U.S. patent application number 10/020886 was filed with the patent office on 2002-07-18 for method for producing an extensible paper having a three-dimensional pattern.
Invention is credited to Billgren, Thomas, Hollmark, Holger, Jarrehult, Bengt, Klerelid, Ingvar, Odhe, Janerik, Reiner, Lennart.
Application Number | 20020092633 10/020886 |
Document ID | / |
Family ID | 27354644 |
Filed Date | 2002-07-18 |
United States Patent
Application |
20020092633 |
Kind Code |
A1 |
Odhe, Janerik ; et
al. |
July 18, 2002 |
Method for producing an extensible paper having a three-dimensional
pattern
Abstract
Method of producing a paper having a three dimensional pattern
which has been given the paper web in connection with drying the
paper web, at which the wet paper web (10) is passed through at
least one press nip (12) comprising a rotatable roll (13) which is
heated and that the paper web during the passage through the press
nip is given said three dimensional pattern either by means of a
pattern provided on the heated roll (13), alternatively on a member
surrounding the roll or by means of a patterned wire, band or belt
and where said pattern is pressed into the paper web against a
counter means (11,14). After said press nip (12) the paper web (10)
is taken off from the heated roll (13) by means of a detaching roll
(16) and is creped against said detaching roll.
Inventors: |
Odhe, Janerik;
(Kristinehamn, SE) ; Jarrehult, Bengt; (Goteborg,
SE) ; Hollmark, Holger; (Stockholm, SE) ;
Reiner, Lennart; (Karlstad, SE) ; Billgren,
Thomas; (Kullavik, SE) ; Klerelid, Ingvar;
(Karlstad, SE) |
Correspondence
Address: |
Ronald L. Grudziecki
BURNS, DOANE, SWECKER & MATHIS, L.L.P.
P.O. Box 1404
Alexandria
VA
22313-1404
US
|
Family ID: |
27354644 |
Appl. No.: |
10/020886 |
Filed: |
December 19, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60256331 |
Dec 19, 2000 |
|
|
|
Current U.S.
Class: |
162/111 ;
162/224; 162/226; 162/362 |
Current CPC
Class: |
D21F 11/14 20130101;
D21F 11/006 20130101; D21F 3/0218 20130101; D21F 3/0281
20130101 |
Class at
Publication: |
162/111 ;
162/224; 162/226; 162/362 |
International
Class: |
D21F 011/12; D21H
025/00; D21H 025/04; D21H 025/10 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 19, 2000 |
SE |
0004719-1 |
Claims
1. Method of producing a paper having a three dimensional pattern
of alternating raised and recessed portions, which has been
provided in connection with drying of the paper web, at which the
wet paper web (10) is passed through at least one press nip (12)
comprising a rotatable roll (13) which is heated and that the paper
web during the passage through the press nip is given said three
dimensional pattern either by means of a pattern provided on the
heated roll (13), alternatively on a member surrounding the roll or
by a patterned wire, band or belt and where said pattern is pressed
into the paper web against a counter means (11,14), characterized
in that the paper web (10) after said press nip (12) is taken off
from the heated roll (13) by means of a detaching roll (16) and
that the paper web is creped against said detaching roll.
2. Method as claimed in claim 1, characterized in that the paper
web (10) between the press nip (12) and the detaching roll (16) is
led around a part of the periphery of the heated roll (13) in order
to provide an after-drying of the paper web while this is still in
contact with the three-dimensional pattern of the roll(13).
3. Method as claimed in claim 1 or 2, characterized in that the
detaching roll (16) is heated and that final drying of the paper
web takes place on the detaching roll.
4. Method as claimed in any of the preceding claims, characterized
in that the counter means (11, 14) is provided with a non-rigid
surface so that the paper web is given a three dimensional
structure having a total thickness greater than the thickness of
the unpressed paper web.
5. Method as claimed in claim 4, characterized in that the paper
web is supported by a compressible press felt (11) through the
press nip (12), said press felt makes said non-rigid counter
means.
6. Method as claimed in claim 5, characterized in that the press
felt (11) is pressed against a resilient surface (14) in the press
nip (12).
Description
TECHNICAL FIELD
[0001] The present invention refers to a method of producing a
paper having a three dimensional pattern of alternating raised and
recessed portions, which has been provided in connection with
drying of the paper web, at which the wet paper web is passed
through at least one press nip comprising a rotatable roll which is
heated and that the paper web during the passage through the press
nip is given said three dimensional pattern either by means of a
pattern provided on the heated roll, alternatively on a member
surrounding the roll or by a patterned wire, band or belt and where
said pattern is pressed into the paper web against a counter
means.
