Plasma treatment apparatus and method

Abstract

A plasma treated gas permeable material is produced by applying an alternating voltage between 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, to generate plasma microdischarges between the spaced electrodes. A gas permeable material is passed between or adjacent to the spaced electrodes. A gas is moved between the electrode segments into and through the space between the electrodes and through the gas permeable material. The gas flows over plasma generation surfaces of the respective electrode segments and is moved at a rate whereby the gas flow between the spaced electrodes is turbulent and so randomises the plasma microdischarges and disperses plasma products that would otherwise give rise to burning instabilities in the gas permeable material, whereby the randomized plasma microdischarges provide a generally uniform plasma treatment of the gas permeable material. Also disclosed is an apparatus for laying out the process.

1 . Apparatus for plasma treating a gas permeable material, the apparatus including: 
 (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 plasma microdischarges between said spaced electrodes;    (c) means enabling the passage of the gas permeable material between or adjacent to said spaced electrodes; and    (d) means for moving a gas between said electrode segments into and through the space between said electrodes and through the gas permeable material, the gas flowing over plasma generation surfaces of the respective electrode segments and being moved at a rate whereby the gas flow between the spaced electrodes is turbulent and so randomises the plasma microdischarges and disperses plasma products that would otherwise give rise to burning instabilities in the gas permeable material;    whereby the randomised microdischarges provide a generally uniform plasma treatment of the gas permeable material.    
   
   
       2 . Apparatus according to  claim 1  wherein a first of the spaced electrodes is gas permeable.  
   
   
       3 . Apparatus according to  claim 2  wherein said first electrode is a mesh electrode.  
   
   
       4 . Apparatus according to  claim 3 , wherein said mesh electrode comprises a course mesh supporting an overlying layer of fine mesh.  
   
   
       5 . Apparatus according to  claim 2 , wherein said first electrode is a curved surface of a rotatable drum electrode, the second electrode comprising said electrode segments being concentrically arranged about the drum whereby the gas permeable material rides on the first electrode between the first and second electrodes.  
   
   
       6 . Apparatus according to  claim 5 , wherein said drum is a hollow rotatable drum.  
   
   
       7 . Apparatus according to  claim 1  wherein said plasma generation surfaces of said electrode segments are opposed to the other of said spaced electrodes, being transversely curved elongate surfaces.  
   
   
       8 . Apparatus according to  claim 1 , wherein said electrode segments are respective rod electrodes.  
   
   
       9 . Apparatus according to  claim 1 , wherein neighbouring electrodes segments of said discrete electrode segments are spaced apart about 0.5 to 2 mm.  
   
   
       10 . Apparatus according to  claim 1 , wherein said means for applying an alternating voltage is arranged to apply the voltage to the electrodes at a frequency that enables the dispersion and/or removal, in the moving gas, of plasma by-products, which cause localisation of the plasma microdischarges.  
   
   
       11 . Apparatus according to  claim 10  wherein said frequency is in the range 1-20 kHz.  
   
   
       12 . Apparatus according to  claim 10  wherein said frequency is in the range 1-5 kHz.  
   
   
       13 . Apparatus according to  claim 1 , wherein the spacing between said electrodes is in the range 2 to 10 mm.  
   
   
       14 . Apparatus according to  claim 1 , wherein said spaced electrodes are shaped to permit the movement of the gas through the gas permeable material in a direction transverse to the direction of passage of the material between the spaced electrodes.  
   
   
       15 . A method of producing a plasma treated gas permeable material, including the steps of: 
 (a) applying an alternating voltage between 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, to generate plasma microdischarges between the spaced electrodes;    (b) passing a gas permeable material between or adjacent to said spaced electrodes; and    (c) moving a gas between said electrode segments into and through the space between the electrodes and through the gas permeable material, the gas flowing over plasma generation surfaces of the respective electrode segments and being moved at a rate whereby the gas flow between the spaced electrodes is turbulent and so randomises the plasma microdischarges and disperses plasma products that would otherwise give rise to burning instabilities in the gas permeable material;    whereby the randomized plasma microdischarges provide a generally uniform plasma treatment of the gas permeable material.    
   
   
       16 . A method according to  claim 15 , including moving the gas through a first of the spaced electrodes, which first electrode is gas permeable.  
   
   
       17 . A method according to  claim 15  wherein said plasma generation surfaces of said electrode segments are opposed to the other of said spaced electrodes, being transversely curved elongate surfaces.  
   
   
       18 . A method according to any  claim 15 , wherein said electrode segments are respective rod electrodes.  
   
   
       19 . A method according to  claim 15 , wherein said alternating voltage is applied at a frequency that enables the dispersion and/or removal, in the moving gas, of plasma by-products, which cause localisation of the plasma microdischarges.  
   
   
       20 . A method according to  claim 19 , wherein said frequency is in the range 1-20 kHz.  
   
   
       21 . A method according to  claim 19 , wherein said frequency is in the range 1-5 kHz.  
   
   
       22 . A method according to  claim 15 , wherein said gas is moved through the gas permeable material in a direction transverse to the direction of passage of the material between said spaced electrodes.  
   
   
       23 . A method according to  claim 15  wherein said gas is air.  
   
   
       24 . A method according to  claim 23  wherein the air pressure of said air as it moves through the space between said electrodes and through the gas permeable material is substantially atmospheric pressure.  
   
   
       25 . A method according to  claim 15  wherein the voltage applied to the spaced electrodes is in the range 10-25 kV.  
   
   
       26 . A method according to  claim 15 , wherein said gas permeable material is a fibrous material.  
   
   
       27 . A method according to  claim 26 , wherein said fibrous material is wool.  
   
   
       28 . A method according to  claim 27 , wherein said fibrous material is wool sliver.  
   
   
       29 . Apparatus according to  claim 1 , wherein said each of said electrode segments comprises: 
 (a) an electrically conductive element;    (b) a dielectric sheath about the electrically conductive element; and    (c) an electrically conductive liquid medium contacting both the electrically conductive element and the dielectric sheath, whereby the liquid medium forms a uniform contact with the dielectric sheath.    
   
   
       30 . Apparatus according to  claim 29  wherein said liquid medium is between the electrically conductive element and the dielectric sheath.  
   
   
       31 . Apparatus according to  claim 30 , wherein said dielectric sheath substantially surrounds or encloses the electrically conductive elements so that the latter forms a core of the electrode segment.  
   
   
       32 . Apparatus according to  claim 29 , wherein said liquid medium is transparent.  
   
   
       33 . Apparatus according to  claim 29 , wherein said liquid medium has a controllably variable electrical conductivity depending on the composition.  
   
   
       34 . Apparatus according to  claim 29 , wherein said electrode segment is elongate and generally cylindrical.  
   
   
       35 . Apparatus according to  claim 3  wherein said first electrode is a curved surface of a rotatable drum electrode, the second electrode comprising said electrode segments being concentrically arranged about the drum whereby the gas permeable material rides on the first electrode between the first and second electrodes.  
   
   
       36 . Apparatus according to  claim 35 , wherein said drum is a hollow rotatable drum.  
   
   
       37 . Apparatus according to  claim 2  wherein said plasma generation surfaces of said electrode segments are opposed to the other said spaced electrodes, being transversely curved elongated surfaces.  
   
   
       38 . Apparatus according to  claim 3 , wherein said electrode segments are respective rod electrodes.  
   
   
       39 . Apparatus according to  claim 35 , wherein said electrode segments are respective rod electrodes.  
   
   
       40 . Apparatus according to  claim 8  wherein neighbouring electrodes segments of said discrete electrode segments are spaced apart about 0.5 to 2 mm.  
   
   
       41 . Apparatus according to  claim 38  wherein neighbouring electrodes segments of said discrete electrode segments are spaced apart about 0.5 to 2 mm.  
   
   
       42 . Apparatus according to  claim 3 , wherein said means for applying an alternating voltage is arranged to apply the voltage to the electrodes at a frequency that enables the dispersion and/or removal, in the moving gas, of plasma by-products, which cause localisation of the plasma microdischarges.  
   
   
       43 . Apparatus according to  claim 42  wherein said frequency is in the range 1-20 kHz.  
   
   
       44 . Apparatus according to  claim 43 , wherein said electrode segments are respective rod electrodes.  
   
   
       45 . Apparatus according to  claim 3 , wherein the spacing between said electrodes is in the range 2 to 10 mm.  
   
   
       46 . Apparatus according to  claim 5 , wherein the spacing between said electrodes is in the range 2 to 10 mm.  
   
   
       47 . Apparatus according to  claim 46 , wherein said electrode segments are respective rod electrodes.  
   
   
       48 . A method according to  claim 16 , wherein said electrode segments are respective rod electrodes.  
   
   
       49 . A method according to  claim 18 , wherein said alternating voltage is applied at a frequency that enables the dispersion and/or removal, in the moving gas, of plasma by-products, which cause localisation of the plasma microdischarges.  
   
   
       50 . A method according to  claim 49 , wherein said frequency is in the range 1-20 kHz.  
   
   
       51 . A method according to  claim 19 , wherein said fibrous material is wool.  
   
   
       52 . A method according to  claim 51 , wherein said frequency is in the range 1-20 kHz.