JPH02215871A - Hydrophilic coating agent, aluminum or aluminum-alloy plate for fin and heat exchanger - Google Patents

Abstract

PURPOSE:To prepare a hydrophilic coating agent exhibiting a good adhesion with aluminum, excellent coating film properties, and no change with time in hydrophilicity by using a copolymer of an alpha,beta-unsatd. monomer contg. a sulfonic acid group, an alpha,beta-unsatd. monomer contg. a carboxyl group, and a (meth)acrylic ester as the resin component. CONSTITUTION:An alpha,beta-unsatd. monomer (A) contg. a sulfonic acid group (e.g. 2-acrylamido-2-methylpropanesulfonic acid), an alpha,beta-unsatd. monomer (B) contg. a carboxyl group (e.g. acrylic acid), a (meth)acrylic acid lower alcohol ester (C) (e.g. methyl methacrylate), and if necessary an alpha,beta-unsatd. monomer (D) contg. a nitrogen (e.g. N,N-dimethylaminoethyl acrylate) are radical-polymerized in a wt.% ratio of A/B/C or A/B/C/D of 10-40/45-70/5-25 or 10-40/40-70/5-20/5-15. Resulting copolymer is used as a hydrophilic coating agent for Al or an Al alloy.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to a coating method for forming a hydrophilic film on the surface of a metal, particularly an aluminum material or an aluminum alloy material (hereinafter simply referred to as an aluminum alloy material). The present invention relates to a composition made of aluminum alloy, an aluminum alloy plate prepared by thermosetting the composition, and a heat exchanger coated with the same.

[Conventional technology]

Since the surface of metal materials is poor in hydrophilicity, fins of heat exchangers and planographic printing plates for printing are coated with a hydrophilic film. Hereinafter, in this specification, the case of the fins of a heat exchanger will be described using an air conditioner as an example.

Recent air conditioning heat exchangers are required to have improved thermal efficiency and be more compact in order to reduce weight, and designs have been adopted in which the spacing between fins is made as narrow as possible. In air conditioning heat exchangers, moisture in the air becomes condensed water and adheres to the surface of aluminum fins during cooling operation. Since the surface of a metal material generally has poor hydrophilicity, this condensed water exists on the fin surface in the form of a semicircle or in the form of a bridge between the fins, as shown in FIG.

This obstructs the flow of air between the fins, increases ventilation resistance, and causes a significant decrease in heat exchange efficiency.

To improve the thermal efficiency of the heat exchanger, it is necessary to quickly eliminate condensed water on the fin surface. As a solution to this problem, (1) a highly hydrophilic film is formed on the surface of the aluminum alloy fin, allowing the condensed water to flow down as a thin water film; (2) a water-repellent film is formed on the surface of the aluminum alloy fin, and the condensed water is directed to the surface. Although it is possible to prevent the adhesion, method (2) is currently extremely difficult.

In order to obtain hydrophilic properties, a coating film is applied to the surface, and the composition of the hydrophilic film prevents the formation of condensed water droplets on the surface of the material and maintains the water film on the surface of the material. is used for.

Therefore, various methods for forming hydrophilic films have been proposed and put into practice. For example, a method of forming an alkali silicate film on the surface of an aluminum fin (Japanese Patent Publication No. 53
-48177), a method of applying a composition containing a water-based paint resin, a surfactant, and synthetic silica to form a hydrophilic film (Japanese Patent Application Laid-Open No. 164264/1982), A method of forming a hydrophilic film by coating a composition containing a low-molecular organic compound and a water-soluble organic polymer compound (Japanese Unexamined Patent Publication No. 60-101
No. 158) has been proposed.

[Problems to be Solved by the Invention] However, the method of forming an alkali silicate film in order to impart hydrophilicity has a drawback that the hydrophilicity does not last long over time, and that it When made into fins, the hardness of the coating is high, which increases the wear of the mold, and the coating tends to crack when formed into fins.

