JPS58195747A - Coating composition for selective absorption of solar heat - Google Patents

Abstract

PURPOSE:To obtain a coating composition of high-efficiency, by decreasing the radiating rate and increasing the absorption rate of solar rays by forming a coating film thinner, by composing the pigment of a mixture of specific oxide or compound oxide mixed with metallic ultrafine powder, in the titled coating composition composed by blending a resin and a pigment with a solvent. CONSTITUTION:In a coating composition of selectively absorbing solar heat, composed of a resin and a pigment mixed with a solvent, the mixture of an oxide or a compound oxide composed of more than one element selected from a group of Fe, Mn, Cu, Cr, Co, and Ni, mixed with metallic ultrafine powder is used as a pigment. By this method, a coating film can be formed thinner, because the covering-up effect of a coating film can be increased, in respects of a solar rays absorbing ability and a transparency to the infrared rays in the oxide or the compound oxide, and also of a scattering effect and the degrees of blackness in the metallic ultrafine powder. By the complex effect of forming the film thinner and the increase of the absorption rate by scattering solar rays to the inside of a coating film and others, the ideal selective absorption characteristics can be obtained in the coating composition.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a coating composition that is applied to the surface of a heat collector that collects all solar energy, and is mainly applied to a metal heat collector to impart selective absorption of solar heat to the surface. It is related to.

Due to the energy situation in recent years, solar energy utilization technology is attracting more and more attention, and active development and practical application to home water heaters and the like are being promoted.

As a heat collecting plate for collecting solar heat with full solar heat efficiency in a solar heat collector, it is recommended to use a solar radiation energy wavelength range (0.2-2.
6 μm), it is very close to a perfect blackbody.

It is known to use a surface that has optical spectral characteristics, that is, a selective absorption surface, which has a high energy absorption rate and minimizes the amount of heat radiation that occurs when the temperature of F itself increases. .

Conventional selective absorption surfaces include black plating with Or, Mi, etc., black oxide film formed by chemical conversion treatment, and those subjected to B treatment using methods such as vacuum evaporation and sputtering.

However, the plating method requires advanced techniques to always achieve a uniform surface finish, requires complex equipment, and is extremely difficult to process, especially for large items.

Furthermore, in the chemical conversion treatment method, the film lacks heat resistance and adhesion to the base material, and is prone to discoloration, so there are generally problems with durability. Furthermore, management of the processing liquid is extremely complicated.

In addition, vacuum evaporation, sputtering, and the like are difficult to process all large-sized items, as is the plating method. These technologies commonly increase costs and reduce productivity (mass production).
There are problems such as lack of quality and difficulty in obtaining stable quality.

Furthermore, a method has been proposed in which paint is applied all around (c), but although this method is advantageous in terms of productivity and cost, in terms of selective absorption, if you are trying to increase the total absorption rate of solar energy, it is difficult to Therefore, the problem was how to lower the emissivity. In order to form a coating film on a metal substrate using paint to make it a surface that selectively absorbs solar heat, it is necessary to use a black pigment that has excellent absorption of light with a wavelength of 2.6 μm or less. The absorption rate can be relatively high, but it is usually at a wavelength of 2.6μ.
This is because it also absorbs light with a wavelength of m or more, so the emissivity at this wavelength also increases. The general idea of achieving this is that the metal surface is exposed to infrared rays and
In order to reflect well i[1, there is a method of making the coating thickness as thin as possible to reduce infrared base absorption of 2.6 μm or more, that is, keeping the emissivity low. In the case of this method, the selection of paint components such as binders and pigments is extremely important for achieving selective absorption of solar heat, and the properties required for paints for selective absorption of solar heat are as follows: Among the paint components, it has a high absorption rate of sunlight even with the thinnest film thickness, and is as transparent as possible to infrared rays of 2.6 μm or more.
Pigments are particularly important.

Certain metal oxide pigments do not absorb much infrared rays, and although their absorption of sunlight is relatively good, there is still room for further improvement in their absorption properties, especially in the near-infrared region, and there is a need for film thickness and absorption rate. There is a relationship between emissivity and emissivity, and as mentioned above, there is an optimal film thickness range in which the thicker the film, the higher the absorption rate and the higher the emissivity, and conversely, the thinner the film, the lower both are. , there was a limit to the performance of this type of pigment alone.The present invention eliminates these conventional drawbacks;
tjJ, so the emissivity can be further reduced and the film thickness can be reduced...1
' Also, from the viewpoint of further increasing the absorption rate of sunlight, we focused on the pigments that play a central role in the effect, and added improvements and innovations to the above selective absorption. The purpose of this invention is to provide a paint set and photosensitive material for selectively absorbing solar heat with high performance.

6,-7 In order to achieve the above object, the present invention provides a coating composition for selectively absorbing solar heat, which is formed by mixing a resin and a pigment together with a solvent, in which Fe, Mn, and Cu are added to the pigment.

A mixture of one or more oxides or composite oxides selected from the group 0 of Cr, Go, and Ni and ultrafine metal powder is used.

