Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PCT/US93/U7924
..~ 0 94/04243
DEPTH FIL'T'ER CARTRIDGE AND METHOD
AND APPARATUS FOR MAIQNG SAME
BACKGROUND OF TF IE INVENTION
S
1. Field of the Invention
The present invention relates generally to the field of depth filters,
and more particularly to a depth filter cartridge comprising a filter element
constructed of a plurality of substantially continuous discrete filaments
which
IO are collected to form a generally tubular depth filter cartridge. The
present
invention also relates to a method and apparatus for making such a filter
cartridge.
2. DesarinHon of the Prior Art
IS Several processes and apparatus for forming depth filters comprised
of a plurality of substantially continuous filaments currently exist in the
prior
art. In this art, fiber forming devices or fiberizers are used to spray
filaments
of synthetic resinous material toward a rotating collection mandrel to be
formed into a tubular configuration. During this process, jets of air or other
20 gases act on the filaments to attenuate such filaments to a comparatively
fine
diameter and convey the same to the collection device. Several specific
processes have evolved from this general concept.
One of these processes is described in United States Patent No.
3,825,379 issued to Lohkamp et al. and United States Patent No. 3,825,380
25 issued to Herding et al. Both disclose a process die or fiberizer
consisting of a
die head containing separate passages for the filament material and the
attenuating air. During operation, molten resinous material fiber is forced
through small holes in the die head toward a collection device and is
attenuated by air streams positioned on opposite sides of the filament outlet
30 holes. The collection methods utilized with this process include either a
rotating "drum such as shown in these patents to form a continuous mat or a
rotating mandrel together with a press roller to form a tubular depth filter.
This latter process is a non-continuous or semi-continuous process in which
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WO 94/04243 ' ' ~ ~ ~ ~ 8 ~ ~ PCT/IJS93/07929< <:''
2 ,
the diameters of the plurality of filaments is constant throughout the
entirety
of the element.
A second process is exemplified by United States Patent No. 4,240,3b4
issued to Lin et al. This patent discloses a process die or nozzle block Which
delivers a plurality of filaments toward a rotating collection device.
Associated with the filaments are attenuating air streams which function to
attenuate the filaments as they travel toward the collection device. This
patent also discloses a press roll for varying the pressure applied to the
accumulating fibers on the rotating mandrel so as to provide a filtex of
varying fiber density. Like the process of Lohkamp et al. and Handing et al.,
the diameter of the individual filaments in this process is constant
throughout the entirety of the filter element. However, contrary to Lohkamp
et al. and Handing et al., this process is a continuous process in which the
collected filaments are continuously forced off the rotating mandrel via the
noncylindrical press roll to produce a coreless depth filter element.
A third specific process is represented by United Skates Patent
Nos. 4,594,202 and 4,726,901, both issued to Pall et al. Similar to the
processes
described above, the Pall process includes a fiberizer or fiberizer die having
a
plurality of individual nozzles through which the molten filament resin is
forced toward a collection mandrel. Also similar to the other processes
described above, this process discloses the use of air or gas streams for the
purpose of attenuating the filaments as they travel toward the collection
mandrel. This process differs from the processes described above, however,
in that it discloses a means for varying the fiber diameter throughout the
radial dimension of the filter element, while maintaining a substantially
constant voids volume for each level of fiber diameter variance. Pall et al. '
accomplishes this by sequentially altering certain parameters which affect the
finer diameter during collection of the filaments on the rotating mandrel.
