Coating technique for plastic containers

Abstract

The invention relates to the field of plastic coating by means of plasma-enhanced chemical vapor deposition (PECVD). By means of the invention, recyclable plastic containers for the storage of aggressive chemicals can be coated with a stable migration barrier. The invention discloses a process and a coating. With the process, a coating can be deposited from a process gas mixture of at least one precursor and a reaction gas, which is excited to form a plasma. By adjusting the reaction gas content in the process gas mixture and varying the mass-dependent excitation energy, a gradient coating can be deposited on a plastic substrate, which produces a chemically resistant migration barrier.

Description

TECHNICAL FIELD

[0001] The present invention relates to the field of plastic coating by plasma-enhanced chemical vapor deposition (PECVD). BACKGROUND

[0002] In industry, plastic containers, such as bottles or cans, are used for storing various liquids. The properties of the plastic influence the suitability of the material for storing the respective medium and the manufacturing costs of the container.

[0003] The suitability of the material depends, inter alia, on the permeability of the plastic to various gases, such as oxygen from ambient air, solvents, aromatics, dyes or other substances, and the resistance of the plastic to the medium to be stored, such as acidic or basic media.

[0004] In order to store a medium, such as a basic solution, safely, the medium should be protected from the penetration of substances from the environment or the loss of substances. The contents of the container must not enter the environment. Depending on the properties of the container material, however, gases and other substances can diffuse through the container wall (permeability). The barrier performance of the container material describes the degree of impermeability of the container or the stored medium.

[0005] In addition, the medium itself should not leak from the container or damage the container. The material of the container must be able to withstand the long-term storage of the medium and ensure sufficient storage safety. In particular when storing chemicals, many of which are classified as hazardous, there are high demands on the resistance of the container material.

[0006] In principle, it is common practice in the industry to produce containers from plastic, for example by extrusion blow molding, since this allows containers to be manufactured economically and efficiently, and plastic containers are easy to store. However, no plastic known in the prior art is able to provide both sufficient barrier performance and resistance to aggressive media, in particular basic or acidic media, at the same time.

[0007] Therefore, in the prior art, plastics or special composite plastics which are expensive to manufacture or complex to transport or store are generally not used for storing aggressive media.

[0008] Containers produced by co-extrusion blow molding, whose wall consists of several layers of different plastics, are often used. Mixtures of hard polyethylene (HD-PE), polyamide (PA) and / or ethylene-vinyl alcohol copolymer (EVOH) are often used. HD-PE, although very resistant to acids, bases, fats and oils, has a high permeability to certain substances, which is why EVOH and / or PA are used. Such packaging made of composite plastics is not environmentally friendly, since only a single-material solution can be recycled sustainably.

[0009] The only other option for plastic barrier surface treatment, besides using non-recyclable plastic multi-material solutions, is fluorination or coating using plasma technology. In fluorination, the containers are placed in a vacuum chamber and exposed to a mixture of fluorine gases in the absence of atmosphere. Due to its high reactivity, the fluorine partially replaces the hydrogen atoms of the material surface. However, this only forms an adsorbing barrier, which can only prevent the migration of media such as solvents. Fluorine is also toxic and strongly corrosive, which makes this technology unattractive and expensive. Furthermore, more and more studies attribute the negative effects of fluorine-containing plastics on the environment and health to this.

[0010] On the other hand, plasma polymer coatings are not only inexpensive, but can also be produced using harmless chemicals and require only little energy and material. PECVD can be used to produce fluorine-free silicon-based barrier coatings, which can act as passive barriers to prevent the migration of any substances. This makes the coatings suitable as solvent barriers, barriers to prevent any contaminants from migrating from plastic recyclates into the filler material, or as gas barriers, for example, to prevent oxygen, hydrogen or carbon dioxide, thus opening up a wide range of possible applications.

[0011] The patent document DE 3632748 A1 describes a process for PECVD coating of hollow bodies at low pressure, which is currently widely used in industry. First, the entire vacuum chamber is evacuated together with the bottles to be coated to the desired working pressure. Process gases are then introduced into the interior of the bottles and excited using microwaves to form a plasma. The plasma ignites inside the bottles and a barrier coating can be applied.

[0012] Compared to competing permeation-reducing processes, plasma polymer coatings are not only inexpensive, but also environmentally friendly, as their production requires only small amounts of energy and material and can do without solvents or other harmful chemicals. This applies in particular to low-pressure plasma processes, as they have a closed reaction space and use minimal amounts of process gases.

[0013] Silicon oxide SiOx-barrier coatings known from the prior art are extremely hydrolytic, so they decompose even when in contact with filler materials with a slightly elevated pH > 7.

[0014] The patent document DE 102006048658 A1 discloses a multilayer composite coating consisting of a SiOxbarrier layer and an organosilicon passivation layer.

[0015] The disadvantage of these multilayer composite coatings, whose layers are built one after the other (usually in separate process steps), is that due to the typical layer growth mechanism of the PECVD process, defects and pores in the underlying layer are propagated as defects in the subsequent coatings, so such layer systems always have open pores.

[0016] This PECVD process for depositing barrier layers and protective passivation layers on plastic containers to prevent gas permeation, so-called composite coatings, is currently mainly used in the beverage industry.

[0017] For certain fillings, for example aggressive alkaline chemicals which require a high mechanical stability of the container, a high barrier performance against gases and solvents and a high resistance against acidic and alkaline media, the known composite coatings are unsuitable or at least require optimization.

[0018] The growth process of the different layers of the composite coating generates pores at the coating surface. These pores can form, among other things, gaps in the passivation layer through which the underlying barrier layer is exposed to the corrosive medium. The pores can in particular be caused by so-called island growth during the deposition of the coating. Island growth prevents the formation of a homogeneous layer.

[0019] The layer growth in PECVD is a complex process as a whole, which is characterized, among other things, by a competition between kinetics and thermodynamics. At the beginning of the coating process in PECVD, the layer-forming particles are accelerated towards the substrate surface. After the impact, they are reflected back from the surface if the kinetic energy is too low. If the kinetic energy is high enough, they are adsorbed as adsorption atoms. Subsequently, these adsorption atoms diffuse over the substrate surface until they desorb again or condense with other adsorption atoms, nucleate and find their final position in the coating. The surface energy of the coating material and the substrate material has a great influence on the mobility of the adsorption atoms and thus on the type of layer growth. If the surface energies of the coating material and the substrate material are similar, a homogeneous layer growth is favored.

[0020] When the surface energy of the substrate is lower than the layer being formed, island growth occurs first, so the interaction between the substrate and the adsorption atoms is lower than the interaction between the particles. Subsequently, the layer material grows preferentially in the form of three-dimensional islands. Since in this growth mode the condensation of atoms on the substrate is not thermodynamically favorable at first, a closed layer is only formed when the islands grow together with the layer growth during island growth.

[0021] Furthermore, depending on the plasma process and the reactor type, different numbers of collisions occur in the plasma before the reaction particles reach the substrate. When the collisions are rare, only a small number of reactions occur in the gas phase, so the deposition rate is reduced. If the particles or radicals have many impacts or reactions before they reach the substrate, volume polymerization occurs, in which oligomers have already been formed in the gas phase. The larger the particles, the lower the possibility of surface diffusion, so that island growth is more frequent and the layer subsequently closes, since the islands first have to grow together.

