EP1827716B1 - Method for treating a polymer material, device for implementing said method and use of said device for treating hollow bodies - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the technical field of surface treatment processes of polymeric material objects, these objects being intended for the packaging of gaseous products, liquid or solid, or the packaging of mixtures of such products.

The invention more particularly relates to techniques for deposition on the surface of polymeric materials using a precursor gas vapor chemically activated by an electric discharge under a reduced atmosphere, in order to modify the physicochemical properties of the surface. said object made of polymeric material.

The method according to the invention finds an application and an important industrial interest in that it makes it possible to reduce the diffusion of gases and liquids through the wall of the polymer object.

The method according to the invention makes it possible in particular to improve the barrier properties of HDPE containers vis-à-vis gasoline, White Spirit (refined petroleum distillation cup, containing less than 0.05% of benzene) , water, n-butyl acetate, oxygen.

The process of the invention finds, in particular, a major industrial interest in that it makes it possible to increase the hydrocarbon diffusion barrier properties obtained by low-pressure plasma deposition on a given polymer material, by electric discharge under a reduced atmosphere. a fluorinated gas or a gaseous composition comprising at least one fluorinated gas.

STATE OF THE ART

The use of polymers in the field of packaging and preservation of various products, including food products, chemicals, has many advantages.

Polymeric materials are indeed light, flexible, resistant, less expensive and easier to implement compared to metals or glasses.

Unfortunately, their barrier properties relative to the diffusion of certain liquid or gaseous products, such as oxygen or carbon dioxide, are generally poor compared to those of metals and glass.

This is particularly true for the polymers most used in the packaging industry such as PE (polyethylene), PP (polypropylene) or PET (polyethylene terephthalate).

Moreover, the resistance of these polymers is too low for their use to be possible in the packaging of certain solvents and low molecular weight volatile compounds, certain acids such as acetic acid, or surfactant solutions.

Such products packaged in a container of polymeric material may degrade both the surface of the container in contact with said product and, on the other hand, various properties of the polymeric material thus leading in time to irreversible mechanical embrittlement of said container.

Moreover, because of the diffusion phenomena, these same products can migrate slowly and continuously from the inside of the container of polymer material outwards through the wall of said container made of polymeric material and thus propagate in the environment. .

During this migration, more or less important of these products is trapped, thus increasing the initial weight of the container of polymeric material.

The variation in weight can be several percent and, with time, the container wall of polymer material swells, its chemical composition changes.

Its mechanical properties sometimes evolve dramatically and an irreversible mechanical embrittlement of said container can be seen.

The deposition of a thin-layer material, recognized for its barrier properties or its protective properties, on the inner and / or outer surface of a container of polymer material is widely known and has been used for many years as a solution. to the different problems posed above.

This operation of depositing a thin-film material on such substrates made of polymeric material may be carried out for example by high vacuum vapor deposition (commonly referred to as PVD, Physical Vapor Deposition) or plasma phase deposition under primary vacuum ( commonly referred to as PCVD, Plasma Chemical Vapor Deposition or PECVD, Plasma Enhanced Chemical Vapor Deposition).

More specifically, the techniques for depositing a thin film material by plasmas consist in using a gas or a gaseous mixture from which the atomic elements forming the molecular structure of said layered material are present.

Such gases or gas mixtures are called precursors. This gas (s) is (are) introduced into a reaction chamber in the low-pressure vapor state and then decomposed (s) by an electric discharge thus forming the plasma.

The plasma vapor thus created releases atoms and molecules that are more or less unstable but very which recombine and condense in a thin layer on the surface of the polymer to be coated.

The document US 3,485,666 (from 1965) ) discloses a method for producing a barrier layer based on silicon nitride. The document US 3442686 (of 1969) ) discloses a method for producing a barrier layer based on silicon oxide. The documents US 4756964 (of 1986) ) and WO99 / 49991 describe carbon deposits. The document US 4830873 (of 1985 ) describes the realization of a protective layer against chemical and physical aggression, the precursor gas used being a mixture of HMDSO (hexamethyldisiloxane) and oxygen.

