JP2006206760A - Water-based coating composition for aluminum DI can and aluminum DI can having a cured coating layer of the composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum water-based coating composition for DI cans capable of forming a coating film having a design property exhibiting high luster and having adhesion and workability capable of withstanding a pressurized steam treatment process.
A glass flake pigment whose surface is plated with silver, a binder resin having a water-based acrylic resin, a water-based polyester resin, and a water-based amino resin, the pigment having an average particle diameter of 10 to 50 μm, and a binder The water-based paint composition for aluminum DI cans, wherein the pigment content is 1 to 30 parts by mass with respect to 100 parts by mass of the resin solid content.
[Selection figure] None

Description

  The present invention provides an aluminum DI can (squeezed iron can) with an aqueous paint composition for an aluminum DI can, which has a glittering and bright design and exhibits excellent retort resistance, and the paint composition. The present invention relates to an aluminum DI can having a cured coating film.

  2. Description of the Related Art Conventionally, a coating material that forms a coating film having a glittering property with an emphasis on designability has been employed in cosmetic and beverage 3P cans. In recent years, high luster design has been required for aluminum DI cans, and metal pigments such as aluminum paste and aluminum flakes have been used. In the case of aluminum DI beverage cans, pressurized steam treatment for sterilization of the contents is performed, so the coating film is also required to have resistance to such treatment (retort resistance), and an epoxy-amino resin. Solvent-type paints mainly composed of organic solvent solutions such as acrylic-amino resins and polyester-amino resins are used. However, this method causes a large amount of solvent volatilization during drying, which causes air pollution and is not preferable from the viewpoint of resource saving. Therefore, in order to solve these problems, paints substituted with various water-based resins have been proposed. However, attempts have been made to add aluminum flake pigments in an attempt to give the water-based resin a design that exhibits further high brightness. There is a fatal problem that causes outbreaks. Furthermore, the retort resistance tends to deteriorate, and it has been difficult for water-based paints to achieve both high luster design and retort resistance. There is an example in which a high brightness pigment in which a metal thin film is coated on a glass flake by a sputtering method is used for automobile body painting, home appliance painting, etc. (see, for example, Patent Document 1) No water-based paint is known.

JP-A-9-188830

  The object of the present invention is to solve the above-mentioned problems of the prior art, have a design property that exhibits high brightness when coated on the outer surface of an aluminum DI can, and has heat resistance that can withstand a pressurized steam treatment process. , An aqueous DI composition for an aluminum DI can capable of forming a coating film having water resistance, adhesion and processability that can be processed into various can forms, and an aluminum DI having a cured coating film layer of the coating composition To provide a can.

  As a result of intensive studies, the present inventors can form a coating film that can satisfy the above-mentioned characteristics by using a glass flake pigment exhibiting high luster and a specific water-soluble resin subjected to a specific surface treatment. The present inventors have found an aqueous coating composition and have reached the present invention.

  That is, the present invention first comprises a binder resin (B) having a glass flake pigment (A) plated with silver on the surface, an aqueous acrylic resin (a), an aqueous polyester resin (b) and an aqueous amino resin (c). The pigment (A) has an average particle size R (μm) in the range of 10 to 50 μm, and the pigment content relative to 100 parts by mass of the binder resin (B) solid content is 1 to 30 parts by mass. A water-based paint composition for aluminum DI cans is provided.

  In the second aspect of the invention, the aluminum has a coating layer obtained by curing the above-described aqueous coating composition for an aluminum DI can as a base coat layer on the outer side wall of the aluminum DI can. Providing DI cans.

  The water-based coating composition for aluminum DI cans according to the present invention has a heat-resistant, water-resistant, various can forms capable of withstanding the pressurized steam treatment process on the outer surface of the aluminum DI can, which has a design that exhibits high brightness. It is possible to form a cured coating film layer having adhesiveness and workability that can be processed into a thin film.

  The water-based paint composition for aluminum DI cans of the present invention is mainly composed of a glass flake pigment (A) plated with silver on the surface, a water-based acrylic resin (a), and a water-based polyester resin (b), and a water-based amino resin (c). A binder resin (B) having a binder as a curing agent, the average particle size R (μm) of the pigment (A) is in the range of 10 to 50 μm, and the binder resin (B) has a solid content of 100 parts by mass. The pigment content is 1 to 30 parts by mass. In addition, an average particle diameter shall be represented by median D50.

