U.S. patent application number 14/425650 was filed with the patent office on 2015-07-30 for press belt in a paper-making machine.
This patent application is currently assigned to VOITH PATENT GMBH. The applicant listed for this patent is VOITH PATENT GMBH. Invention is credited to Delphine Delmas, Uwe Matuschczyk, Hermann Reichert.
Application Number | 20150211177 14/425650 |
Document ID | / |
Family ID | 49080881 |
Filed Date | 2015-07-30 |
United States Patent
Application |
20150211177 |
Kind Code |
A1 |
Delmas; Delphine ; et
al. |
July 30, 2015 |
Press Belt in a Paper-Making Machine
Abstract
A press belt for a shoe-press device for dewatering or smoothing
a fibrous web, in particular a paper, cardboard, or tissue web. The
press belt has a fiber-reinforced plastic matrix. On account of the
fiber-reinforced plastic matrix containing at least in a partial
region at least one polyurethane material and polydimethyl siloxane
and silicon dioxide microparticles as additives, resistance to
abrasion, the tendency toward developing fissures and toward
fissure growth and/or resistance in relation to media present in a
paper-making machine can be improved.
Inventors: |
Delmas; Delphine;
(Heidenheim, DE) ; Matuschczyk; Uwe; (Geislingen,
DE) ; Reichert; Hermann; (Heidenheim/Oggenhausen,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
VOITH PATENT GMBH |
HEIDENHEIM |
|
DE |
|
|
Assignee: |
VOITH PATENT GMBH
HEIDENHEIM
DE
|
Family ID: |
49080881 |
Appl. No.: |
14/425650 |
Filed: |
August 29, 2013 |
PCT Filed: |
August 29, 2013 |
PCT NO: |
PCT/EP2013/067858 |
371 Date: |
March 4, 2015 |
Current U.S.
Class: |
162/358.2 |
Current CPC
Class: |
D21G 1/0066 20130101;
D21F 1/0027 20130101; D21F 3/0236 20130101; D21F 7/086 20130101;
D21F 3/0227 20130101 |
International
Class: |
D21F 1/00 20060101
D21F001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 4, 2012 |
DE |
10 2012 215 612.7 |
Claims
1-15. (canceled)
16. A press belt for a shoe-press device for dewatering or
smoothing a fibrous web, the press belt comprising: a
fiber-reinforced plastic matrix forming the press belt, said
fiber-reinforced plastic matrix, at least in a part-region thereof,
containing at least one polyurethane material and additives of
polydimethyl siloxane and silicon dioxide microparticles.
17. The press belt according to claim 16, wherein at least one
further part-region of said fiber-reinforced plastic matrix is
configured as foam.
18. The press belt according to claim 16, wherein the at least one
part-region is selected from the group consisting of a layer of the
press belt, a surface layer of the press belt, a peripheral region
of the press belt, and an inner layer of the press belt.
19. The press belt according to claim 16, wherein said polydimethyl
siloxane has a viscosity of between 100 and 100,000 mPa*s.
20. The press belt according to claim 16, wherein said at least one
part-region contains a proportion of said polydimethyl siloxane of
1 to 10% by weight.
21. The press belt according to claim 16, wherein said silicon
dioxide microparticles have a mean particle size of between 10 and
800 .mu.m.
22. The press belt according to claim 16, wherein said at least one
part-region contains a proportion of said silicon dioxide
microparticles of 1 to 10% by weight.
23. The press belt according to claim 16, wherein said at least one
part-region contains silicon dioxide nanoparticles having a mean
particle size of between 10 and 80 nm.
24. The press belt according to claim 23, wherein said at least one
part-region contains a proportion of said silicon dioxide
nanoparticles of 1 to 10% by weight.
25. The press belt according to claim 16, wherein said at least one
polyurethane material is made from at least from a polyurethane
prepolymer and a cross-linking agent, and said polyurethane
prepolymer is an MDI prepolymer and/or a PPDI prepolymer having a
polyol component selected from the group consisting of polyether
and polycarbonates.
26. The press belt according to claim 25, wherein said
cross-linking agent contains at least one polyether polyol material
or is composed thereof.
27. The press belt according to claim 16, configured for processing
paper web, cardboard web, or tissue web.
