HK1089799B - Plasma treatment apparatus and method - Google Patents

Description

Plasma processing apparatus and method

Technical Field

The present invention relates to a method and apparatus for plasma treatment of gas permeable materials, for example: a fibrous material. The invention is particularly useful when used to treat wool.

Background

Plasma is widely used in material processing to alter the surface characteristics of the material. Generally, such treatments are quite useful where the surface of the material is uniformly distributed. When used with wool fibers, plasma treatment is used to oxidize the lipid layer on the surface of the fiber. Oxidation of the lipid layer may make the wool fibres more receptive to subsequent surface treatments, such as: shrink-resistant treatment and pilling resistant treatment.

Removing the lipid layer may also increase the friction between the fibers. This will be more advantageous for the spinning process, since less winding is required for spinning as good as possible. Lower levels of winding can increase the yarn take-off efficiency of the spun yarn, thus enabling the downstream process to run faster, thereby increasing production. In addition, low level wound yarns exhibit softer texture than higher wound yarns and are therefore more conducive to producing softer garments as required by the marketplace than high wound yarns.

Plasma treatment of wool or other fibrous materials must provide a uniform surface treatment to ensure that the material is more acceptable for downstream processing on a production line. If the surface of the material is not uniformly treated, the downstream process cannot achieve the designed effect, and defective products are generated.

Another aspect of plasma treatment is that wool and other fibrous materials are susceptible to localized burn in the plasma treatment. In addition, this is highly undesirable on a production line when a continuous supply of material is required. Therefore, the best plasma treatment should minimize the occurrence of localized burn injury during material handling.

Some existing plasma generation techniques for processing materials include adjusting the applied voltage and frequency to achieve a stable, uniform plasma. Such plasmas are typically generated at gas pressures above or below atmospheric pressure. Recently, developments of plasma treatment techniques performed at atmospheric pressure include using expensive inert gases to stably glow plasma, which is suitable for surface treatment of materials. Both above or below atmospheric pressure plasma treatments and plasma treatments comprising inert gases are economically less feasible due to their cost. Accordingly, plasma processing in air and at atmospheric pressure has been the focus of interest.

Roth et al (Roth et al) in us patent 5403453 states that a uniform glow discharge plasma is generated at one atmosphere of pressure, wherein ions generated by electrically breaking down helium and/or air are trapped between electrodes. Roth indicates that ion trapping increases the lifetime of ions in the plasma, resulting in a lower electrical breakdown threshold and a uniform glow discharge. A similar theory is also proposed by Gherar di et al (Ghera rdi et al) in U.S. Pat. No. 6299948, which is assigned to L' Air Liquide. According to Roth et al, such trapping can be achieved by applying a radio frequency alternating electric field between spaced electrodes. Roth et al gives the relationship between electrode spacing, electrode voltage and applied frequency when ion trapping occurs.

International patent publication WO 02/094455 discloses a plasma treatment at atmospheric pressure in which a spatially homogeneous micro-discharge distribution is obtained on an elongated discharge electrode by introducing a gas flow on a longitudinally symmetrical inclined plane. A relatively complex structure includes a plurality of channels leading from a gas distribution chamber.

Us patent 5403453 describes a plasma treatment station for a polymer strip (strip) at about atmospheric pressure, preferably slightly above atmospheric pressure, in which gas is blown from a set of holes in one of a pair of closed spaced plate electrodes. The turbulent high velocity transport of gas is used to delay and disrupt the formation of filament discharges.

It is an object of the present invention to provide improved plasma processing techniques for processing gas permeable materials.

Disclosure of Invention

The present inventors have recognized that the cause of plasma non-uniformity at normal atmospheric pressure is residual ions generated during the previous plasma generation cycle, causing electrical breakdown to concentrate through these ions, for example: at the same point. A normal dielectric barrier electrodischarge plasma consists of multiple microelectrodes, each lasting a few nanoseconds. The plasma is driven by an alternating high voltage between the electrodes. The alternating voltage plasma of each half cycle is generated by a microdischarge burst. Ions from each microdischarge are generally not readily dispersed and have a lower resistance than the surrounding gas, causing microdischarges to occur repeatedly at the same place. This results in very poor process uniformity and does not allow the use of all available gases to generate useful chemical compositions from the plasma.

