JP3274048B2 - Aluminum member for heat exchanger and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum member for a heat exchanger suitable as a fin for a heat exchanger incorporated in a room air conditioner which is also used for cooling and heating, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Generally, aluminum materials (hereinafter also including aluminum alloy materials) are mainly used as fin materials for heat exchangers of room air conditioners. This is because the aluminum material is excellent in thermal conductivity and moldability. This kind of fin material is subjected to anti-corrosion treatment to prevent corrosion, and at the same time, to prevent water condensed during cooling operation from accumulating between the fins and increasing ventilation resistance, The surface treatment is performed to impart hydrophilicity and improve the water wettability of the fin surface.

[0003] In recent years, the number of room air conditioners that can be used for both cooling and heating has been increasing. However, in a heat pump type heat exchanger used for this type of room air conditioner, the indoor unit becomes an evaporator and the outdoor unit becomes a condenser in summer. Becomes On the other hand, in winter, the indoor unit becomes a condenser and the outdoor unit becomes an evaporator. In such a room air conditioner that is also used for cooling and heating, when heating is performed indoors when the outside air temperature is low in winter, moisture condensed on the fin surface of the heat exchanger provided in the outdoor unit freezes and frost is easily generated. Become. In particular, when a fin material having hydrophilicity is used, frost is easily generated on the fin surface because the fin surface has good water wettability.
If frost is generated on the fin surface of the outdoor unit, the fin blocks the space between the fins, so that the ventilation resistance increases and the heating capacity decreases.

[0004] In view of this, a method has been conceivable in which water repellency is imparted to the fin surface so that water droplets condensed on the surface of the fin are dropped before becoming large, thereby improving the drainage of the fin and the prevention of frost formation. However, when water repellency is imparted to the fin material, a water repellent paint (a paint having a contact angle of 90 ° or more when applied to a smooth surface to form a film) is applied. However, there is a problem in that sufficient water repellency cannot be obtained and frost formation cannot be prevented only by forming the film of No.

On the other hand, a method of forming irregularities directly on the surface of a fin material by a chemical treatment and forming a water-repellent film using the surface as a base (Japanese Patent Application Laid-Open No. 3-45894) has been proposed. (Japanese Patent Application Laid-Open Nos. 3-30939 and 3-44485), after forming a special fluorine-based film on the surface of a fin material, roughening the surface of this film and repelling it. A method of further improving the water solubility (Japanese Patent Application Laid-Open No. 3-45893) and a method of improving the water repellency by blending fine particles with a paint and forming a film with the paint (Japanese Patent Publication No. 3-244680) are proposed. Have been.

As shown in FIG. 1, the contact angle is defined as the tangent 3 drawn from the point where the surface of the water droplet 1 is in contact with the member surface 2. Angle θ
1, the larger the contact angle θ1 (the maximum θ1 = 180
°) Since the area where the water droplet 1 adheres to the member surface 2 becomes smaller, it can be said that the water droplet 1 hardly adheres to the member surface 2. Also,
Regarding the relationship between the roughening of the member surface and the contact angle, the apparent contact angle generally increases with the roughening of the surface of the member having a contact angle of 90 ° or more. On the other hand, it is known that, on a member surface having a contact angle of less than 90 °, the contact angle decreases as the surface is roughened.

[0007]

However, the above-described method has the following disadvantages. That is, in the method of forming the water-repellent film after forming the unevenness on the fin material by the chemical treatment, the thickness of the fin material is reduced by the etching by the chemical treatment, and it is difficult to control the thickness. in addition,
After forming an undercoat by ceramic coating on the surface of the fin material, a water-repellent film is formed on the surface of the undercoat. However, since the undercoat is a fusion coating, the fin material and the undercoat are not bonded to each other. There is no chemical bond between them, and the water-repellent film is easily peeled off from the fin material.

In the method of forming a special fluorine-based film, it is necessary to use a method such as plasma polymerization.
Huge costs are required to introduce manufacturing equipment.
For this reason, the manufacturing cost increases and the product price increases. In addition, in order to form a special fluorine-based film, a batch process is required, so that the productivity is low and it is difficult to actually use the film.

