U.S. patent application number 11/365747 was filed with the patent office on 2007-09-06 for splittable multicomponent fiber with high temperature, corrosion resistant polymer.
This patent application is currently assigned to Fiber Innovation Technology, Inc.. Invention is credited to Jeffrey S. Dugan, Brad Willingham.
Application Number | 20070207317 11/365747 |
Document ID | / |
Family ID | 38328366 |
Filed Date | 2007-09-06 |
United States Patent
Application |
20070207317 |
Kind Code |
A1 |
Willingham; Brad ; et
al. |
September 6, 2007 |
Splittable multicomponent fiber with high temperature, corrosion
resistant polymer
Abstract
The present invention provides a splittable, multicomponent
fiber or filament comprising a first polymer that has a high
melting point and does not degrade in a corrosive environment, and
a second polymer that has a high melting point but that is
degradable in a corrosive environment. The multicomponent fiber or
filament is particularly useful in filtration media.
Inventors: |
Willingham; Brad;
(Kingsport, TN) ; Dugan; Jeffrey S.; (Erwin,
TN) |
Correspondence
Address: |
ALSTON & BIRD LLP
BANK OF AMERICA PLAZA, 101 SOUTH TRYON STREET, SUITE 4000
CHARLOTTE
NC
28280-4000
US
|
Assignee: |
Fiber Innovation Technology,
Inc.
|
Family ID: |
38328366 |
Appl. No.: |
11/365747 |
Filed: |
March 1, 2006 |
Current U.S.
Class: |
428/375 |
Current CPC
Class: |
B01D 39/02 20130101;
B01D 39/1623 20130101; D01F 8/04 20130101; Y10T 428/2933
20150115 |
Class at
Publication: |
428/375 |
International
Class: |
D02G 3/00 20060101
D02G003/00 |
Claims
1. A splittable, multicomponent fiber having an outer surface, said
fiber comprising: a first fiber component comprising a polymer
having a melting point of at least about 200.degree. C. and that
does not degrade in a corrosive environment, said first fiber
component being dimensioned to form a microfilament; and a second
fiber component comprising a polymer having a melting point of at
least about 200.degree. C. and that is degradable in a corrosive
environment; wherein each of said fiber components forms a portion
of the outer surface of said fiber and form distinct, unocclusive
cross-sectional segments along the length of the fiber.
2. The multicomponent fiber according to claim 1, wherein said
first fiber component comprises a polymer selected from the group
consisting of polyphenylene sulfide, fluoropolymers,
chlorofluoropolymers, epoxies, silicones, polymethylpentene,
mixtures thereof, copolymers thereof, and terpolymers thereof.
3. The multicomponent fiber according to claim 1, wherein said
second fiber component comprises a polymer selected from the group
consisting of polyesters and polyamides.
4. The multicomponent fiber according to claim 3, wherein said
second fiber component comprises a polymer selected from the group
consisting of polycyclohexylene dimethyl terephthalate,
polyethylene terephthalate, polybutylene terephthalate,
poly(trimethylene) terephthalate, polyethylene naphthalate, nylon
6, nylon 6,6, mixtures thereof, copolymers thereof, and terpolymers
thereof.
5. The multicomponent fiber according to claim 1, wherein said
first fiber component comprises polyphenylene sulfide and said
second fiber component comprises polyethylene terephthalate.
6. The multicomponent fiber according to claim 1, wherein said
fiber is selected from the group consisting of pie/wedge fibers,
hollow pie/wedge fibers, segmented round fibers, segmented oval
fibers, segmented rectangular fibers, segmented cross fibers, and
segmented multilobal fibers.
7. The multicomponent fiber according to claim 1, wherein said
fiber is selected from the group consisting of continuous
filaments, staple fibers, spunbond fibers, and meltblown
fibers.
8. The multicomponent fiber according to claim 1, wherein said
first fiber component comprises at least about 50% by weight of
said multicomponent fiber.
9. The multicomponent fiber according to claim 1, wherein said
first fiber component comprises at least about 75% by weight of
said multicomponent fiber.
10. The multicomponent fiber according to claim 1, wherein said
fiber is capable of being mechanically dissociated.
11. The multicomponent fiber according to claim 10, wherein said
mechanical dissociation comprises a method selected from the group
consisting of carding, crimping, drawing, and high pressure water
jet impinging.
12. The multicomponent fiber according to claim 1, wherein said
fiber is capable of being chemically dissociated.
13. A fabric comprising a multicomponent fiber according to claim
1.
14. The fabric of claim 13, wherein the fabric is selected from the
group consisting of nonwoven fabrics, woven fabrics, and knit
fabrics.
15. A filtration media comprising a multicomponent fiber according
to claim 1.
16. The filtration media according to claim 15, wherein said
filtration media further comprises one or more non-splittable fiber
comprising a polymer having a melting point of at least about
200.degree. C. and that does not degrade in a corrosive
environment
17. A method for preparing a microfilament filter at a point of
use, said method comprising: a. providing a filtration media
comprising a splittable, multicomponent fiber having an outer
surface, said fiber comprising: i. a first fiber component
comprising a polymer having a melting point of at least about
200.degree. C. and that does not degrade in a corrosive
environment; and ii. a second fiber component comprising a polymer
having a melting point of at least about 200.degree. C. and that
does degrade in a corrosive environment; wherein each of said fiber
components forms a portion of the outer surface of said fiber and
form distinct, unocclusive cross-sectional segments along the
length of the fiber; b. installing said filtration media at said
point of use; and c. flowing a stream for filtration through said
filtration media under high temperature, corrosive conditions such
that said second fiber component degrades and said first fiber
component remains intact as microfilaments having a fineness of
less than or equal to about 1 denier per filament.
18. The method according to claim 17, wherein said filtration media
further comprises one or more non-splittable fibers comprising a
polymer having a melting point of at least about 200.degree. C. and
that does not degrade in a corrosive environment.
19. The method according to claim 17, wherein said microfilament
filter prepared according to said method has a filtration
performance of greater than or equal to about 99%, said filtration
performance being measured as the percentage of particles having a
diameter of 1 micron or greater that are retained by said
microfilament filter.
20. The method according to claim 17, further comprising removing
said degraded second fiber component from said microfilament
filter.
21. The method according to claim 20, wherein said removing step
comprises entraining the degraded second fiber component in the
filtered stream exiting the filtration media such that the degraded
second fiber component is carried away by said filtered stream.
22. The method according to claim 20, wherein said removing step
comprises mechanical cleaning of said microfilament filter.
23. The method according to claim 17, wherein said stream comprises
a gas.
24. The method according to claim 17, wherein said multicomponent
fiber is selected from the group consisting of continuous
filaments, staple fibers, spunbond fibers, and meltblown
fibers.
25. The method according to claim 17, wherein said filtration media
comprises a fabric selected from the group consisting of nonwoven
fabrics, woven fabrics, and knit fabrics.
26. The method according to claim 17, wherein said point of use
comprises a baghouse filter.
27. A microfilament filter prepared according to the method of
claim 17.
