Patent GB-1111740-A (GB)
Title: Glass and other light-transmitting materials and articles
IPC: G03C1/725
Filed: 1966-08-31
Abstract: A light transmitting material or article comprises at least one light transmitting coating layer borne by a sheet or other support of glass or other like transmitting materials which layer consists of or contains at least one chemical compound which when sufficiently irradiated by sunlight reversibly dissociates and yields a dissociation product which reduces the transparancy of said layer to part at least of the incident light, and wherein in said layer or in an adjacent layer there is a substance which when said dissociation occurs acts as an acceptor for the other dissociation product or products until the condition causing the dissociation ceases to obtain.  The dissociating compound or compounds may be photolysable and photosensitive substances which dissociate when sufficiently irradiated.  The substance may be a metal halide or a mixture of two or more metal halides may be used, the acceptor then being a substance capable of releasably storing halogen when this is liberated from said halide or halides.  Examples of halides are chloride, bromide, or iodide of silver, mercury, or thallium, and the acceptor substance may be an oxide or oxides of one or more of silicon, titanium, aluminium and tin.  The support may be provided with more than one layer of a dissociating compound and there may be an intervening or subbing layer say comprising substances serving as acceptor.  The dissociating layer may be formed by the deposit of a metal followed by the halogenation thereof in situ.  The acceptor may be in a layer different from the dissociating compound e.g. in a layer located on the opposite side of the dissociating compound layer and may itself be coated with one or more layers or sheets for protective purposes or to impart particular optical properties to the light transmitting material.  Such further layer or sheet may be coloured.  Such a further layer may be an impermeable layer which may be light dispersing e.g. a layer based on pyrogenated metal or metalloid oxide such as magnesium, zinc, zirconium oxide or a coloured oxide of iron nickel or chromium.  This oxide layer may be produced by applying to the already coated sheet or other support a suspension of a salt or other compound of the metal or metalloid in an organic solvent and then converting such compound to the oxide or hydrated oxide in situ by heating with simultaneous elimination of the solvent.  The response of the light transmitting material to increases in the intensity of incident sunlight can be reduced or eliminated by raising the temperature of the dissociating layer and the layer containing the halogen acceptor.  The acceptor layer may be heated by electrical resistance heating and the said layer may be constituted by an electrically conductive substance and this layer may be connected at opposite margins to a source of electrical current.  A catalyst which promotes the dissociation and/or recombination may be present in the dissociating layer e.g. copper, cadmium and nickel halides.  Cobalt halide can also be used as catalyst say in a layer of mercury or thallium chloride or bromide. The acceptor substance is preferably in a coating layer which is next to the dissociating layer and is substantially impervious to the other dissociation product or products and the acceptor substance takes up the product or products by absorption thereof at the surface of the layer in which the acceptor substance is present.  In one embodiment the support is a sheet and is one of two sheets which are held in spaced facing relationship in such a way that the space between them is enclosed and the acceptor substance is present in gaseous form in said space e.g. nitrogen, chlorine. Other light transmitting materials said to be useful as supports are an acrylic plastics material, celluloid or cellophane ("Celluloid" and "Cellophane" are Trade Marks).  The support may be of laminar-structure and may be a lens.  The dissociation product which is temporarily held by the acceptor may itself decrease the transparency of the material or article to some extent.  The products are used as glazings.