JPS6337862B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for forming a selective solar heat absorption coating that can be applied to a solar heat collector and impart selective solar heat absorption properties to the surface thereof, and particularly relates to a high performance selective absorption coating. The present invention provides a method for realizing a membrane. In general, there is a technology to form a selective absorption film as a technology that contributes to improving the efficiency of solar heat collectors.
In this case, attention has been paid to coatings that are excellent in applicability to large areas and are inexpensive. In order to achieve selective absorption with this coating, the combination of its constituent systems is important. Conventional combinations include paints in which fine lead sulfide powder is dispersed in silicone resin, copper copper, manganese dioxide, cobalt oxide, etc., and resins such as acrylic melamine, vinyl, and silicone. Proposed.
The key to improving selective absorption characteristics with paint methods is how to improve emissivity, which tends to be high. In a conventional combination system with a comprehensively balanced configuration, the solar absorption coefficient α is 0.93 to 0.94 and the infrared emissivity ε is 0.4 to 0.5 (when the base material is stainless steel). The standard was that it had selective absorption. This level is a high level of emissivity compared to selective absorption films other than paint. If you want to improve the emissivity of a conventional composition system, you just need to make the film thinner, but it is very difficult to apply a thin, stable and uniform coating, and if you make the film thinner, , the number of defects such as pinholes increases, the physical properties of the coating film deteriorate, and the solar absorption rate also decreases. In view of the above-mentioned conventional drawbacks, the present invention aims to prevent defects such as pinholes in the coating film as much as possible.
The object of the present invention is to provide a method that improves painting workability and achieves excellent selective absorption. In order to achieve the above object, the present invention combines a carboxylic acid amide copolymer with Fe, Mn, Cu, Cr, Co,
Using a solvent-based paint whose main components are an oxide or composite oxide containing one or more elements selected from the group of Ni and a low molecular weight tetrafluoroethylene resin, the solid content in the paint is adjusted to the weight fraction. As less than 10wt%,
With amino-modified silicone resin added,
It is applied onto a heat collecting surface and then heated and cured. The above-mentioned carboxylic acid amide copolymer is a binder and is used to form a film on a heat-collecting surface material such as metal. That is, it is for adhering to the substrate and for adhering other coating film components to each other. In addition, oxides or composite oxides containing one or more elements selected from the group of Fe, Mn, Cu, Cr, Co, and Ni are black pigments that absorb sunlight and have low absorption of infrared rays. It is used as Regarding absorption of infrared rays, it is inevitable that all resins absorb a considerable amount of infrared rays, but carboxylic acid amide copolymer is a resin that absorbs relatively little infrared rays. Furthermore, the low molecular weight tetrafluoroethylene resin is used to improve the physical properties of the coating film, and by employing this resin, corrosion resistance, abrasion resistance, impact resistance, heat resistance, etc. are improved. In addition, this low molecular weight 4
Fluorinated ethylene resin contributes. Furthermore, in order to lower the emissivity of the heat collecting surface, a material with a low surface emissivity is used and utilized. Furthermore, in order not to impair the low emissivity of the material, it is desirable that the coating film to be formed be as thin as possible. In order to form a stable and uniform thin coating, it is best to apply the coating with a small amount of solids in the coating. In other words, this is why the solid content in the paint is set to 10wt% or less in terms of weight fraction.For example, if the solid content is expressed as awt% in weight fraction, the dilution of the paint is approximately 100/a. If the dilution is 5 wt%, the dilution is approximately 20 times, and it is calculated that a dry film thickness of 1 μm is obtained with a wet film thickness of 20 μm. By doing so, it becomes possible to form a stable thin film. In conventional paints, under such a highly diluted state, the pigment and resin separate, which tends to cause various paint film defects such as pinholes, but in the case of the present invention, amino-modified Since it contains silicone resin and maintains a stable surface tension state, there is no concern about the occurrence of paint film defects and stable painting operations are possible. After coating in this manner, a selective absorption coating film with excellent performance can be easily formed by heating and curing in an ordinary baking oven. The carboxylic acid amide copolymer in the present invention is
Preferably, a copolymer containing acrylamide, an α,β monoethylenically unsaturated carboxylic acid such as methacrylamide, an acrylic acid alkyl ester, or the like as a main component is preferably used. This is because these resins have excellent properties in terms of weather resistance, heat resistance, corrosion resistance, hardness, thin coating properties, and the like. Pigments include Fe ₃ O ₄ , MnO ₂ , CuO, Co ₃ O ₄ , NiO selected from the group of Fe, Mn, Cu, Cr, Co, Ni, etc. alone or in mixtures, especially Fe ₂ O ₃ −
A mixture such as MnO ₂ ·CuO or CuO-Cr ₂ O ₃ is particularly good in terms of transparency in the infrared region and absorption in the sunlight absorption region. Also, for these pigments, the particle size is a particularly important factor, with 0.01
A particle size range of ~0.5 μm is desirable from the standpoint of selective absorption, particularly light scattering. Hereinafter, effects will be explained focusing on examples of the present invention. In addition, evaluation of selective absorption was performed by the following method. Evaluation of absorption rate α is made by Shimadzu Corporation.
Using an MPS-5000 type self-recording spectrophotometer (incident angle 8 degrees, with an integrating sphere reflector), the emissivity of a black body of 6000 was calculated from the measured values at wavelengths between 0.3 and 2.0 μm. . In addition, the evaluation of emissivity (ε) is
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Direct evaluation was performed using an andS AERD type emissivity meter. Example: The test piece is 70mm x 150mm x 0.3mm.
Stainless steel YUS− made by Nippon Steel Corporation with dimensions of
190 (trade name) was used, and the paint was prepared according to the formulation shown in Table 1. This paint has a solids content of approximately 34%. When this paint is diluted with a solvent of the same composition as the paint in order to apply a thin film with a thickness of approximately 1 μm,
It is possible to dilute an area of at most 15% without causing unevenness (pinholes, flutters) on the coated surface.
If this is applied simply by spray painting, it is possible to increase the dilution, but it is difficult to do so by electrostatic painting using a disk. Therefore, coating workability was evaluated by adding 0.2 parts by weight of various surfactants to 15 parts by weight of the paint shown in Table 1 and 85 parts by weight of the solvent. Table 2 shows the results.
Shown below.

