JPS6026943B2 - Selective absorption surface for solar heat - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a selective absorption surface applied as a collector material for collecting solar energy.

Solar energy utilization technology has been attracting attention due to the recent oil crisis, but solar energy can also be used to heat water at home.
From the standpoint of application to heating and cooling, heat collection technology that converts light energy at the entrance into thermal energy is important as a basic technology.

One of the challenges in the heat collection technology is the development of a low-cost, durable, and highly efficient heat collector. The radiant energy of sunlight passing through the atmosphere is approximately 0.2 to 2
．． The short wavelength of 5 m is on the side, and on the other hand, the energy is absorbed as heat, and the temperature rises to 80 to 100.
The radiant energy radiated from the heated surface at midnight is 2.
It is in the infrared region with a long wavelength of 5 to 20 rm.

In order to construct an efficient heat collector, it is sufficient to direct most of the sunlight to the ground and reduce the various forms of energy loss from the heat collector. Regarding the heat collecting surface, wavelength 2.
It has spectral characteristics such that its absorption rate (expressed by a) for sunlight of 5rm or less is close to 1, and its emissivity (expressed by g) for light with a wavelength of 2.5mm or more from its surface is close to 0. It is desirable to be present. That is, it is desirable that the heat collecting surface has selectivity with a wavelength of 2.5 mm as a boundary. A coating formed on a metal surface or the like to impart the selective absorption properties is called a selective absorption film. In order to obtain such a selective absorption surface, methods are known in which a metal surface is subjected to plating or chemical conversion treatment, and a method in which aluminum is colored black using an anodic oxidation method.

All of these methods utilize a metal surface with a low emissivity, and perform a surface treatment on this surface to increase the absorption rate without impairing the emissivity as much as possible. Among these methods, in the case of colored stainless steel, the absorption rate Q
A performance of =0.90 and emissivity =0.10 was obtained. In the case of these methods, if the processing conditions are made stricter in an attempt to increase the absorption rate, there is a problem that the metal surface will be etched and the emissivity will increase. In addition to the complicated management associated with controlling the composition and film thickness, the manufacturing equipment is large-scale, which increases the cost.

On the other hand, the method using paint is expected to have cost advantages in terms of productivity, but regardless of whether the binder that makes up the paint is an organic resin or an inorganic binder,
There is absorption in the infrared region, which increases the emissivity.Although the absorption rate can be improved relatively easily by selecting pigments, it is extremely difficult to maintain a low emissivity, and it is still not practical compared to the colored stainless steel. We haven't found anything that can compete with the competition.

Naturally, mere conventional black paint does not have selective absorption, and has a characteristic of Q = 0.95 x = 0.95, so if you try to increase Q, the absorption will also increase.
It shows the property that if you try to decrease Q, Q will also decrease.

As mentioned above, in order to obtain a selective absorption film by coating, the problem is how to keep the emissivity in the infrared region low.

Since metal surfaces usually have a low emissivity, the general idea is to utilize this base metal surface to obtain a low emissivity.

Therefore, in the development that is proceeding in line with this idea, base metals that have both the physical properties (including durability) of the material that makes up the heat collector and the properties that can provide the low emissivity mentioned above are being developed. Examples of such materials include copper, aluminum, and stainless steel. These metal surfaces have a wavelength range of 0.04 to 0.0 in the wavelength range of 2.5 to 30 meters.
A low emissivity of about 8 can be achieved. Therefore, conventional attempts to obtain a paint-type, low-cost selective absorption membrane have been mostly limited to the metal surfaces. Targeting these materials, using acrylic resin as a binder, Fe, Mn,
Cu, Cte, Co. One or more oxides or composite oxides selected from the group of Ni are made into a paint as a pigment, and this is
By coating the metal surface with the following film thickness, Q=
Performance of 0.94 to 0.95 = 0.2 to 0.3 (aluminum, copper), and 0.4 to 0.5 (stainless steel) can be obtained.

On the other hand, there have been conventional products that have been applied to metal surfaces using chemical conversion treatments such as colored stainless steel or black alumite. is inferior and, as mentioned above, requires the use of relatively expensive materials to obtain the effect, so the cost effectiveness is also reduced. Therefore, when we focused on various types of inexpensive surface-treated steel sheets, we found that many of the surface-treated steel sheets had microscopic irregularities on their surfaces, and therefore had poor emissivity.

For example, when Nippon Steel ■'s "Silver Alloy" (product name) was evaluated as an example of zinc-treated steel sheet, it showed a value of 0.48 to 0.55 in its base state, indicating that sufficient selective absorption performance could not be obtained. . Furthermore, in order to obtain a low emissivity as described above, if one tries to achieve this with a coating film using a metal surface with a low emissivity, the combination with the base metal becomes an issue.
That is, even if the same paint is applied under the same conditions to obtain exactly the same film, the selective absorption will be different if the base metal has a different emissivity. Therefore, the selective absorption properties of the paint itself alone will not solve the problem.

In view of the above, the present invention uses an aluminum-coated steel sheet as its base material, and has obtained extremely excellent characteristics.

That is, an aluminum-coated steel plate is used as a base material, and a coating having a thickness of 51 m or less is formed on the surface of the aluminum-coated steel plate by applying a paint containing a black pigment and an acrylic resin binder as main components. The present invention will be explained in detail below.

The drawings are conceptual diagrams of the present invention.

In the drawings, A is an aluminum coated steel plate, B is a steel plate, and C is an aluminum coating layer. Further, D is a coating film containing a black pigment 1 and an acrylic resin binder 2. Sunlight is absorbed by the black pigment 1 and converted into heat. The emissivity of the infrared radiation from the surface is low because the aluminum-coated surface has a low emissivity, and both the black pigment 1 and the acrylic resin binder 2 are relatively transparent to infrared rays. As the thickness of coating film D increases, the absorption of infrared rays increases and the emissivity increases. Therefore, if the emissivity is to be maintained at a level of 0.5 or less, the film thickness must be 5 m or less. It is. Nisshin Steel's "Ulstar" (product name) was used as the aluminum-coated steel sheet A, and its emissivity (wavelength 2
．． When measuring the emissivity of 5 mm to 30 mm, an emissivity of 0.08 was obtained, and overall, extremely excellent characteristics were obtained as a solar heat collecting material.

By the way, in order to form the coating film D, a binder and a pigment are essential.

The absorption of light with a wavelength of 2.5 Am or less depends solely on the pigment, and the problem is the emission of light with a wavelength of 2.5 Am or more. Since there is no binder that is substantially completely transparent to infrared rays, if absorption of infrared rays is assumed, the thickness of the binder must be as thin as possible. Naturally, it is desirable that the binder itself has low absorption in the infrared region. Acrylic resin binders are suitable in this respect. If a black pigment is blended with an acrylic resin binder as a base (solvents, dispersants, etc. may be added as necessary), a paint can be obtained.

As black pigments, Fe, M
It is preferable to use one or more oxides or composite oxides selected from the group consisting of n, Cu, Co, and Ni. Furthermore, the ratio of the acrylic resin binder to the black pigment is important. When the amount of acrylic resin binder increases, the coating film becomes glossier. Conversely, as the amount of black pigment increases, the gloss decreases. Wavelength 2.
Regarding the absorption of light with a wavelength of 51 m or less, it is preferable that there is no gloss, and with regard to the reflection of light with a wavelength of 2.5 m or more, it is preferable that there is gloss. Usually, a pigment/resin ratio of about 2% to 5% is desirable, and around 3% is best. If the paint obtained in this way is applied to a metal surface with low emissivity at a film thickness of 5 m or less, Q = 0.93 to 0.95, Go = 0.4.
A selective absorption membrane of 0 to 0.50 is obtained. This characteristic is not so much related to the type of acrylic resin, and almost the same level can be obtained. As shown in the following examples, when two or three acrylic resin binders were used to compare the base metals of stainless steel, aluminum, and aluminum-coated steel sheets, excellent performance was obtained in common with aluminum-coated steel sheets. I discovered that.