Further, after forming a fluorine-based water-repellent film on the surface of the fin material and roughening the surface of the film, the sum of the thickness of the water-repellent film and the projection height of the film surface is 0.2 μm. As described above, (the height of the protrusion / the diameter of the bottom of the protrusion) is required to be 0.1 or more. If such a protrusion is provided by machining, a strong force acts on the film and the film is peeled off. For this reason, the water repellency is extremely reduced in the portion where the film has been peeled off, and as a result, it is extremely difficult to form a film having uniform water repellency.

[0010] Furthermore, in the method of blending fine particles with a paint and forming a film with the paint, it is difficult to uniformly disperse the fine particles, and in some cases, precipitation of the fine particles occurs. Is difficult. For this reason,
A fin material having uniform water repellency cannot be obtained. In addition, the fine particles have a weak bonding force in the coating film, and in order to hold the fine particles in the coating film, it is necessary to increase the resin binder component.
The water repellency of the coating film decreases.

The present invention has been made in view of the above problems, and has an object to provide an aluminum member for a heat exchanger which has uniform and excellent water repellency over the entire surface and can prevent frost formation, and a method of manufacturing the same. The purpose is to provide.

[0012]

According to the present invention, there is provided an aluminum member for a heat exchanger according to the present invention, comprising: a chemically treated film having a thickness of 0.1 μm or more formed on the surface of an aluminum substrate; 0.1 to 20 mg / dm ²
And a water-repellent film formed by the method described above, wherein the chemically treated film is characterized in that thin plate-shaped crystals are deposited crossing each other on the outermost surface. Preferably, the crystals have an average distance of 10 μm or less on a plane. Further, the surface of the aluminum substrate is preferably roughened.

[0013] In the method of manufacturing an aluminum member for a heat exchanger according to the present invention, the aluminum substrate is made of Li, Na, K, M
immersed in an aqueous solution containing at least one compound selected from the group consisting of salts, chlorides and hydroxides containing any element selected from the group consisting of g, Ca, Sr, Ba, La and Ce the film thickness and has a step of forming a step of forming the above chemical treatment film 0.1 [mu] m, the water repellent coating 0.1 to 20 mg / dm ² applied to water-repellent film on a surface of said film It is characterized by. Further, the aqueous solution may be sprayed or applied to the aluminum substrate.
Further, the salts are preferably carbonates, bicarbonates or sulfates.

[0014]

The present inventors have developed an aluminum member for a heat exchanger, which has uniform and excellent water repellency over the entire surface and can prevent frost formation, and a method for manufacturing the same.
Various experimental studies were performed. As a result, rather than roughening the surface of the aluminum base material by forming irregularities directly by chemical treatment or the like, thin plate-like crystals intersect and precipitate on the outermost surface to form fine irregularities. An aluminum member having excellent water repellency and frost resistance by forming a chemically treated film on the surface of an aluminum substrate and applying a water repellent paint to the surface of the chemically treated film to form a water repellent film Have been found.

First, the chemical treatment film according to the present invention will be described. The chemical treatment film is a film formed as a base treatment before forming a water-repellent film on the surface of the aluminum substrate. This chemical treatment film is formed as follows. That is, Li, Na, K, Mg, Ca, Sr,
Aqueous solution containing one or more compounds selected from the group consisting of salts, chlorides and hydroxides containing any element selected from the group consisting of Ba, La and Ce (hereinafter referred to as “treatment aqueous solution”) The chemical treatment film is formed on the surface of the base material by dipping the aluminum base material in) or spraying or applying the treatment aqueous solution on the surface of the aluminum base material.