28. A method of manufacturing a plastic matrix for a press belt,
the method comprising forming the plastic matrix from at least one
polyurethane prepolymer, at least one cross-linking agent,
polydimethyl siloxane, and silicon dioxide microparticles.
29. The method according to claim 28, which comprises, prior to
cross-linking the at least one polyurethane prepolymer, mixing
silicon dioxide nanoparticles containing at least part of the
cross-linking agent to form a nanoparticle mixture containing
between 20% and 60% by weight of silicon dioxide nanoparticles.
30. The method according to claim 28, which comprises, in
downstream method steps, replacing the cross-linking agent with the
nanoparticles mixture entirely or by 5 to 40%.
31. The method according to claim 28, which comprises, prior to
cross-linking the at least one polyurethane prepolymer, mixing the
silicon dioxide microparticles with the polydimethyl siloxane and,
optionally, with further additives, to form an additive mixture
that is subsequently mixed with at least part of the cross-linking
agent.
Description
[0001] The invention relates to a press belt for a shoe-press
device, having the features of the preamble of claim 1. The
invention furthermore relates to a method for manufacturing a
plastic matrix for a press belt of a shoe-press device, having the
features of the preamble of claim 12.
[0002] Press belts which may be configured, for example, as a
closed sleeve of a shoe-press roller or as a transfer belt which is
routed as a continuously revolving belt between the fibrous web and
the sleeve of the counter roller, are exposed to high mechanical,
thermal and also chemical stresses. Press belts of this type
typically are composed of a polyurethane matrix which is
fiber-reinforced. The polyurethane matrix here may be configured so
as to be single-layered or multi-layered, such that the press belt
may display a plurality of plies or layers, respectively. The outer
surface of the respective press belt may be provided with a
structure, such as grooves, blind holes, or similar, in order for
dewatering in the press to be optimized. On account of the high
mechanical stresses, fissures may develop in the press belts,
wherein further growth of the fissures may arise, likewise on
account of the high mechanical stress. This occurrence of fissure
growth may increasingly arise also in press belts having grooves or
blind holes. On account of fissure growth, structural and/or
functional failure of the press belt may be incurred. Moreover, the
press belts are also exposed to enormous mechanical-cum-dynamic
stresses, such that the press belts additionally are subjected to
high abrasion. Moreover, on account of the various media present in
the paper-making machine, the press belts are exposed to intense
chemical stresses in the paper-making machine. In this way, the
press belts may be in contact with, for example, water, oil, acids,
bases, solvents, or similar, and are at least partially corroded by
these media.
[0003] For example, a press sleeve is thus disclosed in DE19702138
A1, the hardness and resistance to wear of said press sleeve having
been increased by additives from rock flour, ceramic, or carbon. It
is proposed in DE4411620 A1 to provide only an outer layer of the
press sleeve with additives which increase resistance to wear.
[0004] US2005287373 and US20060118261 disclose press belts which
display polydimethyl siloxane. The paper-making machine belts of
WO2005090429 and of US2008081179 display nanoparticles, in order to
improve resilience in relation to fissure growth, hardness or
resilience to abrasion, for example. Paper-making machine belts
which display silicon dioxide microparticles are described in
EP2330249.
[0005] Despite the embodiments which already exist, there is
ongoing demand for press belts for a shoe-press device, having
improved resilience in relation to mechanical, thermal, and
chemical stress.
[0006] The present invention focuses on the object of providing for
a press belt of a shoe-press device, and for a method for
manufacturing a plastic matrix for a press belt of this type, an
improved or at least an alternative embodiment which is
distinguished, in particular, by higher resilience to abrasion, a
tendency toward fissure formation and toward fissure growth which
is lower or at least not worse, and/or by a lower sensitivity in
relation to media which are present in a paper-making machine.
[0007] According to the invention, this object is achieved by the
subject matter of the independent claims. Advantageous embodiments
are the subject matter of the dependent claims.
[0008] In one aspect of the invention, a press belt for a
shoe-press device for dewatering or smoothing a fibrous web, in
particular a paper, cardboard, or tissue web, is proposed, in which
the press belt displays a fiber-reinforced plastic matrix. The
fiber-reinforced plastic matrix here may at least in a part-region
display a polyurethane material, and polydimethyl siloxane and
silicon dioxide microparticles as additives.
