JPH09328656A - Aqueous coating composition for metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an aqueous coating composition for metals, excellent in water resistance, processability, storage (preservation) stability, solvent resistance and low temperature curability, giving coating films having high hardness and excellent in various kinds of physical properties. SOLUTION: This aqueous coating composition comprises (A) an aqueous polymer having carboxyl groups, a basic compound and (B) an aqueous polymer having oxazoline groups. The aqueous polymer (A) is obtained by polymerizing a monomer composition containing a monomer having a carboxyl group. The aqueous polymer (B) is obtained by polymerizing a monomer composition containing an oxazoline derivative such as 2-isopropenyl-2-oxazoline. The coating composition is suitable e.g. as a coating material for PCM, cans, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aqueous metal coating composition suitable as, for example, a precoat metal coating material or a can coating material.

[0002]

2. Description of the Related Art Conventionally, pre-coated metal (hereinafter referred to as "pre-coated metal" used in various home appliances such as refrigerators and washing machines
The paints for PCM) include amino-acrylic resin type, amino-alkyd resin type, amino-oil-free type
Polyester resin-based or vinyl resin-based coating compositions are known. These coating compositions are required to have excellent stain resistance, chemical resistance and high hardness.
In addition, the coating applied to the steel plate to be processed as the outer plate of the above-mentioned product is a process such as adhesion and flexibility that can withstand processing such as press working, bending, punching etc. of the steel plate in the process after painting. Sex is required.

As the top coat paint to be applied to the steel sheet, there is known a paint containing a polyester resin as a base resin and a composition containing a melamine resin or an isocyanate compound as a curing agent as a resin component. Among them, paints in which a curing catalyst is mixed with a mixture of a polyester resin and a melamine resin, particularly a methyl etherified methylol melamine resin are often used.

Further, for example, in Japanese Patent Application Laid-Open No. 4-342779, a coating material composed of a fluorine-modified epoxy resin, a polyester resin and an amino resin which is excellent in chemical resistance and stain resistance and forms a coating film of high hardness. The composition is PCM
It is disclosed to be used as a paint for a car. Further, Japanese Patent Application Laid-Open No. 4-366187 discloses a coating composition comprising a polyester resin, a melamine resin and a curing catalyst as a coating for a coated steel sheet for processing articles.

[0005]

However, the above-mentioned conventional coating composition has the following problems. That is, for example, in the coating composition, in the case of an aqueous coating composition comprising a carboxyl group-containing aqueous polymer, a water-soluble melamine, and a curing agent, as compared with a solvent-based coating composition, water resistance is poor. Further, there is a problem that equipment or the like for painting work is contaminated by volatilization or evaporation of low molecular weight compounds.

Further, the coating film formed from the above-mentioned coating composition generally lacks hardness and is poor in stain resistance.
It has practical problems. On the other hand, a coating film having a hardness of a certain level or more has good stain resistance, but lacks flexibility, etc., and has a problem that cracks or peeling may occur due to pressing, bending, punching, etc. are doing.

As described above, the conventional paint compositions such as paints for PCM are currently restricted in use for the above reasons, and have a problem that they cannot meet various requirements. There is.

The present invention has been made in view of the above-mentioned conventional problems, and its object is excellent in water resistance, processability, storage (storage) stability, solvent resistance, and low temperature curability, and An object of the present invention is to provide an aqueous metal coating composition having high hardness and excellent physical properties.

[0009]

Means for Solving the Problems The inventors of the present application have made extensive studies on a water-based metal coating composition in order to solve the above-mentioned conventional problems. As a result, a coating composition containing an aqueous polymer having a carboxyl group and an aqueous polymer having an oxazoline group is excellent in water resistance, processability, storage (storage) stability, solvent resistance, and low temperature curability. Therefore, the present invention has been completed.

That is, in order to solve the above-mentioned problems, an aqueous metal coating composition of the present invention comprises a carboxyl group-containing aqueous polymer and an oxazoline group-containing aqueous polymer. It has a feature.

Further, in order to solve the above-mentioned problems, an aqueous metal coating composition according to a second aspect of the present invention is the aqueous metal coating composition according to the first aspect, wherein the aqueous polymer having an oxazoline group is It is characterized by being water-soluble.

In order to solve the above-mentioned problems, the water-based coating composition for metal according to the third aspect of the present invention is provided with the first or second aspect.
In the aqueous coating composition for metal described above, the aqueous polymer having a carboxyl group is a dicarboxylic acid having an ethylene bond, and a copolymerization weight of a monomer composition containing at least one compound selected from the group consisting of derivatives thereof. The aqueous polymer having a combination and having an oxazoline group is further characterized by further having a hydroxyl group.

