JPS58190651A - Collecting plate for solar heat - Google Patents

Abstract

PURPOSE:To improve durability while preventing the lowering of an absorption index by forming a black film consisting of a black opaque heat-resistant resin onto a blackened film as a solar-heat selective absorbing film element formed to the surface of a metallic base body within a range of 0.1-0.8mum thickness. CONSTITUTION:The aluminum plate of the purity of JIS A1030 is degreased by a degreaser such as a non-etching type degreaser, and DC-electrolysed for 10min by 15V DC in an aqueous solution of 100g/l phosphoric acid, and an anodic oxidation film of 0.6mum thickness is formed to the surface. The film is AC electrolysed for 3min by 15V AC in an aqueous solution of 30g/l nickel sulfate and 30g/l boric acid to blacken the film. The blackened film is brought to 1mum thickness or less. The black opaque film is formed onto the black film within the range of 0.1-0.8mum thickness. The comparison of the selective absorption performance of the heat collecting plates in which the films of 0.3mum, 0.5mum and 1.0mum thickness are formed by a polyester denatured silicon resin and an acrylic resin is shown in the table.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solar heat collecting plate, and particularly to a solar heat collecting plate having a metal base and a solar heat selective absorption film formed on the surface thereof by blackening film treatment.

The performance of a solar heat collecting plate mainly depends on the selective absorption performance of the selective absorption film formed on its surface, and its evaluation is generally based on the absorption rate in the large sunlight wavelength range) and the long wavelength range. In the relative relationship with the emissivity (ε) in , the higher α/ε is as large as possible and the closer (c)) is to 1, the better.

By the way, the selective absorption film formed on the surface of a metal substrate is
In general, at the beginning of use, absorption rate ←) and emissivity (
ε) Both exhibit excellent performance that is almost satisfactory, but after long-term use, there is a tendency for the selective absorption performance, especially the emissivity (ε), to deteriorate significantly due to the influence of moisture such as rainwater and the influence of solar heat. This poses a major problem that is difficult to overlook.

Conventionally, in order to improve the durability of the selective absorption membrane, a method of coating the surface of the selective absorption membrane with a transparent heat-resistant resin made of silicone resin, fluororesin, or the like has been known to address this problem. This method can, of course, improve the durability of the selective absorption film due to the protective effect of the transparent resin film, but on the other hand, in terms of selective absorption performance, the emissivity (-) increases as the coating thickness increases. Not only that, but the absorption rate (←) also decreased at the same time.

In view of the above, an object of the present invention is to provide a solar heat collecting plate that can avoid a decrease in selective absorption performance, particularly a decrease in absorption rate←), while improving durability.

In this invention, a black coating film is formed on the surface of a metal substrate as a solar heat selective absorption film element, and a black coating film made of a particularly black opaque heat-resistant resin is applied on the black coating film to a thickness of 0.1 mm. It is characterized by being formed in the range of .about.08μ.

Suitable heat-resistant resins for forming the black coating film include black polyester-modified silicone resin, black noricorn resin, black acrylic-modified silicone resin, river fish urethane-modified silicone resin, black polyester-modified noricorne resin, black fluororesin, etc. I can give an example. There are no particular restrictions on the means for applying these resins.
Any method such as dipping, roll coating, spraying, etc. can be used, but gravure roll coating is particularly preferred since it can advantageously form a coating film with a uniform thickness over the entire surface. be.

However, the thickness of this black coating film should be within the range of 01 to 08 microns (7), and particularly preferably about 02 to 03 microns. If the film thickness is less than O,+μ and is extremely thin, the protective effect of the coating film will be insufficient (and the effect of improving durability cannot be satisfactorily obtained.On the other hand, the reverse (this) If the thickness exceeds 0.8 μm, the emissivity (ε) D increases by 1, making it impossible to obtain good selective absorption performance.

As the material for the metal base, metals with good thermal conductivity such as aluminum, copper, and stainless steel are used. Then, aluminum substrates are blackened by secondary electrolytic coloring or chemical coloring, copper substrates are treated with blank nickel plating, and stainless steel substrates are treated with titanium oxide, etc. , a selective absorption film is formed on the surface by blackening film treatment. However, a selective absorption film is formed on an aluminum plate by electrolytic coloring, that is, the aluminum material is first anodized to form a porous oxide film with a thickness of about 1μ on its surface, and then this is coated with a metal salt. In cases where a blackened film is formed by electrolytically treating the oxide film in an aqueous solution to precipitate and fill the pores of the oxide film, a portion of the black resin coating is filled into the pores of the porous film. At the same time, since the base surface is also roughened, the adhesion of the black coating film becomes extremely strong, which is advantageous in that it can reliably prevent its peeling and further improve durability.

According to this invention, on a blackened film as a solar heat selective absorption film element formed on the surface of a metal substrate in a series,
Historically, a black coating film made of heat-resistant resin has been formed, and the protective effect of the coating film maintains the selective absorption performance of the selective absorption film well over a long period of time, and can significantly improve durability. However, since this protective coating is particularly black and opaque, and has a thickness of 01 to 08μ, it reduces the selective absorption performance of the blackened coating; rather, it reduces the absorption rate. ), this is further increased to achieve the effect of having even better selective absorption performance.

Next, examples of the present invention will be compared with comparative examples.

Example: After degreasing an aluminum plate having a purity of JIS-A1030 with a non-etching type degreaser, phosphoric acid 100
After performing DC electrolysis for 10 minutes at 15 V DC in a t/l aqueous solution to form an anodic oxide film with a thickness of 06 μm on the surface of the aluminum plate, this was further diluted with nickel sulfate 30 F// and boric acid 30 g/l. AC electrolysis was carried out in an aqueous solution of AC 15 V for 3 minutes to form a blackened film in which the above film was substantially blackened.

Next, a black opaque polyester-modified silicone resin and a black opaque acrylic resin were applied to the blackened film to a coating thickness of 03μ, 05μ, and 10μ, respectively, so that the surface was covered with the black coating. Various samples were obtained.

On the other hand, as comparative examples of coating films, colorless and transparent polyester-modified silicone resins were coated with various film thicknesses as above on the blackened film, and their selective absorption performance was evaluated using the various materials mentioned above. compared with that of The results are shown in Table-■.

Table - ■ As is clear from the results in the above table, the present invention has
In particular, by forming a black coating film, compared to forming a transparent coating film, although the emissivity -) increases to the same extent, the absorption rate ←) does not decrease at all; in fact, it is the opposite. It was confirmed that this product can achieve even better selective absorption performance.

In addition, we measured and compared the changes in the selective absorption performance of the various samples above with a coating thickness of 0.3μ after the moisture resistance test, and the results are shown in the table -■ below. That's right. In addition, this humidity test was conducted at 38℃ on the bottom.
A sample was held in a closed container containing hot water, and the performance was measured after 100 hours while stirring the hot water with air.

(Left below) Table -■ As can be seen from the results in the above table, the present invention shows an improvement effect comparable to that of conventional transparent resin coatings in terms of moisture resistance and durability. It was something.

that's all

Claims (2)

[Claims] (1) A black coating film is formed on the surface of a metal substrate as a solar heat selective absorption film element, and a black coating film with a thickness of 01 to 08 μm made of a black opaque heat-resistant resin is further formed on the black coating film. A solar heat collecting plate characterized by being formed. (2) Claim 1, in which the metal substrate is made of an aluminum material, and the blackened film on its surface is a film colored by electrolyzing an anodic oxide film with a thickness of 1 μm or less in the presence of a metal salt. The solar heat collector plate described.