WO2002036850A2

WO2002036850A2 - Method and device for coating hollow bodies

Info

Publication number: WO2002036850A2
Application number: PCT/EP2001/012689
Authority: WO
Inventors: Rainer Dahlmann
Original assignee: Vereinigung Zur Förderung Des Instituts Für Kunststoffverarbeitung In Industrie Und Handwerk An Der Rheinisch-Westfälischen Rwth Aachen E.V.
Priority date: 2000-11-03
Filing date: 2001-11-02
Publication date: 2002-05-10
Also published as: WO2002036850A3; AU2002216000A1; DE10054653A1

Abstract

The invention relates to a method for coating hollow bodies (1) by means of layer deposition from a plasma, whereby a hollow body (1) in a vacuum chamber (2) is coated from outside with provision of electromagnetic radiation, injected through the interior of the hollow body. In the external volume, surrounding said hollow body (1), gases, vapours or mixtures thereof may be introduced into the vacuum chamber (2) which can be stimulated to give a plasma, whereby the process parameters are chosen such that in the internal volume (6) of the hollow body (1) the generation of a plasma is prevented.

Description

Method and device for coating hollow bodies

The invention relates to a method for coating hollow bodies according to the preamble of claim 1 and a device according to the preamble of claim 25.

Hollow bodies made of plastics are increasingly used primarily for packaging liquid fillers. Depending on the sensitivity of the filling material, such as food, to gases, such as oxygen, or the loss of components in the filling material, such as carbon dioxide, the barrier properties of plastics such as polyethylene or polyethylene terephthalate are often not sufficient to ensure adequate storage stability to reach. For this reason, there is a great need for economically feasible technologies to improve the barrier properties of hollow plastic articles. Starting from typical materials for the production of polymeric hollow bodies such as polyethylene or polyethylene terephthalate, technologies for improving the barrier can be found, for example, in the use of so-called high barrier materials or in combination with high barrier materials in the form of multilayer composites. In both cases, not only the conversion costs for production, but also the manufacturing costs of the hollow bodies are very high. In addition, recycling is generally significantly more difficult, especially since there is already a recycling cycle for standard materials and technologies for reprocessing are already well advanced. As a result, the further development of thin-film technologies with regard to the coating of hollow bodies, which serve as packaging material for liquid foodstuffs, is becoming particularly important. DE 36 32 748 C has already described a CVD process for the internal coating of hollow bodies by means of microwave-excited layer deposition from a plasma. Further developments (WO 99/17334, WO99 / 49991) use the same basic principle and represent solution approaches for the necessary scaling up of the method for the purpose of use for the internal coating of hollow bodies, some of which have already been implemented. However, a disadvantage of the inner coating applied in this way can be that the layer surfaces produced come into contact with food. It cannot be ruled out that layer components get into the filling material and in the simplest case lead to changes in taste. Likewise, the method does not necessarily ensure that layer particles completely detach from the wall of the hollow body and thus get into the food.

This aspect is harmless for the outer coating, as there is no direct contact with the product. On the other hand, the problem is that a coating zone with a sufficiently large volume that is adapted to the geometry of the bottle has to be created. From WO 98/49531 it is known that the hollow bodies are rotated through a plasma zone. This PVD process is additionally supported by a plasma and focused on one zone. A disadvantage of this method is that the wall of the coating chamber is continuously co-coated. In addition, gas supply and plasma source systems can also be coated, so that the process conditions can change in the course of some coating processes. Furthermore, in this system the coating chamber is comparatively large in relation to the volume of the hollow body, so that high pump capacities are required. An opening of the system that is necessary due to a malfunction of the process then takes long evacuation periods. This applies in particular from the point of view that lower pressures are necessary and necessary in PVD processes than in CVD processes. The invention is based on the object of specifying a method and a device for coating hollow bodies in which the evacuation periods and the pump capacity can be reduced for the external coating of hollow bodies.

The features of claims 1 and 25 serve to achieve this object.

The invention advantageously provides that after evacuation of an external space surrounding the hollow body, layer-forming gases, vapors or mixtures thereof are introduced into the vacuum chamber, which can be excited into a plasma, and electromagnetic radiation is coupled in through the interior of the hollow body The process parameters are set such that a plasma is ignited only in the exterior and the ignition of a plasma is prevented in the interior of the hollow body.

The invention enables CVD coating, in particular the outer coating of hollow bodies, with a complex geometry. A plasma is only generated on the outside of the hollow body. The advantage of the invention is that, compared to the PVD method, higher pressures in the range of approximately 10 Pa <p <1000 Pa are possible. Furthermore, since they are surrounded by the hollow body to be coated, the energy sources are not subject to continuous coating, so that the process conditions remain constant from coating to coating. Another advantage is that the size and shape of the vacuum chamber can be adapted to the contour of the hollow body, so that evacuation periods and the pump capacity to be made available can be minimized.

