JP2020041064A - Aqueous coating, and coated can - Google Patents

Abstract

To provide an aqueous coating that can form a coating film that does not contain an epoxy resin having a phenol skeleton such as BPA, has excellent storage stability, and has excellent workability, retort resistance, anticorrosiveness, and a coated can having a coating film of the aqueous coating.SOLUTION: An aqueous coating contains an emulsion (X), and a curing agent (C). The emulsion (X) contains a composite polymer (AB) and an aqueous dispersion medium. The composite polymer (AB) is obtained by polymerizing an acrylic monomer (b) in an aqueous dispersion or aqueous solution containing an olefinic polymer (A) having a carboxyl group and an ethylenically unsaturated bond with an acid value of 50 mgKOH/g or more.SELECTED DRAWING: None

Description

  The present invention relates to a water-based paint and a coated can.

  2. Description of the Related Art Conventionally, an inner surface of a metal can using a metal material such as tinplate, tin-free steel, and aluminum has been provided with a synthetic resin protective coating in order to prevent metal corrosion due to contents (food, beverages, and the like).

  The coating film formed from the coating material used for coating is required to have excellent corrosion resistance, retort resistance and workability due to the contents. "Excellent workability" means that after forming a coating film on a can material (metal substrate for a can), the coating film is not damaged even if the can material and the coating film are molded together. For example, a higher degree of workability is required for a member having many irregularities such as a bottle can having a thread at the neck for fitting with a cap member or a lid member requiring a tab to be attached. As paints that exhibit these required physical properties, aqueous paints using a self-emulsifying epoxy resin of a bisphenol type epoxy resin and an acrylic resin and a phenol resin have been widely used.

  Patent Literature 1 discloses a water-based paint containing a self-emulsifying bisphenol-type epoxy resin (A) and a phenol resin (D). According to Patent Document 1, the coating film of the water-based paint is said to be capable of obtaining a coating film in which flavor components in the beverage are hardly adsorbed, excellent in corrosion resistance to a beverage containing sulfite, and excellent in processability. ing.

However, in recent years, the use of a resin containing bisphenol A (hereinafter referred to as BPA) as a component in containers for infants such as baby bottles is being restricted in other countries due to concerns about toxicity of environmental hormones.
For this reason, in the field of food containers and packaging, in addition to the demand for paints for inner surfaces of cans that do not use BPA-type epoxy resins, the demand for water-based paints is increasing due to the regulation of volatile organic compounds (hereinafter referred to as VOCs). ing

  Patent Document 2 discloses an acrylic-modified polyester resin obtained by graft-polymerizing a specific acrylic monomer containing a carboxyl group onto a polyester resin containing an ethylenically unsaturated bond as an aqueous coating containing no BPA type epoxy resin. An aqueous coating composition for the inner surface of a can is disclosed.

  Patent Document 3 discloses that a monomer (A) is emulsified in water by an acrylic copolymer (B) formed from a specific monomer, and the monomer (A) is subjected to radical polymerization to obtain a polymer emulsion (D1). It is disclosed that the polymer emulsion (D1) and the phenol resin (E) are mixed to obtain an aqueous paint, and that the aqueous paint is used as a can coating.

JP 2006-36964 A JP-A-2002-302639 JP 2015-193834 A

  However, the coating film formed from the can inner surface coating composition described in Patent Literature 2 has insufficient retort resistance. In addition, the water-based paint described in Patent Document 3 has a problem that high workability and corrosion resistance are insufficient.

  The present invention has been made in view of such circumstances, and does not include an epoxy resin having a BPA (bisphenol A) skeleton, is excellent in processability, and is excellent in retort resistance and corrosion resistance. An object of the present invention is to provide a water-based paint that can be formed, and a coated can having a coating film of the water-based paint.

  The aqueous coating composition according to the present invention has an acrylic monomer (A) in an aqueous dispersion or aqueous solution containing an olefin polymer (A) having a carboxyl group and an ethylenically unsaturated bond and having an acid value of 50 mgKOH / g or more. It contains an emulsion (X) containing a composite polymer (AB) obtained by polymerizing b) and an aqueous dispersion medium, and a curing agent (C).

  The coated can according to the present invention has a can material and a coating film of the water-based paint of the embodiment on at least a part of the surface of the can material.

  According to the present invention, a water-based paint that does not contain an epoxy resin having a phenol skeleton such as BPA and that can form a coating film having excellent workability, retort resistance, and corrosion resistance, and coating of the water-based paint It is possible to provide a coated can having a membrane.

FIG. 1 illustrates a method for producing a test piece for a workability test. (A) A schematic diagram before bending a test panel, (b) a schematic diagram for explaining how to produce a test piece by bending the test panel, and (c) a schematic diagram for explaining a method of dropping a weight on the test piece.

Hereinafter, the water-based paint and the coated can of the present invention will be described.
In this embodiment, the monomer and the acrylic monomer are ethylenically unsaturated monomers. In addition, (meth) acrylic acid includes each of acrylic acid and methacrylic acid, and (meth) acrylate includes each of acrylate and methacrylate.
In the present embodiment, “polymer (polymer)” includes “copolymer (copolymer)”.
In the present embodiment, “water-soluble” means that the solubility in water is 1.0 part by mass or more under a condition of 20 ° C. The term "nonionic" refers to a property in which neither a cation portion nor an anion portion can be formed in the molecular structure in water. A property in which at least one of a cation portion and an anion portion can exist in the structure.
Moreover, in this embodiment, a coating film means the coating film after bridge | crosslinking which apply | coated the aqueous coating composition to base materials, such as a metal plate.

[Water-based paint]
As described above, the water-based paint of the present invention has an acrylic dispersion in an aqueous dispersion or an aqueous solution containing an olefin-based polymer (A) having a carboxyl group and an ethylenically unsaturated bond and having an acid value of 50 mgKOH / g or more. An emulsion (X) containing a composite polymer (AB) obtained by polymerizing the system monomer (b) and an aqueous dispersion medium, and a curing agent (C) are included.
The composite polymer (AB) here is not a simple mixture but a resin in which at least a part of the olefin-based polymer (A) and at least a part of the acrylic-based polymer (B) are bonded to each other. It is not possible to directly specify the structure of the composite polymer (AB).

<Olefin polymer (A)>
The olefin polymer (A) used in the present invention is an olefin polymer having a carboxyl group and an ethylenically unsaturated bond and having an acid value of 50 mgKOH / g or more. For example, a modified olefin (co) polymer obtained by modifying a polyolefin such as polyethylene or polypropylene homopolymer with a carboxylic acid, or an olefin copolymer which is a copolymer of an α-olefin monomer and a monomer having a carboxyl group, is used in the following method. Is a polymer having an ethylenically unsaturated bond introduced therein.

