JPH0652158B2 - Heat exchanger fin material - Google Patents

Description

TECHNICAL FIELD The present invention relates to an aluminum heat exchanger fin member having a coating layer formed thereon.

In the specification, aluminum is a generic term for industrial pure aluminum and aluminum alloys.

As is well known in the prior art, aluminum is widely used as a heat exchanger fin material because it is lightweight and has excellent workability and thermal conductivity.

Conventionally, the heat exchanger fin material has been used by processing the thin plate base as it is without performing surface treatment for imparting special properties such as corrosion resistance to the metal surface. However, when using a heat exchanger fin with such a fin material, moisture in the air is condensed on the fin surface during use, aluminum is corroded early by the moisture, and so-called white rust (aluminum hydroxide) is generated, which damages the equipment. There was a drawback that the service life was shortened. Further, the layer of water condensed on the fin surface becomes ventilation resistance and reduces heat exchange efficiency. For this reason, it is necessary to increase the size of the cooling fan, which inevitably increases the size of the entire device, and there is also a drawback that the water layer resonates due to the blowing of air and generates noise. In order to eliminate these drawbacks, white rust is prevented from being generated on the aluminum surface (hereinafter, this performance is referred to as corrosion resistance), the wettability between the aluminum surface and condensed water is improved, and a layer of condensed water is formed. A method of forming a coating layer on the aluminum surface layer that keeps the thickness thin and prevents the reduction of heat exchange efficiency and noise generation is adopted.

There is also a method (post-coating method) of forming this coating layer after fin forming, but recently, from the viewpoint of simplification of the process, uniformity of the coating layer, etc., a film is formed on the aluminum thin plate before fin forming, There is an increasing demand for a molding method (hereinafter referred to as "precoat method"). In adopting this precoat method, the coating layer formed on the fin surface is required to have characteristics called continuous moldability and chemical resistance in addition to the above-mentioned corrosion resistance and hydrophilicity. In other words, when molding a fin material having a coating layer with poor continuous formability, the surface of the forming tool is worn early, causing defective molding of the fin material and shortening the tool life. It causes damage such as generation of cracks and deteriorates properties such as corrosion resistance. Further, during fin formation, a lubricating oil or a lubricant is used in order to facilitate the formation of the fin and to prevent the formation of flaws in the forming material.In order to remove these after forming, organic materials such as trichlene are used. Washed with solvent. If the coating layer is washed off or deteriorates during cleaning, the desired effect described above cannot be obtained, and therefore the coating layer is also required to have chemical resistance.

In response to these requirements, chromate-treated coatings that are inorganic coatings, anodic oxide coatings, boehmite coatings, water glass, etc., have been conventionally used to impart corrosion resistance, and silica and alumina such as silica and alumina are particularly excellent in hydrophilicity. A technique for forming a coating layer in which an inorganic substance is mixed with an organic resin (JP-A-54
No. 142650 and JP-A No. 55-99976) are known. Further, an organic coating layer such as a water-soluble acrylic resin is mentioned as one having excellent continuous moldability and corrosion resistance.

However, conventional inorganic coatings such as chromate-treated coatings are useful for improving corrosion resistance, but their hydrophilicity is insufficient, and in order to obtain sufficient corrosion resistance, they must be thick films and continuous molding is required. There is also a problem with sex. In addition, the coating layer in which an inorganic substance such as silica or alumina is mixed with an organic resin has excellent hydrophilicity, but its continuous moldability and corrosion resistance are very poor, and as described above, corrosion of fins and tool wear occur. There is a problem. Further, the organic coating layer made of a water-soluble acrylic resin or the like is excellent in continuous moldability and corrosion resistance, but it is inferior in hydrophilicity, and similarly, as described above, there are problems in that heat exchange efficiency is lowered and noise is generated.

Therefore, there has never been a heat exchanger fin material excellent in all of corrosion resistance, hydrophilicity, continuous moldability, and chemical resistance.
Moreover, the good hydrophilicity also allows water to easily pass therethrough, resulting in easy corrosion and poor corrosion resistance.
In addition, the good corrosion resistance means that it is easy to repel water by removing it, that is, it is inferior in hydrophilicity, and it is very difficult to obtain a coating layer excellent in both these contradictory hydrophilicity and corrosion resistance. .

