JPH093397A - Highly hydrophilic paint - Google Patents

Abstract

PURPOSE: To provide a highly hydrophilic paint which is suitable for imparting retention of hydrophilicity and corrosion resistance on a high level to the surface of an aluminum fin of a heat exchanger for an air conditioner. CONSTITUTION: This highly hydrophilic paint comprises an alumina sol (a) wherein primary particles are in the form of feather, rod or ramification and have been previously agglomerated by a synthetic method to an average particle diameter of 0.5 to 20μm; and a water-soluble resin (b) prepd. by copolymerizing 10 to 80 pts. α,β-unsatd. monomer having a sulfonic acid or sodium sulfonate group, 10 to 50 pts. α,β-unsatd. monomer having a carboxylic group, and 10 to 50 pts. α,β-unsatd. monomer having an alcoholic hydroxyl group. A coating film formed by drying and curing the hydrophilic paint has very good retention of hydrophilicity and, is excellent also in adhesion and corrosion resistance, and the addition of an alumina sol in the form of amorphous gel minimizes the abrasion of a mold, prolonging the service life of the mold. Thus, the hydrophilic paint can offer a hydrophilic coating suitable for an aluminum fin material or the like for a heat exchanger.

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 suitable highly hydrophilic coating that imparts a high degree of hydrophilic persistence and corrosion resistance to the surface of an aluminum fin of a heat exchanger for an air conditioner. More specifically, it relates to a highly hydrophilic paint containing an alumina sol having a specific shape.

[0002]

2. Description of the Related Art Conventionally, aluminum and its alloys have been widely used for heat exchangers of air conditioners because of their excellent workability and thermal conductivity. In the heat exchanger of an air conditioner, the condensed water generated during cooling becomes water droplets, forming a water bridge between the fins, increasing the ventilation resistance and deteriorating the heat exchange rate, so the surface of the fin material is made hydrophilic. Generally, it is processed. On the other hand, in recent years, home appliances have been strongly required to be downsized, and air conditioners are no exception. In particular, heat exchangers, which occupy a large volume among air conditioners, are most strongly required to be downsized. The tendency of the fin shape to be complicated and the fin spacing to be narrowed due to such requirements imposes further improvement of hydrophilicity on the fins.

As a method for imparting hydrophilicity to the aluminum fin, there are methods such as chemical conversion treatment and coating with a hydrophilic paint. However, since the chemical conversion treatment is generally performed after fining such as drilling, it has a drawback of being inferior in productivity.

In order to solve this problem, there has been proposed a method of applying water glass or hydrophilic paint before fin processing. Examples of such hydrophilic paints include paints made of organic hydrophilic resins and paints containing synthetic silica. However, when an organic hydrophilic resin such as aqueous nylon, aqueous acrylic resin, polyvinyl alcohol, polyvinylpyrrolidone is used, the hydrophilicity is insufficient,
There are problems that the hydrophilicity and the anticorrosiveness cannot be balanced, or that the odor suppressing (preventing) effect is insufficient. On the other hand, when a coating material containing synthetic silica or the like is used to impart hydrophilicity, the hydrophilicity and anticorrosiveness are superior to those of ordinary organic hydrophilic coating materials, but the coating film is hard so that holes such as holes are formed. There are problems that the mold used for processing, the processing tool, etc. are heavily worn and the service life of the tool is shortened, and that the odor suppression (prevention) effect is insufficient.

Further, when water glass is applied, there are drawbacks such that the tool life is shortened or odor is adsorbed as in the case of using a coating material containing synthetic silica or the like.

In view of the above problems, there has been a demand for a coating material which is excellent in hydrophilicity and corrosion resistance and which gives a relatively soft coating film which does not shorten the life of the tool.

On the other hand, as a hydrophilic paint containing no synthetic silica or the like, Japanese Patent Laid-Open No. 5-22234 discloses a poly (meth) acrylic acid and a nitrate such as Al, Sn, Co, La, Ce and Ta. Japanese Patent Application Laid-Open No. 4-366182 discloses a hydrophilic coating film made of polyvinylpyrrolidone and polyvinyl alcohol.

