U.S. patent application number 09/956527 was filed with the patent office on 2002-01-31 for splittable multicomponent polyester fibers.
This patent application is currently assigned to Fiber Innovation Technology, Inc.. Invention is credited to Dugan, Jeffrey S., Harris, Frank O..
Application Number | 20020013111 09/956527 |
Document ID | / |
Family ID | 23568166 |
Filed Date | 2002-01-31 |
United States Patent
Application |
20020013111 |
Kind Code |
A1 |
Dugan, Jeffrey S. ; et
al. |
January 31, 2002 |
Splittable multicomponent polyester fibers
Abstract
Mechanically divisible multicomponent fibers are disclosed
having at least a first component comprised of poly(lactic acid)
polymer and at least a second component comprised of an aromatic
polyester. The multicomponent fibers are particularly useful in the
manufacture of nonwoven structures, and in particular nonwoven
structures used as synthetic suede.
Inventors: |
Dugan, Jeffrey S.; (Erwin,
TN) ; Harris, Frank O.; (Rogersville, 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: |
23568166 |
Appl. No.: |
09/956527 |
Filed: |
September 19, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09956527 |
Sep 19, 2001 |
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09396669 |
Sep 15, 1999 |
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Current U.S.
Class: |
442/335 ;
428/373; 428/374; 428/397; 442/340; 442/341; 442/347; 442/361 |
Current CPC
Class: |
Y10T 428/2929 20150115;
Y10T 442/609 20150401; Y10T 442/614 20150401; D04H 1/435 20130101;
D04H 1/43832 20200501; D01F 8/14 20130101; D04H 1/43912 20200501;
Y10T 442/622 20150401; D06N 3/0015 20130101; D04H 1/43914 20200501;
D04H 1/46 20130101; Y10T 442/637 20150401; Y10T 428/2931 20150115;
D04H 1/495 20130101; Y10T 156/1062 20150115; Y10T 442/615 20150401;
D04H 1/43838 20200501; Y10T 428/2913 20150115; D04H 1/43918
20200501; Y10T 428/2973 20150115 |
Class at
Publication: |
442/335 ;
428/373; 428/397; 428/374; 442/340; 442/341; 442/347; 442/361 |
International
Class: |
D02G 003/04; D04H
003/00; D02G 003/00 |
Claims
That which is claimed:
1. A splittable multicomponent fiber comprising: at least one
polymer component comprising a poly(lactic acid) polymer; and at
least one polymer component comprising an aromatic polyester
polymer, wherein said multicomponent fiber is dissociable by
mechanical means.
2. The fiber of claim 1, wherein said multicomponent fiber is
dissociable into a plurality of poly(lactic acid) microfilaments
and aromatic polyester microfilaments.
3. The fiber of claim 1, wherein said aromatic polyester polymer
comprises a polymer selected from the group consisting of
polyethylene terephthalate, polybutylene terephthalate,
polycyclohexane terephthalate, polyethylene napthalate, and
copolymers and mixtures thereof.
4. The fiber of claim 1, wherein said aromatic polyester is
poly(ethylene terephthalate).
5. The fiber of claim 1, wherein said fiber is selected from the
group consisting of pie/wedge fibers, segmented round fibers,
segmented oval fibers, segmented rectangular fibers, segmented
ribbon fibers, and segmented multilobal fibers.
6. The fiber of claim 5, wherein said fiber is a pie/wedge
fiber.
7. The fiber of claim 1, wherein the weight ratio of said
poly(lactic acid) polymer component to said aromatic polyester
polymer component ranges from about 80/20 to about 20/80.
8. The fiber of claim 7, wherein the weight ratio of said
poly(lactic acid) polymer component to said aromatic polyester
polymer component is about 65:35 to about 35:65.
9. The fiber of claim 1, wherein said fiber is selected from the
group consisting of continuous filaments, staple fibers, and
meltblown fibers.
10. The fiber of claim 9, wherein said fiber is a staple fiber.
11. The fiber of claim 1, wherein said multicomponent fiber is
dissociable by mechanical operations selected from the group
consisting of impinging the multicomponent fiber with high pressure
water, carding the multicomponent fiber, crimping the fiber, and
drawing the multicomponent fiber.
12. The fiber of claim 1, wherein said aromatic polyester polymer
is poly(ethylene terephthalate), the weight ratio of said
poly(lactic acid) polymer component to said poly(ethylene
terephthalate) polymer component is from about 65:35 to about
35:65, and the fiber has a pie/wedge configuration.
13. A fiber bundle comprising a plurality of aliphatic polyester
microfilaments and aromatic polyester microfilaments, said
microfilaments originating from a common multicomponent fiber.
14. The fiber bundle of claim 13, wherein said microfilaments are
prepared by mechanically dissociating aliphatic polyester and
aromatic polyester components of said multicomponent fiber.
15. The fiber bundle of claim 13, wherein said aliphatic polyester
microfilaments comprise poly(lactic acid).
16. The fiber bundle of claim 13, wherein said aliphatic polyester
microfilaments and said aromatic polyester microfilaments are
receptive to dyeing with disperse dye to provide a uniformly dyed
fiber bundle.
