It is fair to say that the selection of a plastic is usually a compromise or a balance of bulk versus surface properties. If the surface of a plastic can be altered down to a depth of just a few molecules, it can make a profound difference in the plastic's suitability for a broad range of applications.

Using a cold gas plasma reactor to redesign the surface by just a few angstroms is an economical and environmentally safe method to change the basic polymer film in many manufacturing applications.

The engineering properties of plastics (abrasion resistance, heat tolerance, strength, and cost) are the primary reasons for selecting a resin. However, secondary engineering characteristics are assuming more critical importance.

In the case of films, designers often must select specially formulated and expensive polymeric materials, or combinations of materials. to provide an appropriate balance of properties. In some cases the polymer that exhibits the desired surface properties lacks the primary engineering attributes.

Often, the requirement is to provide a barrier against gas or liquid permeation through the film, necessitating the use of a costly multilayer construction when a simple coating, properly adhered to the surface, would be a more cost-effective and desirable route. Entire product concepts have been abandoned due to the inability to cost-effectively balance the primary engineering requirements of the bulk structural component with the secondary requirements of chemical inertness, bondability, or barrier characteristics. Whether the engineering problem involves the bonding of two polymers by lamination or multilayer extrusion, the adhesion of applied coatings, or the deposition of barrier coatings to polymer surfaces, gas plasma treatment may offer significant advantages.

Controllable, Reproducible

As early as 1969, claims were made for improved bondability of high density polyethylene, nylon, and polypropylene by exposing their surfaces to a cold plasma of partially-ionized gas 1.2.

Even better, the surface modification did not affect the character of the base material beneath the surface. Bond strength was shown to have improved after such treatment to the extent that failures most often occurred in the unmodified base polymer rather than at the interface. The process was found to be controllable with excellent reproducibility and without any noxious byproducts.

Over the past quarter century, the technique of re-engineering polymer surface properties through exposure to a gas plasma has been extended to virtually all polymers. Producible effects run the gamut from highly wettable surfaces exhibiting superior adhesion characteristics and chemical reactivity to completely unwettable, inert surfaces.

More sophisticated plasma processes permit dissimilar polymers to be "grafted" onto the bulk polymer chain, or the deposition in-situ of a micro-thin coating via plasma polymerization. Plasma polymerization provides pinhole-free films that adhere tenaciously to the substrate.