WO2018234842A1

WO2018234842A1 - Method for producing a multilayer film using core-shell polymeric particles

Info

Publication number: WO2018234842A1
Application number: PCT/IB2017/001004
Authority: WO
Inventors: Keltoum Ouzineb; Thimothy MC KENNA; Barbara REZENDE LARA
Original assignee: Toray Films Europe; Universite Claude Bernard Lyon 1; Centre National De La Recherche Scientifique - Cnrs; Cpe Lyon Fcr - Cpe Lyon Formation Continue Et Recherche
Priority date: 2017-06-23
Filing date: 2017-06-23
Publication date: 2018-12-27
Also published as: EP3642270A1

Abstract

The invention relates to a method for producing a multilayer film. In particular, the invention relates to a method for producing a multilayer film comprising at least one polymer support, at least one bonding primer layer and at least one coating, said method comprising the following steps: a) implementing a polymer support; b) optionally, performing a surface pretreatment on at least one face of said support; c) coating at least one face of said support with a primer dispersion comprising core-shell polymeric particles; d) drying the dispersion in order to produce a bonding primer layer; e) coating the bonding primer layer with at least one coating of at least one metal and/or at least one metal oxide and/or silicon oxide, or at least one layer of ink, or at least one layer of adhesive. The invention also relates to the use of a primer dispersion comprising core-shell polymeric particles to obtain a bonding primer layer that makes it possible to control the barrier properties and/or the adhesion properties of a multilayer film comprising a polymer support, a bonding primer layer and a coating.

Description

METHOD FOR PRODUCING A MULTILAYER FILM USING CORE-SHELL

POLYMERIC PARTICLES

Technical field

The field of the invention is that of plastic films. The invention relates to a method for producing a multilayer film. In particular, the invention relates to a method for producing a multilayer film comprising at least one polymer support, at least one bonding primer layer and at least one coating, using a primer dispersion comprising core-shell polymeric particles.

Background art

Plastic films and in particular polyester films are well known for their excellent properties of thermal stability, dimensional stability, chemical resistance and relatively high surface energy. These are supports that are very strong and particularly desirable for various film-forming coatings resulting in composite materials that find numerous applications: food or non-food packaging, support protection, films or sheets for graphic art (printing or drawing) and metallized films. However, for high-stress applications, these supports have the drawback of insufficient adhesion of said film-forming coatings on the supports, in particular on polyester films, thus making their use ineffective and/or unreliable and therefore unsuitable. In fact, it is known that metallic coatings of PET film do not adhere properly to the film, especially under wet conditions and at high temperature, as it is the case in processes for hot filling, pasteurization and sterilization. This lack or loss of adhesion means that the coating's expected barrier effect to oxygen and water vapour is lost, which causes deterioration of the food contents and a health risk.

In an attempt to solve this problem, several solutions have been proposed for improving the bond between the support and its covering. Thus, physical treatments (flame treatment, corona discharge, abrasive treatment) or physicochemical treatments (treatments with acid, grafting of chemical functions) on the surface of the films have been tested. As these various treatments have many drawbacks, the application of an intermediate coating is actually preferred.

This intermediate coating, also commonly called priming coat or bonding primer layer, is designed to have, on the one hand, good adhesion to the substrate and, on the other hand, good adhesion to the coating. Numerous polymers or copolymers have been proposed for producing this coating, in particular acrylic polymers. For example, patent application WO2014/102487 describes a method for coating a support with a primer layer using an aqueous dispersion. This aqueous dispersion comprises (i) particles of at least one acrylic and/or methacrylic polymer having either a gel content of less than 50 wt. % and an acrylic and/or methacrylic acid copolymer content of at least 10 wt. %, or a gel content of at least 50 wt. %, and (ii) at least one cross-linking agent.

The combination of different types of polymer, like an acrylic polymer with another type of polymer has also been described. For example, patent application EP0260203A1 describes a modified polymer obtained by aqueous-phase radical polymerization of at least one monomer of an acrylic nature in the presence of an effective quantity of a water-dispersible polyester, derived from at least one aromatic dicarboxylic acid and at least one aliphatic diol and comprising a plurality of sulphonyloxy groups. Although the results for adhesion obtained with these formulations are good, further improvement is desirable.

In this context, the invention aims to achieve at least one of the essential aims listed below.

One of the essential aims of the present invention is to provide a method for producing a multilayer film by coating a polymer support with a primer dispersion, making it possible to obtain distinctly enhanced adhesion properties between the support and the final coating, together with enhanced barrier properties, in particular barrier properties towards oxygen and water.

Another essential aim of the present invention is to provide a method for producing a multilayer film comprising a polymer support covered with a layer of metal and/or of metal oxide having enhanced adhesion properties between the support and the metal coating.

