U.S. patent application number 15/330853 was filed with the patent office on 2017-03-02 for dimensionally stable nonwoven fibrous webs and methods of making and using the same.
The applicant listed for this patent is 3M Innovative Properties Company. Invention is credited to Michael R. Berrigan, Sian F. Fennessey, Jay M. Jennen, Korey W. Karls, Kevin D. Landgrebe, Eric M. Moore, Francis E. Porbeni, Matthew T. Scholz, John D. Stelter.
Application Number | 20170058442 15/330853 |
Document ID | / |
Family ID | 42936789 |
Filed Date | 2017-03-02 |
United States Patent
Application |
20170058442 |
Kind Code |
A1 |
Moore; Eric M. ; et
al. |
March 2, 2017 |
Dimensionally stable nonwoven fibrous webs and methods of making
and using the same
Abstract
Dimensionally stable nonwoven fibrous webs include a
multiplicity of continuous fibers formed from one or more
thermoplastic polyesters and polypropylene in an amount greater
than 0% and no more than 10% by weight of the web. The webs have at
least one dimension which decreases by no greater than 10% in the
plane of the web when heated to a temperature above a glass
transition temperature of the fibers. When the thermoplastic
polyester is selected to include aliphatic and aromatic polyesters,
a spunbond process may be used to produce substantially continuous
fibers that exhibit molecular orientation. When the thermoplastic
polyester is selected from aliphatic polyesters, a meltblown
process may be used to produce discontinuous fibers that do not
exhibit molecular orientation. The webs may be used as articles for
filtration, sound absorption, thermal insulation, surface cleaning,
cellular growth support, drug delivery, personal hygiene, medical
apparel, or wound dressing.
Inventors: |
Moore; Eric M.; (Roseville,
MN) ; Stelter; John D.; (Osceola, WI) ;
Berrigan; Michael R.; (Oakdale, MN) ; Porbeni;
Francis E.; (Woodbury, MN) ; Scholz; Matthew T.;
(Woodbury, MN) ; Landgrebe; Kevin D.; (Woodbury,
MN) ; Fennessey; Sian F.; (Winterthur, CH) ;
Jennen; Jay M.; (Forest Lake, MN) ; Karls; Korey
W.; (Woodbury, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
3M Innovative Properties Company |
St. Paul |
MN |
US |
|
|
Family ID: |
42936789 |
Appl. No.: |
15/330853 |
Filed: |
November 7, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13262400 |
Dec 15, 2011 |
9487893 |
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PCT/US2010/028263 |
Mar 23, 2010 |
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15330853 |
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61165316 |
Mar 31, 2009 |
|
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61186374 |
Jun 11, 2009 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
D01F 6/92 20130101; D04H
1/544 20130101; D04H 1/55 20130101; Y10T 442/68 20150401; D04H
1/4291 20130101; D04H 1/435 20130101; D04H 3/011 20130101; Y10T
428/249921 20150401; Y10T 442/681 20150401; Y10T 442/689 20150401;
D01F 1/10 20130101 |
International
Class: |
D04H 1/55 20060101
D04H001/55; D01F 6/92 20060101 D01F006/92; D04H 3/011 20060101
D04H003/011; D04H 1/435 20060101 D04H001/435; D04H 1/544 20060101
D04H001/544; D01F 1/10 20060101 D01F001/10; D04H 1/4291 20060101
D04H001/4291 |
Claims
1-41. (canceled)
42. A nonwoven web including a plurality of continuous fine fibers
comprising: one or more thermoplastic aliphatic polyesters; and
polypropylene in an amount greater than 0% and no more than 10% by
weight of the web; wherein the fibers exhibit molecular orientation
and extend substantially endlessly through the web, and have a
median fiber diameter of no greater than 20 micrometers; further
wherein the web has at least one dimension which decreases by no
greater than 10% when the web is heated to a temperature above a
glass transition temperature of the fibers; wherein the nonwoven
web comprises at least one melt blown layer and at least one
spunbond layer, at least one of which includes the fine fibers;
wherein the meltblown layer has further incorporated therein or
thereon a repellent additive.
43. The nonwoven web of claim 42, wherein the repellent additive
comprises a surface treatment comprising paraffin waxes, fatty
acids, bee's wax, silicones, fluorochemicals, and combinations
thereof.
44. The nonwoven web of claim 42, wherein the repellent additive is
selected from a fluorochemical comprising a perfluoroalkyl group
having at least 4 carbon atoms and a silicone fluid consisting of a
linear polymer having a molecular weight of about 4000 to
25,000.
45. The nonwoven web of claim 42, wherein the nonwoven web
comprises a spunbond-meltblown-spunbond layered construction.
46. The nonwoven web of claim 42, wherein the nonwoven web
comprises a spunbond-meltblown-meltblown-spunbond layered
construction.
47. The nonwoven web of claim 42, wherein the molecular orientation
of the fibers results in a bi-refringence value of at least
0.01.
48. The nonwoven web of claim 42, wherein the thermoplastic
aliphatic polyester is selected from the group consisting of one or
more poly(lactic acid), poly(glycolic acid),
poly(lactic-co-glycolic acid), polybutylene succinate,
polyhydroxybutyrate, polyhydroxyvalerate, blends, and copolymers
thereof.
49. The nonwoven web of claim 48, wherein the aliphatic polyester
is semicrystalline.
50. The nonwoven web of claim 42, further comprising at least one
of a plasticizer, a diluent, a surfactant, a viscosity modifier, an
antimicrobial component, or combinations thereof.
51. The nonwoven web of claim 50, wherein the plasticizer is
selected from poly(ethylene glycol), oligomeric polyesters, fatty
acid monoesters and di-esters, citrate esters, or combinations
thereof.
52. The nonwoven web of claim 50, wherein the diluent is selected
from a fatty acid monoester (FAME), a poly(lactic acid) (PLA)
oligomer, or combinations thereof.
53. The nonwoven web of claim 50, wherein the surfactant is
selected from a nonionic surfactant, an anionic surfactant, a
cationic surfactant, a zwitterionic surfactant, or combinations
thereof.
54. The nonwoven web of claim 50, wherein the viscosity modifier
has the following structure: (R--CO.sub.2.sup.-).sub.nM.sup.n+
where R is alkyl or alkylene of C8-C30, which is branched or
straight chain, or C12-C30 aralkyl and may be optionally
substituted with 0-100 alkylene oxide groups, oligomeric lactic
and/or glycolic acid, or a combination thereof; n is the valency of
M; and M is H, an alkali metal or an alkaline earth metal salt, or
amine salts.
55. The nonwoven web of claim 54, wherein the viscosity modifier is
selected from the group consisting of selected from the group
consisting of alkyl carboxylates, alkenyl carboxylates, aralkyl
carboxylates, alkylethoxylated carboxylates, aralkylethoxylated
carboxylates, alkyl lactylates, alkenyl lactylates, stearoyl
lactylates, stearates, and mixtures thereof.
56. The nonwoven web of claim 50, wherein the antimicrobial
component is selected from a fatty acid monoester, a fatty acid
di-ester, an organic acid, a silver compound, a quaternary ammonium
compound, a cationic (co)polymer, an iodine compound, or
combinations thereof.
57. The nonwoven web of claim 42, further comprising a
thermoplastic (co)polymer distinct from the thermoplastic aliphatic
polyester.
58. The nonwoven web of claim 42, wherein the polypropylene is
present in an amount from about 1% to about 6% by weight of the
web.
59. The nonwoven web of claim 42, wherein the fibers exhibit a
median diameter of no greater than about 15 micrometers.
60. The nonwoven web of claim 42, wherein the web is autogeneously
bonded.
61. A nonwoven web including a plurality of fine fibers comprising:
one or more thermoplastic polyesters selected from aliphatic
polyesters; and polypropylene in an amount greater than 0% and no
more than 10% by weight of the web; wherein the fibers do not
exhibit molecular orientation, and have a median fiber diameter of
no greater than 20 micrometers; further wherein the web has at
least one dimension which decreases by no greater than 10% when the
web is heated to a temperature above a glass transition temperature
of the fibers; wherein the nonwoven web comprises at least one melt
blown layer and at least one spunbond layer, at least one of which
includes the fine fibers; wherein the meltblown layer has further
incorporated therein or thereon a repellent additive.
62. The nonwoven web of claim 61, wherein the repellent additive
comprises a surface treatment comprising paraffin waxes, fatty
acids, bee's wax, silicones, fluorochemicals, and combinations
thereof.
63. The nonwoven web of claim 61, wherein the repellent additive is
selected from a fluorochemical comprising a perfluoroalkyl group
having at least 4 carbon atoms and a silicone fluid consisting of a
linear polymer having a molecular weight of about 4000 to
25,000.
64. The nonwoven web of claim 61, wherein the nonwoven web
comprises a spunbond-meltblown-spunbond layered construction.
65. The nonwoven web of claim 61, wherein the nonwoven web
comprises a spunbond-meltblown-meltblown-spunbond layered
construction.
66. The nonwoven web of claim 61, wherein the thermoplastic
aliphatic polyester is selected from the group consisting of one or
more poly(lactic acid), poly(glycolic acid),
poly(lactic-co-glycolic acid), polybutylene succinate,
polyhydroxybutyrate, polyhydroxyvalerate, blends, and copolymers
thereof.
67. The nonwoven web of claim 66, wherein the aliphatic polyester
is semicrystalline.
68. The nonwoven web of claim 61, further comprising at least one
of a plasticizer, a diluent, a surfactant, a viscosity modifier, an
antimicrobial component, or combinations thereof.
69. The nonwoven web of claim 68, wherein the plasticizer is
selected from poly(ethylene glycol), oligomeric polyesters, fatty
acid monoesters and di-esters, citrate esters, or combinations
thereof.
70. The nonwoven web of claim 68, wherein the diluent is selected
from a fatty acid monoester (FAME), a poly(lactic acid) (PLA)
oligomer, or combinations thereof.
71. The nonwoven web of claim 68, wherein the surfactant is
selected from a nonionic surfactant, an anionic surfactant, a
cationic surfactant, a zwitterionic surfactant, or combinations
thereof.
72. The nonwoven web of claim 68, wherein the viscosity modifier
has the following structure: (R--CO.sub.2.sup.-).sub.nM.sup.n+
where R is alkyl or alkylene of C8-C30, which is branched or
straight chain, or C12-C30 aralkyl and may be optionally
substituted with 0-100 alkylene oxide groups, oligomeric lactic
and/or glycolic acid, or a combination thereof; n is the valency of
M; and M is H, an alkali metal or an alkaline earth metal salt, or
amine salts.
73. The nonwoven web of claim 72, wherein the viscosity modifier is
selected from the group consisting of selected from the group
consisting of alkyl carboxylates, alkenyl carboxylates, aralkyl
carboxylates, alkylethoxylated carboxylates, aralkylethoxylated
carboxylates, alkyl lactylates, alkenyl lactylates, stearoyl
lactylates, stearates, and mixtures thereof.
74. The nonwoven web of claim 68, wherein the antimicrobial
component is selected from a fatty acid monoester, a fatty acid
di-ester, an organic acid, a silver compound, a quaternary ammonium
compound, a cationic (co)polymer, an iodine compound, or
combinations thereof.
75. The nonwoven web of claim 61, further comprising a
thermoplastic (co)polymer distinct from the thermoplastic aliphatic
polyester.
76. The nonwoven web of claim 61, wherein the polypropylene is
present in an amount from about 1% to about 6% by weight of the
web.
77. The nonwoven web of claim 61, wherein the fibers exhibit a
median diameter of no greater than about 15 micrometers.
78. The nonwoven web of claim 61, wherein the web is autogeneously
bonded.
79. An article comprising the nonwoven web of claim 42, wherein the
article is a gas filtration article, a liquid filtration article, a
sound absorption article, a thermal insulation article, a surface
cleaning article, a cellular growth support article, a drug
delivery article, or a personal hygiene article.
80. An article comprising the nonwoven web of claim 42, wherein the
article is a surgical drape, a surgical gown, a sterilization wrap,
or a wound contact material.
81. An article comprising the nonwoven web of claim 42 and a
support layer, wherein the nonwoven web and the support layer are
bonded using thermal bonding, adhesive bonding, powdered binder
bonding, hydroentangling, needlepunching, calendaring, or a
combination thereof.
82. An article comprising the nonwoven web of claim 61, wherein the
article is a gas filtration article, a liquid filtration article, a
sound absorption article, a thermal insulation article, a surface
cleaning article, a cellular growth support article, a drug
delivery article, or a personal hygiene article.
83. An article comprising the nonwoven web of claim 61, wherein the
article is a surgical drape, a surgical gown, a sterilization wrap,
or a wound contact material.
84. An article comprising the nonwoven web of claim 61 and a
support layer, wherein the nonwoven web and the support layer are
bonded using thermal bonding, adhesive bonding, powdered binder
bonding, hydroentangling, needlepunching, calendaring, or a
combination thereof.
85. A method of making a nonwoven web according to claim 42
comprising: forming a mixture of one or more thermoplastic
aliphatic polyesters with polypropylene in an amount greater than
0% and no more than 10% by weight of the mixture; forming a
plurality of fibers from the mixture; and collecting at least a
portion of the fibers to form a web, wherein the fibers exhibit
molecular orientation and extend substantially endlessly through
the web, and further wherein the web has at least one dimension
which decreases by no greater than 10% when the web is heated to a
temperature above a glass transition temperature of the fibers.
86. A method of making a nonwoven web according to claim 61
comprising: forming a mixture of one or more thermoplastic
aliphatic polyesters with polypropylene in an amount greater than
0% and no more than 10% by weight of the mixture; forming a
plurality of fibers from the mixture; and collecting at least a
portion of the fibers to form a web, wherein the fibers do not
exhibit molecular orientation, and further wherein the web has at
least one dimension which decreases by no greater than 10% when the
web is heated to a temperature above a glass transition temperature
of the fibers.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 61/165,316, filed Mar. 31, 2009 and
61/186,374, filed Jun. 11, 2009, the disclosures of which are
incorporated by reference herein in their entirety.
TECHNICAL FIELD
[0002] The present disclosure relates to dimensionally stable
nonwoven fibrous webs and methods of making and using such webs.
The disclosure further relates to dimensionally stable nonwoven
fibrous webs including blends of polypropylene and an aliphatic
and/or aromatic polyester useful in making articles, such as
biodegradable and biocompatible articles.
BACKGROUND
[0003] Melt-spinning (or spunbond processing) is the process of
forming fibers by extruding molten polymer through small orifices
in a die, collecting the spun filaments on a belt in a uniform
random fashion, and bonding the fibers to form a cohesive web.
Melt-blowing (or MB) is the process of forming fibers by extruding
molten polymer through small orifices surrounded by high speed
heated gas jets, and collecting the blown filaments as a cohesive
web. This process is also referred to as a blown micro fiber (or
BMF) process.
[0004] Polyesters such as poly(ethylene) terephthalate (PET) and
polyolefins such as poly(propylene) (PP) are two commonly used
classes of petroleum based polymers in the commercial production of
textile fibers, packaging films, beverage bottles, and injection
molded goods by processes such as BMF and spunbond. Although PET
has a higher melting point and superior mechanical and physical
properties compared to other commercially useful polymers, it
exhibits poor dimensional stability at temperatures above its glass
transition temperature. Polyester fibers, e.g. aromatic polyesters
such as PET and poly(ethylene) terephthalate glycol (PETG), and/or
aliphatic polyesters such as poly(lactic acid) (PLA), and webs
including such fibers, may shrink up to 40% of the original length
when subjected to elevated temperatures due to the relaxation of
the oriented amorphous segments of the molecules to relax upon
exposure to heat (See Narayanan, V.; Bhat, G. S. and L. C.
Wadsworth. TAPPI Proceedings: Nonwovens Conference & Trade
Fair. (1998) 29-36).
[0005] Furthermore, PET has generally not been considered as
suitable for applications involving high-speed processing because
of its slow crystallization from the melt state; at commercial
production rates, the polymer has minimal opportunity to form well
developed crystallites. Articles prepared from PET fibers typically
need to undergo an additional stage of drawing and heat-setting
(e.g. annealing) during the fiber spinning process to dimensionally
stabilize the produced structure.
[0006] Additionally, there is also a growing interest in replacing
petroleum based polymers such as PET and PP with resource renewable
polymers, i.e. polymers derived from plant based materials. Ideal
resource renewable polymers are "carbon dioxide neutral" meaning
that as much carbon dioxide is consumed in growing the plants base
material as is given off when the product is made and disposed of.
Biodegradable materials have adequate properties to permit them to
break down when exposed to conditions which lead to composting.
Examples of materials thought to be biodegradable include aliphatic
polyesters such as PLA, poly(glycolic acid), poly(caprolactone),
copolymers of lactide and glycolide, poly(ethylene succinate), and
combinations thereof.
