Note: Descriptions are shown in the official language in which they were submitted.
1
Process for producing a fibrous material web
Description
The present invention relates to a process for producing a fibrous material
web,
especially a process for producing a decorative paper, to a fibrous material
web,
especially a decorative paper, especially obtainable according to this
process, and
to the use of the fibrous material web as decorative paper.
Decorative papers are usually special papers for surface finishing, for
example of
wood-based materials. Known decorative papers are mainly produced from
hardwood chemical pulp. Such decorative papers can either be used directly in
plain
colours or printed with various designs. They are used, for example, for
furniture
surfaces, flooring and panels.
Decorative papers are generally printed in a gravure printing process. In this
process, printing ink is usually delivered to the paper by an engraved roller.
Due to
the interaction of paper colour and different printing inks, there are hardly
any
limits to the variety of decorative design. The print designs range from wood,
stone
through to fantasy decorations.
Decorative papers can be produced in a multitude of colours and area
densities.
The surface either has a satin finish or is machine-glazed. Further important
properties are high porosity, wet strength, light fastness and colour
consistency.
In order to bond decorative papers to surfaces, for example to wood-based
surfaces, they can be saturated, depending on the application, with melamine,
urea
or acrylate resins (impregnation). Due to their high absorbency and
penetration
capacity, decorative papers are able to absorb twice their own weight in
resins.
Suitable decorative papers are preferably distinguished by a high wet strength
and
thus ensure smooth running through the impregnation unit.
CA 03208542 2023- 8- 15
2
In order to guarantee optimal further processing during impregnation, suitable
decorative papers have a very high absorbency. To cover dark substrate
materials,
such as chipboard or core papers, decorative papers can also be provided with
fillers. Suitable fillers are white and coloured pigments that have a very
high light
fastness and are as chemically resistant as possible.
Decorative papers are usually bonded to the surfaces, especially wood-based
panels, using pressing and laminating equipment. The sometimes high
temperatures
and corresponding pressures in the presses cause the impregnated resin to
cure. In
this process, the decorative paper is bonded to the wood-based material. In
the
laminating process, this is usually done using hot-melt adhesives. Structured
press
plates can be used to give the wood-based materials an almost lifelike surface
feel.
Decorative papers as described above can be produced by known processes. These
processes usually comprise the steps of first producing a material stream,
which is
then fed in succession to at least one headbox, at least one wire section for
forming
the fibrous material web, at least one press section, at least one dryer
section
having drying groups, and then to a reel.
Fibrous material webs, especially decorative papers, obtained by to such
processes
regularly have the features mentioned below. Due to a high dry matter content
after the press section, especially when using a shoe press, the paper is
influenced
in that it experiences less "sticking" to the drying cylinders of the (first)
pre-drying
group in the dryer section. The term "sticking" is understood here to mean
especially the adhesion of the moist paper web to the hot cylinder surface.
The cellulose fibres usually used for paper production swell when
moisture/water is
absorbed and shrink when water is released. As a result, the fibrous material
web
shrinks in the dryer section by approximately 1 - 5% over the entire
dewatering and
drying process. Due to the described "sticking", the paper web is hindered in
its
shrinkage.
When the fibrous material web then comes into contact with printing ink and/or
resin during application to a surface and/or during the printing process, the
paper
can change size again and "grow". This takes place to approximately a similar
degree as shrinkage during drying. Since, when using a shoe press, the paper
web
is drier when it enters the dryer section, it adheres less to the drying
cylinder and
CA 03208542 2023- 8- 15
3
thus shrinks to a greater extent, which leads to higher paper growth in the
subsequent finishing process.
Such paper growth, which can also be referred to as wet elongation, is only
suitable
to a limited extent, especially for dimension-critical decorations.
Therefore, the known processes for producing decorative papers are in need of
improvement.
The present invention addresses this need.
Especially, a process is to be provided with which high-quality fibrous
material webs
can be produced which are distinguished, among other things, by high porosity,
wet
strength, light fastness and colour consistency. The process should be as
simple
and economical as possible. Furthermore, the shrinkage of the paper during the
production process should be as defined as possible, so that the subsequent
"waxing" of the paper during the printing and/or impregnation is as constant
and
reproducible as possible.