,. _:
Although each of the above specific processes are generally
acceptable for certain applications, each also has certain limitations. For
example, one limitation of the Lohkamp et al. and Handing et al. process is
that it is a non-eontinuous or semi-continuous process. In other words, a
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r~~"°~ 94/04243 2 ~, ~ 2 g ~ ( PCT/US93/07924
3
filter element of finite length is formed by building up a mat of attenuated
filaments on a rotating mandrel. When the collected filament material
reaches a desired thickness, the filter strucriare is removed and the process
is
commenced again far the next filter element. A further limitation is that the
filament materials are dispensed from a common manifold. Thus, the
characteristics of the collected filaments, including the filament diameters,
are
substantially identical throughout the entire radial thickness of the filter
element. Still further, such process contemplates forming the filter structure
on a separate core which remains part of the filter element when it is
removed from the mandrel. Tf such a core is not used, a significant limitation
exists in the fiber diameter which is needed to support the filter str~xcture
without collapse. This, in turn, necessarily limits the micron rating of the
resulting filter, or the particle size which can be filtered.
The filter structure of Lin et al. is an improvement over the process
of Lohkamp et al. and Handing et al. in that it is a continuous process for
forming a continuous filter structure of indefinite length. However, Lin et
al., like Lohkamp et al. and lHarding et al. discloses a filter structure in
which
the filaments are all of the same diameter. Further, since the Lin process is
designed for producing a coreless depth filter element (i.e.) a filter without
a
separate core, the central portion of the filter element must be formed from a
filament having a diameter sufficiently large to provide support for the
filter
structure. This also, in turn, necessarily limits the micron rating of the
filter
or minimum particle size which can be filtered.
Although the Pall et al. patents contemplate a depth filter element
comprised of filaments with varying diameters, there are several limitations
which exist. First, the process of Pall et al. is not a continuous process,
but
must be repeated fox each filter manufactured. Second, although some filter
elements of Pall et al. have filaments of varying diameters, the process of
making such elements has limitations. Specifically, the filament diameter is
varied by sequentially changing one of several operating conclitions of the f
filament producing mechanism. Whenever such a change is introduced, t
however, the system takes time to respond to such changes before again
WO 94/04243 ~ g ~ ~ PCT/US93/0792~°~~:
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reaching equilibrium. The time frame for.response is proportional to the
degree of change. Because these changes are introduced during the
manufacture of each individual filter element, a less stable and more variable
a
process results: Further, the changeover from a filament of one diamefer to
that of another occurs gradually as a time related transition, rather than
abruptly such as where the filaments are comprised of two or more discrete
filaments.
Accordingly, although prior art methods exist for manufacturing
depth filters, each of the methods, as well as the products constructed from
such methods, have limitations which tend to limit the wide scale
applicability of products produced by any one particular process. Accordingly,
there is a need in the art for an improved, cost efficient eoreless depth
filter
element, and more particularly, to a set of filter elements having a wide
range
of micron ratings and filtering applications. A need also exists for a
I5 continuous method and apparatus for producing such a filter.
SUMMARY OF THE INVENTION
In contrast to the prior art, the depth filter of the present invention
is a coreless, non-woven depth filter element which is preferably
manufactured on a continuous basis. Further, the filter element in
accordance with the present invention is a graded fiber element which is
provided with filaments of different diameters or filaments constructed of
different materials. The filaments include support filaments at the eentral
area of the filter with diameters which are sufficiently large to thermally
bind :
into a structure which is strong enough to support the remainder of the filter
'
structure without collapse. Such filter element is also provided with one or
more (layers of discrete filtration filaments of different diameters and
preferably diameters smaller than the diameters of the support filaments. ,
These filtration filaments define the ultimate filtration characteristics of
the
filter. Unlike prior art coreless structures, these filtration filament
diameters . I
can be quits small and significantly smaller than the filament diameters .
needed. t~ support the central support portion of the filter element. The
small ;
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_'~'r~.' 94104243
PCT/t,JS93/0792d
filament diameter section or sections can then, if desired, be followed by one
or more layers of a further varied filament diameter to act as a prefilter or
the
like to filter out larger particles. The filter element can also embody a
graded
density structure, if desired. "'
5 The apparatus for making such a filter includes two or more
filament delivery systems spaced side-by-side in a direction parallel to the
axial direction of the collection mandrel. These delivery systems are
independently controlled so that filaments of different diameters or of
different materials or polymers can simultaneously be produeed and directed
to a collection device and thus formed into a filter element. In the preferred
embodiment of the present invention, the material feed passages are
associated with positive displacement independent motor driven pumps in
which the speed is independently and electronically controlled to thereby
effect the material flow rate. The heating blocks for heating the material in
the apparatus and maintaining it at a predetermined temperature are also
independently heated and controlled by appropriate means as are the
mechanisms for providing the attenuating gas.
