JPH0571382B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an aluminum fin material for a heat exchanger made of aluminum or an aluminum alloy, and in particular, by forming a pre-coated coating layer, it has hydrophilicity, corrosion resistance,
This invention relates to an aluminum fin material for heat exchangers that has excellent chemical resistance and formability. [Prior Art] Aluminum or aluminum alloy, which has excellent lightness, workability, and thermal conductivity, is used for the fin material of the heat exchanger of the evaporator of an air conditioner. However, during operation of the evaporator, the surface of the fins becomes below the dew point and condensed water adheres to the surface of the fins, causing problems such as corrosion of the material and increased ventilation resistance. To solve this problem, fin materials with surface treatment coatings that are corrosion resistant and have an affinity for water have come to be used. There are two methods for this surface treatment: one is to perform it after forming the fins (post-coat method), and the other is to perform it on the aluminum plate before forming the fins (pre-coat method).
The pre-coating method has been adopted from the viewpoint of simplifying the heat exchanger manufacturing process and ensuring uniformity of the surface treatment film. However, in the pre-coating method, it is necessary to process the coating into a fin shape after coating, so it is required that the coating be good after molding, that the film will not be destroyed by molding, and that the molding tool will not be worn out. In addition, since organic solvents such as trichlene and alkaline degreasing agents are used to remove lubricating oil during molding after assembly to the fin core, chemical resistance against these is also required. To meet these demands, inorganic films such as chromate-treated films, anodized films, and boehmite films have been used to impart corrosion resistance.
In addition, to impart hydrophilic properties, boehmite films, which are inorganic films, mixed films of inorganic and organic substances such as silica, water glass, and alumina, and organic films such as water-soluble acrylic resins are used. Also,
A method of applying a crosslinking reaction product of an organic compound and an organic curing agent onto the inorganic film (Japanese Patent Laid-Open No. 105629/1983)
) has also been proposed. However, inorganic coatings such as chromate-treated coatings have excellent corrosion resistance but insufficient hydrophilicity, and boehmite coatings have good hydrophilicity but are poor in chemical resistance. Furthermore, in order to obtain sufficient corrosion resistance, these inorganic coatings must be thick, which has the problem of accelerating tool wear during fin forming. Treated films made by mixing inorganic substances such as silica, water glass, and alumina with organic resins have excellent hydrophilic properties, but have difficulty in continuous molding and have problems with wear of molding tools. Organic films such as water-soluble acrylic resins have excellent continuous moldability, but have a problem of poor hydrophilicity. Furthermore, a film with good hydrophilicity easily allows water to permeate and has poor corrosion resistance, and a film with good corrosion resistance easily repels water and has poor hydrophilicity. It is extremely difficult to obtain these conflicting functions of hydrophilicity and corrosion resistance in a single film, so it is important to obtain a film that is hydrophilic and has excellent corrosion resistance, continuous moldability, and chemical resistance. If this is the case, it will have to be a multilayer film, but even if the crosslinking reaction product of the organic compound and organic curing agent described above is coated on an inorganic film, it will compensate for the drawbacks of both. It wasn't completely satisfying. [Problems to be Solved by the Invention] Therefore, the object of the present invention is to provide a coating that is hydrophilic and has excellent corrosion resistance, continuous formability, and chemical resistance, particularly for coating precoated coatings on heat exchanger fin materials. An object of the present invention is to provide an aluminum fin material for a heat exchanger. [Means for Solving the Problems] The present inventor has conducted repeated research in order to solve the above problems, and found that after chemically coating aluminum or aluminum alloy thin plates, a corrosion-resistant composite of a specific composition was applied on the aluminum or aluminum alloy thin plates. It has been found that it is effective to provide an intermediate layer made of a resin film and further provide a specific hydrophilic organic film, leading to the present invention. That is, the present invention provides a lower layer consisting of a chemical film on the surface of an aluminum or aluminum alloy thin plate, and on the chemical film, (a) a polymer of water-soluble unsaturated carboxylic acids, (b) a zirconium compound,
An intermediate layer consisting of a corrosion-resistant composite resin film obtained by coating and drying an aqueous solution consisting of a compound selected from the group consisting of a titanium compound and a silicon compound and (c) a fluoride, and further a water-soluble cellulose resin on top of the intermediate layer. This is an aluminum fin material for a heat exchanger characterized by having a composite film composed of an upper layer made of a hydrophilic organic film made of a reaction product with a water-soluble acrylic resin. The aluminum or aluminum alloy thin plate used in the present invention is used as an aluminum fin material. The chemical film formed on the surface of this aluminum or aluminum alloy thin plate is preferably a chromate film such as a phosphoric acid chromate film or a chromic acid chromate film, but a boehmite film, an anodized film, a water glass treated film or a zirconium treated film may also be used. be able to. In the present invention, the corrosion-resistant composite resin film constituting the intermediate layer is formed by applying and drying an aqueous solution consisting of the above a, b, and c. Examples of polymers of water-soluble unsaturated carboxylic acids as component (a) include (meth)acrylic acid and (meth)acrylic acid.