According to the above constitution, the water-based coating composition for metal is excellent in water resistance, processability, storage (storage) stability, solvent resistance, and low-temperature curing property, and has high hardness and various physical properties. You can get things.

Hereinafter, the present invention will be described in detail. Aqueous metal coating composition according to the present invention (hereinafter referred to as coating composition)
Contains an aqueous polymer having a carboxyl group, an aqueous polymer having an oxazoline group, and, if necessary, a basic compound. The “aqueous polymer” in the present invention means a water-soluble polymer and a water-dispersible polymer.

The above-mentioned aqueous polymer having a carboxyl group (hereinafter referred to as the aqueous polymer (A)) is not particularly limited. The aqueous polymer (A) can be easily obtained by, for example, radically polymerizing a monomer composition containing a monomer having a carboxyl group (hereinafter referred to as a carboxyl group-containing monomer).

Specific examples of the carboxyl group-containing monomer include unsaturated monocarboxylic acids such as (meth) acrylic acid, crotonic acid and cinnamic acid; maleic acid, fumaric acid, itaconic acid and citraconic acid. And unsaturated dicarboxylic acids; monoesters of these unsaturated dicarboxylic acids; monoamides of these unsaturated dicarboxylic acids; and anhydrides of unsaturated dicarboxylic acids such as maleic anhydride, itaconic anhydride, citraconic anhydride and the like. It is not particularly limited. One of these carboxyl group-containing monomers may be used alone, or two or more thereof may be used in combination. Among the above-exemplified carboxyl group-containing monomers, unsaturated dicarboxylic acids, monoesterified products of the dicarboxylic acids, monoamides of the dicarboxylic acids, and anhydrides of the dicarboxylic acids are more preferable. That is, a dicarboxylic acid having an ethylene bond and its derivative are more preferable.

The proportion of the carboxyl group-containing monomer in the monomer composition containing the carboxyl group-containing monomer (hereinafter referred to as the monomer composition (A)) is 1% by weight to 30% by weight.
Is preferably within the range. When the proportion of the carboxyl group-containing monomer is less than 1% by weight, the amount of the carboxyl group contained in the obtained aqueous polymer (A) becomes too small and the oxazoline group cannot be sufficiently reacted, which is preferable. Absent. Further, when the proportion of the carboxyl group-containing monomer exceeds 30% by weight, a cured product (crosslinked polymer) obtained is obtained.
It is not preferable because the water resistance and the like will be reduced.

Monomers other than the carboxyl group-containing monomer contained in the monomer composition (A) are compounds that are copolymerized with the carboxyl group-containing monomer and are inactive to the carboxyl group. There is no particular limitation as long as it is provided.
Specific examples of the monomer include styrene derivatives such as styrene, vinyltoluene, α-methylstyrene, chloromethylstyrene, styrenesulfonic acid and salts thereof; (meth) acrylamide, N-monomethyl (meth). (Meth) acrylamide derivatives such as acrylamide, N-monoethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide; (meth) acrylic acid esterified with an alcohol having 1 to 18 carbon atoms,
(Meth) acrylic acid esters such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, and cyclohexyl (meth) acrylate; 2-hydroxyethyl (meth) acrylate, (meth) Hydroxy group-containing (meth) acrylic acid ester such as 2-hydroxypropyl acrylate, monoester product of (meth) acrylic acid with polypropylene glycol or polyethylene glycol; ethylene, propylene,
Olefins such as n-butene; (meth) acrylic acid-2-
Unsaturated sulfonic acids such as ethyl sulfonate and salts thereof, vinyl sulfonic acid and salts thereof; vinyl esters such as vinyl acetate, vinyl propionate and vinyl stearate;
(Meth) acrylonitrile; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, octyl vinyl ether, lauryl vinyl ether, etc .; dimethylaminoethyl (meth) acrylate, dimethylaminoethyl (meth) acrylamide, dimethylaminopropyl (meth)
Basic unsaturated monomers such as acrylamide, vinyl pyridine, vinyl imidazole, vinyl pyrrolidone; (meth) acrylic acid, for example, ethylene glycol, 1,
3-butylene glycol, diethylene glycol, 1,
A polyfunctional compound having two or more ethylene bonds in the molecule formed by esterification with a polyhydric alcohol such as 6-hexane glycol, neopentyl glycol, polyethylene glycol, polypropylene glycol, trimethylolpropane, pentaerythritol, and dipentaerythritol (meta ) Acrylic ester; N-methylol (meth)
N-substituted (meth) acrylamides such as acrylamide and N-butoxy (meth) acrylamide; vinyltrimethoxysilane, γ- (meth) acryloxypropyltrimethoxysilane, allyltriethoxysilane, trimethoxysilylpropylallylamine and other organosilicones Unsaturated monomer containing; epoxy group-containing monomer such as glycidyl (meth) acrylate, 2-methylglycidyl (meth) acrylate, allylglycidyl ether; (meth) acryloylaziridine, (meth) acrylic acid-2 An aziridinyl group-containing monomer such as aziridinylethyl; vinyl fluoride,
Vinylidene fluoride, vinyl chloride, vinylidene chloride, divinylbenzene, diallyl phthalate; 4- (meth) acryloyloxy-2,2,6,6-tetramethylpiperidine, 4- (meth) acryloylamino-2,2,6,6
6-Tetramethylpiperidine, 4- (meth) acryloyloxy-1,2,2,6,6-pentamethylpiperidine and other piperidine derivatives; and the like. These monomers may be used alone or in combination of two or more.