Further, in JP-A-3-252461, a hydrophilic coating formed by a carboxylmethylcellulose derivative and N-methylolacrylamide is applied on a base coat of polyester urethane, and JP-A-63-17168.
Japanese Patent Publication No. 3 discloses a hydrophilic treatment coating film with polyacrylamide, styrene sulfonic acid, water-soluble urethane (used for both base coat and top coat).

However, these are insufficient in hydrophilicity and are not put to practical use. Generally, aluminum fins are required to have sufficient hydrophilicity not only immediately after forming a coating film, that is, in the initial stage, but also after various tests. The hydrophilicity persistence test assumes not only running water with condensed water / rainwater but also a drying process at 50 ° C with a heating medium at the time of heating, and soaking in running water for 8 hours and drying at 50 ° C for 16 hours as one cycle, and 20 cycles or more. Although evaluation is required, the surface treatment method using each of the above coating films or treatment agents does not sufficiently satisfy hydrophilicity.

In addition to the above, it does not contain synthetic silica or the like,
Those containing alumina sol or alumina are disclosed in JP-A-57 / 57
-134572, JP-A-58-76462, JP-A-59-205596, and JP-A-59-2.
29197, JP-A-60-164168,
JP-A-63-249643, JP-A-63-262
Some proposals have been made, such as JP-A No. 238, JP-A-63-262239, JP-A-2-22047, JP-A-5-70711, and JP-A-6-172777.

Japanese Unexamined Patent Publication (Kokai) No. 57-134572 discloses a method of subjecting an aluminum material to chemical conversion treatment with an acid treatment liquid containing an alumina sol or a silica sol. It seems that the use of alumina sol or silica sol tried to increase the surface area and improve the wettability with water, but the hydrophilicity is insufficient because the alumina sol is not aggregated.

Japanese Unexamined Patent Publication (Kokai) No. 58-76462 discloses an antifogging coating composition in which an alumina sol is combined with one or more kinds selected from the group consisting of specific carboxylates, sulfonates and phosphonates. ing. However, since this is intended for a synthetic resin film, a synthetic resin plate, and a glass plate, the adhesiveness with an aluminum material is poor. Also in this invention, since the alumina sol is not aggregated, the hydrophilicity is insufficient.

In JP-A-59-205596, a corrosion-resistant coating layer is provided on an aluminum plate, and a hydrophilic coating layer made of silicic acid, silicate, silica sol, alumina sol is formed on the surface of the corrosion-resistant coating layer. The disclosed fin material made of aluminum is disclosed. However, this hydrophilic coating layer is a dispersion of silicic acid, silicate, silica sol, alumina sol as it is coated on an aluminum plate,
Since it is baked, when using silicic acid, silicate, silica sol, there is a problem that the life of the tool is shortened as described above because the coating film is hard, and when using alumina sol. However, since it is used without agglomeration, the contact angle with water is 30 to 35 degrees, which is insufficient in terms of hydrophilicity.

Japanese Unexamined Patent Publication (Kokai) No. 59-229197 discloses a surface treatment method for an aluminum heat exchanger in which a corrosion-resistant surface treatment film is formed on an aluminum plate and then a suspension aqueous solution containing alumina fine particles is applied. It is disclosed. However, a suspension aqueous solution containing fine alumina particles is insufficient in hydrophilicity when used alone,
When it is used in combination with a polyethylene oxide thermoplastic polymer resin, hydrophilicity is improved to some extent as compared with a single system, but sufficient hydrophilicity cannot be ensured with an alumina sol that does not aggregate once.

