Note: Descriptions are shown in the official language in which they were submitted.
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High Density Nonwoven Filter Media
BACKGROUND OF THE INVENTION
The present invention is related to a nonwoven web
produced from conjugate fibers. More specifically, the
invention is related to a filter medium of a conjugate fiber
nonwoven web.
Porous nonwoven sheet media, such as composites containing
meltblown or solution sprayed microfiber webs and conventional
spunbond nonwoven webs have been used in various filtration
applications, e.g., coolant filtration, cutting fluid
filtration, swimming pool filtration, transmission fluid
filtration, room air filtration and automotive air filtration.
In liquid filtration applications, especially for large volume
filtration applications, e.g., coolant and cutting fluid
filtration, contaminated liquid typically is pressure driven
onto a horizontally placed filter medium. Consequently, the
filter medium needs to be strong enough to withstand the
weight of the liquid and the applied driving pressure. As
such, liquid filter media need to provide high strength
properties in addition to suitable levels of filter
efficiency, capacity and durability.
Tn general, composite filter media are formed by
laminating a layer of a microfiber web onto a highly porous
supporting layer or between two highly porous supporting
layers since the microfiber layer does not have sufficient
physical strength to be self-supporting. Consequently, the
production process for composite filter media requires not
only different layer materials but also requires elaborate
layer-forming and laminating steps, making the filter media
costly. Although self-supporting single-layer microfiber
filter media can be produced in order to'avoid the complexity
of forming composite filter media by increasing the thickness
of the microfiber filter layer, the pressure drop across such
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thick microfiber filter media is unacceptably high, making the
microfiber media unfit for filter applications, especially for
high throughput filter applications. An additional
disadvantage of existing microfiber filter media and laminate
filter media containing microfiber webs is that they tend to
exhibit weak physical properties. Consequently, these filter
media are not particularly useful for large volume liquid
filtration uses.
Other sheet filter media widely used in the industry are
cellulosic fiber webs of thermomechanically or chemically
processed pulp fibers. Cellulosic fiber media are, for
example, commonly used in automotive oil and fuel filters and
vacuum cleaner filters. However, cellulosic fiber filter
media tend to have a limited filter efficiency and do not
provide the high strength properties that are required for
high pressure, large volume liquid filtration applications.
Yet another group of filter media that have been utilized
in liquid filtration applications are calendered spunbonded
nonwoven webs, especially polyester spunbond webs. For
example, calendered polyester spunbond filter media are
commercially available from Reemay, Inc. under the Reemay
trademark. Typically, spunbond filter media are formed by
melt-spinning a physical blend of structural filaments and
binder filaments, randomly and isotropically depositing the
filaments onto a forming surface to form a nonwoven web, and
then calendering the nonwoven web to activate the binder
filaments to effect adhesive bonds, forming a sheet filter
medium that has a relatively uniform thickness. These
calendered sheet filter media exhibit good strength
properties. However, the filter efficiency of these spunbond
filter media is, in general, significantly lower than that of
microfiber filter media. In addition, the porosity
distribution on the surface of the calendered spunbond filter
media tends to be non-uniform. This is because when the spun
filaments are randomly deposited on the forming surface, the
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filament density, i.e., the number of filament strands
deposited for a given area of surface, of the deposited web
varies from one section to another: and when the deposited
fiber web is calendered and compacted to a uniform thickness,
the sections of high fiber density and low fiber density form
low porosity and high porosity sections, respectively.
Consequently, the calendered spunbond filter media tend to
have a non-uniform porosity distribution.
There remains a need for economical filter media that
provide a highly desirable combination of high filtration
efficiency, capacity and high physical strength.
SUMMARY OF THE INVENTION
The invention provides a sheet filter medium having
autogenously bonded uncrimped conjugate fibers. The filter
medium has a density between about 0.07 g/cm3 and about 0.2
g/cm3 and a Frazier permeability of at least 3.5 m3/min/m2 (50
ft3/min/ft2), and the conjugate fibers have a polyolefin and
another thermoplastic polymer having a melting point higher
than the polyolefin. The medium has a Mullen Burst strength
of at least 3.5 kg/cm2, and the medium is particularly suited
for filtering liquid.
The invention also provides a three dimensionally
thermofonaed filter medium that has autogenously bonded
uncrimped conjugate fibers selected from spunbond fibers and
staple fibers containing a polyolefin and another
thermoplastic polymer, wherein the polyolefin and the
thermoplastic polymer have different differential scanning
calorimetry melting curves such that an exposure to a
temperature that melts about 50% of the lower melting
polyolefin component melts equal to or less than about 10% of
the other thermoplastic component. The thermoformed filter
medium has a density between about 0.07 g/cm3 and about 0.5
g/ cm3 .
