Apparatus for plasma supported coating of the inner surface of tube-like packaging containers made of plastics with the assistance of a non-thermal reactive ambient pressure beam plasma

Technical Field

The invention refers to an apparatus for the treatment of plastics surfaces, in particular for the production of a permeation reducing coating on the inner and/or the outer surface of packaging bodies made of plastics by reactive ambient pressure beam plasma.

Background Art

The treatment of surfaces with low temperature plasma procedures and low temperature plasma appara- tuses can be performed in various embodiments for a broad spectrum of applications in the field of plasma technology. Typical applications of this kind of plasma apparatuses for example comprise the plasma surface activation (control of the features of boundary layers, hydropho- bisation, hydrophilisation) , plasma etching, plasma polymerisation, plasma coating, plasma cleaning and plasma sterilization (see Alfred Rutscher et al . "Wissenschaft- liche Plasmaphysik" VEB Fachbuchverlag Leipzig 1983 and H. Conrads, Plasmatechnologie - Stand und Perspektiven, Endbericht des Projekts Fkz 13N61825 1994) . In the past for these applications primarily low pressure plasma were considered wherein radicals, activated atoms, ions, electrons as well as UV radiation necessary for the effects of these treatments can be suitably implemented. The use of low pressure plasma methods, however, bears the following disadvantages: high investment costs for the vacuum technique (chambers, load locks, vacuum pumps) as

well as the complicate integration into inline processes due to the discontinuous functioning. Therefore, during the last years, various attempts have been made (see U. Kogelschatz, Plasma Chem. Plasma Processing, 23 (1), 1, 2003) to develop much cheaper non-thermal ambient pressure plasma methods, allowing an automated continuous treatment process with high working velocity and therefore simplified integration into existing technological processes. Further advantages of the atmospheric pressure discharge concern the treatment of materials that due to their high vapor pressure cannot be subjected to a vacuum treatment or of substrates/products the outer or inner form of which (e.g. small gaps or cavities) require an adapted plasma geometry. Ambient pressure plasma can for example be generated by the long known corona discharge or barrier discharge (also referred to as silent or dielectric barrier discharge (DBD) ) , spark discharge, arc discharge, torch/flare discharge, as well as micro wave supported discharges (see H . -E . Wagner, R. Brandenburg, K. V. Ko- zlov, A. Sonnenfeld, P. Michel, J. F. Behnke, Vacuum 71, 417-436, 2003) . Such plasma can be thermal or nonthermal. Thermal plasmas are in thermal equilibrium, i.e. electron temperature Te = ion temperature Ti = (neutral) gas temperature Tg (e.g. approximately 1500-2500 K) . Nonthermal plasmas are non-equilibrium plasmas wherein Te » Ti = Tg. In non-thermal plasmas Te may e.g. be 12O00 K and Ti = Tg = 300-500 K. Hitherto of technical significance are in particular corona discharges and DBD. The DBD is operated with alternating voltage (AC voltage) and develops in a very narrow discharge gap between two electrodes, whereby at least one dielectric barrier must be placed between the two electrodes. The DBD is the hitherto most used discharge form for ambient pressure plasma methods . Due to the narrow discharge gap and homogeneity problems due to filament formation, the applicability of this kind of ambient pressure plasma is limited. Corona

discharges function with direct voltage (DC voltage), they are, however, often operated in a pulsed manner and develop - due to the selection of specific arrangements of pointed electrodes - in a very inhomogeneous electri- cal field. In large scale applications, frequently corona discharges are used. From the perspective of surface treatment homogenous, geometrically adapted plasmas are desired. Solutions for such plasmas comprise arrangements of paralelly or serielly operated micro plasma (see E. Kunhardt, IEEE Trans. Plasma Sci., 28, 1, 2000) as well as the homogenous embodiment of the DBD (that in general is present in the filamented inhomogenous form) , also known under the expression "Atmospheric Glow Discharge (ACD)" (see S. Kanazawa, M. Kogoma, T. Moriwaki, S. Okzaki, J. Phys . D: Appl . Phys . 21, 838, 1988). The ACD is characterized by the lack of the characteristic discharge filaments and, due to its homogenous glow appearance, strongly reminds of a low pressure DC glow discharge. Similar thereto a low current Townsend mode and a glow mode can be distinguished (see F. Massines, A. Ra- behi, P. Decomps, R. Ben Gadri, P. Segur, C. Mayoux, J. Appl. Phys. 83, 2950, 1998) that have some similarities to the abnormal glow discharge at low pressure (pseudo neutral column, Faraday dark space) . Some applications of the ACD for cleaning, for coating deposition on aluminum, for adhesion improvement and for corrosion protection already exist (see R. Foest, F. Adler, F. Sigeneger, M. Schmidt, Surf. Coat. Technol . , 163 -164, 323-330, 2003). However, the short distance between the electrodes limits the geometry of the surfaces to be treated to thin and planar substrates. A broadening of the space between the electrodes is achieved by structured electrodes. These arrangements are known as micro hollow cathode arrays and plasma capillary electrodes (see K. H. Schoenbach, R. Ver- happen, T. Tessnov, F. E. Peterkin, and W. W. Byszewski, Appl. Phys. Lett. 68, 13, 1996) and their application in the treatment of polymer films is described (see A. Ig-

