JPH11209448A - Photo-curable resin composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a coating material which provides coating with excellent adhesion, felt pen soil resistance and water resistance by admixing an amino compound-neutralized polyfunctional urethane acrylate having an oxyalkylene group and a carboxyl group, with a photopolymerization initiator and water. SOLUTION: A polyfunctional urethane acrylate is preferably water dispersible one having unsaturated groups at the both ends, which is obtained by reacting a compound having two isocyanate groups in the molecule with a glycol compound, of a mol.wt. of 300-3,000, having a hydroxyl group at an end and a photo-polymerizable, hydroxyl group-containing unsaturated compound having at least one unsaturated double bond, followed by neutralization with an amino group-containing compound free of an active hydrogen. An average mol.wt. of 1,000-7,000 results in good stability in dilution with water. The photopolymerization initiator is compounded in an amount of preferably 3-5 pts.wt. based on 100 pts.wt. of the total of the polyfunctional urethane acrylate and other water soluble photo-polymerizable compounds added as required, and water is added in an amount such that the solids content becomes 20-80 wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-dilutable photocurable resin composition useful as a coating curable by irradiation with ultraviolet rays or electron beams, and a coating composition and a coating composition containing the same. In particular, the resin has excellent stability, and can be washed again with water even after dilution water has been volatilized, and when cured, has excellent coating film adhesion, water resistance, and magic stain resistance. About paint.

[0002]

2. Description of the Related Art Conventionally, a photocurable resin composition containing a polyurethane acrylate is disclosed in
-66596, JP-A-50-94090, JP-A-48-48
25095, JP-A-8-157770, JP-A-8-27
398 and the like. And
Nowadays, the use of these photocurable resin compositions for coating has been increasing for the purpose of improving productivity. In recent years, volatile organic compounds (VOCs) have been developed from the viewpoints of pollution prevention, environmental protection, and work environment improvement.
(Nic Compound) regulations tend to reduce the content of organic solvents in paints, and photocurable resin compositions that can be made solvent-free or high-solid are growing significantly in the coatings market. However, the solventless photocurable resin composition used for coating must be diluted with a photoreactive monomer such as an acrylic monomer in order to adjust the coating viscosity. Many photoreactive monomers for viscosity adjustment are
Because of its low molecular weight, it is highly irritating to the skin, and is apt to cause rashes and chemical wounds when handled by workers. Further, in order to adjust the coating viscosity, it is necessary to incorporate a large amount of a photoreactive monomer, and there is a tendency that the overall physical properties of the obtained cured coating film properties deteriorate. Under such influence, the development of an aqueous photocurable resin composition containing a small amount of an organic solvent and a reactive monomer has been required for a photocurable resin for coating. Particularly in the woodworking, paper, plastic and metal coating fields, there is a strong demand for the development of UV-curable resin compositions and paints having water dilutability, but storage stability after water dilution and adhesion to coating machines, It is possible to wash the dried paint with water, and the obtained cured coating film properties have not yet been provided to provide a photocurable resin composition and a paint having good water resistance, magic stain resistance, adhesion, etc. .

[0003]

DISCLOSURE OF THE INVENTION The present invention is useful for coating plastics, woodwork base materials, etc.
The present invention provides a photocurable resin composition capable of achieving magic stain resistance and water resistance, and further provides a material that can be diluted with water alone and that can be washed again with water even after dilution water is volatilized. It is.

[0004]

