GB2085938A - Needled multi layer fabric - Google Patents

Abstract

A process for producing a non- woven fabric comprising (1) forming a stack of three or more superimposed fibrous layers, in at least one of the layers the fibres being oriented predominantly in the warp direction and in at least one of the other layers the fibres being oriented predominantly in a second direction, which is inclined at an imaginary line which is orthogonal to the warp direction, (2) needle punching the fibrous layers together and, optionally, (3) bonding the needled fibrous layers together. In the example conjugate fibres are air laid onto a layer of longitudinally aligned conjugate fibres to form second and third layers of fibres orientated at + 45 DEG and - 45 DEG respectively to the machine direction, the layers needled together and then anlogenously bonded by heated embossing calender rolls.

Description

SPECIFICATION Needled non-woven fabric This invention relates to a non-woven fabric which is particularly suitable as a drape comprising a needled stack of fibrous layers and to a process for producing such a fabric.

It is already known to produce a non-woven fabric comprising three or more superimposed fibrous layers in which the predominating direction of fibre orientation in the outermost layers is orthogonal to the predominating direction of fibre orientation in the other layers. Usually the predominating direction of fibre orientation in the outermost layers is in the machine of 'warp' direction and the predominating direction of fibre orientation in the other layers is in the 'weft' direction. In such a fabric the layers are bonded together in discrete areas.

Such fabrics have poor extensibility in the 'warp' and 'weft' directions.

It is also known to produce a bonded non-woven fabric comprising a four ply stack of fibrous layers in which the direction of fibre orientation in the first and second plies in the stack are the same and the direction of fibre orientation in the third and fourth plies in the stack are the same and at an angle to the direction of fibre orientation in the first and second plies.

In such a fabric, if the angle is 90 , then the fabric properties will be similar to those of the above 'orthogonal' fabrics. If the angle is substantially less than 90 , then the fabric will exhibit a weakness and a lack of recovery in the direction of the bisector of the angle complementary to the above-stated angle of fibre orientation.

According to the present invention we provide a process for producing a non-woven fabric comprising (1) forming a stack of three or more superimposed fibrous layers, in at least one of the layers the fibres being oriented predominantly in the warp direction, corresponding to the machine direction of the fabric, and in at least one of the other layers the fibres being oriented predominantly in a second direction, which is inclined at an obtuse angle to an imaginary line which is orthogonal to the warp direction, (2) needle punching the fibrous layers together and, optionally, (3) bonding the needled fibrous layers together.

We also provide a needle punched, and optionally bonded, non-woven fabric comprising a stack of three or more superimposed fibrous layers, in at least one of the layers, prior to needle punching, the fibres being oriented predominantly in a warp direction, corresponding to the machine direction of the fabric, and in at least one of the other layers, prior to needle punching, the fibres being oriented predominantly in a second direction, which is inclined at an acute angle to an imaginary line which is orthogonal to the warp direction, and in at least one of the other layers, prior to needle punching, the fibres being oriented in a third direction, which is inclined at an obtuse angle to the imaginary line, the needled fibrous layers having, optionally, been bonded together.

In the non-woven fabric of the invention, it might be desirable, particularly from an appearance point of view, to arrange for both faces of the fabric to have an identical fibre orientation. This necessarily would require a minimum of four fibrous layers in the stack.

We also prefer that in the stack of layers, the second direction is at an angle of between + 25 and + 654, and more preferably at an angle of between + 35 and + 55 , to an imaginary line which is orthogonal to the warp direction, whilst the third direction is at an angle of between + 115 and + 155 and more preferably at an angle of between + 125 and + 145 to the imaginary line.

The several layers may be formed into a stack in any suitable manner. Each of the layers having a fibre orientation in the warp direction are laid in the machine direction of the nonwoven fabric itself. Those layers having a fibre orientation in the second and third directions are introduced into the stack by a cross lapping technique or, alternatively by a cut and place technique. As a further alternative any or all of the layers in the stack may be introduced by a precision air-laying technique.Thus, for example, where the stack comprises four superimposed layers, the outermost layers having a fibre orientation in the warp direction and the two inner layers having fibre orientations in the second and third directions, the innermost layers can be laid on one of the outermost layers by a cross lapping technique and the other outermost layer can then be laid on top of the cross lapped layer. When the stack includes more than one pair of layers having a fibre orientation in the second and third directions then each of these pairs of layers can be introduced into the stack by a cross lapping technique.

