IL29245A - A method of forming an extruded sheet,filamentary or fibrous material - Google Patents

Description

29245/2 A method of funning an extruded sheet, filamentary or fibrous material ybniwn »ny » nan n» 'wy n»*¾? OIE-BEHDT RASMUSSEN C: 27678 The present invention relates to a method of producing yarn, including webs of fibres which are in substantially aligned arrangement, by subdividing sheet material r thicker filaments.

By use of the existing methods of subdividing sheets it is generally not possible to obtain subdivided structures of finer thickness than about o.o5 - o.l mm, or in case the sheet is thinner than this, of a thickness about the same as that of the sheet, without using particularly splittable polymers as raw materials or using particular substances admixed at random in order to promote high splittability. In such cases however the yarn produced will have a low abrasion resistance, since it has a tendency to split further up.

Similar problems exist for subdividing of filaments. The use of particularly thin film in order to produce the flexibilit required for a textile yarn and similar, is generally relatively unpractical, as the manufacture and handling of such fine film is difficult and expensive.

The present invention has for its object to produce a sheet or filament having so to say predetermined planes of cleavage produced by means of foreign material inserted in the form of thin layers, which lie sufficiently close for obtaining the desired flexibility of the subdivided material. Thus the-principal polymer itself need not be splittable, or may' have-only medium spli ttability, for producing textile fibres, an improved abrasion resistance resulting. Furthermore, the thickness of the subdivided material can be predetermined by adjustment of the process, and even extremely great fineness can be obtained without the reduction of -tensile strength which is normal when the splittin has been romoted by substances ad- 29245/2 „ ■ , , - 3 -mixed at random.

The method according to the present invention comprises feeding a molten first extrudable polymeric material, (as herein defined) to a multitude of first orifices opening into an annular collecting chamber having an outlet slot along its length, and distributed around the length dimension of the annulus, feeding a second extrudable material (as herein defined) to a multitude of second orifices likewise opening into the collecting chamber and distributed around the length dimension of the annulus, the first orifices being interspersed with the second orifices, extruding the materials through the orifices into the collecting chamber and collecting them in the chamber to form a fluid material comprising interspersed lamellae of the first and second materials, rotating one side of the chamber relative to the other and thereby dragging out the sides of the lamellae and substantially reducing the thickness of the lamellae to form, on extrusion through the slot, a sheet strrcture in the form of a sandwich-like arrangement of the lamellae of- reduced thickness, and at leas substantially disrupting the connections between adjacent lamellae of the first polymeric material.

This disruption may consist in cracking the second materia or making the interphases between the lamellae slip, or dissolving the second material, at least partly. In any case the cleaving must be carried out in such a manner that it does not substantially harm the first material. All types of mechanical cracking may be promote by including in the second polymeric material a slipping agent, for example an oil which is soluble in the fluid polymer but bleeds out on solidification of the latter. Cracking the second material or in combination, in particular it is effective to produce a longitudinal rubbing action after removal of some part of the second material* The term "first extrudable polymeric material" as used herein refers to a polymeric material selected from polyaraides, polyethylene terephthalates, polyolefins, polystyrene and poly-acrylonitriles« The term"second extrudable material" as used herein refers to any one of the polymers listed above for the irst extrudable polymeric material provided that it is different than the latter, to a blend of two or more of these polymers, to polyethylene oxide or a product obtained by grafting ethylene oxides on cellulose or to a blend of kaolin or another powder dispersed in mineral oil,' mineral wax or in a heat-stabilized polyethylene glycol.

Furthermore, one of the "first extrudable polymeric material" and the "second extrudable material" may be a poly-vinylester or a polyvinylidene ester provided that the other has a melting point sufficiently low to prevent degradation of the former.