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Conjugate fibers as used herein indicate fibers having
at least two different component polymer compositions which
occupy distinct cross sections along substantially the entire
length of the fibers. The term "fibers" as used herein
indicates both continuous filaments and discontinuous fibers,
e.g., staple fibers. The term "spunbond fibers" refers to
fibers formed by extruding molten thermoplastic polymers as
continuous filaments from a plurality of relatively fine,
usually circular, capillaries of a spinneret, and then rapidly
drawing the extruded filaments by an eductive or other well-
known drawing mechanism to impart molecular orientation and
physical strength to the filaments. The drawn continuous
filaments are deposited onto a foraminous forming surface in
a highly random manner to form a nonwoven web having
essentially a uniform density. A vacuum apparatus may be
placed underneath the forming surface around the region where
the fibers are deposited to facilitate an appropriate
placement and distribution of the fibers. Then the deposited
nonwoven web is bonded to impart physical integrity and
strength. The processes for producing spunbond fibers and
webs therefrom are disclosed, for example, in U.S. Patents
4,340,563 to Appel et al.; 3,692,618 to Dorschner et al. and
U.S. patent 3,802,817 to Matsuki et al. In accordance with
the present invention, the filter medium desirably contains
continuous conjugate filaments, e.g., spunbond conjugate
fibers, since continuous filaments provide improved strength
properties and do not tend to produce lint. The term
"uncrimped" as used herein indicates fibers that have not been
subjected to fiber crimping or texturizing processes and
desirably have less than 2 crimps per extended inch as
measured in accordance with ASTM D-3937-82. The term "uniform
fiber coverage" as used herein indicates a uniform or
substantially uniform fiber coverage that is achieved by
random and isotropic fiber or filament depositing processes.
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The nonwoven filter medium of the present invention is
highly suitable for various filter applications that require
high filter efficiency, . physical strength, abrasion
resistance, thermoformabililty and the like. Additionally,
the nonwoven filter medium is highly suitable for converting
it into a high pleat density filter medium.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is DSC melting curves for linear low density
polyethylene and polypropylene.
Figure 2 is DSC melting curves for linear low density
polyethylene and nylon 6.
Figure 3 illustrates a through-air bonder which is
suitable for the present invention.
Figure 4 illustrates a suitable pleating process.
Figure 5 is a graph of the filter efficiencies of various
filter media with respect to their densities.
Figure 6 is a graph of the filter lives of various filter
media with respect to their densities.
Figure 7 is a graph of the initial filter efficiencies of
various filter media with respect to their densities.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a nonwoven sheet filter
medium of uncrimped or substantially uncrimped conjugate
fibers. The filter medium is highly useful for liquid
filtration. The filter medium has a density between about
0.07 g/cm3 and about 0.2 g/cm3, desirably between about 0.08
g/cm3 and about 0.19 g/cm3, more desirably between about 0.1
g/cm3 and about 0.15 g/cm3, and a permeability of at least
about 15 m3/min/mZ (50 ft3/min/ft~) , desirably between about 15
m3/min/m2 and about 90 m3/min/mz, more desirably between about
18 m3/min/mZ and about 76 m3/min/mZ, most desirably between
about 30 m3/min/m2 and about 60 m3/min/m2, as measured in
accordance with Federal Test Method 5440, Standard No 191A.
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The conjugate fiber nonwoven filter medium is characterized
as having a desirable combination of useful filter attributes
including high density, high strength, smooth surface and
relatively uniform porosity distribution. The desirable
characteristics of the present filter medium are attributable
to the unique approach in producing the sheet nonwoven filter
medium. The filter medium of the present invention is
through-air bonded, and not calender bonded, and yet the
filter medium can be produced to have a low loft and high
density that are comparable to calendered nonwoven filter
media.
The conjugate fibers contain at least two component
polymers that have different melting points, a higher melting
polymer and a lower melting polymer, and the lower melting
polymer occupies at least about 25~, desirably at least 40%,
more desirably at least about 50%, of the total peripheral
surface area along the length of the fibers such that the
lower melting polymer can be heat activated to be rendered
adhesive and forms autogenous interfiber bonds, while the
higher melting polymer retains the structural integrity of the
fibers. The present filter medium containing the conjugate
fibers that form autogenous interfiber bonds exhibits high
strength properties, especially multidirectional strength.
Such multidirectional strength can be measured with the ASTM
D3786-87 test, Mullen Burst test. The filter medium has a
Mullen Burst strength of at least 3.5 kg/cm2, desirably at
least 4 kg/cm2, more desirably at least 4.5 kg/cm2.
