JPH1077440A - Water-base coating material for exterior of can - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water-base coating material which is used for the exterior of a can and forms a film excellent in both adhesion even after necking and retorting resistance. SOLUTION: This coating material comprises mainly an aqueous resin composition obtained by neutralizing a coating resin composition consisting of 20-60wt.% alkyl-etherified benzoguanamine resin comprising a formaldehyde (1.5-3mol per mol of the triazine nucleus) adduct and having a solubility parameter of 9.5 to 11 and 80-40wt.% film-forming resin selected from acrylic and polyester resins and having an acid number of 30-100mg/KOH mg and a solubility parameter of 9.5 to 11, and dissolving or dispersing the neutralized composition in water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-based paint for the outer surface of a can. More specifically, the present invention relates to a water-based paint for the outer surface of a can which can be suitably used for a beverage can subjected to squeezing and ironing.

[0002]

2. Description of the Related Art Drink cans containing soft drinks, tea, and the like mainly include a three-piece can divided into a can body, a canopy and a shipping lid, and a two-piece can divided into a bottomed can body and a can lid. is there.

In the case of the two-piece can, as represented by a so-called DI can which is worked by drawing and ironing, aluminum and steel are used for the metal material.

Conventionally, such a DI can has a D
I perform processing and trimming, make a prototype of the container,
A white coat or a size coat is applied from the outer surface side, a printing ink and a top coat are successively applied thereon, then the inner surface is applied, and then necking and flange processing are performed.

[0005] As a two-piece can, a so-called 206-diameter neck-in can is mainly used. In recent years, studies have been made to replace it with a smaller-diameter 202-diameter neck-in can.

[0006] In the case of manufacturing a neck-in can having a diameter of 202 in this manner, since the necking of the bottomed can body becomes deeper, the development of a paint for the outer surface of a can which forms a coating film having excellent adhesion is awaited. Have been.

[0007] Further, since conventionally used paints are organic solvent-based paints, development of water-based paints that do not use organic solvents has been awaited in terms of environmental hygiene and fire safety.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned prior art, and has as its object to provide a water-based paint for an outer surface of a can which forms a coating film having excellent adhesion even after necking. This is the first purpose.

Further, the present invention has been made to provide an aqueous paint for an outer surface of a can which forms a coating film having excellent retort resistance in view of the fact that beverage cans are generally retorted for sterilization. This is the second purpose.

[0010]

According to the present invention, there is provided an alkyl etherified benzoguanamine resin (A) comprising 1.5 to 3 moles of formaldehyde added to 1 mole of a triazine nucleus and having a solubility parameter of 9.5 to 11. ~ 60
% By weight, and (B) an acid value of 30 to 100 mg / KOH.
Aqueous solution formed by dissolving or dispersing in water water a neutralizing resin composition comprising 80 to 40% by weight of a film-forming resin selected from an acrylic resin and a polyester having a solubility parameter of 9.5 to 11 mg. The present invention relates to a water-based paint for the outer surface of a can, comprising a resin composition as a main component.

[0011]

DETAILED DESCRIPTION OF THE INVENTION As described above, the water-based paint for the outer surface of a can of the present invention comprises (A) 1.5 to 3 mol of formaldehyde added per 1 mol of triazine nucleus, and has a solubility parameter (SP value). 20-60% by weight of an alkyl etherified benzoguanamine resin having 9.5-11 and (B) a coating selected from acrylic resins and polyesters having an acid number of 30-100 mg / KOH mg and a solubility parameter of 9.5-11 It is mainly composed of an aqueous resin composition which is obtained by neutralizing a resin composition for a coating consisting of 80 to 40% by weight of a forming resin and dissolving or dispersing in water.

The above-mentioned alkyl etherified benzoguanamine resin is obtained by subjecting benzoguanamine to addition reaction with formaldehyde under basic conditions, acidifying the system, adding excess alcohol to carry out etherification and condensation reactions. It is.

Examples of the alkyl etherified benzoguanamine resin include isopropyl etherified benzoguanamine resin, n-propyl etherified benzoguanamine resin, methyl isopropyl mixed etherified benzoguanamine resin, and methyl n-propyl mixed etherified benzoguanamine resin.

