Studies on the Papermaking by Use of Surface Sizing Techniques (II)

Abstract

If alum is cut back or removed from the wet end, retention of fines and filler in the sheet is generally reduced, which may result in poor formation of the sheet. Thus, in this paper was discussed the filler retention in producing base sheet for surface sizing by both laboratory applications and field pilot scale trials.Calcium carbonate (both ground limestone and precipitated calcium carbonate) was compared with the hitherto generally use clay and with other fillers. In particular, it was thought that ground limestone would be a very advantageous filler, because it had superior optical property and very low abrasiveness, and could be obtained at a low price. Thus, it was evaluated to determine whether it would be useful at filler for base sheet for surface sizing.As a result, it was found that ground limestone of a small particle size (for example, 1.8μ) improved the opacity (scattering coefficient) of the sheets. The use of filler retention aids proved more effectively with the ground limestone than with the precipitated calcium carbonate. The ground limestone was retained up to 80% by adding 0.010.02% cationic or anionic synthetic polymer based on filler weight as a retention aid continuously to the riffler just prior to the headbox. What is more, this was a sheet having a higher optical property and greater strength property as compared with the sheet of a clay/rosin/alum system. It was known that when ground limestone filled sheet was surface-sized at size press, it could be made into a sized paper having a remarkable sizing response just as in the case of precipitated calcium carbonate.Ground limestone filled paper has the following advantages;(1) Ground limestone itself is a lower-priced filler.(2) It has a better optical property and a very low abrasiveness than clay.(3) It has a superior strength property as compared with the sized paper of a clay/rosin/alum system. Thus, more of the expensive pulp weight has been replaced by the low-cost filler.