[0009] Advantageously, chemical resistance in relation to the media
present in the paper-making machine can be increased on account of
the combination of the additives polydimethyl siloxane and silicon
microparticles. Moreover, on account of the listed additives,
resilience to abrasion can be improved, and the tendency toward
fissure formation and toward fissure growth can be held low.
Advantageously, by way of adding the combination of additives, the
swelling behavior of the press belt is not or only slightly
modified.
[0010] In comparison with employing polydimethyl siloxane alone,
the combination of additives leads to improved resilience to
abrasion and to increased chemical resilience. In contrast,
employing silicon dioxide microparticles alone leads to worsened
dispersibility of the reactant of the plastic matrix and, on
account thereof, optionally to an increased tendency toward fissure
formation in the finished press belt. Moreover, it was determinable
that press belts having only silicon dioxide microparticles as an
additive displayed significantly worsened resilience to
abrasion.
[0011] It may thus be established that a balanced stress profile
can be created only by way of the combination of additives, such
that both resistance to chemicals and the tendency toward fissure
formation and toward fissure growth, and resilience to abrasion,
are improved in a mutually balanced ratio, without any
deterioration of one of these properties or in the further required
properties, such as the swelling behavior, for example,
occurring.
[0012] A press belt is to be understood a belt or a sleeve which,
together with a fibrous web, is routed through a shoe-press nip
which is formed between a static press element, the so-called press
shoe, and a cylindrical counter roller. The press shoe is supported
on a fixed yoke and is hydraulically pressed against the counter
roller. In addition to the fibrous web and the press belt, one or a
plurality of continuously revolving felts and/or further
continuously revolving press belts may be routed through the press
nip.
[0013] The press belt may be implemented as a press sleeve of the
shoe-press roller, i.e. as a closed sleeve said press belt is held
by two lateral tension disks and rotates about the fixed press
shoe. In order to reduce the friction of the press belt on the
press shoe, oil for lubricating is applied to the inner side of the
press belt. Instead of being guided by the two lateral tension
disks, the press belt may be routed over the press shoe and a
plurality of guide rollers, as is the case in open shoe presses.
The surface of press sleeves may be provided with grooves and/or
blind holes.
[0014] The press belt may also be implemented as a transfer belt
which, in order to convey the fibrous web through the shoe-press
nip, is routed as a continuously revolving belt between the fibrous
web and the sleeve of the counter roller. After the shoe-press nip,
the fibrous web is then taken off the press belt with the aid of a
suction roller, transferred to another clothing, and supplied to
the downstream machine group. It is thus advantageous for the
surface of the transfer belt to have adequate adhesion in relation
to the fibrous web in order to reliably guide the latter, and for
the surface of the transfer belt to have good smoothness and a low
tendency toward marking. On the other hand, it is likewise
advantageous for the fibrous web to be capable of being easily
taken off again.
[0015] A fiber-reinforced plastic matrix is to be understood as a
plastic matrix in which one-, two-, or three-dimensional fiber
structures are embedded. The term one-dimensional fiber structure
here comprises fibers, endless fibers, yarns, fiber bundles, fiber
strands, filaments, filament bundles, rovings, or hybrid forms. The
term two-dimensional fiber structure comprises woven fabrics,
knitted fabrics, warp-knitted fabrics, non-woven fabrics,
cross-laid structures, unidirectionally deposited fiber layers,
multiaxial cross-laid structures, mats, knitted goods, woven spacer
fabrics, braided hoses, embroideries, sewn goods, peel plies, or
hybrid forms. The term three-dimensional fiber structure is to be
understood as being substantially a plurality of two-dimensional
fiber structures which are layered so as to be on top of one
another. The two-dimensional fiber structures here may be
configured in different manners. In this way it is conceivable, for
example, that a unidirectional fiber layer is followed by a
non-woven fabric as the next layer, while a woven fabric may
complete the three-dimensional fiber structure. However,
unidirectional two-dimensional fiber structures may also be
exclusively used for constructing a three-dimensional fiber
structure. The unidirectional two-dimensional fiber structures here
may be identically oriented or be variably oriented with respect to
their direction. In the event of the latter, a multiaxial
cross-laid structure is present.
[0016] Materials which may be employed for fiber structures are
glass fibers, carbon fibers, plastic fibers, aramid fibers, PBO
fibers, polyethylene fibers, polyester fibers, polyamide fibers,
natural fibers, basalt fibers, quartz fibers, aluminum oxide
fibers, silicon carbide fibers, or hybrid forms.