Another essential aim of the present invention is to provide a method for producing a multilayer film comprising a polymer support covered with a layer of metal and/or of metal oxide having enhanced barrier properties at high temperature and under wet conditions.

Another essential aim of the present invention is to provide a method for producing a multilayer film which is easy to implement. Summary

These objectives, among others, are achieved by the invention which first relates to a method for producing a multilayer film comprising at least one polymer support, at least one bonding primer layer and at least one coating, said method comprising the following steps:

a) implementing a polymer support;

b) optionally, performing a surface pretreatment on at least one face of said support;

c) coating at least one face of said support with a primer dispersion comprising core-shell polymeric particles;

d) drying the dispersion in order to produce a bonding primer layer;

e) coating the bonding primer layer with at least one coating of

at least one metal and/or at least one metal oxide and/or silicon oxide, or at least one layer of ink, or

at least one layer of adhesive.

The use of a primer dispersion comprising core-shell polymeric particles for making the bonding primer layer allows for enhanced barrier properties and adhesion properties of the multilayer film.

The core-shell polymeric particles have a core comprising one type of polymer and a shell comprising a different type of polymer. As the combination of different types of polymer takes place at the molecular level in the core-shell particles, there is no risk of phase separation of the different polymers. Therefore, there is also less risk of a defect on the bonding primer layer and the bonding primer layer is more homogeneous than with a simple combination of different polymers. Thus, the barrier properties of the multilayer film prepared with the core-shell polymeric particles are enhanced. The use of core-shell polymeric particles, also allows for a high concentration of functional groups at the surface of the bonding primer layer which gives a good adhesion of the metal layer, without compromising the barrier properties of the multilayer film. The core-shell polymeric particles used can be easily synthesized using cheap monomers and the process as described above is easy to implement. The invention also relates to the use of a primer dispersion comprising core-shell polymeric particles to obtain a bonding primer layer that makes it possible to control the barrier properties and/or the adhesion properties of a multilayer film comprising a polymer support, a bonding primer layer and a coating.

Brief descriptions of the figures

Figure 1 shows Transmission Electron Microscopy (TEM) pictures of the core-shell polymeric particles. Figure 1 a) shows a TEM picture of the core-shell particles CSEO synthesized according to example 1. Figure 1 b) shows a TEM picture of the core-shell particles CSEl synthesized according to example 1. Figure 1 c) shows a TEM picture of the core-shell particles CSE2 synthesized according to example 1.

Figure 2 shows cryo-TEM pictures of the core-shell polymeric particles and of the core alone. Figure 2 a) shows a cryo-TEM picture of the core alone particle CI synthesized according to example 1. Figure 2 b) shows a cryo-TEM picture of the core-shell particles CSEO synthesized according to example 1. Figure 2 c) shows a cryo-TEM picture of the core-shell particles CSEl synthesized according to example 1. Figure 2 d) shows a cryo-TEM picture of the core-shell particles CSE2 synthesized according to example 1.

Figure 3 shows a diagram of the water permeability of the multilayer film according to the protocol described in example 2. Figure 4 shows a diagram of the oxygen permeability of the multilayer film according to the protocol described in example 2.

Figure 5 shows a diagram of the adhesion of the metal coating on the multilayer film under dry conditions according to the protocol described in example 2.

Figure 6 shows a diagram of the adhesion of the metal coating on the multilayer film under wet conditions (90% relative humidity) according to the protocol described in example 2.

Figure 7 shows an example of a multilayer film according to the present invention. Detailed description

The invention first relates to a method for producing a multilayer film using a primer dispersion comprising core-shell polymeric particles. An example of a multilayer film obtained according to this method is shown in figure 7. The core-shell polymeric particles of the primer dispersion are a key element of the present invention.

Core-shell polymeric particles "Core-shell particles" is intended to mean particles comprising a core (inner material) and a shell (outer material), the core and the shell being in different materials. In the case of core-shell polymeric particles according to the present invention, the polymer comprised in the core is chemically different from the polymer comprised in the shell. Advantageously, the shell of the core-shell polymeric particles is more hydrophilic than the core. In other words, the shell has a higher ability to form hydrogen bonds than the core.

According to a preferred embodiment, the core-shell polymeric particles comprise acrylic and/or methacrylic polymers. The acrylic and/or methacrylic polymers may represent at least 80%, 85%, 90%> or 95% by weight of the total weight of the polymers.