  Since the olefin polymer (A) has a carboxyl group, it becomes possible to stably emulsify the acrylic monomer (b) described later in an aqueous medium. Then, by polymerizing the acrylic monomer (b) and the olefin polymer (A) in a stable emulsified state, the generation of coarse particles of the composite polymer (AB) in the obtained emulsion (X) is suppressed, and the dispersion is stable. Performance can be improved. Further, since the olefin-based polymer (A) in the composite polymer (AB) has a carboxyl group, the adhesion of a coating film obtained by applying an aqueous coating material to a metal material or the like can be improved.

Examples of the polyolefin include, but are not particularly limited to, ethylene, propylene, 1-butene, 3-methyl-1-butene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-heptene, 1-hexene, -Octene, a polymer of an α-olefin monomer such as 1-decene and 1-dodecene, specifically, polyethylene, polypropylene, poly-1-butene, poly-3-methyl-1-butene, poly-4 Olefin homo, such as -methyl-1-pentene, poly-3-methyl-1-pentene, poly-1-heptene, poly-1-hexene, poly-1-octene, poly-1-decene, poly-1-dodecene, etc. polymer,
Olefin copolymers such as ethylene-propylene copolymer, ethylene-1-butene copolymer, and propylene-1-butene copolymer are exemplified.

The carboxyl group of the olefin-based polymer (A) may be obtained by obtaining a polyolefin such as an olefin homopolymer or an olefin copolymer, and then introducing a carboxyl group into a side chain or copolymerizing an olefin monomer with a monomer having a carboxyl group. Can be obtained.
Examples of the carboxylic acid for modifying the polyolefin include maleic anhydride. Specific examples of the modified modified olefin (co) polymer include maleic anhydride-grafted polyethylene, maleic anhydride-grafted polypropylene, and maleic anhydride. Grafted poly-1-butene, maleic anhydride grafted poly-3-methyl-1-butene, maleic anhydride grafted poly-4-methyl-1-pentene, maleic anhydride grafted poly-3-methyl-1-pentene, maleic anhydride grafted poly- 1-heptene, maleic anhydride grafted poly-1-hexene, maleic anhydride grafted poly-1-octene, maleic anhydride grafted poly-1-decene, maleic anhydride grafted poly-1-dodecene, maleic anhydride grafted ethylene-propylene copolymer, Maleic anhydride-grafted ethylene-1-butene copolymer, maleic anhydride-grafted propylene-1-butene copolymer and the like can be mentioned.

Examples of the monomer having a carboxyl group copolymerized with the α-olefin monomer include acrylic acid, methacrylic acid, and maleic anhydride. Specific examples of the obtained copolymer include ethylene-acrylic acid copolymer and ethylene-acrylic acid copolymer. Examples include methacrylic acid copolymers and ethylene-maleic anhydride copolymers.
These olefin (co) polymers having a carboxyl group can be used alone or in combination of two or more.

  As the modified olefin (co) polymer and the olefin (co) polymer having a carboxyl group, commercially available products may be used. Examples of commercially available products that can be preferably used include "PRIMACOR" series manufactured by Dow Chemical Company, and DuPont Mitsui. -The "NUCREL" series manufactured by Polychemical Co., Ltd., and the "Escor" series manufactured by ExxonMobil Co., Ltd. are exemplified.

By introducing an ethylenically unsaturated bond into the olefin (co) polymer, the olefin-based polymer (A) can be obtained.
As a method for introducing an ethylenically unsaturated bond into an olefin (co) polymer, a known method can be used, and a compound having a functional group capable of reacting with a carboxyl group and an ethylenically unsaturated bond is converted into an olefin (co) By reacting with some carboxyl groups in the polymer, an olefin-based polymer (A) is obtained.
These reactions are not particularly limited, but may be any temperature at which the reaction with a carboxyl group starts, and may be performed, for example, at 50 ° C to 150 ° C. The reaction may be performed in the presence of a known catalyst. Furthermore, in order to introduce the ethylenically unsaturated bond more stably, a known polymerization inhibitor may be added to the reaction within a range not to hinder the polymerization of the acrylic polymer (B) described below, and the reaction may be performed.
Examples of the compound having a functional group capable of reacting with a carboxyl group and an ethylenically unsaturated bond include, for example, glycidyl (meth) acrylate, methyl glycidyl (meth) acrylate, 3,4-epoxycyclohexylmethyl (meth) acrylate, 6-methyl Examples thereof include compounds having a glycidyl group such as -3,4-epoxycyclohexylmethyl (meth) acrylate, and compounds having an oxazoline group such as vinyloxazoline and isopropenyl-2-oxazoline.

  The acid value of the olefin polymer (A) is 50 mgKOH / g or more, preferably 300 mgKOH / g or less, more preferably 60 to 200 mgKOH / g. By making it 50 mgKOH / g or more, the olefin polymer (A) is easily dissolved or dispersed in the aqueous dispersion medium, and the dispersion stability of the emulsion (X) described below is improved. Also improves retort resistance.

The ethylenically unsaturated bond in the olefin-based polymer (A) is preferably 0.1 to 1 mmol / g, more preferably 0.2 to 0.8 mmol / g. When the content is 0.1 mmol / g or more, the storage stability of the emulsion (X) containing the composite polymer (AB) is improved, and when the content is 1 mmol / g or less, workability is also improved.
The content of the ethylenically unsaturated bond is calculated from the value measured based on the iodine value measured by the method of JIS K0070: 1992.

<Acrylic polymer (B) part>
The acrylic polymer (B) portion is a portion mainly formed by (co) polymerization of the acrylic monomer (b) in the composite polymer (AB).

As the acrylic monomer (b) used for forming the acrylic polymer (B) part, a monomer (m1) having an amide group (hereinafter sometimes simply referred to as an amide monomer), two or more ethylenically unsaturated monomers A monomer (m2) having a bond (hereinafter sometimes simply referred to as a polyfunctional monomer), a monomer (m3) having a glycidyl group (hereinafter sometimes simply referred to as a glycidyl monomer), and the above (m1) to (m3) )). The acrylic monomers (b) can be used alone or in combination of two or more.
By containing at least one of the above (m1) to (m3), the workability and retort resistance of the formed coating film can be improved. Therefore, the use of the above (m1) to (m3) is preferable.

