DE102020105000A1 - Process for coating containers and coated containers - Google Patents

Abstract

The invention relates to a method for coating containers by means of a PECVD process for microwave-induced plasma reaction for the deposition of SiOx on the inner surface of the container by means of deposition steps in a vacuum with a plasma, the container consisting of a paper substrate which consists of or comprises cellulosic material, and wherein the paper substrate on the inner surface before the deposition of the coating layer has a surface roughness ravon less than 20 nm, preferably less than 10 nm and particularly preferably between 2 nm and 5 nm Surface is coated.

Description

The invention relates to a method for coating containers by means of a PECVD process for microwave-induced plasma reaction for the deposition of SiO _x on the inner surface of the container with the features of the preamble of claim 1. The invention also relates to a method for coating containers by means of an acetylene coating process the features of the preamble of claim 2. Furthermore, the invention relates to a container, in particular in the form of a bottle, made of a paper substrate which has a coating at least on partial areas of its inner surface.

The coating of the inner surfaces of plastic containers using the PECVD process has been known for some time. For example, this is done in the DE 102 58 681 A1 shown. The more precise configuration of such methods and how a device for carrying out such coating methods is constructed by means of a gas lance introduced into the container can be, for example, the DE 10 2016 105 548 A1 can be removed.

In the process gas generator of the WO 2017/102280 A2 the process gas _{mixtures of O 2} , Ar, HMDSO (hexamethyldisiloxane) and HMDSN (hexamethyldisilazane) are mixed. The process gas provided is dosed from the gas phase by means of mass flow controllers and sucked through the coating stations due to the negative pressure of the vacuum system. The process gas is converted in the coating stations to create a barrier layer in the bottles. The pressure conditions in the system are critical for the coating process and are determined by several parameters: gas flow, pumping speed of the vacuum pumps and conductivity values of the pipelines (depending on the pipe length and cross-section). With a favorable design of the system, very uniform conditions can be achieved for a coating process. In general, the highest absolute pressure prevails in the gas generator, the lowest is the suction pressure directly at the inlet of the vacuum pump (s).

A special recipe is created for each type of bottle to be coated, in which, among other things, the process gas _{mixture of O 2} , Ar, HMDSO and HMDSN is defined. This mixture is not changed during operation of the machine (with the selected recipe). Since the relevant pipelines do not change significantly either, very stable pressure conditions result during the coating operation or in the standby phases when no bottles are being coated in the device. The device is only released for coating when a stable state has been reached in the vacuum system. Due to the stability of the system described (pressure gradient), the pressure values to be expected for a given recipe in the normal state can be calculated or predicted and measured for process control.

Instead of using plastic bottles for packaging liquids, a container made of paper or cardboard, the inner surface of which has been made impervious to liquids, can also be used. From CH 60994 it is known to coat the inner surface of the container with paraffin after it has been folded. Alternatively, it is known from AT 135352 to make paper containers impermeable to water by impregnation using rubber latex, rubber, gutta-percha, balata or other vegetable resins and mineral or vegetable waxes, for example beeswax.

Due to the pollution problem and to protect non-renewable resources, the use of alternatives to plastics is very useful

It is an object of the present invention to provide a liquid-impermeable container which is more environmentally friendly than the coated plastic containers described above with equivalent safety, and a method for the production thereof

This object is achieved for the generic container and for the generic method by the features of the respective independent claim.

Advantageous developments of the container according to the invention and of the method according to the invention are mentioned in the dependent claims.

The fact that the invention provides that the containers, which are made of a cellulose-containing material or comprise this - such a material is referred to in the context of this application as a paper substrate - on their inner surface with a coating layer as an adhesion promoter and at least one barrier layer applied thereon by means of a PECVD process are coated, the containers are made liquid-impermeable so that they can be used instead of plastic containers for liquids. A mixture of HMDSO and O ₂ or of HMDSO and Ar or of HMDSO and O ₂ and Ar is used for the coating layer. _{A mixture of HMDSN and O 2} or of HMDSN and Ar or of HMDSN and O ₂ and Ar is used for the barrier layer or the barrier layers. Such coated containers made of paper substrate has the advantage over plastic containers such as PET, PE, PP, POC - which are used today - that it is more environmentally friendly because it can be made from renewable raw materials and is more easily biodegraded. The application of such a barrier layer is well known from the prior art for containers made of plastic and can - as surprisingly shown after extensive experiments - also be carried out for containers made of paper substrate with the known coating devices.

The term roughness used in this application relates to the mean roughness value, represented by the symbol R _a . It indicates the mean distance of a measuring point - on the surface - to the center line. The center line intersects the real profile within the reference section in such a way that the sum of the profile deviations in a plane parallel to the center line is distributed over the length of the measuring section. The mean roughness corresponds to the arithmetic mean of the absolute deviation from the mean line. Put simply, the mean roughness (in one dimension) is the height of the rectangle, which has the same length as the line to be examined and the same area as the area between the reference height and profile.