Further, the localization of the micro-emitters increases the possibility of generating high temperature instabilities in the plasma, thus burning the material to be treated. It appears that this occurs due to the local release of plasma of specific chemical species on the surface of the material, where there may be a high concentration of contaminants. The generation of these chemicals changes the properties of the plasma, resulting in local excessive absorption of plasma energy and rapid temperature rise. Localization of microdischarges can lead to two effects. First, ions that are stationary relative to the electrodes result in localization of plasma microdischarges between the electrodes and result in uneven, less pronounced surface treatment. Second, the trapping of ions and plasma material by-products moving relative to the electrode in the gas permeable material causes plasma localization of the opposing material, resulting in material burn.

It is further recognized that the localization of plasma microdischarges prevents the full utilization of the gas available when generating the plasma, thereby limiting the concentration of active ingredients that contribute to the improvement of the surface chemistry of the material.

Thus, the present invention uses a strong gas flow through the gas permeable material and prevents localized formation of plasma microdischarges by dispersing and/or removing ions and unwanted chemicals between the electrodes or within the gas permeable material during and between the voltage crossover cycles. Thus, the present invention can provide uniform, efficient plasma processing where the voltage, frequency and electrode spacing parameters used are outside the range specified by the Roth theory. The uniform, efficient plasma treatment provided by embodiments of the present invention uses a filamentary, but randomly distributed, dielectric barrier to discharge the plasma and does not burn the material to be treated; rather than producing a uniform glow discharge as described by Roth and others.

In a first aspect, the present invention provides a method of producing a plasma treated gas permeable material comprising the steps of:

(a) applying an alternating voltage between spaced electrodes to generate plasma microdischarges between the spaced electrodes, at least one of the spaced electrodes being covered with a dielectric barrier and at least one of the spaced electrodes comprising a plurality of discrete electrode segments;

(b) passing a gas permeable material between or adjacent to said spaced electrodes; and

(c) gas is passed between the electrode segments into and through the space between the electrodes and the gas permeable material, the gas flowing over the plasma generating surfaces of the respective electrode segments and at a specific rate to ensure that the gas flow between the spaced electrodes is in a turbulent state, thereby randomizing the plasma microdischarges and dispersing the plasma products which would otherwise cause burn instability in the gas permeable material.

The thus randomized plasma microdischarges provide a uniformly distributed plasma treatment of the gas permeable material.

It will be appreciated that the gas in the space between the electrodes is used to disperse and/or remove residual ions that are stationary relative to the electrodes. Further, ions trapped by the gas permeable material are dispersed and/or removed by passing the gas through the material. Therefore, the plasma microdischarge generated next time does not repeat at the same point as the previous plasma microdischarge. The randomized plasma microdischarge also therefore provides a time-averaged, uniform plasma that is suitable for uniformly treating the surface of gas permeable materials. Accordingly, the gas permeable material treated in this way has better uniformity of surface properties and is less likely to be burned by localized plasma micro-emitters.

In a preferred embodiment, the gas moves in a direction across the passage of gas permeable material between the spaced electrodes.

In a particularly preferred embodiment, the treatment process can be facilitated by the following steps: applying a voltage alternating at a frequency between the electrodes enables the dissipation and/or removal of plasma by-products in the flowing gas that would otherwise cause localization of the plasma microdischarges. Any frequency may be used, but typically the frequency range used is 1kHz to 20kHz, with the preferred frequency range being 1kHz to 5 kHz.

As an additional advantage, the flowing gas can remove not only ions, but also harmful plasma by-products, such as: o is₃And NO₂。

The gas used in the method may be any gas suitable for electrical breakdown to generate a plasma, for example: inert gases or gases which do not interact with the material, but air is preferred. In addition, the pressure of the gas used in the process may be above atmospheric pressure or below atmospheric pressure. Advantageously, the gas pressure is atmospheric pressure.

A typical voltage range applied between the spaced electrodes is 10kV to 25 kV.

