Abstract:
Process and apparatus for atmospheric pressure plasma enhanced chemical vapor deposition coating using a first and second electrode, the second electrode being positioned apart from the first electrode thereby creating a volume space between the first and second electrodes which volume space is covered by a duct sealed to the electrodes. Gas is flowed from the volume space between the first and second electrodes at the same or at a greater rate than the sum of the gaseous coating precursor mixtures of the first and second electrodes. 
     In addition, an improved electrode assembly for use in an atmospheric pressure plasma enhanced chemical vapor deposition coating system that includes a means for distributing a gaseous coating precursor mixture to emerge from an electrode assembly. The improvement relates to a gas distributing subassembly of the electrode assembly.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The instant invention is in the field of plasma enhanced chemical vapor deposition (PECVD) methods and apparatus for coating substrates and more specifically to PECVD methods and apparatus for applying two successive PECVD coatings. 
         [0002]    A Plasma is an ionized form of gas that can be obtained by ionizing a gas or liquid medium using an AC or DC power source. A plasma, commonly referred to as the fourth state of matter, is an ensemble of randomly moving charged particles with sufficient density to remain, on average, electrically neutral. Plasmas are used in very diverse processing applications, ranging from the manufacture of integrated circuits for the microelectronics industry, to the treatment of fabric and the destruction of toxic wastes. 
         [0003]    Plasmas are widely used for the treatment of organic and inorganic surfaces to promote adhesion between various materials. For example, polymers that have chemically inert surfaces with low surface energies do not allow good bonding with coatings and adhesives. Thus, these surfaces need to be treated in some way, such as by chemical treatment, corona treatment, flame treatment, and vacuum plasma treatment, to make them receptive to bonding with other substrates, coatings, adhesives and printing inks. Corona discharge, physical sputtering, plasma etching, reactive ion etching, sputter deposition, PECVD, ashing, ion plating, reactive sputter deposition, and a range of ion beam-based techniques, all rely on the formation and properties of plasmas. 
         [0004]    The use of PECVD techniques to coat an object with, for example, a silicon oxide layer and/or a polyorganosiloxane layer by introducing a “precursor” into a plasma adjacent to the object to be coated is well known as described, for example, in WO 2004/044039 A2. PECVD can be conducted in a reduced pressure chamber or in the open at or near atmospheric pressure. PECVD conducted at or near atmospheric pressure has the advantage of lower equipment costs and more convenient manipulation of the substrates to be coated. 
         [0005]    Two different types of electrode systems are generally used for atmospheric pressure PECVD coating. The first such system is termed a “top-down” electrode system wherein the object to be coated is positioned between a working electrode and a grounded electrode. The plasma is generated between the working electrode and the object to be coated and the precursor is introduced into the plasma by way of a carrier gas usually comprising oxygen and an inert gas such as argon. The second such electrode system is termed a “side-by-side” electrode system and comprises a grounded electrode(s) and a working electrode(s) embedded in a dielectric material such as a ceramic. The plasma is generated adjacent the surface of the dielectric material. The surface of the object to be coated is exposed to the plasma while the precursor is introduced into the plasma by way of a carrier gas usually comprising oxygen and an inert gas such as argon. The mixture of precursor material(s) with the carrier gas is called a “gaseous precursor mixture”. 
         [0006]    Atmospheric pressure PECVD coating systems can produce irritating or toxic emissions as a byproduct resulting from the passage of the gaseous precursor mixture through the plasma. Such emissions are traditionally vented in a safe manner from a hood placed over the atmospheric pressure PECVD coating system. However, the use of such hoods can interfere with desired flow patterns as well as air contamination of the gaseous precursor mixture through the plasma especially when two or more electrodes are used to sequentially generate two or more PECVD coatings on a substrate. 
       SUMMARY OF THE INVENTION 
       [0007]    The instant invention provides a process and apparatus for venting gases from an atmospheric pressure PECVD coating system employing two or more electrodes while maintaining excellent flow patterns of and elimination of air contamination of the gaseous precursor mixtures through the plasmas and eliminating thereby improving the uniformity of and chemistry of the coatings on the substrate. More specifically, the instant invention is process for operating an atmospheric pressure plasma enhanced chemical vapor deposition coating system comprising introducing a first and second gaseous coating precursor mixture into a first and second plasma electrically generated adjacent to a plasma surface of a first and second electrode, the second electrode being positioned apart from the first electrode so that the plasma surface of the first electrode is substantially parallel with the plasma surface of the second electrode thereby creating a volume space between the first and second electrodes, comprising the step of; flowing gas from the volume space between the first and second electrodes at the same or at a greater rate than the sum of the first and second gaseous coating precursor mixtures are introduced into the first and second plasmas. 
         [0008]    In another embodiment, the instant invention is an apparatus for an atmospheric pressure plasma enhanced chemical vapor deposition coating system, comprising: a first electrode and a second electrode, means for introducing a first gaseous coating precursor mixture into a plasma generated adjacent to a plasma surface of the first electrode, means for introducing a second gaseous coating precursor mixture into a plasma generated adjacent to a plasma surface of the second electrode, the second electrode being positioned apart from the first electrode so that the plasma surface of the first electrode is substantially parallel with the plasma surface of the second electrode thereby creating a volume space between the first and second electrodes, a duct positioned over the volume space between the first and second electrodes, the duct sealed to the first and second electrodes so that when the apparatus is placed on a sheet of material, the volume space between the first and second electrodes is substantially bounded by the electrodes, the duct and the sheet of material. 
         [0009]    In yet another embodiment, the instant invention is an improved electrode assembly for use in an atmospheric pressure plasma enhanced chemical vapor deposition coating system comprising a means for distributing a gaseous coating precursor mixture to emerge from an electrode assembly, wherein the improvement comprises a subassembly of the electrode assembly, the subassembly comprising at least one planar surface having an endless groove and a ledge therein, the endless groove having a straight section, the ledge being positioned between the straight section of the groove and the edge of the subassembly, the surface of the ledge being below the planar surface and extending from the straight section of the groove to the edge of the subassembly, the subassembly further comprising a first and a second passageway therethrough for the passage of a gaseous coating precursor mixture therethrough, the first passageway terminating at one end thereof at a position substantially at the center of the straight section of the groove, the second passageway terminating at one end thereof at a position substantially equidistant along the groove in either direction from the center of the straight section of the groove. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a cross-sectional side view of a prior art two electrode atmospheric pressure PECVD coating system employing a hood to evacuate fumes from the system; 
           [0011]      FIG. 2  is a cross-sectional side view of a two electrode atmospheric pressure PECVD coating system of the instant invention employing a duct to evacuate fumes from the system and wherein the gaseous coating precursor mixtures emerge from apertures in the electrode assemblies; 
           [0012]      FIG. 3  is an end view of the system shown in  FIG. 2 ; 
           [0013]      FIG. 4  is a cross-sectional side view of a two electrode atmospheric pressure PECVD coating system of the instant invention employing a duct to evacuate fumes from the system and wherein the gaseous coating precursor mixtures are flowed under the electrode assemblies from plenums positioned above and to one side of the electrode assemblies; 
           [0014]      FIG. 5  is an end view of the system shown in  FIG. 3 ; 
           [0015]      FIG. 6  is a cross-sectional end view of a preferred side-by-side electrode assembly for use in the instant invention comprising a central ceramic section containing alternate ground and high voltage rods and metal side sections for coolant passageways, one of which side section comprises a preferred distributor for flowing the gaseous coating precursor mixture from the electrode assembly; 
           [0016]      FIG. 7  is a top view of the preferred distributor for flowing the gaseous coating precursor mixture from the electrode assembly of  FIG. 6 ; 
           [0017]      FIG. 8  is a cross-sectional side view of the preferred distributor of  FIG. 7 ; 
           [0018]      FIG. 9  is a cross-sectional end view of a preferred top-down electrode assembly for use in the instant invention comprising a central metallic high voltage section and ceramic side sections for coolant passageways, one of which side section comprises a preferred distributor for flowing the gaseous coating precursor mixture from the electrode assembly and a ground electrode positioned under the substrate to be coated; and 
           [0019]      FIG. 10  is a bottom view of a top-down electrode assembly for use in the instant invention comprising a central metallic high voltage section and ceramic side sections for coolant passageways, one of which side section comprises apertures for flowing the gaseous coating precursor mixture from the electrode assembly. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    Referring now to  FIG. 1 , therein is shown a cross-sectional side view of a prior art two electrode atmospheric pressure PECVD coating system  10  employing a hood  11  to evacuate fumes from the system. The system  10  includes a first electrode assembly  12  and a second electrode assembly  13 . A first plasma  14  is generated adjacent the plasma surface of the first electrode  12 . A first gaseous coating precursor mixture  15  is flowed from a slot  16  in the electrode assembly  12 . The first gaseous coating precursor mixture  15  passes through the plasma  14  to coat a moving substrate  17  with a first PECVD coating. Fumes  18  from the plasma  14  are drawn out the outlet  19  of the hood  11 . A second plasma  20  is generated adjacent the plasma surface of the second electrode  13 . A second gaseous coating precursor mixture  21  is flowed from a slot  22  in the electrode assembly  13 . The second gaseous coating precursor mixture  21  passes through the plasma  20  to coat a moving substrate  17  with a second PECVD coating. Fumes  23  from the plasma  20  are drawn out the outlet  19  of the hood  11 . The flow rate out of the outlet  19  of the hood  11  is significantly greater than the sum of the flow rates of the first and second gaseous coating precursor mixtures  15  and  21  to ensure that excess air  24  flows under the edge of the hood  11  so that no fumes escape the edges of the hood. Some of the excess air  24  undesirably flows with the gaseous coating precursor mixtures  15  and  21  into the plasmas  14  and  20  respectively. 
         [0021]    Referring now to  FIG. 2 , therein is shown a cross-sectional side view of a two electrode atmospheric pressure PECVD coating system  30  of the instant invention employing a duct  31  to evacuate fume gas  32  from the system  30 . The system  30  comprises a first electrode assembly  33  and a second electrode assembly  34 . The term “electrode assembly” means an assembly comprising an electrode and optionally additional elements for, for example, cooling the electrode assembly and for introducing gaseous coating precursor mixtures into a plasma electrically generated adjacent a surface of the electrode. A first gaseous coating precursor mixture  35  is flowed through conduit  36 , through the electrode assembly  33 , through a plasma  36  to produce a first PECVD coating on a moving substrate sheet  37  and fumes  32 . A second gaseous coating precursor mixture  38  is flowed through conduit  39 , through the electrode assembly  34 , through a plasma  40  to produce a second PECVD coating on the moving substrate sheet  37  and fumes  32 . The first electrode assembly  34  is positioned apart from the first electrode assembly  33  so that the plasma surface  40  of the first electrode assembly  33  is substantially parallel with and substantially in the same plane as the plasma surface  41  of the first electrode assembly  34  thereby creating a volume space  42  between the first and second electrodes. The duct  31  is positioned over the volume space  42  between the first and second electrode assemblies  33  and  34 . The duct  31  is sealed to the first and second electrode assemblies  33  and  34  so that when the system  30  is placed on a sheet of material (such as the substrate sheet  37 ), the volume space  42  between the first and second electrode assemblies  33  and  34  is substantially bounded by the electrode assemblies  33  and  34 , the duct  31  and the sheet of material. The flow rate of fume gas  32  from the volume space  42  between the first and second electrode assemblies  33  and  34  is at the same or at a greater flow rate than the sum of the flow rates of the first and second gaseous coating precursor mixtures  35  and  38 . 
         [0022]    Preferably, the flow rate of fume gas  32  from the volume space  42  between the first and second electrode assemblies  33  and  34  is from equal to 1.1 times greater than the sum of the flow rates of the first and second gaseous coating precursor mixtures  35  and  38 . More preferably, the flow rate of fume gas  32  from the volume space  42  between the first and second electrode assemblies  33  and  34  is from equal to 1.01 times greater than the sum of the flow rates of the first and second gaseous coating precursor mixtures  35  and  38 . Referring now to  FIG. 3 , therein is shown an end view of the system  30  of  FIG. 2 . 
         [0023]    Referring now to  FIG. 4 , therein is shown a cross-sectional side view of a two electrode atmospheric pressure PECVD coating system  50  of the instant invention employing a duct  51  to evacuate fume gas  52  from the system  50 . The system  50  comprises a first plenum  53  into which a first gaseous coating precursor mixture  54  is flowed. The system  50  comprises a second plenum  55  into which a second gaseous coating precursor mixture  56  is flowed. The system  50  comprises a first electrode assembly  57  and a second electrode assembly  58 . The first gaseous coating precursor mixture  54  is flowed through a plasma  59  to produce a first PECVD coating on a moving substrate sheet  60  and fumes  52 . The second gaseous coating precursor mixture  56  is flowed through a plasma  61  to produce a second PECVD coating on the moving substrate sheet  60  and fumes  52 . The second electrode assembly  58  is positioned apart from the first electrode assembly  57  so that the plasma surface  62  of the first electrode assembly  57  is substantially parallel with and substantially in the same plane as the plasma surface  63  of the second electrode assembly  58  thereby creating a volume space  64  between the first and second electrode assemblies  57  and  58 . The duct  31  is positioned over the volume space  42  between the first and second electrode assemblies  33  and  34 . The duct  51  is sealed to the first and second electrode assemblies  57  and  58  so that when the system  50  is placed on a sheet of material (such as the substrate sheet  60 ), the volume space  64  between the first and second electrode assemblies  57  and  58  is substantially bounded by the electrode assemblies  57  and  58 , the duct  51  and the sheet of material. The flow rate of fume gas  52  from the volume space  64  between the first and second electrode assemblies  57  and  58  is at the same or at a greater flow rate than the sum of the flow rates of the first and second gaseous coating precursor mixtures  54  and  56 . Preferably, the flow rate of fume gas  52  from the volume space  64  between the first and second electrode assemblies  57  and  58  is from equal to 1.1 times greater than the sum of the flow rates of the first and second gaseous coating precursor mixtures  54  and  56 . More preferably, the flow rate of fume gas  52  from the volume space  64  between the first and second electrode assemblies  57  and  58  is from equal to 1.01 times greater than the sum of the flow rates of the first and second gaseous coating precursor mixtures  54  and  56 . Referring now to  FIG. 5 , therein is shown an end view of the system  50  of  FIG. 4 . 
         [0024]    Referring now to  FIG. 6 , therein is shown a cross-sectional end view of a preferred side-by-side electrode assembly  70  for use in the instant invention comprising a central ceramic section  71  containing alternate ground  72  and high voltage  73  metallic rods, a first metallic side section  74  and a second metallic side section  75 . In use, a coolant fluid is passed through passageways in the electrode assembly  70  one of which passageway is shown as passageway  76 . The second metallic side section  75  comprises a preferred distributor  78  for flowing a gaseous coating precursor mixture from the electrode assembly by way of slot  77 . 
         [0025]    Referring now to  FIG. 7 , therein is shown a top view of the distributor  78  of  FIG. 6  showing holes  79  through which screws are passed to attach the distributor  78  to the second metallic side section  75 . An oval track  80  is machined into the distributor  78 . A gaseous coating precursor mixture is flowed via passageways (not shown) through the second metallic side section  75  into the center of each straight leg of the oval track  80 . The gaseous coating precursor mixture flows over the ledge  81  and into the slot  77  shown in  FIG. 6 . Referring now to  FIG. 8 , therein is shown a cross-sectional end view of the distributor  78 . 
         [0026]    Referring now to  FIG. 9 , therein is shown a cross-sectional end view of a preferred side-by-side electrode assembly  90  for use in the instant invention comprising a central high voltage metallic section  91 , a first ceramic side section  92  and a second ceramic side section  93 . In use, a coolant fluid is passed through passageways in the electrode assembly  90  one of which passageway is shown as passageway  94 . The second ceramic side section  93  comprises the preferred distributor  78  of  FIGS. 6 ,  7  and  8  for flowing a gaseous coating precursor mixture  95  from the electrode assembly  90 . In practice, a plasma  96  is generated adjacent the electrode  91 , above a moving substrate sheet  98  which is moved above a ground electrode  97 . Passage of the gaseous coating precursor mixture  95  through the plasma  96  generates a PECVD coating on a moving substrate sheet  98 . 
         [0027]    Referring now to  FIG. 10 , therein is shown a bottom view of a top-down electrode assembly  100  for use in the instant invention comprising a central metallic high voltage section a first ceramic side section  102 , and a second side section  103 . The second side section  103  has a plurality of apertures  104  thereinto for flowing a gaseous coating precursor mixture from the electrode assembly  100 . 
       Conclusion  
       [0028]    While the instant invention has been described above according to its preferred embodiments, it can be modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the instant invention using the general principles disclosed herein. Further, the instant application is intended to cover such departures from the present disclosure as come within the known or customary practice in the art to which this invention pertains and which fall within the limits of the following claims.