[0007] However, difficulty is often encountered in the use of
aliphatic polyesters such as poly(lactic acid) for BMF due to
aliphatic polyester thermoplastics having relatively high melt
viscosities which yields nonwoven webs that generally cannot be
made at the same fiber diameters that polypropylene can. The
coarser fiber diameters of polyester webs can limit their
application as many final product properties are controlled by
fiber diameter. For example, course fibers lead to a noticeably
stiffer and less appealing feel for skin contact applications.
Furthermore, course fibers produce webs with larger porosity that
can lead to webs that have less of a barrier property, e.g., less
repellency to aqueous fluids.
[0008] The processing of aliphatic polyesters as microfibers has
been described in U.S. Pat. No. 6,645,618 (Hobbs et al.). U.S. Pat.
No. 6,111,160 (Gruber et al.) discloses the use of melt stable
polylactides to form nonwoven articles via melt blown and spunbound
processes. JP6466943A (Shigemitsu et al.) describes a low
shrinkage-characteristic polyester system and its manufacture
approach. U.S. Patent Application Publication No. 2008/0160861
(Berrigan et al.) describes a method for making a bonded nonwoven
fibrous web comprising extruding melt blown fibers of a
polyethylene terephthalate and polylactic acid, collecting the melt
blown fibers as an initial nonwoven fibrous web, and annealing the
initial nonwoven fibrous web with a controlled heating and cooling
operation. U.S. Pat. No. 5,364,694 (Okada et al.) describes a
polyethylene terephthalate (PET) based meltblown nonwoven fabric
and its manufacture. U.S. Pat. No. 5,753,736 (Bhat et al.)
describes the manufacture of polyethylene terephthalate fiber with
reduced shrinkage through the use of nucleation agent, reinforcer
and a combination of both. U.S. Pat. Nos. 5,585,056 and 6,005,019
describe a surgical article comprising absorbable polymer fibers
and a plasticizer containing stearic acid and its salts.
SUMMARY
[0009] In general, the presently disclosed invention relates to
dimensionally stable nonwoven fibrous webs and methods of making
and using such webs. In one aspect, the disclosure relates to a web
including a plurality of continuous fibers comprising one or more
thermoplastic polyesters selected from aliphatic polyesters and
aromatic polyesters; and polypropylene in an amount greater than 0%
and no more than 10% by weight of the web, wherein the fibers
exhibit molecular orientation and extend substantially endlessly
through the web, and further wherein the web has at least one
dimension which decreases by no greater than 10% in the plane of
the web when the web is heated to a temperature above a glass
transition temperature of the fibers, but below the melting point
of the fibers. In some exemplary embodiments, the molecular
orientation of the fibers results in a bi-refringence value of at
least 0.01. In most embodiments, the fibers are microfibers, and
particularly fine fibers.
[0010] In some exemplary embodiments, the thermoplastic polyester
comprises at least one aromatic polyester. In certain exemplary
embodiments, the aromatic polyester is selected from poly(ethylene)
terephthalate (PET), poly(ethylene) terephthalate glycol (PETG),
poly(butylene) terephthalate (PBT), poly(trimethyl) terephthalate
(PTT), their copolymers, or combinations thereof. In other
exemplary embodiments, the thermoplastic polyester comprises at
least one aliphatic polyester. In certain exemplary embodiments,
the aliphatic polymer is selected from one or more poly(lactic
acid), poly(glycolic acid), poly(lactic-co-glycolic acid),
polybutylene succinate, polyhydroxy-butyrate, polyhydroxyvalerate,
blends, and copolymers thereof. In certain exemplary embodiments,
the aliphatic polyester is semicrystalline.
[0011] In another aspect, the disclosure relates to a web including
a plurality of fibers comprising one or more thermoplastic
polyesters selected from aliphatic polyesters; and polypropylene in
an amount greater than 0% and no more than 10% by weight of the
web, wherein the fibers do not exhibit molecular orientation, and
further wherein the web has at least one dimension which decreases
by no greater than 10% in the plane of the web when the web is
heated to a temperature above a glass transition temperature of the
fibers, but below the melting point of the fibers. In certain
exemplary embodiments, the thermoplastic polyester comprises at
least one aliphatic polyester selected from the group consisting of
one or more poly(lactic acid), poly(glycolic acid),
poly(lactic-co-glycolic acid), polybutylene succinate,
polyhydroxy-butyrate, polyhydroxyvalerate, blends, and copolymers
thereof. In certain exemplary embodiments, the aliphatic polyester
is semicrystalline. In most embodiments, the fibers are
microfibers, particularly fine fibers.
[0012] In additional exemplary embodiments related to both of the
previously described aspects of the disclosure, the plurality of
fibers may comprise a thermoplastic (co)polymer distinct from the
thermoplastic polyester. In further exemplary embodiments, the
fibers may comprise at least one of a plasticizer, a diluent, a
surfactant, a viscosity modifier, an antimicrobial component, or
combinations thereof. In some particular exemplary embodiments, the
fibers exhibit a median fiber diameter of no greater than about 25
.mu.m. In certain of these embodiments, the fibers exhibit a median
fiber diameter of at least 1 .mu.m. In additional exemplary
embodiments, the web is biocompatible.
[0013] In further embodiments, dimensionally stable fibrous
nonwoven webs may be formed by use of a viscosity modifier to
reduce the viscosity of aliphatic polyesters, such as PLA. In
certain exemplary embodiments, the viscosity modifier is selected
from the group consisting of alkyl carboxylates, alkenyl
carboxylates, aralkyl carboxylates, alkylethoxylated carboxylates,
aralkylethoxylated carboxylates, alkyl lactylates, alkenyl
lactylates, and mixtures thereof.
[0014] In some exemplary embodiments, the web is a dimensionally
stable nonwoven fibrous web formed from a molten mixture of the
thermoplastic polyester and the polypropylene. In further exemplary
embodiments, the dimensionally stable nonwoven fibrous web is
selected from the group consisting of a spunbond web, a blown
microfiber web, a hydroentangled web, or combinations thereof.
[0015] In a further aspect, the disclosure relates to a method of
making a dimensionally stable nonwoven fibrous web comprising
forming a mixture of one or more thermoplastic polyesters selected
from aliphatic polyesters and aromatic polyesters with
polypropylene in an amount greater than 0% and no more than 10% by
weight of the mixture; forming a plurality of fibers from the
mixture; and collecting at least a portion of the fibers to form a
web, wherein the fibers exhibit molecular orientation and extend
substantially endlessly through the web, and further wherein the
web has at least one dimension in the plane of the web which
decreases by no greater than 10% when the web is heated to a
temperature above a glass transition temperature of the fibers, but
below the melting point of the fibers. In some embodiments, the
fibers may be formed using melt-spinning, filament extrusion,
electrospinning, gas jet fibrillation or combinations thereof.
[0016] In still another aspect, the disclosure relates to a method
of making a dimensionally stable nonwoven fibrous web comprising
forming a mixture of one or more thermoplastic aliphatic polyesters
with polypropylene in an amount greater than 0% and no more than
10% by weight of the mixture; forming a plurality of fibers from
the mixture; and collecting at least a portion of the fibers to
form a web, wherein the fibers do not exhibit molecular
orientation, and further wherein the web has at least one dimension
which decreases by no greater than 10% in the plane of the web when
the web is heated to a temperature above a glass transition
temperature of the fibers, but below the melting point of the
fibers. In some exemplary embodiments, the fibers may be formed
using a melt-blowing (e.g. BMF) process.
[0017] In some exemplary embodiments, the methods may further
comprise post healing the dimensionally stable nonwoven fibrous
web, for example, by controlled heating or cooling of the web.
[0018] In a further aspect, the disclosure relates to an article
comprising a dimensionally stable nonwoven fibrous web as described
above, wherein the article is selected from a gas filtration
article, a liquid filtration article, a sound absorption article, a
thermal insulation article, a surface cleaning article, a cellular
growth support article, a drug delivery article, a personal hygiene
article, a wound dressing article, and a dental hygiene article. In
certain exemplary embodiments, the article may be a surgical drape.
In other exemplary embodiments, the article may be a surgical gown.
In other exemplary embodiments, the article may be a sterilization
wrap. In further exemplary embodiments, the article may be a wound
contact material.
[0019] Exemplary embodiments of the dimensionally stable nonwoven
fibrous webs according to the present disclosure may have
structural features that enable their use in a variety of
applications, have exceptional absorbent properties, exhibit high
porosity and permeability due to their low Solidity, and/or be
manufactured in a cost-effective manner. Due to the small diameter
of the fibers formed, the webs may have a soft feel similar to
polyolefin webs but in many cases exhibit superior tensile strength
due to the higher modulus of the polyester used.
[0020] Bi-component fibers, such as core-sheath or side-by-side
bi-component fibers, may be prepared, as may be bicomponent
microfibers, including sub-micrometer fibers. However, exemplary
embodiments of the disclosure may be particularly useful and
advantageous with monocomponent fibers. Among other benefits, the
ability to use monocomponent fibers reduces complexity of
manufacturing and places fewer limitations on use of the web.
[0021] Exemplary methods of producing dimensionally stable nonwoven
fibrous webs according to the present disclosure may have
advantages in terms of higher production rate, higher production
efficiency, lower production cost, and the like.
[0022] Various aspects and advantages of exemplary embodiments of
the present invention have been summarized. The above Summary is
not intended to describe each illustrated embodiment or every
implementation of the present invention. The Detailed Description
and the Examples that follow more particularly exemplify certain
presently preferred embodiments using the principles disclosed
herein.
DETAILED DESCRIPTION
[0023] The present disclosure relates generally to dimensionally
stable nonwoven fibrous webs or fabrics. The webs include a
plurality of fibers formed from a (co)polymer mixture that is
preferably melt processable, such that the (co)polymer mixture is
capable of being extruded. Dimensionally stable nonwoven fibrous
webs may be prepared by blending an aliphatic and/or aromatic
polyester with polypropylene (PP) in an amount greater than 0% and
no more than 10% by weight of the web, before or during extrusion.
The resulting webs have at least one dimension which decreases by
no greater than 10% in the plane of the web, when the web is heated
to a temperature above a glass transition temperature of the
fibers. In certain embodiments, the fibers may exhibit molecular
orientation.
[0024] In the plane of the web refers to the x-y plane of the web,
which may also be referred to as the machine direction and/or cross
direction of the web. Thus, fibers and webs described herein have
at least one dimension in the plane of the web, e.g., the machine
or the cross direction, that decreases by no greater than 10%, when
the web is heated to a temperature above a glass transition
temperature of the fibers.
[0025] The fibrous webs or fabrics as described herein are
dimensionally stable when the web is heated to a temperature above
a glass transition temperature of the fibers. The webs may be
heated 15.degree. C., 20.degree. C., 30.degree. C., 45.degree. C.
and even 55.degree. C. above the glass transition temperature of
the aromatic and/or aliphatic polyester fibers, and the web will
remain dimensionally stable, e.g., having at least one dimension
which decreases by no greater than 10% in the plane of the web. The
web should not be heated to a temperature that melts the fibers, or
causes the fibers to appreciably degrade, as demonstrated by such
characteristics as loss of molecular weight or discoloration.
[0026] While not intending to be bound by theory, it is believed
that aggregates of PP may thereby be evenly distributed through the
core of the filament; the polyolefin is believed to act as a
selectively miscible additive. At low weight percents of the web,
PP mixes with the polyester and physically inhibits chain movement,
thereby suppressing cold crystallization, and macroscopic shrinkage
is not observed. If the weight percent of the PP is increased
further beyond 10 percent by weight, the PP and polyester phase
separate and rearrangement of the polyester is not affected.
[0027] As used in this specification and the appended claims, the
singular forms "a", "an", and "the" include plural referents unless
the content clearly dictates otherwise. Thus, for example,
reference to fine fibers containing "a compound" includes a mixture
of two or more compounds. As used in this specification and the
appended claims, the term "or" is generally employed in its sense
including "and/or" unless the content clearly dictates
otherwise.
[0028] As used in this specification, the recitation of numerical
ranges by endpoints includes all numbers subsumed within that range
(e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.8, 4, and 5).
[0029] Unless otherwise indicated, all numbers expressing
quantities or ingredients, measurement of properties and so forth
used in the specification and claims are to be understood as being
modified in all instances by the term "about." Accordingly, unless
indicated to the contrary, the numerical parameters set forth in
the foregoing specification and attached claims are approximations
that can vary depending upon the desired properties sought to be
obtained by those skilled in the art utilizing the teachings of the
present invention. At the very least, and not as an attempt to
limit the application of the doctrine of equivalents to the scope
of the claims, each numerical parameter should at least be
construed in light of the number of reported significant digits and
by applying ordinary rounding techniques.
[0030] For the following defined terms, these definitions shall be
applied, unless a different definition is given in the claims or
elsewhere in the specification.
GLOSSARY
[0031] The term "bi-component fiber" or "multi-component fiber"
means fibers with two or more components, each component occupying
a part of the cross-sectional area of the fiber and extending over
a substantial length of the fiber. Suitable multi-component fiber
configurations include, but are not limited to, a sheath-core
configuration, a side-by-side configuration, and an
"islands-in-the-sea" configuration (for example, fibers produced by
Kuraray Company, Ltd., Okayama, Japan).
[0032] The term "monocomponent fiber" means fibers in which the
fibers have essentially the same composition across their
cross-section, but monocomponent includes blends or
additive-containing materials, in which a continuous phase of
substantially uniform composition extends across the cross-section
and over the length of the fiber.
[0033] The term "biodegradable" means degradable by the action of
naturally occurring microorganisms such as bacteria, fungi and
algae and/or natural environmental factors such as hydrolysis,
transesterification, exposure to ultraviolet or visible light
(photodegradable) and enzymatic mechanisms or combinations
thereof.
[0034] The term "biocompatible" means biologically compatible by
not producing toxic, injurious or immunological response in living
tissue. Biocompatible materials may also be broken down by
biochemical and/or hydrolytic processes and absorbed by living
tissue. Test methods used include ASTM F719 for applications where
the fine fibers contact tissue such as skin, wounds, mucosal tissue
including in an orifice such as the esophagus or urethra, and ASTM
F763 for applications where the fine fibers are implanted in
tissue.
[0035] The term "median fiber diameter" means fiber diameter
determined by producing one or more images of the fiber structure,
such as by using a scanning electron microscope; measuring the
fiber diameter of clearly visible fibers in the one or more images
resulting in a total number of fiber diameters, x; and calculating
the median fiber diameter of the x fiber diameters. Typically, x is
greater than about 20, more preferably greater than about 50, and
desirably ranges from about 50 to about 200.
[0036] The term "fine fiber" generally refers to fibers having a
median fiber diameter of no greater than about 50 micrometers
(.mu.m), preferably no greater than 25 .mu.m, more preferably no
greater than 20 .mu.m, still more preferably no greater than 15
.mu.m, even more preferably no greater than 10 .mu.m, and most
preferably no greater than 5 .mu.m.
[0037] "Microfibers" are a population of fibers having a median
fiber diameter of at least one .mu.m but no greater than 100
.mu.m.
[0038] "Ultrafine microfibers" are a population of microfibers
having a median fiber diameter of 2 .mu.m or less.
[0039] "Sub-micrometer fibers" are a population of fibers having a
median fiber diameter of no greater than one .mu.m.
[0040] When reference is made herein to a batch, group, array, etc.
of a particular kind of microfiber, e.g., "an array of
sub-micrometer fibers," it means the complete population of
microfibers in that array, or the complete population of a single
batch of microfibers, and not only that portion of the array or
batch that is of sub-micrometer dimensions.
[0041] "Continuous oriented microfibers" herein refers to
essentially continuous fibers issuing from a die and traveling
through a processing station in which the fibers are drawn and at
least portions of the molecules within the fibers are oriented into
alignment with the longitudinal axis of the fibers ("oriented" as
used with respect to fibers means that at least portions of the
molecules of the fibers are aligned along the longitudinal axis of
the fibers).
[0042] "Melt-blown fibers" herein refers to fibers prepared by
extruding molten fiber-forming material through orifices in a die
into a high-velocity gaseous stream, where the extruded material is
first attenuated and then solidifies as a mass of fibers.
[0043] "Separately prepared sub-micrometer fibers" means a stream
of sub-micrometer fibers produced from a sub-micrometer
fiber-forming apparatus (e.g., a die) positioned such that the
sub-micrometer fiber stream is initially spatially separate (e.g.,
over a distance of about 1 inch (25 mm) or more from, but will
merge in flight and disperse into, a stream of larger size
microfibers.
[0044] "Autogenous bonding" is defined as bonding between fibers at
an elevated temperature as obtained in an oven or with a
through-air bonder without application of direct contact pressure
such as in point-bonding or calendering.
[0045] "Molecularly same" polymer refers to polymers that have
essentially the same repeating molecular unit, but which may differ
in molecular weight, method of manufacture, commercial form,
etc.
[0046] "Self supporting" or "self sustaining" in describing a web
means that the web can be held, handled and processed by itself,
e.g., without support layers or other support aids.
