U.S. patent application number 11/290145 was filed with the patent office on 2007-05-31 for surface modified bi-component polymeric fiber.
This patent application is currently assigned to The Dow Chemical Company. Invention is credited to Edward Knickerbocker, Hong Peng, Randy E. Pepper, Jozef J. Van Dun.
Application Number | 20070122614 11/290145 |
Document ID | / |
Family ID | 37769418 |
Filed Date | 2007-05-31 |
United States Patent
Application |
20070122614 |
Kind Code |
A1 |
Peng; Hong ; et al. |
May 31, 2007 |
Surface modified bi-component polymeric fiber
Abstract
The present invention provides a bicomponent fiber having
increased surface roughness. The fiber includes a first polymer and
a composite, wherein the composite forms a layer which forms at
least a portion of the fiber's surface. The composite is formed by
a second polymer and a filler, where an average particle size of
the filler can be greater than a thickness of the layer formed by
the composite. The fibers can have a round, oval, trilobal,
triangular, dog-boned, flat or hollow shape and a symmetrical or
asymmetrical sheath/core or side-by-side configuration. When the
fiber has a sheath/core configuration, the composite can form the
sheath, and the average particle size of the filler can be greater
than the thickness of the sheath.
Inventors: |
Peng; Hong; (Lake Jackson,
TX) ; Van Dun; Jozef J.; (Zandhoven, BE) ;
Pepper; Randy E.; (Lake Jackson, TX) ; Knickerbocker;
Edward; (Lake Jackson, TX) |
Correspondence
Address: |
OSHA LIANG L.L.P.
1221 MCKINNEY STREET
SUITE 2800
HOUSTON
TX
77010
US
|
Assignee: |
The Dow Chemical Company
Midland
MI
|
Family ID: |
37769418 |
Appl. No.: |
11/290145 |
Filed: |
November 30, 2005 |
Current U.S.
Class: |
428/374 ;
264/464; 428/373 |
Current CPC
Class: |
D01F 8/06 20130101; Y10T
428/2931 20150115; Y10T 428/2929 20150115; D01F 1/10 20130101 |
Class at
Publication: |
428/374 ;
428/373; 264/464 |
International
Class: |
D02G 3/36 20060101
D02G003/36; D02G 3/02 20060101 D02G003/02; D02G 3/22 20060101
D02G003/22 |
Claims
1. A bicomponent fiber having increased surface roughness
comprising: a first polymer; and a composite comprising a second
polymer and a filler, wherein the composite forms a layer that
forms at least a portion of the fiber's surface, and wherein an
average particle size of the filler is greater than a thickness of
the layer formed by the composite.
2. The bicomponent fiber of claim 1, wherein the bicomponent fiber
has a sheath/core configuration, the sheath comprising the
composite, the core comprising the first polymer, and wherein a
thickness of the sheath is less than an average particle size of
the filler.
3. The bicomponent fiber of claim 1, wherein the first polymer is
selected from the group consisting of a polyolefin, a di-block,
tri-block or multi-block elastomeric copolymer, a polyurethane, a
polyamide, a polyester, or combinations thereof.
4. The bicomponent fiber of claim 3, wherein the di-block,
tri-block, or multi-block elastomeric copolymer is selected from
the group consisting of styrene-isoprene-styrene,
styrene-butadiene-styrene, styrene-ethylene/butylene-styrene,
styrene-ethylene/propylene-styrene, or combinations thereof.
5. The bicomponent fiber of claim 1, wherein the first polymer
comprises a polyolefin.
6. The bicomponent fiber of claim 5, wherein the polyolefin is a
homogenously branched polyolefin.
7. The bicomponent fiber of claim 5, wherein the polyolefin is
derived from at least one monomer selected from the group
consisting of ethylene, propylene, 1-butene, 1-hexene, 1-octene,
4-methyl-1-pentene, butadiene, cyclohexene, dicyclopentadiene,
styrene, toluene, alpha-methylstyrene, or combinations thereof.
8. The bicomponent fiber of claim 1, wherein the composite
comprises an elastomeric polymer.
9. The bicomponent fiber of claim 8, wherein the elastomeric
polymer is selected from the group consisting of a homogenously
branched polyolefin, a di-block, tri-block or multi-block
elastomeric copolymer, a polyurethane, a polyamide, a polyester, or
combinations thereof.
10. The bicomponent fiber of claim 9, wherein the polyolefin is
derived from at least one monomer selected from the group
consisting of ethylene, propylene, 1-butene, 1-hexene, 1-octene,
4-methyl-1-pentene, butadiene, cyclohexene, dicyclopentadiene,
styrene, toluene, alpha-methylstyrene, or combinations thereof.
11. The bicomponent fiber of claim 1, wherein the filler is
selected form the group consisting of silica, alumina, calcium
carbonate, silicon dioxide, a clay, or combinations thereof.
12. The bicomponent fiber of claim 1, wherein the filler comprises
calcium carbonate.
13. The bicomponent fiber of claim 1 1, wherein the filler is
coated with a compatibilizer.
14. The bicomponent fiber of claim 13, wherein the compatibilizer
is stearic acid.
15. The bicomponent fiber of claim 1, wherein the composite
comprises from about 1 to about 20 weight percent of the fiber.
16. The bicomponent fiber of claim 15, wherein the composite
comprises from about 5 to about 15 weight percent of the fiber.
17. The bicomponent fiber of claim 1, wherein the filler comprises
from about 1 to about 25 weight percent of the composite.
18. The bicomponent fiber of claim 1, wherein the filler comprises
from about 3 to about 15 weight percent of the composite.
19. The bicomponent fiber of claim 1, wherein the average particle
size of the filler ranges from about 0.1 to about 20 microns.
20. The bicomponent fiber of claim 1, wherein a ratio of the
average particle size of the filler to the composite layer
thickness is greater than 1 and less than 2.
21. The bicomponent fiber of claim 20, wherein a ratio of the
average particle size of the filler to the composite layer
thickness is from 1.2 to 1.8.
22. The bicomponent fiber of claim 1, wherein a particle size
distribution of the filler is less than 3.0.
23. The bicomponent fiber of claim 22, wherein a particle size
distribution of the filler is less than 2.0.
24. The bicomponent fiber of claim 1: wherein a ratio of a filler
particle center to center distance (L) to the average particle size
(d) of the filler a) is between about 3 and about 6 when the
average particle size is less than 1 micron, or b) is between about
2 and about 4 when the average particle size of the filler is 1
micron or greater; wherein the center to center distance (L) is
calculated as equal to (0.8/.alpha..sub.av).sup.1/2d, where aav is
the ratio of particle volume percentage to the polymer matrix
volume percentage.
25. The bicomponent fiber of claim 1, wherein the fiber is
elastic.
26. The bicomponent fiber of claim 1, wherein the fiber is
crosslinked.
27. An article comprising the fiber of claim 1.
28. A method of forming a bicomponent fiber comprising: blending a
first polymer and a filler to form a composite; coextruding under
thermal bonding conditions a second polymer and the composite to
form the bicomponent fiber; wherein the second polymer forms the
polymeric core and the composite forms a layer that forms at least
a portion of a surface of the fiber; and wherein an average
particle size of the filler is greater than a thickness of the
composite layer.