The process of the present invention is a continuous process which
includes providing two or more independently controlled filament
dispensers or dispensing means and operating the dispensers simultaneously
during the manufacture of a filter element to produce a depth filter having
filaments of at least two different diameters or two different materials.
Accordingly, it is an object of the present invention to provide an
improved coreless depth filter constructed of filaments having different
diameters or filaments of different materials.
Another object of the present invention is to provide a set of
coreless depth filter elements having an enhanced micron rating and thus the
ability to filter a greater range of particle sizes.
Another object of the present invention is to provide a coreless
depth filter having an innermost layer constructed of filaments of a first
diameter and one or more outer, filter layers constructed of filaments of
diameters less than the first diameter.
CA 02142857 2004-O1-23
6
Another object of the present invention is to provide a depth filter having
filaments of different diameters in which the specific filament diameters are
selected to
provide filter support as well as filtering capability.
A further object of the present invention is to provide a coreless depth
filter
constructed of filaments made from different materials.
A still further object of the present invention is to provide an improved
method
and apparatus for making a depth filter which includes at least two
independently
controlled filament producing means or dispensers functioning simultaneously
to produce
a continuous depth filter cartridge.
Accordingly, in one aspect the present invention resides in an apparatus for
making a continuous, coreless non-woven, generally tubular, depth filter
element
comprising: first filament forming means for producing a first substantially
continuous
molten filament of synthetic resinous material having a first diameter for
conveying said
first filament in a stream along a first predetermined path, said first
filament forming
means including a first filament delivery system; second filament forming
means for
simultaneously producing a second substantially continuous molten filament of
synthetic
resinous material having a second diameter for conveying said second filament
in a
stream along a second predetermined path, said second filament forming means
including
a second filament delivery system, said first and second filament forming
means
producing discrete filaments and said first and second filament delivery
systems being
independently controlled; a collection means positioned in said first and
second
predetermined paths, said collection means including a rotating mandrel
operable to
receive said first and second filaments for continuously forming the filter
element, said
mandrel having an axial length and an outer collection surface.
In another aspect the present invention resides in a continuous process of
making
a coreless non-woven, generally tubular depth filter element comprising the
steps of:
simultaneously producing first and second substantially continuous, but
discrete molten
filaments of synthetic resinous material by providing first and second
filament delivery
systems and independently controlling said first and second filament delivery
systems
and conveying said first and second filaments in streams along first and
second
CA 02142857 2004-O1-07
6a
predetermined paths toward a collection means, respectively, said first and
second
filaments having first and second diameters, respectively; collecting said
first and second
filaments on said collection means with a rotating mandrel with an axial
length and an
outer collection surface.
These and other objects of the present invention will become apparent with
reference to the drawings, the description of the preferred and alternate
embodiments and
the appended claims.
DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic diagram illustrating the apparatus of the preferred
embodiment of the present invention.
Figure 2 is a plan view of the collection device as viewed from the source of
the
filaments.
Figure 3 is a schematic illustration of an alternate apparatus embodying more
than
two independent filament delivery systems.
Figure 4 is a pictorial view of a depth filter element in accordance with the
present invention which has been made via the method and apparatus of the
present
invention, and in particular, an apparatus such as that of Figure 1.
Figure 5 is a sectional view as viewed along the section line 5-5 of Figure 4.
Figure 6 is a sectional view similar to Figure 5 of an alternate depth filter
embodiment constructed in accordance with the present invention, and in
particular from
an apparatus such as that of Figure 3.
