Paper making and fiber liberation – Processes and products – Non-fiber additive
Reexamination Certificate
1999-05-21
2001-05-29
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-fiber additive
C162S158000, C162S164300, C162S164600, C162S168100, C162S168200, C162S168300, C162S181600, C162S181800, C162S175000, C162S183000
Reexamination Certificate
active
06238521
ABSTRACT:
FIELD OF THE INVENTION
The present invention is in the technical field of papermaking. More specifically, this invention is in the technical field of wet-end additives to papermaking slurries.
BACKGROUND OF THE INVENTION
Retention and drainage are important properties of a papermaking process that papermakers are always seeking to optimize.
One method of improving the retention of cellulosic fines, mineral fillers and other furnish components on the fiber mat is the use of a coagulant/flocculant system, added ahead of the paper machine. To use such a system, a papermaking slurry (or furnish) is created out of a pulp. To this slurry is added a coagulant, with said coagulant being selected from the group consisting of low molecular weight cationic synthetic polymers, starch and alum. The coagulant generally reduces the negative surface charges present on the particles in the slurry, particularly cellulosic fines and mineral fillers, and thereby accomplishes a degree of agglomeration of such particles. The next item added is a flocculant. Flocculants typically are high molecular weight anionic synthetic polymers which bridge the particles and/or agglomerates, from one surface to another, binding the particles into large agglomerates. The presence of such large agglomerates in the slurry as the fiber mat of the paper sheet is being formed increases retention.
While a flocculated agglomerate usually does not interfere with the drainage of the fiber mat to the extent that would occur if the furnish were gelled or contained an amount of gelatinous material, there is a noticeable reduction in drainage efficiency when such flocculated agglomerates are filtered by the fiber web, because the pores thereof are to a degree reduced. Hence, retention usually is increased with some degree of deleterious effect on the drainage.
Another system employed to provide an improved combination of retention and drainage (or dewatering as it is sometime known) is described in U.S. Pat. Nos. 4,753,710 and 4,913,775, the disclosures of both of these patents being incorporated herein by reference. In brief, such method first adds to the aqueous cellulosic papermaking suspension a high molecular weight linear cationic polymer before shearing the suspension, followed by the addition of bentonite after shearing. The shearing generally is provided by one or more of the cleaning, mixing and pumping stages of the papermaking process. The shearing breaks down the large flocs formed by the high molecular weight polymer into microflocs. Further agglomeration then ensues with the addition of the bentonite clay particles.
Another system uses the combination of cationic starch followed by dispersed silica to increase the amount of material retained on the web by the method of charge neutralization and adsorption of smaller agglomerates. This system is described in U.S. Pat. No. 4,388,150, inventors Sunden et al., issued Jun. 14, 1983.
In another system, a high molecular weight cationic polymer is added to the slurry before shearing. Then an organic microparticle is added to the slurry after the introduction of shear. The organic microparticle is a medium molecular weight anionic polymer such as the copolymers of acrylic acid described in U.S. Pat. No. 5,098,520, the disclosure of which is incorporated herein by reference. Or the organic microparticle can be a medium molecular weight anionic sulfonated polymers such as those described in U.S. Pat. No. 5,185,062, the disclosure of which is herein incorporated by reference.
There continues to be a need to identify new additive or additives that when added in specific combinations result in improvement in retention and drainage in a papermaking process.
SUMMARY OF THE INVENTION
The claimed invention is:
in a papermaking process consisting essentially of:
forming an aqueous cellulosic papermaking slurry;
adding to the slurry certain additives, with said certain additives selected from the group including: coagulants; sizing agents; and mineral fillers;
draining the slurry to form a sheet; and
drying the sheet to form a paper sheet;
the improvement comprising adding to the slurry, prior to it being drained; an effective amount of a cationic dispersion polymer; which cationic dispersion polymer is a copolymer comprising about 30 mole % diallyldimethylammonium chloride (DADMAC) and about 70 mole % acrylamide (AcAm); and
adding to the slurry, either before or after said cationic dispersion polymer is added and the slurry is drained,
a microparticle selected from the group consisting of
a) copolymers of acrylic acid and acrylamide;
b) bentonite; and
c) dispersed silica;
with the proviso that said coagulant cannot be a cationic dispersion copolymer comprising about 30 mole % diallyldimethylammonium chloride (DADMAC) and about 70 mole % acrylamide (AcAm).
REFERENCES:
patent: 4388150 (1983-06-01), Sunden et al.
patent: 4753710 (1988-06-01), Langley et al.
patent: 4913775 (1990-04-01), Langley et al.
patent: 4929655 (1990-05-01), Takeda et al.
patent: 5006590 (1991-04-01), Takeda et al.
patent: 5098520 (1992-03-01), Begala
patent: 5178730 (1993-01-01), Bixler et al.
patent: 5185062 (1993-02-01), Begala
patent: 2180404 (1997-01-01), None
patent: 202780 (1986-11-01), None
patent: 277728 (1988-08-01), None
patent: 0805234 (1997-11-01), None
patent: 57-77399 (1982-05-01), None
patent: 59-137600 (1984-08-01), None
patent: 61-6397 (1986-01-01), None
patent: WO 97/18351 (1997-05-01), None
Maltesh Chidambaram
Nagarajan Ramasubramanyam
Shing Jane B. Wong
Breininger Thomas M.
Brumm Margaret M.
Chin Peter
Nalco Chemical Company
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