JPH049597A - Aluminum fin material for heat exchanger and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve adhesion of a paint film and prevent cracks and separation of the paint film due to processing by forming an oxidized film with a specific thickness on a material for use in fins by effecting AC electrolysis in an alkaline aqueous solution. CONSTITUTION:An aluminum or aluminum alloy is subjected to AC electrolysis in an alkaline aqueous solution at pH 9-3, temperatures 35-85 deg.C, current density 4-50A/dm<2>, and quantity of electricity exceeding 80C/dm<2> to form an oxidized film with a thickness of 500-5,000Angstrom . Either or both anti-correction film and hydrophilic film are applied to the oxidized film thus formed. Since the oxidized film has a large pore diameter and a large number of branches, a strong adhesion is achieved between a paint film and an aluminum plate when an organic substance such as coating resin etc., or an inorganic substance such as water glass etc., is applied to the oxidized film. The oxidized film is flexible and hence cracks or separation is not formed therein, so that cracks or separation is not caused by processing in the resins or inorganic paint films applied to the surface of the oxidized film.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to aluminum fins used for heat exchanger fins used in condensers (condensers) for household, commercial and car air conditioners, evaporator noters, etc. Regarding materials.

The aluminum fin material of the present invention, which is made by coating and baking an inorganic film such as resin or water glass on aluminum or an aluminum alloy material, is formed into a fin by drawing or annealing, degreasing and cleaning (removal of press oil), assembly(
When used as a heat exchanger fin by inserting a copper vibrator or expanding the tube, it has excellent adhesion between the aluminum or aluminum alloy material and the coating film, and has high corrosion resistance and chemical resistance (solvent resistance, alkali chemical resistance), Furthermore, the present invention provides an aluminum fin material for a heat exchanger with high productivity (short processing time, low cost) and a method for manufacturing the same.

[Conventional technology] Aluminum fin materials are used in heat exchangers such as evaporators and condensers for air conditioners and coolers, whether for home or commercial use, because they have excellent workability and heat dissipation, and are lightweight and have good corrosion resistance. ing.

In recent years, as heat exchangers have become smaller and more energy efficient, they have been processed into complex shapes to increase thermal efficiency, increasing the surface area per unit weight, and reducing condensation of moisture in the air on the fin surfaces during cooling operation. In order to prevent the increase in ventilation resistance associated with this, the aluminum fin surface is subjected to hydrophilic treatment (resin coating, etc.).
In addition, in order to further improve corrosion resistance, a treatment such as coating with a corrosion-resistant paint film is applied.

These coating treatments include post-coating, which involves painting the molded material, and pre-coating, which involves painting the pre-painted aluminum plate before forming it, but painting after forming it into a complex shape is difficult. Needless to say, it is extremely difficult to apply a pre-coat to the step corners of the board.

However, coated aluminum plates generally must undergo the following process of forming into fins.

Forming (drawing or ironing) - Cutting - Copper pipe insertion - Copper vibrator expansion - Degreasing - Drying - Product The forming performed here is done by drawing or ironing, but deep drawing or harsh forming is not enough. There it is,
Normally, the processing rate (handling thickness reduction rate) of fin material is 50% or more.

Therefore, if the adhesion between the aluminum plate and the coating film is insufficient, the coating film may crack or peel.

Under such conditions, white rust and pitting corrosion are likely to occur in the defective areas of the coating film due to condensation during cooling operation of the heat exchanger (and electrolytic corrosion is also likely to occur due to direct contact with the copper vibrator).

Furthermore, since press oil is used in heat exchanger molding, degreasing and cleaning is required after molding. For degreasing, ], 1
．． 1-) Lichloryukun, ■1.2-Organic solvents such as trichlorethylene, alkaline degreasers such as alkali silicate, nonionic or anionic activator Aqueous solutions are immersed in the solution and/or cleaning is performed in a steam bath5. When.

If the adhesion between the aluminum plate and the paint film is insufficient, the degreaser will get into the adhesive surface between the aluminum plate and the paint film, causing damage to the fins,
This causes problems such as peeling and other problems, and the degreasing agent remains in the final product, causing unpleasant odors.

