JPH10176122A - Water-based coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a water-based coating composition having excellent film- forming properties and giving a coating film excellent in adhesion to substrates, low-temperature flexibility and staining resistance by mixing two emulsions of vinyl polymers having specified grass transition temperatures (Tg) so that the Tg of the resultant polymer of the mixed emulsion may have a specified Tg. SOLUTION: This composition is formed by mixing emulsion A containing a polymer having a Tg of 40-80 deg.C and obtained by polymerizing a vinyl monomer in an aqueous medium with emulsion B containing a polymer of a Tg of -10 to 20 deg.C and obtained in the similar manner so that the Tg of the resultant polymer in the mixed emulsion may be 25-50 deg.C. It is desirable that the polymer in each of emulsions A and B is a copolymer comprising the above monomer and 0.1-10wt.%, based on the polymer, an amido-bond-containing vinyl monomer represented by the formula (wherein X is H or methyl; R is a 1-10C group; Y is a 1-6C group; and Z is H or a 1-6C group) and still having the above specified Tg in order to improve the water-resistant adhesion of a coating film formed from the water-based coating composition to a substrate in a wet state.

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, and more particularly, to an aqueous coating composition having good film-forming properties, good adhesion to various substrates such as metals, plastics, woods, and papers. The present invention relates to an aqueous coating composition having excellent flexibility and capable of forming an excellent coating film, such as having less adhesion of dirt due to contaminants contained in rainfall.

[0002]

2. Description of the Related Art In recent years, from the viewpoint of the environment, the need for aqueous coating compositions has been greatly increased, and various aqueous coatings have been developed. For example, aqueous dispersions such as emulsions and dispersions are present because the polymer is dispersed in water.
It has a feature that a high molecular weight polymer can be used, and has an advantage that an aqueous coating composition having excellent coating film properties after coating can be prepared.

However, recently, in paints used for outdoor use, in addition to weather resistance, contamination of the paint film due to rainfall has become a problem, and it is desired to solve this problem regardless of whether it is a solvent or water system. ing. One method of solving this problem is to set the glass transition temperature of the resin constituting the coating film high to harden the coating film, but the aqueous coating takes a form such as an emulsion or dispersion. In the composition, generally, when the glass transition temperature of the resin is set high, the film-forming property is significantly reduced, and the film-forming aid added to compensate for this, on the contrary, promotes the contamination of the coating film, It has problems such as losing flexibility at low temperatures and cracking of the coating film at low temperatures in winter.

[0004]

The inventors of the present invention have conducted intensive studies with the aim of solving the above-mentioned problems, and as a result, have used an emulsion having a glass transition temperature in a specific range, and set the emulsion within a specific range. The inventor has found that an aqueous coating composition that can solve the above-mentioned problems can be obtained by blending, and the present invention has been completed.

That is, according to the present invention, a polymer obtained by polymerizing a vinyl monomer in an aqueous medium has a glass transition temperature of 4
An emulsion (A) having a temperature of 0 to 80C and an emulsion (B) having a glass transition temperature of -10 to 20C of a polymer obtained by polymerizing a vinyl monomer in an aqueous medium are blended. An aqueous coating composition characterized in that the glass transition temperature of the polymer in the emulsion obtained by blending is 25 to 50 ° C.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail.

[0007] The aqueous coating composition of the present invention is an emulsion in which a polymer obtained by polymerizing a vinyl monomer in an aqueous medium has a glass transition temperature (hereinafter abbreviated as Tg) of 40 to 80 ° C. (A) (hereinafter referred to as emulsion (A)) and an emulsion (B) (hereinafter referred to as emulsion) having a Tg of -10 to 20 ° C of a polymer obtained by polymerizing a vinyl monomer in an aqueous medium. (B)).

Emulsion (A) and emulsion (B)
The vinyl polymerizable monomer used to constitute the above has at least one polymerizable vinyl group.
Preferred examples of the vinyl monomer that can be used include a monomer selected from methyl methacrylate, ethyl acrylate, 2-ethylhexyl acrylate, methacrylic acid, and the like. The body can also be used.

