Patent GB-502931-A (GB)
Title: A process for the production of smooth edges in electro-deposited coatings on non-conductors
IPC: C25D5/54
Filed: 1938-03-23
Abstract: 502,931. Electrodeposition of metal on non-conductors; glass and earthenware pipes ; medical syringes; bottles. HOCHWALD, F. March 23, 1938, No. 8948. [Class 41] [Also in Groups VI, XVII, and XXVIII] In the produotion of metallic coatings over parts of non-con. ductors, such as glass, porcelain or artificial resin, means are adopted to prevent the formation of ridges at the margins. This may be done by means of screening devices such that the current density on the surface to be metallized is diminished in the neighbourhood of the margin. Electrodeposition may be effected beyond the desired margin and the undesired metal removed afterwards ; removal of this is facilitated by forming scratches transverse to the margin in the conducting layer first applied or in the initial eleetrodeposited layer. The margin itself may be marked by such a scratch; this may be bridged, or independent electric connection to the surface may be made on both sides of the scratch. In this case screening means are not necessary ; the width of the scratch should be enough to prevent coalescence of the deposits on the two sides while not enough to permit ridge formation. The same result may be produced by forming the non-conductive surface with a narrow ridge which is not covered in the preliminary application of a conducting layer. When an article is to be coated up to its edge removaple extension pieces which also receive a deposit are applied during the electrodeposition. A recess may be formed in the non-conducting surface at the desired margin in which the screening means such as a wire may be disposed.. The screening means may consist of a non-conductor, for example a rubber ring, a strip of varnish or lacquer, a silk thread or a layer of fat or the like or of an enamelled wire laid over the preliminary conductive layer. A textile thread impregnated with electrolyte may also be employed. In coating a tube a rubber ring is applied at the desired margin and a conductive layer applied over the whole; after electrodeposition the ring is removed. Electrodeposition is effected at normal current densities, which may be increased a few hours before removal of the articles from the bath. In coating the lower part of a glass sphere 2, a conductive layer of graphite or silver is applied extending be yond the desired' edge. Contact is made by a wire, not shown, at the upper part and an enamelled wire 6 is applied at the desired edge. A gap 7 is made in the conductive layer. After electrodeposition the upper part of the coating at the top of which a ridge 8 is formed is removed together with the wire 6 leaving the lower part without a boundary ridge. A vessel may be provided with one or more inequalities below the coating to prevent displacement thereof when loosened by heat expansion. The end of a glass or porcelain pipe may be provided with a metal coating in which a screw thread is cut ; a thin pliable intermediate layer of rubber, lacquer or varnish may be applied before the metal. The glass nozzle of a medical syringe which is to be inserted in a hollow metal needle and the lower part of the glass barrel may be plated by the process.