GB742530A - Improvements in or relating to heat reflecting filters and methods for the manufacture thereof - Google Patents

Abstract

742,530. Coating by vapour deposition. VOGT, A. Sept. 5, 1952 [Sept. 5, 1951], No. 22394/52. Class 82(2). [Also in Group XX] A base of plastic material which has a residual vapour pressure not greater than 1 x 10- 4 mm. Hg. is coated with two or more layers to form an interference filter by vapour deposition. The base may be of polystyrene such as Styroflex, Styrofol, " Styrafoil " (Registered Trade Mark) or Polyflex, or of polymethacrylic acid esters such as " Plexi-glass " (Registered Trade Mark) provided these have the required residual vapour pressure. Preferably two different materials are applied in alternate layers, and a suitable pair of substances is titanium dioxide and magnesium fluoride. As shown, a roll of film base 1 may be run in either direction through the vacuum chamber 2 by means of conveyer belts 5, 6 which pass over and round rolls 7, 8 and 9, 10 respectively. The inlet 3 and outlet 4 are provided with lock chambers 24-29 which are connected with preliminary vacuum pumps 36-38 which produce an increasing degree of vacuum, thus enabling the high vacuum pump 39 to produce a very high vacuum in chamber 2 while the base is continuously introduced and removed. The materials to be deposited are contained in vessels 40, 41 and 42 which are heated electrically. The film is given a preliminary run through the vacuum chamber to remove any occluded gases, and it is then passed through in the opposite direction while one of the vessels 40-42 is heated to deposit the first layer. The other layers are similarly deposited. If desired, three layers may be deposited in one run by heating all three vessels and using screens 56-59. Specifications 730,640 and 730,642, [both in Group XX], are referred to.