The method for producing the aqueous polymer (A), that is, the method for polymerizing the monomer composition (A) is not particularly limited, and various known polymerization methods can be adopted.
Examples of the polymerization method include a solution polymerization method, an emulsion polymerization method, a suspension polymerization method, and a bulk polymerization method in a solvent that is uniformly mixed with water.

Specific examples of the above solvent include lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol and t-butyl alcohol;
Examples thereof include glycols such as ethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol and propylene glycol monomethyl ether; ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone; and the like. These solvents may be used alone or as a mixture of two or more.

The reaction conditions may be set according to the composition of the monomer composition (A) and the like, and are not particularly limited. For example, the reaction temperature is preferably room temperature to 200 ° C. . Further, the monomer composition (A) may be charged into the reactor all at once, or may be charged continuously or sequentially by a method such as dropping. The above polymerization reaction is more preferably carried out in an atmosphere of an inert gas such as nitrogen gas.

In the above polymerization reaction, 2,2'-azobisisobutyronitrile and 2,2'-azobis (2-
Azo compounds such as amidinopropane) dihydrochloride; persulfates such as potassium persulfate; peroxides such as benzoyl peroxide and di-t-butyl peroxide; and other polymerization initiators. The amount of the polymerization initiator used may be set according to the composition of the monomer composition (A) and the like, and is not particularly limited, but it is 0.1% by weight of the monomer composition (A).
About 10 to 10% by weight is preferable. The polymerization initiator may be charged into the reactor together with the monomer composition (A),
It may be charged continuously or sequentially by a method such as dropping.

Further, in the above-mentioned polymerization reaction, a surfactant, a chain transfer agent, a chain regulator or the like can be used if necessary. By the above-mentioned polymerization reaction, the aqueous polymer (A) is obtained in a state of being dissolved or dispersed in the solvent. The water-based polymer (A) may be used alone, or
Two or more types may be used in combination. The average molecular weight (degree of polymerization) of the aqueous polymer (A) is not particularly limited. Moreover, you may distill off some or all of a solvent as needed.

The above aqueous polymer (A) is, for example, a water-dispersible acrylic resin, a water-soluble acrylic resin, a water-dispersible fluororesin, a water-soluble fluororesin, a water-dispersible acrylic silicone resin or a water-soluble acrylic. Known aqueous resins such as silicone resin, water-dispersible polyester, water-soluble polyester, water-dispersible polyurethane, water-soluble polyurethane, and water-dispersible polyolefin can also be used.

The above-mentioned aqueous polymer having an oxazoline group (hereinafter referred to as the aqueous polymer (B)) has the general formula (1)

[0026]

Embedded image

(Wherein R ₁ , R ₂ , R ₃ and R ₄ are each independently a hydrogen atom, a halogen atom, an alkyl group, a cycloalkyl group, an aralkyl group, a cycloalkenyl group,
It is not particularly limited as long as it is an aqueous polymer having an oxazoline group represented by an aryl group or a substituted aryl group).

The above aqueous polymer (B) has the general formula (2)

[0029]

Embedded image

(In the formula, R ₁ , R ₂ , R ₃ and R ₄ are each independently a hydrogen atom, a halogen atom, an alkyl group, a cycloalkyl group, an aralkyl group, a cycloalkenyl group,
An aryl group or a substituted aryl group, R ₅ represents an acyclic organic residue having an unsaturated bond having an addition polymerization property), and polymerizing a monomer composition containing the oxazoline derivative. Can be easily obtained. R above
_The substituent represented by ₅ is more preferably an alkenyl group or a cycloalkenyl group.

Specific examples of the above oxazoline derivative include 2-vinyl-2-oxazoline and 2-
Vinyl-4-methyl-2-oxazoline, 2-vinyl-
5-methyl-2-oxazoline, 2-isopropenyl-
2-oxazoline, 2-isopropenyl-4-methyl-
2-oxazoline, 2-isopropenyl-5-methyl-
2-oxazoline, 2-isopropenyl-5-ethyl-
2-oxazoline etc. are mentioned. These oxazoline derivatives may be used alone or in combination of two or more. Among the above-exemplified oxazoline derivatives, 2-isopropenyl-2-oxazoline is industrially easily available and is more preferable.

