JP2012184370A - Aqueous coating composition, and method for manufacturing the same - Google Patents

Abstract

The present invention is capable of forming a coating film excellent in polymerization stability during production and storage stability after production, and excellent in processability and adhesion without using any BPA-derived components. An object is to provide a water-based paint, a method for producing the same, and a coated can.
An aqueous paint containing an acrylic modified polyester resin (A), a basic compound (B), and a curing agent (C), wherein the acrylic modified polyester resin (A) is a polyester resin (D). A polyester resin (F) obtained by reacting an aromatic vinyl monomer, an amide monomer, and a (meth) acrylic acid alkyl ester monomer in the presence of a water-insoluble polymerization initiator (E); Aqueous paint which is a resin obtained by reacting an aromatic vinyl monomer, a carboxyl group-containing monomer, and a (meth) acrylic acid alkyl ester monomer in the presence of a water-insoluble polymerization initiator (E).
[Selection figure] None

Description

  The present invention relates to a water-based paint and an object to be coated using the water-based paint, and relates to an aqueous paint composition suitably used for coating on a metal material or a base paint. Specifically, the present invention relates to an aqueous coating composition for covering a beverage packaging container that contains a beverage. More specifically, the present invention relates to an aqueous coating composition suitable for coating a lid member for a can that requires high processability and corrosion resistance among beverage packaging containers.

A paint containing a BPA type epoxy resin synthesized from bisphenol A (hereinafter abbreviated as “BPA”) and epichlorohydrin has good adhesion to the metal of the coating film, and also has steam sterilization resistance, workability, etc. Since it is good, it is suitably used as a paint for coating inner and outer surfaces of cans.
In the coating material, it is common to use a water-dispersed acrylic modified epoxy resin in which a carboxyl group or the like is introduced into the molecule by modifying the BPA type epoxy resin with an acrylic resin.

  However, in recent years, research results have been reported that BPA has endocrine disrupting effects on organisms, and it has been listed in 67 substances in the list of “chemical substances suspected of having endocrine disrupting effects” published by the Ministry of the Environment. In response to this, the elution of BPA from the inner surface coating film of the can into the contents has become a serious problem. From such a background, a water-based paint for coating the inner surface of a can that does not use any component derived from BPA is desired.

  Therefore, other than the BPA type epoxy resin, as a resin having processability and adhesion similar to those of the BPA type epoxy resin, for example, there is an emulsion type acrylic resin synthesized by an emulsion polymerization method. It is known that an emulsion type acrylic resin generally has a very high molecular weight as compared with an acrylic resin synthesized by a solution polymerization method. This is presumably because the emulsion type acrylic resin has a very high molecular weight, so that good processability and adhesion can be obtained.

  However, since a surfactant is generally used in the emulsion polymerization method, a surfactant is contained in the cured coating film. Since the presence of this surfactant causes deterioration of the steam sterilization resistance of the coating film, at present, the emulsion type acrylic resin synthesized by the emulsion polymerization method is not used in the paint for coating the inner surface of the can.

  Therefore, instead of using a surfactant that causes deterioration in steam sterilization resistance, instead using a water-based acrylic resin having a carboxyl group and a crosslinkable functional group other than a carboxyl group and a base compound, a mixture of acrylic monomers is used. A method in which an aqueous dispersion (pre-emulsion) of a monomer is obtained by preliminarily dispersing in an aqueous medium, and the aqueous dispersion of the monomer is radically polymerized in the presence of a separately prepared aqueous resin having a carboxyl group (hereinafter referred to as a “polymerization”) , Also referred to as “pre-emulsification method”) (see Patent Document 1).

  That is, Patent Document 1 states that a soap-free acrylic resin emulsion obtained by dropwise polymerization of an aqueous dispersion of an acrylic monomer in the presence of an aqueous resin having a carboxyl group can be used in an aqueous coating composition for cans. Are listed. Further, Patent Document 1 describes a water-based coating composition for cans that can form a coating film having excellent processability, adhesion, and boiling resistance.

  However, depending on the type of contents, the can covered with the paint for cans may be subjected to a steam sterilization process more severe than boiling. When a can coated with the aqueous coating composition of Patent Document 1 is steam sterilized, the coating film may be whitened or blistered (dotted peeling).

  Further, the beverage can filled with the carbonated beverage is filled with the contents at a low temperature of about 5 ° C. and attached to the lid, and then returned to room temperature. During this process, the carbonic acid volatilizes and the pressure inside the can increases, so the lid portion of the can swells outward due to the pressure from inside. Even after this, the volatilization from the filler of carbonic acid and the dissolution in the filler are repeated due to the change in the ambient temperature, and the lid repeats the change in the uneven shape. As a result, the lid is deformed in a state where the contents are filled, and corrosion of the deformed portion is likely to occur. Therefore, various processes are performed on the lid portion in consideration of such deformation due to pressure. Since these various processes are performed after providing a double-sided coating film on the lid material, the coating composition has high processability so as not to cause a coating film defect in various processes, and the lid is uneven after filling the contents. High corrosion resistance is required so that corrosion does not occur even if this change is repeated. When the aqueous coating composition of Patent Document 1 is applied, these high processability and corrosion resistance cannot be obtained.

  Further, an aqueous resin dispersion composed of a polyester resin having a carboxyl group, a basic compound, and water is used as a polymer emulsifier component, and a polyester resin and an ethylenically unsaturated monomer are used as an emulsified component. A composite polymer was proposed (see Patent Document 2). In the method exemplified in Patent Document 2, polyester and ethylenically unsaturated monomers that are to be emulsified are pre-emulsified with a polymer emulsifier, and this is emulsion-polymerized and combined in an aqueous medium with a water-soluble initiator. It is to become. In general, emulsion polymerization is explained by a special mechanism in which a solubilized monomer reacts in a micelle and the monomer is sequentially supplied from dispersed monomer droplets. From this point of view, it is difficult to say that the polyester and the ethylenically unsaturated monomer are necessarily combined in the reaction. With the composite polymer described in Patent Document 2, there are many variations in properties between production lots, and a uniform quality paint can be obtained. Difficult to get. Furthermore, when the polyester resin content in the emulsified component is increased, the compatibility between the polyester resin that is the emulsified component, the ethylenically unsaturated monomer, and the polymer thereof decreases, so that the polymerization stability, and There arises a problem that the resulting emulsion lacks dispersion stability.

  In addition, when crystalline polyester is used as an emulsified component, an operation process for dissolving the polyester in a solvent or a monomer becomes indispensable, and the production process becomes complicated and takes a long time. Become.

JP 2002-155234 A Japanese Patent Laid-Open No. 2005-60460

  The object of the present invention is to provide a can that can form a coating film having excellent polymerization stability during production and storage stability after production, and excellent workability and adhesion without using any BPA-derived components. An aqueous coating composition for coating an inner surface lid, a method for producing the same, and a coated can formed by coating the inner surface of the lid portion of the can using the same.

