U.S. patent application number 12/558496 was filed with the patent office on 2010-07-15 for polyamide fine fibers.
Invention is credited to Ismael Ferrer, Castro S. Laicer.
Application Number | 20100178507 12/558496 |
Document ID | / |
Family ID | 26923964 |
Filed Date | 2010-07-15 |
United States Patent
Application |
20100178507 |
Kind Code |
A1 |
Ferrer; Ismael ; et
al. |
July 15, 2010 |
Polyamide Fine Fibers
Abstract
Improved microfiber and nanofiber properties can be obtained
from a novel nylon material. Such nylon comprises alkyl modified
nylon 6, a methoxy modified nylon 8, a methoxy modified nylon 12 or
other similar nylons prepared from a cyclic lactam.
Inventors: |
Ferrer; Ismael;
(Minneapolis, MN) ; Laicer; Castro S.;
(Minneapolis, MN) |
Correspondence
Address: |
PAULY, DEVRIES SMITH & DEFFNER, L.L.C.
Plaza VII-Suite 3000, 45 South Seventh Street
MINNEAPOLIS
MN
55402-1630
US
|
Family ID: |
26923964 |
Appl. No.: |
12/558496 |
Filed: |
September 12, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12008919 |
Jan 14, 2008 |
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12558496 |
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11398788 |
Apr 6, 2006 |
7318852 |
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12008919 |
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10894848 |
Jul 19, 2004 |
7179317 |
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11398788 |
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10676189 |
Sep 30, 2003 |
6924028 |
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10894848 |
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09871583 |
May 31, 2001 |
6743273 |
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10676189 |
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61096513 |
Sep 12, 2008 |
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60230138 |
Sep 5, 2000 |
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Current U.S.
Class: |
428/401 |
Current CPC
Class: |
B01D 2239/065 20130101;
B01D 2239/1258 20130101; Y10T 442/659 20150401; B01D 2239/0613
20130101; D01D 5/0007 20130101; D01F 1/10 20130101; D01F 6/90
20130101; D01F 6/92 20130101; Y10T 428/26 20150115; B01D 2239/0428
20130101; D01F 6/80 20130101; Y10T 442/16 20150401; Y10T 428/2969
20150115; B01D 46/546 20130101; B01D 2239/1233 20130101; D01D 5/003
20130101; B01D 2239/0654 20130101; C08L 65/00 20130101; B01D
2275/10 20130101; B01D 2239/064 20130101; B01D 46/523 20130101;
B01D 2239/0492 20130101; Y10T 428/24686 20150115; B01D 2239/0618
20130101; C08L 77/00 20130101; B01D 46/521 20130101; Y10S 428/903
20130101; Y10T 428/24942 20150115; Y10T 428/2915 20150115; Y10T
428/2967 20150115; B01D 39/04 20130101; D01D 5/0084 20130101; B01D
39/1623 20130101; B01D 46/02 20130101; B01D 39/163 20130101; B01D
2239/0627 20130101; Y10T 428/2933 20150115; D04H 3/02 20130101;
Y10T 442/626 20150401; B01D 39/18 20130101; Y10T 428/1362 20150115;
Y10T 428/29 20150115; Y10T 442/614 20150401; B01D 46/0001 20130101;
B01D 2239/025 20130101; B01D 39/086 20130101; Y10T 428/2938
20150115; B01D 46/10 20130101; B01D 46/2411 20130101; Y10T 428/298
20150115 |
Class at
Publication: |
428/401 |
International
Class: |
B32B 27/34 20060101
B32B027/34 |
Claims
1. A fiber comprising a polyamide polymer, the fiber comprising a
diameter of about 0.001 to about 5 microns; wherein the polyamide
comprises an N-modified nylon of the formula I: ##STR00002##
wherein CO represents a carbonyl, R.sup.1 is either a hydrogen
atom, a lower alkyl, such as methyl, ethyl, propyl, a vinyl
containing chain, such as ethylene, allyl, etc., a hydroxyl group,
an alkoxy group, such as lower alkyl chain oxides, such as methoxy,
ethoxy, butoxy, etc., m and n is independently an integer number
from 2 to 12 and p+q is an integer number from about 10 to 5000,
and the ratio of p to p+q is a number between 0.05 to 0.99.
2. The fiber of claim 1 wherein the nylon comprises a alkylol or a
alkoxyalkyl modified nylon 6.
3. The fiber of claim 2 wherein the diameter of the fiber is about
0.01 to about 2 microns.
