Multi-layer structure

Abstract

The present invention relates to a multi-layer structure comprising: - an adhesive layer consisting of a composition A comprising a copolyester resin having a glass transition temperature of less than 0°C and a degree of crystallinity of less than 10%; - a heat-sealable polyester polymer layer; and - a complexable polyester polymer layer, wherein the adhesive layer is located between the heat-sealable layer and the complexable layer. In addition, the present invention relates to a method for producing the multi-layer structure according to the invention. The present invention also relates to resealable packaging. Finally, the present invention relates to the use of the multi-layer structure according to the invention.

Description

[0001] Multi-layer structure

[0002] Field of invention

[0003] The present invention relates to a multi-layer structure, its method of manufacture and its use, as well as a resealable package.

[0004] Technical background

[0005] Multi-layered products (or laminated products) are used in many fields for packaging a wide variety of products, particularly in the food, cosmetics, and detergent industries. Depending on the requirements, these products can be flexible or rigid. These include flexible packaging. These products are generally made of different materials (composite multi-layered products). The materials can be chosen from paper, metal, or thermoplastic polymers.

[0006] The characteristics and properties of multi-layer articles will depend in particular on the materials used to obtain the layers. Thus, it is common to combine layers comprising different materials in order to obtain multi-layer articles, very generally composite multi-layer articles, combining the characteristics and properties of the different individual layers and therefore having particular characteristics and properties.

[0007] Among the multi-layer articles, there are resealable packages that are used in the food industry and mass distribution to package foodstuffs, particularly fresh products. These packages generally comprise a container (or receptacle) and a lid (or lidding film) forming a cover, which are hermetically attached to each other by heat sealing. After an initial opening of the lid and consumption of a portion of the food product contained in the receptacle, the user can reposition the lid on the receptacle, so as to reseal the package in a substantially hermetic manner, and ensure the preservation of the remaining portion of the product. A succession of reopenings and reclosings is also possible.

[0008] The receptacle of these packages generally comprises a sheet of polyethylene terephthalate (PET), thermoformed so as to have a flat base on which the food product rests and a perimeter in the form of a flat strip. This perimeter, generally parallel to the base, is heat-sealed to the lid, which is made of a multi-layer film. When the consumer opens the package, the lidding film is manually separated from the receptacle at the level of the flat strip of its perimeter. This operation reveals the adhesive layer initially included in the lidding film.

[0009] A simple manual pressure then allows the packaging to be resealed, once the seal has been repositioned on the receptacle in accordance with their position in the packaging before opening.

[0010] In most resealable packaging available on the market, the lidding film is a multi-layer structure that includes an HMPSA (Hot Melt Pressure Sensitive Adhesive) layer bonding a complexable layer and a heat-sealable layer.

[0011] The complexable layer can be complexed with other layers to produce the sealing film, for example with a rigid layer to improve the mechanical strength of said film.

[0012] The HMPSA layer typically comprises one or more tackifying resins and one or more styrenic block copolymers. Applied in the molten state, it solidifies upon cooling, forming an adhesive layer that ensures the bonding of the complexable and heat-sealable layers.

[0013] The heat-sealable layer allows the lidding film to be sealed to the container by heat sealing. It is often made of a polyolefin, particularly polyethylene, due to its heat sealability at low temperatures. However, since the PET in the container has a much higher softening temperature, it is necessary to use a container made from PET coextruded with a polyolefin in order to be able to heat seal the lidding film at low temperatures.

[0014] The resulting packaging therefore includes materials of very different natures (styrene block copolymer, polyolefin, polyester), which are very difficult to separate from each other, which poses a problem for recycling them.

[0015] The present invention aims to remedy this recycling problem.

[0016] Thus, the present invention aims to provide a multi-layer structure that is fully recyclable, as well as a fully recyclable resealable package.

[0017] Furthermore, the present invention aims to improve the resealing quality of a resealable package, in particular to limit the risk of the package opening during storage or transport.

[0018] Summary of the Invention The present invention relates to a multilayer structure comprising:

[0019] - an adhesive layer consisting of a composition A comprising a copolyester resin having a glass transition temperature of less than 0°C and a degree of crystallinity of less than 10%,

[0020] - a heat-sealable layer based on polyester polymer, and

[0021] - a complexable layer based on polyester polymer, in which the adhesive layer is located between the heat-sealable layer and the complexable layer.

[0022] In addition, the present invention relates to a method for manufacturing the multilayer structure according to the invention comprising: a step of coating an adhesive comprising composition A on a surface of a first film, then a step of laminating (laminating) a surface of a second film on the coated surface of the first film, in which one of the films comprises the heat-sealable layer or is bonded to the heat-sealable layer after the laminating step, and in which one of the films comprises the complexable layer or is bonded to the complexable layer after the laminating step.

[0023] The present invention also relates to resealable packaging comprising the multi-layer structure according to the invention.

[0024] Finally, the present invention relates to the use of the multilayer structure according to the invention for the manufacture of a resealable package.

[0025] The multilayer structure according to the invention makes it possible to overcome the problem of separating layers of different materials, which makes it easier to recycle. In particular, it is not necessary to use a styrene block copolymer in the adhesive layer of the multilayer structure according to the invention. Furthermore, the multilayer structure according to the invention can be heat-sealed directly to a PET container, which avoids prior coextrusion with a polyolefin (of a different nature) and therefore allows the container to be recycled. In addition, the multilayer structure according to the invention leads to improved resealing quality compared to a conventional multilayer structure (comprising a layer based on a styrene block copolymer, and polyolefin layers).

[0026] Description of the invention

[0027] Multilayer structure By “polyester polymer” we mean a polymer comprising at least two ester groups, which may be a homopolyester or a copolyester.

[0028] The term "homopolyester polymer" means a polyester polymer whose main chain comprises i) ester bonds linking a single unit derived from polyol and a single unit derived from polycarboxylic acid, or ii) ester bonds linking a single unit derived from hydroxylated carboxylic acid, said units being repeated several times.

[0029] By “polyol” is meant a compound comprising at least two hydroxyl groups (-OH). Preferably, the polyol is a diol.

[0030] By "polycarboxylic acid" is meant a compound comprising at least two carboxylic acid groups (-C(=O)-OH). Preferably, the polycarboxylic acid is a dicarboxylic acid.

[0031] A homopolyester polymer according to i) may be obtained by polymerization of a single type of polyol monomer and a single type of polycarboxylic acid monomer (or one of its ester-forming derivatives such as anhydride or (m)ethyl ester, preferably methyl ester).

[0032] In particular, a homopolyester polymer according to i) may be a polymer whose main chain comprises ester bonds connecting a single unit derived from diol and a single unit derived from dicarboxylic acid.

