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Timestamp: 2015-01-31 06:27:23
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Patent US4229394 - Multi-layer products - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsFibrous products, including single fibers, yarn and fibrous webs, of improved fineness are produced from extruded sheet material extruding in the form of a sheet-like, multi-layer composite stream a plurality of extrudable materials, at least one of which is a synthetic thermoplastic fiber-forming polymer...http://www.google.com/patents/US4229394?utm_source=gb-gplus-sharePatent US4229394 - Multi-layer productsAdvanced Patent SearchPublication numberUS4229394 APublication typeGrantApplication numberUS 05/926,244Publication dateOct 21, 1980Filing dateJul 20, 1978Priority dateDec 30, 1966Also published asUS4125581, US4430284Publication number05926244, 926244, US 4229394 A, US 4229394A, US-A-4229394, US4229394 A, US4229394AInventorsOle-Bendt RasmussenOriginal AssigneeRasmussen O BExport CitationBiBTeX, EndNote, RefManPatent Citations (4), Referenced by (9), Classifications (50) External Links: USPTO, USPTO Assignment, EspacenetMulti-layer productsUS 4229394 AAbstract Fibrous products, including single fibers, yarn and fibrous webs, of improved fineness are produced from extruded sheet material extruding in the form of a sheet-like, multi-layer composite stream a plurality of extrudable materials, at least one of which is a synthetic thermoplastic fiber-forming polymer and another of which is expandable or swellable in nature, which layers extend generally parallel to the faces of the stream, with each such layer containing either a fiber-forming polymer or an expandable or swellable extrudable material with the different layers being interspersed in the composite stream; solidifying this composite stream into a multi-layer sheet, not earlier than during such solidification subjecting the multi-layer sheet to a swelling or expanding treatment to aid in its mechanical disruption, and then mechanically disrupting the swollen or expanded sheet to produce a fibrous product of increased fineness. Alternatively, the other extrudable material can be incompatible with the polymer so as to separate therefrom during mechanical disruption. Instead of solidifying the extruded stream while intact, the stream can be divided during extrusion along spaced generally parallel planes extending through the stream at an angle to its faces and solidified in this divided state to form separate strips each containing a section of the multi-layer composite stream. These separate strips are then treated as indicated to at least partially remove the removable material and at least partially separate the polymeric layers therein. Alternatively, the stream can be divided and re-united before solidification.
I claim: 1. A method of producing fibrous products, including single fibers, yarn and fibrous webs, of improved fineness from extruded sheet material which comprises the steps of extruding in the form of a sheet-like, multi-layer composite stream a plurality of extrudable materials, at least one of which is a synthetic thermoplastic fiber-forming polymer and another of which is expandable or swellable, said layers extending generally parallel to the faces of said stream, some of such layers containing said fiber-forming polymer and others said expandable or swellable extrudable material with the different layers being interspersed in said composite stream, solidifying said composite stream into a multi-layer sheet, subjecting the multi-layer sheet not earlier than during such solidification to a swelling or expanding treatment to aid in its mechanical disruption, and then mechanically disrupting the swollen or expanded sheet to produce a fibrous product of increased fineness.
2. The method of claim 1, wherein said solidified sheet is subjected to orientation before said swelling or expanding treatment.
3. The method of claim 1, wherein layers are extruded of at least two different synthetic thermoplastic fiber-forming polymers which intimately adhere together in the solid state, said different polymeric layers being arranged in groups of at least two such layers with the groups being separated by a layer of said expandable or swellable material.
4. The method of claim 3, wherein said groups of two such layers include at least one intermediate layer of a third mutually adhesive synthetic polymer.
5. The method of claim 1, wherein said multi-layer composite stream is divided along spaced apart generally parallel planes extending through said sheet at an angle to the sheet faces, said divided streams are merged again with the layers thereof generally intact into sheet form which is then solidified.
6. A method of producing fibrous products, including single fibers, yarn and fibrous webs, of improved fineness from extruded sheet material which comprises the steps of extruding in the form of a sheet-like, multi-layer composite stream a plurality of extrudable materials, at least one of which is a synthetic thermoplastic fiber-forming polymer and another of which is substantially incompatible with said polymer, said layers extending generally parallel to the faces of said stream, some of said layers containing said fiber-forming polymer and others containing said incompatible material with the different layers being interspersed in said composite stream with at least one surface of a polymer containing layer in direct face-to-face contact with one surface of a layer containing said incompatible material, solidifying said composite stream into a multi-layer sheet, and then mechanically disrupting the solidifed sheet to produce a fibrous product of increased fineness.
7. The method of claim 6, wherein said solidifed sheet is subjected to orientation before said disrupting treatment.
8. The method of claim 6, wherein layers are extruded of at least two different synthetic thermoplastic fiber-forming polymers which intimately adhere together in the solid state, said different polymeric layers being arranged in groups of at least two such layers with the groups being separated by a layer of said incompatible material.
9. The method of claim 8, wherein said groups of two such layers include at least one intermediate layer of a third mutually adhesive synthetic polymer.
10. The method of claim 6, wherein said multi-layer composite stream is divided along spaced apart generally parallel planes extending through said sheet at an angle to the sheet faces, said divided streams are merged again with the layers thereof generally intact into sheet form which is then solidified.
11. The method of claim 1 wherein before solidification, said multi-layer composite stream is divided along spaced apart generally parallel planes extending through the stream at an angle to the faces thereof, and the thus-divided stream is then solidified.
12. The method of claim 11 wherein the divided stream is subjected to orientation after solidification but before said treatment.