natkov, A. Schwabedissen, G. F. Leu and J. Engemann, Contributed Papers Hakone VIII (Puhajarve, Estonia), 1, 58, 2002) . The plasma treatment of small cavities within dielectric materials by DBD is applied in plasma printing (see C. Penache, C. Gessner, T. Betker, V. Bartels, A. Hollaender, and C-P. Klages, IEE Proceedings - Nanobio- technology - August 2004 - Volume 151, Issue 4, p. 139- 144) . Plasma generated by microwave play a role in the surface treatment at enhanced pressure (50-1000 hPa) (see R. Foest, D. Baumann, and A. OhI, Proc. Vth Int. Workshop on Microwave Discharges: Fundam. and Appl . , 201, 2003). One possibility to achieve a plasma that is not limited to a narrow space between the electrodes and with conservation of the necessary homogeneity to a lar- ger extent is to generate a non-thermal beam plasma outside the discharge room by a combination of the electrical field with a directed stream of the working gases. Ambient pressure beam plasma of this type can be generated with arc discharges as well as with spark dis- charges, corona discharges and barrier discharges (see A. Schϋtze, J. Y. Yeong, S. E. Babayan, J. Park, G. S. Selwyn, and R. F. Hicks, IEEE Trans. Plasma Sci . , 26, (6), 1685, 1998 and the original documents cited therein) . For example in the DDR-patent 101929 a method for the treatment of fiber material utilizing a single polar high frequency RF- discharge or an electrode less RF-discharge, respectively, are described. In this method either a rod electrode or a hollow electrode can be used on which the RF- plasma torch starts that, without counter-electrode, un- disturbedly extends freely into the space. In the patent specification DE 3733492 an apparatus for the generation of a beam plasma by means of Corona discharge is presented that is suitable for the plasma treatment of surfaces. Thereby a gas stream is guided through the Corona discharge space between a rod like inner electrode and a tube like outer electrode. A further method for the plasma treatment of surfaces that is based on the genera-

tion of a plasma beam by means of an arc discharge under supply of a working gas is described in the patent specification DE 19532412. In another patent specification (EP 881 865, 1998) an apparatus for the generation of a plu- rality of low temperature plasma-jets is described that are generated by RF-excitation making use of the hollow cathode effect, however, working under low pressure conditions .

Other arrangements based on the RF-excitation of an ambient pressure plasma are described by Gary S. Selwyn et al. (see US 6,194,036, US 6,262,523, 2001). Such arrangements can be used for different plasma technological applications dependent on the choice of the process conditions and process gases. As two different embodiments of said arrangement one variant with plan parallel electrodes for large-surface applications and one variant with a central inner electrode were proposed. An ambient pressure plasma-jet activated with 27.17 MHz has been used for the treatment of surfaces and for coating (see F. Adler, R. Foest, E. Kindel, M. Stie- ber, K. -D. Weltmann, Proc. Gas discharges X, 2004) . In this application the substrate temperatures remain at room temperature or in a temperature range between 50 ⁰ C and 100 ⁰ C. As process gases for atmospheric jets serve gases or their mixtures, respectively, known from low pressure plasma procedures, namely: rare gases (e.g. Ar, He) , oxygen, nitrogen, air, hydrogen, hydrocarbons and silanes or silicon organic compounds as admixtures. Some of the mentioned methods for the generation of beam plasma have considerable disadvantages with regard to the multivalent usability for surface treatments, namely

- insufficient lifetime of the electrodes due to their erosion,

- unhandy construction of the treatment devices due to high operating voltages,

- high construction expenses in case of full surface treatments,

- restrictions in the choice of the materials and workpieces to be treated, - damage of the material to be treated due to filaments or electric breakdown or sparkover, respectively,

- high consumption of process gases,

- partially high temperature exposure of the substrates (e.g. arc discharge).

A permeation inhibiting coating of surfaces can be achieved by a metallisation, by deposition of amorphous hydrocarbon coatings and by silica layers. As alternatives to the plasma based methods there exist gas phase methods such as chemical vapor deposition (CVD) , electron beam methods as well as sol-gel-methods . Thin metal layers can additionally be applied by sputter physical vapor deposition (Sputter-PVD) .

Thus, there still exists a need for an im- proved plasma beam method for the application of permeation reducing coatings, in particular for the application of permeation reducing coatings to the inner surface of radial symmetric plastics packagings, that does not have the above outlined disadvantages.

Disclosure of the Invention

Hence, it is a general object of the inven- tion to provide an apparatus suitable for the plasma supported coating of the inner and/or the outer surface of packaging containers, in particular packaging containers made of plastics such as bottles and (collapsible) tubes.

It is a further object of the present inven- tion to provide a low-temperature, ambient pressure plasma beam method for the application of permeation reducing coatings, in particular for the application of

permeation reducing coatings to the inner and/or the outer surface of radial symmetric plastics packaging containers such as bottles and (collapsible) tubes, wherein said method does not have the above outlined disadvan- tages.