Although the present conjugate fibers may contain more
than two component polymers, the present invention is
hereinafter illustrated with conjugate fibers having two
component polymers (bicomponent fibers). The component
polymers are selected from fiber-forming thermoplastic
polymers, and the polymers have a melting point difference of
at least about 5°C, desirably at least about 10°C. Since
thermoplastic polymers generally do not melt at a specific
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temperature, but instead melt over a span of temperature, the
melting temperature difference between the lower melting
polymer component and the higher melting component polymer can
be better defined by the melting curve measurements in a
conventional differential scanning calorimetry (DSC). Even
. if two polymers may have significantly different melting
points, which is generally defined as the peak of the DSC
melting curve, the polymers may melt simultaneously over a
range of temperatures due to overlap of the melting curve
l0 temperature ranges. In accordance with the present invention,
the component polymers are selected so that at the temperature
where 50% of the lower melting polymer is melted, as defined
by the DSC melting curve of the polymer, the higher melting
polymer melts equal to or less than 10%, desirably equal to
or less than 5%. More desirably, the DSC melting curves of
the component polymers do not overlap at all; and most
desirably, the DSC melting curves of the component polymers
are separated by at least some degree. The component polymers
selected in accordance with the melting point selection
criterion of the present invention provide a beneficial
combination of thermal and physical properties such that the
lower melting component polymer can be thermally rendered
adhesive while the other component polymers maintain the
physical integrity of the fibers, thereby forming strong
interfiber bonds without sacrificing the physical integrity
of the nonwoven web or requiring compaction pressure.
Moreover, when the DSC melting curves do not overlap, the
difference in melting temperature ranges enables the nonwoven
web to be heated even to a temperature at which the lower
melting component polymer is melted and allowed to flow and
spread within the fiber structure without loosing the
structural integrity of the web. The flow of the lower
melting polymer, in general, improves the abrasion resistance
and strength and increases the density of the web, producing
a more compacted filter medium. For example, linear low
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density polyethylene and polypropylene are highly suitable
component polymers for the conjugate fibers since the DSC
melting curves of the polymers do not overlap at all, as shown
in Figure 1. The first dip in the melting curve of Figure 1
is the melting curve of linear low density polyethylene and
the second dip is the melting curve of polypropylene. Figure
2 is another example of a suitable polymer combination for the
conjugate fibers. The DSC melting curves, as shown in Figure
2, for linear low density polyethylene and nylon 6 are
l0 significantly separated. The first significant dip in the
melting curve of Figure 2 is the melting curve of linear low
density polyethylene and the second dip is the melting curve
of nylon 6. The melting curves show that the melting
temperature ranges of the two polymers are significantly
different, making the polymers highly suitable for the present
invention.
In accordance with the present invention, the lower
melting component polymer is selected from polyolefins, and
the lower melting polymer constitutes between about 10 wt% and
about 90 wt%, desirably between about 30 wt% and about 80 wt%,
more desirably between about 40 wt% and about 70 wt%, of the
fibers based on the total weight of the fibers. The
polyolefin is selected from polyethylene, e.g., linear low
density polyethylene, high density polyethylene, low density
polyethylene and medium density polyethylene; polypropylene,
e.g., isotactic polypropylene, syndiotactic polypropylene,
blends thereof and blends of isotactic polypropylene and
atactic polypropylene; polybutylene, e.g., poly(1-butene) and
poly(2-butene); and polypentene, e.g., poly-4-methylpentene-
1 and poly(2-pentene); as well as blends and copolymers
thereof, e.g., ethylene-propylene copolymer, ethylene-butylene
copolymer and the like.
The other component polymers for the conj agate fibers are
selected from polyolefins, polyamides, polyesters,
polycarbonate, and blends and copolymers thereof, as well as
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copolymers containing acrylic monomers, provided that the
other component polymers are selected in accordance with the
above-described melting point selection criterion. Suitable
polyolefins include polyethylene, e.g., linear low density
polyethylene, high density polyethylene, low density
- polyethylene and medium density polyethylene: polypropylene,
e.g., isotactic polypropylene, syndiotactic polypropylene,
blends thereof and blends of isotactic polypropylene and
atactic polypropylene; polybutylene, e.g., poly(1-butene) and
poly(2-butene); and polypentene, e.g., poly-4-methylpentene-
1 and poly(2-pentene); as well as blends and copolymers
thereof. Suitable polyamides include nylon 6, nylon 6/6,
nylon 10, nylon 4/6, nylon 10/10, nylon 12, nylon 6/12, nylon
12/12, and hydrophilic polyamide copolymers, such as
copolymers of caprolactam and an alkylene oxide diamine and
copolymers of hexamethylene adipamide and an alkylene oxide,
as well as blends and copolymers thereof. Suitable polyesters
include polyethylene terephthalate, polybutylene
terephthalate,polycyclohexylenedimethylene terephthalate,and
blends and copolymers thereof. Acrylic copolymers suitable
for the present invention include ethylene acrylic acid,
ethylene methacrylic acid, ethylene methylacrylate, ethylene
ethylacrylate, ethylene butylacrylate and blends thereof.
