JPS621511B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a solar heat selective absorption surface that is applied to the surface of a solar heat collector to impart selective absorption properties. Most of the radiant energy of sunlight passing through the atmosphere is on the short wavelength side of 0.2 to 2.5 μm, and on the other hand, by absorbing that energy and converting it into heat, it is heated to, for example, 80 to 100 degrees Celsius. The radiation energy radiated from the surface is in the infrared region with long wavelengths of 2.5 μm or more. A surface that takes advantage of this wavelength shift and has an absorption rate close to 1 at short wavelengths of 2.5 μm or less and an emissivity close to 0 at long wavelengths of 2.5 μm or more is called a selective absorption surface. As a treatment for imparting such selective absorptivity to a metal surface, blackening treatment of colored stainless steel and the like has already been put into practical use. Characteristically, solar absorption rate α is 0.88 to 0.90, and infrared emissivity ε is 0.15.
However, the drawback is that the processing cost is high. On the other hand, the method using paint is expected to have cost advantages in terms of industrial production, but it is difficult to impart selective absorption properties itself, and many of the methods are still at the research stage. In order to form a paint film on a metal surface and make it a surface that selectively absorbs solar heat, the absorption rate can be relatively reduced by using a black pigment that has excellent absorption of light with a wavelength of 2.5 μm or less. Although it is easy to increase the emissivity, ordinary coatings also absorb light with wavelengths of 2.5 μm or more, so the emissivity of wavelengths of 2.5 μm or more is high, and it is difficult to find a way to lower the emissivity. This will be a challenge. The general idea for achieving this is
Taking advantage of the fact that metal surfaces reflect infrared rays well,
The thickness of the coating film is made as thin as possible to a few μm or less, and the wavelength is 2.5.
There is a method of reducing the absorption of infrared rays of μm or more, that is, lowering the emissivity. In the case of this method, even if selective absorption can be achieved, the physical properties of the coating film are not stable, such as poor adhesion to the metal, and
Although it has been difficult to put this into practical use, the inventors have already proposed a coating composition that achieves a good balance between selective absorption and coating film properties. According to this proposal, in order to achieve selective absorption, it is undesirable to use organic pigments that absorb particularly large amounts of infrared rays with wavelengths of 2.5 μm or more, and that inorganic pigments are preferable. Particularly good examples include oxides or composite oxides of at least one metal selected from the group of Fe, Mn, Ni, Cu, Cr, and Co. In addition, in order to obtain stable hiding power for thin film formation, less scattering and absorption of infrared rays, and small emissivity, we especially
A particle size of 0.5 μm is desirable. This is extremely fine compared to the particle size of ordinary pigments, which is 0.5 to 1.5 μm. On the other hand, a resin is used as a binder for forming a coating film.Although most resins have absorption in the infrared region, acrylic resin is cited as a resin that is relatively advantageous in this respect. This has many advantages in terms of coating film properties such as weather resistance and adhesion, and cost. Especially when considering the physical properties of the coating film, thermosetting acrylic resins are good, and those modified with silicone are also useful. Furthermore, various resins are added as necessary for the purpose of improving the physical properties of the coating film. In addition, in order to achieve both selective absorption and coating film properties, the blending ratio of pigment and resin is also important.
It is said that the weight ratio of pigment to resin solid content is preferably in the range of 45/100 to 65/100. The selective absorption performance of these configurations is as follows when stainless steel is used as the support.
If the film thickness is 5 μm or less, solar absorption rate α=
Achieves 0.93-0.94 infrared emissivity ε = 0.40-0.45. The present invention provides a selective absorption surface that satisfies the physical properties of the coating film and has further improved selective absorption properties than those described above. That is, on a support made of a metal with low infrared emissivity, the main components are the already proposed inorganic black pigment and acrylic resin, and the weight ratio of the pigment to the resin is 45/100 to 65/2. The first layer is formed by applying a paint having a ratio of 100 to 100, and the second layer is further formed by applying a paint having a ratio of 65/100 to 80/100. The total film thickness at this time is preferably 5 μm or less. In order to maintain the physical properties of the coating film such as adhesion, the resin as a binder makes a large contribution, so in terms of the blending ratio of pigment and resin, it is desirable to have a large resin content, but in terms of selective absorption, the resin content is The fewer the minutes, the better. The blending ratio of pigment and resin was determined based on the balance between the two, and this is the case when one layer of coating film is formed on the support. The present invention makes good use of both the physical properties of the coating film and selective absorption, and the first layer on the support is formed with a paint made from a blend of pigment and resin that emphasizes the physical properties of the coating film, and the second layer
The layer focuses on selective absorption, and by forming a coating film with a paint containing a small amount of resin, a practical and high-performance selective absorption surface is realized. The present invention will be explained below using examples. The base material for forming the painted surface is Nippon Steel Corporation's stainless steel "YUS-190" (PB finish).
A product with a size of 70 x 150 mm and a thickness of 0.3 mm was used after degreasing with alkaline. The infrared emissivity of this was ε=0.10. In addition, the spectral characteristics of the selectively absorbing coating film were determined by measuring the spectral reflectance using a Shimadzu spectrophotometer model MPS-5000, and evaluating the absorption rate α from the ratio to the black body radioactivity of 6000〓. The external emissivity is
Measured using an emissivity meter manufactured by DEVICES & SERVICES CONPANY. "Dipyroxide Color #9550" by Dainichiseika Co., Ltd. was used as the Fe ₂ O ₃ / MnO ₂ / CuO-based black pigment, and thermosetting acrylic resin "Dyanal SE-5661" by Mitsubishi Rayon Co., Ltd. was used as the binder. used, resin 50
Paints with different blending ratios of pigment and resin were prepared as shown in Table 1 in terms of weight percent. The paint was mixed and dispersed for 24 hours using a ball mill. The solvent used was 29% by weight of n-butanol, 21% by weight of xylene, and 50% by weight of "Solbetsuso #100" manufactured by Esso Standard Oil Co., Ltd.

