CA1187638A - Paint for applying spectral-selective coatings and process for the preparation thereof, solar heat absorbing device and solar collector containing such a device - Google Patents
Paint for applying spectral-selective coatings and process for the preparation thereof, solar heat absorbing device and solar collector containing such a deviceInfo
- Publication number
- CA1187638A CA1187638A CA000371182A CA371182A CA1187638A CA 1187638 A CA1187638 A CA 1187638A CA 000371182 A CA000371182 A CA 000371182A CA 371182 A CA371182 A CA 371182A CA 1187638 A CA1187638 A CA 1187638A
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- Prior art keywords
- pigment
- oxide
- resins
- copper
- sulfide
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
- C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
- C09D5/32—Radiation-absorbing paints
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24S—SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
- F24S70/00—Details of absorbing elements
- F24S70/30—Auxiliary coatings, e.g. anti-reflective coatings
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/40—Solar thermal energy, e.g. solar towers
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Sustainable Development (AREA)
- Sustainable Energy (AREA)
- Thermal Sciences (AREA)
- Physics & Mathematics (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Wood Science & Technology (AREA)
- Organic Chemistry (AREA)
- Paints Or Removers (AREA)
Abstract
Abstract of the Disclosure An inexpensive and easily used paint for applying spectral-selective coatings consists of spectral-selective pigment, reflective metal particles, binder and, if desired, other components with or without a liquid vehicle, the spectral-selective pigment being combined with a binder and, if desired, a liquid vehicle, and the reflective metal particles being added to the resulting pigment dispersion.
A coating of the paint on a base provides a solar heat absorbing device for use in a solar collector.
A coating of the paint on a base provides a solar heat absorbing device for use in a solar collector.
Description
~7631 3 Paint for applying spectral-selective coatings and process for the preparation thereof, solar heat absorbing device and solar collector containing such a devlce.
Background of the Invention.
The invention relates to a paint for applying spectral-selective coatings, to a process for the preparation of such a paint, to a so-lar heat absorbing device containing such a spectral-selective coat-ing and to a solar collector containing such a device.
From the book of F.Daniels "Dlrect use of the sun's energy",Yale Universlty Press9 New Haven, London, 196~, chapter 12, pages 209-223 it ls known to manufacture solar heat absorbing devices by applying a layer of a black semiconductor havlng a thlckness of 0.1-1/um upon a plate having a reflecting metal surface. This black semiconductor layer absorbs solar light (wave length 0.3-2.5/um) almost completely, but does not absorb or emit much heat radiation (wave length ,~ 2.5/um). The reflecting metal layer does not emit heat radiation either.Thus the temperature of the plate increases and ]5 the plate is suitable to be incorporated into a solar collector.
t ~ According to an artlcle of Henry Y.B.Mar et al. ln Thin Solid Films 39 (1976), pages 95 - 103~black coatings can be applied upon metal surfaces by means of electroplating or as a paint con~aining the desired pigment together with a polymeric blnder in an organic solvent, which solvent is removed after the application of the paint by mearls of drying and, if necessary, baking, so that a layer of black pigment in the binder remains on the metal. The electroplated coatlngs show the best optical performance, but the application of pigments as a paint is much cheaper. N
According to the U.S.Patent ~ee~ }~L~ ~,011,190 reflectlve metal particles are coated with a layer of selectlve black material, whereafter the coated particles are mixed with a liquid vehicle and an organic polymer to form a paint, which can be brushed or sprayed onto a substrate, which can be metal, wood, masonry or other desired material. The particles of reflective metal are usually available in the form of flakes, powder or dust. The reflective metal particles are coated with the layer of black selective material for instance by electroless chemical deposition of an other metal and o~ ~ ation or ` ~
~1 8~;3~3 sulfidation of the metal layer deposited in this way.
According to the U.S. Patent No. 4,082,~13 a device for absorption oE selected radiation wavelengths, such as solar radiation, is manufactureA by applying upon a substrate of metal or glass a layer of a mixture of metal particles and a dielectric material, the concentration of the metal in this :La~er varying from one boundary surface to the opposite boundary surface gradually from 0~ to 100%. The dielectric material is in general transparent to radiation, although it may absorb some radiation, whereas the`metal absorbs and reflects radiation. The heat built up in the layer as radia-tion is absorbed is withdrawn by means of a heat transfer agent flowing through a conduit in thermal contact with the layer or with the substrate on which the layer is deposited.
According to the published Netherlands patent appli-cation No. 7400292 a coating composition is prepared, which provides a metallic appearance when applied to a substrate, by mixing a finely divided metal powder and pulverulent graphite with an organic polymeric binder. The coated sub-strate reflects radiation and does not absorb it. If desired, other additives, such as asbestos, bentonite, chalk or pigments may be incorporated in the composition but only in very small amounts in order to avoid deterioration of the metallic appearance.
From the published German patent application No. 2,056,211 a heat reflecting paint is known, which consists of metal particles reflecting radiation of a wavelength of 3-20/um and an organic binder absorbing radiation of a wave-length of 3-20/um only slightly.
Summary of the Invention It has now been found that a very cheap and easily handable paint for applying spectral-selective coatings consists of spectral-selective piyment, reflective metal particles and binder and, if desired, other components with or without a liquid vehicle. Thus, reflective metal particles coated with a black pigment layer as described in the U.S.
3~
Patent No. 4,011,190 are not presen~ in this paint. The advantage thereof is that the separate step of coating metal particles with a very thin film of spectral-selective material, which step is the most difficult step in the preparation of the pain-t from a technological point of view, has become superEluous The pigmentr the metal particles and the binders, whlch are incorporated in the apints according to the inven-tion, may be conventional commercial products, which can be mixed together in a simple way to form a paint. Thus, the preparation and the use of such a paint has become possible in areas where the use of advanced technologies is not possible.
In accordance with one aspect of the present invention there is provided a paint suitable for spectral-selective coatings which comprises spectral-selective pigment selected from the group consisting of copper oxide-chromium oxide, iron oxide-manganese oxide-copper oxide, molybdenum oxide, lead oxidel copper sulfide, chromium sulfide, iron sulfide, manganese sulfide, molybdenum sulfide, lead sulfide, blacks, organic dyes and pigments, and mixtures of one or more thereof, uncoated particles of reflective metal selected from the group consisting of aluminum, nickel, copper, zinc, alloys thereof, and stainless steel, and binder selected from the group consisting of polyethylene, polypropylene, ethylene-propylene copolymers, ethylene-propylene-diene terpolymers, polysiloxane resins, alkyd resins, polyester resins, styrene-butadiene-copolymers, polyacrylates, vinyl resins, chlorinated rubber, phenolic resins, amino resins, epoxy resins, polyurethanes, elastomeric fluorohydrocarbons, siloxane-modified alkyd resins, siloxane-modified polyester resins, inorganic silicates, and organic silicic acid esters, the pigments having a pigment volume concentration of from about 1% to about 60%, and the metal particles having a pigment volume concentration of from about 5% to about 95%.
In accordance with a further aspect of the present invention there is provided a process for preparing a paint suitable for spectral-selective coatings which comprises combining a spectral-selective pigment selected from the ~.a~S7~3~
-3a-group consisting of copper oxide-chromium oxide, iron oxide-manganese oxide-copper oxide, molybdenumoxide, lead oxide copper sulfide, chromium sulfide, iron sulfide, manganese sulfide, molybdenum sulfide, lead sulfide, blacks, organic d~es and pigments, and mixtures of one or more thereof, with a binder selected from the group consisting of polyethylene, pol~prop~lene, ethylene-propylene copolymers, ethylene-propylene-diene terpolymers, polysiloxane resins, alkyd resins, polyester resins, styrene-butadiene-copolymers, polyacrylates, vinyl resins, chlorinated rubbers, phenolic resins, amino resins, epoxy resins, polyurethanes, elastomeric fluorohydrocarbons, siloxane-modified alkyd resins, siloxane-modified polyester resins, inorganic silicates, and organic silicic acid esters, and adding to the resulting pigment dispersion uncoated particles of reflective metal selected from the group consisting of aluminum, nickel, copper, zinc alloys thereoE, and stainless steel, the pigment having a pigment volume concentration of from about 1% to about 60%, and the metal particles having a pigment volume concentration of from about 5% to about 95%.
The results obtained with the paints according to the invention are about the same as the results obtained with the paints according to the U.S. Patent No. 4,011,190. For instance paints have been prepared, in which the pigment volume concentration of metal flakes was 20% and of black pigment was 10% or 20~ respectively, this concentration being based on the total content of non-volatile components of the pigment. Substrates coated with paints prepared in this way showed an absorption coefficient of solar light (as) between 30 about 0.84 and about 0.90 and an emittance coefficient (~) between about 0.35 and about 0.50 Detailed description of the invention . .
In the paint according to the invention as spectral-selective pigments in most cases pigments l~aving a high absorption for solar radiation are used. Examples thereof are among others conventional black pigments, such as copper oxide-chromium oxide, iron oxide-manganese oxide-~r ~8763~
- 3b -copper oxide, molybdenum oxide and lead oxide as well as the sulfides of the metals present in the oxides, especially lead sulfide. Also certain blacks, organic dyes and pi~ments are suitable, mixtures of one or more of these substances being also useful.
Examples of the metals in -the reflective metal particles are e.g. aluminium, nickel, copper and zinc or alloys of these metals, especially of copper and zinc, and also stainless steel. In many cases the metal particles are used as flakes. Especially flakes of aluminium, copper or copper-zinc alloys are preferred, because they vield excellent results and moreover are not expensive and avail-able as commercial products. When drying and/or baking the paint the 1akes appear to orient parallel to the surface of the substrate.
The binders, which may be used in the paints accordin~ to the invention, can be binders conven-tional for this purpose. Examples ~3 ~.
thereof are e.g. polyethylene, polypropylene, ethylene-propylene co-polymers, ethylene-propylene-diene terpolymers, polysiloxane resins, such as methylphenylpolysiloxane polymer, alkyd resins, polyester re-SillS, styrene-butadiene-copolymers, polyacrylates, vinyl resins, chlorinated ruhber, phenolic resins, amino resins, epoxy resinsl po lyuretllanes, elastomeric fluorohydrocarbons, siloxane-modified alkyd reslns or polyester resins, inorganic silicates and organic silicic acid esters.
Polysiloxane resins, siloxane-modified alkyd resins and polyes-ter resins as well as fluoro hydrocarbonelastomers have the advantagethat they are resistant to high temperatures and weathering.
In the paint according to the invention also other components may be present, such as auxiliary agents, e.g. disperslng agents, wetting agents, thickening agents, siccatives, antiskinning agents and flux agents.
When a liquid vehicle is used in the paint, it consists e.g. of an organic solvent or water. As or~anic solvents aliphatic, cycloali-phatic and aromatic hydrocarbons and chlorinated hydrocarbons, alco-hols, ketones and esters are suitable. In case of the use of aqueous binder dispersions water is employed as a liquid vehicle. These binder dispersions often contain emulsifying agents or wetting agents and other auxiliary agents.
When using a binder having a sufficiently low viscosity the paint may contain no liquid vehicle at all or only a small amount of vehicle.
The concentration of the spectral-selective pigment and the re-flective metal particles in the paint according to the invention is expressed in the pigment volume concentration (pvc) normally used in the paint industry, which pvc is based on the total content of non-f volatile components. The pvc of the spectral-selective pigment i5 in general from about 1% to about 60~, and preferably from about 10% to about 30~. The pvc of the reflective metal particles is in general from about 5~ to about 95~ and preferably from about 10% to about 30~.
The preparation of a paint according to the invention may take place in a conventional way. By way of example the spectral-selective pigment may be dispersed in such a way in a portion of the binder or of the binder solution, that the greatest particles are smaller than e.g. about 10 /um. To the resulting dispersion first the remaining amount of binder or binder solution is added under agitation and thereafter the reflective metal particles are added as such or in the form of a paster In some cases the metal particles or paste are pre-wettecl with an amount of solvent to facilitate the incorporation thereoE.
The paint according to the invention is applied on a substrate ln a conventlonal way and subsequently dried and, if desired, baked.
As a substrate for the paint metal, wood, masonry,plastics or any other material may be used. If desired, first a layer is applied on the substrate, which effects protection against corrosion and/or a better adhesion of the spectral selective-paint coating. This is es-pecially desirable if the substrate is formed by a metal or a plastic. Upon this first layer the paint of the invention is applied.
The thickness of the applied paint coating may vary within broad limits and is e.g. after drying about 5 - 100/um and particularly about 20 - 50 /um.
Substrates with spectral-selective coatings on the base of the paint according to the invention are very suitable to be used in all kind of types of solar collectors.
From experiments of the coated substrates it has appeared, that the coatings possess an excellent durability upon heating at 200C
for 14 days, especially when polysiloxane resins and siloxane-modi-fied alkyd resins and polyester resins are used. It has also appearedthat with experiments in an atlas weatherometer after 10 ~ no re-duction of the durability of the coating could be determined. These experiments have been carried out without a glass plate retaining ul-traviolet light, which glass plate in general will be present in solar collectors, in which the ccated substrates are used.
The following examples illustrate the invention without limiting it. The compositions described in these examples were prepared in the way as described in the above.
Example I.
A paint of the following composition was prepared:
component weight %
soja alkyd resin 20.09 ~l~763~3 pigment Ferro Black F 6331a) 12.90 Cu/Zn flakes 30.28 white spirit 34.55 acetone 0.22 S nentone 34 b) 0.37 Pb naphtenate, 32% Pb0.29 Co nnphtenate, 10% Co0.12 Ca naphtenate, 4% Ca1.18 100 . 00 .
The pvc of the pigment was about 10%, the pvc of the Cu/Zn flakes was about 20%. The paint was applied to an aluminium plate with the aid of a doctor's blade. The thickness of the layer after drying was about 30 - 40/um~ After 14 days of drying were measured: ~ s =
0.88 and ~ =
Example II.
A paint of the following composition was prepared:
component weight %
20 styrene-butadiene-copolymer 10.30 chlorinated paraffin1.14 pigment Ferro ~lack F 6331 a) 17.32 aluminium flakes 9.73 xylene 55.28 25 solvent in aluminium paste 5.24 polysiloxane oil O.Ol Coloral F c) 0.98 100 . 00 The pvc of the pigment was about 20%, the pvc of the aluminium was also about 20%.
The paint was applied on an aluminium plate with the aid of a doctor's blade. The thickness of the layer after drying was about 30 to 40 jum. After 14 days drying were measured:~s = 0.90 en ~ -0.44.
Example III.
A paint of the following composition was prepared:
component weight %
. . _ ~7~
siloxane modified polyester resin 19.75 plgment Ferro Black F 6331 a) 23.03 aluminium flakes 19.36 ethylglycolacetate 13.16 5 xylene 15.92 solvent in aluminium paste 8.30 Bentone 38 b) 0.26 Dispersing agent 0.22 100 . 00 .
The pvc of the pigment was about 16%, the pvc of the aluminium was about 24%.
The paint was applied on an aluminium plate with the aid of a doctor's blade. The layer was predried for 30 minutes at 20C and subsequently baked for 60 minutes at 200C. The thickness of the re-sulting coating was about 40 - 50/um. Thereafter were measured:
s = 0-84 and ~ = 0.41.
a) iron oxide-manganese oxide-copper oxide plgment, commercial pro-duct of Ferro Holland b) bentonite modified with quaternary ammonium compounds c) modified so~a lecithine.
Background of the Invention.
The invention relates to a paint for applying spectral-selective coatings, to a process for the preparation of such a paint, to a so-lar heat absorbing device containing such a spectral-selective coat-ing and to a solar collector containing such a device.
From the book of F.Daniels "Dlrect use of the sun's energy",Yale Universlty Press9 New Haven, London, 196~, chapter 12, pages 209-223 it ls known to manufacture solar heat absorbing devices by applying a layer of a black semiconductor havlng a thlckness of 0.1-1/um upon a plate having a reflecting metal surface. This black semiconductor layer absorbs solar light (wave length 0.3-2.5/um) almost completely, but does not absorb or emit much heat radiation (wave length ,~ 2.5/um). The reflecting metal layer does not emit heat radiation either.Thus the temperature of the plate increases and ]5 the plate is suitable to be incorporated into a solar collector.
t ~ According to an artlcle of Henry Y.B.Mar et al. ln Thin Solid Films 39 (1976), pages 95 - 103~black coatings can be applied upon metal surfaces by means of electroplating or as a paint con~aining the desired pigment together with a polymeric blnder in an organic solvent, which solvent is removed after the application of the paint by mearls of drying and, if necessary, baking, so that a layer of black pigment in the binder remains on the metal. The electroplated coatlngs show the best optical performance, but the application of pigments as a paint is much cheaper. N
According to the U.S.Patent ~ee~ }~L~ ~,011,190 reflectlve metal particles are coated with a layer of selectlve black material, whereafter the coated particles are mixed with a liquid vehicle and an organic polymer to form a paint, which can be brushed or sprayed onto a substrate, which can be metal, wood, masonry or other desired material. The particles of reflective metal are usually available in the form of flakes, powder or dust. The reflective metal particles are coated with the layer of black selective material for instance by electroless chemical deposition of an other metal and o~ ~ ation or ` ~
~1 8~;3~3 sulfidation of the metal layer deposited in this way.
According to the U.S. Patent No. 4,082,~13 a device for absorption oE selected radiation wavelengths, such as solar radiation, is manufactureA by applying upon a substrate of metal or glass a layer of a mixture of metal particles and a dielectric material, the concentration of the metal in this :La~er varying from one boundary surface to the opposite boundary surface gradually from 0~ to 100%. The dielectric material is in general transparent to radiation, although it may absorb some radiation, whereas the`metal absorbs and reflects radiation. The heat built up in the layer as radia-tion is absorbed is withdrawn by means of a heat transfer agent flowing through a conduit in thermal contact with the layer or with the substrate on which the layer is deposited.
According to the published Netherlands patent appli-cation No. 7400292 a coating composition is prepared, which provides a metallic appearance when applied to a substrate, by mixing a finely divided metal powder and pulverulent graphite with an organic polymeric binder. The coated sub-strate reflects radiation and does not absorb it. If desired, other additives, such as asbestos, bentonite, chalk or pigments may be incorporated in the composition but only in very small amounts in order to avoid deterioration of the metallic appearance.
From the published German patent application No. 2,056,211 a heat reflecting paint is known, which consists of metal particles reflecting radiation of a wavelength of 3-20/um and an organic binder absorbing radiation of a wave-length of 3-20/um only slightly.
Summary of the Invention It has now been found that a very cheap and easily handable paint for applying spectral-selective coatings consists of spectral-selective piyment, reflective metal particles and binder and, if desired, other components with or without a liquid vehicle. Thus, reflective metal particles coated with a black pigment layer as described in the U.S.
3~
Patent No. 4,011,190 are not presen~ in this paint. The advantage thereof is that the separate step of coating metal particles with a very thin film of spectral-selective material, which step is the most difficult step in the preparation of the pain-t from a technological point of view, has become superEluous The pigmentr the metal particles and the binders, whlch are incorporated in the apints according to the inven-tion, may be conventional commercial products, which can be mixed together in a simple way to form a paint. Thus, the preparation and the use of such a paint has become possible in areas where the use of advanced technologies is not possible.
In accordance with one aspect of the present invention there is provided a paint suitable for spectral-selective coatings which comprises spectral-selective pigment selected from the group consisting of copper oxide-chromium oxide, iron oxide-manganese oxide-copper oxide, molybdenum oxide, lead oxidel copper sulfide, chromium sulfide, iron sulfide, manganese sulfide, molybdenum sulfide, lead sulfide, blacks, organic dyes and pigments, and mixtures of one or more thereof, uncoated particles of reflective metal selected from the group consisting of aluminum, nickel, copper, zinc, alloys thereof, and stainless steel, and binder selected from the group consisting of polyethylene, polypropylene, ethylene-propylene copolymers, ethylene-propylene-diene terpolymers, polysiloxane resins, alkyd resins, polyester resins, styrene-butadiene-copolymers, polyacrylates, vinyl resins, chlorinated rubber, phenolic resins, amino resins, epoxy resins, polyurethanes, elastomeric fluorohydrocarbons, siloxane-modified alkyd resins, siloxane-modified polyester resins, inorganic silicates, and organic silicic acid esters, the pigments having a pigment volume concentration of from about 1% to about 60%, and the metal particles having a pigment volume concentration of from about 5% to about 95%.
In accordance with a further aspect of the present invention there is provided a process for preparing a paint suitable for spectral-selective coatings which comprises combining a spectral-selective pigment selected from the ~.a~S7~3~
-3a-group consisting of copper oxide-chromium oxide, iron oxide-manganese oxide-copper oxide, molybdenumoxide, lead oxide copper sulfide, chromium sulfide, iron sulfide, manganese sulfide, molybdenum sulfide, lead sulfide, blacks, organic d~es and pigments, and mixtures of one or more thereof, with a binder selected from the group consisting of polyethylene, pol~prop~lene, ethylene-propylene copolymers, ethylene-propylene-diene terpolymers, polysiloxane resins, alkyd resins, polyester resins, styrene-butadiene-copolymers, polyacrylates, vinyl resins, chlorinated rubbers, phenolic resins, amino resins, epoxy resins, polyurethanes, elastomeric fluorohydrocarbons, siloxane-modified alkyd resins, siloxane-modified polyester resins, inorganic silicates, and organic silicic acid esters, and adding to the resulting pigment dispersion uncoated particles of reflective metal selected from the group consisting of aluminum, nickel, copper, zinc alloys thereoE, and stainless steel, the pigment having a pigment volume concentration of from about 1% to about 60%, and the metal particles having a pigment volume concentration of from about 5% to about 95%.
The results obtained with the paints according to the invention are about the same as the results obtained with the paints according to the U.S. Patent No. 4,011,190. For instance paints have been prepared, in which the pigment volume concentration of metal flakes was 20% and of black pigment was 10% or 20~ respectively, this concentration being based on the total content of non-volatile components of the pigment. Substrates coated with paints prepared in this way showed an absorption coefficient of solar light (as) between 30 about 0.84 and about 0.90 and an emittance coefficient (~) between about 0.35 and about 0.50 Detailed description of the invention . .
In the paint according to the invention as spectral-selective pigments in most cases pigments l~aving a high absorption for solar radiation are used. Examples thereof are among others conventional black pigments, such as copper oxide-chromium oxide, iron oxide-manganese oxide-~r ~8763~
- 3b -copper oxide, molybdenum oxide and lead oxide as well as the sulfides of the metals present in the oxides, especially lead sulfide. Also certain blacks, organic dyes and pi~ments are suitable, mixtures of one or more of these substances being also useful.
Examples of the metals in -the reflective metal particles are e.g. aluminium, nickel, copper and zinc or alloys of these metals, especially of copper and zinc, and also stainless steel. In many cases the metal particles are used as flakes. Especially flakes of aluminium, copper or copper-zinc alloys are preferred, because they vield excellent results and moreover are not expensive and avail-able as commercial products. When drying and/or baking the paint the 1akes appear to orient parallel to the surface of the substrate.
The binders, which may be used in the paints accordin~ to the invention, can be binders conven-tional for this purpose. Examples ~3 ~.
thereof are e.g. polyethylene, polypropylene, ethylene-propylene co-polymers, ethylene-propylene-diene terpolymers, polysiloxane resins, such as methylphenylpolysiloxane polymer, alkyd resins, polyester re-SillS, styrene-butadiene-copolymers, polyacrylates, vinyl resins, chlorinated ruhber, phenolic resins, amino resins, epoxy resinsl po lyuretllanes, elastomeric fluorohydrocarbons, siloxane-modified alkyd reslns or polyester resins, inorganic silicates and organic silicic acid esters.
Polysiloxane resins, siloxane-modified alkyd resins and polyes-ter resins as well as fluoro hydrocarbonelastomers have the advantagethat they are resistant to high temperatures and weathering.
In the paint according to the invention also other components may be present, such as auxiliary agents, e.g. disperslng agents, wetting agents, thickening agents, siccatives, antiskinning agents and flux agents.
When a liquid vehicle is used in the paint, it consists e.g. of an organic solvent or water. As or~anic solvents aliphatic, cycloali-phatic and aromatic hydrocarbons and chlorinated hydrocarbons, alco-hols, ketones and esters are suitable. In case of the use of aqueous binder dispersions water is employed as a liquid vehicle. These binder dispersions often contain emulsifying agents or wetting agents and other auxiliary agents.
When using a binder having a sufficiently low viscosity the paint may contain no liquid vehicle at all or only a small amount of vehicle.
The concentration of the spectral-selective pigment and the re-flective metal particles in the paint according to the invention is expressed in the pigment volume concentration (pvc) normally used in the paint industry, which pvc is based on the total content of non-f volatile components. The pvc of the spectral-selective pigment i5 in general from about 1% to about 60~, and preferably from about 10% to about 30~. The pvc of the reflective metal particles is in general from about 5~ to about 95~ and preferably from about 10% to about 30~.
The preparation of a paint according to the invention may take place in a conventional way. By way of example the spectral-selective pigment may be dispersed in such a way in a portion of the binder or of the binder solution, that the greatest particles are smaller than e.g. about 10 /um. To the resulting dispersion first the remaining amount of binder or binder solution is added under agitation and thereafter the reflective metal particles are added as such or in the form of a paster In some cases the metal particles or paste are pre-wettecl with an amount of solvent to facilitate the incorporation thereoE.
The paint according to the invention is applied on a substrate ln a conventlonal way and subsequently dried and, if desired, baked.
As a substrate for the paint metal, wood, masonry,plastics or any other material may be used. If desired, first a layer is applied on the substrate, which effects protection against corrosion and/or a better adhesion of the spectral selective-paint coating. This is es-pecially desirable if the substrate is formed by a metal or a plastic. Upon this first layer the paint of the invention is applied.
The thickness of the applied paint coating may vary within broad limits and is e.g. after drying about 5 - 100/um and particularly about 20 - 50 /um.
Substrates with spectral-selective coatings on the base of the paint according to the invention are very suitable to be used in all kind of types of solar collectors.
From experiments of the coated substrates it has appeared, that the coatings possess an excellent durability upon heating at 200C
for 14 days, especially when polysiloxane resins and siloxane-modi-fied alkyd resins and polyester resins are used. It has also appearedthat with experiments in an atlas weatherometer after 10 ~ no re-duction of the durability of the coating could be determined. These experiments have been carried out without a glass plate retaining ul-traviolet light, which glass plate in general will be present in solar collectors, in which the ccated substrates are used.
The following examples illustrate the invention without limiting it. The compositions described in these examples were prepared in the way as described in the above.
Example I.
A paint of the following composition was prepared:
component weight %
soja alkyd resin 20.09 ~l~763~3 pigment Ferro Black F 6331a) 12.90 Cu/Zn flakes 30.28 white spirit 34.55 acetone 0.22 S nentone 34 b) 0.37 Pb naphtenate, 32% Pb0.29 Co nnphtenate, 10% Co0.12 Ca naphtenate, 4% Ca1.18 100 . 00 .
The pvc of the pigment was about 10%, the pvc of the Cu/Zn flakes was about 20%. The paint was applied to an aluminium plate with the aid of a doctor's blade. The thickness of the layer after drying was about 30 - 40/um~ After 14 days of drying were measured: ~ s =
0.88 and ~ =
Example II.
A paint of the following composition was prepared:
component weight %
20 styrene-butadiene-copolymer 10.30 chlorinated paraffin1.14 pigment Ferro ~lack F 6331 a) 17.32 aluminium flakes 9.73 xylene 55.28 25 solvent in aluminium paste 5.24 polysiloxane oil O.Ol Coloral F c) 0.98 100 . 00 The pvc of the pigment was about 20%, the pvc of the aluminium was also about 20%.
The paint was applied on an aluminium plate with the aid of a doctor's blade. The thickness of the layer after drying was about 30 to 40 jum. After 14 days drying were measured:~s = 0.90 en ~ -0.44.
Example III.
A paint of the following composition was prepared:
component weight %
. . _ ~7~
siloxane modified polyester resin 19.75 plgment Ferro Black F 6331 a) 23.03 aluminium flakes 19.36 ethylglycolacetate 13.16 5 xylene 15.92 solvent in aluminium paste 8.30 Bentone 38 b) 0.26 Dispersing agent 0.22 100 . 00 .
The pvc of the pigment was about 16%, the pvc of the aluminium was about 24%.
The paint was applied on an aluminium plate with the aid of a doctor's blade. The layer was predried for 30 minutes at 20C and subsequently baked for 60 minutes at 200C. The thickness of the re-sulting coating was about 40 - 50/um. Thereafter were measured:
s = 0-84 and ~ = 0.41.
a) iron oxide-manganese oxide-copper oxide plgment, commercial pro-duct of Ferro Holland b) bentonite modified with quaternary ammonium compounds c) modified so~a lecithine.
Claims (14)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A paint suitable for spectral-selective coatings which comprises spectral-selective pigment selected from the group consisting of copper oxide-chromium oxide, iron oxide-manganese oxide-copper oxide, molybdenum oxide, lead oxide, copper sulfide, chromium sulfide, iron sulfide, manganese sulfide, molybdenum sulfide, lead sulfide, blacks, organic dyes and pigments, and mixtures of one or more thereof, uncoated particles of reflective metal selected from the group consisting of aluminum, nickel, copper, zinc, alloys thereof, and stainless steel, and binder selected from the group consisting of polyethylene, polypropylene, ethylene-propylene copolymers, ethylene-propylene-diene terpolymers, polysiloxane resins, alkyd resins, polyester resins, styrene-butadiene-copolymers, polyacrylates, vinyl resins, chlorinated rubber, phenolic resins, amino resins, epoxy resins, polyurethanes, elastomeric fluorohydrocarbons, siloxane-modified alkyd resins, siloxane-modified polyester resins, inorganic silicates, and organic silicic acid esters, the pigment having a pigment volume concentration of from about 1% to about 60%, and the metal particles having a pigment volume concentration of from about 5% to about 95%.
2. The paint according to claim 1, wherein the reflective metal particles are flakes of metal selected from the group consisting of aluminum, copper and copper-zinc alloys.
3. The paint according to claim 1, wherein the pigment volume concentration of the spectral-selective pigment is from about 10% to about 30%.
4. The paint according to claim 1, wherein the pigment volume concentration of the reflective metal particles is from about 10% to about 30%.
5. A process for preparing a paint suitable for spectral-selective coating which comprises combining a spectral-selective pigment selected from the group consisting of copper oxide-chromium oxide, iron oxide-manganese oxide-copper oxide, molybdenum oxide, lead oxide, copper sulfide, chromium sulfide, iron sulfide, manganese sulfide, molbdenum sulfide, lead sulfide, blacks, organic dyes and pigment, and mixtures of one or more thereof, with a binder selected from the group consisting of polyethylene, polypropylene, ethylene-propylene copolymers, ethylene-propylene-diene terpolymers, polysil-oxane resins, alkyd resins, polyester resins, styrene-butadiene-copolymers, polyacrylates, vinyl resins, chlorinated rubber, phenolic resins, amino resins, epoxy resins, poly-urethanes, elastomeric fluorohydrocarbons, siloxane-modified alkyd resins, siloxane-modified polyester resins, inorganic silicates, and organic silicic acid esters, and adding to the resulting pigment dispersion uncoated particles of reflective metal selected from the group consisting of aluminum, nickel, copper, zinc, alloys thereof, and stainless steel, the pigment having a pigment volume concentration of from about 1% to about 60%, and the metal particles having a pigment volume concentration of from about 5% to about 95%.
6. In a solar heat absorbing device, wherein the improvement comprises a coating on the base of a paint according to claim 1.
7. In a solar collector, wherein the improvement comprises a solar heat absorbing device according to claim 6.
8. The paint according to claim 1 which further comprises a liquid vehicle which is selected from the group consisting of water, aliphatic hydrocarbons, cyclo-aliphatic hydrocarbons, aromatic hydrocarbons, chlorinated hydrocarbons, alcohols, ketones and esters.
9. The process according to claim 5 which further comprises adding a liquid vehicle to the spectral-selective pigment and binder combination.
10. A paint according to claim 1, wherein the pigment comprises an iron oxide-manganese oxide-copper oxide pigment, the particles of reflective metal comprise a copper-zinc alloy, and the binder comprises soja alkyd resin.
11. A paint according to claim 1, wherein the pigment comprises an iron oxide-manganese oxide-copper oxide pigment, the particles of reflective metal comprise aluminum flakes, and the binder comprises a styrene-butadiene copolymer.
12. A paint according to claim 1, wherein the pigment comprises an iron oxide-manganese oxide-copper oxide pigment, the particles of reflective metal comprise aluminum flakes, and the binder comprises a siloxane modified polyester resin.
13. In a process of preparing a solar heat absorbing device, wherein the improvement comprises coating the base with a paint according to claim 1.
14. In a process of preparing a solar collector, wherein the improvement comprises using a solar heat absorbing device according to claim 13.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL8000986A NL8000986A (en) | 1980-02-18 | 1980-02-18 | PAINT FOR APPLICATION OF SPECTRAL-SELECTIVE COATINGS AND METHOD OF PREPARING THE SAME, SOLAR HEAT ABSORBING DEVICE AND SOLAR COLLECTOR CONTAINING SUCH A DEVICE. |
| NL8000986 | 1980-02-18 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1187638A true CA1187638A (en) | 1985-05-21 |
Family
ID=19834849
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000371182A Expired CA1187638A (en) | 1980-02-18 | 1981-02-18 | Paint for applying spectral-selective coatings and process for the preparation thereof, solar heat absorbing device and solar collector containing such a device |
Country Status (6)
| Country | Link |
|---|---|
| AU (1) | AU541490B2 (en) |
| CA (1) | CA1187638A (en) |
| DE (1) | DE3105963A1 (en) |
| IL (1) | IL62137A (en) |
| NL (1) | NL8000986A (en) |
| ZA (1) | ZA811044B (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4753829A (en) * | 1986-11-19 | 1988-06-28 | Basf Corporation | Opalescent automotive paint compositions containing microtitanium dioxide pigment |
| HRP20030926B1 (en) * | 2003-06-17 | 2012-12-31 | Kemijski inštitut | Spectrally selective coatings for absorbers in solar collectors |
| US20210348023A1 (en) * | 2018-08-17 | 2021-11-11 | The Trustees Of Dartmouth College | Solar receiver, selectively absorbing material, and associated fabrication methods |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3432998C3 (en) * | 1984-09-07 | 1993-12-02 | Gerd Hugo | Camouflage color |
| JP4871951B2 (en) | 2008-12-26 | 2012-02-08 | 大島工業株式会社 | Heat resistant paint |
| CN106756899A (en) * | 2016-11-28 | 2017-05-31 | 江南大学 | A kind of preparation method of high temperature resistant spectral selective absorbing coating |
-
1980
- 1980-02-18 NL NL8000986A patent/NL8000986A/en not_active Application Discontinuation
-
1981
- 1981-02-13 IL IL62137A patent/IL62137A/en unknown
- 1981-02-17 ZA ZA00811044A patent/ZA811044B/en unknown
- 1981-02-17 AU AU67357/81A patent/AU541490B2/en not_active Ceased
- 1981-02-18 CA CA000371182A patent/CA1187638A/en not_active Expired
- 1981-02-18 DE DE19813105963 patent/DE3105963A1/en not_active Withdrawn
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4753829A (en) * | 1986-11-19 | 1988-06-28 | Basf Corporation | Opalescent automotive paint compositions containing microtitanium dioxide pigment |
| HRP20030926B1 (en) * | 2003-06-17 | 2012-12-31 | Kemijski inštitut | Spectrally selective coatings for absorbers in solar collectors |
| US20210348023A1 (en) * | 2018-08-17 | 2021-11-11 | The Trustees Of Dartmouth College | Solar receiver, selectively absorbing material, and associated fabrication methods |
Also Published As
| Publication number | Publication date |
|---|---|
| DE3105963A1 (en) | 1981-11-19 |
| ZA811044B (en) | 1982-03-31 |
| AU6735781A (en) | 1981-08-27 |
| IL62137A0 (en) | 1981-03-31 |
| AU541490B2 (en) | 1985-01-10 |
| NL8000986A (en) | 1981-09-16 |
| IL62137A (en) | 1984-07-31 |
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