JP5129012B2 - Water-based paint for can exterior - Google Patents

Description

  The present invention is a water-based paint having a high solid content and low viscosity, which is excellent in coating workability, has a small resin content elution amount after retort treatment, is easy to treat waste water, and is obtained by coating the water-based paint. The coated film relates to a water-based paint for outer surfaces of cans, which is a high-hardness coating film that is difficult to be damaged in the process of transport, adhesion, and retort treatment, and that can form a coating film having excellent scratch resistance.

Metal cans are widely used as containers for packaging various beverages and foods, and the outer surface of the metal cans is used for the purpose of preventing corrosion originating from the external environment, aesthetics, and marking contents. UV-curable silver printing, ink printing, and a clear coating is applied on the printing ink.
As this type of clear paint, organic solvent solutions such as acrylic resin / amino resin, polyester / amino resin, and resin resin in which an epoxy resin is added to these resins are widely used.

  Conventionally, water-based paints for the outer surface of metal cans include α, β-monoethylenically unsaturated carboxylic acid, N-alkoxymethyl (meth) acrylamide having an alkoxy group having 4 or less carbon atoms, and aromatic vinyl monomer or alkyl (meta ) Aqueous resin copolymerized with acrylate, and a reaction product of an amino compound having active hydrogen, formaldehyde and an alcohol having 1 to 4 carbon atoms, and containing an amino resin having one or more imino groups per molecule A coating composition is disclosed (Patent Document 1).

  However, in Patent Document 1, since the imino group in the amino resin is 1 or more, the crosslinking reactivity is inferior, and further, the carboxyl group in the aqueous resin remains unreacted in the coating film. There were problems such as a large amount of elution, a low hardness after retort treatment, and the coating film was easily damaged.

  In addition, 1.5 to 3 mol of formaldehyde is added per mol of triazine nucleus, and the alkyl etherated benzoguanamine resin having a solubility parameter of 9.5 to 11 is 20 to 60% by weight, and the acid value is 30 to 100 mg / KOH mg. A water-based paint for can outer surfaces is disclosed in which a resin composition comprising 80 to 40% by weight of an acrylic resin and / or polyester resin having a solubility parameter of 9.5 to 11 is neutralized and dissolved or dispersed in water. (Patent Document 2).

  However, Patent Document 2 discloses that a benzoguanamine resin has a small amount of formalin addition and the number of imino groups per mole of triazine nucleus is 1 or more, so that the cross-linking reaction of the resin is insufficient, and the carboxyl resin of the acrylic resin and / or the polyester resin. Since the group remained in the coating film, the amount of resin elution during retort treatment was large, and the wastewater treatment was troublesome. In addition, the hardness after retorting is low, and the coating film is easily damaged in the can transporting process. Furthermore, since the solubility parameter of the alkyl etherated benzoguanamine resin is in the range of 9.5 to 11, when the solid content of the paint is increased (50% by mass <), the viscosity of the paint is also increased and the workability of the paint is inferior. There was a problem.

  In addition, it contains 1 to 25% by weight of α, β-monoethylenically unsaturated carboxylic acid and 20 to 100% by weight of N-methylolalkoxy (meth) acrylamide formed by etherification with a specific alcohol having a boiling point of 120 ° C. or higher. N-methylolalkoxy (meth) acrylamide 5 to 60% by weight, and other monomers 10 to 60% by weight of an acrylic copolymer obtained by copolymerization reaction 30 to 85% by weight, and 0.1 per benzoguanamine nucleus. An aqueous coating composition containing 15 to 70% by weight of an imino group-type benzoguanamine resin having 5 to 2.0 imino groups is disclosed (Patent Document 3).

  Further, 20 to 80% by weight of the alkoxy group in the N-alkoxymethyl (meth) acrylamide portion constituting the acrylic copolymer is ether-exchanged with ethylene glycol monoalkyl ether or the like, and a plurality of different boiling points are obtained. An aqueous coating composition using an acrylic copolymer as an alkoxy moiety of alcohol is disclosed (Patent Document 4).

  However, in patent document 3 and patent document 4, since the alcohol part (-OR) of N-alkoxymethyl (meth) acrylamide which comprises an acryl-type copolymer is high molecular weight, crosslinkability is inadequate. Furthermore, the coating film hardness after the retort treatment is low, and the coating film is easily damaged especially during the can conveyance process. Further, when the solid content of the paint is increased, the viscosity of the paint is also increased and the workability of the paint is inferior.

  The ultraviolet curable resin composition contains a radical polymerizable acrylate and / or methacrylate compound (A), a non-radical polymerizable compound (B), a vinyl ether compound (C), and a photo radical polymerization initiator (D). Thus, [0019] in the specification discloses a xylene formaldehyde resin (Patent Document 5). However, the invention of Patent Document 5 relates to an ultraviolet curable resin composition for obtaining a coating film having adhesion, workability, heat resistance, and hardness to a metal can or a polyester film-coated drawn metal can, and is cured with the present invention. The method is also different, and it is not aimed at high solidification of the paint or improvement in painting workability.

  Because of this, it is a water-based paint that has a high solid content and low viscosity, and is excellent in coating workability, and has a small amount of resin elution after retort treatment, and can be easily treated with waste water. There has been a demand for a water-based paint for outer surfaces of cans that can form a coating film having high scratch resistance and high hardness, which is hard to be damaged in the process of transport, adhesion and retort treatment.

Japanese Patent Laid-Open No. 5-320564 Japanese Patent Laid-Open No. 10-77440 JP-A-11-106700 JP 2006-299139 A JP-A-9-143395

  The object of the present invention is a high solid content and excellent coating workability, and the obtained coating film is a high hardness coating film that is hard to be damaged in the process of conveyance, adhesion and retort processing, and is scratch resistant. It is possible to form an excellent coating film. Furthermore, it is providing the water-based paint for can outer surfaces with little resin elution amount after a retort process.

  As a result of intensive studies by the inventors to solve the above problems, a carboxyl group-containing vinyl copolymer obtained by copolymerizing a monomer component containing a specific nitrogen-containing radical polymerizable unsaturated monomer (a1) Resin (A), an amino resin (b1) having a triazine nucleus structure having less than 1 mole of imino group per mole of triazine nucleus, and an oxazoline group-containing compound having a number average molecular weight of 1,500 or more and less than 40,000 ( It has been found that this can be achieved by a water-based paint for outer surfaces of cans containing a cross-linking agent (B) containing b2) and a xylene formaldehyde resin (C) having an average molecular weight of 250 to 500, and the present invention has been completed.

  The effects of the present invention are as follows: (1) A paint having a high solid content and a low viscosity, and having a low volatile organic compound (low VOC) and excellent coating workability. (2) A can body having a coating film excellent in workability and adhesion after retorting treatment and scratch resistance can be provided. In particular, the can body is hardly damaged even during the transport process after the retort processing. (3) Good wettability and excellent finish. (4) Less resin elution after retort treatment and excellent retort resistance.

  In the carboxyl group-containing vinyl copolymer resin (A), a specific amount of the specific nitrogen-containing radical polymerizable unsaturated monomer (a1) and the hydroxyl group-containing radical polymerizable unsaturated monomer (a3) are blended. The nitrogen-containing radically polymerizable unsaturated monomer (a1) and the hydroxyl group-containing radically polymerizable unsaturated monomer (a3) react to improve the crosslinkability, and the amount of resin elution after retort treatment is small and waste water It is easy to process and has excellent resistance to retort processing.

