JP2006036978A - Aqueous coating composition and can for alcoholic drink - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aqueous coating composition forming a coating film which hardly adsorbs flavoring components in an alcoholic drink and exhibits excellent corrosion resistance against alcoholic drinks containing a sulfite salt and excellent processability, and a can for alcoholic drinks with its inner surface coated with a coating comprising the aqueous coating composition. <P>SOLUTION: The aqueous coating composition comprises an aqueous medium and, dispersed therein in the presence of an amine or ammonia, a self-emulsifying bisphenol-type epoxy resin (A), obtained by reacting a carboxy group-containing acrylic copolymer (A1) obtained by copolymerizing methacrylic acid/styrene/ethyl acrylate/methyl methacrylate in a composition (wt%) of (50-70)/(1-20)/(1-20)/(0-20) with a specific epoxy resin (A2), and a resol-type phenolic resin (D) obtained from a trifunctional phenol as a monomer and having a content of a mononuclear component bearing one benzene ring in the resin of at most 1 wt%, a number-average molecular weight of 250-1,000 and a total amount of methylol groups, alkoxylated methyl groups, methylene bonds and dimethylene ether bonds per one phenyl group of 1.5-2.5. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an aqueous paint composition and a can for alcoholic beverages having an inner surface coated with a paint containing the aqueous paint composition. More specifically, it is an aqueous coating composition that is applied directly to a metal material or on a base coating, and particularly an aqueous coating composition that is suitably used for coating an inner surface of a metal can and a coating containing the aqueous coating composition. The present invention relates to a can for alcoholic beverages coated on the surface.

  Conventionally, a metal cover such as tinplate, tin-free steel, and aluminum is usually provided with a thin synthetic resin protective coating to prevent direct contact with the contents and corrosion.

As an aqueous coating composition for inner surface coating, a so-called self-emulsifying bisphenol type epoxy resin in which a bisphenol type epoxy resin and an acrylic resin are partially bonded and a phenol resin are dissolved or dispersed in an aqueous medium. Known coating compositions are known.
The aqueous coating composition containing the self-emulsifying bisphenol type epoxy resin can be obtained by the method shown in the following (1) to (3), for example.

(1) Esterification method A bisphenol-type epoxy resin is esterified with an acrylic resin containing a carboxyl group, neutralized with a base, and dispersed in an aqueous medium (Patent Document 1: Japanese Patent Publication No. 59-37026) See the official gazette).
(2) Grafting method An acrylic monomer mixture containing a carboxyl group-containing polymerizable monomer such as acrylic acid or methacrylic acid as an essential component is grafted onto a bisphenol-type epoxy resin using a free radical generator, It is dispersed in the medium (see Patent Document 2: Japanese Patent Publication No. 63-17869).
(3) Direct method (modified esterification method)
Reacting acrylic acid or methacrylic acid to a part of the epoxy group of the bisphenol type epoxy resin to obtain an epoxy resin having a (meth) acryloyl group, and then an acrylic monomer containing the epoxy resin and acrylic acid or methacrylic acid And the obtained copolymer is dispersed in water by the same method as above (see Patent Document 3: Japanese Patent Publication No. 62-7213).

  Further, for the purpose of improving the workability of the coating film, an aqueous coating composition containing a combined product of both resins and an acrylic resin part in combination with a phenoxy resin in addition to an epoxy resin is disclosed in Patent Document 4: -145593.

  In addition, an aqueous coating composition containing a combination of an acrylic resin portion having a specific composition and an epoxy resin for the purpose of preventing adsorption of aroma components in food is disclosed in Patent Document 5: JP-A-2003-292883. Proposed.

In alcoholic beverages, since flavor flavor components in beverages are generally easily adsorbed to the coating film, low absorptivity of flavor flavor components is desired for the coating film in order to preserve the flavor of alcoholic beverages.
Among alcoholic beverages, fruit fermented liquors such as wine generally contain highly corrosive sulfites such as potassium metabisulfite as antioxidants. The coating film formed from the conventional aqueous bisphenol-type epoxy resin-based coating composition has a high molecular weight between crosslinks (low crosslink density), and therefore has a property that it is easily corroded by alcoholic beverages containing such sulfites. ing. Moreover, when a sulfite ion touches a base metal according to deterioration of a coating film, hydrogen sulfide will be produced and a bad odor similar to a rotting odor will be generated. On the other hand, the decrease in sulfite ions accompanying the generation of hydrogen sulfide causes a decrease in the antioxidant effect required for the contents, and causes the contents to be altered.

Patent Document 6: Japanese Patent Application Laid-Open No. 2002-361784 includes a phenol resin blended with an epoxy acrylic copolymer formed by copolymerizing an acrylic resin having a specific composition and an epoxy resin containing a certain amount of a phenoxy resin. It is disclosed that the coating film obtained from the resin composition is suitable for beverages containing sulfurous acid.
Patent Document 7: Japanese Patent Application Laid-Open No. 2004-292883 also discloses an aqueous coating composition containing a combination of an acrylic resin portion having a specific composition and an epoxy resin having a specific structure and a resol type phenol resin in an alcoholic beverage. It is disclosed that it is difficult to adsorb the flavor component of this product and it is possible to form a coating film having excellent resistance to alcoholic beverages containing potassium metabisulfite.

  However, the coating film formed from the coating composition disclosed in Patent Document 6 is not satisfactory in terms of corrosion resistance to alcoholic beverages containing potassium metabisulfite, particularly corrosion resistance under long-term storage.

Moreover, the coating material disclosed by patent document 7 uses resin which uses bisphenol A and / or bisphenol F as a monomer as a resol type phenol resin.
Bisphenol A and bisphenol F are tetrafunctional phenol monomers and have high reactivity, but also high self-condensation, so that the part derived from the epoxy resin of the self-emulsifying bisphenol type epoxy resin, which is the main component of the coating composition, The self-condensation reaction tends to proceed prior to the crosslinking reaction with the acrylic resin-derived portion. When the self-condensation reaction proceeds, the molecular weight between crosslinks of the cured coating film increases and the crosslink density decreases. However, when the molecular weight between crosslinks is large, the coating film becomes rough and flavor components are easily adsorbed.

Furthermore, as the self-condensation cured product of the phenol resin increases, the coating film becomes brittle and the workability tends to decrease. That is, a can containing beverages and foods is formed by winding and joining a can body member and a can lid, but the can body member is subjected to bending processing at the time of joining, In some cases, cracks and corrosion occurred in the coating film of the tightened portion. In particular, when a highly corrosive beverage such as an alcoholic beverage containing sulfite such as wine is filled, corrosion tends to occur in the processed part, and improvement is required in terms of corrosion resistance, particularly corrosion resistance under long-term storage. It was.
Japanese Patent Publication No.59-37026 Japanese Patent Publication No. 63-17869 Japanese Patent Publication No.62-7213 Japanese Patent Laid-Open No. 06-145593 JP 2003-292883 A JP 2002-361784 A JP 2004-155835 A

  The present invention relates to an aqueous coating composition that is difficult to adsorb flavor aroma components in alcoholic beverages, has excellent corrosion resistance to alcoholic beverages containing sulfites, and can form a coating film excellent in processability, and the aqueous coating composition. It aims at providing the can for alcoholic beverages formed by coat | covering the coating material containing a can inside.

  The present inventors have repeatedly studied adsorption of flavor aroma components in alcoholic beverages with water-based paint compositions, and further, as a result of repeated resistance tests against alcoholic beverages containing sulfites such as wine, acrylic resin having a specific composition and Self-emulsifying bisphenol-type epoxy resin composed of specific epoxy resin and trifunctional phenol as monomer, low benzene ring mononuclear content in resin, structure with narrow molecular weight distribution, high functional group concentration By using an aqueous coating composition containing a resol type phenol resin which is a highly reactive resin, it has excellent workability and has a very dense structure with a low molecular weight between crosslinks. It has been found that a coating film suitable for coating the inner surface of can be obtained.