[0017] Additives are to be understood as materials which are added
to the plastic matrix in order to modify the properties of the
latter in the desired way and manner. In this way, additives are
added to the plastic matrix in order to, for example, influence in
a targeted manner resilience to abrasion, a low tendency toward
fissure formation, a low fissure growth, high resilience in
relation to media present in the paper-making machine, such as, for
example, water, oil, acids, bases, solvents, or similar, desired
surface properties, such as, for example the adhesive capability in
relation to a fibrous web, hardness, or similar. Here, likewise
properties which are achieved by way of the fiber reinforcement may
be influenced by the additives. In this way, for example, pigments,
microfibers, such as, for example, carbon fibers, glass fibers, or
similar, powdered glass, carbon black, clay, montmorillonite,
saponite, hectorite, mica, vermiculite, bentonite, nontronite,
beidellite, volkonskoite, manadiite, kenyaite, smectite, bederite,
silicon carbide, silicic acid salt, metal oxides, or arbitrary
mixtures of the aforementioned compounds can be used as further
addivitives.
[0018] A fibrous web is to be understood as a cross-laid structure
or a random structure of fibers, respectively, comprising wood
fibers, plastic fibers, glass fibers, carbon fibers, additives,
auxiliaries, or similar. In this way, the fibrous web may be
configured as a paper, cardboard, or tissue web, for example, which
is substantially composed of wood fibers, with small amounts of
other fibers or also additives and auxiliaries being present.
[0019] Furthermore, at least one further part-region of the
fiber-reinforced plastic matrix may be configured as foam. On
account of configuring a further part-region of the
fiber-reinforced plastic matrix as foam, higher elasticity and
softness of the press belt may advantageously be established. On
account of the press belt displaying less hardness, the compressive
force may be adjusted in a more exact manner. Moreover, in the case
of unevenness in the fibrous web or other components of the
paper-making machine, the compressive force fluctuates less
intensely. Foam here is to be understood as bubbles which are
separated by walls. If the foam has open pores, the walls are at
least in part breached, while in a closed foam the individual
bubbles are closed off by the walls.
[0020] The part-region which displays at least polyurethane, and
polydimethyl siloxane and silicon dioxide microparticles as
additives, or the further part-region which is configured as foam,
may comprise a layer of the press belt, a surface layer of the
press belt, a peripheral region of the press belt, or an inner
layer of the press belt, for example.
[0021] If the part-region comprises a surface layer of the press
belt, the press belt may thus be equipped with the desired surface
property but, on account of layers of the press belt which lie on
the inside and which are configured in various manners, may be
equipped with further advantageous properties. By way of a surface
layer which is designed in such a manner, abrasion resistance, an
advantageous fissure behavior, and high resilience in relation to
the media present in the paper-making machine may be achieved, for
example, while sufficiently high elasticity and tear strength can
be established by way of inner layers. In an analogous manner, this
also applies to the peripheral regions of the press belt. An inner
layer, for example configured from a foam, may positively influence
elastic behavior and softness of the press belt, without the
demanded high resilience of the surface of the press belt
deteriorating.
[0022] A layer or a ply, respectively, of the press belt here is
understood to be a region which is delimitable in the direction of
thickness in relation to other layers or plies. Delimiting may be
performed, for example, by the fiber reinforcement, by the
construction of the plastic matrix, by the additive proportions
and/or by mechanical properties.
[0023] Furthermore, the employed polydimethyl siloxane may display
a viscosity of 100 to 100,000 mPa*s. Polydimethyl siloxane having a
viscosity of 500 to 50,000 mPa*s, optionally of 1000 to 10,000
mPa*s, in particular of 1500 to 5000 mPa*s, and of 2000 to 3000
mPa*s, for example, may also be employed. This relates to a
temperature of 25.degree. C.
[0024] On account of employing polydimethyl siloxane having a
viscosity of this type a reduction of the surface interferences in
the press belt may advantageously be performed. Moreover,
dispersibility of the reactants of the plastic matrix may be
improved on account of a viscosity of the polydimethyl siloxane of
this type.
