U.S. patent application number 10/823001 was filed with the patent office on 2005-10-13 for anti-rewet press fabric or filter media comprising a fine porous layer of splittable microfibers.
Invention is credited to Kenney, Maryann C..
Application Number | 20050227561 10/823001 |
Document ID | / |
Family ID | 34965898 |
Filed Date | 2005-10-13 |
United States Patent
Application |
20050227561 |
Kind Code |
A1 |
Kenney, Maryann C. |
October 13, 2005 |
Anti-rewet press fabric or filter media comprising a fine porous
layer of splittable microfibers
Abstract
An anti-rewet fabric for a paper machine including a base fabric
in the form of an endless loop. A fine porous layer is incorporated
into the press fabric and is composed of split microfibers. The
present invention provides good anti-rewet properties and exhibits
a reduced start-up period and controlled wear. The present
invention is also applicable to other fabrics, such as fabrics used
for filtration.
Inventors: |
Kenney, Maryann C.;
(Foxboro, MA) |
Correspondence
Address: |
FROMMER LAWRENCE & HAUG
745 FIFTH AVENUE- 10TH FL.
NEW YORK
NY
10151
US
|
Family ID: |
34965898 |
Appl. No.: |
10/823001 |
Filed: |
April 13, 2004 |
Current U.S.
Class: |
442/189 ;
162/358.1 |
Current CPC
Class: |
D21F 7/083 20130101;
Y10T 442/3065 20150401 |
Class at
Publication: |
442/189 ;
162/358.1 |
International
Class: |
D03D 015/00 |
Claims
What is claimed is:
1. An anti-rewet press fabric for a paper machine, said fabric
comprising: a base fabric, said base fabric being in the form of an
endless loop and having an outer side and an inner side; and a fine
porous layer applied to said base fabric, wherein said fine porous
layer comprises split microfibers.
2. The anti-rewet press fabric as claimed in claim 1, further
comprising at least one additional layer of material disposed
between said fine porous layer and said base fabric.
3. The anti-rewet press fabric as claimed in claim 1, further
comprising at least one additional layer of material applied to an
outer side of said fine porous layer.
4. The anti-rewet press fabric as claimed in claim 1, wherein said
base fabric is a fabric selected from the group consisting of
woven, nonwoven, nonwoven arrays of MD or CD oriented yarns,
knitted and braided fabrics.
5. The anti-rewet press fabric as claimed in claim 4, wherein said
base fabric is an extruded mesh fabric.
6. The anti-rewet press fabric as claimed in claim 1, wherein said
base fabric is a strip of material spirally wound in a plurality of
turns, each turn being joined to those adjacent thereto by a
continuous seam, said base fabric being endless in a longitudinal
direction, said strip material being selected from the group
consisting of woven fabrics, nonwoven fabrics, knitted fabrics,
braided fabrics and extruded mesh fabrics.
7. The anti-rewet press fabric as claimed in claim 1, wherein said
base fabric is an on-machine seamable fabric.
8. The anti-rewet press fabric as claimed in claim 2, wherein said
at least one additional layer of material comprises fiber batt.
9. The anti-rewet press fabric as claimed in claim 2, wherein said
at least one additional layer of material is comprised of a fine
woven base.
10. The anti-rewet press fabric as claimed in claim 2, wherein said
at least one additional layer of material is comprised of a
non-woven structure.
11. The anti-rewet press fabric as claimed in claim 3, wherein said
at least one additional layer of material comprises fiber batt.
12. The anti-rewet press fabric as claimed in claim 3, wherein said
at least one additional layer of material is comprised of a fine
woven base.
13. The anti-rewet press fabric as claimed in claim 3, wherein said
at least one additional layer of material is comprised of a
non-woven structure.
14. The anti-rewet press fabric as claimed in claim 1, wherein at
least one of said splittable microfibers comprise polyamide and
polyester in the at least one fiber.