That is, the first invention is an aqueous coating composition comprising a self-emulsifying bisphenol type epoxy resin (A) and a phenol resin (D) dispersed in an aqueous medium in the presence of amine or ammonia,
The self-emulsifying bisphenol type epoxy resin (A)
A carboxyl group-containing acrylic copolymer (A1) obtained by copolymerizing methacrylic acid / styrene / ethyl acrylate / methyl methacrylate with a composition of 50 to 70/1 to 30/1 to 20/0 to 20 (% by weight); ,
A bisphenol-type epoxy resin (A2) having an epoxy equivalent of 1500-5000 and a number-average molecular weight of 2,000-6000 as an essential component;
Carboxyl group-containing acrylic copolymer (A1) / epoxy resin (A2) = self-emulsifying bisphenol type epoxy resin (A) obtained by esterification at a weight ratio of 30/70 to 10/90,
The phenol resin (D) has a trifunctional phenol as a monomer, the benzene ring mononuclear content in the resin is 1% by weight or less, the number average molecular weight is 250 to 1000, methylol groups per phenyl group, alkoxyl A resol type phenolic resin having a total value of methyl group, methylene bond and dimethylene ether bond of 1.5 to 2.5,
The present invention relates to a water-based coating composition characterized in that self-emulsifying bisphenol type epoxy resin (A) / phenol resin (D) = 90/10 to 99/1 (weight ratio).

A second invention is an aqueous coating composition comprising a self-emulsifying bisphenol type epoxy resin (B) and a phenol resin (D) dispersed in an aqueous medium in the presence of an amine or ammonia. Type epoxy resin (B)
A radical polymerizable monomer (b1) containing methacrylic acid / styrene / ethyl acrylate / methyl methacrylate in a composition of 50 to 70/1 to 30/1 to 20/0 to 20 (wt%),
(B1) / (A2) using a free radical generator in a bisphenol type epoxy resin (A2) containing a bisphenol type epoxy resin having an epoxy equivalent of 1500 to 5000 and a number average molecular weight of 2000 to 6000 as an essential component. = Self-emulsifying bisphenol type epoxy resin (B) grafted under conditions of 30/70 to 10/90 (weight ratio),
The phenol resin (D) has a trifunctional phenol as a monomer, the benzene ring mononuclear content in the resin is 1% by weight or less, the number average molecular weight is 250 to 1000, a methylol group per phenyl group, A resol type phenolic resin having a total value of alkoxylated methyl group, methylene bond and dimethylene ether bond of 1.5 to 2.5;
The present invention relates to a water-based coating composition characterized in that self-emulsifying bisphenol type epoxy resin (A) / phenol resin (D) = 90/10 to 99/1 (weight ratio).

A third invention is an aqueous coating composition comprising a self-emulsifying bisphenol type epoxy resin (C) and a phenol resin (D) dispersed in an aqueous medium in the presence of an amine or ammonia, the self-emulsifying bisphenol Type epoxy resin (C)
A methacryloyl group obtained by reacting methacrylic acid (c1) with a part of a bisphenol type epoxy resin (A2) containing an epoxy equivalent of 1500 to 5000 and a number average molecular weight of 2000 to 6000 as an essential component. A copolymer (C) obtained by copolymerizing an epoxy resin (c2) having a methacrylic acid (c3) / radical polymerizable monomer (c4) containing styrene / ethyl acrylate / methyl methacrylate,
Methacrylic acid (c1) + (c3) / styrene / ethyl acrylate / methyl methacrylate is 50 to 70/10 to 30/1 to 20/0 to 20 (% by weight),
Methacrylic acid (c1), radical polymerizable monomer (c4), and epoxy resin (A2) provided for the constitution of the copolymer (C) are [(c1) + (c4)] / (A2) = 30 / 70 to 10/90 (weight ratio),
The phenol resin (D) has a trifunctional phenol as a monomer, the benzene ring mononuclear content in the resin is 1% by weight or less, the number average molecular weight is 250 to 1000, a methylol group per phenyl group, A resol type phenolic resin having a total value of alkoxylated methyl group, methylene bond and dimethylene ether bond of 1.5 to 2.5;
The present invention relates to a water-based coating composition characterized in that self-emulsifying bisphenol type epoxy resin (A) / phenol resin (D) = 90/10 to 99/1 (weight ratio).

  In any one of the above-mentioned present inventions, the trifunctional phenol in the phenol resin (D) is preferably carboxylic acid or m-cresol.

  Another can for alcoholic beverages according to the present invention is characterized in that the inner surface is coated with a paint containing the aqueous paint composition according to any one of the above inventions.

  The can for alcoholic beverages according to another invention is characterized in that the inner surface is coated with a paint containing the aqueous paint composition according to any one of the above inventions, and the minimum molecular weight between crosslinks of the coated film is 150 to 300. It is what.

  According to the present invention, the processability is excellent, the amount of flavor components adsorbed in alcoholic beverages is small, the flavor retention and flavor retention are extremely excellent, and the highly corrosive contents containing sulfite are also included. An aqueous coating composition capable of forming a coating film excellent in corrosion resistance and excellent in flavor and hygiene, and a can for alcoholic beverages whose inner surface is coated with a coating containing the coating composition are obtained.

  As described above, the aqueous coating composition of the present invention contains one of the self-emulsifying bisphenol type epoxy resins (A) to (C) and the phenol resin (D), and is self-emulsifying bisphenol. There are first to third modes depending on the method of forming the type epoxy resins (A) to (C).

First, the first aspect will be described.
A 1st aspect is a case where the self-emulsifiable bisphenol-type epoxy resin (A) obtained by what is called an esterification method is contained.
Self-emulsifying bisphenol type epoxy resin (A)
In a carboxyl group-containing acrylic copolymer (A1) obtained by copolymerizing methacrylic acid / styrene / ethyl acrylate / methyl methacrylate with a composition of 50 to 70/1 to 30/1 to 20/0 to 20 (wt%). A part of the carboxyl group of
An epoxy equivalent is 1500-5000, and a part of the epoxy group or hydroxyl group in the bisphenol-type epoxy resin (A2) containing a bisphenol-type epoxy resin having a number average molecular weight of 2000-6000 as an essential component,
Carboxyl group-containing acrylic copolymer (A1) / epoxy resin (A2) = 30/70 to 10/90, and is an esterification reaction, 25/75 to 15/85 It is preferable to carry out an esterification reaction.

When the amount of the carboxyl group-containing acrylic copolymer (A1), which is a hydrophilic resin, exceeds the above range compared to the epoxy resin (A2), which is a hydrophobic resin, the ester reaction between the epoxy resin and the acrylic resin proceeds. It becomes difficult to obtain a stable aqueous resin dispersion. Further, when the amount of the acrylic copolymer (A1) is excessive as compared with the epoxy resin (A2), the hydrophilicity of the self-emulsifying bisphenol type epoxy resin (A) to be formed becomes too high, and the water resistance in the coating film performance is increased. Inferior problems arise.
On the other hand, when the carboxyl group-containing acrylic copolymer (A1) is less than the above range as compared with the epoxy resin (A2), the hydrophilicity of the produced self-emulsifying bisphenol type epoxy resin (A) is low. It becomes too much to become a stable dispersion in water, and there arises a problem that the resulting epoxy resin (A) settles with time.

  Examples of esterification catalysts used for esterification include alcohol amines such as dimethylethanolamine, ethanolamine, diethanolamine, and aminomethylpropanol, alkylamines such as trimethylamine, triethylamine, and butylamine, and volatile amines such as morpholine. Can be mentioned.

