U.S. patent application number 12/746790 was filed with the patent office on 2010-10-07 for arrangement in connection with the press section of a web-forming machine and board or paper produced in such arrangement.
This patent application is currently assigned to STORA ENSO OYJ. Invention is credited to Pekka Kylliainen, Kari Raisanen.
Application Number | 20100252215 12/746790 |
Document ID | / |
Family ID | 39387107 |
Filed Date | 2010-10-07 |
United States Patent
Application |
20100252215 |
Kind Code |
A1 |
Kylliainen; Pekka ; et
al. |
October 7, 2010 |
ARRANGEMENT IN CONNECTION WITH THE PRESS SECTION OF A WEB-FORMING
MACHINE AND BOARD OR PAPER PRODUCED IN SUCH ARRANGEMENT
Abstract
The invention relates to an arrangement in connection with the
press section of a web-forming machine. The arrangement includes at
least one press nip (10) for dewatering the web (11) manufactured
on a web-forming machine. The arrangement also includes a smoothing
press (12) including a soothing roll (13) arranged after the press
nip (10). The smoothing press (12) includes smooth heat carrying
means (14') arranged as a loop around at least two guide rolls
(15). The smoothing roll (13) is arranged into contact with the
means (14') between two guide rolls (15). The smoothing roll (13)
and/or at least one of the guide rolls (15) is a steam heated
drying cylinder or a steam heated roll modified thereof. The
invention aldo relates to a board or paper produced in such
arrangement.
Inventors: |
Kylliainen; Pekka; (Imatra,
FI) ; Raisanen; Kari; (Jyvaskyla, FI) |
Correspondence
Address: |
FILDES & OUTLAND, P.C.
20916 MACK AVENUE, SUITE 2
GROSSE POINTE WOODS
MI
48236
US
|
Assignee: |
STORA ENSO OYJ
Helsinki
FI
METSO PAPER, INC.
Helsinki
FI
|
Family ID: |
39387107 |
Appl. No.: |
12/746790 |
Filed: |
December 10, 2008 |
PCT Filed: |
December 10, 2008 |
PCT NO: |
PCT/FI08/50724 |
371 Date: |
June 8, 2010 |
Current U.S.
Class: |
162/100 ;
162/359.1 |
Current CPC
Class: |
D21F 5/04 20130101; D21F
3/0281 20130101; D21F 3/045 20130101; D21G 1/0066 20130101 |
Class at
Publication: |
162/100 ;
162/359.1 |
International
Class: |
D21H 11/00 20060101
D21H011/00; D21F 3/00 20060101 D21F003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 20, 2007 |
EP |
07150199.3 |
Claims
1. Arrangement in connection with the press section of a
web-forming machine, which arrangement includes at least one press
nip for dewatering the web manufactured on a web-forming machine,
and a smoothing press including a smoothing roll arranged after the
press nip, characterized in that the smoothing press includes
smooth heat carrying means arranged as a loop around at least two
guide rolls, and the smoothing roll is arranged into contact with
the means between two guide rolls, and the smoothing roll and/or at
least one of the guide rolls is a steam heated drying cylinder or a
steam heated roll modified thereof.
2. Arrangement according to claim 1, characterized in that the
smoothing press is arranged in the direction of motion of the web
when the dry content of the web is 60% or more.
3. Arrangement according to claim 1, characterized in that the
smooth heat carrying means consist of a belt made of metal.
4. Arrangement according to claim 1, characterized in that the
smoothing roll and/or at least one of the guide rolls is arranged
to be heated by steam, infrared, resistive, inductive or
gas-burning heating means.
5. Arrangement according to claim 1, characterized in that all
guide rolls are steam cylinders or steam heated rolls modified
thereof.
6. Arrangement according to claim 1, characterized in that the
diameter of the smoothing roll and/or the guide roll is 1000-2500
mm, preferably 1300-2000 mm.
7. Arrangement according to claim 1, characterized in that the
smoothing press has a hood.
8. Arrangement according to claim 3, characterized in that the
tension of the belt is 0.3-15 kN/m, preferably 5-10 kN/m.
9. Arrangement according to claim 3, characterized in that in
connection with both smoothing roll and belt there are cleaning
equipments which include high-pressure water cleaners.
