抄録
Alkylketene dimer (AKD) based emulsion sizing agent has been widely used in alkaline papermaking systems, because of its excellent sizing performance. However, the use of AKD sometimes causes deposit problems and affects on the runnability of paper machines. Such deposits are often observed on the inner side of the pipe from stuff box to head box, or on the press/smoothing rolls. To prevent these problems, a better understanding of AKD sizing is necessary. This paper deals with the factors of AKD sizing, such as pH, alkalinity, cationic starch, alum, cationic polymer, filler, pulp, and drying condition. Under the papermaking conditions using calcium carbonate as a filler, the use of cationic starch is necessary to achieve effective AKD sizing. Some cationic polymers work not only to improve AKD sizing performance, but also to prevent press/smoothing roll deposits.
Some mill experiences of deposit problems with AKD and the countermeasures are also shown. Deposit problems sometimes occur on press/smoothing roll, when running temperature is increased, especially in summer. It has been found that such kind of deposits could be decreased by replacing with higher melting point AKD. When first pass retentions of SS and AKD are low, deposit problems tend to occur. One of the reason will be that the AKD concentration in pulp slurry becomes higher. Another reason will be the hydrolysis of AKD by the requirement of longer retention time, which makes AKD emulsion particles unstable in pulp slurry. The better retention system helps to solve deposit problems.