[0047] "Solidity" is a nonwoven web property inversely related to
density and characteristic of web permeability and porosity (low
Solidity corresponds to high permeability and high porosity), and
is defined by the equation:
Solidity ( % ) = [ 3.937 * Web Basis Weight ( g / m 2 ) ] [ Web
Thickness ( mils ) * Bulk Density ( g / cm 3 ) ] ##EQU00001##
[0048] "Web Basis Weight" is calculated from the weight of a 10
cm.times.10 cm web sample.
[0049] "Web Thickness" is measured on a 10 cm.times.10 cm web
sample using a thickness testing gauge having a tester foot with
dimensions of 5 cm.times.12.5 cm at an applied pressure of 150
Pa.
[0050] "Bulk Density" is the bulk density of the polymer or polymer
blend that makes up the web, taken from the literature.
[0051] Various exemplary embodiments of the disclosure will now be
described. Exemplary embodiments of the present invention may take
on various modifications and alterations without departing from the
spirit and scope of the disclosure. Accordingly, it is to be
understood that the embodiments of the present invention are not to
be limited to the following described exemplary embodiments, but is
to be controlled by the limitations set forth in the claims and any
equivalents thereof.
[0052] Reference throughout this specification to "one embodiment,"
"certain embodiments," "one or more embodiments" or "an
embodiment," whether or not including the term "exemplary"
preceding the term "embodiment," means that a particular feature,
structure, material, or characteristic described in connection with
the embodiment is included in at least one embodiment of the
present invention. Thus, the appearances of the phrases such as "in
one or more embodiments," "iii certain embodiments," "in one
embodiment" or "in an embodiment" in various places throughout this
specification are not necessarily referring to the same embodiment
of the present invention. Furthermore, the particular features,
structures, materials, or characteristics may be combined in any
suitable manner in one or more embodiments.
A. Dimensionally Stable Nonwoven Fibrous Webs
[0053] In some embodiments, dimensionally stable nonwoven webs may
be formed from a molten mixture of a thermoplastic polyester and a
polypropylene. In certain embodiments, the dimensionally stable
nonwoven webs may be a spunbond web, a blown microfiber web, a
hydroentangled web, or combinations thereof.
[0054] 1. Molecularly Oriented Fibers
[0055] In certain embodiments, dimensionally stable nonwoven
fibrous webs can be prepared by fiber-forming processes in which
filaments of fiber-forming material are formed by extrusion of a
mixture of one or more thermoplastic polyesters selected from
aliphatic and aromatic polyesters with polypropylene in an amount
greater than 0% and no more than 10% by weight of the mixture,
subjected to orienting forces, and passed through a turbulent field
of gaseous currents while at least some of the extruded filaments
are in a softened condition and reach their freezing temperature
(e.g., the temperature at which the fiber-forming material of the
filaments solidifies) while in the turbulent field. Such fiber
formations processes include, for example, melt-spinning (i.e.
spunbond), filament extrusion, electrospinning, gas jet
fibrillation or combinations thereof.
[0056] The resulting webs have at least one dimension which
decreases by no greater than 10% in the plane of the web when the
web is heated to a temperature above a glass transition temperature
of the fibers. The glass transition temperature of the fibers may
be determined conventionally as is known in the art, for example,
using differential scanning calorimetry (DSC), or modulated DSC. In
certain exemplary embodiments, the thermoplastic polyester may be
selected to include at least one aromatic polyester. In other
exemplary embodiments, the aromatic polyester may be selected from
PET, PETG, poly(butylene) terephthalate (PBT), poly(trimethyl)
terephthalate (PTT), or combinations thereof.
[0057] As noted above, the fibers are preferably molecularly
oriented; i.e., the fibers preferably comprise molecules that are
aligned lengthwise of the fibers and are locked into (i.e., are
thermally trapped into) that alignment. Oriented fibers are fibers
where there is molecular orientation within the fiber. Fully
oriented and partially oriented polymeric fibers are known and
commercially available. Orientation of fibers can be measured in a
number of ways, including birefringence, heat shrinkage, X-ray
scattering, and elastic modulus (see e.g., Principles of Polymer
Processing, Zehev Tadmor and Costas Gogos, John Wiley and Sons, New
York, 1979, pp. 77-84). It is important to note that molecular
orientation is distinct from crystallinity, as both crystalline and
amorphous materials can exhibit molecular orientation independent
from crystallization. Thus, even though commercially known
sub-micrometer fibers made by melt-blowing or electrospinning are
not oriented, there are known methods of imparting molecular
orientation to fibers made using those processes.
[0058] Oriented fibers prepared according exemplary embodiments of
the disclosure may show a difference in birefringence from segment
to segment. By viewing a single fiber through a polarized
microscope and estimating retardation number using the Michel-Levy
chart (see, "On-Line Determination of Density and Crystallinity
During Melt Spinning", Vishal Bansal et al, Polymer Engineering and
Science, November 1996, Vol. 36, No. 2, pp. 2785-2798),
birefringence is obtained with the following formula:
birefringence=retardation (nm)/1000 D, where D is the fiber
diameter in micrometers. We have found that exemplary fibers
susceptible to birefringence measurements generally include
segments that differ in birefringence number by at least 5%, and
preferably at least 10%. Some exemplary fibers may include segments
that differ in birefringence number by 20 or even 50 percent. In
some exemplary embodiments, the molecular orientation of the fibers
results in a bi-refringence value of at least 0.00001, more
preferably at least about 0.0001, still more preferably at least
about 0.001, most preferably at least about 0.01.
[0059] Different oriented fibers or portions of an oriented fiber
also may exhibit differences in properties as measured by
differential scanning calorimetry (DSC). For example, DSC tests on
exemplary webs prepared according to the disclosure may reveal the
presence of chain-extended crystallization by the presence of a
dual melting peak. A higher-temperature peak may be obtained for
the melting point for a chain-extended, or strain-induced,
crystalline portion; and another, generally lower-temperature peak
may occur at the melting point for a non-chain-extended, or
less-ordered, crystalline portion. The term "peak" herein means
that portion of a heating curve that is attributable to a single
process, e.g., melting of a specific molecular portion of a fiber
such as a chain-extended portion. The peaks may be sufficiently
close to one another that one peak has the appearance of a shoulder
of the curve defining the other peak, but they are still regarded
as separate peaks, because they represent melting points of
distinct molecular fractions.
[0060] In certain exemplary embodiments, the passive longitudinal
segments of the fibers may be oriented to a degree exhibited by
typical spunbond fibrous webs. In crystalline or semi-crystalline
polymers, such segments preferably exhibit strain-induced or
chain-extended crystallization (i.e., molecular chains within the
fiber have a crystalline order aligned generally along the fiber
axis). As a whole, the web can exhibit strength properties like
those obtained in spunbond webs, while being strongly bondable in
ways that a typical spunbond web cannot be bonded. And autogenously
bonded webs of the invention can have a loft and uniformity through
the web that are not available with the point-bonding or
calendering generally used with spunbond webs.
[0061] While not intending to be bound by theory, it is believed
that molecular orientation is improved through the use of fiber
attenuation as is known in the art (See U. W. Gedde, Polymer
Physics, 1st Ed. Chapman & Hall, London, 1995, 298). An
increase in percent crystallinity of the attenuated fibers may thus
be observed. The crystallites stabilize the filaments by acting as
anchoring which inhibit chain motion, and rearrangement and
crystallization of the rigid amorphous fraction; as the percentage
of crystallinity is increased the rigid amorphous and amorphous
fraction is decreased. Semi-crystalline, linear polymers consist of
a crystalline and an amorphous phase with both phases being
connected by tie molecules. The tie-molecule appears in both
phases; strain builds at the coupled interface and it appears
particularly obvious in the amorphous phase as observed in the
broadening of the glass transition to higher temperatures in
semi-crystalline polymers. In cases of strong coupling, the
affected molecular segments are produce a separate intermediate
phase of the amorphous phase called the rigid amorphous fraction.
The intermediate phase, forming the extended boundary between the
crystalline and amorphous phases, is characterized by lower local
entropy than that of the fully amorphous phase.
[0062] At temperatures above the glass transition and below the
melting temperature of the material, the rigid amorphous fraction
rearranges and crystallizes; it undergoes cold crystallization. The
percentages of crystalline and rigid amorphous material present in
the fibers determine the macroscopic shrinkage value. The presence
of crystallites may act to stabilize the filaments by acting as
anchoring or tie points and inhibit chain motion.
[0063] Furthermore, it is presently believed that a total percent
crystallinity of at least about 30% is required for PET to show
dimensional stability at elevated temperatures; this level of
crystallinity can generally only be obtained in a pure polyester
system by thermally annealing the web after the fiber forming
process. Additionally, in conventional melt spinning, 0.08 g/denier
stress is generally required to induce crystallization in-line
without any type of additive. In a typical spunbonding operation at
production rates of 1 g/die hole/minute, spinning speeds of 6000
meters per minute are generally needed to produce the required
thread-line tension. However, most spunbonding systems provide only
filament speeds from 3,000-5,000 meters per minute (m/min).
[0064] Thus, exemplary embodiments of the present disclosure may be
particularly useful in forming dimensionally stable nonwoven
fibrous webs including molecularly oriented fibers using a high
production rate spunbonding process. For example, dimensionally
stable nonwoven fibrous webs of the present disclosure may, in some
embodiments, be prepared using a spunbonding process at rates of at
least 5,000 m/min, more preferably at least 6,000 m/min.
[0065] 2. Non-Molecularly Oriented Fibers
[0066] In alternative embodiments, dimensionally stable nonwoven
fibrous webs can be prepared by fiber-forming processes in which
substantially non-molecularly oriented filaments of fiber-forming
material are formed from a mixture of one or more thermoplastic
polyesters selected from aliphatic polyesters with polypropylene in
an amount greater than 0% and no more than 10% by weight of the
mixture, before or during extrusion. The resulting webs have at
least one dimension which decreases by no greater than 10% in the
plane of the web when the web is heated to a temperature above a
glass transition temperature of the fibers. In some exemplary
embodiments, the fibers may be formed using a melt-blowing (e.g.
BMF) process.
[0067] 3. Fiber Sizes
[0068] In some exemplary embodiments of the above referenced
fiber-forming processes used to produce dimensionally stable
nonwoven fibrous webs, a preferred fiber component is a fine fiber.
In certain more preferred embodiments, a fine fiber component is a
sub-micrometer fiber component comprising fibers having a median
fiber diameter of no greater than one micrometer (.mu.m). Thus, in
certain exemplary embodiments, the fibers exhibit a median diameter
of no greater than about one micrometer (.mu.m). In some exemplary
embodiments, the sub-micrometer fiber component comprises fibers
have a median fiber diameter ranging from about 0.2 .mu.m to about
0.9 .mu.m. In other exemplary embodiments, the sub-micrometer fiber
component comprises fibers have a median fiber diameter ranging
from about 0.5 .mu.m to about 0.7 .mu.m.
[0069] The sub-micrometer fiber component may comprise
monocomponent fibers comprising the above-mentioned polymers or
copolymers (i.e., (co)polymers. In this exemplary embodiment, the
monocomponent fibers may also contain additives as described below.
Alternatively, the fibers formed may be multi-component fibers.
[0070] In other exemplary embodiments, the nonwoven fibrous webs of
the present disclosure may additionally or alternatively comprise
one or more coarse fiber components such as microfiber component.
In some exemplary embodiments, the coarse fiber component may
exhibit a median diameter of no greater than about 50 .mu.m, more
preferably no greater than 25 .mu.m, more preferably no greater
than 20 .mu.m, even more preferably no greater than 15 .mu.m, still
more preferably no greater than 10 .mu.m, and most preferably no
greater than 5 .mu.m. In other exemplary embodiments, a preferred
coarse fiber component is a microfiber component comprising fibers
having a median fiber diameter of at least 1 .mu.m, more preferably
at least 5 .mu.m, more preferably still at least 10 .mu.m, even
more preferably at least 20 .mu.m, and most preferably at least 25
.mu.m. In certain exemplary embodiments, the microfiber component
comprises fibers having a median fiber diameter ranging from about
1 .mu.m to about 100 .mu.m. In other exemplary embodiments, the
microfiber component comprises fibers have a median fiber diameter
ranging from about 5 .mu.m to about 50 .mu.m.
[0071] 4. Layered Structures
[0072] In other exemplary embodiments, a multi-layer nonwoven
fibrous web may be formed by overlaying on a support layer a
dimensionally stable dimensionally stable nonwoven fibrous web
comprising an overlayer of microfibers on an underlayer comprising
a population of sub-micrometer fibers, such that at least a portion
of the sub-micrometer fibers contact the support layer at a major
surface of the single-layer nonwoven web. In such embodiments of a
multi-layer nonwoven fibrous web, it will be understood that the
term "overlayer" is intended to describe an embodiment wherein at
least one layer overlays another layer in a multi-layer composite
web. However, it will be understood that by flipping any
multi-layer nonwoven fibrous web 180 degrees about a centerline,
what has been described as an overlayer may become an underlayer,
and the disclosure is intended to cover such modification to the
illustrated embodiments. Furthermore, reference to "a layer" is
intended to mean at least one layer, and therefore each illustrated
embodiment of a multi-layer nonwoven fibrous web may include one or
more additional layers (not shown) within the scope of the
disclosure. In addition, reference to "a layer" is intended to
describe a layer at least partially covering one or more additional
layers (not shown).
[0073] For any of the previously described exemplary embodiments of
a dimensionally stable nonwoven fibrous web according to the
present disclosure, the web will exhibit a basis weight, which may
be varied depending upon the particular end use of the web.
Typically, the dimensionally stable nonwoven fibrous web has a
basis weight of no greater than about 1000 grams per square meter
(gsm). In some embodiments, the nonwoven fibrous web has a basis
weight of from about 1.0 gsm to about 500 gsm. In other
embodiments, the dimensionally stable nonwoven fibrous web has a
basis weight of from about 10 gsm to about 300 gsm.
[0074] As with the basis weight, the nonwoven fibrous web will
exhibit a thickness, which may be varied depending upon the
particular end use of the web. Typically, the dimensionally stable
nonwoven fibrous web has a thickness of no greater than about 300
millimeters (mm). In some embodiments, the dimensionally stable
nonwoven fibrous web has a thickness of from about 0.5 mm to about
150 mm. In other embodiments, the dimensionally stable nonwoven
fibrous web has a thickness of from about 1.0 mm to about 50
mm.
[0075] 5. Optional Support Layer
[0076] The dimensionally stable nonwoven fibrous webs of the
present disclosure may further comprise a support layer. When
present, the support layer may provide most of the strength of the
nonwoven fibrous article. In some embodiments, the above-described
sub-micrometer fiber component tends to have very low strength, and
can be damaged during normal handling. Attachment of the
sub-micrometer fiber component to a support layer lends strength to
the sub-micrometer fiber component, while retaining the low
Solidity and hence the desired absorbent properties of the
sub-micrometer fiber component. A multi-layer dimensionally stable
nonwoven fibrous web structure may also provide sufficient strength
for further processing, which may include, but is not limited to,
winding the web into roll form, removing the web from a roll,
molding, pleating, folding, stapling, weaving, and the like.
[0077] A variety of support layers may be used in the present
disclosure. Suitable support layers include, but are not limited
to, a nonwoven fabric, a woven fabric, a knitted fabric, a foam
layer, a film, a paper layer, an adhesive-backed layer, a foil, a
mesh, an elastic fabric (i.e., any of the above-described woven,
knitted or nonwoven fabrics having elastic properties), an
apertured web, an adhesive-backed layer, or any combination
thereof. In one exemplary embodiment, the support layer comprises a
polymeric nonwoven fabric. Suitable nonwoven polymeric fabrics
include, but are not limited to, a spunbonded fabric, a meltblown
fabric, a carded web of staple length fibers (i.e., fibers having a
fiber length of no greater than about 100 mm), a needle-punched
fabric, a split film web, a hydroentangled web, an airlaid staple
fiber web, or a combination thereof. In certain exemplary
embodiments, the support layer comprises a web of bonded staple
fibers. As described further below, bonding may be effected using,
for example, thermal bonding, adhesive bonding, powdered binder
bonding, hydroentangling, needlepunching, calendering, or a
combination thereof.
[0078] The support layer may have a basis weight and thickness
depending upon the particular end use of the nonwoven fibrous
article. In some embodiments of the present disclosure, it is
desirable for the overall basis weight and/or thickness of the
nonwoven fibrous article to be kept at a minimum level. In other
embodiments, an overall minimum basis weight and/or thickness may
be required for a given application. Typically, the support layer
has a basis weight of no greater than about 150 grams per square
meter (gsm). In some embodiments, the support layer has a basis
weight of from about 5.0 gsm to about 100 gsm. In other
embodiments, the support layer has a basis weight of from about 10
gsm to about 75 gsm.
[0079] As with the basis weight, the support layer may have a
thickness, which varies depending upon the particular end use of
the nonwoven fibrous article. Typically, the support layer has a
thickness of no greater than about 150 millimeters (mm). In some
embodiments, the support layer has a thickness of from about 1.0 mm
to about 35 mm. In other embodiments, the support layer has a
thickness of from about 2.0 mm to about 25 mm.
