MXPA01005682A - Hollow cathode array for plasma generation - Google Patents

Abstract

This invention relates to a cathode assembly for use in the creation of a discharge plasma. The cathode comprises a plurality of electrically conductive hollow plasma generating cells in an array, the cells being electrically connected to each other. The plasma generated can be used to modify surface properties of substrates, such as films, fibers, particles and other articles.

Description

ARRANGEMENT OF HOLLOW CATHODES FOR THE GENERATION OF PLASMA BACKGROUND OF THE INVENTION This invention describes a hollow cathode array for use in the creation of a discharge plasma. The generated plasma can be used to modify the surface properties of the substrates, such as films, fibers, particles and other articles. The treatment of various substrates, such as polymers, to impart new surface properties through physical or chemical modification is important for many industries, including the film industry. Wet methods have been used successfully for such treatment; however, such wet methods are associated with problems, such as the residual elimination of solvents. Dry methods, such as corona treatments, UV treatments, laser treatments, X-ray and gamma treatments have also been used with some successes. Crown treatments have had industrial use for several decades but are generally restricted to Ref: 129005 simple surface geometries, such as mesh structures. In addition, in some materials the effects of corona treatments disappear over time. In addition, there is little control over which functional groups can end up on the surface of a treated substrate, and the close distance between the electrode and the substrate can lead to an undesired formation of small holes or burn spots. UV, X-ray, gamma-ray and laser treatments are point sources and can not be easily used to treat large areas. In addition, these treatments are subject to intensity variations or shading effects, which may result in some regions receiving less treatment or even being blocked by the darkening of the line of sight. The treatment of rigid polymer containers, formed or molded to impart improved surface properties and gas barrier properties is important for the food and beverage industries. Various methods of application have been proposed to coat such containers with a variety of compositions and thereby improve their gas barrier properties. However, it continues to be a need to further increase the gas barrier properties of such containers to make them capable of better retarding the transmission of gases, such as oxygen and carbon dioxide. Improved surface properties, especially related to the printability, in relation to improving the recyclability of such containers also continues to be a necessity. Plasma technology has been used in the laboratory for more than 50 years, but only recently has it been practiced on a commercial scale, mainly driven by the semiconductor industries. In the treatment of polymer plasma, energetic particles and photons generated in plasma interact strongly with the surface of the polymer, usually via the chemistry of free radicals. A major advantage of the plasma surface treatment compared with other treatment processes is the lack of harmful by-products. Generally, there are no toxic or dangerous liquids or gases that must be eliminated. Usually, by-products of the main process for plasma treatment are CO, C02 and water vapor, none of which is present in toxic amounts. Theoretically, plasmas can be applied to objects of all possible geometries with varying success, using conventional apparatus and processes. Such objects include fabrics, films, solid and large objects with complex shapes, and small and discrete parts in large quantities, such as a powder. A major impediment to using plasma processes on an industrial scale is to achieve economically acceptable proportions of production. The utility of plasma processes is easily apparent, but the yield is so low that the processes are economically feasible only for products that acquire a greatly increased value from the process. Limiting factors include a low plasma density and lack of plasma confinement. A plasma modification or polymerization system with a capacity for high production ratios can lead to a rapid growth in the use of plasma technology on a commercial scale. Most of the devices used to generate plasmas for plasma polymerization and plasma modification are variations of two basic types of electrode configurations: internal parallel plate electrodes and external electrodes. The utility of these two processes is limited by the ease in which they can be progressively increased to treat large areas while maintaining a high plasma density, so that a minimum residence time can be obtained. The existing hollow cathode plasma reactors for DC offer a high plasma density and a higher degree of plasma confinement than the external and internal parallel plate electrodes. However, these can not be used to treat large areas because a large hollow cathode reactor is inherently difficult to scale or increase progressively. In order to achieve a desirable plasma density with a large hollow cathode reactor necessary to accommodate treatment of large areas, such substrates with a width of 60" (152.4 cm), an extremely high voltage is required. EP 634 778 discloses an arrangement of hollow cathodes that generates a plasma for surface etching and the removal of "rolling oils" on metal sheets. The hollow cathode arrangement system comprises a housing having a plurality of uniformly spaced openings along a wall of the housing. The plasma of the hollow cathodes is basically generated in the housing and is transported through the openings. The arrangement of such openings serves as a distributor, however the intensity and uniformity of the plasma are not increased. Each opening is about 1/16 inch (0.15 cm) in diameter. The pressure used in the system of document EP'778 is within the range of 0.1 to 5.0 torrs (13.33 to 666.61 Pascals), and the energy input is in the range of 0.5 to 3.0 k.