That is, the present invention provides:
The present invention relates to a photocurable resin composition containing (A) a polyfunctional urethane acrylate having a oxyalkylene group and a carboxyl group neutralized with an amino compound, (D) a photopolymerization initiator, and water.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, (A) used in the present invention
The polyfunctional urethane acrylate having an oxyalkylene group and a carboxyl group neutralized with an amino compound (hereinafter, referred to as component (A)) will be described in detail. The component (A)
A water-dispersible polyfunctional urethane acrylate having unsaturated groups at both ends is preferred. The component (A) includes, for example, 1
Isocyanate compound having two isocyanate groups in the molecule (component (a)), diol compound having at least one carboxyl group and two hydroxyl groups in the molecule (component (b)), molecular weight of 300 to 3,000 And a hydroxyl group-containing glycol compound having a terminal group (component (c)), and a hydroxyl-containing unsaturated compound having one or more unsaturated double bonds capable of being photopolymerized (component (d))
And further reacting the carboxyl group-containing polyfunctional urethane acrylate compound having two or more unsaturated double bonds at one end with a compound having an amino group having no active hydrogen to thereby neutralize the compound. Can be prepared. Diisocyanate compound having two isocyanate groups in one molecule (a) used in the present invention
Components include tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, trimethyl hexamethylene diisocyanate, tetramethyl xylylene diisocyanate, isophorone diisocyanate, norbornane diisocyanate, hydrogenated tolylene diisocyanate, and hydrogenated xylylene diisocyanate. Examples thereof include diisocyanate and hydrogenated diphenylmethane diisocyanate, and preferably include tolylene diisocyanate, isophorone diisocyanate, and norbornane diisocyanate. These compounds can be used alone or in combination of two or more.

The diol compound (b) having at least one carboxyl group and two hydroxyl groups in one molecule includes dimethylolpropionic acid, dimethylolbutanoic acid, trimethylolpropane, glycerin and the like.
A trifunctional polyol obtained by addition polymerization of caprolactone and a cyclic acid anhydride such as maleic anhydride, phthalic anhydride or succinic anhydride have at least one or more carboxyl groups in one molecule obtained by a ring-opening addition reaction; Half-ester compound having two hydroxyl groups, dimethylolpropionic acid modified with ε-caprolactone, compound having two hydroxyl groups in one molecule, dimethylolbutanoic acid is ε-
Examples thereof include compounds modified with caprolactone and having two hydroxyl groups in one molecule, and can be used alone or in combination of two or more.

The glycol compound containing a hydroxyl group at the terminal (c) includes, for example, polyethylene glycol,
Polyether polyols such as polypropylene glycol and polytetramethylene glycol, ethylene oxide-modified bisphenol, propylene oxide-modified bisphenol, polyglycol obtained by copolymerization of ethylene oxide and propylene oxide, 1-6 hexanediol, 4-5 pen Tangyl, 3-methyl-
1,5 pentanediol, 1,9-nonanediol, 2
And aliphatic polycarbonate polyols obtained from one or more diols selected from -methyl-1,8-octanediol and dimethyl carbonate. The number average molecular weight of the glycol compound (c) is 30 in order to provide the obtained photocurable resin composition with storage stability, sufficient adhesion, water resistance, magic stain resistance and the like to the obtained coating film.
0 to 3000 is preferred. That is, if it is less than 300, the adhesion is inferior, and if it exceeds 3000, the magic stain resistance and the water resistance decrease.

The hydroxyl group-containing unsaturated compound (d) which is photopolymerizable and has at least one unsaturated double bond includes, for example, 2-hydroxyethyl acrylate,
-Hydroxypropyl acrylate, 4-hydroxybutyl acrylate, ethylene oxide-modified compounds thereof, propylene oxide-modified compounds, dimethyl trimethylene carbonate-modified hydroxy acrylate (for example, HEAC-1 manufactured by Daicel Chemical Industries, Ltd .; hydroxyl value = 170, etc.), poly Caprolactone-modified hydroxy acrylate (for example, PLAC manufactured by Daicel Chemical Industries, Ltd.)
Hydroxyalkyl (meth) acrylates such as CEL FA-1,2,3,4,5) and pentaerythritol triacrylate are preferred.

Here, the components (a) to (d) are
For example, a carboxyl group-containing polyfunctional urethane acrylate compound having two or more unsaturated double bonds at one terminal can be obtained by reacting at a temperature of 60 to 90 ° C. under normal pressure for 1 to 20 hours. The polymerization average molecular weight of the urethane acrylate compound is preferably from 1,000 to 15,000,
Furthermore, 1000 to 7000 is more preferable in terms of storage stability when diluted with water and strength of the coating film when cured.