4. The fiber of claim 3 where the fiber polymer is crosslinked.
5. The fiber of claim 1 wherein the alkoxy group is derived from a
lower alkyl oxide comprising methoxy, ethoxy, butoxy.
6. The fiber of claim 1 wherein the hydrocarbyl group is a lower
alkyl.
7. The fiber of claim 13 wherein the lower alkyl group is methyl,
ethyl or propyl.
8. The fiber of claim 12 wherein the nylon comprises a methoxy
modified nylon.
9. A fiber comprising a polyamide polymer, the fiber comprising a
diameter of about 0.001 to about 5 microns; wherein the polyamide
comprises an N-modified nylon of the formula II:
--[NR.sup.1--(CH.sub.2).sub.m--CO--].sub.p--[NH--(CH2).sub.n--CO].sub.q--
II wherein CO represents a carbonyl, R.sup.1 is an alkoxy group, m
and n is independently an integer number from 2 to 12 and p+q is an
integer number from about 10 to 5000, and the ratio of p to p+q is
a number between 0.05 to 0.99.
10. The fiber of claim 9 wherein the nylon comprises a methoxy,
ethoxy, butoxy, modified nylon 6.
11. The fiber of claim 10 wherein the diameter of the fiber is
about 0.01 to about 2 microns.
12. The fiber of claim 11 where the fiber polymer is
crosslinked.
13. The fiber of claim 9 wherein the alkoxy group is methoxy.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority from U.S. Pat. App. No.
61,096,513, filed Sep. 12, 2008, and to U.S. patent application
Ser. No. 12/008,919, filed Jan. 14, 2008, which is a continuation
of U.S. patent application Ser. No. 11/398,788, filed Apr. 6, 2006,
now U.S. Pat. No. 7,318,852; which is a continuation of U.S. patent
application Ser. No. 10/894,848, filed Jul. 19, 2004, now U.S. Pat.
No. 7,179,317; which is a divisional of U.S. patent application
Ser. No. 10/676,189, filed Sep. 30, 2003, now U.S. Pat. No.
6,924,028; which is a divisional of U.S. patent application Ser.
No. 09/871,583, filed May 31, 2001, now U.S. Pat. No. 6,743,273,
which claims benefit of U.S. Pat. App. No. 60/230,138, filed Sep.
5, 2000, which are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The Invention is in fibers having small or micro- and
nano-scale, diameters and to methods of forming such fibers. These
fibers have substantially improved properties. The fibers can be
used in filtration applications.
BACKGROUND
[0003] Microfiber and nanofiber have been prepared from polyamides
in the past. Depending on their applications, such fibers have had
some success. Polyamides belong to a class of engineering polymers
that have found a wide variety of successful thermoplastic
commercial applications including in the synthetic fiber industry.
In this class of materials, certain polyamide have been most widely
used because of their desirable combination of physical properties
which include high strength, toughness, flexibility, thermal
resistance, and chemical resistance.
[0004] Polyamides are condensation polymers typically polymerized
from a lactam and from a diacid and a diamine and processed in to
useful forms. In certain types of processing where the solubility
of the material is important, the poor solubility of these
materials in common organic and environmentally friendly solvents
limits their applications if they must be processed from solution.
Strategies to dissolve these materials have included strong acids
such as formic acid and sulfuric acid, fluorinated solvents such as
2,2,2-trifluoroethanol (TFE) and hexafluoroisopropanol (HFIP), and
mixtures of TFE and methylene chloride. These solvents are
hazardous and can add significant processing costs and in some
cases can be detrimental to the material. For example, acidic
solvents have been shown to degrade aliphatic polyamides and
fluorinated solvents are considerably more expensive than commonly
used organic solvents.
[0005] The use of nylon-6 6 in combination with other materials to
electrospin nanofibers for filtration applications has been
described in U.S. Pat. No. 6,743,273. However, the ability to
produce nanofibers from this material was limited by its poor
solution stability in EtOH/H.sub.2O cosolvent mixtures and the
formation of non-homogeneous nanofiber structures. Better nanofiber
formation was only achieved after this material was blended with an
alcohol soluble Nylon 6 Nylon 6 6 Nylon 6 10 polyamide copolymer.
As will be discussed later, many of these solution blends still
suffer from poor solution stability which limits their use in fiber
forming processes.