On the other hand, during use, heat exchangers become contaminated with dust, oil floating in the air, dirt, etc. This can lead to clogging, the growth of bacteria and mold, and a decrease in heat exchange performance. Therefore, the fin surface may be washed with an alkaline detergent once every few years to several times a year. In this case too, if the adhesion between the aluminum surface and the paint film is poor, the cleaning solution will come into contact with the adhesion defects between the aluminum and the paint film and react with the aluminum.
Image erasure, corrosion, fins, and paint peeling occur (such defects occur regardless of post-coat or pre-coat).

In order to eliminate such inconveniences and to improve the adhesion between the aluminum plate and the coating film, conventional coating substrate surface treatments have been carried out on the aluminum plate.

For example, JP 60-13428 (JP 57-19
381) or in JP-A-59-215564, the aluminum surface is anodized in a solution such as sulfuric acid, ceric acid, or phosphoric acid.

The anodic oxide film formed in such an acidic solution is dense and certainly has high corrosion resistance, and if no sealing treatment is performed, an anchoring effect can be expected due to the diffusion and assimilation of the resin into the pores. Improves paint film adhesion.

However, the anodic oxide film formed in such an acidic solution is dense and hard, and is prone to cracking when subjected to severe forming processes such as deep drawing and ironing, resulting in corrosion, paint film peeling, etc. It causes In addition, a film thickness of several micrometers or more is required to satisfy the monophagous property, and to achieve this film thickness, a long processing time of several minutes to several tens of minutes is required, which has the disadvantage of low productivity. be. Furthermore, there are many problems, such as high drug prices, leading to increased costs.

Also, JP-A-59-211578 and JP-A-58-48
No. 676 proposes treating the aluminum surface with demineralized water or a basic aqueous solution of p ) (= 9 to I2) to form a hydrated oxide film (boehmite film) on the aluminum surface.

This hydrated oxide film has needle-like crystals, and when the resin penetrates into the gaps between the crystals, it exerts an anchoring effect and improves coating adhesion.

However, even with this method, in order to obtain a film thickness with sufficient corrosion resistance, a thick boehmite film is required, and a processing time of several minutes to JO is required, resulting in poor productivity. In addition, since the coating film is thick and hard, if it is touched deeply or subjected to severe shaping such as ironing, cracks may occur, causing corrosion and peeling of the coating film.

In addition, equity 8t ¥53-48177, JP-A-54-29
In No. 45, it is proposed to treat the surface of an aluminum plate with an alkanosilicate aqueous solution or an alkali silicate M salt solution to which an organic Thai acid compound of type 1 is added.

In this case, corrosion resistance is improved by covering the aluminum surface with a silicate compound, but the formed silicate compound is brittle, so it cracks and peels during the forming process, becoming a starting point for corrosion and causing paint film to peel off. This makes it extremely difficult to use as a precoat.

Furthermore, in Japanese Patent Publication No. 60-13429, aluminum was treated with acid-based treatment solutions (chromic acid, chromate, dichromate,
Chromic acid/phosphoric acid, titanate, tannic acid-titanate) for a few seconds to 20 minutes.7 This process forms a corrosion-resistant film of chromic acid, chromium phosphate, etc. on the aluminum surface. 1ttt,
However, in this case too, if severe molding is performed with an ironing rate of 50% or more, cracks will appear in the -F film, which may become a starting point for corrosion or cause peeling of the paint film.

In addition, when using chemically formed chromate, a large amount of wastewater containing chromium is generated, which requires washing with water after chemical treatment, so wastewater treatment equipment with large capacity is required, which requires a large amount of money and is difficult to handle. It is disadvantageous in terms of pollution, safety, and cost, as it requires special care.

[Problems to be Solved by the Invention] The purpose of the present invention is to develop an aluminum fin material for pre-coating with high productivity. ■ High adhesion between the base and the coating film, and a reduction of 50% or more or 50% or more. To obtain a coating base that does not cause defects such as cracking or peeling in the painted coating even when subjected to rolling processing, and maintains high corrosion resistance even after processing and forming. To obtain a coating base that does not cause blistering or peeling of the paint film even after degreasing and cleaning after press molding.■ The adhesion between the base and the paint film is high, and the paint film does not peel or peel even when washed or immersed in an alkaline solution. To obtain a coating base that does not cause corrosion, etc. ■ To obtain a coating base that requires short processing time and is highly productive ■ A coating that is low in toxicity, high in safety and h, and low pollution in terms of waste liquid treatment, etc. The present invention was completed after conducting research with the following goals: (1) Obtaining a method for manufacturing a coating base that uses low chemicals and is low in cost.