U.S. Patent 5,686,789 discloses a discharge device having a cathode with a micro-hole array for use in sub-miniature fluorescent lamps. This patent includes devices with dimensions in the scale of the free path medium of the electrons, which is not viable for the treatment of large areas. The electrons are subjected to an oscillatory movement within the microvoids, which produces a microhole discharge that results in an increase in current capacity. In use the system of document US'789 uses a pressure of 0.1 torr at 200 torrs (13.33 to 26.664.48 Pascal). The patent does not mention a reactive plasma, plasma polymerization, or surface modification of materials. H. Koch et al., In an article entitled "Hollow cathode discharge sputtering device for uniform large area thin film deposition", (J. Vac. Sol. Technol.A9 (4), Jul / Aug 1991, p.2374) describe hollow cathode discharge devices which produce higher densities of electron deposition particles than conventional discharges. In the process of electron deposition of the hollow cathode plasma described herein, a production obtained by electronic deposition, for example of Cu, is used as the cathode. The process is mainly a physical process where a moment transfer takes place. The article does not mention the use of hollow cathode discharge devices in the creation of reactive plasma for surface modification or polymerization of the conduction plasma to deposit a thin layer on the surface layers of the substrate. The need continues for a process for surface treatment that among others (1) is free of solvents and / or free of harmful byproducts, (2) that is versatile in adapting the treatment to any surface structure, any size, and / or chemistry of a given article, (3) that provides a uniform treatment, (4) that is capable of high speed and high performance, (5) that can be used in a batch or continuous process, and ( 6) that can operate at a low pressure or under other desirable conditions.

BRIEF DESCRIPTION OF THE INVENTION The present invention concerns a cathode assembly for generating a plasma, comprising a plurality of hollow cells, which generate a plasma, electrically conductive in an array, the cells are electrically connected to each other. The present invention also relates to an apparatus that generates plasma comprising at least one cathode assembly described above; means for supplying a plasma precursor gas to the cathode assembly, and means for supplying power to the cathode assembly. The present invention further relates to a method of treating a surface of a substrate comprising placing the substrate in close proximity to at least one cathode assembly described above; supplying at least one plasma precursor gas in the vicinity of the cathode assembly and the substrate, generating a plasma by means of power supply to the cathode assembly; and the exposure of the substrate surface to the plasma, for a sufficient time to form a treated surface.

The present invention also relates to a method for packaging a liquid in a biaxially oriented, polymeric molded container (a) forming a biaxially oriented, polymeric molded container; (b) exposing at least one surface of the container to a plasma generated from a plasma precursor gas, comprising a hydrocarbon using the cathode assembly of the present invention described herein, wherein the arrangement is formed: (c) introducing a liquid to the container; and (d) sealing the container. The present invention further relates to a method for reducing gas permeability of a polyester substrate, comprising exposing a polyester substrate to a plasma generated from a plasma precursor gas, comprising a hydrocarbon using the cathode assembly of the present invention described herein.

