U.S. patent application number 12/197803 was filed with the patent office on 2009-03-05 for condensation dryer fabric.
This patent application is currently assigned to VOITH FABRICS PATENT GMBH. Invention is credited to Antony Morton.
Application Number | 20090056901 12/197803 |
Document ID | / |
Family ID | 32178878 |
Filed Date | 2009-03-05 |
United States Patent
Application |
20090056901 |
Kind Code |
A1 |
Morton; Antony |
March 5, 2009 |
CONDENSATION DRYER FABRIC
Abstract
Apparatus includes a multi-layer dewatering fabric and a dynamic
condensation drying apparatus having a hot surface. The multi-layer
dewatering fabric is arranged to sandwich a paper web onto the hot
surface.
Inventors: |
Morton; Antony; (West
Yorkshire, GB) |
Correspondence
Address: |
GREENBLUM & BERNSTEIN, P.L.C.
1950 ROLAND CLARKE PLACE
RESTON
VA
20191
US
|
Assignee: |
VOITH FABRICS PATENT GMBH
Heidenheim
DE
|
Family ID: |
32178878 |
Appl. No.: |
12/197803 |
Filed: |
August 25, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10532208 |
Apr 28, 2005 |
|
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PCT/GB2003/004585 |
Oct 24, 2003 |
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12197803 |
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Current U.S.
Class: |
162/358.2 ;
162/359.1 |
Current CPC
Class: |
Y10T 428/249953
20150401; Y10T 428/24322 20150115; Y10T 442/3724 20150401; Y10T
428/24942 20150115; D21F 1/0063 20130101; D21F 1/0036 20130101;
Y10T 442/3293 20150401; D21F 1/0072 20130101; Y10T 442/682
20150401; Y10T 442/3325 20150401; Y10T 442/3764 20150401; Y10T
428/24273 20150115 |
Class at
Publication: |
162/358.2 ;
162/359.1 |
International
Class: |
D21F 3/00 20060101
D21F003/00; D21F 5/00 20060101 D21F005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 24, 2002 |
GB |
0224749.2 |
Dec 27, 2002 |
GB |
0230211.5 |
Claims
1. An apparatus comprising: a multi-layer dewatering fabric; a
dynamic condensation drying apparatus having a hot surface, wherein
the multi-layer dewatering fabric is arranged to sandwich a paper
web onto the hot surface.
2. The apparatus according to claim 1, wherein the multi-layer
fabric comprises a paper contacting surface layer and a core having
a higher void volume than that of the paper contacting surface
layer, the core having a machine side surface.
3. The apparatus according to claim 2, wherein a third layer
comprising a machine side surface layer is provided on the machine
side surface of said core.
4. The apparatus according to claim 3, wherein the paper contacting
surface layer is relatively the finest of the layers, being
composed of closely spaced yarns, fibers or particles of small
diameter, while the machine side surface layer, which is coarser
than the paper contacting surface layer and finer than the core,
comprises yarns, fibers or particles of a larger diameter and more
loosely spaced than those of the paper contacting surface
layer.
5. The apparatus according to claim 3, wherein the core is composed
of widely spaced yarns, fibers or particles, or of a perforated
sheet or membrane layer.
6. The apparatus according to claim 1, wherein regions of the
multi-layer fabric are treated to render said regions more, or less
hydrophilic.
7. The apparatus according to claim 2, wherein the multilayer
fabric can include a core of a woven base cloth, a single or
composite perforated membrane or a spiral-link base cloth, and a
batt of staple fibers needled to each face of the base cloth.
8. The apparatus according to claim 7 wherein the core is filled
with a porous material.
9. The apparatus according to claim 8, wherein said porous material
filling the core comprises an open celled foam or a sintered
plastics material.
10. The apparatus according to claim 7, wherein the fibrous batt is
coated with a resin and then perforated.
11. The apparatus according to claim 2 wherein at least one layer
of the multi-layer fabric comprises a sintered structure formed
from beads, fibers or other particles of thermoplastics or metal,
partially melted and fused together.
12. The apparatus according to claim 11 wherein the sintered
structure further contains a textile reinforcement such as chopped
fibers, a woven fabric felt, a non-woven fabric, membrane or yarns,
at least partially encapsulated in the sintered structure.
13. The apparatus according to claim 2 wherein at least one layer
of the multi-layer fabric comprises a microporous open cell foam
coated structure.
14. The apparatus according to claim 2, wherein the multi-layer
fabric comprises a laminate of a sintered polymer, coating, fine
staple batt layer or composite membrane on a core of a spiral link
or open structure with a further fine layer of the same or
different material as the upper layer on the underside.
