Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS FOR PRODUCING PAPER OR PAPERBOARD, IN PARTICULAR LABEL PAPER
OR PAPERBOARD SUITED FOR USE AS PACKAGING MATERIAL FOR BEVERAGE
CONTAINERS, AND PAPER OR PAPERBOARD PRODUCED BY THIS PROCESS
Field of the Invention
The present invention concerns a process for producing paper or paperboard, in
particular label
paper or paperboard suited for use as packaging material for beverage
containers.
Background to the Invention
Label paper and paperboard suited for use as packaging material for beverage
cans or bottles need
to meet specific requirements to ensure full functionality of the packaging
material (secondary
packaging material holding typically 2 or more beverage containers such as
cans or bottles
together). The same applies for beverage labels intended to be glued on for
example glass bottles.
The major requirement for label paper is resistance to humidity as often
condensation may arise on
the outer surface of beverage containers and beverage bottles are typically
stored outdoors for
extended periods of time. Clearly exposure to humidity should not affect the
label quality in terms
of printability nor damage the integrity of the label paper. Therefore high
wet tear resistance and
high wet tensile strength characteristics are a major requirement of label
papers.
The same applies to paperboard designed to be used as packaging material. Such
paperboard should
meet strict requirements of wet tensile strength and wet tear resistance as
the structural integrity
of the packaging is to be ensured over the lifetime of such (secondary)
packaging product,
otherwise, the beverage container risk falling out of the packaging upon
lifting it.
In industrial paper making, the use of wet-strength additives is well known
and common additives
used for this purpose include epichlorohydrin, melamine and urea formaldehyde.
Other typical additives to wood pulp in the paper making process include: i)
dry strength additives
such as cationic starch; ii) binders to increase printability such as
carboxymethyl cellulose, iii)
retention aids allowing binding filler materials to the paper such as
polyacrylamide.
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The present invention addresses the above industry demands and provides a
method allowing
producing label paper and packaging paperboard having increased wet tensile
strength and wet tear
resistance of paper whilst maintaining the paper! paperboard basis weight
constant.
Summary of the Invention
The present invention concerns a method for producing label paper or paper for
corrugated board
or folding carton for packaging of beverage containers, comprising the steps
of:
- feeding wood fiber pulps into a paper-making process;
- forming a web mixture comprising the wood fiber pulp, a cationic polymer, an
anionic polymer
and a cationic starch;
characterized in that the cationic starch is added to the wood fiber pulp only
after the addition of
the anionic polymer and cationic polymer.
The cationic polymer is preferably added to the wood fiber pulp prior to the
addition of the anionic
polymer.
According to a preferred method of the invention, the cationic polymer
comprises or is
polyamideamine epichlorohydrin (PAE), which is added to the wood fiber pulp
ranging between 1
and 40 kg/ton of wood fiber pulp (dry weight), preferably between 1,5 and 4,5
kg/ton of wood fiber
pulp (dry weight).
The anionic polymer preferably comprises carboxy methyl cellulose (CMC), which
may be added to
the wood fiber pulp ranging between 0,1 and 10 kg/ton of wood fiber pulp (dry
weight), preferably
between 0,5 and 2 kg/ton of wood fiber pulp (dry weight).
The amount of cationic starch added to the wood fiber pulp preferably ranges
between 1 and 40
kg/ton of wood fiber pulp (dry weight), more preferably between 5 and 15
kg/ton of wood fiber
pulp (dry weight).
The method of the present invention preferably comprises providing a reaction
time in between the
addition of cationic polymer and the addition of anionic polymer to the web
mixture of wood fiber
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pulp and/or providing a reaction time in between the addition of anionic
polymer and the addition
of cationic starch to the web mixture of wood fiber pulp.
The present invention also concerns a fiber product, comprising:
a fiber web; and
an at least partially cured resin composition, wherein, preferably prior to
curing, the resin
composition comprises:
a cationic polymer, preferably polyamide-epichlorohydrin (resin);
an anionic polymer, preferably carboxymethyl cellulose (resin); and
cationic starch, wherein the cationic starch is added after the addition of
the anionic polymer and
the cationic polymer.
In a preferred embodiment, the PEC polymer is a PEC resin.
In a preferred embodiment, the CMC polymer is a CMC resin.
Note that the term "curing" refers to the step of mixing the chemicals (resin
composition) with the
fibers (fiber web).
The fiber product according to the present invention preferably has a wet
tensile strength of at least
7 N=m/g (1503781:2011) and/or a wet tear resistance of at least 9 mN=m2/g,
preferably at least 9,5
mN=m2/g (1501794:2012).
Brief description of the Drawings
.. Figures 1 and 2 illustrate two alternative process schemes of a method
according to the present
invention;
Figure 3 shows a set-up of a forming section of a paper making machine that
can be used in a method
according to the present invention;
Figures 4 to 10 show characteristics of specific fiber products made during
trials of the method of
.. the present invention.
The following components are shown in the drawings:
1: Wire pit 2: Front chest 3: Storage chest
4: Headbox pump 5 : Screen 6: Headbox
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7: Fibers out of process 8: Fibers back to chest 9: Driven roll
10: Steering guide, tension measurement 11: High Vacuum
12: Vacuum box with friction measurement 13: Transfer
vacuum box
14: Vacuum box 1 15: MB unit 16: Apron board
Description of a preferred Embodiment
The present invention concerns a method for producing label paper or
corrugated board or folding
carton for packaging of beverage containers, comprising the steps of:
- feeding wood fiber pulps into a paper-making process;
- forming a web mixture comprising the wood fiber pulp, a cationic polymer, an
anionic polymer
and a cationic starch;
characterized in that the cationic starch is added to the wood fiber pulp only
after the addition of
the anionic polymer and cationic polymer.
Figures 1 and 2 show two alternative preferred process schemes of a method
according to the
present invention, wherein in Figure 1, the chemicals in particular a cationic
polymer (such as
polyamideamine epichlorohydrin (PAE)); an anionic polymer (preferably
comprising carboxy methyl
cellulose (CMC)); and cationic starch are dosed online to the furnish between
a front chest and a
headbox. In Figure 2, the chemicals are dosed into the furnish sequentially
yet in batch to a storage
chest for the furnish, downstream of the front chest and the further
downstream headbox.
Both process schemes were used for some trials of papermaking as discussed in
more detail below.
RAW MATERIALS AND APPLICATION OF CHEMICALS
In the trials a furnish was used consisting of 80% 'southern pine, Alabama
river' and 20% hardwood
(birch). The pulp mixture was refined in one batch to freeness 495 ml (refined
1000 kg in Valmet,
Rautpohja). Clearly, this furnish is only provided as an example, as numerous
variants can be used
without departing from the present invention.
The applied chemicals for the trials were:
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= PAE: Kymene 25 X-Cel (Solenis), 1.5, 3.0 or 4.5 kg/ton
= CMC: Finnfix 5 (CP Celco), 1.0 or 2.0 kg/ton
= Cationic Starch: Raisamyl 50021 (Chemigate), 5 or 15 kg/ton
= Retention aid: cationic polyacrylamide cPAM, Fennopol 3400 (Kemira), 200
g/ton
The chemicals were alternatively dosed online before the headbox (Fig. 1) or
to the batch of furnish
(Fig. 2).
In the online addition of the chemicals (Fig. 1) the interaction time between
chemicals with each
other and pulp mixture (or furnish) was some seconds whereas in batch dosage
(Fig. 2) interaction
time was several of minutes. In both cases the addition order of the chemicals
was the same: 1. PAE
(cationic polymer), 2. CMC (anionic polymer), 3. Cationic starch, 4. C-PAM
(retention aid). The
addition places and interaction time of additives before forming section (head
box) are presented in
schematic layout pictures of online dosage (Fig. 1) and batch dosage (Fig. 2).
FORMING SECTION SET-UP AND RUNNING PARAMETERS
The pilot machine consists of an approach system with different kind of
containers, a forming
section (Fig. 3) that can be run in gap, hybrid or fourdrinier mode, and of a
press section (not shown).
In the trial, the pilot machine was run in the hybrid-forming mode at speed of
400 m/min. The
consistency of furnish in head box was 0.6%. The forming section configuration
is shown in the figure
3.
The press section (Fig. 3) consisted of a 1-nip shoe press having a 350 mm
extended nip. The nip
pressure was varied at three different levels: 400, 800 and 1200 kN/m. After
the wet pressing, the
paper web was reeled and sheet samples were collected and dried in cylinder
drier for the
laboratory analyses.
MEASUREMENTS FROM WIRE WATER, FURNISH IN HEADBOX, WET WEB AND DRY
SHEET
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Process conditions and process inputs were measured and recorded on-line in
Wedge data
acquisition system.
In order to make easier to view the results the geometric average values were
calculated from the
machine direct (MD) and cross direct (CD) data.
PRODUCED CONDITIONS
Different conditions were produced and sampled in the pilot machine trial. The
total 22 trial points
are listed in table 1. During the trials some trial points were rejected based
on too low or high
basis weight (missing numbers in the table 1).
M -
-= - -=_ ,
Online - CMC to
Online - PAE
0 Trial between of
fu Target Additives to former's
< Point head box pump
front chest
and screen
-I- _________________________________________________________ -F
,
AER, PAE PAE addition CMC, Finnfix CMC addition
Kymene 25 consistency 5 dosage consistentcy
X-Cel (25% active
dosage material
content)
_ _ + _ + _
[kg/tri] [%] [kg/tri] [cy]
t -F ___________
,
1 Reference 1 -
1 Online dosage 2 1,5 0,5 I -
1 Reference 3 - ______________________________ -
-t
-
1 Online dosage 4 1,5 0,5 1,0 i 0,35
New furnish
1 Reference 5 -
1 Online dosage 6 3,0 0,5 I
-
1 Reference 9 - - ___ I -
1 ___________________________________________________________________________
1 Online dosage 10 3,0 0,5 2,0 0,35
New furnish
I_ 1 I Reference _L 12 - - -
_____________________________________________________________ _L -
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1 Online dosage 14 4,5 1,0 -
1 Reference 15 - - ___ t -
________________________________________________________ + ___________ -
1 Online dosage 16 4,5 1,0 2,0 0,35
______________________________________________________________________
1 Online dosage 17 4,5 1,0 2,0 0,35
_ +
PAE, kg/tn Batch - PAE to CMC, kg/tn Batch - CMC to
Sampo's wire Sampo's wire pit
pit
i _________________________________________________________
Batch add Batch add consistency
treatment consistency % treatment %
=
First - 10 min treatment Second - 15 min treatment time
time
2 Run through trials 18 3,0 1,0 -
_
2 Run through trials+ 19 3,0 1,0 -
2 Run through trials 20 3,0 1,0 I -
____________________ -
2 Run through trials 21 3,0 1,0 __ t -
New furnish
2 , Run through trials 22 3,0 1,0 2 0,35
-+ -k
2 Run through trials 23 3,0 1,0 2 0,35
-I- -F ______________________________________________________________ -
2 Run through trials 24 3,0 1,0 2 0,35
-r _____________________________________________________________________
2 Run through trials 25 3,0 1,0 2 0,35
2 Run through trials 26 3,0 1,0 2 0,35
_ --h _______________________________________________________________ .,
NOTE: 20 sheets / trial point, heat treatment of the dry samples; 10
min in 105C I
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1 1 1 1 ____________________________________________________________
Online - Starch C-PAM to
0 Trial to Retamixer, Retamixer,
tU Target
Pressing
< Point farther to closer to
headbox headbox
I ______________________________________________________________________
Starch, Starch addition C-PAM
Line Load
Raisamyl consistancy [%] Fennopol
50021 dosage 3400
1 ___________________________________________________ _
__ I _______________________________________________________ f _______
[kg/tri] [sy] [g/tri] [kN/m]
1 Reference 1 200
800
+ ¨ _________________________________________ + _______ _
1 Online dosage 2 5 1,1 200 800
1 Reference 3 - - 200 --
800
_____________________________________________________________ I __
1 Online dosage 4 5 1,1 200 800
New furnish
1 Reference 5 200
800
1 + Online dosage 6 15 1,1 200 800
Reference 9 - - 200 800
1 Online dosage 10
15
1,1 _
200 800
New furnish
1 Reference 12 200
800
_ _ ___
1 Online dosage 14 15 1,1 200 800
_
1 Reference 15 - - 200
800
1 Online dosage 16 15 1,1 200 800
_____________________________________________________________ -h _____
1 Online dosage 17 15 1,1 200 800
Starch, kg/tn Batch - CMC to C-PAM, g/tn
Sampo's wire pit
Batch add consistency
treatment %
______________________ I. _____________________________________________
Third - 30 min Online
-h- _____
2 Run through trials I- 18 15 1,1
200 800
F ________________________________________ +-
2 Run through trials 19 15 1,1 200 --
1200
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2 Run through trials 20 15 1,1 200
400
2 Run through trials 21 15 1,1 200
800
New furnish
2 Run through trials 22 15 1,1 200 -
- 800
- _________________________
2 Run through trials 23 15 1,1 200 -
- 1200
_ __________________________________________________________________________
2 Run through trials 24 15 1,1 200
400
2 Run through trials 25 15 1,1 200
800
- - -
2 Run through trials 26 15 1,1 200 -
- 800
NOTE: 20 sheets / trial point, heat treatment of the dry samples; 10 min in
105C
TABLE 1 (table split in 2 parts)
FURNISH ANALYSES
The pH or conductivity of the furnish were not chemically modified in the
trials. The pH of the furnish
(measured from the headbox furnish sample) was between 7.7 and 8.1 in all
trial points. It is known
that PAE (wet strength agent) works best in neutral or alkaline pH area.
Correspondingly, the
conductivity was -180 uS in all trial points. The pH and conductivity values
were very close to what
was applied in the preliminary laboratory scale trials.
The freeness of the original refined pulp mixture was 475 ml. In the figure 4
are presented freeness
values measured from the furnish samples sampled from the headbox. On the
online dosage day
the freeness value was found to level to around 500 ml. In the first trial
points (reference points only
measured) 1 and 3 was probably less fines washed to the white water when the
pulp was recycled
in the pilot compared to the trial points from 5 to 15. In the batch dosing
day (run through trials)
was new fresh pulp and waters changed after running reference point 18 thus,
the furnish base in
18 and 22 should be comparable.
BETA-FORMATION
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In the figure 5 can be seen that the method of the present invention did not
significantly influence
the beta-formation values. The furnish consisted 80% of very long southern
pine fibers thus the
increased flocculation of the furnish would have seen in big increase of beta-
formation value.
Because the formation remained in same level no significant changes in
coatability or printability of
the product are expected when the new strength aid solution would be utilized
in the paper! board
mills.
DEWATERING CHARACTERISTICS
In the Figure 6 and 7 are presented dryness values after forming section and
pressing section. Based
on the online dosing trial points the method of the present invention had only
minor effect on the
total vacuum level in the forming section (samples from the batch dosing trial
day were not taken).
Correspondingly, the after wet pressing dryness was not significantly changed
by the method
according to the present invention in online dosing or in batch dosing trial
points.
STRUCTURAL CHARACTERISTICS
The average grammage of the trial points (Figure 8) was in online dosing
points 100 5 g/m2. In the
batch dosing trial points (run through trials) the grammage was lower 91 3
g/m2. Additionally, a
very low grammage trial point 53 g/m2 was executed. The low grammage trial
point offers possibility
to preliminary estimate the potential to reduce grammage with the method
according to the
present invention.
.. The method according to the present invention did not significantly
influence on the bulk of the
sheet. Thus, no change expected in the bending resistance of the product.
Further in the batch
dosage trial points the air permeance was not changed by the method according
to the present
invention.
WET SHEET STRENGTH PROPERTIES
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The conventional wet and dry strength solution: PAE with starch was found to
increase wet tear
index up to 250% compared to reference with no strength aids. The method
according to the
present invention increased wet tear resistance further by 28% (Fig 9). The
results indicate that
online dosage with short interaction times of the chemicals could be possible.
Likewise, the method
according to the present invention increased wet tensile index (16%). (Fig 10)
CONCLUSIONS
A method according to the present invention was found to have no or no
significant influence on
dewatering in forming and pressing sections. Additionally, sheet formation was
not affected by the
dosing strategy of the chemicals in accordance with the present invention. The
results indicates that
wet and dry strength aids could be applied in online or in batch dosing
system.
Overall, in the pilot trials was demonstrated that method of the present
invention could bring end
product quality benefits over conventional strength aid solution. Wet strength
properties of the
sheet increased significantly (wet tear index +28% and wet tensile index
+16%). Alternatively, the
grammage could be decreased by 25% (from 95 to 70 g/m2) without decrease in
wet tear strength.
The above characteristics of the, make the fiber product according to the
present invention suitable
for use as label paper or corrugated board or folding carton for packaging of
beverage containers,
where wet tear strength and wet tensile strength are key features.
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