28. A filter comprising polyphenylene sulfide microfilaments having
a fineness of less than or equal to about 1 denier per filament,
wherein said filter has a filtration performance of greater than or
equal to about 95%, said filtration performance being measured as
the percentage of particles having a diameter of 1 micron or
greater that are retained by said filter.
29. The filter according to claim 28, wherein said filter has a
filtration performance of greater than or equal to about 99%.
Description
FIELD OF THE INVENTION
[0001] The present invention is related to multicomponent fibers.
In particular, the invention is related to multicomponent fibers
comprising at least one high melting point, corrosion resistant
polymer and fabrics made from such fibers and from microfilaments
obtainable from such multicomponent fibers.
BACKGROUND
[0002] Filtration processes are used to separate specific compounds
(often of one phase) from a fluid stream (often of another phase)
by passing the fluid stream through filtration media, which traps
the specific compounds for separation, such as by entrainment or
suspension. For example, the fluid stream may be a liquid stream
containing a solid particulate. Likewise, the fluid stream may be a
gas stream containing a liquid or solid aerosol. Many properties
may be considered in selecting a particular filtration media,
including the ability of the media to retain the compounds to be
filtered, temperature stability, chemical stability (e.g.,
corrosion resistance), physical strength of the media to withstand
filtering conditions, and cost.
[0003] Filtration media commonly include fabrics formed of natural,
synthetic, metallic, and glass fibers. For use in corrosive
environments, filters are generally formed of fibers having
chemical resistance. For example, power plants often employ
baghouse filters, which are subject to a stream for filtration
characterized by a high temperature, corrosive environment. U.S.
Pat. No. 5,586,997, which is incorporated by reference in its
entirety, provides further disclosure related to bag filters.
[0004] A wide range of fabric constructions can be used in
filtration media, such as woven, knit, and nonwoven fabrics,
including meltspun webs. Non-limiting examples of webs useful in
filtration media include carded fiber webs, air-laid fiber webs,
wet-laid fiber webs, meltblown fiber webs, and spunbond fiber
webs.
[0005] Fine denier fibers in filtration media can provide benefits
in the filtration of extremely small particulates. Fine denier
fibers may be used to produce fabrics having smaller pore sizes,
thus allowing smaller particulates to be filtered from a fluid
stream. In addition, fine denier fibers can provide a greater
surface area per unit weight of fiber, which can be beneficial in
filtration applications.
[0006] One method for preparing fabric from fine denier filaments
is meltblown technology. Fine denier meltblown webs have been
widely used as filter media as the densely packed fibers of such
webs are conducive to providing high filter efficiency (i.e.,
removal of a high percentage of particles of a given size).
Meltblown webs, however typically do not have good physical
strength, primarily because less orientation is imparted to the
polymer during processing and lower molecular weight resins are
generally used. Accordingly, in general practice, meltblown filter
media are laminated to at least one separate, self-supporting
layer, which adds costs and complexity to the manufacturing
process.
[0007] Continuous filament or spunbond melt extrusion processes can
provide higher strength fibers than meltblown fibers; however, it
can be difficult to prepare fine denier fibers, particularly fibers
of 2 denier or less, using conventional continuous filament or
spunbond melt extrusion processes. Therefore, while filter media
produced from nonwoven webs of coarser fibers, such as spunbond and
staple fiber webs, have been used in filtration applications, such
as stove hood filters, they have not been used as filter media for
fine particles.
[0008] One method for overcoming such difficulties in continuous
filament melt extrusion is to split multicomponent continuous
filament or staple fiber into fine denier filaments, or
microfilaments, in which each fine denier filament has only one
polymer component. Multicomponent fibers, also referred to as
composite fibers, may be split into fine denier fibers comprised of
the respective components if the composite fiber is formed from
polymers which are incompatible in some respect. The single
composite filament thus becomes a bundle of individual
microfilaments. See, for example, U.S. Pat. Nos. 5,783,503 and
5,759,926, which are incorporated herein by reference, and which
disclose splittable multicomponent fibers containing polypropylene,
such as splittable polyester/polypropylene and nylon/polypropylene
fibers.
[0009] A number of processes are known for separating the fine
denier filaments from multicomponent fibers. The particular process
employed depends upon the specific combination of components
comprising the fiber, as well as their configuration. One common
process by which to divide a multicomponent fiber involves
mechanically working the fiber. For example, hydroentangling is
commonly employed to effect fiber separation during fabric
formation. Other, non-limiting examples of mechanical means for
fiber separation include needle punching, beating, and carding. In
some cases drawing on godet rolls may be sufficient for fiber
separation. When mechanical action is to be used to separate
multicomponent fibers, the fiber components are generally selected
to bond poorly with each other to facilitate subsequent
separation.
[0010] As previously noted, filters employing synthetic fibers are
often used in extreme conditions, including high temperature and
corrosive environments. Synthetic fibers suitable for use in such
environments are often costly. Further, as pollution reduction
standards become more stringent, the need for more efficient
filtration media increases. Accordingly, there is an increased need
to find methods of producing small denier synthetic fibers suitable
for high efficiency filters used in high temperature, corrosive
environments.
SUMMARY OF THE INVENTION
[0011] The present invention provides a segmented, multicomponent
fiber or filament that is splittable into a plurality of filaments.
The fiber is preferentially splittable into a plurality of
microfilaments. The multicomponent fiber, and the microfilaments
obtainable therefrom, find various applications in the area of
textiles and industry, as well as other areas. The invention also
provides various materials formed of the multicomponent fibers and
microfilaments, including yarns and fabrics, particularly
filtration media.
[0012] In one aspect, the invention is directed to a splittable,
multicomponent fiber. In a particular embodiment, the
multicomponent fiber comprises a first fiber component comprising a
polymer with a high melting point and that does not degrade in a
corrosive environment. The multicomponent fiber further comprises a
second fiber component comprising a polymer having a high melting
point but that is degradable in a corrosive environment.
Preferentially, the polymers used in the first and second fiber
components have a melting point of at least about 180.degree. C. In
a preferred embodiment, the multicomponent fiber is segmented, each
of the fiber components forming a portion of the outer surface of
the fiber, thereby forming distinct, unocclusive cross-sectional
segments along the length of the fiber. Further, preferably, the
first fiber component is dimensioned to form one or more
microfilaments upon splitting of the fiber components, and
optionally removing the second fiber component.
[0013] The multicomponent fiber is capable of splitting, or
dissociation, by various methods. In one embodiment, the fiber is
capable of being mechanically dissociated. For example, such
mechanical dissociation can include methods, such as carding,
crimping, drawing, and high pressure water jet impinging. According
to another embodiment, the fiber is capable of being chemically
dissociated. For example, the fiber can be subjected to a high
temperature, corrosive environment that degrades the second fiber
component.
[0014] The invention also encompasses various articles
incorporating the multicomponent fiber. In one embodiment, there is
provided a fabric comprising a multicomponent fiber according to
the invention. Preferentially, the fabric includes nonwoven
fabrics, woven fabrics, and knit fabrics.