[0022] Thus, island growth leads to a granular surface structure and subsequently to nanoscale pores at the grain boundaries of the coalesced islands. When several grain boundaries meet, a pore is formed. The lateral extent of the pores is in the range of a few nanometers. This means that these layer defects are much larger than, for example, molecular oxygen or ions in alkaline solutions and thus represent a weak point in the layer system.

[0023] If such pores are located in the underlying SiOxlayer (barrier layer), nucleation is increased at these pores, so that agglomerates are formed there, which leads to the continuation of these layer defects into possible subsequent protective layers (passivation layers).

[0024] Experiments have shown that a large number of nanoscale pores always form in the SiOxlayer deposited on a plastic or organosilicon adhesion-promoting layer, which can be detected using electrochemical methods such as cyclic voltammetry or electrochemical impedance spectroscopy.

[0025] This can be explained in particular by the different surface energies and chemical configurations of the materials and the increasing volume polymerization. Measurements on existing pores after the further application of an organosilicon passivation layer on the SiOxlayer show that the number of nanoscale pores hardly decreases as a result of the further coating.

[0026] When using composite coatings known from the prior art, the system fails in a pore- or defect-driven manner when exposed to chemically aggressive media. Through the open pores, the chemically aggressive media can reach the barrier layer below the passivation layer, which is susceptible to hydrolysis, and begin to break it down. This leads to the permeation of the protective layer and the failure of the entire system. Such a layer system is therefore not suitable for the industrial storage of chemicals.

[0027] One approach to solving these problems of composite coatings is the use of so-called gradient coatings, in which the chemical configuration gradually changes along the layer thickness between the organic (passivation or adhesion promotion) and the oxide (migration barrier). In contrast to composite coatings, which consist of several (micro)layers of materials with a clear difference in material, the material components of a gradient coating have a continuous gradient along the thickness of the coating.

[0028] Gradient coatings are widely known in other technical fields, for example as anti-scratch layers on plastic spectacle lenses.

[0029] It is known from the patent document EP 0 718 418 A1 that the plasma pulsation parameter can be used to generate PECVD gradient coatings with other constant parameters. However, this parameter is only suitable for the deposition of scratch protection layers, for example, for which no major differences in chemical configuration are required, so that the same gas components can be used throughout the layer deposition.

[0030] The patent document DE 42 38 279 A1 discloses another coating process for producing an anti-scratch coating.

[0031] Patent document EP2630273B1 discloses a process for the plasma treatment of workpieces, in which pulsed microwave energy is used to ignite the plasma, whereby the ratio of the duration of the on phase to the off phase is varied. In the coating process the ratio of the on time to the off time is first increased and then reduced again, in order to first reduce the carbon content in the barrier layer and then to increase it again.

[0032] Patent document DE19732217C2 discloses a plasma coating of a photovoltaic semiconductor device with a gradient coating, which gradually changes the coating properties by varying the plasma parameters and the gas supply. The gradient coating comprises a diffusion barrier layer, an elastic polymer protection layer zone and a scratch-resistant surface layer. The deposition is carried out in a microwave plasma. The process is not suitable for producing the desired layer properties on plastic substrates for plastic containers for corrosive media such as chemicals. In particular, it is not explained how and on the basis of which process parameters the plasma power is to be controlled in order to produce the desired gradient coating.

[0033] From patent document DE10139305A1 a PICVD process in pulsed microwave plasma for pharmaceutical packaging is known, but does not include a sufficient passivation layer.

[0034] Patent document WO01 / 94448A2 discloses a coating for beverage bottles with an improved gas permeation barrier, low wall thickness and good recyclability. A coating is proposed which has a SiO x C y H z base layer and a barrier layer applied on top. As one of the embodiments, a SiO x C y H z continuous layer structure is disclosed which gradually changes from the SiO x x on the surface of the substrate to the SiO

[0035] Patent document US2009 / 148633A1 discloses a plasma CVD coating on plastic bottles with a binding layer of higher carbon concentration, an intermediate barrier layer of lower carbon concentration and a surface protection layer of higher carbon concentration. The technology can be used to produce a beverage bottle coating which can withstand the influence of slightly alkaline mineral water (pH 7.3), but also fails when exposed to more corrosive media.

[0036] The known processes are not sufficient to produce a pore-free gradient coating which can encompass a wide range of chemical configurations from high oxidation (SiOx) for the barrier to organosilicon (SiOCH) for the corrosion protection.

[0037] In particular, merely changing the pulse ratio is not sufficient to achieve the desired bandwidth between the barrier effect and the passivation effect in a continuous gradient coating, while at the same time ensuring uniform coating growth and the absence of pores.

[0038] With reference to the technical solution known from patent document EP 2630273 B1, it is possible to achieve a deposition of a favorable gradient coating, in which the ratio of the pulse parameters, in particular the on-time and the off-time, is not necessarily increased first and then decreased. Rather, it has been shown that a targeted control of the energy density in the plasma depending on the gas composition has a significant influence on the coating properties. The energy density in the plasma can be controlled, for example, by the energy supply, the absolute duration of the pulses and / or the gas composition, at least as long as the ratio between the on-time and the off-time of the pulses remains constant.

[0039] Gradient coatings known from the prior art, such as scratch-resistant coatings, are also not suitable due to their mechanical properties. Scratch protection layers with a thickness of more than one micrometer, often more than two or three micrometers, are susceptible to cracking under mechanical stress or breaking at points of force, thus impairing the protective effect.

[0040] Further developments of the gradient coating deposition process developed in the 1990s are also limited by the high reaction times of about 0.5 seconds of the mass flow controllers on the market. It is not possible to form pore-free gradient coatings with a gradient resolution of a few nanometers using the currently available technology. SUMMARY

[0041] It is therefore the task of the present invention to present an improved plastic container coating technology.

[0042] It has been shown that special process conditions and coating properties are necessary for the formation of a chemically resistant coating with good barrier properties.

[0043] In order to be able to form a sufficiently high chemical resistance for the storage of chemicals, it is necessary to produce a high carbon content of the organic silicon coating, preferably by preserving the methyl groups in the precursor.

[0044] Plasma polymer layers deposited from organic silicon precursors, such as silicon oxide barrier layers, consist of silicon, carbon, hydrogen, oxygen and / or nitrogen. The typical resistance of such layers to alkaline media, for example, is due to the high difference in electronegativity between oxygen / nitrogen and silicon, as the ions in the solution mainly destroy the bonds with high partial charge transfer. The more inorganic or the higher the degree of oxidation of the layer, the more positive partial charge on the carbon, in particular on the silicon atoms. Since silicon has the largest positive partial charge due to the greater difference in electronegativity between silicon and oxygen than between silicon and carbon, these bonds and thus the commonly used SiOx barrier layers are particularly susceptible to attack.

