U.S. patent application number 11/920328 was filed with the patent office on 2009-04-30 for process for the production of a paper and a paper produced according to the process.
This patent application is currently assigned to STORA ENSO AB. Invention is credited to Elisabeth Dolff, Bjorn Legnerfalt, Jan Olausson.
Application Number | 20090107645 11/920328 |
Document ID | / |
Family ID | 36754154 |
Filed Date | 2009-04-30 |
United States Patent
Application |
20090107645 |
Kind Code |
A1 |
Legnerfalt; Bjorn ; et
al. |
April 30, 2009 |
Process for the Production of a Paper and a Paper Produced
According to the Process
Abstract
A process for producing paper from a furnish comprising fillers
and fibers, wherein the furnish is treated with polymers in at
least three steps and said furnish contains fillers in such an
amount that the paper product obtained by the process contains at
least 15% by weight of fillers. The invention also relates to a
paper product produced according to the process of the present
invention.
Inventors: |
Legnerfalt; Bjorn; (Falun,
SE) ; Dolff; Elisabeth; (Falun, SE) ;
Olausson; Jan; (Falun, SE) |
Correspondence
Address: |
GREER, BURNS & CRAIN
300 S WACKER DR, 25TH FLOOR
CHICAGO
IL
60606
US
|
Assignee: |
STORA ENSO AB
Falun
SE
|
Family ID: |
36754154 |
Appl. No.: |
11/920328 |
Filed: |
May 11, 2006 |
PCT Filed: |
May 11, 2006 |
PCT NO: |
PCT/EP2006/062255 |
371 Date: |
November 9, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60679734 |
May 11, 2005 |
|
|
|
Current U.S.
Class: |
162/176 ;
162/158; 162/175 |
Current CPC
Class: |
D21H 17/29 20130101;
D21H 23/04 20130101; D21H 17/67 20130101; D21H 17/26 20130101 |
Class at
Publication: |
162/176 ;
162/158; 162/175 |
International
Class: |
D21H 17/25 20060101
D21H017/25; D21H 17/00 20060101 D21H017/00; D21H 17/28 20060101
D21H017/28 |
Claims
1. A process for the production of a paper product, which process
comprises: providing a furnish comprising fillers and fibers;
subjecting said furnish to polymer treatment, in which polymers are
added to the furnish in at least three steps; dewatering the
furnish on a wire to form a fiber web; pressing said fiber web;
drying the fiber web to form said paper product, said furnish
containing fillers in such an amount that the paper product
obtained by the process contains at least 15% by weight of
fillers.
2. The process as claimed in claim 1, wherein the paper product
contains 15-70% by weight of fillers.
3. The process as claimed in claim 1 or 2, wherein the polymer used
in each of the consecutive polymer treatment steps interacts with
the polymer used in the subsequent step.
4. The process as claimed in any of the preceding claims, wherein
at least one of the polymer treatment steps includes the addition
of an anionic polymer, and at least one of the polymer treatment
steps includes the addition of a cationic polymer.
5. The process as claimed in claim 4, wherein the anionic polymer
is CMC.
6. The process as claimed in claim 4, wherein the cationic polymer
is cationic starch.
7. The process as claimed in any of the preceding claims, wherein
the polymer treatment comprises three to seven steps.
8. A paper product produced according to the process of claim 1.
Description
[0001] The present invention relates to a process for the
production of a paper product with high filler content wherein the
furnish used is treated with polymers in steps.
BACKGROUND OF THE INVENTION
[0002] In papermaking processes there is an ongoing concern to find
ways to produce paper at reduced costs. Since fillers are cheaper
than fibers, one way is to increase the filler content of the paper
and thus be able to reduce the amount of fibers in the paper.
Besides being economically beneficial, fillers also improve the
opacity and printability properties of the paper. However, large
amount of fillers in the paper decreases the strength of the paper.
Thus, there is a balance between the possible amount of fillers
added and the required strength of the paper produced. Current
levels of fillers in paper vary depending on paper grade, for
example the filler content of newsprint may be up to about 12-14%.
The maximum filler content today, considering available publication
paper grades and fine paper grades, is about 35%, as it is in
uncoated magazine paper.