Specific examples of other copolymerizable vinyl monomers that can be used in combination include methyl acrylate, ethyl methacrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, and t-butyl (meth). C1 such as acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl methacrylate, lauryl (meth) acrylate, and stearyl (meth) acrylate
(Meth) acrylic acid alkyl ester having an alkyl group of from 18 to 18; aromatic vinyl compounds such as styrene, α-methylstyrene and p-methylstyrene; 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate Hydroxyalkyl (meta)
Acrylates; glycol di (meth) acrylates such as ethylene glycol di (meth) acrylate and butylene glycol di (meth) acrylate; alkylamino (meth) such as dimethylaminoethyl (meth) acrylate
Acrylate; dimethylaminoethyl (meth) acrylate methyl chloride salt, allyl (meth) acrylate, trimethylolpropane tri (meth) acrylate, glycidyl (meth) acrylate, vinyl acetate, vinyl propionate, (meth) acrylonitrile, benzyl (meth) Examples include a polymerizable vinyl monomer such as acrylate.

The emulsion (A) and the emulsion (B) are composed of at least one of the above-mentioned vinyl monomers. In the emulsion (A), the Tg of the polymer is between 40 and 80 ° C., preferably It is necessary that the Tg of the polymer be between 45 and 70 ° C., and in the emulsion (B), the Tg of the polymer must be between -10 and 20 ° C., preferably between -5 and 15 ° C. is there.

This is because when the Tg of the emulsion (A) is lower than this range, there is no effect on the improvement of stain resistance. On the other hand, when the Tg is higher, the aqueous coating composition is obtained by blending with the emulsion (B). This is because the glossiness of the paint tends to decrease, and the T of the emulsion (B) is reduced.
If the value of g is higher than this range, the flexibility at low temperatures decreases, while if the value of Tg decreases, the stain resistance decreases.

Emulsion (A) and emulsion (B)
Is required to be such that the Tg of the polymer in the emulsion obtained by blending is 25 to 50 ° C., preferably 30 to 45 ° C. This is because if Tg exceeds the above range, the flexibility decreases, while if Tg is below the above range, the effect of improving the stain resistance decreases.

In the present invention, the Tg of the polymer in the emulsion (A) and the emulsion (B) means a theoretical value calculated by the following Fox equation.

[0014]

1 / Tg = Σ (Wi / Tgi)

(Wherein, Wi: weight fraction of each copolymer component,
Tgi: represents Tg of a homopolymer of each copolymer component. )

The Tg of the polymer in the emulsion obtained by blending the emulsion (A) and the emulsion (B) is as follows: the Tg of the polymer of the emulsion (A) and the polymer of the emulsion (B) and the blend thereof. It can be calculated from the amount (polymer blending ratio).

The aqueous coating composition of the present invention basically comprises an emulsion (A) and an emulsion (B) of a polymer comprising the above-mentioned monomers. In order to improve the water-resistant adhesion to a substrate in a wet state, an amide bond-containing vinyl system having a ureide ring represented by the following general formula (I) and a ring structure similar thereto within the range of Tg defined above. It is preferable to copolymerize the monomer (a).

[0018]

Embedded image

Wherein X is a hydrogen atom or a methyl group;
Represents a group containing 1 to 10 carbons, Y represents a group containing 1 to 6 carbons, Z represents a hydrogen atom or a group containing 1 to 6 carbons. )

In the above formula (I), R is preferably a hydrocarbon group. More preferably, it is a hydrocarbon group having 1 to 4 carbon atoms. In the general formula (I), Y is preferably an alkylene group, more preferably an alkylene group having 1 to 4 carbon atoms. Z is preferably a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. Amide bond-containing vinyl monomer (a) represented by the above general formula (I)
Specific examples of (meth) acrylamide-methyl-
Methylene urea, (meth) acrylamido-ethyl-methylene urea, (meth) acrylamido-ethyl-ethylene urea, (meth) acrylamido-ethyl-butylene urea, (meth) acrylamido-butyl-ethylene urea and the like. Meth) acrylamide-R-ethylene urea (R is a group containing 1 to 10 carbons) is preferred from the viewpoint of copolymerizability. These monomers can be used alone or in combination of two or more.

The copolymerization amount of the amide bond-containing vinyl monomer (a) is preferably in the range of 0.1 to 10% by weight, more preferably 0.3 to 8% by weight, based on the polymer. And more preferably in the range of 0.3 to 5% by weight.

This is because when the copolymerization amount of the amide bond-containing vinyl monomer (a) is less than 0.1% by weight, there is no effect in improving the adhesion of the coating film to the base material in a wet state, and 10% by weight. If the copolymerization exceeds the above, the stability of the dispersion is impaired during the polymerization, and there is a possibility that the polymerization may not be performed stably.

