U.S. patent application number 16/096839 was filed with the patent office on 2019-04-25 for dry processed cellulose fibers for papermaking.
The applicant listed for this patent is WestRock MWV, LLC. Invention is credited to Peter W. Hart, Nichole Kilgore, David E. Knox, Humphery J. Moynihan.
Application Number | 20190119854 16/096839 |
Document ID | / |
Family ID | 58745517 |
Filed Date | 2019-04-25 |
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United States Patent
Application |
20190119854 |
Kind Code |
A1 |
Knox; David E. ; et
al. |
April 25, 2019 |
DRY PROCESSED CELLULOSE FIBERS FOR PAPERMAKING
Abstract
Dry processing of cellulose fibers in an attritor mill produces
small cellulose particles with properties useful for increasing the
bulk of paperboard products. In contrast with the usual behaviour
of small particles, the dry attritor-processed particles exhibit a
further benefit of good drainage on a paper machine. Comparisons
are made for the modulus, smoothness, and density of paperboard
made with and without the dry-attrited cellulose particles.
Inventors: |
Knox; David E.; (Apex,
NC) ; Hart; Peter W.; (Atlanta, GA) ;
Moynihan; Humphery J.; (Covington, VA) ; Kilgore;
Nichole; (Richmond, VA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
WestRock MWV, LLC |
Atlanta |
GA |
US |
|
|
Family ID: |
58745517 |
Appl. No.: |
16/096839 |
Filed: |
May 15, 2017 |
PCT Filed: |
May 15, 2017 |
PCT NO: |
PCT/US2017/032648 |
371 Date: |
October 26, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62335935 |
May 13, 2016 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
D21H 17/25 20130101;
D21H 11/16 20130101; D21H 27/38 20130101; D21H 21/52 20130101; C08L
1/02 20130101; D21H 19/00 20130101; C08L 2205/18 20130101; D21H
27/30 20130101; D21H 21/22 20130101 |
International
Class: |
D21H 17/25 20060101
D21H017/25; D21H 21/52 20060101 D21H021/52; D21H 27/38 20060101
D21H027/38; D21H 11/16 20060101 D21H011/16; D21H 19/00 20060101
D21H019/00 |
Claims
1. A composition, comprising: a dry processed collection of
cellulose particles having a particle size distribution, wherein
95% of the particles are between 20 microns and 500 microns.
2. The composition of claim 1, wherein the cellulose particles show
no tendency to hydrate.
3. The composition of claim 1, wherein 90% of the particles are
between 25 and 350 microns.
4. The composition of claim 1, wherein 80% of the particles are
between 35 and 300 microns.
5. The composition of claim 1, where substantially all of the
particles are between 10 and 1000 microns.
6. The composition of claim 1, wherein the particle size
distribution is a unimodal distribution.
7. The composition of claim 1, wherein the cellulose particles are
softwood.
8. The composition of claim 7, wherein the cellulose particles are
unbleached.
9. The composition of claim 7, wherein the cellulose particles are
bleached.
10. The composition of claim 1, wherein the cellulose particles are
hardwood.
11. A specialized papermaking furnish, comprising: a cellulosic
composition comprising a dry processed collection of cellulose
particles having a particle size distribution, wherein 95% of the
particles are between 20 microns and 500 microns; and a
conventionally refined papermaking furnish; wherein the cellulosic
composition is used in an amount between 3 20 parts per 90 parts of
the conventionally refined papermaking furnish.
12. The specialized papermaking furnish of claim 11, wherein the
cellulosic composition is used in an amount between 5 15 parts per
90 parts of conventionally refined papermaking furnish.
13. The specialized papermaking furnish of claim 11, wherein the
cellulosic composition is used in an amount between 8 12 parts per
90 parts of conventionally refined papermaking furnish.
14. A raw stock comprising the composition of claim 1.
15. A base stock comprising the composition of claim 1.
16. A paperboard comprising the composition of claim 1.
17. A multi-ply paperboard having a plurality of plies, wherein at
least one ply comprises the composition of claim 1.