[0006] Other approaches in improving the solubility of polyamides
have involved N-alkylation and N-allylation in which amide
hydrogens were deprotonated to form dimethyl sulfoxide (DMSO)
soluble polyanions that were subsequently converted to N-alkylated
and N-allylated products with heat or by reacting with allyl
bromide.
[0007] A substantial need exists to show that improved materials
can achieve, particularly in nanofiber sizes, increased
environmental stability, increased processability including
solubility in environmentally safe solvent systems, electrical
conductivity for electrospinning and viscosity control. Lastly,
when the fiber is used in a filter structure, the fiber must obtain
effective filtration efficiency over an array of conditions
including fluid type, type of particulate, particulate
concentration, temperature and fluid velocity through the fiber
mass.
SUMMARY OF THE INVENTION
[0008] The invention comprises a micro- or nano-fiber comprising a
novel nylon polymer. The fibers can be made into a layer or layers
comprising a distribution of micro- or nano-fibers. The polymer in
the fibers in any one layer can be crosslinked.
[0009] The invention comprises a fiber comprising an N-modified
nylon of the formula (I or II):
##STR00001##
The fiber can consist of the nylon of the invention; wherein in I
or II, CO represents a carbonyl, R.sup.1 is a lower alkyl, such as
methyl, ethyl, propyl, a vinyl containing chain, such as ethylene,
allyl, etc., a hydroxyl group, an alkoxy group, such as lower alkyl
only groups, such as methoxy, ethoxy, butoxy, etc., m and n is
independently an integer number from 2 to 12 and p+q is an integer
number from about 10 to 5000, and the ratio of p to p+q is a number
between 0.05 to 0.99. Formula I shows that a fraction of the --N--
amide nitrogens are N-modified. In use, in this aspect, the
N-modified nylon can be used as a single component or blended with
another polymer in the fine fiber materials. A preferred aspect is
a fiber consisting of a methoxy, ethoxy, N-methylol or
N-methoxymethyl modified nylon-6 such as the nylon polymer derived
from s-caprolactam.
BRIEF DISCUSSIONS OF THE FIGURES
[0010] FIG. 1 is an .sup.1H-NMR spectrum of the substituted Nylon 6
material.
[0011] FIG. 2 is a DSC scan of the substituted Nylon 6
material.
[0012] FIGS. 3 and 4 show viscosity measurements of polymer
solutions of the polymer materials disclosed.
[0013] FIG. 5 shows conductivity measurements of polymer solutions
of the polymer materials disclosed.
[0014] FIG. 6 shows pH measurements of polymer solutions of the
polymer materials disclosed.
[0015] FIGS. 7 through 8 show scanning electron micrographs of
fibers made from the polymer materials disclosed.
DETAILED DESCRIPTION OF THE INVENTION
[0016] We have also found that nanofibers from an N-modified or
N-substituted (e.g.) an N-alkylol, N-alkoxy, or N-alkoxy alkyl
nylon-X.sup.1, wherein X.sup.1 is an integer from 5 to 15, and the
degree of substitution on the nitrogen is less than about 50% and
is often about 2 to 40% can be formed into a fiber. These modified
nylons include modified polymers made of Nylon 5, Nylon 6, Nylon 7
and Nylon 12. Preferred are N-methoxymethyl-nylon-6, or
N-ethoxymethyl-nylon-6. These materials can surprisingly be
crosslinked under heat in the absence of acid catalysts without any
loss of solvent resistance characteristics. The high filtration
efficiency of these structures demonstrates their use in a variety
of particulate filtration applications that require material
resistance to elevated temperatures, high humidity, and chemical
exposure.
[0017] We have demonstrated that the solutions of these improved
nylon materials have significantly improved solution stability in
EtOH/H.sub.2O cosolvent mixtures and that homogenous nanofiber
structures were produced from homopolymer solutions of
N-methoxymethyl-nylon-6 and solution blends with nylon-6,66,PACM 6.
The molecular weights of the polymers are: M.sub.n=1 to
6.times.10.sup.4 g/mol, M.sub.w=2 to 10.times.10.sup.5 g/mol.
[0018] Because of their small diameter and high surface area,
polymer nanofibers are highly susceptible to mechanical damage and
chemical or thermal degradation under high temperature, high
humidity, and chemical exposure. Under these conditions,
crosslinking the polymer matrix helps to stabilize the fiber and to
retain the filtration characteristics of the nanofiber
structures.
