CA1181017A - High performance fibrillated film wound filter cartridge - Google Patents

Abstract

Abstract The invention relates to filters of the helical precision wound type in which the strands are of a yarn formed from highly fibrillated polymer film. In one form of the invention a conventional filter cartridge of about 2-7/16 inch overall diameter on a core of about 1-1/8 inch diameter is prepared by winding a highly fibrillated film yarn or 10,000 total bundle denier, a fibril denier of less than 50 and greater than three percent broken fibrils onto a cartridge of any desired length.
This cartridge exhibits much higher life and efficiency than previously available fibrillated film filter cartridges.

Description

Field of the Invention This invention relates to improvements in the construction of filtering devices. It particularly relates to precision wound filter tubes comprising helically wound layers of yarn or 5 roving.
Description of Prior Practices It has been long known that filters may be formed by constructing a tubular element comprising a foraminous core precisiQn wound with a multiplicity of layers of spaced con-lo volutions of strand applled in criss-cross fashion to form a plurality of diamond shaped filtering passages through the sidewall of the element ~hrough which the fluid to be filtered is caused to pass. The fluid passing through khe filter is clarified as particles in fluid adhere to the fibrous strands.

15 The cartridge may be napped durlng winding to create additional loosely held fibers which occupy the passages and capture dirt partlcles. Reissue Patent No. 22,651 to Hastings et al is an example of such a filter. Such filters suffer from the disad-vantage that when being used the filter suffers failure by 20 excessive pressure drop prior to the fibers being totally or predominantly coated with the particles being filtered from the fluid. The loading of the filter is generally thought to occur by large particles which coat and block the outer portion of the filter. Ordinarily the filtering direction is from the 25 outside to the inner portion of the filter.

i11) 1'7 It has also been known to wind filter cartridges using yarns made from fibrlllated f`ilms ordinarily of polypropylene.
While these cartridges of polypropylene are advantageous in that they do not have a finish on the fiber and therefore are very suitable for filtering food materials, they suffer from the disadvantage that they do not have the ability to trap as large an amount of dirt in the cartridge as a cartridge wound with textile roving and further they do not have as high an efficiency which means that they do not filter as much dirt, especially fine particles, from the material fed to the cartridge as would be desirable.
U.S. Patent No. 3,~28,934 to Green et al suggests that filters can be wound using a filter material composed of fibers attached to a substrate, such as by flocking. The method disclosed by Green et al calls for providing a windable strand material with a plurality of fibers attached thereto by one fiber end only. The fibers are attached to the strand by an adhesive. Choice of the adhesive must vary according to the chemical nature of the fluid being filtered to avoid situations wherein the fluid being filtered would dissolve the adhesive.
In addition, the cost of adhesively bonding the fibers to the strands has been found to be economically prohibitive.
Therefore, there is a need to provide a highly fibrillated winding material that is both economically viable and which can be used for filtering a broad variety of chemically active fluids while still providing good filtration performance and filter medla integrity.
In addition to the wound cartridges utilitzing fibrillated film yarn, there also has been proposed such as shown in United States Patent ~o. 3,904,798 to Vogt et al that filters of variable density be formed by extrusion of flbers dlrectly onto a rotating collection device. However, such a process is expenslve to control for unlrormity, the process is llmited to extruded ~lbers rather than roving or napped fibers and the S process does not readlly lend ltself to the formatlon of well defined efficiency rating categories in comparison to the con-ventional filters produced on the presently available winding equipment used to form precislon wound cartridges.
In ~eneral, precislon wound ~ilters are formed by mounting the core, horizontally, on a motor driven spindle. One end Or the strand of filtering material can be tled or otherwise fixed to one end of the sidewall of that core. The strand passes through a guide which is set up, through a gear train or simi-lar arrangement to maintain a precise relationship between rotations of the core and traverse o~ the ~uide, to move back and forth along the length of the core, as the core is rotated.
As the guide travels in one directlon along the rotating core, ~
a spiral of strand is wrapped around the core from one end to the other. When the gulde reaches the far end of the core, it reverses in direction and travel~ back to the beginning point.
During this travel in the reverse direction, the core contlnues to rotate in the same direction. Thus a reverse spiral of strand is laid down on the core overlaying the original strand spiral, forming a succession of diamond patterned layers.
Brief Description of the Drawlngs Fig. l illustrates the complete diamond pattern layer of a precision wound filter cartridge whlch has been split longitu-~
dinally along one surface of the cartridge, opened up and laid rlat .
Fig. 2 is a pro~ection illustration of a diamond ~rom the diamond pattern of Fig. l, showing the arrangement of the filter strand overlays.
Fig.l 3 ls a side view Or Fig. 2 illustrating the depth dimension of a diamond as well as the arrangement of the filter strand overlays.