[0003] One way to compensate for the decrease in strength caused
when filler is added is to improve the fiber bonding properties
between the fibers in the paper, thereby maintaining the strength
of the paper. With increased strength of the paper it is possible
to increase the filler content. The predominant treatment for
improving paper strength, particularly dry strength, of paper has
so far been to add a strength agent, preferably cationic starch, to
the pulp fiber slurry prior to the sheet forming operation.
Cationic starch molecules added to the pulp slurries can adhere to
the naturally anionic pulp fibers by electrostatic attraction and
thus be retained in the wet fiber mat and remain in the final paper
or board. It is however difficult to adsorb large amounts of
cationic starch to the fibers.
[0004] When adding large amounts of cationic starch to a
papermaking furnish, in order to achieve high resulting paper
strength, two major problems arise. The first is that the cationic
starch molecules tend to saturate the anionic charge on the
cellulose fibers, thus setting a limit to the amount of cationic
starch which can be added to the slurry. If an excess of cationic
starch is added, only a portion of the starch added will be
retained in the sheet, and the rest will circulate in the paper or
board machine white water system. A second problem is that fibers
which are made cationic by excessive cationic starch addition, will
not be able to adsorb other cationic additives which are commonly
added to the pulp slurry, such as sizing agents and retention
aids.
[0005] Another method to enhance the strength properties of paper
is to treat the fibers with polymers in consecutive steps. The
international application WO 2006041401 describes such method where
a part of a furnish is treated with polymers in consecutive steps,
whereby a paper or board with improved strength and with reduced
amount of polymers is obtained.
[0006] Yet another method to enhance the strength properties of
paper is described in WO 0032702, in which particles (such as
fibers or fillers) are provided with a multilayer coating of
interacting polymers.
[0007] It is however still a need for a process by which paper
products having a maintained or improved strength could be produced
at a lower cost.
SUMMARY OF THE INVENTION
[0008] The object of the invention is to provide a process by which
a paper product having a high strength can be produced at low
cost.
[0009] It has now surprisingly been found that by subjecting both
fillers and fibers of a furnish to polymer treatment as set out in
claim 1, the strength of the resulting paper product is
significantly improved even though the filler content is high. The
above object is thus achieved by the present invention as defined
by the appended independent claims. Preferred embodiments are set
forth in the dependent claims and in the following description.
[0010] The present invention concerns a process for the production
of a paper product, which process comprises providing a furnish
comprising fillers and fibers; subjecting the furnish to polymer
treatment, in which polymers are added to the furnish in at least
three steps; dewatering the furnish on a wire to form a fiber web,
pressing said fiber web and drying the fiber web to form said paper
product; said furnish containing fillers in such an amount that the
paper product obtained by the process contains at least 15% by
weight of fillers. By treating the furnish, which contains fibers
and a high amount of fillers, with polymers, a paper product with
high strength is obtained.
[0011] The paper product produced preferably contains 15-70%
fillers by weight of the total paper weight.
[0012] The polymer used in each of the consecutive polymer
treatment steps is preferably interacting with the polymer used in
the subsequent step. The polymer treatment preferably includes one
step in which cationic polymer is added, and at least one step in
which anionic polymer is added. By alternating cationic and anionic
polymer additions it is believed that interacting polymer layers
are obtained. The cationic polymer is preferably cationic starch
and the anionic polymer is preferably CMC. The polymer treatment
preferably comprises three to seven consecutive steps.
[0013] The invention also relates to a paper product produced
according to the process of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0014] The invention relates to a process for the production of a
paper product from a furnish comprising fillers and fibers, wherein
the furnish is treated with polymers in at least three steps and of
which said furnish contains fillers in such an amount that the
paper product produced contains at least 15% by weight of fillers.
The invention also relates to a paper product produced according to
the process of the present invention.
[0015] It is possible to produce a paper or board with high amounts
of cationic starch and consequently receive a strong product. This
is shown in both WO 0032702 and in WO 2006041401.