The number average molecular weight of the alkyl etherified benzoguanamine resin is set at 30 to prevent a large amount of volatile components from being generated when the formed coating film is cured.
0 or more, preferably 400 or more,
Further, in order to improve the water solubility, it is preferably at most 1,000, particularly preferably at most 700.

The amount of added formaldehyde per mole of the triazine nucleus of the alkyl etherified benzoguanamine resin is determined by improving the reactivity between the film-forming resin as the main ingredient and the alkyl etherified benzoguanamine resin as the curing agent, and improving the hardness after retorting. The amount is set to 1.5 mol or more in order to prevent physical properties such as damage resistance from decreasing, and to 3 mol or less in order to improve the adhesion of the formed coating film.

The alcohol used in preparing the alkyl etherified benzoguanamine resin includes, for example, aliphatic alcohols such as methanol, ethanol, n-propanol and isopropanol, as well as ethylene glycol monoisopropyl ether and ethylene glycol mono-n-propyl. Examples thereof include ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, and propylene glycol monomethyl ether. These alcohols are used alone or in combination of two or more.

The condensation reaction is carried out by adding formaldehyde to the triazine nucleus and then performing heat condensation with alcohol. At this time, the amount of formaldehyde added was determined by gel permission chromatography (GP
C).

The content of the mononuclear component of the triazine nucleus is preferably not less than 20% by weight, especially not less than 35% by weight, in order to improve the water solubility. In order to improve the retort resistance, the content is preferably 50% by weight or less, particularly preferably 40% by weight or less.

The solubility parameter (SP value) of the alkyl etherified benzoguanamine resin is set to 9.5 or more from the viewpoint of water solubility of the water-based paint for the outer surface of a can. It is 11 or less from the viewpoint of the water resistance of the coating film.

The content of the alkyl etherified benzoguanamine resin in the resin composition for coating is determined so as to increase the hardness of the formed coating film and to improve its water resistance.
The content is 20% by weight or more, preferably 30% by weight or more, and from the viewpoint of water solubility and processability, it is 60% by weight or less, preferably 50% by weight or less.

In the present invention, as the film-forming resin, those selected from acrylic resins and polyesters having an acid value of 30 to 100 mg / KOH mg and a solubility parameter of 9.5 to 11 are used.

Examples of the raw material monomer for the acrylic resin include vinyl monomers containing a carboxyl group such as (meth) acrylic acid, maleic acid, fumaric acid, and itaconic acid; hydroxymethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate , 2-hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate and other hydroxyl-containing vinyl monomers; methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl The alkyl group of (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate or the like has 1 to 20 carbon atoms.
Alkyl (meth) acrylates; aromatic vinyl monomers such as styrene and α-methylstyrene; and (meth) acrylamides such as N-butoxy (meth) acrylamide and N-methylol (meth) acrylamide. These raw material monomers are used alone or in combination of two or more. Among the alkyl (meth) acrylates, from the viewpoint of water solubility, the alkyl group has 1 to 8 carbon atoms, preferably 4 to 8 alkyl (meth) acrylates.
Acrylates are preferred.

As a method for preparing an acrylic resin using the raw material monomers, for example, a solution polymerization method and the like can be mentioned.

As the solvent used in the solution polymerization method, for example, ethylene glycol monomethyl ether,
Examples thereof include ethylene glycol monobutyl ether, ethylene glycol monoisopropyl ether, propylene glycol monomethyl ether acetate, and propylene glycol monoethyl ether acetate. These solvents are used alone or as a mixture of two or more.

In the polymerization, for example, benzoyl peroxide, di-t-butyl peroxide, t-
Organic peroxides such as -butylperoxybenzoate and t-butylperoxy-2-ethylhexanoate; radical polymerization initiators represented by azo compounds such as azobisisobutyronitrile and azobismethylvaleronitrile Can be used.

The acid value of the acrylic resin thus obtained is
30mg / KOHmg to give sufficient water solubility
As described above, the content is preferably 50 mg / KOH mg or more. In order to improve the water resistance of the formed coating film, 100
mg / KOHmg or less, preferably 75 mg / KOHm
g or less.

The solubility parameter of the acrylic resin (S
P value) is 9.5 from the viewpoint of water solubility of the water-based paint for the outer surface of a can.
From the viewpoint of the reactivity with the alkyl etherified benzoguanamine resin as a curing agent and the water resistance of the coating film, it is set to 11 or less.

