Note: Descriptions are shown in the official language in which they were submitted.
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~ol~r~l of tlle Tnvention
1. Field of the Tnv~ntion
The present invention re:lates to a p~rm~king method, and, more particularly, to
a method of paper board m~nnf~-~.tllre.
S
2.1Description of the Prior ~rt
European Patent Specifi.cation publication number 0 041 056 teaches a method of
paper m~mlf~c~lre in which inorgarlic filler, colloidal silica and cationic starch are added
to an aqueous suspension of ce]lulose fibers U~SLIealll of the inlet to the pap~rm~king
m~r.hine for the purpose of enh~neing paper strength and improving filler retention on the
wire. Swedish Patent Application 850016206 teaches a method of paper manufacture in
which an aqueous suspension of an inorganic filler is first mixed with pulp fines,
whereafter a retention agent is added (coflocculation) and the flocs thus formed are
introduced into the pulp suspen,sion at a location upstrearn of the paper m~chine thereby
improving filler retention and enh~nçing paper properties. U.S. Patent No. 4,889,594,
issued to Gavelin, teaches the use of an app~dL~Is ~ che~l to a paper m~-ehine for use in
co-flocculating filler and fine pulp.
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- Although the method tallght by EP 0 041 056 provides a very good result it has
the drawback of requiring the use of large q l~ntities of ~ c~ive starch and is very
difficult to apply in practice due to the complexity of the added ingredi~ nts and their
reactions with locally occllrrin~ sllbst~nces. Thus, the results may vary from plant to
plant. The method according tc, the Swedish Patent Application 85001~j2-6, although
presentmg a simpler solution, still causes problems in achieving a resull: which can be
reproduced in practice. It has been found that the resultant flocs or filler and fine pulp are
broken down to some extent prior to being charged to the pulp suspension, resulting in
impaired retention and nece~sil~llhlg careful control of flocculation and degradation in a
particular manner and with the aid of special a~p~ s in order to achieve the result
desired.
U.S. Patent No. 4,889,~!34, issued to Gavelin, teaches the use of an appdl~Lus
aKached to a paper machine to provide a suitable environment for mixing a retention
agent and inorganic filler for use in the manufacture of fine papers. These patents address
the problem of strength loss when the level of inorganic filler is increased.
Many compositions and applications which are useful in the m~nllf~r*lre of fine
paper are inapplo~liate for use in the m~n~lf~hlre of paper board. Several factors
contribute to this incompatibility. Traditionally, no retention aid is use,1 in the
manufacture of paper board since retention aid tends to hurt formation when it is added to
whole furnish. This is because paper board uses the longest fiber to achieve increased
CA 02219332 1997-10-24
strength and long fiber is most susceptible to flocculation
leading to formation loss. Poor formation causes loss in
strength and poor dewatering o~ the sheet.
Secondly, the manufacture of paper board does not
incorporate the use of any fillers since it is unbleached fiher
and does not require the brightness conveyed b~ the addition of
fillers. The use of fillers would, in fact, hurt the overall
strength of the paper board, which is its most important sheet
propert~. Since paper board is primarily designed for strength,
the use of a filler would not be appropriate. Accordingly, it
is an object of this invention to provide an improved method
of flocculating fines in the manufacture o~ paper board.
Summary of the Inv~ntion
The present invention relates to a method i-or manu-
facturing paper board, which contains no inorganic filler.
Pulp fines from the white water s~stem of the paper machine are
mixed with one or more retention agents and then ~ed to the
stock upstream of the paper machine. This introduces the
fine/retention aid mixture prior to blending with the long
fiber stock. Once flocculation takes placer~the stock is
drained to form a sheet and the sheet is dried.
According to the present invention, there is provided
a method oi- manufacturing ~aper board using a paper machine in
which stock is fed to a headbox of the paper machine to form
the paper board, the method comprising the steps of: mixing
white water pulp fines from the stock with a retention aid to
66530-633
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form flocst feeding the flocs to the long fiber stoc]~ upstream
of the headbox; draini~g the stock to form a sheet, and drying
the sheet.
In a preferred embodiment at least one flo~ of fine
pulp is delivered to at le!ast one headbox in a paper machine
provided with multiple headboxes.
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D~s~ ,liolr ofthePreferred]Embo-limPnts
When carrying out the process of the invention, fine pulp is floc:culated with the
aid of one or more retention agents, prior to the pulp being introduced into the long fiber
stock fed to ~e paper m~hine. This results in flocculation of the fine particles without
flocculation of the long fiber with r~slllting loss of formation.
~uitable retention agenl s for use in accordance with the present invention are any
of the typical retention agents used in papçrm~king, including high molecular weight
polymers which provide an irreversible bridge formation bet~,veen particles. Anionic,
cationic and nonionic polymers can be used herein. In order to charge the polymer to the
system effectively and to obtain effective flocculation, it is necessary f~r each polymer
molecule to come into contact with the largest nurnber of particles possible. When
flocculating in accordance with the invention, flocculation is effected in the presence of a
small proportion of the total headbox furnish and when the flocs come into contact with
the long fiber stock, at a later stage, the retention agent has already reacted and is, to a
great extent, bound to active groups on the fine pulp.
Retention of the flocs in the paper board is caused by two mutually contributoryreaction.processes. According to the first of these processes, the flocs are filtered out and
fasten in the meshes of the fiber network on those sites at which they are located when
the fiber network is consolidated during the process of dewatering the stock on the wire
of the paper m~chine According to the second of these processes, which applies when
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using a cationic retention agent, the cationic flocs are attracted to anionic fiber surfaces in
the fiber network, which ampli:Eies the filtt~rin~ process and contributes towards uniform
distribution of the flocs in the clirection of the Z-axis of the paper.
The method according to the invention is not dependent on the use Qf any
particular kind of retention agemt. The choice of retçntinn agent depends on those
demands placed on the process and on paper quality. A few retention agents which can
be used in accordance with the invention are given below.
Floccnl~nt~ such as copolymers of acrylamide with cationic or anionic monomers,
which can be obtained at various molecular weights and degrees of substitution.
Coagulants, including DADMACs, epi-DMAs, con-len~tion products ~f ethylene
dichloride and ~minçs, polyethylene imine, modified polyethylene amines and polyamido
amines. These coagulants may be used alone or in conjunction with flocculants in dual
polymer programs. Nonionic flocculants such as polyacrylamide and polyethylene oxide.
Both may be used with an enh~mcer such as phenol formaldehyde resins. Cationic starch
can be added to the stock in order to increase the dry strength of the paper or to reduce the
Z-potential of the system and cause coagulation of fine fraction.
C~ther polymers of the type polyamide, polyami~lç~mine con(lçn~tç7 cationic
polystyrene latex, and inorganic compounds of the type alum, polyalurninum chloride and
sodium alnmin~t~ can also be used as retention agents in accordance with the present
invention.
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It is also possible when practicing the invention to use combinalions of dirre,c ~1~
retention agents, e.g. two-complonent systems or three-cc,..,~onent systems. For example,
a cationic retention agent can be combined with an anionic agent, in which case the
ca~ionic agent is preferably prior to the addition of the anionic agent.
S A microparticle may also be added to any of the single or dual polymer programs
described above. Particles cu~lc;lllly in use include colloidal silica, bent~nite, other
smectite clays and anionic latex polymers.
Suitable three-component systems for use in accordance with the invention are the
combination cationic starch/aniionic polyacrylamide/cationic polyacrylarnide and the
combination bentonite or colloidal silica/anionic polymer/cationic polymer.
Suitable addition points for adding the retention aid according to the invention are
any paper machine locations cont~ining only fines, e.g., the tray, white water silo and
suction side of the fan pump. P'referably, the addition occurs at a poinl where at least a
low level of turbulence occurs, e.g., the suction side of the fan pump.
Numerous advantages are realized as a result of lltili7.in~ the method of the
invention. The foremost advantage is the increase in retention that occ urs without a loss
of dewatering, while increasing runnability and tensile/crush strength of the end product.
These benefits cannot be achieved by adding the retention aid to the whole furnish (long
fiber plus ~mes) because long fiber flocculation will lead to loss in fon nation, with
resulting loss in dewatering, rlmnability and strength.
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A second advantage is the reduced amount of retention aid that is required for use
throughout the paper m~hine system. This reduction is realized because long fiber is not
heated, as is done to paper fibers used in the production of finer paper g;rades.
The following examples are presented to describe ~l~r~.,ed emborliment~ and
utilities of the invention and are not meant to limit t]he invention unless otherwise stated
in the claims appended hereto.
Example 1
The effect of adding Nalco~ 7523, a low charge density (0.14 Irleq/g) cationic
flocculant, was meaLsured at a paper board m~nuf~r*-ring facility m~mlf~rtllringcorrugated medium from semi-chemical pulp. The 7523 was fed to the wire pit (fines
only) and compared to pre-screen (conventional method - whole furnis]h).
Although addition of the Nalco'l9 7523 in a conventional manner to the whole
fumish is beneficial, wire pit addition reduced total wet-end breaks by 59.2% (from an
average of 9.7 breaks/day down to 3.9 breaks/day). Total wet-end breaks reflects both the
fabric (wire) and press section breaks. On average, fabric breaks were reduced by ~72%
when Nalco~ 7523 was being run through the wire pit on the paper m~ rhine. Likewise,
the break level in the press secl:ion (lst and 2nd presses) was reduced by ~42% when the
polymer was being fed to the paper machine at the wire pit.
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The lost time resl-lhng firom all wet-end breaks was reduced by ~58% when
co"~p~ g the periods that the polymer was fed at the wire pit vs. those times when it
was fed pre-screen. The avera~e total lost minl-tes, when combining all wire pit vs. Pre-
screen feed evaluation periods, was 70.3 ~i"~ /day with normal polymer feed and 29.9
minutes/day with wire pit polymer feed. This represents a net gain in production time of
40.4 minutes/day or 0.675 hours/day. Using a production rate of 15.66 TPH, there is an
increase in daily production of 10.54 Tons per Day (~ 100% operating efficiency).
During the Nalco 7523 evaluation periods, the data suggests that the steam usageon the paper machine was reduced by ~5% when polymer was being fed at the wirepit.
As a result, first-pass retention levels (during 26# medium production) increased from an
average range of 70% - 72% ta, an average range of 79% - 81% with polymer added at the
wlre pit.
There appears to be a significant improvement in the polymer performance by
ch~nging the feed point to the drive-side of the wire pit (fines only) relative to pre-screen
(whole furnish). In many instances, feeding the polymer to the white water essentially
"pre-flocculates" the fines before being brought back into the headbox By targeting the
polymer at initially only recircul~ting tray water solids, this aims a very high initial
dosage of chemical at the fines which are difficult to retain and that have the most
detrimental impact on the paper machine drainage (due to their high relative surface area
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and water holding capabilities). More ~~ lly, it provides improvements in retention
and drainage, without potentially cc~ "ising sheet formation.
~Hi ~ ; . lcr good form;~tion means that forming area vacuums ~vvill rernain at
higher effective levels (less light and heavy areas where vacuum integri.ty can be lost),
S sending a more ulliro~ sheet of higher cor~ tency and wet web strengrth into the press
section.- This can mean less opportunity for press picking, fewer wet-end breaks, and
better opport~it,v for the wet p~resses to remove water and build intern,~l sheet strength.
F,xample 2
The drainage and dryin,g effects of Nalco~' 7523 on paper board m~n~lf~c~lring
machinery were measured. Effects of the polymer on reel moisture, sl:eam pressure,
flatbox vacuums, and reel speed were calculated. Differences before, during, and after
this evaluation on 33# heavyweights regarding average C~CO tests, average m~rhine
speeds, and average tons/hour were then measured. Nalco 7523 was added to the drive
side of the wire pit at a target addition rate of 2 Ib/ton. Three days later, Nalco 7523
flocculant was removed from the paper m~chine system at least at the same, if not
slower,-rate than it was taken out during previous evaluations. Some of the observations
made during this time period where the feed rate was reduced from 2 Ib/ton down to O
Ib/ton are as follows.
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The effect of reduced polymer dosages on the reel moisture levels was measured.
Before each subsequent polymer dosage reduction, the reel moisture was allowed to
stabilize below 8.8% via increases in the 4th and 5th section steam pressure, changes in
the rush-drag to reduce the amount of water being carried down the table, reduced
dilution water, or through reductions in m~5hine speed, before the feed. rate was further
reduced. Reel moistures were at 8.2% at a 2 lb/ton dosage and soared to a maximum
moisture level of 13.3% when the polymer was removed entirely from the addition to the
wlre pit.
Prior to decreasing the polymer dosage (i.e., 2 lb/ton), the steam pressure was at ~
43 psi. Upon making the final reduction in dosage from 0.5 lb/ton) down to 0 lb/ton, the
steam pressure reached a maximum level of~ 94 psi. The 3rd section steam increased
slightly from ~ 1 12 psi up to ~ 1 16 psi, throughout the removal of the polymer from the
paper machine.