17. The fiber bundle of claim 13, wherein said aromatic polyester
microfilaments are formed of a polymer selected from the group
consisting of polyethylene terephthalate, polybutylene
terephthalate, polycyclohexane terephthalate, polyethylene
napthalate, and copolymers and mixtures thereof.
18. The fiber bundle of claim 17, wherein said aromatic polyester
is poly(ethylene terephthalate).
19. The fiber bundle of claim 18, wherein said microfilaments have
an average size ranging from about 0.05 to about 1.5 denier.
20. The fiber bundle of claim 13, wherein said fiber bundle
comprises about 8 to about 48 aliphatic polyester and aromatic
polyester microfilaments.
21. The fiber bundle of claim 13, wherein said fiber bundle is in
the form of staple fiber.
22. A yarn comprising the fiber bundle of claim 13.
23. A microfilament comprising poly(lactic acid), said
microfilament having an average size ranging from about 0.05 to
about 1.5 denier and a tenacity ranging from about 1.0 to about 5.5
gpd tenacity.
24. The microfilament of claim 23, wherein said poly(lactic acid)
microfilament is a continuous filament.
25. A yarn comprising the poly(lactic acid) microfilament of claim
23.
26. A fabric comprising a plurality of splittable multicomponent
fibers comprising at least one polymer component comprising a
poly(lactic acid) polymer and at least one polymer component
comprising an aromatic polyester polymer, wherein said
multicomponent fibers are dissociable by mechanical means.
27. A fabric comprising a plurality of poly(lactic acid)
microfilaments and aromatic polyester microfilaments.
28. The fabric of claim 27, wherein at least some of said
poly(lactic acid) microfilaments and said aromatic polyester
microfilaments originate from a common multicomponent fiber.
29. The fabric of claim 28, wherein at least some of said
poly(lactic acid) microfilaments and said aromatic polyester
microfilaments are prepared by mechanically dissociating
poly(lactic acid) components and aromatic polyester components of
said multicomponent fiber.
30. The fabric of claim 26 or 27, wherein said fabric is selected
from the group consisting of nonwoven fabrics, woven fabrics, and
knit fabrics.
31. The fabric of claim 26 or 27, wherein said fabric is a nonwoven
fabric selected from the group consisting of wet-laid nonwoven
fabrics, dry-laid nonwoven fabrics, and direct-laid nonwoven
fabrics.
32. The fabric of claim 26 or 27, wherein said fabric is a dry-laid
nonwoven fabric.
33. The fabric of claim 26 or 27, wherein said fabric is a
hydroentangled dry-laid nonwoven fabric.
34. The fabric of claim 26 or 27, wherein said fabric further
comprises a disperse dye.
35. A product comprising the fabric of claim 27, selected from the
group consisting of synthetic suede and filtration media.
36. The product of claim 35, wherein said product is synthetic
suede.
37. A method for producing uniformly dyeable microfilament fibers,
said method comprising: extruding a plurality of multicomponent
fibers comprising at least one polymer component comprising a
poly(lactic acid) polymer and at least one polymer component
comprising an aromatic polyester polymer; and mechanically
separating said multicomponent fibers to form a fiber bundle
comprising a plurality of poly(lactic acid) microfilaments and
aromatic polyester microfilaments.
38. The method of claim 37, further comprising the step of disperse
dyeing said poly(lactic acid) microfilaments and said aromatic
polyester microfilaments simultaneously.
39. The method of claim 38, further comprising the step of forming
a yarn of said microfilaments prior to said dyeing step.
40. A method for producing fabric, said method comprising:
extruding a plurality of multicomponent fibers comprising at least
one polymer component comprising a poly(lactic acid) polymer and at
least one polymer component comprising an aromatic polyester
polymer; forming a fabric from said multicomponent fibers; and
mechanically separating said multicomponent fibers to form a
plurality of poly(lactic acid) microfilaments and aromatic
polyester microfilaments, said separating step occurring prior to,
during, or after said fabric forming step.
41. The method of claim 40, further comprising the step of forming
a yarn of said multicomponent fibers following said extrusion step
and prior to said fabric forming step.
42. The method of claim 40, wherein said step of forming a fabric
comprises forming a woven fabric, forming a knit fabric, or forming
a nonwoven fabric.
43. The method of claim 40, further comprising after said extruding
step the steps of: forming a tow from a plurality of said
multicomponent fibers; drawing said tow; crimping said fibers;
chopping said drawn tow into staple fibers; and carding said
crimped staple fibers to form a carded fiber web.
44. The method of claim 43, further comprising the step of bonding
said carded fiber web to form a unitary nonwoven fabric.
45. The method of claim 44, wherein said bonding step is selected
from the group consisting of needle punching and
hydroentangling.
46. The method of claim 44, wherein said separating step occurs
simultaneously with at least one of said drawing step, crimping
step, chopping step, carding step and bonding step.
47. The method of claim 40, wherein said separating step occurs
prior to said fabric forming step.
48. The method of claim 40, wherein said separating step occurs
after said fabric forming step.
Description
FIELD OF THE INVENTION
[0001] The present invention is related to fine denier polyester
fibers. In particular, the invention is related to fine denier
polyester fibers obtained by splitting multi-component polyester
fibers and to fabrics made from such fine fibers.