[Table] Apply the above paint so that the first layer has a film thickness of 2 μm, air dry for 30 minutes, and then apply the second layer to a thickness of 2 μm.
It was coated to a film thickness of m and baked at 200°C for 10 minutes. Tables 2 and 3 show the results of evaluating the selective absorption and coating film properties of the test pieces thus prepared.

【table】

[Table] The physical properties of the coating film were evaluated by the following tests. Adhesion: Goban taping test (1mm square) Flexibility: 1φmm x 180℃ bending test Erichsen: Taping test after extruding 5mm using an Erichsen tester Impact resistance: Dupont type 1/2", 500g steel ball of 50cm Taping test after dropping from a height (front and back) Salt spray test: Taping test after continuously spraying 5% NaCl aqueous solution for 500 hours in an atmosphere at 35°C Here, the second layer coating was evaluated, but the first layer There was no abnormality in the physical properties of the coating film.Therefore, even if the second layer were to disappear, there would be no functional problem because the first layer would be stable.However, if the second layer In order to improve selective absorption, it is not practical for No. 1, which had extremely poor physical properties of these coatings. Although some peeling was observed for Nos. 2 and 3, the physical properties of the coating were tested. The selective absorption after the test was at the same level as before the test, and it was found that there was no functional problem as the second layer.The blending ratio of pigment and resin in the paint forming the first layer is as follows: The higher the resin content, the higher the resin content. Although the physical properties of the coating film are good, the present inventors have already made efforts to lower the total emissivity and to maintain selective absorption when the first layer is exposed due to shedding of the second layer. The blending ratio of pigment and resin solids proposed by should be in the range of 45/100 to 65/100 by weight.From the above, as the first layer on the support, the ratio of pigment to resin should be in the range of 45/100 to 65/100. A paint film with a ratio of 45/100 to 65/100 is applied to form a coating, and the same ratio is 65/100 as the second layer.
By applying a paint in the range of 100 to 80/100 to form a coating film, it is possible to stably obtain a solar absorption rate α of 0.94 or more and an infrared radiation emissivity ε of 0.40 or less. Further, the total thickness of the first layer and the second layer at this time is preferably 5 μm or less. Although stainless steel was used as the support here, it can also be applied to copper, aluminum, etc., which have good infrared reflection, and since these have better infrared reflection than stainless steel, An excellent selective absorption surface can be obtained. As described above, according to the present invention, the following effects can be obtained. (1) The first coating film has selective absorption with emphasis on adhesion to the support, corrosion resistance, etc., and the second coating has emphasis on selective absorption, so it has excellent reliability over a long period of time. It is possible to realize the flexibility and selective absorbency. (2) Even if the second coating peels off, the first coating has excellent physical properties such as corrosion resistance, so it can prevent damage and deterioration of the support and has selective absorption properties. Therefore, it is possible to prevent a decrease in the ability to collect solar heat.

Claims (1)

[Claims] 1 The main components are an inorganic pigment and an acrylic resin, and the weight ratio of the pigment and the resin is 45/
A first coating film formed by applying a paint having a ratio of 100 to 65/100 (pigment/resin), and a blending ratio of the pigment and resin on this first coating film is 65/100 to 80/100. A surface that selectively absorbs solar heat and has a second coating formed by applying paint.