JPH0718206A - Highly hydrophilic coating material - Google Patents

Abstract

PURPOSE:To provide the material suitable for imparting hydrophilicity and corrosion protective performance to the surface of an aluminum fin of the heat exchanger for an air conditioner. CONSTITUTION:The material contains: fine resin particles having a swelling degree with water of at most 50wt.% and having a hydrophilic functional group on the surface thereof; water; a water-soluble or water-dispersible resin; and an alkali metal zirconium carbonate or ammonium zirconium carbonate. The aluminum fin of the heat exchanger for an air conditioner, treated with this coating material to make it hydrophilic is free from lowering of the corrosion protective and hydrophilic effects over a long period of time.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a highly hydrophilic paint. More specifically, the present invention relates to a highly hydrophilic coating suitable for imparting hydrophilicity and anticorrosiveness to the aluminum fin surface of a heat exchanger for an air conditioner.

[0002]

2. Description of the Related Art Conventionally, aluminum fins for heat exchangers for air conditioners have their surfaces treated with boehmite, acrylic coating liquid or water glass. The purpose of such treatment is to prevent corrosion of aluminum, and to prevent condensed water droplets generated during the operation of the air conditioner from quickly flowing on the fin surface and becoming water droplets on the fin surface. Since recent heat exchangers have become smaller and the spacing between aluminum fins has been narrowed to 1.5 to 3 mm, a bridge will be created between the fins due to water droplets of condensed water during operation unless hydrophilic treatment is applied, resulting in poor ventilation. Heat exchange efficiency decreases.

However, it is pointed out that the boehmite treatment is inferior in productivity although it is sufficient in terms of hydrophilic treatment since it is generally performed after fining. In order to solve this problem, a method of coating a large amount of aluminum surface by coating an acrylic coating liquid or water glass before fin processing was devised. For example, JP-A-55-164264 discloses a coating material containing an aqueous resin, a surfactant and synthetic silica. However, although fins hydrophilically treated with such a coating are sufficiently excellent in hydrophilicity and anticorrosion, there is a problem in that when the fins are punched, the machining tool wears sharply and shortens the tool life. Came. This problem also occurred in the water glass treatment. It has also been found that fins treated with water glass are severely damaged by acid rain.

Therefore, a paint has been developed which imparts hydrophilicity and anticorrosion property, does not wear a processing tool, and is resistant to acid rain.
For example, as disclosed in JP-A-63-258966,
It is a highly hydrophilic coating material comprising water, a water-soluble resin, a water-absorbent microgel, an alkali metal zirconium carbonate or an ammonium salt, and a surfactant if necessary. This paint can almost solve the above problems, and has hydrophilicity, corrosion resistance, and
And although the processability is satisfied, there is a problem that the water-absorbent microgel absorbs water that is condensed during operation of the heat exchanger and swells because the water-absorbent microgel has too good water absorbency, and the coating strength becomes weak. .

[0005]

DISCLOSURE OF THE INVENTION The present inventors have conducted extensive studies to solve the above problems, and as a result, water swelling rate is 50% by weight or less, resin fine particles having a hydrophilic functional group on the surface of fine particles, water, A highly hydrophilic coating containing an aqueous resin and zirconium carbonate alkali metal salt or ammonia salt is hydrophilic,
The inventors have found that they have excellent corrosion resistance, acid rain resistance, and workability, and have reached the present invention.

[0006]

The present invention has a water swelling ratio of 50.
Resin particles (a), water (b), water-soluble resin or water-dispersible resin having a hydrophilic functional group on the surface of fine particles in an amount of not more than 10% by weight.
(c) A highly hydrophilic coating material containing zirconium carbonate alkali metal salt or ammonia salt (d) is provided.

The resin fine particles (a) having a hydrophilic functional group on the surface of the fine particles have no or little water absorption inside the fine particles because the inside of the fine particles are lipophilic, but since they have a hydrophilic functional group on the surface of the fine particles, The hydrophilicity of the surface of the fine particles is not reduced. The water swelling rate of the resin fine particles (a) is 50% by weight or less, but 20% by weight or less is preferable from the viewpoint of coating film strength. When the water swelling rate exceeds 50% by weight, if used for a long period of time, dew condensation water is absorbed and the coating film becomes weak, so that it cannot withstand long-term use.