(Monomer Having Amide Group (m1))
The monomer having an amide group is preferably N-alkoxyalkyl (meth) acrylamide, N-hydroxyalkyl (meth) acrylamide, or (meth) acrylamide. Specifically, for example, N-hydroxyalkyl (meth) acrylamide such as N-hydroxymethyl (meth) acrylamide, N-hydroxyethyl (meth) acrylamide, N-hydroxybutyl (meth) acrylamide;
N-methoxymethyl (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, N- (n-, iso) butoxymethyl (meth) acrylamide, N-methoxyethyl (meth) acrylamide, N-ethoxyethyl (meth) acrylamide N-alkoxyalkyl (meth) acrylamides such as, N- (n-, iso) butoxyethyl (meth) acrylamide;
And (meth) acrylamide.
Among them, N-alkoxyalkyl (meth) acrylamide and N-hydroxyalkyl (meth) acrylamide are preferable because the crosslinking is apt to proceed.
The amide monomers (m1) can be used alone or in combination of two or more.

(Monomer having two or more ethylenically unsaturated bonds (m2))
Examples of the monomer (m2) having two or more ethylenically unsaturated bonds include ethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, 1,10-decane Examples thereof include diol di (meth) acrylate and tricyclodecane dimethylol di (meth) acrylate.

(Monomer having glycidyl group (m3))
Examples of the monomer (m3) having a glycidyl group include glycidyl (meth) acrylate, methyl glycidyl (meth) acrylate, 3,4-epoxycyclohexylmethyl (meth) acrylate, and 6-methyl-3,4-epoxycyclohexylmethyl (meth). Acrylate and the like.

In the present invention, monomers other than the above (m1) to (m3) can be used as appropriate.
For example, methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, Alkyl (meth) acrylate monomers such as hexyl (meth) acrylate and ethylhexyl (meth) acrylate;
Monomers having a carboxyl group such as (meth) acrylic acid, crotonic acid, maleic acid, itaconic acid, fumaric acid, citraconic acid, and mesaconic acid;
Hydroxymethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 3-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) Monomers having a hydroxyl group such as acrylate, hydroxypentyl (meth) acrylate, and hydroxyhexyl (meth) acrylate;
Examples include aromatic monomers such as styrene and α-methylstyrene.
These can be used alone or in combination of two or more.

The emulsion (X) contains a composite polymer (AB) in which a portion derived from the olefin-based polymer (A) and an acrylic polymer (B) are bonded, and an aqueous dispersion medium. It is considered that the portion derived from the olefin-based polymer (A) surrounds the acrylic polymer (B) portion and has a function of dispersing the particles of the composite polymer (AB) in the aqueous dispersion medium.
More specifically, a portion derived from the olefin polymer (A) functions as a kind of emulsifier, surrounds the acrylic monomer (b), and the olefin polymer (A) is polymerized in the course of polymerization of the acrylic monomer (b). It is considered that the composite polymer (AB) is generated by the reaction of the ethylenically unsaturated bond contained in the polymer with the acrylic polymer (B) part and is dispersed in the aqueous dispersion medium.

Such an emulsion (X) containing the composite polymer (AB) polymerizes the acrylic monomer (b) using a radical initiator in, for example, an aqueous dispersion or an aqueous solution containing the olefin-based polymer (A). Can be obtained.
More specifically, an aqueous dispersion medium and an olefin-based polymer (A) are charged into a reaction vessel, and then emulsion polymerization is performed while adding an acrylic-based monomer (b) to synthesize an acrylic-based polymer (B) portion and simultaneously form a composite. A method for obtaining the polymer (AB) may be mentioned. The radical initiator and the reducing agent described below can be put in the reaction tank, or can be put in the dropping tank together with the acrylic monomer (b), and dropped into the reaction tank together with the acrylic monomer (b). However, it is also possible to put it in a dropping layer different from the acrylic monomer (b) and drop it into the reaction tank.

  As another method, an acrylic monomer (b) is emulsified in an aqueous dispersion medium using an olefin polymer (A) and a basic compound (referred to as pre-emulsion), and then the pre-emulsified product is placed in a reaction vessel. To obtain a composite polymer (AB) at the same time as synthesizing the acrylic polymer (B) by emulsion polymerization. The radical initiator and the reducing agent described below can be put in the reaction tank together with a part of the aqueous dispersion medium, can be put in the pre-emulsion, or can be put in a dropping tank different from the pre-emulsion. It can also be dropped and dropped into the reaction tank.

  In the emulsion polymerization, a water-soluble or water-dispersible resin may be used together with the olefin-based polymer (A). As the water-soluble or water-dispersible resin, a polyester resin containing a carboxyl group, an acryl-modified polyester resin, a cellulose resin, polyvinyl alcohol, and derivatives thereof can be used as appropriate.

(Aqueous dispersion medium)
Examples of the aqueous dispersion medium include, in addition to water, hydrophilic solvents among so-called organic solvents. The combined use of water and a hydrophilic organic solvent is preferred from the viewpoint of improving the dispersion stability of the emulsion (X).
As the hydrophilic ones among the so-called organic solvents, specifically, for example, ethanol, n-propanol, isopropal, n-butyl alcohol, isobutyl alcohol, n-amyl alcohol, amyl alcohol, methyl amyl alcohol, octanol, Alcohols such as 2-ethylhexanol;
Glycols such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, and 1,3-butylene glycol;
Ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, ethylene glycol diethyl ether, ethylene glycol mono (iso) propyl ether, ethylene glycol di (iso) propyl ether, ethylene glycol mono (iso) butyl ether, ethylene glycol di ( Iso) butyl ether, ethylene glycol mono-tert-butyl ether, ethylene glycol monohexyl ether, 1,3-butylene glycol-3-monomethyl ether, 3-methoxybutanol, 3-methyl-3-methoxybutanol, diethylene glycol monomethyl ether, diethylene glycol dimethyl ether , Diethylene glycol monoethyl ether, diethylene glycol Diethyl ether, diethylene glycol mono (iso) propyl ether, diethylene glycol di (iso) propyl ether, diethylene glycol mono (iso) butyl ether, diethylene glycol di (iso) butyl ether, diethylene glycol monohexyl ether, diethylene glycol dihexyl ether, triethylene glycol dimethyl ether, propylene Glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono (iso) propyl ether, propylene glycol mono (iso) butyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol di (iso) propyl ether, propylene glycol di (a ) Butyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono (iso) propyl ether, dipropylene glycol mono (iso) butyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, diethylene glycol di (iso ) Various ether alcohols or ethers such as propyl ether and dipropylene glycol di (iso) butyl ether;
Organic solvents such as acetates such as ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, 3-methoxybutyl acetate, ethylene glycol monobutyl ether acetate, and 3-methyl-3-methoxybutyl acetate are appropriately used. Can be used.
The organic solvent can be used alone or in combination of two or more.

(Radical initiator)
In the synthesis of the emulsion (X), the acrylic monomer (b) is polymerized using a radical initiator, and among them, a nonionic water-soluble radical initiator is preferably used. By using the nonionic water-soluble radical initiator, it is possible to suppress the hydrophilicity of the emulsion (X) from being too high, and to suppress the water resistance, retort resistance, and peeling of the coating film.