BACKGROUND OF THE INVENTION
[0002] Moist paper webs are usually dried against one or more
heated rolls. A method which is commonly used for tissue paper is
so called Yankee drying. At Yankee drying the moist paper web is
pressed against a steam-heated Yankee cylinder, which can have a
very large diameter. Further heat for drying is supplied by blowing
of heated air. If the paper to be produced is soft paper the paper
web is usually creped against the Yankee cylinder. The drying
against the Yankee cylinder is preceded by a vacuum dewatering and
a wet pressing, in which the water is mechanically pressed out of
the paper web.
[0003] Another drying method is so called through-air-drying (TAD).
In this method the paper is dried by means of hot air which is
blown through the moist paper web, often without a preceding wet
pressing. The paper web which enters the through-air-dryer is then
only vacuum dewatered and has a dry content of about 25-30% and is
dried in the through-air-dryer to a dry content of about 65-95%.
The paper web is transferred to a special drying fabric and is
passed over a so called TAD cylinder having an open structure, Hot
air is blown through the paper web during its passage over the TAD
cylinder. Paper produced in this way, mainly soft paper, becomes
very soft and bulky. The method however is very energy-consuming
since all water that is removed has to be evaporated. In connection
with the TAD drying the pattern structure of the drying fabric is
transferred to the paper web. This structure is essentially
maintained also in wet condition of the paper, since it has been
imparted to the wet paper web. A description of the TAD technique
can be found in e g U.S. Pat. No. 3,301,746.
[0004] Impulse drying of a paper web is disclosed in e g SE-B-423
118 and shortly involves that the moist paper web is passed through
the press nip between a press roll and a heated roll, which is
heated to such a high temperature that a quick and strong steam
generation occurs in the interface between the moist paper web and
the heated roll. The heating of the roll is e g accomplished by gas
burners or other healing devices, e g by means of electromagnetic
induction. By the fact that the heat transfer to the paper mainly
occurs in a press nip an extraordinarily high heat transfer speed
is obtained. According to a theory all water that is removed from
the paper web during the impulse drying is not evaporated, but the
steam on its way through the paper web carries along water from the
pores between the fibers in the paper web. The drying efficiency
becomes by this very high.
[0005] In EP-A-0 490 655 there is disclosed the production of a
paper web, especially soft paper, where the paper simultaneously
with impulse drying is given an embossed surface. This embossment
is made by pressing a pattern into the paper from one or both sides
against a hard holder-on. This gives a compression of the paper and
by this a higher density in certain portions just opposite the
impressions and a lower density in the intermediate portions.
[0006] In the international patent application no. PCT/SE98/02461
there is disclosed a method for producing an impulse dried paper,
especially soft paper, having a three-dimensional pattern, said
paper having high bulk and softness. The paper is produced
according to the method stated in the introduction, at which the
counter means against which the paper is pressed in connection with
the simultaneous impulse drying and shaping, has a non-rigid
surface so that the paper is given a three-dimensional structure
having a total thickness greater than the thickness of the
unpressed paper web.
THE OBJECT AND MOST IMPORTANT FEATURES OF THE INVENTION
[0007] There is however still a need to further improve and adapt
the paper quality to special fields of application. The object of
the present invention is to provide a method of producing a paper
that has been dried at a high temperature in a press nip and having
a three-dimensional pattern, e g a soft paper intended as toilet
paper, kitchen rolls, paper handkerchiefs, table napkins and other
wiping material, and where the paper besides a high bulk and a high
softness also has a high extensibility. This has according to the
invention been provided by the fact that the paper web after said
press nip is taken off from the heated roll by means of a detaching
roll and that the paper web is creped against said detaching
roll.
[0008] According to a preferred embodiment of the invention the
paper web is led between the press nip and the detaching roll
around a part of the periphery of the heated roll in order to
provide an after-drying of the paper web while this is still in
contact with the three-dimensional pattern of the roll.
[0009] The counter means against which the paper web is pressed in
connection with the simultaneous drying and shaping has preferably
a non-rigid surface so that the paper web is given a
three-dimensional structure having a total thickness which is
greater than the thickness of the unpressed paper web.
[0010] Further features and advantages of the invention are
disclosed in the following description and in the dependant
claims.
DESCRIPTION OF THE DRAWING
[0011] The invention will in the following be closer described with
reference to an embodiment shown in the accompanying drawing.
[0012] FIG. 1 is a schematic side view of an drying device
according to the invention.
DESCRIPTION OF THE INVENTION
[0013] FIG. 1 shows schematically a device for producing a paper
according to the invention. The wet paper web 10 which is dewatered
over suction boxes (not shown) and possibly also slightly pressed,
is supported by a wire or felt 11 and is led into a press nip 12
between a rotatable roll 13 and a counter means 14 in the form of a
rotatable roll or a press band running over a stationary press
shoe, at which the roll 13 which is in direct contact with the
paper web is by a heating device 15 heated to a temperature which
is sufficiently high for providing drying of the paper web. The
surface temperature of the heated roll can vary depending on such
factors as the moisture content of the paper web, thickness of the
paper web, the contact time between the paper web and the roll and
the desired moisture content of the completed paper web. The
surface temperature should of course not be so high the paper web
is damaged. An appropriate temperature should be in the interval
100-400.degree. C., preferably 150-350.degree. C. and most
preferably 200-350.degree. C.
[0014] By the fact that the heat transfer to the paper mainly takes
place in a press nip a very rapid heat transfer rate an by that an
effective drying is obtained. A very rapid, violent and almost
explosive steam generation takes place in the interface between the
heated roll 13 and the moist paper web. This drying procedure is
often called impulse drying. The paper is at the exit of the press
nip strongly heated, which means that the water that normally flows
back into the paper web from the felt at the exit from a press nip,
in this case is heated and surrounded by a protecting steam film,
which prevents the water from being sucked back into the paper web
again.
[0015] Besides the heated roll 13 the press nip also comprises a
press shoe 14 or a counter roll. The press nip may be a common roll
nip or a so called extended press nip in order to provide a more
effective drying of the paper web. Two and more press devices may
also be arranged after each other. It is also possible that the
paper web 11 is brought into the press nip unsupported, i e not
supported by any wire or felt.
[0016] The paper web 10 can according to an alternative embodiment
after said press nip 12 be led around an essential part of the
periphery of the heated roll 13 in order to provide an after-drying
of the paper web while this is still in contact with three
dimensional pattern of the roll 13. The paper is taken off from the
heated pattern roll 13 by means of a detaching roll 16, which is
located at a small distance from or in contact with the pattern
roll 13, and is creped on the detaching roll 16 by means of a
doctor blade 17. The doctor blade 17 can be of any optional type,
flat as well a patterned, and the doctor blade angle can be
adjusted for providing small or large creping creases. Through the
creping the extensibility and softness of the paper is improved.
Creping chemicals can in a per se known manner be applied, e g
sprayed, on the detaching roll 16, the detaching roll 16 by means
of an applicator means 19.
[0017] Alternatively the detaching roll 16 can be heated and the
moisture content of the paper web when it reaches the detaching
roll can be at least 10%, preferably at least 20%, at which final
drying takes place on the detaching roll 16.
[0018] The angular distance between the press nip 12 and the
detaching roll 16, with respect to the roll 13, corresponding to
the distance that the paper web is led around the periphery of the
pattern roll 13, is preferably at least 45.degree., more preferably
at least 60.degree..
[0019] A further advantage with this arrangement is that the
problem with taking off the paper web from the pattern roll 13 is
solved. Since the paper web is pressed into the surface structure
of the pattern roll it can sometimes be difficult to remove the
paper from the roll 13. The removal of the paper web from the
pattern roll 13 is considerably facilitated by the roll 16, which
thus fills the function of both a detaching roll and a creping
cylinder. The paper is after drying and creping rolled up on a
wind-up roll 18.
[0020] Simultaneously with the drying in the press nip the paper is
given a three-dimensional structure. This can be made as shown in
FIG. 1 by the fact that the heated roll 13 is provided with an
embossing pattern consisting of alternating raised and recessed
areas. This pattern may be provided on a sleeve applied around the
roll. This structure is substantially maintained also in a later
wetted condition of the paper, since it has been imparted the wet
paper web in connection with drying thereof. Since the term
embossing is normally used for a shaping performed on dried paper
we have in the following used the term press moulding for the
three-dimensional shaping of the paper that occurs simultaneously
with the drying in the press nip. By this press moulding the bulk
and absorption capacity of the paper is increased, which are
important qualities for soft paper.
[0021] The paper can at the drying in the press nip be pressed
against a non-rigid surface, i e a compressible press felt 11. The
band that runs over the press shoe 14 or the like can also have an
elastically yielding surface, e g an envelope surface of rubber.
The paper is herewith given a three-dimensional structure, the
total thickness of which is greater than the thickness of the
unpressed paper. By this the paper is imparted a high bulk and by
that a high absorption capacity and a high softness. Besides the
paper will be elastic. At the same time a locally varying density
is obtained in the paper.
[0022] The paper can also be pressed against a hard surface, e g a
wire 11 and/or a roll 14 having a hard surface, at which the
pattern of the heated roll 13 is pressed into the paper web under a
heavy compression of the paper opposite the impressions, while the
portions therebetween are kept uncompressed.
[0023] The pattern structure in the paper can also be made by means
of a pattern band or belt (not shown) which extends around and is
heated by the roll 13 and is led through the press nip 12 between
the roll 13 and the paper web 10.
[0024] Alternatively the paper web 10 may during the drying be
supported by a wire 11 having a pattern, which is press moulded
into the paper web when this passes through the press nip 12. The
paper web will in this case pass the press nip 12 between the roll
13 and the pattern wire. The roll 13 can either be smooth or have
an embossing pattern. In the case the roll 13 is smooth the press
moulded paper will have one smooth surface and one surface with
impressions. In the case the roll 13 has an embossing pattern this
will also be pressed into the paper, which thus on one side will
have a pattern corresponding to the structure of the wire 11 and on
the opposite side having a pattern corresponding to the embossing
pattern of the roll. The patterns may but need not coincide and/or
be the same or different.
[0025] Possibly the paper web can after the first press nip and
before winding on the wind-up roll 16 be passed through a second
press nip (not shown) where a second drying of the paper web takes
place. This implies of course that the paper web before the second
press nip is not completely dry but has a moisture content of at
least 10 and preferably at least 20 weight %. This can be achieved
if the drying in the first drying step in the press nip 12 is not
complete and/or by moistening the paper web before the second
drying step.
[0026] Simultaneously with the two drying steps the paper web is
given a three-dimensional structure. The patterns can be pressed
into the paper web from opposite sides. It is of course also
possible to press different patterns into the paper web from the
same side. The patterns pressed into the paper web in the two
drying steps are preferably different.
[0027] According to one embodiment of the invention a material may
be added to the paper web, said material softens or melts in the
temperature interval 100-400.degree. C. Said material can be
synthetic or natural polymers with thermoplastic properties,
chemically modified lignin and/or synthetic or natural polymers in
the presence of softening agents. The material cm either be in the
form of powder, flakes, fibers or an aqueous suspension, e g a
latex dispersion. Examples of thermoplastic polymers are
polyolefines such as polyethylene and polypropylene, polyesters
etc. The material can either be supplied to the entire paper web or
only to the portions thereof that are intended to be located
closest to the heated roll 13.
[0028] By adding to the paper web said material which is brought to
soften or melt, there is achieved an increased amount of bonding
sites in the paper web. By this the basis weight variation and
three-dimensional structure, that has been imparted to the paper
web in connection with the combined drying and press moulding, is
effectively permanented. This structure is maintained also in the
wet condition of the paper.
[0029] Paper can be produced by a number of different pulp types.
If one disregards recovery pulp, which today is used to a great
extent mainly for toilet paper and kitchen rolls. the most commonly
used pulp type for soft paper is chemical pulp The lignin content
in such pulp is practically zero and the fibers, which mainly
consist of pure cellulose, are relatively thin and flexible.
Chemical pulp is a low yield pulp since it gives a yield of only
about 50% calculated on the wooden raw material used. It is
therefore a relatively expensive pulp.
[0030] It is therefore common to use cheaper so called high yield
pulps, e g mechanical, thermomechanical pulp, chemomechanical pulp
(CMP) or chemothermomechanical pulp (CTMP) in soft paper as well as
in other types of paper, e g newsprint paper, cardboard etc. In
high yield pulps the fibers are coarser and contain a high amount
of lignin, resins and hemicellulose. The lignin and the resins
gives the fibers more hydrophobic properties and a reduced ability
to form hydrogen bonds. The addition of a certain amount of
chemothermomechanical pulp in soft paper has due to the reduced
fiber-fiber bonding a positive effect on properties like bulk and
absorption capacity.