The resin fine particles (a) are produced, for example, by the following method. (1) A lipophilic compound having an α, β-ethylenically unsaturated double bond and a hydrophilic compound having an α, β-ethylenically unsaturated double bond are emulsion-polymerized in water. (2) A lipophilic compound having an α, β-ethylenically unsaturated double bond is solution-polymerized in a solvent, and then a hydrophilic compound having an α, β-ethylenically unsaturated double bond is used. Seed polymerize with solution. (3) A lipophilic compound having an α, β-ethylenically unsaturated double bond is solution polymerized in a solvent, and a hydrophilic α, β-ethylenically unsaturated double bond is present in the presence of this polymer. Graft polymerization of the compound having

(4) A lipophilic compound having an α, β-ethylenically unsaturated double bond is emulsion-polymerized by using a compound containing a tertiary ammonium salt as an emulsifier (JP-A-2-263805). By this method, cationic resin fine particles are obtained. Furthermore, the tertiary functional ammonium salt of the obtained resin fine particles may be reacted with a compound having an epoxy group and other reactive functional groups to introduce a reactive functional group on the surface of the fine particles. (5) Emulsion polymerization of a lipophilic compound having an α, β-ethylenically unsaturated double bond using a carboxylate-containing compound as an emulsifier. By this method, anionic resin fine particles are obtained. Further, the carboxylic acid of the obtained resin fine particles may be reacted with a compound having an epoxy group and another reactive functional group to introduce a reactive functional group on the fine particle surface.

Examples of the lipophilic compound having an α, β-ethylenically unsaturated double bond include (meth) acrylic acid such as methyl (meth) acrylate, ethyl (meth) acrylate and butyl (meth) acrylate. Alkyl ester, alkenyl ester of (meth) acrylic acid such as glycidyl (meth) acrylate, hydroxy (meth) acrylate, styrene, acrylonitrile, monofunctional monomer such as vinyl acetate, bifunctional monomer such as acrylic acid ester of ethylene glycol, Examples thereof include bifunctional oligomers or polyfunctional prepolymers obtained by extending polyethylene glycol with isocyanate and reacting hydroxyethyl (meth) acrylate at the terminals. These are one type or two types.
A combination of two or more species can be used.

Examples of the hydrophilic compound having an α, β-ethylenically unsaturated double bond include acrylic acid, tacrylic acid,
Anionic monomers such as maleic acid and itaconic acid, 2,
One or more kinds of monomers selected from cationic monomers such as 2-dimethylaminoethyl (meth) acrylate and diethylaminoethyl (meth) acrylate can be used. When an anionic monomer is used, anionic resin fine particles are obtained, but these anionic monomers may be neutralized with an alkali metal, aqueous ammonia, amines or the like before the polymerization, or after the polymerization. You can mix them up. Further, when a cationic monomer is used, cationic resin fine particles are obtained, but these cationic monomers may be neutralized with an acid, a carboxylic acid or the like before the polymerization, or may be neutralized after the polymerization. Is also good.

When the resin fine particles (a) are polymerized, an anionic or nonionic low molecular surface active agent may be used within the range where physical properties such as water resistance are not impaired for the purpose of assisting emulsification. These emulsifiers are contained in an amount of 0.1 to 50% by weight based on the compound having an α, β-ethylenically unsaturated double bond, preferably
It is used in a proportion of 0.1 to 20% by weight, and the temperature for polymerizing the resin fine particles is 50 to 95 ° C, preferably 65 to 80 ° C.

Resin fine particles produced by various methods
The particle size of (a) is usually 0.003 to 10 μm as measured by the light scattering method.
m, but a suitable range for use in the highly hydrophilic coating material of the present invention is 0.05 to 5 μm. When the average particle size exceeds 5 μm, the coating film is as thin as 1 to 3 μm, and therefore the coating film strength is weakened by the amount necessary to obtain a sufficient hydrophilic effect. In order to bond the resin fine particles (a) firmly to the coating film, a hydroxyl group or a carboxyl group is introduced on the surface of the resin fine particles (a), and zirconium carbonate alkali metal salt or ammonium salt (d) It may be chelated to the resin.

