Method for coating reusable containers, containers produced by means of said method, and container coating machine for coating reusable plastic containers

Abstract

The invention relates to methods for coating reusable containers (5) made of a thermoplastic plastic, in particular PET, with a protective layer (TC) against cleaning agents, wherein the protective layer is deposited on the inner surface of the container (5) by means of a PECVD method for microwave-induced plasma reaction under a negative pressure, wherein at least one container (5) with a container interior (5.1) is inserted into and positioned in a plasma chamber (17) of a plasma station (3). The plasma chamber (17) and the at least one container interior (5.1) are at least partially evacuated. Within the at least partially evacuated plasma chamber (17), at least the one container interior (5.1) of the container (5) is provided with an inner coating by means of plasma treatment under the negative pressure, and a process gas mixture is used, which is introduced into the container interior (5.1). During the deposition of the protective layer (TC), at least two of the following features a) to c) are implemented in any combination, preferably all three: a) the negative pressure in the container interior (5.1) is held below 0.3 mbar, preferably below 0.25 mbar, more preferably between 0.1 and 0.25 mbar and most preferably between 0.15 and 0.2 mbar (+ / - 10%); b) the microwave power is introduced in pulses and the average microwave power P_mittel is less than 50 watts, preferably less than 40 watts and more preferably between 25 and 30 watts (+ / - 10); c) a process gas mixture composed of a monomer gas and a carrier gas is used, the process gas mixture having a carrier gas fraction of less than 50%, preferably less than 25%, more preferably less than 10%. In particular, it is preferred that the process gas used is a pure monomer gas without a carrier gas fraction. The invention also relates to containers produced by means of methods of this type and to a coating machine in which methods of this type are carried out.

Description

[0001] Method for coating reusable containers, containers manufactured according to this method and container coating machine for coating reusable plastic containers

[0002] The invention relates to methods for coating reusable containers made of a thermoplastic, in particular PET, according to the preamble of claim 1. Furthermore, the invention relates to a container coating machine on which such methods are carried out and containers are coated. Finally, the invention relates to reusable plastic containers produced by such a method.

[0003] Single-use containers are known in the prior art. Containers for multiple use, also known as reusable containers, are also known. Reusable containers made of glass are known, as well as plastics, e.g., thermoplastics, particularly PET. It is also known that applying coatings to such reusable containers improves their suitability for multiple use.

[0004] DE 31 44 457 A1 discloses reusable glass bottles coated on their outer surface with a fast-curing, thin layer of siloxane or polysiloxane. This layer protects the outer surface against scratching. WO 2017 / 102280 A2 discloses the use of process gas mixtures of O2, Ar, HMDSO (hexamethyldisiloxane), and HMDSN (hexamethyldisilazane) for coating PET containers. The provided process gas is metered from the gas phase using mass flow controllers and drawn through the coating stations due to the negative pressure of the vacuum system. In the coating stations, the process gas is converted to create a barrier layer and additional layers in the containers. The pressure conditions in the system are determined by several parameters: gas flow, pumping speed of the vacuum pumps, and conductivity of the pipelines (depending on pipe length and cross-section).A special recipe is created for each container type to be coated, which defines, among other things, the process gas mixture of O2, Ar, HMDSO, and HMDSN. This mixture remains unchanged during machine operation (with the selected recipe). Since the relevant piping also remains unchanged, very stable pressure conditions are achieved during coating operation or during standby phases when no container is currently being coated in the device.

[0005] It is known to clean reusable PET containers using cleaning agents, e.g. caustic soda, before refilling. One such cleaning step is required for each refilling of the reusable container. The standard industry cleaning process in container cleaning machines with highly concentrated caustic soda at high temperatures has a severely negative impact on two characteristics of the reusable PET containers, resulting in premature wear and thus in the premature removal of the reusable PET containers from the reusable cycle. These characteristics are the roughness of the surfaces and the internal volume of the containers, which is undesirably reduced by container shrinkage. The well-known and common washing process leads to a roughening of the surfaces of the reusable PET containers by the caustic, a process known as PET corrosion.The increasing roughness of the surface with each cycle makes it increasingly difficult to wash away or remove biofilms and foreign substances, as these unwanted deposits accumulate in ever deeper recesses. To reliably remove these films and foreign substances, aggressive washing processes at elevated temperatures are required. The disadvantage of this is that high temperatures with correspondingly long exposure times cause reusable PET containers to shrink, which is detrimental. To keep shrinkage of reusable PET containers within acceptable limits, they are given greater dimensional stability through greater wall thickness. This, however, is disadvantageous due to the required increased material usage and the associated higher costs.

[0006] The terms "cleaning" and "washing" are used synonymously in this application. Damage to the PET surface occurs primarily due to the long residence time of the reusable PET containers in the caustic soda solution of the cleaning machine – the residence time typically ranges from 6-8 minutes in Germany to 10-12 minutes in South America. The minimum residence time in the cleaning machine is also determined by the time required to remove the label, which is typically 3-4 minutes.

[0007] It is known from the state of the art to use a cleaning agent such as 2% sodium hydroxide solution with a pH of 13.7 and a temperature of 55-60°C, as this allows for economical cleaning times. Other concentrations, pH values, and temperatures are also known. The operating costs are significantly lower than with alternatives such as the complexing agents ethylenediaminetetraacetate (EDTA) or nitrilotriacetic acid (NTA).

[0008] If, for example, a biofilm or foreign matter can no longer be completely removed, the reusable PET container is removed from the reusable cycle. Furthermore, the use of a highly concentrated caustic soda solution causes the reusable PET container to become "blind." This is optically detected, and the corresponding reusable PET containers are also removed.

[0009] Furthermore, in the logistics of the reusable cycle, it is necessary to record which beverage type the reusable PET container was filled with in the previous cycle or in one of the previous cycles before refilling. In doing so, a distinction must be made between reusable PET containers filled with flavored beverages and other reusable PET containers filled with mineral water, for example. This is necessary because certain flavors, such as lemonade, initially migrate from the beverage into the plastic wall and become deposited there. If such a reusable PET container is subsequently filled with water, the flavorings from the plastic wall migrate into the beverage, which negatively influences or changes the inherent taste of the water, which is undesirable in practice.A variable or alternating use of reusable PET containers for flavored and unflavored beverages is desirable, as this reduces the logistical effort.

[0010] Cleaning machines, coating machines and methods for cleaning or coating reusable plastic containers are well known from the prior art, for example from DE 10 2016 105 548 A1, DE 10 2018 1 14 776 A1 and DE 10 2018 129 694 A1. WO 2022 / 106350 A1 describes reusable PET containers and how they are to be cleaned. It is described that a protective layer is deposited on the inside, and possibly also on the outside, of the container, which shields the PET material from the cleaning agent, e.g. caustic soda. On the one hand, it is proposed that this protective layer is completely removed during a washing process and reapplied before refilling. Alternatively, it is proposed that the protective layer is only completely washed off after several washing cycles and is reapplied, for example, after 10 or 20 washing cycles. The protective layer should, for example,made of HMDSO, HMDSN, or HMDS, or a mixture of at least two of these materials. This prior art provides further details on the protective layer.

[0011] The object of the invention is to provide reusable containers as well as methods and devices for coating reusable containers with protective layers that are particularly suitable for use in a reusable recycling system. In particular, the disadvantages of the prior art mentioned above are to be avoided and the cost-effectiveness of reusable containers made of a thermoplastic, in particular PET, is to be improved compared to disposable containers and compared to glass or metal as reusable container materials.

[0012] The invention solves the problem according to a first aspect by a method having the features of claim 1. Advantageous method embodiments are specified in the subclaims.