Therefore, the inventors of the present invention have conducted extensive studies to obtain a heat exchanger fin material having excellent properties in any of corrosion resistance, hydrophilicity, continuous formability, and chemical resistance, and particularly to obtain a fin material by a precoat method. It has come to do.

Means for Solving the Problems That is, the present invention, a corrosion-resistant film is formed on the surface of an aluminum thin plate, the coating layer formed by compounding a chromium compound in an organic compound having hydrophilicity is formed on the upper layer of the film. It is characterized by being

As the organic compound having hydrophilicity, one or two kinds of water-soluble cellulose resin or polyvinyl alcohol are used. The amount of chromium compound that cross-links with the hydrophilic organic compound is 0.1 based on the solid content of the organic compound in terms of CrO _3.
It is desirable that the content is ˜50 wt%.

Furthermore, it is desirable to use a chromate-treated film as the corrosion resistant film.

Effect According to the present invention, the corrosion-resistant coating is formed on the surface of the aluminum thin plate, and the coating layer formed by mixing the organic compound having hydrophilicity with the chromium compound is formed as the upper layer of the coating. In the upper layer, a cross-linking reaction occurs between the organic compound and the chromium compound to form a coating layer having a cross-linked structure. Since the organic compound has hydrophilicity, it is easily compatible with water, but therefore, the corrosion resistance of the organic compound alone is inferior. However, the coexistence of a chromium compound with a hydrophilic organic compound causes a cross-linking reaction between the chromium compound and the hydrophilic group of the organic compound, thereby improving corrosion resistance without impairing desired hydrophilicity. The chemical resistance can also be improved by polymerizing by this crosslinking reaction. The organic compound alone is excellent in continuous moldability, but the chromium compound alone, for example, a chromic acid film, is inferior in continuous moldability. However, since the chromium compound coexisting with the organic compound causes a crosslinking reaction with the organic compound, it exists in the coating layer as a part of the reaction product and does not deteriorate the original continuous moldability of the organic compound.

Further, since the lower layer coating is a corrosion resistant coating, it is possible to obtain a heat exchanger fin material having excellent corrosion resistance in combination with the upper coating layer. Such a lower layer film is not limited to one layer, and may be two or more layers. Also, when the corrosion resistant film is an organic film, it does not have any adverse effect on the continuous formability of the fin material,
Even if it is a hard inorganic film, the film of the lower layer can be formed into a thin film by the function of the above-mentioned upper layer,
Does not impair the continuous formability of the fin material.

That is, according to the present invention, it is possible to obtain a heat exchanger fin material having excellent corrosion resistance, hydrophilicity, continuous moldability, and chemical resistance.

If the lower corrosion resistant film is a chromate treated film,
Not only the original corrosion resistance of the coating but also the interaction such as a cross-linking reaction between the chromium compound in the chromate-treated coating and the organic compound of the upper layer increases the corrosion resistance, and the corrosion resistance more than the sum of the effects of both layers can be obtained.

Moreover, the effect of improving the adhesion between the upper layer and the lower layer can be obtained by the above-mentioned crosslinking reaction and the like. Further, after forming the chromate-treated film which is a corrosion resistant film, the upper layer according to the present invention can be continuously worked on the same line, and the working efficiency can be improved.

Detailed Description for Carrying Out the Invention The lower corrosion-resistant coating may be either an organic coating or an inorganic coating. Examples of the organic coating include water-soluble epoxy resin, water-soluble acrylic resin, water-soluble urethane resin, water-soluble There are alkyd resins, water-soluble vinyl acetate resins and the like and their derivatives. Examples of the inorganic film include the above-mentioned chromate-treated coating, anodized coating, boehmite coating, water glass and the like. The amount of organic coating is 0.3-3.0g
/ M ² is desirable, and in the case of the inorganic coating, the amount of Cr in the chromate treatment coating is 3 mg / m ^{2 to} 2000 mg / m ² , boehmite coating, anodizing coating, and water glass 0.1 μm to 3.0 μm. If the coating amount is less than the lower limit, the corrosion resistance is insufficient, and if the coating amount exceeds the upper limit, the corrosion resistance is slightly improved, but not only the production cost is increased, but also the moldability is deteriorated. Therefore, the coating amount of each coating layer is preferably within the above range.

