IE43991B1 - Biaxially oriented nonwoven fabric including long and short fibres - Google Patents

Abstract

1510580 Biaxially orientated non-woven fabric KENDALL CO 8 Dec 1976 [19 Dec 1975] 51270/76 Headings DIN and D1R A biaxially orientated non-woven fabric composed of long fibres of length 0.5in. or more and short fibres of length less than 0.5in. comprises areas 12 of low fibre density having a finger-like configuration and areas 11 of high fibre density, the majority of the fibres in the areas 12 of low fibre density being long fibres which are orientated in a direction substantially normal to the fingers, the majority of the fibres in the portions of the high fibre density areas 12 directly adjacent the fingers 11 being orientated substantially parallel to the fingers and the majority of the short fibres being disposed in high density areas 11. Preferably, slivers 14 of long fibres are drafted by rolls 15 and propelled by air from blower 16 through venturi 17 to distributor chamber 21 whilst short fibres are fed by a further air stream from feeder 18. Suction box 29 collects the fibres on moving conveyor screen 22. Preferably fixed finger-like striping bars 23 are disposed at regular intervals above and across the width of the screen, e.g. 0.125in. wide bars are located at 4 in between their centers. The deflection of air between the bars deposits the majority of the fibres on the screen between the bars and orientated in the machine direction. The minority of fibres which are not deflected will straddle a bar. Their ends will be orientated longitudinally in dense areas 11 and this will straighten the middle portion and orientate it transversely. As the fibre weight per unit area is increased the bars have less effect so that a thick web has an upper layer of randomly aligned fibres. In alternative embodiments the stripping bars are orientated transversely or replaced by impervious areas e.g. star shaped areas (61, Fig. 6, not shown) formed on screen 22 with paint or plastics. The web may contain thermoplastic fibres which bond it when softened by heater 25. In example 1 the web comprises 14 g/yd2 of 1 9/16" 3 denier rayon, 8 g/yd2 of “" 3 denier vinylacetate/vinylchloride thermoplastic copolymer fibres and 4 g/yd2 of wood-pulp fibres. A plaid fabric (Fig. 7, n.s.) may be obtained by superimposing two layers with their stripes at right angles.

Description

Prtce 12|p describes and claims Patent Specification No. 41606 a biaxially oriented nonwoven fabric, and apparatus for making the same, said fabric being formed of staple fibres and comprising areas of low fibre density having a fingerlike configuration with a majority of the fibres therein having their axes oriented in a direction substantially normal to the fingers and immediately adjoining areas of high fibre density in which a majority of the fibres directly adjacent the areas of low fibre density have their axes oriented in a direction substantially parallel to the fingers the fibres being superposed in the fabric without twisting and interlooping in a knit-stitch manner. In its preferred form, the areas of high and low fibre density in this fabric are alternating stripes which extend lengthwise of the fabric.

The present invention is based on the appreciation of the fact that biaxially oriented nonwoven fabrics as described in Patent Specification No. 41606 can be produced more cheaply by forming the fabric from a mixture of long fibres and short inexpensive fibres, such for example as wood pulp fibres or cotton linters.

The invention accordingly provides a biaxially oriented nonwoven fabric, composed of long fibres having a length of half an inch or more and short fibres having a length less than half an inch and comprising areas of low fibre density having a fingerlike configuration and areas of high fibre density, the majority of the fibres in the areas of low fibre density being long fibres which are oriented in a direction substantially normal to the fingers, the majority of the fibres in the portions of the areas of high fibre density which are directly adjacent the areas of low fibre density being oriented in a direction substantially parallel to the fingers and the majority of the short fibres being disposed within the areas of high fibre density.

Preferably the areas of high and low fibre density are alternating stripes which extend lengthwise of the fabric, the majority of the fibres in the Stripes of low fibre density being oriented in a substantially cross direction and comprising long fibres bridging said stripes, the majority of the fibres in the stripes of high fibre density being oriented in a direction substantially parallel to the stripes, and the spacing between the stripes of high fibre density being at least the width of a stripe of high fibre density.