  As a result of intensive studies, the present inventors have determined that the polyester resin is modified in two steps using a radical polymerizable unsaturated monomer in the presence of a radical polymerizable initiator, thereby stabilizing the polymerization during production. The present invention has been completed by finding that it is possible to provide a water-based paint excellent in workability and storage stability after production, and excellent in processability and adhesion, a method for producing the same, and a coated can.

  That is, the first invention is an aqueous paint containing an acrylic modified polyester resin (A), a basic compound (B), and a curing agent (C), wherein the acrylic modified polyester resin (A) is a polyester. Polyester resin formed by reacting resin (D), aromatic vinyl monomer, amide monomer, and (meth) acrylic acid alkyl ester monomer in the presence of a water-insoluble polymerization initiator (E) ( F) a resin obtained by reacting an aromatic vinyl monomer, a carboxyl group-containing monomer, and a (meth) acrylic acid alkyl ester monomer in the presence of a water-insoluble polymerization initiator (E). Is a water-based paint characterized by

  A second invention is the water-based paint according to the first invention, wherein the polyester resin (D) is obtained by reacting a polyhydric alcohol and a polyvalent carboxylic acid.

  A third invention is the water-based paint according to the second invention, wherein the polyhydric alcohol is a proportion of 60 to 80 mol% of a dihydric alcohol and 20 to 40 mol% of a trihydric alcohol.

  The fourth invention is a step (1) of obtaining a polyester resin (D) by reacting a polyhydric alcohol and a polyvalent carboxylic acid, and in the presence of the obtained polyester resin (D), an aromatic vinyl. A polyester resin (F) is obtained by reacting a monomer, an amide monomer, a (meth) acrylic acid alkyl ester monomer, and a water-insoluble polymerization initiator (E), and then an aromatic vinyl monomer, A step (2) of obtaining an acrylic-modified polyester resin (A) by adding a carboxyl group-containing monomer, a (meth) acrylic acid alkyl ester monomer, and a water-insoluble polymerization initiator (E) and reacting them is obtained. Water comprising a step (3) of obtaining a water-based paint by blending the acrylic-modified polyester resin (A), the basic compound (B), and the curing agent (C). It is a manufacturing method of paint.

  A fifth invention is characterized in that, in the step (1), the polyhydric alcohol is a proportion of 60 to 80 mol% of a dihydric alcohol and 20 to 40 mol% of a trihydric alcohol. It is a manufacturing method of a coating material.

  In a sixth aspect of the invention, in step (2), in the presence of the polyester resin (D), an aromatic vinyl monomer, an amide monomer, and a (meth) acrylic acid alkyl ester monomer are water-insoluble polymerized. Initiator (E) is added and reacted to obtain polyester resin (F), then aromatic vinyl monomer, carboxyl group-containing monomer, (meth) acrylic acid alkyl ester monomer, and water-insoluble polymerization The method for producing a water-based paint according to the fourth or fifth invention, wherein the initiator (E) is added and reacted.

  The seventh invention is characterized in that the amide monomer is at least one monomer selected from the group consisting of N-alkoxyalkyl (meth) acrylamide, N-hydroxyalkyl (meth) acrylamide and (meth) acrylamide. The water-based paint according to any one of the first to third inventions.

  The eighth invention is the water-based paint according to any one of the first to third inventions and the seventh invention, characterized in that the number average molecular weight of the polyester resin (D) is 2,000 to 7,000. It is.

  A ninth invention is a coated can having an inner surface with a coating film formed from the water-based paint according to any one of the first to third inventions, the seventh and eighth inventions.

  A tenth invention is a coated can characterized by having a coating film formed from the water-based paint according to any one of the first to third inventions, the seventh and eighth inventions on the inner surface of the lid.

  According to the present invention, a can inner surface lid capable of forming a coating film having excellent polymerization stability during production and storage stability after production, and excellent workability and adhesion without using any BPA-derived constituent components. An aqueous coating composition for coating, a method for producing the same, and a coated can formed by coating the inner surface of the lid of the can with the coating composition can be provided.

<Acrylic modified polyester resin (A)>
First, acrylic modified polyester resin (A) is described.
In the present invention, “acrylic modification” refers to reacting a polyester resin and a radical polymerizable monomer in the presence of a non-polymerization initiator. This reaction is preferably performed by heating a solution obtained by dissolving a polyester resin in a solvent.

  In the present invention, by heating the polyester resin (D), the aromatic vinyl monomer, the amide monomer, and the (meth) acrylic acid alkyl ester monomer, a part of the hydroxyl group of the polyester resin (D) Acrylic modification is performed by reaction of a part of the amide group of the amide monomer. At the same time, a copolymerization reaction of the amide monomer and another radical polymerizable monomer proceeds. By these reactions, a polyester resin (F) is first obtained. By reacting the obtained polyester (F) with a carboxyl group-containing monomer and a (meth) acrylic acid ester monomer in the presence of a water-insoluble polymerization initiator at a certain temperature, an acrylic-modified polyester resin ( A) is obtained.

  Since the obtained acrylic modified polyester resin (A) contains a carboxyl group, an acrylic modified polyester resin having a carboxyl group is obtained by neutralizing a part or all of the carboxyl group using the basic compound (B). (A) can be dissolved in water or dispersed in water. The acrylic paint-modified polyester resin (A) partially or wholly neutralized with the basic compound (B) is stirred while adding water little by little, and further the curing agent (C) is added, whereby the aqueous paint of the present invention is obtained. Obtainable.

  In the present invention, the (meth) acrylic acid alkyl ester monomer is not particularly limited, and one or more kinds of monomers can be used in combination. 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 (meta ) Acrylate, lauryl (meth) acrylate, benzyl (meth) acrylate, stearyl (meth) acrylate, cetyl (meth) acrylate, cyclohexyl (meth) acrylate, alkyl ester of acrylic acid or methacrylic acid such as isobornyl (meth) acrylate, hydroxy Ethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, hydroxyamyl (meth) acrylate, hydroxyhexyl (meth) acrylate, etc. Such as hydroxyalkyl (meth) acrylate.

  Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, vinyl toluene, and the like. Here, “(meth) acrylate” at the end of each compound in the present invention means “acrylate or methacrylate”.

  Examples of amide monomers include acrylamide, methacrylamide, N-methoxymethyl (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, Nn-propoxymethyl (meth) acrylamide, N-isopropoxymethyl (meth) acrylamide, Examples include Nn-butoxymethyl (meth) acrylamide, N-sec-butoxymethyl (meth) acrylamide, N-tert-butoxymethyl (meth) acrylamide, etc. In the present invention, the crosslinking reaction during coating film formation As a result of considering the properties, it is more preferable to use at least one of N-alkoxyalkyl (meth) acrylamide, N-hydroxyalkyl (meth) acrylamide and (meth) acrylamide.