(Example 1) Using Asahi Kasei's acrylic emulsion binder "Polydron E-300" (trade name), 100 parts by weight of this binder and Dainichiseika's Fe-M
25 parts by weight of an n-Cu oxide black binder "Dipyroxide Color #9550" (trade name) was dispersed and mixed using a ball mill to form a paint.

This paint is applied to pure aluminum plate, stainless steel (
SUS430), aluminum plated steel plate respectively
It was applied to a film thickness of about 4 Am and cured at room temperature. All of these films have a Q of 0.93 to 0. The absorption rate of the base is shown. The emissivity (measured with an emissivity meter) was 0.42 for pure aluminum, 0.48 for stainless steel, and 0.45 for aluminum plated steel plate. (Example 2) Kyowa Hakko ■'s dawn hardening type acrylic emulsion binder
20 parts by weight of "Hopsol YS-2 Paper" (trade name),
Sumitomo Chemical's water-soluble melamine resin "Sumimar 40W"
j (trade name), 25 parts by weight of butyl carbitol 3, 10 parts by weight of "Texanol" (trade name) by Eastman Chemical ■, and 4 parts by weight of the pigment of Example 1, and a ball mill. A paint was obtained by dispersion-mixing.

Approximately 4 mounds of this paint was applied to three types of boards in the same manner as in Example 1.
It was painted at a film thickness of 160 oo and competed for 30 minutes. All of these films showed an absorption rate of Q=0.91 to 0.93. Note that pure aluminum has an emissivity of 0.4.
5. Stainless steel showed 0.48, and aluminum plated steel plate showed 0.45. (Example 3) 5 parts by weight of Mitsubishi Rayon's thermosetting acrylic resin "Duracroso #5661" (trade name) and 1 part by weight of the above pigment.
The paint obtained by dispersing and mixing 5 parts by weight was diluted with a solvent and applied to three types of plates in the same manner as in Example 1 to a film thickness of about 4 m, and baked at 180q0 for 30 minutes.

All of these films have a Q of 0.93 to 0. The absorption rate is shown below. The emissivity of pure aluminum is 0.
0.43 with paper stainless steel plate with aluminum plated steel plate,
It showed 0.35. The following tests were conducted on the above system, and the results are shown in the table below.

1 Adhesion: Vertical taping test 2 Flexibility: IC rib x 1800 bending test 3 Eriksen: 5 side extrusion 4 Impact resistance: Typhon type, 1/2,
Drop a 500mm steel ball from a height of 2:1 5 Hardness: Pencil hardness 6 Boiling water resistance: Leave in boiling water for 10 hours 7 Salt spray: Leave 240b in continuous fog 8 Weather resistance: Sunshine type carbon arc Heat resistance reliability: After being left in a 200qo furnace for 50 hours, adhesion, selective absorption performance, and coating film performance test results show that boiling water resistance , aluminum-plated steel sheet, aluminum, and stainless steel, and this is thought to be related to the influence of silicone contained in the aluminum coating layer of the aluminum-plated steel sheet.

As mentioned above, the selective absorption surface of the present invention is inexpensive and is extremely superior to the painted absorption surface.Selective absorption surface Q:
0.93 to 0.94, 0.35, and the coating film is dense, has high adhesion to the substrate, and has high corrosion resistance, and has extremely large industrial merits. BRIEF DESCRIPTION OF THE DRAWINGS The drawing is a cross-sectional view of a selective absorption surface according to an embodiment of the invention.

A... Aluminum coated steel plate, B... Steel plate, C... Aluminum coating layer, D...
Coating film, 1... Satiro pigment, 2... Acrylic resin binder.

Claims (1)

[Scope of Claims] 1. An aluminum-coated steel plate is used as a substrate, and a coating is formed on the surface of the substrate by coating a paint containing a black pigment and an acrylic resin binder as main components to a thickness of 5 μm or less, and the above-mentioned black pigment As, Fe, Mn, Cu, Cr, C
A surface for selectively absorbing solar heat using one or more oxides/composite oxides selected from the group of Ni. 2. The solar heat selective absorption surface according to claim 1, which uses a thermosetting acrylic resin as the acrylic resin binder.