A decrease in wire drainage was observed after removing the retention and
drainage aid on the wire. This decrease in wire drainage was shown by the significant
increase in the #3 Flatbox vacuum level. At the 2 lb/ton dosage, the #3 Flatbox vacuum
was ~7.35"Hg. This increased by ~ 27% up to a vacuum reading of 9.3"Hg when the
polymer had been completely shut off. This increase remained at this high level even
after the machine tender attempted to compensate through reductions in rush-drag (-60
fpm to -75 fpm) and machine speed. The wet line position carried ~ I feet further down
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the m~-hin~: (toward the press section) when co",l.~, ;"g the 2 lb/ton dosage to no
polymer addition. In addition, the CD moisture 2-sigma moisture profile was muchpoorer after the removal of the polymer (1.30% (~ 2 lb/ton versus 1.85 %+ ~ ~ lb/ton).
As to m~f.hine speed, at the 2 lb/ton dosage, the m~-~hine was rum~ing at a reelS speed of 1,370 fpm. Once the polymer had been completely removed, the reel speed had
been reduced down to 1,355 fpm for a net reduction in speed of 15 fpm (while running at
significantly higher steam pressures).
Pre-trial, trial, and post-trial period CFCO test averages during l~e 33#
heavyweight run were as follows:
~ Pre-Trial 74.4 psi
~ Nalco 7523 Trial 77.2 psi
~ Post-Trial 72.8 psi
Average machine speeds during the pre-trial, trial, and post-trial periods during
the evaluation of Nalco(~ 752:3 polymer while running 33# medium were as follows:
~ Pre-Trial 1449 fpm
~ Nalco 7523 l'rial 1461 fpm
~ Post-Trial 1442 fpm
The production rates (tons/hour) when co.l,l,~hlg the pre-trial, trial, and post-trial
periods are as follows:
~ Pre-Trial 15.72 tons/hour
~ Nalco 7~23 Trial 17.22 tons/hour
~ Post-Trial 16.09 tons/hour
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In summary, when co" .p ~ g ~e effects of a 2 lb/ton polymer i'eed rate with no
polymer addition, the following observations were docllm~nte~ To achieve the same reel
moisture levels without polymer, a~ ux.illlately 41 psi of additional 4tll and 5th section
dryer steam pressure was required (~43 psi (~ 2 lb/ton versus 84 psi (~ O lb/ton).
Additionally, a reduction in m~hin~ speed of 15 feet per minute (fpm) was also
necessary due to the poorer wire drainage and higher moistures/poorer moisture profiles.
It was also n~ce~s~ry to reduce the rush-drag from -60 fpm to -75 fpm l~hile re~lucing the
dilution valve position from 78% down to 69%.
Fxample 3
T~RT,F 1
Item Pre-Trial During Trial
CSF,mls 350 400
FPR, % 85 93
Freeness Drop,ml 100 150
MD Tensile Strength, 71-73 78-81
lbf/0.5in
MK Formation Better
Flock Count 70 100+
Flock Size 19 14.8
FlockArea, % 70 50
At this mill, linerboard for gypsum wallboard is produced on a Fourdrinier using~ 100% recycle furnish. The initial retention/drainage program consistel~ of a flocc~ nt
CA 02219332 1997-10-24
fed pre-screen, a coagulant and alum fed nn the suction side of the fan purnp and a
microparticle fed post-screen. lllis is the pre-trial column shown in Table 1 above. The
trial consicte~ of ch~nging the i~occulant feed point from pre-screen (whole furnish
including long fiber) to the white water silo (fines orlly). This configurcltion is denoted as
S "During Trial" in Table 1 above. This change in feed point resulted in increased drainage
as measured by C~n~ n standard freeness (CSF), increased first pass retention (FPR),
increased m~rl~in~ direction sheet strength and improved formation.
F~mple 4
The retention/drainage program of the invention was incorporated into a dual
headbox Fourdrinier m~chine producing virgin unbleached kraft linerboard. It was found
that by feeding the dual polymer retention program that had been in use at the m~rhine to
the wire pit (fines only) production was increased from 850 to over 90t) tons per day.
Significantly, a 2% reduction in white top liner furnish was realized as a result of
improved retention of the brown unbleached kraft fines gained by the change in feed
1 5 points.
Changes can be made in the composition, operation and arrangement of the
method of the present invention described herein without departing from the concept and
scope of the invention as defined in the following claims:
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