15. The apparatus according to claim 1, wherein the multi-layer
fabric comprises materials having high resistance to high
temperature and hydrolysis, such as poly(phenylene sulfide) (PPS),
poly(etheretherketone) (PEEK), polyetherketone (PEK), polyamide,
fluoropolymer, glass, metal, poly(ethylene naphthalate) (PEN) or
propylene butene copolymer (PBM).
16. The apparatus according to claim 15, wherein the multi-layer
fabric further comprises a high temperature resistant material,
such as nylon, poly(ethylene terephthalate) (PET), polybutylene
terephthalate (PBT), polythrimethyleneterephthalate (PTT),
poly(cyclohexyylene dimethylene therephtalate) (PCTA) or
polyesteramides, arranged to at least partially insulate parts of
the fabric not composed of the materials having high resistance to
high temperature and hydrolysis.
17. The apparatus according to claim 2, wherein the paper
contacting surface layer and the core are constituted by a single
structure providing zones of differing mean void volume.
18. The apparatus according to claim 17, wherein the multi-layer
fabric comprises a two-ply woven core zone of relatively coarse
cross-machine direction or weft yarns and superposed thereon on the
paper side of the fabric, a two-ply woven zone of relatively fine
cross-machine direction or weft yarns.
19. The apparatus according to claim 18 wherein the layers are
interwoven with warp yarns which interlink the weft yarn plies into
a single woven structure.
20. The apparatus according to claim 18, wherein the multi-layer
fabric comprises a further ply of finer weft yarns on the machine
side of the core zone which are bound into a weave structure by
warp yarns which pass about the further ply of finer weft yarns and
the lower ply of the core yarns.
21. The apparatus according to claim 17, wherein the core zone
comprises a single ply of larger diameter weft yarns relative to
the paper contacting surface layer zone.
22. The apparatus according to claim 2, wherein the multi-layer
fabric comprises a relatively fine woven layer laminated to the
paper side of a perforated membrane of synthetic plastics material
or resin impregnated fibrous material.
23. The apparatus according to claim 22, wherein the perforations
of the membrane are tapered with their wider ends adjacent the fine
woven layer, and their narrower ends opening from the surface of
the membrane at the cooling cylinder side.
24. The apparatus according to claim 23, wherein the tapering
perforations comprise two notional zones of different void volume,
the wider ends forming a core zone of greater void volume, and the
narrower ends a cylinder side zone of lower void volume.
25. The apparatus according to claim 22, wherein the perforations
are stepped.
26. The apparatus according to claim 2, wherein the multi-layer
fabric comprises a structure of sintered particles bonded together
by fusion over contact zones, with interstices between the
particles, the structure providing a core zone of relatively large
particles with large spaces between them and an outer zone on the
paper side with relatively fine particles defining a paper
contacting surface.
27. The apparatus according to claim 26, wherein the multi-layer
fabric comprises a further zone on the cylinder side, of relatively
fine particles which define a cylinder contacting surface, these
zones being created by laying down different sized particles as the
structure is built up.
28. The apparatus according to claim 26, wherein the zones are
merged by transition regions wherein the particle size decreases
towards the respective surface.
29. The apparatus according to claim 26, wherein the structure of
sintered particles includes reinforcing fibers.
30. The apparatus according to claim 1, wherein the hot surface
comprises an outer surface of a heated roll.
31. The apparatus according to claim 1, wherein the multi-layer
fabric is sandwiched between the paper web and a belt exposed to
temperatures lower than the that of the hot surface.
32. The apparatus according to claim 31, wherein the belt is
structured and arranged to contact at least one of ambient air,
forced ventilation, refrigerated air, and a reservoir of cooled
water.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a Continuation of U.S. patent
application Ser. No. 10/532,208 filed Oct. 24, 2003, which is a
U.S. National Stage of International Patent Application No.
PCT/GB2003/004585 filed Oct. 24, 2003, and claims priority of Great
Britain Patent Application No. 0224749.2 filed Oct. 24, 2002 and
Great Britain Patent Application No. 0230211.5 filed Dec. 27, 2002.
The disclosures of U.S. patent application Ser. No. 10/532,208 and
International Application No. PCT/GB2003/004585 are expressly
incorporated by reference herein in their entireties.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to a fabric for use in a so-called
dynamic condensation drying apparatus or other similar condensation
drying processes in the manufacture of paper and board.
[0004] 2. Discussion of Background Information
[0005] A dynamic condensation drying apparatus involves the
utilization of a heat source to generate water vapor within the wet
web. This leads to an increase in vapor pressure and a
thermodynamic drive for such moisture to leave the web.
[0006] The moisture is then condensed by cooling, the water then
being retained by the fabric to avoid re-wetting of the web. In
such dynamic condensation drying apparatus, a hot steam heated
solid steel roll or belt is pressed against B moist paper web which
is transported on a fine fabric. The fine fabric in turn lies
immediately adjacent a coarse fabric. The coarse fabric is located
next to a water-cooled solid steel or other composite impermeable
belt.
