Dynamic Shear Modulus Degradation Limits in High Speed Recyclable UV Resin Formulations
Dynamic shear degradation limits UV resin velocity at 280 m/min to prevent oligomer scission, balancing resin costs against full EPR fee savings.
UV Resin Degradation
Polymer Breakdown
Permanent loss of chemical and physical properties in a cured coating due to prolonged exposure to high energy radiation characterizes a failure in the binder system. The uv resin degradation appears as a shortening of the polymer chains and a reduction in the crosslink density of the film.
Photo-Oxidation Process
Interaction between the polymer matrix, oxygen, heat and residual photoinitiators creates reactive radicals that attack the molecular structure. During uv resin degradation, these radicals cause chain scission or unwanted additional crosslinking, making the film either soft and tacky or hard and brittle. Speed of this reaction depends on the intensity of the light and the presence of stabilizers like hindered amine light stabilizers.
Moisture can accelerate the breakdown by facilitating the migration of degradative byproducts.
Visual Failure
Change in the optical properties of the coating often indicates a problem. The uv resin degradation typically leads to yellowing or a loss of gloss as the surface becomes microscopically rough. In severe cases, the coating may crack or peel away from the substrate because it can no longer accommodate the expansion and contraction of the board.
Selecting resins with higher aromatic content or specialized additives is necessary for packaging intended for long term display in sunlight.