BRIEF DESCRIPTION OF THE DRAWINGS. Figure 1 is a diagram of one embodiment of a cathode assembly of the present invention, showing cells having a generally square cross-sectional shape. Figure 2 is a diagram of one embodiment of a cathode assembly of the present invention, showing cells having a generally circular cross-sectional shape. Figure 3 is a diagram of one embodiment of a cathode assembly of the present invention, showing cells having a generally quadrilateral cross sectional shape. Figure 4 is a diagram of one embodiment of a cathode assembly of the present invention, showing cells having a generally triangular cross-sectional shape. Figure 5 is a diagram of one embodiment of a cathode assembly of the present invention, showing cells having a generally hexagonal cross sectional shape. Figure 6 is a diagram of one embodiment of a cathode assembly of the present invention, showing cells having a generally elliptical cross-sectional shape.

Figure 7 is a diagram of one embodiment of a cathode assembly of the present invention, showing a cross section of cells having a flat bottom end portion. Figure 8 is a diagram of one embodiment of a cathode assembly of the present invention, showing a cross section of cells having various shapes as an end portion. Figure 9 is a diagram of one embodiment of a cathode assembly of the present invention, showing a cross section of cells having various shapes as an end portion. Figure 10 is a diagram of one embodiment of a cathode assembly of the present invention showing the cells in a shaped array, configured to treat a formed substrate. Figure 11 is a diagram of one embodiment of a plasma generating apparatus of the present invention showing two cathode assemblies, one having a dielectric material lining its walls, the other having a dielectric material placed adjacent to at least one cell. Means for supplying a plasma precursor gas, means for supplying power to the cathode assemblies, and a substrate are also shown. Figure 12 is a sectional, perspective view of one embodiment of a cathode assembly of the present invention, configured to treat a bottle-shaped container. Figure 13 is a cross-sectional view of the embodiment of Figure 12. DETAILED DESCRIPTION OF THE INVENTION With reference initially to Figures 1-6 and -13, the alternative embodiments of the cathode assembly of the present invention are shown in a general manner. The cathode 1 assembly includes a plurality of cells 2 which together form an array of individual plasma generators. Each cell is defined by a wall or walls 3. The cathode assembly comprises a plurality of cells that generate plasma, hollow, electrically conductive, mounted in an array; the cells are electrically connected to each other with such cells which are effective in providing a uniform plasma treatment to a variety of substrates having a large or small treatment area. By "plasma generation cells, hollow" is meant a plurality of cells, each cell defined by at least one wall. The cells defined by the wall or walls can have any shape. However, for easy fabrication, the cells preferably have a generally circular cross-sectional shape, a generally elliptical cross-sectional shape, a generally regular or irregular polygonal cross-sectional shape, or any combination of such shapes (see FIG. 1-6 and 10-13). By "regular polygonal" is meant a cross-sectional shape selected from a group consisting of shapes: triangular, quadrilateral, pentagonal, hexagonal, heptagonal, octagonal and combinations thereof. For cells having irregular polygonal cross-sectional shapes, such shapes may be the same or different. The cells can be like tubes that have two open ends. Alternatively, the cells can also be defined either by a base 5 (see in particular Fig. 10) on which an open end of the cell is mounted, or each cell can also be defined by an end portion 6 of the end that encloses one end of the cell. In this way, the cell can further comprise an end portion enclosing one end of the cell, wherein said end portion is flat, flat-bottomed, U-shaped, V-shaped, or other (see FIG. 7-9). Cells such as tubes or other cells further defined by an end portion may be mounted on the flat or shaped base. For easy handling and / or connection to a power source, the cathode assembly may further comprise one or more side pieces 8 which may surround the arrangement of the cells. In certain embodiments, the side pieces 8 may form all or a portion of the wall of a cell. The side pieces 8 can be attached to at least a portion of the cells on the periphery of the array and / or can be attached to the optional base 5. The holes 4 in the side pieces can facilitate the connection to a power source.

