FIELD OF THE INVENTION

The technical field of the invention is that of plastic films, in particular polyester films. More specifically, the invention relates to polyester/metal composite films (laminates), comprising a support formed by one or more polyester layers, said support being covered over at least one of its faces by a metallic film.

Even more particularly, the invention relates to a composite film containing an adhesion primer at the metal/polyester interface.

The production of these polyester/metal composite films, using at least one interfacial layer of at least one adhesion primer layer, is a further subject of the present invention, as well as the adhesion primer composition intended to coat the polymer films and making it possible, on the one hand, to improve the adhesion under conditions of high temperature and humidity between the film and a final covering of metallic type, and on the other hand to give the covered film good gas barrier properties.

The polyesters more specifically concerned are the semi-aromatic copolymers such as: polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN); the aromatic copolymers such as Vectran.

TECHNOLOGICAL BACKGROUND

Plastic films, and in particular polyester films, are well known for the excellent properties thereof in terms of thermal stability, dimensional stability, chemical resistance and relatively high surface energy. These are very resistant materials and are particularly sought as supports for various coverings. Composite films comprising a plastic film as support and a covering have many applications: packaging, in particular food packaging, the protection of various objects (white goods, window panes, etc.), thermal insulation and damp protection in the building sector (vacuum insulation panel).

The food packaging applications of these polyester/metal composite films require, in particular, barrier properties to the gases oxygen and water vapour. But these barrier properties are not the only specifications required for these polyester/metal composite films. It is also important for them to be cohesive and not to delaminate, during handling, production, use and storage of the products for which they are intended.

Now, these composite films have the drawback of insufficient adhesion between the supports, in particular the polyester supports, and the metallic covering, thus rendering use thereof ineffective and/or unreliable and thus unsuitable. These problems of adhesion are particularly acute when the composite material is subject to high stresses. For example, in the field of food production, packaging can be subject to high temperature and humidity conditions in the hot filling, pasteurization or sterilization processes. It is known that, in these situations, the metallic coverings do not properly adhere to the polyester film, for example PET. This absence or this loss of adhesion means that the required barrier effect to oxygen and water vapour is lost, which causes deterioration of the food contained and a risk to the health of consumers.

In order to attempt to overcome this problem of the bond between the support and its metallic covering, several solutions have been proposed in the past. Thus physical (flame treatment, corona discharge, abrasive treatment) or physico-chemical treatments (acid treatments, grafting of chemical functions) at the surface of the films have been tested. As these various treatments have many drawbacks, the application of an intermediate coating was preferred for being more durable. This intermediate coating, also commonly called adhesion primer layer, is designed so as to have on the one hand, good adhesion to the support, and on the other hand, good adhesion to the metallic covering, and is conventionally based on acrylic (co)polymers. Placing this adhesion primer layer on the support is carried out by coating with an aqueous emulsion of acrylic (co)polymers.

Patent application PCT WO2014/102487A1 thus describes a PET film coated with an adhesion primer layer and covered with an aluminium layer obtained by evaporation under vacuum.

The coating of the adhesion primer is carried out using an acrylic latex A or an acrylic latex B (15 or 20% dry extract) cross-linked with or without Cymel 303 LF or Cymel 1123 crosslinking agent from Cytec Industries Inc.

The latex A is prepared according to Example 1 of patent EP0260203B1.

Its gel content is less than 50% by weight with respect to the total weight of acrylic and/or methacrylic polymer(s) and its content of acrylic and/or methacrylic acid copolymer(s) is at least 10% of the total weight of polymers.

The adhesion primer obtained from latex A makes it possible to obtain composite films with metal adhesions, under dry conditions (ambient temperature/hygrometry<50%), of at least 1000 gF/38 mm, while they are only 200, 280 or 480 gF/38 mm under wet conditions; in an adhesion test AT is measured according to the recommendations of AIMCAL TP-105-92 (Metallizing Technical Reference published by the Association of Industrial Metallizers, Coaters and Laminators).

Latex B, marketed under the name BT-67 by the company DSM, comprises particles of acrylic and/or methacrylic polymer(s) and has a gel content of at least 50% by weight with respect to the total weight of acrylic and/or methacrylic polymer(s).

The adhesion primer obtained from latex B makes it possible to obtain composite films with metal adhesions, under dry conditions, of at least 1000 gF/38 mm, while they are only 280, 400, 480 or 800 gF/38 mm under wet conditions, in the adhesion test AT.