[0019] The materials of the invention are derived from the generic
polymer class consisting of the polyamides and copolyamides
including linear homopolyamides and copolyamides which are prepared
in a known manner from cyclic lactams, lactams or suitable
derivatives of these compounds. Useful monomers are those used in
polymerization of such polyamides and copolyamides as nylon 3, 4,
5, 6, 8, 11, 12, 13, 6 6, 6 10 or 6 13; or a polyamide obtained
from cyclic lactams and from other monomers including
metaxylylenediamine and adipic acid or from
trimethylhexamethylenediamine or isophoronediamine and adipic acid;
nylon 6, 6 6, 6 10 or nylon 6, 6 6, 6 12; or a polyamide of
.epsilon.-caprolactam/adipic
acid/hexamethylenediamine/bis(4-aminocyclohexyl)methane, which are
produced by copolymerizing equal amounts of adipic acid,
caprolactam and hexamethylene diamine comonomers with
bis(4-aminocyclohexyl)methane. The materials of this invention also
include N-modified derivatives of all these homopolyamides and
copolyamides which include N-alkyl, an N-vinyl containing chain,
such as ethylene, allyl, etc., an N-methylol group, or an
N-alkoxymethyl group.
[0020] The invention provides a range of improved polymeric
materials. These polymers have improved physical and chemical
stability. The polymer fine fiber (microfiber and nanofiber) can be
fashioned into useful product formats. Nanofiber is a fiber with
diameter less than 200 nanometer or 0.2 micron. Microfiber is a
fiber with diameter larger than 0.2 micron, but not larger than 5
microns. This fine fiber can be made and then made into the form of
an improved layered or multi-layer microfiltration media structure.
The fine fiber layers of the invention comprise a random
distribution of fine fibers which can be bonded to form an
interlocking net. Such layers or nets can be formed on a filter
substrate layer. Such layers are cellulosic, synthetic or mixed
cellulosic/synthetic. Filtration performance is obtained largely as
a result of the cooperation between the fine fiber barrier to the
passage of particulate and contribution of the of filter substrate
barrier. Structural properties of stiffness, strength, pleatability
are provided by the substrate to which the fine fiber adhered. The
fine fiber interlocking fiber networks provide important
characteristics to a fiber layer. Fine fiber layers consist of
relatively small spaces between the fibers and form pores in the
layer at pore sizes that are useful in filter applications. Such
spaces typically range, between fibers, of about 0.01 to about 25
microns or often about 0.1 to about 10 microns. The filter products
comprising a fine fiber layer are combined with a choice of
appropriate substrate. The fine fiber adds less than few microns
and often less than a micron in thickness to the overall fine fiber
layer on the substrate filter media. In service, the filters can
stop incident particulate from passing through the fine fiber layer
and can attain substantial surface loadings of trapped particles.
The particles comprising dust or other incident particulates can
form a dust cake on the fine fiber surface and maintain high
initial and overall efficiency of particulate removal. Even with
relatively fine contaminants having a particle size of about 0.01
to about 1 micron, the filter media comprising the fine fiber has a
very high dust capacity.
[0021] The polymer materials as disclosed herein have substantially
improved resistance to the undesirable effects of heat, humidity,
high flow rates, reverse pulse cleaning, operational abrasion,
submicron particulate penetration, cleaning of filters in use and
other demanding conditions. The improved microfiber and nanofiber
performance is a result of the improved character of the polymeric
materials forming the microfiber or nanofiber. Further, the filter
media of the invention using the improved polymeric materials of
the invention provides a number of advantageous features including
higher efficiency, lower flow restriction, high durability (stress
related or environmentally related) in the presence of abrasive
particulates and a smooth outer surface free of loose fibers or
fibrils. The overall structure of the filter materials provides an
overall thinner media allowing improved media area per unit volume,
reduced velocity through the media, improved media efficiency and
reduced flow restrictions.
[0022] A particularly preferred material of the invention comprises
a small diameter fiber material having a dimension of about 5 to
0.005 microns, about 2 to 0.01 micron or between 0.8 to 0.05
micron. Such fibers with the preferred size provide excellent
filter activity, ease of back or reverse pulse cleaning and other
aspects.