The invention will now be further described with reference to the accompanying drawings, in which:Figure 1 is a plan view of a nonwoven fabric according to the invention, Figure 2 is a perspective view of an apparatus for making this nonwoven fabric, Figure 3 shows a diagrammatic view of the striping bars used in this apparatus, Figure 4 is a plan view of another embodiment of nonwoven fabric according to the invention, Figure 5 is a perspective view of another embodiment of nonwoven fabric according to the invention, Figure 6 shows another embodiment of the nonwoven fabric according to the invention made with resist areas moving with the screen, and Figure 7 is a plan view of still another embodiment of the invention which includes superposed layers of nonwoven fabric.

Figure 1 shows a nonwoven fabric 10 having alternating stripes 11 of high fibre density and stripes 12’of low fibre density. As can be seen, the majority of the fibres in the stripes 11 are oriented in a direction that follows the direction of a moving conveyor belt upon which the fabric has been made (the machine direction). In 3 9 91 other words these fibres are aligned substantially parallel to the length of the fabric. However, the majority of the fibres in the stripes 12 are oriented in a' direction that is substantially across the width of the fabric 10 (cross direction orientation). In other words, these fibres are aligned substantially normal to the fibres in the stripes 11 and in bridging relationship with those stripes. These alternating striped portions of varying orientation are formed simultaneously as described below.

The apparatus shown in Figure 2 is similar to that described in Patent Specification No. 41606 . As shown, textilelength fibres 14 are drafted through a draw frame 15, and are then propelled by a high velocity air stream provided by an input blower 16. The airborne stream of fibres is then guided through a venturi 17 and passed into a distributor chamber 21, further aided by free air pulled in from without the chamber 21. Short fibres are also delivered into the chamber 21 by means of a short fibre feeder 18 of any conventional type. An airborne stream of both types of fibres passes through the chamber 21 and falls onto a moving conveyor screen 22. Fixed finger-like striping bars 23, which extend parallel to the length of the screen, are disposed at regular intervals across the width of the screen 22 and a suction box 29 is positioned beneath the screen 22 in the region of the striping bars 23 to aid in causing the airborne stream of fibres to be directed at the striping bars as so facilitate the simultaneous formation of crosswise and maohinewise orientation of the fibres in the airborne stream. - 4 43991 As the airborne stream of fibres falls on the striping bars and the screen they align themselves to produce a striped nonwoven web 24 as described above with reference to Figure 1.

The web 24 is carried by the screen 22 through a heater 25, which serves to melt thermoplastic fibres present in the web 24 and so bond the fibres of the web together. Of course, the web may alternatively be bonded by any other conventional bonding procedure. The web is picked up by a takeup roll (not shown) beyond the heater 25· While it is not entirely certain what causes the formation of the striped fabric, the following is believed to be a likely explanation. As the airborne stream of fibres approaches the screen 22 propelled by a positive pressure induced velocity above the screen and a low pressure below 15 the screen, the fluid must diverge to avoid the striping bars 23 positioned above the screen. This divergence will be centred along the centre line of each striping bar and above that striping bar. The air along each side of that line of divergence will be induced to move outward from the centre line of the striping bar. As a result, a fibre approaching the screen will be carried by this divergent air and thus follow its divergence. If a fibre 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 25 line of divergence, it will suffer a straightening action as its two portions on opposite sides on the line of divergence are forced outwardly with respect to the striping bar. The fibres are then carried down to the moving screen 22 with one portion of the fibre on one side of the . 439® 1 striping bar and another portion of the fibre on the other side of the bar. Bridging these two portions of the fibre will be a relatively straight section of fibre which bridges the striping bar at approximately 90° to its axis.

