Paper making and fiber liberation – Processes and products – Non-fiber additive
Reexamination Certificate
2000-03-15
2002-04-16
Fortuna, Jose (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-fiber additive
C162S164100, C162S158000, C162S183000, C210S728000, C210S727000, C210S725000
Reexamination Certificate
active
06372088
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of Invention
The present invention is directed towards the papermaking process, and, more particularly, to the technical field of wet-end additives to the papermaking furnish. More importantly, the present invention relates to a process for increasing the retention of fines, fillers, and pigments during the manufacture of paper in a mill water system. The invention also provides a novel retention aid system and novel aromatic resin cofactors for such system.
2. Description of Prior Art
In the papermaking process the largest amount of water in a pulp suspension is removed from the fibres, fillers and pigments by filtration. The filtrate, which is commonly called whitewater, contains many fines which may be fibre fragments, mineral fillers, or pigment particles. Poor fines retention is a serious problem because it results in the loss of valuable material to the water system, a possible overloading of the waste water treatment facilities and, in the finished paper sheet, reduced strength properties. To alleviate such problems in the manufacture of fine paper, polymeric flocculants which are called retention aids are commonly added to a suspension of fibres, fines, and fillers prior to the formation of the wet sheet by drainage over a paper machine wire.
Many of the polymers traditionally used for the retention of fillers in fine papermaking are cationic, i.e. they carry a positive charge. Unfortunately mechanical pulp furnishes have high levels of dissolved and colloidal substances, DCS, which are anionic, i.e. negatively charged. It can be anticipated that the DCS preferentially interact with the cationic polymers rendering them less cost-effective in the retention of fines and fillers. Different polymers are needed as retention aids with mechanical pulp furnishes. U.S. Pat. No. 3,141,815, of Nalco Chemical Company, issued Jul. 21, 1964 teaches that poly(ethylene oxide), PEO, can increase the fines retention in certain commercial newsprint furnishes. PEO is nonionic and thus, is less affected by DCS. Furthermore, U.S. Pat. No. 4,070,236 to Carrard and Plummer teaches that PEO is much more effective as a retention aid for mechanical pulp furnishes, upon the addition of water soluble phenolic polymers. Pelton et al., U.S. Pat. No. 4,313,790, teach that other types of polymeric resins such as lignin products derived from kraft pulping processes can also enhance the performance of PEO towards the retention of fines and fillers. The additives which, by themselves do not retain fines, but enhance the retention performance of PEO, are termed cofactors or enhancers and the combination of PEO with a cofactor forms a dual retention aid system.
The practice of mixing a cofactor, i.e. a polymeric phenolic resin, into a furnish prior to the addition of PEO has become widespread and has greatly reduced any variability in the performance of PEO based retention aids. Other benefits of such dual retention aids are that they improve the retention and the cofactors for PEO are relatively inexpensive. More recently, as more mills began to introduce significant amounts of deinked pulp as part of their furnish, the performance of the traditional dual PEO/cofactor retention aids suffered (Tay, S., Tappi J., 80(9):149-156 (1997); Stack, K. R., Dunn, L. A., and Maughan, S., Appita, 48(4): 275-283 (1995)). Other drawbacks of these retention aids are that both phenol formaldehyde resins and lignin products have poor solubility in mill whitewater. Although an evaluation of various phenol formaldehyde resins as enhancers for PEO showed that the higher the molar mass of the resin, the greater the improvement in the retention, such benefits may be lost when using a resin of very high molar mass (molecular weight) due to reduced solubility (Stack, K. R., Dunn, L. A., and Roberts, N. K., J. Wood Chem. Technol.,13(2): 283 (1993)).
It would be advantageous for papermaking to have a cofactor for PEO which can be manufactured to high molar mass while retaining good solubility in mill whitewater systems. U.S. Pat. No. 5,538,596 assigned to Allied Colloids Limited teaches that resins based on a phenol sulphone formaldehyde chemistry may possess such a combination of properties. A possible disadvantage of this combination of polymers for mechanical pulp furnishes is a poor retention of mineral fillers and higher costs for the production of the phenol sulphone formaldehyde resin. Yet another chemistry for a dual retention aid system is disclosed in U.S. Pat. No. 5,554,260, assigned on Sep. 10, 1996 to E.QU.I.P. International, which uses in addition to poly(ethylene oxide), naphthalene sulphonate salts.
U.S. Pat. No. 5,670,021 assigned to Kenura Kemi Aktiebolag teaches that phenolic resins become activated as enhancers for PEO when mixed with soluble alkali metal silicates. However, the introduction of silicates into mill whitewater could lead to problems because silicates form complexes with chemical substances already in the whitewater system. Some silicate containing complexes have poor solubilities and may deposit on papermaking equipment in the form of “stickies”.
Recent trends in the manufacture of newsprint or mechanical printing grades of paper are towards a greater use of calcium carbonate fillers to increase opacity, inclusion of deinked pulp in the furnish, greater recirculation of water within a mill and furnishes based on thermomechanical pulp bleached with hydrogen peroxide. Each of these can be expected to significantly modify the chemistry of papermaking. For example, recent investigations on the effects of system closure on newsprint manufacture have found that the concentrations of ionic species build up and that the performance of many traditional retention and drainage aids deteriorate with increasing system closure (Allen, L., Polverari, M., Levesque, B., and Francis, B., in “Coating/Papermakers Conference Proceedings”, TAPPI Press, Atlanta, pp. 497-513 (1998)). The combination of high ionic strength and low acidity in a whitewater adversely affects the performance of the traditional PEO plus phenol formaldehyde retention aids because phenol formaldehyde resins precipitate from such whitewater (Stack, K., Dunn, L., and Roberts, N., Colloids and Surfaces A: Physicochemical and Engineering Aspects, 70: 23-31 (1993)).
SUMMARY OF INVENTION
In accordance with one aspect of the invention there is provided in a method of increasing the retention of pulp components and pulp additives in an aqueous papermaking furnish which comprises the pulp components and pulp additives in an aqueous vehicle in which a retention aid is added to the furnish, the improvement wherein the retention aid comprises a poly(oxyethylene) having a molecular weight of at least 10
6
and an aromatic resin cofactor for said poly(oxyethylene); said aromatic resin cofactor being derived from an aromatic resin which is insoluble or sparingly soluble in said aqueous vehicle and modified to enhance the solubility in the aqueous vehicle.
In accordance with another aspect of the invention there is provided in a method of increasing the retention of pulp components and pulp additives in an aqueous papermaking furnish which comprises the pulp components and pulp additives in an aqueous vehicle in which a retention aid is added to the furnish, the improvement wherein the retention aid comprises a poly(oxyethylene) having a molecular weight of at least 10
6
and an aromatic resin cofactor for said poly(oxyethylene); said aromatic resin cofactor containing aryloxy groups.
The methods of the invention may be exploited in a process of making paper which comprises: a) forming an aqueous papermaking suspension comprising pulp fibres, fines and papermaking additives in an aqueous vehicle; b) adding a retention aid to the suspension; c) draining the suspension through a screen to form a sheet; and d) drying the sheet; the retention aid being as set forth in the methods of the invention hereinbefore.
In accordance with another aspect of the invention there is provided a retention aid system for use in a papermaking furnis
Laivins Gunar V.
Polverari Marco
Fortuna Jose
Pulp and Paper Reserch Institute of Canada
Renault Ogilvy
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