[0007] The drying process begins as the paper web contacts the hot
steel roll or belt, generating water vapor which passes through the
fine fabric. This is collected as it condenses in the voids of the
much cooler coarse fabric (as this is in contact with the water
cooled belt). The temperature gradient between the two restraining
elements, for example the hot and cold steel belts drives the
drying equilibrium, since the more water removed from the gaseous
state as condensate in the coarse fabric, the more water can be
evaporated into vapor from the web. Air removal from the drying
system and application of physical pressure to the web may also be
a feature. The drying rate has been quoted as being typically 5-10
times higher than for cylinder drying, and the hot steel belt or
roller may be used at 120.degree.-180.degree. C., and the cold
steel or composite belt at 20.degree.-90.degree..
[0008] The fine fabric serves to transmit uniform pressure to the
paper web, as it is pressed between the two restraining elements;
since a coarse fabric alone would mark the web. The coarse fabric
is present to provide plenty of void volume in which water from the
web can condense and be subsequently removed.
[0009] U.S. Pat. No. 6,397,493 (Voith-Sulzer) discloses one example
of a dynamic condensation drying apparatus wherein a steel or
composite belt seals the cooling chamber and the paper web is
pressed against the heated cylinder by one or more fabrics.
[0010] U.S. Pat. No. 5,778,565 {Valmet} discloses a machine and
process for carrying out the CONDEBELT (Registered Trade Mark)
process, which consists of drying the web between two steel belts,
one of which is heated and the other cooled. U.S. Pat. No.
5,706,587 and EP-A-0,727,521 disclose modifications thereof.
[0011] EP-A-0,962,588 and 0,962,589 disclose a two fabric
arrangement, wherein a fine woven fabric is propelled on the paper
side of a coarser fabric, the latter being modified by
incorporation on the machine side face of additional finer
cross-direction yarns in the spaces between the main
cross-direction yarns to provide a fine woven surface against the
cooled belt.
[0012] The term "fabric" as used above and hereinafter in practice
refers to web support fabrics which are typically synthetic woven
fabrics, although woven metal fabrics or hybrid metal/synthetic
woven fabrics or non-woven fabrics, including membranes, may also
be used.
[0013] The use of a fine and a coarse fabric as in the last example
above however presents a number of problems notably:--
[0014] a). The vapor passes through the fine top cloth and into the
coarse cloth t1nd condenses, due to the fact that the coarse cloth
is in contact with the cold steel surface. The coarse cloth is
intended to retain the moisture, but there is potential for rewet
to occur due to capillary action.about.of the fine top cloth
drawing water back from the coarse cloth. The cold belt contacting
side of the coarse cloth may be made finer by in-filling the weave
with additional weft threads, while retaining a two-fabric
arrangement (as in EP-A-0,962,588 above), which addressed the
problem to some extent.
[0015] b). The fine structure of the top fabric means that it is
not possible to incorporate a seam which can be joined on the paper
machine using a pintle wire or any interconnecting technique, since
the seam loops will be proud of the paper contacting surface of the
fabric and will mark the web, since fine structures involve the use
of thin fabrics. As a consequence, the top fabric has to be
provided in endless form. To make an endless fabric involves either
exceptionally wide and expensive weaving machinery, or the time
consuming process of weaving a flat piece of fabric and then
rendering it endless in a seaming machine, before delivery to the
customer.
[0016] Highly complicated cantilevered machine structures are
needed to install the top fabric in to such dryer systems. It may
take several days to install the fabrics as compared to a number of
hours if both of the fabrics were on machine joinable, for example
by inserting a pintle wire through the fabric seaming loops or by
effecting a join by other means.
[0017] c). The presence of two fabrics with different structures,
which are simply laid one on top of the other, can lead to
interference patterns when they are pressed between the belt and
roll or between two belts. This is caused by the coincidence of
weave knuckles in the upper and lower belts overlying each other.
This interference can mark the web and/or lead to aggravated
abrasion between the two fabrics. The latter is a particular
problem where the two fabrics diverge at the end of the condenser
belt dryer due to the difference in modulus between the two
fabrics. The use of two fabrics also gives rise to problems such as
increased wear and abrasion.
[0018] d). The presence of two fabrics holds additional.
complications in that each fabric requires its own set of return,
guide and stretch rolls, as well as conditioning systems.
SUMMARY OF THE INVENTION
[0019] The present invention overcomes the problems set out above
so far as is possible by providing a single fabric for transport
and dewatering of a paper web through a dynamic condensation drying
apparatus as hereinbefore defined.
[0020] According to the invention, a dewatering fabric for use in
dynamic condensation drying apparatus comprises a three layer
fabric. The fabric preferably has a paper contacting surface layer,
a core having a high void volume, and a machine side surface layer.