  The polyester resin (D) is not dispersed or dissolved in water as it is and is essentially insoluble in water, but hydrophilicity is imparted by modification with a radically polymerizable monomer having a hydrophilic group. As the hydrophilic group, there are a carboxyl group, a sulfonic acid group, a hydroxyl group, a quaternary ammonium salt, and the like, and a carboxyl group is preferable in terms of easy adjustment of water dispersibility by changing the acid value. Examples of the radical polymerizable monomer having a carboxyl group include acrylic acid, methacrylic acid, maleic acid, fumaric acid, and itaconic acid.

<Polyester resin (D)>
In the present invention, the polyester resin (D) means a copolymer having an ester bond generally obtained by condensation or transesterification of a dicarboxylic acid or dicarboxylic acid ester and an alcohol.

  As the dicarboxylic acid, aromatic dicarboxylic acid, aliphatic dicarboxylic acid, alicyclic dicarboxylic acid and the like are preferable.

  Examples of the alcohol include aliphatic diols having 2 to 10 carbon atoms having 2 hydroxyl groups, alicyclic diols having 6 to 12 carbon atoms having 2 hydroxyl groups, and 2 hydroxyl groups and ether bonds. A diol containing, and those having 3 or more hydroxyl groups are preferred.

  Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, orthophthalic acid, naphthalene dicarboxylic acid, and biphenyl dicarboxylic acid.

  Examples of the aliphatic dicarboxylic acid include succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, and dimer acid.

  Examples of the alicyclic dicarboxylic acid include 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid and its anhydride. Examples of the dicarboxylic acid having a polymerizable double bond include α, β-unsaturated dicarboxylic acids such as fumaric acid, maleic acid, maleic anhydride, itaconic acid and citraconic acid, and other 2,5-norbornene dicarboxylic acid anhydrides. And tetrahydrophthalic anhydride.

  Examples of the aliphatic diol having 2 to 10 carbon atoms include ethylene glycol, 1,2-propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1, Examples of the alicyclic diol having 6 to 12 carbon atoms such as 6-hexanediol, 3-methyl-1,5-pentanediol, 1,9-nonanediol, 2-ethyl-2-butylpropanediol, Examples include 4-cyclohexanedimethanol.

  Examples of the diol containing an ether bond include diethylene glycol, triethylene glycol and dipropylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like.

  Examples of alcohols having 3 or more hydroxyl groups include glycerin, trimethylolethane, trimethylolpropane, and pentaerythritol.

  In the present invention, the polyester resin (D) can be produced by arbitrarily combining one or more of the above dicarboxylic acids and alcohols. Among these, considering the physical properties such as water resistance and hardness of the coating film, it is preferable to use an aromatic dicarboxylic acid or an alicyclic dicarboxylic acid and an aliphatic dicarboxylic acid in combination as the dicarboxylic acid component.

  On the other hand, with respect to alcohols, it is necessary to use an alcohol having two or more hydroxyl groups in order to ensure physical properties such as processability of the coating film after drying and baking. Furthermore, it is more preferable to use an alcohol having three or more hydroxyl groups in combination from the viewpoint of ensuring the storage stability of the obtained water-based paint. However, if a polyhydric alcohol having 4 or more hydroxyl groups is used, gelation may occur during the copolymerization reaction. Therefore, in the present invention, it is desirable to use a trihydric alcohol having three hydroxyl groups in combination. As a usage-amount of a trihydric alcohol, although 0-60 mol% in all the alcohol components can be used, it is preferable to use at 10-50 mol%. If it is more than 60 mol%, gelation occurs during the copolymerization reaction. When the amount is less than 10 mol%, the above-described acrylic modification reaction does not proceed or is difficult to proceed, and it becomes difficult to obtain a polymer emulsion having excellent storage stability.

  In the present invention, the number average molecular weight of the polyester resin (D) is preferably 1000 to 10,000. If the number average molecular weight is less than 1000, physical properties such as workability of the coating film after drying and baking may be deteriorated. On the other hand, when the number average molecular weight is more than 10,000, it is difficult to disperse in water, and it becomes difficult to obtain a stable polymer emulsion. The acid value of the polyester resin (D) is preferably 20 or less, more preferably 10 or less. When the acid value is 20 or more, gelation is likely to occur during the acrylic modification reaction, and it becomes difficult to obtain a stable polymer emulsion. In the present invention, the number average molecular weight is a value in terms of standard polystyrene in gel permeation chromatography (hereinafter referred to as GPC).

  When the polyester resin (D) is dissolved in advance with an arbitrary solvent that can be dissolved, it becomes easy to handle. Specifically, for example, ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, ethylene glycol diethyl ether, ethylene glycol mono (iso) propyl ether, ethylene glycol di (iso) propyl ether, ethylene glycol mono (iso) Butyl ether, ethylene glycol di (iso) butyl ether, ethylene glycol mono-tert-butyl ether, ethylene glycol monohexyl ether, 1,3-butylene glycol-3-monomethyl ether, 3-methoxybutanol, 3-methyl-3-methoxybutanol, Diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, diethylene glycol monoethyl ether , Diethylene glycol diethyl ether, diethylene glycol mono (iso) propyl ether, diethylene glycol di (iso) propyl ether, diethylene glycol mono (iso) butyl ether, diethylene glycol di (iso) butyl ether, diethylene glycol monohexyl ether, diethylene glycol dihexyl ether, triethylene glycol dimethyl ether, propylene Glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono (iso) propyl ether, propylene glycol mono (iso) butyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol di (iso) propyl ether, propylene Glycol di (iso) butyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono (iso) propyl ether, dipropylene glycol mono (iso) butyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, Various ether alcohols or ethers such as diethylene glycol di (iso) propyl ether and dipropylene glycol di (iso) butyl ether; methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol, isobutyl alcohol, sec-butyl alcohol, tert -Alcohols such as butyl alcohol and furfuryl alcohol; methyl ethyl Ketones such as ruketone, dimethyl ketone and diacetone alcohol; glycols such as ethylene glycol, diethylene glycol, propylene glycol and dipropylene glycol; ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, 1-methoxy-2-propyl acetate And alkoxyesters such as propylene glycol monomethyl ether acetate. These may be used alone or in combination of two or more. The non-volatile content of the polyester resin (D) dissolved in the solvent is preferably as high as possible in consideration of the reaction solid content concentration in acrylic modification, but the viscosity is too high to make actual handling difficult. Therefore, it is preferably about 70 to 80%.