13. The method of claim 6 wherein before solidification, said multi-layer composite stream is divided along spaced apart generally parallel planes extending through the stream at an angle to the faces thereof, and the thus-divided stream is then solidified.
14. The method of claim 13 wherein the divided stream is subjected to orientation after solidification but before said treatment.
This application is a division of application Ser. No. 607,695, filed Aug. 25, 1975, now U.S. Pat. No. 4,125,581, which in turn is a continuation of application Ser. No. 421,270, filed Dec. 3, 1973, and now abandoned, which in turn is a continuation of application Ser. No. 75,229, filed Sept. 24, 1970, and now abandoned, which is a composite continuation-in-part of application Ser. No. 871,688, filed Nov. 19, 1969, and now abandoned, which is in turn a continuation application of application Ser. No. 694,433, filed Dec. 29, 1967 and now abandoned; application Ser. No. 694,660, filed Dec. 29, 1967, now U.S. Pat. No. 3,547,761, issued Dec. 15, 1970; application Ser. No. 751,205, filed Aug. 8, 1968, and now abandoned, of which continuation-in-part application Ser. No. 147,496 was filed on May 27, 1971 and is now U.S. Pat. No. 3,778,333, issued Dec. 11, 1973; and application Ser. No. 757,237 filed Aug. 8, 1968, and now abandoned.
BACKGROUND OF THE INVENTION The production of fibres from films by splitting has hitherto in practice been confined to the use of polypropylene and high density polyethylene films which possess high splittability in an oriented state. Furthermore, the fibre fineness has been limited by the thickness of the films and because of the complications encountered in the film-making process it has not yet been found practical to use very thin sheets generally more desirable.
The invention further comprises a method for forming by oc-extrusion a multi-layer sheet or film which is particularly suitable in connection with the subsequent cleaving step but which also can be used independently for the production of laminates.
SUMMARY OF THE INVENTION The first aspect of the present invention relates to a process of producing multi-layer thermoplastic products.
The combination of reinforcing material and filling material in a sheet is usually made by simple compounding before the formation of the sheet, or by using the reinforcement material in the form of a woven, knitted or non-woven fabric to which the filling material is adhered, or by laminating the filler to one or several films of the reinforcement material. In the first case the reinforcement material is substantially weakened at least with respect to creep resistance, whereas the production of the second kind of sheet material is relatively complicated and expensive, and the third kind of sheet material generally has low abrasion resistance or a tendency to delamination on bending. The basic object of the present invention is to overcome the above-mentioned drawbacks by use of two extrudable thermoplastic materials in a new, suitable laminated arrangement which easily can be produced by extrusion.
In the extruded sheet material according to my invention the two extrudable materials are present in the sheet material in the form of interspersed intimately adhering thin lamellae, the former having an overall thickness between 0.1 and 10 microns and traversing the flat dimension of the sheet at an overall angle of less than 2� to the surfaces of the sheet. The said range of thickness is actually about the marginal range between dimensions which with regard to dispersions are considered to be colloidal, and dimensions which in the same respect are considered to be macrodimensions. It has been found that a laminate of such materials tends to behave more and more as an undisruptable whole when the thickness of the layers of the former material approaches or reaches colloidal dimensions. If, on the other hand, the thickness of one of the set of layers actually takes on colloidal dimensions, surface irregularities will play an essential role to weaken the material. The indicated range of thickness has been found generally suitable, and more particularly, the range between 0.5 and 5 microns is generally preferable. The use of the colloidal or almost colloidal thickness of the layers has a further advantage in that local failures in the raw materials as well as scratches in the surface made by abrasion, have very little influence on the tensile strength of the sheet. It would be very difficult and uneconomical to produce, handle and laminate film material of such fine thickness in conventional manner in order to make laminates of the thickness which is generally required for packaging and other purposes. A preferred embodiment of the process of the invention comprises feeding fluid first extrudable, polymeric material to first orifices in a row of orifices in an extruding device, feeding a fluid second extrudable material to second orifices in the row, extruding the fluid materials through the orifices into a collecting chamber that extends along the length of the row and has an outlet slot extending along the length of the row, and while extruding said fluid materials through said collecting chamber and slot, subjecting the extruded sheet to a transverse smearing action.
The shape of the lamellae will depend at least in part upon the relationship between the viscosities of the particular polymeric materials that are used as well as their deviatons from Newtonian behaviour, and upon the movement and shape of the devices establishing drag and shear.
Comparing the effect of the different forms of the lamellae, the S-form, or those mixed forms which are predominantly S-formed, generally are more suitable than the U-form and those mixed forms which are predominantly U-formed. This is due to the fact that in a certain, central layer of the sheet of U-formed lamellae the latter gradually change their traversal angle from the indicated marginal value of 2� to 90� and back to 2� and coincidentally the thickness of the reinforcing lamellae generally will be greater than the indicated margin of 10 microns at least within a portion of this layer. Such deviations in a central layer decreases the strength. If, however, the sheet of U-shaped lamellae (hereunder mixed forms still having a U-like cross-section) is cleaved through the core, the resulting sheets, in which the lamellae have the form of a half U, hereinafter called the J-form, will have improved abrasion resistance on the surface which formerly was in the core, wherein the lamellae are arranged in a kind of pile intimately connected by the filling material. This cleavage can with advantage take place during haul-off by means of a blade inserted into and parallel to the long slot of the extrusion device, but it can also take place after haul-off by means of a band saw or the like.
