Coating having solar control properties for a substrate, and method and system for depositing said coating on the substrate

Abstract

The present invention relates to coating glass for architectural or automotive use, either monolithic or laminated, having solar control properties. The coating consists of several layers of different metal oxide semiconductors (TiO.sub.2, ZnO, ZrO.sub.2, SnO.sub.2, AlO.sub.x) and a layer of metallic nanoparticles, which when superimposed on a pre-established order give the glass solar control properties. In particular the use of protective layers of n-type semiconductors around the metallic nanoparticles layer. It also relates to the method for obtaining the coating by means of the aerosol-assisted chemical vapor deposition technique, using precursor solutions containing an organic or inorganic salt (acetates, acetylacetonates, halides, nitrates) of the applicable elements and an appropriate solvent (water, alcohol, acetone, acetylacetone, etc.). The synthesis is performed at a temperature between 100 and 600° C. depending on the material to be deposited. A nebulizer converts the precursor solution into an aerosol which is submitted with a gas to the substrate surface, where due to the temperature the thermal decomposition of the precursor occurs and the deposition of each layer of the coating occurs.

Claims

1. A method for depositing a solar control coating on a substrate comprising the steps of: a) placing the substrate in a clamping area; b) heating the substrate in a heater chamber to a predetermined temperature; c) preparing a mixture of a precursor solution and a solvent; d) depositing the mixture of precursor solution and solvent in the heating chamber to form the solar control coating composed of active n-type protective semiconductor layers deposited one below and the other one above a layer of metal nanoparticles having a diameter of less than 30 nm on the recently heated substrate, wherein the temperature in the heating chamber produces the evaporation of the solvent and deposits the precursor solution on the substrate surface, forming the solar control coating on the substrate; and e) removing the substrate from the clamping area once the coating layer is formed.

2. A method according to claim 1, wherein the step of depositing the mixture of precursor solution and solvent to form at least one coating layer on the substrate comprises: producing a micrometric drop cloud or aerosol of the precursor solution on the substrate.

3. The method according to claim 2, wherein the micrometric drop cloud is applied with a diameter of between 1 to 20 microns.

4. The method according to claim 1, wherein the precursor solution comprises organometallic precursors or inorganic compounds.

5. The method according to claim 4, wherein the inorganic or organometallic precursors are acetates, acetylacetonates, chlorides, nitrates, or halides.

6. The method according to claim 1, wherein the solvent being water, distilled water, methanol, ethanol, acetone, or a mixture thereof.

7. The method according to claim 1, wherein the substrate temperature is between 100° C. and 600° C.

8. The method according to claim 1, wherein the concentration of the precursor solution is from 0.001 to 0.2 mol.Math.dm.sup.−3.

9. The method according to claim 1, wherein the step of depositing the precursor solution mixture and solvent of step c) comprises: introducing said mixture into the heating chamber by means of a carrier gas with a flow of between 1 and 10 L min.sup.−1.

10. The method according to claim 9, wherein the carrier gas is air, argon, nitrogen, or a similar gas.

11. The method according to claim 1, wherein the step of depositing the mixture of precursor solution and solvent is performed by the aerosol-assisted chemical vapor deposition technique (AACVD).

12. The method according to claim 1, wherein the solar control coating comprises: i) a first active protective layer residing over one surface of the substrate; ii) a non-continuous metallic nanoparticle layer residing over said first active protective layer; iii) a second active protective layer residing over said metallic nanoparticle layer; and iv) a dielectric layer.

13. The method according to claim 12, wherein the non-continuous metallic nanoparticle layer comprises metallic nanoparticles having a diameter of less than 30 nm.

14. The method according to claim 12, wherein the dielectric layer comprises Al.sub.2O.sub.3.

15. The method according to claim 12, wherein the first active protective layer and second active protective layer comprise a metal oxide, wherein said metal oxide comprises titanium or zinc.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows the schematic diagram of a coating with solar control properties, comprising a substrate (1), four layers of metal oxides (2), (4), (5), (6) and a layer composed of evenly distributed metal nanoparticles (3).

(2) FIG. 2 shows the schematic diagram of a coating with solar control properties, comprising a substrate (7), six layers of metal oxides (8), (9) (10) (12) (13), (14) and a layer composed of uniformly distributed metal nanoparticles (11).

(3) FIG. 3 shows a diagram of the system used for depositing the different layers of solar control coating of the present invention.

(4) FIG. 4 shows the cross section of a typical solar control coating, where the different component layers can be seen, particularly the uniform layer of metal nanoparticles surrounded above and below by the protective layer of n-type semiconductor.

