US20160091225A1

US20160091225A1 - Radiation selective absorbing coating and process for obtaining the same at room temperature

Info

Publication number: US20160091225A1
Application number: US14/958,237
Authority: US
Inventors: Juan Manuel CAMACHO PEREZ; Araceli RIOS FLORES; Fatima Guadalupe ROCHA ARGUELLES
Original assignee: Energia Suministros E Instalaciones Sa De C V; ENERGIA SUMINISTROS E INSTALACIONES SA de CV
Current assignee: Energia Suministros E Instalaciones Sa De C V; ENERGIA SUMINISTROS E INSTALACIONES SA de CV
Priority date: 2014-01-29
Filing date: 2015-12-03
Publication date: 2016-03-31

Abstract

The present invention relates to materials and its thermal applications in different uses. More specifically, it relates to the use of a selective absorbing coating which is obtained at room temperature and is deposited on metal, which is additionally used for capturing solar energy or artificial light and converting it into thermal energy. The novelty of the present invention is related to its production process and its use and industrial application in meshes, fabrics, threads, fibers or metallic wires used in the textile industry for the manufacture of jackets, trousers, scarves, shirts, hats, gloves, mittens and mitts, sleeping bags, tents, to provide properties to absorb sunlight or artificial radiation and convert it into heat for heating said fibers or a body.

Description

REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No. 14/895,362 filed Dec. 2, 2015, entitled, RADIATION SELECTIVE ABSORBING COATING AND PROCESS FOR OBTAINING THE SAME AT ROOM TEMPERATURE, pending, the content of which is incorporated herein by reference, which is a US national stage entry of PCT/MX2014/000173 filed Nov. 4, 2014, under the International Convention, which claims priority over Mexican patent application No. MX/a/001213 filed Jan. 29, 2014.

FIELD OF THE INVENTION

The instant invention relates to materials and their thermal applications in different purposes. More specifically, it relates to the employment of a selective absorbing coating obtained at room temperature and deposited on metal, used for harnessing solar energy and converting it into thermal energy. Said coating improves the efficiency in the collection of thermal energy, optimizing visible and near infrared light harnessing and minimizing heat emission of the metal towards environment.

OBJECT OF THE INVENTION

The object of the instant invention is to present the process for obtaining a solar and/or artificial radiation selective absorbing coating at room temperature which can operate in the temperature range from 0° C. to 300° C. and its application on metallic substrates with different shape and geometry configurations such as smooth, rough, porous, tubular or laminar, as non-limiting exemplary embodiments of the instant application, generating heat through solar radiation and/or artificial illumination.
It also relates to different uses and applications that can be given to it, for example, such technology can be used to coat metal fibers used in the manufacture of coats, jackets, sweaters, hats, gloves, fabric for tents, shoes, boots, etc. without limiting the scope of the present application, specifically as an inner linning (interlining) which is constructed in each of the clothing designs or applications that can integrate it so that these garments have the capacity to absorb solar and/or artificial radiation, convert it into heat, keep the calorific energy and transmit said energy to the human body.

BACKGROUND OF THE INVENTION

In the field of solar energy, the selective absorbing coatings efficiently capture solar radiation in the spectral region of high intensity visible light and near infrared. Consequently, a selective coating will absorb and retain a substantial amount of solar radiation, while a non-selective surface, such as an ordinary black body, will lose a high percentage of the energy absorbed by re-radiation.
Absorbers with black surfaces absorb 95% of incident solar radiation. The reflection loss is only 5%. However, black surfaces give off much of this energy in the form of thermal radiation and wasting 45% of the absorbed energy. Thus, the total yield of the collectors with black coatings is less than 50%. For high solar absorption applications, the selective coating must be thermally stable around 400° C., ideally in the air and have an absorbency greater than 0.95 and a thermal emittance below 0.15 at 400° C.
The object of the selective absorbing coatings is to increase the efficiency of solar collectors and are generally used in thermosolar applications. Said coatings have a large power of absorption of solar energy and low emissivity characteristics in order to reduce energy losses through thermal radiation in the remote infrared region. Whatever their application, the selective absorbing coatings play an essential part in increasing the efficiency of heat absorbing materials.
There are two magnitudes denominated absorbance (α) in the UV_VIS region of the spectre (200-1000 nm) and emittance (ε) in the infrared region (1-15 μm) used for evaluating the efficiency of selective absorbing coatings. The greater a and the smaller c, the higher is the efficacy of the coating.
The selective coatings for the efficient absorption of solar energy and its conversion into heat are characterized because they have a reflectance spectrum that changes abruptly according to the wavelength value. Thus, with wavelength values below certain value (about 2 μm, corresponding to the infrared region), the intensity of solar radiation is null or with a very low value (about 5%), while with wavelengths greater than this value the intensity reaches a very high value (greater than 90%) which corresponds to the infrared spectral region. This ensures that the heat acquired by the metallic element is not lost through thermal radiation.
Several patents and patent applications related to solar selective coatings are known. Usually, the coatings are made of a metal, dielectric or ceramic material substrate, at least one reflecting metallic layer and at least one anti-reflection layer and their direct application is in absorbing pipes for parabolic-trough solar collectors and in absorbing sheets for solar panels, such as those described in patents ES2316321B2, ES2317796B2 and patent application WO2012172148A1. The main advantage is an absorbance greater than 95% and an emittance lower than 0.20 in the range from 400° C. to 550° C. However, their compositions and methods for obtaining thereof are very complex and thus would not be economically sound in industries such as: food, textile, among others, because of their high production costs and thus the high price of the final product would be high for such markets.
Specifically, the inventions described in patents ES2317796B2 or ES2316321B2, report very acceptable absorbance values but their emittance values are not so favorable, leading to a selectivity ratio of α/ε 400° C.=0.975/0.15 and α/ε 400° C.=0.975/0.08.
Patent ES2317796B2 patent discloses a selective coating for solar applications with a reflective coating in the infrared region between two aluminum oxide layers, which allows any material of the reflective layer to not diffused in the infrared region in the superimposed absorption layer; causing it to have a high absorption capacity α>95.5% and a reduced emissivity with ε<9% at an operating temperature of 550° C. under vacuum for a period of time of 250 hours, reporting a selectivity ratio of α/ε=10.61; but at medium and low temperatures there are no reported results, or absorption operation and implementation capacity.
Meanwhile patent application WO2012172148A1 refers to a selective absorbing coating to visible and infrared radiation comprising: (a) a first non diffusing barrier layer (2); (b) an IR reflective metallic layer (3) of at least one metallic element selected from a group consisting of Au, Ag, Al, Cu, Ti and Pt; (c) at least one second non diffusing barrier layer (4) formed by oxidation of the layer (3); (d) an absorbent structure in the UV-VIS comprising at least a first film (5) and a second film (6) of cermet, which itself comprises a metal fraction of a metal selected from Pt, Cr, Mo, W, Zr, Nb, Ta and Pd, or any alloy thereof, and a ceramic comprising a free oxygen nitride constituted by a metallic oxide selected from aluminum, silicon and chromium; and (e) an antireflective dielectric layer in the UV-VIS region comprising a nitride of at least one metal selected from silicon, aluminum and chromium. Another object of the invention is the method for obtaining such a coating and its use in solar thermal collectors.
The ES2316321 patent reports that the methods for obtaining a selective coating in which the different layers of the coating are deposited by techniques of physical vapor deposition in vacuum (PVD, physical vapor deposition) such as are thermal evaporation, electron gun, ionic implantation or “sputtering”, by chemical vapor deposition (CVD) or through electrolytic baths, being the sputtering technique preferred for this purpose. It also has a refractive index of between 1.4 and 2.4 of the dielectric material layers of the absorbent multilayered structure comprising metallic oxides and/or nitrides of metallic elements.
The U.S. Pat. No. 4,104,134 describes a process for obtaining an aluminum absorber panel through a chemical bath in an aqueous solution with an alkaline cleaner from 5 to 10 minutes at a temperature of 60° C. and 80° C. to be then immersed in a brilliant solution from 5 and 10 minutes at 82° C. and 93° C.
Patent application WO2002072918 suggests a process and method for stripping a metal piece after welding to increase its corrosion resistance, indicating that the novelty of the invention resides in using an acid and an alkaline stripping agent for the process containing heavy metals and subsequently adding sodium hydroxide to the process for a chemical precipitation; afterwards, in the passivation process for creating an anticorrosion protective layer to the metal, it is possible to maintained a temperature above 35° C.
The EP Patent 0317838 defines a method of manufacturing an ultra-black coating; detailing that the process of preparation is carried out through a chemical bath in electrolytic solution of phosphorus and nickel alloy to form the coating based, which is immersed generally at temperatures of between 80 and 95° C. from 1 to 5 hours. For the black finish, it is required to soak it into a nitric acid solution between a 20° C. to 100° C. temperature from 5 seconds to 5 minutes, depending on the phosphorus content in the base, which indicates that usually at a concentration of 1 to 1 of phosphorus to nitric acid at a temperature of 50° C. the coating base blackens, the typical process temperature varies from 30 to 80° C. with a time from 5 seconds to 5 minutes, achieving a very stable coating with excellent mechanical strength, moisture resistance, and a spectrum reflectance from 0.1-0.4%, a wavelength width from 380-1800 nm and a wavelength range of 0.1% or less.
Particularly, in each one of these patents a large number of selective coatings have been described that use cermets formed by some of the following metals: Cu, Ni, Co, Pt, Cr, Mo, W, Al or Ag; and as ceramic matrix, the following compounds: SiO, SiO₂, Al₂O₃, AlN or MgO. In order to improve their efficacy, these cermets must be covered with a layer of a material having very good transparent qualities such as the following oxides: Cr₂O₃, MoO₃, WO_x, H_fO_xor SiO₂, where said layer acts as anti-reflection layer. Additionally, the cermet must be deposited on the metal acting as infrared mirror, which is usually achieved with Ag, Cu, Al, Au or Pt.
Unlike the state of art, the present invention introduces a method for obtaining a coating at room temperature, and the invention presented is not comprised of multiple layers. Nevertheless, very good results are obtained in the absorbent and reflective properties of the material. On the other hand, in any patent application or patent granted in our knowledge, it is proposed depositing a selective coating into fibers, threads, wires or metallic mesh with minimum thickness from 0.03 mm, which expands the applicability of the invention to other industries mainly textiles for making clothing that use solar selective coatings that provide solar and artificial radiation absorbent qualities.
The following patents disclose the background in the use of metallic fibers where we have found the following methods, processes and fiber products that integrate solar selective coatings.
The document U.S. Pat. No. 8,187,984 B2, Temperature sensitive intelligent textiles, relates to a textile fabric that includes a smooth surface with one or more regions (layers) of material having a variable behavior of thermal expansion or contraction, adjusting the insulation performance of the textile fabric in response to ambient conditions, yet the patent does not teach the use of radiation-absorbing coatings.
The document KR101386765, Electrically conductive fiber of graphene and method of production thereof, relates to a method for manufacturing a graphene electronic conductive fiber coated using a cotton thread of modified surface and the grapheneosin solution. The electronic conductive fiber manufactured by such method has very high conductivity, thereby being used for the intelligent electronic fiber (e-textile and e-fiber); but its application is limited to the transmission of electricity.
The document KR101373633, Method for manufacturing a conductive metal fiber, that has a higher elastic resistance, method of manufacturing products with the metal fiber composition with use of the same. The document relates to a method for manufacturing a fiber of a complex conductive metal that can be applied to an intelligent textile, made by combining the use of technologies such as electricity, computers, and electronics technology. In order to increase the limit of elasticity of the fiber by collecting multiple pieces of a first twisted thread twisted into a thread and a conductive fiber. The method for manufacturing the conductive complex fiber comprises the steps of: a first process that manufactures the fiber by winding the thread with the coated conductive fiber; a second process that makes the first twisted stranded thread; and a third process that produces fiber reinforced having a higher creep strength for winding the thread onto the surface of multiple pieces of the first coated stranded thread. This patent reflects the intention to bring to market intelligent fibers that integrate advanced technology for making clothing.
Finally, the document WO 2010129923 A2 entitled Pattern for controlling heating in materials, relates to method and apparatus using an array of heat elements coupled to a base material to maintain close body heat, while maintaining the desired transfer properties of the base material. In some embodiments, the material elements that manage or control the heat include elements that reflect or conduct heat; the mainly used materials are aluminum as reflective and can be glued, sewn or ironed to the clothes so that they can be addressed into the body of a wearer or away from the same in the inside of the garment; its method of preparation involves the sputtering technique for the precipitation of the material onto the fabric; unlike the present invention, this patent must be superimposed by the inner layer of the clothing to reflect infrared from the body, and it does not have the ability to absorb heat as the present invention does.
Overall, the patents discussed, analyze and give detail in the method of making intelligent textile fibers with different applications; however no one deepens on the ability to use a selective coating method that will provide to mesh fibers, threads, fibers, and metallic wire, capacity to absorb solar and artificial radiation and to generate heat. At the same time, these patents propose processes that cannot be done at room temperature, which involves high costs processes. Finally, unlike prior art documents, this invention discloses a method for deposing a selective coating into fibers or metallic meshes in thicknesses from 0.03mm without affecting the substrate.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1: shows a cross sectional view of the radiation selective absorbing coating of the present invention comprising a substrate of metallic material (1) and a radiation absorbing metallic layer (2), which to exemplify it is a cross section of a coated metallic pipe;