It is in particular an object of the present invention to provide an apparatus suitable for performing a plasma beam coating method and such coating method that have at least one of the following advantages, preferably several thereof, most preferred all:

- good lifetime or little erosion, respectively, of the electrodes,

- handy construction of the treatment devices, - low construction expenses even for full treatment of the inner surface of hollow bodies,

- applicability to a large choice of materials, in particular heat sensitive materials such as plastics, - no damage of the material to be treated due to filaments or electric breakdown or sparkover, respectively

- low consumption of process gases

- no high temperature exposure of the sub- strates (e.g. due to arc discharge),

- good implementation in continuously working production lines.

Now, in order to implement these and still further objects of the invention, which will become more readily apparent as the description proceeds, the apparatus suitable for the plasma supported coating of inner and/or outer surfaces of packaging containers made of plastics is manifested by the features that it comprises at least one set of capillaries, each set comprising at least two beam plasma capillaries,

said beam plasma capillaries being or comprising tubes or forming channels with narrow inner diameter and/or capillaries that are positioned radially within one another, said beam plasma capillaries being axially extending, said beam plasma capillaries comprising a first or inner beam plasma capillary that is the beam plasma capillary positioned closest to the axis, said first beam plasma capillary being made of an electrically conducting material, in particular metal, and forming a first electrode, said first beam plasma capillary being connected to a voltage source leading to an electrical con- nection to which a defined electrical potential is applied, preferably a high frequency generator and more preferably the earth connection of a high frequency generator, said beam plasma capillaries comprising a second beam plasma capillary and optionally one or more further beam plasma capillaries, said second and optionally further beam plasma capillaries being made of electrically insulating material, the plasma beam capillary most distant from the axis being the outer beam plasma capillary, said outer beam plasma capillary comprising either at least 3, preferably at least 5, most preferred at least 6 axially extending capillaries in its jacket, or it is comprised of two tubes-fitted into each other such that there is a small annular slit between both, the proximal end of said axially extending capillaries being connected to a pumping device for removing excess gases and waste gases (both together also termed exhaust gases) , at least said first capillary being fed from its proximal end with at least one process gas, said pro-

cess gas being a plasma supporting and/or surface treating gas and/or a coating gas.

In general and preferred, the apparatus of the present invention has 3 beam plasma capillaries, a first or inner beam plasma capillary, an outer beam plasma capillary and a second beam plasma capillary positioned between the inner and the outer beam plasma capillary. The first and second beam plasma capillaries are in general connected to first and second process gas sup- plies, although connections to only one process gas supply might for some applications be provided, namely if the same gas composition at different velocities should be supplied and provided that suitable velocity regulating valves are positioned between the capillaries and the process gas sources.

The part termed outer beam plasma capillary, in one embodiment is rather a jacket comprising a plurality of regularly distributed capillaries, in general at least 3 capillaries, whereby the number of capillaries as a rule has to be as high as to ensure a sufficiently homogeneous (in radial-symmetrical respect) and controllable removal of excess and waste gases through said jacket. In another embodiment, the outer beam plasma capillary is comprised of two tubes fitted into each other (one of said tubes may be the wall limiting the next inner beam plasma capillary) such that there is a small annular slit between both which acts as channel for removing exhaust gas . In an improved version of this second embodiment, a ring with rectangular toroidal cross- section can be fitted tightly into the annular slit, carrying the aforementioned axial holes, thus simplifying the mechanical construction of an alternative to the capillaries. Capillaries or at least a ring are preferred in view of mechanical stability of the plasma beam appara- tus.

In a preferred embodiment of the apparatus, each of the capillaries extends into a basic body, said

basic body providing a connection to a process gas source and/or a pumping device. The connection of the basic body- to the process gas source or the pumping device can e.g. be made by providing the basic body with a bore that tightly fits to a capillary and to a tube serving the connection to a process gas supply/process gas storage container or to the pumping device. Thus, in general, the capillary receiving basic bodies also provide a mechanical fixation for their capillary. The first beam plasma capillary is made of an electrically conductive material, in particular a metal, especially molybdenum, tungsten, tantalum or high- grade/stainless steel, most advantageously tungsten. Dependent on the process gases used, it may be advantageous to protect the metal by applying a protective layer to the inner and/or the outer surface of the first beam plasma capillary, preferably at least to the outer surface, since the more reactive gases are in general provided through the second capillary. Suitable coatings for the surfaces of the inner beam plasma capillary are e.g. coatings made of ceramic oxides or temperature resistant polymers .

The second and any further beam plasma capillaries are made of a thermally stable inert insulating material, in particular a material selected from ceramics and duroplastic materials, e.g. polyimides and polyether ketones. The thickness of the total of insulating materials and the gas spaces must be such that ignition and maintenance of the plasma is guaranteed. The wall thick- ness of the walls defining the second and further beam plasma capillaries is not critical. For an apparatus with three beam plasma capillaries intended for coating tubes with a diameter of 13.5 mm, a total wall thickness of about 10 mm has proved to be preferred. The material for the basic bodies is not critical provided that it does not interfere with the plasma generation. In general, for an embodiment with

three beam plasma capillaries a basic body consisting of 5 parts is provided. Further conducting, not conducting or semi-conducting areas that can be capacitively loaded in order to get an optimal electric field strength can be provided to ensure that no discharge at an undesired place occurs . The dimensions of the embodiments are not critical, the preferred material is a metal in the case of electrically grounded potential or a non conducting material, preferably polyetheretherketone (PEEK) in case the inner electrode carries high voltage.

