Colorless topcoats applied over litho-printed materials are designed to provide:

• Increased gloss
• Rub resistance
• Chemical resistance

Functional improvements such as heast-sealable blister packaging The three types of coatings are (1) Overprint varnishes, (2) Water-based, and (3) UV and Electron Beam-cured coatings.

Overprint varnishes are solvent-based, inexpensive, lower quality coatings which are easy to use. This segment is seeing declining market share.

Water-based coatings provide higher quality than Overprint. They contain 30-50% solids and are made up of acrylic and styrene/acrylic polymers and some water-based urethanes along with specialty additives peculiar to a particular task. The acrylics have a far lower yellowing tendency than Overprint. Forced air or infrared heating is required to dry them. Water-based coatings are expanding their market share.

UV and Electron beam-cured coatings offer the highest performance of the three options at the highest price. They are made from energy-cured polymers and monomers with specialty additives. Like Overprint, they can be applied on a standard printing press, and like water-based, require a separate curing unit. They are expanding from a small market share.

Author: Don P. Duncan
Source: GATF 1999 Technology Forecast, p. 30.