Polyethylene thermoforming

Sheet Extrusion and Thermoforming. Sheet for thermoforming and analogous operations is usually formed by extmding the melt through a slot die onto a set of poHshed chill roUs. The sheet is usually approximately 150 cm wide. After rapid cooling, the web is coiled or cut into sheets. Polystyrene, PVC, polyethylene, polypropylene, and filled polypropylene are prepared in sheet form by extmsion. 

Thermoforming, of high density polyethylene, 20 174 Thermoforming process, 23 398-399 Thermographic black and white developers, 79 347... 

Polyethylene terephthalate) (PET) has become a major synthetic polymer during the past forty years. Significant commercial markets [1] have been developed for its application in textile and industrial fibers, films, and foamed articles, containers for carbonated beverages, water and other liquids, and thermoformed applications (e.g. dual ovenable containers). 

A new approach was proposed for making effective helmets which could replace the former British army steel helmet. Essentially the new helmet used modified phenolic resins reinforced with nylon, and the crown cap inside was thermoformed from polyethylene. Formerly the crown cap was attached to the steel by rivets—not an appropriate method for fixing polyethylene to reinforced plastics. Instead a method was developed with a hot-melt adhesive based on ethylene-vinyl acetate copolymers cast as film on release paper. For assembly, the cast film is cut in advance to match the intricate shape required and activated by heat to bond under light pressure subsequently, a further heat activation is employed to fix the crown cap in place (Figure 52 illustrates this). 

Polyethylene Terephthalate (PET) A plastic resin of the polyester family and one of the most common thermoformed plastics. Plastic soda bottle are a common PET product. PET is also fully recyclable. 

Polyethylene, polyvinyl chloride and polypropylene are easily worked utilizing ordinary wood or metal working hand and power tools. Being thermoplastic, these materials can be easily thermo-formed as well as cut, sawed, drilled and tapped. In the heat forming process, electric ovens are generally used which can maintain good thermal control. Of the three thermoplastics, polypropylene requires the more finite thermal control. Table III provides approximate time and temperature relationship required for thermoforming these three plastics. 

Petrothene . [Quantum/USI] Polyethylene or polyprc ylene resins for inj., rotational, and blow molding, sheet and proHle extrusion, vacuumforming, thermoforming, film, wire and cable, industrial containers, closures, toys, foamed parts, pipe, food [dig., house-wares, a esives, coatings. 

Since fully cured thermoset sheets cannot be resoftened, forming is not appKcable to them. Common materials subjected to thermoforming are thermoplastics such as polystyrene, cellulose acetate, cellulose acetate butyrate, PVC, ABS, poly(methyl methacrylate), low- and high-density polyethylene, and polypropylene. The bulk of the forming is done with extruded sheets, although cast, calendered, or laminated sheets can also be formed. 

Thermoformed high density polyethylene (PE) and low density PE foams that can be molded into a variety of complex shapes are being increasingly used in supporting devices in the treatment of orthopaedic and disabling conditions. Some examples are wheelchair seats, spinal jackets, medical shoe inserts, and splint supports. 

Olefinic Thermoplastic Elastomers Blends of EPDM or EP rubbers with polypropylene or polyethylene, optionally eross-linked. Has low density, good dielectric and mechanical properties, and processibility but low oil resistance and high flammability. Processed by extrusion, injection and blow-molding, thermoforming, and calendering. Used in auto parts, construction, wire jackets, and sporting goods. Also called TPO. 

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