Heat generation at photopolymerization by multiple-spot exposure with bluelight

In this paper, heat generation in an acrylate monomer during photopolymeriz ation in multiple-LED photographic curing (MPC) is studied. During the expo sure process, an array of multiple beams of light are projected simultaneou sly on to the resin surface while the projector moves across the resin vat. In this way, exposure occurs through raster scanning. It was found that th e heat generated by the polymerization process causes the resin temperature to increase in steps to a maximum of 25 degrees C when scanning at a veloc ity of 0.5 mm/s. Heat from the light source itself is not induced. At 3 mm/ s, excess temperature decreases to only approximately 4.5 degrees C. For on e layer, three-dimensional temperature profiles show that excess temperatur e is distributed equally, perpendicular to the scan direction. The polymerization process occurs slowly. Using spectrophotometry, the cour se of absorbance of the photoinitiators can be observed. At 470 nm, the abs orbance increases from 0.4 to 1.2 in the liquid state. The absorbance of th e photoinitiators decreases to 0.1. After 30 min of exposure, the polymeriz ation process is complete. This necessitates post-curing after the actual b uild process.