JP4521169B2 - Water-based paint composition for outer surface of seamless metal can, and seamless metal can having cured coating layer of the paint composition - Google Patents

Description

  The present invention relates to an aqueous coating composition for the outer surface of a seamless metal can for forming a coating layer having color flip-flop properties and retort resistance on the outer surface of the seamless metal can, and a dry-cured coating layer of the coating composition. The present invention relates to a seamless metal can.

In recent years, in order to enhance the design of metal cans used for cosmetics, food and drinks, etc., a coating film is formed on the surface of metal cans with varnishes containing pearl pigments and paints with added light interference pigments. It has been proposed to do. (For example, see Patent Documents 1 and 2)
We also propose a coating composition that gives color flip-flop properties that change the color tone of the coating film to two or more colors depending on the position of the light source or the position of the viewer on articles that require high design, such as automobile bodies. Has been. (See Patent Documents 3 and 4)

JP-A-8-225756 JP 2000-95973 A JP 2002-285093 A Japanese Patent No. 3056253

  In metal cans containing beverages and foods, pressurized water vapor treatment (retort treatment) is performed under conditions such as 120 ° C. for 30 minutes in order to sterilize the contents after filling and sealing the contents. Therefore, the coating film formed on the surface of the metal can needs to have resistance to such retort treatment. From such a viewpoint, as a conventional paint for metal can, epoxy-amino resin, acrylic-amino resin A solvent-type paint in which a polyester-amino resin is dissolved in an organic solvent is used. However, when a solvent-type paint is used, a large amount of solvent is volatilized when the coating film is dried, which causes air pollution and wastes resources.

In order to eliminate the disadvantages of such solvent-based paints, various water-based paints mainly composed of an aqueous film-forming resin such as an acrylic resin or a polyester resin and an amino resin have been proposed. When a water-based paint was used, the water resistance of the coating film was inferior, and a coating film that could withstand retort treatment could not be obtained.
Especially for paints with pearl luster and color flip-flop properties to which pearl pigments and light interference pigments are added in order to improve the design of the paint film, the paint film obtained by blending these pigments in the aqueous paint However, it was extremely difficult to produce a water-based paint composition for the outer surface of a metal can that has both retort resistance and design properties. In particular, it is substantially impossible to obtain an aqueous coating composition that can be applied to seamless cans (DI cans, thin-walled deep-drawn cans, etc.) that are formed by squeezing and squeezing metal, which have restrictions on the painting method and process. It was possible.

  Therefore, the present invention solves the above-mentioned problems of the prior art, and when coated on the outer surface of the seamless metal can, while giving a color flip-flop property that the color tone of the coating film changes greatly depending on the position of the light source and the viewing angle, A water-based coating composition for the outer surface of a seamless metal can that has heat resistance, water resistance, adhesion and processability to withstand retort treatment, and has a low environmental load, and a seamless metal can having a cured and dried coating film layer of the coating composition The purpose is to provide.

  As a result of intensive studies, the present inventors have selected (A) a specific color flip-flop pigment as the pigment component, (B) (a) an acrylic aqueous resin having a specific structure as the binder resin component, and (b) The present invention has been completed by discovering that the above problems can be solved by using an aqueous resin containing an amino resin having a specific structure.

