U.S. patent application number 16/792848 was filed with the patent office on 2020-12-17 for filter media including a waved filtration layer.
This patent application is currently assigned to Hollingsworth & Vose Company. The applicant listed for this patent is Hollingsworth & Vose Company. Invention is credited to David T. Healey, Ingrid Ruckert, Bruce Smith, Siqiang Zhu.
Application Number | 20200391148 16/792848 |
Document ID | / |
Family ID | 1000005059298 |
Filed Date | 2020-12-17 |
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United States Patent
Application |
20200391148 |
Kind Code |
A1 |
Smith; Bruce ; et
al. |
December 17, 2020 |
FILTER MEDIA INCLUDING A WAVED FILTRATION LAYER
Abstract
Filter media including a waved filtration layer are described
herein. The filtration layer may be held in a waved configuration
by a support layer. In some cases, the filtration layer may have a
combination of characteristics (e.g., mean flow pore size, basis
weight, amongst others) that can lead to enhanced filtration
performance (e.g., reduced air permeability decrease), in
particular, in high humidity environments. The filter media may be
used to form a variety of filter elements for use in various
applications. In some embodiments, at least a surface of the
filtration layer is hydrophilic.
Inventors: |
Smith; Bruce; (Copper Hill,
VA) ; Healey; David T.; (Bellingham, MA) ;
Ruckert; Ingrid; (Hatzfeld, DE) ; Zhu; Siqiang;
(Christiansburg, VA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hollingsworth & Vose Company |
East Walpole |
MA |
US |
|
|
Assignee: |
Hollingsworth & Vose
Company
East Walpole
MA
|
Family ID: |
1000005059298 |
Appl. No.: |
16/792848 |
Filed: |
February 17, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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|
15466799 |
Mar 22, 2017 |
10561972 |
|
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16792848 |
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14858398 |
Sep 18, 2015 |
10449474 |
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15466799 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01D 2239/1266 20130101;
B01D 46/522 20130101; B01D 2239/0421 20130101; B01D 2239/1216
20130101; B01D 39/1623 20130101; A62B 23/025 20130101; B01D 46/521
20130101; B01D 2239/1233 20130101; B01D 39/2017 20130101; B01D
46/10 20130101; B01D 2239/0492 20130101; B01D 2275/10 20130101;
B01D 2239/10 20130101; B01D 2239/0622 20130101; B01D 39/18
20130101; B01D 46/023 20130101 |
International
Class: |
B01D 39/18 20060101
B01D039/18; B01D 39/20 20060101 B01D039/20; B01D 46/10 20060101
B01D046/10; B01D 46/52 20060101 B01D046/52; B01D 46/02 20060101
B01D046/02; A62B 23/02 20060101 A62B023/02; B01D 39/16 20060101
B01D039/16 |
Claims
1. A filter media, comprising: a fiber filtration layer and a
support layer that holds the fiber filtration layer in a waved
configuration and maintains separation of peaks and troughs of
adjacent waves of the fiber filtration layer, and wherein at least
a surface of the fiber filtration layer is hydrophilic, having a
water contact angle of less than or equal to 60 degrees.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 15/466,799, filed Mar. 22, 2017, which is a
continuation-in-part of U.S. patent application Ser. No. 14/858,398
(now U.S. Pat. No. 10,449,474), filed Sep. 18, 2015, which are
incorporated herein by reference in their entirety for all
purposes.
FIELD OF THE INVENTION
[0002] The present invention relates to filtration and, more
particularly, to filter media that include a waved filtration
layer.
BACKGROUND
[0003] Filter media can be used to remove contamination in a
variety of applications. In general, filter media include one or
more fiber webs. The fiber web provides a porous structure that
permits fluid (e.g., air) to flow through the web. Contaminant
particles contained within the fluid may be trapped on the fiber
web. Fiber web characteristics (e.g., pore size, fiber dimensions,
fiber composition, basis weight, amongst others) affect filtration
performance of the media. Although different types of filter media
are available, improvements are needed.
SUMMARY
[0004] In one aspect, a filter media is provided. In some
embodiments, the filter media comprises a fiber filtration layer
and a support layer that holds the fiber filtration layer in a
waved configuration and maintains separation of peaks and troughs
of adjacent waves of the fiber filtration layer, wherein at least a
surface of the fiber filtration layer is hydrophilic.
[0005] In some embodiments, the filter media comprises a fiber
filtration layer and a support layer that holds the fiber
filtration layer in a waved configuration and maintains separation
of peaks and troughs of adjacent waves of the fiber filtration
layer, wherein at least a surface of the fiber filtration layer is
hydrophilic and wherein the filter media has a decrease in air
permeability of less than or equal to 20% after humidity loading at
95%.
[0006] In some embodiments, the filter media comprises a fiber
filtration layer and a support layer that holds the fiber
filtration layer in a waved configuration and maintains separation
of peaks and troughs of adjacent waves of the fiber filtration
layer. The fiber filtration layer has a mean flow pore size of at
least about 11.5 microns. The filter media has a minimum DEHS
particle filtration efficiency of at least about 25%.
[0007] In some embodiments, the filter media comprises a fiber
filtration layer and a support layer that holds the fiber
filtration layer in a waved configuration and maintains separation
of peaks and troughs of adjacent waves of the fiber filtration
layer. The fiber filtration layer in the waved configuration is
formed from a fiber layer having a planar configuration and a
transition salt load of at least about 2.0 gsm. The filter media
has a minimum DEHS particle filtration efficiency of at least about
25%.
[0008] Other aspects and novel features of the present invention
will become apparent from the following detailed description of
various non-limiting embodiments of the invention when considered
in conjunction with the accompanying figures. In cases where the
present specification and a document incorporated by reference
include conflicting and/or inconsistent disclosure, the present
specification shall control. If two or more documents incorporated
by reference include conflicting and/or inconsistent disclosure
with respect to each other, then the document having the later
effective date shall control.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1A is a side view illustration of one embodiment of a
filter media;
[0010] FIG. 1B is a side view illustration of another embodiment of
a filter media;
[0011] FIG. 1C is a side view illustration of one layer of the
filter media of FIG. 1A;
[0012] FIG. 2A is a plot showing resistance pressure versus salt
loading for various fiber filtration layers;
[0013] FIG. 2B is a plot showing transition salt loading versus
mean flow pore size for various fiber filtration layers;
[0014] FIG. 2C is a plot showing cake pressure slope versus mean
flow pore size for various fiber filtration layers;
[0015] FIG. 3A is a plot the specific natural log of penetration
(i.e., the natural log of the penetration divided by the basis
weight) versus mean flow pore size for various fiber filtration
layers;
[0016] FIG. 3B is a plot showing basis weight versus mean flow pore
size for various fiber filtration layers;
[0017] FIG. 4 is a plot showing the percentage difference between
the maximum air permeability minus the minimum air permeability
value expressed as a percentage of the maximum value versus mean
flow pore size for various filter media in a humid environment;
and
[0018] FIG. 5 is a plot showing the percent decrease in air
permeability after humidity loading versus the type of hydrophilic
treatment for various filter media.
DETAILED DESCRIPTION
[0019] Filter media including a waved filtration layer are
described herein. The filtration layer may be held in a waved
configuration by a support layer. As described further below, the
filtration layer may have a combination of characteristics (e.g.,
mean flow pore size and/or basis weight and/or hydrophilic
surface(s), amongst others) that can lead to enhanced filtration
performance (e.g., efficiency), in particular, in high humidity
environments. The filter media may be used to form a variety of
filter elements for use in various applications.
[0020] Media
[0021] In general, various filter media are provided having at
least one filtration (e.g., fibrous) layer that is held in a waved
or curvilinear configuration by one or more additional support
layers (e.g., fibrous). As a result of the waved configuration, the
filter media has an increased surface area which can result in
improved filtration properties. The filter media can include
various layers, and only some or all of the layers can be
waved.
[0022] FIG. 1A illustrates one exemplary embodiment of a filter
media 10 having at least one filtration layer and at least one
support layer that holds the filtration layer in a waved
configuration to maintain separation of peaks and troughs of
adjacent waves of the filtration layer. In the illustrated
embodiment, the filter media 10 includes a fiber filtration layer
(e.g., a fine fiber filtration layer) 12, a first, downstream
support layer 14, and a second, upstream support layer 16 disposed
on opposite sides of the fiber filtration layer 12. The support
layers 14, 16 can help maintain the fiber filtration layer 12, and
optionally any additional filtration layers, in the waved
configuration. While two support layers 14, 16 are shown, the
filter media 10 need not include both support layers. Where only
one support layer is provided, the support layer can be disposed
upstream or downstream of the filtration layer(s).
[0023] The filter media 10 can also optionally include one or more
outer or cover layers located on the upstream-most and/or
downstream-most sides of the filter media 10. FIG. 1A illustrates a
top layer 18 disposed on the upstream side of the filter media 10
to function, for example, as an upstream dust holding layer. The
top layer 18 can also function as an aesthetic layer, which will be
discussed in more detail below. The layers in the illustrated
embodiment are arranged so that the top layer 18 is disposed on the
air entering side, labeled I, the second support layer 16 is just
downstream of the top layer 18, the fiber filtration layer 12 is
disposed just downstream of the second support layer 16, and the
first support layer 14 is disposed downstream of the first layer 12
on the air outflow side, labeled O. The direction of air flow,
i.e., from air entering I to air outflow O, is indicated by the
arrows marked with reference A.
[0024] The outer or cover layer can alternatively or additionally
be a bottom layer disposed on the downstream side of the filter
media 10 to function as a strengthening component that provides
structural integrity to the filter media 10 to help maintain the
waved configuration. The outer or cover layer(s) can also function
to offer abrasion resistance. FIG. 1B illustrates another
embodiment of a filter media 10B that is similar to filter media 10
of FIG. 1B. In this embodiment, the filter media 10B does not
include a top layer, but rather has a fiber filtration layer 12B, a
first support layer 14B disposed just downstream of the fiber
filtration layer 12B, a second support layer 16B disposed just
upstream of the fiber filtration layer 12B on the air entering side
I, and a bottom layer 18B disposed just downstream of the first
support layer 14B on the air exiting side O. Furthermore, as shown
in the exemplary embodiments of FIGS. 1A and 1B, the outer or cover
layer(s) can have a topography different from the topographies of
the fiber filtration layer and/or any support layers. For example,
in either a pleated or non-pleated configuration, the outer or
cover layer(s) may be non-waved (e.g., substantially planar),
whereas the fiber filtration layer and/or any support layers may
have a waved configuration. A person skilled in the art will
appreciate that a variety of other configurations are possible, and
that the filter media can include any number of layers in various
arrangements.
[0025] Fiber Filtration Layer
[0026] As indicated above, in an exemplary embodiment the filter
media 10 includes at least one fiber filtration layer 12, which may
optionally be hydrophobic or hydrophilic. In an exemplary
embodiment, a single filtration layer 12 formed from fine fibers is
used, however the filter media 10 can include any number of
additional filtration layers disposed between the downstream
support layer and the upstream support layer, adjacent to the fiber
filtration layer 12, or disposed elsewhere within the filter media.
While not shown, the additional filtration layer(s) can be
maintained in a waved configuration with the fiber filtration layer
12. In certain exemplary embodiment the filter media 10 can include
one or more additional filtration layers disposed upstream of the
fiber filtration layer 12. The additional filtration layer(s) can
be formed from fine fibers, or can be formed from fibers having an
average fiber diameter that is greater than an average fiber
diameter of the fibers that form the fiber filtration layer 12.
[0027] The fiber filtration layer may be designed to have a
particular mean flow pore size. Advantageously, fiber filtration
layers having a mean flow pore size of 11.5 microns or greater may,
in some embodiments, have increased NaCl loading, improved high
humidity performance, and/or smaller reduction in air permeability
after NaCl loading as compared to fiber filtration layers having
smaller mean flow pore sizes. However, a mean flow pore size of
11.5 microns or greater is not intended to be limiting and other
embodiments may include other ranges (e.g., between about 5 microns
and about 45 microns).
[0028] In some embodiments, the fiber filtration layer has a mean
flow pore size of at least about 5 microns, at least about 6
microns, at least about 8 microns, at least about 10 microns, at
least about 11 microns, at least about 11.5 microns, at least about
13 microns, at least about 15 microns, at least about 16 microns,
at least about 20 microns, at least about 25 microns, at least
about 30 microns, at least about 35 microns, or at least about 40
microns. In certain embodiments, the fiber filtration layer has a
mean flow pore size less than or equal to about 45 microns, less
than or equal to about 40 microns, less than or equal to about 35
microns, less than or equal to about 30 microns, less than or equal
to about 25 microns, less than or equal to about 20 microns, less
than or equal to about 16 microns, less than or equal to about 15
microns, less than or equal to about 13 microns, less than or equal
to 11.5 microns, less than or equal to 11 microns, less than or
equal to 10 microns, less than or equal to 8 microns, or less than
or equal to 6 microns. Combinations of the above referenced ranges
are also possible (e.g., between about 5 microns and about 45
microns, between about 11.5 microns and about 45 microns, between
about 11.5 microns and about 25 microns, between about 11.5 microns
and about 16 microns). Other ranges are also possible including, in
some embodiments, less than 11.5 microns (e.g., between about 5
microns and about 11 microns).