[Means for Solving the Problems] The present invention provides an aluminum fin material for a heat exchanger, characterized in that an oxide film with a thickness of 500 to 5,000 is formed by alternating current electrolysis treatment in an alkaline aqueous solution. This aluminum material for heat exchanger is made of aluminum or aluminum alloy material at a pH of 9.
~13. In an alkaline aqueous solution with a bath temperature of 35 to 85 °C, at a current density of 4 to 50 A/d m'', the amount of electricity is 8
Obtained by a method for producing an aluminum fin material for a heat exchanger, which is characterized by performing alternating current electrolytic treatment for a period of time exceeding 0 C/dm2 and an oxide film thickness of 5,000 g, and on the oxide film of the obtained aluminum fin material. Provided is an aluminum fin material for a heat exchanger in which a corrosion-resistant film or a hydrophilic film is provided, or a corrosion-resistant film is first provided and a hydrophilic film is provided thereon.

The oxide film obtained by alkaline AC electrolysis according to the present invention is
It has a large bore diameter (approximately 200 diameter diameter, about 50 diameter for normal sulfuric acid anodized coating) and has a large number of branched structures. Therefore, when organic substances such as paint resin or inorganic substances such as water glass are applied, these substances easily penetrate into the bore, resulting in a high anchoring effect and strong adhesion between the coating film and the aluminum plate. is obtained.

In the present invention, the thickness of the oxide film is 500 to 5000 times thinner, and the pores 11 have branching! As a result of its structure, the oxide film is highly flexible and does not crack or peel off even if it is drawn by more than 50% or ironed by more than 50%, and as a result, the oxide film is not coated on the surface. This prevents cracks and peeling from occurring in resins, inorganic coatings, etc.

However, if the film thickness is less than 500 Å, the length of the bore is short, so a sufficient anchoring effect cannot be obtained, resulting in poor adhesion.

In addition, if the number of workers exceeds 5,000, not only will the adhesion of the coating not improve significantly compared to when the number of workers is 5,000, but the flexibility of the oxide film will decrease as the film becomes thicker, making it more likely to cause cracks during molding. 6. It's wasteful The alkaline source for the alkaline aqueous solution is not particularly limited, but those containing phosphates such as sodium phosphate, potassium phosphate, sodium birophosphate, potassium birophosphate, and phosphoric acid + sodium hydroxide are preferred. In the case of a liquid containing phosphate, the bore diameter tends to be large, so particularly high adhesion can be obtained. In addition, alkali or alkaline earth carbonates such as sodium carbonate, aqueous solutions of alkali or alkaline earth hydroxides such as sodium hydroxide, or a mixture of two or more of these may also be used.

In addition, a surfactant may be included in order to improve wettability with the aluminum surface and degreasing property. Preferably the pH is 0 to 12.

If the pH is less than 9, the degreasing properties will be poor, and if the pH is particularly acidic, it will not be possible to dissolve and remove the rolling oil on the surface of the aluminum plate and the oxide film formed during rolling. ) is likely to occur and equipment costs are high. pH is 1
If it exceeds 3, the solubility of the generated oxide film will be too strong, and a porous film with excellent adhesion will not be formed.

The bath temperature is preferably in the range of 35 to 85°C, preferably in the range of 60 to 80°C. If the bath temperature is less than 35°C, the degreasing and cleaning effects will be insufficient and the treatment will take a long time.

On the other hand, if the bath temperature exceeds 85° C., monolysis is too strong, making it difficult to obtain an anodic oxide film of the required thickness, and a porous film with excellent adhesion cannot be formed.

The current density during AC electrolysis is 4-50 A/d m'
Preferably it is 5 to 30 A/dm''.

If the current density is less than 4 A/d m'', the amount of bubbles generated during electrolysis will be insufficient, the surface cleaning effect will be poor, and the formation of a porous oxide film with excellent adhesion will be insufficient, which is undesirable. If it exceeds /dm2, the electrolysis voltage becomes too high, which tends to cause production problems such as electric leakage, and uneven electrolysis (burning) due to reaction heat, which increases equipment costs.

electricity! (total amount of electricity) needs to exceed 80 c/dm''.

When the amount of electricity is equal to or less than 80 c/d m 2 , the porous oxide film is thin, the adhesion to the coating film formed thereon is insufficient, and the cleaning action is also poor.