However, the preferred way of achieving such cleaving, particularly with view to production of the J-form, is to avoid any extrusion of the first polymeric material in a core or interior region of the sheet material. This embodiment can be done by use of an extrusion device in which first orifices are located in zones on both sides and spaced from an interior plane parallel to the margins of the row of orifices. Because of the absence of any first polymeric material in a core stratum, the cleaving will be very much facilitated, and can often be carried out by simple peeling apart. In case the filling material has lower melting point than the first polymeric material, peeling preferably is carried out at a temperature where the second extrudable material is fluid or semi-fluid, but the first polymeric material is solid.
The sheet material according to the present invention may comprise lamellae of at least one further extrudable material interspersed with the lamellae of the first polymeric material and the lamellae of the second extrudable material. This may be an adhesive suitable for bonding the lamellae of said two materials together, such as, for instance, a mixture of the principal polymeric components of said two materials, or a graft- or block-copolymer of both. Of these possibilities, the graft- or block-polymers generally exhibit the best cohesive strength, whereas the mixture generally is cheaper. In order to increase the cohesive strength of the said mixture, the components should have relatively high molecular weight and should be relatively soft modifications of the respective polymers.
In another embodiment of the present invention, said second extrudable material is a cellular polymer material. In this form of the invention, there is obtained a combination of strength and volume which for instance makes the material suitable for bookprint paper and several kinds of wrapping material. The volume facilitates the handling of thin sheet material through an increase of stiffness, and with regard to packaging uses the material is suited for protection against impact actions. Because of the very limited number of actually available polymer substances for making cellular products, it will normally be difficult to find suitable combinations of first polymeric material and cellular material which are capable of uniting directly, thus it is normally necessary to interpose a set of adhesive lamellae. The expansion to form the cellular structure can take place by well-known methods either during haul-off or later, however, the last mentioned possibility seems to be preferable in most cases, as the expansion tends to weaken the lamellae of the first polymeric material when carried out while the latter are fluid. The lamellae of the first polymeric material may, in fact, facilitate the expansion by setting up a barrier against diffusion of the expansion agent. The materials may be selected with regard to this effect.
In another embodiment of the present invention, the lamellae of the second extrudable material comprise a split-fibre network. This provides for a material of high absorbing power. Suitable materials for producing such split-fibre networks are well known in the art. It should be understood, that the term split-fibre networks also comprises fibres in the form of needle- to thread-formed crystal formations of a crystalline polymer bunched together to a network structure, even when the splitting has been carried out without any molecular orientation being present.
In a further development of this embodiment also the first polymeric material comprises split-fibre network material, however, of higher strength and lower average fibre fineness than that forming the lamellae of the second extrudable material. In this form, the product is suitable as layer(s) in non-woven fabric or even as an independent non-woven fabric either for disposable apparel, table cloth, window curtains and the like, or for sanitary textiles or filter materials. The methods of producing the fibrous networks by suitable choice of raw materials (generally intimate mixtures of different polymers) and by processes subsequent to the extrusion of the sheet (such as drawing and swelling and/or leaching) can easily be carried out by an expert by adaption of the known art.
The flexible filling material can, in order to establish the intimate adhesive bonding, be a co-polymeric modificaton of the principal polymeric component of the first polymeric material. Thus it can, with great advantage, be a block-copolymer containing segments of the principal polymeric component of the first polymeric material and segments of an elastomer, or alternatively, a graft-polymer having branches of the principal polymeric component of the first polymeric material grafted upon an elastomeric backbone.
The lamellae of second extrudable material may extend beyond the lamellae of first polymeric material to constitute at least one surface layer of the sheet. This is often useful when the second material has a lower melting range than the first material, as it enables sealing together of two sheets without ruining the orientation in the lamellae of the first material. This extension of the lamellae is obtained by making the orifices in the row extend correspondingly one set beyond the other. However, a material suitable for the flexible filling lamellae will often be too sticky for being suitable as a surface layer. It is preferable to intersperse with the lamellae of said two materials lamellae of a crystalline polymeric material having a substantially lower melting range than the first polymeric material. This lower melting, crystalline material should be adjacent at least one surface and extend beyond both to form at least one surface layer of the sheet. Because of its lower melting range it serves the sealing of the material, and because of its crystallinity it is non-sticky and will exhibit a suitable cohesive strength. Preferably this surface material should only overlap the adjacent lamellae of the first polymeric material over a relatively small distance. For obtaining such arrangements, the slots in the row are constructed correspondingly.
Alternatively, the first polymeric material may with advantage consist of isotactic or syndiotactic polypropylene, whereas the corresponding second extrudable material may, for instance, be a block-copolymer having segments of polypropylene and segments of randomly o-polymerized ethylene/propylene. Other suitable combinations for any particular purpose can easily be selected by an expert. By use of the existing methods of subdividing sheets, it is generally not possible to obtain subdivided structures of finer thickness than about 0.05-0.1 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.
In another aspect 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 splittability, for producing textile fibres with improved abrasion resistance. 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 usually occurs when the splitting has been promoted by substances admixed at random.
