JPS63213681A - Treatment of aluminum for providing hydrophilic property - Google Patents

Abstract

PURPOSE:To form a hydrophilic film having superior corrosion resistance when an org. polymer film is formed on the surface of an Al material and treated with an aq. silicate soln., by incorporating a hardening agent which makes the silicate insoluble in water into the org. polymer film. CONSTITUTION:A film of an org. polymer having >=about 5,000mol.wt. such as polyvinyl acetate, polyacrylic acid or polybutadiene is formed on the surface of an Al material to <=about 10mum thickness. An aq. silicate soln. such as water glass having about 2-5 ratio of SiO2 to Na2O is then applied to form a film of about 0.1-5mum thickness and to make the surface of the Al material hydrophilic. At this time, a hardening agent which makes the silicate insoluble in water, e.g., Mg(OH)2, phosphoric acid, tartaric acid or sodium silicofluoride is incorporated into the org. polymer film. Thus, a hydrophilic film having superior hydrophilic property in the early stage and after the lapse of time and superior corrosion resistance is obtd. The film is useful to provide hydrophilic property to the surfaces of fins forming the heat radiating and cooling parts of a heat exchanger made of Al.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to hydrophilic treatment of the surface of aluminum or aluminum alloy, and more specifically, the heat radiation part and cooling part of an aluminum heat exchanger. The present invention relates to a method of hydrophilizing the surface of the fins constituting the fin.

[Conventional technology]

Conventionally, aluminum or aluminum alloy (hereinafter referred to as
For the fins of aluminum heat exchangers made of aluminum (collectively referred to as "aluminum"), surface treatments such as anodic oxide coating, boehmite coating, and resin coating are performed to prevent white rust. The surface of the film formed by these treatments has almost no water wettability, and is rather water repellent. In addition, chromate conversion coating treatment is also performed to prevent white rust. Although chromate conversion coatings have some water wettability in the initial stage of coating formation, sufficient wood-philicity cannot be obtained with chromate treatment alone. In addition, chromate conversion coatings tend to change from hydrophilic to hydrophobic over time, especially under heated and dry conditions, so they are problematic as coatings for heat exchanger fins.

On the other hand, most heat exchangers are designed to have as large an area as possible for the heat radiating section and the cooling section in order to improve the heat dissipation or cooling effect, so the spacing between the fins is extremely narrow. Therefore, when used for cooling, moisture in the atmosphere condenses on the surface of the heat exchanger, particularly in the gaps between the fins. The more hydrophobic the fin surface is, the more condensed water becomes water droplets, and the fin gaps become clogged, increasing ventilation resistance.
Reduces heat exchange rate.

In addition, the water droplets accumulated in the fin gaps are easily scattered by the blower of the heat exchanger, and the water droplets are dissipated in the water droplet tray installed at the bottom of the heat exchanger, staining the vicinity of the heat exchanger with water.

Therefore, in order to prevent water droplets remaining in the fin gaps from causing clogging, a treatment has been proposed to impart hydrophilicity to the aluminum surface and improve water wettability. In particular, many methods have been proposed for treating fins with silicates such as water glass because they have high water wettability, high heat resistance, and are inexpensive.

One method is to apply a silicate aqueous solution directly to the chemically treated aluminum surface and dry it. This method is described, for example, in Japanese Patent Application Laid-Open No. 50-38645.

As an alternative method, a method has been proposed in which an organic polymer film is previously formed on the aluminum surface, a silicate solution is applied thereon, and the film is dried. This method is used, for example, in JP-A-60-11
This is proposed in Publication No. 7098.

As another alternative method, it has been proposed to apply a mixture of an organic polymer compound and an inorganic silicate to the aluminum surface. This proposal can be found, for example, in the following publication:

JP-A-61-8598 discloses that styrene-maleic acid copolymer, polyacrylamide, butylene-maleic acid copolymer, polyacrylic acid or a salt thereof, and XM2O
・ySiOz (M=Li, Na, K,
y/x≧2) as a coating layer and a fin material.

JP-A-60-101156 discloses a hydrophilic film-forming agent for aluminum containing an alkali silicate and a compound containing a carbonyl group (aldehydes, esters, amides, etc.).

JP-A No. 60-221582 discloses that a hydrophilic inorganic film layer made of silicate, boehmite, etc. is formed on an aluminum plate, and a hydrophilic organic polymer film with a degree of polymerization of 50 or more is formed on top of the hydrophilic inorganic film layer. discloses a fin material made of

[Problem that the invention seeks to solve]

The film formed by the conventional hydrophilic treatment method (directly applying a silicate aqueous solution to chemically treated aluminum) mentioned in the first section is only a hydrophilic film and not a corrosion-resistant film. There were disadvantages such as a decrease in the corrosion resistance and an increase in the tendency for white rust to occur.

The conventional hydrophilic treatment method mentioned in the second section (forming an organic polymer film and then forming a silicate film) provides sufficient corrosion resistance and initial hydrophilicity, but the silicate in the upper layer is washed away by condensed water. Because it is easy to grow, it has the disadvantage of poor persistence of parent trees.

The silicate contained in the film formed on aluminum by the conventional hydrophilic treatment method (coating a mixture of organic polymer and silicate) mentioned in the third point is hydrophilic, so fins treated with this method tends to promote the formation of white rust on aluminum. In addition, the silicate and organic polymer undergo phase separation when the mixture is applied to aluminum and dried, resulting in wide variations in performance depending on manufacturing conditions (and the hydrophilicity of the fin becomes insufficient).

[Means for solving problems]

Therefore, as a result of various studies, the present inventors adopted the process of the conventional hydrophilic treatment method described in the second section, and found that the most excellent and stable hydrophilic coating that solves the problems of this method. In addition, we determined that this was the best way to eliminate the occurrence of white rust on aluminum, and added a hardening agent, especially a water-soluble one, to the organic polymer film applied to aluminum to make the silicate that will be applied later non-water-soluble. It has been found that hydrophilicity sustainability can be greatly improved by including a curing agent of

The curing agent contained in the organic polymer, which is the most characteristic feature of the present invention, includes (a) hydroxides and salts of polyvalent metals such as Mg(OH)z aluminum nitrate and alum; Inorganic acids and their ammonium salts such as phosphoric acid, polyphosphoric acid, and boric acid; (c) organic acids such as tartaric acid, malic acid, organic sulfonic acids, phosphonic acids, restrictive acids, and polyacrylic acids;
In particular, carboxylic acids, hydroxycarboxylic acids and their ammonium salts, (di)silifluorides such as sodium silicofluoride, titanium fluoride, and titanium fluorides can be used.

It is known that water glass can be cured (made non-water soluble) by the above-mentioned curing agents (for example, Science and Industry Up: 1.77
178.184-185 (1983), Japan Adhesive Association Journal 12394 (1976), etc.), these compounds are used in paints and adhesives to harden water glass, which is a component of inorganic heat-resistant paints and heat-resistant adhesives. In most conventional examples, it is contained in Only, the above-mentioned Japanese Patent Application Publication No. 60-101156
The publication describes the formation of a hydrophilic film on aluminum from a mixed solution of glyoxal and alkali silicate, but this method has the following problems in addition to the problems of the third conventional method mentioned above. The water glass hardening reaction (insolubilization reaction) has not been effectively used industrially for hydrophilic treatment because the mixed liquid gels immediately or after a while after mixing and is difficult to coat. The present inventors conducted various experiments and found that, surprisingly, the curing agent contained in the heat-dried organic polymer film was removed from the silicate layer during the process of forming a silicate film using an aqueous silicate solution. It was discovered that the required performance of the fin material was completely satisfied by insolubilizing the silicate to such an extent that the silicate was not washed away. As the hardening agent for water glass, a water-soluble one is preferable.

The components, conditions, etc. of the hydrophilic treatment agent will be explained in detail below.

Most of the organic polymer resins that are currently industrialized and used can be used as the organic polymer film, including vinyl-based resins such as vinyl acetate, vinyl chloride, and vinylidene chloride, and their copolymers, acrylic acid, methacrylic acid, and their esters, acrylics and their copolymers such as acrylamide, alkyds, epoxys, urethanes, polyesters, styrenes, olefins and their copolymers, synthetic rubbers such as butadiene, and natural polymers. and mixtures thereof are used.

The molecular weight of the organic polymer resin is preferably 5,000 or more.
, less than 5,000, particularly in the case of a highly hydrophilic resin, it is preferable to polymerize it by oxidation reaction, addition reaction, vinyl polymerization reaction, etc. during film formation to form a water-insoluble and corrosion-resistant film.

Further, in the present invention, since the resin for surface treatment is mainly used for the heat exchanger, it is necessary to select a resin that forms a thin resin film with good corrosion resistance on the surface of aluminum and its alloy. The thickness of the coating used in the heat exchanger is preferably as thin as possible, usually 10 microns or less, and most preferably 0.1 micron to 2 microns. Paints in the form of organic solvent solutions or organosols may be used, but
Considering air pollution and flammability caused by solvents, the most desirable undercoat composition is a combination of a water-soluble polymer and a water-soluble crosslinking agent, or a water-based emulsion.

Water-soluble polymers for film formation include polyvinyl alcohol,
Glucose derivatives, hydroxyethylcellulose, polyvinylphenol, polyethylene glycol, poly(
meth)acrylic acid, maleic acid (itaconic acid) copolymer, polystyrene phosphate, salicylic acid resin, polystyrene sulfonate, phenol sulfonate, polyethyleneimine, aminated polystyrene, polyvinylpyridine, polyacrylamide, water-soluble polyamide, polyvinylpyridine, polyvinylpyrrolidone Polymers obtained from natural or synthetic polymers such as starch, gelatin, casein, and gum arabic, and monomers and oligomers such as methylol acrylamide, methylol melamine, methylol phenol, hydroxyethyl methacrylate, resol, and p-aminobenzenesulfonic acid. can be used.

Various types of crosslinking agents are used depending on the base polymer. For example, in the case of a polymer containing active hydrogen,
A compound that can react with active hydrogen, such as two or more isocyanate groups, aziridyl groups, glycidyl groups, and methylol groups, is also an unsaturated compound that can be copolymerized with oligomers and polymers that contain unsaturated groups. compound is used. Z
n, Al.

An inorganic compound such as a Ti compound forms a complex with an organic polymer containing O and N, and acts as a crosslinking insolubilizer. As a method for applying the organic polymer, any method such as spraying, brushing, roll coating, flow coating, dip coating, powder coating, etc. can be adopted.

Next, the most common method for drying organic polymer coatings is by heating, but of course, in addition to air drying, UV, EB
Drying by thermal radiation may also be used.

As the silicate of the silicate aqueous solution applied onto the organic polymer coating film, silicates of Li, Na, K, and amine can be used, but so-called water glass is generally used from the viewpoint of cost. The 5ift/NazO ratio of water glass is not particularly limited, but a ratio of 2 to 5 is generally used. The concentration of the silicate aqueous solution may be determined to facilitate application, and there are no particular limitations on the performance of the hydrophilic surface. The coating amount of the silicate aqueous solution is preferably such that a silicate film having a thickness of 0.1 to 5 μm is formed after heating and drying. If the thickness of the film is less than 0.1 μm, the hydrophilic effect will not be sufficient, and if it exceeds 5 μm, the silicate will not be sufficiently hardened (insoluble in water), and heat exchange will be difficult due to cracking and peeling. There is concern that this may have an adverse effect on the performance of the device.

The heating drying temperature of silicate is within the range of 100 to 200℃ and 10 seconds to IO minutes, high and low) and short (long) in Wenzhou.
Heat for an hour.

[For production]

The silicate aqueous solution applied as a topcoat is applied evenly,
Even after drying, a homogeneous silicate degree IQ is formed.

The coating film used as an undercoat allows for uniform topcoating and exhibits water resistance after drying.

A homogeneous silicate film exhibits excellent hydrophilicity, and the wood-philicity of the silicate film does not deteriorate over time due to the action of the curing agent contained in the undercoat film. Therefore, the corrosion resistance of the upper and lower coatings is also improved.

The present invention will be further explained below with reference to Examples.

〔Example〕

The test methods in the following examples are as follows.

1.9 The contact angle of a small water droplet with a diameter of 1 to 21 M placed on a solid surface was measured using a FACE contact angle meter C type (Kyowa Kaimen Kagaku Products).

■Kou Yu Salt water spray test method Measurements are carried out based on JIS Z-2371, and the spray test time is shown as the spray test time until the white rust area reaches 5%.

Yarizutama Yodogo - Soaked in running water for 8 hours at room temperature, then 8 hours for 16 hours
The process of drying at 0°C is 1 cycle, and 5 cycles!
It is expressed as the contact angle with water after e.

Example 1 22 g/l of water-soluble nylon (AQ-Nylon, Toshi ■) was used as an organic polymer for film formation, and water-soluble polyurethane (Elastron H-38,
(Daiichi Kogyo Seiyaku) in terms of solid content, 5 g/l, and phosphoric acid as a hardening agent for water-soluble silicate, 8 g/l! A mixed aqueous solution containing l,
It was applied onto the surface of a degreased aluminum plate (A-1100) and dried for 3 minutes in an air drying layer at 180°C to obtain a coating film with an average thickness of 0.8 μm.

A 10% aqueous solution of No. 3 water glass was applied thereon and dried in the same manner as above to form a coating film with an average thickness of 0.3 μm.

Comparative Example 1 The same process as in Example 1 was carried out except that the curing agent phosphoric acid was omitted.

In the following margin [Effects of the Invention] As explained hereinafter, according to the present invention, initial hydrophilicity,
A hydrophilic film with excellent aging properties and corrosion resistance can be obtained. Such a coating is useful not only for the fins of aluminum heat exchangers, but also for anti-corona discharge treatment of aluminum power transmission lines (Japanese Patent Laid-Open No. 57-49110).

Claims (1)

[Claims] 1. A hydrophilic treatment method in which an organic polymer film is formed on the surface of an aluminum material and then treated with a silicate aqueous solution, characterized by containing a hardening agent that makes the silicate insoluble in water in the organic polymer film. Hydrophilic treatment method.