JP2003213204A - Coating material for external surface of can - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a coating material for external surfaces of cans, free from toxicity, or the like, having rapid curing rate, not causing shrinkage in polymerization and capable of providing a coating film excellent in corrosion resistance, water resistance, adhesion, or the like, and processability. <P>SOLUTION: This coating material for the external surfaces of cans is obtained by irradiating a coating material composition for the external surfaces of cans comprising a compound having two oxetane rings and/or three oxetane rings and a photo cation polymerization initiator, and optionally further containing a compound having an epoxy group or a compound having vinyl ether group and/or optionally further containing a compound having (meth) acryloyl group and a photoradical polymerization initiator with an active energy. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a paint for the outer surface of a can, which is composed of a compound having an oxetane ring and has excellent film properties and processability. In addition, in this specification, an acryloyl group or a methacryloyl group is represented as a (meth) acryloyl group.

[0002]

2. Description of the Related Art The outer surface of beverage cans containing soft drinks and food cans for packaging foods has a cured film of a coating composition for the outer surface of the cans in order to prevent corrosion of the can material and enhance aesthetic commercial value. Is covered by. Beverage cans, food cans, and the like are sterilized by heat treatment, so that the coating film of the coating composition for an outer surface of the can is required to withstand the heat treatment process. Conventionally, these coating compositions have a method of coating an organic solvent solution of epoxy / amino resin, acrylic / amino resin, polyester / amino resin, etc. on a steel plate with a roll coater and baking and curing in a gas oven. It is taken. However, this method has a problem of environmental pollution because it causes a large amount of solvent volatilization during baking, and requires a large space for installing an oven.
It has problems such as low energy efficiency such as requiring a large amount of heat for curing the coating composition. In recent years, active energy ray-curable coating compositions have come to be used as coating compositions that solve these problems. Since the active energy ray-curable coating composition is essentially solvent-free, there is no risk of environmental pollution, and the active energy ray irradiation apparatus can significantly reduce energy consumption and required space for a gas oven. it can.

[0003]

The majority of conventional active energy ray-curable coating compositions are concentrated on polyfunctional acrylates and unsaturated polyesters, which are cured by active energy ray-initiated radical polymerization, and are used today. However, these compounds are still used in large quantities. However, when these compounds are used as a coating composition for the outer surface of a can, the film thickness in this application generally needs to be around several μm, so that the effect of polymerization inhibition by oxygen during curing is large, and the curability of the composition is high. Or, the scratch resistance and surface smoothness of the coating film tended to be impaired. Further, as an active energy ray curing technique other than the active energy ray initiated radical polymerization, an active energy ray initiated cationic polymerization technique has been put into practical use. In particular, the active energy ray-initiated cationic polymerization does not have to be carried out under an inert atmosphere because the polymerization is not hindered by oxygen, and rapid and complete polymerization can be carried out in air. Has the advantage. To date, the development of active energy ray initiated cationic polymerization technology has focused on two types of monomers: epoxy resins and vinyl ethers. Particularly, the photocurable epoxy resin has excellent adhesiveness, and the coating film has good heat resistance and chemical resistance. However, in the conventional photocurable epoxy resin,
Since it has a defect that the photopolymerization rate is relatively slow, it could not be used in applications requiring rapid photocuring. The low molecular weight photo-curable epoxy resin is
Mutagenicity and other toxicities have been pointed out, and their risk is being questioned. On the other hand, photocurable vinyl ether
Many of them are volatile and have a strong odor, and many of them show shrinkage during curing as compared with photocurable epoxies. In particular, in the production of a coating composition for a can, which cannot be expected to improve adhesion due to a phenomenon of sucking into a base material or a graft reaction with a base material, the adhesion may be impaired due to shrinkage during curing. Further, when the conventional active energy ray-curable coating composition is used as a coating composition for a can, the coating film does not have sufficient performance such as corrosion resistance, water resistance and processability.

In view of the above circumstances, the inventors of the present invention have no toxicity or the like, have a high curing speed, and do not shrink during polymerization.
The coating film was thoroughly studied in order to find a paint for the outer surface of a can which is excellent in corrosion resistance, water resistance, adhesion, etc. and workability.