According to a first aspect, the present invention further provides apparatus for treating a plasma of a gas permeable material, the apparatus comprising:

(a) spaced electrodes, at least one of which is covered with a dielectric barrier and at least one of which comprises a plurality of discrete electrode segments;

(b) means for applying an alternating voltage between said spaced electrodes to generate a plasma microdischarge between said spaced electrodes;

(c) means for effecting a pathway of gas permeable material between or adjacent said spaced electrodes; and

(d) means for passing a gas between said electrode segments and through the passage between the electrodes and the gas permeable material as described above, the gas flowing over the plasma generating surface of each electrode segment and moving at a rate such that the gas flow between the spaced electrodes is turbulent, thereby randomizing the plasma microdischarges and dissipating plasma products which would otherwise cause burn instability in the gas permeable material;

thus, randomized microelectrodes can provide an overall uniform plasma treatment of the gas permeable material.

The voltage application means preferably applies a frequency electrode which enables the dissipation and/or removal of plasma by-products from the moving gas which cause localisation of the plasma microdischarges; any frequency may be used, but a typical applied frequency range may be 1kHz to 20kHz, and a preferred frequency range is 1kHz to 5 kHz.

The electrodes are advantageously spaced to allow relative movement of materials therebetween and the power required to generate the plasma can be minimized. Preferably, the electrode spacing is in the range of 2mm to 10mm, most preferably around 4 mm.

In a preferred embodiment, the spaced electrodes are preferably shaped to allow gas to pass through the gas permeable material in a direction transverse to the direction of passage of material between the spaced electrodes.

In particular, a first electrode of the spaced electrodes is gas permeable, preferably in the form of a mesh.

Adjacent separated electrode segments are preferably spaced apart by about 0.5mm to 2 mm.

The means for opening gas passages in the gas permeable material may comprise a rotatable drum (drum), the curved surface of which comprises a first electrode and the second electrode comprises said separate electrode segments, which are arranged concentrically around the drum, whereby the gas permeable material bridges over the first electrode between the first and second electrodes.

The apparatus of the invention, in either of the above aspects, is particularly suitable for fibrous materials and textiles, such as: treatment of wool, especially wool slivers.

Each of the foregoing electrode segments may comprise:

(a) a conductive element;

(b) a dielectric cover around the conductive element; and

(c) a liquid conductive medium connecting the conductive element and the dielectric cap, whereby the liquid medium forms a uniform contact with the dielectric cap.

The liquid medium is preferably between the conductive element and the dielectric cover. The dielectric cover preferably substantially surrounds or encloses the conductive element, for example so that the latter forms the core of the electrode.

The uniform contact between the liquid medium and the dielectric cap ensures that the current is evenly distributed over the surface of the dielectric cap. This promotes randomization of the electrical breakdown of the gas between the electrode segments, thereby achieving a more uniform plasma. This also avoids undesirable electric field concentrations at the peak points within the electrode structure, which increases the probability of electrical breakdown. This is particularly important when using a dielectric medium, which is preferred in order to maximise the efficiency of coupling of the electric field energy into the plasma. The liquid conductor also helps to evenly distribute the heat in the electrode segments, thereby minimizing thermal stresses.

The liquid conductor may be transparent so that observations and/or optical measurements can be made of the plasma, which is not possible with conventional electrodes.

Preferably, the conductivity of the liquid medium is a controlled variable that varies in dependence on the composition.

Although the electrode segments may be of any shape, they are preferably elongate and may be cylindrical.

Drawings

Preferred embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings.

FIG. 1 is a schematic cross-sectional view of a plasma treatment apparatus, particularly suitable for treating wool slivers, according to a preferred embodiment of the invention;

FIG. 2 is an enlarged cross-sectional view of a portion of the apparatus of FIG. 1;

FIG. 3 is a schematic perspective view of the apparatus of FIG. 1 with the second electrode removed;

FIG. 4 is a fragmentary perspective view of a section of the second electrode portion;

FIG. 5 is a perspective view of an alternative arrangement of second electrodes; and

fig. 6 is a cross-sectional view of a plasma processing apparatus according to an alternative embodiment of the present invention.

