Paper making and fiber liberation – Processes and products – Non-fiber additive
Patent
1994-01-03
1996-03-05
Chin, Peter
Paper making and fiber liberation
Processes and products
Non-fiber additive
162175, 1621811, 1621812, 1621814, 1621815, 1621816, 1621818, 162183, D21H 2110
Patent
active
054964407
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for improved dewatering and retention in the paper, where a retention agent containing anionic groups and being based on a polysaccharide or being an acrylamide-based polymer, and an alkaline solution of an aluminate are added to the stock containing lignocellulose-containing fibres and optionally fillers. The pH of the stock prior to the addition of the aluminate should be below about 7 to obtain the desired cationic aluminium hydroxide complexes in the stock. The present invention is cost effective and insensitive to the content of calcium in the white water.
BACKGROUND
In the production of paper, a stock consisting of papermaking fibres, water and normally one or more additives is brought to the headbox of the paper machine. The headbox distributes the stock evenly across the width of the wire, so that a uniform paper web can be formed by dewatering, pressing and drying. The pH of the stock is important for the possibility to produce certain paper qualities and for the choice of additives. A large number of paper mills throughout the world have changed, in the last decade, from acidic stocks to neutral or alkaline conditions. However, this change sometimes requires expensive investments for which reason several mills are still manufacturing paper under acidic conditions.
In the production of paper, improved dewatering and retention are desired. Improved dewatering (drainage) means that the speed of the paper machine can be increased and/or the energy consumption reduced in the following pressing and drying sections. Furthermore, improved retention of fines, fillers, sizing agents and other additives will reduce the amounts added and simplify the recycling of white water.
Fibres and most fillers--the major papermaking components--carry a negative surface charge by nature, i.e. they are anionic. It is previously known to improve the dewatering and retention effect by altering the net value and distribution of these charges. Commonly, starch where cationic groups have been introduced, has been added to the stock because of its strong attraction to the anionic cellulose-containing fibres. This effect has, however, been reduced in mills where the white water is hard, due to the competition for the anionic sites between the cationic starch and calcium ions. For most effective results, it has been thought that there must be a suitable balance between cationic and anionic groups in the starch. Starches, where both cationic and anionic groups are introduced are termed amphoteric and are well known in papermaking.
It is previously known to combine starch with aluminium compounds to further improve the effect. In P. H. Brouwer, Tappi Journal, 74(1), pp. 170-179 (1991) alum is combined with anionic starch to improve the dewatering as well as gloss and strength of packaging paper. In this case the pH of the pulp as well as the white water is 4.4 and the addition of alum 50 kg/ton of pulp.
THE INVENTION
The invention relates to a process for improved dewatering and retention of fines, fillers, sizing agents and other additives in the manufacture of paper, where a retention agent containing anionic groups and an aluminate are added to the stock of lignocellulose-containing fibres.
The invention thus concerns a process for the manufacture of paper on a wire by forming and dewatering a stock of lignocellulose-containing fibres, and optional fillers, whereby a retention agent containing anionic groups, where said retention agent is based on a polysaccharide or is an acrylamide-based polymer, and an alkaline solution of an aluminate are added to the stock, which stock prior to the addition of the aluminate has a pH in the range of from about 3 up to about 7.
According to the present invention it has been found that by adding an alkaline solution containing an aluminate to a stock with a pH below about 7, it is possible to get an interaction between the cationic aluminium hydroxide complexes developed in the stock and the anionic groups of the retention agent and cellulose f
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Carlson Ulf
Carre/ Bruno
Chin Peter
Eka Nobel AB
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