In an embodiment of the invention, the shell of the core-shell polymeric particles comprises at least a polymer made from at least a hydrophilic monomer, preferably selected from the group consisting of alkyl acrylates and alkyl methacrylates, in which the alkyl moiety has 1 or 2 carbon atoms. The preferred monomers are methyl acrylate, methyl methacrylate, ethyl acrylate, and mixtures thereof, methyl methacrylate and ethyl acrylate being the most preferred. These hydrophilic monomers have a high affinity with the final coating, especially if it is a layer of metal or metal oxide. These hydrophilic monomers being on the shell of the particles, and therefore on the surface of the bonding primer layer, allows for a good adhesion of the metal coating on the polymer support. The hydrophilic monomers may represent at least 50%, 70% or 80% by weight of the total weight of the monomers of the shell. According to an embodiment of the invention, the shell of the core-shell polymeric particles comprises less than or equal to 20%> by weight of a cross-linking agent, relative to the total weight of monomers in the shell, preferably less than or equal to 10% by weight. For example, the shell comprises between 0.01 and 10% of a cross-linking agent. The cross-linking agent can be selected from the group consisting of bifunctional ethylenically unsaturated monomers. The bifunctional ethylenically unsaturated monomers that may be used in the present invention include diacrylate compounds, like glycol dimethacrylate, and divinylbenzenes. In some cases, the shell does not comprise a cross-linking agent.

According to an embodiment of the invention, the shell of the core-shell polymeric particles comprises at least a polymer made from at least a monomer selected from the group consisting of acrylic acid and methacrylic acid, and mixture thereof. The shell can comprises less than or equal to 5% by weight of this monomer, relative to the total weight of monomers in the shell. Typically, the shell comprises around 2% of this monomer.

According to an embodiment, the shell of the core-shell polymeric particles comprises at least a polymer made from:

at least a hydrophilic monomer selected from the group consisting of alkyl acrylates and alkyl methacrylates, in which the alkyl moiety has 1 or 2 carbon atoms, and

at least a monomer selected from the group consisting of acrylic acid and methacrylic acid.

According to an embodiment of the invention, the core of the core-shell polymeric particles comprises:

i) at least a cross-linked polymer made from at least a hydrophilic monomer, preferably selected from the group consisting of alkyl acrylates and alkyl methacrylate, in which the alkyl moiety has 1 or 2 carbon atoms, or

ii) at least a polymer made from at least a hydrophobic monomer, preferably selected from the group consisting of alkyl acrylates and alkyl methacrylates, in which the alkyl moiety is linear or branched and contains at least 4 carbon atoms.

In the case of i), the preferred hydrophilic monomers are methyl acrylate, methyl methacrylate, ethyl acrylate, and mixtures thereof, methyl methacrylate and ethyl acrylate being the most preferred. In this case, the polymer is cross-linked with at least a cross-linking agent and the core comprises less than or equal to 5 % by weight of a cross-linking agent, relative to the total weight of monomers in the core, preferably less than or equal to 1 % by weight. Typically, the core comprises between 0.5 and 1 % by weight of a cross-linking agent. The cross-linking agent can be selected from the group consisting of bifunctional ethylenically unsaturated monomers. The bifunctional ethylenically unsaturated monomers that may be used in the present invention include diacrylate compounds, like glycol dimethacrylate, and divinylbenzenes. In the case of ii), the hydrophobic monomers that may be used for the present invention include alkyl acrylates and alkyl methacrylates where the alkyl moiety is linear or branched and contains at least 4 carbon atoms. The alkyl moiety may be selected from the group constituted of n-butyl, isobutyl, t-butyl, n-pentyl, n-hexyl, ethyl-2-hexyl, decyl, dodecyl, and octadecyl. The preferred hydrophobic monomers are butyl acrylate, butyl methacrylate and mixtures thereof. In some cases, the core of the core-shell polymeric particles comprises a co-polymer made from:

at least a hydrophobic monomer selected from the group consisting of alkyl acrylates and alkyl methacrylates, where the alkyl moiety is linear or branched and contains at least 4 carbon atoms; and

- at least a hydrophobic monomer selected from the group consisting of ethylenically unsaturated aromatic compounds, like styrenic, butadiene, ethylene, vinylidene difluoride, and mixtures thereof.

The ratio of the hydrophobic monomer selected from the group consisting of alkyl acrylates and alkyl methacrylates, where the alkyl moiety is linear or branched and contains at least 4 carbon atoms to the hydrophobic monomer selected from the group consisting of ethylenically unsaturated aromatic compounds can, for example, be comprised between 5/95 and 95/5, between 10/90 and 80/20 or between 15/85 and 50/50. The core/shell ratio of the core-shell polymeric particles can be comprised between 50/50 and 10/90 relative to the total weight of monomers. For example, the core/shell ratio is comprised between 40/60 and 20/80, or is around 30/70.

The core-shell polymeric particles are typically spherical particles. The diameter of the core-shell polymeric particles can be comprised between 30 and 800 nm, or between 50 and 500, or between 75 and 200 nm. The diameter can be determined, for example, by Dynamic-Light- Scattering (DLS), TEM or cryo-TEM.