The component (A) used in the present invention neutralizes the carboxyl group-containing polyfunctional urethane acrylate compound thus obtained by further reacting with a compound having an amino group having no active hydrogen. Can be obtained. As the compound having an amino group, triethylamine, triethanolamine, diethylaminoethanol, N-methyldiethylamine and the like are preferable. In this reaction, for example, the equivalent ratio of (the compound having an amino group having no active hydrogen) / (the carboxyl group in the urethane acrylate compound) is 1.0 to 1.4,
Preferably, the reaction is performed under the conditions of 1.1 to 1.3.

In the component (A) used in the present invention, a carboxyl group neutralized with an amino compound is provided by the reaction of the component (b) with the compound having an amino group having no active hydrogen. , (C) component,
An oxyalkylene group can be provided.

The photocurable resin composition of the present invention can further contain, if necessary, a water-soluble photopolymerizable compound (B) having one or more photopolymerizable unsaturated double bonds per molecule. . As the water-soluble photopolymerizable compound (B), a monofunctional or polyfunctional acrylate compound or the like can be preferably used. Examples of these water-soluble photopolymerizable monomers include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxydiethylene glycol (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, and N, N- Dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, polyethylene glycol di (meth) acrylate,
Diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, ethylene oxide-added trimethylolpropane tri (meth) acrylate [(meth) acrylate means methacrylate and acrylate, the same applies hereinafter), N-vinylpyrrolidone, Acryloyl morpholine, N-vinylcaprolactam, and the like, among which acryloylmorpholine, N-vinylpyrrolidone and N-vinylcaprolactam have good storage stability of the resin composition when a photopolymerization initiator is blended. Is preferred. These components may be used alone or as a mixture of two or more, and preferably 0 to 5 based on the sum of the components (A).
0% by mass is blended, and particularly preferably 25% by mass or less. When this amount exceeds 50% by mass, the storage stability of the resin composition and the properties of the obtained coating film tend to be generally deteriorated.

Further, the photocurable resin composition of the present invention comprises
(D) It contains a photopolymerization initiator as a component. Examples of the photopolymerization initiator include, for example, carbonyl [benzophenone, diacetyl, benzyl, benzoin, ω-bromoacetophenone, chloroacetone, acetophenone,
2-diethoxyacetophenone, 2,2-dimethoxy-
2-phenylacetone, p-dimethylaminoacetophenone, p-dimethylaminopropiophenone, 2-chlorobenzophenone, p, p'-bisdiethylaminobenzophenone, Michler's ketone, benzoin methyl ether, benzoin isobutyl ether, benzoin-n-
Butyl ether, benzyldimethyl ketal, 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methyl-1-one, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1- (4-isopropylphenyl) -2-hydroxy-2-methylpropan-1-one, methylbenzoyl formate, 2,2-
Diethoxyacetophenone, 4-N, N'-dimethylacetophenones], sulfides (such as diphenyl disulfide and dibenzyl disulfide), quinones (such as benzoquinone and anthraquinone), and azo (azobisisobutyronitrile, 2,2) '-Azobispropane, hydrazine, etc.), sulfochlorides (such as thioxanthone), peroxides (such as benzoyl peroxide, di-t-butyl peroxide), isoamyl o-dimethylaminobenzoate and the like. 2-hydroxy-
2-methyl-1-one, 2-hydroxy-2-methyl-
1-phenylpropan-1-one, 1- (4-isopropylphenyl) -2-hydroxy-2-methylpropan-1-one, 1-hydroxycyclohexylphenyl ketone, and the like are preferable in terms of solubility. These photopolymerization initiators can be used alone or in combination of two or more.

These photopolymerization initiators (D) are used with respect to 100 parts by weight of the total of the components (A) and (B).
It is preferably used in an amount of 1 to 10 parts by weight, in particular 3 to 5 parts by weight. If the amount is less than 1 part by weight, the photocurability is not sufficient, and if it exceeds 10 parts by weight, the physical properties of the obtained coating film tend to be generally reduced.

Further, the photocurable resin composition of the present invention comprises
Contains water. The amount of water in the photocurable resin composition is preferably such that the solid concentration of the photocurable resin composition is 20 to 80% by weight.

