JP2001247818A - Aqueous coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an aqueous coating composition which has good coating workability and coating film performance and, in addition, can solve the problem of endocrine disrupting chemicals such as bisphenols. SOLUTION: This aqueous coating composition is obtained by neutralizing (B) a carboxyl group-containing acrylic modified resin to be obtained by reacting (A) an epoxy modified polyester resin obtained by the esterification reaction of (a) a carboxyl group-containing polyester resin having a number average molecular weight of 1,000-30,000 and an acid value of 5-200 mgKOH/g and (b) a novolak type epoxy resin with (c) a Carboxyl group-containing acrylic resin, and dispersing the resulting resin in an aqueous medium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an aqueous coating composition,
In particular, the present invention relates to a novel water-based coating composition suitable for coating the inner surface of a can corresponding to environmental hormone problems.

[0002]

2. Description of the Related Art In order to solve the problem of global environmental pollution caused by the volatilization of organic solvents, organic solvent type paints are being replaced with water-based paints in the field of paints for inner surfaces of cans such as edible cans.
JP-B-63-41934 and JP-A-7-138523 propose an epoxy-modified acrylic resin-based aqueous coating obtained by reacting or mixing an epoxy resin with a carboxyl group-containing acrylic resin. ing.

[0003] However, in these conventional water-based paints, the epoxy resin as a raw material is generally obtained by reacting bisphenol A with a low molecular weight epoxy resin from the viewpoint of obtaining good coating workability and coating film performance. Since unreacted bisphenol A remains in the paint because of the use of the obtained high molecular weight epoxy resin, the remaining bisphenol A causes a problem of environmental hormone. In order to avoid this problem, when a low-molecular-weight epoxy resin in which bisphenols are not detected is used as it is as a raw material epoxy resin, the obtained water-based paint has a coating workability, a substrate adhesion, a flavor property and the like. The coating film performance will be reduced, and it is unsuitable as a paint for the inner surface of a can.

Therefore, at present, there is no fundamental solution to the problem of environmental hormones caused by bisphenols in epoxy-modified acrylic resin-based water-based paints.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide an aqueous coating composition capable of solving the problem of environmental hormones caused by bisphenols while having good coating workability and coating performance.

[0006]

Means for Solving the Problems The present inventor has conducted intensive studies to develop an aqueous coating composition suitable for the inner surface of a can which can solve the problem of environmental hormones caused by bisphenols. Using a group-containing polyester resin, a novolak-type epoxy resin and a carboxyl group-containing acrylic resin, and neutralizing the resin obtained by sequentially reacting them, and dispersing the water-based paint, it does not contain free bisphenols, and It has been found that the same coating workability and coating film performance as in the case of the conventional epoxy-modified acrylic resin-based water-based paint can be exhibited, and based on this, the present invention has been completed.

That is, the present invention provides a number average molecular weight of 1,000.
An epoxy-modified polyester resin (A) obtained by subjecting a carboxyl group-containing polyester resin (a) and a novolak type epoxy resin (b) having an acid value of from 5 to 30,000 and an acid value of from 5 to 200 mgKOH / g to a carboxyl group The present invention relates to an aqueous coating composition characterized in that a carboxyl group-containing acrylic-modified polyester resin (B) obtained by reacting with an acrylic resin (c) is neutralized and dispersed in an aqueous medium.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The epoxy-modified polyester resin (A) in the aqueous coating composition of the present invention has a number average molecular weight of 1,000 to 30,000 and an acid value of 5 to 200 mg KO.
It is obtained by subjecting a carboxyl group-containing polyester resin (a) of H / g and a novolak type epoxy resin (b) to an esterification reaction.

The carboxyl group-containing polyester resin (a) must have a number average molecular weight of 1,000 to 30,000 and an acid value of 5 to 200 mgKOH / g. When the number average molecular weight is less than 1,000 or when the acid value exceeds 200 mgKOH / g, a side reaction is liable to occur during the addition reaction between the carboxyl group and the epoxy group, increasing the viscosity and making the production difficult. On the other hand, when the number average molecular weight exceeds 30,000 or when the acid value is less than 5 mgKOH / g, it is difficult to disperse in a subsequent step in water, and neither is preferable.

