Patent GB-461716-A (GB)
Title: Improvements in metallic screens, stencils and the like and formation thereof
IPC: C25D1/08
Filed: 1935-12-06
Abstract: 461,716. Photographic stencils. NORRIS, Inc., E. O. Dec. 6, 1935, No. 33888. Convention date, Dec. 6, 1934. [Class 98 (ii)] [Also in Groups XXII, XVI, and XXXVI] A matrix for the electrodeposition of a perforated sheet such as a screen or stencil is formed by imposing a resistant material on a metal sheet in a design, removing portions of the sheet in accordance with the design to form depressions, removing the resistant material, filling the depressions with a resistant material, applying a layer of covering material, and removing the remainder of the sheet A matrix for the electrodeposition of a screen is formed by securing a sheet 10, Fig. 3, of electrolytic copper to a glass plate by adhesive tape, polishing the surface of the sheet and applying thereto a sensitized glue containing specified quantities of ammonium bichromate, albumen, and ammonia, which is dried by heat. A design is printed thereon by arc or sunlight using a negative comprising a series of opaque dots, it is immersed in methyl violet solution and washed in water, dried, examined for faults which are rectified by hand, and heated over a gas or flame forming lines 11 of developed glue. After applying a back coating of tinted shellac 12, depressions 13 are formed by etching in ferric chloride, and after washing a resistant material 14 such as an acid resistant paint, not capable of being electroplated, is applied to the depressions 13 and dusted with copper powder and dried. The glue 11 is sandpapered off, the whole surface plated with copper 16, Fig. 7, the shellac 12 dissolved off and a shellac layer 17 applied to the other face. The article is then immersed in an etching bath producing a sheet 16, Fig. 10, with protuberances 14 of nonconducting material. The screen 19 is electrodeposited on the matrix so formed and peeled off. An alternative method of forming a matrix comprises the formation of raised lines 11 on a surface, forming a wax casting therefrom, inserting a non-conductor in the depressions, sprinkling a conducting powder thereover, electrodepositing a layer of metal, and melting out the wax. The valleys in the matrix may be coated with a material such as platinum, enabling any sticking deposit to be removed by etching. The stripping of the screen may be facilitated by a thin layer 18 of oxide or of beeswax and naphtha, to which a thin coat of graphite may be applied. The deposit may be carried nearly to the tops of the protuberances, the faces coated with stencilling paste or printers' ink, and the article then immersed in an etching bath. In a further modification, the protuberances may be completely covered, the lower points given a resistant coating, the back covered with shellac, and the thin portions etched through. A synthetic rubber composition may be used to form the protuberances. In the production of thick screens, deep matrices are produced from a thin sheet of electrolytic copper, the thickness of which may be further reduced by grinding, electro-corrosion, or etching. While mounted on a glass plate 20, Fig. 11, a pattern 11 is applied thereto by means of sensitized glue, it is removed from the plate 20, a layer of shellac 12a is applied, it is placed again on the plate 20, and etched in ferric chloride completely through its thickness. Such a form, Fig. 12, may be itself used as a screen, or in the formation of a thicker screen or of a matrix, is electroplated with copper, coated with resistant ink, etched to enlarge the holes, and the coating and etching steps are repeated until the required thickness is obtained. A matrix is obtained from such a screen by applying a sheet of glued paper 22, filling the holes with synthetic rubber or other material 23, dusting with metallic powder, electrodepositing a layer 26, and finally etching to produce the matrix, Fig. 17. Alternatively, the rubber is caused also to form a coating on the surface, and the matrix is formed entirely of rubber. The surface is rendered conducting by dusting metal powder 30, Fig. 21, on to a wax solution 31, the tops being treated with a greasy ink 33. A coating of silver may, alternatively, be formed by precipitation. The inking 33, Fig. 23, may be effected after deposition has been commenced, the small deposit on the protuberances being removed to form perforations. This method is employed to provide perforated portions 35, Fig. 25, and imperforate areas 32, as in the production of a stencil which is employed in a process wherein a viscous ink is forced by a squeegee through the perforated areas.