Note: Descriptions are shown in the official language in which they were submitted.
BACRGROUND OF THE INVENTION
Field of the Invention
This invention relates to nonwoven fibrous filter
material used for the filtration, under pressure, of fluid
containing sediment. More particularly to a milk filter
that has the capability of both surface filtration and
in-depth filtration of fluid contaminants.
Prior Art
In the processing of aqueous fluids, particularly
fluids such as milk and other dairy products, it is
customary to perform a preliminary filtration operation
close to the source of production so as to remove solid
impurities which may serve to contaminate the milk. This is
in many cases done at the dairy farm. Raw milk as it is
produced is filtered before the milk is collected in a bulk
cooling tank.
The sediment or impurities removed by this process
include coarse material such as hair, straw, shavings, etc.,
down to very finely divided dirt or soil, which varies in
amount. It is customary for milk collected at the farm to
be periodically tested for sediment by an inspector or
sanitarian, and unless an efficient filtration has been
performed, the milk producer is liable to suffer an economic
loss. Efficient removal of fine sediment, therefore is
desirable both from sanitary and economic reasons~ Such
removal, however, must be effected without unduly prolonging
the time requlred to filter a given guantity of mil~.
2 --
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Historically, milk has for many years been filtered on
the farm by in-line filtration devices, wherein milk is
drawn from the cows by a milking machine, and is transferred
to a pipeline system where it is forced under pressure
through a filtering device, to remove sediment. The
filtered milk then passes to a bulk cooling or holding tank.
The fluid milk is then pumped from the holding tank into a
tank truck.
Such in-line installations are for convenience,
improved sanitation, and to reduce manpower needed.
In U.S.Patent No. 3,831,766 there is described a filter
media that is used in an in-line filtration device. The
filter media is a blend of fibers which combine the effect
of hydrophilic, water-swellable fibers with hydrophobic,
non-swellable fibers, with the latter serving as high
tensile load bearing fibers. These fibers are an intimate
blend in the fiber media, and are not stratified in layers
of different composition. A chemical system binds the blend
of fibers together.
A disadvantage with this prior art filter media is that
it only has in-depth filtration, thus permits a substantial
amount of fine sediment to pass through it. In addition,
the filter may become so clogged that it has to be replaced
frequently. Additionally, because this prior art filter
does not have a reinforcing element therein, rupture may
occur in the walls of the filter while it is in use, causing
sediment to pass through into a holding tank. Furthermore,
because this prior art does not have secondary filtration
such as in the form of surface filtration, some fine
particles may not be retained within the filter media. This
occurs especially in thin or weak areas of the filter.
Other known processess to make milk filters involve the
layering of fibrous webs, where each web may bg ~r , _se~; Of
a fiber or fibers of different deniers from the ~recee~in~
web. This construction permits different particle sizes of
contaminants in the milk to be entrapped at different
levels of the fiber stratification. A disadvantage with
this filter is its low cross direction tensile strength of
the fabric. This is due to the fact the fibers in the
individual webs are carded predominantly in the machine
direction, which produces a fabric with low cross direction
tensiles. A low tensile filter is not adapatable nor fit
for in-line filtration where pressure is used because it is
not strong enough to withstand pressure.
In dealing with the sanitation of milk by eliminating
the sediment in the milk it is desirous to obtain a filter
that will have: "primary or in-depth filtration" to retain
dirt, grass and vegetation particles, leaves or particles of
skin disloged from the cow's udders during the milking
process; "high tensile strength", both in the machine
direction and the cross direction of the fabric so as to be
able to withstand hydrostatic pressures that impinge on its
surface when it is mounted in-line between a vacuum
reservoir in the milking device and a storage tank for
pre-pasteurized milk; and a "secondary or surface
filtration" layer to remove sediment that has passed through
the in-depth filtration layer, and before the sediment
reaches a holding tank. Prior art has not been able to
accomplish this, but the present invention has.
It is the primary object of the present invention to
provide a fibrous, nonwoven fluid filter which will remove
sediment from sediment containing fluids by both surface
filtration and in-depth filtration.
An additional object of the present invention is to
provide a nonwoven filter in which the wet tenacity, denier,
and wet stiffness of the fibers combine to effect efficient
filtration under pressures of 20 pounds per square inch or
more. ~
Still another object of the present invention is to
provide a nonwoven that is economical to make and use.
Other objects of the invention will be more apparent
from the following description and drawings.
5-
SUHMARY OF THE INVENTION
A nonwoven milk filter material for use in the
filtration of fluid comprised of an inner layer of a plurality
of continuous 4 denier polyester filaments in surface to
surface contact with at least one layer of a blend of 1.5
denier staple po]yester fibers and 1.5 and 5.5 denier staple
rayon viscose fibers. The filaments and the blend of polyester
and rayon viscose fibers are bonded together by an aqueous
anionic dispersion of co-polymers of acrylic esters carboxy
modified binder. The aqueous anionic dispersion of co-polymers
of acrylic esters carboxy modified binder provides adhesion
between the staple fibers and the continuous filaments. The
continuous filaments serve as a base material giving the filter
strength and support. The present invention constructed in
this manner permits both surface filtration and in-depth
filtration of fluid contaminants.
In its broadest aspect, the present invention
comprises a nonwoven filter material for use in filtering
contaminants from fluid comprising:
an inner layer having a plurality of continuous polymeric
filaments;
at least one outer layer in surface to surface contact
with said inner layer, said outer layer comprising a blended
fibrous web having a uniform pore distribution; and
an aqueous hinder bonding said inner layer to said outer
layer:
wherein the filter is capable of both surface filtration
and in-depth filtration.
_ ~ ~
Brief Description of the Drawings
The objects and advantages of the present invention
will become more apparent when viewed in conjunction with
the following drawings, in which:
Figure 1 is a side elevational view of a tubular filter
made from the filter material of this invention;
Figure 2 is an elevational view of the filtering
section of an in-line filter system, showing the filter tube
of Figure 1 in place;
Figure 3 is a view of the present invention
illustrating the layers of fibers;
Figure 4 is a view through "IV-IV"' of Figure 3;
Figure 5 is a graph illustrating the pore distribution
of the prior art filter with the trademark "Tuffy";
Figure 6 is a graph illustrating the pore distribution
of the prior art filter with the trademark "Milk Check";
Figure 7 is a graph illustrating the pore distribution
of the present invention; and
Figure 8 is a graph illustrating the corresponding
standard range of contaminants that are found in milk.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to Figure l, the filter material 10 of this
invention for use in pressurized in-line filtration systems
are commonly formed in elongated tubes, commonly called
"socks", by folding a strip of the nonwoven fabric 10 on
itself, and sealing the edges of the lengthwise portion, as
at 12 and one end, as at 14, leaving one end, 16, open.
Referring to Figure 2, the filter sock 10 is shown in
place in a representative pressure filter system. Numerous
types of such in line systems are made by various
manufacturers. The representation of Figure 2 is not meant
to depict any particular system, but only to convey the
working relationship of the elements common to all such
systems. No part of the partial system shown in Figure 2 is
claimed as an element of this invention apart from the
filter sock 10.
Milk under pressure is pumped into a milking chamber
20, from whence it is forced through the nonwoven filter 10,
supported against collapse by being mounted on an open
armature 18. Various types of armatures are used, the
illustration here being of a semi rigid metal coil. The
milk chamber 20 is totally enclosed, the closed end of the
chamber and the sealed end 14 of the sock 10 not being
shown. Milk passing through the sock 10, as at A and B,
passes into the armature 18, and under pressure is forced
out of the exit end 26 of the armature 18. The open end of
the sock 16 is held tightly into the system by a gasket
arrangement 24.
It has been found that in order to obtain the desired
balance between fast flow time and acceptable se~ -nt
retention under pressurized flow o~ 20 polln~c or more per~
square inch a composite fabric as disclosed herein must be
used.
Figure 3, illustrates the present invention which has
an inner layer of continuous filaments 28 and an outer layer
of a fibrous web 30 having a blend of staple fibers bonded
together by an aqueous binder 32. The continuous filaments
28, may be purchased under the trademark Remay 2011, which
is made by E.I.DuPont Company of Kingsport, Tennessee. For
the purpose of this specification, the inner layer is
defined as the layer on the inside of the filter which is in
contact with the open`armature 18 while the outer layer is
the layer that comes into contact with the fluid first, as
shown in Figure 2, whereby the fluid is flowing into the
filter as at A and B. The continuous filaments consist of
continuously extruded hot melt polymeric fibers of a
polyester polymer or a co-extrusion containing up to 10% of
low temperature melt fibers which act to stabilize the
filaments. The weight of the inner layer of filaments may
be between 0.6 ounces per square yard (oz./sq.yd.) and 1.3
oz./sq.yd. Although the preferred denier is 4 for the
continuous filaments the denier may be between 4 and 12.
