JPH04363179A - Can inner surface painted metal can - Google Patents

Abstract

PURPOSE:To provide the internally coated metallic can and more particularly internally coated two-piece steel can having higher content-resistant properties, such as resistance to flavors, water, corrosion and beer clouding and more particularly higher corrosion resistance in the part subjected to impact working than metallic cans and more particularly two-piece steel cans coated on the inside surfaces with the conventional water-based coating materials. CONSTITUTION:The internally coated metallic can is obtd. by coating the inside surface of the metallic can with the water-based coating material compsn. prepd. by dispersing and dissolving into an aq. medium (A) 100 pts.wt. carboxyl group-contg. acryl resin-modified epoxy resin and (B) 5 to 30 pts.wt. phenol formaldehyde resin which is obtd. by bringing carbolic acid and formaldehyde into reaction, has 250 to 700 weight average mol. wt., has 1.5 to 2.0mol addition quantity of the formaldehyde per 1 nucleus of benzene nuclei and <0.2mol per 1 benzene nucleus of alkoxy groups and contains at least 10wt.% water-soluble component.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to metal cans with coated inner surfaces. More specifically, the present invention provides content resistance (flavor resistance, water resistance, corrosion resistance, beer cloudiness resistance, etc.), particularly,
This invention relates to a metal can whose inner surface is coated with a water-based paint that has excellent corrosion resistance.

0002

BACKGROUND OF THE INVENTION Conventionally, beverage cans for beer, carbonated drinks, fruit juice drinks, etc. have been coated with a protective paint on their inner surfaces to prevent metal elution and corrosion. Conventionally, solvent-based paints have been used as such protective paints. In recent years, these paints are being converted to water-based paints for reasons such as resource saving and low pollution. However, with water-based paints, especially when the material is a two-piece steel (hereinafter abbreviated as DIS) can, the corrosion resistance of the impact-treated parts is insufficient, and in some cases the can There is a problem with holes being created. For this reason, there is a demand for the development of metal cans whose inner surfaces are coated with water-based paints that have better resistance to contents, especially corrosion resistance in areas subjected to impact processing.

0003

[Means for Solving the Problems] The present inventors have conducted extensive research in order to develop a metal can that surpasses conventional water-based paint inner-coated metal cans in terms of resistance to contents, especially corrosion resistance of parts that have undergone impact processing. As a result of repeated experiments, it has been found that the intended purpose of the present invention can be achieved by using a composition comprising an acrylic modified epoxy resin and a specific phenol formaldehyde resin as a water-based paint for the inside of a can. The present invention was completed based on this knowledge.

Thus, according to the present invention, (A) 100 parts by weight of a carboxyl group-containing acrylic resin and (B) a weight average molecular weight of 250 to 700 obtained by reacting carboxyl group-containing acrylic resin and formaldehyde, and a concentration of formaldehyde per benzene nucleus. Phenol formaldehyde resin 5 to 30 having an addition amount in the range of 1.5 to 2.0 mol, having less than 0.2 mol of alkoxy groups per benzene nucleus, and containing at least 10% by weight of water-soluble components. There is provided a metal can whose inner surface is coated, characterized in that the inner surface of the metal can is coated with an aqueous coating composition in which parts by weight are dispersed and dissolved in an aqueous medium.

[0005] As the metal constituting the inner-coated metal can of the present invention, for example, a simple substance such as iron or aluminum, or a surface-treated steel plate such as a tin-plated steel plate, a nickel-plated steel plate, or a chrome-plated steel plate is used. It is also possible to use the surface-treated steel plate whose surface is plated with Fe, Zn, Mn, etc.

The present invention was completed based on the development of a new water-based paint composition that can be applied to the above-mentioned metals.The water-based paint composition, which is an important part of the present invention, will be explained below.

[0007] The aqueous coating composition used for the inner-coated metal can of the present invention uses a carboxyl group-containing acrylic resin-modified epoxy resin and a phenol formaldehyde resin as the film-forming resin.

