Note: Descriptions are shown in the official language in which they were submitted.
28,666
MANUFACTURE OF PAPER USING COPOLYMERS OF
2-ACRYLAMIDO-2-METH~LPROPANE SULFO~IC ACID FOR INCREASING
. . . _
RATE OF DEWATERING OF HIG~ MECHANICAL/THERM~MECHANICAL
PULP FURNISHES
Background of the Invention
Field of the Invention
This invention generally relates to a process for
increasing rate of dewatering of furnish in the manufacture
of paper, and specifically to such a process wherein the
pulp constituent of the furnish contains a high content of
mechanical and/or thermomechanical pulps.
Description of the Prior Art
In the general practice of papermaking, an aqueous
pulp suspension, or "furnish", of cellulosic fibers resulting
from pulping of the feed wood stock is hydraulically and
mechanically conveyed onto a wire grid or screen which is
in motion to produce a wet web of cellulosic fibers. The
wet fiber web is dewatered on the screen, by drainage of
liquid therefrom, following which the wet web may be further
treated, dried, calendared, and subjected to additional
treatments as desired.
In general practice, a number of additives are
contained in the furnish which is passed to the wire sub-
strate (wet web forming means). These additives may include
processing aids for improving operation of the papermaking
machinery, as well as chemicals for improvement of the
properties oE the finished paper product. Suitable pro-
cessing aids may include retention aids for the retention
oE Eiller additives in and on the resultingly formed web
and reduction of loss of paper pulp fincs from the furni~n
during the dewatering step and drainage aids for improvir,g
the rate of dewatering of the furnish on the wire for~ing
means. Other additives may include formation aids, floccu-
lants, defoamers, wet and dry strength additives, pitchcontrol agents, slimicides, creping aids, and the like, as
is well known to those skilled in the art.
Functional additives may include fillers as men-
tioned, sizing aids, strenghtening additives and the like.
The fillers may include optical brighteners, opacifiers,
and pigments. Sizing agents are employed to provide the
paper product with resistance to wetting by liquids,such as
ink,,water and the like, and rosin or waxes are typically
employed for such purpose.
Based on considerations of efficiency and ease of
processing, it is desirable to add drainage aids to the
furnish prior to the wet web formation step, to provide in-
creased capacity or processing rate in the papermaking pro-
cess in systems where dewatering or liquid drainage is the
rate-limiting step in the process.
Although it is desirable to maximize drainage
rates in the papermkaing system, the additives which here-
tofore have been employed for such purpose give rise to low
levels of activity when used in newsprint furnishes, which
generally are made under strongly acidic and high shear
conditions. These include conventional drainage aids contain-
ing as anionic substituents -COOH groups, as well as copo-
lymeric additives containing -SO3H groups.
As used herein, "newsprint furnish" means a fur-
nish for the manufacture of paper and paperboard, particu-
larly newsprint, coating raw stock grades and fine paper
grades, containing fines and fillers and made under acid
conditions, whose pulp constituent comprises at least 40%
by weight of a wood pulp selected from the group consisting
of mechanical wood pulp, thermomechanical wood pulp and
mixtures thereof.
Accordingly, there is a containing need for im-
7 ''i ~
proved dewatering additives for newsprint furnishes char-
acterized by stability and high activity
It is therefore an object of the present inven-
tion to provide a process for increasing rate of dewatering
in newsprint Eurnishes at the low pH conditions c'naracter-
istic of such furnishes.