Among various combinations of the above illustrated suitable
component polymers, because of the economical availability and
desirable physical properties, particularly suitable conjugate
fibers contain a combination of different polyolefins having
the above-discussed melting point differential. More
particularly suitable conjugate fibers are bicomponent
polyolefin conjugate fibers having a polyethylene component,
e.g., high density polyethylene, linear low density
polyethylene and blends thereof, and a polypropylene
component, e.g., isotactic propylene, syndiotactic propylene
and blends thereof.
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Suitable conjugate fiber configurations include concentric
sheath-core, eccentric sheath-core, island-in-sea and side-
by-side configurations. Particularly suitable for the present
invention are conjugate fibers having symmetrically arranged
component polymers, e.g., concentric sheath-core conjugate
fibers, since fibers having a symmetric polymer arrangement
do not possess potential or latent crimpability. In general,
asymmetric conjugate fibers, such as side-by-side conjugate
fibers, that contain component polymers having different
l0 crystallization and/or shrinkage properties possess latent
crimpability, which can be thermally or mechanically
activated. It is believed that the latent crimpability is
.imparted in the conjugate fibers because of the shrinkage
disparity of the component polymers. When such conjugate
fibers are exposed to a heat treatment or a drawing process,
the shrinkage disparity among the component polymers of the
conjugate fibers during the heat treatment or drawing process
causes the fibers to crimp. As such, when fibers having an
eccentric sheath-core or a side-by-side configuration are
used, the fibers may need to be processed in such a manner as
to prevent the fibers from possessing or activating latent
crimpability. For example, U.S. Pat. No. 4,315,881 to
Nakajima et al. discloses a process for producing
polyethylene-polypropylene side-by-~.ide staple cwonjugate
fibers that do not have crimps and latent crimpab.lit~.
The process employs a specific wt_retchinc~ ratio and temperature
to obtain conjugate fibers having rzo crimp and .Latent
crimpability. As for spunbond ccnj!.rgate fibers, the production
process for 1=he fiber;:; ~::an be ~u~just:ect to prevent crimps and
latent crimpability. F'or example, conjugate fibers having
polypropylene and polyet;~ylene c:an be drawn with a high drawing
stress during the spi.ar.bond fi.bc.r forming process, e.g., by
providing a low polymer throughput rate and increasing the
fiber drawing
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force, to produce conjugate fibers that do not have crimps and
latent crimpability.
A nonwoven web suitable for the present invention, which
- has a relatively uniform fiber coverage, can be formed by
isotropically depositing the uncrimped conjugate fibers onto
a forming surface. The deposited, unbonded nonwoven web of
conjugate fibers is carried on a foraminous support surface
and then bonded in a through-air bonder. Figure 3 illustrates
an exemplary through-air bonder 10 that is suitable for the
present invention. The bonder 10 receives an unbonded
nonwoven web 12 on a foraminous supporting surface 14. The
through-air bonder 10 is equipped with a temperature
adjustable heated air source 16 that heats air and directs the
heated air toward the nonwoven web 12, and a vacuum apparatus
18 that is placed below the supporting surface 14 and directly
underneath the heated air source 16. The vacuum apparatus 18
facilitates the heated air to travel through the nonwoven web
12. Unlike a conventional or hot air oven, or a radiant
heater, which applies heat only on the surface of the nonwoven
and relies on the web thermal conductivity to heat the
interior of the web, a through-air bonder forces heated air
through the nonwoven web to quickly and evenly raise the
temperature of the web to a desired level. Although the flow
rate of the heated air may be varied to accommodate the
caliper and fiber density of each nonwoven web, a velocity
from about 100 feet per minute to about 500 feet per minute
is highly desirable. The temperature of the heated air and
the dwell time of the nonwoven web in the bonder are adjusted
to heat the web to a temperature that is higher than the
melting temperature, i.e., the peak melting temperature
determined with a DSC, of the low melting polyolefin component
but lower than the melting point of the highest melting
component polymer of the conjugate fibers. Desirably, the
bonder heats the web to a temperature that is high enough to
melt at least about 50% of the olefin component polymer but
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not as high as to melt more than 10% of the highest melting
component polymer, as defined by the DSC melting curves. More
desirably, the bonder heats the web to a temperature that
completely melts the low melting polyolefin component but that
melts less than about 10% of the highest melting component
polymer, as defined by the DSC melting curve of the highest
melting component polymer of the conjugate fibers. For
example, when a nonwoven web of bicomponent conjugate fibers
having polypropylene and linear low density polyethylene is
used, the through-air bonder desirably applies a flow of
heated air that has a temperature between about 260°F and
about 300°F, and the dwell time of the web in the bonder is
desirably between about 0.1 seconds and about 6 seconds. It
is to be noted that a short dwell time in the bonder is highly
desirable since any latent crimpability that may be imparted
during the fiber forming process, in general, does not
manifest if the bonding duration is brief. In addition, the
flow rate of the heated air can be adjusted to control the
caliper and porosity of the nonwoven web. Generally, a higher
flow rate produces a bonded web having a lower caliper and a
lower porosity.