[0015] According to another embodiment, there is provided
filtration media comprising a multicomponent fiber of the
invention. The filtration media can take on various embodiments
employable in multiple environments. In a particular embodiment,
the filtration media comprises a multicomponent fiber of the
invention, wherein the fiber is unsplit or has been split into a
plurality of microfilaments, either before or after formation of
the filtration media. In one preferred embodiment, the filtration
media further comprises one or more non-splittable fibers.
Preferentially, the non-splittable fiber comprises a polymer that
has a high melting point and does not degrade in a corrosive
environment.
[0016] In another aspect, the invention is directed to a method for
preparing a microfilament filter. The method is particularly
characterized in that the microfilament filter is capable of
preparation at a point of use. In one embodiment, the method of
preparing a microfilament filter comprises providing a filtration
media comprising a splittable, multicomponent fiber; installing the
filtration media at a point of use; and flowing a stream for
filtration through the filtration media. Preferably, the
multicomponent fiber used in the filtration media comprises a first
fiber component comprising a polymer that has a melting point of at
least about 200.degree. C. and that does not degrade in a corrosive
environment, and further comprises a second fiber component
comprising a polymer that has a melting point of at least about
200.degree. C. and that is degradable in a corrosive
environment.
[0017] The microfilament filter is capable of preparation at the
point of use in that, under high temperature, corrosive conditions,
the second fiber component degrades and the first fiber component
remains intact as microfilaments. In a particularly preferred
embodiment, the microfilaments have a fineness of less than or
equal to about 1 denier per filament. In another preferred
embodiment, the filtration media further comprises one or more
non-splittable fibers comprising a polymer that has a melting point
of at least about 200.degree. C. and that does not degrade in a
corrosive environment.
[0018] The microfilament filter prepared according to the above
method is particularly beneficial in that it provides a high
efficiency filter capable of use in a high temperature, corrosive
environment. Filter performance for a high efficiency filter can be
measured as the percentage of particles having a diameter of 1
micron or greater that are retained by the filter. Preferably, the
microfilament filter prepared according to the method has a
filtration performance of greater than or equal to about 95%.
[0019] In yet another embodiment, the invention provides a
microfilament filter. Preferably, the microfilament filter is a
high efficiency filter adapted for use in a high temperature,
corrosive environment, such as in a baghouse filter for use in a
power plant.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] In order to assist the understanding of embodiments of the
invention, reference will now be made to the appended drawings,
which are not necessarily drawn to scale. The drawings are
exemplary only, and should not be construed as limiting the
invention in any way.
[0021] FIGS. 1A-1F provide cross-sectional views of exemplary
embodiments of multicomponent fibers according to the present
invention;
[0022] FIGS. 2A-2B provide cross-sectional and longitudinal views,
respectively, of an exemplary fiber according to one embodiment of
the invention, wherein the fiber has been mechanically
dissociated;
[0023] FIG. 3 provides a flow diagram illustrating a fabric
formation process according to one embodiment of the invention;
and
[0024] FIG. 4 schematically illustrates one fabric formation
process of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0025] The present invention will be described more fully
hereinafter in connection with illustrative embodiments of the
invention which are given so that the present disclosure will be
thorough and complete and will fully convey the scope of the
invention to those skilled in the art. However, it is to be
understood that this invention may be embodied in many different
forms and should not be construed as being limited to the specific
embodiments described and illustrated herein. Although specific
terms are used in the following description, these terms are merely
for purposes of illustration and are not intended to define or
limit the scope of the invention. Like numbers refer to like
elements throughout. As used in this specification and the claims,
the singular forms "a," "an," and "the" include plural referents
unless the context clearly dictates otherwise.
[0026] The present invention is directed to a segmented,
splittable, multicomponent fiber or filament comprising two or more
fiber components. In general, multicomponent fibers are formed of
two or more fiber components (preferentially, polymeric materials)
which have been extruded together to provide continuous, contiguous
polymer segments extending down the length of the multicomponent
fiber. In a particular embodiment, the multicomponent fiber of the
invention comprises a first fiber component and a second fiber
component. While the invention may be described herein in terms of
the first and second fiber components, it is understood that the
multicomponent fiber is not limited to two fiber components.
Rather, the invention encompasses fibers comprising two or more
fiber components. Furthermore, while the invention may be described
herein in relation to a "fiber", it is understood that the term
encompasses fibers of finite length, such as conventional staple
fiber, as well as substantially continuous structures, such as
filaments. In one embodiment, the multicomponent fiber of the
invention comprises a fiber selected from the group consisting of
continuous filaments, staple fibers, spunbond fibers, and meltblown
fibers.
[0027] The multicomponent fiber of the invention can take on a
number of structural configurations, and any configurations
allowing for free dissociation of the individual fiber components
are acceptable according to the present invention. Generally, the
fiber components are arranged so as to form distinct, unocclusive
cross-sectional segments along the length of the fiber so that the
first fiber component is not impeded from being separated from the
second fiber component (or further fiber components, as desired).
In one particularly advantageous embodiment, the multicomponent
fiber of the invention takes on a pie-wedge arrangement, such as
that illustrated in FIG. 1A. The pie-wedge fiber arrangement
illustrated in FIG. 1A is a bicomponent filament 4 having eight
alternating segments of triangular shaped wedges comprising the
overall "pie". The wedges comprise a first fiber component 6 and a
second fiber component 8. While the pie-wedge filament illustrated
in FIG. 1A is a non-hollow fiber, the invention also encompasses
embodiments wherein the pie-wedge filament is hollow. Further,
while the pie-wedge fiber of FIG. 1A comprises eight wedge
segments, it should be recognized that filaments according to the
invention can comprise more or less than eight segments.
[0028] In addition to the pie-wedge configuration illustrated in
FIG. 1A, the multicomponent fiber of the invention can also take on
other segmented, splittable fiber configurations. For example, the
multicomponent fiber of the invention could take on the
configuration illustrated in FIG. 1B, which shows a round fiber 4
segmented into four alternating sections, comprising a first fiber
component 6 and a second fiber component 8. Description of further
multicomponent fiber construction that may be useful according to
the present invention can be found in U.S. Pat. No. 5,108,820; U.S.
Pat. No. 5,336,553; and U.S. Pat. No. 5,382,400; which are all
incorporated herein by reference.
[0029] The multicomponent fibers of the present invention are
further advantageous in that they are not limited to configuration
as conventional round fibers. Rather, the multicomponent fibers can
take on other useful shapes. For example, the inventive
multicomponent fiber can take on a segmented rectangular (or
ribbon) configuration, as illustrated in FIG. 1C, a segmented oval
configuration, as illustrated in FIG. 1D, a multilobal
configuration, as illustrated in FIG. 1E, and a segmented cross
configuration, as illustrated in FIG. 1F. Further description of
multicomponent fibers of unconventional shape that may be useful
according to the present invention can be found in U.S. Pat. No.
5,277,976; U.S. Pat. No. 5,057,368; and U.S. Pat. No. 5,069,970;
which are all incorporated herein by reference.
[0030] Both the shape of the fiber and the configuration of the
components therein can depend upon various factors including, but
not necessarily limited to, the equipment used in the preparation
of the multicomponent fiber, the process conditions, and the melt
viscosities of the various fiber components. Accordingly, a wide
variety of fiber configurations are possible.