SVMMARY OF THE INVENTION
The present invention relates to a process for
increasing rate of dewatering in the manufacture of paper
from a furnish whose pulp constituent comprises at least
40% by weight of a wood pulp selected from the group con-
sisting of mechanical wood pulp, thermomechanical ~ood
pulp, and mixtures thereof comprising:
(a) adding to said furnish prior to said dewater-
ing thereof (1) from about 0.5 to about 5 percent by weight,
based on weight of cellulosic fibers in said furnish, of an
aluminum salt, and (2) from about 0.01 to about 0.5 percent
by weight, based on weight of cellulosic fibers in said
furnish, of a water-soluble copolymer containing from about
2 to about 30 mole percent repeating units derived from 2-
acrylamido-2-methylpropanesulfonic acid, from 0 to about 25
mole percent repeating units derived from acrylic acid, and
from about 45 to about 98 mole percent repeating units
derived from acrylamide; and
(b) maintaining pH of said furnish during step
(a) and through said dewatering in the range of from about
3.5 to about 6.5.
DESCRIPTION OF THE DRAWINGS
Fig. 1 is a graph of drainage change, i.e., the
change in amount of drained liquid, in milliliters, for a
Eurnish containing various drainage additives relative to a
furnish containing no drainage additives, plotted as a
function of furnish pH, for 3% addition of aluminum sulfate
(alum) to the furnish.
Fig. 2 is a graph a drainage change, ml, as a
function of pH, for 1% alum addition.
Fig. 3 is a graph of drainage change, ml, as a
function of alum addition, at pH = 4.5.
Fig. 4 is a graph~of drainage change, ml, as a
function of pH, showing parametrically the effect of variant
levels of alum addition and of elevated temperature.
DETAILED DESCRIPTION OF THE INVENTIO~l
In connection with the present invention, it has
surprisingly and unexpectedly been discovered that the use
of a water-soluble copolymer containing from about 2 to
about 30 mole percent repeating units derived from 2-acryl-
amido-2-methylpropanesulfonic acid (hereinafter denoted as
"AMPS"), from O to about 25 mole percent repeating units
derived from acrylic acid, and from about 45 to about 98
mole percent repeating units derived from acrylamide, in
combination with addition of an aluminum salt, as for exam-
ple aluminum sulfate (alum), aluminum chloride or aluminum
nitrate, at low pH conditions on the order of from about
3.5 to about 5.5 is remarkably effective in increasing the
rate of dewatering of a furnish whose pulp constituent
comprises at least 40 percent by weight of a wood pulp
selected from the group consisting of mechanical wood pulp,
thermomechanical wood pulp, and mixtures thereof.
The process of the present invention provides
high rate and extent of drainage of newsprint furnishes,
under strongly acidic conditions, where conventional anion-
ic or cationic polymers are not effective. As indicated,
conventional drainage aids which contain carboxylic acid
groups (and those which contain sulfonic acid groups) are
ineffective under such acidic conditions and cationic high
molecular weight polymers do not produce adequate effect
conditions. Although AMPS polymers and copolymers have
been taught as drainage aids in the prior art, e.g., German
Offenlegungsschrift 2,248,752, in combination with alum at
low pH conditions for treatment of hardwood/softwood kraft
pulp furnishes, there has been no recognition that such
additives could be used in newsprint-type furnishes as
contemplated in the present invention since experience has
shown that dewatering aids that work ~ell in bieached pulp
furnishes are not effective in groundwood-containing pulps.
In view of the fact that most additives which are satisfac-
tory for enhancement of drainage in neutral or alkaline
furnish media and kraft pulps are characterized by e~treme-
ly poor performance in strongly acidic newsprint-type fur-
nishes, it is indeed unexpected that the process of the
present invention may be employed to advantage to produce
superior levels of drainage.
The AMPS copolymer employed in the present inven-
tion contains from about 2 to about 30 mole percent repeat-
ing units derived from AMPS, from 0 to about 25 mole percent
repeating units derived from acrylic acid, and from about
45 to about 98 mole percent repeating units derived from
acrylamide. As used herein, AMPS is intended broadly to
refer to 2-acrylamido-2-methylpropanesulfonic acid as well
as any suitable salts thereof.
