IL27207A - Non-woven filamentary structures and process and apparatus for the manufacture thereof - Google Patents

Description

J3AJENTS_ _AN_D _DE_SiqNS_ ORDINANCE S P E C I F I C A TI O N NON-WOVEN FILAMENTARY STRUCTURES AND PROCESS AND APPARATUS FOR THE MANUFACTURE THEREOF ΟΠΧ» » We. IMPERIAL CHEMICAL INDUSTRIES LIMITED, a British Company of Imperial Chemical House, Millbank, London, S. W.1. England DO HEREBY DECLARE the nature of this invention and in what manner the same is to be performed, to be particularly described and ascertained in and by the following statement :- Shs present inven i on s concerned with non-woven filamentary structures o continuous filaments and wit a process and an apparatus for making such structures.

Processes are known in which continuous filaments are made in a controlled manner by the use of traversing mechanism, "shulfler" plates and like mechanisms. Air ejectors which may be traversed, have also been described* Using these variuus traversing means, there is a tendency for filaments to be deposited in bundles in the filamentary web so that a so-called "stringy" appearance is given to the web. It has also been proposed to separate bundles cf filaments by repulsion effects produced when electro-static charges of similar polarity are induced on the filaments.

Those processes which involve the use of electro-static charges are affected by changes in atmospheric conditions and changes in the condition of the surfaces over which the filaments pass, so that difficulties arise in achieving consistent control. This particularly applies when, in the interests of economical working, large bundles of filaments are to be separated and deposited to form a web, since it becomes difficult to charge a fast moving bundle uniformly as the number of filaments is increased.

One object of the present invention is to reduce the disadvantages of the previously proposed method's whilst avoiding the xise of traversing mechanisms or electro-static repulsion.

According to the present invention, a non-woven filamentary structure comprises a plurality of substantially parallel filamentary bunds, each band oeing formed of one or more filaments disposed in a random configuration uniformly another by random overlapping1 and irtteriaingling with the filaments thereof, and said structure having folded portions thereof of substantially equal length overlapping in the direction of substantial parallelism of the filamentary band and each overlapping portion extending across the structure in a direction substantially at right angles to said direction and parallel to its neighbouring portions.

The present invention also includes a process for making a non-woven filamentary structure which comprises forwarding a bundle of continuous filaments under tension towards a moving receiving surface, wherein the filaments are banded .Into a substantially uniform filamentary ribbon in v/hich the filaments are aligned in parallel relationship, the so-formed ribbon is spread into a diverging curtain of separated filaments, and the curtain of filaments is overfed onto the receiving surface as it moves in a direction substantially at right-angles to the plane of the curtain of filaments so that the filaments are collected thereon as a non-woven web. The bundle of filaments is passed through a banding stage where, in a restricted space, it is subjected to the action of at least two non-parallel streams of gas which are arranged to impinge on the filaments whereby the filaments are aligned into the substantially uniform filamentary ribbon; and the so-formed ribbon of filaments is passed through a spreading stage where, in a restricted space, the filaments are subjected to the action of at least one stream , - fv of gas ^/substantially arcuately shaped cross-section arranged to impinge on the ribbon of filaments over the width thereof and whereby the filaments are forwarded to the moving receiving surface and spread into the diverging curtain of filaments, formed from a plurality of filar*lenta hic are continuously extruded from the spinneret forming part of a spinning unit.

A capstan roll/nip roll arrangement my be interposed between the banding stage and the spreading stage. The capstan roll is arranged to run at a constant surface speed and draws the freshly spun filament away from the spinneret and through the banding stage. The effect of thisis to apply a low tension to the filaments, which is not sufficient to draw them, and to control the denier of the filaments. The same effect may also be achieved by substituting gas- ejector means for' the capstan roll/nip roll arrangement.

In order to obtain a web of drawn filaments a drawing stage may be introduced into the process before or after the banding stage. The filaments may be heat set during the drawing stage to facilitate subsequent processing.

A web comprising of a mixture of undrawn and draxvn filaments may be obtained by allowing a proportion of the freshly spun filaments to by-pass the drawing stage and then passing the drawn and undrawn filaments to the banding stage.

The drasri and undrawn filaments may be processed by separate banding stages into two filamentary ribbons of equal width before passing them through a common spreading stage.

