JPS623184B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is applied to the surface of a solar heat collector, mainly by coating the surface of a metal heat collector.
The present invention relates to a coating composition for imparting selective absorption of solar heat to its surface.

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 characteristics for the surface of a solar collector that collects solar thermal energy are those that absorb as much solar energy as possible and minimize the amount of radiant energy that is dissipated from the surface whose temperature has increased due to the absorbed solar energy (selection). absorbency).

In general, most of the radiant energy of sunlight that passes through the atmosphere is on the short wavelength side of 0.2 to 2.5 μm, and on the other hand, that energy is absorbed as heat and released from surfaces heated to 80 to 1000 degrees Celsius. The radiant energy dissipated is in the infrared region with long wavelengths of 2.5 μm or more. Taking advantage of this wavelength shift,
Below 2.5 μm, the closer the absorption rate is to 1, the more
It becomes an ideal selective absorption surface.

In addition, in order to form a coating film on a metal surface using paint to make it a surface that selectively absorbs solar heat, it is possible to use a black pigment that has excellent absorption of light with a wavelength of 2.5 μm or less. Although the absorption rate can be increased relatively easily, since a typical coating film also absorbs light with a wavelength of 2.5 μm or more, the emissivity of light with a wavelength of 2.5 μm or more also increases. Therefore, the problem is how to lower the emissivity.

The general idea to achieve this is to make the coating film as thin as possible, to a few μm or less, since metal surfaces reflect infrared rays well.
There is a method to reduce the absorption of infrared rays of m or more, that is, to keep the emissivity low.

In this method, selective absorption can be achieved by selecting the paint components to a certain extent, but the adhesion of the paint film to the metal is poor, or
It has not yet been put to practical use because it is extremely difficult to apply a thin coating film in an industrially stable manner.

The present invention provides a coating composition for selectively absorbing solar heat that achieves both selective absorption and physical properties of the coating film in a well-balanced manner and is also excellent in coating workability.

The surface to be coated to which the coating composition of the present invention is applied is advantageously a metal surface with a low emissivity, such as copper, aluminum, stainless steel, etc.

The paint of the present invention is made of iron, manganese, copper, nickel,
It can be obtained by mixing a pigment supporting one or more oxides or composite oxides selected from the group of chromium and cobalt and a transparent resin with a solvent, and then dispersing the mixture using a dispersing machine such as a ball mill or an attritor. Furthermore, if necessary, auxiliary agents such as surfactants and fillers can be added to this paint, and about 10% of the transparent resin can also be added to modify the resin. can.

As already mentioned, the properties required of the paint of the present invention include high absorption of sunlight even at the thinnest film thickness, and transparency as much as possible to infrared rays of 2.5 μm or more. Since the binder is an organic resin, absorption of infrared rays due to molecular rotation and vibration is unavoidable. Among the organic resins that can be used as binders in paints,
Examples of transparent resins that can be used in coatings for solar heat absorption include acrylic resins, silicone resins, and fluorine resins. Resins are classified into different types depending on the heat resistance required for use as a solar heat collector, but acrylic resins are considered to be sufficient for domestic hot water supply.

In addition, preferable pigments for selective absorption include iron,
Examples include one or more oxides or composite oxides selected from the group of manganese, copper, nickel, chromium, and cobalt. This is because there is little absorption of infrared rays and good absorption of sunlight, but there is a relationship between film thickness, absorption rate, and emissivity.
As the film thickness increases, both absorption rate and emissivity increase, and as the film thickness decreases, both absorption rate and emissivity decrease. Therefore, there is an optimum film thickness.
As long as this type of inorganic pigment is used, there are limits to its performance, with an absorption rate α of 0.93 to 0.94 and an emissivity ε.
The limit was 0.35 to 0.45 (the range varies depending on the base material).

The present invention focuses on pigments, which play a central role in this effect, from the viewpoint of increasing the absorption rate even with a low film thickness.

Next, the method for producing the pigment used in the present invention will be described in detail. Silica, alumina, titanium dioxide, talc,
Fine particles of inorganic compounds such as kaolin and calcium carbonate are used. Using these inorganic compounds as a carrier,
On this support, one or more oxides or composite oxides selected from the group of iron, manganese, copper, nickel, chromium, and cobalt are supported. The method is
The above-mentioned inorganic compound is immersed in an aqueous solution of nitrates of iron, manganese, copper, nickel, chromium, and cobalt, and is impregnated and dried. After such manipulation, it is placed in ammonia water. As a result, the metal nitrate becomes a hydroxide. After washing with water and drying, it is fired in air at approximately 500°C. In this way, a pigment is prepared in which one or more oxides or composite oxides selected from the group of iron, manganese, copper, nickel, chromium, and cobalt are supported on an inorganic compound.

The effects will be described below, focusing on examples.

Example Fine powder of γ-alumina was used as the inorganic compound fine particles. Classify this to 0.2μ ~ 0.5μ, 0.1
It was divided into three types: ~0.2 μm and 0.1 μm or less. After drying this at 100°C for 1 hour, it was immersed in an aqueous solution containing 1N manganese nitrate and 1N ferric nitrate all day and night, and then dried at 100°C for 2 hours. This was transferred onto a Bronner funnel, washed with 2N ammonia water, washed with water until there was no trace of ammonia, dried at 100°C for 1 hour, and then heated to 500°C.
It was baked for 2 hours. Pigments prepared in this way
25 parts by weight, Mitsubishi Rayon as acrylic resin
100 parts by weight of “Dianal SE-5661” manufactured by Co., Ltd.
100 parts by weight of Solbetuso #100 as a solvent, n-
58 parts by weight of butanol and 42 parts by weight of xylene were added and mixed, and dispersed for 6 hours using an attritor to form a paint. The paint prepared in this way was diluted 2.5 times with a solvent and painted on a pure aluminum plate to a film thickness of 1 μm, and its absorption rate α and emissivity ε were evaluated. As a result, 0.2μ ~ 0.5
For initial particle size of μ, α=0.85, ε=0.35, 0.1~
For particle size of 0.2μm, α=0.95, ε=0.25, 0.1
In the case of particle sizes of μm or less, results of α=0.95 and ε=0.24 were obtained.

The reason why a high absorption rate of α=0.95 was obtained when the particle size was 0.2 μm or less was due to the formation of a stable composite oxide of iron and manganese on the surface of the central core containing the inorganic compound particles. is for light absorption,
It is thought that it exerts an effect like an interference film and improves the absorption rate.

There was a concern that such a surface structure would be destroyed during the dispersion operation for making it into a paint, but such an effect did not actually occur.

As described above, the coating composition of the present invention has a particle size of
A pigment supporting one or more oxides or composite oxides selected from the group of iron, manganese, copper, nickel, chromium, and cobalt and a transparent resin are mixed with a solvent on inorganic compound fine powder of 0.2 μm or less. Therefore, by coating and baking this coating composition on a metal surface with a low emissivity, it is possible to obtain an excellent selective absorption surface of solar heat at a very economical and low cost.

Claims (1)

[Claims] 1. One or more oxides or composite oxides selected from the group of iron, manganese, copper, nickel, chromium, and cobalt are supported on inorganic compound fine powder with a particle size of 0.2 μm or less. A paint composition for selectively absorbing solar heat, which is made by mixing a pigment and a transparent resin with a solvent. 2. The coating composition for selectively absorbing solar heat according to claim 1, wherein the transparent resin is one or more selected from the group of acrylic resins, silicone resins, and fluororesins.