JPS624626B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heat collection plate for a solar heat collector, and aims to improve heat collection efficiency. In recent years, solar energy has attracted attention from the viewpoint of energy conservation and oil alternative energy, and active development and practical application to home water heaters and the like are being promoted. Solar heat collectors have been developed as the core of solar heat utilization systems for various solar applications, and flat plate, tubular, vacuum-insulated tubular, heat pipe, and concentrator types have been proposed and put into practical use. has been done. Among these, flat plate solar heat collectors are the main type used for domestic hot water supply. Home solar water heating systems are pump-type,
They are broadly divided into natural circulation type and forced circulation type, but natural circulation type is currently becoming mainstream, and it is predicted that forced circulation type will also increase in the future. In a natural circulation type or forced circulation type single water circuit, the water channels of the heat collecting plate are required to be corrosion resistant, so stainless steel, copper, etc. are used as materials. In addition, in a two-water circuit system, water containing a closed system corrosion inhibitor or antifreeze containing propylene glycol is passed through a heat collector, and hot water is heated through a heat exchanger in a hot water storage tank. The choice of materials for the heat collecting plate is widened, and for example, inexpensive materials such as galvanized steel sheets can be used. Types of galvanized steel sheets include steel sheets that are electrolytically galvanized, hot-dip galvanized, and then subjected to iron-zinc alloying treatment. From the viewpoint of workability as a heat collecting plate of a heat collector, that is, drawing, welding, etc., galvanized steel sheets subjected to iron-zinc alloying treatment are best. A heat collecting plate for a solar heat collector constructed using a galvanized steel plate subjected to the iron-zinc alloying treatment has excellent economical merits. In order to impart sunlight absorption ability to the thus formed heat collecting plate, conventionally, a black paint was applied onto the surface of a galvanized steel plate. This black paint is made of a black pigment such as carbon black and a resin such as silicone resin or acrylic resin.In the case of this paint, the absorption rate of sunlight (0.3 to 2.0 μm) is about 0.95. , because it absorbs infrared light well, the emissivity (3 to 30 μm)
It was also high, around 0.95. Furthermore, since zinc-treated steel sheets do not have very good corrosion resistance, corrosion-resistant paint has been used as an undercoat for black paint in order to improve the corrosion resistance. The present invention aims to impart selective absorption properties to an economically superior heat collecting plate for a solar heat collector from the viewpoint of improving heat collecting efficiency. Galvanized steel sheets subjected to iron-zinc alloying treatment, which is optimal in terms of workability, have a high emissivity of 0.45 or higher. Therefore, if a coating film is formed on top of this, absorption in the infrared region will be added to it, so even if a film with a thickness of 2 to 3 μm is formed with very little absorption in the infrared region, the emissivity will be less than 0.7. There is a problem with overcoming it. The present invention attempts to solve these problems all at once. Figure 1 shows the structure of a typical flat plate solar collector, where 1 is a transparent cover, 2 is a heat collecting plate, and 3 is a transparent cover.
is an insulating material. The main point of the present invention is that the heat collecting plate 2
However, A, which is the heat receiving surface side of the sunlight,
FIG. 2 shows a cross-sectional view of the surface and the B surface on the back surface side. In FIG. 2, layer a is the iron base portion, and layer b is the galvanized layer. Surface A, which is the solar heat receiving surface, is as shown in Figure 2A.
On the galvanized layer b, a corrosion-resistant paint layer containing 15 wt % or more of fine aluminum powder, ie, a layer c, is formed to reduce the emissivity of the surface.
Further, on the back surface side B, only the C layer is processed as shown in FIG. 2B. Regarding the A side, as shown in Figure 2 A, there is a coating layer on top of the c layer, with a thickness of 5 μm or less, containing black pigment and an acrylic resin binder as main components, that is, a d layer. form. In the above configuration, when sunlight, most of which is light with a wavelength of 2.5 μm or less, enters the A plane, it is mainly absorbed by the d layer and converted into heat. This heat is transmitted through the c layer by thermal conduction, and further transmitted to water or the heat medium via the b→a layer. In an equilibrium state where the temperature is increased, infrared radiation of 2.5 μm or more has a relatively low emissivity due to the effect of aluminum arranged on the surface side of the C layer, and the radiation of infrared rays from the surface is considerably suppressed. The d layer is 5μ
Since it is a thin film of less than m and is composed of a binder and pigment that absorb little infrared rays, it does not significantly increase the emissivity of the C layer. That is, the d layer is made of a pigment made of one or more oxides or composite oxides selected from the group of iron, manganese, copper, chromium, cobalt, and nickel, and an acrylic resin binder. The fine aluminum powder used for the c-layer has good leafing properties and tends to float and be arranged in parallel on the surface of the c-layer coating. Further, as the binder to be applied to the c layer, various binders can be used from the viewpoint of corrosion resistance, heat resistance, painting workability, etc. Particularly preferred binders include epoxy resins. By applying such treatment, radiation from the back side (B side) of the solar collector is reduced, and the heat receiving side (A side) maintains selective absorption, and the overall corrosion resistance is also excellent. A heat collection plate for a solar heat collector is obtained. Examples of the present invention will be described in detail below. Evaluation of selective absorption was performed by the following method. The absorption rate α was evaluated using a Shimadzu MPS-5000 type self-recording spectrophotometer (incident angle 8°, with an integrating sphere reflector) from the measured value at a wavelength of 0.3 to 2.0 μm. Calculated for the blackbody emissivity of
This was taken as the characteristic value of the coating film. In addition, the evaluation of emissivity ε is
The emissivity of the sample surface was directly evaluated using a D and S AERD type emissivity meter manufactured by DEVICES & SERVICES COMPANY. (Example) "Silver Alloy" (trade name) manufactured by Nippon Steel Corporation was used as the zinc-treated steel sheet, and this was
It was cut into a size of x100mm x 0.8mmt and used as a test piece. The emissivity of the sample as a substrate is
It was 0.58. Polyester-modified silicone resin is used as a binder for this undercoat, but this polyester-modified silicone resin is used by Dainippon Ink.
Rhodosil resin #9031 manufactured by Co., Ltd. was used. Then, this polyester-modified silicone resin and aluminum powder (Alpaste #0215M manufactured by Toyo Aluminum Co., Ltd.) were mixed at different blending ratios and dispersed and mixed for 24 hours using a ball mill to prepare a paint. In this case, ethylene glycol diacetate was used to adjust the viscosity as necessary. The thus prepared paint was applied to the surface of a zinc-treated steel sheet to a film thickness of approximately 30 μm. The following table shows the aluminum content ratio (wt
%) and emissivity. As seen in this table, as the amount of aluminum increases,
Emissivity ε becomes lower. It tends to become saturated at 15wt% or more. It is thought that the surface will be almost completely hidden if it is 15wt% or more.

[Table] Next, the same silicone binder was used and the aluminum content was set to 20 wt%, and the coating was applied to a film thickness of approximately 30μ. This coating was performed by a spray method after degreasing the base material with trichlene, allowing it to stand at room temperature for 15 minutes, and then baking it at 200°C for 30 minutes. The samples in this case were also prepared in the same manner as the samples in the table above. And this sample showed an emissivity in the range of 0.22-0.26. The above sample was also tested for adhesion, steam resistance, water resistance, heat resistance, and corrosion resistance, and showed extremely excellent surface properties. In addition, as another example, a product manufactured by Dainichiseika Co., Ltd.
25 parts by weight of "Dipyroxide Color #9550" (trade name), which is a Fe ₂ O ₃ / MnO ₂ / CuO pigment, and Nippon Gosei as a methacrylate ester resin.
"Coponil AZ-40T" (product name) manufactured by Co., Ltd.
100 parts by weight and 40 parts by weight of toluene were added, and these were dispersed and mixed for 12 hours using a ball mill to prepare a paint. Then, this paint was applied to a film thickness of about 4 μm on top of the coating film that had already been undercoated with silicone resin, and dried at 50° C. for 5 minutes. This sample has an absorption rate α=0.93~0.94 and an emissivity ε=0.41~
It showed a performance of 0.44. This coating also showed good adhesion, heat resistance, and weather resistance (weather meter and outdoor exposure). Regarding the solar heat collector model that adopted the heat collector plate shown in the above example, we evaluated the case where it was applied to a forced circulation system by simulation calculation, and compared to the case of conventional black paint, it was found that
The result was that the annual heat collection amount improved by 10%. As described above, the heat collecting plate of the present invention has fine aluminum powder applied to both the front and back sides of the galvanized steel plate.
A corrosion-resistant paint layer containing 15 wt% or more is formed, and further, only on the side that receives sunlight, on the corrosion-resistant paint layer is a film thickness of 5 μm or less and a black pigment,
Since it forms a layer mainly composed of acrylic resin and binder, it can significantly improve heat collection efficiency compared to conventional black paint coatings.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a flat plate type solar collector employing a heat collecting plate according to an embodiment of the present invention, Fig. 2 A,
B is a diagram showing the cross-sectional structure of the heat collecting plate.

Claims (1)

[Claims] 1. A corrosion-resistant paint layer containing 15 wt% or more of aluminum fine powder is formed on both the front and back sides of a zinc-treated steel sheet, and a film thickness of 100% is applied on the corrosion-resistant paint layer only on the surface that receives sunlight. 5 μm or less, and a layer containing a black pigment, an acrylic resin, and a binder as main components is formed.