29. The method of claim 28 wherein the coextruding comprises
forming a fiber having a round, oval, trilobal, triangular,
dog-boned, flat or hollow shape and a symmetrical or asymmetrical
sheath/core or side-by-side configuration.
30. The method of claim 29 wherein the bicomponent fiber has a
round shape and a sheath/core configuration.
31. In a method for manufacturing a bicomponent fiber by
coextruding under thermal bonding conditions (a) a first polymer,
and (b) a second polymer which forms a layer which forms at least a
portion of the fiber's surface, the improvement comprising:
blending a filler with the second polymer to form a composite;
wherein the average particle size of the filler is greater than a
thickness of the layer formed by the composite.
32. A bicomponent fiber comprising a composite comprising a polymer
and a filler wherein a composite forms a layer that forms at least
a portion of the fiber's surface, and wherein an average particle
size of the filler is greater than a thickness of the layer formed
by the composite.
Description
BACKGROUND OF INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates generally to fibers and processes to
produce the same. More specifically, the invention relates to
synthetic fibers having increased surface roughness and an improved
hand feel.
[0003] 2. Background Art
[0004] Many forms of fibers and fabrics have been made from
thermoplastics. The properties of the fibers and fabrics are a
function, at least in part, of the polymer(s) from and the
processes by which they are made. Representative of these various
polymers, fiber and fabric types, and processes for making the
fibers and fabrics are those described in U.S. Pat. Nos. 4,076,698,
4,644,045, 4,830,907, 4,909,975, 4,578,414, 4,842,922, 4,990,204,
5,112,686, 5,322,728, 4,425,393, 5,068,141 and 6,190,768. the
entirety of each is incorporated herein by reference.
[0005] Mineral additives can advantageously be used to affect the
properties of the fibers produced from thermoplastics. For example,
in U.S. Pat. No. 4,254,182 fibers are produced by incorporating
silica ranging in size from 10 to 200 millimicrons. The silica is
then extracted from the fiber to produce surface irregularities or
recesses in the fiber.
[0006] As a result, the effective fiber surface area and
coefficient of friction can be increased, which can reduce the
slick, waxy feel, the glossy appearance, and the perception of
color depth of the fiber.
[0007] Minerals have also been encapsulated in a polymer to form a
composite and to achieve a desired physical property benefit. U.S.
Pat. No. 6,797,377 describes fibers made from a thermoplastic
polymer (particularly polypropylene) containing titanium dioxide,
wax and at least one mineral filler, such as kaolin or calcium
carbonate. The fillers are added in an amount such that the fillers
become encapsulated within the polymeric material. It is also noted
from the patent that when a mixture of oil and minerals is added
together to the polypropylene, the softness of web is improved
while the tensile strength of the web is generally reduced.
[0008] U.S. Pat. Nos. 5,413,655 and 5,344,862 describe the use of
silica as an encapsulated additive in mono-component fibers for
nonwoven applications. The additive system includes two components:
polysiloxane polyether and hydrophobic fumed silica. The silica is
added in an amount from 3 to 1500 ppm of the thermoplastic
polyolefin, and the polyether is added in an amount from 0.1 to 3
weight percent of the thermoplastic polyolefin. The claimed benefit
is a significant increase of tensile strength of spunbond nonwoven
fabrics.
[0009] Accordingly, there exists a need to improve the cloth-like
perception (natural fiber feel) of synthetic fibers.
SUMMARY OF INVENTION
[0010] In one aspect, the present invention relates to a
bicomponent fiber having increased surface roughness. The
bicomponent fiber can comprise a first polymer and a composite. The
composite can form a layer which forms at least a portion of the
fiber's surface. The composite can comprise a second polymer and a
filler. An average particle size of the filler can be greater than
a thickness of the layer formed by the composite.
[0011] The present invention also provides a method of forming a
bicomponent fiber including the steps of blending a first polymer
and a filler to form a composite, and coextruding under thermal
bonding conditions a second polymer and the composite to form the
bicomponent fiber. The second polymer may form the polymeric core,
and the composite may form a layer that forms at least a portion of
a surface of the fiber. An average particle size of the filler may
be greater than a thickness of the composite layer.
[0012] The present invention also provides an improvement of a
method for manufacturing a bicomponent fiber including coextruding
under thermal bonding conditions (a) a first polymer, and (b) a
second polymer which forms a layer which forms at least a portion
of the fiber's surface. The improvement includes blending a filler
with the second polymer to form a composite, wherein the average
particle size of the filler is greater than a thickness of the
layer formed by the composite.
[0013] Other aspects and advantages of the invention will be
apparent from the following description and the appended
claims.
BRIEF DESCRIPTION OF DRAWINGS
[0014] FIG. 1 is a schematic representation of an embodiment of the
core/sheath bicomponent fibers of the present invention.
[0015] FIG. 2 is a schematic representation of an embodiment of the
side-by-side bicomponent fibers of the present invention.
[0016] FIG. 3 illustrates simplified particle distribution formats
used in developing a model useful in manufacturing embodiments of
the bicomponent fibers of the present invention.
[0017] FIGS. 4 through 6 are SEM pictures of embodiments of the
bicomponent fibers of the present invention.
DETAILED DESCRIPTION
[0018] Typical synthetic fibers, which are extruded and drawn, have
a very smooth surface with very few imperfections, thus creating a
slick, oily feel. In one aspect, embodiments of the invention
relate to modifying fiber surface roughness to improve the hand
feeling perception of synthetic fibers. The present invention
provides a method to impart surface roughness to synthetic fibers,
where the surface roughness extending out of the sheath of a
bicomponent fiber results in an improved hand feel perception,
decreasing the slick, oily feel of the fiber. In one embodiment,
adding mineral fillers such as calcium carbonate (CaCO.sub.3) to
the polymeric sheath, where the mineral fillers have an average
particle size being greater than sheath thickness, can provide a
"stick-out" effect, providing a rougher surface, and improving the
hand feel perception.
[0019] General Definitions
[0020] As used herein, a "fiber" means a material in which the
length to diameter ratio is greater than about 10. Fibers are
typically classified according to their diameter. A filament fiber
is generally defined as having an individual fiber diameter greater
than about 15 denier, usually greater than about 30 denier. A fine
denier fiber generally refers to a fiber having a diameter less
than about 15 denier. Microdenier fiber is generally defined as
fiber having a diameter less than about 100 microns.
[0021] "Filament fiber" or "monofilament fiber" means a continuous
strand of material of indefinite (i.e., not predetermined) length,
as opposed to a "staple fiber" which is a discontinuous strand of
material of definite length (i.e., a strand which has been cut or
otherwise divided into segments of a predetermined length).
[0022] "Polyolefin polymer" means a thermoplastic polymer derived
from one or more olefins. The polyolefin polymer can bear one or
more substituents, e.g., a functional group such as a carbonyl,
sulfide, etc. For purposes of this invention, "olefins" include
aliphatic, alicyclic and aromatic compounds having one or more
double bonds.
