MATERIAL

FIELD OF THE INVENTION

The Invention relates to an improved method for producing an arc treated carbon fibre material and an arc treated carbon fibre material produced thereby,

BACKGROUND US patent 7923077 discloses an electric arc discharge-based method for producing a carbon nanotube-bearing carbon fabric. The carbon nanotubes are present in an arc treated track on the fabric.

International patent application publication WO03/082733 discloses an electric arc discharge-based method for producing an activated carbon fabric. The fabric is activated in an arc treated track on the fabric,

SUMMARY OF INVENTION

The invention provides an improved or at least alternative method for producing an arc treated carbon fibre material and an arc treated carbon fibre material produced thereby.

Method & Reactor - Low thermal conductivity cathode(s)

In one aspect the invention broadly comprises a method for treating a carbon fibre material which includes moving the carbon fibre material within a reaction chamber either through an electric arc in a gap between two electrodes one of which is a cathode, or adjacent an electrode which is a cathode so that an electric arc exists between the electrode and the material, which cathode has a thermal conductivity of less than about 30 watts per meter Kelvin (when measured at about room temperature). In another aspect the invention broadly comprises an electric arc discharge apparatus for treating a carbon fibre material, comprising a cathode having a thermal conductivity of less than about 30 watts per meter Kelvin (when measured at about room temperature). Preferably the cathode has a thermal conductivity of less than about 25 or less than about 20 watts per meter Kelvin and/or electrical resistivity of at least about 5 or at least about 10 ohms per mm. Preferably the cathode provides dimensional control of the arc in width and length planes of the carbon fibre material and through a depth of the carbon fibre material.

In another aspect the invention broadly comprises a method for treating a carbon fibre material which includes moving the carbon fibre material within a reaction chamber either through an electric arc In a gap between two electrodes one of which Is a cathode, or adjacent an electrode which Is a cathode so that an electric arc exists between the electrode and the material, which cathode has a thermal conductivity of less than about 30 watts per meter Kelvin (when measured at about room temperature) and electrical resistivity of at least about 5 ohms per mm.

Method & Reactor - Multiple electrode set

In another aspect the invention broadly comprises a method for treating a carbon fibre material which includes moving the carbon fibre material within a reaction chamber in a machine direction either through an electric arc in a gap between electrodes including multiple adjacent electrodes on at least one side of the material, or past multiple adjacent electrodes so that an electric arc exists between each of the electrodes and the material.

Preferably the electrodes on one or both sides of the material are spaced from one another both In and across the machine direction.

In another aspect the invention broadly comprises an electric arc-discharge apparatus for treating a carbon fibre material comprising a reaction chamber through which the carbon fibre material moves in a machine direction through an electric arc either in a gap between electrodes including multiple adjacent electrodes on at least one side of the material, or past multiple adjacent electrodes so that an electric arc exists between each of the electrodes and the material,

Preferably the electrodes on one or both sides of the material are spaced from one another both in and across the machine direction,

Materials

In a further aspect the invention may broadly consist in an electric arc-discharge processed carbon fibre fabric comprising one or multiple adjacent activation tracks produced by electric arc-discharge, and minimum tensile strength of about 40N/m across substantially all of the width and/or length of the fabric,

Preferably the useable area has a minimum uniform tensile strength of about 50N/m across substantially all of the width and/or length of the fabric. Preferably the carbon fibre fabric has a minimum tensile strength of about 40 N/m or about 50N/m across at least about 70% or about 80% or about 90% or about 95% or about 98% or all of the width or length of the fabric.

