JPH0679820A - Member excellent in water repellency and anti-frosting properties and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain member excellent in water repellency and anti-frosting properties suitable for a heat exchanger fan, which is installed in a room air conditioner by the type of both air cooling and heating in combination. CONSTITUTION:First of all, metallic plate material such as aluminum or the like is etched so as to realize the percentage of portion not subjected to erode of 10% or less and the surface area of 20cm<2> or more per one cm<2>, which is area shown in plan view, of the metallic plate material. Next, on the surface of the metallic plate material, water repellent film, under the application of which on the flat surface the contacting angle of water drop is 90 deg.C or more, is formed by the thickness of 1-20mg/dm<2>.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a member having excellent water repellency and anti-frosting property suitable for use as an aluminum fin for a heat exchanger incorporated in a room air conditioner for both heating and cooling, and a method for manufacturing the member.

[0002]

2. Description of the Related Art Conventionally, a fin material for a heat exchanger of a room air conditioner is mainly made of aluminum (including an aluminum alloy) because of its excellent thermal conductivity and moldability. Usually, this kind of fin material is subjected to anticorrosion treatment in order to prevent corrosion. In addition, in order to prevent the water that has condensed during cooling operation from accumulating between the fins and increasing ventilation resistance, a surface treatment is applied to impart hydrophilicity to improve the water wettability of the fin surface and improve drainage. Is improving.

As a surface treatment for imparting anticorrosion and hydrophilicity, a treatment using silicate (Japanese Patent Laid-Open No. 61-8598).
No.) and a method of coating a hydrophilic resin, and fins for heat exchangers that have been subjected to these treatments have been put to practical use.
Further, it contributes to the performance improvement of the heat exchanger such as reduction of ventilation resistance at the time of blowing air in the room air conditioner and improvement of heat exchange efficiency.

By the way, recently, room air conditioners which are both heating and cooling type are increasing. In the heat pump type heat exchanger used in this type of room air conditioner, the indoor unit becomes the evaporator and the outdoor unit becomes the condenser in the summer. On the other hand, in winter, the indoor unit serves as a condenser and the outdoor unit serves as an evaporator.

In such a room air conditioner for both air conditioning and heating, when the heating operation is performed in the winter when the outside air temperature is low, the water condensed on the surfaces of the fins of the heat exchanger provided in the outdoor unit is frozen to form frost. Is likely to occur. In particular, when a fin that has been subjected to a hydrophilic treatment is used, the fin surface has good wettability with water, so that frost is likely to be generated on the entire fin surface. When frost forms on the fin surface of the outdoor unit, the frost blocks the fins, increasing ventilation resistance and reducing the heating capacity. Further, when the frost is significant, the device may break down, so it is necessary to stop the heating operation to remove the frost adhering to the fins.

The fins that have been subjected to the hydrophilic treatment have an advantage that the frost easily dissolves during defrosting and becomes a water film more easily than the fins that have not been subjected to the hydrophilic treatment. However, since the entire surface of the fin is wet with water even after the frost is melted, when the heating operation is restarted, frost is generated on the entire surface of the fin in a short time.

Therefore, the surface of the fin is subjected to a water repellent treatment,
A technique has been proposed in which the water droplets condensed on the fin surface are dropped before they become large (that is, the falling property is improved), thereby obtaining good water drainage property and improving anti-frosting property. In this case, as the water-repellent treatment, for example, a method of providing a special fluorine-based water-repellent coating on the surface of the fin has been proposed (for example, JP-A-3-30939 and JP-A-3-44485). Also, a method has been proposed in which a fluorine-based water-repellent coating is provided on the surface of the fin and then the surface of the coating is roughened to further improve the water repellency (JP-A-3-54).
No. 893). When the contact angle of the surface of the member with respect to water droplets (hereinafter simply referred to as “contact angle”) is 90 ° or more, the rougher the surface of the member, the larger the apparent contact angle becomes, and the water repellency is improved. It is known that if the angle is less than 90 °, the apparent contact angle decreases as the surface of the member is roughened (for example, Kozo Sato, "Coating of coating film-theory and explanation of its mechanism"). Page 157 Riko Publisher).