Further, in the emulsion (A) and the emulsion (B) used in the present invention, an emulsion of a polymer obtained by copolymerizing a vinyl monomer (b) containing a carbonyl group and / or an aldehyde group is used. In addition, it is preferable that an organic hydrazine compound having two or more hydrazine residues is contained in an aqueous medium which is a main dispersion medium of the emulsion.

This further improves the flexibility and stain resistance of the coating film formed from the aqueous coating composition, and maintains more water- and solvent-resistance while maintaining high substrate adhesion in a wet state. This is because it can be improved.

The carbonyl group and / or aldehyde group-containing vinyl monomer (b) referred to in the present invention has at least one carboxylic acid group, ester group or amide group in the molecule.
It is a monomer having two keto groups or aldehyde groups and a polymerizable double bond. The type of such a monomer is not particularly limited as long as it can be copolymerized with other monomer components to be used, and is preferably used in an amount of 1 to 20% by weight based on the polymer. Preferably it is in the range of 2 to 13% by weight, more preferably 2 to 10% by weight.

This is because if the copolymerization amount is less than 1% by weight, the resulting coating film does not sufficiently improve the solvent resistance, water resistance, etc.
When the copolymerization exceeds 20% by weight, the reaction with the organic hydrazine compound present in water, which is the main dispersion medium, proceeds remarkably in water, and it tends to be difficult to stably store in one liquid for a long time. To be seen.

Specific examples of the carbonyl group and / or aldehyde group-containing vinyl monomer (b) include acrolein, diacetone acrylamide, formylstyrene, vinyl alkyl ketone, and the following general formula (II):

[0028]

Embedded image

Wherein X is a hydrogen atom or a methyl group;
₁ , R ₂ is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms,
R ₃ represents an alkyl group having 1 to 4 carbon atoms. (Meth) acryloxyalkylpropanal, (meth) acrylamidopivalinaldehyde, diacetone (meth) acrylate, acetonitrile acrylate, 2-hydroxypropyl acrylate-acetyl acetate, acetoacetoxyethyl (meth) acrylate, butanediol- Examples thereof include 1,4-acrylate-acetyl acetate and acrylamidomethylanisaldehyde, among which acrolein, diacetone acrylamide, vinyl methyl ketone having 4 to 7 carbon atoms,
The use of vinyl alkyl ketones such as vinyl ethyl ketone and vinyl isobutyl ketone is preferred. These monomers can be used alone or in combination of two or more.

Further, in order to improve the stability of the obtained vinyl polymer dispersion in a dispersion medium, a carboxyl group-containing vinyl monomer (c) is added to the vinyl monomers to be copolymerized. It can also be copolymerized.

The carboxyl group-containing vinyl monomer (c) used herein is represented by the following general formulas (II) and (III).

[0032]

Embedded image

[0033]

Embedded image

(Where X is a hydrogen atom or a methyl group, R is
₄ represents a group containing ₄ to 30 carbon atoms. )

The carboxyl group-containing vinyl monomer (c) represented by the above general formulas (III) and (IV), if it can be copolymerized with other monomer components to be used, particularly the kind and the amount of the monomer. Is not limited, but when it is necessary to particularly improve the adhesion to the substrate, it is preferable to select and use from the carboxyl group-containing vinyl monomer represented by the general formula (IV).

When the pH of the system needs to be in an alkaline region (pH> 7) by performing a treatment such as neutralization to improve the stability of the emulsion, a neutralizing agent is required. Partial dissolution of the polymer dispersion occurs, resulting in significant thickening of the entire system over time. Therefore, from the viewpoint of preventing this, the carboxyl group-containing vinyl monomer (c) is 0.5 to 20% by weight based on the polymer.
It is preferable to copolymerize in the range of.

Specific examples of the carboxyl group-containing vinyl monomer (c) represented by the general formulas (III) and (IV) include (meth) acrylic acid and monohydroxyethyl 1,2-cyclohexanedicarboxylate ( (Meth) acrylate, monohydroxypropyl (meth) acrylate 1,2-cyclohexanedicarboxylate, monohydroxypropyl (meth) acrylate tetrahydrophthalate, 5-
Methyl-1,2-cyclohexanedicarboxylate monohydroxyethyl (meth) acrylate, phthalate monohydroxyethyl (meth) acrylate, monohydroxypropyl phthalate (meth) acrylate, monohydroxyethyl oxalate (meth) acrylate, hexahydrophthalate And 2-methacryloyloxyethyl acid. These monomers can be used alone or in combination of two or more.