Unlike conventional calender bonded sheet nonwoven webs
that have non-uniform porosity and pore size distributions,
as discussed above, the present through-air bonded filter
medium provides highly improved porosity and pore size
distribution and the medium does not contain mechanically
compacted regions that impede the filtration function of the
medium. In addition, unlike a calender bonding process that
applies mechanical compaction pressure and non-uniformly
alters the pore size and pore configuration of different
sections of the nonwoven web, depending on the caliper of
different sections of the unbonded web, the through-air
bonding process in conjunction with the uncrimped and
uncrimping nature of the present conjugate fibers allow the
nonwoven web to be bonded without imparting significant non-
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uniform changes in the pore size and configuration of the
nonwoven web.
One additional advantage of the present nonwoven filter
medium is that the porosity and density of the filter medium
can be controlled not only with conventionally known
approaches, e.g., varying the basis weight of the filter
medium and varying the thickness of the conjugate fibers, but
also during the bonding process. The polymer selection
criteria, especially the melting point criterion, of the
present invention provides an additional approach that can be
conveniently utilized to control the porosity and density of
the filter medium. As discussed above, because of the melting
point difference between the low melting and high melting
component polymers of the conjugate fibers, the nonwoven web
produced from the fibers can be exposed to a temperature that
is not only high enough to melt the low melting component
polymer but also sufficiently high enough to allow the melt
viscosity of the melted polymer to be lowered such that the
melted polymer spreads while preserving the physical integrity
of the higher melting component polymer and of the nonwoven
web. In general, a bonding temperature that is measurably
higher than the temperature at which the low melting
polyolefin component completely melts facilitates and induces
the melted polyolefin to spread, thereby reducing the porosity
and increasing the density of the nonwoven web. It is to be
noted that the present high density filter medium has a low
caliper and high abrasion resistance that are highly suitable
for processing the medium into a highly pleated filter medium.
As an additional embodiment of the present invention, the
porosity and density of the nonwoven filter medium can also
be controlled by varying the level of the low melting
polyolefin content of the conjugate fibers. Generally,
conjugate fibers having a higher level of the low melting
polyolefin content form a nonwoven filter medium that has a
lower porosity, higher density and higher abrasion resistance.
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In addition, the porosity and caliper of the nonwoven filter
medium can be controlled during the bonding process by
adjusting the flow rate of the heated air. Generally, a
higher heated air flow rate produces a bonded filter medium
having a lower caliper and a lower porosity.
The present filter medium is heretofore illustrated with
a single layer medium. However, the filter medium can have
more than one layer. For example, conjugate fiber filter
media of the present invention that have different fiber
thicknesses and/or densities can be laminated or sequentially
deposited and then bonded to form a filter having a porosity
gradient. Additionally, the conjugate fiber filter medium can
be laminated to a microfiber filter media.
Although the filter medium is illustrated in conjunction
with liquid filtration applications, the medium is also highly
suitable for gas filtration applications. Moreover, for gas
filtration applications, the density of the filter medium can
be even higher in order to increase the efficiency of the
filter medium. Even though the throughput capacity of such
a high density filter medium is low, the throughput of the
medium can be accommodated by three-dimensionally forming or
pleating the filter medium since, as discussed above, the
filter medium is highly thermoformable. The pleated filter
medium has an increased effective filtration surface area and
thus has an increased throughput rate. Consequently, the
filter medium for gas filtration may have a density up to
about 0.5 g/cm3, desirably between about 0.1 g/cm3 and about
0.5 g/cm3, more desirably between about 0.11 g/cm3 and about
0.45 g/cm3, most desirably between about 0.12 g/cm3 and about
3 0 0 . 4 g/ cm3 .