Japanese Unexamined Patent Publication (Kokai) No. 60-164168 discloses a heat exchanger having a coating layer composed of a glass frit containing polyamide imide resin, Al ₂ O ₃ and calcium phosphate as main components. However, the heat exchanger in this invention is not a heat exchanger for an air conditioner,
Therefore, since the coating layer is not intended to improve hydrophilicity or anticorrosion property but is intended to improve heat resistance, even if this coating composition is used for an aluminum fin heat exchanger of an air conditioner, the coating layer Water bridge formation cannot be prevented. In addition, Al ₂ O shown here
₃ is alumina, which forms a hard film like synthetic silica, and is not suitable for aluminum fin heat exchangers of air conditioners because it shortens the tool life.

In Japanese Patent Laid-Open No. 63-249643, after a corrosion resistant film is formed on both sides of an aluminum plate, a hydrophilic inorganic material and a low molecular organic compound having a carbonyl group are formed on the surface of one of the corrosion resistant films. A hydrophilic first film is formed, and a hydrophilic second film composed of a water-soluble organic polymer compound or a water-soluble organic polymer compound and a low molecular weight organic compound having a carbonyl group is formed on the surface of the other corrosion-resistant film. Disclosed fin material for a heat exchanger. Alumina sol is mentioned as an example of the hydrophilic inorganic material forming the hydrophilic first film. However, sufficient hydrophilicity cannot be ensured with an alumina sol that does not aggregate once.

Further, since the hydrophilic first film uses a low molecular weight organic compound, it has a problem that the film forming performance is poor and only a brittle film can be formed.

In Japanese Patent Laid-Open No. 63-262238, an organic or inorganic corrosion resistant film is formed on a thin plate of aluminum or aluminum alloy, and water-soluble cellulose (or polyvinyl alcohol), alumina sol, melamine resin, urea is formed on the film. Disclosed is a heat exchanger fin member having a coating layer formed of a resin, an amino resin such as benzoguanamine resin, or the like. However, sufficient hydrophilicity cannot be ensured with an alumina sol that does not aggregate once.

Japanese Patent Laid-Open No. 63-262239 discloses a heat exchanger fin in which a coating layer made of water-soluble cellulose (or polyvinyl alcohol), alumina sol and chromium compound is formed on a thin plate of aluminum or aluminum alloy. The material is disclosed. However, sufficient hydrophilicity cannot be ensured with an alumina sol that does not aggregate once.

Japanese Patent Laid-Open No. 22047/1990 discloses a heat exchange in which a coating layer made of activated alumina fine particles and one of styrene-modified acrylic-melamine resin, epoxy resin and styrene-methacrylic acid ester resin is formed. A fin material is disclosed. However, the fine particles shown here are alumina, which forms a hard coating like synthetic silica and causes significant tool damage, and the hydrophilicity of such binder resin is also insufficient, so it is not suitable for aluminum fin heat exchangers of air conditioners. Is.

Japanese Patent Laid-Open No. 5-70711 discloses an aluminum-containing metal containing a hydrophilizing component made of alkali silicate, colloidal silica, alumina sol, or hydrophilic organic polymer material and a lubricating component made of siloxane compound. A hydrophilic treatment agent for a material is disclosed. However, sufficient hydrophilicity cannot be obtained with an alumina sol that does not aggregate once.

Japanese Unexamined Patent Publication (Kokai) No. 6-172777 discloses lubrication with a treatment liquid containing a siloxane compound on a hydrophilic coating containing at least one kind of alkali silicate, colloidal silica, alumina sol or hydrophilic organic polymer material. A coated, hydrophilic, lubricious aluminum-containing metallic material is disclosed. However, sufficient hydrophilicity cannot be obtained with an alumina sol that does not aggregate once.

As a result of repeated studies in view of the above-mentioned various problems, a non-silica or non-aqueous glass system which is excellent in hydrophilicity and anticorrosion and gives a relatively soft coating film which does not shorten the life of the tool. The inventors have found a highly hydrophilic paint and have reached the present invention.