Examples include polymers of esters of acrylic acid or copolymers of these and other vinyl monomers, and it is desirable that the aqueous solution contains 0.3 to 30 g/g. Examples of the zirconium compound used as component (b) include fluorozirconic acid and its alkali metal salts, zirconium fluoride, zirconium oxide, and ammonium salts of zirconium carbonate. As the titanium compound, fluorotitanic acid and its alkali metal salts, ammonium fluorotitanate, titanium oxide, etc. are used. As the silicon compound, fluorosilicic acid and its alkali metal salt, silicon fluoride, silicon oxide, etc. are used, and component (b) is contained in an aqueous solution containing 0.1
It is desirable to contain ~15g/. (c) Examples of the fluoride component include fluoric acid,
Potassium hydrofluoride, sodium hydrofluoride, etc. can be mentioned. It is desirable that component (c) is contained in the aqueous solution in an amount of 0.05 to 10 g. The intermediate layer forming liquid may be applied onto the chemical film by any method such as a roll method, a dipping method, or a spray method.
It is dried for 1 to 60 seconds at ℃ to form an intermediate layer. In the present invention, the hydrophilic organic film constituting the upper layer is composed of a water-soluble cellulose resin and a water-soluble acrylic resin. Water-soluble cellulose resins include cellulose,
The esters or ethers or mixtures thereof can be used. Water-soluble acrylic resins generally have hydrophilic functional groups such as carboxyl groups, hydroxyl groups, and amino groups in their acrylic polymers.
Polymers of acrylic acid, (meth)acrylic acid esters, (meth)acrylamide, etc., copolymers of these unsaturated compounds, or copolymers or hydration of these unsaturated compounds with other unsaturated compounds The carboxyl group is removed by decomposition etc.
Examples include acrylic polymers into which hydrophilic groups such as hydroxyl groups or amino groups are introduced. It is preferable to use these water-soluble cellulose resin and water-soluble acrylic resin in a ratio of 1:4 to 4:1. After applying these mixtures on the intermediate layer,
The upper layer is formed by baking at 200-280°C for 5-60 seconds. [Function] According to the present invention, corrosion resistance is imparted by a chemical film such as a chromate film on the surface of an aluminum or aluminum alloy thin plate. In addition, the corrosion-resistant composite resin film of the intermediate layer is formed by uniformly covering the chemical film with a film made of a polymer through a crosslinking reaction between a polymer of unsaturated carboxylic acid and a zirconium compound. Due to the action of the fluoride present in free form in the intermediate layer, organic compounds are effectively removed from the defective areas of the chemical film.
