Paper making and fiber liberation – Processes and products – Non-fiber additive
Reexamination Certificate
2001-12-17
2004-03-23
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-fiber additive
C162S168200, C162S168300, C524S140000, C524S141000, C524S145000, C524S386000, C524S460000, C526S258000
Reexamination Certificate
active
06709551
ABSTRACT:
TECHNICAL FIELD
This invention is directed to high molecular weight water-soluble polymers derived from zwitterionic monomer units, nonionic monomer units and at least one cationic or anionic monomer unit, and to the use of the polymers in papermaking processes.
BACKGROUND OF THE INVENTION
In the manufacture of paper, an aqueous cellulosic suspension or slurry is formed into a paper sheet. The cellulosic slurry is generally diluted to a consistency (percent dry weight of solids in the slurry) of less than 1 percent, and often below 0.5 percent, ahead of the paper machine, while the finished sheet must have less than 6 weight percent water. Hence, the dewatering aspects of papermaking are extremely important to the efficiency and cost of the manufacture.
The least costly dewatering method is drainage, and thereafter more expensive methods are used, including vacuum pressing, felt blanket blotting and pressing, evaporation and the like, and any combination of such methods. Because drainage is both the first dewatering method employed and the least expensive, improvements in the efficiency of drainage will decrease the amount of water required to be removed by other methods and improve the overall efficiency of dewatering, thereby reducing the cost thereof.
Another aspect of papermaking that is extremely important to the efficiency and cost of manufacture is the retention of furnish components on and within the fiber mat being formed during papermaking. A papermaking furnish contains particles that range in size from about the 2 to 3 millimeter size of cellulosic fibers to fillers measuring only a few microns. Within this range are 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 pass through the spaces (pores) between the cellulosic fibers in the fiber mat being formed.
Typical retention aids include high molecular weight cationic or anionic synthetic polymer flocculants, composed of one or more nonionic monomers and one or more cationic or anionic monomers. The flocculant functions by binding the particles into large agglomerates. The presence of such large agglomerates in the furnish increases retention and drainage. The agglomerates are filtered out of the water onto the fiber web, where unagglomerated particles would otherwise generally pass. The presence of agglomerates allows water to pass more easily from the furnish through the pores surrounding them.
Other points in the papermaking process where material savings are important include pulp washers or thickeners. These processes filter the pulp with the purpose of displacing unwanted soluble or colloidal materials out of the pulp suspension, or thickening the pulp for a subsequent processing step. Valuable filler or cellulose fines can be lost during either thickening or washing processes. The addition of treatment additives, such as coagulants or flocculants, can be beneficial to the efficiency of these processes.
In many papermaking furnishes, particularly furnishes containing recycled fibers, there may be anionic substances that compete with the target anionic materials to be flocculated. When the target filler and fiber surfaces must compete for polymer with anionic solutes or colloids (anionic “trash”), the flocculation efficiency is dramatically decreased because of the reduction in available cationic sites within the polymer. To circumvent this problem, one has traditionally complexed the detrimental anionic substances using a cationic coagulant. When the coagulant neutralizes the anionic charge on the high surface area of the detrimental anionic substances, the flocculant then remains “free” to aggregate the remaining anionic fiber and filler surfaces, which is the desired result. However, fluctuations in charge demand of the process water owing to varying levels of the soluble detrimental anionic substances means that the coagulant dose will have to change in order to achieve the same extent of neutralization. Although eliminating the variations in flocculation performance is critical to maintaining process control and consistent operation, maintaining a constant solution charge prior to flocculant addition can be quite difficult in practice. An alternative approach to charge neutralization using coagulant addition is adding a flocculant that, by design, is resistant to changes in anionic trash levels and concentrations of charged species in solution.
One example of such a flocculant is poly(acrylamide), which is a neutral, uncharged homopolymer. Another example is uncharged polymers composed of one or more zwitterionic monomers and one or more nonionic monomers, disclosed in published International Application Number PCT/US00/17841.
SUMMARY OF THE INVENTION
We have discovered that high molecular weight, charged polymers made from one or more nonionic monomers, one or more zwitterionic monomers, and one or more cationic or anionic monomers are unexpectedly effective for flocculating aqueous suspensions with high conductivity or containing high levels of soluble or colloidal anionic components.
Accordingly, in its principal aspect, this invention is directed to a high molecular weight water-soluble charged polymer comprising from about 50 to about 99.8 mole percent one or more nonionic monomers, from about 0.1 to 9.9 mole percent of one or more cationic or anionic monomers, and from about 0.1 to about 49.9 mole percent of one or more zwitterionic monomers of formula
wherein
L
+
is a group of formula
L
−
is a group of formula
W
+
is —S
+
R
3
— or —N
+
R
2
R
3
—;
Z
+
is —N
+
R
5
R
6
R
7
;
R
1
and R
8
are independently hydrogen or methyl;
R
2
, R
3
, R
4
, R
5
, R
6
and R
7
are independently selected from hydrogen and C
1
-C
4
alkyl;
Y
1
, Y
2
, and Y
3
are independently selected from O or NR
2
;
m is 2 or 3; and
n is 1-5.
DETAILED DESCRIPTION OF THE INVENTION
“Alkyl” means a monovalent group derived from a straight or branched chain saturated hydrocarbon by the removal of a single hydrogen atom. Representative alkyl groups include methyl, ethyl, n- and iso-propyl, n-, sec-, iso- and tert-butyl, and the like. A preferred alkyl group is methyl.
“Reduced specific viscosity” (RSV) is an indication of polymer chain length and average molecular weight. The RSV is measured at a given polymer concentration and temperature and calculated as follows:
RSV
=
[
(
η
η
o
)
-
1
]
c
wherein &eegr;=viscosity of polymer solution;
&eegr;
o
=viscosity of solvent at the same temperature; and
c=concentration of polymer in solution.
As used herein, the units of concentration “c” are (grams/100 ml or g/deciliter). Therefore, the units of RSV are dl/g. The RSV is measured at 30° C. The viscosities &eegr; and &eegr;
o
are measured using a Cannon-Ubbelohde semimicro dilution viscometer, size 75. The viscometer is mounted in a perfectly vertical position in a constant temperature bath adjusted to 30±0.02° C. The error inherent in the calculation of RSV is about 2 dl/g. Similar RSVs measured for two linear polymers of identical or very similar composition is one indication that the polymers have similar molecular weights, provided that the polymer samples are treated identically and that the RSVs are measured under identical conditions.
IV stands for intrinsic viscosity, which is RSV in the limit of infinite polymer dilution (i.e. the polymer concentration is equal to zero). The IV, as used herein, is obtained from the y-intercept of the plot of RSV versus polymer concentration in the range of 0.015-0.045 wt % polymer.
“Charged polymer” means a polymer having a net positive or negative charge. The charged polymers of this invention are composed of one or more zwitterionic monomers, one or more nonionic monomers and one or more cationic or anionic monomers. The charged polymers of this invention have a RSV of greater than 5 dl/g when measured at 450 ppm in 1M NaNO
3
as described herein. Preferred cha
Begala Arthur J.
Coffey Martin J.
Govoni Steven T.
Gray Ross T.
Murray Patrick G.
Breininger Thomas M.
Chin Peter
Martin Michael B.
Ondeo Nalco Company
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