[0008]

However, the fin provided with the fluorine-based water repellent coating has a problem that the manufacturing cost is high because the fluorine coating material is expensive. In addition, simply providing a fluorine-based water-repellent coating on the surface of the fin material does not sufficiently increase the contact angle, and when applied to the outdoor unit of a room air conditioner, water droplets are partially accumulated and There is a problem that the ventilation resistance is higher than that of the fin that has been subjected to the heat treatment.

Further, a fin having a fluorine-based water-repellent coating on the surface of the fin material and roughening the coating surface has a problem that the contact angle is not sufficiently improved and the production is difficult. is there. That is, if a fluorine-based water-repellent paint is applied on the surface of the fin material to roughen the surface of the coating film and then the fin material is formed into a fin shape, the forming process is difficult. Further, if the coating film surface is to be roughened after being formed into a fin shape, the roughening treatment is difficult. Therefore, at present, fins having a roughened surface of a fluorine-based water-repellent coating have not been put into practical use.

For this reason, it has a water-drainage property equivalent to or higher than that of the hydrophilic treatment, has a small ventilation resistance at the time of ventilation, and
There is a demand for fin materials that produce less frost.

The present invention has been made in view of the above problems, and provides a member excellent in water repellency and frost prevention, which is suitable as a fin for a heat exchanger of a room air conditioner that is also used for cooling and heating, and a manufacturing method thereof. The purpose is to do.

[0012]

A member excellent in water repellency and frost prevention according to the present invention is formed on a surface of a metal plate material having a roughened surface. 1 cm ^{2 in} plan view of the metal plate material
The surface area per contact is 20 cm ² or more, and the film thickness of the water-repellent coating is 1 to 20 mg / dm ² .

According to the method for producing a member having excellent water repellency and anti-frosting property according to the present invention, the surface of the metal plate material is subjected to etching so as not to be dissolved and the proportion of the portion is 10% or less and the flat surface of the metal plate material. The surface area per cm ² is 20c
m ² or more, and a water-repellent coating having a contact angle of water droplets of 90 ° or more when formed on a flat surface is formed on the surface of the metal plate material in a thickness of 1 to 20 mg / dm ^2. And a process.

[0014]

The inventors of the present application investigated the change in the apparent contact angle by variously changing the surface roughness of the member in order to obtain a heat exchanger fin excellent in water drainage and frost prevention. As a result, it has been theoretically said that the rougher the surface of the member is, the higher the apparent contact angle becomes, but in reality, it may be difficult to uniformly coat the surface following the roughening. Yes,
The roughness does not necessarily correspond to the apparent contact angle, and the roughened surface did not result in an improvement in the apparent contact angle. Therefore, the inventors of the present application repeated various experimental studies in order to investigate factors that affect the apparent contact angle in addition to the roughness, and found that the microscopic surface area affects the improvement of the apparent contact angle. . The present invention has been made based on such experimental results.

In the present invention, a water-repellent film is formed on the surface of the metal plate material which has been roughened. Therefore, fine unevenness is provided on the surface of the water-repellent coating, and the apparent contact angle is improved as compared with the case where the water-repellent coating is formed on a flat surface, and good water repellency can be obtained. Therefore, for example, when the member according to the present invention is applied to a heat exchanger of a room air conditioner that also serves as a cooling and heating type, the water droplets that have condensed on the surface of the member fall while being relatively small. This makes it possible to obtain good drainage and suppress frost formation. However, the surface area per 1 cm ² in a plan view of the metal sheet is less than 20 cm ^2, it is impossible to obtain the effect of improving the apparent contact angle of the hydrophobic film sufficiently. Therefore, the surface area of the metal plate material per 1 cm ² in plan view needs to be 20 cm ² or more. In the present invention, the surface area means the surface area measured by the BET method. This bet
The method uses the BET adsorption formula proposed by S. Brunauer, PHEmmett, and E. Taylor, etc., and based on the adsorption of gas (gas such as nitrogen, krypton, and xenon) molecules on the surface of a porous solid, the surface area of the solid Is a method of calculating.