[0005]

DISCLOSURE OF THE INVENTION The inventors of the present invention have made various investigations and found that a composition comprising a cyclic ether having a specific structure can solve the above problems as a coating composition for an outer surface of a can. Heading The present invention has been completed. That is, the first invention of the present invention is a compound having two oxetane rings and / or a compound having three oxetane rings,
And a can external surface coating comprising a cationic photopolymerization initiator, a second invention is a can external surface coating of the first invention further containing a compound having an epoxy group, and a third invention is a first invention further containing a compound having a vinyl ether group. The can outer surface coating of the invention, the fourth invention is a can outer surface coating of the first invention, the can outer surface coating of the second invention or the third invention, which further contains a compound having a (meth) acryloyl group and a photoradical polymerization initiator. This is a paint for the outer surface of a can. Hereinafter, the present invention will be described in detail.

Compounds Having 1-4 Oxetane Rings The compounds having an oxetane ring used in the present invention have 1 to 4 oxetane rings. When a compound having 5 or more oxetane rings is used, the coating film of the composition loses flexibility and may crack when the steel sheet having the coating film of the composition is processed into a can. As the compound having an oxetane ring used in the present invention, various compounds can be used as long as they are compounds having two oxetane rings and / or compounds having three oxetane rings. Specific examples of the compound having one oxetane ring include compounds represented by the following general formula (1).

[0007]

[Chemical 1]

In the formula (1), R ¹ is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms such as a methyl group, an ethyl group, a propyl group or a butyl group, a fluoroalkyl group having 1 to 6 carbon atoms, It is an allyl group, an aryl group, a furyl group or a thienyl group. R ² is an alkyl group having 1 to 6 carbon atoms such as a methyl group, an ethyl group, a propyl group or a butyl group, 1-
Alkenyl having 2 to 6 carbon atoms such as propenyl group, 2-propenyl group, 2-methyl-1-propenyl group, 2-methyl-2-propenyl group, 1-butenyl group, 2-butenyl group or 3-butenyl group. Group, phenyl group, benzyl group,
A group having an aromatic ring such as fluorobenzyl group, methoxybenzyl group or phenoxyethyl group, alkylcarbonyl group having 2 to 6 carbon atoms such as ethylcarbonyl group, propylcarbonyl group or butylcarbonyl group, ethoxycarbonyl group, propoxycarbonyl group Alternatively, it is an alkoxycarbonyl group having 2 to 6 carbon atoms such as butoxycarbonyl group, or an N-alkylcarbamoyl group having 2 to 6 carbon atoms such as ethylcarbamoyl group, propylcarbamoyl group, butylcarbamoyl group or pentylcarbamoyl group. .

Next, examples of the compound having two oxetane rings include compounds represented by the following general formula (2).

[0010]

[Chemical 2]

In the formula (2), R ¹ is the same group as in the general formula (1). R ³ is, for example, a linear or branched alkylene group such as ethylene group, propylene group or butylene group, poly (ethyleneoxy)
Group or a linear or branched poly (alkyleneoxy) group such as a poly (propyleneoxy) group, a propenylene group, a linear or branched unsaturated hydrocarbon group such as a methylpropenylene group or a butenylene group, a carbonyl group, An alkylene group containing a carbonyl group, an alkylene group containing a carboxyl group, an alkylene group containing a carbamoyl group, and the like.
R ³ is also a polyvalent group selected from the groups represented by the following formulas (3), (4) and (5).

[0012]

[Chemical 3]

In the formula (3), R ⁴ is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, a propyl group or a butyl group, a methoxy group, an ethoxy group, a propoxy group or a butoxy group. An alkoxy group having 1 to 4 carbon atoms such as, a halogen atom such as a chlorine atom or a bromine atom,
It is a nitro group, a cyano group, a mercapto group, a lower alkylcarboxyl group, a carboxyl group, or a carbamoyl group.

[0014]

[Chemical 4]

In the formula (4), R ⁵ is an oxygen atom, a sulfur atom, a methylene group, NH, SO, SO ₂ , C (CF ₃ ).
₂ or C (CH ₃ ) ₂ .

