GB2047912A - Glass Plate Light Stop and Method for its Production - Google Patents

Abstract

A glass plate is made pervious to light in at least one direction and impervious to light in at least one other direction by thin parallel equidistantly spaced light-absorbing which extend substantially through the plate and whose function is comparable to a jalousie. According to one method, the lamina are formed by impressing into a glass plate a prismatic grating structure whose indentations are to be made light opaque and the lands therebetween which are to remain light permeable, are masked with thin adhesive strips. The entire plate surface is then covered with a light impermeable layer, the adhesive strips are removed, and the impressions are filled with a glass plumb to provide a smooth surface. According to another method a plate 53 of photosensitive glass is temporarily masked with spaced parallel strips 52 of radiation-shielding material and then the plate 53 is irradiated with UV light 51 and heat treated until the glass between the masked strips 52 becomes light opaque. <IMAGE>

Description

SPECIFICATION Glass Plate Light Stop and Method for its Production The object of this invention is to produce a plate-shaped light stop element made of glass which is impervious to light in at least one direction, and which is light pervious in at least one other direction. Partial light perviousness is achieved by the fact that a large number of thin, light absorbing (e.g. black) lamina are arranged parallel to each other in a glass plate in such a way that light falling in one direction is completely absorbed. Thus when looking in one direction the glass plate is non-transparent, while in the other direction it is largely transparent-up to the places where the thin lamellae are found.

The glass plate thus works like a jalousie. There is an increasing need for such diaphragm elements, especially in optical indicating instruments, for example, those which operate with liquid crystals.

Plastic foils are already known which serve to reinforce picture contrast as well as reduce reflections and light stop effects and in which equidistant, light-absoring lamellae are arranged so that the light is almost completely let through in one direction, but is increasingly absorbed by the lamellae with a change of the angle of incidence, and finally is completely blocked in a certain angular range. However, these foils have the disadvantage of small mechanical and thermal load carrying capacity and moreover must mostly be used between glass covers.

According to the invention, two different ways are proposed for the production of such light stop elements. According to the first mode, parallel glass plates of a few mm thickness are used. The desired surface structures are obtained after heating to temperatures of incipient softening by pressing with suitable profiled matrices.

Preferably by means of an automatically working mechanism, the grid surfaces, which should remain light permeable, are covered with thin adhesive strips; subsequently, the entire profile of the grid plate is covered with a light impermeable layer. This can be done for example, by vapor deposition in a vacuum with absorbing metal sulfides, oxides or so-called cermets such as, for example, the Cr-SiO mixture. Likewise, other layering methods can be used such as by moistening with solutions of colloidal graphite.

The use of opaque lacquers with organic components is prohibited generally because of the temperatures occurring with further processing or in use. After layering, the adhesive strips are again removed from the covered surfaces so that they are light permeable whereas the portions of the plate between them are light impermeable.

The second grid plate required for a complete light stop element can be obtained in the same way by pressing in with a suitable profile. The grid plates must then be fitted together with an optical cement, which in the case of larger surfaces can lead to difficulties. The problem is better solved according to the invention in that the depressions of the grid plate are filled with a glass plumb in such a way that after melting in of the plumb9 a shiny surface originates parallel to the under side of the plate. If one selects a commercial lime soda-silicate glass for the grid plate, then preferably a non-crystalline glass plumb is suitable, whose transformation temperature Tg lies between 500 and 530 OC, whereby the expansion coefficient should amount to approximately 9.10-6/K.For example the glass plumb 8467 of Schott Mainz fulfills these conditions, which is advantageously used in grain sizes < 40,um. At temperatures near the Tg point of the glass of the grid plate, the melting glass powder is pressed into the profile in such a way that a level surface results. A polished steel plate for example, is suitable as a pressing tool which is protected against the adhering of glass by graphiting or covering with a vitreous carbon.

In cases where a small thickness ( < 3 mm) is desired for a glass plate containing the light stop element according to the invention, a correspondingly fine grid structure of the glass surface often is no longer to be attained because of the surface stress of the glass. Experiments have shown that in such cases one method achieves the desired results which consists in the use of photosensitive glasses, which precipitate light-absorbing particles after UV-irradiation with subsequent temperature treatment. Such light sensitive glasses have been known for a long time; for example they are described in the DE PS 809 847 glasses, which contain gold, silver or copper or else cerium oxide and are suitable for the production of developable dark or colored pictures in glass.In the following design example, this method for the purpose of producing the light stop elements according to the invention wiil be described more closely with reference to the drawing in which: Fig. 1 is a diagramatic side elevation of a glass plate undergoing irradiation; and Fig. 2 is a diagramatic cross-section through the plate after irradiation is completed.

From a mixture of the composition (in wt. %) SiO2 78.7 B203 0.2 At203 4.2 Li2O 9.5 Na2O 1.7 K2O 4.0 ZnO 1.0 AgCI 0.2 CeO2 0.03 Sb203 0.5 at temperatures of about 1 5000C, a photosensitive glass is melted and from this a disk 53 of 2-3 mm thickness is produced. This is covered with a mask 50 constituted by a series of radiation-shielding strips 52 of a width c which are spaced by narrow, equidistant gaps b at regularly spaced intervals, and irradiated with as parallel as possible UV-light 51 of a Hg-high pressure burner. The irradiation period varies from 2 to 5 hours according to the intensity and glass thickness. By means of a subsequent heat treatment, the irradiated strips 54 are converted into glass ceramics which are opaque. The nucleus formation is induced at 500+1 00C within 1 hour and at 580-6000C within 45 to 90 minutes for the required crystal growth and the precipitation of colloidal silver. The portions 53a of disk 53 which lie between strips 54 remain transparent.

Claims (6)

Claims

1. Method for the production of a glass plate which is pervious to light rays in at least one direction and impervious to light in at least one other direction, and which exhibits a large number of thin, light absorbing lamina substantially parallel and spaced equidistant from each other, which lamina extend substantially from one surface of this glass to the opposite-lying surface, characterized by the fact that a prismatic grating structure is impressed in one plane-parallel glass plate at a temperature at which the glass begins to soften by pressing with profiled matrices, and subsequently the surfaces determined as impervious to light are covered with a light absorbing layer, whereupon the depressions of the grid structure are filled with a non-crystallized glass plumb in such a way that an essentially parallel shiny surface results.

2. Method for the production of a glass plate, which is pervious to light in at least one direction and impervious to light in at least one other direction, and which exhibits a large number of thin, light-absorbing lamina arranged essentially parallel and equidistant to each other and which extend essentially from one surface of this glass plate to the opposite lying surface, characterized by the fact that a) a thin plate of a light-sensitive glass is covered with a mask comprised of a plurality of equidistantly spaced radiation-shielding strips, b) the portion of glass plate not covered by a mask is irradiated with an essentially parallel UVlight, and c) the glass plate is then subjected to a heat treatment until the irradiated strips are impervious to light

3.Glass plate which is pervious to light in at least one direction and impervious to light in at least one other direction, and which comprises a large plurality of thin, light-absorbing lamina arranged essentially parallel and equidistant to each other, said lamina extending essentially from one surface of the glass plate to the opposite lying surface, characterized by the fact that it consists of a photo-sensitive glass.

4. Glass plate, which is light-pervious in at least one direction and light-impervious in at least one other direction, and which comprises a plurality of thin, light-absorbant lamina arranged essentially parallel and equidistant to each other, said lamina extending essentially from one surface of this glass plate to the opposite lying surface, characterized by the fact that it consists of a glass containing silver halides.

5. A method as claimed in claim 2, substantially as hereinbefore described with reference to the accompanying drawings.

6. A glass plate when produced by a method as claimed in claim 1,2 or 5.