Radiation curing: giving films a smoother profile
A new paper investigates the film quality of electron beam curable varnish coatings on polymer web substrates. Properties were found to be affected by monomer level, EB dose and EB current. Also, some crosslinkable surfactants improved properties.
Polymer webs are important substrates for all kinds of flexible applications such as food packaging, decorative products and flexible electronics. If the polymer web is intended to be coated with functional thin films, which are deposited by chemical or physical vapour deposition (CVD, PVD) techniques, the surface of the polymer films must be smooth and defect-free.
Scientist from Fraunhofer Institute for Organic Electrons, Electron Beam and Plasma Technology investigated a formulation consisting an aliphatic urethane diacrylate oligomer and 1,6 hexanediol diacrylate (HDDA) in differing ratios. Different surface additives were also examined. The varnishes were also cured by EB with different parameters.
Influence on surface roughness
Influence of the fraction of monomer in the formulation on the average surface roughness
They found that the arithmetic average surface roughness and the fractional defect area increased with increasing monomer content in the formulation. Also the fractional defect area rises with increasing electron beam dose. However, a high electron beam current and hence a high motion speed on a line leads to a lower fractional defect area.
Furthermore, certain surfactants, designed to crosslink into the film, could also decrease the fractional defect area.