[0045] Studies have shown that within a narrow process window of energy density, gas composition, process pressure and temperature in the plasma, the methyl groups contained in the precursors (e.g. hexamethyldisiloxane (HMDSO) molecules) can be preserved in the plasma to prevent volume polymerization and thus integrate them into the layer. Given the structural formula and binding energy of the HMDSO molecule, PECVD of HMDSO in the plasma first causes cleavage of the methyl groups, followed by hydrogen cleavage. Typically, these groups are split in the plasma, react with other particles to form volatile components and then leave the reaction space without participating in the formation of the layer.

[0046] By preserving the methyl groups, an increase in layer stability can be achieved by the mechanism of action of the steric hindrance effect. Steric hindrance is the steric shielding of weak bonds by adjacent steric filling substituents. In organic chemistry, a substituent is a group of atoms (organic or other residues) that replace a hydrogen atom in a molecule (here: methyl groups).

[0047] Therefore, the use of oxygen as a reaction gas for depositing a chemically resistant passivation layer must be limited or even avoided. However, the addition of large amounts of oxygen is absolutely necessary to produce an oxidic SiOx layer (barrier layer). Therefore, it is not sufficient to generate both functional layers only by controlling the energy introduced in the process (e.g. by the pulse parameters of the plasma excitation).

[0048] The present invention relates to both a coating and a process for producing the coating.

[0049] A first aspect of the present invention is the use of a gradient coating deposited by PECVD, which has at least one barrier zone with oxidic properties and one passivation zone with organic properties, for the coating of plastic containers for aggressive media (e.g. alkali metals).

[0050] The gradient coating consists of a large number of nanolayers with a resolution of a few nanometers (up to 1 nm), whose material composition gradually changes from nanolayer to nanolayer. Along the layer thickness, the material composition gradually changes from organic to oxidic and vice versa. In a nanolayer, the material composition of the layer is essentially homogeneous. The material composition of an individual nanolayer is determined by the process control of the PECVD process.

[0051] The barrier zone is characterized by being oxidic and providing high barrier properties to prevent gas penetration through the container wall. Preferably, the barrier zone has a high concentration of Si-O-Si compounds.

[0052] The passivation zone has organic properties and is highly resistant to aggressive media, in particular to alkaline media. The passivation zone is preferably arranged on the barrier zone and protects the barrier zone from the environment, in particular from aggressive media in the container. Preferably, the passivation zone has a high concentration of organic compounds, preferably CH3 and / or CH2 compounds, and a low concentration of oxidic compounds, in particular a low concentration of Si-OH and Si-O-Si compounds.

[0053] Depending on the type of plastic substrate to be coated, it is advantageous to deposit an adhesion zone with organic properties between the plastic substrate and the oxidation barrier zone.

[0054] The coating with the adhesion zone is usually applied on polyolefins. On certain plastics, such as PET, the adhesion zone can be dispensed with.

[0055] In a first embodiment, the gradient coating comprises at least one oxidation barrier zone and an organic passivation zone (2-zone layer). In another embodiment, the gradient coating comprises an organic adhesion zone, an oxidation barrier zone and an organic passivation zone (3-zone layer).

[0056] The different zones gradually merge into one another. The zones form a continuous gradient coating with a smooth transition between the zones. The zones preferably have an oxidic or organic center, depending on whether it is an edge zone of the gradient coating or a zone within the gradient coating, which is located in the middle region of the zone or in the edge region of the zone. In certain embodiments, the coating can comprise a plurality of gradient coatings. The gradient coating can also comprise a plurality of zones of the same type (passivation zone, barrier zone or adhesion zone).

[0057] One particular advantage of the gradient coating compared to the composite coating is that the coating can be formed particularly uniformly, i.e. without pores and with low residual stress. During the deposition of the individual nanolayers, nanolayers of similar chemical properties always meet, thus preventing island growth.

[0058] The gradually merging zones can be separated from one another in different ways. Preferably, the zones are separated from one another by the proportion of organic or oxidic compounds. The gradient coating consists of a large number (approximately 80-1000) of nanolayers with a thickness of a few nanometers. If the proportion of oxidic compounds predominates in a nanolayer, the nanolayer can be assigned to the barrier zone. If the proportion of organic compounds predominates in a nanolayer, the nanolayer can be assigned to the passivation zone or the adhesion zone.

[0059] Another aspect of the application is to vary the concentration of the reaction gas used (preferably oxygen) during the deposition of the gradient coating in order to achieve a sufficiently strong gradient between the oxidation barrier zone and the organic passivation zone or adhesion zone.

[0060] For depositing a gradient coating in a PECVD process, a process gas mixture is fed into a pre-evacuated reaction space in which a plastic substrate is arranged. The process gas mixture comprises one or more silicon-containing precursors, preferably hexamethyldisiloxane (HMDSO) and / or hexamethyldisilazane (HMDSN). The process gas mixture also comprises one or more reaction gases, preferably oxygen, at least intermittently. In certain embodiments, further auxiliary gases, such as inert gases, can be added.

[0061] The composition of the process gas mixture, i.e. the mixing ratio, is dynamically adjustable, preferably by means of mass flow controllers. In particular, the reaction gas mass flow, the precursor mass flow and the ratio of the two mass flows can be adjusted. In certain embodiments, several precursors and / or reaction gases can be used. In these cases, the ratio between the individual precursor mass flows can also be controlled. Preferably, the ratio between the reaction gas mass flow and the precursor mass flow is adjusted.

[0062] The reaction gas content C can in particular be described by the following formula:

[0063]

[0064] C: reaction gas content

[0065] RGF: reaction gas mass flow

[0066] PGF: precursor mass flow

[0067] The precursor mass flow can be obtained from the sum of the mass flows of the individual precursors.

[0068] Increasing the amount of reaction gas, in particular oxygen, added in the process, i.e. increasing the reaction gas content C, leads to a higher degree of fragmentation of the silicon-containing monomers and a greater oxidation of the deposited layer. The oxidation of the layer in turn correlates with the barrier effect and the hydrolytic stability of the layer.

[0069] By controlling the reaction gas content, preferably the oxygen content, it is possible to control the material composition over a wider spectrum and thus the function of the deposited nanolayer. In this way, a high barrier effect and strong passivation can be achieved by means of a uniform, i.e. pore-free, layer structure.

[0070] A further aspect of the present application is to control the excitation energy during the deposition of the gradient coating, in particular in relation to the process gases involved in the reaction. In particular, the excitation energy is controlled on a mass-related basis in accordance with the composition of the process gas mixture. The targeted adjustment of the mass-related excitation energy prevents volume polymerization and thus the formation of pores.

[0071] In plasma-assisted chemical vapor deposition, a process gas mixture is excited by an energy source to form a plasma. Preferably, a magnetron is used as the energy source. The excitation is preferably carried out by microwaves. Preferably, the plasma is excited in a pulsed manner. Pulsed excitation can prevent the plastic substrate from being heated too much by the plasma.

[0072] The plasma excitation provides energy for the reactions of the process gas. The mass-dependent excitation energy describes the energy provided by the mass of the particles to the reactions. By specifically adjusting the energy provided by the mass of the particles, a particularly homogeneous layer deposition can be achieved.

