Patent GB-724087-A (GB)
Title: Conductive articles
Inventor: LYTLE WILLIAM ORLAND
IPC: H01B1/08
Filed: 1951-04-30
Abstract: <PICT:0724087/III/1> <PICT:0724087/III/2> <PICT:0724087/III/3> A sheet of glass or refractory material is provided with a transparent electroconductive film by heating the sheet to at least 400 DEG F. but below the temperature at which it becomes molten, passing it edgewise constantly forward through a spray of the filming composition while holding it at an angle to the direction of spray, and removing it from the spray before the film thickness exceeds 800 millimicrons.  The resistivity of the resultant film is not uniform, being highest at the leading edge, and may be further varied so as to give a required resistivity at various parts of the sheets which may be of various and non-uniform shapes.  As shown the panel 14 has bus bars 16, usually provided before the coating operation but if necessary intermediate a pair of cooling operations.  The spray gun 10 is adjusted to give a spray having a width at least equal to the width of the panel, the spray pattern normally being oval as in Fig. 1.  More than one gun may be required.  The film compositions, several of which are described, preferably comprise a hydrolysable tin compound such as a halide, desirably stannic chloride, but may include stannous acetate, zinc acetate, cadmium acetate, cadmium bromide, or indium trichloride.  Fig. 4 shows the application of a spray 12 at an angle of approach a  of 90 degrees, whereby the film is thinner, and therefore has a higher resistivity, at the leading edge 18, and this condition may be exaggerated by increasing the angle of approach above 90 degrees, or minimized by making the angle a  substantially below 90 degrees but not less than about 10-15 degrees.  The bus bars may be formed by fusing together 70 parts litharge, 16 parts boric acid, and 14 parts silica, and mixing 10 parts of the milled frit with 70 parts flake silver, 12.5 parts French fat oil, and 7.5 parts turpentine, and applying the resultant to the panel edges to a thickness up to 0.0025 inch but preferably less than 0,0025 inch.  The bus bars are tapered to a point at the edge of the panel beyond the centre of the curve at the corners, as in Fig. 5.  Alternatively the bars may be formed by using an adherent metal spray to deposit metal on the glass base, which may be roughened previously by grinding, etching, &c.  The panel shown in Fig. 5, after formation of the bus bars, was heated at 1150-1250 DEG F. for two minutes and then passed with an angle of approximately 90 degrees before a dumb-bell type spray which is wider and more dense adjacent the upper and lower ends than in the centre.  The resultant surface resistance in ohms per unit square were as follows, A 92, B 136, C 97, D 92, E 102, F 77, G 138, H 175, I 140.  A further example is also described.  The invention is particularly suitable for application to panels having uneven widths, e.g. as in Fig. 1, or having curved sides, to ensure that the current density is more uniform, thus avoiding the establishment of high current densities, e.g. where the bus bars are closer together, with resultant strain and fracture of the panel.  The thickness of the film, and hence the resistivity, may also be varied by passing the panel through the spray at non-uniform speed.  The spray may be directed horizontally and the sheet held more or less perpendicularly thereto, or the sheet held horizontally, and the spray directed vertically upward or downward.  The panels may be formed of lime-soda glass, borosilicate glass, china, porcelain, mica, phosphate glass, stone, lead X-ray glass, tungsten carbide, aluminium oxide, marble, tungsten &c. Windscreens may be made by this method, the coating being used as a heating element.  Specification 724,086, [Group XI], is referred to.