[0016]

[Chemical 5]

In equation (5), R⁶Is a methyl group,
1 to 4 carbon atoms such as chill, propyl or butyl
Is an alkyl group or an aryl group. n is 0 to 20
It is an integer of 00 and the coating film of the composition requires high surface hardness.
When it is carried out, n is preferably 0 to 6,
When the coating film of the product requires high tensile strength, n is
It is preferably 100 to 200. R⁷Is methyl
1 carbon atom such as group, ethyl group, propyl group or butyl group
~ 4 alkyl groups or aryl groups. R ₇Is
A polyvalent group selected from the groups represented by the following formula (6)
It

[0018]

[Chemical 6]

In the formula (6), R ⁸ is an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, a propyl group and a butyl group, or an aryl group. m is 0 to 100
Is an integer. Specific examples of the compound having two oxetane rings include compounds represented by the following formulas (7) and (8).

[0020]

[Chemical 7]

The compound represented by the formula (7) is a compound of the formula (2) in which R ¹ is an ethyl group and R ³ is a carboxyl group.

[0022]

[Chemical 8]

The compound represented by the formula (8) is the compound represented by the general formula (2), wherein R ¹ is an ethyl group, R ³ is a group represented by the formula (5) and R ⁶
And R ⁷ is a methyl group, and n is 1.

Of the compounds having two oxetane rings, preferred examples other than the above compounds include compounds represented by the following general formula (9).

[0025]

[Chemical 9]

Examples of the compound having 3 to 4 oxetane rings include compounds represented by the following general formula (10).

[0027]

[Chemical 10]

In the formula (10), R ¹ is the same group as in the general formula (1). R ⁹ represents, for example, a group represented by the following formulas (11) to (13) having 1 to 1 carbon atoms.
And 12 branched alkylene groups, branched poly (alkyleneoxy) groups such as the group represented by the following formula (14), branched polysiloxy groups such as the group represented by the following formula (15), and the like. . j is 3 or 4.

[0029]

[Chemical 11]

[In the formula (11), R ¹⁰ is a methyl group,
A lower alkyl group such as an ethyl group or a propyl group. ]

[0031]

[Chemical 12]

[0032]

[Chemical 13]

[0033]

[Chemical 14]

[In the formula (14), l is an integer of 1 to 10. ]

[0035]

[Chemical 15]

Specific examples of the compound having 3 to 4 oxetane rings include compounds represented by the following formula (16).

[0037]

[Chemical 16]

Further, as an example of the compound having 1 to 4 oxetane rings other than the above, there is a compound represented by the following formula (17).

[0039]

[Chemical 17]

In the formula (17), R ⁸ is the same group as in the formula (6). R ¹¹ is an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, a propyl group or a butyl group, or a trialkylsilyl group, and r is 1 to 4.

More preferred examples of the compound having two oxetane rings and / or the compound having three oxetane rings used in the present invention include the compounds shown below.

[0042]

[Chemical 18]

[0043]

[Chemical 19]

[0044]

[Chemical 20]

[0045]

[Chemical 21]

In addition to these, the molecular weight is from 1000 to 5
A compound having two oxetane rings and / or a compound having three oxetane rings having a high molecular weight of about 000 is also included. Examples of these include the following compounds.

[0047]

[Chemical formula 22] Here, p is 20 to 200.

[0048]

[Chemical formula 23] Here, q is 15 to 100.

[0049]

[Chemical formula 24] Here, s is 20 to 200.

Photocationic Polymerization Initiator As the photocationic polymerization initiator used in the composition of the present invention, various kinds can be used. Preferred examples of these initiators include diaryliodonium salts and triarylsulfonium salts. A typical cationic photopolymerization initiator is shown below.

[0051]

[Chemical 25]

[0052]

[Chemical formula 26]

[0053]

[Chemical 27]

[0054]

[Chemical 28]

In the formula, R ¹² is a hydrogen atom and has 1 to 18 carbon atoms.
Or an alkoxy group having 1 to 18 carbon atoms, R ¹³ is a hydrogen atom, a hydroxyalkyl group or a hydroxyalkoxy group, and preferably a hydroxyethoxy group. M is a metal, preferably antimony,
X is halogen, preferably fluorine, and k is the valence of the metal, for example 5 in the case of antimony. The cationic photopolymerization initiator is preferably contained in the compound having an oxetane ring in a proportion of 0.1 to 20% by weight, more preferably 0.1 to 10% by weight. When the composition of the first invention further contains a compound having an epoxy group and / or a compound having a vinyl ether group, which will be described later, a compound having an oxetane ring, a compound having an epoxy group and / or a compound having a vinyl ether group can be used. The content is preferably 0.1 to 20% by weight, more preferably 0.1 to 10% by weight, based on the total amount. If it is less than 0.1% by weight, the curability is not sufficient, while if it exceeds 20% by weight, the light transmission becomes poor and uniform curing cannot be performed or the coating surface is not smooth. The sex may be lost.

Other Blends In addition to the above-mentioned essential ingredients, other ingredients may be blended into the composition of the present invention as required. A second invention of the present invention is a paint for the outer surface of a can, wherein the composition of the first invention further contains a compound having an epoxy group. in this case,
By including the epoxy compound in the composition, the curing rate of the composition can be further improved. Various compounds can be used as the compound having an epoxy group. For example, examples of the epoxy compound having one epoxy group include phenylglycidyl ether and butylglycidyl ether, and examples of the epoxy compound having two or more epoxy groups include hexanediol diglycidyl ether, tetraethylene glycol diglycidyl ether, triglyceride. Examples thereof include methylolpropane triglycidyl ether, bisphenol A diglycidyl ether and novolac type epoxy compounds. Particularly in the present invention, it is preferable to use an alicyclic epoxy compound, and examples thereof include the compounds shown below.

[0057]

[Chemical 29]

[0058]

[Chemical 30]

[0059]

[Chemical 31]

In this case, the compounding ratio of the compound having an epoxy group is 5 to 95 parts by weight based on 100 parts by weight of the total amount of the compound having 1 to 4 oxetane rings and the compound having an epoxy group. preferable.

The third invention of the present invention is a coating material for the outer surface of a can, which further comprises a compound having a vinyl ether group in the composition of the first invention. In this case, by including the compound having a vinyl ether group in the composition, the curing rate of the composition can be further improved. Various compounds can be used as the compound having a vinyl ether group. For example, examples of the compound having one vinyl ether group include hydroxyethyl vinyl ether, hydroxybutyl vinyl ether, dodecyl vinyl ether, propenyl ether propylene carbonate and cyclohexyl vinyl ether. Examples of the compound having two or more vinyl ether groups include cyclohexanedimethanol divinyl ether, triethylene glycol divinyl ether, and novolak type divinyl ether. In this case, the compounding ratio of the compound having a vinyl ether group is preferably 5 to 95 parts by weight based on 100 parts by weight of the total amount of the compound having 1 to 4 oxetane rings and the compound having a vinyl ether group.

The fourth invention of the present invention relates to the composition of the first invention, the composition of the second invention, or the composition of the third invention,
Further, it is a paint for the outer surface of a can, which contains a compound having a (meth) acryloyl group and a photoradical polymerization initiator. In this case, by including a compound having a (meth) acryloyl group in the composition, the composition viscosity can be adjusted and the coating film hardness of the composition can be modified. Various compounds can be used as the compound having a (meth) acryloyl group. For example, compounds having one (meth) acryloyl group include phenol, nonylphenol and 2-
Examples thereof include (meth) acrylate of ethylhexanol, and (meth) acrylate of alkylene oxide adduct of these alcohols. Examples of the compound having two (meth) acryloyl groups include bisphenol A,
Examples include isocyanuric acid, di (meth) acrylates of ethylene glycol and propylene glycol, and di (meth) acrylates of alkylene oxide adducts of these alcohols. 3 (meth) acryloyl groups
Examples of the compound having pentaerythritol, trimethylolpropane and isocyanuric acid tri (meth)
There are acrylates and alkylene oxide adducts of these alcohols such as tri (meth) acrylate,
Examples of the compound having four or more (meth) acryloyl groups include pentaerythritol and poly (meth) acrylate of dipentaerythritol. In addition, conventionally known acrylic monomers and oligomers such as urethane acrylate having a urethane bond as a main chain, polyester acrylate having an ester bond as a main chain, and epoxy (meth) acrylate obtained by adding acrylic acid to an epoxy compound can also be used. In this case, the compounding ratio of the compound having a (meth) acryloyl group is 5 to 95 with respect to 100 parts by weight of the total amount of the compound having 1 to 4 oxetane rings and the compound having a (meth) acryloyl group. Parts by weight are preferred. In the fourth aspect of the present invention, a photoradical polymerization initiator is added to the composition. As the photo-radical polymerization initiator, various ones can be used, and preferred ones are benzophenone and its derivatives, benzoin alkyl ether, 2-methyl [4- (methylthio) phenyl] -2-morpholino-1-propanone. ,
Benzyl dimethyl ketal, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1
-Phenylpropan-1-one, alkylphenylglyoxylate, diethoxyacetophenone, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -1-butanone, acylphosphine oxide and the like can be mentioned. The content of these photoradical polymerization initiators is preferably 0.01 to 20% by weight based on the compound having a (meth) acryloyl group.

In the present invention, the composition of the first invention is selected from the above-mentioned compound having an epoxy group, compound having a vinyl ether group and [compound having a (meth) acryloyl group and photoradical polymerization initiator]. It is also possible to mix two or more of the above. In this case, the compounding ratio of these compounds is a compound having two oxetane rings and / or a compound having three oxetane rings, a compound having an epoxy group, a compound having a vinyl ether group and a (meth) acryloyl group. A compound having an epoxy group, based on 100 parts by weight of the total amount of the compound,
The total amount of the compound having a vinyl ether group and the compound having a (meth) acryloyl group is preferably 5 to 95 parts by weight.

The composition of the present invention contains 10 parts in addition to the above components.
Inert ingredients such as inorganic fillers, dyes, pigments, viscosity modifiers, treating agents, organic solvents and UV blockers can be incorporated in amounts of up to 100 parts by weight per 0 parts by weight of curable components.

In addition to the photocationic polymerization initiator and / or photoradical polymerization initiator, a photosensitizer may be added to the composition of the present invention to adjust the wavelength in the UV region. Typical sensitizers that can be used in the present invention include Clevero [JV Crivello, Adv. In Polymer Sc
i., 62, 1 (1984)], and specific examples thereof include pyrene, perylene, acridine orange, thioxanthone, 2-chlorothioxanthone and benzoflavin.

○ Method of Use As a base steel sheet for which the coating composition of the present invention can be used,
It can be applied to various things. For example, electro-positive steel plate,
Examples include chin-free steel and aluminum, and those whose surface is oxidized, and those in which an oil layer such as cottonseed oil, dioctyl sebacate or acetyltributyl citrate is electrostatically formed. The method of using the coating composition of the present invention may be appropriately selected depending on the structure of the can. For example, in the case of producing a three-piece can that is formed by coating a coating composition on a substrate, the sheet substrate is coated or printed by roll coating, spray coating or offset printing, and then irradiated with active energy rays. Examples of the method include, and in the case of manufacturing a two-piece can that is molded before coating, the molded substrate is sprayed or curved surface is coated or printed with a roller or the like, and then irradiated with active energy rays. Methods and the like. When a composition containing a solvent is used as the composition, it is heated by a heating furnace, far infrared rays or ultra far infrared rays to evaporate the solvent before irradiation with the active energy rays. Examples of active energy rays include ultraviolet rays, X-rays, and electron rays. A variety of light sources can be used as the light source that can be used for curing with ultraviolet rays, and examples thereof include a mercury arc lamp, a xenon arc lamp, a fluorescent lamp, a carbon arc lamp, and a tungsten-halogen copying lamp. In the case of curing with an electron beam, it is usually cured with an electron beam having an energy of 300 eV or less, but it is also possible to cure instantly with an irradiation dose of 1 Mrad to 5 Mrad. In the present invention, it is preferable to use ultraviolet rays for curing the composition, because an inexpensive device can be used.

On the coating film of the coating composition for an outer surface of a can of the present invention, other coating materials can be further applied.

[0068]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples below. The parts in the following examples are based on weight.