<Water-insoluble polymerization initiator (E)>
The water-insoluble polymerization initiator (E) used in the present invention will be described. The radical polymerization initiator is roughly classified into a water-soluble initiator and a water-insoluble initiator. These polymerization initiators react with radically polymerizable unsaturated monomers to produce polymers that are aggregates of molecules with various degrees of polymerization. Then, a part of the structure forming the initiator molecule is introduced to the end of the polymer molecule. In the present invention, it is important to use a water-insoluble radical polymerization initiator. Since the water-insoluble polymerization initiator does not contain a functional group having high hydrophilicity in the molecule, the terminal of the obtained polymer molecule is not hydrophilic. Therefore, even if it is a polymer molecule with a small molecular weight, the polymer molecule does not exhibit surfactant properties. Therefore, a polymer obtained using a water-insoluble initiator is likely to form a coating film excellent in retort resistance, specifically, a coating film that is not easily whitened even by retort treatment.

  In the present invention, the water-insoluble polymerization initiator (E) is a ketone peroxide such as cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, methylcyclohexanone peroxide, acetylacetone peroxide; 1,1 bis (tert- Butylperoxy) 3,3,5-trimethylcyclohexane, 1,1-bis (tert-butylperoxy) cyclohexane, 2,2-bis (tert-butylperoxy) octane, n-butyl-4,4-bis Peroxyketals such as (tert-butylperoxy) valerate and 2,2-bis (tert-butylperoxy) butane; di-tert-butyl peroxide, tert-butylcumyl peroxide, dicumyl peroxide, α, α'-bis (tert -Butylperoxy-i-propyl) benzene, 2,5-dimethyl-2,5-di (tert-butylperoxy) hexane, 2,5-dimethyl2,5-di (tert-butylperoxy) hexyne-3 Dialkyl peroxides such as: acetyl peroxide, i-butyryl peroxide, octanoyl peroxide, decanoyl peroxide, lauroyl peroxide, 3,5,5-trimethylhexanoyl peroxide, succinic acid peroxide, benzoyl peroxide Diacyl peroxides such as 2,4-dichlorobenzoyl peroxide; di-i-propyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, di-n-propyl peroxydicarbonate, bis- (4- tert-Butyl Rohexyl) peroxydicarbonate, dimyristyl peroxydicarbonate, di-2-ethoxyethyl peroxydicarbonate, dimethoxy-i-propyl peroxydicarbonate, di (3-methyl-3-methoxybutyl) peroxydicarbonate Peroxydicarbonates such as diallyl peroxydicarbonate; tert-butyl peroxyacetate, tert-butylperoxy-i-butyrate, tert-butylperoxypivalate, cumylperoxyneodecanoate, tert-butylper Various peracids such as peroxyesters such as oxylaurate, tert-butyl peroxybenzoate, cumyl peroxyoctate, tert-hexyl peroxypivalate, cumyl peroxyneohexanoate Compound-based initiators, azobis-i-butyronitrile, azobismethylbutyronitrile, azobis- (2,4-dimethylvaleronitrile), 2,2′-azobis- (4-methoxy-2,4-dimethyl) Various azo initiators such as valeronitrile), 1,1′-azobis- (cyclohexane-1-carbonitrile), dimethyl 2,2′-azobisisobutyrate are used, and peroxide initiators are preferred.

  The amount of the water-insoluble polymerization initiator (E) used is preferably about 1 to 3 parts by weight, more preferably 1.5 to 2.5 parts by weight, based on 100 parts by weight of the radical polymerizable unsaturated monomer. . When the amount is less than 1 part by weight, gelation tends to occur during acrylic modification. Moreover, when more than 3 weight part, sufficient molecular weight as an acrylic modified polyester resin (A) cannot be obtained, and there exists a tendency for physical properties, such as workability at the time of coating-film formation, to be inferior.

<Basic compound (B)>
The basic compound (B) is one of the carboxyl groups when the polyester resin (D) is acrylic-modified and at the same time, a radical polymerizable unsaturated monomer having a carboxyl group and another radical polymerizable unsaturated monomer are copolymerized. It is used for neutralizing a part or all of the polymer and water-solubilizing or dispersing the acrylic-modified polyester resin (A) having a carboxyl group in water.

  In the present invention, examples of the basic compound (B) include organic amine compounds, ammonia, alkali metal hydroxides, and the like. Examples of organic amine compounds include monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monopropylamine, dipropylamine, monoethanolamine, diethanolamine, triethanolamine, N, N-dimethyl-ethanolamine, N, N-diethyl-ethanolamine, 2-dimethylamino-2-methyl-1-propanol, 2-amino-2-methyl-1-propanol, N-methyldiethanolamine, N-ethyldiethanolamine, monoisopropanolamine, diisopropanol Examples include amines and triisopropanolamine. Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, and potassium hydroxide. These basic compounds (B) are preferably used in an amount of 10 to 150 mol% with respect to 100 mol% of the carboxyl group having a carboxyl group.

<Curing agent (C)>
In addition to the polymer emulsion described above, the water-based paint of the present invention further improves the curability and adhesion of the coating film as required, such as phenol resin, amino resin, polyvinyl alcohol, polyvinyl alcohol derivatives, etc. One or more curing agents can be added.

  The phenol resin or amino resin can react with a carboxyl group in the acrylic-modified polyester resin (A) in addition to self-crosslinking reaction. Moreover, the hydroxyl group in a polyester resin (D), a phenol resin, and an amino resin can also react with those hydroxyl groups. Furthermore, since the radically polymerizable unsaturated monomer has a crosslinkable functional group derived from an amide monomer, it can also react with these crosslinkable functional groups.

  In the present invention, the phenol resin is a trifunctional phenolic compound such as carboxylic acid, metacresol, 3,5-xylenol, or a bifunctional phenolic compound such as orthocresol, paracresol, paratertiary butylphenol and formaldehyde in the presence of an alkali catalyst. Can be mentioned.

  In the present invention, examples of the amino resin include urea, melamine, and benzoguanamine added with formalin. As the phenol resin and amino resin, those obtained by etherifying some or all of the methylol groups generated by addition of formalin with alcohols having 1 to 12 carbon atoms are also preferably used. When phenol resin or amino resin is used, 0.5 to 20 parts by weight should be added to 100 parts by weight of the total of acrylic modified polyester resin (A), basic compound (B) and curing agent (C). It is preferable to add 2 to 10 parts by weight.

  A hydrophilic organic solvent can be added to the water-based paint of the present invention for the purpose of improving paintability. Examples of hydrophilic organic solvents include ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, ethylene glycol diethyl ether, ethylene glycol mono (iso) propyl ether, ethylene glycol di (iso) propyl ether, ethylene glycol mono (iso ) Butyl ether, ethylene glycol di (iso) butyl ether, ethylene glycol mono-tert-butyl ether, ethylene glycol monohexyl ether, 1,3-butylene glycol-3-monomethyl ether, 3-methoxybutanol, 3-methyl-3-methoxybutanol , Diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, diethylene glycol monoethyl Ether, diethylene glycol diethyl ether, diethylene glycol mono (iso) propyl ether, diethylene glycol di (iso) propyl ether, diethylene glycol mono (iso) butyl ether, diethylene glycol di (iso) butyl ether, diethylene glycol monohexyl ether, diethylene glycol dihexyl ether, triethylene glycol dimethyl ether, Propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono (iso) propyl ether, propylene glycol mono (iso) butyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol di (iso) propyl ether, Pyrene glycol di (iso) butyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono (iso) propyl ether, dipropylene glycol mono (iso) butyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether Various ether alcohols or ethers such as diethylene glycol di (iso) propyl ether and dipropylene glycol di (iso) butyl ether; methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol, isobutyl alcohol, sec-butyl alcohol, alcohols such as tert-butyl alcohol and furfuryl alcohol; Ketones such as ruethyl ketone, dimethyl ketone, diacetone alcohol; glycols such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol; ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, 1-methoxy-2-propyl acetate And alkoxyesters such as propylene glycol monomethyl ether acetate. These may be used alone or in combination of two or more.

