GB458736A - Improvements in or relating to metal mesh screens for example for use in cathode ray tubes - Google Patents

Abstract

458,736. Making mesh screens; electrodeposition. HOLMAN, H. E., 4, Fairway Avenue, Garden City, Yiewsley, Middlesex. May 23, 1935, No. 17164/36. Divided out of 458,675, [Group IX]. [Class 83 (ii)] [See also Groups XXXVI and XL] A metal mesh screen for use in an electron discharge device is formed by a process including the steps of forming an electrically-conducting matrix 30 having ribs 30a corresponding to the finished screen, applying a layer 31 of an insulating material such as an asphalt varnish, removing the layer 31 until the tops of the ribs appear, and then lapping until the exposed copper surface corresponds to the desired form of the screen, depositing a gold or other metal layer on the tops 30a of the ribs and then removing the remainder of the insulating medium and the matrix 30 to leave a screen 32, a supporting member being attached to the screen before complete removal of the matrix. The deposit may be applied to two plates placed back-to-back and soldered at their edges. An asphalt coating is removed by boiling in ether. A screen may be secured to a nickel frame by methods described in Specification 458,675. Alternatively, a screen 32, Fig. 13, is secured to a mosaic screen for cathode-ray tubes such as used in the electrical transmission of pictures and comprising crossed wires 35b each insulated by a glass tube 36 and having gold cups 38 in the interstices, the screen 32 acting as a potential stabilizer and preventing the spreading of secondary electrons. In the production of the composite screen, the matrix 30 and deposited screen 32, have a film of nickel deposited thereon and then a thick deposit of silver 34, the copper matrix being removed by dissolving in acid, electrolytically, or by ammonium persulphate as described in Specification 458,675. The matrix so formed is employed with a matrix 37 in a process similar to that described in Specifications 447,824, [Group XL], and 455,233 whereby the crossed insulated wires 35b are subjected to heat and pressure, causing adhesion of the glass tubes 36 at the junctions and applying the gold cups 38 to the interstices. The screen 32 is also caused to adhere to the glass tubes 36, after which the layers 37, 33, 34 are removed by acid.