WO2002026401A1

WO2002026401A1 - Method for deposition of an internal coating in a plastic container

Info

Publication number: WO2002026401A1
Application number: PCT/FR2001/002992
Authority: WO
Inventors: Mohamed Benmalek; Alain Jupin
Original assignee: Cebal Sa
Priority date: 2000-09-28
Filing date: 2001-09-27
Publication date: 2002-04-04
Also published as: FR2814382A1; FR2814382B1; AU2001293923A1

Abstract

The invention concerns a method for making plastic containers, which includes shaping the container, deposition of a coating having barrier properties to diffusion on an internal surface, said method being plasma-assisted under pressure close to atmospheric pressure. The invention is characterised in that said coating has a thickness ranging between 150 and 1500 Å and comprises a material or a mixture of materials belonging to the following group: amorphous carbon, hydrogenated or not, nitrogenous or not, oxides, nitrides or carbides or their mixture or their combination of one or several of the following metals (Si, Mg, Al, Ti, Zr, Nb, Ta, Mo, W, V). Preferably the coating is a mixture comprising carbon with polymeric trend and silicon oxide and the substrate is a thermoplastic material such as polyolefin, typically polyethylene or polypropylene, or a polyester, typically, PET or PEN.

Description

METHOD FOR DEPOSITING AN INTERNAL COATING IN A CONTAINER

PLASTIC MATERIAL

TECHNICAL AREA

The invention relates to a method of depositing an internal coating in a plastic container. These containers are intended to contain liquid to pasty products such as pharmaceuticals, parapharmaceuticals, cosmetics and food.

STATE OF THE ART

Plastic containers are generally known for their good chemical stability at low temperatures. On the other hand, the relatively high permeability of plastics conventionally used for the preparation of containers did not make it possible to obtain containers of a single polymeric material effectively protecting the product against a possible loss of aroma or oxidation by ambient air.

Known from US 4,712,990, US 4,518,344, US 4,512,730, US 4,554,190 and US 4,497,621 a process for obtaining fully plastic containers, easy to recycle, satisfactorily protecting food products against possible loss of aroma and pollution by ambient air in the event of prolonged storage. These containers are produced by co-injection molding of several polymeric materials, for example one or more polyolefins and a material with improved barrier property such as EVOH (ethylene-vinyl alcohol copolymer).

W09522413, FR 2 776 540, DE 43 16 349 and EP 0 773 166 disclose methods for obtaining the deposition of a coating, essentially consisting of amorphous carbon on the internal surface of plastic containers such as a polyolefin or a polyester such as PET (polyethylene terephthalate) or PEN (polyethylene naphthalate). It has in fact been observed that the amorphous carbon layer has good diffusion barrier properties which could advantageously supplement those, which are not negligible, of materials such as PET.

PROBLEM

The first method, consisting of co-injecting different polymeric materials is a complex process requiring the installation of sophisticated machines with molding tools comprising a very large number of feed channels which must lead the right material to be injected in the right place. The viscosity of a material being very sensitive to temperature, the simultaneous flow of the same polymeric material in a large number of channels requires perfect control of the temperature prevailing in the multiple injection tool. In addition, the simultaneous injection of several polymeric materials of very different viscosities - at equal temperature, EVOH is much more viscous than the polyolefins that it comes into contact with - makes the problem of controlling structural stability even more complex (distribution thicknesses) and geometric of co-injected products. The development of such devices is therefore delicate and costly. It can only be justified for containers produced in very large series.

The second type of process is based on a deposit assisted by a plasma generated in a vacuum enclosure. This type of process is not very compatible with production at high rates and requires the use of complex devices for its implementation in the context of production in large series (sealed enclosures, pumps for achieving high voids in a very short time, high frequency generators, automated handling devices, etc.). The Applicant has therefore sought a more economical process enabling the same goal to be achieved: obtaining fully polymeric containers capable of preserving, sheltered from ambient air and of preserving the aromas of products such as pharmaceuticals, parapharmaceuticals, cosmetics and food.