The barrier effect with respect to O2 is given by a minimum P O2 (50% HR 23° C. in cc/m2/d) of 1 for latex B with L/R=80/20, and <0.3 for latex A with L/R=80/20.

The barrier effect with respect to H2O is given by a minimum P112O (90% HR 38° C. in g/m2/d) of 0.27 for latex B with L/R=80/20, and <0.3 for latex A with L/R=80/20.

Patent application PCT WO2015092329A1 thus describes a PET film coated with an adhesion primer layer and covered with an aluminium layer obtained by evaporation under vacuum.

The coating of the adhesion primer is carried out using an acrylic latex B (15 or 20% dry extract) cross-linked with a Cymel 303 LF crosslinking agent from Cytec Industries Inc.

This latex B, marketed under the name BT-67 by the company DSM, comprises particles of acrylic and/or methacrylic polymer(s) and has a gel content of at least 50% by weight with respect to the total weight of acrylic and/or methacrylic polymer(s).

The adhesion primer obtained from latex B, according to latex dry extract/dry crosslinking agent ratios (L/R) of F1:100/0, F2:80/20, F3:75/25, F4:70/30 makes it possible to obtain composite films with metal adhesions, under dry conditions (ambient temperature/hygrometry<50%), of at least 1500 gF/38 mm, and 360 gF/38 mm under wet conditions, for F4, in an adhesion test AT measured according to the recommendations of AIMCAL TP-105-92 (Metallizing Technical Reference published by the Association of Industrial Metallizers, Coaters and Laminators).

The barrier effect with respect to O2 is given by a minimum PO2 (50% HR 23° C. in cc/m2/d) of 1.76 for F4.

The addition of 5 and 10% of sulphonated polyester to the adhesion primers F2, F3, F4 leads to formulations F5 and F6, F7 and F8, F9 and F10, respectively.

F6 makes it possible to obtain composite films with metal adhesions of at least 1500 gF/38 mm, under dry conditions, and 1400 gF/38 mm under wet conditions.

The barrier effect with respect to O2 is given by a minimum PO2 (50% HR 23° C. in cc/m2/d) of 0.86 for F6.

OBJECTIVES OF THE INVENTION

In this context, the invention aims to achieve at least one of the essential objectives listed below:i further improve, in particular, the following specifications from the required product specification for composite films with polyester/primer/metallic covering, namely:Adhesion of the metallic covering is maintained after heat treatment of the packaging (laminate comprising a metallized coated PET composite film and a polyolefin: polyethylene or polypropylene, film);Adhesion of the covering is maintained under wet conditions: Wet Metal Adhesion greater than or equal to 500 gF/38 mm;Gas barrier of the metallized coated PET composite film: Oxygen permeability (23° C., 50% relative humidity) less than or equal to 0.8 cc/m2/d—Water vapour permeability (38° C., 90% relative humidity) less than or equal to 0.3 g/m2/d;ii providing a novel composite film comprising a polymer support, preferably polyester, at least one adhesive covering on at least one of the faces of the support, and at least one layer of cross-linked adhesion primer between the support and the covering, said film having improved barrier properties with respect to gases as well as for adhesion of the covering onto the support;iii providing a novel composite film such as defined in the aforementioned objective and in which an interfacial cross-linking takes place be interposing the adhesion primer, in such a way as to promote adhesion between layers of materials of a different nature (for example polyester and metal) and to improve the gas barrier properties of the composite;iv providing a novel composite film formed by a support (for example polyester), coated with at least one coat of adhesion primer and covered with at least one layer of metal and/or metal oxide, or at least one layer of ink, or a layer of adhesive;v providing a novel polyester composite film meeting at least one of the aforementioned objectives and impervious to water;vi providing a novel coating method for a support, preferably a polyester film, with an adhesion primer layer making it possible to obtain markedly increased adhesion properties between the support and the final covering;vii providing a novel adhesion primer coating composition, which is universal with respect to the supports and the coverings to be firmly fixed together, and which moreover has good performance is terms of improvement in the adhesion properties and the gas barrier properties of the composite films produced by means of this adhesion primer;viii providing a novel method for the production, in in-line or batch production, preferably in-line production, of a composite film comprising a polymer support, preferably polyester, at least one adhesive covering on at least one of the faces of the support, and at least one cross-linked adhesion primer layer between the support and the covering, said film having improved barrier properties with respect to gases as well as for adhesion of the covering onto the support;ix proposing novel uses for a composite film formed by a support (for example polyester), coated with at least one adhesion primer layer and covered with at least one layer of metal and/or metal oxide, or at least one layer of ink, or a layer of adhesive, these novel uses being in particular packaging, preferably of food, decoration, printing and/or the protection of various supports.