[0024]

That is, according to the present invention, the primary particles have a feather-like, rod-like or dendritic shape / morphology, and they are agglomerated in advance by a synthetic method and have an average particle diameter of 0.5 to Alumina sol (a) which is 20 μm, and α having sulfonic acid or sodium sulfonate groups,
10 to 80 parts of β unsaturated monomer, 10 to 50 parts of α and β unsaturated monomers having a carboxylic acid group, and 10 to 50 parts of α and β unsaturated monomers having an alcoholic hydroxyl group. It is a highly hydrophilic coating material containing a water-soluble resin (b) obtained by copolymerizing parts.

Alumina sol (a) used in the present invention
Is a primary particle is an aqueous dispersion of hydrated alumina, having a colloidal size obtained by dispersing an anion in water as a stabilizer, in a form in which the primary particles are agglomerated in advance by a synthetic method, The average particle size of the aggregated particles is 0.5 to 20 μ.
m. Specifically, “Cataloid AS-3” manufactured by Catalyst Kasei Co., Ltd. may be mentioned.

In the present invention, a relatively large alumina sol having a specific shape and form is preferably used. That is,
By having a feather-like, rod-like or dendritic shape / morphology, the specific surface area is increased, and since the primary particles of these alumina sols are in an aggregated form,
The wettability to water could be improved by the capillary phenomenon. As a commercially available product of the alumina sol that can obtain such a special shape and form, the above-mentioned "Cataloid AS-3" manufactured by Catalyst Kasei Co., Ltd. can be mentioned.

[Cataloid AS manufactured by Catalysts & Chemicals Co., Ltd.
-1 "," Cataloid AS-2 "," Alumina sol-100 "manufactured by Nissan Chemical Industries, Ltd.," Alumina sol-20 "
0 "," alumina sol-520 ", Kawaken Fine Chemicals Co., Ltd." alumina clear sol "," aluminum sol- "
90 "of alumina sol and" Cataloid AS-3 "dispersed as primary particles having an average particle size of 2 to 100 nm.
The same form can be obtained by mixing with a composition of 10 parts to 0 parts / 100 parts and forming a coating.

Alumina sol (a) used in the present invention
Is in the process of transitioning from the amorphous gel to boehmite, and this state does not change in the aggregation process and the usual coil coat coating baking conditions (for example, 250 ° C. × 20 seconds). The alumina sol at the stage of transition from the amorphous gel to boehmite is softer than colloidal silica, and therefore, the abrasion of the blade of the press machine when processing the coating containing the alumina sol is extremely small.

Alumina sol (a) used in the present invention
Has an average particle diameter of 0.5 to 20 μm. In the present invention, by using the alumina sol (a), a film thickness of 0.
It has succeeded in increasing the contact surface area with water by roughening the surface of a hydrophilic coating film of 5 to 2 μm. Those having an average particle size of less than 0.5 μm are buried in the coating film, and those having an average particle size of more than 20 μm cause defects in the coating film such as lumps and are not suitable for use.

When the mixture of "Cataloid AS-3" and the alumina sol exemplified above is too large, it can be used after being classified by means such as centrifugation or filtration. Alternatively, the particle size can be adjusted by crushing with a high-pressure homogenizer or the like after forming the paint.

Alumina sol (a) used in the present invention
Is preferably contained in an amount of 0.1 to 50 parts by weight in 100 parts by weight of the coating solid content. If the amount is less than 0.1 part by weight, the hydrophilicity is insufficient, and if the amount is more than 50 parts by weight, the viscosity increases and the coatability deteriorates.

The water-soluble resin (b) used in the present invention means 10 to 80 parts of an α, β unsaturated monomer having a sulfonic acid group or a sodium sulfonate group, and an α, β unsaturated monomer having a carboxylic acid group. It is obtained by copolymerizing 10 to 50 parts of a saturated monomer and 10 to 50 parts of an α, β unsaturated monomer having an alcoholic hydroxyl group. The water-soluble resin is added to the substrate to form an essentially hydrophilic coating film and fix the alumina sol (a) in the coating film.