  In addition, for the purpose of improving the paintability, the water-based paint of the present invention may contain various auxiliary agents such as a hydrophobic organic solvent, a surfactant, and an antifoaming agent.

  The method for producing a water-based paint in the present invention will be specifically described below. First, step (1) is performed as a step of obtaining the polyester resin (D). This step has been described in detail in the portion related to the polyester resin (D).

  Next, step (2) is performed as a step of obtaining the acrylic-modified polyester resin (A). The acrylic modification is performed in a state where the polyester resin (D) is dissolved in an organic solvent, and is performed by reacting a mixture of a radical initiator and a radical polymerizable monomer at a certain temperature. What is important here is that the acrylic modification is carried out in two stages. In the first stage, an amide monomer is essential, and in the second stage, a carboxyl group-containing monomer is essential.

  In the acrylic modification, in both the first stage and the second stage, the radically polymerizable unsaturated monomer and the radically polymerizable initiator are dissolved in an organic solvent in advance if necessary, and the organic solvent is previously removed. In addition, it is added dropwise to the dissolved polyester resin (D) and polyester resin (D-1) over a certain temperature and a certain time. Further, after the radically polymerizable unsaturated monomer and the radically polymerizable initiator are separately dropped over a certain period of time, the reaction can be continued by further heating while stirring for a certain period of time. In addition, after adding a part of the radical polymerizable unsaturated monomer at a time, and then dropping the remaining radical polymerizable unsaturated monomer and the radical polymerizable initiator separately over a certain period of time, further a certain period of time The reaction can be allowed to proceed by continuing heating while stirring.

  The reaction nonvolatile concentration in the first and second stage acrylic modification, that is, the ratio of the total amount of the polyester resin (D) or polyester resin (F) and the radical polymerizable unsaturated monomer in the reaction solution is particularly limited. However, it is preferably about 50 to 85% by weight, more preferably 60 to 75% by weight. In order to satisfy this condition, the organic solvent dissolved in the radically polymerizable unsaturated monomer can be the organic solvent necessary for dissolving the polyester resin (D) mentioned above, or the solvent for dissolving the polyester resin (D). May be the same or different. In order to sufficiently proceed with the acrylic modification, the reaction temperature during modification is preferably 80 to 130 ° C., and the reaction time is preferably about 1 to 5 hours.

  As the weight ratio of the total amount of the first-stage and second-stage radically polymerizable unsaturated monomers and the polyester resin (D), the former / the latter is preferably 40/60 to 60/40, and 45/55 to 55. / 45 is more preferable. When the amount of the radical polymerizable unsaturated monomer is more than 60% by weight, the ratio of the polyester resin is relatively low, and the polyester resin has excellent performance, that is, high processability, excellent water resistance, and excellent resistance to various substrates. Adhesiveness tends to be insufficient, and there is a possibility that the undesirable performance of the acrylic polymer formed by radical polymerization, that is, processability and water resistance, may decrease. On the other hand, when the ratio of the radically polymerizable unsaturated monomer is less than 40% by weight, a hydrophilic group such as a carboxyl group is relatively insufficient, and it becomes difficult to obtain a stable polymer emulsion.

  The first stage of acrylic modification in the step (2) has been described above that an amide-based monomer is essential. This is because part of the hydroxyl group contained in the polyester resin (D) is Part of the amide monomer contained in the mixture of the radically polymerizable unsaturated monomer in the second stage, that is, the mixture of the aromatic vinyl monomer and the amide monomer and the (meth) acrylic acid alkyl ester monomer. This is because the reaction of acrylic modification proceeds by the reaction of the amide group. Therefore, as described above, the amount of the amide monomer is important. If this amount is too small, acrylic modification is not performed and water-based treatment cannot be performed. On the other hand, if the content of the amide monomer is too large, the viscosity increases during the modification reaction, resulting in gelation, which also makes it impossible to make it aqueous. In the present invention, the total radical polymerizable unsaturated monomer is preferably about 100 parts by weight and 2 to 23 parts by weight, more preferably 5 to 20 parts by weight. Here, other radical polymerizable unsaturated monomers can be arbitrarily selected, but it is desirable not to use a carboxyl group-containing monomer. This is because the amide group in the amide monomer reacts preferentially with the carboxyl group in the carboxyl group-containing monomer, and the carboxyl group necessary for the aqueous treatment in step (3), which will be described later, disappears. This is because it is difficult or impossible. Therefore, even when the acrylic modification is carried out in one stage without dividing it into the first stage and the second stage, it is similarly difficult to make the aqueous solution, and a stable polymer emulsion cannot be obtained.

  The acrylic modification in the second step in the step (2) is described above that the carboxyl group-containing monomer is essential. The reason for this is that by using the carboxyl group-containing polymerizable unsaturated monomer, This is to produce a stable polymer emulsion. As content of a carboxyl group-containing monomer, about 10-50 weight part is desirable in 100 weight part of all radically polymerizable unsaturated monomers, and 20-40 weight part is more preferable. When the amount is more than 50 parts by weight, the water resistance after the formation of the coating film is deteriorated, and when the amount is less than 10 parts by weight, the hydrophilic group becomes insufficient and the aqueous solution becomes difficult, and a stable polymer emulsion cannot be obtained. For the reason described above, it is desirable not to contain an amide monomer in the second stage. Other radical polymerizable unsaturated monomers are not particularly limited, and may be one or more of the (meth) acrylic acid alkyl ester monomers and aromatic vinyl monomers listed above. Arbitrarily selected.

  In step (3), the carboxyl group in the acrylic-modified polyester resin (A) solution is partially or completely neutralized with the basic compound (B), and then water is gradually added dropwise to form a polymer emulsion. The amount of water is preferably 40 to 50 parts by weight with respect to 100 parts by weight of the acrylic-modified polyester resin (A) solution.

  The water-based paint of the present invention can be widely used for general metal materials or metal products, but can be suitably used as a paint for coating the inner and outer surfaces of cans that contain beverages and foods. It is suitable for.

  As the metal, aluminum, tin-plated steel plate, chrome-treated steel plate, nickel-treated steel plate or the like is used, and these materials may be subjected to surface treatment such as zirconium treatment or phosphoric acid treatment.