BRIEF DESCRIPTION OF THE INVENTION

It is to the inventors' credit that, seeking to improve on the state of the art, they have developed a novel adhesion primer making it possible to achieve the aforementioned objectives, among others.

Thus, according to a first aspect, a purpose of the invention is a composite film comprising a polymer support, preferably polyester, at least one adhesive covering on at least one of the faces of the support, and at least one cross-linked adhesion primer layer between the support and the covering;said film having improved barrier properties with respect to gases as well as for adhesion of the covering onto the support, characterized in thatthis primer comprises at least one acrylic and/or methacrylic polymer P1, at least one acrylic and/or methacrylic polymer P2 different from P1, at least one crosslinking agent, and, preferably, at least one polyester that is soluble or dispersible in water;P1 having a gel content TG1 greater than or equal to—in % dry weight and in an increasing order of preference—70, 80, 85, with respect to the total dry weight of P1;P2 having a gel content TG2 less than or equal to TG1 and less than or equal to—in % dry weight and in an increasing order of preference—20, 40, 70 by weight with respect to the total dry weight of P2;P1, having a surface-grafted free weak acid content greater than or equal to—in microequivalent per gram of polymer and in an increasing order of preference—0.8; 0.9; 1.0;

the mass concentration of P2 is less than or equal to—in % dry weight with respect to the total dry mass of P1 and P2 and is given hereinafter in an increasing order of preference, 60, 50, 40.

The invention is thus based on a novel assembly of acrylic and/or methacrylic polymers, having different gel contents and situated in opposite domains, this novel assembly resulting, in a surprisingly unexpected way, in significant and concomitant improvements in the wet metal adhesion and gas barrier properties of the composite film.

According to a second aspect, a purpose of the invention is a production method, in in-line or batch production, preferably in-line, of the film according to the invention, this method being characterized by the implementation of the following steps:a—utilizing a support as defined in the present description;b—optionally, carrying out a physical surface treatment of said substrate;c—optionally, stretching the film in a given direction or in 2 perpendicular directions;d—coating at least one face of said support with a coating composition making it possible to obtain at least one layer of cross-linked adhesion primer as defined in the present description;e—cross-linking the coating in order to obtain the layer of adhesion primer;f—optionally, stretching the film in a given direction, the latter being perpendicular to that envisaged in step c in the case where this step is implemented with unidirectional stretching, or stretching in 2 perpendicular directions;g—optionally, subjecting the coated and stretched support to a thermosetting;h—applying a covering as defined in the present description on the layer of cross-linked adhesion primer;i—subjecting the composite support/primer/covering assembly to heat curing, advantageously for 1 to 50 days, preferably 5 to 20 days, and even more preferably, for 8 to 15 days, at a temperature comprised between 10 and 120° C., preferably between 30 and 90° C., and even more preferentially, between 50 and 80° C., at ambient atmospheric pressure.

According to a third aspect, the invention relates to an adhesion primer coating composition, in particular utilized in the aforementioned method, characterized in that it comprises:a mixture of at least two acrylic latexes L1, L2:L1 comprising at least one acrylic and/or methacrylic polymer P1; P1 having a gel content TG1 greater than or equal to—in % by dry weight and in an increasing order of preference—70, 80, 85, with respect to the total dry weight of P1;L2 comprising at least one acrylic and/or methacrylic polymer P2 different from P1, P2 having a gel content TG2 less than or equal to TG1 and less than or equal to—in % by dry weight and in an increasing order of preference—20, 40, 70 by weight with respect to the total dry weight of P2;P1 having a surface-grafted free weak acid content greater than or equal to—in microequivalent per gram of polymer and in an increasing order of preference—0.8; 0.9; 1.0;the mass concentration of P2 is less than or equal to—in % by dry weight with respect to the total dry mass of P1 and P2 and is given hereinafter in an increasing order of preference, 60, 50, 40;at least one crosslinking agent;preferably, at least one polymer that is soluble or dispersible in water;and preferably water.

According to a fourth aspect, the invention relates to an article chosen from the group constituted by food and non-food packaging, films or foils for support protection and films or foils for thermal insulation and protection against humidity in the building sector, characterized in that it comprises at least one film according to the invention or such as obtained at the end of the method according to the invention.

