Peter Palasz, Ph.D.
Business Scientist
Henkel R&D

Ultra Violet Cationic Acrylic PSA

Solvent based acrylic PSA are well known as the premium system in the market place due to their durability and high performance either as one or two pack formulations.  With increasing pressures on improved environmental emissions from factories the industry is seeking alternative approaches to solvent based adhesives.  UV cured acrylic hotmelts are well known in the market place and offer a solution.  These hot melts use a bound photo-initiator usually based around grafting benzophenone functional groups.  Existing hot melts give good properties up to @80 gsm, but at greater coat weights the heat resistance tends to decline.  This paper will report on the recent work at Henkel to achieve good performance at higher coat weights of @150 gsm.  The approach has been to design novel UV cationic cured acrylic polymers.  The polymers have a pendant reactive epoxy functional groups.  The chemical nature of the epoxy group is critical for good thermal stability for the resulting hot melt typically at 130C. On exposure to UV radiation the epoxy groups ring open and crosslink the polymer chains. Then through a process known as dark cure the polymer reaction continues until no more epoxy functionality is left ensuring effective through cure.  This process allows for thick coatings to be made with good hot shear.  An additional advantage is that the level of UV dose required is less than that required for existing UV acrylic cured hotmelts resulting in coating lines running twice as fast.