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, is 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 splits in each of the lamellae is performed at least in part before or during the haul-off from the extruding 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 terminated whereby any of the lamellae will be subdivided into sandwich-like strips or filaments. By the said methods the ribbons or filaments can get a cleaner edge as compared to cutting in solid state, and further, 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 will be understood, these methods of splitting, as well as simple cutting are carried out without requiring fragility of the first polymeric material. Thus it is possible 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 in the melted state (as described above) or by cutting in solid state with very closely spaced knives can be used directly as a textile yarn, no chopping to staple with subsequent carding being necessary. So can the cleaved material when it has first been split to ribbons and subsequently split further to a splitfibre network. Normally, however, a twisting process is desirable. Alternatively, the split and cleaved material either in form of yarn or wet can be chopped to staples and may be mixed with other 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 socalled bicomponent fibres, which, as is well known, are suitable for obtaining a very effective crimp, or which may be used for obtaining composite properties of the fibres, e.g. to apply to one or both surfaces of the fibre a more hydrophilic sutstance suitable for dyeing or to increase the ability of transporting moisture. In this connection the present invention provides for a much simpler and cheaper method than the known art, in which each filament has to be formed separately in a bicomponent nozzle. 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 system are used for each material. The choice of materials for obtaining the desired properties as well as for avoiding cleaving of the layers within each bicomponent fibre can easily be made by an expert. This embodiment can also with advantage be used to produce 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 is 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.
By the extrusion method described above, the lamellae will be in the form of continuous 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 halices, or splitting the tube helically, or both, it is possible to obtain an angle between the continuous dimension of each lamellae and the direction of splitting, thus producing staple material of substantially constant length.
The existing processes for splitting up strips to staple fibres or to yarn make use of a fissility formed either by molecular orientation or by a fiber-formed or fibre-like oriented morphology depending on the presence of two or more different phases or materials. It is known that the morphology most suitable for easy splitting is one which predominantly produces splitplanes transversal to the first dimension of the strip, preferably under an angle relatively near to 90�. The aim of the present invention is to produce such a morphology in a particular efficient manner.
A simplified method of producing said sandwich-like arrangement consists in mixing the materials at random, but only to form a relatively coarse dispersion of the materials in one another, and flattening the shape of each of the particles of this dispersion to form elongated flakes by passage through a sheetforming chamber.
Generally the disruption should not be carried so far that the fibres become completely separated from one another, but at least some interconnection in network-form, as obtained by incomplete splitting, is preferable in order to ease the handling of the yarn or web.
If one material is split-resistant and another is either directly splittable or rendered splittable by a suitable treatment, and furthermore the adhesive bond between the two materials is sufficient for preventing them from separating totally from each other during the splitting, then the resulting fibres will be of bi-component nature and consist of structurally undisrupted strands in combination with strands in structurally disrupted state. This provides for a suitable combination of properties, as the split-resistant strand provides abrsion resistance whereas the disrupted material provides surface properties which are suitable for textile fibres.
An embodiment of the present invention is characterised in that a polyamide is used as one of the materials, and a polyester as another of the materials. Thus both constituents will exhibit high abrasion resistance, and a differential shrinkage due to the different moisture absorbance gives high curling effect. Furthermore, the polyester contributes with high crease resistance whereas the polyamide contributes with relatively high dyeability. The polyester can with advantage be polyethyleneterephthalate and the polyamide either polycaprolactame or polyhexamethyleneadipamide.
In combination with one of more polymeric materials a non-polymeric material, e.g. a paste may be used for facilitating the separation of the layers.
The filamentary strands can also be in the form of ribbon-like strips of pleated cross sectional configuration fitting into that of the strips of said first material. This product presents the advantage of having a particularly high bulk and high elasticity when compressed or flexed.
It should be understood that the invention applies not only to thermoplastic polymers, but also to other polymers, which are capable of being shaped in said sandwich-like arrangement, e.g. cross-linked polymers polymerized in situ or polymers which decompose below their melting point, but are capable of forming a homogeneous film from dispersion of solution. Furthermore, it should be understood that the invention applies not only to organic polymers, but also to glass, which because of its thermoplastic properties can be processed by extrusion on principle in similar manner as thermoplastic organic polymer substances.
The strips of pleated cross-sectional configuration and the filamentary strands may be united by means of an adhesive layer. In the case of polymeric materials, this adhesive layer may consist of a mixture of the first polymeric material and the second polymeric material or may be graft polymers or block copolymers of said polymeric materials.
The two polymeric materials forming the fibrous product according to the invention need not be chemically different by may be chemically identical provided that they have been manufactured in such a way as to have different physical properties. E.g. the filamentary strands may be in the form of micro fibrils, while the pleated strips are in the form of a continuous structure of a chemically identical substance.
At the stage just before compression and expansion, the sandwich-like product can either be a relatively thick filament or a flat structure such as a ribbon or a relatively wide sheet which may be tubular. The layers may be parallel or practically parallel to the flat dimension of the product or may traverse over a part of the thickness of the product or the whole thickness of the product and may even by perpendicular to the flat dimension of the product.
The sandwich-like product consisting of alternating layers of at least two materials may be produced by extruding alternating layers of said materials. It is generally most practical to extrude a multitude of the layers into a common chamber where they unite. Extruder heads for simultaneous extrusion and lamination of two or a small number of layers of different polymeric materials have since long been used for the production of complete packaging film materials. Similar dies but constructed for simultaneous extrusion of a great number of layers are suitable for carrying out the method according to the invention.
If the material in film-form is to be subject to the compression after termination of the full extrusion process it is preferable to units the sandwich-like strips leaving said grid to as to form a tubular structure. The sandwich-like strips may be united during the transversal shearing produced by continuously rotating the two lips of a last section of a ring die in opposite directions.
If the sandwich-like product is formed by the smearingout of materials from a multitude of orifices as described above, and if the said grid is steady in relation to said row of orifices, the grid will divide each layer into continuous strips, whereas discontinuous strips will be formed if the grid rotates relative to the row of orifices. Such product consisting of discontinuous strips is suitable for the production of staple fibres according to the invention.