In order to prevent the material from changing its character essentially through a continuous cleaving produced by the normal use the cleavage during processing should preferably go so far that each of the lamellae of the first polymeric material is separated almost totally from its neighbours. Thus, the character of the product is substantially changed as a result of said cleavage, In order to obtain the most regular thickness of the lamellae, the orifices for extrusion of the latter into the collection chamber are preferably closely spaced, elongated slots, forming an angle with the direction of the row. a spacing of 2 - 3 MI is preferable for constructional reasons. If the extrusion velocities of the two polymeric materials are equal, the original thickness of the lamellae will equal the distance between the slots, however it is easy to obtain the desired small thickness of the lamellae by the dragging or shearing action described. This thickness is generally below 10 jxs and may even be below 1 u.

I use the term lamellae to signify any body in which one dimension is very much greater than one at least of its other dimensions, and in my extruded product at least one dimension is very much less than the other two dimensions.

If the process of manufacture only comprises the steps disclosed above, flake-formed structures will be produced rather than fibre-like structures, but the product will still be suitable for many yarn purposes after twisting, because of the extremely small thickness which is made possible by the invention. However, the invention preferably involves a further step of producing substantially parallel splits in each of the lamellae of the first polymeric material in order to convert the latter to thin ribbons, strips, staple fibres or splitfibre networks. It is most expedient to perform the production of said splits at least in part before the cleaving of the sandwich arrangement is completed, as the coherence of the material facilitates -the splitting. This production of splits can, for instance, be carried out by cutting with knives, or tearing with needles, e.g. during passage over a needle roller. Furthermore it may be advantageous to make a first splitting in form of cutting the extruded sheet to ribbons and subsequently to form splits in each of the lamellae, provided the latter are oriented by a lateral drawing between rubber belts (this splitting method being in itself well-known in the art) or, alternatively, by lateral rolling between rubber surfaces. The final cleaving of the sandwich structure may follow by a rubbing in the longitudinal direction. In any case it is generally preferable to. orient the material before the cleaving, as this facilitates the separation of the lamellae from one another.

In an embodiment of the invention the production of split in each of the lamellae is performed at least in part before or durin the haul-off from the extrudin device. This can be carried out by passing the fluid materials through a kind of grid, situated at a place in the extrusion device where the formation of the sandwich-like structure is practically terminat whereby any of the lamellae will be subdivided into sandwichlike strips or filaments- Alternatively, this grid may be replac by a comb-like device which will divide only a certain portion of each lamellae, thus initiating a further splitting. By the said methods the ribbons or filaments can get a cleaner edge as compared to cutting in solid state, and furthermore the ribbons or filaments can be made finer in this way, as the material can generally be deeply drawn down in connection with the haul-off. As v/ill be understood, these methods of splitting, as well as simple butting are carried out without requiring fragility of the first polymeric material. Thus it is possibke to use a tough polymer of high abrasion resistance, such as for instance the normal polyamides or polyethyleneterephthalate . The second material may in these cases be, for instance, small amounts of polyethylene or polypropylene, which may be leached by means of hot toluene, or xylene, or another solvent, and may be recovered on cooling of said solvent. However, it is also possible to use, as the second material, a very fragile material such as polystyrene, which may become almost powdered during a rubbing action or other suitable mechanical cleaving process, whereafter the main part of the brittle material may be removed by means of vacuum cleaning or by sweeping with an air jet.

After collection it may be re-used, since small amounts of the first polymeric material, which may also have gone into dust, make no harm.

A- cleaved strip or filament produced either by splitting state with very closely spaced knives can be used directly as a textile yarn, no chopping to staples with subsequent carding being necessary. So can the cleaved material when it has first been split to ribbons and subsequently split further to a split-fibre network. Normally, however, a twisting process is desirabl Alternatively, the split and cleaved material either in form of yarn or web can be chopped to staples and may be mixed with othe fibre material. Furthermore, a web of the material according to the invention can be used as a layer in a non-woven fabric.

Another embodiment of the present invention further comprises feeding at least one additional extrudable polymeric material to orifices interspersed with those for the first and second extrudable materials, said additional material being capable of strongly adhering to the lamellae of the first polymeric material and of remaining in such adhesive connection upon the cleaving. This provides for a very simple method of producing the sojcalled bicomponent fibres, which, as is well known, are suitable for obtaining a very effective crimp, or whi may be used for obtaining composite properties of the fibres e. to apply to one or both surfaces of the fibre a more hydrophilic substance suitable for dyeing or to increase the ability of tran porting moisture. In this connection the present invention provi for a much simpler and cheaper method than the known art, in whi each filament has to be formed separately in a bicomponent nozzl By use of the present invention, it is furthermore possible to apply up to a rather great number, say 6, different components in each fibre.. A separate extruder and- a separate channel syste are used for each material.- The choice of materials for obtainin the desired properties as well as for avoiding cleaving of the layers within such bicomponent fibres can easily be made by an expert. This embodiment can also with advantage be. used to produ fibres having very fine "hair" on their surface or surfaces. For this purpose the materials and treatments are so chosen that the additional material is disrupted into fibre-like particles still intimately adhering to the lamellae of the first material. This best obtained by using, as additional material, a polymer in. a polymer emulsion of which one of the components is on principle the same as., or at least very closely related to, the principal polymer of the first polymeric material. The other component or components of said emulsion . should be leached or disrupted in swollen state.

In similar manner fibres with "hair" can be obtained with use of additional material, when the second material is a polyme in a polymer emulsion suitable for the purpose, however it is difficult to obtain a similar quality in this way, which on the other hand is simpler.

In fact, lamellae of the. second material can also remain in the yarn or web as useful separate fibres, provided the cleav is produced by slipping apart the two sets lamellae without any substantial damage being made to either of them. As an example, lamellae of the normal, commercial polyamides such as hexamethy-leneadipamide or polycaprolactame can easily be cracked away fro lamellae of polyethyleheterephthalate, a useful two-fibre yarn o web resulting. In similar way many other combinations can be made by an expert. It is to be understood that the term "first polymeric material" and "second material" each can comprise, several different materials each being extruded through a separa channel system and separate orifices of the row.

By the extrusion method described above, the lamellae will become continuous like ribbons, all being substantially parallel. Normally the lamellae will be arranged longitudinally in the ■■ extruded tube, but may also form helices by suitable rotations of the devices, if desired. By forming the lamellae in helices, or splitting the tube helically, or both, it is possible to obtai an angle between the continuous dimension of each lamellae and the direction of splitting, thus producing staple material of substantially constant length.

The invention will now be described with reference to the accompanying drawings. In these ' Figure 1 is a section through sheet material capable of being disrupted according to the invention and having lamellae of a flattened S-form, the section being transverse to the continuous dimension of the lamellae, normally but not necessaril being the direction of extrusion. The splitting of each of the lamellae is also indicated, Figure 2 is a diagrammatic perspective view, partly in section, of a ring die comprising a circula row of extrusion slots, a collecting chamber the two sides of which are rotated relative to each other (normally both are rotated in opposite directions) and a slot part, normally steady, supplied with dividing walls in a grid-like arrangement to split the lamellae in fluid state, Figure is a diagrammatic view through the collecting chamber of the same apparatus, further showing the drive as well as the dragging of the lamellae during the advance through the chamber to S-form of fine thickness.

In fig. 1 as well as the other figures the sheet material is shown, for simplicity, as being made of solely two materials, Ό material. For clarity, the lamellae are represented by lines, but in actual fact they have of course a thickness corresponding to the spacing of the full and dotted lines. Their thickness and their angles to the plane of the sheet are grossly exaggerated. Normally the overall thickness will be about or below lo ja and may even be below 1 u, and the overall angle to the plane of the sheet will normally be about or below 1°. Figure 1 furthe shows how each lamella of material 1 can be split through lines , either by cutting or tearing with needles, or by subdividing in fluid state, or by any of the mechanical methods known for splitting an oriented film.

If this splitting is carried out before any substantial cleaving of the lamellae structure has taken place, the result will normally be split-planes which traverse the sheet from surface to surface as shown (although not necessarily with the indicated regularity) hereby crossing the planes of cleavage. If the material is first cleaved, however, the splitting will often be more irregular.