This pigment composition allows thinning of the coating to improve the hiding power of the coating in terms of the sunlight absorption ability and infrared transparency of oxides and composite oxides, the scattering effect of ultrafine metal powder, and blackness. , ideal selective absorption has been achieved through a combination of effects such as increased absorption due to sunlight scattering inside the coating.

Examples of the present invention will be described below.

Example (1) Thermosetting acrylic resin [Diall 5K
100 parts by weight of -5661j (trade name), 100 parts by weight of Tsurupetz #100J (trade name), 60 M parts of n-butanol, 40 parts by weight of xylene as a solvent, 40 parts by weight of xylene with an average particle size of 0.6μ as a pigment, FeMnCu type Complex oxide [y
-6331J (trade name) 49.4 parts by weight, particle size is so
A paint 'f' was prepared by dispersing and mixing 2.6 parts by weight of ultrafine Cu powder in a ball mill for 24 hours.

The base material is pure aluminum with an emissivity of 0.04 f 150 ml x 70 mm x 0.8
Using a test piece cut to a size of mm, the above paint was sprayed onto the surface of the test piece and baked at 200°C for 10 minutes to form a coating film.

Example (2) Resin Dial 8 -5661100 parts by weight Solvent Tsurupetz #100 100 parts by weight n-butanol 60 parts by weight xylene
40 overlapping parts Pigment F-633149,4
Part by weight: 300 AFe ultrafine powder 2.6 parts by weight A coating film was obtained using the same mixing, painting, and baking methods as in Example (1) using a ball mill.

Example (3) All other conditions were the same as in Example (1), and only the pigment was added at a ratio of [F-6331J46.8 parts by weight, 500 parts by weight]
The ACu ultrafine powder was 6.2 parts by weight. , 4 Example (4) All other conditions were the same as in Example (2), and only the pigment was added at a ratio of [F-6331J46.8 parts by weight, 300 parts by weight].
The JF15 ultrafine powder was 6.2 parts by weight.

The absorption and emissivity results for the above are shown in the table below along with the film thickness.

The absorption rate in the table above is based on the spectrophotometer MP manufactured by Seitsu Seisakusho.
The spectral reflectance was measured using S-6000 model i, and 60,000
It is evaluated from the ratio of the black body emissivity of DKVICICa, --, 8KRV I CTC.
S OOMP ANY H) Emissivity meter tJ1'l Ite 7 The number of test samples for both absorption and emissivity is n=s, and the average value is expressed.

In addition, the level of selective absorption by the conventional coating method is the best one with an absorption rate of 0.94. The emissivity is about 0.36.

As is clear from the table above, in the examples of the present invention, extremely high performance selective absorption was obtained. This is because the pigment that plays a central role in the selective absorption of sunlight is a mixture of oxides, composite oxides, and ultrafine metal powder, which significantly increases the hiding power of the material. By improving the thinner film, lowering the emissivity, and uniformly dispersing the ultrafine metal powder inside the coating,
Without sunlight being guided through the paint film, this ultrafine metal powder is scattered like a mirror and forms oxides, metal oxidation, and oxidation.

4. It seems that by absorbing -4° pigments and solar chips, a high level of sunlight absorption was achieved even with such a thin film thickness.

In addition, the oxide and composite oxide pigments used in the present invention play an important role as described above.

In order to achieve selective absorption, absorption of infrared rays of 2.6 μm or more is particularly undesirable.

For this reason, organic pigments are not desirable, and good ones include Fe, Mn, Cu, Cr, and Co.
.

Examples include one or more oxides selected from the group of Ni and metal oxides. This is due to the above-mentioned properties against infrared rays, but these pigments include CoO*Cr20sa
Mno2Cr20sa, Fe20s*MnO*CuO
, CuO-0r203, etc., among which T/
Pigments such as re20s, MnO, and CuO are optimal, and it is thought that the selective absorption property is further improved by combining them with ultrafine metal powder (mixing system).

It goes without saying that when applied to the heat collection plate of a solar heat collector, it is important to achieve a good balance of selective absorption, coating film properties, and surface treatment reliability. In particular, there are concerns about corrosion resistance with thinner films, but because the dispersion and hiding power in the paint film is improved, corrosion resistance and adhesion (
(tape peeling, rough edges, impact from falling balls, etc.), heat resistance, and weather resistance were extremely good.

As described above, according to the present invention, the absorption rate is 0.947 to 0.
．． 95B with an emissivity of 0.14 to 0.20, which is an unprecedented level of selective absorption, and which also has reliability as a surface treatment, making it possible to obtain a material of extremely high practical value.

Claims (1)

[Scope of Claims] A paint composition for selectively absorbing solar heat, comprising a resin, a pigment, and a total solvent, wherein the pigment is Fe. A coating composition for selectively absorbing solar heat, which is a mixture of one or more oxides or composite oxides selected from the group consisting of Mn, Cu, Or, Go, and Ni0, and ultrafine metal powder.