Abstract:
An improved electrode ( 44 ) useful for modifying a substrate using corona or plasma treatment or coating a substrate using plasma enhanced chemical vapor deposition under atmospheric or near atmospheric pressure conditions, the electrode comprising a body ( 10 ) defining at least a first cavity therein, the body having at least one inlet passageway ( 12 ) therein in gaseous communication with the first cavity ( 11 ) so that a gas mixture can be flowed into the first cavity by way of the at least one inlet passageway ( 12 ), the electrode having at least one outlet passageway ( 43 ) therein in gaseous communication with the first cavity so that a gas that is flowed into the first cavity can flow out of the cavity by way of the at least one outlet passageway. The improvement of the instant invention requires that the at least one outlet passageway be a slot ( 43 ) and that the body ( 10 ) include at least a first removable portion thereof, one edge of the first removable portion ( 30, 31 ) defining one side of the at least one outlet passageway ( 43 ).

Description:
CROSS REFERENCE STATEMENT 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/849,157, filed Oct. 3, 2006. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The instant invention relates to an improved electrode useful for modifying a substrate using corona or plasma treatment or coating a substrate using plasma enhanced chemical vapor deposition under atmospheric or near atmospheric pressure conditions. 
         [0003]    Numerous prior art electrode configurations have been developed for atmospheric or near atmospheric pressure operation. The prior art configurations can be classified into two major types. The first type is intended to be used with a ground electrode positioned on the other side of the substrate from the working electrode. Examples of the first type of electrode are disclosed in WO 2006/049794 and WO 2006/049865. The second type uses a ground electrode position of the same side of the substrate as the working electrode. Examples of the second type of electrode are discussed in WO02/23960, U.S. Pat. No. 6,441,553 and U.S. Pat. No. 7,067,405. 
         [0004]    Despite the significant advances provided by prior art electrodes, it would be an advance in the art if an electrode could be developed that permitted control of electric field intensity over a defined area, easily adjustable working gas velocity and flow characteristics and easy removal and replacement of the exposed working portion of the electrode. 
       SUMMARY OF THE INVENTION 
       [0005]    The instant invention is a solution to the above-mentioned problems. The electrodes of the instant invention permit control of electric field intensity over a defined area provide easily adjustable working gas velocity and flow characteristics and easy removal and replacement of the exposed working portion(s) of the electrode. More specifically, in one embodiment the instant invention is an improved electrode useful for modifying a substrate using corona or plasma treatment or coating a substrate using plasma enhanced chemical vapor deposition under atmospheric or near atmospheric pressure conditions, the electrode comprising a body defining at least a first cavity therein, the body having at least one inlet passageway therein in gaseous communication with the first cavity so that a gas mixture can be flowed into the first cavity by way of the at least one inlet passageway, the electrode having at least one outlet passageway in gaseous communication with the first cavity so that a gas that is flowed into the first cavity can flow out of the first cavity by way of the at least one outlet passageway, wherein the improvement comprises the at least one outlet passageway being a slot, the body comprised of at least a first removable portion thereof, one edge of the first removable portion defining one side of the at least one outlet passageway. 
         [0006]    In another embodiment, the instant invention is an improved method for modifying a substrate by plasma or corona treatment or for coating a substrate using plasma enhanced chemical vapor deposition under atmospheric or near atmospheric pressure conditions wherein a gas is flowed from an electrode and into an electric field region adjacent the electrode, the electrode being defined by a body defining at least a first cavity therein, the body having at least one inlet passageway therein in gaseous communication with the first cavity so that a gas mixture can be flowed into the first cavity by way of the at least one inlet passageway, the electrode having at least one outlet passageway in gaseous communication with the first cavity so that a gas that is flowed into the first cavity can flow out of the first cavity by way of the at least one outlet passageway, wherein the improvement comprises controlling the temperature of the body. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0007]      FIG. 1  is a perspective view of an electrode body of a preferred embodiment of the instant invention; 
           [0008]      FIG. 2  is a perspective view of a pair of removable electric field plate portions of a preferred embodiment of the instant invention; 
           [0009]      FIG. 3  is a perspective view of the pair of removable electric field plate portions of  FIG. 2  installed on the body of  FIG. 1 ; 
           [0010]      FIG. 4   a, b, c  and  d  show alternative cross section shapes for the removable electric field plate portions of  FIG. 2 ; and 
           [0011]      FIG. 5  shows a system for forming a plasma polymerized coating on a substrate using an electrode of the instant invention; and 
           [0012]      FIG. 6  is an end view of another electrode embodiment of the instant invention. 
       
    
    
     DETAILED DESCRIPTION  
       [0013]    Referring now to  FIG. 1 , therein is shown a perspective view of an electrode body  10  of a preferred embodiment of the instant invention. The body  10  is made of metal and defines a first cavity  11  therein. The body  10  has a first inlet passageway  12 , made of structural dielectric material, therein in gaseous communication with the cavity  11 . The body  10  has a second inlet passageway  13 , also made of structural dielectric material, therein in gaseous communication with the cavity  11 . The body  10  also defines a second cavity  16  therein. The body  10  has an inlet  14  and outlet  18  each in fluid communication with the second cavity  16 . The body  10  also defines a third cavity  17  therein. The body  10  has an inlet  15  and outlet  19  each in fluid communication with the third cavity  17 . The body  10  defines a first channel  28  and a second channel  29  therein. Holes  20 ,  21 ,  22 ,  23 ,  24 ,  25 ,  26  and  27  are bored through the body  10  and into the channels  28  and  29  as shown. 