Figure 7 is a schematic illustration of a further embodiment of the present
invention showing a single material delivery system with two independently
controlled
filament dispensing means.
CA 02142857 2004-O1-07
7
DESCRI>''ITON OF THE PREF'FRRED EMBODIMENT AND METHQD
The present invention relates to an improved non-woven depth
filter element, and more particularly a coreless depth filter element, as well
as
an apparatus and a method for making such element. Throughout the
specification and claims the term "coreless" is used to describe certain depth
filter elements. Unless otherwise indicated, the term "coreless" refers to a
filter element which is not provided with a separate support core.
Reference is first made to Figure I illustrating an apparatus which is
used to continuously manufacture a depth filter element of indefinite length
in which the depth filter is comprised of at least two discrete sets of
thermally
bound continuous filament material of different diameters or of different
materials. The preferred embodiment of the apparatus includes a motor
driven screw type extruder IO which is supplied with thermoplastic
I5 polymeric material from a source (not shown). A single extruder 10 can
function for both delivery systems as shown, or where filaments of different
materials are contemplated, separate extruders can be provided for each
delivery system. The particular thermo plastic polymeric material may be any
one of a variety of synthetic resinous materials which can produce the
filaments used in manufacturing the depth filter element of the present
invention. Although the class of polymeric materials known as
polypropylenes are preferred, polyesters, NylonTM, polyurethanes and other
materials may be used as well. Within the extruder 10, the polymeric
material is heated to a molten state, at which time it is metered and conveyed
into a heated delivery line 11. The material is maintained or further heated
in the line I1 and is ultimately fed into a common manifold 12. The heated
molten polymeric material is then directed by the manifold 12 to two
substantially identical filament forming means in the form of two filament
delivery systems which are illustrated by the general reference characters 14
and 16. Each of the delivery systems 14 and 16 is substantially. identical and
functions to produce one or more substantially continuous filaments of the
CA 02142857 2004-O1-07
resinous material and to direct the same along a predetermined path toward a
collection means as will be described in greater detail below.
The filament delivery system 14 includes a motor driven gear type
positive displacement metering pump 18 which receives molten polymeric
material from the manifold 12 and directs it to the heater block 24. The speed
of the motor 19 which drives the metering pump 18, and thus the rate at
which the material is metered through the pump 18 is electronically
controlled by an appropriate control means 20.
The block 24 is independently heated via heater means (not shown).
Such heater means, and thus the temperature of the polymeric material
with the block 24, is controlled by the temperature control means 26. The
block 24 is provided with a plurality of filament dispensers or filament
dispensing means in the form of a plurality of removable orifices or
nozzles 25, 25 and associate gas attenuating mechanisms 28, 28. The size
of the orifices 25, 25 may be selected as desired to assist in achieving
desired filament size or diameter. The molten material is fed to the nozzles
25, 25 through internal passages (not shown) within the block 24.
The filament attenuating mechanisms 28, 28 provide a plurality of
gas or air jets to attenuate the filaments exiting from the nozzles 25 in a
20 manner known in the art. The gas attenuating mechanisms 28, 28
accordingly may be of any design known in the art including that described in
United States Patent No. 4,173,443.
Each of the attenuation mechanisms 28, 28 is associated with a gas
25 heater means 29 and gas supply 31. The attenuating gas is supplied from the
supply 31 via the conduit 32 and appropriate valves and regulators to the
heater 29 where its temperature is elevated or lowered to the desired
temperature via the temperature control 30. The gas is then fed from the
heater 29 through the conduit 34 to the attenuating means 28, 28. In the
30 preferred embodiment of Figure 1, the mechanisms 28, 28 are provided with
attenuating gas from a common supply and control means. However, it is
CA 02142857 2004-O1-07
9
contemplated that each of the mechanisms 28, 28 could be provided with
separately controlled gas sources such as that shown in Figure 7.