[0029] As used herein, the mean flow pore size refers to the mean
flow pore size measured by a capillary flow porometer (e.g., Model
CFP-34RTF 8A-X-6 manufactured by Porous Materials, Inc.) in
accordance with the ASTM F316-03 standard using a
1,1,2,3,3,3-hexafluoropropene low surface tension fluid. The mean
flow pore size of a fiber filtration layer may be designed by
selecting an average fiber diameter, basis weight, and/or thickness
of the layer as known to those of ordinary skill in the art. In
some cases, mean flow pore size may be designed by adjusting
processing parameters such as air flow rate and/or temperature
during manufacturing (e.g., using meltblowing techniques) of the
fiber filtration layer. In some embodiments, a combination of
filtration layers may have a mean flow pore size in one or more of
the above-referenced ranges. Additionally, in embodiments in which
more than one filtration layers are present in a media, each
filtration layer may have a mean flow pore size having one or more
of the above-referenced ranges.
[0030] The basis weight of the fiber filtration layer can be
designed by adjusting processing parameters such as the number of
fibers included in the filtration layer. In some embodiments, the
basis weight of the fiber filtration layer may be greater than or
equal to about 3 g/m.sup.2, greater than or equal to about 5
g/m.sup.2, greater than or equal to about 8 g/m.sup.2, greater than
or equal to about 10 g/m.sup.2, greater than or equal to about 12
g/m.sup.2, greater than or equal to about 14 g/m.sup.2, greater
than or equal to about 15 g/m.sup.2, greater than or equal to about
16 g/m.sup.2, greater than or equal to about 18 g/m.sup.2, greater
than or equal to about 20 g/m.sup.2, greater than or equal to about
25 g/m.sup.2, greater than or equal to about 30 g/m.sup.2, greater
than or equal to about 35 g/m.sup.2, greater than or equal to about
40 g/m.sup.2, or greater than or equal to about 45 g/m.sup.2. In
some cases, the basis weight of the fiber filtration layer may be
less than or equal to about 50 g/m.sup.2 (e.g., less than or equal
to about 50 g/m.sup.2, less than or equal to about 45 g/m.sup.2,
less than or equal to 40 g/m.sup.2, less than or equal to about 35
g/m.sup.2, less than or equal to about 30 g/m.sup.2, less than or
equal to about 25 g/m.sup.2, less than or equal to about 20
g/m.sup.2, less than or equal to about 18 g/m.sup.2, less than or
equal to about 16 g/m.sup.2, less than or equal to about 15
g/m.sup.2, less than or equal to about 14 g/m.sup.2, less than or
equal to about 12 g/m.sup.2, less than or equal to 10 g/m.sup.2,
less than or equal to 8 g/m.sup.2, or less than or equal to 5
g/m.sup.2. Combinations of the above-referenced ranges are also
possible (e.g., a basis weight greater than or equal to about 3
g/m.sup.2 and less than or equal to about 50 g/m.sup.2, of greater
than or equal to about 10 g/m.sup.2 and less than or equal to about
40 g/m.sup.2, or greater than or equal to about 14 and less than or
equal to about 20 g/m.sup.2). Other ranges are also possible. In
some embodiments, a combination of filtration layers may have a
combined basis weight in one or more of the above-referenced
ranges. As determined herein, the basis weight of the filtration
layer is measured according to the Edana WSP 130.1 Standard.
Additionally, in embodiments in which more than one filtration
layers are present in a media, each filtration layer may have a
basis weight having one or more of the above-referenced ranges.
[0031] In some embodiments, the basis weight and/or mean flow pore
size may be tuned such that the fiber filtration layer has a
desired minimum DEHS (diethyl-hexyl-sebacate) particle filtration
efficiency. In some cases, the basis weight of the fiber filtration
layer and/or the mean flow pore size of the fiber filtration layer
may be increased or decreased, such that the fiber filtration layer
has a particular minimum DEHS particle filtration efficiency (e.g.,
a minimum DEHS particle filtration efficiency of at least about
25%). For example, in some embodiments, the basis weight may be
adjusted (e.g., increased) for a fiber filtration layer having a
mean flow pore size of at least about 11.5 microns such that the
fiber filtration layer has a minimum DEHS particle filtration
efficiency of at least about 25%. In some embodiments and as
described further in Example 1, the relationship between the basis
weight, mean flow pore size, and efficiency of the fiber filtration
layer may be expressed as:
BW > - MP a ln ( 1 - E ) b ##EQU00001##
[0032] wherein BW is the basis weight (in grams per square meter)
of the fiber filtration layer, MP is the mean pore size (in
microns) of the fiber filtration layer, a and b are coefficients,
and E is the minimum DEHS particle filtration efficiency (expressed
as a fraction) of the fiber filtration layer. In some embodiments,
a is 2 and b is 6.5. In some embodiments, a is a number greater
than or equal to 2 and less than or equal to 2.3, and b is a number
greater than or equal to 6.5 and less than or equal to about 8. For
example, in some other embodiments, a is 2, 2.1, 2.25, or 2.28 and
b is 6.5, 7, 7.5, or 8. In some cases, the parameters may be
selected (e.g., basis weight) to obtain a particular minimum DEHS
particle filtration efficiency (e.g., a minimum DEHS particle
filtration efficiency of at least about 0.25 (i.e., 25%) or at
least about 0.35 (i.e., 35%)) for a given mean flow pore size. For
example, in some cases, the fiber filtration layer has a particular
minimum DEHS particle filtration efficiency (e.g., at least about
25% or at least about 35%) and a particular mean flow pore size
(e.g., at least about 11.5 microns), and the basis weight may be
designed to be at least about 8.76 g/m.sup.2, when a is 2 and b is
6.5. Without wishing to be bound by theory, the equation above
demonstrates a relationship between basis weight, mean flow pore
size, and efficiency of a fiber filtration layer which can be used
to design fiber filtration layer(s) that provide desirable
performance under humid conditions, including a smaller decrease in
air permeability in humid environments as compared to certain
traditional fiber filtration layers. Air permeability in humid
environments is described in more detail below.
[0033] The fiber filtration layers and/or filter media described
herein (e.g., having a mean flow pore size of at least about 11.5
microns) may have a wide range of minimum DEHS particle filtration
efficiencies. In some embodiments, the minimum DEHS particle
filtration efficiency of the fiber filtration layer and/or filter
media is between about 25% and about 75%, between about 30% and
75%, or between about 35% and about 55%. In some embodiments, the
fiber filtration layer and/or filter media has a minimum DEHS
particle filtration efficiency of greater than or equal to about
25%, greater than or equal to about 30%, greater than or equal to
about 35%, greater than or equal to about 45%, greater than or
equal to about 55%, or greater than or equal to about 65%. Other
minimum DEHS particle filtration efficiencies are also possible. In
some embodiments, the fiber filtration layer and/or filter media
has a minimum DEHS particle filtration efficiency of less than or
equal to 75%, less than or equal to 65%, less than or equal to 55%,
or less than or equal to 45%. In some embodiments, a combination of
fiber filtration layers may have a minimum DEHS particle filtration
efficiency in one or more of the above-referenced ranges. In some
embodiments, the minimum DEHS particle efficiency of the filter
media may be greater than that of the fiber filtration layer,
because additional layers added to the media (e.g., an outer or
cover layer) may help to trap particles, thereby increasing the
minimum DEHS particle of the overall filter media.
[0034] In some embodiments, the fiber filtration layers and/or
filter media described herein (e.g., having a mean flow pore size
of at least about 11.5 microns) may have a wide range of average
DEHS particle filtration efficiencies. In some embodiments, the
average DEHS efficiency of the fiber filtration layer and/or filter
media is greater than or equal to about 25%, greater than or equal
to about 30%, greater than or equal to about 35%, greater than or
equal to about 40%, greater than or equal to about 45%, greater
than or equal to about 50%, greater than or equal to about 55%,
greater than or equal to about 60%, greater than or equal to about
65%, greater than or equal to about 70%, greater than or equal to
about 75%, or greater than or equal to about 80%. Other
efficiencies are also possible. In some embodiments, the fiber
filtration layer and/or filter media has an average DEHS efficiency
of less than or equal to 99.9%, less than or equal to 99.8%, less
than or equal to 99.7%, less than or equal to 99.5%, less than or
equal to 99%, less than or equal to 98%, less than or equal to 95%,
less than or equal to 90%, less than or equal to 85%, less than or
equal to 80%, less than or equal to 70%, less than or equal to 60%,
or less than or equal to 50%. In some embodiments, the average DEHS
particle efficiency of the filter media may be greater than that of
the fiber filtration layer, because additional layers added to the
media (e.g., an outer or cover layer) may help to trap particles,
thereby increasing the average DEHS particle efficiency of the
overall filter media.
[0035] The minimum and average DEHS particle filtration efficiency
of a filtration layer or a filter media, as referred to herein, are
tested following the EN779-2012 standard and using 0.4 micron or
larger. The testing uses an air flow of 0.944 m.sup.3/s. The
testing begins by initially measuring the pressure drop and DEHS
particle efficiency of a sample. The testing then involves
progressively loading the sample with standard test dust
(ANSI/ASHRAE 52.2) in 30 g increments and measuring the pressure
drop and DEHS particle efficiency after each loading increment
until a pressure drop of 450 Pa or greater is reached at which
point the testing is complete. The minimum DEHS particle filtration
efficiency, as used herein, refers to the lowest DEHS particle
efficiency obtained throughout the test. The average DEHS particle
filtration efficiency, as used herein, is determined as the average
of the DEHS particle efficiencies obtained throughout the test
(including the DEHS particle efficiency measured initially prior to
standard test dust loading and the DEHS particle efficiencies at
all loading levels including the particle DEHS efficiency at the
maximum test pressure of 450 Pa or greater).
[0036] As described herein, the fiber filtration layers (e.g.,
having a mean flow pore size greater than about 11.5 microns)
and/or filter media may advantageously have improved performance
(e.g., reduced air permeability decrease) in high humidity
environments as compared to certain traditional fiber filtration
layers (e.g., having mean flow pore sizes less than about 11.5
microns). Without wishing to be bound by theory, improved humidity
performance may be generally correlated with increased transition
salt loading of a fiber filtration layer. In some cases, transition
salt loading may be measured using a NaCl (sodium chloride)
challenge (or NaCl loading), which employs an automated filter
testing unit (e.g., 8130 CertiTest.TM. from TSI, Inc.) equipped
with a sodium chloride generator. The average particle size created
by the salt particle generator is about 0.3 micron mass mean
diameter. The instrument measures a pressure drop across the
filtration layer and/or filter media and the resultant penetration
value on an instantaneous basis. The testing unit can be run in a
continuous mode with one pressure drop/penetration reading
approximately every minute. The NaCl particles at a concentration
of 23 mg NaCl/m.sup.3 air are continuously loaded onto a 100
cm.sup.2 sample at a flow rate of 5.3 cm/s. The samples are
continuously loaded until 1% (or lower) penetration is achieved.
Penetration, often expressed as a percentage, is defined as
follows:
Pen=C/C.sub.0
where C is the particle concentration after passage through the
filter and C.sub.0 is the particle concentration before passage
through the filter.
[0037] In some embodiments, the fiber filtration layer and/or the
filter media has a transition salt load of at least about 2.0 gsm
(grams per square meter). Transition salt load may be determined by
performing NaCl loading as described above on a planar fiber
filtration layer or on the filter media as a whole, and plotting
the resistance pressure (in mm H.sub.2O) as a function of NaCl load
(gsm (i.e., grams per square meter)). Referring now to FIG. 2A, an
initial depth loading line is calculated by fitting a simple linear
regression line to the initial ten minute region (i.e., initial ten
consecutive data points) of the NaCl loading curve (i.e.,
resistance pressure versus NaCl load) which begins with the first
reading taken at one minute after the onset of testing. A cake
loading line (see FIG. 2A) is calculated by fitting a simple linear
regression line to ten consecutive data points of the NaCl loading
curve, wherein the first through tenth data points are selected
such that penetration of the fiber filtration layer and/or filter
media is less than 1% and the eleventh data point (not included in
the simple linear regression fit) is greater than or equal to 1%
penetration (e.g., drawn through 10 data points preceding and
including the one at which measured penetration drops below 1%).
The transition salt load described herein is defined as the value
of NaCl load (in grams) per unit area (in square meters) of the
fiber filtration layer at the intersection of the initial depth
loading line and the cake loading line.
[0038] In some embodiments, the transition salt load of a planar
fiber filtration media is at least about 2.0 gsm, at least about
2.5 gsm, at least about 3.0 gsm, at least about 3.5 gsm, at least
about 4.0 gsm, or at least about 5.0 gsm. In some embodiments, the
transition salt load is less than or equal to about 10.0 gsm, less
than or equal to about 5.0 gsm, less than or equal to about 4.0
gsm, less than or equal to about 3.5 gsm, less than or equal to
about 3.0 gsm, or less than or equal to about 2.5 gsm. Combinations
of the above referenced ranges are also possible (e.g., between
about 2.0 gsm and about 10.0 gsm). The fiber filtration layers and
filter media described herein generally have increased transition
salt loads as compared to traditional filtration layers and filter
media which, generally, corresponds to lower resistance pressures
for an equivalent amount of NaCl loading.
