A pulp furnish containing predominantly wood-containing fibers (mechanical) and natural calcium carbonate as a filler is formed into a paper in a paper forming section of a paper machine at a neutral pH in the range of 6.7 to 7.5. Bentonite plus a suitable polymer such as a polyacrylamide produces a pulp stock that has exceptionally high drainage characteristics particularly when used with chalk as the filler. The pH of the stock in the headbox is maintained at the desired level of pH 6.7-7.3 by monitoring the pH in the headbox and adjusting the flow of pH reducing and buffering agent, preferably phosphoric acid, into the pulp prior to the headbox to obtain the desired pH in the stock.
The present invention relates to an acid-stabilized calcium carbonate slurry having a pH of less than 7, preferably between about 6 and about 7, containing water, calcium carbonate, preferably precipitated calcium carbonate, and an acid-stabilizer of a water soluble calcium salt, a weak acid, a chelating agent, a weak acid capable of chelating calcium ion, or a mixture thereof. The acid-stabilizer is present in an amount sufficient to provide an aqueous calcium carbonate slurry having an increased calcium ion concentration and an acidic pH. In a typical acid-stabilized calcium carbonate slurry of the invention, the acid-stabilizer is present in an amount sufficient to provide a calcium ion concentration of about 1 millimolar to about 5 molar, preferably from about 1 to about 120 millimolar. The invention also relates to a method of making the acid-stabilized calcium carbonate slurry of the invention, to a method of forming a filled paper, that includes the step of adding the acid-stabilized calcium carbonate slurry of the invention to a papermaking pulp in a process for making acid paper, and to a filled paper produced according to the method of the invention.
The invention relates to papermaking processes wherein calcium carbonate is included in a pulp suspension. The dissolution of the calcium carbonate in the papermaking system is prevented or substantially retarded by the introduction of carbon dioxide to said pulp suspension in connection with subjecting said calcium carbonate in said papermaking system to pH conditions of about 8 or lower. The invention also provides processes for the production of paper or board in papermaking systems wherein solid calcium carbonate is present as a filler and/or pigment.
A papermaking process wherein calcium carbonate is included in a pulp suspension. The dissolution of the calcium carbonate in the papermaking system is substantially retarded by the introduction of carbon dioxide to said pulp suspension. The invention also provides processes for the production of paper or board in papermaking systems wherein solid calcium carbonate is present as a filler and/or pigment.
A method for the manufacture of paper products includes the feeding of a carbon dioxide stream to a product flow which includes a material containing an aluminum compound. The material is preferably wastepaper containing aluminum sulfate or papermaker's alum. The material may also be a product flow of wastepaper (containing aluminum sulfate) to which a supply of virgin pulp has been added. The carbon dioxide addition to the product flow reduces the pH of the product flow to a level of acidity which allows a dissolution of the aluminum compound and incorporation thereof throughout the product flow.
A wet part of a paper making machine includes a distributor to which a main stream of a stock suspension is fed and which has a number of connections. The connections are connected by means of split stream lines to a machine-wide flow box which has a machine-wide slice nozzle (headbox). The split stream lines are connected (directly or indirectly) to the flow box. The slice nozzle is connected to at least one continuous web-forming screen. At least one collection trough is connected to the screen, as well as, optionally, to a backwater tank to accept the backwater trapped by the collection trough. Dilution water lines are provided to introduce backwater into the split stream lines to adjust the stock density of the split streams. The dilution water lines are connected directly to the collection trough.
