GB2031044A

GB2031044A - Non-woven Fabric

Info

Publication number: GB2031044A
Application number: GB7927058A
Authority: GB
Original assignee: Courtaulds PLC
Current assignee: Akzo Nobel UK PLC
Priority date: 1978-08-04
Filing date: 1979-08-03
Publication date: 1980-04-16

Abstract

A web comprises continuous carbon filaments which extend in the same general direction in overlapping sinuous paths. It may be made by suspending a tow 1 of carbon filaments in a stream of liquid in a chamber 3 and forwarding it with the stream while spreading it in a fish-tail device 7 to a generally planar array. The spread array is fed onto an endless conveyor 12 which is pervious to the liquid and is moving in the same general direction as the array, but more slowly, so that the carbon filaments are deposited on the support in sinuous, overlapping paths to form a web. The web can be used to make an electrode for an electrolytic cell or as a reinforcement or a chemically- resistant liner for the resin wall of a vessel, pipe or duct. <IMAGE>

Description

SPECIFICATION Non-woven Fabric This invention relates to a non-woven fabric comprising continuous carbon filaments and to a process for making such a fabric from carbon filament tow.

Carbon filaments are used as a reinforcement for resins in the manufacture of composite structures. They are presented in various forms depending upon the end use including unidirectional tapes and sheets in prepreg form, woven fabric, staple fibres in moulding compounds, and non-woven tissue made from staple fibres. A woven fabric utilises the strength of the carbon filaments in more than one direction and being a fabric is easier to handle than nonfabric forms such as tow. However, it is difficult to produce because of the brittleness of carbon filaments, and is expensive. Non-woven tissues are cheaper to produce but being made of staple fibres are much weaker.

According to this invention, a non-woven fabric comprises a web of continuous carbon filaments which extend in the same general direction in overlapping sinuous paths. This non-woven fabric is stronger than non-woven tissue, is easy to handle and can be produced directly from tow by a wet-laying process.

The invention includes a process for making a non-woven fabric comprising suspending a tow of carbon filaments in a flowing stream of liquid and forwarding it with the stream whilst spreading it to a generally planar array, feeding the array onto a support which is pervious to the liquid stream and which is moving in the same general direction as the array but at a slower speed so that the carbon filaments are deposited on the support in sinuous, overlapping paths to form a web.

The liquid stream in which the tow is suspended is conveniently water. It provides lubrication and support for the suspended filaments to allow uniform spreading and also assists in the deposition of a uniform web on the porous support through which it drains. The tow may be spread to the desired array simply by flowing the liquid through a channel which is wider than the suspended tow, whereupon the fluid forces act to spread the tow to a width approaching that of the channel. The channel can be made to diverge like a 'fish-tail' to promote diverging liquid flow but this is not essential for effective tow spreading. Preferably the tow is spread to an array in which the filaments are contiguous with no large gaps between them.

The array of filaments produced by spreading is deposited on a moving pervious support, thereby being separated from the liquid stream which drains through both the deposited web and the pervious support. The latter may be a woven screen fabric in the form of a continuous moving belt, similar to the 'wire' of a paper-making machine. The filaments are overfed onto the pervious support so that they are forced to take sinuous, overlapping paths as they are deposited on the support, and the liquid flow through the support assists this disposition of the filaments.

Suction may be applied underneath the pervious support to assist drainage and to influence the sinuous configurations in which the filaments are laid.

The degree of overfeed of the array of filaments is preferably at least 2 per cent, that is to say the speed of the filaments just prior to deposition is 2 per cent greater than the speed of the moving support. The degree of overfeed can be as high as 200 per cent or more; however, we prefer an overfeed of 10 to 100 per cent which we have found produces a fairly uniform web of filaments on the support with sufficient filament overlap to give a coherent structure after further treatment.

The web of filaments produced is preferably given a treatment for improving its cohesion. This treatment may be the application to the web of an adhesive material which bonds together at least some of the carbon filaments at locations where they overlap. The adhesive material may be applied to the web in overall manner as by dipping or spraying with emulsions or solutions of adhesive material such as emulsions of polyvinyl acetate, polyester, and epoxy or epoxy ester compounds, or an aqueous solution of sodium carboxymethyl cellulose. Thermoplastic materials may be sprinkled onto the web in powder form and activated by applied heat and pressure. An alternative to overall bonding is pattern bonding, for example in spot, stripe or grid patterns, using the adhesive material in the form of a print paste, and applying it by roller or screen printing.

The adhesive material may comprise thermoplastic filaments, for example nylon 6 filaments, distributed amongst the carbon filaments and activated to bond themselves and the carbon filaments into a coherent web structure by heat applied to the web. Bonding is assisted by applied pressure and is conveniently effected by passing the web between heated nip rollers.