This aim was addressed by a process according to claim 1, i.e. by a process
for
producing a fibrous material web, especially a decorative paper, the process
comprising the following steps:
- providing a fibrous material stream
- supplying the fibrous material stream in this sequence into at least one
fibrous
material headbox, into at least one wire section for forming a fibrous
material web,
into at least one press section, and into at least one dryer section having
drying
groups,
characterised in that
a dry matter content of the fibrous material web in the range from 45 wt.% to
60 wt.% is established in the press section, and in that the fibrous material
web is
moistened after or in the dryer section partially or completely by means of an
aqueous medium, wherein from 2% to 30%, especially from 4% to 20%, preferably
from 6% to 15%, in relation to the area density of the fibrous material web,
of
water is applied to the fibrous material web.
The expression "in relation to the area density of the fibrous material web"
refers to
the area density of the fibrous material web produced according to the process
and
CA 03208542 2023- 8- 15
4
not to the area density of the fibrous material web at the location of the
moistening.
In other words, for a fibrous material web produced according to the process
with
an area density of 100 g/m2, a total of 2 g/m2 to 30 g/m2 of water is applied
to the
fibrous material web (moistened).
The feature "partially or completely moistened by means of a water-containing
medium" means that the fibrous material web is moistened in the running
direction
of the fibrous material web transversely or longitudinally either only in
predetermined regions (partially) or over the entire width, so that especially
by
these two measures - targeted strong drying and targeted re-moistening of the
fibrous material web - a wet elongation behaviour of the fibrous material web
according to Miitek of 2.0% to 4.0% transversely to the machine running
direction
and of 0.5% to 1.5% longitudinally in the machine running direction can be
established, moreover preferably at very high speeds of the fibrous material
web of
up to 1100 nn/min.
In conventional press concepts, the dry matter content is preferably
established in
the range of 46 wt.% to 53 wt.%, and in shoe presses preferably in the range
of
52 wt.% to 58 wt.%.
Subsequently, the fibrous material web can first be smoothed, if necessary,
and
then fed to a reel for easier storage and/or easier transport.
The fibrous material web thus produced is especially a decorative paper.
In the present text, the term "comprise" shall also mean "consisting of".
All norms and standards mentioned in this text and in the examples and claims
refer to those valid on the priority date. If no priority is claimed, the
standards and
norms referred to in the text and in the examples and claims refer to those in
force
on the filing date.
The process according to the invention is characterised especially in that the
amount of water/moisture applied after or in the dryer section re-creates the
"sticking" described above, which reduces subsequent elongation in the event
of
liquid contact, e.g. during the printing process or during impregnation.
CA 03208542 2023- 8- 15
5
Furthermore, the process is kept simple and allows for an economically
advantageous implementation due to high web speeds. The fibrous material webs
produced in this way are additionally characterised by high porosity, wet
strength,
light fastness and colour consistency.
In the process according to the invention, a fibrous material stream is first
provided. This fibrous material stream is preferably characterised in that it
comprises or consists of pulp fibres of hardwoods or softwoods, or a mixture
thereof, the fibre length of which is preferably in the range of 0.6 mm to 3
mm,
especially in the range of 0.8 mm to 2 mm. Furthermore, the fibrous material
stream may contain various fillers, such as titanium dioxide, kaolin, etc.
and/or
colour pigments and/or other additives and/or various functional chemicals,
such as
wet-strength agents, or the like and/or production aids, such as retention
agents
and defoamers. The usual consistency in the headbox is usually 0.5 wt.% to
2 wt.%, especially 0.8 wt.% to 1.5 wt.%.
In the process according to the invention, the fibrous material stream is then
passed into at least one headbox and into at least one wire section to form a
fibrous material web.
The headbox is usually a type of nozzle by means of which the fibrous material
stream is applied evenly across the width in quantity and consistency to an
endless
circulating wire, through which the solids are separated from the water
content.
During the dewatering process, a uniform fibre mat forms on the wire, which is
the
starting point for the subsequent paper. The solids content at the end of the
wire
section is preferably 15 wt.% to 25 wt.%, especially in the range of 18 wt.%
to
22 wt.%.
In the process according to the invention, the fibrous material web is then
fed into
at least one press section.
In the press section, the fibre mat produced in the wire section is preferably
further
dewatered. For this purpose, it is usually pressed out with the support of
felts. This
can be done, for example, between two rollers pressed against each other. The
felts used here have the function of transporting the web through the press
section
without destroying it and of absorbing the pressed-out water in the press nip.
