紙塗工用ラテックスの新しい品質設計

Abstract

Two types of the newly improved SB-latex can provide good performance for coated paper. The first one is the latex which provides better balance between blistering resistance and picking strength for web off-set printing coated paper. It is difficult to reconcile blistering resistance with picking strength only by controlling gel content of latex. Reducing gel contents can give good blistering resistance with the porous coated layer. But the porous structure causes poor picking strength, and vice versa. The newly devised latex has greater thermal sensitivity to the melt flow of latex polymer by changing the quality of gel into higher homogeneous molecular distribution and carboxyl group distribution. This sensitivity results in not only a small pore coating structure which gives good picking strength but also large deformation of pores under high temperature in order to attain good blistering resistance. Dynamic viscoelasticity both of latex film and coating layer was measured. Usefulness of the dynamic viscoelastic measurements in characterizing latex polymer and coating layer is demonstrated. Another one is a newly developed cationic modified latex. Controlling surface electric state of latex can provide suitable interaction between latex and pigment in coating. Such interaction gives coating structure adequate porosity for less print mottle of coated paper. Generally, Tg is the key factor to improve print mottle. Lower Tg latex provides less print mottle due to the produced bulky and porous coating structure. However, lower Tg latex tends to provide poor wet picking strength and poor stiffness. The moderate cationic latex performed less print mottle without reducing Tg. The effect of the moderate cationic latex on print mottle was verified by pilot coating and commercial press.