Abstract: In a process for producing kraft pulp, the process is made closed, the yield of pulp is improved and environmental problems are minimized. An alkaline solution containing Na2S which flows in a process of producing kraft pulp, is electrolyzed by an electrolytic oxidation method; a liquid which is formed at an anode side and contains a polysulfide type sulfur in an amount of 6 g/l or more, is added, as it is or after being causticized, to the process before a chip has the maximum temperature, and a NaOH solution formed at a cathode side, is added to at least one step of the process after the chip has the maximum temperature till a final bleaching stage; and at least chemicals in the step wherein NaOH is added, among chemicals discharged in all steps from a cooking step till the final bleaching stage, are recovered and reused.

Abstract: Inexpensive spindle- or rice-like calcium carbonate giving useful properties for brightness, opacity and wire abrasion resistance as a paper filler is provided by taking advantage of the causticization step. When a white liquor is used for slaking a quick lime, the quick lime used in the slaking reaction of a first step has a calcium carbonate content of 10% by weight or less and is slaked with the white liquor at a concentration of 20 to 60% to prepare a milk of lime. When a green liquor is used for slaking a quick lime, the quick lime used in the slaking reaction of a first step has a calcium carbonate content of 0.1 to 10% by weight and is slaked with the green liquor at a concentration of 20 to 60% to prepare a milk of lime. In a second step, causticization reaction takes place at a green liquor loading rate of 0.02 to 0.5 cc (green liquor)/min/g (quick lime) at a reaction temperature of 20 to 105° C. to afford spindle- or rice-like calcium carbonate.

Abstract: Calcium carbonate in the form of aragonite crystals suitable for use as a filler for papermaking to give useful properties for bulk, whiteness, opacity, wire abrasion and yield is obtained by taking advantage of the causticization step.

Abstract: The present invention has an object to obtain a cooking liquor containing polysulfide-sulfur at a high concentration by minimizing by-production of thiosulfate ions. The present invention is a method for producing polysulfides, which comprises introducing a solution containing sulfide ions into an anode compartment of an electrolytic cell comprising the anode compartment provided with a porous anode, a cathode compartment provided with a cathode, and a diaphragm partitioning the anode compartment and the cathode compartment, for electrolytic oxidation to obtain polysulfide ions, characterized in that the porous anode is disposed so that a space is provided at least partly between the porous anode and the diaphragm, and the apparent volume of the porous anode is from 60% to 99% based on the volume of the anode compartment.

Abstract: A lignocellulose material is cooked by means of an alkaline cooking liquor containing polysulfides in the presence of a quinone-hydroquinone compound, of which the oxidation-reduction potential in the form present during the cooking, which potential is a value calculated as a standard oxidation-reduction potential (Ea) with a hydrogen ion activity of 1, is within a range of from 0.12 to 0.25V to the standard hydrogen electrode potential. It is thereby possible to cook the lignocellulose material with a low Kappa number and in good yield and at the same time, to reduce the amount of the chemical solution used and to reduce the load on a recovery boiler.

Abstract: The present invention has an object to obtain a cooking liquor containing polysulfide-sulfur at a high concentration by minimizing by-production of thiosulfate ions. The present invention is a method for producing polysulfides, which comprises introducing a solution containing sulfide ions into an anode compartment of an electrolytic cell comprising the anode compartment provided with a porous anode, a cathode compartment provided with a cathode, and a diaphragm partitioning the anode compartment and the cathode compartment, for electrolytic oxidation to obtain polysulfide ions, characterized in that the porous anode is disposed so that a space is provided at least partly between the porous anode and the diaphragm, and the apparent volume of the porous anode is from 60% to 99% based on the volume of the anode compartment.

Abstract: Inexpensive spindle- or needle-like calcium carbonate giving useful properties for bulk, brightness, opacity, wire abrasion resistance and yield as a paper filler is provided by taking advantage of the causticization step. In a first step, a quick lime having a calcium carbonate content of 10% by weight or less is slaked with a liquor having a pH of 5.5 to 13.5 at a concentration of 20 to 60% to prepare a milk of lime. In a second step, causticization reaction takes place at a green liquor loading rate of 0.02 to 0.5 cc (green liquor)/min/g (quick lime) at a reaction temperature of 20 to 105° C. to afford spindle- or needle-like calcium carbonate.

Abstract: A process for preparing a coated printing paper by applying a coating solution containing a pigment and an adhesive to a base paper, which comprises coating the base paper with the coating solution containing 30 to 90% by weight, based on 100% by weight of pigment components, of rice grain- or spindle-shaped precipitated calcium carbonate as a pigment component, the precipitated calcium carbonate being produced by slaking calcium oxide with a white liquor, followed by causticization with a green liquor, at a causticizing step during pulp production by the sulfate process or the soda process; whereby the coated printing paper free from uneven gloss, mottling, and trapping unevenness, and excellent in ink drying properties and operability with a blade coater is provided.

Abstract: Provided are an ink jet recording paper which is provided with a recording layer having a coverage rate of from 0.1 to 10 g/m.sup.2 on at least one side of a base paper and has a basis weight of from 50 to 100 g/m.sup.2, with the recording paper having an irreversible shrinkage factor of from -0.05% to 0.10% in the CD direction when it is put under an environment that the relative humidity thereof is raised to 95% from 35% and then lowered to 35% and further showing a shrinking rate of from 0.15% to 0.25% in the CD direction by the change in relative humidity of the environment from 75% to 60% during the process of lowering the relative humidity from 90% to 35%.

Abstract: Provided is a recording paper having a feeling of plain paper suitable for ink jet recording with water-base ink, with the recording paper having in both machine and cross directions an irreversible shrinkage factor of from -0.10% to +0.10% when it is put under an environment that the relative humidity thereof is changed from 35% to 90% and further changed to 35%.

Abstract: Provided are a cast-coated paper suitable for ink jet recording and a production method thereof, with the cast-coated paper having an irreversible shrinkage factor in the crossing direction within the range of 0.00% to 0.20% when it is put under an environment that the relative humidity thereof is changed from 35% to 95% and further changed to 35%.

Abstract: A process for producing coated paper comprises applying an aqueous coating solution onto coating base paper and drying the coating base paper, wherein a steam provided for drying or gas composed mainly of a steam is brought into direct contact with paper sheet, heated for regeneration, and then circulation for re-use, in which owing to the improvements in the heat efficiency and drying rate in the drying step, not only the productivity is improved, but also a high-quality coated paper is stably produced with a good efficiency.