The resin composition and paint of the present invention include metal materials such as iron and aluminum, calcium silicate plates, lightweight concrete plates, asbestos cement plates, inorganic building materials such as mortar, wood, paper, and plastic base materials. It can be used as a UV curable paint or printing ink. When used as a paint, a photopolymerizable monomer, an organic solvent, a leveling agent, a polymerization inhibitor and other modifiers described below other than the water-soluble polymerizable compound (B) may be added. it can.

The photopolymerizable monomers include, for example, methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, t-butyl acrylate, isobutyl acrylate, ethylhexyl acrylate, isodecyl acrylate, n-hexyl acrylate, stearyl Acrylate, lauryl acrylate, tridecyl acrylate, ethoxyethyl acrylate, methoxyethyl acrylate, glycidyl acrylate, butoxyethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-methoxyethoxy acrylate, 2-ethoxyethoxyethyl acrylate, Methoxydiethylene glycol acrylate, ethoxydiethylene glycol acrylate, Toki Siji propylene glycol acrylate, octafluoropentyl acrylate, N,
N-dimethylaminoethyl acrylate, N, N-diethylaminoethyl acrylate, allyl acrylate,
1,3-butanediol acrylate, 1,4-butanediol acrylate, 1,6-hexanediol acrylate, polyethylene glycol diacrylate, diethylene glycol diacrylate, neopentyl glycol diacrylate, triethylene glycol diacrylate, tripropylene glycol diacrylate ,
Hydroxypivalic acid ester neopentyl glycol diacrylate, trimethylolpropane diacrylate, 1,3-bis (hydroxyethyl) -5,5-dimethylhydantoin, 3-methylpentanediol acrylate, α-, ω-diacrylbisdiethylene glycol phthalate , Trimethylolpropane triacrylate, pentaerythritol acrylate, pentaerythritol hexaacrylate, dipentaerythritol monohydroxypentaacrylate, α, ω-tetraallylbistrimethylolpropane tetrahydrophthalate, 2
-Hydroxyethyl acryloyl phosphate, trimethylolpropane trimethacrylate, ethylene glycol di (meth) acrylate, [(meth) acrylate means methacrylate and acrylate, the same applies hereinafter), tetraethylene glycol di (meth) acrylate, polyethylene glycol Di (meth) acrylate, 1,4-butanediol di (meth) acrylate,
1,6-hexanediol di (meth) acrylate, neopentyl glycol dimethacrylate, diacryloxyethyl phosphate, and the like.

The photocurable resin composition of the present invention may further contain (i) a hydrophilic organic solvent such as an alcohol-based organic solvent or a ketone-based organic solvent, or (ii) polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl formamide, aqueous Polyurethane resin (for example, U-coat UWS- manufactured by Sanyo Chemical Industry Co., Ltd.)
Aqueous organic compounds such as 140, 145 and Samprene series, Daiichi Kogyo Seiyaku's Superflex series, Zeneca's Neoretz series, Mitsui Toatsu Chemical's Orester series, etc.) (iii) Carbonic acid Calcium, talc, mica, clay,
Various fillers and pigments such as silica powder, colloidal silica, barium sulfate, aluminum hydroxide, zinc stearate, zinc white, red pepper, azo pigment, etc .; (iv) hydroquinone, hydroquinone monomethyl ether, benzoquinone, pt-butylcatechol;
A coating material can be obtained by adding a polymerization inhibitor such as 2,6-di-t-butyl-4-methylphenol.

Examples of the leveling agent include polyether-modified dimethylpolysiloxane copolymer, polyester-modified dimethylpolysiloxane copolymer, polyether-modified methylalkylpolysiloxane copolymer, aralkyl-modified methylalkylpolysiloxane copolymer, And polyether-modified methylalkylpolysiloxane copolymers.

[0020]

EXAMPLES Next, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto. In the following, "part" and "%"
All are by weight unless otherwise specified.