That is, the present invention has the following configuration.
1. In the water-based coating composition for the outer surface of a seamless metal can containing (A) a pigment component and (B) a binder resin component,
(A) The pigment component is
It contains a color flip-flop pigment that is coated with a metal oxide on the surface of silicon dioxide flakes and further surface-treated with a silane coupling agent and zirconium oxide,
(B) the binder resin component is
(A) α, β-monoethylenically unsaturated carboxylic acid (I), N-alkoxymethyl (meth) acrylamide (II) containing an alkoxy group having 1 to 4 carbon atoms, and an aromatic vinyl monomer or alkyl (meta An aqueous resin obtained by copolymerization of acrylate (III), and (b) a reaction product of an amino compound having active hydrogen, formaldehyde, and an alcohol having 1 to 4 carbon atoms, per structural unit of the amino compound An amino resin having one or more imino groups,
An aqueous coating composition for an outer surface of a seamless metal can, characterized in that the aqueous coating composition contains an aqueous resin.
2. 2. The aqueous coating composition for an outer surface of a seamless metal can according to 1, wherein the metal oxide coated on the surface of the silicon dioxide flake is one or more metal oxides selected from tin dioxide, titanium dioxide and iron oxide. object.
3. (B) The water-based coating composition for a seamless metal can outer surface according to 1 or 2, comprising 1 to 30 parts by mass of the pigment component (A) with respect to 100 parts by mass of the solid content of the binder resin component.
4). A seamless metal can having a dry-cured coating film layer of the aqueous coating composition for a seamless metal can outer surface described in any one of 1 to 3 on an outer surface of a side wall of the seamless metal can.
5). 5. The seamless metal can according to 4, wherein the amount of the dried coating film of the aqueous coating composition layer for the outer surface of the seamless metal can is 30 to 70 mg / 100 cm ² .
6). The seamless metal can according to 4 or 5, wherein a desired printed layer is provided on the outer surface of the side wall of the seamless metal can.

  According to the present invention, when applied to the outer surface of a seamless metal can, the color tone of the coating film changes greatly, for example, from purple to green, or from red to green, depending on the position of the light source and the viewing angle, thereby enhancing the design. A water-based coating composition for the outer surface of a seamless metal can that can form a coating film that can withstand the retort treatment and has a low environmental impact, and a highly retort-resistant resist having a hard coating layer formed from the coating composition. A seamless metal can having the following can be obtained.

In the aqueous coating composition for the outer surface of a seamless metal can according to the present invention, (A) a color flip-flop in which a metal oxide is coated on a silicon dioxide flake surface as a pigment component, and surface treatment is performed with a silane coupling agent and zirconium oxide Use pigments.
As the metal oxide, it is preferable to use one or more metal oxides selected from tin dioxide, titanium dioxide and iron oxide. For example, the surface of silicon dioxide flakes is coated with tin dioxide and further coated with titanium dioxide. As a result, a color flip-flop pigment whose color tone changes from purple to green can be obtained. Further, by coating iron oxide on the surface of silicon dioxide flakes and controlling the film thickness of the iron oxide, a color flip-flop pigment in which the color tone of the coating film changes from red to green can be obtained.

  The silicon dioxide flake whose surface is coated with a metal oxide can further improve the retort resistance of the coating film formed on the outer surface of the seamless metal can by further surface treatment with a silane coupling agent and zirconium oxide. There is no restriction | limiting in particular as a silane coupling agent, Any normal silane coupling agent can be used.

The average particle size distribution of the color flip-flop pigment used in the aqueous coating composition of the present invention is preferably in the range of 5 to 40 μm. The average particle size distribution in this case means that 90% by mass or more of the pigment falls within the above particle size range.
The color flip-flop pigment used in the present invention can be obtained as a commercial product. For example, as an iron oxide coating type, “Color stream T20-01 WNT Via Fantasy” manufactured by Merck Ltd., or a titanium oxide coating type is available. Examples thereof include “Color stream F20-00 WNT Automatic Mystery” manufactured by Merck & Co., Inc. Examples of pigments exhibiting a strong color flip-flop include “HELICONE HC” and “HELICONE HC XL” manufactured by Wacker Chemie. These color flip-flop pigments can be used alone or in combination of two or more. Further, it can be used in combination with an ordinary pigment having no color flip-flop property.

  The content of the color flip-flop pigment in the aqueous coating composition is preferably 1 to 30 parts by mass, particularly 1.5 to 20 parts by mass with respect to 100 parts by mass of the solid content of the (B) binder resin component. When the content of the color flip-flop pigment is less than 1 part by mass, it becomes difficult to impart color flip-flop properties to the coating film formed on the outer surface of the seamless metal can. On the other hand, when content exceeds 30 mass parts, the retort resistance of a coating film will fall.

