Paper making and fiber liberation – Processes and products – Non-fiber additive
Reexamination Certificate
2000-12-20
2002-09-17
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-fiber additive
C162S164600, C162S168300, C162S181600, C162S181800, C162S183000
Reexamination Certificate
active
06451169
ABSTRACT:
TECHNICAL FIELD
This invention is directed to a method for increasing retention and drainage in a papermaking furnish using structurally rigid polymeric coagulants in combination with a flocculant and a microparticle.
BACKGROUND OF THE INVENTION
In the manufacture of paper, a papermaking furnish is formed into a paper sheet. The to papermaking furnish is an aqueous slurry of cellulosic fiber having a fiber content of about 4 weight percent (percent dry weight of solids in the furnish) or less, and generally around 1.5% or less, and often below 1.0% ahead of the paper machine, while the finished sheet typically has less than 6 weight percent water. Hence the dewatering and retention aspects of papermaking are extremely important to the efficiency and cost of the manufacture.
Gravity dewatering is the preferred method of drainage because of its relatively low cost. After gravity drainage more expensive methods are used for dewatering, for instance vacuum, pressing, felt blanket blotting and pressing, evaporation and the like. In actual practice a combination of such methods is employed to dewater, or dry, the sheet to the desired water content. Since gravity drainage is both the first dewatering method employed and the least expensive, an improvement in the efficiency of this drainage process will decrease the amount of water required to be removed by other methods and hence improve the overall efficiency of dewatering and reduce the cost thereof.
Another aspect of papermaking that is extremely important to the efficiency and cost is retention of furnish components on and within the fiber mat. The papermaking furnish represents a system containing significant amounts of small particles stabilized by colloidal forces. The papermaking furnish generally contains, in addition to cellulosic fibers, particles ranging in size from about 5 to about 1000 nm consisting of, for example, cellulosic fines, mineral fillers (employed to increase opacity, brightness and other paper characteristics) and other small particles that generally, without the inclusion of one or more retention aids, would in significant portion pass through the spaces (pores) between the mat formed by the cellulosic fibers on the papermachine.
Greater retention of fines, fillers, and other components of the furnish permits, for a given grade of paper, a reduction in the cellulosic fiber content of such paper. As pulps of lower quality are employed to reduce papermaking costs, the retention aspect of papermaking becomes more important because the fines content of such lower quality pulps is generally greater. Greater retention also decreases the amount of such substances lost to the whitewater and hence reduces the amount of material costs, the cost of waste disposal and the adverse environmental effects therefrom. It is generally desirable to reduce the amount of material employed in a papermaking process for a given purpose, without diminishing the result sought. Such add-on reductions may realize both a material cost savings and handling and processing benefits.
An important method of enhancing dewatering while improving the retention of cellulosic fines, mineral fillers and other furnish components on the fiber mat employs an inorganic microparticle in combination with a coagulant and a polymeric flocculant. In such a system a coagulant is first added, followed by the flocculant and the microparticle.
The coagulant is generally a low molecular weight synthetic cationic polymer or cationic starch. The coagulant may also be an inorganic coagulant such as alum or polyaluminum chlorides. The coagulant addition can take place at one or several points within the furnish make up system, including but not limited to the thick stock, white water system, or thin stock of a machine. The coagulant generally reduces the negative surface charges present on the particles in the furnish, such as cellulosic fines and mineral fillers, and thereby accomplishes a degree of agglomeration of such particles. Further, in the presence of other detrimental anionic species, the coagulant serves to neutralize the interfering species enabling aggregation with the subsequent addition of a flocculant.
The flocculant generally is a high molecular weight synthetic polymer which bridges the particles and/or agglomerates, from one surface to another, binding the particles into larger agglomerates. The presence of such large agglomerates in the furnish, as the fiber mat of the paper sheet is being formed, increases retention. The agglomerates are filtered out of the water onto the fiber web, whereas unagglomerated particles would, to a great extent, pass through such a paper web. In such a program the order of addition of the microparticle and flocculant can be reversed successfully.
However, there is continuing need to develop improved agents for improving the retention and drainage performance of the papermaking furnish, thereby increasing the efficiency of pulp or paper manufacture.
SUMMARY OF THE INVENTION
Structurally rigid polymers have been used as substitutes for pulp in papermaking (U.S. Pat. No. 4,749,753; Japanese Patent Application 1987-29251), but not as process additives. We have discovered that adding structurally rigid polymeric coagulants to papermaking furnishes results in a substantial improvement of the retention and drainage properties of the furnishes.
Accordingly, in its principal embodiment, this invention is directed to a method of increasing retention and drainage in a papermaking furnish comprising adding to the furnish an effective amount of a structurally rigid polymeric coagulant and an effective flocculating amount of a flocculant and a microparticle.
DETAILED DESCRIPTION OF THE INVENTION
Definitions of Terms
“Structurally rigid polymers” means polymers having a structure where the rotational conformation (degrees of freedom) of the polymer are restricted compared with common flexible polymeric materials. Structural rigidity is imparted to the polymeric coagulants described herein by incorporating rigid components such as alkenyl, alkynyl, cyloalkyl, heterocyclyl, aryl and heteroaryl groups along the main chain of the polymer. The structurally rigid polymers may be composed entirely of rigid components, or the rigid components may be connected by flexible chains such as alkyl or ether groups, so long as introduction of the flexible groups does not substantially effect the overall rigidity of the polymer. Further, the structurally rigid polymers should be water-soluble or water-dispersable and have cationic charge.
“Cyclic ditertiary amine” means an aromatic or aliphatic monocyclic or multicyclic ring system of formula
where “A” and “B” denote, respectively, a monocyclic, bicyclic or fused aromatic or aliphatic ring system of from about 5 to about 10 ring atoms and R
9
and R
10
are alkyl of from one to about 4 carbon atoms. The nitrogen atoms are separated by at least one ring atom, preferably by at least two ring atoms. Where the cyclic ditertiary amine is aliphatic, the nitrogen atoms are further substituted with alkyl. Preferably, the alkyl groups are connected to form a bridged heterocylic ring. The cyclic ditertiary amine is optionally substituted with one or more substituents selected from alkyl, alkoxy and haloalkyl. Preferred cyclic ditertiary amines are 1,4-diazabicyclo[2.2.2]octane, 4,4-dipyridine, pyrazine and 1,4-dimethylpiperazine. A more preferred cyclic ditertiary amine is 1,4-diazabicyclo[2.2.2]octane.
“Acyclic ditertiary amine” means an amine of formula
where R
1
-R
4
are alkyl and L
1
is C
1
-C
6
alkylene, C
2
-C
6
alkenylene, C
2
-C
6
alkynylene, arylene, heteroarylene heterocycylene or cycloalkylene. Preferred acyclic ditertiary amines are N,N,N′,N′-tetramethyl-2-butene-1,4-diamine, N,N,N′,N′-tetramethyldiaminomethane, N,N,N′,N′-tetramethyl-2,2-diaminopropane and N,N,N′,N′-tetramethyl-1,4-diaminocyclohexane. N,N,N′,N′-Tetramethyl-1,4-diaminocyclohexane is more preferred.
“Cyclic dihalide” means an aliphatic cylcoa
Dunham Andrew J.
Ward William J.
Breininger Thomas M.
Chin Peter
Martin Michael B.
Nalco Chemical Company
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