V~7 Fig. 4 is a cross sectional view of a conventional filter cartrid~e sectioned in a plane perpendicular to its longltudi-nal axis.
Flg. 5 is an lllustration of an enlarged section of an example of standard ~ibrlllated polypropylene film.
Fig. 6 is an illustration o~ an enlarged section of an example of highly ~ibrillated fllm accordin~ to the present inventlon.
The diamond pattern, as it is wound on the core as described above, is illustrated in Fig. 1 of the drawings.
Fig. l shows a cylindrical core which has been cut axially alon~ one wall and then rlattened out. Keeping in mind that the strand is continuous, each strand spiral wound on the core, by the traverse of the gulde ln a single direction, is designated by~ a letter. The order in which each strand spiral -3a-n.~ ~

has been wound is alphabe-tical. Thus, beglnning in the lower left hand corner of Fig. 1, the strand is tied to the end o~
the core and is designated as spiral a. It is wound around the core as the guide moves in a direction from the bottom of Fig.
1 to the top. Thus it will be noted, in Fig. 1, that every fourth line sloping upwardly from left to right is designated as spiral a. When the guide reaches the far end of the core, represented by the top of Fig. 1, the end of spiral a is reached and spiral b begins as the guide reverses direction.
This is designated as a-~b at the top of Figo 1. Spiral b ls wound in the reverse direction from spiral a and is shown by lines sloping downwardly from left to right, and every fourth of these lines is designated as spiral b.
When spiral a has been wound and spiral b has been wound in overlay on top o~ spiral a, the guide has traveled the length of the core twice, from the beginning end of the core to the far end, then revers~ng directions, back to the beginning end. Thus the guide has traveled through one cycle, from its beginning point back to that same end of the core. It will be noted that spiral a has made precisely 3-5/6 complete winds on the core and that spiral b also has made precisely 3-5/6 complete winds. Adding this together, it will be apparent that the core has been rotated precisely 7-2/3 tirnes during one cycle of the guide.
Again referring to Fig. 1, the guide, during one complete cycle, returns to the beginning end of the core, however, not to the same point on the circumference of the core at which it began. Along the bottom of ~ig. 1, it will be noted that spiral b does not end at the same point at which spiral a began; spiral b transcends into spiral c, designated as b-~c, at a polnt which is to be precisely two-thirds of the circum-ference away from the beginning of spiral a in the direction of rotation of the core. At this point, the guide direction of traverse again reverses, winding splral c. At the far end of the core, the guide direction again reverses and spiral d is wound to complete the second cycle of the guide. Again, the core has rotated precisely 7-2/3 times during this second cycle of the guide~ for a total of precisely 15-1/3 revolutions for precisely two guide cycles. Spiral c transcends into spiral d, designated as c-~d, at the far end o~ the core9 at the top of Fig. l, and spiral d is wound in the re~erse direction of spiral c. At this point four spirals have been wound, spirals a and c being in the same direction and generally parallel to each other, and spirals b and d being in the same direction, opposite to the direction of spirals a and c, and also generally parallel to each other, as depicted in ~ig. 1. And spiral d ends at a point-which is to be precisely two-thirds of -the circumference away from the beginning of spiral c in the direction of rotatlon of the core.
At the end of the second cycle of the guide traverse, spiral d transcends into spiral e, designated as d~e at the bottom of Fig. 1 and a third guide traverse cycle begins, winding spiral e which transcends into spiral f at e-~f as shown at the top of Fig. 1. Again, the guide reverses its direction of traverse at the far end of the core and winds spiral f in the opposite direction to the winding of spiral e.
At the end of the third guide traverse cycle, spiral f ter-minates at a point which is to be at precisely the same point on the beginning end of that core where spiral a began. At this point one complete layer of diamond patterns has been i~ )l'7 wound. During the thlrd cycle of spindle traverse, the core has, again, been rotated precisely 7-2/3 times, now totalling precisely 23 revolutions for three complete guide traverse cycles.
In the parlance of the filter lndustry, the "wind number"
of the filter cartridge shown in Fig. 1 is three, equal to the number of guide traverse cycles required to wind one complete layer of diamond patterns. The number of circumferential diamonds which appear on the filter cartridge is equal to the wind number. Another term that ls used in the industry is "wind ratio". This ratio is set up as a fraction with the "wind number" on the bottom and the number of revolutions, which were turned by the core during the winding of one complete layer of diamond patterns, being on top. The filter cartridge shown in Fig. l was rotated 23 times, during three guide traverse cycles, to form one complete diamond pattern.
Thus the "wind ratio" is-23/3 or 7-2/3~ This is equal to pre- -cisely the number of revolutions which the core turned to complete a single guide traverse cycle, from one end to the other and back along the rotating core.
It turns out that the number of "axial diamonds", or the number of diamonds along the longitudlnal axis of the filter cartridge, is one-half of the number of times the core was ~`
rotated to wind one complete diamond pattern layer. For the filter cartridge illustrated in Fig. 1, the core was rotated 23 times to wind one complete diamond pattern layerg thus the number of 'laxial diamonds" is meant to be precisely 11 1/2. It also turns out that the total number of diamonds on the face or surface of the cartridge is the product of multiplying the number of revolutions required to wind one complete diamond pattern layer, with the number o~ guide traverse cycles required to wind one complete diamond pattern layer. For the filter cartridge illustrated in Fig. 1, the core was rotated precisely 23 times and the guide went through precisely three traverse cycles to form one complete diamond pattern layer.
Thus 23 x 3 = 69, precisely the number of diamonds to be formed on the surface of the filter cartridge, including half diamonds at the ends of the core.
Again, referring to Fig. lg initially, spiral a was wound, followed by spiral b in a reverse directionP This formed a diamond pattern which was three times the size Or the diamonds which ultimately form the first diamond pattern layer. This is shown in dotted outline about the vertical center of FigD 1.
Spiral b overlaps spiral a. Next spirals c and d were wound, with spiral c overlapping spirals a and b and spiral d overlapping spirals a, b and c. What was then formed within that original large diamQnd pattern were two parallelograms, one small diamond and another diamond twice its size. This is shown in dashed outline in combination with the dotted outline of Fig. 1. Flnally spirals e and f were wound, with spiral e overlapping all of the foregoing spirals and spiral f overlapping all those other spirals including spiral e. What was finally formed are nine essentially equivalent diamonds within the original large diamond. This is shown in dot-dash outline, combined with the dotted outline and dashed outline of Fig. 1. One of those diamonds, having the letter "d" appearing on it, was formed of spiral a, crossed by spiral b, which in turn were both crossed by spiral c, and finally spirals a, b and c were crossed by spiral do This criss-cross formation is illustrated in Fig. 2, in enlarged section, projection view.

Ii~1017 Because of this criss-cross formation, a third dimension, depth, is added to the diamond pattern, each diamond approachingg in depth, about an average of 2-1/2 times the nominal diameter of the strand material of each spiral, as illustrated in Fig. 3 which shows an elevational, or side view, of the diamond illustrated in Fig. 2.
Typical filter cartridges have a core with an outside diameter of about 1~ inches and an outside diameter of about

2~7/16 inches with a filtering medlum, or build up of strands, that is about 11/16 inch thick, give or take about 1/16 inch on all dimensions. The filter is wound in a range of approx-imately 15~ to 200 guide traverse cycles, and for the standard ten inch long filter, the ratio of circumferential diamonds to a~ial diamonds is usually within the range of about two to about five. That is, for each circumferential diamond, there are about two to five axial diamondsO Among the commonly available filters, the coarsest winds have a wind number of about six and the finest winds have a wind number of about 39, and the number of complete diamond pattern layers ranges from as many as about 25 to as few as about four.
Of course, as each successive complete diamond pattern layer is wound on the one before it, the overall diameter of the cartridge increases, and the distance around the circum- ~-ference increases, but the number of diamonds around the cir-cumference remains constant, because the wind number, or number of guide traverse cycles, is set as a constant at the beginning, as is the number of core rotations for each complete diamond pattern layer. The shape of the diamond changes as the diameter of the filter cartridge increases with each suc-cessive complete diamond pattern layer. Referring to Fig. 1, the diamonds increase in length, sideways, as the circumference dimension lncreases, but the height of the diamonds remains constant because the length of the cartrid~e does not change.
Thus, the cross sectional areas of the diamonds increase, As viewed from the circular end of a filter cartridge, or more precisely, looking towards the cut end of a cartridge which had been sectioned perpendicular to the longitudinal axis of the cartridge, as shown in Fig. 4, it is noted that the diamonds, in addition to increasing in size along the circum-ference of the cartridge, as each successive complete diamond pattern layer is wound, also are symetrically displaced. The centers of each successive diamond, going from the center of the core to the outside diameter of the cartridge, are not aligned on a radius line. Rather, the centers are displaced to ~orm a compound curve, or a helix, generally analogous to a snail shell as shown in Fig. 4. Thus the centerline of the passageway formed by the_successive diamond layers, from the core to the outside diameter of the filter cartridge, does not track a straight line, but rather~ follows the helix curve.
This phenomenon is caused by the displacement of the transition points, one spiral to the other, about the circumference of the filter cartridge, as each successive complete diamond pattern layer is wound. Such filter cartrldges are referred to as "helical" cartridges or "helically" wound cartridges. It is believed, by those with skill in the art, that this helix pat-tern of displacement of`the diamonds serves to create a tortuous path in the flow of fluids therethrou~h, thus aiding in the exposure of the diamond sidewalls to more particles of dirt, resulting in the entrapment of more dirt particles aOainst those sidewalls. Thus, as the theory goes, dirt particles which would otherwise pass through a larger diamond cross sec-tional area, would tend to cling to the sidewalls of that diamond, while the fluid flows on through. This is thought to increase ~ilter cartridge life by trapping, in the larger diamonds, dirt particles which would otherwise more rapidly clog up the lesser cross sectional areas of the smaller diamonds ln the layers nearer the cartridge core.
For each successive complete diamond pattern layer, one on top of the other, the cross sectional areas of the diamonds increase, and the voids inside of each diamond increase in size, resulting in additional space, in each such layer, for the pass-through of dirt particles to the layers beneath.
Where the diamond cross sectional areas become too large, for example where the overall diameter of the filter cartridge is increased too much, in comparison with the core diameter, the filter cartridge is known to loose its ability to trap dirt particles within those cQ~plete outer layers of diamond pat- -ternsO Simply, the dirt particles are too small and the holes through which they travel are too big. This problem can be overcome, generally, by using fibrillated strand material wikh fibrils extending from the strands to position a portion of the filterin~ media within the voids of the complete outer layers of diamond patterns. However, strand fibrillation has been a costly and difficult process as detailed in the above mentioned prior art. There remains a need for an economical improved highly ~ibrillated film cartridge of great efficiency, extended life and dirt holding capacity.
Summary of the Invention It is an ob~ect of this invention to overcome disadvan tages of prior filters made from fibrillated film yarns and processes using these filters.

It is an additlonal obJect of this lnvention to create an improved helically wound fibrillated film cartrldge.
It is an addltional obJeet of this invention to provlde improved dirt holdlng eapaeity ln a wound fibrillated film S fllter cartrldge.
It is another further obJeet of thls lnvention to provlde a fibrillated fllm eartridge of lncreased effieiency.
These and other ob~ects of the inventlon are generally accomplished by providing filters of the preeislon wound type in whieh the strands are of a yarn formed from hlghly flbrillated film.
¦ In a particularly preferred form of the invention a eon-¦ ventional filter cartridge of about 2-7~16 inch overall I diameter on a core of about 1-1/18 inch dlameter was prepared ¦ by windlng a highly ribrillated film yarn of 10,000 total bundle denler J having a f~bril denler of less than 50 and con taining greater than three percent broken fibrils, onto a cartridge Or any desired length. This cartrldge exhibits much higher llfe and efficiency than previously available fibrlllated film filter cartridges.

