U.S. patent application number 10/344227 was filed with the patent office on 2004-02-12 for method for manufacturing a coated fibre web, improved paper or board machine and coated paper or board.
Invention is credited to Ilmoniemi, Erkki, Kinnunen, Juha S, Lipponen, Juha.
Application Number | 20040026054 10/344227 |
Document ID | / |
Family ID | 8558870 |
Filed Date | 2004-02-12 |
United States Patent
Application |
20040026054 |
Kind Code |
A1 |
Ilmoniemi, Erkki ; et
al. |
February 12, 2004 |
Method for manufacturing a coated fibre web, improved paper or
board machine and coated paper or board
Abstract
A surface-sized paper web is made by supplying pulp from a
headbox (100) where additives and/or fillers and/or fines are
admixed into the pulp, to the wire section (200), where water is
removed. The web is guided from the wire section (200), to the
press section (300), the front drying section (400), is
surface-coated in the coating section (500) dried in the
post-drying section (600), and reeled by a reeler (800). In the
headbox (100) starch and optionally hydrofobic size are admixed or
layered into the pulp, so that on at least one side of the web an
essentially dense surface is formed, on which in surface-coating a
coating paste is spread out, which has a high dry matter content,
whereby a bond is achieved in direction z inside the web in between
the base paper and the surface-coating layer spread out on the
surface.
Inventors: |
Ilmoniemi, Erkki;
(Vaajakoski, FI) ; Kinnunen, Juha S; (Jyvaskyla,
FI) ; Lipponen, Juha; (Kerava, FI) |
Correspondence
Address: |
LATHROP & CLARK LLP
740 REGENT STREET SUITE 400
P.O. BOX 1507
MADISON
WI
537011507
|
Family ID: |
8558870 |
Appl. No.: |
10/344227 |
Filed: |
August 4, 2003 |
PCT Filed: |
August 6, 2001 |
PCT NO: |
PCT/FI01/00696 |
Current U.S.
Class: |
162/135 ; 118/56;
162/158; 162/175; 162/204; 162/289; 427/391 |
Current CPC
Class: |
D21H 23/28 20130101;
D21H 21/16 20130101; D21H 17/28 20130101; D21H 23/30 20130101; D21H
19/12 20130101; D21F 9/006 20130101 |
Class at
Publication: |
162/135 ;
162/175; 162/158; 162/204; 162/289; 427/391; 118/56 |
International
Class: |
D21H 019/54; D21F
011/04 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 10, 2000 |
FI |
20001773 |
Claims
1. Method for making a coated fibre web, such as a paper or board
web, in which method the pulp, in which additives, fillers and
fines as well as retention matter are mixed, is supplied from the
headbox (100) on to a wire section (200), where water is removed
from the web (W); the web (W) is guided from the wire section (200)
to the press section (300) for removing water from the web (W); the
web (W) is dried in a front drying section (400); the web (W) is
coated in a coating section (500); the web (W) is dried in a
post-drying section (600); and the web (W) is reeled by a reeler
(800), characterised in that into the pulp to be fed from the
headbox (100) to the wire section (200) starch and/or hydrofobic
size or sizes are admixed or layered, so that into at least one
layer of the web (W) to be guided through the wire section (200)
and press section (300) and front drying section (400) into the
coating section (500) an essentially dense surface (10) is formed,
on to which such a coating paste or starch is spread out, which has
a high dry matter content, whereby a bond (2) is achieved in
direction z inside the web (W) between the base or body layer (1),
that is, the base paper or board, and the coating paste or starch
layer (11) spread out on the surface.
2. Method according to claim 1, characterised in that the base
paper or board (1) is formed by layering in the pulp flows to be
conducted into the headbox (100) filler, starch and/or hydrofobic
sizes by a system for layering additives, so that an essentially
dense and hydrofobic surface (10) is achieved for surface-coating,
preferably surface sizing, included in the further treatment.
3. Method according to claim 1 and 2, characterised in that in the
surface coating such surface-coating or sizing paste is spread out,
the dry matter content of which is >15%, preferably 15-25%.
4. Method according to claim 2, characterised in that in the
headbox (100) starch and optionally size is conducted into the base
paper or board (1) to be formed in order to bring about a dense and
hydrofobic surface (10) for surface coating.
5. Method according to claim 4, characterised in that starch and
optionally size is supplied into at least one layer in a
multi-layer headbox (100).
6. Method according to claim 5, characterised in that starch and
optionally size is layered mainly in the middle layer of the pulp
forming the base paper or board (1), when the headbox (100) is a
3-layer headbox.
7. Method according to claim 4, characterised in that starch and
optionally size is admixed into the pulp forming the base paper or
board (1), when the headbox (100) is a 1-layer headbox.
8. Method according to any one of claims 2-7, characterised in that
surface sizing of the essentially dense and hydrofobic surface of
the base paper or board (1) is performed in the coating section
(500) with high consistence coating paste, wherein the quantity of
starch has been reduced and/or where the dry matter content of the
size has been increased.
9. Method according to any one of claims 1-8, characterised in that
the surface coating is performed in connection with the press
section (300).