By "Plasma" is meant a partially or totally ionized gas, generated under the influence of extreme thermal conditions or an electric / magnetic field. A plasma is a volume of high-energy electric and magnetic fields that rapidly dissociate any present gas to form energetic ions, photons, electrons, highly reactive chemical species, stable neutral species, excited molecules, and atoms. By "arrangement" is meant any configured group of cells. This may include a flat arrangement or a shaped arrangement. An array may also include any random treatment of cells where the cells are arranged in such a way as to provide a treatment for only selected areas of a substrate. By "electrically conductive" is meant that the wall, walls, and / or end portions of the optional or an optional base that defines the cells or on which the cells can be mounted, comprises a material that can conduct electricity. By "electrically connected to each other" is meant that when the cathode assembly is connected to a power source, by virtue of the fact that the electrically conductive material defines each cell, the cells are capable of electrical contact with each other. The materials useful in the manufacture of the cathode assembly of the present invention include any electrically conductive material that does not adversely affect the plasma process, such as stainless steel, aluminum, titanium, copper, tungsten, platinum, chromium, nickel, zirconium, molybdenum or alloys thereof with each other or with other known elements. The orifices of the cells may be of varying cross-sectional dimensions, but it is preferred that a plurality of the cells in the array have a ratio of the cross-sectional area of the cell to the depth of the cell in the range of about 0.1 to about 5.0, preferring even more the range of around 0.25 to about 4.0. Preferably, the ranges of the cross-sectional area of each cell is from about 0.25 to about 10 pig2 (about 1.6 to about 64.5 cm2).

Each cell can be defined by a discrete wall or walls, such walls are not shared with an adjacent cell (see Figures 2,5,6 and 10). Such cells can be separated from at least one adjacent cell (see Fig 6), or they can have walls that are in contact with at least one wall of at least one adjacent cell (see Fig. 2), or any combination of the same. Alternatively, adjacent cells can share at least one wall in common (see Figures 1,3,4 and 11). Preferably, adjacent cells of regular or irregular polygonal shape share at least one common wall or have walls that are in contact with at least one wall of at least one adjacent cell. Each wall has the ability to drive and is of such thickness that it has its mechanical integrity. All or a portion of at least one wall of at least one cell of the cathode assembly of the present invention can be coated with a dielectric material (see Fig. 11, cathode assembly on the left). In addition or alternatively, a dielectric material 10 may be placed adjacent to at least one cell of the cathode assembly of the present invention (see Fig. 11, cathode assembly to the right). Such dielectric material may include mica, ceramic, or a polymeric material having a high dielectric constant. The dielectric material can be coated around the edge of the cell, covering all or a portion of the cell wall surface, or covering surfaces immediately adjacent to the cell. The dielectric material prevents the formation of the electric arc and forms short circuits and can dampen discharges. The dielectric material can be used to cover certain cells thus preventing the generation of plasma from the cell when the cathode assembly is in use. Decorative effects are performed on a substrate by covering certain cells during the plasma treatment of the substrate. In order to provide a more uniform plasma treatment, it has been found to be advantageous to provide at least a portion of the cells adjacent to the periphery of the array that are smaller in area cross section than the cells inside the array. This modality is compensated by the loss of diffusion (see Fig. 2,3,4,5 and 6). The cathode cells may be arranged in a generally flat array, a preferred embodiment for the treatment of flat substrates 12 (see Fig. 11). Alternatively, the cells of the cathode assembly may be arranged in a molded array to accommodate the shape of an article to be treated, for example an article having a ring-like, curved or otherwise shaped shape (see FIG. 10), such as a bottle (see Figs 12 and 13). Such molded, curved arrangements can be configured, for example, in a concave or convex shape. In Figures 12 and 13, the cathode 1 assembly is placed inside the container 20 in the form of a bottle for the treatment of the plasma of the inner surface of the container. The outer electrode 30 is shown having a cell configuration but which could have a simple flat surface. In the embodiment shown in FIGS. 12 and 13, the polarity can be reversed and a gas supply provided for the electrode 30 whereby the outer surface of the container 20 can be treated in the form of a bottle. One or more walls of a cell may be substantially perpendicular to the plane of the total array (see Fig. 7), or the plane of that portion of the array where the particular cell is placed. Alternatively, one or more walls of each cell has at least a portion of a wall that forms an obtuse angle with the plane of the array (see Figs 8 and 9), or for the plane of this portion of the array in which the cell particular is located. It is preferred that the arrangement configuration conform to the shape of the substrate to maintain a reasonably uniform separation between the assembly of the cells and the portion of the substrate to be treated. Such a reasonably uniform separation allows an even more uniform treatment. The cathode assemblies of the present invention can be realized by means of a machine that cuts the conductive material into pieces of desired length, width and thickness and placing these pieces in a desired arrangement arrangement. The pieces can be adjusted together in a slot arrangement, placed in a tight configuration to be fitted together, or welded by a spot welding process of a typical metal sheet. Other methods of making the cathode assemblies of the present invention may be readily apparent to one of ordinary skill in the art. The present invention also concerns a plasma generating apparatus, comprising the cathode assembly described above; means for supplying a plasma precursor gas for the cathode assembly; and the means for supplying energy for the cathode assembly (see Fig. 11).

The precursor gas of the plasma can be supplied by a gas jet 16 (see Figs 7, 12 and 13) arranged in relation to the cathode assembly such that the precursor gas diffuses into approximately one cell. Fig. 7 shows a multiple tube 16M connected to a jet pump 16 of individual gas, each located in a cell. Figs. 12 and 13 also show a manifold 16M connected to an individual gas jet pump 16 located at the center electrode which is placed inside the bottle 20. The plasma gas can be fed through a gas supply line of plasma (not shown) and the gas mass flow rate or rate can be controlled by using an appropriate plasma gas flow controller, such as a KS type 1179 A, available from MKS Instruments Inc. The rate or speed of flow depends on the application. Many applications can be handled appropriately using flow rates of about 0.1 to about 100 standard cubic centimeters per minute (ccem), preferably about 0.5 to about 15 ccem. Other applications can be handled using proportions or high or low speeds. The power source 18 (see Fig. 11) can be a DC source, or an AC source operated in an audio frequency (AF), or radio frequency (RF). The power source is connected to the cathode assembly by means of fasteners (not shown) which can be, in one embodiment, inserted in the holes 4. For many treatment applications, less than 1 KW of energy is needed, preferably approximately from 1 to about 1000 Kw is used, more preferably from about 5 to about 200 watts. However, there are applications where energy input greater than lKw is required to achieve the desired results. A cooling system of the liquid electrode can be used in such cases. Low pressure (with vacuum) is used in the plasma treatment here. In this way, the current plasma generating apparatus further comprises a vacuum chamber within which the cathode assembly resides, and the means for providing a vacuum. A suitable vacuum chamber such as a cylindrical stainless steel vacuum chamber is indicated. Commercially available vacuum pumps comprising a booster pump in combination with a rotary pump, such as the E2M80 / EH 500, available from Edwards High Vacuum International can be used. The pressures useful in the present invention may be from about 1 millitor to about 100 torrs (0.1333 to 13.332.24 Pa), preferably about 1 millitor to about 1 torr (0.1333 to 133.32 Pa). A batch or continuous process is possible when using the apparatus or the current plasma generation method. Although vacuum systems tend to provide a batch process by themselves, a continuous operation can be maintained by subatmospheric pressures through the use of a staggered interlock system. By "staggered interlock system" is meant a series of chambers at differential pressures. The present invention also concerns a method of treating at least one surface comprising the position of at least one surface of the substrate in close proximity to at least one cathode assembly described above; the supply of at least one plasma precursor gas to the vicinity of the cathode assembly and the substrate; the generation of a plasma by supplying energy to the cathode assembly; and exposing at least one surface of the substrate to the plasma for a sufficient time to form a treated surface. First, at least one surface of a substrate is placed in close proximity to at least one cathode assembly described above. By "close proximity" it is meant that the substrate is separated at an appropriate distance from the cathode assembly, enough to receive the plasma treatment. One or more cathode mounts can be used to treat a substrate. Substrates useful for the treatment herein include fibers, films, particles, and molded articles, such as bottles or other containers. The substrate can be mounted parallel to and spaced from a preselected distance of at least one cathode assembly of the present invention. In using the molded cathode assemblies, it is preferred that a reasonably uniform distance be maintained between the substrate and the cells in order to provide a uniform treatment to the substrate. The fiber, film, particle or molded article substrates can be made of thermoplastic polymeric materials. The film and rigid containers contemplated for use in the present invention include those formed of conventional thermoplastic polymers, such as polyolefins, polyamides, and engineered polymers, such as polycarbonates, and the like. The invention is applicable to films and rigid, that is to say shaped containers, hollow, biaxially oriented, blow molded, injection expansion, thermoplastic containers, such as bottles, formed from synthetic linear polyesters, such as polyethylene terephthalate. (PET), polybutylene terephthalate (PBT), polyethylene naphthalene (PEN), and the like, including polymers and copolymers of ethylene terephthalate and ethylene naphthalate wherein up to about 50 mole percent or more of the copolymer can be prepared from the diethylene glycol monomer units; propane-1,3-diol; butane-1,4-diol; polytetramethylene glycol; polyethylene glycol; propylene glycol and 1,4-hydroxymethylcyclohexane substituted by the glycol radical in the preparation of the copolymer; or isophthalic acid, dibenzoic; 1,4 or 2,6-dicarboxylic naphthalene; adipic; sebacic and decane-1, 10-dicarboxylic substituted by the acid radical in the preparation of the copolymer. The foregoing description is for the purpose of illustrating the applicable polymeric substrates and not as a limitation of the field of the invention. Second, in the present method, at least one plasma precursor gas is supplied in the vicinity of the cathode assembly and the substrate. Plasma can be classified into three categories (1) plasma not chemically reactive; (2) chemically reactive plasma but without polymer formation; and (3) chemically reactive plasma with polymer formation. The plasma precursor gas employed can be selected based on the desired treatment provided by the plasma. A suitable precursor gas can be, for example, nitrogen, hydrogen, ozone; nitrous oxide; a gas comprising a hydrocarbon, such as methane, ethylene, butadiene, or acetylene; argon; helium; ammonia; and the similar; and mixtures of gases such as hydrocarbon / nitrogen mixtures; air, halides; halocarbons, and polymerizable monomers. For example, the polymer particles can be treated with virtually any organic compound or organic metal capable of being introduced into the plasma discharge zone. The gas or precursor gases are fed into the vacuum chamber at a desired gas flow rate via a gas jet. A plasma is generated by supplying energy to the cathode assembly. The cathode assembly is connected to a power supply, and the power supply is turned on to start the plasma state. The energy then adjusts to a desired level of energy. The energy level may vary depending on the gas flow rate, the size of the substrate, the distance of the cathode assembly to the anode, a molecular weight of the plasma precursor gas and pressure. The electrical energy and the gas flow rates can be adjusted so as to form a heavy plasma discharge in all the desired cells of the cathode assembly. Optionally, the magnetic enhancement can be used to focus the plasma as it leaves the cells. Finally, at least one surface of the substrate is exposed to the plasma for a sufficient time to form a treated surface. The plasma treatment can be maintained for a desired period of time which can take several seconds to several minutes. The treatment time depends on the characteristics of the plasma and its interaction with the surface of the substrate which depends on the operational parameters under which the plasma is maintained. Such parameters include a proportion of the gas flow, the input energy, the pressure, the discharge energy and the position of the substrate. The treatment may also depend on the nature of the substrate. The present invention is useful for bottling beverages. Thus, the present invention also concerns a method for bottling a liquid in a molded, biaxially oriented, polymeric container, comprising the formation of a container; exposing at least one surface of the container to a plasma generated from plasma precursor gas, comprising a hydrocarbon using the cathode assembly of the present invention described herein, wherein the array is molded; by introducing a liquid into the container, and sealing the container. This method further comprises purging the gas from the container prior to the introduction of the liquid. This method may be suitable for carbonated liquids. The present invention is suitable for improving the effectiveness of the gas barrier of poly (ethylene terephthalate) films and rigid containers used for packaging food and beverages, and blow molded PET bottles, which are expanded by injection, used to bottle carbonated soft drinks and beer. Therefore, the present invention includes a method for reducing the gas permeability of a polyester substrate, comprising exposing at least one surface of a polyester substrate to a plasma generated from a plasma precursor gas, which it comprises a hydrocarbon using the cathode assembly of the present invention, described herein. The present invention is useful in the process that includes cleaning (removal of organic contamination); chemical attack or wear (removal of a weak boundary layer and increase in surface area); cross-linking or branching of molecules near the surface, which can cohesively strengthen the surface layer and consequently the physical properties, the chemical / injurious modification by the deliberate alteration of the surface region with new chemical functionalities; and the deposition, alteration of the surface properties of a substrate to suit the adhesion needs or a barrier coating to capitalize on the volume properties of a thin film, free of holes and highly adherent in the permeating selective membranes. Example 1 Increase of Adhesion for a copper polyimide film. Two cathode assemblies of 12 pig x 12 pig (30.48 cm x 30.48 cm) are fabricated having a square cell model similar to that shown in Fig. 1, of stainless steel. Each cell measures 1 pig x 1 pig x 1 pig (2.54 cm x 2.54 cm x 2.54 cm), and the ratio of the cross-sectional area of the cell to the depth of the cell is equal to 1.0. The cathode mounts are mounted parallel to each other in a vacuum chamber and each cathode is connected to a DC power supply. The Kapton® polyimide film, available from E.l. du Pont de Neumours and Company, Wilmington, DE, is placed between the cathodes at a distance of approximately 2 pigs (5.08 cm) from each cathode. A vacuum is induced with a pressure of 150 millitor. Ammonia is introduced into the chamber at a flow rate of 12 standard cubic centimeters per minute (ccem) and the power is supplied at a voltage of 560 v. The film is exposed to the ammonia plasma for 1 minute. Using a conventional post-extruder cylinder process, the treated film is then laminated with adhesive and copper. The accumulation consists of 1 oz (28.34 grams) of copper, a layer of 1 thousand (0.0254 grams) of copper, a layer of 1 thousand (0.0254 mm) of a Piralux® adhesive sheet, the polyamide film strip, another 1 mil layer of adhesive sheet and another layer of 1 oz (28.34 grams) of copper to form a coating. In order to test the strength of the copper adhesion for the rest of the coating, the copper is placed in the upper jaw of an Instron machine and the rest of the coating is adhered with a tape sticking on both sides to a German wheel. The wheel rotates as the copper comes off in an attempt to maintain a 90 degree peel angle. The stretch ratio is 2 in / min (5.08 cm / min). The link values in pounds per linear inch (pli) (newtons per meter (N / m)) and the surface energies for the control and the sample treated with ammonia plasma are listed below: Example 2 Increase in barrier properties for poly (ethylene terephthalate) (PET) films The 5 x 5"(12.7 cm x 12.7 cm) PET films of MYLINEX® type 5, available from DuPont Co., Wilmington, DE, between the assemblies, as described in Example 1, for the deposition of the thin plasma film to create an upper barrier for oxygen permeation through the PET films. A vacuum is introduced with a pressure of 150 millitor. Acetylene is introduced into the chamber at a flow rate of 25 saan and power is supplied at a voltage of 640 V. The film is exposed to the acetylene plasma for 10 minutes. The treated films are then evaluated for an Oxygen Permeation Ratio (OTR) when using OXTRAN ® 1000 manufactured by Mocon, Inc., following ASTM 03985 with a relative humidity of 50% (RH) at 30 ° C. The results are listed below: It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention

Claims (15)

1. CLAIMS Having described the foregoing as claimed is claimed as property contained in the following claims: 1. An apparatus that generates plasma, characterized in that it comprises: at least one assembly of the cathode to generate plasma, comprising: a plurality of cells that generate plasma , hollow, conductive or electrically conductive, in a cylindrical arrangement, arranged on the surface of a cylinder, the cells are electrically connected to each other; means for supplying a precursor gas to at least one cathode assembly; and means for supplying power to the cathode assembly.
2. 2. The apparatus that generates plasma according to claim 1, characterized in that the precursor gas is supplied adjacent to the cathode assembly according to which the gas diffuses into the vicinity of the cells.
3. 3. The apparatus that generates plasma according to claim 1, characterized in that, the cathode assembly further comprises a multiple and one or more passages in communication with the cells, and the precursor gas is supplied to the cathode assembly through said passages to the cells according to which the gas diffuses to the vicinity of the cells.
4. 4. The apparatus that generates plasma according to claim 1, characterized in that the cells are arranged in a cylindrical arrangement on an inner surface of the cylinder.
5. The apparatus that generates plasma according to claim 1, characterized in that the cells are arranged in a cylindrical arrangement on an outer surface of the cylinder.
6. The apparatus that generates plasma according to claim 1, characterized in that the plurality of the cells have a cylindrical cross-sectional shape or a regular or irregular polygonal cross-sectional shape.
7. The apparatus that generates plasma according to claim 1, characterized in that, a plurality of cells have a regular polygonal cross-sectional shape, selected from the group consisting of the forms; triangular, quadrilateral, pentagonal, hexagonal, heptagonal, octagonal, and combinations thereof.
8. A method for treating at least one surface of a generally cylindrical substrate, characterized in that it comprises: (a) placing at least one surface of the substrate in close proximity to at least one cathode assembly of the plasma generating apparatus of the claim 1; (b) supplying at least one plasma precursor gas in the vicinity of the cathode and substrate assembly; (c) generate a plasma by the energy supply to the cathode assembly. (d) exposing the at least one surface of the substrate to the plasma for a sufficient time to form a treated surface.
9. 9. The method according to claim 8, characterized in that the substrate is a polyimide.
10. The method according to claim 8, characterized in that the substrate is a polyester.
11. 11. The method according to claim 8, characterized in that the substrate is a polyester selected from the homopolymer of polyethylene terephthalate or a copolymer of ethylene terephthalate wherein up to about 50 percent of the copolymer is prepared from the monomer units of diethylene glycol; propane-1,3-diol; butane-1,4-diol; polytetramet i 1eng1 i col; polyethylene glycol; propylene glycol and 1/4-hydroxymethylcyclohexane substituted by the glycol radical in the preparation of the copolymer; or isophthalic acid, dibenzoic acid; 1,4 or 2,6-dicarboxylic naphthalene; adipic; sebacic and decane-1, 10-dicarboxylic substituted by the acid radical in the preparation of the copolymer.
12. The method according to claim 11, characterized in that the substrate is a container of biaxially oriented poly (ethylene) terephthalate.
13. 13. A method for packaging a liquid in a polyester container of cylindrical, molded, biaxially oriented general form, characterized in that it comprises: (a) forming a biaxially oriented, molded polyester container; (b) exposing at least one surface of the container to a plasma generated from a plasma precursor gas comprising a hydrocarbon using the cathode assembly of the plasma generating apparatus of claim 1; (c) introducing a liquid into a container; and (d) sealing the container.
14. 14. The method according to claim 13, characterized in that it further comprises purging the precursor gas from the plasma of the container before introducing the liquid.
15. 15. A method for reducing the gas permeability of a polyester substrate of general cylindrical shape, characterized in that it comprises: exposing at least one surface of the polyester substrate to a plasma generated from a plasma precursor gas comprising a hydrocarbon using the cathode assembly of the plasma generating apparatus of claim 1. ARRANGEMENT OF HOLLOW CATHODES FOR THE GENERATION OF PLASMA SUMMARY OF THE INVENTION This invention relates to a cathode assembly for use in the creation of a discharge plasma. The cathode comprises a plurality of cells that generate plasma, electrically conductive hollows in an array, the cells are electrically connected to each other. The generated plasma can be used to modify the surface properties of substrates, such as films, fibers, particles and other articles.