The organic compound has hydrophilicity, and as described above, it is desirable that the organic compound has many hydroxyl groups (—OH) such as water-soluble cellulose resin and polyvinyl alcohol. Here, the water-soluble cellulose resin is a general term for cellulose and its derivatives such as esters and ethers, and may refer to a mixture thereof. In addition, polyvinyl alcohol includes water-soluble polyvinyl alcohol having a partially saponified polymer chain. The hydroxyl group increases hydrophilicity as described above, but the carboxyl group (—COOH) also increases hydrophilicity, and the organic compound is not limited to those having many hydroxyl groups as described above. Absent. What is essential is that the organic compound has excellent hydrophilicity.

Further, the chromium compound includes, for example, chromic acid, dichromic acid or these acids, and chromate, which may be either trivalent chromium or hexavalent chromium.
It may be a valence and is not limited by the ionic valence.
Examples of the trivalent chromium compound include chromium hydroxide, chromium nitrate, chromium fluoride, chromium phosphate, chromium sulfate, and chromium acetate, and examples of the hexavalent chromium compound include chromic acid (CrO ₃ ) and magnesium chromate. There are chromate salts such as zinc chromate, calcium chromate, ammonium chromate, potassium chromate, sodium chromate, lithium chromate, etc., and further dichromic acid, magnesium dichromate, zinc dichromate, calcium dichromate. , Ammonium dichromate, potassium dichromate, sodium dichromate, lithium dichromate and the like. If trivalent chromium is desired, for example, a hexavalent chromium compound may be reduced to trivalent and then used.

The content of the chromium compound in the coating layer is preferably in the range of 0.1 to 50 wt% in terms of CrO _{3 with} respect to the solid content of the organic compound. If the content is less than 0.1%, the hydrophilicity is good, but the crosslinking reaction is insufficient, resulting in poor corrosion resistance.
On the other hand, if the content exceeds 50 wt%, crosslinking reaction occurs excessively and corrosion resistance is good, but hydrophilicity is exhibited, for example, hydroxyl groups are consumed by excessive crosslinking reaction, resulting in impairing hydrophilicity. Therefore, the content of the chromium compound is preferably set within the above range in which the hydrophilicity and the corrosion resistance of the coating layer are good. Here, the coating layer is formed by forming a corrosion-resistant film, further applying, for example, a coating component, and then baking and drying. The coating amount of the coating layer is 0.
It is preferably in the range of 3 to 3.0 g / m ² . This is because when the coating amount is less than 0.3 g / m ² , the corrosion resistance and chemical resistance are inferior, and when it exceeds 3.0 g / m ² , the corrosion resistance is slightly improved.
This is because the manufacturing cost will increase. Therefore, it is preferable that the coating amount be within the above range.

The coating layer is desirably baked at 130 ° C. to 310 ° C. for 5 to 60 seconds. If the baking is performed at less than (130 ° C. × 5 seconds), the baking will be insufficient and the crosslinking reaction will be incomplete, so that desired corrosion resistance cannot be obtained. Also (310 ℃ × 6
If baking is performed for more than 0 seconds, over-baking will occur, and the coating layer will deteriorate or become brittle, and the corrosion resistance, chemical resistance, etc. will deteriorate, and the desired coating film performance will be obtained by cracking or peeling of the coating layer. Absent. Further, such over-baking may lead to softening of the aluminum itself, which may reduce the product strength after fin forming. Therefore, the coating baking conditions are preferably within the above range.

However, the content of the above-mentioned chromium compound, the coating film amount,
Further, the baking conditions can be changed depending on the material of the thin plate for fin material, the type of organic compound, the chromium compound and the usage environment of the heat exchanger, and the point is that desired effects such as corrosion resistance can be obtained under the usage conditions. Anything will do.

Example An example of the present invention will be described below in comparison with a conventional fin material having only a coating layer made of an organic compound containing a chromium compound. The examples of the present invention consist of Examples 1 to 8 as described below, and the conventional example consists of Comparative Example 1.

In Example 1, as shown in Table 1, a 0.12 mm-thick industrial pure aluminum (JIS A1100) thin plate material was degreased and cleaned, and then a chromate chromate-based chemical conversion bath liquid (trade name: Bonderite # 713, Nippon Parkerizing Co., Ltd.). Product) to form a corrosion resistant film consisting of a chromate conversion film (r amount is 3 mg / m ² ) and then washed with water and dried. Water-soluble cellulose resin (10% aqueous solution,
Mitsui Toatsu Chemical Co., Ltd., trade name Solidite WH-1
0) containing 0.1% of chromic anhydride based on the resin solid content was applied by a bar coater and baked at 260 ° C. for 20 seconds to form a coating layer of 0.3 g / m ² and a heat exchanger fin material. It was created.

In Examples 2 to 8, heat exchanger fin materials were similarly prepared according to Table 1.

Comparative Example 1 is Example 1 except that there is no corrosion resistant coating underlayer.
The same fin material was created.

The following characteristics were evaluated for the heat exchanger fin materials of Examples 1 to 8 and Comparative Example.

(1) Corrosion resistance The white rust occurrence area (%) after 600 hours of the salt spray test was evaluated. In the table, ⊚ is excellent (1% or less), ◯ is good (1% or more and 5% or less), and x is poor (5% or more).

(2) Hydrophilicity One cycle consists of holding at a relative humidity of 95% or more at 50 ° C. for 7 hours and then at room temperature in a dry atmosphere for 17 hours, and the contact angle after 10 cycles was evaluated. In the table,
⊚ is excellent (water contact angle is within 20 °), ◯ is good (water contact angle is 20 ° to 40 °), and x is poor (water contact angle is 40 ° or more).

(3) Continuous Formability The state of wear of the tool (punch and die) after the fin press and the forming defect of the fin material after forming were visually observed and evaluated by the number of punches until the wear or the occurrence of the defect. In the table, ◎
Was excellent (2 million punches), and ◯ was good (1.5 million punches).

(4) Chemical resistance After washing with trichlene, coating weight loss (%) relative to the total coating weight
It was evaluated by. ⊚ is excellent (within 5%), ◯ is good (5% to 10%), and x is poor (10% or more).

Table 2 shows the results obtained by measuring the above characteristics of each example and comparative example.
Shown in.

As is clear from Table 2, Examples 1 to 8 of the present invention are excellent in any of corrosion resistance, hydrophilicity, continuous moldability, and chemical resistance, but the conventional example of Comparative Example 1 is hydrophilic. , Continuous moldability and chemical resistance are excellent, but corrosion resistance is slightly inferior.

EFFECTS OF THE INVENTION As described above, according to the present invention, a corrosion resistant film is formed on the surface of an aluminum thin plate, and a coating layer formed by compounding a hydrophilic organic compound with a chromium compound is formed as an upper layer of the film. Therefore, a heat-exchanger fin material having excellent corrosion resistance, hydrophilicity, continuous moldability, and chemical resistance, particularly excellent corrosion resistance, can be obtained by the lower layer corrosion-resistant film and the upper layer coating.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shotaro Takemura 4-1-1 Nihombashi Muromachi, Chuo-ku, Tokyo Inside Sky Aluminum Co., Ltd. (56) Reference JP-A-59-196782 (JP, A)

Claims (4)

[Claims] 1. A heat treatment characterized in that a corrosion-resistant coating is formed on the surface of a thin aluminum plate, and a coating layer formed by mixing a hydrophilic organic compound with a chromium compound is formed on the coating. Exchanger fin material. 2. The heat exchanger fin material according to claim 1, wherein the organic compound is one or two of water-soluble cellulose resin and polyvinyl alcohol. 3. The heat exchanger fin member according to claim 1, wherein the corrosion resistant film is a chromate treated film. 4. The content of the chromium compound in terms of CrO ₃ is 0.1 to 50 wt% with respect to the solid content of the organic compound, and the content of the chromium compound is any one of claims 1 to 3. Heat exchanger fin material.