[0073] It has been shown that if the excitation energy provided to the reactions is controlled in accordance with the process gas mixture, a layer can be deposited that is completely free of porosities. Preferably, the mass-dependent excitation energy in the individual zones of the gradient coating is set in a specific process window in accordance with the respective reaction gas content.

[0074] For the calculation of the mass-dependent excitation energy, the mass flow of the process gas involved in the reaction is preferably corrected using a correction factor to take into account the reactivity of the reaction gas. The correction factor for oxygen is K = 0.6 and for nitrogen K = 0.5.

[0075] The mass-dependent excitation energy, also referred to as the energy density, can be described by the following equation:

[0076]

[0077] E: mass-dependent excitation energy (energy density) [J / kg]

[0078] P p : average pulse power [J / s]

[0079] F c : corrected process gas flow [kg / s]

[0080] P: power [J / s]

[0081] t on : pulse-on time [s]

[0082] t off : pulse-off time [s]

[0083] PGF: precursor mass flow [kg / s]

[0084] RGF: reaction gas mass flow [kg / s]

[0085] In a preferred embodiment, at a relatively high reactant gas content, preferably 25 < C < 250, particularly preferably 50 < C < 100, a relatively high mass-related excitation energy, preferably 400 kJ / kg < E < 2700 kJ / kg, particularly preferably 1800 kJ / kg < E < 2200 kJ / kg, is provided for depositing the barrier region.

[0086] For depositing the passivation region, at a relatively low to medium reactant gas content, preferably 0 < C < 20, particularly preferably 0 < C < 10, a relatively low to medium mass-related excitation energy, preferably 30 kJ / kg < E < 1700 kJ / kg, particularly preferably 500 kJ / kg < E < 800 kJ / kg, is provided.

[0087] For depositing the optional adhesion region, at a relatively low to medium reactant gas content, preferably 0 < C < 50, particularly preferably 0 < C < 30, a relatively low mass-related excitation energy, preferably 20 kJ / kg < E < 200 kJ / kg, particularly preferably 30 kJ / kg < E < 140 kJ / kg, is provided.

[0088] The intervals mentioned here are disclosed in combination and individually and contribute to the technical effect of the invention. The respective lower or upper limit of the interval is therefore also explicitly disclosed individually.

[0089] A further aspect of the invention is to form the gradient coating, in particular the individual regions, sufficiently thin. Advantageously, the total thickness of the coating is less than 1000 nanometers. Preferably, the thickness of the coating is at most 500 nanometers.

[0090] Thin coatings have a lower layer stress. Lower layer stress reduces the risk of cracks forming in the coating or the coating breaking under mechanical stress. In the field of plastic containers, the requirements in terms of mechanical load capacity are higher than in the area of scratch protection coatings, for example for spectacle lenses. Thin-walled plastic containers are generally soft. Deformations of the container can occur during storage or transport, for example in the event of impacts or stacking. Such deformations must not lead to failure of the coating. It has proven to be particularly advantageous for plastic containers, in particular for storing aggressive media, to have a thin coating with a thickness of less than 1000 nanometers, preferably less than 500 nanometers.

[0091] The regions formed in the gradient coating also preferably have a thickness that is optimized for their function and / or the coating formation process.

[0092] The optional adhesion zone preferably has a thickness of at most 10 nanometers. The adhesion zone is preferably thinner than the barrier zone or the passivation zone. Such a thin adhesion zone is sufficient to protect the plastic substrate from oxidative degradation by the oxygen-rich plasma used for depositing the barrier zone. Increasing the thickness of the adhesion zone can result in increased pore formation during subsequent barrier zone deposition. Therefore, a thin adhesion zone with a maximum thickness of 10 nanometers facilitates uniform layer formation. Such a thin adhesion zone forms the basis for as uniform as possible subsequent barrier zone deposition.

[0093] The barrier zone preferably has a maximum thickness of 100 nanometers. A thin barrier zone is sufficient to form a sufficient migration barrier. At the same time, uniform layer growth is possible. Preferably, the barrier zone is thinner than the passivation zone. A thinner barrier zone facilitates crack-free layer growth.

[0094] The growth of highly oxidized layers is accompanied by intrinsic layer stress. On the other hand, passivation layers of organic nature are hardly affected by layer stress when growing, and can therefore be thicker.

[0095] The passivation zone preferably has a thickness of at most 800 nanometers. Since the passivation zone must ensure that the barrier zone is sufficiently protected from the aggressive medium in the container, the passivation zone can be thicker than the barrier zone.

[0096] The coating can consist of one or more gradient coatings. The structure of the gradient coatings described above can be repeated in several adjacent gradient coatings to increase the protective effect. Zones located at the edge of the coating usually have their organic or oxidic center at the outer end, i.e. facing the medium or the substrate. Zones located in the interior of the gradient coating usually have an oxidic or organic center in the middle.

[0097] In contrast to the successive application of different types of layers in a composite layer, the coating material in a gradient coating always has a chemically similar surface, thus facilitating layer growth and preventing pore formation at coalesced islands.

[0098] Adjustment of the gas flow, i.e. the composition of the process gas mixture, will allow setting the desired chemical configuration of the barrier zone and the passivation zone. Targeted adjustment of the energy introduced per molecule from the process gas mixture further prevents volume polymerization, thus preventing large oligomers from participating in layer formation and creating pores.

[0099] The process according to the application can therefore be used to produce layers with high barrier properties against gases and other penetrants, while at the same time having high stability against aggressive media or other environmental influences, since the layers above are chemically stable at the same time as being pore-free.

[0100] The barrier properties of polyethylene containers coated with gradient coatings can be increased by a factor of 50 to 2000, depending on the surface quality, volume and weight of the container, in relation to the oxygen permeation rate. Furthermore, the gradient coatings remain resistant even after long storage in strongly alkaline NaOH solutions or similar aggressive chemicals, and the barrier remains intact. This means that they can be used to manufacture packaging made of conventional packaging plastics such as PE or PET, suitable for storing sensitive chemicals.

[0101] In addition to silicon, other suitable semimetals or metals can also be envisaged for the present application. The present application is not limited to silicon-based starting materials or coatings. Instead of or in addition to the preferred precursors HMDSO and HMDSN, other (semi)metal monomers can also be used. Instead of or in addition to oxygen, other reaction gases can also be used, for example nitrogen. The present disclosure also includes embodiments in which a PECVD alternative mentioned herein or known to the person skilled in the art is used instead of the preferred process gases.

[0102] Further advantageous embodiments will be described below with reference to the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0103] The application is described in the drawings in a schematic and exemplary manner. Therein:

[0104] Figure 1 The structure of the reactor is shown;

[0105] Figure 2 The structure of the gradient coating (3-zone coating) is shown;

[0106] Figure 3 The structure of a coating with several gradient coatings is shown;

[0107] Figure 4 The advantageous progression of the process parameters C and E during deposition of the gradient layer is shown;

[0108] Figure 5 The FT-IR spectrum at the center of the adhesion zone (EH) and the barrier zone (WB) is shown;

[0109] Figure 6 The FT-IR spectrum at the center of the passivation zone is shown. DETAILED DESCRIPTION

[0110] Figure 1A schematic structure of the reactor (300) is shown. The reactor (300) comprises a process chamber (301). The substrate (100) is arranged in the process chamber (301). A reaction space (302) is formed in or on the plastic substrate (100). The reaction space (302) can be evacuated by a pump (310). In the shown embodiment, the reaction space is formed inside the container (100) in order to coat the interior of the plastic container (100), e.g. a can.