[0013] The method according to the invention is used to coat reusable containers made of a thermoplastic, in particular PET. The container is provided with a protective layer, which is also commonly referred to as a top coat (TC). The protective layer is intended to protect the underlying areas against cleaning agents, in particular against caustic soda. The cleaning agents in question are those commonly used for cleaning plastic bottles on an industrial scale, e.g., caustic soda in the usual concentration and at the usual temperature; see the general description and the known prior art for cleaning machines for plastic bottles. The method involves depositing the protective layer on the inner surface of the container. For this purpose, a PECVD process for microwave-induced plasma reaction under reduced pressure is used.At least one container with an interior is inserted and positioned into a plasma chamber of a plasma station. To generate a sufficiently stable plasma, negative pressure conditions must be set so that the plasma chamber and the at least one interior container are at least partially evacuated. The primary purpose of evacuating the plasma chamber is to prevent the pressure difference between the interior and exterior of the container from becoming so great that the container is damaged due to the pressure difference. In this respect, the pressure inside the container and the pressure in the surrounding container chamber can be quite different. The pressure in the surrounding chamber is often deliberately set higher, on the one hand to achieve this negative pressure more quickly and on the other hand to avoid plasma generation in the surrounding chamber.The container interior is then provided with an internal coating within the at least partially evacuated plasma chamber by means of plasma treatment at the negative pressure. For this purpose, a process gas is used which is introduced into the container interior. The invention is particularly aimed at coatings in which silicon-based monomers are used as the process gas, in particular the monomers HMDSO, HMDSN or HMDS or a mixture of at least two of these gases. Noble gases, e.g., argon or helium, or gases such as oxygen or nitrogen can be added as the carrier gas. The silicon-based monomers and the container coating therewith are known in the prior art. In particular, it is known in the prior art that HMDSO as a process gas, optionally with a carrier gas, provides good protective layer properties. However, other precursors are also known for depositing coatings on plastic containers, e.g.,carbon-based monomers such as ethyne, also known as acetylene.

[0014] According to the invention and in the course of investigations, it was found that particularly suitable protective layers are created when at least two of the following three features are implemented in any combination during the deposition of the protective layer. It is preferred that all three features be implemented, as this has led to particularly good results.

[0015] The first of the three features relates to the negative pressure in the container interior during deposition of the protective layer. It has been recognized that the resulting layers exhibit the desired increased resistance to cleaning agents if this negative pressure in the container interior is kept below 0.3 mbar, preferably below 0.25 mbar, more preferably between 0.1 and 0.25 mbar, and especially preferably between 0.15 and 0.2 mbar, whereby the lower and upper limit values ​​can deviate by 10% (+ / - 10%). Even lower negative pressures, e.g., below 0.1 mbar, have not led to a further significant increase in resistance that justifies the additional effort required to achieve such a negative pressure. Previously, typical negative pressures were in the range of 0.5 mbar or higher.While setting lower pressure values ​​either requires more powerful vacuum pumps or requires more time for extraction, resulting in longer process times and lower container throughput, this additional effort or time proves to be justified within the specified vacuum range by the significant increase in the protective layer's resistance to common cleaning agents such as caustic soda.

[0016] The second of the three features relates to the power with which the microwave radiation is applied during the deposition of the protective layer. As in the prior art, the microwave radiation is used in pulses, i.e. the microwave radiation is switched on and off in a repeating sequence. The irradiation occurs at a specific power, which is also referred to as the pulse power. The decisive factor for this second feature is that the average microwave power is less than 50 watts, preferably less than 40 watts, and more preferably between 25-30 watts (+ / -10). This average power P_average is calculated from the pulse power PJmpuls according to the formula P_average = PJmpuls x t_on / (t_on + t_off). t_on is the pulse duration, and t_off is the pause time between two pulses. In other words, t_on is the time during which radiation is irradiated, and t_off is the time without microwave irradiation.Particularly good resistance properties have been observed for the average power values ​​specified above. The pulse power is preferably between 750 and 1500 watts, preferably less than 1000 watts. Furthermore, the time t_on is preferably between 0.5 and 4 ms, preferably less than 2 ms. These values ​​have also been shown in studies to be advantageous in terms of the protective properties of the resulting layers and in terms of process times.

[0017] The third of the three characteristics finally concerns the process gas that is fed into the vessel interior during the deposition of the protective layer and from which the layer is deposited, or rather the composition of this process gas. It has proven advantageous if this process gas mixture is supplied with a low carrier gas content, in other words with a high monomer content. It has been recognized that a carrier gas content of less than 50%, preferably less than 25%, and particularly preferably less than 10% results in favorable resistance of the protective layer, for example against sodium hydroxide solution. The % specification refers to the mass flow in sccm. If the carrier gas content is 50%, the mass flow of carrier gas and monomer are the same. The most durable protective layers could be achieved if a pure monomer gas without a carrier gas was used as the process gas, e.g. pure HMDSO without the otherwise usual addition of a noble gas such as argon as a carrier gas.Previously common process gas mixtures for depositing a protective layer, for example, require a larger amount of carrier gas than monomer. For water bottles, for example, a mixing ratio of two to one was used, meaning twice the amount of carrier gas (e.g., argon) compared to the amount of monomer (e.g., HMDSO), each based on the mass flow in sccm. For CSD containers, the amount of carrier gas is further increased compared to the amount of monomer and can easily be 100 times the amount of monomer. However, these common process gas mixtures are not optimized for the resistance of the resulting layer to cleaning agents.

[0018] The protective layer produced in the method according to the invention protects the reusable plastic container, in particular a PET bottle, at the coated areas against attack by cleaning agents, e.g. caustic soda, during the cleaning process. This prevents the cleaning agents from damaging the surface of the container's base body and thus from exacerbating existing unevenness, thus preventing the formation of large-scale adhesions of biofilms and foreign substances. Since the protective layer retains its protective effect for several cleaning cycles, e.g. in a caustic bath, any biofilms or similar adhering to the surface of the protective layer can be easily removed in a single washing step. This means that the container can be refilled after each washing cycle. The container only needs to be provided with a new protective layer after several cleaning and filling cycles.Each of the three features mentioned above, taken individually, leads to improved properties of the protective coatings in terms of resistance to typical cleaning agents. However, the combination of the features leads to a further significant increase in resistance, while the protective coatings can be applied within acceptable process times. These process times are significant, because on an industrial scale, hundreds, if not thousands, of containers must be coated per hour. The highest resistance, while still maintaining acceptable process times, was observed when all three features were implemented.

[0019] It was also found that the resulting protective layers according to the invention described above have increased hydrophobic properties compared to conventional coatings, thus reducing the adhesion of contaminants and the growth of biofilm. Relative to water, the contact angle is thus further increased toward 90°. This effect has been noticeable, for example, when rinsing a container after a cleaning step: it was found that virtually no water adheres to the protective layers after rinsing. It was even found that this can be used as a criterion for the quality of the protective layer.The observed increased hydrophobic properties of the protective layer potentially allow modification of conventional industrial cleaning processes by shortening throughput times, reducing alkali concentrations, or lowering cleaning temperatures. This would also have a positive impact on the durability of the applied layers: the damaging effects of the cleaning process would be reduced. The protective layers according to the invention therefore exhibit, on the one hand, better resistance to conventional cleaning fluids. Furthermore, the protective layers according to the invention are easier to clean due to their increased hydrophobic properties, meaning fewer aggressive washing steps are required, thus further increasing the durability of the protective layer.

[0020] The protective layers according to the claims could be deposited directly onto the container material. While this protective layer would then protect the container material against the damaging effects of cleaning agents as intended, the protective layer would not, for example, simultaneously be able to prevent the transfer of certain aromas into the plastic container wall as required. As explained in the general description, this would limit the variable or alternating use of, for example, reusable PET bottles. In this respect, it is advantageously proposed that an adhesion promoter layer (HV) and a barrier layer (BA) be deposited on the inside of the container before the protective layer (TC) is deposited. A layer structure of HV-BA-TC is therefore proposed, and the barrier layer would prevent the transfer of aromas into the plastic container wall and also the ingress of oxygen from outside into the container.This proposed layer structure would increase the shelf life of filled products, and after a washing cycle, a reusable container could safely hold either flavored or unflavored beverages. The same reusable container can therefore be filled with different liquids over the course of its multiple uses, including water after lemonade was in the container in the previous cycle. This would only be possible without a barrier layer if the protective layer were resistant to aromatic migration, which it generally is not. The barrier layer itself is protected from the damaging effects of a cleaning or washing agent by the protective layer applied to the inside of the container, i.e. the protective layer protects both the barrier layer and the container material.A further advantage of an adhesion promoter layer and a barrier layer is a weight reduction of the container without negatively impacting the barrier function due to the savings in PET material; this can even increase it many times over. It is also advantageous for the layers added to the protective layer if the negative pressure inside the container is kept below 0.3 mbar during the deposition of the respective layer, preferably below 0.25 mbar, more preferably between 0.1 and 0.25 mbar, and especially preferably between 0.15 and 0.2 mbar (plus -10%).

