CA1042172A - Apparatus for making a biaxially oriented nonwoven fabric - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
An apparatus is disclosed for manufacturing a nonwoven fabric having alternating stripes of high fiber density and low fiber density with substantially all of the fibers in the stripes of high fiber density oriented in substantially one direction, for example the machine direction, and substantially all of the fibers in the adjacent stripes of low fiber density oriented in a direction substantially normal to that direction. This phenomenon can be produced by a fluid propelling means for carry-ing discretely separated fibers in a fluid-borne stream, and a set of finger-like striping bars that are disposed, equidistantly from each other, directly over a moving conveyor screen or by a set of impervious resist areas in the shape of bars, or the like, disposed directly on the moving screen. As the fluid-borne stream passes onto the section having the striping bars or resist areas, a majority of the fibers in the stream are attracted to the spaces between the bars and are generally disposed in an orientation that follows the direction of the striping bars, while a lesser number of fibers are disposed across the bars and remain in a generally cross direction to those bars after the thusly formed web of fibers moves entirely onto the moving conveyor screen. Some of the fibers in the fabric may advantageously be of a thermo-plastic nature so that when heated, they will provide a binder for the fabric.

Description

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This application is a division of application No. 223,778, filed April 3, 1975.
This invention relates to apparatus for making biaxially oriented striped nonwoven fabrics, and more particularly, to apparatus for making a nonwoven fabric having alternating high fiber density and low fiber density striped portions wherein the low fiber density stripes are substantially oriented in one direction and the high fiber density stripes are substantially oriented in a direction normal to that direction. Such a fabric and a method for its manufacture are the subject matter of the parent application No.
223,778.
Nonwoven fabrics are now used for a variety of purposes in a ~ number of industries. These fabrics have been made traditionally by methods - such as carding, garnetting, air-laying and the like. Nonwoven webs have been made to have most of the fibers therein oriented in the machine direction; other nonwoven webs have been made to have some cross orientation;
and still other webs have been produced having a randomized fiber distribution.
However, substantially all of these webs are lacking in any surface character or natural decorative effect.
Parent application 223,778 relates to a biaxially oriented non-woven fabric of textile-length fibers comprising areas of low fiber density and areas of high fiber density, a majority of the fibers in said low fiber density areas having a particular configuration and being oriented in a direction substantially normal to the axis of said configuration and, a majority sf the fibers in the high fiber density area that lies directly adjacent said low fiber density areas b~ing oriented in a direction substan- ~, tially parallel with the contours of said configuration of the low fiber density area.
me areas of high fiber density and low fiber density may be alter-;-3 nating stripes of high fiber density and low fiber d~sity, running ~g the ~ . .

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length of the fabric with a majority of the fibers in th~ low fiber density stripes oriented in a substantially cross direction and a majority of the fibers in the high fiber density stripes oriented in a direction substantially parallel to the low fiber density stripes.
The parent application also relates to a method of producing such a biaxially oriented nonwoven fabric.
According to the present invention there is provided an apparatus for making a biaxially oriented nonwoven fabric having areas of high fiber density and low fiber density wherein a majority of the fibers in said low fiber density areas are oriented in a substantially cross direction and a majority of the fibers in said high fiber density areas that lie directly adjacent said low fiber density areas are oriented in a direction substan-tially parallel with the contours of the configuration of said low fiber - density areas comprising: fluid propelling means for carrying discretely ~ separated textile-length fibers in a fluid-borne stream; a distributor i chamber having an opening on the bottom thereof for receiving said fluid-borne ,! stream and being workably disposed with said propelling means; a moving air-permeable conveyor screen disposed under said chamber; at least one imper-vious resist area disposed across said moving screen; a vacuum means disposed under said moving screen and said chamber for aiding said `f~uid-borne stream to locate in fibers on said screen in a particular manner; and, a pick-up means for collecting a biaxially oriented striped nonwoven fabric, said pick-d Up means disposed at the end of said moving conveyor screen.
, In the accompanying drawings which illustrate exemplary embodiments .d of the present invention:
Figure 1 is a plan view of a nonwoven fabric;
c Figure 2 is a perspective view of an apparatus used to make such a nonwoven fabric;
, Figure 3 shows a partial view of striping bars;

