U.S. patent application number 16/681147 was filed with the patent office on 2021-05-13 for papermaking system and method.
The applicant listed for this patent is John H. Klungness. Invention is credited to John H. Klungness.
Application Number | 20210140113 16/681147 |
Document ID | / |
Family ID | 1000004777299 |
Filed Date | 2021-05-13 |
![](/patent/app/20210140113/US20210140113A1-20210513\US20210140113A1-2021051)
United States Patent
Application |
20210140113 |
Kind Code |
A1 |
Klungness; John H. |
May 13, 2021 |
PAPERMAKING SYSTEM AND METHOD
Abstract
A method of making paper is described. The method includes
providing a cellulosic fibrous material, the cellulosic fibrous
material comprising a plurality of elongated fibers having a fiber
wall surrounding a hollow interior, the fibrous material having
moisture content. The method also includes adding calcium
bicarbonate solution to the cellulosic fibrous material to form a
pulp mixture, the calcium bicarbonate solution containing up to the
saturation level of about 16% solids of calcium bicarbonate, the
resulting pulp mixture having between 0.1% to 65% total solids by
weight. Further, the method includes refining the pulp mixture such
that at least some of the calcium ions become associated with the
reactive sites in the fiber walls. Further still, the method
includes forming a web from the pulp mixture and wet pressing the
web.
Inventors: |
Klungness; John H.;
(Bayfield, WI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Klungness; John H. |
Bayfield |
WI |
US |
|
|
Family ID: |
1000004777299 |
Appl. No.: |
16/681147 |
Filed: |
November 12, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
D21F 3/02 20130101; D21H
15/02 20130101; D21F 7/008 20130101; D21H 17/675 20130101; D21H
17/70 20130101; D21H 23/04 20130101; D21D 1/20 20130101 |
International
Class: |
D21H 23/04 20060101
D21H023/04; D21D 1/20 20060101 D21D001/20; D21H 15/02 20060101
D21H015/02; D21H 17/67 20060101 D21H017/67; D21F 3/02 20060101
D21F003/02; D21F 7/00 20060101 D21F007/00 |
Claims
1. A method of making paper comprising: combining carbon dioxide,
calcium carbonate, and water in a reactor to produce calcium
bicarbonate; providing a cellulosic fibrous material, the
cellulosic fibrous material comprising a plurality of elongated
fibers having a fiber wall surrounding a hollow interior, the
fibrous material having moisture content; adding calcium
bicarbonate solution to the cellulosic fibrous material to form a
pulp mixture, the calcium bicarbonate solution containing between
0.5% to 16% solids of calcium bicarbonate by weight, the resulting
pulp mixture having between 0.1% to 65% total solids by weight;
refining the pulp mixture such that at least some of the calcium
ions become associated with the reactive sites in the fiber walls;
forming a web from the pulp mixture; and wet pressing the web.
2. The method of claim 1, further comprising: drying the web.
3. The method of claim 1, further comprising: adding energy in a
steam box prior to wet pressing the web.
4. A method of making paper comprising: providing a cellulosic
fibrous material, the cellulosic fibrous material comprising a
plurality of elongated fibers having a fiber wall surrounding a
hollow interior, the fibrous material having moisture content;
adding calcium bicarbonate solution to the cellulosic fibrous
material to form a pulp mixture, the calcium bicarbonate solution
containing between 0.5% to 16% solids of carbon bicarbonate, the
resulting pulp mixture having between 0.1% to 5% total solids by
weight; refining the pulp mixture such that at least some of the
calcium ions become associated with the reactive sites in the fiber
walls; forming a web from the pulp mixture; and wet pressing the
web.
5. The method of claim 4, further comprising: drying the web.
6. The method of claim 4, further comprising: adding energy in a
steam box prior to wet pressing the web.
Description
REFERENCE TO PRIORITY APPLICATIONS
[0001] This application claims priority to U.S. Provisional
Application No. 62/760,543, to inventor John H. Klungness, filed on
Nov. 13, 2018, the entirety of which is herein incorporated by
reference.
BACKGROUND
[0002] Over the past half century, there has been considerable
research into the parameters controlling press dewatering. Previous
efforts to improve press dewatering have, with limited success,
focused on changing the equipment used in the process. Out of
necessity, this requires significant capital investment for
development and commercialization. The last major improvement in
press dewatering, extended nip pressing, requires complete
replacement of a portion of the press section. It was introduced in
the early 1980's and still has not reached full market saturation.