Production Example 1 (Urethane acrylate compound
1) After introducing air gas into a reaction vessel equipped with a stirrer, thermometer, cooling pipe and air gas introduction pipe, 38.3 parts of 2-hydroxyethyl acrylate, tetramethylol methane triacrylate (Shin-Nakamura Chemical Co., Ltd.) NK ester A-TMM-3L, hydroxyl value 460mgKOH /
g) 167 parts, polyoxytetramethylene glycol (manufactured by Hodogaya Chemical Co., Ltd., PTG650SN, molecular weight: about 68)
2) 236 parts, dimethylolbutanoic acid (manufactured by Mitsubishi Chemical Corporation)
Hydroxyl value 751mgKOH / g, acid value = 382mgK
(OH / g) 49.5 parts, hydroquinone monomethyl ether 0.25 parts, dibutyltin dilaurate (L101 manufactured by Tokyo Fine Chemical Co., Ltd.) 0.50 parts, triethylamine (Mitsubishi Gas Chemical Co., molecular weight 101.1) 1
6.7 parts, tripropylene glycol diacrylate (ACTILANE424, manufactured by AKCROS) 173
Acryloylmorpholine (ACM manufactured by Kojin Co., Ltd.)
O) 100 parts were charged, the temperature was raised to 70 ° C, the temperature was kept at 70 to 75 ° C, and 172 parts of tolylene diisocyanate (Coronate T80, manufactured by Nippon Polyurethane Industry Co., Ltd.) was uniformly dropped in 3 hours to carry out a reaction. When the reaction was continued for about 15 hours after completion of the dropwise addition, IR measurement confirmed that the isocyanate had disappeared, and the reaction was terminated. The weight average molecular weight was 3400 and the acid value was 2
0 urethane acrylate compound was obtained. Then 60 ° C
, 1165 parts of distilled water and triethylamine.
A mixture of 5 parts was uniformly dropped for 2 hours, and the resin content was 45% by mass.
A water-dispersed urethane acrylate compound was obtained.

Production Example 2 (Urethane acrylate compound
2) After introducing air gas into a reaction vessel equipped with a stirrer, a thermometer, a cooling pipe and an air gas introduction pipe, 30.2 butyl 2-hydroxyethyl acrylate and tetramethylol methane triacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.) , NK ester A-TMM-3L hydroxyl value 460mgKOH / g)
131.6 parts, 236 parts of polycarbonate diol (PLACCEL CD210PL, manufactured by Daicel Chemical Industries, hydroxyl value = 113.3 mgKOH / g), dimethylolbutanoic acid (hydroxyl value of 751 mgKO manufactured by Mitsubishi Chemical Corporation)
H / g, acid value = 382 mg KOH / g) 39 parts, hydroquinone monomethyl ether 0.3 parts, dibutyltin dilaurate (L10 manufactured by Tokyo Fine Chemical Co., Ltd.)
1) 0.6 parts, triethylamine (manufactured by Mitsubishi Gas Chemical Company,
13.1 parts of tripropylene glycol diacrylate (ACTILA manufactured by AKCROS)
NE424) 184 parts and acryloyl morpholine (ACMO manufactured by Kojin Co., Ltd.) 92 parts were charged, heated to 70 ° C., and then kept at 70 to 75 ° C., and isophorone diisocyanate (Vestanat IPDI manufactured by Huls) 1
73.2 parts were uniformly dropped in 3 hours to carry out a reaction. When the reaction was continued for about 15 hours after the completion of the dropwise addition, IR measurement confirmed that the isocyanate had disappeared, and the reaction was terminated. Thus, a urethane acrylate compound having a weight average molecular weight of 8000 and an acid value of 16.5 was obtained. Thereafter, the temperature is maintained at 60 ° C. and distilled water 11
A mixture of 00 parts and 19 parts of triethylamine was uniformly dropped for 2 hours to obtain a water-dispersed urethane acrylate compound having a resin content of 45%.