10. Improved paper or board machine for making a coated fibre web,
such as a paper or board web, which paper machine includes a
headbox (100), and into the pulp to be supplied to the headbox
additives, fillers and fines have been admixed as well as retention
matter, a wire section (200) for forming the web (W) and for
removing water from the web (W); a press section (300) for pressing
water from the web (W); a front drying section (400) for drying the
pressed web (W); a coating section (500) for surface-coating of the
web (W); a post-drying section (600) for drying the coated web (W);
and a reeler (800) for reeling the web (W), characterised in that
the pulp to be supplied contains starch and/or hydrofobic size or
sizes, so that into at least one layer of the web (W) to be guided
through the wire section (200) and the press section (300) and the
front drying section (400) into the coating section (500) an
essentially dense surface (10) is formed, on which in the surface
coating a coating paste or starch is spread out, which has a high
dry matter content, whereby a bond (2) is achieved inside the web
(W) in direction z between the base or body layer (1), that is, the
base paper or board, and the coating paste or starch layer (11)
spread out on the surface.
11. Paper or board machine according to claim 10, characterised in
that the base paper or board (1) is formed by layering in a
multi-layer headbox (100) filler, starch and optionally hydrofobic
sizes by a system for layering additives, so that in the web (W) an
essentially dense and hydrofobic surface (10) is formed for further
treatment, which includes surface coating, preferably surface
sizing.
12. Paper or board machine according to claim 10, characterised in
that the dry matter content of the surface-coating paste to be
spread out on the web surface (10) in the surface-coating section
(500) is >15%, preferably 15-25%.
13. Paper or board machine according to claim 10 and/or 11,
characterised in that there is starch and optionally size in the
base paper or board to be supplied from the headbox (100) into the
wire section (200).
14. Paper or board machine according to claim 11, characterised in
that in the multi-layer headbox (100) starch and optionally size
have been supplied at least through one layer of the multi-layer
headbox (100).
15. Paper or board machine according to claim 14, characterised in
that starch and optionally size have been layered mainly in the
middle layer of the pulp forming the base paper or board (1)
through the middle layer of a 3-layer headbox.
16. Paper or board machine according to claim 10, characterised in
that a 1-layer headbox (100) admixes starch and optionally size
into pulp forming the base paper or board (1).
17. Paper or board machine according to any one of claims 11-16,
characterised in that surface coating of the essentially dense and
hydrofobic surface of the base paper or board has been performed in
the coating section (500) with a high consistence coating paste,
wherein the quantity of starch has been reduced and/or wherein the
dry matter content of the size has been increased.
18. Paper or board machine according to any one of claims 10-17,
characterised in that the surface coating is integrated into the
press section (300).
19. Coated paper or board, including the paper product's base or
body layer (1), that is, the base paper or board, and at least one
surface-coating layer (11), characterised in that an internal bond
(2), which is located in between the base or body layer (1) and the
surface-coating layer (11) and which holds the layers (1, 11)
together affects the paper's or board's strength characteristics in
direction z.
20. Paper or board according to claim 19, characterised in that the
surface-coating layer (11) is starch.
21. Paper or board according to claim 19, characterised in that the
surface-coating layer (11) is hydrofobic size.
22. Paper or board according to any one of claims 19-21,
characterised in that in the base paper or board (1) of the paper
or board at least one layer is starch and optionally hydrofobic
size, that on the essentially dense and hydrofobic surface (10) of
the base paper or board there is a surface-coating layer (11),
which extends over a part of the thickness of the base paper or
board web and forms a bond (2) in between the base paper or board
(1) and the surface-coasting layer (11).
23. Paper or board according to any one of claims 17-20,
characterised in that the high dry matter content of the
surface-coating paste has been achieved by a reduced quantity of
starch and/or by an increased dry matter content of the size.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] This application is a U.S. national stage application of
International Application No. PCT/FI01/00696, filed Aug. 6, 2001,
and claims priority on Finnish Application No. 20001773, filed Aug.
10, 2000, the disclosures of both of which applications are
incorporated by reference herein.
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED
RESEARCH AND DEVELOPMENT
[0002] Not applicable.
BACKGROUND OF THE INVENTION
[0003] The present invention concerns a method and apparatus for
making a coated fibre web, such as a paper or board web.
[0004] The method and paper or board machine according to the
invention may be applied very largely to the manufacture of such
different paper and board grades, where the conventional method
would improve the quality of the paper or board by pre-coating.
Typical such writing and printing papers are fine grade paper, LWC
base paper or improved newsprint, which as such are known to the
professional in the field. Coating of various board grades has also
increased in recent years. However, in the following the invention
will be described mainly in connection with fine grade paper, but
without limiting the invention hereto in any way.
[0005] In this presentation, fine grade paper means uncoated fine
grade paper and coated fine grade paper. The grammage of uncoated
fine grade paper is usually 40-230 g/m.sup.2, while of coated fine
grade paper it is 60-250 g/m.sup.2. The typical pulp for making
fine grade paper includes chemical fibre: short fibre obtained e.g.
from birch and eucalyptus wood, and to this is usually added
long-fibred material obtained from softwood.