10. Arrangement according to claim 1, characterized in that the
smoothing press has a linear load which is 1-150 kN/m, preferably
5-100 kN/m.
11. Arrangement according to claim 3, characterized in that the
smoothing roll has a counter roll which is arranged inside the belt
arranged as a loop.
12. Arrangement according to claim 3, characterized in that the
smoothing roll and the belt form two gaps which open downwards.
13. Arrangement according claim 1, characterized in that in
connection with the smoothing press there are auxiliary heating
means for heating the web and/or the smooth heat carrying
means.
14. Arrangement according to claim 1, characterized in that the
arrangement is intended for dewatering and/or processing board
webs, especially liquid packaging board or cup board.
15. Board or paper produced in the arrangement according to claim
1, for use as a liquid packaging board, having an initial roughness
before pre-calendering or calendering Bendtsen value below 1000
ml/min, a Scott Bond of 120-350 J/m.sup.2, a bending resistance
index of 8-25 Nm.sup.6/kg.sup.3, a hexanal value below 600 ppb when
measured within one week from the board manufacture and an EWT
(lactic acid) value below 2 kg/m.sup.2 and/or an EWT (hydrogen
peroxide) value below 2 kg.sup.2/m.sup.2.
16. Board or paper produced in the arrangement according to claim
1, for use in the manufacture of cups for holding liquids, said
board having an initial roughness before pre-calendering or
calendering Bendtsen value below 1000 ml/min, a bending resistance
index of at least 5 Nm.sup.6/kg.sup.3, a Scott Bond value of at
least 160 J/m.sup.2, a CD stretch to break of at least 2.5%,
preferably at least 3.5%, a hexanal value below 600 ppb when
measured within one week from the board manufacture, preferably
below 400 ppb, and a EWT (cream coffee) value below 1.8
kg.sup.2/m.sup.2.
17. Board or paper produced in the arrangement according to claim
1, for use as a graphical board wherein said board having an
initial roughness before pre-calendering or calendering Bendtsen
value below 1000 ml/min, a Scott Bond value of at least 130
J/m.sup.2, a hexanal value below 1000 ppb when measured within one
week from the board manufacture and a brightness (ISO-UV; measured
with 420 nm filter) of at least 82% for the uncoated board.
18. Board or paper produced in the arrangement according to claim
1, for use as food service board, said board having an initial
roughness before pre-calendering or calendering Bendtsen value
below 1000 ml/min, a bending resistance index of at least 5
Nm.sup.6/kg.sup.3, a Scott Bond value of at least 130 J/m.sup.2, a
CD stretch to break of at least 2.5%, preferably at least 3.5% and
a hexanal value below 600 ppb when measured within one week from
the board manufacture, preferably below 400 ppb.
Description
[0001] The present invention relates to an arrangement in
connection with the press section of a web-forming machine, which
arrangement includes [0002] at least one press nip for dewatering
the web manufactured on a web-forming machine, and [0003] a
smoothing press including a smoothing roll arranged after the press
nip.
[0004] The present invention also relates to a board or paper
produced in such arrangement.
[0005] In the press section of a web-forming machine lots of water
is rapidly removed from the web. The press section has usually one
or two press nips and press felts are also used. The press nip is
often formed of two rolls arranged to be loaded against each
other.
[0006] The quick removing of water causes surface densification of
the same side of the web where the water is removed.
Simultaneously, an oil absorption reduction appears and the print
quality degrades. To avoid these problems a smoothing press is
arranged after the press section. Traditionally the smoothing press
includes two rolls forming a nip. The web is thus pressed in the
nip without any press felt. Due to this fact water is not removed
from the web in the smoothing press. However, both surfaces of the
wet web get smoother which improves drying of the web in the drying
section.
[0007] One target in the web-forming is to maintain both sides of
the web as symmetrical as possible. However, this has occasionally
required very complicated structures in the press sections and
smoothing presses. Also, when heating the paper or board some
problems have occurred. In the conventional short heated smoothing
nip the water may turn to steam with a sudden heat or press
impulse. This leads to delamination of the web. Furthermore the
brightness and opacity of the web may decrease and the web can
stick to the surfaces, for example to the surface of the roll.
[0008] The invention is intended to create a new type of
arrangement in connection with the press section of a web-forming
machine by means of which arrangement the quality of the surfaces
of the web can be improved together with better drying properties.
The characteristic features of this invention are stated in the
accompanying Claims. The arrangement according to the invention is
a new kind of combination of a press nip and a smoothing press. In
the smoothing press according to the invention the web is heated
efficiently without any risk of delamination. Simultaneously, both
surfaces of the web get smooth which intensifies drying of the web.
Other properties and advantages of the arrangement are discussed
later. The paper or board produced in the arrangement according to
the invention has surprisingly improved properties, above all, the
initial smoothness of the paper or board product is improved
resulting in improved stiffness and more efficient drying of the
paper or board. Dry content of 60% or more enables smoothing with
lower nip loads and without the need of moisturising. However, the
smoothing press can be applied for paper or board products
independent of the of content with appropriate moisturising and
even just before reeling.
[0009] In the following, the invention is described in detail with
reference to the accompanying drawings showing two embodiments of
the invention, in which
[0010] FIG. 1 shows a schematic drawing of a side view of the
arrangement according to the invention,
[0011] FIG. 2 shows a schematic drawing of a side view of the
embodiment of the arrangement according to the invention.
[0012] FIG. 1 shows an arrangement according to the invention in
connection with the press section of a web-forming machine. The
arrangement includes at least one press nip 10 for dewatering the
web 11 manufactured on a web-forming machine. In FIG. 1 there is
actually three press nips. The arrangement also includes a
smoothing press 12 including a smoothing roll 13. The smoothing
press 12 is arranged after the press nip 10. When arriving to the
smoothing press, the web has a dry content of 60% or more.
According to the invention the smoothing press 12 also includes
smooth heat carrying means 14', such as a belt 14. The belt is
preferably made of metal. The metal belt is smooth and has no void
volume for water removal. The belt 14 is arranged as a loop around
at least two guide rolls 15. The smoothing roll 13 is then arranged
into contact with the belt 14 between two guide rolls 15. Thus, a
non-water removing long nip area is formed with the metal belt.
During the processing of the web, the web is guided between the
belt and the smoothing roll. Then both surfaces of the web will be
smoothened in this long wrap metal belt smoothing nip. In addition,
the smoothing roll 13 and/or at least one of the guide rolls 15 is
arranged to be heated by steam. Thus, the web is also heated in an
efficient way. In practice the rolls are internally heated, for
example, with steam.
[0013] According to the invention, the press nip 10 is a roll nip
or a long nip press. A long nip and low specific pressure in the
press nip is very beneficial to the final bulk and bending
stiffness of the paper or board. Preferably, the long nip press is
a shoe press. With the shoe press high amount of water can be
removed from the web. This increases both bulk and dry content of
the paper or board but it can make the surfaces of the web porous.
However, the web is then smoothened in the smoothing press
according to the invention. This results in a paper or board with
improved bulk or in a paper or board with improved surface
properties with standard bulk. Simultaneously, drying efficiency
can be improved since the contact between the web and the drying
rolls is improved. This results in, for example, reduced drying
shrinkage in the cross direction of the paper or board. The belt
and the smoothing roll have very smooth surfaces which is important
in view of smoothing. Due to the long nip area in the smoothing
press heat has time to penetrate through the web and thus also to
increasing the temperature of the middle layer of the web.
[0014] Heating of a web influences the smoothness of the web. The
smoothing press according to the invention has a more efficient
heating equipment compared to prior art. First, the smoothing roll
13 can be a steam cylinder or a steam heated roll modified thereof.
Secondly, at least one of the guide rolls 15 can be a steam
cylinder or steam heated roll modified thereof. A combination of
the first two embodiments is also possible. Also all guide rolls 15
can be steam cylinders or steam heated rolls modified thereof.
Steam is very efficient source of heat and the structure of a steam
cylinder is simple. The required temperatures can be achieved with
a steam system of 1-10 bar. Temperatures of smoothing press are
around 20-300.degree. C., preferably 50-170.degree. C. If needed,
there can be also some auxiliary heating means 21 for the rolls 13,
15. The auxiliary heating means can include, for example infrared,
resistive, inductive or gas-burner heater. There can be also a
combination of the above mentioned heaters and the belt can also be
heated. Some special arrangements can also be equipped with above
mentioned auxiliary heating means without any steam heated
solutions. In practise the diameter of the smoothing roll 13 and/or
the guide roll 15 is 1000-2500 mm, preferably 1300-2000 mm. Thus,
the nip area becomes long and the rolls are stiff. In spite of
large rolls the actual size of the smoothing press stays quite
small. Preferably the smoothing press 12 also has an own hood 16.
In this way it is possible to independently control the smoothing
press and runaway heat flows can be avoided. Also excess or extra
moisture can be handled with removal of moist air. The hood can
also be common with the hood of the drying section.
[0015] In FIG. 1 there is an open draw from the press nip 10 to the
smoothing press 12. The tail threading is handled for example by
ropes arranged to the side of the press section. However, vacuum
belt conveyors and air blowings can be used.
[0016] The belt can be made of metal, for example of steel. The
thickness of the metal belt is about 1 mm. In order to achieve a
stable run of the belt quite high tensions are needed. According to
the invention, the tension of the belt 14 is 0.3-15 kN/m,
preferably 5-10 kN/m. The position and alignment of one or more
guide rolls can be adjusted. Thus, the smoothing press can be
controlled for every situation.
[0017] The web may dust during smoothing. Also fibres, fines,
chemical deposit or stickies can stick to the surface of the rolls
or belt. According to one preferred embodiment of the invention,
there are cleaning equipments 17 which include high-pressure water
cleaners preferably in connection with both the smoothing roll 13
and the belt 14. The cleaners are used continuously and bigger
particles are removed with doctors 18. For better cleaning results
the temperature of the cleaning medium can be risen close to
100.degree. C. which also reduces the cooling effect of the
cleaners.
[0018] The smoothing effect of the smoothing press is achieved by
long wrap metal belt nip area together with smooth surfaces of the
belt 14 and the smoothing roll 13, and heating. The length of the
nip is 500-2500 mm, preferably 1000-2000 mm. There is no need to
press the web which would decrease the bulk. Thus, the smoothing
press 12 has a linear load which is 1-150 kN/m, preferably 5-100
kN/m. This nip pressure can be adjusted for example by moving one
guide roll. If additional pressing is needed the smoothing roll 13
can be equipped with a counter roll 20 which is arranged inside the
belt 14 arranged as a loop. By loading the counter roll against the
smoothing roll, the nip pressure is locally increased. The counter
roll is preferably a crowned or tube a roll.
[0019] The smoothing roll 13 is arranged into contact with the belt
14 between two guide rolls 15. The rolls are situated in such a way
that the smoothing roll 13 and the belt 14 form two gaps 19 which
open downwards. The gaps are under the loop which keeps the
smoothing press clean if threading tail breaks. Also, if something
else than the web enters into the closing gap, it will come out and
fall underneath the smoothing press by way of gravity.
[0020] The second embodiment of the present invention shown in FIG.
2 includes a dryer 22 arranged between the press section and the
smoothing press 12. The dryer 22 is for increasing the temperature
of the web and decreasing the water content therein. Thus the
smoothing process becomes more effective. Here the dryer 22
includes four steam cylinders and one drying wire. This
web-preheating arrangement according to FIG. 2 also enables less or
no heating in the actual smoothing press.
[0021] In FIG. 1 and FIG. 2 the web is guided from the smoothing
press to the drying section. Due to the smoothing press according
to the invention the first drying cylinder can be warmer than
previously. The above mentioned arrangement is advantageous when
forming board and especially board with one or more plies. In known
web-forming machines, the drying of the different plies of the
board will occur at different times, i.e. the middle ply will have
a different drying time than the top plies. Also, the shrinking
forces of different plies are different in the top and middle of
the web. In other words, when the top ply shrinks, the middle ply
is still wet and can not resist shrinkage. This causes defects of
the surface properties of the board and especially in the edge
areas of the board where the board can dry freely. With the
smoothing press the temperature of the web can be raised. Thus, the
effect of z-directional shrinkage difference can be minimized.
Simultaneously, higher initial cylinder temperatures can be used in
the drying section. This improves the drying capacity of the drying
section as a whole. Also the improved smoothness of the web will
increase the friction between drying cylinders and drying fabrics.
This will improve the surface properties of the board especially in
the edge areas.
[0022] The arrangement according to the invention is compact and it
has many advantageous features. Due to the long wrap metal
smoothing nip, the web has higher dry content than in the ordinary
smoothing press. Also, the surfaces of both sides of the web are
very similar. The components of this arrangement are simple so the
founding costs are low. Also, there are only minor press felt
markings on the web after leaving the smoothing press. The web has
very good smoothness and bulk both after the press section and also
for the end product. As mentioned earlier, this leads to improved
contact between drying cylinders and drying fabrics. Also the
drying shrinkage is reduced and the temperature transmission from
drying cylinders to the web is improved. When the drying efficiency
gets higher the production capacity can be improved or higher bulk
can be achieved after the press section. When the smoothness is
improved in the metal belt smoothing press there is less need for
calendaring after the drying section. This leads to improved
bending stiffness because the caliper of the web is improved. Also,
the reduced z-directional temperature gradient leads to reduced
drying roughening which improves the cross direction uniformity of
the web.
[0023] The press section has few press nips. The structure of the
press section is thus simple which improves the runnability of the
press section and reduces the investment costs. This gives a short
payback period for the smoothing press arrangement according to the
invention. Also, the space needed for the press section is reduced.
The metal belt smoothing press has also effect on the strength
properties of the end product. In practise, a minimum web stretch
on the press section keeps the md/cd strength property ratio down.
This kind of ratio is desirable for packaging board end uses. Also,
both sides of the board have improved similarity. The smoothing
press also changes the surface properties of the web. Also, it is
possible to adjust the temperatures of the sides of the paper or
board in the smoothing press. Hence, it is easy to change the
sidedness of the paper or board. When the web is already preheated
in the smoothing press, higher initial cylinder temperature can be
used in the drying section without fibre picking and dusting or
linting problems.
[0024] The press section is intended for dewatering and/or
processing paper of board webs. The board can have one or more
plies. Liquid packaging board and cup stock board are preferable
end products. In spite of the end use, the board has no warpages or
curlings and it has a good stiffness. According to the invention,
the heating means or heat carrying means or cleaning equipments
includes one or more suitable device for heating, heat carrying or
cleaning, respectively.
[0025] The boards are divided into a number of different types,
depending on their intended end use. Each application makes
different demands on the properties of the board and each board
type therefore implies certain characteristics, such as strength
properties, internal bonding (Scott Bond (J/m.sup.2), bending
resistance index (Nm.sup.6/kg.sup.3), taint/odour (hexanal value
(ppb)); brightness (ISO) (%) and edge penetration. The different
board applications of this invention are therefore characterized by
means of parameters, which correspond to their intended end use.
The following methods and standards apply both to the definitions
of the appended claims.
[0026] The edge penetration is a measure of hydrophobicity and
sizability and is measured by an edge penetration test EWT (Edge
Wick Test) according to the following method: board samples are
conditioned at 23.degree. C., 50% RH for 10 minutes. The samples
are then cut to a specific size and the thickness of the samples is
measured. The samples are then covered on both sides with a
waterproof tape, the edges of the samples are thus uncovered, and
the weight of the samples is measured. The size of the samples is
for example 25.times.75 mm. Thereafter, the samples are put into a
test solution (bath) for a certain period of time: lactic acid
(concentration 1%, 1 hour), hydrogen peroxide (concentration 35%,
70.degree. C., 10 minutes), cream coffee (1 l tap water, 9.5 g
instant coffee, 17.5 g dry cream, 80.degree. C., 10 minutes). The
weight of the samples is measured after the samples have been in
the bath. The wick index is then calculated by the formula:
E = W 2 - W 1 t l ##EQU00001##
where E=Wick index [kg/m.sup.2] W.sub.1=weight before bath [mg]
W.sub.2=weight after bath [mg] t=thickness (.mu.m) l=total length
of the edges of the samples [m]
[0027] Hexanal is measured within one week from production of the
board according a gas chromatography method, in which a sample is
heated in a headspace (Perkin Elmer HS 40XL) to a temperature of
90.degree. C. for 40 minutes, and the gas formed is conducted to
the gas chromatograph (AutoSystem XL with a FID), where the
components of the sample are separated. The amount of hexanal is
measured in ppb (.mu.g/kg).
[0028] Bending resistance is measured according to SCAN-P
29:95(L&W 15 degrees). Bending resistance index (F) is
calculated: F=10.sup.6*F.sub.b/w.sup.3 (Nm.sup.6/kg.sup.3), where w
grammage (g/m.sup.2) and F.sub.b is bending resistance (mN). The
bending resistance index refers to the geometrical bending
resistance index, which is calculated
F.sub.geom=(F.sub.md*F.sub.cd).sup.0.5, where F.sub.md is the
bending resistance index in the machine direction and F.sub.cd is
the bending resistance index cross the machine direction.
[0029] The following properties are measured according to the
standards indicated:
Scott Bond: TAPPI UM-403,
Roughness Bendtsen; SCAN-P 84,
Brightness (ISO): ISO 2470,
[0030] CD stretch to break: SCAN-P 67.
[0031] The value of roughness is measured before the board is
pre-calendered or calendered. The roughness can either be measured
on the web by open the calender and then measure the roughness or a
sample can be cut out of the web and the roughness can then be
measured on the sample. The other parameters, such as Scott Bond,
bending resistance, hexanal and EWT are measured on the finished
board.
[0032] In one preferred embodiment of the invention the board has
an initial roughness Bendtsen value below 1000 ml/min, a Scott Bond
of 120-350 J/m.sup.2, a bending resistance index of 8-25
Nm.sup.6/kg.sup.3, a hexanal value below 600 ppb when measured
within one week from the board manufacture and an EWT (lactic acid)
value below 2 kg/m.sup.2 and/or an EWT (hydrogen peroxide) value
below 2 kg/m.sup.2. The board of this embodiment has high
cleanliness, high strength and good hydrogen peroxide and/or lactic
acid penetration values, all which is important for packages
containing liquid. It fulfils the demands for use as a liquid
packaging board, and is thus suitable for the manufacture of
packages for holding liquids, such as milk or juice cartons.
[0033] In another embodiment of the invention, the board has an
initial roughness Bendtsen value below 1000 ml/min, a bending
resistance index of at least 5 Nm.sup.6/kg.sup.3, a Scott Bond
value of at least 160 J/m.sup.2, a CD (cross direction) stretch to
break of at least 2.5%, preferably 3.5%, a hexanal value below 600
ppb when measured within one week from the board manufacture,
preferably below 400 ppb, and an EWT (cream coffee) value below 1.8
kg.sup.2/m.sup.2. This board grade has high formation, high
cleanliness as well as a good CD stretch value, which fulfils the
demands of cup stock board, and is thus suitable for use in the
manufacture of cups for holding liquids, such as coffee or other
beverages.
[0034] In a further embodiment of the invention, the board has an
initial roughness Bendtsen value below 1000 ml/min, a Scott Bond
value of at least 130 J/m.sup.2, a hexanal value below 1000 ppb
when measured within one week from the board manufacture and a
brightness (ISO-UV; measured with 420 nm filter) of at least 82%
for the uncoated board. The board of this embodiment has good
strength and optical properties and fulfils the demands of a
graphical paperboard, and is thus suitable for use as a graphical
board and for packages holding for example pharmaceuticals or
cosmetics.
[0035] In yet another embodiment of the invention, the board has an
initial roughness Bendtsen value below 1000 ml/min, a bending
resistance index of at least 5 Nm.sup.6/kg.sup.3, a Scott Bond
value of at least 130 J/m.sup.2, a CD stretch to break of at least
2.5%, preferably 3.5% and a hexanal value below 600 ppb when
measured within one week from the board manufacture, preferably
below 400 ppb. The board of this embodiment has high cleanliness in
combination with good strength and CD stretch, and fulfils the
demands of food service board, which makes it suitable for use as
food service board and in the manufacture of packages for
foodstuff, especially packages in which the foodstuff comes into
direct contact with the board.
* * * * *