GB2068427A - Producing ordered webs - Google Patents

Abstract

A process and apparatus for simultaneously laying down two or more individual fibrous strands 1, 2 in an ordered manner comprising means for supplying the individual strands, individual means 4, 5 for forwarding each of the strands, individual means for imparting an oscillatory motion to each forwarding strand in a synchronised manner which causes all of the strands, at any instance, to move in the same direction, two closely spaced plates 3 providing a path for all of the oscillating strands between the oscillatory means and a movable collecting surface whereon the strands are laid. <IMAGE>

Description

SPECIFICATION Process and apparatus for the production of ordered fibrous webs This invention relates to a process for the production of fibrous webs having a high degree of orientation of the fibrous strands in the web, comprising forwarding two or more fibrous strands towards a collecting surface and imparting an oscillatory motion to the strands at a point above the collecting surface.

Fibrous webs have been made from staple fibres by carding or by random air laying processes, the former process imparting some degree of isotropic arrangement of the fibres. Fibrous webs have also been made by collecting a mat of synthetic continuous filaments in which the filaments are more or less randomly intermingled in the mat.

However in order that a fabric made from one or more webs should have properties which resemble more closely the properties of conventional woven or knitted fabrics it is considered desirable to introduce a high degree of orientation of the fibrous material comprising the web, as for example, a high degree of parallelism in staple fibre yarns or filamentary strands oriented in, for example, the machine or cross directions or in both these directions. Methods which have been proposed for introducing the desired orientation into a web of filamentary strands include those in which the extruded multifilamentary strands are forwarded and drawn by means of air jets and the issuing filaments are given an oscillatory motion before freely falling onto a collecting brattice or support.UK specification 1 244 753 describes such a method wherein gas oscillating jets are applied to already drawn filaments. It has also been proposed in Japanese patent publication 75 007 1 78 to oscillate the outlet of the forwarding jet to impart the desired oscillatory motion to the emerging filaments. These methods have not in practice proved entirely satisfactory in producing webs of as high a degree of parallelism and order as desired. Thus it is an object of this invention to provide a method in which movement of a strand in the laying down of a web is more fully controlled so as to approach more nearly the desired high degree of parallelism and order.

In Patent Application 40027/78 we have described a process for the production of an ordered web from at least one fibrous strand, comprising forwarding a strand towards a collecting surface, imparting an oscillatory motion to the strand at a point above the collecting surface, the strand being passed between two closely spaced planar plates which are substantially parallel to each other and to the plane of strand oscillation, the plates extending from the place of oscillation down to the collecting surface.

The strand is laid in substantially straight lines on the collecting surface, successive lengths of strand being laid substantially parallel to previous lengths of strand. Also in Patent Application 7928435 (filed 15.8.79) we have described an improvement of the process described in Patent Application 40027/78, in which shaped rather than planar plates are used so allowing the strand to be laid in non-straight lines on the collecting surface.

In Patent Application 40027/78 and Patent Application 7928435 it is contemplated that a number of the strand laying devices, each laying a single strand, may be used in conjunction to produce a single or multi-layer web. We have now found that improved webs can be produced by a process in which two or more individual oscillating strands are simultaneously passed between a single pair of closely spaced plates.

According to the present invention, therefore, we provide a process for the production of an ordered web from two or more individual fibrous strands comprising forwarding the strands towards a moving collecting surface and imparting an oscillatory motion to each strand at a position above the collecting surface characterised in that all of the strands are passed between a single pair of closely spaced plates which extend substantially from the position of oscillation down to the collecting surface, the oscillatory motion imparted to each strand being synchronised with the oscillatory motion imparted to the remaining strands so that at any instance ail of the strands are caused to move in the same direction.