OBJECT OF THE INVENTION

A first object of the invention is a method of manufacturing plastic containers including, after the container has been shaped, the deposition on the internal surface of a coating having barrier properties to diffusion, said method being carried out by plasma assistance at a pressure close to atmospheric pressure characterized in that said coating has a thickness of between 150 and 1500 Å and comprises a material or a mixture of materials belonging to the following group: amorphous carbon, hydrogenated or not, nitrogenous or not, oxides, nitrides or carbides or their mixture or combination of one or more of the following metals (Si, Mg, Al, Ti, Zr, Nb, Ta, Mo, W, V).

Preferably, this deposition is carried out on the internal surface of the container at a speed compatible with industrial production rates, typically of one or more hundreds of units per minute.

More particularly, the deposit can comprise amorphous carbon, hydrogenated or not, nitrogenous or not, that is to say a material with a polymer tendency, characterized by a network of chains of amorphous carbon capable of comprising hydrogen or nitrogen bonds. The Applicant has found that such a deposit has very good diffusion barrier properties. aromas such as those introduced into pharmaceutical, parapharmaceutical, cosmetic and food products. The product can thus retain all of its aromas.

It can also comprise silicon oxide, typically an SiOx compound, where x is between 1.7 and 2.1 depending on the ratio of the oxygen and silicon concentrations in the plasma formed. The Applicant has found that such a deposit has very good barrier properties to the diffusion of oxygen. The product thus remains protected from oxidation by ambient air in the event of prolonged storage.

Comparable results can be achieved with an aluminum oxide deposit, but the latter must preferably be in a mixture with the carbon and / or silicon oxide mentioned above. In fact, a layer comprising only alumina is more fragile and risks becoming faience if it has a thickness greater than lOOO.angstroms.

Preferably, the deposit is a mixture comprising carbon with a polymer tendency and silicon oxide (which we will call hereinafter "silica" for simplicity) and / or aluminum oxide. The product can thus retain all of its aromas and remains protected from oxidation by ambient air in the event of prolonged storage. The mixture can be homogeneous throughout the thickness of the coating. It can also be very rich in carbon (concentration up to 100%) in the vicinity of the substrate and very rich in silica (concentration up to 100%) on the surface, the concentration of the respective elements varying continuously between these extreme points of the coating. In this way, one obtains a gradual deposition of layers first rich in amorphous carbon then rich in silica. The hydrogenated amorphous carbon, located in a sublayer, ensures better bonding on the thermoplastic polymeric substrate and ensures greater flexibility in coating obtained. The silicon oxide or aluminum oxide layer completes the barrier effect of the carbon layer while limiting the coloring due to carbon.

The deposition is carried out on the internal surface of the container made of polymeric material, the latter being a thermoplastic material such as a polyolefin or a polyester, typically PET or PEN. The wall of such a container can thus be free of a polymeric layer with barrier properties, rigid and difficult to inject simultaneously with the other constituent layers of the wall. The coating according to the invention gives the structure of the wall of the tube satisfactory barrier properties. The thickness of the coating is variable depending on the material chosen. It must be thick enough to give the structure barrier properties that translate

• for oxygen, by a permeability of less than 1 ml / m / day / atmosphere (standard ASTMD3985)

• for water vapor, with a permeability of less than 2 g / m ² / day / atmosphere (standard ASTM F327)

• and for aromas, by a permeability of less than 0.5 10- ° g / m ² / day / mmHg

Until now, the plastic containers envisaged for use in the field of the invention were, even if that were not enough, made of a material chosen from polymeric materials having barrier properties to the diffusion of improved gases ( for example PET). With the deposit produced in the preferred embodiment of the invention, that is to say a coating composed of a mixture of amorphous carbon and silica, homogeneous or with gradual composition, we can obtain, even with a small thickness of the coating, satisfactory barrier properties so that it is not necessary to choose a particular material for the substrate (basic material of the container wall) and that less material can be taken efficient with regard to their permeability but easier to implement. Thus, a simple polyolefin may suffice, in particular polypropylene. Unlike PET, this has the advantage of being much easier to shape: it is not necessary to make preforms and control the shaping process to obtain a bi-oriented material. The cost of manufacturing such containers is significantly reduced.