15. The anti-rewet press fabric as claimed in claim 14, wherein
said polyamide fibers are poly[imino(1-oxo-1,6-hexanediyl)].
16. The anti-rewet press fabric as claimed in claim 1, wherein said
fine porous layer further comprising nonsplittable fiber.
17. The anti-rewet press fabric as claimed in claim 16, wherein
said nonsplittable fiber is present in an amount sufficient to
insure the integrity of the press fabric structure.
18. An industrial filtration fabric comprising: a base fabric, said
base fabric being in the form of an endless loop and having an
outer side and an inner side; and a fine porous layer applied to
said outer side of said base fabric, wherein said fine porous layer
comprises split microfibers.
19. The industrial filtration fabric as claimed in claim 18,
wherein said base fabric is a fabric selected from the group
consisting of woven, nonwoven, knitted and braided fabrics.
20. The industrial filtration fabric as claimed in claim 18,
wherein said fine porous layer is needle punched to said base
fabric.
21. The industrial filtration fabric as claimed in claim 18,
wherein at least one of said splittable microfibers comprise
polyester.
22. The industrial filtration fabric as claimed in claim 18,
wherein said fine porous layer further comprising nonsplittable
fiber.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to industrial fabrics for the
papermaking arts. More specifically, the present invention relates
to press fabrics for the press section of a paper machine. In
addition, the present invention relates to filtration fabrics.
[0003] 2. Description of the Related Art
[0004] During the papermaking process, a cellulosic fibrous web is
formed by depositing a fibrous slurry, that is, an aqueous
dispersion of cellulose fibers, onto a moving forming fabric in the
forming section of a paper machine.
[0005] A large amount of water is drained from the slurry through
the forming fabric, leaving the cellulosic fibrous web on the
surface of the forming fabric.
[0006] The newly formed cellulosic fibrous web proceeds from the
forming section to a press section, which includes a series of
press nips. The cellulosic fibrous web passes through the press
nips supported by a press fabric, or, as is often the case, between
two such press fabrics. In the press nips, the cellulosic fibrous
web is subjected to compressive forces which squeeze water
therefrom, and which adhere the cellulosic fibers in the web to one
another to turn the cellulosic fibrous web into a paper sheet. The
water is accepted by the press fabric or fabrics and, ideally, does
not return to the paper sheet.
[0007] The paper sheet finally proceeds to a dryer section, which
includes at least one series of rotatable dryer drums or cylinders,
which are internally heated by steam. The newly formed paper sheet
is directed in a serpentine path sequentially around each in the
series of drums by a dryer fabric, which holds the paper sheet
closely against the surfaces of the drums. The heated drums reduce
the water content of the paper sheet to a desirable level through
evaporation.
[0008] It should be appreciated that the forming, press and dryer
fabrics all take the form of endless loops on the paper machine and
function in the manner of conveyors. It should further be
appreciated that paper manufacture is a continuous process which
proceeds at considerable speeds. That is to say, the fibrous slurry
is continuously deposited onto the forming fabric in the forming
section, while a newly manufactured paper sheet is continuously
wound onto rolls after it exits from the dryer section.
[0009] The present invention relates to the press fabrics used in
the press section. Press fabrics play a critical role during the
paper manufacturing process. One of their functions, as implied
above, is to support and to carry the paper product being
manufactured through the press nips.
[0010] Press fabrics also participate in the finishing of the
surface of the paper sheet. That is, press fabrics are designed to
have smooth surfaces and uniformly resilient structures, so that,
in the course of passing through the press nips, a smooth,
mark-free surface is imparted to the paper.
[0011] Traditionally, press sections have included a series of nips
formed by pairs of adjacent cylindrical press rolls. In recent
years, the use of long press nips of the shoe type has been found
to be more advantageous than the use of nips formed by pairs of
adjacent press rolls. This is because the web takes longer to pass
through a long press nip than through one formed by press rolls.
The longer the time a web can be subjected to pressure in the nip,
the more water can be removed there, and, consequently, the less
water will remain behind in the web for removal through evaporation
in the dryer section.