The proportion of the oxazoline derivative in the monomer composition containing the oxazoline derivative (hereinafter referred to as the monomer composition (B)) is not particularly limited,
The amount of the structural unit derived from the oxazoline derivative in the aqueous polymer (B) is more preferably 5% by weight or more. If the amount of the structural unit derived from the oxazoline derivative is less than 5% by weight, the amount of the oxazoline group contained in the obtained aqueous polymer (B) will be too small, and sufficient reaction with the carboxyl group may not be possible.

The monomer other than the oxazoline derivative contained in the monomer composition (B) may be any compound as long as it is a compound which copolymerizes with the oxazoline derivative and is inactive to the oxazoline group, and is not particularly limited. Not a thing. Specific examples of the monomer include methyl (meth) acrylate, ethyl (meth) acrylate, (meth) acrylic acid-
n-butyl, isobutyl (meth) acrylate, (meth)
-T-butyl acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate,
Methoxy polyethylene glycol (meth) acrylate,
Lauryl (meth) acrylate, stearyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate,
2-Hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, monoester product of (meth) acrylic acid and polypropylene glycol or polyethylene glycol, and 2-aminoethyl (meth) acrylate and This salt, a caprolactone modified product of (meth) acrylic acid, (meth) acrylic acid-2,
(Meth) acrylic acid esters such as 2,6,6-tetramethylpiperidine and (meth) acrylic acid-1,2,2,6,6-pentamethylpiperidine; sodium (meth) acrylate, (meth) acrylic acid (Meth) acrylic acid salts such as potassium and ammonium (meth) acrylate; unsaturated nitriles such as acrylonitrile and methacrylonitrile;
Unsaturated amides such as (meth) acrylamide, N-methylol (meth) acrylamide, N- (2-hydroxyethyl) (meth) acrylamide; vinyl esters such as vinyl acetate and vinyl propionate; vinyl ethers such as methyl vinyl ether and ethyl vinyl ether. Α-olefins such as ethylene and propylene; halogen-containing α, β- such as vinyl chloride, vinylidene chloride and vinyl fluoride
Unsaturated aliphatic hydrocarbons; styrene, α-methylstyrene, α, β-unsaturated aromatic hydrocarbons such as sodium styrenesulfonate, and the like. These monomers may be used alone or in combination of two or more.

The method for producing the aqueous polymer (B), that is, the method for polymerizing the monomer composition (B) is not particularly limited, and various known polymerization methods can be adopted.
Examples of the polymerization method include a solution polymerization method, an emulsion polymerization method, a suspension polymerization method, and a bulk polymerization method in the above-mentioned solvent. The reaction conditions may be set according to the composition of the monomer composition (B) and the like, and are not particularly limited, but for example, the reaction temperature is preferably about 20 ° C to 150 ° C and the reaction time. Is preferably about 1 to 24 hours.
Further, the monomer composition (B) may be charged into the reactor all at once, or may be charged continuously or sequentially by a method such as dropping. The above polymerization reaction is more preferably carried out in an atmosphere of an inert gas such as nitrogen gas.

In the above polymerization reaction, the above-mentioned polymerization initiator is used. The amount of the polymerization initiator used may be set according to the composition of the monomer composition (B) and the like, and is not particularly limited. The polymerization initiator may be charged together with the monomer composition (B) into the reactor at once, or may be continuously or sequentially charged by a method such as dropping.

Further, in the above polymerization reaction, a surfactant, a chain transfer agent, a chain regulator or the like can be used if necessary. By the above polymerization reaction, the aqueous polymer (B) is obtained in a state of being dissolved or dispersed in the solvent. Only one kind of the aqueous polymer (B) may be used, and
Two or more types may be used in combination. The average molecular weight (degree of polymerization) of the aqueous polymer (B) is not particularly limited. Moreover, you may distill off some or all of a solvent as needed.

Of the above-mentioned aqueous polymers (B), the water-dispersible polymer is more preferably a water-soluble polymer, since a large amount of carboxyl groups and oxazoline groups may remain and the physical properties may be deteriorated. Further, when the above-mentioned aqueous polymer (B) further has a hydroxyl group, various physical properties such as storage stability and low temperature curability are further improved, and the adhesiveness to a base or a top coating is further improved. Further improve.

The above basic compound is not particularly limited as long as it is a compound which can be dissolved or dispersed in an aqueous medium. The basic compound further improves the storage stability of the coating composition by neutralizing the carboxyl group contained in the aqueous polymer (A).