As the carboxyl group-containing acrylic resin-modified epoxy resin (A), for example, the following can be preferably used, but the invention is not limited thereto. (1) As disclosed in JP-A No. 53-1228, obtained by graft polymerizing an acrylic monomer containing a carboxyl group-containing monomer to the main chain of an epoxy resin using a radical generating catalyst such as benzoyl peroxide. and (2) high acid value acrylic resins which have been polymerized in advance with a radical generating catalyst such as benzoyl peroxide as disclosed in JP-A-55-3481 and JP-A-55-3482. and an epoxy resin in the presence of an esterification catalyst.

Epoxy resins constituting the carboxyl group-containing acrylic resin-modified epoxy resin (A) include bisphenol A type epoxy resins having an epoxy equivalent of 2,500 to 100,000, such as Epicote 1007 (number average molecular weight approximately 2,700), Epicote 1009 (number average molecular weight: about 3,700), Epicoat 1010 (number average molecular weight: about 4,500), etc. can be suitably used.

The monomer composition constituting the carboxyl group-containing acrylic resin is disclosed in JP-A-53-1228, JP-A-55-3481, and JP-A-55-348.
It is possible to use various materials disclosed in Publication No. 2, etc., such as (1) methyl methacrylate/2-ethylhexyl acrylate/acrylic acid, (2) styrene/
Combinations such as methyl methacrylate/ether acrylate/methacrylic acid, (3) styrene/ethyl acrylate/methacrylic acid, and (4) methyl methacrylate/ethyl acrylate/acrylic acid can be suitably used.

When producing resin (A) by graft polymerizing an acrylic monomer mixture to the bisphenol A type epoxy resin described above in the presence of a radical generator such as benzoyl peroxide, the molecular weight of the carboxyl group-containing acrylic resin component is Although difficult to measure accurately,
It is preferable to adjust the approximate number average molecular weight to 5,000 to 30,000 and the acid value to a range of 100 to 500 based on resin solid content.

Number average molecular weight and acid value of the carboxyl group-containing acrylic resin when the resin (A) is produced by esterifying a bisphenol A type epoxy resin and a carboxyl group-containing acrylic resin in the presence of a tertiary amine. can be easily adjusted when the acrylic monomer mixture is produced by a solution polymerization method in the presence of a radical polymerization initiator. The carboxyl group-containing acrylic resin preferably has a number average molecular weight of 5,000 to 30,000 and an acid value of 100 to 500.

The ratio of the acrylic resin component/epoxy resin component of the carboxyl group-containing acrylic resin-modified epoxy resin (A) is 10/90 to 40/60, preferably 15/85 to 25/75, by weight.

Phenol-formaldehyde resin (B), which is another component of the film-forming resin, uses carbolic acid as the phenol component, and undergoes a condensation reaction in the presence of formaldehyde and an alkali metal hydroxide, such as sodium hydroxide or potassium hydroxide. This is a phenol formaldehyde resin obtained by The structure of the phenol formaldehyde resin is very important in order to obtain a coating composition that forms a coating film with good corrosion resistance on areas subjected to impact processing, which is the object of the present invention.

The phenol formaldehyde resin according to the present invention is a carbolic acid resol resin, and has a number average molecular weight of 25
0 to 700, the amount of formaldehyde added per benzene nucleus is 1.5 to 2.0 mol, the alkoxy group is less than 0.2 mol per 1 benzene nucleus, and 10% by weight or more,
Preferably, the resin should be a phenol formaldehyde resin containing 10 to 25% by weight of water-soluble components. If the above range is exceeded, it may not be possible to obtain a water-based coating composition that forms a coating film with good corrosion resistance on the impact-processed part, which is the objective of the present invention, or it may not be possible to obtain a water-based coating composition that can be used for the inside of cans in terms of processability, sanitary properties, flavor properties, etc. A defect occurs in at least one or more of the essential performances of a paint.

The conditions for the condensation reaction of carbolic acid and formaldehyde are not particularly limited and can be appropriately selected from a wide range, but are generally 60 to 130°C and 1 to 20°C.
It is sufficient to perform heating for about an hour. The phenolic resin thus produced is separated and purified from the reaction mixture by means known per se.

