SHRINKAGE EFFECTS IN PHOTOPOLYMERIZABLE RESINS CONTAINING FILLING AGENTS - APPLICATION TO STEREOPHOTOLITHOGRAPHY

The influence of porous additives with various structures on the shrinkage of resins used for stereolithographic applications was studied by measuring the dependence of the specific gravity of the charged polymer material as a function of the charge fraction. The investigations were conducted on difunctional monomers photopolymerized either by a radical (acrylate) or a cationic (epoxy) mechanism. The improvement resulting from the incorporation of charges in the formulation is accounted for in a semi-quantitative way by an adsorption-desorption equilibrium of monomer molecules between the pores and the bulk phase. Thus, the pores of the charges which are initially filled with monomer molecules play the role of buffers which discharge their content as the photopolymerization develops in the liquid phase. It is also worth mentioning that the viscosities of the photosensitive charged resins used in these experiments are quite suitable for use in stereophotolithography.