IE43992B1 - A method of making biaxially oriented nonwoven fabrics - Google Patents

Abstract

An aqueous dispersion of long and short fibres is slurried by stripe-forming elements onto a moving endless wire. The long fibres have a minimum length of 12.7 mm. The short fibres are shorter than 12.7 mm. The stripe-forming elements extend in the direction of movement of the endless wire. They are either formed on the longitudinal wire itself by stripy liquid-impermeable coverings over the wire apertures or fixed in place as stripe-forming strips above the endless wire. The distance between the stripe-forming elements is less than the average length of the long fibres. The fibre web thus produced has successive alternating regions (11, 12) of higher and lower fibre density. The fibres in the regions (11) of higher fibre density are aligned in a parallel arrangement in the longitudinal direction of the fibre web. The fibres in the regions (12) of lower fibre density are aligned transversely to the longitudinal direction of the fibre web. The fibres in the stripe-structured fibre web are fixed, for example by applying an adhesive to the composite (10) or, if thermoplastifiable fibres are present, by heating the composite (10).

Description

This invention provides a method of making a biaxially oriented nonwoven fabric having alternating stripes of high and low fibre density, which comprises preparing a stock of blended long and short fibres, the long fibres having a.length of at least half an inch and the short fibres having a length less than half an inch, maintaining the stock in an agitated state, causing the stock to flow into a headbox in which the stock becomes stabilized, flowing the stabilized stock onto a moving Fourdrinier ]_0 screen having approximately equidistantiy spaced fluidimpervious, finger-like resist areas disposed above or on the screen and extending parallel to the direction of travel of the screen the width and spacing of the resist areas being such that the majority of the long and short fibres in the stock become located on the screen between the resist areas to form the stripes of high fibre density with the fibres orienting in a direction substantially 43982 parallel to the length of the resist areas, while the remainder of the fibres become located across the resist areas and oriented in a direction substantially normal to the length of the resist areas to form the stripes of low fibre density, securing in such orientations the fibres of the biaxially oriented nonwoven fabric so obtained, and carrying the fabric on the moving screen to a pick-up device for collection thereon.

Preferably the resist areas are approximately equidistantly spaced finger-like striping bars disposed over the screen.

This invention will now be further explained with reference to the accompanying drawing, in which:Figure 1 is a plan view of a nonwoven fabric made by the method according to the invention, and Figure 2 is a flow chart illustrating the method.

Figure 1 shows a single-layer 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 obtained in a direction that substantially follows the direction of a moving Fourdrinier screen upon which the fabric is made (the machine direction), i.e. these fibres extend 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 (the cross direction orientation), i.e. these fibres are disposed substantially normal to the fibres in the stripes 11 and bridge those stripes. These alternating striped portions of varying orientation are formed simultaneously as described below.

A nonwoven fabric such as that shown in Figure 1 is made by a papermaking technique, wherein a stock of blended long and short fibres is prepared and held in a chest at a particular consistency, while being agitated to prevent settling and separation of the solids. The 3S-9 2 stock then flows to an inlet distribution systems which spreads the flow to the full machine width, discharging the stock into a headbox, wherein the flow becomes stabilized.

The stabilized stock then flows onto a moving Fourdrinier wire screen, which travels around a perforated couch roll and suction is applied to the screen to drain the water away and cause the fibres to become deposited on the screen.

The screen carries fluid-impervious resist areas in the form of continuous, parallel stripes extending lengthwise of the screen. Alternatively, parallel striping bars extending lengthwise of the screen may be disposed above the screen in the path of flow of the stock onto the screen. These striping bars are similar to those used in the apparatus described in Patent Specification No. 41606 · which forms a nonwoven fabric by depositing an airborne stream of fibres onto a moving screen. As the stock flows onto the screen, a majority of both the long and short fibres are drawn to the areas thereon on opposite sides of the fluid-impervious areas constituted by the resist areas or striping bars. This is especially true of the short fibres since they are not subject to forces arising from more than one such area and do not therefore attempt to bridge a fluid-impervious area.

Indeed, because of the movement of the screen, they are increasingly drawn to the portions of the screen between the fluid-impervious areas and become oriented parallel to the machine direction of the web of fibres formed on the screen.

