Paper making and fiber liberation – Processes and products – Non-fiber additive
Patent
1999-01-08
2000-10-17
Chin, Peter
Paper making and fiber liberation
Processes and products
Non-fiber additive
1621682, 1621683, 162175, 1621816, 1621818, 162183, D21H 2110
Patent
active
061325589
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for the production of paper and cardboard by draining pulps, with sheet formation and drying of the sheets, two different water-soluble cationic polymers being added in succession to the pulps and the latter then being subjected to at least one shearing stage and then being flocculated by adding bentonite, colloidal silica or clay.
2. Description of the Background
The process described at the outset is disclosed in EP-A-0 335 575. In this process, first a low molecular weight, water-soluble, cationic polymer and then a high molecular weight, water-soluble cationic polymer are added to the pulp. The low molecular weight water-soluble cationic polymers have a molar mass of less than 500,000. Suitable low molecular weight cationic polymers are, for example, polyethyleneimines, polyamines, polycyandiamide, formaldehyde condensates and polymers of diallyldimethylammonium chloride, dialkylaminoalkyl (meth)acrylates and dialkylaminoalkyl(meth)acrylamides. The suitable high molecular weight cationic polymers have molar masses of more than 500,000. These polymers are high molecular weight retention aids usually used in papermaking, such as cationic polyacrylamides. After the addition of the cationic polymers, the flocculated fiber suspension is subjected to a shearing stage, for example in a pulper, refiner, wire or screen, the hard giant flocks present in the paper stock being destroyed. Bentonite, colloidal silica or clay is then added, with the result that the destroyed flock constituents are collected by adsorption to give a soft microflock. It is only thereafter that the draining of the pulp with sheet formation on a wire and drying of the sheets are carried out.
EP-A-0 235 893 discloses a process for the production of paper and cardboard, more than 0.03% by weight, based on the dry weight of the suspension, of an essentially linear synthetic cationic polymer having a molar mass of more than 500,000 first being added to an aqueous fiber suspension, the mixture then being subjected to shearing in a shear field with formation of microflocks, from 0.03 to 0.5% by weight of bentonite then being metered and the pulp thus obtained being drained.
EP-A 0 223 223 discloses a process for the production of paper and cardboard by draining a paper stock, bentonite being added to a paper stock having a consistency of from 2.5 to 5% by weight, the consistency then being brought to 0.3-2% by weight by diluting with water, polyelectrolyte having a charge density of at least 4 meq per g of polyelectrolyte then being added, then being metered into the mixture, and the pulp thus obtained being drained after thorough mixing.
It is an object of the present invention further to increase the drainage rate and hence the rate of production in papermaking.
This object is achieved, according to the invention, by a process for the production of paper and cardboard by draining pulps, with sheet formation and drying of the sheets, two different water-soluble, cationic polymers being added in succession to the pulps and the latter then being subjected to at least one shearing stage and then being flocculated by adding bentonite, colloidal silica or clay, if first polymers containing vinylamine units and having a molar mass M.sub.w of from 5000 to 3 million and then vinylamine units, the molar masses M.sub.w of the polymers each being at least 4 million,
Unexpectedly, the use of polyethyleneimines having a molar mass M.sub.w of more than 500,000 or of polymers containing vinylamine units and having a molar mass M.sub.w of from 5000 to 3 million as cationic polymers of group a), which are initially added to the paper stock, leads to an increase in the drainage rate compared with the prior art, according to which polyethyleneimines having a molar mass of less than 500,000 are used.
According to the invention, suitable polymers of group a) are polyethyleneimines having a molar mass M.sub.w of more than 500,000, preferably more than 700,000. The poly
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patent: 5876563 (1999-03-01), Greenwood
Baumann Peter
Dirks Bernd
Dyllick-Brenzinger Rainer
Gerber Klaus-Dieter
Linhart Friedrich
BASF - Aktiengesellschaft
Chin Peter
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