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Printing on Specialty Substrates

(April 2010) posted on Tue Mar 23, 2010

Managing variables associated with the substrates you use is critical to quality. Find out how to work with some popular, but picky, materials.


By Gail Flower, Johnny Shell

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Polypropylene Plastic bottles, corrugated-plastic sheeting, real-estate signs, storage boxes, and many other temporary indoor or outdoor point-of-sale/point-of-purchase displays are made from it. Low surface energy necessitates pretreament or ink modification to facilitate ink adhesion.

PVC (polyvinylchloride) PVC is highly popular because of its durability and strength. Display graphics, ID cards, containers, and medical supplies are a few examples of applications suited to PVC.

Ink compatibility
Inks for thermoplastics establish a chemical bond on the substrate’s surface, in addition to the mechanical bond created when the ink dries or cures. Solvent-based, multipurpose inks make adhesion on a majority of thermoplastics much easier.
 

Ink fails to adhere adequately to substrates that have a surface energy that is lower than the surface tension of the ink printed on the material. Surface energy is expressed in dynes. Using a dyne pen will help you determine the substrate’s level of surface energy. The objective is to test the surface of the substrate with one of several pens in a set until the ink begins to flow out and not bead like water on a waxed surface. You can change the ink’s wetting properties by using a special modifier or adjust the substrate’s surface energy by treating the plastic with an air-plasma (corona) system before going to press.

UV ink can also be used with thermoplastics as the curing action of the acrylic monomer forms a hard, mechanical bond that is useful when vacuum-forming screen-printed thermoplastics. Whatever the ink system, communicate with the manufacturer to ensure proper curing parameters.

Vinyls will leach out plasticizers, especially when encapsulated in an airtight package or subjected to prolonged heat. Plasticizer is a contaminant and will cause fish eyes, blurred printing, or ink delamination during and after drying. Wiping the surface of cast vinyl with 70% isopropyl alcohol just before printing usually removes most surface plasticizer.

Metal
Metal is an extremely durable substrate but needs a high degree of preparation. Some of the more popular metal products that are screen printed include member cards, discount cards, nameplates for desks, offices and restaurant signs, awards, clock faces, dials, appliances, point-of-sale graphics, and outdoor signage.


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