Continuous mfr. of acrylic fresnel lenses - with embossing section with high pressure heating and low pressure cooling zones

摘要

Fresnel lenses are made on a continuous process by extruding thermoplastic material (2) into a three roll smoothing calender (3) followed by an embossing section (23) consisting of embossing and pressure rolls (8,5) and roller conveyors (4). At least half of the embossing roll (8) is wrapped by an endless steel belt (9) and it has an insulating layer and temp. control channels. The material is exposed to a high pressure/temp. zone to form the lens shape followed by cooling in a low pressure zone. Polymethylmethacrylate enters the calender (3) at 150-200 deg.C leaves at 85-110 deg.C and enters the embossing section (23) in the same temp. range. In the high pressure zone the side facing the embossing roll is heated to 250-300 deg.C while the other side with at least 50% of the material thickness is kept at 85-100 deg.C. The embossed material leaves the high pressure zone at a max. surface temp. of 100 deg.C. The pressure in the high pressure zone is 200-600 bar pref. 300-500 bar, while in the low pressure zone it is 3-8 bar, pref. 4-6 bar. USE/ADVANTAGE - Produces acrylic Fresnel lenses with high dimensional accuracy in a continuous process.