1.  Field of the Invention
This invention relates to optical screens, and, more particularly, to optical screens having relatively thin alternating layers of clear, light transmitting elements and opaque elements and to a method of making such screens by extrusion. 
2.  Description of the Prior Art
U.S. Pat.  No.  5,381,502, U.S. Pat.  No.  5,625,736, and U.S. Pat.  No.  5,668,907, all by Veligdon, disclose optical panels having waveguides interleaved with opaque elements to provide optical display panels, with the opaque elements interleaved with the optical waveguides for purposes of increasing the resolution of images on the panels.  The panels are conventional with respect to the prior art in the sense that they are generally flat, sheet type panels, coextruded generally perpendicular to a viewer, and generally parallel to a major surface, the viewing surface. 
The invention described and claimed herein comprises extruded polymer elements, with light transmitting polymer elements and opaque polymer elements interleaved, or alternating with, the light transmitting elements to comprise an optical screen apparatus, and a method of making the screen apparatus.  The optical screen apparatus is extruded in ribbons, as opposed to the prior art sheet elements.  Several embodiments are disclosed.  The screen apparatus has an appearance of being opaque because the apparatus includes many alternating small layers or ribbons.  Due to well known principles of total internal reflection, light that enters the apparatus is efficiently transmitted to the front surface for observation by a viewer.  The ribbon layers are generally parallel to a viewer, and generally perpendicular to the plane of a major surface, namely the front viewing surface.  The appearance of the extruded screen apparatus prior to illumination by an appropriate light source, is opaque.  Diffusion and light directing elements and ultraviolet protection may be coextruded or formed with the basic light directing and opaque elements or they may be added to the basic screen after the screen has been extruded.  Included in the embodiments of the present invention are angled and curved elements.  Since their and curve are relatively small, they are still considered to be generally parallel and perpendicular, as referred to above. 
Among the objects of the present invention are the following:
To provide a new and useful optical screen apparatus;
To provide a new and useful screen apparatus having alternating light transmitting and opaque elements;
To provide new and useful optical screen apparatus including a plurality of extruded ribbons of alternating light transmitting and opaque elements;
To provide new and useful optical screen apparatus having light directing elements;
To provide new and useful optical screen apparatus having light diffusing elements;
To provide new and useful optical screen apparatus having light directing and light diffusing elements;
To provide new and useful optical screen apparatus including an ultraviolet light inhibiting layer;
To provide a new and useful method of making an optical screen apparatus;
To provide a new and useful method of extruding an optical screen apparatus;
To provide a new and useful method of extruding polymer elements having alternating ribbons of light transmitting and opaque elements;
To provide a new and useful method of forming an optical screen apparatus having light directing and light diffusing elements; and
To provide a new and useful method of forming an optical screen apparatus having an ultraviolet protective layer.