[0033] A homopolyester polymer according to ii) may be obtained by polymerization of a compound comprising at least one ester bond engaged in a cycle (for example a lactone or a cyclic diester such as glycolide or lactide), or a polymer obtained by polymerization of a hydroxylated carboxylic acid.

[0034] The term "copolyester polymer" refers to a polyester polymer whose main chain comprises i) ester bonds linking units derived from polyol(s) and polycarboxylic acid(s), at least one unit derived from polyol and / or at least one unit derived from polycarboxylic acid being different from the others (i.e. the copolyester polymer comprises at least two different units derived from polyols and / or at least two different units derived from polycarboxylic acids), or ii) ester bonds linking different units derived from hydroxylated carboxylic acids, said units being repeated several times.

[0035] A copolyester polymer according to i) may be obtained by polymerization of one or more types of polyol monomers and one or more types of polycarboxylic acid monomers (or one of their ester-forming derivatives such as anhydride or (m)ethyl ester, preferably methyl ester), at least one polyol monomer and / or at least one polycarboxylic acid monomer (or derivative) being different from the others.

[0036] In particular, a copolyester polymer according to i) may be a polymer whose main chain comprises ester bonds connecting one or more diol-derived units and one or more dicarboxylic acid-derived units, at least one diol-derived unit and / or at least one dicarboxylic acid-derived unit being different from the others.

[0037] A copolyester polymer according to ii) may be obtained by polymerization of several compounds comprising at least one ester bond engaged in a cycle (each compound being for example a lactone or a cyclic diester such as glycolide or lactide), or a polymer obtained by polymerization of several hydroxylated carboxylic acids.

[0038] Adhesive layer

[0039] The adhesive layer allows the heat-sealable layer and the complexable layer to be bonded directly or indirectly. Indeed, other layers may be present in the multi-layer structure, particularly between the adhesive layer and the heat-sealable layer.

[0040] The adhesive layer consists of a composition A comprising a copolyester resin having a glass transition temperature below 0°C and a degree of crystallinity below 10%.

[0041] The copolyester resin makes it possible to give composition A adhesive properties, in particular pressure-sensitive adhesive.

[0042] A pressure-sensitive adhesive can be generally defined as a substance that gives the substrate coated with it an immediate tack, which allows it to adhere instantly to another substrate under the effect of brief, light pressure at room temperature or at a lower temperature (for example, between 3°C and 25°C).

[0043] By "copolyester resin" is meant the reaction product obtained from the synthesis of a copolyester polymer or a mixture of different reaction products obtained from syntheses of different copolyester polymers, preferably the reaction product obtained from the synthesis of a copolyester polymer.

[0044] As a reaction product, the copolyester resin therefore comprises one or more copolyester polymers, but may also comprise, for example, an unreacted monomer, a possible catalyst (to accelerate the synthesis of the copolyester polymer) and / or a monomer formed in situ by reaction of other monomers which may be part of the backbone of the copolyester polymer. Generally, the relative amounts of the monomer residues constituting the copolyester polymer are identical or very similar to the relative amounts of the monomers used to manufacture it. However, it may happen that other monomers are formed during the production of the copolyester polymer and these formed monomers may be part of the final copolyester polymer.For example, when monoethylene glycol is used, a small amount of diethylene glycol may be formed in situ and its residue may be incorporated into the structure of the copolyester polymer, as is known to those skilled in the art.

[0045] The glass transition temperature (Tg) of a copolyester resin can be measured by differential scanning calorimetry (DSC), for example according to ASTM E1356-08 with the modification that a scanning temperature of 15°C per minute instead of 10°C per minute is used.

[0046] Unless otherwise indicated, the standards referred to throughout the application are those in effect on the date the application was filed.

[0047] Advantageously, the glass transition temperature of the copolyester resin is less than -4°C, preferably between -5°C and -20°C.

[0048] The degree of crystallinity of a copolyester resin can be measured by DSC, for example according to ASTM E793-06.

[0049] Preferably, the copolyester resin of composition A is amorphous (i.e., it does not exhibit a melting point by DSC).

[0050] The softening temperature of the copolyester resin may be between 50°C and 150°C, preferably between 70°C and 130°C, more preferably between 80°C and 110°C. The softening temperature may be measured according to ASTM E28-67.

[0051] Composition A may have a storage modulus G' at 25°C of less than 1 MPa, preferably less than 0.7 MPa.

[0052] In the context of the present invention, the storage modulus G' can be measured with a rheometer, in particular according to the ASTM D4440 standard, for example by varying the temperature from 140°C to -40°C at 10 rad / sec using 25 mm parallel plates.

[0053] The copolyester polymer(s) of the copolyester resin may have a weight-average molecular weight of between 5000 g / mol and 150000 g / mol, preferably between 30000 g / mol and 100000 g / mol, more preferably between 60000 g / mol and 90000 g / mol. In the present invention, the number-average or weight-average molecular weights may be measured by size exclusion chromatography, in particular with a polystyrene standard, for example with tetrahydrofuran as solvent.

[0054] The copolyester polymer(s) of the copolyester resin may be obtained by reacting at least one polyol with at least one polycarboxylic acid or one of its ester-forming derivatives (such as anhydride or (m)ethyl ester, preferably methyl ester).

[0055] This reaction can be carried out by any conventional method for obtaining a copolyester, in particular by transesterification and / or esterification. In particular, a catalyst can be used, in particular an organometallic catalyst such as an organozinc, organotitanium and / or an organotin (preferably an organozinc and / or an organotitanium), for example zinc acetate dihydrate, butyltin tris(2-ethylhexanoate), dibutyltin diacetate, tetra(2-ethylhexyl)titanate, tetra-n-butyl titanate and / or dibutyltin oxide.

[0056] The molar equivalent ratio of polyol(s) / polycarboxylic acid(s) (or ester-forming derivative(s)) used during the preparation of the copolyester polymer may be between 1.1 and 2.5, preferably between 1.2 and 2, more preferably between 1.3 and 1.8.

[0057] The molar equivalent ratio of polyol(s) / polycarboxylic acid(s) (or ester-forming derivative(s)) is defined as being equal to the molar equivalent number of -OH groups of the polyol(s) divided by the molar equivalent number of -C(O)OH groups of the polycarboxylic acid(s) (or ester-forming groups) used during the preparation of the copolyester polymer.

[0058] The molar equivalent number of -OH groups in a polyol is equal to: f(-OH )*(m poiyoï / Mpoiyoi), where f(-OH) is the number of -OH groups in the polyol, m po iyoi is the mass introduced in g of the polyol and M po iyoi is the molar mass in g / mol of the polyol. Preferably, the polyol is a diol and f(-OH) is therefore equal to 2.

[0059] The molar equivalent number of -C(O)OH groups in a polycarboxylic acid is equal to: f(-C(O)OH)*(m a cide / M a cide), where f(-C(O)OH) is the number of -C(O)OH groups in the polycarboxylic acid, m aCide is the mass introduced in g of the polycarboxylic acid and M aC ide is the molar mass in g / mol of the polycarboxylic acid. The molar equivalent number of ester-forming groups of an ester-forming polycarboxylic acid derivative is calculated in a similar manner. Preferably, the polycarboxylic acid is a dicarboxylic acid (or one of its ester-forming derivatives) and f(-C(O)OH) (or f(ester-forming groups)) is therefore equal to 2.

[0060] Advantageously, the copolyester polymer(s) of the copolyester resin is (are) obtained by reaction of at least one diol with at least one dicarboxylic acid or one of its ester-forming derivatives.

[0061] Preferably, the copolyester polymer(s) of the copolyester resin is (are) obtained by reaction of at least one acyclic diol with at least one cyclic dicarboxylic acid or one of its ester-forming derivatives, and at least one acyclic dicarboxylic acid comprising at least 4 (preferably between 4 and 15, more preferably between 6 and 12) carbon atoms or one of its ester-forming derivatives (the at least 4 carbon atoms being the carbon atoms of the carbonyls (C=O) and between the carbonyls; for example, the carbon atoms of the alkoxy groups of an ester are not taken into account).

[0062] By "acyclic" is meant not including a cycle (aromatic or non-aromatic).

[0063] By "cyclic dicarboxylic acid" is meant a dicarboxylic acid comprising at least one cycle (aromatic or cycloaliphatic).

[0064] For example, the copolyester polymer(s) of the copolyester resin may be obtained by reacting 52-80 mol% (preferably 54-76 mol%, more preferably 56-66 mol%) of acyclic diol(s) with 10-24 mol% (preferably 12-23 mol%, more preferably 17-22 mol%) of cyclic dicarboxylic acid(s) (or ester-forming derivative(s)), and 10-24 mol% (preferably 12-23 mol%, more preferably 17-22 mol%) of acyclic dicarboxylic acid(s) comprising at least 4 carbon atoms (or ester-forming derivative(s), the mol% contents being calculated on the basis of the total number of moles of acyclic diol(s), of cyclic dicarboxylic acid(s) (or ester-forming derivative(s)) and of acyclic dicarboxylic acid(s) comprising at least 4 carbon atoms (or ester-forming derivative(s)) used.

[0065] Preferably, the at least one acyclic diol is chosen from monoethylene glycol, polyethylene glycol (preferably having a number-average molecular weight less than or equal to 10,000 g / mol, more preferably between 350 g / mol and 450 g / mol), propane-1,3-diol, butane-1,4-diol, pentane-1,5-diol, hexane-1,6-diol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, polytetrahydrofuran (also called polytetramethylene glycol, preferably having a number-average molecular weight less than or equal to 3,000 g / mol, more preferably between 950 g / mol and 1,050 g / mol), and mixtures thereof, more preferably from monoethylene glycol, 2,2-dimethyl-1,3-propanediol, and mixtures thereof, in particular monoethylene glycol.

[0066] Advantageously, the at least one cyclic dicarboxylic acid (or one of its ester-forming derivatives) comprises a cycloaliphatic dicarboxylic acid (or one of its ester-forming derivatives), for example 1,4-cyclohexanedicarboxylic acid, and / or an aromatic dicarboxylic acid (or one of its ester-forming derivatives) comprising an aromatic ring whose two functional groups (carboxylic acid, methyl ester, etc.) are in the meta or ortho position relative to each other, in particular meta. Preferably, the at least one cyclic dicarboxylic acid comprises isophthalic acid (or one of its ester-forming derivatives) and / or phthalic acid (or one of its ester-forming derivatives), in particular isophthalic acid (or one of its ester-forming derivatives). More preferably, the at least one cyclic dicarboxylic acid is a mixture of aromatic dicarboxylic acids (or ester-forming derivatives) comprising isophthalic acid or one of its ester-forming derivatives.In particular, the at least one cyclic dicarboxylic acid is a mixture of terephthalic acid (or one of its ester-forming derivatives, in particular dimethyl terephthalate) and isophthalic acid (or one of its ester-forming derivatives).

[0067] Advantageously, the at least one acyclic dicarboxylic acid (or one of its ester-forming derivatives) comprising at least 4 (preferably between 4 and 15, more preferably between 6 and 12) carbon atoms is linear. Preferably, the at least one linear dicarboxylic acid is chosen from succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, 1,12-dodecanedioic acid, one of their ester-forming derivatives, and mixtures thereof, more preferably from azelaic acid, sebacic acid, one of their ester-forming derivatives, and mixtures thereof, in particular azelaic acid or one of its ester-forming derivatives.

[0068] According to one embodiment, the copolyester polymer(s) of the copolyester resin is (are) obtained by reaction of: at least one acyclic diol with at least one cyclic dicarboxylic acid (or one of its ester-forming derivatives) comprising a cycloaliphatic dicarboxylic acid (or one of its ester-forming derivatives) and / or an aromatic dicarboxylic acid (or one of its ester-forming derivatives) comprising an aromatic ring whose two functional groups are in the meta position relative to each other, and at least one acyclic dicarboxylic acid (or one of its ester-forming derivatives) comprising at least 4 (preferably between 4 and 15, more preferably between 6 and 12) carbon atoms and being linear.

[0069] Preferably, the copolyester polymer(s) of the copolyester resin is (are) obtained by reaction of: at least one acyclic diol chosen from monoethylene glycol, polyethylene glycol (preferably having a number-average molecular weight less than or equal to 10,000 g / mol, more preferably between 350 g / mol and 450 g / mol), propane-1,3-diol, butane-1,4-diol, pentane-1,5-diol, hexane-1,6-diol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, polytetrahydrofuran (preferably having a number-average molecular weight less than or equal to 3,000 g / mol, more preferably between 950 g / mol and 1050 g / mol), and mixtures thereof, with at least one cyclic dicarboxylic acid comprising isophthalic acid (or one of its ester-forming derivatives) and / or phthalic acid (or one of its ester-forming derivatives), and at least one linear dicarboxylic acid chosen from succinic acid,glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, 1,12-dodecanedioic acid, one of their ester-forming derivatives, and mixtures thereof.,

[0070] In particular, the copolyester polymer(s) of the copolyester resin is (are) obtained by reaction of: monoethylene glycol, with terephthalic acid (or one of its ester-forming derivatives, in particular dimethyl terephthalate), isophthalic acid (or one of its ester-forming derivatives), and azelaic acid (or one of its ester-forming derivatives).

