Note: Descriptions are shown in the official language in which they were submitted.
CA 02581898 2007-03-15
METHOD FOR MAKING A LOW DENSITY MULTI-PLY PAPERBOARD WITH
HIGH INTERNAL BOND STRENGTH
FIELD
The present application relates to a method for increasing the bond strength
in a
multi-ply paperboard that has high crosslinked cellulose fiber present in at
least one of
the plies.
SUMMARY
This application is directed to a method improving the internal bond strength
of
paperboard with greater than 25 percent crosslinked fiber in at least one ply.
In the
method, additives are added to the slurry in various combinations and order
while
maintaining the ionic demand of the slurry at less than zero. Paperboard with
high ZDT,
Scott Bond and Taber Stiffness is obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a schematic diagram of the pilot line.
DESCRIPTION
In single or multi-ply paperboard where the inner plies contain greater than
approximately 25 percent crosslinked cellulose fiber the density of the
stratum will
drop below 0.4 g/cc. As a result, the internal bond strength can drop so low
as to not
only be well below levels required for converting the paperboard into
packaging
products but also below the level where conventional methods of increasing the
internal
strength cannot provide enough increase to meet minimum levels needed for
converting. This effect can occur either in the entire structure or some
fraction within
the structure. The present application provides a method for increasing the
internal
bond of low density paperboard back into the range which is useable for
converting.
I
CA 02581898 2007-03-15
In this application, the use of high concentrations of wet end additives have
been demonstrated while producing low density paperboard.
A distinguishing characteristic of the present application is that at least
one ply of
the paperboard, whether a single-ply or a multiple-ply structure, contains
crosslinked
cellulose fibers and strength enhancing additives such as mechanically refined
fiber,
anionic and cationic starches and other additives to offset the board strength
lost by
adding the crosslinked cellulosic fibers. The crosslinked cellulosic fibers
increase the
bulk density of the insulating paperboard characteristics of the board. The
paperboard
also contains chemical pulp fibers. As defined herein, chemical pulp fibers
useable in the
present application are derived primarily from wood pulp. Suitable wood pulp
fibers for
use with the application can be obtained from well-known chemical processes
such as the
kraft and sulfite processes, with or without subsequent bleaching. Softwoods
and
hardwoods can be used. Details of the selection of wood pulp fibers are well
known to
those skilled in the art. For example, suitable cellulosic fibers produced
from southern
pine that are useable in the present application are available froma number of
companies
including Weyerhaeuser Company under the designations C-Pine, Chinook, CF416,
FR416, and NB416. A bleached Kraft Douglas Fir pulp (D. Fir), and Grande
Prairie
Softwood, all manufactured by Weyerhaeuser are examples of northern softwoods
that
can be used. Mercerized fibers such as HPZ and mercerized flash dried fibers
such as
HPZ III, both manufactured by Buckeye Technologies, Memphis TN, and Porosinier-
J-
HP available from Rayonier Performance Fibers Division, Jessup, GA are also
suitable
for use in the present application when used with crosslinked cellulose
fibers. Other non
crosslinked cellulose fibers include chemithermomechanical pulp fibers (CTMP),
bleached chemithermomechanical pulp fibers (BCTMP), thermomechanical pulp
fibers
(TMP), refiner groundwood pulp fibers, groundwood pulp fibers, TMP
(thermomechanical pulp) made by Weyerhaeuser, Federal Way, WA, and CTMP
( chemi-thermomechanical pulp) obtained from NORPAC, Longview, WA, sold as a
CTMP NORPAC Newsprint Grade, jet dried cellulosic fibers and treated jet dried
cellulosic fibers manufactured by the Weyerhaeuser Company by the method
described
in U.S. Application No.10/923,447 filed August 20, 2004. These fibers are
twisted kinked
2
CA 02581898 2007-03-15
and curled. Additional fibers include flash dried and treated flash dried
fibers as
described in U.S. 6,837,970,
Suitable crosslinking agents for making crosslinked fibers include carboxylic
acid
crosslinking agents such as polycarboxylic acids. Polycarboxylic acid
crosslinking agents
(e.g., citric acid, propane tricarboxylic acid, and butane tetracarboxylic
acid) and catalysts
are described in U.S. Patent Nos. 3,526,048; 4,820,307; 4,936,865; 4,975,209;
and
5,221,285 The use of C2-C9 polycarboxylic acids that contain at least three
carboxyl
groups (e.g., citric acid and oxydisuccinic acid) as crosslinking agents is
described in
U.S. Patent Nos. 5,137,537; 5,183,707; 5,190,563; 5,562,740; and 5,873,979.
Polymeric polycarboxylic acids are also suitable crosslinking agents for
making
crosslinked fibers. These include polymeric polycarboxylic acid crosslinking
agents are
described in U.S. Patent Nos. 4,391,878; 4,420,368; 4,431,481; 5,049,235;
5,160,789;
5,442,899; 5,698,074; 5,496,476; 5,496,477; 5,728,771; 5,705,475; and
5,981,739.
Polyacrylic acid and related copolymers as crosslinking agents are described
U.S. Patent
Nos. 5,549,791 and 5,998,511. Polymaleic acid crosslinking agents are
described in U.S.
Patent No. 5,998,511 and U.S. 6,582,553. CHB405, a citric acid crosslinked
cellulose
fiber and CHB505, a polyacrylic acid crosslinked cellulose, both commercially
available
from Weyerhaeuser Company, Federal Way, WA were used in this work.
In single or multi-ply paperboard construction a mixture of wood pulp fibers
and
crosslinked cellulose fibers are used. In one embodiment the crosslinked
cellulosic fibers
are present in at least one layer at a level of 25 to 80 percent by total
fiber weight of the
ply. In another embodiment the crosslinked fibers are present at a level of 40
to 75
percent by total fiber weight of the layer and in yet another embodiment they
are present
at a level of 50 to 70 percent by total fiber weight of the layer.