[0025] The at least one part-region furthermore may display 0.1 to
10% by weight polydimethyl siloxane. It is also conceivable that
the at least one part-region displays 0.1 to 8% by weight, in
particular 0.1 to 5% by weight, optionally 0.1 to 3% by weight, and
0.2 to 1.5% by weight polydimethyl siloxane, for example.
[0026] On account of a proportion of polydimethyl siloxane of this
type the aforementioned advantages may be advantageously
achieved.
[0027] Furthermore, the silicon dioxide microparticles may display
a mean particle size of 2 to 800 .mu.m. It is also conceivable for
the silicon dioxide microparticles which display a mean particle
size of 5 to 500 .mu.m, in particular of 5 to 50 .mu.m, for example
of 10 to 30 .mu.m, and optionally of 10 to 20 .mu.m, to be
employed.
[0028] On account of a mean particle size of the silicon dioxide
microparticles of this type, dispersibility of the reactants of the
plastic matrix may be advantageously improved.
[0029] Furthermore, the at least one part-region may display 0.01
to 10% by weight silicon dioxide microparticles. It is also
conceivable for the at least one part-region to display 0.01 to 5%
by weight, in particular 0.05 to 3% by weight, optionally 0.05 to
0.5% by weight, and for example 0.05 to 2% by weight silicon
dioxide microparticles.
[0030] On account of a proportion of silicon dioxide microparticles
of this type, the aforementioned advantages may be advantageously
achieved
[0031] Furthermore, silicon dioxide nanoparticles having a mean
particle size of 10 to 80 nm may be employed in the at least one
part-region. It is also conceivable for silicon dioxide
nanoparticles which have a mean particle size of 12 to 60 nm, in
particular of 14 to 40 nm, for example of 16 to 30 nm, and
optionally of 18 to 25 nm, to be employed.
[0032] On account of employing silicon dioxide nanoparticles, the
tendency toward fissure formation may be advantageously reduced.
Possibly, the tendency toward fissure growth likewise may be
reduced. Employing silicon dioxide nanoparticles alone does in turn
improve the tendency toward fissure formation, but leads to a
deterioration in the resilience to abrasion. By combining the
additives, resilience to abrasion of the at least one part-region
is increased.
[0033] Furthermore, the at least one part-region may display 0.01
to 10% by weight silicon dioxide nanoparticles.
[0034] By means of a proportion of silicon dioxide nanoparticles of
this type in the at least one part-region, the aforementioned
advantages may be achieved.
[0035] Furthermore, the at least one polyurethane material may be
manufactured from a polyurethane polymer and a cross-linking agent.
The polyurethane polymer here may be configured as an MDI
prepolymer and/or as a PPDI prepolymer having polyether and/or
polycarbonates and/or polycaprolactones as a polyol component. On
account of a configuration of the polyurethane component of the
plastic matrix of this type, the desired durability and resilience
in relation to the wear of the press belt may be advantageously
established. Moreover, a plastic matrix of this type is
distinguished by high resilience in relation to media present in
the paper-making machine.
[0036] Furthermore, the cross-linking agent may contain at least
one polyether polyol. It is also conceivable for linear polyether
polyol, and also linear polypropylene etherpolyol, for example, to
be employed.
[0037] On account of cross-linking agents of this type, the
properties of the plastic matrix with respect to elasticity,
hardness, and resilience to media present in the paper-making
machine may be advantageously influenced.
[0038] In a further aspect of the invention, a method for
manufacturing a plastic matrix for a press belt of a shoe-press
device for dewatering or smoothing a fibrous web, in particular a
paper, cardboard, or tissue web as described above, is proposed.
Here, the plastic matrix is manufactured from at least one
polyurethane prepolymer, at least one cross-linking agent,
polydimethyl siloxane, and silicon dioxide microparticles.
[0039] On account of a method of this type, press belts which
display the abovementioned advantages may be advantageously
manufactured.
[0040] Furthermore, prior to cross-linking of the at least one
polyurethane prepolymer, silicon dioxide nanoparticles having at
least part of the cross-linking agent are mixed to form a
nanoparticles mixture which contains 20 to 60% by weight silicon
dioxide nanoparticles. It is also conceivable for the nanoparticles
mixture to contain 25 to 55% by weight, for example 30 to 50% by
weight, in particular 35 to 45% by weight, and optionally 38 to 42%
by weight silicon dioxide nanoparticles.