The core-shell polymeric particles can easily be synthesized using free-radical emulsion polymerisation.

According to an embodiment, the core-shell polymeric particles comprise a shell comprising at least a polymer made from at least a hydrophilic monomer, preferably selected from the group consisting of alkyl acrylates and alkyl methacrylates, in which the alkyl moiety has 1 or 2 carbon atoms, and a core comprising

(i) at least a cross-linked polymer made from a hydrophilic monomer, preferably selected from the group consisting of alkyl acrylates and alkyl methacrylate, in which the alkyl moiety has 1 or 2 carbon atoms, or

(ii) at least a polymer made from at least a hydrophobic monomer, preferably selected from the group consisting of alkyl acrylates and alkyl methacrylates, in which the alkyl moiety is linear or branched and contains at least 4 carbon atoms.

Method for producing a multilayer film

The method comprises the following steps:

a) implementing a polymer support;

b) optionally, performing a physical or physicochemical treatment on at least one face of said support;

d) drying the dispersion in order to produce a bonding primer layer;

e) coating the bonding primer layer with at least one coating of

at least one layer of adhesive.

Step a)

The support implemented in the present method is a solid polymer support. Quite particularly, a polyester film and/or a polyolefm film is used.

The polymer support implemented for the present invention is preferably a film, more preferably a film with a thickness A such that:

A < 150 μιη (micrometres),

preferably 4 μιη < A < 100 μιη,

more preferably 4 μιη < A < 40 μιη,

even more preferably 4 μιη < A < 12 μιη. The polymer support according to the invention may advantageously partly comprise recycled product originating from the support itself and/or from the coated support. The support may contain up to 80% by weight of this recycled product relative to the total weight of the final support. This makes it possible to reduce the costs of production of the film and avoid economic losses due to the non-use of scraps of support and/or of coated support.

The polymer support implemented in the present invention is a film that may be oriented or not. Preferably, it is oriented. Advantageously, the film used is bi-axially oriented.

The stretching sequences for obtaining an oriented film may be different depending on the machines used, without affecting the properties obtained by means of the invention. For example, so-called inverse-sequence machines or multistep machines, machines with alternating sequences or machines with simultaneous stretching, etc., may usefully be used.

The stretching temperature is for example comprised between the glass transition temperature Tg and a temperature at most equal to Tg + 60°C in the longitudinal direction as well as in the transverse direction.

Longitudinal stretching is carried out for example by 3 to 6 times and transverse stretching for example by 3 to 5 times. In general, following the stretching operation or operations, the film undergoes a step of thermosetting. As an example, for PET, thermosetting is carried out between 180°C and 250°C (for example at 240°C) for 1 to 60 seconds for example and then at a lower temperature in order to stabilize the film. Preferably, for the implementation of the invention, film-forming linear polyesters, crystallizable by orientation, are used, and obtained in standard fashion starting from one or more aromatic dicarboxylic acids or derivatives thereof (esters of lower aliphatic alcohols or halides for example) and from one or more aliphatic diols (glycols). The polyester constituting the polymer support may be selected from the polyesters that are usually used for obtaining bi-oriented semi crystalline films.

As examples of aromatic acids, mention may be made of the phthalic, terephthalic, isophthalic, naphthalene-2,5-dicarboxylic, and naphthalene-2,6-dicarboxylic acids. These acids may be combined with a minor quantity of one or more aliphatic or cycloaliphatic dicarboxylic acids, such as the adipic, azelaic, tetra- or hexahydroterephthalic acids. As non- limitative examples of aliphatic diols, mention may be made of ethylene glycol, propane- 1,3-diol and butane- 1,4-diol. These diols may be combined with a minor quantity of one or more aliphatic diols of more condensed carbon (neopentylglycol for example) or cycloaliphatic diols (cyclohexanedimethanol for example). Preferably, the crystallizable film- forming polyesters are polyterephthalates or alkylenediol polynaphthalenedicarboxylates and, in particular, polyethylene terephthalate of ethylene glycol (PET) or of butane- 1,4-diol or copolyesters comprising at least 80 mole percent of ethylene glycol terephthalate units. Advantageously, the polyester is a poly(ethylene terephthalate) glycol the intrinsic viscosity of which measured at 25°C in ortho-chlorophenol is between 0.6 dl/g and 0.75 dl/g.

The bi-oriented polyester films are for example:

either constituted by polyethylene terephthalate;

or constituted by mixtures, or not, of polyethylene terephthalate copolyesters containing cyclohexyl dimethylol units in place of the ethylene units;

or composed of mixtures, or not, of polyethylene terephthalate copolyesters with a proportion of polyester having isophthalate units;

or constituted by several layers of polyesters of different chemical natures, as described previously, obtained by coextrusion.

Specific examples of aromatic polyesters are in particular polyethylene terephthalate (PET), polyethylene isophthalate, polybutylene terephthalate, poly(dimethyl-l,4- cyclohexyleneterephthalate) and polyethylene-2,6-naphthalenedicarboxylate. The aromatic polyester may be a copolymer of these polymers or a mixture of these polymers with a small quantity of other resins, a non- limitative example being polybutylene terephthalate (PBT). Among these polyesters, polyethylene terephthalate (PET) and polyethylene-2,6-naphthalenedicarboxylate (PEN) are particularly preferred as they offer a good balance between the physical properties, the mechanical properties and the optical properties. Preferably, the content of terephthalic acid, expressed in moles per hundred moles of acid, is at least 80. In the preferred embodiments of the invention, the support is a film of polyethylene terephthalate PET (for example bi- axially oriented) or polyethylene naphthalate (PEN) or polybutylene terephthalate (PBT). The polymer support according to the invention may be monolayer, bi-layer or tri-layer. Each of the layers is composed of polyesters as defined above, preferably of PET, PBT or PEN, and/or of the copolyesters described above and/or of mixtures of polyesters/copolyesters. The layer or layers may be of a structure M, MN, MNM or MNO, where M is different from N and O, N is different from O. The main layer may be sandwiched between one or two layers, identical or not in terms of thickness and/or of composition. In this structure, the support may be symmetric or asymmetric. One of these layers of the support may increase the adhesion of the future coating described below.

The polymer support can also be a polyolefm film, like a biaxially oriented polypropylene film.

Step b)

For further improvement of the adhesion properties of the metal coating to the support, it can be envisaged that at least a portion of the surface of the film according to the invention is subjected to a physical treatment by electric discharge of the corona type and/or to a treatment of the plasma type. This treatment is carried out before the coating of step c).

Said treatment of the corona type is a corona discharge under ambient air at atmospheric pressure or under gases at high partial pressures, preferably between 100 mbar and 3000 mbar, even more preferably at atmospheric pressure.

Step c)

The primer dispersion comprising core-shell polymeric particles is preferably in the form of an aqueous dispersion.

Coating of the polymer support with the primer dispersion, may be carried out by the various techniques known to a person skilled in the art. Thus, the dispersion may be deposited by gravity from a slot-orifice coater, or by passing the film through the dispersion, by means of transfer rollers, by in-line coating with a reverse gravure process. Preferably, coating of the polymer support, according to the present invention, is carried out in-line, which not only allows simplification of industrial implementation but also a considerable saving of time and money. The thickness of the coating depends in particular on the dry extract of the dispersion used and the conditions of drying of the coating. Of course, the thickness also depends on the quantity of coating deposited.

Coating of the support is carried out on at least one face of the polymer support. It may of course be carried out on both faces of the polymer support.

Step d)

The drying of the coating can be done at room temperature or by heating. For example, infrared radiation can be used to dry the primer dispersion.

Step e)

This coating step is done by coating the bonding primer layer with at least one coating of

at least one layer of adhesive. The presence of strong acids at the interface, supplied by the monomers such as the acrylic and/or methacrylic acid of the bonding primer layer, allows favourable interaction of the coating of acrylic copolymer with the particles of the coating, for example metal during the step of metallizing of the coated film. The higher the polarity at the surface of the film, the stronger is the adhesion of the covering, regardless of the type of coating.

The coating may be made on the bonding primer layer that is present on one or both faces of the support. The multilayer film coated with a layer of metal and/or metal oxide and/or silicon oxide offers very good barrier properties, especially to oxygen and steam, under conditions of high temperature and humidity. The conditions for hot filling or packaging, for example of food products such as tomato sauce, are conditions under high temperature and wet conditions.

The metallization can be carried out under vacuum. It consists of vaporizing under vacuum (4x10^~4 mbar) a thin metallic layer (typically aluminium) on the film. Evaporation is carried out in ceramic crucibles heated by the Joule effect (1400°C to 1500°C). The metal is then sprayed onto the surface of the film which is in contact with a cooled roller called a coating roller. It then condenses immediately, thus forming a thin layer from 20 nm to 100 nm. During metallizing, the thickness of the layer of metal is monitored by measuring the optical density (OD, measurement of the transparency of the film).

Advantageously, the metal is selected from the group consisting of aluminium, copper, chromium, nickel, silver, gold, alloys thereof, and mixtures thereof. According to an embodiment, the metal oxide is selected from the oxides of aluminium, silicon, copper, nickel, silver and mixtures thereof. Coating the support with zinc sulphide may also be envisaged.

With respect to the application of a covering of ink and adhesive, this is carried out according to the methods known to a person skilled in the art, in particular printing/ co mp lexing .

According to one of its embodiment, the method comprises the following steps:

a) implementing a polyester film;

c) coating at least one face of said support with a primer dispersion comprising core-shell polymeric particles comprising

o a shell comprising at least a polymer made from at least a hydrophilic monomer, preferably selected from the group consisting of alkyl acrylates and alkyl methacrylates, in which the alkyl moiety has 1 or 2 carbon atoms, and

o a core comprising

(i) at least a cross-linked polymer made from a hydrophilic monomer, preferably selected from the group consisting of alkyl acrylates and alkyl methacrylate, in which the alkyl moiety has 1 or 2 carbon atoms, or (ii) at least a polymer made from at least a hydrophobic monomer, preferably selected from the group consisting of alkyl acrylates and alkyl methacrylates, in which the alkyl moiety is linear or branched and contains at least 4 carbon atoms;

d) drying the dispersion in order to produce a bonding primer layer;

e) coating the bonding primer layer with at least one coating of at least one metal and/or at least one metal oxide and/or silicon oxide.

Applications of the multilayer film

The applications of the multilayer film according to the present invention are in particular food packaging, medical packaging and the so-called industrial applications (e.g. electrical insulation, electronic components and protective films, optical films, films filtering a part of the light spectrum, films for agriculture or building), printable films or else the decoration or protection of supports.

Regarding packaging, it may be packaging of food products from their manufacture/production site to their arrival with the final consumer. These films have been developed quite especially for providing a barrier either to gases (oxygen, nitrogen, helium, water vapour, etc.) or to aromas. This may also be a packaging film for cooking foodstuffs in a microwave oven.

It may also be packaging for protecting various industrial products such as domestic electrical appliances, electronic components, etc.

Regarding decoration, these films are used for creating surfaces of the simulated wood type, for example.

Regarding films or sheets for graphic art, they may be printable supports, covered with inks or not.

The applications of the multilayer film obtained by the above described method are in particular food packaging. Examples

For TEM analysis, the diluted latex samples were dropped on a carbon/formvar-coated copper grid and dried under air and for cryo-ΎΈΜ, the diluted latex samples were placed on carbon-coated copper grid treated with plasma, and frozen with liquid nitrogen. TEM and cryo-ΎΈΜ images were recorded at an accelerating voltage of 80 and 120 kV respectively, with a Philips CM 120 transmission electron microscope at the Centre Technologique des Microstructures (^Τμ), platform at the Universite Claude Bernard Lyon 1 , Villeurbanne, France

Example 1: Core-shell particles

1 Synthesis of the core-shell particles

The first step is the synthesis of a poly(styrene-co-butyl acrylate) P(S-co-BA) core (CI), the composition of which was set to obtain a copolymer with a T_g of approximately 80°C, via batch emulsion polymerization in a 1 L double jacketed reactor. The emulsifier and the buffer were separately solubilized in 150 and 100 mL (respectively) of distilled deionized (DDI) water and added to the reactor with the monomers (styrene (Sty) and butyl acrylate (BA)) and water. The system was heated by means of a thermostatic bath under nitrogen flow. The initiator was solubilized in 50 mL of DDI water and kept under nitrogen flow during 30 min. When the temperature of the reactor reached 72°C the initiator solubilized in the water was added into the reactor. The temperature of the reactor was set to 75°C and stirring speed was kept constant at 250 rpm. The reactor vessel was kept under nitrogen flow until the polymerization was complete.

The second step is the synthesis of the shell of acrylates around the core. Monomers, buffer and emulsifier were then added to the reactor containing the poly(styrene-co- butyl acrylate) copolymer core (CI) using two tanks. The reaction media, feeding tanks one and two were purged for 30min with nitrogen prior the start of the reaction and they were kept under N₂ flow until the end of the process.

The first tank containing a mixture of MMA (methyl methacrylate), EA (ethyl acrylate), MAA (methacrylic acid) and EGDMA (ethylene glycol dimethacrylate) in proportions chosen to obtain determined T_g values, was added into the reactor by means of a piston pump. The addition time ranged from 100 to 180 minutes.

The second tank containing a solution of the salt SDS (sodium dodecyl sulfate) and APS (ammonium persulfate), all solubilized in 60mL of DDI water, was added into the reactor using a peristaltic pump. This solution was added at a rate of 15mL of solution per hour.

When the temperature inside of the reactor reached 72°C the initiator was added by using a syringe. The monomer started to be fed into the reactor right after the initiator shot and the buffer/surfactant/initiator solution started to be fed 10 minutes after. The reaction was considered started when the first drop of monomer touched the reaction medium. Samples were periodically withdrawn and polymerization was quenched by immersing sample flasks into an ice bath.

The different compositions of the particles are shown in table 1.

