U.S. patent application number 13/513410 was filed with the patent office on 2012-09-27 for process for production of a paper or paperboard product.
This patent application is currently assigned to STORA ENSO OYJ. Invention is credited to Lars Axrup, Isto Heiskanen, Mika Riikonen.
Application Number | 20120241114 13/513410 |
Document ID | / |
Family ID | 44115154 |
Filed Date | 2012-09-27 |
United States Patent
Application |
20120241114 |
Kind Code |
A1 |
Axrup; Lars ; et
al. |
September 27, 2012 |
PROCESS FOR PRODUCTION OF A PAPER OR PAPERBOARD PRODUCT
Abstract
The present invention relates to a process for producing a paper
or paperboard product which process comprises the steps of,
providing a furnish comprising fibers, adding starch to the
furnish, adding microfibrillated cellulose to the furnish,
conducting the furnish to a wire in order to form a web, wherein
the starch and microfibrillated cellulose is added separately to
the furnish.
Inventors: |
Axrup; Lars; (Hammaro,
SE) ; Heiskanen; Isto; (Imatra, FI) ;
Riikonen; Mika; (Lappeenranta, FI) |
Assignee: |
STORA ENSO OYJ
Helsinki
FI
|
Family ID: |
44115154 |
Appl. No.: |
13/513410 |
Filed: |
November 30, 2010 |
PCT Filed: |
November 30, 2010 |
PCT NO: |
PCT/SE10/51322 |
371 Date: |
June 1, 2012 |
Current U.S.
Class: |
162/127 ;
162/175 |
Current CPC
Class: |
D21H 21/18 20130101;
D21H 17/28 20130101; D21H 27/30 20130101; D21H 11/18 20130101 |
Class at
Publication: |
162/127 ;
162/175 |
International
Class: |
D21H 23/04 20060101
D21H023/04; D21H 17/28 20060101 D21H017/28 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 3, 2009 |
SE |
0950930-8 |
Claims
1. A process for producing a paper or paperboard product which
process comprises the steps of: providing a furnish comprising
fibers, adding starch to the furnish, adding microfibrillated
cellulose to the furnish, conducting the furnish to a wire in order
to form a web, wherein the starch and microfibrillated cellulose is
added separately to the furnish.
2. The process according to claim 1 wherein 2-15% by weight of
starch and 1-15% by weight of microfibrillated cellulose is
added.
3. The process according to claim 1 wherein the web being formed by
said furnish comprising starch and microfibrillated cellulose forms
a layer of the paper or paperboard product.
4. The process according to claim 3 wherein the web forms a middle
layer of the paper or paperboard product.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a process for production of
a paper or paperboard product comprising a furnish which comprises
starch and microfibrillated cellulose.
BACKGROUND
[0002] In papermaking processes there is an ongoing concern to find
ways to produce paper or paperboard at reduced costs without
impairing the properties of the product, e.g. without decreasing
the strength of the product.
[0003] One way to reduce the cost is to increase the filler content
of a paper or paperboard product and thus be able to reduce the
amount of fibers in the paper or paperboard. Besides being
economically beneficial, fillers also improve the opacity and
printability properties of the product. However, large amount of
fillers in the product decreases the strength. Thus, there is a
balance between the possible amount of fillers added and the
required strength of the paper or paperboard produced.
[0004] Furthermore, during production of paperboard there is a
desire to produce a strong but yet low density product. When
increasing the strength of a paperboard the density normally
increases. There is thus a balance between the desired strength and
the density of the paperboard product.
[0005] It is possible to compensate for the decrease in strength,
caused for example by addition of large amount of filler or by
increased bulk, by improving the fiber bonding properties between
the fibers in the paper or paperboard, thereby maintaining the
strength. The predominant treatment for improving paper or
paperboard strength, particularly dry strength, has so far been to
add a strength agent, preferably cationic starch, to the furnish
prior to the sheet forming operation. Cationic starch molecules
added to the furnish 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 paperboard.
[0006] 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.