BACKGROUND OF THE INVENTION
[0002] Polyester has long been recognized as a desirable material
for textile applications. Polyester fibers are readily formed into
woven, knit, and nonwoven fabrics. Polyester fabrics are
particularly attractive because they are economical, resilient,
insensitive to moisture, and have superior tensile properties. It
is further known that use of very fine denier polyester fibers
produces a softer fabric, among other benefits. As would be
expected, softness is considered to be a highly beneficial
attribute in apparel applications.
[0003] Melt extrusion processes for spinning continuous filament
and spunbond filaments from thermoplastic resins such as polyester
are well known in the art. Meltblown processes are also known for
spinning thermoplastic resins into fiber, in particular fine denier
fiber. In general, melt extrusion processes provide higher strength
fibers than microfibers produced using meltblown methods, which
impart less orientation to the polymer and employ a lower molecular
weight resin. However, it is difficult to produce fine denier
fibers, in particular fibers of 2 denier or less, using
conventional melt extrusion processes.
[0004] One avenue by which to overcome this difficulty 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. It is now widely known that
multicomponent fiber, also referred to as composite fiber, may be
split into fine 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 component microfilaments.
[0005] Typical known splittable multicomponent fibers containing
polyester include the polyester/nylon fibers described in U.S. Pat.
Nos. 4,239,720, 4,118,534, and 4,364,983.
[0006] Composite splittable polyester/olefin fibers are likewise
described in U.S. Pat. No. 5,783,503. Tricomponent dividable fibers
containing polyester are taught in U.S. Pat. No. 4,663,221.
[0007] A number of processes are known for separating 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.
[0008] A common process by which to divide a multicomponent fiber
involves mechanically working the fiber. Methods commonly employed
to work the fiber include drawing on godet rolls, beating or
carding. It is also known that fabric formation processes such as
needle punching or hydroentangling may supply sufficient energy to
a multicomponent fiber to effect separation. When mechanical action
is used to separate multicomponent fibers, the fiber components
must be selected to bond poorly with each other to facilitate
subsequent separation. In that vein, conventional opinion has been
that the polymer components must differ from each other
significantly to ensure minimal interfilamentary bonding. It is for
this reason that polymers having disparate chemistries, i.e., from
different chemical families, have been chosen as components for
mechanically dissociable composite fibers to date.
[0009] However, the use of such disparate chemistries is
problematic, as polymers from different chemical families accept
and retain dyestuffs differently. As an example, a nylon/polyester
multicomponent fiber would typically be dyed using two dyestuffs,
an acid dye for the nylon component and a disperse dye for the
polyester component. Typically, the dye processes required for
these dyestuffs are quite different, introducing process
inefficiencies. In addition, it is extraordinarily difficult to
match the color imparted to the respective components using
differing dyes. This dyeing phenomenon is noted in U.S. Pat. No.
4,118,534, in which a nylon/copolyester multicomponent fiber was
dyed with the "same color" acid and cationic dyes for the nylon and
copolyester components, respectively. The dyes produced different
colors on their respective microfilaments, giving rise to a "halo"
effect.
[0010] Currently, to produce fine denier fabrics having uniform
color, a multicomponent fiber comprised of a desired polymer and a
soluble polymer is formed. The soluble polymer is then dissolved
out of the composite fiber, leaving the desired microfilaments to
be dyed. U.S. Pat. No. 5,593,778 utilizes such a process, in which
a poly(lactic acid) copolymer component is dissolved away, thereby
providing fine denier copolyester filaments. A comparable process
is given in U.S. Pat. No. 4,663,221, in which a matrix component is
dissolved away using a solvent such as toluene, to yield a fiber
bundle comprised of polyurethane and polyester microfilaments. U.S.
Pat. No. 5,162,074 also describes this method in general terms,
recommending the use of polystyrene as a soluble component in the
production of fine denier filaments. In general, polystyrene is
soluble in hydrocarbon solvents, such as toluene.
[0011] The use of dissolvable matrixes to produce fine denier
filaments is problematic. First, the manufacturing yields are
inherently low because a significant portion of the
multiconstituent fiber must be destroyed to produce the
microfilaments. Secondly, the wastewater or spent hydrocarbon
solvent generated by such processes poses an environmental issue.
Third, the time required to dissolve the matrix component out of
the composite fiber further exacerbates manufacturing
inefficiencies.
[0012] Based on the foregoing, although a number of methods for
splitting multicomponent fibers to obtain fine denier filaments are
known, there is still need for improvement.
SUMMARY OF THE INVENTION
[0013] The present invention provides splittable multicomponent
fibers and fiber bundles which include a plurality of fine denier
filaments having many varied applications in the textile and
industrial sector. The fibers can exhibit many advantageous
properties, such as a soft, silk-like hand, high covering power,
and the like. Further the fiber bundles can be uniformly dyeable.
The present invention further provides fabrics formed of the
multicomponent fibers and fiber bundles, as well as an economical,
environmentally friendly process by which to produce fine denier
polyester filaments.
[0014] In particular, the invention provides mechanically divisible
or splittable fibers formed of polyester components. The fibers can
have a variety of configurations, including pie/wedge fibers,
segmented round fibers, segmented oval fibers, segmented
rectangular fibers, segmented ribbon fibers, and segmented
multilobal fibers. Further, the mechanically splittable
multicomponent fibers can be in the form of continuous filaments,
staple fibers, or meltblown fibers. The splittable fibers may be
dissociated by a variety of mechanical actions, such as impinging
with high pressure water, carding, crimping, drawing, and the
like.
[0015] In one particularly advantageous aspect of the invention,
the divisible multicomponent fiber includes at least one aliphatic
polyester component, advantageously poly(lactic acid), and at least
one aromatic polyester component. The polymer components are
dissociable by mechanical means to form a bundle of fine denier
polyester fibers. A particularly advantageous embodiment is a
splittable multicomponent fiber formed of equal parts of
poly(lactic acid) and poly(ethylene terephthalate) in a pie/wedge
configuration.
[0016] The instant invention also provides a fiber bundle which
includes a plurality of dissociated polyester microfibers of
different polyester compositions. Specifically the fiber bundle
include a plurality of aliphatic polyester microfilaments,
advantageously poly(lactic acid) microfilaments, and aromatic
polyester microfilaments. In general, the microfilaments of the
present invention range in size from 0.05 to 1.5 denier.
[0017] The multicomponent fibers can be formed into a variety of
textile structures, including nonwoven webs, either prior to or
after fiber dissociation. Fabrics made using the fine denier fibers
of the present invention are both economical to produce and behave
in important ways as fabrics made entirely of polyester. As noted
previously, earlier fabrics containing mechanically splittable
composite filaments were based on disparate component chemistries.
A typical conventional fabric produced from mechanically splittable
composite fibers includes nylon and poly(ethylene terephthalate)
microfilaments. As noted previously, such fabric must be dyed with
one dye for the polyester microfilaments and a second dye for the
nylon microfilaments. Often, this would require two separate dyeing
processes, and it is very difficult to match the shade of the two
fine denier fibers.
[0018] However, previous attempts to overcome this difficulty by
making mechanically splittable fibers from pairs of polyesters have
failed, because most polyesters have too high an affinity for each
other to allow the segments to be split easily. Surprisingly, the
inventors have found that an aliphatic polyester polymer,
advantageously poly(lactic acid), can be made into an
easily-splittable segmented fiber with aromatic polyesters, such as
poly(ethylene terephthalate). The resulting composite fiber can be
dyed with disperse dyes before or after splitting, thereby allowing
a one-step "union" dyeing. Union dyeing is a process in which the
same color is imparted to different fibers contained in a fabric by
means of a one bath process, thus providing fabric having a uniform
color.
[0019] Another aspect of the invention teaches fabrics formed from
mechanically splittable multicomponent fibers of poly(lactic acid)
and aromatic polyester components, as well as the methods by which
to produce such fabrics. In this aspect of the invention, the
multicomponent fibers can be divided into microfilaments either
prior to, during, or following fabric formation. Fabrics of the
present invention may generally be formed by weaving, knitting, or
nonwoven processes. Advantageously the fabric is a dry-laid
nonwoven fabric formed from the multicomponent fibers of the
present invention. Another advantageous fabric is a dry-laid
nonwoven fabric bonded by hydroentangling.
[0020] Products comprising the fabric of the present invention
provide further advantageous embodiments. Particularly preferred
products include synthetic suede fabrics and filtration media.
[0021] By providing fiber bundles comprised entirely of fine denier
polyester filaments, the present invention permits soft, uniformly
dyeable fabrics having a high degree of coverage to be economically
produced. In specific, the multiconstituent fibers of the present
invention allow the production of fabrics containing fine denier
polyester filaments which may be formed without hydrocarbon
solvents or extraordinary waste, and which may be dyed to a uniform
shade in a single dyeing operation.
[0022] Further understanding of the processes and systems of the
invention will be understood with reference to the brief
description of the drawings and detailed description which follows
herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIGS. 1A-1E are cross sectional views of exemplary
embodiments of multicomponent fibers in accordance with the present
invention;
[0024] FIGS. 2A and 2B are cross sectional and longitudinal views,
respectively, of an exemplary dissociated fiber in accordance with
one embodiment of the present invention;
[0025] FIG. 3 is a flow diagram illustrating a fabric formation
process according to one embodiment of the present invention;
and
[0026] FIG. 4 schematically illustrates one fabric formation
process of the invention which includes carding and hydroentangling
steps.
DETAILED DESCRIPTION OF THE INVENTION
[0027] 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. As an additional note, like
numbers refer to like elements throughout.
[0028] Referring now to FIG. 1, cross sectional views of exemplary
multicomponent fibers of the present invention are provided. The
multicomponent fibers of the invention, designated generally as 4,
include at least two structured polymeric components, a first
component 6, advantageously comprised of a poly(lactic acid)
polymer, and a second component 8, comprised of an aromatic
polyester polymer.