18. The multi-ply paperboard of claim 17, wherein at least one ply
does not contain the cellulose particles.
19. A process for making a cellulosic composition, comprising:
providing an attritor device; introducing dry cellulose fibers into
the attritor device, the dry cellulose fibers having an initial
size distribution; subjecting the dry cellulose fibers to
communition in the attritor device to create smaller cellulose
particles; and collecting the cellulose particles that are below a
specific size.
20. The process of claim 19, wherein the mean particle size of the
cellulose fibers following communition is not more than 50% that of
the cellulose fibers when introduced to the attritor device.
21. The process of claim 19, wherein the specific size is 1000
microns.
22. The process of claim 19, wherein the collected cellulose
particles have a particle size distribution with 95% of the
particles between 20 microns and 500 microns.
23. The process of claim 19, further comprising the addition of the
collected cellulose particles in an amount between 3-20 parts to 90
parts of a conventionally papermaking furnish to create a
specialized papermaking furnish.
24. The process of claim 23, further comprising forming the
specialized papermaking furnish into a web.
25. The process of claim 24, wherein the web comprises at least two
plies.
26. The process of claim 25, wherein at least one ply does not
contain the cellulose particles.
27. The process of claim 24, further comprising coating the web to
improve its smoothness.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] This application is a National Phase application of PCT
Application PCT/US2017/032648, filed May 15, 2017, which claims the
benefit of U.S. Provisional Patent Application No. 62/335,935,
filed May 13, 2016, both of which are incorporated herein by
reference in their entirety.
TECHNICAL FIELD
[0002] This disclosure relates to a method to treat cellulose
fibers by dry grinding (attrition) to yield cellulose materials
suitable for producing desired attributes such as lower density in
paperboard products.
BACKGROUND
[0003] This disclosure relates to cellulose particles produced by
dry attrition. The cellulose particles may be incorporated into
various products. Such products may include paperboard. Paperboard
incorporating the cellulose particles is expected to exhibit
reduced density.
[0004] Treatment of cellulose fibers is usually done by wet
processing methods. Wet processing may have certain drawbacks when
processing cellulose. For example, excessive wet refining of
cellulose pulp may lead to poor drainage of the pulp, which is
undesirable on a paper machine.
[0005] In the art of paper making, particularly for the manufacture
of paperboard (e.g. heavier paper grades in the caliper range from
about 8 pts to about 40 pts (0.008-0.040 inches), it is often
desired to make a particular grade of paperboard while minimizing
the amount of cellulose fiber, a major cost component of the
paperboard. Methods are sought which can lower the product density
for example by reduced calendaring or dry finishing, or using
specialized coatings such as described in U.S. Pat. Nos. 8,142,887;
8,916,636; and 8,349,443. The current invention offers another
method for lowering paperboard density.
SUMMARY
[0006] The general purpose of the invention is the utilization in a
paperboard product of a certain amount of fine cellulose particles
that have been produced from dry cellulose fiber, which are
produced with dry processing.
[0007] In one embodiment, a composition of the paperboard is
disclosed which includes a dry processed collection of cellulose
particles having a particle size distribution, wherein 95% of the
particles are between 20 microns and 500 microns. In certain
embodiments, the cellulose particles show little tendency to
hydrate. In certain embodiments, 90% of the particles are between
25 and 350 microns.
[0008] In another embodiment, a process is disclosed for making a
cellulosic composition, the process including providing an attritor
device; introducing dry cellulose fibers into the attritor device,
the dry cellulose fibers having an initial size distribution;
subjecting the dry cellulose fibers to communition in the attritor
device to create smaller cellulose particles; and collecting the
cellulose particles that are below a specific size. In certain
embodiments, the specific size is 1000 microns.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 illustrates a dry attritor device producing a fine
cellulose particles from a dry cellulose feed;
[0010] FIG. 2 illustrates a paper machine using the fine cellulose
particles produced using the dry attritor device of FIG. 1;
[0011] FIG. 3 compares median particle sizes achieved using various
specific energy inputs for three different types of grinding
including an attritor;
[0012] FIG. 4 is a graph of hardwood mean particle diameter at
varying amounts of energy input;
[0013] FIG. 5 is a graph comparing particle size distributions for
control hardwood and dry-attrited hardwood;
[0014] FIG. 6 is a graph comparing particle size distributions for
control softwood and dry-attrited softwood;
[0015] FIG. 7 is a graph comparing modulus vs density for softwood
pulp with and without addition of dry-attrited pulp;
[0016] FIG. 8 is a graph comparing Sheffield Smoothness vs density
for softwood pulp with and without addition of dry-attrited
pulp;
[0017] FIG. 9 shows cross-sectional micrographs of paperboard
sheets made with and without addition of dry-attrited pulp;
[0018] FIG. 10 is a graph comparing Young's Modulus vs density for
bleached softwood pulp with and without addition of dry-attrited
bleached softwood pulp;
[0019] FIG. 11 is a graph comparing Young's Modulus vs density for
bleached hardwood pulp with and without addition of dry-attrited
bleached hardwood pulp;
[0020] FIG. 12 is a graph comparing Young's Modulus vs density for
bleached hardwood pulp with and without addition of dry-attrited
coated bleached hardwood pulp;
[0021] FIG. 13 is a graph comparing Young's Modulus vs density for
bleached hardwood pulp with and without addition of dry-attrited
unbleached softwood pulp;
[0022] FIG. 14 is a graph comparing Young's Modulus vs density for
unbleached softwood pulp with and without addition of dry-attrited
coated unbleached softwood pulp;
[0023] FIG. 15 is a graph comparing Young's Modulus vs density for
OCC pulp with and without addition of dry-attrited semi-chemical
hardwood pulp;
[0024] FIG. 16 is a graph comparing Young's Modulus vs density for
bleached softwood pulp with and without addition of dry-attrited
bleached softwood pulp;
[0025] FIG. 17 is a graph comparing Young's Modulus vs density for
bleached hardwood pulp with and without addition of dry-attrited
bleached hardwood pulp;
[0026] FIG. 18 is a graph comparing Young's Modulus vs density for
bleached hardwood pulp with and without addition of dry-attrited
coated bleached hardwood pulp;
[0027] FIG. 19 is a graph comparing Young's Modulus vs density for
bleached hardwood pulp with and without addition of dry-attrited
unbleached softwood pulp;
[0028] FIG. 20 is a graph comparing Young's Modulus vs density for
unbleached softwood pulp with and without addition of dry-attrited
coated unbleached softwood pulp;
[0029] FIG. 21 is a graph comparing Young's Modulus vs density for
OCC pulp with and without addition of dry-attrited semi-chemical
hardwood pulp;
[0030] FIG. 22 is a graph comparing Tensile Index vs density for
bleached softwood pulp with and without addition of dry-attrited
bleached softwood pulp;
[0031] FIG. 23 is a graph comparing Tensile Index vs density for
bleached hardwood pulp with and without addition of dry-attrited
bleached hardwood pulp;
[0032] FIG. 24 is a graph comparing Tensile Index vs density for
bleached hardwood pulp with and without addition of dry-attrited
coated bleached hardwood pulp;
[0033] FIG. 25 is a graph comparing Tensile Index vs density for
bleached hardwood pulp with and without addition of dry-attrited
unbleached softwood pulp;
[0034] FIG. 26 is a graph comparing Tensile Index vs density for
bleached softwood pulp with and without addition of dry-attrited
bleached softwood pulp;
[0035] FIG. 27 is a graph comparing Tensile Index vs density for
bleached hardwood pulp with and without addition of dry-attrited
bleached hardwood pulp;