Other technologies (impulse drying and displacement dewatering)
have not fared well either, at least in part due to the significant
capital investment required.
[0003] During the same time period, there has also been
considerable research into the manipulation of sheet physical
properties through refining, chemical addition, and filler
addition. These studies sometimes address the impact on sheet
formation, but usually from the standpoint of final sheet
properties. This work generally ignores the impact of sheet and
fiber changes on sheet dewatering.
[0004] There is a need for a system and method of fiber loading (in
situ formation of precipitated calcium carbonate) that can enhance
sheet properties relative to sheets made using traditional filler
addition methods as well as enhancing wet pressing water removal.
Present knowledge needs to be synthesized to optimize press
dewatering of filler loaded fibers.
SUMMARY
[0005] An exemplary embodiment relates to a method of making paper.
The method includes providing a cellulosic fibrous material, the
cellulosic fibrous material comprising a plurality of elongated
fibers having a fiber wall surrounding a hollow interior, the
fibrous material having moisture content. The method also includes
adding calcium bicarbonate solution to the cellulosic fibrous
material to form a pulp mixture, the calcium bicarbonate solution
containing up to the saturation level of about 16% solids of
calcium bicarbonate, the resulting pulp mixture having between 0.1%
to 65% total solids by weight. Further, the method includes
refining the pulp mixture such that at least some of the calcium
ions become associated with the reactive sites in the fiber walls.
Further still, the method includes forming a web from the pulp
mixture and wet pressing the web.
[0006] Another exemplary embodiment relates to a method of making
paper. The method includes providing a cellulosic fibrous material,
the cellulosic fibrous material comprising a plurality of elongated
fibers having a fiber wall surrounding a hollow interior, the
fibrous material having moisture content. The method also includes
adding calcium bicarbonate solution to the cellulosic fibrous
material to form a pulp mixture, the calcium bicarbonate solution
containing up to the saturation level of about 16% solids of
calcium bicarbonate, the resulting pulp mixture having between 0.1%
to 5% total solids by weight. Further, the method includes refining
the pulp mixture such that at least some of the calcium ions become
associated with the reactive sites in the fiber walls. Further
still, the method includes forming a web from the pulp mixture and
wet pressing the web.
[0007] In addition to the foregoing, other system aspects are
described in the claims, drawings, and text forming a part of the
disclosure set forth herein. The foregoing is a summary and thus
may contain simplifications, generalizations, inclusions, and/or
omissions of detail; consequently, those skilled in the art will
appreciate that the summary is illustrative only and is NOT
intended to be in any way limiting. Other aspects, features, and
advantages of the devices and/or processes and/or other subject
matter described herein will become apparent in the disclosures set
forth herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a process diagram of an embodiment of the paper
making process in accordance with the invention.
[0009] FIG. 2 is a machine diagram of papermaking machine
configured for the process of FIG. 1.
[0010] The use of the same symbols in different drawings typically
indicates similar or identical items unless context dictates
otherwise.
DETAILED DESCRIPTION
[0011] Referring to FIG. 1, a generalized process for papermaking
in accordance with exemplary embodiments is depicted. The process
provides a method of combining precipitated calcium carbonate (PCC)
with a pulp slurry (pulp and water mixture). The method then causes
the dissolving of the PCC in the presence of added CO2. The entire
mixture is then refined to cause reprecipitation of PCC.
[0012] The method of FIG. 1 may be carried out in a papermaking
machine generally depicted in FIG. 2. The Papermaking machine may
include, but is not limited to a Paper Machine Head Box, where the
mixture is formed, a wet press, where at least some of the water
may be removed. The Papermaking machine may also include a dryer
section configured to remove any excess water still remaining
within the sheet.
Rewetting
[0013] One of the most interesting and controversial subjects in
wet pressing research is the rewetting phenomena. Rewetting refers
to the re-adsorption of water into the web (nip rewetting) in the
later part of the press nip or subsequently before the web is
separated from the felt (post-nip rewetting).
[0014] Walstrom (1969) showed that felt batt diameter was the most
important factor for rewetting and that grammage and paper machine
speed had no effect on rewetting. Post nip rewetting occurs after
the press nip if paper web is in contact with the press felt
(Busker, Cronin 1984).
[0015] The mechanism of nip rewetting is less clear due in part
that it is difficult to measure. It has been suggested that felt
expansion after mid-nip is controlling mechanism that limits
rewetting, opposing the effect of web expansion based on studies
where an incompressible pressing media was used (Jaavidaan et al.
1988; Luotonen, Sampi 1995).
[0016] McDonald and Kerekes (1991) complied rewetting from earlier
studies and found them varying in the range from 2 to 72 g/m2. They
developed a permeability model and found good agreement with mill
scale measurements.
Sheet and Fiber Water
[0017] In conventional pressing, water removal is induced by
compressing the sheet. Sheet compression results in a decrease in
average pore size and increase in apparent density. Using peak
pressures of up to 7,000 kPa (1000 psi), the maximum solids
attainable in most press sections is 45% to 50%. Sheet property
constraints and lifetime limitations often prohibit using press
loads of that magnitude. The 40% to 45% solids level represents
about the same amount of water as is found in the inter-fiber
pores, i.e., inter-fiber water or free water (Maloney et al.,
1998).
[0018] Inter-fiber water is contained in the pore spaces between
the fibers. These pores generally have diameters of 1 .mu.m or
greater.
[0019] Intra-fiber water is the water contained in pores that exist
in the fibers. These pores generally have diameters that range in
size from <0.01 to about 0.05 .mu.m. Water in pore spaces
ranging in size from 0.025 to 0.05 .mu.m is not bonded to the fiber
and can be removed mechanically.
[0020] The amount of unbonded intra-fiber in fiber is about 1.4 to
1.5 g/g (42% solids) (Carlsson, Lindstrom, Soremark, 1977). A
portion of intra-fiber water (about 0.4 g/g) forms hydrogen bonds
with the fibers and is contained in the fiber wall in pores smaller
than 25 .ANG. (or 0.0025 .mu.m) (Stone et al., 1966). The amount of
hydrogen bonded water does not vary significantly for different
pulps or different levels of refining. This water cannot be removed
mechanically, as its removal requires heating to break the hydrogen
bonds. It constitutes the limit of water removal by mechanical
means and represents a sheet solids content of 1/(1+moisture
ratio))=1/(1+0.4)=0.71 or 71% (Fiber Saturation Point).
[0021] Is only inter-fiber water removed in the press section?
Experiments indicate that intra-fiber water is also removed in the
nip (Carlsson, 1983). Therefore, the low solids levels attained in
conventional pressing imply that the water removal process is not a
serial process in which all the free water is removed and then the
intra-fiber water is removed. As the sheet is compressed, some
intra-fiber water is pushed into the inter-fiber spaces and a
portion of it may reach the felt. Some of the inter-fiber water
also enters the felt. However, some inter-fiber water may be
absorbed by the fibers, thus becoming intra-fiber water. This
process is beneficial for development of sheet strength but at the
same time limits water removal by conventional pressing.
Eventually, all the inter-fiber water is removed, although in
actual practice some of it may be removed by drying.
[0022] Robertson (1963) described what happens to the web as the
water is removed: The saturated web that is first formed derives
its strength from fiber entanglement and inter-fiber friction
forces. Fiber flexibility contributes to increased floc strength
and wet web strength. The removal of water produces increased
strength by compression of the pad by surface tension effects up to
the point of air intrusion. Air intrusion is determined by the web
compressibility and pore size distribution. Pore size distribution
is a function of fiber size and fibrillation.
[0023] As the inter-fiber pores are emptied of water, the web may
expand or contract, depending on whether it is predominantly
plastic or elastic. Webs made of high yield pulp tend to be more
elastic.
[0024] As the inter-fiber water is removed, further water removal
requires collapse of fiber structure. Surface tension tends to draw
the fiber together, increasing fiber-fiber contacts. Fibrils
collapse onto the parent fiber or each other; fiber walls are
flattened to form extended areas of inter-fiber contact. Caliper
reduction occurs and with highly fibrillated fibers planar
shrinkage occurs. The strength of the web is still a result of
surface tension forces, but the forces are now acting on large
surfaces in close contact and the radii of curvature of the menisci
are small.
[0025] Hydrogen bonding does not occur until after the fibers are
collapsed and the lumen water is removed.
