SOLAR HEAT SELECTIVE ABSORBING MATERIAL AND ITS MANUFACTURING METHOD

Abstract: An object of this invention is to provide a solar heat selective absorbing material of high performance which is prepared by using a diversity substrate by simple manufactur­ ing methods. The construction of the solar heat selective absorbing material is such that a carbide of a transition metal belonging to the IV group of periodic table or a mixed powder of the carbide and the aluminum is applied directly or by means of a binder on the surface of the substrate to form a film. This solar heat selective absorbing material is manufactured by a method of forming a film of material, for example, ZrC on the surface of the substrate by high fre­ quency sputtering or a method of mixing a mixed powder of the ZrC and Al with a resin binder and coating or printing the mixed material on the surface of the substrate.

Description: BACKGROUND OF THE INVENTION This invention relates to a solar heat selective absorbing material that absorbs solar energy efficiently and having a minimum loss by thermal radiation, and more particularly to a solar heat selective absorbing material prepared by forming a film of a material whose essential component belongs to a carbide of a transition metal belonging to the IV group of periodic table on the surface of a substrate, and to a method of manufacturing said material. Recently, techniques of utilizing solar energy have attracted the attention of those in the art and developments of thermoelectric power generation system using selective absorption films are in progress. The radiation spectrum of the sun is such that its peak is present in the vicinity of 0.5 µm, and over 95% of total energy is contained between 0.3 to 2.0 µm. For this reason, a material that selectively absorbs solar heat must have high absorption in a wavelength region of 0.3 - 2.0 µm, and also, rate of radiation of heat is small in an infrared region of more than 2.0 µm. Heretofore, a material of the multifilm group such as a metal-dielectric multilayer film or semiconductor reflection preventive film has been developed as a solar heat selective absorbing surface. The solar heat selective absorbing surface of the multifilm group is involved with a complicated process of forming the film so that a method of using a single material is effective for the simple formation of the film. A single material having excellent heat resistance, carbon, has heretofore been known, and also, recently, carbides of metals and the like which are advantageous in view of their heat resistance have been employed. However, these materials have problems that cannot be sufficiently satisfied with respect to the performances. So far the solar heat selective absorbing material having satisfactory performance, prepared by a simple method using the conventional film material, has not been developed. SUMMARY OF THE INVENTION An object of this invention is to provide a solar heat selective absorbing material using a diversity substrate by a simple manufacturing method. Another object of this invention is to provide a solar heat selective absorbing performance to interior goods such as curtain material and the like and sport and leisure clothing. These objects are achieved by providing a material constructed of a solar heat selective absorbing material which is prepared by applying a carbide of a transition metal belonging to the IV group of the periodic table or a mixed powder of the said carbide and aluminum directly or by means of a binder onto the surface of the substrate to form a film. The carbide of the transition metal belonging to the IV group of the periodic table such as the TiC, ZrC, HfC and a mixture of said carbide and aluminum has qualities of absorbing the photoenergy of more than about 0.6 eV, and reflecting the low energy light, and works effectively for the selective absorption of the solar energy whose wavelength is 0.3 - 2.0 µm. BRIEF DESCRIPTION OF THE DRAWINGS The drawings show a thermo pattern by a thermoviewer camera which is measured for embodiment of this invention. Among the drawings, FIG. 1 shows a thermo pattern in the case of irradiation of the film formed surface of the solar heat selective absorbing material with an illuminating lamp of 500 W at a distance of 1.5 meters which is prepared by coating a fine powder of the ZrC on the substrate of Nylon fiber cloth by means of a polyurethane resin binder; FIG. 2 shows a thermo pattern of the surface (opposite surface of the film formation) of an untreated material in the same condition; and FIG. 3 shows a thermo pattern in the case of irradiation of the film formed surface of the solar heat selective absorbing material with an illuminating lamp of 500 W at a distance of 1.3 meters which is prepared by coating a mixed powder of ZrC and Al on the surface of a substrate of Nylon fiber cloth by means of a polyurethane resin binder. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The solar heat selective absorbing material according to this invention is characterized in the construction of the material prepared by forming a film of a carbide of a transition metal belonging to the IV group of the periodic table or a mixed powder of the said carbide and aluminum on the surface of the substrate directly or by means of a binder. As the carbide of the transition metal belonging to the IV group of the periodic table, the TiC, ZrC, HfC are used but among these materials, the ZrC has the most effective solar heat selective absorbing property so that the ZrC is effectively used. The foregoing carbide is used in the fine powder condition as the single material or is used in the mixed powder condition in which the metal aluminum is blended as the second component. These components are preferably in as fine a powder as possible and it is desirably so adjusted that the particle diameter of the powder is less than 15 µm. In the case where the carbide is mixed with aluminum, the mixing ratio of the aluminum to carbide is set at 1 : 0.3 - 1.0, and when the ratio is out of this range, the degree of improvement of the solar heat selective absorbing property deteriorates. As the substrates, woven fabric produced from organic material such as natural fiber, synthetic fiber or synthetic resin, or inorganic materials such as carbon or ceramics, or metallic materials, and clothing material such as knitted goods and non-woven fabric, are enumerated. On the surfaces of these substrates, films consisting of single carbide chosen from TiC, ZrC and HfC, or compounds of the carbide and aluminum are formed, the formation of the films is carried out directly or by means of the binder as will be desired in the following. The direct method is a method of forming the film by the high frequency chemical sputtering, whereby a thin film of the TiC, ZrC or HfC is formed on the surface of the substrate by using the high frequency sputtering device and feeding the Ar-CH₄ mixed gases into the system using Ti, Zr or Hf as the target. A method of interposing the binder is performed by mixing uniformly and dispersing a fine powder of the TiC, ZrC, HfC or a mixed powder of the Al with said fine powder in the binder, for example, polyurethane, polyacrylate, and other resins, and coating or printing the mixture on the surface of the substrate, and fixing the film formed thereof. The film formation using this binder is not subjected to limitations such as the size of the substrate, shape and heat resistance and the like as compared with the direct method by the sputtering and, moreover, it has the advantage of making continuous film formation possible. For this reason, for example, when a thin woven fabric that allows the transmission of the visible light is used as the substrate, and the film is formed on the reverse surface by using the foregoing method, the film provides the feature of solar heat selective absorption without changing the condition of the surface material. Accordingly, the resulting substrates are useful for ski wear, winter clothes which require heat insulation and waterproofing or interior goods such as curtains and the like. This invention will be described in the following by referring to embodiments but the scope of this invention is not limited to them. EXAMPLE 1 20 weight parts of the fine powder of ZrC were mixed to 100 weight parts of the polyurethane resin binder, and the mixture was mixed uniformly by a stirrer. This dispersion solution was coated on one surface of a cloth substrate of Nylon fiber, and then, the binder component was hardened. For comparison purpose, a film of only polyurethane resin binder was also formed (blank material). The ZrC film material and the blank material which were formed with the films by the foregoing method were irradiated with the illuminating lamp of 500 W for photography at a distance of 1.5 meters, and the heat distribution condition of the surface was photographed by the thermoviewer camera in about 3 minutes. FIG. 1 shows the thermo pattern in case the film formed surface was irradiated, and also, FIG. 2 shows the thermo pattern in case the surface of an untreated material (opposite surface of the film formed surface). In FIG. 1 and FIG. 2, (1) denotes the ZrC film material and (2) denotes the blank material. From the results of FIG. 1 and FIG. 2, the thermal absorption of the ZrC film is found to be extremely good in comparison with the blank material. EXAMPLE 2 5 parts of the ZrC powder, of particle diameter less than 3 µm, was blended with 3 parts of the aluminum powder, of particle diameter was less than 1 µm, and 20 weight parts of the mixed powder was mixed to 100 weight parts of the polyurethane resin binder, and the mixture was uniformly mixed in the stirrer. The dispersion solution was coated on one surface of the cloth substrate of the Nylon fiber, and the binder component was hardened. For comparison, the film formation was carried out only with the polyurethane resin binder not mixed with the ZrC-Al component (blank material). The film formed ZrC + Al film material and the blank material were irradiated with the illuminating lamp of 500 W for photography at a distance of 1.3 meters, and the thermal distribution condition of the surface was photographed by the thermoviewer camera in about 3 minutes. FIG. 3 shows the thermo pattern of the irradiated film. In FIG. 3, (1) denotes the ZrC + Al film material, and (2) denotes the blank material. From the result of FIG. 3, the heat absorption of the ZrC + Al film material is recognized to be much better than that of the blank material.

Claims: A solar heat selective absorbing material in which a film of carbide of a transition metal belonging to the IV group of the periodic table or a mixed powder of the said carbide and the aluminum is coated on the surface of a substrate directly or by means of a binder. A solar heat selective absorbing material according to claim 1 in which the carbide of the transition metal belonging to the IV group of the periodic table is ZrC. A solar heat selective absorbing material according to claim 1 in which the substrate is cloth such as woven fabric, knitted goods or non-woven fabric. A method of manufacturing a solar heat selective absorbing material comprising forming a film of carbide of a transition metal belonging to the IV group of the periodic table on the surface of the substrate by a high frequency chemical sputtering. A method of manufacturing a solar heat selective absorbing material comprising coating or printing carbide powder of a transition metal belonging to the IV group of the periodic table or a mixed material prepared by mixing a mixed powder of the said carbide and aluminum in a resin binder on the surface of the substrate, and fixing the film formed thereof. A method of manufacturing a solar heat selective absorbing material according to claim 5 in which a mixing ratio of the aluminum powder against the carbide powder of the transition metal belonging to the IV group of the periodic table is 1 : 0.3 - 1.0. A method of manufacturing a solar heat selective absorbing material according to claim 5 in which the mixed powder whose particle diameter is less than 15 µm which is prepared by blending the carbide powder of the transition metal belonging to the IV group of the periodic table and the aluminum powder is mixed with the resin binder.

Inventors: FUJIMOTO, MASANORI, KAGECHI, SHUNSAKU
Applicants: DESCENTE LTD.
Application year: 1987
Main classification: D06Q1
IPC codes: D06M11, D06Q1, F24J2