[0031] As can be seen in FIGS. 1A-F, the multicomponent fiber of
the invention is typically formed to have a configuration such that
one component does not fully surround, or encapsulate, the other
components. One example of a configuration where one fiber
component completely surrounds the other fiber components is an
islands-in-the-sea configuration. While such embodiments are not
specifically excluded by the present invention, it is generally
preferred that the multicomponent fiber of the invention take on a
configuration wherein each fiber component forms a portion of the
outer surface of the fiber.
[0032] In conventional multicomponent fibers, so as to provide
dissociable properties to the composite fiber, the fiber components
are generally chosen so as to be mutually incompatible. In
particular, the polymers used for the fiber components do not
substantially mix together and are not chemically reactive one with
the other. Specifically, when spun together to form a composite
fiber, the polymer components exhibit a distinct phase boundary
between them so that substantially no blend polymers are formed
that may prevent dissociation. Additionally, a balance of
adhesion/incompatibility between the components of the composite
fiber is considered highly beneficial. The components
advantageously adhere sufficiently to each other to allow the
unsplit multicomponent fiber to be subjected to conventional
textile processing, such as winding, twisting, weaving, or knitting
without any appreciable separation of the components until desired.
Conversely, it is generally desirable that the polymers be
sufficiently incompatible so that adhesion between the components
is relatively weak, thereby allowing ready separation at the
desired time.
[0033] The multicomponent fibers of the present invention can also
be subject to the above considerations in that the present
multicomponent fibers may be mechanically dissociated, which is
described in greater detail below. The multicomponent fiber of the
present invention is further characterized, however, in that the
fiber is also subject to chemical dissociation, the mechanism of
which is made evident according to the following description of the
inventive fiber.
[0034] In one embodiment of the invention, the multicomponent fiber
comprises a first fiber component and a second fiber component.
Both fiber components are preferably polymers, however, the fiber
components are clearly distinguishable according to the physical
properties of the polymers. In particular, the first fiber
component comprises a polymer that has a high melting point and
that does not degrade in a corrosive environment, and the second
fiber component comprises a polymer that also has a high melting
point, but that is degradable in a corrosive environment.
[0035] The phrase "high melting point" as used herein is intended
to refer to melting points above a specified range, particularly
melting points above the operating temperatures to which synthetic
fibers are exposed in harsh industrial environments, such as in the
case of fibers in baghouse filters used in power plants,
particularly coal-fired power plants. Accordingly, as applied to
the present invention, the phrase "high melting point" is intended
to refer to melting point temperatures of about 160.degree. C. or
greater, preferably about 170.degree. C. or greater, more
preferably about 180.degree. C. or greater, still more preferably
about 190.degree. C. or greater, and most preferably about
200.degree. C. or greater. In one embodiment, "high melting point"
refers to a melting point temperature in the range of about
160.degree. C. to about 300.degree. C., preferably about
180.degree. C. to about 280.degree. C., more preferably about
200.degree. C. to about 250.degree. C.
[0036] As previously noted, the first fiber component of the
inventive fiber is distinguishable from the other fiber components
in that the first fiber component does not degrade in a corrosive
environment. The phrase "corrosive environment" is generally
understood to refer to an atmosphere having conditions present for
facilitating a physical breakdown of an item through chemical
interactions of the environment with the item. A corrosive
environment may be correlated to the presence of various chemical
agents, including alkalies, acids, oxidizing agents, and organic
solvents. For example, in the baghouse of a coal-fired power plant,
sulfuric acid is formed when sulfur released from the coal reacts
with moisture, such as condensation on the baghouse filter.
Accordingly, a corrosive environment could refer to an environment
where sulfuric acid is present.
[0037] The polymer comprising the first fiber component does not
degrade in a corrosive environment. Accordingly, the polymer used
in the first fiber component would be expected to resist
degradation in the presence of corrosive agents. In particular, the
polymer used in the first fiber component does not degrade in the
presence of strong bases, mineral acids, organic acids, oxidizing
agents, or organic solvents. Conversely, the polymer comprising the
second fiber component does degrade in a corrosive environment.
Accordingly, the polymer used in the second fiber component would
be expected to be degradable in the presence of corrosive agents.
In particular, the polymer used in the second fiber component is
degradable in the presence of strong bases, mineral acids, organic
acids, oxidizing agents, or organic solvents. In one particular
embodiment, the polymer used in the second fiber component is
degradable in the presence of acids, and specifically acids formed
as by-products of the combustion of coal, such as sulfuric
acid.
[0038] In one particular embodiment of the invention, the first
fiber component comprises a polymer that has a melting point of at
least about 200.degree. C. Preferably, the first fiber component
comprises a polymer that has a melting point of at least about
225.degree. C., more preferably at least about 250.degree. C.,
still more preferably at least about 275.degree. C., even more
preferably at least about 285.degree. C., and most preferably at
least about 300.degree. C.
[0039] As would be recognizable to the skilled artisan, many
different polymers could be used in the first fiber component
according to the invention. Any polymer exhibiting the physical
properties described herein with respect to melting point and
degradation resistance in a corrosive environment could be used as
the first polymer component in the multicomponent fiber of the
invention. In one embodiment, the first fiber component comprises a
polymer selected from the group consisting of polyphenylene
sulfide, fluoropolymers (e.g., polytetrafluoroethylene),
chlorofluoropolymers, (e.g., HALAR.RTM., which is an
ethylene/chlorotrifluoroethylene copolymer), epoxies, silicones,
polymethylpentene, mixtures thereof, copolymers thereof, and
terpolymers thereof.
[0040] In another particular embodiment of the invention, the
multicomponent fiber further comprises a second fiber component
also comprising a polymer that has a melting point of at least
about 200.degree. C. Preferably, the second fiber component
comprises a polymer that has a melting point of at least about
225.degree. C., more preferably at least about 250.degree. C.,
still more preferably at least about 275.degree. C., even more
preferably at least about 285.degree. C., and most preferably at
least about 300.degree. C. While the polymers used in the first and
second fiber components exhibit similar melt characteristics, the
polymer used in the second fiber component is different from the
polymer used in the first fiber component.
[0041] As would again be recognizable to the skilled artisan, many
different polymers could be used in the second fiber component
according to the invention. In particular, any polymer exhibiting
the physical properties described herein with respect to melting
point and degradation in a corrosive environment could be used as
the second polymer component in the multicomponent fiber of the
invention. In one embodiment, the second fiber component comprises
a polymer selected from the group of polyesters and polyamides.
Preferably, the second fiber component comprises a polymer selected
from the group consisting of polycyclohexylene dimethyl
terephthalate (PCT), polyethylene terephthalate (PET), polybutylene
terephthalate (PBT), poly(trimethylene) terephthalate (PTT),
polyethylene naphthalate (PEN), nylon 6, and nylon 6,6.
[0042] Preferentially, the first fiber component and the second
fiber component of the inventive multicomponent fiber are present
in defined ratios based on the overall weight of the multicomponent
fiber. In one embodiment, the first fiber component comprises at
least about 50% by weight of the multicomponent fiber. Preferably,
the first fiber component comprises at least about 60% by weight of
the multicomponent fiber, more preferably at least about 70% by
weight, and most preferably at least about 75% by weight of the
multicomponent fiber.