In the present invention, the aqueous coating composition used contains 5 to 30 parts by weight, preferably 5 parts by weight, of the phenol formaldehyde resin (B) per 100 parts by weight of the carboxyl group-containing acrylic resin-modified epoxy resin (A).
~15 parts by weight were dispersed and dissolved in an aqueous medium.

More specifically, the water-based coating composition is prepared by mixing the carbonic acid resol resin in a ratio of 5 to 30 parts by weight with respect to 100 parts by weight of the solid content of the carboxyl group-containing acrylic resin-modified epoxy resin solution. It is produced by neutralizing it with ammonia, amines, etc., adding water to form an emulsion, and then adding a solvent, water, amines, etc. to adjust the solid content, viscosity, etc.

The following adjustment method is also possible. A carboxyl group-containing acrylic resin-modified epoxy resin solution is neutralized by adding ammonia, amine, etc., and water is added to form an emulsion. Next, the solid content of this emulsion is 1
To 00 parts by weight, add the necessary amount of the carbonic acid resol resin diluted with a solvent such as butanol so that the solid content is 10 to 50 weight % to give a solid content of 5 to 30 parts by weight, and add a solvent, It can also be produced by adding water, amine, etc. to adjust the solid content, viscosity, etc.

[0020] The organic solvent used in the graft polymerization reaction and ester addition reaction in producing the resin (A) dissolves the bisphenol type epoxy resin and the carboxyl group-containing acrylic resin, and also dissolves the reactants of these resins. When neutralizing with ammonia, amine, etc. and adding water to form an emulsion, conventionally known materials that are miscible with water and do not cause any problems can be used, such as n-butanol, ethylene glycol monobutyl ether, etc. Can be used suitably. It is also possible to use organic solvents that are immiscible or hardly soluble in water. Examples of such organic solvents include aromatic hydrocarbons such as toluene and xylene, esters such as ethyl acetate and butyl acetate, ketones such as methyl ethyl ketone and methyl isobutyl ketone, alcohols such as hexanol, and ethylene glycol monohexyl. Examples include glycol ethers such as ether.

The tertiary amine used in the esterification addition reaction between the epoxy resin and the carboxyl group-containing acrylic resin of the present invention includes triethylamine, dimethylethanolamine (dimethylaminoethanol), methyldiethanolamine, ethylmethylethanolamine, and dimethylethylamine. , dimethylpropylamine, dimethyl-
3-hydroxy-1-propylamine, dimethylbenzylamine, dimethyl-2-hydroxy-1-propylamine, diethylmethylamine, dimethyl-1-hydroxy-2-propylamine and mixtures thereof can be used. Preferably triethylamine or dimethylethanolamine is used.

As the basic compound used to neutralize the carboxyl group of the carboxyl group-containing acrylic resin-modified epoxy resin, a wide range of conventionally known basic compounds can be used as long as it is normally used for neutralizing carboxyl groups. Examples include arbitrary primary amines, secondary amines, tertiary amines, monofunctional quaternary ammonium salts, and the like. More specifically, methylamine, ethylamine, n-propylamine, isopropylamine, n-hexylamine, monoethanolamine, propanolamine, benzylamine, dimethylamine, dibutylamine, dihexylamine, methylethanolamine, diethanolamine,
These include triethylamine, diethylethanolamine, dimethylcyclohexylamine, triethanolamine, tributylamine, dimethyl n-butylamine, tripropylamine, γ-picoline, and tetrahexylammonium hydroxide. The amount of such a neutralizing agent to be used is usually 0.1 to 2 with respect to the carboxyl group in the reactant.
It is best to use the neutralization equivalent of . Treatment with the neutralizing agent also
This can be done by conventionally known methods.