[0023] Representative olefins include ethylene, propylene,
1-butene, 1-hexene, 1-octene, 4-methyl-1-pentene, butadiene,
cyclohexene, dicyclopentadiene, styrene, toluene,
alpha-methylstyrene and the like.
[0024] "Temperature-stable" and similar terms mean that the fiber
or other structure or article comprising the polyolefin polymer of
this invention will substantially maintain its elasticity during
repeated extensions and retractions after exposure to about
90.degree. C. (about 200.degree. F.), e.g., temperatures such as
those experienced during the manufacture, processing (e.g., dying)
and/or cleaning of a fabric made from the structure or article.
[0025] "Elastic" means that a fiber will recover at least about 50
percent of its stretched length after the first pull and after the
fourth to 100 percent strain (doubled the length). Elasticity can
also be described by the "permanent set" of the fiber. Permanent
set is the converse of elasticity. A fiber is stretched to a
certain point and subsequently released to the original position
before stretch, and then stretched again. The point at which the
fiber begins to pull a load is designated as the percent permanent
set. "Elastic materials" are also referred to in the art as
"elastomers" and "elastomeric". Elastic material (sometimes
referred to as an elastic article) includes a polyolefin polymer
itself as well as, but not limited to, the polyolefin polymer in
the form of a fiber, film, strip, tape, ribbon, sheet, coating,
molding and the like. The preferred elastic material is fiber. The
elastic material can be cured or uncured, radiated or unradiated,
and/or crosslinked or uncrosslinked.
[0026] "Nonelastic material" means a material, such as a fiber,
that is not elastic as defined above.
[0027] "Substantially crosslinked" and similar terms mean that the
polyolefin polymer, shaped or in the form of an article, has xylene
extractables of less than or equal to 70 weight percent (i.e.,
greater than or equal to 30 weight percent gel content), preferably
less than or equal to 40 weight percent (i.e., greater than or
equal to 60 weight percent gel content). Xylene extractables (and
gel content) are determined in accordance with ASTM D-2765.
[0028] "Cured" and "substantially cured" mean that the polyolefin
polymer, shaped or in the form of an article, was subjected or
exposed to a treatment which induced substantial crosslinking. The
fibers of the present invention can be cured or crosslinked by
various methods known to those skilled in the art.
[0029] "Curable" and "crosslinkable" mean that the polyolefin
polymer, shaped or in the form of an article, is not cured or
crosslinked and has not been subjected or exposed to treatment that
has induced substantial crosslinking (although the polyolefin
polymer, shaped or in the form of an article, comprises additive(s)
or functionality which will effectuate substantial crosslinking
upon subjection or exposure to such treatment). In the practice of
this invention, curing, irradiation or crosslinking can be
accomplished by UV-radiation.
[0030] "Homofil fiber" means a fiber that has a single polymer
region or domain, and that does not have any other distinct polymer
regions (as do bicomponent fibers).
[0031] "Bicomponent fiber" means a fiber that has two or more
distinct polymer regions or domains. Bicomponent fibers are also
known as conjugated or multicomponent fibers.
[0032] The polymers are usually different from each other although
two or more components may comprise the same polymer. The polymers
are arranged in substantially distinct zones across the
cross-section of the bicomponent fiber, and usually extend
continuously along the length of the bicomponent fiber. The
configuration of a bicomponent fiber can be, for example, a
sheath/core arrangement (in which one polymer is surrounded by
another), a side by side arrangement, a pie arrangement or an
"islands-in-the sea" arrangement. Bicomponent fibers are further
described in U.S. Pat. Nos. 6,225,243, 6,140,442, 5,382,400,
5,336,552 and 5,108,820. These patents are incorporated by
reference in their entirety.
[0033] "Meltblown fibers" are fibers formed by extruding a molten
thermoplastic polymer composition through a plurality of fine,
usually circular, die capillaries as molten threads or filaments
into converging high velocity gas streams (e.g. air) which function
to attenuate the threads or filaments to reduced diameters. The
filaments or threads are carried by the high velocity gas streams
and deposited on a collecting surface to form a web of randomly
dispersed fibers with average diameters generally smaller than 10
microns.
[0034] "Meltspun fibers" are fibers formed by melting at least one
polymer and then drawing the fiber in the melt to a diameter (or
other cross-section shape) less than the diameter (or other
cross-section shape) of the die.
[0035] "Spunbond fibers" are fibers formed by extruding a molten
thermoplastic polymer composition as filaments through a plurality
of fine, usually circular, die capillaries of a spinneret. The
diameter of the extruded filaments is rapidly reduced, and then the
filaments are deposited onto a collecting surface to form a web of
randomly dispersed fibers with average diameters generally between
about 7 and about 30 microns.
[0036] "Nonwoven" means a web or fabric having a structure of
individual fibers or threads which are randomly interlaid, but not
in an identifiable manner as is the case of a knitted fabric. The
elastic fiber of the present invention can be employed to prepare
nonwoven structures as well as composite structures of elastic
nonwoven fabric in combination with nonelastic materials.
[0037] "Yam" means a continuous length of twisted or otherwise
entangled filaments which can be used in the manufacture of woven
or knitted fabrics and other articles. Yarn can be covered or
uncovered. Covered yarn is yarn at least partially wrapped within
an outer covering of another fiber or material, typically a natural
fiber such as cotton or wool. As here used, "fiber" or "fibrous"
means a particulate material in which the length to diameter ratio
of such material is greater than about 10. Conversely, "nonfiber"
or "nonfibrous" means a particulate material in which the length to
diameter ratio is about 10 or less.
[0038] Fiber and other Article Manufacture
[0039] The present inventors have advantageously discovered that
bicomponent fibers having improved hand feel can be manufactured by
modifying the fiber surface roughness. A bicomponent fiber may
include at least two components, i.e., those having at least two
distinct polymeric regimes. The first component, i.e., "Component
A", serves the purpose of generally retaining the fiber form during
thermal bonding at elevated temperatures. The second component,
i.e., "Component B", serves the function of an adhesive. Component
A can have a higher melting point than Component B. For example, in
one embodiment, Component A can have a melt temperature at least
about 20.degree. C., preferably at least 40.degree. C., higher than
the temperature at which component B will melt. In other
embodiments, Component A and Component B can have similar melting
points. In yet other embodiments, component B can have a higher
melting point than Component A.
[0040] For simplicity, the structure of the bicomponent fibers will
be referred to herein as a core/sheath structure. However, the
structure of the fiber can have any one of a number of
multi-component configurations, as described above, such as
core/sheath, side by side, pie or "islands-in-the sea"
arrangements, where Component B forms a layer which forms at least
a portion of the surface of the fiber.
[0041] In some embodiments, the core (Component A) may include a
thermoplastic polymer, such as a polyolefin. In other embodiments,
the core may include an elastomeric polymer illustrative of which
are homogenously branched polyolefins, di-block, tri-block or
multi-block elastomeric copolymers such as olefinic copolymers such
as styrene-isoprene-styrene, styrene-butadiene-styrene,
styrene-ethylene/butylene-styrene or
styrene-ethylene/propylene-styrene; polyurethanes; polyamides; and
polyesters. In certain embodiments, the core may include the olefin
block copolymers disclosed in WO2005/090427, herein incorporated by
reference.
[0042] The sheath (the adhesive or Component B) may also be
elastomeric, such as a homogeneously branched polyolefin,
preferably a homogeneously branched ethylene or propylene. These
materials are well known. For example, U.S. Pat. No. 6,140,442
provides an excellent description of homogeneously branched,
substantially linear polyolefins, especially ethylene polymers; the
contents of which are herein incorporated by reference.
[0043] Mineral fillers may be added to the sheath to form a
composite and to enhance desired properties. In preferred
embodiments, the average particle size of the mineral filler is
greater than the sheath thickness, providing a "stick-out" effect.
The "stick-out" effect can be illustrated for a core/sheath
bicomponent fiber as shown in FIG. 1, where a polymeric core 10 is
surrounded by a composite sheath that includes a polymeric matrix
12 and mineral filler 14. FIG. 2 illustrates the "stick-out" effect
for a side-by-side bicomponent fiber. Other forms of bicomponent
fibers will have similar characteristics, where the composite
Component B will form at least a portion of the surface of the
fiber so as to provide a "stick-out" effect, generating surface
roughness on the fiber.
[0044] In certain embodiments, the mineral filler may make up from
about 1 to about 25 percent by weight of the sheath. In other
embodiments, the mineral filler may make up from about 2 to about
20 percent; from about 3 to about 15 percent; or, from about 5 to
about 10 percent by weight of the sheath. The sheath may also
include other additives, ranging from about 0 to about 5 weight
percent of the sheath, including plasticizers, compatibilizers, and
other additives common in the art.
[0045] Fillers useful in the present invention to enhance
coefficient of friction characteristics of the fiber or to produce
a "stick-out" effect include, but are not limited to, untreated and
treated silica, alumina, silicon dioxide, talc, calcium carbonate,
and clay. In certain embodiments, the preferred mineral filler is a
calcium carbonate (CaCO.sub.3). In other embodiments, the mineral
filler may be a compatibilized mineral, where the mineral is coated
with a compound to enhance the dispersibility and compatibility of
the mineral in the polymer matrix. For example, the mineral may be
calcium carbonate, where the calcium carbonate is coated with
stearic acid to enhance the dispersibility and compatibility of the
calcium carbonate in the polymer matrix.
[0046] The average particle size of the mineral filler used in the
sheath composite may be selected based upon the desired sheath
thickness, and may typically range from about 0.1 to about 20
microns. For example, for a fiber having a sheath thickness of 1
micron, mineral filler having an average particle size greater than
about 1 micron can produce the desired "stick-out" effect. In some
embodiment, a ratio of the average particle size of the mineral
filler to the sheath thickness may be equal to or greater than
about 1.0. In other embodiments, the ratio may be greater than
about 1 but less than about 2; in other embodiments, the ratio may
be greater than about 1.2 but less than about 1.8.
[0047] The mineral filler may have a particle size distribution,
where some particles are smaller than the average particle size and
other particles are larger than the average particle size. The
particle size distribution may affect the "stick-out" effect
realized; for example, many particles smaller than then sheath
thickness may be encapsulated within the sheath, such as particles
16 in FIGS. 1 and 2. Particles having a size well in excess of the
sheath thickness may result in adhesion problems, where the
particles do not remain in the composite matrix. A larger particle
size distribution may also lead to a greater spacing between
particles sticking out from the sheath (as described further
below). In some embodiments of the present invention, a preferred
particle size distribution may be less than about 5. In other
embodiments, a preferred particle size distribution may be less
than about 3; less than about 2.5, less than about 2.0, or less
than about 1.5 in other embodiments.
[0048] Fiber diameter can be measured and reported in a variety of
fashions. Generally, fiber diameter is measured in denier per
filament. Denier is a textile term which is defined as the grams of
the fiber per 9000 meters of that fiber's length. Monofilament
generally refers to an extruded strand having a denier per filament
greater than 15, usually greater than 30. Fine denier fiber
generally refers to fiber having a denier of about 15 or less.
Microdenier (or microfiber) generally refers to fiber having a
diameter not greater than about 100 micrometers. For the fibers of
this invention, the diameter may be widely varied, with little
impact upon the elasticity of the fiber. The fiber denier, however,
may be adjusted to suit the capabilities of the finished article
and as such, would preferably be from about 0.5 to about 30
denier/filament for melt blown fiber; from about 1 to about 30
denier/filament for spunbond fiber; and, from about 1 to about
20,000 denier/filament for continuous wound filament. The sheath
thickness and mineral filler average particle size may be selected
based upon the desired filament diameter or denier.
[0049] The bicomponent fibers of the present invention can have a
core that comprises from 80 to 99 percent by weight of the fiber.
In other embodiments, the core can be from 85 to 95 percent by
weight of the fiber. The bicomponent fibers of the present
invention can have a sheath that comprises from about 1 to about 20
percent by weight of the fiber. In other embodiments, the sheath
comprises from about 5 to about 15 percent by weight of the
fiber.
[0050] The shape of the fiber is not limited. For example, typical
fibers have a circular cross-sectional shape, but sometimes fibers
have different shapes, such as a trilobal shape, or a flat (i.e.,
"ribbon" like) shape. The bicomponent fibers disclosed herein are
not limited by the shape of the fiber.
[0051] The bicomponent fiber of the present invention may be used
with other fibers such as PET, nylon, cotton, KEVLAR.RTM.
(available from E.I. Du Pont de Nemours Co.), etc. to make elastic
fabrics. As an added advantage, the heat (and moisture) resistance
of certain bicomponent fibers can enable polyester-PET fibers to be
dyed at ordinary PET dyeing conditions. Other commonly used elastic
fibers, especially spandex (e.g., LYCRA.RTM., a spandex available
from E. I. Du Pont de Nemours Co.), are typically used at less
severe PET dyeing conditions to prevent degradation of
properties.
[0052] Fabrics made from the bicomponent fibers of this invention
include woven, nonwoven and knit fabrics. Nonwoven fabrics can be
made by various methods, e.g., spunlaced (or hydrodynamically
entangled) fabrics as disclosed in U.S. Pat. Nos. 3,485,706 and
4,939,016, carding and thermally bonding staple fibers; spunbonding
continuous fibers in one continuous operation; or by melt blowing
fibers into fabric and subsequently calendering or thermally
bonding the resultant web. These various nonwoven fabric
manufacturing techniques are well known to those skilled in the art
and the scope of the present invention is not limited to any
particular method. Other structures made from such fibers are also
included within the scope of the invention, including, for example,
blends of the fibers of the present invention with other fibers
(e.g., PET, cotton, etc.).
[0053] Fabricated articles which may be made using the bicomponent
fibers and fabrics of this invention include elastic composite
articles (e.g., diapers) that have elastic portions. For example,
elastic portions are typically constructed into diaper waist band
portions to prevent the diaper from falling and leg band portions
to prevent leakage (as shown in U.S. Pat. No. 4,381,781, which is
herein incorporated by reference in its entirety). Often, the
elastic portions promote better form fitting and/or fastening
systems for a good combination of comfort and reliability. The
fibers and fabrics of the present invention may also produce
structures that combine elasticity with breathability. For example,
the inventive elastic fibers, fabrics and/or films may be
incorporated into the structures disclosed in U.S. Pat. No.