The outer beam plasma capillary consists of a jacket that in one embodiment tightly abuts the next inner beam plasma capillary and comprises a plurality of at least 3, preferably at least 5, most preferred at least 6 capillaries. Since it is technically complicated to produce long capillaries, it is also possible to form the outer beam plasma capillary as a lumen similar to the second beam plasma capillary. In this embodiment it is also possible and - e.g. for stability reasons preferred - to tightly fit a ring with rectangular toroidal cross section into the annular slit (opening of the outer beam plasma capillary lumen) , wherein such a ring carries axial holes .

In order to get a well shaped plasma, the flow velocity of the process gases, the excess and waste gases, the high frequency and the voltage applied as well as the dimensions of the capillaries must be adapted to one another. In general, for treating/coating the inner surface of a tube of 9 mm to 33 mm diameter, in particu- lar a tube of 13,5 mm diameter, the inner beam plasma capillary has diameters ranging from about 2 mm to about 3 mm, said plurality of capillaries in said outer beam plasma capillary have diameters ranging from about 1 mm to about 2 mm, and preferably have diameters of about 1.5mm, and said lumen of said second capillary placed between said outer and said inner beam plasma capillary has a width of about 2 mm to about 10 mm. The thickness of

the insulating material of the second and further beam plasma capillaries is not critical, however their combined thickness should be at least about 5 mm.

Whether the outer beam plasma capillary is formed with a plurality of capillaries or with an annular lumen or with an annular lumen partially closed with a ring is not critical as long as the sum of the cross- sections of the capillaries or the area of the lumen in cross-section or the sum of the cross-sections of the openings in the ring are such that the gas volume to be removed through said outer plasma beam capillary can be regulated through the suction force.

If inner surfaces of tubes or bottles with larger diameters shall be treated/coated, the following kinds of adaptation have to be made. The size of the outer diameter of the jacket which carries the capillaries or defines the lumen of the outer beam plasma capillary must be adjusted such that it fits to the diameter of the tube or bottle to be treated. The size of the in- ner beam capillary is enlarged such that a maximal lumen cross section of 10 mm is ensured.

If treatment of the inner surface of smaller tubes is at issue, the same parameters have to be changed in the opposite direction, i.e. the size of the outer di- ameter of jacket which carries the outer beam capillaries must be adjusted such that it fits to the tube diameter. The size of the inner beam capillary is decreased accordingly such that a radial lumen cross section between inner and 2 ⁿ d capillary of 0.5 mm is ensured. The ratio of the active area of the annular cross-section of the lumen of the second beam plasma capillary (Fa) to the active area of the circular cross- section of the inner beam plasma capillary (Fi) is in the range of 0.7-1.4. For an apparatus for coating tubes of 13.5 mm diameter, Fa : Fi is preferably about 1.2.

When the inner capillary is connected to high voltage, it may act as the only explicit electrode. In

this case, the substrate that is to be coated acts as a reference electrode. For the coating of inner surfaces of a tube, it is preferred to have a 2 ^n< ^ electrode in front of the tube tip that in the case of high voltage applied to the inner capillary is grounded, or, most preferably, this 2 ^nc ^ electrode carries the high voltage whereas the inner capillary is grounded.

Thus, in a preferred embodiment of the present invention, the inventive apparatus comprises a sec- ond electrode. The second electrode is separated from the plasma by the surface to be coated. In one embodiment with two electrodes the inner beam plasma capillary carries high voltage while the second electrode is connected to mass. In a preferred embodiment, the second electrode carries high voltage and the inner beam plasma capillary is grounded.

In an apparatus for the coating of e.g. the inner surface of a tube-like container made of plastics, in particular a tube, the second electrode is preferably a formed body positioned at the upper end of the body to be coated, i.e. the end distal from the capillaries. The form of the second electrode is not necessarily form- fitting, but preferably form-following, whereby a sealing with respect to the gas is necessary. The term tube or tube-like as used in connection with the container to be surface treated means a container with a cylindrical body part (such as a bottle or a (collapsible) tube) that - if applied to the plasma beam apparatus - in distal direction from said plasma ap- paratus narrows towards an outlet; in general, the tube in distal direction ends in an elongated neck forming part .

In order to provide more possibilities to optimize the plasma generation and distribution, the hole or bore of said second electrode can be connected to a pumping device for pumping off excess gases and waste gases. This allows to control the back flow of excess

gases and waste gases through the outer beam plasma capillary, the pressure in the plasma and the flow of gas through the outlet of the tube as well as the extension of the plasma into said usually elongated neck forming part of said outlet such that also said neck can be plasma treated and/or plasma coated, respectively.