In those containing a surfactant, it is impossible to prevent the bleeding phenomenon because the surfactant basically migrates toward the surface of the film. As a result, the hydrophilicity of the fin surface decreases over time. Also, since it contains synthetic silica, when it is applied to a material and processed into fins, it acts like an abrasive and increases wear on the mold. The method of forming a hydrophilic film by applying a composition containing a low-molecular organic compound having an alkali silicate and a carbonyl compound and a water-soluble organic polymer compound has been improved in terms of sustainability of hydrophilicity. In order to expect sufficient wettability of the film, the content of alkali silicate must be high. Increase wear.

Therefore, an object of the present invention is to provide a film composition that has good adhesion to aluminum and excellent film physical properties, has no change in hydrophilicity over time, and has good wettability to water. It is an object of the present invention to provide a coating agent that forms a hydrophilic film that does not cause significant wear on a mold when it is applied and processed.

[Means for Solving the Problems] The present inventors have conducted repeated research to solve the above problems. In order for the coating on an aluminum plate to be sufficiently wetted by water, the coating itself needs to have excellent hydrophilic properties, but this depends on the mechanical properties such as the toughness of the coating itself and the adhesion. It was found that it is important to achieve both of these characteristics.

Therefore, as a result of further research, it was found that by selecting a combination of constituent monomers of the polymer that forms the coating material, it was possible to achieve both the above-mentioned contradictory properties, that is, the wettability of the formed film and other properties. They discovered that it is possible to do this, and completed the present invention.

The gist of the present invention is that A, an α,β unsaturated monomer having a sulfonic acid group, and an α,β unsaturated monomer having a B carboxyl group.
A hydrophilic coating obtained by polymerizing a β-unsaturated monomer, a lower alcohol ester of C(meth)acrylic acid, or a lower alcohol ester of (meth)acrylic acid, and a nitrogen-containing α,β-unsaturated monomer. The first aspect of the present invention is an α, β unsaturated monomer having a sulfonic acid group, B an α, β unsaturated monomer having a carboxyl group, a lower alcohol ester of (meth)acrylic acid, or a lower alcohol ester of (meth)acrylic acid. ) A thermosetting hydrophilic coating consisting of a hydrophilic coating obtained by polymerizing a lower alcohol ester of acrylic acid and a nitrogen-containing α, β unsaturated monomer is applied to an aluminum or aluminum alloy plate material, and heated. A second invention is a hardened aluminum or aluminum alloy plate material for fins, which has an A sulfonic acid group.

β-unsaturated monomer, B-carboxyl group-containing α, β-unsaturated monomer, C (meth)acrylic acid lower alcohol ester or (meth)acrylic acid lower alcohol ester and nitrogen-containing α, β-unsaturated A third invention provides a heat exchanger comprising a hydrophilic thermosetting coating formed from a hydrophilic coating material obtained by polymerizing a monomer on the surface of an aluminum or aluminum alloy fin. be.

The monomers used in the production of the polymer constituting the hydrophilic coating material of the present invention will be explained.

The α, β unsaturated monomer component having a sulfonic acid group of component A has strong anionic hydrophilicity and functions to make the polymer water-soluble. Improves wettability. Examples of the component A include 2-acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid, and styrenesulfonic acid, with 2-acrylamido-2-methylpropanesulfonic acid being particularly preferred.

The α,β unsaturated monomer component having a carboxyl group, component B, plays a role in providing adhesiveness to the aluminum plate. As this B component, for example, (meta)
Examples include acrylic acid, maleic anhydride, crotonic acid, itaconic acid, fumaric acid, maleic acid, fumaric acid, and itaconic acid half esters, among which acrylic acid,
Methacrylic acid is particularly preferred.

The lower alcohol ester of (meth)acrylic acid, component C, imparts toughness and flexibility to the formed film.

Examples of this C component include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, and among these, (meth)acrylate Methyl, (meta)
Particularly preferred is ethyl acrylate.

In addition, nitrogen-containing α may be used together with lower alcohol ester of (meth)acrylic acid.

The β-unsaturated monomer contributes to the softness and flexibility of the formed film, as well as to the adhesion to the aluminum plate.

The nitrogen-containing α,β unsaturated monomer used in the present invention includes:
For example, N,N-dimethylaminoethyl (meth)acryle), N,N-diethyl urea.

Minoethyl (meth)acrylate, vinylpyrrolidone,
Examples include vinylimidacillin, among which N
, N-dimethylaminoethyl (meth)acrylate, N
, N-diethylaminoethyl (meth)acrylate, and vinylpyrrolidone are particularly preferred.

