JPS624625B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a selective solar heat absorption surface in a solar heat collector or the like. Due to the energy situation in recent years, solar heat utilization technology has attracted attention, and it is already being put into practical use for household purposes such as hot water heating. Desirable properties for the surface of a heat collector that collects solar energy include the ability to absorb as much solar energy as possible, as well as to minimize the amount of radiant energy radiated from the surface that absorbs solar energy and whose temperature has increased (selective absorption). gender). Most of the radiant energy of sunlight passing through the atmosphere is at the short wavelength side of 0.2 to 2.5 μm, and on the other hand, that energy is absorbed as heat,
For example, the radiant energy radiated from a surface heated to 80 to 100°C is in the infrared region with a long wavelength of 2.5 μm or more. Therefore, by making use of this shift in the wavelengths of ingress and egress, ideal selective absorption can be achieved by making the absorption rate close to 1 below 2.5 μm and the emissivity close to 0 above 2.5 μm. It becomes a surface. In order to form a coating film on a metal surface using paint and make this coating film a surface that selectively absorbs solar heat, 2.5
The absorption rate can be relatively easily increased by using a black pigment that has excellent absorption of light at wavelengths below μm.
2.5 μm because it absorbs light of μm or more.
At the same time, the emissivity of light with wavelengths higher than that also increases. Therefore, the problem is how to lower the emissivity. The basic components of the coating film are resins and pigments, but since most resins strongly absorb light of 2.5 μm or more, that is, infrared rays, it is difficult to lower the emissivity. Regarding pigments, if inorganic pigments are used, this inorganic pigment does not absorb much infrared rays, so it is very advantageous in terms of emissivity. Therefore, if a coating film is formed with a relatively small amount of resin, it will be advantageous in terms of selective absorption, but the adhesion to the metal base and the adhesion between pigments will be poor, and therefore it will be very difficult to form a coating. This will result in a paint film with poor adhesion. In addition, when the ratio of resin and pigment is set within a range that maintains adhesion as a coating film to the base material, if the emissivity is to be lowered, the resin and pigment should be adjusted so that the infrared absorption is as low as possible. It is necessary to select the desired amount and to form the coating film as thinly as possible. In the case of this method, it is naturally assumed that the base metal is a metal surface with low emissivity. As the metal with low emissivity, aluminum, copper, stainless steel, etc. are most suitable. In reality,
If it is attempted to form a thin coating film on these metal surfaces on an industrial basis, there are many difficulties associated with controlling the film thickness. Ordinary paints use pigments with a particle size of 1.0 μm or more from the viewpoint of coloring power, hiding power, dispersibility, hue, etc., so if you want to form a continuous film, you will inevitably end up with a film thickness of 10 μm or more. I end up. It is extremely difficult to exhibit selective absorption ability with this film thickness. Further, carbon black has a very fine particle size, and a particle size of 0.01 μm is possible, but it is difficult to obtain selective absorption properties because of its poor infrared transparency as a pigment. Furthermore, when spray painting with regular paints, there is an optimal solids content range from the perspective of improving painting workability, and it is rare to paint with a low solids content of 20wt% or less, for example. . This is because when the viscosity is low, sagging occurs, secondary aggregation of the pigment occurs, and boiling occurs. In the present invention, Fe (iron),
Mn (manganese), Cu (copper), Cr (chromium), Co
1 selected from the (cobalt), Ni (nickel) group
More than one type of oxide or composite oxide is used. All of these materials have almost no infrared absorption, so they exhibit good sunlight absorption. for example,
CoO・Cr ₂ O ₃・MnO ₂・Fe ₂ O ₃ , Fe ₂ O ₃・MnO・
CuO, CuO, Cr ₂ O ₃ etc. are excellent. The particle size is important in order to exhibit stable hiding power for forming a thin film and at the same time to reduce scattering and absorption of infrared rays. Pigments with a particle size of 0.01-0.5 μm exhibit optimal properties. Hereinafter, the present invention will be explained based on examples. Examples (1) Using commercially available Fe ₂ O ₃ .MnO.CuO pigments, the particle sizes of the pigments were classified and tested as 6 types. First, we made a prototype paint using thermosetting acrylic resin containing 52% by weight of each pigment based on the solid content of the resin, and sprayed this paint onto a stainless steel substrate to a film thickness of approximately 3 μm. Painted at 200℃
Baked for 10 minutes. The relationship between pigment particle size and selective absorption is shown in the table below.

