VINTAGE OWNER'S MANUALS, SERVICE MANUALS, BROCHURES AND PUBLICATIONS
FAQ
Your Recent Purchases
Contact Us
Home
Welcome to Automatic Ephemera, an independent organization/library for historical research and education, sharing public domain manuals, brochures and periodicals relating to vintage products.
Modern Packaging Magazine - September 1958 - Return to Main Search
Preview Page 152 of 236 Preview Pages
Text Summary via OCR:

gradual loss of properties. Thus, the ideal area for effective orientation is under the C-D portion of the curve, which actually is rather narrow. The exact location of the "ideal" area may vary considerably, as this depends upon the processing conditions.

Packaging properties

Polystyrene film, oriented under ideal conditions, has properties which are highly suited to many flexible and semi-rigid packaging requirements. This market in 1955 consumed an estimated 500 to 550 million pounds of various films (9). It is still growing. Polyethylene and cellophane accounted for most of this volume. These are relatively low-cost materials and any new film will need to be competitive in cost if it is to make its way in this field.

Since the supply of polystyrene resin is plentiful, cost is low and the density is favorable, it is finding a place in this field. The area factor for oriented polystyrene film is approximately 26,000 sq. in. per pound for a 1-mil film. This compares to about 19*500 for moistureproof cellophane, 22,000 for cellulose acetate and about 30,000 for polyethylene film of the same thickness.

The area factors must be combined with costs to be significant. The bar chart shown as Figure 3 illustrates relative costs for films of the same thickness. The open bars represent the area yield per pound; the cross-hatched bars, the yield per dollar. Thus polyethylene is seen to be the lowest-cost film, gauge for gauge. The specific cost for a given application will depend upon the film thickness required. Although other factors may affect the cost, the comparisons based upon equal thickness are valid to illustrate the competitive position of oriented polystyrene film.

Figure 4 shows the relative water-vapor transmission and gas-permeability rates of oriented polystyrene, cellulose acetate and polyethylene films. Tests have shown that the degree of orientation does not affect the permeability of polystyrene.

The water-vapor transmission rate of polystyrene, which is 6.2, is not so low as that of polyethylene, although it is considerably better than that of cellulose acetate.

Since the gas permeability of oriented polystyrene is lower than that of polyethylene and slightly higher than that of cellulose acetate, oriented polystyrene is suited for wrapping many fruits and vegetables. Many of these products require a certain minimum level of respiration and, if not allowed to "breathe," will soon discolor, lose their taste, develop off-flavors and then rot.

The overwrapped molded polystyrene and paper-board tomato cartons shown in Figure 5 are good examples of typical vegetable-package overwraps in

EFFECT OF ORIENTATION ON FILM PROPERTIES

DEGREE OF ORIENTATION

Figure 2, Amount of orientation is very critical in effect on the physical properties of polystyrene film. There is no improvement up to B; then an almost vertical rise to the desirable area C-D, and a gradual loss occurs beyond D.

which oriented polystyrene film is showing considerable progress. The high gloss and excellent transparency are apparent.

Oriented polystyrene has many other good properties, too, as shown in Table I. Its water absorption is nil; it ages well indoors, although its outdoor life in sunlight is limited. Its specific gravity is favorable, which classifies it as a "high-coverage" film. The tensile strength in the (LW) or roll direction is good, as is its strength in the (CW) or crossroll direction. Tear and burst strengths are satisfactory. The melting point is rather high compared to the softening point. However, the critical temperature is shrink point, since the film is highly oriented. Chemical resistance to acids, alkalis, greases, oils (both vegetable and mineral) and alcohols is very good, although polystyrene has poor

KH

[yTeloI    COMPARATIVE FILM YIELD

(per area end per dollar)

60,000-------

CELLULOSE CELLOPHANE POLYSTYRENE POLYETHYLENE

ACETATE

I-1 SQ. IN./LB./MIL THK'NESS. m SQ. IN./DOLLAR/MIL THK'NESS.