The α, β unsaturated monomer having a sulfonic acid group or a sodium sulfonate group exhibits anionic strong hydrophilicity and improves the wettability of the surface of the formed film with water.
Examples thereof include vinyl sulfonic acid, aryl sulfonic acid, 2-acrylamido-2-methyl sulfonic acid, styrene sulfonic acid, methacryloyloxyethyl sulfonic acid and all of these sodium salts, potassium salts, lithium salts and the like.

The α, β unsaturated monomer having a carboxylic acid group shows some hydrophilicity and adhesion to an aluminum substrate. Examples thereof include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid and the like.

The α, β-unsaturated monomer having an alcoholic hydroxyl group shows some hydrophilicity and further causes crosslinking with the active hydroxyl group on the alumina sol particles, so that the entire water-soluble resin fixes the alumina sol particles. It acts as a binder for doing so. Examples thereof include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, N-methylol (meth) acrylamide and the like.

The water-soluble resin (b) is preferably contained in an amount of 30 to 99.9 parts by weight based on 100 parts by weight of the coating solid content. If it is less than 30 parts by weight, the content of the alumina sol (a) becomes relatively large, the viscosity increases, and the coatability deteriorates.
On the other hand, when it exceeds 99.9 parts by weight, the content of the alumina sol (a) becomes relatively small and the hydrophilicity becomes insufficient.

The coating composition of the present invention comprises the above-mentioned component (a),
In addition to (b), one or more of water-soluble resins or water-dispersible resins such as cellulose-based, polyurethane-based, polyester-based, polyether polyol-based, polyamide-based, and epoxy-resin-based resins, and further, if necessary. Depending on the surfactant, hydrophilic organic particles or inorganic particles, antibacterial agents, lubricants,
You may mix | blend a coloring agent, a solvent, etc.

The highly hydrophilic coating material of the present invention can be used not only as a precoat coating material for coating aluminum fin materials, but also as a postcoat coating material for coating processed fins.

[0039]

Next, the present invention will be described by way of examples.

Synthesis Example 1 A 500 cc three-necked flask was charged with 6 g of 220 g of deionized water.
Stir at 0 ° C. 0.4 g of ammonium persulfate was charged, and 160 g of a 50% aqueous solution of 2-acrylamido-2-methylpropanesulfonic acid (2AA2MPSA) and 2 g of 2% were added.
-A mixed solution of 10 g of hydroxyethyl acrylate (HEA) and 10 g of acrylic acid (AA) is added dropwise over 1 hour. 0.4 g (5% aqueous solution) of ammonium persulfate was added 4 times every 50 minutes to complete the polymerization to obtain a water-soluble acrylic resin.

Synthesis Examples 2 to 6 (water-soluble acrylic resin-
Synthesis Example 1) Aqueous polymerization was carried out in the same manner as in Synthesis Example 1 with the composition (weight ratio) shown in Table 1 to obtain a water-soluble acrylic resin.

[0042]

[Table 1]

Example 1 The particle size of Cataloid AS-3 manufactured by Catalyst Kasei Co., Ltd. was measured by Microtrac MK-II particle size analyzer manufactured by Nikkiso Co., Ltd., and the average particle size was 0.8 μm. . Synthesis Example 1
70 parts by dry weight of the water-soluble acrylic resin obtained in
30 parts of the aggregate was mixed under stirring and diluted with ion-exchanged water to prepare a hydrophilic coating material having a nonvolatile content of 10%. Bar coater N is applied to an aluminum plate which has been subjected to phosphoric acid chromate treatment in advance.
After coating according to No. 6, it was baked for 20 seconds in a 250 ° C. gas oven (wind speed: 2 m / sec) to obtain an aluminum coating material having a coating thickness of about 1 μm.