[0039] The slope of the cake loading line, described herein, may
have a particular value. In some embodiments, the slope of the cake
loading line of the fiber filtration layer may be less than or
equal to about 7.5 mm H.sub.2O/gsm salt load, less than or equal to
about 7 mm H.sub.2O/gsm salt load, less than or equal to about 6 mm
H.sub.2O/gsm salt load, less than or equal to about 5.5 mm
H.sub.2O/gsm salt load, less than or equal to about 5 mm
H.sub.2O/gsm salt load, less than or equal to about 4.5 mm
H.sub.2O/gsm salt load, less than or equal to about 4 mm
H.sub.2O/gsm salt load, or less than or equal to about 3.5 mm
H.sub.2O/gsm salt load. In some embodiments, the slope of the cake
loading line of the fiber filtration layer may be greater than or
equal to 0 mm H.sub.2O/gsm salt load, greater than or equal to
about 1 mm H.sub.2O/gsm salt load, greater than or equal to about 2
mm H.sub.2O/gsm salt load, greater than or equal to about 3 mm
H.sub.2O/gsm salt load, greater than or equal to about 4 mm
H.sub.2O/gsm salt load, greater than or equal to about 4.5 mm
H.sub.2O/gsm salt load, greater than or equal to about 5 mm
H.sub.2O/gsm salt load, greater than or equal to about 5.5 mm
H.sub.2O/gsm salt load, or greater than or equal to about 6 mm
H.sub.2O/gsm salt load, or greater than or equal to about 7 mm
H.sub.2O/gsm salt load. Combinations of the above referenced ranges
are also possible (e.g., between 0 mm H.sub.2O/gsm salt load and
about 7 mm H.sub.2O/gsm salt load, between 1 mm H.sub.2O/gsm salt
load and about 7 mm H.sub.2O/gsm salt load, between about 3 mm
H.sub.2O/gsm salt load and about 6 mm H.sub.2O/gsm salt load,
between about 5 mm H.sub.2O/gsm salt load and about 6 mm
H.sub.2O/gsm salt load). Other ranges are also possible.
[0040] Advantageously, in some embodiments, the fiber filtration
layers described herein (e.g., having a mean flow pore size greater
than about 11.5 microns) and/or filter media may have relatively
lower decrease in air permeability in humid environments as
compared to certain traditional fiber filtration layers (e.g.,
having a mean flow pore size less than about 11.5 microns) and/or
filter media. In some embodiments, the percent decrease in air
permeability after humidity loading is less than or equal to about
50%, less than or equal to about 45%, less than or equal to about
44%, less than or equal to about 42%, less than or equal to about
40%, less than or equal to about 35%, less than or equal to about
30%, or less than or equal to about 25%. In certain embodiments,
the percent decrease in air permeability after humidity loading is
at least about 25%, at least about 35%, at least about 40%, at
least about 42%, at least about 44%, or at least about 45%.
Combinations of the above-referenced ranges are also possible
(e.g., a decrease in air permeability after humidity loading of
between about 35% and 50%, between about 42% and about 45%, between
about 42% and about 50%). Other ranges are also possible.
[0041] Air permeability after humidity loading, as referred to
herein, is determined by performing a humidity challenge after
loading a 100 cm.sup.2 sample with NaCl aerosol (23 mg NaCL/m.sup.3
air) of approximately 0.3 micron particle for 30 minutes using an
automated filter testing unit (e.g., TSI 8130 CertiTest.TM. from
TSI, Inc.) equipped with a sodium chloride generator. Samples
(e.g., filter media in a waved configuration including a fiber
filtration layer and a support layer) are loaded at a face velocity
of 14.1 cm/sec for 30 minutes. Once loaded with NaCl, the samples
are placed into a sample holder connected to an Frazier air
permeability machine and enclosed in a chamber containing a steam
generator to generate humidity. A hygrometer probe is inserted into
the box to measure the temperature and humidity within the chamber.
At the beginning of the test the relative humidity in the chamber
is 50% and the test is conducted by taking initial air permeability
readings at pressure drop of 0.5'' water column, after which the
steam generator is turned on and air permeability and humidity
readings are taken every 30 seconds. Once humidity reaches 90% (or,
in some cases, 95%), the readings are continued for approximately
12 minutes, after which the steam generator is turned off. Readings
are continued until the relative humidity in the chamber returns to
its level at the beginning of the test (i.e., 50%), at which point
the air permeability has stabilized. The percent decrease in air
permeability after humidity loading is the difference between the
maximum air permeability value (which is the air permeability value
measured when the relative humidity has returned to its level at
the beginning of the test, i.e., 50%) minus the minimum air
permeability value (at either 90% or 95%, as the case may be)
expressed as a percentage of the maximum air permeability
value.
[0042] In some cases, the fiber filtration layer may have a
particular solidity. Solidity, as used herein, generally refers the
basis weight of the fiber filtration layer divided by the average
density of the fibers times the uncompressed thickness of the fiber
filtration layer (i.e. BW/(.rho.*t)), where BW is the basis weight,
.rho. is the density, and t is the uncompressed thickness).
Uncompressed thickness, as used herein, refers to the thickness of
the fiber filtration layer as determined from a measurement of the
thickness of the fiber filtration layer with a micrometer under a
series of different loads) and extrapolating to determine the
thickness under zero loading. In some embodiments, the fiber
filtration layer has a solidity of at least about 1%, at least
about 2%, at least about 2.5%, at least about 5%, at least about
10%, at least about 13%, or at least about 15%. In certain
embodiments, the fiber filtration layer has a solidity of less than
or equal to about 20%, less than or equal to about 15%, less than
or equal to about 13%, less than or equal to about 10%, less than
or equal to about 5%, less than or equal to about 4%, less than or
equal to about 3.5%, less than or equal to 3%, less than or equal
to about 2.5%, or less than or equal to about 2%. Combinations of
the above-referenced ranges are also possible (e.g., between about
1% and about 20%, between about 2.5% and about 13%, between about
5% and about 20%). Other ranges are also possible.
[0043] In some embodiments, the fiber filtration layer may have a
particular surface area. In some cases, the surface area of the
fiber filtration layer may be between about 0.8 square meters per
gram and about 2.5 square meters per gram. For example, the surface
area may be between about 1.2 square meters per gram and about 1.6
square meters per gram. Surface area can be determined by any
suitable method known in the art including, for example, BET gas
adsorption.
[0044] The fiber filtration layer 12 can be formed from a variety
of fibers, but in an exemplary embodiment the fiber filtration
layer 12 is formed from fibers having an average fiber diameter
that is less than or equal to about 10 microns, less than or equal
to about 8 microns, less than about 5 microns, less than about 4
microns, less than about 3 microns, less than about 2 microns, less
than about 1.6 microns, less than about 1.2 microns, less than
about 1 micron, less than about 0.8 microns, less than about 0.5
microns, less than about 0.4 microns, or less than about 0.3
microns. In certain embodiments, the fiber filtration layer has an
average fiber diameter of at least 0.2 microns, at least 0.3
microns, at least 0.4 microns, at least about 0.5 microns, at least
about 0.8 microns, at least about 1 micron, at least about 1.2
microns, at least about 1.6 microns, at least about 2 microns, at
least about 3 microns, at least about 4 microns, at least about 5
microns, or at least about 8 microns. Combinations of the above
referenced ranges are also possible (e.g., between about 0.5
microns and about 10 microns, between about 1 micron and about 5
microns, between about 1.6 microns and about 3 microns, between
about 0.2 microns and about 10 microns). Other ranges are also
possible. The average diameter of a fiber can be determined, for
example, by scanning electron microscopy.
[0045] Various materials can also be used to form the fibers,
including synthetic and non-synthetic materials. In one exemplary
embodiment, the fiber filtration layer 12, and any additional
filtration layer(s), is formed from meltblown fibers. Certain
suitable meltblown processes have been described in commonly-owned
U.S. Pat. No. 8,608,817, which is incorporated herein by reference
in its entirety. In some embodiments, the fiber filtration layer
may be formed by wet laid techniques, air laid techniques,
electrospinning, spunbonding, centrifugal spinning or carding.
Exemplary materials include, by way of non-limiting example,
polyolefins, such as polypropylene and polyethylene; polyesters,
such as polybutylene terephthalate and polyethylene terephthalate;
polyamides, such as Nylon; polycarbonate; polyphenylene sulfide;
polystyrene; and polyurethane.
[0046] The fiber filtration layer may include a suitable percentage
of synthetic fibers. For example, in some embodiments, the weight
percentage of synthetic fibers in the filtration layer may be
between about 50 wt % and about 100 wt % of all fibers in the
filtration layer. In some embodiments, the weight percentage of
synthetic fibers in the filtration layer may be greater than or
equal to about 50 wt %, greater than or equal to about 60 wt %,
greater than or equal to about 70 wt %, greater than or equal to
about 80 wt %, greater than or equal to about 90 wt %, or greater
than or equal to about 95 wt %. In some embodiments, the weight
percentage of the synthetic fibers in the filtration layer may be
less than or equal to about 100 wt %, less than or equal to about
95 wt %, less than or equal to about 90 wt %, less than or equal to
about 80 wt %, less than or equal to about 70 wt %, or less than or
equal to about 50 wt %. Combinations of the above-referenced ranges
are also possible (e.g., a weight percentage of greater than or
equal to about 90 wt % and less than or equal to about 100 wt %).
Other ranges are also possible. In some embodiments, a filtration
layer includes 100 wt % of synthetic fibers. In some embodiments, a
filtration layer includes the above-noted ranges of synthetic
fibers with respect to the total weight of the filtration layer
(e.g., including any resins). In some embodiments, a combination of
filtration layers may have a percentage of synthetic fibers in one
or more of the above-referenced ranges. Additionally, in
embodiments in which more than one filtration layers are present in
a media, each filtration layer may have a percentage of synthetic
fibers having one or more of the above-referenced ranges. In
another embodiment, the above-referenced ranges of fibers may apply
to the entire filter media (which may include multiple filtration
layers). The remaining fibers of the filtration layer and/or filter
media may be non-synthetic fibers, such as glass fibers, glass wool
fibers, and/or cellulose pulp fibers (e.g., wood pulp fibers).
[0047] In some embodiments, the fiber filtration layer 12 may
include glass fibers (e.g., microglass fibers, chopped strand glass
fibers, or a combination thereof). The type and size of glass fiber
can also vary, but in an exemplary embodiment, the fiber is a
microglass fiber, such as A-type or E-type glass fibers made using
a rotary or flame attenuation process and having an average fiber
diameter in the range of about 0.2 .mu.m to 5 .mu.m. Microglass
fibers and chopped strand glass fibers are known to those of
ordinary skill in the art. One of ordinary skill in the art is able
to determine whether a glass fiber is microglass or chopped strand
by observation (e.g., optical microscopy, electron microscopy).
Microglass fibers may also have chemical differences from chopped
strand glass fibers. In some cases, though not required, chopped
strand glass fibers may contain a greater content of calcium or
sodium than microglass fibers. For example, chopped strand glass
fibers may be close to alkali free with high calcium oxide and
alumina content. Microglass fibers may contain 10-15% alkali (e.g.,
sodium, magnesium oxides) and have relatively lower melting and
processing temperatures. The terms refer to the technique(s) used
to manufacture the glass fibers. Such techniques impart the glass
fibers with certain characteristics. In general, chopped strand
glass fibers are drawn from bushing tips and cut into fibers in a
process similar to textile production. Chopped strand glass fibers
are produced in a more controlled manner than microglass fibers,
and as a result, chopped strand glass fibers will generally have
less variation in fiber diameter and length than microglass fibers.
Microglass fibers are drawn from bushing tips and further subjected
to flame blowing or rotary spinning processes. In some cases, fine
microglass fibers may be made using a remelting process. In this
respect, microglass fibers may be fine or coarse. As used herein,
fine microglass fibers are less than or equal to 1 micron in
diameter and coarse microglass fibers are greater than or equal to
1 micron in diameter.
[0048] The microglass fibers may have small diameters. For
instance, in some embodiments, the average diameter of the
microglass fibers may be less than or equal to about 10 microns,
less than or equal to about 9 microns, less than or equal to about
7 microns, less than or equal to about 5 microns, less than or
equal to about 3 microns, or less than or equal to about 1 micron.
In some instances, the microglass fibers may have an average fiber
diameter of greater than or equal to about 0.1 microns, greater
than or equal to about 0.3 microns, greater than or equal to about
1 micron, greater than or equal to about 3 microns, or greater than
or equal to about 7 microns. Combinations of the above-referenced
ranges are also possible (e.g., greater than or equal to about 0.1
microns and less than or equal to about 10 microns, greater than or
equal to about 0.1 microns and less than or equal to about 5
microns, greater than or equal to about 0.3 microns and less than
or equal to about 3 microns). Other values of average fiber
diameter are also possible. Average diameter distributions for
microglass fibers are generally log-normal. However, it can be
appreciated that microglass fibers may be provided in any other
appropriate average diameter distribution (e.g., Gaussian
distribution).