Preferably multiple adjacent activation tracks extend in a length of the fabric and having a minimum tensile strength of about 40 N/m or about 50N/m across a width of the fabric substantially transverse to said length. Preferably the fabric has an average weight of between 10 to 35% less than, and an average thickness (through a plane of the fabric) of between 5 to 10% less than, the same carbon fibre fabric not comprising said one or multiple adjacent activation tracks produced by electric arc-discharge, In a further aspect the invention broadly comprises in an electric arc-discharge processed carbon fibre fabric comprising one or multiple adjacent activation tracks produced by electric arc-discharge, and having an average weight of between 10 to 35% less than, and an average thickness (through a plane of the fabric) of between 5 to 10% less than, the same carbon fibre fabric not comprising said multiple adjacent activation tracks.

In a further aspect the Invention broadly comprises an electric arc-discharge processed carbon fibre fabric comprising one or multiple adjacent activation tracks produced by electric arc-discharge extending along a length of the fabric and each said activation track having a substantially constant width.

Preferably the or each activation track is between about 6mm and about 20mm in width. Alternatively the width of the or each activation track is between about 12mm and about 17mm if the fabric is woven. If the fabric is non woven, then the width of the or each activation track is between about 15mm to 25mm. Ideally, the width of the or each multiple activation track is about 15mrn. Furthermore, the width of the or each activation track is substantially constant along its length.

Preferably the one or more adjacent activation tracks are substantially consistent and/or constant in width across and/or depth through the fabric. Preferably the or each track does not vary in width across and/or depth by more than about 30% along its length. Alternatively, the width and/or depth of the or each activation track does not vary by more than about 20% along its length. Ideally, the width and/or depth of the or each activation track does not vary by more than about 10% or more than about 5% along Its length. The or each track should not burn through the fabric to cause a hole to be formed in the fabric.

Preferably the carbon fibre fabric Is a woven, knitted, or non-woven including felted carbon fibre material.

The material produced may be a graphitlzed and/or activated and/or a carbon nanotube bearing carbon fibre material. Definitions

By "graphltization" is meant enlargement of crystalline graphitic areas in carbon so that conductivity (both electrical and thermal) is enhanced.

By "activation" Is meant the creation of pores typically of nanoscale and typically up to 50nm in diameter, and typically also coarser corridor pores up to 100 nm in diameter in the material, or features on the surface of the material, by the arc treatment, and by vaporising or removing in the arc some matter of the carbon substrate and preferably non- graphitic carbon or a sufficient part or a major part of the non-graphitic carbon of the substrate. The interior pores can be termed 'internal activation' and "activation" is intended to also include the creation of exterior nanostructures on the surface of the material such as nanotubes ie 'external activation', deposited by the arc treatment process.

As used herein the term "and/or" means "and" or "or", or both.

As used herein "(s)" following a noun means the plural and/or singular forms of the noun,

The term "comprising" as used in this specification means "consisting at least in part of". When interpreting statements in this specification which include that term, the features, prefaced by that term in each statement, all need to be present but other features can also be present. Related terms such as "comprise" and "comprised" are to be interpreted in the same manner. BRIEF DESCRIPTION OF THE FIGURES

The invention will now be described by way of example only and with reference to the accompanying figures in which:

Figure 1 shows a section of electric arc-discharge processed carbon fibre material comprising one activation track produced by the method set out in WO03/082733, Figure 2 shows a section of electric arc-discharge processed carbon fibre material comprising multiple adjacent activation tracks,

Figure 3 is a schematic perspective vertical cutaway view of an arc reactor,

Figure 4 is an illustration of the material that may be produced by an arc reactor with multiple adjacent electrodes,

Figure 5 is a graph of cathode thermal conductivity versus resistivity of a number of cathodes,