According to the invention, this deposition is carried out using a plasma surface treatment reactor. Plasma can be generated under different types of discharge: discharge through a dielectric barrier or corona type discharge or luminescent discharge, with different types of excitation: low frequency microwaves, medium frequency alternating current. These types of plasma generation have the advantage of being able to be carried out under a pressure close to atmospheric pressure.

The coating is obtained by condensation after decomposition of a body or a gaseous compound. The plasma can be generated by dielectric barrier discharge or corona discharge. In this case, the working pressure can be close to atmospheric pressure, which is appreciable because the treatment time can be considerably reduced and the operation can be integrated more in the normal cycle of a large-scale production. cadences.

A particularly advantageous embodiment of the invention consists in placing the container in a device comprising two electrodes: an external one conforming as best as possible to the shape of the container and another intended to enter the container. The device also has a supply means injecting a precursor gas inside the container. After a certain time necessary to evacuate the ambient air and replace it with gas precursor, the electrode introduced inside the container is brought to an alternating voltage of about ten kV, the external electrode being connected to earth, to generate the plasma.

If the container is a body provided with a bottom connected to a vertical wall and a neck connected to said vertical wall by a shoulder, the external electrode can have a simple shape (vertical wall and bottom matching the shape of the bottom of the container) but, in this case, the coating on the shoulder and the neck may be irregular and not very thick. One can then envisage improving the device either by constructing the external electrode in several radially movable parts, said parts having an internal surface matching the external shape of the container, shoulder and neck included. The radial displacement is defined so that the diameter of the opening offered when said moving parts are in the extreme position is greater than the maximum diameter of the vertical wall of the container.

If this vertical wall is cylindrical, it is also possible to envisage a device similar to that illustrated in FIGS. 10e and 1 Of and presented in example 3 of the application WO 99/46964: as the container has a symmetry of revolution, it is done rotate around its axis of symmetry and the internal surface of the wall of the container is passed through a confined plasma in the form of a bead. ^" The electrodes have in this case a simpler form, the installation of the container is faster and does not require a complex device with parts moving radially; finally the plasma generated has a more stable spatial extent.

This process has the advantage of being able to be carried out under a pressure close to atmospheric pressure, preferably between 200 and 760 millimeters of mercury. A slightly lower pressure than atmospheric pressure allows better control of the purity of the gas circulating in the container. Preferably, a preliminary sweep is carried out with an inert gas, of the argon type, to avoid the formation of impurities (risk of reaction with nitrogen in the air, water vapor, etc.) liable to deteriorate the quality. of the adhesion of the layer thus deposited.

We are targeting a deposit thickness between 150 Å and 1500 Å, preferably less than 300 Å. The material to be deposited can be any material having good barrier properties to the diffusion of aromas and gases. To obtain an alumina deposit, tributyl aluminum AI (CH <?) 3 is preferably used as precursor gas. circulated diluted in an argon and oxygen mixture. To obtain an amorphous carbon deposition, a stream of carburetted gas is passed, typically acetylene C ₂ H or carbon fluoride CF. To obtain a deposit of silicon oxide, a gas such as HMDSO (hexamethyldisiloxane) or TMDSO (tetramethyldisiloxane) is circulated. Finally, to obtain the deposition of a mixed carbon + silica coating, a mixture of carburetted gas and precursor gas is circulated for the deposition of silica. This mixture has a constant composition or, in the "gradual deposition" variant mentioned above, a variable composition passing continuously from 100% of fuel gas at the start of treatment to 100% of precursor gas for the deposition of silica (hexa- or tetramethyldisiloxane for example) at the end of treatment.

The figure shows schematically in axial section a first device intended to implement the method according to the invention. A second device, particularly well suited to axisymmetric containers, is described in Example 3 of application WO 99/46964 and illustrated in Figures 10e and 10f of this same document. EXAMPLE (Figure)

The internal wall of the container of this example, made of polypropylene, was covered with a coating whose thickness is between 250 and 300 angstroms and comprising an amorphous carbon and silica mixture. The coating was deposited by plasma assistance using the device illustrated in the figure.