6,176,952, which is herein incorporated by reference in its
entirety.
[0054] The inventive elastic fibers and fabrics can also be used in
various structures as described in U.S. Pat. No. 2,957,512 (the
'512 Patent), which is herein incorporated by reference in its
entirety. For example, layer 50 of the structure described in the
'512 Patent (i.e., the elastic component) may be replaced with the
inventive elastic fibers and fabrics, especially where flat,
pleated, creped, crimped, etc., nonelastic materials are made into
elastic structures. Attachment of the inventive elastic fibers
and/or fabric to nonelastic fibers, fabrics or other structures may
be performed by melt bonding or with adhesives. Gathered or shirted
elastic structures may be produced from the inventive elastic
fibers and/or fabrics and nonelastic components by pleating the
non-elastic component (as described in the '512 Patent) prior to
attachment, pre-stretching the elastic component prior to
attachment, or heat shrinking the elastic component after
attachment.
[0055] The inventive fibers may also be used in a spunlaced (or
hydrodynamically entangled) process to make novel structures. For
example, U.S. Pat. No. 4,801,482, which is herein incorporated by
reference in its entirety, discloses an elastic sheet (12) which
can now be made with the novel elastic fibers and/or fabric
described herein.
[0056] Continuous elastic filaments as described herein may also be
used in woven applications where high resilience is desired.
[0057] U.S. Pat. No. 5,037,416 (the '416 Patent), which is herein
incorporated by reference in its entirety, describes the advantages
of a form fitting top sheet by using elastic ribbons (see member 19
of the '416 Patent). The inventive elastic fibers may serve the
function of member 19 of the '416 Patent, or could be used in
fabric form to provide the desired elasticity.
[0058] Elastic panels may also be made from the inventive elastic
fibers and fabrics disclosed herein, and may be used, for example,
as members 18, 20, 14, and/or 26 of U.S.
[0059] Pat. No. 4,940,464 (the '464 Patent), which is herein
incorporated by reference in its entirety. The inventive elastic
fibers and fabrics described herein may also be used as elastic
components of composite side panels (e.g., layer 86 of the '464
Patent).
[0060] The elastic materials of the present invention may also be
rendered pervious or "breathable" by any method well known in the
art including by aperturing, slitting, microperforating, mixing
with fibers or foams, or the like and combinations thereof.
[0061] Examples of such methods include, U.S. Pat. No. 3,156,242 by
Crowe, Jr., U.S. Pat. No. 3,881,489 by Hartwell, U.S. Pat. No.
3,989,867 by Sisson, and U.S. Pat. No. 5,085,654 by Buell, each of
which is herein incorporated by reference in their entirety.
[0062] Surface Roughness Model of Calcium Carbonate Filled
Sheath
[0063] As described above, the bicomponent fibers of the present
invention may include a sheath that includes a polymeric material
and a filler producing a "stick-out" effect. A simple model
describing the fiber surface roughness in terms of the ratio of
particle size to sheath thickness and the particle spacing distance
in sheath is presented below to allow a better understanding of the
present invention.
[0064] The hand-feel perception of a PP nonwoven fabric can be
related to the surface roughness of the fabrics at the microscopic
level, as in the Kawabata measurement system. The surface roughness
may be defined as the departure of the surface shape from some
ideal or prescribed form. Thus, for a nominally flat surface, the
roughness could be defined in terms of the ratio of the true
overall area of the projected nominal area, or as the slope of a
profile taken along some prescribed line, or as the distance
between high points and low points on the surface. Two terms are
used herein to describe the roughness of a fiber surface: the ratio
of average particle size to sheath thickness and the particle
spacing in the sheath. As will be shown below, the roughness is
directly correlated to the physical properties of the fiber and
filler. To establish a simple mathematical model for the thickness
of micro composite sheath, the sheath is assumed to be a two-phase
filled composite system, while the core is assumed to be a
homogeneous polymeric resin, such as homogeneous polypropylene
(hPP).
[0065] Correlation between Weight and Volume Content of a Component
in Two-Phased Composite.
[0066] For a two-phased composite system, it can be shown that to
convert weight percentage to volume percentage, the following
formulation can be used:
.alpha..sub.av=1/(1+(1/.alpha..sub.aw-1).rho..sub.a/.rho..sub.b)
(1) or, equation (2) can be used to convert from volume percentage
to weight percentage:
.alpha..sub.aw=1/(1+(1/.alpha..sub.av-1).rho..sub.b/.rho..sub.a)
(2) where: .alpha..sub.av is the volume percentage of component
`a`, .alpha..sub.aw is the weight percentage of component `a`,
.rho..sub.a is the density of the component `a`, and .rho..sub.b is
the density of component `b`.
[0067] For example, for a calcium carbonate filled hPP composite,
the density of PP is assumed as 0.90, the density of calcium
carbonate is 2.7, and the volume percentage of CaCO.sub.3 to be
used is 2 percent. From equation (2), the filling level of this
calcium carbonate filled hPP composite is equivalent to 5.77
percent by weight.
[0068] Prediction of Thickness of Two-Phased Composite Sheath for a
Bi-component Fiber
[0069] Assumptions used for the prediction of thickness include:
(1) the cross section of a bicomponent fiber consists of two
perfect concentric circles; and, (2) the composite sheath and
homogeneous core sections of the bi-component fiber form as two
distinctive phases without intrusion from one to another.
[0070] When the sheath content in the bicomponent fiber is given by
a weight percentage, the requisite formulas for estimating the
thickness of the composite sheath are:
[0071] .rho..sub.s=A.sub.f
.rho..sub.filler+(1-A.sub.f).rho..sub.m
[0072] k=0.5 {(.rho..sub.c w.sub.s/.rho..sub.s
w.sub.c+1).sup.0.5-1}
[0073] h=11.894 k [dpf/(.rho..sub.c+4.rho..sub.s
k(1+k))].sub.0.5
[0074] D.sub.c=h/k
[0075] D.sub.f=D.sub.c+2h
[0076] where .rho..sub.filler is the density of the filler in
g/cm.sup.3; .rho..sub.m is the density of the polymer matrix in
g/cm.sup.3; A.sub.f is the volume percent of the filler in the
microcomposite; w.sub.f is the weight percent of the filler in the
microcomposite; .rho..sub.c is the density of the polymer in the
core section of a bicomponent fiber in g/cm.sup.3; .rho..sub.s is
the density of the polymer in the sheath section of a bicomponent
fiber in g/cm.sup.3; w.sub.c is the weight percent of the core
section; w.sub.s is the weight percent of the sheath section (note
that: w.sub.c+w.sub.s=1); V.sub.c is the volume percent of the core
section; V.sub.s is the volume percent of the sheath section (note
that: V.sub.c+V.sub.s=1);
[0077] dpf is denier per filament, or grams of a filament in 9000
meters; k is a parameter relating the sheath to the core; h is the
thickness of the sheath in microns; D.sub.c is the diameter of the
core section in microns; and, D.sub.f is the diameter of the
bicomponent fiber in microns.