The internal pressure of the gas located in the interior of the hollow body is preferably set such that ignition of a plasma in the interior is prevented.

Microwaves are introduced into the interior of the hollow body as electromagnetic radiation. Rod antennas are preferably used to couple the microwaves. The rod antennas are partially provided with an electromagnetic shield which serves to homogenize the plasma fire in the axial direction of the antenna and / or to adapt the radiation intensity to complex hollow body geometries.

The antenna can be made of a cylinder made of a non-microwave active material, e.g. Quartz glass.

The layer deposition can be homogenized by adjusting the ratio of layer-forming gases and carrier gases.

For example, hydrocarbons or silicon-containing starting materials are introduced as layer-forming gases or vapors.

Argon and / or oxygen can also be used as carrier gases.

The hollow body, e.g. a bottle consists at least partially of a polymer material.

According to a variant of the method, a higher pressure is set in the interior of the hollow body than in the exterior of the hollow body and the hollow body is coated with stretching. The pressure in the interior of the hollow body can be several times the atmospheric pressure. During the coating process, the excess pressure in the interior stretches the hollow body.

The coating under stretch has the advantage that the stretch that is applied when the hollow body is subsequently filled does not lead to the layers being torn open. In general, however, the invention is designed in such a way that negative pressures can also be generated in the interior of the hollow body if pre-stretching does not appear expedient.

In one embodiment, the hollow body is fixed in the receptacle, the cup-shaped vacuum chamber is lowered above it and the Outside space evacuated via the pump. Suitable gases, such as silicon-containing or hydrocarbon-containing or fluorohydrocarbon-containing gases, vapors or mixtures, are then passed into the space between the bottle and the chamber housing and a plasma is generated on the outside of the hollow body by switching on the microwave generator, so that the coating process is initiated , Possibly. plasma or plasma post-treatments can be carried out, for example to clean the surface or to saturate radicals in the surface of the layer. The vacuum chamber is then vented and opened.

If necessary, the microwave intensity can be homogenized on the outside of the hollow body contour by means of partial metallic covers of the antenna. Further access to the homogenization of the layer deposition is possible by adapting the process parameters and using carrier gases.

The electromagnetic shielding can consist, for example, of metal sheets or foils which taper to a point towards the free end of the rod antenna and thus only partially cover the circumference of the rod antenna.

The interior of the hollow body can be filled or flowed with a gas or a liquid before, during and / or after the coating process, with the aim of cooling, cleaning or sterilizing the inside of the bottle.

The electromagnetic radiation can pulsate in time, i.e. be coupled in with time-varying power.

By varying process parameters, for example gas composition, process pressure and / or microwave power, gradient layers can be applied during the coating process, the properties of which change continuously or step by step as the layer thickness increases. This process variant allows gradients in the internal tension of the layers to be built up or compensated for, for example with the aim of improving the behavior of the layers under mechanical stress (elongation / bending). The outside of the hollow body can be provided with a scratch-resistant layer, which can be used, for example, for decorative purposes and / or to protect a barrier layer from partial destruction by mechanical loads. The rod antenna can be inserted into the hollow body, and the housing forming the vacuum chamber can consist of two movable half-shells (or of several shells) which enclose the hollow body with the aid of a locking mechanism and thus produce a closed volume which defines the hollow body and the exterior surrounds in which a negative pressure is generated.

The inner contour of the vacuum chamber can be adapted to the outer contour of the hollow body, for example in order to minimize pumping volumes and / or to optimize gas flows.

The manufacturing process of the hollow body (e.g. injection molding, stretch blow molding and / or blow molding process) can be combined with the outer coating in terms of plant technology, for example by using the blow mold by slightly opening it as a vacuum chamber and the expanding mandrel by modification as an antenna for coupling in the electromagnetic radiation.

The coating of the hollow body can be combined with a fluid injection process for producing the hollow body.

For coating a non-hollow body-shaped component with the method according to the invention, a hollow body can be formed by connecting additional elements to the component which form a hollow body in combination with the component and are therefore suitable for coating with this method. For example, shell-shaped or cup-shaped components are particularly suitable which, in combination with at least one additional element temporarily provided for coating, for example a lid, form a hollow body. Also tubular or tubular components are also suitable, which also form a hollow body by closing all openings. Of course, almost any component shape can be supplemented with additional elements to form a hollow body. After coating, the supplementary elements can be removed. An exemplary embodiment of the invention is explained in more detail below with reference to the single drawing.