After the esterification reaction, the self-emulsifiable bisphenol type epoxy resin (A) can be dispersed in an aqueous medium by neutralizing at least a part of the remaining carboxyl groups with amine or ammonia.
Examples of the amine used include alcohol amines such as dimethylethanolamine, ethanolamine, diethanolamine, and aminomethylpropanol, alkylamines such as trimethylamine, triethylamine, and butylamine, and volatile amines such as morpholine.

  The aqueous medium in the present invention is a mixture of water and a hydrophilic solvent in which at least 50% by volume, preferably 80% by volume or more is water. Examples of hydrophilic solvents include alcohol solvents such as ethanol, isopropanol, n-propanol, n-butanol, iso-butanol and pentanol, and ethylene glycol alkyl ether solvents such as ethylene glycol monoethyl ether and ethylene glycol monobutyl ether. , Esterified products of diethylene glycol alkyl ether solvents such as diethylene glycol monobutyl ether, propylene glycol alkyl ether solvents such as propylene glycol monomethyl ether and propylene glycol monoethyl ether, and a series of glycol alkyl ether solvents such as ethylene glycol monoethyl ether acetate Etc.

Next, the carboxyl group-containing acrylic copolymer (A1), which is one of the components constituting the self-emulsifying bisphenol type epoxy resin (A), will be described.
The carboxyl group-containing acrylic copolymer (A1) is obtained by copolymerizing methacrylic acid / styrene / ethyl acrylate / methyl methacrylate with a composition of 50 to 70/1 to 30/1 to 20/0 to 20 (wt%). It will be.
Among the flavor components in alcoholic beverages, particularly in sensory evaluation, 50 to methacrylic acid is used because it reduces the amount of adsorption of the ester compound that is a component that easily perceives flavor change due to its adsorption (low sensory threshold). It is important to copolymerize a relatively large amount of 70% by weight, which is one of the features of the present invention.

If the copolymerization ratio of methacrylic acid is less than 50% by weight, the cross-linking density of the coating film is not sufficient for alcoholic beverage applications, and the amount of flavor components adsorbed cannot be reduced, and alcoholic beverages containing sulfites Corrosion resistance is not ensured.
On the other hand, if it exceeds 70% by weight, the copolymerizability of the acrylic resin becomes non-uniform, the amount of homopolymer of methacrylic acid increases and the water resistance is inferior, and the reaction does not occur in the esterification reaction with the epoxy resin. It becomes uniform and gelation is likely to occur during the reaction, and the viscosity behavior at the time of coating and over time, such as an increase in viscosity of the coating, becomes unstable.
From the viewpoint of making it aqueous after reacting with the epoxy resin (A2) described later, and from the viewpoint of processability of the formed coating film, the carboxyl group-containing acrylic copolymer (A1) is a copolymer as described above. It is important that they are copolymerized at a polymerization ratio.

In the copolymerization, an azobis-based polymerization initiator, a peroxide-based polymerization initiator, or the like can be appropriately used according to a conventional method.
Examples of the azobis polymerization initiator include azobisisobutyronitrile and azobisisovaleronitrile, and examples of the peroxide polymerization initiator include benzoyl peroxide.
In the copolymerization, an organic solvent such as alkyl alcohol, ethylene glycol monoalkyl ether, ethylene glycol dialkyl ether, diethylene glycol monoalkyl ether, diethylene glycol dialkyl ether, or propylene glycol monoalkyl ether can be appropriately used.

Next, the bisphenol type epoxy resin (A2), which is another component constituting the self-emulsifying bisphenol type epoxy resin (A), will be described.
This epoxy resin (A2) has an epoxy equivalent of 1500 to 5000 and includes a bisphenol type epoxy resin having a number average molecular weight of 2000 to 6000 as an essential component.
Here, the number average molecular weight of the epoxy resin and the number average molecular weight of the phenol resin described later are those measured by the GPC method (standard polystyrene conversion).

When a bisphenol type epoxy resin having an epoxy equivalent of less than 1500 is used, the processability of the coating film is lowered and the corrosion resistance is deteriorated. On the other hand, if the epoxy equivalent exceeds 5000, the reactivity of the resulting self-emulsifying bisphenol type epoxy resin (A) is lowered, and the crosslinking density of the coating film after baking and drying is lowered. When used as an inner coating for cans of alcoholic beverages, the amount of flavor aroma components adsorbed increases, and in alcoholic beverages containing sulfites, the coating film deteriorates significantly, generating hydrogen sulfide, altering the contents, etc. .
In addition, when a bisphenol type epoxy resin having a number average molecular weight lower than 2000 is used, the processability of the coating film is lowered, and when used as an inner paint of a can body portion of a can for alcoholic beverages, the coating film is formed at a tightening portion with a lid. Cracks are likely to occur, and corrosion is likely to occur from the tightened portion. On the other hand, when the number average molecular weight exceeds 6000, the viscosity of the resin solution of the self-emulsifying bisphenol type epoxy resin (A) during the production of the aqueous resin dispersion becomes high and the production becomes difficult. This is not preferable because problems such as the inability to obtain a coating resin composition occur.

  Bisphenol-type epoxy resins are manufactured for industrial use and are manufactured by a one-step method in which bis (4-hydroxyphenyl) alkanes and epichlorohydrin are reacted in the presence of strong alkali, or by this one-step method. It is obtained by a two-stage method in which a bis (4-hydroxyphenyl) alkane is further added to an epoxy resin.

  Examples of the bisphenol type epoxy resin include bisphenol F type, brominated bisphenol A type, hydrogenated bisphenol A type, and bisphenol S type in addition to the bisphenol A type having the structure represented by the following formula (1).

（ただし、ｎは、０以上の整数。）

(However, n is an integer of 0 or more.)

  As such a bisphenol type epoxy resin (A2), a commercially available bisphenol type epoxy resin such as Epicoat 1007 (epoxy equivalent (hereinafter referred to as Eeq) = 2000, number average molecular weight (hereinafter referred to as Mn) = 2600). Epicoat 1009 (Eeq = 2900, Mn = 3700), Epicoat 1010 (Eeq = 4000, Mn = 4900) (manufactured by Japan Epoxy Resins Co., Ltd.), AER-6017 (Eeq = 1900, Mn = 2700), AER -6019 (Eeq = 2500, Mn = 3900) (above, manufactured by Asahi Kasei Epoxy Co., Ltd.), Epototo YD-017 (Eeq = 1900, Mn = 2600), Epototo YD-019 (Eeq = 2900, Mn = 3600), Epototo YD-020 (Eeq = 5000, Mn = 5200), There is Toto Kasei Co., Ltd.), and the like.

  In the present invention, when the carboxyl group-containing acrylic copolymer (A1) and the epoxy resin (A2) are reacted to produce the self-emulsifying bisphenol type epoxy resin (A), the epoxy resin (A2) In addition to the bisphenol type epoxy resin, a bisphenol type high molecular weight epoxy resin generally called a phenoxy resin can also be contained.

As the phenoxy resin, a resin containing substantially no epoxy equivalent is also known. In the present invention, in order to ensure the reactivity with the resol type phenol resin (D) described later, the bisphenol type used in the present invention is used. The epoxy equivalent of the high molecular weight epoxy resin is desirably 6000 to 20000. Moreover, it is preferable that a number average molecular weight is 8000-20000.
As such a high molecular weight epoxy resin, for example, Japan Epoxy Resin Co., Ltd. product name Epicoat 1256 (Eeq = 8000, Mn = 12000), Toto Kasei Co., Ltd. product name Fenototo YP-50S (Eeq = 20000, Mn = 14000) or the like is preferably used.