The document WO 03/035154 A discloses a method for coating an article of polymeric material comprising creating a discharge plasma in a 1,1,1,2-tetrafluoroethane gas. There is no mention of a preparation of the surface using an acetylene plasma.

Fluorinated thin film material deposits on polymer surfaces improve the hydrocarbon diffusion barrier effect of said polymer surface (see document US 4869,922 )

In order to provide a diffusion barrier for the surface hydrocarbons in polymer mentioned above, the use of the plasma deposition technique can be very advantageous and constitute an extremely interesting alternative to the conventional fluorination method.

Indeed, said conventional fluorination method conventionally consists in exposing the polymer material surface to a fluorinated gas under precise pressure and temperature conditions, for a very long time, up to several hours.

This fluorination technique, which is a very expensive investment, requires the use of fluorinated gases in large quantities that must be reprocessed at the end of the fluorination phase.

Plasma deposition makes it possible to obtain hydrocarbon diffusion barrier performances comparable to those obtained by conventional fluorination, while using however very small amounts of precursor gas and generally very long completion times. shorter.

However, the two major drawbacks of the plasma deposition technique are the use of generally very expensive precursor gases and the often complex methods of implementation which make it a very difficult industrialization technique.

Achieving a barrier to the diffusion of surface hydrocarbons made of polymer finds an important application in the field of automobile tanks.

The document DE 3027531 (of 1980 ) discloses a method of treating such high density PE polymer fuel tanks (HDPE or HDPE) by a PECVD plasma technique in which the precursor is a fluorinated gas vapor or a mixture of fluorinated gases introduced at low pressure. The document DE3908418 describes the use of the mixture of a fluorinated precursor CHF ₃ and C ₄ H ₆ . The document EP 0739655 describes the production of multilayer from the precursors C ₂ H ₄ CF ₃ H.

The industrial implementation of the aforementioned techniques remains delicate and poorly adapted to techno-economic constraints, particularly because of the high cost of precursor gases and high cycle times.

Prior to performing the deposition of a diffusion barrier thin layer on a polymer surface, it is often carried out a preparation of said polymer surface with for example the same technique of low pressure plasma generation as that used to make said thin film deposition.

The gases or gas mixtures used in this case must change the energy state and sometimes even the chemical state of the polymer surface without, if possible, causing the growth of a thin layer of an amorphous material.

Among these gases, it is possible to cite, in a non exhaustive, argon, oxygen, carbon dioxide, hydrogen or a combination of these gases.

The document US 4536271 (of 1983) ) describes for example the use of an oxygen plasma. The patent EP 0460966 (of 1991 ) describes the generation of atmospheric pressure plasma, such as a corona treatment, to prepare the surface.

SUMMARY PRESENTATION OF THE INVENTION

In a presently preferred embodiment of the present invention, the polymeric material coating is obtained at low pressure from a gaseous plasma of 1,1,1,2-tetrafluoroethane (C ₂ H ₂ F ₄ , or H ₂ FC-CF ₃ ), conventionally referred to as HFC R134a.

In a second presently preferred embodiment of the present invention, the coating on polymeric material is obtained at low pressure from a gaseous plasma of pentafluoroethane (C ₂ HF ₅ or HF ₂ C-CF ₃ ), a product conventionally referred to as the name HFC R125.

Other objects and advantages of the present invention will become apparent from the detailed description below.

The invention makes it possible, inter alia, to obtain a coating having barrier properties to several compounds simultaneously under very advantageous technical-economic conditions.

DETAILED DESCRIPTION OF THE INVENTION

The inventors have surprisingly discovered that the improvement of the hydrocarbon diffusion barrier properties obtained by low pressure plasma deposition on a given polymer material can vary in a very wide range of gain, ranging from one to several tens, depending on the fluorinated gas or the gaseous composition comprising at least one fluorinated gas brought to the plasma state employed, and this for otherwise identical operating conditions ( gas flow, pressure, temperature, electric discharge power for plasma generation, plasma generation technique, plasma application time).