The water-repellent coating has a thickness of 1 to 2
It should be 0 mg / dm ² . When the film thickness of the water-repellent film is less than 1 mg / dm ² , the metal plate material cannot be sufficiently covered and sufficient water repellency cannot be obtained. On the other hand, when the film thickness of the water-repellent coating exceeds 20 mg / dm ² ,
Fine irregularities on the surface of the metal plate material are embedded, and the effect of improving the apparent contact angle is reduced. Therefore, the film thickness of the water repellent coating needs to be 1 to 20 mg / dm ² .

On the other hand, in the method of the present invention, first, the surface of the metal plate material is etched to form a large number of fine depressions. As such an etching process, an electrolytic etching method in which an electrolytic current is applied to the metal plate material or a chemical etching method utilizing a chemical reaction is suitable. According to this electrolytic etching method or chemical etching method, it is possible to form a large number of uniform and fine depressions on the surface of the metal plate material, and to form a water-repellent film on the surface of the metal plate material as described later. In addition, the apparent contact angle of the water-repellent coating can be significantly improved. Although it is possible to form irregularities on the surface of the metal plate material by mechanical polishing with sandpaper or a rolling roll, the irregularities formed by these methods have an excessively large unevenness interval or become uneven. Even if a water-repellent film is formed on the surface, the effect of improving the contact angle of the film cannot be sufficiently obtained. Therefore, it is necessary to form fine recesses on the surface of the metal plate material by the etching method.

Further, in the surface of the metal plate material, in this etching step, the proportion of the flat portion which is not dissolved by etching is 10% or less of the area of the flat surface before etching, and 1 cm ² of the metal plate material in plan view. It is necessary to make the microscopic surface area per hit be 20 cm ² or more. When the proportion of the flat portion after etching exceeds 10% of the area of the flat surface before etching, the effect of increasing the contact angle is small even if the surface area is increased in other portions. In addition, the surface area of the metal member after etching has a surface area of ² per cm ^{2 in} a plan view.
If it is less than 0 cm ^2, the effect of improving the apparent contact angle of the water-repellent coating formed on the surface of the metal plate in the subsequent step cannot be sufficiently obtained. Therefore, the proportion of the flat portion that is not dissolved after etching is 10% or less of the area of the flat surface before etching, and the microscopic surface area per 1 cm ² of the metal plate material is 20 cm ^{2 in} plan view.
It is necessary to do the above.

Then, a water-repellent film is formed on the surface of the metal plate material having a large number of fine depressions formed on the surface by etching.
The thickness is about 20 mg / dm ² . In this case, the water-repellent coating needs to have a contact angle of 90 ° or more when it is formed on a flat surface by coating or the like or when baking is performed after coating. In the case of a film having a contact angle of less than 90 ° on a flat surface, the apparent contact angle is not improved even if it is formed on the surface of the above-mentioned metal plate material that has been subjected to the etching treatment. Therefore, the water-repellent coating needs to have a contact angle of 90 ° or more when formed on a flat surface. Such a water-repellent film can be formed, for example, by applying a fluorine-based paint containing ethylene tetrafluoride or a copolymer of ethylene tetrafluoride and ethylene. Furthermore, Si-based water-repellent paint, paint and perfluoroalkyl group {(-CF containing a compound having a Tomekishi group (-CH ₃₎ is hydrophobic group
₂ -) _n -CF ₃ water-repellent agent having a} may also be used. However, the fluorine-based paint is disadvantageous in that it is expensive and the baking temperature is high. On the other hand, the water repellent agent having a perfluoroalkyl group has the advantages that it can obtain water repellency even when applied in a small amount and does not require drying at high temperature.

