Cure-Shrinkage Stress at the Coating-Substrate Interface: Substrate Modulus, Thermal Mismatch and Adhesion Failure in Radiation-Curable Coatings

Radiation-curable coatings develop internal stress when polymerisation shrinkage is constrained after gelation. The observable consequence depends not only on free shrinkage, but also on the evolving coating modulus, relaxation before vitrification, coating thickness, substrate stiffness, laminate symmetry, cure rate and thermal history. Direct studies show that formulation and irradiation intensity alter gelation, vitrification and stress development in UV-curable acrylates; that coupled kinetic-mechanical models can reproduce some stress regimes while failing in early non-equilibrium or post-vitrification regimes; and that substrate compliance and annealing can strongly change curl in a UV-coated semi-rigid laminate [1-4]. A two-step photocuring study further demonstrates that constraint stiffness is an experimental coordinate, not a background constant [5]. ER-195 converts this evidence into a bounded qualification framework for coatings on inert substrates. No universal stress, modulus, thickness, coefficient-of-thermal-expansion, adhesion or cure-schedule limit is proposed. Curl is treated as a system response, not a direct stress measurement, and adhesion failure is treated as a competing-mechanism diagnosis.