Paper making and fiber liberation – Processes and products – Non-fiber additive
Patent
1997-05-27
1999-05-11
Chin, Peter
Paper making and fiber liberation
Processes and products
Non-fiber additive
1621681, 1621682, 1621683, 1621818, 162183, D21H21/10
Patent
active
059024550
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a process for the manufacture of paper, board and the like; it also relates to a retaining agent for the application of this process.
The invention relates more particularly to a specific combination of retaining agents and of operating conditions promoting the retention of the fines and of the fillers when the sheet is being formed.
The process according to the invention and the compositions according to the invention additionally improve some properties of the paper itself, like the opacity in particular.
DISCUSSION OF PRIOR ART
When paper, board or the like is manufactured, it is well known to introduce into the cellulose pulp retaining agents whose function is to retain a maximum of fines and of fillers in the sheet. The beneficial effects that stem from the use of retaining agents are essentially: saving, steadier running of the machine, higher yield of fibers, fines, fillers and anionic processing products, lower acidity in the circuit, connected with a decrease in the use of aluminium sulphate and hence reduction in corrosion problems, in the moisture content on sheet, in opacity, in smoothness, in absorbency and decrease in the porosity of the paper.
There are very many publications on this subject, as well as a certain number of products and processes employed in the industry. This is therefore a technical field which has formed the subject matter of numerous investigations, some parameters of which are well known but other parameters of which are less well known.
The invention relates to a system whose general concept is known, namely the addition to the cellulose paper pulp (containing the usual additives and prepared upstream in traditional manner) of a cationic polymer of high molecular weight, as first retaining agent, sometimes known in the literature as "main retaining agent", and then of a second retaining agent, sometimes known in the literature as "secondary retaining agent", which is microparticulate and essentially inorganic and anionic. Shearing of the pulp which is flocculated or being flocculated is next performed between the two points of addition, and the pulp thus treated is next brought to the flow box of the papermaking machine.
EP-A-0 348 366 thus describes an addition of an aluminum compound to the pulp, followed by a cationic polymer, followed by a polysilicic acid, itself characterized by a very high specific surface of at least 1050 m.sup.2 /g. However, this last product is relatively costly.
EP-A-0 235 893 describes the use as first retaining agent of a cationic polymer of high molecular weight (a million and more), and then a shearing stage, then the addition of bentonite as second agent, a well-known disadvantage of which is that it presents environmental problems and, subsidiarily, that it risks affecting the brightness of the paper. According to this document the polymer is essentially linear. Microflocs are obtained after the shearing stage, and their cationicity is sufficient to interact with the bentonite. A considerable disadvantage of this technique is that it is tricky to apply. It involves, in fact, the use of an extremely fine powder which is difficult to disperse. Furthermore, the ability of bentonite to swell entails a serious risk of loss of control of the rise in viscosity, even with a risk of gelling. Example 4 of this document illustrates, furthermore, the extent to which the polymer/bentonite proportioning ratio is sensitive.
EP-B-0 373 306 recommends the addition of a cationic polymer of high molecular weight and of an association or combination of a microparticulate colloidal siliceous material (like bentonite or the like) with a water-soluble organic polymer of molecular weight lower than 100 000 and whose characteristic is based on a high anionic or cationic charge density of 4 to 24 meq/g. This polymer is used for the purpose of modifying the ionicity of the bentonite. The examples in this document are as a general rule with 10% by weight of polymer of low molecular weight in relation to the bentonite, s
REFERENCES:
patent: 4913775 (1990-04-01), Langley et al.
patent: 5068276 (1991-11-01), Suitch et al.
"Ash in Wood, Pulp, Paper and Paperboard: Combustion at 525.degree. C., " Tappi, pp. 1-3, 1993.
Hund Rene
Jehn-Rendu Christian
Chin Peter
S.N.F.
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