  The glass flake pigment (A) used for the water-based paint composition for aluminum DI cans according to the present invention is plated with silver on glass flakes having a thickness of about 1 to 2 μm and an average particle size of about 10 to 50 μm. Glass flake pigment. The silver surface may be further subjected to a surface coating treatment with a silane coupling agent or the like, and may be a glass flake pigment exhibiting stronger high luminance. If the average particle size is less than 10 μm, sufficient high brightness is difficult to obtain, and if it exceeds 50 μm, high brightness can be obtained, but damage to the rubber roll or scraper tends to occur due to restrictions on coating conditions.

  The preferable average particle diameter and content of the pigment described above are such that the particle diameter is in the range of 25 to 40 μm, and the content of the pigment with respect to the binder resin solid content is 5 to 20 mass%.

  Examples of commercially available pigment components include Metashine ME2025PS (Median D50: 25 μm) manufactured by Nippon Sheet Glass Co., Ltd., and Metashine ME2040PS (Median D50: 40 μm) manufactured by the same company. These have a glass thickness of about 1 μm and a silver plating thickness of about 0.05 μm.

  The binder resin used in the water-based paint composition for aluminum DI cans of the present invention contains a water-based acrylic resin (a), a water-based polyester resin (b), and a water-based amino resin (c).

  For example, when the total resin solid content is 100 parts by mass, the aqueous acrylic resin (a) 30 to 40 parts by mass, the aqueous polyester resin (b) 20 to 30 parts by mass, and the aqueous amino resin (c) 40 to 50 parts by mass. Can be used in combination and an acid catalyst can be added as a catalyst.

  As the aqueous acrylic resin (a) constituting the binder resin (B), for example, a monomer mixture composed of a vinyl monomer containing a carboxyl group and a vinyl monomer containing a functional group for crosslinking is used as a radical in various organic solvents. Examples thereof include a copolymer obtained by polymerization and having a number average molecular weight of about 1,000 to 3,000. The functional group for crosslinking here is a functional group capable of reacting with a so-called crosslinking agent component such as amino resin, epoxy resin, polyisocyanate compound or polycarboxylic acid when used as a functional group for thermosetting. Means. Of course, it is also possible to use an aqueous acrylic resin having a low organic solvent content obtained by distilling off an excess organic solvent under reduced pressure from the copolymer solution thus obtained.

  Typical examples of the carboxyl group-containing vinyl monomer used in preparing the aqueous acrylic resin (a) include acrylic acid, methacrylic acid, maleic acid, and fumaric acid. Or use of methacrylic acid or the like is desirable. The amount of the carboxyl group-containing vinyl monomer used is about 1 to 25% by mass, preferably about 2 to 15% by mass, based on the total amount of monomers.

  Among the functional group-containing vinyl monomers for crosslinking, typical examples of the hydroxyl group-containing vinyl monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, and 4-hydroxybutyl (meth) acrylate. , Hydroxypentyl (meth) acrylate, hydroxyhexyl (meth) acrylate, and the like. An appropriate amount of these hydroxyl group-containing vinyl monomers is about 1 to 40% by mass.

  Furthermore, typical examples of other vinyl monomers copolymerizable with these vinyl monomers include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, Various (meth) acrylic acids such as tert-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, cyclohexyl (meth) acrylate, or benzyl (meth) acrylate Esters; various N-alkoxyalkyl-substituted amide-containing vinyl monomers such as N-methoxymethyl (meth) acrylamide, N-isobutoxymethyl (meth) acrylamide or Nn-butoxymethyl (meth) acrylamide Various aromatic vinyl monomers such as styrene, vinyltoluene, or α-methylstyrene; such as dimethyl maleate, dibutyl maleate, dimethyl fumarate, dibutyl fumarate, dimethyl itaconate or dibutyl itaconate And dialkyl esters of various unsaturated dibasic acids; or various vinyl esters such as vinyl acetate, vinyl propionate, vinyl pivalate or vinyl versatate.

  As the aqueous polyester resin (b) constituting the binder resin (B), for example, polyol and polycarboxylic acid (anhydride) are heated and melted, and the reaction product has an acid value of about 160 to 270 ° C. If necessary, dehydration condensation is performed under reduced pressure until it becomes about 1 to 40 (mgKOH / g), and after obtaining a dehydration condensate having a number average molecular weight of about 500 to 25,000, it is dissolved in various organic solvents. Examples include those prepared by caulking.

  Typical examples of polyols used in preparing the aqueous polyester resin (b) include ethylene glycol, propylene glycol, 1.3-butylene glycol, 1.4-butylene glycol, 1.6-hexanediol. Or various dihydric alcohols such as diethylene glycol, dipropylene glycol, neopentyl glycol, triethylene glycol or hydrogenated bisphenol A, bisphenol A ethylene oxide adduct or bisphenol A propylene oxide adduct; and glycerin, trimethylol Various trivalent or higher alcohols such as ethane, trimethylolpropane, trishydroxymethylaminomethane, pentaerythritol, dipentaerythritol or diglycerin Kind, and the like.

  Typical examples of the polycarboxylic acid (anhydride) used in preparing the aqueous polyester resin (b) include propanetricarboxylic acid, butanetetracarboxylic acid, adipic acid, phthalic acid, terephthalic acid or trimellit Examples thereof include various aliphatic or aromatic polycarboxylic acids such as acids, (anhydrous) trimellitic acid, methylcyclohexentricarboxylic acid (anhydride), and (anhydrous) pyromellitic acid. Further, various monobasic acids such as benzoic acid and tert-butylbenzoic acid can be used in combination as the acid component as necessary.

  Examples of the aqueous amino resin (c) constituting the binder resin (B) include an alkyl etherified melamine resin, an alkyl etherified benzoguanamine resin, an alkyl etherified urea resin, an alkyl having a number average molecular weight of about 300 to 2,000. Examples include etherified acetoguanamine resins, alkyletherified spiroguanamine resins, and alkyletherified cyclohexylguanamine resins.

  Typical examples of alcohols for etherification include methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, sec-butyl alcohol, tert-butyl alcohol, cyclohexanol, and n-octyl alcohol. , Sec-octyl alcohol or 2-ethylhexyl alcohol, various C1-C8 alcohols; various ether alcohols such as ethylene glycol monomethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, or diethylene glycol monomethyl ether Or various ketone alcohols such as ketobutanol, diacetone alcohol or acetoin . These may be used alone or in combination other than two kinds.

  As the alkyl etherified amino resin, a butyl etherified amino resin is preferable, and examples thereof include use of a butyl etherified melamine resin, a butyl etherified benzoguanamine resin, a butyl etherified spiroguanamine resin, a butyl etherified acetoguanamine resin, or a butyl etherified cyclohexylguanamine resin. Particularly desirable.

  The aqueous coating composition for aluminum DI cans of the present invention is an aqueous coating composition in which a coating component is dissolved in a water-soluble solvent. Examples of such water-soluble solvents include various ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, or diacetone alcohol; ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, ethylene Glycol diethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol diethyl ether, diethylene glycol monoethyl ether, diethylene glycol diethyl ether, diethylene glycol monobutyl ether, triethylene glycol dimethyl ether, propylene glycol monomethyl ether Or various glycols such as propylene glycol dimethyl ether; or, i- propanol, n- butanol, various alcohols such as i- butanol. Of course, these may be used alone or in combination of two or more, and may also be in a form in which a small amount of other water-insoluble solvent is mixed.

  If necessary, the water-based paint composition for aluminum DI cans of the present invention may have various acid catalysts such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthylene disulfonic acid, or phosphoric acid; Various amine salts and the like may be added as a curing catalyst. The amount of the curing catalyst is usually about 0.1 to 1.0 part by mass with respect to 100 parts by mass of the binder resin solid content. Furthermore, various additives such as leveling agents, antifoaming agents, and lubricants that are usually used in paints can also be blended.

  The aluminum water-based paint composition for DI cans of the present invention can be produced by a conventional method, for example, using a mixing device such as a turbo mill or a dispersion stirrer.

The aqueous coating composition for aluminum DI cans of the present invention is preferably used for a base coat layer on the outer surface of an aluminum DI can. In order to apply to an aluminum DI can, for example, after applying 60 to 200 mg / dm ² (about 6 to 20 μm in dry film thickness) to the outer surface of the can by using a roller or the like with a body coater for DI can, etc. By baking at a temperature of about 130 to 250 ° C. under a heating condition of about 5 seconds to 10 minutes, a desired cured coating film can be formed. Preferably, it is 200 ° C. for 15 seconds, which is the baking condition for the aluminum DI can. The resulting coating film has high brightness and excellent gloss, is highly brilliant in design, and is suitable as a printing foundation.

  When a desired pattern, label logo, or the like is printed on the base coat layer, a clear print layer can be formed. On the printed layer, a top coat layer can be formed by a conventional method if necessary.

  Hereinafter, the present invention will be described specifically by way of examples. Unless otherwise specified, “part” and “%” in the examples represent “part by mass” and “% by mass”.

Synthesis Example 1 [Synthesis of aqueous acrylic resin (solution) (a)]
Into a four-necked flask reaction vessel equipped with a stirrer, reflux condenser, dropping funnel, nitrogen gas inlet tube, and thermometer, 483 parts of ethylene glycol monoisopropyl ether was charged and heated to 110 ° C. While maintaining the same temperature, 223 parts of ethyl acrylate, 130 parts of n-butyl acrylate, 279 parts of methyl methacrylate, 102 parts of 2-ethylhexyl acrylate, 52 parts of 2-hydroxyethyl methacrylate, N- (isobutoxy) A mixture comprising 47 parts of methyl) acrylamide, 56 parts of acrylic acid, 19 parts of 2,2′-azobis (2-methylbutyronitrile), and 9 parts of di-tert-butyl peroxide was continuously added dropwise over 4 hours. One hour after completion of the dropwise addition, 9 parts of di-tert-butyl peroxide was added, and the reaction was further performed at the same temperature for 2 hours. The resulting resin solution was distilled off 326 parts of ethylene glycol monoisopropyl ether, and the residual solvent was neutralized with 66 parts of dimethylethanolamine, and 149 parts of butyl diglycol and 422 parts of ion-exchanged water were added. Dilution was performed to obtain a transparent viscous aqueous acrylic resin (aqueous solution) (a) having a nonvolatile content of 50.0%, a viscosity (Gardner bubble viscosity of 25 ° C.) of W, and a weight average molecular weight of 10,000.

Synthesis Example 2 [Synthesis of aqueous polyester resin (solution) (b)]
In a reaction vessel equipped with a stirrer, reflux condenser, rectification tube, decanter, nitrogen gas introduction tube and thermometer, 684 parts of hexahydrophthalic anhydride, 122 parts of 1,6-hexanediol, 404 parts of trimethylolpropane, 51 diethylene glycol 51 The portion was charged and heated to 160 ° C. to dissolve the contents. From the same temperature, the temperature was raised to 200 ° C. in 4 hours while distilling condensed water out of the system. The reaction was carried out at the same temperature for 5 hours. When the acid value of the reaction product reached 50.0 (mgKOH / g), it was cooled to 130 ° C., and 368 parts of ethylene glycol monoisopropyl ether and 241 parts of diethylene glycol monobutyl ether were added to obtain a uniform solution. The temperature was further lowered to 90 ° C. and neutralized with 94 parts of dimethylethanolamine to obtain a water-soluble polyester resin (solution) (b). The non-volatile content is 61.0%, the viscosity (Gardner bubble viscosity 25 ° C.) is W, the acid value (solid content) is 50.0 (mgKOH / g), and the hydroxyl value (solid content) is 100.5 (mgKOH / g). )Met.

Synthesis Example 3 [Synthesis of aqueous amino resin (c)]
A four-necked flask reaction vessel equipped with a stirrer, reflux condenser, dropping funnel, nitrogen gas inlet tube and thermometer was charged with 384 parts of methanol, 91.8 parts of 92% paraformaldehyde, and 187 parts of benzoguanamine and heated with stirring. The temperature was raised to 70 ° C., and the reaction solution became uniform 10 minutes after reaching the same temperature. Furthermore, after reacting at the same temperature for 1 hour, the temperature was lowered to 60 ° C. Next, 5 parts of 85% phosphoric acid was added, the reaction temperature was raised to 70 ° C., the reaction was carried out for 2 hours after reaching this temperature, the temperature was lowered to 60 ° C., and pH was adjusted to 8. with 40% sodium hydroxide. The reaction mixture was adjusted to 0, and unreacted methanol, formaldehyde and water were distilled off under reduced pressure (10 kgPa), and 150 parts of ethylene glycol monobutyl ether was added and filtered. A colorless aqueous amino resin (solution) (c) having a nonvolatile content (measurement condition = 108 ° C./1 hour) of 70.0% was obtained. The viscosity (Gardner bubble viscosity 25 ° C.) was Y, and the number of colors by the Gardner method was 1 or less.

Examples 1-12, Comparative Examples 1-15
25 parts of aqueous acrylic resin (a) obtained in Synthesis Example 1, 13.1 parts of aqueous polyester resin (b) obtained in Synthesis Example 2, 21.6 parts of amino resin (c) obtained in Synthesis Example 3, and catalyst 0.06 part of acid catalyst "Nicure 2500" (manufactured by King), 7.8 parts of butyl diglycol, and 34.0 parts of ion-exchanged water are mixed and stirred with a turbo mill, the amount of organic solvent is 28%, non-volatile content 35% work-in-process paint composition was obtained. To this work-in-process coating composition, the following high-brightness glass flake pigment was added in the amount shown in Table 1 (binder resin component (B) per 100 parts by mass of solid content), and mixed with a disper for 10 minutes for coating. Each paint composition was obtained by adjusting the viscosity so as to have an appropriate viscosity.

