Abstract
High filler-containing papers were prepared by incorporating mixtures of two kinds of silica fillers carrying different particle size. The filler particles were silicas, SD-8 with an average diameter of 9 pm and PW-20 of 26 μm. The ratio of both silicas in the filler mixtures was 1: 3 (ratio of weight, SD-8 to PW-20), 1: 1 or 3: 1, respectively. The filler contents in the paper were 10 wt% to 65 wt%. The effects of the silica mixtures and the filler contents on the mechanical strength and the porous structure of the papers were investigated. The pore-size distributions were measured by a mercury intrusion porosimeter and the pore structures were observed by a scanning electron microscope. The pore volume increased for papers in which SD-8 ratios in the filler were high and the filler contents increased. The highest pore volume of the sample sheets was one for a paper with filler ratio of 3: 1 and the filler content of 60 wt%, and it was 3.8 times as much as that of the filler-free sheet. The pore volume below 2 μm in diameter remarkably increased with an increased SD-8 ratio in the filler. The tensile strength and the folding endurance were measured by the Schopper's machines. The mechanical strength of the papers decreased dramatically when the filler contents increased, and it decreased a lot for papers in which the SD-8 ratio in the filler increased. The moisture content of the papers increased with the filler content increase in the paper and when the SD-8 ratio in the filler increased. The effects of SD-8 were higher than those of PW-20, especially in high humidity air.