It will be realised that in layers which have been introduced into the stack by a cross lapping technique that the fibres in those portions of the shim which emanate from one longitudinal edge of the non-woven fabric will be inclined at a positive angle to the aforementiond imaginary line and that the fibres in those portions of the shim which emanate from the other longitudinal edge of the non-woven fabric will be inclined at negative angle to the aforementioned imaginary line.

In this specification, unless otherwise indicated, the terms "fibres" and "fibrous layers" are used broadly to include both staple fibres and continuous filaments and layers thereof.

Furthermore, it should be understood that the fibres or filments in a layer can be textured or non-textured or may be potentially crimpable so that if it is desired to bond the layers together by heat, the crimp in such fibres or filaments is developed.

When we use a term such as "the fibres in a layer are oriented predominantly in one direction" we mean that the fibres within the layer have a degree of parallellism in excess of 95% which is significantly higher than that obtained by a simple carding process as applied to staple fibres. This high degree of parallelism is characterised in a layer of staple fibres by a fibre direction coherence of 1 g/cm/g/m2, a cross fibre direction coherence of less than 0.2g/cm/g/m2 and a tweezer separation distance of at least 5 cm. Such an enhanced degree of parallelism of staple fibres may be obtained by subjecting a carded layer to an additional fibre orienting step during the carding operation.Continuous filament layers may be produced, for example, by arranging a number of spinnerets side-by-side and collecting the extruded filaments on a moving conveyor having means to maintain the required degree of predominant orientation of the fibres. Alternatively continuous filament layers may be produced by an air laying technique in which one or more continuous filaments are laid on a moving conveyor. As a further alternative a tow of continuous filaments can be opened to form a layer of filaments using the threaded roll apparatus described in British Patent Specification No. 1 105 968.

In one embodiment of the invention, the fibrous layer is produced by a process which consists of subjecting a plurality of staple fibre slivers including at least some potentially crimpable fibres to a treatment in which the slivers are spread and merged into a web and then subjected to a heat treatment. A process of this kind is described in British Patent Specification No 1 558 402.

In the process the slivers are led between at least three pairs of rollers which draft the fibres and spread and merge the slivers laterally into a single web which is then subjected to a heat treatment under conditions allowing some contraction of the fibres to effect crimping of the crimpable fibres and formation of a coherent highly ordered layer.

Fibre coherence in a staple layer is conveniently measured using a flexible tensile test machine such as the Instron machine. For both fibre and cross-fibre direction measurements a sample width of 2.5 cm equal to the width of the machine clamping jaws which are operated at a crosshead speed of 20 cm/min together with a chart speed of 1 Ocm/min. For fibre direction coherence samples having a length 1.5 times the nominal or mean fibre length plus the clamping length are cut and weighed carefully so as not to disturb the delicate fibre structure and then mounted in the test machine.For cross-fibre direction coherence measurements a test sample length of 1 cm (plus clamping length) is used and for both measurements the coherence is calculated from the measured load as follows: B L W 1 Coherence = --- X ---- X --- X g/cm/g/m2 2.5 100 100 M Where B is the measured breaking load in grams L is the sample length in cm W is the sample width in cm and M is the sample weight in grams.

For measurement of tweezer separation distance stainless steel tweezers are selected measuring 1 3 cm end to end and 11 cm from the hinge point to the tweezer tips, the hinge resilience being such that there is 1 cm separation of the tips from beginning to end of a test. One limb of the tweezers is attached rigidly to the measuring arm of a rotary tensiometer for example of the "Zivy" type having a full scale deflection of 3Qg. To effect a measurement the tweezer tips (sharpened to fine points if necessary), are inserted in the closed position into the sample to the specified depth, the sample having been suitably supported in a horizontal plane under slight tension.The tips are then allowed to open to 1 cm separation in the cross fibre direction and the gauge moved horizontally and parallel to the fibre direction along the web until the initial zero reading rises to 20 g. The distance moved in cm between these points is the tweezer separation distance which is approximately independent of sample weight at least for values in the range 40110 g/m2.

The fibres in a layer may be natural fibres or synthetic fibres derived from linear organic polymeric materials, as for example melt spinnable polyesters, polyamides and copolymers of such linear organic polymers. We prefer that at least some of the fibres in a layer are synthetic Il-iormoplastic fibres since these allow the several layers to be bonded together by simple and efr:ctive thermal means and may be produced in both staple fibre and continuous filament fornl., and potentially crimpable forms, as for example bicomponent fibres in which at least part otjf uni component present at the surface of the fibres is of lower softening or melting point and dllft;ut;nt shrinkage propensity than the other component.

rrle sjt,'ml ray fibrous layers in the stack may, optionally, be bonded together for example by thermal, ultrasonic or adhesive bonding or by stitiching. We prefer, however, to effect point or segmental bonding of the shims by heat and pressure, for example by passing a needled stack of fibrous layers through the nip of a hot calendar press, at least one roll of which bears a pattern of projections which corresponds to the desired pattern of bonded areas.

Preferably the bonded area should be between 5 and 25% and more preferably between 8 and 15% of the total area. The bond spacing should preferably be between 1 and 10 mm.

Preferably the bonded areas are arranged with their longitudinal axes orthogonal to the warp direction.

EXAMPLE A fibrous shim, 1 m wide, was prepared continuously by the method described in BP 1 558 402 starting with 100 ends of 3g/m sliver, from 100% staple fibre having a decitex of 3.3 and a staple length of 90-125 mm. The individual fibres were eccentric core/sheath (67/33), the sheath being composed of 1 5 mole % polyethylene isophthalate/polyethylene terephthalate copolymer. The shim had a weight of 30 g/m2.

After manufacture, the shim was laid directly onto a foraminous conveyor and passed under two sets of air laying devices as described in Patent Application No 40027/78 (Publication No 2006844). To each air laying device, a core/sheath (67/33) heterofoil yarn of 200 decitex and containing 60 filaments composed of a polyethylene terephthalate core and a 1 5 mole % polyethylene isophthalate/polyethylene terephthalate copolymer sheath were fed at a speed of 4000m/min. The plates of each air laying device were 1.6 m wide and the rotary valve speed was 1 330 m/min. The threadline was laid with an efficiency of 95-97% as defined in Patent Application No 40027/78 (Publication No 2006844).The first air laying device was positioned so that the threadline was laid on top of shim to give a filament direction at an angle of + 45 to an imaginary line which is orthogonal to the machine direction of the fabric and the second air laying device was positioned so the threadline was laid to give a filament direction at an angle of + 135 to an imaginary line which is orthogonal to the machine direction of the final fabric. The weight of material laid in each of the latter two directions was 50 g/m2.

The web was then passed through a Bywater needleloom, the first board of which was fitted with 36 gauge standard needles and the second board of which was fitted with 36 gauge fine needles. The web was needled at a rate of 100 punches/sq cm. The needled web was then heat set at 160"C for 2 mins (to partially crystallise the sheath polymer) and then bonded at 197"C and a pressure of 50 psi. The bonding matter was produced using a bottom roll pattern of splines of width 0.04 cm and a separation of 0.1 9 cm and a top roll pattern of rings of laid width 1.7 mm and a groove width of 1.9 mm. The bonded fabric had good aesthetic properties with good dimensional stability in both the warp and 'bias' direction but would stretch in the weft direction. It showed good recovery from stretching in the weft direction.

Claims (6)

1. A process for producing a non-woven fabric comprising (1) forming a stack of three or more superimposed fibrous layers, in at least one of the layers the fibres being oriented predominantly in the warp direction, corresponding to the machine direction of the fabric, and in at least one of the other layers the fibres being oriented predominantly in a second direction, which is inclined at an obtuse angle to an imaginary line which is orthogonal to the warp direction, (2) needle punching the fibrous layers together and, optionally, (3) bonding the needled fibrous layers together.

2. A needle punched, and optionally bonded, non-woven fabric comprising a stack of three or more superimposed fibrous layers, in at least one of the layers, prior to needle punching, the fibres being oriented predominantly in a warp direction, corresponding to the machine direction of the fabric, and in at least one of the other layers, prior to needle punching, the fibres being oriented predominantly in a second direction, which is inclined at an acute angle to an imaginary line which is orthogonal to the warp direction, and in at least one of the other layers, prior to needle punching, the fibres being oriented in a third direction, which is inclined at an obtuse angle to the imaginary line, the needled fibrous layers having, optionally, been bonded together.

3. A needle punched non-woven fabric as claimed in Claim 2 in which the second direction is at an angle of between + 25 and + 65 to an imaginary line which is orthogonal to the warp direction.

4. A needle punched non-woven fabric as claimed in Claim 3 in which the second direction is at an angle of between + 35 and + 55 to an imaginary line which is orthogonal to the warp direction.

5. A needle punched non-woven fabric as claimed in any one of claims 2 to 4 in which the third direction is at an angle of between + 115 and + 155 to the imaginary line.

6. A needle punched non-woven fabric as claimed in Claim 5 in which the third direction is at an angle of between + 125 and + 145 to the imaginary line.