Detailed Description

Referring first to fig. 1 and 2, it can be seen that the plasma treatment apparatus 30 comprises a hollow, rotatable drum 40 having a first electrode formed on the curved outer surface of the drum 40 in the form of a mesh electrode 60. The device 30 further includes a second electrode formed as a plurality of rod electrodes 70 spaced radially outwardly from the mesh electrode 60.

The mesh electrode 60 includes a coarse mesh 62 that supports an overlying fine mesh 64. The fine grid 64 prevents localization of plasma microdischarges by providing a large array of potential plasma formation sites, where a reduced number of potential plasma formation sites will typically result in plasma microdischarge localization as compared to the coarse grid 62.

As shown in fig. 1 and 3, the drum 40 has a tubular core 44 and a wedge shaped baffle 42, the wedge shaped baffle 42 extending from the core to the periphery of the drum 40. A core 44 extends through the drum 40 and has openings 46 to allow gas to flow from the hollow of the drum 40 to the interior of the core 44. The core 44 is secured by a conduit 48 to a suction device 50 in the form of an industrial blower. Also, motor 52 drives wheel 54, and wheel 54 drivingly engages roller 40 to rotate roller 40 relative to rod electrode 70.

A gas permeable material, in this case wool slivers (wool silver)56, is fed from a source of stock material to the apparatus 30 by rollers 58. The wool 56 is conveyed to the space between the mesh electrode 60 and the rod electrode 70, where the wool 56 is subjected to plasma treatment. Finally, the treated wool 56 exits the space and is conveyed by rollers 58 to downstream processing equipment.

Although suitable plasma treatment of the material depends on the residence time of the material in the plasma, suitable plasma treatment using apparatus 30 is provided in which rod-like electrode 70 covers a surface of drum 40 of 0.8m to 1m and drum 40 is rotated at a rate such that wool sliver 56 passes through apparatus 30 at a rate of about 20 m/min.

In operation, the suction device 50 draws gas, preferably air at ambient atmospheric pressure, between the rod electrodes 70, through the space between the rod electrodes 70 and the mesh electrode 60, and through the mesh electrode 60 into the hollow of the drum 40 and then into the tubular core 44 via the opening 46. Otherwise, alternative gases, such as inert gases, may be used. Although the preferred gas pressure is ambient atmospheric pressure, pressures above or below ambient atmospheric pressure may also be used. The details of the gas flow between the rod electrode 70 and the mesh electrode 60 will be discussed in detail in the following section.

As the wool 56 comes into contact with the mesh electrode 60, the air flowing into the hollow of the drum 40 acts to keep the wool 56 in contact with the mesh electrode 60. In this way, wool 60 or other similar air permeable material remains on mesh electrode 60 and no bunching or folding of wool 56 occurs during movement relative to rod electrode 70. The baffle 42 facilitates removal of the wool 56 from the mesh electrode 60 because air does not flow over the segments of the mesh electrode 60 near the baffle 42. No air flowing through the length of mesh electrode 60 releases the wool 56 which contacts the mesh electrode 60.

Satisfactory plasma treatment of the material can be achieved by applying an alternating voltage of between 10kV and 20kV between the mesh electrode 60 and the rod electrode 70, the frequency of which is arbitrary but preferably in the range of 1 to 5 kHz. While the mesh electrode 60 is grounded, an alternating voltage is applied from a power source 85 to the rod electrode 70 via a cable 82 from a suitable busbar.

As can be seen in fig. 2, the air streams a, B and C traverse the direction of movement of the wool 56, which is indicated by arrow M for the wool 56. In this way, the gas flows through the space between the mesh electrode 60 and the rod electrode 70, and enters the hollow of the drum 40 through the wool 56. Air flowing through the material during passage through the plasma-free region serves to disperse or remove plasma products, such as ions and unwanted chemicals, that are stationary relative to the material, thereby preventing the occurrence of moving burn instabilities. In an alternative embodiment, the air flow may pass through the space between mesh electrode 60 and rod electrode 70 and through wool 56 in a direction parallel or anti-parallel to the direction of movement of wool 56 as indicated by arrow M.

