Coating processes – Coating has x-ray – ultraviolet – or infrared properties
Utility Patent
1999-11-02
2001-01-02
Cameron, Erma (Department: 1762)
Coating processes
Coating has x-ray, ultraviolet, or infrared properties
C427S163100, C427S164000, C427S165000, C427S368000, C427S369000, C427S426000
Utility Patent
active
06168825
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates in general to the production of uniform, tightly adhered, thin, transparent gold coatings, and, in particular, to the efficient and economical production of such films on surfaces. More particularly, this invention relates to the production of thin transparent blue to blue-green gold coatings on nonmetallic surfaces using an electroless spraying process for deposition resulting in films which transmit a high degree of visible light, while still blocking a large amount of infrared light.
2. Description of the Prior Art
Gold coatings can be deposited onto substrate materials through the use of electroless chemical deposition processes. A good review of the prior art before 1960 is given in a two part article by Samuel Wein (“Gold Films,” The Glass Industry, May 1959 p. 280 and June 1959, p. 330). Here a variety of formulations are presented as well as techniques involving both dipping and spraying methods of application. The methods described are relatively slow requiring five minutes to twenty four hours for reaction to occur, and many require the procedure to be carried out at elevated temperatures.
Levy was awarded U.S. Pat. No. 3,515,571, which describes the simultaneous spraying of two solutions onto substrates. The gold solution is made of a gold salt (gold chloride, gold bromide, or sodium gold thiosulfate) neutralized with sodium hydroxide or other metal hydroxides to which is added a ligand solution of diethylenetriamine neutralized with acid (hydroboric acid). The reducing solution contains hydrazine and an alkali metal hydroxide. The two solutions are simultaneously sprayed onto a sensitized (using a solution of stannous chloride) substrate with a dualhead spray set-up. The technique was used to provide gold mirror films for use in heat shielding in various NASA spacecraft applications. The thickness of the films described both in the patent as well as other related literature (Levy, The Lockspray-Gold Process Technical Data Bulletin, Lockheed Palo Alto Research Laboratory, April
1966
) ranged from 0.4-80 micro-inches (100-20,300 Angstroms) in thickness. The literature reports that it is difficult to control the deposition of thin films (less than 200 Angstroms) without modification to the procedure. In addition, no mention of chemical deposition onto polycarbonate as a substrate was described.
In U.S. Pat. No. 3,484,263, Kushashi et al. form semi-transparent gold coatings on glass by using an alkaline solution containing a gold salt, a reducing agent, and an alkali carbonate to contact the glass. The system is maintained at less than 10 degrees centigrade for 0.5-5 minutes, then irradiated with a mercury lamp of 2500-5000 nanometers wavelengths to cause reduction. This is reported to give good uniformity for the resulting film, but requires temperature control, and a light source to initiate reduction.
Miller and Cavitt in U.S. Pat. No. 4,005.229 describe the rapid deposition of gold films at ambient temperature using a delivery system similar to Levy. The glass is prepared as described by Miller et al. in U.S. Pat. No. 3,723,158, sensitized with stannous chloride, and activated with a dilute solution of palladium chloride or a thin catalytic metal film, typically silver, through a spray reduction process. The gold solution employed consists of gold chloride, sodium carbonate, and a surfactant. The solution is then aged. The reducing agent is hydrazine tartrate with a source of divalent ion added, preferably lead nitrate. Miller in U.S. Pat. No. 4,091,128 describes a method involving cleaning of the glass substrate as described by Miller et al. in U.S. Pat. No. 3,723,158, followed by sensitizing with a stannous chloride solution, then an activation step using either silver ions or palladium chloride in solution. A gold chloride with sodium carbonate solution is reduced by hydrazine reducing agents with a small amount of surfactant added to the solution using a double nozzled spray gun. The resulting coating is then rinsed and a film of silver is added through a similar spray process involving a silver solution contacted by a reducing solution. It is reported that the resulting film has a more intense gold color and superior durability compared to simply a deposited gold film. Both patents describe techniques for rapid deposition, but require an activation step before film deposition. The patents report films produced with luminous transmittance percent values up to 45 percent. In addition, glass is the only substrate described in either patent.
Very thin deposits of gold, for example, deposits with thicknesses of less than approximately 300, and preferably, 200 Angstroms, are more or less transparent to visible light. The nature of the deposit determines to a significant degree how much visible light is transmitted. Some gold deposits appear pink to golden as soon as they become visible to either incident or transmitted light, and others appear blue to blue-green or blue-gray until they reach a thickness of several hundred Angstroms. Of the various forms of gold, the blue to blue-green to blue-gray deposits are the most transparent to visible light. For ease of reference, as used herein, unless otherwise indicated, it will be understood that the use of “blue” describes and includes all shades of blue, including the blue-green to blue-gray deposits. Such blue deposits generally transmit approximately half as much infrared energy as they do visible light. The pink colored gold deposits generally transmit more infrared than visible energy. The blue deposits are thus much preferred over the pink colored gold deposits for use in applications where visible light is to be transmitted and infrared energy is to be blocked. The inexpensive production of satisfactory blue deposits under desirable production conditions and restraints had generally been impossible or impractical. Uniformity and tight adherence of the deposits to the substrate, ease of production and repeatability had generally been unsatisfactory.
The physical properties of thin transparent gold films include the transmittance of significant amounts of visible light while blocking much of the infrared light from passing through the substrate. This is accomplished through a highly reflective process. For use as windshields in automobiles, the law requires the glass to have at least 70 percent transmittance of visible light. At least 20 percent, and, prefereably as much as 40 percent of the infrared energy should be blocked. This was reported to be a problem in the Levy's Lockspray process, and was not achievable in the Miller patents. In order to achieve a 50 percent or greater transmittance, it is necessary for the gold film to be less than approximately 200 angstroms in thickness. Achieving a uniform, tightly adhered coating at thicknesses of approximately 200 angstroms or less inexpensively, rapidly and simply had generally been considered to be impractical.
Sputtering has been proposed as a preferred way of producing thin gold coatings. Sputtering operations require that they be performed in very closely controlled environments. They can not be performed in ambient conditions, which limits their use to fixed location manufacturing sites with significant capital investment in equipment. They can not, for example, be used to coat a window at the location of a construction project or in a manufacturing station that is open to the ambient environment.
Those concerned with these problems recognize the need for improvement.
BRIEF SUMMARY OF THE INVENTION
A preferred embodiment of the process of gold deposition according to the present invention comprises selecting a substrate and cleaning the surface upon which the thin film of gold is to be deposited. Preferably, as a part of the cleaning, the surface is lightly etched so that a fresh debris free surface is presented. The etching can be accomplished chemically, for example, with an etching solution, or mechanically, for example, with a polishing compound, or both. The etching is so l
Jakubowski Gerald S.
Landry James M.
O'Brien Dudley
Vogler Jerry
Cameron Erma
Jagger Bruce A.
LandOfFree
Process for producing thin transparent gold coatings does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for producing thin transparent gold coatings, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for producing thin transparent gold coatings will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2446289