[0111] The process gas mixture (PGM) is fed into the reaction space (302) through a line. The reactor comprises a gas supply (320) and one or more gas flow controllers (321), preferably mass flow controllers. The process gas mixture (PGM) consists of one or more process gases (PG1, PG2, RG), the mixing ratio of which can be controlled.

[0112] In a preferred embodiment, two precursors are used. The first precursor (PG1) is preferably HMDSN. The second precursor (PG2) is preferably HDMSO.

[0113] One or more precursors (PG1, PG2) can be used specifically for certain regions of the gradient coating. It is particularly preferred to use (mainly) HMDSO as the first precursor for the deposition of the adhesion zone (201) and / or the passivation zone (203). Alternatively or additionally, it is particularly preferred to use (mainly) HMDSN as the second precursor for the deposition of the barrier zone (202).

[0114] In particular in the transition between two zones of the gradient coating, two or more precursors can be mixed at least temporarily.

[0115] The precursor gas mass flow is preferably related to the sum of the mass flows of the various precursors. In the case of chemically similar precursors (e.g. HMDSN and HMDSO), the mass flows of the individual precursors in the process gas mixture can be combined to form a calculated precursor gas mass flow for determining the mass-dependent excitation energy. In some embodiments, it can be useful to weight the individual gas mass flows with a factor.

[0116] Preferably, oxygen is used as the reaction gas (RG). Alternatively or additionally, nitrogen can be used as (further) reaction gas (RG).

[0117] In the reaction space (302), the process gas mixture (PGM) is excited by an energy source (350). Preferably, a magnetron is used as the energy source (350). The plasma is preferably excited by pulsed microwaves (351). Alternatively or additionally, an ICP plasma can also be used.

[0118] The coating (200) is deposited on the plastic container (100) from a process gas mixture which is excited into a plasma (352).

[0119] The process chamber (301) can comprise one or more reaction spaces (302). The reaction space (302) can occupy the entire process chamber or only a portion thereof. In particular, the reaction space (302) can be formed in the interior of the plastic container (100). Preferably, the container is sealed. Alternatively or additionally, a further reaction space can be formed, for example on the outside of the container.

[0120] The reactor (300) can also comprise a plurality of process chambers (301) with one or more reaction spaces (302).

[0121] The coating (200) is preferably deposited within a time of about 5-60 seconds, depending on the structure of the coating (200), the dimensions of the substrate (100) and the process control. In the case of particularly large containers, longer process times can also occur. At least one gradient coating is deposited during the deposition process.

[0122] The mixing ratio of the process gas mixture (PGM) changes during the process sequence. In particular, the mass flow of the precursors (PG1, PG2) and / or the reaction gas (RG) changes. By changing the process gas, the material composition of the coating (200) is influenced.

[0123] An advantageous course of the process parameters is shown in Figure 4

[0124] Preferably, the reaction gas content (C) and / or the mass-dependent excitation energy (E) between the adhesion zone (201) and the barrier zone (202) gradually increases along the layer build direction (x).

[0125] Alternatively or additionally, the reaction gas content (C) and / or the mass-dependent excitation energy (E) between the barrier zone (202) and the passivation zone (203) gradually decreases along the layer build direction (x).

[0126] The change in the reaction gas content (C) and the mass-dependent excitation energy (E) is preferably uniform, in particular smooth.

[0127] It is particularly advantageous to control the excitation energy (E) depending on the composition of the process gas mixture (PGM), in particular depending on the precursor gas mass flow and / or the reaction gas mass flow.

[0128] ​Those skilled in the art can use a variety of options to control the mass-related excitation energy. In particular, the average pulse power can be set. Preferably, the power of the energy source and / or pulse parameters can be controlled. Particularly preferably, a setpoint of the mass-related excitation energy (E) is calculated and controlled or adjusted by one or more manipulated variables, such as those selected from (nominal) power supply, pulse on-time, pulse off-time, or pulse rate, or combinations thereof.

[0129] Figure 2 A schematic structure of a coating (200) is shown, which has a gradient coating (200') of three regions. The coating (200) is deposited on a plastic substrate (100). The deposition of the coating, i.e., the stacking of nanolayers (L), proceeds along the layer stacking direction (x).

[0130] The thickness of a suitable coating (d) is preferably between 80 and 1000 nanometers. The thickness of the plastic substrate (100) is several orders of magnitude greater. Common wall thicknesses of plastic containers are in the millimeter range. Therefore, for ease of demonstration, the plastic substrate is shown broken.

[0131] In Zone 3 ( Figure 2 In this process, an organic adhesion region (201) is first deposited on a substrate (100). Subsequently, an oxidation barrier region (202) is deposited on the adhesion region (201), where these regions are smoothly merged together. An organic passivation region (203) is deposited on the barrier region (202).

[0132] In the case of a 2-zone layer, the barrier region (202) can also be directly deposited on the substrate.

[0133] The gradient coating (200') includes at least one barrier region (202) and a passivation region (203). The passivation region (203) is disposed between the ambient surface (211) of the coating (200) and the barrier region (202). The passivation region (203) protects the barrier region (202). The passivation region resists the effects of corrosive media (M).

[0134] The coating (200) forms a migration barrier, i.e., a diffusion barrier, against ambient gases (A) capable of diffusing through the plastic substrate (100). The permeation path is interrupted by forming one or more barrier regions (202). The oxide barrier region (202) serves as a migration barrier.

[0135] The gradient coating (200') is formed by the deposition of a large number of nanolayers (L) during the deposition process. The material composition of each individual nanolayer (L) gradually changes along the stacking direction (x).

[0136] The gradient (G) schematic illustrates the gradual change in the material composition of the gradient coating.

[0137] The individual zones, i.e. the adhesion zone (201), the barrier zone (202) and the passivation zone (203), can be described in terms of their material composition and the proportion of specific bond types. The respective center of a zone can be considered to represent a gradual change in composition in the respective zone. The respective center (S1, S2, S3) of a zone can be considered to be a nanolayer (L) at an extremum of a certain characteristic curve (e.g. gradient (G)) along the layer build direction (x).

[0138] The chemical structure of a gradient coating is defined by extrema (centers), in particular local or global maxima or minima, at which the maximum coating property of the respective coating type has been set and the process control will therefore remain constant until the next extremum is reached. The chemical structure at the extrema (S1, S2, S3) will be described in more detail later. Table 1 shows the preferred elemental composition of the layers at the extrema, which was determined using X-ray photoelectron spectroscopy (XPS).