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- 2 -Figure 4 is a photomicrograph of a sectional view of a nonwoven fabric taken at the interface of a high fiber density stripe and a low fiber density stripe;
Figure 5 shows a plan view of another embodiment of the nonwoven fabric;
Figure 6 shows another embodiment of the nonwoven fabric made with resist areas moving with the screen; and, Figure 7 is a chart for showing the process steps and conditions ; for air-laying the web.
; 10 Referring to Figure 1 of the drawings, there is shown a nonwoven fabric 10 having alternating high fiber density stripes 11 and low fiber density stripes 12. As can be seen in the drawing, the majority of the fibers in the high fiber density stripes 11 are oriented in a direction that substantiall~ follows the direction of a moving conveyor belt upon which such -~ a fabric is made (machine direction), that is toosay, that those fibers are aligned substantially parallel to the length of the fabric. However, the majority of the fibers in the low fiber density stripes 12 are oriented in a ~ direction that is substantially across the width of the fabric 10 (cross `~ direction orientation), that is to say, these fibers are aligned substantially normal to the fibers in the high fiber density stripes 11. These alternating striped portions of varying orientation are formed simultaneously as described ;
below.
As shown in Figure 2, a fluid-borne stream of textile length fibers can be produced by an air lay such as the device described in my U.S. Patent

3,727,270, wherein textile-length fibers 14 are drafted through a draw frame ;
~ such as at 15 and are then propelled by a high velocity air stream provided by .
input blower 16. The bluid-borne stream of fibers is then guided through a : . ~:
~enturi 17 and passed into a distributor chamber 21, further aided by free air pulled in from without the chamber 21. The fluid-borne stream of fibers passes ,~ ,... .

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through the chamber 21 and falls onto a moving conveyor screen 2Z. Finger-like striping bars 23 are disposed at regular intervals across the width of the moving conveyor screen 22 in a per~,anent manner and a vacuum means in the form of suction box 29, is positioned beneath the screen 22 and in the area of striping bars 23 so as to aid in causing the fluid-borne stream of fibers to be directed at the striping bars and so as to facilitate the simultaneous formation of crosswise and machinewise orientation of the fibers in the fluid-borne stream. As the fluid-borne stream of fibers falls on the striping bars and the screen they align themselves in a fashion that pro-duces the nonwoven fabric described above. The thusly formed striped web 24 then proceeds to move along the screen 22 and passes through a heating means 25, which serves to cause a melting of thermoplastic fibers present within the web 24 so as to serve as a means for binding the fibers of the web together. m e formed web may alternatively be bonded by any other conven-tional bonding means known to those skilled in the art of nonwoven fabrics.
m e web then continues until it is picked up by the takeup roll 26 at the end of the line.
While it is not entirely certain what causes this novel striped fabric to be formed, one theory is now offered. As the fluid-borne stream approaches the moving screen 22 propelled by a positive pressure induced velocity above the screen and a low pressure below the screen, the air must diverge to avoid the stripes positioned across the screen. m is divergence would be centered along the center line of each striping bar and above that striping bar. m e air along either side of that line of divergence would be induced to move outward from the center line of the striping bar. As a result, a fiber approaching the screen would be carried by this divergent air and would thus fbllow its divergence. If a fiber has a portion of its length ~ -on one side of the line of divergence and another portion of its length on the other side of the line of divergence, it will suffer a straightening ', ", ':

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action as its two portions on opposite sides on the line of divergence are forced outward from the striping bars 23. The fibers are then carried down to the moving screen 22 with one portion of the fiber~on one side of the striping bar and another portion of the fiber on the other side of the bar.
- Bridging these two portions of the fiber will be a relatively straight sec-tion of fiber that bridges the striping bar at approximately 90 to its axis.
Accordingly, it then becomes apparent that it is desirable to have the width of the striping bar less than the length of the fiber to provide a bridging length and two portions of the fibers on either side of the striping 10 bar. It has been noted, however, that there will still be some straightening action and cross orientation effected whenever a fiber bridges both sides of the line of divergence. Further, the striping bars should be of sufficient width so as to cause a divergence that is substantial when compared to a fiber length so as to have a substantial portion of the fiber length straight and oriented along the striping bar.
A majority of fibers, however, will be propelled toward the spaces between the striping bars and those fibers will be pulled forward along the moving screen 22 oriented substantially in a direction parallel to the striping bars 23, thereby producing a webbed fabric as shown and described in 20 Figure 1 above.
It has been found, for example, that a 3/8" wide striping bar produces a high degree of cross orientation with 1 1/2" fibers, since it is a substantial width co~pared to a fiber length, but it is still small enough to permit a number of fibers to both bridge the striping bar and still have length remaining to distribute on either side of the striping bar. If the ~ striping bars are close together so that the distance between the bars is less j than a fiber length, and preferably less than 1/2 a fiber length, the fibers that do not bridge the striping bars will be carried into a high fiber density stripe or space that lies between the striping bars. As described earlier ' 1 '', ~

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herein, a high fiber density stripe formed by a majority of the fibers is therefore induced to have a primary orientation along the axis of the striping bar. This most probably occurs because there is no restraint on the orien-tation of a fiber lying parallel to the axis of the stripe, but any fiber attempting to lie across the striping bars is pushed by the divergent air from the striping bars into a conformed position along the striping bar.
Under this theory, the high fiber density stripes that are formed between the blocking or resisting striping bars will be increasingly oriented in the direction of the stripe as the distance between the striping bars is decreased.
Figure 3 is a close-up of the striping bars 23 andJnows a majority of the fibers falling between the striping bars at 27 and being oriented in a - direction that is substantially parallel to the striping bars.23. Simultan-eously, a minority of the fibers become disposed across the striping bars so as to be oriented in a direction substantially across the width of the fabric, and normal to the axis of the bars, such as is shown at 28.
In all but thellightest weight fabrics, the top of the fabric, that is the portion of the fabric furthest removed from the conveyor screen, appears to be covered by a minor portion of fibers positioned generally across the entire width of the webs. As the fluid-borne stream of fibers positions itself on the screen and striping bars, and becomes increasingly thick and passes off the striping bars, the falling fibers become less generally controlled by the diverging air, and then fall on the uppermost portions of the fabric in a somewhat randomized or cross oriented fashion (partly because some cross orientation is caused by theefluid~borne stream of fibers being thrown toward the forward wall of the curved chamber 21). The web at this point can best be described as having high and low fiber density stripes having a somewhat randomi~ed ccoering layer of fibers integrated therewith. However, a majority of the fibers are still positioned in a striped ~--' i - 6 - ~

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fashion and in an orientation parallel to the length of the web.
If the striping bars are moved closer together and arranged so that they are spaced 3/4" on center rather than on 1" centers as described herein earlier, a much more pronounced ribbed structure is formed. By "ribbed structure", it is meant that the high fiber density stripes have so many fibers therein that this portion of the web structure becomes almost semi-circular in its construction, while the low fiber density areas remains rather flat. m is arrangement could well be described as being a wash-board configuration.
Furthermore, two web fabrics may be superimposed one on top of the other in a manner that the stripes of one web 31 will be at substantially 90 to the stripes of the second web thereby forming a "plaid" fabric such as i shown at 30 in Figure 5. m e fabrics have a variety of uses and could be ;~ used as disposable curtains or drapes, decorative narrow ribbons and/or florist ribbons; sweatbands; cling type bandages; disposable tablecloths, and the like.
Other designs of striping bars can be used in different arrange-~ ments to provide similarly biaxially oriented nonwoven fabrics. For example, .'3 , -.
-x~ impervious resist areas can be designed into the moving conveyor screen as a -;~ .
~ substitute for the striping bars. As shown in Figure 6, a resist area 41 is - 20 formed in the shape of a star, directly on the moving screen 42, so that as the portion of the screen carrying the resist areas passes under the curved chamber and over the suction box, the biaxial orientation of fibers will occur on and around the resist area on the screen. The resist area 41 will have low fiber density areas 43 wherein the fibers are oriented in a direction substantially across each ofhthe finger-like extensions on the star, while the area of the fabric web directly adjacent the resist area will have fibers oriented in a direction substantially parallel with the contours of the configuration of the resist area, and the fibers on the rest of the web not affected by resist areas will have a random, cross or machine orientation as .~ :

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desired. Other configurations could also be made on the screen to produce other similar biaxially oriented patterns thereof.
The above webs can be produced by passing fluid-borne streams of fibers through the apparatus outlined herein before by any method of air-laying fiber webs that is known to those skilled in the art, however, the preferred method is as follows:
Eight vacuum drafting jets of type C as described fully in my earlier patent U.S. Letters Patent 3,727,270, of common assignee, having a throat diameter of 0.562" were operated at 45 PSIG to 50 PSIG of compressed air at an air consumption of 60 SC~M per jet or at 15 PSIG at an air con-- sumption of 30 SCFM per jet. The jets were supplied with a conventional second draw 60 grain sliver, and the sliver was fed from a conventiDnal 4 over 4 draw frame set to a draft of 10.
The Jets set on 5" cen~ers were used to "seed" a column of blower air 40" wide and 4 1/2" deep. At a distance of 40" downstream from the jet the 40" wide column of air was reduced by a venturi from 4 1/2" deep to 2"
deep to form a sheet of air travelling at 6,000 feet per minute or 3,333 - CFII. This velocity can be adjusted to this level by means of controlling the output of the positive pressure blower.
After leaving the venturi, the sheet of air passed through an open space and was then fed into a distributor chamber having a collection screen approximately 40" wide. A suction blower powered by a suction box under the collection screen was adjuted to collect approximately 4,000 C~M
~i per inch of width. Since the suction system was removing more air thanwas being supplied by the venturi, that amounttof free air from the room was drawn in the air gap between the venturi and the distributor. Such a machine i operating in the above manner handles 18,000 pounds of air per hour of 4,000 ~ C~M. All of the air but for the 240 C~M used in the jets at 15 PSIG, was `~ supplied by blowers.
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The operation of this airlaid system can be further shown by referring to Figure 7 of the drawings by taking an example of a sliver feed rate of 24 feet per minute at the input end of the draw frame. In this case, the original sliver containing approximately 38,265 denier would be drawn down to 3,826 denier by the draw frame and would be about 3/4" wide and travel at 240 feet per minute.
Assuming that the jet was operating at 15 PSIG it would accelerate the fibers to 24,000 feet per minute and reduce the sliver weight tooan aver~ge of approximately 38 denier spread over the area of the jet exit 0.6"
in diameter. This stream of fibers would be expanded and then fed to the venturi where it would contract to 153 denier spread over a venturi exit cross section of 10 square inches or 15~3 denier per square inch.
When eight ends of sliver at 24 feet per minute are fed (one to each jet) over the 40 inch width, the feed rate of the sliver to the machine is 28 grams per square yard and the exit rate at the venturi is 0.112 grams per square yard. The draft factors, in process web weights, and the velocities are outlined in Figure 7.
The machine was operated on 3 denier and 1 1/2 denier fibers of about 1 1/2" length. Theequality level areas observed the -various rates of feed ant the various jet pressures. From these experi~nts the generalized conditions for runiing these fibers were determined in the form of the ratios of pounds per hour, horsepower, air volume, etc. These generalized conditions can be shown on the following cha~:

