Patent ID: 7198696

Claim:
A method for manufacturing paper with a constant filler content, comprising a) passing a thick pulp suspension containing water, pulp fibres, optionally filler derived from slurrying paper broke, and optionally diverse paper chemicals towards a head box in a paper machine; b) adding further water to the thick pulp suspension on its way to the head box, so as to form a stock; c) adding at least one filler to at least one of the thick pulp suspension, the stock and said further water; d) adding at least one retention agent to at least one of the thick pulp suspension, the stock and said further water; e) spreading finally prepared stock on a wet apparatus via the head box, so as to form a wet paper web, and collecting resultant drainage water, designated white water, beneath the wet apparatus and passing said white water back in the paper production process for delivery to fresh thick pulp suspension divided and included in two liquid-based flows of material designated the short circulation and the long circulation respectively; f) causing the wet paper web to leave the wet apparatus and then optionally pressing and drying said web in at least one stage and subjecting said web optionally to aftertreatment and/or collecting said web on rolls or converting the web into sheets and g) measuring the filler content of the paper; h) measuring the concentration of filler in the white water or in the stock; in a position in the short circulation or in direct connection therewith, characterised by adding the filler in an amount such that the system will be buffered with filler to a predetermined concentration level which is the control value, said level being followed via measurement (h); basing the continuing addition of filler exclusively on the measured concentration level of filler in the white water or in the stock, such that when the measured level is lower than the control value, the addition of filler is increased, and such that when said measured level is higher than the control value the addition of filler is reduced, so that the white water system or the buffer system will always have available sufficient filler to enable the paper web to adsorb the intended amount of filler; and basing the continuing addition of retention agent exclusively on the newly measured amount of filler in the paper (g), so that when the measured amount of filler in the paper is lower than the level that shall be held constant, the addition of retention agent is increased, and so that when the measured amount of filler in the paper is higher than the level that shall be kept constant, the addition of retention agent is reduced, therewith resulting in rapid correction of the filler content of the paper back to the level that shall be held constant.