Uniformity of Conversion and Improvements in Film Properties as a Function of Absorbed Light Intensity ― A Light Intensity Dependence Study

摘要

For most photoinduced free radical based polymerizations, the uniformity of double bond conversion as a function of coating thickness as well as a high total degree of conversion are crucial for the performance characteristics of the photopolymerized coating. In this study, the influence of irradiance (I_0) and photoinitiator concentration ([PhI]) was evaluated with respect to the depth profile of conversion (C_d). The investigation was performed at a constant absorbed light intensity (I_a). This was accomplished by variation of the irradiance and photoinitiator concentration simply by using the direct proportionality relation I_a=Const.·I_0·[PhI]. The purpose of the study was simply to define conditions for optimization and predictions for control of C_d. The photopolymerizations were performed under laminated and un-laminated conditions at various film thicknesses. Degrees of conversion were obtained by the use of FTIR. The apparent technical benefits are therefore quite obvious, such as possibility of controlling C_d. As a practical result a dramatic reduction of [PhI] and higher degrees of conversion at low [PhI] and high I_0 can be achieved.