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Modern Packaging Magazine - September 1958 - Return to Main Search
Preview Page 154 of 236 Preview Pages
Text Summary via OCR:

TRANSMISSION RATE COMPARISON OF METALLIZED 8 PLAIN POLYSTYRENE FILM

PLAIN

POLYSTYRENE

METALLIZED

POLYSTYRENE

GAS TRANS, cc/100 SQ IN./mil/24 HRS.-ATM 23°C

02

275

15

Hz

38

3

C02

>1000

80

W.V.T.R. gms/100 SQ IN./

24 HRS/mil AT 95°R,H 90° F METALLIZED SIDE AWAY

6.2

0.9

W.V.T.R. gms/100 SO IN./ 24 HRS/mil AT 95°R.H 90°F METALLIZED SIDE TOWARD

6.2

0.45

have found the thinner gauges of oriented film to be an excellent material to produce a glossy sheet by lamination. The laminating bond is accomplished by utilizing the heat of the high-impact sheet at the time of extrusion. Thus, the processing cost of the material is very low.

If desired, the thin oriented film can be reverse printed prior to laminating, to produce an unlimited number of "locked-in" designs or colors. This eliminates the possibility of the ink contaminating the product in a package if used in this manner, since the ink cannot touch the product. It also protects the ink film from abrasion. This makes it possible to produce on a continuous basis predecorated containers by vacuum or pressure-forming techniques, as shown in Figure 7.

Sheet

Film in thicknesses of 3 mils or heavier is commonly called sheeting. It can be produced by methods somewhat similar to those used to produce the film. The combination of good properties and low cost has made possible new uses for this rigid plastic sheet. While oriented polystyrene sheet cannot replace all applications presently using other plastics, it can be used for many of them. Fabrication can be accomplished by present practices being used for rigid thermoplastic sheet.

Limitations

Like many other plastic materials, oriented polystyrene has some shortcomings. It acquires a static charge and can be somewhat difficult to "machine" in packaging equipment. It can be scratched and it is not the easiest film to heat seal. However, it can be easily cemented to itself and is readily adhered to paperboard or other materials. It is tasteless and odorless, doesn't discolor on aging and its properties remain practically unchanged even when the material is subject to very low temperatures.

Some of the drawbacks mentioned may be overcome by using surface coatings. Heat sealing, scratch-resistant, non-fogging films and films having less static attraction can be expected. These are not commercially available at the present time, but they have been produced experimentally. Of course, the coatings will add to the cost of the base film and their use will depend on the demand for such material and the price limitations.

Copolymers

Copolymers, such as styrene-acrylonitrile, provide films and sheets possessing properties considerably different from those of polystyrene. The products produced from this copolymer are more flexible and exhibit better scratch resistance. The chemical resistance is generally improved in the copolymer sheet. This product has higher tensile strength, greater elongation and added toughness, and is more easily adapted to fabrication methods presently being used, especially those which are being used for cellulose acetate.

In a tray-type package produced by the Plax Corp., the lids are regular polystyrene, whereas the vacuum-formed bottoms are fabricated of copolymer sheet, since it has the necessary toughness and impact resistance and also is well suited to the vacuum-forming process.

Other copolymers will eventually extend the uses of the polystyrene family of films and sheeting beyond the existing hori- I Continued on page 226]

Figure 7, Thermoformed containers made of laminated polystyrene film with decorative pattern reverse-printed on one sheet of film prior to laminating and "locked in." This eliminates all possibility of ink contact with the product.