FIG. 4 is a micrograph (acceleration) showing the crystal structure of the outermost surface of a chemically treated film formed on the surface of an aluminum substrate by immersing the aluminum substrate in a treatment aqueous solution containing magnesium sulfate and sodium hydrogen carbonate. Voltage: 1
5KV, magnification: 20000x, working focal length: 24m
m). As shown in the photomicrograph of FIG. 4, on the outermost surface of the chemically treated film, thin plate-like crystals are deposited in a shape crossing each other. Due to such fine irregularities of the crystal, an aluminum substrate has a roughening effect. That is, when a water-repellent coating is formed by applying a water-repellent paint to an aluminum substrate having a chemically treated film having fine irregularities formed on the surface, the water-repellency is improved, and the anti-frosting property is improved. An excellent aluminum member can be obtained.

The thickness of the chemically treated film: 0.1 μm or more The thickness of the chemically treated film affects the water repellency of the aluminum member. That is, if the thickness of the chemically treated film is less than 0.1 μm, there may be a case where the coating of the aluminum base is insufficient and fine irregularities are not formed. For this reason,
Even if a water repellent film is formed on the surface of the chemically treated film, the water repellency becomes non-uniform, and as a result, the water repellency of the aluminum member cannot be sufficiently improved. Therefore, the thickness of the chemical treatment film is set to 0.1 μm or more.

The upper limit of the thickness of the chemically treated film is not particularly limited. However, when the thickness exceeds 3 μm,
It takes a long time to form it. For this reason, the upper limit thickness of the chemical treatment film is preferably about 3 μm. However, when the corrosion resistance is further required, the film can be easily thickened by lengthening the forming time.

Average distance between crystals: 10 μm or less The average distance between the thin plate-shaped crystals deposited on the outermost surface of the chemically treated film affects the water repellency of the aluminum member, particularly the falling angle. That is, when the average distance between the crystals is longer than 10 μm, fine irregularities due to the crystals cannot sufficiently improve the water repellency of the water-repellent film, and particularly the falling angle becomes large, and water droplets adhering to the member surface are reduced. It is difficult to fall. Therefore, the average distance between crystals precipitated on the outermost surface of the chemically treated film is set to 10 μm or less. Preferably 0.05 to 0.5
μm.

As shown in FIG. 2, when the water droplet 1 adheres to the member surface 2 as shown in FIG. 2, the angle between the horizontal plane and the member surface 2 with the end of the member as a fulcrum is gradually increased. It means the angle θ2 when the water drop falls.

As described above, the chemical treatment film can be formed on the surface of the aluminum substrate by immersing the aluminum substrate in a treatment aqueous solution or the like, thereby simplifying the process of manufacturing a water-repellent aluminum member. can do.
Further, since the chemically treated film is chemically bonded to the surface of the base material, the adhesion is further improved. Furthermore, since the chemically treated film also has corrosion resistance, by forming it on the surface of the substrate, it is possible to obtain an aluminum member having excellent corrosion resistance in addition to water repellency.

Next, the water-repellent film will be described. In order to improve the water repellency of the surface of the aluminum member, a water repellent paint is applied to the surface of the above-mentioned chemically treated film formed on the surface of the aluminum substrate, and baked to form a water repellent film. The water-repellent paint at this time may have a contact angle of 90 ° or more of the water-repellent film formed on the smooth surface. This is because, if the contact angle is less than 90 °, in a chemically treated film having fine irregularities on the surface, the contact angle is reduced even if a water-repellent film is formed on the surface.

As the water-repellent paint having a contact angle of the water-repellent film formed on the smooth surface of 90 ° or more, a fluorine-based paint such as ethylene tetrafluoride or a copolymer of ethylene tetrafluoride and ethylene And the like, and a silicon-based water-repellent paint or a hydrophobic methyl group (-CH
₃ ) a paint containing a compound having the formula:
And water-repellent paints having a perfluoroalkyl group.

[0024]

Embedded image ((—CF ₂ —) _n —CF ₃ )

As a method of applying these paints to the surface of a chemically treated film formed on the surface of an aluminum substrate,
For example, there are spray coating, dip coating, roll coating, bar coating, brush coating, and the like. In addition to these methods, any method that can form a water-repellent film may be used.