However, whichever paint is used, it is necessary to form the water-repellent coating in a thickness of 1 to 20 mg / dm ² . If the thickness of the coating is less than 1 mg / dm ² , the coating of the surface of the metal plate material becomes insufficient and sufficient water repellency cannot be obtained. In addition, the film thickness is 20 mg /
If it exceeds dm ² , the paint will fill the minute pits,
The effect of improving water repellency and frost prevention by forming fine irregularities on the base (metal plate material) becomes small. Therefore, it is necessary to form the water-repellent coating with a thickness of 1 to 20 mg / dm ² .

The surface of the member thus treated is
The contact angle of water drops exceeds 150 °, and the water drops easily fall off, and even if water in the atmosphere is condensed, it does not freeze immediately. This is because the apparent contact angle of the surface is high, and because the surface has many depressions, the contact area between the fins and the water droplets of the condensed water is small, and the latent heat of the condensed water does not escape to the fin side and is maintained. It is thought to be because.

It is to be noted that the present invention is mainly intended to simultaneously improve the water drainage property and the frost prevention property in a fin material for a heat exchanger, but the heat exchanger which requires the frost prevention property and the water repelling property. It is also applicable to other uses.
Further, the metal plate material to be subjected to the surface treatment is not limited to aluminum used for the heat exchanger fin material, and minute irregularities can be formed by etching, and water repellency on the surface can be achieved. Other materials may be used as long as the film can be formed by a method such as coating. Further, when the metal plate material is aluminum, there is no great difference in effect as long as it is a commonly used aluminum alloy, and it can be applied to various aluminum alloys. However, in the method of the present invention, since the thickness of the metal plate material is slightly reduced by etching, it is necessary to determine the plate thickness before etching in consideration of the etching margin.

[0023]

EXAMPLES Next, examples of the present invention will be described in comparison with comparative examples.

First, an aluminum plate material (JIS 1100H26) having a length of 10 cm, a width of 20 cm and a thickness of 0.12 mm.
Was etched by the etching method shown in Table 1 below. However, the treatment A was performed by immersing it in an etching solution containing iron chloride at 20% by weight (temperature: 70 ° C.). Further, the treatment B uses an etching solution containing 5% by weight of hydrochloric acid (temperature is 70 ° C.),
A current of 10 A is applied for electrolytic etching. Next, commercially available fluorine-based water repellents (contact angle when coated on a flat surface was about 120 °) were coated in various film thicknesses. Thereby, the specimens of Examples 1 to 6 and Comparative Examples 3 to 6 were obtained.

As Comparative Example 1, a test piece prepared by subjecting the above aluminum plate material to a hydrophilic treatment was prepared. Also,
As Comparative Example 2, a specimen was also prepared by coating the above aluminum plate material with a water-repellent coating material having a contact angle of about 80 ° when coated on a flat surface. In Comparative Examples 1 and 2,
The surface of the aluminum plate is not etched.

Next, the contact angle and the falling angle were examined in order to examine the water drainage property of each of the specimens of Examples and Comparative Examples. The results are shown in Table 2 below. The contact angle is an angle θ1 formed by the tangent line of the water droplet 1 and the plate surface as shown in FIG. As shown in FIG. 2, the falling angle is the angle θ2 at which the water droplet 1 starts to fall, and the smaller the falling angle, the easier the water droplet is to fall. The amount of water in the water droplet 1 at the time of measuring the contact angle and the falling angle is 0.03 g.

[0027]

[Table 1]

Next, the frosting property of each of the samples of Examples and Comparative Examples was examined. FIG. 3 is a schematic diagram showing a test device used for examining the frosting property. This test equipment is a cold water tank 1
1, a circulation pump 12, an aluminum container 13, and a pipe 14 connecting these components.