[0080] In certain exemplary embodiments, the support layer may
comprise a microfiber component, for example, a plurality of
microfibers. In such embodiments, it may be preferred to deposit
the above-described sub-micrometer fiber population directly onto
the microfiber support layer to form a multi-layer dimensionally
stable nonwoven fibrous web. Optionally, the above-described
microfiber population may deposited with or over the sub-micrometer
fiber population on the microfiber support layer. In certain
exemplary embodiments, the plurality of microfibers comprising the
support layer is compositionally the same as the population of
microfibers forming the overlayer.
[0081] The sub-micrometer fiber component may be permanently or
temporarily bonded to a given support layer. In some embodiments of
the present disclosure, the sub-micrometer fiber component is
permanently bonded to the support layer (i.e., the sub-micrometer
fiber component is attached to the support layer with the intention
of being permanently bonded thereto).
[0082] In some embodiments of the present disclosure, the
above-described sub-micrometer fiber component may be temporarily
bonded to (i.e., removable from) a support layer, such as a release
liner. In such embodiments, the sub-micrometer fiber component may
be supported for a desired length of time on a temporary support
layer, and optionally further processed on a temporary support
layer, and subsequently permanently bonded to a second support
layer.
[0083] In one exemplary embodiment of the present disclosure, the
support layer comprises a spunbonded fabric comprising
polypropylene fibers. In a further exemplary embodiment of the
present disclosure, the support layer comprises a carded web of
staple length fibers, wherein the staple length fibers comprise:
(i) low-melting point or binder fibers; and (ii) high-melting point
or structural fibers. Typically, the binder fibers have a melting
point of at least 10.degree. C. greater than a melting point of the
structural fibers, although the difference between the melting
point of the binder fibers and structural fibers may be greater
than 10.degree. C. Suitable binder fibers include, but are not
limited to, any of the above-mentioned polymeric fibers. Suitable
structural fibers include, but are not limited to, any of the
above-mentioned polymeric fibers, as well as inorganic fibers such
as ceramic fibers, glass fibers, and metal fibers; and organic
fibers such as cellulosic fibers.
[0084] As described above, the support layer may comprise one or
more layers in combination with one another. In one exemplary
embodiment, the support layer comprises a first layer, such as a
nonwoven fabric or a film, and an adhesive layer on the first layer
opposite the sub-micrometer fiber component. In this embodiment,
the adhesive layer may cover a portion of or the entire outer
surface of the first layer. The adhesive may comprise any known
adhesive including pressure-sensitive adhesives, heat activatable
adhesives, etc. When the adhesive layer comprises a
pressure-sensitive adhesive, the nonwoven fibrous article may
further comprise a release liner to provide temporary protection of
the pressure-sensitive adhesive.
[0085] 6. Optional Additional Layers
[0086] The dimensionally stable nonwoven fibrous webs of the
present disclosure may comprise additional layers in combination
with the sub-micrometer fiber component, the support layer, or
both. One or more additional layers may be present over or under an
outer surface of the sub-micrometer fiber component, under an outer
surface of the support layer, or both.
[0087] Suitable additional layers include, but are not limited to,
a color-containing layer (e.g., a print layer); any of the
above-described support layers; one or more additional
sub-micrometer fiber components having a distinct median fiber
diameter and/or physical composition; one or more secondary fine
sub-micrometer fiber layers for additional insulation performance
(such as a melt-blown web or a fiberglass fabric); foams; layers of
particles; foil layers; films; decorative fabric layers; membranes
(i.e., films with controlled permeability, such as dialysis
membranes, reverse osmosis membranes, etc.); netting; mesh; wiring
and tubing networks (i.e., layers of wires for conveying
electricity or groups of tubes/pipes for conveying various fluids,
such as wiring networks for heating blankets, and tubing networks
for coolant flow through cooling blankets); or a combination
thereof.
[0088] 7. Optional Attachment Devices
[0089] In certain exemplary embodiments, the dimensionally stable
nonwoven fibrous webs of the present disclosure may further
comprise one or more attachment devices to enable the nonwoven
fibrous article to be attached to a substrate. As discussed above,
an adhesive may be used to attach the nonwoven fibrous article. In
addition to adhesives, other attachment devices may be used.
Suitable attachment devices include, but are not limited to, any
mechanical fastener such as screws, nails, clips, staples,
stitching, thread, hook and loop materials, etc.
[0090] The one or more attachment devices may be used to attach the
nonwoven fibrous article to a variety of substrates. Exemplary
substrates include, but are not limited to, a vehicle component; an
interior of a vehicle (i.e., the passenger compartment, the motor
compartment, the trunk, etc.); a wall of a building (i.e., interior
wall surface or exterior wall surface); a ceiling of a building
(i.e., interior ceiling surface or exterior ceiling surface); a
building material for forming a wall or ceiling of a building
(e.g., a ceiling tile, wood component, gypsum board, etc.); a room
partition; a metal sheet; a glass substrate; a door; a window; a
machinery component; an appliance component (i.e., interior
appliance surface or exterior appliance surface); a surface of a
pipe or hose; a computer or electronic component; a sound recording
or reproduction device; a housing or case for an appliance,
computer, etc.
B. Dimensionally Stable Nonwoven Fibrous Web Components
[0091] Various components of exemplary dimensionally stable
nonwoven fibrous webs according to the present disclosure will now
be described. In some exemplary embodiments, the dimensionally
stable nonwoven fibrous webs may include a plurality of continuous
fibers comprising one or more thermoplastic polyesters selected
from aliphatic polyesters and aromatic polyesters; and
polypropylene in an amount greater than 0% and no more than 10% by
weight of the web, wherein the fibers exhibit molecular orientation
and extend substantially endlessly through the web, and further
wherein the web has at least one dimension which decreases by no
greater than 10% in the plane of the web when the web is heated to
a temperature above a glass transition temperature of the fibers.
Such dimensionally stable nonwoven fibrous webs may be produced, in
certain exemplary embodiments, using a spunbond or melt spinning
process.
[0092] In other exemplary embodiments, the dimensionally stable
nonwoven fibrous webs may include a plurality of fibers comprising
one or more thermoplastic polyesters selected from aliphatic
polyesters; and polypropylene in an amount greater than 0% and no
more than 10% by weight of the web, wherein the fibers do not
exhibit molecular orientation, and further wherein the web has at
least one dimension in the plane of the web which decreases by no
greater than 10% in the plane of the web when the web is heated to
a temperature above a glass transition temperature of the fibers.
Such dimensionally stable nonwoven fibrous webs may be produced, in
certain exemplary embodiments, using a meltblown or BMF
process.
[0093] 1. Thermoplastic Polyesters
[0094] The fibrous webs of the present disclosure include at least
one thermoplastic polyester. In some exemplary embodiments an
aromatic polyester is used as a major component in the
fiber-forming mixture. In certain exemplary embodiments, the
aromatic polyester is selected poly(ethylene) terephthalate (PET),
poly(ethylene) terephthalate glycol (PETG), polybutylene)
terephthalate (PBT), poly(trimethyl) terephthalate (PTT), their
copolymers, and combinations thereof.
[0095] In other exemplary embodiments, an aliphatic polyester is
used as a major component in the fiber-forming mixture. Aliphatic
polyesters useful in practicing embodiments of the present
invention include homo- and copolymers of poly(hydroxyalkanoates)
and homo- and copolymers of those aliphatic polyesters derived from
the reaction product of one or more polyols with one or more
polycarboxylic acids that is typically formed from the reaction
product of one or more alkanediols with one or more
alkanedicarboxylic acids (or acyl derivatives). Polyesters may
further be derived from multifunctional polyols, e.g. glycerin,
sorbitol, pentaerythritol, and combinations thereof, to form
branched, star, and graft homo- and copolymers. Miscible and
immiscible blends of aliphatic polyesters with one or more
additional semicrystalline or amorphous polymers may also be
used.
[0096] Exemplary aliphatic polyesters are poly(lactic acid),
poly(glycolic acid), poly(lactic-co-glycolic acid), polybutylene
succinate, polyhydroxybutyrate, polyhydroxyvalerate, blends, and
copolymers thereof. One particularly useful class of aliphatic
polyesters are poly(hydroxyalkanoates), derived by condensation or
ring-opening polymerization of hydroxy acids, or derivatives
thereof. Suitable poly(hydroxyalkanoates) may be represented by the
formula:
II(O--R--C(O)--).sub.nOH,
where R is an alkylene moiety that may be linear or branched having
1 to 20 carbon atoms, preferably 1 to 12 carbon atoms optionally
substituted by catenary (bonded to carbon atoms in a carbon chain)
oxygen atoms; n is a number such that the ester is polymeric, and
is preferably a number such that the molecular weight of the
aliphatic polyester is at least 10,000, preferably at least 30,000,
and most preferably at least 50,000 daltons. Although higher
molecular weight polymers generally yield films with better
mechanical properties, for both melt processed and solvent cast
polymers excessive viscosity is undesirable. The molecular weight
of the aliphatic polyester is typically no greater than 1,000,000,
preferably no greater than 500,000, and most preferably no greater
than 300,000 daltons. R may further comprise one or more caternary
(i.e., in chain) ether oxygen atoms. Generally, the R group of the
hydroxy acid is such that the pendant hydroxyl group is a primary
or secondary hydroxyl group.
[0097] Useful poly(hydroxyalkanoates) include, for example, homo-
and copolymers of poly(3-hydroxybutyrate), poly(4-hydroxybutyrate),
poly(3-hydroxyvalerate), poly(lactic acid) (as known as
polylactide), poly(3-hydroxypropanoate), poly(4-hydropentanoate),
poly(3-hydroxypentanoate), poly(3-hydroxyhexanoate),
poly(3-hydroxyheptanoate), poly(3-hydroxyoctanoate), polydioxanone,
polycaprolactone, and polyglycolic acid (i.e., polyglycolide).
Copolymers of two or more of the above hydroxy acids may also be
used, for example, poly(3-hydroxybutyrate-co-3-hydroxyvalerate),
poly(lactate-co-3-hydroxypropanoate),
poly(glycolide-co-p-dioxanone), and poly(lactic acid-co-glycolic
acid). Blends of two or more of the poly(hydroxyalkanoates) may
also be used, as well as blends with one or more polymers and/or
copolymers.
[0098] The aliphatic polyester may be a block copolymer of
poly(lactic acid-co-glycolic acid). Aliphatic polyesters useful in
the inventive fine fibers may include homopolymers, random
copolymers, block copolymers, star-branched random copolymers,
star-branched block copolymers, dendritic copolymers, hyperbranched
copolymers, graft copolymers, and combinations thereof.
[0099] Another useful class of aliphatic polyesters includes those
aliphatic polyesters derived from the reaction product of one or
more alkanediols with one or more alkanedicarboxylic acids (or acyl
derivatives). Such polyesters have the general formula:
##STR00001##
where R' and R'' each represent an alkylene moiety that may be
linear or branched having from 1 to 20 carbon atoms, preferably 1
to 12 carbon atoms, and m is a number such that the ester is
polymeric, and is preferably a number such that the molecular
weight of the aliphatic polyester is at least 10,000, preferably at
least 30,000, and most preferably at least 50,000 daltons, but no
greater than 1,000,000, preferably no greater than 500,000 and most
preferably no greater than 300,000 daltons. Each n is independently
0 or 1. R' and R'' may further comprise one or more caternary (i.e.
in chain) ether oxygen atoms.
[0100] Examples of aliphatic polyesters include those homo- and
copolymers derived from (a) one or more of the following diacids
(or derivative thereof): succinic acid; adipic acid; 1,12
dicarboxydodecane; fumaric acid; glutartic acid; diglycolic acid;
and maleic acid; and (b) one of more of the following diols:
ethylene glycol; polyethylene glycol; 1,2-propane diol;
1,3-propanediol; 1,2-propanediol; 1,2-butanediol; 1,3-butanediol;
1,4-butanediol; 2,3-butanediol; 1,6-hexanediol; 1,2 alkane diols
having 5 to 12 carbon atoms; diethylene glycol; polyethylene
glycols having a molecular weight of 300 to 10,000 daltons,
preferably 400 to 8,000 daltons; propylene glycols having a
molecular weight of 300 to 4000 daltons; block or random copolymers
derived from ethylene oxide, propylene oxide, or butylene oxide;
dipropylene glycol; and polypropylene glycol, and (c) optionally a
small amount, i.e., 0.5-7.0-mole % of a polyol with a functionality
greater than two such as glycerol, neopentyl glycol, and
pentaerythritol.
[0101] Such polymers may include polybutylenesuccinate homopolymer,
polybutylene adipate homopolymer, polybutyleneadipate-succinate
copolymer, polyethylenesuccinate-adipate copolymer, polyethylene
glycol succinate homopolymer and polyethylene adipate
homopolymer.
[0102] Commercially available aliphatic polyesters include
poly(lactide), poly(glycolide), poly(lactide-co-glycolide),
poly(L-lactide-co-trimethylene carbonate), poly(dioxanone),
poly(butylene succinate), and poly(butylene adipate),
[0103] Useful aliphatic polyesters include those derived from
semicrystalline polylactic acid. Poly(lactic acid) or polylactide
has lactic acid as its principle degradation product, which is
commonly found in nature, is non-toxic and is widely used in the
food, pharmaceutical and medical industries. The polymer may be
prepared by ring-opening polymerization of the lactic acid dimer,
lactide. Lactic acid is optically active and the dimer appears in
four different forms: L,L-lactide, D,D-lactide, D,L-lactide (meso
lactide) and a racemic mixture of L,L- and D,D-. By polymerizing
these lactides as pure compounds or as blends, poly(lactide)
polymers may be obtained having different stereochemistries and
different physical properties, including crystallinity. The L,L- or
D,D-lactide yields semicrystalline poly(lactide), while the
poly(lactide) derived from the D,L-lactide is amorphous.
[0104] The polylactide preferably has a high enantiomeric ratio to
maximize the intrinsic crystallinity of the polymer. The degree of
crystallinity of a poly(lactic acid) is based on the regularity of
the polymer backbone and the ability to crystallize with other
polymer chains. If relatively small amounts of one enantiomer (such
as D-) is copolymerized with the opposite enantiomer (such as L-)
the polymer chain becomes irregularly shaped, and becomes less
crystalline. For these reasons, when crystallinity is favored, it
is desirable to have a poly(lactic acid) that is at least 85% of
one isomer, at least 90% of one isomer, or at least 95% of one
isomer in order to maximize the crystallinity.
[0105] An approximately equimolar blend of D-polylactide and
L-polylactide is also useful. This blend forms a unique crystal
structure having a higher melting point (.about.210.degree. C.)
than does either the D-poly(lactide) and L-(polylactide) alone
(.about.160.degree. C.), and has improved thermal stability, see H.
Tsuji et. al., Polymer, 40 (1999) 6699-6708.
[0106] Copolymers, including block and random copolymers, of
poly(lactic acid) with other aliphatic polyesters may also be used.
Useful co-monomers include glycolide, beta-propiolactone,
tetramethylglycolide, beta-butyrolactone, gamma-butyrolactone,
pivalolactone, 2-hydroxybutyric acid, alpha-hydroxyisobutyric acid,
alpha-hydroxyvaleric acid, alpha-hydroxyisovaleric acid,
alpha-hydroxycaproic acid, alpha-hydroxyethylbutyric acid,
alpha-hydroxyisocaproic acid, alpha-hydroxy-beta-methylvaleric
acid, alpha-hydroxyoctanoic acid, alpha-hydroxydecanoic acid,
alpha-hydroxymyristic acid, and alpha-hydroxystearic acid.
[0107] Blends of poly(lactic acid) and one or more other aliphatic
polyesters, or one or more other polymers may also be used.
Examples of useful blends include poly(lactic acid) and poly(vinyl
alcohol), polyethylene glycol/polysuccinate, polyethylene oxide,
polycaprolactone and polyglycolide.
[0108] Poly(lactide)s may be prepared as described in U.S. Pat. No.
6,111,060 (Gruber, et al.), U.S. Pat. No. 5,997,568 (Liu), U.S.
Pat. No. 4,744,365 (Kaplan et al.), U.S. Pat. No. 5,475,063 (Kaplan
et al.), U.S. Pat. No. 6,143,863 (Gruber et al.), U.S. Pat. No.
6,093,792 (Gross et al.), U.S. Pat. No. 6,075,118 (Wang et al.),
U.S. Pat. No. 5,952,433 (Wang et al.), U.S. Pat. No. 6,117,928
(Hiltunen et al.), and U.S. Pat. No. 5,883,199 (McCarthy et al.),
WO 98/24951 (Tsai et al.), WO 00/12606 (Tsai et al.), WO 84/04311
(Lin), WO 99/50345 (Kolstad et al.), WO 99/06456 (Wang et al.), WO
94/07949 (Gruber et al.), WO 96/22330 (Randall et al.), and WO
98/50611 (Ryan et al.). Reference may also be made to J. W.
Leenslag, et al., J. Appl. Polymer Science, vol. 29 (1984), pp
2829-2842, and H. R. Kricheldorf, Chemosphere, vol. 43, (2001)
49-54.
[0109] The molecular weight of the polymer should be chosen so that
the polymer may be processed as a melt. For polylactide, for
example, the molecular weight may be from about 10,000 to 1,000,000
daltons, and is preferably from about 30,000 to 300,000 daltons. By
"melt-processible", it is meant that the aliphatic polyesters are
fluid or can be pumped or extruded at the temperatures used to
process the articles (e.g. make the fine fibers in BMF), and do not
degrade or gel at those temperatures to the extent that the
physical properties are so poor as to be unusable for the intended
application. Thus, many of the materials can be made into nonwovens
using melt processes such as spun bond, blown microfiber, and the
like. Certain embodiments also may be injection molded. The
aliphatic polyester may be blended with other polymers but
typically comprises at least 50 weight percent, preferably at least
60 weight percent, and most preferably at least 65 weight percent
of the fine fibers.
[0110] 2. Polypropylenes
[0111] Polypropylene (homo)polymers and copolymers useful in
practicing embodiments of the present disclosure may be selected
from polypropylene homopolymers, polypropylene copolymers, and
blends thereof (collectively polypropylene (co)polymers). The
homopolymers may be atactic polypropylene, isotactic polypropylene,
syndiotactic polypropylene and blends thereof. The copolymer can be
a random copolymer, a statistical copolymer, a block copolymer, and
blends thereof. In particular, the inventive polymer blends
described herein include impact (co)polymers, elastomers and
plastomers, any of which may be physical blends or in situ blends
with the polypropylene.
[0112] The method of making the polypropylene (co)polymer is not
critical, as it can be made by slurry, solution, gas phase or other
suitable processes, and by using catalyst systems appropriate for
the polymerization of polyolefins, such as Ziegler-Natta-type
catalysts, metallocene-type catalysts, other appropriate catalyst
systems or combinations thereof. In a preferred embodiment the
propylene (co)polymers are made by the catalysts, activators and
processes described in U.S. Pat. Nos. 6,342,566; 6,384,142; and
5,741,563; and WO 03/040201; WO 97/19991. Likewise, (co)polymers
may be prepared by the process described in U.S. Pat. Nos.
6,342,566 and 6,384,142. Such catalysts are well known in the art,
and are described in, for example, ZIEGLER CATALYSTS (Gerhard Fink,
Rolf Mulhaupt and Hans H. Brintzinger, eds., Springer-Verlag 1995);
Resconi et al., Selectivity in Propene Polymerization with
Metallocene Catalysts, 100 CHEM. REV. 1253-1345 (2000); and I, II
METALLOCENE-BASED POLYOLEFINS (Wiley & Sons 2000).
[0113] Propylene (co)polymers that are useful in practicing some
embodiments of the presently disclosed invention include those sold
under the tradenames ACHIEVE and ESCORENE by Exxon-Mobil Chemical
Company (Houston, Tex.), and various propylene (co)polymers sold by
Total Petrochemicals (Hoston, Tex.).
[0114] Presently preferred propylene homopolymers and copolymers
useful in this invention typically have: 1) a weight average
molecular weight (Mw) of at least 30,000 Da, preferably at least
50,000 Da, more preferably at least 90,000 Da, as measured by gel
permeation chromatography (GPC), and/or no more than 2,000,000 Da,
preferably no more than 1,000,000 Da, more preferably no more than
500,000 Da, as measured by gel permeation chromatography (GPC);
and/or 2) a polydispersity (defined as Mw/Mn, wherein Mn is the
number average molecular weight determined by GPC) of 1, preferably
1.6, and more preferably 1.8, and/or no more than 40, preferably no
more than 20, more preferably no more than 10, and even more
preferably no more than 3; and/or 3) a melting temperature Tm
(second melt) of at least 30.degree. C., preferably at least
50.degree. C., and more preferably at least 60.degree. C. as
measured by using differential scanning calorimetry (DSC), and/or
no more than 200.degree. C., preferably no more than 185.degree.
C., more preferably no more than 175.degree. C., and even more
preferably no more than 170.degree. C. as measured by using
differential scanning calorimetry (DSC); and/or 4) a crystallinity
of at least 5%, preferably at least 10%, more preferably at least
20% as measured using DSC, and/or no more than 80%, preferably no
more than 70%, more preferably no more than 60% as measured using
DSC; and/or 5) a glass transition temperature (T.sub.g) of at least
-40.degree. C., preferably at least -10.degree. C., more preferably
at least -10.degree. C., as measured by dynamic mechanical thermal
analysis (DMTA), and/or no more than 20.degree. C., preferably no
more than 10.degree. C., more preferably no more than 5.degree. C.,
as measured by dynamic mechanical thermal analysis (DMTA); and/or
6) a heat of fusion (Hf) of 180 J/g or less, preferably 150 J/g or
less, more preferably 120 J/g or less as measured by DSC and/or at
least 20 J/g, more preferably at least 40 J/g as measured by DSC;
and/or 7) a crystallization temperature (Tc) of at least 15.degree.
C., preferably at least 20.degree. C., more preferably at least
25.degree. C., even more preferably at least 60.degree. C. and/or,
no more than 120.degree. C., preferably no more than 115.degree.
C., more preferably no more than 110.degree. C., even more
preferably no more than 145.degree. C.
[0115] Exemplary webs of the present disclosure may include
propylene (co)polymers (including both poly(propylene) homopolymers
and copolymers) in an amount of at least 1% by weight of the web,
more preferably at least about 2% by weight of the web, most
preferably at least 3% by weight of the web. Other exemplary webs
may include propylene (co)polymers (including both poly(propylene)
homopolymers and copolymers) in an amount no more than 10% by
weight of the web, more preferably in an amount no more than 8% by
weight of the web, most preferably in an amount no more than 6% by
weight of the web. In certain presently preferred embodiments, the
webs comprise polypropylene from about 1% to about 6% by weight of
the web, more preferably from about 3% to no more than 5% by weight
of the web.
[0116] 3. Optional Additives
[0117] Fibers also may be formed from blends of materials,
including materials into which certain additives have been blended,
such as pigments or dyes. In addition to the fiber-forming
materials mentioned above, various additives may be added to the
fiber melt and extruded to incorporate the additive into the fiber.
Typically, the amount of additives is no greater than about 25 wt
%, desirably, up to about 5.0 wt %, based on a total weight of the
fiber. Suitable additives include, but are not limited to,
particulates, fillers, stabilizers, plasticizers, tackifiers, flow
control agents, cure rate retarders, adhesion promoters (for
example, silanes and titanates), adjuvants, impact modifiers,
expandable microspheres, thermally conductive particles,
electrically conductive particles, silica, glass, clay, talc,
pigments, colorants, glass beads or bubbles, antioxidants, optical
brighteners, antimicrobial agents, surfactants, wetting agents,
fire retardants, and repellents such as hydrocarbon waxes,
silicones, and fluorochemicals.
[0118] One or more of the above-described additives may be used to
reduce the weight and/or cost of the resulting fiber and layer,
adjust viscosity, or modify the thermal properties of the fiber or
confer a range of physical properties derived from the physical
property activity of the additive including electrical, optical,
density-related, liquid barrier or adhesive tack related
properties.
[0119] i) Plasticizers
[0120] In some exemplary embodiments, a plasticizer for the
thermoplastic polyester may be used in forming the fine fibers. In
some exemplary embodiments, the plasticizer for the thermoplastic
polyester is selected from poly(ethylene glycol), oligomeric
polyesters, fatty acid monoesters and di-esters, citrate esters, or
combinations thereof. Suitable plasticizers that may be used with
the aliphatic polyesters include, for example, glycols such
glycerin; propylene glycol, polyethoxylated phenols, mono or
polysubstituted polyethylene glycols, higher alkyl substituted
N-alkylpyrrolidones, sulfonamides, triglycerides, citrate esters,
esters of tartaric acid, benzoate esters, polyethylene glycols and
ethylene oxide propylene oxide random and block copolymers having a
molecular weight no greater than 10,000 Daltons (Da), preferably no
greater than about 5,000 Da, more preferably no greater than about
2,500 Da; and combinations thereof.
[0121] ii) Diluent
[0122] In some exemplary embodiments, a diluent may be added to the
mixture used to form the fine fibers. In certain exemplary
embodiments, the diluent may be selected from a fatty acid
monoester (FAME), a PLA oligomer, or combinations thereof. Diluent
as used herein generally refers to a material that inhibits,
delays, or otherwise affects crystallinity as compared to the
crystallinity that would occur in the absence of the diluent.
Diluents may also function as plasticizers.
[0123] iii) Surfactants
[0124] In certain exemplary embodiments, it may be desirable to add
a surfactant to the mixture used to form the fine fibers. In
particular exemplary embodiments, the surfactant may be selected
from a nonionic surfactant, an anionic surfactant, a cationic
surfactant, a zwitterionic surfactant, or combinations thereof. In
additional exemplary embodiments, the surfactant may be selected
from a fluoro-organic surfactant, a silicone-functional surfactant,
an organic wax, or a salt of anionic surfactants such as
dioctylsulfosuccinate.
[0125] In one presently preferred embodiment, the fine fibers may
comprise anionic surfactants that impart durable hydrophilicity.
Examples of anionic surfactants suitable for use in the prescnt
invention include those described in U.S. Patent Application
Publication No. US 2008/0200890 A1; and U.S. Ser. No. 61/061,088,
filed Jun. 12, 2008.
[0126] iv) Viscosity Modifiers
[0127] In some exemplary embodiments, fine fibers comprising a
thermoplastic aliphatic polyester polymer, e.g., polylactic acid,
polyhydroxybutyrate and the like, greater than 0% but 10% or less
by weight of polypropylene, and one or more viscosity modifiers
selected from the group of alkyl, alkenyl, aralkyl, or alkaryl
carboxylates, or combinations thereof, are formed using a fiber
forming process.
[0128] The fine fibers disclosed herein may include one or more
viscosity modifier(s) to reduce the average diameter of the fiber
during the melt process (e.g. blown microfiber (BMF), spunbond, or
injection molding). By reducing the viscosity of the aliphatic
polyester during the BMF process, the average diameter of the
fibers may be reduced, resulting in fine fibers, typically no
greater than 20 micrometers, in the melt blown web.
[0129] We have found that the addition of traditional plasticizers
for the aliphatic polyester thermoplastics result in a very gradual
viscosity reduction. This is generally not useful for producing
fine fibers of sufficient mechanical strength since the
plasticizers degrade polymer strength.
[0130] Viscosity reduction can be detected in the extrusion/BMF
equipment by recording the pressures within the equipment. The
viscosity modifiers of the present invention result in a dramatic
viscosity reduction and thus back pressure during extrusion or
thermal processing. In many cases, the viscosity reduction is so
great that the melt processing temperature must be reduced in order
to maintain sufficient melt strength. Often the melt temperature is
reduced 30.degree. C. or more.
[0131] In applications in which biodegradability is important, it
may be desirable to incorporate biodegradable viscosity modifiers,
which typically include ester and/or amide groups that may be
hydrolytically or enzymatically cleaved. Exemplary viscosity
modifiers useful in the fine fibers described herein include
viscosity modifiers with the following structure:
R--CO.sub.2.sup.-M.sup.+
[0132] where R is alkyl or alkylene of C8-C30 which is branched or
straight chain or C12-C30 aralkyl and may be optionally substituted
with 0-100 alkylene oxide groups such as ethylene oxide, propylene
oxide groups, oligameric lactic and/or glycolic acid or a
combination thereof; and
[0133] M is H, an alkali metals or an alkaline earth metal salt,
preferably Na+, K+, or Ca++, or amine salts including tertiary and
quaternary amines such as protonated triethanolamine,
tetramethylammonium and the like.
[0134] In the formula above, the ethylene oxide groups and
propylene oxide groups can occur in reverse order as well as in a
random, sequential, or block arrangement.
[0135] In certain preferred embodiments, the viscosity modifiers
useful to form fine fibers are selected from the group consisting
of alkyl carboxylates, alkenyl carboxylates, aralkyl carboxylates,
alkylethoxylated carboxylates, aralkylethoxylated carboxylates,
alkyl lactylates, alkenyl lactylates, and mixtures thereof. The
carboxylic acid equivalents of the carboxylates may also function
as viscosity modifiers. Combinations of various viscosity modifiers
can also be used. As used herein a lactylate is a surfactant having
a hydrophobe and a hydrophile wherein the hydrophile is at least in
part an oligamer of lactic acid having 1-5 lactic acid units and
typically having 1-3 lactic acid units. A preferred lactylate is
calcium stearoyl lactylate from Rita Corp. which is reported to
have the following structure:
[CH.sub.3(CH.sub.2).sub.16C(O)O--CH(CH.sub.3)--C(O)O--
CH(CH3)--C(O)O.sup.-].sub.2 Ca.sup.++. Alkyl lactylates are a
preferred class of viscosity modifiers since these also are made
from resource renewable materials.
[0136] The viscosity modifiers typically melt at or below the
extrusion temperature of the thermoplastic aliphatic polyester
composition. This greatly facilitates dispersing or dissolving the
viscosity modifier in the polymer composition. Mixtures of
viscosity modifiers may be employed to modify the melting point.
For example, mixtures of alkyl carboxylates may be preformed or an
alkyl carboxylate may be blended with a nonionic surfactant such as
a polyethoxylated surfactant. The necessary processing temperature
may be altered by addition of nonsurfactant components as well such
as plasticizers for the thermoplastics aliphatic polyester. For
example, when added to polylactic acid compositions, the viscosity
modifiers preferably have a melting point of no greater than
200.degree. C., preferably no greater than 180.degree. C., more
preferably no greater than 170.degree. C., and even more preferably
no greater than 160.degree. C.
[0137] The viscosity modifier can be conveniently compounded with
the resin in the hopper or elsewhere along the extruder as long as
good mixing is achieved to render a substantially uniform mixture.
Alternatively, the viscosity modifier may be added into the
extruder directly (without pre-compounding), for example, using a
positive displacement pump or weight loss feeder.
[0138] In some embodiments, when used in the fine fibers, the
viscosity modifiers are present in a total amount of at least 0.25
wt. %, at least 0.5 wt. %, at least 1.0 wt. %, or at least 2.0 wt.
%, based on the total weight of the fine fibers. In certain
embodiments, in which a very low viscosity melt is desired and/or a
low melt temperature is preferred, the fine fibers comprise greater
than 2 wt. %, greater than 3 wt. %, or even greater than 5 wt. % of
the viscosity modifier based on the weight of the aliphatic
polyester polymer in the fine fibers.
[0139] For melt processing, preferred viscosity modifiers have low
volatility and do not decompose appreciably under process
conditions. The preferred viscosity modifiers contain no greater
than 10 wt. % water, preferably no greater than 5% water, and more
preferably no greater than 2 wt. % and even more preferably no
greater than 1% water (determined by Karl Fischer analysis).
Moisture content is kept low in order to prevent hydrolysis of the
aliphatic polyester or other hydrolytically sensitive compounds in
the fine fibers.
[0140] The viscosity modifiers may be carried in a nonvolatile
carrier. Importantly, the carrier is typically thermally stable and
can resist chemical breakdown at processing temperatures which may
be as high as 150.degree. C., 200.degree. C., 250.degree. C., or
even as high as 300.degree. C. Preferred carriers for hydrophilic
articles include polyalkylene oxides such as polyethylene glycol,
polypropylene glycol, random and block copolymers of ethylene oxide
and propylene oxide, thermally stable polyhydric alcohols such as
propylene glycol, glycerin, polyglycerin, and the like. The
polyalkylene oxides/polyalkylene glycols may be linear or branched
depending on the initiating polyol. For example, a polyethylene
glycol initiated using ethylene glycol would be linear but one
initiated with glycerin, trimethylolpropane, or pentaerythritol
would be branched.
[0141] The viscosity modifier may be present in the melt extruded
fiber in an amount sufficient to modify the melt viscosity of
aliphatic polyester. Typically, the viscosity modifier is present
at no greater than 10 weight %, preferably no greater than 8 weight
%, more preferably no greater than 7%, more preferably no greater
than 6 weight %, more preferably no greater than 3 weight %, and
most preferably no greater than 2% by weight based on the combined
weight of the aliphatic polyester and viscosity modifier.
[0142] v) Antimicrobials
[0143] An antimicrobial component may be added to impart
antimicrobial activity to the fine fibers. The antimicrobial
component is the component that provides at least part of the
antimicrobial activity, i.e., it has at least some antimicrobial
activity for at least one microorganism. It is preferably present
in a large enough quantity to be released from the fine fibers and
kill bacteria. It may also be biodegradable and/or made or derived
from renewable resources such as plants or plant products.
Biodegradable antimicrobial components can include at least one
functional linkage such as an ester or amide linkage that can be
hydrolytically or enzymatically degraded.