[0139]

[0140] Table 1: XPS data at the extrema of the material composition when using HMDSO and HMDSN as precursors

[0141] Fourier-transform infrared spectroscopy (FT-IR) was used to further characterize the chemical structure of the individual zones, in particular the centers of the individual zones. Table 2 lists the vibration modes that are important for the evaluation of the FTIR measurements.

[0142]

[0143] Table 2: Vibration modes and FT-IR peak positions

[0144] In Table 2, the prefix: S = stretch; b = bend; r = rock; subscript: sym = symmetric.

[0145] Figure 5 and Figure 6 Exemplary FT-IR spectra showing the extrema of the individual zones are shown. The parameter W represents the wave number in cm-1, the dimensionless parameter X represents the extinction. -1

[0146] Figure 5 FT-IR spectra at the centroid of the adhesion-promoting zone (EH) based on HMDSO and at the centroid of the barrier zone (WB) based on HMDSN are shown.

[0147] The coating at the extremum of the barrier zone (WB), in contrast to the centroid S2 in Figure 2 , exhibits a very pronounced Si-O-Si network structure (440 cm-1 and 1070 cm-1). -1 -1 ​​). 900 and 1300 cm -1 The broad band peak between 900 and 1300 cm -1 may mainly correspond to three asymmetric Si-O stretching vibrations in the Si-O-Si compound. The peak at about 1135 cm -1 may correspond to a Si-O-Si cage structure with a bond angle of about 150°. The network structure with a bond angle of about 144° corresponds to a peak at about 1070 cm -1 If the structure has a bond angle of less than 144°, it is assumed that there is a suboxide in the network (1010-1030 cm -1 The peak at 839 cm -1 is characteristic of stretching and rocking vibrations of methyl groups and indicates that at the focal point of the adhesion promoting zone (EH) a higher retention of monomer functional groups is achieved compared to the barrier zone (WB) which imparts the organic character to this zone.

[0148] The intensity of the peak of the Si-O-Si network and the exact peak position provide information about the degree of layer crosslinking. A higher maximum peak position indicates a higher Si-O-Si crosslinking. This peak shift can be clearly seen in the comparison of the two spectra. The barrier zone (WB) is a highly crosslinked coating with a clear Si-O-Si network structure with almost no C and C-H bonding.

[0149] Figure 6 An exemplary FT-IR spectrum of the center of the passivation zone is shown. The figure shows the FT-IR spectrum of a HMDSO-based passivation zone (EP).

[0150] Similar to the spectrum of the adhesion zone (EH) in Figure 5 , Figure 6 the spectrum of the passivation zone in -1 is composed of a superposition of a series of individual peaks. The peak at 1070 cm -1 is also due to the stretching vibration of the Si-O-Si network. The peak at 1257 cm -1 is characteristic of the symmetric stretching vibration of the methyl groups.

[0151] The chemical structure of these zones is of great importance, especially with regard to the barrier properties of the barrier zone and the hydrolysis stability of the passivation zone.

[0152] Therefore, in order to characterize the chemical structure of these zones, a structure parameter V was also introduced, which represents the ratio of the area (Gaussian curve) under the peaks measured by FT-IR, where each peak can clearly correspond to a CH3 or Si-O group (the assignment of the peaks can be found in Table 2):

[0153]

[0154] V: structure parameter [-]

[0155] A: extinction X [-], W = 1376 cm -1

[0156] B: extinction X [-], W = 1257 cm -1

[0157] E: extinction X [-], W = 839 cm -1

[0158] C: extinction X [-], W = 440 cm -1 , 1010 cm -1 to 1035 cm -1 , 1070 cm -1

[0159] D: extinction X [-], W = 930 cm -1

[0160] In terms of chemical structure, the barrier properties of the barrier zone are mainly dependent on the degree of crosslinking and oxidation of the layer. For the extreme value of the barrier zone (WB), a favorable range V < 0.2 and a particularly favorable range V < 0.05 have been determined.

[0161] The chemical resistance of the passivation zone is explained by considering the electronegativity of the relevant elements in the coating material, which can be used to assess the partial partial charge transfer in the bond. The greater the difference in electronegativity of the bonding partners, the more strongly the bonding electron is localized on the bonding partner with the higher electronegativity. As a result, this element experiences an electron enhancement.

[0162] In the bonds present in the layer, the oxygen in Si-O is particularly subject to the greatest electron enhancement. As a result, the oxygen carries a negative partial charge (δ - ) and the silicon carries a positive partial charge (δ + ). The silicon therefore experiences an electron deficiency. Negatively charged ions in the solution therefore attack the silicon bound to the oxygen due to its positive partial charge. The Si-CH3 bond in turn has a low partial charge. The layer is therefore, for example, subject to nucleophilic attack by ions at Si-O. This leads to the formation of Si-OH bonds in the case of bond rupture of the Si-O-Si bond. As a result, more and more gaps are created within the Si-O network with the introduction of anionic end groups. The weak bonds are spatially shielded by the CH3 groups, which can significantly slow down or completely terminate the reaction. The greater the proportion of CH3 groups to Si-O, the slower the degradation of the layer. The greater V, the more resistant the coating. Preferably, for the extreme value of the passivation zone, at least one structure parameter V > 0.20 is achieved, particularly advantageously V > 0.35, in order to be able to provide the necessary protective properties.

[0163] To deposit a beneficial adhesion promoting layer, a structure parameter V of 0.1 < V < 0.3 is achieved at the extrema of the adhesion promoting zone (EH).

[0164] The structure parameter V can be used to determine the oxidic or organic center and / or the functional zones of the gradient coating. For example, in Figure 2 A schematic curve of the structure parameter V(x) is plotted along the layer build-up direction x. The extrema (S1, S2, S3) of the structure parameter V(x) can be used to determine the center of the gradient coating and the individual functional zones of the gradient coating.

[0165] The respective oxidic or organic center of the zones can be located at the edge or in the middle of the zones, in particular depending on the layer architecture. The transitions between the zones are fluent.

[0166] The zones are preferably determined by their material composition. The material composition of the individual nanolayers determines the functionality of the layer zone.

[0167] Various types of analysis can be used to delimit the zones (201, 202, 203), for example to determine the thickness (d1, d2, d3). For example, the material composition of the individual nanolayers can be determined in a SIMS process (secondary ion mass spectroscopy), or further in a nanoSIMS process. By bombarding the surface with ions, the layers can be removed and analyzed with nanometer resolution.

[0168] To define the thickness of the zones, the structure parameter V or the elemental composition of the nanolayers along the layer build-up direction can be determined. If the proportion of organic compounds predominates, the location can be assigned to a passivation zone or an adhesion zone. If oxidic compounds predominate, the location can be assigned to a barrier zone.

[0169] The material composition of two adjacent nanolayers (L) is always similar. The material similarity of the individual nanolayers (L) favors uniform layer growth.

[0170] The advantage of the gradual structure of the zones of the gradient coating is that each nanolayer (L) finds a chemical similarity during the deposition process. The chemical properties of the nanolayers only change gradually. This prevents island growth.

[0171] Figure 3 An exemplary structure of the coating (200) is shown, which has a plurality of gradient coatings (200', 200", 200'"). The structure of the gradient coating or the individual zones can be repeated along the layer build-up direction. Preferably, the zones between two consecutive gradient coatings (200', 200") also gradually merge into one another.

