According to the invention, in producing coloured cardboard, carbon dioxide is injected and dissolved in a mixture of pulp and at least a sulphur dye, while the mixture is pumped with a delivery pressure higher than 200 kPa out of a first pulp reservoir (11) towards a second pulp reservoir (12), and in such manner that the mixture is acidified by the carbon dioxide to become an acidified coloured pulp mixture (14) with a pH-value between 6.5 and 7.0. The acidified coloured pulp is injected under high pressure out of a pulp duct structure (7) into the second pulp reservoir (12) at a distance of at least 2 meter below a level (15) of the acidified coloured pulp mixture (14) in the second pulp reservoir (12). Accordingly, the invention provides a high-quality colouring of cardboard, wherein environmental problems are prevented.

An on-line control and reaction process for pH adjustment and a control device for automatically adjusting pH value are provided. The process includes mixing a first enhancer and a second enhancer, optionally after diluting the first enhancer and/or the second enhancer with water, to form a mixture, setting a base pH value (δ1) and a target pH value (δ2), and adding pH adjuster into the mixture via a pH control unit and mixing to obtain a product with the target pH value. The pH control unit adjusts the adding of the pH adjuster by measuring or inputting certain parameters.

A method for producing a modified lignocellulosic pulp having improved wet-strength properties and a modified lignocellulosic pulp obtainable by the method.

An accumulating unit that discharges fibers by rotating a drum unit in which a plurality of openings are formed, a second web forming unit that forms a second web by operating a mesh belt, a sheet forming unit that forms a sheet from the second web, and a control unit that performs a start control for operating the accumulating unit and the second web forming unit from the stop state are included. In a case where the start control is performed from a state where the fibers are present in the drum unit, the control unit adjusts a thickness of the second web by controlling at least one of a timing at which rotation of the drum unit is initiated, a rotational speed of the drum unit, a timing at which movement of the mesh belt is initiated, and a movement speed of the mesh belt.

An accumulating unit that discharges fibers by rotating a drum unit in which a plurality of openings are formed, a second web forming unit that forms a second web by operating a mesh belt, a sheet forming unit that forms a sheet from the second web, and a control unit that performs a start control for operating the accumulating unit and the second web forming unit from the stop state are included. In a case where the start control is performed from a state where the fibers are present in the drum unit, the control unit adjusts a thickness of the second web by controlling at least one of a timing at which rotation of the drum unit is initiated, a rotational speed of the drum unit, a timing at which movement of the mesh belt is initiated, and a movement speed of the mesh belt.

A method for producing a modified lignocellulosic pulp having improved wet-strength properties and a modified lignocellulosic pulp obtainable by the method.

This invention relates to a method for manufacturing a sheet of paper or cardboard, comprising the addition of a water-soluble polymer P with a weight-average molecular weight greater than 750,000 Dalton to a fibrous suspension. This method comprises the following successive steps: preparing an aqueous solution A containing at least one water-soluble polymer P at a concentration C of between 0.1 and 0.5% by weight, said polymer P having a factor F(C) strictly greater than 4, with F.sub.(C)=Δ600/C, Δ600 being the slope to reach 90% of the viscosity developed by aqueous solution A at 600 seconds at 25° C., obtained from the viscosity curve of aqueous solution A as a function of time, at the given concentration C, at 25° C., adding aqueous solution A to the fibrous suspension, at one or more injection points, forming a sheet of paper or cardboard.

This invention relates to a method for manufacturing a sheet of paper or cardboard, comprising the addition of a water-soluble polymer P with a weight-average molecular weight greater than 750,000 Dalton to a fibrous suspension. This method comprises the following successive steps: preparing an aqueous solution A containing at least one water-soluble polymer P at a concentration C of between 0.1 and 0.5% by weight, said polymer P having a factor F(C) strictly greater than 4, with F.sub.(C)=Δ600/C, Δ600 being the slope to reach 90% of the viscosity developed by aqueous solution A at 600 seconds at 25° C., obtained from the viscosity curve of aqueous solution A as a function of time, at the given concentration C, at 25° C., adding aqueous solution A to the fibrous suspension, at one or more injection points, forming a sheet of paper or cardboard.

Absorbent sheet is manufactured utilizing a low charge density debonder composition comprising an imidazolinium surfactant-containing constituent selected from the group consisting of: (i) cationic imidazolinium surfactants with alkylalkenylhydroxy substitution; (ii) zwitterionic imidazolinium surfactants; and (iii) an ion paired surfactant mixture including a zwitterionic imidazolinium surfactant and a cationic surfactant and, in admixture with the imidazolinium surfactant-containing constituent, (iv) a nonionic surfactant.

Absorbent sheet is manufactured utilizing a low charge density debonder composition comprising an imidazolinium surfactant-containing constituent selected from the group consisting of: (i) cationic imidazolinium surfactants with alkylalkenylhydroxy substitution; (ii) zwitterionic imidazolinium surfactants; and (iii) an ion paired surfactant mixture including a zwitterionic imidazolinium surfactant and a cationic surfactant and, in admixture with the imidazolinium surfactant-containing constituent, (iv) a nonionic surfactant.