The emulsion (A) and the emulsion (B) used in the present invention are produced by emulsion polymerization.
As the emulsion polymerization method, a method in which polymerization is carried out using a water-soluble initiator using an emulsifier, or a method in which soap-free polymerization is carried out using a redox initiator such as an inorganic peroxide and a reducing agent such as sodium thiosulfate. Known methods such as a polymerization method using a chain transfer agent can be used for these polymerization methods.

The emulsifier used in the emulsion polymerization is not particularly limited, and commercially available emulsifiers can be used. Examples of the emulsifier include anionic surfactants such as alkali metal salts of alkylbenzenesulfonic acid and alkali metal salts of alkali sulfate, and polyoxyethylene lauryl. Nonionic surfactants such as ether and polyoxyethylene nonylphenyl ether are exemplified. These emulsifiers may be used alone or as a mixture.

Examples of the polymerization initiator used in the emulsion polymerization include persulfate initiators such as potassium persulfate and ammonium persulfate, and redox of a monomer-soluble peroxide with a reducing agent such as Rongalite. Known initiators such as an initiator system and the like are mentioned, and these are appropriately selected and used according to the purpose.

If necessary, a chain transfer agent such as n-dodecylmercaptan or α-methylstyrene dimer may be added to the above vinyl monomer mixture in order to adjust the molecular weight of the emulsion particles.

The method of supplying the monomer into the polymerization system at the time of emulsion polymerization is not particularly limited, and may be a known method, for example, a method of charging monomers all at once, a method of dropping monomers, a method of supplying monomers, Can be used.

The emulsion obtained by emulsion polymerization is
It is preferable from the viewpoint of the stability of the system that the pH of the system is set in a range from neutral to weakly alkaline, that is, the pH is in the range of 6.5 to 10.0, by the base after the polymerization.

Examples of the base to be added include ammonia, trimethylamine, 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
-Dimethylamino-2-propanol, 3-dimethylamino-1-propanol, 2-propylaminoethanol, ethoxypropylamine, aminobenzyl alcohol, morpholine, sodium hydroxide, potassium hydroxide and the like.

For obtaining the aqueous coating composition of the present invention, the emulsion (A) and the emulsion (B) are blended in the following manner.
From the viewpoint of the coating process, the solid content in the mixed emulsion is 40 to
It is preferable that the content be 60% by weight.

In the emulsions (A) and (B) used in the present invention, when a polymer containing a specific amount of a vinyl monomer (b) containing a carbonyl group and / or an aldehyde group is used as a dispersion, By containing an organic hydrazine compound having two or more hydrazine residues in water as a main dispersion medium, a film having improved water resistance and solvent resistance while maintaining high substrate adhesion in a wet state. And a room temperature crosslinkable one-pack type aqueous coating composition which can be obtained.

The organic hydrazine compound having two or more hydrazine residues used in the present invention can be obtained by mixing the number of moles of carbonyl groups (M) in the vinyl polymer with the number of moles of hydrazine residues (N) in the dispersion medium. ) Is 0.1 / 1 ≦ (M) /
It is preferable to add so that (N) ≦ 1 / 0.1, more preferably 0.8 / 1 ≦ (M) /
(N) ≦ 1 / 0.5. (M) / (N)
When the ratio is less than 0.1 / 1, the obtained aqueous coating composition has poor stability and tends to be difficult to store for a long period of time, and (M) / (N) is 1 / 0.1. If the ratio exceeds the above range, the solvent resistance of the formed coating film will be reduced.

Examples of the organic hydrazine compound added to the dispersion medium include 2 to 10 carbon atoms, preferably 4 to 6 carbon atoms.
Dicarboxylic acid hydrazide having a carbon number of, for example, oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, adipic acid dihydrazide, sebacic acid dihydrazide, maleic acid dihydrazide, fumaric acid dihydrazide, isophthalic acid dihydrazide, and isophthalic dihydrazide And aliphatic water-soluble dihydrazines having 2 to 4 carbon atoms, for example, ethylene-1,2-dihydrazine, propylene-1,3-
Examples thereof include dihydrazine and butylene-1,4-dihydrazine. Among these, adipic dihydrazide,
Preference is given to using sebacic dihydrazide, isophthalic dihydrazide and succinic dihydrazide.
These compounds can be used alone or in combination of two or more.