Examples of the acid component of the polyester raw material include phthalic acid, isophthalic acid, terephthalic acid,
Dicarboxylic acids such as adipic acid, sebacic acid, maleic acid, fumaric acid, succinic acid, and itaconic acid; tricarboxylic or higher polycarboxylic acids such as trimellitic acid; and their acid anhydrides and alkyl esters such as methyl esters These acid components are used alone or in combination of two or more.

Examples of the alcohol component as a raw material of the polyester include ethylene glycol, propylene glycol, neopentyl glycol, 3-methyl-1,
Dihydric alcohols such as 5-pentanediol; trihydric or higher polyhydric alcohols such as trimethylolpropane and pentaerythritol; these polyhydric alcohols are used alone or in combination of two or more.

The polyester is obtained by polycondensing an acid component and an alcohol component. The polyester may be an oil-free polyester, or may be an oil-free polyester modified with an oil fatty acid. The polycondensation of the acid component and the alcohol component can be prepared by a known method, for example, by heating to 180 to 250 ° C in the presence of an ester conversion catalyst.

The acid value of the polyester thus obtained is
30mg / KOHmg to give sufficient water solubility
As described above, the content is preferably 50 mg / KOH mg or more. In order to improve the water resistance of the formed coating film, 100
mg / KOHmg or less, preferably 75 mg / KOHm
g or less.

The solubility parameter of the polyester (S
P value) is 9.5 from the viewpoint of water solubility of the water-based paint for the outer surface of a can.
From the viewpoint of the reactivity with the alkyl etherified benzoguanamine resin as a curing agent and the water resistance of the coating film, it is set to 11 or less.

The acrylic resin and the polyester may be used alone or in combination.

One of the major features of the present invention is that the solubility parameter (S) of the alkyl etherified benzoguanamine resin
P value) and solubility parameter (SP value) of the film-forming resin
In that they have been adjusted to be approximately equal. Although the alkyl etherified benzoguanamine resin has a small number of reaction points, the film forming resin compensates for the small number of reaction points. Thus, the solubility parameter (SP value) of the alkyl etherified benzoguanamine resin and the film forming resin By making the solubility parameter (SP value) of these resins substantially equal, the compatibility of both resins is improved, so that the reactivity and water resistance are enhanced.

From the viewpoint of water solubility and processability, the content of the film-forming resin in the coating resin composition is 40% by weight.
As described above, the content is preferably at least 50% by weight, and is 80% by weight or less, preferably 70% by weight or less in order to increase the hardness of the formed coating film and improve its water resistance.

An aqueous resin composition is obtained by neutralizing the resin composition for coatings comprising the alkyl etherified benzoguanamine resin and the film-forming resin and dissolving or dispersing in water.

In neutralizing the resin composition for coating, a volatile base component can be used.

Representative examples of the volatile base component include, for example, triethanolamine, dimethylethanolamine, diethylethanolamine, morpholine and the like.

The neutralization ratio of the resin composition for coating is preferably 50 to 150 mol% of the remaining carboxyl groups from the viewpoint of the stability of the obtained water-based coating for can outer surfaces.

Next, an aqueous resin composition is obtained by dissolving or dispersing the neutralized paint resin composition in water. At this time, the neutralized paint resin composition is mixed with water. It is preferable that the ratio is appropriately adjusted so that the aqueous resin composition does not correspond to the dangerous goods regulation specified by the Fire Service Law.

The aqueous coating composition for the outer surface of a can of the present invention comprises an aqueous resin composition as a main component. If necessary, sulfonic acids such as p-toluenesulfonic acid and dodecylbenzenesulfonic acid, and alkylphosphoric acids and the like can be used. An acid catalyst such as phosphoric acid, a curing aid such as an amine block of the acid catalyst, an additive such as a leveling agent, an antifoaming agent, a lubricant, and a coloring agent such as a pigment may be blended.

The coating of the water-based paint for the outer surface of a can of the present invention can be performed by a known method such as a roll coating method and a spray coating method.

The water-based paint for outer surface of a can of the present invention forms a coating film having excellent adhesion, and does not cause any deterioration even if retort treatment is performed for sterilization.
It can be suitably used as a paint for the outer surface of a neck that has been subjected to necking.

[0044]

Next, the aqueous coating composition for the outer surface of a can of the present invention will be described in more detail with reference to Examples, but the present invention is not limited to only these Examples.