Also according to the invention an apparatus for simultaneously laying down two or more individual fibrous strands in an ordered manner comprises means for supplying the individual strands, individual means for forwarding each of the strands, individual means for imparting an oscillatory motion to each forwarding strand in a synchronised manner which causes all of the strands, at any instance, to move in the same direction, two closely spaced plates providing a path for all of the oscillating strands extending between the oscillatory means and a movable collecting surface whereon the strands are laid.

The term "closely spaced" is used herein to mean less than 75 mm.

The plates used may be spaced apart by a distance of between 0.5 mm and 75 mm.

Preferably, however, the plates are spaced apart by a distance of between 1 mm and 10 mm and more preferably are spaced apart by a distance of between 1 mm and 5 mm.

The plates may be planar or may have any other suitable shape including a curvilinear, for example sinusoidal corrugation, shape, a zig-zag shape, a castellated shape or some other shape which serves to lay the strand in a patterned arrangement on the collecting surface.

If desired the plates may have the same shape throughout their height. Alternatively the plates may have two or more different shapes at different heights, the different shapes merging into one another. In one embodiment an upper portion of each plate is planar and the remaining portion has a corrugated, for example zig-zag or sinusoidal, shape, the two portions merging into one another.

The plates used may be uniformly spaced apart throughout their height but preferably they are arranged so that the space between them converges in a downward direction. Typically the spacing at the upper end of the plates is selected in the range 2 mm to 75 mm and at the lower end of the plates in the range 0.5 mm to 10 mm as for example from a spacing at the upper end of 4 mm to a spacing of 2 mm at the lower end. This convergence of the space assists the sideways exhaust of gas from the space and this reduces the possible disturbance of strands on the collector.

Likewise the distance between the lower ends of the plates and the collector is minimised consistent with maximising the efficiency and precision of laying that is to say so as to give maximum control of the strand while it is moving and immediately after it is laid. For higher strand speeds and web widths the function of the plates becomes increasingly important.

It is preferred to use continuous filamentary strands in the present invention since these may be produced directly from a synthetic polymeric substance as for example by melt spinning. Staple fibre strands, preferably having only a low degree of twist, may also be used and the term "fibrous strand" as used herein includes both these and similar materials.

In producing a mutifilamentary strand by melt extrusion of a synthetic polymer it is desirable to draw or orient the filaments to improve their strength and other physical properties. This may be done by forwarding the freshly extruded filaments at a high speed such that when they have cooled sufficiently any further drawing down of the still plastic filaments will cause orientation and alignment of the polymer chains which is set in on further cooling of the filaments to a temperature below the glass transition point. Gas forwarding jets as described in more detail in Patent Application 40027/78 and Patent Application 7928435, are a convenient means for forwarding the strands and to produce this orientation. The means used to impart an oscillatory motion to each strand may also utilise a compressed gas.Thus jets may be located on opposite sides of each of the forwarding jet outlets and operated alternately so as to direct the issuing strands first in one direction and then in the opposite direction. Jets of this type are described in more detail in Patent Application 40027/78 and Patent Application 7928435. Alternatively a single intermittently operated jet may be used to impart the oscillatory motion to each strand.

A single or two part rotary valve may be conveniently used to provide the alternate or intermittent operation of the two jets or the single jet and the speed of rotation of this valve provides a simple control over the amplitude of oscillation described by a strand; the rotation speed bearing an inverse relationship to the strand amplitude when other conditions are constant. Thus the length of the courses of each strand laid on the collecting surface may be set within at least the range 0.5-4 m by adjustment of the rotary valve speed of each individual jet particularly because the use of closely spaced plates between the oscillating jets and the collecting surface allows changes to have their full effect on strand movement. Oscillating jets may have a single orifice or number of orifices in line or preferably a narrow slot for exit of the compressed gas.It is preferred to mount the deflecting jets so that both the angle between the jets, if two are used, and the angle of the, or each, jet in relation to an issuing strand may be adjusted as a further means of controlling strand oscillation.

While deflecting gas jets are preferred, other devices may be used to impart oscillation to each strand provided they can induce a sufficiently large amplitude of oscillation at the collecting surface. Such alternative devices may be rotating or oscillating opposed pairs of coanda surfaces which are alternatively brought into contact with an issuing strand.

Forwarding jets are all well known in the art consisting of entry and exit passages for the strand and means to introduce the forwarding gas.

The exit passage may be convergent or divergent but it is preferred to use a parallel passage to maintain the integrity of the issuing strand passing to the place of oscillation.

Because closely spaced plates are provided between the forwarding/oscillating means and the collecting surface each strand will assume a wave form oscillation the amplitude of which will be dependent upon the forces involved and will maintain this wave form until it reaches the collecting surface whereon it is laid in substantially parallel courses the contour of which is dependent on the shape of the plates used.

We have already mentioned that the oscillatory motion imparted to each strand is synchronised with the oscillatory motion imparted to the remaiming strands. The object of this is to ensure that the several strands passing between the plates move independently of, and without interfering with one another. Thus the several strands moving between the single pair of plates will, at one instance, be cause to move in the same direction.

Nevertheless it should be understood that each individual strand may be laid in a superimposed manner on an adjoining strand. Indeed it is advantageous for this to occur because a more integrated web is produced.

Conveniently this synchronisation of oscillatory motion between the strands as they move between the plates is achieved by using a common drive for the individual means for imparting an oscillatory motion to each forwarding strand.

The method and apparatus of this invention make it possible to lay highly oriented webs in which several strands are laid simultaneously with an exactitude and precision hitherto impossible.

Furthermore the several strands can be laid with such precision at a strand speed of at least 3600 m/min with an overall efficiency of 96% or more.

In a preferred embodiment of the invention the parallel plates are positioned with their medial planes parallel to the direction of movement of the collecting surface so that the individual strands are laid on the collecting surface in a generally warp-wise manner. In the preferred embodiment the plates, the means for supplying the individual strands and the means for imparting an oscillatory motion to each strand are adapted to move together with a reciprocating movement so that they traverse substantially the total width of the collecting surface. In this way the individual strands are laid in a warp-wise manner across substantially the whole width of the collecting surface.It will, of course, be realised that because of the relative movement of the collecting surface and the several means for supplying the individual strands each individual strand will be laid in such a manner that it is displaced with respect to an adjoining strand and this achieves uniform cover of the collecting surface.

The laying of strands on the collecting surface may be conducted with a very high precision to produce a web of substantially uniform thickness.

It will be realised that when the plates are shaped, that the strands will not be laid on the collecting surface in straight lines. Instead, with suitably shaped plates, portions along the length of a strand will be laid in a warp-wise direction and portions along the length of a strand will be laid in a weft-wise direction.

This produces a web exhibiting two directional properties which is very desirable in fabrics for use as apparel textiles.

Webs made according to this invention require to be bonded in some manner to convert them into useful fabrics and for this purpose it is preferred to use some form of segmental or spot bonding method so as to preserve the directional properties introduced in making the web. It is further preferred to include in the web at least a proportion of thermoplastic filaments or fibres and to employ a thermal or ultrasonic segmental bonding method for making the final fabric. Such thermal segmental bonding methods are described in for example United Kingdom patent specifications 1 245088, 1 474 101 and 1 474 102. Thermoplastic synthetic filaments or fibres of many kinds are suitable for use in this invention either alone or in a mixture with natural or other non-thermoplastic fibres.It is most preferred that the webs include or are composed of bicomponent synthetic fibres in which one of the components present at least in part at the surface of the fibre or filament is of lower softening or melting point, than the other and forms a strong bond under suitable conditions of heat and pressure. Alternatively or in addition to the foregoing segmental or spot bonding methods other processes may be used as for example, stitch bonding in which the web is held together by chains of stitching using a separate thread or part of the web itself and machinery which is capable of operating at fast production rates.