[0016] It has now been found that by treating a furnish containing
both fillers and fibers with polymers in three or more polymer
treatments steps, the amount of fillers in the produced paper
product can be increased and the strength of the paper is very good
in spite of the high filler content of the paper. Surprisingly, the
filler content can be increased even more when the furnish treated
contains both fillers and fibers as compared to only treating the
fibers or the fillers of the furnish with polymers in consecutive
steps. One theory behind this is that when a furnish containing
both fillers and fibers is treated with polymers according to the
invention, the filler particles bind stronger to other filler
particles or to the fibers, and the filler content can consequently
be increased without affecting the strength of the paper
negatively. By treating the entire furnish with polymers in
consecutive steps and not only one part of the furnish as done in
WO 2006041401, it has even more surprisingly been seen that the
strength of the paper is maintained or even increased, even though
the filler content of the paper is increased.
[0017] The present process for producing a paper or board product
comprises, providing a furnish comprising fillers and fibers;
subjecting the furnish to polymer treatment, in which polymers are
added to the furnish in at least three steps; dewatering the
furnish on a wire to form a fiber web; pressing said fiber web and
drying the fiber web to form said paper product; said furnish
containing fillers in such an amount that the paper product
obtained by the process contains at least 15% by weight of fillers.
By treating the entire furnish, which comprises both fillers and
fibers, the filler content of resulting paper product, can be
increased and the strength of the resulting paper is still
surprisingly significantly good.
[0018] The filler content of the paper product is at least 15% by
weight of the total paper sheet weight, preferably 15-70% and even
more preferably 20-70% or 20-50% by weight, since it has been seen
that the strength of the paper still is high, even if the filler
content is increased, and it thus makes it possible to produce a
paper product at lower cost. The filler content is even more
preferably between 30-50% by weight since the strength of the paper
is good even at this high filler content, this can bee seen in
table 1. The filler content is adjusted in order to achieve the
desired strength of the paper product. It is desirable to have as
high filler content as possible without decreasing the strength to
unacceptable levels. The appropriate amount of fillers depends on
the properties of the furnish and on the quality demands of the
paper product. The amount of fillers added to the furnish, in order
to receive a paper product with a desired filler content, depends
on the filler retention of the fiber web, i.e. how much of the
added fillers that are retained in the resulting paper product. The
filler retention varies a lot and there are many factors that
affect it, some examples are: the grammage of the paper, the
formation unit of the paper machine, the fiber components of the
furnish and the use and amount of added retention agents.
Consequently, there is a wide range of what the filler retention
can be, normally the filler retention is about 20-70%, i.e. 20-70%
of the added fillers are retained in the paper product. To treat
the furnish with polymers according to the invention might also
affect the filler retention, however it is believed that the
polymer treatment affects the filler retention in a positively way.
This is due to the fact that both filler particles and fibers form
complexes and that these complexes might improve the fillers
ability to bind to the fibers in the paper and thus improve the
fillers ability to remain in the paper.
[0019] The polymer used in each of the consecutive polymer
treatment steps is preferably interacting with the polymer used in
the subsequent step, thereby enabling a larger amount of polymers
to be attached to the fillers and fibers and thus result in
increased strength of the final paper product. The polymer
treatment preferably includes one step in which anionic polymer is
added, and at least one step in which cationic polymer is added. By
alternating anionic and cationic polymer coatings interacting
polymer layers may be obtained.
[0020] The anionic polymer used may be one or more chosen from the
group consisting of: carboxy methyl cellulose (CMC), polyvinyl
sulphate, anionic galactoglucomannan, anionic starch,
polyphosphoric acid, alginate and polymethacrylic acid. The anionic
polymer is preferably CMC, since it has high charge density, which
reduces the amount of CMC needed in each addition, and which is
therefore economically beneficial. CMC also interacts very well
with cationic polymers, and especially cationic starch. Thus, the
use of CMC is very economically beneficial both due to its low
price as well as the reduced amount needed. The cationic polymer
used may be one or more chosen from the group consisting of:
cationic starch, polyvinyl amine, chitosan, primary and secondary
amines, polyethylene imines, polyvinyl pyrrolidone and modified
polyacryl amides. The cationic polymer is preferably cationic
starch, which is advantageous because it results in a paper having
enhanced strength properties and it is economically beneficial, due
to its low price and easy availability. It is preferable to use
cationic starch in combination with CMC since these two polymers
have been found to interact well with each other, resulting in
paper with good strength at a low cost.
[0021] The polymer treatment preferably comprises three to seven
consecutive steps. The optimal number of steps depends on what
properties of the paper that are desired and on the properties of
the furnish being treated. The more steps the treatment consists
of, the larger amount of polymers are added and thus retained in
the paper. Often it is a balance between the cost and the desired
properties, for example strength of the paper. There is usually a
limit when it is no longer cost effective to add more polymers with
respect to the improvement of the desired properties, for example
increase of strength or filler content of the paper manufactured.
It is preferred to add cationic polymer in a first step of the
polymer treatment and to add anionic polymer in a subsequent and to
continue with alternating additions of cationic and anionic
polymers, until the desired amount of polymers has been added in
the desired number of steps.
[0022] The furnish need not be washed between each polymer
treatment steps. Any unabsorbed excess of polymer added in the
preceding step can remain in the furnish and need not be rinsed
away. Washing between the polymer treatment steps has not been
shown to enhance the properties of the resulting product. It is
thus advantageous to subject the furnish to each of the polymer
treatment steps without any intermediate washing. Thereby, washing
between the polymer treatment steps is unnecessary and may be
excluded, thus a faster process is achieved which, in addition, has
lower water consumption.
[0023] After each polymer treatment step there should be sufficient
time and mixing for the polymer to be absorbed to the fillers and
fibers of the furnish. A time period of at least 5 seconds between
each polymer treatment step is suitable. The optimal time period
depends on the capacity of the mixing of the equipment.
[0024] The polymer of each polymer treatment step can be added to
the furnish in a pulp vessel, such as a pulp chest, or in-line in a
furnish transport pipe, or a combination thereof. The point of
addition of the polymer depends on the equipment available and
where it is practically possible to make the addition. When
carrying out three or more polymer treatment steps by in-line
addition of polymer it needs to be ensured that the pipe is long
enough to allow both thorough blending of polymer, filler and
fibers, and to allow enough time between each addition step for
absorption of the polymer. Alternatively an in-line mixer can be
used to ensure good mixing in the pipe.
[0025] The amount of polymer to be added varies depending of the
properties of the furnish. When cationic starch and CMC are used
for the polymer treatment the amount of cationic starch added in
each step is typically between 5-30 kg/ton and the amount of CMC
added in each step is typically between 0.25-3 kg/ton. The amount
of polymers added to the furnish may be decided by measuring the
charge of the pulp or the process water. Even if an excess amount
of added polymer is not detrimental to the final result, it may be
advantageous to add an amount of polymer that is close to what can
be absorbed by the pulp, both for economical and environmental
reasons. However, for some paper products it has been seen that an
excess of polymers added to the furnish results in an improved
paper product, i.e. a stronger product or a product with higher
filler content with remained strength. This might be explained by
that the polymers form polyelectrolyte complexes that could have
favorable affects on the properties of the paper product.
[0026] The furnish typically contains a mixture of different kinds
of pulp, for example chemical pulp (hardwood pulp, softwood pulp,
sulphate pulp or sulfite pulp) or mechanical pulp (CTMP or
TMP).
[0027] Examples of fillers used in the furnish are; kaolin, calcium
carbonate, precipitated calcium carbonate, talcum, gypsum and
synthetic fillers.
[0028] The paper product produced can be of any paper grade at any
grammage, for example fine paper, magazine paper or newsprint.
[0029] If necessary, additional generally known paper process
steps, such as coating and calendering, can be used in order to
produce the paper product according to claim 1.
EXAMPLE
[0030] Ten different furnish samples 1-10 were used to evaluate the
process. The furnish used was a mixture of groundwood and kraft
pulp in the ratio 2.5:1. In six of the samples only the fiber part
of the furnish was treated with polymers and in the remaining four
samples the entire furnish was treated with polymers. Clay was used
as filler and the filler content of the paper product was either
30% or 50%. For comparison, some samples were treated with cationic
starch in one step and the other samples were treated with cationic
starch and CMC in consecutive steps according to the invention.
[0031] The three sequential steps of the polymer treatment
were:
I. addition of cationic starch to the furnish sample; II. addition
of CMC to the furnish sample; and III. addition of cationic starch
to the furnish sample.
[0032] The charge of the furnish was measured after each addition,
and the amount of polymer added in each subsequent step was decided
based on these measurements. The polymers were added in excess as
compared to the amount determined on basis of the charge
measurement.
[0033] In samples 1-6 only the fiber part was subjected to polymer
treatment and thereafter fillers were added, and the fibers and
fillers were mixed into a furnish. Samples 7-10 were subjected as a
whole to the polymer treatment, i.e. the entire furnish comprising
both fibers and fillers were subjected to the polymer
treatment.
[0034] Sheets were then prepared by dewatering the furnish,
pressing and drying the fiber web and the density (ISO 5270),
tensile index (ISO 5270) and z-strength (SCAN P 80) were determined
for all sheets. Prior to testing the sheets were conditioned at
23.degree. C./50% RH. The results are shown in Table 1.
TABLE-US-00001 TABLE 1 Starch- Starch Filler CMC- z- analyzed Paper
content Starch Density Tensile strength in paper sheets Treatment
(%) (kg/ton) (kg/m3) index (Nm/g) (kPa) (%) 1 Fiber part 30 10-0-0
513 24.7 436 0.79 2 Fiber part 30 20-0-0 497 22.4 433 1.3 3 Fiber
part 30 25-0-0 486 23.1 427 1.3 4 Fiber part 30 25-2-20 502 22.4
485 2.6 5 Fiber part 50 25-0-0 512 11.5 334 0.97 6 Fiber part 50
25-2-20 512 11.7 373 2.1 7 Entire furnish 30 22-0-0 544 35.7 540
1.8 8 Entire furnish 30 22-2-22 554 41.3 720 3.1 9 Entire furnish
50 20-0-0 582 20.9 454 1.6 10 Entire furnish 50 20-2-20 620 25.6
634 3.2
[0035] Table 1 shows an increase in z-strength and tensile index
for the resulting paper product when the entire furnish is
subjected to polymer treatment, as compared to if only the fiber
part of the furnish were treated. It can also be seen that
treatment with polymers in consecutive steps improves both the
z-strength and the tensile index.
[0036] The density was also measured and it can be seen that in
many cases there is an increase of density as the amount of starch
in the sheet increases. However, the density increase is not large
enough to explain the increase of tensile index.
[0037] In order to get a better view of the results, they are also
shown in Diagram 1, Diagram 2 and Diagram 3. The abbreviation st,
as can bee seen in the diagrams stands for addition of cationic
starch in kg/ton.
[0038] The results of the z-strength measurements are shown in
Diagram 1.
[0039] Diagram 1 shows that the z-strength of the paper sheets
increases when the entire furnish is treated with polymers. The
highest z-strength can be found when the furnish is treated with
polymers in consecutive steps according to the invention.
Surprisingly, the z-strength of the paper sheets with a filler
content of 50% is very high.
[0040] The results of the tensile index are shown in Diagram 2.
[0041] Diagram 2 shows that the tensile index of the paper sheets
increases when the entire furnish is treated with polymers. The
highest value of the tensile index can be found when the furnish is
treated with polymers in consecutive steps according to the
invention.
[0042] Diagram 3 shows the tensile index compared to the amount of
starch in the paper sheets.
[0043] Diagram 3 shows that the tensile index of the sheets is best
for those sheets for which the entire furnish was treated with
polymers, even if the amount of starch in the sheets is not so
high. The tensile index of sheets with a filler content of 50%
where the entire furnish has been treated, is comparable to the
sheets with a filler content of 30% where only the fiber part of
the furnish has been treated with polymers.
[0044] Consequently, these tests presented in table 1, Diagram 1, 2
and 3 show that it is advantageous to treat the entire furnish
since it results in a paper having high strength at the same time
as the filler content can be increased.
* * * * *