The quality of a substrate's surface is solely dependent on what the substrate is to be used for. This spills over into the type of substrate such as paper, polyester (PET) film or oriented polypropylene (OPP) film, or shrink film to name a few. What do I mean? Well, with PET film the applications are oftentimes technical or industrial applications, and you are purchasing the film for its surface quality, while for shrink film or OPP you are buying the film for its surface area and perhaps some special attributes such as saleability or printability. In some cases, you are purchasing the film for both its surface area and its surface quality as in packaging labels. The choice between coverage and quality is sometimes controlled by the polymer density as lower densities give more square inches of film for pound of polymer (the yield, in2/lb or m2/km). In the case of labels the overlap comes from the need, or desire, for a graphic-arts quality printing surface with large yields as compared to the reverse surface printing of packaging by flexo or gravure, which appears to allow more surface defects in the films.
However, there are several overarching substrate properties, in no particular order, which will define the surface “quality” of the substrate (for the application). First is the freedom from contamination, second is the surface texture (smoothness or matte at the extremes), next might be freedom from physical blemishes (gels, bubbles, degraded polymer, foreign particles, and scratches), surface-energy level (treatment or polymer type), and adhesion level. Other properties will be important based on the application. We will begin to explore these surface quality features in more detail in future posts. Of course, if you have a particular interest in one, let me know and I can start with that one.
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