[Table] As is clear from the table above, the pigment particle size is
A range of 0.01 to 0.5 μm is good. This is related to the light scattering of particles, and the range of 0.01 to 0.5 μm is related to selective absorption, which means that light with long wavelengths of 2.0 μm or more is not scattered much, and light with wavelengths of 2.0 μm or less is well scattered. It is presumed that this is to show its properties. Furthermore, it is considered that the reactivity of the particles with smaller diameters became stronger and secondary aggregation occurred. Furthermore, as the resin for forming the selective solar heat absorption film as a coating film, acrylic resins and silicone resins are preferable because they have relatively low absorption in the infrared region. The method for forming the selective absorption film (coating film) will be described below. Using acrylic resin or silicone resin,
50 to 60wt% of the resin solid content (weight)
An inorganic black pigment, i.e. Fe, having a weight of
One or more oxides or composite oxides selected from the group of Mn, Cu, Cr, Co, and Ni, with a particle size of 0.01 to
Add and mix 0.5 μm and disperse well. In order to perform this dispersion well, it is desirable to dilute with a solvent so that the solid content concentration during dispersion is 25 to 50 wt%. Furthermore, when painting by spray painting, the total solid content (wt%) of resin and pigment is 10
Dilute with a solvent and paint to a concentration of ~17wt%. When these resins and pigment systems are used and the total solid content (wt%) in the paint is 10 to 17 wt%, the specific gravity of the paint is approximately 1. Further, since the specific gravity of these dry coating films is approximately 1, the ratio of the dry film thickness to the wet film thickness matches the ratio of the total solid content to the total amount of paint. 10 times for 10wt%, about 5.9 for 17wt%
It will be doubled. The paint viscosity is approximately 1 poise at 12.5 wt% (that is, around 8 times as much). This is because the particle size of the pigment is fine, so the paint viscosity is lower than the normal particle size (0.5
This is because it does not decrease as much as in the case of pigments with a diameter of ~1.5 μm). In addition, in order to obtain a dry film thickness of 2 to 5 μm,
The coating may be applied to obtain a wet film thickness of 20 to 50 μm at a total solids content of 10 wt%. Also, at 17wt%,
It is sufficient to aim for a wet film thickness of approximately 12 to 30 μm. Furthermore, if the total solids content is less than 10wt%, the wet coating will tend to float or sag, making it difficult to handle. In the above case, it becomes difficult to stably obtain a film thickness of 2 to 5 μm. In this case, the total solids content is
A range of 12.5-15wt% is best. If a coating film is formed by the method of the present invention as described above, the absorption rate α will depend on the combination with the underlying metal.
= 0.93 to 0.95, and a coating film with emissivity ε = 0.35 to 0.50 can be stably obtained. Furthermore, the method of the present invention is extremely practical because it can be applied directly using painting equipment such as air spray and electrostatic painting that has been conventionally used in industrial production.

Claims (1)

[Claims] 1 One or more resins selected from the group of acrylic resins and silicone resins and one or more oxides or composite oxides selected from the group of iron, manganese, copper, chromium, cobalt, and nickel, and the particle size is 0.01
A paint whose main solid content is an inorganic black pigment of ~0.5 μm is used, and the total solid content of the paint is
A solar heat selective absorption surface characterized by diluting the paint with a solvent to a range of 10wt% to 17wt%, applying the diluted paint to the metal surface to be treated, and then heating to form a 2.5μm coating film. manufacturing method.