Synthetic polymeric filamentary strands being nonconductors and hydrophobic tend to accumulate static charges when in frictional contact with processing surfaces and as such charges may disturb the even oscillation or laying of a falling strand. It may be necessary to eliminate or reduce the accumulation of such charges by the provision of static discharging means at or near the point of oscillation or by surface treatment of the filaments with an appropriate chemical agent.

It is preferred, when using a gas forwarding jet, that a small amount of the issuing gas is allowed to pass in a gentle current down between the plates to assist the passage of an oscillating strand down to the collecting surface. It is also preferred that the collecting surface is a pervious brattice to allow escape of gas and if necessary the application of suction to the underside at the place of contact with a newly laid strand and thus to ensure its complete contact with the brattice.

The invention will now be described with reference to the accompanying drawings in which Figure 1 is a diagrammatic representation of the invention in which two strands are passed between a pair of closely spaced plates.

Figure 2 shows the boundary lines formed by joining consecutive points of reversal of a strand as it is laid on the moving collector surface as the plates and strand forwarding/oscillatory means traverse substantially the whole width of the collector surface.

Figure 3 shows the path of the strand within the boundary lines shown in Figure 2.

Figure 4 shows the paths followed by two strands as they are simultaneously laid on a moving conveyor surface in accordance with the invention.

In Figure 1, two strands, 1 and 2, are forwarded between plates 3 and on to a moving collector surface (not shown) by means of gas forwarding jets 4, 5 which are described in more detail in Patent Application 40027/78 and Patent Application 7928435.

Before entering between the plates, which are positioned parallel to the direction of movement of the collector surface, an oscillatory motion is imparted to each strand in a synchronised manner by compressed gas deflector jets (now shown but described in Patent Application 40027/78 and Patent Application 7928435). For clarity the limits of movement of the strands within the plates are shown as dotted lines.

In Figure 2 is shown imaginary boundary lines 6, 6A formed by the points of reversal of a strand as the plates shown in Figure 1 and associated forwarding/deflector jets simultaneously traverse from left to right the width of a collecting surface moving in the direction indicated by the arrow.

Also shown are imaginary boundary lines 7, 7A formed by the points of reversal of a strand as the plates and associated forwarding/deflector jets simultaneously traverse from right to left the width of the collecting surface.

In this Figure, W denotes the width of the web produced and L denotes the overall strand path length along the length of the collecting surface.

Figure 3 shows the path of the strand 8 as it is laid on the conveyor in the manner described with respect to Figures 1 and 2. Again the points of reversal of the strand fall on imaginary boundary lines 6, 6A and 7, 7A.

In Figure 4 the path of strand 8 is shown in a full line and the path of strand 9 is shown in a broken line. The imaginary boundary lines 10, 1 OA 101, 1 0A1 are formed by joining the points of reversal of strands 8 and 9 respectively as the plates and forwarding/deflector jets move from left to right across the collecting surface and the imaginary boundary lines 11,11 A, T, 1 1 AT are formed by joining the points of reversal of strands 8 and 9 respectively as the plates and forwarding/deflector jets move from right to left across the collecting-surface.

For ease of understanding we have shown diagrammatically in section the plates 3 and locatiori of the gas forwarding jets 4, 5 with respect to the plates in order to achieve a laid strand pattern as shown.

The invention will now be described with reference to the following Example:- EXAMPLE Two strands, each composed of 60 synthetic filaments and with a final decitex of 200, spun direct from a spinneret, were led by way of rolls rotating at a speed of 4,000 m/min to the entries of forwarding jets (items 4, 5 in Figure 1) supplied with compressed gas at a pressure of 1758 g/cm2 gauge. A pair of motorised rotary valves, supplied with compressed gas at a pressure of 5625 g/cm2 gauge, each served to give impulses of compressed gas to a pair of deflector jets. Each pair of deflector jets was located immediately below a forwarding jet and symmetrically in reflation thereto with an included angle of 1650 between the jets.Each valve served to give an impulse of compressed gas in turn to each of the jets in a pair of jets, each jet receiving compressed gas from the rotary valve for 50% of the valve revolution. Each rotary valve rotated at a speed of 2000 rpm.

The two strands emerging from the forwarding/deflector jets were passed between a pair of plates 3, 1.5 m wide and 0.5 m high. The forwarding jets were spaced equidistant from opposed edges of the plates and equidistant apart i.e. the forwarding jets were 0.5 m apart and 0.5 m from each opposed edge of each plate. The tops of the plates were 1 cm below the forwarding jets and the plates were spaced 4 mm apart at the top and 2.5 mm apart at the bottom. The bottoms of the plates were 3 cm above a horizontally disposed 150 cm wide foraminous conveyor moving at a speed of 4 m/min.

The plates, forwarding jets and both pairs of deflector jets were arranged to traverse the width of the conveyor in a to and fro manner at a speed of 10 m/min (which is equivalent to a traverse cycle rate of 4 cycles/min) so that the two strands issuing from between the plates were laid on the conveyor in the manner shown in Figure 4.

The overall strand path length laid down was 0.97 m compared with a theoretical length (calculated from the strand and rotary valve speeds) of 1.0 m thus giving an overall laying efficiency of 97%.

The above Example was achieved using a prototype apparatus in accordance with the invention.

At the output speeds envisaged for a production machine, higher traverse speeds, up to, say, 100 m/min, would be required in order that each strand nominally covers the whole area of the web. At such speeds, the distance between adjacent strand reversals will be relatively large e.g. 50 mm. Accordingly it will be necessary to ensure that successive strands are laid so as to fill in the gaps left by previous strands. In order to obtain a uniform web, the strand forwarding/deflector jets must be arranged with respect to the plates in accordance with the following equation:- Distance between adjacent strand forwarding/deflector jet assemblies Strand cycle length Number of forwarding/deflector jet assembles and the length of the plates by the equation:- Plate length 3 Strand cycle length + (Number of strands - 1) x Distance between adjacent forwarding/deflector jet assemblies

Claims (7)

1. A process for the production of an ordered web from two or more individual fibrous strands comprising forwarding the strands towards a moving collecting surface and imparting an oscillatory motion to each strand at a position above the collecting surface characterised in that all of the strands are passed between a single pair of closely spaced plates which extend substantially from the position of oscillation down to the collecting surface, the oscillatory motion imparted to each strand being synchronised with the oscillatory motion imparted to the remaining strands so that at any instance all of the strands are caused to move in the same direction.

2. A process as claimed in claim 1 characterised in that that closely spaced plates are positioned with their medial planes parallel to the direction of movement of the collecting surface so that the individual strands are laid on the collecting surface in a generally warp-wise manner.

3. A process as claimed in Claim 2 characterised in that the plates move together with a reciprocating movement so that they traverse substantially the total width of the collecting surface.

4. An apparatus for simultaneously laying down two or more individual fibrous strands in an ordered manner characterised by means for supplying the individual strands, individual means for forwarding each of the strands, individual means for imparting an oscillatory motion to each forwarding strand in a synchronised manner which causes all of the strands, at any instance, to move in the same direction, and two closely spaced plates providing a path for all of the oscillating strands extending between the oscillatory means and a movable collecting surface whereon the strands are laid.

5. An apparatus as claimed in claim 4 characterised in that the individual means for imparting an oscillatory motion to each forwarding strand use a common drive.

6. An apparatus as claimed in either claim 4 or claim 5 characterised in that the parallel plates are positioned with their medial planes parallel to the direction of movement of the collecting surface so that individual strands are laid on the collecting surface in a generally warp-wise manner;

7. An apparatus as claimed in claim 6 characterised in that the plates, the means for supplying the individual strands and the means for imparting an oscillatory motion to each strand are adapted to move together with a reciprocating movement so that they traverse substantially the total width of the collecting surface.