Looking more closely, the amount of electricity when the polarity is positive (referred to as the amount of electricity at the anode) is preferably in a range exceeding 40 c/dm2. If the amount of electricity at the anode is equal to or less than 40C/dm, the growth of the porous oxide film will be insufficient and the cleaning action will not be sufficient.6 The amount of electricity when the polarity is negative (referred to as the amount of cathode electricity )
is preferably 40 c/dm"lJ or more. If the cathode electricity amount is less than 40 c/dm2, the cleaning action will be insufficient.

The current waveform may be an alternating current waveform, such as a sine wave alternating current, a rectangular wave, a trapezoidal wave, a triangular wave, etc., and the amount of electricity at the anode and the amount of electricity at the cathode may be different.

The electrolysis time may be set based on the relationship between the required amount of electricity and the current density. If the current density is high, the process can be done in a short time.

For aluminum alloys such as 5182, which have a thick natural oxide film, it is recommended to remove the natural oxide film with an acid solution before electrolytic treatment, which will extend the life of the electrolyte and form a porous film due to electrolysis. This is effective because it increases uniformity.

Cleaning treatment before electrolysis may be performed as necessary. For example, if a very large amount of rolling oil is present, cleaning with a solvent such as trichloroethane or immersion cleaning with an alkaline solution such as an aqueous solution of caustic soda is effective.

As the corrosion-resistant coating used in the present invention, any one of polyacrylic acid, polymethacrylic acid, polyacrylic a derivative, polymethacrylic acid derivative, urethane resin urethane resin derivative, epoxy resin, epoxy resin derivative, polyamide, polyamide derivative, etc. Alternatively, it may be a copolymer or a mixture of two or more of these, and may further contain trivalent chromium, hexavalent chromium, S i 02) silicate, zirconium salt, etc.

For example, acrylic copolymer melamine resin as disclosed in JP-A-61-101798, JP-A-1-174
438, an acrylic resin as disclosed in JP-A No. 6
Examples include a mixture of hexavalent chromium and polyacrylamide as disclosed in No. 3-168473.

The coating thickness is preferably 5 g/m2 or less; if it exceeds 5 g/m2, the thermal conductivity decreases, which is not preferable.

The temperature for baking can be selected as appropriate depending on the paint to be applied.1 Normally, a temperature in the range of 80 to 320°C is selected.6 The baking time can also be selected as appropriate depending on the paint, but in consideration of productivity, It is preferable to select a paint that lasts about seconds.

The coating method may be dipping, roll coater, or the like.

The hydrophilic film used in the present invention includes silicates, polyacrylic acid derivatives, and polyamide derivatives.

Examples include cellulose derivatives, but are not limited to 1
For example, any one of polyvinyl alcohol and polyvinyl alcohol derivatives, or a copolymer or mixture of two or more of these may be used, and polyoxyethylene derivatives, sorbitan derivatives, sucrose fatty acid esters, sulfuric acid esters, sulfonic acid esters, IN of surfactants such as phosphate esters! Or it may contain 2J4 or more.

For example, Tokukaihei! -201487, polyacrylic acid, polymethacrylic acid, or a mixture thereof having a degree of polymerization in the range of 1000 to +0000, and styrene-maleic acid as disclosed in JP-A-61-8598. Mixture of one or more water-soluble organic polymers and silicate compounds of acid copolymer, polyacrylamide, butylene-maleic acid copolymer, polyacrylic acid or salts thereof, JP-B-1973- S IO2/M 20 (M = L
i, Na, Ca, etc.) ratio of 1 or more, a polyvinyl alcohol, polyamide resin, urea resin mixture as disclosed in JP-A-1-299877, exemplified in JP-A-61-101798 There are cellulose derivatives, etc.

Examples of the surfactant include phosphate ester surfactants whose hydrophobic group has a molecular weight of 400 or less, as exemplified in JP-A No. 64-61239, JP-A No. 64-61239, JP-A-64-61239;
Examples include nonionic surfactants having an HL B value of 8 to 20 as disclosed in Japanese Patent No. 4067.

The thickness of the hydrophilic bamboo film is preferably 01 to 5 g/m2.

If it is less than 0.1 g/m2, hydrophilicity is insufficient, and 5 g/m2
If it exceeds 2, the thermal conductivity decreases, which is not preferable.