(5) FIG. 5 shows the spectra percentage of transmittance (% T), reflectance (% R) and absorbency (% A) of a typical solar control coating, with the structure shown in Example 2 (VC/TO.sub.2/Al.sub.2O.sub.3/TiO.sub.2/Nano-Au/TiO.sub.2/Al.sub.2O.sub.3/TiO.sub.2). A vertical arrow indicates the position of the absorption peak in the IRC around 1000 nm.

(6) FIG. 6 presents the spectra percentage of transmittance (% T), reflectance (% R) and absorbency (% A) of a typical solar control coating, with the structure shown in Example 3 (VC/ZnO/ZrO.sub.2/Al.sub.2O.sub.3/TiO.sub.2/Nano-Ag/TiO.sub.2/Al.sub.2O.sub.3/SnO.sub.2). A vertical arrow indicates the position of the reflection peak around 800 run.

(7) FIG. 7 includes a schematic showing the methodology for the preparation of substrates and coating deposition by means of the AACVD technique.

DETAILED DESCRIPTION OF THE INVENTION

(8) The present invention describes coatings with solar control properties deposited on glass for architectural or automotive use, either monolithic or laminated. Solar control refers to the ability to modify the amount of transmitted, reflected and absorbed solar radiation in the solar range comprised between 300 and 2500 nm. Generally low transmittance is pursued in the UV and IRC (near-IR) ranges, while transmittance in the VIS should be high (>70%) for automotive applications or low for architectural applications. The coating is composed of two or more layers of different semiconductor metal oxides (TiO.sub.2, ZnO, ZrO.sub.2, SnO.sub.2 or Al.sub.2O.sub.3) and one or more layers of metal nanoparticles selected from Gold (Au), Silver (Ag), platinum (Pt) and palladium (Pd), uniform, non-continuous and homogenously distributed over the entire surface of the coated substrate.

(9) As exemplified in FIG. 1, the CS solar control coating of the present invention is deposited on a surface of a glass substrate 1 by the technique of aerosol-assisted chemical vapor deposition technique (AACVD). In the example shown in FIG. 1, the CS solar control coating is deposited on at least one surface of the substrate 1. As described herein, the term “solar control coating” refers to a coating comprising one or more layers or films that affect the solar properties of the coated article, but not limited to the amount of solar radiation, for example, visible, infrared, or ultraviolet radiation. The CS solar control coating can block, absorb or filter selected portions of the solar spectrum, such as IR, UV and/or visible spectrum.

(10) Examples of CS solar control structures are shown in FIGS. 1 and 2, representing 5 and 7 layer coatings, respectively. In the example illustrated in FIG. 1, the CS solar control coating comprises 5 layers: There is substrate (1) on which layer (2), consisting of TiO.sub.2 or ZnO, but mainly TiO.sub.2, is deposited first. Its thickness shall be between 10 and 70 nm. This first layer also serves as a support for the metal nanoparticles (3) and further as an active protector, given its n-type semiconductor character, to prevent oxidation of the nanoparticles, as well as increase their adhesion. The metal nanoparticles layer (3) is deposited so that the size of the nanoparticles is less than 30 nm, its distribution is uniform and covers a large part of the surface (>80%). The function of the metal layer (3) including Au and/or Ag metals, is to increase IR blocking by absorption and/or reflection (see FIGS. 5 and 6). Subsequently, a second active protective layer (4), consisting of TiO.sub.2 or ZnO, but mainly TiO.sub.2, whose thickness is similar to the first protective layer, i.e. between 10 and 70 nm, is deposited on it, whose function is to protect the metal nanoparticles from oxidation. Then one or more dielectric layers are superimposed, in order to increase solar control properties, in particular to increase transmittance in the visible range. Therefore, in FIG. 1 layer (5) corresponds to an Al oxide (Al.sub.2O.sub.3); its thickness shall be between 10-150 nm. The final layer (6) corresponds to a mechanically resistant material, such as ZrO.sub.2, SnO.sub.2, TiO.sub.2 or a compound of them, preferably including the stronger material (ZrO.sub.2).

(11) The example illustrated in FIG. 2, schematically shows a CS solar control coating made up by 7 layers. FIG. 2 shows a glass substrate (7) on which the first layer (8) is deposited, corresponding to the diffusion consisting of TiO.sub.2 or ZnO with a thickness between 10-70 nm. Subsequently, layer (9) corresponds to one or more dielectrics, e.g. ZrO.sub.2 or Al.sub.2O.sub.3 or both sequentially deposited, its thickness may be between 10-150 nm. Then, the support layer (10) follows, which promotes better adhesion of nanoparticles and also plays the role of active protector, given its n-type semiconductor character, to prevent oxidation of the nanoparticles. Support layer (10) may be composed of TiO.sub.2 or ZnO, but mainly TiO.sub.2. Its thickness shall be between 10 and 70 nm. The layer of metal nanoparticles (11) is deposited so that the nanoparticle size is 8 to 30 nm, with a uniform non-continuous distribution and covering a large part of the surface (>80%). The function of the metal layer (11) including Au and/or Ag metals, is to increase the IRC blocking, by absorption and/or reflection. This is apparent in FIG. 5, where the spectra are shown as percent of transmittance (% T), reflectance (% R) and absorbency (% A) of a typical solar control coating (structure of example 2) where a vertical arrow indicates the peak position of IRC absorption. Then a second active protective layer (12), consisting of TiO.sub.2 or ZnO, but mainly TiO.sub.2, whose thickness is similar to that of the first protective layer, i.e. between 10 and 70 nm, is deposited on layer (11). The last dielectric layers are then superimposed, whose function is mainly to increase transmittance in the visible range. Therefore in FIG. 2, layer (13) corresponds to one or more dielectrics, for example Al.sub.2O.sub.3, whose thickness is similar to that of the first Al.sub.2O.sub.3 layer, that is, between 10-150 nm and other dielectrics such as TiO.sub.2, with thickness between 10-120 nm, may be added on it. The final layer (14) is resistant to abrasion, for example ZrO.sub.2, SnO.sub.2, TiO.sub.2 or a compound of them, preferentially including the stronger material (ZrO.sub.2).

(12) These properly deposited structures, with the required thickness, confer to glass solar control properties, particularly IR blocking and adequate transmittance in the VIS. In particular the use of active n-type metal-semiconductor junctions, allows injection of negative charges from the semiconductor to the metal (Schottky junction) protecting it from oxidation and also preventing its agglomeration; this allows obtaining uniform layers of homogeneously distributed metal nanoparticles over a large portion of the solar control coating intermediate surface.

(13) Additionally, it is intended that the developed product has high mechanical, thermal and chemical resistance, sufficient to support the manufacturing processes of tempered and/or laminated glass without making changes that impair the performance of solar control. The coated products were subjected to various tests to determine industrial tempering capability by means of fracture tests, laminating (Pummel tests and boiling under customer standards and ANSI/SAE Z26.1-1996) and chemical contact resistance of samples to acid solutions. Coated glasses successfully passed all of these tests, confirming the feasibility of integrating the developed product to tempering and laminating glass manufacturing processes.

(14) Obtention of Glasses with Solar Control

(15) The aerosol-assisted CVD method (AACVD) is an economical, efficient and useful process for obtaining relatively thin coatings, with maximum thickness of several micrometers. It consists in producing a cloud of micrometric drops, whose diameter is in the range of 1 to 20 mm, from a solution made up by organometallic precursors (acetates, acetylacetonates) or inorganic compounds (halides, nitrates), dissolved in a particular solvent for each type of compound (water, alcohol, acetone, acetylacetone, etc.). The aerosol can be generated by pneumatic, electrostatic or ultrasonic methods. Among the most effective are ultrasonic nebulizers which generate drops with size of a few micrometers and with a closed distribution of sizes (FWHM˜10%). In these nebulizers, a drop cloud is produced by vibration (a few MHz) of a piezoelectric crystal, whose ultrasonic waves are concentrated on the surface of the solution, which generates the micrometric drop cloud by means of cavitation. Droplet size depends primarily on the frequency of the piezoelectric (inversely), as well as on surface tension and density of the solution. Drop size and essentially its size distribution decisively influences the conditions (substrate temperature, carrier gas flow) of the tank and the quality of the obtained material. A widespread drop size distribution prevents optimizing synthesis conditions, because a large drop requires different conditions to those of a droplet; resulting in an inhomogeneous and shoddy coating. The precursor solution aerosol must be transported to the storage area by a carrier gas. In the deposition area, is the glass substrate, which is heated to a specific temperature depending on the material to be deposited. The substrate temperature is the key parameter controlling the deposition of material. The optimum temperature of the process depends on the precursors used, consequently on the material to be deposited, but in general it can be said that these are relatively low, between 373 K (100° C.) and 873 K (600° C.). In obtaining a coating, in addition to the thermodynamic conditions it is necessary to verify the kinetics of the process. Since growth of the film depends on: a) the process of transporting the reactant(s) to the vicinity of the substrate surface; where as the cloud approaches the substrate it warms up initially causing solvent evaporation, melting, evaporation or eventually sublimation, or thermal decomposition of the precursor compound, and thereafter its diffusion towards the surface. b) kinetic processes on the substrate surface, where the following processes are required in succession: reactant adsorption, diffusion and convergence on the substrate surface, chemical reaction, diffusion and desorption off the surface of the chemical reaction products and disposal away from the surface, to avoid contamination of the deposited material.

(16) Description of the Obtention System:

(17) FIG. 3 shows a schematic diagram of the system used in the process of the present invention. The system consists of the following parts:

(18) a) A heating plate or chamber (23) for elevating the temperature of the glass substrate to the deposition temperature between 100 and 600° C. The heating system comprises a temperature control (not shown in the figure) that allows keeping temperature constant throughout the deposition process. Moreover, heating shall be uniform throughout the glass surface.

(19) b) A nebulizer (19) which may be of pneumatic, electrostatic or ultrasonic type. The carrier gas (16) with its pressure regulator (17) and flow controller (18) and finally the aerosol exit nozzle (20) towards the substrate surface (22).

(20) c) The nozzle drive system of the (21) permits distributing the precursor solution over the entire surface of the substrate in order to obtain uniform coatings. The nozzle (20) is mounted on the nozzle drive system (21) having controlled movement (0.1 to 5 cm) allowing even distribution of the precursor solution over the whole substrate surface, in order to obtain uniform coatings.

(21) d) The gas extraction system (24) to prevent contamination of the deposited coating.

(22) Preparation of the precursor solution.

(23) The precursors are mainly organometallic salts of the elements of interest and as solvent, one suited to each salt was used, preferably aqueous or alcoholic solutions were used due to their advantageous features for aspersion (methanol, ethanol, triple distilled water), concentrations used were from 0.001 to 0.2 mol/dm.sup.3. Precursors for introducing dopants were also organometallic salts. Dopant concentration will range from 1% atomic up to the solubility limit of the dopant relative to the base material, which may be up to 10-40% atomic. Complete dissolution of the precursor used by means of suitable stirring, heating and/or ultrasound shall be ensured.

(24) Application Method

(25) The synthesis starts with the preparation of the precursor solution containing an organic or inorganic salt containing the element of interest, for example a chloride, nitrate, acetate or acetylacetonate, tin tetrachloride, zinc nitrate, zinc acetate, aluminum acetylacetonate, zirconium acetylacetonate; and a suitable solvent such as methanol, ethanol, acetone, water or a mixture thereof. The concentration of the solution is in the range of 0.001 to 1.0 mol.Math.dm.sup.−3.

(26) The substrate (22) is fastened to the heating plate (23). The deposition temperature between 100 and 600° C. is set, and the substrate system is turned on (22) to stabilize substrate temperature. The remaining parts of the AACVD system are configured: nebulizer (19) and nozzle (20). The carrier gas (16) is connected. It is important that the couplings are tight to prevent leakage of aerosol. Additionally the nozzle motion speed (20) is set between 0.1 and 5 cm/min, which allows varying the thickness of the deposited coatings. Nozzle total travel length is also set, depending on the portion of the substrate that is to be covered. The gas extraction system (24) is also turned on to stabilize the temperature in the entire system.

(27) The introduction of carrier gas (which may be air but depending on the coating argon, nitrogen or other similar gas may be used) is also started. For thermal stabilization, the flow is set between 1 and 10 L min.sup.−1. The particular value of the flow of carrier gas and the deposition temperature depend on the material to be deposited.

(28) Additionally, the precursor solution is introduced in the nebulizer (19). If necessary for long deposition times a larger amount of solution can be added during deposition, using a peristaltic pump (15). A commercial ultrasonic nebulizer (19), operating at 2.4 MHz high frequency was used in tests.

(29) Upon reaching the thermal stability of the whole system, the process proceeds by turning on the nebulizer (19), generating the aerosol cloud of the precursor solution; simultaneously displacement of nozzle (20) via the nozzle drive system (21) is started. The generated cloud enters the nozzle (21). In the nozzle, the precursor solution and carrier gas mixture rises in temperature to between 50 and 150° C.; this preheating to a temperature lower than synthesis temperature ensures that the precursor reach the substrate surface (22) in the reaction zone at the temperature required for thermal decomposition and coating deposition is carried out in optimal conditions. In the substrate surface (22), physical transformations and precursor chemical decomposition are carried out by action of the temperature, yielding a well bonded, high purity coating on its surface. Forming of the thin film on the substrate surface occurs after the thermal decomposition of the precursor, for this reason the surface temperature has a major role in obtaining the material of interest. Additionally, changing the nozzle travel speed allows obtaining thin films of different thicknesses.

(30) Once the chemical reaction takes place and reaction gases are generated, they are evacuated by an extraction system (24), to avoid contamination of the deposited material and thus obtain high purity coatings. The process is repeated with each precursor to deposit all the different layers of the coating.

Examples of Coated Substrates

EXAMPLE 1

(31) Using a 4 mm-thick clear glass (VC), five coating layers were deposited by the AACVD method with the following structure:

(32) TABLE-US-00001 Material Thickness [nm] ZrO.sub.2 35 Al.sub.2O.sub.3 45 TiO.sub.2 Nano-Au 75 TiO.sub.2 VC 4 mm
Optical properties in this coating solar range are summarized in the following table. Transmittances are presented in the ultraviolet (UV 300-380 nm), solar (SOL 300-2500 nm) and visible (VIS 380-780 nm) intervals.

(33) TABLE-US-00002 % T UV SOL VIS 43 52 62

EXAMPLE 2

(34) Using a 4 mm-thick clear glass, seven coating layers were deposited by the AACVD method, with the following structure:

(35) TABLE-US-00003 Material Thickness TiO.sub.2 134 Al.sub.2O.sub.3 106 TiO.sub.2 97 Nano-Au TiO.sub.2 Al.sub.2O.sub.3 101 TiO.sub.2 68 VC 4 mm
The transmittance values at ultraviolet (UV 300-380 nm), solar (SOL 300-2500 nm) and visible

(36) (VIS 380-780 nm) intervals of this coating are:

(37) TABLE-US-00004 % T UV SOL VIS 36 42 56

(38) FIG. 5 shows the spectra in percentage of transmittance (% T), reflectance (% R) and absorbance (% A) of a typical solar control coating, with the structure of Example 2 (VC/TiO.sub.2/Al.sub.2O.sub.3/TiO.sub.2/Nano-Au/TiO.sub.2/Al.sub.2O.sub.3/TiO.sub.2). A vertical arrow indicates the position of the absorption peak in the IRC around 1000 nm.

(39) FIG. 4 shows the cross section of a typical solar control coating, with a similar structure to Example 2, wherein the glass substrate is represented by the number 25; a first layer (26) acting as anti-diffusion barrier (ZnO, ZrO.sub.2); a second layer (27) of a first dielectric (Al.sub.2O.sub.3, TiO.sub.2, ZrO.sub.2); a third layer 28 of n-type semiconductor, adhesive-protector (ZnO, TiO.sub.2); a fourth layer (29) of metal nanoparticles (Ag, Au, Pt, Pd); a fifth layer (30) of an n-type semiconductor, protector (ZnO, TiO.sub.2); a sixth layer (31) of a second dielectric Al.sub.2O.sub.3, TiO.sub.2 or ZrO.sub.2; and seventh layer of materials to improve mechanical strength selected from SnO.sub.2 or ZrO.sub.2. In said FIG. 4 the different component layers, particularly the uniform layer of metal nanoparticles surrounded above and below by the protective layer of n-type semiconductor, may be seen.

EXAMPLE 3

(40) Using a 4 mm thick clear glass, eight coating layers were deposited by the AACVD coating method under the following structure:

(41) TABLE-US-00005 Material Thickness SnO2 66 Al.sub.2O.sub.3 249 TiO.sub.2 86 Nano-Ag TiO.sub.2 Al.sub.2O.sub.3 114 ZrO.sub.2 69 ZnO 54 VC 4 mm
The transmittances at ultraviolet (UV 300-380 nm), solar (SOL 300-2500 nm) and visible (VIS 380-780 nm) intervals of this coating are:

(42) TABLE-US-00006 % T UV SOL VIS 31 52 63

(43) FIG. 6 presents the spectra in percent transmittance (% T), reflectance (% R) and absorbance (% A) of a typical solar control coating, with the structure of Example 3 (VC/ZnO/ZrO.sub.2/Al.sub.2O.sub.3/TiO.sub.2/Nano-Ag/TiO.sub.2/Al.sub.2O.sub.3/SnO.sub.2). The vertical arrow indicates the position of the reflection peak around 800 nm.