[0049] In some embodiments, the average length of microglass fibers
may be less than or equal to about 10 mm, less than or equal to
about 10 mm, less than or equal to about 8 mm, less than or equal
to about 6 mm, less than or equal to about 5 mm, less than or equal
to about 4 mm, less than or equal to about 3 mm, or less than or
equal to about 2 mm. In certain embodiments, the average length of
microglass fibers may be greater than or equal to about 1 mm,
greater than or equal to about 2 mm, greater than or equal to about
4 mm, greater than or equal to about 5 mm, greater than equal to
about 6 mm, or greater than or equal to about 8 mm. Combinations of
the above referenced ranges are also possible (e.g., microglass
fibers having an average length of greater than or equal to about 4
mm and less than about 6 mm). Other ranges are also possible.
[0050] In general, chopped strand glass fibers may have an average
fiber diameter that is greater than the diameter of the microglass
fibers. For instance, in some embodiments, the average diameter of
the chopped strand glass fibers may be greater than or equal to
about 5 microns, greater than or equal to about 7 microns, greater
than or equal to about 9 microns, greater than or equal to about 11
microns, or greater than or equal to about 20 microns. In some
instances, the chopped strand glass fibers may have an average
fiber diameter of less than or equal to about 30 microns, less than
or equal to about 25 microns, less than or equal to about 15
microns, less than or equal to about 12 microns, or less than or
equal to about 10 microns. Combinations of the above-referenced
ranges are also possible (e.g., greater than or equal to about 5
microns and less than or equal to about 12 microns). Other values
of average fiber diameter are also possible. Chopped strand
diameters tend to follow a normal distribution. Though, it can be
appreciated that chopped strand glass fibers may be provided in any
appropriate average diameter distribution (e.g., Gaussian
distribution).
[0051] In some embodiments, chopped strand glass fibers may have a
length in the range of between about 3 mm and about 25 mm (e.g.,
about 6 mm, or about 12 mm). In some embodiments, the average
length of chopped strand glass fibers may be less than or equal to
about 25 mm, less than or equal to about 20 mm, less than or equal
to about 15 mm, less than or equal to about 12 mm, less than or
equal to about 10 mm, less than or equal to about 7 mm, or less
than or equal to about 5 mm. In certain embodiments, the average
length of chopped strand glass fibers may be greater than or equal
to about 3 mm, greater than or equal to about 5 mm, greater than or
equal to about 10 mm, greater than or equal to about 12 mm, greater
than equal to about 15 mm, or greater than or equal to about 20 mm.
Combinations of the above referenced ranges are also possible
(e.g., chopped strand glass fibers having an average length of
greater than or equal to about 3 mm and less than about 25 mm).
Other ranges are also possible.
[0052] It should be appreciated that the above-noted dimensions are
not limiting and that the microglass and/or chopped strand fibers,
as well as the other fibers described herein, may also have other
dimensions.
[0053] In some embodiments, the average diameter of the glass
fibers (e.g., regardless of whether the glass fibers are
microglass, chopped strand, or another type) in the fiber
filtration layer may be greater than or equal to about 1.5 microns,
greater than or equal to about 2 microns, greater than or equal to
about 2.5 microns, greater than or equal to about 3 microns,
greater than or equal to about 4.5 microns, greater than or equal
to about 5 microns, greater than or equal to about 6 microns,
greater than or equal to about 7 microns, or greater than or equal
to about 9 microns. In some instances, the average diameter of the
glass fibers in the fiber filtration layer may have an average
fiber diameter of less than or equal to about 10 microns, less than
or equal to about 9 microns, less than or equal to about 7 microns,
less than or equal to about 6 microns, less than or equal to about
5 microns, less than or equal to about 4.5 microns, less than or
equal to about 3 microns, less than or equal to about 2.5 microns,
or less than or equal to about 2 microns. Combinations of the
above-referenced ranges are also possible (e.g., greater than or
equal to about 1.5 microns and less than or equal to about 10
microns, greater than or equal to about 2 microns and less than or
equal to about 9 microns, greater than or equal to about 2 microns
and less than or equal to about 5 microns, greater than or equal to
about 2.5 microns and less than or equal to about 4.5 microns).
[0054] In some embodiments, the average length of the glass fibers
in the fiber filtration layer (e.g., regardless of whether the
glass fibers are microglass, chopped strand, or another type) may
be less than or equal to about 25 mm, less than or equal to about
20 mm, less than or equal to about 15 mm, less than or equal to
about 12 mm, less than or equal to about 10 mm, less than or equal
to about 8 mm, less than or equal to about 5 mm, less than or equal
to about 3 mm, or less than or equal to about 1 mm. In certain
embodiments, the average length of the glass fibers in the fiber
filtration layer may be greater than or equal to about 0.05 mm,
greater than or equal to about 0.1 mm, greater than or equal to
about 0.3 mm, greater than or equal to about 0.5 mm, greater than
equal to about 1 mm, greater than or equal to about 5 mm, greater
than equal to about 10 mm, greater than or equal to about 15 mm,
greater than equal to about 20 mm, greater than or equal to about
30 mm, or greater than or equal to about 40 mm. Combinations of the
above referenced ranges are also possible (e.g., greater than or
equal to about 1 mm and less than about 25 mm, greater than or
equal to about 0.3 mm and less than about 20 mm, greater than or
equal to about 0.1 mm and less than about 12 mm, greater than or
equal to about 0.2 mm and less than about 6 mm, greater than or
equal to about 0.5 mm and less than about 3 mm). Other ranges are
also possible.
[0055] The resulting fiber filtration layer 12, as well as any
additional filtration layer(s), can also have a variety of
thicknesses, air permeabilities, basis weights, and filtration
efficiencies depending upon the requirements of a desired
application.
[0056] In one exemplary embodiment, the fiber filtration layer 12,
as measured in a planar configuration, has a thickness in the range
of about 6 mils to 22 mils; for example, between about 10 mils and
about 18 mils, or between about 12 mils to 16 mils. Thickness, as
referred to herein, is determined according to the Edana WSP 120.1
Standard on a planar layer under approximately 1 ounce load per
square foot. Additionally, in embodiments in which more than one
filtration layers are present in a media, each filtration layer may
have a thickness having one or more of the above-referenced
ranges.
[0057] The fiber filtration layer may have an air permeability in
the range of about 30 CFM to 150 CFM. For example, the air
permeability may be at least about 30 CFM, at least about 50 CFM,
at least about 65 CFM, at least about 75 CFM, at least about 100
CFM, or at least about 125 CFM. In some embodiments, the air
permeability of the fiber filtration layer may be less than or
equal to about 150 CFM, less than or equal to about 125 CFM, less
than or equal to about 100 CFM, less than or equal to about 75 CFM,
less than or equal to about 65 CFM, or less than or equal about 50
CFM. Combinations of the above-referenced ranges are also possible
(e.g., between about 30 CFM to 150 CFM, between about 65 CFM to 100
CFM). Other ranges are also possible. As determined herein, the air
permeability is measured according to ASTM D737-04 (2012). The air
permeability of a filtration layer or filter media is an inverse
function of flow resistance and can be measured with a Frazier
Permeability Tester. The Frazier Permeability Tester measures the
volume of air per unit of time that passes through a unit area of
sample at a fixed differential pressure across the sample.
Permeability can be expressed in cubic feet per minute per square
foot at a 0.5 inch water differential.
[0058] Support Layers
[0059] As also indicated above, the filter media 10 can include at
least one support layer. In an exemplary embodiment, the filter
media 10 includes a downstream support layer 14 disposed on the air
outflow side O of the fiber filtration layer 12 and that is
effective to hold the fiber filtration layer 12 in the waved
configuration. The filter media 10 can also include an upstream
support layer 16 that is disposed on the air entering side I of the
fiber filtration layer 12 opposite to the downstream support layer
14. The upstream support layer 16 can likewise help maintain the
fiber filtration layer 12 in a waved configuration. As indicated
above, a person skilled in the art will appreciate that the filter
media 10 can include any number of layers, and it need not include
two support layers, or a top layer. In certain exemplary
embodiments, the filter media 10 can be formed from a fiber
filtration layer 12 and a single, adjacent support layer 14 or 16.
In other embodiments, the filter media can include any number of
additional layers arranged in various configurations. The
particular number and type of layers will depend on the intended
use of the filter media.
[0060] The support layers 14, 16 can be formed from a variety of
fibers types and sizes. In an exemplary embodiment, the downstream
support layer 14 is formed from fibers having an average fiber
diameter that is greater than or equal to an average fiber diameter
of the fiber filtration layer 12, the upstream support layer 16,
and the top layer 18, if provided. In some cases, the upstream
support layer 16 is formed from fibers having an average fiber
diameter that is less than or equal to an average fiber diameter of
the downstream support layer 14, but that is greater than an
average fiber diameter of the fiber filtration layer 12 and the top
layer 18. In certain exemplary embodiments, the downstream support
layer 14 and/or the upstream support layer 16 can be formed from
fibers having an average fiber diameter in the range of about 10
.mu.m to 32 .mu.m, or 12 .mu.m to 32 .mu.m. For example, the
average fiber diameter of the downstream support layer and/or the
upstream support layer may be in the range of about 18 .mu.m to 22
.mu.m. In some cases, the downstream and/or the upstream support
layer may comprise relatively finer fibers than traditional support
layers. For example, in some embodiments, the finer downstream
and/or finer upstream support layer can be formed from fibers
having an average fiber diameter in the range of about 9 .mu.m to
18 .mu.m. For example, the finer downstream and/or finer upstream
support layer average fiber diameter may be in the range of about
12 .mu.m to 15 .mu.m.
[0061] The fibers of the support layer (e.g., the downstream
support layer, the upstream support layer) may have an average
fiber length of, for example, between about 1.0 inches and about
3.0 inches (e.g., between about 1.5 inches and about 2 inches). In
some embodiments, the fibers of the support layer may have an
average fiber length of less than or equal to about 3 inches, less
than or equal to about 2.5 inches, less than or equal to about 2
inches, less than or equal to about 1.5 inch, or less than or equal
to about 1.1 inches. In some embodiments, the fibers of the support
layer may have an average fiber length of greater than or equal to
about 1 inch, greater than or equal to about 1.5 inches, greater
than or equal to about 2.0 inches, or greater than or equal to
about 2.5. Combinations of the above referenced ranges are also
possible (e.g., fibers having an average fiber length of greater
than or equal to about 1.5 inches and less than about 2 inches).
Other ranges are also possible.
[0062] Various materials can also be used to form the fibers of the
support layers 14, 16, including synthetic and non-synthetic
materials. In one exemplary embodiment, the support layers 14, 16
are formed from staple fibers, and in particular from a combination
of binder fibers and non-binder fibers. One suitable fiber
composition is a blend of at least about 20% binder fiber and a
balance of non-binder fiber. A variety of types of binder and
non-binder fibers can be used to form the media of the present
invention. The binder fibers can be formed from any material that
is effective to facilitate thermal bonding between the layers, and
will thus have an activation temperature that is lower than the
melting temperature of the non-binder fibers. The binder fibers can
be monocomponent fibers or any one of a number of bicomponent
binder fibers. In one embodiment, the binder fibers can be
bicomponent fibers, and each component can have a different melting
temperature. For example, the binder fibers can include a core and
a sheath where the activation temperature of the sheath is lower
than the melting temperature of the core. This allows the sheath to
melt prior to the core, such that the sheath binds to other fibers
in the layer, while the core maintains its structural integrity.
This may be particularly advantageous in that it creates a more
cohesive layer for trapping filtrate. The core/sheath binder fibers
can be concentric or non-concentric, and exemplary core/sheath
binder fibers can include the following: a polyester
core/copolyester sheath, a polyester core/polyethylene sheath, a
polyester core/polypropylene sheath, a polypropylene
core/polyethylene sheath, a polyamide core/polyethylene sheath, and
combinations thereof. Other exemplary bicomponent binder fibers can
include split fiber fibers, side-by-side fibers, and/or "island in
the sea" fibers.
[0063] The non-binder fibers can be synthetic and/or non-synthetic,
and in an exemplary embodiment the non-binder fibers can be about
100 percent synthetic. In general, synthetic fibers are preferred
over non-synthetic fibers for resistance to moisture, heat,
long-term aging, and microbiological degradation. Exemplary
synthetic non-binder fibers can include polyesters, acrylics,
polyolefins, nylons, rayons, and combinations thereof.
Alternatively, the non-binder fibers used to form the media can
include non-synthetic fibers such as glass fibers, glass wool
fibers, cellulose pulp fibers, such as wood pulp fibers, and
combinations thereof.
[0064] The support layer may include a suitable percentage of
synthetic fibers. For example, in some embodiments, the weight
percentage of synthetic fibers in the support layer may be between
about 80 wt % and about 100 wt % of all fibers in the support
layer. In some embodiments, the weight percentage of synthetic
fibers in the support layer may be greater than or equal to about
80 wt %, greater than or equal to about 90 wt %, or greater than or
equal to about 95 wt %. In some embodiments, the weight percentage
of the synthetic fibers in the support layer may be less than or
equal to about 100 wt %, less than or equal to about 95 wt %, less
than or equal to about 90 wt %, or less than or equal to about 85
wt %. Combinations of the above-referenced ranges are also possible
(e.g., a weight percentage of greater than or equal to about 80 wt
% and less than or equal to about 100 wt %). Other ranges are also
possible. In some embodiments, a support layer includes 100 wt % of
synthetic fibers. In some embodiments, a support layer includes the
above-noted ranges of synthetic fibers with respect to the total
weight of the support layer (e.g., including any resins).