[0026] Fiber/Lumen Loading
[0027] In conventional papermaking, fillers are added for two
primary purposes (1) modify the final sheet physical properties
(optical properties or print quality properties), and (2) replace
fiber with lower cost nonfiber materials. Fillers used just to
modify physical properties can be expensive (e.g., titanium dioxide
used for sheet brightness and opacity). Filler used for fiber
replacement are of necessity low cost (e.g., kaolin clay, calcium
carbonate).
[0028] In using fillers, the primary problem is retention of filler
particles in the forming section of the paper machine. Polymers are
used to modify the filler and/or the fiber surfaces charges and
promote attachment of the filler particles to the fiber surfaces.
Always some filler materials drain through the web and enter the
paper machine white water system, not all of which is recovered. An
additional problem is that sheet strength is reduced when
conventional filler techniques are used. The filler particles
adhere to the exterior of the fibers and decrease the surface area
available for fiber-fiber bonding.
[0029] The shift to alkaline conditions in papermaking was prompted
by the increased level of filler permitted in alkaline-sized
papers. Because alkaline conditions enhance paper strength, a
higher level of filler can be incorporated into the sheet. Calcium
carbonate, filler that could not be used in acid-sized papers, is
popular as filler in alkaline-sized papers because of its high
brightness level (Gill and Scott, 1987; Downs, 1990).
[0030] A method to incorporate filler into the lumen of wood fibers
has been the subject of extensive research. Scallan and associates
(Green et al., 1982; Scallan and Middelton, 1985) reported the
first studies as lumen loading. An excess of titanium dioxide was
mechanically mixed with a pulp slurry depositing titanium dioxide
within the fiber lumen. However, limitations of this method were
the large excess of titanium dioxide required for lumen loading and
the need of a separate process for recycling the excess filler.
More recent studies on cell wall loading have been reported by
Allan and associates (Allan et al., 1992). Their approach was to
saturate pulp fibers with sodium carbonate and react the resulting
a pulp mixture with a salt-containing calcium (e.g., calcium
chloride). However, additional processing was required to remove
the salt remaining in the mixture.
[0031] The fiber-loading technology, developed at the USDA Forest
Service, Forest Products Laboratory, consists of two steps
(Klungness et al., 1993). First, calcium hydroxide is mixed into
pulp fiber slurry. Then, the pulp and calcium hydroxide mixture are
reacted using a high consistency pressurized reactor (refiner or
disk disperser) under carbon dioxide pressure to precipitate
calcium carbonate. The calcium carbonate formed is termed
fiber-loaded precipitated calcium carbonate (FLPCC). The technology
increases brightness, opacity, bonding properties, and runnability
of the paper machine.
[0032] We estimated the capital effectiveness of fiber loading with
regard to producing lightweight high-opacity newsprint. Fiber
loading allows fiber bonding at increased precipitated calcium
carbonate levels without significant loss in Canadian Standard
Freeness (CSF) (an arbitrary measurement of water drainage) or
additional use of energy. We investigated the return on investment
(ROI) for FLPCC for a hypothetical 600 metric ton/day newsprint
mill. Savings were obtained from substituting lower cost FLPCC for
higher cost fiber, reducing grammage and drying energy costs, and
obtaining a premium for lightweight paper. Fiber loading produces a
positive ROI, given typical engineering costs. Assuming that a
4-g/m2 reduction in fiber and a 6% addition of precipitated calcium
carbonate is a reasonable goal for fiber-loaded newsprint, high
ROIs can be reached. Assuming that FLPCC is available at
$150/metric ton and 1% hydrogen peroxide is added along with
typical stabilizing chemicals, the ROI is estimated to be 59.7%. If
the cost of FLPCC is $75/metric ton, the ROI is estimated to be
73.4% (Klungness et al., 1999). The above economics are based on
using expensive high consistency fiber-loading reactors. If
conventional equipment, such as double-disk refiners, can be used
at consistencies of about 5%, the ROIs are very much improved. This
work did not have as its primary objective to decrease dryer
section energy use.
[0033] Fiber/Lumen Loading--Previous Pilot-Scale Work
[0034] There are two published industrial evaluations of fiber
loading. The first evaluation (Klungness et al., 1995) involved
fiber loading virgin never-dried birch hardwood bleached Kraft
pulp. The fiber-loaded pulp was processed on a pilot-scale paper
machine. The paper machine trials revealed some technical
obstacles. Changes in color and brightness, cross machine web
shrinkage, and apparent density increases were observed and became
the focus of the follow-up laboratory evaluations following these
trials. The problems were duplicated in the laboratory, and methods
for preventing or overcoming the obstacles were developed.
[0035] It was demonstrated that including a low level of hydrogen
peroxide prevented brightness loss and yellowing of the
fiber-loaded pulp. Web shrinkage was tracked to greatly improved
water removal for fiber-loaded pulps compared to the conventional.
Web shrinkage occurred before the paper machine
cross-machine-direction restraint rolls. This was due to improved
water removal. Filler retention was shown not to be a problem with
fiber-loaded pulps. Apparent density was increased by about 10% for
fiber-loaded pulps. Laboratory hand sheet experiments demonstrated
that increased use of TMP pulp restored the loss in bulk.
[0036] The second published industrial evaluation of fiber loading
involved deinked mixed office waste (Heise et al., 1996).
Conventional deinking mill conditions were simulated.
Industrial-scale fiber loading was technically successful; calcium
hydroxide was completely converted to calcium carbonate and
deposited on the external and internal surfaces of pulp fibers. The
fiber-loading processes used in the trials needed to be modified to
obtain optimum conversion to calcium carbonate.
[0037] The term "hot pressing" has been used to refer to two
different technologies, both of which have the objective of
reducing water viscosity and fiber compressive strength. These, in
turn, result in increased water removal due to reduced hydraulic
pressures in the web and reduced fiber/web springback. One
technique referred to as "hot pressing" is the use of multiple
steam boxes before and in the press section of the paper machine
(Cutshall, 1987). There are two primary complications to this
technology. Modern paper machines have extremely compact press
sections and it is difficult to fit multiple steam boxes into a
machine that was not specifically designed for that purpose. A
second potential problem is decreased web permeability due to
refining; high recycle content, or both.
[0038] The second technique of "hot pressing" is to use a heated
pressing surface. Hot pressing differs from impulse drying in that
the pressing surface is kept at temperature below the boiling
temperature of water. The delamination issues associated with
impulse drying are therefore not of concern.
Advances in the Art
[0039] We have determined that using pulp mixture solids from 0.1%
to 5% solids provides significant benefits to what has previously
conceived. The use of pulp mixtures between 5% and 60% solids has
been previously (Klungness 2014). In accordance with an exemplary
embodiment the pulp to be processed is to be in the form of a crumb
pulp, i.e. the fibrous material has a moisture present at a level
sufficient said cellulose fibrous material in the form of dewatered
crumb pulp.
[0040] However, a great deal of wood pulp is processed as a slurry,
below the claimed solids and thus it would be advantage to use
existing conditions and processing equipment for our method to use
lower solids. Using lower solids (0.1% to 5%) is unexpected as
prior to this high solids (5% to 60%) have been used in order to
permit near field reaction to occur in order to result in calcium
being deposited within the cell wall of wood pulp fibers. However,
it has been shown that high solids pulp is produced very briefly
during processing in a pressurized refiner between rotating refiner
plates.
[0041] Unexpectedly, low solids pulp mixtures as a feed to pulp
refiners result, under proper refiner plate gap, temperature, and
chemical addition, in calcium depositing within the fiber cell
walls thus displacing bound water from the cell walls. The
resulting solids of wet pressed pulp web are higher than without
this method using lower solids.
[0042] Scanning electron microscopy (SEM) analysis revealed the
presence of PCC crystals on both external fiber surfaces and within
the cell lumen. X-ray microprobe analysis identified the presence
of calcium within the cell wall (Klungness et al., 1994). Also, it
was observed that the FLPCC crystals on the surface if the fibers
were very small and the FLPCC crystals within the lumen larger
(standard 1.4 .mu.m). This shows that not only were the FLPCC
particles formed by reacting calcium hydroxide and carbon dioxide,
that excess carbon dioxide reacted with water for form carbonic
acid. The carbonic acid formed then reacted with the FLPCC to form
calcium bicarbonate. Calcium bicarbonate is only soluble in water
to about 16%. During processing in wet pressing the pulsing action
of the pressing would repeatedly raise and lower the water solids
between the 16% solubility of calcium bicarbonate. The calcium
bicarbonate would precipitate as fine particles of PCC (and
possibly dissolve again). The calcium ions from the calcium
bicarbonate have then also displaced bound water attached to
carboxyl and carbonyl reactive groups within the fiber wall.
[0043] In summary these observations indicate three reactions occur
during fiber loading:
[0044] PCC is formed as normal 1.4 .mu.m diameter PCC particles
[0045] PCC is formed on the surface of the fibers as small as 0.05
.mu.m (or lower) PCC particles
[0046] Calcium ions have been deposited in the cell walls.
[0047] These (non-obvious) observations suggest that adding calcium
bicarbonate directly will result in simplifying and improve water
removal in wet pressing.
[0048] Calcium ions which displace and release bound water from
within the fiber wall also prevent rewetting. This includes both
nip and post nip rewetting. Reactive hydroxyl and carboxyl sites
within the fiber wall are bound with calcium ions and compounds
which effectively reduce or prevent rewetting of wet paper webs in
the wet pressing process. Preventing rewetting is due in part to
stearic hindrances of the calcium ions and compounds deposited in
the fiber loading process. The prevention or reduction of rewetting
is also facilitated by the neutralization of reactive groups within
and on the surface of the cellulose fibers.
[0049] When using lower solids, not only does the PCC formed in the
reaction displace the bound water, but it prevents rewetting of the
eventually wet pressed formed web from this fiber loaded pulp. That
is, the water removed during wet pressing becomes more effective by
preventing the rewetting during pressing. Such that, as the free
water is removed, then the intra-fiber water removed, and finally
(as the sheet is compressed), the inter-water is removed from the
wet web; all water removed reaches the felt with greatly reduced
re-wetting of the wet pressed formed web. This serial process is
repeated (pulsed) many times during refining and wet pressing
resulting in greatly enhanced water removal during the wet pressing
operation.
[0050] In accordance with exemplary embodiments, the repeated
pulsing of the solids during stock preparation causes small PCC
particles to repeatedly and simultaneously form and bond strongly
with the fibers. These small and well bonded PCC particles cause
higher solids to be reached during wet pressing as well as
preventing re wetting during the release of wet pressing.
[0051] In our following experiments we focus on dissolving a
portion of typical particle sized PCC used in producing paper
thereby producing soluble calcium bicarbonate. Then reprecipitating
much smaller PCC particles (from the soluble calcium bicarbonate)
on and within the fiber walls. By so doing we desire to reduce
rewetting during wet pressing of the fiber web, in order to reduce
subsequent drying energy during paper manufacture.
Materials
[0052] Pulp--The pulp used was a commercial bleached hardwood
market pulp supplied by Verso.
[0053] Calcium carbonate (PCC)--Commercial paper grade precipitated
calcium carbonate was supplied by Specialty Minerals Inc.
[0054] Synthetic wet press felts (fabrics) were supplied by Albany
International.
[0055] Retention aid-Nalco 7546 was supplied by Nalco Inc.
[0056] Carbon dioxide-Commercial grade pressurized gaseous carbon
dioxide was used.
Equipment
[0057] Pulp beating-A commercial laboratory scale Valley beater was
used for adjusting the pulp freeness.
[0058] Producing calcium bicarbonate-A standard laboratory scale
mixer and stainless-steel container was used to bubble carbon
dioxide into a mixture of PCC and water.
[0059] British Disintegrator-Standard fiberizer used in TAPPI
standard procedures for fiberizing pulp for handsheets.
[0060] Wet pressing-A pilot scale wet press was used to press
handsheets. The wet press was single bottom felted only. The second
wet press was used for pressing.
Procedure
[0061] Treating PCC-Prepared a mixture of PCC in water sufficient
to end with 30% on the weight of pulp to be used in the Valley
beater. Bubbled carbon dioxide into the stirred mixture for 4-6
hours or until pH measurement stabilizes around 6.0.
[0062] Combined pulp, PCC, and water in the Valley beater at 3.0%
consistency and run for 1.5 hours until the freeness is about 350
ml CSF. Diluted pulp mixture to 0.6% consistency. Added Nalco 7546
(mixed under shear at 1% aged for 5 minutes, diluted to 0.1%.
Dosage of 1 lb./ton on total dry solids).
[0063] Prepared 2.4 g handsheets in Tappi hand sheet mold. Place
each hand sheet between two metal hand sheet plates and place in
plastic bag to prevent drying. Stored in oven at 1200F until ready
to press on the paper machine wet press.
[0064] The paper machine wet felt was conditioned by running with a
felt washer and pressing before experiments. The felt pads were
conditioned before each hand sheet pressing by washing with a hose,
pressing and running through a Uhle vacuum box.
[0065] Pressed hand sheets in a sandwich (paper machine wet press
felt, hand sheet, sample wet press felt). Passed through until a
pre-determined number of passes to reach 6.0 g wet weight (40%
solids). All the handsheets for a given experimental condition were
given the same number of passes. Pressed 25 handsheets per
experimental condition.
[0066] After pressing each hand sheet was placed in a plastic bag.
Determined the dry weight by oven drying. Calculated the water
removal for each hand sheet.
[0067] The untreated experiment was repeated as the treated PCC
experiment except for omitting the carbon dioxide treatment.
Results
TABLE-US-00001 [0068] TABLE 1 pH and Freeness values for Pulps
Processed with Untreated and Treated PCC Untreated PCC Treated PCC
PCC plus H.sub.2O PCC plus H.sub.2O plus CO.sub.2 pH 9.68 6.09 pH
Add pulp Add pulp 6.74 pH Beat 1.5 hr. Beat 1.5 hr. 8.49 8.51 CSF,
ml 350 380
[0069] Adding PCC to pulp resulted in a pH of 9.68 (Table 1).
Beating at 3.0% consistency reduced the pH to 8.49- and freeness to
350-ml CSF. An identical pulp mixture was treated with CO2 which
lowered the pH from 9.68 to 6.09 due to the formation of calcium
bicarbonate from the carbonic acid formed by CO2 and water plus
PCC. After again beating the pulp with treated PCC for 1.5 hours,
the pH reached 8.51 (close to the 8.49 reached by beating the pulp
with the untreated PCC). The similar pH values indicate the treated
pulp had much of the calcium bicarbonate converted to PCC.
TABLE-US-00002 TABLE 2 Ash Content of Hand Sheet Mold Mixture and
Dried Hand Sheets Untreated Treated Hand sheet mold, ash % 25.6
21.3 Dried hand sheet, ash % 23.0 25.4 Retention, ash % 89.8
119.2
[0070] Retention of ash from the untreated PCC pulp sample before
and after hand sheet preparation was 89.8%. This level of retention
of PCC was expected. The retention for the treated PCC containing
pulp sample was much higher than expected, at 119.2%. The result
for the treated PCC suggests that the high solids reached during
wet pressing caused further precipitation of unprecipitated calcium
bicarbonate during the wet pressing operation. That is, a longer
beating time, higher pulp consistency, or both during beating would
precipitate more of the calcium bicarbonate (prior to pressing)
formed during CO2 treatment.
TABLE-US-00003 TABLE 3 Wet Press Water Removal Results for
Handsheets Containing Untreated and Treated 23% PCC Untreated
Treated Dry Weight, g 2.44 (0.06) 2.43 (0.05) (Std. Dev.) Water
removed, g 1.79 (0.19) 1.87 (0.16) (Std. Dev.) Water 0.7324 0.769
removed/dry wt. (g/g) Apparent density, 0.0123 0.0124
(g/cm.sup.3)
[0071] The weight of the dried handsheets and the apparent density
of the pressed and dried handsheets were similar at 2.44 and 2.43 g
and 0.0123 and 0.0124 g/cm3 (Table 3). The ratio of water removed
per gm of dry pulp for the treated pulp with respect to the value
for untreated pup was 0.769/07324 or 1.05. That is, there was a 5%
drying energy saving realized by treating PCC at the 23% PCC based
on total hand sheet weight.
[0072] Wet webs containing treated PCC demonstrate improved water
removal during wet pressing compared to identical wet webs with
untreated PCC. The improvement in wet pressing is due to an
increase in filtration resistance of pulp webs containing treated
PCC. Treating PCC creates smaller particle size reprecipitated PCC
(from calcium bicarbonate) (Klungness et al. 1994). Filtration
resistance is proportional to specific surface area which increases
with the smaller size of the treated PCC.
[0073] During wet pressing wet webs of both treated and untreated
PCC perhaps reach similar solids at high mid press nip pressure.
But the treated PCC webs leaving the mid nip, have an increased
filtration resistance at the reduced pressure, impeding rewetting.
The increased filtration resistance results in reduced water
rewetting during wet pressing.
[0074] In some instances, one or more components may be referred to
herein as "configured to," "configured by," "configurable to,"
"operable/operative to," "adapted/adaptable," "able to,"
"conformable/conformed to," etc. Those skilled in the art will
recognize that such terms (e.g. "configured to") generally
encompass active-state components and/or inactive-state components
and/or standby-state components, unless context requires
otherwise.
[0075] While particular aspects of the present subject matter
described herein have been shown and described, it will be apparent
to those skilled in the art that, based upon the teachings herein,
changes and modifications may be made without departing from the
subject matter described herein and its broader aspects and,
therefore, the appended claims are to encompass within their scope
all such changes and modifications as are within the true spirit
and scope of the subject matter described herein. It will be
understood by those within the art that, in general, terms used
herein, and especially in the appended claims (e.g., bodies of the
appended claims) are generally intended as "open" terms (e.g., the
term "including" should be interpreted as "including but not
limited to," the term "having" should be interpreted as "having at
least," the term "includes" should be interpreted as "includes but
is not limited to," etc.). It will be further understood by those
within the art that if a specific number of an introduced claim
recitation is intended, such an intent will be explicitly recited
in the claim, and in the absence of such recitation no such intent
is present. For example, as an aid to understanding, the following
appended claims may contain usage of the introductory phrases "at
least one" and "one or more" to introduce claim recitations.
However, the use of such phrases should not be construed to imply
that the introduction of a claim recitation by the indefinite
articles "a" or "an" limits any particular claim containing such
introduced claim recitation to claims containing only one such
recitation, even when the same claim includes the introductory
phrases "one or more" or "at least one" and indefinite articles
such as "a" or "an" (e.g., "a" and/or "an" should typically be
interpreted to mean "at least one" or "one or more"); the same
holds true for the use of definite articles used to introduce claim
recitations. In addition, even if a specific number of an
introduced claim recitation is explicitly recited, those skilled in
the art will recognize that such recitation should typically be
interpreted to mean at least the recited number (e.g., the bare
recitation of "two recitations," without other modifiers, typically
means at least two recitations, or two or more recitations).
Furthermore, in those instances where a convention analogous to "at
least one of A, B, and C, etc." is used, in general such a
construction is intended in the sense one having skill in the art
would understand the convention (e.g., "a system having at least
one of A, B, and C" would include but not be limited to systems
that have A alone, B alone, C alone, A and B together, A and C
together, B and C together, and/or A, B, and C together, etc.). In
those instances where a convention analogous to "at least one of A,
B, or C, etc." is used, in general such a construction is intended
in the sense one having skill in the art would understand the
convention (e.g., "a system having at least one of A, B, or C"
would include but not be limited to systems that have A alone, B
alone, C alone, A and B together, A and C together, B and C
together, and/or A, B, and C together, etc.). It will be further
understood by those within the art that typically a disjunctive
word and/or phrase presenting two or more alternative terms,
whether in the description, claims, or drawings, should be
understood to contemplate the possibilities of including one of the
terms, either of the terms, or both terms unless context dictates
otherwise. For example, the phrase "A or B" will be typically
understood to include the possibilities of "A" or "B" or "A and
B."
[0076] With respect to the appended claims, those skilled in the
art will appreciate that recited operations therein may generally
be performed in any order. Also, although various operational flows
are presented in a sequence(s), it should be understood that the
various operations may be performed in other orders than those
which are illustrated, or may be performed concurrently. Examples
of such alternate orderings may include overlapping, interleaved,
interrupted, reordered, incremental, preparatory, supplemental,
simultaneous, reverse, or other variant orderings, unless context
dictates otherwise. Furthermore, terms like "responsive to,"
"related to," or other past-tense adjectives are generally not
intended to exclude such variants, unless context dictates
otherwise.
BIBLIOGRAPHY & CITED REFERENCES
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[0078] Busker, L. H., and Cronin, D. C. (1984). The relative
importance of wet press variables in water removal, Pulp Pap. Can.
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of Wet Pressing of Paper Source: Royal Inst. Technol. (Stockholm),
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