Detailed Descrlption of the Invention The filter cartridge and filtering process of the inven-tion has a decided advantage over pr~or art fibrillated film cartridges. The cartridges of the invention have up to about 3 times longer llfe while exhibiting greater efficiency than pre-vious cartridges using standard fibrillated fllm yarns as shown in Fig. 5. The cartridges have greater dirt holding capacity and are able to trap more fine particles of matter from the fluid passing through it ~han prlor cartridges. Further the lo instant cartridges have the advantage that the technique of forming the cartrldge remains the same as for prior wound cartridges, therefore making the increase ln performance possible wlth no addltional capital outlay for winding equipment.
In the instant specification the following terms of art are utllized ln accordance wlth the deflnitlons below which are considered to be in accordance with their accepted meaning in the cartridge filtering art:
efficiency (particle size) percentage removal of a given size particle as determined from the ratio of downstream number or ~ 7 weight of partlcles of that particular size to the number or weight of that particular si~e particle ln S the upstream fluid from a filter. An efficiency rating would be stated 9 for example~ as "90% at 10 microns".
wind number number of circumferential diamonds on the surface of a cartridge taken at the locus of points creating a circle in a plane perpen-dicular to the axis of the filter.
wind ratio _ equals spindle revolutions -divided by guide traverse cycles (complete traverse cycles of the guide mecha nism up and back to the starting end of the core).
dirt holding capacity (DHC) the amount or quantity of ~
dirt fed to a filter cartridge up to the point where the pressure drop between the inlet and outlet of that filter reaches 30 psi. (also referred to as life of the cartridge). This term does not mean the amount of dirt held by the cartridge as of the point where the pressure drop reaches , 30 psi, pressure drop the change in pressure between input fluid and fluid exiting a cartridge during filtering.
diamond the area defined by a first pair of adjacent, spaced-apart substantially parallel strands and a second pair of adjacent, spaced-apart substantially _ parallel strands that crosses said ~irst pair in . a precision wlnding on a filter cartridge. The extension of this defini-tion to fractional half-diamonds at the end of the filter cartridge will be apparent.
diamond pattern is the complete winding to form one layer of circum-ferential diamonds, i.e., 13 cycles of the traverse are required to form a 101~ ~

complete diamond pattern for a 13 I'wind number"
cartridge.
flbrillated film yarn a yarn made by orienting a polymeric film suf~iciently to cause it to separate into a fibrous structure (fibrils). The geometry and degree of separating into fibrils can be controlled and/or enhanced by several techniques known to those in the art, such as embossing or perforating.
highly fibrillated film yarn a fibrillated film yarn in whi.ch about 3% or more of - the auxiliary fibrlls are broken on one end from the main fibril strands, in which the auxiliary fibrils are about one-half lnch (1.25 cm) or more in length and are of an average denier of about 70 or less.
~5 It is known that in a precision wound filter, increasing the number of circumferential diamonds (finer winding) provides higher efficiency, but that it usually shortens the cartridge life. Conversely decreasing the number of circumferential diamonds (coarser winding) provides greater cartridge life but with lower efficiency.

.017 By way of example only the following table provides a com-parison of the properties of typical highly fibrillated yarns as compared to typical standard fibrillated yarns.
PROPERTY HIGHLY FIBRILLATED STANDARD FIBRILLATED
Yarn denier lO,OOO average 10,000 average Total fibrils in 200-600 50-75 cross section Total main 8-25 percent 30~50 percent fibrils Total aux. 75-92 percent 50 70 percent fibrils Aux. fibril 1/2 in. to 3/1~ in. 1/8 in. to 3/8 in.
length Aux. fibrils 6-10 1-4 per inch of main fibril Percentage of 3-50 percent 0-1 percent broken aux.
fibrils ~ilm thickness l.O to 1.75 mil 2.0 to 2.5 mil avg. 3~ micrometers avg. 57 micrometers avg. ~i5 mil avg. 2.25 mil It is well ~nown that reducing the average cross-sectional area (denier) of a fibrous assemblage reduces 1ts bending modu-lus (stiffness). Ordinary fibrillated film yarns are usually produced such that the bending modulus is reduced while main-taining tensile properties of the strands. The highly fibrillated film yarns used to make the cartridges of the pre-sent invention are produced with stretching of the film to an extent sueh that only tensile properties sufficient to permit winding are retained while significantly reducing the average cross-sectional area (denier) of the individual fibrils. Thus the preferred highly fibrillated film yarns have an average fibril denier less than about 50 and more than 3 percent of the fibrils are broken. The total bundle denier may be any denier ``\ ~ o~

that gives good filter performance. A total bundle denier of about lO,000 has been found to be satisfactory.
Filter cartridges made from highly fibrillated yarns have been found to be much more efficient in removing particles than cartridges of the same wind number made with ordinary fibrillated film yarn. Additionally, the life of the highly fibrillated film yarn cartridge usually increases relative to those made with ordinary fibrillated film yarns. It has been found that a significant increase in life without loss in effi-ciency is achieved with highly fibrillated film yarns when the wind number is reduced (coarser winding). Improvements in life of up to threefold that of those made from ordinary fibrillated film yarn are possible. This amount of improvement in both life and efficiency generally can be achieved be forming the highly fibrillated cartridges at one or kwo wind numbers lower (coarser) than those made with ordinary fibrillated film yarn.
The preferred highl~ fibrillated film yarns of the inven- -tion may be formed of any film forming polymer. Typical are polyesters, polyethers, polyethylenes, polysulfides, polyacry-lics, fluorinated polymers, polyvinyl chlorides, polypropy-lenes, rubberized styrenes and polyamides. A preferred material has been found to be the polyolefins as they are low in cost, are easily fibrillated and are suitable for use in food products. The optimum material has been found to be polypropylene as it is lowest in cost and is easily worked to form fibrillated films and is safe for food products.
It has been found that for the conventional, about 2-7/16"
diameter, cartridges a wind number of between about lO and about 13 is preferred, for A.C. coarse test dust, as the highest performance is in this range with greatly increased life and higher efficiency. As is apparent from the above set ~ 7 for~h definitions a specific wind number cartridge has that specific number of circumferential diamonds at any circumferen-tial circle, i.e. a 13 wind number cartridge has 13 circum-ferential dlamonds. The ratio of axial diamonds to circum-ferential diamonds per 10 inch length of the cartridge is typi-cally kept about between about 2 and about 5. The preferred ratio is between 2.5 and about ~ for good filtering perfor-mance. The optimum ratio is between about 3 and about 3.5 as this ratio gives the best filtering performance and ease of winding.
Because fibrillated film yarns are derived ~rom films, even though the yarns may be nearly circular in cross section, ¦ when they are wound under tension, they tend to flatten out.
Thus, the effeckive strand width is greater than textile lS rovings and the opening of any given diamond, vis-a-vis a corresponding textile roving diamond, is smaller for fibrillated fllm yarn where comparable bundle deniers and the same wind numbers are used. Above about 13 wind number, lOgO00 total denier fibrillated film yarn produces overlapping diamonds because of this flattening phenomenon and filtration performance (life) is significantly reduced. By using a fibrillated film yarn with a relatively smaller cross-section (lower total denier) it is believed that more definite but ~-relatively smaller diamonds (greater wind number) would be possible. It is believed that highly fibrillated film yarns of even lower denier could be utilized at even higher wind numbers as the packing of the finer yarns would not be as tight.
The following examples illustrate the dramatic improvement in performance obtained by the instant invention, Three different fibrillated film yarns were made by extruding polypropylene films, orienting (stretching) the ~ilms, generally contactin~ the films with embosslng rolls to cause separations into a fiberous-like structure (fibrillation), slitting the films into appropriate widths to yield lO,OOO total bundle deniers, and winding the yarns onto supply bobbins.
The first yarn was used to make standard fibrillated film yarn filter cartridges which are identified as "ORD" in the following examples. It was made from a polypropylene film about 0.00225 inches thick (2.25 mil approx.) Orientation and embossing produced a network of main support strands and auxi-liary fibrils about as shown in Fig. 5, the main strands averaging about 173 denier There were about four auxiliary fibrils per linear inch of main strand. The auxiliary fibrils averaged about 22.5 denier and were about 3/8 inch long~