The filament delivery system 16 is substantially identical to that of
the system 14 described above. Specifically, the system 16 includes a heater
head 38 corresponding to the heater block 24, an independently driven positive
displacement metering pump 36 corresponding to the metering pump 18 and
pump and pump control elements 39 and 40 corresponding to the
elements 19 and 20. The head 38 is provided with a plurality of nozzles 42, 42
and temperature control means 4I corresponding to the nozzles 25, 25 and
temperature control 26 of system 14. The system 16 is also provided with
attenuating mechanisms 44, 44 associated with the nozzles 42, 42. The
attenuating mechanisms 44, 44 are provided with attenuating air from an air
supply 45 through a heater 48 similar to the air supply 31 and heater 29.
Appropriate conduit means 46 and 49 and temperature control means 50 are
also provided for the attenuating air in the filament producing means 16.
Each of the delivery systems 14 and 16 is capable of producing a
plurality of discrete, continuous filaments 51, 51 and 52, 52, respectively
which are directed from the orifices 25, 25 and 42, 42 toward the filament
collection means 54 illustrated in Figures 1 and 2. The collection means 54
includes a central, rotatable mandrel 55 supported for rotation via the
rotation means 58. Adjacent to the mandrel 55 and spaced therefrom is a
press roll member 56 rotatable about the axis 57. During operation, the
plurality of filaments 51, 51 and 52, 52 are directed toward the rotating
mandrel 55 and collected thereon in a manner known in the art. The rotating
press roller 56 engages the filaments which have been wound onto the
rotating mandrel 55. As sufficient filaments are built up on the mandrel 55,
the press roller 56 forces the finished filter element 59 off the axial end of
the
mandrel 55 in the direction of the arrow 53 (Figure 2) to produce a continuous
filter element 59 of indefinite length. The entire collection means 54 is
known to those skilled in the art and may be similar to that desczibed in
United States Patent No. 4,240,864
CA 02142857 2004-O1-07
1U
In the preferred embodiment the press roller 56 is
contoured, thus resulting in a filter element of graded density.
The preferred apparatus illustrated in Figure 1 includes two
independent filament delivery systems 14 and Ib capable of forming
filaments of different diameters or different materials. Such an apparatus can
be used to construct the filter element of Figure 4 having filaments of
different diameters or materials. It is contemplated, however, that the
apparatus may embody a filament forming means embodying one or more
additional independent filament delivery systems such as the system 15
illustrated schematically in Figure 3. With the apparatus of Figure 3,
filaments of additional diameters or materials can be added to the filter
element structure such as that shown in Figure 6. The number of
independent filament delivery systems in the apparatus is dictated by the
particular filter element desired.
With the apparatus of Figures 1-3, depth filter elements of the type
contemplated by the present invention can be made. This is accomplished by
altering or controlling certain structural components and/or operating
conditions of each of the filament producing means 14 and 16 (Figure 1 ) or
14,
I5 and 16 (Figure 3) to produce filaments having the desired filament
diameters or other characteristics or filaments of different materials. For
example, the filament size can be controlled to some extent by the orifice
size.
In general, the smaller the orifice, the smaller the filament diameter. The
temperature of the filament material and the pressure at which it is forced
through the orifice also has a bearing on filament size. In general, and
within
limits, higher temperatures and lower pressures will lead to smaller filament
diameters. Further, the conditions of the attenuating gas, including the
pressure, velocity and temperature of such gas, can be used to control
filament size and characteristics. Generally, increased pressure, velocity and
temperature of the attenuating gas will result in smaller filament diameter.
It should also be noted that certain of the structural components or
operating conditions within each of the filament producing means 14, 15 or
I6 can also be controlled. For example, the size of the orifices 25, 25 can be
CA 02142857 2004-O1-23
1I
adjusted to produce filaments of different sizes from the means I4. Similarly,
as shown in Figure 7, it is contemplated that one or more of the filament
delivery systems such as the system of Figure 7 can be provided with one or
more individual attenuating gas supply and control means 72 and ~3. Each of
these means T2 and 73 is associated with one or more of the gas attenuating
mechanisms to individually control the size and characteristics of the
resulting filaments.