FIG. 2: shows a graphic of the reflectance value measured in a sample of the present invention;

FIGS. 3A and 3B: show values of temperature increase of the selective coating obtained at room temperature when the sample is illuminated with a radiation of 1000 watts/m2. By varying the treatment time in the process of obtaining the selective coating, various surface colors of the coating according to the graph (FIG. 3A) and colors of the coating (FIG. 3B) are obtained: blue (3), gray (4), black (5), blue-purple (6), green (7), gold (8), lilac (9). Based on the rate of temperature rise it was determined that the blue-purple has the highest ability to absorb radiation;

FIG. 4. shows a Mesh, wire, thread or metallic fiber (10) and its mesh-shaped cross section (11) with the layer of radiation selective absorbent (12);

FIG. 5: shows a preferred application of the metallic fiber with the solar and/or artificial radiation selective absorbing coating at room temperature of the present invention, in the conformation of a fabric consisting of an exterior layer of any type (13), fiber or metallic mesh with the solar and/or artificial radiation selective absorbing coating at room temperature of the present invention (14), and the inner lining or insulating of the garment of any type (15);

FIG. 6: shows the integration of the fiber, thread, mesh or steel wire with solar selective coating at room temperature as an interlining in jackets (16), using the system described in FIG. 5.

FIG. 7: shows the integration of the fiber, thread, mesh or steel wire with selective absorbing coating for use in shoes (17), gloves (18) caps (19) and tents (20) using the system described in FIG. 5;

FIG. 8: shows a comparative plot of temperature increase using the following configuration, the mesh, fiber, fabric, or metallic wire with the selective absorbing coating in the middle in a sandwich-type or tandem configuration with a polyester-cotton fabric with a weight of 235 g/m², and insulating lining (21) and one of a similar configuration without the fiber, mesh, thread or wire with the selective absorbing coating of the present invention as interlining between the polyester-cotton fabric and the insulating lining (22).

FIG. 9: shows an outside temperature graph of a test at 3° C. of two pieces: a composite with the system described in FIG. 5 of the present invention (23) and another with aluminum and/or copper reflective dot technology in the interior lining to allow recycle the infrared from human body (24), indicating the temperature increase that jackets allow that integrate the fiber mesh, thread or wire with the present invention;

FIG. 10: shows a photo with an infrared camera of the system described in FIG. 5 with different components: without using mesh, fiber, thread, or metallic wire with the selective absorbing coating (25), using the mesh, fiber, thread, or metallic wire with the selective absorbing coating (26) and using the mesh, fiber, thread or metallic wire without the selective absorbing coating (27);

FIG. 11: shows a graph of the absorption spectrum of the present invention in the UV (28), visible (29) and infrared (30) range; and

FIG. 12: shows a graph of transmittance of UV rays on the selective absorbing coating obtained at room temperature, representing the values of UV rays that the present invention passes upon contact with light.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an absorbent and selective coating of solar and/or artificial and infrared radiation. In the present invention, the term radiation is to be understood broadly and without limitation, as the total electromagnetic spectrum, including sunlight, ultraviolet, infrared and artificial lighting, also called selective surface, which refers to a material or coating exhibiting optical selectivity; said coating material has optical properties which extremely vary from one spectral region to another, and it is characterized by its production process at room temperature. In the present invention, the term ambient temperature should be understood as the temperature from the 20° C. to 40° C., including standard room temperature of 25° C. Said coating is and may be permanently secured or fixed to a base material in a plurality of forms, such as, without limiting the scope of the methods: by chemical solution, cathodic spraying (sputtering), thermal evaporation, electrochemical and spray or sol-gel.
This coating acts as a heat trap, as it absorbs solar and/or artificial radiation and transforms it into heat. It also has the ability to reflect infrared radiation generated by a body.
Said coating comprises a substrate (1 and 10) of metallic material, that may present, without limitation, certain dielectric or ceramic characteristics, and at least a metallic layer (2 and 12) providing low emittance properties and because of its features it has various uses, for example as selective absorbent on metallic surfaces or substrates for thermosolar applications, in the textile industry.
The substrate (1 and 10) of metallic material may have surfaces of various shapes, geometry and texture configurations, including, without limitation, smooth, rough, porous, tubular, sheet, wire, threads, filaments, meshes, spheres and this without limiting the type of base material that can be used, provided it complies with the basic features for the material or selective absorbing coating adheres to and coat the surface maintaining the physical and chemical properties and performance (12).
For the above mentioned uses and applications, the solar and/or artificial radiation selective absorbing coating operates within the temperature range from 0° C. to 300° C., in the case of solar thermal applications, generating a range in the ratio of selectivity from α/ε=5.33 to α/ε=4.23 between such temperatures; enough for its employment in devices generating heat through solar radiation or artificial illumination.
The steps in the process of obtaining the proposed invention comprises (a) at least one cleaning stage, (b) at least one first stage of immersion and standing in aqueous solution, (c) at least one first rinsing stage, (d) at least one second stage of immersion in aqueous solution and (e) at least one second rinsing stage.
In said cleaning stage, the metallic substrate or surface to be coated is cleaned with solvents that are selected from the group comprising, without limiting the scope of the invention, the following substances:
A mixture of silicates, phosphates, carbonates and sulfates, to remove impurities such as dust and some greases;
Trichloroethylene for removing greases and oils that may be present on the metallic surface;
Acetone, for removing inorganic greases and polymer coatings that are different from oxides.
After the cleaning stage, the substrate to a stripping process in an aqueous solution of hydrofluoric acid is subjected in a concentration range of 0% to 5% plus nitric acid at a concentration ranging from 5% to 15%.
After the cleaning stage, the substrate is subjected to a stripping process in a hydrofluoric acid aqueous solution at a concentration ranging from 0% to 5% plus nitric acid at a concentration ranging from 5% to 15%. In a period of time from 8 to 16 minutes, the surface to be coated is allowed to stand immersed in the solution.
Then, the water rinsing stage is conducted (distilled water may be used).
After the cleaning stage and immersion in aqueous solution, in the second immersion stage, the pre-treated substrate is immersed in a chromic acid aqueous solution at a concentration ranging from 200 g/L to 300 g/L and sulfuric acid at a concentration ranging from 350 g/L to 450 g/L, during 9 to 10.5 hours obtaining coatings 3 blue, 4 gray, 5 black, 6 blue-purple according to FIGS. 3A and 3B with an absorption rate of 80 to 89% of solar radiation, or more during a time from 13 hours up to 24 hours obtaining coatings 7 green, 8 gold, 9 lilac according to FIGS. 3A and 3B with an absorption rate of 75% to 80% of solar radiation, and wherein an optimum coating is obtained preferably within 9.5 and 10.5 hours (3, 4, 5).
This coating is generated by applying the indicated ranges and with a room temperature, between 20° C. and 40° C., and at a humidity ranging from 0% RH to 80% RH, preferably between 20-80% RH, because out of this range precipitation would be generated in the solution.
Once obtained the first coatings, chromic acid solution can be kept at room temperature and used repeatedly for more coatings without affecting the absorption properties of coatings to be developed afterwards, which presents big savings on the cost of the solution.
Finally, the substrate with the coating is withdrawn and is submitted to a rinsing stage that can be conducted with water or with an impurity removing liquid.
Then, the metal substrate (1, 10) is coated with one single layer (2, 12) of chromium oxide having simultaneously reflecting and anti-reflecting characteristics.
The process may employ a step (f) or additional polishing process, to improve the coating, whereas sheets, tubes and spheres can be polished (2), however, if this additional step is not used, as in the case of wires, threads, fabric or metallic fiber, this does not drastically reduced absorbance values.
The usage of acetone is not mandatory in this procedure, this component ensures the cleaning of the metallic substrate (1) but it does not affect the efficacy values obtained.
The absorption level in the wavelength from 0.25 to 1.0 μm is in the range from 80 to 89%, the reflectance level in the wavelength from 2 to 15 μm which is in the range from 15 to 21%.
The thickness of the obtained film of chromium oxide is 100 nm to 200 nm.
Also and despite it is performed with hydrofluoric acid and nitric acid in the pretreatment and chromic acid to the pre-treated substrate to generate the selective coating at room temperature, the process allows its application on metallic substrate with thicknesses smaller than 0.03 mm up to thicknesses greater than 1.2 mm keeping their absorbance and reflectance properties for the applications described (12, 16, 17, 18, 19, 20).
A variation is that the present invention can be depose equally on reels of fiber, filament or metallic wire before being woven into a fabric woven with points or planes, without limiting the scope of the woven fabric, and having the same properties.
The tests conducted on the selective absorbing coating with a typical optical test of reflectance generate a high reflectance spectrum result such as the one shown in FIG. 2. The reflectance spectrum abruptly changes according to the value of the wavelength (approximately 1 μm), the intensity of the reflected solar radiation has a very low value, whereas at wavelengths greater than 1 μm, the intensity of the reflected radiation reaches a very high value. This ensures that the heating acquire by the metal element is not lost by thermal radiation.
The tests performed in FIG. 8, with the following configuration, mesh, fiber, fabric or metallic with the selective absorbing coating in the middle in a sandwich-type or tandem configuration with a polyester-cotton fabric with a weight of 235 g/m², and interior insulating lining (21) and one of a similar configuration without the fiber, mesh, thread or wire with the selective absorbing coating of the present invention as interlining between the polyester-cotton fabric and the insulating lining (22), both exposed to a radiation of 1000 W/m²emitted by two 500 W halogen lamps each at room temperature of 24° C. with an infrared filter, reflect a differential of 21.2° C. in just 5 minutes of exposure to radiation, being better and superior the garment that includes fiber, mesh, thread, wire with the present invention (21) demonstrating the advantages of integrating the meshes, fibers, thread or metallic wire with the present invention to traditional fibers to improve the thermal and energy absorption properties.
According to FIG. 9, where the external temperature of two pieces of garment is exposed, the one which includes fiber, thread, mesh or wire with the present invention (23) and one which includes the reflective dot technology of the infrared from human body (24), both exposed to radiation of 1000 W/m²emitted by two 500 W halogen lamps each at room temperature of 3° C., demonstrating a temperature differential of up to 5° C. in a time of 5 minutes, demonstrating that the present invention has advantages in the heat absorption and thermal storage, that comparatively with the traditional jackets among others, do not offer.
As it can be observed, the instant invention has the advantage of being a simple process that however has not been previously used for solving situations of cost reduction implemented in industries where process heat is required in the manufacturing process and where fossil fuels are mainly used, and it is thus considered a novelty for its simplicity but with a technical degree of good results.
Another advantage is that solvents and solutions can be reused, thus optimizing the use of these supplies.
Also in FIG. 10 we note that the present invention (26) substantially improves the uptake of radiation from traditional clothing (25), including those which are added only a fiber, mesh, thread or metallic wire beneath the outer fabric without the present invention (27). In FIG. 10, where we observe a thermal photo at different sandwich-type compositions similar to FIG. 5, the temperature differential (26) is 22° C. higher than (25) which does not have any fiber, thread, mesh or metallic wire and 10° C. higher than the one having only a fiber, thread, mesh or metallic wire but without the selective absorbing coating (27), so we see that the novelty of the present invention also resides in the fact that the temperature of the garments and traditional textile fibers increases and therefore improve comfort when using the present invention. According to the values reported in FIG. 11, the present invention has the ability to absorb light in the range of the wavelength spectrum up to 60% of the ultraviolet region (28), up to 73% in the visible spectrum (29), and up to 89% in the infrared spectrum (30). This means that the present invention absorbs in these three intervals of the electromagnetic spectrum: UV, visible, IR and turns it into heat for use in the human body.
A big advantage is that the present invention integrated on mesh, thread, wire or metallic fabric functions as a protective shield against ultraviolet rays as the tests conducted to measure the transmittance indicate that it only allows 27.6% of ultraviolet light incident on the same as shown in FIG. 12, thus improving protection against ultraviolet rays of jackets (16), caps (19), gloves (20), shoes (17), trousers, coats, tents (20), increasing a further 73% to the protection of the fabrics to be used outdoors and exposed to ultraviolet rays.
Another advantage is that it can be applied into substrates with thicknesses below 0.03 mm (10, 11, 12) and can be applied to configurations where selective coatings have never been applied as in the case of fibers, wire, threads or metallic meshes for use in textiles wherein jackets (16), trousers, scarves, shirts, hats (19), shoes (17) gloves (18), mittens and mitts, sleeping bags, tents (20), without limiting the scope of the invention, can be made up, and that in conjunction with insulating textiles enhance absorption and retention of body heat and solar radiation.
Thus, one of the main uses of the selective coating obtained at room temperature is on fibers, threads, wire and/or metallic meshes (10) and an example of its direct industrial application is for making jackets (16), sweaters, hats (19), gloves (18), fabric for tents (20), shoes (17) boots (17) among others without limiting the scope of the invention. Unlike the application on other substrates for other uses it does not require additional procedures in order to integrate the invention into fabrics with different characteristics, qualities and compositions as an interlining (14); the union of these absorb solar radiation, convert it into heat and maintain heat (26), which is equivalent to the use of bulky garments without the need of having thermal insulation around the garment to protect from the cold. The main advantages of a fabric of the present invention are: lighter textiles and garments, less bulky, externally generated heat and retention thereof in the garment, convenience, added value for the producer of textiles and superior aesthetics.

Claims

What is claimed is:

1. A radiation selective absorbing coating obtained at room temperature comprising:

a metallic substrate; and

at least one metal layer of chromium oxide;

wherein said metal layer has an optical absorption selectivity in the electromagnetic spectrum, reflective and antireflective characteristics and absorbance values between 80%-89% and reflectance between 15%-21%.

2. The radiation selective absorbing coating according to claim 1, wherein the metal layer of chromium oxide layer is 100 nm to 300 nm.

3. The radiation selective absorbing coating according to claim 1, wherein the optical absorption selectivity in the electromagnetic spectrum is up to 60% in the ultraviolet region, up to 73% in the visible spectrum and up to 89% in the infrared spectrum.

4. A process for obtaining at room temperature a radiation selective absorbing coating of claim 1, comprising the steps of:

(a) at least one cleaning stage;

(b) at least one first stage of immersion and standing in aqueous solution of a metallic substrate to be coated;

(c) at least one first rinsing stage;

(d) at least one second stage of immersion in aqueous solution; and

(e) at least one second rinsing stage,

(f) optionally, a polishing step,

and wherein the above steps (a)-(e) are performed between 20° C. and 40° C., and between 0% and 80% relative humidity.

5. The process according to claim 4, wherein in the at least one cleaning stage (a), the metallic substrate to be coated is cleaned with solvents that remove dirt, dust, grease, inorganic fats, polymeric coatings, coatings different from oxides and oils.

6. The process according to claim 5, wherein the solvent is selected from the group comprising silicates, phosphates, carbonates, sulfates, trichloroethylene, and/or optionally acetone.

7. The process according to claim 4, wherein in the at least one first stage of immersion and standing in aqueous solution (b), the metallic substrate to be coated is immersed in an aqueous solution of hydrofluoric acid in a concentration range from 0% to 5%, plus nitric acid in a concentration of 5% to 15%.

8. The process according to claim 7, wherein the standing in aqueous solution of a metallic substrate to be coated is for a time between 8 and 16 minutes.

9. The process according to claim 7, wherein the metallic substrate to be coated has a minimum thickness from 0.03 mm up to thicknesses greater than 1.2 mm.

10. The process according to claim 4, wherein the at least a first rinsing step (c) is performed with water.

11. The process for according to claim 10, wherein the rinse water is distilled water.

12. The process according to claim 4, wherein the at least one second stage of immersion (d), the pretreated metal substrate is immersed for 9 to 24 hours in an aqueous solution of chromic acid and sulfuric acid.

13. The process according to claim 12, wherein the chromic acid and sulfuric acid have a concentration of 200 g/L to 300 g/L and 350 g/L to 450 g/L respectively.

14. The process according to claim 12, wherein the pre-treated metallic substrate is immersed from 13 to 24 hours.

15. The process according to claim 12, wherein the pre-treated metallic substrate is preferably immersed from 9.5 to 10.5 hours.

16. The process according to claim 4, wherein the at least one second rinsing stage (e) is performed with water or with a liquid that removes impurities.

17. The process according to claim 4, wherein a humidity is between 20-80% RH.

18. A radiation selective absorbing coating obtained from the process claim 4.

19. The radiation selective absorbing coating according to claim 1, wherein the coating is deposited on metallic substrates with different configurations, shape and geometry.

20. The radiation selective absorbing coating according to claim 19, wherein the metallic substrate is selected from a metallic fiber, mesh, wire, fabric or steel wire for making interlining for coats, jackets, sweaters, hats, gloves, tents, shoes, boots.

21. The radiation selective absorbing coating according to claim 19, wherein the configuration is tandem type to capture solar radiation and/or artificial light and convert it into heat to increase the temperature of the garment and the body.

22. The radiation selective absorbing coating according to claim 19, wherein the shape and geometry can be smooth, rough, porous, tubular or laminar.

23. The radiation selective absorbing coating according to claim 1, wherein the coating increases protection of jackets, trousers, scarves, shirts, hats, gloves, mittens and mitts, sleeping bags, tents, against UV with 73% additional protection for each application.

24. The radiation selective absorbing coating according to claim 1, wherein the coating is apply to clothing, tents, shoes, or boots to capture solar radiation and/or artificial light, convert it into heat, retain the calorific energy and transmit it to the human body.

25. The radiation selective absorbing coating according to claim 24, wherein the radiation selective absorbing coating obtained at room temperature further reflects infrared from human body.

26. The radiation selective absorbing coating according to claim 1, wherein the coating is apply to thermosolar applications in the textile industry.