Essentially all of the auxiliary fibrils were connected at both ends between main strands as shown in Fig. 5. The yarn pro-duced with this film is similar to yarns available, for example, from Blue Mountain Industries, Anniston, Alabama (Type 1300) and EB Industries, Inc., Senisbury, Connecticut (Type 6700).
The second yarn was used to make the fibrillated film yarn cartridges which are identified as "HIGH" in the following examples. It was made from a polypropylene film about 0.0015 ~
inches thick (1.5 mil approx.). Orientation and embossing were essentiall~ identical to that used to produce the first film yarn as described above. However, the orientation and embossing produced a network of main strands and auxiliary fibrils about as shown in Fig. 6. The main strands averaged about 107 denier. There were about eight auxiliary fibrils per ~ ~ 7 linear inch of main strand. The auxiliary ~ibrils averaged about 5/8 inch in length and were about 22.4 denier.
Approximately 10% of the auxiliary fibrils were broken from the main strands on at least one end.
A third yarn was used to make the fibrillated film yarn cartridges which are identified as "EXTRA HIGH" in the following examples. It was also made from a polypropylene film about 0~0015 inches thich (1.5 mil approx.). Orientation was essentially identical to that used to produce the first and second film yarns. However, the contact area of the embossing rolls with the film was increased. This resulted in main strands which averaged about 107 denier, as in the second yarn described above. -There were about eight auxiliary fibrils per linear inch of main strand. However, the auxillary fibrils averaged only about 12 denier and were about 7/8 inch in length. And about 50% of the auxiliary fibrils were broken from the main strands on~at least one end.
A series of precision wound filter cartridges were formed from each of the three yarns described above utilizing a cartridge core of per~orated tinned steel of a diameter of about 1-1/8 inch, The cartridges were wound in 10 inch lengths to an overall dlameter of about 2-7/16 inches. All of the cartridges were formed at a spindle speed of about 650 rpm.
The cartridges were formed with a ratio of total diamonds of between 3 and 3.5 axial diamonds to circumferential diamonds on the 10 inch cartridge. The roving tension was between about 400 and 800 grams for winding of all cartridges. The winder was a Leesona winder which utilized a back plate which pressed against the turning cartridge after about the formation of the first 8th inch of windings. The cartridges average about 200 gms of yarn. Back plate pressure was adjusted to give finished `~` ~ 7 cartridges with air density as shown ln the table below~ ~ir density is the pressure drop measured in inches of water at 3.9 scfm airflow.
After formation, each cartridge was tested in flow.ng water containing A.C. Coarse Test Dust from the A.C. Spark Plug Company. A.C. Coarse Test Dust as available from A.C. Spark Plug Company contains particle size distribution as follows:
weight percent at micrometer: 12% at 0-5; 12% at 5-10; 14% at 10-20; 23% at 20-40; 30% at 40-80; 9% at 80-200. The water was flowing at a rate of about 3.5 gallons per minute during testing and the test was stopped at a pressure drop across the cartridge of about 30 pounds or when no increase in the pressure drop was occuring. The test results f'rom each cartridge are displayed in the listing below. This listlng illustrates that highly fibrillated film yarn filter cartridges exhibit greater efficiency and generally greater dirt holding capacity than those made ~ith ordinary fibrillated film.
Additionally, when the wind number of the highly fibrillated film yarn filter cartridges is reduced as much as two values both the efficiency and dirt holding capacity are still higher relative to the finer wound ordinary fibrillated film cartridges.