The depth filter element 59 illustrated pictorially in Figure 4 and
sectionally in Figure 5 is a generally elongated depth filter element which is
coreless and which can be constructed of indefinite length via the continuous
process of the present invention. The coreless nature of the filter element 59
is due to the fact that as the filter is forced off the rotating mandrel 55 by
the
press roll 56, the center hollow portion 60 of the filament 59 is defined by
the
inner surface of the iruiermost portion 61 of intertwined filaments of
resinous material. This is in contrast to a filter element in which the
intertwined filaments are supported by a separate, hollow support core
constructed of plastic or the like.
In the preferred embodiment, the filter element 59 is an elongated
generally tubular element of indefinite length having a generally tubular
hollow interior 60 and a generally cylindrical external surface 64. The
preferred element 59 of Figures 4 and 5 also includes a filter portion
rnmprised of a plurality of substantially continuous, thermally bound,
intertwined filaments of synthetic resinous material. This filter portion
includes a central support zone 61 comprised of a plurality of support zone
filaments having a first diameter and a filtering zone 62 comprised of one or
more filtering levels, each comprised of a plurality of filtration filaments
having a second or more diameters different than the diameter of the support
zone filaments. In the embodiment of Figures 4 and 5, the filtering zone 62 is
comprised of a single filtering level.
The support zone filaments of Figures 4 and 5 have a diameter
which is sufficiently large to provide support for the filter element during
the
filtering process, and in particular, support for the filtering zone
filaments.
CA 02142857 2004-O1-07
1z
The support zone filaments should also be of a size that facilitates the
thermal
bondings of such filaments to one another. Preferably the diameter of such
support filaments should be greater than about 15 microns and between about
15-50 microns. Most preferably such diameters should be about 20-40
microns. The filtering zone of the element 59 of Figures 4 and 5 is comprised
of a single filtering level identified by the reference numeral 62. The
filtering
zone filaments of this level 62 have a diameter which is dictated by the
desired filtering characteristics of the filter element 59. Although these
filtration filaments can be of any desired diameter, the preferred embodiment
contemplates that they will be smaller than the support filaments forming
the support zone 61 and generally in the range of about 1 to 15 micTOns. More
preferably such filaments will have a diameter in the range of about 1 - 8
microns. With filtration filament diameters in this range, a coreless depth
filter can be constructed which is capable of filtering particles much smaller
than prior art coreless depth filters. In addition to the variance in filament
diameter, the density of such filaments in the filter element can also be
varied
in accordance with the prior art via the press roller as taught in United
States
Patent No. 4,240,864.
A modified depth filter construction 65 is illustrated in Figure 6.
This construction 65 differs from that illustrated in Figures 4 and 5 by the
number of layers or levels in the filtering zone. Specifically, the embodiment
of Figure 6 is constructed using an apparatus such as that of Figure 3. The
element 65 includes a hollow center 66, a central support zone comprised of
the layer 68 and a filtering zone comprised of the two filtering layers 69 and
70. Each of the layers 68, 69 and 70 is constructed of a plurality of discrete
resinous filaments with differing diameters. Similar to the support layer 61
of the embodiment of Figures 4 and 5, the support zone filaments of the
layer 68 have a diameter sufficiently large to support the filtering zone
filaments and thus preferably have a diameter greater than about 15 microns
or about 15 - 50 microns, and most preferably, a diameter of about 20 -
microns.
CA 02142857 2004-O1-23
13
Also, similar to the filtering zone 62 of Figures 4 and 5, the diameter
of the filtration filaments forming the layers 69 and 70 is generally smaller
than the filaments of the support zone layer 68. Preferably, the filtration
filaments of the filter layer 69 have a diameter of approximately 1 -15
microns, while the filtration filaments of the filter layer 70 have a diameter
of
approximately 3 - 10 micTOns larger to serve as a prefilter layer for the
filter
layer 69.