3
CA 02581898 2007-03-15
Ionic Demand Balance
The technology relies on the ability to balance the ionic demand in the wet
end of
the paper machine such that 1) anionic polymeric materials can be retained on
the fibers
and fines without excess remaining in the water system, 2) the fibers and
system do not
pass through the zero charge point which destabilizes retention and drainage
3) since pulp
fibers are anionic, some cationic material can be added, however, adding too
much
cationic material without balancing the excess anionic demand will either
cause the fibers
to flocculate reducing formation and/or cause the drainage to drop, impacting
the
runnability.
Each of the components used in the paperboard containing crosslinked fiber in
this disclosure has a specific charge density typically measured by ionic
demand titration.
A Mutek PCD -Titrator was used for the particle charge titration coupled with
the PCD
02 Particle Charge Detector for measuring the ionic demand of the component or
fiber
fumish. The method was performed according to a procedure from A.E. Staley
Manufacturing, a subsidiary of Tate and Lyle, Decatur, IL The method is as
follows.
1. Turn the Mutek on using the power switch on the back of the instrument.
2. Place 10 mL of a well mixed sample in the sample vessel. Insert the plunger
and
washer into the vessel. The sample consistency should be no more than 0.83.
Thick stock
samples should be diluted.
3. With the instrument turned on, the plunger should move up and down and a mV
potential should be displayed. The sign of the potential (+ or -) indicates
whether the
sample is cationic (+) or anionic (-).
4. Titrate the sample with the appropriate titrant until the mV potential
reads 0 mV
(PoIyDADMAC is the. cationic polymer and is used to titrate anionic samples;
PVSK or
PESNa are the anionic polymers used to titrate the cationic samples). A buret
or syringe
can be used to deliver the titrant to the sample. Titration should not be
conducted with
more than 4 mL of titrant since higher volumes will give inaccurate
measurements. If the
sample requires more than 4 mL of titrant, the sample should be diluted or
more
concentrated titrant should be used.
3o 5. Record the amount of titrant used to titrate the sample. To calculate
the demand of
the system, use the following equation:
4
CA 02581898 2007-03-15
"Ionic Demand" (ueq/L) (mL titrant) x (% titrant dilution) x (sample
dilution)
Ionic Demand refers to the amount of anionic or cationic charge required to
neutralize the counter ion charge and is expressed in meq/g or ueq/kg. For
example, an
additive with an ionic demand of +2.2 meq/g has an anionic demand of 2.2
meq/g; an
additive with an ionic demand of -1.8 meq/g has a cationic demand of 1.8
meq/g.
Specific components whose ionic demand was measured by the Mutek method
are noted in Table 1, other component values are from suppliers.
TABLE I
Component Ionic Demand
Fully bleached Softwood kraft pulp - -0.015 meq/g total
Fully bleached Softwood kraft pulp -0.0015 meq/g available
CHB405 - -0.43 meq/g total
CHB405 -0.015 meq/g available
Kymene 557H - +2.2 meq/g
Hercobond 2000 ~ -1.8 meq/g
STA-LOK 300 ---+-0.3
RediBOND 3050 -0.19 meq/g
RediBOND 2038 - +0.24 meq/g
STA-LOK 330 - +0.41 meq/g
PPD M-5133 -+ 16 meq/g
GALACTASOL SP813D - + 2.3 meq/g
With reference to the table, the difference between the total and available
ionic
demand represents the amount of charge that is internal to the fiber that is
not accessible
to polymers of molecular weight above 300,000 g/mole. For papermaking, the
available
5
CA 02581898 2007-03-15
ionic demand is more representative of the results obtained in practice than
the total ionic
demand.
The situation is further complicated in a paper machine wet-end where dilution
water from outside sources and/or wash water from pulp mill bleaching stages
contain
ionic materials, (both dissolved and dispersed), is used to control
consistency of the pulp
slurry. In integrated mills where excess ionic materials are present,
materials added to the
pulp slurry to increase internal bond strength can be consumed by the excess
ionic
materials. Also, the available ionic sites on pulp will also depend on how
much refining
has been done and on the basic fiber morphology, i.e. the smaller the fiber or
partial fiber
l0 the higher available surface area, and therefore the higher available ionic
demand.
In general it may be stated that the fiber slurry is anionic to start with and
should
remain anionic through the paper making process i.e. the ionic demand of the
slurry
should less than zero.
Mechanically refined fiber can be added to the slurry to increase the strength
of the
paperboard. In one embodiment the mecharrically refined fiber has a Canadian
Standard
Freeness of less than 125 mL CSF, a curl index of 1/3 or less of the unrefined
fiber and a
kink angle of 1/2 or less of the unrefined fiber.
In one embodiment mechanically refined fiber is added to the slurry followed
by
the addition of an anionic starch and then followed by addition of a cationic
fixative.
2o After each addition step the slurry ionic demand is less than zero. The
slurry is deposited
on a foraminous support, dewatered forming a web and dried to form a
paperboard.
In one embodiment the total starch level on dry fiber is from 50 to 120 lb/t.
In
another embodiment the total starch level on dry fiber is from 60 to 100 lb/t.
In yet
another embodiment the total stach level is 80 to 90 lb/t.
Cationic fixatives such as cationic starch (e.g. STA-LOK 300, STA-LOK 330
and RediBOND 2038) have a low anionic demand i.e. less than 1 meq/g. Other
cationic
additives such as Kymene 557H have a high anionic demand (+2.2 meq/g). In one
embodiment the cationic fixative has an anionic demand of greater than zero
but less than
one meq/g. In another embodiment the cationic fixative has an anionic demand
of from 1
meq/g to 10 meq/g.