The carboxyl group-containing polyester resin (a) has a number average molecular weight of preferably from 2,000 to 1.
000, and the acid value is preferably 20 to 150 mg.
KOH / g.

The carboxyl group-containing polyester resin (a) is obtained by a polycondensation reaction between a polyhydric alcohol and a polybasic acid. Polyhydric alcohols are polyols such as alkane polyols, oxyalkylene polyols, polyoxyalkylene polyols, and alicyclic polyols. Typical examples thereof include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, , 4
-Butanediol, 1,3-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, 1,3-pentanediol, 1,6-hexanediol, 1,5-hexanediol, Alkane polyols such as neopentyl glycol, glycerin, 2-methylglycerin, trimethylolpropane, trimethylolethane, and pentaerythritol; oxyalkylene polyols such as diethylene glycol; triethylene glycol, tetraethylene glycol, polyethylene glycol, dipropylene glycol, and tripropylene Polyoxyalkylene polyols such as glycol and polypropylene glycol; and alicyclic polyols such as 1,4-cyclohexanedimethanol. Further, as polybasic acids, for example, adipic acid, sebacic acid, glutaric acid, phthalic acid, isophthalic acid, terephthalic acid, maleic acid, fumaric acid, succinic acid, pimelic acid, azelaic acid,
Dodecandioic acid, cyclohexanedicarboxylic acid, tetrahydrophthalic acid, methyltetrahydrophthalic acid, endomethylenetetrahydrophthalic acid, methylendmethylenetetrahydrophthalic acid, hexahydrophthalic acid, naphthalenedicarboxylic acid, trimellitic acid, butanetricarboxylic acid or anhydrides thereof Objects and the like.

In the polycondensation reaction between a polyhydric alcohol and a polybasic acid, a strong protonic acid, a heavy metal oxide or the like can be used as a polycondensation catalyst. Examples of strong protic acids include sulfuric acid, benzenesulfonic acid, and paratoluenesulfonic acid. Examples of the heavy metal oxide include tetrabutyl titanate, dibutyltin oxide, antimony trioxide, and manganese dioxide.

The above polyester resin (a) can be produced by condensing a polyhydric alcohol and a polybasic acid so as to have a carboxyl group in the molecule so as to have the acid value specified in the present invention. The resin (a) may be produced by first producing a hydroxyl group-containing polyester resin and adding an acid anhydride to the hydroxyl group to give a specific acid value. Examples of the acid anhydride include phthalic anhydride, trimellitic anhydride, succinic anhydride, maleic anhydride, hexahydrophthalic anhydride, and pyromellitic anhydride.

The novolak type epoxy resin (b) in the present invention preferably has a number average molecular weight of 200 to 8,000 and has an average of less than 3 epoxy groups in the molecule. When the molecule has an average of three or more epoxy groups, or when the number average molecular weight is 8,000 or more, the viscosity increases during the esterification reaction with the carboxyl group-containing polyester resin (a). This is not preferable because the production tends to be difficult. The resin (b) more preferably has an average of about 1 to 2.7 epoxy groups in the molecule.

The novolak type epoxy resin (b) does not contain bisphenols. By modifying the carboxyl group-containing polyester resin (a) using the bisphenols, the water-based paint finally obtained can be used for coating workability. In addition, since the coating film performance is good and free bisphenols are not contained, the problem of environmental hormones is solved.

As the novolak type epoxy resin (b), specifically, orthocresol novolak type epoxy resin can be suitably used.

The epoxy-modified polyester resin (A) in the composition of the present invention is obtained by combining a carboxyl group-containing polyester resin (a) and a novolak type epoxy resin (b) with a carboxyl group of the resin (a): an epoxy group of the resin (b). Can be suitably prepared by performing an esterification reaction at a mixing ratio of 1: 1 to 1: 3 in a molar ratio. The epoxy equivalent of the resulting epoxy-modified polyester resin (A) is about 2,000 to 10,000, and the number average molecular weight is about 4,000 to 100,000. The epoxy-modified polyester resin (A) preferably has an epoxy equivalent and a number average molecular weight within the above ranges from the viewpoints of stability, coating workability, coating film performance and the like of the obtained water-based paint.

The epoxy equivalent of the polyester resin (A) is preferably about 2,500 to 7,000, and the number average molecular weight is preferably about 5,000 to 50,000.

