Paper making and fiber liberation – Processes and products – Non-fiber additive
Patent
1994-01-03
1996-04-30
Chin, Peter
Paper making and fiber liberation
Processes and products
Non-fiber additive
1621812, 1621813, 1621815, 162183, D21H 2106
Patent
active
055121357
DESCRIPTION:
BRIEF SUMMARY
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. This is inter alia due to the possibility to use calcium carbonate as filler, which produces a highly white paper at a very competitive price.
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, 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 cationic potato starch or amphoteric starch with aluminium compounds to further improve the effect. In R. Trksak, Tappi Papermakers Conference 1990, pp. 229-237 systems of cationic potato starch or amphoteric maize starch and polyaluminium chloride PAC), alum or aluminium chloride are used to improve the drainage and retention under alkaline conditions. 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 production of paper, where an anionic retention agent having no cationic groups and an acidic solution of an aluminium compound are added to the stock of lignocellulose-containing fibres.
The invention thus concerns a process for the production of paper on a wire by forming and dewatering a stock of lignocellulose-containing fibres, and optional fillers, whereby an anionic retention agent based on starches, cellulose derivatives or guar gums having no cationic groups and an acidic solution of an aluminium compound are added to the stock, which stock prior to the addition of the aluminium compound has a pH in the range of from about 6 up to about 11.
According to the present invention it has been found that by adding an acidic solution containing an aluminium compound to a stock with a pH of at least about 6, 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 fibres.
As stated above, conventionally starch where cationic groups have been introduced is used in papermaking. It is advantageous, however, to use anionic starch since it is much easier and less expensive to introduce anionic groups, such as phosphate groups, than it is to introduce cati
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R. M. Trksak, "Aluminum compounds as cationic donors in alkaline papermaking systems", 1990 Papermakers Conference, pp. 229-237.
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Carlson Ulf
Carre Bruno
Chin Peter
Eka Nobel AB
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