A Holistic Approach to Papermaking Additives for Coated Paper Grades

摘要

Chemicals used in the papermaking process can be divided into two groups, the functional chemicals that remain in the paper and influence the paper properties and the process chemicals that are used to improve control of the paper making process. Functional chemicals can add to value of the finished paper by introducing superior properties to that of untreated papers. This value can be quantified in terms of paper properties such as strength, resistance to water or solvents and absorption of lotions, inks or water. The cost of the paper making process itself can be controlled through the effective use of process chemicals. Process chemicals can reduce the number of sheet defects, minimise breaks and lower downtime caused by deposit build-up. Deposits form in the paper making process usually as a consequence of the system becoming unstable either as a result of pH or charge shocks, incompatibility between additives or the concentration of a particular species reaching critical levels. The nature of the deposits depends very much on the process. Generally deposit forming materials (troublesome substances) enter the system through a variety of routes including the broke system, the process waters or the recycled fibre line. Many of these troublesome substances are anionic in charge when dispersed in water. Several of the most troublesome deposit formers such as coating binders as well as certain types of pitch and sticky carry a neutral charge.