[0031] A special variant of chemothermomechanical pulp (CTMP) is so
called high temperature chemothermomechanical pulp (HT-CTMP), the
production of which differs from the production of CTMP of
conventional type mainly by using a higher temperature for
impregnation, preheating and refining, preferably no lower than
140.degree. C. For a more detailed description of the production
method for HT-CTMP reference is made to WO 95/34711. Characterizing
for HT-CTMP. is that it is a long fibrous-, easily dewatered- and
bulky high yield pulp with a low shives content and low fines
content.
[0032] It has according to the invention been found that high yield
pulp is especially suitable for impulse drying since it is pressure
insensitive, easily dewatered and has an open structure which
admits the generated steam to pass through. This minimizes the risk
for the paper to be overheated and destroyed during the impulse
drying, which is performed at considerably higher temperatures than
in other drying methods. The pressure insensitivity and the open
structure depends On that the fibers in high yield pulp are
relatively coarse and stiff as compared to the fibers in chemical
pulp.
[0033] A further advantage is that the three-dimensional pattern
and the creping structure given the paper is essentially maintained
also in wet condition of the paper, since it is imparted to the wet
paper web in connection with drying thereof. Impulse drying further
takes place at a considerably higher temperature than e g Yankee
drying or through-air-drying, at which according to a theory, to
which however the invention is not bound, the softening temperature
of the lignin present in the high yield pulp is reached during the
simultaneous impulse drying and press moulding. When the paper
becomes cooler the lignin stiffens again and contributes in
permanenting the three-dimensional structure that has been given
the paper. This is therefore essentially maintained also in the wet
condition of the paper, which strongly improves the bulk and
absorption qualities of the paper.
[0034] According to an embodiment of the inventionthe wet paper web
is before said press nip exerted to a creping- or other
foreshortening procedure which shortens the length of the paper
web. This creping is a wet creping as the paper web at the creping
is still wet or at least moist. This wet creping will result in a
very fine creasing of the paper web, which is essentially
maintained also in the dried paper web. By this the extensibility
and toughness of the paper in the machine direction is
improved.
[0035] According to one embodiment of the invention the paper
contains a certain amount of a high yield pulp, said amount should
be at least 10 weight % calculated on the dry fiber weight,
preferably at least 30 weight % and more preferably at least 50
weight %. Admixture of a certain amount of another pulp with high
strength properties, such as chemical pulp, preferably long-fibrous
kraft pulp, or recycled pulp, is an advantage if a high strength of
the paper is aimed at. The invention is however not bound to the
use of a certain type of pulp in the paper, but can be applied with
any optional pulp type or mixture of pulp types.
[0036] According to a further embodiment of the invention the paper
web 10 can in connection with forming and dewatering be given a
variation in basis weight in a non-random pattern This can for
example be provided by forming and dewatering the paper web on a
wire, belt or band the dewatering capacity of which varies
according to a certain pattern and where the differences in
dewatering capacity involves a certain displacement of fibers and
by that a local change of the basis weight of the paper web.
[0037] The basis weight variation that is given the paper web 10 in
connection with forming and dewatering is permanented in the
subsequent drying step, at which the structure is essentially
maintained also in the wet condition of the paper.
[0038] According to a further embodiment of the invention the paper
web has a varying material composition as seen in its thickness
direction, in such a way that it at least in the layer(s) that will
be located closest to heated roll 13 in connection with the drying
contains a certain amount of a material which softens, melts or
hardens in the temperature interval 100-400.degree. C. By this the
paper will get a surface layer which contributes in reinforcing the
structural stability of the paper also in wet condition. The pulp
composition in the rest of the paper layers can on the other hand
be chosen for optimizing other properties such as softness,
strength, bulk and draping qualities.
[0039] Said material which in connection with drying in the press
nip softens, melts or hardens can consist of a wet strength agent,
synthetic or natural polymers with thermoplastic properties,
chemically modified lignin and/or synthetic or natural polymers in
the presence of softening agents or of a lignin-containing high
yield pulp.
[0040] Common additives such as wet strength agents, softening
agents, fillers etc may of course also be used in the paper. The
paper web can after drying in the press nip undergo different types
of per se known treatments such as addition of different chemicals,
further embossing, lamination etc.
* * * * *