[0144] In some exemplary embodiments, a suitable antimicrobial
component may be selected from a fatty acid monoester, a fatty acid
di-ester, an organic acid, a silver compound, a quaternary ammonium
compound, a cationic (co)polymer, an iodine compound, or
combinations thereof. Other examples of antimicrobial components
suitable for use in the present invention include those described
in U.S. Patent Application Publication No. 2008/0142023.
[0145] Certain antimicrobial components are uncharged and have an
alkyl or alkenyl hydrocarbon chain containing at least 7 carbon
atoms. For melt processing, preferred antimicrobial components have
low volatility and do not decompose under process conditions. The
preferred antimicrobial components contain no greater than 2 wt. %
water, and more preferably no greater than 0.10 wt. % (determined
by Karl Fischer analysis). Moisture content is kept low in order to
prevent hydrolysis of the aliphatic polyester during extrusion.
[0146] When used, the antimicrobial component content (as it is
ready to use) is typically at least 1 wt. %, 2 wt. %, 5 wt. %, 10
wt. % and sometimes greater than 15 wt. %. In certain embodiments,
in which a low strength is desired, the antimicrobial component
comprises greater than 20 wt. %, greater than 25 wt. %, or even
greater than 30 wt. % of the fine fibers.
[0147] Certain antimicrobial components are amphiphiles and may be
surface active. For example, certain antimicrobial alkyl
monoglycerides are surface active. For certain embodiments of the
invention that include antimicrobial components, the antimicrobial
component is considered distinct from a viscosity modifier
component.
[0148] vi) Particulate Phase
[0149] The fine fibers may further comprise organic and inorganic
fillers present as either an internal particulate phase within the
fibers, or as an external particulate phase on or near the surface
of the fine fibers. For implantable applications biodegradable,
resorbable, or bioerodible inorganic fillers may be particularly
appealing. These materials may help to control the degradation rate
of the polymer fine fibers. For example, many calcium salts and
phosphate salts may be suitable. Exemplary biocompatible resorbable
fillers include calcium carbonate, calcium sulfate, calcium
phosphate, calcium sodium phosphates, calcium potassium phosphates,
tetra-calcium phosphate, alpha-tri-calcium phosphate,
beta-tri-calcium phosphate, calcium phosphate apatite, octa-calcium
phosphate, di-calcium phosphate, calcium carbonate, calcium oxide,
calcium hydroxide, calcium sulfate di-hydrate, calcium sulfate
hemihydrate, calcium fluoride, calcium citrate, magnesium oxide,
and magnesium hydroxide. A particularly suitable filler is
tri-basic calcium phosphate (hydroxy apatite).
[0150] Other additional components include antioxidants, colorants
such as dyes and/or pigments, antistatic agents, fluorescent
brightening agents, odor control agents, perfumes and fragrances,
active ingredients to promote wound healing or other dermatological
activity, combinations thereof, and the like.
C. Methods of Making Dimensionally Stable Nonwoven Fibrous Webs
[0151] Exemplary processes that are capable of producing oriented
fine fibers include: oriented film filament formation,
melt-spinning, plexifilament formation, spunbonding, wet spinning,
and dry spinning. Suitable processes for producing oriented fibers
are also known in the art (see, for example, Ziabicki, Andrzej,
Fundamentals of Fibre Formation: The Science of Fibre Spinning and
Drawing, Wiley, London, 1976.). Orientation does not need to be
imparted within a fiber during initial fiber formation, and may be
imparted after fiber formation, most commonly using drawing or
stretching processes.
[0152] The dimensionally stable nonwoven fibrous webs may include
fine fibers that are substantially sub-micrometer fibers, fine
fibers that are substantially microfibers, or combinations thereof.
In some exemplary embodiments, a dimensionally stable nonwoven
fibrous web may be formed of sub-micrometer fibers commingled with
coarser microfibers providing a support structure for the
sub-micrometer nonwoven fibers. The support structure may provide
the resiliency and strength to hold the fine sub-micrometer fibers
in the preferred low Solidity form. The support structure could be
made from a number of different components, either singly or in
concert. Examples of supporting components include, for example,
microfibers, discontinuous oriented fibers, natural fibers, foamed
porous cellular materials, and continuous or discontinuous non
oriented fibers.
[0153] Sub-micrometer fibers are typically very long, though they
are generally regarded as discontinuous. Their long lengths--with a
length-to-diameter ratio approaching infinity in contrast to the
finite lengths of staple fibers--causes them to be better held
within the matrix of microfibers. They are usually organic and
polymeric and often of the molecularly same polymer as the
microfibers. As the streams of sub-micrometer fiber and microfibers
merge, the sub-micrometer fibers become dispersed among the
microfibers. A rather uniform mixture may be obtained, especially
in the x-y dimensions, or plane of the web, with the distribution
in the z dimension being controlled by particular process steps
such as control of the distance, the angle, and the mass and
velocity of the merging streams.
[0154] The relative amount of sub-micrometer fibers to microfibers
included in a blended nonwoven composite fibrous web of the present
disclosure can be varied depending on the intended use of the web.
An effective amount, i.e., an amount effective to accomplish
desired performance, need not be large in weight amount. Usually
the microfibers account for at least one weight percent and no
greater than about 75 weight percent of the fibers of the web.
Because of the high surface area of the microfibers, a small weight
amount may accomplish desired performance. In the case of webs that
include very small microfibers, the microfibers generally account
for at least 5 percent of the fibrous surface area of the web, and
more typically 10 or 20 percent or more of the fibrous surface
area. A particular advantage of exemplary embodiments of the
present invention is the ability to present small-diameter fibers
to a needed application such as filtration or thermal or acoustic
insulation.
[0155] In one exemplary embodiment, a microfiber stream is formed
and a sub-micrometer fiber stream is separately formed and added to
the microfiber stream to form the dimensionally stable nonwoven
fibrous web. In another exemplary embodiment, a sub-micrometer
fiber stream is formed and a microfiber stream is separately formed
and added to the sub-micrometer fiber stream to form the
dimensionally stable nonwoven fibrous web. In these exemplary
embodiments, either one or both of the sub-micrometer fiber stream
and the microfiber stream is oriented. In an additional embodiment,
an oriented sub-micrometer fiber stream is formed and discontinuous
microfibers are added to the sub-micrometer fiber stream, e.g.
using a process as described in U.S. Pat. No. 4,118,531
(Hauser).
[0156] In some exemplary embodiments, the method of making a
dimensionally stable nonwoven fibrous web comprises combining the
sub-micrometer fiber population and the microfiber population into
a dimensionally stable nonwoven fibrous web by mixing fiber
streams, hydroentangling, wet forming, plexifilament formation, or
a combination thereof. In combining the sub-micrometer fiber
population with the microfiber population, multiple streams of one
or both types of fibers may be used, and the streams may be
combined in any order. In this manner, nonwoven composite fibrous
webs may be formed exhibiting various desired concentration
gradients and/or layered structures.
[0157] For example, in certain exemplary embodiments, the
population of sub-micrometer fibers may be combined with the
population of microfibers to form an inhomogenous mixture of
fibers. In other exemplary embodiments, the population of
sub-micrometer fibers may be formed as an overlayer on an
underlayer comprising the population of microfibers. In certain
other exemplary embodiments, the population of microfibers may be
formed as an overlayer on an underlayer comprising the population
of sub-micrometer fibers.
[0158] In other exemplary embodiments, the nonwoven fibrous article
may be formed by depositing the population of sub-micrometer fibers
onto a support layer, the support layer optionally comprising
microfibers, so as to form a population of sub-micrometer fibers on
the support layer or substrate. The method may comprise a step
wherein the support layer, which optionally comprises polymeric
microfibers, is passed through a fiber stream of sub-micrometer
fibers having a median fiber diameter of no greater than 1
micrometer (.mu.m). While passing through the fiber stream,
sub-micrometer fibers may be deposited onto the support layer so as
to be temporarily or permanently bonded to the support layer. When
the fibers are deposited onto the support layer, the fibers may
optionally bond to one another, and may further harden while on the
support layer.
[0159] In certain presently preferred embodiments, the
sub-micrometer fiber population is combined with an optional
support layer that comprises at least a portion of the microfiber
population. In other presently preferred embodiments, the
sub-micrometer fiber population is combined with an optional
support layer and subsequently combined with at least a portion of
the microfiber population.
[0160] 1. Formation of Sub-Micrometer Fibers
[0161] A number of processes may be used to produce and deposit
sub-micrometer fibers, including, but not limited to melt blowing,
melt spinning, or combination thereof. Particularly suitable
processes include, but are not limited to, processes disclosed in
U.S. Pat. No. 3,874,886 (Levecque et al.), U.S. Pat. No. 4,363,646
(Torobin), U.S. Pat. No. 4,536,361 (Torobin), U.S. Pat. No.
5,227,107 (Dickenson et al.), U.S. Pat. No. 6,183,670 (Torobin),
U.S. Pat. No. 6,743,273 (Chung et al.), and U.S. Pat. No. 6,800,226
(Gerking), and DE 19929709 C2 (Gerking).
[0162] Suitable processes for forming sub-micrometer fibers also
include electrospinning processes, for example, those processes
described in U.S. Pat. No. 1,975,504 (Formhals). Other suitable
processes for forming sub-micrometer fibers are described in U.S.
Pat. No. 6,114,017 (Fabbricante et al.); U.S. Pat. No. 6,382,526 B1
(Reneker et al.); and U.S. Pat. No. 6,861,025 B2 (Erickson et
al.).
[0163] The methods of making dimensionally stable nonwoven fibrous
webs of the present disclosure may be used to form a sub-micrometer
fiber component containing fibers formed from any of the
above-mentioned polymeric materials. Typically, the sub-micrometer
fiber forming method step involves melt extruding a thermoformable
material at a melt extrusion temperature ranging from about
130.degree. C. to about 350.degree. C. A die assembly and/or
coaxial nozzle assembly (see, for example, the Torobin process
referenced above) comprises a population of spinnerets and/or
coaxial nozzles through which molten thermoformable material is
extruded. In one exemplary embodiment, the coaxial nozzle assembly
comprises a population of coaxial nozzles formed into an array so
as to extrude multiple streams of fibers onto a support layer or
substrate. See, for example, U.S. Pat. No. 4,536,361 (FIG. 2) and
U.S. Pat. No. 6,183,670 (FIGS. 1-2).
[0164] 2. Formation of Microfibers
[0165] A number of processes may be used to produce and deposit
microfibers, including, but not limited to, melt blowing, melt
spinning, filament extrusion, plexifilament formation, spunbonding,
wet spinning, dry spinning, or a combination thereof. Suitable
processes for forming microfibers are described in U.S. Pat. No.
6,315,806 (Torobin); U.S. Pat. No. 6,114,017 (Fabbricante et al.);
U.S. Pat. No. 6,382,526 B1 (Reneker et al.); and U.S. Pat. No.
6,861,025 B2 (Erickson et al.). Alternatively, a population of
microfibers may be formed or converted to staple fibers and
combined with a population of sub-micrometer fibers using, for
example, using a process as described in U.S. Pat. No. 4,118,531
(Hauser). In certain exemplary embodiments, the population of
microfibers comprises a web of bonded microfibers, wherein bonding
is achieved using thermal bonding, adhesive bonding, powdered
binder, hydroentangling, needlepunching, calendering, or a
combination thereof, as described below.
[0166] 3. Apparatus for Forming Dimensionally Stable Nonwoven
Fibrous Webs
[0167] A variety of equipment and techniques are known in the art
for melt processing polymeric fine fibers. Such equipment and
techniques are disclosed, for example, in U.S. Pat. No. 3,565,985
(Schrenk et al.); U.S. Pat. No. 5,427,842 (Bland et. al.); U.S.
Pat. Nos. 5,589,122 and 5,599,602 (Leonard); and U.S. Pat. No.
5,660,922 (Henidge et al.). Examples of melt processing equipment
include, but are not limited to, extruders (single and twin screw),
Banbury mixers, and Brabender extruders for melt processing the
inventive fine fibers.
[0168] The (BMF) meltblowing process is one particular exemplary
method of forming a nonwoven web of molecularly unoriented fibers
where a polymer fluid, either molten or as a solution, is extruded
through one or more rows of holes then impinged by a high velocity
gas jet. The gas jet, typically heated air, entrains and draws the
polymer fluid and helps to solidify the polymer into a fiber. The
solid fiber is then collected on solid or porous surface as a
nonwoven web. This process is described by Van Wente in "Superfine
Thermoplastic Fibers", Industrial Engineering Chemistry, vol. 48,
pp. 1342-1346. An improved version of the meltblowing process is
described by Buntin et al. as described in U.S. Pat. No.
3,849,241.
[0169] As part of an exemplary BMF process for making fine fibers,
a thermoplastic polyester and polypropylene in a melt form may be
mixed in a sufficient amount relative to an optional viscosity
modifier to yield fine fibers having average diameter
characteristics as described hereinabove. The ingredients of the
fine fibers may be mixed in and conveyed through an extruder to
yield a polymer, preferably without substantial polymer degradation
or uncontrolled side reactions in the melt. The processing
temperature is sufficient to mix the biodegradable aliphatic
polyester viscosity modifier, and allow extruding the polymer.
Potential degradation reactions include transesterification,
hydrolysis, chain scission and radical chain define fibers, and
process conditions should minimize such reactions.
[0170] The viscosity modifiers in the present disclosure need not
be added to the fiber extrusion process in a pure state. The
viscosity modifiers may be compounded with the aliphatic polyester,
or other materials prior to extrusion. Commonly, when additives
such as viscosity modifiers are compounded prior to extrusion, they
are compounded at a higher concentration than desired for the final
fiber. This high concentration compound is referred to as a master
batch. When a master batch is used, the master batch will generally
be diluted with pure polymer prior to entering the fiber extrusion
process. Multiple additives may be present in a masterbatch, and
multiple master batches may be used in the fiber extrusion
process.
[0171] An alternative melt blown process that may benefit from the
use of viscosity modifiers as provided herein is described in U.S.
Patent Application Publication No. 2008/0160861.
[0172] Depending on the condition of the microfibers and
sub-micrometer fibers, some bonding may occur between the fibers
during collection. However, further bonding between the microfibers
in the collected web is usually needed to provide a matrix of
desired coherency, making the web more handleable and better able
to hold the sub-micrometer fibers within the matrix ("bonding"
fibers means adhering the fibers together firmly, so they generally
do not separate when the web is subjected to normal handling).
[0173] Conventional bonding techniques using heat and pressure
applied in a point-bonding process or by smooth calender rolls can
be used, though such processes may cause undesired deformation of
fibers or compaction of the web. A more preferred technique for
bonding the microfibers is taught in U.S. Patent Application
Publication No. 2008/0038976. Apparatus for performing this
technique is illustrated in FIGS. 1, 5 and 6 of the drawings.
[0174] In brief summary, as applied to the present disclosure, this
preferred technique involves subjecting the collected web of
microfibers and sub-micrometer fibers to a controlled heating and
quenching operation that includes a) forcefully passing through the
web a gaseous stream heated to a temperature sufficient to soften
the microfibers sufficiently to cause the microfibers to bond
together at points of fiber intersection (e.g., at sufficient
points of intersection to form a coherent or bonded matrix), the
heated stream being applied for a discrete time too short to wholly
melt the fibers, and b) immediately forcefully passing through the
web a gaseous stream at a temperature at least 50.degree. C. no
greater than the heated stream to quench the fibers (as defined in
the above-mentioned U.S. Patent Application Publication No.
2008/0038976, "forcefully" means that a force in addition to normal
room pressure is applied to the gaseous stream to propel the stream
through the web; "immediately" means as part of the same operation,
i.e., without an intervening time of storage as occurs when a web
is wound into a roll before the next processing step). As a
shorthand term this technique is described as the quenched flow
heating technique, and the apparatus as a quenched flow heater.
[0175] It has been found that the sub-micrometer fibers do not
substantially melt or lose their fiber structure during the bonding
operation, but remain as discrete microfibers with their original
fiber dimensions. Without wishing to be bound by any particular
theory, Applicant's believe that sub-micrometer fibers have a
different, less crystalline morphology than microfibers, and we
theorize that the limited heat applied to the web during the
bonding operation is exhausted in developing crystalline growth
within the sub-micrometer fibers before melting of the
sub-micrometer fibers occurs. Whether this theory is correct or
not, bonding of the microfibers without substantial melting or
distortion of the sub-micrometer fibers does occur and may be
beneficial to the properties of the finished web.
[0176] A variation of the described method, taught in more detail
in the aforementioned U.S. Patent Application Publication No.
2008/0038976, takes advantage of the presence of two different
kinds of molecular phases within microfibers--one kind called
crystallite-characterized molecular phases because of a relatively
large presence of chain-extended, or strain-induced, crystalline
domains, and a second kind called amorphous-characterized phases
because of a relatively large presence of domains of lower
crystalline order (i.e., not chain-extended) and domains that are
amorphous, though the latter may have some order or orientation of
a degree insufficient for crystallinity. These two different kinds
of phases, which need not have sharp boundaries and can exist in
mixture with one another, have different kinds of properties,
including different melting and/or softening characteristics: the
first phase characterized by a larger presence of chain-extended
crystalline domains melts at a temperature (e.g., the melting point
of the chain-extended crystalline domain) that is higher than the
temperature at which the second phase melts or softens (e.g., the
glass transition temperature of the amorphous domain as modified by
the melting points of the lower-order crystalline domains).