The micro-pleating caused by the compression will of course result in some irregularity of the thickness within a cross-section of each of the layers, no matter whether the compression and expansion take place in fluid or semifluid or in a more solid state. In this connection the most fluid material will tend to adapt its shape to the deformation which the less fluid material tends to determine, thus said irregularities of thickness will be most pronounced in the layers formed by the more fluid material. These irregularities increase the splittability of the individual layers. Thus the material which is intended to retain the highest resistance to splitting is generally chosen to have the lowest fluidity at the temperature where the compression and expansion are carried out.
The process step of disruption can also be carried out in different ways, some being particularly cheap and some being directed particularly to the creation of suitable fibre surface properties. In any case, the treatment must be so chosen in relation to the materials that at least one of the materials retains a continuous or practically continuous structure within areas which are sufficiently big for still exhibiting the micro-pleated configuration. The disruption generally involves a mechanical treatment which either splits the structure of one of the materials or makes the inter-faces between the lamellae slip. Additionally to or in some cases independently of the mechanical disruption leaching out of a part of the product may be applied. Furthermore, the mechanical disruption either in the inter-faces or internally in one of the materials can with great advantage be promoted by including in one of the materials a slipping agent, for instance an oil which is soluble in the material while this is melted or semimelted, but bleeds out when the latter solidifies. Alternative or supplementary agents to aid the disruption are swelling agents and expansion agents, such as volatile solvents which are preferably applied to the product after extrusion, micropleating and solidification of the product. Mechanical treatments suitable for the disruption are in particular rubbing actions, but also twisting, drawing, rolling, impacting, bending, brushinng, or acoustic splitting actions. In any case, the disruption treatment or treatments must of course be so restricted that it leaves fibres of the first material in the form of micropleated strips laminated with filamentary strands of the second material, at least spot-wise.
As mentioned in connection with the description of the fibrous product, the pleated strips and the fibamentary strands may be laminated with an adhesive layer in between. In this case, the disruption treatment generally should be so chosen that said adhesive bond is substantially unaffected, whereas the disruption may for instance take place in the filamentary strand material or by means of a fourth material also forming part of the sandwich structure. Thus said fourth material will be used particularly with a view to an easy production of fibres from the thicker product, whereas the adhesive material is used with a view to the properties of the final fibrous material.
If the strips are formed in the extrusion process or by a cutting action it is generally preferable to use a split resistant polymeric material as the first material. The reason for this choice is partly that it enables vigorous disrupting forces to be applied without risk of ruining the pleated configuration, but also and particularly that the pleated configuration is prone to abrasion during the use of the fibrous product. Examples of suitable splitresistant polymers are: polyamides, polyesters, block copolymers of alternate crystalline and elastomer segments graft copolymers having an elastomer backbone and crystalline grafts.
If the fiber material is split resistant and the second material is either directly splittable or rendered splittable by a suitable treatment, and furthermore the adhesive bond between the first and second material is sufficient for preventing the two materials from separating totally from each other during the splitting, then the resulting fibrous product will consist of split-resistant pleated strips laminated with filamentary strands in a structurally disrupted state. This makes a suitable combination of properties, as the splitresistant strip provides abrasion resistance whereas the disrupted material provides surface properties which are suitable for textile fibres.
In such structurally disrupted state the filamentary strands may with advantage consist of micro-fabrillar crystal formation disrupted from one another. Such formations may be formed from crystalline polymers when an oil is dissolved in the latter in melted state and bleeds out on crystallisation during drawing. The oil can subsequently be leached out.
An embodiment of the present invention is characterized in that either the first or the second material is a polyamide and the other a polyester. Thus both constituents will exhibit high abrasion resistance, and a differential shrinkage due to the different moisture absorbance gives high curling effect. Furthermore, the polyester contributes with high crease resistance whereas the polyamide contribute with relatively high dyeability. The polyester can with advantage be polyethyleneterephthalate and the polyamide either polycaprolactone or polyhexamethylenedipamide.
As described above adhesion can be increased by imparting a "cross-crimped" configuration to the strps, but the aspect described is not limited to this configuration.
Generally the multi-layer structure is prepared from a sheet built up from fluid layers, and subsequently each of the layers is longitudinally subdivided to fibres or fibre-like products. The formation of this sheet preferably takes place by co-extrusion of at least three extrudable materials, at least two of which being synthetic polymers. The third component may also be a synthetic polymer, but may alternatively be a non-polymeric, but co-extrudable separating component. The components are extruded in interspersed relationship, each forming a plurality of thin layers extending substantially parallel to the faces of the sheet. For further details of making the sandwich structure reference is made to pg 18, line 28-pg 19, line 2. When using the rotary device for subjecting the interspersed streams to a shearing action the melt viscosities of the major components should be at generally similar level.
Although it will generally be possible to find an adhesive component for any selection of A and B, e.g. a graft or block copolymer between A and B, ther may be practical or commercial limitations, and it may often be advantageous to use two adhesive components C1 and C2 of which C1 is mainly capable of bonding to A, and C2 to B, while C1 and C2 adhere to one another. The succession would then be as follows: AC1 C2 BAC1 C2 B.
There are practically no constructional difficulties in co-extruding five instead of four components, and thus two adhesive components (C1 and C2) ca be used together with the separating component D, viz.
AC1 C2 BDAC1 C2 BDAC1 C2 B
Thus one of the polymers may be highly hydrophobic and possessing high wet strength, while the other is hydrophilic and water-absorbing. Alternatively, the difference between the melting points of said polymers may be particularly high and permit the fusing of one of the components of the fibre (in the manufacture of paper or non-woven fabrics) without substantially affecting the molecular orientation of the other components. Although similar significant differences can be achieved by conventional spinning methods, this generally requires use of an expensive copolymer as one of the major components, because only two polymers can be co-extruded and these must satisfy both the requirement for adhesion and the specific requirements for the application. By use of the present invention as described in the foregoing the desirable combinations of properties may generally be achieved by means of cheap polymers, generally homopolymers, while the generally more expensive copolymers which are used or adhesive purposes are used in small concentrations in the form of thinner layers.