The above epoxy-modified polyester resin (A)
The esterification reaction between the polyester resin (a) and the novolak-type epoxy resin (b) for obtaining a mixture is carried out, for example, by mixing these mixtures with a catalyst such as a tertiary alkylamine or a tetraalkylammonium halide and an organic solvent. Can be carried out at a reaction temperature of 100 to 150 ° C. for about 1 to 8 hours, whereby the target resin (A) can be obtained.

The above epoxy-modified polyester resin (A)
Is usually obtained by an addition reaction between the carboxyl group at the terminal of the polyester resin (a) and the 1,2-epoxy group at the terminal of the epoxy resin (b), so that a hydroxyl group is generated on the molecular side chain. The hydroxyl group in the molecular side chain is advantageous for improving the adhesion to the substrate and the corrosion resistance of the obtained coating film by improving the adhesion to the metal substrate.

In the present invention, the carboxyl group-containing acrylic resin (c) used for producing the carboxyl group-containing acrylic modified polyester resin (B) by reacting with the above-mentioned modified polyester resin (A) includes acrylic acid and methacrylic acid. And acrylic polymers containing a polymerizable unsaturated carboxylic acid such as itaconic acid or fumaric acid as an essential monomer component. This polymer has an acid value of 100 to 500 mgKOH / g.
It is preferable from the viewpoints of stability in an aqueous medium, processability of an obtained coating film, corrosion resistance, water resistance and the like.

Other monomer components other than the polymerizable unsaturated carboxylic acid used in the polymerization of the acrylic resin (c) include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, benzyl (meth) acrylate, stearyl (meth) acrylate, Cetyl (meta)
C1-C15 alkyl esters of acrylic acid or methacrylic acid such as acrylate; cyclohexyl (meth) acrylate, isobornyl (meth) acrylate; aromatic vinyl monomers such as styrene, α-methylstyrene, and vinyltoluene; Hydroxyalkyl (meth) such as hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, hydroxyamyl (meth) acrylate, and hydroxyhexyl (meth) acrylate
Acrylate, a hydroxyl group-containing polymerizable unsaturated monomer such as a caprolactone-modified alkyl (meth) acrylate having a hydroxyl group, which is obtained by subjecting 1 mol to 5 mol of ε-caprolactone to 1 mol of the hydroxyalkyl (meth) acrylate. Body: acrylamide, methacrylamide, N-methoxymethyl (meth) acrylamide, N-
Ethoxymethyl (meth) acrylamide, Nn-propoxymethyl (meth) acrylamide, N-isopropoxymethyl (meth) acrylamide, Nn-butoxymethyl (meth) acrylamide, N-sec-butoxymethyl (meth) acrylamide, Acrylamide monomers such as N-tert-butoxymethyl (meth) acrylamide; acrylonitrile, methacrylonitrile, vinyl acetate, ethylene, butadiene and the like.

The acrylic resin (c) is prepared by mixing a monomer mixture of the polymerizable unsaturated carboxylic acid with the other monomer components in, for example, an organic solvent in the presence of a radical polymerization initiator or a chain transfer agent. 1-1 at 80-150 ° C
It can be obtained by heating and copolymerizing for about 0 hours. As the above-mentioned polymerization initiator, an organic peroxide type, an azo type or the like can be used. Examples of the organic peroxide-based polymerization initiator include, for example, benzoyl peroxide, t-butylperoxy-2-ethylhexanoate, di-t-
Butyl peroxide, t-butyl peroxybenzoate, t-amyl peroxy-2-ethylhexanoate and the like. Examples of the azo polymerization initiator include, for example, azobisisobutyronitrile, azobisdimethylvaleronitrile and the like. Is mentioned. Examples of the chain transfer agent include α-methylstyrene dimer and mercaptans.

The above epoxy-modified polyester resin (A)
And the carboxyl group-containing acrylic resin (c) reacts with
Usually, in an organic solvent, for example, in the presence of a catalyst such as a tertiary amine such as triethylamine or dimethylethanolamine, heated at a temperature of about 80 to 120 ° C. for about 0.5 to 8 hours to cause a reaction. The carboxyl group-containing acrylic-modified polyester resin (B) can be suitably obtained. In this reaction, esterification usually occurs mainly, but further reactions such as onium chloride occur.

The epoxy-modified polyester resin (A) and the carboxyl group-containing acrylic resin (c) in the above reaction
May be appropriately selected depending on coating workability, coating film performance, and the like, but usually 60/40 to 90/10 in terms of the solid content weight ratio of resin (A) / resin (c). Preferred, 7
More preferably, it is in the range of 0/30 to 90/10.

The carboxyl group-containing acrylic-modified polyester resin (B) obtained by the above reaction has an acid value of 15
It is preferable that it is within the range of 200 mgKOH / g from the viewpoints of dispersion stability in an aqueous medium, water resistance of the obtained coating film, and the like. In addition, it is usually desirable to have substantially no epoxy group from the viewpoint of storage stability.

The above acrylic-modified polyester resin (B)
Is neutralized and dispersed in an aqueous medium. As a neutralizing agent used for neutralization, amines and ammonia are suitably used. Representative examples of the above amines include, for example, triethylamine, triethanolamine, dimethylethanolamine, diethylethanolamine, morpholine and the like. Among them, triethylamine and dimethylethanolamine are particularly preferable. Although the degree of neutralization of the acrylic-modified polyester resin (B) is not particularly limited, it is usually 0.3 to 3% based on carboxyl groups in the resin.
It is desirable to be in the range of 1.0 equivalent neutralization.

The aqueous medium in which the carboxyl group-containing acrylic-modified polyester resin (B) is dispersed may be water alone or a mixture of water and an organic solvent. As the organic solvent, any conventionally known organic solvent can be used as long as it is a water-miscible organic solvent that does not affect the stability of the carboxyl group-containing acrylic-modified polyester resin (B) in an aqueous medium. it can.

As the organic solvent, alcohol solvents, cellosolve solvents, carbitol solvents and the like are preferable. Specific examples of the organic solvent include alcohol solvents such as n-butanol; cellosolve solvents such as ethylene glycol monobutyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monomethyl ether, and propylene glycol monomethyl ether; diethylene glycol monoethyl ether and the like. And carbitol solvents. In addition, as the organic solvent, an inert organic solvent that is not mixed with water other than the above can be used as long as the stability of the acrylic-modified polyester resin in the aqueous medium is not hindered. Examples thereof include aromatic hydrocarbon solvents such as toluene and xylene, ester solvents such as ethyl acetate and butyl acetate, and ketone solvents such as methyl ethyl ketone. The amount of the organic solvent in the aqueous coating composition of the present invention is desirably in the range of 50% by weight or less in the aqueous medium from the viewpoint of environmental protection.

The carboxyl group-containing acrylic-modified polyester resin (B) can be neutralized and dispersed in an aqueous medium by a conventional method. For example, the polyester resin is stirred under stirring in an aqueous medium containing a neutralizing agent. (B) a method of gradually adding, after neutralizing the polyester resin (B) with a neutralizing agent, adding an aqueous medium to the neutralized product under stirring or adding the neutralized product to the aqueous medium And the like.

The composition of the present invention may further contain a crosslinking agent in addition to the neutralized carboxyl group-containing acrylic-modified polyester resin (B). Examples of the crosslinking agent include a resol type phenol resin, a melamine resin, and a benzoguanamine resin. As a phenol component constituting the phenol resin, for example, o
Bifunctionality such as -cresol, p-cresol, p-tert-butylphenol, p-ethylphenol, 2,3-xylenol, 2,5-xylenol, p-tert-aminophenol, p-nonylphenol, p-cyclohexylphenol Phenols, phenolic acid, trifunctional phenols such as m-cresol, m-ethylphenol, 3,5-xylenol, m-methoxyphenol, and monofunctional phenols such as 2,4-xylenol and 2,6-xylenol , Bisphenol B, bisphenol F, and other four-functional phenols alone or in combination of two or more. However, it is desirable not to use bisphenol-type phenol resins due to environmental hormone problems. Further, if necessary, a surfactant, an antifoaming agent, etc. may be contained.

In general, the aqueous coating composition of the present invention desirably has a solid content of about 15 to 40% by weight.