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CA 02581898 2007-03-15
The paperboard of the present application may be one of several structures. In
one embodiment the paperboard is a single ply structure, in another the
paperboard is a
two-ply structure and in yet another embodiment the paperboard is a multi-ply
structure.
In the method, the addition order of the additive can vary. As stated earlier,
in one
embodiment, mechanically refined fiber is added to the slurry followed by the
addition of
an anionic starch and then followed by addition of a cationic fixative. After
each addition
step the slurry ionic demand is less than zero. The slurry is deposited on a
foraminous
support, dewatered forming a web and dried to form a paperboard. In another
embodiment mechanically refined fiber is added to the slurry followed by the
addition of
a cationic fixative and then followed by addition of an anionic starch. After
each addition
step the slurry ionic demand is less than zero. The slurry is deposited on a
foraminous
support, dewatered forming a web and dried to form a paperboard. In yet
another
embodiment, mechanically refined fiber is added to the slurry followed by the
addition of
an anionic starch and then followed by addition of first cationic fixative,
followed by
adding a second cationic fixative. After each addition step the slurry ionic
demand is less
than zero. The slurry is deposited on a foraminous support, dewatered forming
a web and
dried to form a paperboard. In each case, the first cationic fixative may have
an anionic
demand of from 1 meq/g to 10 meq/g and the second fixant may have an anionic
demand
of greater than zero but less than 1.
Mechanically Refined Fiber and Hia Levels of Starch
Fiber and polymer binders were applied to low density board so that
internal bond strength increases by 100% or more with 10% or less increase in
density.
The effect of refining on freeness and ionic demand is shown in Table 11.
30
7
CA 02581898 2007-03-15
Table II
Effect Of Refining On Ionic Demand
Kink Ionic
CSF, Curl angle, Demand,*
#Test Fiber Description mL Index /mm meq/g
1 LV Lodgepole Pine - Unrefined 720 0.25 92 -0.0008
2 LV Lodgepole Pine - EW 550 0.10 46 -0.0069
3 LV Lodgepole Pine - EW 275 0.07 31 -0.0118
4 LV Doug. Fir - Unrefined 675 0.23 64
LV Doug. Fir - EW 85 0.07 28 -0.0114
6 LV Lodgepole Pine - EW 65 0.05 18 -0.0167
7 LV Lodgepole Pine 33 0.05 21 -0.0114
*Fiber only
LV, Longview
5 EW, Escher Wyss
VB, Valley Beater
Each of the following Examples were generated as follows:
1. Handsheets formed using typical handsheet making equipment with an
extension to
reduce the forming consistency.
2. 250 gsm OD fiber.
3. 60% CHB405 (crosslinked fiber), dispersed independently; several methods
were
used interchangeably (Valley beater with no load, lab disk refiner with 1-2
amps
over no load and a pilot scale deflaker. Mechanical dispersion was done to
improve
formation.
4. 40% Douglas Fir refined to 400 ml CSF; pH was adjusted to 7.
6. 4 #/t Aquapel sizing agent.
7. 5 #/t Kymene 557H.
8. 25 #/t cationic starch, (STA-LOK 300)
The above formulation serves as a control; adjustments to the chemistry are
noted in each
Example.
As defined herein, mechanically refined fiber (MRF) is mechanically refined
wood pulp for example, Lodgepole Pine having a Canadian Standard Freeness <125
mL,
8
CA 02581898 2007-03-15
a index 1/2 or less of unrefined starting fiber and a kink angle of 1/2 or
less of the
unrefined starting fiber. Curl Index and kink angle were determined using a
Fiber Quality
Analyzer (FQA) as published in the Journal of Pulp and Paper Science
21(11):J367
(1995). Mechanically refined fiber can be generated to meet these criteria by
different
refining methods which have different impact on conventional fiber properties.
Table III
shows the effect on Z-direction tensile and density of various formulations
with
mechanically refined fiber. ZDT was determined by TAPPI 541.
Table III
Effect Of Mechanically Refined Fiber Addition On Strength Properties
Density Change in ZDT, A ZDT,
Description g/cc Density kPa %
100 % D. Fir 0.628 138 498 1138
Control (as above) 0.264 40.22
10% valley beater mechanically 0.292 10.6% 95.38 137
refined fiber replacing 10 % D. Fir
5% Escher Wyss mechanically refined 0.274 3.7% 78.14 94
fiber replacing 5 % D. Fir
5% Escher Wyss mechanically refined 0.274 3.7% 110 174
fiber replacing 5 % D. Fir
5% Escher Wyss mechanically refined 0.259 -1.9% 52.86 31.4
fiber replacing 5 % D. Fir
Control 0.232 24.8
5% Escher Wyss mechanically refined 0.238 2.5% 68.95 178
fiber replacing D. Fir
5% mechanically refined fiber 0.242 4.3% 85.5 244
replacing D. Fir (double disk refined)
Control 0.255 40.22
5% Valley Beater mechanically refined 0.265 3.9 69.81 73.5
fiber replacing D. Fir
9
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Density Change in ZDT, A ZDT,
Description g/cc Density kPa %
5% Valley Beater mechanically refined 0.256 0.4 80.15 99.3
fiber replacing D. Fir
A indicates "change in"
Internal bond strength can be increased by replacing some of the cationic
starch with a
higher ionic strength molecule such as Kymene as shown in the following
example.
50% CHB405.
50% Lodgepole Pine refined to 400 mL CSF.
#/t Kymene 557H from Hercules.
10 #/t Stalok 400 cationic starch from Staley.
Mechanically refined Lodgepole pine fiber refined at 50 ml CSF using an Escher
Wyss
laboratory refiner.