[0041] On account of process management of this type good
dispersibility may be advantageously achieved. If silicon dioxide
nanoparticles which have been created by a sol-gel process, wherein
the OH groups on the surface of the particles may be blocked by
means of silanization, are employed, dispersibility of the
reactants of the plastic matrix may be further improved.
[0042] Furthermore, the nanoparticles mixture in the downstream
method steps may replace the cross-linking agent entirely or by 5
to 40%. Furthermore, it is also conceivable for the nanoparticles
mixture to replace the cross-linking agent by 6 to 35%, in
particular by 7 to 30%, for example by 9 to 30%, and optionally by
10 to 25%.
[0043] On account of process management of this type,
dispersibility of the reactants of the plastic matrix likewise may
be further enhanced. Furthermore, better mixing of the individual
reactants of the plastic matrix is also possible on account
thereof.
[0044] Furthermore, prior to cross-linking of the at least one
polyurethane prepolymer, the silicon dioxide microparticles can be
mixed with the polydimethyl siloxane and, if applicable, with
further additives, to form an additive mixture. The latter may
subsequently be mixed with at least part of the cross-linking
agent. It is conceivable here for silicon dioxide nanoparticles to
have already been previously mixed into the cross-linking
agent.
[0045] On account of process management of this type, a homogenous
mixture of the reactants of the plastic matrix may advantageously
be achieved and both dispersibility and the mixing behavior may be
improved.
[0046] The mean particle size may be determined, for example, by
way of laser scattered light methods or by means of dynamic image
analysis. By means of dynamic image analysis, particle sizes from 1
.mu.m to 30 mm may be determined. The laser scattered light methods
allow an analysis of particle sizes from 0.3 nm to 1 .mu.m. Here,
the mean particle size is defined according to the measuring method
employed according to the respective size range
[0047] Further important features and advantages of the invention
are derived from the dependent claims, from the drawings, and from
the associated description of the figures by means of the drawings
and the example. Preferred exemplary embodiments of the invention
are illustrated in the drawings and are explained in more detail in
the following description, wherein identical reference signs relate
to identical or similar or functionally identical components.
[0048] In the drawings, in each case in a schematic manner:
[0049] FIG. 1 shows a view of a shoe press having a press sleeve
according to one exemplary embodiment of the present invention,
and
[0050] FIG. 2 shows a view of a press section of a paper-making
machine, comprising a shoe press and a conveyor belt, according to
one exemplary embodiment of the present invention.
[0051] In FIG. 1 a shoe press 10 which comprises a shoe roller 12
and a counter roller 14 is illustrated. While the counter roller 14
is composed of a rotating roller which is designed in a cylindrical
manner, the shoe roller 12 is assembled from a shoe 16, a static
yoke 18 carrying said shoe 16, and a press sleeve 20. The shoe 16
here is supported by the yoke 18 and by way of hydraulic press
elements (not illustrated) pressed onto the press sleeve 20
revolving around said shoe 16. On account of the concave design of
the shoe 16 on that side which is opposite the counter roller 14, a
comparatively long press nip 22 results. The shoe press 10 is
particularly suitable for dewatering fibrous webs 24. During
operation of the shoe press a fibrous web 24 having one or two
press films 26, 26' is routed through the press nip 22, wherein the
fluid which, on account of the pressure exerted in the press nip 22
on the fibrous web 24, leaks from the fibrous web 24 and which,
apart from water, contains dissolved and undissolved compounds,
such as, for example, fibers, fiber fragments, additives and/or
auxiliaries, is temporarily received by the press felt or felts 26,
26', respectively, and by depressions (not illustrated) which are
provided in the press sleeve surface. After leaving the press nip
22 the fluid which has been received by the press sleeve 20 is
thrown off from the press sleeve 20, before the press sleeve 20
again enters into the press nip 22. Moreover, water received by the
press felt 26, 26' is removed by way of suction elements, after
having left the press nip 22.
[0052] On account of the comparatively long press nip 22, which is
due to the concave design of the shoe 16 on that side which is
opposite the counter roller 14, considerably better dewatering of
the fibrous web 24 is achieved by such a shoe press as compared
with a press composed of two rotating rollers, such that subsequent
thermal drying may be correspondingly curtailed. In this way,
particularly gentle dewatering of the fibrous web 24 is
achieved.