The paper contacting surface layer preferably is relatively the
finest of the three layers, that is, it is comprised of closely
spaced yarns or fibers of small diameter. The machine side surface
layer is preferably of intermediate fineness, being composed of
yarns or fibers of a larger diameter and more loosely spaced, than
those of the paper contacting surface layer. The high void volume
of the core may be provided for example by wide spacing of the
constituent yarns or fibers, or by incorporation of a perforated
sheet or membrane layer.
[0021] The invention makes possible an apparatus with a single
dryer fabric for transporting the paper web through a dynamic
condensation drying apparatus or similar installation, in place of
the two fabrics heretofore considered necessary.
[0022] The finer surface of the paper contacting side serves to
provide good support to the web, to allow for high heat transfer
due to densely spaced contact points and to help prevent marking of
the web. The opposite, fine surface which faces the cold belt is
preferably not as fine as the web support surface, put is
preferably sufficiently fine to encourage the condensed water to
remain in the fabric without any tendency to be drawn back through
the structure to cause web rewetting. To aid this, the core of the
fabric may comprise a permeable structure containing relatively
large pores with low capillary force.
[0023] Regions of the fabric may be treated so as to render them
more, or less, hydrophilic to ensure preferential movement of
moisture from the heated (web contacting) side to the cooled
side.
[0024] The fabric may be endless or seamed, and if seamed is
preferably capable of being joined on the machine, thereby
overcoming many difficulties experienced at present.
[0025] The dryer fabric in accordance with the invention will be
thicker than the fine fabric used heretofore in the condensation
dryer apparatus and thus there will be no associated seaming
problems as the seams need not lie proud of the surface.
[0026] The dryer fabric of the invention may comprise a core of
woven base cloth, a single or composite perforated membrane or a
spiral-link base cloth, having a batt of staple fibers needled to
each face of the base cloth, or alternatively it may be filled with
an open-celled foam, or a sintered or otherwise porous synthetic
plastics material, which may be proud of the paper contacting side.
Such structures can have the advantage of containing relatively
large pores with low capillary forces.
[0027] The fibrous batt or porous medium may be coated with a resin
such as an epoxy, phenoxy, fluoropolymer or silicone, and then
perforated. The perforations may be carried out using laser,
waterjet, mechanical punching or other cutting techniques or may
result from the coating process, e.g. by coagulation chemistry or
by transfer coating a reticular coating onto the batt or medium.
The latter can give an optimum pore volume, surface tension,
contact ratio and smoothness properties.
[0028] At least one layer of the dryer fabric may comprise a
sintered structure formed from beads, fibers or other particles of
thermoplastics, metal or the like, partially melted and fused
together. The sintered structure may also contain chopped fibers
and/or a textile reinforcement in the form of a woven fabric felt,
non-woven fabric, membrane or yarn, at least partially encapsulated
in the sintered structure.
[0029] At least one layer of the fabric may be microporous open
cell foam coated structure.
[0030] The dryer fabric may comprise a laminate or sintered
polymer, a coating or a fine staple batt layer, or a composite
membrane supported by a spiral link or other open structure such as
a coarse woven base cloth, with a further fine layer an the
underside.
[0031] Preferably, the fabric is made from materials with high
temperature and hydrolysis resistance, for example poly(phenylene
sulfide) (PPS), poly(etheretherketone) (PEEK), polyamide,
fluoropolymer, glass, metal poly(ethylene naphthalate) (PEN) or
propylene butene copolymer (PBM). Conventional dryer fabric
materials may be used in parts of the fabric which are insulated to
a certain extent from the hot felt or roll by the high temperature
resistant material. These may include nylon, poly(ethylene
terephthalate) (PET), polybutylene terephthalate (PBT),
polythrimethyleneterephthalate (PTT), poly(cyclohexyylene
dimethylene therephtalate) (PCTA) or polyetheramides (such 56 Elf
Atochem's PEBAX (Registered Trademark)).
[0032] The fabric according to the invention may also be used on
conventional steam-heated dryer sections or on air-impingement
dryer sections. A key requirement of a fabric for a dynamic
condensation drying apparatus is to prevent rewetting of the paper
web by water already expelled from the web into the fabric.
Therefore hydrophobic materials are preferably used to make surface
components of the fabric, although hydrophilic materials are of
advantage in the lower regions away from the paper contacting
surface, in order to provide good water storage capacity.
[0033] A further embodiment of the invention is based on the
realization that the dryer or dewatering fabric may be comprised of
zones of differing mean void volume, preferably also of differing
void size or yarn diameter, rather than distinct layers; and also
that the machine side surface zone of intermediate fineness, whilst
highly desirable, can in some circumstances be omitted so that the
machine side of the high void volume core may rest directly on the
cold cylinder of the condensation drying apparatus.