[0029] In general, multicomponent fibers are formed of two or more
polymeric materials which have been extruded together to provide
continuous contiguous polymer segments which extend down the length
of the fiber. For purposes of illustration only, the present
invention will generally be described in terms of a bicomponent
fiber. However, it should be understood that the scope of the
present invention is meant to include fibers with two or more
components. In addition, the term "fiber" as used herein means both
fibers of finite length, such as conventional staple fiber, as well
as substantially continuous structures, such as filaments, unless
otherwise indicated.
[0030] As illustrated in FIGS. 1A-1E, a wide variety of fiber
configurations that allow the polymer components to be free to
dissociate are acceptable. Typically, the fiber components are
arranged so as to form distinct unocclusive cross-sectional
segments along the length of the fiber so that none of the
components is physically impeded from being separated. One
advantageous embodiment of such a configuration is the pie/wedge
arrangement, shown in FIG. 1A. The pie/wedge fibers can be hollow
or non-hollow fibers. In particular, FIG. 1A provides a bicomponent
filament having eight alternating segments of triangular shaped
wedges of poly(lactic acid) components 6 and aromatic polyester
components 8. It should be recognized that more than eight or less
than eight segments can be produced in filaments made in accordance
with the invention. Other fiber configurations as known in the art
may be used, such as but not limited to, the segmented
configuration shown in FIG. 1B. Reference is made to U.S. Pat. No.
5,108,820 to Kaneko et al., U.S. Pat. No. 5,336,552 to Strack et
al., and U.S. Pat. No. 5,382,400 to Pike et al. for a further
discussion of multicomponent fiber constructions.
[0031] Further, the multicomponent fibers need not be conventional
round fibers. Other useful shapes include the segmented rectangular
configuration shown in FIG. 1C, the segmented oval configuration in
FIG. 1D, and the multilobal configuration of FIG. 1E. Such
unconventional shapes are further described in U.S. Pat. No.
5,277,976 to Hogle et al., and U.S. Pat. Nos. 5,057,368 and
5,069,970 to Largman et al.
[0032] Both the shape of the fiber and the configuration of the
components therein will depend upon the equipment which is used in
the preparation of the fiber, the process conditions, and the melt
viscosities of the two components. A wide variety of fiber
configurations are possible. As will be appreciated by the skilled
artisan, typically the fiber configuration is chosen such that one
component does not encapsulate, or only partially encapsulates,
other components.
[0033] Further, to provide dissociable properties to the composite
fiber, the polymer components are chosen so as to be mutually
incompatible. In particular, the polymer components do not
substantially mix together or enter into chemical reactions with
each 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,
preventing dissociation. In addition, 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, the polymers should be sufficiently incompatible so
that adhesion between the components is sufficiently weak, thereby
allowing ready separation upon the application of sufficient
external force.
[0034] In general, a first component of the fibers of the invention
includes an aliphatic polyester polymer. A particularly
advantageous component is comprised of poly(lactic acid) (PLA).
Further examples of aliphatic polyesters which may be useful in the
present invention include without limitation fiber forming polymer
formed from (1) a combination of an aliphatic glycol (e.g.,
ethylene, glycol, propylene glycol, butylene glycol, hexanediol,
octanediol or decanediol) or an oligomer of ethylene glycol (e.g.,
diethylene glycol or triethylene glycol) with an aliphatic
diarboxylic acid (e.g., succinic acid, adipic acid,
hexanedicarboxylic acid or decaneolicarboxylic acid) or (2) the
self condensation of hydroxy carboxylic acids other than
poly(lactic acid), such as polyhydroxy butyrate, polyethylene
adipate, polybutylene adipate, polyhexane adipate, and copolymers
containing them.
[0035] Poly(lactic acid) is particularly attractive for use in the
present invention because it is a relatively inexpensive
thermoplastic polyester resin having adequate heat resistance, with
a melting point of approximately 178.degree. C. In addition, the
use of poly(lactic acid) in splittable fibers is especially
advantageous because poly(lactic acid) develops tensile properties
which are comparable or improved in comparison to the polyester and
polyamide polymers traditionally employed in splittable fibers.
[0036] Poly(lactic acid) polymer is generally prepared by the
self-condensation of lactic acid. However, it will be recognized by
one skilled in the art that a chemically equivalent material may
also be prepared by the polymerization of lactide. Therefore, as
used herein, the term "poly(lactic acid) polymer" is intended to
represent the polymer that is prepared by either the polymerization
of lactic acid or lactide. Reference is made to U.S. Pat. Nos.
5,698,322; 5,142,023; 5,760,144; 5,593,778; 5,807,973; and
5,010,145, the entire disclosure of each of which is hereby
incorporated by reference.
[0037] Lactic acid and lactide are known to be asymmetrical
molecules, having two optical isomers referred to, respectively as
the levorotatory (hereinafter referred to as "L") enantiomer and
the dextrorotatory (hereinafter referred to as "D") enantiomer. As
a result, by polymerizing a particular enantiomer or by using a
mixture of the two enantiomers, it is possible to prepare polymers
that are chemically similar yet which have widely differing
properties. In particular, it has been found that by modifying the
stereochemistry of a poly(lactic acid) polymer, it is possible to
control the crystallinity of the polymer.
[0038] The degree of crystallinity of a PLA polymer is based on the
regularity of the polymer backbone and its ability to line up with
similarly shaped sections of itself or other chains. If even a
relatively small amount of D-enantiomer (of either lactic acid or
lactide), such as about 3 to about 4 weight percent, is
copolymerized with L-enantiomer (of either lactic acid or lactide),
the polymer backbone generally becomes irregularly shaped enough
that it cannot line up and orient itself with other backbone
segments of pure L-enantiomer polymer, thus reducing the
crystallinity of the polymer. Based on the foregoing, preferably
the amount of D-enantiomer present in the instant invention is such
that it lowers the fiber crystallinity sufficiently to provide
adequate toughness, yet does not detrimentally impact the fiber
formation process or resulting fabric properties. In addition,
hydrolyzed poly(lactic acid) is biodegradable. Polymer morphology
strongly effects the rate of biodegradation of the hydrolyzed
polymer. Therefore, as a precautionary measure, in applications in
which a minimal rate of degradation is desirable, the use of higher
molecular weight, highly crystalline PLA is recommended.
[0039] Advantageously, the PLA polymer also exhibits residual
monomer percents effective to provide desirable melt strength,
fiber mechanical strength, and fiber spinning properties. As used
herein, "residual monomer percent" refers to the amount of lactic
acid or lactide monomer that is unreacted yet which remains
entrapped within the structure of the entangled PLA polymer chain.
In general, if the residual monomer percent of a PLA polymer in a
component is too high, the component may be difficult to process
due to inconsistent processing properties caused by a large amount
of monomer vapor being released during processing that cause
variations in extrusion pressures. However, a minor amount of
residual monomer in a PLA polymer in a component may be beneficial
due to such residual monomer functioning as a plasticizer during a
spinning process. Thus, the PLA polymer generally exhibits a
residual monomer percent that is less than about 15 percent,
preferably less than about 10 percent, and more preferably less
than about 7 percent.
[0040] The second component of the fibers of the invention includes
an aromatic polyester polymer. As used herein, the term aromatic
polyester means a thermoplastic polyester polymer in which at least
one monomer contains at least one aromatic ring. Thermoplastic
aromatic polymers that are preferred include: (1) polyesters of
alkylene glycols having 2-10 carbon atoms and aromatic diacids; (2)
poly(alkylene naphthalates), which are polyesters of
2,6-naphthalenedicarboxylic acid and alkylene glycols, as for
example poly(ethylene naphthalate); and (3) polyesters derived from
1,4,-cyclohexanedimethanol and terephthalic acid, as for example
polycyclohexane terephthalate. In particular, the use of
poly(alkylene terephthalates), especially poly(ethylene
terephthalate) and poly(butylene terephthalate), is considered
beneficial. Poly(ethylene terephthalate) (PET) is particularly
advantageous. See also polymers set forth in WO 97/24916, the
entire disclosure of which is hereby incorporated by reference. PET
and other aromatic polyesters are commercially available from many
manufacturers, including Eastman Chemical Co.
[0041] Each of the polymeric components can optionally include
other components not adversely effecting the desired properties
thereof. Exemplary materials which could be used as additional
components would include, without limitation, pigments,
antioxidants, stabilizers, surfactants, waxes, flow promoters,
solid solvents, particulates, and other materials added to enhance
processability of the first and the second components. For example,
a stabilizing agent may be added to the poly(lactic acid) polymer
to reduce thermal degradation which might otherwise occur during
the poly(lactic acid) spinning process. The use of such stabilizing
agents is disclosed in U.S. Pat. No. 5,807,973, hereby incorporated
by reference. These and other additives can be used in conventional
amounts.
[0042] The weight ratio of the poly(lactic acid) component and the
aromatic polyester component can vary. Preferably the weight ratio
is in the range of about 10:90 to 90:10, more preferably from about
20:80 to about 80:20, and most preferably from about 35:65 to about
65:35. In addition, the dissociable multicomponent fibers of the
invention can be provided as staple fibers, continuous filaments,
or meltblown fibers.
[0043] In general, staple, multi-filament, and spunbond
multicomponent fibers formed in accordance with the present
invention can have a fineness of about 0.5 to about 100 denier.
Meltblown multicomponent filaments can have a fineness of about
0.001 to about 10.0 denier. Monofilament multicomponent fibers can
have a fineness of about 50 to about 10,000 denier. Denier, defined
as grams per 9000 meters of fiber, is a frequently used expression
of fiber diameter. A lower denier indicates a finer fiber and a
higher denier indicates a thicker or heavier fiber, as is known in
the art.
[0044] Dissociation of the multicomponent fibers provides a
plurality of fine denier filaments or microfilaments, each formed
of the different polymer components of the multicomponent fiber. As
used herein, the terms "fine denier filaments" and "microfilaments"
include sub-denier filaments and ultra-fine filaments. Sub-denier
filaments typically have deniers in the range of 1 denier per
filament or less. Ultra-fine filaments typically have deniers in
the range of from about 0.1 to 0.3 denier per filament. As
discussed previously, fine denier filaments of low orientation have
previously been obtained from relatively low molecular weight
polymers by meltblowing. The present invention provides much finer
polyester meltspun filament than previously available without the
use of solvents. In addition, the invention provides continuous
fine denier polyester filaments to be produced at commercial
throughputs from relatively high molecular weight polymers with
acceptable manufacturing yields.