The polymerization of these A, B%C components is carried out by radical polymerization in an aqueous medium. The composition ratio of the copolymer is A/B/C in weight% 1O~40/45~7015~25, and C
When using both of the above components, 1O~40/4
The range of 0 to 7015 to 2015 to 15 (nitrogen-containing compound) is preferable.

As the polymerization initiator, those generally used in the polymerization of vinyl monomers can be used, but water-soluble ammonium persulfate and potassium persulfate are particularly preferred, and these can be used alone or in combination with sodium metabisulfite or sodium thiosulfate. The polymerization may be carried out using a sodium redox system using a combination of the following, or an oil-soluble initiator such as azobisisobutyronitrile may be dissolved in a small amount of alcohol and finely dispersed in the polymerization system. The radical polymerization initiator is preferably used in an amount of 0.1 to 5% by weight based on the monomer.

The polymerization temperature is preferably 20 to 40°C in the case of a redox system, and 60 to 80°C in other cases.

Moreover, the monomer concentration in the aqueous medium is preferably 10 to 30%. A water-soluble organic solvent is used as the polymerization regulator. Examples of such organic solvents include lower alcohols such as methanol, ethanol, and isopropanol, and monoalkyl ethers of glycols such as ethylene glycol monoethyl ether and diethylene glycol monoethyl ether. In addition, acetone, dioxane, etc. can also be used. .

The hydrophilic resin obtained in this way contains a sulfonic acid group and a carboxyl group in its polymer chain, but among these, the sulfonic acid group is limited to the extent that the resin film exhibits sufficient hydrophilicity. Some or all of the carboxy groups are neutralized, and some or all of the carboxy groups are also neutralized. This neutralization can be performed at any time, ie, after polymerization, or in the monomer state before polymerization.

As the neutralizing agent, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, aqueous ammonia, or organic amines such as triethylamine and diethylamine ethanol can be used.

In the case of organic amines such as aqueous ammonia and triethylamine, they may be added in excess because they evaporate and volatilize during baking.

The coating material of the present invention is of a so-called wave type and does not use a hardening agent, so that the troubles and troubles related to pot life, which is a bottleneck in the work process, can be avoided. Furthermore, since no curing agent is used, there is no reduction in hydrophilicity due to three-dimensionalization due to crosslinking reaction with the curing agent. Therefore, it is possible to make the base polymer's own hydrophilicity-hydrophobicity balance more hydrophobic, and to increase the amount of (meth)acrylic acid lower alcohol ester in component C compared to those using a curing agent. Can be done.

The hydrophilic coating agent of the present invention can form a hydrophilic film on an object to be coated, and in particular can be coated on aluminum and aluminum alloy plates and chemically treated surfaces thereof.

Moreover, when a higher degree of corrosion resistance is required, a corrosion-resistant organic resin can be coated between the hydrophilic coating agent of the present invention and the surface to be coated.

As a coating method for the hydrophilic coating material of the present invention, various known methods such as dipping, dipping, spraying, electrostatic coating, and roll coater can be applied. Further, a coloring agent or the like may be added to the coating film for aesthetic purposes or other purposes.

The drying temperature and time for curing of the coated hydrophilic coating should be taken into account to suit the speed of the production line, but water-soluble polymers should be dried on aluminum plates until the film has hardened. Bye.

In this manner, the coating material of the present invention allows a resin film to be formed on a coated object with excellent hydrophilicity, adhesion, film physical properties, and corrosion resistance.

Further, processing of the fin material into a heat exchanger can be performed by a known method, and coating of the coating material of the present invention on the heat exchanger fins may be performed by either a pre-coating method or a post-coating method.

〔Example] Hereinafter, the present invention will be explained in more detail with reference to Examples.

Industrial pure aluminum (A10) with a thickness of 0.120s
50-H22) was degreased and washed using a commercially available weak alkaline degreaser. Next, a phosphoric acid chromate-based chemical solution (
The product was sprayed with Allozin 401/45 (trade name, manufactured by Nippon Paint Company) to form a phosphoric acid romate skin (ICCr amount: 20 B/m'), and then washed with water and dried. Next, a hydrophilic coating agent shown in the following example was applied onto this chemical conversion coating using a roll coater, and the coating was heated at a temperature of 200°C using a hot air circulation drying oven.
℃ for 20 seconds to form a hydrophilic resin film layer (thickness 1
μm) was obtained.