Baking ("Fade temperature" can be selected appropriately depending on the paint to be applied, but it is usually selected from the range of 150 to 300 degrees Celsius.15
Below 0°C, baking tends to be insufficient (up to 300°C).
If it exceeds this amount, the hydrophilic groups are destroyed, resulting in a decrease in hydrophilicity.

The baking time may be appropriately selected depending on the paint, but it is preferable to select a baking time in the range of about 5 to 300 seconds in consideration of productivity.

The amount of surfactant added is preferably about 0 to 50%, preferably about 0 to 20%, based on the resin solid content. If it exceeds 50%, curing of the paint will be hindered.

The coating method may be dipping, roll coater, etc. In addition, the above corrosion-resistant film and wood-friendly film may be coated with one or more of fungicides, preservatives, and deodorants. May contain.

As antifungal agents, TBZ, 2-(2-furyl)-3-(5-nitro-2-furyl)-acrylic acid amide, and 5,6-titrachloro are exemplified in JP-A-58-102073. Examples include isophthalonitrile, N-dimethyl-N-phenol-(N-fluorodichloromethylthione-acrylic acid sulfamide), and the like.

Examples of preservatives include benzoic acid or its salts, sorbic acid or its salts, and salicylic acid or its salts, as exemplified in JP-A-62-129695.

Examples of deodorants include sodium percarbonate, calcium peroxide, penyl peroxide, etc., as exemplified in JP-A No. 61-129694.

The amount of each added is preferably 50% or less, and if it exceeds 50%, film formation will be hindered, which is inappropriate.

[Function] The present invention degreases and cleans the surface of aluminum (A) by electrolytically treating it in an alkaline solution at 35 to 85°C using alternating current, and also forms a porous film with excellent layer properties. The present invention will be described in detail below at step 6, when the oxide film is formed.

(1) Alkaline i= itself has degreasing properties. Historically, electrolytic treatment using an AC waveform has been used in the same way, which has a stronger cleaning action5.In other words, since oxygen gas is generated during the anode reaction, organic substances such as rolling oil adhering to the aluminum surface are oxidized and removed, resulting in a stronger cleaning action. Demonstrates degreasing and cleaning properties. Further, during cathode cleaning, hydrogen bubbles are generated, and the expansion of the bubbles acts as a mechanical cleaning action, making it difficult for smut to adhere, which is the case in normal degreasing, and thus exhibiting a strong cleaning action.

Since this anode reaction and cathode reaction are alternating current, the above-mentioned effects work alternately, making the cleaning effect extremely strong.

The synergistic effect of each of the above actions produces a powerful degreasing and cleaning effect, and in a short period of time removes rolling oil, sludge, etc. from the aluminum plate surface that can adversely affect paint film adhesion, and at the same time creates a clean and uniform surface. A porous oxide film is formed.

On the other hand, in direct current electrolysis in an irradiated acidic bath, the bath voltage rises rapidly after one hour, making it difficult to conduct electrolysis at the high current density required for high-speed processing. Furthermore, since the oxide film does not have a branched structure, the film lacks flexibility compared to an oxide film from an alkaline bath.

When using an acidic aqueous solution, the barrier type oxide film tends to become thicker, and if you try to process it at high current density for a short time,
A voltage five times higher than that required for alkaline water is required. Also, if you forcefully apply a high voltage in such a liquid,
A non-uniform reaction (called "burning") is likely to occur due to heat generation due to concentration of current due to localized non-uniform electrical resistance, which not only impairs the appearance but also causes poor paint film adhesion and sparks. There are also many problems in terms of safety such as occurrence.
In acidic aqueous solutions, the acid concentration is usually 10% or more, pH = 1 to 2.
Below, there are also conflicts in terms of waste liquid treatment and chemical solution handling.

■ Reaction time can be shortened due to high temperature and high current density electrolysis.

Normal anodization is often carried out at temperatures below 35°C, while sulfur # anodizing is often carried out at temperatures below 20°C.In contrast, this paper uses alternating current electrolysis at a high temperature of 35 to 85°C. Electrolysis at high current densities becomes possible, allowing high-speed chemical reactions to occur. That is, because the electrolyte temperature is high, the liquid resistance is low (and the current density can be set to a high value, so the oxide film formation rate is high).

■ Characteristics of oxide film The oxide film formed by alternating current in an alkaline solution has a higher etching property than the oxide film formed by anodic oxidation by direct current electrolysis in an acidic aqueous solution. Because of its large diameter, it is extremely porous and has a large bore diameter, and because it uses AC electrolysis, it has a branched structure.