When an anionic resin is used as the water-soluble resin or the water-dispersed resin (c), the anionic resin fine particles can be used as an aqueous dispersion or after being dried.
The cationic resin fine particles must be dried before use. When a nonionic resin is used as the water-soluble resin or the water-dispersed resin (c), both the anionic resin fine particles and the cationic resin fine particles can be used either as an aqueous dispersion or as a dried powder. The aqueous dispersion of the resin fine particles (a) can be dried using a hot air oven, a thin film evaporator, a spray dryer or the like.

Resin fine particles having hydrophilic functional groups on the surface
(a) is the solid content of the water-soluble resin or water-dispersible resin (c)
It is preferable to add 1 to 200 parts by weight in terms of solid content to 100 parts by weight. If it exceeds 200 parts by weight, sufficient water resistance cannot be obtained and sufficient coating strength cannot be obtained.

The water-soluble resin or water-dispersible resin (c) is
An essentially hydrophilic film is formed on a substrate, and resin fine particles (a) having a water swelling ratio of 50% by weight or less and having a hydrophilic functional group on the surface of the fine particles are mixed in order to be fixed in this film. As the water-soluble resin, polyvinyl alcohol-based, methyl cellulose-based, carboxydimethyl cellulose-based, hydroxyethyl cellulose-based, polyacrylic acid, acrylic acid-vinyl alcohol copolymer, polyacrylic acid soda-based, acrylic acid-soda-acrylic acid amide copolymer Examples thereof include polymers and the like, and they are used as one kind or as a mixture of two or more kinds.

As the water-dispersible resin, a monomer having both an α, β-ethylenically unsaturated double bond and a carboxyl group, and another monomer having an α, β-ethylenically unsaturated double bond in water are used. Examples thereof include acrylic resin aqueous dispersions obtained by emulsion polymerization or suspension polymerization. Examples of the monomer having both the α, β-ethylenically unsaturated double bond and the carboxyl group include acrylic acid, methacrylic acid, maleic acid and itaconic acid.

Other monomers having an α, β-ethylenically unsaturated double bond include (meth) acrylate-based: methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate. , (Meth) acrylate, butyl (meth) acrylate, (meth)
Hexyl acrylate, Octyl (meth) acrylate,
C ₁ -C ₁₈ alkyl ester of (meth) acrylic acid such as lauryl (meth) acrylate, C ₂ -C ₂₀ alkenyl ester of (meth) acrylic acid such as glycidyl (meth) acrylate, allyl (meth) acrylate, hydroxyl ethyl (meth) acrylate, hydroxyl ethyl (meth) acrylate, hydroxypropyl (meth) acrylate, C ₂ -C ₂₀ hydroxyalkyl esters, allyl oxyl ethyl (meth) acrylate (meth) acrylic acid such as hydroxyethyl (meth) acrylate (meth) C ₃ -C ₁₉ alkenyloxy Le alkyl esters of acrylic acid and the like, styrene, alpha-methyl styrene, vinyl toluene, p- chlorostyrene, acrylonitrile, methacrylonitrile, methyl isopropenyl Niruketon, vinyl acetate, Sulfonyl propionate and the like.

In the highly hydrophilic coating material of the present invention, an alkali metal zirconium carbonate or an ammonia salt (d) is further used. Zirconium carbonate carbonate or ammonia salt (d) is known to cross-link with OH group, COOH group, etc., and acts as an insolubilizing agent for water-soluble resin or water-dispersible resin, that is, as a cross-linking agent. Contributes to the corrosion resistance of the material. Zirconium carbonate alkali metal or ammonia salt (d), ₂₀ to 300 parts by weight of the alkali metal zirconium carbonate or ammonia salt (d) converted to ZrO ₂ with respect to 100 parts by weight of the water-soluble resin or water-dispersible resin, It is preferably used in the range of 30 to 200 parts by weight. If it is less than 20 parts by weight, it is difficult to obtain the water resistance and corrosion resistance of the coating film, and if it exceeds 300 parts by weight, it is difficult to obtain the hydrophilicity and processability of the coating film.

When preparing the highly hydrophilic paint, a surfactant is optionally used. When the water-soluble resin or water-dispersible resin (c) is anionic or nonionic and the resin fine particles (a) is anionic, a nonionic or anionic surfactant can be used. When the water-soluble resin or water-dispersible resin (c) is a cationic or nonionic resin and the resin fine particles (a) is a cationic resin, a nonionic or cationic surfactant can be used.

