Flat Film or Sheet Extrusion

Another process for producing plastic films is flat, or cast, film extrusion. In this process the extruder pumps molten resin through a flat film or sheet die. The melt leaves the die in the form of a wide film, or sheet. This is typically fed into a chill-roll assembly which stretches and cools the film. After the film passes through the rolls, the film is wound up on a roll. 

Numerous types of dies are available depending on the extrusion process and the type of product being produced. Compounders use strand dies to make continuous strands that are chopped into pellets. Sheet and cast film producers use flat dies. A schematic of a flat film or sheet die is shown in Fig. 12.53. This produces a flat web of a specific thickness that passes through a three-roll stack or lays flat on a cast roll. Blown film producers use circular dies as shown in Fig. 12.54. Tubing and pipe cross head dies are similar to that shown in Fig. 12.55A where... 

Melt Extrusion. By far the most important method for producing film and sheeting materials reties on one or another of the various melt extmsion techniques (5). The main variations of melt extmsion are the slot (or flat) die-cast film process, the blown films process, and the flat die sheeting-stack process. These may be combined with one or more steps such as coextmsion wherein multilayer film or sheet is formed, biaxial orientation, and in-line coating (6). 

Extrusion A plastic processing technique to produce pipe, film or sheeting. The plastic is fed through a flat or preformed annular die, which gives the object its definitive shape. 

The Extrusion Die. The die is placed at the discharge end of the extruder. Its function is to form the flowing plastic into the desired shape of the extruded product. Dies can be categorized by the shape of the product that they produce. Annular dies are used to make tubing, pipe, and wire coating. Slit dies are used to make flat film and sheet. Circular dies are used to make fiber and rod. Profile dies are used to make shapes other than annular, circular, or rectangular. Dies are also named by the product that they produce. So, we talk about tubing dies, flat film dies, blown film dies, etc. 

Water quenching can be used for wire insulation, tubing, and pipe. Sheet and film extruded from slit dies are frequently crystallized on polished steel rolls operating at 65°C-145°C. Extruded, blown, or flat film can be uniaxially or biaxially oriented to submil thickness. Monofilament is extrusion spun into a water bath, and then oriented and heat set at an elevated temperature. 

Film blowing or sheet extmsion Continuous melt extrusion through a flat or circular die (PE, ionomers, PP, PS, PMMA, PEST, PA, etc.)... 

Extrusion process is used in major pipe, profile, sheet, and flat film manufacturing process. In this process, an extruder (of one or two screws) moves molten materials through a barrel by pushing it through a die to produce uniform shape of products [26]. 

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