U.S. patent application number 11/901686 was filed with the patent office on 2008-01-17 for air filtration arrangements having fluted media constructions and methods.
This patent application is currently assigned to Donaldson Company, Inc.. Invention is credited to Gary R. Gillingham, Mark A. Gogins, Thomas M. Weik.
Application Number | 20080010959 11/901686 |
Document ID | / |
Family ID | 26923965 |
Filed Date | 2008-01-17 |
United States Patent
Application |
20080010959 |
Kind Code |
A1 |
Gillingham; Gary R. ; et
al. |
January 17, 2008 |
Air filtration arrangements having fluted media constructions and
methods
Abstract
Filter arrangements include a barrier media in the form of
fluted media treated with a deposit of fine fibers. The media is
particularly advantageous in high temperature (greater than 140 to
240.degree. F.) systems. Such systems may include engine systems,
gas turbine systems, and fuel cell systems. Filter arrangements may
take the form of media packs having a circular cross-section or a
racetrack shaped cross-section, or media packs formed in a panel
configuration.
Inventors: |
Gillingham; Gary R.; (Prior
Lake, MN) ; Gogins; Mark A.; (Roseville, MN) ;
Weik; Thomas M.; (Deephaven, MN) |
Correspondence
Address: |
MERCHANT & GOULD PC
P.O. BOX 2903
MINNEAPOLIS
MN
55402-0903
US
|
Assignee: |
Donaldson Company, Inc.
Minneapolis
MN
|
Family ID: |
26923965 |
Appl. No.: |
11/901686 |
Filed: |
September 18, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11411577 |
Apr 25, 2006 |
7270692 |
|
|
11901686 |
Sep 18, 2007 |
|
|
|
11110625 |
Apr 20, 2005 |
7090712 |
|
|
11411577 |
Apr 25, 2006 |
|
|
|
10741788 |
Dec 19, 2003 |
6974490 |
|
|
11110625 |
Apr 20, 2005 |
|
|
|
09871590 |
May 31, 2001 |
6673136 |
|
|
10741788 |
Dec 19, 2003 |
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60230138 |
Sep 5, 2000 |
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Current U.S.
Class: |
55/486 |
Current CPC
Class: |
B01D 2265/028 20130101;
Y10S 977/963 20130101; B01D 46/525 20130101; D04H 1/728 20130101;
Y10S 977/89 20130101; Y10S 977/902 20130101; B01D 46/002 20130101;
B01D 2271/027 20130101; B01D 46/546 20130101; D01F 6/90 20130101;
B01D 46/527 20130101; B01D 2273/20 20130101; D01D 5/0038 20130101;
D01F 6/92 20130101; D01D 5/0084 20130101; B01D 46/10 20130101; B01D
39/1623 20130101; B01D 46/0005 20130101; B01D 46/0001 20130101 |
Class at
Publication: |
055/486 |
International
Class: |
B01D 46/02 20060101
B01D046/02 |
Claims
1. A filter element arrangement comprising: (a) a media pack having
a substrate comprising first and second opposite flow faces and a
plurality of flutes wherein in said media pack; (i) each of said
flutes have a first end portion adjacent to said first flow face
and a second end portion adjacent to said second flow face; (ii)
selected ones of said flutes being open at said first end portion
and closed at said second end portion; and selected ones of said
flutes being closed at said first end portion and open at said
second end portion (iii) said substrate at least partially covered
by a layer comprising fine fiber comprising a fiber with a diameter
of about 0.01 to 0.5 microns such that the fiber, when tested under
conditions of exposure for a test period of 16 hours to test
conditions of 140.degree. F. air at a relative humidity of 100%,
retains greater than 30% of the fiber unchanged for filtration
purposes
Description
RELATED APPLICATION
[0001] This application is a continuation of application Ser. No.
11/411,577, filed Apr. 25, 2006, which application is a
continuation of application Ser. No. 11/110,625, filed Apr. 20,
2005, which application is a continuation of application Ser. No.
10/741,788, filed Dec. 19, 2003, now U.S. Pat. No. 6,974,490, which
application is a continuation of application Ser. No. 09/871,590,
filed May 31, 2001, now U.S. Pat. No. 6,673,136, which application
claims priority under 35 U.S.C. .sctn. 119(e) to U.S. provisional
application Ser. No. 60/230,138, filed on Sep. 5, 2000, which
applications are incorporated by reference herein.
FIELD OF THE INVENTION
[0002] The invention relates to a filter arrangement and filtration
method. More specifically, it concerns an arrangement for filtering
particulate material from a gas flow stream, for example, an air
stream. The invention also concerns a method for achieving the
desirable removal of particulate material from such a gas flow
stream.
[0003] The present invention is an on-going development of
Donaldson Company Inc., of Minneapolis, Minn., the assignee of the
present invention. The disclosure concerns continuing technology
development related, in part, to the subjects characterized in U.S.
Pat. Nos. 4,720,292; Des 416,308; 5,613,992; 4,020,783; and
5,112,372. Each of the patents identified in the previous sentence
is also owned by Donaldson, Inc., of Minneapolis, Minn.; and, the
complete disclosure of each is incorporated herein by
reference.
[0004] The invention also relates to filters comprising a substrate
having a fine fiber layer made of polymer materials that can be
manufactured with improved environmental stability to heat,
humidity, reactive materials and mechanical stress. Such materials
can be used in the formation of fine fibers such as microfibers and
nanofiber materials with improved stability and strength. As the
size of fiber is reduced the survivability of the materials is
increasingly more of a problem. Such fine fibers are useful in a
variety of applications. In one application, filter structures can
be prepared using this fine fiber technology. The invention relates
to polymers, polymeric composition, fiber, filters, filter
constructions, and methods of filtering. Applications of the
invention particularly concern filtering of particles from fluid
streams, for example from air streams and liquid (e.g. non-aqueous
and aqueous) streams. The techniques described concern structures
having one or more layers of fine fibers in the filter media. The
compositions and fiber sizes are selected for a combination of
properties and survivability.
BACKGROUND OF THE INVENTION
[0005] Gas streams often carry particulate material therein. In
many instances, it is desirable to remove some or all of the
particulate material from a gas flow stream. For example, air
intake streams to engines for motorized vehicles or power
generation equipment, gas streams directed to gas turbines, and air
streams to various combustion furnaces, often include particulate
material therein. The particulate material, should it reach the
internal workings of the various mechanisms involved, can cause
substantial damage thereto. Removal of the particulate material
from the gas flow upstream of the engine, turbine, furnace or other
equipment involved is often needed.
[0006] The invention relates to polymeric compositions with
improved properties that can be used in a variety of applications
including the formation of fibers, microfibers, nanofibers, fiber
webs, fibrous mats, permeable structures such as membranes,
coatings or films. The polymeric materials of the invention are
compositions that have physical properties that permit the
polymeric material, in a variety of physical shapes or forms, to
have resistance to the degradative effects of humidity, heat, air
flow, chemicals and mechanical stress or impact.
[0007] In making fine fiber filter media, a variety of materials
have been used including fiberglass, metal, ceramics and a range of
polymeric compositions. A variety of fiber forming methods or
techniques have been used for the manufacture of small diameter
micro- and nanofibers. One method involves passing the material
through a fine capillary or opening either as a melted material or
in a solution that is subsequently evaporated. Fibers can also be
formed by using "spinnerets" typical for the manufacture of
synthetic fiber such as nylon. Electrostatic spinning is also
known. Such techniques involve the use of a hypodermic needle,
nozzle, capillary or movable emitter. These structures provide
liquid solutions of the polymer that are then attracted to a
collection zone by a high voltage electrostatic field. As the
materials are pulled from the emitter and accelerate through the
electrostatic zone, the fiber becomes very thin and can be formed
in a fiber structure by solvent evaporation.
[0008] As more demanding applications are envisioned for filtration
media, significantly improved materials are required to withstand
the rigors of high temperature 100.degree. F. to 250.degree. F.,
often 140.degree. F. to 240.degree. F. and up to 300.degree. F.,
high humidity 10% to 90% up to 100% RH, high flow rates of both gas
and liquid, and filtering micron and submicron particulates
(ranging from about 0.01 to over 10 microns) and removing both
abrasive and non-abrasive and reactive and non-reactive particulate
from the fluid stream.
[0009] Accordingly, a substantial need exists for polymeric
materials, micro- and nanofiber materials and filter structures
that provide improved properties for filtering streams with higher
temperatures, higher humidities, high flow rates and said micron
and submicron particulate materials.
[0010] A variety of air filter or gas filter arrangements have been
developed for particulate removal. However, in general, continued
improvements are sought.
SUMMARY OF THE INVENTION
[0011] Herein, general techniques for the design and application of
air cleaner arrangements are provided. The techniques include
preferred filter element design, as well as the preferred methods
of application and filtering.
[0012] In general, the preferred applications concern utilization,
within an air filter, of Z-shaped media, including a composite of a
substrate and fine fibers, to advantage.
[0013] The filter media includes at least a micro- or nanofiber web
layer in combination with a substrate material in a mechanically
stable filter structure. These layers together provide excellent
filtering, high particle capture, and efficiency at minimum flow
restriction when a fluid such as a gas or liquid passes through the
filter media. The substrate can be positioned in the fluid stream
upstream, downstream or in an internal layer. The fiber can be
positioned on the upstream, the down stream or both sides of a
filter substrate, regardless of filter geometry. The fiber is
generally placed on the upstream side. However is certain
applications downstream placement can be useful. In certain
applications, double sided structure is useful. A variety of
industries have directed substantial attention in recent years to
the use of filtration media for filtration, i.e. the removal of
unwanted particles from a fluid such as gas or liquid. The common
filtration process removes particulate from fluids including an air
stream or other gaseous stream or from a liquid stream such as a
hydraulic fluid, lubricant oil, fuel, water stream or other fluids.
Such filtration processes require the mechanical strength, chemical
and physical stability of the microfiber and the substrate
materials. The filter media can be exposed to a broad range of
temperature conditions, humidity, mechanical vibration and shock
and both reactive and non-reactive, abrasive or non-abrasive
particulates entrained in the fluid flow. When in normal operation,
the filter is generally exposed to air at or near ambient
conditions or at slightly elevated temperature. The filter can be
exposed to higher temperature when the engine is operated
abnormally or when the engine is shut down after extended service.
If the engine is not in operation, air does not pass through the
filter. The filter rapidly reaches under hood temperature. Further,
the filtration media often require the self-cleaning ability of
exposing the filter media to a reverse pressure pulse (a short
reversal of fluid flow to remove surface coating of particulate) or
other cleaning mechanism that can remove entrained particulate from
the surface of the filter media. Such reverse cleaning can result
in substantially improved (i.e.) reduced pressure drop after the
pulse cleaning. Particle capture efficiency typically is not
improved after pulse cleaning, however pulse cleaning will reduce
pressure drop, saving energy for filtration operation. Such filters
can be removed for service and cleaned in aqueous or non-aqueous
cleaning compositions. Such media are often manufactured by
spinning fine fiber and then forming an interlocking web of
microfiber on a porous substrate. In the spinning process the fiber
can form physical bonds between fibers to interlock the fiber mat
into a integrated layer. Such a material can then be fabricated
into the desired filter format such as cartridges, flat disks,
canisters, panels, bags and pouches. Within such structures, the
media can be substantially pleated, rolled or otherwise positioned
on support structures.
[0014] The filter arrangements described herein can be utilized in
a wide variety of applications including, for example, dust
collection, air compressors, on-road and off-road engines, gas
turbine systems, power generators such as fuel cells and
others.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 depicts a typical electrostatic emitter driven
apparatus for production of the fine fibers of the invention.
[0016] FIG. 2 shows the apparatus used to introduce fine fiber onto
filter substrate into the fine fiber forming technology shown in
FIG. 1.
[0017] FIG. 3 is a depiction of the typical internal structure of a
support material and a separate depiction of the fine fiber
material of the invention compared to small, i.e. 2 and 5 micron
particulate materials.
[0018] FIGS. 4 through 11 are analytical ESCA spectra relating to
Example 13.
[0019] FIG. 12 shows the stability of the 0.23 and 0.45 microfiber
material of the invention from Example 5.
[0020] FIGS. 13 through 16 show the improved temperature and
humidity stability of the materials of Examples 5 and 6 when
compared to unmodified nylon copolymer solvent soluble
polyamide.
[0021] FIGS. 17 through 20 demonstrate that the blend of two
copolymers, a nylon homopolymer and a nylon copolymer, once heat
treated and combined with additives form a single component
material that does not display distinguishable characteristics of
two separate polymer materials, but appears to be a crosslinked or
otherwise chemically joined single phase.
[0022] FIG. 21 is a schematic view of an engine system in which air
cleaners according to the present disclose may be utilized;
[0023] FIG. 22 is a schematic, perspective view of one embodiment
of a filter element that may be utilized in the system depicted in
FIG. 21;
[0024] FIG. 23 is a schematic, perspective view of a portion of
filter media (Z-media) useable in the arrangement of FIG. 22;
[0025] FIG. 24 is a schematic, cross-sectional view of the filter
element depicted in FIG. 22 installed within a housing;
[0026] FIG. 25 is a fragmented, enlarged, schematic view of one
embodiment of a compressible seal member utilized in a sealing
system for the filter element of FIG. 22;
[0027] FIG. 26 is a schematic, perspective view of another
embodiment of a filter element that may be utilized in the engine
system of FIG. 21;
[0028] FIG. 27 is a schematic, cross-sectional view of the filter
element of FIG. 26 installed within a housing;
[0029] FIG. 28 is a schematic, exploded, perspective view of
another embodiment of a filter element and housing that may be
utilized in the engine system of FIG. 21;
[0030] FIG. 29 is a schematic depiction of a gas turbine system in
which filter elements according to the present disclosure may be
utilized;
[0031] FIG. 30 is a schematic, perspective view of one embodiment
of a filter element that may be useable in gas turbine air intake
systems depicted in FIG. 29;
[0032] FIG. 31 is a rear elevational view of the filter element
depicted in FIG. 30 installed within a tube sheet, and having a
prefilter installed upstream of the filter element of FIG. 30;
[0033] FIG. 32 is an enlarged, schematic, fragmented,
cross-sectional view of the air filter arrangement of FIG. 31,
taken along the line 12-12 of FIG. 31;
[0034] FIG. 33 is a schematic view of an air intake system for a
microturbine system, in which filter elements of the present
disclosure may be utilized;
[0035] FIG. 34 is a schematic, cross-sectional view of a filter
element in an operable installation to clean intake air in a gas
turbine system, the cross-section being taken along the line 14-14
of FIG. 35, but in an assembled state;
[0036] FIG. 35 is an exploded, side elevational view of the filter
arrangement of FIG. 34, and in an unassembled state;
[0037] FIG. 36 is a fragmented, schematic, cross-sectional view
showing the filter element sealed within a filter housing;
[0038] FIG. 37 is a schematic view of an air intake for a fuel cell
system, which may utilize filter elements disclosed herein;
[0039] FIG. 38 is a schematic, cross-sectional view of a filter
assembly that may be utilized in the fuel cell air intake system of
FIG. 37; and
[0040] FIG. 39 is a schematic, cross-sectional view of another
embodiment of a filter assembly that may be utilized in the air
intake for a fuel cell system.
DETAILED DESCRIPTION OF THE INVENTION
A. Micro Fiber or Fine Fiber Polymer Materials
[0041] The invention provides an improved polymeric material. This
polymer has improved physical and chemical stability. The polymer
fine fiber (microfiber and nanofiber) can be fashioned into useful
product formats. The fiber can have a diameter of about 0.001 to 10
microns, about 0.005 to 5 microns, about 0.01 to 0.5 micron.
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 10 microns.
[0042] This fine fiber can be made in the form of an improved
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. Filtration
performance is obtained largely as a result of the fine fiber
barrier to the passage of particulate. Structural properties of
stiffness, strength, pleatability are provided by the substrate to
which the fine fiber adhered. The fine fiber interlocking networks
have as important characteristics, fine fibers in the form of
microfibers or nanofibers and relatively small spaces between the
fibers. Such interfiber spaces in the layer typically range,
between fibers, of about 0.01 to about 25 microns or often about
0.1 to about 10 microns. The filter products comprise a fine fiber
layer on a choice of appropriate substrate such as a synthetic
layer, a natural layer or a mixed natural/synthetic substrate. The
fine fiber adds less than 5 microns, often less than 3 microns of
thickness. The fine fiber in certain applications adds about 1 to
10 or 1 to 5 fine fiber diameters in thickness to the overall fine
fiber plus substrate filter media. In service, the filters can stop
incident particulate from passing to the substrate or through the
fine fiber layer and can attain substantial surface loadings of
trapped particles. The particles comprising dust or other incident
particulates rapidly form a dust cake on the fine fiber surface and
maintains 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.
[0043] 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 particulates, 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.