Thus homopolyamides such as nylon 4, nylon 6, nylon 66, nylon 11 or 12 can be combined with homopolyolefins such as polyethylene or polypropylene by means of a thin layer of polyolefin/acrylic acid copolymer (or a suitable salt of the latter). And polyethyleneterephthalate can be combined with homopolyamides such as nylon 4, nylon 6, nylon 66 by means of a layer of a suitable adhesive component which may be a blend of a copolymer based on polyamide and one based on polyethyleneterephthalate.
ABEABEABE . . . or . . . ABAEABAEABA
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a section through the extruded sheet material transverse to the continuous dimension of the lamellae (or the continuous dimension of the rows of chopped lamellae), showing lamellae of flattened S-form,
FIG. 18 is a schematical illustration in perspective view of a method of making a similar inversion of the position of the sandwich arrangement by means of a circular row of chambers but without inverting the cross-sectional dimensions of the strips,
FIG. 29 is a cross-sectional view along the line XIII-XIII in FIG. 28.
DESCRIPTIONS OF THE PREFERRED EMBODIMENTS In FIGS. 1, 2, and 3, the film material is shown, for simplicity, as being made of solely two materials, 1 being the reinforcing material and 2 being the filling 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 the angles to the plane of the sheet are grossly exaggerated, as in fact the overall angle between the lamellae and the dimension of the sheet is below 2�, and the thickness of the reinforcing lamellae is in the range between 0.1 and 10 microns. In FIG. 3 it is further shown that material 1 is absent in a layer in the core of the sheet, whereas material 2 is present all over.
The apparatus shown in FIG. 4 comprises a row of slots, three for the reinforcement material and four for the filling material, above which is a collecting chamber consisting of parts 5 and 6 which narrow down to an extrusion slot. The two parts of the collecting chamber may be rotated together relative to the row of slots so that the drag exerted by the bottom of the collecting chamber on the lamellae 1 and 2 as they are extruded from slots 5 and 6 causes the lamellae to be laid substantially flat along the row. Simultaneously, however, the lamellae are forced upwards by fresh polymeric material being extruded through the slots and as they are forced upwards their sides drag against the sides of the collecting chamber, as indicated in FIG. 4, and in particular against the neck 7 (not shown in FIG. 4), and the U-form of FIG. 2 results.
In FIG. 7, the slots for material 1 are split so that material 2 from slots 4 will be smeared in between the two half-parts of the lamellae of 1. This arrangement is preferably used in connection with the process for making the U-form of the lamellae, which will, however, in this case turn out in the split form, shown in FIG. 3, (the J form). It is not essential that the orifice parts 3 lie adjacent to each other in the form of a split slot. In fact they can be orifices dislocated from one another.
In the following examples, the indications of melt indexes refer to ASTM D 1238 - 62T.
In FIG. 10 as well as the other figures the sheet material is shown, for simplicity, as being made of solely two materials, 11 being the first polymeric material and 12 being the second 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 10 microns and may even be below 1 micron, and the overall angle to the plane of the sheet will normally be about or below 1�. FIG. 10 further shows how each lamella of material 11 can be split through lines 13, 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.
In case the extrusion takes place at the same speed at different portions of the cross-section of each of the orifices 14 and 15, the parts 16 and 17 preferably ought to rotate at the same speeds but in opposite directions. In practice, however, there will normally be differences between the extrusion velocities over the cross-section of each of the orifices, and this in combination with the fact that the viscosities of the materials are unequal tends to produce different dragging at the two surfaces. In order to compensate for such differences the parts 16 and 17 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 18 and 19 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.
Within the scope of the invention the first material may be 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 applied 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 suitable viscosity.
In FIG. 12, 21 and 22 represent two different materials in sandwich-arrangement at the stage when the composite product is extruded through a chamber in sheet form and is subdivided to form many strips, in which the sandwich-structure will lie transversely. The blades 23 to produce the subdivision are shown, while the other apparatus parts are omitted. If instead of blades, wedges widening in the direction of flow are used, tapering chambers will be formed between the wedges, and the fluid product will therefore be compressed in the lateral direction of the sheet during the subdividing step.
FIG. 13 shows a morphology where the layers themselves are strips with their flat dimension transversal in relation to the flat dimension of the extruded laminated strip, whereas each layer in FIG. 14 tends to be a strip with its flat dimension parallel to the flat dimensions of the extruded laminated strip. Whether the structure of FIG. 13 or that of FIG. 14 is formed depends on the number and relative thickness of layers in the sandwich, the dimensions of the extrusion devices, and the draw-down ratio after extrusion. In FIG. 13 the layers are shown thinner near the edges than at the middle. Such differences will generally occur when the layers are formed by smearing action as described.
FIG. 15 shows the morphology resulting when a grid has been inserted in the extrusion device to subdivide the layers before the fluid product reaches the subdividing means, which in this case should be of the wedge type so as to compress the strips in the dimension which originally was the lateral dimension of the sheet. In the case shown, three rows of lamella-formed layers are formed, corresponding to four blades or wires per strip-forming chamber. This can for instance correspond to a grid division of one millimeter and a chamber division of 4 millimeters. If furthermore, the width of each of the slots at the end of the chambers is one millimeter, the width of each small lamella will be 1/3 millimeter at the time when it leaves the extrusion device. If by drawing-down, partly in melted and partly in solid state, the thickness of each laminated strip is brought down to for instance 0.03 millimeter, the width of each of the small lamellae will beocme 0.01 millimeter. The thickness of each lamella can be essentially smaller.