-\ ~ 7 Chart No. 1 EFFICIENCY
Yarn (Percent at Fibrillation Wind Air Micrometers) Ex. Degree No. Density DHC~ 5~m 10~m ?0~m 30~m 50~m la ORD 8 0.3 no Too low to measure lb EXTRA HIGH8 0.4 2 PSID 10 14 20 25 30 2a ORD 10 0.4 0.2PSID -- 9 12 15 18 2b HIGH 10 1.0 227g 2040 55 62 75 2c HIGH 9 o.6 5PSID 2025 30 38 56 3a ORD 11 o.6 3PSID 2023 28 32 35 3b HIGH 11 1~5 35g 8996 9999.4 99O9 4a ORD 13 3.3 13g 3744 5458 64 4b EXTRA HIGH13 5.1 57g 6894 98100 100 4c HIGH 12 2.0 79g 5465 7679 89 *Dirt Holding Capacity (DHC) is expressed in grams fed to achieve 30 psld (pounds per square inch drop). Some cartridges do not achieve 30 psid. In such cases cartridges achieving higher pressure drop are considered to have higher dirt holding capacity. Those not achieving 30 psid substantially cease to provide filtering and me~ely pass dust fed after trapping an initial amount. In chart No. l, where filter cartridges failed to reach 30 psid, DHC is expressed in psid reach rather than grams fed to achieve 30 psid.
In Chart No. 1, examples la through 4c each illustrate that, at a given wind number, use of a highly fibrillated film yarn increases life (DHC) and concurrently provides signifi-cantly increased particle removal efficiency. In example 4, the highly fibrillated film yarn wound cartridges (4b and 4c) exhibit greater than four times the DHC, in comparison to those wound with standard fibrillated film yarn (4a), and, con-currently, about twice the particle removal efficiency.
Examples 2 and 4 demonstrate that because of the improved filtering characteristics of the highly fibrillated film yarn of the present invention~ filter cartridges can be made at wind numbers which are lower than those used for standard fibrillated film yarn` cartridges and still provide more effi-ciency and life (DHC) in comparison. By comparlng example 4a with 3b and example 3a with 2c, it can be seen that a filter cartridge made from a highly fibrillated film yarn provides a greater life (DHC) and a greater efficiency than a filter cartridge wound from standard fibrillated film yarn at two wind numbers higher.
Numerous modifications of this invention may be made without departing from the spirit and scope of the invention.
For instance, the cartridges may be formed in irregular shapes I rather than onto tuhes. ~urther, while the invention is set forth primarily with the conventional 2-7/16 nominal diameter filter tube, the invention is viable for any diameter tubeO
Further, the invention is viable for any length tubular filter and the invention may be utilized with highly fibrillated yarns of materials other than the demonstrated polypropylenes such as polyethylenes or polyestersO Further highly fibrillated yarns may be utilized of higher or lower total bundle denier which would result in a shift of wind number values to account for the change in dimensions of the diamond opening caused by yarn~
size difference. For instance lower bundle denier highly fibrillated yarns would be expected to reach best filter per-formance at higher wind numbers. The important factors of high fibrillated yarns which are low average fibril denier and the presence of broken fibrils are present at other total bundle deniers.
These and other modifications will be apparent to the per-son with skill in the filter art. For instance, the core 1.~
material also could be modified ko be other than tin material such as plastic or stainless steel, both of which are par-ticularly desirable in the food industry. Such modifications are within the scope of the invention. Accordingly, the inven tion is not to be limited except as set forth in the appended claims.

Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A filter cartridge comprising:
(a) a cylindrical tubular foraminous core, (b) a highly fibrillated polymer yarn stretched along an axis thereof to provide a yarn containing about 3%
or more integral broken fibrils having average denier of about 70 or less, and (c) said highly fibrillated polymer yarn helically wound about the outer surface of said foraminous core to form a continuous filtration surface thereon.

2. The device of Claim 1 wherein said fibrillated polymer film is less than 0.002 inches in thickness (2 mil.).

3. The device of Claim 1 wherein said fibrillated polymer film yarn is formed from a material selected from the group consisting essentially of polypropylene, polyethylene, polyester, polyvinyl chloride and rubberized styrene.

4. The invention of Claim 1 wherein said fibrillated polymer film yarn is formed from a material selected from the group consisting of polyolefins, polyethers, polyesters, polysulfide, polyamides, fluorinated polymers, and polyacrylics and mixtures thereof.

5. A method of forming a filter media of a highly fibrillated yarn comprising the steps of:
(a) extruding a polymer film to provide an elongated yarn, (b) orienting the film along its longitudinal axis, (c) contacting the film with an embossing roll to cause separations into a fibrous-like structure which contain about 3% or more broken fibrils having an average denier of about 70 or less, (d) slitting the film into preselected widths to yield 10,000 total bundle deniers, and (e) winding the film onto supply bobbins.

6. The method of Claim 5 wherein said fibrillated polymer film yarn is formed from a material selected from the group consisting essentially of polypropylene, polyethylene, polyester, polyvinyl chloride and rubberized styrene.

7. The method of Claim 5 wherein said fibrillated polymer film yarn is formed from a material selected from the group consisting of polyolefins, polyethers, polyesters, polysulfide, polyamides, fluorinated polymers, and polyacrylics and mixtures thereof.