[0044] The polymer can be an additive polymer, a condensation
polymer or mixtures or blends thereof. A preferred mode of the
invention is a polymer blend comprising a first polymer and a
second, but different polymer (differing in polymer type, molecular
weight or physical property) that is conditioned or treated at
elevated temperature. The polymer blend can be reacted and formed
into a single chemical specie or can be physically combined into a
blended composition by an annealing process. Annealing implies a
physical change, like crystallinity, stress relaxation or
orientation. Preferred materials are chemically reacted into a
single polymeric specie such that a Differential Scanning
Calorimeter analysis reveals a single polymeric material. Such a
material, when combined with a preferred additive material, can
form a surface coating of the additive on the microfiber that
provides oleophobicity, hydrophobicity or other associated improved
stability when contacted with high temperature, high humidity and
difficult operating conditions. The fine fiber of the class of
materials can have a diameter of 0.001 micron to 10 microns. Useful
sizes include 0.001 to 2 microns, 0.005 to 5 microns, 0.01 to 5
microns, depending on bonding, substrate and application. Such
microfibers can have a smooth surface comprising a discrete layer
of the additive material or an outer coating of the additive
material that is partly solubilized or alloyed in the polymer
surface, or both. Preferred materials for use in the blended
polymeric systems include nylon 6; nylon 66; nylon 6-10; nylon
(6-66-610) copolymers and other linear generally aliphatic nylon
compositions. A preferred nylon copolymer resin (SVP-651) was
analyzed for molecular weight by the end group titration. (J. E.
Walz and G. B. Taylor, determination of the molecular weight of
nylon, Anal. Chem. Vol. 19, Number 7, pp 448-450 (1947). A number
average molecular weight (Mn) was between 21,500 and 24,800. The
composition was estimated by the phase diagram of melt temperature
of three component nylon, nylon 6 about 45%, nylon 66 about 20% and
nylon 610 about 25%. (Page 286, Nylon Plastics Handbook, Melvin
Kohan ed. Hanser Publisher, New York (1995)).
[0045] Reported physical properties of SVP 651 resin are:
TABLE-US-00001 Property ASTM Method Units Typical Value Specific
Gravity D-792 -- 1.08 Water Absorption D-570 % 2.5 (24 hr
immersion) Hardness D-240 Shore D 65 Melting Point DSC .degree. C.
(.degree. F.) 154 (309) Tensile Strength D-638 MPa (kpsi) 50 (7.3)
@ Yield Elongation at Break D-638 % 350 Flexural Modulus D-790 MPa
(kpsi) 180 (26) Volume Resistivity D-257 ohm-cm 10.sup.12
[0046] A polyvinylalcohol having a hydrolysis degree of from 87 to
99.9+% can be used in such polymer systems. These are preferably
cross linked. And they are most preferably crosslinked and combined
with substantial quantities of the oleophobic and hydrophobic
additive materials.
[0047] Another preferred mode of the invention involves a single
polymeric material combined with an additive composition to improve
fiber lifetime or operational properties. The preferred polymers
useful in this aspect of the invention include nylon polymers,
polyvinylidene chloride polymers, polyvinylidene fluoride polymers,
polyvinylalcohol polymers and, in particular, those listed
materials when combined with strongly oleophobic and hydrophobic
additives that can result in a microfiber or nanofiber with the
additive materials formed in a coating on the fine fiber surface.
Again, blends of similar polymers such as a blend of similar
nylons, similar polyvinylchloride polymers, blends of
polyvinylidene chloride polymers are useful in this invention.
Further, polymeric blends or alloys of differing polymers are also
contemplated by the invention. In this regard, compatible mixtures
of polymers are useful in forming the microfiber materials of the
invention. Additive composition such a fluoro-surfactant, a
nonionic surfactant, low molecular weight resins (e.g.) tertiary
butylphenol resin having a molecular weight of less than about 3000
can be used. The resin is characterized by oligomeric bonding
between phenol nuclei in the absence of methylene bridging groups.
The positions of the hydroxyl and the tertiary butyl group can be
randomly positioned around the rings. Bonding between phenolic
nuclei always occurs next to hydroxyl group, not randomly.
Similarly, the polymeric material can be combined with an alcohol
soluble non-linear polymerized resin formed from bis-phenol A. Such
material is similar to the tertiary butylphenol resin described
above in that it is formed using oligomeric bonds that directly
connect aromatic ring to aromatic ring in the absence of any
bridging groups such as alkylene or methylene groups.
[0048] Preferred polymer systems of the invention have adhering
characteristic such that when contacted with a cellulosic substrate
adheres to the substrate with sufficient strength such that it is
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 except 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 Tg, and the polymer formulation including additives. Polymers
plasticized with solvent or steam at the time of adhesion can have
increased adhesion.
[0049] 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 are
formed on 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 30%, preferably 50%
of the fine fiber formed on the surface of the substrate. Retention
of at least 30%, preferably 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%.
The thickness of the typical fine fiber filtration layer ranges
from about 1 to 100 times the fiber diameter with a basis weight
ranging from about 0.01 to 240 micrograms-cm.sup.-2.
[0050] Fluid streams such as air and gas streams often carry
particulate material therein. The removal of some or all of the
particulate material from the fluid stream is needed. For example,
air intake streams to the cabins of motorized vehicles, air in
computer disk drives, HVAC air, aircraft cabin ventilation, clean
room ventilation and applications using filter bags, barrier
fabrics, woven materials, air to engines for motorized vehicles, or
to power generation equipment; gas streams directed to gas
turbines; and, air streams to various combustion furnaces, often
include particulate material therein. In the case of cabin air
filters it is desirable to remove the particulate matter for
comfort of the passengers and/or for aesthetics. With respect to
air and gas intake streams to engines, gas turbines and combustion
furnaces, it is desirable to remove the particulate material
because particulate can cause substantial damage to the internal
workings to the various mechanisms involved. In other instances,
production gases or off gases from industrial processes or engines
may contain particulate material therein. Before such gases can be,
or should be, discharged through various downstream equipment to
the atmosphere, it may be desirable to obtain a substantial removal
of particulate material from those streams.
[0051] A general understanding of some of the basic principles and
problems of air filter design can be understood by consideration of
the following types of filter media: 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.
[0052] The "lifetime" of a filter is typically defined according to
a selected limiting pressure drop across the filter. The pressure
buildup across the filter defines the lifetime at a defined level
for that application or design. Since this buildup of pressure is a
result of load, for systems of equal efficiency a longer life is
typically directly associated with higher capacity. Efficiency is
the propensity of the media to trap, rather than pass,
particulates. It should be apparent that typically the more
efficient a filter media is at removing particulates from a gas
flow stream, in general the more rapidly the filter media will
approach the "lifetime" pressure differential (assuming other
variables to be held constant).
DETAILED DESCRIPTION OF CERTAIN DRAWINGS
[0053] The microfiber or nanofiber of the unit can be formed by the
electrostatic spinning process. A suitable apparatus for forming
the fiber is illustrated in FIG. 1. This apparatus includes a
reservoir 80 in which the fine fiber forming polymer solution is
contained, a pump 81 and a rotary type emitting device or emitter
40 to which the polymeric solution is pumped. The emitter 40
generally consists of a rotating union 41, a rotating portion 42
including a plurality of offset holes 44 and a shaft 43 connecting
the forward facing portion and the rotating union. The rotating
union 41 provides for introduction of the polymer solution to the
forward facing portion 42 through the hollow shaft 43. The holes 44
are spaced around the periphery of the forward facing portion 42.
Alternatively, the rotating portion 42 can be immersed into a
reservoir of polymer fed by reservoir 80 and pump 81. The rotating
portion 42 then obtains polymer solution from the reservoir and as
it rotates in the electrostatic field, a droplet of the solution is
accelerated by the electrostatic field toward the collecting media
70 as discussed below.
[0054] Facing the emitter 40, but spaced apart therefrom, is a
substantially planar grid 60 upon which the collecting media 70
(i.e. substrate or combined substrate is positioned. Air can be
drawn through the grid. The collecting media 70 is passed around
rollers 71 and 72 which are positioned adjacent opposite ends of
grid 60. A high voltage electrostatic potential is maintained
between emitter 40 and grid 60 by means of a suitable electrostatic
voltage source 61 and connections 62 and 63 which connect
respectively to the grid 60 and emitter 40.
[0055] In use, the polymer solution is pumped to the rotating union
41 or reservoir from reservoir 80. The forward facing portion 42
rotates while liquid exits from holes 44, or is picked up from a
reservoir, and moves from the outer edge of the emitter toward
collecting media 70 positioned on grid 60. Specifically, the
electrostatic potential between grid 60 and the emitter 40 imparts
a charge to the material which cause liquid to be emitted therefrom
as thin fibers which are drawn toward grid 60 where they arrive and
are collected on substrate 12 or an efficiency layer 14. In the
case of the polymer in solution, solvent is evaporated off the
fibers during their flight to the grid 60; therefore, the fibers
arrive at the substrate 12 or efficiency layer 14. The fine fibers
bond to the substrate fibers first encountered at the grid 60.
Electrostatic field strength is selected to ensure that the polymer
material as it is accelerated from the emitter to the collecting
media 70, the acceleration is sufficient to render the material
into a very thin microfiber or nanofiber structure. 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. The
rotating portion 42 can have a variety of beneficial positions. The
rotating portion 42 can be placed in a plane of rotation such that
the plane is perpendicular to the surface of the collecting media
70 or positioned at any arbitrary angle. The rotating media can be
positioned parallel to or slightly offset from parallel
orientation.
[0056] FIG. 2 is a general schematic diagram of a process and
apparatus for forming a layer of fine fiber on a sheet-like
substrate or media. In FIG. 2, the sheet-like substrate is unwound
at station 20. The sheet-like substrate 20a is then directed to a
splicing station 21 wherein multiple lengths of the substrate can
be spliced for continuous operation. The continuous length of
sheet-like substrate is directed to a fine fiber technology station
22 comprising the spinning technology of FIG. 1 wherein a spinning
device forms the fine fiber and lays the fine fiber in a filtering
layer on the sheet-like substrate. After the fine fiber layer is
formed on the sheet-like substrate in the formation zone 22, the
fine fiber layer and substrate are directed to a heat treatment
station 23 for appropriate processing. The sheet-like substrate and
fine fiber layer is then tested in an efficiency monitor 24 and
nipped if necessary at a nip station 25. The sheet-like substrate
and fiber layer is then steered to the appropriate winding station
to be wound onto the appropriate spindle for further processing 26
and 27.
[0057] FIG. 3 is a scanning electromicrograph image showing the
relationship of typical dust particles having a diameter of about 2
and about 5 microns with respect to the sizes of pores in typical
cellulose media and in the typical fine fiber structures. In FIG.
3a, the 2 micron particle 31 and the 5 micron particle 32 is shown
in a cellulosic media 33 with pore sizes that are shown to be quite
a bit larger than the typical particle diameters. In sharp
contrast, in FIG. 3B, the 2 micron particle 31 appears to be
approximately equal to or greater than the typical openings between
the fibers in the fiber web 35 while the 5 micron particle 32
appears to be larger than any of the openings in the fine fiber web
35.
[0058] The foregoing general description of the various aspects of
the polymeric materials of the invention, the fine fiber materials
of the invention including both microfibers and nanofibers and the
construction of useful filter structures from the fine fiber
materials of the invention provides an understanding of the general
technological principles of the operation of the invention. The
following specific exemplary materials are examples of materials
that can be used in the formation of the fine fiber materials of
the invention and the following materials disclose a best mode. The
following exemplary materials were manufactured with the following
characteristics and process conditions in mind. Electrospinning
small diameter fiber less than 10 micron is obtained using an
electrostatic force from a strong electric field acting as a
pulling force to stretch a polymer jet into a very fine filament. A
polymer melt can be used in the electrospinning process, however,
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. Choice
of solvent is critical for several reasons. If solvent dries too
quickly, then fibers tends to be flat and large in diameter. If the
solvent dries too slowly, solvent will redissolve the formed
fibers. Therefore matching drying rate and fiber formation is
critical. At high production rates, large quantities of exhaust air
flow helps to prevent a flammable atmosphere, and to reduce the
risk of fire. A solvent that is not combustible is helpful. In a
production environment the processing equipment will require
occasional cleaning. Safe low toxicity solvents minimize worker
exposure to hazardous chemicals. Electrostatic spinning can be done
at a flow rate of 1.5 ml/min per emitter, a target distance of 8
inches, an emitter voltage of 88 kV, an emitter rpm of 200 and a
relative humidity of 45%.
[0059] The choice of polymer system is important for a given
application. For pulse cleaning application, an extremely thin
layer of microfiber can help to minimize pressure loss and provide
an outer surface for particle capture and release. A thin layer of
fibers of less than 2-micron diameter, preferably less than
0.3-micron diameter is preferred. Good adhesion between microfiber
or nanofiber and substrates upon which the microfibers or
nanofibers are deposited is important. When filters are made of
composites of substrate and thin layer of micro- and nanofibers,
such composite makes an excellent filter medium for self-cleaning
application. Cleaning the surface by back pulsing repeatedly
rejuvenates the filter medium. As a great force is exerted on the
surface, fine fiber with poor adhesion to substrates can delaminate
upon a back pulse that passes from the interior of a filter through
a substrate to the micro fiber. Therefore, good cohesion between
micro fibers and adhesion between substrate fibers and electrospun
fibers is critical for successful use.
[0060] Products that meet the above requirements can be obtained
using fibers made from different polymer materials. Small fibers
with good adhesion properties can be made from such polymers like
polyvinylidene chloride, poly vinyl alcohol and polymers and
copolymers comprising various nylons such as nylon 6, nylon 4,6;
nylon 6,6; nylon 6,10 and copolymers thereof. Excellent fibers can
be made from PVDF, but to make sufficiently small fiber diameters
requires chlorinated solvents. Nylon 6, Nylon 66 and Nylon 6,10 can
be electrospun. But, solvents such as formic acid, m-cresol,
tri-fluoro ethanol, hexafluoro isopropanol are either difficult to
handle or very expensive. Preferred solvents include water,
ethanol, isopropanol, acetone and N-methylpyrrolidone due to their
low toxicity. Polymers compatible with such solvent systems have
been extensively evaluated. We have found that fibers made from
PVC, PVDC, polystyrene, polyacrylonitrile, PMMA, PVDF require
additional adhesion means to attain structural properties. We also
found that when polymers are dissolved in water, ethanol,
isopropanol, acetone, methanol and mixtures thereof and
successfully made into fibers, they have excellent adhesion to the
substrate, thereby making an excellent filter medium for
self-cleaning application. Self-cleaning via back air pulse or
twist is useful when filer medium is used for very high dust
concentration. Fibers from alcohol soluble polyamides and
poly(vinyl alcohol)s have been used successfully in such
applications. Examples of alcohol soluble polyamides include
Macromelt 6238, 6239, and 6900 from Henkel, Elvamide 8061 and 8063
from duPont and SVP 637 and 651 from Shakespeare Monofilament
Company. Another group of alcohol soluble polyamide is type 8
nylon, alkoxy alkyl modifies nylon 66 (Ref. Page 447, Nylon
Plastics handbook, Melvin Kohan ed. Hanser Publisher, New York,
1995). Examples of poly(vinyl alcohol) include PVA-217, 224 from
Kuraray, Japan and Vinol 540 from Air Products and Chemical
Company.
[0061] We have found that filters can be exposed to extremes in
environmental conditions. Filters in Saudi Arabian desert can be
exposed to temperature as high as 150 F..degree. or higher. Filters
installed in Indonesia or Gulf Coast of US can be exposed high
humidity above 90% RH and high temperature of 100 F..degree.. Or,
they can be exposed to rain. We have found that filters used under
the hood of mobile equipment like cars, trucks, buses, tractors,
and construction equipment can be exposed to high temperature
(+200.degree. F.), high relative humidity and other chemical
environment. We have developed test methods to evaluate
survivability of microfiber systems under harsh conditions. Soaking
the filter media samples in hot water (140 F..degree.) for 5
minutes or exposure to high humidity, high temperature and air
flow.
B. General Principles Relating to Air Cleaner Design
[0062] Herein, the term "air cleaner" will be used in reference to
a system which functions to remove particulate material from an air
flow stream. The term "air filter" references a system in which
removal is conducted by passage of the air, carrying particulate
therein, through filter media. The term "filter media" or "media"
refers to a material or collection of material through which the
air passes, with a concomitant deposition of the particles in or on
the media. The term "surface loading media" or "barrier media"
refers to a system in which as the air passes through the media,
the particulate material is primarily deposited on the surface of
the media, forming a filter cake, as opposed to into or through the
depth of the media.
[0063] Herein the term "filter element" is generally meant to refer
to a portion of the air cleaner which includes the filter media
therein. In general, a filter element will be designed as a
removable and replaceable, i.e. serviceable, portion of the air
cleaner. That is, the filter media will be carried by the filter
element and be separable from the remainder portion of the air
cleaner so that periodically the air cleaner can be rejuvenated by
removing a loaded or partially loaded filter element and replacing
it with a new, or cleaned, filter element. Preferably, the air
cleaner is designed so that the removal and replacement can be
conducted by hand. By the term "loaded" or variants thereof in this
context, reference is meant to an air cleaner which has been
on-line a sufficient period of time to contain a significant amount
of trapped particles or particulates thereon. In many instances,
during normal operation, a filter element will increase in weight,
due to particulate loading therein, of two or three times (or more)
its original weight.
[0064] In general, specifications for the performance of an air
cleaner system are, generated by the preferences of the original
equipment manufacturer (OEM) for the engine involved and/or the OEM
of the truck or other equipment involved. While a wide variety of
specifications may be involved, some of the major ones are the
following: [0065] 1. Engine air intake need (rated flow) [0066] 2.