[0021] The durability of the protective layer can be further increased by depositing the protective layer with a layer thickness greater than 40 nm, preferably greater than 60 nm, more preferably greater than 80 nm, and most preferably greater than 100 nm. Even greater layer thicknesses are of course also possible. Typical coating thicknesses, e.g. for CSD containers (CSD = carbonated soft drink), are 25-30 nm. This already concerns a layer structure consisting of an adhesion promoter (HV), a barrier layer (BA), and finally a protective layer (top coat (TC)). The adhesion promoter and the top coat are usually thicker than the barrier layer, but each regularly thinner than 20 nm.

[0022] It has also been recognized as advantageous for the durability of the protective layer that the build-up of the protective layer takes place more slowly than is usual in the prior art, in particular slower than the build-up of any other coatings present, such as HV and / or BA. In this respect, it is advantageously proposed that the coating time for the protective layer is greater than 4000 ms, preferably greater than 5000 ms, more preferably greater than 7500 ms, and finally preferably greater than 10,000 ms. The coating time refers to the duration of the deposition process for the protective layer. If an adhesion promoter layer and then a barrier layer are applied before the protective layer is applied, it is advantageous that the coating time for the protective layer is more than twice as long as the coating time for the two other layers combined.

[0023] Furthermore, investigations have shown it to be advantageous to deposit a second protective layer TC2 inside the container in addition to a first protective layer TC1 and, after its deposition, to do so. It is possible for this second protective layer TC2 to be deposited, for example, directly onto the first protective layer TC1, resulting in a layer structure HV-BA-TC1-TC2. Regarding layer thicknesses for the protective layer and / or coating times for the protective layer, in the case of such a structure consisting of multiple protective layers TC1 and TC2, this refers to the sum of the protective layers TC1 and TC2, i.e. the protective layers taken together meet the established criteria for layer thickness and coating time.In a continuation of this embodiment variant, it has been found to be advantageous that an adhesion promoter layer (HV2) and a barrier layer (BA2) are deposited as an intermediate layer between the first protective layer (TC1) and the second protective layer (TC2), thus creating a layer structure HV1 - BA1 - TC1 - HV2 - BA2 - TC2, provided that the protective layer TC1 is not deposited directly onto the inner wall of the container (in which case a layer structure TC1-HV1-BA1-TC2 would be present). If an adhesion promoter layer HV1 and a barrier layer BA1 are first deposited onto the inner wall of the container, then it is preferred that the proportion of oxygen as a carrier gas in the process gas used for the adhesion promoter layer (HV2) and / or the barrier layer (BV2) of the intermediate layer is reduced compared to the process gas for the adhesion promoter layer HV1 orBarrier layer BA1 between the first protective layer (TC1) and the container material, particularly in that oxygen is partially substituted by a noble gas, e.g., argon. It is generally advantageous to keep the oxygen content within the process gas low when depositing an intermediate layer between two protective layers, as it has been found that oxygen negatively affects the resistance of the already deposited protective layer to detergents, e.g., caustic soda.

[0024] In a further development of the aforementioned embodiments, it has proven advantageous that after the second protective layer (TC2) has been deposited, a third protective layer (TC3) is deposited inside the container, wherein an adhesion promoter layer (HV3) and a barrier layer (BA3) are preferably deposited on the container as a second intermediate layer between the second and third protective layers (TC3). Once again, it has proven advantageous to have little oxygen in the process gas when depositing this second intermediate layer, preferably by reducing the proportion of O2 in the process gas used for the adhesion promoter layer (HV3) and / or the barrier layer (BV3) of the second intermediate layer compared to the process gas for the adhesion promoter layer HV1 or barrier layer BA1 between the first protective layer TC1 and the container material, in particular by substituting O2 with a noble gas, e.g. with argon.

[0025] It is known in the prior art that the adhesion promoter layer is deposited, for example, from a process gas mixture of HMDSO and oxygen (O2) or of HMDSO and argon (Ar). With regard to the intermediate layers mentioned above, a mixture of HMDSO and argon would be preferable. If an oxygen content is to be included in the process gas, e.g. because this is desired for the layer properties of the adhesion promoter layer, the oxygen content can be reduced by at least partially substituting oxygen with argon, i.e., by using a mixture of HMDSO, oxygen, and argon. A typical adhesion promoter layer according to the prior art has a layer thickness of between 5 and 20 nm.

[0026] It is known in the prior art that the barrier layer is deposited, for example, from a process gas mixture of HMDSN and O2 or of HMDSN and O2 and Ar. If a barrier layer is to be deposited as an intermediate layer between two protective layers, it is advantageous to keep the oxygen content low in this barrier layer and the process gas mixture used, for example, by substituting oxygen with argon. A typical barrier layer according to the prior art has a layer thickness of 5-20 nm, preferably in the order of 10 nm. This improves the elongation properties and provides additional protection for the contents against migration from the PET material.

[0027] An advantageous development of the method according to the invention provides for all embodiments that the PET material used for the container contains a proportion of recycled PET material, in particular a proportion greater than 50%, particularly preferably a proportion between 80-100%, in particular 100%. Since the protective layer according to the invention eliminates the surface roughness of the inner surface of the container with regard to the adhesion of biofilms or foreign substances, the use of recycled PET material is possible, which increases environmental compatibility.

[0028] The invention solves the problem according to a second aspect by a container coating machine having the features of claim 9. The advantages of the machine result from the above-mentioned advantages of the method.

[0029] Finally, the invention solves the problem according to a third aspect by means of a reusable plastic container having the features of claim 10. It is further preferred that the protective layer (TC) covers the entire interior of the base body of the container, preferably additionally also at least part of the outer surface of the base body of the container, wherein the protective layer (TC) is preferably formed from HMDSO, HMDSN or HMDS or a mixture of at least two of these substances. Finally, it is also advantageous for the container if it consists of a PET material with a proportion of recycled PET material, in particular with a proportion greater than 50%, particularly preferably a proportion between 80-100%, in particular 100%. The invention, with the aspects mentioned above, provides the person skilled in the art with tools to provide reusable containers with coatings of specific resistance or a minimum resistance. With knowledge of or when specifying the cleaning agent orDuring the cleaning procedure, the coating process can specify a minimum number of cycles that the container can withstand due to the coating. For example, the expert can design the protective layer so that it can withstand at least ten cycles of a standard industrial washing process. It is also possible to specify larger cycle numbers, although this increases the time required to apply the coating. With smaller cycle numbers, the time required to apply the coating is shorter. The expert can select an economically viable number of cycles from these constraints.

[0030] The invention is explained in more detail below using preferred embodiments and the accompanying figures. Experimental results are also presented in excerpts. The drawings are not necessarily to scale, but are to be understood as schematic representations. In the figures, identical or essentially functionally identical or similar elements are designated by the same reference numerals. Without limiting generality, bottles are a typical application for a container. Therefore, the following description often refers to bottles. Furthermore, to explain the invention, reference is made in particular, and also without limiting generality, to containers made of PET, without excluding other thermoplastics. The figures show:

[0031] Fig. 1 is a schematic plan view of a coating system as is known in its basic structure and basically in the prior art;

[0032] Fig. 2 is a perspective view of an example of a single coating station as is generally known in the prior art;

[0033] Fig. 3 is a sectional view through an example of a single coating station with a double chamber and as basically known in the prior art;

[0034] Fig. 4a, b a schematic representation of a coated container inner wall and an SEM image of a cross section through a coated container inner wall;

[0035] Fig. 5 shows images of three bottles; Fig. 6 shows a schematic diagram explaining the experimental procedure;

[0036] Fig. 7 is a diagram showing the determined influence of layer thickness on the resistance of the protective layer to caustic soda;

[0037] Fig. 8 Measurement results for OTR measurements on different containers;

[0038] Fig. 9a-c Principle representations of multi-layer coatings;

[0039] Tables 1 to 9 summarize experimental parameters and measurement results for different coating variants.

[0040] The illustration in Fig. 1 shows a coating system, more precisely a PECVD system 10, which is equipped with a rotating coating wheel 2. A plurality of coating stations 1 are arranged at circumferential spacing along the circumference of the coating wheel 2. Since plasma-based coating processes are involved, the following will also refer to a plasma wheel 2, plasma stations 1, and plasma chambers 17. Since coating processes are involved, the terms coating wheel 2, coating chambers 17, and coating stations 1 could also be used synonymously.