The following pigments were used as silver-plated glass flakes.
(A1) Glass flake pigment with silver plating on the glass surface: average particle size 25 μm
(Nippon Sheet Glass Co., Ltd. Metashine ME2025PS Median D50: 25 μm)
(A2) Glass flake pigment with silver plating on the glass surface: average particle size of 40 μm
(Metashine ME2040PS made by Nippon Sheet Glass Co., Ltd. Median D50: 40 μm)
(A3) Glass flake pigment with silver plated on the glass surface: average particle size of 80 μm
(Metashine ME2080PS Median D50: 80 μm manufactured by Nippon Sheet Glass Co., Ltd.)

About the coating compositions of Examples 1 to 12 and Comparative Examples 1 to 15 obtained in each of the above rows, using a 9-inch test coater and a mandrel, collected from a can can manufacturer's actual can line, before paint printing 350 ml of aluminum DI base can (base plate: thickness 0.30 mm, 3004 aluminum alloy thin plate, DI molding ironing rate of about 60%), so that the dry coating amount is 100 mg / dm ² And then cured by heating in a hot-air circulating gas oven at 200 ° C. for 15 seconds. Furthermore, after applying the inner surface coating material to the inner surface of the can, it was dried in a hot air circulating gas oven at 200 ° C. for 60 seconds to prepare a test can. The test can was opened and the panel was used for the next test.

(High brightness)
By visual evaluation

(Missing property)
A small paint tester is used as a misting tester and black paper is placed before and after the composition roll. Rotate the misting tester at 1000 revolutions / minute in the same manner as painting. A 1-minute mist is attached to black paper and visually judged.

(Flow property)
The aluminum plate is coated with the misting tester and baked in an oven at a set time of 0. The flowability is visually determined on the surface of the cured coating.

(Scraper scratches)
Set a scraper that has been ground and smoothed with a grindstone on a 9-inch test coater, and operate the coater in the same manner as painting. Lightly touch the scraper with the impression roll and scrape the paint. Immediately after starting, paint is applied to the aluminum plate after 5 minutes and 10 minutes. Since the back surface dirt (dirty back) of the paint plate occurs according to the scratch of the scraper, the degree of dirt and the scratch of the scraper blade is visually determined.

(Boiling water resistance test)
After immersing the test panel in boiling water for 30 minutes, the state of the coating film is evaluated.

(Retort resistance test)
After exposing the test panel to water vapor at 130 ° C. for 30 minutes in a pressurized container, the state of the coating film is evaluated.

(Workability test)
According to the Eriksen test.

(Impact resistance test)
The state of the coating film after processing is evaluated under the conditions of a DuPont impact test, 500 g-10 cm, 20 cm, and 30 cm.

The evaluation criteria are as follows.
○: Good △: Somewhat bad ×: Bad

The cured coating film obtained from the aluminum DI can outer surface aqueous paint composition of the present invention has heat resistance that can withstand the pressurized steam treatment process, water resistance, and adhesion and workability that can be processed into various can forms, Since it has a design that exhibits a strong and high brightness of the reflected light, it is widely used for various beverage cans and food cans.

Claims (6)

A pigment flake pigment (A) plated with silver on the surface, a binder resin (B) having an aqueous acrylic resin (a), an aqueous polyester resin (b) and an aqueous amino resin (c), and the pigment (A) described above The average particle size R (μm) of the aluminum is in the range of 10 to 50 μm, and the pigment content is 1 to 30 parts by mass with respect to 100 parts by mass of the binder resin (B) solid content. Water-based paint composition for cans. 2. The aluminum DI can according to claim 1, wherein the average particle diameter R (μm) of the pigment is in the range of 25 to 40 μm, and the content of the pigment with respect to the binder resin solid content is 5 to 20% by mass. Water-based paint composition. The water-based coating composition for aluminum DI cans according to claim 1 or 2, which is used for an outer surface base coat of an aluminum DI can. It has the coating-film layer obtained by hardening | curing the water-based coating composition for aluminum DI cans described in any one of Claims 1-3 as a basecoat layer in the side wall outer surface of aluminum DI cans. Aluminum DI can. The aluminum DI can according to claim 4, wherein the amount of the cured coating film of the aluminum aqueous DI paint composition for DI can is 60 to 200 mg / dm ² . The aluminum DI can according to claim 4 or 5, wherein the aluminum DI can has a desired printed layer on an outer surface of the side wall of the aluminum DI can.