Process for the manufacture of paper

Details Process for the manufacture of paper Process for the manufacture of paper

1997-01-13

1999-04-06

Chin, Peter

Paper making and fiber liberation

Processes and products

Non-fiber additive

1621811, 1621812, 1621813, 162183, D21H 1729

Patent

active

058913050

DESCRIPTION:

BRIEF SUMMARY
The subject of the invention is a new process for the manufacture of paper, the term "paper" denoting, in the following text, any plane or sheet structure based not only on cellulose fibres, the most frequently used raw material in the paper and fibreboard industry, but also based:
on synthetic fibres, such as polyamide, polyester and polyacrylic resin fibres,
on inorganic fibres, such as asbestos, ceramic and glass fibres,
on any combination of cellulose, synthetic and inorganic fibres.
The use, which is well known, of cationic starches which are introduced into the mass of fibres before the formation of the sheet has made it possible overall to increase the retention of the fibres and fillers, to improve the draining and to enhance the physical characteristics of the paper. Indeed, the preferential fixation of these starches to the anionic reaction sites of the fibres and fillers, made possible by their cationic nature or cationicity, enables the number of bonds between fibres and between fibres and fillers to be increased, resulting in a greater strength of the paper. By virtue of this greater strength of the paper, it became possible to decrease the concentration of the mass of fibres and to resort to fibres of lower quality.
However, it has been known for several years that the abovementioned advantages provided by the use of cationic starches do not always make it possible to compensate for the increasing disadvantages created by the increasing deterioration in the quality of the raw materials.
In fact, in the face of increasingly severe concerns about economic profitability, not only has the semi-chemical pulp conventionally used, for example for the manufacture of paper for corrugated fibreboard, seen its share reduced to the advantage of pulps made from recovered cellulose fibres, commonly known as RCFs, but the quality even of these RCFs is furthermore increasingly mediocre due to the increasing number of recyclings of "old papers".
To this may be added the fact that, as regards paper machines, the trend is increasingly towards the systematic closure of circuits, resulting in the process waters becoming enriched in suspended matter, both organic and inorganic. This undesirable or polluting matter contains, in particular, extremely varied physicochemical species, including those of colloidal nature, which exhibit an anionic nature and which are commonly grouped under the generic term of "anionic trash".
Their forever increasing presence in the process waters means that any cationic starch used is increasingly drawn towards neutralizing or becoming fixed to the said anionic trash and, correlatively, increasingly less available for becoming fixed to the reaction sites of the fibres, resulting in a decrease in the level of starch retained on the sheet and a decreased strength of the latter.
Generally, whatever the degree of cationicity of the starches, the closure of the circuits and the deterioration in the quality of the fibres are reflected in an inevitable fall in the effectiveness (including retention on the sheet) of the starches and in the strength of the papers, as well as in a virtually automatic increase in the purification requirements of the backwaters of the paper machines, also known as "white waters".
Starting from the principle that the effectiveness of a cationic starch had to increase as its probability of fixation to the fibres increased, recourse was had, in order to increase this probability of fixation, to combinations of the "cationic starch - polyacrylamide" type (U.S. Pat. No. 4,066,495), "cationic starch - aluminium sulphate" type or "cationic starch - basic alumina salt" type (Patent FR 2,418,297).
Recourse was also had, as described in European Patent EP 0,139,597 granted in the name of the Applicant Company, to "cationic cereal starch - cationic tuber starch" combinations, the said cationic starches advantageously having, according to the examples of the said patent, a relatively low level of fixed nitrogen on a dry basis, namely lying between 0.20 and 0.30%.
The abovemen

REFERENCES:
patent: 4066495 (1978-01-01), Voigt et al.
patent: 4332935 (1982-06-01), Fischer et al.
patent: 4613407 (1986-09-01), Hughette et al.
patent: 4902382 (1990-02-01), Sakabe et al.
patent: 4911790 (1990-03-01), Lindstrom et al.
patent: 4992536 (1991-02-01), Billmers et al.
Paper Technology Sep. 1994 vol. 35--No. 7 "Cationic Starches" pp. 18-27.

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