In the water-based paint composition for the outer surface of the seamless metal can of the present invention, (B) the binder resin component contains (a) α, β-monoethylenically unsaturated carboxylic acid (I), and an alkoxy group having 1 to 4 carbon atoms. N-alkoxymethyl (meth) acrylamide (II) and an aqueous resin obtained by copolymerizing an aromatic vinyl monomer or alkyl (meth) acrylate (III), and (b) an amino compound having active hydrogen, formaldehyde, And an aqueous resin containing an amino resin that is a reaction product of an alcohol having 1 to 4 carbon atoms and having one or more imino groups per structural unit of the amino compound.
In addition, in this application, it shall describe like (meth) acrylamide as description showing both acrylic acid and methacrylic acid, or those derivatives.

This (a) acrylic water-based resin can be produced, for example, by the following method.
(I) Vinyl containing α, β-monoethylenically unsaturated carboxylic acid, (II) N-alkoxymethyl (meth) acrylamide, and (III) vinyl monomer copolymerizable with (I) and (II) above A method in which an excess organic solvent is distilled off from a copolymer solution obtained by radical polymerization of a monomer mixture in an organic solvent under reduced pressure, and then made aqueous with a volatile base such as ammonia or organic amine, or the copolymer A method in which a volatile base and water are added to a combined solution, and then an excess organic solvent is distilled off together with water under reduced pressure.

Examples of (I) α, β-monoethylenically inert carboxylic acid include acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid and the like, and acrylic acid and methacrylic acid are preferable. The amount of these used is preferably in the range of 5 to 20% by mass of the whole monomer. If the amount used is less than 5% by mass, it is difficult to make the resulting resin water-based, and if it exceeds 20% by mass, the water resistance of the coating film decreases.

Examples of (II) N-alkoxymethyl (meth) acrylamide include methoxymethyl (meth) acrylamide, ethoxymethyl (meth) acrylamide, n-butoxymethyl (meth) acrylamide, and isobutoxymethyl (meth) acrylamide. The amount of these used is preferably in the range of 5 to 40% by mass of the whole monomer. If the amount used is less than 5% by mass, the retort resistance of the coating film is insufficient due to insufficient curing, and if it exceeds 40% by mass, it is cured too much and the base adhesion and workability of the coating film are impaired.

(III) Examples of the aromatic vinyl monomer copolymerizable with the above (I) and (II) include styrene, p-methylstyrene, α-methylstyrene, vinyltoluene and the like. Examples of the alkyl (meth) acrylate include ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, methyl methacrylate, butyl methacrylate, stearyl methacrylate, cyclohexyl methacrylate, and the like. These monomers can be used in an amount of 40 to 90% by mass of the whole monomer, and the type and copolymerization amount can be selected in consideration of the hardness and flexibility of the coating film.
(A) It is preferable to use an acrylic aqueous resin having a molecular weight of about 5,000 to 30,000, particularly about 10,000 to 25,000.

Monomers essential for the (a) acrylic aqueous resin used in the aqueous coating composition of the present invention are the above (I), (II), and (III), but in addition to these monomers, hydroxyalkyl (meth) acrylate, Monomers copolymerizable with (I) and (II) such as vinyl carboxylate and vinyl alkyl ether can also be used.
Solvents used in the polymerization include alcohol solvents such as isopropyl alcohol, n-butyl alcohol and isobutyl alcohol, cellosolve solvents such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether and ethylene glycol monobutyl ether. A solvent, 3-methoxybutanol, 3-methyl 3-methoxybutanol, etc. are mentioned.