The lowest possible roughness is advantageous so that a largely closed and homogeneous layer can grow. Excessively large pores or sudden differences in height in the surface either cannot be completely covered or create natural layer boundaries at which cracks may begin.

In principle, the same also applies to containers made of paper substrate that are coated by means of PECVD, with acetylene (C ₂ H ₂ ) being used for the coating. This creates a CH _x layer that acts as a coating layer and / or as a barrier layer.

A protective layer made of HMDSO and Ar or of acetylene can advantageously be applied to the barrier layer or the barrier layers. The application of such a protective layer is well known from the prior art for containers made of plastic and can also be easily implemented for containers made of paper substrate with the known coating devices.

The paper substrate can advantageously have a rigidity at which the volume of the container increases by at most 10%, preferably by no more than 3%, at a pressure of up to 5 bar. It has been shown that from this stiffness onwards, micro-cracking in the coating can be effectively avoided when there is internal pressure in the container.

The inner surface of the paper substrate can advantageously be coated with a floating or sprayed fluid, such as a lacquer or a paint, preferably a water-soluble, particularly preferably an organic-water-soluble lacquer, such as shellac or paint. This is particularly advantageous if the paper substrate is very porous, so that a leveled, uniform surface is created effectively and economically with a fluid in a first coating step, which can then be finally coated with high quality. The color or lacquer layer has the great advantage that it significantly reduces the roughness of the substrate.

In conventional coating processes, the container is placed in a vacuum chamber, which is brought to a normal process vacuum level, in particular to a medium to high vacuum level, before the actual deposition process. It has been shown that cavities and air inclusions in the paper substrate are disadvantageous and a defined gradient of the pore volume is advantageous and a measure of the damage-free, rapid removal of gas components in the interior of the paper substrate. The paper substrate can therefore advantageously have at least 60%, preferably at least 80% and particularly preferably at least 90%, from the inner surface to the outer surface, an at least sectionally constant and / or steadily increasing average pore volume. The paper substrate advantageously has no internal, closed cavities, apart from any gas drainage pores that may be present. Such a pore volume or such a course of pore volumes has the advantage that when a vacuum is generated, the internal gas components can more easily escape from the interior of the paper substrate. Trapped gas volumes that cannot flow away expand under vacuum and can lead to the formation of cracks or major damage to the paper substrate.

It goes without saying that the features and embodiments explained above and below are not only disclosed in the respectively specified combinations, but are also to be regarded as belonging to the disclosure on their own and in other combinations.

The invention is explained in more detail below on the basis of preferred embodiments.

The containers made of paper substrate - in the following a paper bottle is described as a representative for all of them - are for example via a rotating plasma wheel, as it is for example from the above WO 2017/102280 A2 is known, promoted in plasma stations. However, the invention is by no means limited to a rotating plasma wheel, but includes in particular all rotating or non-rotating coating machines that have one or more process steps with fixed process gas mixtures and continuous process gas consumption. The plasma wheel is fed with uncoated paper bottles by means of an input wheel, which receives the uncoated paper bottles from an input section via a separation wheel. After the treatment has been carried out, the treated coated paper bottles are removed from the area of the plasma wheel by an output wheel and transferred to the area of an output path.

The structure of the plasma stations is known from the prior art for coating devices for plastic containers and, for the specific design, reference is only made to FIG DE 10 2016 105 548 A1 referenced. The plasma stations have microwave generators. A rotary distributor can be provided in the center of the plasma wheel, via which the plasma stations are supplied with operating resources, such as process gas, as well as energy. In particular, the rotary distributor can interact with a central process gas generator with a plurality of gas mixing units.

The paper bottle is inserted and positioned gas-tight and / or airtight in the plasma station. A gas lance can be inserted into the interior of the paper bottle via a vacuum channel. Depending on the design of the coating station, the interior of the container is sealed against the reactor by moving the gas lance into the interior of the container and / or by closing the process reactor. When the gas lance is lowered or the reactor is open, however, there is a gas-permeable connection between the interior of the container and the reactor.

The gas lance is coupled, for example, to a central process gas line with, for example, three process gas lines, via which different process gas compositions, in particular, can be supplied to the container interior by means of the gas lance.

• Zuerst wird der Behälterinnenraum der in die Plasmastation eingeförderten Papierflasche mitsamt dem Kammerinnenraum evakuiert.

A typical coating process at a plasma station is explained below:

• First, the interior of the container of the paper bottle conveyed into the plasma station, including the interior of the chamber, is evacuated.

The gas lance is then moved into the interior of the container of the paper bottle and the interior of the container is sealed off from the interior of the chamber. It is also possible that the gas lance is already moved into the paper bottle synchronously with the beginning of the evacuation of the chamber interior. The pressure in the interior of the container can then be further reduced. In addition, it is also contemplated that the positioning movement of the gas lance should already be carried out at least partially parallel to the positioning of the chamber wall. After a sufficiently low negative pressure has been reached, process gas is introduced into the interior of the container of the paper bottle via the central process gas line and the plasma is ignited with the aid of a microwave generator. As a first layer, an adhesion promoter - also called a coating layer - is deposited on the rough inner surface of the container of the paper bottle, which has a roughness R _a of 10 nm, for example. The process gas used for this is, for example, a mixture of HMDSO and O ₂ .

After the coating layer has been deposited, the actual barrier layer made of silicon oxides is deposited on this coating layer. The process gas used for this is, for example, a mixture of HMDSN and O ₂ . Otherwise, this deposition process corresponds to that for the deposition of the coating layer.

After the barrier layer or the barrier layers have been deposited, the gas lance is lowered from the interior of the container. After the interior of the container and the plasma station have been adequately ventilated to preferably atmospheric pressure or ambient pressure, the plasma station is opened and the coated paper bottle is removed or transferred to an output wheel.

When using acetylene, only acetylene is admitted into the chamber instead of HMDSO with O ₂ or HMDSN with O _2. The plasma is usually generated by means of a microwave, a CH _x layer being deposited as a result.

Typically only one process is used to _{deposit one or more CH x} layers. Among other things, it is also possible to create several layers that differ, for example, in terms of flow and microwave power.

The invention was described above using exemplary embodiments. It goes without saying that numerous changes and modifications are possible without thereby departing from the inventive concept on which the invention is based.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 10258681 A1 [0002]
• DE 102016105548 A1 [0002, 0021]
• WO 2017/102280 A2 [0003, 0020]

Claims (13)

Process for coating containers by means of a PECVD process for microwave-induced plasma reaction for the deposition of SiO _x on the inner surface of the container, including the following deposition steps in the plasma: Deposition of a coating layer as an adhesion promoter on the inner surface of the container, which is produced by plasma reaction from a mixture of HMDSO and O ₂ or from HMDSO and Ar or from HMDSO and O ₂ and Ar, then depositing at least one barrier layer on the coating layer, which is formed by plasma reaction from a mixture of HMDSN and O ₂ or from HMDSN and Ar or from HMDSN and O ₂ and Ar arises, characterized in that the container consists of a paper substrate which consists of or comprises cellulosic material, the paper substrate having a surface roughness R _a of less than 20 nm, preferably less than 10 nm and particularly preferred, on the inner surface before the coating layer is deposited between 2 nm and 5 nm, having. A method for coating containers by means of an acetylene coating process on the container inner surface, the following deposition steps being comprised: Deposition of at least one layer on the inner surface of the container by plasma reaction from acetylene, characterized in that the container consists of a paper substrate made of cellulose-containing material consists or comprises this, the paper substrate having a surface roughness R _a of less than 80 nm, preferably less than 50 nm and particularly preferably between 2 nm and 20 nm, on the inner surface before the coating layer is deposited. Procedure according to Claim 1 or 2 , wherein after the barrier layer or the barrier layers have been deposited, a protective layer is deposited which is applied by plasma reaction from a mixture of HMDSO and Ar or from acetylene. Method according to one of the Claims 1 until 3 , the paper substrate having a rigidity at which the volume of the container increases by at most 10%, preferably by not more than 3%, at a pressure of up to 5 bar. Method according to one of the Claims 1 until 4th , wherein the inner surface of the paper substrate is coated with a floating or sprayed fluid, such as a lacquer or paint, preferably a water-soluble, particularly preferably an organic-water-soluble lacquer, such as shellac or paint. Method according to one of the Claims 1 until 5 , wherein the paper substrate from the inner surface to the outer surface has at least 60%, preferably at least 80% and particularly preferably at least 90%, an at least partially constant and / or steadily increasing average pore volume. Procedure according to Claim 6 , wherein the paper substrate has no internal, closed cavities, except for any gas drainage pores that may be present. Container, in particular in the form of a bottle, made of a paper substrate, which has a coating at least on partial areas of its inner surface, characterized in that a coating layer is present as an adhesion promoter directly on the inner surface, which is composed of a mixture of HMDSO and O ₂ or from HMDSO and Ar or from HMDSO and O ₂ and Ar or from a polyacetylene deposited by means of an acetylene coating process, and on the coating layer at least one barrier layer made from a mixture of HMDSN and O ₂ or from a mixture of HMDSN and Ar or from a mixture of HMDSN and O ₂ and Ar or from a polyacetylene. Container after Claim 8 , a protective layer made of HMDSO and Ar or of polyacetylene being applied to the barrier layer or the barrier layers. Container after Claim 8 or 9 , the paper substrate having a rigidity at which the volume of the container increases by at most 10%, preferably by no more than 3%, at a pressure of up to 5 bar. Container according to one of the Claims 8 until 10 , wherein the inner surface of the paper substrate is coated with a floated or sprayed varnish or paint, preferably a water-soluble, particularly preferably an organic-water-soluble varnish or paint. Container according to one of the Claims 8 until 11 , wherein the paper substrate from the inner surface to the outer surface has at least 60%, preferably at least 80% and particularly preferably at least 90%, an at least partially constant and / or steadily increasing average pore volume. Container according to one of the Claims 8 until 12th , wherein the paper substrate has no internal, closed cavities, except for any gas drainage pores that may be present.