Specific examples of the basic compound include ammonia; primary amines such as methylamine, ethylamine, n-butylamine and cyclohexylamine, secondary amines such as dimethylamine and diethylamine, trimethylamine, triethylamine and dimethylethanol. Aliphatic amines such as tertiary amines such as amines; Heterocyclic amines such as piperidine, morpholine, N-ethylpiperidine, N-ethylmorpholine and pyridine; benzylamine
Aromatic amines such as N-methylaniline and N, N-dimethylaniline; Tetraalkylammonium halides such as tetramethylammonium chloride and tetraethylammonium chloride; Organic acid tetraalkylammonium salts such as tetramethylammonium acetate; Tetramethylammonium hydrogen sulfate Inorganic acid tetraalkylammonium salt such as tetraethylammonium hydrogen sulfate; (hydroxy) alkylammonium hydroxide such as tetramethylammonium hydroxide, tetraethylammonium hydroxide, monohydroxyethyltrimethylammonium hydroxide; sodium hydroxide, potassium hydroxide Alkali metal hydroxides such as barium hydroxide, strontium hydroxide, calcium hydroxide, lanthanum hydroxide, etc. Genus hydroxide; hexaammine platinum (I
V) A free salt of a complex salt such as hydroxide "[Pt (NH ₃ ) ₆ ] (OH) ₄ "; and the like. These basic compounds are
Only one type may be used, or two or more types may be used in combination. Of the above-exemplified basic compounds, ammonia, tertiary amines, and quaternary ammonium salts are more preferable.

When a basic compound is used, the amount of the basic compound used is preferably in the range of 0.3 times to 3 times the molar amount of the carboxyl group of the aqueous polymer (A). If the amount of the basic compound used is less than 0.3 times the molar amount, the storage stability of the coating composition may decrease. On the other hand, if the amount of the basic compound used is more than 3 times by mole, the coating composition becomes difficult to cure, and the weather resistance of the cured product decreases, which is not preferable.

The above aqueous polymer (A) in the coating composition
The ratio of the aqueous polymer (B) and the aqueous polymer (B) is not particularly limited, but is preferably within the range of 95: 5 to 5:95 by weight. Further, the equivalent ratio of the carboxyl group and the oxazoline group is more preferably within the range of 1:20 to 20: 1. If the ratio of the aqueous polymer (A) and the aqueous polymer (B) is out of the above range, the functional group of either one of the carboxyl group and the oxazoline group is extremely insufficient,
The cross-linking reaction may not proceed sufficiently. That is,
At least one of physical properties such as mechanical strength, water resistance, and solvent resistance of the obtained coating film may be deteriorated. Incidentally, when the crosslinking reaction has not proceeded sufficiently, the cured product is rubbed with an organic solvent such as methyl ethyl ketone, or the cured product is immersed in the organic solvent,
The cured product melts or peels off.

The method for preparing the coating composition containing the above-mentioned aqueous polymer (A), aqueous polymer (B) and, if necessary, a basic compound is not particularly limited. That is, the mixing method and mixing order of the aqueous polymer (A), the aqueous polymer (B), and the basic compound are not particularly limited, but the aqueous polymer (A) and the basic compound are mixed. After that, the method of mixing the aqueous polymer (B) with this mixture is more preferable because the storage stability and other physical properties are further improved.

Further, the coating composition may optionally contain a known curing agent and a catalyst for promoting curing,
Further, additives such as pigments, pigment dispersants, fillers (fillers), leveling agents, UV absorbers, UV stabilizers, plasticizers, antioxidants, and surfactants may be included. Incidentally, these additives, depending on the application of the coating composition,
It may be appropriately selected and used.

Examples of the curing agent include aqueous amino resins, aqueous polyisocyanate compounds and blocked polyisocyanate compounds. Examples of the catalyst include quaternary salts such as quaternary ammonium salts and quaternary phosphonium salts. As the pigment, an organic pigment or an inorganic pigment used in known paints and the like can be adopted. As the filler, it is possible to use a filler used in known paints and the like.

As a method of forming a coating film using the coating composition having the above-mentioned structure, that is, a coating method, specifically, for example, after coating the coating composition on a base material such as an iron plate or a steel plate, the coating composition is coated. The composition may be dried. As a result, the aqueous medium evaporates, and the carboxyl group of the aqueous polymer (A) and the oxazoline group of the aqueous polymer (B) undergo a crosslinking reaction to cure the coating composition. That is, a coating film is obtained. The method of applying the coating composition to the substrate is
The method is not particularly limited, and known methods such as brush coating, roll coating, and spray coating can be adopted. The method of drying the coating composition is not particularly limited. The coating composition having the above configuration, for example,
By heating to 170 ° C. to 240 ° C., it cures even faster. The thickness of the coating film is not particularly limited.