[0172] Such a multi-layer structure of the gradient coating can be particularly advantageous for enhancing the migration barrier and / or chemical resistance (i.e. protective barrier zone). Alternatively or additionally, a low thickness of the individual zones can still be maintained, which is beneficial for uniform layer growth and mechanical properties of the coating (e.g. low layer stress).

[0173] In one embodiment not specifically shown, the coating (200) can also comprise a gradient coating (200'") with only one barrier zone (202) and one passivation zone (203). Especially for PET substrates, the adhesion zone (201) can be omitted.

[0174] In case of a 2-zone layer (200'"), the barrier zone (202) is preferably arranged directly on the plastic substrate (100) or on an intermediate gradient coating (200', 200'). In case of a 2-zone layer, the barrier zone (202) can especially have oxidation centers at the edges of the zone.

[0175] Figure 4 A favorable progression of the reactive gas content (C) or mass-dependent excitation energy (E) during deposition of a gradient coating (200') with an adhesion zone (201), a barrier zone (202) and a passivation zone (203) is shown.

[0176] In particular, both process variables C and E can be controlled or adjusted in a specific process window (W).

[0177] The adhesion zone (201) is deposited with a low to moderate reactive gas content (C). In one advantageous embodiment, at least a small amount of oxygen is added at the beginning of the process. The surface of the plastic substrate (210) is activated by the resulting oxygen-rich plasma. In this way, a previous surface activation of the substrate (100) can be omitted, which can shorten the process time. The activation of the surface improves the adhesion of the coating (200) to the substrate surface.

[0178] The adhesion zone (201) protects the sensitive plastic substrate (100), especially polyolefins, from the oxidizing barrier zone (202). Here, the adhesion zone (201) has a protective effect on the plastic substrate.

[0179] The gradual change of the reactive gas content (C) and / or the mass-dependent excitation energy (E) controls the gradient (G) of the material composition of the deposited layer and is beneficial for uniform and pore-free layer growth.

[0180] At certain stages of the deposition process, the proportion of the reaction gas (RG) in the process gas mixture can be between 0 and 100%. In order to deposit strongly oxidizing regions, it is appropriate to apply a very high reaction gas content (C), preferably 50 < C < 100. Alternatively or additionally, for the organic regions of the gradient coating, it can be appropriate to use a lower reaction gas content (C) or not to use a reaction gas at all.

[0181] In a particularly preferred embodiment, the excitation energy (E) of the plasma is controlled in dependence on the current process gas composition. Particularly preferably, the energy introduced by the particle mass is kept within a range and this range is adapted to the varying reaction gas content.

[0182] By varying the reaction gas content, a wide range of material compositions can be achieved between the oxidizing and the organic center of the gradient coating. As a result, particularly strong barrier effects and passivation effects can be achieved, which provide a sufficient migration barrier and chemical resistance for containers for aggressive media.

[0183] By adjusting the mass-dependent excitation energy (E), it is possible to keep the excitation and the reaction within the optimum range for uniform layer growth, despite a strong change in the gas composition. This means that, in particular, volume polymerization can be avoided. This makes it possible to achieve pore-free layer deposition.

[0184] The individual features of the embodiments described, illustrated or claimed here can also be combined with one another. The features can be replaced or supplemented by individual features of other embodiments.

[0185] List of reference signs

[0186] 100 plastic substrate

[0187] 200 coating

[0188] 200' gradient coat

[0189] 201 contact zone

[0190] 202 barrier zone

[0191] 203 passivation zone

[0192] 210 substrate face, substrate surface

[0193] 211 environment face

[0194] S1 organic center

[0195] S2 oxidic center

[0196] S3 organic center

[0197] 300 reactor

[0198] 301 process chamber

[0199] 302 reaction space

[0200] 310 pump

[0201] 320 gas supply

[0202] 321 gas flow controller

[0203] 350 energy source, magnetron

[0204] 351 microwaves

[0205] 352 plasma

[0206] PG process gas mixture

[0207] PG precursor, polysiloxane

[0208] PG1 (first) precursor, HMDSN

[0209] PG2 (second) precursor, HMDSO

[0210] RG reactive gas, oxygen

[0211] A ambient gases

[0212] C reactive gas content

[0213] E Excitation energy, mass-related Fc Correction factor

[0214] K Correction factor

[0215] L Nanolayer

[0216] M Medium

[0217] P Power supply

[0218] r Resolution

[0219] RGF Reactive gas mass flow PGF Precursor gas mass flow ton Pulse on-time

[0220] toff Pulse off-time

[0221] W Process window

[0222] x Layer build-up direction

Claims

1. A process for making a coating on a plastic substrate (100) by plasma- enhanced chemical vapor deposition (PECVD) for creating a chemically resistant migration barrier, wherein, A process gas mixture (PGM) is introduced into a reaction space (302) and excited by an energy source (350) to form a plasma (352), the process gas mixture (PGM) having an adjustable composition made of one or more precursors (PG) and / or one or more reaction gases (RG), wherein a gradient coating having an adhesion zone (201), a barrier zone (202) and a passivation zone (203) and a gradient coating having a barrier zone (202) and a passivation zone (203) are deposited on the plastic substrate (100), characterized in that the deposition of the gradient coating is controlled by varying the reaction gas content (C) in the process gas mixture (PGM) and varying the mass-dependent excitation energy (E) of the plasma, and the excitation energy (E) is controlled on a mass-dependent basis as a function of the composition of the process gas mixture (PGM), the mass-dependent excitation energy (E) gradually decreasing between the barrier zone (202) and the passivation zone (203) along the layer build direction (x).

2. The process of claim 1, wherein, The plastic substrate (100) is a plastic container.

3. The process of claim 1, wherein, The excitation energy (E) is controlled on a mass-dependent basis as a function of the precursor gas mass flow and the reaction gas mass flow.

4. The process of claim 1, wherein, During the deposition of the gradient coating, one or more pulse parameters of the energy source (350) remain constant at least temporarily.

5. The process of claim 4, wherein, The deposition of the gradient coating is the deposition of the adhesion zone (201) and / or the barrier zone (202), and / or the pulse parameter of the energy source (350) is the ratio of the pulse-on time to the pulse-off time of the excitation pulses.

6. The process of claim 1, wherein, The reaction gas content (C) and / or the mass-dependent excitation energy (E) gradually increases between the adhesion zone (201) and the barrier zone (202) along the layer build direction (x).

7. The process of claim 1, wherein, The reaction gas content (C) gradually decreases between the barrier zone (202) and the passivation zone (203) along the layer build direction (x).

8. The process of claim 1, wherein, The excitation energy (E) is adjusted as a function of the mass of the particles involved in the deposition reaction.

9. The process of claim 8, wherein, The excitation energy (E) is controlled as a function of the mass of the particles involved in the deposition reaction.

10. The process according to claim 1, wherein, The plasma is excited by pulsed microwaves (351).

11. The process of claim 4, wherein, The power supply (P) for controlling the plasma excitation and / or the pulse parameters are controlled in order to vary the excitation energy (E).