In order to enhance the runnability -Bad control of the process any electro-static charges on the filaments may be at least reduced, say by means of an electro-static eliminator before the filaments enter the spreading stage. The separation of the filaments is then achieved by the action of the gas stream of the spreading stage, Bonding of the web may subsequently be carried out super-calendering. Bonding ag tits having lower softening points than the filaments in.the v;e"b may "be used for this purpose, or the web may he fornetl of .a·mixture of filaments having different softening points in which the filaments with the lowest softening point serve as binder filaments when subjected to heat treatment. The tinder filaments nay be Qo-spun into the bundle of filaments» Alternatively, heterofilaents formed from two polymers of different softening points may be used to form the wen, the polymer having the lower softening point serving as the bonding agent during a heat treatment at a temperature sufficient to soften it. Cold bonding may also be used.

Potentially crimpaMe filaments may be formed into webs using the process of the invention and the crimp may be developed in the filement in the banding stags or the spreading stage by heating the gaseous fluid used therein.

Although a continuous process has been so far described, that is, in which the continuous filaments are processed directly from a spinnerex, the invention is also applicable to continuous filaments which are- spun from a spinneret, and possibly drawn, and then wound up onto packages whereafter the continuous filaments are unwound from the packages as a bundle and formed into a web by the process of the invention.

The process of the invention can be used to make webs from all types of non-tacky filaments, that is, filaments which have a. state of non-tackiness such that on passing through the banding and spreading stages they do not stick to one another or to the apparatus. Examples of such non-tscky filaments are made from polyethylene terephthalate, polyhexamethylene adipamide, polycaprolactam, polypropylene, dry viscose, cellulose acetate, The pre-sent invention, .further includes apparatus for use in the production of a non-woven filainentary structure which comprises: means for supplying a "bundle of continuous filaments; a banding device for forming the bundle of filaments into a substantially uniform filamentary ribbon comprising a pair of substantially parallel, flat surfaces, defining a restricted filament passageway and tnrough which in operation the filaments are passed, one of said surfaces having at least two non-parallel slots therein which open into the filament passageway and which ere arranged on opposite sides of the path of the filaments through the banding device, said slots being adapted for correction to a source of gas under pressure; a spreading device for foraing the filamentary ribbon into a diverging curtain of filaments comprising a pair of substantially flat surfaces defining a restricted filaiaent passageway and through which in operation the ribbon of filaments is passed,an arcuate slot in one of said surfaces which opens into E&id filament passageway and which is adapted to be supplied with gas under pressure so that, in operation, the filaments passing over the arcuate slot are acted on by a stream of gas isauing therefrom in such a manner as to forward the filaments and spread then into a diverging curtain and a receiving surface arranged to be moveable in a direction substantially at right angles to the plane of the curtain of filaments whereby in operation the filaments are collected thereon as a non-woven web.

The width of the filamentary ribbon can be varied to suit certain requirements during operations of the boundi device by varying the velocity of the gas issui from the slots. The maximum effectiveness of the banding device is best realised at filaments over a roll situated iBmeai teiy after the banding device, assists in keeping the uniformity of the filamentary ribbon..

Unlike the prior kn wn devices, such as gas eiectors, which have been described for separating the filaments into a diverging shroud of filanents, the spreading device of the invention separates the filaments into- a diverging curtain in which the filaments over a large part of their travel to the receiving surface are substantially contained in a single plane.

This, arrangement of the filanents when deposited on the receiving surface gives rise tc a filament geometry in the so-formed web which is quite different from thab of a web formed from a shroud of filaments.

The banding device nay be provided with a further straight slot in said one surface containing the non-parallel slots, and said further slot extends transversely to the path of the filaments through the banding device. The stream of gas issuing from this slot serves to distribute the filanents more uniformly across the width of the filamentary ribbon0 An additional the uniformity of the filament/ ribbon leavin /draw rolls 7hich may be present to draw the filaments, and before it enters the spreading device. This may be required when the distance between the feed roll and the d aw roll systems is sufficient to allow disturbance of the ribbon during the drawing of the filaments thereof.

The arc of the slot of the spreading device is arranged in the direction of travel of the filaments and the desired radius 01 the arcuate slot can be determined in a manner hereinafter described.

The surface of the apreading device not having the arcuate slot is slot, so that the angle of divergence of the filamentary curtain can be altered to some extent.