Table 1 - Recipes used on the described runs.

a^" Related to total amount of monomer

2 Hydrodynamic diameter (D¾), Particle Size and Particle Size distribution of the core-shell particles The hydrodynamic diameter (D¾), particle size and particle size distribution of the core- shell particles were determined by Dynamic Light Scattering (DLS), TEM and (cryo)- TEM analysis. The results obtained are presented in Table 2.

Hydrodynamic diameters (¾) were determined using a Malvern Zeta-Sizer Nano-ZS instrument. Samples were diluted in DDI water prior the analysis. For each sample, 3 measurements of 12 runs each were performed at 25°C to obtain the average ¾ and polydispersity index (PDI). The angle from the scattering of the light when it finds an object of determined size is measured and ¾ is then calculated using the Rayleigh equation (Berne, B. J.; Pecora, R., Dynamic light scattering: with applications to chemistry, biology, and physics. Courier Corporation, 1976). The PDI is a value provided by the instrument and is used to describe the width of the particle size distribution around a central value (Xu, R., Electrophoretic light scattering. Particle Characterization: Light Scattering Methods 2002, 289-343). ¾ is heavily weighted towards big particles and it reflects the effects of swelling and shrinking from polar groups present in the particles. Poly is the measurement of the dispersion from the ¾ data obtained from this analysis.

As the DLS technique is very likely to not take into account small particles and its results are influenced by the existence of polar groups, the TEM technique was also used to determine the particle size. D_w and D_n were determined by measuring the diameter of 400 particles and finding the average values in terms of volume and number respectively. I_p is the polydispersity index given by D D_n.

The results show that the I_p is close to 1 and that the Poly is largely under 0.1, these indexes indicate that the synthesized core-shell polymeric particles are monodispersed particles.

Table 2 - Comparison of particle diameter by DLS and TEM / cryo-TEM.

3 TEM Analysis

TEM and Cryo TEM pictures of the different particles synthesized were recorded. The pictures are shown in Figure 1 for the TEM and figure 2 for the Cryo TEM. These pictures confirm that the synthesized particles are monodispersed particles.

4 Thermal analysis and gel content Thermal properties were analyzed by Differential Scanning Calorimetry (DSC) using a DSC 3 from Mettler Toledo in a temperature range between -10°C and 200°C. Heating rate was 15°C/min and first scan was considered. Minimum film formation temperature (MFFT) was measured according to ASTM D2354. The latex was placed on a metallic substrate to which a temperature gradient, ranging from 25 to 60°C, was applied using two thermostatic baths. MFFT is the temperature at which the film goes from a brittle white powder to a transparent uniform material. Gel content was determined by Soxhlet extraction with tetrahydroiuran (THF) as solvent, under nitrogen flow. The extraction was carried out for 24h at 100°C. Gel content is determined as shown on Equation 1.

G. C. (%) = ^{Ms ~ Md} . 100 Equation 1

M_s

Where:

M_s - initial mass of the dried sample;

M_d - dried mass after the extraction.

The results obtained are shown in Table 3. These results show that there is a good correlation between the calculated Tg and the measured ones. It is therefore possible to prepare a latex comprising core-shell particles with a controlled Tg by choosing the monomers used for synthesizing the particles and their quantity.

Table 3 - Core-shell properties evaluation.

a^~ Calculated by the difference between P(S-co-BA) diameter and final particle diameter measured by TEM and cryo-ΎΈΜ respectively

b^" Measured on TEM pictures

c^~ Determined by Fox Equation.

Example 2: Multilayer film synthesis using the core-shell particles

1. Synthesis of the multi-layer film

A bonding primer dispersion comprising core-shell polymeric particles or simple acrylic polymers according to example 1 is implemented. This dispersion is coated on the support by an in-line heliographic coating process (pilot machine Toray Film Europe). The rotating helio roller leads to dispersion coating on the PET film. The coating is dried using infrared radiation at a wavelength of the order of 2 μιη. In some cases, the PET film coated with a bonding primer layer is coated with a layer of aluminium obtained by evaporation under vacuum (4x10^"4 mbar) in a conventional industrial metallizing process (TopMet machine from Applied Materials). In the course of metallizing, the thickness of the layer of metal is monitored by a measurement of film transparency expressed in terms of optical density OD. The OD selected for the present example is between 2.4 and 3.0, which corresponds to a thickness of the metal layer from 30 to 60 nm.

By a similar method and using the same equipment, it is possible to prepare a PET film coated with a coat of bonding primer and a layer of aluminium oxide with a thickness of about 10 nm. 2. Water permeability

The measurements of permeability to water vapour are carried out according to standard ASTM F-1249 "Standard Test Method for Water Vapour Transmission Rate through Plastic Film and Sheeting using a Modulated Infrared Sensor"; the results are expressed in g/m²/day. The measurements of permeability to water vapour of the films are carried out on the Permatran-W®3/31 with the Mocon - Water Vapor Permeation Analysis System software.

