JP4665425B2 - Aqueous coating composition, process for producing the same, and can body and can lid having coating film made of the aqueous coating composition - Google Patents

Description

  The present invention relates to an aqueous coating composition capable of forming a coating film having excellent corrosion resistance and hardly affecting the flavor of the contents, and a method for producing the same. More specifically, the coating film can be formed without using a curing agent. In addition, the present invention relates to a water-based coating composition remarkably excellent in processing adhesion, corrosion resistance, and dent resistance of a coating film and a method for producing the same.

  Conventionally, water-based paints composed of a combination of epoxy acrylic resins and hardeners have been applied as internal paints used for can-making paints, particularly aluminum squeezed iron cans (hereinafter sometimes referred to as ADI cans). . Paints using such epoxy acrylic resins have little influence on the flavor of the contents and are excellent in corrosion resistance, and have been widely put into practical use as internal paints for cans such as coffee drinks, acidic drinks, and tea drinks that require retort sterilization. Yes.

  Such a paint is, for example, a reaction product of an epoxy resin containing a 1,2-epoxy group and a preformed first addition polymer containing a carboxyl group, and the 1,2-epoxy group and the carboxyl group described above. An ionic polymer component A comprising a hydroxy ester group from the reaction with and substantially free of unreacted 1,2-epoxy groups, and a second addition polymer different from the first addition polymer, A second addition polymer B different from the first addition polymer and an ammonia or organic amine neutralizing agent polymerized in an aqueous dispersion of the ionic polymer with an addition polymerization product of an ethylenically unsaturated monomer There has been proposed an aqueous coating composition comprising (Patent Document 1).

Japanese Patent Publication No. 4-12309

Conventionally, beverages that cannot be filled into metal cans are known to be beverages containing a high content of sulfite such as wine. Most wines are added with sulfurous acid during brewing for the purpose of facilitating fermentation or preventing alteration by microorganisms, etc., and this sulfurous acid causes corrosion of metal cans and flavor deterioration. . For this reason, wine-based beverages with a significantly reduced sulfurous acid concentration have been put to practical use in metal cans, but ordinary wines could not be filled into metal cans.
Even in a metal can provided with the water-based paint described in Patent Document 1, it was difficult to develop satisfactory corrosion resistance when the contents were ordinary wine containing a relatively large amount of sulfurous acid. As a result of studying this cause, in the water-based paint described in Patent Document 1, it is necessary to use a curing agent to form a coating film. It was found that the coating film was cracked at a site where the degree of processing was high, and the processing adhesion was poor.

  Moreover, there is what is called dent resistance as a performance required for an actual can. This means that even if the canned products fall or if the canned products collide with each other and the dents called dents are generated in the canned products, the adhesion and coverage of the coating are completely maintained. Although it is a characteristic, the metal can which gave the water-based paint of the said patent document 1 also had the problem that this dent resistance was inferior.

Accordingly, an object of the present invention is to provide a coating composition capable of forming a coating film that does not cause corrosion of a metal can even if ordinary wine containing sulfurous acid is filled as it is.
Another object of the present invention is to provide a coating composition capable of forming a coating film having little influence on the content flavor and excellent in dent resistance and work adhesion.
Still another object of the present invention is to provide a production method capable of efficiently preparing the coating composition.
Still another object of the present invention is to provide a can body and a can lid which are remarkably excellent in dent resistance and corrosion resistance and can be filled with ordinary wine as it is.

According to the present invention, a reaction capable of self-dispersing in water in a neutralized form by reacting an epoxy resin having a weight average molecular weight in the range of 5000 to 15000 and an acrylic resin having a weight average molecular weight in the range of 3000 to 20000. After preparing the product (A) and adding ammonia or an organic amine neutralizing agent to the reaction product to prepare an aqueous dispersion, the aqueous dispersion does not contain an epoxy resin and has a carboxyl group. The ethylenically unsaturated monomer (B) not contained is added in a weight ratio of (A) :( B) = 30: 70 to 80:20, and bulk polymerization is performed so that the weight average molecular weight becomes 20000 to 200000. Provided is a method for producing an aqueous coating composition for use in a metal can filled with a featured high sulfurous acid content beverage .

According to the present invention, (A) a reaction product based on an epoxy resin / acrylic resin that is self-dispersible in water in a neutralized form, (B) does not contain an epoxy resin and contains a carboxyl group An aqueous coating composition used for metal cans filled with acrylic resin and (C) ammonia or an organic amine neutralizing agent, and filled with a beverage containing high content of sulfurous acid. The weight average molecular weight is in the range of 3000-20000, the weight average molecular weight of the epoxy resin in (A) is in the range of 5000-15000, the weight average molecular weight of the acrylic resin in (B) is in the range of 20000-200000, A) and (B) are contained in a weight ratio of (A) :( B) = 30: 70 to 80:20, and the acrylic resin of (B) is There is provided an aqueous coating composition characterized in that the reaction product (A) is incorporated in a dispersed state and no curing agent is used in forming a coating film .