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GENERALIZED CONDITIONS FOR AN AIRLAY DISTRIBUTOR
(A) AT A REINFORCING GRADE QUALITY~LEVEL
3-Den. 1-1/2-Den.
1-1/2" 1-1/2"
Distributor Conditions Number of Fibers/Cubic foot of air6,000 12,000 Number of Fibers/Cubic inch of air3.5 7 Lbs. of air/lb. of fiber 450 450 CFM of air/lb. of fiber per hour 100 100 Tet Conditions at 15 PSIG
Compressor HP per lb. of fiber/hour0.6 ___ Lbs. of fiber per hour per jet 5 _ _ Iet Conditions at 50 PSIG
Compressor HP per lb. of fiber/hour_ _ 2 Lbs. per fiber per hour per jet _ _ 5 (B) AT A GOOD QUALITY LEVEL
- 3-Den. 1-1/2-Den.
lfl/2" 1-1/2"
Distributor Conditions ~-~ Number of Fibers/Cubic foot of air3,000 6,000 -~ Number of Fibers/Cubic inch of air11755 3.5 Lbs. of air/lb. of fiber 900 900 CFM of air/lb. of fiber per hour 200 200 L t Conditions at 15 PSIG
Compressor HP per lb. of fiber/hour1.2 Lbs. of Fiber per hour per jet 2.5 4~-L t Conditions at 50 PSIG
Compressor HP per lb. of fiber/hour_ _ 4 Lbs. of Fiber per hour per jet _ _ 2.5 This invention will be further explained by means of the following examples:
Example 1 Eight ends of 38l265 denier rayon sliver of 3 denier per filament --1 1/2" long were fed into a fluid-borne stream through 8 jet nozzles at an .. . .

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air pressure of approximately 17 PSIG. The rayon is fed into the stream at a rate of 24.9 grams per square yard and Vinyon fibers of 3 denier and 1/4" in length (Vinyon is the trade name for a polymer of vinyl acetate and vinyl chloride by AmericanilViscose) are simultaneously fed therein by a ninth jet at a rate of 17.1 grams per square yard giving a total weight of 42.0 grams per square yard. The stream passes into a curved chamber and the stream of fibers is thrown onto a moving conveyor screen having finger-like striping bars equidistantly disposed from each other across the 42" width of the conveyor screen. The striping bars are 3/~' wide and are located on 1"
centers. Forty-two stripes result from this particular web. In this particular example the suction under the screen was 2.5 inches of water. me web was then processed into a nonwoven by passing the web through an oven at 420F.
, E~camPle 2 e same fluid-borne stream of fibers as described in E~ample Dwas ~l fed through the same equipment at 17 PSIG, and thrown onto the screen under ;~ which a suction box or the like exerted a pressure of 2 inches of water.
;~ me rayon is fed at a rate of 14.00grams per square yard while the Vinyon is fed at a rate of 9.0 grams per square yard giving a total fabric weight of 23 gram~ per square yard. mis fabric is also run l~hro~gh an oven at approximately 420 F, and a finished nonwoven fabric is produced thereby having 42 stripes thereon.
xample 3 The fluid-borne stream as described in Example 1 was prepared and run through the same apparatus as described therein at 17 PSIG. The rayon was fed at a rate of approximately 28 grams per square yard while the Vinyon was fed at approximately 35 grams per square yard giving a total fabric weight of 63 grams per square yard. me fabric was once more passed through ~ -an oven at 420 F producing a rather hea;vy and somewhat boardy striped fabric '~ ' .

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having 42 stripes thereon. 1l)4Z172 Example 4 The fluid-borne stream described in Example 1 is passed into the curved chamber described therein at 17 PSIG. The striping bars, however, still 3/8" wide, were placed on 3/4" centers over a width of 42". A
striped fabric was formed having 56 stripes thereon and wherein the heavy fiber density stripes are raised above the plane of the fabric so as to form a ribbed structure thereon.
It is to be understood that many variations on the fabric described herein can be formed by varying the width of the striping bars, the shape of - the bars or resist areas, and the distances between same. Also the speed of the moving conveyor (the weight of the fabric) may also alter the characteristics of the web. For example, and as was discussed earlier, a somewhat heavier weight web will have a layer of generally randomized or cross oriented fibers across the uppermost portion of the web fabric. This can be shown by reference to Figure 4 of the drawings. Figure 4 is a photo-~, .
; micrograph taken on an AMR-1000 Scanning Electron Microscope made by AMR
~$ Corporation~ Burlington, Massachusetts. This photomierograph, taken at the interface between a low fiber density stripe and a high fiber density stripe, i 20 shows that the fibers in the low fiber density stripes are substantially cross oriented, that the fibers in the high fiber density stripes are substantially machine direction oriented, and theefibers in the uppermost j portion of the fabric extend beyond the interface and are somewhat cross oriented onto the high fiber density stripe portion. However, it can also be . .- . -. .
seen that a majority of the fibers are located in the high fiber density 1 stripe and are oriented at approximately 90 to the orientation of the low .~ ~ ~ .. .. ..
fiber density fibers. -~

