IE45153B1 - Biaxially orientated nonwoven fabrics - Google Patents

Abstract

Fibres of limited length form strip-shaped regions of higher and lower fibre density which are arranged in an alternating sequence adjacent and parallel to one another. The fibres are present in a uniform distribution in the said regions. At least some of the fibres extend beyond the limits of adjacent regions. The majority of the fibres or fibre parts (20) in the strip-shaped regions of higher fibre density are folded transversely to the strip in a zigzag-like manner (22). The segments of the folded fibres are arranged at least approximately parallel to one another and are oriented virtually in the longitudinal direction of the strips. The majority of the fibres or fibre parts in the strip-shaped regions of lower fibre density are oriented transversely to the strip. The quotient Tensile strength transversely to the strip direction DIVIDED Tensile strength in the strip direction always has a value of less than 2. The composite textile material is produced by introducing a carded fibre fleece (31) between a stretched screen (32) and a set of strip-forming bars (33) and by directing, for example via nozzles (35), a flowable medium, preferably water, onto the strip-forming bars.

Description

The fibres in a carded web are normally aligned in a direction substantially parallel to the direction of the web within the carding machine normally used to make nonwoven fabrics.

Consequently, the machine direction strength of a carded web is generally a high multiple of the cross direction strength. Moreover, the conventional processing of bonded nonwoven fabrics involves conveying, saturating, drying and x-zinding stages, all of which impose a further drafting and parallelizing effect on the fibrous web. This procedure yields a product in which the MD/CD strength ratio, i.e. the ratio of the tensile strength of the web in the machine direction to that in the cross direction, is 10 to 20:1.

Attempts to bring the MD/CD ratio closer to 1 have included the use of a cross-laying device, whereby a fullwidth web of oriented fibres is mechanically pleated back and forth across a conveyor belt to build up a composite batt in which the average angular displacement of the fibres is alternated. Such a device is slow and cumbersome and is suitable only for batts of substantial thickness where fold marks and overlap ridges are not objectionable.

In Patent Specification No. 41606 we have described the production of a biaxially oriented nonwoven fabric having alternating stripes of high and low fibre '41 S3 density which extend lengthwise of the fabric, a majority of the fibres in the stripes of lew fibre density being oriented in a substantially cross direction and a majority of the fibres n the stripes of high fibre density being oriented in a direction substantially parallel to the length of the stripes, by passing an airborne stream of discrete staple fibres downwardly onto a moving airpermeable conveyor screen through spaced striping bars disposed over the. screen and extending lengthwise of the screen and apply >.ng suction beneath the screen. This procedure does not, however, produce a fabric having a low MD/CD strength ratio.

It is the primary object of the present invention to produc·· from a carded web of textile fibres a biaxially S3 oriented nonwoven fabric having an MD/CD strength ratio which approaches unity.

The invention provides a biaxially oriented nonwoven fabric having an lid/CD strength ratio of less than 2:1 and composed of adjacent and alternating stripes of high and low fibre density extending in the cross direction of the fabric, the majority of the fibres in the stripes of low fibre density being pulled across the stripes and oriented in a direction substantially normal to the length of the stripes and the majority of the fibres in the stripes of high fibre density being accordion folded so that portions of the fibres are aligned substantially parallel to one another and being oriented in a direction substantially parallel to the stripes of low fibre density.

The invention includes a method of making such a fabric which comprises sandwiching a carded web of textile fibres between a tensioned pervious screen and a set of spaced impervious striping bars extending in the cross direction of the web, and directing a stream of fluid onto the striping bars to cause the portions of the fibres in 3b the gaps between the striping bars to be straightened 5153 - 4 across the gaps at 90° to the striping bars and tha remaining portions of the fibres to become accordion folded under said striping bars, while leaving substantially all the portions of the fibres orginally under the striping bars extending substantially parallel to the length of the striping bars.

The invention also includes apparatus for producing such a fabric comprising a rotary drum carrying on its periphery spaced, axially extending striping bars, a tensioned pervious screen extending around a portion of the drum to define a passage for a carded nonwoven fibrous web between the screen and the drum with the stripping bars extending in the cross direction of the carded web, and means within the drum for directing a stream of fluid onto the web sandwiched between the screen and the drum.

