Prevention of Vessel Picking Trouble in Tropical Hardwood Pulps IV.

In the previous paper (1), it was shown that the vessel pick number of a handsheet decreased effectively with high consistency beating (PFI mill) treatment for vessel-rich pulp which was separated with a hydrocyclone from tropical hardwood pulps. This paper describes the prepara-tion of bleached kraft pulp from mixed tropical hardwood chips and the effects of various beating methods on the vessel picking during offset printing on pilot machine made paper. Beateing was carried out using 12-and 20-inch single disc refiner, Deluxe Finer (Aikawa Iron Work Co. Ltd.) and PFI mill.It was found that printing paper made from hardwood pulps beaten at low consistency to the freeness value lower than conventional 400ml CSF was most suitable for offset print among the beating conditions tested. Printing papers made from high consistency refined pulps has lower vessel picking tendency only for laboratory scale printability testers.The accepted pulp obtained by hydrocyclone treatment, which containes fewer and smaller vessel elements, showed low vessel picking tendency under the conventional low consistency refining.Sulfate cooking of hardwood chips with lower active alkali addtion produced higher quality pulps, which resulted in superior printablity.The results obtained from the comparison of handsheets vessel picking tendency suggest that though high consistency refined pulp produces high density sheets, the inter-fiber bonding is not so firm that it easily loses bonding strength under the filler addition, calendering during paper making and moisture during offset printing.