with a stirrer, thermometer, reflux condenser and capable of both heating and cooling. 100 parts of water, 2 parts of polyoxyethylene nonylphenyl ether having 35 oxyethylene units, 1 part of sodium lauryl sulfate
And 0.5 part of potassium persulfate were dissolved, stirring was started and the temperature was raised to 70 ° C. Then, a mixture of 57 parts of methyl methacrylate, 25 parts of n-butyl methacrylate, 15 parts of n-butyl acrylate, and 3 parts of methacrylic acid was added to 4 parts.
The temperature was raised to 80 ° C., and the temperature was maintained for 2 hours to terminate the reaction, thereby obtaining an aqueous polymer dispersion.
The resulting polymer had a second transition temperature of 52 ° C., a weight average molecular weight of 1,000,000, and an aqueous dispersion thereof had a solid content of 50% and a viscosity of 3,000 cps.

Preparation of Aqueous Polymer Dispersion (b) By a production method similar to that for the above aqueous polymer dispersion (a), a vinyl monomer comprising 85 parts of styrene, 14 parts of ethylhexyl acrylate and 1 part of methacrylic acid was prepared. When the mixture was polymerized, the secondary transition temperature was 67 ° C., and the weight average molecular weight was 500,0.
00 polymer was obtained, the aqueous dispersion of which had a solids content of 50
% And a viscosity of 800 cps.

Preparation of Polymer Aqueous Dispersion (c) 25 parts of isopropyl alcohol, 42 parts of methyl methacrylate, and styrene were placed in a polymerization apparatus equipped with a stirrer, a thermometer, a reflux condenser and capable of both heating and cooling. 23
Parts, n-butyl methacrylate 28 parts, a vinyl monomer mixture of acrylic acid 7 parts, and azobisisobutyronitrile 0.1 part. Thereafter, the temperature was raised to 80 ° C., and the temperature was maintained for 7 hours while adding 0.1 part of azobisisobutyronitrile every other hour, and then cooled to 50 ° C. Then, 3.1 parts of 28% ammonia water and 150 parts of deionized water are gradually added, and then the temperature is raised to 95 ° C. over 3 hours, and isopropyl alcohol is distilled off to about 1% of the initial charge, and heavy water is removed. A combined aqueous dispersion was obtained. The resulting polymer had a secondary transition temperature of 76 ° C. and a weight average molecular weight of 350,000, and the aqueous dispersion had a solid content of 40% and a viscosity of 200 cps. Production of Polymer Dispersion (d) In a 1000 mL reaction vessel equipped with a stirrer, thermometer, and condenser, 13 parts of dimethylolpropionic acid, 80 parts of N-methyl-2-pyrrolidone, 100 parts of polytetramethylene glycol, and trimethylol Add 5 parts of propane,
The mixture was heated and dissolved at 90 ° C. Next, 48 parts of isophorone diisocyanate was added, and after stirring for 10 minutes, 0.1 part of dibutyltin dilaurate was added, the temperature was raised to 95 ° C., and the reaction was carried out for 1 hour.

After the above hydrophilic group-containing oligomer was neutralized with 5 parts of triethylamine, 300 parts of deionized water was added, and the mixture was stirred for 1 hour to obtain an aqueous dispersion. The resulting polymer had a secondary transition temperature of 40 ° C., a weight average molecular weight of 220,
000 and the aqueous dispersion had a solids content of 29% and a viscosity of 8000 cps.

Production of Polymer Dispersion (e) 25 parts of isopropyl alcohol, 42 parts of methyl methacrylate, and 2 parts of styrene were placed in a polymerization apparatus equipped with a stirrer, a thermometer, and a condenser and capable of both heating and cooling.
3 parts, 28 parts of n-butyl methacrylate, 7 parts of acrylic acid, a vinyl monomer mixture, and 2 parts of azobisisobutyronitrile were added. Then, the temperature was raised to 80 ° C., and azobis The temperature was maintained for 7 hours while charging 0.1 part of isobutyronitrile. Thereafter, it is cooled to 50 ° C., and 3.1 parts of 28% ammonia water and 1 part of deionized water
50 parts were gradually charged. Subsequently, the temperature was raised to 95 ° C. over 3 hours, and isopropyl alcohol was added to 1% of the initial charge.
After distilling off to an extent, an aqueous dispersion of the polymer was obtained. The secondary transition temperature of the obtained polymer was 76 ° C., the weight average molecular weight was 80,000, and the aqueous dispersion had a solid content of 50% and a viscosity of 200 cps.