The thermoplastic filaments may be combined with the carbon filaments by suspending a tow of the thermoplastic filaments in the flowing stream of liquid together with the tow of carbon filaments and spreading them together to form an array of filaments in which the thermoplastic filaments are distributed amongst the carbon filaments. This distribution is carried through to the web formed when the array is deposited on the moving pervious support.

As an alternative or in addition to adhesive bonding, the cohesion of the web may be improved by threads stitched into it. These are preferably spaced lines of stitching substantially parallel to and/or substantially at right angles to a side margin of the fabric.

Another means of improving the cohesion of the web is to laminate a sheet material to it. This may be, for example, a thermoplastic film or a nonwoven fabric of thermoplastic fibres which can be laminated to one or both faces of the web by passing them together through heated nip rollers so that the carbon filaments of the web are pressed into and bonded to the softened thermoplastic sheet(s). Suitable thermoplastic materials for the sheet include polyamides such as nylon 6 and nylon 66, polyesters such as poly(ethylene terephthalate), acrylic polymers formed mainly from acrylonitrile units and polyurethanes. The thermoplastic material is generally chosen to be compatible in usewith any matrix which the non-woven fabric of the invention is to reinforce; for example, polyamides generally bond well to epoxy resins.

One way of bringing the web of carbon filaments and the sheet material together is to use a sheet material which is pervious to the liquid from which the array of carbon filaments is deposited, and to feed the sheet onto the moving pervious support so that the web is formed directly on the sheet. A perforated plastics film may be used or a woven, knitted or non-woven fabric of the requisite porosity. One particular type of sheet which we have found effective is a randomly fibrillated film produced by extruding a plastics film and simultaneously activating a blowing agent contained in the film to rupture it into a fibrillar, network structure.

It is convenient for production purposes to form the web in a given thickness, and to build up greater thicknesses by stacking the non-woven fabric of the invention in layers to form fabric assemblies to suit the desired end-use. This also allows different filament orientation in different layers to produce strength in more than one direction. For example, the component filaments of one layer may extend in a general direction substantially at right angles to that of the component filaments of another layer.

The non-woven fabric of the invention or an assembly thereof may be used as a reinforcement for resin layers to form a composite structure. For this purpose it may be embedded in the resin layer, for example an epoxy resin layer, or bonded to a surface of that layer. One arrangement which is suitable for forming a chemically-resistant liner on the surface of the wall of a vessel, pipe or duct, is to embed the non-woven fabric of the invention in a surface layer of resin. The remaining part of the wall may comprise glassfibre reinforced resin, for example, polyester or furane resin. For this purpose the web of carbon filaments needs to be densely formed, or built up in layers to a dense assembly.

The non-woven fabric of the invention is particularly useful for reinforcing the surface layer of a composite structure. Such 'skin' structures are a cost effective way of adding strength and stiffness to a component, and have been found useful for sports equipment such as skis.

The invention also provides an electrode suitable for use in an electrolytic cell and comprising a non-woven fabric according to the invention, or an assembly thereof, a mounting for the fabric and terminal means for connecting the web of carbon filaments to an electrical power supply.

It has been proposed to use a tow of carbon filaments as an electrode in an electrolyte cell as described in British Patent No. 1,514,935.

However, the form of the non-woven fabric of the invention is better suited for this purpose, being easy to handle, more resistant against mechanical damage, and enabling economic use of cell space because a battery of electrodes with intervening spacers can form a compact assembly.

The mounting for the fabric may comprise a full or partial frame clamped around the fabric, or a pair of spacers, for example a pair of nonconductive grids, holding the fabric clamped between them. The terminal means may be separate from the mounting or may be part of it. A suitable terminal is a metal clamp which clamps directly onto the web of carbon filaments. An alternative is a conductive thread, for example of carbon filaments, stitched into the web and leading to a terminal screw or suchlike.

The fact that the carbon filaments are continuous rather than of staple length and are constrained in fabric form helps to prevent loose fibres floating about the cell and causing shortcircuiting. A further protection from this may be provided by holding the nonwoven carbon filament fabric within an envelope of a fabric which is pervious to the requisite electrolyte solution. A suitable fabric for this purpose is a non-woven fabric made by rupturing a thermoplastic film, for example polypropylene or polyethylene film, into a fibrillar network structure. The envelope can be made by laying the carbon filament fabric between two layers of the non-woven thermoplastic fabric and heat sealing the margins. Electrical connection can be made through the envelope by having a clamp which pierces it or by threading a connecting carbon filament thread through it.

The carbon filaments used to make the electrode of the invention are preferably high modulus filaments having an essentially graphitic structure because these have greater electrical conductivity and a better resistance to degradation during use of the electrode. The latter is particularly necessary when the electrode is used as an anode.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which Figure 1 is a diagrammatic side elevation of an apparatus for carrying out the process of the invention, Figure 2 is a plan of the spreading device used in the apparatus of Figure 1, Figure 3 is a plan of a non-woven fabric according to the invention, Figure 4 is a side elevational view of an electrode according to the invention, Figure 5 is a sectional view taken on the line V-V of Figure 4, and Figure 6 is a sectional view of a composite structure according to the invention.

Referring to Figures 1 and 2, a tow 1 of unsized carbon filaments is overfed to a spreading device 2. The spreading device consists of a chamber 3 containing water continuously fed in through an inlet 4 and a fish-tail device 5 which forms the outlet of the spreading device. The fish-tail is of substantially square cross-section at the point 6 where it joins the chamber 3 but its outlet 7 is in the form of a long slit.

A pervious sheet 10 of plastics material, for example a randomly fibrillated film of nylon 6, is fed from a reel 11 to the upper flight of a water pervious, endless conveyor 12, for example a wire mesh conveyor, passing over rollers 1 3 and 14 in the direction shown. The spread tow of carbon filaments emerging from the fish-tail device 5 is laid on the plastics sheet 10 as the tow passes from the outlet 7 of the fish-tail. The speed of the carbon filaments emerging from the outlet 7 is arranged to be greater, for example from 10 to 100 per cent greater, than the speed of the conveyor 12 and the plastics sheet 10. The water carrying the carbon filaments drains through the plastics sheet 10 and the pervious conveyor 12 into a receptacle 1 5 under the upper flight of the conveyor from which it can, if desired, be recycled to the inlet 4 of the spreading device.Suction may be applied to increase the drainage rate.

The plastics sheet 10 supporting the tow 1 of carbon filaments parts from the conveyor at the roller 14 and passes through a heater 1 7 where it is heated to soften the sheet 10 and thence to heated calender rolls 1 8 and 1 9 which press the filaments and the sheet sufficiently for the filaments to become embedded in one surface of the plastics sheet.

Figure 3 shows a non-woven fabric according to the invention in which the carbon filaments 20 follow overlapping, sinuous paths to constitute a web. The cohesion of the web and its lateral strength is increased by spaced lines of stitching 21 running at right angles to the general direction in which the carbon filaments extend, i.e. at right angles to the machine direction.

Referring to Figures 4 and 5, an electrode suitable for an electrolytic cell comprises a carbon filament fabric 22 of the invention enclosed in an envelope 23 of a pervious non-woven fabric, for example of polypropylene. The envelope 23 is supported by two frame members 24, 25 which clamp the margins of the envelope between them.

These frame members may also act as spacers between adjacent electrodes arranged as a battery.

A terminal connection is provided by a carbon filament thread 26 of which one end is stitched into the carbon filament fabric 22 and the other end is connected to a terminal block 27.

Figure 6 shows a cross-section of a composite wall structure in which the main body of the wall is a staple-fibre reinforced resin layer 28 such as a furane resin reinforced with glass fibre in chopped strand mat form. A non-woven fabric of carbon filaments according to the invention is embedded in a surface layer 29. This surface layer 29 constitutes a chemically-resistant liner for the wall, which may be part of a vessel, pipe or duct, for example, a spin bath for the viscose process.

The invention is illustrated by the following Examples Example t Four unsized carbon filament tows ('Grafil'- Type A-R.T.M.) each weighing approximately 1 g/m and containing 10,000 filaments were fed to the apparatus shown in Figures 1 and 2 of the drawings and spread into a unitary array of width 1 5 cm in the fish-tail device. The fish-tail device fed the carbon filaments onto a randomlyfibrillated, polyurethane film having a basis weight of 20 g/m2 to form a web of overlapping sinuous filaments. The feed rate of the carbon filaments was 1.2 times faster than the speed of the conveyor and polyurethane film, i.e. an overfeed of 20 per cent.The assembly of the polyurethane film and the carbon filaments was heated and pressed to form a coherent web in which the carbon filaments were embedded in one surface of the polyurethane fibrillated film and formed substantially the whole of that surface of the film. The web as a whole contained 61 per cent by weight of carbon filaments and 39 per cent by weight of polyurethane.

Example 2 Four unsized tows of high modulus carbon filaments having an essentially graphitic structure ('Grafil'-Type HM) and each comprising 10,000 filaments, were formed into a web by the process described in Example 1 but with the omission of the polyurethane film, and using an overfeed of 60 per cent. The resulting dense web of overlapping, sinuous filaments had a basis weight of 37 g/m2.

Added cohesion was given to the web by passing it through a dip bath of an 8 per cent by weight aqueous emulsion of a short-chain polyester (Neoxil 952) and then drying it. A rectangular assembly of eight layers of this web was made to produce a dense, substantially even structure. A continuous carbon filament yarn was stitched into a margin of this fabric assembly and extended from that margin. The assembly was then sandwiched between two rectangular sheets of a fibrillated polyolefin film (a 60:40 mixture of polypropylene and polyethylene) of basis weight 18 g/m2. These were heat sealed around the margins to enclose the carbon filament assembly in an envelope, with only the carbon filament yarn protruding.

The resulting product was suitable for mounting as an electrode in an electrolytic cell as described in relation to Figures 4 and 5 of the drawings.

Claims

1. A non-woven fabric comprising a web of continuous carbon filaments which extend in the same general direction in overlapping sinuous paths.

2. A fabric as claimed in claim 1 provided with means for improving the cohesion of the web.

3. A fabric as claimed in claim 2 in which the means for improving the cohesion of the web comprises an adhesive material which bonds together at least some of the carbon filaments at locations where they overlap.

4. A fabric as claimed in claim 3 in which the adhesive material comprises thermoplastic filaments distributed amongst the carbon filaments.

5. A fabric as claimed in any of claims 2 to 4 in which the means for improving the cohesion of the web comprises threads stitched into the web.

6. A fabric as claimed in claim 5 in which the threads are stitched in spaced lines substantially parallel to and/or substantially at right angles to a side margin of the fabric.

7. A fabric as claimed in any of claims 2 to 6 in which the means for improving the cohesion of the web comprises a sheet material laminate bonded to the web.

8. A fabric as claimed in claim 7 in which the sheet material comprises a thermoplastic film or a nonwoven fabric of thermoplastic fibres.

9. A non-woven fabric comprising a web of continuous carbon filaments substantially as hereinbefore described in Example 1 or Example 2.

10. A fabric assembly comprises two or more non-woven fabrics as claimed in any of claims 1 to 9 stacked in layers.

11. A fabric assembly as claimed in claim 10 in which one layer has its component filaments extending in a general direction substantially at right angles to that of the component filaments of another layer.

12. An electrode suitable for use in an electrolytic cell comprising a non-woven fabric, or assembly thereof, as claimed in any of claims 1 to 11, a mounting for the fabric, and terminal means for connecting the web of carbon filaments to an electrical power supply.

13. An electrode as claimed in claim 12 in which the carbon filaments have an essentially graphitic structure.

14. An electrode as claimed in claim 12 or claim 1 3 in which the non-woven fabric, or assembly thereof, is held within an envelope of a fabric which is pervious to an electrolyte solution.

1 5. An electrode substantially as hereinbefore described with reference to, and as illustrated in, Figures 4 and 5 of the accompanying drawings.

1 6. An electrode substantially as hereinbefore described in Example 2.

1 7. A composite structure comprising a nonwoven fabric, or an assembly thereof, as claimed in any of claims 1 to 11, which is embedded in, or bonded to the surface of, a layer of resin material.

18. A composite structure as claimed in claim 1 7 in the form of a vessel, pipe or duct having a wall comprising the layer of resin material with the non-woven fabric, or an assembly thereof, embedded in a surface layer of the wall as a chemically-resistant liner.

19. A process for making a non-woven fabric comprising suspending a tow of carbon filaments in a flowing stream of liquid and forwarding it with the stream whilst spreading it to a generally planar array, feeding the array onto a support which is pervious to the liquid stream and which is moving in the same general direction as the array but at a slower speed so that the carbon filaments are deposited on the support in sinuous, overlapping paths to form a web.

20. A process as claimed in claim 1 9 in which the web is treated to improve its cohesion.

21. A process as claimed in claim 20 in which the web isseaSd by applying to itanedhesive material to bond together at least some of the carbon filaments at locations where they overlap.

22. A process as claimed in claim 20 in which the web is treated by stitching threads into it.

23. A process as claimedjnciaim 20 in which a tow of thermoplastic filaments is suspended in the flowing stream of liquid together with the tow of carbon filaments, and the tows are spread together to form an array of filaments in which the thermoplastic filaments are distributed amongst the carbon filaments, and in which the resulting deposited web is heat treated to cause the thermoplastic filaments to bond themselves and the carbon filaments into a coherent web.

24. A process as claimed in claim 20 in which a sheet of thermoplastic material pervious to the liquid stream is fed to the pervious support so that the array of carbon filaments is deposited as a web on the sheet, the web and the sheet being forwarded together and bonded to each other using heat and pressure.

25. A process for making a non-woven fabric comprising a web of carbon filaments substantially as hereinbefore described with reference to, and as illustrated in, Figures 1 and 2 of the accompanying drawings.

26. A process for making a non-woven fabric comprising a web of carbon filaments substantially as hereinbefore described in Example 1 or Example 2.