The filter media of the nonwoven web of the present
invention can be easily thermoformed into three dimensional
shapes without measurably changing the porosity and physical
properties of the media. The conjugate fiber nonwoven web for
the present filter media can be thermoformed immediately after
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the web is through-air bonded but before the web is cooled
since the bonded web that exits the through-air bonder is
highly pliable. Consequently, the unquenched web can be
managed into desired shapes before the web is cooled to retain
the applied shape. For example, the unquenched web can be
pleated using a known pleating process. Figure 4 illustrates
an example of suitable pleating processes. The web 52 can be
passed through a set of intermeshing pleating plates or
pressed between two intermeshing pleating plates, 54 and 56,
that have equally spaced, perpendicularly attached equal
length shims 58: and then cooled to solidify the low melting
polyolefin polymer while the web is retained in the pleating
plates to permanently set the pleat configuration into the
nonwoven web.
The conjugate fiber filter medium is self-supporting,
highly abrasion resistant filter media that have high filter
efficiency and desirable strength properties. As such, the
present filter medium is highly suitable for large volume
liquid filtration applications. The filter medium can be used
as a roll filter medium, which is continuously supplied to a
filtering device, e.g., a flat bed filter, or as a sheet
filter medium. The filter medium can also be fitted in a
filter frame.
The filter media can also be conveniently
electrostatically treated to form electret filter media and
are highly thermoformable without sacrificing the physical and
electret properties of the media. Consequently, the nonwoven
filter medium are highly suitable for forming three
dimensional filter media in a conventional thermoforming
apparatus and for forming high pleat density filter media.
The three dimensional thermoformed filter media, which are
firm and self-supporting, can easily be fitted into a
conventional filter frame or housing in a conventional manner.
The filter media are highly suitable for various filtration
applications. More particularly, the filter media are highly
CA 02203567 2003-04-24
usefnl for liquid and gas filtration applications including
water filters, oil f~.lters, various gas filters and the like;
and the electrostatically treated filter media are
particularly suitable for gas filtration applications
including industrial. air cleaner filters, HVAC filters,
automotive air filters, vacuum cleaner filters, and the' like.
The following examples are provided for illustration
purposes.
1G EZampl~~:
The following test procedures were utilized to
determine various properties of the filter media.
Filter Efficiency Test: The efficiency and service life
of the filter samples were tested as follows. The filter
testing apparatus had a 90 mm diameter filter holder assembly,
which has an inlet and an outlet and directs the influent
fluid entering from the inlet to pass through the sample
filter medium, a gear pump and flow meter/regulator unit,
which supplies the influent fluid to the filter holder
assembly and is capable of maintaining 2 gallons per minute
per square inch flow rate (1.2 liter/min/cm2), and a pressure
gauge, which is placed on the inlet side of the filter holder
assembly. Samples of filter media were prepared by cutting
filter webs to fit a 90 mm diameter filter holder. Each
filter medium was weighed and fitted in the filter holder
assembly. A test fluid, which contains 40 ml of QP 24
soap/oil emulsion and 1200m1 o.f deionized water, was placed
in a beaker and then 1 g of an AC fine test particles was
added to the test fluid. The test particles had the following
particle size distributions:
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Size (less than) Volume
5.5 ~,m 38
11 ~,m 5 4
2 2 /1m 71
44 ~Cm g9
176 ~Cm 100.
. The test, fluid was continuously stirred with a magnetic
stirrer and maintained at 38°C. The inlet of the pump was
placed in the beaker, and the testing fluid was pumped through
the sample filter and then returned to the beaker, forming a
continuous loop, at a flow rate of 800 ml/min. The initial
pressure and time were noted. The flow regulator was
constantly adjusted to maintain a constant flow rate as the
test particle accumulated on the test filter medium and the
inlet pressure increased. 1 g of the test particles was added
to the beaker at an interval of 5 minutes until the inlet
pressure reached 30 psi (2.1 kg/cmz) , at which time the filter
medium was considered plugged.
The plugged time was noted and the filter medium was
removed. The removed filter medium was weighed to determine
the amount of the test particles captured after completely
drying it in an oven set at 180°F. The efficiency of the
filter medium was determined by dividing the weight of the
captured test particles by the weight of the total test
particles added to the beaker. This efficiency test
determines the overall efficiency of the filter medium over
its entire service-life.
Initial Filter Efficiency: The initial filter efficiency
measures the filter efficiency of sample filter media before
a significant amount of the test particles is accumulated on
the media, thereby measuring the inherent filter efficiency
of the media. For this efficiency test, the above-described
efficiency testing procedure was repeated, except the testing
setup was changed to an openloop system. 1240 ml of the
above-described test fluid, which contained 40 ml of QP 24
17
CA 02203567 2003-04-24
soap~oil emulsion, 1.200 ml of deionized water and 1 gv of the
AC fine test particles, was passed through the test filter,
and then the filter efficiency was measured.
Frazier Permeability: The Frazier permeability, which
expresses the permeability of a fabric in terms of cubic feet
per minute of air per square foot of medium at a pressure drop
of 0.5 inch (1.27 c:m) of water, was determined utilizing a
Frazier Air Permeab:i.lity Tester available from the Frazier
Precision Instrument Company and measured in accordance with
Federal Test Method 5:50, Standard No. 191A.
Density: The density of each filter medium was calculated
from the basis weight and the caliper, which was measured at
0.5 psi (35 g/cmZ) with a Starret-type bulk tester.
Mullen Burst: This test measures the strength of a medium
against a multidimensional stretching force. The test was
conducted in accordance with ASTM D3786-87»
Ezample 1 (Ezi)
A low loft nonwoven web was produced from linear low
density polyethylene sheath - polypropylene core spunbond
bicomponent conjugate fibers using two single screw extruders
2!5 and a sheath-care :pinning pack. The bicomponent fiber
contained 2U wt% linear low densit~r polyethylene (LLDPE) and
80 wt% polypropylene... LLDPE, Aspua~'~~~811A, which is available
from Dow Chemical, was blended with 2 wt% of a Ti02
concentrate containing 50 wt% of Ti02 and 50 wt% of
polypropylene, and the mixture was fed into a first single
.screw extruder. Polypropylene, PD3443, which is available
from Exxon, was blended with 2 wt% of the above-described Ti02
concentrate, and the: mixture was fed inta a second single
screw extruder. Using a bicomponent spinning die, which had
3'.i a 0.6 mm spinhole diameter and a 6:1 L/D ratio, the extruded
18
CA 02203567 1997-04-23
WO 96/13319 PCT/US95/13090
polymers were spun into round bicomponent fibers having a
concentric sheath-core configuration. The temperatures of the
molten polymers fed into the spinning die were kept at 450°F
(232°C), and the spinhole throughput rate was 0.5
gram/hole/minute. The bicomponent fibers exiting the spinning
die were quenched by a flow of air having a flow of air having
a flow rate of 45 ft3/min/inch spinneret width (0.5 m3/min/cm)
and a temperature of 65 ° F ( 18 ° C) . The fibers entering the
aspirator were drawn with the feed air at a flow rate of about
19 ft3/minute/inch width (0.21 m3/min/cm). The weight-per-
unit-length measurement of the drawn fibers was about 2.5
denier per filament. The drawn fibers were then deposited on
a foraminous forming surface with the assist of a vacuum flow
to form a first unbonded fiber web. An identical bicomponent
fiber spinning unit was consecutively positioned next to the
first fiber spinning unit and deposited the drawn fibers on
top of the first unbonded fiber web, forming a unitary
nonwoven web.
The unbonded fiber web was bonded by passing the web on
a foraminous supporting surface through a through-air bonder
that applied a flow of heated air at a temperature of 280°F
(138°C) and a velocity of 500 feet/min (152 m/min). The
residence time in the bonder was about 2 seconds. The
resulting nonwoven web had a 3 osy (102 g/m2) basis weight
and had a uniformly bonded sheet-like configuration. The
nonwoven filter medium was tested for various properties as
shown in Table 1.
Euample 2 (Eu2)
A low loft nonwoven web was produced from LLDPE sheath
polypropylene core spunbond bicomponent conjugate fibers in
accordance Example 1, except the weight ratio of
LLDPE:polypropylene was 50:50. The test results are shown in
Table 1.
19
CA 02203567 1997-04-23
WO 96/13319 PCT/US95113090
Example 3 (Ex3)
A low loft nonwoven web was produced from side-by-side
bicomponent conjugate fibers of LLDPE and polypropylene having
a 50:50 weight ratio. The production procedure outlined in
Example 1 was repeated, except a side-by-side spinning die was
used to produce conjugate fibers having a side-by-side
configuration. The feed air flow rate was increased to
prevent the fibers from having crimps and latent crimpability,
and the flow rate was about 0.22 m3/minute/cm width. The
results are shown in Table 1.
Example 4 (Ex4)
A low loft nonwoven web of polypropylene sheath - nylon
6 core was produced in accordance with the procedure outlined
in Example 1, except the bonding air temperature was 149°C.
The weight ratio between polypropylene and nylon 6 was 90:10.
The nylon was obtained from Custom Resin and had a sulfuric
acid viscosity of 2.2. The results are shown in Table 1.
Example 5 (Eu5)
A high density filter medium of LLDPE-sheath / nylon 6-
core spunbond fibers was prepared in accordance with Example
4, except the weight ratio between LLDPE and nylon 6 was
80:20. Example 5 is a comparative example for the purpose of
the present sheet filter illustration although the filter
medium is highly suitable for pleated filter applications.