The composition of the present invention can be suitably used as a paint for the inner surface of a can such as an edible can, for example, a metal plate such as an aluminum plate or a steel plate, or zinc, chromium, tin, or the like on the surface of a steel plate.
The present invention can be applied to various metal materials such as a plated steel sheet plated with aluminum or the like and a treated steel sheet whose surface is chemically converted with chromic acid, iron phosphate, or zinc phosphate. As a means for applying the composition to the surface of the metal material, any known method such as roll coating, spray coating, brush coating, spray coating, and immersion electrodeposition can be used. Further, the coating film thickness is usually sufficient in the range of 2 to 30 μm, and the baking of the coating film is generally performed at about 150 to about 28 μm.
0 ° C., preferably from about 180 ° C. to about 220 ° C., from about 20 to 6
It is carried out for 00 seconds, preferably for about 30 to 300 seconds.

[0034]

EXAMPLES Hereinafter, Production Examples, Examples and Comparative Examples will be given,
The present invention will be described more specifically. In each case, parts and%
Is, in principle, by weight.

Production Example 1 Production of Carboxyl Group-Containing Acrylic Resin Ethylene glycol monobutyl ether 1 was placed in a reaction vessel.
200 parts were blended, and the temperature was raised to 100 ° C. and maintained. Among them, 400 parts of methacrylic acid, 500 parts of styrene, 100 parts of ethyl acrylate, "Perbutyl O" (Nippon Oil & Fats Co., Ltd.)
A mixed solution of 35 parts of a peroxide-based polymerization initiator) and 140 parts of ethylene glycol monobutyl ether was added dropwise over 3 hours. After completion of the dropwise addition, the mixture was aged at 100 ° C. for 2 hours.
% Of a carboxyl group-containing acrylic resin solution was obtained. The obtained resin had a number average molecular weight of about 7,000 and a resin acid value of 26.
It had 0 mg KOH / g.

Production Example 2 Production of carboxyl group-containing polyester resin In a reaction vessel, 146 parts of ethylene glycol, 179 parts of propylene glycol, 269 parts of adipic acid, 376 parts of isophthalic acid, 199 parts of terephthalic acid and 0.5 part of dibutyltin oxide were added. After mixing, the temperature was raised to 230 ° C. over 3 hours with stirring and maintained for 2 hours, 50 parts of xylene was added, and the temperature was maintained for 5 hours. Next, after cooling to 140 ° C., 200 parts of cyclohexanone was added to obtain a polyester resin solution having a solid content of 80% by weight. The obtained resin had an acid value of 70 mgKOH / g and a number average molecular weight of about 2,000.

Production Example 3 Production of carboxyl group-containing polyester resin In a reaction vessel, 151 parts of ethylene glycol, 185 parts of propylene glycol, 163 parts of adipic acid, 389 parts of isophthalic acid, 287 parts of terephthalic acid, 50 parts of xylene and 0 parts of dibutyltin oxide were added. .5 parts, 2 parts with stirring
After the temperature was raised to 30 ° C. over 3 hours and maintained for 2 hours, 50 parts of xylene was added and the temperature was maintained at the same temperature for 8 hours. Then, after cooling to 140 ° C, cyclohexanone 200
To obtain a polyester resin solution having a solid content weight ratio of 80%. The obtained resin has an acid value of 30 mgKOH /
g, had a number average molecular weight of about 4,000.

Production Example 4 Production of carboxyl group-containing polyester resin In a reaction vessel, 136 parts of ethylene glycol, 167 parts of propylene glycol, 129 parts of adipic acid, 263 parts of isophthalic acid, 278 parts of terephthalic acid, 50 parts of xylene and 0 parts of dibutyltin oxide were added. .5 parts, 2 parts with stirring
After the temperature was raised to 30 ° C. over 3 hours and maintained for 2 hours, 50 parts of xylene was added and the temperature was maintained at the same temperature for 8 hours. Then, after cooling to 160 ° C., hexahydrophthalic acid 1
76 parts were added and kept at the same temperature for 3 hours. Then 1
After cooling to 40 ° C., 200 parts of cyclohexanone was added to obtain a polyester resin solution having a solid content of 80% by weight. The obtained resin had an acid value of 35 mgKOH / g and a number average molecular weight of about 3,500.