Additionally, in embodiments in which more than one filtration
layers are present in a media, each filtration layer and/or support
layer may have a percentage of synthetic fibers having one or more
of the above-referenced ranges. In other embodiments, the
above-referenced ranges of fibers may apply to the entire filter
media (which may include multiple filtration layers). The remaining
fibers of the filtration layer and/or filter media may be
non-synthetic fibers, such as glass fibers, glass wool fibers,
and/or cellulose pulp fibers (e.g., wood pulp fibers).
[0065] The support layers 14, 16 can also be formed using various
techniques known in the art, including meltblowing, wet laid
techniques, air laid techniques, carding, electrospinning, and
spunbonding. In an exemplary embodiment, however, the support
layers 14, 16 are carded or airlaid webs. The resulting layers 14,
16 can also have a variety of thicknesses, air permeabilities, and
basis weights depending upon the requirements of a desired
application. In one exemplary embodiment, the downstream support
layer 14 and the upstream support layer 16, as measured in a planar
configuration, each have a thickness in the range of about 8 mil to
30 mil (e.g., between about 12 mil to 20 mil), a basis weight in
the range of about 10 gsm to 99 gsm (e.g., between about 22 gsm and
about 99 gsm, between about 33 gsm and 70 gsm), and a mean flow
pore size in the range of about 30 microns to 150 microns (e.g.,
between about 50 microns and about 120 microns).
[0066] For example, In some embodiments, the support layer(s) each
have a thickness of at least about 8 mil, at least about 10 mil, at
least about 12 mil, at least about 15 mil, at least about 20 mil,
or at least about 25 mil. In certain embodiments, the support
layer(s) may have a thickness of less than or equal to about 30
mil, less than or equal to about 25 mil, less than or equal to
about 20 mil, less than or equal to about 15 mil, less than or
equal to about 12 mil, or less than or equal to about 10 mil.
Combinations of the above-referenced ranges are also possible
(e.g., between about 8 mil and about 30 mil, between about 12 mil
and about 20 mil). Other ranges are also possible. Thickness of the
support layer(s) is determined as described herein according to the
Edana WSP 120.1 Standard on a planar layer under approximately 1
ounce load per square foot.
[0067] In certain embodiments, the support layer(s) each have a
basis weight of at least about 10 gsm, at least about 20 gsm, at
least about 22 gsm, at least about 33 gsm, at least about 50 gsm,
at least about 60 gsm, at least about 70 gsm, at least about 80
gsm, or at least about 90 gsm. In some embodiments, the support
layer(s) each have a basis weight of less than or equal to about 99
gsm, less than or equal to about 90 gsm, less than or equal to
about 80 gsm, less than or equal to about 70 gsm, less than or
equal to about 60 gsm, less than or equal to about 50 gsm, less
than or equal to about 33 gsm, less than or equal to about 22 gsm,
or less than or equal to about 22 gsm. Combinations of the
above-referenced ranges are also possible (e.g., between about 10
gsm and about 99 gsm, between about 33 gsm and about 70 gsm). Other
ranges are also possible. As described herein, the basis weight of
the support layer(s) is measured according to the Edana WSP 130.1
Standard.
[0068] In some embodiments, the support layer(s) have a mean flow
pore size of at least about 30 microns, at least about 40 microns,
at least about 50 microns, at least about 75 microns, at least
about 100 microns, or at least about 120 microns. In certain
embodiments, the support layer(s) have a mean flow pore size of
less than or equal to about 150 microns, less than or equal to
about 120 microns, less than or equal to about 100 microns, less
than or equal to about 75 microns, less than or equal to about 50
microns, or less than or equal to about 40 microns. Combinations of
the above-referenced ranges are also possible (e.g., between about
30 microns to 150 microns, between about 50 microns and about 120
microns). Other ranges are also possible. Mean flow pore size may
be determined by a capillary flow porometer, as described
above.
[0069] Outer or Cover Layer
[0070] As previously indicated, the filter media 10 can also
optionally include one or more outer or cover layers disposed on
the air entering side I and/or the air outflow side O. FIG. 1A
illustrates a top layer 18 disposed on the air entering side I of
the filter media 10. The top layer 18 can function as a dust
loading layer and/or it can function as an aesthetic layer. In an
exemplary embodiment, the top layer 18 is a planar layer that is
mated to the filter media 10 after the fiber filtration layer 12
and the support layers 14, 16 are waved. The top layer 18 thus
provides a top surface that is aesthetically pleasing. The top
layer 18 can be formed from a variety of fiber types and sizes, but
in an exemplary embodiment the top layer 18 is formed from fibers
having an average fiber diameter that is less than an average fiber
diameter of the upstream support layer 16 disposed immediately
downstream of the top layer 18, but that is greater than an average
fiber diameter of the fiber filtration layer 12. In certain
exemplary embodiments, the top layer 18 is formed from fibers
having an average fiber diameter in the range of about 5 .mu.m to
20 .mu.m. As a result, the top layer 18 can function as a dust
holding layer without affecting the alpha value of the filter media
10, as will be discussed in more detail below.
[0071] As shown in FIG. 1B, the filter media 10B can alternatively
or in addition include a bottom layer 18B disposed on the air
outflow side O of the filter media 10B. The bottom layer 18B can
function as strengthening component that provides structural
integrity to the filter media 10B to help maintain the waved
configuration. The bottom layer 18B can also function to offer
abrasion resistance. This may be particularly desirable in ASHRAE
bag applications where the outermost layer is subject to abrasion
during use. The bottom layer 18B can have a configuration similar
to the top layer 18, as discussed above. In an exemplary
embodiment, however, the bottom layer 18B is the coarsest layer,
i.e., it is formed from fibers having an average fiber diameter
that is greater than an average fiber diameter of fibers forming
all of the other layers of the filter media. One exemplary bottom
layer is a spunbond layer, however various other layers can be used
having various configurations.
[0072] Various materials can also be used to form the fibers of the
outer or cover layer, including synthetic and non-synthetic
materials. In one exemplary embodiment, the outer or cover layer,
e.g., top layer 18 and/or bottom layer 18B, is formed from staple
fibers, and in particular from a combination of binder fibers and
non-binder fibers. One suitable fiber composition is a blend of at
least about 20% binder fiber and a balance of non-binder fiber. A
variety of types of binder and non-binder fibers can be used to
form the media of the present invention, including those previously
discussed above with respect to the support layers 14, 16.
[0073] The outer or cover layer, e.g., top layer 18 and/or any
bottom layer, can also be formed using various techniques known in
the art, including meltblowing, wet laid techniques, air laid
techniques, carding, electrospinning, and spunbonding. In an
exemplary embodiment, however, the top layer 18 is an airlaid layer
and the bottom layer 18B is a spunbond layer. The resulting layer
can also have a variety of thicknesses, air permeabilities, and
basis weights depending upon the requirements of a desired
application. In one exemplary embodiment, the outer or cover layer,
as measured in a planar configuration, has a thickness in the range
of about 2 mil to 50 mil, an air permeability in the range of about
100 CFM to 1200 CFM, and a basis weight in the range of about 10
gsm to 50 gsm.
[0074] A person skilled in the art will appreciate that, while FIG.
1A illustrates a four layer filter media, the media can include any
number of layers in various configurations. Various layers can be
added to enhance filtration, to provide support, to alter
structure, or for various other purposes. By way of non-limiting
example, the filter media can include various spunbond, wetlaid
cellulose, drylaid synthetic nonwoven, wetlaid synthetic, and
wetlaid microglass layers.
[0075] Method of Manufacturing
[0076] Some or all of the layers can be formed into a waved
configuration using various manufacturing techniques, but in an
exemplary embodiment the filtration layer 12 (e.g., fine fiber),
any additional filtration layers, and at least one of the support
layers 14, 16, are positioned adjacent to one another in a desired
arrangement from air entering side to air outflow side, and the
combined layers are conveyed between first and second moving
surfaces that are traveling at different speeds, such as with the
second surface traveling at a speed that is slower than the speed
of the first surface. A suction force, such as a vacuum force, can
be used to pull the layers toward the first moving surface, and
then toward the second moving surface as the layers travel from the
first to the second moving surfaces. The speed difference causes
the layers to form z-direction waves as they pass onto the second
moving surface, thus forming peaks and troughs in the layers. The
speed of each surface can be altered to obtain the desired number
of waves per inch. The distance between the surfaces can also be
altered to determine the amplitude of the peaks and troughs, and in
an exemplary embodiment the distance is adjusted between 0.025'' to
4''. For example, the amplitude of the peaks and waves may be
between about 0.1'' to 4.0'', e.g., between about 0.1'' to 1.0'',
between about 0.1'' to 2.0'', or between about 3.0'' to 4.0''. For
certain applications, the amplitude of the peaks and waves may be
between about 0.1'' and 1.0'', between about 0.1'' and 0.5'', or
between about 0.1'' and 0.3''. The properties of the different
layers can also be altered to obtain a desired filter media
configuration. In an exemplary embodiment the filter media has
about 2 to 6 waves per inch, with a height (overall thickness) in
the range of about 0.025'' to 2'', however this can vary
significantly depending on the intended application. For instance,
in other embodiments, the filter media may have about 2 to 4 waves
per inch, e.g., about 3 waves per inch. The overall thickness of
the media may be between about 0.025'' to 4.0'', e.g., between
about 0.1'' to 1.0'', between about 0.1'' to 2.0'' or between about
3.0'' to 4.0''. For certain applications, the overall thickness of
the media may be between about 0.1'' and 0.5'', or between about
0.1'' and 0.3''. As shown in FIG. 1A, a single wave W extends from
the middle of one peak to the middle of an adjacent peak. Thickness
of the (waved) filter media can be determined as described above
according to the Edana WSP 120.1 Standard under approximately 1
ounce load per 1 square inch pressure foot.
[0077] In the embodiment shown in FIG. 1A, when the fiber
filtration layer 12 and the support layers 14, 16 are waved, the
resulting fiber filtration layer 12 will have a plurality of peaks
P and troughs T on each surface (i.e., air entering side I and air
outflow side O) thereof, as shown in FIG. 1C. The support layers
14, 16 will extend across the peaks P and into the troughs T so
that the support layers 14, 16 also have waved configurations. A
person skilled in the art will appreciate that a peak P on the air
entering side I of the fiber filtration layer 12 will have a
corresponding trough T on the air outflow side O. Thus, the
downstream support layer 14 will extend into a trough T, and
exactly opposite that same trough T is a peak P, across which the
upstream support layer 16 will extend. Since the downstream support
layer 14 extends into the troughs T on the air outflow side O of
the fiber filtration layer 12, the downstream coarse layer 14 will
maintain adjacent peaks P on the air outflow side O at a distance
apart from one another and will maintain adjacent troughs T on the
air outflow side O at a distance apart from one another. The
upstream support layer 16, if provided, can likewise maintain
adjacent peaks P on the air entering side I of the fiber filtration
layer 12 at a distance apart from one another and can maintain
adjacent troughs T on the air entry side I of the fiber filtration
layer 12 at a distance apart from one another. As a result, the
fiber filtration layer 12 has a surface area that is significantly
increased, as compared to a surface area of the fiber filtration
layer in the planar configuration. In certain exemplary
embodiments, the surface area in the waved configuration is
increased by at least about 50%, and in some instances as much as
120%, as compared to the surface area of the same layer in a planar
configuration.
[0078] In embodiments in which the upstream and/or downstream
support layers hold the fiber filtration layer in a waved
configuration, it may be desirable to reduce the amount of free
volume (e.g., volume that is unoccupied by any fibers) in the
troughs. That is, a relatively high percentage of the volume in the
troughs may be occupied by the support layer(s) to give the fiber
layer structural support. For example, at least 95% or
substantially all of the available volume in the troughs may be
filled with the support layer and the support layer may have a
solidity ranging between about 1% to 90%, between about 1% to 50%,
between about 10% to 50%, or between about 20% to 50%.
Additionally, as shown in the exemplary embodiments of FIG. 1A, the
extension of the support layer(s) across the peaks and into the
troughs may be such that the surface area of the support layer in
contact with a top layer 18A is similar across the peaks as it is
across the troughs. Similarly, the surface area of the support
layer in contact with a bottom layer 18B (FIG. 1B) may be similar
across the peaks as it is across the troughs. For example, the
surface area of the support layer in contact with a top or bottom
layer across a peak may differ from the surface area of the support
layer in contact with the top or bottom layer across a trough by
less than about 70%, less than about 50%, less than about 30%, less
than about 20%, less than about 10%, or less than about 5%.