For getting a homogeneous plasma treatment and/or plasma coating of a large inner surface area of a container, in particular a tube, in longitudinal exten- sion, it may be advantageous to arrange the beam plasma capillaries such that they can be moved in axial direction relative to the packaging container.

The apparatus described above can also be used for external treatment, in particular for treating the outer surface of a container, such as a bottle and in particular a tube, especially the outer surface in the area around the container mouth, in particular the elongated neck part of a tube. For external treatment, the body to be treated is positioned at an appropriate dis- tance from the distal end of the apparatus, i.e. the end where the plasma beam is generated. In case of a container, such as a bottle or tube, said container is positioned coaxially with the plasma beam apparatus .

Although not absolutely necessary, it is much preferred that both, the distal end of the plasma beam apparatus and the container end to be treated are positioned opposite to each other in a casing, in particular a tubular casing that at least at its ends fits to the container wall and the plasma beam apparatus. In a cen- tral part, said casing can have a larger diameter, in particular a diameter larger than the outer diameter of the container body. Such larger diameter allows that also part of the outer surface of the container body is surface treated and not only the neck part. This casing preferably is made of insulating material .

Thus, the apparatus of the present invention allows for the treatment of the inner or outer surface of a container or, in subsequent steps for the threatment of the inner and outer surface. If both surfaces shall be treated, either first the outer surface can be treated and then the inner surface or first the inner surface is treated and then the outer surface .

If the container to be coated is too large for being homogeneously coated with one set of concentric capillaries as described above, several such sets of capillaries can be combined for use within one container, e.g. by providing mechanical fixation means such as fitting bores for several sets of concentric capillaries within each basic body. If several containers shall be simultaneously treated, plasma treating and/or coating devices can be provided comprising a plurality of one set apparatuses or multiple set apparatuses as described above. Such apparatuses may be serially or circularly arranged. Several or all of the apparatuses can be connected to a common gas source for a first process gas and/or a common gas source for a second or further process gas and/or common pumping devices and/or common RF generators.

For the plasma coating device of the present invention it is possible to form the apparatuses as modules. Such modules can be made such that they easily fit to one another, e.g. in that the basic bodies are shaped to together form a circle that can be hold in a circular holder, or in that each of the basic bodies fits to a re- ceptacle within a holder, whereby said holder can provide connections to gas sources, pumping devices, RF generator or mass, etc.

The modular embodiment has the advantage of simplified change, be it that one plasma beam apparatus is defect and needs replacement, be it that the whole device shall be changed to another container size. The modular embodiment has the advantage that apparatuses

with differently sized capillaries as well as one set and multiple set apparatuses can be provided with identically shaped basic bodies such that one and the same holder - that preferably is connected to the different supply means as well as pumping devices - can be used for coating different container shapes at different times.

It is also within the present invention to provide plasma treating/plasma coating devices wherein at least some of the apparatuses and/or a part of some of them is formed in one common block. Such embodiments comprise embodiments wherein several apparatuses are fixed together, e.g. by joining common basic bodies and/or common second electrodes .

Due to the specific arrangement of the elec- trodes and the chosen high frequency excitation neither problems with the lifetime of the electrodes nor problems with damages of the material due to discharge filaments or electric flashover to the material to be treated exist. The excitation/activation of previously inert gases and vapours by the plasma effect to chemically reactive species such as radicals and unsaturated molecules can be used to achieve a surface coating. Suitable coating materials are those that vaporize below about 200 ⁰ C at ambient pressure (about 1 + 0.1 atmosphere) . Compounds with higher vaporization temperatures can also be used, however, they in general necessitate the use of lower pressures. Such vaporized compounds herein are also referred to as process gases. A method for the beam plasma treatment and/or beam plasma coating of a plastics surface and using an apparatus or device of the present invention comprises the steps of positioning the surface to be treated above the apparatus of the present invention, applying at least one plasma supporting and/or surface treating gas and optionally at least one coating gas at least through the inner beam plasma capillary during high frequency excita-

tion applied to the inner capillary or to the second electrode, and applying a suction force to the outer beam plasma capillary.

The high frequency electric field applied must be such that it is sufficient to ignite and support/maintain the plasma.

In a preferred embodiment, the surface to be treated/coated is the inner surface of a packaging container made of plastics. In this embodiment, said con- tainer is applied to the outer surface of the outer beam plasma capillary or to the outer surfaces of the outer beam plasma capillaries of a set of beam plasma capillaries, and then at least one plasma supporting and/or surface treating gas and optionally at least one coating gas are applied at least through the inner beam plasma capillary during high frequency excitation applied to either the inner capillary or a second electrode, and applying a suction force to the outer beam plasma capillary.

In another preferred embodiment, the surface to be treated is the outer surface of a packaging container, such as a bottle and in particular a tube, especially the outer surface in the area around the container mouth, in particular the elongated neck part of a tube. In this embodiment, said container is positioned at an appropriate distance from the distal end of the apparatus and coaxially with the apparatus . Preferably, the distal end of the plasma beam apparatus and the container end to be treated are positioned opposite to each other in a casing, in particular a tubular casing that at least at its ends fits to the container wall and the plasma beam apparatus . Then at least one plasma supporting and/or surface treating gas and optionally at least one coating gas are applied at least through the inner beam plasma capillary during high frequency excitation applied to ei- ther the inner capillary or a second electrode, and applying a suction force to the outer beam plasma capillary. Optionally, the other end of the container, i.e.

the end that is not surface treated, can be connected to a suction apparatus .

For plasma coating, besides of the at least one plasma supporting and/or surface treating gas at least one plasma coating gas is provided. The at least one plasma supporting/surface treating gas and the at least one coating gas can be fed through different beam plasma capillaries or, preferred, are fed admixed.

If an apparatus with three beam plasma capil- laries is used, in general a first process gas is fed through the inner capillary, a second process gas is fed through a second beam plasma capillary and at least part and preferably only part of the excess gases and the waste gases are removed via the outer beam plasma capil- lary.

The first process gas in general comprises gases selected from the group comprising rare gases, oxygen, nitrogen, hydrogen and mixtures thereof. It can be admixed with further compounds such as e.g. alcohols, in particular aliphatic alcohols, aldehydes, silanes, disi- lanes, disiloxanes, disilazanes and mixtures thereof, however, such admixture is less preferred unless the surface of the inner beam plasma capillary is inert (or made inert) to such admixtures. The second process gases in general comprise gases selected from silicon comprising compounds (e.g. silanes) and hydrocarbons, wherein silicon organic compounds are preferred. In general, the compounds are selected from the group comprising alcohols, in particular aliphatic alcohols, aldehydes, silanes, disilanes, disiloxanes, disilazanes and mixtures thereof, optionally in combination with gases as mentioned above.

In a much preferred embodiment of the present invention the surface treatment leads to ^' a reduced oxygen permeability of the plastics substrate, in particular the tube. For providing an oxygen barrier silicon comprising compounds are preferred, in particular hexamethyldisilox-

ane (CH ₃ ) ₃ -Si-O-Si- (CH ₃ ) 3, hexamethyldisilazane (CH ₃ ) ₃ -Si- HN-Si- (CH ₃ ) _3/ tetramethylsilane (CH ₃ ) 4-Si, tetramethydisi- loxane H (CH ₃ ) ₂ -Si-O-Si- (CH ₃ ) ₂ H, tetraethoxysilane (C ₂ H ₅ O) ₄ - Si, and mixtures of two or more of these compounds. Such silicon comprising compounds are preferably provided in the second process gas, optionally admixed with oxygen or nitrogen whereby preferred concentrations/ratios are: compound: optional gas = 1:20.

In order to get a good plasma a total gas flow per module for the treatment of the inner surface of a plastics tube of a diameter of 13.5 mm is:

- at atmospheric pressure 2-15 slm (standard liters per minute) , preferred 4-7 slm,

- at reduced pressure (10 mbar) 2-100 seem (standard cubic centimeters per minute), preferred 10-20 seem.

The method of the present invention is preferably performed at pressures close to atmospheric pressure, in general ambient pressure, although for certain applications reduced pressure can be provided. Besides of about atmospheric pressure, a pressure range of 5 mbar to 800 mbar is preferred.

From an economic point of view ambient pressure or slightly reduced pressure that can be easily achieved with common pumping devices is much preferred in an inventive method for the plasma treatment/plasma coating of the inner and/or outer surface of tubes since no evacuation prior to plasma treatment is necessary and no vacuum chamber to avoid collapsing of the tubes is neces- sary, thereby saving investment costs and time.

The voltage to get ignition must be high enough to meet the so called Paschen's Law. Said law states that the breakdown characteristics V of a gap are a (generally not linear) function of the product of the gas pressure p [in atin] and the gap length d [in cm] , namely V = f {pd) . This equation applies at pd products less than 1000 torr cm. Minimum sparking potentials Vs

for some gases can be found in Naidu, M.S. and Kamaraju, V., High Voltage Engineering, 2nd ed . , McGraw Hill, 1995, ISBN 0-07-462286-2.

The values given in the table apply for dc breakdown. They are slightly lower in the case of RF voltages . Suitable frequences of the voltage applied are from 50 Hz to 10 GHz, preferably from 1 kHz to 9 GHz, much preferred from 5 kHz to 50 MHz, most preferred about 27.12 MHz, and the effective voltage in general ranges from 100 V _e ff to 10kV _e ff, preferably from 500 V _e ff to 5 kV _e ff, much preferred from 0.8 kV _e ff to 1.5kV _e ff.

If a plasma coating is applied, this coating can be and preferably is applied in pulsed mode, most preferably at a frequency of 100 Hz and duty cycle of 0.1 for an operating frequency of 27.12 MHz. During the plasma treatment/plasma coating of inner surfaces said packaging container and/or said beam plasma capillaries can be axially moved with regard to each other either in a stepwise or in continuous mode. The velocity of the relative movement allows the regula- tion of e.g. the surface treatment intensity and the coating thickness.

A great advantage of the inventive beam plasma method is that it can be performed at temperatures between 30 ⁰ C and 100 ⁰ C which makes it perfectly suitable

for a broad variety of plasties such as polyethylene and polypropylene, polyethylene terephthalate, and polyethylene naphthalate .

The regulation of the plasma temperature can be made through the process gas temperature.

The inventive plasma treatment and/or plasma coating method can be applied in one step or in consecutive steps.

If desired, the inventive method can be used in combination with chemical methods such as the subsequent or previous application of antifungal/antibacterial coatings, heat sealable layers etc.

The inventive method can be used to homogeneously coat the whole circumferential area of a certain extent in axial direction of the container or of the whole container. If for the main body forming part of the container a compound material comprising a diffusion barrier, e.g. an aluminium layer, is used, the plasma treatment/plasma coating can be more intense at the (elon- gated) neck part, the seams etc.

A container with a surface treated according to the present invention can then be filled and closed according to conventional methods . In the case of a collapsible tube, in particular since it is preferred to have the elongated neck already fixed on the top of the tube body, the filling in general is performed from the bottom part prior to sealing it. In the case of bottles it is possible to first fill them from the bottom and then seal them by connecting a bottom part to the tube- like side wall, or to first connect a bottom part to the tube-like side wall and then fill the bottle from the top.

Brief Description of the Drawings

The invention will be better understood and objects other than those set forth above will become ap- parent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings, wherein:

Figure 1 shows a plasma beam apparatus of the present invention (with a second electrode shown) used for applying a permeation resistant layer to the inner surface of a plastic tube in a section along the longitudinal axis.

Figure 2 shows a preferred embodiment of the plasma beam apparatus (with the second electrode not shown) in a section along the longitudinal axis, said beam apparatus having an outer capillary with circular bores fully surrounded by insulator material.

Figure 3 is a cross section along line A-A of Figure 2. Figure 4 is another preferred embodiment of the beam apparatus (with the second electrode not shown) in a section along the longitudinal axis, said beam apparatus having an outer capillary with peripheral semicircular bores. Figure 5 is a cross section along line A-A of

Figure 4.

Figure 6 is a schematic presentation of an apparatus with multiple sets of capillaries within a tube in cross-section perpendicular to the longitudinal axis. Figure 7 shows a device of the present invention with two sets of capillaries joining the same body parts and the same counter electrode in section along the longitudinal axis .

Figure 8 is a schematic presentation of a de- vice of the present invention with a circular arrangement of inventive apparatuses in cross-section perpendicular

to the longitudinal axis, each apparatus shown in a cut at a position as shown in- Figure 1 by line A-A.

Figure 9 is a schematic presentation of a device of the present invention with a circular arrangement of modules of inventive apparatuses, each apparatus shown in a cut at a position as shown in Figure 1 by line B-B.

Figure 10 is a schematic presentation of a plasma beam apparatus arranged for the treatment of outer surfaces in a section along the longitudinal axis .

Legend

1 body to be treated

2 outer capillary forming a lumen or with bore holes 2a, 2b in the jacket

3 gas supply 1

4 gas supply 2

5 basic body gas 1

6 basic body gas 2 with mechanical recepta- cle of capillary (9)

7 basic body exhaust gas with mechanical receptacle capillary (10) and electrical supply

8 basic body with mechanical receptacle capillary (2) 9 inner capillary (metal)

10 central capillary (insulator material)

11a to the voltage source or to ground potential lib to ground potential or to the voltage source

12 dome for pumping off gas and counter electrode

13 exhaust gas line

14 beam plasma 15 set of capillaries

16 modules

17 gasket for holding/sealing the tube-like container

18 gasket sealing the connection between two body parts

19 sealing connection

20 casing

21 hollow holder 100 plasma apparatus

Modes for Carrying Out the Invention

The invention is now further described with regard to some specific preferred embodiments shown in the Figures. The Figures are, however, not intended to limit the scope of the invention as it is shown by the claims .

An apparatus 100 with one set of capillaries that is suitable for the plasma treatment/plasma coating of small containers, in particular small bottles or especially small tubes, with two electrodes 9, 12 in an arrangement for the treatment of inner surfaces of containers, especially bottles and in particular tubes, is shown in Figures 1 to 5. As shown in Figures 1, 2 and 4, the inner beam plasma capillary 9 is at its proximal end hold in a fitting bore in the basic body 6 and extends into a larger bore in basic body 5, said bore in basic body 5 forms part of the gas supply for the first process gas 3. Capillary 9 extends axially from its proximal end, where it extends over the second beam plasma capillary 10, to its distal end, where, in the preferred embodiments shown in Figures 1 to 5, it ends within the second beam plasma capillary 10 thereby ensuring suitable mixing of the first and second process gases. Plasma generation is pre- ferred at the distal end of the second beam plasma capillary 10. Said second beam plasma capillary 10 at its proximal end is hold in a fitting bore in basic body 7 and extends into a larger bore forming part of basic body 6 and of the gas supply for the second process gas 4. The basic bodies 5, 6, 7 and 8 are connected to each other by any suitable connecting means such as a screw and preferably sealed to each other by a gasket.

As shown in Figures 2, 3, 4 and 5 the outer beam plasma capillary 2 is a body of electrically insu- lating material that comprises a plurality of (e.g. 8) capillaries arranged either within and completely bound by said material 2a (Figures 2, 3) or peripherally 2b

(Figures 4, 5) such that the capillaries are formed by the outer beam plasma capillary in combination with the tube. The outer beam capillary 2 is such that - except for peripheral capillaries 2b - it tightly fits to the tube-like container 1, and the tube-like container 1 is hold in the basic body 8 by any suitable holding or sealing means, preferably by a gasket 17.

Body part 6 includes an electrical connection to the inner capillary 9, the capillary made of metal, in particular molybdenum or tungsten, or tantalum or steel, most advantageously tungsten. This electrical connection is either connected to the RF-power supply unit 11a (preferably providing 13.56 MHz or 27.17 MHz) via an impedance adaptation network, or it is connected to ground potential. In the second case a second electrode 12 must be present that is connected to the RF-power supply lib.

The several body parts 5, 6, 7, 8 can be fixed by e.g. screws and sealed by there between positioned gaskets 18. As already mentioned above, a second electrode 12, may or must be present. In the case where the second electrode is optional, it is connected to mass lib. Said second electrode 12 comprises a bore fitting the elongated neck of the tube 1 to be coated. Said bore goes through the whole electrode allowing excess and waste gases to leave the apparatus by this way. The distant opening 13 of the bore in the second electrode 12 can be connected and preferably is connected to an exhaust gas line that can be connected to a pumping device. The whole device is provided with valves allowing the regulation of the specific flows and optionally with flow meters and/or pressure indicators. The whole apparatus can in addition be connected to an automatic regulation device regulating the treatment/coating conditions and speeds .

Such a plasma apparatus is used as follows:

First the tube to be treated is applied to the plasma beam apparatus to provide an arrangement as shown in Figures 1, 2 and 4. The tube body 1 is pushed onto the outer plasma beam capillary 2 such that it forms therewith a gas tight seal. The gas supply occurs via gas support tubes 3, 4 that lead to the disc like basic bodies 5, 6. As described above, the disc-like basic bodies serve the fixation of the beam capillaries 9, 10 that are arranged one within the other. The excess and waste gases of the process on the one hand are guided through capillaries 2a, 2b in the outer plasma beam capillary 2 to the body part 7, on the other hand they exhaust through the shaped/formed part that simultaneously acts as counter electrode 12 and that is connected to mass and to the outlet of the tube-like container in a gas-tight manner. If a vacuum pump is connected to the outlet of the tube-like container, or rather the shaped/formed part tightly connected thereto, the exhaust gas 13 can be sucked off and collected for possible recovery and recycling.

By applying an electrical voltage on the inner capillary or voltage on the outer block at the tube tip (second electrode 12), the plasma 14 is ignited and extends from the capillaries in a beam-like shape such that it is suitable to treat the inner surface of the container 1 in a defined manner.

Such an arrangement can be used with all the above outlined gases and vapors, preferably, however, it is used with argon, oxygen and admixtures of silanes, disilanes and disiloxanes although it can also be used with pure nitrogen or nitrogen-oxygen mixtures.

Figure 6 schematically shows an apparatus with multiple sets of capillaries within a tube in cross- section perpendicular to the longitudinal axis. By such an arrangement, tube-like containers with much larger diameter can be treated/coated. In such embodiment it might be advantageous to not only provide an axial movement of

the container relative to the capillaries, but also a rotational movement.

Figure 7 shows a device of the present invention with two sets of capillaries joining the same body parts and the same counter electrode. Both sets of capillaries are simultaneously used. In stead of a linear arrangement more than two such plasma beam apparatuses can also be circularly arranged. Such an arrangement is schematically shown in cross-section perpendicular to the longitudinal axis in Figure 8.

The apparatuses of the present invention can also be formed as modules, such that each can easily be replaced, e.g. in case of damage. A modular arrangement is also advantageous if one and the same device shall be used for the treatment of different tube diameters. A device in an intermediate state with two of the six modules exchanged is shown in Figure 9. In view of the different tube lengths in general all modules will be changed from one kind to another. Thus, Figure 9 rather shows an in- termediate state than a final state.

Figure 10 shows an arrangement of an apparatus 100 of the present invention for the treatment of the outer surface of a container 1, especially the mouth part of said container 1. For this treatment, the distal end of the capillaries and the container mouth both are positioned in a casing 20 tightly fitting to the outer surface otf the container as well as to the outer surface of the outer capillary of the plasma beam apparatus 100. If the container is e.g. a collapsible tube, the tube body may be tightly positioned on a preferably hollow holder 21 that at one end is open towards the area defined by casing 20, the mouth end of container 1 and the distal end of apparatus 100 and at the other end connected to a suction device suitable for assisting in the removal of excess and exhaust gases.

The modular device preferably comprises totally independent modules, i.e. each module has its own

connections to power and gas supplies, although it is also possible that the modules are provided with connect- able bores for gas distribution or power connections . In this case, however, valves must be provided to ensure ho- mogeneous gas and pressure distribution over all apparatuses .

While there are shown and described presently preferred embodiments of the invention, it is to be dis- tinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims .