Title of Invention	AN ATMOSPHERIC PRESSURE PLASMA ASSEMBLY
Abstract	An atmospheric pressure plasma assembly (1) comprising a first and second pair of vertically arrayed, parallel spaced-apart planar electrodes (36) with at least one dielectric plate (31) between said first pair, adjacent one electrode and at least one dielectric plate (31) between said second pair adjacent one electrode, the spacing between the dielectric plate and the other dielectric plate or electrode of each of the first and second pairs of electrodes forming a first and second plasma regions (25, 60) characterized in that the assembly further comprises a means of transporting a substrate (70, 71, 72) successively through said first and second plasma regions (25, 60) and an atomizer (74) adapted to introduce an atomized liquid or solid coating making material into one of said first or second plasma regions

Title of Invention

AN ATMOSPHERIC PRESSURE PLASMA ASSEMBLY

Abstract

An atmospheric pressure plasma assembly (1) comprising a first and second pair of vertically arrayed, parallel spaced-apart planar electrodes (36) with at least one dielectric plate (31) between said first pair, adjacent one electrode and at least one dielectric plate (31) between said second pair adjacent one electrode, the spacing between the dielectric plate and the other dielectric plate or electrode of each of the first and second pairs of electrodes forming a first and second plasma regions (25, 60) characterized in that the assembly further comprises a means of transporting a substrate (70, 71, 72) successively through said first and second plasma regions (25, 60) and an atomizer (74) adapted to introduce an atomized liquid or solid coating making material into one of said first or second plasma regions

Full Text	AN ATMOSPHERIC PRESSURE PLASMA ASSEMBLY [0001] The present inyention ralates to an atmospheric pressure plasma assembly and a method of treating a substrate using said assembly. [0002] When matter is continually supplied with energy, its temperature increases and it typically transforms from a solid to a liquid and, then, to a gaseous state. Continuing to supply energy causes the system to undergo yet a further change of state in which neutral atoms or molecules of the gas are broken up by energetic collisions to produce negatively charged electrons, positive or negatively charged ions and other species. This mix of charged particles exhibiting collective behaviour is called "plasma", the fourth state of matter. Due to their electrical charge, plasmas are highly influenced by external electromagnetic fields, which makes them readily controllable. Furthermore, their high energy content allows them to achieve processes which are impossible or difficult through the other states of matter, such as by liquid or gas processing. №003] The term "plasma" covers a huge range of systems whose density and temperature vary by many orders of magnitude. Some plasmas are very hot and all their microscopic species (ions, electrons, etc.) are in approximate thermal equilibrium, the energy input into the system being widely distributed through atomic/molecular level collisions. Other plasmas, however, particular those at low pressure (e.g. 100 Pa) where collisions are relatively infrequent, have their constituent species at widely different temperatures and are called "non- thermal equilibrium" plasmas. In these non-thermal plasmas the free electrons are very hot with temperatures of many thousands of Kelvin (K) whilst the neutral and ionic species remain cool. Because the free electrons have almost negligible mass, the total system heat content is low and the plasma operates close to room temperature thus allowing the processing of temperature sensitive materials, such as plastics or polymers, without imposing a damaging thermal burden onto the sample. However, the hot electrons create, through high energy collisions, a rich source of radicals and excited species with a high chemical potential energy capable of profound chemical and physical reactivity. It is this combination of low temperature operation plus high reactivity which makes non-thermal plasma technologically important and a very powerful tool for manufacturing and material processing, capable of achieving processes which, if achievable at all without plasma, would require very high temperatures or noxious and aggressive chemicals. [0004] For industrial applications of plasma technology, a convenient method is to couple electromagnetic power into a volume of process gas, which can be mixtures of gases and vapours in which the workpieces/samples to be treated are immersed or passed through. The gas becomes ionised into plasma, generating chemical radicals, UV-radiation, and ions, which react with the surface of the samples. By correct selection of process gas composition, driving power frequency, power coupling mode, pressure and other control parameters, the plasma process can be tailored to the specific application required by a manufacturer. [0005] Because of the huge chemical and thermal range of plasmas, they are suitable for many technological applications. Non-thermal equilibrium plasmas are particularly effective for surface activation, surface cleaning, material etching and coating of surfaces. [0006] The surface activation of polymeric materials is a widely used industrial plasma technology pioneered by the automotive industry. Thus, for example, polyolefins, such as polyethylene and polypropylene, which are favoured for their recylability, have a non-polar surface and consequently a poor disposition to coating or gluing. However, treatment by oxygen plasma results in the formation of surface polar groups giving high wettability and consequently excellent coverage and adhesion to metal paints, adhesives or other coatings. Thus, for example, plasma surface engineering is becoming increasingly important in the manufacture of vehicle fascias, dashboards, bumpers and the like as well as in component assembly in the toy and like industries. Many other applications are available in the printing, painting, gluing, laminating and general coating of components of all geometries in polymer, plastic, ceramic/inorganic, metal and other materials. [0007] The increasing pervasiveness and strength of environmental legislation world- wide is creating substantial pressure on industry to reduce or eliminate the use of solvents and other wet chemicals in manufacturing, particularly for component/surface cleaning. In particular, CFC-based degreasing operations have been largely replaced by plasma cleaning technology operating with oxygen, air and other non-toxic gases. Combining water based pre- cleaning operations with plasma allows even heavily soiled components to be cleaned; the resulting surface qualities obtained being generally superior to those resulting from traditional methods. Any organic surface contamination is rapidly scavenged by room temperature plasma and converted to gaseous CO2 and water, which can be safely exhausted. [0003] Plasmas can also carry out etching of a bulk material, i.e. for the removal of unwanted material therefrom. Thus, for example, an oxygen based plasma will etch polymers, a process used in the production of circuit boards, etc. Different materials such as metals, ceramics and inorganics are etched by careful selection of precursor gas and attention to the plasma chemistry. Structures down to nanometer critical dimensions are now being produced by plasma etching technology. [0089] A plasma technology that is rapidly emerging into mainstream industry is that of plasma coating/thin film deposition. Typically, a high level of polymerisation is achieved by application of plasma to monomelic gases and vapours. Thus, a dense, tightly knit and three- dimensionally connected film can be formed which is thermally stable, chemically very resistant and mechanically robust. Such films are deposited conformally on even the most intricate of surfaces and at a temperature which ensures a low thermal burden on the substrate. Plasmas are therefore ideal for the coating of delicate and heat sensitive, as well as robust materials. Plasma coatings are free of micropores even with thin layers. The optical properties, e.g. colour, of the coating can often be customised and plasma coatings adhere well to even non-polar materials, e.g. polyethylene, as well as steel (e.g. anti-corrosion films on metal reflectors), ceramics, semiconductors, textiles, etc. [0010] In all these processes, plasma engineering produces a surface effect customised to the desired application or product without affecting the material bulk in any way. Plasma processing thus offers the manufacturer a versatile and powerful tool allowing choice of a material for its bulk technical and commercial properties while giving the freedom to independently engineer its surface to meet a totally different set of needs. Plasma technology thus confers greatly enhanced product functionality, performance, lifetime and quality and gives the manufacturing company significant added value to its production capability. [0011] These properties provide a strong motivation for industry to adopt plasma-based processing, and this move has been led since the 1960s by the microelectronics community which has developed the low pressure Glow Discharge plasma into an ultra-high technology and high capital cost engineering tool for semiconductor, metal and dielectric processing. The same low pressure Glow Discharge type plasma has increasingly penetrated other industrial sectors since the 1980s offering, at more moderate cost, processes such as polymer surface activation for increased adhesion/bond strength, high quality degreasing/cleaning and the deposition of high performance coatings. Thus, there has been a substantial take-up of plasma technology. Glow discharges can be achieved at both vacuum and atmospheric pressures. In the case of atmospheric pressure glow discharge, gases such as helium or argon are utilised as diluents and a high frequency (e.g.> 1kHz) power supply is used to generate a homogeneous glow discharge at atmospheric pressure via a Penning ionisation mechanism, (see for example, Kanazawa et al, J.Phys. D: Appl. Phys. 1988,21,838, Okazaki et al, Proc. Jpn. Symp. Plasma Chem. 1989,2,95, Kanazawa et al, Nuclear Instruments and Methods in Physical Research 1989, B37/38,842, and Yokoyama et al., J. Phys. D: Appl. Phys. 1990,23,374). [0012] However, adoption of plasma technology has been limited by a major constraint on most industrial plasma systems, namely, their need to operate at low pressure. Partial vacuum operation means a closed perimeter, sealed reactor system providing only off-line, batch processing of discrete workpieces. Throughput is low or moderate and the need for vacuum adds capital and running costs. [0013] Atmospheric pressure plasmas, however, offer industry open port or perimeter systems providing free ingress into and exit from the plasma region by workpieces/webs and, hence, on-line, continuous processing of large or small area webs or conveyor-carried discrete workpieces. Throughput is high, reinforced by the high species flux obtained from high pressure operation. Many industrial sectors, such as textiles, packaging, paper, medical, automotive, aerospace, etc., rely almost entirely upon continuous, on-line processing so that open port/perimeter configuration plasmas at atmospheric pressure offer a new industrial processing capability. [0014] Corona and flame (also a plasma) treatment systems have provided industry with a limited form of atmospheric pressure plasma processing capability for about 30 years. However, despite their high manufacturability, these systems have failed to penetrate the market or be taken up by industry to anything like the same extent as the lower pressure, bath- processing-only plasma type. The reason is that corona/flame systems have significant limitations. They operate in ambient air offering a single surface activation process and have a negligible effect on many materials and a weak effect on most. The treatment is often non- uniform and the corona process is incompatible with thick webs or 3D workpieces while the flame process is incompatible with heat sensitive substrates. [0015] Significant advances have been made in plasma treatment at atmospheric pressure. Considerable work has been done on the stabilisation of atmospheric pressure glow discharges, such as in Okazaki et al., J. Phys. D: Appl. Phys. 26 (1993) 889-892. Further, there is described in US Patent Specification No. 5414324 (Roth et al) the generation of a steady-state glow discharge plasma at atmospheric pressure between a pair of insulated metal plate electrodes spaced up to 5 cm apart and radio frequency (KF) energised with a root mean square (rms) potential of 1 to 5 kV at 1 to 100 kHz. This patent specification describes the use of electrically insulated metallic plate electrodes and also the problems of electrode plates and the need to discourage electrical breakdown at the edge of electrodes. It further describes the use of the electrodes, which in this case are copper plates, and a water cooling system, which is supplied through fluid flow conduits bonded to the electrodes and as such, water does not come into direct contact with any electrode surface. [0016] In US Patent Specification No. 5185132, (Horiike et al), there is described an atmospheric plasma reaction method in which plate electrodes are used in a vertical configuration. However, they are merely used in the vertical configuration to prepare the plasma and then the plasma is directed out from between the plates onto a horizontal surface below the vertically arranged electrodes and downstream from the plasma source. [0016] In EP 0809275 and JP 11 -29873 here are provided atmospheric pressure glow discharge systems having at least two sets of horizontally arrayed pairs of electrodes through which a substrate web may be passed continuously by means of rollers. JP 11-241165 and JP 2000-212753 describe electric discharge type plasma system using pulsed electric fields. In all four of these documents the substrate is treated with gases. [0018] In the applicants co-pending application WO 02/35576, which was published after the priority date of the present application, a plasma system of the type comprising a pair of parallel spaced-apart planar electrodes with at least one dielectric plate therebetween and adjacent one electrode, the spacing between the dielectric plate and the other dielectric plate or electrodes forming a plasma region for a precursor gas wherein a cooling liquid distribution system is provided for directing a cooling conductive liquid onto the exterior of at least one of the electrodes to cover a planar face of the at least one electrode. [0019] According to the present invention there is provided an atmospheric pressure plasma assembly comprising a first and second pair of vertically arrayed, parallel spaced-apart planar electrodes with at least one dielectric plate between said first pair, adjacent one electrode and at least one dielectric plate between said second pair adjacent one electrode, the spacing between the dielectric plate and the other dielectric plate or electrode of each of the first and second pairs of electrodes forming a first and second plasma region characterised in that the assembly further comprises a means of transporting a substrate successively through said first and second plasma regions and an atomiser adapted to introduce an atomised liquid or solid coating making material into one of said first or second plasma regions. [0020] The terms "comprise, comprises, comprised and comprising" or any variation thereof and the terms "include, includes, included and including" or any variation thereof are considered to be totally interchangeable and they should all be afforded the widest possible interpretation. [0021] It should be understood that the term vertical is intended to include substantially vertical and should not be restricted solely to electrodes positioned at 90 degrees to the horizontal. [0022] Preferably the means of transporting the substrate is by a reel to reel based process. The substrate may be transported through the first plasma region in an upwardly or downwardly direction. Preferably when the substrate passes through one plasma zone in an upwardly direction and the other in a downwardly direction one or more guide rollers are provided to guide the substrate from the end of the first reel into the first plasma zone, from the first plasma zone to and into the second plasma zone and from the second plasma zone to the second reel or next plasma zone dependent on the number of plasma zones being used. The substrate residence time in each plasma region may be predetermined prior to coating and rather than varying the speed of the substrate, through each plasma zone, the path length a substrate has to travel through each plasma region may be altered such that the substrate may pass through both regions at the same speed but may spend a different period of time in each plasma region due to differing path lengths through the respective plasma regions. [0023] In view of the fact that the electrodes in the present invention are vertically orientated it is preferred that a substrate be transported through an atmospheric pressure plasma assembly in accordance with the present invention upwardly through one plasma region and downwardly though the other plasma region. On the basis of the distance between adjacent electrodes, as will be discussed below, it will be appreciated that the substrate is generally transported through a plasma region in a vertical or diagonal direction although in most cases it will be vertical or substantially vertical. [0024] Preferably each substrate needs only to be subjected to one pass through the assembly but if required the substrate may be returned to the first reel for further passages through the assembly. [0025] Additional pairs of electrodes may be added to the system to form further successive plasma regions through which a substrate would pass. The additional pairs of electrodes may be situated before or after said first and second pair of electrodes such that substrate would be subjected to pre-treatment or post-treatment steps. Said additional pairs of electrodes are preferably situated before or after and most preferably after said first and second pairs of electrodes. Treatments applied in the plasma regions formed by the additional pairs of electrodes may be the same or different from that undertaken in the first and second plasma regions. In the case when additional plasma regions are provided for pre-treatment or post- treatment the necessary number of guides and/or rollers will be provided in order to ensure the passage of the substrate through the assembly. Similarly preferably the substrate will be transported alternatively upwardly and downwardly through all neighbouring plasma regions in the assembly. [0026] Each electrode may comprise any suitable geometry and construction. Metal electrodes may be used and may be in for example the form of metallic plates or a mesh. The metal electrodes may be bonded to the dielectric material either by adhesive or by some application of heat and fusion of the metal of the electrode to the dielectric material. Alternatively one or more of the electrodes may be encapsulated within the dielectric material or may be in the form of a dielectric material with a metallic coating such as, for example a dielectric, preferably a glass dielectric with a sputtered metallic coating. [0027] In one embodiment of the invention each electrode is of the type described in the applicants co-pending application WO 02/35576 wherein there are provided electrode units containing an electrode and an adjacent a dielectric plate and a cooling liquid distribution system for directing a cooling conductive liquid onto the exterior of the electrode to cover a planar face of the electrode. Each electrode unit may comprise a watertight box having a side formed by a dielectric plate having bonded thereto on the interior of the box the planar electrode together with a liquid inlet and a liquid outlet. The liquid distribution system may comprise a cooler and a recirculation pump and/or a sparge pipe incorporating spray nozzles. [0028] Ideally the cooling liquid covers the face of the electrode remote from the dielectric plate. The cooling conductive liquid is preferably water and may contain conductivity controlling compounds such as metal salts or soluble organic additives. Ideally, the electrode is a metal electrode in contact with the dielectric plate. In one embodiment, there is a pair of metal electrodes each in contact with a dielectric plate. The water in accordance with the present invention acts as well as being an extremely efficient cooling agent to also assist in providing an efficient electrode. [0029] Ideally the dielectric plate extends beyond the perimeter of the electrode and the cooling liquid is also directed across the dielectric plate to cover at least that portion of dielectric bordering the periphery of the electrode. Preferably, all the dielectric plate is covered with cooling liquid. The electrode may be in the form of a metal mesh The water also acts to electrically passivate any boundaries, singularities or non-uniformity in the metal electrodes such as edges, corners or mesh ends where the wire mesh electrodes are used. Effectively the water acts as an electrode of limited conductivity. Further, by having a vertical arrangement, the weight of large areas of electric systems are now placed so that there is not the same sag or distortion or deformation that there might otherwise be. [0030] The assembly is preferably retained in an outer casing as defined in the applicant's co-pending application WO 02/59809 in which a lid is provided to prevent escape of a process gas, which is required in order to activate the plasma. The lid may be situated on top of the outer casing, i.e. covering the top of all the electrodes or may be situated at the bottom of the casing, i.e. covering the base of all the electrodes, dependent on whether the process gas used is lighter or heavier than air (e.g. helium and argon respectively). [0051] The dielectric materials used in accordance with the present invention may be made from any suitable dielectric, examples include but are not restricted to polycarbonate, polyethylene, glass, glass laminates, epoxy filled glass laminates and the like. [0932] The process gas for use in plasma treatment processes using the electrodes of the present invention may be any suitable gas but is preferably an inert gas or inert gas based mixture such as, for example helium, a mixture of helium and argon and an argon based mixture additionally containing ketones and/or related compounds. These process gases may be utilized alone or in combination with potentially reactive gases such as, for example, nitrogen, ammonia, O2, H2O, NO2, air or hydrogen. Most preferably, the process gas will be Helium alone or in combination with an oxidizing or reducing gas. The selection of gas depends upon the plasma processes to be undertaken. When an oxidizing or reducing process gas is required, it will preferably be utilized in a mixture comprising 90 - 99% noble gas and 1 to 10% oxidizing or reducing gas. [0033] Under oxidising conditions the present method may be used to form an oxygen containing coating on the substrate. For example, silica-based coatings can be formed on the substrate surface from atomised silicon-containing coating-forming materials. Under reducing conditions, the present method may be used to form oxygen free coatings, for example, silicon carbide based coatings may be formed from atomised silicon containing coating forming materials. [0034] In a nitrogen containing atmosphere nitrogen can bind to the substrate surface, and in an atmosphere containing both nitrogen and oxygen, nitrates can bind to and/or form on the substrate surface. Such gases may also be used to pre-treat the substrate surface prior to exposure to a coating forming substance. For example, oxygen containing plasma treatment of the substrate may provide improved adhesion with the applied coating. The oxygen containing plasma being generated by introducing oxygen containing materials to the plasma such as oxygen gas or water. [0035] A wide variety of plasma treatments are currently available, those of particular importance to the present invention are surface activation, surface cleaning and coating applications. Typically the substrate may be subjected to any appropriate treatment for example whilst passing through the first plasma region a substrate might be cleaned and when passing through the second plasma region the substrate might be surface activated, coated or etched and in the case when further plasma regions are provided after the first and second plasma regions said additional plasma regions may, when the second plasma region is utilised to activate a surface, further activate the surface, or apply a coating and when the second plasma region is utilised to coat the substrate surface, the additional plasma regions might be utilised to activated the coated surface and then re-coat the surface, apply a one or more further coatings or the like, dependent on the application for which the substrate is intended. For example, a coating formed on a substrate may be post treated in a range of plasma conditions. For example, siloxane derived coatings may be further oxidised by oxygen containing plasma treatment. The oxygen containing plasma being generated by introducing oxygen containing materials to the plasma such as oxygen gas or water. [0036] Any appropriate combination of plasma treatments may be used, for example the first plasma region may be utilised to clean the surface of the substrate by plasma treating using a helium gas plasma and the second plasma region is utilised to apply a coating, for example, by application of a liquid or solid spray through an atomiser or nebuliser as described in the applicants co-pending application 339/KOLNP/2003, which was published after the priority date of this application. The application of a coating of a liquid spray is particularly suited as the droplets in the spray will be subjected to gravitational feed unlike a gas such that the nebuliser is positioned in the assembly such that gravity feed of the coating material results in the coating precursor only passing through the second plasma region, thereby relying on gravity to prevent transfer of coating precursor into the first plasma region [0001] Alternatively the first plasma region might be utilised as a means of oxidation (in for example, an oxygen/Helium process gas) or the application of coating and the second plasma region is utilised to apply a second coating using a different precursor. As an example having a pre-treatment and post-treatment step is the following process adapted for the preparation of a SiOx barrier with a soil/fuel resistant outer surface which may be utilised for solar cells or in auto applications in which the substrate is first pretreated by He cleaning/activation of substrate, followed by deposition of SiOx from a polydimethylsiloxane precursor in the first plasma region Further Helium plasma treatment to provide extra crosslinking of the SiOx layer and finally applying a coating utilizing a perfluorinated precursor. Any appropriate pre-treatments may be undertaken for example the substrate may be washed, dried, cleaned or gas purged using the process gas, for example helium [0002] The coating-forming material may be atomised using any conventional means, for example an ultrasonic nozzle. The atomiser preferably produces a coating-forming material drop size of from 10 to 100μm, more preferably from 10 to 50μm. Suitable atomisers for use in the present invention are ultrasonic nozzles from Sono-Tek Corporation, Milton, New York, USA or Lechler GmbH of Metzingen Germany. The apparatus of the present invention may include a plurality of atomisers, which may be of particular utility, for example, where the apparatus is to be used to form a copolymer coating on a substrate from two different coating-forming materials, where the monomers are immiscible or are in different phases, e.g. the first is a solid and the second is gaseous or liquid. [0003] The present invention may be used to form many different types of substrate coatings. The type of coating which is formed on the substrate is determined by the coating- forming material(s) used, and the present method may be used to (co)polymerise coating- forming monomer material(s) onto the substrate surface. The coating-forming material may be organic or inorganic, solid, liquid or gaseous, or mixtures thereof. Suitable organic coating-forming materials include carboxylates, methacrylates, acrylates, styrenes, methacrylonitriles, alkenes and dienes, for example methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, and other alkyl methacrylates, and the corresponding acrylates, including organofunctional methacrylates and acrylates, including glycidyl methacrylate, trimethoxysilyl propyl methacrylate, allyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, dialkylaminoalkyl methacrylates, and fluoroalkyl (meth)acrylates, methacrylic acid, acrylic acid, fumaric acid and esters, itaconic acid (and esters), maleic anhydride, styrene, α-methylstyrene, halogenated alkenes, for example, vinyl halides, such as vinyl chlorides and vinyl fluorides, and fluorinated alkenes, for example perfluoroalkenes, acrylonitrile, methacrylonitrile, ethylene, propylene, allyl amine, vinylidene halides, butadienes, acrylamide, such as N-isopropylacrylamide, methacrylamide, epoxy compounds, for example glycidoxypropyltrimethoxysilane, glycidol, styrene oxide, butadiene monoxide, ethyleneglycol diglycidylether, glycidyl methacrylate, bisphenol A diglycidylether (and its oligomers), vinylcyclohexene oxide, conducting polymers such as pyrrole and thiophene and their derivatives, and phosphorus-containing compounds, for example dimethylallylphosphonate. Suitable inorganic coating-forming materials include metals and metal oxides, including colloidal metals. Organometallic compounds may also be suitable coating-forming materials, including metal alkoxides such as titanates, tin alkoxides, zirconates and alkoxides of germanium and erbium. [0040] Substrates may alternatively be provided with silica- or siloxane-based coatings using coating-forming compositions comprising silicon-containing materials. Suitable silicon-containing materials include silanes (for example, si lane, alkylsilanes alkylhalosilanes, alkoxysilanes) and linear (for example, polydimethylsiloxane) and cyclic siloxanes (for example, octamethylcyclotetrasiloxane), including organo-functional linear and cyclic siloxanes (for example, Si-H containing, halo-functional, and haloalkyl-functional linear and cyclic siloxanes, e.g. tetramethylcyclotetrasijoxane and tri(nonofluorobutyl)trimethylcyclotrisiloxane). A mixture of different silicon-containing materials may be used, for example to tailor the physical properties of the substrate coating for a specified need (e.g. thermal properties, optical properties, such as refractive index, and viscoelastic properties). [0041] An advantage of the present invention over the prior art is that both liquid and solid atomised coating-forming materials may be used to form substrate coatings, due to the method of the present invention taking place under conditions of atmospheric pressure. Furthermore the coating-forming materials can be introduced into the plasma discharge or resulting stream in the absence of a carrier gas, i.e. they can be introduced directly by, for example, direct injection, whereby the coating forming materials are injected directly into the plasma. [0042] The substrate to be coated may comprise any material, sufficiently flexible to be transported through the assembly as hereinbefore described, for example plastics for example thermoplastics such as polyolefins e.g. polyethylene, and polypropylene, polycarbonates, polyurethanes, polyvinylchloride, polyesters (for example polyalkylene terephthalates, particularly polyethylene terephthalate), polymethacrylates (for example polymethylmethacrylate and polymers of hydroxyethylmethacrylate), polyepoxides, polysulphones, polyphenylenes, polyetherketones, polyimides, polyamides, polystyrenes, phenolic, epoxy and melamine-formaldehyde resins, and blends and copolymers thereof. Preferred organic polymeric materials are polyolefins, in particular polyethylene and polypropylene. Other substrates include metallic thin films made from e.g. aluminium, steel, stainless steel and copper or the like. [0043] The substrate may be in the form of synthetic and/or, natural fibres, woven or non-woven fibres, powder, siloxane, fabrics, woven or non-woven fibres, natural fibres, synthetic fibres cellulosic material and powder or a blend of an organic polymeric material and a organosilicon-containing additive which is miscible or substantially non-miscible with the organic polymeric material as described in the applicants co-pending patent application WO 01/40359. For the avoidance of doubt "substantially non-miscible" means that the organosilicon-containing additive and the organic material have sufficiently different interaction parameters so as to be non-miscible in equilibrium conditions. This will typically, but not exclusively, be the case when the Solubility Parameters of the organosilicon- containing additive and the organic material differ by more than 0.5 MPal/2. However, the size of the substrate is limited by the dimensions of the volume within which the atmospheric pressure plasma discharge is generated, i.e. the distance between the electrodes of the means for generating the plasma. [0044] In one particularly preferred embodiment of the invention there is provided an atmospheric plasma assembly for preparing multilayer coatings upon flexible substrates. The plasma is generated by vertically orientated electrodes, which can be arranged in series, enabling single pass, multiple treatment or multilayer coating. Coating forming material or coating precursor is introduced as an atomised liquid into the top of the chamber, the precursor then enters the plasma zone under gravity. Advantages are mat the different plasma zones require no physical barrier separation, and each operates as an open perimeter process. [0045] For typical plasma generating apparatus, the plasma is generated within a gap of from 3 to 50mm, for example 5 to 25mm. Thus, the present invention has particular utility for coating films, fibres and powders. The generation of steady-state glow discharge plasma at atmospheric pressure is preferably obtained between adjacent electrodes which may be spaced up to 5 cm apart, dependent on the process gas used. The electrodes being radio frequency energised with a root mean square (rms) potential of 1 to 100 kV, preferably between 1 and 30 kV at 1 to 100 kHz, preferably at 15 to 50 kHz. The voltage used to form the plasma will typically be between 1 and 30 kVolts, most preferably between 2.5 and 10 kV however the actual value will depend on the chemistry/gas choice and plasma region size between the electrodes. Whilst the atmospheric pressure glow discharge assembly may operate at any suitable temperature, it preferably will operate at a temperature between room temperature (20 ° C) and 70° C and is typically utilized at a temperature in the region of 30 to 50 °C. [0046] Substrates coated by the method of the present invention may have various uses. For example, a silica-based coating, generated in an oxidising atmosphere, may enhance the barrier and/or diffusion properties of the substrate, and may enhance the ability of additional materials to adhere to the substrate surface. A halo-functional organic or siloxane coating (e.g. perfluoroalkenes) may increase hydrophobicity, oleophobicity, fuel and soil resistance, enhance gas and liquid filtration properties and/or the release properties of the substrate. A polydimethylsiloxane coating may enhance water resistance and release properties of the substrate, and may enhance the softness of fabrics to touch; apolyacrylic acid polymeric coating may be used as a water wettable coating, bio-compatible coating or an adhesive layer to promote adhesion to substrate surface or as part of laminated structure. The inclusion of colloidal metal species in the coatings may provide surface conductivity to the substrate, or enhance its optical properties. Polythiophene and polypyrrole give electrically conductive polymeric coatings which may also provide corrosion resistance on metallic substrates. Acidic or basic functionality coatings will provide surfaces with controlled pH, and controlled interaction with biologically important molecules such as amino acids and proteins. [0047] The invention will be more clearly understood from the following description of some embodiments thereof given by way of example only with reference to the accompanying drawings, in which :- Fig. 1 is a front view of an atmospheric pressure plasma system according to the invention, Fig. 2 is a partially exploded perspective view of portion of the system illustrated in Fig. 1, Fig. 3 is a plan view of the plasma assembly in accordance with the present invention Fig. 4a and 4b are views of a further the plasma assembly in accordance with the present invention [0048] Referring to the drawings, In Fig. 1 there is provided an atmospheric plasma system, indicated generally by the reference numeral 1 comprising an atmospheric pressure plasma assembly 2 fed by cables 3 by a power source 4 and also fed by a cooling water assembly feeding a cooling liquid distribution system mounted within the plasma assembly 2 and described in more detail later. The cooling water assembly comprises a water pump 5, a cooler in the form of a heat exchanger 6 and mam water distribution pipes 7. One of the main water distribution pipes 7 feeds an inlet manifold 8, which in turn feeds, through feed water hoses 9 and liquid inlets 14, into the plasma assembly 2. Return water hoses 10 connect through liquid outlets 15, to a further return output manifold 11, which in turn is connected to another of the water distribution pipes 7 which feeds the pump 5. Pressure release pipes 13 are mounted in the plasma assembly 2. [0049] Referring now to Fig 2 in which there are provided three watertight boxes 20, 26. The watertight boxes indicated generally by the reference numeral 20 are joined by vertical insulated spacers in the form of spacer plates 21 which form between the watertight boxes 20 an open top 22 and an open bottom 23. Each watertight box 20 comprises a rear plate 30 and a spaced apart front plate 31 mounted on a water containment frame 32 having a crossbar 33 in which are provided drain-off holes 34. The rear plate 30 and the front plate 31 are connected to the water containment frame 32 by gaskets 35. Two sets of wire electrodes 36 are mounted in the box 20 on the front plate 31. The rear plate 30, front plate 31 and water containment frame 32 are manufactured of a suitable dielectric material. A pair of sparge poles 40 formed from pipes of an insulation material, such as a plastics material, carrying a plurality of nozzles 41 are mounted within the box 20 and are connected to the feed water hoses 9. [0050] Between the watertight boxes 20 and the spacer plates 21, is a third watertight box 26 of substantially the same construction as the boxes 20, in which parts similar to those described for watertight box 20 below. The only difference between the box 26 and the box 20 is that it carries effectively two front plates 31 and carries electrodes 36 on each front plate 31 since the plates 31 act as front plates in respect of the boxes 20 on either side of the box 26. In this embodiment, the nozzles 41 of the sparge poles 40 direct water onto both plates 31. [0051] In operation, a workpiece may be led up through plasma region 25 in the direction of the arrow A and then down through plasma region 60 in direction B. Process gas can be injected into the plasma regions 25,60 and suitable power can be provided to the electrodes 36 in the plasma regions 25,60 to affect a plasma. Water is delivered from the inlet manifold 8 through the feed water hoses 9 into the sparge poles 40 where the water is delivered in a spray out the nozzles 41 onto the wire electrodes 36 and also across the exposed interior face of the front plate 31. I [0052] Referring now to Fig.3, there is provided a figure showing how a flexible substrate is treated in accordance with the present invention. A means of transporting a substrate through the assembly is provided in the form of guide rollers 70, 71 and 72, a process gas inlet 75, an assembly lid 76 and an ultrasonic nozzle 74 for introducing an atomised liquid into plasma region 60 are provided. The process gas inlet 75 may be found in the assembly lid 76 instead of the side as shown in Fig. 3) [0053] In use a flexible substrate is transported to and over guide roller 70 and is thereby guided through plasma region 25 between watertight boxes 20a and 26. The plasma in the plasma region 25 is a cleaning helium plasma, i.e. no reactive agent is directed into plasma region 25. The helium is introduced into the system by way of inlet 75. Lid 76 is placed over the top of the system to prevent the escape of helium as it is lighter than air. Upon leaving plasma region 25 the plasma cleaned substrate passes over guide 71 and is directed down through plasma region 60, between electrodes 26 and 20b and over roller 72 and then may pass to further units of the same type for further treatment. However, plasma region 60 generates a coating for the substrate by means of the injection of a liquid or sold coating making material through ultrasonic nozzle 74. An important aspect of the fact that the reactive agent being coated is a liquid or solid is that said atomised liquid or solid travels under gravity through plasma region 60 and is kept separate from plasma region 25 and as such no coating occurs in plasma region 25. The coated substrate then passes through plasma region 60 and is coated and then is transported over roller 72 and is collected or further treated with additional plasma treatments. Rollers 70 and 72 may be reels as opposed to rollers. Having passed through is adapted to guide the substrate into plasma region25 and on to roller 71. [0054] It has been found surprisingly that in addition to cooling, the water in accordance with the present invention, also acts to electrically passivate any boundaries, singularities or non-uniformities in the metal electrodes such as edges, comers or mesh ends where wire mesh electrodes are used. It will be appreciated that these, without passivation, can discharge a Corona or other plasma, causing power loss and local heating leading potentially to breakdown. Essentially, the water itself acts as an electrode of limited conductivity to smooth out potential differences and damp out unwanted electrical discharges inside the electrode box. Typically, the plasma generated in the inter-electrode gap will extend about 5 cm beyond the edge of the metal electrode due to water conductivity. Further, there are major advantages in longer residence time in the plasma region which allows the plasma to access all parts of a workpiece surface enhancing uniformity of treatment. This is particularly important with intricately formed workpieces. It has been found with the present invention that it is possible to maintain low electrode temperatures even with high plasma power densities ensuring long equipment lifetimes and elimination of excessive thermal burdens on the workpiece. Radio Frequency power was applied using a power supply to the electrodes via matching transformers at approximately 40 kHz and about 30 kW of RF power. [0055] Figs.4a and 4b are intended to show an assembly in accordance with the present invention in which there are provided four plasma zones a, b, c and d. In this assembly, there are two types of watertight box electrodes used. Two single electrode boxes 37a and 37b are used at the exterior of the assembly and three double electrode watertight boxes 38 are provided for interior plasma regions as will be described below. Each watertight box 37 comprises a polypropylene body with an glass dielectric window 47 external to the systems and a second glass dielectric window 49 which forms one edge of a plasma zone (zones a and d in the present examples). Adhered to glass dielectric window 49 is a mesh electrode 48. A water inlet 53 is provided for provision of a means of spraying the mesh electrode 48. A water outlet is also provided for drainage purposes but is not shown. [0056] Double electrodes 38a 38b and 38c are similar in construction to electrodes 37a and 37b, in that they comprise polypropylene bodies, and two glass dielectric windows 51, but have a mesh electrode 52 attached to both windows 51. Again, a water inlet 53 is provided for spraying water on both mesh electrodes 51. [0057] Rollers and guides 42,43,44,45 and 46 are provided to guide the substrate through the plasma regions a, b, c and d respectively. [0058] In use, a substrate is provided on roller 42 and is transported to roller 46 via the pathway identified by the arrows and dotted lines. The substrate travels upwardly from roller 42 to guide 43 through plasma region a formed between electrodes 37a and 38a. It then passes over guide 43 and into plasma region b between electrodes 38a and 38b to guide 44, upwardly to guide 45 and finally through plasma region d to roller 46. Typically plasma regions a and c are utilised for cleaning, the substrate, initially and after application of the first coating respectively and plasma regions b and d are utilised to for the applications of coatings using atomised liquid or solid coating forming materials in accordance with the process of the present invention via an atomiser (not shown). The atomiser is retained above the plasma regions b and d and relies upon gravity for the atomised liquid or solid to enter the its respective plasma region b and d. windows 47 49 and 51 are provided using glass to enable the operator to view the formation and operation of the plasma formed between the electrodes which is useful when problems within the assembly occur. [0059] It is to be appreciated that any suitable electrode system may be utilised and that the system described above is used merely for example. Example: Multilayer Coating on Polypropylene Film [0060] As an example of the potential utility of the present invention there is provided the following example in which a 25 μm thick polypropylene film was coated twice using the apparatus in accordance with the present invention. The first coating was a hydrophilic polyacrylic acid coating, the second coating being an oleophobic and hydrophobic fluoropolymer coating. A KSV CAM200 Optical Contact Angle Meter was used to characterise i) The untreated film which is hydrophobic but not oleophobic ii) the acrylic acid treated film (i) and iii) the fluoropolymer treated film (ii) by sessile drop contact angle. The untreated polypropylene film is hydrophobic but not oleophobic, as shown in [0061] The film is then coated using the described atmospheric pressure glow discharge (APGD) apparatus. The operating conditions used were the same for the application of both coatings Both pairs of electrodes used were made from a steel mesh and were adhered to a glass dielectric plate. The distance between the glass dielectric plates attached to the two electrodes was 6mm and the surface area thereof was (10cm x 60cm). The process gas used was helium. The plasma power to both zones 0.4kW, voltage was 4kV and the frequency was 29 kHz. The operating temperature was below 40° C. The substrate was passed through both the first and second plasma zones using a reel to reel mechanism of the type described in Fig. 3 with a guide means being utilised to assist in the transport of the substrate out of the first and into the second plasma regions. The speed of the substrate passing through both plasma zones was 2m min-1. Application of acrylic acid coating [0062] The substrate was transported through a first plasma region in which it is activated by means of an atmospheric pressure glow discharge using helium as the process gas. Upon leaving the first plasma region the guide was utilised to direct the activated substrate into the second plasma zone into which an acrylic acid precursor is introduced via Sonotec ultrasonic nozzle into the coating zone at a rate of 50 μl min-1. Contact angle analysis was undertaken on the resulting coated substrate and the results thereof are provided in Table 2 below. It will be noted that the hydrophilicity of the resulting coated substrate has significantly increased. Application of Fluoropolymer [0063] The second coating was applied in a similar fashion, with the first plasma zone being utilised to activate the surface and the second plasma zone being used to further coat the substrate with a layer of heptadecafluorodecyl acrylate. Contact angle analysis of the resulting coated film is presented in Table 3. The resulting double coated polypropylene substrate is now both hydrophobic and oleophobic. WE CLAIM : 1. An atmospheric pressure plasma assembly (1) comprising a first and second pair of vertically arrayed, parallel spaced-apart planar electrodes (36) with at least one dielectric plate (31) between said first pair, adjacent one electrode and at least one dielectric plate (31) between said second pair adjacent one electrode, the spacing between the dielectric plate and the other dielectric plate or electrode of each of the first and second pairs of electrodes forming a first and second plasma regions (25,60) characterised in that the assembly further comprises a means of transporting a substrate (70,71,72) successively through said first and second plasma regions (25,60) and an atomiser (74) adapted to introduce an atomised liquid or solid coating making material into one of said first or second plasma regions. 2. An assembly as claimed in claim 1 wherein the substrate is transported through said first and second plasma regions by means of guide rollers and/or guide reels (70,71,72). 3. An assembly as claimed in any preceding claim wherein each electrode comprises an electrode unit containing an electrode (36), an adjacent dielectric plate (31) and a cooling liquid distribution system (20,26) for directing a cooling conductive liquid onto the exterior of the electrode (36) to cover a planar face of the electrode (36) 4. An assembly as claimed in claim 3 wherein the cooling conductive liquid is water. 5. An assembly as claimed in claim 3 or 4 wherein the electrode unit is in the form of a watertight box (20, 20a, 26) having a side formed by a dielectric plate (31) having bonded thereto, on the interior of the box (20,20a, 26), a planar electrode (36) together with a liquid inlet (14) and a liquid outlet (15). 6. An assembly as claimed in any preceding claim retained in an outer casing in which a lid (76) is provided to prevent escape of a process gas which is required in order to activate the plasma. 7. An assembly as claimed in any preceding claim wherein the atomizer (74) is an ultrasonic nozzle. 8. An assembly as claimed in any preceding claim wherein the electrode (36) is a dielectric with a metallic coating. 9. An assembly as claimed in any preceding claim wherein said assembly is an atmospheric pressure glow discharge assembly. 10. An atmospheric plasma assembly for preparing multilayer coatings upon flexible substrates as claimed in any one of claims 1 to 9 wherein plasma is generated between vertically orientated electrodes (36), which are arranged in series and adapted to enable single pass, multiple treatment or multilayer coatings. 11. An assembly as claimed in any preceding claim wherein the assembly comprises one or more additional pairs of vertically oriented electrodes (36) situated before or after said first and second pair of electrodes. 12. A method of atmospheric plasma treating a substrate comprising using the apparatus described in any preceding claim, wherein the atomised solid or liquid coating making material is transferred from the atomiser (74) into the plasma region (60) by means of gravitational feed. 13. A method as claimed in claim 12 wherein the atomised solid or liquid coating material is introduced into the plasma region in the absence of a carrier gas. 14. A method as claimed in claim 12 or 13 wherein the substrate is synthetic and/or, natural fibres, woven or non-woven fibres, powder, siloxane, fabrics, woven or non-woven fibres, natural fibres, synthetic fibres cellulosic material and powder or a blend of an organic polymeric material and an organosilicon- containing additive. 15. A method of atmospheric plasma treating a substrate comprising, transporting a substrate through an atmospheric pressure plasma assembly as claimed in any one of claims 1 to 11 upwardly through one plasma region (25,60) and downwardly though the other plasma region (25,60). 16. A method as claimed in any one of claims 12 to 15 wherein the first plasma region (25) through which the substrate passes is a cleaning plasma and the second plasma region (60) through which the substrate passes effects a coating on the substrate by means of the atomised liquid or solid coating forming material. 17 A method as claimed in claim 16 wherein the gravitational feed of the atomised liquid or solid coating forming material into the second plasma region (60) prevents transfer of said atomised liquid or solid coating forming material into the first plasma region (25). 18. A method as claimed in any one of claims 12 to 17 wherein, in use, the temperature of the assembly is maintained in the range of from room temperature to 70° C 19. A treated substrate obtainable as claimed in the method as described in any one of claims 12 to 18. 20 A treated substrate as claimed in claim 19, the coating there on being capable of enhancing the barrier and/or diffusion properties of the substrate, and/or enhancing the ability of additional materials to adhere to the substrate surface. 21. A treated substrate as claimed in claim 19, the coating there on being capable of increasing hydrophobicity, oleophobicity, fuel and soil resistance, enhancing gas and liquid filtration properties and/or the release properties of the substrate. 22. A treated substrate as claimed in claim 19, the coating there on being capable of enhancing water resistance and release properties of the substrate, and/or enhancing the softness of fabrics to touch. 23. A treated substrate as claimed in claim 19, the coating there on being capable of being used as a water wettable coating, bio-compatible coating or an adhesive layer to promote adhesion to substrate surface or as part of laminated structure. 24. A treated substrate as claimed in claim 19, the coating there on being capable of providing surface conductivity to the substrate and/or enhance its optical properties. 25. A treated substrate as claimed in claim 19, the coating there on being capable of providing surfaces with controlled pH, and/or controlled interaction with biologically important molecules such as amino acids and proteins An atmospheric pressure plasma assembly (1) comprising a first and second pair of vertically arrayed, parallel spaced-apart planar electrodes (36) with at least one dielectric plate (31) between said first pair, adjacent one electrode and at least one dielectric plate (31) between said second pair adjacent one electrode, the spacing between the dielectric plate and the other dielectric plate or electrode of each of the first and second pairs of electrodes forming a first and second plasma regions (25, 60) characterized in that the assembly further comprises a means of transporting a substrate (70, 71, 72) successively through said first and second plasma regions (25, 60) and an atomizer (74) adapted to introduce an atomized liquid or solid coating making material into one of said first or second plasma regions

Full Text

AN ATMOSPHERIC PRESSURE PLASMA ASSEMBLY
[0001] The present inyention ralates to an atmospheric pressure plasma assembly and
a method of treating a substrate using said assembly.
[0002] When matter is continually supplied with energy, its temperature increases and it
typically transforms from a solid to a liquid and, then, to a gaseous state. Continuing to supply
energy causes the system to undergo yet a further change of state in which neutral atoms or
molecules of the gas are broken up by energetic collisions to produce negatively charged
electrons, positive or negatively charged ions and other species. This mix of charged particles
exhibiting collective behaviour is called "plasma", the fourth state of matter. Due to their
electrical charge, plasmas are highly influenced by external electromagnetic fields, which makes
them readily controllable. Furthermore, their high energy content allows them to achieve
processes which are impossible or difficult through the other states of matter, such as by liquid
or gas processing.
№003] The term "plasma" covers a huge range of systems whose density and
temperature vary by many orders of magnitude. Some plasmas are very hot and all their
microscopic species (ions, electrons, etc.) are in approximate thermal equilibrium, the energy
input into the system being widely distributed through atomic/molecular level collisions. Other
plasmas, however, particular those at low pressure (e.g. 100 Pa) where collisions are relatively
infrequent, have their constituent species at widely different temperatures and are called "non-
thermal equilibrium" plasmas. In these non-thermal plasmas the free electrons are very hot with
temperatures of many thousands of Kelvin (K) whilst the neutral and ionic species remain cool.
Because the free electrons have almost negligible mass, the total system heat content is low and
the plasma operates close to room temperature thus allowing the processing of temperature
sensitive materials, such as plastics or polymers, without imposing a damaging thermal burden
onto the sample. However, the hot electrons create, through high energy collisions, a rich
source of radicals and excited species with a high chemical potential energy capable of profound
chemical and physical reactivity. It is this combination of low temperature operation plus high
reactivity which makes non-thermal plasma technologically important and a very powerful tool
for manufacturing and material processing, capable of achieving processes which, if achievable

at all without plasma, would require very high temperatures or noxious and aggressive
chemicals.
[0004] For industrial applications of plasma technology, a convenient method is to
couple electromagnetic power into a volume of process gas, which can be mixtures of gases and
vapours in which the workpieces/samples to be treated are immersed or passed through. The
gas becomes ionised into plasma, generating chemical radicals, UV-radiation, and ions, which
react with the surface of the samples. By correct selection of process gas composition, driving
power frequency, power coupling mode, pressure and other control parameters, the plasma
process can be tailored to the specific application required by a manufacturer.
[0005] Because of the huge chemical and thermal range of plasmas, they are suitable for
many technological applications. Non-thermal equilibrium plasmas are particularly effective for
surface activation, surface cleaning, material etching and coating of surfaces.
[0006] The surface activation of polymeric materials is a widely used industrial plasma
technology pioneered by the automotive industry. Thus, for example, polyolefins, such as
polyethylene and polypropylene, which are favoured for their recylability, have a non-polar
surface and consequently a poor disposition to coating or gluing. However, treatment by
oxygen plasma results in the formation of surface polar groups giving high wettability and
consequently excellent coverage and adhesion to metal paints, adhesives or other coatings.
Thus, for example, plasma surface engineering is becoming increasingly important in the
manufacture of vehicle fascias, dashboards, bumpers and the like as well as in component
assembly in the toy and like industries. Many other applications are available in the printing,
painting, gluing, laminating and general coating of components of all geometries in polymer,
plastic, ceramic/inorganic, metal and other materials.
[0007] The increasing pervasiveness and strength of environmental legislation world-
wide is creating substantial pressure on industry to reduce or eliminate the use of solvents and
other wet chemicals in manufacturing, particularly for component/surface cleaning. In
particular, CFC-based degreasing operations have been largely replaced by plasma cleaning
technology operating with oxygen, air and other non-toxic gases. Combining water based pre-

cleaning operations with plasma allows even heavily soiled components to be cleaned; the
resulting surface qualities obtained being generally superior to those resulting from traditional
methods. Any organic surface contamination is rapidly scavenged by room temperature plasma
and converted to gaseous CO2 and water, which can be safely exhausted.
[0003] Plasmas can also carry out etching of a bulk material, i.e. for the removal of
unwanted material therefrom. Thus, for example, an oxygen based plasma will etch polymers, a
process used in the production of circuit boards, etc. Different materials such as metals,
ceramics and inorganics are etched by careful selection of precursor gas and attention to the
plasma chemistry. Structures down to nanometer critical dimensions are now being produced
by plasma etching technology.
[0089] A plasma technology that is rapidly emerging into mainstream industry is that of
plasma coating/thin film deposition. Typically, a high level of polymerisation is achieved by
application of plasma to monomelic gases and vapours. Thus, a dense, tightly knit and three-
dimensionally connected film can be formed which is thermally stable, chemically very resistant
and mechanically robust. Such films are deposited conformally on even the most intricate of
surfaces and at a temperature which ensures a low thermal burden on the substrate. Plasmas are
therefore ideal for the coating of delicate and heat sensitive, as well as robust materials. Plasma
coatings are free of micropores even with thin layers. The optical properties, e.g. colour, of the
coating can often be customised and plasma coatings adhere well to even non-polar materials,
e.g. polyethylene, as well as steel (e.g. anti-corrosion films on metal reflectors), ceramics,
semiconductors, textiles, etc.
[0010] In all these processes, plasma engineering produces a surface effect customised
to the desired application or product without affecting the material bulk in any way. Plasma
processing thus offers the manufacturer a versatile and powerful tool allowing choice of a
material for its bulk technical and commercial properties while giving the freedom to
independently engineer its surface to meet a totally different set of needs. Plasma technology
thus confers greatly enhanced product functionality, performance, lifetime and quality and gives
the manufacturing company significant added value to its production capability.

[0011] These properties provide a strong motivation for industry to adopt plasma-based
processing, and this move has been led since the 1960s by the microelectronics community
which has developed the low pressure Glow Discharge plasma into an ultra-high technology and
high capital cost engineering tool for semiconductor, metal and dielectric processing. The same
low pressure Glow Discharge type plasma has increasingly penetrated other industrial sectors
since the 1980s offering, at more moderate cost, processes such as polymer surface activation
for increased adhesion/bond strength, high quality degreasing/cleaning and the deposition of
high performance coatings. Thus, there has been a substantial take-up of plasma technology.
Glow discharges can be achieved at both vacuum and atmospheric pressures. In the case of
atmospheric pressure glow discharge, gases such as helium or argon are utilised as diluents
and a high frequency (e.g.> 1kHz) power supply is used to generate a homogeneous glow
discharge at atmospheric pressure via a Penning ionisation mechanism, (see for example,
Kanazawa et al, J.Phys. D: Appl. Phys. 1988,21,838, Okazaki et al, Proc. Jpn. Symp. Plasma
Chem. 1989,2,95, Kanazawa et al, Nuclear Instruments and Methods in Physical Research
1989, B37/38,842, and Yokoyama et al., J. Phys. D: Appl. Phys. 1990,23,374).
[0012] However, adoption of plasma technology has been limited by a major constraint
on most industrial plasma systems, namely, their need to operate at low pressure. Partial
vacuum operation means a closed perimeter, sealed reactor system providing only off-line,
batch processing of discrete workpieces. Throughput is low or moderate and the need for
vacuum adds capital and running costs.
[0013] Atmospheric pressure plasmas, however, offer industry open port or perimeter
systems providing free ingress into and exit from the plasma region by workpieces/webs and,
hence, on-line, continuous processing of large or small area webs or conveyor-carried discrete
workpieces. Throughput is high, reinforced by the high species flux obtained from high
pressure operation. Many industrial sectors, such as textiles, packaging, paper, medical,
automotive, aerospace, etc., rely almost entirely upon continuous, on-line processing so that
open port/perimeter configuration plasmas at atmospheric pressure offer a new industrial
processing capability.

[0014] Corona and flame (also a plasma) treatment systems have provided industry with
a limited form of atmospheric pressure plasma processing capability for about 30 years.
However, despite their high manufacturability, these systems have failed to penetrate the market
or be taken up by industry to anything like the same extent as the lower pressure, bath-
processing-only plasma type. The reason is that corona/flame systems have significant
limitations. They operate in ambient air offering a single surface activation process and have a
negligible effect on many materials and a weak effect on most. The treatment is often non-
uniform and the corona process is incompatible with thick webs or 3D workpieces while the
flame process is incompatible with heat sensitive substrates.
[0015] Significant advances have been made in plasma treatment at atmospheric
pressure. Considerable work has been done on the stabilisation of atmospheric pressure glow
discharges, such as in Okazaki et al., J. Phys. D: Appl. Phys. 26 (1993) 889-892. Further,
there is described in US Patent Specification No. 5414324 (Roth et al) the generation of a
steady-state glow discharge plasma at atmospheric pressure between a pair of insulated metal
plate electrodes spaced up to 5 cm apart and radio frequency (KF) energised with a root mean
square (rms) potential of 1 to 5 kV at 1 to 100 kHz. This patent specification describes the
use of electrically insulated metallic plate electrodes and also the problems of electrode plates
and the need to discourage electrical breakdown at the edge of electrodes. It further describes
the use of the electrodes, which in this case are copper plates, and a water cooling system,
which is supplied through fluid flow conduits bonded to the electrodes and as such, water
does not come into direct contact with any electrode surface.
[0016] In US Patent Specification No. 5185132, (Horiike et al), there is described an
atmospheric plasma reaction method in which plate electrodes are used in a vertical
configuration. However, they are merely used in the vertical configuration to prepare the
plasma and then the plasma is directed out from between the plates onto a horizontal surface
below the vertically arranged electrodes and downstream from the plasma source.
[0016] In EP 0809275 and JP 11 -29873 here are provided atmospheric pressure glow
discharge systems having at least two sets of horizontally arrayed pairs of electrodes through
which a substrate web may be passed continuously by means of rollers. JP 11-241165 and JP

2000-212753 describe electric discharge type plasma system using pulsed electric fields. In all
four of these documents the substrate is treated with gases.
[0018] In the applicants co-pending application WO 02/35576, which was published
after the priority date of the present application, a plasma system of the type comprising a pair
of parallel spaced-apart planar electrodes with at least one dielectric plate therebetween and
adjacent one electrode, the spacing between the dielectric plate and the other dielectric plate
or electrodes forming a plasma region for a precursor gas wherein a cooling liquid distribution
system is provided for directing a cooling conductive liquid onto the exterior of at least one of
the electrodes to cover a planar face of the at least one electrode.
[0019] According to the present invention there is provided an atmospheric pressure
plasma assembly comprising a first and second pair of vertically arrayed, parallel spaced-apart
planar electrodes with at least one dielectric plate between said first pair, adjacent one electrode
and at least one dielectric plate between said second pair adjacent one electrode, the spacing
between the dielectric plate and the other dielectric plate or electrode of each of the first and
second pairs of electrodes forming a first and second plasma region characterised in that the
assembly further comprises a means of transporting a substrate successively through said first
and second plasma regions and an atomiser adapted to introduce an atomised liquid or solid
coating making material into one of said first or second plasma regions.
[0020] The terms "comprise, comprises, comprised and comprising" or any variation
thereof and the terms "include, includes, included and including" or any variation thereof are
considered to be totally interchangeable and they should all be afforded the widest possible
interpretation.
[0021] It should be understood that the term vertical is intended to include substantially
vertical and should not be restricted solely to electrodes positioned at 90 degrees to the
horizontal.
[0022] Preferably the means of transporting the substrate is by a reel to reel based
process. The substrate may be transported through the first plasma region in an upwardly or

downwardly direction. Preferably when the substrate passes through one plasma zone in an
upwardly direction and the other in a downwardly direction one or more guide rollers are
provided to guide the substrate from the end of the first reel into the first plasma zone, from the
first plasma zone to and into the second plasma zone and from the second plasma zone to the
second reel or next plasma zone dependent on the number of plasma zones being used. The
substrate residence time in each plasma region may be predetermined prior to coating and
rather than varying the speed of the substrate, through each plasma zone, the path length a
substrate has to travel through each plasma region may be altered such that the substrate may
pass through both regions at the same speed but may spend a different period of time in each
plasma region due to differing path lengths through the respective plasma regions.
[0023] In view of the fact that the electrodes in the present invention are vertically
orientated it is preferred that a substrate be transported through an atmospheric pressure plasma
assembly in accordance with the present invention upwardly through one plasma region and
downwardly though the other plasma region. On the basis of the distance between adjacent
electrodes, as will be discussed below, it will be appreciated that the substrate is generally
transported through a plasma region in a vertical or diagonal direction although in most cases it
will be vertical or substantially vertical.
[0024] Preferably each substrate needs only to be subjected to one pass through the
assembly but if required the substrate may be returned to the first reel for further passages
through the assembly.
[0025] Additional pairs of electrodes may be added to the system to form further
successive plasma regions through which a substrate would pass. The additional pairs of
electrodes may be situated before or after said first and second pair of electrodes such that
substrate would be subjected to pre-treatment or post-treatment steps. Said additional pairs of
electrodes are preferably situated before or after and most preferably after said first and second
pairs of electrodes. Treatments applied in the plasma regions formed by the additional pairs of
electrodes may be the same or different from that undertaken in the first and second plasma
regions. In the case when additional plasma regions are provided for pre-treatment or post-
treatment the necessary number of guides and/or rollers will be provided in order to ensure the

passage of the substrate through the assembly. Similarly preferably the substrate will be
transported alternatively upwardly and downwardly through all neighbouring plasma regions in
the assembly.
[0026] Each electrode may comprise any suitable geometry and construction. Metal
electrodes may be used and may be in for example the form of metallic plates or a mesh. The
metal electrodes may be bonded to the dielectric material either by adhesive or by some
application of heat and fusion of the metal of the electrode to the dielectric material.
Alternatively one or more of the electrodes may be encapsulated within the dielectric material or
may be in the form of a dielectric material with a metallic coating such as, for example a
dielectric, preferably a glass dielectric with a sputtered metallic coating.
[0027] In one embodiment of the invention each electrode is of the type described in
the applicants co-pending application WO 02/35576 wherein there are provided electrode
units containing an electrode and an adjacent a dielectric plate and a cooling liquid
distribution system for directing a cooling conductive liquid onto the exterior of the electrode
to cover a planar face of the electrode. Each electrode unit may comprise a watertight box
having a side formed by a dielectric plate having bonded thereto on the interior of the box the
planar electrode together with a liquid inlet and a liquid outlet. The liquid distribution system
may comprise a cooler and a recirculation pump and/or a sparge pipe incorporating spray
nozzles.
[0028] Ideally the cooling liquid covers the face of the electrode remote from the
dielectric plate. The cooling conductive liquid is preferably water and may contain conductivity
controlling compounds such as metal salts or soluble organic additives. Ideally, the electrode is
a metal electrode in contact with the dielectric plate. In one embodiment, there is a pair of metal
electrodes each in contact with a dielectric plate. The water in accordance with the present
invention acts as well as being an extremely efficient cooling agent to also assist in providing an
efficient electrode.
[0029] Ideally the dielectric plate extends beyond the perimeter of the electrode and
the cooling liquid is also directed across the dielectric plate to cover at least that portion of

dielectric bordering the periphery of the electrode. Preferably, all the dielectric plate is
covered with cooling liquid. The electrode may be in the form of a metal mesh The water
also acts to electrically passivate any boundaries, singularities or non-uniformity in the metal
electrodes such as edges, corners or mesh ends where the wire mesh electrodes are used.
Effectively the water acts as an electrode of limited conductivity. Further, by having a
vertical arrangement, the weight of large areas of electric systems are now placed so that there
is not the same sag or distortion or deformation that there might otherwise be.
[0030] The assembly is preferably retained in an outer casing as defined in the
applicant's co-pending application WO 02/59809 in which a lid is provided to prevent escape
of a process gas, which is required in order to activate the plasma. The lid may be situated on
top of the outer casing, i.e. covering the top of all the electrodes or may be situated at the
bottom of the casing, i.e. covering the base of all the electrodes, dependent on whether the
process gas used is lighter or heavier than air (e.g. helium and argon respectively).
[0051] The dielectric materials used in accordance with the present invention may be
made from any suitable dielectric, examples include but are not restricted to polycarbonate,
polyethylene, glass, glass laminates, epoxy filled glass laminates and the like.
[0932] The process gas for use in plasma treatment processes using the electrodes of
the present invention may be any suitable gas but is preferably an inert gas or inert gas based
mixture such as, for example helium, a mixture of helium and argon and an argon based
mixture additionally containing ketones and/or related compounds. These process gases may
be utilized alone or in combination with potentially reactive gases such as, for example,
nitrogen, ammonia, O2, H2O, NO2, air or hydrogen. Most preferably, the process gas will be
Helium alone or in combination with an oxidizing or reducing gas. The selection of gas
depends upon the plasma processes to be undertaken. When an oxidizing or reducing process
gas is required, it will preferably be utilized in a mixture comprising 90 - 99% noble gas and
1 to 10% oxidizing or reducing gas.
[0033] Under oxidising conditions the present method may be used to form an oxygen
containing coating on the substrate. For example, silica-based coatings can be formed on the

substrate surface from atomised silicon-containing coating-forming materials. Under
reducing conditions, the present method may be used to form oxygen free coatings, for
example, silicon carbide based coatings may be formed from atomised silicon containing
coating forming materials.
[0034] In a nitrogen containing atmosphere nitrogen can bind to the substrate surface,
and in an atmosphere containing both nitrogen and oxygen, nitrates can bind to and/or form
on the substrate surface. Such gases may also be used to pre-treat the substrate surface prior
to exposure to a coating forming substance. For example, oxygen containing plasma
treatment of the substrate may provide improved adhesion with the applied coating. The
oxygen containing plasma being generated by introducing oxygen containing materials to the
plasma such as oxygen gas or water.
[0035] A wide variety of plasma treatments are currently available, those of particular
importance to the present invention are surface activation, surface cleaning and coating
applications. Typically the substrate may be subjected to any appropriate treatment for example
whilst passing through the first plasma region a substrate might be cleaned and when passing
through the second plasma region the substrate might be surface activated, coated or etched and
in the case when further plasma regions are provided after the first and second plasma regions
said additional plasma regions may, when the second plasma region is utilised to activate a
surface, further activate the surface, or apply a coating and when the second plasma region is
utilised to coat the substrate surface, the additional plasma regions might be utilised to activated
the coated surface and then re-coat the surface, apply a one or more further coatings or the like,
dependent on the application for which the substrate is intended. For example, a coating
formed on a substrate may be post treated in a range of plasma conditions. For example,
siloxane derived coatings may be further oxidised by oxygen containing plasma treatment.
The oxygen containing plasma being generated by introducing oxygen containing materials to
the plasma such as oxygen gas or water.
[0036] Any appropriate combination of plasma treatments may be used, for example the
first plasma region may be utilised to clean the surface of the substrate by plasma treating using
a helium gas plasma and the second plasma region is utilised to apply a coating, for example, by

application of a liquid or solid spray through an atomiser or nebuliser as described in the
applicants co-pending application 339/KOLNP/2003, which was published after the priority
date of this application. The application of a coating of a liquid spray is particularly suited as
the droplets in the spray will be subjected to gravitational feed unlike a gas such that the
nebuliser is positioned in the assembly such that gravity feed of the coating material results in
the coating precursor only passing through the second plasma region, thereby relying on gravity
to prevent transfer of coating precursor into the first plasma region
[0001] Alternatively the first plasma region might be utilised as a means of oxidation
(in for example, an oxygen/Helium process gas) or the application of coating and the second
plasma region is utilised to apply a second coating using a different precursor. As an example
having a pre-treatment and post-treatment step is the following process adapted for the
preparation of a SiOx barrier with a soil/fuel resistant outer surface which may be utilised for
solar cells or in auto applications in which the substrate is first pretreated by He
cleaning/activation of substrate, followed by deposition of SiOx from a polydimethylsiloxane
precursor in the first plasma region Further Helium plasma treatment to provide extra
crosslinking of the SiOx layer and finally applying a coating utilizing a perfluorinated
precursor. Any appropriate pre-treatments may be undertaken for example the substrate may
be washed, dried, cleaned or gas purged using the process gas, for example helium
[0002] The coating-forming material may be atomised using any conventional means,
for example an ultrasonic nozzle. The atomiser preferably produces a coating-forming
material drop size of from 10 to 100μm, more preferably from 10 to 50μm. Suitable
atomisers for use in the present invention are ultrasonic nozzles from Sono-Tek Corporation,
Milton, New York, USA or Lechler GmbH of Metzingen Germany. The apparatus of the
present invention may include a plurality of atomisers, which may be of particular utility, for
example, where the apparatus is to be used to form a copolymer coating on a substrate from
two different coating-forming materials, where the monomers are immiscible or are in
different phases, e.g. the first is a solid and the second is gaseous or liquid.
[0003] The present invention may be used to form many different types of substrate
coatings. The type of coating which is formed on the substrate is determined by the coating-

forming material(s) used, and the present method may be used to (co)polymerise coating-
forming monomer material(s) onto the substrate surface. The coating-forming material may
be organic or inorganic, solid, liquid or gaseous, or mixtures thereof. Suitable organic
coating-forming materials include carboxylates, methacrylates, acrylates, styrenes,
methacrylonitriles, alkenes and dienes, for example methyl methacrylate, ethyl methacrylate,
propyl methacrylate, butyl methacrylate, and other alkyl methacrylates, and the corresponding
acrylates, including organofunctional methacrylates and acrylates, including glycidyl
methacrylate, trimethoxysilyl propyl methacrylate, allyl methacrylate, hydroxyethyl
methacrylate, hydroxypropyl methacrylate, dialkylaminoalkyl methacrylates, and fluoroalkyl
(meth)acrylates, methacrylic acid, acrylic acid, fumaric acid and esters, itaconic acid (and
esters), maleic anhydride, styrene, α-methylstyrene, halogenated alkenes, for example, vinyl
halides, such as vinyl chlorides and vinyl fluorides, and fluorinated alkenes, for example
perfluoroalkenes, acrylonitrile, methacrylonitrile, ethylene, propylene, allyl amine, vinylidene
halides, butadienes, acrylamide, such as N-isopropylacrylamide, methacrylamide, epoxy
compounds, for example glycidoxypropyltrimethoxysilane, glycidol, styrene oxide, butadiene
monoxide, ethyleneglycol diglycidylether, glycidyl methacrylate, bisphenol A diglycidylether
(and its oligomers), vinylcyclohexene oxide, conducting polymers such as pyrrole and
thiophene and their derivatives, and phosphorus-containing compounds, for example
dimethylallylphosphonate. Suitable inorganic coating-forming materials include metals and
metal oxides, including colloidal metals. Organometallic compounds may also be suitable
coating-forming materials, including metal alkoxides such as titanates, tin alkoxides,
zirconates and alkoxides of germanium and erbium.
[0040] Substrates may alternatively be provided with silica- or siloxane-based
coatings using coating-forming compositions comprising silicon-containing materials.
Suitable silicon-containing materials include silanes (for example, si lane, alkylsilanes
alkylhalosilanes, alkoxysilanes) and linear (for example, polydimethylsiloxane) and cyclic
siloxanes (for example, octamethylcyclotetrasiloxane), including organo-functional linear and
cyclic siloxanes (for example, Si-H containing, halo-functional, and haloalkyl-functional
linear and cyclic siloxanes, e.g. tetramethylcyclotetrasijoxane and
tri(nonofluorobutyl)trimethylcyclotrisiloxane). A mixture of different silicon-containing
materials may be used, for example to tailor the physical properties of the substrate coating

for a specified need (e.g. thermal properties, optical properties, such as refractive index, and
viscoelastic properties).
[0041] An advantage of the present invention over the prior art is that both liquid and
solid atomised coating-forming materials may be used to form substrate coatings, due to the
method of the present invention taking place under conditions of atmospheric pressure.
Furthermore the coating-forming materials can be introduced into the plasma discharge or
resulting stream in the absence of a carrier gas, i.e. they can be introduced directly by, for
example, direct injection, whereby the coating forming materials are injected directly into the
plasma.
[0042] The substrate to be coated may comprise any material, sufficiently flexible to
be transported through the assembly as hereinbefore described, for example plastics for
example thermoplastics such as polyolefins e.g. polyethylene, and polypropylene,
polycarbonates, polyurethanes, polyvinylchloride, polyesters (for example polyalkylene
terephthalates, particularly polyethylene terephthalate), polymethacrylates (for example
polymethylmethacrylate and polymers of hydroxyethylmethacrylate), polyepoxides,
polysulphones, polyphenylenes, polyetherketones, polyimides, polyamides, polystyrenes,
phenolic, epoxy and melamine-formaldehyde resins, and blends and copolymers thereof.
Preferred organic polymeric materials are polyolefins, in particular polyethylene and
polypropylene. Other substrates include metallic thin films made from e.g. aluminium, steel,
stainless steel and copper or the like.
[0043] The substrate may be in the form of synthetic and/or, natural fibres, woven or
non-woven fibres, powder, siloxane, fabrics, woven or non-woven fibres, natural fibres,
synthetic fibres cellulosic material and powder or a blend of an organic polymeric material
and a organosilicon-containing additive which is miscible or substantially non-miscible with
the organic polymeric material as described in the applicants co-pending patent application
WO 01/40359. For the avoidance of doubt "substantially non-miscible" means that the
organosilicon-containing additive and the organic material have sufficiently different
interaction parameters so as to be non-miscible in equilibrium conditions. This will typically,
but not exclusively, be the case when the Solubility Parameters of the organosilicon-

containing additive and the organic material differ by more than 0.5 MPal/2. However, the
size of the substrate is limited by the dimensions of the volume within which the atmospheric
pressure plasma discharge is generated, i.e. the distance between the electrodes of the means
for generating the plasma.
[0044] In one particularly preferred embodiment of the invention there is provided an
atmospheric plasma assembly for preparing multilayer coatings upon flexible substrates. The
plasma is generated by vertically orientated electrodes, which can be arranged in series,
enabling single pass, multiple treatment or multilayer coating. Coating forming material or
coating precursor is introduced as an atomised liquid into the top of the chamber, the
precursor then enters the plasma zone under gravity. Advantages are mat the different plasma
zones require no physical barrier separation, and each operates as an open perimeter process.
[0045] For typical plasma generating apparatus, the plasma is generated within a gap
of from 3 to 50mm, for example 5 to 25mm. Thus, the present invention has particular utility
for coating films, fibres and powders. The generation of steady-state glow discharge plasma
at atmospheric pressure is preferably obtained between adjacent electrodes which may be
spaced up to 5 cm apart, dependent on the process gas used. The electrodes being radio
frequency energised with a root mean square (rms) potential of 1 to 100 kV, preferably
between 1 and 30 kV at 1 to 100 kHz, preferably at 15 to 50 kHz. The voltage used to form
the plasma will typically be between 1 and 30 kVolts, most preferably between 2.5 and 10 kV
however the actual value will depend on the chemistry/gas choice and plasma region size
between the electrodes. Whilst the atmospheric pressure glow discharge assembly may
operate at any suitable temperature, it preferably will operate at a temperature between room
temperature (20 ° C) and 70° C and is typically utilized at a temperature in the region of 30 to
50 °C.
[0046] Substrates coated by the method of the present invention may have various
uses. For example, a silica-based coating, generated in an oxidising atmosphere, may
enhance the barrier and/or diffusion properties of the substrate, and may enhance the ability of
additional materials to adhere to the substrate surface. A halo-functional organic or siloxane
coating (e.g. perfluoroalkenes) may increase hydrophobicity, oleophobicity, fuel and soil

resistance, enhance gas and liquid filtration properties and/or the release properties of the
substrate. A polydimethylsiloxane coating may enhance water resistance and release
properties of the substrate, and may enhance the softness of fabrics to touch; apolyacrylic
acid polymeric coating may be used as a water wettable coating, bio-compatible coating or an
adhesive layer to promote adhesion to substrate surface or as part of laminated structure. The
inclusion of colloidal metal species in the coatings may provide surface conductivity to the
substrate, or enhance its optical properties. Polythiophene and polypyrrole give electrically
conductive polymeric coatings which may also provide corrosion resistance on metallic
substrates. Acidic or basic functionality coatings will provide surfaces with controlled pH,
and controlled interaction with biologically important molecules such as amino acids and
proteins.
[0047] The invention will be more clearly understood from the following description
of some embodiments thereof given by way of example only with reference to the
accompanying drawings, in which :-
Fig. 1 is a front view of an atmospheric pressure plasma system according to the
invention,
Fig. 2 is a partially exploded perspective view of portion of the system illustrated in Fig.
1,
Fig. 3 is a plan view of the plasma assembly in accordance with the present invention
Fig. 4a and 4b are views of a further the plasma assembly in accordance with the present
invention
[0048] Referring to the drawings, In Fig. 1 there is provided an atmospheric plasma
system, indicated generally by the reference numeral 1 comprising an atmospheric pressure
plasma assembly 2 fed by cables 3 by a power source 4 and also fed by a cooling water
assembly feeding a cooling liquid distribution system mounted within the plasma assembly 2
and described in more detail later. The cooling water assembly comprises a water pump 5, a

cooler in the form of a heat exchanger 6 and mam water distribution pipes 7. One of the main
water distribution pipes 7 feeds an inlet manifold 8, which in turn feeds, through feed water
hoses 9 and liquid inlets 14, into the plasma assembly 2. Return water hoses 10 connect
through liquid outlets 15, to a further return output manifold 11, which in turn is connected to
another of the water distribution pipes 7 which feeds the pump 5. Pressure release pipes 13
are mounted in the plasma assembly 2.
[0049] Referring now to Fig 2 in which there are provided three watertight boxes 20,
26. The watertight boxes indicated generally by the reference numeral 20 are joined by vertical
insulated spacers in the form of spacer plates 21 which form between the watertight boxes 20 an
open top 22 and an open bottom 23. Each watertight box 20 comprises a rear plate 30 and a
spaced apart front plate 31 mounted on a water containment frame 32 having a crossbar 33 in
which are provided drain-off holes 34. The rear plate 30 and the front plate 31 are connected to
the water containment frame 32 by gaskets 35. Two sets of wire electrodes 36 are mounted in
the box 20 on the front plate 31. The rear plate 30, front plate 31 and water containment frame
32 are manufactured of a suitable dielectric material. A pair of sparge poles 40 formed from
pipes of an insulation material, such as a plastics material, carrying a plurality of nozzles 41 are
mounted within the box 20 and are connected to the feed water hoses 9.
[0050] Between the watertight boxes 20 and the spacer plates 21, is a third watertight
box 26 of substantially the same construction as the boxes 20, in which parts similar to those
described for watertight box 20 below. The only difference between the box 26 and the box 20
is that it carries effectively two front plates 31 and carries electrodes 36 on each front plate 31
since the plates 31 act as front plates in respect of the boxes 20 on either side of the box 26. In
this embodiment, the nozzles 41 of the sparge poles 40 direct water onto both plates 31.
[0051] In operation, a workpiece may be led up through plasma region 25 in the
direction of the arrow A and then down through plasma region 60 in direction B. Process gas
can be injected into the plasma regions 25,60 and suitable power can be provided to the
electrodes 36 in the plasma regions 25,60 to affect a plasma. Water is delivered from the inlet
manifold 8 through the feed water hoses 9 into the sparge poles 40 where the water is delivered

in a spray out the nozzles 41 onto the wire electrodes 36 and also across the exposed interior
face of the front plate 31.
I
[0052] Referring now to Fig.3, there is provided a figure showing how a flexible
substrate is treated in accordance with the present invention. A means of transporting a
substrate through the assembly is provided in the form of guide rollers 70, 71 and 72, a process
gas inlet 75, an assembly lid 76 and an ultrasonic nozzle 74 for introducing an atomised liquid
into plasma region 60 are provided. The process gas inlet 75 may be found in the assembly lid
76 instead of the side as shown in Fig. 3)
[0053] In use a flexible substrate is transported to and over guide roller 70 and is
thereby guided through plasma region 25 between watertight boxes 20a and 26. The plasma in
the plasma region 25 is a cleaning helium plasma, i.e. no reactive agent is directed into plasma
region 25. The helium is introduced into the system by way of inlet 75. Lid 76 is placed over
the top of the system to prevent the escape of helium as it is lighter than air. Upon leaving
plasma region 25 the plasma cleaned substrate passes over guide 71 and is directed down
through plasma region 60, between electrodes 26 and 20b and over roller 72 and then may pass
to further units of the same type for further treatment. However, plasma region 60 generates a
coating for the substrate by means of the injection of a liquid or sold coating making material
through ultrasonic nozzle 74. An important aspect of the fact that the reactive agent being
coated is a liquid or solid is that said atomised liquid or solid travels under gravity through
plasma region 60 and is kept separate from plasma region 25 and as such no coating occurs in
plasma region 25. The coated substrate then passes through plasma region 60 and is coated and
then is transported over roller 72 and is collected or further treated with additional plasma
treatments. Rollers 70 and 72 may be reels as opposed to rollers. Having passed through is
adapted to guide the substrate into plasma region25 and on to roller 71.
[0054] It has been found surprisingly that in addition to cooling, the water in accordance
with the present invention, also acts to electrically passivate any boundaries, singularities or
non-uniformities in the metal electrodes such as edges, comers or mesh ends where wire mesh
electrodes are used. It will be appreciated that these, without passivation, can discharge a
Corona or other plasma, causing power loss and local heating leading potentially to breakdown.

Essentially, the water itself acts as an electrode of limited conductivity to smooth out potential
differences and damp out unwanted electrical discharges inside the electrode box. Typically,
the plasma generated in the inter-electrode gap will extend about 5 cm beyond the edge of the
metal electrode due to water conductivity. Further, there are major advantages in longer
residence time in the plasma region which allows the plasma to access all parts of a workpiece
surface enhancing uniformity of treatment. This is particularly important with intricately
formed workpieces. It has been found with the present invention that it is possible to maintain
low electrode temperatures even with high plasma power densities ensuring long equipment
lifetimes and elimination of excessive thermal burdens on the workpiece. Radio Frequency
power was applied using a power supply to the electrodes via matching transformers at
approximately 40 kHz and about 30 kW of RF power.
[0055] Figs.4a and 4b are intended to show an assembly in accordance with the present
invention in which there are provided four plasma zones a, b, c and d. In this assembly, there
are two types of watertight box electrodes used. Two single electrode boxes 37a and 37b are
used at the exterior of the assembly and three double electrode watertight boxes 38 are provided
for interior plasma regions as will be described below. Each watertight box 37 comprises a
polypropylene body with an glass dielectric window 47 external to the systems and a second
glass dielectric window 49 which forms one edge of a plasma zone (zones a and d in the present
examples). Adhered to glass dielectric window 49 is a mesh electrode 48. A water inlet 53 is
provided for provision of a means of spraying the mesh electrode 48. A water outlet is also
provided for drainage purposes but is not shown.
[0056] Double electrodes 38a 38b and 38c are similar in construction to electrodes 37a
and 37b, in that they comprise polypropylene bodies, and two glass dielectric windows 51, but
have a mesh electrode 52 attached to both windows 51. Again, a water inlet 53 is provided for
spraying water on both mesh electrodes 51.
[0057] Rollers and guides 42,43,44,45 and 46 are provided to guide the substrate
through the plasma regions a, b, c and d respectively.

[0058] In use, a substrate is provided on roller 42 and is transported to roller 46 via the
pathway identified by the arrows and dotted lines. The substrate travels upwardly from roller 42
to guide 43 through plasma region a formed between electrodes 37a and 38a. It then passes
over guide 43 and into plasma region b between electrodes 38a and 38b to guide 44, upwardly
to guide 45 and finally through plasma region d to roller 46. Typically plasma regions a and c
are utilised for cleaning, the substrate, initially and after application of the first coating
respectively and plasma regions b and d are utilised to for the applications of coatings using
atomised liquid or solid coating forming materials in accordance with the process of the present
invention via an atomiser (not shown). The atomiser is retained above the plasma regions b and
d and relies upon gravity for the atomised liquid or solid to enter the its respective plasma region
b and d. windows 47 49 and 51 are provided using glass to enable the operator to view the
formation and operation of the plasma formed between the electrodes which is useful when
problems within the assembly occur.
[0059] It is to be appreciated that any suitable electrode system may be utilised and that
the system described above is used merely for example.
Example: Multilayer Coating on Polypropylene Film
[0060] As an example of the potential utility of the present invention there is provided
the following example in which a 25 μm thick polypropylene film was coated twice using the
apparatus in accordance with the present invention. The first coating was a hydrophilic
polyacrylic acid coating, the second coating being an oleophobic and hydrophobic
fluoropolymer coating. A KSV CAM200 Optical Contact Angle Meter was used to characterise
i) The untreated film which is hydrophobic but not oleophobic
ii) the acrylic acid treated film (i) and
iii) the fluoropolymer treated film (ii)
by sessile drop contact angle.
The untreated polypropylene film is hydrophobic but not oleophobic, as shown in

[0061] The film is then coated using the described atmospheric pressure glow
discharge (APGD) apparatus. The operating conditions used were the same for the
application of both coatings Both pairs of electrodes used were made from a steel mesh and
were adhered to a glass dielectric plate. The distance between the glass dielectric plates
attached to the two electrodes was 6mm and the surface area thereof was (10cm x 60cm).
The process gas used was helium. The plasma power to both zones 0.4kW, voltage was 4kV
and the frequency was 29 kHz. The operating temperature was below 40° C. The substrate
was passed through both the first and second plasma zones using a reel to reel mechanism of
the type described in Fig. 3 with a guide means being utilised to assist in the transport of the
substrate out of the first and into the second plasma regions. The speed of the substrate
passing through both plasma zones was 2m min-1.
Application of acrylic acid coating
[0062] The substrate was transported through a first plasma region in which it is
activated by means of an atmospheric pressure glow discharge using helium as the process gas.
Upon leaving the first plasma region the guide was utilised to direct the activated substrate into
the second plasma zone into which an acrylic acid precursor is introduced via Sonotec
ultrasonic nozzle into the coating zone at a rate of 50 μl min-1. Contact angle analysis was

undertaken on the resulting coated substrate and the results thereof are provided in Table 2
below. It will be noted that the hydrophilicity of the resulting coated substrate has significantly
increased.

Application of Fluoropolymer
[0063] The second coating was applied in a similar fashion, with the first plasma zone
being utilised to activate the surface and the second plasma zone being used to further coat the
substrate with a layer of heptadecafluorodecyl acrylate. Contact angle analysis of the resulting
coated film is presented in Table 3. The resulting double coated polypropylene substrate is now
both hydrophobic and oleophobic.

WE CLAIM :
1. An atmospheric pressure plasma assembly (1) comprising a first and second pair
of vertically arrayed, parallel spaced-apart planar electrodes (36) with at least
one dielectric plate (31) between said first pair, adjacent one electrode and at
least one dielectric plate (31) between said second pair adjacent one electrode,
the spacing between the dielectric plate and the other dielectric plate or electrode
of each of the first and second pairs of electrodes forming a first and second
plasma regions (25,60) characterised in that the assembly further comprises a
means of transporting a substrate (70,71,72) successively through said first and
second plasma regions (25,60) and an atomiser (74) adapted to introduce an
atomised liquid or solid coating making material into one of said first or second
plasma regions.
2. An assembly as claimed in claim 1 wherein the substrate is transported through
said first and second plasma regions by means of guide rollers and/or guide reels
(70,71,72).
3. An assembly as claimed in any preceding claim wherein each electrode
comprises an electrode unit containing an electrode (36), an adjacent dielectric
plate (31) and a cooling liquid distribution system (20,26) for directing a
cooling conductive liquid onto the exterior of the electrode (36) to cover a
planar face of the electrode (36)
4. An assembly as claimed in claim 3 wherein the cooling conductive liquid is
water.
5. An assembly as claimed in claim 3 or 4 wherein the electrode unit is in the form
of a watertight box (20, 20a, 26) having a side formed by a dielectric plate (31)
having bonded thereto, on the interior of the box (20,20a, 26), a planar
electrode (36) together with a liquid inlet (14) and a liquid outlet (15).

6. An assembly as claimed in any preceding claim retained in an outer casing in
which a lid (76) is provided to prevent escape of a process gas which is
required in order to activate the plasma.
7. An assembly as claimed in any preceding claim wherein the atomizer (74) is
an ultrasonic nozzle.
8. An assembly as claimed in any preceding claim wherein the electrode (36) is a
dielectric with a metallic coating.
9. An assembly as claimed in any preceding claim wherein said assembly is an
atmospheric pressure glow discharge assembly.
10. An atmospheric plasma assembly for preparing multilayer coatings upon
flexible substrates as claimed in any one of claims 1 to 9 wherein plasma is
generated between vertically orientated electrodes (36), which are arranged in
series and adapted to enable single pass, multiple treatment or multilayer
coatings.
11. An assembly as claimed in any preceding claim wherein the assembly
comprises one or more additional pairs of vertically oriented electrodes (36)
situated before or after said first and second pair of electrodes.
12. A method of atmospheric plasma treating a substrate comprising using the
apparatus described in any preceding claim, wherein the atomised solid or
liquid coating making material is transferred from the atomiser (74) into the
plasma region (60) by means of gravitational feed.
13. A method as claimed in claim 12 wherein the atomised solid or liquid coating
material is introduced into the plasma region in the absence of a carrier gas.

14. A method as claimed in claim 12 or 13 wherein the substrate is synthetic
and/or, natural fibres, woven or non-woven fibres, powder, siloxane, fabrics,
woven or non-woven fibres, natural fibres, synthetic fibres cellulosic material
and powder or a blend of an organic polymeric material and an organosilicon-
containing additive.
15. A method of atmospheric plasma treating a substrate comprising, transporting
a substrate through an atmospheric pressure plasma assembly as claimed in any
one of claims 1 to 11 upwardly through one plasma region (25,60) and
downwardly though the other plasma region (25,60).
16. A method as claimed in any one of claims 12 to 15 wherein the first plasma
region (25) through which the substrate passes is a cleaning plasma and the
second plasma region (60) through which the substrate passes effects a coating
on the substrate by means of the atomised liquid or solid coating forming
material.
17 A method as claimed in claim 16 wherein the gravitational feed of the
atomised liquid or solid coating forming material into the second plasma
region (60) prevents transfer of said atomised liquid or solid coating forming
material into the first plasma region (25).
18. A method as claimed in any one of claims 12 to 17 wherein, in use, the
temperature of the assembly is maintained in the range of from room
temperature to 70° C
19. A treated substrate obtainable as claimed in the method as described in any
one of claims 12 to 18.
20 A treated substrate as claimed in claim 19, the coating there on being capable
of enhancing the barrier and/or diffusion properties of the substrate, and/or
enhancing the ability of additional materials to adhere to the substrate surface.

21. A treated substrate as claimed in claim 19, the coating there on being capable
of increasing hydrophobicity, oleophobicity, fuel and soil resistance,
enhancing gas and liquid filtration properties and/or the release properties of
the substrate.
22. A treated substrate as claimed in claim 19, the coating there on being capable
of enhancing water resistance and release properties of the substrate, and/or
enhancing the softness of fabrics to touch.
23. A treated substrate as claimed in claim 19, the coating there on being capable
of being used as a water wettable coating, bio-compatible coating or an
adhesive layer to promote adhesion to substrate surface or as part of laminated
structure.
24. A treated substrate as claimed in claim 19, the coating there on being capable
of providing surface conductivity to the substrate and/or enhance its optical
properties.
25. A treated substrate as claimed in claim 19, the coating there on being capable
of providing surfaces with controlled pH, and/or controlled interaction with
biologically important molecules such as amino acids and proteins

An atmospheric pressure plasma assembly (1) comprising a first and second pair of vertically arrayed, parallel
spaced-apart planar electrodes (36) with at least one dielectric plate (31) between said first pair, adjacent one electrode and at least
one dielectric plate (31) between said second pair adjacent one electrode, the spacing between the dielectric plate and the other
dielectric plate or electrode of each of the first and second pairs of electrodes forming a first and second plasma regions (25, 60)
characterized in that the assembly further comprises a means of transporting a substrate (70, 71, 72) successively through said first
and second plasma regions (25, 60) and an atomizer (74) adapted to introduce an atomized liquid or solid coating making material
into one of said first or second plasma regions

Documents:

1213-kolnp-2004-granted-abstract.pdf

1213-kolnp-2004-granted-assignment.pdf

1213-kolnp-2004-granted-claims.pdf

1213-kolnp-2004-granted-correspondence.pdf

1213-kolnp-2004-granted-description (complete).pdf

1213-kolnp-2004-granted-drawings.pdf

1213-kolnp-2004-granted-examination report.pdf

1213-kolnp-2004-granted-form 1.pdf

1213-kolnp-2004-granted-form 13.pdf

1213-kolnp-2004-granted-form 18.pdf

1213-kolnp-2004-granted-form 3.pdf

1213-kolnp-2004-granted-form 5.pdf

1213-kolnp-2004-granted-gpa.pdf

1213-kolnp-2004-granted-reply to examination report.pdf

1213-kolnp-2004-granted-specification.pdf

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Patent Number

226140

Indian Patent Application Number

1213/KOLNP/2004

PG Journal Number

50/2008

Publication Date

12-Dec-2008

Grant Date

08-Dec-2008

Date of Filing

19-Aug-2004

Name of Patentee

DOW CORNING IRELAND LIMITED

Applicant Address

UNIT 12, OWENACURRA BUSINESS PARK, MIDLETON, COUNTY CORK

Inventors:

#	Inventor's Name	Inventor's Address
1	DOBBYN PETER	HIGHRANGE ROSTELLAN, MIDDLETON, CO. CORK.
2	GOODWIN ANDREW JAMES	MELROSE, MONEYGOURNEY, DOUGLAS, COUNTY CORK
3	LEADLEY STUART	30 LAURISTON, THE PARK, MIDLETON, CO. CORK.
4	SWALLOW FRANK	SEA VIEW HOUSE, CARRIGNAFOY, COBH, CO. CORK.

PCT International Classification Number

H05H 1/24

PCT International Application Number

PCT/EP03/04349

PCT International Filing date

2003-04-08

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	0208261.8	2002-04-10	U.K.