The rod electrodes 70 are spaced apart by a distance S such that the gas a flowing inwardly, as indicated by arrows B, exhibits turbulence at the plasma generating surface of the rod electrodes 70, with the rod electrodes 70 being in the vicinity of or opposite the mesh electrode 60. If the distance S is too great, the flow rate of the gas A flowing inwardly is slower and will pass more directly between the adjacent spaced rod electrodes 70 through the showerhead electrode 60 with a lower gas flow rate over the surface of the rod electrodes 70. However, if the distance S is too small, the load on the pumping device 50 increases, requiring a more powerful pumping device 50 to achieve a gas flow rate that removes residual ions and randomizes the plasma microdischarge. The applicant has found that a spacing S of the wand electrodes 70 of between 0.5mm and 2mm ensures an acceptable turbulent airflow and an acceptable airflow rate over the surface of the wand electrodes 70 adjacent the mesh electrode 60.

Rod electrode 70 and mesh electrode 60 are optimally spaced to allow wool 56 to move therein while also minimizing the power required to generate plasma microdischarges over this distance. When wool sliver 56 is used in apparatus 30, rod electrode 70 and mesh electrode 60 are spaced approximately 4mm apart. However, this distance will vary from 1mm to 10mm depending on the gas permeable material in the device.

The air flowing through the space between the mesh electrode 60 and the rod electrode 70 disperses and/or removes ions remaining from the previous plasma generation cycle so that the subsequent plasma microdischarges are generated at random positions between the rod electrode 70 and the mesh electrode 60, rather than repeatedly at the positions of the remaining ions. Thus, the dissipation and/or removal of residual ions that are stationary relative to the electrodes can randomize the plasma microdischarges, thereby providing a generally randomized plasma for treating wool 56. Furthermore, the high velocity gas flow through wool 56 also enables dissipation and/or removal of ions and other plasma products trapped in wool 56, thus avoiding burn-in of wool 56 due to the localized intense thermal plasma relative to wool 56. Avoiding burn instability allows the use of higher energy densities and thus higher levels of treatment or higher treatment speeds for a given treatment length and/or transport speed.

Further benefits of gas movement include: (i) turbulent mixing of the gases to better utilize the available gases to produce higher concentrations of short-lived actives for surface treatment of wool 56; (ii) fresh air is supplied to generate active species from the plasma, thus promoting the quality of plasma-treated wool 56; and (iii) removing harmful by-products of the plasma, such as O3, NO2, and other fumes.

By way of example, for an electrode spacing of 2mm, the desired gas flow rate between the rod electrodes 70 is greater than 1.8 m/s. In general, the minimum gas flow rate depends on various parameters including power, voltage, frequency, and interaction of the materials being processed.

As shown in fig. 4, each rod-like electrode 70 includes a conductive core 72, which is preferably made of a metallic conductor such as: copper is formed. Around the periphery of the core 72 there is a dielectric cap, which in this case is formed by a glass tube 76 closed at one end. A conductive medium 74 separates the core 72 from the glass tube 76. The material filling the space between the electrical conductor and the glass may be electrically conductive or non-conductive, however, in order to minimize the thickness of the dielectric barrier and maximize the uniformity of the electrode, a conductive material is preferred.

In an embodiment of the second aspect of the invention, the conductive medium 74 is a liquid conductive medium 74. The liquid conductive medium 74 may be comprised of water and other suitable conductive liquids.

The liquid conductive medium 74, in this case water, takes the shape of the inner surface of the glass tube 76 so that a consistent, intimate contact can be made over the entire inner surface of the glass tube. The uniformity of the contact ensures a more uniform distribution of the current and thus a uniform distribution of the charge in the glass tube. Such a uniformly distributed current facilitates randomization of the plasma microdischarges, thereby providing a more uniform plasma treatment of the material. The intimate contact of the liquid conductive medium 74 and the glass tube 76 also maximizes the smoothness of contact between the conductive body and the dielectric body, reducing local concentrations of electric fields that may result in electrical breakdown of the dielectric material. The liquid conductor also more uniformly dissipates heat, reducing thermally induced stresses in the glass or ceramic electrodes. Voids, not shown, may be provided at suitable locations to accommodate expansion and contraction of the liquid with changes in temperature. The use of liquid conductors also facilitates the use of dielectric covered electrodes of more complex shapes than would otherwise be possible. The dielectric material can be processed into complex shaped structures by any method, for example: the glass tube is wound and then easily filled with a liquid conductor.