[0071] For example, the copolyester polymer(s) of the copolyester resin is (are) obtained by reaction of:

[0072] 52-80 mol% (preferably 54-76 mol%, more preferably 56-66 mol%) of monoethylene glycol, with

[0073] 5-12 mol% (preferably 6-13 mol%, more preferably 10-12 mol%) of terephthalic acid (or one of its ester-forming derivatives), 5-12 mol% (preferably 6-10 mol%, more preferably 7-10 mol%) of isophthalic acid (or one of its ester-forming derivatives), and

[0074] 10-24 mol% (preferably 12-23 mol%, more preferably 17-22 mol%) azelaic acid (or one of its ester-forming derivatives), the mol% contents being calculated on the basis of the total number of moles of acyclic diol(s), cyclic dicarboxylic acid(s) (or ester-forming derivative(s)) and acyclic dicarboxylic acid(s) comprising at least 4 carbon atoms (or ester-forming derivative(s)) used.

[0075] Advantageously, composition A comprises at least 90% by weight of copolyester resin relative to the total weight of composition A, preferably at least 95% by weight, more preferably at least 99% by weight.

[0076] Composition A may further comprise one or more additives, for example chosen from anti-fog agents, slip / anti-blocking agents, UV stabilizers (or antioxidants), tackifying resins, preferably from UV stabilizers (or antioxidants). These additives do not intervene in the synthesis reaction of a copolyester polymer, and may therefore be introduced before, simultaneously or after obtaining the copolyester resin.

[0077] The total content of additive(s) may be up to 10% by weight relative to the total weight of composition A, preferably up to 5% by weight, more preferably between 0.1% and 1% by weight.

[0078] The anti-fogging agent may be chosen from sorbitan esters, glycerol esters, poly(oxyethylene) esters, alkylbenzene sulfonates, and mixtures thereof; said esters are in particular esters of fatty acid(s).

[0079] The anti-fog agent content can be up to 5% by weight relative to the total weight of composition A.

[0080] The glidant / anti-blocking agent may be selected from erucamide, oleamide, docosanamide, stearamide, palmitamide, ethylene bis-stearamide, ethylene bis-oleamide, and mixtures thereof.

[0081] The content of slip agent / anti-blocking agent can be up to 5% by weight relative to the total weight of composition A.

[0082] A UV stabilizer is typically introduced to prevent degradation resulting from a reaction with oxygen that is likely to form under the action of heat or light. UV stabilizers may include antioxidants capable of scavenging free radicals.The UV stabilizer (or antioxidant) may be chosen from benzotriazoles, benzophenones, so-called hindered phenols such as octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (CAS: 2082-79-3), pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (CAS: 6683-19-8) and ethylenebis(oxyethylene) bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate] (CAS: 36443-68-2), so-called hindered amines such as bis(1-octyloxy-2,2,6,6-tetramethyl-4-piperidyl)sebacate, bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate, bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate (CAS No. 41556-26-7), methyl 1,2,2,6,6-pentamethyl-4-piperidyl sebacate (CAS No. 82919-37-7) and 4,4'-bis(a,a-dimethylbenzyl)diphenylamine, and mixtures thereof.

[0083] Preferably, the UV stabilizer (or antioxidant) is chosen from so-called hindered phenols, so-called hindered amines, and mixtures thereof, more preferably from so-called hindered phenols. So-called hindered phenols are generally phenols substituted by at least one bulky group (such as tert-butyl) preferably in the ortho position relative to the hydroxy group.

[0084] The content of UV stabilizer(s) (or antioxidant(s)) can be up to 5% by weight relative to the total weight of composition A, preferably between 0.1% and 1% by weight.

[0085] The tackifying resin can be chosen from natural and modified rosin esters, including glycerol and pentaerythritol esters.

[0086] Composition A may also include possible traces (for example less than 0.05% by weight relative to the total weight of composition A) of solvent previously used to facilitate the coating of composition A on one of the layers of the multilayer structure.

[0087] The solvent used to dilute the copolyester resin may be an organic solvent, for example butanone, toluene, xylene, benzene, monochlorobenzene, dichloromethane, 2-nitropropane, nitroethane, nitrobenzene, dichlorobenzene, dioxolane, tetrahydrofuran, an ester (ethyl acetate, n-butyl acetate, 2-ethoxyethyl acetate), cyclohexanone and / or dioxane, including an ester such as ethyl acetate, n-butyl acetate, 2-ethoxyethyl acetate, etc.

[0088] However, composition A constituting the adhesive layer of the multilayer structure only comprises possible traces of solvent because, if a solvent is used to facilitate the coating of composition A on one of the layers of the multilayer structure, it is evaporated after coating.

[0089] Advantageously, composition A does not comprise styrenic block copolymers or saturated aliphatic polymers (such as polyethylene or polypropylene). Indeed, these compounds could hinder the recyclability of the multilayer structure. In addition, composition A preferably does not comprise a crosslinking agent such as a polyisocyanate.

[0090] According to a preferred embodiment, composition A comprises (preferably consists of) at least 95% by weight of copolyester resin and up to 5% by weight of UV stabilizer(s) (or antioxidant(s)), preferably at least 99% by weight of copolyester resin and between 0.1% and 1% by weight of UV stabilizer(s) (or antioxidant(s)), the percentages being relative to the total weight of composition A.

[0091] The copolyester resin and the UV stabilizer(s) (or antioxidant(s)) are as defined above.

[0092] The amount of composition A per unit area in the multilayer structure can vary over a very wide range, for example from 1 g / m 2 at 30 g / m 2 , preferably 2 g / m 2 at 20 g / m 2 , in particular 4 g / m 2 at 16 g / m 2 .

[0093] Heat-sealable layer

[0094] The heat-sealable layer is different from the adhesive layer. In particular, it is not a pressure-sensitive adhesive.

[0095] The heat-sealable layer allows the multi-layer structure to be sealed to a substrate when heated, particularly at a temperature between 80°C and 180°C, preferably between 100°C and 160°C. Thus, the heat-sealable layer advantageously has a softening temperature between 80°C and 180°C. The softening temperature can be measured according to ASTM E28-67.

[0096] The heat-sealable layer may have a storage modulus G' at 25°C greater than 1 MPa, or even be too rigid for G' to be measured accurately.

[0097] The heat-sealable layer is based on polyester polymer. In particular, the heat-sealable layer comprises at least 90% by weight of one or more polyester polymers relative to the total weight of said layer, preferably at least 95% by weight, more preferably at least 99% by weight.

