Solvent-Recovery Mass Balances in Photopolymer Processing: Contaminant Build-Up, Separation Efficiency and Reuse Limits

Wash solvent in vat-photopolymer processing is a circulating process material, not an indefinitely reusable utility. Each cleaning cycle transfers uncured resin, monomers, oligomers, photoinitiator-related species, pigments, particles and water into the bath while solvent is also lost by evaporation, drag-out and disposal. Recovery by settling, filtration, photochemical treatment, distillation or other separation can reduce contaminant load, but recovered volume alone does not establish reuse quality. This review develops a mass-balance framework that closes solvent, dissolved resin and separated-residue flows around washing and recovery. It distinguishes contamination concentration from cleaning performance, recovery yield from contaminant rejection, and nominal purity from fitness for the next wash stage. Recent studies show that resin contamination in IPA can measurably affect printed-part accuracy, supporting the need for state-based solvent control. The framework uses staged baths, representative sampling, contaminant indicators, solvent-loss accounting and challenge testing on printed geometries. The central conclusion is that reuse limits should be defined by the effect of solvent state on the downstream part and process, while the recovery system is qualified by both mass closure and restored cleaning performance.

ER-272 · Version 0.2.