[0041] The plasma stations 1 are provided with cavities or plasma chambers 17, which will be shown later, for accommodating bottles 5 to be treated. As an example, each plasma station 1 has four treatment stations within each plasma chamber 17. This PECVD system 10 is purely exemplary for all coating systems that perform coating processes on containers using process gases. Furthermore, the containers below are formed by bottles 5 only as an example.

[0042] The bottles 5 to be treated are fed to the plasma wheel 2 in the area of ​​an input 8 and passed on via a separating wheel 7 to a transfer wheel 6 which is equipped with support arms which can, for example, be designed to be positionable. The support arms can, for example, be arranged so as to be pivotable relative to a base of the transfer wheel 6 so that the distance between the bottles 5 can be changed. This transfers the bottles 5 from the transfer wheel 6 to the plasma wheel 2. After the treatment has been carried out during rotation on the plasma wheel 2, the treated bottles 5 are removed from the area of ​​the plasma wheel 2 by an output wheel 3 and transferred to the area of ​​an output section 4. Two options are known in the prior art: coating the workpieces 5, which are designed, for example, as bottles 5, with the mouth area facing upwards or downwards.Since the transport of the bottles 5 is easier when the mouth area points upwards, the bottles 5 could, for example, be fed into the area of ​​the input 8 with the mouth area pointing upwards and the bottle 5 could, for example, be turned on the transfer wheel 6 into a position with the mouth area facing downwards. Working wheels with such a turning function are known in the art. In this positioning, the bottle 5 would be transferred to the plasma wheel 2 and also removed from the plasma wheel 2 after treatment. The output wheel 3 could then turn the bottle 5 again and the bottle 5 could then be fed to the output section 4 with a positioning with the mouth area facing upwards. Without limiting the generality, the following figures show the bottle 5 being positioned with the mouth area facing downwards.It is also possible, of course, for the treatment to be carried out on plasma wheel 2 with the mouth area facing upwards and for no turning process to be performed before or after plasma wheel 2. A different orientation of the bottles during the coating process is also not fundamentally excluded.

[0043] In a manner not shown, as this is sufficiently known in the prior art, process gases are generated, e.g. by evaporating liquid precursors, e.g. by mixing them with other gases. The process gases generated in this way reach the plasma wheel 2 and are guided to the plasma wheel 2 via rotary feedthroughs known in the prior art. The process gases transferred to the plasma wheel 2 have the required composition upon transfer and are provided by a gas supply device arranged outside the plasma wheel 2, which will not be described further as it is not essential to the subject matter of the invention. The supply usually takes place in a center of the plasma wheel 2 and via a rotary distributor arranged there, via which the plasma stations 1 are also supplied with operating materials and energy.For the distribution of process gases and operating materials, ring lines are used in particular, which supply the process gases required for the coating process to the several plasma stations 1 rotating with the plasma wheel 2.

[0044] To illustrate a possible basic design of a plasma station 1, Fig. 2 shows a perspective view of a station with a single treatment station. A station frame 16 is provided with guide rods 23, on which a carriage 24 is guided to hold the cylindrical chamber wall 18. Fig. 2 shows the carriage 24 with the chamber wall 18 in a raised state, so that the upside-down container in the form of a bottle 5 is exposed. When the chamber wall 18 is raised, the plasma chamber 17 is in an open position; when the chamber wall 18 is lowered, the plasma chamber 17 is in a closed position.

[0045] A microwave generator 19 is arranged in the upper area of ​​the plasma station 1. The microwave generator 19 is connected via a deflector 25 and an adapter 26 to a coupling channel 27, which opens into the plasma chamber 17. The adapter 26 functions as a transition element. The deflector 25 is designed as a waveguide. The bottle 5 is positioned in the area of ​​a tong-like holding and sealing element 28, which is arranged in the area of ​​a chamber floor 29 and which can be designed, for example, as described in DE 10 2022 119 836. The chamber floor 29 is formed as part of a chamber base 30.

[0046] To close the plasma chamber 17, the carriage 24 with the cylindrical chamber wall 18 can be lowered along the rails 23 until the chamber wall 18 has moved against the chamber floor 29. In this closed positioning state, the plasma coating of the bottle 5, which is then enclosed in the closed cavity 17, can be carried out. In the closed positioning state, the required negative pressure in the chamber 17 and in the bottle 5 is also adjusted in order to generate a plasma and carry out the microwave-induced plasma coating. In the closed positioning state, the chamber 17 and the bottle 5 accommodated in the chamber 17 are also vented to ambient pressure so that the chamber 17 can be opened.

[0047] In the raised position of the chamber wall 18 shown in Fig. 2, it is possible without problems to remove the treated bottle 5 from the area of ​​the plasma station 1 and to insert a new bottle 5 to be treated, e.g. by means of the wheels 6 and 3 shown in Fig. 1.

[0048] Fig. 3 shows an example of a plasma station 1 with a plasma chamber 17 for the simultaneous plasma treatment of two bottles 5. For this purpose, the chamber 17 is divided into two sub-chambers 17a, 17b. Alternatively, the subdivision by a partition could also be omitted. Each of the sub-chambers 17a, 17b is connected to a microwave generator 19 via a coupling channel 27 as well as an adapter 26 and a deflector 25. In principle, it is also conceivable to use a common microwave generator 19 for two or more sub-chambers 17a, 17b and to divide the generated microwave radiation via a branch (not shown) in order to ensure uniform ignition of the plasma in each of the sub-chambers 17a, 17b.

[0049] Supply channels 54 for adjusting the chamber pressure open into the subchambers 17a, 17b. Each of these channels is connected to a branch 55 for distributing the suction power provided by the pumps. If more than two plasma chambers 17 are used, the branch 55 is either provided with a corresponding number of outlets, or several sub-branches are arranged in cascade. Negative pressure, for example, can be supplied via these channels 54, 55.

[0050] The two cylinders 5 are supplied with process gases via gas lines 74, which in the embodiment shown have been split from a central line at a branch 75.

[0051] Also shown for each treatment station is a gas lance 36 that can be moved vertically into and out of the bottle 5, e.g., in a manner not shown, by being arranged on a lance carriage that can be guided vertically and, e.g., can perform a cam-controlled vertical movement. In the position shown, the plasma chamber 17 is closed, and the lance 36 is arranged inside the bottle 5 for discharging the process gases into the interior of the container 5. The gas lances 36 assume the coating position.

[0052] In the area of ​​the chamber base 30, the plasma chambers 17 and the containers 5 are subjected to negative pressure via the aforementioned channels 54, 55; venting is also possible. Process gases are supplied to the gas lances 36 via a process gas line 66 and the lines 74 connecting behind the branch 75 and guided into the container interior. The supply is valve-controlled in each case. The process gas line 66 is connected to a gas supply device (not shown) and carries the process gases provided by this gas supply device to the gas lances 36.

[0053] Fig. 3 shows, in a highly schematic representation and with additional representations of switchable valves 59, the control and adjustment of the pressure conditions and the process gas supply. Starting from a supply line, both the process gas and the negative pressure are distributed at branch points to several sub-lines. Also visible are quartz glass windows 68 for sealing the interiors of the plasma chambers 17 relative to the interiors of the coupling channels 27 while simultaneously allowing the microwave radiation to pass through. According to the purely exemplary embodiment shown, a primary vacuum valve 60 is used to supply a first negative pressure stage, and a secondary vacuum valve 61 is used to supply a negative pressure that is lower than the first negative pressure stage. The addition of further negative pressure stages is possible.To maintain the vacuum synchronously with the process gas supply, a process vacuum valve 62 is also provided. The process vacuum valve 62 prevents the extracted process gas from entering the supply circuits for the primary vacuum and the secondary vacuum.

[0054] To support the selective or joint supply of negative pressure to the interior of the bottle 5 and / or to the further interior of the plasma chamber 17, a chamber vacuum valve 63 is used, which performs a corresponding shut-off function. In particular, the idea is to supply the respective supply vacuum directly to the interior of the bottle 5 via the valves 60, 61, 62, and to connect the further interior of the plasma chamber 17 as needed, controlled by the chamber vacuum valve 63.