The extruder head shown in FIG. 16 comprises two ducts 25 and 26 communicating with extrusion slots 27 and 28, respectively. An extrusion chamber 29 comprising two parts 30 and 31 which can be rotated around a common axis in opposite directions is located along the length of the circular row of extrusion slots. The radially arranged lamellae produced by the slots 27 and 28 are subjected to a smearing action during the passage between the oppositely rotating walls of the chamber 28. This smearing action causes the lamellae to be drawn out to form a sa dwich-like arrangement in which the layers will traverse the thickness of the sheet, but under a very small angle. The layers thus formed may be divided into very narrow ribbons by means of a row of radial wires or thin blades provided in the path of the extruded tube (not shown in FIG. 16) and is finally formed to ribbons in the manner previously described.
In the fibrous product shown in FIG. 19, 41 defines internally pleated layers of a first polymeric material and 42 defines layers of a second polymeric material laminated with the first polymeric material. The fibrous product shown in FIG. 20 also comprises layers 41 of a first polymeric materal and layers 42 of a second polymeric material. The sandwich-like product shown in FIG. 20 has been divided in fluid state to narrow ribbons before being compressed.
The bi-component bulked fibre shown in FIG. 21--formed by disruption of the product of FIG. 19 or 20--comprises a pleated layer 41 of a first polymeric material and another pleated layer 42 of a second polymeric material.
The stretching device shown in FIG. 22 comprises a first set of rubber-coated nip-rollers, the nip zone of which is indicated by the line a-a. It also comprises a second and a third set of nip-rollers, the nip zones of which being indicated by the lines b-b and c-c, respectively. A sandwich-like product 43 in ribbon form is fed into the nip zone of the first set of nip-rollers in a direction perpendicular to the axis of the rollers and is drawn off by the second set of rollers in a direction almost perpendicular to the feeding direction. Simultaneously with said change of direction the ribbon is strongly stretched in its longitudinal direction, the peripheral speed of the second set of rollers being chosen several times higher than that of the first set of rollers. Owing to said strong longitudinal drawing in combination with the extra narrowing resulting from the change of direction, a tension is produced which is capable of imparting to the ribbon relatively fine external longitudinal pleats which pleats are converted to internal pleating, when the ribbons subsequently pass the second set of rollers. In order to obtain said pleating the ribbon should not be too thin and generally not below 100 microns during the feeding into the device. The third set of nip-rollers driven so as to produce a small further elongation serves to maintain a high longitudinal tension in the ribbon during the full passage between the second set of rollers. The device shown preferably also comprises a hot-air oven (not shown) located immediately before the first set of rollers, heating elements provided within said first set of rollers and a second hot-air even located between the zone a-a and b-b. The device may also comprise a cooling device located between the zone b-b and c-c.
If the change of direction is α, the ratio of reduction of width will be sin (90�-α). The sandwich-like product stretched at a ratio n will exhibit a tendency to obtain a reduction of width of a ratio about 1:√n as it tends to obtain about equal reductions of width and thickness when it is stretched n times whereas the volume of the product is kept practically constant. Thus, in order to obtain the intended internal pleating, sin (90�-α) must be significantly smaller than 1:√n. In practice the change of direction should preferably be chosen so that sin (90�-α) will be between 1:2√n and 1:3√n.
The radially arranged lamellae, of. FIG. 24, e.g. produced by the slots 27 and 28 in FIG. 16, are subjected to a smearing action during the passage between the oppositely rotating walls 30,31 of FIG. 16. This smearing action causes the lamellae to be drawn out so as to get the form shown in FIG. 25. The layers thus formed may be divided into very narrow ribbons by means of a row of radial wires or thin blades provided in the path of the extruded tube, of. FIG. 11. In this case, the product will get the form shown in FIG. 26. If the material thus formed is subjected to a further smearing action although less vigorous than the first smearing treatment it will get the form shown in FIG. 27. The reason for subjecting the material to this further treatment is to make the structure sufficiently coherent in sheet form to be capable of being treated on the stretching devices shown in FIG. 22 and 23. This extruder head can easily be modified to co-extrude three or four materials instead of only two materials.
FIG. 17 illustrates a method of compressing (micro-pleating) a sheet-like product by passage through two chambers in an extruder head which gradually changes the dimensions of the cross section. The increase of the width, however, is not strictly necessary for obtaining the effect of internal pleating. Furthermore, the grid can be omitted if use is made of a rather great number of relatively small chambers to produce the internal pleating.
EXAMPLE 1 Production of a sheet with high contents of an inorganic filler for use as substitute of book-print paper.
The sheet material should be biaxially drawn at about 110� C. at a ratio of 1:2 in both directions. Thickness before drawing about 0.1 millimeter.
EXAMPLE 2 Production of a light and stiff expanded sheet for packaging purposes.
Adhesive component: A mixture between (a) the same polyethylene and (b) a polystyrene with small contents of copolymerized butadiene, melt index 0.5 (same condition).
The expansion takes place during haul-off. Temperature of the circular slot: 120� C. (but higher temperature at the start of the run).
EXAMPLE 3 Production of a wrapping material consisting of crystalline, oriented lamellae and flexible lamellae.