  Furthermore, according to the present invention, a can body and a can lid characterized by having a coating film made of the above-mentioned aqueous coating composition on the inner surface of the can or the lid, particularly a can body in which the coating film is formed on an aluminum substrate. And a can lid is provided.

According to the coating composition of the present invention, a water-based coating comprising a reaction product based on an epoxy resin / acrylic resin, a high molecular weight acrylic resin containing no epoxy group and no carboxyl group, and a neutralizing agent In the composition, a coating film can be formed without using a curing agent by incorporating a high molecular weight acrylic resin into a dispersion state of a reaction product composed of an epoxy resin and an acrylic resin. A coating film can be formed without increasing the cross-linking density of the film, and the formed coating film has high flexibility while being a cured coating film. For this reason, it is excellent in the adhesiveness of a coating film also in a severely processed part such as a tightening part or a part subjected to an impact, and is remarkably excellent in processing adhesiveness, dent resistance, and corrosion resistance.
In addition, cans and can lids having an inner surface coating film made of this coating composition do not cause corrosion even when filled with normal wine containing sulfurous acid as it is, and are ordinary wines that have been limited to conventional glass bottles. Can also be filled.

In the aqueous coating composition of the present invention, (A) a reaction product based on an epoxy resin / acrylic resin that is self-dispersible in water in a neutralized form, and (B) an epoxy resin that does not contain an epoxy resin In an aqueous coating composition comprising an acrylic resin not containing a group and (C) ammonia or an organic amine neutralizing agent, the acrylic resin in (A) has a weight average molecular weight in the range of 3000 to 20000, and the epoxy in (A). It is important that the weight average molecular weight of the resin is in the range of 5000 to 15000, the weight average molecular weight of the acrylic resin in (B) is in the range of 20000 to 200000, and that no curing agent is used in forming the coating film.
As described above, an aqueous coating composition comprising a reaction product based on an epoxy resin / acrylic resin system, an addition polymerization product of an ethylenically unsaturated monomer, and a neutralizing agent has been conventionally known. In order to form a coating film in the composition, since the use of a curing agent is essential, the crosslinking density is high, and the formed coating film is hard, that is, lacks flexibility. For this reason, it is thought that the corrosion progresses remarkably when the coating film cracks at the part to be subjected to severe processing such as the coiling part or the dent part and the contents contain corrosive components like wine. .

  In the present invention, from such a viewpoint, it is important to use a high molecular weight acrylic resin having a weight average molecular weight of 20,000 to 200,000 in order to enable formation of a flexible coating film without using a curing agent. It is. This high molecular weight acrylic resin is incorporated into the dispersion state of the reaction product of the epoxy resin and the acrylic resin, and it is possible to form a coating film without increasing the crosslinking density of the coating film like a curing agent. Therefore, although the coating film to be formed is a cured coating film, it has a high flexibility and is remarkably excellent in work adhesion and dent resistance.

The excellent effect of the aqueous coating composition of the present invention is also apparent from the results of Examples described later.
That is, in a can body having a coating film formed using a curing agent, satisfactory results were not obtained in terms of influence on processing adhesion, corrosion resistance, dent resistance, and content flavor (comparative example). 23 to 25), the can body having the coating film made of the aqueous coating composition of the present invention has obtained satisfactory results in all of processing adhesion and corrosion resistance (Examples 1 to 29).

In the present invention, it is also important that each component constituting the coating composition has a predetermined weight average molecular weight, and this point is also apparent from the results of the examples.
That is, when the weight average molecular weight of the acrylic resin in (A) is smaller than 3000, the boiling water resistance, processing adhesion, and corrosion resistance are inferior (Comparative Example 1). Since it is inferior, manufacture of a coating material becomes difficult and also it becomes inferior to the stability of a coating material (Comparative Examples 20-22). Further, when the weight average molecular weight of the epoxy resin in (A) is smaller than 5000, the boiling water resistance, the bending adhesion, and the corrosion resistance are inferior (Comparative Examples 6, 14, 20). Since the compatibility is inferior, the production of the paint becomes difficult and the stability of the paint is also inferior (Comparative Examples 11, 19, and 22). Furthermore, when the weight average molecular weight of the acrylic resin in (B) is smaller than 20000, it becomes difficult to form a sufficiently cured coating film, and the bending adhesion and corrosion resistance are poor (Comparative Examples 2 and 4). On the other hand, when it is larger than 200000, the compatibility is inferior, so that the production of the paint becomes difficult and the stability of the paint is also inferior (Comparative Examples 3, 5, 8, etc.).

In the aqueous coating composition of the present invention, in order to enable the formation of a coating film having excellent work adhesion and corrosion resistance, in the coating composition, (B) It is important that the acrylic resin is in a state of being taken in, so that it is not necessary to use a curing agent as described above, so that it has excellent work adhesion, corrosion resistance and dent resistance, and is flexible. A cured coating film can be formed.
Therefore, in the present invention, an aqueous dispersion is prepared by adding ammonia or an organic amine neutralizing agent (C) to the reaction product of (A) above, and then an epoxy resin is contained in the aqueous dispersion. In addition, an ethylenically unsaturated monomer that does not contain a carboxyl group is added and bulk polymerization is performed so that the weight average molecular weight is 20000 to 200000, and the acrylic resin of (B) is contained in the dispersed state of the resin of (A). It is important to prepare the coating composition in the incorporated state.

  The fact that it is important that the coating composition of the present invention is prepared by such a production method is also apparent from the results of Examples described later. That is, in the coating composition prepared by the above method, since no curing agent is used, excellent process adhesion and corrosion resistance are obtained (Examples 1 to 29), even if the same components are used, When an acrylic resin that has been polymerized in advance by solution polymerization is added to the aqueous dispersions (A) and (C), the work adhesion is poor, and as a result, the corrosion resistance is also reduced (Comparative Examples 28 and 29). Further, when the acrylic resin and epoxy resin (A) and (B) acrylic resin and (C) neutralizing agent are all mixed at the same time, the compatibility is inferior and the coating cannot be stabilized.

  In the coating composition of the present invention, the blending ratio of (A) a reaction product based on an epoxy resin / acrylic resin and (B) an acrylic resin not containing an epoxy resin and not containing a carboxyl group is a weight ratio, (A) :( B) = 30: 70 to 80:20, particularly 40:60 to 80:20. If the component (B) is less than the above range, satisfactory processability cannot be obtained, and if the component (B) is more than the above range, a stable coating composition cannot be prepared and coating properties are poor. None (Comparative Examples 26 and 27).

(A) Reaction product based on epoxy resin / acrylic resin system The component (A) of the present invention comprises an epoxy resin and an acrylic resin, and an aqueous dispersion is obtained mainly by an esterification reaction of the epoxy resin and the acrylic resin. The necessary epoxy acrylate is prepared.
The blending ratio of the epoxy resin and the acrylic resin is preferably in the range of 10:90 to 80:20, particularly 50:50 to 75:25, by weight. When the amount of the epoxy resin is less than the above range, the resulting coating film is inferior in processing adhesion, whereas when the amount of the epoxy resin is more than the above range, it becomes difficult to form an aqueous dispersion.

(Epoxy resin)
The epoxy resin used in the present invention is a resin having one or more epoxy groups in one molecule, and generally a reaction product of a polyhydric phenol compound having two or more phenolic hydroxyl groups in one molecule and epichlorohydrin. Is preferred.
Specific examples of the polyhydric phenol compound include 2,2′-bis (4-hydroxyphenyl) propane (hereinafter sometimes referred to as “bisphenol A”), halogenated bisphenol A, and bis (4-hydroxyphenyl). Methane (hereinafter sometimes referred to as “bisphenol F”), 2,2′-bis (4-hydroxyphenyl) butyl, bis (4-hydroxyphenyl) sulfone (hereinafter sometimes referred to as “bisphenol S”), resorcinol, phenol Or the novolak type polyfunctional phenol etc. which are condensed from cresol and formalin are mentioned. Of these, bisphenol A and bisphenol F are preferred, and a mixture of both may be used.
Moreover, as an epoxy resin, the epoxy ester resin which combined the dibasic acid with the reaction product of the said polyhydric phenol compound and epichlorohydrin may be sufficient. Specifically, as the dibasic acid, succinic acid, adipic acid, pimelic acid, azelaic acid, sebacic acid, etc., hexahydrophthalic acid and the like can be preferably used.
The weight average molecular weight of the epoxy resin used in the present invention is in the range of 5000 to 15000, particularly 8000 to 15000, which is important from the viewpoint of balance between workability and corrosion resistance.
Moreover, it is preferable that the epoxy equivalent of an epoxy resin exists in the range of 1500-5000.

(acrylic resin)
As the acrylic resin used in the component (A) of the present invention, (i) carboxyl group-containing radicals such as α, β-ethylenically unsaturated carboxylic acid such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, and crotonic acid (Ii) 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, which is copolymerizable with at least one of the polymerizable unsaturated monomers or in addition to such monomers A hydroxyalkyl ester of 1 to 8 carbon atoms of acrylic acid or methacrylic acid such as: methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate Acrylic or methacrylic acid such as relate, tert-butyl acrylate, tert-butyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, lauryl acrylate, lauryl methacrylate, stearyl acrylate, stearyl methacrylate, decyl acrylate, etc. C1-C24 alkyl or cycloalkyl ester of acid; acrylamide, methacrylamide, N-methylacrylamide, N-ethylmethacrylamide, diacetoneacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, N-methoxy Acrylic or methacrylate such as methylacrylamide, N-butoxymethylacrylamide, etc. Amides or derivatives thereof; aromatic vinyl monomers such as styrene, vinyltoluene, α-methylstyrene; radicals such as vinyl monomers such as vinyl propionate, vinyl acetate, acrylonitrile, methacrylonitrile, vinyl pivalate; Examples thereof include acrylic resins obtained by polymerizing a polymerizable unsaturated monomer with a polymerization method such as emulsion polymerization, solution polymerization, bulk polymerization and the like.

It is important from the viewpoint of corrosion resistance, retort resistance, etc. that the acrylic resin has a weight average molecular weight in the range of 3000-20000, particularly 5000-20000.
Moreover, it is preferable that the acid value of an acrylic resin exists in the range of 50-300 mgKOH / g from viewpoints, such as stability in an aqueous medium, retort resistance of the coating film obtained, and flavor resistance.

The reaction product of component (A) can be obtained by reacting an epoxy resin and an acrylic resin in the presence of a tertiary amine. In this reaction, mainly in the presence of a tertiary amine, an esterification reaction between a carboxyl group in an acrylic resin and an epoxy group in an epoxy resin, and a carboxyl group in an acrylic resin and an epoxy group in an epoxy resin It is considered that either one of the quaternary ammonium chloride reactions with the tertiary amine or both of these reactions are performed simultaneously.
As the tertiary amine that promotes the reaction, for example, dimethylethanolamine, dimethylbenzylamine, triethanolamine, monomethyldiethanolamine, morpholine, and the like are preferably used, and the amount used is the carboxyl in the reaction product. It is preferably used in the range of usually 0.2 to 2.0 chemical equivalents relative to the base amount.

(B) Acrylic resin The acrylic resin used for component (B) in the present invention is an acrylic resin composed of an ethylenically unsaturated monomer that does not contain an epoxy resin and does not contain a carboxyl group. The above-mentioned (ii) radical polymerizable unsaturated monomer exemplified as the one forming the acrylic resin can be used.

(C) Ammonia or organic amine neutralizing agent As the neutralizing agent for stably dispersing the reaction product of (A) described above in water, N-methylpyrrolidine, N-methylmorpholine, pyridine, N-methylpyrrole , N-methylpiperidine, ammonia, and a mixture of any of these, specifically, trimethylamine, dimethylethanolamine (dimethylaminoethanol), methyldiethanolamine, ethylmethylethanolamine Dimethylethylamine, dimethylpropylamine, dimethyl-3-hydroxy-1-propylamine, dimethylbenzylamine, dimethyl-2-hydroxy-1-propylamine, diethylmethylamine, dimethyl-1-hydroxy-2-propylamine, and this It can include any of the mixtures. Among these, particularly preferred are N-methylmorpholine, dimethylethanolamine, ethylmethylethanolamine and the like.
The amount used may be dispersed in an aqueous medium by adding a neutralizing agent in an amount such that the final aqueous resin dispersion has a pH of 6 to 10.

(Other)
In the aqueous coating composition of the present invention, if necessary, a conventionally known coating compounding agent such as a lubricant, an anti-agglomeration agent, a fluidity modifier and the like, a pigment, and a conventionally known coating compounding agent are appropriately added according to a conventionally known formulation. Can be blended.
The aqueous coating composition of the present invention generally preferably has a solid content of 10 to 40%, and the coating viscosity is preferably in the range of 100 to 1000 centipoise from the viewpoint of coating properties.

(Method for producing coating composition)
In the coating composition of the present invention, as described above, ammonia or an organic amine neutralizing agent (C) is added to the reaction product (A) to prepare an aqueous dispersion, and then the aqueous dispersion is added to the aqueous dispersion. An ethylenically unsaturated monomer that does not contain an epoxy resin and does not contain a carboxyl group is added and bulk polymerization is performed so that the weight average molecular weight is 20000 to 200000, and the dispersion state of the resin (A) ( A coating composition in a state in which the ethylenic addition polymerization product of B) is incorporated is prepared.
As described above, the reaction product (A) of the epoxy resin and the acrylic resin can be obtained by reacting the epoxy resin and the acrylic resin in the presence of a tertiary amine in an organic solvent solution. An aqueous dispersion of the reaction product (A) can be obtained by dispersing it in the aqueous medium using the neutralizing agent (C).

Although it does not limit to this as an organic solvent used for reaction which produces | generates the reaction product of (A), An alcohol type organic solvent can be used conveniently. For example, isopropanol, n-butyl alcohol, 2-hydroxy-4-methylpentane, 2-ethylhexyl alcohol, cyclohexanol, ethylene glycol, diethylene glycol, 1,3-butylene glycol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol Examples thereof include monomethyl ether, propylene glycol monopropyl ether, and propylene glycol monobutyl ether.
In addition to the alcohol organic solvents described above, for example, aromatic hydrocarbons such as toluene and xylene; esters such as ethyl acetate and butyl acetate; low boiling points such as ketones such as acetone, methyl isobutyl ketone and methyl ethyl ketone A combination of organic solvents can be used.
The reaction temperature and time of the acrylic resin and epoxy resin vary depending on the type of resin used, the type of solvent, and the like, but generally the reaction temperature is in the range of 80 to 120 ° C., and the reaction time is in the range of 0.5 to 10 hours. It is preferable.

Next, an ethylenically unsaturated monomer that does not contain a carboxyl group is blended in the aqueous dispersion, and polymerization is performed by bulk polymerization so that an ethylenic addition polymerization product having a weight average molecular weight of 20,000 to 200,000 is taken into the aqueous dispersion. .
The amount of the ethylenically unsaturated monomer to be added to the reaction product (A) is preferably 20 to 70% by weight, particularly 40 to 60% by weight based on the total weight of both components.
Polymerization catalysts such as benzoyl peroxide, perbutyl octate, t-butyl hydroperoxide, azobisisobutyronitrile, azobisisovaleronitrile, 2,2′-azobis (2-aminopropane) hydrochloride during polymerization These can generally be used in an amount of 0.1 to 3 parts by weight per 100 parts by weight of the ethylenically unsaturated monomer.
In the polymerization reaction of the ethylenically unsaturated monomer, the reaction temperature and time vary depending on the type of the ethylenically unsaturated monomer used, but generally the reaction temperature is 60 to 100 ° C. and the reaction time is 0.5 to 5 hours. A range is preferable.

(Can body and can lid)
The can body and the can lid having the coating film made of the aqueous coating composition of the present invention on the inner surface are obtained by coating the metal substrate with the aqueous coating composition of the present invention.
Usable metal substrates can be used for all conventionally known metal substrates, such as black plates, various coated steel plates, such as plated steel plates plated with tin, chromium, aluminum, zinc, etc. Examples of steel plates that have been chemically or cathodically electrolyzed with phosphoric acid, etc., and light metal plates such as aluminum alloys, can be mentioned. Is preferred.
The can body and can lid of the present invention comprise a coated metal plate formed on the surface of the metal substrate on which the aqueous coating composition of the present invention should be formed at least on the inner surface side. It can obtain by forming in a desired shape by a conventionally well-known manufacturing method so that it may become a desired shape.
Of course, the order can be reversed, and a coating film can be formed by applying and baking a pre-formed can body and can lid by spray coating or the like. This paint may be provided as a single coat or may be provided as a double coat.
The aqueous coating composition of the present invention can form a coating film by drying or baking after coating, generally at a temperature of about 180 to 220 ° C. for about 0.5 to 10 minutes.

Below, the manufacturing method of the can body and can lid | cover of this invention is demonstrated.
For example, in the case of a three-piece can having a side seam, the can body is preliminarily applied with the coating composition of the present invention to the above-described metal base can material, and then baked, and then soldered, welded, or adhesived. Joined by means such as joining to make a can. In the case of a seamless seamless seamless can, a painted metal plate is subjected to deep drawing or thinning deep drawing to form a painted seamless can body. Further, the can material may be subjected to drawing or drawing-ironing processing, the paint may be applied to the can after molding, and baked to form a painted seamless can.

  For the can lid, the paint of the present invention can be applied by coil coating, and it is coated on pure aluminum, aluminum alloy or the like to obtain a coated metal material having a high degree of workability. The coated metal material is punched, and press molding, or score processing, rivet molding, tab attachment, etc. are performed so that the coating film surface is the inner surface side, and the can is formed into a can lid or an easy open can lid.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, the following specific examples do not limit this invention. Unless otherwise specified, “part” and “%” in Examples represent “part by mass” and “% by mass”.

(Synthesis of aqueous acrylic resin solution)
A four-necked flask reaction vessel having a capacity of 1 liter equipped with a stirrer, reflux condenser, dropping funnel, nitrogen gas inlet tube and thermometer is prepared. Next, a mixed liquid of 60 parts of styrene, 80 parts of methacrylic acid, 24 parts of ethyl acrylate, and 4 parts of benzoyl peroxide was prepared, and charged into a four-necked flask in which 30% and 240 parts of n-butanol were replaced with nitrogen gas. And heated to 90 ° C. Subsequently, the remaining 70% of the above-mentioned mixed solution was added dropwise over 2 hours while maintaining the same temperature. After completion of dropping, the mixture was further stirred at that temperature for 2 hours to obtain an acrylic resin solution (a1) having a solid content of 40% and a weight average molecular weight of 2050.
Moreover, the acrylic resin solution (a2) having a solid content of 40% and a weight average molecular weight of 3080 by adjusting the addition amount of benzoyl peroxide, holding temperature, dropping time, last holding time, and the like under the same conditions as above. 5030 acrylic resin solution (a3), 9850 acrylic resin solution (a4), 19700 acrylic resin solution (a5), and 35800 acrylic resin solution (a6).

(Manufacture of epoxy resin)
・ Production example 1
A mixture of 300 parts of Epicoat 828 (trade name of Yuka Shell Epoxy Co., Ltd.), 90 parts of bisphenol A and 0.4 part of ethyltriphenylphosphonium chloride was reacted at 160 ° C. for 2 hours to obtain 390 parts of an epoxy resin having a weight average molecular weight of 1980. Obtained. 300 parts of the obtained epoxy resin was heated to 250 to 260 ° C. and purified by repeating vacuum distillation three times under the condition of 0.2 mmHg, and the weight average molecular weight of the obtained epoxy resin was 2120. This epoxy resin was used as an intermediate in the epoxy resin production described below.
Moreover, diethylene glycol monobutyl ether was added to the epoxy resin similarly produced by said method, and the epoxy resin solution (e1) of 60% of solid content was obtained.
・ Production example 2
A mixture of 300 parts of the aforementioned epoxy resin intermediate, 95 parts of bisphenol A, 0.05 part of tetramethylammonium chloride and 50 parts of cyclohexanone was reacted at 170 ° C. for 2 hours to obtain an epoxy resin having a weight average molecular weight of 5180, and diethylene glycol monobutyl ether Was added to prepare an epoxy resin solution (e2) having a solid content of 60%.
・ Production example 3
A mixture of 300 parts of the aforementioned epoxy resin intermediate, 65 parts of bisphenol A, 0.3 part of ethyltriphenylphosphonium chloride and 50 parts of cyclohexanone was reacted at 170 ° C. for 2 hours to obtain an epoxy resin having a weight average molecular weight of 10120, and diethylene glycol mono Butyl ether was added to prepare an epoxy resin solution (e3) having a solid content of 60%.
・ Production example 4
A mixture of 310 parts of the above epoxy resin intermediate, 70 parts of bisphenol A, 0.2 part of tetramethylammonium chloride and 100 parts of cyclohexanone was reacted at 160 ° C. for 6 hours to obtain an epoxy resin having a weight average molecular weight of 14950, and diethylene glycol monobutyl ether was added. In addition, an epoxy resin solution (e4) having a solid content of 60% was prepared.
・ Production example 5
A mixture of 300 parts of the aforementioned epoxy resin intermediate, 105 parts of bisphenol A, 0.2 part of tetramethylammonium chloride and 100 parts of cyclohexanone was reacted at 160 ° C. for 7 hours to obtain an epoxy resin having a weight average molecular weight of 20250, and diethylene glycol monobutyl ether was added. In addition, an epoxy resin solution (e5) having a solid content of 60% was prepared.

(Adjustment of aqueous resin dispersion (esterification of acrylic resin and epoxy resin))
In a four-necked flask reaction vessel having a capacity of 1 liter equipped with a stirrer, reflux condenser, dropping funnel, nitrogen gas inlet tube, thermometer, 120 parts of the acrylic resin solution (a1) and 80 parts of the epoxy resin solution (e3). Was heated to a liquid temperature of 80 ° C. and held at that temperature for 30 minutes, and then 5 parts of 2-dimethylethanolamine was added and reacted for 2 hours. After the reaction, the mixture was cooled to 55 ° C. and 250 parts of deionized water was added with stirring. This aqueous dispersion was subjected to vacuum distillation at a liquid temperature of 50 ° C. under a reduced pressure of 10 cmHg, and then adjusted to pH 7 to 8 by addition of amine to impart dispersion stability, and an aqueous resin dispersion having a final solid content of 40% was obtained. A body (A01) was obtained.
Various aqueous resin dispersions were prepared in the same manner, and the details are shown in Table 1.

(Preparation of acrylic resin B in various aqueous dispersions described above)
In a 1 liter four-necked flask reaction vessel equipped with a stirrer, reflux condenser, dropping funnel, nitrogen gas inlet tube, thermometer, 240 parts of aqueous dispersion A01, 125 parts of deionized water, 2-dimethylethanolamine 2 parts were charged, and 65 parts of a mixed solution of styrene / butyl acrylate = 1/1 was further added with stirring. Add 1 part of 20% mixture of t-butyl hydroperoxide diluted with deionized water to bring the reaction temperature to 65 ° C, then add 3 parts of 10% mixture of ammonium bisulfite diluted with deionized water and hold at 65 ° C for 1 hour. did. After completion of the reaction, 450 parts of deionized water was added, and then a neutralizing agent was added and adjusted so that the reaction system had a pH of 7 to 8 to obtain an aqueous paint. The weight average molecular weight of the synthesized acrylic resin B1 was 10150.
With the above formulation, various acrylic resins B were synthesized using various aqueous dispersions A01 to A19 while changing the reaction temperature and reaction time to prepare an aqueous paint. The weight average molecular weight of the acrylic resin B obtained by each synthesis was as follows.
Acrylic resin B2: 20250 Acrylic resin B3: 50530
Acrylic resin B4: 102110 Acrylic resin B5: 199000
Acrylic resin B6: 305400

(Adjustment of acrylic resin D by solution polymerization)
Into a 1-liter four-necked flask reaction vessel equipped with a stirrer, reflux condenser, dropping funnel, nitrogen gas inlet tube and thermometer, 50 parts of n-butanol and 170 parts of ethylene glycol monobutyl ether were charged, and further styrene / butyl. 100 parts of a mixed solution of acrylate = 1/1 was added, and the temperature of the reaction system was adjusted to 130 ° C. In that state, 400 parts of a mixed solution of styrene / butyl acrylate = 1/1 was added with stirring for 1 hour, and maintained at 130 ° C. for 30 minutes after the addition was completed. After completion of the holding, the resin was cooled to room temperature to obtain an acrylic resin D1, and the resin had a solid content of 70% and a weight average molecular weight of 50,300.
An acrylic resin D2 was obtained by changing the additional styrene / butyl acrylate = 1/1 solution addition time to 2 hours and the reaction time to 3 hours with the same formulation. The solid content of the resin at that time was 70%, and the weight average molecular weight was 205500.

(Production example of phenol resin solution)
In a 1-liter four-necked flask reaction vessel equipped with a stirrer, reflux condenser, dropping funnel, nitrogen gas inlet tube and thermometer, 150 parts of bisphenol A, 65 parts of P-cresol, 250 parts of 37% formalin, 25% ammonia 17 parts of water was charged, heated to around 95 ° C. and reacted for 1 hour. After the reaction, the system was cooled, extracted into a mixed solvent of n-butanol / butyl acetate = 1/1, washed with water, heated to azeotropic dehydration, and water was fractionated until the liquid temperature reached 110 ° C. After azeotropic dehydration, the mixture was further diluted with 200 parts of n-butanol to obtain a phenol resin solution (Ph) having a weight average molecular weight of 1500 and a solid content of 50%.

(Example of production of benzoguanamine resin solution)
A 1-liter four-necked flask reaction vessel equipped with a stirrer, reflux condenser, dropping funnel, nitrogen gas inlet tube and thermometer was charged with 187 parts of benzoguanamine, 281 parts of 80% paraformaldehyde, and 320 parts of methanol, 25% After adding 0.7 part of sodium hydroxide solution, it heated at 60 degreeC for 3 hours. Thereafter, 60% nitric acid solution was added until the pH of the reaction system solution reached 3.5, and the reaction was continued for 4 hours. After completion of the reaction, the reaction mixture was neutralized with 25% sodium hydroxide solution, and methanol water was removed under reduced pressure at 70 ° C. or lower. Thereafter, after filtration under reduced pressure, ethylene glycol monoisopropyl ether was added to obtain a benzoguanamine resin solution (Am) having a solid content of 50%.

(Paint adjustment)
The adjustment of the water-based paint corresponding to the present invention is as described in the above paragraph [0038].
Regarding the adjustment of other water-based paints, there are a case where the acrylic resin B is not used and a case where a curing agent is used.
When the acrylic resin B is not used, a necessary amount of deionized water is dispersed in the mixed state of the aqueous resin dispersion A and the acrylic resin D while stirring with a high-speed stirrer so that the solid content of the paint becomes 18%. It was. To impart dispersion stability, the pH was adjusted to 7-8 by adding an amine.
Moreover, when using a hardening | curing agent, it added in the ratio of 2 parts of hardening | curing agents (a phenol resin solution or a benzoquamine resin solution) with respect to 100 parts of water-based paints created based on the description in the item of [0037]. Thereafter, a required amount of deionized water was dispersed so that the solid content of the paint was 18% while stirring with a high-speed stirrer. To impart dispersion stability, the pH was adjusted to 7-8 by adding an amine.
About the composition content of the produced coating material, it showed in the table | surface of the evaluation result of Table 2-5.

(Creating a paint sample)
A variety of prototype water-based paints were used to coat ADI cans with a spray machine and baked at 200 ° C. for 3 minutes to prepare test samples. The coating amount on the can inner coating was 150 mg (dry coating weight) per 350 ml can, and the following confirmation items were evaluated.

(Confirmation items and test method)
The test methods that are various confirmation items are as follows.
The evaluation was performed with each of the following scores, but when there are two scores in the results table, it indicates that the score was in the middle of both scores.

-About the manufacturability and stability of paint When performing paint, from the viewpoint of manufacturability, the compatibility of the resin and the setting of the initial viscosity of the paint were observed. Furthermore, the stability over time when the coating was stored at a high temperature (37 ° C.) was investigated.
○: No problem in terms of both production and stability over time △: Slightly difficult in terms of production or stability over time ×: Particularly difficult in setting compatibility and initial viscosity of paint

-Flavor properties After filling the test cans with ion-exchanged water and performing heat treatment (treatment at 100 ° C for 30 minutes), the effect on the content flavor of the current product was compared.
○: No significant difference from current product △: Slightly inferior to current product in nasty taste / odour, etc. ×: Very different in current taste / odour, etc.