[0006] The share of mechanical pulp is usually less than 10%. About
15-30% of filler is added to the pulp, and the filler may be stone,
calcium carbonate, kaolin and/or other suitable mineral pigments.
Lately, makers of fine grade paper have also begun using more and
more recycling fibre.
[0007] As was mentioned above, the method and paper machine
according to the invention may be used advantageously for making
paper equivalent to pre-coated fine grade paper. In this
application, traditional pre-coating is used with a view of
providing the web surface with certain properties advantageous in
the further treatment of the web. Such properties are e.g. the
desired surface porosity and pore size distribution along with the
desired oil absorption level, e.g. measuring with the Cobb-Unger
method. The degree of pigment coverage is also one property which
should be observed. With the process of making fine grade paper
according to the invention, wherein traditional pre-coating is not
applied, equal values are thus achieved for the said properties as
when using a conventional manufacturing process including a
pre-coating step.
[0008] As with coated fine grade paper, the invention may also be
advantageously applied to paper grades containing mechanical pulp,
which are coated in the final stage of the manufacturing process.
LWC and MWC are typical such paper grades.
[0009] With the method and equipment according to the invention it
is also possible to make better newsprint than before without any
surface-sizing unit. This significance of the invention becomes
more significant with increasingly speedy newsprint machines or
with newsprint which becomes more and more thin. Four-color
printing requires a harder and denser surface than before. As is
known, it has been proposed earlier that this can be achieved by
surface-treatment of the web.
[0010] A better printing surface than before is more and more often
demanded of boards. The invention offers good possibilities in this
regard without any expensive investments in the dry end of the
board machine. For the manufacturing of multi-layer board, the
invention also offers an advantageous solution to improve the
printing characteristics of the webs forming the surface layers of
multi-layer board. The inter-laminar strength of multi-layer board
can also be improved by supplying e.g. starch on to the web
surfaces.
[0011] In known state-of-the-art paper or board machines, the short
circulation and the other pulp system is usually constructed in
such a way that it mixes the fibres, fillers, fines and additives
into a pulp as homogenous as possible to be supplied to the headbox
of the paper or board machine. It is also known in multi-layer web
formation to use several separate pulp systems in order to supply
different fibre suspensions to either one headbox or more
headboxes. The headbox spreads the resulting pulp suspension evenly
on to the wire section, where dewatering and couching of the web
will begin. The state of the art knows several wire sections or
formers of various types which are known as such to the
professional in the field; Fourdrinier wires, hybrid formers and
jaw formers. Board machines may even have several wire units. From
the viewpoint of the invention, the most advantageous former is the
jaw former, wherein a lip discharge formed by the headbox is run in
between two wires and most of the water is removed in between the
said wires in two directions. An advantageous jaw former solution
was described in the paper L. Verkasalo: Efficient Forming at High
Speeds, XI Valmet Paper Technology Days 1998. In known
state-of-the-art solutions, it is possible only in part to control
the fibre and filler distribution in the thickness direction of the
web, e.g. by the location of the former's dewatering elements and
by negative pressures. Fillers often enrich on web surfaces in the
dewatering stage.
[0012] Multi-layer headboxes are known as such in the state of the
art, one of which is presented e.g. in the paper M. Odell:
Multilayering, Method or Madness?, XI Valmet Paper Technology Days
1998 and one of which was also described in the paper P. Ahonen:
Challenges for Digital Printing Paper, XI Valmet Paper Technology
Days 1998. Using multi-layer headboxes, desired layer structures
are brought about in the web by feeding the layered pulp into the
space between wires. Especially with some board grades several
different headboxes and wire units have been used instead of a
multi-layer headbox in order to bring about a layered
structure.
[0013] From the wire section the web is taken to the press section,
wherein water is removed from the web by pressing it against one
felt or two felts. The professional knows several different
state-of-the-art press solutions, e.g. Metso Paper, Inc.'s press
marketed with the SymPress.TM. II trademark, which is based on roll
nips. Lately there has been an increasing use with all paper and
board grades of a long nip known as such in the art instead of roll
nips due to its better dewatering ability and/or due to the web's
bulk preservation ability.
[0014] In known state-of-the-art paper and board machines, the
drying section is usually formed by a conventional drying section
using single and/or two wire transfer, by which drying mainly takes
place as cylinder drying as the wire presses the web against a
heated cylinder surface. In recent years the use of single-wire
transfer through the entire drying section has increased with high
running speeds. As the latest solution e.g. patent application
PCT/FI98/00945 proposes a combination of blowing-on with cylinder
drying in order to achieve a higher evaporation speed and a shorter
drying section.
[0015] In some known state-of-the-art solutions, the paper web is
guided from the drying section to a pre-calender, which in the
known solutions may be a calender with a hard or soft nip, wherein
the paper web is guided from the nip between rolls in order to
achieve a smooth paper web surface. The pre-calender is also used
for fastening loose fibres or other pulp components to the web
surface, but at the same time possibly also causing density
differences in the base paper and losing web bulkiness, which is
important to many grades. Pre-calendering is especially important
before the web is coated when using blade coating to avoid
so-called blade lines.
[0016] According to the known technology, the web surfaces are
pre-coated with a starch or pigment solution after the drying
section or after pre-calendering, for example, using an applying
device of the film size press type marketed under Metso Paper,
Inc.'s trademark OptiSizer.TM.. In this step, pre-coating is
typically done on both sides of the web at the same time, but the
web surfaces may also be pre-coated separately in successive units.
The paper web is then dried using infra driers and airborne web
driers and a short bank of cylinders following after these.
[0017] Then, as is known in the art, the web is surface-coated by
blade, roll or jet coating units known as such in the art, and it
is dried using infra and air-borne web driers as well as cylinder
drying. The dried paper or board web is reeled, whereupon a
multi-nip calender follows, which is used to give the paper or
board the desired grade of smoothness and gloss. On-line
calendering has also become more widely used lately.
[0018] On the other hand, in some known state-of-the-art solutions
a calender and reel-up often follows after the drying section. An
unwinder then follows, from which the web is guided to an off-line
coating station. There are different known state-of the-art coating
stations. In one known solution pre-coating of one side of the
paper web is first performed, whereupon the drying section follows,
and then the other side of the paper web is pre-coated, whereupon
the drying section follows. The resulting pre-coated web is finally
coated with other coating layers and the web is then dried and
reeled. Unwinding then follows as well as calendering and reeling
of the web. The final machine after the drying section may thus be
an on-line or an off-line machine.
[0019] Before coating, the paper may thus be very porous, as is
known in the art, so after dewatering and drying treatments the
paper web must be pre-coated before the actual surface coating.
This also means that the paper web must be dried after pre-coating,
so that the coating proper can be added to the paper web surface.
The equipment and web transfers needed for these steps add
considerably to the length of the fine grade paper manufacturing
line. This double coating, that is, pre-coating and actual surface
coating, of fine grade paper has aimed at achieving a coated paper
surface, which is physically and visually even, as a printing
basis. The most important task of the pre-coating in the said
coating process is suitably to diminish pores existing in the
surface structure of the base paper or board, so that the surface
coating will remain on the surface and will not sink into the paper
or board structure. If the coating is distributed very unevenly in
the paper or board surface, then the paper or board will be uneven
even after it has been surface-coated, and it may have e.g. gloss
spottiness or other visual faults. E.g. with a film transfer
technique it is possible to achieve an even surface-coating layer
and thus good coverage, which is a desirable property especially in
the pre-coating stage, because an even pre-coating is a
precondition for an even surface coating. After pre-coating,
surface coating of the web is performed in known state-of-the-art
blade coating in order to achieve an even surface. However, this
makes space demands on the paper or board finishing line, because
the paper or board is coated in 3-4 different steps, since the
different sides of the paper or board web are often coated in
different steps.
[0020] In known state-of-the-art paper and board machines, a size
press or a coater of the film transfer type is thus generally used
for pre-coating of the web. Hereby surface size or some equivalent
coating material is supplied as an aqueous solution on to both
sides of the paper web in one or two steps with the purpose to bind
fines and fibres into the web surface and thus bring about
favourable conditions for a possible following coating. In known
state-of-the-art solutions, where a separate pre-coater is thus
used, it is a problem that the length of the paper or board machine
or of the coating line increases. This adds to the investment costs
of both the machine itself and also of the building. Lack of space
in renewals may actually prevent introduction of new technology.
When aqueous matter is spread out on the web, drying will be
needed, which both increases the machine length and adds to the
investment costs and which also increases the need of drying
energy. In addition, open transfers must be arranged in the paper
machine, which may cause web breaks and other runability problems,
especially with lighter paper grades and at high running
speeds.
[0021] As regards the state of the art relating to the invention,
reference is also made to Metso Paper, Inc.'s FI patent
applications 981330 and 981331. Of these, FI patent application
981330 presents an integrated paper machine, which may be used for
making paper of a good quality and with a high coefficient of
efficiency at a speed in excess of 2000 m/min and which is shorter
than the paper machine of today.
[0022] FI patent application 981331 presents a paper machine
intended especially for making such paper, which has copying paper
properties as well as good gloss and suitable porosity for color
powder printing.
[0023] FIG. 1 is a cross-sectional view of traditional paper
according to the known state of the art. In order to get surface
sizing layers 11, the present-day surface sizing of base paper 1
for fine grade paper typically uses pastes of a low dry matter
content (8-12%), in order to ensure penetration of the coating
paste through the paper; this means, that the size pressed into the
paper from different sides must "meet" in the middle of the paper
and form a bond 2 increasing the strength of the paper. Thus, the
purpose of using a paste with a low dry matter content (8-12%) is
to lower the viscosity of the coating paste to be applied. With the
present-day technique this is necessary to achieve sufficient
strength characteristics, because when increasing the dry matter
content of the paste the size will remain in the surface layers of
the paper and desired bonds are not formed in the internal parts of
the paper or board.
[0024] The use of pastes with a low dry matter content (8-12%)
means that the paper is wetted "throughout" and thus much drying is
needed afterwards and runability problems will result in the
post-drying section. The increase of the coating paper's dry matter
content alone reduces the paste's penetration into the paper or
board and thus causes poorer strength characteristics in direction
z. On the other hand, a reduction of the viscosity of a
high-consistence paste by only changing the characteristics of the
starch easily leads to increased curling and waviness
tendencies.
[0025] The problems with base paper or board in office papers are
distributions of the paper or board in direction z, especially
filler distribution, which in copying paper ought to be of such a
type that there is less filler on the surfaces in view of dusting.
On the other hand, with office papers the aim is to use the paper
or board in many ways, that is, the paper or board should also be
suitable for use in ink-jet printing, whereby filler is needed in
the surface to achieve a dense surface.
SUMMARY OF THE INVENTION
[0026] It is an objective of the invention to bring about an
inventive method of a new kind for making a surface-sized paper or
board web in such a way that pastes with a higher dry matter
content (>15%, preferably 15-25%) can be used without having to
be content with poorer strength characteristics of the produced web
or with poorer web runability. It is a particular objective of the
invention to reduce investment costs by developing a paper and
board machine, which is shorter than the known solutions, for
making paper and board grades traditionally requiring pre-coating
and thus bring about an improved paper or board machine. In
addition, it is an objective of the invention to bring about an
inventive paper or board with a new kind of structure and with good
strength characteristics and suitable for very different purposes
of use.
[0027] Considerable advantages are achieved with the invention:
[0028] 1. From the high dry matter content (>15%, preferably
15-25%) of the coating paste follows, when it is desirable to apply
into the web and press into its surface layer or layers a smaller
amount of coating paste (g/m.sup.2), a higher dry matter content
after the surface-coating section, which results in less need for
post-drying and in a better runability of the post-drying
section,
[0029] 2. The chemicals of the intermediate layer (strength
characteristics in direction z) and the surface layer (surface
strength) can be optimised independently of each other.
[0030] 3. When single-wire transfer is used, the curling tendency
caused by the post-drying section is reduced, as less post drying
is needed. The required curling control equipment based on wetting
can also be abandoned, which further reduces the need for post
drying.
[0031] 4. The paper to be produced has multi-use characteristics
(copying, ink-jet).
[0032] According to the invention, additive and filler layering
into the pulp is used in a multi-layer headbox and admixing of
additives or fillers into the pulp is used in a single-layer
headbox, which replaces the state-of-the-art pre-coating to be
performed in the finishing section. In additive and filler
layering, the pulp can be divided into three different pulp flows
for the body or base layer, that is, for the base paper's or
board's surface layers and middle layer, whereby the desired
additives and fillers are conducted into each, especially starch to
bring about layer structures of different kinds. When required, the
additive and filler may be supplied from several different points
or in several different steps into the pulp flow. According to an
advantageous application of the invention, fines may also be added.
In addition, fibre layering may advantageously be used in
connection with the invention, where the fibre pulp is separated
for the surface and middle layers of the base paper or board
separately, so that a fibre pulp of the desired type is led into
the surface layer of the base paper or board, or correspondingly,
into the middle layer of the base paper or board. In addition,
retention matter known in the state of the art may be used to bind
the filler and fines into the surface, which will prevent them from
moving away together with the water from the surface layers of the
paper or board. The retention matter may also be supplied
layer-wise.
[0033] Thus, according to the invention, pre-coating is integrated
in the first part of the paper or board machine and additives and
fillers are led into the web surface immediately in the early stage
of the web manufacture. In this way a sufficiently small pore size
is achieved in the surface of the body or base layer, that is, the
base paper or board, so that the actual surface-coating paste,
preferably a surface-sizing paste, to be applied stays in the
surface of the base paper or board. In this way an advantageous
surface for a printing process is also achieved, from which
printing color will not penetrate deeply into the web.
[0034] With the invention, such a pore size can be achieved in the
paper or board, which is {fraction (1/10)} of its original value.
An optimum surface sizing coverage is attained, when the pores in
the surface of the base paper or board are so small that surface
sizing will not penetrate into them and thus remains on the
surface. This is achieved by adding the additives and fillers into
the pulp flows even before the headbox, and advantageously by using
at the same time fibre layering and possibly by adding fines into
the pulp flows to be supplied into the surface layers of the base
paper or board.
[0035] Thus, in the invention pre-coating is replaced by layering
of additives and fillers into the pulp flows to be supplied to the
headbox, whereby process efficiency is improved and investment
costs are reduced. According to an advantageous application, the
paper or board machine according to the invention, wherein
pre-coating is replaced by an additive and filler layering
technique into the pulp flows of the headbox, includes a
multi-layer headbox, a jaw former, a press section, a drying
section, a surface-coating station/stations and a multi-nip
calender and a reeler.
[0036] In the method according to the invention, short circulation
and a headbox can be applied, which allows layering of additives,
fillers and/or fines. One such pulp supply arrangement advantageous
for application in the invention is presented in FI Patent 92729.
The fillers, fines and additives can also-be supplied only in the
headbox itself. One such arrangement is described in printed patent
specification EP 824157. Short circulation arrangements may be
generally known already as such in the state of the art, but it is
especially advantageous in connection with the invention to apply
such a short circulation marketed by Metso Paper, Inc. under the
trademark OptiFeed.TM., which is described e.g. in FI Patent
103676. By using the OptiFeed.TM. arrangement pulp volumes are
minimized in the short circulation, for which reason e.g. grade
exchange can be made quickly on a paper or board machine according
to our invention without any long troubles e.g. in pulp
proportioning.
[0037] Thus, in the paper or board machine according to the
invention there are a short circulation and a multi-layer headbox
or single-layer headbox, which allow at least layering or mixing of
fillers. The former used is preferably a jaw former, which allows
higher speeds than formers of other types and a possibility to
perform dewatering bilaterally, whereby a symmetrical paper is
obtained. One such jaw former is e.g. the wire section marketed
under Metso Paper, Inc.'s trademark OptiFormer.TM. or a former of a
corresponding type, which is described in the mentioned paper L.
Verkasalo: Efficient Forming at High Speeds, XI Valmet Paper
Technology Days 1998.
[0038] In the paper or board machine according to the invention,
known press solutions can be utilized, but in several cases it is
most advantageous to use long-nip pressing. With a so-called shoe
press good bulk and high dry matter are achieved and also as little
asymmetry as possible in the web. When using e.g. Metso Paper,
Inc.'s double-felt OptiPress.TM. press section, symmetrical
dewatering is achieved as well as a web having symmetrical surface
characteristics. When aiming at high dry matters, it can be
advantageous to replace one felt with a fabric, a so-called
transfer belt, which does not receive water and which transfers the
web well. Although the invention does essentially reduce the need
for separate coating equipment, it may be advantageous in some
applications to combine the press section with surface sizing,
whereby a separate surface sizing unit after the drying section and
the associated further treatments are not necessarily needed. One
such solution (wet end sizing) is described e.g. in U.S. Pat. No.
4,793,899.
[0039] The invention makes no special demands on the drying
section, but it is possible in connection with the invention to
apply known state-of-the-art drying solutions, e.g. a drying
section applying single-wire transfer, with which on-blowing can
also be combined in order to achieve drying efficiency, profiling
or a swift grade exchange. Such a modern drying section is
presented e.g. in the international patent application
PCT/FI98/00945. With paper grades in particular it is advantageous
to use the drying section marketed under Metso Paper, Inc.'s
trademark OptiDry.TM. or a drying section of a similar type. When
desired, such pre-calendering may be used on the drying section,
which is presented e.g. in FI Patent 104434, wherein calendering
drying against a cylinder is presented. Naturally, pre-calendering
may also be performed between two rolls. When needed,
pre-calendering can of course be done traditionally after the
drying section.
[0040] There is no pre-coating in the final end of the paper
machine or board machine according to the invention, because
coating was done in the headbox, whereby fillers and/or starch was
layered, and no surface sizing was done, except a possible wet end
surface sizing in the press section. Under these circumstances, as
the paper or board arrives from the actual drying section, it is
surface-coated at one or more surface-coating stations, which is
followed by an on-line or off-line multi-nip calender.
[0041] In those applications of the invention, where the web is
also coated separately at a coating station, e.g. a blade coater,
or a coater of the jet, film transfer or spray type is used in the
coating. Using the coater, the coating matter is transferred freely
on to the web surface either as a coherent jet or as a spray, or
the coating is applied by a roll. It is advantageous to use e.g.
the coater marketed by Metso Paper, Inc. under the tradename
OptiCoat Jet.TM. or a coater of a corresponding type.
[0042] In order to eliminate web breaks, the web may be coated
supported by a belt. Supported coating is presented e.g. in Metso
Paper, Inc.'s Finnish patent FI 101489 and in article 1998
Coating/Paper Machine Makers Conference, TAPPI Proceedings.
[0043] The drying after surface coating may be started by
non-contact drying, e.g. by using the drier marketed by Metso
Paper, Inc. under the tradename PowerDry.TM. or a drier of a
corresponding type, with which a high drying power is achieved and
a quick change of drying power when required. In actual fact,
thanks to the invention, non-contact drying may even form the main
form of drying, so that the following short bank of cylinders after
it mainly functions as a driving bank.
[0044] Then advantageously follows a multi-nip calender, which is
preferably an on-line calender marketed by Metso Paper, Inc. under
the trademark OptiLoad.TM. or a calender of a corresponding type,
which differs from the ordinary super calenders in that its linear
loads in each nip can be controlled separately. Thus it is possible
to save bulk, but to achieve a good gloss and smoothness. As
regards a calender of this type, reference is made to FI Patent
96334. In connection with the invention it is of course also
possible to apply off-machine calenders.
[0045] Then follows the reeler, preferably the reeler marketed by
Metso Paper, Inc. under the trademark OptiReel.RTM. or a reeler of
the same type, which is suitable for uniform reeling of the
web.
[0046] With the method according to the invention it is possible to
make paper or board that is similar to a web made with a
state-of-the-art machine equipped with a pre-coating unit. However,
the paper or board machine according to the invention includes no
pre-coating unit, therein differing from the state of the art.
According to an advantageous application of the invention, neither
is a surface sizing unit needed, nor preferably any
pre-calender.
[0047] In the paper or board machine according to the invention,
the need for post-drying is reduced essentially in comparison with
the traditional post-drying section. Assume that the paper machine
capacities remain the same and that the normal low dry matter
content of the coating paste is approximately 10%. As according to
the invention the dry matter content of the coating paste can be
increased highly, e.g. to about 20%, and assuming that the base
paper is dry when arriving in the surface-coating section, the
post-drying section can be shortened to one-half of its present
length, because the water quantity to be removed is only one-half
of the normal quantity. If one-half of the coating paste is layered
in the web already at the headbox, the water quantity to be removed
in the post-drying section is further reduced to one-half. Thus, in
a paper machine according to the invention, the need for post
drying is only 25% of the present need, that is, only one cylinder
bank is sufficient as the post-drying section instead of the
earlier 12 cylinders in several banks, instead of the post-drying
section. It should be noted in this context that it follows from
the high dry matter content (>15%, preferably 15-25%) of the
coating paste, when a smaller quantity of paste (g/m.sup.2) should
be applied into the web, that the dry matter content is higher
after the surface coating section, which results in less need for
post-drying and in a better runability of the post-drying section,
and when single-wire transfer is used the curling tendency caused
by the post-drying section is reduced, when the need for
post-drying is reduced. Hereby curling control equipment based on
wetting can be abandoned, which further reduces the need for
post-drying.
[0048] It should be noted in particular in connection with the
invention that several techniques to be used in the method and in
the paper or board machine according to the invention have become
separately known only in recent days.
[0049] In the following, the invention will be described in greater
detail referring to the figures in the appended drawing, but the
purpose is not to restrict the invention in any strict manner to
the details shown in the figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0050] FIG. 1 is a cross-sectional view of traditional paper
according to the known state of the art.
[0051] FIG. 2 is a schematic view of the improved paper or board
machine according to the invention.
[0052] FIG. 3 is a cross-sectional view of the paper or board
according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0053] The advantageous example shown in FIG. 2 of the paper or
board machine according to the invention for implementing the
method according to the invention includes, first, a headbox 100,
which is preferably a multi-layer headbox as shown FIG. 2.
[0054] In the multi-layer headbox 100, the pulp is layered in such
a way that the pulp flows to be conducted into the surface layers
include fillers and additives, e.g. starches and hydrofobic sizes
and possibly a retention matter. In addition to the layering of
additives and fillers, fines may be layered into the surface layers
when required or fibre layering may be used at the same time. If it
is advantageous for the final product, the arrangement according to
the invention in the multi-layer headbox allows desired fillers,
additives and fines to be conducted into the desired layer, e.g. a
supply of any required fillers and additives and other such matter
into the middle layer. However, it is essential for the invention
that in the multi-layer headbox starch and optionally hydrofobic
size is conducted into the pulp through at least one layer in the
multi-layer headbox. When the multi-layer headbox is a 3-layer
headbox, a conventional quantity of starch is layered into the
middle layer part of the base or body layer 1 (compare with FIG.
3), that is, of the base paper or board. But when the headbox is a
1-layer headbox, a quantity of starch in excess of the normal
quantity is admixed into the base paper or board.
[0055] The headbox is followed by a wire section 200. The headbox
100 and the wire section 200 have such a structure that in
direction z a layered structure of the paper or board web is
achieved and/or a desired distribution of additives or fillers is
achieved in direction z (see Metso Paper, Inc.'s patent EP 0 651
092). The occurrence of porosity can be enhanced by using either
one or a negative pressure suitable for the purpose in support of
the retention matter added before the headbox 100. However, it is
also important that a good formation is achieved. The wire section
200 should be such that it will not damage the achieved layering.
The jaw former 250 shown in FIG. 2 is well suitable for this
purpose, but formers of other types are suitable at least partly
for use.
[0056] Wire section 200 is followed by a press section 300. As
shown in FIG. 2, a long-nip press, e.g. a shoe press 350, 360, is
used in the press section 300, and in this way preconditions are
brought about for preservation of the porosity. The press section
300 shown includes two presses 350, 360.
[0057] The front drying section 400, which follows after press
section 300, is formed by an on-blowing drying section 450 and a
conventional cylinder drying section 460, which includes drying
banks R.sub.1-N applying single-wire transfer. Of the drying banks
at least one is formed by a large-diameter cylinder 420 located in
a cellar space and by on-blowing drying equipment 422 placed in
connection with the cylinder 420.
[0058] After the front drying section 400, a film size press 500 is
located, which is followed by a post-drying section 600 formed by
drying banks R.sub.J applying single-wire transfer, a shoe calender
700 and a reeler 800.
[0059] In the paper or board machine according to FIG. 2, the fibre
web W, such as a paper or board web, travels as follows. From the
multi-layer headbox 100 the pulp is supplied into a jaw between the
former rolls 210, 220 of the jaw former 250 of wire section 200,
from which jaw it is conducted in between wires 215 and 216 past
dewatering equipment 230 and further supported by wire 215 on to
the press section 300. Press section 300 includes two presses 350
and 360, and at the top fabric 315 of the first press the web W is
conducted between press rolls 311, 310 of press 350 supported by
bottom fabric 316. From bottom fabric 316 the web W is conducted on
to the top fabric 317 of the next press 360 and further in between
top fabric 317 and bottom fabric 318 in between press rolls 321,
320 of press 360. Each press 350, 360 is formed as a shoe
press.