Example 1 To 953 parts of the carboxyl group-containing polyester resin solution obtained in Production Example 2 was added an ortho-cresol novolak type epoxy resin (epoxy equivalent: about 190, number average molecular weight: about 40
0, having an average of about 2.2 epoxy groups in the molecule) 23
Eight parts, 54 parts of cyclohexanone, and 5 parts of tri-n-butylamine were blended and kept at 120 ° C. for 3 hours with stirring to obtain an epoxy-modified polyester resin solution having a solid content of 80% by weight. The obtained resin has an epoxy equivalent of about 3,000.
0, had a number average molecular weight of about 20,000.

Next, 833 parts of the carboxyl group-containing acrylic resin solution obtained in Production Example 1 was mixed with 875 parts of the epoxy-modified polyester resin solution. At this time, the molar ratio of the carboxyl group to the epoxy group is 1: 1.32.
Subsequently, after the mixed resin solution was uniformly stirred and mixed, 74 parts of dimethylethanolamine was added, and the mixture was maintained at 90 ° C. for 1 hour. Then, 2,217 parts of deionized water was added dropwise over 1 hour, and the resin acid value was 68 mgKOH / g, the solid content ratio was 25%, the viscosity was 4,000 mPas, and the particle diameter was 260 n.
Thus, an aqueous coating composition of the present invention, which was an aqueous dispersion of m, was obtained.

Example 2 Orthocresol novolak type epoxy resin (epoxy equivalent: about 1,500, number average molecular weight: about 7,000, epoxy group in the molecule) was added to 239 parts of the carboxyl group-containing polyester resin solution obtained in Production Example 2. 809 parts, cyclohexanone 202 parts, tri-n-
Five parts of butylamine were mixed and kept at 120 ° C. for 3 hours with stirring to obtain an epoxy-modified polyester resin solution having a solid content of 80% by weight. The resulting resin had an epoxy equivalent of about 3,000 and a number average molecular weight of about 26,000.

Next, 833 parts of the carboxyl group-containing acrylic resin solution obtained in Production Example 1 was mixed with 875 parts of the epoxy-modified polyester resin solution. At this time, the molar ratio between the carboxyl group and the epoxy group is 1: 2.26.
Subsequently, after the mixed resin solution was uniformly stirred and mixed, 74 parts of dimethylethanolamine was added, and the mixture was maintained at 90 ° C. for 1 hour. Then, 2,217 parts of deionized water was added dropwise over 1 hour, and the resin acid value was 70 mgKOH / g, the solid content weight ratio was 25%, the viscosity was 3,000 mPas, and the particle diameter was 240 n.
Thus, an aqueous coating composition of the present invention, which was an aqueous dispersion of m, was obtained.

Example 3 To 1,070 parts of the carboxyl group-containing polyester resin solution obtained in Production Example 3 was added an ortho-cresol novolak-type epoxy resin (epoxy equivalent: about 190, number average molecular weight: about 400, average epoxy group in the molecule) Has about 2.2)
144 parts, 31 parts of cyclohexanone, and 5 parts of tri-n-butylamine were blended and kept at 120 ° C. for 3 hours with stirring to obtain an epoxy-modified polyester resin solution having a solid content of 80% by weight. The obtained resin has an epoxy equivalent of about 3,
000, a number average molecular weight of about 18,000.

Next, 833 parts of the carboxyl group-containing acrylic resin solution obtained in Production Example 1 was mixed with 875 parts of the epoxy-modified polyester resin solution. At this time, the molar ratio of the carboxyl group to the epoxy group is 1: 1.66.
Subsequently, after the mixed resin solution was uniformly stirred and mixed, 74 parts of dimethylethanolamine was added, and the mixture was maintained at 90 ° C. for 1 hour. Then, 2,217 parts of deionized water was added dropwise over 1 hour, the resin acid value was 70 mgKOH / g, the solid content ratio was 25%, the viscosity was 4,000 mPas, and the particle diameter was 220 n.
Thus, an aqueous coating composition of the present invention, which was an aqueous dispersion of m, was obtained.