The single figure shows a device for coating hollow bodies 1 made of plastic with a vacuum chamber 2 surrounded by a housing 3, in which the hollow body 1 is arranged. The hollow body 1 consists, for example, of a PET bottle, which is kept upside down and sealed in a base 5 of the device. The vacuum chamber 2 can be evacuated in the area of an outer space 4 relative to the hollow body 1 with the aid of a vacuum pump 10. Furthermore, gases, vapors or mixtures thereof, which can be excited into a plasma as a result of electromagnetic radiation, can be introduced into the outer space 4 via a gas feed device 14. The gas supply device 14 has a riser pipe 7 in the vacuum chamber 2, which ends at the upper end of the housing 3, so that the introduced gases and vapors reach the outside space 4 from above.

Preferably, the bell-shaped housing 3 can be removed upwards to populate the hollow body receptacle, while the base 5 is fixed.

A device 12 for generating electromagnetic radiation, preferably a microwave generator, couples microwaves via at least one rod antenna 8, which extends coaxially to the hollow body 1 into an interior space 6 of the hollow body 1.

The rod antenna 8 is partially provided with an electromagnetic shield 20, which is either cylindrical, as shown in the single figure, or consists of elements tapering towards the free end of the rod antenna 8. The electromagnetic shielding from a metallic cover 20 serves to emit the radiation only at the level of the hollow body and to homogenize the plasma fire in the axial direction of the antenna. It enables the radiation intensity to be adapted to complex hollow body geometries.

The rod antenna 8 and the partial metallic cover 20 are surrounded by a sleeve-shaped cylinder 22 made of a non-microwave-active material, for example quartz glass. After the coating device has been equipped with a hollow body 1, the outer space 4 of the hollow body 1 is evacuated. Then gases or vapors or their mixtures that can be excited by a plasma are introduced into the outer space 4 of the hollow body 1 and then a plasma is ignited by coupling the electromagnetic radiation from the inner space 6. In this way, only an outer coating is produced on the outside of the hollow body 1.

The interior 6 can only contain air under atmospheric pressure or can be pressurized to achieve a higher elongation of the hollow body. If an expansion of the hollow body 1 is not desired, the interior 6 can also be evacuated.

In any case, the inner pressure in the interior 6 is set in the outer coating in such a way that ignition of a plasma is prevented.

With the help of a second gas supply device 16, it is also possible to carry out an inner coating sequentially in addition to the outer coating, by introducing gases, vapors or their mixtures, which can be excited into a plasma, into the interior 6 of the hollow body 1 and by a second , conventional device for generating electromagnetic radiation is used, which for example couples microwaves from the outside.

Claims

claims

1. A method for coating hollow bodies (1) by means of the layer deposition from a plasma, in which a hollow body (1) is coated from the outside in a vacuum chamber (2), characterized in that after evacuation of an outer space surrounding the hollow body (1) (4) into the vacuum chamber (2) layer-forming gases, vapors or mixtures thereof are introduced into the exterior (4), which can be excited into a plasma, and that electromagnetic radiation is injected through the interior of the hollow body (1), the Process parameters are set such that a plasma is ignited only in the outer space (4) and the ignition of a plasma is prevented in the inner space (6) of the hollow body (1).

2. The method according to claim 1, characterized in that the pressure in the gas located in the interior (6) is set such that ignition of a plasma is prevented.

3. The method according to claim 1 or 2, characterized in that microwaves are introduced as electromagnetic radiation into the interior of the hollow body (1).

4. The method according to claims 1 to 3, characterized in that rod antennas (8) are used for coupling the microwaves.

5. The method according to claim 4, characterized in that the rod antenna (8) is partially shielded.

6. The method according to claims 4 or 5, characterized in that the rod antenna (8) is surrounded by a cylinder (22) made of a non-microwave active material.

7. The method according to claims 1 to 6, characterized in that the layer deposition is homogenized by adjusting the ratio of layer-forming gases to carrier gases.

8. The method according to claims 1 to 7, characterized in that hydrocarbons or silicon-containing starting materials are introduced as layer-forming gases or vapors.

9. The method according to claims 1 to 8, characterized in that as an additional carrier gases such as Argon and / or oxygen can be used.

10. The method according to claims 1 to 9, characterized in that the hollow body (1) consists at least partially of a polymeric material.

11. The method according to claim 1 to 10, characterized in that a higher pressure is set in the interior (6) of the hollow body (1) than in the outer space (4) of the hollow body (1) and the hollow body (1) is coated with stretching.

12. The method according to claims 1 to 10, characterized in that the interior (6) of the bottle is evacuated, so that an expansion of the hollow body (1) is prevented.

13. The method according to claims 1 to 12, characterized in that the hollow body surface is subjected to a plasma pretreatment or plasma post-treatment.

14. The method according to claims 1 to 12, characterized in that after or before an outer coating by introducing gases into the interior (6) of the hollow body (1) and by coupling electromagnetic radiation from the outside through the outer space (4) of the hollow body (1) an internal coating of the hollow body (1) is carried out sequentially.