Example 1 60 g of a 25% solids aqueous solution of a vinyl polymer (1), and an aqueous polymer dispersion (a) 120
g and 0.3 g of adipic dihydrazide were charged into a beaker, and mixed gently with a stick to prepare a blend. In this case, the polymer ratio between the vinyl polymer (1) and the aqueous polymer dispersion (a) is 20:80. Further, the ratio of the hydrazine residue is 1 mol per 1 mol of the carbonyl group in the vinyl polymer (1).

No precipitate was observed immediately after blending, and the compatibility as a solution was very good.

Further, the blend was applied to a zinc phosphate-treated steel sheet (Bonderite # 144 manufactured by Japan Test Panel) so as to have a solid film thickness of 25 μm, dried at 25 ° C. and 60% RH for 6 hours, and then measured for pencil hardness. As a result, the initial hardness was as good as 3B.

After drying the coating film in this state for 7 days,
A rubbing test was carried out 30 times with a gauze containing the aqueous ammonia solution No. 1, and the coating film was good with no damage such as scratches or abrasion. Further, a 0T bend test was carried out, and no cracks were generated and the test was good.

<Examples 2 to 20, Comparative Examples 1 to 15> Tables 3 to 8 show the results of tests performed in the same manner as in Example 1. In addition, the evaluation result of each test shows the following contents. ○ Good compatibility: no precipitates are seen from the beginning of blending. Slightly good: precipitates are seen at the beginning of blending but disappear after one day. Poor: there are precipitates. ○ Alkali resistance is good. No damage such as scratches, abrasion, etc. is seen. Slightly good: The coating film is not damaged by rubbing 15 times or more, but is damaged by rubbing 30 times or more. Defective: Damage occurs by rubbing less than 15 times. ○ Good flexibility: no cracks are generated. Bad: cracks are generated. ○ Initial hardness is good: 4B and harder than 4B. Bad: 5B or softer than 5B.

[0055]

[Table 3]

[0056]

[Table 4]

[0057]

[Table 5]

[0058]

[Table 6]

[0059]

[Table 7]

[0060]

[Table 8]

[0061]

As described above, the aqueous coating composition of the present invention has excellent initial hardness, flexibility and alkali resistance.

The aqueous coating composition of the present invention contains a specific vinyl polymer, and an aqueous solution of the vinyl polymer is well compatible with various aqueous polymer dispersions. Therefore, according to the present invention, an aqueous coating composition having such excellent performance can be provided by a simple blend of an aqueous solution of a vinyl polymer and various polymer aqueous dispersions. . This is a breakthrough in the art where hybridization of both was desired.

Claims (2)

[Claims] (1) a methyl methacrylate unit of 20 to
90% by weight, (b) 0 to 40% by weight of styrene unit,
(C) at least one carbonyl group and / or
Or a vinyl monomer unit having an aldehyde group 0.5
10 to 10% by weight, (d) 3 to 40% by weight of a vinyl monomer unit having an acid group, (e) Other vinyl monomer unit 1
0-70% by weight, having a secondary transition temperature of 0-120.
Aqueous solution of a vinyl polymer obtained by neutralizing a vinyl polymer [I] having a weight average molecular weight of 6,000 to 60,000 and an acid value of 30 to 200 mgKOH / g with a base and dissolving the same in water. Dissolution [A], Polymer [I] having a weight average molecular weight of 100,000 or more
I] an aqueous dispersion [B], and an organic hydrazine derivative [C] having two or more hydrazine residues,
The mixing ratio [I] / [II] of the polymer is 1/99 to 70
/ 30, characterized in that the hydrazine residue of the organic hydrazine derivative is 0.1 to 2 mol per 1 mol of the carbonyl group and / or aldehyde group contained in the polymer [I]. Aqueous coating composition. 2. The aqueous coating composition according to claim 1, wherein the vinyl polymer [I] is produced by a suspension polymerization method.