  Examples of the coated can of the present invention include food cans, beverage cans, and aerosol cans according to the contents. In addition, there are two types of cans, a two-piece can composed of two parts, a lid part and a body part integrated with the bottom part, and a three-piece can composed of three parts, a lid part, a bottom part, and a body part. Each is further divided into an outer surface side and an inner surface side.

  The coated can of the present invention can be produced by coating the metal plate or the can with the aqueous paint described above. As the coating method, roll coater coating is desirable, but spray coating such as air spray, airless spray, electrostatic spray, etc., dip coating, electrodeposition coating, etc. can also be applied.

In the present invention, the coating film depends on the form, part, contents, etc. of the can used, but the coating film weight after drying is 5 to 300 mg / dm ² , especially about 50 to 150 mg / dm ² especially for the lid. It is. The water-based paint of the present invention can form a coating film only by volatilization of volatile components after coating, but it is better to add a baking process in order to obtain excellent steam sterilization resistance, processability and adhesion. . As conditions for baking, baking at a temperature of 150 ° C. to 280 ° C. for 10 seconds to 30 minutes is desirable.

  Hereinafter, the present invention will be described more specifically with reference to synthesis examples, comparative synthesis examples, examples, and comparative examples. In each example, parts and% are based on weight unless otherwise specified.

<Synthesis of polyester resin (D)>
(Synthesis Example 1) [Synthesis of Polyester Resin (D-1)]
Based on the composition shown in Table 1, 88 parts of isophthalic acid, 44 parts of terephthalic acid, 373 parts of sebacic acid, 197 parts of propylene glycol, and 99 parts of trimethylolpropane are respectively weighed and prepared, and charged into a flask equipped with a fractionator. The mixture was heated with stirring under a nitrogen stream and dehydrated and transesterified at 160 to 230 ° C. When the acid value became 10 or less, the reaction vessel was gradually depressurized using a vacuum pump, and the pressure was reduced at 100 Torr and 210 ° C. for 1 hour. As a result, a polyester resin having a number average molecular weight of 5000 and an acid value of 4.1 (D -1) was obtained.
(Synthesis Examples 2-5) [Synthesis of Polyester Resins (D-2) to (D-5)]
Based on the composition shown in Table 1, the preparation weight was calculated in the same manner as the polyester resin (D-1) so that the total amount of each component was 800 parts, and the polyester resin (D-2) to ( D-5) was obtained.

(Example 1) [Synthesis of acrylic modified polyester resin (A-1) and preparation of water-based paint]
100 parts of the polyester resin (D-1) obtained in Synthesis Example 1 and 45 parts of diethylene glycol monobutyl ether are charged into a flask and heated to 110 ° C. and dissolved. In a separate container, 12 parts of N-butoxymethylacrylamide, 12 parts of styrene, 16 parts of ethyl acrylate, 21 parts of diethylene glycol monobutyl ether and 1.1 parts of benzoyl peroxide are mixed, stirred, and poured into a dropping funnel. This was dropped and reacted in the first stage over 1 hour to a solution containing the polyester resin (D-1) in the flask. 30 minutes after the completion of the dropping, 0.1 part of benzoyl peroxide is added, and the reaction is further performed for 30 minutes. Next, 27 parts of methacrylic acid, 15 parts of styrene, 18 parts of ethyl acrylate, 29 parts of ethylene glycol monoisobutyl ether and 1.6 parts of benzoyl peroxide are mixed and stirred in a separate container in advance and poured into a dropping funnel. . This was dropped and reacted in the second stage to the solution containing the polyester resin (D-1) in the flask over 1 hour. 30 minutes after the completion of the dropping, 0.2 part of benzoyl peroxide is added, and the reaction is further performed for 30 minutes. After completion of the reaction, the mixture is cooled to 90 ° C., 13 parts of a 50% aqueous solution of N, N-dimethyl-ethanolamine is added, and the mixture is stirred for 10 minutes. 261 parts of ion exchange water was poured into a dropping funnel in advance, and this was dropped into the flask over 1 hour to obtain an aqueous dispersion of acrylic modified polyester resin (A-1) having a nonvolatile content of 33%. 145 parts of this aqueous dispersion are weighed, and 1 part (non-volatile content 50%) of a phenol resin-based curing agent “Shonol BKS-368” manufactured by Showa Polymer Co., Ltd. is added and stirred as a curing agent. Further, ion exchange water was added to adjust the non-volatile content to 30% to obtain an aqueous paint.

Examples 2 to 5 [Synthesis of acrylic modified polyester resins (A-2) to (A-5) and preparation of water-based paint]
Except that the polyester resin (D-1) in Example 1 was replaced with the polyester resins (D-2) to (D-5) obtained in Synthesis Examples 2 to 5, respectively, all were the same as in Example 1. Carried out.

(Example 6) [Synthesis of acrylic modified polyester resin (A-6), preparation of water-based paint]
90 parts of the polyester resin (D-1) obtained in Synthesis Example 1 and 40 parts of diethylene glycol monobutyl ether are charged into a flask and heated to 110 ° C. and dissolved. In a separate container, 13 parts of N-butoxymethylacrylamide, 13 parts of styrene, 18 parts of ethyl acrylate, 23 parts of diethylene glycol monobutyl ether and 1.2 parts of benzoyl peroxide are mixed, stirred, and poured into a dropping funnel. This was dropped and reacted in the first stage over 1 hour to a solution containing the polyester resin (D-1) in the flask. 30 minutes after the completion of the dropping, 0.1 part of benzoyl peroxide is added, and the reaction is further performed for 30 minutes. Next, 30 parts of methacrylic acid, 17 parts of styrene, 20 parts of ethyl acrylate, 31 parts of ethylene glycol monoisobutyl ether and 1.8 parts of benzoyl peroxide are mixed and stirred in a separate container in advance and poured into a dropping funnel. . This was dropped and reacted in the second stage to the solution containing the polyester resin (D-1) in the flask over 1 hour. 30 minutes after the completion of the dropping, 0.2 part of benzoyl peroxide is added, and the reaction is further performed for 30 minutes. After completion of the reaction, the mixture is cooled to 90 ° C., 15 parts of a 50% aqueous solution of N, N-dimethyl-ethanolamine is added, and the mixture is stirred for 10 minutes. 259 parts of ion exchange water was poured into a dropping funnel in advance, and this was dropped into the flask over 1 hour to obtain an aqueous dispersion of an acrylic-modified polyester resin (A-6) having a nonvolatile content of 33%. 145 parts of this aqueous dispersion is weighed, and 1 part (Shonol BKS-368) manufactured by Showa Polymer Co., Ltd. is added as a curing agent (50% nonvolatile content) and stirred. Further, ion exchange water was added to adjust the non-volatile content to 30% to obtain an aqueous paint.
(Example 7) [Synthesis of acrylic modified polyester resin (A-7) and preparation of water-based paint]
110 parts of the polyester resin (D-1) obtained in Synthesis Example 1 and 49 parts of diethylene glycol monobutyl ether are charged into a flask and heated to 110 ° C. and dissolved. In a separate container, 11 parts of N-butoxymethylacrylamide, 11 parts of styrene, 14 parts of ethyl acrylate, 19 parts of diethylene glycol monobutyl ether and 1.0 part of benzoyl peroxide are mixed, stirred, and poured into a dropping funnel. This was dropped and reacted in the first stage over 1 hour to a solution containing the polyester resin (D-1) in the flask. 30 minutes after the completion of the dropping, 0.1 part of benzoyl peroxide is added, and the reaction is further performed for 30 minutes. Next, 24 parts of methacrylic acid, 14 parts of styrene, 16 parts of ethyl acrylate, 25 parts of ethylene glycol monoisobutyl ether, and 1.4 parts of benzoyl peroxide are mixed and stirred in a separate container in advance and poured into a dropping funnel. . This was dropped and reacted in the second stage to the solution containing the polyester resin (D-1) in the flask over 1 hour. 30 minutes after the completion of the dropping, 0.2 part of benzoyl peroxide is added, and the reaction is further performed for 30 minutes. When the reaction is completed, the mixture is cooled to 90 ° C., 12 parts of a 50% aqueous solution of N, N-dimethyl-ethanolamine is added, and the mixture is stirred for 10 minutes. Ion-exchanged water (263 parts) was poured into a dropping funnel in advance and dropped into the flask over 1 hour to obtain an aqueous dispersion of an acrylic-modified polyester resin (A-7) having a nonvolatile content of 33%. 145 parts of this aqueous dispersion is weighed, and 1 part (Shonol BKS-368) manufactured by Showa Polymer Co., Ltd. is added as a curing agent (50% nonvolatile content) and stirred. Further, ion exchange water was added to adjust the non-volatile content to 30% to obtain an aqueous paint.

(Examples 8 to 10) [Synthesis of acrylic modified polyester resins (A-8) to (A-10) and preparation of water-based paint]
The same procedure as in Example 1 was conducted except that the radical polymerizable unsaturated monomer in Example 1 was replaced with the composition shown in Table 2.
(Comparative Example 1) [Synthesis of acrylic modified polyester resin (A-811) and preparation of water-based paint]
100 parts of the polyester resin (D-1) obtained in Synthesis Example 1 and 45 parts of diethylene glycol monobutyl ether are charged into a flask and heated to 110 ° C. and dissolved. In a separate container, 12 parts of N-butoxymethylacrylamide, 34 parts of styrene, 27 parts of ethyl acrylate, 27 parts of methacrylic acid, 21 parts of diethylene glycol monobutyl ether, 29 parts of ethylene glycol monoisobutyl ether, and 2.6 parts of benzoyl peroxide are mixed. Stir and pour into dropping funnel. This was dropped and reacted for 2 hours to a solution containing the polyester resin (D-1) in the flask. One hour after the completion of the dropwise addition, 0.3 part of benzoyl peroxide is added, and the mixture is further reacted for one hour. After completion of the reaction, the mixture is cooled to 90 ° C., 13 parts of a 50% aqueous solution of N, N-dimethyl-ethanolamine is added, and the mixture is stirred for 10 minutes. 261 parts of ion exchange water was poured into a dropping funnel in advance, and this was dropped into the flask over 1 hour to obtain an aqueous dispersion of an acrylic modified polyester resin (A-811) having a nonvolatile content of 33%. 145 parts of this aqueous dispersion is weighed, and 1 part (Shonol BKS-368) manufactured by Showa Polymer Co., Ltd. is added as a curing agent (50% nonvolatile content) and stirred. Further, ion exchange water was added to adjust the non-volatile content to 30% to obtain an aqueous paint.

(Comparative Examples 2 to 5) [Synthesis of acrylic modified polyester resins (A-12) to (A-15) and preparation of water-based paint]
The same procedure as in Example 1 was conducted except that the radical polymerizable unsaturated monomer in Example 1 was replaced with the composition shown in Table 3.
(Comparative Example 6) [Synthesis of acrylic resin and preparation of water-based paint]
Charge 190 parts of diethylene glycol monobutyl ether to a flask and heat to 110 ° C. to dissolve. In a separate container, 120 parts of N-butoxymethylacrylamide, 120 parts of styrene, 160 parts of ethyl acrylate, and 11 parts of benzoyl peroxide are mixed, stirred, and poured into a dropping funnel. This was dropped into the diethylene glycol monobutyl ether in the flask for 1 hour to carry out the first stage dropping and reaction. 30 minutes after the completion of the dropwise addition, 1.1 parts of benzoyl peroxide is added and the reaction is continued for another 30 minutes. Next, 270 parts of methacrylic acid, 150 parts of styrene, 180 parts of ethyl acrylate, 280 parts of ethylene glycol monoisobutyl ether, and 16 parts of benzoyl peroxide are mixed and stirred in a separate container in advance and poured into a dropping funnel. This was dropped and reacted in the second stage to the solution containing the polyester resin (D-1) in the flask over 1 hour. 30 minutes after the completion of the dropping, 1.6 parts of benzoyl peroxide is added, and the reaction is further performed for 30 minutes. When the reaction is completed, the reaction solution is cooled to 90 ° C., and 130 parts of a 50% aqueous solution of N, N-dimethyl-ethanolamine is added, followed by stirring for 10 minutes. 1430 parts of ion-exchanged water was poured into a dropping funnel in advance, and this was dropped into the flask over 1 hour to obtain an aqueous solution of an acrylic resin having a nonvolatile content of 33%. 145 parts of this aqueous dispersion is weighed, and 1 part (Shonol BKS-368) manufactured by Showa Polymer Co., Ltd. is added as a curing agent (50% nonvolatile content) and stirred. Further, ion exchange water was added to adjust the non-volatile content to 30% to obtain an aqueous paint.

[Evaluation of paint to storage stability]
Each aqueous coating composition obtained in Examples 1 to 10 and Comparative Examples 1 to 6 is stored in an incubator at 37 ° C., and the appearance such as the presence or absence of separation is evaluated.
◎: No separation over 1 month ○: Separation within 1 week to 1 month △: Separation within 4 days to 1 week ×: Separation within 3 days

[Evaluation of coating film]
Using each of the aqueous coating compositions obtained in Examples 1 to 10 and Comparative Examples 1 to 6, coating was performed on an aluminum plate having a thickness of 0.26 mm so that the dry film thickness was 5 to 6 μm. The test panel for evaluation was obtained by baking at an ambient temperature of 250 ° C. for 3 minutes, and the performance of the coating film was evaluated as follows. The results are shown in Tables 2 and 3.

  Each evaluation method will be described below.

<Gel fraction>
The test panel is cut into 15 cm × 15 cm, boiled in methyl ethyl ketone (MEK) for 60 minutes, and the gel fraction is calculated from the weight change before and after boiling.
◎: 85% or more ○: 75% or more and less than 85% △: 65% or more and less than 75% ×: less than 65%

<Processability>
The test panel is cut to a size of 30 mm × 50 mm, the coating is on the outside, the test site is folded in advance by hand so that the width of the test site is 30 mm, and the thickness of 0.26 mm is between the two folded test pieces. After sandwiching two aluminum plates and dropping a 1kg weight from a height of 40cm onto a folded part and completely folding it, the end of the folded part was energized for 6.0V x 6 seconds, and a workability of 30mm width current value (mA) Was measured.
◎: Less than 1.0 mA ○: 1.0 mA or more and less than 10 mA △: 10 mA or more and less than 20 mA ×: 20 mA or more

<Adhesion>
According to JIS K-5400 cross cut tape method, after creating 100 squares of 1mm x 1mm on the test panel, the number of peeled cross cut coatings after sticking cellophane tape and peeling off rapidly Were evaluated according to the following criteria.
◎: 0 pieces ○: 1 to 5 pieces △: 6 to 39 pieces ×: 40 pieces or more

<Corrosion resistance>
The test panel is cut to 30 × 50 mm, the coating film is on the outside, the test site is previously folded by hand so that the width of the test site is 30 mm, and these test pieces are wrapped with gauze. Add and dissolve 80 ppm potassium pyrosulfite manufactured by Kanto Chemical Co., Ltd., carbonated drink “Coca Cola” manufactured by Coca-Cola Japan Co., Ltd., and transfer to a suitable glass bottle. A test piece wrapped with gauze is put in this, and it is sealed and stored at 37 ° C. for one week. When one week has passed, the test piece is taken out and washed with water. Three aluminum plates with a thickness of 0.26 mm are sandwiched between the test pieces folded in half, and a 1 kg weight is dropped from a height of 40 cm onto the bent portion and completely bent, and then 6.0 V is applied to the bent tip portion. * Electricity was applied for 6 seconds, and a current value (mA) with a workability of 30 mm width was measured.
◎: Less than 1.0 mA ○: 1.0 mA or more and less than 10 mA △: 10 mA or more and less than 20 mA ×: 20 mA or more

<Retort resistance>
While the test panel was immersed in water, a retort treatment was performed in a retort kettle at 125 ° C. for 30 minutes, and the appearance of the coating film was visually evaluated.
◎: Untreated coating and no change ○: Very thin whitening △: Slightly whitening ×: Remarkably whitening

<Feathering>
Feathering is a term used to describe the loss of adhesion of a coating on a tab of a beverage can lid. When the beverage can is opened, if the coating loses adhesion at the tub, there will be a film across the mouth of the can. This is feathering. The following describes the testing and evaluation methods for feathering properties. The test panel is cut to 40 × 50 mm, and the lid of the test piece is processed using a lid-making press toward the coating film side. After immersing the can lid in boiling water at 100 ° C. for 10 minutes, the coating surface Was opened so that the opening of the lid was pulled upward, and the peeling width of the coating film from the opening edge was evaluated according to the following criteria.
A: Maximum peel width of coating film is less than 0.2 mm ○: Maximum peel width of coating film is 0.2 mm or more and less than 0.5 mm Δ: Maximum peel width of coating film is 0.5 mm or more and less than 1.0 mm × : Maximum peel width of coating film is 1.0 mm or more

  The ratios of acid component and alcohol component in Table 1 are all molar ratios (mol%).

  The units of numbers in Tables 2 and 3 are all by weight.

  As shown in Table 2 and Table 3, the storage stability, gel fraction, workability, corrosion resistance, retort resistance, and feathering resistance of Examples 1 to 10 were all good, whereas Comparative Example 1 Nos. 6 to 6 were poor in storage stability, gel fraction, processability, corrosion resistance, retort resistance, and feathering properties, and all of them were not good.

Claims (10)

An aqueous paint containing an acrylic-modified polyester resin (A), a basic compound (B), and a curing agent (C),
The acrylic modified polyester resin (A) comprises a polyester resin (D), an aromatic vinyl monomer, an amide monomer, and a (meth) acrylic acid alkyl ester monomer as a water-insoluble polymerization initiator (E). A polyester resin (F) obtained by reacting in the presence;
An aqueous resin characterized by reacting an aromatic vinyl monomer, a carboxyl group-containing monomer, and a (meth) acrylic acid alkyl ester monomer in the presence of a water-insoluble polymerization initiator (E) paint.   The water-based paint according to claim 1, wherein the polyester resin (D) is obtained by reacting a polyhydric alcohol and a polyvalent carboxylic acid.   The water-based paint according to claim 2, wherein the polyhydric alcohol is a proportion of 60 to 80 mol% of a dihydric alcohol and 20 to 40 mol% of a trihydric alcohol.   Step (1) of obtaining a polyester resin (D) by reacting a polyhydric alcohol and a polyvalent carboxylic acid, and an aromatic vinyl monomer and an amide monomer in the presence of the obtained polyester resin (D) And a (meth) acrylic acid alkyl ester monomer and a water-insoluble polymerization initiator (E) to obtain a polyester resin (F), then an aromatic vinyl monomer, a carboxyl group-containing monomer, Step (2) of obtaining an acrylic modified polyester resin (A) by adding and reacting a (meth) acrylic acid alkyl ester monomer and a water-insoluble polymerization initiator (E), and the resulting acrylic modified polyester resin ( A method for producing a water-based paint comprising the step (3) of obtaining a water-based paint by blending A), a basic compound (B) and a curing agent (C) .   The method for producing a water-based paint according to claim 4, wherein in step (1), the polyhydric alcohol is in a proportion of 60 to 80 mol% of dihydric alcohol and 20 to 40 mol% of trihydric alcohol.   In step (2), in the presence of the polyester resin (D), an aromatic vinyl monomer, an amide monomer, and a (meth) acrylic acid alkyl ester monomer are combined with a water-insoluble polymerization initiator (E). And react to obtain a polyester resin (F), then an aromatic vinyl monomer, a carboxyl group-containing monomer, a (meth) acrylic acid alkyl ester monomer, a water-insoluble polymerization initiator (E), The method for producing a water-based paint according to claim 4, wherein the reaction is carried out.   The amide monomer is at least one monomer selected from the group consisting of N-alkoxyalkyl (meth) acrylamide, N-hydroxyalkyl (meth) acrylamide and (meth) acrylamide. 3. The water-based paint according to any one of 3.   The water-based paint according to claim 1, wherein the polyester resin (D) has a number average molecular weight of 2,000 to 7,000.   A coated can having an inner surface with a coating film formed from the water-based paint according to any one of claims 1 to 3, 7, and 8. A coated can having a coating film formed from the water-based paint according to any one of claims 1 to 3, 7, and 8 on an inner surface of a lid.