Example 1 (1) Synthesis of IQ water-based resin A-1 1 equipped with a stirrer, thermometer, cooling tube and nitrogen gas introduction tube
A separable flask was charged with 25 parts of 2-acrylamido-2-methylpropanesulfonic acid, 60 parts of methacrylic acid, and 15 parts of methyl methacrylate, and 100 parts of ethanol and 400 parts of demineralized water were added thereto and uniformly dissolved.

Under a nitrogen gas atmosphere, 0.5 part of lauroyl peroxide was added, and polymerization was carried out at 75° C. for 7 hours. Three hours after the start of polymerization, 0.3 part of lauroyl peroxide was added.

After the polymerization was completed, neutralization was performed with 8 parts of caustic soda. The solids content was then adjusted to 10% concentration with demineralized water.

(2) Preparation of hydrophilic coating agent Hydrophilic resin A-1 was adjusted to pH-7 with aqueous ammonia, and the solid content was brought to 5% with ion-exchanged water.

Example 2 (1) Synthesis of hydrophilic resin A-2 2-acrylamido-2-methylpropanesulfonic acid 1
5 parts of styrene sulfonic acid, 15 parts of styrene sulfonic acid, 50 parts of methacrylic acid, and 20 parts of methyl methacrylate were uniformly dissolved in 400 parts of demineralized water and 100 parts of ethanol.

After neutralization with 11.3 parts of caustic soda, under nitrogen gas atmosphere,
Add 0.4 parts of potassium persulfate and 0.2 parts of sodium sulfite, and polymerize in a redox system at 30°C for 6 hours. Thereafter, the concentration was adjusted to 10% with demineralized water.

(2) Preparation of hydrophilic coating agent Hydrophilic resin A-2 was adjusted to pH-7 with aqueous ammonia, and the solid content was brought to 5% with ion-exchanged water.

Example 3 (1) Synthesis of hydrophilic resin A-3 15 parts of styrene sulfonic acid, 2-acrylamide-2-
10 parts of methylpropanesulfonic acid, 40 parts of acrylic acid,
25 parts of itaconic acid and 10 parts of butyl acrylate in 4 parts of demineralized water
00 parts and 100 parts of ethanol were added and uniformly dissolved.

After neutralization with 9.6 parts of caustic soda, 0.5 part of benzoyl peroxide was added in a nitrogen gas atmosphere, and polymerization was carried out at 75°C for 7 hours. Three hours after the start of polymerization, 0.3 part of benzoyl peroxide was added. Then lO was added with demineralized water.
% concentration.

(2) Preparation of hydrophilic coating agent Hydrophilic resin A-3 was adjusted to pH=7 with aqueous ammonia, and the solid content was adjusted to 5% with ion-exchanged water.

Example 4 (1) Synthesis of hydrophilic resin A-4 2-acrylamido-2-methylpropanesulfonic acid 1
5 parts, 70 parts of methacrylic acid, 5 parts of methyl methacrylate,
10 parts of vinylpyrrolidone was uniformly dissolved in 4008B of demineralized water and 100 parts of ethanol.

After neutralizing with 126 parts of triethylamine, 0.5 part of azobisisobutyronitrile was added under nitrogen gas atmosphere, and 7 parts of azobisisobutyronitrile was added.
Polymerization was carried out at 5°C for 7 hours.

0.3 azobisisobutylnitrile 3 hours after the start of polymerization
Added section. Thereafter, the concentration was adjusted to 10 parts with demineralized water.

(2) Preparation of hydrophilic coating agent Hydrophilic resin A-4 was adjusted to pH-7 with aqueous ammonia, and the total solid content was adjusted to 5% with ion-exchanged water.

Example 5 (1) Synthesis of hydrophilic resin A-5 2-acrylamido-2-methylpropanesulfonic acid 2
0 parts, 60 parts of methacrylic acid, 15 parts of methyl methacrylate, and 5 parts of dimethylaminoethyl methacrylate were uniformly dissolved in 400 parts of demineralized water and 100 parts of ethanol.