         [0014]    Referring now to  FIG. 2 , therein is shown a perspective view of a pair of removable aluminum electric field plate portions  30  and  31  of a preferred embodiment of the instant invention. Electric field plate portion  30  has a ridge portion  32  drilled and tapped to produce threaded holes  34 ,  35 ,  36  and  37 . A threaded screw  42  is shown engaged in threaded hole  37 . Electric field plate portion  31  has a ridge portion  33  drilled and tapped to produce threaded holes  38 ,  39 ,  40  and  41 . The width of the ridge portions  32  and  33  is less than the width of the channels  28  and  29  of the body  10  shown in  FIG. 1 . The height of the ridge portions  32  and  33  is less than the depth of the channels  28  and  29  of the body  10  shown in  FIG. 1 . 
         [0015]    Referring now to  FIG. 3 , therein is shown a perspective view of the pair of removable electric field plate portions  30  and  31  of  FIG. 2  installed on the body  10  of  FIG. 1  by way of screws like the screw  42  shown in  FIG. 2  inserted from the bottom of the body  10  through the holes  20 ,  21 ,  22 ,  23 ,  24 ,  25 ,  26  and  27  shown in  FIG. 1  and engaging with the threaded holes  34 ,  35 ,  36 ,  37 ,  38 ,  39 ,  40  and  41  of the plate portions  30  and  31  shown in  FIG. 2  to produce a preferred electrode  44  according to the instant invention. The plate portions  30  and  31  form a slot  43  so that when a gas is flowed into the cavity  11  by way of inlets  12  and  13 , the gas flows out of the electrode  44  through the slot  43 . A pair of feeler gauges of the same thickness are preferably inserted in each end of the slot  43  so that the width of the slot  43  can be established before tightening the screws that clamp the plate portions  30  and  31  to the body  10 . The width of the slot  43  can thereby be adjusted from, for example and without limitation thereto, 0.001 inches to 0.050 inches. The width of the slot  43  is preferably adjusted to be relatively small, for example in the range of from 0.001 to 0.01 inches to minimize the consumption of working gas, to improve the evenness of the plasma polymerized coating and to optimize the quality of such coating. In operation a heated, cooled or temperature controlled fluid can be flowed into and out of the second and third cavities  16  and  17  by way of inlets  14  and  15  and outlets  18  and  19  to control the temperature of the electrode  44 . 
         [0016]    Referring now to  FIG. 4   a, b, c  and  d , therein is show a cross-sectional view of alternative shapes for the removable electric field plate portions  30  and  31  of  FIG. 2 .  FIG. 4   a  shows a planar external surface and a chamfered edge.  FIG. 4   b  shows a planar external surface and a rounded edge.  FIG. 4   c  shows a planar external surface and a square edge.  FIG. 4   d  shows a rounded external surface and a square edge. In many applications, the configuration shown in  FIG. 4   c  is preferred. The shape of the edge influences the flow characteristics of working gas flowing from the slot towards the substrate to be coated. The shape of the external surface influences the electric field intensity over the exposed surface. 
         [0017]    Referring now to  FIG. 5 , therein is shown a system for forming a plasma polymerized coating on a substrate using the electrode  44  of  FIG. 3 . The electrode  44  requires sufficient power and frequency via power source  45  to be applied to electrode  44  to create and maintain, for example and without limitation thereto, a corona discharge  46  in a spacing between the electrode  44  and a substrate  51  positioned on a counter electrode  47 . The instant invention will operate between 0 watts and 20,000 watts. The operating frequency is between 0 Hz and 100 kHz. The maximum power to be delivered to the electrode should not exceed 50,000 watts. The maximum frequency for the instant invention can be in the tens of giga-hertz. Changing spatial dimensions will, of course, require changes to the operating ranges for power and frequency as is well understood in the art. 
         [0018]    Referring still to  FIG. 5 , a mixture of gases  48  including a balance gas  53  and a working gas  50  is flowed into the inlet  12  the electrode  44  and then out the slot  43  to be plasma polymerized by the corona discharge  46  to form a coating onto the moving substrate  51 . As used herein, the term “working gas” refers to a reactive substance, which may or may not be gaseous at standard temperature and pressure, that is capable of polymerizing to form a coating onto the substrate. As used herein, the term “balance gas” is reactive or non-reactive gas that carries the working gas through the electrode and ultimately to the substrate. 