[0034] A two zoned structure may for example comprise a woven core
zone of relatively coarse warp and weft yarns, and on the paper
side of the fabric, a woven zone of relatively fine warp and weft
yarns. The layers are woven and interconnected by means of binder
yarns in one weaving process, so giving a single woven entity. To
achieve a three zoned structure, this woven entity may be modified
by incorporation of a further ply of finer weft yarns, on the
cylinder side of the core zone "below" the yarns of the core
zone.
[0035] In a further embodiment, the zoned woven fabric may have a
void volume, which increases from the fine paper side down through
the fabric. This therefore would mean that the nominal or actual
middle zone does not have the highest void volume. Such a zoned
fabric would be of particular importance if coarse yarns were
required in the bottom layer in order to give the fabric increased
mechanical resistance and so longevity.
[0036] In a further embodiment, it may the case that a zoned fabric
may have a middle and bottom layer that are of similar or identical
void volume.
[0037] The weaves could be the same in all layers or different in
at least one layer. Examples of possible weaves are plaint twill,
satins etc with 16, 20, 24, 28, 32 end 40 shaft weaves especially
preferred. In addition, the number of md and cd yarns per cm, as
well as their diameters have a large number of possible variations.
Also, the yarns need not be necessarily round, they could be
square, rectangular, ovate, bi-nodal, etc. in order to modify the
openness, smoothness, caliper etc. Also, weaving with md and/or cod
yarns in one or more layers as paired yarns is also a possible
technique to modify void volume, whilst minimizing the effect on
caliper. Also, it is possible that the fabrics could be calendered
to give increased surface contact area and smoothness. Any of the
zones can be made of any desired number of plies.
[0038] Examples of possible alternative multizone structures
include a two layer fabric comprising a relatively fine woven layer
laminated to a perforated membrane of synthetic plastics material,
or resin impregnated fibrous material. The perforations of the
membrane may be preferably tapered, for example frustoconical, with
their wider ends adjacent the fine woven layer, and their narrower
ends opening from the surface of the membrane at the cooling
cylinder side. The tapering perforations may comprise two notional
zones of different void volume, the wide ends forming a core zone
of greater void volume and the narrower ends a cylinder side zone
of lower void volume, despite the fact that there is no precise
demarcation between the zones. Alternatively the perforations may
be stepped, giving a quasi-three layer fabric.
[0039] Another possible embodiment of the fabric comprises a
structure of sintered particles, bonded together by fusion over
contact zones, after having been subjected to heating sufficient to
soften their outer layers to the point of tackiness, and to
pressure sufficient to ensure area rather than point contact
between the particles, but low enough to leave significant void
space in interstices between the particles. The sintered particle
structure is preferably made as a single unit and comprising a core
zone of relatively large particles with large spaces remaining
between them, and an outer zone on the paper side with relatively
fine particles defining a paper contacting surface, and also
preferably a further zone on the cylinder side of relatively fine
particles (possibly coarser than those on the paper side) which
define a cylinder contacting surface, these zones created by laying
down particles of differing sizes as the structure is built up.
[0040] The sintered particle structure may, or may not, incorporate
reinforcing fibers.
[0041] According to embodiments of the invention, an apparatus
includes a multi-layer dewatering fabric and a dynamic condensation
drying apparatus having a hot surface. The multi-layer dewatering
fabric is arranged to sandwich a paper web onto the hot
surface.
[0042] In accordance with features of the invention, the
multi-layer fabric can include a paper contacting surface layer and
a core having a higher void volume than that of the paper
contacting surface layer, the core having a machine side surface. A
third layer may include a machine side surface layer is provided on
the machine side surface of said core. The paper contacting surface
layer can be relatively the finest of the layers, being composed of
closely spaced yarns, fibers or particles of small diameter, while
the machine side surface layer, which is coarser than the paper
contacting surface layer and finer than the core, comprises yarns,
fibers or particles of a larger diameter and more loosely spaced
than those of the paper contacting surface layer. Further, the core
may be composed of widely spaced yarns, fibers or particles, or of
a perforated sheet or membrane layer.
[0043] According to other features of the invention, regions of the
multi-layer fabric can be treated to render said regions more, or
less hydrophilic.
[0044] In accordance with still other features, the multilayer
fabric can include a core of a woven base cloth, a single or
composite perforated membrane or a spiral-link base cloth, and a
batt of staple fibers needled to each face of the base cloth. The
core may be filled with a porous material. The porous material
filling the core can include an open celled foam or a sintered
plastics material. Further, the fibrous batt may be coated with a
resin and then perforated.
[0045] According to other aspects of the invention, at least one
layer of the multi-layer fabric can include a sintered structure
formed from beads, fibers or other particles of thermoplastics or
metal, partially melted and fused together. The sintered structure
may further contain a textile reinforcement such as chopped fibers,
a woven fabric felt, a non-woven fabric, membrane or yarns, at
least partially encapsulated in the sintered structure.