Simultaneously, a minority of the fibres, especially ) the long fibres, will be subject to forces arising from areas on opposite sides of fluid-impervious areas, which cause some of the long fibres to form bridges between a pair of fluid-impervious areas and become oriented in a direction substantially normal to the lengthwise direction ; of the screen.

Provided the striping bars or resist areas are disposed sufficiently close together, and in practice the spacing between them should generally be less than the average length, and preferably less than half the average length, of long fibre, the frbres that do not bridge the striping bars or resist areas will be carried into a stripe of high fibre density which lies between the striping bars or resist areas. In a stripe of high fibee density the majority of the fibres are oriented along the length of the web.

As already explained the long fibres have a length of at least half an inch, while the short fibres , which may be paper fibres, cotton linters or short thermoplastic fibres, or combinations thereof, have a length less than half an inch. If short thermoplastic fibres are used, either alone or with short fibres, they will be drawn into the stripes of high fibre density and when activated by heat, will bond the long bridging fibres at the ends which are incorporated into these stripes, but will leave the bridging substantially free of bonding between the stripes of high fibre density, thus enhancing drape and softness in those areas, and in the total fabric.

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 be disposed within the stripes of high fibre density.

In all but the lightest weight fabrics, the top of the fabric, that is the portion of the fabric furthest removed from the Fourdrinier screen, will be covered by a minor portion of long and short fibres positioned more or less at random across the entire width of the web. As the fibres in the stock flow position themselves on the screen and resist areas, or form an increasingly thick layer and pass off the striping bars, the fibres become less generally controlled by the diverging action of the water between fluid-pervious and fluid-impervious areas, and fall on the uppermost portions of the web in a somewhat random fashion. The web at this point can best be -described as having stripes of high and low fibre density having a somewhat random covering of long and short fibres integrated therewith. However, a majority 43992 of the fibres are nevertheless positioned in a striped fashion and in an orientation parallel to the length of the web.

If the striping bars or resist areas are disposed sufficiently close together, the fabric assumes a pronounced ribbed structure. By ribbed structure" is meant that the stripes of the high fibre density contain so many fibres that they become almost semicircular in configuration, while the stripes of low fibre density remain more or less flat.

The web is carried on by the screen to a zone at which the fibres are secured by bonding in the above described orientation, e.g. by deposition of adhesive on the web or, in the case when some of the fibres are thermoplastic, by passage beneath a heater. Finally the bonded non-woven web is collected from the screen by a suitable pickup device.

The nonwoven fabrics produced by this invention have a variety of uses and may be used as disposable curtains or drapes, as decorative narrow ribbons and for florist ribbons, as sweatbands, as cling type bandages or as disposable tablecloths.

If the striping bars or resist areas extend over part only of the width of the screen, a substantially random web will be formed on the unblocked surface of the screen which will be integrally connected to the bi-axially oriented striped portion of the web.

Claims (4)

1. A method of making a biaxially oriented nonwoven fabric having alternating stripes of high and low fibre density, which comprises preparing a stock of blended long and short fibres, the long fibres having a length of at least half an inch and the short fibres having a length less than half an inch, maintaining the stock in an agitated state, causing the stock to flow into a headbox in which the stock becomes stabilized, flowing the stabilized stock onto a moving Fourdrinier screen having approximately equidistantiy spaced fluid-impervious, finger-like resist areas disposed above or on the screen and extending parallel to the direction of travel of the screen, the width and spacing of the resist areas being such that the majority of the long and short fibres in the stock become located on the screen between the resist areas to form the stripes of high fibre density with the fibres oriented in a direction substantially parallel to the length of the resist areas, while the remainder of the fibres become located across the resist areas and oriented in a direction substantially normal to the length of the resist areas to form the stripes of low fibre density, securing in such orientations the fibres of the biaxially oriented nonwoven fabric so obtained, and carrying the fabric on the moving screen to a pick-up device for collection thereon.

2. A method according to claim 1, wherein the resist areas are finger-like striping bars disposed over the screen.

3. A method according to claim 1 or claim 2, wherein the distance between the edges of adjacent resist areas is less than an average length of a long fibre.

4. A method according to claim 1, in which the fabric includes generally cross-oriented or randomly disposed fibres disposed on top of and integral with the striped portion of the fabric.