         [0019]    Examples of suitable working gases include organosilicon compounds such as silanes, siloxanes, and silazanes generated from the headspace of a contained volatile liquid  52  of such material and carried by a carrier gas  49  from the headspace and merged with balance gas  53  to form the mixture of gases  48 . Examples of silanes include dimethoxydimethylsilane, methyltrimethoxysilane, tetramethoxysilane, methyltriethoxysilane, diethoxydimethylsilane, methyltriethoxysilane, triethoxyvinylsilane, tetraethoxysilane, dimethoxymethylphenylsilane, phenyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-methacrylpropyltrimethoxysilane, diethoxymethylphenylsilane, tris(2-methoxyethoxy)vinylsilane, phenyltriethoxysilane, and dimethoxydiphenylilane. Examples of siloxanes include tetramethyldisiloxane, hexamethyldisiloxane, octamethyltrisiloxane, and tetraethylorthosilicate. Examples of silazanes include hexamethylsilazanes and tetramethylsilazanes. Siloxanes are preferred working gases, with tetramethyldisiloxane being especially preferred. 
         [0020]    The working gas is preferably diluted with a carrier gas  49  such as air or nitrogen before being merged with the balance gas. The v/v concentration of the working gas in the carrier gas is related to the vapor pressure of the working gas, and is preferably not less than 1%, more preferably not less than 5%, and most preferably not less than 10%; and preferably not greater than 50%, more preferably not greater than 30%, and most preferably not greater than 20%. 
         [0021]    Examples of suitable balance gases include air, oxygen, nitrogen, helium, and argon, as well as combinations thereof. The flow rate of the balance gas is sufficiently high to drive the plasma polymerizing working gas to the substrate to form a contiguous film, as opposed to a powder. Preferably the flow rate of the balance gas is such that the velocity of the balance gas passing through the slot of at least 1000 feet per minute, more preferably at least 2000 feet per minute, and most preferably at least 4000 feet per minute; and preferably not greater than 10000 feet per minute, more preferably not greater than 8000 feet per minute, and most preferably not greater than 6000 feet per minute. Control of the relative flow rates of the balance gas and the working gas also contributes to the quality of the coating formed on the substrate. Preferably, the flow rates are adjusted such that v/v ratio of balance gas to working gas is at least 0.002%, more preferably at least 0.02%, and most preferably at least 0.2%; and preferably not greater than 10%, more preferably not greater than 6%, and most preferably not greater than 1%. The actual numeral values for gas injection speed, concentrations, and compositions depends, of course, on the type of coating that is being put down on the substrate as is well understood in the art. It should be understood that the use of the instant invention is not restricted to the above-mentioned values. 
         [0022]    Although it is possible to carry out the process of the present by applying a vacuum or partial vacuum in, for example and without limitation thereto, the corona discharge region, (i.e, the region where the corona discharge is formed) the process is preferably carried out so that the corona discharge region is not subject to any vacuum or partial vacuum, that is, carried out at atmospheric or near atmospheric pressure. 
         [0023]    The substrate to be coated or treated by the electrodes of the instant invention is not limited. Examples of substrates include, polyolefins such as polyethylene and polypropylene, polystyrenes, polycarbonates, and polyesters such as polyethylene terephthalate and polybutylene terephthalate. 
         [0024]    Referring again to  FIG. 5 , temperature control gas  54  is flowed through heat exchanger  55  and into inlets  14  and  15 . Thermister  57  embedded in the body of electrode  44  is connected to temperature control system  56 . Temperature control system  56  controls heat exchanger  55  to control the temperature of the electrode  44 . Preferably, the temperature of the electrode  44  is controlled to be in the range of from fifty to seventy degrees Celsius. 
         [0025]    As discussed above, a flat or planar exterior surface is preferred for the electric field plates  30  and  31 . A curved surface as shown in  FIG. 4   d  increases the electric field in the plasma region near the slot and may be preferable in some applications. The electric field plates  30  and  31  are easily removable for cleaning, to change from a planar to a curved exposed surface and to change the shape of the slot. 
         [0026]    Referring now to  FIG. 6 , therein is shown an end view of another electrode  58  embodiment of the instant invention comprising an aluminum body  61  and a removable portion  59  bolted to the body  61 . The body  61  has a working gas inlet  60  so that working gas can be flowed into a first cavity defined by body  61  and removable portion  59  and then flow from a slot defined by the gap between the portion  59  and the body  61 . Dielectric portions  62  and  63  are attached to the body  61  and contain ground rods  66  and  67 . When appropriately powered, a plasma generated by the electric field between the body  61  and portion  59  and the ground rods  66  and  67  is formed there between. Cooling inlets  64  and  65  are used in the same manner as the inlets  14  and  15  of the electrode  44  of  FIG. 5 . In the embodiment shown in  FIG. 6 , the slot width is not adjustable and is controlled by careful machining of the body  61  and/or the removable portion  59  that define the slot. Preferably the width of the slot is in the range of from 0.001 to 0.01 inches. 
       CONCLUSION 
       [0027]    In conclusion, it should be readily apparent that although the invention has been described above in relation with its preferred embodiments, it should be understood that the instant invention is not limited thereby but is intended to cover all alternatives, modifications and equivalents that are included within the scope of the invention as defined by the following claims.