The amount of the water-repellent film: 0.1 to 20 mg
/ Dm ² Further, when the coating amount of the hydrophobic film is less than 0.1 mg / dm ^2, can not be sufficiently covered the chemical treatment film,
A portion having poor water repellency may occur. Therefore, uniform water repellency cannot be obtained on the surface of the aluminum member. On the other hand, if the amount of the water-repellent film exceeds 20 mg / dm ² , the surface roughening effect of the underlying chemically treated film cannot be sufficiently enjoyed, and the water repellency and the anti-frosting property of the aluminum member are improved. Can not do. Therefore,
The amount of the water-repellent film is 0.1 to 20 mg / dm ² .

Next, the aluminum base will be described. The aluminum substrate in the present invention may be an aluminum alloy containing 90% by weight or more of aluminum in addition to aluminum alone. The surface of this aluminum base material is subjected to a cleaning treatment by degreasing, shot blasting, sputter etching, brush processing, electrolytic or immersion etching, or the like. When the surface of the base material is roughened at the same time as the cleaning treatment, the water repellency is further improved, and accordingly, the anti-frosting property is further improved.

The aluminum member according to the present invention comprises:
It is mainly used as a fin material for heat exchangers, but it can also be applied to places other than heat exchangers where frost formation prevention, drainage, and water repellency (water repellency) are required.

[0029]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples that fall outside the scope of the claims of the present invention.

First Embodiment In this embodiment, a degreased aluminum plate (JIS 1100H26, plate thickness: 0.12 mm, vertical ×
A 10 cm × 20 cm width was immersed in a treatment aqueous solution containing various salts shown in Table 1 below to form a chemically treated film (hereinafter, referred to as “base film”) on the surface of the aluminum plate. Then, a perfluoroalkylsilane-based paint was applied to this aluminum plate using a bar coater # 4.
And baked at 100 ° C. for 10 minutes to form a water-repellent film.

Table 1 below shows the thickness of the undercoat, the presence or absence of fine irregularities on the surface of the undercoat, and the amount of the water-repellent film contained in the treatment aqueous solution.

[0032]

[Table 1]

A 1.8 μL water droplet was dropped on the aluminum plate on which the water-repellent film was formed, and the contact angle and the falling angle were measured. Regarding the adhesion, a cellophane tape was attached to the aluminum plate, and the contact angle and the falling angle after peeling off (tape peeling test) were measured. The results are shown in Table 2 below. In the comprehensive evaluation, when the contact angle is 160 ° or more and the falling angle is 20 ° or less, the contact angle is 160 ° or more, but the falling angle is 2 °.
A case exceeding 0 ° and a case where the contact angle is 155 ° or less and the falling angle is 90 ° (does not fall) are evaluated as “excellent”, “good” and “poor”, respectively, and are “◎”, “○” and “×”, respectively. Indicated by In addition, more than 90 ° refers to a case where a water drop does not fall even at 90 °.

[0034]

[Table 2]

As shown in Table 2 above, Examples Nos. 1 to 4
In each case, the contact angle is 160 ° or more, which is superior to the contact angle (about 120 °) of the film formed by the conventional water-repellent paint, and the falling angle is also 30 ° or less, It can be seen that the falling property of water droplets is excellent. Further, the contact angle and the falling angle after the tape peeling test were almost the same as those before the test, indicating that the adhesion was good.

On the other hand, in Comparative Examples Nos. 1 to 4, the thickness of the undercoat was as thin as less than 0.1 μm, and there were some places where the coating of the aluminum plate was insufficient locally. For this reason, the contact angles were all 150 ° or less, and even when the falling angle was 90 °, water droplets did not fall, and good water repellency could not be obtained.

In Comparative Examples Nos. 5 to 7, the undercoating film was formed using an aqueous solution of a salt of an element not defined in the claims of the present invention. Did not precipitate. Therefore, even if a water-repellent film was formed using these films as a base film, sufficient water repellency could not be obtained.

Second Embodiment In this embodiment, a degreased aluminum plate (JIS 1100H26, plate thickness: 0.12 mm, vertical ×
(Width: 10 cm × 20 cm) was immersed in a treatment aqueous solution containing various salts shown in Table 3 below to form a base coat on the surface of the aluminum plate. Thereafter, a perfluoroalkylsilane-based paint was applied to the aluminum plate and baked at a temperature of 100 ° C. for 10 minutes to form water-repellent films having various thicknesses.

