Thermoforming orientation

Different processes take advantage in applying orientation to gain certain properties in certain products. Major product lines include stretched blow molded bottles/containers (Chapter 6), thermoformed oriented containers (used for such products as fruits, vegetables, and baked goods) (Chapter 7), tapes, etc. 

Extruded sheet is cheaper than cast sheet but because there is some residual molecular orientation, is somewhat less satisfactory optically and more difficult to machine. On the other hand, no doubt a function of its lower molecular weight, it may be thermoformed more easily. 

Plastic films represent the largest worldwide market for plastics with practically all extruded (6). They are used to meet different performance requirements particularly for its major packaging market. Worldwide just for biaxial oriented (Chapter 8) polypropylene consumption is about 5 /2 billion lb. Their use includes tape, food, tobacco, and confectionery. Thermoforming film (and extruded sheets) is a major processing technique producing all kinds of products. 

Chicago, II., 29th Aug-2nd Sept.l993,p.403-6. 6A MULTILAYER EXTRUSION DIE GEOMETRY FOR THERMOFORMED POLYPROPYLENE FOAM SHEETS AND BIAXIALLY ORIENTED FOAM FILMS Raukola J Savolainen A Tampere,University of Technology (TAPPI)... 

Techniques commonly used to manufacture advanced composites from prepregs, which are available in unidirectional fiber or fabric form, include compression molding, vacuum-bag autoclave molding, stamp molding, thermoforming, and on-line (in situ) consolidation [3]. In compression and vacuum-bag autoclave molding techniques, the prepreg is cut to the dimensions of the structure, and the fiber directions are oriented to obtain the required... 

However, it has been found that a filler can be added within a specified range to provide a suitably tearable filled thermoformed HIPS container lid when the tear back portion of the lid is oriented in the extrusion direction of the PS, when the tear back lid comprises two sets of tear indentations and a tab portion. In this way, the lid is prepared from a HIPS composition consisting essentially of from 10-15% calcium carbonate as filler (28). 

Packaging applications are the most extensive. Meat, poultry, and egg containers arc thermoformed from extruded foamed polystyrene sheet. The fast-food market also accounts for a substantial amount of polystyrene for takeout containers where the insulation value of a foamed container is an advantage. Containers, tubs, and trays formed from extruded impact polystyrene sheets are used for packaging a large variety of food. Biaxially oriented polystyrene film is thermoformed into blister packs, meat trays, container lids, and cookie, candy, pastiy, and other food packages where clarity is required. 

Sheet can be produced by extrusion or calendering. For use in thermoforming, the sheet must be extremely uniform. For improved properties, the sheet may be biaxially stretch-oriented up to 300 percent. For large automatic production runs, it is fed continuously off a roll for short runs, large, and/or specialty jobs, it may be cut into individual sheets and fed one at a time. 

Dow s patented scrapless forming process is identified as the SFP process. An extruder produce a biaxially oriented sheet (Chapter 5). In turn the sheet is slit and cut into square blanks. These blanks are heated and pressed into circular disc with a lip. Immediately or latter after reheating, the disc is thermoformed into a shape such as a cup. 

Insert molding, or in-mold decoration, helps overcome the flow lines common to metallic colored intricate injection-molded parts. By this process a film with a uniform orientation is thermoformed and fused with the surface of the injection-molded part. 

NatureWorks PLA can be extruded, cast or biaxially oriented, and thermoformed using conventional processing equipment. The company claims that NatureWorks PLA performs like traditional petroleum-based plastics, and in some cases offers better performance characteristics, including gloss, clarity, strength, and flavour and aroma barrier. 

Where a clear, thermoformed product is desired, many fabricators use OPS. Because of the low elongation of general-purpose polystyrene, it is necessary to orient the sheet biaxially to obtain the required physical properties for satisfactory part trimming and end use. If there is insufficient elongation in the... 

OPS is commercially available in 0.13-0.76 mm gauge. The tenter frame process for manufacturing OPS is the most common process used today. A typical tenter frame process is shown in Figure 11.1. Tentered OPS is distinguished from polystyrene blown films (which are also biaxially oriented) in that the tenter frame process can produce heavier gauge films than the blown-film process. Blown films (0.025-0.13 mm) are used primarily in window envelopes, lamination, and printed applications tentered OPS is typically used in thermoformed trays, lids, and containers for rigid food packaging applications. 

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