The liquid conductor may be transparent so that it can be used for observation and/or optical measurements of the plasma, which is not possible with conventional electrodes.

The liquid medium preferably has a controllably variable conductivity depending on the composition. For example, the inclusion of selected additives in the liquid controls conductivity. Controlled conductivity can be used to prevent transient localization of electrical energy density over the electrode area, which can produce destructive instability on a time scale.

The liquid conductive medium 74 is held inside a glass tube 76 by a plug (not shown) that extends from the glass tube beyond the exposed end of the wick 72. The end of the core 72 is connected to a power source via a wire 82 to provide an alternating voltage to the rod electrode 70.

One particular arrangement of rod electrodes 70 is shown in fig. 4. The rod electrodes 70 are located in openings in the wall 90 that extend radially outward from the drum 40. The seal 80 electrically insulates the exposed end 75 of the core 72, which is connected to the power supply by a wire 82, from discharging with the mesh electrode 60 located opposite the wall 90. This arrangement applies to the same alternating voltage applied to the rod electrode 70 while maintaining the mesh electrode 60 grounded so as to generate plasma microdischarges between the rod electrode 70 and the mesh electrode 60.

In an alternative arrangement shown in fig. 5, the rod electrodes 70 are crossed so that when an alternating voltage is applied, the magnitude of the potential on adjacent rod electrodes 70 is the same, but the polarity is opposite. The sliver 56 moves along the vicinity of the spaced rod-like electrodes 70. In this way, plasma microdischarges are generated between adjacent rod electrodes 70, rather than between rod electrodes 70 and mesh electrode 60. Thus, compared to the layout in fig. 4, the applied alternating voltage can be halved, i.e.: +/-10kV so that a potential difference of 20kV can still be generated between adjacent rod electrodes 70.

Electrical excitation to generate plasma may be applied by grounding either of the electrodes 60 or 70 while applying a full time-domain varying voltage across the other electrode 70 or 60, respectively. Alternatively, voltages of any combination of frequency and voltage may be applied simultaneously to both electrodes so that there is a sufficient time-varying potential difference between the electrodes to generate the required plasma.

One security feature that may be used on device 30 is a pair of windows mounted adjacent the baffle through which wool 56 may pass to and from the space between rod electrode 70 and mesh electrode 60. The size of the window allows the wool 56 to pass through, but the size and shape of the window is selected to prevent a user from inserting a hand or finger into the space between the rod-shaped electrode and the mesh electrode, thereby preventing the user from getting an electric shock.

The apparatus may further include a lockable door security feature that opposes the sheet of drum 40 adjacent to the baffle 42. The door preferably includes a logic switch that enables the device to be operated only when the door is locked, thus preventing a user from entering the drum 40 while the device 30 is in operation.

While the baffle 42 assists in the release of the wool 56 from the mesh electrode 60, occasionally a portion of the wool 56 remains attached and continues to re-enter the plasma processing space between the rod electrode 70 and the mesh electrode 60. In this case, the adhered wool 56 portion overlaps with the newly introduced wool 56 portion. The combined thickness may exceed the spacing between the rod electrode 70 and the mesh electrode 60 and may result in damage or even complete destruction of the rod electrode 70. To prevent said overlap, an optical sensor may be provided opposite the baffle to shut down the device 30 when wool 56 with adsorbed portions is detected. To avoid the device being continuously shut down by stray wool fibers or other dust particles, the sensor may be programmed to trigger the device to shut down only when the optical interference of the sensor exceeds 0.25 seconds.