[0177] In the stated variation of the described method, heating is
at a temperature and for a time sufficient for the
amorphous-characterized phase of the fibers to melt or soften while
the crystallite-characterized phase remains unmelted. Generally,
the heated gaseous stream is at a temperature greater than the
onset melting temperature of the polymeric material of the fibers.
Following heating, the web is rapidly quenched as discussed
above.
[0178] Treatment of the collected web at such a temperature is
found to cause the microfibers to become morphologically refined,
which is understood as follows (we do not wish to be bound by
statements herein of our "understanding," which generally involve
some theoretical considerations). As to the amorphous-characterized
phase, the amount of molecular material of the phase susceptible to
undesirable (softening-impeding) crystal growth is not as great as
it was before treatment. The amorphous-characterized phase is
understood to have experienced a kind of cleansing or reduction of
molecular structure that would lead to undesirable increases in
crystallinity in conventional untreated fibers during a thermal
bonding operation. Treated fibers of certain exemplary embodiments
of the present invention may be capable of a kind of "repeatable
softening," meaning that the fibers, and particularly the
amorphous-characterized phase of the fibers, will undergo to some
degree a repeated cycle of softening and resolidifying as the
fibers are exposed to a cycle of raised and lowered temperature
within a temperature region lower than that which would cause
melting of the whole fiber.
[0179] In practical terms, repeatable softening is indicated when a
treated web (which already generally exhibits a useful bonding as a
result of the heating and quenching treatment) can be heated to
cause further autogenous bonding of the fibers. The cycling of
softening and resolidifying may not continue indefinitely, but it
is generally sufficient that the fibers may be initially bonded by
exposure to heat, e.g., during a heat treatment according to
certain exemplary embodiments of the present invention, and later
heated again to cause re-softening and further bonding, or, if
desired, other operations, such as calendering or re-shaping. For
example, a web may be calendered to a smooth surface or given a
nonplanar shape, e.g., molded into a face mask, taking advantage of
the improved bonding capability of the fibers (though in such cases
the bonding is not limited to autogenous bonding).
[0180] While the amorphous-characterized, or bonding, phase has the
described softening role during web-bonding, calendering, shaping
or other like operation, the crystallite-characterized phase of the
fiber also may have an important role, namely to reinforce the
basic fiber structure of the fibers. The crystallite-characterized
phase generally can remain unmelted during a bonding or like
operation because its melting point is higher than the
melting/softening point of the amorphous-characterized phase, and
it thus remains as an intact matrix that extends throughout the
fiber and supports the fiber structure and fiber dimensions.
[0181] Thus, although heating the web in an autogenous bonding
operation may cause fibers to weld together by undergoing some flow
and coalescence at points of fiber intersection, the basic discrete
fiber structure is substantially retained over the length of the
fibers between intersections and bonds; preferably, the
cross-section of the fibers remains unchanged over the length of
the fibers between intersections or bonds formed during the
operation. Similarly, although calendering of a web may cause
fibers to be reconfigured by the pressure and heat of the
calendering operation (thereby causing the fibers to permanently
retain the shape pressed upon them during calendering and make the
web more uniform in thickness), the fibers generally remain as
discrete fibers with a consequent retention of desired web
porosity, filtration, and insulating properties.
[0182] One aim of the quenching is to withdraw heat before
undesired changes occur in the microfibers contained in the web.
Another aim of the quenching is to rapidly remove heat from the web
and the fibers and thereby limit the extent and nature of
crystallization or molecular ordering that will subsequently occur
in the fibers. By rapid quenching from the molten/softened state to
a solidified state, the amorphous-characterized phase is understood
to be frozen into a more purified crystalline form, with reduced
molecular material that can interfere with softening, or repeatable
softening, of the fibers. For some purposes, quenching may not be
absolutely required though it is strongly preferred for most
purposes.
[0183] To achieve quenching the mass is desirably cooled by a gas
at a temperature at least 50.degree. C. no greater than the nominal
melting point; also the quenching gas is desirably applied for a
time on the order of at least one second (the nominal melting point
is often stated by a polymer supplier; it can also be identified
with differential scanning calorimetry, and for purposes herein,
the "Nominal Melting Point" for a polymer is defined as the peak
maximum of a second-heat, total-heat-flow DSC plot in the melting
region of a polymer if there is only one maximum in that region;
and, if there are more than one maximum indicating more than one
melting point (e.g., because of the presence of two distinct
crystalline phases), as the temperature at which the
highest-amplitude melting peak occurs). In any event the quenching
gas or other fluid has sufficient heat capacity to rapidly solidify
the fibers.
[0184] One advantage of certain exemplary embodiments of the
present invention may be that the sub-micrometer fibers held within
a microfiber web may be better protected against compaction than
they would be if present in an all-sub-micrometer fiber layer. The
microfibers are generally larger, stiffer and stronger than the
sub-micrometer fibers, and they can be made from material different
from that of the microfibers. The presence of the microfibers
between the sub-micrometer fibers and an object applying pressure
may limit the application of crushing force on the sub-micrometer
fibers. Especially in the case of sub-micrometer fibers, which can
be quite fragile, the increased resistance against compaction or
crushing that may be provided by certain exemplary embodiments of
the present invention offers an important benefit. Even when webs
according to the present disclosure are subjected to pressure,
e.g., by being rolled up in jumbo storage rolls or in secondary
processing, webs of the present disclosure may offer good
resistance to compaction of the web, which could otherwise lead to
increased pressure drop and poor loading performance for filters.
The presence of the microfibers also may add other properties such
as web strength, stiffness and handling properties.
[0185] The diameters of the fibers can be tailored to provide
needed filtration, acoustic absorption, and other properties. For
example it may be desirable for the microfibers to have a median
diameter of 5 to 50 micrometers (.mu.m) and the sub-micrometer
fibers to have a median diameter from 0.1 .mu.m to no greater than
1 .mu.m, for example, 0.9 .mu.m. Preferably the microfibers have a
median diameter between 5 .mu.m and 50 .mu.m, whereas the
sub-micrometer fibers preferably have a median diameter of 0.5
.mu.m to no greater than 1 .mu.m, for example, 0.9 .mu.m.
[0186] As previously stated, certain exemplary embodiments of the
present invention may be particularly useful to combine very small
microfibers, for example ultrafine microfibers having a median
diameter of from 1 .mu.m to about 2 .mu.m, with the sub-micrometer
fibers. Also, as discussed above, it may be desirable to form a
gradient through the web, e.g., in the relative proportion of
sub-micrometer fibers to microfibers over the thickness of the web,
which may be achieved by varying process conditions such as the air
velocity or mass rate of the sub-micrometer fiber stream or the
geometry of the intersection of the microfiber and sub-micrometer
fiber streams, including the distance of the die from the
microfiber stream and the angle of the sub-micrometer fiber stream.
A higher concentration of sub-micrometer fibers near one edge of a
dimensionally stable nonwoven fibrous web according to the present
disclosure may be particularly advantageous for gas and/or liquid
filtration applications.
[0187] In preparing microfibers or sub-micrometer fibers according
to various embodiments of the present disclosure, different
fiber-forming materials may be extruded through different orifices
of a meltspinning extrusion head or meltblowing die so as to
prepare webs that comprise a mixture of fibers. Various procedures
are also available for electrically charging a dimensionally stable
nonwoven fibrous web to enhance its filtration capacity: see e.g.,
U.S. Pat. No. 5,496,507 (Angadjivand).
[0188] If a web could be prepared from the sub-micrometer fibers
themselves, such a web would be flimsy and weak. However, by
incorporating the population of sub-micrometer fibers with a
population of microfibers in a coherent, bonded, oriented composite
fibrous structure, a strong and self-supporting web or sheet
material can be obtained, either with or without an optional
support layer.
[0189] In addition to the foregoing methods of making a
dimensionally stable nonwoven fibrous web, one or more of the
following process steps may be carried out on the web once
formed:
[0190] (1) advancing the dimensionally stable nonwoven fibrous web
along a process pathway toward further processing operations;
[0191] (2) bringing one or more additional layers into contact with
an outer surface of the sub-micrometer fiber component, the
microfiber component, and/or the optional support layer;
[0192] (3) calendering the dimensionally stable nonwoven fibrous
web;
[0193] (4) coating the dimensionally stable nonwoven fibrous web
with a surface treatment or other composition (e.g., a fire
retardant composition, an adhesive composition, or a print
layer);
[0194] (5) attaching the dimensionally stable nonwoven fibrous web
to a cardboard or plastic tube;
[0195] (6) winding-up the dimensionally stable nonwoven fibrous web
in the form of a roll;
[0196] (7) slitting the dimensionally stable nonwoven fibrous web
to form two or more slit rolls and/or a plurality of slit
sheets;
[0197] (8) placing the dimensionally stable nonwoven fibrous web in
a mold and molding the dimensionally stable nonwoven fibrous web
into a new shape;
[0198] (9) applying a release liner over an exposed optional
pressure-sensitive adhesive layer, when present; and
[0199] (10) attaching the dimensionally stable nonwoven fibrous web
to another substrate via an adhesive or any other attachment device
including, but not limited to, clips, brackets, bolts/screws,
nails, and straps.
D. Articles Formed from Dimensionally Stable Nonwoven Fibrous
Webs
[0200] The present disclosure is also directed to methods of using
the dimensionally stable nonwoven fibrous webs of the present
disclosure in a variety of applications. In a further aspect, the
disclosure relates to an article comprising a dimensionally stable
nonwoven fibrous web according to the present disclosure. In
exemplary embodiments, the article may be used as a gas filtration
article, a liquid filtration article, a sound absorption article, a
thermal insulation article, a surface cleaning article, a cellular
growth support article, a drug delivery article, a personal hygiene
article, a dental hygiene article, a surgical drape, a surgical
equipment isolation drape, a surgical gown, a medical gown,
healthcare patient gowns and attire, an apron or other apparel, a
sterilization wrap, a wipe, agricultural fabrics, food packaging,
packaging, or a wound dressing article.
[0201] For example, a dimensionally stable nonwoven fibrous web of
the present disclosure may be advantageous in gas filtration
applications due to the reduced pressure drop that results from
lower Solidity. Decreasing the Solidity of a sub-micrometer fiber
web will generally reduce its pressure drop. Lower pressure drop
increase upon particulate loading of low Solidity sub-micrometer
dimensionally stable nonwoven fibrous web of the present disclosure
may also result. Current technology for forming particle-loaded
sub-micrometer fibers results in much higher pressure drop than for
coarser microfiber webs, partially due to the higher Solidity of
the fine sub-micrometer fiber web.
[0202] In addition, the use of sub-micrometer fibers in gas
filtration may be particularly advantageous due to the improved
particle capture efficiency that sub-micrometer fibers may provide.
In particular, sub-micrometer fibers may capture small diameter
airborne particulates better than coarser fibers. For example,
sub-micrometer fibers may more efficiently capture airborne
particulates having a dimension smaller than about 1000 nanometers
(nm), more preferably smaller than about 500 nm, even more
preferably smaller than about 100 nm, and most preferably below
about 50 nm. Gas filters such as this may be particularly useful in
personal protection respirators; heating, ventilation and air
conditioning (HVAC) filters; automotive air filters (e.g.
automotive engine air cleaners, automotive exhaust gas filtration,
automotive passenger compartment air filtration); and other
gas-particulate filtration applications.
[0203] Liquid filters containing sub-micrometer fibers in the form
of dimensionally stable nonwoven fibrous webs of the present
disclosure may also have the advantage of improved depth loading
while maintaining small pore size for capture of sub-micrometer,
liquid-borne particulates. These properties improve the loading
performance of the filter by allowing the filter to capture more of
the challenge particulates without plugging.
[0204] A fiber-containing dimensionally stable nonwoven fibrous web
of the present disclosure may also be a preferred substrate for
supporting a membrane. The low Solidity fine web could act a both a
physical support for the membrane, but also as a depth pre-filter,
enhancing the life of the membrane. The use of such a system could
act as a highly effective symmetric or asymmetric membrane.
Applications for such membranes include ion-rejection,
ultrafiltration, reverse osmosis, selective binding and/or
adsorption, and fuel cell transport and reaction systems.
[0205] Dimensionally stable nonwoven fibrous webs of the present
disclosure may also be useful synthetic matrices for promoting
cellular growth. The open structure with fine sub-micrometer fibers
may mimic naturally occurring systems and promotes more in
vivo-like behavior. This is in contrast to current products (such
as Donaldson ULTRA-WEB.TM. Synthetic ECM, available from Donaldson
Corp., Minneapolis, Minn.) where high Solidity fiber webs act as a
synthetic support membrane, with little or no penetration of cells
within the fiber matrix.
[0206] The structure provided by the dimensionally stable nonwoven
fibrous webs of the present disclosure may also be an effective
wipe for surface cleaning, where the fine sub-micrometer fibers
form a soft wipe, while low Solidity may have the advantage of
providing a reservoir for cleaning agents and high pore volume for
trapping debris.
[0207] For acoustic and thermal insulation applications, providing
the fine sub-micrometer fibers in a low Solidity form improves
acoustic absorbance by exposing more of the surface area of the
sub-micrometer fibers, as well as specifically improving low
frequency acoustic absorbance by allowing for a thicker web for a
given basis weight. In thermal insulation applications in
particular, a fine sub-micrometer fiber insulation containing
sub-micrometer fibers would have a soft feel and high drapability,
while providing a very low Solidity web for trapping insulating
air. In some embodiments, the nonwoven web may comprise hollow
fibers or filaments or fibers containing gas voids. A spunbond
process may be used to prepare nonwoven fabric of continuous,
hollow fibers or filaments containing voids that are particularly
useful for acoustic and thermal insulation; the voids may allow for
an improvement in acoustic damping, reduction in thermal
conductivity, and a reduction in weight of the dimensionally stable
nonwoven fibrous webs and articles made therefrom.
[0208] In some embodiments of a use of such an acoustic and/or
thermal insulation article, an entire area may be surrounded by a
dimensionally stable nonwoven fibrous web prepared according to
embodiments of the present disclosure, provided alone or on a
support layer. The support structure and the fibers comprising the
dimensionally stable nonwoven fibrous web may, but need not be
homogeneously dispersed within one another. There may be advantages
in cushioning, resiliency and filter loading for asymmetric loading
to provide ranges of pore sizes, higher density regions, exterior
skins or flow channels.
[0209] The fine fibers are particularly useful for making absorbent
or repellent aliphatic polyester nonwoven gowns and film laminate
drapes used in surgery as well as personal care absorbents such as
feminine hygiene pads, diapers, incontinence pads, wipes, fluid
filters, insulation and the like.
[0210] Various embodiments of the presently disclosed invention
also provides useful articles made from fabrics and webs of fine
fibers including medical drapes, medical gowns, aprons, filter
media, industrial wipes and personal care and home care products
such as diapers, facial tissue, facial wipes, wet wipes, dry wipes,
disposable absorbent articles and garments such as disposable and
reusable garments including infant diapers or training pants, adult
incontinence products, feminine hygiene products such as sanitary
napkins and panty liners and the like. The fine fibers of this
invention also may be useful for producing thermal insulation for
garments such as coats, jackets, gloves, cold weather pants, boots,
and the like as well as acoustical insulation.
[0211] In yet another aspect, this invention provides multi-layer,
aqueous liquid-absorbent articles comprising an aqueous media
impervious backing sheet. For example, importantly some surgical
drapes are liquid impervious to prevent liquid that is absorbed
into the top sheet from wicking through to the skin surface where
it would be contaminated with bacteria present on the skin. In
other embodiments the construction may further comprise an aqueous
media permeable topsheet, and an aqueous liquid-absorbent (i.e.,
hydrophilic) layer constructed of the above-described web or fabric
juxtaposed there between useful, for instance, in constructing
disposable diapers, wipes or towels, sanitary napkins, and
incontinence pads.
[0212] In yet another aspect, a single or multi-layer aqueous
repellent article such as a surgical or medical gown or apron can
be formed at least in part of a web of fine fibers described
herein, and having aqueous fluid repellent properties. For example,
an SMS web may be formed having fine fibers in at least the M (melt
blown, blow microfiber) layer but they may also comprise the S
(spunbond layer as well). The M layer may have further incorporated
therein a repellent additive such as a fluorochemical. In this
manner, the gown is rendered fluid repellent to avoid absorption of
blood or other body fluids that may contain pathogenic
microorganisms. Alternatively, the web may be post treated with a
repellent finish such as a fluorochemical.