The width of the striping bar should clearly be less than the length of the fibre to provide a bridging length and a portion of fibre on each side of the striping bar. However, the striping bars should be of sufficient width to cause a divergence that is substantial when com10 'pared to a fibre length so as to have a substantial portion of the fibre length straight and oriented along the striping bar.

A majority of fibres, however, will be propelled towards the spaces between the striping bars and those fibres will be pulled forward along the moving screen 22 oriented substantially in a direction parallel to the striping bars 23, thereby producing a striped fabric as shown in Figure 1 and described above.

It has been found, for example, that a striping bar 20 3/8 wide produces a high degree of cross orientation with fibres having a length of 1£, since its width is substantial compared with the fibre length, but it is still small enough to permit a number of fibres to bridge the striping har and have ends disposed on opposite sides of the striping bar. If the striping bars are close together so that the distance between the edges of the bars is less than a fibre length, and preferably less than half a fibre length, the fibres that do not bridge the striping bars will be carried into a stripe of high fibre density that lies 6. between the striping bars. As described earlier, a stripe of high fibre density formed by a majority of the fibres has a primary orientation along the axis of the striping bar. This most probably occurs because there is no re5 straint on the orientation of a fibre lying parallel to the axis of the stripe, but any fibre attempting to lie across the striping bars is pushed by the divergent air from the striping bars into a conformed position aligned with the striping bars. 1° On this basis, therefore, it is to be expected that the stripes of high fibre density that are formed between tne striping bars will be increasingly oriented in the direction of the stripe as the distance between the striping bars is decreased.

Figure 3 is an enlarged view of the striping bars 23 and shows a majority of the fibres falling between the striping bars at 27 and being oriented in a direction substantially parallel to the striping bars 23 and a minority of the fibres disposed across tne 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 as shown at 28.

The nonwoven fabric according to the invention is made from a blend of long fibres having a length of one25 half an inch or more and short fibres having a lengtn less -than half an inch and preferably less than quarter of an inch. The short fibres in the blend are unable to bridge the striping bars and will, therefore, be deposited with substantially their full length contained within the areas on the screen of high fibre density. This greatly enhances the sharpness or resolution of the stripes as well as increasing the bulk of the fabric.

The short fibres may, for example.be wood pulp fibres, cotton linters, short thermoplastic fibres, or combinations thereof. The use of these short fibres reduces the cost of the final fabric. When the short fibres consist of, or include, thermoplastic fibres, these fibres will be drawn into the stripes of high fibre density and, when 0 heated, will bond the long bridging fibres at their ends where they are incorporated into the stripes but will leave the bridging fibres substantially free of bonding between the stripes of high fibre density, thus enhancing the drape and softness in those areas.

These stripes of high fibre density comprising long and short fibres are referred to herein as twistless ribbon strands. While it is true that some short fibres will be found in the stripes of low fibre density mixed with the long bridging fibres, a majority of the short fibres will 3 be disposed within the twistless ribbon strands.

Figure 4 shows a nonwoven fabric 30, in which the stripes 31 of high fibre density contain the majority of the short fibres and form the twistless ribbon strands.

The stripes 32 of low fibre density contain the majority ' of long bridging fibres which are oriented in a direction across the wrath of the fabric and normal to the fibres in the stripes 31 The majority of the fibres in the stripes 31, whether long or short, are oriented substantially parallel to the length of the fabric 30· The spacing between the twistless ribbon strands 31 is at least the width of a strand, and long fibres, most of which have at least a portion of their length in adjacent strands, bridge and so connect the twistless strands.

Figure 5 shows a heavier weight nonwoven fabric 40, having stripes 41 of high fibre density containing both long and short fibres running parallel with the length of the fabric, and stripes 42 of low fibre density containing the bridging long fibres and some short fibres, the majority of the fibres in the stripes 42 being oriented in a direction substantially normal to the stripes 41. However, in all but the lightest weight fabrics and as shown in Figure 4, the top of the fabric 43, that is the portion of the fabric furthest removed from the conveyor screen, appears to be covered by a minor number of long and short fibres.