Production Example 1 (Production of methyl isopropyl mixed etherified benzoguanamine resin (a1)) 256 g of methanol was placed in a two-liter four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a solvent by-product recovery device. (8 mol), 85% paraformaldehyde 8
8 g (2.5 mol as formaldehyde) and 187 g (1 mol) of benzoguanamine were charged and 30% by weight.
After adjusting the pH to 10.5 with an aqueous sodium hydroxide solution, the temperature was raised to 70 ° C., and the methylolation reaction was performed for 1 hour. After the completion of the reaction, the reaction mixture is cooled and p
H was adjusted to 1.0, and a primary methyl etherification reaction was performed at 40 ° C. for 30 minutes. The pH was adjusted to 10.5 with a 30% by weight aqueous sodium hydroxide solution, and excess formaldehyde, methanol and water were removed under reduced pressure.

Next, 300 g (5 mol) of isopropanol was charged, the pH was adjusted to 1.0 with a 50% by weight aqueous sulfuric acid solution, and an isopropyl etherification reaction was carried out at 80 ° C. for 1 hour. Thereafter, the pH was adjusted to 8.5 with a 30% by weight aqueous solution of sodium hydroxide, and after isopropanol and water were removed under reduced pressure, the precipitated salts were separated by filtration.
A methyl isopropyl mixed etherified benzoguanamine resin was obtained.

The methyl isopropyl mixed etherified benzoguanamine resin thus obtained was a colorless and transparent viscous liquid.

Next, the physical properties of the obtained methylisopropyl mixed etherified benzoguanamine resin include solid content, Gardner-Holt viscosity, mononuclear component content, number average molecular weight, solubility parameter, formaldehyde bond amount and etherification. Was determined according to the following method.

As a result, the solid content was 98.0% by weight, the Gardner-Holdt viscosity (25 ° C.) was Z, the mononuclear component content was 35% by weight, the number average molecular weight was 500, and the solubility parameter was 10. 5. The formaldehyde binding amount was 2.0 moles per mole of triazine nucleus, and the etherification ratio was 70% by weight of methyl and 30% by weight of isopropyl.

(Solid Content) A sample is placed in an aluminum dish and heated at 135 ° C. for 2 hours.

(Gardner-Holt viscosity) Gardner-
It is measured at 25 ° C. using a Holt foam viscometer.

(Content and Number Average Molecular Weight of Mononuclear Component) The content and number average molecular weight of the mononuclear component are examined by gel permission chromatography of a sample under the following measurement conditions. The number average molecular weight is calculated by a calibration curve using standard polystyrene.

GPC: LC-6A (manufactured by Shimadzu Corporation) Detector (UV): SPD-6A (manufactured by Shimadzu Corporation) Chromatopack: CR-6A (manufactured by Shimadzu Corporation) Column: Shim -Pack GPC-802 (manufactured by Shimadzu Corporation) Shim-pack GPC-801 (manufactured by Shimadzu Corporation) Solvent: THF (tetrahydrofuran) Flow rate: 0.5 ml / min Temperature: 25 ° C (solubility parameter) high A non-solvent is added to the molecular solution, and the amount of the non-solvent required until turbidity is generated is determined. At this time, the non-solvent having a high SP value (solubility parameter) and the non-solvent having a low SP value are separately measured, and the volume of the non-solvent having a high SP value (V _mh ) and the volume of the non-solvent having a low SP value (V _ml ), The SP value (δ _s ) of the polymer is obtained based on the following equation. Note that water (SP value (δ _mh ): 23.5) is used as a non-solvent having a high SP value, and n-hexane (SP value (δ _ml ): 7.24) is used as a non-solvent having a low SP value.

[0054]

(Equation 1)

(Formaldehyde Bonding Amount and Etherification Ratio) The sample was subjected to ¹ H-NMR analysis under the following measurement conditions to determine the formaldehyde bonding amount and the etherification ratio.

NMR: JNM-FX-100 (manufactured by JEOL Ltd.) Solvent: CDCl ₃ (chloroform-d) Reference: tetramethylsilane Sample tube: 5 mmφ Temperature: 25 ° C. Production Example 2 (n-propyl etherified benzoguanamine) Production of Resin (a2)) In a 2-liter four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a solvent by-product recovery device, 300 g (5 mol) of n-propanol and 109 g of 85% paraformaldehyde ( 3.1 mol of formaldehyde) and 187 g (1 mol) of benzoguanamine were charged.
After adjusting the pH to 10.5 with a 0% by weight aqueous sodium hydroxide solution, the temperature was raised to 70 ° C., and the methylolation reaction was performed for 1 hour.