As described above, the coating composition according to the present invention comprises the aqueous polymer (A) having a carboxyl group and the aqueous polymer (B) having an oxazoline group.

As a result, it is possible to provide a coating composition which is excellent in water resistance, processability, storage (storage) stability, solvent resistance, and low temperature curability, has high hardness, and is excellent in various physical properties. .

[0048]

The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited to these examples. Various physical properties of the coating composition were measured or evaluated by the methods described below. In the Examples and Comparative Examples, “parts” indicates “parts by weight” and “%”
Indicates "% by weight".

(A) Storage stability The coating composition was stored at 40 ° C. for 30 days. Then, the storage stability was evaluated by measuring the viscosity of the coating composition and comparing it with the viscosity measured before storage. Evaluation standard is 3
When there is no change in viscosity before and after storage, there is no change (marked by ⊚ in Table 1), and when viscosity increases after storage, “thickening” (same as ◯). When the coating composition gelled after storage, it was evaluated as "gelling" (the same is noted by x).

(B) Minimum Curing Conditions First, the coating composition is applied to the surface of a mild steel plate and forcedly dried at a temperature of 220 ° C. for a certain time to form a coating film which is a cured product. Next, the coating film is rubbed with absorbent cotton containing methyl ethyl ketone 50 times at a predetermined pressure (so-called rubbing). After rubbing, it is confirmed whether the coating film is dissolved.

The above operation was repeated a plurality of times while changing the time for forced drying, and the minimum drying time at which a coating film which was not dissolved in methyl ethyl ketone was obtained was defined as the minimum curing time (second).

(C) Solvent resistance The coating composition was applied to the surface of a mild steel plate and forcedly dried at 200 ° C. for 30 seconds to form a coating film as a cured product. Next, the coating film was rubbed (rubbing) with absorbent cotton containing methyl ethyl ketone 50 times at a predetermined pressure. Then, the state of the coating film after rubbing was visually evaluated. The evaluation criteria were three levels, and when no change was observed in the coating film, “no change” (marked with ⊚ in Table 1),
"Glossy" when the gloss of the coating film surface has decreased (same as ○
, And the case where the coating film was dissolved or disappeared was evaluated as “dissolved” (same as above, marked with x).

(D) Pencil hardness A coating film was formed by applying the coating composition onto the surface of a mild steel plate and forcibly drying it at 140 ° C. for 20 minutes. Next, the coating film was tested based on the hand scratching method defined in JIS K 5400 84.2, and the coating film was evaluated by scratches.

(E) Workability A test plate was placed in a room at 20 ° C. with the coated surface facing outside.
After bending at 0 °, the number of sheets in which no crack was generated in the bent portion, that is, the T number was obtained. The T number is 0T when 180 ° bending can be performed without sandwiching anything inside the bent portion, and 180 ° bending can be performed by sandwiching one plate having the same thickness as the test plate. 1 if
The case where 180 ° bending was possible by sandwiching T and n sheets was defined as nT.

(F) Fume property A tin plate having a thickness of 0.23 mm was cut into 15 × 20 cm and precisely weighed (this weight is defined as W ₁ ), and then the coating composition was applied to 1
It is applied to the surface of the tin plate so as to be 0 g / m ² . Next, after drying the coating composition at 100 ° C. for 60 minutes, the tin plate is precisely weighed (this weight is defined as W ₂ ). After further drying the coated tin plate at 200 ° C. for 10 minutes, the tin plate is precisely weighed (this weight is defined as W ₃ ). Then, the heating loss rate M (%) was obtained from the above weights W ₁ , W ₂ and W ₃ according to the following equation.

M = 100 × (W ₂ −W ₃ ) / (W ₂ −W ₁ ) The heating loss rate M was reduced by volatilization or evaporation of components in the coating composition when heated under a certain condition. The ratio of the weight to the weight of the coating composition is shown. Then, the fume generation amount was evaluated based on the heating loss rate M. The evaluation criteria are three levels, and when the heating loss rate M is more than 0% and 3% or less, the fume property is “good” (marked with ⊚ in Table 1), and the heating loss rate M is more than 3% and 6%. The following cases were evaluated as fumeability "OK" (same as "○"), and when the heating loss rate M exceeds 6% as fumes "impossible" (same as "X").

Example 1 First, an aqueous polymer (A) was produced. That is, a thermometer, a nitrogen gas introduction pipe, a reflux condenser,
A flask equipped with a dropping funnel and a stirrer was used as a reactor. This reactor was charged with deionized water 78 as an aqueous medium.
2.4 parts and 128 parts of a 15% aqueous solution of a surfactant (polyoxyethylene nonylphenyl ether sulfate ammonium salt; manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., trade name Hitenol N-08) were charged. On the other hand, the dropping funnel was charged with a monomer composition (A) obtained by mixing 32 parts of acrylic acid as a carboxyl group-containing monomer, 320 parts of butyl acrylate and 288 parts of styrene.