Because the oxide film has such a structure, when a corrosion-resistant film or a hydrophilic film is provided on top of it, the flexibility of the oxide film itself and the anchor effect derived from its shape make it difficult to draw. It is possible to obtain an aluminum fin material that does not cause defects in corrosion resistance due to cracks or peeling of the painted film even when subjected to a high degree of processing.

■ Oxide film thickness The aluminum fin material of the present invention has an oxide film thickness of 5
00 to 5,000 people, it is thin so that electrolysis time is short and productivity can be maintained at a high level, and because it is thin, it is flexible and does not easily crack even if the fin material is processed at a high degree. Furthermore, although this oxide film is thinner than usual, high adhesion with the paint film is obtained, which is thought to be due to the anchor effect.

[Example 1 (Test method) ■ Solvent resistance test A test piece was subjected to 1.1. To l-trichloroethane】0
After being immersed for a minute, it was dried at room temperature for 1 hour. The appearance of this test piece was observed and the adhesion test was conducted. 11, and the number of H cases where the coating film remained was counted.

■ Alkali cleaner resistance test The test piece was washed with trichloroethane and dried according to method (■). Next, it was diluted with Aluminum Fin Cleaner (manufactured by Seiso Kogyo, Aluminum Fin Cleaner W 5 times diluted solution, pH = 12-13).
After being immersed for 0 minutes (at room temperature) and then washed with running water for 15 minutes (one cycle) for a total of 10 cycles, the external appearance was observed and a goblin adhesion test was conducted using the method (2).

■ Formability test The painted test piece was formed into fins with a fin pitch of 25 mm and a colored hide of 2 mm using a fin press machine (manufactured by Hidaka Seiki) so that the ironing rate (thickness reduction rate) was 50% or more. , the state of coating film adhesion on the fin surface and the inner and outer surfaces of the collar
Observed by EM. Paint film adhesion surface fii100% is 0.100
% not 7 @ 80% or more △, less than 80% 50% or more,
Less than 50% was rated as "X".

■ Corrosion Resistance Test After passing a 9.8 mmφ copper vibrator through the fins formed in ■, the copper vibrator was expanded to create a model heat exchanger. After degreasing and cleaning this model heat exchanger using method ■,
T test (35°C, N a CQ concentration = 5%, 200 h,
JIS-22371-1988) and evaluated based on the corrosion area.

(Example 1, Comparative Example 1) JIS Al2O2-1 (24 (0,115 mmt)
Alkaline AC electrolysis (sine wave,
2%-sodium birophosphate aqueous solution, frequency 50Hz,
(pH adjusted with NaOH).

After washing with water and drying, acrylic resin (Nisvia A 1., -50 B manufactured by Shinto Toyo Co., Ltd.) was applied to each surface-treated board (coating amount = 1 g/m") and baked at 290°C to prepare a test piece.
I did various tests. The results are shown in Table 1.

(Margin below) (Example 2) Alkaline AC electrolysis (sine wave, 2
%-sodium birophosphate aqueous solution, frequency 50t1z,
pt-1=10.5).

After washing with water and drying, each surface treatment board is coated with acrylic resin and 3102.
(Nippon Paint Co., Ltd. Garfal Coat 131)
) was coated (coating amount = 0.3 g/m'') and baked at 250°C to prepare test pieces, which were subjected to various tests. The results are shown in Table 2.

(Comparative Example 2) JIS A1200-H24 (0.15 mmt) was caustic etched (10% aqueous sodium hydroxide solution, 4
0°C, 2 minutes), water washing, desmutting (30% nitric acid, room temperature, 1 minute), and after washing with water, DC electrolysis treatment (20% sulfuric acid,
20°C, current density = 1. 5A/dm", 5 minutes, film thickness =
20,000 people).

This surface-treated board was coated in the same manner as in Example 2, and the same tests were conducted. The results are shown in Table 2 6 (Comparative Example 3) JIS A1200-H24 (0,ll5mm')
Solvent cleaning (1,],]l-trichloroethane 70
℃, 5 minutes), then phosphoric acid chromate treatment (Cr amount = 3
0 mg/m21.

This surface-treated board was coated in the same manner as in Example 2 and tested. The results are shown in Table 2.