Furthermore, high amounts of starch often cause problems with
runnability, microbiology and foaming during the production
process.
[0007] It has recently been found that addition of microfibrillated
cellulose to a paper or board will increase the strength of the
product, probably due to the improved fiber bonding.
[0008] However, there is still a need for a cost efficient product
with good strength properties.
SUMMARY OF THE INVENTION
[0009] It is an object of the present invention to provide a
process which in an easy and cost efficient way will be able to
produce a paper or paperboard with improved strength and
density.
[0010] These objects and other advantages are achieved by the paper
or paperboard product according to claim 1. The present invention
relates to a process for producing a paper or paperboard product
which process comprises the steps of; providing a furnish
comprising fibers, adding starch to the furnish, adding
microfibrillated cellulose to the furnish and conducting the
furnish to a wire in order to form a web, wherein the starch and
microfibrillated cellulose is added separately to the furnish. It
has been shown that a product comprising both starch and
microfibrillated cellulose (MFC) increases the strength of the
product since the amount of starch can be increased without
increasing the density of the paper or paperboard product.
[0011] It is preferred that the furnish comprises 2-15% by weight
of starch and 1-15% by weight of microfibrillated cellulose. The
amount of starch respectively MFC of the product depends on the end
use and the corresponded desired properties of the product. High
amounts of starch will increase the strength of the product and it
has been shown that the combination of MFC and starch makes it
possible for the product to retain larger amounts of starch.
[0012] The web being formed by said furnish comprising starch and
microfibrillated cellulose preferably forms a layer of the paper or
paperboard product. The paper or paperboard product is preferably a
multilayer product which comprises at least two layers. It may be
preferred that the product comprises at least three layers and that
the layer located in the middle of the product comprises furnish
comprising starch and microfibrillated cellulose, i.e. the web
being formed by the furnish that comprises starch and MFC, forms a
middle layer of the paper or paperboard.
DETAILED DESCRIPTION
[0013] The invention relates to a process for production of a paper
or paperboard product comprising a furnish which comprises starch
and microfibrillated cellulose. The furnish comprises starch in an
amount of 2-15% by weight, preferably between 3-5% by weight.
Consequently, the product thus comprises starch of an amount of
2-15% by weight, preferably between 3-5% by weight.
[0014] The furnish preferably comprises cellulosic fibers. The
cellulosic fibers may be hardwood and/or softwood fibers. The
cellulosic fibers may be mechanically, chemimechanically and/or
chemically treated. The fibers may also be bleached or
unbleached.
[0015] It has been found that the addition of starch and
microfibrillated cellulose (MFC) to a furnish has a very good
effect on the strength of the paper or paperboard. Products
comprising both starch in large amounts and MFC, makes it possible
for the product to retain larger amount of starch. Surprisingly, it
has also been found that the addition of both starch, in large
amounts, and MFC do not increase the densification of the product.
The combination of MFC and starch thus has a synergistic effect
when it comes to boosting the strength of a paper or paperboard
product without increasing the density of the product to the same
extend. It is thus possible to decrease the density of the paper or
paperboard product but still be able to produce a strong product.
In this way a much cheaper product can be produced since the fiber
content of the product can be decreased and the strength can be
remained (compared to products produced according to prior art).
Furthermore, the weight of the product will be decreased which will
reduce costs during transportation and handling.
[0016] Microfibrillated cellulose (MFC) (also known as
nanocellulose) is a material made from wood cellulose fibers, where
the individual microfibrils have been partly or totally detached
from each other. MFC is normally very thin (.about.20 nm) and the
length is often between 100 nm to 10 .mu.m. However, the
microfibrils may also be longer, for example between 10-100 .mu.m
but lengths up to 200 .mu.m can also be used. Fibers that has been
fibrillated and which have microfibrils on the surface and
microfibrils that are separated and located in a water phase of a
slurry are included in the definition MFC.