The aqueous coating composition of the present invention thus obtained exhibits a high level of performance as a coating material, and therefore includes additives such as known pigments, defoamers, pigment dispersants, preservatives, and urethane. A known resin such as water-soluble chlorinated polyolefin or the like may be added for use.

Examples of substrates to which the aqueous coating composition of the present invention can be applied and coated include iron, stainless steel, aluminum and other metals, and cement, glass and plastic.

The coating method for forming a coating film on a substrate surface of various materials using the aqueous coating composition of the present invention includes spray coating, roller coating, bar coating, air knife coating, and flow coating. Conventional known methods such as a drawing method, a brush coating method, and a dipping method can be appropriately selected and used, and there is no particular limitation.

When the aqueous coating composition of the present invention is used as a coating material, it is usually dried at a temperature in the range of room temperature to about 120 ° C. for about 10 seconds to about 24 hours to obtain a sufficiently formed coating film. Can be.

[0053]

The present invention will be described below in detail with reference to examples and comparative examples. “Parts” and “%” in the examples indicate “parts by weight” and “% by weight”, respectively.

The evaluation of each coating film performance was performed by the following method.

The coating film for evaluating the substrate adhesion, water adhesion and solvent resistance was prepared by applying an aqueous coating composition prepared according to the following formulation to a steel plate using a bar coater No. 40 and then applying the coating at room temperature. What was dried for 1 hour was used. Emulsion (single or mixed emulsion) 40 g Butyl cellosolve 2 g Kyowanol M (manufactured by Kyowa Hakko Co., Ltd., plasticizer) 2 g RHEOLATE 350 (manufactured by RHEOX, thickener) 0.6 g

(1) Substrate Adhesion A crosscut cellophane tape peeling test was performed and evaluated according to the following criteria. A: The peeled portion is less than 10%. ：: The peeled portion is 10% or more and less than 30%. Δ: The peeled portion is 30% or more and less than 90%. X: 90% or more of the peeled portion.

(2) Water Adhesion Resistance The coating surface coated on the steel sheet was allowed to stand in an environment of 50 ° C. and 98% RH for 3 days, and then subjected to a cross-cut cellophane tape peeling test, which was evaluated according to the following criteria. A: The peeled portion is less than 10%. ：: The peeled portion is 10% or more and less than 30%. Δ: The peeled portion is 30% or more and less than 90%. X: 90% or more of the peeled portion.

(3) Solvent resistance The coated surface of the steel plate was rubbed with a gauze impregnated with methyl ethyl ketone under a load of 200 g / cm ² and evaluated according to the following criteria. ：: Not melted up to the steel plate surface by double rubbing 50 times. Δ: Dissolved up to the steel plate surface by double rubbing 30 to 50 times. ×: Dissolved to the steel plate surface by double rubbing less than 30 times.

(4) Stain resistance Emulsion alone or mixed emulsion and mill base (75% titanium oxide, 20% butyl cellosolve, 5% deionized water), plasticizer (Kyowanol M Kyowa Hakko Co., Ltd.) Viscous agent (RHEOLATE350 RHE
OX) was blended at the following ratio to prepare a white gloss paint, which was coated on a steel plate using a bar coater # 40.
After drying at room temperature for one week, the gloss (60 ° gloss) and the like were measured, an exposure test was performed outdoors at 45 ° on the south side, and the color difference (Δ
L) was used as an index to evaluate the contamination. Mixing conditions: Mill base 48 g Emulsion (solid content 50% basis) 128 g Kyowanol M 10 g Thickener 2 g

(5) Low temperature flexibility Spraying white gloss paint prepared for evaluating stain resistance on a microelastic polymer cement-based main material and a waterproof multi-layer coating material according to JIS A 6909 in accordance with JIS A 6909. The coated and left standing at room temperature for one week and dried was used as an evaluation sample, and subjected to 10 cycles of a cooling / heating cycle test in which one cycle was immersion in water for 18 hours, −20 ° C. × 3 hours, and 50 ° C. × 3 hours. The evaluation was based on the following criteria. ：: No peeling, cracking, etc. occurred. ×: Peeling, cracking, etc. occurred.