The nonionic surfactants include polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, polyoxyethylene cetyl ether and other polyoxyethylene alkyl ethers, polyoxyethylene octyl phenyl ether, polyoxyethylene alkyl allyl ether, Polyoxyethylene derivative,
Examples thereof include sorbitan fatty acid esters such as oxyethylene / oxypropylene block copolymers, sorbitan monolaurate, sorbitan monostearate, and sorbitan trioleate, glycerin fatty acid esters, and polyoxyethylene fatty acid esters.

Examples of the anionic surfactant include fatty acid salts such as sodium stearate and potassium oleate, sodium lauryl sulfate, triethanolamine lauryl sulfate, alkyl sulfates such as ammonium lauryl sulfate, alkylbenzene sulfonates, and alkylnaphthalene sulfone. Acid salt, alkyl sulfosuccinate,
Examples thereof include alkyl diphenyl ether disulphonate, alkyl phosphate, and polyoxyethylene alkyl sulfate ester salt.

Examples of the cationic surfactant include stearylamine acetate, alkylamine salts such as stearylamine hydrochloride, lauryltrimethylammonium chloride, stearyltrimethylammonium chloride,
Examples thereof include quaternary ammonium salts such as distearyldimethylammonium, alkyl betaines such as lauryl betaine and stearyl betaine, and amine oxides.

Further, a coloring agent such as a pigment or a dye, a filler, a lubricant, an antifoaming agent, a leveling agent and the like can be added to the highly hydrophilic coating material of the present invention, if necessary. The highly hydrophilic coating composition of the present invention can be used not only as a precoat coating composition for coating aluminum fin materials, but also as a postcoat coating composition for coating processed fins.

[0025]

EXAMPLES The present invention will be described in more detail with reference to examples. In the examples, "part" and "%" mean "part by weight" and "% by weight", respectively. First, a synthesis example of each component used in the examples will be described. (A) Synthesis of Reactive Polymer Emulsifier 70 parts of acrylic acid, 70 parts of 2-ethylhexyl acrylate and 140 parts of 2-propanol were heated to 80 ° C. in a nitrogen atmosphere while stirring in a 1 liter reaction vessel. 1.1 parts of azobisisobutyronitrile (hereinafter abbreviated as AIBN) was added as a polymerization initiator, and the mixture was kept at 80 ° C. for 2 hours to complete the polymerization. Then, a mixture of 272.2 parts of a 10% aqueous sodium hydroxide solution and 200 parts of water was added, and heated to remove 2-propanol and a part of water by azeotropic distillation to obtain a polymeric emulsifier. After left standing overnight, 13.3 parts of glycidyl methacrylate was added, and the mixture was heated to 80 ° C. in an air atmosphere and kept for 4 hours. Then, the solid content was adjusted to 25% to obtain a reactive polymer emulsifier solution (a).

(B) Synthesis of reactive polymer emulsifier 70 parts of acrylic acid (70 mol% neutralized with sodium hydroxide),
30 parts of butyl acrylate and 400 parts of deionized water were heated to 80 ° C. in a nitrogen atmosphere while stirring in a 1 liter reaction vessel. 16 parts of 5% AAPD aqueous solution was added and maintained for 2 hours, then 4 parts of 5% AAPD aqueous solution was added, and after the addition was completed, the reaction was continued for 4 hours to complete the polymerization to obtain a polymeric emulsifier. Next, 100 parts of the obtained polymer emulsifier and 14.6 parts of glycidyl methacrylate (hereinafter abbreviated as GMA) were heated to 80 ° C. with stirring in a 1 liter reaction vessel and kept for 4 hours. Then, the solid content was adjusted to 20% to obtain a reactive polymer emulsifier solution (b).

(C) Synthesis of anionic resin fine particles 50 parts styrene, 40 parts ethyl methacrylate, 10 parts divinylbenzene, reactive polymer emulsifier solution (a) 80 parts (solid content)
20 parts) and 200 parts of deionized water were heated to 80 ° C. in a nitrogen atmosphere under stirring in a 1 liter reaction vessel. 5% azobisamidinopropane dihydrochloride (hereinafter abbreviated as AAPD)
Add 16 parts of aqueous solution and hold for 2 hours, then 5% AAPD
After adding 4 parts of the aqueous solution, the reaction mixture was heated to 80 ° C after the addition was completed.
Hold for time to complete the polymerization. 25% solids with deionized water
% To obtain an anionic resin fine particle water dispersion (c). The measurement result of the resin fine particle diameter in the water dispersion by the light scattering method was about 0.1 μm. The obtained anionic resin fine particle water dispersion was dried, powdered and immersed in water at 25 ° C. for 1 day. As a result, the water swelling ratio was 9%.