Initial Restriction [0067] 3. Initial efficiency [0068] 4. Average
or overall operating restriction [0069] 5. Overall efficiency
[0070] 6. Filter service life
[0071] The engine air intake need is a function of the engine size,
i.e. displacement and rpm at maximum, full or "rated" load. In
general, it is the product of displacement and rated rpm, modified
by the volumetric efficiency, a factor which reflects turbo
efficiency, duct efficiency, etc. In general, it is a measurement
of the volume of air, per unit time, required by the engine or
other system involved, during rated operation or full load. While
air intake need will vary depending upon rpm, the air intake
requirement is defined at a rated rpm, often at 1800 rpm or 2100
rpm for many typical truck engines. Herein this will be
characterized as the "rated air flow" or by similar terms. In
general, principles characterized herein can be applied to air
cleaner arrangements used with systems specified for operation over
a wide range of ratings or demands, including, for example, ones in
the range of about 3 cubic feet/min. (cfm) up to 10,000 cfm often
50 to 500 cfm. Such equipment includes, for example: small utility
engines (motorcycles, lawn mowers, etc.), automotive engines,
pickup trucks and sport utility vehicle engines, engines for small
trucks and delivery vehicles, buses, over-the-highway trucks,
agricultural equipment (for example tractors), construction
equipment, mining equipment, marine engines, a variety of generator
engines, and, in some instances, gas turbines and air
compressors.
[0072] Air cleaner overall efficiency is generally a reflection of
the amount of "filterable" solids which pass into the air cleaner
during use, and which are retained by the air cleaner. It is
typically represented as the percentage of solids passing into the
air cleaner which are retained by the air cleaner in normal use, on
a weight basis. It is evaluated and reported for many systems by
using SAE standards, which techniques are generally characterized
in U.S. Pat. No. 5,423,892 at Column 25, line 60-Column 26, line
59; Column 27, lines 1-40. A typical standard used is SAE J726,
incorporated herein by reference.
[0073] With respect to efficiency, engine manufacturer and/or
equipment manufacturer specifications will vary, in many instances,
with efficiency demands (based on either SAE J726 or field testing)
for overall operation often being set at 99.5% or higher, typically
at 99.8% or higher. With typical vehicle engines having air flow
demands of 500 cfm or above, specifications of 99.8% overall
average, or higher, are not uncommon.
[0074] Initial efficiency is the measurable efficiency of the
filter when it is first put on line. As explained in U.S. Pat. No.
5,423,892 at Column 27, lines 1-40, especially with conventional
pleated paper (barrier type or surface-loading) filters, initial
efficiency is generally substantially lower than the overall
average efficiency during use. This is because the "dust cake" or
contaminant build-up on the surface of such a filter during
operation, increases the efficiency of the filter. Initial
efficiency is also often specified by the engine manufacturer
and/or the vehicle manufacturer. With typical vehicle engines
having air flow demands of 500 cfm or above, specifications of 98%
or above (typically 98.5% or above) are common.
[0075] Restriction is the pressure differential across an air
cleaner or air cleaner system during operation. Contributors to the
restriction include: the filter media through which the air is
directed; duct size through which the air is directed; and,
structural features against which or around which the air is
directed as it flows through the air cleaner and into the engine.
With respect to air cleaners, initial restriction limits are often
part of the specifications and demands of the engine manufacturer
and/or equipment manufacturer. This initial restriction would be
the pressure differential measured across the air cleaner when the
system is put on line with a clean air filter therein and before
significant loading occurs. Typically, the specifications for any
given system have a maximum initial restriction requirement.
[0076] In general, engine and equipment manufacturers design
equipment with specifications for air cleaner efficiency up to a
maximum restriction. As reported in U.S. Pat. No. 5,423,892, at
Column 2, lines 19-29; and, column 6, line 47, column 7, line 3,
the limiting restriction: for typical truck engines is a pressure
drop of about 20-30 inches of water, often about 25 inches of
water; for automotive internal combustion engines is about 20-25
inches of water; for gas turbines, is typically about 5 inches of
water; and, for industrial ventilation systems, is typically about
3 inches of water.
[0077] In general, some of the principal variables of concern in
air cleaner design in order to develop systems to meet the types of
specifications characterized in the previous section, are the
following: [0078] 1. filter media type, geometry and efficiency;
[0079] 2. air cleaner shape and structure; and [0080] 3. filter
element size.
[0081] For example, conventional cellulose fiber media or similar
media is generally a "barrier" filter. An example is paper media.
In general, the operation of such media is through surface loading,
i.e., when air is directed through the media, the surface of the
media acts as a barrier or sieve, preventing passage of particulate
material therethrough. In time, a dust cake builds on the surface
of the media, increasing media efficiency. In general, the
"tightness" or "porosity" of the fiber construction determines the
efficiency, especially the initial efficiency, of the system. In
time, the filter cake will effect (increase) the efficiency.
[0082] In general, such media is often defined or specified by its
permeability. The permeability test for media is generally
characterized in U.S. Pat. No. 5,672,399 at Col. 19, lines 27-39.
In general, it is the media face velocity (air) required to induce
a 0.50 inch water restriction across a flat sheet of the referenced
material, media or composite. Permeability, as used herein, is
assessed by a Frazier Perm Test, according to ASTM D737
incorporated herein by reference, for example using a Frazier Perm
Tester available from Frazier Precision Instrument Co., Inc.,
Gaithersburg, Md., or by some analogous test.
[0083] The permeability of cellulose fiber media used in many types
of engine filters for trucks having rated air flows of 50 cfm or
more manufactured by Donaldson Company, is media having a
permeability of less than about 15 fpm, typically around 13 fpm. In
general, in the engine filtration market, for such equipment, a
variety of barrier media (pleated media) having permeability values
of less than about 25 fpm, and typically somewhere within the range
of 10-25 fpm, have been widely utilized by various element
manufacturers.
[0084] With respect to efficiency, principles vary with respect to
the type of media involved. For example, cellulose fiber or similar
barrier media is generally varied, with respect to efficiency, by
varying overall general porosity or permeability.
C. Typical System; Engine Air Intake
[0085] In FIG. 21, a schematic view of a system is shown generally
at 130. System 130 is one example type of system in which air
cleaner arrangements and constructions described herein is usable.
In FIG. 21, equipment 131, such as a vehicle, having an engine 132
with some defined rated air flow demand, for example, at least 370
cfm, is shown schematically. Equipment 131 may comprise a bus, an
over the highway truck, an off-road vehicle, a tractor, or marine
application such as a power boat. Engine 132 powers equipment 131,
through use of an air, fuel mixture. In FIG. 21, air flow is shown
drawn into engine 132 at an intake region 133. An optional turbo
134 is shown in phantom, as optionally boosting the air intake into
the engine 132. An air cleaner 135 having a media pack 136 is
upstream of the engine 132 and turbo 134. In general, in operation,
air is drawn in at arrow 137 into the air cleaner 135 and through
media pack 136. There, particles and contaminants are removed from
the air. The cleaned air flows at arrow 137 into the intake 133.
From there, the air flows into engine 132, to power vehicle
131.
[0086] In engine systems, during operation of the engine, the
temperature, under the hood, typically is at least 120.degree. F.,
and often is in the range of 140.degree. F.-220.degree. F. or more
depending on operating conditions. The temperature may adversely
affect the operating efficiency of the filter element. Regulations
on emissions can increase the restriction on the engine exhaust,
causing further increased temperatures. As explained below,
constructing the filter media in the form of a composite of a
barrier media and at least a single layer, and in some instances,
multiple layers of "fine fiber" can improve the performance (the
operating efficiency, in particular) of the filter element over
prior art filter elements that are not constructed from such media
composites.
D. Example Air Cleaners
[0087] Attention is directed to FIG. 22. FIG. 22 is a perspective
view of a first embodiment of a media pack 140. The preferred media
pack 140 depicted includes filter media 142 and a sealing system
144. In preferred constructions, the filter media 142 is designed
to remove particulates from a fluid, such as air, passing through
the filter media 142, while the sealing system 144 is designed to
seal the media pack 140 against a sidewall of a housing or duct, as
shown in FIG. 24.
[0088] This media pack 140 of FIGS. 22-25 is generally described in
U.S. Pat. No. 6,190,432, which is incorporated by reference
herein.
[0089] In certain preferred arrangements, the filter media 142 will
be configured for straight-through flow. By "straight-through
flow," it is meant that the filter media 142 is configured in a
construction 146 with a first flow face 148 (corresponding to an
inlet end, in the illustrated embodiment) and an opposite, second
flow face 150 (corresponding to an outlet end, in the illustrated
embodiment), with fluid flow entering in one direction 152 through
the first flow face 148 and exiting in the same direction 154 from
the second flow face 150. When used with an inline-flow housing, in
general, the fluid will enter through the inlet of the housing in
one direction, enter the filter construction 146 through the first
flow face 148 in the same direction, exit the filter construction
146 in the same direction from the second flow face 150, and exit
the housing through the housing outlet also in the same
direction.
[0090] In FIG. 22, the first flow face 148 and the second flow face
150 are depicted as planar and as parallel. In other embodiments,
the first flow face 148 and the second flow face 150 can be
non-planar, for example, frusto-conical. Further, the first flow
face 148 and second flow face 150 need not be parallel to each
other.
[0091] Generally, the filter construction 146 will be a wound
construction. That is, the construction 146 will typically include
a layer of filter media that is turned completely or repeatedly
about a center point. Typically, the wound construction will be a
coil, in that a layer of filter media will be rolled a series of
turns around a center point. In arrangements where a wound, coiled
construction is used, the filter construction 146 will be a roll of
filter media, typically permeable fluted filter media.
[0092] Attention is now directed to FIG. 23. FIG. 23 is schematic,
perspective view demonstrating the principles of operation of
certain preferred media usable in the filter constructions herein.
In FIG. 23, a fluted construction of Z-media is generally
designated at 156. Preferably, the fluted construction 156
includes: a layer 157 of corrugations having a plurality of flutes
158 and a face sheet 160. The FIG. 22 embodiment shows two sections
of the face sheet 160, at 160A (depicted on top of the corrugated
layer 157) and at 160B (depicted below the corrugated layer 157).
Typically, the preferred media construction 162 used in
arrangements described herein will include the corrugated layer 157
secured to the bottom face sheet 160B. When using this media
construction 162 in a rolled construction, it typically will be
wound around itself, such that the bottom face sheet 160B will
cover the top of the corrugated layer 157. The face sheet 160
covering the top of the corrugated layer is depicted as 160A. It
should be understood that the face sheet 160A and 160B are the same
sheet 160.
[0093] When using this type of media construction 162, the flute
chambers 158 preferably form alternating peaks 164 and troughs 166.
The troughs 166 and peaks 164 divide the flutes into an upper row
and lower row. In the particular configuration shown in FIG. 23,
the upper flutes form flute chambers 168 closed at the downstream
end 178, while flute chambers 170 having their upstream end 181
closed form the lower row of flutes. The fluted chambers 170 are
closed by a first end bead 172 that fills a portion of the upstream
end 181 of the flute between the fluting sheet 171 and the second
facing sheet 160B. Similarly, a second end bead 174 closes the
downstream end 178 of alternating flutes 168.
[0094] When using media constructed in the form of media
construction 162, during use, unfiltered fluid, such as air, enters
the flute chambers 168 as indicated by the shaded arrows 176. The
flute chambers 168 have their upstream ends 169 open. The
unfiltered fluid flow is not permitted to pass through the
downstream ends 178 of the flute chambers 168 because their
downstream ends 178 are closed by the second end bead 174.
Therefore, the fluid is forced to proceed through the fluting sheet
171 or face sheets 160. As the unfiltered fluid passes through the
fluting sheet 171 or face sheets 160, the fluid is cleaned or
filtered. The cleaned fluid is indicated by the unshaded arrow 180.
The fluid then passes through the flute chambers 170 (which have
their upstream ends 181 closed) to flow through the open downstream
end 184 out the fluted construction 156. With the configuration
shown, the unfiltered fluid can flow through the fluted sheet 171,
the upper facing sheet 160A, or lower facing sheet 160B, and into a
flute chamber 170.
[0095] Typically, the media construction 162 will be prepared and
then wound to form a rolled construction 146 of filter media. When
this type of media is selected for use, the media construction 162
prepared includes the sheet of corrugations 157 secured with the
end bead 172 to the bottom face sheet 160B (as shown in FIG. 23,
but without the top face sheet 160A).
[0096] Attention is again directed to FIG. 22. In FIG. 22, the
second flow face 150 is shown schematically. There is a portion at
182 in which the flutes including the open ends 184 and closed ends
178 are depicted. It should be understood that this section 182 is
representative of the entire flow face 50. For the sake of clarity
and simplicity, the flutes are not depicted in the other remaining
portions 183 of the flow face 150. Top and bottom plan views, as
well as side elevational views of a media pack 140 usable in the
systems and arrangements described herein are depicted in copending
and commonly assigned U.S. patent application Ser. No. 29/101,193,
filed Feb. 26, 1999, and entitled, "Filter Element Having Sealing
System," herein incorporated by reference.
[0097] Turning now to FIG. 24, the filter construction 146 is shown
installed in a housing 186 (which can be part of an air intake duct
into an engine or turbo of an air cleaner 179). In the arrangement
shown, air flows into the housing 186 at 187, through the filter
construction 146, and out of the housing 186 at 188. When media
constructions such as filter constructions 46 of the type shown are
used in a duct or housing 186, the sealing system 144 will be
needed to ensure that air flows through the media construction 146,
rather than bypass it.
[0098] The particular sealing system 144 depicted includes a frame
construction 190 and a seal member 192. When this type of sealing
system 144 is used, the frame construction 190 provides a support
structure or backing against which the seal member 192 can be
compressed against to form a radial seal 194 with the duct or
housing 186.
[0099] Still in reference to FIG. 24, in the particular embodiment
shown, the frame construction 190 includes a rigid projection 196
that projects or extends from at least a portion of one of the
first and second flow faces 148, 150 of the filter construction
146. The rigid projection 196, in the particular arrangement shown
in FIG. 24, extends axially from the second flow face 150 of the
filter construction 146.
[0100] The projection 196 shown has a pair of opposite sides 198,
102 joined by an end tip 104. In preferred arrangements, one of the
first and second sides 198, 102 will provide a support or backing
to the seal member 192 such that seal 194 can be formed between and
against the selected side 198 or 102 and the appropriate surface of
the housing or duct. When this type of construction is used, the
projection 196 will be a continuous member forming a closed hoop
structure 106 (FIG. 22).
[0101] When this type of construction is used, a housing or duct
may circumscribe the projection 196 and hoop structure 106
including the seal member 192 to form seal 194 between and against
the outer side 102 of the projection 196 and an inner surface 110
of the housing or duct.
[0102] In the particular embodiment shown in FIG. 24, the seal
member 192 engages the end tip 104 of the projection 196 as well,
such that the seal member 192 covers the projection 196 from the
exterior side 102, over the end tip 104, and to the interior side
198.
[0103] Referring now to FIGS. 22 and 24, the frame 190 has a band,
skirt, or depending lip 107 that is used to secure the frame 190 to
the media construction 146. The depending lip 107 depends or
extends down a first distance from cross braces 108.
[0104] During use of frames 190 of the type depicted herein, inward
forces are exerted around the circumference of the frame 190. Cross
braces 108 support the frame 190. By the term "support," it is
meant that the cross braces 108 prevent the frame 190 from radially
collapsing under the forces exerted around the circumference of the
frame 190.
[0105] The tip portion 104 provides support for the compressible
seal member 192. The compressible seal member 192 is preferably
constructed and arranged to be sufficiently compressible to be
compressed between the tip portion 104 of the frame 190 and
sidewall 110 of a housing or duct. When sufficiently compressed
between the tip portion 104 and the sidewall 110, radial seal 194
is formed between the media pack 140 and the sidewall 110.
[0106] One preferred configuration for seal member 192 is shown in
FIG. 25. The tip portion 104 of the frame 190 defines a wall or
support structure between and against which radial seal 194 may be
formed by the compressible seal member 192. The compression of the
compressible seal member 192 at the sealing system 144 is
preferably sufficient to form a radial seal under insertion
pressures of no greater than 80 lbs., typically, no greater than 50
lbs., for example, about 20-40 lbs., and light enough to permit
convenient and easy change out by hand.
[0107] In the preferred embodiment shown in FIG. 25, the seal
member 192 is a stepped cross-sectional configuration of decreasing
outermost dimensions (diameter, when circular) from a first end 112
to a second end 113, to achieve desirable sealing. Preferred
specifications for the profile of the particular arrangement shown
in FIG. 25 are as follows: a polyurethane foam material having a
plurality of (preferably at least three) progressively larger steps
configured to interface with the sidewall 110 and provide a
fluid-tight seal.
[0108] The compressible seal member 192 defines a gradient of
increasing internal diameters of surfaces for interfacing with the
sidewall 110. Specifically, in the example shown in FIG. 25, the
compressible seal member 192 defines three steps 114, 115, 116. The
cross-sectional dimension or width of the steps 114, 115, 116
increases the further the step 114, 115, 116 is from the second end
113 of the compressible seal member 192. The smaller diameter at
the second end 113 allows for easy insertion into a duct or
housing. The larger diameter at the first end 112 ensures a tight
seal.
[0109] In general, the media pack 140 can be arranged and
configured to be press-fit against the sidewall 110 of the housing
186 or duct. In the specific embodiment shown in FIG. 24, the
compressible seal member 192 is compressed between the sidewall 110
and the tip portion 104 of the frame 190. After compression, the
compressible seal member 192 exerts a force against the sidewall
110 as the compressible seal member 192 tries to expand outwardly
to its natural state, forming radial seal 94 between and against
the tip portion 104 and the sidewall 110.