Example 4 To 1,054 parts of the carboxyl group-containing polyester resin solution obtained in Production Example 4 was added an ortho-cresol novolak type epoxy resin (epoxy equivalent: about 190, number average molecular weight: about 400, average epoxy group in the molecule) Has about 2.2)
157 parts, 34 parts of cyclohexanone, and 5 parts of tri-n-butylamine were blended, and the mixture was kept at 120 ° C. for 3 hours with stirring to obtain an epoxy-modified polyester resin solution having a solid content of 80% by weight. The obtained resin has an epoxy equivalent of about 3,
000, a number average molecular weight of about 24,000.

Then, 833 parts of the carboxyl group-containing acrylic resin solution obtained in Production Example 1 was mixed with 875 parts of the epoxy-modified polyester resin solution. At this time, the molar ratio between the carboxyl group and the epoxy group is 1: 1.57.
Subsequently, after the mixed resin solution was uniformly stirred and mixed, 74 parts of dimethylethanolamine was added, and the mixture was maintained at 90 ° C. for 1 hour. Then, 2,217 parts of deionized water is added dropwise over 1 hour, and the aqueous coating composition of the present invention is an aqueous dispersion having a resin acid value of 70 mgKOH / g, a solid content weight ratio of 25%, a viscosity of 900 mPas, and a particle diameter of 220 nm. I got

Comparative Example 1 "Epicoat 828EL" (trade name, manufactured by Yuka Shell Epoxy Co., Ltd., bisphenol A type epoxy resin, epoxy equivalent: about 190, number average molecular weight: about 350) was placed in a reaction vessel.
1,000 parts, 556 parts of bisphenol A, 172 parts of ethylene glycol monobutyl ether and 1.6 parts of a 50% aqueous solution of tetramethylammonium were added, and the mixture was stirred.
The temperature was raised to 40 ° C. and kept at the same temperature for 5 hours to obtain a high molecular weight epoxy resin solution. The obtained resin had a solid content of 90%, an epoxy equivalent of 3,000, and a number average molecular weight of 8.0.
00.

Next, 630 parts of the acrylic resin solution containing a carboxyl group obtained in Production Example 1 and 110 parts of ethylene glycol monobutyl ether were added to 1,000 parts of the above epoxy resin solution, and the mixture was uniformly stirred and mixed. 50 parts of deionized water and 6 parts of dimethylethanolamine
0 parts were added and kept for 1 hour. Then, deionized water 2,
600 parts were added dropwise over 1 hour to obtain a comparative aqueous coating composition as a water dispersion having a solid content of 25%, a resin acid value of 36 mgKOH / g, a viscosity of 3,000 mPas, and a particle diameter of 180 nm.

Performance Test of Aqueous Coating Composition Each of the aqueous coating compositions obtained in Examples 1 to 4 and Comparative Example 1 was applied to a clean chin-free steel having a thickness of 0.23 mm to have a dry coating thickness of 10 μm. Spray paint like 20
Various coating film performance tests were performed using the coated plate baked and cured at 0 ° C. for 3 minutes based on the following test methods. Also,
The bisphenol A concentration in each aqueous coating composition was measured.

Test method Gel fraction: The weight percentage (%) of the weight of the unextracted coating film after extraction with respect to the weight of the coating film before extraction when the cured coating film was subjected to solvent extraction under acetone reflux for 6 hours. is there.

Substrate adhesion: two painted plates (150 mm ×
5 mm) with the coated film surface as an adherend surface, sandwiching a nylon film, heating this at 200 ° C. for 60 seconds,
A test piece was obtained by applying pressure at 0 ° C. for 30 seconds and fusing the above nylon film to both coating films. Next, the T
Peel adhesion strength tensile tester ("Autograph AGS
-500A "(trade name, manufactured by Shimadzu Corporation). The tensile conditions were as follows: a temperature of 20 ° C. and a tensile speed of 2.
00 mm / min.

Workability: A coated plate is cut into a size of 40 mm × 50 mm, folded in two so that the coating surface is on the outside, and a 3 kg weight is dropped from the height of 42 cm on the bent portion. Then, the portion from the bent portion to the width of 20 mm in length is immersed in a 1% aqueous solution of sodium chloride, and 6.5 V
The current value was measured when the voltage was applied for 6 seconds. The smaller the current value, the better the workability.

Corrosion resistance: A coated plate was cut into a size of 150 × 70 mm, and a cross-cut was made on the coated film so as to reach a base material. Then, the coated plate was subjected to a salt spray test for 3 weeks. The coated plate after the test was visually evaluated according to the following criteria.