[0060] From the press section 300, the web W is guided on the
transfer fabric 390, whereby a vacuum box 391 keeps the web W on
the fabric, into an on-blowing drying unit of drying section 400,
wherein the web W travels supported by a bottom fabric 451 past an
on-blowing drying unit 450 into R.sub.1-R.sub.N of drying section
400, which apply single-wire transfer. Of the cylinder drying banks
R.sub.2 is formed in such a way that it includes a large-diameter
cylinder 420, which is placed in the cellar and in connection with
which on-blowing drying 422 is arranged, in which drying bank the
web travels supported by a wire 425. The drying wire of drying
banks applying single-wire transfer is indicated by reference
number 415 and the heated drying cylinders of the top row are
indicated by reference number 410, while the hitch cylinders or
rolls of the bottom row are indicated by reference number 411.
[0061] The web W travels in a zigzag fashion from the hitch
cylinders/rolls 411 of the bottom row on to the heated drying
cylinders 410 of the top row, on which the web W is in direct
contact against the heated cylinder surface. Then the web W is
guided through measuring equipment 490 on to the film size press
500, the rolls of which are indicated by reference numbers 545 and
547, while the film transfer devices are indicated by reference
numbers 548 and 549. The web W is guided through a non-contact
reversing device 580 to the post-drying section 600, which
according to the invention includes one drying bank R.sub.J, which
preferably applies single-wire transfer and includes a drying wire
615 and heated drying cylinders 610 and hitch cylinders/rolls
611.
[0062] After the post-drying section, the web is wetted by either
water fog or steam in order to eliminate any curling with the aid
of device 650. The web W is then guided into the calender 700,
which is formed as a shoe calender and whose rolls are indicated by
reference numbers 750, 751. After the calender 700, the web W is
guided on to a reeler, wherein the web W is reeled by the reeler's
reeling rolls 809, 810 into reels 811, 812.
[0063] According to the invention, the base paper or board, from
which the base or body layer 1 of the paper product is formed, is
optimally formed by in the headbox 100 layering filler, starch and
possibly hydrofobic sizes with a system for layering additives, so
that a suitable dense and hydrofobic surface 10 is achieved for
further treatment, such as surface sizing.
[0064] By layering in the surface-coating section 500, such as in a
film size press, a surface-sizing layer 11 into the surface 10 a
bond/bonds 2 keeping the layer/layers 1, 11 together are formed in
between the base or body layer 1 and the surface-sizing
layer/layers 11. Bond 2 also affects the strength characteristics
of the paper or board in direction z. When the surface-sizing layer
11 is starch, the dusting problems of normal copying paper are
avoided as the pulp starch improves the surface strength as well as
the binding of fillers and fines. When the surface-sizing layer 11
is hydrofobic size, a suitable hydrofobic surface is brought about
for penetration of the sizing into the paper or board (water
retention) and for the important uniform absorption of ink into the
surface of inkjet paper, by which the ink is prevented from
penetrating too deeply or from spreading out on the paper or board
surface.
[0065] When in the multi-layer headbox 100 a base paper or board
web W has been formed by layering, which web has essentially dense
and hydrofobic surfaces 10 and which has been taken through wire
section 200 and press section 300 and front drying section 400 to
the surface-coating section 500, surface sizing of the essentially
dense and hydrofobic surface of the base paper or board 1 can be
performed in the surface-coating section 500 with a high
consistence coating paste, wherein the increased dry matter content
has been achieved by a reduced quantity of starch and/or by an
increased dry matter content of the size and which penetrates
inside from the surface 10 of the base paper web or base board web
forming a bond 2 between base paper or board 1 and surface sizing
layer 11.
[0066] As is illustrated in FIG. 3, in the surface coating to be
performed after the front drying section, preferably in surface
sizing, the coating paste is pressed only into the surface 10 of
the layered base or body layer 1 of the paper or board in such a
way that the bonds 2 in direction z of the paper or board are
brought about in the internal parts of the paper or board in
between the layered base or body layer 1 and the layers of
chemicals 11 applied from the surface. Thus, in the paper or board
product according to the invention the surface-coating layer 11
extends only to a part of the thickness of the base paper or board
web and it forms a bond 2 in between the base paper or board 1 and
the surface-coating layer 11.
[0067] Thus, chemicals to be surface sized need not be pressed
through the entire paper or board. In addition, it is an advantage
that the chemicals of the base or middle layer 1 (strength
characteristics in direction z) and of the surface layer 11
(surface strength) can be optimised independently of each other and
it is possible to make such paper or board which has multi-use
characteristics (copying, ink-jet).
[0068] The invention was described in the foregoing only with the
aid of its one embodiment, which is considered advantageous. Of
course, this is not intended to limit the invention in any way to
concern such an individual embodiment only. Thus, as is obvious to
the professional in the field, many alternative solutions and
modifications are possible within the scope of the inventive idea
defined in the appended claims.
* * * * *