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 shows a section of electric arc-discharge processed woven carbon fibre material which comprises one activation track 501 produced by electric arc-discharge. The material may be a woven material (comprising intersecting warp and weft fibres), a knitted material, or a non-woven material, such as a woven or knitted or non-woven Including a felt material, The material example shown Is produced by the method and reactor disclosed in international patent application publication WO03/082733 but an Improved single activation track material of the invention may be produced by a method and reactor as will be described with reference to Figure 3. In particular Improved single activation track material may be produced by arc discharge by moving the carbon fibre material within a reaction chamber through an electric arc between two electrodes, or between a cathode and the material, where the cathode is formed from a low thermally conductive material so that the cathode has a thermal conductivity of less than about 30 watts per meter Kelvin (when measured at about room temperature) and an electrical resistivity of at least 5 ohms per mm. It has been found that arc attachment to the cathode tip can be a function of cathode thermal conductivity and electrical resistivity, and that with cathodes with thermal conductivity and electrical resistivity in this range exhibit a relatively stable arc attachment to the cathode tip. This In turn produces an activation track on the material of relatively consistent width and/or position on the material. Figure 5 is a graph of cathode thermal conductivity versus resistivity of a number of cathodes, In which unfilled circles Indicate combinations of cathode thermal conductivity and electrical resistivity which result in a relatively stable arc attachment to the cathode tip and filled circles Indicate relatively unstable arc attachment. Preferably the cathode has a thermal conductivity of less than about 30 watts per meter Kelvin and electrical resistivity of at least 10 ohms per mm, or less than about 25 watts per meter Kelvin and at least 10 ohms per mm, or less than about 20 watts per meter Kelvin and at least 10 ohms per mm. It is believed that with such a cathode, as arc energy is released at the tip of the cathode electrons are easily emitted at the tip and the arc remains more constrained to the tip of the cathode, which can stabilise the arc attachment to the cathode, reducing any wandering of the arc on the cathode. As stated this In turn produces an activation track on the material of relatively consistent width and/or position on the material. A higher proportion of the material may be substantially defect free, and therefore usable, as electrode material for example ie arc- treated fabric of the invention may be of higher quality, because of the higher arc stability. The strength of non-woven material may also be increased. An unstable arc is one in which the cathode hot spot moves with respect to the cathode rod. This movement is either of the form of a rotation at almost constant frequency, or apparent "sticking" where the hot spot maintains the same position on the cathode tip. This periodic or erratic behaviour of the cathode spot induces corresponding movement of the arc as a whole, so that the arc attachment on the anode moves laterally in a periodic or erratic fashion as the anode material moves past. "Sticking" of the cathode spot thus corresponds to a constant deviation of the arc track on the moving anode material for a period of time (up to 5 s has been observed). When the wandering/ rotating behaviour is observed non-uniform tracks are produced so that instead of the centre of the track being directly above the cathode, the edge of the arc track may be directly above the cathode or even past it. This causes great difficulty In producing tracks bordering on each other. The ^" "sticking" behaviour can be greatly damaging, as the arc is in one position of an extended period of time and the resulting treatment damages the anode material. Sticking times of greater than about 0.5 s have been found to cause the material to be destroyed during pasting. This gives two objective measures of arc stability, the frequency of arc rotation, and the duration of any sticking. A stable arc is one in which neither of these phenomena are observed. Moderately stable is one in which no sticking is observed, and rotation frequency is of the order of about 1/3 Hz or less. In order to maintain an arc the surface of the cathode needs to be able to easily emit electrons and therefore has to be hot. The arc can originate from any point at which the cathode is hot enough. It will then propagate perpendicular to the surface at this point. This is due to the movement of a concentrated flow of electrons from the surface, that induces a magnetic field which then pumps the arc plasma directly away from the surface. The arc is often in constant lateral motion on the cathode surface, but will stay In one place if there is a sufficient thermal gradient along the surface to keep it there. The arc attachment itself heats the cathode. If the material making up the cathode has a high thermal conductivity we have found that the arc movement is over a large area (and the arc track is "unstable") and conversely when the thermal conductivity is low the arc attachment is small (and the arc track is "stable"). The other major property of the cathode material is electrical resistivity which must be sufficiently low to allow the arc current to flow. With a vertical carbon cathode, the carbon erodes and oxidises from the heated surface so that a pointed tip is formed. The formation of the tip appears to result from evaporation from the shank combined with deposit on the tip. For materials of lower thermal conductivity the stable arc attachment is developed on the small radius of the tip and the arc is vertical. For materials above a limiting thermal conductivity the hot area expands and becomes overall cooler, resulting in no strongly preferred location for electron emission.