Example 1 Production of Composition As a compound having an oxetane ring, the following compound (32) having two oxetane rings shown below (hereinafter referred to as component A)
100 parts and 4 parts of the following compound (33) (hereinafter referred to as component G) as a cationic photopolymerization initiator were mixed with stirring to produce a coating composition for the outer surface of a can.

[0070]

[Chemical 32]

[0071]

[Chemical 33]

Evaluation The following evaluation was performed on the obtained composition. The results are shown in Table 2 below. O An electroplated tin plate having a thickness of 0.2 mm is used as a curable substrate, and the composition is applied to this with a bar coater to give a coating film thickness of 10
It was coated so that it had a thickness of μm, and it was repeatedly passed under the mercury lamp at 80 W / cm, at a position 10 cm below the concentrating high-pressure mercury lamp, and at a conveyor speed of 10 m / min. It was evaluated by the number of passes (the number of passes) until the tackiness disappeared.

[Adhesion] The obtained coating film was cut at 1 mm intervals in a grid pattern, and the adhesion was evaluated according to JISK5400.
In Table 2, ◯, Δ and × have the following meanings. ◯: Almost no peeling Δ: 50% or more remains ×: Peeling exceeds 50%

〇 Corrosion resistance The base plate coated is immersed in activated carbon-treated water and immersed at 3 ° C.
I kept it for 6 months. The corrosion state of the base material under the coating film after the test was evaluated. ○: No corrosion △: Slight corrosion was observed ×: Corrosion was remarkable

The substrate plate coated with the hot water resistant coating was immersed in water and heat-treated at 100 ° C. for 30 minutes, and then the whitening state of the coating film was evaluated. ○: No whitening △: Slight whitening is observed ×: Whitening is observed on the entire surface

Erichsen processability Using the Erichsen molding test test model 142-20, the diameter of the cylinder head was 2.6 cm (drawing ratio 2.4) and the wrinkle holding pressure was 300 kg. A deep drawing test was conducted under the conditions of a drawing speed of 3.0 cm / sec.
At this time, cracks in the coating film formed on the coated surface of the cylindrical head were visually evaluated. In Table 2, ◯, Δ and × have the following meanings. ◯: No cracks △: Slight cracks are generated ×: Peeling occurs

Examples 2 to 7 Compositions were produced in the same manner as in Example 1 except that the components having the compositions shown in Table 1 were used. The obtained composition was evaluated in the same manner as in Example 1. The results are shown in Table 2.

Comparative Examples 1 to 3 Compositions were produced in the same manner as in Example 1 except that the components having the compositions shown in Table 1 were used. The obtained composition was evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0079]

[Table 1]

In Table 1, each numeral indicates a part. Further, in Table 1, components B to H represent the following compounds.

Component B (compound having 3 oxetane rings)

[0082]

[Chemical 34]

Component C (compound having one oxetane ring)

[0084]

[Chemical 35]

Component D (compound having two epoxy groups)

[0086]

[Chemical 36]

Component E (compound having two vinyl ether groups)

[0088]

[Chemical 37]

Component F (compound having two acryloyl groups)

[0090]

[Chemical 38]

Component H (photoradical polymerization initiator)

[0092]

[Chemical Formula 39]

[0093]

[Table 2]

[0094]

EFFECTS OF THE INVENTION The coating composition for an outer surface of a can of the present invention has a high curing rate and does not shrink during polymerization, and the coating film has excellent properties such as corrosion resistance, water resistance, adhesion and processability. I have.

Claims (4)

[Claims] 1. A compound having two oxetane rings and / or
Alternatively, a can outer surface coating composition obtained by irradiating a can outer surface coating composition containing a compound having three oxetane rings and a photocationic polymerization initiator with an active energy ray. 2. A can outer surface coating composition obtained by irradiating the can outer surface coating composition according to claim 1 with an active energy ray, which further contains a compound having an epoxy group. 3. A can outer surface coating composition obtained by irradiating the can outer surface coating composition according to claim 1 with an active energy ray, which further comprises a compound having a vinyl ether group. 4. A coating composition for an outer surface of a can, which further comprises a compound having a (meth) acryloyl group and a photoradical polymerization initiator, is irradiated with active energy rays. Paint for the outer surface of the can.