The (b) amino resin used in the aqueous coating composition of the present invention is a reaction product of an amino compound having active hydrogen, formaldehyde, and an alcohol having 1 to 4 carbon atoms, and has an alkoxy group as a functional group in the molecular structure. And one or more imino groups (NH) per structural unit of an amino compound together with a methylol group.
Examples of the amino compound include compounds such as melamine, benzoguanamine, urea, ethylene urea, acetoguanamine, tetramethylene diguanamine, phthaloguanamine, and spiroguanamine. Examples of the alcohol having 1 to 4 carbon atoms include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, sec-butyl alcohol, and t-butyl alcohol.
(B) It is preferable to use an amino resin having a molecular weight of about 400 to 2,000, particularly about 500 to 1,500. When the molecular weight is less than 400, the low molecular weight amino resin component is scattered when the paint is baked and contaminates the baking oven. On the other hand, when the molecular weight exceeds 2,000, it becomes difficult to make an aqueous paint.

  (B) A preferred use ratio of (a) an acrylic aqueous resin constituting the binder resin and (b) an amino resin having an imino group is a resin solid content ratio, and (a) 40 to 80% by mass: (b ) 20 to 60% by mass. When the amount of (b) used is less than 20% by mass, the hardness and water resistance of the coating film are insufficient. On the other hand, when it exceeds 60% by mass, the workability decreases.

  As a solvent that can be used in the water-based coating composition of the present invention, water as a main component can be used together with the solvent used at the time of polymerization of the above (a) acrylic water-based resin, if necessary.

(B) The binder resin is a low molecular polyol such as polyether polyol, polyester polyol, polyurethane polyol, or bisphenol A ethylene oxide or propylene oxide adduct for the purpose of lowering the viscosity of the paint or improving the adhesion of the undercoat of the coating film. Can be used as the third resin component in addition to the above (a) and (b). In this case, the amount of the low-molecular polyols used is preferably 30% by mass or less in the total resin solid content from the viewpoint of maintaining the water resistance of the coating film.

In order to prepare the aqueous coating composition of the present invention, the above (a), (b) and, if necessary, polyols are mixed, and if necessary, p-toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonyl. What is necessary is just to add 0.02-0.2 mass part with respect to 100 mass parts of resin solid content by using dinaphthalenedisulfonic acid or these amine salts as a curing catalyst.
Conventionally known antifoaming agents, leveling agents, lubricants, ultraviolet absorbers and the like can be added to the aqueous coating composition of the present invention.

The aqueous coating composition of the present invention can be efficiently prepared by the following method.
(B) Add the color flip-flop pigment (A) to the binder resin component, and stir and mix with a dispersion stirrer. It is desirable to disperse the color flip-flop pigment only by stirring without kneading.

The aqueous coating composition of the present invention is a seamless metal can produced by drawing and ironing from a metal substrate such as an electrotin-plated steel plate, a chrome-treated steel plate, and an aluminum plate by known means such as roll coating, spray coating, brush coating, etc. Can be painted on the outside.
As a preferred example, a coating film exhibiting strong color flip-flop properties can be formed by applying the gloss and smoothness of the aluminum base by, for example, coating on an aluminum DI can with a two-piece coater.

  The water-based coating composition of the present invention can be applied to a wide range of drying conditions from 150 to 200 ° C. for about 10 minutes to 250 ° C. for about 10 seconds after being applied to the outer surface of a seamless metal can. A cured coating film with good performance can be formed. As a preferable drying condition, for example, in the case of an aluminum DI can, a general baking condition is 200 ° C. for 15 seconds.

The aqueous coating composition of the present invention is preferably applied to the outer surface of the seamless metal can so that the dry mass of the coating film formed on the outer surface of the seamless metal can is 30 to 70 mg / 100 cm ² , particularly 35 to 60 mg / 100 cm ^2. . When the dry mass is less than 30 mg / 100 cm ² , the color flip-flop property tends to be reduced. On the other hand, when the dry mass exceeds 70 mg / 100 cm ² , the tendency to decrease the retort resistance is recognized.
This coating film can be formed on the outer surface of the side wall of the seamless metal can as a base coat layer or a top coat layer. In addition to forming this coating film on the entire outer surface, it may be used for forming a printed pattern such as a logo mark. When a dark or opaque ink layer is provided as the base of this coating film, light is reflected by the base layer, and the color flip-flop effect is further enhanced.