[0023] The highly preferred polymer systems of the invention have
adhering characteristic such that when fibers are contacted with a
cellulosic or other synthetic or mixed cellulosic/synthetic
substrate, they adhere to the substrate with sufficient strength
such that they are securely bonded to the substrate and can resist
the delaminating effects of a reverse pulse cleaning technique and
other mechanical stresses. In such a mode, the polymer material
must stay attached to the substrate while undergoing a pulse clean
input that is substantially equal to the typical filtration
conditions in a reverse direction across the filter structure. Such
adhesion can arise from solvent effects of fiber formation as the
fiber is contacted with the substrate or the post treatment of the
fiber on the substrate with heat or pressure. However, polymer
characteristics appear to play an important role in determining
adhesion, such as specific chemical interactions like hydrogen
bonding, contact between polymer and substrate occurring above or
below T.sub.g, and the polymer formulation such as conductivity
stability and viscosity. Polymers plasticized with solvent or steam
at the time of adhesion can have increased adhesion.
[0024] We have found that additive materials can improve the
properties of certain of the copolymer materials in the form of a
fine fiber. The resistance to the effects of heat, humidity,
impact, mechanical stress and other negative environmental effect
can be substantially improved by the presence of additive
materials. We have found that while processing the microfiber
materials of the invention, that the additive materials can improve
the oleophobic character, the hydrophobic character and can appear
to aid in improving the chemical stability of the materials. We
believe that the fine fibers of the invention in the form of a
microfiber are improved by the presence of these oleophobic and
hydrophobic additives as these additives form a protective layer
coating, ablative surface or penetrate the surface to some depth to
improve the nature of the polymeric material. We believe the
important characteristics of these materials are the presence of a
strongly hydrophobic group that can preferably also have oleophobic
character. Strongly hydrophobic groups include fluorocarbon groups,
hydrophobic hydrocarbon surfactants or blocks and substantially
hydrocarbon oligomeric compositions. These materials are
manufactured in compositions that have a portion of the molecule
that tends to be compatible with the polymer material affording
typically a physical bond or association with the polymer while the
strongly hydrophobic or oleophobic group, as a result of the
association of the additive with the polymer, forms a protective
surface layer that resides on the surface or becomes alloyed with
or mixed with the polymer surface layers. Additive layers can range
form 10 to 200 angstroms.
[0025] An important aspect of the invention is the utility of such
microfiber or nanofiber materials formed into a filter structure.
In such a structure, the fine fiber materials of the invention can
consist of stand alone fiber layers or the polymer fiber material
can be formed onto and adhered to a filter substrate. Natural fiber
and synthetic fiber substrates, like spun bonded fabrics, non-woven
fabrics of synthetic fiber and non-wovens made from the blends of
cellulosics, synthetic and glass fibers, non-woven and woven glass
fabrics, plastic screen like materials both extruded and hole
punched, UF and MF membranes of organic polymers can be used.
Sheet-like substrate or cellulosic non-woven web can then be formed
into a filter structure that is placed in a fluid stream including
an air stream or liquid stream for the purpose of removing
suspended or entrained particulate from that stream. The shape and
structure of the filter material is up to the design engineer. One
important parameter of the filter elements after formation is its
resistance to the effects of heat, humidity or both. One aspect of
the filter media of the invention is a test of the ability of the
filter media to survive immersion in warm water for a significant
period of time. The immersion test can provide valuable information
regarding the ability of the fine fiber to survive hot humid
conditions and to survive the cleaning of the filter element in
aqueous solutions that can contain substantial proportions of
strong cleaning surfactants and strong alkalinity materials.
Preferably, the fine fiber materials of the invention can survive
immersion in hot water while retaining at least 50% of the fine
fiber formed on the surface of the substrate. Retention of at least
50% of the fine fiber can maintain substantial fiber efficiency
without loss of filtration capacity or increased back pressure,
most preferably retaining at least 75% of the fiber for filtration
purposes.
[0026] All of these materials and admixtures of materials can be
crosslinked using appropriate crosslinking agents, processes or
mechanisms. Nylons can be crosslinked using crosslinking agents
that are reactive with the nitrogen atom in the amide linkage. Such
reactive materials include monoaldehydes, such as formaldehyde,
ureas, melamine-formaldehyde resin and its analogues, boric acids
and other inorganic compounds. dialdehydes, diacids, urethanes,
epoxies and other known crosslinking agents. Crosslinking can be
accomplished using radiation source to bond adjacent polymer
chains. Simple heating processes can act to crosslink. A preferred
crosslinking agent for polyamide materials is p-toluene sulfonic
acid (p-TSA). Crosslinking technology is a well known and
understood phenomenon in which a crosslinking reagent reacts and
forms covalent bonds between polymer chains to substantially
improve molecular weight, chemical resistance, overall strength and
resistance to mechanical degradation.