[0055] A container vent valve 64 and a chamber vent valve 65 are used for a predeterminable and independent venting of both the interior of the bottle 5 and the further interior of the plasma chamber 17. A first process gas valve 66 and a second process gas valve 67 are used to supply different process gas compositions. It is also conceivable to supply additional process gas mixtures, so that additional lines and additional valves could be added. The process gas mixtures are provided by a gas supply device.

[0056] The following describes a typical coating process sequence on a coating station. The explanation refers to one bottle, meaning the process is described in the singular. When treating multiple bottles simultaneously, the described processes occur simultaneously for all bottles.

[0057] A typical treatment process is carried out, for example, in such a way that the bottle 5 is first transported to the plasma wheel 2 as explained in relation to Figure 1, and the bottle 5 is inserted into the plasma station 1 with the sleeve-like chamber wall 18 pushed up. After the insertion process has been completed, the chamber wall 18 is lowered into its sealed position. For sealing purposes, the chamber wall 18 has circumferential sealing rings on its front side as a sealing device 41. First, an evacuation of both the cavity 17 and an interior of the bottle 5 is carried out simultaneously; if necessary, only a pre-evacuation of the cavity 17 takes place first, before the evacuation of the interior of the bottle 5 is also switched on.

[0058] After sufficient evacuation of the interior of the cavity 17, the gas lance 36 is moved into the interior of the bottle 5 and the interior of the bottle 5 is sealed off from the interior of the cavity 17. It is also possible to move the gas lance 36 into the bottle 5 synchronously with the beginning of the evacuation of the interior of the cavity 17. The pressure in the interior of the bottle 5 is then reduced even further. Furthermore, it is also conceivable to carry out the positioning movement of the gas lance 36 at least partially parallel to the positioning of the chamber wall 18. After a sufficiently low negative pressure has been reached, process gas is introduced into the interior of the bottle 5 and the plasma is ignited with the aid of the microwave generator 19. In particular, it is conceivable to use the plasma to apply both an adhesion promoter to an inner surface of the bottle 5 and the actual barrier layer, e.g.from silicon oxides. An additional third layer, such as a protective layer, can also be deposited using plasma, e.g., also from silicon oxides.

[0059] After the coating process is completed, the gas lance 36 is removed from the interior of the bottle 5, and the plasma chamber 17 and the interior of the bottle 5 are ventilated. After ambient pressure has been reached within the cavity of the plasma chamber 17, the chamber wall 18 is raised again to remove the coated bottle 5 and insert a new bottle 5 to be coated. The coating process described proceeds while the bottle 5 rotates on the plasma wheel 2 in the plasma station 1.

[0060] Positioning of the chamber wall 18 and / or the gas lance 36 can be achieved using various drive units. In principle, the use of pneumatic drives and / or electric drives, particularly in a linear motor embodiment, is conceivable. However, it is particularly contemplated to implement a cam control system to support precise movement coordination with a rotation of the plasma wheel 2. The cam control system can, for example, be designed such that control cams are arranged along a circumference of the plasma wheel, along which cam rollers are guided. The cam rollers are coupled to the respective components to be positioned. The valves 59 are preferably actuated via a programmable electronic controller 45.First, after the plasma chamber 17 has been closed, the primary vacuum valve 60 is opened and the interior of the bottle 5 and the interior of the plasma chamber 17 are evacuated simultaneously or partially at different times. In this case, a pressure level in the range of 20 mbar to 50 mbar is reached. After the primary vacuum valve 60 has been closed, the secondary vacuum valve 61 is opened and the interior of the bottle 5 and the interior of the plasma chamber 17 are initially connected simultaneously to a vacuum source with a lower pressure level. After the interior of the plasma chamber 17 surrounding the bottle 5 has been sufficiently evacuated, the chamber vacuum valve 63 closes and only the interior of the bottle 5 is further evacuated. In this case, a pressure level of approximately 0.1 mbar is reached.

[0061] After the chamber vacuum valve 63 has been closed and the gas lance 36 has usually already been positioned beforehand within the interior of the bottle 5, the first process gas valve 66, also called the primary process gas valve, opens and a process gas of a first composition is supplied. After a sufficient supply of process gas, the microwave generator 19 ignites the plasma in the interior of the bottle 5. At a predeterminable time, the primary process gas valve 66 closes and the secondary process gas valve 67 opens to supply a process gas of a second composition. At least temporarily, parallel to the opening of the process gas valves 66, 67, the process vacuum valve 62 also opens in order to maintain a sufficiently low negative pressure in the interior of the bottle 5. A pressure level in the range according to the invention proves to be advantageous here, e.g., a pressure level of approximately 0.2 mbar.

[0062] After the plasma coating process is complete, the container vent valve 64 opens first, connecting the interior of the bottle 5 to ambient pressure. With a predeterminable time delay after the container vent valve 64 opens, the chamber vent valve 65 also opens to completely raise the interior of the plasma chamber 17 back to ambient pressure. Once the ambient pressure within the plasma chamber 17 has at least approximately been reached, the plasma chamber 17 can open, and the coated bottle 5 is removed and replaced with a new bottle 5 to be coated.

[0063] The processes described above take place in a plasma chamber with multiple container treatment stations, simultaneously for each of the treatment stations and thus simultaneously for each container 5 arranged at one of the multiple treatment stations. The invention is explained below using further figures, and tables present the tests conducted and the results obtained therefrom. The tests were carried out on a laboratory coating station, which structurally corresponds to a station on the InnoPET Plasmax 20Q coating machine from KHS GmbH, which has been available on the market for many years. This machine has twenty stations arranged on a plasma wheel, each of which simultaneously accommodates and coats four containers. The laboratory coating station corresponds to one of these 20 stations.The coating process basically corresponds to the previously described process sequence with regard to setting negative pressure conditions, supplying process gases and igniting a plasma by microwave radiation.

[0064] Figures 4a and 4b explain, in a schematic representation (Figure 4a) and in a scanning electron microscope image (Figure 4b), on the one hand, the problem to be solved by the present invention and, on the other hand, a first approach to solving the problem. Figure 4a schematically shows that the PET material of a plastic bottle is first provided with a barrier layer (BA) on the inside of the container; an adhesion promoter layer (HV) between the PET material and the barrier layer (BA) is also provided and is not shown separately. The barrier layer (BA) and also the PET material are to be protected against the cleaning agent caustic soda (NaOH), which is filled, for example, into the interior of the container during a washing process in order to remove impurities and residues from the container before a subsequent filling process.The barrier layer (BA), which is specified with a layer thickness of 30 nm, which also includes the thickness of the adhesion promoter layer (HV), is intended to prevent the penetration of oxygen and water into the container interior and the contents filled therein. In the case of carbonated beverages as the contents, the barrier layer is also intended to prevent the escape of carbon dioxide. Conventional barrier layers (BA) are not resistant to typical cleaning agents used in container washing machines. A barrier layer (BA) known in the prior art would therefore not survive such a washing process, e.g., with caustic soda. A new coating would be necessary after each wash cycle. For this reason, a topcoat is applied to the barrier layer (BA), which is referred to below as TC and in the claims as the protective layer. In the diagram shown, this topcoat (TC) is many times thicker than the barrier layer (BA), and this can, for example,approximately 150 nm. This protective layer (TC) should be able to withstand washing with sodium hydroxide solution to such an extent that the barrier layer (BA) and thus also the PET material are not attacked by the sodium hydroxide solution. Figure 4b shows an SEM image of a cross-section through a coated container, initially on the left side of the image the PET material of the coated bottle. This is followed by a coating on the inside of the container with a total thickness of 210 nm, with a 35 nm thick coating consisting of an adhesion promoter (HV) and a barrier layer (BA) being applied directly onto the PET material. The protective layer (TC) applied to these two layers on the inside of the container therefore has a thickness of approximately 175 nm. Such a layer thickness is unusual, as previous protective layers are usually well below 40 nm and are, for example, between 20 and 30 nm.One reason for this is that the deposition process for a coating takes longer the thicker the layer is required. A thicker layer thickness therefore contradicts the need for short process times to coat as many bottles as possible in a given time. The layers mentioned were deposited starting from silicon-based monomers (HDMSO, HMDSN). Examples of how and under which process conditions these layers can be deposited will be given later.

