Flexographic Printing & Packaging

PP films can be made by either blow or cast-extrusion methods. As a plain, unoriented, uncoated film, PP possesses superior optical properties, excellent moisture barrier properties, good dimensional stability, and good heat seal strength, although in a narrow temperature range. It also has low tensile and impact strength, high gas permeability and poor low temperature durability; it has only fair chemical resistance, machine performance and abrasion resistance.

PP film comes in a variety of forms and classifications and can be enhanced with different coatings such as PVDC, Acrylic, EVOH, low temperature seal coatings, white, or cavitated, and is even produced in metallized versions.

PET films are manufactured by cast extrusion and are usually biaxially oriented. PET films have high tensile strength, low elongations, high melting point, excellent grease/oil barrier properties, low gas and moisture permeability, good printing characteristics, a high-use temperature range, high impact strength, high scuff resistance and excellent dimensional stability.

Polyamide or Nylon (former DuPont trade name) can come in Biax or Cast version. Cast versions are less common and used mostly in forming applications. Unoriented Nylon (sometimes known as Nylon 6) is widely used in meat and cheese vacuum packaging because of its good oxygen barrier, grease resistance, and ability to be easily drawn into a thermoformed shape. Oriented nylons are most commonly combined with PE in a laminated structure to form the outer layer of a package. Both types of nylons have excellent optical properties, resist grease, oil, and many chemicals, and are physically very durable, resisting impact, puncture, and cracking when repeatedly flexed. Nylon is not heat-sealable and naturally provides a good barrier to aromatics, oxygen, nitrogen, and carbon dioxide, but it also has poor water vapor (WVTR) properties. This can, however, be improved with a coating such as PVDC.

At one time, cellophane was the only clear packaging film available, and thus also the most widely used. This material is composed of wood cellulose transfer rather than petrochemicals. Although not used in many modern applications, its compostable property is renewing brand and consumer interest in cellophane, which comes in many versions and has superior dead fold properties and machineability. It does have good natural barrier properties on its own, but the use of coatings can enhance this ability even further.

PVC alone is hard, brittle, has low thermal stability, and is practically useless unless compounded with other additives. These additives can include slip agents, plasticizers, pigments, waxes, fillers, processing aids, impact modifiers, and liquid epoxy stabilizers. Specific application requirements will determine which PVC film will be optimal. Most PVC films have high impact strength, scuff resistance, dimensional stability, good opticals, and excellent grease and oil barrier properties. Highly plasticized PVC films have excellent stretch properties, making them good for hand-wrapping meats and produce. PVC films can be made with superior shrink properties, making PVC the preferred material for tamper-evident bands and shrink-label stock.

All of these acronyms fall under the polyethylene family of films, but the films differ so greatly from each other that their applications are completely different, and different polyethylene films are often treated as if they belonged to different plastic families. Most grades of film in the polyethylene family are considered low-cost and have a good moisture barrier, sealability, seal strength, high elongation, and softness. However, PE grade films in general do not have good clarity. PE films are used in a variety of applications such as bread bags, shipping sacks, mulch, frozen foods, consumer products, garment bags, bag liners and more. PE is also offered in white versions and can be coextruded with other resins to enhanced performance of the moisture barrier, lower film sealing temperatures, and increase durability for extreme processing applications.

Metal foil holds a strong position among flexible packaging materials. Although itself not considered a plastic or film, foil is considered to have the perfect barrier to moisture and gas and also has no light transmission. Foil comes in different hardness or softness levels, with softer foil possessing better dead fold characteristics. Foil is generally used as the inner or middle layer of a multi-ply lamination because it is susceptible to scratching, abrasion and flex crack when exposed. Usually a high-cost material, foil can be difficult to work with in the converting process, but its appeal and superior characteristics can make it a good choice in some applications.