As the airborne stream of fibres positions itself on the striping bars, and becomes increasingly thick and passes off the striping bars, the fibres become less subject to control by the diverging air and fall on the uppermost portion of the fabric in a partly random and a partly cross oriented fashion, some tendency towards cross orientation being caused by the airborne stream of fibres being thrown towards the forward wall of the chamber 21. When the fibres are thrown towards this wall at a relatively low speed the fibres will tend to be randomly disposed but when the velocity of the airborne stream is increased the tendency towards cross orientation of the fibres will also increase. The web at this point can best be described as having stripes of high and low fibre density having a generally random covering layer of long and short fibres integrated therewith. However, a majority of the fibres are still positioned in a striped fashion and in an orientation parallel to the length of the web. 439S1 lf the striping bars are moved closer together and spaced at a.» centre distance rather than 1 as described above, a much more pronounced ribbed structure is formed. By ribbed structure is meant that the stripes of high fibre 5 density contain so many fibres that they become almost semi-circular in configuration, while the stripes of low fibre density remain more or less flat.

Two layers of fabric may be superimposed as shown in Figure 7, with the stripes 51 of one layer at right angles 10 to the stripes 52 of the other layer thereby forming a plaid fabric 50. The fabrics according to the invention have a variety of uses, for example as disposable curtains or drapes, as decorative narrow ribbons and/or florist ribbons, as sweatbands, as cling type bandages and as dis15 posable tablecloths.

Biaxially oriented nonwoven fabrics may be produced by providing impervious resist areas on the moving screen instead of by using striping bars. These resist areas may extend parallel to the length of the screen, in which case 20 a striped pattern will be produced as in the case of the striping bars, or they can assume other configurations.

Thus, as shown in Figure 6, resist areas 61 can he formed in the shape of a star directly on the moving screen 62, so that as the portion of the screen carrying a resist area 25 passes under the curved chamber and over the suction box, the biaxial orientation of fibres will occur on and around the resist areas. Areas 65 of low fibre density will be formed above the resist area 61 wherein the fibres are oriented in a direction substantially across each of the . 43881 finger-like extensions of the star, while the area of the web directly adjacent the resist area, e.g. at 64, will contain fibres oriented in a direction substantially parallel with the configuration of the resist area, and the fibres in the rest of the web not affected by resist areas will have an orientation that is partly randan and partly cross or machine oriented-. Other confiourations of resist area can be provided on the screen to produce other similar biaxially oriented patterns in the web. 1° The above-described apparatus is preferably operated as follows :Eight vacuum drafting jets of type C as described in U.S.Patent 3,727,.270 and having a throat diameter Of 0.562 were operated at 45 PSIG to 30 PSIG of compressed air at an 15 air consumption of 60 CFM per jet or at 15 PSIG at an air consumption of 30 CFM per jet. The jets were supplied with a conventional second draw 60 grain sliver, and the sliver was fed from a conventional 4 over 4 draw frame set to a draft of 10.

The jets set on 3 centres were used to seed a column of blower air 40 wide and 4J deep. At a distance of 40 downstream from the jet the 40 wide column of air was reduced by a venturi from 4J deep to 2 deep to form a sheet of air travelling at 6,000 feet per minute or 3»333 25 CFM. The velocity can be adjusted to this level by 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 through the distributor chamber onto a screen approximately 40 wide. A 11. 43991 suction blower powered by a suction box under the collection screen was adjusted to collect approximately 4,000 CFM per 40 inch of width. Since the suction system was removing more air than was being supplied by the venturi, the corresponding amount of free air from the room was drawn in the air gap between the venturi and the distributor chamber. When operating in the above manner, the machine handles 18,000 pounds of air per hour or 4,000 CFM. All of the air apart from the 240 CFM used in the jets at 15 PSIG was supplied by blowers.