Examples 2 to 5 In the same manner as in Example 1, except that the type and mixing ratio of Cataloid AS-3 and other alumina sols were changed, the water-soluble acrylic resin according to Synthesis Example 1 was used. Then, the hydrophilic coating material was adjusted to obtain an aluminum coating material. In Example 2, 70 parts / 30 parts by dry weight ratio of Cataloid AS-3 and Cataloid AS-1 manufactured by Catalyst Kasei Co., Ltd. was used, and in Example 3, Cataloid AS-3 and Aluminasol-200 manufactured by Nissan Kagaku Co., Ltd. In a dry weight ratio of 70 parts / 30 parts, Example 4
Is 50 parts / 50 parts by dry weight ratio of Cataloid AS-3 and Nissan Chemical Co., Ltd. alumina sol-200, and Example 5 is a dry weight ratio of Cataloid AS-3 and Kawaken Fine Chemical Co., Ltd. alumina sol-10. 70 parts / 30 parts were mixed and used.

The average particle size of each alumina sol mixture particle in the paint after being made into a paint is 6 μm, 6 μm, 18 μm and 3 μm, respectively.
m.

Examples 6 to 7 Hydrophilic paints were prepared by changing the composition ratio of the cataloid AS-3 and the water-soluble acrylic resin according to Synthesis Example 1 to obtain aluminum coating agents. Example 6 was dry weight, 99.9 parts of water-soluble acrylic resin and 0.1 part of Cataloid AS-3 were mixed, and Example 7 was dry weight, 50 parts of water-soluble acrylic resin and Cataloid AS-3. Was mixed in an amount of 50 parts, and the hydrophilic coating material was prepared in the same manner as in Example 1 to obtain an aluminum coating material.

Examples 8 to 10 Example 1 was repeated except that the water-soluble acrylic resins obtained in Synthesis Examples 2 to 4 were used in place of the water-soluble acrylic resin.
In the same manner as above, a hydrophilic coating material was prepared to obtain an aluminum coating material.

Example 11 The water-soluble acrylic resin of Synthesis Example 1 was used in a dry weight of 60.
Parts, 30 parts of Cataloid AS-3 and 10 parts of hydroxyethyl cellulose (SP-250: Daicel Chemical Industries, Ltd.) were mixed and hydrophilic coating was prepared and aluminum coating was carried out in the same manner as in Example 1 below. I got the material.

Example 12 The water-soluble acrylic resin of Synthesis Example 1 was used in a dry weight of 60.
Parts, 30 parts of Cataloid AS-3 and 10 parts of polyvinyl alcohol (GL-5: Nippon Synthetic Chemical Industry Co., Ltd.) manufactured by Nippon Synthetic Chemical Industry Co., Ltd. were mixed, and then, in the same manner as in Example 1, The hydrophilic paint was adjusted to obtain an aluminum coating material.

Example 13 The water-soluble acrylic resin of Synthesis Example 1 was used in a dry weight of 60.
Parts, 30 parts of Cataloid AS-3, and 10 parts of polyethylene glycol (Paogen PP-15: manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) were mixed, and a hydrophilic coating material was prepared in the same manner as in Example 1 below. An aluminum coating material was obtained.

Example 14 The water-soluble acrylic resin of Synthesis Example 1 was used in a dry weight of 50.
Part, 30 parts of Cataloid AS-3, and 20 parts of a polyurethane emulsion (Super Flex 110: manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) were mixed, and a hydrophilic coating material was prepared in the same manner as in Example 1 below. Then, an aluminum coating material was obtained.

Example 15 The water-soluble acrylic resin of Synthesis Example 1 was used in a dry weight of 60.
Parts, 30 parts of Cataloid AS-3, and 10 parts of non-swelling synthetic mica (MK-100: manufactured by Cop Chemical Co., Ltd.) were mixed, and a hydrophilic paint was prepared in the same manner as in Example 1 below. An aluminum coating material was obtained. Example 16 The water-soluble acrylic resin according to Synthesis Example 1 was used in a dry weight of 60.
Part, 30 parts of Cataloid AS-3, water-soluble nylon (A
Q-Nylon A-90: 10 parts of Toray Co., Ltd. are mixed,
Thereafter, a hydrophilic coating material was prepared in the same manner as in Example 1 to obtain an aluminum coating material.