The abbreviations in Table 1 represent the following monomers. MMA: methyl methacrylate MAA: methacrylic acid 2-EHA: 2-ethylhexyl acrylate t-BMA: t-butyl methacrylate i-BMA: i-butyl methacrylate n-BA: n-butyl acrylate CHMA: cyclohexyl methacrylate St: styrene DAAm: di Acetone acrylamide MAEEU: methacrylamide-ethyl-ethylene urea HH: 2-methacryloyloxyethyl hexahydrophthalate

[Production Example of Emulsion] Production of Emulsions Em1 to Em12 An aqueous solution containing 100 parts of deionized water and 40% sodium polyoxyethylene alkylphenyl ether sulfate was placed in a polymerization apparatus equipped with a stirrer, a thermometer, and a reflux condenser. 5 parts and 1 part of sodium persulfate were added, the temperature was raised to 80 ° C. while stirring, and then a monomer mixture having the composition shown in Table 1 was added dropwise over 4 hours. After completion of the dropwise addition, the temperature was maintained at 80 ° C. for 1 hour, and then the temperature was raised to 90 ° C., and the reaction was terminated after 1 hour.

After the completion of the reaction, the pH of the emulsion was adjusted to 6.5.
25% ammonia water was added so as to be in a region of about 10.0, and gradually cooled to around room temperature, and cullet and the like were removed through a 100 mesh nylon gauze to obtain an emulsion Em.
1 to Em12 were obtained. The theoretical solid content of the emulsion produced by this method was 50%, and the theoretical value was used for calculating the mixing ratio when blending the emulsion unless otherwise specified.

[0064]

[Table 1]

[Examples 1 to 7, Comparative Examples 1 to 8] Emulsions Em1 to E obtained in the above-mentioned emulsion production examples
Using m12, these were blended in the proportions shown in Table 2 to obtain various aqueous coating compositions. Table 3 shows the evaluation results of the mixed emulsion at low temperature flexibility, substrate adhesion, water adhesion, solvent resistance, and stain resistance. In Comparative Example 1, no coating film was formed.

[0066]

[Table 2]

[0067]

[Table 3]

As is apparent from Table 3, the coating films of the aqueous coating compositions of Examples 1 to 7 exhibited excellent coating performance. On the other hand, the coating films of the aqueous coating compositions of Comparative Examples 1 to 8 that did not satisfy the requirements specified in the present invention were insufficient in either low-temperature flexibility or stain resistance.

[0069]

The aqueous coating composition of the present invention has excellent film-forming properties, adhesion, low-temperature flexibility, and stain resistance, and can be used for various substrates.
For example, it is extremely useful for coating metal, plastic, wood, paper and the like.

Claims (4)

[Claims] An emulsion (A) in which a polymer obtained by polymerizing a vinyl monomer in an aqueous medium has a glass transition temperature of 40 to 80 ° C., and a vinyl monomer in an aqueous medium. The glass transition temperature of the polymer obtained by polymerization is -10 to 2
The emulsion (B) at 0 ° C. is blended, and the glass transition temperature of the polymer in the resulting emulsion is 25.
Aqueous coating composition characterized in that the temperature is adjusted to -50 ° C. 2. An emulsion (A) and an emulsion (B) are obtained by copolymerizing an amide bond-containing vinyl monomer (a) represented by the following general formula (I) with 0.1 to 10% by weight based on a polymer. The aqueous coating composition according to claim 1, which is an emulsion of a polymer. Embedded image (Wherein X is a hydrogen atom or a methyl group, R is a group containing 1 to 10 carbons, Y is a group containing 1 to 6 carbons, Z
Represents a hydrogen atom or a group containing 1 to 6 carbon atoms. ) 3. An emulsion of a polymer obtained by copolymerizing the emulsion (A) and the emulsion (B) with a vinyl monomer having a carbonyl group and / or an aldehyde group (b) in an amount of 1 to 20% by weight based on the polymer. The aqueous coating composition according to claim 1 or 2, wherein an organic hydrazine compound having two or more hydrazine residues is contained in an aqueous medium of the emulsion. 4. The emulsion (A) and the emulsion (B) are polymer emulsions obtained by copolymerizing a carboxyl group-containing vinyl monomer (c) in an amount of 0.5 to 20% by weight based on the polymer. The aqueous coating composition according to claim 1, 2 or 3, wherein: