Cast Film Dies

The main components of a die include the inlet channel, which delivers the plastic from the extruder to the die the manifold, which is designed to evenly distribute the melt within the die the approach or land, which carries the melt from the manifold to the die opening and the die lips, which perform the final shaping of the melt as it exits the die. For cast film or sheet, the die opening is slit-shaped, producing a thin, wide exiting stream of plastic. 

The most common die configuration for production of cast film and sheet is a coat-hanger die (Fig. 7.7), named because of its resemblance to a common coat hanger. T-shaped dies are also used. The die opening is wider and thicker than the finished film. As the film is drawn down between the die and the chill roll, it contracts in width and thins, due to tension on the film being produced and polymer relaxation effects. 

Internals of coat hanger die for cast film and sheet 

The dies are generally equipped with flow modifiers such as restrictor bars and adjustable lips, to adjust for processing variations such as changes in resin, extrusion temperature, and flow rates. As mentioned, sometimes the lip adjustments are computer-controlled and linked to in-line thickness measurements. 

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Eig. 7. Extmsion of roU-cast film A, die inlet B, cast-film die C, air gap with molten web D, casting roU E, stripping roU E, idler roU G, edge-trim sHtter ... 

Many characteristics of cast film dies carry over into sheet dies but because of generally thicker materials, die lip openings are much larger and do not generate enough back pressure for accurate distribution of melt (Figure 17.6). Therefore, many sheet dies have a restrictor bar.143... 

Fig. 3-12a. Examples of dies with nomenclature. (1) Pipe or tubing die for in-line extrusion. (2) Pipe or tubing die for crosshead extrusion. (3) Cast film die. (4) Sheet extrusion die.

Extruder diameter, mm Blown film die diameter, mm Cast film die width, mm Extrusion coating die width, mm... 

With a given die cross-sectional area, there is only 1 ratio of puller speed to extruder throughput rate that produces a product with the correct cross-sectional dimensions. If the extruder throughput is increased, the puller speed must be increased proportionally to maintain the same finished product dimensions. Likewise if the throughput is decreased the puller speed must be decreased proportionally to maintain the same finished product cross-sectional area. The draw ratio and molecular orientation can only be increased or decreased by changing the die cross-sectional area relative to the puller speed assuming the final product dimensions are kept constant. This is easily done with sheet dies, cast film dies, or blown film dies that have adjustable die lips. Profile and cross head dies... 

The PP monolayer cast film was processed using a ThermoHaake PolyLab extruder (RC300P/R600) with a cast film die the processing conditions are shown in Table 2. 

Two commercial disazo disperse dyes of relatively simple structure were selected for a recent study of photolytic mechanisms [180]. Both dyes were found to undergo photoisomerism in dimethyl phthalate solution and in films cast from a mixture of dye and cellulose acetate. Light-induced isomerisation did not occur in polyester film dyed with the two products, however. The prolonged irradiation of Cl Disperse Yellow 23 (3.161 X = Y = H) either in solution or in the polymer matrix yielded azobenzene and various monosubstituted azobenzenes. Under similar conditions the important derivative Orange 29 (3.161 X = N02, Y = OCH3) was degraded to a mixture of p-nitroaniline and partially reduced disubstituted azobenzenes. 

Use Packaging film molded parts for automobiles, appliances, housewares, etc. wire and cable coating food container closures coated and laminated products bottles artificial grass and turfs plastic pipe wearing apparel (acid-dyed) fish nets surgical casts strapping synthetic paper reinforced plastics nonwoven disposable filters. 

Finishing of aluminium-alloy die-castings is usually for decorative purposes and includes anodising, which can be dyed a wide variety of colours painting and electroplating. The more usual electroplating material is chromium, which involves fairly complicated pre-treatment to prevent the formation of an oxide film which would make it difficult for the plated metal to bond to the aluminium. 

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