Extruded sheet process

The co-polyester sheet process involves the extrusion of molten polymers through a flat die to form a thick film. This film is “pinned” to the surface of a chill roll with another roll to ensure proper clarity and gauge control. A series of 2 to 3 rolls is used to quench the molten polymer immediately creating a very clear sheet with thicknesses greater than 10 mils.

• Example of extruded sheet (flexible) line

As in film processing, coextrusion can also be utilized to create multilayer structures. Use a coat-hanger, flexible-lip die with a 1 in. land and 30-40 mil lip opening (or at least 25% greater than the desired film thickness). All flow surfaces should be hard chrome plated and highly polished (no dead zones, nicks, or scratches). The face of the die should be tapered instead of square to permit a short die to chill roll air gap. Restrictor-bar dies are not recommended.

• Cooling

Use standard 3-roll sheet-casting stacks with a 12-inch minimum roll diameter for producing nip-polished high quality film/sheet. The casting-stack temperature and polish roll pressure should be balanced to eliminate sticking and maintain high quality aesthetics. The surface roughness or RMS values of the sheet-casting stack-cooling rollers can have a highly polished, embossed, or matte finish.

• Finishing

Use sharp, rigidly mounted razor blades for trimming film edges. Use a winder with good tension control and a proximity lay-on roll. Use static reduction devices prior to winding or as needed throughout the line.