The apparatus shown in Figure 2 comprises a circular row of slots H- and 5 for extrusion of materials 1 and 2, respectivel into the collecting chamber consisting of parts 6 and 13 which are rotated relative to each other, as indicated in Figure 3.

The collecting chamber is shown as being defined by the walls of the mutually movable parts 6 and 7 which narrow down smoothly. This narrowing down seems to be preferable with respect to the regulatiry of the structure obtained, however it is not very essential. Furthermore this zone of shear (chamber parts 6 and 7) is shown as following immediately after the row of slots. This too is a preferable, but not very essential feature, two sets of lamellae are extruded even into a relatively long ch ber where no transversal shear is applied from there advancing i to the sone of shear (parts 6 and 7)· In the slot part 8 the slot" 9 is interrupted by dividing walls lo forming a kind of grid which splits the fluid sheet-formed material to ribbons, strips or filaments, hereby splittin each of the lamellae. However, said walls need not interrupt the slot entirely but may form the arrangement of a ccmb, or may for two combs extending from either side of the slot. The teeth in one of the combs can for instance advantageously intermesh with the teeth of the other comb. Even when the fluid material is only combed, it will generally split to separate filaments (ribb or strips) during the haul-off. If the material is to be extrude in sheet form, the part 8 is removed. Extremely fine denie s of the individual lamellae can be obtained by such splitting carried out in connection with the haul-off. If the row of slots 4 and 5 and the slot part 8 are stationary in relation to each other, the lamellae will generally remain continuous after said splitting, whereas if the two parts are rotated relative to one another, the lamellae will generally be chopped to staples, but remain in adhesive connection till the cleaving process is carried out. The most practical arrangement of such relative rotation is to keep part 8 stationary in order to avoid a . rotation of the haul-off devices with respect to the axis of the extrusion device whereas the row of slots 4 and 5 is rotate Consequently, polymers 1 and 2 must be extruded into the main channels which feed 4 and 5 through revolving fittings or the like.

The shape of the lamellae will depend at least in part upo materials used, as well as their deviation from Newtonian behavior, and upon the movements and shape of the devices establishing the shear. Generally the materials should have rather similar viscosities, but the use of different viscosities is facilitated by making a sudden reduction of the flow area of the extrusion nozzle at the orifices, so that a substantial pressure drop is produced within these orifices.

In case the extrusion takes place at the same speed at different portions of the cross-section of each of the orifices 4 and 5* the parts 6 and 7 preferably ought to rotate at the same speeds but in opposite directions. In practice, however, there will normally be differences betv/een the extrusion velocities ove the cross-section of each of the orifices, and this in combinatio with the fact that the viscosities of the materials are unequal tends to produce different dragging at the two surfaces. In order to compen ate for such differences the parts 6 and should normally not move exactly at numerically equal speeds (as seen in relation to the row of orifices which may be stationary or may move), but the speeds should preferably be suitably adjusted to make the structure as regular as possible. However, this is not an essential feature of the invention, and in fact it is possible even to rotate parts 8 and 9 in the same direction (as seen in relation to the row of slots) but at different speeds. This will normally produce a wide range of fibre thickness, which may under certain circumstances be aimed at.

It is within the scope of the invention to make the row of slots 4 and 5 either in the wall of 6 or in the wall of 7-In these cases again, there will normally be produced a wide rang of fibre thicknesses.

Within the scope of the invention the first material may fee any extrudable thermoplastic polymeric material suitable for producing fibrous materials, either of a fully synthetic or a semi-synthetic type, and furthermore the invention can be applie to prepolymers, such as polyisocyanate/polyol - compositions. Curing of the prepolymers should preferably be carried out before the cleaving. As for the second material, this may even be a non-polymeric material, in this case generally a paste of 3i-'.i table vi scosi fcy.

Claims (1)

1. 8. A method according to claim 7 in which the lamellae of first polymeric material are fibrillated, after solidification, into a split fibre network. 9. A method according to any preceding claim in which the second extrudable material includes a slipping agent. For the Applicants DR. REINHOLD COM AND PARTNERS By: