JPH0818005B2 - Method for hydrophilic treatment of aluminum surface - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for hydrophobizing a metal surface, particularly an aluminum or aluminum alloy (hereinafter collectively referred to as aluminum) surface, to prevent corrosion. The present invention relates to an anticorrosive hydrophilic surface treatment method for an aluminum material used in a heat exchanger.

[Prior art]

BACKGROUND ART Conventionally, aluminum heat exchangers, fins thereof, and the like have been subjected to surface treatment for the purpose of preventing white rust. As the surface treatment, an anodic oxide film, a boehmite film, and a resin film treatment (hexavalent chromium) However, the surface of these coatings has almost no wettability and is rather water-repellent. Further, although chromate conversion film treatment is also performed, the chromate conversion film has some wettability at the initial stage of film formation, but that is not enough. The chromate conversion film tends to change from a hydrophilic surface to a hydrophobic surface with the lapse of time, particularly under a heating and drying condition.

On the other hand, many heat exchangers are designed so that the areas of the heat radiating portion and the cooling portion are as large as possible in order to improve the heat radiating or cooling effect. For this reason, when used for cooling, water in the atmosphere where water is condensed on the heat exchanger surface, especially on the fin gap,
The more hydrophobic the fin surface is, the more likely it is to form water drops, and the fin gap causes clogging to increase ventilation resistance and reduce the heat exchange rate.

Further, the water droplets accumulated in the fin gap are easily scattered by the blower of the heat exchanger, and cannot be received by the water droplet receiving tray installed in the lower part of the heat exchanger, so that the vicinity of the heat exchanger is soiled with water.

Therefore, in order to prevent the water droplets from remaining in the fin gaps and causing clogging due to the water droplets, a treatment for imparting hydrophilicity to the aluminum surface and improving water wettability has been proposed.

In particular, a method of treating an aluminum surface with a silicate such as water glass is widely used as a hydrophilic treatment because it has high wettability and heat resistance and is inexpensive. As the treatment method, there has been proposed a method in which an aqueous silicate solution is directly applied to the chemical conversion-treated aluminum, or an organic polymer film is previously formed on the aluminum and then the silicate solution is applied thereto.

For example, in JP-A-59-205,596, a corrosion resistant coating layer made of an organic polymer resin is formed on the surface of an aluminum plate, and a hydrophilic coating layer made of a hydrophilic inorganic material is formed on the surface of the corrosion resistant coating layer. The present invention relates to an aluminum fin material for a heat exchanger.

Further, JP-A-61-8598 proposes a fin material for a heat exchanger having excellent hydrophilicity, which is characterized by providing a mixture coating layer of a specific organic polymer and an alkali silicate on the aluminum surface. It also states that a coating layer selected from among chromate, boehmite and organic silicate coatings can be provided as an underlayer for this mixture coating layer.

In particular, no primer is used, but JP-A-57-
In No. 82,467, water-soluble alkaline siliceous material is applied to the surface of aluminum material, dried, and then neutralized with an acid such as nitric acid to form an anticorrosion film, which can prevent discoloration of the aluminum surface due to hot water. It is said that the corrosion resistance is also improved [Technical Lecture Meeting of Metal Surface Technology Association p.46 Sho 5
7] There is a proposal to try to improve the physical properties by post-treatment.

JP-A-49-24,446 and 52-52,135 do not aim at hydrophilicity, but a method for producing an aluminum material for a reflector for a lighting fixture using an alkali metal silicate solution coating pickling step has been proposed. There is.

JP-A-61-84,383 is characterized in that an aqueous solution of an alkali metal silicate added with borate is applied to the surface of an aluminum material and dried, and then an aqueous solution of an inorganic acid, an organic acid and an acidic salt thereof is applied. There is a proposal of a method for surface treatment of the aluminum material for the heat exchanger described above, but the use of polyvalent metal ions is not explicitly stated.

In JP-A-54-57264, an aluminum plate fin type heat exchanger is first treated with an aqueous solution (A) containing a silicic acid compound and then with an alkaline aqueous solution (B) containing an alkaline earth metal compound. There is provided a heat exchanger in which a chemical conversion film is formed on the aluminum surface by treatment to impart corrosion resistance and hydrophilicity at the same time.

[Problems to be solved by the invention]

As described above, the surface of the aluminum fin material for the heat exchanger is first coated with an organic primer, then treated with a water-soluble silicate or a mixed aqueous solution of a water-soluble silicate and an organic polymer, and then dried to form a hydrophilic film. The method of forming is known. However, these methods have the following drawbacks.

First, 0.1-0.2 mm thick aluminum plate for heat exchanger fin material is subjected to hydrophilic treatment, and then perforation processing is performed on this plate to assemble the heat exchanger. In order to facilitate the processing and reduce the wear of the jig, apply lubricating oil and wash it off after processing.However, if you use a material made by applying water glass on the surface to make it hydrophilic, it repels the lubricating oil. There is a problem that it is difficult to apply it uniformly and so-called "riding" is poor. Further, there is a drawback that fatty acid soap is generated due to hydrolysis of lubricating oil by strongly alkaline water glass.

As described in JP-A-57-82,467, acid cleaning after treatment with water glass eliminates the above-mentioned drawbacks, but the fin material treated with acid has a better adhesion and hydrophilic film than the one without acid cleaning. A new problem has been found that not only the hydrophilicity is poor, especially after the solvent is washed after applying the lubricating oil, but also the odor during operation of the heat exchanger assembled using this fin is remarkable.

Generally, the cause of the bad odor during operation of the heat exchanger has not been clarified yet, but it is considered to be due to fine particles scattered from the aluminum surface of the heat exchanger or bacteria propagated on the surface, especially in the case of a new heat exchanger. It is said that.

The above-mentioned drawbacks can be alleviated to some extent when the organic polymer is used in combination, but they cannot be completely improved as compared with the case where water glass is used alone.

Japanese Unexamined Patent Publication No. 54-57,264 describes that the aqueous solution A is treated and washed. In this method, the solution A forms a chemisorption film on the aluminum surface, but there is a part where physical adsorption is formed. In this method, since the solution A is treated and washed with water, the partially adsorbed A
The solution was washed away, and a part where the solution A did not remain was generated, and the thickness of the adhered part seems to be extremely thin. Therefore, even if it was treated with the solution B, a uniform chemical conversion film was not necessarily formed on the aluminum surface, and the hydrophilicity, film adhesion, odor and workability were not necessarily sufficiently improved.

For this reason, the present inventor has conducted earnest studies for the purpose of establishing a treatment method for maintaining the corrosion resistance of the aluminum surface and forming a film having sufficient hydrophilicity, odor, film adhesion and processability.

[Means for solving problems]

As a result of various investigations to solve the above problems, a water glass type hydrophilic treatment agent was applied to an aluminum material coated with a primer, and dried without washing with water to form a water glass type hydrophilic film. By further treating this with an aqueous solution of a polyvalent metal compound, it becomes possible to manufacture an aluminum heat exchanger with good hydrophilicity, film adhesion, and post-processability and low odor, or an aluminum fin material for heat exchangers. The present inventors have found a hydrophilic treatment method for aluminum materials.

That is, according to the present invention, the surface of aluminum is applied with or without chemical conversion treatment to form a film by applying an organic polymer-based undercoat paint, and further, an alkali metal salt of silicic acid and / or a quaternary grade. A silicate-based hydrophilic film formed by applying an amine salt-containing hydrophilic treatment solution and heating and drying it,
The present invention provides a hydrophilic treatment method for an aluminum surface, which is characterized by treating with a solution containing a polyvalent metal ion.

The water glass hydrophilic treatment agent used here is SiO ₂
/ M ₂ O (M is one selected from Li, Na, K) molar ratio is 1 to 17 Usually, M is Na or K and 2 to 4 alcalcyl silicate (hereinafter collectively referred to as water glass ) Aqueous solution mainly composed of quaternary amine water glass [for example, Nissan Chemical Co., Ltd.'s KYAS-40-25 (trade name)], and optionally water-soluble organic solvent capable of forming a mixed aqueous solution with the water glass. Molecules, for example, polymers of unsaturated acids such as polyvinylpyrrolidone, polyacrylic acid, polymethacrylic acid, maleic acid, itaconic acid,
Water-soluble salts of copolymers, polymers and copolymers of polyacrylamide, methacrylamide and their derivatives; polyacrylamide, partial hydrolysates of methacrylamide, polyvinyl alcohol, poly-2-hydroxyacrylate, alkali salts of polystyrenesulfonic acid , Pullulan, etc. are mixed.

Furthermore, hydrophilic metal oxides such as silica sol and alumina sol can be added to water glass. The content of water glass when these organic polymers and sols are mixed is not particularly limited, but when the water glass content is 50% or more of the total solid content, the water-soluble salt of a polyvalent metal, which is the essence of the present application. The effect of the treatment becomes remarkably remarkable.

Of course, in addition to the above, surfactants, leveling agents, antibacterial agents,
It is also possible to add fragrances, coloring agents, antifoaming agents, rust preventives and the like.

The primer is applied to the aluminum material directly or after being subjected to an appropriate chemical conversion treatment. The chemical conversion treatment method is not particularly limited, and known chemical conversion treatment methods such as the MBW method, the EW method, the boehmite method, the chromate chromate method, and the phosphoric acid chromate method are used. Of course, a coating type chromate containing chromic acid and dichromate ions in the primer can be used, and the type of primer is not particularly limited. However, it is necessary that the water glass-based hydrophilic treatment aqueous solution to be applied thereon is uniformly applied, and in order to maintain high hydrophilicity as the aluminum fin material subjected to hydrophilic treatment, the primer itself may be used. It is desirable that it has hydrophilicity.

The greatest feature of the present invention is that the aluminum surface coated with the water glass hydrophilic treatment agent is heated and dried without being washed with water to form a water glass hydrophilic film.

That is, the aluminum material or aluminum heat exchanger coated with the water glass hydrophilic treatment agent is not washed with water, but a water glass hydrophilic treatment film is formed by heating and drying. The thickness of this film is not particularly limited, but usually 0.02
˜2 μ, preferably about 0.05 to 1 μ.

The heat drying is usually carried out in a hot air drying furnace, but infrared drying or the like is also used.

The hot air drying furnace has a hole for blowing hot air, and the hot air is blown through the hole to pass through an aluminum heat exchanger or the like to dry the air.

The drying conditions are slightly different depending on the part to be dried,
Perform at 80 ° to 300 ° C for 5 seconds to 30 minutes.

In this case, naturally, the time is long at low temperature and short at high temperature.

This water glass hydrophilic coating is subsequently treated with a water soluble salt of a polyvalent metal. As the treatment method, various methods such as dipping, spraying, rolling, and curtain coating can be adopted.

As the polyvalent metal, magnesium, calcium, strontium, barium, aluminum, titanium, zirconium, chromium, molybdenum, manganese, iron, cobalt, copper, zinc, tin, etc. can be used, but environmental problems, potential, cost Considering the above, magnesium, calcium,
Barium and iron are preferable, and an aqueous solution of magnesium, calcium, and barium compound is most suitable, but it is of course possible to mix a water-soluble solvent such as alcohol. The counter ion is not particularly limited as long as it is water-soluble, but (nitrous) nitric acid, hydrofluoric acid, (bi) carbonate and hydroxide are suitable from the viewpoint of corrosion resistance. Here, the solution concentration can be treated with a metal ion having a solubility of 0.01 mol / · H ₂ O or more, but 0.1 mol / · H ₂ O or more is effective. Since the case the amount of adhered as the upper concentration not economical viewpoint and water washing is too large heat exchanger performance decreases, preferably 3mol / · H ₂ O or less with a metal ion, more preferably 2 mol / · H
Used below ₂ O.

When the flat plate is subjected to a dipping treatment, a slurry such as lime milk can be used as long as it has a certain degree of solubility.

Although the liquid property is not particularly limited, a strong acidic liquid that decomposes a polyvalent metal silicate is not preferable. Preferably
An aqueous solution having a pH of 3 to 13, and more preferably a pH of 4 to 12 is used.

Various additives may be added to the aqueous solution of the polyvalent metal salt as long as the post-treatment effect of the present application is not impaired.

For example, in addition to surfactants, defoamers, antibacterial agents, fragrances, colorants, etc., when chromate chromate conversion treatment is carried out, addition of a reducing agent of Cr ⁶⁺ , such as a hydrazine salt, is added to chromium. Effective in preventing elution.

Further, when an aqueous solution of polymetal salt is applied onto an aluminum flat plate by roll coating, it is effective to add a thickening agent, a leveling agent, a surfactant and the like.

Furthermore, when an aqueous calcium hydroxide solution or slurry is used, a hydroxyl group-containing organic compound may be added to increase the solubility and then used.

There are also no particular restrictions on processing conditions such as processing temperature and time. It is better to raise the temperature in a shorter time, but from the viewpoint of cost, room temperature treatment is preferable.

[Action]

Although the mechanism of formation of the water glass-based hydrophilic film by heating and drying is not always clear, a uniform water glass-based hydrophilic film is formed on the organic polymer-based undercoat paint film by chemical adsorption instead of physical adsorption. It seems to be.
Further on the film by an aqueous solution containing polyvalent metal ions,
It seems to form a polymer film.

The cause of the post-treatment effect exerted by the polyvalent metal ion-containing aqueous solution is not always clear, but the polymer film is formed by the ion exchange between the alkali ion of the low-molecular-weight alkali silicate and the polyvalent metal ion to form a metal crosslink. It is thought to be for making. In particular, when acid treatment is applied to the water glass film, -O ^- Na ⁺ in the water glass becomes OH, and the film becomes porous and brittle, and it becomes easy to scatter with fine powder of silicic acid, resulting in poor adhesion. It seems that the odor also increases.

In addition, the alkali metal salt has sufficient hydrophilicity but the lipophilicity is extremely poor, so that the lubricating oil is hard to ride, but the polyvalent metal silicate retains hydrophilicity to some extent, and the lipophilicity is also higher than the alkali metal salt. Therefore, the oil can ride well, and since the alkalinity is low, the hydrolysis of oil is difficult to occur.

In addition, since the alkali metal salt has too high water solubility, it easily dissolves and flows out in the immersion-drying cycle, whereas the polyvalent metal salt has low solubility in water and thus has high hydrophilic durability. Thus, magnesium seems to have the best balance of these properties.

When a polymer containing an acid group such as a carboxyl group, such as polyacrylic acid, is added to water glass, an ionic bond due to a polyvalent metal is formed between the polymer and silicic acid to enhance the same effect as described above. It seems to be.

 The present invention will be further described with reference to the following examples.

〔Example〕

 The test methods in the examples were as follows.

Test method ・ Contact angle (hydrophilicity) F is the contact angle of a small water droplet with a diameter of 1 to 2 mm that is statically placed on a solid surface.
It measured using ACE contact angle meter CA-P type (Kyowa Interface Chemistry).

The measurement was performed for each of the initial one after processing and one week after immersion in running water.

- flowing water stability after 8H _R immersed in flowing water at (hydrophilic) at room temperature, the process of drying 16H _R, 80 ° C. and 1 cycle, indicated by the water contact angle after 5 cycles.

・ Corrosion resistance White rust area based on salt spray test method JIS Z-2371 is 5%
It shows in the spray test time until it reaches.

・ Odor: The odor when blown with humid air to the treated plate is measured by the 5-point method.
Evaluated by people.

-Adhesiveness Cellotape was attached to a hydrophilic coating film, and it was judged from the appearance when it was rapidly peeled off.

・ Lubricant oil coatability (processability) Dipped in punching oil AF-8F [Idemitsu Petroleum Co., Ltd.],
The wettability of the oil after standing for 1 minute was visually evaluated.

Example 1 An aqueous primer prepared by dissolving 10 g of polyacrylamide having an average molecular weight of about 200,000, 3.84 g of chromic anhydride, and 4.54 g of zircon hydrofluoric acid on the surface of a 0.1 mm thick aluminum plate (standard A-1100) was dried. The coating was applied so that the film thickness would be 0.2 μm, and dried by heating in an oven at 200 ° C. for 3 minutes. Next, a 5% aqueous solution of a 1: 1 (solid content weight ratio) mixture of potash water glass having a SiO ₂ / K ₂ O molar ratio of 3 and polyacrylic acid soda was dried on this primer to a dry film thickness of 0.2μ. Apply to 200
It was dried by heating in an oven at ℃ for 3 minutes.