In addition to a coreless depth filter element having filaments of
different diameters, the filaments can also be constructed of different
materials. For example, filaments of a first material such as a polypropylene
or polyethylene could be used to form the support zone 61 (Figures 4 and 5) or
68 (Figure 6), while filaments of a second or third material, such as a Nylon
or
a polyester could be used to form the filter layers 62 (Figures 4 and 5) or
69, 70
(Figure 6).
It should be noted that the filament forming means contemplated by
the present invention is not capable of producing filaments of an exact and
constant diameter. For example, during the production of filaments having
diameters of about 15 microns, some will be larger, while some will be
smaller. Most, however, will be about 15 microns. The same is true for the
ranges of filament sizes set forth above and in the claims.
Having described the apparatus of the present invention and the
structure of the depth filter element in detail, the general operation of the
apparatus and the method of the present invention can be best understood as
follows.
First, molten resinous material is supplied to the extruder 10 of
Figure 1 where it is heated to a desired temperature. This material is then
conveyed to the manifold 12 where it is directed to each of the filament
delivery systems 14 and 16. With this structure, the material which is fed to
the systems 14 is the same as that which is fed to the system 16. Thus, the
material forming the filaments 51, 51 and 52, 52 is the same. It is
contemplated, however, that if desired, the filaments 51, 51 and 52, 52 can be
made from different materials, such as one from a polypropylene and a
CA 02142857 2004-O1-07
14
second from a polyester or other polymer. .In such a case, a separate
extruder 10 would be provided for each system 14 and I6.
The apparatus of Figure 1 is designed to produce filaments 51, 51 and
52, 52 having two different diameters or of two different materials. Thus, the
apparatus of Figure I may be used to make the depth filter element illustrated
in Figures 4 and 5. To produce a depth filter element as illustrated in Figure
6
having more than two layers of filaments with different diameters or
constructed from filaments of more than two different materials, a third
independent filament delivery system I5 such as shown in Figure 3 is
employed. This third filament producing means 15 can also be served by a
common extruder similar to the extruder 10, or can be provided with its own
separate corresponding extruder.
Because of the fact that the filament delivery systems 14 and 16 of
Figure 1 or 14, 15 and I6 of Figure 3 are independently controlled, the
various
factors affecting filament size, including temperature, orifice size,
pressure,
resin throughput rate, attenuating gas conditions, etc. can be set and
controlled to produce filaments having desired diameters to function either
as support filaments for a coreless depth filter or as filtration or
prefiltration
filaments for the filtering levels.
In constructing the depth filter of the present invention, the
filaments 5I, 5I and 52, 52 (Figure I) are directed toward the rotating
mandrel 55 such that they accumulate on the mandrel. It should be noted
that the filaments 51, 51 and 52, 52 are directed toward the mandrel 55 along
its axial length. With the press roll 56 in the position illustrated in
Figures 1
and 2, the filaments 5I, 5I would normally be the coarser filaments or those
with a greater diameter sufficient to form the support portion of the filter
element 59. As the filter element is moved axially along the rotating
mandrel 55 by the press roll 56 in the direction 'g3 (Figure 2), the filaments
52,
52 are laid and collected on top of the previously collected filaments 5I, 5I,
thereby forming the outer or filtering layer. Tf other filaments of further
differing diameters or materials are desired, the filament dispensing means
CA 02142857 2004-O1-07
for dispensing such filaments can be added axially next to the dispenser
forming the filaments 52, 52.
Although the description of the preferred embodiment and method
has been quite specific, it is contemplated that various modifications could
be
5 made without deviating from the spirit of the present invention.
Accordingly, it is intended that the scope of the present invention be
dictated
by the appended claims rather than by the description of the preferred
embodiment.
