Patent GB-705934-A (GB)
Title: Conductive article and production thereof
Inventor: OLSON EARL RICHARD
IPC: H05B3/84
Filed: 1951-05-17
Abstract: 705,934. Electro-conductive coatings on glass. PITTSBURGH PLATE GLASS CO. May 17, 1951, No. 11597/51. Class 56 A sheet of soda lime glass is provided with a transparent electro-conductive coating by first providing the base with a surface which has a Na 2 O/SiO 2  ratio lower than that of untreated soda lime glass after heating the untreated glass at 1,150‹F. for 4 minutes, and then applying a transparent electro-conductive coating to the surface. The preliminary treatment, which is said to eliminate much of the haze which, previously occurred in the finished product, may be carried out by removing alkali from the glass surface or by coating the surface with a film which has a low removable-alkali content. Thus the surface Na 2 O may be reduced by exposure to the action of an acid or acidic gas which does not etch the glass, for example the glass may be heated above 400‹F. but below the melting temperature and exposed to SO 2  for about 30 minutes, or treated with solutions of, for example, hydrochloric, boric, nitric, oxalic, acetic, phosphoric, phosphorous, sulphurous, or sulphuric acids, the gases chlorine, chlorine monoxide, chlorine dioxide, phosgene, phosphorus pentoxide, hydrogen chloride, bromine, iodine vapour, hydrogen bromide, or phosphorus oxychloride or aqueous solutions of liquid acid halides such as thionyl chloride, sulphuryl chloride, thionyl bromide &c. It is frequently desirable to include methanol in the solution to improve the contact of the solution with the glass. In a further method'the glass. is coated with a base exchange agent such as clay which can combine with the Na 2 O or exchange other ions for the Naions, heated above about 500‹F. but below the melting temperature (800-1,250‹F.), cooled, and the clay removed by washing. Alkali may also be removed by heating the glass to 400-550‹F. and exposing it to a vaporized metal halide e.g. cupric chloride, cuprous chloride, or thallous chloride, in the absence of oxygen for several hours, and washing. It is advantageous to perform the alkali removal process at temperatures above about 400‹F. and usually not more than 100‹F. below the temperature to which the glass is heated for electroconductive coating, but may be performed without heating, but over a longer time, e.g. by soaking the glass in aqueous hydrochloric or sulphuric acid at room temperature for several hours. Alternatively a film, such as SiO 2  or transparent metal oxide of 100-300 millimicrons, may be deposited on the glass in lieu of removing the alkali or after such treatment, e.g. by repeatedly wetting the surface with a solution of silicon tetrachloride or tetrabromide or of silico-chloroform in a volatile non-aqueous solvent, drying each coating in the atmosphere, and rubbing each dried coating until it is bright, the wetting solution preferably containing a volatile ketone; by dipping the glass in a partially hydrolized silicic-acid ester such as ethyl ortho silicate or equivalent lower alkyl ester, and drying, by heating the glass to 220‹C. and spraying, in moist air, with titanium tetrachloride, or by depositing calcium or magnesium fluoride films by vacuum evaporation. The glass with low alkali surface is heated, e.g. for 1-10 minutes, above about 500‹F., preferably 800-1,250‹F., treated with a metal compound such as stannic chloride, excessively long heating being avoided to prevent migration of the alkali from the interior to the surface. The temperature and time of heating in the surface preparation are preferably correlated to those of the final coating operation, e.g. the former time being two to five times the latter, and the former temperature not substantially below, preferably not more than 100‹F. below, the latter. The coating solutions may be applied by a spray gun in the presence of an oxygen source such as water, air, or oxygen. Films resulting from treatment with SnCl 4  contain 95-99 per cent. SnO, with Cl 2 , C, Si, and Sn as impurities. The electro-conductivity of the coating is improved by the addition of methanol, phenyl hydrozine hydrochloride, or antimony chloride, and a wide variety of other agents of this character may be used such as those described in U.S.A. Specification 2,614,944. SnCl 4  may be used in solution or as a vapour. Other suitable tin compounds are SnBr 4 , SnBr 3 Cl, SnBrCl 3 , Sncl 2 I 2 , SnI 4 , stannic sulphate, stannic phosphate, stannic nitrate, stannous acetate, stannous oxalate, stannous chloride, stannous nitrate, stannous tartrate, organic tin compounds having the structure RmSnXn, where R is a monovalent aryl, aliphatic, or aryl aliphatic radicle linked to the tin atom through carbon and X is another monovalent aryl, aliphatic, or aryl aliphatic radical linked to the tin through carbon or is a radical such as hydride, hydroxyl, chloride, bromide, iodide, etc., and the sum of m and n is 4, examples being given, or tin compounds such as diphenyl tin, diethyl tin, stannic biacetylacetone dichloride or dibromide. Tin compounds are usually used which are liquid, vaporize readily, or dissolve in solvents such as water, benzene, xylene, toluene, acetone, methanol, ethanol, methyl ethyl ketone, etc. such solutions normally contain 10-50 parts by weight of tin compound per 100 parts by weight of solution. Other metallic compounds may be used with the tin compounds, e.g. indium chloride, cadmium bromide, cadmium acetate, zinc bromide, zinc acetate, thallium nitrate, chromium chloride, ferric chloride. The electro-conductive coatings may also be formed from metals other than tin, e.g. solutions containing indium trichloride, cadmium acetate, cadmium bromide, or cadmium chloride may be used. Typical base glasses contain in percentages by weight, Na 2 O 10-15, CaO 5-15, SiO 2  70-75, MgO 2-10, a typical example being SiO 2  71.38, Na 2 O 12.79, CaO 9.67, MgO 4.33, Na 2 SO 4  0.75, NaCl 0.12, Fe 2 O 3  0.15, Al 2 O 3  0.81. The colour characteristic of the film is determined by the thickness of the film which generally does not exceed 800 microns. The film intermediate the base and the coating may thus contain no Na 2 O or less surface Na 2 O than that of untreated glass, this is not essential however so long as the surface removable Na 2 O is below that of untreated glass which has been heated to the temperature at which the final coating is applied. The available surface Na 2 O content before coating, determined by immersing a 6 in. by 6 in. by # in. base in 350 ccs. of water for two hours and calculating the Na 2 O content of the water as sodium magnesium uranyl acetate, is less than 1. and preferably less than 0.5. Properties of the treated glass, and the preparation of several examples are given. The resultant glass may be used as windscreens, when heating caused by passage of an electric current through the coating prevents the formation of ice and fog on the glass, electrical insulators, grid leaks, space heaters, and mirrors. Specifications 604,878, 632,227, 632,256, and 639,561 are referred to.