[0043] Each of the fiber components can optionally include
additional ingredients. Examples of materials that could be used as
additional components include, but are not limited to,
antioxidants, stabilizers, surfactants, waxes, flow promoters,
solid solvents, particulates, and other materials added to enhance
processability of the first fiber component or the second fiber
component of the inventive multicomponent fiber. In particular, it
may be useful to use pigments with one or both of the first and
second fiber components. The same pigment may be employed in both
fiber components, or, in an alternative embodiment, the components
may each contain pigments of differing colors. Further, the
invention encompasses the addition of other additives that may be
useful for providing beneficial properties to the finished product,
such as antimicrobials, flame retardants, UV absorbers, and the
like. These and other additives can be used in conventional
amounts.
[0044] As previously noted, the multicomponent fiber of the present
invention can be provided as staple fibers of varying finite
lengths, continuous filaments, spunbond fibers, and meltblown
fibers. The fibers can also be described in terms of fiber fineness
on a denier scale, which is a commonly used expression of fiber
diameter, and which is defined as the weight in grams of 9000
meters of the fiber. As understood in the art, a lower denier value
indicates a finer fiber, while a higher denier value indicates a
thicker, or heavier, fiber. The fineness of the multicomponent
fibers prepared according to the present invention can vary
depending upon the fiber formation. Generally, the multicomponent
fibers of the invention can have a fineness of about 1 denier per
filament (dpf) to about 60 dpf, more preferably about 1.5 dpf to
about 20 dpf, most preferably about 2 dpf to about 10 dpf.
[0045] The multicomponent fiber of the present invention is
characterized, in one aspect, in that the overall fiber is
splittable, through mechanical dissociation or chemical
dissociation, to provide a plurality or fine denier filaments, or
microfilaments, each formed of the individual fiber components that
make up the overall multicomponent fiber. In particular, the first
fiber component of the multicomponent fiber is dimensioned so as to
form a microfilament upon dissociation from the second fiber
component (which is understood to mean the same as the second fiber
component being dissociated from the first fiber component). As
used herein, the terms "fine denier filaments" and "microfilaments"
are interchangeable and are intended to include sub-denier
filaments and ultra-fine filaments. Sub-denier filaments typically
have denier values in the range of 1 dpf or less. Ultra-fine
filaments typically have denier values in the range of about 0.1
dpf to about 0.3 dpf. It is also understood according to the
invention that the term microfilaments relates to continuous
filaments, as well as staple fibers. In one embodiment, the
microfilaments formed by dissociation of the multicomponent fiber
exhibit have a fineness in the range of about 0.05 dpf to about 1.0
dpf, preferably about 0.1 dpf to about 0.7 dpf, more preferably
about 0.1 dpf to about 0.5 dpf.
[0046] FIG. 2 illustrates one embodiment of a multicomponent fiber
of the invention that has been separated into a fiber bundle 10 of
microfilaments. As seen in FIG. 2, the multicomponent fiber has
been split into four microfilaments 6 comprising the first fiber
component and four microfilaments 8 comprising the second fiber
component, thereby providing an eight filament fiber bundle 10. In
one embodiment of the invention, the multicomponent fiber is
splittable, either mechanically or chemically, into 4 to 48
microfilaments. Preferably, the multicomponent fiber is splittable
into 6 to 36 microfilaments, more preferably 8 to 20
microfilaments. In one embodiment, the multicomponent fiber is
splittable into 16 to 32 microfilaments.
[0047] As the multicomponent fibers of the invention, and the
microfilaments produced therefrom, are subject to mechanical and/or
chemical stresses to facilitate splitting, it is preferable for the
fibers, and microfilaments, to have a suitable tenacity. As is
understood in the art, tenacity describes the tensile strength of a
fiber (i.e., the force at which the fiber ruptures or breaks) and
is generally provided in terms of grams per denier (gpd), or the
force in grams required to break a given filament or fiber bundle
divided by that filament or fiber bundle's denier value. In one
embodiment, the multicomponent fibers and microfilaments of the
invention exhibit a tenacity of about 1.0 gpd to about 5 gpd,
preferably about 1.5 gpd to about 4.5 gpd, more preferably about 2
gpd to about 4 gpd.
[0048] As noted above, the multicomponent fiber of the invention,
in one embodiment, is capable of being mechanically dissociated
into the separate fiber component microfilaments. In particular,
the first fiber component is dimensioned to form a microfilament
upon dissociation. Mechanical dissociation can be by any means that
provides sufficient flex or mechanical action to the multicomponent
fiber to fracture and separate the individual fiber components of
the composite fiber. As used herein, the terms "splitting,"
dissociating," or "dividing" are intended to mean that at least one
of the fiber components is separated completely or partially from
the original multicomponent fiber. Partial splitting can mean
dissociation of some individual segments from the fiber, or
dissociation of pairs or groups of segments (which remain together
in these pairs or groups) from other individual segments, or pairs
or groups of segments from the original fiber. As seen in FIG. 2,
the resultant microfilaments can remain in proximity to the
remaining components, thereby providing a coherent fiber bundle 10
of microfilaments 6 and 8, originating from a common multicomponent
fiber. However, as the skilled artisan will appreciate, in some
processing techniques, such as hydroentanglement, or where the
fibers are split prior to fabric formation, the microfilaments
originating from a common fiber source may be further removed from
one another.
[0049] According to another embodiment of the invention, there is
provided a fabric comprising a multicomponent fiber, as described
herein. A fabric according to the invention can be prepared through
any method recognizable in the art as useful for preparing fabrics
using synthetic fibers. In particular, the fabric according to the
invention comprises nonwoven fabrics, woven fabrics, and knit
fabrics.
[0050] One process for making a fabric in accordance with one
embodiment of the invention is illustrated diagrammatically in FIG.
3. Specifically, FIG. 3 illustrates an extrusion process 14,
followed by a draw process 16, a staple process 18, a carding
process 20, and a fabric formation process 22.
[0051] Extrusion processes for making multicomponent continuous
filament fibers are known and need not be described here in detail.
Generally, to form a multicomponent fiber, at least two polymers
are extruded separately and fed into a polymer distribution system
wherein the polymers are introduced into a spinneret plate. The
polymers follow separate paths to the fiber spinneret and are
combined in a spinneret hole. The spinneret is configured so that
the extrudant has the desired overall fiber cross section (e.g.,
round, trilobal, etc.). Such a process is described, for example,
in U.S. Pat. No. 5,162,074, which is incorporated herein by
reference in its entirety.
[0052] In the present invention, a first polymer that has a high
melting point and that does not degrade in a corrosive environment,
such as polyphenylene sulfide, and a second polymer that has a high
melting point and that is degradable in a corrosive environment,
such as polyethylene terephthalate, are fed into the polymer
distribution system. The polymers typically are selected to have
melting points such that the polymers can be spun as a polymer
throughput that enables the spinning of the components through a
common capillary at substantially the same temperature without
degrading one of the components.