Using this test apparatus, the frosting property was examined by the method described below. That is, the temperature of the refrigerant stored in the cold water tank 11 is maintained at −10 ° C., and the circulation pump 12
This refrigerant was circulated between the aluminum container 13 and the cold water tank 11. Also, the aluminum container 13
Each of the specimens 10 of the example and the comparative example is attached so that the treated surface is on the outside, and the dry bulb temperature is 2 ° C. and the wet bulb temperature is 1.
The occurrence of frost was investigated in an atmosphere of ℃. Then, the frosting property was evaluated by measuring the time until the entire surface of the test piece was covered with frost. The results are also shown in Table 2.

[0030]

[Table 2]

As is clear from Table 2, in each of Examples 1 to 6, the contact angle exceeds 150 °, the falling angle is extremely small, and the water repellency and the falling property are excellent.
In addition, in Examples 1 to 6, the frost formation time is as long as 85 minutes or more, and the frost formation prevention property is excellent.

On the other hand, in Comparative Example 1, the entire surface was covered with frost in a short time after passing the coolant, and the frost-preventing property was not satisfactory. Further, Comparative Example 2 was not able to satisfy both the falling property of water droplets and the frost prevention property. Further, Comparative Examples 3 to 6 all have a low contact angle and have good frost prevention properties as compared with those subjected to the hydrophilic treatment (Comparative Example 1), but they cannot be said to be sufficient.

Next, a heat exchanger was manufactured using the surface-treated molding fins in the same manner as in Example 1, and the ventilation resistance and frost formation of this heat exchanger were examined.

First, a corrugated fin having 2 rows and 10 stages and having a water-repellent coating similar to that of Example 1 was formed.
This forming fin has a width of 25.4 mm and a length of 254 m.
m, and the color height (height of the portion where the copper tube is inserted) is 1.60 mm. The overhang height by corrugation (waveform overhang) processing is 1.5 mm. And the heat exchanger was manufactured using this fin (Example 7). The size of this heat exchanger is 254 mm in length and 250 mm in width. Further, as Comparative Example 7, a heat exchanger was manufactured using the same fins as in Example 7 except that the silica-based hydrophilic treatment was applied. Further, as Comparative Example 8, a heat exchanger was manufactured using the same fins as in Example 7 except that a water repellent paint having a contact angle on a flat surface of 80 ° was used.

Next, with respect to these examples and comparative examples, the measurement of ventilation resistance and the anti-frosting property were examined under the conditions according to JIS C9612.

FIG. 4 is a schematic view showing a wind tunnel device used for the test of ventilation resistance and frost prevention. In this wind tunnel device, the heat exchanger 20 of the embodiment and the comparative example is arranged on the intake side, and by driving the suction fan 21, air flows at a predetermined wind speed in the wind tunnel 22. In addition, this wind tunnel device can measure the pressure difference before and after the heat exchanger 20. Further, the wind tunnel device is provided with an anemometer 23 so that the wind speed behind the heat exchanger 20 can be measured. On the other hand, the refrigerant stored in the cold water tank 24 is supplied to the heat exchanger 20 by the cold water pump 25. The water temperature in the cold water tank 24 is maintained at a constant temperature. The water that has passed through the heat exchanger 20 is returned to the cold water tank 24.

Using the thus constructed wind tunnel device, the ventilation resistance and frosting time of the heat exchangers according to the examples and comparative examples were measured.

However, the ventilation resistance was evaluated as follows. First, the temperature of the refrigerant is set to 50 ° C. and the fins of the heat exchanger 20 are set to a state where no dew condensation occurs, and the heat exchanger 20
The pressure difference .DELTA.P1 before and after was calculated. Next, a pressure difference .DELTA.P2 before and after the heat exchanger 20 was obtained when a refrigerant having a temperature of 5.degree. C. was passed through the heat exchanger 20 at a flow rate of 10 l / min to cause dew condensation. At this time, the dry-bulb temperature of the atmosphere is 27.
° C, the wet bulb temperature is 19.5 ° C. And this ΔP1
The ratio of ΔP2 and ΔP2 (ΔP2 / ΔP1) was determined. The results are shown in Table 3 below as the ventilation resistance ratio.