The movable surface upon which the filaments are deposited is conveniently constituted fcy the upper ru of an endless conveyor, which allows the free flow of gas therethrough. The provision of such a receiving surface reduces any turbulence which may be caused by the gas in which the filaments are suspended and hence at least greatly reduces the likelihood of the structure of the web being disturbed. 4Ή^ ί-^I'44Φ^Ιί^ I'$4^ kU4 MH>bM li tekb-m®M/WW tUUM PkUH mtiUMMJ fiH/b/./ J-f JSf/fi L The speed of the receiving surface of the conveyor is controlled to allow overfeeding thereon of the filamenta to make a we& of the desired thickness.

Ideally the filaments delivered into the web on the receiving surface should be equally separated and distributed uniformly over the width of the web. However, as a result of slight imperfections which may occur in the banding and spreading device¾ and/or currents of imperfectly directed gas, the uniformity of filament separation and distribution may be somewhat disturbed and may throughout any operating period. These variations which may occur are at high frequency and the general effect is towards compensation of the variations, so that good uniformity of web thickness and cover is achieved with overfeeding of the filaments.

Due to the fact that the web is generated from an overfed curtain of filaments in which the filaments are substantially equally spaced apart (the majority not migrating extensively across the curtain over short periods) the form taken by the filaments in the web is such that they exhibit an overall pattern of parallelism. The overfeeding of the filaments causes individual filaments each with neighbouring filaments. More than one filament ·, of course, nay occupy or overlap the sane proportion of the web width (or band), but this depends to a large extent on the number of filaments and their spacing apart in tho curtain.

When the filaments have the sane colour the bands formed thereby are not discernable by the naked eye. However, when one (or more) of the filaments is coloured differently then it can be seen to randomly occupy a proportion of the web width.

Overfeeding of the curtain filanents also causes it to oscillate so that the filaments in the τ/eb are deposited in a manner such that in cross section the web is seen to be built up from folded overlapping portions of substantially equal length which overlap in the direction of travel of the receiving surface, that is, the web is built up in the form of crude TZl laminations.

Preferred embodiments of the invention will be further described, by way of example, with reference tc the accompanying drawings, wherein;- Figure 1 shows, diagrammatically, a banding device of the invention part of which has been omitted to enable the slots to be seen; Figure 2 is a section tkken along the line II II of Figure 1.

Figures 3 and 4 show modifications of the slots of the device illustrated in Figure lj Figure 5 s a diagrammatic representation of filaments bding spread by the spreading device of the invention; Figure 6 is a side view of Figure 5? Figures 7, 8 and 9 shows alternative apparatus assemblies for carrying out the process of the invention; and static field meter for measuring the electro-static eharge.

In the drawings, like parts have the same reference numerals.

The basic apparatus of the invention comprises a banding device which takes a bundle of continuous filaments and converts it into a substantially uniform ribbon of parallel filaments, and a spreading device ¾hich converts the ribbon of filaments into a diverging curtain of filaments and forwards the filaments to a receiving surface -where they are collected as a non-woven filamentary web.

A typical banding device of the invention is illustrated in Figures 1 and 2. The banding device, generally designated 10 comprises a rectangular impingement plate 12 which is arranged substantially parallel to a rectangular plate 14 so that a restricted space 16, i.e. a filament passageway, is defined between the plates. The plate 14 constitutes the front wall of the banding device 10 and has slots 16, 20 and 22 therein which communicate, with separate compartments, 2 , 26 end 28, conneoted to a common expansion chamber 30 by a valve port 32 controllable by an adjustable valve member 34 . (Only one valve port 32 and its valve member 34 a e shewn in Figure 2 ) . The expansion chamber has an inlet 36 for the supply of conpressied air.

In operation, compressed air is admitted through the inlet 36 into the expansion chamber 30 and passes through valve ports 32 into the compartments 24 , 26 and 28 from whence it issues at a high velocity through slots 18, 20 and 22, respectively into the filament passageway 16 and impinges against the flat surface of the plate 12. ien a bundle of filaments 39 is ed under tension between the plates 12 and 14 it is acted upon by the streams of sir The air stream issuing from the slot 20, which is arranged transversely to the path of thefilaments 38 , spreads the filaments substantially uniformly across its length. The non-parallel slots 18 and 22 have air streams issuing therefrom which control the spread of the filaments 36. The total effect of air turbulence in the filament passageway 16 and the current set up of air escapes between the plates 12, 14 sustain the filaments 38 in a substantial parallel relationship as a ribbon of filaments..