【table】

[Table] As is clear from Table 2, the addition of amino-modified silicone was effective in improving painting workability. It was confirmed that similar effects can be obtained even when added at the paint formulation stage. It is believed that these additives change the surface tension and somehow suppress the separation of the pigment and resin system with respect to the migration phenomenon accompanying solvent evaporation. Note that the amount of these additives added was effective from 0.05 wt%. When the amount added is 1 wt%, there is a tendency to have an adverse effect on the physical properties of the coating film, that is, to deteriorate the vapor resistance of the coating film. With such a combination system, for the first time approximately 1μ
It becomes possible to form a stable selective absorption coating film at a film thickness level of m. The drawing shows the relationship between the film thickness and selective absorption properties (α, ε) of a coating film formed on a stainless steel (YUS-190) plate by the method of the present invention. In this case, extremely excellent selective absorption was obtained with α of 0.92 and ε of 0.26. As described above, the method of the present invention can be easily mass-produced industrially using existing coating equipment, and its practical effects are extremely large.

[Brief explanation of the drawing]

The figure is a graph showing the relationship between the film thickness and selective absorption property of the selective absorption coating film formed by the method of the present invention.

Claims (1)

[Claims] 1 Carboxylic acid amide copolymer, Fe, Mn,
An oxide or composite oxide containing one or more elements selected from the group of Cu, Cr, Co, and Ni, and a low molecular weight 4
Using a solvent-based paint whose main component is fluorinated ethylene resin, the solid content in the paint is reduced to 10wt% by weight.
The following is a method for forming a solar heat selective absorption coating film, which is coated on a heat collecting surface in a state in which an amino-modified silicone resin is added, and then heated and cured.