Fig. 6 shows an alternative apparatus 100 for treating wool slivers 56 with plasma. Without rotating rollers, the apparatus 100 carries wool slivers 56 on an endless conveyor belt 104 forming a grid 104 of electrodes. Alternatively, the grid may have an electrically insulating material and cover the structure forming the second electrode. Spaced above the mesh conveyor 104 is a rod electrode 102, the rod electrode 102 being formed in the same manner as the rod electrode 70 in the previous embodiment. The spacing between the electrodes 102 and the mesh 104, and the spacing between adjacent electrodes 102, is set to have the same effect on gas flow as described in the previous embodiment. The structure of the support grid may be shaped such that it directs the gas flow preferentially around the dielectric covering the rod electrode, for example, laid out in a similar manner to the rod electrode, but with space directly beneath the dielectric covering the rod electrode. The suction device 106 causes the gas to flow in the direction indicated by F in the figure so that the gas flow passes through the sliver 56 and traverses the direction of movement of the sliver 56. In this manner, the plasma generated reactive species between the electrode 102 and the mesh 104 are drawn through the sliver 56 to treat the sliver 56.

The electrode 70 cross-fitting concept shown in fig. 5 can also be used in the apparatus 100 to generate plasma between adjacent electrodes 102. In addition, the cross-flow F generated by the pumping arrangement 106 drives the plasma products through the sliver 56 moving adjacent the electrode 102. This arrangement creates a treatment gradient in the sliver 56, i.e., the fibers receive a greater surface treatment at the top of the sliver 56 than at the interior of the sliver where the fibers are deeper. If uniform fiber treatment is desired, the sliver may be reversed and passed through the apparatus again, or the second apparatus 106 may be used after reversing the sliver.

Claims (39)

1. An apparatus for plasma treating a gas permeable material, the apparatus comprising:

(a) spaced electrodes, at least one of which is covered with a dielectric barrier and at least one of which comprises a plurality of discrete electrode segments;

(b) means for applying an alternating voltage across said spaced electrodes to generate plasma microdischarges between said spaced electrodes;

(c) means for passing a gas permeable material between or adjacent to the spaced electrodes; and

(d) means for passing gas between said electrode segments through the space between said electrodes and through the gas permeable material, the gas flowing over the plasma generating surface of each electrode segment and moving at a rate such that the gas flow between the spaced electrodes is turbulent, thereby randomizing plasma microdischarges and dissipating plasma products which would otherwise cause burn instability in the gas permeable material;

thus, randomized microelectrodes can provide an overall uniform plasma treatment of the gas permeable material.

2. The apparatus as recited in claim 1, wherein the first spaced apart electrodes are gas permeable.

3. The apparatus as recited in claim 2, wherein said first electrode is a mesh electrode.

4. The apparatus as claimed in claim 3, wherein said mesh electrode comprises a coarse mesh supporting a fine mesh superimposed thereon.

5. An apparatus as claimed in claim 2, wherein the first electrode is a curved surface of a rotatable drum electrode and the second electrode comprises said electrode segments arranged concentrically around the drum such that the gas permeable material bridges the first electrode between the first and second electrodes.

6. The apparatus as claimed in claim 5, wherein said drum is a hollow rotatable drum.

7. An apparatus as claimed in claim 3, wherein the first electrode is a curved surface of a rotatable drum electrode and the second electrode comprises said electrode segments arranged concentrically around the drum such that the gas permeable material bridges the first electrode between the first and second electrodes.

8. The apparatus as claimed in claim 7, wherein said drum is a hollow rotatable drum.

9. Apparatus as claimed in any one of claims 1 to 8, wherein said plasma generating surface of said electrode section and said further spaced electrode are opposed and are transversely curved elongate surfaces.

10. Apparatus as claimed in any one of claims 1 to 8, wherein the electrode segments are rod-like electrodes.

11. The apparatus of any one of claims 1 to 8, wherein adjacent ones of the separated electrode segments are spaced apart by about 0.5mm to 2 mm.

12. Apparatus as claimed in any one of claims 1 to 8, wherein said means for applying an alternating voltage is arranged to apply a voltage to the electrodes at a frequency which enables the dissipation and/or removal of plasma by-products from the flowing gas which cause localisation of plasma microdischarges.