Suit.able AMPS copolymers include those containing
for example from about 2 to about 20 mole percent repeating
units derived from AMPS and from about 80 to about 98 mole
percent repeating units derived from acrylamide As used
herein, "acrylamide" is intended to be broadly construed to
include acrylamide per se as well as acrylamide derivatives,
e.g., substituted acrylamides. Such copolymer compositions
may be used to particular advantage in furnishes where an
aluminum salt, e.g., aluminum sulfate, aluminum nitrate, or
aluminum chloride, is added to the furnish in an amount of
from about 2 to about 4 percent by weight, based on weight
of cellulosic fibers in the furnish. With such weight
percent addition of aluminum salt, the pH of the furnish is
preferably maintained during the copolymer addition and
through the dewatering of the furnish in a range of from
about 4.1 to about 6.5.
The aluminum salt is employed in the process of
the present invention as a source of polyvalent metal ions,
to enhance the effectiveness of the AMPS copolymer and the
specific dosage of the aluminum salt which is required in
any given system can readily be determined ~lithout Jndue
experimentation by simple tests such as Canadian Standard
Freeness (CSP) or Britt jar drainage determinations on t'ne
furnish which is to be treated. The preferred alumin~m
salt is aluminum sulfate (alum).
In systems where the above-described AMPS/acryla-
mide copolymer is employed with additions to the furnish of
the aluminum salt in the amount of from about 0.5 to about
2 percent by weight, based on weight of cellulosic fibers
in the furnish, is satisfactory, it is desirable to maintain
pH of the furnish during the copolymer addition and through
the dewatering in a range of from about 4.8 to about 6.5,
to achieve optimal performance of the drainage additives.
Particularly preferred in the broad practice of
the present invention are AMPS copolymers containing from
about 2 to about 30 mole percent repeating units derived
from AMPS, from about 5 to about 25 mole percent repeating
units derived from acrylic acid, and from about 45 to 93
mole percent repeating units derived from acrylamide. Such
terpolymer system, as discussed hereinaEter in greater
detail, has been found to provide particularly enhanced
drainage performance when the furnish temperature is main-
tained during the terpolymer/aluminum salt addition and
through the dewatering in a range of from about 20 to about
60C. Most preferably, enhanced performance has been found
to be particularly enhanced at elevated temperatures in the
range of from about 40 to about 60C.
The above terpolymer composition has particular
utility when the pH of the furnish is maintained during the
terpolymer/aluminum salt addition and through the dewatering
in a range of from about 4 to about 6.5.
In papermaking systems using the preferred alumi-
num salt, aluminum sulfate (alum), where the amount of alum
employed for optimum drainage enhancement by the terpolymer
is in the range of from about 2 to about 4 percent by weight,
based on weight of cellulosic Eibers in the furnish, the pH
of the furnish is desirably maintained through the terpoly-
A4~
mer/alum addition and dewatering steps in the range of from
about 4.5 to about 6.3. When lower amounts of alum addition
are most effective, e.g., in a range of from about 0.5 to
about 2 percent by weight addition of alum, based on weight
5 of cellulosic fibers in the furnish, furnish pH is desirably
maintained during the terpolymer/alum addition and through
the dewatering steps in a range of from about 4.5 to about
5.6. These relationships may vary somewhat for different
furnishes, temperature conditions and the presence or absen-
ce of recycling in the papermaking system. In practice,
the optimum pH conditions can be accurately determined by
actual mill trials without undue experimentation.
As indicated, the process of the present invention
has particular ut;lity in application to newsprint-type
furnishes, whose pulp constituent is mechanical wood pulp
and/or thermomechanical wood pulp. Especial utility is
realized in application of the process of the invention to
stone grou~dwood mechanical pulps.
Preferably, the AMPS copolymer or terpolymer has
a molecular weight of from about two million to about twen-
ty million. Particularly preferred copolymers may for
example have a Standard Brookfield viscosity7 measured in a
0.20 percent solution at 25C. in 0.33 M NaCl with a number
one spindle rotating at 60 rpm, of Z-10 centipoises.
Although the present invention in preferred prac-
tice employs alum as a source of polyvalent metal cations
in the treatment of the furnish with AMPS-containing copoly-
mers, it is possible to employ other sources of cationic
metal (aluminum) sols having capability to bond with the
sulfonic acid groups or carboxylic acid groups as an alter-
native to the alum constituent. Other aluminum salts
having potential utility in combination with the AMPS co-
polymer at low pH conditions include aluminum chloride and
aluminum nitrate.
As indicated, heating of the furnish medium, to
maintain same at elevated temperature through the AMPS
copolymer/alum addition and dewatering, further improves
- ~ -
the dewaterability of the furnish7 presumably becau~e ~r~
of the necessary cationic alumina complex forms through
olation of aluminum ~ydroxide groups to an Al~-0-Al+ type
configuration, which forms at lower pH and is favored by
higher stock temperatures.
In the manufacture of newsprint it is of utmost
importance to improve drainage or water removal and to mini-
mize pitch deposition problems. Both problems can be alle-
viated to a great extent by using an appropriate drainage
aid which flocculates the groundwood fines as well as
retaining the pitch particles on fibers under the strongly
acidic conditions characteristic of newsprint furnishes.
Typically, a newsprint furnish will contain approx-
imately 25% of long fiber chemical pulp, such as bleached
sulfite or bleached kraft and about 75% by weight of high
yield mechanical pulps, such as stone groundwood (GW) or
a mixture of stone groundwood and thermomechanical (TMP)
pulp. Upon forming a sheet (wet-web) on a high spedd com-
mercial papermaking machine, much of the fine fibers, con-
sisting primarily of the fine fraction of the GW or TMPpulp components, passes through the paper machine wire and
characteristically the first pass retention in such systems
is low, on the order of about 50-60%. Accordingly, such
fines are returned back to the wet-web forming portion of
the process system, by recycle of the tray water. By such
expedient, the majority of the fines in the initial furnish
is finally retained in the sheet after multiple recycles.
High speed paper machines in general are very sen-
sitive to any changes in drainage rate and it is most essen-
tial to produce flocculation of fines and pitch particles onlong fibers since such flocculation minimizes pitch deposi-
tion problems and enhances the rate of water removal. Drain-
age aids that perform adequately in fine paper grades gen-
erally do not produce perceptible beneficial results in
newsprint-type furnishes Such inefficiency may be due to
the considerable surface area oÇ the high yield pulps (due
to the fines content thereof) and the substantially reduced
(inhibited) bonding capacity of the polymeric additive~ on
the lignin-rich fiber surfaces of mechanical pulps.
Another factor which precludes the achievement o~
good drainage and high fines retention in ne~sprint-type
furnishes is the high hydrodynamic shear of a high speed
papermaking machine such as conventionally employed for
production of newsprint.
In summary, it has not been possible to translate
the performance characteristics of polymeric drainage/re-
tention aid additives in fine paper furnishes (see the
aforementioned German Offenlegungsschrift 2,248,752, dis-
cussed hereinabove) to furnishes containing high percentages
of high yield pulps. Accordingly, the present invention
representa a substantial advance in the art, in the provi-
sion of a furnish treatment (furnish additive) providing
a substantial, surprising and wholly unexpected enhancement
in the rate of dewatering of furnishes containing signifi-
cant content of mechanical wood pulp and/or thermomechanical
wood pulp.
The following specific examples illustrate specific
aspects of the present invention. These examples are set
forth by way of illustration only and are not to be construed
as limiting on the scope of the present invention except
as set forth in the appended claims. In all examples set
forth hereinafter, parts and percentages are by weight
unless otherwise specified.