After completion of the reaction, the reaction mixture was cooled, the pH was adjusted to 1.0 with a 50% by weight aqueous sulfuric acid solution, and n-propyl etherification was carried out at 70 ° C. for 1 hour. The pH was adjusted to 10.5 with a 30% by weight aqueous sodium hydroxide solution and excess formaldehyde, n-propanol and water were removed under reduced pressure.

Next, 300 g (5 mol) of n-propanol was charged, the pH was adjusted to 1.0 with a 50% by weight aqueous sulfuric acid solution, and a secondary n-propyl etherification reaction was carried out at 70 ° C. for 30 minutes. Thereafter, the pH was adjusted to 8.5 with a 30% by weight aqueous sodium hydroxide solution, n-propanol and water were removed under reduced pressure, and the precipitated salts were separated by filtration to obtain an n-propyl etherified benzoguanamine resin. .

The n-propyl etherified benzoguanamine resin thus obtained was a colorless and transparent viscous liquid.

Next, as the physical properties of the obtained n-propyl etherified benzoguanamine resin, the solid content, Gardner-Holt viscosity, mononuclear component content, number average molecular weight, solubility parameter and formaldehyde binding amount were prepared. The test was conducted in the same manner as in Example 1.

As a result, the solid content was 98.0% by weight, the Gardner-Holt viscosity (25 ° C.) was Z, the mononuclear component content was 40% by weight, the number average molecular weight was 500, and the solubility parameter was 10. 0, the formaldehyde binding amount was 2.5 moles per mole of triazine nucleus.

Production Example 3 (Production of methyl isopropyl mixed etherified benzoguanamine resin (a3)) A 2-liter four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a solvent by-product recovery device was charged with 320 g of methanol. (10 mol), 176 g (5.0 mol as formaldehyde) of 85% paraformaldehyde and 187 g (1 mol) of benzoguanamine were added, and the pH was adjusted to 10.5 with a 30% by weight aqueous sodium hydroxide solution. After heating, the methylolation reaction was performed for 1 hour. After completion of the reaction, the reaction mixture was cooled, adjusted to pH 1.0 with a 50% by weight aqueous sulfuric acid solution, and subjected to a methyl etherification reaction at 40 ° C. for 1 hour. The pH was adjusted to 10.5 with a 30% by weight aqueous sodium hydroxide solution, and excess formaldehyde, methanol and water were removed under reduced pressure.

Next, 300 g (5 mol) of isopropanol was charged, the pH was adjusted to 1.0 with a 50% by weight aqueous sulfuric acid solution, and an isopropyl etherification reaction was carried out at 70 ° C. for 1 hour. Thereafter, the pH was adjusted to 8.5 with a 30% by weight aqueous solution of sodium hydroxide, and after isopropanol and water were removed under reduced pressure, the precipitated salts were separated by filtration.
A methyl isopropyl mixed etherified benzoguanamine resin was obtained.

The methyl isopropyl mixed etherified benzoguanamine resin thus obtained was a colorless and transparent viscous liquid.

Next, as the physical properties of the obtained methyl isopropyl mixed etherified benzoguanamine resin, the solid content, Gardner-Holt viscosity, mononuclear component content, number average molecular weight, solubility parameter and formaldehyde binding amount were prepared. The test was conducted in the same manner as in Example 1.

As a result, the solid content was 98.0% by weight, the Gardner-Holt viscosity (25 ° C.) was Y, the mononuclear component content was 45% by weight, the number average molecular weight was 400, and the solubility parameter was 10. 5. The formaldehyde binding amount was 4.0 mol per 1 mol of triazine nucleus.

Production Example 4 (Production of Methyl Etherified Benzoguanamine Resin (a4)) A 2-liter four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a solvent by-product recovery device was charged with 256 g of methanol (8 g). Mol), 85% paraformaldehyde 8
8 g (2.5 mol as formaldehyde) and 187 g (1 mol) of benzoguanamine were charged and 30% by weight.
After adjusting the pH to 10.5 with an aqueous sodium hydroxide solution, the temperature was raised to 70 ° C., and the methylolation reaction was performed for 1 hour.

After completion of the reaction, the reaction mixture was cooled, the pH was adjusted to 1.0 with a 50% by weight aqueous sulfuric acid solution, and the primary methyl etherification reaction was carried out at 40 ° C. for 1 hour. The pH was adjusted to 10.5 with a 30% by weight aqueous sodium hydroxide solution, and excess formaldehyde, methanol and water were removed under reduced pressure.

Next, 256 g (8 mol) of methanol was charged, the pH was adjusted to 1.0 with a 50% by weight aqueous sulfuric acid solution, and a secondary methyl etherification reaction was carried out at 40 ° C. for 30 minutes. Thereafter, the pH was adjusted to 8.5 with a 30% by weight aqueous sodium hydroxide solution, methanol and water were removed under reduced pressure, and the precipitated salts were separated by filtration to obtain a methyl etherified benzoguanamine resin.

The methyl etherified benzoguanamine resin thus obtained was a colorless and transparent viscous liquid.

Next, the physical properties of the obtained methyl etherified benzoguanamine resin were as follows: solid content, Gardner
Production Example 1: Holt viscosity, mononuclear component content, number average molecular weight, solubility parameter and formaldehyde binding amount
It investigated similarly to.

As a result, the solid content was 98.0% by weight, the Gardner-Holt viscosity (25 ° C.) was Y, the mononuclear component content was 50% by weight, the number average molecular weight was 350, and the solubility parameter was 11.1%. 5. The amount of formaldehyde bond was 2.0 mol per 1 mol of triazine nucleus.

Production Examples 5 to 9 (Acrylic resin (b1))
(Production of (b5)) After charging 40.0 g of butyl cellosolve into a 0.3-liter four-necked flask equipped with a thermometer, a stirrer, a reflux condenser, a dropping funnel and a nitrogen gas introducing tube, 14
The temperature was raised to 0 ° C., and the components for polymerization shown in Table 1 were added dropwise over 5 hours and polymerized to obtain an acrylic resin.

As the physical properties of the obtained acrylic resin, an acid value and a solubility parameter were examined.

The acid value was determined according to the following method, and the solubility parameter was determined in the same manner as in Production Example 1. Table 1 shows the results.

(Acid value) 1 g of an acrylic resin was dissolved in 5 ml of a toluene / butanol mixed solution (weight ratio: 1/1), and neutralized and titrated with a 0.1N methanolic potassium hydroxide solution using a phenolphthalein indicator. Ask.

The abbreviations in Table 1 mean the following.

MA: methacrylic acid 2HEMA: 2-hydroxyethyl methacrylate St: styrene EA: ethyl acrylate BA: butyl acrylate 2EHM: 2-ethylhexyl methacrylate SM: stearyl methacrylate MS: α-methylstyrene dimer (chain transfer agent) TBP: t -Butyl peroxy-2-ethylhexanoate

[0079]

[Table 1]

Production Example 10 (Production of Polyester (b6)) 174.3 g of terephthalic acid was placed in a 1-liter four-necked flask equipped with a thermometer, a stirrer, a reflux condenser equipped with a separator, and a nitrogen gas blowing tube. Adipic acid 51.1
g, 3-methyl-1,5-pentanediol 206.5
g and 95.2 g of pentaerythritol, and heated to 230 ° C. while stirring while introducing nitrogen gas.
The reaction was continued until the oxidation became 1 mg / KOHmg or less.
Then, after cooling to 160 ° C, adipic acid 20
4.4 g was added, the temperature was raised to 200 ° C. while stirring, and the reaction was further continued. When the acid value reached 35 mg / KOH mg, the reaction was terminated. After cooling to 100 ° C. or lower, 163.3 g of butyl cellosolve was added, and the nonvolatile content was 80% by weight, the resin acid value was 65 mg / KOH mg, and the number average molecular weight was 2
A water-soluble polyester (b6) having a solubility parameter of 10.5 was obtained.

Examples 1 to 6 and Comparative Examples 1 to 5 The benzoguanamine resin obtained in Production Examples 1 to 4 and the film-forming resin obtained in Production Examples 5 to 10 were used in the proportions (parts by weight) shown in Table 2. Mix and use dimethylethanolamine as a base component for neutralization, and add 0.5% by weight of paratoluenesulfonic acid and 0.5% by weight of a silicone-based leveling agent to the coating resin to obtain a resin solid content. A 40% by weight aqueous paint was obtained. As an organic solvent in the paint,
Using butyl cellosolve, the coating was prepared so that the sum with the neutralized amine was 30% by weight in the paint.