Many other designs could be achieved using the methods described ;

i above by also varying the placement of the striping bars so as to be directly - 12 - ;

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on the collection screen as described above or to be of a more stationary nature and be positioned over the screen. Either will produce various fiber patterns in the area that is covered by the striping bars or resist areas that is highly oriented in a direction substantially normal to the axis of the striping bar.
Op*imum results can be obtained when the striping bars have a width of less than a fiber length but of more than 1/8". A width of 3/8"
has been found to be particularly preferable using 1 1/2" long fibers of 1 1/2 and 3 denier.
If the length of the striping bars blocking the screen is reduced so that they do not extend so far as to cover the entire screen collecting surface, then a substantially random web will be formed on the unblocked collection surface causing a random web to become superimposed over and . , .
integrally connected with the striped web. The proportion of web weight that is striped and has been biaxially oriented, to the proportion of super-imposed web that is random can, of course, be varied by adjusting the proportion of the-screen that is blocked by the striping bars.
The striping bars described as preferred can, of course, be replaced, ~ as described earlier herein, by placing resist areas~cf impermeability on the 1 20 screen in the form of barsj or the like. This may be accomplished by placing, for example, strips of tape across the screen or by blocking the openings in the screen in aelected areas with a plastic or paint. If these bars are positioned so as to be along the screen's direction of travel, then the ~ resulting striped fabric will be as described in the examples above.
i ~owever, if the bars are placed across the width of the screen, then the pattern will be reversed so that the stripes will be disposed across the width of the fabric.
Of course, as stated and described herein earlier, resist areas may also be placed at any other angles, other than parallel or normal to the .; ..

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direction of travel of the screen to produce fabrics with stripe~ at a bias to the direction of tra~el of the fabrics.

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Claims (7)

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

1. Apparatus for making a biaxially oriented nonwoven fabric having areas of high fiber density and low fiber density wherein a majority of the fibers in said low fiber density areas are oriented in a substantially cross direction and a majority of the fibers in said high fiber density areas that lie directly adjacent said low fiber density areas are oriented in a direc-tion substantially parallel with the contours of the configuration of said low fiber density areas comprising: fluid propelling means for carrying discretely separated textile-length fibers in a fluid-borne stream; a distri-butor chamber having an opening on the bottom thereof for receiving said fluid-borne stream and being workably disposed with said propelling means;
a moving air-permeable conveyor screen disposed under said chamber; at least one impervious resist area disposed across said moving screen; a vacuum means disposed under said moving screen and said chamber for aiding said fluid-borne stream to locate in fibers on said screen in a particular manner; and, a pick-up means for collecting a biaxially oriented striped nonwoven fabric, said pick-up means disposed at the end of said moving conveyor screen.

2. The apparatus of claim 1 wherein said at least one impervious resist area is a plurality of equidistantly spaced-apart finger-like striping bars disposed across said screen directly under the opening on said chamber.

3. me apparatus of claim 2 wherein said striping bars are 3/8" wide.

4. The apparatus of claim 2 wherein the distance between said striping bars is less than a fiber length.

5. The apparatus of claim 2 wherein said striping bars are positioned so as to be on 1" centers across said moving screen.

6. The apparatus of claim 2 wherein said striping bars are positioned so as to be on 3/4" centers across said moving screen.

7. The apparatus of claim 2 wherein the distance between said striping bars is less than 1/2 of an average fiber length.