[0017] MFC can be produced in a number of different ways. It is
possible to mechanically treat cellulosic fibers so that
microfibrils are formed. The production of nanocellulose or
microfibrillated cellulose with bacteria is another option. It is
also possible to produce microfibrils from cellulose by the aid of
different chemicals and/or enzymes which will break or dissolve the
fibers.
[0018] One example of production of MFC is shown in WO2007091942
which describes production of MFC by the aid of refining in
combination with addition of an enzyme.
[0019] It is also possible to modify the microfibrillated cellulose
before addition to the furnish. In this way it is possible to
change its interaction and affinity to other substances. For
example, by introducing more anionic charges to MFC the stability
of the fibril and fibril aggregates of the MFC are increased. How
the modification of the microfibrillated fibers is done depends,
for example on the other components present in the furnish.
[0020] The furnish comprises 2-15% by weight of starch, preferably
between 3-5% by weight, and it is preferred that the furnish
further comprises MFC in an amount of 1-15% by weight. The chosen
amount of starch respectively MFC added to the furnish depends on
the final product produced and the desired properties of the
product. Higher amounts of starch will increase the strength of the
product. However, it is not possible to increase the amount of
starch too much since other problems then may occur. Also, the
amount of MFC must be regulated based on the amount of starch and
of course also on the end use of the product. Too high amounts of
MFC may cause dewatering problems since MFC is a very fine material
which easily absorbs water and increased content will make it more
difficult to dewater the product.
[0021] The paper or paperboard product is preferably a multilayer
product comprising at least two layers. It may be preferred that
the product comprises at least three layers and that the layer
located in the middle of the product comprises furnish comprising
starch and microfibrillated cellulose. However, it is also possible
that at least one outer layer of the product or even all layers of
the product comprises furnish comprising starch and MFC. For some
products it might be advantageous that at least one of the outer
layers comprises furnish comprising starch and MFC. In this way it
is possible to increase the strength and/or the bulk of this layer.
Consequently, depending on the end use of the product, it is
decided which and how many of the layers that will comprise furnish
comprising starch and MFC.
[0022] It is not necessary that the entire furnish in a layer of
the paper or paperboard product comprises starch and MFC, but it is
preferred that the starch and MFC is added to the majority of the
furnish of the layer. However, the layer may also comprise other
components, such as broke pulp which does not comprise starch and
MFC.
[0023] The furnish may also contain various amounts of fillers to
increase for example runnability and cost-efficiency of the process
and the produced substrate. Other commonly used additives used in
the production of paper or paperboard can also be added.
[0024] The paperboard product is preferably a high quality
paperboard product, such a liquid packaging board, graphical board
or food service board. The paper product is preferably a high
quality paper, such as copy paper of grades A or B, graphical
papers, LWC, SC or news paper for high speed printing machines.
[0025] The process for producing a paper or paperboard product
which process comprises the steps of providing a furnish comprising
fibers, adding starch to the furnish, adding microfibrillated
cellulose to the furnish and conducting the furnish to a wire in
order to form a web. The addition of starch and MFC is preferably
done in the machine chest or before the fan pump. It may also be
possible to do the addition to the circulation water which later on
is added to the furnish. However, all practical points of addition
for the starch and MFC can be used as long as there is enough time
and mixing of the starch and MFC with the furnish before it is
conducted to the wire.
[0026] The starch and MFC is added separately. It is preferred to
first add starch followed by addition of MFC. It could be possible
to mix the starch and MFC before addition to the furnish, however
the result is then not as good as when starch and MFC is added
separately. It is then possible to mix starch and MFC before
addition to the furnish by cooking them, preferably by the use of a
jet-cooker. It has been shown that by cooking the mixture of starch
and MFC, the MFC shows less tendency to flocculate. Furthermore, by
altering the charge and charge density of e.g. starch, different
degrees of flocculation can be obtained and it would thus be
possible to neutralize the charge of MFC. This might affect
dewatering and retention of the fibers and eventual fillers in the
product. It may also be possible to add a layer of starch on the
MFC and then add this mixture to the furnish, i.e. a multilayering
effect can be created.
EXAMPLES
Material Used
[0027] Bleached chemothermomechanical pulp (BCTMP) at 570 CSF.
[0028] Microfibrillated cellulose (MFC) was prepared by refining
bleached hardwood sulphite pulp of 4% consistency with edge load of
2 Ws/m to 28 SR. The pulp were thereafter enzymatically treated
with Endoglucanase (Novozym 476) with the activity of 0.85 ECU/g.
The enzymes were dosed to the pulp and which thereafter was treated
at 50.degree. C. for 2 hours, at pH 7. After the enzymatic
treatment, the pulp was washed and enzymes were deactivated at
80.degree. C. for 30 min. The pulp was thereafter refined once more
to 90-95 SR and the refined pulp was then fluidized
(Microfluidizer, Microfuidics corp.) by letting pulp of 3%
consistency pass through a 400 .mu.m chamber followed by a 100
.mu.m chamber wherein the MFC used were formed.
[0029] Starch used was cationized starch, Raisamyl 70021, Ciba (now
BASF). C-PAM used was Percol 292 NS, Ciba (now BASF).
[0030] BMA used was Eka NP495, Eka Chemicals.
Example 1
[0031] The dried BCTMP were soaked in water over night and then
dispersed in hot water. The BCTMP suspension was thereafter diluted
to a concentration of 0.3%.
[0032] The produced MFC was also diluted to a concentration of 0.3%
and dispersed using a kitchen mixer.
[0033] A formette sheet former was used to prepare the sheets for
testing. The sheets were prepared according to the following
procedure; Pulp suspension measured to produce a 150 gsm sheet was
added to the stock tank. During agitation, starch if used, and MFC
if used, was added. After 30 seconds, 500 g/t C-PAM was added and
after another 30 seconds was 300 g/t BMA added to the stock and the
sheet forming was thereafter started.
[0034] The formed sheet was wet pressed and dried while the
shrinkage was constrained. The dried sheet was tested for
structural density according to SCAN P 88:01, z-strength according
to SCAN P 80:88 and tensile strength index according to ISO
1924-3.
TABLE-US-00001 TABLE 1 Results of strength and density tests.
Tensile strength Structural Index density z-strength geometrical
mean Sample (kg/m3) (kPa) (Nm/g) Reference 570CSF 388 103 27
Addition of 5% MFC 459 218 40 Addition of 5% Starch 396 142 32
Addition of 5% MFC and 436 240 44 2.5% Starch Addition of 5% MFC
and 426 256 47 5% Starch
[0035] As can be seen from table 1 above it is clear that the
addition of the combination of MFC and starch strongly increases
the strength, both the z-strength and the tensile index.
Furthermore, the densification of the sheets has decreased compared
to if only MFC was added.
Example 2
[0036] Tests were also performed where MFC and cationic starch
either was pre-mixed or added separately to the stock.
[0037] When pre-mixed, the MFC and cationic starch was well mixed
before addition to the stock. When added separately, cationic
starch was first added and well mixed with the stock for 5 minutes
followed by addition of MFC.
[0038] MFC in an amount of 25 kg/t and cationic starch in an amount
of 20 kg/t were added in both samples, both the pre-mixed and the
separately added.
[0039] After addition of the MFC and cationic starch to the stock,
a formette sheet former was used in the same manner as described in
Example 1.
[0040] As a reference the stock without any MFC and cationic starch
was used.
[0041] Scott Bond was measured according to TAPPI UM-403.
TABLE-US-00002 TABLE 2 Results of strength and density tests.
Structural density z-strength Scott Bond Sample (kg/m3) (kPa)
(J/m2) Reference 310 170 100 Pre-mixed sample 320 210 125
Separately added sample 320 225 145
[0042] As can be seen from Table 2, both z-strength and Scott Bond
is increased when cationic starch and MFC is separately added to
the stock.
[0043] In view of the above detailed description of the present
invention, other modifications and variations will become apparent
to those skilled in the art. However, it should be apparent that
such other modifications and variations may be effected without
departing from the spirit and scope of the invention.
* * * * *