The results obtained are shown in figure 3. They show that the metallized film produced using a primer dispersion comprising core-shell polymeric particles has a lower water transmission rate than the metallized film produced using a primer dispersion comprising simple acrylic polymers. In the case of the metallized film according to the invention, the water transmission rate is lower than 0.5 g/(m².day). 3. Oxygen permeability

The measurements of permeability to oxygen are carried out with the OXTRAN 2/20 according to standard ASTM F-1927 "Standard Test Method for determination of Oxygen Gas Transmission Rate, Permeance at Controlled Relative Humidity through Barrier Materials using a Coulometric Detector"; the results are expressed in cm³/m²/day. The results obtained are shown in figure 4. They show that the metallized films have a lower oxygen transmission rate than the non-metallized films.

4. Adhesion tests under dry and wet conditions

The adhesion test AT is measured according to the AIMCAL TP- 105-92 recommendations (Metallizing Technical Reference published by the Association of Industrial Metallizers, Coaters and Laminators). It is described for metal but it is suitable for the other types of covering intended to be applied on the coated support according to the invention.

The AT test allows the adhesive strength between metal and PET to be measured, using a dynamometer. This test is carried out under dry and wet conditions. The metallized PET film is sealed with a treated polyethylene film. A test specimen with a width of 38 mm is then cut out of the sample and will be used for the measurement. The test specimen is tested under tension using an INSTRON dynamometer in order to determine the force to be applied to detach the layer of aluminium from the coated film. The PET film is fixed in the lower jaws and the treated polyethylene film film is fixed in the upper jaws. In this way, tension is exerted at 180° at a velocity of 100 mm/min on the sealed zone and the force required for delamination is measured (according to standard NF T 54-122, "Assessment of the quality of a weld or bond between two sheet elements by means of a tensile test"). The result of this AT test is an adhesive strength expressed in N/38 mm. For each sample, a minimum of 3 test specimens is tested in this way, and each film is cut into six wide strips. The force required at the dynamometer for detaching the layer of metal from the PET film under dry and wet conditions is measured. The difficulty is to maintain the forces of PET/metal adhesion under wet conditions. For measurement in a wet environment, the operator applies a small quantity of water to simulate a moisture-laden environment. The results are shown in figures 5 (dry conditions) and 6 (wet conditions).

Claims

1. Method for producing a multilayer film comprising at least one polymer support, at least one bonding primer layer and at least one coating, said method comprising the following steps:

a) implementing a polymer support;

d) drying the dispersion in order to produce a bonding primer layer;

e) coating the bonding primer layer with at least one coating of

at least one metal and/or at least one metal oxide and/or silicon oxide, or - at least one layer of ink, or

at least one layer of adhesive.

2. Method according to claim 1 characterized in that the shell of the core-shell polymeric particles is more hydrophilic than the core.

3. Method according to any of the preceding claims characterized in that the core- shell polymeric particles comprise acrylic and/or methacrylic polymers.

4. Method according to any of the preceding claims characterized in that the shell of the core-shell polymeric particles comprises at least a polymer made from at least a hydrophilic monomer, preferably selected from the group consisting of alkyl acrylates and alkyl methacrylates, in which the alkyl moiety has 1 or 2 carbon atoms. 5. Method according to any of the preceding claims characterized in that the shell of the core-shell polymeric particles comprises less than or equal to 20% by weight of a cross-linking agent, relative to the total weight of monomers in the shell, preferably less than or equal to 10%> by weight. 6. Method according to any of the preceding claims characterized in that the shell of the core-shell polymeric particles comprises at least a polymer made from at least a monomer selected from the group consisting of acrylic acid and methacrylic acid. Method according to any of the preceding claims characterized in that the core of the core-shell polymeric particles comprises:

ii) at least a polymer made from at least a hydrophobic monomer, preferably selected from the group consisting of alkyl acrylates and alkyl methacrylates, where the alkyl moiety is linear or branched and contains at least 4 carbon atoms.

8. Method according to any of the preceding claims characterized in that the core/shell ratio of the core-shell polymeric particles is comprised between 50/50 and 10/90 relative to the total weight of monomers.

9. Method according to any of the preceding claims characterized in that the diameter of the core-shell polymeric particles is comprised between 30 and 800 nm.

10. Method according to any of the preceding claims characterized in that the support is a polyester and/or polyolefm film.

11. Method according to any of the preceding claims characterized in that the metal is selected from the group consisting of aluminium, copper, chromium, nickel, silver, gold, alloys thereof, and mixtures thereof.

12. Use of a primer dispersion comprising core-shell polymeric particles to obtain a bonding primer layer that makes it possible to control the barrier properties and/or the adhesion properties of a multilayer film comprising a polymer support, a bonding primer layer and a coating.