[0110] A variety of housings are usable with the media pack 140. In
the particular embodiment depicted in FIG. 24, the housing 186
includes a body member or a first housing compartment 118 and a
removable cover or second housing compartment 120. In some
arrangements, the first housing compartment 118 is affixed to an
object, such as a truck. The second housing compartment 120 is
removably secured to the first housing compartment 118 by a
latching device 122.
[0111] In the illustrated embodiment in FIG. 24, the second end 150
of the media pack 140 with the attached frame 190 and compressible
seal member 192 is inserted into the first housing compartment 118.
The media pack 140 is press-fit into the first housing compartment
118 such that the compressible seal member 192 is compressed
between and against the tip portion 104 of the frame 190 and the
sidewall 110 of the first housing compartment 118, to form radial
seal 194 therebetween.
[0112] During use of the arrangement depicted in FIG. 24, the fluid
enters the housing assembly 185 at the inlet region 124 of the
second housing compartment 120, in the direction shown at 187. The
fluid passes through the filter construction 146. As the fluid
passes through the filter construction 146, contaminants are
removed from the fluid. The fluid exits the housing assembly 185 at
the outlet region 128, in the direction of 188. The compressible
seal member 192 of the sealing system 144 forms radial seal 194 to
prevent contaminated fluid from exiting the housing assembly 185,
without first passing through the filter construction 146.
[0113] FIG. 26 is a perspective view of another embodiment of a
media pack 130. In the construction depicted, the media pack 130
includes filter media 132 and a sealing system 134. The filter
media 132 is designed to remove contaminants from a fluid, such as
air, passing through the filter media 132. The sealing system 134
is designed to seal the filter media 134 to a housing or duct.
[0114] The construction and geometry of the media pack 130 of FIGS.
26-27, with the exception of preferred media formulations given in
Section H below, is described in U.S. Pat. No. 6,190,432, which is
incorporated by reference herein.
[0115] In certain preferred arrangements, the filter media 132 will
be configured in a filter construction 136 with a first flow face
138 and an opposite, second flow face 140.
[0116] The filter construction 136 can have a variety of
configurations and cross-sectional shapes. In the particular
embodiment illustrated in FIG. 26, the filter construction 136 has
a non-circular cross-section. In particular, the FIG. 26 embodiment
of the filter construction 136 has an ob-round or "racetrack"
cross-sectional shape. By "racetrack" cross-sectional shape, it is
meant that the filter construction 136 includes first and second
semicircular ends 141, 142 joined by a pair of straight segments
143, 144.
[0117] In FIG. 26, certain portions 146 are depicted showing the
flutes, including the open and closed ends. It should be understood
that this portion or section 146 is representative of the entire
flow face 140 (as well as the first flow face 138). For the sake of
clarity and simplicity, the flutes are not depicted in the other
remaining portions 149 of the flow face 140. Top and bottom plan
views, as well as side elevational views of the media pack 130
usable in the systems and arrangements described herein are
depicted in copending and commonly assigned U.S. patent application
Ser. No. 29/101,193, filed Feb. 26, 1999, and entitled, "Filter
Element Having Sealing System," herein and incorporated by
reference.
[0118] As with the embodiment of FIG. 22, the media pack 130
includes sealing system 134. In preferred constructions, the
sealing system 134 includes a frame 148 and a seal member 150.
[0119] The frame 148 has a non-circular, for example, obround and
in particular, a racetrack shape and is arranged and configured for
attachment to the end of the filter media 132. In particular, the
frame 148 has a band or skirt or depending lip 151 that is
generally racetrack shaped. The depending lip 151 depends or
extends down a distance from cross braces 152 and is used to secure
the frame 148 to the media pack 130.
[0120] During use of the arrangements depicted, inward forces are
exerted around the circumference of the frame 148. Inward forces
exerted against the semicircular ends 141, 142 can cause the
straight segments 143, 144 to bow or bend. Cross braces 152 are
provided to provide structural rigidity and support to the straight
segments 143, 144. As can be seen in FIG. 26, the particular cross
braces 152 depicted form a truss system 154 between the opposing
straight segments 143, 144. The truss system 154 includes a
plurality of rigid struts 156, preferably molded as a single piece
with the remaining portions of the frame 148.
[0121] The frame 148 is constructed analogously to the frame 90. As
such, the frame 148 includes a tip portion 158 (FIG. 27). In
preferred arrangements, the tip portion 158 acts as an annular
sealing support. In preferred systems, the compressible seal member
150 has structure analogous to the that of the compressible seal
member 92 of FIG. 5.
[0122] Preferably, the media pack 130 will be installed in a duct
or an air cleaner housing. In FIG. 27, the housing depicted is a
two-piece housing including a cover 160 and a body member 162. The
cover 160 defines an airflow inlet 164. The body member 162 defines
an airflow outlet 166. The housing further includes a pre-cleaner
arrangement 167 upstream of the media pack 130, such as that
described in U.S. Pat. Nos. 2,887,177 and 4,162,906, incorporated
by reference herein. In the one depicted, the pre-cleaner
arrangement 167 is in the cover 160. The cover 160 includes a dust
ejector 168 that expels dust and debris collected in the
pre-cleaner 167.
[0123] The compressible seal member 150 is compressed between the
sidewall 170 and the tip portion 158 of the frame 150. As the media
pack 130 is press-fit, the compressible seal member 150 is
compressed between and against the frame 148 (specifically, in the
particular embodiment shown, the tip portion 158) and the sidewall
170. After compression, the compressible seal member 150 exerts a
force against the sidewall 170 as the compressible seal member 150
tries to expand outwardly to its natural state, forming a radial
seal 171 with the sidewall 170.
[0124] Preferred formulations for media 132 are described in
Section H, below.
[0125] Another filter arrangement is shown in FIG. 28, generally at
174. With the exception of preferred media formulations described
in Section H below, the filter arrangement 174 is described in U.S.
Pat. No. 5,820,646, incorporated by reference herein.
[0126] The filter arrangement 174 includes a media pack 176 mounted
in, held by and supported by a panel construction 178. Filter
arrangement 174 also includes a housing 180, which includes a body
181 and a removable cover member 182. The panel construction 178
holding the media pack 176 seals within the housing 180, and is
removable and replaceable therefrom.
[0127] The media pack 176 includes fluted filter media 184
constructed as described above with respect to FIG. 23.
E. Typical System; Gas Turbine Air Intake
[0128] In FIG. 29, the air intake of a gas turbine system is shown
generally at 200. Airflow is shown drawn into an air intake system
200 at arrows 201. The air intake system 200 includes a plurality
of air filter arrangements 202 generally held in a tube sheet 203.
In preferred systems, the tube sheet 203 will be constructed to
hold the filter arrangements 202 at an angle, relative to a
vertical axis. Preferred angles will be between 5-25.degree., for
example, about 7.degree.. This permits liquid to drain from the
filter arrangements 202 when the system 200 is not operating.
[0129] The air is cleaned in the air filter arrangements 202, and
then it flows downstream at arrows 204 into gas turbine generator
205, where it is used to generate power.
[0130] In FIG. 33, an example of the air intake of a microturbine
is illustrated generally at 210. In general, microturbines are
smaller versions of gas turbines typically used as stand-by
generators. In some instances, such microturbines are approximately
24 inches by 18 inches and have electrical power output typically
between 30 kilowatts and 100 kilowatts. These systems typically
have air flow between 1000 cfm and 10,000 cfm.
[0131] In FIG. 33, airflow is shown drawn into an air intake system
211 at arrows 212. The air intake system 211 includes a filter
arrangement 213. As the air is drawn through the filter arrangement
213, the air is cleaned in the air filter arrangement 213, and then
flows downstream at arrows 214 into a gas turbine 215. The gas
turbine then typically powers an electrical generator, a fluid
compressor, or a fluid pump. As explained below, constructing the
filter arrangement in the form of a composite of a barrier media
and at least a single layer, and in some instances, multiple layers
of "fine fiber" can improve the performance (the operating
efficiency, in particular) of the filter arrangement over prior art
filters that are not constructed from such media composites.
F. Example Filter Arrangements for Gas Turbine Systems
[0132] One example of an air filter arrangement 202 usable in
system 200 or system 210 is shown in FIGS. 30-32. Other than
preferred media formulations given in Section H, the air filter
arrangement 202 is described in commonly assigned U.S. Ser. No.
09/437,867, filed Nov. 10, 1999, incorporated by reference herein.
In general, the air filter arrangement 202 includes a first, or
primary filter element 220 (FIGS. 30 and 32) and a second filter
element 222 (FIGS. 31 and 32), which acts as a prefilter. By the
term "prefilter", it is meant a separator that is positioned
upstream of the main, primary filter element 220, that functions to
remove large particles from the gas stream. The primary filter
element 220 and the prefilter element 222 are preferably secured
within a sleeve member 224 that is removably mountable in an
aperture 226 in tube sheet 203. In general, air flow is taken into
the system 200 and flows first through the prefilter element 222
and then through the primary filter element 220. After exiting the
primary filter element 220, the air is directed into the generator
205.
[0133] In general, the element 220 is constructed from fluted or
z-shaped media 230, as described above in connection with FIGS. 2
and 3. In FIG. 30, it should be understood that the outlet face 228
is shown schematically. That is, only a portion of the face 228 is
shown with flutes. It should be understood that, in typical
systems, the entire face 228 will be fluted.
[0134] The filter element 220 has a first end 232 and an opposite,
second end 234. In the arrangement depicted in FIG. 30, the first
end 232 will correspond to an upstream end inlet face 227, while
the second end 234 will correspond to a downstream end outlet face
228. The straight through flow allows gas to flow into the first
end 232 and exit the second end 234, such that the direction of the
air flow into the first end 232 is the same direction of air flow
that is exiting the second end 234. Straight through flow patterns
can reduce the amount of turbulence in the gas flow.
[0135] The media 230 can be a polyester synthetic media, a media
made from cellulose, or blends of these types of materials and
treated with fine fiber.
[0136] Preferably, the prefilter element 222 is a pleated
construction 236 comprising a plurality of individual pleats 237.
The pleats 237 are arranged in a zig-zag fashion. Preferred
prefilter elements 222 will have a generally circular
cross-section.
[0137] The prefilter element 222 is configured to permit straight
through flow. In other words, the air flows directly through the
prefilter element 222, entering at an inlet face 238 and exiting at
an oppositely disposed outlet face 239, wherein the direction of
fluid flow entering the inlet face 238 is in the same direction of
fluid flow exiting the outlet face 239.
[0138] In certain preferred embodiments, there will be at least 15
pleats 237, no greater than 80 pleats 237, and typically 30-50
pleats 237. The pleated construction 236 is made from a media 240
that is folded in the form of pleats 237 centered around a central
core 241. Useable types of media 240 includes fiberglass, or
alternatively, an air laid media. Specific properties of usable
media 240 include: a dry laid filter medium made from polyester
fibers randomly oriented to form a web having a weight of 2.7-3.3
oz./yd.sup.3 (92-112 g/m.sup.3); a free thickness (i.e., thickness
at 0.002 psi compression) of 0.25-0.40 in. (6.4-10.2 mm); and a
permeability of at least 400 ft./min (122 m/min).
[0139] In general, the prefilter element 222 is removably and
replaceably mountable in the sleeve member 224. The sleeve member
224 is described in further detail below. In certain systems, the
prefilter element 222 is held within the sleeve member 224 by
squeezing or compressing end tips of the media 240 against the
inside wall of the sleeve member 224.
[0140] Preferred filter arrangements 202 constructed according to
principles herein will have sleeve member 224 secured to and
circumscribing the primary filter element 220. In general, the
sleeve member 224 functions to hold the primary element 220 in
place in the system 200. Preferred sleeve members 224 will also
hold the prefilter element 222 in place upstream of the primary
element 220.
[0141] As can be seen in FIGS. 30 and 31, the sleeve member 224
preferably has a cross-section that matches the cross-section of
the primary filter element. The sleeve member 224 includes a
surrounding wall 244 that is curved in a form to result in a
surrounding ring 245. The sleeve member 224 is preferably oriented
relative to the primary filter element 220 to extend at least 30%
of the axial length of the primary filter element 220. In many
typical arrangements, the sleeve member 224 will extend greater
than 50% of the axial length of the primary filter element 220.
Indeed, in most preferred arrangements, the sleeve member 224 will
extend at least the entire length (that is, 100%) of the axial
length of the primary filter element 220. In many typical
applications, the sleeve member 224 will have a radius of at least
10 inches, typically 15-30 inches, and in some instances, no
greater than 50 inches.
[0142] The sleeve member 224 is preferably constructed and arranged
with a sealing system to allow for securing the primary filter
element 220 to the tube sheet 203, to inhibit air from bypassing
the primary element 220. In the illustrated embodiment, the sleeve
member 224 includes a seal member pressure flange 246. The flange
246 at least partially, and in many embodiments fully,
circumscribes the wall 244 of the sleeve member 224. The seal
member pressure flange 246 operates as a backstop to support a seal
member 248 in order to create a seal 250 between and against the
flange 246 and the tube sheet 203. The flange 246 extends radially
from the wall 244 of the sleeve member 224 and fully circumscribes
the seal member 224. The flange 246 will extend radially from the
wall 244 a distance sufficient to support the seal member 248.
[0143] A patch or retaining clip 252 (FIG. 30) extends over a joint
254 to secure the sleeve member 224 in its final configuration
Preferably, the retaining clip 252 is secured in a permanent way to
the sleeve member 224; for example, by ultrasonic welding.
[0144] Attention is directed to FIG. 32. It can be seen that the
flange 246 supports the seal member 248 on the axial side 256. The
seal member 248 generally comprises a circular gasket 258. The
gasket 258 is preferably secured to the flange 246, by adhesive
between the gasket 258 and the side 256 of the flange 246. The
gasket 258 is positioned on the flange 246, such that the gasket
258 completely circumscribes the wall 244 and the primary element
220.
[0145] The arrangement depicted also includes a system for clamping
the sleeve member 224 to the tube sheet 203. In the illustrated
embodiment, the clamping system includes a plurality of latches or
clamps 260. There should be enough latches or clamps 260 to form a
good, tight seal 250 between the flange 246 and the tube sheet 203,
when the sleeve member 224 is operably installed in the tube sheet
203; for example, illustrated is 4 clamps 260. In FIG. 32, the
clamp 260 is shown in cross-section. Each of the clamps 260
includes a lever 261, a nose 262, and a plate 263. The plate 263
includes apertures for accommodating a fastener, such as a bolt 264
to secure the clamp 260 to the tube sheet 203. The nose 262
operates to apply pressure to the flange 246 and compress the seal
member 248 against the tube sheet 203. The lever 261 operates to
selectively move the nose 262 toward and away from the tube sheet
203. In other embodiments, the clamps 260 can be hand-tightened,
such as using wing nuts.
[0146] In typical operation, there is an overall pressure drop
across the filter arrangement 202 of about 0.6-1.6 inches of water.
This includes both the primary filter element 220 and the prefilter
222. Typically, the pressure drop across the prefilter 222 alone
will be about 0.2-0.6 inches of water, while the pressure drop
across the primary element 220 alone will be about 0.4-1 inch of
water.
[0147] Another example of an air filter arrangement 213 usable in
the system 304 or system 302 is shown in FIGS. 34-36. With the
exception of preferred media formulations provided in Section H
below, the air filter arrangement is described in commonly assigned
U.S. patent application Ser. No. 09/593,257 filed Jun. 13, 2000,
incorporated by reference herein.
[0148] FIG. 35 illustrates the filter arrangement 213 in an
exploded, unassembled form, while FIG. 14 illustrates the filter
arrangement 213 assembled for use. In general, the air filter
arrangement 213 includes a moisture separator 270, a filter
assembly 272, and a filter housing 274. The filter housing 274 is
typically secured within a tube sheet 276 when assembled for use.
Preferably, the filter housing 274 is secured within the tube sheet
276 by welding the housing 274 to the tube sheet 276 or by bolting
the housing 274 to the tube sheet 276.
[0149] An access door 278 provides access to the filter arrangement
213 when assembled and allows air to be drawn into the system 302.
In general, the access door 278 is designed and constructed to fit
the particular housing of the system, such as the system 302, of
FIG. 33, it is to be installed in and to provide access to the
filter arrangement 213, when assembled. The access door 278 is also
designed and constructed to allow air to enter the system 210, FIG.
33.
[0150] The access door 278 preferably includes an air flow
resistance arrangement 280. In general, the air flow resistance
arrangement 280 directs air flow into the filter arrangement 213 in
a particular direction to reduce resistance through the system 302.
The air flow resistance arrangement 280 also aids in noise
attenuation. In the embodiment depicted in FIG. 34, the air flow
resistance arrangement is depicted as a plurality of louvers 282.
The louvers 282 also aid in protecting the system 210 from entry of
large objects and moisture into the system 302, FIG. 33. The
louvers 282 further aid in noise attenuation.
[0151] Moisture in the incoming air stream can damage the integrity
of the filter assembly 272, and damage, i.e. contribute to rusting,
the internal mechanisms of the system 302. To address this, the
filter arrangement includes moisture separator 270. In general, the
moisture separator 270 separates and collects moisture from the
incoming air stream prior to reaching the filter assembly 272. In
one embodiment, the moisture separator 270 includes a plurality of
flat screens, e.g., wire mesh.
[0152] In general, the filter assembly 272 removes contaminants
from the incoming air stream 212, FIG. 33, prior to entry into the
internal mechanisms of the system 302. Preferably, the filter
assembly 272 is configured to permit straight through flow directly
through the filter assembly 272, entering at an inlet face 284 and
exiting at an oppositely disposed outlet face 285, wherein the
direction of fluid flow entering the inlet face 284 is in the same
direction of fluid flow exiting the outlet face 285.
[0153] The filter assembly 272 includes a media pack 286 formed
from fluted media 288 rolled into a cylinder, as explained above in
connection with FIGS. 22 and 23. The media 288 can be a polyester
synthetic media, a media made from cellulose, or blends of these
types of materials and treated with a coating or a layer of fine
fiber. Preferred media formulations are given in Section H
below.
[0154] The filter assembly 272 depicted includes a pull mechanism
290. The pull mechanism 290 is constructed to allow a user to
easily remove the filter assembly 272 from the filter housing 274.
In the one shown, the pull mechanism 290 includes a handle 292 and
a retention mechanism 294 (FIG. 34). Typically, the handle 292 is a
knob 296. In the one shown in FIG. 34, the retention mechanism 294
includes a bolt 298 attached to the knob 296 and a nut 299 at the
other end of the bolt. Alternatively, the pull mechanism and the
core of the filter media could be one integrated unit.
[0155] In general, the filter housing 274 is constructed to receive
and hold the filter assembly 272 and to facilitate sealing with the
filter assembly 272. In the one shown in FIG. 16, the filter
housing 274 includes a transition area 302 angled from an outer
wall 304 at an angle of at least 10 degrees, preferably between 10
and 210 degrees, and most preferably about 15 degrees. The
transition area 302 aids in sealing the filter assembly 272 as will
be explained in more detail below.
[0156] The filter housing 274 further includes a mounting flange
306. The mounting flange 306 secures the filter housing 274 to the
tube sheet 276 through a fastener arrangement (e.g., bolts). The
housing 274 also includes a stopping arrangement 308. The stopping
arrangement 308 seats the filter assembly 272 within the housing
274 to prevent the filter assembly 272 from being pushed too far
into the housing 274. The stopping arrangement 308 also helps in
ensuring a proper seal between the filter assembly 272 and the
housing 274.
[0157] The stopping arrangement 308 includes a stop 310.
Preferably, the stop 310 projects from the outer wall 304 a
distance sufficient to prevent the filter assembly 272 from
bypassing the stop 310. During use, the filter assembly 272 rests
upon a top surface 311 of the stop 310.
[0158] The filter assembly 272 also includes a sealing gasket 312.
The sealing gasket 312 seals the filter assembly 272 in the filter
housing 274, inhibiting air from entering the system 302 between
the filter assembly 272 and the filter housing 274 and bypassing
the filter assembly 272. This ensures that the air stream goes
substantially through the filter assembly 272. In the one
illustrated, the sealing gasket 312 extends circumferentially
around the radial edge of the filter assembly 272. In one
embodiment, the sealing gasket 312 comprises closed cell foam; of
course, the sealing gasket 312 can comprise other suitable
material.
[0159] During use, the sealing gasket 312 seals a joint 314 between
the filter assembly 272 and the filter housing 274. During
installation, the filter assembly 272 is inserted into the housing
274 until an end 315 rests against the stop 310. As the filter
assembly 272 is installed, the sealing gasket 312 is compressed in
the transition area 302 between the filter assembly 272 and the
housing 274, sealing the joint 314.
[0160] During assembly, the filter housing 274 is slid into the
tube sheet 276 until the mounting flange 306 of the filter housing
274 is seated against the tube sheet 276. Next, the filter assembly
272 is seated within the filter housing 274. The filter assembly
272 is slid into the filter housing 274 until the end 315 of the
filter assembly 272 rests against the stop 310. The sealing gasket
312 is partially compressed and the filter assembly 272 is snugly
held with the filter housing 274.
[0161] In operation, the filter arrangement 213 is used as follows:
Air to be filtered in the system 302 is directed at arrows 212 into
the intake system 211. The air flows through the filter assembly
272. The air enters at the inlet face 284, passes through the
fluted construction 288, and exits through the outlet face 285.
From there, the air is taken into the turbine or generator 215.
G. Typical System; Fuel Cell Air Intake
[0162] A fuel cell air intake is shown schematically in FIG. 37 at
330. As depicted in FIG. 37, atmospheric or ambient air 331 enters
filter assembly 332 via an inlet 333. Prior to entering filter
assembly 332, atmospheric air 331 is dirty air having various
physical (e.g., particulate) and chemical contaminants. Filter
assembly 332 is constructed to remove various contaminants from the
dirty air to provide clean air 334 that exits from filter assembly
332. Clean air 334 is the intake air for a fuel cell 335, used to
generate power.
[0163] Referring still to FIG. 37, atmospheric air 331 enters
filter assembly 332 as dirty air through inlet 333 in housing 336
and progresses to dirty air side 337 of filter element 338. As the
air passes through filter element 338 to clean air side 339,
contaminants are removed by filter element 338 to provide filtered
air 334. Filtered air 334 exits filter assembly 332 through outlet
340 of housing 336 and is used by equipment 341.
[0164] Filter assembly 332 also optionally includes a noise
suppression element 342 to reduce or suppress the level of noise or
sound emanating from equipment 341. Suppression element 342 may be
positioned within housing 336, and in some embodiments, suppression
element 342 is defined by housing 336.
[0165] Equipment 341 includes a compressor 343 that provides air to
fuel cell 335 to use in its catalytic reaction. Compressor 343
emits noise, typically in the range of 3 Hertz to 30,000 Hertz,
sometimes as high as 50,000 Hertz, at a level of 85 to 110 dB at
one meter. Suppression element 342, reduces the level of sound
traveling upstream from compressor 343 by at least 3 dB, typically
by at least 6 dB, and preferably by at least 25 dB.
[0166] The fuel cell 335 takes in hydrogen fuel 345, emits a
by-product of water and carbon dioxide 346, and generates power
347. In general, fuel cells are devices consisting of two
electrodes (an anode and a cathode) that sandwich an electrolyte. A
fuel containing hydrogen flows to the anode, where the hydrogen
electrons are freed, leaving positively charged ions. The electrons
travel through an external circuit in which the ions diffuse
through the electrolyte. At the cathode, the electrons combine with
the hydrogen ions and oxygen to form water and carbon dioxide,
by-products. A common oxygen source is air. To speed the cathodic
reaction, a catalyst is often used. Examples of catalysts often
used in the fuel cell reaction include nickel, platinum, palladium,
cobalt, cesium, neodymium, and other rare earth metals. The
reactants in the fuel cell are the hydrogen fuel and an
oxidizer.
[0167] Typically, "low temperature fuel cells" operate at
temperatures, typically about 70 to 100.degree. C., sometimes as
high as 200.degree. C. High temperature fuel cells are typically
not as sensitive to chemical contamination due to their higher
operating temperature. High temperature fuel cells are, however,
sensitive to particulate contamination, and some forms of chemical
contamination, and thus high temperature fuel cells benefit from
the filtering features as described herein. One type of low
temperature fuel cell is commonly referred to as a "PEM", is named
for its use of a proton exchange membrane. Examples of other
various types of fuel cells that can be used in combination with
the filter assembly of the present invention include, for example,
U.S. Pat. Nos. 6,110,611; 6,117,579; 6,103,415; and 6,083,637, the
disclosures of which are incorporated here by reference. Various
fuel cells are commercially available from, for example, Ballard
Power Systems, Inc. of Vancouver, Canada; International Fuel Cells,
of Connecticut; Proton Energy Systems, Inc. of Rocky Hill, Conn.;
American Fuel Cell Corp. of Massachusetts; Siemans A G of Erlangen,
Germany; Energy Partners, L.C. of Florida; General Motors of
Detroit, Mich.; and Toyota Motor Corporation of Japan.
[0168] The filter assemblies, as described below, remove
contaminants from the atmospheric air before the air is used in the
fuel cell operation. As explained below, constructing the filter
assembly in the form of a composite of a barrier media and at least
a single layer, and in some instances, multiple layers of "fine
fiber" can enhance the performance (the operating efficiency, in
particular) of the filter assembly. The fine fiber treatment is
advantageous in improving filter efficiency in most filter geometry
and environment. In certain harsh environments with a filter
temperature over 120.degree. F., which includes both low
temperature and high temperature fuel cells the fine fiber can
often survive and provide extended lifetime filtration.
H. Example Filter Arrangement for Fuel Cell Air Intake Systems
[0169] FIG. 38 illustrates a filter assembly 350 usable in the
system of FIG. 37. Filter assembly 350 includes a housing 352 which
defines an inlet 354 and an outlet 356. Dirty air enters filter
assembly 350 via inlet 354, and clean air exits via outlet 356.
[0170] Positioned within housing 352 is a filter element 358 and a
noise suppression element 360. Suppression element 360 comprises a
first resonator 361 and a second resonator 362. First resonator 361
is configured to attenuate a peak of about 900 Hz, and second
resonator 362 is configured to attenuate a peak of about 550
Hz.
[0171] Filter element 358 of FIG. 38 is generally constructed
analogously as the filter element construction 40 (FIG. 22). As
such, it includes a media pack 364 of fluted media 366 (as
described with respect to FIG. 3) rolled into filter element
358.
[0172] When filter element 358 is used with inline-flow housing
352, the air will enter through inlet 354 of housing 352 in one
direction, enter filter element 358 through first flow face 368 in
the same direction, exit filter element 358 in the same direction
from second flow face 370, and exit housing 352 through outlet 356
also in the same direction.
[0173] As with the embodiment of FIGS. 22 and 24, a radial seal 372
is formed by compression of the sealing gasket 374 between and
against a frame 376 and an inner sealing surface 378 of the
housing.
[0174] Filter assembly 350 preferably also includes a portion
designed to remove contaminants from the atmosphere by either
adsorption or absorption. As used herein, the terms "adsorb",
"adsorption", "adsorbent" and the like, are intended to also
include the mechanisms of absorption and adsorption.
[0175] The chemical removal portion typically includes a
physisorbent or chemisorbent material, such as, for example,
desiccants (i.e., materials that adsorb or absorb water or water
vapor) or materials that adsorb or absorb volatile organic
compounds and/or acid gases and/or basic gases. The terms
"adsorbent material," "adsorption material," "adsorptive material,"
"absorbent material," absorption material, "absorptive material,"
and any variations thereof, are intended to cover any material that
removes chemical contaminants by adsorption or absorption. Suitable
adsorbent materials include, for example, activated carbon,
activated carbon fibers, impregnated carbon, activated alumina,
molecular sieves, ion-exchange resins, ion-exchange fibers, silica
gel, alumina, and silica. Any of these materials can be combined
with, coated with, or impregnated with materials such as potassium
permanganate, calcium carbonate, potassium carbonate, sodium
carbonate, calcium sulfate, citric acid, or mixtures thereof. In
some embodiments, the adsorbent material can be combined or
impregnated with a second material.
[0176] The adsorbent material typically includes particulates or
granulated material and can be present as granules, beads, fibers,
fine powders, nanostructures, nanotubes, aerogels, or can be
present as a coating on a base material such as a ceramic bead,
monolithic structures, paper media, or metallic surface. Typically,
the adsorbent materials, especially particulate or granulated
materials, are provided as a bed of material.
[0177] Alternately, the adsorbent material can be shaped into a
monolithic or unitary form, such as a large tablet, granule, bead,
or pleatable or honeycomb structure that optionally can be further
shaped. In at least some instances, the shaped adsorbent material
substantially retains its shape during the normal or expected
lifetime of the filter assembly. The shaped adsorbent material can
be formed from a free-flowing particulate material combined with a
solid or liquid binder that is then shaped into a non-free-flowing
article. The shaped adsorbent material can be formed by, for
example, a molding, a compression molding, or an extrusion process.
Shaped adsorbent articles are taught, for example, in U.S. Pat. No.
5,189,092 (Koslow), and U.S. Pat. No. 5,331,037 (Koslow), which are
incorporated herein by reference.
[0178] The binder used for providing shaped articles can be dry,
that is, in powdered and/or granular form, or the binder can be a
liquid, solvated, or dispersed binder. Certain binders, such as
moisture curable urethanes and materials typically referred to as
"hot melts", can be applied directly to the adsorbent material by a
spray process. In some embodiments, a temporary liquid binder,
including a solvent or dispersant which can be removed during the
molding process, is used. Suitable binders include, for example,
latex, microcrystalline cellulose, polyvinyl alcohol,
ethylene-vinyl acetate, starch, carboxylmethyl cellulose,
polyvinylpyrrolidone, dicalcium phosphate dihydrate, and sodium
silicate. Preferably the composition of a shaped material includes
at least about 70%, by weight, and typically not more than about
98%, by weight, adsorbent material. In some instances, the shaped
adsorbent includes 85 to 95%, preferably, approximately 90%, by
weight, adsorbent material. The shaped adsorbent typically includes
not less than about 2%, by weight, binder and not more than about
30%, by weight, binder.
[0179] Another embodiment of a suitable adsorbent material for use
in the chemical removal portion is an adsorbent material that
includes a carrier. For example, a mesh or scrim can be used to
hold the adsorbent material and binder. Polyester and other
suitable materials can be used as the mesh or scrim. Typically, any
carrier is not more than about 50% of the weight of the adsorbent
material, and is more often about 20 to 40% of the total adsorbent
weight. The amount of binder in the shaped adsorbed article with
the carrier typically ranges about 10 to 50% of the total adsorbent
weight and the amount of adsorbent material typically ranges about
20 to 60% of the total adsorbent weight.
[0180] The chemical removal portion can include strongly basic
materials for the removal of acid contaminants from the air, or
strongly acidic materials for the removal of basic contaminants
from the air, or both. Preferably, the basic materials and acidic
materials are removed from each other so that they do not cancel
each other. In some embodiments, the adsorbent material itself may
be the strongly acidic or strong basic material. Examples of such
materials include materials such as polymer particulates, activated
carbon media, zeolites, clays, silica gels, and metal oxides. In
other embodiments, the strongly acidic materials and the strongly
basic materials can be provided as surface coatings on carriers
such as granular particulate, beads, fibers, fine powders,
nanotubes, and aerogels. Alternately or additionally, the acidic
and basic material that forms the acidic and basic surfaces may be
present throughout at least a portion of the carrier; this can be
done, for example, by coating or impregnating the carrier material
with the acidic or basic material.
[0181] Both basic and acidic materials may be present in the
chemical removal portion of the filter element; however, it is
preferable that the two types of materials are spaced from each
other so that they do not react with and neutralize one another. In
some embodiments, the basic material, acidic material, or both, may
be spaced from an adsorbent material, such as activated carbon.
[0182] Examples of acidic compounds that are often present in
atmospheric air and are considered as contaminants for fuel cells
include sulfur oxides, nitrogen oxides, hydrogen sulfide, hydrogen
chloride, and volatile organic acids and nonvolatile organic acids.
Examples of basic compounds that are often present in atmospheric
air and are considered as contaminants for fuel cells include
ammonia, amines, amides, sodium hydroxides, lithium hydroxides,
potassium hydroxides, volatile organic bases and nonvolatile
organic bases.
[0183] For PEM fuel cells, the cathodic reaction occurs under
acidic conditions, thus, it is undesirable to have basic
contaminants present. An example of a preferred material for
removing basic contaminants, such as ammonia, is a bed of activated
carbon granules impregnated with citric acid.
[0184] A second example of a filter assembly usable in the system
of FIG. 37 is shown in fragmented cross-section in FIG. 39 as a
filter assembly 380. Filter assembly 380 includes a housing 382
which defines an inlet 384 and an outlet 386. Dirty air enters
filter assembly 380 via inlet 384, and clean air exits via outlet
386. Sound suppression element 388 comprises a resonator 390. A
filter element 391 is mounted within the housing 382 and is
analogous to filter element 358.
[0185] Filter assembly 380 also includes an adsorbent element 392.
Adsorbent element 392 comprises a cylindrical mass of carbon 393
between ends 394, 395. In the one depicted, mass of carbon 393 is a
hollow, circular extension 397 of activated carbon held together by
a thermoplastic binder. Carbon 393 can be produced, for example, by
the teachings of U.S. Pat. No. 5,189,092 (Koslow), and U.S. Pat.
No. 5,331,037 (Koslow). Positioned at first end 394 is a sealing
system 396 and positioned at second end 395 is a cap 398.
[0186] Sealing system 396 provides an air-tight seal between
adsorbent element 392 and baffle 401. Sealing system 396 is
designed to seal adsorbent element 392 against baffle 401, and,
under normal conditions, inhibit air from passing through a region
between adsorbent element 392 and the sidewall of housing 382.
Sealing system 396 inhibits air flow from avoiding passing through
carbon 393 of adsorbent element 392. Sealing system 396 is
typically made from a flexible, compressible material, such as
polyurethane.
[0187] Cap 398 diverts air exiting filter element 358 so that it
enters adsorbent element 392 through carbon 393 rather than passing
axially through the cylindrical extension of carbon 393. Air from
filter element 391 impinges on an exposed surface 402 of cap 398
and is rerouted from its "straight-line" flow to a flow having a
radial component. Cap 398 includes apertures 404 therein for
passage of air through cap 398 so that the air can reach carbon
393. In addition to managing air flow, cap 398 provides anchoring
of absorbent element 392 to filter element 391.
[0188] Adsorbent element 392 functions both as a chemical removal
portion and as an element of sound suppression element 388. Other
arrangements of adsorbent elements and adsorbent materials may also
have both a chemical removal quality and a sound suppression
quality.
[0189] I. Preferred Media Construction for Filter Elements
Disclosed Above
[0190] A fine fiber filter structure includes a bi-layer or
multi-layer structure wherein the filter contains one or more fine
fiber layers combined with or separated by one or more synthetic,
cellulosic or blended webs. Another preferred motif is a structure
including fine fiber in a matrix or blend of other fibers.
[0191] We believe important characteristics of the fiber and
microfiber layers in the filter structure relate to temperature
resistance, humidity or moisture resistance and solvent resistance,
particularly when the microfiber is contacted with humidity,
moisture or a solvent at elevated temperatures. Further, a second
important property of the materials of the invention relates to the
adhesion of the material to a substrate structure. The microfiber
layer adhesion is an important characteristic of the filter
material such that the material can be manufactured without
delaminating the microfiber layer from the substrate, the
microfiber layer plus substrate can be processed into a filter
structure including pleats, rolled materials and other structures
without significant delamination. We have found that the heating
step of the manufacturing process wherein the temperature is raised
to a temperature at or near but just below melt temperature of one
polymer material, typically lower than the lowest melt temperature
substantially improves the adhesion of the fibers to each other and
the substrate. At or above the melt temperature, the fine fiber can
lose its fibrous structure. It is also critical to control heating
rate. If the fiber is exposed to its crystallization temperature
for extended period of time, it is also possible to lose fibrous
structure. Careful heat treatment also improved polymer properties
that result from the formation of the exterior additive layers as
additive materials migrate to the surface and expose hydrophobic or
oleophobic groups on the fiber surface.
[0192] The criteria for performance is that the material be capable
of surviving intact various operating temperatures, i.e. a
temperature of 140.degree. F., 160.degree. F., 270.degree. F.,
300.degree. F. for a period of time of 1 hour or 3 hours, depending
on end use, while retaining 30%, 50%, 80% or 90% of filter
efficiency. An alternative criteria for performances that the
material is capable of surviving intact at various operating
temperatures, i.e. temperatures of 140.degree. F., 160.degree. F.,
270.degree. F., 300.degree. F., for a period of time of 1 hours or
3 hours depending on end use, while retaining, depending on end
use, 30%, 50%, 80% or 90% of effective fine fibers in a filter
layer. Survival at these temperatures is important at low humidity,
high humidity, and in water saturated air. The microfiber and
filter material of the invention are deemed moisture resistant
where the material can survive immersion at a temperature of
greater than 160.degree. F. while maintaining efficiency for a time
greater than about 5 minutes. Similarly, solvent resistance in the
microfiber material and the filter material of the invention is
obtained from a material that can survive contact with a solvent
such as ethanol, a hydrocarbon, a hydraulic fluid, or an aromatic
solvent for a period of time greater than about 5 minutes at
70.degree. F. while maintaining 50% efficiency.
[0193] 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; vehicle cabin air; off
road vehicle cabin air, disk drive air, photocopier-toner removal;
HVAC filters in both commercial or residential filtration
applications. Paper filter elements are widely used forms of
surface loading media. In general, paper elements comprise dense
mats of cellulose, synthetic or other fibers oriented across a gas
stream carrying particulate material. The paper is generally
constructed to be permeable to the gas flow, and to also have a
sufficiently fine pore size and appropriate porosity to inhibit the
passage of particles greater than a selected size therethrough. As
the gases (fluids) pass through the filter paper, the upstream side
of the filter paper operates through diffusion and interception to
capture and retain selected sized particles from the gas (fluid)
stream. The particles are collected as a dust cake on the upstream
side of the filter paper. In time, the dust cake also begins to
operate as a filter, increasing efficiency. This is sometimes
referred to as "seasoning," i.e. development of an efficiency
greater than initial efficiency.
[0194] A simple filter design such as that described above is
subject to at least two types of problems. First, a relatively
simple flaw, i.e. rupture of the paper, results in failure of the
system. Secondly, particulate material rapidly builds up on the
upstream side of the filter, as a thin dust cake or layer,
increasing the pressure drop. Various methods have been applied to
increase the "lifetime" of surface-loaded filter systems, such as
paper filters. One method is to provide the media in a pleated
construction, so that the surface area of media encountered by the
gas flow stream is increased relative to a flat, non-pleated
construction. While this increases filter lifetime, it is still
substantially limited. For this reason, surface loaded media has
primarily found use in applications wherein relatively low
velocities through the filter media are involved, generally not
higher than about 20-30 feet per minute and typically on the order
of about 10 feet per minute or less. The term "velocity" in this
context is the average velocity through the media (i.e. flow volume
per media area).
[0195] In general, as air flow velocity is increased through a
pleated paper media, filter life is decreased by a factor
proportional to the square of the velocity. Thus, when a pleated
paper, surface loaded, filter system is used as a particulate
filter for a system that requires substantial flows of air, a
relatively large surface area for the filter media is needed. For
example, a typical cylindrical pleated paper filter element of an
over-the-highway diesel truck will be about 9-15 inches in diameter
and about 12-24 inches long, with pleats about 1-2 inches deep.
Thus, the filtering surface area of media (one side) is typically
30 to 300 square feet.
[0196] In many applications, especially those involving relatively
high flow rates, an alternative type of filter media, sometimes
generally referred to as "depth" media, is used. A typical depth
media comprises a relatively thick tangle of fibrous material.
Depth media is generally defined in terms of its porosity, density
or percent solids content. For example, a 2-3% solidity media would
be a depth media mat of fibers arranged such that approximately
2-3% of the overall volume comprises fibrous materials (solids),
the remainder being air or gas space.
[0197] Another useful parameter for defining depth media is fiber
diameter. If percent solidity is held constant, but fiber diameter
(size) is reduced, pore size or interfiber space is reduced; i.e.
the filter becomes more efficient and will more effectively trap
smaller particles.
[0198] A typical conventional depth media filter is a deep,
relatively constant (or uniform) density, media, i.e. a system in
which the solidity of the depth media remains substantially
constant throughout its thickness. By "substantially constant" in
this context, it is meant that only relatively minor fluctuations
in density, if any, are found throughout the depth of the media.
Such fluctuations, for example, may result from a slight
compression of an outer engaged surface, by a container in which
the filter media is positioned.
[0199] Gradient density depth media arrangements have been
developed. some such arrangements are described, for example, in
U.S. Pat. Nos. 4,082,476; 5,238,474; and 5,364,456. In general, a
depth media arrangement can be designed to provide "loading" of
particulate materials substantially throughout its volume or depth.
Thus, such arrangements can be designed to load with a higher
amount of particulate material, relative to surface loaded systems,
when full filter lifetime is reached. However, in general the
tradeoff for such arrangements has been efficiency, since, for
substantial loading, a relatively low solidity media is desired.
Gradient density systems such as those in the patents referred to
above, have been designed to provide for substantial efficiency and
longer life. In some instances, surface loading media is utilized
as a "polish" filter in such arrangements.
[0200] A filter media construction according to the present
invention includes a first layer of permeable coarse fibrous media
or substrate having a first surface. A first layer of fine fiber
media is secured to the first surface of the first layer of
permeable coarse fibrous media. Preferably the first layer of
permeable coarse fibrous material comprises fibers having an
average diameter of at least 10 microns, typically and preferably
about 12 (or 14) to 30 microns. Also preferably the first layer of
permeable coarse fibrous material comprises a media having a basis
weight of no greater than about 200 grams/meter.sup.2, preferably
about 0.50 to 150 g/m.sup.2, and most preferably at least 8
g/m.sup.2. Preferably the first layer of permeable coarse fibrous
media is at least 0.0005 inch (12 microns) thick, and typically
0.0006 to 0.02 (15 to 500 microns) thick and preferably is about
0.001 to 0.030 inch (25-800 microns) thick.
[0201] In preferred arrangements, the first layer of permeable
coarse fibrous material comprises a material which, if evaluated
separately from a remainder of the construction by the Frazier
permeability test, would exhibit a permeability of at least 1
meter(s)/min, and typically and preferably about 2-900 meters/min.
Herein when reference is made to efficiency, unless otherwise
specified, reference is meant to efficiency when measured according
to ASTM-1215-89, with 0.78.mu. monodisperse polystyrene spherical
particles, at 20 fpm (6.1 meters/min) as described herein.
[0202] Preferably the layer of fine fiber material secured to the
first surface of the layer of permeable coarse fibrous media is a
layer of nano- and microfiber media wherein the fibers have average
fiber diameters of no greater than about 2 microns, generally and
preferably no greater than about 1 micron, and typically and
preferably have fiber diameters smaller than 0.5 micron and within
the range of about 0.05 to 0.5 micron. Also, preferably the first
layer of fine fiber material secured to the first surface of the
first layer of permeable coarse fibrous material has an overall
thickness that is no greater than about 30 microns, more preferably
no more than 20 microns, most preferably no greater than about 10
microns, and typically and preferably that is within a thickness of
about 1-8 times (and more preferably no more than 5 times) the fine
fiber average diameter of the layer.
[0203] Certain preferred arrangements according to the present
invention include filter media as generally defined, in an overall
filter construction. Some preferred arrangements for such use
comprise the media arranged in a cylindrical, pleated configuration
with the pleats extending generally longitudinally, i.e. in the
same direction as a longitudinal axis of the cylindrical pattern.
For such arrangements, the media may be imbedded in end caps, as
with conventional filters. Such arrangements may include upstream
liners and downstream liners if desired, for typical conventional
purposes.
[0204] In some applications, media according to the present
invention may be used in conjunction with other types of media, for
example conventional media, to improve overall filtering
performance or lifetime. For example, media according to the
present invention may be laminated to conventional media, be
utilized in stack arrangements; or be incorporated (an integral
feature) into media structures including one or more regions of
conventional media. It may be used upstream of such media, for good
load; and/or, it may be used downstream from conventional media, as
a high efficiency polishing filter.
[0205] Certain arrangements according to the present invention may
also be utilized in liquid filter systems, i.e. wherein the
particulate material to be filtered is carried in a liquid. Also,
certain arrangements according to the present invention may be used
in mist collectors, for example arrangements for filtering fine
mists from air.
[0206] According to the present invention, methods are provided for
filtering. The methods generally involve utilization of media as
described to advantage, for filtering. As will be seen from the
descriptions and examples below, media according to the present
invention can be specifically configured and constructed to provide
relatively long life in relatively efficient systems, to
advantage.
[0207] 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.
The following materials were produced using the following
electrospin process conditions.
[0208] The following materials were spun using either a rotating
emitter system or a capillary needle system. Both were found to
produce substantially the same fibrous materials.
[0209] Using the device generally a fiber is made. The flow rate
was 1.5 mil/min per emitter, a target distance of 8 inches, an
emitter voltage of 88 kV, a relative humidity of 45%, and for the
rotating emitter an rpm of 35.
EXAMPLE 1
Effect of Fiber Size
[0210] Fine fiber samples were prepared from a copolymer of nylon
6, 66, 610 nylon copolymer resin (SVP-651) was analyzed for
molecular weight by the end group titration. (J. E. Walz and G. B.
Taylor, determination of the molecular weight of nylon, Anal. Chem.
Vol. 19, Number 7, pp 448-450 (1947). Number average molecular
weight was between 21,500 and 24,800. The composition was estimated
by the phase diagram of melt temperature of three component nylon,
nylon 6 about 45%, nylon 66 about 20% and nylon 610 about 25%.
(Page 286, Nylon Plastics Handbook, Melvin Kohan ed. Hanser
Publisher, New York (1995)). Reported physical properties of SVP
651 resin are: TABLE-US-00002 Property ASTM Method Units Typical
Value Specific Gravity D-792 -- 1.08 Water Absorption D-570 % 2.5
(24 hr immersion) Hardness D-240 Shore D 65 Melting Point DSC
.degree. C. (.degree. F.) 154 (309) Tensile Strength D-638 MPa
(kpsi) 50 (7.3) @ Yield Elongation at Break D-638 % 350 Flexural
Modulus D-790 MPa (kpsi) 180 (26) Volume Resistivity D-257 ohm-cm
10.sup.12
to produce fiber of 0.23 and 0.45 micron in diameter. Samples were
soaked in room temperature water, air-dried and its efficiency was
measured. Bigger fiber takes longer time to degrade and the level
of degradation was less as can be seen in the plot of FIG. 12.
While wishing not to be limited by certain theory, it appears that
smaller fibers with a higher surface/volume ratio are more
susceptible to degradation due to environmental effects. However,
bigger fibers do not make as efficient filter medium.
EXAMPLE 2
Cross-Linking of Nylon Fibers with Phenolic Resin and Epoxy
Resin
[0211] In order to improve chemical resistance of fibers, chemical
cross-linking of nylon fibers was attempted. Copolyamide (nylon 6,
66, 610) described earlier is mixed with phenolic resin, identified
as Georgia Pacific 5137 and spun into fiber. Nylon:Phenolic Resin
ratio and its melt temperature of blends are shown here;
TABLE-US-00003 Composition Melting Temperature (.degree. F.)
Polyamide:Phenolic = 100:0 150 Polyamide:Phenolic = 80:20 110
Polyamide:Phenolic = 65:35 94 Polyamide:Phenolic = 50:50 65
[0212] We were able to produce comparable fiber from the blends.
The 50:50 blend could not be cross-linked via heat as the fibrous
structure was destroyed. Heating 65:35 blend below 90 degree C. for
12 hours improves the chemical resistance of the resultant fibers
to resist dissolution in alcohol. Blends of polyamide with epoxy
resin, such Epon 828 from Shell and Epi-Rez 510 can be used.
EXAMPLE 3
Surface Modification Though Fluoro Additive (Scotchgard.RTM.)
Repellant
[0213] Alcohol miscible Scotchgard.RTM. FC-430 and 431 from 3M
Company were added to polyamide before spinning. Add-on amount was
10% of solids. Addition of Scotchgard did not hinder fiber
formation. THC bench shows that Scotchgard-like high molecular
weight repellant finish did not improve water resistance.
Scotchgard added samples were heated at 300 F..degree. for 10
minutes as suggested by manufacturer.
EXAMPLE 4
Modification with Coupling Agents
[0214] Polymeric films were cast from polyamides with tinanate
coupling agents from Kenrich Petrochemicals, Inc. They include
isopropyl triisostearoyl titanate (KR TTS),
neopentyl(diallyl)oxytri(dioctyl)phosphate titanate (LICA12),
neopentyl(dially)oxy, tri(N-ethylene diamino)ethyl zirconate
(NZ44). Cast films were soaked in boiling water. Control sample
without coupling agent loses its strength immediately, while
coupling agent added samples maintained its form for up to ten
minutes. These coupling agents added samples were spun into fiber
(0.2 micron fiber).
EXAMPLE 5
Modification with Low Molecular Weight p-Tert-Butyl Phenol
Polymer
[0215] Oligomers of para-tert-butyl phenol, molecular weight range
400 to 1100, was purchased from Enzymol International, Columbus,
Ohio. These low molecular weight polymers are soluble in low
alcohols, such as ethanol, isopropanol and butanol. These polymers
were added to co-polyamide described earlier and electrospun into
0.2 micron fibers without adverse consequences. Some polymers and
additives hinder the electrospinning process. Unlike the
conventional phenolic resin described in Example 2, we have found
that this group of polymers does not interfere with fiber forming
process.
[0216] We have found that this group of additive protects fine
fibers from wet environment as see in the plot. FIGS. 13-16 show
that oligomers provide a very good protection at 140 F..degree.,
100% humidity and the performance is not very good at 160
F..degree.. We have added this additive between 5% and 15% of
polymer used. We have found that they are equally effective
protecting fibers from exposure to high humidity at 140 F..degree..
We have also found out that performance is enhanced when the fibers
are subjected to 150 C..degree. for short period of time.
[0217] The table 1 shows the effect of temperature and time
exposure of 10% add-on to polyamide fibers. TABLE-US-00004 TABLE 1
Efficiency Retained (%) After 140 deg. F. Soak: Heating Time
Temperature 1 min 3 min 10 min 150.degree. C. 98.9 98.8 98.5 98.8
98.9 98.8 130.degree. C. 95.4 98.7 99.8 96.7 98.6 99.6 110.degree.
C. 82.8 90.5 91.7 86.2 90.9 85.7
[0218] This was a surprising result. We saw dramatic improvement in
water resistance with this family of additives. In order to
understand how this group of additive works, we have analyzed the
fine fiber mat with surface analysis techniques called ESCA. 10%
add-on samples shown in Table 1 were analyzed with ESCA at the
University of Minnesota with the results shown in Table 2.
TABLE-US-00005 TABLE 2 Surface Composition (Polymer:Additive Ratio)
Heating Time Temperature 1 min 3 min 10 min 150.degree. C. 40:60
40:60 50:50 130.degree. C. 60:40 56:44 62:82 110.degree. C. 63:37
64:36 59:41 No Heat 77:23
[0219] Initially, it did not seem to make sense to find surface
concentration of additive more than twice of bulk concentration.
However, we believe that this can be explained by the molecular
weight of the additives. Molecular weight of the additive of about
600 is much smaller than that of host fiber forming polymer. As
they are smaller in size, they can move along evaporating solvent
molecules. Thus, we achieve higher surface concentration of
additives. Further treatment increases the surface concentration of
the protective additive. However, at 10 min exposure, 150
C..degree., did not increase concentration. This may be an
indication that mixing of two components of copolyamide and
oligomer molecules is happening as long chain polymer has a time to
move around. What this analysis has taught us is that proper
selection of post treatment time and temperature can enhance
performance, while too long exposure could have a negative
influence.
[0220] We further examined the surface of these additive laden
microfibers using techniques called Time of Flight SIMS. This
technique involves bombarding the subject with electrons and
observes what is coming from the surface. The samples without
additives show organic nitrogen species are coming off upon
bombardment with electron. This is an indication that polyamide
species are broken off. It also shows presence of small quantity of
impurities, such as sodium and silicone. Samples with additive
without heat treatment (23% additive concentration on surface) show
a dominant species of t-butyl fragment, and small but unambiguous
peaks observed peaks observed for the polyamides. Also observed are
high mass peaks with mass differences of 148 amu, corresponding to
t-butyl phenol. For the sample treated at 10 min at 150 C..degree.
(50% surface additive concentration by ESCA analysis), inspection
shows dominance of t-butyl fragments and trace, if at all, of peaks
for polyamide. It does not show peaks associated with whole t-butyl
phenol and its polymers. It also shows a peak associated with
C.sub.2H.sub.3O fragments.
[0221] The ToF SIMS analysis shows us that bare polyamide fibers
will give off broken nitrogen fragment from exposed polymer chain
and contaminants on the surface with ion bombardment. Additive
without heat treatment shows incomplete coverage, indicating that
additives do not cover portions of surface. The t-butyl oligomers
are loosely organized on the surface. When ion beam hits the
surface, whole molecules can come off along with labile t-butyl
fragment. Additive with heat treatment promotes complete coverage
on the surface. In addition, the molecules are tightly arranged so
that only labile fragments such as t-butyl-, and possibly
CH.dbd.CH--OH, are coming off and the whole molecules of t-butyl
phenol are not coming off. ESCA and ToF SIMS look at different
depths of surface. ESCA looks at deeper surface up to 100 Angstrom
while ToF SIMS only looks at 110-Angstrom depth. These analyses
agree.
EXAMPLE 6
Development of Surface Coated Interpolymer
[0222] Type 8 Nylon was originally developed to prepare soluble and
crosslinkable resin for coating and adhesive application. This type
of polymer is made by the reaction of polyamide 66 with
formaldehyde and alcohol in the presence of acid. (Ref. Cairns, T.
L.; Foster, H. D.; Larcher, A. W.; Schneider, A. K.; Schreiber, R.
S. J. Am. Chem. Soc. 1949, 71, 651). This type of polymer can be
electrospun and can be cross-linked. However, formation of fiber
from this polymer is inferior to copolyamides and crosslinking can
be tricky.
[0223] In order to prepare type 8 nylon, 10-gallon high-pressure
reactor was charged with the following ratio: TABLE-US-00006 Nylon
66 (duPont Zytel 101) 10 pounds Methanol 15.1 pounds Water 2.0
pounds Formaldehyde 12.0 pounds
[0224] The reactor is then flushed with nitrogen and is heated to
at least 135 C..degree.. under pressure. When the desired
temperature was reached, small quantity of acid was added as
catalyst. Acidic catalysts include trifluoroacetic acid, formic
acid, toluene sulfonic acid, maleic acid, maleic anhydride,
phthalic acid, phthalic anhydride, phosphoric acid, citric acid and
mixtures thereof. Nafion.RTM. polymer can also be used as a
catalyst. After addition of catalyst, reaction proceeds up to 30
minutes. Viscous homogeneous polymer solution is formed at this
stage. After the specified reaction time, the content of the high
pressure vessel is transferred to a bath containing methanol, water
and base, like ammonium hydroxide or sodium hydroxide to shortstop
the reaction. After the solution is sufficiently quenched, the
solution is precipitated in deionized water. Fluffy granules of
polymer are formed. Polymer granules are then centrifuged and
vacuum dried. This polymer is soluble in, methanol, ethanol,
propanol, butanol and their mixtures with water of varying
proportion. They are also soluble in blends of different
alcohols.
[0225] Thus formed alkoxy alkyl modified type 8 polyamide is
dissolved in ethanol/water mixture. Polymer solution is electrospun
in a manner described in Barris U.S. Pat. No. 4,650,516. Polymer
solution viscosity tends to increase with time. It is generally
known that polymer viscosity has a great influence in determining
fiber sizes. Thus, it is difficult to control the process in
commercial scale, continuous production. Furthermore, under same
conditions, type 8 polyamides do not form microfibers as
efficiently as copolyamides. However, when the solution is prepared
with addition of acidic catalyst, such as toluene sulfonic acid,
maleic anhydride, trifluoro methane sulfonic acid, citric acid,
ascorbic acid and the like, and fiber mats are carefully
heat-treated after fiber formation, the resultant fiber has a very
good chemical resistance. (FIG. 13). Care must be taken during the
crosslinking stage, so that one does not destroy fibrous
structure.
[0226] We have found a surprising result when type 8 polyamide
(polymer B) is blended with alcohol soluble copolyamides. By
replacing 30% by weight of alkoxy alkyl modified polyamide 66 with
alcohol soluble copolyamide like SVP 637 or 651 (polymer A),
Elvamide 8061, synergistic effects were found. Fiber formation of
the blend is more efficient than either of the components alone.
Soaking in ethanol and measuring filtration efficiency shows better
than 98% filtration efficiency retention, THC bench testing showing
comparable results with Type 8 polyamide alone. This type blend
shows that we can obtain advantage of efficient fiber formation and
excellent filtration characteristic of copolyamide with advantage
of excellent chemical resistance of crosslinked type 8 polyamide.
Alcohol soak test strongly suggests that non-crosslinkable
copolyamide has participated in crosslinking to maintain 98% of
filtration efficiency.
[0227] DSC (see FIGS. 17-20) of blends of polymer A and B become
indistinguishable from that of polymer A alone after they are
heated to 250 C..degree.. (fully crosslinked) with no distinct melt
temperature. This strongly suggests that blends of polymer A and B
are a fully integrated polymer by polymer B crosslinking with
polymer A. This is a completely new class of polyamide.
[0228] Similarly, melt-blend poly(ethylene terephthalate) with
poly(butylene terephthalate) can have similar properties. During
the melt processing at temperatures higher than melt temperature of
either component, ester group exchange occurs and inter polymer of
PET and PBT formed. Furthermore, our crosslinking temperature is
lower than either of single component. One would not have expected
that such group exchange occur at this low temperature. Therefore,
we believe that we found a new family of polyamide through solution
blending of Type A and Type B polyamide and crosslinking at
temperature lower than the melting point of either component.
[0229] When we added 10% by weight of t-butyl phenol oligomer
(Additive 7) and heat treated at temperature necessary for
crosslinking temperature, we have found even better results. We
theorized that hydroxyl functional group of t-butyl phenol
oligomers would participate in reaction with functional group of
type 8 nylons. What we have found is this component system provides
good fiber formation, improved resistance to high temperature and
high humidity and hydrophobicity to the surface of fine fiber
layers.
[0230] We have prepared samples of mixture of Polymer A and Polymer
B (Sample 6A) and another sample of mixture of Polymer A, Polymer B
and Additive & (Sample 6B). We then formed fiber by
electrospinning process, exposed the fiber mat at 300.degree. F.
for 10 minutes and evaluated the surface composition by ESCA
surface analysis.
[0231] Table shows ESCA analysis of Samples 6A and 6B.
TABLE-US-00007 Composition (%) Sample 6A Sample 6B Polymer A 30 30
Polymer B 70 70 Additive 7 0 10 Surface Composition W/O Heat W/Heat
W/O Heat W/Heat Polymer A&B (%) 100 100 68.9 43.0 Additive 7 0
0 31.1 57.0
[0232] ESCA provides information regarding surface composition,
except the concentration of hydrogen. It provides information on
carbon, nitrogen and oxygen. Since the Additive 7 does not contain
nitrogen, we can estimate the ratio of nitrogen containing
polyamides and additive that does not contain nitrogen by comparing
concentration of nitrogen. Additional qualitative information is
available by examining O 1s spectrum of binding energy between 535
and 527 eV. C.dbd.O bond has a binding energy at around 531 eV and
C--O bond has a binding energy at 533 eV. By comparing peak heights
at these two peaks, one can estimate relative concentration of
polyamide with predominant C.dbd.O and additive with solely C--O
groups. Polymer B has C--O linkage due to modification and upon
crosslinking the concentration of C--O will decrease. ESCA confirms
such reaction had indeed occurred, showing relative decrease of
C--O linkage. (FIG. 4 for non heat treated mixture fiber of Polymer
A and Polymer B, FIG. 5 for heat treated mixture fiber of Polymer A
and Polymer B). When Additive 7 molecules are present on the
surface, one can expect more of C--O linkage. This is indeed the
case as can be seen in FIGS. 6 and 7. (FIG. 6 for as-spun mixture
fibers of Polymer A, Polymer B and Additive 7. FIG. 7 for heat
treated mixture fibers of Polymer A, Polymer B and Additive 7).
FIG. 6 shows that the concentration of C--O linkage increases for
Example 7. The finding is consistent with the surface concentration
based on XPS multiplex spectrum of FIGS. 8 through 11.
[0233] The t-butyl oligomer molecules migrate toward the surface of
the fine fibers and form hydrophobic coating of about 50 .ANG..
Type 8 nylon has functional groups such as --CH.sub.2OH and
--CH.sub.2OCH.sub.3, which we expected to react with --OH group of
t-butyl phenol. Thus, we expected to see less oligomer molecules on
the surface of the fibers. We have found that our hypothesis was
not correct and we found the surface of the interpolymer has a thin
coating.
[0234] Samples 6A, 6B and a repeat of sample described in Section 5
have been exposed THC bench at 160.degree. F. at 100% RH. In
previous section, the samples were exposed to 140.degree. F. and
100% RH. Under these conditions, t-butyl phenol protected
terpolymer copolyamide from degradation. However, if the
temperature is raised to 160.degree. F. and 100% RH, then the
t-butyl phenol oligomer is not as good in protecting the underlying
terpolymer copolyamide fibers. We have compared samples at
160.degree. F. and 100% RH. TABLE-US-00008 TABLE Retained Fine
Fiber Efficiency after Exposure to 160.degree. F. and 100% RH
Sample After 1 Hr. After 2 Hrs. After 3 Hrs. Sample 6A 82.6 82.6
85.9 Sample 6B 82.4 88.4 91.6 Sample 5 10.1
The table shows that Sample 6B helps protect exposure to high
temperature and high humidity.
[0235] More striking difference shows when we exposed to droplets
of water on a fiber mat. When we place a drop of DI water in the
surface of Sample 6A, the water drops immediately spread across the
fiber mat and they wet the substrate paper as well. On the other
hand, when we place a drop of water on the surface of Sample 6B,
the water drop forms a bead and did not spread on the surface of
the mat. We have modified the surface of Sample 16 to be
hydrophobic by addition of oligomers of p-t-butyl phenol. This type
of product can be used as a water mist eliminator, as water drops
will not go through the fine fiber surface layer of Sample 6B.
[0236] Samples 6A, 6B and a repeat sample of Section 5 were placed
in an oven where the temperature was set at 310.degree. F. Table
shows that both Samples 6A and 6B remain intact while Sample of
Section 5 was severely damaged. TABLE-US-00009 TABLE Retained Fine
Fiber Efficiency after Exposure to 310.degree. F. Sample After 6
Hrs. After 77 Hrs. Sample 6A 100% 100% Sample 6B 100% 100% Sample 5
34% 33%
[0237] While addition of oligomer to Polymer A alone improved the
high temperature resistance of fine fiber layer, the addition of
Additive 7 has a neutral effect on the high temperature
exposure.
[0238] We have clearly shown that the mixture of terpolymer
copolyamide, alkoxy alkyl modified nylon 66 and oligomers of
t-butyl phenol provides a superior products in helping fine fibers
under severe environment with improved productivity in
manufacturing over either mixture of terpolymer copolyamide and
t-butyl phenol oligomer or the mixture of terpolymer copolyamide
and alkoxy alkyl modified nylon 66. These two components mixture
are also improvement over single component system.
EXAMPLE 7
Compatible Blend of Polyamides and Bisphenol A polymers
[0239] A new family of polymers can be prepared by oxidative
coupling of phenolic ring (Pecora, A; Cyrus, W. U.S. Pat. No.
4,900,671 (1990) and Pecora, A; Cyrus, W.; Johnson, M. U.S. Pat.
No. 5,153,298 (1992)). Of particular interest is polymer made of
Bisphenol A sold by Enzymol Corp. Soybean Peroxidase catalyzed
oxidation of Bisphenol A can start from either side of two --OH
groups in Bisphenol A. Unlike Bisphenol A based polycarbonate,
which is linear, this type of Bisphenol A polymer forms
hyperbranched polymers. Because of hyperbranched nature of this
polymer, they can lower viscosity of polymer blend.
[0240] We have found that this type of Bisphenol A polymer can be
solution blended with polyamides. Reported Hansen's solubility
parameter for nylon is 18.6. (Page 317, Handbook of Solubility
Parameters and other cohesion parameters, A. Barton ed., CRC Press,
Boca Raton Fla., 1985) If one calculates solubility parameter (page
61, Handbook of Solubility Parameters), then the calculated
solubility parameter is 28.0. Due to the differences in solubility
parameter, one would not expect that they would be miscible with
each other. However, we found that they are quite miscible and
provide unexpected properties.
[0241] 50:50 blend of Bisphenol A resin of M.W. 3,000 and
copolyamide was made in ethanol solution. Total concentration in
solution was 10%. Copolyamide alone would have resulted in 0.2
micron fiber diameter. Blend resulted in lofty layer of fibers
around 1 micron. Bisphenol A of 7,000 M.W. is not stable with
copolyamide and tends to precipitate.
[0242] DSC of 50:50 blend shows lack of melting temperature.
Copolyamide has melting temperature around 150 degree C. and
Bisphenol A resin is a glassy polymer with Tg of about 100. The
blend shows lack of distinct melting. When the fiber mat is exposed
to 100 degree C., the fiber mat disappears. This blend would make
an excellent filter media where upper use temperature is not very
high, but low-pressure drop is required. This polymer system could
not be crosslinked with a reasonable manner.
EXAMPLE 8
Dual Roles of Bisphenol A Polymer As Solvent and Solid in Blend
[0243] A surprising feature of Bisphenol A polymer blend is that in
solution form Bisphenol A polymer acts like a solvent and in solid
form the polymer acts as a solid. We find dual role of Bisphenol A
polymer truly unique.
[0244] The following formulation is made: TABLE-US-00010 Alkoxy
alkyl modified PA 66: Polymer B 180 g Bisphenol A Resin (3,000 MW):
Polymer C 108 g Ethanol 190 Grade 827 g Acetone 218 8 DI water 167
g Catalyst 9.3 g
[0245] The viscosity of this blend was 32.6 centipoise by
Brookfield viscometer. Total polymer concentration was be 19.2%.
Viscosity of Polymer B at 19.2% is over 200 centipoise. Viscosity
of 12% polymer B alone in similar solvent is around 60 centipoise.
This is a clear example that Bisphenol A resin acts like a solvent
because the viscosity of the total solution was lower than
expected. Resultant fiber diameter was 0.157 micron. If polymer B
alone participated in fiber formation, the expected fiber size
would be less than 0.1 micron. In other words, Polymer C
participated in fiber formation. We do not know of any other case
of such dramatic dual role of a component. After soaking the sample
in ethanol, the filtration efficiency and fiber size was measured.
After alcohol soak, 85.6% of filtration efficiency was retained and
the fiber size was unchanged. This indicates that Polymer C has
participated in crosslinking acting like a polymer solid.
[0246] Another polymer solution was prepared in the following
manner: TABLE-US-00011 Alkoxy alkyl Modified PA66: Polymer B 225 g
Bisphenol A Resin (3,000 MW): Polymer C 135 g Ethanol 190 Grade 778
g Acetone 205 g DI Water 157 g Catalyst 11.6 g
[0247] Viscosity of this blend was 90.2 centipoise. This is a very
low viscosity value for 24% solid. Again, this is an indication
Polymer C acts like a solvent in the solution. However, when they
are electrospun into fiber, the fiber diameter is 0.438 micron. 15%
solution of Polymer B alone would have produced around 0.2-micron
fibers. In final state, Polymer C contributes to enlarging fiber
sizes. Again, this example illustrates that this type of branched
polymer acts as a solvent in solution and acts as a solid in final
state. After soaking in ethanol solution, 77.9% of filtration
efficiency was retained and fiber size was unchanged.
EXAMPLE 9
Development of Crosslinked Polyamides/Bisphenol A Polymer
Blends
[0248] Three different samples were prepared by combining resins,
alcohols and water, stirring 2 hours at 60 degree C. The solution
is cooled to room temperature and catalyst was added to solution
and the mixture was stirred another 15 minutes. Afterward,
viscosity of solution was measured and spun into fibers.
[0249] The following table shows these examples: TABLE-US-00012
Recipe (g) Sample 9A Sample 9B Sample 9C Polymer B 8.4 12.6 14.7
Polymer A 3.6 5.4 6.3 Polymer C 7.2 10.8 12.6 Ethanol 190 Grade
89.3 82.7 79.5 Isopropanol 23.5 21.8 21.0 DI Water 18.0 16.7 15.9
Catalyst .45 0.58 0.79 Viscosity (cP) 22.5 73.5 134.2 Fiber Size
(micron) 0.14 0.258 0.496
[0250] We have found out that this blend generates fibers
efficiently, producing about 50% more mass of fiber compared to
Polymer A recipe. In addition, resultant polymeric microfibers
produce a more chemically resistant fiber. After alcohol soak, a
filter made from these fibers maintained more than 90% filtration
efficiency and unchanged fiber diameter even though inherently
crosslinkable polymer is only 44% of the solid composition. This
three-polymer composition of co-polyamide, alkoxy alkyl modified
Nylon 66 and Bisphenol A creates excellent fiber forming,
chemically resistant material.
EXAMPLE 10
Alkoxy Alkyl Modified Co-Polymer of Nylon 66 and Nylon 46
[0251] In a 10-gallon high-pressure reactor, the following
reactions were made, and resultant polymers were analyzed. After
reaction temperature was reached, catalyst were added and reacted
for 15 minutes. Afterward, the polymer solution was quenched,
precipitated, washed and dried. TABLE-US-00013 Reactor Charge (LB)
Run 10A Run 10B Run 10C Run 10D Run 10E Nylon 4,6 (duPont Zytel
101) 10 5 5 5 5 Nylon 6,6 (DSM Stanyl 300) 0 5 5 5 5 Formaldehyde 8
10 8 10 8 DI Water 0.2 0.2 2 0.2 2 Methanol 22 20 20 20 20 Reaction
Temp (.degree. C.) 140 140 140 150 150 Tg (.degree. C.) 56.7 38.8
37.7 38.5 31.8 Tm (.degree. C.) 241.1 162.3 184.9 175.4 189.5 Level
of Substitution Alkoxy (wt. %) 11.9 11.7 7.1 11.1 8.4 Methylol (wt
%) 0.14 0.13 0.14 0.26 0.24
[0252] DSC of the polymer made with Nylon 46 and Nylon 66 shows
broad single melt temperature, which are lower than the melting
temperature of modified Nylon 46 (241 C..degree.) or modified Nylon
66 (210 C..degree.). This is an indication that during the
reaction, both components are randomly distributed along the
polymer chain. Thus, we believe that we have achieved random
copolymer of Nylon 46 and Nylon 66 with alkoxy alkyl modification.
These polymers are soluble in alcohols and mixtures of alcohol and
water. TABLE-US-00014 Property ASTM Nylon 6.6 Nylon 4.6 T.sub.m
265.degree. C. 295.degree. C. Tensile Strength D638 13.700 8.500
Elongation at Break D638 15-80 60 Tensile Yield Strength D638
8000-12,000 Flexural Strength D790 17,8000 11,500 Tensile Modulus
.times. 10.sup.3 psi D638 230-550 250 Izod Impact ft-lb/in of notch
D256A 0.55-1.0 17 Deflection Temp Under D648 158 194 Flexural Load
264 psi
Both are highly crystalline and are not soluble in common alcohols.
Source: Modern Plastics Encyclopedia 1998
EXAMPLE 11
Development of Interpolymer of Coplyamides and Alkoxyalkyl Modified
Nylon 46/66 Copolymer and Formation of Electrospun Fibers
[0253] Runs 10B and 10D samples were made into fibers by methods
described in above. Alkoxy alkyl modified Nylon 46/66 (Polymer D)
alone were successfully electrospun. Blending Polymer D with
Polymer A brings additional benefits of more efficient fiber
formation and ability to make bigger fibers without sacrificing the
crosslinkability of Polymer D as can be seen in the following
table: TABLE-US-00015 Polymer 10B Polymer 10D w/30% w/30% Alone
Polymer A Alone Polymer A Fiber Size(micron) 0.183 0.464 0.19 0.3
Fiber Mass Ratio 1 3 1 2 Filtration Effi. 87 90 92 90
Retention(%)
Fiber Mass Ratio is calculated by (total length of fiber times
cross sectional area). Filtration Efficiency Retention is measured
soaking filter sample in ethanol. Fiber size was unchanged by
alcohol soak.
EXAMPLE 12
Crosslinked, Electrospun PVA
[0254] PVA powders were purchased from Aldrich Chemicals. They were
dissolved either in water or 50/50 mixture of methanol and water.
They were mixed with crosslinking agent and toluene sulfonic acid
catalyst before electrospinning. The resulting fiber mat was
crosslinked in an oven at 150.degree. C. for 10 minutes before
exposing to THC bench. TABLE-US-00016 Sample 12A Sample 12B Sample
12C Sample 12D PVA Hydrolysis 98-99 87-89 87-89 87-89 M.W. 31,500-
31,500- 31,500- 31,500- 50,000 50,000 50,000 50,000 PVA 10 10 10 10
Conc. (%) Solvent Water Mixture Mixture(c) Mixture(d) Other Polymer
None None Acrylic Acid Cymel 385 Other Polymer/ 0 0 30 30 PVA (%) %
Fiber 0(a) 0(a, b) 95(b) 20(b) Retained THC, 1 hr. % Fiber 90(a)
Retained THC, 3 hr. (a): Temperature 160.degree. F., 100% humidity
(b): Temperature 140.degree. F., 100% humidity (c): Molecular
Weight 2000 (d): Melamine formaldehyde resin from Cytec
EXAMPLE 13
[0255] A conventional cellulose air filter media was used as the
substrate. This substrate had a basis weight of 67 pounds per 3000
square feet, a Frazier permeability of 16 feet per minute at 0.5
inches of water pressure drop, a thickness of 0.012 inches, and a
LEFS efficiency of 41.6%. A fine fiber layer of Example 1 was added
to the surface using the process described with a nominal fiber
diameter of 0.2 microns. The resulting composite had a LEFS
efficiency of 63.7%. After exposure to 140 F air at 100% relative
humidity for 1 hour the substrate only sample was allowed to cool
and dry, it then had a LEFS efficiency of 36.5%. After exposure to
140 F air at 100% relative humidity for 1 hour the composite sample
was allowed to cool and dry, it then had a LEFS efficiency of
39.7%. Using the mathematical formulas described, the fine fiber
layer efficiency retained after 1 hour of exposure was 13%, the
number of effective fine fibers retained was 11%.
EXAMPLE 14
[0256] A conventional cellulose air filter media was used as the
substrate. This substrate had a basis weight of 67 pounds per 3000
square feet, a Frazier permeability of 16 feet per minute at 0.5
inches of water pressure drop, a thickness of 0.012 inches, and a
LEFS efficiency of 41.6%. A fine fiber layer of Example 5 was added
to the surface using the process described with a nominal fiber
diameter of 0.2 microns. The resulting composite had a LEFS
efficiency of 96.0%. After exposure to 160 F air at 100% relative
humidity for 3 hours the substrate only sample was allowed to cool
and dry, it then had a LEFS efficiency of 35.3%. After exposure to
160 F air at 100% relative humidity for 3 hours the composite
sample was allowed to cool and dry, it then had a LEFS efficiency
of 68.0%. Using the mathematical formulas described, the fine fiber
layer efficiency retained after 3 hours of exposure was 58%, the
number of effective fine fibers retained was 29%.
EXAMPLE 15
[0257] A conventional cellulose air filter media was used as the
substrate. This substrate had a basis weight of 67 pounds per 3000
square feet, a Frazier permeability of 16 feet per minute at 0.5
inches of water pressure drop, a thickness of 0.012 inches, and a
LEFS efficiency of 41.6%. A fine fiber layer of a blend of Polymer
A and Polymer B as described in Example 6 was added to the surface
using the process described with a nominal fiber diameter of 0.2
microns. The resulting composite had a LEFS efficiency of 92.9%.
After exposure to 160 F air at 100% relative humidity for 3 hours
the substrate only sample was allowed to cool and dry, it then had
a LEFS efficiency of 35.3%. After exposure to 160 F air at 100%
relative humidity for 3 hours the composite sample was allowed to
cool and dry, it then had a LEFS efficiency of 86.0%. Using the
mathematical formulas described, the fine fiber layer efficiency
retained after 3 hours of exposure was 96%, the number of effective
fine fibers retained was 89%.
EXAMPLE 16
[0258] A conventional cellulose air filter media was used as the
substrate. This substrate had a basis weight of 67 pounds per 3000
square feet, a Frazier permeability of 16 feet per minute at 0.5
inches of water pressure drop, a thickness of 0.012 inches, and a
LEFS efficiency of 41.6%. A fine fiber layer of Polymer A, Polymer
B, t-butyl phenol oligomer as described in Example 6 was added to
the surface using the process described with a nominal fiber
diameter of 0.2 microns. The resulting composite had a LEFS
efficiency of 90.4%. After exposure to 160 F air at 100% relative
humidity for 3 hours the substrate only sample was allowed to cool
and dry, it then had a LEFS efficiency of 35.3%. After exposure to
160 F air at 100% relative humidity for 3 hours the composite
sample was allowed to cool and dry, it then had a LEFS efficiency
of 87.3%. Using the mathematical formulas described, the fine fiber
layer efficiency retained after 3 hours of exposure was 97%, the
number of effective fine fibers retained was 92%.
EXAMPLE 17
[0259] A conventional cellulose air filter media was used as the
substrate. This substrate had a basis weight of 67 pounds per 3000
square feet, a Frazier permeability of 16 feet per minute at 0.5
inches of water pressure drop, a thickness of 0.012 inches, and a
LEFS efficiency of 41.6%. A fine fiber layer of crosslinked PVA
with polyacrylic acid of Example 12 was added to the surface using
the process described with a nominal fiber diameter of 0.2 microns.
The resulting composite had a LEFS efficiency of 92.9%. After
exposure to 160 F air at 100% relative humidity for 2 hours the
substrate only sample was allowed to cool and dry, it then had a
LEFS efficiency of 35.3%. After exposure to 160 F air at 100%
relative humidity for 2 hours the composite sample was allowed to
cool and dry, it then had a LEFS efficiency of 83.1%. Using the
mathematical formulas described, the fine fiber layer efficiency
retained after 2 hours of exposure was 89%, the number of effective
fine fibers retained was 76%.
EXAMPLE 18
[0260] The following filter composite materials have been made with
the listed substrate using the methods described in Example 1-17.
TABLE-US-00017 Filter Examples Substrate Substrate Substrate
Substrate Composite perm Substrate Basis wt Thickness Eff Eff
(Frazier) (lbs/3000 sq ft) (in) (LEFS) (LEFS) Single fine fiber
layer (+/-10%) (+/-10%) (+/-25%) (+/-5%) (+/-5%) on single
substrate (flow either direction through media) Cellulose air
filter media 58 67 0.012 11% 50% Cellulose air filter media 16 67
0.012 43% 58% Cellulose air filter media 58 67 0.012 11% 65%
Cellulose air filter media 16 67 0.012 43% 70% Cellulose air filter
media 22 52 0.010 17% 70% Cellulose air filter media 16 67 0.012
43% 72% Cellulose/synthetic 14 70 0.012 30% 70% blend with moisture
resistant resin Flame retardant 17 77 0.012 31% 58% cellulose air
filter media Flame retardant cellulose 17 77 0.012 31% 72% air
filter media Flame retardant synthetic 27 83 0.012 77% air filter
media Spunbond Reemay 1200 15 0.007 5% 55% (polyester)
Synthetic/cellulose air filter 260 76 0.015 6% 17% media
Synthetic/glass air filter 31 70 0.012 55% 77% media
Synthetic/glass air filter 31 70 0.012 50% 90% media Synthetic
(Lutrador- 300 25 0.008 3% 65% polyester) Synthetic (Lutrador-
0.016 90% polyester)
[0261] Media has been used flat, corrugated, pleated, corrugated
and pleated, in flatsheets, pleated flat panels, pleated round
filters, and other filter structures and configurations.
Test Methods
Hot Water Soak Test
[0262] Using filtration efficiency as the measure of the number of
fine fibers effectively and functionally retained in structure has
a number of advantages over other possible methods such as SEM
evaluation. [0263] the filtration measure evaluates several square
inches of media yielding a better average than the tiny area seen
in SEM photomicrographs (usually less than 0.0001 square inch
[0264] the filtration measurement quantifies the number of fibers
remaining functional in the structure. Those fibers that remain,
but are clumped together or otherwise existing in an altered
structure are only included by their measured effectiveness and
functionality.
[0265] Nevertheless, in fibrous structures where the filtration
efficiency is not easily measured, other methods can be used to
measure the percent of fiber remaining and evaluated against the
50% retention criteria.
[0266] Description: This test is an accelerated indicator of filter
media moisture resistance. The test uses the LEFS test bench to
measure filter media performance changes upon immersion in water.
Water temperature is a critical parameter and is chosen based on
the survivability history of the media under investigation, the
desire to minimize the test time and the ability of the test to
discriminate between media types. Typical water temperatures re
70.degree. F., 140.degree. F. or 160.degree. F.
Procedure:
[0267] A 4'' diameter sample is cut from the media. Particle
capture efficiency of the test specimen is calculated using 0.8
.mu.m latex spheres as a test challenge contaminant in the LEFS
(for a description of the LEFS test, see ASTM Standard F1215-89)
bench operating at 20 FPM. The sample is then submerged in
(typically 140.degree. F.) distilled water for 5 minutes. The
sample is then placed on a drying rack and dried at room
temperature (typically overnight). Once it is dry the sample is
then retested for efficiency on the LEFS bench using the same
conditions for the initial calculation.
[0268] The previous steps are repeated for the fine fiber
supporting substrate without fine fiber.
[0269] From the above information one can calculate the efficiency
component due only to the fine fiber and the resulting loss in
efficiency due to water damage. Once the loss in efficiency due to
the fine fiber is determined one can calculate the amount of
efficiency retained.
Calculations:
[0270] Fine fiber layer efficiency: [0271] E.sub.i=Initial
Composite Efficiency; [0272] E.sub.s=Initial Substrate Efficiency;
[0273] F.sub.e=Fine Fiber Layer
F.sub.e=1-EXP(Ln(1-E.sub.i)-Ln(1-E.sub.x))
[0274] Fine fiber layer efficiency retained: [0275] F.sub.i=Initial
fine fiber layer efficiency; [0276] F.sub.x=Post soak fine fiber
layer efficiency; [0277] F.sub.r=Fine fiber retained
F.sub.r=F.sub.x/F.sub.i
[0278] The percentage of the fine fibers retained with effective
functionality can also be calculated by:
%=log(1-F.sub.x)/log(1-F.sub.i)
[0279] Pass/Fail Criteria: >50% efficiency retention
[0280] In most industrial pulse cleaning filter applications the
filter would perform adequately if at least 50% of the fine fiber
efficiency is retained.
THC Bench (Temperature, Humidity
[0281] Description: The purpose of this bench is to evaluate fine
fiber media resistance to the affects of elevated temperature and
high humidity under dynamic flow conditions. The test is intended
to simulate extreme operating conditions of either an industrial
filtration application, gas turbine inlet application, or heavy
duty engine air intake environments. Samples are taken out, dried
and LEFS tested at intervals. This system is mostly used to
simulate hot humid conditions but can also be used to simulate
hot/cold dry situations. TABLE-US-00018 Temperature -31 to
390.degree. F. Humidity 0 to 100% RH (Max temp for 100% RH is
160.degree. F. and max continuous duration at this condition is 16
hours) Flow Rate 1 to 35 FPM
Procedure:
[0282] A 4'' diameter sample is cut from the media.
[0283] Particle capture efficiency of the test specimen is
calculated using 0.8 .mu.m latex spheres as a test challenge
contaminant in the LEFS bench operating at 20 FPM.
[0284] The sample is then inserted into the THC media chuck.
[0285] Test times can be from minutes to days depending on testing
conditions.
[0286] The sample is then placed on a drying rack and dried at room
temperature (typically overnight). Once it is dry the sample is
then retested for efficiency on the LEFS bench using the same
conditions for the initial calculation.
[0287] The previous steps are repeated for the fine fiber
supporting substrate without fine fiber. From the above information
one can calculate the efficiency component due only to the fine
fiber and the resulting loss in efficiency due to alcohol
damage.
[0288] Once the loss in efficiency due to the fine fiber is
determined one can calculate the amount of efficiency retained.
[0289] Pass/Fail Criteria: >50% efficiency retention
[0290] In most industrial pulse cleaning filter applications the
filter would perform adequately if at least 50% of the fine fiber
efficiency is retained.
Alcohol (Ethanol) Soak Test
[0291] Description: The test uses the LEFS test bench to measure
filter media performance changes upon immersion in room temperature
ethanol.
Procedure:
[0292] A 4'' diameter sample is cut from the media. Particle
capture efficiency of the test specimen is calculated using 0.8
.mu.m latex spheres as a test challenge contaminant in the LEFS
bench operating at 20 FPM. The sample is then submerged in alcohol
for 1 minute.
[0293] The sample is then placed on a drying rack and dried at room
temperature (typically overnight). Once it is dry the sample is
then retested for efficiency on the LEFS bench using the same
conditions for the initial calculation. The previous steps are
repeated for the fine fiber supporting substrate without fine
fiber. From the above information one can calculate the efficiency
component due only to the fine fiber and the resulting loss in
efficiency due to alcohol damage. Once the loss in efficiency due
to the fine fiber is determined one can calculate the amount of
efficiency retained.
[0294] Pass/Fail Criteria: >50% efficiency retention.
[0295] The above specification, examples and data provide an
explanation of the invention. However, many variations and
embodiments can be made to the disclosed invention. The invention
is embodied in the claims herein after appended.
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