Thermoforming plastic materials

This is another version of cold forming by utilizing a thermoformed plastic skin to impart an excellent surface and other characteristics (for weather resistance, etc.) to a cold-molded RP. For example, a TP sheet is placed in a matched mold cavity with an RP uncured material placed against the sheet. The mold is closed and the fast, room temperature curing plastic system hardens. The finished product has a smooth TP-formed sheet backed-up with RP. 

Thermoforming a material for a unit change in temperature. Values for plastics range from 0.01 to 0.2 mil/in. Any process of forming thermoplastic sheet which consists of heating the sheet and pulling it down onto a mould surface. 

Film and sheet are the major forms in which PE is used, including shrink/stretch film, food packaging, pouches, and blown-film bags and liners. In North America, PE is by far the most-used film/sheet plastic material followed by PP. For shrink/stretch film in the United States, for example, over 75% is LDPE, rather than PVC. PE film and sheet also sees significant use in industrial thermoforming applications, as does PP for thermoformed packaging [2-19, 2-20]. 

Processing involves the conversion of the solid polymer into a desirable size and shape. There are a number of methods to shape the polymer, including injection molding, extrusion, thermoforming, blow molding, and rotational molding. The plastic material is heated to the appropriate temperature for it to flow, the material is shaped, and then it is cooled so... 

Foams are versatile both in their applications and in the way in which the materials are made. These include the production of various shapes by casting, extruding, injection molding, thermoforming, and reaction injection molding. Foam versatihty also includes the fact that any plastic material, thermoplastic or thermoset, may be produced in cellular form. 

Plastic materials have low thermal conductivities, hence during heating, even relatively thin sheets can have surface temperatures that are substantially higher than the interior temperatures. Therefore, plastic sheets must be heated to an optimum forming temperature in order to achieve uniform and repeatable drawdown. Figure 4.5 illustrates continuous sheet forming extrusion via the thermoforming process. 

The thermoforming process is the method for annealing a sheet of thermoplastic resin to manufacture the final product by vacuum or air pressure, as shown in Fig. 6.9. It has these advantages The cost of equipment is inexpensive, the processing of multilayer sheets can be readily achieved, and the production of thin products is possible. The disadvantages of this process are that the procedure for preparing sheets is necessary, the selection of available plastic material is limited, and manufacturing with accurate dimensions is difficult. 

Blow Molding. The process of blow molding also applies only to thermoplastics. It is similar to thermoforming in that it uses a difference in pressure to force softened thermoplastic material to adopt the shape of a mold. Blow molding uses three-dimensional molds, however, and is typically used to produce open structures such as plastic bags, bottles, and other similar objects. In blow molding, a metered quantity of plastic material is set into a mold, where it is then blown outward by a sudden blast of heated air to the shape of the mold. The method is most suitable for open, three-dimensional shapes having little or no surface detail. 

Fig. 16. U.S. plastic materials consumption for thin-gauge (2.1 million metric tons) and heavy-gauge (682,000 t) thermoforming (32). PE = Polyethylene ABS = acrylonitrile-butadiene-styrene PS = polystyrene PP = polyproplyene PMMA = poly(methyl methylacrylate) PVC = poly(vinyl Chloride) PET = poly(ethylene terephthalate). Redrawn and used with permission of SPE Thermoforming Division.

The most common use of P LA is for compostable sugarcane trays and in punnets or pallets. A starch derivative, PLA can be manufactured from maize and other plants and is a biodegradable, compostable plastic material. The material is obtainable in a range of blends and can be used in sheet or film form for a diverse range of products including food containers. It can be used for rigid thermoforms, films. 

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