This plate was immersed in a 3% aqueous solution of magnesium acetate for 30 seconds, washed with water, and dried in an oven at 200 ° C. for 2 minutes.

Examples 2 to 8 Samples were prepared in the same manner as in Example 1 except that the aqueous solution of the polyvalent metal compound shown in Table 1 was used instead of the magnesium acetate in Example 1.

Example 9 A water-soluble polyurethane (Elastron A-42 manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) was applied to the same aluminum plate treated with chromate chromate and dried at 200 ° C. for 3 minutes. The coating thickness was about 0.3μ.

A sample was prepared in the same manner as in Example 1 except that No. 3 water glass was used.

Comparative Example 1a The procedure of Example 1 was repeated, except that nitric acid was used instead of magnesium acetate.

Comparative Example 1b Example 1b was repeated except that the treatment with magnesium acetate was omitted.

Comparative Example 2a The procedure of Example 9 was repeated, except that nitric acid was used instead of magnesium acetate.

Comparative Example 2b The procedure of Example 9 was repeated, except that the treatment with magnesium acetate was omitted.

Example 10 An aluminum heat exchanger was treated with phosphoric acid chromate by a conventional method, washed with water, dried, and then treated with water-soluble polyurethane.

Comparative Example 3 Example 10 except that no magnesium acetate treatment was performed.
The same process was carried out.

Table 1 summarizes the results of Examples 1 to 10 and Comparatives 1 to 3.
It was shown to.

From these results, corrosion resistance, hydrophilicity (contact angle), odor,
Comprehensive evaluation of film adhesion and workability (lubricant coating property) shows that in Comparative Examples, any of them is inferior except corrosion resistance, but in the present invention, all performances show good results, and particularly hydrophilic Shows remarkable improvement effect on the odor, odor and film adhesion.

〔The invention's effect〕

The effect of the present invention is excellent, and the extremely useful point is specifically shown in the above Examples and Comparative Examples.
The summary is as follows.

(1) The aluminum surface treated according to the present invention is
In proportion to the conventional one, it has good overall performance in terms of corrosion resistance, hydrophilicity, odorous film adhesion and workability, and especially a remarkable improvement effect on hydrophilicity, odor and film adhesion. Indicates.

(2) The method of the present invention is particularly effective as an anticorrosive hydrophilic surface treatment method for an aluminum material used in an aluminum heat exchanger.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B05D 7/24 302 Y 7415-4F F28F 1/32 H 19/02 501 Z (72) Inventor Okita Hiroshi Nihonbashi 1-15-1, Chuo-ku, Tokyo Japan, Parkerizing Co., Ltd. (72) Inventor Yasunobu Matsushima 1-15-1 Nihonbashi, Chuo-ku, Tokyo Japan, Parkerizing Co., Ltd. (56) Reference JP-A-54- 57264 (JP, A) JP-A-61-261483 (JP, A)

Claims (5)

[Claims] 1. A surface of aluminum is subjected to a chemical conversion treatment or not to a chemical conversion treatment, and an organic polymer based undercoat paint is applied to form a film, and further, an alkali metal salt of silicic acid and / or a quaternary grade. A hydrophilic treatment method for an aluminum surface, which comprises applying a hydrophilic treatment liquid containing an amine salt, heating and drying, and treating the formed silicate-based hydrophilic film with a solution containing a polyvalent metal ion. 2. The hydrophilic treatment method for an aluminum surface according to claim 1, wherein the heat drying is hot air drying. 3. The heating and drying at 80 ° to 300 ° C. for 5 seconds to 30
The method for hydrophilic treatment of an aluminum surface according to claim (1) or (2), wherein the method is carried out for minutes. 4. The method for hydrophilic treatment of an aluminum surface according to claim 1, wherein the polyvalent metal is magnesium, calcium or barium. 5. The surface of aluminum is applied with or without chemical conversion treatment with an organic polymer based undercoat paint to form a film, and further, an alkali metal salt of silicic acid and / or quaternary. A hydrophilic treatment liquid containing an amine salt and a water-soluble polymer is applied, dried by heating, and the formed silicate hydrophilic film is treated with a solution containing a polyvalent metal ion. Method for hydrophilic treatment of aluminum surface.