The invention will now be further described with refe rence to the accompanying drawings, in which:Figure 1 is a plan view of a portion of a biaxially oriented nonwoven fabric according to the invention.

Figure 2 is a plan view of a normal textile fibre in its relaxed state.

Figure 3 is a plan view of the fibre shown ih Figure 2 after it has been rearranged by fluid forces in accordance v/ith the invention.

Figure 4 shows a portion of a nonwoven fabric according to the invention, wherein fibres in the web have alternating straight and accordion folded portions, Figure 5 is a perspective view of apparatus for producing a nonwoven fabric according to the invention.

Figure 6 is a side view of the drum and hydroforming portion of the apparatus shown in Figure 5, Figure 7 is a photograph of a fabric according to the invention, and Figure 8 is a diagrammatic sectional view showing a nonwoven web disposed between a tensioned screen and another screen having striping bars as an integral part thereof.

The nonwoven fabric 10 shown in Figure 1 has alternating stripes 11 of high fibre density and stripes 12 of low fibre density which extend in the cross direction of thi· Γ.:!.ι-1ι·. Λ majority of the fibre.-, in the 3tripes 1.1 are substantially lir.lformly distributed therein and are oriented in a direction substantially parallel to the length of the stripes, and a majority of the fibres in the areas 12 are substantially uniformly distributed therein, and are oriented in a direction substantially normal to the length of the stripe.

The striped nonwoven fabric is made from a carded web and has an MD/CD strength ratio which approaches unity. Tha carded web, which may be cross stretched carded web, is passed through aa apparatus, described in more detail below with reference tc figures 5 and 6, in which the web is interposed between a travelling tensioned pervious screen and a rotating arum carrying on its periphery spaced striping r ·· extending in the cross direction of the wei,. streams of water are directed onto the web from the interior of the drum and the resulting fluid forces push the ends of the fibres located between the striping bars to the areas under the bars, sc forming in the portions of the web opposite the gaps between the striping bars areas of low fibre density in which the fibres are drawn very straight. Simultaneously, the portions of the fibres which are moved hydraulically from the areas of low fibre density to the areas of high fibre density which are formed in tiie portions of the web in contact with the striping bars become accordion folded when pushed’ together by forces on either side of a striping bar, thereby resulting in a higher cross direction orientation of the portions 4S153 Of the fibres in the areas of high fibre density than was present in the original carded web. The fabric leaving the apparatus accordingly has stripes of high fibre density running across the fabric to maximize the cross direction strength.

Figures 2, 3 and 4 show, in an exaggerated manner, how the fluid forces act on an individual fibre. Figure 2 shows a normal individual fibre 20 in a carded web. Such a fibre is present in the web as a series of cursive twists and turns and has substantially no straight portions. When such a fibre, extending generally in the length of the carded web, crosses adjacent striping bars on the drum, the effect on the fibre of the fluid forces is shown, somewhat exaggerated, in Figure 3. The portions 21 of the fibre between the striping bars are drawn straight and; the portions of tha fibre in contact with the striping bars become pushed, together in accordion folds 22. Therefore, as shown in Figure 4, the portions of the fibres 21 in the areas of low fibre density are straight and highly orien20 tad in the machine direction of the carded web so as to maximize the MD strength per unit of fabric weight in these areas, while the portions 22 of the fibres in the areas of high fibre density are accordion folded to give a higher CD orientation, with the result that the MD/CD strength ratio comes close to unity.

The cross direction strength can be further enhanced by saturating the web with binder. For example, when binder is added to the web while still wet and suction is applied to remove excess binder, a majority of the binder in the 30 areas of low fibre density passes through the web. Consequently, more binder is present in the areas of high fibre density than in those of lov? fibre density which further enhances the CD strength.

Striping bars of varying widths can be used, and the number of striping bars per inch can be varied, as descri- 7 bet! later In the Examples. Thus the bars may be 1/8 inch wide on 1/4 Inch centres or 1/16 inch wide on 1/8 inch centres.

It should be noted that fibres or portions of fibres forced to lie in a narrow stripe opposite a gap between the striping bars must become increasingly oriented along the length of the stripe as the width of the stripe is decreased. For example, imagining a hypothetical stripe cf width only a few times the diameter of a fibre, any x->ortior. of a fibre of reasonable length would be forced into a cross direction orientation of absolute precision wi.th its axis deviating from a straight line by an amount equal to only a few fibre diameters.

In use of the apparatus shown in Figures 5 and 6, a carded .je'-i 31 is sandwiched between a moving tensioned pervious screen 32 and spaced, axially extending striping oars 33 disposed o?. the periphery of a rotating drum 34. Water nozzles 35 are mount'd on a shaft 36 so that the carded web 31 passes through a striking zone opposite the nozzles 35 and is ait ly jets of wafer to cause the fibres to become rearranged ss described above. As the water passes the web, it pushes the fibres located between the striping bars to the areas under tha bars, thereby causing the fibres in the newly formed areas of low fibre density to be very straight, since they are pulled in opposite directions towards the adjacent areas of high fibre density under the bars. At the same rime, the portions of the fibres that are moved hydraulically from the areas of low fibre density to those of high fibre density become somewhat accordion folded to produce a higher cross direction orientation of the portions of the fibres in the areas of high fibre density than was present in the original carded web. ’he drum 34, cradled by freely rotatable rollers 38, carries the v?eb past a suction box 37, which further — 8 rearranges the fibres in the web and removes the excess water from the web. Another suction box 39 is preferably also positioned directly behind the screen 32 in the striking zone. It is not essential to use water to provide the fluid forces; other fluids such as gas or air can be used to produce similar although possibly somewhat less successful results. If the web contains a proportion Cf thermoplastic fibres, it may be desirable to use live steam as the fluid in order to produce a thermoplastically bonded fabric simultaneously with rearrangement of the fibres. ' The nozzles 35 should preferably be arranged in six banks and should preferably produce a water flow rate of approximately 10 cc/sec per inch of width per bank of nozzles. The nozzles can be conventional solid cone nozzles in overlapping relation. The above-described pulling action on the fibres in the density areas between the striping bars and simultaneous accordion folding action under the bars is totally different from the results achieved by a somewhat similar apparatus described in O.S. Patent No. 2,862,251, which produces uniformly apertured fabrics having spaced interconnected packed fibrous portions cf starting material and apertures arranged in a predetermined pattern which are separated by interconnected packed portions in yarn-like bundles. The different fibre structure achieved by the present invention results in a nonwoven fabric possessing an MD/CD strength ratio that approaches unity.

Figure 7 shows a half-tone3/11^! a striped fabric according^ to, the invention. As can be observed from this half-tone/ e iif the areas of low fibre density a majority of the fibres are drawn relatively straight between the stripes of high fibre density. While in the stripes of high fibre density the accordion folds are not as pronounced as in Figure 3, the folding of the fibres in the 4-5183 stripes nevertheless gives the particular fibre orientation described. Furthermore, although apertures are present in the web, they are randomly distributed and are not surrounded by yarn-like bundles of fibres.

EXAMPLE X A carded web weighing 12.28 gms/sq. yard was made in the conventional manner using 3 denier 1 9/15 type 40 rayon fibres supplied by FMC Corporation. The MD/CD strength ratio of such a web is over 10 to 1. The carded web was put through an apparatus as described above wherein the drum carried metal striping bars of width 1/8" positioned on the drum on 1/4 centres. The web was struck with water droplets having a flow rate of approximately 10 cc/sec per inch of width per bank of solid cone type spray nozzles using six banks of nozzles. The web, after subjection to suction to remove excess water, was saturated with HA 8 binder (tradename for an acrylic binder composition sold by Rohm a Hass). Tho rc 1.15 pounds per inch of width, i.e, an MD/CD strength ratio of about 1.7 to 1. This provided an improvement in the strength ratio over the carded web of 5.84 times.

EXAMPLE IX A carded web weighing 20 grams/sq. yard was prepared of the fibrous material described in Example I. Again, the MD/CD strength ratio of this was in excess of 10 to 1. The web was treated as in Example I and under the same conditions, also using che HA 8 binder. The resulting striped fabric had a machine direction tensile strength of 2.4 pounds per inch of width and a cross direction tensile strength of 2.1 pounds per inch of width, i.e. an MD/CD strength ratio of about 1.14 to 1. This provided an improvement in the strength ratio over the carded web of more than eight times 43153 - 10 Reference has hitherto been made to the use of a drum carrying rigid striping bars. Figure 8 shows another form of apparatus which may be used to make a nonwoven fabric according to the invention. A tensioned pervious screen 54 serves as a backing for a carded web 53, which is sandwiched between the screen 54 and another pervious screen 51 having striping bars 52 as an integral part thereof. The striping bars 52 can either be imprinted on the screen 51 or woven into the screen. When the water spray is directed onro the web from below, as seen in Figure 8, the fibres are rearranged as described above with reference to the drum. However, if the water spray were to be directed from above, the fibres would be washed away from the impervious striped areas 52 and into the open areas between the stripes to produce the reverse effect to that described.