10 In this formulation the level of the Kymene 557H with an ionic demand of
+2.2
meq/g was doubled and the STA-LOK 300 cationic starch with an ionic demand of
+
0.3 meq/g was reduced by 60 %. As noted from the table, significant increases
in ZDT
bond strength and Scott Bond can be obtained by this method
Table IV
Effect On Strength Of Partial Replacement Of Cationic Starch With A Higher
Ionic
Demand Polymer
Mechanically
refined fiber Density % ZDT % Scott Bond %
% by wt. g/cc Increase kPa Increase J/m2 Increase
0% 0.222 23 98
10% 0.234 +5.4% 62 +170% 135 +38%
20% 0.260 +14.6% 125 +443% 173 +76.5%
A third technology is use of a starch excess. The general approach was to
overcome the normal limits of effective wet-end starch, balancing the charge
in the wet-
end by adding excess anionic starch and fixing it to the fibers by adding
cationic starch or
CA 02581898 2007-03-15
other high charge density cationic polymers thus balancing the system to near
neutral
charge density. The neutralization was important to prevent excessive
flocculation and
large impacts on drainage.
Specifically, total starch content added to the wet can be increased to 2% to
5%
based on dry fiber. Anionic starch such as RediBOND 3050 supplied by National
Starch & Chemical or Aniofax AP25 supplied by Carolina Starches can be used.
Cationic fixatives include common cationic starches like STA-LOK 300 supplied
by
Staley Corp., Poly Aluminum Chloride (PAC) like Nalco ULTRION 8187. or high
charge density cationic polymers like M5133 and M5134, GALACTAOL SP813D
(anionic guar) and Kymene 557H supplied by Hercules Corp. and Nalco NALKATS
62060 (branched EPEDMA) Nalco NALKAT 2020 (poly DADMAC). As used herein,
a high ionic demand is represented by a polymer that has an ionic demand of 1
meq/g to
17 meq/g, either as an anionic demand or as a cationic demand. For example,
Kymene 557H has an anionic demand of 2.2 meq/g and Hercobond 2000 has a
cationic
demand of 1.8 meq/g.
The level of anionic starch needed to obtain high strength development depends
on the charge density and more importantly on the retention. Typically, 2% to
5%
addition level based on dry fiber is adequate. The amount of cationic fixative
depends
entirely on the size of the polymer and the cationic charge density. As
defined herein, a
fixative is a charged polymer that ionically bonds to a molecule of the
opposite charge. In
general the higher the charge density the smaller the amount required and for
equal
charge density the larger the polymer the smaller the amount required.
The following data was based on laboratory handsheets of the following
formulation:
1. Handsheets formed using typical handsheet making equipment with an
extension to
reduce the forming consistency.
2. 250 gsm OD fiber.
3. 60% CHB405, dispersed independently; several methods were used
interchangeably, (Valley Beater with no load, lab disk refiner with 1-2 amps
over
no load condition, and a pilot scale deflaker). Mechanical dispersion is done
to
improve formation.
11
CA 02581898 2007-03-15
4. 40% Douglas Fir refined to 400 ml CSF.
5. pH adjusted to 7.
6. 5#/t Kymene 557H.
7. 4#/t Aquapel 625 sizing agent.
8. 25#/t cationic starch (STA-LOK 300)
Adjustments to the chemistry are noted in each Example.
Example I
The above described handsheet is the control. The following adjustments were
made to the non-fiber portion of the furnish, 80 lbs/t (4%) Aniofac AP25 was
mixed
with the fibers, followed by 20 lbs/t cationic starch STA-LOK 300. Then
Kymene8557H was added and the amount increased to 10 lbs/t. Last, before sheet
making a blend of cationic starch STA-LOK 300 and Aquapel 625 were added, the
cationic starch was reduced to 20 lbs/t and the Aquapel was kept constant at 4
lbs/t.
Handsheets were evaluated for density, ZDT and Scott Bond the results are in
Table V.
Table V
Density ZDT Scott Bond
Description g/cc kPa J/m2
Control 0.243 45 80
4% Anionic Starch Example 1 0.273 204 119
(Aniofac AP25)
Example 2
The control handsheet as described above was adjusted as follows to the non-
fiber
portion. 40 1 bs/t Aniofax AP25 was mixed with the fibers, followed by 20
lbs/t STA-
LOK 300 cationic starch. Kyrnene 557H at 5#/t was added and the same
combination
of Stalok 300 and Aquape1625 as in Example 1, i.e. 20 lb/t and 41b/t,
respectively.
Handsheets were evaluated for density, ZDT and Scott Bond; the results are in
Table V1
combined with the results from Example 1.
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CA 02581898 2007-03-15
Table VI
Density ZDT Scott Bond
Description g/cc kPa J/m2
Control 0.243 45 80
4% Anionic Starch* Example 1 0.273 204 119
2% Anionic Starch* Example 2 0.262 85 113
*Aniofac AP25
Example 3.
The handsheet formulation described in Example 2 was altered to contain
mechanically refined fiber fibers so that the fiber portion of the furnish is:
60% CHB405.
35% Fully Bleached D. Fir refined to 400 mL CSF.
5% Valley beater mechanically refined fiber - fully bleached kraft Lodgepole
Pine at -50
mL CSF.
1 o The remainder of the additives are the same as in Example #2. The results
are shown in
Table V11.
Table VII
Density ZDT Scott Bond
Description g/cc kPa J/m2
Control 0.243 45 80
4% Anionic Starch* Example 1 0.273 204 119
2% Anionic Starch* Example 2 0.262 85 113
Control + 5% Mechanically 0.274 78 106
refined fiber
2% anionic starch + 5% Example 3 0.283 122 148
mechanically refined fiber
*Aniofac AP25
Example 4
Adjustments were made to the non-fiber portion of the of the handsheet
formulation described in Example 3 (containing mechanically refined fiber) as
follows:
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CA 02581898 2007-03-15
100 lb/t Aniofax AP25 (was blended with the fibers followed by 90 lb/t Nalco
8187
PAC, then 5 lb/t Kymene 557H, 5 lb/t STA-LOK 300 and 4 lb/t Aquapel 625. The
results are shown in Table VIII.