[0012] Perhaps most importantly, the press fabrics accept the large
quantities of water extracted from the wet paper in the press nip.
In order to fulfill this function, there literally must be space,
commonly referred to as void volume, within the press fabric for
the water to go, and the fabric must have adequate permeability to
both water and air for its entire useful life. Finally, press
fabrics must be able to prevent the water accepted from the wet
paper from returning to and rewetting the paper upon exit from the
press nip.
[0013] Contemporary press fabrics are produced in a wide variety of
styles designed to meet the requirements of the paper machines on
which they are installed for the paper grades being manufactured.
Generally, they comprise a woven base fabric into which has been
needled a batt of fine, nonwoven fibrous material. The base fabrics
may be woven from monofilament, plied monofilament, multifilament
or plied multifilament yarns, and may be single-layered,
multi-layered or laminated. The yarns are typically extruded from
any one of the synthetic polymeric resins, such as polyamide and
polyester resins, used for this purpose by those of ordinary skill
in the paper machine clothing arts.
[0014] The woven base fabrics themselves take many different forms.
For example, they may be woven endless, or flat woven and
subsequently rendered into endless form with a woven seam.
Alternatively, they may be produced by a process commonly known as
modified endless weaving, wherein the widthwise edges of the base
fabric are provided with seaming loops using the machine-direction
(MD) yarns thereof. In this process, the MD yarns weave
continuously back-and-forth between the widthwise edges of the
fabric, at each edge turning back and forming a seaming loop. A
base fabric produced in this fashion is placed into endless form
during installation on a paper machine, and for this reason is
referred to as an on-machine-seamable fabric. To place such a
fabric into endless form, the two widthwise edges are brought
together, the seaming loops at the two edges are interdigitated
with one another, and a seaming pin or pintle is directed through
the passage formed by the interdigitated seaming loops.
[0015] Further, the woven base fabrics may be laminated by placing
at least one base fabric within the endless loop formed by another,
and by needling a staple fiber batt through these base fabrics to
join them to one another. One or more of these woven base fabrics
may be of the on-machine-seamable type. This is now a well known
laminated press fabric with a multiple base support structure.
[0016] In any event, the woven base fabrics are in the form of
endless loops, or are seamable into such forms, having a specific
length, measured longitudinally therearound, and a specific width,
measured transversely thereacross. Because paper machine
configurations vary widely, paper machine clothing manufacturers
are required to produce press fabrics, and other paper machine
clothing, to the dimensions required to fit particular positions in
the paper machines of their customers. Needless to say, this
requirement makes it difficult to streamline the manufacturing
process, as each press fabric must typically be made to order.
[0017] In response to this need to produce press fabrics in a
variety of lengths and widths more quickly and efficiently, press
fabrics have been produced in recent years using a spiral technique
disclosed in commonly assigned U.S. Pat. No. 5,360,656 to Rexfelt
et al., the teachings of which are incorporated herein by
reference.
[0018] U.S. Pat. No. 5,360,656 shows a press fabric comprising a
base fabric having one or more layers of staple fiber material
needled thereinto. The base fabric comprises at least one layer
composed of a spirally wound strip of woven fabric having a width
which is smaller than the width of the base fabric. The base fabric
is endless in the longitudinal, or machine, direction. Lengthwise
threads of the spirally wound strip make an angle with the
longitudinal direction of the press fabric. The strip of woven
fabric may be flat-woven on a loom which is narrower than those
typically used in the production of paper machine clothing.
[0019] The base fabric comprises a plurality of spirally wound and
joined turns of the relatively narrow woven fabric strip. The
fabric strip is woven from lengthwise (warp) and crosswise
(filling) yarns. Adjacent turns of the spirally wound fabric strip
may be abutted against one another, and the helically continuous
seam so produced may be closed by sewing, stitching, melting or
welding. Alternatively, adjacent longitudinal edge portions of
adjoining spiral turns may be arranged overlappingly, so long as
the edges have a reduced thickness, so as not to give rise to an
increased thickness in the area of the overlap. Further, the
spacing between lengthwise yarns may be increased at the edges of
the strip, so that, when adjoining spiral turns are arranged
overlappingly, there may be an unchanged spacing between lengthwise
threads in the area of the overlap.
[0020] In any event, in the press section of the papermaking
machine, the formed sheet is pressed to a higher dry content
through consecutive press nips. The sheet is carried through the
press nip together with one or several endless textile fabrics,
that are commonly referred to as press fabrics.
[0021] The paper web, or sheet, and press fabric probably reach
minimum thickness at the same time somewhat near mid nip. The sheet
is considered to reach its maximum dry content at the very same
moment. After that, the sheet, as well as the fabric, begin to
expand. During this expansion, a vacuum is created in the paper web
and in the surface layer of the press fabric, both of which have
been compressed to a minimum thickness at a maximum pressure. In
response to this vacuum, water flows back from the inside and
possibly base layers of the fabric to the surface layer of the
fabric and into the paper sheet to reestablish the pressure
balance. This expansion phase provides the driving force of the
rewetting of the paper sheet inside the press nip.
[0022] Another factor that is important in press fabrics is the
amount of time required before the press fabric reaches its maximum
ability to extract water from the paper web (i.e., dewater the
paper sheets) after the press fabric is newly installed in the
paper machine. This time period is termed "start-up" period for the
press fabric. This period may last from a couple of hours to
several days. Factors that are believed in the art to be
responsible for the start-up period include the fabric being too
thick, too open, or the surface of the new press fabric being too
non-uniform. Over time, while the fabric becomes thinner, less
open, more dense and smoother, the ability of the press fabric to
appropriately extract water from the paper web increases until it
reaches its optimum or steady state level.
[0023] Minimizing or eliminating the start-up period is a desired
feature for a press fabric. Methods known in the art include
pre-compacting the finished, needled press fabric, using finer
(smaller denier) fibers on the surface or less batt within the
base. However, none of these methods has been totally successful
and there is a need in the art to develop a press fabric with
reduced or no start-up time.
[0024] Forming a fine porous layer on or within a fabric in the
production of a contemporary press fabric is highly desirable.
Formation of this surface characteristic has been previously
attempted by a variety of techniques such as incorporating a foam
layer or a fine nonwoven layer on or within the needle felt
structure. Both of these techniques while desirable, have process
drawbacks. Applying a foam layer requires wet chemistry application
with careful control of foam density, penetration and substrate
adhesion. Incorporating a nonwoven layer such as a meltblown or a
spunbond layer requires careful attention to surface layer
adhesion. If such a layer is placed within a structure subsequent
needling of additional layers may disrupt porosity of the
fabric.
[0025] Microfibers may also be formed on or incorporated within the
surface of the fabric but microfibers of this type are difficult to
process by conventional techniques. Further, the range of deniers
that may be added to the fabric using conventional processing
techniques may be limited, with increasing difficulty encountered
under 10 microns in diameter.
SUMMARY OF THE INVENTION
[0026] Accordingly, the present invention provides an anti-rewet
press fabric which is in the form of an endless loop having an
outer side and an inner side. A fine porous layer composed of split
microfibers is applied to the outer side of the base fabric.
[0027] The present invention, unlike the prior art, provides a
splittable fiber with extremely fine fiber cross-sections that
allows for easy application on or within a fabric by conventional
processes. Further, the present invention provides good anti-rewet
properties and exhibits a reduced startup period, controlled wear
and near constant density.
[0028] The present invention will now be described in more complete
detail with reference being made to the figures wherein like
reference numerals denote like elements and parts, which are
identified below.
BRIEF DESCRIPTION OF THE DRAWING
[0029] FIG. 1 is a perspective view of an anti-rewet press fabric
in accordance with an embodiment of the present invention;
[0030] FIG. 2 is a like view of an another embodiment in accordance
with the present invention;
[0031] FIG. 3 is a cross-sectional view in accordance with an
embodiment the present invention;
[0032] FIG. 4 is a like view in accordance with an embodiment of
the present invention; and
[0033] FIG. 5 is a photograph of splittable microfibers in
accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0034] A preferred embodiment of the present invention will be
described in the context of a press fabric. However, it should be
noted that the invention is applicable to other processes, such as
industrial filtration fabrics. For example, fine splittable
microfibers may be applied to the outer side or surface of an
industrial filtration fabric. The fine porous layer offers high
permeability and hence low pressure drops. Thus, higher filtration
velocities may be applied resulting in a smaller required effective
filtration surface. Further, the splittable microfibers of the
present invention are able to filter fine, smaller sized
particulates from liquid or gaseous fluid streams.
[0035] Turning now to the figures, FIG. 1 is a schematic
perspective view of press fabric 10 of the present invention. Press
fabric 10 is of the on-machine-seamable variety and takes the form
of an endless loop once its two ends 12, 14 have been joined to one
another at seam 16.
[0036] In an alternate embodiment, as shown in schematic
perspective view in FIG. 2, press fabric 20 has no seam and is in
the form of an endless loop having an inner and outer surface.
[0037] In its simplest form, the anti-rewet fabric of the present
invention includes a fine porous layer which may be applied to a
base fabric. That is, the fine porous layer is disposed on, formed
on or incorporated within a base fabric. The fine porous layer is
composed of split microfibers which may be effectively split by
needling or carding alone. FIG. 3 illustrates such a fabric with
fine porous layer 22 located on outer side or surface 26 of base
fabric 24. In general, base fabric 24 is in the form of an endless
loop having inner surface 25 and outer surface 26. Base fabric 24
may be woven, nonwoven, nonwoven arrays of MD or CD oriented yarns
knitted or braided structure of yarns of the varieties used in the
production of paper machine clothing, such as monofilament, plied
monofilament and/or multifilament yarns extruded from polymeric
resin materials. Resins from the families of polyamide, polyester,
polyurethane, polyaramid and polyolefin resins may be used for this
purpose. However, other materials for forming base fabric 24 would
be readily apparent to a practitioner in this art and the selection
of a particular material would be within the purview of the skilled
practitioner.
[0038] Base fabric 24 may alternatively be composed of mesh
fabrics, such as those shown in commonly assigned U.S. Pat. No.
4,427,734 to Johnson, the teachings of which are incorporated
herein by reference. Further, base fabric 24 may be produced by
spirally winding a strip of woven, nonwoven, knitted, braided or
mesh material according to the methods shown in commonly assigned
U.S. Pat. No. 5,360,656 to Rexfelt et al., the teachings of which
are incorporated herein by reference. Base fabric 24 may
accordingly comprise a spirally wound strip, wherein each spiral
turn is joined to the next by a continuous seam making base fabric
24 endless in a longitudinal direction. Base fabric 24 may also be
endless, or on-machine-seamable.
[0039] As shown, base fabric 24 is woven from monofilament yarns in
a single layer weave. Machine-direction yarns 28, which are the
warp yarns in the base fabric 24 and cross-machine direction yarns
30 which are the weft yarns during the weaving of the base fabric
24, are, like the machine-direction yarns 28, shown to be
monofilament yarns for the purposes of illustration. As is to be
appreciated, other possible ways to form base fabric 24 would be
readily be apparent to those so skilled in the art.
[0040] Fine porous layer 22 may then be applied to, or formed on,
an outer side of the base fabric 24 as illustrated in FIG. 3, or
optionally to the inside as well, and constituent fibers thereof
may be driven into the interior of base fabric 24 by needling. As
is to be appreciated, other possible ways of applying or forming
fine porous layer 22 onto base fabric 24 would be apparent to those
so skilled in the art, for example, melting, fusing or the like.
Fine porous layer 22 is composed of splittable microfibers, which
may be split during a carding and/or a needling process.
Microfibers are fibers having a small average diameter of not
greater than, for example, 12 microns. Microfibers having an
average diameter from about 3 microns to about 8 microns are
especially preferred. Suitable material for the microfibers
include, for example, polyolefins, polyesters and polyamides.
Especially preferred are microfibers comprising two different
materials. Preferred materials include polyamides, such as nylon-6,
nylon 33, nylon-11 and nylon 12, with nylon-6 or
poly[imino(1-oxo-1,6-hexanediyl) being especially preferred. Other
preferred microfibers are those made from polyethylene
terpephthalates (PET). Especially preferred are microfibers
comprising nylon-6 and PET, or polyester, with the fibers being
present in a 1:1 ratio being most especially preferred.
[0041] In addition, as described in FIG. 3, splittable microfibers
applied to the surface or outer side of the press fabric may
provide a smoother surface so that, in the course of passing
through a press nip, sheet marking is reduced.
[0042] Although spilttable microfibers applied to, or formed on,
the surface of a press fabric is preferred, the present invention
is as aforesaid not so limited. For example, spilttable microfibers
may be incorporated as an interior layer within the press fabric to
provide a microporous anti-rewet layer. For example, FIG. 4 is
another embodiment in accordance with the present invention. As
shown, press fabric 10 includes base fabric 24, fine porous layer
22 and at least one additional layer 32. That is, one or more
additional layer(s) 32 may be applied to, or formed on, an outer
side 34 of fine porous layer 22 or, optionally to the inside of,
any layer of press fabric 10. Layer(s) 32 may be composed of
needled batt, a fine woven fabric or a non-woven structure. For
example, needled batt may comprise staple fibers of any polymeric
resin used in the production of paper machine clothing, but are
preferably of a polyamide resin. As is to be appreciated, other
possible ways to apply layer(s) 32 to fabric 10 would readily be
apparent to one skilled in the art, for example, layer 32 may be
applied or disposed between fine porous layer 22 and base fabric
24, and/or to the inside of base fabric 26.
[0043] Among the advantages of press fabric 10 are its good
anti-rewet properties. Further, the press fabrics of the present
invention may exhibit reduced start-up period and controlled
wear.
[0044] Press fabric 10 may minimize rewet because the homogeneity
of fine porous layer 22 permits less water to return to the paper
web following exit from a press nip compared to the press fabrics
of the prior art. The same uniformity of the pressing surface may
maximize the dryness of the paper sheet following exit from the
nip. Moreover, the fine, homogeneous, smooth porous layer makes
press fabric 10 less prone to sheet blowing upon approach to a
press nip. Further, controlled wear of the fibers compensates for
the reduction of permeability caused by clogging of the fabric
during the startup period, that is, some microfibers may be
composed of material selected to ensure that some of the fiber will
be removed continuously or discontinuously during start-up.
Accordingly fine porous layer 22 may provide optimum operation
efficiency at start-up or minimize the start-up period.
[0045] Split microfibers of the present invention may be
incorporated as a start-up aid in a press fabric on a tissue making
machine. The split microfibers may be formed by passing fiber
product, for example, T-512 manufactured by Fiber Innovation
Technology, Inc. and commercially available, through a carding
apparatus. As the commercial carding process is robust enough to
split these fibers, quantities of fiber may be processed
efficiently.
[0046] A fine porous layer composed of these split microfibers may
be incorporated onto the surface of the press fabric as described
in FIG. 3. The fibers may be comprised of nylon-6 and PET, or
polyester, and may have a denier of about 3 dpf. FIG. 5 is a
photograph of such fibers after carding that could be used on the
surface of the fabric. At this denier, the fibers may be readily
processed in a fabric by conventional processes and may exhibit
excellent start-up. That is, the fine porous layer may provide
optimum operation efficiency at start-up or minimize the start-up
period. As mentioned above, pores formed by the fine microfibers
retain water inside the press fabric without causing rewetting when
the felt expands while exiting the press nip. At the same time, the
extremely fine fibers provide a fabric surface which may result in
optimum distribution of the pressure against the paper web, thus
improving paper quality and dewatering effects right from the
beginning of fabric running or pressing.
[0047] Additionally, incorporating both nylon 6 and polyester or
PET in the same splittable fiber, or in a side-to-side
relationship, may allow for improved controlled wear rate, with the
PET or polyester fibers disappearing first. That is, the PET or
polyester fibers which are less abrasion resistant are successively
worn off from the surface layer. This results in a fabric that
maintains its relative density as it compacts, a concept as taught
in commonly assigned U.S. Pat. No. 4,882,217, which teachings are
incorporated herein by reference. For this reason, these fibers are
suitable for use in accordance with the invention, however, any
other material or combination of materials suitable for this
purpose as known to those skilled in the art may be used.
[0048] Furthermore, each layer containing the splittable microfiber
may also contain nonsplittable fiber as well that is blended in as
part of the carding process in amounts required to insure the
integrity of the press fabric structure. The amounts of
nonsplittable fiber sufficient to insure the integrity of the press
fabric structure would be readily apparent to those so skilled in
the art.
[0049] As mentioned above, the present invention is also applicable
to industrial filtration fabrics. Filters have wide commercial
applications and utility. Filters generally involve the use of a
filter media, which, depending upon its construction may or may not
require a supporting structure or reinforcement means. For example,
the filter media may be an industrial filtration fabric and the
reinforcement means may be a wire made of metal or other suitable
material formed into a desired shape.
[0050] Industrial filtration fabrics may be woven, non-woven,
laminate, foam coated or coated with polymeric or metallic material
having a high or low melting temperature depending upon the
particular application, which is then possibly further processed by
attaching a fibrous batt layer by needling.
[0051] One application of a filtration fabric is to remove
particulate matter from a gas stream which flows from the outside
of a filter into the filter with the particulate accumulated on the
outside of the filter. The particulate may then be collected in a
hopper at the base of the filter system. However, other
applications of industrial filtration fabrics may be apparent to
those so skilled in the art.
[0052] Such filter arrangements can be found in U.S. Pat. Nos.
5,951,726, and 6,706,085 the disclosures of which are incorporated
herein by reference, where filter bags are described. As noted
therein, such filters and their support members can be relatively
large (i.e. 20-30 feet or more in length) depending upon the
application. The bag is usually fabricated from any conventionally
employed filter fabric conventionally used to filter solids
entrained in a gas.
[0053] For example, needle punch filters may be used to remove
particulate matter in bag houses. The preferred method of forming
the fabric is to needle punch an assembly of layers together to
provide a plurality of points in which the fibers in the layers
interlock to hold the layers and the assembly together without
reducing the permeability of the composite.
[0054] Accordingly, fine splittable microfibers of the present
invention may be applied to the outer side or surface of an
industrial filtration fabric. Preferred materials for the
microfiber include polyester. Needle punching or the like may be
used to apply the fine splittable microfibers or to cause existing
fibers in the fabric to split. However, any other method suitable
for this purpose as known to those skilled in the art may be used.
For example, a woven filtration fabric may be used for the filter
media. The processing of yarns (twisting, weaving, etc.) may cause
the fibers to spit, giving increased filtering area.
[0055] A fine porous layer including splittable microfibers offers
high permeability and hence low pressure drops. Thus, higher
filtration velocities may be applied resulting in a smaller
required effective filtration surface. Further, the splittable
microfibers of the present invention are able to filter fine,
smaller sized particulates from liquid or gaseous fluid streams. In
addition, the fine porous layer containing the splittable
microfiber may also contain nonsplittable fiber.
[0056] Modifications to the above would be obvious to those of
ordinary skill in the art, but would not bring the invention so
modified beyond the scope of the appended claims
* * * * *