[0027] A fine fiber filter structure includes a bi-layer or
multi-layer structure wherein the filter contains one or more fine
fiber layers. Such layers can be used as is or can be combined with
or separated by one or more synthetic, cellulosic or blended
substrate webs. Another preferred motif is a structure including
fine fiber in a matrix or blend of other fibers.
[0028] Electrospinning can be achieved in apparatus that includes a
reservoir of fine fiber forming polymer solution in contact with an
emitter. An emitter can be immersed into a reservoir of polymer. A
droplet of the solution from the emitter is accelerated by an
applied electrostatic field toward the collecting media. Facing the
emitter, but spaced apart therefrom, is a substantially planar grid
upon which the collecting media, substrate or combined substrate is
positioned. The collecting media is passed over the grid at a rate
to form the fiber in a continuous layer. Air can be drawn through
the grid. A high voltage electrostatic potential is maintained
between emitter and grid. In use, the electrostatic potential
between grid and emitter imparts a charge to the polymer solution
which causes liquid droplets to be emitted therefrom as thin
fibers. Solvent is evaporated off the fibers during their flight.
The fine fibers are directed to and bond to the substrate fibers as
they form. Electrostatic field strength is selected to ensure that
the acceleration of the polymer material is sufficient to render
the material into a very thin microfiber or nanofiber structure as
it is accelerated from the emitter to the collecting media.
Increasing or slowing the advance rate of the collecting media can
deposit more or less emitted fibers on the forming media, thereby
allowing control of the thickness of each layer deposited thereon.
Fibers smaller than 1 micron are best made from polymer solution.
As the polymer mass is drawn down to smaller diameter, solvent
evaporates and contributes to the reduction of fiber size.
Electrostatic spinning can be done at a polymer solution flow rate
of 0.001 to 5 ml/min per emitter, a target distance of 1 to 20 cm,
and an emitter voltage of 1 to 60 kV.
[0029] The fine fiber materials of the invention can be used in a
variety of filter applications including pulse clean and non-pulse
cleaned filters for dust collection, gas turbines and engine air
intake or induction systems; gas turbine intake or induction
systems, heavy duty engine intake or induction systems, light
vehicle engine intake or induction systems; "Z" filter; vehicle
cabin air; off road vehicle cabin air, disk drive air,
photocopier-toner removal; HVAC filters in both commercial or
residential filtration applications.
[0030] Various filter designs are shown in patents disclosing and
claiming various aspects of filter structure and structures used
with the filter materials. Engel et al., U.S. Pat. No. 4,720,292,
disclose a radial seal design for a filter assembly having a
generally cylindrical filter element design, the filter element
being sealed by a relatively soft, rubber-like end cap having a
cylindrical, radially inwardly facing surface. Kahlbaugh et al.,
U.S. Pat. No. 5,082,476, disclose a filter design using a depth
media comprising a foam substrate with pleated components combined
with the microfiber materials of the invention. Stifelman et al.,
U.S. Pat. No. 5,104,537, relate to a filter structure useful for
filtering liquid media. Liquid is entrained into the filter
housing, passes through the exterior of the filter into an interior
annular core and then returns to active use in the structure. Such
filters are highly useful for filtering hydraulic fluids. Engel et
al., U.S. Pat. No. 5,613,992, show a typical diesel engine air
intake filter structure. The structure obtains air from the
external aspect of the housing that may or may not contain
entrained moisture. The air passes through the filter while the
moisture can pass to the bottom of the housing and can drain from
the housing. Gillingham et al., U.S. Pat. No. 5,820,646, disclose a
Z filter structure that uses a specific pleated filter design
involving plugged passages that require a fluid stream to pass
through at least one layer of filter media in a "Z" shaped path to
obtain proper filtering performance. The filter media formed into
the pleated Z shaped format can contain the fine fiber media of the
invention. Glen et al., U.S. Pat. No. 5,853,442, disclose a bag
house structure having filter elements that can contain the fine
fiber structures of the invention. Berkhoel et al., U.S. Pat. No.
5,954,849, show a dust collector structure useful in processing
typically air having large dust loads to filter dust from an air
stream after processing a workpiece generates a significant dust
load in an environmental air. Lastly, Gillingham, U.S. Design Pat.
No. 425,189, discloses a panel filter using the Z filter design. A
general understanding of some of the basic principles and problems
of air filter design can be understood by consideration of the
following of filter media types including surface loading media
and, depth media. Each of these types of media has been well
studied, and each has been widely utilized. Certain principles
relating to them are described, for example, in U.S. Pat. Nos.
5,082,476; 5,238,474; and 5,364,456. The complete disclosures of
these three patents are incorporated herein by reference.
Example 1
[0031] One hundred and fifty grams of a methoxy methyl N-modified
nylon 6 with a molecular weight of about 20,000, were added to
743.5 grams of Ethanol with 106.5 grams of distilled water and 4.5
ml of a 40% solution of para-toluene sulfonic acid in
isopropanol.
Electrospinning
[0032] Nanofibers were electrospun from solutions described in
Example 1 by applying a voltage of 10.7 to 16.6 kV to polymer
solutions eluted from syringe needles at a flow rate of 0.10
mL/min. The distance from the emitter to collector substrate was
fixed at 3 inches. Nanofibers were electrospun onto a cellulose
substrate (product no. FF6168; Hollingworth and Vose Company) and
thermally crosslinked by annealing in a 150.degree. C. oven for 10
min.
Differential Scanning Calorimetry (DSC)
[0033] Polymer thermal transitions were obtained with a DSC 2920
instrument (TA Instruments). Scans were obtained at a rate of
10.degree. C./min over a temperature range of 0-300.degree. C. The
sample chamber was purged with N.sub.2 during analysis. Data
acquisition and analysis was performed with TA Universal Analysis
software (TA Instruments). Melting peak transitions were;
T.sub.m=185.degree. C. for nylon-6,66,PACM6,
T.sub.m=199.degree. C. for N-PEO-b-PA, and
T.sub.m=205.degree. C. for PEO-b-PA.
See FIGS. 2 and 5.
Proton-NMR and DSC Analysis
[0034] Proton (.sup.1H-NMR) NMR analysis was used to determine the
degree of N-substitution in N-substituted polyamide (nylon 6)
[N-PA-6]. FIG. 1 shows the .sup.1H-NMR spectrum of N-PA-6 of
Example 4. Proton resonance peaks for this material were assigned
according to FIG. 1 which shows distinct peaks at .about.3.55 ppm,
.about.2.55 ppm, and .about.1.6-2 ppm. The resonance peak at 3.55
ppm was consistent with methylene protons attached alpha to amide
nitrogen atoms.
[0035] [--CH.sub.2--NH(C.dbd.O)--], and the peak at 2.55 ppm was
consistent with methylene protons attached alpha to amide carbonyl
atoms [--CH.sub.2--(C.dbd.O)--NH--]. The peaks in the higher field
region .about.1.6-2 ppm were consistent with methylene protons that
were further removed from the electron withdrawing amide nitrogen
and amide carbonyl groups. Consistent with previous .sup.1H-NMR
reports on N-modified nylon-6, FIG. 1 also shows additional peaks
at 2.8 ppm and 3.7 ppm caused by downfield shifts for protons alpha
to the carbonyl and nitrogen groups in the substituted carbonamide
groups. The peak at 5.2 ppm was attributed to absorbed water, and
the multiple pattern at 4.7 ppm was caused by splitting of the
2-carbon hydrogen by the six neighboring fluorine atoms in the HFIP
solvent. The degree of N-substitution was calculated to be 35%
using equation 1:
% N - substitution ( 1 H - NMR ) = I es I es + I e Equation 1
##EQU00001##
where I.sub.es and I.sub.e are integration intensities of the
protons alpha to the carbonyl group in the substituted and
unsubstituted carbonamide groups, respectively.
[0036] DSC analysis of N-PA-6 shown in FIG. 2 did not show a
distinct melting peak due to polymer crosslinking via the
N-methoxymethyl groups in the DSC heating cycle. Qualitatively, the
suppression of polymer crystallization was evident in the
material's soft and rubbery physical properties.
Scanning Electron Microscopy (SEM)
[0037] Scanning electron microscopy was performed on samples that
were first mounted onto aluminum stubs with carbon tape and then
sputtered with gold. Images were obtained with a JEOL JSM-5900LV
scanning electron microscope.
Electrospinning and LEFS Measurements
[0038] Nanofibers were prepared by electrospinning solutions of
Example I and blends with nylon-6,66,PACM6 (see copending U.S.
application Ser. No. 12/558,499) in EtOH/H.sub.2O. FIG. 10 shows
SEM images of nanofibers prepared from 10 wt % solutions of (FIG. 7
a,b) N-PA-6 with 7.09.times.10.sup.-3 M p-TSA and blends of (FIG. 7
c,d) 50/50 wt % N-PA-6/nylon-6,66,PACM6 with 4.15.times.10.sup.-3M
p-TSA and (FIG. 7 e,f) 70/30 wt % N-PA-6/nylon-6,66,PACM6 with
5.36.times.10.sup.-3M p-TSA. Nanofibers (FIG. 7 a,c,e) were
annealed at 150.degree. C. for 10 min and (FIG. 10 b,d,f) annealed
at 150.degree. C. for 10 min and immersed in EtOH for 10 min. We
found that these solutions produced nanofibers with homogenous
morphology regardless of the composition of N-PA-6 and
nylon-6,66,PACM6. For example, SEM results show that solutions of
N-PA-6 produced well-defined nanofibers without blending with
nylon-6,66,PACM6 (FIG. 7 a,b). We also found that nanofibers were
undamaged from EtOH immersion after crosslinking at 150.degree. C.
for 10 min (FIG. 7 b,d,f). Surprisingly, nanofibers from N-PA-6
also crosslinked at annealing temperature without addition of p-TSA
catalyst. FIG. 8 shows SEM images of nanofibers prepared from 10 wt
% polymer solutions of N-PA-6 with 0 M p-TSA. Nanofibers were
annealed at 150.degree. C. for 10 min (FIG. 8a) and annealed at
150.degree. C. for 10 min and soaked in EtOH for 10 min (FIG. 8b).
FIG. 9 shows SEM images of nanofibers prepared from solutions of
N-PEO-b-PA in 82/18 wt % EtOH/H.sub.2O. Images were obtained after
nanofibers were (FIG. 9 a,c) annealed at 150.degree. C. for 10 min
and (FIG. 9 b,d) annealed at 150.degree. C. for 10 min and immersed
in EtOH for 10 min. p-TSA concentrations were (FIG. 9 a,b) 0 M and
(FIG. 9 c,d) 1.37.times.10.sup.-2M. Nanofibers prepared from
solutions of N-PEO-b-PA also crosslinked from thermal annealing
without adding p-TSA catalyst (FIG. 9 a,b). However, for this
material, the extent of nanofiber crosslinking and resistance to
EtOH solvent was improved with p-TSA addition (FIG. 9 c,d).
[0039] The LEFS measurement were done according to ASTM1215-89.
Particle capture efficiency was measured on a LEFS bench using 0.80
.mu.m latex spheres with velocity of 20 ft/min as a test challenge
contaminant. Measurements were made on substrate and nanofiber
composite samples that were annealed at 150.degree. C. for 10 min.
Measurements were also made on substrate and nanofiber composite
samples that were annealed at 150.degree. C. for 10 min and soaked
in EtOH for 10 min. Samples soaked in EtOH were air dried for at
least 3 h prior to measurement. Filter efficiency (LEFS)
measurements (Table 1) of nanofibers from Example 1 showed high
particle capture efficiency. LEFS measurements of samples that were
immersed in EtOH for 10 min showed a substantial efficiency
retention. The efficiency retained from nanofibers alone (F.sub.r)
in EtOH immersed samples was calculated using equation 2:
F r = F x F i Equation 2 ##EQU00002##
where F.sub.x is the post EtOH soak nanofiber efficiency, and
F.sub.i is the initial nanofiber layer efficiency. F.sub.i and
F.sub.x are expressed by equations 3 and 4:
F.sub.i=1-e.sup.ln(1-E.sup.i.sup.)-ln(1-E.sup.is.sup.) Equation
3
F.sub.x=1-e.sup.ln(1-E.sup.x.sup.)-ln(1-E.sup.sx.sup.) Equation
4
where E.sub.i=initial composite efficiency, E.sub.x=post EtOH soak
composite efficiency, E.sub.is=initial substrate efficiency, and
E.sub.xs=post EtOH soak efficiency.
% = log ( 1 - F x ) log ( 1 - F i ) Equation 5 ##EQU00003##
The solution of claim 1 was electrospun at four different web
speeds -5, 10, 15, and 20 fpm and was tested for efficiency.
TABLE-US-00001 % FF Web Speed Efficiency (fpm) LEFS % LEFS % (EtOH)
Retained 5 84.0 81.5 96.1 PASS 10 72.7 67.0 88.5 PASS 15 64.9 57.9
83.0 PASS 20 56.3 49.3 79.0 PASS Substrate Efficiency = 27% pre
& 26% post EtOH Soak
* * * * *