：: The rust width from the cut portion is less than 2 mm on one side, Δ: the rust width from the cut portion is 2 mm or more and less than 5 mm on one side, ×: the rust width from the cut portion is 5 mm or more on one side.

Acid resistance: The coated surface after sealing the back and cut surfaces of the coated plate in a 10% aqueous hydrochloric acid solution at 20 ° C. for one week was visually evaluated according to the following criteria.

：: no abnormality is observed, Δ: slight whitening is observed, ×: remarkable whitening is observed.

Alkali resistance: The coated surface after sealing the back and cut surfaces of the coated plate in a 10% aqueous sodium hydroxide solution at 20 ° C. for 1 week was visually evaluated according to the following criteria.

：: No abnormality is observed, Δ: Slight whitening is observed, ×: Extremely whitening is observed.

Bisphenol A concentration: The concentration of bisphenol A in the aqueous coating composition when the aqueous coating composition obtained in each example was dissolved in tetrahydrofuran and analyzed by high performance liquid chromatography is indicated.

Table 1 shows the test results.

[0061]

[Table 1]

[0062]

The aqueous coating composition of the present invention contains free bisphenols in a coating material by using a specific carboxyl group-containing polyester resin, a novolak type epoxy resin and a carboxyl group-containing acrylic resin as raw materials. The problem of environmental hormones has been solved. Moreover, it has excellent paint workability,
It has excellent coating properties such as processability, corrosion resistance, acid resistance, alkali resistance, and flavor.

Therefore, it can be suitably used as an inner surface of a can such as a food can.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Keiji Inomata 4-171-1, Higashi-Hachiman, Hiratsuka-shi, Kanagawa Prefecture Inside Kansai Paint Co., Ltd. (72) Yoshinori Hirano 4-1-1, Higashi-Hachiman, Hiratsuka-shi, Kanagawa Kansai Paint Co., Ltd. (72) Inventor Hideo Yokoi 4-171-1, Higashiyawata, Hiratsuka-shi, Kanagawa F Kansai Paint Co., Ltd. F-term (reference) 4J031 AA20 AA47 AA49 AB01 AC03 AD03 AF12 4J038 CG001 CG021 CG031 DB071 DB471 DD001 DD231 GA06 KA03 MA08 MA10 MA14 PB04 PC02

Claims (8)

[Claims] 1. A carboxyl group-containing polyester resin (a) having a number average molecular weight of 1,000 to 30,000 and an acid value of 5 to 200 mg KOH / g, and a novolak type epoxy resin (b) obtained by an esterification reaction. The carboxyl group-containing acrylic modified polyester resin (B) obtained by reacting the epoxy-modified polyester resin (A) with the carboxyl group-containing acrylic resin (c) is neutralized and dispersed in an aqueous medium. Aqueous coating composition. 2. The composition according to claim 1, wherein the novolak type epoxy resin (b) has a number average molecular weight of 200 to 8,000 and an average of less than 3 epoxy groups in the molecule. 3. The novolak epoxy resin (b) is an orthocresol novolak epoxy resin.
A composition according to claim 1. 4. A carboxyl group-containing polyester resin (a) and a novolak type epoxy resin (b), wherein the carboxyl group of the resin (a) and the epoxy group of the resin (b) have a molar ratio of 1: 1 to 1: 3. The composition according to claim 1, wherein the epoxy-modified polyester resin (A) obtained by the esterification reaction at a mixing ratio of 2,000 to 10,000 and the number average molecular weight of 4,000 to 100,000 is obtained. object. 5. A carboxyl group-containing acrylic resin (c)
The composition according to claim 1, which has an acid value of 100 to 500 mgKOH / g. 6. An epoxy-modified polyester resin (A) and a carboxyl group-containing acrylic resin (c),
/ Resin (c) is 60/40 to 90/10 in terms of solid content weight ratio
The composition according to claim 1, wherein the polyester resin (B) is obtained by reacting at a mixing ratio of: 7. The composition according to claim 1, wherein the carboxyl group-containing acrylic-modified polyester resin (B) has an acid value of 15 to 200 mgKOH / g. 8. The composition according to claim 1, further comprising a crosslinking agent.