After neutralization with 6.7 parts of caustic soda, under nitrogen gas atmosphere,
0.5 part of azobisisobutyronitrile was added and polymerization was carried out at 75°C for 7 hours. 3 hours after the start of polymerization, 0.3 part of azobisisobutyronitrile was added. Thereafter, the concentration was adjusted to 10% with demineralized water.

(2) Preparation of hydrophilic coating agent Hydrophilic resin A-5 was adjusted to pH-7 with aqueous ammonia, and the solid content was brought to 5% with ion-exchanged water.

The film properties (hydrophilicity, adhesion, continuous formability) of each of the fin materials with the various hydrophilic films thus obtained were investigated, and the results are shown in Table 1.

Here, hydrophilicity was evaluated by measuring the contact angle with water after 500 cycles of a combination of immersion in water at room temperature for 2 minutes and then drying with cold air for 6 minutes. ◎ is very good (contact angle 20° or less), O is good (contact angle 20-40@), and X is poor (contact angle over 40'').

Adhesion was evaluated by performing a cross-cut tape peeling test and determining the number of pieces that did not peel off.

Continuous moldability was determined by visually observing the wear condition of the molding tool and the appearance of the fin after molding after 100,000 punch fin presses were performed continuously.

Comparative Examples 1 and 2 After forming a chemical conversion film in the same volume as in the example, in Comparative Example 1, a water-soluble coating agent consisting of colloidal silica, water-soluble acrylic/melamine resin, and a surfactant was applied on the chemical conversion film. Dry with 250"CX 30"1
A hydrophilic film of μ was obtained. In Comparative Example 2, a water-soluble coating agent consisting of sodium-based water glass, polyacrylic acid, and a hardening agent was dried at 240°C x 30'' to obtain a hydrophilic film with a thickness of 701 g/a' in terms of Si content. Ta.

The properties of the obtained film were investigated in the same manner as in the Examples, and the results are shown in Table 1.

A cured film without mold wear can be formed.

In addition, the hydrophilicity of the aluminum plate material for fins coated with this coating material is significantly improved, and heat exchangers manufactured using this material show the formation of half-moon-shaped water droplets, bridges, etc. that obstruct ventilation between the fins. heat exchange efficiency can be improved.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating a state in which water droplets adhere between the fins of a conventional heat exchanger. [Effects of the Invention] As explained above, the hydrophilic coating material according to the structure of the present invention has excellent wettability with water, good adhesion with the substrate, and furthermore, the hydrophilic coating material according to the structure of the present invention has excellent wettability with respect to water, and has good adhesion with the substrate, and also Sumitomo Light Metal Industries Co., Ltd. Patent applicant Kyoeisha Oil and Fat Chemical Industry Co., Ltd. Agent Patent attorney Hide Komatsu Agent Patent attorney Hiroshi Asahi

Claims (3)

[Claims] (1) A α, β unsaturated monomer having a sulfonic acid group, B
α, β unsaturated monomer having a carboxyl group, lower alcohol ester of C(meth)acrylic acid or (meth)
A hydrophilic coating material obtained by polymerizing a lower alcohol ester of acrylic acid and a nitrogen-containing α,β unsaturated monomer. (2) A α, β unsaturated monomer having a sulfonic acid group, B
α, β unsaturated monomer having a carboxyl group, lower alcohol ester of C(meth)acrylic acid or (meth)
For fins, characterized in that a hydrophilic coating obtained by polymerizing a lower alcohol ester of acrylic acid and a nitrogen-containing α, β unsaturated monomer is applied to an aluminum or aluminum alloy plate material and heat-cured. Aluminum or aluminum alloy plate material. (3) A α, β unsaturated monomer having a sulfonic acid group, B
α, β unsaturated monomer having a carboxyl group, lower alcohol ester of C(meth)acrylic acid or (meth)
The aluminum or aluminum alloy fin has a hydrophilic thermosetting coating formed from a hydrophilic coating material obtained by polymerizing a lower alcohol ester of acrylic acid and a nitrogen-containing α, β unsaturated monomer on the surface of the aluminum or aluminum alloy fin. A heat exchanger characterized by: