Tham khảo tài liệu 'plastic product material and process selection handbook part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 404 Plastic Product Material and Process Selection Handbook Solvent casting of film . While the capital equipment for solvent casting is expensive and the process considerably more complex than extrusion167 or calendering certain types of film can be produced that would be difficult or impossible to manufacture by any of the other film processes. In PVC acrylic and other plastics solvent casting film the formation depends upon solubility not melting of the plastic. Therefore the process requires only moderate amounts of heat. PVC solvent cast film is extensively used. An example of a solvent used with PVC is tetrahydrofuran THF . To produce PVC films by this process the plastic plasticizers and other materials are added to the solvent in an inert gas-blanketed mixing tank. Thorough mixing uniform viscosity of the solution and thorough degassing are critical for producing a quality film. After mixing and then cooling the solution below its boiling point it is pumped to the casting tank. This solution is filtered to 5 microns to remove any undissolved particles and is then pumped to a specially designed flat die where the solution is cast onto a stainless steel conveyor belt. The belt then enters an oven where the solvent is evaporated from the film the film is cooled stripped from the belt and wound into rolls. Control of the gauge of the film is via die opening pumping pressure and speed of the belt. In-line monitoring equipment is used for gauge control and for quick gauge changes. Heated air traveling counter to the direction of the conveyor belt carries the solvent vapors from the drying oven to the solvent recovery system through large ducts. Different designed solvent recovery systems are used. As an example there is the solvent system that consists of fixed bed adsorbers containing activated carbon and a distillation system. The carbon adsorbs the solvent vapors. Then the beds are steamed in sequence to remove the solvent. The solvent and steam are condensed