By adjustement of the valve members 34 "the flow of pressurised air to the separate compartments 24 , 26 and 28 can be controlled and hence the width of the filamentary ribbon can be regulated. For example, by reducing the air flow to compartment 26 and increasing the air flow to compartments 24 and 28, the velocity of the air stream issuing from the slots 18 and 22, is greater than that of the air stream issuing from the sloe 20, and thus the width of the ribbon of filaments is reduced.

In a modific tion of the banding device just described, the slot 20 is omitted and the compartments 24 , 26 and 28 are combined into a single air chest. The control of the width of filamentary ribbon is then achieved by adjustement of the air flow into the air chest which supplies pressurised air to the oblique slots 18 and 22, Modifications to the positioning and shp„pe of the slots in plate 14 may be effected as shown in Figures 3 and 4 , In Figure 3 the slot which is of uniform cross section ispositioned such that its longitudinal axis makes an angle Y with a normal to the plate 14. This increases the forsaard component of velocity of the air stream issuing from the slot and facilitates the advancement of the filaraents 38 through the banding device and also In Figure 4 the slot is slightly displaced from the normal and diminishes in cross-section in the direction cf the air flow therethrough such that, as shown in section, the sides of the slot subtend an angle X. This shape of slot tends to reduce the fractional losses in the passage of the air through the slot without loss of air velocity as it issues from the slot.

The pressure of the air supplied to the handing device is controllable by an adjustable valve positioned in the air supply system between a source of pressurised air, such as an air compressor, and the inlet to the banding device The gap between the plates 12 and I4 should be as snail as possible consistent with the free passage of the filaments therebetween.

An embodiment of the spreading device of the invention is shown in Figures 5 and 6, and comprises an air chest 0 having a front wall formed by a rectangular plate 42.. The plate 42 has an arcuate slot 44 therein which communicates with the air chest 40, Inlet pipes 46 are connected to the air chest 4^ at opposite sides thereof for supplying compressed air into the air chest. An impingement plate 43 s spaced from the plate 4 so that a restricted space i.e. a filament passageway $0, is defined Therebetween. The plate 4S is movable angularly relative to the plate 42.

In operation, a ribbon of continuous filament having a width W is fed between the plate 4 of the air eheat 40 and the impingement plate 48· Air under pressure is fed into the air chest 40 through the pipes 46 and issues from the arcuate slot 44» which is positioned and shaped as indicated in Figures 3 and 4« The passage of the air through the filament passageway 50 in the direction, of filament travel applies tension to the filaments. iha angle Y at which, the slot/is positioned, and thieknc-ss of the filanents 3S0 The action of the air stream, iissuing from the slot 44 and fanning out in the filament passageway 50 between the plates 42 and 48, is to spread the filaments 38 across the length of the slot 44 (as shown in Figure 5)· T e exhaust air fron the spreading device advances the filanents by air entrainment as a diverging filamentary curtain (as distinct fron -a cone-shaped filamentary shroud) towards a collecting surface 52. The surface 2 moves in the direction of the arrow Z (Figure 6) and collects the filamenta as a continuous non-woven 54· The desired radius of the arcuate slot 54 is depdndant upon its distance from the point of delivery of the ribbon of filaments and upon the width ¥ (Figure 4 ) o 'the ribbon. The width of the web produced depends upon the angle of diverganoe on the filamentary curtain and upon the distance between the collecting surface and the spreading device. The angle of divergence of the filamentary curtain can be adjusted to some extent by angularly moving the plate 48 ^ith respect to the plate 42. For example, assuming the diverganoe of the filaments is such as to produce a web having a width Δ-Α (Figure 5) with the plate 48 in the full line position (Figure 6) , movement of the plate 48 towards its dotted line position causes deflection of constriction the path of the filaments, due to the further hiid^i ki-O- of the airflow in that part of the filament passageway 0 below the slot 44 thereby increasing the angle of divergence of the curtain below the slot 44 "to produce a web of greater width B-B (Figure 5) .

The convenient radius and length of the arcuate slot 44 f°r any arrangement in the apparatus of the invention may be determined from a geometrical drawing to scale of the triangle AWA spreading device is the distance from tho apex of th© ixli ugle to the desired position before the slot, and the length of the slot is the length of the arc between the sides AW of the triangle. The dimensions of the triangle Δ Α -Bill be governed by the desired width of the web, the desired width of the filamentary ribbon, and the distance between the delivery point of the filamentary ribbon to the spreading device and the collecting surface fof the web. This method of determination is, howevdr, dependent on the fact that the curtain of filaments is deposited under the major influence of the gas from the spreading device so that the curtain is kept triangular.