Production Example 3 (Urethane acrylate compound
3) After introducing air gas into a reaction vessel equipped with a stirrer, thermometer, cooling pipe and air gas introduction pipe, 30.2 parts of 2-hydroxyethyl acrylate and tetramethylol methane triacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.) , NK ester A-TMM-3L hydroxyl value 460mgKOH / g)
131.6 parts, polyoxytetramethylene glycol (manufactured by Hodogaya Chemical Co., Ltd., PTG650SN, molecular weight: about 68)
2) 236 parts, dimethylolbutanoic acid (manufactured by Mitsubishi Chemical Corporation)
Hydroxyl value 751mgKOH / g, acid value = 382mgK
(OH / g) 39 parts, hydroquinone monomethyl ether 0.3 parts, dibutyltin dilaurate (L101 manufactured by Tokyo Fine Chemical Co., Ltd.) 0.6 parts, triethylamine (Mitsubishi Gas Chemical Co., molecular weight 101.1) 13.1
Parts, tripropylene glycol diacrylate (AKC
ACTILANE 424 manufactured by ROS) 184 parts, acryloyl morpholine (ACMO manufactured by Kojin Co., Ltd.) 92
Then, the mixture was heated to 70 ° C. and kept at 70 to 75 ° C., and 160.8 parts of norbornane diisocyanate (trade name: NBDI% NCO 40.8, Mitsui Toatsu Chemicals, Inc.) was uniformly dropped in 3 hours to carry out a reaction. . When the reaction was carried out for about 15 hours after the completion of the dropwise addition, IR measurement confirmed that the isocyanate had disappeared, and the reaction was terminated. Thus, a urethane acrylate compound having a number average molecular weight of 7,000 and an acid value of 17 was obtained. Then 6
Keep at 0 ° C, 1085 parts of distilled water and triethylamine 1
The mixture with 9.5 parts was uniformly dropped for 2 hours to obtain a water-dispersed urethane acrylate compound.

Examples 1 to 3 Using the water-dispersed urethane acrylate compounds obtained in Production Examples 1 to 3, 2-hydroxy-2-methyl-1-amine was used as a photopolymerization initiator for the resin component of each resin. A curable resin composition according to the present invention was prepared by mixing and uniformly mixing 3% by weight of phenylpropan-1-one (trade name: Darocur 1173, manufactured by Ciba Geigy). Table 1 lists the formulations.

[0025]

[Table 1]

Application Example The curable resin composition obtained in each of the above Examples was applied to a transparent hard PVC plate (150 mm × 70 mm, manufactured by Nippon Test Panel Co., Ltd.).
× 2 mm). 20 and dried in a hot air dryer heated to 60 ° C. for about 5 minutes to volatilize the dilution water, and then an ultraviolet irradiation device (6 kW, 80 w / cm × 2)
Lamp, UV irradiation device; manufactured by Nippon Battery Co., Ltd.)
m 1 high pressure mercury lamp, irradiation distance 15cm, conveyor speed 1
Irradiation was performed at 0 m / min (approximate dose of about 250 mJ / cm2 at one time). The coating film thus obtained was subjected to the following various performance tests. (1) Paint stability: The stability after storage at room temperature for one month was visually observed. (2) Water resistance: half of the coating base material was placed in tap water at 40 ° C for 24 hours.
After soaking for an hour, the appearance of the coating film surface was visually observed. (3) Adhesion: Based on JIS-K5400 cross cut test. (4) Magic stainability: After contaminating the coating film with red and black oily magic, leaving it at room temperature for 6 hours, n-
The extent and condition of the stain on the coating film wiped with butanol was comprehensively visually determined. (5) Water washability: about 5 in a hot air dryer heated to 60 ° C.
After drying for 5 minutes to evaporate the dilution water, the coated plate was immersed in tap water for 1 hour, and the resin remaining on the surface of the coated plate was visually observed. Table 2 shows the results.

[0027]

[Table 2]

[0028]

The curable resin composition of the present invention is most suitable as a water-based paint, is inexpensive, has excellent cleaning properties for uncured paint adhered to coating equipment, and has excellent adhesion, magic stain and water resistance. Produces an excellent cured coating.

Claims (1)

[Claims] 1. A photocurable resin composition comprising (A) a polyfunctional urethane acrylate having a carboxyl group neutralized with an oxyalkylene group and an amino compound, (D) a photopolymerization initiator, and water.