The aqueous coating composition of the present invention needs to contain a phenol resin (D) as a crosslinking agent for the self-emulsifying bisphenol type epoxy resin (A).
The phenol resin (D) is formed from a trifunctional phenol monomer such as carboxylic acid or m-cresol, has a benzene ring mononuclear content of 1% by weight or less, and has a number average molecular weight of 250 to 1,000. It is important that the resol type phenolic resin has a total value of 1.5 to 2.5 of methylol group per phenyl group, alkoxylated methyl group (alkoxylmethyl group), methylene bond, and dimethylene ether bond. is there.

  When the number average molecular weight of the resol type phenol resin (D) is as small as 250 to 1,000, generally, the benzene ring mononuclear body is contained in an amount of more than 1% by weight. Here, the benzene ring mononuclear body has a structure composed of a trifunctional phenol monomer such as carboxylic acid or m-cresol and one benzene ring in which a methylol group or an alkoxymethyl group is added to the monomer, The content is determined by the GPC method. Such a mononuclear body is likely to be eluted from the coating film, and may deteriorate the flavor of the contents of the can for alcoholic beverages. Also, the benzene ring mononuclear has a strong odor and skin irritation and is not desirable from a hygienic viewpoint.

  Although the resol type phenol resin (D) used in the present invention has a small number average molecular weight of 250 to 1000, the benzene ring mononuclear content is as low as 1% by weight or less. That is, the phenol resin (D) inevitably has a low benzene ring dinuclear content, and has a very narrow molecular weight distribution centering on the benzene ring trinuclear to hexanuclear. Such a resol type phenol resin (D) is difficult to be extracted from the coating film and has sufficient reactivity.

Further, in the resol type phenol resin (D) used in the present invention, it is important that the total value of methylol group, alkoxylmethyl group, methylene bond and dimethylene ether bond per phenyl group is 1.5 to 2.5. It is. The total amount of methylol groups and alkoxylated methyl groups, which are functional groups involved in the crosslinking reaction with the self-emulsifying bisphenol type epoxy resin, is preferably 1.0 or more per phenyl group. When the concentration of functional groups involved in the crosslinking reaction is sufficiently high, a dense coating with a low molecular weight between crosslinks (high crosslink density) can be obtained. When used as an inner coating for food cans, adsorption of flavor aroma components It exhibits low tolerance and exhibits sufficient resistance against alcoholic beverages containing sulfites. The concentration of each functional group can be determined quantitatively by ¹³ C-NMR method.

  There are various methods for reducing the mononuclear benzene ring contained in the resol-type phenolic resin. As one of them, first, the content of the mononuclear benzene ring having a number average molecular weight of 250 to 800 under an acidic catalyst is 1 weight. % Novolak type phenol resin is prepared, and then formaldehyde is added by basic catalysis, and alkoxylation is performed as necessary.

The novolak type phenol resin having a benzene ring mononuclear content of 1% by weight or less can be obtained by removing low molecular weight components typified by the benzene ring mononuclear substance from the novolak type phenol resin. For example, a method of removing low molecular weight components under high temperature and reduced pressure, a method of removing low molecular weight components by steam distillation, and using a special acid catalyst such as tartaric acid or citric acid, A technique for obtaining a narrow resin is known as a representative technique.
The novolak-type phenol resin having a benzene ring mononuclear content of 1% by weight or less thus obtained is subjected to a basic catalyst such as sodium hydroxide, magnesium hydroxide, ammonia, triethylamine, or the like, and a methylol group or alkoxyl group per phenyl group. Formaldehyde is added so that the total value of the methyl group, methylene bond, and dimethylene ether bond is 1.5 to 2.5, and the methylol group is alkoxylated with alcohol such as methanol or n-butanol as necessary. By methylation, a resol type phenol resin (D) having a benzene ring mononuclear content of 1% by weight or less can be obtained.

  In order to obtain the resol type phenol resin (D), it is important to use a trifunctional phenol as a phenol monomer. Examples of the trifunctional phenol include carboxylic acid, m-cresol, m-ethylphenol, m-ethoxyphenol, 3,5-xylenol, and carboxylic acid or m-cresol is particularly preferable from the viewpoint of reactivity and hygiene. By using these trifunctional phenol monomers, a highly reactive phenol resin having a total value of methylol group, alkoxylmethyl group, methylene bond and dimethylene ether bond per phenyl group of 1.5 to 2.5 is obtained. And the high crosslink density associated therewith can be ensured.

  Phenol monomers other than trifunctional phenols such as monofunctional 2,4-xylenol, 2,6-xylenol, bifunctional p-cresol, p-ter-butylphenol, p-ethylphenol, o-cresol, When phenolic monomers such as 2,3-xylenol, 2,5-xylenol, and p-nonylphenol are used, the functional group concentration is low, and it is difficult to ensure desirable reactivity and molecular weight (crosslinking density) between crosslinks. .

Moreover, it is not preferable to use a tetrafunctional phenol monomer such as bisphenol A or bisphenol F as the phenol monomer because the self-condensation property of the phenol resin becomes too high. A resol type phenol resin containing bisphenol A or bisphenol F as a monomer tends to cause a self-condensation reaction before the reaction with the self-emulsifying bisphenol type epoxy resin (A), and it becomes difficult to function as a cross-linking component. May be difficult to form. Furthermore, phenol resin self-condensates generally have hard and brittle properties and tend to degrade the processability of the coating. Deterioration of the workability of the coating film is not preferable because it tends to cause cracks in the processed parts such as the above-described lid tightening part.
In addition, a phenol monomer other than the trifunctional phenol can be used in combination with the trifunctional phenol within the range in which the above problems do not occur, and a phenol resin formed from a phenol monomer other than the trifunctional phenol and 3 Can also be used in combination with phenolic resins formed from functional phenols

  The ratio of the self-emulsifying bisphenol type epoxy resin (A) / phenolic resin (D) is preferably 90/10 to 99/1 (weight ratio), and if less than 1 part by weight, the phenolic resin (D) is cured. As a result, it is difficult to recognize the contribution to water, and the crosslink density is lowered, and the adsorptivity of flavor aroma components and the corrosion resistance to alcoholic beverages containing sulfites are not ensured. Moreover, when it exceeds 10 weight part, the workability of a coating film falls and it becomes unpreferable since it becomes easy to produce a crack in processed parts, such as the above-mentioned lid winding part.

Next, a 2nd aspect is demonstrated.
The second embodiment is an aqueous coating composition containing a self-emulsifying bisphenol type epoxy resin (B) obtained by a so-called graft method, and is self-emulsifying bisphenol instead of the self-emulsifying bisphenol type epoxy resin (A). Except for the use of the type epoxy resin (B), it is the same as in the case of the first aspect.
The self-emulsifying bisphenol type epoxy resin (B) is a methacrylic acid / styrene / ethyl acrylate / methyl methacrylate 50-70 / 1-30 / 1-20 / to the epoxy resin (A2) using a free radical generator. It is obtained by grafting a radically polymerizable monomer (b1) contained in a composition of 0 to 20 (% by weight). Generally, the radically polymerizable monomer (b1) is graft-polymerized to the secondary carbon in the epoxy resin (A2).

As the free radical generator, an organic peroxide is suitable among the polymerization initiators exemplified when obtaining the acrylic copolymer (A1) used for forming the self-emulsifying bisphenol type epoxy resin (A). In particular, benzoyl peroxide is preferred.
Examples of the organic solvent used in the graft reaction include those exemplified for obtaining the acrylic copolymer (A1) used for forming the self-emulsifying bisphenol type epoxy resin (A).

Self-emulsifying bisphenol-type epoxy resin (B) is different from self-emulsifying bisphenol-type epoxy resin (A) in the formation process, but as a result, radical polymerization that requires epoxy resin (A2) and acrylic acid or methacrylic acid as essential. And a part derived from a sex monomer.
Accordingly, the ratio of the epoxy resin (A2) constituting the self-emulsifying bisphenol type epoxy resin (B) to the portion derived from the radical polymerizable monomer (b1) is determined by the self-emulsifying bisphenol type epoxy resin (A). It is important to be the same as in the case of. That is, the radical polymerizable monomer (b1) containing methacrylic acid / styrene / ethyl acrylate / methyl methacrylate in a specific composition ratio is converted into epoxy resin (A2), and (b1) / (A2) = 30/70 to 10/90. It is important to graft at a ratio of (weight ratio).

Next, a 3rd aspect is demonstrated.
A third aspect is an aqueous coating composition containing a self-emulsifying bisphenol type epoxy resin (C) obtained by a so-called direct method (modified esterification method), which is a self-emulsifying bisphenol type epoxy resin (A), Except for using a self-emulsifying bisphenol type epoxy resin (C) instead of (B), it is the same as the first and second aspects.
Self-emulsifying bisphenol-type epoxy resin (C) is obtained by reacting methacrylic acid (c1) with a part of bisphenol-type epoxy resin (A2) to obtain an epoxy resin (c2) having a methacryloyl group. It is a copolymer (C) obtained by copolymerizing (c2) and a radical polymerizable monomer (c4) containing methacrylic acid (c3) / styrene / ethyl acrylate / methyl methacrylate.
As an esterification catalyst that can be used in the reaction of the epoxy resin (A2) and methacrylic acid (c1), an esterification catalyst that can be used in forming the self-emulsifying bisphenol type epoxy resin (A) can be exemplified similarly. .
Moreover, as a polymerization initiator used when copolymerizing an epoxy resin (c2) having a methacryloyl group and a radical polymerizable monomer (c4) containing methacrylic acid (c3) as an essential component, a self-emulsifying bisphenol type is used. What was illustrated when obtaining the acrylic copolymer (A1) used for formation of an epoxy resin (A) can be illustrated similarly.
Further, examples of the organic solvent used in the direct method include those exemplified when obtaining the acrylic copolymer (A1) used for forming the self-emulsifying bisphenol type epoxy resin (A).

Self-emulsifying bisphenol-type epoxy resin (C) is different from self-emulsifying bisphenol-type epoxy resins (A) and (B), but, as a result, specific that requires epoxy resin (A2) and methacrylic acid as essential. A part derived from a radical polymerizable monomer of the composition is bonded.
Accordingly, the ratio of the epoxy resin (A2) constituting the self-emulsifying bisphenol type epoxy resin (C) to the portion derived from the radical polymerizable monomer is determined by the self-emulsifying bisphenol type epoxy resin (A), (B It is important to be the same as in the case of). That is, the total amount (c1) + (c4) of methacrylic acid (c1) used for esterification and radical polymerizable monomer (c4) containing methacrylic acid (c3) used for copolymerization as an essential component. ) Is in a relationship of [(c1) + (c4)] / (A2) = 30/70 to 10/90 (weight ratio) with the epoxy resin (A2).
In addition, the portion derived from the radical polymerizable monomer is also methacrylic acid (c1) + (c3) / styrene / ethyl acrylate / methyl methacrylate of 50 to 70/1 to 30/1 to 20/0 to 20 (wt%). It is important that

  The aqueous coating composition of the present invention is preferably used as a coating, particularly a coating for the inner surface of a can, as it is or by adding a surfactant, an antifoaming agent or the like for improving coating properties as necessary. be able to.

As the base material to which the aqueous coating composition of the present invention is applied, a metal plate such as an untreated steel plate, a treated steel plate, a galvanized iron plate, a tin plate, and an aluminum plate is suitable. As a coating method, an air spray or an airless spray is used. In addition to spray coating such as electrostatic spraying, dip coating roll coater coating and electrodeposition coating are also possible.
The baking conditions for fixing the coating film on the substrate can be selected from the range of 150 ° C. to 230 ° C. and the time of 10 seconds to 30 minutes.

Next, the molecular weight between crosslinks of the coating film formed from the coating composition of the present invention will be described.
The molecular weight between crosslinks of the coating film is an index of the crosslink density of the coating film, and it can be said that the lower the molecular weight between crosslinks, the denser the crosslink density based on chemical bonds. The minimum molecular weight between crosslinks of the coating film formed from the coating composition of the present invention is preferably 150 to 300.
The molecular weight between crosslinks can be determined by a method using a storage elastic modulus value described in Examples described later.
When the molecular weight between crosslinks is as low as 300 or less, the coating film is dense, chemically stable as coating film properties, difficult to adsorb other substances, and exhibits good gas barrier properties. Therefore, for foods with a high concentration of corrosive ions such as sulfurous acid, foods with a high concentration of acid components such as citric acid (low pH), and foods with ethanol. A coating film exhibiting excellent resistance can be obtained.
On the other hand, when the molecular weight between crosslinks is larger than 150, the crosslink density is moderate, and the flexibility of the coating film is obtained and the processability is improved. It is done.

  When forming a coating film from the coating composition of the present invention, it is desirable to bake and dry under the conditions that the molecular weight between crosslinks is the lowest. In the formation of a coating film by baking and drying, when the baking condition is under-baking, the crosslinking reaction does not proceed sufficiently, so that the molecular weight between crosslinking is increased. On the other hand, even when excessive baking and drying are performed, the molecular weight between crosslinks becomes high due to disappearance of crosslink points accompanying decomposition of the resin. That is, it is preferable to measure the molecular weight between crosslinks and appropriately set the baking and drying conditions so that the molecular weight between crosslinks is the lowest. The term “minimum molecular weight between crosslinks” as used in the present invention is a value obtained by baking and drying under the baking and drying conditions such that the molecular weight between crosslinks is the lowest.

  By using the coating composition of the present invention as described above, it is a dense coating film having excellent workability and low molecular weight between crosslinks, and has flavor retention, corrosion resistance, heat resistance, and alcohol resistance to the contents. And a coating film having excellent resistance to alcoholic beverages containing sulfites.

The can for alcoholic beverages of the present invention is an inner surface coated with the aqueous coating composition of the present invention as described above. After filling the cans with alcoholic beverages by a predetermined process, the coating film is stored during storage. Since it is difficult to adsorb flavor components in alcoholic beverages, particularly ester compounds and limonene, the flavor retention of alcoholic beverages is excellent.
The ester compound in the alcoholic beverage according to the present invention includes ethyl acetate, ethyl caproate, ethyl caprylate, isoamyl acetate, as described in “List of brewing ingredients (edited by the Japan Brewing Association)”, Examples include 2-phenylethyl acetate. Various flavor substances are contained in alcoholic beverages, and it is considered important for the coating film to have a low adsorptivity of the ester compound as described above, particularly because of its high content and low sensory threshold.

Hereinafter, the present invention will be described with reference to examples. In the examples, “parts” and “%” indicate “parts by weight” and “% by weight”, respectively. In the following phenol resin production methods, the number average molecular weight was determined by the GPC method (standard polystyrene conversion), the functional group concentration was determined by the ¹³ C-NMR method, and the benzene ring mononuclear content was determined by the GPC method.

Production Example 1 (Production of carboxyl group-containing acrylic copolymer (A1-1) solution)
For production, 1) butyl cellosolve 400 parts, 2) n-butanol 300 parts, 3) methacrylic acid 200 parts, 4) styrene 40 parts, 5) ethyl acrylate 30 parts, 6) methyl methacrylate 30 parts, 7) benzoyl peroxide. 5 parts were used.
A four-necked flask purged with nitrogen gas was charged with 400 parts of butyl cellosolve, 300 parts of n-butanol, and 1/4 of a mixed liquid composed of monomers 3) to 7) and a polymerization initiator. Next, the mixture was heated to 100 ° C. and stirred for 30 minutes, and the remaining 3/4 of the mixed solution composed of the monomer and the polymerization initiator was added dropwise over 2 hours while maintaining 100 ° C. After completion of the dropping, the mixture was further stirred at 2O 0 C for 2 hours, cooled and taken out to obtain an acrylic copolymer (A1-1) solution having a solid content of 30.0%.

Production Examples 2 to 4 [Production of carboxyl group-containing acrylic copolymer (A1-2 to A1-4)]
In the same manner as in Production Example 1, acrylic copolymer (A1-3) to (A1-4) solutions having a solid content of 30.0% were obtained from the monomer mixture shown in Table 1.

Production Example 5 [Production of phenol resin (D-1) solution]
A 4-necked flask purged with nitrogen gas was charged with 1) 500 parts of coal acid, 2) 237 parts of 37% formalin, and 3) 5 parts of oxalic acid, heated to 95 ° C., and reacted for 3 hours. Next, after reducing the pressure to 60 mmHg and heating to 150 ° C. while performing dehydration, the dehydration was continued while blowing nitrogen gas, the internal temperature was heated to 210 ° C., and this state was maintained for 4 hours. Subsequently, vacuum dehydration was performed for 1 hour under a reduced pressure of 20 mmHg to obtain 383 parts of a solid novolak type phenol resin having a benzene ring mononuclear content of 0.1% and a number average molecular weight of 440.
Next, 4) ion-exchanged water 200 parts, 5) 20% sodium hydroxide aqueous solution 200 parts, and 6) 37% formalin 800 parts were charged in the flask, and the novolac type phenol resin was dissolved, followed by reaction at 60 ° C. for 3 hours. A reddish brown transparent solution was obtained. After cooling to 40 ° C., 190 parts of 7) 20% hydrochloric acid was added to the reddish brown transparent solution and stirred, and the upper layer was separated into a colorless and transparent aqueous layer and the lower layer was separated into a reddish brown organic layer in about 10 minutes. After separating and removing the upper layer by decantation, 8) 490 parts of n-butanol was added, the benzene ring mononuclear content was 0.1%, the number average molecular weight was 680, the methylol group per phenyl group was 1.6, n -Resol-type phenolic resin having a solid content of 50% (butoxy (alkoxylated) methyl group is 0.1, methylene bond is 0.8, dimethylene ether bond is 0.0, total functional group total value is 2.5) D-1) A solution was obtained.

Production Example 6 [Production of phenol resin (D-2) solution]
A 4-necked flask purged with nitrogen gas was charged with 1) 450 parts of m-cresol, 2) 130 parts of 86% paraformaldehyde, 3) 250 parts of citric acid, heated to 120 ° C., and reacted for 4 hours. After completion of the reaction, 4) citric acid was removed by washing with 500 g of ion exchange water. Subsequently, dehydration was performed under reduced pressure of 60 mmHg to obtain 383 parts of a novolak type phenol resin having a benzene ring mononuclear content of 0.4% and a number average molecular weight of 650.
Next, 5 parts of ion-exchanged water 220 parts, 6) 20% sodium hydroxide aqueous solution 180 parts, and 7) 37% formalin 700 parts were charged into a 4-necked flask to dissolve the novolak type phenol resin, and then at 60 ° C. for 3 hours. When reacted, a reddish brown transparent solution was obtained. Then, after cooling to 40 ° C., 180 parts of 8) 20% hydrochloric acid was added to this reddish brown transparent solution and stirred, and in about 10 minutes, the upper layer was separated into a colorless and transparent aqueous layer, and the lower layer was separated into a reddish brown organic layer. After separating and removing the upper layer by decantation, 9) 490 parts of n-butanol was added and reacted at 60 ° C. for 3 hours to obtain a benzene ring mononuclear content of 0.1%, a number average molecular weight of 840, and methylol per phenyl group. Solid content 50 having a group of 0.5, an n-butoxy (alkoxylated) methyl group of 0.6, a methylene bond of 0.6, a dimethylene ether bond of 0.3, and a total value of all functional groups of 2.0 % Phenol resin (D-2) solution was obtained.

Production Example 7 [Production of phenol resin (D-3) solution]
In a four-necked flask purged with nitrogen gas, 1) ion exchange water 60 parts, 2) 20% sodium hydroxide aqueous solution 60 parts, 3) bisphenol A 50 parts, 4) bisphenol F 50 parts, 5) 37% formalin 300 parts Was reacted at 60 ° C. for 3 hours to obtain a brown transparent solution. Then, after cooling to 40 ° C., 5) 55 parts of 20% hydrochloric acid was added to this brown transparent solution and stirred, and in about 10 minutes, the upper layer was separated into a colorless and transparent aqueous layer, and the lower layer was separated into a brown organic layer. After separating and removing the upper layer by decantation, 7) n-butanol 140 is added, benzene ring mononuclear content is 0.0% (theoretical does not exist), number average molecular weight is 320, methylol per phenyl group Solid content 50 having a group of 1.3, an n-butoxy (alkoxylated) methyl group of 0.1, a methylene bond of 0.3, a dimethylene ether bond of 0.1 and a total value of all functional groups of 1.8 % Phenol resin (D-3) solution was obtained.

Production Example 8 [Production of phenol resin (D-4) solution]
A 4-necked flask purged with nitrogen gas was charged with 1) 60 parts of ion-exchanged water, 2) 60 parts of a 20% aqueous sodium hydroxide solution, 3) 100 parts of coal acid, and 4) 200 parts of 37% formalin at 70 ° C. for 3 hours. When reacted, a brown transparent solution was obtained. Then, after cooling to 40 ° C., 5) 55 parts of 20% hydrochloric acid was added to this brown transparent solution and stirred, and in about 10 minutes, the upper layer was separated into a colorless and transparent aqueous layer, and the lower layer was separated into a brown organic layer. After separating and removing the upper layer by decantation, 6) n-butanol 140 was added and then reacted at 60 ° C. for 3 hours. The benzene ring mononuclear content was 4.8%, the number average molecular weight was 580, per phenyl group A solid having a methylol group of 0.4, an n-butoxy (alkoxylated) methyl group of 0.3, a methylene bond of 0.5, a dimethylene ether bond of 0.1, and a total value of all functional groups of 1.3 A 50% phenol resin (D-4) solution was obtained.

Production Example 9 [Production of phenol resin (D-5) solution]
P-cresol was used instead of m-cresol in Production Example 6, and the others were the same in the same manner, with a benzene ring mononuclear content of 0.2%, a number average molecular weight of 670, and a methylol group per phenyl group of 0.3, A phenol resin (D) having a solid content of 50% having an n-butoxy (alkoxylated) methyl group of 0.3, a methylene bond of 0.4, a dimethylene ether bond of 0.1, and a total value of all functional groups of 1.1. -5) A solution was obtained.

Production Example 10 [Production of phenol resin (D-6) solution]
Using o-cresol in place of the coalic acid of Production Example 8, except that the benzene ring mononuclear content is 3.3%, the number average molecular weight is 720, the methylol group per phenyl group is 0.5, n- A phenol resin (D-6) having a butoxy (alkoxylated) methyl group of 0.1, a methylene bond of 0.5, a dimethylene ether bond of 0.1 and a total value of all functional groups of 1.2 and a total content of 1.2% ) A solution was obtained.