Figure 2 shows a section of electric arc-discharge processed carbon fibre material similar to that of Figure 1 but which comprises multiple, such as two or more or three or more or five or more or ten or more, adjacent activation tracks produced by electric arc- discharge. In Figure 2, three adjacent activation tracks are indicated at 2a, 2b and 2c. It can be seen that the tracks are generally constant in width across the material, and quality, along the length of the material, as indicated also by the consistent colour of the tracks along the length of the material, Indicating control of the arc through the plane of the material.

The multi-track carbon fibre material may be produced by arc discharge by moving the carbon fibre material within a reaction chamber through multiple electric arcs formed either between multiple electrode pairs, or each between a cathode and the material itself.

In preferred embodiments the electrode pairs are spaced from one another in a machine direction as will be further described. This reduces inconsistencies in the width and/or quality of the arc tracks (as can occur when the multiple electrode pairs are placed within the reaction chamber adjacent one another, as then or in other situations the arcs may have a tendency to wander and interact with one another). The tensile strength of the material may be more consistent across the length and width of the material and In the depth (through the plane) of the material due to the electrode pairs being spaced from one another in the machine direction.

Again preferably the cathode is formed from a material having a thermal conductivity of less than about 30 watts per meter Kelvin and electrical resistivity of at least 5 ohms per mm, as described above. Such single or multiple arc track materials may have a useable area of 50 percent of treated material, where the useable area may have a minimum uniform tensile strength of about 40 N/m or about 50N/m across substantially all of, or about 70%, 80%, 90%, 95%, 98%, or all of the width or length of the material. The minimum uniform tensile strength may be across a width W of the material substantially transverse to a length L along which the tensile force is applied and further preferably through the plane of the material. The material may have an average weight of between about 10 to about 35% less than, and an average thickness (through a plane of the material) of between about 5 to about 10% less than, the same carbon fibre material not comprising the multiple adjacent activation tracks 2a-c produced by electric arc-discharge. The purpose of such a weight loss of the material Is to improve the performance of the material. Optimum levels of weight loss may give the best possible morphology of the material.

In preferred embodiments the width of the activation tracks may be between about 6mm and about 40mm, or about 12mm and about 17mm when the material is a woven fabric, or 15mm to 25mm when the material Is a non-woven fabric. In some embodiments the width of each activation track is about 15mm. The width of each of the activation tracks 2a-c is substantially constant along Its length, and preferably does not vary by more than about 30%, 20%, or 10% along its length.

Figure 3 is a schematic view of an arc reactor having a reactor chamber 1 in which one or more discharge arcs are created. Electrodes 2 and 3 project into the reactor chamber and are typically mounted by electrode-feeding mechanisms so that the position of electrode 2, which may be an anode support, and electrode 3, which may be the cathode, may be adjusted to create the arc, and in operation to maintain or if required adjust the arc. One electrode pair is shown but in an alternative embodiment the reactor may comprise multiple electrode pairs for producing a material as shown in Figure 2. In multiple electrode pair reactors preferably the individual cathode-anode electrode pair are spaced from one another both in and across the machine direction (the direction of movement of the carbon fabric through the reactor). The cathode 3 may be a motor fed consumable cathode, The reactor chamber preferably includes a surrounding water jacket 4 through which water is circulated to cool the walls of the reactor chamber during operation, or other suitable cooling system. Carbon fibre material 8 passes between the electrodes and through the arc formed by these electrodes during operation of the reactor. The carbon fibre material is typically a high purity flat carbon tape or belt or similar, The material 8 enters the reactor chamber through a slit 41 In the inlet side of the reactor chamber and leaves through a similar slit 42 in the outlet side of the reactor chamber. A mechanism usually a motor or the like is provided to feed the material, usually from a spool 9, through the reactor chamber. This is arranged such that the motor unwinds the material at a slow constant speed during a production run. After passing through the reactor, the now arc treated material exits and is then suitably collected, for example on another spool for further processing. The current density through the electrodes should be sufficiently low to avoid structural damage to the material (i.e. damage that would significantly affect the structural Integrity of the material) but sufficient to achieve a current density at the contact point of each arc on the material that Is sufficient to form an activation track on the material. The current density may be sufficient to cause some vaporisation of the material (again without structurally damaging the material).

An example of a section of material 300 that has been treated through an arc reactor comprising eight electrode pairs is schematically shown in Figure 4, As the material 300 moves through the arc reactor it passes through two electric arcs between a first set of cathodes on one side of the material and a common anode on the other, at dashed line 301, forming adjacent horizontal arc tracks 310 and 311, At a second set of cathodes and anode, further on in the machine direction at dashed line 302, the material 300 moves through two further electric arcs forming arc tracks 320, 321. At a third set of cathodes and anode, further on again in the machine direction at dashed line 303, the material moves through two further electric arcs forming arc tracks 330and 331. Finally, at a fourth set of cathodes and anode, further on again in the machine direction at dashed line 304, the material moves through two more electric arcs forming arc tracks 440 and 441. The resultant adjacent arc tracks are substantially consistent In width and are substantially parallel with one another. The electrodes may be positioned such that the whole width of the material is covered by activation tracks and/or the electrodes may be arranged such that the tracks overlap or gaps between each of the tracks are minimised. EXPERIMENTAL

Example 1 - Cathode

Carbon fibre fabric (a polyacrylonitrite based woven carbon fibre tape CWIOOI manufactured by TaiCarbon, Taiwan sold under the brand name KoTHmex of the specific weight 220 g/m ² , thickness was 0.7 mm, and a carbon content of 99.98) was electric arc- discharge processed by moving the carbon fibre material through three electric arcs between three electrode pairs, in a reactor similar to that described with reference to Figure 3. Each cathode had a thermal conductivity of about 13 W/mK, and an electrical resistivity of about 47 Ohm mm. An arc gap of 9mm existed between the cathodes and anodes. The electrode pairs were spaced from one another In the machine direction. The fabric was fed through the reactor at 5mm/second.

The arc-treated material produced was similar in appearance to that of Figure 2. A relatively high proportion of the material was considered defect free and usable as electrode material le the material arc-treated in accordance with the invention was considered to be of higher quality, because of the higher arc stability. Example 2 -Tensile Strength of Processed Carbon Fibre Fabric

The tensile strength of fabric was measured, both before arc treatment and post arc treatment generally as described in Example 1, by the use of tensile force meters in the following way. Samples of fabric 55mm wide by 150mm long were subjected to an even tensile stress each across its width and length. The stress applied was increased slowly increasing at a rate of IN every 5 seconds until the material tore. Tearing was generally observed across the width of the fabric shortly after the material had become taut i.e., tearing occurred shortly after the fabric came under tension. The tensile strength of the fabric was then calculated by dividing the measured maximum force value applied to the fabric by the width of the fabric sample.

Table 1 below sets out the results for three fabric samples tested, where the measurements taken were in the length direction (machine direction of arc treatment of the arc reactor) or width of the sample (perpendicular to the machi ne direction) . The results are expressed as a tensile strength measurement, which is calculated by taking the maximum tensile force applied before the fabric tore and dividing by the width (0.055m) of the fabric. Table 1 - Tensile Strength

Table 2 sets out the characteristics of the carbon fabrics tested. Table 2 - Carbon Fabric Characteristics

The foregoing describes the invention including preferred forms thereof and alterations and modifications as will be obvious to one skilled in the art are intended to be incorporated in the scope thereof as defined In the accompanying claims.