Next, the above aqueous solution was heated to 70 ° C. with stirring under a nitrogen gas stream, and then 64 parts of a 5% aqueous solution of potassium persulfate as a polymerization initiator was mixed with the aqueous solution. Then, the above monomer composition (A) was added dropwise to the aqueous solution over 3 hours while stirring at 70 ± 1 ° C. under a nitrogen gas stream.

After completion of dropping, the reaction solution was reacted at 70 ± 1 ° C. for 2 hours while stirring under a nitrogen gas stream, and further, 8
The polymerization reaction was completed by continuing to stir at 0 ° C. for 1 hour and reacting.

After completion of the reaction, the reaction solution was cooled and the pH of the reaction solution was adjusted to 8.5 with 28% aqueous ammonia. As a result, the nonvolatile content (aqueous polymer (A)) becomes 3
An aqueous polymer (A) aqueous solution containing 9.8% was obtained.

Next, an aqueous polymer (B) was produced. That is, in a reactor having the same configuration as the above reactor, 116 parts of deionized water as an aqueous medium, and a polymerization initiator (2,2′-azobis (2-amidinopropane) dihydrochloride; Wako Pure Chemical Industries, Ltd., trade name V-50) 4
The department was charged. On the other hand, 2-isopropenyl-2-oxazoline 40 as an oxazoline derivative was added to the dropping funnel.
Part and methoxypolyethylene glycol acrylate (average number of moles of ethylene glycol added: 9 moles; manufactured by Shin Nakamura Chemical Co., Ltd., trade name: NK ester AM-90)
A monomer composition (B) prepared by mixing 40 parts of G) was charged.

Next, the above aqueous solution was heated to 70 ° C. with stirring under a nitrogen gas stream. Then, the above monomer composition (B) was added dropwise to the aqueous solution over 1 hour while stirring at 70 ± 1 ° C. under a nitrogen gas stream.

After completion of the dropping, the reaction solution was stirred at 70 ± 1 ° C. for 9 hours while stirring under a nitrogen gas stream to carry out the reaction to complete the polymerization reaction.

After completion of the reaction, the reaction solution was cooled, whereby an aqueous polymer (B) aqueous solution having a nonvolatile content of 41.5%, a pH of 6.5 and a viscosity of 67 centipoise (cP.) Was obtained. It was

Next, a coating composition was prepared using the obtained aqueous polymer (A) aqueous solution and aqueous polymer (B) aqueous solution. That is, by mixing 100 parts of the aqueous polymer (A) aqueous solution and 15 parts of the aqueous polymer (B) aqueous solution,
A coating composition was prepared.

Various physical properties of the obtained coating composition were measured or evaluated by the above-mentioned methods. As a result, the storage stability is "no change", the minimum curing time is 5 seconds,
The solvent resistance was “no change”, the pencil hardness was 2H, the workability was 1T, and the fume property was “good”. Table 1 shows the composition of the coating composition and the measurement results and evaluation of various physical properties.

Example 2 First, an aqueous polymer (A) was produced in the same manner as in Example 1. Next, the aqueous polymer (B) was produced. That is, instead of 116 parts of deionized water in a reactor having the same configuration as the reactor of Example 1,
A monomer composition (B) comprising a mixture of 58 parts of deionized water and 58 parts of isopropanol and 16 parts of 2-isopropenyl-2-oxazoline, 32 parts of methoxypolyethylene glycol acrylate and 32 parts of methyl methacrylate. The same operation as in Example 1 was performed except that the non-volatile component was 41.6% and the pH was 6.
7, an aqueous polymer (B) aqueous solution having a viscosity of 360 centipoise (cP.) Was obtained.

Next, a coating composition was prepared using the obtained aqueous polymer (A) aqueous solution and aqueous polymer (B) aqueous solution. That is, by mixing 100 parts of the aqueous polymer (A) aqueous solution and 30 parts of the aqueous polymer (B) aqueous solution,
A coating composition was prepared.

Various physical properties of the obtained coating composition were measured or evaluated by the methods described above. As a result, the storage stability is "no change", the minimum curing time is 5 seconds,
The solvent resistance was “no change”, the pencil hardness was 2H, the workability was 1T, and the fume property was “good”. Table 1 shows the composition of the coating composition and the measurement results and evaluation of various physical properties.

Comparative Example 1 First, an aqueous polymer (A) was produced in the same manner as in Example 1. Next, a comparative aqueous polymer (B) was produced. That is, 782.4 parts of deionized water was added to a reactor having the same structure as the reactor of Example 1.
Further, 128 parts of a 15% aqueous solution of a surfactant (same as above) was charged, and the pH of the aqueous solution was adjusted to 9.0 using 28% aqueous ammonia. On the other hand, a monomer composition (B) obtained by mixing 128 parts of 2-isopropenyl-2-oxazoline, 288 parts of butyl acrylate, and 224 parts of styrene was charged into the dropping funnel.

Next, the above aqueous solution was heated to 70 ° C. with stirring under a nitrogen gas stream, and then 64 parts of a 5% aqueous solution of potassium persulfate was mixed with the aqueous solution. Then, the above monomer composition (B) was added dropwise to the aqueous solution over 3 hours while stirring at 70 ± 1 ° C. under a nitrogen gas stream.

After completion of dropping, the reaction solution was reacted at 70 ± 1 ° C. for 2 hours while stirring under a nitrogen gas stream, and further, 8
The polymerization reaction was completed by reacting at 0 ° C. for 1 hour.

After the completion of the reaction, the reaction solution was cooled, whereby a comparative aqueous polymer (B) aqueous solution having a nonvolatile content of 39.8% and a pH of 8.0 was obtained.

Next, a comparative coating composition was prepared using the obtained aqueous polymer (A) aqueous solution and comparative aqueous polymer (B) aqueous solution. That is, aqueous polymer (A) aqueous solution 1
A coating composition for comparison was prepared by mixing 00 parts with 30 parts of an aqueous solution of the aqueous polymer (B) for comparison.

Various physical properties of the obtained comparative coating composition are
It was measured or evaluated by the method described above. As a result, the storage stability was “no change”, the pencil hardness was 2H, and the fume property was “good”, but the minimum curing time was 1
5 seconds, solvent resistance is "glossy", processability is 2
It was T. Therefore, the comparative coating composition was inferior to the coating composition according to the present invention. Table 1 shows the composition of the coating composition for comparison, and the measurement results and evaluation of various physical properties.

Comparative Example 2 First, an aqueous polymer (A) was produced in the same manner as in Example 1. Next, a coating composition for comparison was prepared using the obtained aqueous polymer (A) aqueous solution and a water-soluble melamine resin (hexamethoxymethylated melamine resin; manufactured by Mitsui Cytec Co., Ltd., trade name: Cymel 303). did. That is, the aqueous polymer (A) aqueous solution 10
A comparative coating composition was prepared by mixing 0 parts with 15 parts of water-soluble melamine.

Various physical properties of the obtained comparative coating composition are
It was measured or evaluated by the method described above. As a result, the storage stability was "no change" and the pencil hardness was 2H, but the fuming property was "poor" and the minimum curing time was 2
0 seconds, solvent resistance is "glossy", workability is 3
It was T. Therefore, the comparative coating composition was inferior to the coating composition according to the present invention. Table 1 shows the composition of the coating composition for comparison, and the measurement results and evaluation of various physical properties.

[0078]

[Table 1]

[0079]

As described above, the aqueous metal coating composition according to the first aspect of the present invention is a composition containing an aqueous polymer having a carboxyl group and an aqueous polymer having an oxazoline group.

As described above, the aqueous metal coating composition according to the second aspect of the present invention is such that the aqueous polymer having an oxazoline group is water-soluble.

The aqueous metal coating composition according to claim 3 of the present invention is, as described above, a dicarboxylic acid in which the aqueous polymer having a carboxyl group has an ethylene bond, and
An aqueous polymer having a oxazoline group, which is a copolymer of a monomer composition containing at least one compound selected from the group consisting of derivatives thereof, further has a hydroxyl group.

As a result, it is excellent in water resistance, processability, storage (storage) stability, solvent resistance, and low-temperature curing property, and has high hardness and various physical properties. For example, for PCM paints and cans. The metal coating composition suitable for paints can be provided.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hironobu Akutagawa 5-8 Nishimitabicho Suita City, Osaka Prefecture Nippon Shokubai Co., Ltd. (72) Inventor Kenta Kaneda 5-8 Nishiomitabicho Suita City, Osaka Stocks Company Nippon Catalyst

Claims (3)

[Claims] 1. An aqueous coating composition for a metal, comprising an aqueous polymer having a carboxyl group and an aqueous polymer having an oxazoline group. 2. The aqueous coating composition for metals according to claim 1, wherein the aqueous polymer having an oxazoline group is water-soluble. 3. An aqueous polymer having a carboxyl group is a copolymer of a monomer composition containing at least one compound selected from the group consisting of a dicarboxylic acid having an ethylene bond and a derivative thereof, and The aqueous coating composition for metals according to claim 1 or 2, wherein the aqueous polymer having an oxazoline group further has a hydroxyl group.