Table 3 below shows the thickness of the base film, the average distance between the plate-like crystals deposited on the surface of the base film, and the amount of the water-repellent film, such as salts contained in the treatment aqueous solution. Note that, regarding the aluminum plate of the present embodiment having the water-repellent film defined in the claims of the present invention, since the conditions for forming each water-repellent film are the same as those of the first embodiment, the same reference numerals are used below. (Example Nos. 1 to 4) will be described.

[0040]

[Table 3]

With respect to the aluminum plate on which the water-repellent film was formed under the conditions shown in Table 3, the contact angle and the falling angle were measured in the same manner as in the first embodiment, and the results are shown in Table 4 below. Since the results of Examples Nos. 1 to 4 are the same as the results shown in Table 2, only Comparative Examples Nos. 8 to 15 are shown in Table 4 below.

[0042]

[Table 4]

In Comparative Examples Nos. 8 to 11, the amount of the water-repellent film was smaller than the predetermined amount.
And 13 are cases where the amount of the water-repellent film is larger than a predetermined amount. Therefore, as shown in Table 4 above, the contact angles were all 150 ° or less, and even when the falling angle was 90 °, water droplets did not fall, and good water repellency could not be obtained.

In Comparative Examples 14 and 15, the average distance between the crystals was 10 μm or more, and good water repellency could not be obtained as in the above-mentioned Comparative Example.

In this example, the frosting time of each aluminum plate was measured in order to evaluate the anti-frosting property.

FIG. 3 is a schematic diagram showing a test apparatus used for measuring the frosting time. This test apparatus is provided with a cold water tank 11 for storing a refrigerant. A circulation pump 12 is connected to the cold water tank 11, and the circulation pump 12 supplies a refrigerant to the aluminum container 13 via a pipe 14a. Then, the refrigerant flowing out of the aluminum container 13 flows into the cold water tank 11 via the pipe 14b.

Using such a test apparatus, the above-described aluminum plate test plate 10 was attached to the outer surface of the aluminum container 13 so that the treated surface was on the outside. And
Aluminum container 1 while maintaining the temperature of the refrigerant at −10 ° C.
3 was supplied with refrigerant. At this time, the dry bulb temperature and the wet bulb temperature of the hygrometer were 2 ° C. and 1 ° C., respectively.

The test plate 10 was cooled as described above, and the time from the start of cooling until the entire surface of the test plate 10 was covered with frost was measured. The results are shown in Table 5 below. In the evaluation, when the entire surface frosting time of the test plate exceeds 120 minutes, 100 minutes or more and 120 minutes or less, 60 minutes or more and less than 100 minutes and 60 minutes or less, excellent, good, slightly poor, It was evaluated as defective and indicated by “◎”, “○”, “△”, and “×”, respectively.

[0049]

[Table 5]

As shown in Table 5, Examples Nos. 1 to 4
For all, the frosting time is 120 minutes or more,
It can be seen that it has excellent frost prevention properties.

On the other hand, in Comparative Examples 8 to 11, the amount of the water-repellent film was smaller than the predetermined amount, and a film having a uniform thickness could not be formed. For this reason, the frosting time was short, and the entire surface of the test plate was covered with frost in all cases within 30 minutes.

Comparative Examples Nos. 12 and 13 are cases where the amount of the water-repellent film is larger than the predetermined amount, and Comparative Examples Nos. 14 and 15 are cases where the distance between the crystals is larger than 10 μm. In each of these cases, the frosting time was shorter than in the examples.

Third Embodiment In the present embodiment, JIS 1100H26 plate, A5083 rolled plate, and A
After subjecting the 6N01 extruded plate to surface treatment or surface treatment, these were immersed in a salt solution containing lithium for 20 minutes to form a base coat. At this time, the thickness of the undercoat is 3
μm, and the average distance between the precipitated crystals was 0.3 μm. Thereafter, various paints shown in Table 6 below were applied to the surface of each aluminum plate using a bar coater to form a water-repellent film having a thickness of 2 μm.