Table VIII
Density ZDT Scott Bond
Description g/cc kPa J/m2
Control 0.243 45 80
Control + 5% mechanically 0.274 78 106
refined fiber
5% Anionic starch* + 4.5% Example 4 0.304 142 214
PAC
*Aniofac AP25
Example 5
Adjustments were made to the non-fiber portion of the of the handsheet
formulation described in Example 3 (containing mechanically refined fiber) as
follows:
lo 50 lb/t Aniofax AP25 was blended with the fibers followed by 8 lb/t Nalco
62060 poly,
then 5 lb/t Kymene 557H, 5 lb/t STA-LOK 300 and 4 lb/t Aquapel 625. The
results
are shown in the Table IX.
Table IX
Density ZDT Scott Bond
Description g/cc kPa J/mZ
Control 0.243 45 80
Control + 5% Mechanically refined fiber 0.274 78 106
5% Anionic starch* + 4.5% PAC Example 4 0.304 142 214
2.5% Anionic starch* + 0.4% Poly Example 5 0.284 109 138
DADMAC
*Aniofac AP25
Example 6
14
CA 02581898 2007-03-15
Adjustments were made to the non-fiber portion of the of the handsheet
formulation described in Example 3 (containing mechanically refined fiber) as
follows:1001b/t Aniofax AP25 was blended with the fibers followed by 61b/t
Nalco
2020 poly, then 51b/t Kymene 557H, 51b/t STA-LOK 300 and 4 lb/t Aquape1625.
The results are shown in Table X.
Table X
Density ZDT Scott Bond
Description g/cc kPa J/mZ
Control 0.243 45 80
Control + 5% Mechanically refined fiber 0.274 78 106
5% Anionic starch* + 4.5% PAC Example 4 0.304 142 214
2.5% Anionic starch* + 0.4% Poly Example 5 0.284 109 138
DADMAC
5% Anionic Starch* + 0.3% Poly Example 6 0.279 218 215
*Aniofac AP25
Single-ply handsheets designed to simulate the mid-ply of low density multi-
ply
lo paperboard were made. A 0.015 percent to 0.035 percent consistency slurry
was used in
these studies. Handsheet making equipment was standard 8" x 8" sheet mold
modified
with an extended headbox so that twice the normal volume of stock was used.
This
modification was necessary to improve handsheet formation when using materials
designed to generate high bulk (e.g. crosslink fiber such as CHB405 and
CHB505). Fiber
weights are expressed as a weight percent of the total fiber dry weight;
additives are
based on weight of dry fiber.
A series of handsheets were made using different levels of wet-end additives,
different addition order and some changes in fiber furnish to demonstrate the
level of
internal bond strength that could be generated by starch loading the web. The
additives
were added to the slurry in the order across each sample row and the slurry
stirred after
each addition.
CA 02581898 2007-03-15
Series 1.
The Table XI below shows the conditions and formulations used when making the
series of handsheets
16
Table XI-A. Handsheet Formulation And Addition Order.
Code Target CHB405 D. PVOH Mechanically Anionic Cationic Anionic Kymene
Cationic Aquapel
Basis Fir Celanese Refined Starch Starch Starch 557H Starch 650
wt. Celvol Fiber* Avebe STA- Avebe STA-
165SF Aniofax LOK Aniofax LOK
AP25 300 AP25 300
g/m % % % % #/t #/t #/t #/t #/t #/t
1 250 60% 30% 5% 5% 0 0 0 5 25 4
2 250 60% 35% 0% 5% 0 0 0 5 25 4
3 250 60% 40% 0% 0% 40 20 0 5 20 4
4 250 60% 35% 0% 5% 40 20 0 5 20 4
250 60% 35% 0% 5% 0 20 40 5 20 4 0
6 250 60% 35% 0% 0% 80 20 0 10 10 4 1 .3
7 250 60% 35% 0% 5% 80 20 0 10 10 4 w
8 250 60% 35% 0% 5% 0 10 80 15 10 4 'n
9 250 60% 40% 0% 0% 0 0 0 5 25 4
5 * Lodgepole Pine refined with Valley Beater to 33 CSF
17
Table XI-B. Calculated Ionic Demand As Chemical Additions Are Made In Table XI-
A
Code Ionic lonic Ionic Ionic Ionic Ionic Ionic Ionic Ionic Ionic Ionic
demand demand demand demand demand, strength strength strength strength
strength strength
CHB405 D. Fir PVOH MRF total with with with with with with
pulp and Aniofax STA- Aniofax Kymene STA- Aquapel
particles AP25 LOK AP25 557H LOK 650 - end
300 300 point
u/ ueq/g u/ ueq/g u/ ueq/g ueq/g ueg/g ueq/g ueg/g u!