The operation of this system can be further appreciated 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 15 denier would be drawn down to 3,826 denier by the draw frame and would be about J wide and travel at 240 feet per minute.

Assuming that the jet was operating at 15 PSIG it would accelerate the fibres to 24,000 feet per minute and !0 reduce the sliver weight to an average of approximately 38 denier spread over the area of the jet exit, which has a diameter of 0.6. This stream of fibres 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 5 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 12. square yard.

The machine was operated on 5 denier and 14 denier fibres having a length of about ij, Various rates of feed and various jet pressures were tested. From these experiments the generalized conditions for running these fibres were determined: GENERALIZED CONDITIONS FOR AN AIRLAY DISTRIBUTOR (A) AT A REINFORCING GRADE QUALITY LEVEL 3-Den. 1-4-Den. 1-4 1-4 Distributor Conditions Number of Fibres/Cubic foot of air 6,000 12,000 Number of Fibres/Cubic inch of air 3.5 7 Lbs. of air/lb. of fibre 450 450 CFM of air/lb. of fibre per hour 100 100 Jet Conditions at 15 PSIG Compressor HP per lb. of fibre/hour 0.6 Lbs. of fibre per hour per jet 5 Jet Conditions at 50 PSIG Compressor HP per lb. of fibre/hour 20 Lbs. af,fibre per hour per jet (B) AT A GOOD QUALITY LEVEL Distributor Conditions Number of Fibres/Cubic foot Number of Fibres/Cubic inch Lbs. of air/lb. of fibre CFM of air/lb. of fibre per Jet Conditions at 15 PSIG of air 3,000 6,000 of air 1.75 3.5 900 900 hour 200 200 Compressor HP per lb. of fibre/hour 1.2 Lbs. of Fibre per hour per jet 2.5 439s1 3-Den. 1-i-Den. 1-¾11 Jet Conditions at 50 PSIG Compressor HP per lb. of fibre/hour --- 4 Lbs. of Fibre per hour per jet --- 2.5 The invention will be further explained by means of the following examples: Example 1 Eight ends of 58,265 denier rayon sliver of 5 denier per filament 1 9/16 long were fed into an airborne stream 10 through eight jet nozzles at an air pressure of approximately 17 PSIG. The rayon is fed into the stream at a rate of 10 grams per square yard and Vinyon ('Trade Mark) fibres of 5 denier and in length (Vinyon is a tradename for a polymer of vinylacetate and vinylchloride made by American Viscose) were simultaneously fed into the stream by a ninth jet at a rate of 8 grams per square yard. The stream passed into a curved distributor chamber and the stream of fibres was thrown onto a moving conveyor screen having finger-like striping bars equidistantly disposed from each other across the 42 width of the screen. The striping bars were 1/8 wide and are located on 4 centres. Simultaneously, wood pulp fibres that had been separated in a pin-type fiberizer or a hammer-mill were passed into the distributor chamber in a second air25 borne stream and were simultaneously thrown onto the screen The suction under the screen was 6 of water. The web was then processed into a nonwoven fabric by passing the web through an oven at 450°F. The nonwoven fabric had 168 4308 1 stripes and weighed 26 grams per square yard.

Example II The airborne stream of rayon and Vinyon fibres described in Example I was fed through the same equipment at 5 17 PSIG, and thrown onto the screen under which a suction box exerted a suction of approximately 6 of water. The rayon was fed at a rate of 14 grams per square yard while the Vinyon was fed at a rate of 6 grams per square yard. Simultaneously, a second airborne stream of wood pulp fibres was fed into the distributor chamber at a rate of grams per square yard. The resulting fabric weighed 26 grams per square yard, had 168 stripes and was also passed through an oven at 45O°P.