15. The method according to claims 1 to 14, characterized in that the hollow body consists of a non-microwave active material.

16. The method according to any one of claims 1 to 15, characterized in that the interior (6) of the hollow body (1) before, during and / or after the coating process is filled or flowed through with a gas or a liquid around the inside of the bottle to cool, clean or sterilize.

17. The method according to any one of claims 1 to 16, characterized in that the electromagnetic radiation pulsates in time, i.e. is coupled with time-varying power.

18. The method according to any one of claims 1 to 17, characterized in that gradient layers are applied by varying process parameters during the coating process, the properties of which change continuously or step-wise as the layer thickness increases.

19. The method according to any one of claims 1 or 18, characterized in that the hollow body (1) is provided on the outside with a scratch-resistant layer as a decorative layer or barrier layer.

20. The method according to any one of claims 1 to 19, characterized in that the rod antenna (8) is inserted into the hollow body (1), and the vacuum chamber (2) of at least two movable shell parts, e.g. Half shells, is enclosed and thus a closed outer space (4) is formed, which surrounds the hollow body (1) and in which a negative pressure is generated.

21. The method according to any one of claims 1 to 20, characterized in that a vacuum chamber (2) with an inner contour adapted to the outer contour of the hollow body (1) is used.

22. The method according to any one of claims 1 to 21, characterized in that the manufacture of the hollow body (1) with the coating of the hollow body (1) is combined on the outside, for example by using the blow mold by opening a certain amount as a vacuum chamber (2) and the stretching mandrel by modification as an antenna for coupling the electromagnetic radiation.

23. The method according to any one of claims 1 to 22, characterized in that the coating of the hollow body (1) is combined with a fluid injection method for producing the hollow body (1).

24. The method according to any one of claims 1 to 23, characterized in that for coating a component, a hollow body (1) is formed in that the component is supplemented with additional elements to be removed later to form a hollow body (1).

25. Device for coating hollow bodies (1) with a vacuum chamber (2) surrounded by a housing (3), in which the hollow body (1) is arranged and which can be evacuated by means of a vacuum pump (10), with a device (12 ) for generating an electromagnetic radiation and with a first gas supply device (14) for layer-forming gases, vapors or mixtures thereof, which can be excited into a plasma due to the electromagnetic radiation, characterized in that the first gas supply device (14) layer-forming gases, vapors or mixtures thereof feeds the outer space (4) surrounding the hollow body (1) in the vacuum chamber (2), and that the device (12) couples the electromagnetic radiation through the inner space (6) of the hollow body (1) and exclusively a plasma in the outer space (4 ) between the hollow body (1) and the housing (3), in which the internal pressure in the interior (6) is set such that a Z ligand is a plasma prevented in the interior (6).

26. The device according to claim 25, characterized in that the housing (3) of the shape of the hollow body (1) is adapted in size and / or shape.

27. The apparatus of claim 25 or 26, characterized in that the device (12) uses microwaves.

28. Device according to claims 25 to 27, characterized in that the device (12) for generating the electromagnetic radiation has at least one rod antenna (8) which is inserted into the hollow body (1).

29. The device according to claim 28, characterized in that the rod antenna (8) is provided with a shield (20).

30. The device according to claim 29, characterized in that the shield consists of a partial metallic cover (20) of the rod antenna (8).

31. The device according to claim 30, characterized in that the surface of the metallic cover (20) decreases over the length of the rod antenna (8) towards its free end.

32. Device according to one of claims 25 to 31, characterized in that the interior (6) of the hollow body (1) is subjected to an excess pressure.

33. Device according to one of claims 25 to 31, characterized in that the interior (6) of the hollow body (1) can be evacuated.

34. Device according to one of claims 28 to 33, characterized in that the rod antenna (8) is surrounded by a cylinder (22) made of a non-microwave active material.

35. Device according to one of claims 25 to 34, characterized in that for sequential implementation of an additional inner coating of the hollow body (1), a second gas supply device (16) gases to the interior (6) of the hollow body (1) and a second electromagnetic radiation from can be coupled into the outside of the vacuum chamber (2).

36. Device according to one of claims 25 to 35, characterized in that the device (12) for generating electromagnetic radiation couples the electromagnetic radiation in a pulsating manner and with a time-varying power.

37. Device according to one of claims 25 to 36, characterized in that the housing (3) from at least two movable shell parts, e.g. There are half shells that enclose the hollow body (1) and the outer space (4).

38. Component for coating according to one of the methods according to claim 1 to 24, characterized in that the component is provided with supplementary elements to be removed later, the combination of the component and the supplementary elements resulting in a hollow body (1).