12. The process of claim 11, wherein, The pulse parameters are the pulse-on time (ton) and / or the pulse-off time (toff), the pulse rate or the pulse ratio.

13. The process according to any one of claims 1 to 12, wherein, During the deposition of the barrier zone (202), the reaction gas content (C) is 25 ≤ C ≤ 250, and / or the mass-dependent excitation energy (E) is 400 kJ / kg ≤ E ≤ 2700 kJ / kg.

14. The process of claim 13, wherein, During the deposition of the barrier zone (202), the reaction gas content (C) is 50 ≤ C ≤ 100, and / or the mass-dependent excitation energy (E) is 1800 kJ / kg ≤ E ≤ 2200 kJ / kg.

15. The process according to any one of claims 1 to 12, wherein, During deposition of the passivation zone (203), the reactive gas content (C) is 0 < C < 20 and / or the mass-related excitation energy (E) is 30 kJ / kg < E < 1700 kJ / kg.

16. The process of claim 15, wherein, During deposition of the passivation zone (203), the reactive gas content (C) is 0 < C < 10 and / or the mass-related excitation energy (E) is 500 kJ / kg < E < 800 kJ / kg.

17. The process according to any one of claims 1 to 12, wherein, During deposition of the adhesion zone (201), the reactive gas content (C) is 0 < C < 50 and / or the mass-related excitation energy (E) is 20 kJ / kg < E < 200 kJ / kg.

18. The process of claim 17, wherein, During deposition of the adhesion zone (201), the reactive gas content (C) is 0 < C < 30 and / or the mass-related excitation energy (E) is 30 kJ / kg < E < 140 kJ / kg.

19. The process according to any one of claims 1 to 12, wherein, The process gas mixture (PGM) comprises one or more silicon-containing precursors (PG, PG1, PG2).

20. The process of claim 19, wherein, The silicon-containing precursor (PG, PG1, PG2) is an organosilicon compound.

21. The process of claim 20, wherein, The silicon-containing precursor (PG, PG1, PG2) is a siloxane, silazane or silane.

22. The process of claim 21, wherein, The silicon-containing precursor (PG, PG1, PG2) is hexamethyldisiloxane (HMDSO) and / or hexamethyldisilazane (HMDSN).

23. The process according to any one of claims 1 to 12, wherein, The reactive gas (RG) comprises oxygen and / or nitrogen.

24. The process according to any one of claims 1 to 12, wherein, Hexamethyldisilazane (HMDSN) or hexamethyldisiloxane (HMDSO) is used as a precursor (PG1) for depositing the barrier zone (202).

25. The process of claim 24, wherein, Hexamethyldisilazane (HMDSN) is used as a precursor (PG1) for depositing the barrier zone (202).

26. The process of any one of claims 1 to 12, wherein, Hexamethyldisilazane (HMDSN) or hexamethyldisiloxane (HMDSO) is used as a precursor (PG2) for depositing the adhesion zone (201) and / or the passivation zone (203).

27. The process of claim 26, wherein, Hexamethyldisiloxane (HMDSO) is used as a precursor (PG2) for depositing the adhesion zone (201) and / or the passivation zone (203).

28. A coating on a plastic substrate (100) for producing a chemical resistance migration barrier, wherein the coating comprises one or more gradient coatings, wherein at least one gradient coating comprises at least one barrier zone (202) of oxidic character and a passivation zone (203) of organic character, wherein the chemical configuration of the gradient coating gradually changes from the substrate side of the coating along the layer build direction (x) and from the at least one barrier zone (202) to the passivation zone (203), wherein the chemical structure of the gradient coating is determined by a structure parameter V which can be measured using Fourier transform infrared spectroscopy (FT-IR): A: extinction X [-], W = 1376 cm -1 B: extinction X [-], W = 1257 cm -1 E: extinction X [-], W = 839 cm -1 C: extinction X [-], W = 440 cm -1 , 1010 cm -1 to 1035 cm -1 , 1070 cm -1 D: extinction X [-], W = 930 cm -1 , characterized in that For the passivation zone (203), at least one of the structure parameters V is V > 0.

2.

29. The coating of claim 28, wherein, The plastic substrate (100) is a plastic container.

30. The coating of claim 28, wherein, A gradient coating further comprises at least one adhesion zone (201) of organic character between the barrier zone (202) and the substrate side (210).

31. The coating of claim 30, wherein, The thickness (d1) of the adhesion zone (201) is at most 10 nanometers.

32. The coating of claim 28, wherein, The thickness (d) of the coating and / or the thickness (d) of the at least one gradient coating is less than 1000 nanometers.

33. The coating of claim 32, wherein, The thickness (d) of the coating and / or the thickness (d) of the at least one gradient coating is less than 500 nanometers.

34. The coating of claim 28, wherein, The thickness (d2) of the barrier zone (202) is less than 100 nanometers.

35. The coating of claim 34, wherein, The thickness (d2) of the barrier zone (202) is less than 60 nanometers.

36. The coating of claim 35, wherein, The thickness (d2) of the barrier zone (202) is less than 40 nanometers.

37. The coating according to claim 28, wherein, The thickness (d3) of the passivation zone (203) is at least 20 nanometers and / or at most 800 nanometers.

38. The coating according to claim 37, wherein, The thickness (d3) of the passivation zone (203) is at least 200 nanometers.

39. The coating of claim 28, wherein, The chemical configuration of the gradient coating is formed by a plurality of nanolayers (L, L') stacked along the layer stacking direction (x) with a resolution (r) of less than 50 nanometers.

40. The coating of claim 39, wherein, The chemical configuration of the gradient coating is formed by a plurality of nanolayers (L, L') stacked along the layer stacking direction (x) with a resolution (r) of less than 10 nanometers.

41. The coating of claim 40, wherein, The chemical configuration of the gradient coating is formed by a plurality of nanolayers (L, L') stacked along the layer stacking direction (x) with a resolution (r) of 1 to 5 nanometers.

42. The coating of claim 39, wherein, Each nanolayer (L, L') has a different adjusted elemental composition and / or composition of organic compounds and oxidic compounds, respectively.

43. The coating of claim 42, wherein, The organic compound is an organosilicon compound SiO x C y H z , and / or the oxidic compound is an oxidic silicon compound SiO x .

44. The coating of claim 28, wherein, The structure parameter V at the extreme value (S2) of the barrier zone (202) is smaller than the structure parameter V at the extreme value (S3) of the passivation zone (203).

45. The coating of claim 28, wherein, The structure parameter V at the extreme value (S2) of the barrier zone (202) is V < 0.

2.

46. The coating of claim 45, wherein, The structure parameter V at the extreme value (S2) of the barrier zone (202) is V < 0.

05.

47. The coating of claim 28, wherein, The structure parameter V at the extreme value (S3) of the passivation zone (203) is V > 0.

35.

48. The coating of the preceding claim 30 or 31, wherein, The structure parameter V at the extreme value (S1) of the adhesion zone (201) is 0.1 < V < 0.

3.

49. A plastic container having a coating according to any one of claims 28 to 48.

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