The inner layer may have an air permeability of no less than
600 cubic feet air per square feet minute
(cu.ft./sq.ft.min.) at a differential pressure of 0.5 inches
of water. The inner continuous filament layer weight
contribution to the finished filter fabric is 20%-35% by
weight of the fabric. The continuous filament contributes
50-65% of the tensile strength in the cross direction of the
fabric and 35-45% of the tensile strength in the machine
direction of the fabric. The remaining tensile strength
both in the machine direction and the cross direction of the
fabric is derived from the chemical aqueous binder that
produces adhesion between the carded fibrous web fibers and
the continuous filaments.
g
The blend of the outer fibrous web comprise between 40
and 55% of the total weight of the filter. Three different
denier fibers are blended together in the composition of the
outer fibrous web. The fibers that are in the blend may
consist of about 1.1 to 1.5 denier polyester fiber, about a
3.0 to 3.5 denier rayon viscose fiber and about a 5.5 to 12
denier rayon viscose fiber. The 1.1 to 1.5 denier polyester
fibers and the 3.0 to 3.5 denier rayon viscose fibers are
the pore controlling elements in the fibrous web. The size
of the pores in the fibrous web are controlled by varying
the amount and ratio of the aforementioned fibers used. The
5.5 to 12 denier rayon viscose fibers permit larger paths
for the fluid to flow through. This is accomplished by
varying the amount of fiber. By varying the amount of this
fiber, the flow time of the fluid can be controlled. Thus,
making the present invention superior to the prior art. To
acheive the maximum retention and flow time the following
amounts and ratios of the aforementioned fibers were used in
the present invention. The preferred fibers of this
invention that are blended together consist of a 1.5 denier
1.5 inch long staple 100% polyester fiber, crimped, without
an optical brightener and with a finish on the fibers that
is approved by the Food and Drug Administration (FDA), a 3.0
denier rayon viscose fiber, 1.5 inch long staple, crimped,
without brighteners and with a finish approved by the FDA,
and a 5.5 denier rayon viscose fiber, 1.5 inch long staple,
crimped, without optical brightener and with a finish
approved by the FDA.
The percent of each fiber used in the present invention
to acheive effective filtration and practical flow rates may
be about 15-35% of 1.5 denier Polyester fiber, about 25-50%
of 3.0 denier rayon fiber and about 15-40% of 5.5 denier
rayon viscose fiber. The combination of the above providing
100% of the outer layer fiber weight.
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The total weight of the filter fabric may be between
about 40 and 80 grams per square yard (g/sq.yd.) with the
preferred wei~ht being about 75 grams/sq.yd..
The chemical binder is preferrably an aqueous anionic
dispersion of copolymers of acrylic esters carboxy modified,
heat reactive self crosslinking or crosslinked with urea
formaldehyde with adhesion affinity both to Polyester fiber
and rayon viscose fibers. The preferred being the self
crosslinking binder. Although the preferred content of
active binder in the dry and finished filter is 25% of the
finished product weight, the content of active binder in the
finished product weight may range between 20-35%. The
purpose of the binder is to produce adhesion areas between
the rayon viscose fibers and polyester fibers of the outer
layer, and between the inner continuous filaments and the
outer layers of fibers without substantially decreasing the
flow of the milk as it is filtered through the filter
material.
The preferred finished filter weight composition is 48%
fibers, 27% continuous filaments and 25% binder. The
percentage of finished fiber weight may range between 40-55%
of fibers, 20-35% of continuous filaments and 20-35%.of
binder.
The per cent retention of solid contaminants in the
milk that are retained in the filter and the flow rate
expressed as flow time are the determining factors of the
functionality of the in-line milk filter. They are the
limiting factors in which to obtain the optimum pore size
distribution, and the number of pores per unit area. These
limiting factors are obtained by the proper proportion of
the different denier type fiber, the fiber density on the
continuous filament layer and the ratio o~ binder to the
fiber weight.
J /
The flow Rate and retention limits for end use filters
in the filtration of milk consist of the following
established industry specifications:
Flow Time (seconds)------------ 25 seconds maximum.
Retention (Alundum -280 mesh)-- 70-80%
In testing filter material for filtration efficiency,
it is desirable to use a reproducible laboratory test, since
the amount and fineness of natural sediment encountered in
actual farm filtration will vary widely from day to day.
For this purpose a finely divided silicon carbide is used,
in a fineness of 280 mesh, which has an average particle
size of about 70 microns. Five grams of this silicon
carbide are suspended in 5 gallons of water and filtered
through a wet-out piece of filter material mounted in a
conventional metal milk strainer. The time necessary to
complete the five gallon filtration is recorded, after which
the filter, containing retained sediment, is dried to a bone
dry condition in a microwave oven. The amount of silicon
carbide after drying, divided by 5, is the percent sediment
retained, and is expressed as percent efficiency of sediment
removal.
A test was made of the present invention which
comprised an intimate preferred fiber blend of 20% l.S
denier polyester fibers, 50% 3 denier rayon fiber, and 30%
of 5.5% denier rayon viscose carded into a fibrous web
weighing 38 grams per square yard. The fibrous web was then
laid onto a layer of continuous filaments and then bonded by
means of a dispersion of an acrylic polymer, and dried. The
final dried product weighted 74 grams and consisted of 75%
fiber, 25% binder. The web had a wet tensile strength, per
inch-wide strip, of 14 pounds in the machine direction, 8
ds in the cross direction, and a wet Mullen burst
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strength of 36 pounds. The thickness of the web was 28
mils, indicating a density of 0.127 grams per cubic
centimeter.
The flow time in the above-described test was 23
seconds, with 74% of the sediment being retained. When
fashioned into a filter sock, this filter material withstood
the pressures involved in a heavy duty, high pressure
system, in actual farm tests on sediment-laden milk, without
rupture or other signs of failure.
The present invention filter was also tested under
pressure using a DeLaval closed loop pilot unit. This pilot
unit is made by DeLaval Separator Company, located in Kansas
City, Missouri. Water was pumped through the filter in
line. The water was at room temperature and contained about
10 grams of suspended soil particles contaminant per 10
gallons of circulating water. A cycling to start and stop
the circulating pump produced maximum pressures of 18-20
psi. The filter was subjected to 10 cycles without
rupturing.
To illustrate that the present invention was superior
to the prior art, a comparison test was made using the same
test described above, between the present invention and two
(2) prior art filters that are prominent in the market
place. One of the prior art filters is a filter made by
Schwartz Company of Two Rivers, Wisconsin, under the
trademark "Tuffy". The other prior art filter is one made
by KleenTest Products of Milwaukee, Wisconsin, under the
trademark "Milk-Check". It should be pointed out that the
prior art filter from Schwartz only has in-depth filtration
capability to filter sediment within the filter media, and
the prior art filter from KleenTest only has surface
filtration capability to filter sediment on the surface of
the filter. There is no prior art with the capabilities to
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filtrate both at the surface and within the filter, as does
the present invention.
The following is a table showing the comparative data
of the test.
COMPARATIVE TABLE OF PHYSICAL PROPERTIES
Milk-Check Tuffy Present
invention
WEIGHT (gr./sq. yd.) 37 119 74
THICKNESS (mils) g.3 42 28
TENSILES (lb./in.)
MD (Wet) 9.6 10.4 14.0
CD (Wet) 9.0 9-0 8.0
FLOW TIME (sec.) 42 25 23
RETENTION (%) 86 8S 74
The importance of the presented data is to show that
the present invention acheived a lower flow time, higher
tensile strength while having in-depth and surface
filtration and a substantial retention rate. It may be seen
from the data that the-present invention is superior over
the prior art. Although the prior art "Milk-Check" had low
weight, low thickness, and a high retention rate, it had a
high flow time, which was double that of the present
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invention. Thus, the prior art filter would clog with
sediment faster than the present invention, and have to be
changed more often, making it expensive to use. The present
invention is superior to the prior art "Tuffy" because the
"Tuffy" filter had to have 61% higher weight and 66% thicker
material than the present invention to acheive substantially
the same flow time and retention as the present invention.
The present invention is therefore more economical than the
aforementioned prior art.
The innovative aspect of the present invention material
is in the fact that the amount of sediment removed from the
fluid remains substantially the same while the flow time is
reduced. This is caused by the entrapment of particles by
pores in the inner layer and outer layer of the present
invention filter. Entrapment of particles between the inner
and outer layers is referred to as "surface filtration".