In addition to the obvious advantage of an increased strength ratio provided by the fabric according to the invention, it should also be pointed out that, since the fabric consists of alternating stripes of high and lov? fibre density, the stripes of low fibre density act in the manner of hinges, so greatly enhancing the feel and drape of the fabric.

While the Examples refer to a web made of rayon, other fibre suitable for the production of nonwoven fabrics can be utilized. For example, as mentioned earlier, the web may contain thermoplastic fibres and be subjected to live steam to bind the web simultaneously with rearrangement of the fibres. Further, a carded web made from continuous filaments of reshuffled spread tow web can be used with similar results.

While the water pressures and flow rates mentioned above are preferred, it is possible to use pressures in the range of 20 PSIG to 10,000 PSIG.

Furthermore, if a CD strength higher than the MD /»SiS3 - 11 strength is the desired end product, a random web can be used initially in place of a carded web and will result in a nonwoven fabric having an MD/CD strength ratio of less than one.

Claims (15)

1. A biaxially oriented nonwoven fabric having an MD/CD strength, ratio of less than 2:1 and composed of adjacent and alternating stripes of high and low fibre 5 density extending in the cross direction of the fabric, the majority of the fibres in the stripes of low fibre density being pulled across the stripes and oriented in a direction substantially normal to the length of the stripes and the majority of the fibres in the stripes of high 10 fibre density being accordion folded so that portions of the fibres are aligned substantially parallel to one another and being oriented in a direction substantially parallel to the stripes of low fibre density.

2. A fabric according to Claim 1, wherein the 15 fibres are rayon fibres.

3. A fibre according to Claim 1, which contains a proportion of thermoplastic fibres.

4. A fabric according to Claim 1, wherein the stripes are approximately 1/8 inch wide on approximately 20 1/4 inch centres.

5. A fabric according to Claim 1 wherein the MD/CD strength ratio is less than 1.

6. A method of making a nonwoven fabric according to Claim 1, which comprises sandwiching a carded web of 25 textile fibres between a tensioned pervious screen and a set of spaced impervious striping bars extending in the cross direction of the web, and directing a stream of fluid onto the striping bars to cause the portions of the fibres in the gaps between the striping bars to be 30 straightened across the gaps at 90° to the striping bars and the remaining portions of the fibres to become accordion folded under said striping bars, while leaving substantially all the portions of the fibres originally under the striping bars extending substantially parallel to the length of the striping bars.

7. A method according to Claim 6, wherein the stream of fluid is a stream of water.

8. A method according to Claim 6, wherein the carded web has been cross stretched prior to being sandwiched between the screen and the striping bars.

9. A method according to Claim 6, wherein the water is directed onto the striping bars from a series of nozzles.

10. Apparatus for producing nonwoven fabric as claimed in Claim 1, comprising a rotary drum carrying on its periphery spaced,axially extending striping bars, a tensioned pervious screen extending around a portion of the drum to define a passage for a carded nonwoven fibrous web between the screen and the drum with the striping bars extending in the cross direction of the carded web, and means within the drum for directing a stream of fluid onto rhe web sandwiched between the screen and the drum,

11. Apparatus according to Claim 10, wherein the striping bars are 1/8 inch wide and are located on 1/4 inch centres on the drum.

12. Apparatus according to Claim 10, wherein the drum contains a bank of nozzles for spraying water on the drum.

13. Apparatus according to Claim 12, which includes a suction box disposed beyond the nozzles for removing excess water from the web.

14. Apparatus according to Claim 13, which includes a further suction box behind the screen and opposite the nozzles.

15. A nonwoven fabric according to Claim 1, substantially as described herein with reference to the accompanying drawings.