In practice it may be found that under certain operating conditions the filaments do not spread out to span the full length of the arcuate slot, so that adjustement of the impingement plate is relied upon to achieve the desired width of tho web. If it is desired to spread filaments wider at the slot, this can be achieved by modifying the vertical profile of the face impingement plate tfejsfc from the straight profile illustrated in Hgure 6, Increased spreading effect at the slot can be produced by causing the air discharged from the slot to enter a more confined space in the filament passageway, which later widens out to allow the air to discharge adequately without excessive back pressure .

The delivery point 56 of the ribbon of filaments 38, shown in Figure 5i is constituted by the banding device 10, in the apparatus hereinbefore described, but it may be constituted by other delivery means interposed between the banding and spreading devices, in modifications of the apparatus to be hereinafter described, in the Examples, The important factors to be taken into consideration across the cuxtain thereof issuing; from the spreading device are (a) central alignment of the filamentary ribbon with respect to the spreading device, and (b) adj stnent-: of the spreading device so as to keep the triangle AWA syinmetrical, In order that the invention nay be more fully understood, the following examples are given by way of illustration only- EX&MPLE 1 Using the apparatus shown in Figure 7> a one hundred and fifty- wo continuous filaments 38 of polyethylene terephthalate were melt spun and fed directly from a spinneret (not shown) to an air-operated banding device 10 regulated to form the bundle of filaments 38 into a substantially uniform ribbon of filaments of 3/θ of an inch width. The ribbon of filaments was forwarded to an air-operated spreading device 40 situated a distance of 12 inches below the banding device. This distance was determined in the manner outlined above, though in this case the dimensions of the slot 44 we e known. The filaments 38 were spread and delivered as The diverging- curtain from the spreading device 40 onto a moving conveyor surface ?2 forming a continuous web 54 with a width of 10 inches. The collection surface of the conveyor 2 was formed by a plurality of parallel wares which allowed free flow of air therethrough.

Any elecbro-static charges on the filaments 38 were reduced to a ininimum by means of an eloctro-static eliminator 58. was The banding device 14 operated at an air pressure of 5 p.s.i. and the spreading device at 14 p.s.i* Th9 mean denier per filament of the filaments in the web were found to be 3.0 which, by calculation on the spinning provided by spreading de-vice fed een equivalent to that produced by a roll winding speed of /, 000 ft./mins, EXAMPLE 2 Using the apparatus illustrated in Figure 8, one hundred and forty-four freshly melt spun, continuous filaments 38 of polyethylene terephthalate were fed directly from a spinneret (not shown), to an air-operatdd banding device 10 and formed into a substantially uniform ¾- inula wide ribbon. Tie ribbon of filaments passed to a capstan roll 60 running at a surface speed of 4 , 000 ffc./min. and made more than half a turn around the circumference of the capstan roll before passing over a nip roll 62. On leaving the nip roll, any electro-static charges present on the filaments were substantially removed by an elirqinator 58 before the filaments reached the air-operated spreading device 0 (which provided the tension necessary to remove the filaments from the nip roll). The filaments were sprayed as a substantially uniform diverging curtain, entrained in the exhaust air of xhe spreading device and were collected as a 12 inch wide web on the surface of a conveyor 52 moving at a linear speed of 15ft./ in. in a direction substantially at right angles to the plane of the curtain of filaments. The structure of the conveyor surface was designed o that the majority of the exhaust air passed through it leaving the deposite of filaments forming the web 54 · The web 54 comprising the undrawn polyethylene terephthalate filaments was calendered using a bowl temperature 110°C. and a pressure of 0.57 ' ns per linear inch on two steel bowls of 7*5 inch diameter. The product was paper-like material having good tensile strength and e strength properties.

It was found, howov r, that for some particular like material fofned of -undrawn polyethylene terephthalate filanents was unsuitable, for vrhen subjected to a temperature of 150°C. the material had a shirnkage of around 5070 and became very brittle. This disadvantage was overcome by drawing, to at least some extent, the filaments prior to them entering the spreading device, EXAMPLE 3 An adjustable drawing stage was added to the apparatus as described in Example 2 providing adjustments of the draw ratio up to 5.5: 1 at a draw speed of 1, 000 feet per minute. Electrically heated feed rolls were used to control the draw point of the filaments.

One hundred and fifty-two continuous filaments of polyethylene terephthalate were melt spun and passed as a bundle directly from the spinneret to an air-operated banding device by which the bundle of filaments was formed into a substantially uniform ribbon of filaments. The filaments were then passed over three feed rolls in turn, the last of which was held at a temperature of 95°C. and all of which were running a¾ a peripheral speed of 7 0 ft./rain. The filaments were next passed onto a draw roll and after threequarters of a turn round its circumference were taken over a nip roll and finally wound up on a sample bobbin winder.

This process was repeated with the draw ratio as given in Table 1„ Sample lengths of the filaments of the various ribbons were taken and their shrinkages measured in water at a temperature of 100°C.

A TABLE I The samples were also dyed and it was found that the partxally drawn filaments exhibited heavy dye flecks at frequent intervals along their length in the lower draw ratio sanples. As the draw ratio increased the dye flecks became smaller and occurred more frequently until at a draw ratio of »0s "the flecks were substantially removed. The existance of the flecks indicated that the filaments possessed intermittently occurring portions of substantially undrawn material, which would have a lower softening point than the portions of drawn material. was The process Lis then continued. The ribbon of filaments was taken from the nip roll and, instead of being wound up on the bobbins winder, was fed to an air-operating spreading device which diverging forwarded the filaments as a substantially uniform β,^^Ψ^α curtain onto a moving conveyor where they were collecting in the form of a non-woven web. Several webs were made in this manner from filaments drawn at draw ratios of 2,0, 2.5, 3.0, 3.33» 4-° anc14.66:1. The webs were calendered at a mean botsl temperature of 170°C. and with a nip pressure of 0,57 tons per linear inchtetween steel bowls. As could be predicted, from the shlvnkage figures given in Table 1, the webs shrank on con+act with the heated calender bowl, A occurred im a draw ratio range of 2.0*1 to 3.3:1 under the spinning conditions and the feed speeds used. The b©nd strengths were found to diminish progressively as the draw ratio was increased above 3.33 si.

The apparatus used in carrying out the continuous process of this Example is illustrated inPigure 9 and comprises a guide-peg 64 around which the filaments 38 pass to the banding device 10. Δ drawing stage follows the banding device and comprises 3 heatable feed rolls 66, 68 and O and a capstan and draw roll 60 and a nip drs,w roll 62. Δη electrostatic eligiinator 58 is positioned after the nip roll 62 to remove electro-static charges from the filaments before they reach the spreading device / Q„ The filaments are collected on a moving conveyor surface, EXAMPLE 4 One hundred and fifty two continuous filaments of polyethylene terephthalate were melt spun and passed through the continuous process of the previous Example, except that seventy- six of the filaments were made to by-pass the drawing stage. For those that passed through the drawing stage a draw ratio of 4 · 7ϊ1 was used. The undrawn and drawn filaments were reassembled into a ribbon before passing through the spreading device and being collected as a non-woven web. The web thus contained an even mixture of substantially drawn filaments having a relatively high softenin g point and undrawn filaments having a relatively low softening point.

The web was calendered at a temperature of 140°C. on a steel bowl of the calender having a heated steel bowl and an unheated elastic bowl. A nip pressure of 0.5 tons per linear ΒΧΔΜΓΙιΒ 5.

In this Example the continuous filaments were heterofilanents formed from equal portions of polyethylene isoghthalate/ torephthalate polyner and polyethylene/ierophthalate copolymer (20 nols )» The copolyner had a lower softening point than the polymer.

The freshly spun heterofilaments were wound up directly from a spinning unit onto bobbins using a surface driven package winder, The bobbins were then side unwound and the bundle of neurofilaments therefrom were formed into a non-woven web using the apparatus shown in Figure 9, The web was calendered between two heateu steel bovils at a temperature of 190°C. and a nip pressure of 0.57 tons per linear inch. The low softening point copolyner of the heterofilament served to bind the filaments in the paper-like material produced.

EXAMPLE 6 ■Whilst carrying out the continuous process described in Example 3 , the electro-static charge on the web was continuously monitored. An eleostro-static field meter 72 (Figure IO) operating from B.C. mains and feeding and alternating potential, proportional to the field of the web, to a phase sensitive rectifier, was used to measure the charge. Δ detailed description of an instrument similar to the one used is given in Supplement No. 2 of the British Jouunal of Applied Physics, 1953 , pages 547-549· -he charge indication scale incorporated in this instrument was divided into 600 divisions, 0-300 positive and 0-300 negative and the instrument waa equipped with a sensitivity control so that charges of the order of the full scale reading xl, x2 , x3 and x30 could be measured.