CA 03208542 2023- 8- 15
6
In the process according to the invention, the pressed fibrous material web is
then
fed into at least one dryer section with drying groups.
The dryer section usually consists mainly of steam-heated cylinders that are
brought into contact with the paper web in order to heat it to such an extent
that
the water still in the paper web evaporates to the desired final moisture
content.
These successive drying cylinders are preferably combined to form so-called
drying
groups. These drying groups can be supplied with steam in different ways in
order
to control the drying process.
In the process according to the invention, a dry matter content of the fibrous
material web in the range of about 45 wt.% to 60 wt.% is established in the
press
section.
From an energy perspective, the aim is usually to achieve the highest possible
dry
matter content. From a technical perspective, however, there are limitations.
In
conventional rollers/presses, dry matter contents from 46 wt.% to 53 wt.% can
be
achieved, depending on the material input.
When using one or more shoe presses, dry matter contents of up to 60 wt.% can
be
achieved, especially in the range from 52 wt.% to 58 wt.%. Too much pressure
can
destroy the paper web, whilst excessively low dry matter contents can lead to
running problems or result in higher steam consumption in the subsequent dryer
section, which in turn leads to higher drying costs.
According to the process of the invention, the fibrous material web is
moistened in
the dryer section. Here, a water application from 0.8 g/m2 to 45 g/m2 or 1
nril/rn2 to
30 ml/m2 is preferred. Preferred ranges include, especially: 1 nril/rn2 to 15
ml/m2,
2 nril/rn2 to 15 ml/m2, 1 nril/rn2 to 10 nril/rn2 or 2 nril/rn2 to 6 ml/m2.
Depending on the area density of the fibrous material web, the amount of water
to
be applied, and thus also the water content of the medium, can be adjusted in
relation to the area density of the fibrous material web in the range from 2%
to
30%, especially in the range from 4% to 20%, preferably in the range from 6%
to
15%.
The process according to the invention is further preferably characterised in
that
the press section comprises a laying press, especially a shoe press.
CA 03208542 2023- 8- 15
7
After the formation of a fibrous material web in the wire section, the fibrous
material web must be further dewatered. The dry matter content is usually
increased here by mechanical pressure perpendicular to the surface of the
fibrous
material web. This is done in the so-called press section. Here, the fibrous
material
web is usually treated between rollers with special pressures. The water
pressed
out of the fibrous material web is regularly absorbed here by felts that are
applied
to the corresponding rollers.
For this purpose, presses in conventional roller-roller or shoe-roller design
are
preferably used.
Shoe presses are known in paper production and usually comprise a shoe that
presses against a rotating counter roller. A flexible plastic sleeve supported
by an
oil film can float here on the shoe. The rotating counter roller is usually
covered
with a felt to remove the pressed-out water.
After pressing the fibrous material web, during which dry matter contents from
45 wt.% to 60 wt.% are achieved, the moisture remaining in the fibrous
material
web must be further removed. This is usually done by evaporation and/or the
effect
of vacuum. The most common process here is contact drying on steam-heated
cylinders. Here, the thermal energy is transferred by direct contact from the
outer
walls of the drying cylinders to the surface of the fibrous material web. The
dryer
section consists of multiple drying cylinders, over which the fibrous material
web is
usually brought alternately once with the top side and once with the bottom
side.
Single-row as well as conventional double-row drying groups can be used for
this
purpose.
The process according to the invention is further preferably characterised in
that
the moistening with the water-containing medium is carried out by means of a
nozzle moistening, especially by atomising a water-air mixture, especially via
a two-
substance nozzle.
In a practical embodiment, a nozzle moistener with two-substance nozzles
and/or
with pneumatic atomiser nozzles is used as a contactless application unit. The
flow
rate of the water-air mixture is preferably adjustable and/or controllable
sectionally
in the running direction of the fibrous material web and/or in the transverse
CA 03208542 2023- 8- 15
8
direction. Preferably, each nozzle is individually adjustable and/or
controllable. The
temperature of the water is expediently 20 to 95 C, preferably 40 C to 90 C,
for
good atomisation.
The aqueous medium is preferably free of dyes so that the colour of the
fibrous
material web is not changed.
