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Pressure-Sensitive Adhesives for Decals and Labels

(October 2012) posted on Mon Oct 01, 2012

This article talks about adhesives, looks at various polymer chemistries and curing options available, and provides information.

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By Julia Goldstein, Ph.D.

Current trends
When suppliers are asked what customers are demanding, cost reduction is a common theme. One example is the trend toward thinner label films and liners to reduce cost. These changes in substrates introduce new challenges for manufacturers. The adhesive may not coat the same on a thinner substrate, so it is important for the adhesive supplier to work with the customer to determine an optimum solution that will meet both cost and performance requirements. There is also a drive toward reducing coating thicknesses in cases where adhesion performance will not suffer as a result.
Another cost saving approach is improving throughput, which may favor adhesives with 100% solids that do not require oven drying to cure. Many of these, however, are hot melts. The processing temperature required to apply these adhesives may limit their use on some of the newer label films that have low melting or softening points.
There is also shift from paper to film substrates, giving designers more creative options. Clear labels (Figure 5) that enhance graphics with a no-label look are becoming more popular. These require colorless adhesives that will not yellow over the life of the label, and many manufacturers produce PSAs that meet this requirement.
Even if an adhesive is designed to adhere to a new type of substrate, there can be other concerns for label manufacturers. One example is labels for powder-coated, painted surfaces. The adhesive may bond well, but there can be issues with oozing of adhesive. The adhesive supplier, label manufacturer, and end customer may need to work together to achieve an optimum solution.

Future directions
What does the future hold for the label printing industry? There is a push toward digital printing of adhesives. Adhesives are not yet available for printing through an inkjet nozzle, but there is a race in the industry to add that capability. The challenge is depositing enough adhesive for a strong bond while avoiding the problem of excess adhesive drying inside the printer.
Labels are being applied to more and more products. One new development is clear labels applied to drinking glasses as an alternative to painted decorations. Here the challenge is developing an adhesive that can withstand the heat and chemical exposure of automatic dishwashing. Some companies report demand for adhesives that can withstand extremely high temperatures that are beyond even the capabilities of silicone materials. Long-term UV resistance is also on the wish list.
The ideal adhesive of the future will be environmentally friendly, low cost, and very strong. It will be able to be applied to any label material attached to any surface under demanding environmental conditions. In reality, of course, many different adhesives will be needed to meet an ever-expanding list of requirements. The industry will continue to innovate and develop a range of products designed to meet customer needs in the years ahead.

Julia Goldstein, Ph.D., is a freelance writer with a background in materials science. She provides commercial writing for companies in the semiconductor and printed-electronics industries.

The author wishes to thank Ingrid Brase (Henkel), Lisa Castillo (KIWO), Shannon Cook (Craig Adhesives), Kyle Rhodes (Dow Corning), Jeffrey Stadelman (MACtac Graphic Products), Randy White (J.N. White Designs) and Mike Witte (Franklin Adhesives) for providing information for this article. 


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