Process for manufacture of plastic sheets

A method of making a thin sheet of plastic material from a liquid mixture of components which react during formation of the sheet, comprising the steps of:

• providing a flat, substantially horizontal substrate moving at a uniform rate;
• continuously feeding a thin sheet-like flow of the liquid mixture onto the upper surface of the moving substrate with the plane of the sheet-like flow being disposed transversely to the direction of movement of the substrate;
• providing sheet forming means downstream of the zone of introduction of the mixture onto the substrate, the sheet forming means extending transversely to the direction of substrate movement and controlling the thickness of the sheet formed on the substrate;
• forming a stable pocket of the mixture on the substrate extending upstream from the zone of introduction of the mixture, and controlling the viscosity, pressure, and flow rate of the material, and degree of adherence between the flowable material and the substrate whereby all the material in the pocket is continuously in motion;
• feeding the mixture to provide a greater flow at the center of the substrate then toward the edges thereof;
• establishing a continuous flow in the upper portion of the pocket in a direction essentially opposite the direction of movement of the substrate in order to come in contact with and be entrained by the substrate in the direction of substrate movement, thus forming the lower portion of the sheet-forming layer;
• establishing a flow of a direct stream of the mixture from the zone of introduction in a downstream tangential relation to the pocket in order to form the upper portion of the sheet-forming layer;
• and
• simultaneously establishing continuous flows of the mixture forming the central portion of the pocket in directions essentially transverse to the direction of substrate movement, the latter flows moving along oppositely directed flow paths from substantially the center of the substrate toward the opposite side edges thereof, whereby the mixture from the central portion of the pocket forms the outer edges of the sheet.