[0053] In FIG. 2 a detail of a press section of a paper-making
machine 30 which comprises a shoe press 10 is shown. As is also the
case in the embodiment illustrated in FIG. 1, the shoe press 10
here comprises a shoe roller 12 which comprises a press sleeve 20
and a press element or shoe 16, respectively, and a counter roller
14, wherein a press nip is configured between the shoe 16 and the
counter roller 14. Moreover, this part of the paper-making machine
comprises two suction rollers 28, 28' and two deflection rollers
30, 30'. During operation of the paper-making machine a felt 26,
which is guided by the suction rollers 28, 28' and which receives
the fibrous web 24 on the suction roller 28, is routed through the
press nip. Moreover, a routed conveyor belt or transfer belt 32,
respectively, is routed through the press nip by the deflection
rollers 30, 30' below the felt 26 which guides the fibrous web 24,
wherein the transfer belt 32 in the press nip takes over the
fibrous web 24 from the felt 26 and conveys away said fibrous web
24 from the press nip via the deflection roller 30'. On account of
the pressure exerted on the fibrous web 24 in the press nip, fluid
leaks from the fibrous web 24, which fluid apart from water
contains dissolved and undissolved compounds, for example fibers,
fiber fragments, additives and/or auxiliaries, and is temporarily
received by the felt 26 and by depressions which are provided in
the press sleeve surface. After having left the press nip, the
fluid which has been received by the press sleeve is thrown off by
the press sleeve 20, before the press sleeve 20 again enters into
the press nip. Moreover, water which has been received by the felt
26 is removed after leaving the press nip by suction elements which
are provided on the suction roller 28'. On account of the
comparatively long press nip due to the concave design of the shoe
16, significantly better dewatering of the fibrous web 24 is
achieved by such a shoe press as compared with a press composed of
two rotating rollers, such that subsequent thermal drying can be
correspondingly curtailed. In this way, particularly gentle
dewatering of the fibrous web 24 is achieved.
EXAMPLE
TABLE-US-00001 [0054] Mixture O HV AV AN VAV VAN RB 1% by weight
poly- smooth 93.0 29 26 26 47 0.40 dimethyl siloxane- SiO.sub.2
microparticles Comparative plate 92.3 39 49 0.35 without additives
Caption: HV hardness prior to water storage [ShA] AV abrasion prior
to water storage [mm] AN abrasion post water storage 150 h at
95.degree. C. [mm] VAV improvement of resilience to abrasion prior
to water storage [%] VAN improvement of resilience to abrasion post
water storage [%] RB mean value of fissure growth at 1 million
cycles in a flexural fatigue machine [mm]
[0055] In comparison with a comparative plate without additives,
resilience to abrasion is significantly improved, in particular
post water storage, on account of adding polydimethyl
siloxane--silicon dioxide microparticles. The tendency toward
fissure formation here is substantially unchanged. Thus, by way of
adding polydimethyl siloxane--silicon dioxide microparticles,
resilience to abrasion can be improved while the tendency toward
fissure growth remains almost unchanged.
[0056] Manufacturing of the Specimens:
[0057] An MDI-polyether-prepolymer having an NCO content of approx.
6% is employed. MCDEA and PTHF200 are used as a cross-linking
agent, and cross-linking is performed at a temperature of
90.degree. C.
[0058] The prepolymer, the MCDEA and the PTHF200 are separately
degassed, using a vacuum evaporator. Polydimethyl
siloxane-SiO.sub.2 microparticles are added to the cross-linking
agent. Then all components are mixed in a vortex mixer. The mixture
is poured into steel molds and tempered.
[0059] Determination of Resilience to Abrasion:
[0060] Resilience to abrasion determination was performed according
to DIN 5316 and ISO 4649. To this end, a specimen piece having a
diameter of 16 mm was impinged with a testing force of 10 N. The
grinding length was 40 m at an angular speed of 40 revolutions per
min.
[0061] Determination of the Mean Value of Fissure Growth:
[0062] Fissure growth determination is performed in a flexural
fatigue machine. To this end, the specimen is flexed 1,000,000
times at a frequency of 7.5 Hz, at an angle of +/-40.degree.. A
section in the specimen displays a width of 6 mm and a depth of 2.5
mm.
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