The results are shown in Table 1.
Example 6 (Ex6)
A high density filter medium of 80 wt% LLDPE / 20 wt%
polypropylene sheath/core spunbond fibers was prepared in
accordance with Example 3. Example 6 is a comparative example
for the purpose of the present sheet filter illustration
although the filter medium is highly suitable for pleated
filter applications. The results are shown in Table 1.
CA 02203567 2003-04-24
Comparative Example 1 (C1)
A crimped side-by-side spunbond conjugate fiber web was
prepared by repeating the production procedure of Example 3,
except the aspirating air used was heated to about 350°F and
had a flow rate of '3 ft~/minrin width. The unbonded fiber
web was bonded by passing the webs through a through-air
bonder having an air temperature of 272'F and a air velocity
of 200 feetfmin. The results are shown in Table 1.
comparative Example 2~ (C2)
A point bonded polypropylene spunbond fiber web, which is
commercially available from Kimberly-Clark under the trade-mark
AccordT" and has a bonded area of about 25%, was tested for its
initial filter efficiency. The results are shown in Table 1.
Comparative Examples 3-6 (C3-C6)
Comparative Examples 3 and 4 were ReemayT~ filters, style
numbers 2033 and 2440, respectively. ReemayT" filters are
calender bonded webs of polyethylene terephthalate polyester
spunbond fibers and capolyester spunbond fibers. Comparative
Example 5 was Typarrr~30$, which is a polypropylene spunbond
nonwoven web. Reemayt" and TyparT" ate commercially available
from Reemay, Inc., Old Hickory, Tenn.
Comparative Example 6 was a commercial liquid filter
medium available from Auchenbach of Germany. The filter
medium is calendered polyester spunbond nonwoven web that is
spot bonded with an acrylic binder. The results are shown in
Table 1.
Comparative Example 7 (CT)
A unbonded three layers laminate of Reemay 2 011 ~ia.~ tested
for the initial filter efficiency. ReemaymM20;~1 r,~as selected
since the density of the material is within the range of the
present filter medium. The result is shown in Table 1.
21
CA 02203567 1997-04-23
WO 96/13319 PCT/US95/13090
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22
CA 02203567 1997-04-23
WO 96/13319 PCT/US95/13090
The results clearly indicate that the filter media of
the present invention exhibit a highly desirable
combination of good filter efficiency, filter life and
strength properties, especially for liquid filtration.
Compared to the prior art polyester and polypropylene
spunbond filter media, the conjugate fiber filter media of
the present invention have a combination of highly improved
overall and initial efficiencies, and filter life, as well
as provide high strength properties.
In addition, the examples of the present filter media
also demonstrate that the physical properties, e.g.,
density, permeability and strength, of the filter media can
easily be modified by changing various elements of the
filter media manufacturing process. For example, by
changing the weight ratio of the component polymers,
changing the component polymers and/or changing the bonding
conditions, the filter media can be produced to have
different physical and filtration properties.
In order to more clearly demonstrate the highly useful
combination of efficiency and life of the present filter
media, the filter efficiency data and the filter life data
for Examples 1-6 and Comparative Examples 3-5 were
graphically plotted, since the examples have a similar
basis weight and thus should be directly comparable.
Figure 5 illustrates the filter efficiencies with respect
to the densities of the example filter media; Figure 6
illustrates the filter life with respect to the densities
of the filter media; and Figure 7 illustrates the initial
filter efficiencies of the example filter media.
Figure 5 illustrates that the filter efficiencies of
the present filter media are significantly better than the
commercial polyester filter media; Figure 6 shows that the
present filter media have a long service life; and Figure
7 shows that the present filter media have a highly
improved initial filter efficiency. It is to be noted that
although the filter life of the commercial polyester filter
media may appear to be beneficial from Figure 6, Figure 5
23
CA 02203567 1997-04-23
WO 96/13319 PCT/US95/13090
and Figure 7 clearly demonstrates that the extended life of
these filter media are the result of poor filter
efficiency. Alternatively stated, these commercial filter
media allow a large portion of the contaminant particles to
pass through the media and, thus, lessening the contaminant
cake build up on the filter surface, extending the service-
life while providing a poor filter efficiency.
From Figures 5 and 6, it can be seen that, for liquid
filtration applications, the present filter media provide
an especially desirable combination of filter efficiency
and life when the media have a density between about 0.07
g/cm3 and about 0.2 g/cm3.
As can be seem from the above, the through-air bonded
conjugate fiber filter media of the present invention
highly desirable filter attributes, such as filter
efficiency, strength, life and the like. Accordingly, the
filter media is highly useful for various filtration
applications that require filter attributes including self-
support, high efficiency, long filter life and strength.
24
