Oji Paper Co., Ltd.

Shigeru Eimaeda

Isao Wada

Yoichi Shin

Junichiro Kido

Shinji Seto

Kunihiko Aida

Takao Suzuki

An improved paper-making hydrous acid filler is prepared by classifying or pulverizing a slurry containing fine particles of hydrous silicic acid, which is obtained by neutralizing sodium silicate with sulfuric acid, by a wet classifier or a wet pulverizer, so that the proportion of particles having a particles size of 1 to 30 .mu.m is at least 80% and the proportion of particles having a particle size of at least 70 .mu.m is not more than 0.4%. The filler has a function of improving the ink receptivity of the paper of the internal additive type and is capable of improving the opacity of the paper after printing.

Process for preparation of paper-making hydrous silicic acid filler

Lignocellulosic material is pulped by a process comprising the steps of: introducing a molecular oxygen-containing gas, such as air, into an alkaline sulfide solution containing NaOH, Na.sub.2 S and at least one cyclic organic compound selected from quinone, hydroquinone, 9,10-diketohydroanthracene and 9,10-dihydroxyhydroanthracene compounds, to oxidize at least a portion of Na.sub.2 S; delignifying the lignocellulosic material with an alkaline sulfide cooking liquor containing the oxidized alkaline sulfide solution at an elevated temperature and; then, recovering the resultant pulp from the delignification mixture.

Process for pulping lignocellulosic material with a preoxidized alkaline

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Tomakomai, Japan

Shigeru Eimaeda