[0053] Following extrusion through the die, the resulting thin
fluid strands, or filaments, remain in the molten state for some
distance before they are solidified by cooling in a surrounding
fluid medium, which may be chilled air blown through the strands.
Once solidified, the filaments are taken up on a godet or other
take-up surface. In a continuous filament process, the strands are
taken up on a godet, which draws down the thin fluid streams in
proportion to the speed of the take-up godet. Continuous filament
fiber may further be processed into staple fiber. In processing
staple fibers, large numbers (e.g., 10,000 to 1,000,000 strands) of
continuous filament are gathered together following extrusion to
form a tow for use in further processing.
[0054] Rather than being taken up on a godet, continuous
multicomponent fiber may also be melt spun as a direct laid,
nonwoven web via a jet process. For example, in a spunbonding
process, the strands are collected in a jet following extrusion
through the die, such as for example, an air attenuator, and then
blown onto a take-up surface, such as a roller or a moving belt, to
form a spunbond web. Alternatively, direct laid composite fiber
webs may be prepared by a meltblown process, in which air is
ejected at the surface of a spinneret to simultaneously draw down
and cool the thin fluid polymer streams, which are subsequently
deposited on a take-up surface in the path of cooling air to form a
fiber web.
[0055] Regardless of the type of melt spinning procedure which is
used, the thin fluid streams are typically melt drawn in a molten
state (i.e., before solidification occurs) to orient the polymer
molecules for good tenacity. Typical melt draw down ratios known in
the art may be utilized. The skilled artisan will appreciate that
specific melt draw down is not required for meltblowing
processes.
[0056] When a continuous filament or staple process is employed, it
may be desirable to subject the strands to a draw process. In the
draw process, the strands are typically heated past their glass
transition point and stretched to several times their original
length using conventional drawing equipment, such as, for example,
sequential godet rolls operating at differential speeds. Typical
draw ratios can depend upon polymer type. For example, draw ratios
of about 2 to about 5 times are typical for polyolefin fibers.
Optionally, the drawn strands may be heat set to reduce any latent
shrinkage imparted to the fiber during processing.
[0057] If staple fiber is being prepared, following drawing in the
solid state, the continuous filaments are cut into a desirable
fiber length. The length of the staple fibers generally ranges from
about 25 to about 50 millimeters, although the fibers can be longer
or shorter as desired. See, for example, U.S. Pat. No. 4,789,592
and U.S. Pat. No. 5,336,552, which are incorporated herein by
reference. Optionally, the fibers may be subjected to a crimping
process prior to the formation of staple. Crimped composite fibers
are highly useful for producing lofty woven and nonwoven fabrics
since the microfilaments split from the multicomponent fibers
largely retain the crimps of the composite fibers, and the crimps
increase the bulk, or loft, of the fabric. Such lofty fine fiber
fabric of the present invention exhibits cloth-like textural
properties (e.g., softness, drapability, and hand) as well as the
desirable strength properties of a fabric containing highly
oriented fibers.
[0058] The staple fiber thus formed is then fed into a carding
process. A more detailed schematic illustration of a carding
process is provided in FIG. 4. As shown therein, the carding
process can include the step of passing spun yarns 26 comprising
staple fibers through a carding machine 28 to align the fibers of
the yarn as desired, typically to lay the fibers in roughly
parallel rows, although the staple fibers may be oriented
differently. The carding machine 28 is comprised of a series of
revolving cylinders 34 with surfaces covered in teeth. These teeth
pass through the yarn as it is conveyed through the carding machine
on a moving surface, such as a drum 30. The carding process
produces a fiber web 32.
[0059] The carded fiber web 32 can be subjected to a fabric
formation process to impart cohesion to the fiber web. In one
embodiment, the fabric formation process includes the step of
bonding the fibers of fiber web 32 together to form a coherent
unitary nonwoven fabric. The bonding step can be any known in the
art, such as mechanical bonding, thermal bonding, and chemical
bonding. Typical methods of mechanical bonding include
hydroentanglement and needle punching.
[0060] FIG. 4 further illustrates a schematic of one
hydroentangling process suitable for use in the present invention.
As shown in FIG. 4, the fiber web 32 is conveyed longitudinally to
a hydroentangling station 40 wherein a plurality of manifolds 42,
each including one or more rows of fine orifices, direct high
pressure water jets through fiber web 32 to intimately
hydroentangle the staple fibers, thereby providing a cohesive,
nonwoven fabric 52.
[0061] The hydroentangling station 40 is constructed in a
conventional manner as known to the skilled artisan and as
described, for example, in U.S. Pat. No. 3,485,706, which is hereby
incorporated by reference. As known to the skilled artisan, fiber
hydroentanglement is accomplished by jetting liquid, typically
water, supplied at a pressure of from about 200 psig up to 4000
psig or greater to form fine, essentially columnar, liquid streams.
The high pressure liquid streams are directed toward at least one
surface of the composite web. In one embodiment of the invention
water at ambient temperature and 200 bar is directed towards both
surfaces of the web. The composite web is supported on a foraminous
support screen 44 which can have a pattern to form a nonwoven
structure with a pattern or with apertures or the screen can be
designed and arranged to form a hydraulically entangled composite
which is not patterned or apertured. The fiber web 32 can be passed
through the hydraulic entangling station 40 a number of times for
hydraulic entanglement on one or both sides of the composite web or
to provide any desired degree of hydroentanglement.
[0062] Optionally, the nonwoven webs and fabrics of the present
invention may be thermally bonded. In thermal bonding, heat and/or
pressure are applied to the fiber web or nonwoven fabric to
increase its strength. Two common methods of thermal bonding are
air heating, used to produce low-density fabrics, and calendering,
which produces strong, low-loft fabrics. Hot melt adhesive fibers
may optionally be included in the web of the present invention to
provide further cohesion to the web at lower thermal bonding
temperatures.
[0063] As an alternative to producing a dry-laid nonwoven fabric,
such as previously described, a nonwoven fabric may be formed in
accordance with the instant invention by direct-laid means. In one
embodiment of direct laid fabric, continuous filament is spun
directly into nonwoven webs by a spunbonding process. In an
alternative embodiment of direct laid fabric, multicomponent fibers
of the invention are incorporated into a meltblown fabric. The
techniques of spunbonding and meltblowing are known in the art and
are discussed in various patents, e.g., U.S. Pat. No. 3,987,185;
U.S. Pat. No. 3,972,759; and U.S. Pat. No. 4,622,259; which are
incorporated herein by reference. The fiber of the present
invention may also be formed into a wet-laid nonwoven fabric, via
any suitable technique known in that art.
[0064] While particularly useful in the production of nonwoven
fabrics, the fibers of the invention can also be used to make other
textile structures such as but not limited to woven and knit
fabrics. Yarns prepared for use in forming such woven and knit
fabrics are similarly included within the scope of the present
invention. Such yarns may be prepared from the continuous filament
or spun yarns comprising staple fibers of the present invention by
methods known in the art, such as twisting or air entanglement.
