GB1301746A - - Google Patents

Abstract

1301746 Uses of photochromism CARLZEISS - STIFTUNG [trading as JENAER GLASWERK SCHOTT & GEN] 30 Jan 1970 [31 Jan 1969] 4588/70 Heading C4S [Also in Division G2] An article of a light transmissive phototropic material comprises phototropic glass 5 and a radiation reflective solid oxidic backing layer 7 comprising one or more of TiO 2 , SiO 2 , Ce 2 O 3 and capable of reflecting back into the phototropic material at least a part of the exciting radiation 1 incident upon the surface remote from the backing layer and which has passed through the phototropic material. The reflection improves uniformity of darkening or colour change response for example. The phototropic material may be laminated synthetic plastics glass sheet or phototropic boron-containing glass, e.g. lead borate glass, borosilicate glass, or the phototropic property may be due to the presence of silver halide, e.g. AgCl and/or AgBr (e.g. 50 to 600 Š particles). Visible or U.V. exciting radiation is instanced, and reflection of wavelengths other than the exciting radiation may have secondary undesired effects, e.g. reflected red or infra may heat and cancel out the phototropic mechanism. In examples, phototropic alkaline earth/Al/lead borate glass with AgCl and AgBr, 3 mm. thick, is ground, polished, etched in 3% hydrofluoric acid, washed, cleaned further in alkali soap solution at 100‹ C., terminated in methyl alcohol wash, multiple #/4 films of TiO 2 and SiO 2 obtained by dipping in organic titanic and silicic acid ester solutions, followed by hydrolytic or pyrolytic decomposition. Alternatively, the material may be a laminated material of phototropic borosilicate glass with silver halides, and polystyrene, in translucent form as a disc 5 mm thick, cleaned and vapour coated with Ce 2 O 3 - TiO 2 . Reference is made to Specification 1,213,798.