[0045] FIG. 2 illustrates an exemplary multicomponent fiber of the
present invention which has been separated into a fiber bundle 10
of microfilaments as described above. In the illustrated example,
the multicomponent fiber has been divided into four poly(lactic
acid) microfilaments 6 and four aromatic polyester microfilaments
8, thereby providing an eight filament fiber bundle. In a typical
example, a multicomponent fiber having 4 to 24, preferably 8 to 20,
segments is produced. Generally, the tenacity of the multicomponent
fiber ranges from about 1 to about 5.5, advantageously from about
2.0 to about 4.5 grams/denier (gpd). The tenacity of the
poly(lactic acid) microfilaments produced in accordance with the
present invention can range from about 1.0 to about 5.5 gpd, and
typically from about 2.5 to about 4.5, while tenacity for the
aromatic polyester fine denier filaments can range from about 1 to
about 5.5, typically from about 2.0 to about 4.0 gpd. Grams per
denier, a unit well known in the art to characterize fiber tensile
strength, refers to the force in grams required to break a given
filament or fiber bundle divided by that filament or fiber bundle's
denier.
[0046] It was altogether unexpected that this particular
combination of polymer components would readily dissociate when
subjected to sufficient mechanical action. Heretofore, mechanically
divisible fibers have been comprised of widely differing polymer
types to ensure adequate dissociation. It is surprising that the
multicomponent fibers of the present invention, comprised of
components from the same chemical family, namely polyesters, would
be capable of splitting into fine denier component filaments. While
not wishing to be bound by any theory, it is believed that,
although both components are polyesters, the difference in aromatic
character between the components gives rise to sufficient
incompatibility to allow mechanical splitting-to occur.
[0047] The multicomponent fibers of the present invention may be
dissociated into separate aliphatic polyester microfilaments (such
as poly(lactic acid) microfilaments) and aromatic polyester
microfilaments by any means that provides sufficient flex or
mechanical action to the fiber to fracture and separate the
components of the composite fiber. As used herein, the terms
"splitting," "dissociating," or "dividing" 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 illustrated in
FIG. 2, the fine denier components can remain in proximity to the
remaining components as a coherent fiber bundle 10 of fine denier
poly(lactic acid) microfilaments 6 and aromatic polyester
microfilaments 8. 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 fibers
originating from a common fiber source may be further removed from
one another. Further, the terms "splitting," dissociating," or
"dividing" as used herein also include partial splitting.
[0048] Turning now to FIG. 3, an exemplary process for making a
fabric in accordance with one embodiment of the invention is
illustrated. 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.
[0049] The extrusion process 14 for making multicomponent
continuous filament fibers is well 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 Hills U.S. Pat. No. 5,162,074, the
contents of which are incorporated herein by reference in their
entirety.
[0050] In the present invention, an aliphatic polyester polymer,
such as poly(lactic acid) polymer, stream and an aromatic polyester
polymer stream are fed into the polymer distribution system. In one
advantageous embodiment, a polylactic acid polymer stream and a
poly(ethylene terephthalate) stream are employed. The polymers
typically are selected to have melting temperatures such that the
polymers can be spun at 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.
[0051] 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, as is known in that
art.
[0052] Rather than being taken up on a godet, continuous
multicomponent fiber may also be melt spun as a direct laid
nonwoven web. In a spunbond process, for example, the strands are
collected in a jet, such as an air jet or air attenuator, following
extrusion through the die and then blown onto a take-up surface
such as a roller or a moving belt to form a spunbond web. As an
alternative, 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.
[0053] Regardless of the type of melt spinning procedure which is
used, typically the thin fluid streams are 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.
[0054] When a continuous filament or staple process is employed, it
may be desirable to subject the strands to a draw process 16. 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. As is
known in the art, draw ratios of 2.0 to 5.0 times are typical for
polyester fibers. Optionally, the drawn strands may be heat set, to
reduce any latent shrinkage imparted to the fiber during
processing, as is further known in the art.
[0055] Following drawing in the solid state, the continuous
filaments can be cut into a desirable fiber length in a staple
process 18. 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 to
Taniguchi et al. and U.S. Pat. No. 5,336,552 to Strack et al.
Optionally, the fibers may be subjected to a crimping process prior
to the formation of staple fibers, as is known in the art. Crimped
composite fibers are 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.
[0056] The staple fiber thus formed is then fed into a carding
process 20. A more detailed schematic illustration of a carding
process is provided in FIG. 4. As shown in FIG. 4, the carding
process can include the step of passing staple tow 26 through a
carding machine 28 to align the fibers of the staple tow 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 staple tow
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.
[0057] Referring back to FIG. 3, in one advantageous embodiment of
the invention, carded fiber web 32 is subjected to a fabric
formation process to impart cohesion to the fiber web. In one
aspect of that 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.
[0058] In a preferred embodiment of the present invention, a
hydroentangled nonwoven fabric is provided. A schematic of one
hydroentangling process suitable for use in the present invention
is provided in FIG. 4. As shown in FIG. 4, 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.
[0059] 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 to Evans, 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 1800 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.
[0060] 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. Such methods are well known in the art.
[0061] In addition, rather than producing a dry-laid nonwoven
fabric, an aspect of which was previously described, a nonwoven 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., Buntin et al., U.S. Pat.
No. 3,987,185; Buntin, U.S. Pat. No. 3,972,759; and McAmish et al.,
U.S. Pat. No. 4,622,259. The fiber of the present invention may
also be formed into a wet-laid nonwoven fabric, via any suitable
technique known in that art.
[0062] 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 continuous filaments or
spun yarns comprising staple fibers of the present invention by
methods known in the art, such as twisting or air entanglement.
[0063] In one advantageous embodiment of the invention, the fabric
formation process is used to dissociate the multicomponent fiber
into microfilaments. 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 shown in FIG. 2,
and described previously. In a particularly advantageous aspect of
the invention, the hydroentangling process used to form the
nonwoven fabric dissociates the composite fiber. In the
alternative, the carding, drawing, or crimping processes previously
described may be used to split the multicomponent fiber.
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.
[0064] Fabrics and yarns produced in accordance with the instant
invention may optionally be dyed. In general, polyester fibers lack
the reactive cites possessed by many types of fibers, and are thus
typically dyed with disperse dyes. The disperse dyeing process
physically entraps dye in the fiber, and is performed at high
temperatures or by the use of swelling agents and carriers, as is
well known in that art. A wide variety of polyesters may be dyed
using disperse dye processes, including the poly(lactic acid) and
aromatic polyesters employed in the present invention. In
particular, the fabrics of the present invention may be dyed by
means of a thermosol process, in which a disperse dye is applied to
the fabric as a water emulsion, dried, and passed through a hot
flue or over heated rollers at about 400.degree. F. to sublime the
dyestuff into the polyester fiber. See the Encyclopedia of Science
and Technology.
[0065] Because they are simultaneously dyed by a common dye in a
common dye process, the poly(lactic acid) and aromatic polyester
components comprising the composite fiber are dyed uniformly, that
is, to the same hue. Non-uniform dyeing, in which microfilaments of
disparate chemistries resulting from splitting a multicomponent
fiber are dyed to different shades, gives rise to an unwanted
heather or "halo" appearance. In addition to a uniform initial
appearance, the poly(lactic acid) and aromatic polyester
microfilarnents of the present invention are expected to maintain
an equivalent hue to one another as the fabric which they comprise
is exposed to light, laundering, abrasion, and aging.
[0066] The fabrics of the present invention provide a combination
of desirable properties of conventional fine denier fabrics and
highly oriented fiber fabrics. These properties include fabric
uniformity, uniform fiber coverage, good barrier properties and
high fiber surface area. The fabrics of the present invention also
exhibit highly desirable strength properties, desirable hand and
softness, and can be produced to have different levels of loft. In
addition to the foregoing benefits, fabric of the present invention
may also be uniformly dyed and economically produced.
[0067] Beneficial products can be produced with the fabrics of the
present invention, as well. In particular, nonwoven fabrics formed
from the multicomponent fibers of the invention are suitable for a
wide variety of end uses. In one particularly advantageous
embodiment, nonwoven fabric of the instant invention may be used as
a synthetic suede. In this embodiment, the microfilaments
comprising the nonwoven fabric provide the recovery properties,
appealing hand, and tight texture required in synthetic suedes. In
addition, nonwoven articles produced in accordance with the
invention possess adequate strength, superior barrier and cover.
Based on these properties, nonwoven fabrics made with the
splittable filaments of the instant invention should readily find
use as filtration media, producing long life filters for filtering
lubrication oils and the like. Other applications include garments
(especially synthetic suedes), upholstery and wiping cloths.
[0068] The present invention will be further illustrated by the
following non-limiting example.
EXAMPLE 1
[0069] Continuous multifilament melt spun fiber is produced using a
bicomponent extrusion system. A sixteen segment pie/wedge
bicomponent fiber is produced having eight segments of poly(lactic
acid) polymer and eight segments of PET polymer. The weight ratio
of PET polymer to poly(lactic acid) polymer in the bicomponent
fibers is 50/50. The PET employed is a 0.55 I.V. polyester,
commercially available as Tairilyn polyester from Nan Ya. The
poly(lactic acid) polymer is EcoPLA 5019B from Cargill Dow
Polymers.
[0070] Following extrusion, the filaments are subsequently drawn
3.2 times, thereby yielding a 3 denier multifilament multicomponent
fiber. The fiber is then crimped and cut to 11/2 inch length staple
fiber. This staple fiber is carded to form a web that is
subsequently hydroentangled using water jets operating at 200 bar
pressure. The water jets simultaneously entangle the fibers to give
the web strength and split the fibers substantially into individual
poly(lactic acid) and polyester microfibers. The resulting fabric
has a luxurious hand and drape and a small pore size.
[0071] Many modifications and other embodiments of the invention
will come to mind to one skilled in the art to which this invention
pertains having the benefit of the teachings presented in the
foregoing descriptions and the associated drawings. Therefore, it
is to be understood that the invention is 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.
* * * * *