E~AMPI.E I
A laboratory drainage test procedure was developed,
for use in the examples which follow. It is typically very
difficult to obtain accurate measurements of drainage chan-
ges in high groundwood content pulps, due to the slow drain-
ing character of such pulps. As indicated, the composition
of typical commercial newsprint furnishes is approximately
75~/o by weight groundwood and 25~o by weight chemical long
fiber pulps. For the measurements carried out in the sub-
sequent examples, the furnish was 5()~:50~ I>y wei~ht Or each
- 10 -
fiber component, i.e., groundwood and chemical lorlg fi3er
pulp. The long fiber pulp portion of the furnish consi~ted
of equal parts of~bleached softwood and hard~ood kraft that
had been beated to about 450 CS~. The groundwood portion
of this experimental Eurnish represented a typical stone
groundwood, produced for newsprint production by Bowaters
Paper Company, Calhoun, Tennessee, at a pH of 4.7 and con-
taining about 1.0 percent by weight of alum, based on the
weight of fibers, the alum being added during the ground-
wood production to reduce pitch deposition in the subsequentpapermaking operation.
In each of the tests described hereinafter, the
50:50 percent by weight mixture of the chemical long fiber
pulp and groundwood pulp was diluted to 0.5 percent fiber
consistency and treated with addition alum, to carry out
the process of the present invention, with the pH of such
furnish being adjusted by addition of dilute sodium hydrox-
ide to the furnish.
To the furnish stock prepared as described above
was added a 0.1% solution of the specific polymer or co-
polymer drainage additive at a dosage level of 0.025% actual
polymer based on total fiber weight. This furnish then
was mixed by transferring same from one container to ano-
ther for six times. A 500 milliliter (ml) aliquot of the
treated furnish then was transferred into a drainage tube,
equipped with paper machine wire at the bottom end. The
furnish was allowed to drain for fifteen seconds and the
filtrate co]lected during such period of time was quanti-
tatively measured. ~ large increase in the amount of
filtrate during a given run relative to the control fur-
nish containing no drainage aid is indicative of signi-
ficantly improved water release or drainage by the forming
web.
In each experiment in the examples to follow,
a blank test run was made wherein the furnish contained
no additives, other than alum. An increase or a decrease
in the amount of collected filtrate, as compared to the
~ 3.
blank, is indicative of an increase or a decrea~e, re~pec-
tively, in the rate oE drainage of the furnish.
In the evaluations of the process of the present
invention for newsprint manufacture, a typical cationic and
a typical anionic polyacrylamide retention/drainage aid ~as
included in separate drainage tes~ runs for compari~on.
These conventional cationic and anionic polyacrylamide ad-
ditives had molecular weights in the range of 4-15 million.
EXAMPLE II
Figure I is a graph of draingae change, i.e., the
change in amount of drained liquid, in milliliters (ml), for
a furnish containing various drainage additives relative to
a furnish containing no additives (blank), as a function of
furnish pH, for 3% addition of alum to the furnish. In
Figure I, curve A is the drainage curve for the above-des-
cribed furnish, containing as the drainage aid a copolymercontaining 15% by weight AMPS and 85% by weight acrylamide
(AM~. Curve B is the drainge curve for a furnish contain-
ing 5% by weight AMPS, 10% by weight acrylic acid (AA) and
85% by weight AM. Curve C represents the drainage perform~
ance of a furnish containing the aforementioned convention-
al anionic polyacrylamide drainage/retention agent, and
Curve D is the performance curve for a furnish containing
the conventional cationic polyacrylamide drainage/retention
agent previously described.