(D) Synthesis of anionic resin fine particles Anionic resin fine particles were prepared in the same manner as in the anionic resin fine particle water dispersion (c) except that 200 parts of deionized water was replaced with 120 parts of isopropyl alcohol and 140 parts of deionized water. An aqueous dispersion of resin fine particles (d) was obtained. The measurement result of the resin fine particle diameter in the water dispersion by the light scattering method was about 10 μm. The water swelling ratio of the resin fine particles was 12%.

(E) Synthesis of anionic resin fine particles 25 parts of styrene, 20 parts of ethyl methacrylate, 5 parts of divinylbenzene, 200 parts of reactive polymer emulsifier solution (a) (solid content)
50 parts) and 100 parts of deionized water were used to obtain an anionic resin particle water dispersion (e) in the same manner as the anionic resin particle water dispersion (c). The measurement result of the resin fine particle diameter in the water dispersion by the light scattering method was about 0.1 μm. The water swelling ratio of the resin fine particles was 70%.

(F) Synthesis of Cationic Resin Fine Particles 95 parts of styrene, 5 parts of divinylbenzene, 250 parts of polymer emulsifier solution (b) (50 parts of solid content) and 250 parts of deionized water were added to 1 part.
The mixture was heated to 80 ° C. in a nitrogen atmosphere while stirring in a liter reaction vessel. 16 parts of 5% AAPD aqueous solution was added and kept for 2 hours, then 4 parts of 5% AAPD aqueous solution was added, and after the addition was completed, the reaction temperature was kept at 80 ° C. for 4 hours to complete the polymerization, and the cationic resin fine particles An aqueous dispersion was obtained. The measurement result of the resin fine particle diameter in the water dispersion by the light scattering method was about 0.1 μm. Thereafter, the obtained aqueous dispersion of cationic resin fine particles was placed in a vat and dried at 50 ° C. in an oven dryer to obtain a cationic resin fine particle powder (f). The water swelling ratio of the resin fine particles was 8%.

(G) Synthesis of acrylic resin 30 parts of acrylic acid completely neutralized with diethanolamine,
20 parts of styrene, 20 parts of methyl methacrylate, 30 parts of 2-hydroxyethyl methacrylate and 200 parts of water were charged into a 1 liter reaction vessel and heated to 80 ° C. in a nitrogen atmosphere while stirring. Next, 20 parts of 5% AAPD aqueous solution was added and reacted for 6 hours, and then the solid content was adjusted to 25% to obtain an acrylic resin aqueous dispersion (g).

[Example 1] Vinyl alcohol acrylate copolymer (“Sumikagel L-5H” manufactured by Sumitomo Chemical Co., Ltd.) 50
Parts, hydroxyethyl cellulose resin 50 parts, anionic resin fine particle water dispersion (c) 200 parts (solid content 50 parts), surfactant (Daiichi Kogyo Seiyaku Co., Ltd. “New Frontier 250”)
Z ") and 50 parts of zirconium ammonium carbonate salt were mixed, the solid content was adjusted to 4% with ion-exchanged water, and the aluminum plate for aluminum fins was coated with a bar coater No. 10. This was baked in an electric drying oven at 260 ° C. for 20 seconds to obtain an aluminum fin material having a hydrophilic treatment layer of about 1 μm.

[Example 2] Vinyl alcohol acrylate copolymer "Sumikagel L-5H" 100 parts, cationic resin fine particle powder (f) 50 parts, surfactant "New Frontier 25"
[0Z] 50 parts and zirconium ammonium carbonate 50 parts were mixed to obtain an aluminum filler having a hydrophilic treatment layer of about 1 μm in the same manner as in Example 1. Example 3 An aluminum fin material having a hydrophilic treatment layer of about 1 μm was obtained in the same manner as in Example 1 except that the surfactant “New Frontier 250Z” was omitted.