[0065] Figure 5 shows three reusable bottles, namely on the far left a PET bottle which has no coating and which has not been subjected to a washing process. On the right-hand side of the image, the same bottle is shown, also an uncoated PET bottle, but which has been exposed to a caustic soda solution. The bottle was filled with caustic soda and placed in a water bath for twelve days at 57°C, which corresponds to a normal washing temperature. The caustic soda had a concentration typical for washing processes, for example 1.8%. It is immediately apparent that the PET material has been attacked by the solution. This is known as PET corrosion, which is reflected in the cloudy, milky appearance of the bottle. In contrast, the middle bottle has retained its transparency despite the same treatment with caustic soda. Apparently, no PET corrosion has occurred.This is due to the fact that a protective coating (TC) was applied to the middle bottle before the caustic soda solution was poured in, as shown in Figures 4a and 4b. The protective coating apparently prevented the caustic soda solution from attacking the PET material.

[0066] Figure 6 shows a schematic representation of how, as part of tests conducted, a washing step was simulated in an industrial washing machine for reusable containers in order to evaluate the effects of several consecutive washing steps on containers with different coatings. The lower part of Figure 6 shows a typical industrial washing machine in which reusable containers are washed before being refilled. In such washing machines, it is customary to first carry out a pre-cleaning process, primarily to remove coarse contaminants, then carry out the actual washing process and finally rinse the containers with water to remove any residues of the cleaning agent and any detached contaminants. Accordingly, on a laboratory scale, a pre-cleaning process was first carried out using a less aggressive cleaning agent, e.g., a sodium hydroxide solution with a pH of 12 and a temperature of 45°C.The pre-cleaning was performed over a period of approximately 30 seconds. The actual washing process was carried out with a more aggressive caustic soda solution, namely a caustic soda solution with a concentration of 1.8% and a temperature of 58°C. The washing process lasted a total of 10 minutes per wash cycle. Specifically, the container was filled with this caustic soda solution and kept at a constant temperature in a water bath. Finally, the washed container was rinsed in a rinser with water at a temperature of 20°C. The rinsing process lasted approximately 1 minute.

[0067] All tests were conducted with identical bottles. The bottles had a filling volume of 500 ml and a weight of 42 g, meaning a reusable PET bottle with a thick wall was used.

[0068] HMDSN and HMDSO were used as monomers for the various layers. The protective layer was always deposited starting with the HMDSO monomer, with the process gas sometimes also containing argon as a carrier gas. In preliminary tests, a mixing ratio of 2 to 1 was used, meaning twice the amount of argon carrier gas was used compared to the HMDSO monomer, based on the mass flow in sccm. In the test series presented later, no carrier gas was used during the deposition of the top coat (TC).

[0069] In initial preliminary tests, the influence of the layer thickness of the protective layer (TC) on the durability of the layer over multiple wash cycles was examined. For this purpose, bottles were each provided with an adhesion promoter layer (HV) and a barrier layer (BA) in an identical manner. Finally, a protective layer (TC) was applied, and the thickness of the protective layer (TC) was varied. Containers were coated with a protective layer thickness of approximately 10 nm, approximately 20 nm, approximately 40 nm, and approximately 80 nm, and even greater protective layer thicknesses were deposited. However, Figure 7 no longer shows the results for layer thicknesses greater than 80 nm, as no significant improvement was observed at even greater layer thicknesses for the number of wash cycles shown.Figure 7 shows the measured oxygen permeation (so-called OTR (Oxygen Transfer Rate)) for the containers with the different layer thicknesses plotted against the number of washing cycles to which the container was subjected at the time of the measurement. For comparison, an uncoated PET bottle was also measured. The OTR measurement measures the permeability of the bottle wall to oxygen. Commercial devices are available for this purpose, e.g. the OX-TRAN device family from Mocon. The lower the measured oxygen permeation, the greater the barrier effect of the wall against oxygen. The main barrier effect is provided by the barrier layer. The measured oxygen permeation is therefore a suitable indicator of whether the deposited barrier layer (BA) still fulfills its original barrier effect or whether this barrier effect has been impaired due to the washing cycles, i.e. the protective layer (TC) no longer fully develops its protective effect.Since the measurements do not concern the absolute values ​​obtained, but rather the change in the measured values ​​over the number of washing cycles, further explanations on the measurement of oxygen permeation are not necessary, especially since this is a common and well-known measurement method for containers.

[0070] The diagram in Figure 7 shows that the durability of the protective layer (TC) increases with increasing layer thickness, i.e. an increase in oxygen permeation sets in later and is less pronounced. In the case of the TopCoat (TC) with a layer thickness of 10 nm, the oxygen permeation increases significantly after the first wash cycle and continues to rise during subsequent wash cycles. This means that the sodium hydroxide solution is no longer reliably kept away from the barrier layer (BA) after the first wash cycle, but increasingly damages the barrier layer (BA), which is primarily responsible for the oxygen barrier effect. In contrast, with the greater layer thicknesses, an increase in oxygen permeation is only clearly visible in later wash cycles. Quite surprisingly, no major difference was found in the preliminary test between the coating with a 40 nm protective layer and an 80 nm protective layer.However, in later investigations, the impression resulting from Figure 7 that virtually no difference could be detected could not be verified. Rather, the expected effect occurred that the 80 nm protective layer only loses its protective effect at longer wash cycles than the 40 nm protective layer, i.e. it is measurably below the measurement curve for the 40 nm layer. However, the trend resulting from Figure 7 could be confirmed that even greater layer thicknesses no longer lead to significant improvements within the observed range of 20 wash cycles. The trend resulting from Figure 7 could also be confirmed that the increase in protective effect decreases with increasing layer thickness of the protective layer (TC). Figure 8 shows a representation similar to Figure 7, namely measured oxygen permeation values ​​plotted against the number of wash cycles.A "Generation 1" protective layer (TC) is compared with a "Generation 2" protective layer (TC). As already described for Figure 7, the containers were first coated internally with an adhesion promoter layer (HV) and then with a barrier layer (BA). Finally, a Generation 1 or Generation 2 protective layer (TC) was deposited. Both protective layers (TC) had an identical layer thickness, and both protective layers (TC) were deposited using a low proportion of argon as the carrier gas in the process gas. While a negative pressure of approximately 0.5 mbar was set for the Generation 1 protective layer (TC), a significantly lower process pressure of approximately 0.2 mbar was set for the Generation 2 protective layer (TC).The significantly different courses of the measurement curves for the two protective coatings (TC) show, on the one hand, that the protective coating (TC) of generation 2 loses its protective effect later and that there is no significant increase in oxygen permeation up to about 10 wash cycles. Overall, the measurement curve for the protective layer (TC) of generation 2 is significantly below the curve for the protective layer (TC) of generation 1. From these measurements, it can be concluded that the negative pressure during the deposition of the protective layer (TC) is an important factor influencing its resistance to cleaning agents. The increase in resistance to, for example, caustic soda is well related to the time required during coating.

[0071] Experiments were also conducted to investigate the influence of the layer structure. Figures 9a-9c provide a general overview of the different layer structures considered.

[0072] The layer structure in Figure 9a is characterized by the usual initial structure of adhesion promoter layer (HV), barrier layer (BA) and protective layer (TC). A further protective layer (TC2) was deposited on top of this first protective layer (TC1), and finally a third protective layer (TC3). So-called pinholes occur in a protective layer (TC) as a result of layer defects, through which, for example, sodium hydroxide solution can penetrate to the barrier layer (BA) and cause damage there. The basic idea of ​​the multiple coating with several consecutive protective layers (TC1, TC2, TC3) is to cover these pinholes from layer to layer and create a type of labyrinth effect so that, for example, sodium hydroxide solution has no, or at least no direct, access to the barrier layer (BA). Further tests were carried out with a layer structure as shown in Figure 9b.Between the several protective layers (TC1, TC2, TC3) only one intermediate layer in the form of an adhesion promoter (HV2, HV3) was deposited.

[0073] Layer structures as shown in Figure 9c were also investigated, namely the deposition of an adhesion promoter layer (HV2, HV3) and a barrier layer (BA2, BA3) between the multiple protective layers (TC1, TC2, TC2). This layer structure is characterized by the recurring triple sequence of adhesion promoter (HV), barrier (BA), and top coat (TC).

[0074] After several preliminary tests, a series of tests was conducted with a total of 18 different coating variants, all produced at the aforementioned laboratory station. Two batches of four containers each were produced, thus providing eight containers with internal coatings per coating test run.