[0065] In one embodiment of the invention, the fabric formation
process itself is used to mechanically dissociate the
multicomponent fiber of the invention into microfilaments
comprising the individual fiber components. Stated differently,
forces applied to the multicomponent fibers of the invention during
fabric formation in effect split or dissociate the polymer
components to form microfilaments. The resultant fabric thus formed
is comprised, for example, of a plurality of microfilaments 6 and
8, such as shown in FIG. 2, and described previously. Mechanical
dissociation can take place during one or more aspects of the
fabric forming process. In a particular, complete or partial
mechanical dissociation can be achieved through carding, crimping,
drawing, and high pressure water jet impinging, such as the
hydroentangling process. Optionally, the composite fiber may be
divided after the fabric has been formed by application of
mechanical forces thereto. In addition, the multicomponent fiber of
the present invention may be separated into microfilaments before
or after formation into a yarn. Still further, the multicomponent
fiber may be separated into the individual fiber component
microfilaments prior to implementation of any of the
above-described fabric formation process steps, or other fabric
formation process steps as may be known in the art.
[0066] As noted above, the multicomponent fiber of the invention,
in another embodiment, is capable of being chemically dissociated.
The multicomponent fiber generally comprises a first fiber
component comprising a polymer that has a high melting point and
that does not degrade in a corrosive environment. The
multicomponent fiber further comprises a second fiber component
comprising a polymer that also has a high melting point but that is
degradable in a corrosive environment. Accordingly, the
multicomponent fiber is capable of being chemically dissociated by
introducing the fiber to a corrosive environment. For example, in
one embodiment, the second fiber component can comprise a polymer
that is degradable in an acidic environment. By introducing the
multicomponent fiber to an acidic environment, the second fiber
component, being degradable in such an environment, degrades. The
first fiber component, not being degradable in such an environment,
remains intact. Therefore, the multicomponent fiber is chemically
dissociated by chemically degrading the second fiber component to
free the first fiber component, which preferably is dimensioned to
form microfilaments.
[0067] The multicomponent fibers, the microfilaments prepared
therefrom, and the fabrics prepared from the multicomponent fibers
and the microfilaments, as described above, are particularly
beneficial in that a variety of useful products can be prepared
using the fibers, microfilaments, and fabrics of the invention. In
particular, the various products prepared according to the
invention are further useful in the preparation of filtration
media.
[0068] Many types of filtration media are known in the art and find
a variety of uses in industry, as well as in public and private
structures, such as homes and commercial buildings. Non-limiting
examples of industrial uses for filtration media include bag
filters, air filters, mist eliminators, and the like. Bag filters
are known for use in filtering paints and coatings, especially
hydrocarbon-based paints and primers, chemicals, petrochemical
products, and the like. Air filters are useful in filtering large
or small volumes of air. Small air volume applications include face
mask filters. Large volumes of air are advantageously filtered
using electret filters. Electret air filters are particularly
useful in applications such as furnace filters, automotive cabin
filters, and room air cleaner filters. Mist eliminators, used to
remove liquid or solid airborne particles, are employed in a wide
range of industrial applications generating waste gas streams.
Filtration media prepared according to the present invention would
find use in all of the above, as well as other areas that would be
recognizable to the skilled artisan.
[0069] Generally speaking, filtration media are useful for removing
an undesirable component of a moving stream, which is usually a gas
or a liquid. Fabric filter media are particularly useful for
removing particulate matter from a gas stream. Performance of
fabric filter media is strongly dependant upon the type of fabric
used. In the case of nonwoven fabrics, particularly, performance
can be dictated by the characteristics of the individual fibers or
microfilaments used in the preparation thereof. A fabric for use as
filtration media must be able to efficiently collect the matter
desired for removal from a stream, must be compatible with the
stream flowing through the filter media, and is preferably easily
amenable to cleaning and re-use.
[0070] Filtration media according to the present invention can be
prepared using the multicomponent fiber, microfilaments obtainable
from the multicomponent fiber, or fabric incorporating the
multicomponent fiber or microfilaments of the invention.
Preferably, when the multicomponent fiber is used in preparing
filtration media, the fiber is either mechanically or chemically
dissociated to form microfilaments, said dissociation occurring
either before or after formation of the filtration media. In one
particular embodiment, the invention provides a filtration media
comprising a multicomponent fiber comprising a first fiber
component comprising a polymer that has a melting point of at least
about 200.degree. C. and that does not degrade in a corrosive
environment, the first fiber component being dimensioned to form a
microfilament, and a second fiber component comprising a polymer
that has a melting point of at least about 200.degree. C. and that
is degradable in a corrosive environment, wherein each of the fiber
components forms a portion of the outer surface of the fiber and
form distinct, unocclusive cross-sectional segments along the
length of the fiber. In yet a further embodiment, the invention
provides a filter media as described above, wherein the filtration
media further comprises one or more non-splittable fiber.
Preferably, the non-splittable fiber has a melting point of at
least about 200.degree. C. and does not degrade in a corrosive
environment. Non-limiting examples of non-splittable fibers useful
for incorporation into the filtration media of the invention
include polyimides, aromatic polyamides (aramids), such as
NOMEX.RTM., glass fibers, and imidazoles, such as polybenzimidazole
(PBI).
[0071] The microfilaments of the invention are particularly useful
in preparing filtration media as they provide the tensile
properties, insensitivity to moisture, and high surface area
considered beneficial in filtration media. In addition, articles,
such as filter media, prepared according to the invention and
comprising microfilaments of the first fiber component, as
described herein, possess superior chemical resistance and are
advantageously used in corrosive environments.
[0072] Accordingly, in one embodiment of the invention, there is
provided a microfilament filter comprising a polymer that has a
high melting point and that does not degrade in a corrosive
environment. Preferably, the microfilaments in the filter have a
fineness of less than or equal to about 1 dpf. In one preferred
embodiment, the polymer used in the microfilaments comprises
polyphenylene sulfide.
[0073] Filtration media prepared according to the present invention
is further characterized in that it provides high efficiency
filtration performance. Filtration performance can generally be
described, or rated, in terms of the percentage of particles of a
defined size that are retained by the filter when a stream carrying
the particles passes through the filter. Accordingly, filter
performance is understood to be improved by retaining a higher
percentage of particles of smaller size.
[0074] Filtration media including microfilaments, as described, are
particularly efficient and exhibit a high performance rating.
Accordingly, in one embodiment, the microfilament filter of the
invention has a filtration performance such that greater than or
equal to about 95% of particles having a diameter of 1 micron or
greater are retained by the filter. Preferably, greater than or
equal to about 99% of particles having a diameter of 1 micron or
greater are retained by the filter. In one particularly preferred
embodiment, greater than or equal to about 99.9% of particles
having a diameter of 1 micron or greater are retained by the
filter.
[0075] Such high efficiency filters are particularly beneficial in
that they meet standards set by the United States Environmental
Protection Agency (EPA) under the PM2.5 designation. According to
EPA National Ambient Air Quality Standards (NAAQS), particulate
matter having a size of 2.5 microns or less are designated PM2.5,
and emissions of such particulates are monitored to ensure levels
remain below set standards. The filtration media of the present,
arising the unique microfiber construction, is further beneficial
in that it prevents small particulates from penetrating deeply into
the filtration media. Accordingly, the filtration media allows for
easier cleaning and removal of trapped particulate matter.
[0076] One particular application where filtration media according
to the present invention finds use is the field of baghouse
filters. Baghouse filters are well understood in the art and
therefore do not require detailed discussion herein. A baghouse
filter generally comprises one or a series of fabric bags, or flat
supported envelopes, contained within a housing, which has a stream
inlet, a stream outlet, a collection hopper, and typically a
cleaning mechanism for periodic removal of filtrate from the
filter. In operation, a stream (such as a gas) containing
particulate matter flows through the bag filters, which remove the
particulate matter from the stream. In industrial use, baghouse
filters are capable of filtering in excess of one million cubic
feet of air per minute.
[0077] As baghouse filters generally find use in industrial
settings, the stream for filtration often presents an inhospitable
environment. As previously noted, baghouse filters are often used
in power plants, particularly those wherein power production
include combustion of a carbon-containing fuel, such as coal-fired
and oil-fired power plants. For example, in coal-fired or oil-fired
power plants, a baghouse filter system may be positioned to receive
exhaust directly from a stoker boiler. Primary problems encountered
with such applications include the presence of sulfur in the fuel
(e.g., coal or oil), which leads to the formation of acids from
sulfur dioxide (SO.sub.2) and sulfur trioxide (SO.sub.3) in the
exhaust. Further, alkaline additives (such as dolomite and
limestone) may be injected upstream of baghouse inlets to reduce
the SO.sub.2 and SO.sub.3 present in the exhaust. Such exhaust may
also include nitrates (NO.sub.3) and nitrites (NO.sub.2), as well
as significant amounts of hydrochloric acid (HCl). Accordingly,
fabric filter media used in baghouse filters encounter high
temperatures, as well as corrosive conditions, such as high acidity
or alkalinity.
[0078] The multicomponent fiber of the present invention, as well
as fabric made therefrom, is particularly useful in such
environments. As noted above, the multicomponent fiber of the
invention comprises a first fiber component comprising a polymer
that has a high melting point and that does not degrade in a
corrosive environment, such as the acidic or alkaline conditions
encountered in a baghouse filter. Therefore, in one embodiment, the
invention provides filtration media comprising the multicomponent
fiber as described herein. In another embodiment, the invention
provides a fabric comprising the multicomponent fiber, wherein the
fabric is particularly useful as filtration media. In yet another
embodiment, the invention provides a microfilament filter
comprising a microfilament obtained through dissociation of the
multicomponent fiber of the invention.
[0079] In light of the novel composition of the multicomponent
fiber, as described herein the invention is further characterized
in that, in one particular aspect, there is provided a method for
preparing a microfilament filter at a point of use. Preferably, the
point of use wherein the microfilament filter is prepared exhibits
high temperature, corrosive conditions. In one particular
embodiment, the point of use is a baghouse filter.
[0080] In a preferred embodiment according to this aspect of the
invention, there is provided a method of preparing a microfilament
filter, wherein the method comprises providing a filtration media
comprising a splittable, multicomponent fiber as described herein
comprising a first fiber component and a second fiber component,
installing the filtration media at the desired point of use, and
flowing a stream for filtration through the filtration media under
conditions such that the second fiber component degrades and the
first fiber component remains intact as microfilaments.
Preferentially, the microfilaments have a fineness of less than or
equal to about 1 dpf.
[0081] In a particularly preferred embodiment, the first fiber
component of the multicomponent fiber comprises a polymer that has
a melting point of at least about 200.degree. C. and that does not
degrade in a corrosive environment; and the second fiber component
comprises a polymer that has a melting point of at least about
200.degree. C. and that is degradable in a corrosive environment.
Preferentially, each of the fiber components forms a portion of the
outer surface of the multicomponent fiber and form distinct,
unocclusive cross-sectional segments along the length of the
fiber.
[0082] In yet a further embodiment, the method incorporates the use
of a filter media as described above, wherein the filtration media
further comprises one or more non-splittable fiber. Preferably, the
non-splittable fiber has a melting point of at least about
200.degree. C. and does not degrade in a corrosive environment.
[0083] The method described above allows for in situ preparation of
a microfilament filter through use of a filter media comprised of a
multicomponent fiber due to the unique composition of the
multicomponent fiber of the invention. Preparation of
microfilaments, particularly microfilaments comprising polymers
useful in high temperature, corrosive environments, can be costly
and difficult. Further, direct preparation of filtration media from
microfilaments can also be difficult and costly. The method of the
invention overcomes these obstacles. According to the method, it is
possible to prepare a multicomponent fiber wherein one of the fiber
components will degrade at the conditions of the desired
application and the remaining components will remain intact at the
application conditions. The multicomponent fiber is used to prepare
a filtration media appropriate for the point of use (i.e., the
application site), and the filtration media is installed. A stream
for filtration is then passed through the filtration media under
application conditions (e.g., high temperature, corrosive
conditions). As the second fiber component is designed to degrade
at the application conditions, the second fiber component degrades,
leaving behind the first fiber component, which is preferentially
dimensioned to form a microfilament. Accordingly, the
multicomponent fiber is chemically dissociated, thereby forming a
microfilament filter at the point of use.
[0084] The novel composition of the multicomponent fiber of the
invention makes it particularly beneficial in the inventive method.
Preparation of the filter media as a larger fiber, instead of the
microfilament, simplifies preparation of the filtration media.
Further, the degraded second fiber component is easily removed
after degradation occurs at the application conditions. For
instance, in one embodiment, the degraded second fiber component is
entrained within filtered stream exiting the filtration media and
is thereby carried away from the filtration media by the stream
exiting the filter. In another embodiment, the degraded second
fiber component remains entrapped in the formed microfilament
filter as part of the filtered matter that is easily removed in a
later cleaning step. The later cleaning step can include any
cleaning method generally used in the art, such as mechanical
shaking, reverse flow (with or without heating), and pulse-jet
methods.
[0085] The method of the invention also lends itself to
customization of the pore size of the resultant microfilament
filter, thereby controlling the efficiency of the filter. Such
customization can occur through varying the ratio of the first
fiber component to the second fiber component in the multicomponent
fiber. Such ratio is generally within the ranges previously
described in relation to the multicomponent fiber. Preferably, the
ratio is such that the change in the porosity of the filtration
media through degradation of the second fiber component is not
sufficient to hinder the filtration performance of the resultant
microfilament filter. In a particular embodiment, the microfilament
filter prepared according to the method described herein exhibits a
filtration performance such that greater than or equal to about 99%
of particles having a diameter of 1 micron or greater are retained
by the microfilament filter.
[0086] Many modifications and other embodiments of the inventions
set forth herein will come to mind to one skilled in the art to
which these inventions pertain having the benefit of the teaching
presented in the foregoing descriptions and the associated
drawings. Therefore, it is to be understood that the inventions are
not to be limited to the specific embodiments disclosed and that
modifications and other embodiments are intended to be included
within the scope of the appended claims. Although specific terms
are employed herein, they are used in a generic and descriptive
sense only and not for purposes of limitation.
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