13. The apparatus as recited in claim 12, wherein said frequency range is 1kHz to 20 kHz.

14. The apparatus as recited in claim 12, wherein said frequency range is 1kHz to 5 kHz.

15. Apparatus as claimed in any one of claims 1 to 8, wherein the electrodes are spaced apart by a distance in the range 2mm to 10 mm.

16. An apparatus as claimed in any one of claims 1 to 8, wherein the spaced electrodes are shaped so as to allow gas flowing through the gas permeable material to move in a direction transverse to the direction of material passage between the spaced electrodes.

17. The apparatus of any one of claims 1 to 8, wherein each electrode segment comprises:

(a) a conductive element;

(b) a dielectric cover around the conductive element; and

(c) a liquid conductive medium connecting the conductive element and the dielectric cap, whereby the liquid medium forms a uniform contact with the dielectric cap.

18. The apparatus as claimed in claim 17, wherein the liquid medium is located between the conductive element and the dielectric housing.

19. The apparatus as recited in claim 18, wherein the dielectric shield substantially surrounds or encloses the conductive element so that the latter forms a core of the electrode segment.

20. The apparatus as claimed in claim 17, wherein said liquid medium is transparent.

21. The apparatus as claimed in claim 17, wherein said liquid medium has a conductivity which is controllably variable depending on the composition.

22. The apparatus as recited in claim 17, wherein the electrode segments are elongated and generally cylindrical.

23. The apparatus as claimed in claim 22, wherein the liquid medium is located between the conductive element and the dielectric housing.

24. The apparatus as claimed in claim 23, wherein the dielectric shield substantially surrounds or encloses the conductive element so that the latter forms a core of the electrode segments.

25. The apparatus as claimed in claim 24, wherein said liquid medium has a conductivity which is controllably variable depending on the composition.

26. A method of making a plasma treated gas permeable material comprising the steps of:

(a) applying an alternating voltage between spaced electrodes to generate plasma microdischarges between the spaced electrodes, at least one of the spaced electrodes having a dielectric barrier coated thereon and at least one of the electrodes comprising a plurality of discrete electrode segments;

(b) passing a gas permeable material between or adjacent said spaced electrodes; and

(c) passing a gas between said electrode segments and through the space between the electrodes and through the gas permeable material, the gas flowing over the plasma generating surface of each electrode segment and at a rate such that the gas flow between the spaced electrodes is turbulent and randomizes plasma microdischarges and disperses plasma products which would otherwise cause burn instability in the gas permeable material;

the randomized plasma microdischarges thereby provide a generally uniform plasma treatment of the gas permeable material.

27. The method as recited in claim 26, including moving the gas past a first spaced apart electrode, wherein the first electrode is gas permeable.

28. The method of claim 26 wherein the plasma generating surface of the electrode segment and the other of the spaced electrodes are opposed and are transversely curved elongated surfaces.

29. The method as recited in claim 26, wherein said electrode segments are rod electrodes, respectively.

30. The method as set forth in claim 26, wherein said alternating voltage is applied at a frequency at which plasma by-products in the flowing gas are dissipated and/or removed, said plasma by-products causing localization of plasma micro-emitters.

31. The method as set forth in claim 30, wherein said frequency range is 1kHz to 20 kHz.

32. The method as recited in claim 30, wherein said frequency range is 1kHz to 5 kHz.

33. The method as recited in claim 26 wherein said gas is air.

34. A method as claimed in claim 33, wherein the pressure of said air is substantially atmospheric as it passes through the space between said electrodes and the air permeable material.

35. A method as claimed in any one of claims 26 to 34, wherein the gas moves through the gas permeable material in a direction transverse to the direction of passage of material between the spaced electrodes.

36. A method as claimed in any one of claims 26 to 34, wherein the voltage applied to the spaced apart electrodes is in the range 10kV to 25 kV.

37. A method as claimed in any one of claims 26 to 34, wherein the gas permeable material is a fibrous material.

38. A method as claimed in claim 37, wherein the fibrous material is wool.

39. A method as claimed in claim 37, wherein the fibrous material is wool sliver.