As the physical properties of the obtained water-based paint, the paint state and the performance of the paint film were examined according to the following methods. The results are also shown in Table 2.

(1) Paint Condition After the obtained water-based paint is stored in an atmosphere at 55 ° C. for one month, the paint condition is visually observed and evaluated based on the following evaluation criteria.

Evaluation criteria for transparency A: Transparent.

B: Although slightly turbid, no separation was observed, and it could not be practically used.

C: White turbid and separated.

Evaluation criteria for stability A: No change in viscosity.

B: A slight decrease in viscosity is observed, but it is practically impossible.

C: The viscosity is remarkably reduced, and separation is observed.

D: Separated and does not return to its original state even if stirred.

(2) Film Performance The obtained water-based paint was applied to an unpainted aluminum can (350 ml) using a mini roll coater so that the dry film weight was 120 mg per can, and high-speed hot air It was baked in an oven at 200 ° C. for 30 seconds (metal temperature) and cured. Furthermore, it was baked at the same temperature for 2 minutes and cured to obtain a test can of the coating film.

Each test method of the coating film performance is as follows.

Pencil hardness: Determined according to the method described in JIS K-5400 using Uni (trade name) manufactured by Mitsubishi Pencil Co., Ltd.

Hardness in Hot Water After the test can was immersed in hot water at 80 ° C. for 30 minutes,
The determination is made in the hot water in the same manner as the pencil hardness.

Retort resistance After the test can was left in steam at 130 ° C. for 30 minutes, the following performance was examined.

(I) Appearance After the retort treatment, a phenomenon called overall whitening and partial water spot of the coating film is evaluated based on the following evaluation criteria.

(Evaluation Criteria) A: No discoloration.

B: Some discoloration is seen partially.

C: Whitening is observed as a whole.

(Ii) Hardness in Hot Water Determination is made in the same manner as the hardness in the hot water.

(Iii) Adhesion After scribing was put on the 202 neck processed part of the test can body, it was left in steam at 130 ° C. for 30 minutes.
Nichiban Cellotape (registered trademark) is affixed, and this is rapidly peeled in a direction of 90 degrees with respect to the tangent line of the can body.
The state of the painted surface of the can body is visually observed and evaluated based on the following evaluation criteria.

(Evaluation Criteria) A: No peeling was observed.

B: Slight whisker-like peeling with a length of less than 0.5 mm was observed, but it could not be practically used.

C: Peeling with a length of 0.5 mm or more is observed.

D: Peeling was already observed before sticking the cellophane tape.

[0106]

[Table 2]

From the results shown in Table 2, all of the water-based paints obtained in Examples 1 to 6 were in good paint condition.
It can be seen that the formed coating film has high hardness and excellent adhesion even after retort.

[0108]

The water-based paint for outer surface of a can of the present invention forms a coating film having excellent adhesion even after necking, and the coating film formed even when retorted. It has the effect of excellent adhesion.

Claims (3)

[Claims] (A) 20 to 60% by weight of an alkyl etherified benzoguanamine resin having 1.5 to 3 moles of formaldehyde added per mole of a triazine nucleus and having a solubility parameter of 9.5 to 11, and (B) ) Neutralize a resin composition for coatings consisting of 80 to 40% by weight of a film-forming resin selected from acrylic resins and polyesters having an acid value of 30 to 100 mg / KOH mg and a solubility parameter of 9.5 to 11, A water-based paint for the outer surface of a can, comprising a water-based resin composition dissolved or dispersed as a main component. 2. The method according to claim 1, wherein the alkyl etherified benzoguanamine resin is an isopropyl etherified benzoguanamine resin.
The water-based coating composition for an outer surface of a can according to claim 1, which is -propyl etherified benzoguanamine resin, methyl isopropyl mixed etherified benzoguanamine resin or methyl n-propyl mixed etherified benzoguanamine resin. 3. The water-based paint for an outer surface of a can according to claim 1, wherein the acrylic resin is an alkyl (meth) acrylate having an alkyl group having 4 to 8 carbon atoms as a raw material monomer.