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

[Synthesis Example 1: Synthesis of aqueous acrylic resin solution a-1]
To a 1-liter four-necked flask reaction vessel equipped with a stirrer, a reflux condenser, a dropping funnel, a nitrogen gas inlet tube, and a thermometer, 420 parts of ethylene glycol monoisopropyl ether was charged and heated to 120 ° C. While maintaining the same temperature, a mixture of 40 parts of acrylic acid, 160 parts of n-butoxymethylacrylamide, 120 parts of methyl methacrylate, 80 parts of ethyl acrylate, and 16 parts of azobisisobutylnitrile is added over 4 hours from the dropping funnel. Continuous dripping. One hour after the completion of dropping, 3 parts of di-t-butyl peroxide was added, and the reaction was further performed for 2 hours. The resulting solution was cooled to 80 ° C., and 300 parts of the synthetic solvent was distilled off under reduced pressure. Then, 40 parts of dimethylaminoethanol and 252 parts of water were added and mixed to obtain a non-volatile content of 50% and a residual organic solvent of 14.6%. A transparent viscous acrylic resin aqueous solution a-1 was obtained.

[Synthesis Example 2: Synthesis of aqueous acrylic resin solution a-2]
To a 1-liter four-necked flask reaction vessel equipped with a stirrer, a reflux condenser, a dropping funnel, a nitrogen gas inlet tube, and a thermometer, 420 parts of ethylene glycol monoisopropyl ether was charged and heated to 120 ° C. While maintaining the same temperature, a mixture of 40 parts of acrylic acid, 80 parts of n-butoxymethylacrylamide, 120 parts of methyl methacrylate, 80 parts of ethyl acrylate, 80 parts of butyl acrylate and 16 parts of azobisisobutylnitrile from the dropping funnel Was continuously added dropwise over 4 hours. One hour after the completion of dropping, 3 parts of di-t-butyl peroxide was added, and the reaction was further performed for 2 hours. The resulting solution was cooled to 80 ° C., and 300 parts of the synthetic solvent was distilled off under reduced pressure. Then, 40 parts of dimethylaminoethanol and 252 parts of water were added and mixed to obtain a non-volatile content of 50% and a residual organic solvent of 14.6%. A transparent viscous acrylic resin aqueous solution a-2 was obtained.

[Comparative Synthesis Example 1: Synthesis of aqueous acrylic resin solution a-3]
To a 1-liter four-necked flask reaction vessel equipped with a stirrer, a reflux condenser, a dropping funnel, a nitrogen gas inlet tube, and a thermometer, 420 parts of ethylene glycol monoisopropyl ether was charged and heated to 120 ° C. While maintaining the same temperature, a mixture of 60 parts of acrylic acid, 120 parts of methyl methacrylate, 112 parts of ethyl acrylate, 108 parts of butyl acrylate, and 16 parts of azobisisobutylnitrile was continuously dropped over 4 hours from the dropping funnel. did. One hour after the completion of dropping, 3 parts of di-t-butyl peroxide was added, and the reaction was further performed for 2 hours. The resulting solution was cooled to 80 ° C., and 300 parts of the synthetic solvent was distilled off under reduced pressure. Then, 60 parts of dimethylaminoethanol and 232 parts of water were added and mixed to obtain a non-volatile content of 50% and a residual organic solvent of 14.6%. A transparent viscous acrylic resin aqueous solution a-3 was obtained.

[Synthesis Example 3: Synthesis of imino group-containing methyl etherified benzoguanamine resin b-1]
640 parts (20 moles) of methanol, 130.4 parts (4 moles) of 92% paraformaldehyde, 4 parts of benzoguanamine in a 2-liter four-necked flask equipped with a stirrer, reflux condenser, dropping funnel, thermometer, and nitrogen gas inlet tube 374 parts (1 mole) and 0.3 part of a 10% aqueous sodium hydroxide solution were charged, and the temperature was raised to 70 ° C. After carrying out the reaction at the same temperature for 1 hour, the temperature was lowered to 30 ° C., the pH was adjusted to 3.0 with 36% hydrochloric acid, and the reaction was carried out for 2 hours. Next, after adjusting the pH to 8.0 with 50% sodium hydroxide, unreacted methanol and formaldehyde were distilled off under heating and reduced pressure, and diluted with ethylene glycol monobutyl ether. The product had a non-volatile content of 80.1% and a Gardner viscosity of Z7.

