It is rare that the polymers used in film packaging applications will meet end-use needs without modification of some kind. A wide variety of additives and modifiers is available, and the following list describes broad categories and the performance reasons they are employed. The film producer typically adds them at the time the main polymers are melted in the extrusion process.
COF Modifiers - adjust the coefficient of friction (COF) to match converting, packaging, and end-use requirements, generally by reducing the COF of tacky films. Slip agents work by blooming from the bulk of the polymer to the surface and provide lubrication without degrading clarity, but can interfere with adhesion in printing and laminating. Antiblock agents are small inert particles that act through roughening the surface of the film to reduce contact area and force needed to slide; while they do not generally impact adhesion, they do increase film haze.
Colorants - used to create opacity, to either increase the impact of printed graphics, protect products sensitive to light, hide products that are not particularly attractive at time of sale, or create a unique color for marketing purposes.
Antioxidants - while some amount of antioxidants is generally formulated in the resin by the resin manufacturer to protect the resin from oxidation during the heat of the extrusion operation, film makers may choose to increase the amount if excessive thermal abuse is anticipated, or in some cases, it is added to the film with the intent of small amounts transferring to the product to protect it from oxidative spoilage.
Fillers - used to reduce the cost of the film by substituting a lower-cost material, generally a small particle-size mineral, for some of the polymer. Can also improve dimensional stability at higher temperatures. Caution must be used to prevent excessive loss of strength properties.
Antistats - primarily used for electronics packaging, as polymer films tend to develop static charges when moved over stationary or even rotating surfaces. If not dissipated, those charges can damage sensitive electronic components.
Oxygen Scavengers - used in packages for highly oxygen-sensitive products to intercept permeating oxygen molecules and prevent them from reaching the package interior. Newer technology permits activation of the scavenging functionality at the time of packaging, maximizing the effectiveness of the additive.
Desiccants - think of them as moisture scavengers; desiccants are sometimes added in coextruded layers adjacent to high-performance layers whose key properties are susceptible to deterioration from exposure to water. Desiccant-containing layers in ethylene vinyl alcohol-containing structures are most common.
UV Absorbers - the resin manufacturer generally formulates in the amount of UV absorber needed to protect the polymer itself. In unique cases, UV absorbers can be added to protect food that is highly sensitive to UV exposure.
Nanoparticles - a burgeoning field of exploration and development, with film makers attempting to take advantage of nanometer-scale particles to cause significant property increases in films. The most work done thus far shows that small amounts of high aspect-ration synthetic clays added to PA6 and PEs or PP can increase oxygen and moisture vapor barrier as well as stiffness and thermal stability. Commercial products for these systems are available.