Among the nonionic water-soluble radical initiators, peroxides or azo initiators are preferable.
Examples of the peroxide include hydrogen peroxide, tert-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, p-menthane hydroperoxide and the like.
Examples of the azo initiator include 2,2′-azobis [2- (2-imidazolin-2-yl) propane] and 2,2′-azobis {2-methyl-N- [1,1-bis (hydroxy Methyl) -2-hydroxyethyl] propionamide {, 2,2′-azobis [2-methyl-N- (2-hydroxyethyl) propionamide], and the like.
Of these, peroxides are preferred, and hydrogen peroxide and tert-butyl hydroperoxide are more preferred.
The nonionic water-soluble radical initiator can be used alone or in combination of two or more.

  In the polymerization of the acrylic polymer (B), redox polymerization is preferably performed by combining the nonionic water-soluble radical initiator and a reducing agent. In this case, the nonionic water-soluble radical initiator acts as an oxidizing agent. By conducting the polymerization reaction by redox polymerization, the polymerization rate can be increased and the polymerization reaction can be performed at a low temperature.

(Reducing agent)
As the reducing agent, any of a reducing organic compound and a reducing inorganic compound can be suitably used. Examples of the reducing organic compound include benzoin and metal salts (sodium salt, potassium salt, calcium salt, etc.) such as ascorbic acid, erythorbic acid, tartaric acid, citric acid, glucose, and formaldehyde sulfoxylate.
Examples of the reducing inorganic compound include sodium thiosulfate, sodium sulfite, sodium bisulfite, and sodium metabisulfite.
The reducing agent is particularly preferably a reducing organic compound, more preferably a metal salt of ascorbic acid or erythorbic acid, and even more preferably sodium ascorbate or sodium erythorbate.
The reducing agents can be used alone or in combination of two or more.

The nonionic water-soluble radical initiator is preferably 0.01 to 1% by mass based on 100% by mass of the acrylic monomer (b).
Moreover, it is preferable that a reducing agent is 0.01-2 mass% with respect to 100 mass% of acrylic monomers (b).
The method of adding the nonionic water-soluble radical polymerization initiator or reducing agent may be any method such as intermittent, continuous, and batch addition.

(Basic compound)
When polymerizing the acrylic monomer (b) to obtain the emulsion (X), a basic compound may be contained as necessary.
By containing the basic compound, at least a part of the carboxyl groups in the olefin polymer (A) can be neutralized, and the solubility of the olefin polymer (A) in the aqueous dispersion medium and the pre-emulsification can be achieved. The stability of the product, the dispersion stability of the emulsion (X) and the like may be improved.
As the basic compound, organic amine compounds, ammonia, hydroxides of alkali metals and the like are preferable.
Examples of the organic amine compound include monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monopropylamine, dipropylamine, monoethanolamine, diethanolamine, triethanolamine, N, N-dimethyl-ethanolamine. , N, N-diethyl-ethanolamine, 2-dimethylamino-2-methyl-1-propanol, 2-amino-2-methyl-1-propanol, N-methyldiethanolamine, N-ethyldiethanolamine, monoisopropanolamine, Isopropanolamine, triisopropanolamine and the like.
Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, and potassium hydroxide.
The basic compounds can be used alone or in combination of two or more.

In this way, the emulsion (X) containing the composite polymer (AB) is obtained at the same time as the acrylic polymer (B) is synthesized by emulsion polymerization.
The mass ratio of the portion derived from the olefin polymer (A) and the acrylic polymer (B) contained in the emulsion (X) may be (A) / (B) = 10/90 to 60/40. More preferably, it is 20/80 to 50/50. That is, the olefin-based polymer (A) and the acrylic-based monomer (b) are preferably polymerized in the range of (A) / (b) = 10/90 to 60/40, and 20/80 to 50/50. It is more preferable to polymerize within the range.
When the ratio of the portion derived from the olefin-based polymer (A) is 10 or more, the dispersion stability of the emulsion (X) is improved. When the ratio is 60 or less, the processability of the coating film and the retort resistance are improved. Is improved.
Further, the glass transition temperature (Tg) of the acrylic polymer (B) in the emulsion (X) is preferably from 10C to 100C, more preferably from 30C to 70C. When the Tg is 10 ° C or higher, the coating film has more excellent scratch resistance, and when the Tg is 100 ° C or lower, the processability of the coating film is more excellent.
In addition, Tg is a calculated value calculated from Tg of each homopolymer of the acrylic monomer (b) to be used and the compounding ratio. In the present invention, a value using the FOX equation is used. The value described in the Polymer Handbook (1975, Second Edition) is used as the Tg of the homopolymer of the monomer. Further, the monomer having two or more ethylenically unsaturated groups described above as the acrylic monomer (b) may be used in a small amount (for example, 1.0% by mass or less in 100% by mass of the acrylic monomer (b)). However, since it is a small amount, it is not considered in calculating the Tg of the acrylic polymer (B).

<Curing agent (C)>
The aqueous paint of the present invention contains a curing agent (C) for the purpose of improving the curability of the coating film and the metal adhesion.
As the curing agent (C), a compound which is self-crosslinkable or which reacts with a reactive functional group such as a carboxyl group, an amide group, or a hydroxyl group contained in the emulsion (X) (composite polymer (AB)) can be used. Phenol resin (c1), amino resin (c2), β-hydroxyalkylamide compound (c3) and the like.

(Phenol resin (c1))
As the phenol resin (c1), a resin synthesized by an addition condensation reaction of a phenol compound and an aldehyde such as formaldehyde is preferably used.
Examples of the phenol compound include phenol, o-cresol, p-cresol, p-tert-butylphenol, p-phenylphenol, p-nonylphenol, 2,3-xylenol, 2,5-xylenol, m-cresol, 3, 5-xylenol, resorcinol, hydroquinone, and the like. In this case, the phenol compounds may be used alone or in combination of two or more.
The phenol resin may be a commercially available product. Examples of commercially available products that can be preferably used include, for example, Phenodur PR285, PR516, PR566, PR612, and VPR1785 manufactured by Allnex; Sumilite resin PR-55317, PR-55819 manufactured by Sumitomo Bakelite; PR-53893A; Shaunol BKS-368, CKS-3898, manufactured by Aika SDK Phenol, and the like.

(Amino resin (c2))
Examples of the amino resin (c2) include those obtained by adding formaldehyde to an amino compound such as urea, melamine, or benzoguanamine. In this case, the amino compound can be used alone or in combination of two or more.

  As the amino resin (c2), a commercially available product may be used. Commercially available products that can be preferably used include, for example, Cymel 301, 303LF, 304, 323, 325, 328, 370, 659, 1123 manufactured by Allnex; and Luwipal014, 015, 018, 066, 070, 052, B017 manufactured by BASF. Can be mentioned.

  As the phenol resin (c1) and the amino resin (c2), those in which a part or all of a methylol group formed by addition of formaldehyde is etherified with an alcohol having 1 to 12 carbon atoms are preferably used. Can be

(Β-hydroxyalkylamide compound (c3))
As the β-hydroxyalkylamide compound (c3), a compound having a functional group capable of reacting with a carboxyl group and represented by the following general formula (1) is used.

(In the formula (1), R ₁ represents a hydrogen atom which may be the same or different, a methyl group or an ethyl group, and R ₂ represents a hydrogen atom which may be the same or different, and has 1 to 5 carbon atoms. alkyl group, or _{-CH 2 - (R 1) -CH} -OH, X represents an alkyl group having 2 to 6 carbon atoms).

  As the β-hydroxyalkylamide compound (c3), a commercially available product may be used. Examples of commercially available products that can be preferably used include, for example, PRIMID XL-552 (N, N, N ', N'-tetrakis (2-hydroxyethyl) adipamide), QM-1260, SF-4510, etc., manufactured by Ms. Chemie Japan. Can be mentioned.

  In addition, other than the curing agent (C), any compound that reacts with a reactive functional group contained in the emulsion (X) (composite polymer (AB)) can be used in the same manner, and an oxazoline compound, a carbodiimide compound, Metal chelate compounds and the like.

(Oxazoline compound)
As the oxazoline compound, a compound having two or more oxazoline groups in a molecule is preferably used. For example, 2′-methylenebis (2-oxazoline), 2,2′-ethenebis (2-oxazoline), 2,2′- Ethenebis (4-methyl-2-oxazoline), 2,2'-propenebis (2-oxazoline), 2,2'-tetramethylenebis (2-oxazoline), 2,2'-hexamethylenebis (2-oxazoline) , 2,2'-octamethylenebis (2-oxazoline), 2,2'-p-phenylenebis (2-oxazoline), 2,2'-p-phenylenebis (4,4'-dimethyl-2-oxazoline ), 2,2′-p-phenylenebis (4-methyl-2-oxazoline), 2,2′-p-phenylenebis (4-phenyl-2-oxazoline) and the like. It is possible. Alternatively, a copolymer of a vinyl monomer such as 2-isopropenyl-2-oxazoline or 2-isopropenyl-4,4-dimethyl-2-oxazoline and another monomer copolymerizable with the vinyl monomer. May be.

(Carbodiimide compound)
As the carbodiimide compound, a compound having two or more carbodiimide groups (-N = C = N-) in a molecule is preferably used, and a known polycarbodiimide can be used. Further, as the carbodiimide compound, a high-molecular-weight polycarbodiimide produced by subjecting a diisocyanate to a decarboxylation reaction can also be used. Examples of such compounds include those obtained by subjecting the following diisocyanates to a decarboxylation condensation reaction.
As the diisocyanate, 4,4'-diphenylmethane diisocyanate, 3,3'-dimethoxy-4,4'-diphenylmethane diisocyanate, 3,3'-dimethyl-4,4'-diphenylmethane diisocyanate, 4,4'-diphenyl ether diisocyanate, 3,3′-dimethyl-4,4′-diphenyl ether diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 1-methoxyphenyl-2,4-diisocyanate, isophorone diisocyanate, 4,4′- One of dicyclohexylmethane diisocyanate, tetramethylxylylene diisocyanate, or a mixture thereof can be used.

(Metal chelate compound)
Examples of metal chelate compounds include polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, titanium, nickel, antimony, magnesium, vanadium, chromium, and zirconium, such as 2,4-pentanedione, ethyl acetoacetate, and acetylacetone. Are coordinated.
When a metal chelate compound is used as a crosslinking agent, the reactivity with the functional group in the emulsion (X) (composite polymer (AB)) is further delayed, and the storage stability in a coating solution is improved. A coordinating compound may be used in combination.
Examples of the coordinating compound include acetylacetone, dimethylglyoxime, oxine, dithizone, polyaminooxy acids such as ethylenediaminetetraacetic acid (alias: EDTA), oxycarboxylic acids such as citric acid, and condensed phosphoric acid. Among them, acetylacetone is preferable because of its volatility and easy removal.

  The curing agent (C) is preferably added in an amount of 0.1 to 20 parts by mass, more preferably 1 to 10 parts by mass, based on 100 parts by mass of the composite polymer (AB), and has a retort resistance and a corrosion resistance. , Workability and the like are improved.

Other Components The aqueous coating composition of the present invention usually contains an aqueous dispersion medium such as water for dispersing the emulsion (X), and may further contain other components as necessary within a range that does not impair the effects of the present embodiment. May be contained. Hereinafter, components that can be suitably included will be described.

Further, the water-based paint of the present invention may contain a lubricant such as wax, a curing catalyst, and the like, if necessary, for the purpose of preventing a coating film from being damaged in a can-making process.
Examples of the wax include animal and plant waxes such as beeswax, lanolin wax, spermaceti, candelilla wax, carnauba wax, rice wax, wood wax, jojoba oil, and palm oil;
Minerals such as montan wax, ozogenite, ceresin, paraffin wax, microcrystalline wax, petrolatum, and petroleum wax;
Synthetic waxes such as Fischer-Tropsch wax, polyethylene wax, polyethylene oxide wax, polypropylene oxide wax, montan wax derivatives, paraffin wax derivatives, microcrystalline wax derivatives, and Teflon (registered trademark) wax.
Examples of the curing catalyst include dodecylbenzenesulfonic acid, methanesulfonic acid, p-toluenesulfonic acid, dinonylnaphthalenedisulfonic acid, trifluoromethanesulfonic acid, and sulfuric acid, and neutralized products thereof.

  Further, the water-based paint of the present invention may contain various components such as a surfactant, an antifoaming agent, and a leveling agent for the purpose of improving the coatability, if necessary.

<Use of water-based coating composition>
The aqueous coating composition of the present invention can be suitably used for the purpose of forming a coating film for covering members such as metals and plastics. In particular, it is preferable to coat a storage container such as a can for storing drinks and foods, and it can be used regardless of its inner surface and outer surface.However, it is more preferable to coat the inner surface of the can by taking advantage of its high workability. Preferably, it is particularly preferably used for the inner surface of a beverage can. Further, it can be suitably used for storage containers other than food applications such as engine oil. It goes without saying that the water-based coating composition of the present embodiment can also be used for coating the outer surface of a can.

  The metal is preferably, for example, aluminum, tin-plated steel sheet, chromium-treated steel sheet, nickel-treated steel sheet, or the like, and can be subjected to surface treatment such as zirconium treatment or phosphoric acid treatment. The plastics are preferably made of polyolefin such as polyethylene and polypropylene, and polyester such as polyethylene terephthalate.