[0036] FIG. 28 is a graph comparing Tensile Index vs density for
bleached hardwood pulp with and without addition of dry-attrited
coated bleached hardwood pulp;
[0037] FIG. 29 is a graph comparing Tensile Index vs density for
bleached hardwood pulp with and without addition of dry-attrited
unbleached softwood pulp;
[0038] FIG. 30 is a graph comparing Tensile Index vs density for
unbleached softwood pulp with and without addition of dry-attrited
coated unbleached softwood pulp;
[0039] FIG. 31 is a graph comparing Tensile Index vs density for
OCC pulp with and without addition of dry-attrited semi-chemical
hardwood pulp;
[0040] FIG. 32 is a graph comparing Sheffield Smoothness vs density
for bleached softwood pulp with and without addition of
dry-attrited bleached softwood pulp;
[0041] FIG. 33 is a graph comparing Sheffield Smoothness vs density
for bleached hardwood pulp with and without addition of
dry-attrited bleached hardwood pulp;
[0042] FIG. 34 is a graph comparing Sheffield Smoothness vs density
for unbleached softwood pulp with and without addition of
dry-attrited unbleached softwood pulp;
[0043] FIG. 35 is a graph comparing Sheffield Smoothness vs density
for unbleached softwood pulp with and without addition of
dry-attrited coated unbleached softwood pulp; and
[0044] FIG. 36 is a graph comparing Sheffield Smoothness vs density
for OCC pulp with and without addition of dry-attrited
semi-chemical hardwood pulp.
DETAILED DESCRIPTION OF EMBODIMENTS
[0045] FIG. 1 is a simplified drawing of an attritor 110 for dry
processing of cellulose pulp. This is one of several methods for
dry processing, and others exist including vibratory ball mills and
conventional ball mills. The attritor includes a shell or housing
120 with an internal volume in which the processing takes place. If
continuous mode processing is used, cellulose fibers (not shown)
are fed into attritor 110 by way of inlet conduit 160 and removed
from the attritor by outlet conduit 170. A screen or other
classification device 180 may be used to permit removal of only
particles below a desired size. One or more flow control valves 190
may be used. Batch processing is also possible in which case the
process is discontinuous. An impeller shaft 130 rotates at high
speed within the housing 120. Attached to shaft 130 are rods 140
that spin with the shaft and drive a large number of attritor media
150 such as ceramic or metal balls. The attritor media 150 collide
with each other, with arms 140, and with the inner wall of housing
120. The cellulose fibers in the attritor are impacted by the
collisions between the media 150, rods 140, and attritor wall. This
results in the cellulose fibers being comminuted (made smaller)
during their residence time in the attritor.
[0046] Attritor 110 may be provided in any desired volume, with
appropriately sized shaft 120 and rods 130, and driven by a
suitably powerful motive force such as an electric motor. If
desired, provision may be made for cooling the attritor or for
introducing other materials besides cellulose fibers, for example
gases, additives, catalysts, etc. Multiple attritors may be used in
parallel and/or in series.
[0047] Several of the key variables in the operation of an attritor
include impeller shaft rotation speeds, potential alteration of the
rod geometry in terms of size and angle, ball size during
attrition, temperature, and energy input. Many attritors are also
equipped with temperature control, but for attrition of cellulose
here the work done by the attritor raised the temperature the
system without any attempt to thermostat the system. The attritor
110 used in this work was made by Union Process of Akron, Ohio.
[0048] Other methods and equipment for dry processing of cellulose
particles may be used successfully with the present invention.
[0049] As a non-limiting example of their usefulness, dry-attrited
cellulose particles produced by attritor 110 of FIG. 1 may be
included in the pulp feed to a paper machine such as the device
shown in FIG. 2. A forming wire 210 in the form of an endless belt
passes over a breast roll 215 that rotates proximate to a headbox
220. The headbox provides a fiber slurry (that may include attrited
cellulose particles) in water with a fairly low consistency (for
example, about 0.5% solids) that passes onto the moving forming
wire 210. During a first distance 230 water drains from the slurry
and through the forming wire 210, forming a web 250 of wet fibers.
The slurry during distance 230 may yet have a wet appearance as
there is free water on its surface. At some point as drainage
continues the free water may disappear from the surface, and over
distance 232, water may continue to drain although the surface
appears free from water. Instead of, or in addition to, introducing
the dry-attrited cellulose particles in the slurry fed to the
headbox, the dry-attrited cellulose particles could be added at a
secondary headbox, size press, coater, and other locations on the
paper machine.
[0050] Eventually the web is carried by a transfer felt or press
felt through one or more pressing devices such as press rolls 240
that help to further dewatering the web, usually with the
application of pressure, vacuum, and sometimes heat. After
pressing, the still relatively wet web 250 is dried, for example
using dryer or drying sections 260, 262 to produce a dry web ("raw
stock") 270 which may then be run through a size press 280 that
applies a surface sizing to produce a sized "base stock" 295 which
may then be run through additional dryer sections 298 to produced
dry base stock 299 that continues on for further processing (not
shown).
[0051] Use on paper machines of cellulose particles wet-processed
to the micro and nano-size range has been reported to cause poorer
drainage, higher board density, and material handling problems.
This invention focuses on the use of dry-processed cellulose. The
general process of dry processing (in particular, attrition) and
the initial stages of the paper machine having been outlined at a
high level in the preceding description and with FIGS. 1-2, we now
turn to more specific details of the present invention.
[0052] The efficiency of attritors is indicated in work that was
originally published by Union Process which is shown on the graph
in FIG. 3. As seen in the graph, at a given specific energy input
(kilowatt-hours per ton of material processed) an attritor can
produce smaller particle sizes (310) than conventional ball mills
(320) or vibratory ball mills (330).
[0053] Attritors may be run in batch, semi-batch, or continuous
modes depending upon the applications. For this work, cellulose
particles were prepared in a semi-continuous mode. The attritor
media 150 were 3/8'' diameter ceramic balls. Pulp flakes of
3/4''.times.3/4'' size were added to the attritor and processed for
a given period of time, usually 15 minutes. The resulting cellulose
powder was sieved through a bottom opening in the attritor. The
cellulose powder was weighed and a corresponding make-up amount of
pulp flakes were replenished into the attritor.
[0054] Work was conducted essentially at 100% (nominal) solids,
that is, with the pulp dry. Due to the energy imparted to the pulp
during the attrition process, the attritor would generally heat to
above 240 F, so it was anticipated that except for very tenaciously
bound water, all the residual moisture would be driven off.
[0055] FIG. 4 shows a graph of the correlation between energy input
in the attritor and the particle size reduction of a commercial
once-dried hardwood market pulp. No dispersants were added during
measurement of the particle size distribution, so agglomeration
tendencies might be greater than is sometimes seen in protocols
where dispersants are added prior to measurement. Particle sizes
were measured by a Microtrac particle size analyzer.
[0056] A relatively good correlation was found over the particle
size range shown. There is an obvious trend that higher energy
inputs result in smaller particle sizes. Despite the results in
FIG. 4 showing some deviation from the trend line in these
semi-continuous experiments, it is likely that one may be able to
tailor the energy inputs to a desired particle size and then use
that particle for building a paperboard product suitable for
various paper machine dynamics and product requirements.
[0057] FIG. 5 shows particle size distributions for standard
hardwood (510) and semi-continuous attritor hardwood (520) at an
energy input of approximately 70 hpdt (horsepower-days per ton).
All samples were diluted to an approximate 1% solution then tested
in a Microtrac particle size analyzer. Each sample was first
sonicated for 1 minute prior to introduction into the measurement
cell, and no dispersant was used.
[0058] There was a significant reduction in the amounts of long
fiber. Correspondingly the particle size distribution which is
bimodal for the control pulp 510 is unimodal for the attritor pulp
520. The presence of a large peak around 100.mu. might possibly be
explained by association factors during measurement solution. At
any rate, there is a significant reduction in the particle size of
the hardwood upon attrition as demonstrated in the graph.
Substantially all of the attritor pulp falls between 10 and 1000
microns. About 95% of the attritor pulp is between (approximately)
13 and 990 microns, about 90% is between 18 and 750 microns, and
about 80% between 24 and 600 microns.
[0059] The remaining description focuses on pine fiber (softwood)
size reduction and the use of attritor-based pine in handsheet
samples. For softwood, a typical particle size distribution
reduction curve is shown in FIG. 6 for standard softwood (610) and
semi-continuous attritor softwood (620) at an energy input of about
100 hpdt. The results here show a large reduction in high end
particle sizes and a shift towards the lower end (ca. 100.mu.)
range. Correspondingly the particle size distribution which is
bimodal for the control pulp 610 is unimodal for the attritor pulp
620. Substantially all of the attritor pulp falls between 10 and
1000 microns. About 95% of the attritor pulp is between
(approximately) 20 and 500 microns, about 90% is between 25 and 350
microns, and about 80% between 35 and 300 microns.
[0060] The use of catalysts appears to have a positive impact on
size reduction of pine fiber as shown below in Table 1. For samples
1-3 without catalyst, increasing the energy reduced the particle
size distribution as measured by the Microtrac in terms of Mean
Diameter. For sample 4, catalyst "A" was used (citric acid) and for
sample 5, catalyst "B" was used (sodium hypophosphite). For samples
6 and 7, a combination of these two catalysts was used to explore
whether a further reduction in particle size could be achieved. A
comparison of sample 3 (no catalyst) with samples 4, 5, and 6
(catalyst) shows that use of catalysts is quite effective in terms
of particle size reduction at essentially equivalent energy
inputs.
TABLE-US-00001 TABLE 1 Particle Size Analysis of Softwood Samples
with and without catalyst Energy Particle Size Sample Catalyst
(HPDT) (Mean Diameter in .mu.) 1 0 0 443 2 0 57 375 3 0 85 268 4 A
78 84 5 B 79 114 6 A + B 82 69 7 A + B 120+ `Aerosol`
[0061] It was possible to make exceptionally finely divided
softwood based attritor pulp as seen with samples 6 and 7. Sample 7
was similar to sample 6, except additional energy was applied by
increasing the processing time. With sample 7 the material became
small enough to be electrically charged and form an aerosol (dry
dust). If the cellulose is attrited to such a degree, care should
be taken in case it might form an explosive dust in which case
proper equipment grounding and suitable dust collection devices
should be used.
[0062] An attempt was made to further develop the attritor-based
fibers using refining, but to process the material in a refiner
would require it being hydrated and this was not achieved as the
particles had no propensity to hydrate. It is speculated that being
once-dried fibers, and in conjunction with attritor processing,
perhaps the fibers have fully hornified. The attritor pulp was
therefore simply used in the as-is state as an additive to an
amount of long fiber fraction softwood pulp.
[0063] Table 2 shows results where dry-attrited pulp was added to
four base softwood pulps made with varying degrees of refining
(refining levels 0-3), as reflected in their Canadian Standard
Freeness (CSF) values. The base pulps had CSF values ranging from
743 to 570 achieved by reducing the gap between the refiner plates.
The added dry-attrited pulp was pine that was treated in the dry
attritor at approximately 85 horsepower-days per ton without any
catalyst.
[0064] Each row in Table 2 shows the sample name, the CSF of the
base softwood pulp, and the density, modulus, and Sheffield
Smoothness of handsheets. Each group of three data points includes
a row with no added attritor pulp, a row with 10% added attritor
pulp, and a row with 20% added attritor pulp. In each group, as
attritor pulp percent increased, the density and modulus decreased,
while the Sheffield Smoothness increased. The handsheets were not
coated and therefore might correspond approximately to an uncoated,
partially pressed stage on a paper machine.
TABLE-US-00002 TABLE 2 Data for Softwood Pulp and Handsheets
Density Modulus Condition CSF (#/mil/3000 ft.sup.2) (GPa) Sheffield
refining level (RL) 743 8.51 3.03 370 0 +10% Attritor Pulp 754 7.98
2.42 388 20% Attritor Pulp 749 7.54 2.24 396 refining level (RL)
671 9.56 4.67 315 1 RL 1 + 10% AP 677 8.62 4.16 379 RL 1 + 20% AP
698 7.87 3.37 395 refining level (RL) 624 9.94 5.29 280 2 RL 2 +
10% AP 648 7.61 4.23 386 RL 2 + 20% AP 652 8.01 3.44 399 refining
level 570 10.29 5.75 271 (RL)3 RL 3 + 10% AP 590 8.58 4.97 365 RL 3
+ 20% AP 620 8.21 4.14 390
[0065] FIG. 7 shows the graph of modulus vs. density for the
handsheets of Table 2. Each curve represents a series of four data
points from Table 2, with the lowest point on each line
corresponding to refining level RL=0, and the highest point
corresponding with refining level RL=3. The curve (710) to the
right is for no addition of dry-attrited pulp. The middle curve
(720) is for 10% addition of dry-attrited pulp, and the left curve
(730 is for 20% addition of dry-attrited pulp.
[0066] Addition of dry-attrited pulp is seen to cause a decrease in
modulus, which is not surprising in the context of the decrease in
density. As seen in FIG. 7, additional refining of the base pulp
increases the modulus, so that it should be possible to regain some
of the lost modulus by such additional refining.
[0067] The data here are for in-plane modulus, however it is
expected that out-of-plane modulus should change as well.
Therefore, over the range of 0% to 20%, the use of attritor pulps
can lower density at a given modulus, provided the modulus
decreases do not impact product quality at an attritor pulp level
of about 20%. Thus, if a product can withstand a decrease in
modulus of about 20%, then addition of 10% dry-attrited pulp could
be tolerated. If a modulus of about 4.5 Gpa is satisfactory, 10%
addition of dry-attrited pulp with added base pulp refining may be
able to achieve lower bulk and perhaps 10% reduction in fiber
usage. Thus, it might be possible to substitute shorter fiber
attritor-based softwood as a furnish in place of hardwood in
certain circumstances. While the testing here was done for lab
handsheets only, the fact that the CSF actually goes up for
attritor-containing pulps offers the intriguing option of putting
small particle size pulps into the sheets without impacting
drainage.
[0068] Perhaps not surprisingly, as more dry-attrited pulp is added
to the sheet and the density is decreased, the surface features of
the handsheets from the board become rougher. In FIG. 8 the
Sheffield Smoothness vs density is shown for the same handsheets
depicted in FIG. 7. The curve (810) to the lower right is for no
addition of dry-attrited pulp. The middle curve (820) is for 10%
addition of dry-attrited pulp, and the upper curve (830 is for 20%
addition of dry-attrited pulp. These data are for raw sheets with
no attempt at coating or calendaring, and therefore are only lab
representations of the potential impact of adding dry-attrited pulp
to the furnish. Since surface properties are a prime qualifier for
many board products, an additional top ply or coating(s) may be
required to regain smoothness.
[0069] FIG. 9 shows scanning electron microscope (SEM) micrographs
of handsheet cross-sections without dry-attrited pulp and with 20%
dry-attrited pulp. All SEM's are shown with a 100 micron scale bar.