[0079] In certain exemplary embodiments, the downstream and/or
upstream support layers 14, 16 can have a fiber density that is
greater at the peaks than it is in the troughs; and, in some
embodiments, a fiber mass that is less at the peaks than it is in
the troughs. This can result from the coarseness of the downstream
and/or upstream support layers 14, 16 relative to the fiber
filtration layer 12. In particular, as the layers are passed from
the first moving surface to the second moving surface, the
relatively fine nature of the fiber filtration layer 12 will allow
the downstream and/or upstream support layers 14, 16 to conform
around the waves formed in the fiber filtration layer 12. As the
support layers 14, 16 extend across a peak P, the distance traveled
will be less than the distance that each layer 14, 16 travels to
fill a trough. As a result, the support layers 14, 16 will compact
at the peaks, thus having an increased fiber density at the peaks
as compared to the troughs, through which the layers will travel to
form a loop-shaped configuration.
[0080] Once the layers are formed into a waved configuration, the
waved shape can be maintained by activating the binder fibers to
effect bonding of the fibers. A variety of techniques can be used
to activate the binder fibers. For example, if bicomponent binder
fibers having a core and sheath are used, the binder fibers can be
activated upon the application of heat. If monocomponent binder
fibers are used, the binder fibers can be activated upon the
application of heat, steam and/or some other form of warm moisture.
A top layer 18 (FIG. 1A) and/or bottom layer 18B (FIG. 1B) can also
be positioned on top of the upstream support layer 16 (FIG. 1A) or
on the bottom of the downstream support layer 14B (FIG. 1B),
respectively, and mated, such as by bonding, to the upstream
support layer 16 or downstream support layer 14B simultaneously or
subsequently. A person skilled in the art will also appreciate that
the layers can optionally be mated to one another using various
techniques other than using binder fibers. The layers can also be
individually bonded layers, and/or they can be mated, including
bonded, to one another prior to being waved.
[0081] A saturant can also optionally be applied to the material
prior to drying the material. A variety of saturants can be used
with the media of the present invention to facilitate the forming
of the layers at a temperature that is less than the melting
temperature of the fibers. Exemplary saturants can include phenolic
resins, melamine resins, urea resins, epoxy resins, polyacrylate
esters, polystyrene/acrylates, polyvinyl chlorides,
polyethylene/vinyl chlorides, polyvinyl acetates, polyvinyl
alcohols, and combinations and copolymers thereof that are present
in an aqueous or organic solvent.
[0082] In some embodiments, the resulting media can also have a
gradient in at least one, and optionally all, of the following
properties: binder and non-binder fibers composition, fiber
diameter, solidity, basis weight, and saturant content. For
example, in one embodiment, the media can have a lightweight,
lofty, coarse-fibered, lightly bonded and lightly saturated sheet
upstream, and a heavier, denser, fine-fibered, heavily bonded and
heavily saturated sheet downstream. This allows the coarser
particles to be trapped in the upstream layer, preventing early
saturation of the bottom layer. In other embodiments, the
upstream-most layer can be lighter and/or loftier than the
downstream-most layer. That is, the upstream layer can have a
solidity (e.g., the solid volume fraction of fibers in the layer)
and a basis weight that is less than that of the downstream layer.
Additionally, in embodiments where the filter media includes a
saturant, the media can have a gradient with respect to the amount
of saturant in the upstream-most and downstream-most layers. One
skilled in the art will appreciate the variety of properties that
the layers of the media can have.
[0083] An electrostatic charge can also optionally be imparted to
the filter media, or to various layers of the media, to form an
electret fiber layer. For example, a charge may be imparted to a
fiber filtration layer prior to joining with one or more support
layers. In another embodiment, a charge is imparted to a filter
media including more than one layer, e.g., a fiber filtration layer
and one or more support layers. Depending on the materials used to
form each of the layers, the amount of charge, and the method of
charging, the charge may either remain in one or more of the layers
or dissipate after a short period of time (e.g., within hours). A
variety of techniques are well known to impart a permanent dipole
to the polymer web in order to form electret filter media. Charging
can be effected through the use of AC and/or DC corona discharge
units and combinations thereof. The particular characteristics of
the discharge are determined by the shape of the electrodes, the
polarity, the size of the gap, and the gas or gas mixture. Charging
can also be accomplished using other techniques, including
friction-based charging techniques.
[0084] In some embodiments, the fiber filtration layer may be made
hydrophobic or hydrophilic. As described further below, in some
cases, the hydrophilicity of a filtration layer may alter the
magnitude of the decrease in air permeability of an NaCl loaded
media as compared to unloaded media, in humid environments. In
certain embodiments, an NaCl loaded media comprising a hydrophilic
fiber filtration layer may have a relatively low decrease in air
permeability after exposure to humid environments.
[0085] Air permeability after humidity loading, as referred to
herein, is determined by performing a humidity challenge after
loading a 100 cm.sup.2 sample with NaCl aerosol (23 mg NaCL/m.sup.3
air) of approximately 0.3 micron particle for 30 minutes using an
automated filter testing unit (e.g., TSI 8130 CertiTest.TM. from
TSI, Inc.) equipped with a sodium chloride generator. Samples
(e.g., filter media in a waved configuration including a fiber
filtration layer and a support layer) are loaded at a face velocity
of 14.1 cm/sec for 30 minutes. Once loaded with NaCl, the samples
are placed into a sample holder connected to an Frazier air
permeability machine and enclosed in a chamber containing a steam
generator to generate humidity. A hygrometer probe is inserted into
the box to measure the temperature and humidity within the chamber.
At the beginning of the test the relative humidity in the chamber
is 50% and the test is conducted by taking initial air permeability
readings at pressure drop of 0.5'' water column, after which the
steam generator is turned on and air permeability and humidity
readings are taken every 30 seconds. Once humidity reaches 90% (or,
in some cases, 95%), the readings are continued for approximately
12 minutes, after which the steam generator is turned off. Readings
are continued until the relative humidity in the chamber returns to
its level at the beginning of the test (i.e., 50%), at which point
the air permeability has stabilized. The percent decrease in air
permeability after humidity loading is the difference between the
maximum air permeability value (which is the air permeability value
measured when the relative humidity has returned to its level at
the beginning of the test, i.e., 50%) minus the minimum air
permeability value (at either 90% or 95%, as the case may be)
expressed as a percentage of the maximum air permeability
value.
[0086] In some embodiments, the fiber filtration layer is
hydrophilic and the decrease in air permeability after humidity
loading may be less than or equal to 20%, less than or equal to
19%, less than or equal to 18%, less than or equal to 17%, less
than or equal to 16%, less than or equal to 15%, less than or equal
to 14%, less than or equal to 13%, less than or equal to 12%, less
than or equal to 11%, less than or equal to 10%, less than or equal
to 9%, less than or equal to 8%, less than or equal to 7%, or less
than or equal to 6%. In certain embodiments, the decrease in air
permeability after humidity loading is greater than or equal to 5%,
greater than or equal to 6%, greater than or equal to 7%, greater
than or equal to 8%, greater than or equal to 9%, greater than or
equal to 10%, greater than or equal to 11%, greater than or equal
to 12%, greater than or equal to 13%, greater than or equal to 14%,
greater than or equal to 15%, greater than or equal to 16%, greater
than or equal to 17%, greater than or equal to 18%, or greater than
or equal to 19%. Combinations of the above-referenced ranges are
also possible (e.g., less than or equal to 20% and greater than or
equal to 5%, less than or equal to 15% and greater than or equal to
10%). Other ranges are also possible.
[0087] In some cases, the fiber filtration layer may be
hydrophobic. In certain embodiments, the fiber filtration layer may
be hydrophilic. Those skilled in the art would be capable of
selecting suitable methods for making the fiber filtration layer
hydrophobic or hydrophilic including, but not limited to, the
addition of a hydrophobic or a hydrophilic coating, inclusion of
additives (e.g., during extrusion of the fibers), and/or selecting
of hydrophobic or hydrophilic fiber materials. In some cases, the
fibers of the support layer may also be selectively made
hydrophobic or hydrophilic. For example, such support layers could
be carded or airlaid webs with topical finishes applied to the
fibers before processing, and/or the fibers could be selected based
on their hydrophobic or hydrophilic properties.
[0088] The decrease in air permeability after humidity loading of a
filter media comprising a hydrophilic fiber filtration layer may be
less than the decrease in air permeability after humidity loading
of a filter media comprising a hydrophobic fiber filtration
layer.
[0089] In some embodiments, a layer (e.g., a fiber filtration
layer, a support layer) of the filter media (and/or at least a
portion of the fibers of the layer) may be modified such that at
least a portion of a surface of the layer (and/or at least a
portion of the surface of the fibers of the layer) is hydrophilic.
In certain embodiments, one or both of the upstream and the
downstream surfaces of a layer (e.g., a fiber filtration layer, a
support layer) are modified. In other embodiments, the layer (e.g.,
fiber filtration layer, a support layer) is modified at a depth
beneath the surface, and in some cases, throughout the thickness of
the layer. In certain embodiments, a layer is modified using
chemical vapor deposition, topical application of a coating (e.g.,
via a spray method, a dip method, flexographic or reverse roll
application), incorporation of hydrophilic melt additives,
incorporation of hydrophilic fibers, or combinations thereof. Other
(surface) modification techniques may also be used. For instance,
the layer (e.g., fiber filtration layer, support layer) may
comprise a chemical vapor deposition coating.
[0090] In some embodiments, the filter media and/or one or more
layers of the filter media (e.g., a fiber filtration layer) to be
modified (e.g., such that at least a surface of the fiber
filtration layer is hydrophilic) may include one or more features,
materials, components, and/or methods described in co-owned U.S.
Pat. No. 7,883,562, entitled "Waved filter Media and Elements",
issued Feb. 8, 2011, which is incorporated herein by reference in
its entirety.
[0091] In some embodiments, the hydrophilic modification of a layer
may be conducted at any suitable time. For example, at least a
surface of a layer (e.g., fiber filtration layer, support layer)
may be modified to be hydrophilic after formation of the layer
and/or during formation of the layer (e.g., during a meltblown
process, an electrospinning process, etc., as described herein). In
certain embodiments, at least a surface of the layer may be
modified to be hydrophilic during and/or after formation of the
waved configuration of the layer.
[0092] In some embodiments, at least one surface of the layer
(e.g., fiber filtration layer, support layer) may be modified to
make the surface hydrophilic or increase the hydrophilicity of the
surface. For example, a hydrophilic surface having a water contact
angle of about 60.degree. may be modified to have a water contact
angle of about 15.degree.. In another example, a hydrophobic
surface having a water contact angle of about 100.degree. may be
modified to have a water contact angle of less than 90.degree.
(e.g., a water contact angle of less than 60.degree.).
[0093] As used herein, the term "hydrophilic" refers to material
that has a water contact angle of less than 90 degrees. A material
generally becomes more hydrophilic as the water contact angle
decreases. Accordingly, a "hydrophilic surface" may refer to a
surface that has a water contact angle of less than 90 degrees. In
some embodiments, the surface may be modified to be hydrophilic
such that the water contact angle is less than 90 degrees, less
than or equal to about 80 degrees, less than or equal to about 75
degrees, less than or equal to about 70 degrees, less than or equal
to about 65 degrees, less than or equal to about 60 degrees, less
than or equal to about 55 degrees, less than or equal to about 50
degrees, less than or equal to about 45 degrees, less than or equal
to about 40 degrees, less than or equal to about 35 degrees, less
than or equal to about 30 degrees, less than or equal to about 25
degrees, less than or equal to about 20 degrees, or less than or
equal to about 15 degrees. In some embodiments, the water contact
angle is greater than or equal to about 0 degrees, greater than or
equal to about 5 degrees, greater than or equal to about 10
degrees, greater than or equal to about 15 degrees, greater than or
equal to about 20 degrees, greater than or equal to about 25
degrees, greater than or equal to about 35 degrees, greater than or
equal to about 45 degrees, or greater than about 60 degrees.
Combinations of the above-referenced ranges are also possible
(e.g., greater than or equal to about 0 degrees and less than about
90 degrees, greater than or equal to about 0 degrees and less than
about 60 degrees). In an exemplary embodiment, the contact angle of
the surface (e.g., after modification) is less than or equal to 60
degrees. The water contact angle may be measured using ASTM
D5946-04. The water contact angle is the angle between the surface
(e.g., a surface of the fiber filtration layer) and the tangent
line drawn to the water droplet surface at the three-phase point,
when a liquid drop is resting on a plane solid surface. A contact
angle meter or goniometer can be used for this determination. In
some embodiments, the hydrophilicity of the surface may be such
that a water droplet placed on the surface completely wets the
surface (e.g., the water droplet is completely absorbed into the
material making the water contact angle 0).
[0094] In some embodiments, the decrease in water contact angle of
at least one surface of the layer upon modification as described
herein is greater than or equal to about 0 degree, greater than or
equal to 1 degree, greater than or equal to about 2 degrees,
greater than or equal to about 5 degrees, greater than or equal to
about 10 degrees, greater than or equal to about 15 degrees,
greater than or equal to about 20 degrees, greater than or equal to
about 25 degrees, greater than or equal to about 35 degrees,
greater than or equal to about 45 degrees, greater than or equal to
about 60 degrees, greater than or equal to about 75 degrees,
greater than or equal to about 80 degrees, or greater than or equal
to about 90 degrees as compared to the water contact angle of the
at least one surface prior to modification. In certain embodiments,
the decrease in water contact angle of at least one surface of the
layer upon modification is less than or equal to about 100 degrees,
less than or equal to about 90 degrees, less than or equal to about
80 degrees, less than or equal to about 75 degrees, less than or
equal to about 70 degrees, less than or equal to about 65 degrees,
less than about 60 degrees, less than or equal to about 55 degrees,
less than or equal to about 50 degrees, less than or equal to about
45 degrees, less than or equal to about 40 degrees, less than or
equal to about 35 degrees, less than or equal to about 30 degrees,
less than or equal to about 25 degrees, less than or equal to about
20 degrees, less than or equal to about 15 degrees, less than or
equal to about 10 degrees, less than or equal to about 5 degrees,
or less than or equal to about 2 degrees as compared to the water
contact angle of the at least one surface prior to modification.
Combinations of the above-referenced ranges are also possible
(e.g., greater than or equal to 0 degrees and less than or equal to
100 degrees). Other ranges are also possible.
[0095] In some embodiments, the fiber filtration layer may comprise
fibers that may be modified such that at least a surface of the
fiber filtration layer comprising said fibers is hydrophilic. In
some cases, the fibers may be hydrophilic. In some embodiments, the
fibers may be hydrophobic and may be modified to be hydrophilic.
Non-limiting examples of fibers that may be may be modified (e.g.,
to enhance or impart hydrophilicity) may comprise a polymer such as
polyolefins (e.g., polypropylene, polyethylene, polybutene,
copolymers of olefinic monomers such as ethylene or propylene),
polyesters (e.g., polybutylene terephthalate (PBT), polyethylene
terephthalate (PET), CoPET, polylactic acid (PLA)), polyamides
(e.g., nylons such as polyamid 6 (PA6), polyamid 11 (PA 11),
aramids), polycarbonates, and combinations thereof (e.g.,
polylactic acid/polystyrene, PEN/PET polyester, copolyamides). In
cases in which the fiber is hydrophilic (e.g., polylactic acid,
PA6), the fiber may be modified to enhance the hydrophilicity of
the fiber. In an exemplary embodiment, the fiber may have a water
contact angle of greater than 60 degrees (e.g., greater than 60
degrees and less than 90 degrees) and is modified such that the
water contact angle is less than or equal to 60 degrees (e.g.,
greater than or equal to 0 degree and less than or equal to 60
degrees).
[0096] In some embodiments, a gas may be used to modify the
hydrophilicity of at least one surface of the layer (e.g., the
filtration layer, the support layer). For example, after layer
formation, the layer may be exposed to a gaseous environment. In
some such cases, the molecules in the gas may react with material
(e.g., fibers, resin, additives) on the surface of the layer to
form functional groups, such as charged moieties, and/or to
increase the oxygen content on the surface of the layer.
Non-limiting examples of functional groups include hydroxyl,
carbonyl, ether, ketone, aldehyde, acid, amide, acetate, phosphate,
sulfite, sulfate, amine, nitrile, and nitro groups. Non-limiting
examples of gases that may be reacted with at least one surface of
the layer includes CO.sub.2, SO.sub.2, SO.sub.3, NH.sub.3,
N.sub.2H.sub.4, N.sub.2, O.sub.2, H.sub.2, He, Ar, NO, air and
combinations thereof.
[0097] In certain embodiments, a coating (e.g., a polymeric
coating) may be used to modify the hydrophilicity of at least a
surface of the layer (e.g., the fiber filtration layer, the support
layer). For example, after layer formation, the coating may be
applied to at least a surface of the layer. In certain embodiments,
the coating comprises an acrylate (e.g., acrylamide,
(Hydroxyethyl)methacrylate), carboxylic acid (e.g., acrylic acid,
citric acid), a sulfonate (e.g., 1,3-propane sultone,
N-hydroxysulfosuccinimide, methyl trifluoromethanesulfonate), a
polyol (e.g., glycerin, pentaerythritol, ethylene glycol, propylene
glycol, sucrose), an amine (e.g., allylamine, ethyleneimine,
oxazoline), a silicon-containing compound (e.g., tetraethyl
orthosilicate, hexamethyldisiloxane, silane), and combinations
thereof. In some embodiments, the coating may be applied
independently, as a mixture of two or more coatings, or
sequentially (e.g., coating a first coating with a second
coating).
[0098] In some embodiments, a wetting agent (e.g., a surfactant)
may be used to modify the hydrophilicity of at least one surface of
the layer. For example, after layer formation, the wetting agent
may be applied to at least a surface of the layer. Non-limiting
examples of suitable wetting agents include anionic surfactants
(e.g., sodium dioctylsulfosuccinate, disodium salts of alkyl
polyglucoside esters), nonionic surfactants (e.g., alkyl phenol
ethoxylates, alcohol ethoxylates, polyglycerol esters,
polyglucosides), cationic surfactants (e.g., quaternary ammonium
compounds of the general formula
R.sup.1R.sup.2R.sup.3R.sup.4N.sup.+X.sup.- where each of R.sup.1,
R.sup.2, R.sup.3, and R.sup.4 represent the same or different alkyl
groups and X.sup.- is a halide such as a chloride ion), amphoteric
surfactants (e.g., surfactants comprising cationic and anionic
groups such as N-alkyl betaines), and combinations thereof.
[0099] In some embodiments, the layer may be dipped in a material
(e.g., a coating, a surfactant). In certain embodiments, the
material may be sprayed on the layer. The weight percent of the
material (e.g., coating, surfactant, functional group) used to
modify at least one surface of the layer (e.g., the fiber
filtration layer, the support layer) may be greater than or equal
to about 0.0001 wt %, greater than or equal to about 0.0005 wt %,
greater than or equal to about 0.001 wt %, greater than or equal to
about 0.005 wt %, greater than or equal to about 0.01 wt %, greater
than or equal to about 0.05 wt %, greater than or equal to about
0.1 wt %, greater than or equal to about 0.5 wt %, greater than or
equal to about 1 wt %, greater than or equal to about 2 wt %, or
greater than or equal to about 4 wt % versus the total weight of
the layer. In some cases, the weight percentage of the material
used to modify at least one surface of the layer may be less than
or equal to about 5 wt %, less than or equal to about 3 wt %, less
than or equal to about 1 wt %, less than or equal to about 0.5 wt
%, less than or equal to about 0.1 wt %, less than or equal to
about 0.05 wt %, less than or equal to about 0.01 wt %, or less
than or equal to about 0.005 wt % versus the total weight of the
layer. Combinations of the above-referenced ranges are also
possible (e.g., a weight percentage of material of greater than or
equal to about 0.0001 wt % and less than about 5 wt %). Other
ranges are also possible. The weight percentage of material in the
layer is based on the dry solids of the layer and can be determined
by weighing the layer before and after the modification of the
surface as described herein.
[0100] In some cases, a melt additive may be incorporated into a
fiber and/or the layer to enhance the hydrophilicity of the layer.
For example, in certain embodiments, a melt additive may be used to
modify the hydrophilicity of at least a surface of the layer (e.g.,
the fiber filtration layer, the support layer). In some cases, the
melt additive (e.g., a hydrophilic melt additive) may be blended
with one or more fibers of the layer (e.g., during formation of the
fibers and/or formation of the layer). Non-limiting examples of
suitable (hydrophilic) melt additives include monoglycerides, mixed
glycerides, di-fatty acid esters of polyethylene oxide, ethoxylated
castor oil, blends of glycerol oleate esters and alkyl phenol
ethoxylates, and polyethylene glycol esters of fatty acids. Other
hydrophilic melt additives are also possible.
[0101] In some cases, the melt additive may comprise a preblended
masterbatch melt additive. Preblended masterbatch melt additives
are known in the art and one of ordinary skill would be capable of
incorporating preblended masterbactch melt additives into a fiber
filtration layer such that at least a surface of the fiber
filtration layer is hydrophilic, based upon the teachings of this
specification.
[0102] The weight percent of the melt additive (or preblended
masterbatch melt additive) used to modify at least one surface of
the layer may be greater than or equal to about 0.0001 wt %,
greater than or equal to about 0.0005 wt %, greater than or equal
to about 0.001 wt %, greater than or equal to about 0.005 wt %,
greater than or equal to about 0.01 wt %, greater than or equal to
about 0.05 wt %, greater than or equal to about 0.1 wt %, greater
than or equal to about 0.5 wt %, greater than or equal to about 1
wt %, greater than or equal to about 2 wt %, greater than or equal
to about 4 wt %, greater than or equal to about 6 wt %, or greater
than or equal to about 8 wt % versus the total weight of the layer.
In some cases, the weight percentage of the melt additive used to
modify at least one surface of the layer may be less than or equal
to about 10 wt %, less than or equal to about 8 wt %, less than or
equal to about 5 wt %, less than or equal to about 3 wt %, less
than or equal to about 1 wt %, less than or equal to about 0.5 wt
%, less than or equal to about 0.1 wt %, less than or equal to
about 0.05 wt %, less than or equal to about 0.01 wt %, or less
than or equal to about 0.005 wt % versus the total weight of the
layer. Combinations of the above-referenced ranges are also
possible (e.g., a weight percentage of material of greater than or
equal to about 0.0001 wt % and less than about 10 wt %, or greater
than or equal to about 0.0001 wt % and less than about 5 wt %).
Other ranges are also possible. The weight percentage of material
in the layer is based on the dry solids of the layer and can be
determined by thermogravimetric analysis.
[0103] The filter media can also be pleated after it is formed into
the waved configuration, and various exemplary configurations will
be discussed in more detail below. A person skilled in the art will
appreciate that virtually any pleating technique known in the art
can be used to pleat the waved filter media. Typically, a filter
media is pleated by forming a plurality of parallel score lines in
the media and forming folds at each score line.
[0104] Filter Media Properties
[0105] As indicated above, the properties of the resulting filter
media can vary depending on the intended use. In some embodiments,
the mean flow pore size of the fiber filtration layer is effective
to improve the performance (e.g., reduced air permeability
decrease) of a filter media in relatively high humidity
environments.
[0106] In some embodiments, the filter media described herein is
classified as a G1, G2, G3, G4, M5, M6, F7, F8, or F9 filter media.
The average efficiency and minimum efficiency ranges for 0.4 micron
or larger DEHS particles for these classifications are listed in
Table 1. As stated below, the testing is performed until a maximum
final pressure drop of 250 Pa or 450 Pa, according to the
EN779-2012 standard described above.
TABLE-US-00001 Final Average Average Minimum test arrestance
efficiency (E.sub.m) Efficiency.sup.a pressure (A.sub.m) of of 0.4
.mu.m of 0.4 .mu.m drop synthetic dust particles particles Group
Class Pa % % % Coarse G1 250 50 .ltoreq. A.sub.m < 65 -- -- G2
250 65 .ltoreq. A.sub.m < 80 -- -- G3 250 80 .ltoreq. A.sub.m
< 90 -- -- G4 250 90 .ltoreq. A.sub.m -- -- Medium M5 450 -- 40
.ltoreq. E.sub.m < 60 -- M6 450 -- 60 .ltoreq. E.sub.m < 80
-- Fine F7 450 -- 80 .ltoreq. E.sub.m < 90 35 F8 450 -- 90
.ltoreq. E.sub.m < 95 55 F9 450 -- 95 .ltoreq. E.sub.m 70
[0107] The resulting media can also have a variety of thicknesses,
air permeabilities, basis weights, and initial efficiencies
depending upon the requirements of a desired application.
Thickness, as referred to herein, is determined according to the
Edana WSP 120.1 Standard using an appropriate caliper gage. Basis
weight, as referred to herein, is determined according to the Edana
WSP 130.1 Standard.
[0108] For example, in one embodiment, the resulting media can have
a thickness t.sub.m, as shown in FIG. 1A, in the range of about
0.025'' to 4'', an amplitude of the peaks and waves of between
about 0.025'' to 4'' (e.g., between about 0.1'' to 1.0'', between
about 0.1'' to 2.0'', or between about 3.0'' to 4.0'' in some
applications, between about 0.1'' and 0.5'', or between about 0.1''
and 0.3'' in other applications), and an air permeability in the
range of about 30 CFM to 400 CFM (e.g., between about 50 CFM to 120
CFM, or between about 70 CFM to 90 CFM). The resulting media can
also have a basis weight in the range of about 125 gsm to 250 gsm
(e.g., about 150 to 250 gsm, or about 135 gm to 160 gsm), and/or a
NaCl loading of less than about 25 mm H.sub.2O after loading
approximately 60 mg/100 cm.sup.2 of about 0.3 .mu.m particles at
5.3 cm/s face velocity (e.g., less than about 20 mm H.sub.2O).
[0109] Filter Elements
[0110] As previously indicated, the filter media disclosed herein
can be incorporated into a variety of filter elements for use in
various applications, including both liquid and air filtration
applications. Exemplary uses include ASHRAE bag filters, pleatable
HVAC filters, gas turbine bag filters, liquid bag filter media,
dust bag house filters, residential furnace filters, paint spray
booth filters, face masks (e.g., surgical face masks and industrial
face masks), cabin air filters, commercial ASHRAE filters,
respirator filters, automotive air intake filters, automotive fuel
filters, automotive lube filters, room air cleaner filters and
vacuum cleaner exhaust filters. The filter elements can have
various configurations, and certain exemplary filter element
configurations are discussed in more detail below. Other exemplary
filter elements include, by way of non-limiting example, radial
filter elements that include cylindrical filter media disposed
therein, micron-rater vessel bag filters (also referred to as sock
filters) for liquid filtration, face masks, etc.
[0111] Panel Filter
[0112] In one exemplary embodiment, the filter media can be used in
a panel filter. In particular, the filter media can include a
housing disposed therearound. The housing can have various
configurations, and the particular configuration can vary based on
the intended application. The housing may be in the form of a frame
that is disposed around the perimeter of the filter media. The
frame may have a generally rectangular configuration such that it
surrounds all four sides of a generally rectangular filter media
10, however the particular shape can vary. The frame can be formed
from various materials, including cardboard, metal, polymers, etc.
In certain exemplary embodiments, the frame can have a thickness
that is about 12'' or less, or about 2'' or less. In another
embodiment, the frame can be formed from the edges of the filter
media. In particular, a perimeter of the filter media 10' can be
thermally sealed to form a frame therearound. The panel filter can
also include a variety of other features known in the art, such as
stabilizing features for stabilizing the filter media relative to
the frame, spacers, etc.
[0113] In use, the panel filter element can be used in a variety of
applications, including commercial and residential HVAC (e.g.,
furnace filters); automotive passenger cabin air; automotive air
intake; and paint spray booth filters. The particular properties of
the filter element can vary based on the intended use, but in
certain exemplary embodiments, the filter element has a MERV rating
in the range of 7 to 20, and may be, for example, greater than
about 13, greater than about 15, greater than about 17, or greater
than about 19. The filter element may have a pressure drop in the
range of about 0.1'' to 5'' H.sub.2O, e.g., between about 0.1'' to
1'' H.sub.2O.
[0114] Pleated Filter
[0115] The waved filter media can also be pleated and used in a
pleated filter. As previously discussed, the waved media, or
various layers thereof, can be pleated by forming score lines at a
predetermined distance apart from one another, and folding the
media. A person skilled in the art will appreciate, however, that
other pleating techniques can be used. Once the media is pleated,
the media can be incorporated into a housing. The media can have
any number of pleats depending on the size of the frame and the
intended use. In certain exemplary embodiment, the filter media has
1-2 pleats per inch, and a pleat height in the range of about
0.75'' to 2''. However, some applications utilize peaks having a
height up to 12''.
[0116] In order to facilitate pleating, the filter media can be
self-supporting, i.e., it can have a stiffness that allows
pleating. In certain exemplary embodiments, the minimum stiffness
of the filter media is about 200 mg with Gurley Stiffness tester to
enable pleating. Alternatively, or in addition, the filter media
can include various stiffening elements (e.g., stabilizing straps,
screen backing, and the like).
[0117] In use, the pleated waved filter element can be used in a
variety of applications, including pleatable HVAC filters,
residential furnace filters, cabin air filters, commercial ASHRAE
filters, automotive air intake filters, automotive fuel filters,
automotive lube filters, room air cleaner filters, and vacuum
cleaner exhaust filters. The particular properties of the filter
element can vary based on the intended use, but in certain
exemplary embodiments, the filter element has a MERV rating in the
range of 7 to 20. For example, the MERV rating may be greater than
about 13, greater than about 15, greater than about 17, or greater
than about 19. The filter element may have a pressure drop in the
range of about 0.1'' to 5'' H.sub.2O, e.g., between about 0.1'' to
1'' H.sub.2O. The filter media can also have a thickness before
pleating of about 0.5'' of less, and a thickness after pleating of
about 2'' or less. However, in certain application the thickness
after pleating can be up to 12''.
[0118] Bag/Pocket Filter
[0119] In yet another embodiment, the filter media can be
incorporated into a bag or pocket filter for use in heating, air
conditioning, ventilation, gas turbine filtration, and/or
refrigeration; and micron rated liquid filter bags. The bag or
pocket filter can be formed by placing two filter media together
(or folding a single filter media in half), and mating three sides
(or two if folded) to one another such that only one side remains
opens, thereby forming a pocket inside the filter. In some
embodiments, multiple filter pockets can be attached to a frame to
form a filter element. Each pocket can be positioned such that the
open end is located in the frame, thus allowing air to flow into
each pocket. The frame can include rectangular rings that extend
into and retain each pocket. A person skilled in the art will
appreciate that the frame can have virtually any configuration, and
various mating techniques known in the art can be used to couple
the pockets to the frame. Moreover, the frame can include any
number of pockets, but bag filters typically include between 6 and
10 pockets.
[0120] The particular properties of the filter element can vary
based on the intended use, but in certain exemplary embodiments,
the filter element has a MERV rating in the range of about 7 to 20
(e.g., 13 to 20). For example, the MERV rating may be greater than
about 13, greater than about 15, greater than about 17, or greater
than about 19. The filter element may have a pressure drop in the
range of about 0.1'' to 5'' H.sub.2O, e.g., between about 0.1'' to
1'' H.sub.2O. The filter media can also have a thickness that is
about 2'' or less, or about 0.5'' or less, however the thickness
can vary depending on the intended application.
[0121] By way of non-limiting example, a standard 8 pocket ASHRAE
bag filter typically has a 30'' deep pocket in a 24''.times.24''
frame, and yields 80 sq. ft. of media. An ASHRAE bag filter having
the same dimensions, but utilizing a waved filter media according
to the present invention, will yield 176 sq. ft. of media.
[0122] Facemask
[0123] In yet another embodiment, the filter media can be
incorporated into a personal protective filtration device, such as
a facemask, that is designed to remove contaminants from breathable
air. In one embodiment, the filter media is used to form an
industrial facemask designed for use in the workplace. The facemask
may include, for example, an outer structural support layer, a
filtration layer, and an inner structural support layer, although
any suitable combination of layers can be used. Each of the layers
may be charged or uncharged. Each of the layers may be hydrophobic
or hydrophilic. The structural support layers may be nonwoven
layers that are thermally moldable under suitable conditions, e.g.,
at a temperature of about 105-110.degree. C. for 6-8 seconds. The
filtration layers may be formed from meltblown or fiberglass
materials. In one set of embodiments, a facemask has a filter area
of approximately 170 cm.sup.2, which is standard in the United
States, or an area of approximately 150 cm.sup.2, which may be
standard in other areas of the world.
[0124] In another embodiment, the filter media is used in a
surgical facemask. A surgical facemask includes a personal
protective filtration device typically worn by medical personnel
for two primary reasons: to prevent the transfer of germs from
medical personnel to patient (and vice versa), and to protect
medical personnel from the strike of insulting bodily fluids. A
surgical facemask may include, for example, an outer structural
support layer, a filtration layer, and an inner structural support
layer, although any suitable combination of layers can be used.
Each of the layers may be charged or uncharged. In some
embodiments, the structural support layers are polypropylene
spunbond and the filtration layers are formed from meltblown or
fiberglass materials. The filter media may be folded for larger
coverage area, and may include a filter area of, for example,
200-1000 cm.sup.2.
[0125] The following non-limiting examples serve to further
illustrate the present invention:
Example 1
[0126] This example illustrates the importance of mean flow pore
size on filtration performance according to some embodiments
described herein.
[0127] Samples A-G are melt blown fiber filtration layer samples
(in a planar configuration without support layer(s)) designed to
have a minimum DEHS efficiency of at least 25%). A number of
properties of the samples were measured and the results are shown
in Table 2.
TABLE-US-00002 TABLE 2 Avg. Basis Mean flow pore size Sample Weight
(gsm) (microns) A 9.3 10.43 B 18.6 16.38 C 15.6 12.83 D 14.2 12.54
E 15.8 13.56 F 4.2 6.1 G 8.7 10.96
[0128] Transition salt load testing was conducted on the samples
following the protocol described above.
[0129] FIG. 2A shows a plot of the Resistance (mm H.sub.2O) vs.
NaCl loading (gsm) for Samples A and B obtained from the transition
salt load testing. The plot also shows the cake loading lines and
initial depth loading lines for Samples A and B. As described
above, the transition salt load is defined as the value of NaCl
load per unit area (gsm) at the intersection of the initial depth
loading line and the cake loading line. Sample A (with a mean flow
pore size of 10.43 microns) had a transition salt load of about
1.2, and Sample B (with a mean flow pore size of 16.38 microns) had
a transition salt load of about 3.6.
[0130] FIG. 2B shows a plot of the transition salt load for Samples
A-G as a function of mean flow pore size. As shown, the samples
having a mean flow pore size of greater than 11.5 microns had a
significantly higher transition salt load than the samples having a
mean flow pore size of less than 11.5 microns. Higher transition
salt loads are generally correlated with improved filtration
performance in high humidity conditions, as well as standard
conditions.
[0131] FIG. 2C shows a plot of the slope of the cake loading line
versus mean flow pore size for Samples A-G. As shown, the samples
having a mean flow pore size of greater than 11.5 microns had lower
slopes of the cake loading line than samples having a mean flow
pore size of less than 11.5 microns. The lower slopes can lead to
higher transition salt loads which generally are correlated with
improved high humidity filtration performance.
[0132] FIGS. 2B-2C demonstrate that fiber filtration layers having
a minimum DEHS efficiency of at least 25% and a mean flow pore size
of at least about 11.5 microns had significantly increased
transition salt loads as compared to fiber filtration layers at
this efficiency with less than 11.5 micron mean flow pore sizes.
Since high transition salt loads are generally correlated with
improved high humidity performance, the fiber filtration layers
having a mean flow pore size of at least about 11.5 microns are
expected to have improved filtration performance in high humidity
environments.
[0133] FIG. 3A is a plot of the specific natural log of penetration
(i.e., the natural log of the penetration divided by the basis
weight) versus mean flow pore size for Samples A-G. The regression
curve shown on the plot demonstrates a relationship between fiber
filtration layer mean flow pore size, fiber filtration layer basis
weight and penetration. Therefore, there is also a relationship
between fiber filtration layer mean flow pore size, fiber
filtration layer basis weight and efficiency. For example, the
following equation has been derived, in part from the latter
relationship, to identify suitable mean pore size and basis weight
values needed to obtain a target minimum DEHS efficiency.
BW > - MP 2 ( Ln ( 1 - E ) ) 6.5 ##EQU00002##
where BW is the basis weight of the fiber filtration layer, MP is
the mean flow pore size, and E is the minimum DEHS efficiency for
the fiber filtration layer that is being targeted.
[0134] FIG. 3B is a plot of the basis weight (gsm) versus mean flow
pore size for Samples A-G. The relationship above is used to define
the curve which is a boundary of the basis weight and mean flow
pore size values at which a minimum DEHS efficiency of 35% (to meet
F7 classification) is met. Fiber filtration layers having
combinations of basis weight and mean flow pore size that lie on or
above the boundary have a minimum DEHS efficiency of 35% or
greater. The fiber filtration layers having a mean flow pore size
of greater than 11.5 microns and lie on or above the boundary also
have improved high humidity performance, as noted above.
Example 2
[0135] This example demonstrates the correlation between
performance of a filter media and mean flow pore size under humid
conditions.
[0136] Filter media samples including a range of mean pore sizes
(from about 10 microns to 16.5 microns) were tested in a humid
environment. The filter media samples included a fiber filtration
layer between two support layers with the combined layers being in
a waved configuration. The testing followed the protocol described
above to measure the percent decrease in air permeability after
humidity loading.
[0137] As noted in the protocol described above, the percent
decrease in air permeability after humidity loading is the
difference between the maximum air permeability (as measured during
the testing) minus the minimum air permeability (as measured during
the testing at 90% humidity) expressed as a percentage of the
maximum air permeability value. FIG. 4 shows a plot of the
difference versus mean flow pore size. As shown on the plot, for
mean flow pore sizes greater than about 11.5 microns, the average
difference was about 44% or less. For mean flow pore sizes less
than 11.5 microns, the average difference was 46% or greater.
[0138] This data shows that filter media including mean flow pore
sizes of greater than 11.5 microns experience smaller differences
between maximum air permeability and minimum air permeability than
filter media including mean flow pore sizes of less than 11.5
microns.
Example 3
[0139] This example demonstrates the modification of a filter media
to enhance the hydrophilicity of at least a surface of a layer of
the filter media. Filter media samples were tested in a humid
environment. The filter media samples included a fiber filtration
layer between two support layers with the combined layers being in
a waved configuration. The testing followed the protocol described
above to measure the decrease in air permeability after humidity
loading (at 95% humidity).
[0140] Two samples were treated with a surfactant (e.g., one using
a topical dip and one using a topical spray) before loading and
humidity and the third sample left untreated, as indicated in FIG.
5. The percent decrease in air permeability after humidity loading
(at 95% humidity) is plotted in FIG. 5. The topical dip and topical
spray of waved samples with hydrophilic treatments comprising a
surfactant showed a lower decrease in pressure drop as compared to
untreated waved samples.
[0141] One skilled in the art will appreciate further features and
advantages of the invention based on the above-described
embodiments. Accordingly, the invention is not to be limited by
what has been particularly shown and described, except as indicated
by the appended claims. All publications and references cited
herein are expressly incorporated herein by reference in their
entirety.
* * * * *