As a coating method, known methods such as spray coating such as air spray, airless spray, and electrostatic spray, roll coater coating, dip coating, and electrodeposition coating can be used.
When coating on metal, baking is preferably performed at a temperature of 150 to 300 ° C. for 10 seconds to 30 minutes, more preferably 20 seconds to 10 minutes.

[Coated can]
The coated can of the present embodiment includes, for example, a so-called bottle can having a can lid and a can body member, a so-called bottle can having a recappable lid and a bottle portion. The coated can is preferably a two-piece can composed of one can lid and one can body member, or a three-piece can composed of two upper and lower lids and one can body member. It is preferable that the bottle part has a drinking spout part having a screw that can be opened and closed by the lid.
The coated can of this embodiment has at least a part of the surface of the can material having a coating film of the water-based paint of this embodiment.
The coated can has excellent workability and retort resistance by having the coating film of the water-based paint of the present embodiment.

  The method for producing the coated can is not particularly limited. For example, a water-based paint may be applied to a metal plate before molding, or a water-based paint may be applied to a metal member formed into a can shape, and trimming may be performed. A water-based paint may be applied later.

The thickness of the coating film is not particularly limited, but is usually about 1 to 50 μm. Coating amount after drying may be appropriately selected depending on the application, but usually preferably 5 to 200 mg / dm ² about, and more preferably 10-150 mg / dm ^2.

  The coated can of the present invention is preferably used for storing beverages such as drinking water, soft drinks, tea beverages, and alcoholic beverages as contents. Further, non-drinks such as fish meat and fruits may be stored.

  Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to these Examples. In the examples, "parts" represents parts by mass, and "%" represents mass%.

[Production Example 1]
<Production of aqueous solution of olefin-based polymer (A-1)>
In a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping tank, and a nitrogen gas inlet pipe, PRIMACOR ™ 5980i (manufactured by Dow Chemical Company, ethylene-acrylic acid copolymer, acid value: about 160 mgKOH / g) ) 100 parts were charged and heated and melted at 120 ° C. Thereafter, under an air atmosphere, 0.03 part of p-methoxyphenol, 4.5 parts of glycidyl methacrylate, and 0.1 part of tetrabutylammonium bromide were added and reacted for 10 hours to introduce an ethylenically unsaturated group. Thereafter, 500 parts of ion-exchanged water and 22.5 parts of dimethylethanolamine were charged and heated at 90 ° C. Thereafter, the mixture was dissolved for 5 hours to obtain an aqueous solution of an olefin-based polymer (A-1) having a nonvolatile content of 20%, an acid value of 145 mgKOH / g, and an ethylenically unsaturated bond of 0.3 mmol / g.

[Production Example 2]
<Production of aqueous solution of olefin-based polymer (A-2)>
An ethylenically unsaturated group was introduced into an olefin-based polymer in the same manner as in Production Example 1 except that the amount of glycidyl methacrylate was changed to 9.4 parts. Then, in the same manner as in Production Example 1 except that the amount of ion-exchanged water was changed to 527.5 parts and the amount of dimethylethanolamine was changed to 19.5 parts, a nonvolatile content was 20%, an acid value was 125 mgKOH / g, and ethylenically unsaturated. An aqueous solution of an olefin-based polymer (A-2) having a bond of 0.6 mmol / g was obtained.

[Production Example 3]
<Production of olefin polymer (A-3) aqueous solution>
In the same manner as in Production Example 1, PRIMACOR® 5980i having an acid value of about 160 mg KOH / g was replaced with Escor® 5200 (an ethylene-acrylic acid copolymer manufactured by ExxonMobil, acid value: about 117 mg KOH / g). g) Using 100 parts, 3.8 parts of glycidyl methacrylate was reacted to introduce an ethylenically unsaturated group. Then, in the same manner as in Production Example 1 except that the amount of ion-exchanged water was changed to 502.8 parts and the amount of dimethylethanolamine was changed to 16.2 parts, a nonvolatile content was 20%, an acid value was 105 mgKOH / g, and ethylenically unsaturated. An aqueous solution of an olefin-based polymer (A-3) having a bond of 0.25 mmol / g was obtained.

[Comparative Production Example 1]
<Synthesis of acrylic copolymer (E-1)>
8 parts of ethylene glycol monobutyl ether and 18.2 parts of ion-exchanged water were charged into a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping tank, and a nitrogen gas introduction pipe, and heating was started to about 100 ° C. At reflux. While maintaining the reflux, a mixture of 10 parts of methacrylic acid, 6 parts of styrene, 4 parts of ethyl acrylate, and 0.3 part of benzoyl peroxide was continuously dropped from the dropping tank over 4 hours to carry out polymerization.
One hour and two hours after the completion of the dropping, 0.03 parts of benzoyl peroxide was added, and the reaction was continued for three hours after the completion of the dropping. Then, by cooling, a solution of an acrylic copolymer having a number average molecular weight of 25,000, a glass transition temperature of 80 ° C, and a nonvolatile content of 41% was obtained.
Next, 5.2 parts of dimethylethanolamine was added, and the mixture was stirred for 10 minutes. Then, 46.3 parts of ion-exchanged water was added to dissolve the acrylic copolymer in water. As a result, an acrylic copolymer (E-1) aqueous solution having a nonvolatile content of 20% and an acid value of 306 mgKOH / g was obtained.

[Comparative Production Example 2]
<Synthesis of acrylic copolymer (E-2)>
In the same manner as in Comparative Production Example 1, 23.0 parts of methyl isobutyl ketone was charged, heating was started, and the mixture was refluxed at about 120 ° C. While maintaining the reflux, a mixture of 10 parts of methacrylic acid, 6 parts of styrene, 4 parts of ethyl acrylate, 1 part of N-butoxymethylacrylamide and 0.35 part of benzoyl peroxide was continuously dropped from the dropping tank for 4 hours to carry out polymerization.
One hour and two hours after the completion of the dropping, 0.03 parts of benzoyl peroxide was added, and the reaction was continued for 5 hours after the completion of the dropping. Next, 0.03 parts of p-methoxyphenol, 3.0 parts of glycidyl methacrylate, and 0.1 part of tetrabutylammonium bromide were added in an air atmosphere, and the mixture was reacted for 10 hours to introduce an ethylenically unsaturated group. Thereafter, while cooling, 85.0 parts of ion-exchanged water, 15.0 parts of acetone, and 4.9 parts of dimethylethanolamine were added and dissolved. Then, the mixture was concentrated under reduced pressure while heating to obtain an acrylic copolymer (E-2) aqueous solution having a nonvolatile content of 20%, an acid value of 160 mgKOH / g, and an ethylenically unsaturated bond of 0.3 mmol / g.