It is clear that the sheets with 20% dry-attrited pulp are
noticeably thicker (less dense) than control sheets with only
normal pulp. Additional samples were prepared as indicated in Table
3 using additional base sheet pulp and attritor-dried pulp
combinations, including bleached softwood and hardwood, unbleached
softwood, and OCC base sheet pulps, along with bleached softwood
and hardwood, coated bleached hardwood, coated and uncoated
unbleached softwood, and semi-chemical hardwood attritor-treated
dry pulp. Improvements in modulus and tensile strength were
demonstrated with 10% and 20% addition rates of the
attritor-treated pulps, as noted. Significant size reduction of the
attritor-treated pulp was seen, as measured by mean particle size,
with the mean particle size of the fibers following communition in
the attritor being not more than 50% that of the fibers when first
introduced to the attritor device The attritor-treated pulp much
less hydrophilic than
TABLE-US-00003 TABLE 3 Base Sheet and Attritor Dried Pulp Type
Combinations Attritor Dried Pulp Type Once-dried Once-dried Coated
Once-dried Coated Semi- Bleached Bleached Bleached Unbleached
Unbleached Chemical Softwood Hardwood Hardwood Softwood Softwood
Hardwood Mean particle size (.mu.m) Before 189 145-148 145 385 511
152 attrition After 91 58-77 56 88 71 62 attrition Base Sheet Pulp
Type Bleached softwood, once-dried FIG. 10 market pulp FIG. 16 FIG.
22 FIG. 26 FIG. 32 Bleached hardwood, never dried FIG. 11 FIG. 12
FIG. 13 FIG. 17 FIG. 18 FIG. 19 FIG. 23 FIG. 24 FIG. 25 FIG. 27
FIG. 28 FIG. 29 FIG. 33 Unbleached softwood, never dried FIG. 34
FIG. 14 FIG. 20 FIG. 30 FIG. 35 OCC FIG. 15 FIG. 21 FIG. 31 FIG.
36
normal pulp, and did not negatively impact pulp drainage
properties, as indicated by measurement of Canadian Standard
Freeness.
[0070] The impact of the addition of attritor-treated dried pulp on
Young's Modulus measured using non-destructive testing for the
Table 3 samples is shown in FIGS. 10-15. The tests were conducted
with protocols similar to those outlined in ASTM E494.
[0071] The impact of the addition of attritor-treated dried pulp on
Young's Modulus measured using destructive testing for the Table 3
samples is shown in FIGS. 16-21. The tests were conducted according
to protocols outlined in TAPPI T494.
[0072] The impact of the addition of attritor-treated dried pulp on
Tensile Index measured using non-destructive testing for the Table
3 samples is shown in FIGS. 22-25. The tests were conducted with
protocols similar to those outlined in ASTM E494.
[0073] The impact of the addition of attritor-treated dried pulp on
Tensile Index measured using destructive testing for the Table 3
samples is shown in FIGS. 26-31. The tests were conducted according
to protocols outlined in TAPPI T494.
[0074] The impact of the addition of attritor-treated dried pulp on
Sheffield Smoothness Tensile Index for the Table 3 samples is shown
in FIGS. 32-36.
[0075] Other combinations of base sheet pulp types and
attritor-treated dried pulp would be expected to show improvements
in modulus and tensile strength.
[0076] In summary, dry processing of fiber to produce
micro-cellulose gives considerably lower sheet density and modulus.
This can be compensated for by refining the base fiber furnish more
aggressively to get higher density and higher modulus sheets.
Balancing these effects offers an opportunity to potentially use
less fiber in paperboard depending upon product needs. The lower
density sheets appear to be particularly sensitive to a roughening
effect as noticed by a considerable increase in Sheffield
Smoothness with no impact of refining the main fibers on the
smoothness properties of the sheet. Such lower density sheets
however might be utilized as a base ply in a multi-ply product or
might be processed (for example with one or more coatings) to
achieve desired product smoothness.
[0077] The examples given above involve the use of dry-attrited
cellulose particles in a papermaking operation. However, the use of
the dry-attrited cellulose particles is not limited to
papermaking.
[0078] Once given the above disclosure, many other features,
modifications or improvements will become apparent to the skilled
artisan. Such features, modifications or improvements are,
therefore, considered to be a part of this invention, the scope of
which is to be determined by the following claims.
[0079] While preferred embodiments of the invention have been
described and illustrated, it should be apparent that many
modifications to the embodiments and implementations of the
invention can be made without departing from the spirit or scope of
the invention. It is to be understood therefore that the invention
is not limited to the particular embodiments disclosed (or apparent
from the disclosure) herein, but only limited by the claims
appended hereto.
* * * * *