-About boiling water resistance After filling a test can with ion-exchange water and heat-processing (processing at 100 degreeC for 30 minutes), the state of the coating film was evaluated.
○: No whitening / lifting of the coating film △: Slight whitening / floatinging of the coating film ×: Whitening / lifting of the coating film

・ Processing adhesiveness Open the inner coated can, and perform a preliminary fold on the can body with the inner coating on the outside. Two aluminum plates with a thickness of 0.3 mm were sandwiched between the folds, and the bent part of the sample was wrapped with a thin plastic film, and an iron block having a flat contact surface and a weight of 3 kg was naturally dropped from a height of 45 cm. . Electric current was measured at an applied voltage of 6.5 V for 6 seconds through the 20 mm width of the bent tip portion subjected to impact processing, and the current value at that time was measured.
○: Very good level with current value less than 1 mA Δ: Almost good level with current value of 1 mA to less than 3 mA Δ: Slightly inferior level with current value of 3 mA to less than 10 mA × Δ: Current value of 10 mA or more ~ Unsatisfactory level at less than 20 mA X: Very inferior level at current value of 20 mA or more

-Corrosion resistance A commercially available wine (Mans wine "Monfrail red") was kept at a low temperature of 5 ° C or less and repacked in a test can. After cooling the filled can by heat treatment (at 60 ° C. for 10 minutes), a 1 kg iron block with a tip of a semi-sphere at the bottom of the can was dropped from a height of 50 mm to the can body. A dented part (dent part) was given. Thereafter, long-term storage at 37 ° C. for 3 months was performed, and the corrosion state of the dent portion was evaluated.
○: Corrosion progression is not observed △: Surface corrosion is observed ×: Deep corrosion progression is recognized

(Examples 1 to 24 and Comparative Examples 1 to 22)
A water-based paint was prepared with the combinations shown in Tables 2 and 3 for the combination of the application resin of the aqueous dispersion A and the acrylic resin B. At the time of forming the water-based paint, the ratio of the acrylic resin a: epoxy resin e of the aqueous resin dispersion A was fixed to 40/60, and the ratio of the aqueous resin dispersion A: acrylic resin B was fixed to 60/40. Table 2 shows the results of Examples 1 to 24 and Table 3 shows the results of Comparative Examples 1 to 22.

(Examples 10 and 25, Comparative Examples 23 to 25)
A water-based paint was prepared with the combinations shown in Tables 2 and 3 for the combination of the application resin of the aqueous dispersion A and the acrylic resin B. At the time of forming the aqueous paint, the ratio of the acrylic resin a: epoxy resin e of the aqueous resin dispersion A was fixed to 40/60, and the ratio of the aqueous resin dispersion A: acrylic resin B was fixed to 50/50. Further, the amount of the curing agent was 2 parts of the curing agent with respect to 100 parts of the mixed system of the aqueous resin dispersion and the acrylic resin B. The results are shown in Table 4.

(Examples 26 to 28, Comparative Examples 26 to 27)
A water-based paint was prepared with the combinations shown in Tables 2 and 3 for the combination of the application resin of the aqueous dispersion A and the acrylic resin B. At the time of forming the aqueous paint, the ratio of the acrylic resin a: epoxy resin e of the aqueous resin dispersion A was fixed to 40/60. The results are shown in Table 5.

(Examples 10 and 29, Comparative Examples 28 and 29)
A water-based paint was prepared with the combinations shown in Tables 2 and 3 for the combination of the application resin of the aqueous dispersion A and the acrylic resin B. At the time of forming the aqueous paint, the ratio of the acrylic resin a: epoxy resin e of the aqueous resin dispersion A was fixed to 40/60, and the ratio of the aqueous resin dispersion A: acrylic resin B was fixed to 50/50. The results are shown in Table 6.

Claims (6)

By reacting an epoxy resin having a weight average molecular weight in the range of 5000 to 15000 with an acrylic resin having a weight average molecular weight in the range of 3000 to 20000, a reaction product (A) that can be self-dispersed in water in a neutralized form. After preparing an aqueous dispersion by adding ammonia or an organic amine neutralizer to the reaction product, ethylenic unsaturation containing no epoxy resin and no carboxyl group in the aqueous dispersion Monomer (b) is added in a weight ratio of (A) :( b) = 30: 70 to 80:20, and bulk polymerization is performed so that the weight average molecular weight is 20000 to 200,000. The manufacturing method of the water-based coating composition used for the metal can filled with a drink. (A) In a neutralized form, a reaction product based on an epoxy resin / acrylic resin that is self-dispersible in water, (B) an acrylic resin that does not contain an epoxy resin and does not contain a carboxyl group, and (C ) A water-based coating composition used for metal cans consisting of ammonia or an organic amine neutralizing agent and filled with a sulfite-rich beverage,
The method according to claim 1, wherein the acrylic resin in (A) has a weight average molecular weight in the range of 3000 to 20000, the epoxy resin in (A) has a weight average molecular weight in the range of 5000 to 15000, and the acrylic in (B). The weight average molecular weight of the resin is in the range of 20,000 to 200,000, and (A) and (B) are contained in a weight ratio of (A) :( B) = 30: 70 to 80:20, An aqueous coating composition, wherein the acrylic resin is in a state of being incorporated in the dispersed state of the reaction product (A), and a curing agent is not used in forming a coating film. A can body comprising a coating film comprising the aqueous coating composition according to claim 2 on an inner surface of the can.   The can according to claim 3, wherein the coating film is formed on an aluminum substrate. A can lid comprising a coating film comprising the aqueous coating composition according to claim 2 on an inner surface of the lid.   The can lid according to claim 5, wherein the coating film is formed on an aluminum substrate.