[Example 1]
<Production of water-based paint (1)>
In a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a plurality of dripping tanks, and a nitrogen gas introducing pipe, 178.1 parts of ion-exchanged water, the olefin-based polymer obtained in Production Example 1 (A-1) An aqueous solution (92.8 parts) was charged and heated to 70 ° C. while stirring under a nitrogen gas atmosphere.
Separately, 51.55 parts of styrene, 50.5 parts of ethyl acrylate, and 3.16 parts of N-butoxymethylacrylamide were charged into the dropping tank 1. Further, 18 parts of a 1% aqueous hydrogen peroxide solution was charged into the dropping tank 2, and 18 parts of a 1% aqueous solution of sodium erythorbate was charged into the dropping tank 3.
While maintaining the temperature in the reaction vessel at 70 ° C. with stirring, monomers and the like are dropped from each dropping tank over 3 hours, and the emulsion is polymerized while emulsifying the monomers, thereby obtaining an emulsion containing the composite polymer (AB-1). (X-1) was obtained.
Thereafter, 37.48 parts of ion-exchanged water, 24.17 parts of n-butanol, 25 parts of ethylene glycol monobutyl ether, and 1.24 parts of a phenolic resin / formaldehyde type phenol resin as the phenol resin (c1) are added, and the mixture is filtered to be nonvolatile. 24.7% of a water-based paint (1).

[Examples 2 to 11]
Aqueous paints (2) to (11) were obtained in the same manner as in Example 1 except that the types and amounts of the components were changed as shown in Tables 1 and 2 in Example 1, and evaluated according to the method described below. did.
Since the amount of 1,4-butanediol diacrylate used in Example 5 was small, it was determined that it did not contribute to the glass transition temperature, and was not considered when calculating.

[Comparative Example 1]
<Production of aqueous coating composition>
In a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping tank, and a nitrogen gas introduction pipe, 45 parts of the aqueous solution of the acrylic copolymer (E-1) obtained in Comparative Production Example 1, ion-exchanged water 18.5 parts were charged and heated to 70 ° C. with stirring in a nitrogen gas atmosphere.
Separately, 5.36 parts of styrene, 15.02 parts of ethyl acrylate, and 1.08 part of N-butoxymethylacrylamide were charged into the dropping tank 1. Further, 0.74 parts of a 1% aqueous hydrogen peroxide solution was charged into the dropping tank 2, and 0.92 parts of a 1% aqueous solution of sodium erythorbate was charged into the dropping tank 3. While maintaining the temperature inside the reaction vessel at 70 ° C. with stirring, the mixture was dropped from each dropping tank over 3 hours to carry out emulsion polymerization to obtain a polymer emulsion.
Thereafter, 57 parts of ion-exchanged water, 13.6 parts of n-butanol, 9.1 parts of ethylene glycol monobutyl ether, 0.16 parts of dodecylbenzenesulfonate, and 2.06 parts of phenolic / formaldehyde type phenol resin were added, followed by filtration. As a result, an aqueous paint (12) having a nonvolatile content of 18.5% was obtained.

[Comparative Example 2]
<Production of aqueous coating composition>
In the same manner as in Comparative Example 1, 45 parts of the aqueous solution of the acrylic copolymer (E-2) obtained in Comparative Production Example 2 and 18.5 parts of ion-exchanged water were charged, and stirred under a nitrogen gas atmosphere. Heated to 70 ° C.
Separately, 5.36 parts of styrene, 15.02 parts of ethyl acrylate, and 1.08 part of N-butoxymethylacrylamide were charged into the dropping tank 1. Further, 0.74 parts of a 1% aqueous hydrogen peroxide solution was charged into the dropping tank 2, and 0.92 parts of a 1% aqueous solution of sodium erythorbate was charged into the dropping tank 3. While maintaining the temperature inside the reaction vessel at 70 ° C. with stirring, the mixture was dropped from each dropping tank over 3 hours to carry out emulsion polymerization to obtain a polymer emulsion.
Thereafter, 57 parts of ion-exchanged water, 13.6 parts of n-butanol, 9.1 parts of ethylene glycol monobutyl ether, 0.16 parts of dodecylbenzenesulfonate, and 2.06 parts of phenolic / formaldehyde type phenol resin were added, followed by filtration. As a result, an aqueous paint (13) having a nonvolatile content of 18.5% was obtained.

[Comparative Example 3]
<Production of olefin-based polymer (A-4) aqueous solution>
In the same manner as in Production Example 1, 100 parts of Escor (trademark) 6000 (manufactured by ExxonMobil, ethylene-acrylic acid copolymer, acid value: about 47 mgKOH / g) was charged, and heated and melted at 120 ° C. Thereafter, under an air atmosphere, 0.03 part of p-methoxyphenol and 3.0 parts of glycidyl methacrylate were added and reacted for 10 hours to introduce an ethylenically unsaturated group. Thereafter, 408.3 parts of ion-exchanged water and 3.7 parts of dimethylethanolamine were charged and heated at 90 ° C. Thereafter, dissolution was attempted for 5 hours, but the production of an aqueous solution of the olefin-based polymer was not completed because insoluble components remained.

<Storage stability test>
The appearance of the water-based paint after storage at 50 ° C. for one month was visually evaluated.
A: No change (good)
B: Slight separation is seen in the upper layer. (Available)
C: Clear separation is observed in the upper layer, or settling of particles is observed. (Usage prohibited)

[Production of Test Panel 1]
The aqueous paints obtained in Examples 1 to 11 and Comparative Examples 1 and 2 were coated on a 0.26 mm thick aluminum plate with a bar coater so that the coating weight after baking and drying was 45 mg / dm ^2. Then, baking and drying were performed at 200 ° C. for 120 seconds to produce a test panel 1 for testing.

[Production of Test Panel 2]
The aqueous paints obtained in Examples 1 to 11 and Comparative Examples 1 and 2 were coated on a 0.26 mm thick aluminum plate with a bar coater so that the coating weight after baking and drying was 80 mg / dm ^2. After passing through a double-type conveyor oven in which the temperature of the first zone was 286 ° C. and the temperature of the second zone was 326 ° C. for 24 seconds, baking and drying were performed to produce a test panel 2 for testing.

<Bendability>
The test panel 1 was prepared to have a size of 30 mm in width and 50 mm in length. Next, as shown in FIG. 1A, a round bar 2 having a diameter of 3 mm was attached to a position having a length of 30 mm with the coating of the test panel 1 facing outward. Next, as shown in FIG. 1B, the test panel was folded in two along the round bar 2 to produce a test piece 3 having a width of 30 mm and a length of about 30 mm. Two aluminum plates having a thickness of 0.26 mm are sandwiched between the two folded test pieces 3, and as shown in FIG. 1 (c), a rectangular parallelepiped 1 kg weight 4 cm × 5 cm × height × 5 cm deep. Was dropped from the height of 40 cm to the bent portion of the test piece 3 and completely bent.
Next, the bent portion of the test piece 4 was immersed in a 1% concentration saline solution. Next, a current value was measured when a voltage of 6.0 V × 4 seconds was passed between the metal portion of the flat portion of the test piece 4 not immersed in the saline solution and the saline solution.
When the workability of the coating film is poor, the coating film in the bent portion is cracked, the underlying metal plate is exposed, and the conductivity increases, so that the current value increases.
A: Less than 0.5 mA (good)
B: 0.5 to less than 5 mA (usable)
C: 5 to less than 15 mA (cannot be used)

<Gel fraction>
Test panel 1 was prepared in a size of 15 cm in width and 15 cm in length. Next, the test panel was immersed in methyl ethyl ketone (MEK) refluxed at 80 ° C. for 60 minutes, and the gel fraction was calculated from the weight change of the test panel before and after immersion.
A: 95% or more (good)
B: 90 to less than 95% (usable)
C: less than 90% (cannot be used)

<Retort resistance test>
While the test panel 1 was immersed in water, retort treatment was performed in a retort pot at 125 ° C. for 30 minutes, and the appearance of the coating film was visually evaluated.
A: No change from untreated coating (good)
B: Very thin whitening (usable)
C: Significant whitening (cannot be used)

<Adhesion test>
While the test panel 1 is immersed in water, retort treatment is performed in a retort pot at 125 ° C. for 1 hour, and after a cross-cut is performed on the coated film surface with a cutter, a cellophane adhesive tape is attached and strongly peeled. The peeling state of the coating film after the evaluation was evaluated.
A: No peeling (good)
B: 5% or less peeling (usable)
C: More than 5% peeling (unusable)

The corrosion resistance was evaluated by an acid resistance test and an alkali resistance test.
<Acid resistance test>
While the test panel 2 was immersed in an aqueous solution having a pH of about 3 using citric acid, a retort treatment was performed in a retort pot at 125 ° C. for 30 minutes, and the appearance of the coating film was visually evaluated.
A: No change from untreated coating (good)
B: Very thin whitening (usable)
C: Significant whitening (cannot be used)

<Alkali resistance test>
While the test panel 2 was immersed in an aqueous solution having a pH of about 10 using sodium hydroxide, the test panel 2 was subjected to a retort treatment at 125 ° C. for 30 minutes in a retort pot, and the appearance of the coating film was visually evaluated.
A: No change from untreated coating (good)
B: Very thin whitening (usable)
C: Significant whitening (cannot be used)

<Opening test>
The test panel 2 was prepared in a size of 5 cm in width and 5 cm in length. The mold having the shape of the opening portion applied to the painted surface of the test panel 2 was pressed by a press machine to form a scheduled opening portion on the painted surface, and used as a sample (test lid material).
After retorting the sample in a retort pot at 125 ° C. for 30 minutes, one end of the portion to be opened is struck with a thin rod-shaped tool from the painted surface side to the unpainted surface side, and the one end of the to-be-opened portion together with the aluminum plate is removed. Protruded to the painted side. Pinch one end of the opening that protrudes to the unpainted surface side with pliers, peel off the aluminum plate along the shape of the opening from the part other than the opening, form the opening, and enlarge the opening with a microscope It was visually determined.
If the opening property is poor, the coating film tends to remain in the periphery of the opening, and the width of the coating film protruding into the opening increases. Good openness means a state in which the coating film does not protrude into the opening at all, or even if it does, the width of the coating is very small. Specifically, as a determination method, a protruding width was measured and evaluated according to the following evaluation criteria.
A: The maximum width of the protruding coating film is less than 50 μm (good).
B: The maximum width of the protruding coating film is 50 μm or more and less than 100 μm (usable)
C: The maximum width of the protruding coating film is 100 μm or more (cannot be used)
Incidentally, the lid of the beverage can is generally of a stay-on tab type in which a mouthpiece is pushed into the inside of the can when opening. However, the evaluation of the opening property of the inner coating film is more strict in the method in which the die is peeled off to the outside of the can, and therefore, in the present invention, the evaluation is made as described above.

In Tables 1 and 2,
Cymel 303LF is an amino resin manufactured by Allnex,
PRIMID XL-552 is a β-hydroxyalkylamide compound manufactured by EMS Chemie (Ms. Chemie Japan),
Respectively.

  As shown in Table 2, it contains a composite polymer (AB) in which an olefin polymer (A) having a carboxyl group and an ethylenically unsaturated bond and an acrylic polymer (B) are bonded, and a curing agent (C). The coating films obtained from the aqueous coating compositions of Examples 1 to 11 were all excellent in workability, and showed good retort resistance and corrosion resistance. In addition, the storage stability of the paint was good. The aqueous paints of Comparative Examples 1 and 2 had good retort resistance, but were insufficient in workability and corrosion resistance, and storage stability of the paints was also insufficient.

1 Test panel 2 Round bar 3 Test piece 4 Weight

Claims (8)

A composite obtained by polymerizing an acrylic monomer (b) in an aqueous dispersion or aqueous solution containing an olefin-based polymer (A) having a carboxyl group and an ethylenically unsaturated bond and having an acid value of 50 mgKOH / g or more. An emulsion (X) containing a polymer (AB) and an aqueous dispersion medium,
And a curing agent (C).   The aqueous paint according to claim 1, wherein the curing agent (C) is at least one selected from the group consisting of a phenol resin (c1), an amino resin (c2), and a β-hydroxyalkylamide compound (c3).   The water-based paint according to claim 1 or 2, wherein the curing agent (C) is contained in an amount of 0.1 to 20 parts by weight based on a total of 100 parts by weight of the olefin-based polymer (A) and the acrylic monomer (b).   The aqueous solution according to any one of claims 1 to 3, wherein the mass ratio between the olefin-based polymer (A) and the acrylic monomer (b) is (A) / (b) = 10/90 to 60/40. paint.   One or more acrylic monomers (b) selected from the group consisting of a monomer (m1) having an amide group, a monomer (m2) having two or more ethylenically unsaturated bonds, and a monomer (m3) having a glycidyl group The water-based paint according to any one of claims 1 to 4, wherein     The aqueous paint according to any one of claims 1 to 5, wherein the acrylic monomer (b) is a monomer capable of forming a polymer having a Tg of 10 to 100.   The water-based paint according to any one of claims 1 to 6, wherein the water-based paint is used for coating a can material for storing a beverage or food. Can material,
Coating at least a part of the surface of the can material, and a cured coating film of the aqueous paint according to any one of claims 1 to 6,
Having a coated can.