GB592177A - Improvements in polarizing screens for use in road vehicles - Google Patents

Abstract

592,177. Polarizing - apparatus. MARKS, A. July 3, 1944, No. 12658. Convention date, May 5, 1943. [Classes 97 (i) and 98 (ii)] [Also in Group XXXII] In a polarizing sheet particularly for attachment to automobile windscreens to prevent glare, the polarization effectiveness varies gradually over the sheet, being greatest at the top and least at the bottom. As shown, the sheet 18 is of stretched polyvinyl butyral, impregnated with iodine by treatment with a solution containing propyl alcohol, iodine and hydrogen iodide, excess iodine being removed by a solution containing isopropyl ether, carbon tetrachloride and propyl. alcohol. The sheet mav also be treated to introduce silica therein, as described in Specification 591,943. To produce gradation of polarizating effect, a source of infra-red and ultra-violet light 25, Fig. 5, illuminates the polarizing sheet 22 through a light filter 24 of varying thickness, the rays, after passing through the filter, vaporize and remove iodine from the sheet in accordance with the thickness of the filter. Alternatively, a localised solvent such as the second solution referred to above may be used, the sheet being dipped therein at a controlled rate, or the sheet may be exposed to vapour comprising ethyl or methyl alcohol and carbon tetrachloride issuing from a curved slit under which the sheet travels at controlled speed. The sheet 18 may be flat or cylindrical and the areas of equal polarization may be circular arcs, Fig. 2, or straight lines. When mounted on windscreens 10, 11, Fig. 1, with its polarizing axis horizontal, it may be used in conjunction with headlamps 13 producing two beams 15, 16 polarized respectively vertically and horizontally, the latter being directed towards the ground and reaching the eye 21 through the lower part of the screen, the direct beam 15 being absorbed by the upper part of the screen.