[Synthesis Example 4: Synthesis of imino group-containing methyl etherified benzoguanamine resin b-2]
The same operation as in Synthesis Example 3 was carried out except that the amount of 92% paraformaldehyde was 195.7 parts (6 moles) to obtain a product having a nonvolatile content of 80.3% and a Gardner viscosity Z4.

[Comparative Synthesis Example 2: Synthesis of methyl etherified benzoguanamine resin b-3]
A product having a nonvolatile content of 79.9% and a Gardner viscosity Z was obtained by performing the same operation as in Synthesis Example 3, except that the amount of 92% paraformaldehyde was 391.3 parts (12 mol).

(Examples 1-4)
The aqueous acrylic resin solution, amino resin solution, and BA-8 glycol (manufactured by Nippon Emulsifier Co., Ltd., bisphenol A-ethylene oxide adduct) obtained in Synthesis Examples 1 to 4 and Comparative Synthesis Examples 1 and 2 were used for each component. The solid content ratio was adjusted as shown in Table 1, and ethylene glycol monoisopropylene ether, water, p-toluenesulfonic acid, and color flip-flop pigment (Color stream T20-01WNT manufactured by Merck) were added thereto. By mixing, a paint having a nonvolatile content of 40%, an organic solvent content of 15%, and a catalyst amount of 0.2 PHR was prepared.

(Comparative Examples 1-5)
In the same manner as in the above Examples, a coating material was prepared so that the solid content ratio of the aqueous acrylic resin, amino resin, and BA-8 glycol was as shown in Table 1.

About the coating material obtained in Examples 1-4 and Comparative Examples 1-5, the following coating-film physical property tests were done, and the result was shown in Table 2.
(Film properties test)
A 9-inch test coater and mandrel were used to coat the outer surface of the aluminum DI can so that the coating weight after drying would be 50 mg / 100 cm ^2, and then for 15 seconds +60 in a 200 ° C. hot-air circulating gas oven. Test cans were prepared by drying for 2 seconds. The test can was cut and used as a panel for the next test.

(Boiling water resistance test)
After immersing the test panel in boiling water for 30 minutes, the state of the coating film was evaluated. A case where the coating film was not whitened or floated was indicated by ○, a case where the coating film was slightly whitened or lifted was indicated by Δ, and a case where the coating film was markedly whitened or floated was indicated by ×.

(Retort resistance test)
After the test panel was exposed to water vapor at 130 ° C. for 30 minutes in a pressurized container, the state of the coating film was evaluated. The evaluation results were shown in the same manner as in the boiling water resistance test.

(Processing adhesion test)
The Eriksen test was performed. The case where the crack of the coating film did not occur was indicated by ○, the case where the crack of the coating film slightly occurred was indicated by Δ, and the case where the crack of the coating film occurred significantly was indicated by ×.

(Shock resistance test)
The state of the coating film after processing was evaluated under the conditions of a DuPont impact test, 500 g-10 cm, 20 cm, and 30 cm. The evaluation results were shown in the same manner as in the work adhesion test.

(Coating hardness test)
The test panel was immersed in hot water at room temperature and 80 ° C., and the pencil hardness was measured by a conventional method. The room temperature pencil hardness was indicated by ◯ for 2H or more, Δ for HB to H, and x for B or less.
On the other hand, the pencil hardness in hot water is indicated by ◯ for 2B or more, Δ for 2B to 4B, and x for 5B or less.

(Color flip-flop property)
Test cans prepared by coating film physical property test are visually observed, ◯ when the color change indicating the design property is sufficient, △ when the color change indicating the design property is recognized, △, insufficient or no color change The thing was shown by x.

(Examples 5 to 10)
The aqueous acrylic resin solution obtained in Synthesis Example 1, the amino resin solution obtained in Synthesis Example 3, and BA-8 glycol (manufactured by Nippon Emulsifier Co., Ltd., bisphenol A-ethylene oxide adduct) The amount of ethylene glycol monoisopropylene ether, water, p-toluenesulfonic acid, and color flip-flop pigment (Merck, Color stream T20-01WNT) was varied. The paints shown in Table 3 (non-volatile content 40%, organic solvent content 15%, catalyst amount 0.2 PHR) were prepared.

  About the coating material obtained in Examples 5-10, said coating-film physical property test was done and the result was shown in Table 4.

(Examples 11 to 16)
The aqueous acrylic resin solution obtained in Synthesis Example 1, the amino resin solution obtained in Synthesis Example 3, and BA-8 glycol (Nippon Emulsifier Co., Ltd., bisphenol A-ethylene oxide adduct) were adjusted to a certain solid content ratio. In addition, a coating material (nonvolatile content 40) containing 5 parts by mass of ethylene glycol monoisopropylene ether, water, p-toluenesulfonic acid, and further color flip-flop pigment (Merck, Color stream T20-01WNT). %, Organic solvent content 15%, catalyst amount 0.2 PHR).
The obtained paint was applied to the outer surface of the side wall of an aluminum DI can by using a 9 inch test coater and a mandrel to prepare a coated plate having the coating film mass after drying described in Table 5. .

  About the coating board produced in Examples 11-16, said coating-film physical property test was done, and the result was described in Table 6.

As seen in each of the above examples, the seamless metal can having the base coat layer or the top coat layer made of the aqueous coating composition for a seamless metal outer surface of the present invention changes greatly in the color tone of the reflected light depending on the position of the light source and the viewing angle. Beverage cans with a pearly luster-like enhanced design that exhibits strong color flip-flop properties, and (a) N-alkoxymethyl groups in acrylic resin and (b) imino groups in amino resin It has heat resistance and water resistance that can withstand the pressurized steam treatment process of food can sterilization treatment, and adhesion and workability that can be processed into various can forms.

Claims (6)

In the water-based coating composition for the outer surface of a seamless metal can containing (A) a pigment component and (B) a binder resin component,
(A) The pigment component is
It contains a color flip-flop pigment that is coated with a metal oxide on the surface of silicon dioxide flakes and further surface-treated with a silane coupling agent and zirconium oxide,
(B) the binder resin component is
(A) α, β-monoethylenically unsaturated carboxylic acid (I), N-alkoxymethyl (meth) acrylamide (II) containing an alkoxy group having 1 to 4 carbon atoms, and an aromatic vinyl monomer or alkyl (meta An aqueous resin obtained by copolymerization of acrylate (III), and (b) a reaction product of an amino compound having active hydrogen, formaldehyde, and an alcohol having 1 to 4 carbon atoms, per structural unit of the amino compound An amino resin having one or more imino groups,
An aqueous coating composition for an outer surface of a seamless metal can, characterized in that the aqueous coating composition contains an aqueous resin. The aqueous metal outer surface of a seamless metal can according to claim 1, wherein the metal oxide coated on the surface of the silicon dioxide flake is one or more metal oxides selected from tin dioxide, titanium dioxide and iron oxide. Paint composition. (B) The water-based paint composition for an outer surface of a seamless metal can according to claim 1, wherein 1 to 30 parts by mass of the pigment component (A) is contained with respect to 100 parts by mass of the solid content of the binder resin component. object. A seamless metal can comprising a dry-cured coating film layer of the aqueous coating composition for a seamless metal can outer surface according to any one of claims 1 to 3 on an outer surface of a side wall of the seamless metal can. Seamless metal can according to claim 4, dry coating amount of the seamless metal can outer surface aqueous coating composition layer is characterized by a 30 to 70 mg / 100 cm ^2. The seamless metal can according to claim 4 or 5, wherein a desired printed layer is provided on an outer surface of the side wall of the seamless metal can.