[0054]

[Table 6]

Table 7 below shows the paint used for forming the water-repellent film, the material of the test plate, and the base treatment of the test plate in each of the test plates manufactured as described above.

[0056]

[Table 7]

The results of measurement of the contact angle, falling angle and frosting time of each test plate shown in Table 7 are shown in Table 8 below.

[0058]

[Table 8]

As shown in Table 8 above, Examples Nos. 5 to 1
About 6, the contact angle is 160 ° or more, and the falling angle is 10 °
Below, when the frosting time was 120 minutes or more, excellent water repellency and anti-frosting properties could be obtained in each case.

On the other hand, the contact angle of Comparative Example No. 16 was 30 ° since the film was formed by the hydrophilic paint.
Although the falling angle is about 40 °, the frosting time is 15
In addition, the anti-frosting property was extremely inferior to the examples.

[0061]

As described above, according to the present invention,
On the surface of the aluminum substrate, a chemically treated film is formed on the outermost surface where thin plate-shaped crystals intersect each other, and a predetermined amount of water-repellent film is formed on the surface of this film. An aluminum member having excellent prevention properties can be obtained.

Further, since the chemically treated film is formed between the aluminum substrate and the water-repellent film, the corrosion resistance of the aluminum member can be improved. To combine
The adhesion between the water-repellent film formed on the surface of the chemically treated film and the aluminum substrate can be further enhanced.

Further, by roughening the surface of the aluminum substrate, the water repellency and the anti-frosting property of the aluminum member can be further improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a contact angle.

FIG. 2 is a schematic diagram showing a falling angle.

FIG. 3 is a schematic diagram showing a test device used for measuring the frosting time.

FIG. 4 is a micrograph showing a crystal structure of the outermost surface of a chemically treated film formed on a surface of a substrate obtained by immersing an aluminum substrate in a treatment aqueous solution containing Mg sulfate and Na hydrogen carbonate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1; Water drop 2; Member surface 10; Test plate (aluminum plate) 11; Cold water tank 12; Circulation pump 13; Aluminum containers 14a, 14b;

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-79820 (JP, A) JP-A-5-223481 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B28F 13/18 B05D 7/14 B32B 1/00-35/00

Claims (6)

(57) [Claims] A film having a thickness of 0.1 on the surface of an aluminum substrate.
μm or more, and a water-repellent film having a coating amount of 0.1 to 20 mg / dm ² on the surface of the chemical treatment film, wherein the chemical treatment film has the outermost surface. An aluminum member for a heat exchanger, wherein thin plate-shaped crystals are intersected with each other. 2. The aluminum member for a heat exchanger according to claim 1, wherein an average distance between the crystals on the plane is 10 μm or less. 3. The aluminum member for a heat exchanger according to claim 1, wherein the surface of the aluminum base material is roughened. 4. An aluminum substrate made of Li, Na, K, M
immersed in an aqueous solution containing at least one compound selected from the group consisting of salts, chlorides and hydroxides containing any element selected from the group consisting of g, Ca, Sr, Ba, La and Ce Forming a chemically treated film having a film thickness of 0.1 μm or more, and applying a water-repellent paint to the surface of the film at 0.1 to 20 mg / dm ² to form a water-repellent film. A method for producing an aluminum member for a heat exchanger. 5. The method according to claim 5, wherein Li, Na,
Aqueous solution containing one or more compounds selected from the group consisting of salts, chlorides and hydroxides containing any element selected from the group consisting of K, Mg, Ca, Sr, Ba, La and Ce Sprayed or coated to a thickness of 0.1μm
An aluminum for a heat exchanger, comprising: a step of forming the above-mentioned chemically treated film; and a step of applying a water-repellent paint to the surface of the film at 0.1 to 20 mg / dm ² to form a water-repellent film. Manufacturing method of the member. 6. The method for manufacturing an aluminum member for a heat exchanger according to claim 4, wherein the salts are carbonates, bicarbonates, or sulfates.