[0078] Examples of estimated values of sheath thickness of a
calcium carbonate filled bicomponent hPP fiber based on known
filler content by weight percent (w.sub.f) are shown in Table 1.
The core is hPP polymer (density=.rho..sub.c=0.90 g/cm.sup.3),
while the sheath is a calcium carbonate (density =2.70 g/cm.sup.3)
filled hPP microcomposite, resulting in a sheath density,
.rho..sub.s, greater than the core density, .rho..sub.c.
TABLE-US-00001 TABLE 1 Estimated sheath thickness for a calcium
carbonate filled PP sheath based on w.sub.f. w.sub.s = 10 w.sub.s =
15 w.sub.s = 20 w.sub.f = 10 dpf 4 2 4 2 4 2 .rho..sub.s 0.931
0.931 0.931 0.931 0.931 0.931 k 0.026 0.026 0.041 0.041 0.057 0.057
h (.mu.m) 0.623 0.440 0.947 0.670 1.282 0.906 D.sub.c (.mu.m) 23.79
16.82 23.12 16.35 22.43 15.86 D.sub.f (.mu.m) 25.03 17.70 25.01
17.69 24.99 17.67 w.sub.f = 20 dpf 4 2 4 2 4 2 .rho..sub.s 0.964
0.964 0.964 0.964 0.964 0.964 k 0.025 0.025 0.040 0.040 0.055 0.055
h (.mu.m) 0.602 0.425 0.916 0.647 1.240 0.877 D.sub.c (.mu.m) 23.79
16.82 23.12 16.35 22.43 15.86 D.sub.f (.mu.m) 24.99 17.67 24.95
17.64 24.91 17.61
[0079] When the sheath content in a bicomponent fiber is known as a
volume percentage, the formulation for calculating the thickness of
composite sheath is modified based upon the relationship between
volume percentage and weight percentage as given above.
[0080] The filler content in the sheath can be expressed either as
a weight percent or as a volume percent, thus the formulas for
estimating sheath thickness can be developed accordingly. It should
be noted that the formulas only approximate sheath thickness as the
volume of the "stick-out" portion of particles was included as if
submerged in the polymer matrix. As a result, the actual sheath
thicknesses should be less than the predicted thickness. However,
because the volume percent of the filler in the sheath is typically
low (15% or less), the error involved is small and can be neglected
in most instances.
[0081] From Table 1 it can be shown that for a constant sheath
content by weight percent in a bicomponent fiber, the larger the
diameter of the bicomponent fiber (or the larger the dpf), the
larger the thickness of the micro-composite sheath will be.
Further, for a constant diameter (or dpf) of a bicomponent fiber,
the higher the weight percentage of the sheath content, the thicker
the sheath will be. Finally, the effect of filler content in the
sheath on the sheath thickness is relatively small. As the filling
level increases, the thickness of the sheath increases in a small
amount. Similar observations can be made relating to the thickness
of sheath when viewed by volume percent.
[0082] The fiber surface roughness represented by the filler
particle "stick-out" effect may be partially described in terms of
the ratio of the filler particle size to the sheath thickness. If
this ratio is less than 1, the particle would be submerged in the
polymeric sheath matrix and less effective in creating surface
unevenness. On other hand, if the ratio exceeds 2, more than
one-half of the volume of a mineral particle could stick out of the
sheath and be exposed to air, possibly causing the sheath to lose
its holding power to the imbedded particle. It should be noted,
however, that this approximation does not consider mechanical and
adhesion effects that, when present, may allow the ratio to be
significantly higher. In one embodiment, the ratio of the filler
particle size to sheath thickness may range from about 1 to about
2. In another embodiment, the ratio may range from about 1.2 to
about 1.8. In yet other embodiments, the ratio may be greater than
about 2.
[0083] Estimation of Particle Spacing in Two-Phased Composite
Sheath of a Bi-component Fiber
[0084] From the above discussions, the importance of selecting a
proper particle size to ensure the "stick-out" effect is clearly
demonstrated. Another factor influencing the perceived hand feel
perception in micro scale is the particle spacing in the sheath,
which can be correlated to the particle size, the volume percentage
of the fillers, and the spatial arrangement of the particles. Wang
et al. proposed the following models representing the mean distance
between spherical filling particles (Meng-Jiao Wang, Siegfried
Wolff, and Ewe-Hong Tan, "Filler-Elastomer Interactions. Part VIII.
The Role of the Distance Between Filler Aggregates in the Dynamic
Properties of Filled Vulcanizates", Rubber Chemistry and
Technology, Vol 66, 178-195 (1993)). In the case of the loosest,
i.e., cubic, form of arrangement of the particle, the particle
center to center distance is given by: L=0.805.phi..sup.-1/3d where
.phi. is the volume percentage of the filler, and d is a
characteristic length of a particle.
[0085] For the closest arrangement of the particles, i.e.,
face-centered cubic arrangement, the particle center to center
distance is given by: L=0.906.phi..sup.-1/3d
[0086] For a random packing arrangement, the averaged value of
0.86.phi..sup.-1/3 d can be used.
[0087] The particle size variation in the thickness direction (or
the z-direction) can be effectively eliminated by assuming that the
particle size is in the same order of magnitude of the thickness of
the sheath, resulting in the model simplifying to a planar or 2
dimensional particle size distribution. Four possible cases are
considered: particle in cubic and spherical shapes, and particle
distribution in square and equilateral triangle arrangements.
[0088] Four assumptions were made to estimate the particle spacing.
First, the thickness of sheath is in same order of average particle
size of CaCO.sub.3 fillers, i.e., if the average particle size is 1
.mu.m, the thickness of the sheath is also 1 .mu.m. Thus, the
distribution of fillers in the sheath can be considered
two-dimensional. Second, filler particles are uniformly distributed
in the polymer matrix of the sheath. Third, all particles are
evenly distributed in the sheath, either formed as squares or
equilateral triangles. And, fourth, the particle sizes are very
narrow distributed, thus only the average particle size is used for
modeling the spacing distance.
