Patent GB-749621-A (GB)
Title: Improvements in the manufacture of electrically conductive elements or coatings
IPC: H05K1/09
Filed: 1950-08-28
Abstract: Electrically conducting compositions comprise an ethoxyline resin (e.g. as sold under the Registered Trade Mark "Araldite") and a finely divided metal.  The metal, e.g. silver, copper or gold, preferably ocnstitutes 50-80 per cent of the solid content of the composition.  The compositions are used for making conducting elements or coatings.  They are cured at a temperature substantially higher than 180 DEG C. but below the decomposition temperature of the resin.  In an example a composition of two varieties of "Araldite" and finely divided silver dissolved in a mixture of diacetone alcohol, toluene, xylene, ethyl and methyl acetate is sprayed on to a glass surface and passed through a muffle furnace with inlet and outlet temperatures of 80 DEG  C. and a maximum temperature in the centre of 300 DEG  C.  The coated glass has half an hour warming up to 300 DEG  C., 1 hour at 300 DEG  C. and half an hour cooling down to the outlet temperature.  A protective layer or varnish film of "Araldite" may be applied and cured normally. Before curing the conducting coating it may be dusted with metal powder or the conductivity may be increased by electroplating or by solder-dipping technique.  By adding carbon, e.g. graphite, to the compositions their resistivities may be increased.ALSO:A mixture of finely divided metal and ethoxylene resin is used to produce an electrically conductive coating, the resin being cured by heat treatment at a temperature substantially above 180 DEG C. but below the decomposition temperature of the resin.  The metal, e.g. silver, copper gold or an alloy preferably constitutes 50-85 per cent of the composition.  The resin may be used in solution, the amount of solvent depending on the desired viscosity which in turn depends on the method of application, the shape and size of the base surface and the thickness of the coating required.  The thicknes of the coating may be controlled by spraying to a definite degree of wetness which may be observed and controlled photo-electrically by the degree of specular reflection.  Other controls or automatic traversing of the spray, variation of the pressure, or of rate of feed.  Dispersion of the spray can be controlled electrostatically.  Curing may be effected as an intermittent process in a muffle furnace or as a continuous process, the coated article passing through a heating-up zone, a zone of maximum temperature (e.g. 300 DEG C.) and a cooling zone.  In the example a solution of two mixed Araldites (R.T.M.) containing silver is sprayed on to glass and passed through a muffle with inlet and outlet temps. of 80 DEG C. and a central zone at 300 DEG C.  The rate of advance is such that the glass warms up for half an hour, remains for 1 hour at 300 DEG C. and cools in the next halfhour.  A protective layer of "Araldite" varnish may be applied and cured at normal temperature.  If desired powdered metal may be dusted on the conductive coating or even on to a plain coating before curing to increase its conductivity.  The coating may be electro-plated or built up by solder dipping technique.