(Comparative Example 4) JIS A1200-H24 (0.115 mm') was degreased (immersed in alkaline degreaser, 70°C, pH 13.5
, 60 seconds), after washing with water, chromate treatment (CrW
k=] 000mg7m) After that, the same coating as in Example 2 was performed and tested.

The results are shown in Table 2.

(Margins below) (Example 3. Comparative Example 5), JIS Al2O2-H24 (0,115mm'1
Alkaline AC electrolysis (2% sodium pyrophosphate aqueous solution 1 frequency 50Hz, liquid temperature 70Hz) was carried out under the conditions shown in Table 1.
℃, pH=l O, 5) L? two.

After washing with water and drying, each surface-treated board was coated with cellulose resin (manufactured by Mitsui Toatsu Co., Ltd., Solitite W [-1-101), a surfactant (phosphate ester type) in an amount of 3% based on the resin solid content, and a melamine curing agent. (Cymel 272 manufactured by Mitsui Toatsu Co., Ltd.) was added to the resin solid content in an amount of 30% (coating amount = l).
g/m”)L.

It was baked at 220°C and used as a test piece. The results are shown in Table 3.

(Left below) (Example 4) Alkaline alternating current electrolysis (sine wave, 2
%-sodium birophosphate aqueous solution, frequency 50) 1
z, pH= ] 0, 5, liquid temperature 70°C).

After washing with water and drying, each surface treated board was coated with Cr”, Cr”51
02 and acrylic resin mixture (NRC manufactured by Nippon Paint Co., Ltd.
-300 ml (coating film thickness = IU), dried at 100°C, and then applied hydrophilic Acnol resin (manufactured by Mitsui Toatsu Co., Ltd.) on top of it.
XCE, -1847) and surfactant (Dai-Kogyo Seiyaku Co., Ltd.)
Apply a mixture of Neugen ET120 (coating amount =) g/
m') and baked at 270°C. The results are shown in Table 4.

(Comparative Example 6), IISA 1200-H24 ([1,115
mm t> degreased (soaked in alkaline degreaser, 70°C,
After washing with water, the same coating as in Example 4 was applied to prepare a test piece.

The results are shown in Table 4.

Effects of the Invention As described above, the oxide film formed by AC electrolysis treatment in alkaline water has a clean surface and is very porous and has a branched structure, which makes it difficult to coat the coating. The adhesion with the paint has been significantly improved, and since it is highly flexible, it will not crack or peel off the paint even when subjected to severe drawing or ironing of 50% or more, resulting in strong paint film adhesion even after processing. This means that it can be maintained.

In addition, degreasing and the generation of a porous oxide film are performed simultaneously in the same tank through the same electrolytic treatment, and because the electrolytic time is short, work time is shorter than before, productivity is improved, and equipment costs are reduced. It will also be cheaper. Furthermore, unlike chemical conversion treatment, it does not use substances harmful to the human body, such as a chromium aqueous solution, which is a great advantage in terms of operation and maintenance.

Claims (6)

[Claims] (1) An aluminum fin material for a heat exchanger, characterized in that an oxide film with a thickness of 500 to 5000 Å is formed by alternating current electrolysis treatment in an alkaline aqueous solution. (2) An aluminum fin material for a heat exchanger, wherein a corrosion-resistant film is provided on the oxide film of the aluminum fin material for a heat exchanger according to claim 1. (3) An aluminum fin material for a heat exchanger, wherein a hydrophilic film is provided on the oxide film of the aluminum fin material for a heat exchanger according to claim 1. (4) An aluminum fin material for a heat exchanger, which has a corrosion-resistant film on the oxide film of the aluminum fin material for a heat exchanger according to claim 1, and further has a hydrophilic film on its surface. (5) Aluminum or aluminum alloy material at pH 9
~13, In an alkaline aqueous solution with a bath temperature of 35 to 85°C, the amount of electricity is 80 c/d at a current density of 4 to 50 A/dm^2.
A method for producing an aluminum fin material for a heat exchanger, characterized by performing AC electrolytic treatment for a time such that the oxide film thickness exceeds m^2 and the oxide film thickness becomes 5000 Å or less. (6) AC electrolysis is carried out for a time such that the anode electrical quantity exceeds 40 c/dm^2, the cathode electrical quantity exceeds 40 c/dm^2, and the oxide film thickness becomes 5000 Å or less. Method for manufacturing aluminum fin material for heat exchangers in Section 1.