Example 1 [Production of aqueous coating composition]
160 parts of Epicoat 1010 (manufactured by Japan Epoxy Resin Co., Ltd.) and 70 parts of butyl cellosolve were charged into a four-necked flask substituted with nitrogen gas, and heated and stirred to 120 ° C. to completely dissolve the epoxy resin.
Thereafter, it was cooled to 80 ° C., and 160 parts of the carboxyl group-containing acrylic copolymer (A1-1) solution and 24 parts of the phenol resin (D-1) solution were charged. Next, 11 parts of dimethylaminoethanol was added and allowed to react for 2 hours while maintaining 80 ° C. Then, after cooling to 60 ° C., 575 parts of ion exchange water was gradually added dropwise over 1 hour to obtain an aqueous coating composition having a solid content of 22.0%.

Example 2 [Production of aqueous coating composition]
In the same manner as in Example 1, the carboxyl group-containing acrylic copolymer (A1-2) solution was used instead of the carboxyl group-containing acrylic copolymer (A1-1) solution. An aqueous coating composition was obtained.

Example 3 [Production of aqueous coating composition]
In the same manner as in Example 1, the phenol resin (D-2) was used in place of the phenol resin (D-1) solution, and an aqueous coating composition of Example 3 was obtained.

Example 4 [Production of water-based coating composition]
A 4-necked flask purged with nitrogen gas was charged with 160 parts of AER-6019 (manufactured by Asahi Kasei Epoxy Co., Ltd.), 80 parts of butyl cellosolve and 80 parts of n-butanol, and heated and stirred to 120 ° C. to completely dissolve the epoxy resin.
An acrylic monomer and a polymerization initiator solution in which 30 parts of methacrylic acid, 10 parts of styrene, 5 parts of ethyl acrylate, 5 parts of methyl methacrylate, and 3 parts of benzoyl peroxide are mixed with the inside of the flask kept at 120 ° C. are dropped over 1 hour. did. After completion of the dropwise addition, the mixture was further maintained at 120 ° C. for 1 hour, cooled to 60 ° C., and 15 parts of dimethylaminoethanol was added. Subsequently, 592 parts of ion exchange water was dropped over 1 hour, and then 20 parts of the phenol resin (D-1) solution was added to obtain an aqueous coating composition having a solid content of 22.0%.

Example 5 [Production of aqueous coating composition]
165 parts of Epototo YD-017 (manufactured by Tohto Kasei Co., Ltd.), 80 parts of butyl cellosolve and 80 parts of n-butanol are charged into a four-necked flask purged with nitrogen gas, heated to 125 ° C. and stirred to completely dissolve the epoxy resin. It was.
While maintaining the interior of the flask at 125 ° C., 1.0 part of methacrylic acid and 0.005 part of hydroquinone were charged, and then 0.2 part of 25% aqueous sodium hydroxide solution was charged and reacted for 3 hours.
After cooling to 90 ° C, an acrylic monomer and a polymerization initiator solution in which 30 parts of methacrylic acid, 10 parts of styrene, 10 parts of ethyl acrylate, and 1 part of N, N-azobisisobutyronitrile were mixed while maintaining the temperature It was added dropwise over time. After further holding at 90 ° C. for 1 hour, the mixture was cooled to 60 ° C. and 10 parts of dimethylaminoethanol was added. Subsequently, 603 parts of ion-exchanged water was added dropwise over 1 hour, and then 10 parts of a phenol resin (D-2) solution was added to obtain an aqueous coating composition having a solid content of 22.0%.

Comparative Examples 1 and 2 [Production of aqueous coating composition]
In the same manner as in Example 1, instead of the carboxyl group-containing acrylic copolymer (A1-1), the carboxyl group-containing acrylic copolymer (A1-3) to (A1-4) solution was used, The aqueous coating composition of Comparative Examples 1-2 was obtained.

Comparative Examples 3 to 6 [Production of aqueous coating composition]
In the same manner as in Example 1, the above phenol resins (D-3) to (D-6) were used in place of the phenol resin (D-1) to obtain aqueous coating compositions of Comparative Examples 3 to 6. .

Comparative Example 7 [Production of aqueous coating composition]
Charge 100 parts of Epicoat 1004 (manufactured by Japan Epoxy Resin Co., Ltd., Eeq = 920, Mn = 1600) and 70 parts of butyl cellosolve into a four-necked flask purged with nitrogen gas, and heat and stir to 120 ° C to completely dissolve the epoxy resin. I let you.
Thereafter, the mixture was cooled to 80 ° C., and 360 parts of the carboxyl group-containing acrylic copolymer (A1-1) solution and 24 parts of the phenol resin (D-1) solution were charged. Next, 11 parts of dimethylaminoethanol was added and allowed to react for 1 hour while maintaining 80 ° C. Then, after cooling to 60 ° C., 435 parts of ion exchange water was gradually added dropwise over 1 hour to obtain an aqueous coating composition having a solid content of 22.0%.

Comparative Example 8 [Production of aqueous coating composition]
160 parts of Epototo YP-50S (manufactured by Toto Kasei Co., Ltd.) and 70 parts of butyl cellosolve were charged into a four-necked flask purged with nitrogen gas, and heated and stirred to 120 ° C. to completely dissolve the epoxy resin.
Thereafter, the mixture was cooled to 80 ° C., and 160 parts of the carboxyl group-containing acrylic copolymer (A1-1) solution and 24 parts of the phenol resin (D-1) solution were charged. Next, 11 parts of dimethylaminoethanol was added and allowed to react for 1 hour while maintaining 80 ° C. After cooling to 60 ° C., 575 parts of ion exchange water was gradually added dropwise over 1 hour, but a stable aqueous coating composition was not obtained, and the resin settled and separated over time.

(Coating performance test panel production)
The aqueous coating composition obtained in Examples 1 to 5 and Comparative Examples 1 to 7 (Comparative Example 8 could not be used for coating performance evaluation because it did not become a coating). A test panel was prepared by painting on an aluminum plate having a thickness of 0.1 mm so as to have a thickness of 5 μm, followed by baking and drying at 200 ° C. for 1 minute (peak temperature holding time). Using each test panel, the coating film performance of the following contents was evaluated, and the test results are shown in Table 3.

(Test items)
The following methods are used to test (1) flavor component adsorption rate, (2) water flavor, (3) TOC, (4) corrosion resistance, and (5) measurement of the minimum cross-linking molecular weight of the paint film after baking and drying. Went.

(1) Flavor component adsorption rate Although various flavor substances are contained in alcoholic beverages, ester compounds are considered to be particularly important because of their high content and low sensory threshold. The ester compound in the alcoholic beverage according to the present invention includes ethyl acetate, ethyl caproate, ethyl caprylate, isoamyl acetate, acetic acid 2 as described in “List of Brewing Components (Edited by Japan Brewing Association)”. Limonene, which is known as a representative component of orange flavor, was used as a flavor standard substance. It can be said that the lower the standard material adsorption rate, the better the flavor retention.
Each test panel 500 cm ² was immersed in 500 cc of a 10% ethanol aqueous solution containing 5 ppm each of various flavor standard substances (6 types of ethyl acetate, ethyl caproate, ethyl caprylate, isoamyl acetate, 2-phenylethyl acetate, and limonene) After sealing, it was allowed to elapse at 37 ° C. for 30 days. Each test panel after 30 days is taken out, washed with distilled water, the film is re-immersed in 100 cc of diethyl ether, each flavor standard substance adsorbed on the test panel is extracted, and the amount of adsorption is determined by gas chromatography. did. Each flavor substance was contained in the immersion liquid (500 cc) in an amount of 0.0025 g. Taking this amount as 100%, the adsorption rate of each flavor component was calculated from the amount adsorbed on the coating film, and evaluated according to the following criteria.
Average adsorption rate of 6 types of flavor substances Less than 2%
6 kinds of flavor substance adsorption rate average value 2% or more and less than 4%
6 kinds of flavor substance adsorption rate average value 4% or more and less than 10%
6 kinds of flavor substance adsorption rate average value 10% or more

(2) Water flavor The water flavor is an evaluation of the taste change with respect to the contents, and it can be said that the smaller the change, the better the performance as a can inner surface paint.
Each test panel 500 cm ² was immersed in 500 cc of activated carbon-treated water containing 5% ethanol, sealed, and then heat-treated at 125 ° C. for 30 minutes. The taste of each treated water was evaluated according to the following criteria, using as a standard activated carbon treated water containing 5% ethanol that was subjected to the same treatment without immersing the coated plate.
No change in taste ...
There is a slight change in taste ...
Taste has changed ...
Significant changes in taste such as resin odor

(3) TOC (total organic carbon)
As a general method for inspecting an organic substance present in water, potassium permanganate consumption or COD is known, but these techniques have different detection sensitivities depending on the structure of the organic substance. On the other hand, the TOC can uniformly detect the amount of all organic substances regardless of the structure. It can be said that the lower the measured value, the better the hygiene.
Each test panel 500 cm ² was immersed in 500 cc of distilled water, sealed, and then heat-treated at 125 ° C. for 30 minutes. The TOC of each treated water was measured and evaluated according to the following criteria.
TOC Less than 0.5ppm ・ ・ ・ ・ ◎
TOC 0.5ppm or more and less than 1.0ppm …… ○
TOC 1.0 ppm or more and less than 2.0 ppm △△
TOC 2.0ppm or more ...

(4) Corrosion resistance Corrosion resistance is an evaluation of the presence or absence of corrosion of the coating film with respect to various contents.
Each test panel is immersed in a 10% aqueous ethanol solution containing potassium metabisulfite (608 ppm as potassium salt) corresponding to 350 ppm sulfite concentration, which is the limit allowable concentration (350 ppm) indicated in the Food Sanitation Law, and 1% citric acid. Then, the surface state of the coating film after aging at 50 ° C. for 3 months was observed and evaluated according to the following criteria.
No change in coating surface condition ...
Slight cloudiness occurs on the coating surface.
The coating surface becomes matte ...
The coating film deteriorates and peels off from the base metal.

(5) Molecular weight between minimum crosslinks Except for Comparative Example 8, the aqueous coating compositions obtained in each Example and each Comparative Example were on a 0.25 mm thick tin plate so that the coating thickness after baking and drying was 10 μm. And baking and drying at 200 ° C. for 1 minute (peak temperature holding time). The coating film was peeled off from the tinplate by making tin on the tinplate amalgam (liquid) using mercury, and the free film of each coating film was obtained. Using a dynamic viscoelasticity measuring device (DMS), the storage elastic modulus measurement value of the rubber-like region (175 ° C.) of each free film is measured, and the molecular weight [g / mol] of the coating film is determined by the following Nielsen equation. It was.
(Nielsen type)
Molecular weight between crosslinks [g / mol] = 293 d / (log (E′h / 3) −7.0)
d: Coating film density [g / cm ³ ],
E′h: storage elastic modulus [dyn / cm ² ] of rubber-like region (175 ° C.)

Claims (6)

A water-based coating composition comprising a self-emulsifying bisphenol type epoxy resin (A) and a phenol resin (D) dispersed in an aqueous medium in the presence of an amine or ammonia,
The self-emulsifying bisphenol type epoxy resin (A)
A carboxyl group-containing acrylic copolymer (A1) obtained by copolymerizing methacrylic acid / styrene / ethyl acrylate / methyl methacrylate with a composition of 50 to 70/1 to 30/1 to 20/0 to 20 (% by weight); ,
A bisphenol-type epoxy resin (A2) having an epoxy equivalent of 1500-5000 and a number-average molecular weight of 2,000-6000 as an essential component;
Self-emulsifying bisphenol type epoxy resin (A) obtained by esterification at a weight ratio of carboxyl group-containing acrylic copolymer (A1) / bisphenol type epoxy resin (A2) = 30/70 to 10/90. Yes,
The phenol resin (D) has a trifunctional phenol as a monomer, the benzene ring mononuclear content in the resin is 1% by weight or less, the number average molecular weight is 250 to 1000, a methylol group per phenyl group, A resol type phenolic resin having a total value of alkoxylated methyl group, methylene bond, and dimethylene ether bond of 1.5 to 2.5;
The self-emulsifying bisphenol type epoxy resin (A) / phenolic resin (D) = 90/10 to 99/1 (weight ratio). A self-emulsifying bisphenol-type epoxy resin (B) and a phenol resin (D), which are dispersed in an aqueous medium in the presence of an amine or ammonia, and comprising the self-emulsifying bisphenol-type epoxy resin (B) But,
A radical polymerizable monomer (b1) containing methacrylic acid / styrene / ethyl acrylate / methyl methacrylate in a composition of 50 to 70/1 to 30/1 to 20/0 to 20 (wt%),
(B1) / (A2) using a free radical generator in a bisphenol type epoxy resin (A2) containing a bisphenol type epoxy resin having an epoxy equivalent of 1500 to 5000 and a number average molecular weight of 2000 to 6000 as an essential component. = Self-emulsifying bisphenol type epoxy resin (B) grafted under conditions of 30/70 to 10/90 (weight ratio),
The phenol resin (D) has a trifunctional phenol as a monomer, the benzene ring mononuclear content in the resin is 1% by weight or less, the number average molecular weight is 250 to 1000, and a methylol group per phenyl group. , A resol type phenolic resin having a total value of alkoxylated methyl group, methylene bond, and dimethylene ether bond of 1.5 to 2.5,
The self-emulsifying bisphenol type epoxy resin (A) / phenolic resin (D) = 90/10 to 99/1 (weight ratio). A self-emulsifying bisphenol-type epoxy resin (C) and a phenol resin (D) are dispersed in an aqueous medium in the presence of an amine or ammonia, and the water-based coating composition comprises the self-emulsifying bisphenol-type epoxy resin (C). But,
A methacryloyl group obtained by reacting methacrylic acid (c1) with a part of a bisphenol type epoxy resin (A2) containing an epoxy equivalent of 1500 to 5000 and a number average molecular weight of 2000 to 6000 as an essential component. A copolymer (C) obtained by copolymerizing an epoxy resin (c2) having a radical polymerizable monomer (c4) containing methacrylic acid (c3) / styrene / ethyl acrylate / methyl methacrylate,
Methacrylic acid (c1) + (c3) / styrene / ethyl acrylate / methyl methacrylate is 50 to 70/1 to 30/1 to 20/0 to 20 (% by weight),
Methacrylic acid (c1), radical polymerizable monomer (c4), and epoxy resin (A2) used for the composition of the copolymer (C) are [(c1) + (c4)] / (A2) = 30 / 70 to 10/90 (weight ratio),
The phenol resin (D) has a trifunctional phenol as a monomer, the benzene ring mononuclear content in the resin is 1% by weight or less, the number average molecular weight is 250 to 1000, and a methylol group per phenyl group. , A resol type phenolic resin having a total value of alkoxylated methyl group, methylene bond, and dimethylene ether bond of 1.5 to 2.5,
The self-emulsifying bisphenol type epoxy resin (A) / phenolic resin (D) = 90/10 to 99/1 (weight ratio). The aqueous coating composition according to any one of claims 1 to 3, wherein the trifunctional phenol in the phenol resin (D) is carboxylic acid or / and m-cresol. A can for alcoholic beverages, the inner surface of which is coated with a paint containing the aqueous paint composition according to any one of claims 1 to 4. A can for alcoholic beverages, wherein the inner surface is coated with a paint containing the aqueous paint composition according to any one of claims 1 to 4, and the minimum molecular weight between crosslinks of the coating film is 150 to 300.