The aqueous coating composition thus obtained is used at a solids content of about 15 to 35% by weight. The amount of organic solvent in the diluent in the aqueous coating composition is not particularly limited, but from the viewpoint of environmental pollution, it is preferably within a range of 10% by weight or less. However, it is not particularly limited. Also, other commonly used additives, such as surfactants,
Anti-agglomerating agents, flow control agents, and the like may be appropriately incorporated into the aqueous coating composition, if deemed necessary or desirable.

The aqueous coating composition thus obtained is spray-coated onto the inner surface of a metal can by a known method and heated to about 180 to 230°C.
The inner surface coated metal can of the present invention is manufactured by heating and curing at a temperature of 0.5 to 5 minutes. The coating film thickness (dry film thickness) is usually preferably in the range of 2 to 10 μm. If it is necessary to increase the film thickness in order to minimize the amount of exposed metal on the inner surface of the can, it is also possible to apply the coating using a two-coat, two-bake method.

[0025]

[Effects of the Invention] According to the present invention, compared to metal cans, especially two-piece steel cans, whose inner surfaces are coated with conventional water-based paints, the content has improved flavor resistance, water resistance, corrosion resistance, and beer clouding resistance. To provide a metal can with an inner surface coating, particularly a two-piece steel can with an inner surface coating, which has excellent physical properties, particularly corrosion resistance in a portion subjected to impact processing.

[0026]

[Example] The present invention will be further clarified with reference to Examples below. Phenol used in the following examples and comparative examples.
An example of synthesis of formaldehyde resin will be explained, and Table 1 shows the characteristics of the resin. In addition, the “part” described in each synthesis example
and "%" indicate "part by weight" and "% by weight".

Synthesis Example 1. 94 parts of carbolic acid, 243 parts of 37% formalin water (manufactured by Koei Chemical Co., Ltd.), 0.4 parts of NaOH
1 part was charged into a reaction vessel equipped with a stirrer and a reflux condenser, and 60
The temperature was raised to ~70°C, and 0.2 parts of NaOH was added every 2 hours to react for 10 hours. Then, phosphoric acid is added to adjust the pH to 6-7. Thereafter, 200 parts of n-butanol was added and concentrated under reduced pressure while heating to perform dehydration, solvent removal, and removal of unreacted formaldehyde. When the concentration reached 70%, it was diluted with n-butanol to obtain a phenol resin solution A with a concentration of 50%. The characteristics of the obtained resin are shown in Table 1.

Synthesis Examples 2 and 3. Phenol resin solutions B (Synthesis Example 2) and C (Synthesis Example 3) each having a concentration of 50% were produced in the same manner as in Synthesis Example 1 using the formulations shown in Table 1.

Synthesis Example 4. 94 parts of carbolic acid, 260 parts of 37% formalin water, and 0.4 parts of NaOH were placed in a reaction vessel equipped with a stirrer and a reflux condenser, and the temperature was raised to 60 to 70°C, and 0.2 parts of NaOH was added every 2 hours. Allow to react for 12 hours. Then, phosphoric acid is added to adjust the pH to 6-7. Thereafter, 200 parts of n-butanol was added and concentrated under reduced pressure while heating to perform dehydration, solvent removal, and removal of unreacted formaldehyde. When the concentration reaches 70%, dilute with n-butanol to 40%, add 0.05 part of formic acid, stir and heat to 60-70°C again, and react for 1 hour. At this time, it is alkoxylated with butanol. Next, vacuum concentration was performed again for dehydration and solvent removal, and when the concentration reached 60%, it was diluted with n-butanol to obtain a phenol resin solution D with a concentration of 50%. The characteristics of the obtained resin are:
It is shown in Table 1.

Synthesis Example 5. Using the formulation shown in Table 1, a phenolic resin solution E with a concentration of 50% was prepared in the same manner as in Synthesis Example 4.
I got it. The characteristics of the obtained resin are shown in Table 1.

Synthesis Examples 6 and 7. Using the formulations shown in Table 1, phenol resin solutions F (Synthesis Example 6) and G (Synthesis Example 7) each having a concentration of 50% were obtained in the same manner as in Synthesis Example 1. Table 1 shows the characteristics of the obtained resin.

Synthesis Example 8. Bisphenol A 228 parts, 3
Charge 365 parts of 7% formalin water and 0.4 parts of NaOH into a reaction vessel equipped with a stirrer and a reflux condenser, raise the temperature to 60-70°C, and add 0.2 parts of NaOH every 2 hours to react for 20 hours. . Then, phosphoric acid is added to adjust the pH to 6-7. Thereafter, 400 parts of n-butanol was added and concentrated under reduced pressure while heating to perform dehydration, solvent removal, and removal of unreacted formaldehyde. When the concentration reached 80%, it was diluted with n-butanol to obtain a phenol resin solution H with a concentration of 50%. The characteristics of the obtained resin are shown in Table 1.

[0033]

[Table 1]

<Production of carboxyl group-containing acrylic resin solution> Production Example 1 400 parts of butanol was weighed into a four-necked flask equipped with a stirrer, a reflux condenser, a thermometer, a dropping funnel, and a nitrogen inlet. Next, 174 parts of methacrylic acid, 87 parts of styrene, 29 parts of ethyl acrylate, and 14.5 parts of benzoyl peroxide (75% water wet product) were weighed into a beaker and thoroughly mixed and stirred to prepare a premix. The temperature of the butanol in the flask was heated to 105° C., and at this temperature the premix was added dropwise from the dropping funnel over a period of 3 hours. The temperature was maintained for an additional 2 hours to complete the copolymerization reaction. Next, 290 parts of 2-butoxyethanol was added to give a viscosity of 370 centipoise, a resin acid value of 390, and a solid content of 30%.
A carboxyl group-containing acrylic resin solution (hereinafter referred to as "acrylic resin solution J") was obtained.

<Production of epoxy resin solution> Production Example 1 Epicote 828 (epoxy resin manufactured by Yuka Shell Co., Ltd., epoxy equivalent 184-194, viscosity 120-150 poise, 25
℃) 500 parts, bisphenol A 286 parts, tri-n-
Butylamine 0.5 part and methyl isobutyl ketone 86
When the mixture was placed in a reaction vessel and heated to 135°C under a nitrogen stream, the contents generated heat to 180°C. this thing 1
It was cooled to 60°C and reacted for about 3 hours, resulting in an epoxy value of 0.025, a number average molecular weight of about 5000, and a solution viscosity (
A 90% epoxy resin solution (hereinafter referred to as "epoxy resin solution K") having a Gardner-Holdt viscosity (Gardner-Holdt viscosity of a butyl carbitol solution with a resin content of 40% at 25°C) Z6 was obtained.

Production Example 2 Epicote 1009 (number average molecular weight approximately 3750) 9
0 part was dissolved in 10 parts of methyl isobutyl ketone to obtain an epoxy resin solution L having a solid content of 90%.

Example 1 Formulation (1) Acrylic resin solution J 150 parts (2
) Epoxy resin solution K 283 parts (3)
n-butanol 86 parts (
4) 2-butoxyethanol 47 parts (5)
Deionized water 3.2 parts (6) Dimethylaminoethanol 5.3 parts (7) Dimethylaminoethanol 9.5 parts (8) Phenol resin solution A 30 parts (9) Deionized water
646 copies──────
────────────────Total 1260 parts of the above (
Add 1) to (4) and heat to 115°C under a nitrogen stream.
The resin component was dissolved. After dissolving, cool to 105℃,
(5) to (6) were added in this order and held at 105°C for 3 hours. The reaction product has a solid content weight ratio of acrylic resin/epoxy resin of 15/85. The reaction was tracked by measuring the acid value, and the acid value was 51 at the end of the reaction. Then, after 3 hours, (7) was added, and after 5 minutes, (8) was added, and the mixture was heated at 105°C.
Hot blended for 30 minutes. Then, add (9) to 30
The mixture was added over a period of minutes to obtain a stable aqueous coating composition with a solids content of 25%.

Example 2 A water-based coating composition was obtained in the same manner as in Example 1, except that 60 parts of phenolic resin solution B was used instead of phenolic resin solution A.

Example 3 A water-based coating composition was obtained in the same manner as in Example 2, except that the same amount of phenolic resin solution E was used in place of phenolic resin solution A.

Example 4 Formulation (1) Acrylic resin solution L 283 parts (2
) n-butanol 121 parts (
3) 2-butoxyethanol 117 parts (4) Methacrylic acid 27 parts (
5) Styrene 13.
5 parts (6) Ethyl acrylate 4.
5 parts (7) Benzoyl peroxide
3 parts (8) dimethylaminoethanol 25
Part (9) Phenol resin solution A 90 parts (10) Deionized water
646 copies────────────────────
Total: 1288.0 parts Put the above (1) to (3) into a reaction container, and add 1288.0 parts under a nitrogen stream.
It was heated to 15°C to dissolve the resin component. Then (4
) to (7) were added dropwise over 1 hour, and the mixture was further reacted at 115°C for 2 hours. Then cooled to 105℃, (8)
was added, and after 5 minutes, (9) was added, followed by hot blending at 105°C for 30 minutes. Thereafter, (10) was added over 30 minutes to obtain a stable aqueous coating composition.

Comparative Example 1 A water-based coating composition was obtained in the same manner as in Example 4, except that the same amount of phenolic resin solution C was used instead of phenolic resin solution A.

Comparative Example 2 A water-based coating composition was obtained in the same manner as in Example 1, except that the same amount of phenolic resin solution D was used instead of phenolic resin solution A.

Comparative Example 3 A water-based coating composition was obtained in the same manner as in Example 1, except that 120 parts of phenol resin solution E was used instead of phenol resin solution A.

Comparative Example 4 A water-based coating composition was obtained in the same manner as in Example 1, except that 30 parts of phenolic resin solution F was used instead of phenolic resin solution A.

Comparative Example 5 A water-based coating composition was obtained in the same manner as in Example 2, except that the same amount of phenolic resin solution G was used instead of phenolic resin solution B.

Comparative Example 6 A water-based coating composition was obtained in the same manner as in Example 2, except that the same amount of phenolic resin solution H was used instead of phenolic resin solution B.

Comparative Example 7 A water-based coating composition was obtained in the same manner as in Example 4, except that 20 parts of phenolic resin solution A was used.

Comparative Example 8 Solvent-based epoxy-urea paint for the inner surface of two-piece steel cans.

Comparative Example 9 Solvent-based epoxy-phenol paint for the inner surface of two-piece steel cans.

<Coating film performance test> The water-based coating compositions obtained in Examples 1 to 4 and Comparative Examples 1 to 7 and the solvent-based coatings of Comparative Examples 8 and 9 were placed in a two-piece steel can with a content capacity of 350 ml. 150-1 per can per coat on the inner surface of
Spray paint evenly to achieve a dry coating of 60mg,
Next, it was dried at an ambient temperature of 200° C. for about 2 minutes to form a base coat. Furthermore, a top coat was applied under the same conditions as the base coat to produce coated cans with a coating film of 300 to 320 mg per can. In addition, 8 to 10 μm of the above water-based paint composition and solvent-based paint were applied to one side of 100 μm aluminum foil.
3 m at an ambient temperature of 200°C.
Dry for 0 seconds. Furthermore, apply the above water-based paint on the back side.
Coat to a thickness of 10 μm, then reduce the ambient temperature to 200°C.
The sample was dried for about 80 seconds to prepare a test panel for aqueous extract flavor test. Furthermore, the above water-based paint composition and solvent-based paint were applied onto a #25 tin plate to a thickness of 8 to 10 μm, and then dried at an ambient temperature of 200° C. for about 2 minutes.
A test panel was created.

Various test methods are shown below. Table 2 shows the test results.

(1) Degree of metal exposure Inject 250 ml of 1% saline solution containing 0.3% interfacial lubricant into various prototype cans whose inner surfaces have been painted by spray painting and baking processes, and energize them under 6 V for 6 seconds. Quantity in milliamps (mA)
Display in .