The sheet is biaxially drawn at about 100� C. at ratios of about 2.5:1 in both directions. It exhibits an improved tear propagation resistance compared to normal biaxially drawn film material.
EXAMPLE 4 Instead of being drawn in balanced manner, the sheet of example 3 is cross-drawn at ratio 1.5:1 and simultaneously length-drawn at ratio 3:1 to about 100� C. The drawing can take place by means of a tenter frame. Another unoriented sheet of example 3 is cross-drawn at ratio 3:1 and simultaneously length-drawn at ratio 1.5:1.
The two plies are laminated betw en nip-rollers, the temperature of the rollers being kept at 80� C. and vapors of toluene being applied to condense into the nip on the sheet surface in order to bind the plies together.
EXAMPLE 5 Production of a textile web.
Cooling during haul-off: Strictly controlled air cooling, hot air being used to keep the temperature of the sheet beyond 160� C. till all the polyamide is crystallized. This temperature control has the purpose of promoting the "growth of the whiskers".
The extruded sheet, having a thickness of about 70 microns should be passed through a bath of mineral oil for about 10 seconds and in immediate succession hereto cross-drawn by means of a tenter frame, while keeping the temperature at 170� C. and allowing a lengthwise contraction. Finally, the oil should be leached.
EXAMPLE 6 Polycaprolactame of a melt index of 3 (ASTM D 1238-57 condition K) and polyethylene of the same melt index under said condition is extruded in a proportion of 40:60 by means of the devices shown in FIGS. 16 and 17. Between the two devices is a grid (not shown) as mentioned in the description of FIG. 16. The length of slots 27 and 28 is 6 millimeters and the chamber 29 has a constant radial width of 6 millimeters, too.
The inlet width of each of the chambers for inversion of the structure is 5 millimeters, the outlet width being 1 millimeter. The products thus formed is then oriented at 165� C. at a draw ratio of 2.5:1. The structure is disrupted to splitfibre networks by flexing and rubbing.
EXAMPLE 7 Polypropylene toughened by block copolymerization with elastomeric segments of ethylene/propylene and having a melt index of 0.3 (ASTM D 1238-57, condition L), and a copolymer of 71% ethylene and 29% vinylacetate having a melt index of 5 (ASTM D 1238-57, condition E) in a ratio of 65:35 are extruded in the extruder head shown in FIG. 16 which, however, is provided with a row of twenty compression chambers, each on principle shown in FIG. 17. The length of slots 27 and 28 is 6 millimeters and the chamber 29 has a constant radial width of 6 millimeters. The inlet width of each of the chambers for internal pleating is 20 millimeters, the outlet cross-sectional dimensions of the chambers are 12 millimeters�2 millimeters. The extruded product is oriented at 120� C. and at a draw ratio of 1:5. It is then swelled with chloroform and subsequently caused to expand by passage through boiling water. Finally, the material is split to individual filaments by rubbing between rubber plates.
EXAMPLE 8 Polycaprolactame of a melt index of 3 (ASTM D 1238-57, condition K) and polyethylene (melt index 7, condition E) are extruded in a proportion of 40:60 by the method described in example 7. The product thus formed is then oriented at 165� C. at a draw ratio of 2.5:1. The structure is disrupted to spitfibre network by flexing and rubbing.
EXAMPLE 9 Objective: To produce a three-layer fibre consisting of two incompatible polymers united by a binding layer and to obtain cleaving at the interfaces between the incompatible polymers.
Sequence of coextrusion: . . . I, II, III, I, II, III, . . . The product tends to cleave at the interfaces between III and I.
Temperature at die outlet: 260� C.
EXAMPLE 10 Objective: See example 9.
Component I (50%): Polyethyleneterephthalat.
Component II (5%) (adhesive): A homogeneous blend of (A) 50% polyethyleneterephthalat copolymerized with blocks of polyethyleneglycol, and (B) 50% copolymerized Nylon 6 and Nylon 66 (socalled Nylon 6 A).
Temperature at the die outlet: 275� C.
Further processing of the tape and examination under microscope: See example 9.
EXAMPLE 11 Objective: To illustrate the production of a four-layer fibre consisting of two incompatible polymers united by a system of two adhesive layers and to make a cheap polyester fiber by combination with polyethylene.
Temperature at die outlet: 275� C.
EXAMPLE 12 Objective: To demonstrate the production of two-layer fibres consisting of components which can bond directly to each other, while using a third polymer as separating component, the separating component being incompatible with the other polymers and forming one-layer fibres by cleaving at the interfaces.
Sequence of coextrusion: . . . I, II, III, I, II, III, . . .
The product tends to cleave at the interfaces II-III and III-I.
EXAMPLE 13 Objective: See example 12.
Component I (35%): Copolymer of 85% vinylidenechloride and 15% polyvinylchloride (Saran).
Temperature at die outlet: About 200� C.
EXAMPLE 14 Objective: To produce three-layer fibres consisting of a strong hydrophobic middle layer and a lower-melting and more hydrophilic component on both sides and to demonstrate the use of a separating component which is fully or partially removed.
Component III (5%) (separating component): Polyethyleneoxide.
Sequence of coextrusion: . . . II, I, II, III, II, I, II, III, . . . The cleaving tends to take place in III by leaching of said component.
Temperature at die outlet: About 230� C.
EXAMPLE 15 Objective: To show the simultaneous production of two different two-layer fibres.
Sequence of coextrusion: . . . I, II, III, IV, I, II, III, IV, . . . The product tends to cleave at the interfaces between II-III and IV-I.
Further extrusion conditions, further processing of the extruded tape, final pruduct, and examination under microscope: See example 9.
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