[0098] The heat-sealable layer therefore comprises one or more polyester polymers, but may also comprise, for example, an unreacted monomer, a possible catalyst and / or a monomer formed in situ by reaction of other monomers which may be part of the backbone of the polyester polymer. Preferably, the heat-sealable layer is based on amorphous polyester polymer.

[0099] Advantageously, the polyester polymer(s) of the heat-sealable layer are chosen from copolyester polymers.

[0100] The copolyester polymer(s) of the heat-sealable layer are in particular chosen from polyester polymers whose main chain comprises ester bonds linking units derived from polyol(s) and polycarboxylic acid(s), at least one unit derived from polyol and / or at least one unit derived from polycarboxylic acid being different from the others.

[0101] It is understood that a “polyol / polycarboxylic acid derived unit” refers to the portion of the polyol / polycarboxylic acid retained in the final structure of the polyester polymer. For example, a polyester polymer consisting of a monoethylene glycol derived unit and a succinic acid derived unit comprises the following structure:

[0102] The polycarboxylic acid-derived unit can therefore be introduced into the polymer chain by reacting a polycarboxylic acid or one of its ester-forming derivatives (such as anhydride or (m)ethyl ester, preferably methyl ester).

[0103] Advantageously, the copolyester polymer(s) comprise at least one unit derived from a cyclic or acyclic diol (preferably acyclic) and at least one unit derived from a cyclic dicarboxylic acid (preferably aromatic). Preferably, the copolyester polymer(s) comprise at least one unit derived from a diol and at least two units derived from cyclic dicarboxylic acids (preferably aromatic).

[0104] For example, the cyclic or acyclic diol-derived unit of the copolyester polymer(s) may be derived from monoethylene glycol, polyethylene glycol (preferably diethylene glycol), propane-1,2-diol, propane-1,3-diol, butanediol (-1,4, -1,3 and / or -1,2), pentanediol, hexanediol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, polytetrahydrofuran and / or cyclohexanedimethanol, preferably monoethylene glycol, polyethylene glycol and / or cyclohexanedimethanol, especially monoethylene glycol and / or diethylene glycol.

[0105] For example, the cyclic dicarboxylic acid derived unit may be derived from cyclohexanedicarboxylic acid, phthalic acid, isophthalic acid and / or terephthalic acid, preferably terephthalic acid and optionally isophthalic acid.

[0106] In addition to the at least one unit derived from a cyclic dicarboxylic acid, the copolyester polymer(s) may also comprise at least one unit derived from an acyclic dicarboxylic acid, for example derived from maleic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid and / or 1,12-dodecanedioic acid, preferably azelaic acid and / or sebacic acid.

[0107] According to one embodiment, the copolyester polymer(s) comprise a unit derived from monoethylene glycol and / or diethylene glycol, a unit derived from terephthalic acid and a unit derived from cyclic dicarboxylic acid (different from terephthalic acid), in particular a unit derived from isophthalic acid.

[0108] The heat-sealable layer may further comprise one or more additives, for example chosen from UV stabilizers (or antioxidants), slip / anti-blocking agents, anti-fogging agents, anti-static agents, manufacturing aids, matting agents, and mixtures thereof, in particular from UV stabilizers (or antioxidants), slip / anti-blocking agents, anti-fogging agents, and mixtures thereof.

[0109] The total content of additive(s) may be up to 10% by weight relative to the total weight of the heat-sealable layer, preferably up to 5% by weight, more preferably up to 1% by weight.

[0110] The UV stabilizer (or antioxidant) may be chosen from benzotriazoles, benzophenones, so-called hindered phenols such as octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) and ethylenebis(oxyethylene) bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate], so-called hindered amines such as bis(1-octyloxy-

[0111] 2.2.6.6-tetramethyl-4-piperidyl)sebacate, bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate, bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate, methyl

[0112] 1,2,2,6,6-pentamethyl-4-piperidyl sebacate and 4,4'-bis(a,a-dimethylbenzyl)diphenylamine, and mixtures thereof.

[0113] The glidant / anti-blocking agent may be selected from organic and / or inorganic, preferably inorganic, glidant / anti-blocking agents. For example, the glidant / anti-blocking agent may be selected from erucamide, oleamide, docosanamide, stearamide, palmitamide, ethylene bis-stearamide, ethylene bis-oleamide, silica, talc, calcium carbonate, glass beads, and mixtures thereof, preferably from silica, talc, calcium carbonate, glass beads, and mixtures thereof.

[0114] The anti-fogging agent may be chosen from sorbitan esters, glycerol esters, poly(oxyethylene) esters, alkylbenzene sulfonates, and mixtures thereof; said esters are in particular esters of fatty acid(s).

[0115] The antistatic agent may be selected from alkali metal sulfonates, polyether-modified polydiorganosiloxanes, polyalkylphenylsiloxanes, tertiary amines, glycerol monostearate, mixtures of glycerol monostearate and tertiary amines, and mixtures thereof.

[0116] The heat-sealable layer is advantageously divisible.

[0117] The heat-sealable layer can be pre-cut along all or part of its thickness, for example using a laser or a cutting plate.

[0118] The heat-sealable layer can be bi-oriented.

[0119] The bi-orientation of one (or more) polyester polymer-based layer(s) can be carried out by stretching the layer(s) under heating (for example by infrared, for example at a temperature above 100°C) in the machine direction (also called axial) and by stretching under heating (for example between 100°C and 135°C) in the direction perpendicular to the machine direction (also called transverse). The layer(s) can then be heated up to 220°C and relaxed at 220-170°C in the transverse direction. The stretch factor can be between 2.0 and 4.0 (especially about 3.0) in the machine direction, and between 3.0 and 4.0 (especially about 3.4) in the transverse direction.

[0120] By "about X", we mean more or less 10% of the value of X.

[0121] The heat-sealable layer may have undergone a surface treatment, such as an embossing treatment (preferably hot), a plasma treatment such as a corona treatment, an atmospheric pressure plasma treatment, a flame plasma treatment, a chemical plasma treatment, in particular a corona treatment.

[0122] The heat-sealable layer may have a thickness of between 0.1 pm and 20 pm, preferably between 0.5 pm and 15 pm.

[0123] Complexable layer

[0124] The complexable layer is different from the adhesive layer. In particular, it is not a pressure-sensitive adhesive.

[0125] The expression “complexable layer” is well known to those skilled in the art and designates in particular a layer which can be complexed (or laminated, or laminated, preferably laminated) with other layers, for example with a rigid layer to improve the mechanical strength of the multilayer structure.

[0126] The complexable layer may have a storage modulus G' at 25°C greater than 1 MPa, or even be too rigid for G' to be measured precisely.

[0127] The complexable layer is based on polyester polymer. In particular, the complexable layer comprises at least 90% by weight of one or more polyester polymers relative to the total weight of said layer, preferably at least 95% by weight, more preferably at least 99% by weight.

[0128] The complexable layer therefore comprises one or more polyester polymers, but may also comprise, for example, an unreacted monomer, a possible catalyst and / or a monomer formed in situ by reaction of other monomers which may be part of the backbone of the polyester polymer.

[0129] The polyester polymer(s) of the complexable layer may be chosen from homopolyester polymers, copolyester polymers, and mixtures thereof, preferably from homopolyester polymers.

[0130] The homopolyester polymer(s) are in particular chosen from polyester polymers whose main chain comprises ester bonds linking a single unit derived from polyol and a single unit derived from polycarboxylic acid.

[0131] Advantageously, the polyol-derived unit of the homopolyester polymer(s) is derived from an acyclic diol. For example, the polyol-derived unit may be derived from monoethylene glycol, polyethylene glycol (preferably diethylene glycol), propane-1,2-diol, propane-1,3-diol, butanediol (-1,4, -1,3 and / or -1,2), pentanediol, hexanediol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol or polytetrahydrofuran, preferably monoethylene glycol or polyethylene glycol, especially monoethylene glycol.

[0132] Advantageously, the polycarboxylic acid-derived unit of the homopolyester polymer(s) is derived from a cyclic dicarboxylic acid, in particular an aromatic dicarboxylic acid. For example, the polycarboxylic acid-derived unit may be derived from phthalic acid, isophthalic acid, terephthalic acid, in particular terephthalic acid.

[0133] According to one embodiment, the homopolyester polymer is poly(ethylene terephthalate).

[0134] The copolyester polymer(s) of the complexable layer are in particular chosen from polyester polymers whose main chain comprises ester bonds linking units derived from polyol(s) and polycarboxylic acid(s), at least one unit derived from polyol and / or at least one unit derived from polycarboxylic acid being different from the others.

[0135] Advantageously, the copolyester polymer(s) comprise at least one unit derived from an acyclic diol and at least one unit derived from a cyclic dicarboxylic acid (preferably aromatic).

[0136] For example, the acyclic diol-derived unit of the copolyester polymer(s) may be derived from monoethylene glycol, polyethylene glycol (preferably diethylene glycol), propane-1,2-diol, propane-1,3-diol, butanediol (-1,4, -1,3 and / or -1,2), pentanediol, hexanediol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol and / or polytetrahydrofuran, preferably monoethylene glycol and / or polyethylene glycol, especially monoethylene glycol.

[0137] For example, the cyclic dicarboxylic acid derived unit may be derived from cyclohexanedicarboxylic acid, phthalic acid, isophthalic acid and / or terephthalic acid, preferably terephthalic acid and optionally isophthalic acid.

[0138] In addition to the at least one unit derived from a cyclic dicarboxylic acid, the copolyester polymer(s) may also comprise at least one unit derived from an acyclic dicarboxylic acid, for example derived from maleic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid and / or 1,12-dodecanedioic acid, preferably azelaic acid and / or sebacic acid.

[0139] According to one embodiment, the copolyester polymer(s) comprise a unit derived from monoethylene glycol, a unit derived from terephthalic acid and a unit derived from cyclic dicarboxylic acid (different from terephthalic acid), in particular a unit derived from isophthalic acid.

[0140] The complexable layer may further comprise one or more additives, for example chosen from UV stabilizers (or antioxidants), slip / anti-blocking agents, antistatic agents, manufacturing aids, matting agents, and mixtures thereof, in particular from UV stabilizers (or antioxidants), slip / anti-blocking agents, and mixtures thereof.

[0141] The total content of additive(s) may be up to 10% by weight relative to the total weight of the complexable layer, preferably up to 5% by weight, more preferably up to 1% by weight. The UV stabilizer (or antioxidant) may be chosen from benzotriazoles, benzophenones, so-called hindered phenols such as octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) and ethylenebis(oxyethylene) bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate], so-called hindered amines such as bis(1-octyloxy-

[0142] 2.2.6.6-tetramethyl-4-piperidyl)sebacate, bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate, bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate, methyl

[0143] 1,2,2,6,6-pentamethyl-4-piperidyl sebacate and 4,4'-bis(a,a-dimethylbenzyl)diphenylamine, and mixtures thereof.

[0144] The glidant / anti-blocking agent may be selected from organic and / or inorganic, preferably inorganic, glidant / anti-blocking agents. For example, the glidant / anti-blocking agent may be selected from erucamide, oleamide, docosanamide, stearamide, palmitamide, ethylene bis-stearamide, ethylene bis-oleamide, silica, talc, calcium carbonate, glass beads, and mixtures thereof, preferably from silica, talc, calcium carbonate, glass beads, and mixtures thereof.

[0145] The antistatic agent may be selected from alkali metal sulfonates, polyether-modified polydiorganosiloxanes, polyalkylphenylsiloxanes, tertiary amines, glycerol monostearate, mixtures of glycerol monostearate and tertiary amines, and mixtures thereof.

[0146] The complexable layer is advantageously bi-oriented.

[0147] The complexable layer may have undergone a surface treatment, such as an embossing treatment (preferably hot), a plasma treatment such as a corona treatment, an atmospheric pressure plasma treatment, a flame plasma treatment, a chemical plasma treatment, in particular a corona treatment.

[0148] The complexable layer may have a thickness of between 5 pm and 100 pm, preferably between 10 pm and 50 pm.

[0149] Additional layers

[0150] The multilayer structure according to the invention may also comprise one or more additional layers (in addition to the adhesive, heat-sealable and complexable layers described above).

[0151] For example, the multilayer structure according to the invention may comprise: one or more additional layers on the heat-sealable layer (preferably between the adhesive layer and the heat-sealable layer), and / or one or more additional layers on the complexable layer (between the adhesive layer and the complexable layer, and / or on the surface not facing the adhesive layer, preferably between the adhesive layer and the complexable layer).

[0152] In this text, the term "heat-sealable film" means the assembly formed by the heat-sealable layer and the additional layer(s) on the heat-sealable layer, and the term "complexable film" means the assembly formed by the complexable layer and the additional layer(s) on the complexable layer.

[0153] Advantageously, the heat-sealable layer has a free face (not covered by another layer); it is therefore an external layer. When the multi-layer structure is used as a lid for a resealable package, the lid is heat-sealed onto the receptacle via the heat-sealable layer.

[0154] Preferably, the multilayer structure comprises one or more additional layers between the adhesive layer and the heat-sealable layer. Thus, the heat-sealable layer preferably has a free face (not covered by another layer). It is not excluded that one or more of the additional layers are also heat-sealable layers, identical to or different from the heat-sealable layer as described above.

[0155] According to one embodiment, the multilayer structure comprises one or more additional layers between the adhesive layer and the heat-sealable layer, and one or more additional layers on the complexable layer, preferably between the adhesive layer and the complexable layer. Advantageously, the heat-sealable layer has a free face.

[0156] Each additional layer is advantageously based on polyester polymer. In particular, each additional layer comprises at least 90% by weight of one or more polyester polymers relative to the total weight of said layer, preferably at least 95% by weight, more preferably at least 99% by weight.

[0157] Each additional layer therefore comprises one or more polyester polymers, but may also comprise, for example, an unreacted monomer, a possible catalyst and / or a monomer formed in situ by reaction of other monomers which may be part of the backbone of the polyester polymer.

[0158] The polyester polymer(s) of each additional layer may be chosen from homopolyester polymers, copolyester polymers, and mixtures thereof. Advantageously, the polyester polymer(s) of each additional layer of the heat-sealable film are chosen from homopolyester polymers, in particular polyethylene terephthalate, each additional layer being between the adhesive layer and the heat-sealable layer. Advantageously, the polyester polymer(s) of each additional layer of the complexable film are chosen from copolyester polymers, each additional layer being between the adhesive layer and the complexable layer.

[0159] The homopolyester polymer(s) are in particular chosen from polyester polymers whose main chain comprises ester bonds linking a single unit derived from polyol and a single unit derived from polycarboxylic acid.

[0160] Advantageously, the polyol-derived unit of the homopolyester polymer(s) is derived from an acyclic diol. For example, the polyol-derived unit may be derived from monoethylene glycol, polyethylene glycol (preferably diethylene glycol), propane-1,2-diol, propane-1,3-diol, butanediol (-1,4, -1,3 and / or -1,2), pentanediol, hexanediol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol or polytetrahydrofuran, preferably monoethylene glycol or polyethylene glycol, especially monoethylene glycol.

[0161] Advantageously, the polycarboxylic acid-derived unit of the homopolyester polymer(s) is derived from a cyclic dicarboxylic acid, in particular an aromatic dicarboxylic acid. For example, the polycarboxylic acid-derived unit may be derived from phthalic acid, isophthalic acid, terephthalic acid, in particular terephthalic acid.

[0162] According to one embodiment, the homopolyester polymer is poly(ethylene terephthalate).

[0163] The copolyester polymer(s) of each additional layer are in particular chosen from polyester polymers whose main chain comprises ester bonds linking units derived from polyol(s) and polycarboxylic acid(s), at least one unit derived from polyol and / or at least one unit derived from polycarboxylic acid being different from the others.

[0164] Advantageously, the copolyester polymer(s) comprise at least one unit derived from an acyclic diol and at least one unit derived from a cyclic dicarboxylic acid (preferably aromatic).

[0165] For example, the acyclic diol-derived unit of the copolyester polymer(s) may be derived from monoethylene glycol, polyethylene glycol (preferably diethylene glycol), propane-1,2-diol, propane-1,3-diol, butanediol (-1,4, -1,3 and / or -1,2), pentanediol, hexanediol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol and / or polytetrahydrofuran, preferably monoethylene glycol and / or polyethylene glycol, especially monoethylene glycol.

[0166] For example, the cyclic dicarboxylic acid derived unit may be derived from cyclohexanedicarboxylic acid, phthalic acid, isophthalic acid and / or terephthalic acid, preferably terephthalic acid and optionally isophthalic acid.

[0167] In addition to the at least one unit derived from a cyclic dicarboxylic acid, the copolyester polymer(s) may also comprise at least one unit derived from an acyclic dicarboxylic acid, for example derived from maleic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid and / or 1,12-dodecanedioic acid.

[0168] Each additional layer may further comprise one or more additives, for example chosen from UV stabilizers (or antioxidants), slip / anti-blocking agents, antistatic agents, manufacturing aids, matting agents, and mixtures thereof, in particular from UV stabilizers (or antioxidants), slip / anti-blocking agents, and mixtures thereof.

[0169] The total content of additive(s) may be up to 10% by weight relative to the total weight of each additional layer, preferably up to 5% by weight, more preferably up to 1% by weight.

[0170] The UV stabilizer (or antioxidant) may be chosen from benzotriazoles, benzophenones, so-called hindered phenols such as octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) and ethylenebis(oxyethylene) bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate], so-called hindered amines such as bis(1-octyloxy-

[0171] 2.2.6.6-tetramethyl-4-piperidyl)sebacate, bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate, bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate, methyl

[0172] 1,2,2,6,6-pentamethyl-4-piperidyl sebacate and 4,4'-bis(a,a-dimethylbenzyl)diphenylamine, and mixtures thereof.

[0173] The glidant / anti-blocking agent may be selected from organic and / or inorganic, preferably inorganic, glidant / anti-blocking agents. For example, the glidant / anti-blocking agent may be selected from erucamide, oleamide, docosanamide, stearamide, palmitamide, ethylene bis-stearamide, ethylene bis-oleamide, silica, talc, calcium carbonate, glass beads, and mixtures thereof, preferably from silica, talc, calcium carbonate, glass beads, and mixtures thereof. The antistatic agent may be selected from alkali metal sulfonates, polyether-modified polydiorganosiloxanes, polyalkylphenylsiloxanes, tertiary amines, glycerol monostearate, mixtures of glycerol monostearate and tertiary amines, and mixtures thereof.

[0174] Each additional layer can be bi-oriented.

[0175] Each additional layer may have undergone a surface treatment, such as an embossing treatment (preferably hot), a plasma treatment such as a corona treatment, an atmospheric pressure plasma treatment, a flame plasma treatment, a chemical plasma treatment, in particular a corona treatment.

[0176] Each additional layer may have a thickness of between 0.1 pm and 100 pm, preferably between 0.5 pm and 40 pm.

[0177] The heat-sealable film may have a thickness of between 2 pm and 100 pm, preferably between 3 pm and 50 pm, more preferably between 4 pm and 12 pm.

[0178] The complexable film may have a thickness of between 5 pm and 100 pm, preferably between 10 pm and 50 pm.

[0179] The heat-sealable film is advantageously divisible.

[0180] The heat-sealable film can be pre-cut along all or part of its thickness, for example using a laser or a cutting plate.

[0181] The heat-sealable film can be bi-oriented.

[0182] The complexable film can be bi-oriented.