While the external electrodes 20 and 21 are placed in the extreme radial position (direction of the arrows 22), the container 10 is placed inside the volume occupied by said electrodes 20 and 21. The container 10 has a bottom 11, a wall vertical 12, a neck 13 and a shoulder 14 connecting the vertical wall to the neck. The external electrodes approach by means of a centripetal radial movement and enclose the container 10. A central electrode 30 is introduced into the internal volume of the container. When this container is a cylindrical case 45 mm in diameter, the electrode 30 preferably has a diameter of 17 mm. When the electrode 30 is depressed, its part 31 facing the shoulder 14 and the neck 13 of the housing is electrically insulated with an insulating sleeve 40. The length of the insulating sleeve, typically made of Teflon, is determined so that there is no preferential deposit at the shoulder or the neck.

The electrode 30 is hollow. It has a dozen small diameter perforations 32 (0 <0.1 mm) in the lower part and a few perforations of the same diameter above. Before the generation of the plasma, argon is injected inside the electrode 30 and entrains the ambient air towards the outside of the container. Then the precursor gas is injected - an acetylene-TMDSO mixture - and the electrode 30 is brought to an alternating voltage of around ten kV (between 10 and 15 kV), the external electrode being connected to earth, to generate the plasma. The gas circulates from bottom to top (arrows 50) and the plasma, generated by an excited source at 250 kHz with an electrical power of 400 W, comes to be flush with the internal surface of the container by bringing the carbon-silica mixture to the coating. Ten seconds is enough to obtain a coating of 250

ADVANTAGES OF THE PROCESS ACCORDING TO THE INVENTION

• possibility of using a cheaper material for the substrate than PET, polypropylene for example;

• possibility of choosing for the coating an optimal mixture of materials with respect to the flexibility - barrier properties compromise; • the deposit is thin and deformable: the barrier properties are maintained even after extensive use of the container.

Claims

1) Method for manufacturing plastic containers including, after the container has been shaped, the deposition on the internal surface of a coating having barrier properties to diffusion, said method being carried out by plasma assistance, characterized in that said plasma is generated under a pressure close to atmospheric pressure and in that said coating, having a thickness of between 150 and 1500 A, comprises a material or a mixture of materials belonging to the following group: amorphous carbon, hydrogenated or not, nitrogenous or no, oxides, nitrides or carbides or their mixture or combination of one or more of the following metals (Si, Mg, Al, Ti, Zr, Nb, Ta, Mo, W, V).

2) Method according to claim 1 wherein the coating is a mixture comprising carbon with a polymer tendency and silicon oxide.

3) Process according to claim 1 wherein the coating is a mixture comprising carbon with a polymer tendency and aluminum oxide.

4) Method according to claim 1 wherein the coating is a mixture comprising carbon with a polymer tendency, silicon oxide and aluminum oxide.

5) Method according to claim 2 wherein the coating deposited is very rich in carbon in the vicinity of the substrate and very rich in silicon oxide at the surface, the concentration of the respective elements varying continuously between these extreme points of the coating 6) Method according to claim 3 wherein the coating deposited is very rich in carbon in the vicinity of the substrate and very rich in aluminum oxide at the surface, the concentration of the respective elements varying continuously between these extreme points of the coating.

7) Method according to any one of claims 1 to 6 wherein the container material is a thermoplastic such as a polyolefin, typically polyethylene or polypropylene, or a polyester, typically PET or PEN. w

8) container capable of being obtained by the method according to any one of claims 1 to 4 characterized in that it is made of polypropylene and that its internal surface is covered with a coating whose thickness is between 150 and 1500 Å and which comprises a material or a mixture of materials belonging to the following group: amorphous carbon, hydrogenated or not, nitrogenous or not, oxides, nitrides or carbides or their mixture or combination of one or more of the following metals (Si , Mg, Al, Ti, Zr, Nb, Ta, Mo, W, V)