1 -9 -0.45 0 -0.57 -10.02 -10.02 -10.02 -10.02 -4.52 -0.89 -0.89
2 -9 -0.53 0 -0.57 -10.1 -10.1 -10.1 -10.1 -4.60 -0.97 -0.97
3 -9 -0.6 0 0 -0.96 -14.2 -11.3 -11.3 -5.8 -2.9 -2.9
4 -9 -0.53 0 -0.57 -10.1 -14.7 -11.8 -11.8 -6.3 -3.40 -3.40
-9 -0.53 0 -0.57 -10.1 -10.1 -7.20 -11.8 -6.3 -3.40 -3.40
6 -9 -0.53 0 0 -9.53 -18.7 -15.8 -15.8 -4.8 -3.38 -3.38
7 -9 -0.53 0 -0.57 -10.1 -19.3 -16.4 -16.4 -5.4 -3.94 -3.94 0
8 -9 -0.53 0 -0.57 -10.1 -10.1 -0.86 -0.86 -1.34 0.11 0.11
0
9 -9 -0.6 0 0 -0.96 -0.96 -0.96 -0.96 -4.1 -0.48 -0.48
Ln
18
CA 02581898 2007-03-15
Each handsheet was then coated with Polyvinyl Alcohol (PVA) coating, Celvol
V24203 supplied by Celanese Ltd. The total coat weight was about 50 g/m2 and
was
divided equally between each side of the sheet. The coating was added to the
surface to
facilitate testing Z-direction tensile (ZDT) and internal Scott Bond because
low density
structures without the coating tend to separate at the tape instead of the
within the sheet.
Each sheet was evaluated for several physical properties including basis
weight,
caliper, ZDT, internal Scott Bond and Taber Stiffness (15 ). Scott Bond and
Taber
Stiffness were determined by TAPPI T 569 om-00 and T 489 om-04, respectively.
Table
XII below shows the results for these key characteristics
Table XII. Physical Characteristics of Laboratory Handsheets as Described in
Table XI
Sample Basis Density Z-direction Scott Taber
Wei t Tensile Bond Stiffness
m g/CM3 kPa J/m cm
1 297 0.267 124 158 375
2 296 0.274 78 106 316
3 306 0.262 85 113 433
4 303 0.283 122 147 387
5 303 0.281 121 142 388
6 305 0.273 204 119 403
7 301 0.284 179 128 374
8 303 0.284 140 116 394
9 301 0.264 40 67 364
Samples 1, 2 and 9 can be considered the controls for this experiment. Sample
number 9 is a fiber formulation designed to deliver low density paper and uses
typical
wet end chemistry (i.e. cationic starch and Kymene 557H). The result is a very
low
Scott Bond, but typical Taber Stiffness. Sample 2, incorporates mechanically
refined
fiber in an effort to increase the internal bond and, by itself, results in an
increase in ZDT
and Scott Bond, but not enough to reach the targets needed for converting
multi-ply
paperboard. It is estimated the minimum necessary ZDT needed for converting is
about
175-190 kPa.
Sample 1 incorporates mechanically refined fiber with a particle PVOH - known
as a good binder but is hindered by issues with retention, cost and process
reliability
impacts. The increase in ZDT and Scott Bond for sample I begins to approach
the
amount needed for converting paperboard. Samples 3 and 4 show that by adding
4%
19
CA 02581898 2007-03-15
total starch to the furnish the ZDT and Scott Bond essentially double. Adding
mechanically refined fiber, Sample 4, gives an increase of about the same
magnitude as
it did to the original structure, Sample 2 v. Sample 4 and Sample 3 v. Sample
9.
Sample 5 shows reversing the order ( i.e. adding cationic starch first then
anionic
starch) in which the cationic and anionic starch are added makes no difference
to the
strength development
Samples 6 and 7 are a case where the amount of anionic starch is doubled while
the cationic starch remains constant. Kymeme 557H, a higher charge density
cationic
polymer, is used to balance the additional anionic charge. The result is
further increase in
internal bond, increasing ZDT by 500%, ( Sample 6) over the control and Scott
Bond is
unaffected by the additional starch and Kymene 557H. Sample 7 shows that by
adding
mechanically refined fiber the effect on ZDT is negative in this case, yet the
Scott Bond
increases.
Sample 8 adjusts the source of cationic charge further, increasing the amount
of
Kymene 557H and decreasing the amount of cationic starch. In Table XI-B the
ionic
demand of the system crosses from negative to positive at the last point of
cationic starch
addition and from Table XII the corresponding ZDT and Scott bond are further
reduced
indicating that when the ionic demand exceeds zero the effectiveness of the
ionic binding
system is reduced.
The ZDT is reduced further, indicating that higher charge density polymer is
less
effective than cationic starch in adding internal bond strength. In general
the impact of
the starch loading on Taber Stiffness at 15 is small. For single ply
handsheets this is
reasonable because caliper is the dominating variable effecting bending
stiffness. The
impact of the starch loading on density is small enough that the increase in
elastic
modulus of the sheets due to the starch loading compensates for the small
changes in
caliper. In a multi-ply web the same response would be expected.
Series 2
A second set of handsheets was produced to determine the impact of using high
charge density cationic polymers to retain additional anionic starch. It is
thought that
using higher charge density polymers less total starch would be necessary to
achieve the
same strength due to better retention. The result would reduce the risk of
affecting
CA 02581898 2007-03-15
drainage and formation by adding excess starch. Table XIII shows the
formulations used
in the experiments.
21
Table XIII. Handsheet Formulation and Addition Order
Code CHB D.Fir @ MRF Anionic Cationic Nalco Nalco Nalco Kymene Cationic
405 500 ml Avebe STA- 8187 62060 2020 557H STA-
CSF Aniofax LOK LOK
AP25 300 300
Wt. % Wt. % Wt. % #/t #/t #/t #/t #/t #/t #/t
1 60 35 5 80 20 5 5
2 60 35 5 50 25 5 5
3 60 35 5 50 40 5 5
4 60 35 5 100 60 5 5
60 35 5 100 90 5 5
ko
6 60 35 5 50 4 5 5 N
7 60 35 5 50 8 5 5
8 60 35 5 100 6 5 5 W
9 60 35 5 100 12 5 5 Ln
60 35 5 50 4 5 5
11 60 35 5 50 8 5 5
12 60 35 5 100 6 5 5
13 60 35 5 100 12 5 5
14 0 100 0 5 25
All Codes at 250 g/m target; all additives are on a dry fiber wt. basis
5 Aquapel 650 at 4#/ton was used in all the studies (dry fiber weight basis)
MRF: Mechanically refined Fiber
22
CA 02581898 2007-03-15
Each handsheet was then coated with Polyvinyl Alcohol (PVA) coating, Celvol
V24203 supplied by Celanese Ltd. The total coat weight was about 50 g/m2 and
was
divided equally between each side of the sheet. The coating was added to the
surface to
facilitate testing Z-direction tensile (ZDT) and internal Scott Bond, because
low density
structures without the coating tend to separate at the tape instead of the
within the sheet.
Each sheet was evaluated for several physical properties including basis
weight,
caliper, ZDT, Internal Scott Bond, Taber Stiffness (15 ) and other. The table
below
shows the results for these key characteristics
lo Table XIV. Physical Characteristics Of Laboratory Handsheets As Described
In Table
XIII
Code Basis Weight Density Z-direction Scott Bond Taber
Tensile Stiffness
m cm kPa J/m cm
1 306 0.287 186 132 392
2 317 0.285 107 137 408
3 314 0.278 83 130 394
4 311 0.287 118 164 388
5 320 0.304 142 214 400
6 303 0.286 87 122 373
7 309 0.284 109 138 392
8 304 0.272 107 104 380
9 306 0.276 118 141 389
305 0.281 100 112 384
11 308 0.282 103 141 394
12 308 0.279 218 215 390
13 307 0.276 122 109 394
14 270 0.628 498 329 116
From Table XII - control with normal strength additives, as a reference.
9 301 0.264 40 67 364
Sample code 9 from Tables X1 and XII above is the base case.
The impact of using PAC such as Nalco 8187 (codes 2-5) to retain the anionic
starch in the presence of mechanically refined fiber is less than that of
using cationic
starch on ZDT, however the impact on Scott Bond is greater, suggesting that
the PAC
improves the retention of the mechanically refined fiber giving greater shear
strength to
the board.
23
CA 02581898 2007-03-15
For codes 6-9 using NALKAT(962060 a branched EPEDMA cationic polymer as
a fixative, the impact at 2.5% anionic starch addition is roughly the same as
the PAC
Nalco 8187) but significantly less ZDT development relative to the cationic
starch, Code
1. At the 5% anionic starch addition level there was no further significant
gain
Use of the polyDADMAC (codes 10-13) as a fixative shows more promise than
the other two cationic polymers at the 5% added starch dose where it exceeded
(Code 12)
the cationic starch in ZDT and Scott Bond development vs Code 1
The last code in Tables XIII and XIV, Code 14, is that of a normal density
board,
included for comparison. The higher ZDT and Scott Bond come at the expense of
bending stiffness.
In general, at equal total starch levels it appears that more ZDT is developed
when
using combination of anionic and cationic starch than when using higher charge
density
cationic polymers in combination with anionic starch. However, both methods
develop
significant ZDT. Scott Bond has the opposite result. The shear strength
appears to
increase at a greater rate than the ZDT when using higher charge density
cationic
polymers in combination with anionic siarch.
Finally, the impact of the starch loading, independent of the cationic
fixative has
little effect on the product density and therefore little impact on the
bending stiffness.
Pilot Trial
The disclosure was further explored using a pilot paper machine where dynamic
drainage and white water re-circulation could be used to improve the
simulation of
commercial application on a paper machine.
The fiber furnish used in all of the following examples was the same, only the
chemical additives and the order of addition were changed. The fiber
components were:
60% Weyerhaeuser CHB405
35% Weyerhaeuser fully bleached kraft D. Fir wet lap refined to -500 mL CSF
5% Douglas Fir refined to 85 ml CSF (Escher Wyss refined)
The chemical components were combinations of some or all of the following,
levels and addition order are shown in Table XV.
Kymene 557H supplied by Hercules Incorporated (cationic wet strength resin)
24
CA 02581898 2007-03-15
Aquapel 650 supplied by Hercules Incorporated (AKD sizing agent)
Hercobond 2000 supplied by Hercules Incorporated (anionic polyacrylamide,
retention
aid)
RediBOND 3050 supplied by Hercules Incorporated (anionic starch)
RediBOND 2038 supplied by Hercules Incorporated (cationic starch)
PPD M-5133 supplied by Hercules Incorporated (cationic high charge density
polymer)
GALACTASOL SP813D supplied by Hercules Incorporated (cationic guar gum)
The pilot paper machine was a standard Fourdrinier type single ply former. The
design is such that there are several chemical addition points so that wet end
additive
lo effects can be studied. Figure 1 shows the basic unit operations with the
chemical
addition points. indicated as lower case letters as in Table XV. The addition
points have
been labeled and should be used as a reference for the formulations shown in
Table XV.
Other unit operations were changed to maximize the bulk, for example, lowering
the
amount of vacuum on the forming table suction boxes, lifting the Dandy rolls
away from
the web using only one wet press, a normal drying profile, no size press
(typical solids
entering dryer 32-36%) no calendaring and finally, samples were taken for
evaluation at
the reel (eliminating effect of reel tension)
For each different formulation, the machine was run 10 to 15 minutes after
making
adjustments and insuring the basis weight was on target. In this way, the
white water was
completely turned over and reach equilibrium with the new chemistry. Target
basis
weight was 200 g/m2.
= Each sample was then coated with Polyvinyl Alcohol (PVA) coating, Celvol
V24203
supplied by Celanese Ltd. The total coat weight was about 22 g/m2 and was
divided
equally between each side of the sheet. The coating was added to the surface
to facilitate
testing Z-direction tensile (ZDT) and Internal Scott Bond, because low density
structures
without the coating tend to separate at the tape instead of the within the
sheet.
Table XV. Wet End Additives for Pilot Paper Machine Starch Loading Trials.
Code
b c d e h
1 5 #/t Kymene 2 #/t Hercobond 10 #/t RediBOND 2038 4.5 #/t Aquape1650
557H 2000
2 20 #/t 20 #/t RediBOND 5 #/t 2#/t Hercobond 10 #/t RediBOND 2038 4.5 #/t
Aquape1650
RediBond2038 3050 Kymene 2000
557H
3 20 #/t RediBond 20 #/t RediBOND 5#/t 10 #/t RediBOND 2038 4.5 #/t Aquape1650
2038 3050 Kymene
557H
4 30 #/t RediBond 40 #/t RediBOND 5 #/t 2 #/t Hercobond 10 #/t RediBOND 2038
4.5 #/t Aquape1650
ko
2038 3050 Kymene 2000
557H
20 #/t RediBond 60 #/t RediBOND 10 #/t 2 #/t Hercobond 10 #/t RediBOND 2038
4.5 #/t Aquape1650
2038 3050 Kymene 2000 W
557H Ln
6 20 #/t RediBond 10 #/t Kymene 20 #/t 2 #/t Hercobond 10 #/t RediBOND 2038
4.5 #/t Aquapel 650
2038 557H RediBOND 2000
3050
7 30 #/t RediBond 10 #/t Kymene 40 #/t 2 #/t Hercobond 10 #/t RediBOND 2038
4.5 #/t Aquape1650
2038 557H RediBOND 2000
3050
8 40 #/t RediBond 20 #/t RediBOND 5 #/t 10 #/t RediBOND 2038 4.5 #/t
Aquape1650
2038 2038 Kymene
557H
5
26
Table XV. Wet End Additives for Pilot Paper Machine Starch Loading Trials.
Code
b c d e h
9 40 #/t 2 #/t 8.2 #/t 10 #/t RediBOND 2038 4.5 #/t Aquape1650
RediBOND 3050 M-5133 Hercobond
2000
5#/t KymeneO 2#/t Hercobond 10 #/t RediBOND 2038 4.5 #/t Aquape1650
557H 2000
11 30 #/t 10 #/t Kymene 40 #/t 2 #/t Hercobond 10 #/t RediBOND 2038 4.5 #/t
Aquape1650
RediBOND 2038 557H RediBOND 2000
3050
12 30 #/t 5 #/t 40 #/t 2 #/t Hercobond 10 #/t RediBOND 2038 4.5 #/t Aquape1650
RediBOND 2038 Kymene 557H RediBOND 2000 Ln
3050
13 30 #/t 2.5 #/t Kymene 40 #/t 2#/t Hercobond 10 #/t RediBOND 2038 4.5 #/t
Aquape1650
RediBOND 2038 557H RediBOND 2000
3050
14 30 #/t 40 #/t RediBOND 5 #/t 2 #/t Hercobond 10 #/t RediBOND 2038 4.5 #/t
Aquapel 650 0
w
RediBOND 2038 3050 Kymene 2000
557H 'n
8 #/t 40 #/t RediBOND 5 #/t 2#/t Hercobond 8 #/t GALACTASOL 4.5 #/t Aquapel
650
GALACTASOL 3050 Kymene 2000 SP813D
SP813D 557H
16 40 #/t 20 #/t RediBOND 5 #/t 4 #/t GALACTASOL 4.5 #/t Aquapel 650
RediBOND 3050 2038 Kymene SP813D
557H
Lower case letters refer to the additive addition points in Figure 1
27
CA 02581898 2007-03-15
Codes number 1 and 10 are controls for two different running days, code 14 is
a repeat of
code 4 on a different day and code 11 is a repeat of code 7 on a different
day. The
physical characteristics of the resultant paper are shown in Table XV.
Table XVI. Physical Characteristics of Pilot Paper Machine Samples in Table XV
Code Basis Weight Density Z-direction Geometric Geometric
Tensile Mean Scott Mean Taber
Bond Stiffness
m cm kPa J/m cm
1 228 0.271 161 198 135
2 256 0.273 194 242 163
3 251 0.283 204 258 161
4 245 0.274 219 252 166
5 237 0.284 265 236 147
6 236 0.276 241 227 146
7 239 0.279 232 236 146
8 262 0.288 199 246 190
9 236 0.260 134 189 156
231 0.271 192 227 140
11 230 0.295 350 354 127
12 229 0.290 360 340 131
13 234 0.288 319 323 131
14 244 0.292 339 340 144
228 0.288 305 297 134
16 243 0.273 269 345 146
Pilot Machine versus control
10 The effect of starch loading is basically the same, it is estimated that
the target
internal bond strength that would be enough for performance during converting
is about
2x of the control samples. For the pilot trial ZDT doubled and Scott Bond
increased 75
%.
By loading the wet-end with between 2% and 4% total starch (anionic and
cationic),
15 ZDT can be increased by approximately 25% to 85% relative to the same
furnish with
conventional levels of cationic starch (Codes 2-8, 11-14).
28
CA 02581898 2007-03-15
Loading up to 2% anionic starch into the wet-end and using high charge density
cationic polymer (code 9) to retain the starch little or no gain in ZDT or
Scott Bond
was achieved.
Loading the wet-end with up to 2% anionic starch and using cationic guar gum
(codes 15 and 16) to improve retention as a substitute for cationic starch
about 40%-
50% increase in ZDT was obtained.
When changing the order of addition, indications were that adding the anionic
starch after the cationic material resulted in better strength efficiency.
Starch loading resulted in an increase in density of < 10% in all cases and
had no
significant impact on stiffness.
20
30
29