This ventilation resistance ratio is greatly related to the drainage of the fin. That is, if the fins are poorly drained, many water droplets accumulate between the fins, the ventilation resistance ratio greatly exceeds 1, and the performance of the heat exchanger deteriorates significantly.

The anti-frost property was evaluated by the following method. That is, first, the dry bulb temperature is 2 ° C and the wet bulb temperature is 1
In an atmosphere of ° C, a refrigerant having a temperature of -10 ° C was supplied to the heat exchanger 20 at a flow rate of 10 l / min. At this time, the rotation speed of the suction fan 21 was adjusted so that the wind speed behind the heat exchanger 20 was 1.0 m / sec. Then, the suction fan 21
The time until the wind speed decreased to 30% of the initial value (frosting time) was examined while maintaining the rotation speed of No. 1 constant. The results are also shown in Table 3.

[0041]

[Table 3]

As is clear from Table 3, the heat exchanger of Example 7 had a ventilation resistance ratio substantially equal to that of the conventional heat exchanger subjected to hydrophilic treatment (Comparative Example 7). In addition, it can be seen that the time taken for the air volume to decrease due to frosting is about twice as long as that for the hydrophilic treatment, and the effect of preventing frosting is high. On the other hand, Comparative Examples 7 and 8 both had a short frost formation time, and Comparative Example 8 had a particularly large ventilation resistance ratio.

[0043]

As described above, according to the present invention, since the predetermined water-repellent film is provided on the surface of the surface-treated metal plate material, the water repellency is extremely good and the drainage property is low. In addition to being excellent, the water condensed on the surface is likely to fall off, and frost formation can be suppressed. Therefore, the member having excellent water repellency and frost formation according to the present invention is suitable for a fin material for a heat exchanger of an air conditioner such as a room air conditioner that also serves as a cooling and heating type.

Further, according to the method of the present invention, the surface area of the metal plate material is set to a predetermined value or more by etching, and then the water repellent film is formed on the surface of the metal plate material. A member suitable for a fin material for a heat exchanger can be manufactured.

[Brief description of 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 view showing a test apparatus used for examining frost formation.

FIG. 4 is a schematic view showing a wind tunnel device used for a test of ventilation resistance and frost prevention.

[Explanation of symbols]

 1; Water drop 10; Specimen 11, 24; Cold water tank 12, 25; Pump 13; Aluminum container 14; Piping 20; Heat exchanger 21; Suction fan 22; Wind tunnel 23; Anemometer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location C09D 5/00 PSD 6904-4J F25B 39/02 V 9335-3L F28F 1/32 G 9141-3L / / C23F 1/20 8414-4K C25F 3/04 A 8414-4K (72) Inventor Kenichi Kamiya 15 Kinugaoka, Moka City, Tochigi Prefecture Kamido Steel Works Moka Works (72) Inventor Hitoshi Mogi Osaka Prefecture 1006 Kadoma, Kadoma-shi, Matsushita Electric Industrial Co., Ltd. (72) Inventor, Shoichi Yokoyama, 1006 Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] 1. A surface area of the metal plate material per 1 cm ^{2 in} a plan view, the metal plate material having a roughened surface and a water-repellent film formed on the surface of the metal plate material. Is 20 cm ² or more, and the film thickness of the water-repellent coating is 1 to 20 mg / dm ² , which is excellent in water repellency and frost prevention. 2. A step of subjecting the surface of a metal plate material to 10% or less of a portion which is not dissolved by etching and a surface area per cm ^{2 of the} metal plate material of 20 cm ² or more in plan view, and a flat surface. A water-repellent coating having a contact angle of water droplets of 90 ° or more when formed on the surface of the metal plate having a thickness of 1 to 20 mg / dm ^2. A method of manufacturing a member having excellent water repellency and frost prevention.