For the purpose of this application surface filtration is
further defined as the entrapment of particles by the
combination of the pores in the inner and outer layers in
the area where the inner and outer layers meet. This
surface filtration is combined with the filtration that
takes place in the outer layer of fibrous web. The outer
filtration is referred to as "in-depth filtration". The
outer fibrous layer of the present invention contains a
blend of different sized denier fibers. The voids between
these fibers are por~s in the outer layer. The pores are a
result of the random alignment of the fibers with each
other. The pores that are formed in the outer layer are 80
microns or smaller. It should be noted that there is a
probability that there would be about lS% of the pores in
the fibrous web that are larger than 80 microns. The larger
pores would permit larger particles to pass through the
fibrous layer, but the larger particles would be trapped at
the intersection of the inner and outer layers. That is the
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reason why surface filtration is important. If there were
no surface filtration, the large particles of sediment would
pass through the filter and stay in the fluid. In-depth
filtration is defined as the entrapment by pores smaller
than the particle flowing through the filter and the
attraction of the particle to the surface of the fibers
within the outer layer. These particles r~- ~i n i ng attached
thereto by electrostatic forces.
In addition to the comparison test between the prior
art and the present invention a pore distribution analysis
was made of the prior art and the present invention to get a
statistical distribution of pores to determine which filter
was more efficient. This analysis was done on an Optimax
system that is made by the Optimax Corporation of Hollis,
New Hamphire. This Optimax system is a television scanning
image analysis which makes two dimensional measurements of
features selected from any image which can be received by a
T. V. camera. It measures area covered by the detected
features, counts the number of selected features, counts the
number of times the scan line crosses a feature trailing
edge, shows the distribution of size based on feature
maximum horizontal chord, and shows the distribution of size
based on feature area. As a result of the analysis, bar
charts were drawn and are illustrated in Figure 5 for the
prior art "Tuffy", Figure 6 for the prior art Milk Check and
Figure 7 for the present invention.
Figure 8 illustrates the use of Alundum 280 in testing
milk filters so as to simulate farm/soil contAminAnts.
Using Alundum 280 as the simulated soil permits the tester
to arrive at the percent retention and flow time of a
filter. The average particle size is 75 microns with 85% of
the pore population ranging up to 110 microns, as show on
Figure 8.
Figure 6, shows the pore size distribution of
"Milk-Check" with the average pore size being 25 microns
with 85% of the pore population ranging up to 75 microns.
Filtration of particles takes place at the surface of this
filter.
Figure 5, shows the pore size distribution of "Tuffy"
with the average pore size being 30 microns with 85% of the
pore population ranging up to 85 microns. Filtration of
particles takes place within the depth of this filter.
Figure 7, shows the pore size distribution of the
present invention with the average pore size being 25
microns with 85% of the pore population no larger than 85
microns. The present invention has both surface and
in-depth filtration.
Of particular interest, and which makes the present
invention substantially`superior to the prior art, is that
the present invention has its highest pore count of 48 at
its average, as compared to 25 for the ~Tuffy" filter and 35
for the "Milk-Check" filter. Three other bars on the graph
for the present invention, respectively at 20, -30, and 35
microns also have high frequencies, thus indicating a tight
and uniform distribution of pores based on the present
inventions dual filtration capability. On the other hand
the prior art graphs illustrate that their pore size spreads
out from the average indicating a loose and scattered
distribution of pores. The present invention therefore has
superior pore distribution making it more efficient than the
prior art. Efficiency being defined as the per cent
retention combined with the flow time.
The construction of filter material such as in the
present invention permits the top fibrous layer to act as a
in-depth retention layer, ret~;n;ng about ~5% of the total
se~ retained in the filter and permits the bottom layer
of continuous filaments to act as a surface filtration and
to retain 15% of the total sediment retained in the filter.
The surface retention and in-depth retention of sediment of
the present invention had the unexpected result of not
interfering with the flow of the fluid as one might expect.
This is evident in the aforementioned comparision test. The
flow time of the fluid was substantially the same or better
than the prior art filters. The aforementioned
characteristics were obtained in the present invention
filter by the use of fibers made of different deniers as
mentioned in previous paragraphs. In addition, the
incorporation of a base of continuous filaments provides
high tensile strength to the present invention filter in
both the cross and machine direction of the filter material.
With this high tensile strength the present invention filter
will not fail when subjected to pressures normally found in
pressurized in-line filtration systems.
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