[0046] In accordance with aspects of the invention, at least one
layer of the multi-layer fabric may include a microporous open cell
foam coated structure.
[0047] In accordance with further aspects of the invention, the
multi-layer fabric can include a laminate of a sintered polymer,
coating, fine staple batt layer or composite membrane on a core of
a spiral link or open structure with a further fine layer of the
same or different material as the upper layer on the underside.
[0048] According to aspects of the invention, the multi-layer
fabric may include materials having high resistance to high
temperature and hydrolysis, such as poly(phenylene sulfide) (PPS),
poly(etheretherketone) (PEEK), polyetherketone (PEK), polyamide,
fluoropolymer, glass, metal, poly(ethylene naphthalate) (PEN) or
propylene butene copolymer (PBM). The multi-layer fabric can
further include a high temperature resistant material, such as
nylon, poly(ethylene terephthalate) (PET), polybutylene
terephthalate (PBT), polythrimethyleneterephthalate (PTT),
poly(cyclohexyylene dimethylene therephtalate) (PCTA) or
polyesteramides, arranged to at least partially insulate parts of
the fabric not composed of the materials having high resistance to
high temperature and hydrolysis.
[0049] Moreover, the paper contacting surface layer and the core
can be constituted by a single structure providing zones of
differing mean void volume. The multi-layer fabric may include a
two-ply woven core zone of relatively coarse cross-machine
direction or weft yarns and superposed thereon on the paper side of
the fabric, a two-ply woven zone of relatively fine cross-machine
direction or weft yarns. The layers can be interwoven with warp
yarns which interlink the weft yarn plies into a single woven
structure. Further, the multi-layer fabric can include a further
ply of finer weft yarns on the machine side of the core zone which
are bound into a weave structure by warp yarns which pass about the
further ply of finer weft yarns and the lower ply of the core
yarns. The core zone may include a single ply of larger diameter
weft yarns relative to the paper contacting surface layer zone.
[0050] The multi-layer fabric can include a relatively fine woven
layer laminated to the paper side of a perforated membrane of
synthetic plastics material or resin impregnated fibrous material.
The perforations of the membrane may be tapered with their wider
ends adjacent the fine woven layer, and their narrower ends opening
from the surface of the membrane at the cooling cylinder side. The
tapering perforations may include two notional zones of different
void volume, the wider ends forming a core zone of greater void
volume, and the narrower ends a cylinder side zone of lower void
volume. Further, the perforations can be stepped.
[0051] According to further aspects of the invention, the
multi-layer fabric may include a structure of sintered particles
bonded together by fusion over contact zones, with interstices
between the particles, the structure providing a core zone of
relatively large particles with large spaces between them and an
outer zone on the paper side with relatively fine particles
defining a paper contacting surface. The multi-layer fabric may
include a further zone on the cylinder side, of relatively fine
particles which define a cylinder contacting surface, these zones
being created by laying down different sized particles as the
structure is built up. The zones can be merged by transition
regions wherein the particle size decreases towards the respective
surface. The structure of sintered particles may include
reinforcing fibers.
[0052] According to still other features of the invention, the hot
surface comprises an outer surface of a heated roll.
[0053] In accordance with still yet other features of the
invention, the multi-layer fabric can be sandwiched between the
paper web and a belt exposed to temperatures lower than the that of
the hot surface. The belt may be structured and arranged to contact
at least one of ambient air, forced ventilation, refrigerated air,
and a reservoir of cooled water.
BRIEF DESCRIPTION OF THE DRAWINGS
[0054] Some embodiments of the invention will now be described by
way of example with reference to the accompanying drawings,
wherein:--
[0055] FIG. 1 is a diagram showing a fragmentary cross-section of a
part of a condensation drying apparatus;
[0056] FIG. 2 is a sectional view of a first embodiment of dryer
fabric according to the invention;
[0057] FIGS. 3,4,5,7,8 and 9 are sectional views of further
embodiments of dryer fabric according to the invention;
[0058] FIG. 6 is a fragment perspective view of a yet further
embodiment of dryer fabric according to the invention;
[0059] FIG. 10 is a structural diagram looking in the machine
direction showing the weave structure of a first fabric embodying a
modified structure according to the invention;
[0060] FIG. 11 is a diagram of the same fabric showing the weave
structure looking in the cross-machine direction;
[0061] FIG. 12 is a cross-sectional view of a composite fabric in
accordance with the invention, and
[0062] FIG. 13 is a cross-sectional view of a further embodiment of
fabric according to the invention comprising a structure of
sintered polymeric particles.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
[0063] FIG. 1 is a diagrammatic sectional view of a roll in a
dynamic condensation drying apparatus. This is a magnified view of
part of the shell of the roll with superposed dryer and carrier
belts, with the curvature exaggerated. The outer wall of the roll
comprises a shell or steel surface 11, which is heated from within
the roll. A paper web 10 is passed over the roll in contact with
the heated shell 11, with a drier fabric 13 pressing if thereon.
The dryer fabric also serves to transport the paper web 10, and to
absorb moisture driven from the web 10. Belt 12 is exposed to lower
temperatures on its outer-side. This may be by contact with ambient
air, forced ventilation, or actively refrigerated air, or more
preferably a reservoir of cooled water, which is sealed by belt 12.
The heated surface of cylinder 11 is between the range 120.degree.
C.-180.degree. C., whilst the belt 12 is maintained in the range
20.degree. C.-90.degree. C., that is below boiling point so that
condensation can take place.
[0064] In the remaining figures several examples of dryer fabrics
13 are shown in diagrammatic cross sections.
[0065] FIG. 2 illustrates a preferred embodiment of a dryer fabric
in a dynamic condensation drying apparatus. The fabric 20 consists
of laminated, superposed, needled together, or interlaced woven
fabric layers, comprising a fine mesh woven layer 21 on the paper
contacting side of the fabric (i.e. towards the heated roll), a
core comprised of a coarse mesh woven layer 22, and a further woven
layer 23 on the reverse side of the fabric, contacting the
impermeable belt 12, and towards the cooled side of the apparatus.
The layer 23 is normally less fine than layer 21, but significantly
less coarse than the core layer 22.
[0066] A further embodiment is illustrated in FIG. 3. In this, a
fabric 30, comprising a fine two-ply woven fabric 31 is provided on
the paper contacting side of the composite fabric. This is
supported by a core 32 of a coarser weave base cloth, with a fine
fiber batt 33 on the reverse side of the fabric, to contact the
cooled impermeable belt 12.
[0067] FIG. 4 shows a yet further embodiment of fabric 40 wherein a
batt 41 of finer fibers is provided on the paper contacting face of
a core comprising a woven support fabric 42. A further batt 43,
predominantly of coarser and higher density fibers is provided on
the cooled impermeable belt side of the fabric 40 (the lower side
in the drawing).
[0068] In FIG. 5, the fabric 50, which includes a paper contacting
membrane layer 51 and a cooled belt contacting side membrane layer
52. The membrane layers 51, 52 are separated by at least one core
layer 53. Membrane layer 51 is provided with relatively fine
perforations or pores 54 of relatively small opening which are also
relatively closely spaced. The membrane layer 52 includes
perforations 55 which are of larger opening than the perforations
in the layer 51. The percentage of void spaces in the two membrane
layers may be equal or approximately equal, or the percentage of
void space in the layer 52 may be greater than that in layer
51.
[0069] The core layer 53 has a higher percentage of void space than
either of the membrane layers and includes a network of
interconnecting passageways to assist the through passage of water.
In the embodiment shown, this is achieved by making the layer 53
from a mass of particles of thermoplastic material which are firmly
fused under pressure to adhere at their tangential surfaces and at
the same time leaving considerable space between the particles.
[0070] The particles may be generally spherical, oblate,
cylindrical (e.g. formed by closely chopping yarns or fibers) or
irregular.
[0071] The above observations concerning the incidence of void
space in the outer and inner layers of the various dryer fabric
structures is applicable to all the particularly described
embodiments of the invention mentioned both above and
hereinafter.
[0072] FIG. 6 shows an example of fabric 60 with a foraminous
honeycombed structure 63, comprising a top membrane layer 61 with
small apertures, and a bottom membrane layer 62, with large
apertures and the honeycomb membrane 63 sandwiched
therebetween.
[0073] The top layer 61 is the paper web contacting layer, and the
bottom layer 62 contacts the cooled impermeable belt 12.
[0074] In FIG. 7, a fabric is shown comprising more than three
layers, and this comprises a base cloth 70 of a coarse woven fabric
which provides sufficient void volume and supports a composite
membrane comprised of two or more superimposed layers 71; 72; each
layer 71,72 has differently sized and spaced apertures 73, 74. The
layer having the greater void spaces preferably adjacent the base
cloth 70. The composite membrane carries a layer 75 of sintered
thermoplastic particles which form the paper contacting layer. A
further layer 76, comprising a non-woven batt of fine fibers is
provided below the base cloth 70. In FIG. 8, the fabric comprises a
fibrous batt 80 of staple fibers on its paper side is needled into
a spiral link base cloth 81, and a second batt 82 of fine fibers
below the base cloth 81. In variations of this embodiment, either
or both of the batts may be surfaced with a resin such as an epoxy,
phenoxy, fluoropolymer or a silicone and/or the link base cloth
filled with a foam plastics material.
[0075] In FIG. 9, a spiral link fabric core 90 has plastics coating
91 on the paper contacting side, this coating penetrating about a
third of the way into the spiral link fabric e.g. to the level of
the cross-machine direction hinge yarns, which hold the links
together. In this embodiment a fine fibrous batt layer 92 is
provided on the belt face of the link fabric.
[0076] FIGS. 10 and 11 are sectional views of a single, three
zoned, woven fabric in accordance with the invention, FIG. 10
looking in the machine direction and FIG. 11 in the cross
direction. The fabric consists of a fine, upper paper contacting
surface (i) consisting of fine diameter md and cd binder yarns
woven together. The cd binder yarns A and B interweave with md
yarns C in a plain weave, whilst also binding with md yarns of the
middle zone (iii). It may also be the case that the upper layer
also consists of standard cd yarns, in addition to the pairs of
binder yarns, which simply form a plain weave with md yarns C. The
middle zone is made up of md yarns D, having a greater diameter,
interwoven with cd yarns E, also having an increased diameter, to
give a fabric middle layer having a significantly larger void
volume than the upper, paper contacting surface (i). The lower zone
(iii) is made up of thicker cd yarns F, which interweave with md
yarns D of the middle layer. Due to the difference in CD yarn
weaves and the CD yarn diameters in layers (ii) and (iii), layer
(iii) probably has the larger void volume.
[0077] FIG. 12 is a sectional view of a composite fabric 130 in
accordance with the invention. The fabric 130 comprises an upper
paper contacting layer, formed by a fine woven material 131 such as
sail cloth, which is bonded by adhesive or thermal bonding for
example to a composite membrane 132. The composite membrane 132 is
of a suitable plastics material, or a resin bonded non-woven
material, or reinforcing fibers encapsulated in a resin matrix. The
membrane 132 is perforated with tapering apertures 133 which may be
frustoconical (with circular end openings) or pyramidal (with
square or rectangular end openings). The wider ends 134 of the
apertures 133 are at the upper face of the membrane 132 where it
abuts the woven material 131, whilst the narrower ends 135 of the
aperture 133 are at the lower face of the membrane 132. Whilst the
material 131, which defines a fine pored upper zone a also has a
discrete and separate layer. The membrane 132, by reason of the
taper of the apertures 133 provides an upper core zone b with high
void space and a lower zone c of reduced void space.
[0078] There is no well defined boundary between the zones, and the
boundary may be taken to be along a line such as X-X in FIG. 12
where for example the void cross-section falls below 50% of that at
the upper face of the membrane.
[0079] FIG. 13 illustrates a further embodiment of the fabric
according to the invention wherein the fabric 140 is comprised of a
layer of polymeric particles which have been thermally bonded at
their contacting surfaces by the action of a degree of pressure to
produce sufficient contact area, but not to impair porosity, and
heating to above the softening point of the polymer; in other words
the particles have been sintered to form a sheet. The particles
comprise a core zone b of relatively large particles 141, which
provide for relatively large void spaces therebetween. An upper
zone a on the paper contacting side of the fabric 140 is made up of
relatively small particles 142, and a lower zone on the cooling
side of the fabric of particles 143 which are smaller than the
large particles 141, but may nevertheless be larger than particles
142. The layer of polymeric particles comprises a single sintered
or thermally bonded structure which falls into three zones of
different particle size and porosity. The structure may include
reinforcing fibers which may be included in the thermal bonding,
serving by their length to link a plurality of particles. The
larger particles 142 may be finely divided polymer sheet or fibrous
material, whilst the finer particles such as 141 or 143 may be
microspheres or micorobeads of the kind used in syntactic plastic
compositions.
[0080] In the above embodiments, the upper fine zone, whether
provided by finer yarns or particles, provides a smooth surface for
paper contact. The core zone b in each case has relatively high
void space and allows drainage of moisture away from the paper. The
cooling belt side finer zone c may as in the case of FIG. 1 be
absent, or as in FIG. 3 be indistinctly demarcated from the core
zone b.
[0081] The FIG. 13 embodiment may be modified by providing a
gradient of particle size inwardly from the surfaces of the fabric
towards the core zone b. This would help to eliminate migration of
fine particles from the outer zones a or c into the voids of zone b
thus avoiding obstruction of the voids, and the sintered structure
could just comprise two of the zones, for example (a) comprising
the finer particles 141 and (b) comprising the coarser particles
142.
[0082] The paper contacting surface of the above described
embodiments can be rendered microporous by coating with a
fluoropolymer, silicone, epoxy or phenoxy resin, which may be
coagulated to form a microporous skin, or a reticulated coating may
be transferred onto the batt or other surface medium.
[0083] The fabrics of the invention provide void space within the
belt; and also help to prevent rewetting of the web by provision of
a fine layer in contact with the cooled condensing belt 12, drawing
moisture away from the web by capillary action.
* * * * *