[0075] Table 1 below contains the process parameter values ​​used for the deposition of the adhesion promoter layer (HV1) directly onto the inside of the PET container. For all coating variants, the adhesion promoter layer (HV1), which was applied directly onto the PET material, was deposited using these process parameters. The adhesion promoter layer (HV1) was deposited using a process gas mixture consisting of HMDSO and oxygen at a vacuum of approximately 0.33 mbar.

[0076] Tab. 1 : Parameters for deposition of adhesion promoter layer (HV1)

[0077] Table 2 below contains the process parameter values ​​used for the deposition of the first barrier layer (BA1) on the first adhesion promoter layer (HV1). For all coating variants, the first barrier layer (BA1) was deposited using these process parameters, where applicable. The first barrier layer (BA1) was deposited using a process gas mixture consisting of HMDSN and oxygen at a vacuum of approximately 0.36 mbar. Table 2: Parameters for deposition barrier layer (BA1)

[0078] Table 3 contains parameter values ​​used for the deposition of the first topcoat (TC1) on the first barrier layer (BA1). These values ​​were set for the first three coating variants of the test series, i.e., deposition was carried out at a constant negative pressure of approximately 0.15 mbar and the HMDSO flow was set at a constant 60 sccm per chamber. The process duration was kept constant at 60,000 ms. The microwave power was varied between the first test run (Run 1) and the second test run (Run 2), increasing from 800 W to 1200 W pulse power. The pulse time t_on and pause time t_off were not changed. In Run 3, the pulse power of the second test run was set to 1200 W and the t_on time was kept at 1.5 ms, but the pause time t-off was increased from 60 ms to 85 ms, so that a lower average power was radiated.

[0079] Tab. 3: Runs 1 to 3: Change in TC by changing MW power Table 4 contains the process values ​​for coating variants 4-6, in which other parameters influencing the coating process were changed compared to the TopCoat (TC) of variants 1-3, see Table 3. In these runs 4-6, the average microwave power was kept constant with a pulse value of 800 W, a t_on time of 1.5 ms and a t_off time of 60 ms. The negative pressure was kept at approx. 0.15 mbar and the HMDSO flow at 60 sccm per chamber. The process duration was changed from 20,000 ms in run 4 to 30,000 ms in run 5 and then 40,000 ms in run 6. In addition, in all three runs, two additional topcoat layers, TC2 and TC3, were deposited on top of the first topcoat layer TC1, using process parameters unchanged from those used for TC1. The process parameters specified in Table 4 were thus maintained equally for TC1-TC3 in every run.The altered processing time resulted in different layer thicknesses. Furthermore, we investigated whether layering multiple TCs on top of each other would increase resistance to cleaning agents.

[0080] Tab. 4: Runs 4-6: Change of the TC by varying the process duration and by depositing three TCs on top of each other:

[0081] Table 5 shows process values ​​for coating variants 7-9. These coating variants were structured as shown in Figure 9b, i.e., a further adhesion promoter layer HV2 was deposited on a first TopCoat layer TC1, followed by another TopCoat layer TC2, then another adhesion promoter layer HV3 and finally a third TopCoat TC3. For TopCoats TC1 -TC3, the process parameters used throughout were the same as in the fourth run, i.e., a process duration of 20,000 ms. For the two adhesion promoter layers HV2 and HV3 arranged between TopCoats, a process duration of 1100 ms was selected in the seventh run and a process gas mixture consisting of HMDSO and oxygen was used. In the eighth run, the process duration for each of the two adhesion promoter layers HV2 and HV3 was increased to 1600 ms, but the other process parameters were retained.Finally, in the ninth run, the process duration of 1600 ms selected in the eighth run was retained for the adhesion promoter layers HV2 and HV3, but the process gas composition was changed. Although an HMDSO flow of 70 sccm per chamber was still set, oxygen was completely substituted by an alternative carrier gas, namely argon. The double specification for the alternative process gas is due to the fact that a mass flow controller standardized for oxygen was used. The actual mass flow for argon at a set mass flow of 520 sccm (for O2) therefore corresponds to approximately 371 sccm (quotient 1.4).

[0082] Tab. 5: Runs 7-9: Investigation of HV2 between TC1 / TC2 and HV3 between TC2 / TC3; variation of the adhesion promoters HV2 and HV3

[0083] Tables 6.1 to 6.3 show process parameter values ​​for runs 10-16. In these runs, layer structures as shown in Figure 9c were investigated, namely a triple layer structure consisting of adhesion promoter HV, barrier layer BA, and topcoat TC. The layer structure therefore has the following structure: HV1-BA1-TC1-HV2-BA2-TC2-HV3-BA3-TC3. The first adhesion promoter layer HV1, the first barrier layer BA1, and the first topcoat layer TC1 were deposited in all runs using the same process parameter values. TC1, TC2, and TC3 were deposited using the same process parameter values ​​as in runs 7-9, see Table 6.1. Exception: in run 16, the process time for TC3 was increased from 20,000 ms to 60,000 ms.

[0084] The process parameter values ​​for adhesion promoters HV2 and HV3 are shown in Table 6.2. Both were deposited under the same conditions in each run. The process duration varied between runs, being 1600 ms in runs 10, 15, and 16 and 650 ms in runs 11-14.

[0085] Finally, Table 6.3 contains the process parameter values ​​for barrier layers BA2 and BA3, which were also deposited within one run under the same conditions. The values ​​used for barrier layer BA1 were initially set in Run 10 (see Table 2). In Runs 11-13, the process gas composition was then changed, and in particular, the oxygen content was reduced by substituting it with the alternative carrier gas argon. The original oxygen mass flow of 1400 sccm per chamber was reduced to 800 sccm in Run 11, to 500 sccm in Run 12, and to 200 sccm in Run 13, and the mass flow of

[0086] Argon was gradually increased. Reference is made to the quotient 1.4 for the conversion of oxygen mass flow and argon mass flow; see the explanation for Table 5. In Run 14, the process parameter values ​​used in Run 10 were used, with the exception of the microwave pulse power, which was reduced from 1800 W to 1300 W. In Runs 15 and 16, this reduced microwave pulse power was maintained, but the oxygen flow was reduced from 1400 sccm to 800 sccm, again using argon as a substitute.

[0087] Tab. 6.1 : Runs 10-16: TC always the same, except in Run 16: TC3 on

[0088] Process duration increased by 60000ms

[0089] Tab. 6.2: Runs 10-16: Variation adhesion promoter: Process duration

[0090] Table 6.3: Runs 10-16: Variation of barrier layers BA2 and BA3: process gas composition / oxygen content; average microwave power. Table 7 shows process parameter values ​​for runs 17 and 18, namely the process parameter values ​​for the deposition process of the topcoat TC1. In run 17, the topcoat TC1 was deposited directly onto the inside of the PET bottle; therefore, neither an adhesion promoter layer HV nor a barrier layer BA was deposited beforehand. In run 18, an adhesion promoter layer HV1 was first deposited onto the inside of the PET bottle as in runs 1-3, and then the topcoat was deposited with the process parameter values ​​shown in Table 7.

[0091] Table 7: Runs 17 and 18: Run 17: TC1 directly on PET; Run 18: HV between PET and TC1

[0092] The following Table 8 summarizes the coating variants generated in runs 1-18 in an overview of the layer structure (column 2) and names the target direction in column 3 that should be investigated with the coating variant.

[0093] Table 8: Overview

[0094] For all runs conducted, the resulting containers were tested for oxygen permeation. First, the oxygen permeation of two containers from each run was measured immediately after coating completion (OTR measurement). Two other containers were then subjected to wash cycles, and the oxygen permeation was tested again after each wash cycle. The remaining four containers from each run were used for other tests (coating thickness tests, flavor migration tests), the results of which are not shown, as they are not critical to the present application.

[0095] Table 9 below summarizes the measured values ​​obtained. The left-hand column contains the run information. In the adjacent columns, an averaged OTR value and the corresponding standard deviation are given in pairs for three configurations (two containers were always measured). These values ​​are given for a measurement before a wash process was carried out (columns 2 and 3), in columns 3 and 4 after six wash cycles, and in columns 5 and 6 after twelve wash cycles. For the first three runs and for run 14, no OTR measurement was performed after 12 wash cycles, as the oxygen permeation values ​​had already deteriorated significantly after 6 wash cycles, and the corresponding layer structures were therefore considered ineffective.