[0213] In yet another aspect, a wrap may be formed that is used to
wrap clean instruments prior to surgery or other procedure
requiring sterile tools. These wraps allow penetration of
sterilizing gasses such as steam, ethylene oxide, hydrogen
peroxide, etc. but they do not allow penetration of bacteria. They
may be made of a single or multi-layer aqueous repellent article
such as a sterilization wrap can be formed at least in part of a
web of fine fibers described herein, and having aqueous fluid
repellent properties. For example, a SMS, SMMS, or other nonwoven
construction web may be formed having fine fibers in at least the M
(melt blown, blown microfiber) layer but they may also comprise the
S (spunbond layer as well). The M layer may have further
incorporated therein or thereon a repellent additive such as a
fluorochemical.
[0214] Preferred fluorochemicals comprise a perfluoroalkyl group
having at least 4 carbon atoms. These fluorochemicals may be small
molecules, oligamers, or polymers. Suitable fluorochemicals may be
found in U.S. Pat. No. 6,127,485 (Klun at al.) and U.S. Pat. No.
6,262,180 (Klun et al). Other suitable repellants may include
fluorochemicals and silicone fluids repellents disclosed in U.S.
Ser. No. 61/061,091, filed Jun. 12, 2008, and PCT Publication No.
WO 2009/152349. In some instances hydrocarbon type repellents may
be suitable.
[0215] A sterilization wrap constructed from such a single or
multi-layer repellent article described herein possesses all of the
properties required of a sterilization wrap; i.e., permeability to
steam or ethylene oxide or other gaseous sterilant during
sterilization (and during drying or aeration) of the articles it
encloses, repellency of liquid water during storage to avoid
contamination of the contents of the wrap by water-borne
contaminants, and a tortuous path barrier to contamination by air-
or water-borne microbes during storage of the sterilized pack.
[0216] The fine fiber webs of exemplary embodiments of the
presently disclosed invention may be rendered more repellent by
treatment with numerous compounds. For example, the fabrics may be
post web forming surface treatments which include paraffin waxes,
fatty acids, bee's wax, silicones, fluorochemicals and combinations
thereof. For example, the repellent finishes may be applied as
disclosed in U.S. Pat. Nos. 5,027,803; 6,960,642; and 7,199,197.
Repellent finishes may also be melt additives such as those
described in U.S. Pat. No. 6,262,180.
[0217] Articles comprising the dimensionally stable nonwoven
fibrous webs of the present disclosure may be made by processes
known in the art for making products like polymer sheets from
polymer resins. For many applications, such articles can be placed
in water at 23.degree. C. without substantial loss of physical
integrity (e.g. tensile strength) after being immersed 2 hours and
dried. Typically, these articles contain little or no water. The
water content in the article after extruding, injection molding or
solvent casting is typically no greater than 10% by weight,
preferably no greater than 5% by weight, more preferably no greater
than 1% by weight and most preferably no greater than 0.2% by
weight.
[0218] Articles that may be made of dimensionally stable nonwoven
fibrous webs of the present disclosure may include medical drapes
and gowns, including surgical drapes, procedural drapes, plastic
specialty drapes, incise drapes, barrier drapes, barrier gowns,
SMS, SMMS, or other nonwoven gowns, SMS, SMMS, or other nonwoven
sterilization wraps, and the like, wound dressings, wound
absorbents, wound contact layers, surgical sponges use to absorb
blood and body fluids during surgery, surgical implants, and other
medical devices. Articles made of the dimensionally stable nonwoven
fibrous webs of the present disclosure may be solvent, heat, or
ultrasonically welded together as well as being welded to other
compatible articles. The dimensionally stable nonwoven fibrous webs
of the present disclosure may be used in conjunction with other
materials to form constructions such as sheath/core materials,
laminates, compound structures of two or more materials, or useful
as coatings on various medical devices. The dimensionally stable
nonwoven fibrous webs described herein may be particularly useful
in the fabrication of surgical sponges.
[0219] Some of the preferred hydrophilic additive surfactants of
the present invention may allow for adhesive, thermal, and/or
ultrasonic bonding of fabrics and films made thereof. Exemplary
dimensionally stable nonwoven fibrous webs of the present
disclosure may be particularly suitable for use in surgical drapes
and gowns. Exemplary non-woven web and sheets comprising the
dimensionally stable nonwoven fibrous webs of the present
disclosure can be heat sealed to form strong bonds allowing
specialty drape fabrication; can be made from renewable resources
which can be important in disposable products; and can have high
surface energy to allow wettability and fluid absorbency in the
case of non-wovens. In other applications a low surface energy may
be desirable to impart fluid repellency.
[0220] It is believed that certain dimensionally stable nonwoven
fibrous webs of the present disclosure can be sterilized by gamma
radiation or electron beam without significant loss of physical
strength (tensile strength for a 1 mil thick film does not decrease
by more than 20% and preferably by not more than 10% after exposure
to 2.5 Mrad gamma radiation from a cobalt gamma radiation source
and aged at 23.degree.-25.degree. C. for 7 days.
[0221] The hydrophilic characteristic of some exemplary
dimensionally stable nonwoven fibrous webs of the present
disclosure may improve articles such as wound and surgical
dressings by improving absorbency. If the fine fibers is used in a
wound dressing backing film, the film may be partially (e.g. zone
or pattern) coated or completely coated with various adhesives,
including but not limited to pressure sensitive adhesives (PSAs),
such as acrylic and block copolymer adhesives, hydrogel adhesives,
hydrocolloid adhesives, and foamed adhesives. PSAs can have a
relatively high moisture vapor transmission rate to allow for
moisture evaporation.
[0222] Suitable pressure sensitive adhesives include those based on
acrylates, polyurethanes, KRATON and other block copolymers,
silicones, rubber based adhesives as well as combinations of these
adhesives. The preferred PSAs are the normal adhesives that are
applied to skin such as the acry late copolymers described in U.S.
Pat. No. RE 24,906, particularly a 97:3 iso-octyl
acrylate:acrylamide copolymer. Also preferred is an 70:15:15
iso-octyl acrylate-ethyleneoxide acrylate:acrylic acid terpolymer,
as described in U.S. Pat. No. 4,737,410 (Example 31). Other useful
adhesives are described in U.S. Pat. Nos. 3,389,827; 4,112,213;
4,310,509 and 4,323,557. Inclusion of medicaments or antimicrobial
agents in the adhesive is also contemplated, as described in U.S.
Pat. Nos. 4,310,509 and 4,323,557.
[0223] Other medical devices that may be made, in whole or in part,
of exemplary dimensionally stable nonwoven fibrous webs of the
present disclosure include: sutures, suture fasteners, surgical
mesh, slings, orthopedic pins (including bone filling augmentation
material), adhesion barriers, stents, guided tissue
repair/regeneration devices, articular cartilage repair devices,
nerve guides, tendon repair devices, atrial septal defect repair
devices, pericardial patches, bulking and filling agents, vein
valves, bone marrow scaffolds, meniscus regeneration devices,
ligament and tendon grafts, ocular cell implants, spinal fusion
cages, skin substitutes, dural substitutes, bone graft substitutes,
bone dowels, and hemostats.
[0224] The dimensionally stable nonwoven fibrous webs of the
present disclosure may also be useful in consumer hygiene products,
such as adult incontinence, infant diapers, feminine hygiene
products, and others as described in U.S. Patent Application
Publication No. 2008/0200890.
EXAMPLES
[0225] Exemplary embodiments of dimensionally stable nonwoven
fibrous webs of the presently disclosed invention will be further
clarified by the following examples which are not intended to limit
the scope of the invention.
Example 1
Spunbond PLA with Polypropylene
[0226] Nonwoven webs were made using the spunbond process from neat
poly(lactic acid) (PLA) and a mixture of PLA and polypropylene
(PP). The PLA used was grade 6202D from Natureworks, LLC
(Minnetonka, Minn.). The PP used was grade 3860X from Total
Petrochemicals (Houston, Tex.). One sample also contained a 50/50
mixture Dioctyl sulfosuccinate sodium salt (DOSS) and poly(ethylene
glycol) (PEG) as a plasticizer, diluent, and hydrophilic
surfactant. The DOSS/PEG mixture was compounded with 6202D PLA and
added as a master batch to the spunbond process.
[0227] The spunbond apparatus used is that described in U.S. Pat.
No. 6,196,752 (Berrigan et al.). The extruder used was a 2 inch
single screw extruder from Davis-Standard (Pawcatuck, Conn.). The
die used had an effective width of 7.875 inches and was fed polymer
melt from a metering pump at the rate of 42 pounds per hour. The
die had 648 holes, each hole being 0.040 inches in diameter with a
L/D of 6. The extrusion temperature was 230.degree. C. The air
attenuator was set at a pressure of 5 pounds per square inch.
Process conditions were kept constant for the different mixtures.
Spinning speed is the filament speed calculated using the final
average fiber diameter, measured microscopically, and the polymer
rate per hole. In all cases the spinning speed is no greater than
2500 meters per minute, the speed at which strain induced
crystallization begins in PLA.
[0228] After extrusion the webs were also measured for shrinkage by
placing an unrestrained 10 cm.times.10 cm square section cut from
the middle of each web using a die cutter onto an aluminum tray in
a convection oven at 80.degree. C. overnight (e.g., for
approximately 14 hours). The Tg of the PLA webs was approximately
54-56.degree. C. The heated samples were then allowed to cool and
measured for length (in the machine direction) and width (in the
cross direction), and the average linear shrinkage of three samples
was reported. The shrinkage reported was the average change of
three samples in sample length and width, as opposed to change in
sample area.
TABLE-US-00001 TABLE I Results for Example 1 Fiber Spinning
80.degree. C. Diameter Speed Shrinkage Material (micrometers)
(m/min) (linear %) Neat 6202D PLA 15 2121 5.56 6202D + 3% PP 17
1651 2.84 6202D + 3% 18 1473 7.61 DOSS/PEG + 3% PP
[0229] Birefringence studies using a polarized microscope were
performed on some of the prepared webs to examine the degree of
orientation within the web and within fibers. Retardation was
estimated using the Michel-Levy chart, and birefringence number
determined. Representative samples were also analyzed to identify
variation in birefringence in fibers at constant diameter. Fibers
of constant diameter were studied, although the fiber sections
studied were not necessarily from the same fiber. The results found
for Example 4 are presented in the following Table 2. As seen,
different colors were also detected. Similar variation in
birefringence at constant diameter was found for the other
examples.
Example 2
Meltblown PLA with Polypropylene
[0230] Nonwoven webs were produced using a meltblowing process from
poly(lactic acid), PEA, and polypropylene, PP. The PLA used was
grade 6251D from Natureworks, LLC, (Minnetonka, Minn.). The PP used
was grade 3960 from Total Petrochemicals (Houston, Tex.).
[0231] The meltblowing apparatus consisted of a twin screw
extruder, and metering pump, and a meltblowing die. The extruder
used was a 31 mm conical twin screw extruder (C. W. Brabender
Instruments (South Hackensack, N.J.). After the extruder a positive
displacement gear pump was used to meter and pressurize the polymer
melt. The metered melt was sent to a drilled orifice meltblowing
die. Drilled orifice meltblowing dies are described in U.S. Pat.
No. 3,825,380. The die used was 10 inches wide with 20 polymer
orifices per inch. of width, each orifice being 0.015 inches in
diameter. The die was operated at a temperature of 225.degree. C.
Different mixtures of polymer pellets were fed to the process with
amounts of PP added to the PLA. Process conditions were kept
constant throughout the experiment.
[0232] The webs were collected on a vacuum collector and wound up
onto cores using a surface winder. Fiber diameter was measured
using the airflow resistance technique described by Davies (Davies,
C. N., The Separation of Airborne Dust and Particles, Inst. of
Mech. Engineers, London, Proceedings 1B, 1952), this measurement is
referred to as Effective Fiber Diameter or EFD. Shrinkage was
measured using the technique described in Example 1. Some samples
expanded during heating, and these samples are reported as having
negative shrinkage values.
TABLE-US-00002 TABLE II Example 2 Results Eff. Fiber 80.degree. C.
Diameter Shrinkage Material (micrometers) (linear %) Neat 6251D PLA
15.7 12.25 1% 3960 PP in 6251D 15.8 2.08 2% 3960 PP in 6251D 15.8
1.83 4% 3960 PP in 6251D 16.4 -0.08 8% 3960 PP in 6251D 15.7
-1.50
Example 3
Meltblown PLA with Viscosity Modifying Salts
[0233] Nonwoven webs were produced using the meltblowing process
using PLA and a number of salts that greatly reduce the apparent
viscosity of the melt during processing. The fiber diameters of the
finished nonwoven webs were also smaller when the salts are added.
Polypropylene was also added to some mixtures to reduce the
shrinkage of the nonwoven webs. The resulting web had the
properties of both reduced fiber diameter and reduced shrinkage.
The polypropylene used was grade 3960 from Total Petrochemicals
(Houston, Tex.). The PLA used was grade 6251D from Natureworks, LLC
(Minnetonka, Minn.). The additives tested included:
[0234] Calcium Stearoyl Lactylate (CSL) (Trade name Pationic CSL,
fom RITA Corp. (Crystal Lake, Ill.);
[0235] Sodium Stearoyl Lactylate (SSL) (trade name Pationic SSL
from RITA Corp. (Crystal Lake, Ill.);
[0236] Calcium Stearate (Ca--S) from Aldrich (St. Louis, Mo.);
[0237] Sodium Behenoyl Lactylate (SBL) (trade name Pationic SBL)
from RITA Corp (Crystal Lake, Ill.).
[0238] The chemical structure of CSL is shown in FIG. 1. The
chemical structure of SBL is shown in FIG. 2.
##STR00002##
[0239] The meltblowing process is the same as that used in Example
2. The process was operated with a die temperature of 225.degree.
C. The salts were added to the system by dry blending the powder
with warm PLA pellets from the polymer dryer. The resin was
predried by heating to 71 C overnight. The salt additive melted on
contact with the warm PLA pellets and was blended by hand to form
slightly sticky pellets that were then fed to, the extruder.
[0240] After extrusion the webs were tested for EFD and thermal
shrinkage using the same methods as in previous examples. The
pressure of the polymer entering the die was recorded as a
surrogate for polymer viscosity. In this manner any decrease in
apparent viscosity of the melt is seen as a decrease in pressure at
the die entrance.
TABLE-US-00003 TABLE III Example 3 Results Die Entrance Eff. Fiber
80.degree. C. Pressure Diameter Shrinkage Material (psi)
(micrometers) (linear %) Neat 6251D PLA 431 16.8 13.16 0.5% CSL in
6251D 142 11.7 13.91 0.75% CSL in 6251D 122 11.1 8.50 1.0% CSL in
6251D 62 8.8 17.50 2% SSL in 6251D 425 12.7 29.0 2% SBL in 6251D 69
5.5 19.25 1% Ca--S in 6251D 83 10.0 10.25 2% Ca--S in 6251D 44 8.0
23.08 0.5% CSL, 4% PP in 6251D 401 13.5 -3.47 1% CSL, 4% PP in
6251D 323 11.4 -1.62 1.5% CSL, 4% PP in 6251D 387 11.3 -0.67 1.0%
CSL, 2% PP in 6251D 415 10.4 -3.47 1.0% CSL, 6% PP in 6251D 292
11.0 -1.93
Example 4
Meltblown PET with Polypropylene
[0241] Fiber webs of were made using the meltblowing process with
blends of PP in PET. The PET resin used was grade 8603A from
Invista (Wichita, Kans.). The polypropylene used was grade 3868
from Total Petrochemicals (Houston, Tex.).
[0242] The meltblowing apparatus used consisted of a single screw
extruder, and metering pump, and a meltblowing die. The extruder
used was a 2'' single screw extruder (David Standard, Pawcatuck,
Conn.). After the extruder a positive displacement gear pump was
used to meter and pressurize the polymer melt. The metered melt was
sent to a drilled orifice meltblowing die. Drilled orifice
meltblowing dies are described in U.S. Pat. No. 3,825,380. The die
used was 20 inches wide with 25 polymer orifices per inch of width,
each orifice being 0.015 inches in diameter. Blending was
accomplished by feeding a dry-blended mixture of the PET and PP
pellets to the extruder. Process conditions were kept constant for
the different mixtures.
[0243] After the nonwoven webs were formed, they were tested for
shrinkage in the same manner as the previous PLA samples. However
due to the higher glass transition of PET the convection oven was
set to 150.degree. C., rather than the previous 80.degree. C.
TABLE-US-00004 TABLE IV Example 4 Results 150.degree. C. Shrinkage
Material (Linear %) Neat 8603F 30.08 8603F + 3% PP 7.17 8603F + 5%
PP 4.17 8603F + 10% PP 2.00
[0244] While the specification has described in detail certain
exemplary embodiments, it will be appreciated that those skilled in
the art, upon attaining an understanding of the foregoing, may
readily conceive of alterations to, variations of, and equivalents
to these embodiments. Accordingly, it should be understood that
this disclosure is not to be unduly limited to the illustrative
embodiments set forth hereinabove. Furthermore, all publications,
published patent applications and issued patents referenced herein
are incorporated by reference in their entirety to the same extent
as if each individual publication or patent was specifically and
individually indicated to be incorporated by reference. Various
exemplary embodiments have been described. These and other
embodiments are within the scope of the following claims.
* * * * *