(2) Adhesion Use a knife to make 11 vertical and horizontal cuts, each about 1.5 mm wide, on the painted surface of a test panel painted on tinplate. A cellophane adhesive tape with a width of 24 mm is attached to the sample, and when it is strongly peeled off, the adhesion of the goblin area is observed. ○: No peeling at all, △: Slight peeling, ×: Significant peeling.

(3) A test panel coated on boiling water-resistant tinplate was treated in water at 100°C for 30 minutes, and the coating was visually inspected and peeled off with cellophane adhesive tape (2
) Judgment is made using the same evaluation as for adhesion.

(4) Flavor retention Various types of test cans were filled with 350 m of tap water treated with activated carbon.
After filling and sealing, sterilizing at 100°C for 30 minutes, storing at 37°C for 6 months, and then conducting a flavor test. ○: No change at all, △: Slight change, ×: Significant change.

(5) Consumption of Potassium Permanganate Fill 350 ml of ion-exchanged water into various inner-coated cans, seal the cans, and heat at 100°C for 30 minutes. No.). The consumption amount is expressed in ppm.

(6) Corrosion resistance evaluation: Add 350 ml of 10% pine juice to various test cans at 98°C.
Filled with a hot pack and sealed, stored at 37°C for 6 months, then opened the can and observed the state of internal corrosion. ○: No corrosion, △: Slight corrosion observed, ×: Significant corrosion.

(7) Corrosion resistance of processed parts Various cans The inner surface of the can was filled with sports drink, the lid was tightened, and 10
After treatment at 0°C for 30 minutes, the mixture was rapidly cooled to 0 to 5°C, and a wedge-shaped weight of 1 kg was dropped from a height of 10 cm into the center of the can body at a 90° angle perpendicular to the upright direction of the can. Force processing. The same can was also dropped from a height of 50 cm at an angle of 60° to process the bottom of the can. This can is 37
After storage for 3 months at ℃--open the can and observe the corrosion state of the processed part. ○: No corrosion, △: Slight corrosion observed, ×: Significant corrosion.

(8) Processability Various types of can interior coating A can was cut open and six test pieces were prepared, each measuring 5 cm from the can body in the direction in which the material was squeezed and 4 cm at right angles thereto. In advance, bend the material gently 180 degrees at right angles to the direction in which it was squeezed, with the coating film facing outward. During this time, 0.34 m larger than the sample (5 cm x 10 cm is suitable)
1 to prevent scratches on the paint film side by sandwiching two sheets of Al material with a size of 1.
Cover the paint film with a soft vinyl sheet of 3K
Impact bending is performed by dropping a weight of g load onto the bending part of the test piece from a height of 42 cm. This processed part 20mm
In order to check for damage to the paint film on the width part, this 20mm
The width is immersed in 1% saline, and the current value (mA) is measured when electricity is applied at 6.5V for 6 seconds. Less than 1mA ○ 1 to less than 10mA △ 10mA or more ×

(9) Flavor properties of water extract A 100 μm aluminum foil coated with the above various water-based paints and solvent-based paints was coated on an area of 4 cm2 of tap water treated with activated carbon.
Pour into a heat-resistant glass bottle to a volume of 1 ml, cover with a lid, and sterilize at 100° C. for 30 minutes, then perform a flavor test on the contents. ○: No change at all, △: Slight change, ×: Significant change.

[0060]

[Table 2]

Claims (1)

[Claims] Claim 1: (A) 100 parts by weight of a carboxyl group-containing acrylic resin-modified epoxy resin and (B) a weight average molecular weight of 2 obtained by reacting carboxyl acid with formaldehyde.
50 to 700, the amount of formaldehyde added per benzene nucleus is 1.5 to 2.0 mol, the alkoxy group is less than 0.2 mol per 1 benzene nucleus, and at least 10% by weight
1. A metal can with an inner surface coated surface, characterized in that the inner surface of the metal can is coated with an aqueous coating composition prepared by dispersing and dissolving 5 to 30 parts by weight of a phenol formaldehyde resin containing a water-soluble component in an aqueous medium.