As is seen from ~igure I that changes in pH dra-
matically effect the performance of all the furnish compo-
sitions tested, particularly the highly anionic A~PS co-
polymers (Curves A and B) and the anionic polyacrylamide
furnish (Curve C). The 15/85 AMPS/AM copolymer (Curve A)
produces the best drainage in the pH range oE 4.3 to 5.7
of all furnishes tested, while the anionic (carboxyl
group-containing) polyacrylamide is relatively unaEEected
by change of pH in this range. The cationic polyacrylamide
(Curve D) has a moderate effect in this pH range. Such pH
range and alum dosage (3% by weight) generally is repre-
- 12 -
sentative of process conditions in numerous ner"sprin~ mills
With both the AMPS copolymer of Curve A and the A~PS ter-
polymer of Curve B, the alum added to the finish should be
partially neutralized, i.e., in the form oE a polymer of
cationic alumina. Since excessive Elocculation may be un-
desirable in a given application, the best composition, as
between a copolymer of the type represented by Curve A and
a terpolymer of the type represented by Curve B may be de-
termined by actual mill trial, as indicated hereinabove.
Nonetheless, as clearly shown by the graph, either type
of AMPS-containing polymer is more effective than the cat-
ionic polyacrylamide (Curve D) heretofore used as a conven-
tional drainage/retention aid.
The anionic polyacrylamide of Curve C becomes
highly active only at high pH where the polymer is more
structurall~ extended. High pH conditions, however, are
not attractive in newsprint manufacture because of pitch
deposition problems associated therewith. On the other
hand, if the pH is reduced to extremely low levels, on the
order of less than 4.0, the AMPS-containing polymers become
significantly less effective, presumably due to the absence
of adequate amounts of cationic polymeric alumina which
probably provides activated bonding sites for such polymers.
EXAMPLE III
Figure II is a graph of drainage change, ml, as
a function of pH, for one percent by weight alum addition
to the furnish. The various curves correspond to the same
furnish compositions and drainage aids as the corresponding-
ly lettered curves of Figure I.
As seen from the graph, the AM~S-containing co-
polymers become highly effective when the pH of the furnish
is increased to a point (approximately 5-5.5) where as suf-
ficient amount of cationic polymeric alumina is for~ed.
The observed shift in optimum pH, as comapred to the results
in Example II is probably due to the lower alum dosage
level in this instance relative to Example II, which de-
creases the erfective concentration or the active cationic
alumina. The results shown in Figure II indicate that ,h~
optimum operating pH is a function of the available cation-
ic alumina (cationic polymeric Al ions) in the furnisn.
EXAMPLE IV
Figure III is a graph of drainage change, ml, as
a function of alum addition, at a pH of 4.5. Curve A re-
fers to a furnish containing as the drainage aid a 15 weight
percent/85 weight percent AMPS/AM copolymer; Curve B refers
to a furnish containing a 5:15:80 weight percent AMPS/AA/A~D
terpolymer; and Curve C refers to a furnish employing as the
drainage aid an anionic polyacrylamide containing 30 percent
free carboxyl groups.
In this experiment, the dosage of alum was varied
from 0.5% to 2.0% by weight based on the weight of fibers
present in the furnish and pH was controlled at ~.5. The
results obtained are cons-istent with the results shown in
Example III in demonstrating at low alum levels (e.g., 0.5
1.0% by weight) the polymer may actually retard drainage.
In this furnish system, a minimum of 1.5-2.0% by weight
appears to be essential for adequate activation of the AMPS-
-containing polymers. The carboxyl group-containing anionic
polyacrylamide is unaffected by change in the alum content
of the furnish.
EXAMPLE V
Figure IV is a graph of drainage change, ml, as
a function of pH, showing parametrically the effect of
variant levels of alum addition and of elevated temperature.
The effect of temperature on the drainage rate to determine
whether heat would affect the alum chemistry by favoring
formation of o~olated (polymeric) species of alumina at in-
creased temperature.
The parametric alum concentration and temperature
conditions are set forth on the draft. The drainage aid
employed in all instances was a terpolymer of 5/15/~0
weight percent AMPS/AA/AM.
In each run, the furnish was adjusted to the spe-
cific temperature by warming a stainless steel beaker con-
taining the furnish in a steam bath. Once the parametric
temperature condition was realized, the furnish was treated
with alum and neutralized with an appropriate amount ot
5 sodium hydroxide and allowed to equilibrate for five min-
utes.