[0096] Table 9: Summary of results

[0097] From this Table 9, which merely represents a condensed summary of the total amount of measured values ​​collected, and from the preliminary tests, test series and variations between the test series, the following conclusions can be drawn regarding the desired resistance of the protective layers to cleaning agents:

[0098] MW power: It is beneficial for the durability of a protective layer (TC) if the deposition process is carried out with a reduced average microwave power. Oxygen: The use of oxygen in the process gas for adhesion promoter (HV2, HV3) and / or barrier layers (BA2, BA3) as intermediate layers between protective layers has a negative impact on the durability of already deposited protective layers (TC1, TC2). Negative pressure: It is beneficial for the durability of a protective layer if the layers are deposited with a reduced negative pressure during the deposition process. This applies particularly to protective layers, and to a lesser extent also to the other layers, adhesion promoter and barrier.

[0099] Layer thickness: The durability of a protective layer increases with layer thickness, although the increase in durability does not increase linearly with layer thickness. The additional time required to deposit the layer is increasingly disproportionate to the resulting increase in durability.

[0100] Multi-layer construction: Both the multiple deposition of protective layers (TC1, TC2, TC3) on top of one another and the other multi-layer constructions lead to improved resistance. The best results are achieved when a three-layer HV-BA-TC construction is applied multiple times, avoiding oxygen in the interlayers between protective layers.

[0101] Process composition of protective layer: The durability of a protective layer is particularly favorable if the monomer content of the process gas is as high as possible during the deposition of the protective layer.

[0102] A review of the empirical values ​​and trends resulting from the measurement results obtained and a combination of this review with the additional investment in time, materials, and equipment shows that setting improved process parameter values ​​for the following three variables influencing the deposition result offers the best cost-benefit ratio: a) negative pressure during deposition of the protective layer, b) average microwave power during deposition of the protective layer, and c) process gas composition during deposition of the protective layer. These influencing variables a) to c) demonstrate the best cost-benefit ratio, thus leading to the greatest improvements in the durability of the protective layer with a reasonable additional effort. In particular, it was found that combining the more optimal settings of two of these three influencing variables produces further significant durability advantages.Applying all three optimal process parameters during the deposition of the protective layer leads to the best overall results while still requiring an acceptable amount of additional effort. In contrast, other optimizations of influencing factors are considered less advantageous, but nevertheless also have a significant impact on durability.

Claims

Claims 1 . Method for coating reusable container (5) made of a thermoplastic, in particular PET, with a protective layer (TC) against cleaning agents, in particular against caustic soda, wherein the protective layer is deposited on the inner surface of the container (5) by means of a PECVD method for microwave-induced plasma reaction at a reduced pressure, wherein at least one container (5) with a container interior (5.1) is inserted and positioned in a plasma chamber (17) of a plasma station (3), - the plasma chamber (17) and the at least one container interior (5.1) are at least partially evacuated, - at least one container interior (5.1) of the container (5) within the at least partially evacuated plasma chamber (17) is provided with an internal coating by means of plasma treatment at the negative pressure, and - wherein a process gas mixture is used which is introduced into the container interior (5.1), wherein the process gas preferably contains HMDSO, HMDSN or HMDS or a mixture of at least two of these gases and argon, oxygen, helium and / or nitrogen is used as the carrier gas, characterized in that during the deposition of the protective layer (TC) at least two of the following features a) to c) are implemented in any desired combination, preferably all three: a) the negative pressure in the container interior (5.1) is kept below 0.3 mbar, preferably below 0.25 mbar, particularly preferably between 0.1 and 0.25 mbar and especially preferably between 0.15-0.2 mbar (+ / - 10%); b) the microwave power is radiated in pulses, and the average microwave power P_mittel (P_mittel = PJmpuls x t_on / (t_on + t_off), where t_on is the pulse duration and t_off is the pause time) is less than 50 watts, preferably less than 40 watts and more preferably between 25-30 watts (+ / - 10); preferably the pulse power PJmpuls is between 750 and 1500 watts, preferably below 1000 watts; preferably the t_on time is between 0.5 and 4 ms, preferably below 2 ms; c) a process gas mixture of a monomer gas and a carrier gas is used, which has a carrier gas content of less than 50%, preferably less than 25%, particularly preferably less than 10%, wherein it is particularly preferred that a pure monomer gas, preferably HMDSO, without a carrier gas content is used as the process gas.

2. The method according to claim 1, characterized in that the protective layer (TC) is deposited with a layer thickness greater than 40 nm, preferably greater than 60 nm, particularly preferably greater than 80 nm.

3. Method according to claim 1 or 2, characterized in that the coating time for the protective layer is greater than 5,000 ms, preferably greater than 10,000 ms and / or the container interior (5.1) is first provided with an inner coating with an adhesion promoter layer (HV) and then with a barrier layer (BA) before the inner coating with the protective layer (TC), onto which the protective layer (TC) is then deposited, wherein the coating time for the protective layer (TC) is more than twice as long as the coating time of the other layers (BA, HV) together.

4. Method according to one of claims 1 to 3, characterized in that before the deposition of the protective layer (TC), an adhesion promoter layer (HV) and a barrier layer (BA) are deposited as an inner coating on the container interior (5.1) of the container (5).

5. Method according to one of the preceding claims, characterized in that after the deposition of the first protective layer (TC1), a further, namely second protective layer (TC2) is deposited as an inner coating.

6. The method according to claim 5, characterized in that an adhesion promoter layer (HV2) and a barrier layer (BA2) are deposited as an intermediate layer in the container interior (5.1) between the first protective layer (TC1) and the second protective layer (TC2), wherein the proportion of oxygen in the process gas mixture used for the adhesion promoter layer (HV2) and / or the barrier layer (BV2) of the intermediate layer is preferably reduced compared to the process gas mixture for the adhesion promoter layer HV1 or barrier layer BA1 between the first protective layer (TC1) and the container material, in particular by substituting oxygen with a noble gas 7. Method according to one of the preceding claims, characterized in that the thickness of the protective layer (TC) or the sum of the thicknesses of the protective layers (TC1, TC2) is at least 60 nm, more preferably at least 80 nm and even more preferably more than 100 nm.

8. The method according to claim 6 or 7, characterized in that after the deposition of the second protective layer (TC2), a third protective layer (TC3) is deposited in the container interior (5.1), wherein preferably between the second and the third protective layer (TC3) an adhesion promoter layer (HV3) and a barrier layer (BA3) are deposited as a second intermediate layer in the container interior (5.1), wherein preferably in the process gas mixture used for the adhesion promoter layer (HV3) and / or the barrier layer (BV3) of the second intermediate layer, the proportion of oxygen is reduced compared to the process gas mixture for the adhesion promoter layer HV1 or barrier layer BA1 between the first protective layer (TC1) and the container material, in particular by substituting oxygen with a noble gas.

9. Container coating machine (10) for depositing a protective layer (TC) in the container interior (5.1) of a container (5) by means of a PECVD method for microwave-induced plasma reaction at a reduced pressure, comprising at least one plasma station (3), preferably arranged on a plasma wheel (2), each having at least one plasma chamber (17) in which at least one container (5) with a container interior (5.1) can be inserted and positioned, wherein the respective plasma chamber (17) is designed to be at least partially evacuatable, wherein the plasma station (3) is designed to provide the at least one container interior (5.1) of the container (5) with an inner coating within the at least partially evacuated plasma chamber (17), wherein the coating machine (10) has a control device (45) which is designed and configured to coat a container (5) by means of a method according to one of claims 1 to 8.

10. Reusable plastic container (5), in particular a PET bottle, with a base body and a protective layer (TC) deposited thereon, wherein the protective layer (TC) at least partially covers the base body, wherein the protective layer (TC) is produced according to a method according to one of claims 1 to 8.

11. Container (5) according to claim 10, wherein the protective layer (TC) covers the entire inner surface of the base body, preferably additionally also at least a part of the outer surface of the base body, wherein the protective layer (TC) is preferably formed from HMDSO, HMDSN or HMDS or a mixture of at least two of these substances.

12. Container (5) according to claim 10 or 11, wherein the PET material used for the base body contains a proportion of recycled PET material, in particular a proportion greater than 50%, particularly preferably a proportion between 80-100%, in particular 100%.

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