  Further, as the crosslinking agent (B), an amino resin (b1) having a triazine nucleus structure having less than 1 mole of imino group per mole of triazine nucleus and an oxazoline group having a number average molecular weight of 1,500 or more and less than 40,000 By using the containing compound (b2) in combination, the coating film hardness after the retort treatment can be made a preferable range as compared with the amino resin (b1) or the oxazoline group-containing compound (b2) alone system, and scratch resistance and processing can be achieved. It can be set as the coating film balanced in the property.

  Furthermore, by using a certain amount of a specific xylene formaldehyde resin (C), it is a paint with a high solid content and a low viscosity, so it is considered that the coating workability is excellent with a low volatile organic compound (low VOC). It is done.

  Hereinafter, the water-based paint for outer surfaces of the can according to the present invention will be described in detail.

[Water-based paint for outer surface of cans]
Carboxyl group-containing vinyl copolymer resin (A):
The carboxyl group-containing vinyl copolymer resin (A) comprises 10 to 30% by mass of a specific nitrogen-containing radical polymerizable unsaturated monomer (a1) and a carboxyl group-containing radical polymerizable unsaturated monomer (a2) 3. 10% by mass, a hydroxyl group-containing radical polymerizable unsaturated monomer (a3) 3-20% by mass, and a weight average molecular weight obtained by radical polymerization reaction of a monomer component containing other radical polymerizable unsaturated monomer Is less than 6,000 carboxyl group-containing vinyl copolymer resin (A).

  The “weight average molecular weight” or “number average molecular weight” or “average molecular weight” in the present specification is based on the method described in JIS K 0124-83, and “TSKgel G4000HXL”, “TSKgel G3000HXL”, “TSKgel” are used as separation columns. G2500HXL ”and“ TSKgel G2000HXL ”(above, manufactured by Tosoh Corporation) were connected and chromatographed with an RI refractometer at 40 ° C. and a flow rate of 1.0 ml / min using tetrahydrofuran for GPC as an eluent. It is a value obtained from a calibration curve of grams and standard polystyrene.

Nitrogen-containing radically polymerizable unsaturated monomer (a1)
The nitrogen-containing radically polymerizable unsaturated monomer (a1) is represented by the following formula (1).

Formula (1)
(In the formula ^{(1), R 1, R} 2 represent the same or different 1-4 good hydrogen atoms or carbon atoms in the alkyl group or the number 1-4 alkanol group having a carbon.)
Specific examples of the nitrogen-containing radically polymerizable unsaturated monomer (a1) include N-methylol (meth) acrylamide, Nn-methoxymethyl (meth) acrylamide, Nn-butoxymethyl (meth) acrylamide, and the like. Is given. These can be used alone or in combination of two or more. The nitrogen-containing radically polymerizable unsaturated monomer (a1) is preferably 10 to 30% by mass with respect to the total amount of the polymerizable monomer components from the viewpoint of retort resistance and workability.

Carboxyl group-containing polymerizable unsaturated monomer (a2)
The carboxyl group-containing polymerizable unsaturated monomer (a2) is, for example, (meth) acrylic acid, maleic acid, crotonic acid, itaconic acid, fumaric acid, 2-carboxyethyl (meth) acrylate, 2-carboxypropyl (meta) ) And monomers such as 5-carboxypentyl (meth) acrylate, and these can be used alone or in combination of two or more.

  The carboxyl group-containing polymerizable unsaturated monomer (a2) is 3 to 10% by mass based on the total amount of the polymerizable monomer components, and is used for scratch resistance after retorting treatment and paint viscosity adjustment. From the aspect, it is preferable.

Hydroxyl group-containing radical polymerizable unsaturated monomer (a3)
Hydroxyl group-containing radical polymerizable unsaturated monomer (a3) includes 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate , Monoethers of polyether polyols such as polyethylene glycol, polypropylene glycol and polybutylene glycol and hydroxyl group-containing unsaturated monomers such as 2-hydroxyethyl (meth) acrylate; α, β-unsaturated carboxylic acid and Cardura E10 (Japan) Epoxy resin), adducts with monoepoxy compounds such as α-olefin epoxides; addition products of 2-hydroxyethyl (meth) acrylate and caprolactone (for example, Plaxel F under the trade name of Daicel Corporation) -2 and FM-3), hydroxyalkyl esters of acrylic acid or methacrylic acid such as hydroxybutyl (meth) acrylate, etc .; a monoester of (meth) acrylic acid and polypropylene glycol or polyethylene glycol; etc. These may be used alone or in combination of two or more.

  The hydroxyl group-containing radical polymerizable unsaturated monomer (a3) is 3 to 20% by mass based on the total amount of the polymerizable monomer components, and has good wettability and finish and retort resistance. From the viewpoint of improving the property.

  In addition to the above nitrogen-containing radical polymerizable unsaturated monomer (a1), carboxyl group-containing polymerizable unsaturated monomer (a2) and hydroxyl group-containing radical polymerizable unsaturated monomer (a3), other These radically polymerizable unsaturated monomers can be blended.

  Other radically polymerizable unsaturated monomers are not particularly limited as long as they can be copolymerized with a carboxyl group-containing monomer. Specific examples include styrene, vinyltoluene, α-methylstyrene, chloromethylstyrene, Styrene derivatives such as styrene sulfonic acid and salts thereof; (meth) acrylamide derivatives such as (meth) acrylamide, N-monomethyl (meth) acrylamide, N-monoethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide Synthesized by esterification of (meth) acrylic acid such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, cyclohexyl (meth) acrylate and alcohols having 1 to 18 carbon atoms (meth) Acrylates: ethylene, propylene, n-butyl Olefins such as 2-sulfonic acid ethyl (meth) acrylate and salts thereof, unsaturated sulfonic acids such as vinyl sulfonic acid and salts thereof; vinyl esters such as vinyl acetate, vinyl propionate and vinyl stearate; ) Acrylonitrile; vinyl ethers of methyl vinyl ether, ethyl vinyl ether, octyl vinyl ether, lauryl vinyl ether; dimethylaminoethyl (meth) acrylate, dimethylaminoethyl (meth) acrylamide, dimethylaminopropyl (meth) acrylamide, vinylpyridine, vinylimidazole, vinyl Basic unsaturated monomers such as pyrrolidone; (meth) acrylic acid and ethylene glycol, 1,3-butylene glycol, diethylene glycol, 1,6-hexane glycol, neope Polyfunctional (meth) acrylates having two or more polymerizable unsaturated groups in the molecule, such as esters with polyhydric alcohols such as ntile glycol, polyethylene glycol, polypropylene glycol, trimethylolpropane, pentaerythritol, dipentaerythritol ; Organosilicon-containing unsaturated monomers such as vinyltrimethoxysilane, γ- (meth) acryloxypropyltrimethoxysilane, allyltriethoxysilane, trimethoxysilylpropylallylamine; glycidyl (meth) acrylate, 2-methylglycidyl Epoxy group-containing polymerizable monomers such as (meth) acrylate and allyl glycidyl ether; aziridinyl group-containing polymerizable monomers such as (meth) acryloylaziridine and 2-aziridinylethyl (meth) acrylate; Bini , Vinylidene fluoride, vinyl chloride, vinylidene chloride, divinylbenzene, diallyl phthalate; 4- (meth) acryloyloxy-2,2,6,6-tetramethylpiperidine, 4- (meth) acryloylamino-2,2 , 6,6-tetramethylpiperidine, monomers such as 4- (meth) acryloyloxy-1,2,2,6,6-pentamethylpiperidine, and the like, and one or more of these are used. be able to.

  10-30% by mass of the nitrogen-containing radical polymerizable unsaturated monomer (a1) listed above, 3-10% by mass of the carboxyl group-containing radical polymerizable unsaturated monomer (a2), and a hydroxyl group-containing radical polymerizable unsaturated monomer. The radical copolymerization reaction containing 3 to 20% by mass of the saturated monomer (a3) and appropriately using other radical polymerizable unsaturated monomer mixture can be carried out by a well-known method, for example, solution polymerization method, suspension weight Examples thereof include a combination method, a bulk polymerization method, and an emulsion polymerization method.

  When the solution polymerization method is adopted, the polymerization solvent is an aromatic solvent having a high boiling point such as toluene or xylene; an ester solvent such as ethyl acetate, butyl acetate or cellosolve acetate; a ketone solvent such as methyl ethyl ketone or methyl isobutyl ketone. Alcohol solvents such as methyl alcohol, ethyl alcohol, isopropyl alcohol and ethylene glycol; alkylene glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monobutyl ether and propylene glycol monomethyl ether can be used alone or in combination.

  Initiation of radical polymerization of azo compounds such as azobisisobutyronitrile and azobis 2-methylbutyronitrile; peroxide compounds such as benzoyl peroxide and di (tertiary butyl) peroxide An agent can be used, and it is preferably used in an amount of 0.1 to 10% by weight based on the total amount of the polymerizable monomer components. The reaction temperature is usually 40 to 200 ° C., preferably 60 to 150 ° C., and the reaction time is 30 minutes to 8 hours, preferably about 2 to 4 hours.

  The weight average molecular weight of the thus obtained carboxyl group-containing vinyl copolymer resin (A) is less than 6,000, preferably in the range of 3,000 to 5,900. By being less than 6000, the viscosity of the paint is within a certain range, which is good for improving the workability and finishing of the painting.

  Moreover, as a solubility parameter of the said carboxyl group-containing vinyl copolymer resin (A), it is preferable from a compatible surface with an amino resin (b1) that it is 9-13, Preferably it is 10-12. The “solubility parameter (hereinafter referred to as“ SP value ”)” of the carboxyl group-containing vinyl copolymer resin (A) is calculated by applying to the following equation.

δ: SP value of acrylic resin copolymerized from n kinds of acrylic monomers δ _i : SP value of acrylic monomer i component [(cal / cm ³ ) ^0.5 ]
Φ _i : Weight fraction of acrylic monomer i component where δi is described by KL Hoy, Journal of Paint Technology, 42 [541], p76, Feb. 1970. Depends on the value.

  The carboxyl group-containing vinyl copolymer resin (A) can be dissolved or dispersed in an aqueous medium by neutralizing at least a part of the carboxyl groups in the resin with a basic compound. As the basic compound used for neutralization of the carboxyl group, amines and ammonia are preferably used. Representative examples of the amines include alkylamines such as trimethylamine, triethylamine, and tributylamine; alkanolamines such as dimethylethanolamine, diethanolamine, and aminomethylpropanol; and cyclic amines such as morpholine.

  The degree of neutralization of the carboxyl group-containing vinyl copolymer resin (A) is such that the carboxyl group of the basic compound / carboxyl group-containing vinyl copolymer resin (A) is neutralized by 1.1 to 2.0 equivalents. The range is also preferable from the viewpoint of paint stability.

Crosslinking agent (B):
The water-based paint for outer surfaces of cans of the present invention is characterized by containing an amino resin (b1) and an oxazoline group-containing compound (b2) as a crosslinking agent (B).

Amino resin (b1)
Amino resin (b1) is a monohydric alcohol having 1 to 8 carbon atoms, for example, methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n-butyl, part or all of the methylol group of methylolated melamine. Partially etherified or fully etherified melamine resin etherified with alcohol, i-butyl alcohol, 2-ethylbutanol, 2-ethylhexanol, etc., methylol of methylolated benzoguanamine having less than 1 mole of imino group per mole of triazine nucleus A part or all of the groups are monohydric alcohols having 1 to 8 carbon atoms, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol, i-butyl alcohol, 2-ethylbutanol, 2-ethylhexanoe Etc., such as etherified partially etherified or full-etherified benzoguanamine resin. Among these, it is preferable to use a partially etherified or fully etherified benzoguanamine resin for improving scratch resistance after retort resistance.

The amino resin (b1) has a triazine nucleus structure and has a mole number of imino groups (Note 1) of less than 1 mole, preferably 0.2 to 0.9 mole, per mole of triazine nucleus. From the point of cross-linking reactivity with the carboxyl group-containing vinyl copolymer resin (A),
It is preferable in terms of improving the retort property by improving the scratch resistance after the retort treatment of the coating film and reducing the resin elution amount.

(Note 1) Number of moles of imino group: The number of moles of imino group of amino resin (b1) is determined by proton NMR by diluting amino resin (b1) with t-butanol, lyophilizing, dissolving in dimethyl sulfoxide-d6. Was measured. Next, the integral value of the proton peak in the measurement result was read and converted into the functional group amount. For details, refer to Polymer Analysis Handbook, edited by Japan Society for Analytical Chemistry, published on January 12, 1995, first edition, Kinokuniya Co., Ltd., p795-800.

  Moreover, when the number of imino group moles per mole of triazine nuclei in the amino resin (b1) is 1 or more, the number of methylol groups or alkoxymethyl groups that react with the carboxyl group-containing vinyl copolymer resin (A) decreases. May be inferior. For this reason, the coating film hardness after retort resistance may decrease, and the resin elution amount during retort may increase.

Furthermore, the SP value (Note 2) of the amino resin (b1) is preferably in the range of 11.1 to 15.0, preferably 11.2 to 14.0, from the viewpoint of the coating viscosity and the coating workability. If it is out of the above range, the viscosity at 23 ° C. when the solid content is 50% by mass becomes difficult to be 150 to 300 mPa · sec (shear rate 383 sec ⁻¹ ), or roll finish and ink May deteriorate the leveling performance.

  (Note 2) SP value: The SP value of the amino resin can be measured by cloud point titration. Specifically, the data obtained by cloud point titration is expressed by the following K.P. W. SUH and J.H. M.M. It can be calculated by fitting to the CORBETT equation (see Journal of Applied Polymer Science, 12, 2359, 1968).

Where V _H is the volume fraction of n-hexane at the turbid point, V _D is the volume fraction of deionized water at the turbid point, δ _H is the SP value of n-hexane, and δ _D is the deionized water. It is SP value of ionic water.

For cloud point titration, n-hexane was gradually added to an acetone solution of a resin in which 0.5 g (solid content) of a dried test resin was dissolved in 10 ml of dimethyl ketone (acetone), and the titration H (ml) at the cloud point. In the same manner, deionized water is gradually added to the acetone solution of the resin, and the titration amount D (ml) at the cloud point is measured. _H , V _D , δ _H and δ _D can be calculated. In addition, SP value of dimethyl ketone (acetone) is 9.75, SP value of n-hexane is 7.24, and SP value of deionized water is 23.43.
V _H = H / (10 + H)
V _D = D / (10 + D),
δ _H = 9.75 × 10 / (10 + H) + 7.24 × H / (10 + H),
δ _D = 9.75 × 10 / (10 + D) + 23.43 × D / (10 + D).
These amino resins (b1) can be used alone or in combination of two or more.

Oxazoline group-containing compound (b2)
On the other hand, as the oxazoline group-containing compound (b2) used for the crosslinking agent (B), the following general formula (3)

Formula (2)
(In Formula (3), R ⁷ , R ⁸ , R ⁹ and R ¹⁰ are the same or different and each represents hydrogen, halogen, alkyl group, aralkyl group, cycloalkyl group, cycloalkenyl group, aryl group, or substituted aryl group. R ¹¹ represents an alkenyl group or a cycloalkenyl group.) And is obtained by polymerizing a monomer component containing an addition polymerizable oxazoline as an essential component.

The addition-polymerizable oxazoline has a double bond capable of radical addition polymerization at the R ¹¹ portion. Specific examples thereof include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline. 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, 2- Examples thereof include isopropenyl-5-ethyl-2-oxazoline, and one or a mixture of two or more selected from these groups can be used. Among them, 2-isopropenyl-2-oxazoline is preferable because it is easily available industrially.

  The oxazoline group-containing compound (b2) is synthesized from a monomer component containing the addition-polymerizable oxazoline as an essential component, but a polymerizable monomer other than the addition-polymerizable oxazoline contained in the monomer component as necessary. Any body can be used without particular limitation as long as it is copolymerizable with an addition-polymerizable oxazoline and does not contain a carboxyl group.

  Specifically, one or more of the monomers exemplified as the monomer component used as necessary when producing the above-described carboxyl group-containing vinyl copolymer resin (A) can be used. . As the synthesis method, a method similar to the means for synthesizing the carboxyl group-containing vinyl copolymer resin (A) can be used. In addition, it is preferable that the ratio of the addition polymerizable oxazoline in the monomer component is 5 to 100% by weight in order to obtain a coating film having excellent curability.

  When carrying out the addition polymerization reaction, the number average molecular weight can be adjusted by using a chain transfer agent or a regulator such as lauryl mercaptan, 2-mercaptoethanol, carbon tetrachloride or the like. The oxazolinyl group-containing compound may have a number average molecular weight in the range of 1,500 to 40,000 from the viewpoint of obtaining a coating film excellent in processability and scratch resistance after retort.

  In the water-based paint for outer surfaces of cans of the present invention, the compounding ratio of the carboxyl group-containing vinyl copolymer resin (A) and the crosslinking agent (B) is usually the carboxyl group-containing vinyl copolymer resin (A) and the crosslinking agent ( In 100 parts by mass of the total solid content with B), the carboxyl group-containing vinyl copolymer resin (A) is in the range of 30 to 85 parts by mass, more preferably in the range of 40 to 70 parts by mass, and the crosslinking agent (B). It is in the range of 15 to 70 parts by mass, more preferably 30 to 60 parts by mass.

  Furthermore, by using the amino resin (b1) and the oxazoline group-containing compound (b2) as the crosslinking agent (B), the hydroxyl group and carboxyl group in the carboxyl group-containing vinyl copolymer resin (A) are sufficiently crosslinked. Thus, the amount of resin elution in the retort treatment is reduced, and a coating film that is not easily damaged can be obtained in the can transporting process (particularly in a hot state after retorting).

  In this case, the amino resin (b1): oxazoline group-containing compound (b2) is preferably used in the range of 99: 1 (mass%) to 50:50 (mass%) based on the total solid content of the crosslinking agent (B). .

Xylene formaldehyde resin (C):
In the present invention, 0.1% of xylene formaldehyde resin (C) having an average molecular weight of 250 to 500 is added to 100 parts by mass of the total solid content of the carboxyl group-containing vinyl copolymer resin (A) and the crosslinking agent (B). 10 to 10 parts by mass, preferably 0.2 to 8 parts by mass, more preferably 0.5 to 6 parts by mass. By blending the xylene formaldehyde resin (C) in the above range, it is blended in the paint as a resin solid without volatilization like an organic solvent, so that it can be made into a paint with a high solid content and a low viscosity. The obtained coating film is excellent in hardness after retort treatment, and a can body excellent in roll finish and leveling on ink can be obtained.

  The xylene formaldehyde resin (C) can be produced by subjecting xylene, formaldehyde, and optionally phenols to a condensation reaction in the presence of an acidic catalyst.

As said formaldehyde, the compound etc. which generate | occur | produce formaldehyde, such as formalin, paraformaldehyde, and trioxane which are industrially easy to acquire, can be illustrated. In the present specification, when a polymer such as paraformaldehyde or trioxane is used, the blending amount is defined based on one molecule of formaldehyde.
Furthermore, the above-mentioned phenols include monovalent or divalent phenolic compounds having 2 or 3 reaction sites. Specifically, for example, phenols, cresols (o-cresol, m-cresol, p-cresol), para-octylphenol, nonylphenol, bisphenolpropane, bisphenolmethane, resorcinol, pyrocatechol, hydroquinone, para-tert-butylphenol, bisphenolsulfone, bisphenol ether, para-phenylphenol and the like. Or it can use combining 2 or more types. Of these, phenol and cresol are particularly preferred.

  Examples of the acidic catalyst used for the condensation reaction of xylene, formaldehyde, and optionally phenols described above include sulfuric acid, hydrochloric acid, paratoluenesulfonic acid, oxalic acid, etc. Sulfuric acid is preferred. The amount used is usually diluted with water in an aqueous formaldehyde solution, so that the concentration in the aqueous solution can be in the range of 10 to 50% by mass.

  The condensation reaction can be performed, for example, by heating to a temperature at which xylene, phenols, water, formalin and the like existing in the reaction system are refluxed, usually about 80 to about 100 ° C. It can be completed in about hours.

  Under the above conditions, xylene-formaldehyde resin can be obtained by heat-reacting xylene and formaldehyde, and optionally and preferably phenols in the presence of an acidic catalyst. The xylene formaldehyde resin can also be obtained by reacting a xylene formaldehyde resin produced in advance with phenols in the presence of an acidic catalyst.

  The xylene formaldehyde resin (C) thus obtained preferably has an average molecular weight of 250 to 500, preferably 340 to 400, in order to obtain a coating composition for can outer surfaces having a high solid content and a low viscosity.

  The xylene formaldehyde resin (C) preferably has a phenolic hydroxyl group, and generally has a viscosity in the range of 20 to 50,000 mPs (25 ° C.), preferably 30 to 15,000 mPs (25 ° C.). It is also preferable to have a phenolic hydroxyl group equivalent within the range of 100 to 50,000, particularly 200 to 10,000, in order to obtain pencil hardness after retorting.

Commercially available products of such xylene formaldehyde resin (C) include Nikanol Y-50 (average molecular weight 350), Nikanol L (average molecular weight 410), Nikanol 3L (340), Nikanol M (average molecular weight 351) (and above, Mitsubishi) Gas Chemical Co., Ltd.).
Furthermore, the viscosity of the aqueous paint for the outer surface of the can when adjusted to a solid content of 50% by mass and a coating temperature of 23 ° C. is 150 to 300 mPa · sec (shear rate 383 sec ⁻¹ ), preferably 200 to 280 mPa · Second (shear rate 383 seconds ⁻¹ ), more preferably 200 to 230 mPa · second (shear rate 383 seconds ⁻¹ ), so that even a high solid paint has low viscosity and excellent workability. You can get things.

  (Note 3) Viscosity of paint: A container containing a water-based paint for outer surfaces of cans adjusted to 23 ° C. is an E-type viscometer “TV-20” based on the cone-plate viscometer method according to JIS K 5600-2-3. Set to “Type H” (trade name, manufactured by Tokimec Co., Ltd.), measure using a rotor No. “1 degree 34 minutes × R24” type for 1 minute at a rotational speed of 100 rpm, and paint viscosity at the time of convergence (mPa・ Second).

Organic solvent (D):
The water-based paint for outer surfaces of the can of the present invention can contain an organic solvent (D) for the purpose of improving the coating workability. As such an organic solvent (D), the solubility in water at 20 ° C. is 20 g or more with respect to 100 g of water, and the SP value is in the range of 8.5 to 11, preferably 10 to 11. (The SP value of the organic solvent (D) is described in “Solvent Handbook” (Kodansha)). The above range is excellent in compatibility with the carboxyl group-containing vinyl copolymer resin (A) and the crosslinking agent (B), and is suitable from the viewpoint of wettability with respect to wet ink.

  Specific examples include ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, and the like. Among these, diethylene glycol monoethyl ether improves wet ink suitability and has excellent finish.

  The amount of the organic solvent (D) is a solid content of the carboxyl group-containing vinyl copolymer resin (A) and the crosslinking agent (B) from the viewpoint of improving the coating workability due to the low volatile organic compound (low VOC) and low viscosity. 0.1-20 mass parts with respect to a total of 100 mass parts, Preferably it is 0.2-10 mass parts, More preferably, 0.5-5 mass parts is good.

Surfactant Moreover, a surfactant can be blended in the water-based paint for outer surfaces of the present invention, if necessary. The wet ink suitability can be improved by blending a gemini type surfactant among the surfactants. The content of such a Gemini-type surfactant is 10 parts by mass or less, preferably 0.8 parts per 100 parts by mass in total of solid contents of the carboxyl group-containing vinyl copolymer resin (A) and the crosslinking agent (B). 1 to 5 parts by mass.

  The gemini type surfactant is a multi-chain polyhydrophilic group type surfactant having a plurality of hydrophilic groups and a plurality of hydrophobic groups in one molecule. For example, a silicone-based surfactant represented by the following general formula (3) An additive is mentioned.

Formula (3)
(In the formula (3), R ³ is an alkyl group having 1 to 4 carbon atoms or an allyl group, R ⁴ represents the following formula (3),

式（４）
（Ｒ^５は水素原子又はアルキル基、Ｒ^６は水素原子又はアルキル基又はカルボキシル基
ａ＝１〜３ ｂ＝０〜２ ｃ＝１〜２０、ｄ＝０〜５０、ｅ＝０〜５０の整数を表す）
なお、ジェミニ型界面活性剤（Ｅ）の市販品としては、ジェミサーフα１４２、ジェミサーフα１０２、ジェミサーフα１８２、（以上、中京油脂社製、商品名）、Ｔｗｉｎ４０００（ＴＥＧＯ社製、商品名）、フローレンＴＷ４０００（共栄社化学社製、商品名）等、が挙げられる。

Formula (4)
(R ⁵ is a hydrogen atom or an alkyl group, R ⁶ is a hydrogen atom, an alkyl group or a carboxyl group a = 1 to 3 b = 0 to 2 c = 1 to 20, d = 0 to 50, and e = 0 to 50. Represents)
In addition, as a commercial item of gemini type surfactant (E), Gemisurf α142, Gemisurf α102, Gemisurf α182 (above, manufactured by Chukyo Yushi Co., Ltd., trade name), Twin4000 (manufactured by TEGO, trade name), Floren TW4000 ( Kyoeisha Chemical Co., Ltd., trade name).

  In addition to the carboxyl group-containing vinyl copolymer resin (A), the cross-linking agent (B), and the xylene formaldehyde resin (C), the water-based paint for the outer surface of the can according to the present invention further includes an organic solvent (D), an interface as necessary. Add activator, wax, curing catalyst, light interference component, fragrance, ester group-containing reactive diluent, adhesion-imparting agent, antifoaming agent, lubricant, surface tension modifier, etc., add basic compound, It is dissolved or dispersed stably in an aqueous medium.

  Examples of the ester group-containing reactive diluent include PLACEL 205 (molecular weight 530, polycaprolactone diol), PLACEL 305 (molecular weight 530, polycaprolactone triol), PLACEL 800 (molecular weight 530, polycaprolactone triol), (above, Daicel Chemical Industries, Ltd.) ), FLEXOREZ188, and FLEXOREZ148 (above, manufactured by KING INDUSTRIES). By blending an ester group-containing reactive diluent, a paint having a high solid content and a low viscosity can be obtained.

  The amount of the ester group-containing reactive diluent is from 0.1 to 15 parts by mass, preferably from 0.1 to 15 parts by mass, based on 100 parts by mass of the total solid content of the carboxyl group-containing vinyl copolymer resin (A) and the crosslinking agent (B). 2-10 mass parts, More preferably, 0.5-5 mass parts is preferable from the surface of coating workability | operativity and stability.

  The basic compound used for neutralization is not particularly limited, but generally, volatile amines, particularly tertiary amines are preferably used. Examples of the tertiary amine include triethylamine, triethanolamine, N, N-dimethylaminoethanol, N, N-diethylaminoethanol, morpholine and the like.

  The degree of neutralization of the carboxyl group-containing vinyl copolymer resin (A) is a ratio of basic compound / carboxyl group of the carboxyl group-containing vinyl copolymer resin (A) = 1.1 to 2.0 (equivalent ratio). Neutralization is also preferable from the viewpoint of improving the stability of the paint.

Wax In the water-based paint for outer surfaces of the can of the present invention, a wax can be blended as necessary. The wax in this case may be any solid that is solid at room temperature and can impart lubricity to the cured coating surface, for example, a fatty acid ester wax that is an esterified product of a polyol compound and a fatty acid, a silicon-based wax, Mention may be made of waxes such as fluorine wax, polyolefin wax, animal wax and plant wax.

  Examples of the polyol compound used as a raw material for the fatty acid ester wax include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,3- or 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, and glycerin. , Di- or higher polyglycerin, trimethylolpropane, pentaerythritol, dipentaerythritol and the like. Among these, a polyol compound having three or more hydroxyl groups in one molecule is preferable, and among them, polyglycerol, trimethylolpropane, and pentaerythritol are preferable.

  Examples of the fatty acid that is the other raw material of the fatty acid ester wax include saturated or unsaturated fatty acids, preferably fatty acids having 6 to 32 carbon atoms. Specific examples of suitable fatty acids include saturated fatty acids such as caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, serotic acid, montanic acid and melicic acid; Mention may be made of unsaturated fatty acids such as acids, undecylenic acid, palmitoleic acid, oleic acid, linoleic acid, linolenic acid, eleostearic acid, cetoleic acid, erucic acid, ricanoic acid, ricinoleic acid, arachidonic acid. The fatty acid ester wax is preferably one in which at least 1/3 of the number of hydroxyl groups of the polyol compound is esterified with a fatty acid.

  Examples of the silicon-based wax include BYK-300, BYK-320, BYK-330 [more, manufactured by BYK Chemie), Sylwet L-77, same L-720, same L-7602 [more, Japan Konica, Inc.], Paintad 29, 32, M [above, manufactured by Dow Corning], Shin-Etsu Silicone KF-96 (manufactured by Shin-Etsu Chemical), and the like.

  Examples of the fluorine-based wax include SST-1MG, SST-3, Fluoroslip 231, Hydrosurf 6099, Hydrosurf 9174, FLUORO AQ60 (manufactured by Shamrock Chemicals); POLYFLUO 120, POLYFLUO150, POLYFLUO400. (The above is manufactured by Micro Powders Co., Ltd.); Also, hydrocarbon wax particles and polytetrafluoroethylene fine particles are mixed with a powerful mixer such as a jet mill to form hydrocarbon wax particles on the surface. Polytetrafluoroethylene-modified hydrocarbon wax obtained by attaching fine particles of polytetrafluoroethylene can also be used.

  Examples of the polytetrafluoroethylene-modified hydrocarbon wax include Lanco wax TEF1778, Lanco wax TEF1780 (manufactured by George M. Langer and Company), and the like.

Examples of the polyolefin wax include Shamrock Wax S-394, S-395 (above, manufactured by Shamrock Chemicals); Hoechst PE-520, PE-521 (above, manufactured by Hoechst), Mitsui High Wax. (Mitsui Petrochemical Co., Ltd.) and the like, and animal waxes include, for example, lanolin and beeswax, and plant waxes include, for example, carnauba wax and water wax. . Among these waxes, in order to obtain a low dynamic friction coefficient, a fluorine-based wax is preferable.
The wax is usually 0.01 to 10 parts by mass, preferably 0.1 to 5 parts by mass, based on 100 parts by mass of the total solid content of the carboxyl group-containing vinyl copolymer resin (A) and the crosslinking agent (B). It is suitable that it is in the range of 0.3 parts by mass, more preferably 0.3-3 parts by mass.

  By blending the wax, the dynamic friction coefficient of the obtained coating film surface can be lowered. The coefficient of dynamic friction on the surface of the coating is 0.01 to 0.2, preferably 0.01 to 0.15, more preferably 0.01 to 0.12, which is suitable in terms of the smoothness during processing. Yes. The dynamic friction coefficient of the coating film surface can be measured by the following method.

  Coefficient of dynamic friction: The temperature of the test coating plate was kept at 60 °, and the coefficient of dynamic friction was measured on the surface of the coating film using MOBILITY / LUBRICITY TESTER MODEL 9505AER (manufactured by Altek) at a pulling speed of 100 mm / min. The smaller the dynamic friction coefficient, the better the smoothness.

Examples of the curing catalyst that can be contained in the water-based paint for outer surfaces of the present invention include acid catalysts such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, and amines of these acids. A neutralized material etc. can be mentioned.
Examples of the light interference component include vapor-deposited aluminum thin film, aluminum oxide flakes, mica flakes, titanium oxide-coated mica flakes, iron oxide-coated mica flakes, and collestec liquid crystal polymer powder (Helicone HC, trade name, manufactured by Wacker Chemie, Germany ) And the like. Among these light interference components, a colestec liquid crystal polymer is preferable from the viewpoint of processability.

  The addition amount is preferably such that the ink layer as a base can be seen through, and 0.001 to 20 mass per 100 mass parts of the total solid content of the carboxyl group-containing vinyl copolymer resin (A) and the crosslinking agent (B). Parts, preferably 0.01 to 15 parts by weight, more preferably 0.02 to 10 parts by weight. In addition, the coating film containing the light interference component causes interference color in the reflected light from the ink layer. For example, depending on the viewing direction such as a three-dimensional luster or glitter, or the pearl surface, Various colors can be presented.

[About coating film formation method]
The method of forming a coating film using the water-based paint for outer surfaces of cans according to the present invention comprises printing ink on the side of the metal object to be the outer surface of the cans and applying the ink according to the present invention on the printed uncured ink surface. A method of forming a coating film on the outer surface of a can by painting and baking an aqueous coating composition for the outer surface of the can. Examples thereof include a method of coating a laminated film-coated metal plate comprising a resin film with the aqueous paint composition for can outer surface of the present invention and baking it to form a coating film on the outer surface of the can.

  The metal object to be coated is not particularly limited, but is a metal used as a base material for cans such as aluminum, tin, and tin-free steel, and a coated metal having a coating film formed on the surface of these metals. And the like can be suitably used. The shape of the article to be coated may be a molded can shape or a sheet shape before molding.

  The ink is printed on the outer surface of the metal object to be coated, and the water-based coating composition of the present invention is applied onto the printed uncured ink surface. Well-known means such as curtain flow coating, spray coating, electrostatic spray coating and the like can be mentioned. The water-based paint composition is applied so that the dry film thickness is about 2 to 15 μm and is usually baked for about 10 seconds to 20 minutes under the condition that the temperature to be coated reaches 140 to 260 ° C. A coating film can be formed.

  The present invention will be described more specifically with reference to examples. Hereinafter, “parts” and “%” mean “parts by mass” and “% by mass”, respectively.

[Carboxyl group-containing vinyl copolymer resin (A)]
Production Example 1 Production of vinyl copolymer A-1 solution A four-necked flask equipped with a stirrer, a reflux condenser, a thermometer, a dropping funnel and a nitrogen inlet, 110 parts of propylene glycol monomethyl ether, 3-methoxy-3- 40 parts of butanol was added and heated to 125 ° C. with stirring while introducing nitrogen gas. Next, 20.0 parts of Nn-butoxymethylacrylamide, 6.0 parts of acrylic acid, 10 parts of 2-hydroxyethyl methacrylate, 5.0 parts of styrene, 31.0 parts of methyl methacrylate, 28.0 parts of ethyl acrylate A mixture of 8 parts of 2,2′-azobisethylvaleronitrile was added dropwise from a dropping tank over 3 hours. After completion of dropping, the mixture was kept at the same temperature for 0.5 hour, and then 4.5 parts of a solution prepared by dissolving 0.5 part of 2,2′-azobisethylvaleronitrile in 4 parts of propylene glycol monomethyl ether was added over 30 minutes. It was dripped. Next, after aging for 2 hours, a vinyl copolymer A-1 solution having a solid content of 70% was obtained through a solvent removal step. The obtained vinyl copolymer A-1 had a weight average molecular weight of 5,000.

Production Examples 2 to 12 Production of Vinyl Copolymer A-2 to A-12 Solution Except for the contents shown in Table 1, the vinyl copolymer solution A-2 to A-12 solution was prepared in the same manner as in Production Example 1. Obtained.

Production Example 13 Production of vinyl copolymer A-13 solution 100 parts of ethylene glycol monobutyl ether was added to a four-necked flask equipped with a stirrer, reflux condenser, thermometer, dropping funnel and nitrogen inlet, and nitrogen gas was introduced. While stirring, the mixture was heated to 105 ° C.
Next, a mixture of 20.0 parts of Nn-methoxymethylacrylamide, 8.0 parts of acrylic acid, 20.0 parts of styrene, 52.0 parts of ethyl acrylate, and 5 parts of benzoyl peroxide was dropped from a dropping tank over 3 hours. did. After completion of the dropwise addition, the mixture was kept at the same temperature for 1 hour, and then 1 part of benzoyl peroxide was added and reacted for another hour. Next, the temperature was raised to 120 ° C., 0.2 part of phthalic acid was added, and the reaction was carried out for 1 hour while distilling off methanol. 50% of the methoxy group derived from Nn-methoxymethylacrylamide was converted to 2-butoxyethylene glycol. To 2-butoxyethyl ether (—O—CH ₂ CH ₂ —O—C ₄ H ₉ ) by exchanging with methanol and methanol and ethylene glycol monobutyl ether at 100 ° C. under reduced pressure until the nonvolatile content was 70%. Was removed to obtain a vinyl copolymer A-13 solution having a solid content of 70%. The resulting copolymer A-13 had a weight average molecular weight of 19,200.

[Crosslinking agent (B)]
Production Example 16 Production of amino resin b1-1 solution In a four-necked flask equipped with a thermometer, stirrer, reflux condenser, dropping tank, nitrogen gas blowing tube, 374 parts of benzoguanamine, 391.3 parts of 92% paraformaldehyde, methanol 640 parts were charged, and after adding 0.7 parts of 25% aqueous sodium hydroxide solution, the mixture was heated at 60 ° C. for 3 hours. Thereafter, a 50% aqueous sulfuric acid solution was charged until the pH reached 3.5, and the reaction was continued at 60 ° C. for 2 hours. After completion of the reaction, the reaction mixture was neutralized with a 25% aqueous sodium hydroxide solution, and methanol water was removed under reduced pressure, followed by filtration under reduced pressure. The solid content was adjusted to 80% with ethylene glycol monoisopropyl ether to obtain an amino resin b1-1 solution.

Production Examples 17 to 18 Production of Amino Resin b1-2 to b1-4 Solution According to Production Example 14, the reaction was carried out in the amounts of benzoguanamine, paraformaldehyde and methanol shown in Table 2, and amino resin b1-2 to amino resin b1- Four solutions were obtained.

Production Example 19 Production of amino resin b1-5 solution In a four-necked flask equipped with a thermometer, stirrer, reflux condenser, dropping tank, nitrogen gas blowing tube, 187 parts of benzoguanamine, 163 parts of 92% paraformaldehyde, 320 parts of methanol Was adjusted to 10.5 with a 30% aqueous sodium hydroxide solution and heated at 70 ° C. for 1 hour. Thereafter, the mixture was cooled, and a 50% aqueous sulfuric acid solution was charged until the pH reached 1.0, followed by reaction at 40 ° C. for 1 hour. After completion of the reaction, the pH was adjusted to 10.5 with a 30% aqueous sodium hydroxide solution, and formalin and methanol water were removed under reduced pressure. Next, 300 parts of isopropanol was charged, the pH was adjusted to 1.0 with a 50% aqueous sulfuric acid solution, and the reaction was performed at 70 ° C. for 1 hour. Thereafter, the pH was adjusted to 8.5 with a 30% aqueous sodium hydroxide solution, and isopropanol and water were removed under reduced pressure. Precipitated salts were separated by filtration and the solid content was adjusted to 80% with ethylene glycol monoisopropyl ether to obtain an amino resin b1-5 solution.
In combination with Table 2, the amounts of benzoguanamine, paraformaldehyde, methanol and isopropanol in Production Examples 16 to 19, and the analytical values of the imino group amounts and solubility parameters of the obtained amino resins b1-1 to b1-5 Indicates.

Production Example 21 Production of Oxazoline Group-Containing Resin b2-1 Solution A 4-necked flask equipped with a stirrer, thermometer, cooler, dropping funnel and nitrogen gas inlet tube was charged with 66.7 parts of ethylene glycol monobutyl ether, up to 100 ° C. The temperature rose. While blowing nitrogen gas there, 25 parts 2-isopropenyl-2-oxazoline, 40 parts methyl methacrylate, 20 parts styrene, 5 parts ethyl acrylate, 10 parts butyl acrylate and 2.0 parts azobisisobutyronitrile. The mixture was dropped from the dropping funnel over 2 hours, and further kept at 100 ° C. for 4 hours, and then cooled to room temperature to obtain an oxazoline group-containing resin b2-1 solution.

Production Example 22 Production of Oxazoline Group-Containing Resin b2-2 Solution 66.7 parts of ethylene glycol monobutyl ether was charged into a four-necked flask equipped with a stirrer, thermometer, cooler, dropping funnel and nitrogen gas introduction tube at 100 ° C. The temperature was raised to. A mixture comprising 6 parts of 2-vinyl-2-oxazoline, 10 parts of methyl methacrylate, 10 parts of styrene, 50 parts of ethyl acrylate, 24 parts of butyl acrylate and 2.0 parts of azobisisobutyronitrile while blowing nitrogen gas there. Was dropped from the dropping funnel over 2 hours, and further kept at 100 ° C. for 4 hours, and then cooled to room temperature to obtain an oxazoline group-containing resin b2-2 solution.

Production Example 23 Xylene formaldehyde resin no. 1) A 2-liter separable flask equipped with a production thermometer, reflux condenser, and stirrer was charged with 480 parts of 50% formalin, 110 parts of phenol, 202 parts of 98% industrial sulfuric acid, and 424 parts of metaxylene. The reaction was carried out at ˜88 ° C. for 4 hours. After completion of the reaction, the xylene solution in which the resin phase is dissolved and the aqueous sulfuric acid phase are separated, and then the resin phase is washed with water three times and treated for 20 minutes at 20-30 mmHg / 120-130 ° C. Unreacted meta-xylene was distilled off to obtain a phenol-modified xylene formaldehyde resin No. 1 having a viscosity of 1050 mPa · s (25 ° C.). 480 parts of 1 solution were obtained. Xylene formaldehyde resin no. The average molecular weight of 1 is 350.

Example 1
50 parts (solid content) of the copolymer A-1 solution obtained in Production Example 1, 5.56 parts (corresponding to 1.5 equivalents) of dimethylaminoethanol, and amino resin b1-1 obtained in Production Example 16 40 parts (solid content), 10 parts (solid content) of the oxazoline group-containing resin b2-1 obtained in Production Example 21,
Nikanol 3L (Note 5) 1 part (solid content), ethylene glycol monobutyl ether 20 parts and BYK345 (Note 9) 1.0 part (solid content), NACURE 5225 (Note 10) 0.5 part (solid content), And deionized water were mixed to adjust the solid content. 1 was obtained.

Examples 2-15
Except for the contents of Table 3 and Table 4, the same as in Example 1, the can coating Nos. 2-No. 15 was obtained.

  (Note 4) Cymel 350: manufactured by Nippon Cytec Industries, Inc., hexamethoxymethylolmelamine, imino group amount 0, solubility parameter 12.2.

  (Note 5) Nicanol 3L: xylene formaldehyde resin, manufactured by Mitsubishi Gas Chemical Company, average molecular weight 340.

  (Note 6) Nicanol Y-50: xylene formaldehyde resin, manufactured by Mitsubishi Gas Chemical Company, Inc., average molecular weight 350.

  (Note 7) Nikanol G: xylene formaldehyde resin, manufactured by Mitsubishi Gas Chemical Co., Inc., average molecular weight 606.

  (Note 8) Floren TW4000: Kyoeisha Chemical Co., Ltd., trade name, Gemini type surfactant.

  (Note 9) BYK-345: manufactured by BYK Chemie Japan, trade name, silicone-based additive.

  (Note 10) NACURE 5225: King Industries (USA), amine-blocked dodecylbenzene sulfonic acid solution, curing catalyst.

Comparative Examples 1-17
Except for the contents of Table 5 and Table 6, the same as in Example 1, the paint No. 1 for cans of Comparative Examples 1-17. 16-No. 30 was obtained.

Creating test plates
An ink having an oil-modified polyester resin as a main component of a vehicle is printed on an aluminum plate having a plate thickness of 0.26 mm (1 μm), and the water-based coating composition is dried by a roll coating method with the ink remaining undried. A test plate was obtained by coating to a thickness of 5 μm and baking so that the aluminum plate temperature was maintained at 200 ° C. for 90 seconds. The test conditions were as follows. The result of an Example is combined with Table 3 and Table 4, and the result of a comparative example is combined with Table 5 and Table 6, and is shown.

(Note 12) Viscosity of paint: VISCONIC EMD E-type rotation manufactured by Tokimec Co., Ltd. according to JIS K 5600-2-3 cone plate viscometer method at a liquid temperature of 25 ° C. after adjusting the paint to a solid content of 50% by mass. The viscosity was measured with a viscometer and a shear rate of 1.0 sec ⁻¹ ).

(Note 13) Retort resistance:
The test plate was subjected to pressurized steam treatment (retort treatment) at 125 ° C. for 30 minutes in an autoclave, and the coating film after the treatment was observed for blistering and whitening of the coating film. The state of the coating film was evaluated according to the following criteria.
A: No blistering or whitening is observed in the coating film.
○: Blister and whitening are hardly recognized in the coating film.
Δ indicates either blistering or whitening of the coating surface is abnormal. × indicates marked blistering or whitening of the coating surface is abnormal.

(Note 14) Pencil hardness after retort processing:
The test plate is subjected to pressurized steam treatment (retort treatment) at 125 ° C. for 30 minutes in an autoclave, and the pencil scratch test prescribed in JIS K 5600-5-4 (1999) is applied to Mitsubishi Uni (pencil Using a scratch value test, manufactured by Mitsubishi Pencil Co., Ltd., in warm water at 80 ° C. Evaluation was performed according to the following standard of the blurring method.
◎ indicates that the coating film hardness is B or more. ○ indicates that the coating film hardness is 2B or more and less than B. Δ indicates that the coating film hardness is 4B or more and less than 2B. X indicates that the coating film hardness is less than 5B.

(Note 15) Processed part adhesion after retort processing:
The coated plate is punched into a cap shape with a diameter of 25 mm and a height of 10 mm, and after being subjected to pressurized steam treatment (retort treatment) at 125 ° C. for 30 minutes in an autoclave, cello tape (registered trademark) Then, the cellophane (registered trademark) was peeled off, and the peeled state of the coating film was evaluated according to the following criteria.
○: no peeling of coating film is observed
Δ indicates slight peeling of the coating film
X: The peeling of the coating film is remarkable.

(Note 16) Roll finish: The finish of the roll on the undried ink of the test plate was visually evaluated according to the following criteria.
○ indicates that the rolls are not noticeable and the finish is good.
Δ is slightly conspicuous in rolls, but “x” which does not cause a problem as a product clearly shows the rolls and significantly impairs the appearance.

(Note 17) Leveling property on ink: The leveling state of the test plate on the undried ink was evaluated according to the following criteria.
A: Good with no paint surface abnormality.
○ indicates that there is a slight scratch skin on the painted surface, but there is no problem as a product.
X is markedly damaged on the painted surface, impairing the appearance.

(Note 18) Elution amount during retort processing:
The test plate was subjected to pressurized steam treatment (retort treatment) at 125 ° C. for 30 minutes in an autoclave, and the elution amount of the coating film during the retort treatment was calculated from the change in the coating weight before and after the retort.
The mass of the aluminum plate was measured. ... (1)
Each paint was applied to the test plate so as to have a dry film thickness of 5 μm, and the weight of the test plate subjected to heat treatment under the conditions of a set temperature of 200 ° C. and a processing time of 90 seconds was measured. ... (2)
The test plate that had been subjected to pressurized steam treatment (retort treatment) at 125 ° C. for 30 minutes was dried at 130 ° C. for 1 hour to evaporate moisture and measure the weight. ... (3)
The elution amount (%) of the coating film during the retort treatment was measured according to the following formula.
Elution amount after retort treatment (%) = [(2) − (3) / (2) − (1)] × 100
○: Elution amount is less than 1.5% △: Elution amount is 1.5% or more and less than 2% ×: Elution amount is 2% or more and less than 2.5% XX is elution The amount is 2.5% or more.

(Note 19) Storage stability: The paint condition after each can paint was stored at 40 ° C. for one month was evaluated according to the following criteria.
◎: No abnormalities ○: Slightly cloudy △: A small amount of sediment ×: A large amount of sediment

  Can that can form a coating film with excellent scratch resistance with a high hardness coating film that has little resin elution after retort treatment, is easy to treat wastewater, and is hard to be damaged in the process of transport, adhesion and retort processing. Can provide.

Claims (5)

10 to 30% by mass of the nitrogen-containing radical polymerizable unsaturated monomer (a1) represented by the following formula (1) and the carboxyl group-containing radical polymerizable unsaturated monomer with respect to the total of the constituent monomer components. Radical polymerization reaction of monomer components containing 3 to 10% by mass of the monomer (a2), 3 to 20% by mass of the hydroxyl group-containing radical polymerizable unsaturated monomer (a3) and other radical polymerizable unsaturated monomer And a carboxyl group-containing vinyl copolymer resin (A) having a weight average molecular weight of less than 6,000, and an amino resin (b1) having a triazine nucleus structure having less than 1 mol of imino group per mol of triazine nucleus A crosslinking agent (B) comprising an oxazoline group-containing compound (b2) having an average molecular weight of 1,500 or more and less than 40,000,
In addition, xylene formaldehyde resin (C) having an average molecular weight of 250 to 500 is 0.1 to 0.1 parts by mass with respect to 100 parts by mass of the solid content of the carboxyl group-containing vinyl copolymer resin (A) and the crosslinking agent (B). A water-based paint for can outer surfaces, containing 10 parts by mass.

Formula (1)
(In the formula ^{(1), R 1, R} 2 represent the same or different 1-4 good hydrogen atoms or carbon atoms in the alkyl group or the number 1-4 alkanol group having a carbon.) The water-based paint for outer surfaces of cans according to claim 1, wherein the solubility parameter of the amino resin (b1) is in the range of 11.1 to 15.0. An organic solvent (D) having a solubility in water at 20 ° C. of 20 g or more per 100 g of water is 0 with respect to 100 parts by mass of the solid content of the carboxyl group-containing vinyl copolymer resin (A) and the crosslinking agent (B). The water-based paint for outer surfaces of cans according to claim 1 or 2, containing 1 to 20 parts by mass. The water-based paint for can outer surfaces according to any one of claims 1 to 3, which is coated as an uppermost layer of the outer surface of the can. The ink is printed on the side of the metal object to be the outer surface of the can, and the water-based paint for the outer surface of the can according to any one of claims 1 to 4 is dried on the printed uncured ink surface. A method for forming a coating film, comprising coating to a thickness of 2 to 15 μm and baking for 10 seconds to 20 minutes under a condition that the temperature to be coated reaches 140 to 260 ° C.