Environmentally Aware Printing – Types of Adhesives (continued)
Tuesday, March 9th, 2010Environmentally Aware Printing - Types of Adhesives (continued) – 10th March 2010
C) Water-dispersible hot melt polymers (continued)
The vinyl monomers used in the vinyl/ graft copolymers may be acrylates or vinyl acetate and the grafted component (s) are hydrophilic in nature. Adjustment of copolymer or graft component type or concentration leads, to a range of compositions with varying glass transition temperature, molecular weight and water sensitivity.
These types of copolymers do not suffer from the inherent oxidative and thermal stability problems of other dispersible systems. Water sensitivity and dispersibility are key factors in the performance of such a product and, using Tappi UM 666, it can be seen that the graft copolymer is significantly more dispersible than standard polyethylene-based hot melt. It is also seen that increasing the processing temperature or the hydrophilic component concentration increases the water sensitivity of the polymers.
Products based on this vinyl graft technology have been developed for a variety of applications including bag making, roll wrap, bookbinding and case/ carton sealing. Laboratory scale tests and trials at recycling mills around the world have revealed excellent results with regards to dispersibility and recyclability. Under the right conditions the product has been proven to be totally dispersible with a large percentage of adhesive by weight (more than 20%) being incorporated into the paper with no adverse effects or stickie problems.
A question of backwater saturation still remains in closed loop systems but calculations indicate that saturation cycle at typical addition levels is several months. This is probably comparable with the usual cleaning cycle in a mill and would therefore not cause significant problems.
To be continued…
Peter Harrison is Joint Managing Director of The Printing House Ltd, and Print Buying Direct of Crewe, Cheshire, UK.
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- Environmentally Aware Printing – Types of Adhesives (continued)
- Environmentally Aware Printing – Types of Adhesives – part 3
- Environmentally Aware Printing – Types of adhesives – part 2
- Environmentally Aware Printing – Types of adhesives – part 1
- Environmentally Aware Printing – Dealing with the stickies problem Part 4
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