The measuring head 74 of "the field meter was placed ■which the w&b was transported and 12 inches fi-on the point of spreading of the filament (see Figure 10) , The field meter was calibrated by placing a sheet of steel 1 foot wide and 3 feet lpng on the conveyor surface and applying a voltage of 300 volts to the plate. A scale reading 65 x 1 was obtained which was considered to be equivalent to a field of 300 volts/foot in the particular environment , It was noted that the ssharge in the web varied from time to time, presumably due to alterations in relative humidity of the surrounding area, and was sufficiently high on some days to cause the width of the web to alter, or even worse, to cause breakage of the filamentary ribbon due to it wrapping round the nip roll. A summary of the effects is given in Table II below.

TABLE II Variation in Web Charges Measured at Different Pdriods of Time In view of these observations it was considered necessary to eliminate as far as possible the electro-static charges on the filaments, A pair of D.C. eliminators (designated as 58 in the drawings), 5 inches long and each having two discharge points were positioned 2 inches below the nip roll, one on either side of and 3/4 inch away from the filament threadline between the nip roll and the spreading device (Figure IO), A variable voltage supply undetectable on the xl scale of the field meter was achieved at about 8Kv, under the prevailing atmospheric conditions. This elimination of the static charges did not produce any deterioration of web quality or width over that produced with a web charge scale reading of 100 x 30.

The webs produced were of consistent quality aad dimensions, and filaient breakages due to high electro-static charges were eliminated.

The geometry of the filaments in the web produced according to the Examples was the sane. Each web collected on a conveyor surface was conposed of the plurality of substantially parallel bands of filaments extending the direction of travel of the conveyor and, when viewed in cross section ras found to be built up from a series of flattened, 'Ζ' laminations. For the most part, each band was found to be a proportion of the web width occupied by one or more filaments disposed in a random configuration uniformly throughout the band. However, it was found that the filaments could be deflected into more than one band so that the web contained randomly distributed bundles of spaced apart parallel filaments, the bundles varying in length from about l/4 inch to about 2¾- inches in length. The size and number of the bundles were insufficient to give a so-called "stringy" appeafance to the structure of the web. Neighbouring bands in the web merged into one another by the random overlapping and intermingling of the filaments thereof, Ea.ch filament in the web randomly meanders about a mean path through the web, and since the mean paths are substantially parallel..tie overall effect is that the structure of the wth exhibits a patterned parallelism of the filaments along its length. An excessive entanglement, by withdrawing the whole array cf filaments last laid down in the web. Individual filaments cannot, however, be pulled out without entanglement taking place.

Due to the folded, overlapping portions or 'Ζ' laminations of the web, it is possible to part the web on a line across its width, and by increasing the parting distance, to draw out the overlapping portionsof the web and to substantially straighten the filaments in the drawn out portion of the web into the approximate mean parallel paths governed by their formation when delivered from the spreading device. The number of filaments per unit width of webmeasured at an arbitrarily chosen point on the web gives the degree of uniformity of the spread of the filaments as they are d¾posited into the web at that point, and by selectiiig a number of the points an overall picture of spread uniformity can be arrived at for the whole web.

It was also found that the lengths of the folded overlapping portions of1 Z'laminations of the web were of substantially the same length in any given web. However, differences in length were noticed between various webs and it was discovered that the length of the overlapping portions or Z laminations was dependent to some extent upon the height of the spreader above the receiving surface from which the filaments were collected.

Using the process of the present invention it is possible to make papers and paper-like material which have high tear-strength, high electric resistivity and enhanced durability under adverse conditions as compared with sonventional paper.

Outlets such as carpet backings, interlinings and quilted materials are also envisaged for bonded products of the invention.

Claims (24)

1. Having now particularly described and ascertained the^ture-of our said invention and in what manner the same is to be performed, . we declare that TfflAT HE CLAIM IS; 1, A non-woven filamentary structure comprising a plurality of pubstantially parallel filamentary bands, each band being formed of one or more filaments disposed in a random configuration unifornly throughout the band, with neighbouring bands merging into one another by rsjidom overlapping and intermingling of the filaments thereof, and said structure having folded portions thereof of substantially equal length overlapping in the direction of parallelism of the , filamentary bands, each overlapping portion also extending across the structure in a direction substantially at right angles to said direction and in substantial parallelism with its neighbouring portions.

2. A non-woven structure according to claim 1, in which the filaments are bonded together.

3. A non-woven structure according to Claim 1 or 2 in which a proportion of the filaments are binder filaments having a sdtening point lower than that of the other filaments.

4. A non-woven structure according to Claim 1 or 2, in which the filaments are hetero-filaments formed from two polymers of different softening points*

5. A non-woven structure according to any of claims 1-4 » in which the filaments comprise a mixture of drawn and undrawn filaments.

6. A non-woven structure according to claim 1 or 2 , in which the filaments have drawn and undrawn portions i termittently along their length.

7. A non-woven structure according to any one of claims 1-6 in which the filaments are crimped.

8. A non-woven structure according to any one of claims 1-7 which has been subjected to heat an;" pressure such as by hot calendering or super-calendering to form a paper-like material.

9. A process for making a non-woven filamentary structure which comprises forwarding a bindle of continuous filaments under tension towards a moving receiving surface, wherein the filaments are banded into a substantially uniform filamentary ribbon in •which the filaments are aligned in parallel relationship, tjse so-formed ribbon is spread into a diverging curtain of separated filaments, and the curtain of filaments is overfed onto the receiving surface as it moves in a direction substantially at right-angles to the plane of the curtain of filaments so that the filaments are collected thereon as a non-woven web.

10. A process according to claim 9, in which the bundle of filaments is passed through the banding stage, where, in a restricted space, it is subjected to the action of at least two non-parallel streams of gas which are arranged to impinge on the filamnnts whereby the filaments are aligned into a substantially uniform filamentary ribbon; and the so-formed ribbon of filaments is passed through a spreading stage where, in a restricted space, the filaments arc subjected to the action of at least one stream of gas of substantially arcuately shaped cross-section arranged to impinge on the ribbon of filaments over the width thereof and whereby the filaments are forwarded to the moving receiving surface and spread into the diverging curtain of filaments.

11. A process according to claim 9 or 10 in which the bundle of filaments is formed from a plurality of filaments which are extruded through a spinneret forming part of a melt spinning unit,

12. A process according to Claims 9, 10 or 11 in which a drawing stage for the filaments is introduced before or after the banding of the filaments.

13. A process according to claim 12 in which the filaments

14. 1 · Δ process according to claim 11, in which binder filaments are co-spun into the bundle, the binder filaments having a softening point lower than that of the other filaments in the bundle,

15. A process according to any of claims 9-14 in which the web is subjected to heat treatment to bond the filaments,

16. A process according to claial5, in which the web is subjected to hot celendering or super-calendering by passage between heated nip rolls to form a paper-like material,

17. A process according to any of claims 9-16 in which crimp is developed in the filaments before or after formation of the web,

18. Apparatus for use in the production of a non-woven filamentary structure which comprises; means for supplying a bundle of continuous filamertB; a banding devioe for forming the bundle of filaments into a substantially uniform filamentary ribbon comprising a pair of substantially parallel, flat-surfaces defining a restricted filament passageway and through which in operation the filaments are passed, oaa of said surfaces having at least two non-parallel slots therein which open into the filament passageway and which are arranged cr. opposite sides of the path of the filaments through the banding device, said slots being adapted for a connection to a source of gas under pressure; a spreading device for forming the filamentary ribbon into a diverging curtain of filaments comprising a pair of substantially flat surfaces defining a restricted filament passageway and through which in operation the ribbon of filaments is passed, an arcuate slot in one of said surfaces v/hich opens into said filament passageway and which is adapted to be supplied with gas under pressure, so that, in operation, the filaments passing over the arcuate slot are acted on by a stream of gas issuing therefrom in such a manner as to forward the filaments and spread them into a diverging curtain; and a receiving surface arranged to be movable in a direction substantially at right angles to the plane of the curtain filaments whereby in operation the

19. Apparatus according to plain 18 in which the arrangement of feed rolls and craw rolls are interposed between the banding device and the spreading device whereby to draw fhe filaments.

20. Apparatus according to claim 19» in which a second banding device is mounted between the draw rolls and the spreading device,

21. A non-woven filamentary structure substantially as hereinbefore described in any of the Examples,

22. A paper-like sheet material formed by hot calendering the structure of claim 21, as described in any one of Examples 1-5.

23. A process for making a non-woven filamentary structure substantially as hereinbefore described with reference to any one of Examples 1-5.

24. Apparatus Jbr use in the production of a no -woven filamentary structure arranged and adapted to operate substantially as hereinbefore deeiccribed with reference to tho accompanying drawings. BATED the 2nd day¾d : January, 1967