The process according to the invention is further preferably characterised in
that
the moistening is adjustable transversely to the fibrous web.
This has the advantage that the adhesion of the web can be controlled over the
width.
According to the invention, the fibrous material web is re-moistened after or
in the
dryer section.
The process according to the invention is further preferably characterised in
that
the moistening takes place at the beginning of the first drying group.
It is preferred that the moistening takes place at a paper web moisture of
between
30 wt.% to 50 wt.%, preferably at 42 to 52 wt.%. Preferably, the moistening
takes
place on a vacuum roller.
The process according to the invention is further preferably characterised in
that
the moistening takes place in a dry matter content range of the paper web from
50 wt.% to 70%, preferably at 48 to 68 wt.%.
The process according to the invention is further preferably characterised in
that
the fibrous material web is guided at a speed in the range from 500 m/min to
1100 nn/min, especially at 700 nn/min to 900 nn/min.
The use of shoe presses especially enables a high speed of the fibrous
material
web.
With the process according to the invention, the fibre orientation is
preferably
longitudinal to transverse to influence the growth. Preferably, this is to be
adjusted
by the V-jet over the headbox. The term V-jet means the difference in velocity
between the material stream exiting the headbox and the wire velocity.
CA 03208542 2023- 8- 15
9
Preferred fibre orientations here are longitudinal to transverse in a ratio of
1.0 to
2.2, preferably 1.2 to 2Ø
The process according to the invention is further preferably characterised in
that
the fibrous material headbox is run over a V-jet in the range from +50 nn/min
to -
50 nn/min, preferably at +40 nn/min to -40 nn/min.
The process according to the invention is further preferably characterised in
that
the paper web has a longitudinal/transverse ratio of breaking strength (ISO
1924-2)
from 1.0 to 2.2, preferably from 1.2 to 2Ø
The process according to the invention is further preferably characterised in
that
the fibrous material stream comprises substantially the following pulp types.
Long-
fibre pulps such as spruce and pine and short-fibre pulps such as birch,
beech,
aspen, oak, eucalyptus or mixtures thereof. Especially, eucalyptus pulp from
the
species Grandis, Urograndis and Globulus or mixtures thereof is used.
The process according to the invention is further preferably characterised in
that
the fibrous material stream is ground to a Schopper fineness of 16 to 40 .
This can
be done together with the filler or exclusively with the pulp. The exclusively
pure
pulp grinding has the advantage that the refiner sets have a significantly
longer
service life.
The process according to the invention is further preferably characterised in
that
the fibrous material stream comprises pulps certified especially according to
FSC
and PFSC.
The present invention also relates to a fibrous material web produced by the
process described above.
The present invention also relates to a decorative paper produced by the
process
described above.
The above preferred embodiments of the process according to the invention
apply
analogously to the fibrous material web or the decorative paper obtainable by
this
process.
CA 03208542 2023- 8- 15
10
The present invention also relates to a fibrous material web, especially a
decorative
paper, preferably obtainable by the process according to the invention, which
has at
least one of the following properties.
- A wet elongation behaviour according to Miitek of 2.0 to 4.0%, especially of
2.2%
to 3.3% transversely to the machine direction and 0.5 to 1.5%, especially of
0.7 to
1.3% longitudinally in the machine direction.
The wet elongation behaviour according to Miitek is determined here with a
Miitek
measuring device WSD 02 (Emtec). The measurement parameters include a
transverse tension of 4N/60mm and a longitudinal tension of 1N/60rnrn after 25
seconds of one-sided water application. The measurement result transversely is
averaged from the measurement locations, in each case 10cm from the edge, from
the centre, and from the centre (centre-centre) of the outer and centre
measurement.
The wet elongation behaviour according to Miitek is calculated as follows:
Miitek wet elongation transverse = (((TS + DS)/2)) + centre-centre + DS)/3.
Miitek wet elongation longitudinally from the "centre-to-centre" position.
TS, DS and centre-centre mean tending side, drive side and centre-centre as
the
position between the centre of the web and the TS.
- A real growth of the web due to impregnation from 0.8% to 1.8%, especially
from
0.9% to 1.7% transversely to the machine direction and 0.2% to 1.2%,
especially
0.3% to 1% longitudinally in the machine direction.
- An area density preferably from 40 g/m2 to 150 g/m2, especially from 45 to
90 g/m2 (ISO 536).
- A porosity according to Gurley from 10 s to 28 s, especially from 14 s to 26
s (ISO
5636-5).
- A filler content of 15 wt.% to 42 wt.%, especially 20 wt.% to 38 wt.% (ISO
2144).
- A Bekk smoothness of 80 s to 220 s, especially 140 s to 210 s on the
decorative
side (ISO 5627).
CA 03208542 2023- 8- 15
11
- A longitudinal/transverse ratio of breaking force MD / breaking force CD
(ISO
1924-2) of 1.0 to 2.2, especially of 1.2 to 2Ø
- A width preferably up to 300 cm or up to 227 cm.
Explicitly disclosed herein are also all of the above-mentioned properties
individually as well as all possible combinations of the above-mentioned
properties.
The above preferred embodiments of the process according to the invention
apply
analogously to the fibrous material web or the decorative paper per se,
especially
to the fibrous material web or the decorative paper obtainable by the process
according to the invention.
The fibrous material web according to the invention, especially the decorative
paper, is preferably characterised in that it is present in the colour shades
white,
cream, beige, brown, grey and/or black.
The present invention also relates to the use of the fibrous material web as a
decorative paper, especially for interior finishing and/or in the furniture
industry,
preferably for surface finishing of wood-based materials, such as coated
boards,
tables, floors, kitchen worktops, window sills and/or for exterior
applications, such
as façades.
The above preferred embodiments of the process according to the invention
apply
analogously to the use according to the invention.
CA 03208542 2023- 8- 15
12
Description of the figures
Figure 1 shows a schematic representation of a possible device suitable for
carrying
out the process according to the invention or for producing the fibrous
material web
according to the invention.
A slalom guidance of the fibrous material web over drying cylinders and vacuum
rollers is shown here. This is especially advantageous because the nozzle
moistener
can be positioned in the lower region of the vacuum rollers, especially
between the
"3 and 9 o'clock position". This allows excess water to simply drip away
downwards
without touching the fibrous material web.
Alternatively, the nozzle moistener can also be positioned on vacuum roller 1
or 3.
A single-tier dryer section is especially suitable for this purpose, as here
there is
free access to the paper web and the water-air mixture can be drawn into the
paper
web from the nozzle moistener with the help of the vacuum rollers.
The invention will be explained in greater detail below by means of non-
limiting
examples.
CA 03208542 2023- 8- 15
13
Examples
To produce a fibrous material web for use as a decorative paper according to
the
present invention with a real growth in the impregnation channel of 1.1%
transversely and 0.45% longitudinally, the following setting parameters were
selected.
Use of a eucalyptus pulp of the Globulus species with a fineness of 21 SR and
a
filler content consisting of titanium dioxide of 32.5 wt.%, a V-jet of -18
rn/rnin, a
shaking index of 2900 [1000/min] at a machine speed of 850 m/min and a line
load
of the shoe press of 850 KN/m. A water flow rate of 360 l/h was set at the
nozzle
moistener. The fibrous material web for use as decorative paper was produced
as
follows:
- providing the fibrous material stream,
- supplying the fibrous material stream in this sequence into the fibrous
material
headbox, into the wire section for forming the fibrous material web, into the
press
section, and into the dryer section with drying groups.
In the press section (shoe press), a dry matter content of 55 wt.% was
established
for the fibrous material web. The fibrous material web was moistened again in
the
dryer section, wherein 4.75%, in relation to the area density of the fibrous
material
web (72 g/m2), of water was applied to the fibrous material web.
With these settings, a fibrous material web with an area density of 72 g/m2
was
produced for use as a decorative paper with a finished roll width of 206 cm,
which
showed a growth according to Miitek of 2.25% transversely and 0.65%
longitudinally (determined as described above) with a Gurley porosity of 14 s
(ISO
5636-5). The longitudinal/transverse ratio of the breaking force (ISO 1924-2)
was
1.25. After further impregnations typical for decorative papers, the fibrous
material
web showed an outstandingly very low real growth of the fibrous material web,
which was always in the range of 0.8% to 1.8% transversely to the machine
direction and in the range of 0.2% to 1.2% longitudinally in the machine
direction.
CA 03208542 2023- 8- 15