Example 17 The water-soluble acrylic resin of Synthesis Example 1 was used in a dry weight of 50.
Part, 30 parts of Cataloid AS-3, and 20 parts of calcium alginate beads (manufactured by Nisshinbo Co., Ltd.) were mixed, and a hydrophilic coating material was prepared in the same manner as in Example 1 to obtain an aluminum coating material. .

Comparative Example 1 In the same manner as in Example 1, the water-soluble acrylic resin obtained in Synthesis Example 1 was applied to and baked on a phosphoric acid chromate treated aluminum plate to obtain an aluminum coating material.

Comparative Example 2 50 parts by dry weight of AQ-nylon A-90, 30 parts by dry weight of Elastron W-11, and 2 parts of alumina sol-200.
0 parts (in the state of the primary dispersion without agglomeration) were mixed and the hydrophilic coating material was prepared in the same manner as in Example 1 to obtain an aluminum coating material.

Comparative Examples 3 to 4 Example 1 was repeated except that the water-soluble acrylic resins obtained in Synthesis Examples 5 to 6 were used in place of the water-soluble acrylic resin.
In the same manner as above, a hydrophilic coating material was prepared to obtain an aluminum coating material.

The compositions of the hydrophilic paints of Examples 1 to 17 and Comparative Examples 1 to 4 are shown in Table 2.

[0058]

[Table 2]

With respect to each of the obtained aluminum coating materials (hydrophilic coating film), a hydrophilic continuation test, an adhesion test, and
A corrosion resistance test was performed.

(1) Hydrophilicity sustaining test A coated aluminum plate was immersed in tap water (flow rate of 1 liter / min / min for a 30 liter plastic container) for 8 hours and then in an electric oven at 50 ° C. Drying for 16 hours was set as one cycle, and the water contact angle was measured continuously for 20 cycles. To measure the water contact angle, place the sample horizontally and drop 5 μl of pure water on it to measure the contact angle (CA
-Z: Measured by Kyowa Interface Science Co., Ltd. The evaluation is as follows.

◎: less than 5 degrees ○: 5 degrees or more and less than 20 degrees Δ: 20 degrees or more and less than 30 degrees x: 30 degrees or more

(2) Adhesion test A coated aluminum plate was wiped with a dry waste cloth and evaluated. ◎: Can not be wiped ○: Surface layer can be wiped off but remains on the base material ×: Can be wiped off

(3) Corrosion resistance test A salt spray test was applied to the painted aluminum plate for 40 times.
This was performed for 0 hour, and the ratio of the area of the corroded portion was evaluated. ：: 0% or more and less than 1% ： １: 1% or more and less than 5% ×: 5% or more

The results of tests (1) to (3) are shown in Table 3.

[0065]

[Table 3]

[0066]

The coating film obtained by drying and curing the hydrophilic coating material of the present invention has extremely good hydrophilic durability, and also has good adhesion and corrosion resistance. The addition of alumina sol, which is in the amorphous gel state, has the effect of significantly reducing the wear of the mold and prolonging the life of the mold, and the hydrophilic paint has a hydrophilic property suitable for aluminum fin materials for heat exchangers. A coating film is provided.

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Claims (1)

[Claims] 1. An alumina sol (a), wherein the primary particles have a feather-like, rod-like or dendritic shape / form and are agglomerated in advance by a synthetic method and have an average particle size of 0.5 to 20 μm, and 10 to 80 parts of an α, β unsaturated monomer having a sulfonic acid or sodium sulfonate group, 10 to 50 parts of an α, β unsaturated monomer having a carboxylic acid group,
An α, β unsaturated monomer having an alcoholic hydroxyl group is used as 10
A highly hydrophilic coating material comprising a water-soluble resin (b) obtained by copolymerizing 50 parts by weight.