Abstract
Radical UV curable resin commonly shrinks during photopolymerization, which is difficult to avoid. This study developed an apparatus to measure the degree of shrinkage under nitrogen and air atmospheres. The apparatus consisted of a laser displacement sensor to detect the height of the spun-cast resin on a sapphire plate, two fused silica windows, a nitrogen purging line, and a UV light source. The initial and final thickness of a mixture of diurethane dimethacrylate/1-hydroxycyclohexyl phenyl ketone showed a linear relationship between 50 and 140 μm. The linear relationship was used to calculate the degree of shrinkage assuming an initial film thickness of 80 μm. The degree of shrinkage in nitrogen atmosphere was 1.3% greater than that in air. The relationship between the degree of shrinkage and UV intensity in the nitrogen atmosphere exhibited a single linear relation, while that in air showed two lines. UV intensities lower than 15 mW/cm2 exerted a more significant influence on the degree of shrinkage.
