MEASUREMENT OF INK PARTICLE-SIZE IN DEINKED STOCKS BY IMAGE-ANALYSIS

A new image analysis procedure has been developed for measuring the residual ink particle size in deinked stock. In this procedure, ink particles are deposited onto slides and viewed with transmitted light. A neighbourhood-contrast detection algorithm distinguishes the ink from most of the fines, and a circularity criterion excludes the remaining fines. Repeatability from day to day is enhanced by adjusting the optical setup to a predetermined contrast level for a reference slide containing carbon particles As a result, coefficients of variation of about 3% were obtained for ink particle measurements of recycled pulps. The average particle size is found to be independent of the mesh of the Dynamic Drainage Jar used in the isolation step, but the method can easily discern the aggregation of ink induced by the addition of CaCl2 during the deinking step.