A strong inorganic film is formed, and corrosion resistance can be greatly improved. Zirconium compounds and the like, which are inorganic substances, undergo a crosslinking reaction with organic compounds and exist as part of the reactive components. Furthermore, due to the effect of improving the corrosion resistance of this film, the underlying chemical film can be kept thin, eliminating the problem of wear of forming tools. Furthermore, since the unsaturated carboxylic acid polymer has very good adhesion to the upper film, the chemical resistance and continuous moldability of the hydrophilic film are improved. Therefore, the film can be made thinner, and manufacturing costs can be reduced. This intermediate layer of corrosion-resistant composite resin film has excellent corrosion resistance even if it is a very thin film, and its thickness is 0.5 to 500 mg/
m ² , preferably 3 to 100 mg/m ² . this is,
If it is less ^than 0.5mg/m2, there is no effect of improving corrosion resistance;
Even if it exceeds mg/m ² , the effect of improving corrosion resistance is small and the manufacturing cost also increases. The first component of the hydrophilic organic film is water-soluble cellulose, and since the cellulose resin has a large number of hydroxyl groups, it has excellent hydrophilicity. Chemical resistance can also be improved by mixing and reacting water-soluble acrylic resins. Also, since it is a completely organic film, there is no need to worry about wear of the molding tool. The thickness of the hydrophilic organic film is preferably 0.05 to 1 g/m ² . This is because if it is less than 0.05 g/m ² , the effect of improving hydrophilicity is small, and even if it exceeds 1 g/m ² , the effect of improving hydrophilicity is small, and the manufacturing cost increases. [Example] The present invention will be described in further detail with reference to Examples below. Example Industrial pure aluminum with a thickness of 0.110 mm (JIS A1100
-H26) The strip was degreased and cleaned using a commercially available weak alkaline degreaser. Next, it was immersed in a phosphoric acid chromate-based chemical bath liquid (trade name: Allozin 401/45, manufactured by Nippon Paint Co., Ltd.) to form a corrosion-resistant chemical film consisting of a phosphoric acid chromate film, and then washed with water and dried. Next, an intermediate layer forming liquid having the formulation shown in Table 1 was applied onto this chemical film using a roll coater, and dried in a hot air drying oven at a temperature of 120°C for 20 seconds to obtain the film thicknesses shown in Table 1. A corrosion-resistant composite resin film was obtained. Next, a paint made of water-soluble cellulose resin and water-soluble acrylic resin is applied onto the corrosion-resistant composite resin film using a roll coater, and heated in a hot air drying oven at a temperature of 250°C.
It was baked for 20 seconds at a temperature of 0.degree. C. to form an organic hydrophilic film having the thickness shown in Table 1. The properties (hydrophilicity/corrosion resistance, chemical resistance, continuous formability) of the resulting composite film were investigated for each of the fin materials on which the various precoat films were formed, and the results are shown in Table 1. Here, hydrophilicity was evaluated by measuring the contact angle with water after 500 cycles in which one cycle was 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), 〇 is good (contact angle 20° to 40°), and × is poor (contact angle over 40°). Corrosion resistance was determined by observing the surface condition of the fins after 500 hours of a salt spray test. ◎ is very good, 〇 is good,
× was determined to be defective. Chemical resistance is determined by soaking in commercially available press oil for 24 hours.
Next, after washing with trichlene, the contact angle with water was measured and evaluated. ◎ is very good (contact angle of 15° or less), 〇 is good (contact angle of 15° to 30°), and × is bad (contact angle of over 30°). Chemical resistance was evaluated by immersing the film in a commercially available alkaline degreasing solution at 50°C for 1 minute and determining the film thickness reduction rate from the film thickness before and after immersion. ◎ is very good (reduction rate of 20% or less), 〇 is good (reduction rate of 40%)
% or less), × indicates poor (reduction rate exceeding 40%). Continuous formability was determined by continuous punching of 100,000 fins.After the fin press, the wear condition of the forming tool and the appearance of the fins after forming were observed with the naked eye. Comparative Example A composite film having the structure shown in Table 1 was formed on the surface of an aluminum strip in the same manner as in the example. In Comparative Example 8, a water-soluble organic resin paint mixed with silica was applied and baked on the chemical film to obtain an organic/inorganic mixed film. In Comparative Example 9, a water-soluble acrylic resin paint was applied and baked on the chemical film to obtain an organic hydrophilic film. The thickness of each coating was 1.5 g/m ² . The properties of the obtained film were investigated in the same manner as in the Examples, and the results are shown in Table 1.

【table】

[Table] [Effects of the Invention] As explained above, the aluminum fin material according to the structure of the present invention has hydrophilicity and is also excellent in water resistance, continuous formability, and chemical resistance, and is suitable for use in heat exchangers. It is very useful as Furthermore, since the surface treatment film of the present invention is a very thin film as a whole, it is possible to suppress an increase in heat transfer resistance due to the film, and also to reduce manufacturing costs.

Claims (1)

[Claims] 1 A lower layer consisting of a chemical film on the surface of an aluminum or aluminum alloy thin plate, and on the chemical film (a) a polymer of water-soluble unsaturated carboxylic acids;
(b) a compound selected from the group consisting of a zirconium compound, a titanium compound, and a silicon compound; and (c) an intermediate layer consisting of a corrosion-resistant composite resin film obtained by applying and drying an aqueous solution consisting of a fluoride;
An aluminum fin material for a heat exchanger, further comprising a composite film comprising an upper layer comprising a hydrophilic organic film made of a reaction product of a water-soluble cellulose resin and a water-soluble acrylic resin.