Getting graphics to conform to curved or irregular surfaces isn’t the only challenge that awaits when you print on three-dimensional parts
By Richard Young, Timothy J. Nimmer
If you’ve attempted to print, label, or otherwise decorate a three-dimensional
(3-D) product, you’ve probably been frustrated by an ink or adhesive that refused to adhere to the part’s surface. You may have tried different types of ink or adhesive formulations to get the job done, perhaps even used chemical primers or batch-treating processes. Still, the ink refused to bond with the material. What you experienced was a phenomenon called low surface energy, a characteristic of some substrates—particularly plastics—that makes them repel printing inks and other coating materials.
Contending with low-surface-energy substrates is a frequent concern for screen- and pad-printing businesses that decorate 3-D parts. But it’s an obstacle that can be overcome most easily with inline surface-treatment technology. This article will reveal the types of treatment systems available today and explain the role they can play in a printing operation.
Why is surface treatment necessary?
Surface treatment is frequently used in printing and other converting processes to alter the surface characteristics of a material. Treatment processes may be designed to improve a substrate’s wetting properties, which influence how well inks and coatings will flow out over the material’s surface (Figure 1). Treatments may also be used to enhance the bonding between the substrate and the applied material or eliminate static charges that have accumulated on the substrate surface. Surface-treatment technologies play a key role in preparing the surfaces of many commonly used packaging materials (paper, plastic, foil, etc.) for subsequent processing steps.
Most inks, paints, coatings, and adhesives resist wetting on the surface of virgin-plastic parts, which are newly thermoformed or molded items characterized by an inert, non-porous, low-energy surface. Virgin-plastic parts that screen and pad printers typically work with include items made from polyethylene, polypropylene, and other polyo-lefins. These materials tend to be very slippery and feel greasy to the touch. Getting coatings to permanently adhere to such materials is unlikely without the intimate contact created through wetting (Figure 2).
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