Example III The airborne stream of rayon and Vinyon fibres described in Example I was run through the same apparatus at 17 PSIG. The rayon was fed at a rate of 8 grams per square yard while the Vinyon was fed at approximately 3 grams per square yard. The wood pulp fibres were sim20 ultaneously fed in at a rate of 3 grams per square yard, to produce a fabric weighing 14 grams per square yard. The fabric was passed through an oven at 450°F and had 168 stripes.

Many variations can be produced in the fabric by vary25 ing the width of the striping bars, the shape of the bars or other resist areas, the distances between same, tne length of the fibres, and the types of fibre used. Also, change in the speed of the moving screen (the weight of the fab15. 43991 ric) may also alter the characteristics of the web. For example, and as was mentioned earlier, a web of somewhat heavier weight will have a layer of generally random or cross-oriented fibres across its surface.

If the striping bars do not cover the entire surface of the screen, a substantially random web will be formed on the portion of the surface not blocked by the bars ana this ranaom web will be integrally connected with the striped web. The ratio of the portion of the web that is striped 0 and has been biaxially oriented to the portion of the web that is random can, of course, be varied by adjusting the extent to which the screen is blocked by the striping bars.

When the striping bars are replaced by forming impervious resist areas this may be achieved by placing strips 5 of tape across the screen or by blocking the openings in the screen in selected areas with a plastics material or paint. If the resist areas take the form of bars positioned in the direction of travel of the screen, the resulting striped fabric will he as aescribed above. How3 ever, if the bars are placed across tne wiath of the screen, trie pattern will be reversed so tnat the stripes will be disposed across the width of the fabric.

Resist areas may also be placed at angles other than parallel or normal to the direction of travel of the screen ' to produce fabrics with stripes at a bias to the machine direction.

Claims (11)

CLAIMS:

1. A biaxially oriented nonwoven fabric, composed of long fibres having a length of half an inch or more and short fibres having a length less than half an inch and comprising areas of low fibre density having a fingerlike config5 uration and areas of high fibre density, the majority of the fibres in the areas of low fibre density being long fibres which are oriented in a direction substantially normal to the fingers, the majority of the fibres in the portions of the areas of high fibre density which are 0 directly adjacent the areas of low fibre density being oriented in a direction substantially parallel to the fingers and the majority of the short fibres being disposed within the areas of high fibre density.

2. A nonwoven fabric according to claim 1, wherein the ’ areas of high and low fibre density are alternating stripes which extend lengthwise of the fabric, the majority of the fibres in the stripes of low fibre density being oriented in a substantially cross direction and comprising long fibres bridging said stripes, the majority of the fibres in the stripes of high fibre density being oriented in a direction substantially parallel to the stripes, and the spacing between the stripes of high fibre density being at least the width of a stripe of high fibre density. 17.

3. A nonwoven fabric according to claim 2, wherein the length of th? short fibres is less than a quarter of an inch.

4. A nonwoven fabric according to claim 3, wherein the short fibres comprise at least a proportion of wood-pulp 5 fibres.

5. A nonwoven fabric according to claim 3, wherein the short fibres comprise at least a proportion of thermoplastic fibres.

6. A nonwoven fabric according to claim 3» wherein the 10 short fibres comprise at least a proportion of cotton linters.

7. A nonwoven fabric according to any one of claims 2 to 6, wherein the stripes of high fibre density are raised above the plane of the fabric on one side only thereof. 15

8. A nonwoven fabric according to any one of claims 2 to 7, which includes both long and short fibres disposed in a partly randan and a partly cross oriented manner across the top of the fabric.

9. 4 nonwoven fabric according to claim 2, which consists 2o of two layers of striped fabric superimposed on one another with the stripes of one layer disposed at right angles to the stripes of the other layer.

10. A nonwoven fabric according to claim 3, wherein the bridging fibres in each stripe of low fibre density !5 extend into stripes of high fibre density and are bonded into the stripes of high fibre density by thermoplastic short fibres. - 18

11. 43981 A nonwoven fabric according to claim 1, substantially as described herein with reference to the accompanying drawings.