The inventors are not able to give an explanation of this surprising discovery.

The inventors have found that, in the field under study, there are no obvious correlations between the hydrocarbon diffusion barrier performance and the ratios between the different quantities of atoms per unit volume of fluorinated gas or composition. gas comprising at least one fluorinated gas.

The inventors have also discovered that, surprisingly, it can be extremely advantageous to make a first deposition layer and then proceed with the deposition of the fluorinated layer, without being able to explain it clearly.

Preferably, the authors propose carrying out a first hydrogenated amorphous carbon deposition with a low-pressure acetylene gas brought to the plasma state, and then producing a second fluorinated carbon deposit using a plasma of R134 (C ₂ H ₂ F ₄ , or H ₂ FC-CF ₃ or 1,1,1,2 Tetrafluoroethane)

In addition to the excellent performance of hydrocarbon diffusion barrier properties obtained, one of the advantages of such a process is that the reaction fluids used are inert, not dangerous and inexpensive, which makes the invention very advantageous from one point of time. from an economic point of view.

The inventors have also been able to verify that the production of the second fluorinated layer from the gas R134 is particularly interesting because the hydrogen and / or the hydrogenated molecules released by this precursor, by their incorporation in said second fluorinated layer, very substantially improve the stability of the layer.

They attribute this behavior to phenomena of saturation of the hanging links which makes it possible to reduce the mechanical stresses at the interfaces.

This particularity was not observed when the second fluorinated layer was made from other fluorocarbon gases such as C ₂ F ₆ , C ₆ F ₆ or C ₄ F ₈ which generally require the addition of hydrogen or else still from other fluorinated gases that are a priori similar to R134 gas.

From the operating point of view, the polymer surface for which it is desired to improve the hydrocarbon diffusion barrier properties is introduced into a vacuum-tight treatment chamber.

The emptying of the air initially contained in said treatment chamber is carried out by conventional pumping means up to a vacuum level of between 0.001 mbar and 1 mbar; preferentially below 0.1 mbar.

Then, a flow of gas or gas mixture is introduced into said processing chamber.

This generally has the effect of increasing the pressure inside the treatment chamber to values between 0.002 mbar and 10 mbar; the flow rate being preferably chosen to reach a pressure below 1 mbar but above 0.01 mbar.

The gas or gas mixture is released near the polymer surface which has been introduced into the treatment chamber which will be called the treatment zone.

In this treatment zone, electrical or electromagnetic energy is applied using specific means for generating and transporting said energy, which generally has the effect of bringing the gas or gas mixture to the plasma state if certain pressure conditions and energy power density are met.

All the reactions described above which occur in the entire volume defined by the presence of the plasma also occurs in the immediate vicinity of the polymer.

They depend on a certain number of process parameters such as the pressure or even the nature of the energy used to create the plasma for example but also and mainly of the gas or gaseous mixture used.

The energies used for the creation of said plasma can come from a DC voltage, a high frequency RF, a radio frequency (13.46 MHz and its harmonics for example) or even microwaves ( 915 MHz, 2,450 MHz).

The volume densities of power involved are between 0.01 W / cm ³ and 10 W / cm ³ , but preferably between 0.1 W / cm ³ and 3 W / cm ³ .

The frequencies preferentially used are those, industrial, of 40 kHz, 13.56 MHz and 2450 MHz.

The plasma state then has the effect of bringing into a partial ionization state of said gas or gas mixture.

The particles resulting from these excitation and decomposition mechanisms can then be recombined with one another to result in more or less unstable particles which can then condense on the surface of the polymer which is immersed in this plasma mixture, or condense on the surface of the polymer.

We then observe, for the deposition process, the realization of a deposition layer whose thickness depends the time of application of the plasma phase.

Therefore, after a sufficient plasma phase time which can be between a second and a few minutes but preferably at least one second and at most thirty seconds, the application of energy is stopped which stops any generation of plasma.

The flow of gas or gas mixture is also stopped, then the chamber is returned to atmospheric pressure.

In a variant, before returning the chamber to atmospheric pressure, a second deposition cycle is performed by reproducing according to the cycle described above from a new gas or gas mixture.

In another variant, several cycles are carried out with different gases or gas mixtures thus making it possible to coat the surface of the polymer with as many layers.

In another variant, the first cycle may be a step of preparing the surface of the polymer which consists in "chemically cleaning" said surface of the polymer.

In this latter variant, the polymer surface is prepared by preferably using an argon plasma or an argon + hydrogen mixture.

The inventors have also found that it could be advantageous to use a carbon dioxide plasma to increase the number of oxidized sites on the surface of the favorable polymer, in particular to obtain better performance of the oxygen barrier deposits by example.

The pressure conditions are then between 0.01 mbar and 5 mbar, but preferably between 0.05 mbar and 1 mbar.

The power conditions are those described above and the plasma preparation times are generally between 1 second and 30 seconds depending on the nature of the polymer surface to be prepared.

After this preparation phase, the barrier layer or the various sub-layers constituting the barrier layer are deposited.

Thus, this barrier layer may consist of a single layer or the superposition of two or more layers of different chemical nature.

Preferably, and according to a preferred variant, the inventors produce two types of sublayers: a first sublayer of hydrogenated amorphous carbon and a second sublayer of fluorinated amorphous carbon.

The first sublayer of hydrogenated amorphous carbon is produced from acetylene gas, the beneficial feature of which is a more or less significant collapse of the pressure when this gas is put into a plasma state, thus favoring the obtaining of a more stable deposit. homogeneous.

The second fluorinated amorphous carbon sublayer is made from the precursor gas R134 of chemical formulation C ₂ F ₄ H ₂ or from the precursor gas R125 of chemical formulation C ₂ F ₅ H according to the application.

R125 is used in some cases, because it allows a better stability and chemical resistance in particular to products having a significant surfactant effect.

RESULTS Results 1

Polyethylene High Density Polyethylene (HDPE) polymer containers, rigid, hollow and with total opening, of a 0.2 liter capacity were treated according to the process of the invention.

Rigid means a container whose wall is of a thickness of at least one mm as is the case in this example.

Such a container is placed in a cylindrical metal processing chamber connected to a microwave emitting device emitting at 2450 MHz with conventional standard size waveguide means.

In practice, the device makes it possible to produce a differential pressure between the internal volume of the container and the external volume so that the external pressure is greater than the internal pressure.

In this way, if the external pressure is large enough, the generation of plasma is only inside the container and the deposit is then formed on the inner wall of the latter.

According to the present invention, the treatment of the container is in several stages.

The pumping circuit is in communication with the treatment chamber and the internal volume of the polymer container.

Vacuum is achieved using a conventional vacuum prime pump.

The pressure inside the container is reduced to a pressure of less than 0.05 mbar while the outside pressure is maintained at about 30 mbar.

A mixing flow of argon gas and hydrogen is introduced into the container in proportions 90/10 although this is not a requirement so that the internal pressure is found at a value between 0.05 and 1 mbar.

A microwave energy is then applied with a power of about 200 W, which allows the creation a surface preparation plasma maintained for a period of 6 seconds. After this time, the microwave energy and the gas mixture flow rate are cut off.

A flow of acetylene gas is introduced into the container so that the internal pressure is found at a value between 0.05 and 0.3 mbar.

Microwave energy is then applied with a power of about 300 W, which allows the creation of a deposition plasma maintained for a period of one second.

After this time, the microwave energy and the gas flow are cut off.

A flow of gas R134 is introduced into the container so that the internal pressure is found at a value between 0.05 and 0.3 mbar.

Microwave energy is then applied with a power of about 300 W, which allows the creation of a deposition plasma maintained for a period of six seconds.

After this time, the microwave energy and the gas flow are cut off.

The pumping circuit is isolated from the treatment chamber and the internal volume of the polymer container.

The treatment chamber and the polymer container are returned to atmospheric pressure.

It was followed a conditioning and measurement protocol that is described in the standards for the transport of hazardous materials.

The containers are filled with a liquid load of about 100 grams, then their openings are closed with a heat-sealable aluminum film.

Thus packaged, the containers are placed in study at 40 ° C for a while. The permeability is measured by weighing at regular intervals of at least 1 day over a period that may extend over several months.

Loss of product by diffusion through the wall of the container is then expressed in mg / day.

Oxygen permeability is measured with an OXTRAN (MOCON) device for a period of at least 24 hours. The permeability is expressed in this case in cm ³ / day.

The performance of barriers to the diffusion of standard products have been measured and are recalled in Table 1.

The product loss values are given after a conditioning time (in days) indicated in parentheses. <b><u> Table 1: Performance barriers to broadcast. </ u></b> O2 (24h) Essence F (40) n-butyl acetate (40) Water (40) White spirit (40) Untreated 0.27 374 96 2.3 250 Treaty 0.05 13 20 0.5 15 Gain 5 28 5 4 17

The containers thus treated have shown a very good barrier to several compounds such as gasoline, white spirit, water, n-butyl acetate, oxygen.

During the diffusion process of the product contained through a polymer wall, a greater or lesser part of said product is trapped in the mass of the polymer thus resulting in weight gain.

The application of the inventive method as described above, on these polymer containers, also give an improvement in their resistance to the setting of weight after 40 days of conditioning. White spirit N butyl acetate Acetic acid Nitric acid Untreated 3.85% 1.87% 0.44% 0.31% Treaty 2.64% 0.95% 0.25% 0.11% Gain 1.46 1.97 1.76 2.82

Similarly, an improvement in abrasion resistance is noted.

These results have been confirmed by an expert report made by the Netherlands Organization for Applied Scientific Reseacr (TNO).

Results 2

Flexible, hollow, 0.5 liter polyethylene high density polyethylene (HDPE) containers were treated according to the method of the invention.

Flexible means a container whose wall is of a thickness less than 1 mm as is the case in this example for which the thickness is 0.5 mm.

Such a container is placed in a cylindrical metal processing chamber connected to a microwave emitting device emitting at 2450 MHz with conventional standard size waveguide means.

These containers are treated similarly to the procedure described in results 1 above.

The power is adjusted in each phase in relation to the surface to be treated.

The containers thus treated have shown a very good barrier to several compounds such as gasoline, White Spirit, water, n-Butyl acetate, oxygen and conventional hydrocarbons.

For example, such untreated containers have a hydrocarbon diffusion barrier of 3000 mg / day, while these same treated containers have a hydrocarbon diffusion barrier of 25 mg / day at 40 ° C.

Results 3 :

Hollow, full opening, high density polyethylene (HDPE) polymer containers having a capacity of 5 liters were treated according to the process of the invention.

Such a container is placed in a cylindrical metal processing chamber connected to a microwave emitting device emitting at 2450 MHz with conventional standard size waveguide means.

These containers are treated similarly to the procedure described in results 1 above.

The power is adjusted in each phase in relation to the surface to be treated.

The containers thus treated have shown a very good barrier to several compounds such as gasoline, White Spirite, water, n-butyl acetate, oxygen and conventional hydrocarbons.

For example, such untreated containers have a 1400 mg / day white spirit diffusion barrier, whereas these same treated containers have a barrier to diffusion of 15 mg / day at 40 ° C and after 2 months of maceration.

Claims (15)

1. Method for treatment of an article made of polymer material in order to deposit on it a coating with a barrier effect on at least one of its surfaces, characterised in that it comprises the creation of a discharge plasma in tetrafluoroethane-1,1,1,2 or pentafluoroethane precursor gas and in that it comprises, before the creation of a discharge plasma in tetrafluoroethane-1,1,1,2 or pentafluoroethane gas, the creation of a discharge plasma in acetylene gas at low pressure.
2. Method for treatment of an article made of polymer material as claimed in claim 1, characterised in that the space densities of power are between 0.01 W/cm³ and 10 W/cm³, preferentially between 0.1 W/cm³ and 3 W/cm³.
3. Method for treatment of an article made of polymer material as claimed in claim 1 or 2, characterised in that the frequencies are 40 kHz, 13.56 MHz or 2,450 MHz.
4. Method for treatment of an article made of polymer material as claimed in any of claims 1 to 3, characterised in that the plasma phase time is between one second and a few minutes, preferentially between one second and thirty seconds.
5. Method for treatment of an article made of polymer material as claimed in any of claims 1 to 4, characterised in that the precursor gas is introduced into the reaction chamber at a flow rate such that the pressure inside this treatment chamber is brought to values between 0.002 mbar and 10 mbar, more preferably between 0.01 mbar and 1 mbar.
6. Method for treatment of an article made of polymer material as claimed in any of claims 1 to 5, characterised in that it comprises, in addition, a prior preparation of the surface of the article made of polymer material that is to be coated, this preparation implementing a low pressure discharge plasma in a gas comprising at least one of the following gases: oxygen, hydrogen, argon, carbon dioxide, helium, nitrogen.
7. Method for treatment of an article made of polymer material as claimed in claim 6, characterised in that, for the surface preparation step, the low pressure discharge plasma is a plasma made of a mixture of argon/hydrogen, the pressure being between 0.01 mbar and 5 mbar, more preferably between 0.05 mbar and 1 mbar.
8. Method for treatment of an article made of polymer material as claimed in claim 7, characterised in that, for the surface preparation, the space densities of power are between 0.01 W/cm³ and 10 W/cm³, preferentially between 0.1 W/cm³ and 3 W/cm³.
9. Method for treatment of an article made of polymer material as claimed in claim 7 or 8, characterised in that the time for surface preparation by the plasma is between one second and thirty seconds.
10. Method for treatment of an article made of polymer material as claimed in any of claims 1 to 9, wherein an additional coating is created with a low pressure discharge plasma in C₂H₂ or pentafluoroethane gas at low pressure.
11. Method for treatment of an article made of polymer material as claimed in any of claims 1 to 10, characterised in that the polymer is a polyethylene, a polypropylene, a polyamide, a PET or a vinyl polychloride.
12. Method for treatment of an article made of polymer material as claimed in any of claims 1 to 11, characterised in that the article is a totally open hollow container.
13. Application of the method as claimed in claim 12 to the treatment of a rigid or flexible container made of high density polyethylene (PEHD), characterised in that the pressure inside the container is brought to a pressure less than 0.05 mbar while the pressure on the outside is maintained at approximately 30 mbar, and in that a flow of a mixture of argon and hydrogen gases is introduced into the container in such a way that the internal pressure attains a value between 0.05 and 1 mbar, microwave energy then being applied with a power of approximately 200 W, causing the creation of a surface preparation plasma that is maintained for a duration of 6 seconds, the microwave energy and the flow of the gas mixture being cut off after this surface preparation time.
14. Application as claimed in claim 13, characterised in that a flow of acetylene gas is then introduced into the container in such a way that the internal pressure attains a value between 0.05 and 0.3 mbar, microwave energy then being applied with a power of approximately 300 W, causing the creation of a deposit plasma that is maintained for a duration of one second, the microwave energy and the gas flow being cut off afterwards.
15. Application as claimed in claim 13 or 14, characterised in that a flow of tetrafluoroethane-1,1,1,2 precursor gas is introduced into the container in such a way that the internal pressure attains a value between 0.05 and 0.3 mbar, microwave energy then being applied with a power of approximately 300 W, causing the creation of a deposit plasma that is maintained for a duration of six seconds, after which the microwave energy and gas flow are cut off.