[0089] Particle spacing can then be estimated based upon the
formatting of the particles in space. Particles can be in a square
format or an equilateral triangle format, as illustrated in the
left and right sides of FIG. 3, respectively. The results also
depend upon whether the particles are assumed to be spheres or
cubes (affecting the characteristic length of the particle). The
resulting formulas to calculate particle spacing are given in Table
2, where L is the particle spacing, d is the particle size
(characteristic length: the side length for a cubic particle or the
diameter for a spherical particle), and .alpha..sub.av is the ratio
of particle volume percentage to the polymer matrix volume
percentage. TABLE-US-00002 TABLE 2 Filler particle spacing
estimates. Particles as Cubes Particles as Spheres Square
Formatting L = (1/.alpha..sub.av).sup.1/2 d L =
(0.524/.alpha..sub.av).sup.1/2 d Equilateral Triangle L =
(1.155/.alpha..sub.av).sup.1/2 d L = (0.605/.alpha..sub.av).sup.1/2
d Formatting
[0090] For each of the above formulas, particle spacing is directly
proportional to the particle size. Thus, at a constant volumetric
filling level, the particle spacing distance is determined by the
characteristic dimension of the particles for each of the above
formulas. The ratio of particle spacing to the particle
characteristic dimension (L/d) is listed in Table 3 for systems
having 3 to 15 weight percent filler. It should be pointed out that
the maximum filling level of particles in the polymer matrix will
also depend on the mixing capacity of the extruder. TABLE-US-00003
TABLE 3 L/d Ratio for 3 to 15 weight percent filler Particles in
Cubes Particles in Spheres Wt. vol. Equilateral Equilateral % %
Square triangle Square triangle Average 3 1.0 9.90 10.64 7.16 7.70
8.85 5 1.7 7.62 8.19 5.51 5.92 6.81 8 2.8 5.96 6.40 4.31 4.63 5.33
10 3.6 5.29 5.69 3.83 4.12 4.73 15 5.6 4.24 4.56 3.07 3.30 3.79
[0091] Several observations can be made from the data shown in
Table 3. First, as the filling content increases, the particle
concentration level increases, thus the distance between particles
becomes shorter. Second, when keeping the loading level, particle
arrangement, and particle characteristic dimensions constant, the
distance between spherical particles is less than that between
cubic particles (by definition, the volume of a cubic particle is
larger than that of a spherical particle having the same
characteristic length d). Conversely, there are a greater number
spherical particles than cubic particles under the same loading
level, thus the particle spacing distance becomes shorter.
[0092] For this simplified model, the particles of the filler are
modeled as small cubes or spheres. The distribution of particles in
the sheath is treated as in arrangement of square or equilateral
triangle. In real life, the particles are most likely random
packed, and the shapes of the particles are more or less irregular.
One way to treat this variation is to use an averaged value for the
packing arrangement. The particle diameter is also replaced by an
aggregate diameter (as described in Wang et al.). For simplicity, a
mean particle spacing distance was adopted for the model by
averaging the four values of particle spacing distances shown in
Table 3 (alternatively,
L/d.apprxeq.(0.8/.alpha..sub.av).sup.1/2).
[0093] It was discovered that the fiber surface roughness in a
scale of 1 to 10 micron would generate an improved hand feel
perception. To generate the desired fiber roughness, the required
ratio of particle spacing to particle size, L/d, may vary based
upon particle size. In particular embodiments the L/d ratio may
range from 1 to 10. For example, if the particle size is less than
1 micron, the ratio may be chosen to be from 3 to 6 to generate the
desired roughness. If the particle size is equal to or greater than
1 micron, the ratio may be chosen to be from 2 to 4. It is thus
seen from Table 3 that when a filler loading level is less than 5
percent by weight, the particle spacing may be too large to be
effective for improving the fiber's tactile properties.
[0094] The actual particle size is typically not the same for all
filling particles, as fillers are generally available having an
average particle size and a particle size distribution, from narrow
to broad. The above calculations relating particle size to the
sheath thickness can be determined by using averaged (or mean)
particle size, noting that particle size distribution will affect
the actual spacing and fiber surface roughness. For mineral fillers
with narrow particle size distribution (less than about 2.0), the
effect of the distribution on particle spacing can be neglected.
For fillers with a broader particle size distribution (greater than
about 3.0), the broader particle size distribution would lead to a
greater distance between the particles. For example, the surface
roughness of a fiber with a narrow particle size distribution will
be different than that with a broader particle size distribution
because the fiber incorporating the broad size distribution has
more particles that are smaller than the average particle size.
Thus these smaller particles could possibly be submerged in the
sheath, potentially resulting in a decreased "stick-out" effect. A
broad size distribution also has a greater number of particles
larger than the average particle size than does a narrow
distribution. However, the effect of having a greater number of
particles larger than the average particle size might be negated by
the increased particle spacing for particles that do in fact create
a "stick-out" effect and the increased likelihood of potential
adhesion problems.
[0095] Although the above model can be used for estimating the
ratio of average particle size to the sheath thickness and the
particle spacing distance in the sheath, the model should be used
qualitatively rather than quantitatively as many approximations
were used to derive the formulas. The general principles for using
mineral filler for changing fiber surface morphology are, however,
clearly represented by the model, and the model can provide initial
design guidance.
EXAMPLES
[0096] A spinning trial was conducted by producing bicomponent
fibers, with the sheath being a calcium carbonate filled polymer
micro-composite. The core was Polypropylene 5D49, a commercially
available homopolymer available from the Dow Chemical Company (38
MFR; 0.90 g/cm.sup.3 density). The sheath was 5D49 compounded with
various grades of calcium carbonate, as shown in Table 4. These
fibers were compared to a 5D49 homofil fiber (2 or 4 dpf, as
appropriate) as a control (comparative) sample.
[0097] Selection of Calcium Carbonate. Three commercially available
grades of calcium carbonate having average particle sizes ranging
from 0.4 to 1.2 micron were selected for studying the "stick-out"
effect: TUFFGARD.RTM. (a precipitated calcium carbonate having a
0.4 micron average particle size and a top cut at about 2 microns,
commercially available from Specialty Minerals Inc., Adams, Mass.);
SUPER-PFLEX.RTM. 200 (a precipitated calcium carbonate having a 0.7
micron average particle size and a top cut at about 4 microns,
surface coated with 2% stearic acid to promote dispersion in the
polymer, also commercially available from Specialty Minerals Inc.,
Adams, Mass.); and, FILMLINK.RTM. 400 (a ground calcium carbonate
having a 1.2 micron average particle size and a top cut at about 8
microns, surface coated with 0.8 to 1.2% stearic acid, commercially
available from Imerys, Roswell, Ga.).
[0098] Compounding. Compounding was performed in two steps to
ensure dispersion of calcium carbonate in the hPP. First, calcium
carbonate was compounded with hPP (5D49) at a 40/60 weight ratio to
form concentrates by using a Banbury.RTM. mixer. Second, the
calcium carbonate-hPP concentrates were diluted to the desired
compositions according to the formulations in Table 4 by using a
HAAKE.RTM. 1'' twin screw extruder at mild torque and mild melt
temperature settings (about 210.degree. C.).
[0099] Fiber Spinning. The fiber samples were prepared with a fiber
spinning line consisting of two 1'' single screw extruders, two
Zenith gear pumps, a 144-hole spinneret, a fiber quenching cabinet,
and a wind-up station. The capillary hole of the spinneret was 0.65
mm in diameter with a length to diameter ratio of 4:1. The melt
temperature was setup at 240.degree. C. The throughput was 0.4
grams per hole per minute. The spinning speed was set at 1000 m/min
for producing 4 dpf (denier per filament) fiber and 2000 m/min for
2 dpf fiber, respectively. Fibers were collected in spools for
subsequent property testing. The fiber spinning ran very smoothly,
and no fiber breaks were detected in producing any of the samples.
TABLE-US-00004 TABLE 4 CaCO.sub.3 Surface Modified Bicomponent
Fiber Samples Filler, Sheath, Estimated wt. % vol. % of Fiber
Particle Sheath Fiber Particle in total Denier, Diameter,
Thickness, d/h Diameter, Spacing, Sample CaCO.sub.3 sheath fiber
dpf d (.mu.m) h (.mu.m) Ratio D (.mu.m) L (.mu.m) 1 TUFFGARD .RTM.
5 10 4 0.4 0.64 0.63 25 3.0 2 TUFFGARD .RTM. 5 10 2 0.4 0.45 0.89
17.7 3.0 3 TUFFGARD .RTM. 10 10 4 0.4 0.58 0.69 24.9 2.1 4 TUFFGARD
.RTM. 10 10 2 0.4 0.45 0.89 17.7 2.1 5 SUPER-PFLEX .RTM. 5 10 4 0.7
0.64 1.09 25 5.3 6 SUPER-PFLEX .RTM. 5 10 2 0.7 0.45 1.56 17.7 5.3
7 SUPER-PFLEX .RTM. 10 10 4 0.7 0.58 1.21 24.9 3.7 8 SUPER-PFLEX
.RTM. 10 10 2 0.7 0.45 1.56 17.7 3.7 9 FILMLINK .RTM. 10 15 4 1.2
0.97 1.24 24.9 6.3 10 FILMLINK .RTM. 10 15 2 1.2 0.69 1.74 17.6
6.3
[0100] SEM Analysis on Fiber Surface Morphology. Small areas of the
fibers were cut and placed on aluminum scanning electron microscopy
(SEM) sample mounts in order to acquire surface and cross sectional
images. Samples were coated with gold palladium twice for 20
seconds. Secondary electron images of the fiber surface were
collected on a Hitachi S4100 scanning electron microscope using a 5
kV accelerating voltage.
[0101] SEM images of the surface of three representative surface
modified bicomponent fibers, Samples 4, 8, and 10, are displayed in
FIGS. 4-6, respectively. All three fibers are 2 dpf (17.7 micron in
diameter) and contain 10% sheath by volume.
[0102] Referring to FIG. 4, the SEM image of fiber Sample 4
indicates that the calcium carbonate particles in this sample were
smaller and more concentrated when compared to the SEM images of
the other two fiber samples (FIGS. 5 and 6). This observation is in
accord with the predictions from the model--because the grade of
calcium carbonate, TUFFGARD.RTM., has a smaller particle size (0.4
micron), and the ratio of particle size to the sheath thickness is
less than 1, the model predicts a less significant "stick-out"
effect, and a closer particle spacing distance. Further, the
differences in topography were not discemable between the 5%
(Sample 2. SEM image not presented) and 10% samples, with the
images of the fiber surfaces appearing very similar.
[0103] Referring to FIG. 5, the image of Sample 8 indicates that
this fiber has the most overall surface roughness. The fiber not
only has calcium carbonate "bumps", but also has craters or
depressions formed around the calcium carbonate particles, which
were not evident in FIG. 4. The calcium carbonate contained in
Sample 8. SUPER-PFLEX.RTM. 100, has a particle size of 0.7 micron.
Thus the ratio of size to sheath thickness is greater than 1, and
the improvement in "stick-out" effect over Sample 4 is anticipated
from model.
[0104] Referring to FIG. 6, the particle size of Sample 10 appears
the largest and the least concentrated on the fiber. There was some
evidence of depressions or craters, but less severe than Sample 8.
The calcium carbonate, FILMLINK.RTM. 400, in this fiber has the
largest particle size (1.2 micron), and the ratio of particle size
to sheath thickness is greater than 1. The SEM images appear to
validate the model, as the "stick-out" effect appears to be the
strongest of the three fiber samples, and the spacing distance also
appears to be the largest.
[0105] The formation of craters or depressions on the fiber surface
is not fully understood. One hypothesis is that craters or
depressions may be generated when some large calcium carbonate
particles are sloughed due to centrifugal force or other causes
encountered during the spinning process. A loss of some calcium
carbonate particles during fiber spinning does not hinder the
creation of surface roughness, as craters left by the discarded
particles do provide surface roughness. However, the discarding of
particles during the spinning process may cause a concern of
dusting. For a spunbond line, dusting should not be an issue, as
there are suction fans underneath the forming web where the fibers
are hitting the web and forming the pre-form nonwovens. In other
applications, improved ventilation conditions around the
fabrication line may be needed; however, as the filling content of
calcium carbonate in the fiber is low, about 1% of fiber by weight,
any dusting that might occur should not be severe and could be
easily overcome.
[0106] Knitted Socks
[0107] The 2 dpf fiber samples, including the hPP control, were
knitted on a Lawson-Hemphill sock knitter. The wales and courses
per inch (wpi and cpi) are a measure of the knit density. The wales
go in the machine direction of the fabric, the courses in the cross
direction. The fabric density is defined as the product of wales
and courses. The wpi and cpi of the six samples were measured as 26
and 32, respectively. The density of each sample was 832.
[0108] The Hand Feel Result. The hand feel perception of the
knitted socks made from the 2 dpf fibers are given in Table 5.
Samples 2 and 4, with a particle to sheath thickness ratio less
than 1, did not generate a significant improvement in hand feel.
There is no significant "stick-out" effect, as predicted by the
model and observed in the SEM image of Sample 4 in FIG. 4. Samples
8 and 10 did have an improved hand feel perception as compared to
the control sample, which is made of hPP (5D49) mono fibers without
the surface modifications. TABLE-US-00005 TABLE 5 Hand Feel Ranking
for Select Fiber Samples Particle Sheath Particle Diameter,
Thickness, d/h Spacing, Hand Feel of Sample d (.mu.m) h (.mu.m)
Ratio L (.mu.m knitted socks Control -- -- -- -- Slick, wet 2 0.4
0.45 0.89 3.0 No difference from Control 4 0.4 0.45 0.89 2.1 A
little slick 6 0.7 0.45 1.56 5.3 A little slick 8 0.7 0.45 1.56 3.7
Soft and Dry (best of those tested) 10 1.2 0.69 1.74 6.3 Less
slick, dry, better than the control sample
[0109] As shown by the description and examples above, bicomponent
fibers having a micro-composite surface component can improve the
hand feel perception of synthetic fibers. By incorporating mineral
fillers having a particle size larger than the thickness of the
micro-composite polymer matrix, a "stick-out" effect can be
obtained, resulting in surface roughness and an improved feel. In
certain embodiments, the bicomponent fibers having an improved feel
are useful in end products such as carpets, synthetic hair,
feminine hygiene products, diapers, athletic sportswear, apparel,
upholstery, bandages and sterilizable medical apparel and
instrument wraps
[0110] While the invention has been described with respect to a
limited number of embodiments, those skilled in the art, having
benefit of this disclosure, will appreciate that other embodiments
can be devised which do not depart from the scope of the invention
as disclosed herein. Accordingly, the scope of the invention should
be limited only by the attached claims.
[0111] All priority documents are herein fully incorporated by
reference for all jurisdictions in which such incorporation is
permitted. Further, all documents cited herein, including testing
procedures, are herein fully incorporated by reference for all
jurisdictions in which such incorporation is permitted.
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