Paper making and fiber liberation – Processes and products – Plural fiber containing
Utility Patent
1998-08-19
2001-01-02
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Plural fiber containing
C162S150000, C162S158000, C162S164100, C162S164300, C162S164600, C162S168200, C162S168300, C162S175000, C162S181200, C162S181400, C162S181500, C162S183000
Utility Patent
active
06168686
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the production of paper or paperboard, and more particularly, to a method for improving the retention and/or drainage properties of mechanical pulp-based furnish in the formation of newsprint, directory stock, ground wood specialty stock.
BACKGROUND OF THE INVENTION
Paper production involves the formation and dewatering of a web of cellulose fibers and optional fillers, and is generally performed in the presence of additives which can improve the end product or the papermaking operation. Many grades of paper include substantial levels of inorganic fillers such as kaolinite, calcium carbonate and titanium dioxide. For example, good quality paper, often referred to as fine paper, may be made from high grade, bleached chemical pulp, and may contain 5 to 35%, by weight of dry paper, of inorganic fillers. In the production of such paper, it is common to use retention aids and drainage aids. Such retention and drainage aids have proven to be cost effective in the production of filled or fine paper for some time.
There is, however, a very large scale production of paper that is substantially unfilled. For instance, the production of newsprint. The unfilled paper is substantially free of filler, and often there is no deliberate addition of filler to the pulp from which the paper is made. Over the past few years, the use of retention aids in the production of newsprint and other mechanical pulp containing grades of paper has become increasingly common. The most common treatments are cationic polyacrylamides, poly(ethylene oxides), and poly(ethyleneimines).
U.S. Pat. No. 4,305,781 discloses a process for enhancing drainage and retention of substantially unfilled paper which comprises including in the suspension a combination of a water soluble, high molecular weight substantially nonionic polymer and a bentonite-type clay.
The effectiveness of a nonionic poly(ethyleneoxide) of high molecular weight for fines retention in newsprint stock was disclosed in “Application of Polymeric Flocculant in Newsprint Stock Systems for Fines Retention Improvement”, C. H. Tay, Tappi, Volume 63, No. 6, June 1980. This article also notes that anionic retention aids tend to impair stock drainage characteristics.
In “Retention Aids for Quality Improvements in Newsprint”, D. S. Honig, 1988 Paper Makers Conference at 219, it is stated that based upon a large number of research articles on retention aids for newsprint, the overall conclusions have been that conventional polyacrylamides (as single or multiple component systems) are ineffective or uneconomical. This paper goes on to discuss the use of cationic polyacrylamides as well as a dual component low molecular weight cationic polymer/low pKa anionic polyacrylamide treatment as a retention aid in newsprint production. The author concludes that cationic polyacrylamides are less complex, equal or more effective, and in particular, effective at lower dose level than the alternative treatment.
In treatments shown to enhance drainage and fines retention which employ anionic polyacrylamides, a silicate (such as colloidal silica or polysilicate microgel) or bentonite is a required component. See for example, U.S. Pat. Nos. 4,643,801; 5,584,966 and 5,595,630.
SUMMARY OF THE INVENTION
The present inventors have discovered a novel drainage and retention aid treatment which is effective in newsprint-type furnish without a silicalbentonite-type particle. The novel drainage and retention aid treatment of the present invention comprises the sequential or concurrent addition of (i) a cationic or amphoteric starch and (ii) a cationic polyelectrolyte followed by the addition of a high molecular weight anionic polyacrylamide.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a process for the manufacture of paper which provides rapid water drainage and good retention of fines during the forming and dewatering of a paper furnish. The present invention relates to improved water drainage and retention of fines in the formation of paper from a mechanical pulp containing furnish which is substantially unfilled. This refers to papers such as newsprint, directory, and ground wood specialty. Unfilled paper is substantially free of filler, generally containing less than 5%, by weight of dry paper, of filler, and often there is no deliberate addition of filler to the pulp from which the paper or board is made. The paper often contains recycled fiber as a furnish component which may incorporate small (<5%) levels of fillers in the finished sheet.
The present invention relates to an additive combination for unfilled paper processing which enhances water drainage and retention of fines. The additive combination of the present invention is substantially free of microparticle treatment materials such as silica, polysilicate, polysilicate microgels, and clays such as bentonite. The term “substantially free” as used herein means that while a trace amount of such materials may be present, they are not intentionally added to and are not necessary to achieve the efficacy of the treatment combination of the present invention.
The treatment combination of the present invention comprises: an anionic, high molecular weight polyacrylamide; a cationic or amphoteric starch and an organic or inorganic cationic polyelectrolyte. The treatment combination of the present invention is added to an unfilled pulp furnish in a dosage (on an active product basis) of from about 2.5 to 20 lbs. per ton of starch, about 0.25 to 1 lbs. per ton of cationic organic polyelectrolyte, or about 5 lbs. per ton inorganic cationic polyelectrolyte, and a 0.25 to 0.75 lbs. per ton of high molecular weight anionic polyacrylamide. In use of the treatment combination, the order of addition between the starch and the cationic polyelectrolyte is interchangeable, although it is preferred to add the starch first. Both the starch and the cationic polyelectrolyte must be added prior to addition of the anionic polyacrylamide.
The starch component of the treatment combination of the present invention may be dent corn, waxy maize, or potato-based and either cationic or amphoteric in nature. The degree of quaternary ammonium substitution on the starch is preferably between about 0.1 and 0.4%, with about 0.3 to 0.4% most preferred.
The cationic polyelectrolyte component of the treatment combination of the present invention may be organic in nature, such as an epichlorohydrin-dimethylamine (EPI-DMA) condensate polymer, an EPI-DMA-ethylenediamine (EDA) condensation polymer, diallyidimethylammonium chloride (poly DADMAC) a polyethylene-imine, or a polyamidoamine-based material. It may also be inorganic in nature such alum, polyaluminum chloride or other aluminum-based compounds.
The high molecular weight, anionic acrylamide of the present invention is preferably an essentially linear acrylamide/sodium acrylate copolymer. Other anionic acrylamide copolymers such as 2-acrylamido-2-methyl propane sulfonic acid (AMPS, a registered trademark of Lubrizol) would also be effective. By high molecular weight we referred to molecular weights preferably above 1,000,000 and most preferably above about 10,000,000. The mole percent anionic charge of the anionic acrylamide component can range from about 20 to 70% with a 30 mole percent negative charge material found to be particularly effective.
The present invention will now be further described with reference to a number of specific examples, which are to be regarded solely as illustrative and not as restricting the scope of the present invention.
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patent: 5431
Hobirk Richard A.
Sutman Frank J.
BetzDearborn Inc.
Chin Peter
Woodcock Washburn Kurtz Mackiewicz & Norris LLP
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