Example 4 An aluminum filler having a hydrophilically treated layer of about 1 μm was obtained in the same manner as in Example 1 except that zirconium carbonate potassium salt was used instead of zirconium ammonium carbonate salt. [Example 5] Acrylic resin aqueous dispersion in place of 50 parts of vinyl acrylate copolymer "Sumikagel L-5H"
(g) An aluminum fin material having a hydrophilic treatment layer of about 1 μm was obtained in the same manner as in Example 1 except that 200 parts (50 parts by solid content) was used.

[Example 6] Example 6 was carried out except that 400 parts of an acrylic resin water dispersion (g) (100 parts by solid content) was used in place of 100 parts of the vinyl acrylate acrylate copolymer "Sumikagel L-5H". In the same manner as in Example 2, an aluminum fin material having a hydrophilic treatment layer of about 1 μm was obtained. Example 7 A hydrophilic treatment layer of about 1 μm was prepared in the same manner as in Example 1 except that the anionic resin fine particle water dispersion (d) was used in place of the anionic resin fine particle water dispersion (c). An aluminum fin material was obtained.

Comparative Example 1 About 1 μm was obtained in the same manner as in Example 1 except that the anionic resin fine particle water dispersion (c) was omitted.
An aluminum fin material having a hydrophilic treatment layer of m was obtained. [Comparative Example 2] An aluminum fin material having a hydrophilic treatment layer of about 1 µm was obtained in the same manner as in Example 6 except that the cationic resin fine particle powder (e) was removed. [Comparative Example 3] A hydrophilic treatment layer having a thickness of about 1 µm was obtained in the same manner as in Example 1 except that the anionic resin fine particle water dispersion (e) was used in place of the anionic resin fine particle water dispersion (c). An aluminum fin material was obtained.

The aluminum fin materials obtained in Examples and Comparative Examples were treated with 1,1,1-trichloroethane,
The following hydrophilicity test, corrosion resistance test, moldability test, and mold abrasion test were performed. The evaluation results are shown in Table 1. Hydrophilicity test: The surface condition of the aluminum fin material was visually observed. Continuity of hydrophilicity: After being immersed in running water for 8 hours under running water and dried in an electric drying oven at 80 ° C for 16 hours, 10 cycles were performed, and water wettability was visually observed.

Corrosion resistance test: Salt water was sprayed on the aluminum fin material, and the surface of the aluminum fin material after 10 days was visually observed. Formability test: Burning was applied to the aluminum fin material, and the occurrence of cracks in the bent portion was visually evaluated. Mold wear resistance: The wear state of the mold when the aluminum fin material was molded into a fixed shape using the mold was visually observed.

[0039]

[Table 1] ◎ ・ ・ ・ very good, ○ ・ ・ ・ good, △ ・ ・ ・ somewhat good, × ・ ・ ・ bad

[0040]

The aluminum fin of the heat exchanger for an air conditioner, which has been hydrophilized using the highly hydrophilic coating material of the present invention, has a sufficient anticorrosion effect for a long period of time and sufficient initial hydrophilicity, It is possible to prevent the hydrophilicity from deteriorating over time.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location C09D 133/00 PGB 133/02 PGE

Claims (5)

[Claims] 1. Resin fine particles (a), water (b), water-soluble resin or water-dispersible resin (c), which has a water-swelling rate of 50% by weight or less and which has hydrophilic functional groups on the surface of fine particles, alkali metal zirconium carbonate. Highly hydrophilic paint containing salt or ammonia salt (d). 2. The highly hydrophilic coating composition according to claim 1, wherein the resin fine particles (a) have a particle size of 0.05 to 5 μm. 3. The highly hydrophilic coating composition according to claim 1, wherein the resin fine particles (a) are microgel fine particles in which the inside of the fine particles is three-dimensionally crosslinked. 4. The water-soluble resin (c) is an acrylic acid-vinyl alcohol copolymer or a mixture of an acrylic acid-vinyl alcohol copolymer and water-soluble cellulose, according to any one of claims 1 to 3. Highly hydrophilic paint. 5. The water-dispersible resin (c) comprises a monomer having both an α, β-ethylenically unsaturated double bond and a carboxyl group and another monomer having an α, β-ethylenically unsaturated double bond. The highly hydrophilic coating composition according to claim 1, which is a resin obtained by emulsion polymerization or suspension polymerization in water.