[0183] Other features

[0184] Advantageously, each of the layers of the multilayer structure according to the invention is based on polyester polymer. In particular, each of the layers of the multilayer structure comprises at least 90% by weight of one or more polyester polymers relative to the total weight of said layer, preferably at least 95% by weight, more preferably at least 99% by weight. The polyester polymers of each type of layer (adhesive, heat-sealable, complexable, additional) are as described above.

[0185] Each layer therefore comprises one or more polyester polymers, but may also comprise, for example, an unreacted monomer, a possible catalyst and / or a monomer formed in situ by reaction of other monomers which may be part of the backbone of the polyester polymer.

[0186] Furthermore, one or more of the layers of the multilayer structure according to the invention may be covered in whole or in part by an ink. Advantageously, the multilayer structure does not comprise a styrene block copolymer, a copolymer of ethylene and vinyl acetate, a copolymer of ethylene and (meth)acrylate ester(s), a copolymer of ethylene and (meth)acrylic acid and / or a polyolefin polymer (i.e. obtained by the polymerization of one or more alkene-type monomers, such as polyethylene, polypropylene, ethylene-propylene copolymer), in particular none of these compounds.

[0187] Advantageously, the multilayer structure does not comprise a styrenic block copolymer and / or a polyolefin polymer, in particular none of these compounds.

[0188] According to one embodiment, the quantity of composition A per unit area in the multilayer structure according to the invention is between 1 g / m 2 and 30 g / m 2 , the thickness of the heat-sealable layer is between 0.1 pm and 20 pm and the thickness of the complexable layer is between 5 pm and 100 pm.

[0189] The total thickness of the multilayer structure according to the invention may be between 5 pm and 200 pm, preferably between 10 pm and 100 pm, more preferably between 14 pm and 62 pm.

[0190] According to one embodiment, the multilayer structure according to the invention comprises: an adhesive layer consisting of a composition A comprising a copolyester resin having a glass transition temperature of less than 0°C, a degree of crystallinity of less than 10% and being amorphous, the copolyester polymer(s) of the copolyester resin is (are) preferably obtained by reaction of: o at least one acyclic diol with o at least one cyclic dicarboxylic acid (or one of its ester-forming derivatives) comprising a cycloaliphatic dicarboxylic acid (or one of its ester-forming derivatives) and / or an aromatic dicarboxylic acid (or one of its ester-forming derivatives) comprising an aromatic ring whose two functional groups are in the meta position relative to each other, and o at least one acyclic dicarboxylic acid (or one of its ester-forming derivatives) comprising at least 4 (preferably between 4 and 15,more preferably between 6 and 12) carbon atoms and being linear, a heat-sealable and breakable layer based on copolyester polymer, preferably amorphous, a complexable layer based on polyester polymer, preferably homopolyester, and optionally one or more additional layers based on polyester polymer.,

[0191] The layers of this embodiment are as described above, including preferred embodiments and features.

[0192] The multilayer structure according to the invention advantageously has a second peel opening force greater than or equal to 0.8 N / 10 mm for a quantity of composition A per unit area in said structure greater than or equal to 6 g / m 2, preferably greater than or equal to 1.0 N / 10 mm, more preferably greater than or equal to 1.3 N / 10 mm, in particular when it is previously heat-sealed on an amorphous PET sheet. The second opening force can for example be measured in accordance with Example 3.

[0193] The multilayer structure according to the invention advantageously has a fifth peel opening force greater than or equal to 0.6 N / 10 mm for a quantity of composition A per unit area in said structure greater than or equal to 6 g / m 2 , preferably greater than or equal to 0.90 N / 10 mm, in particular when it is previously heat-sealed on an amorphous PET sheet. The fifth opening force can for example be measured in accordance with Example 3.

[0194] The multilayer structure according to the invention can be used as a cover for a package comprising a receptacle. In this case, it is understood that the multilayer structure does not comprise the receptacle.

[0195] Manufacturing process of the multilayer structure

[0196] The present invention also relates to a method for manufacturing the multilayer structure according to the invention comprising: a step of coating an adhesive comprising composition A on a surface of a first film, then a step of laminating (laminating) a surface of a second film on the coated surface of the first film, in which one of the films comprises the heat-sealable layer or is bonded to the heat-sealable layer after the laminating step, and in which one of the films comprises the complexable layer or is bonded to the complexable layer after the laminating step. The multilayer structure, composition A, the heat-sealable layer and the complexable layer are as described above, including the preferred embodiments and characteristics. In particular, the heat-sealable layer preferably has a free face.

[0197] The first film and the second film can each be single-layer or multi-layer.

[0198] The coating step may be carried out on all or part of the surface of the first film, preferably in a continuous or substantially continuous manner.

[0199] To facilitate the coating of composition A, the adhesive may further comprise an organic solvent, for example butanone, toluene, xylene, benzene, monochlorobenzene, dichloromethane, 2-nitropropane, nitroethane, nitrobenzene, dichlorobenzene, dioxolane, tetrahydrofuran, an ester (ethyl acetate, n-butyl acetate, 2-ethoxyethyl acetate), cyclohexanone and / or dioxane, in particular an ester such as ethyl acetate, n-butyl acetate, 2-ethoxyethyl acetate, etc.

[0200] When the adhesive comprises a solvent, its content may be between 10% and 95% by weight relative to the total weight of the adhesive, preferably between 50% and 90% by weight.

[0201] When the adhesive comprises a solvent, the method for manufacturing the multilayer structure according to the invention advantageously comprises a step of drying the adhesive after the coating step and before the laminating step. The drying step can be carried out at a temperature between 25°C and 100°C, preferably between 35°C and 95°C, more preferably between 45°C and 90°C, for a period sufficient to allow the solvent to evaporate.

[0202] When one or more additional layers (as described above) are present in the multilayer structure, they can be obtained by coextrusion, coating and / or lamination with one or more layers of the multilayer structure.

[0203] Resealable packaging

[0204] The present invention also relates to a resealable package comprising the multi-layer structure according to the invention.

[0205] In particular, the resealable packaging comprises a polyester polymer-based receptacle and a lid made of the multi-layer structure according to the invention.

[0206] Advantageously, the seal is heat-sealed around the perimeter of the receptacle. Advantageously, the receptacle comprises at least 90% by weight of polyester polymer relative to the total weight of the receptacle, preferably at least 95% by weight, more preferably at least 99% by weight. The receptacle therefore comprises one or more polyester polymers, but may also comprise, for example, an unreacted monomer, a possible catalyst and / or a monomer formed in situ by reaction of other monomers which may be part of the backbone of the polyester polymer.

[0207] Preferably, the receptacle comprises at least one amorphous polyester polymer, more preferably the receptacle is based on amorphous polyester polymer (in particular, at least 90% by weight of amorphous polyester polymer relative to the total weight of the receptacle, preferably at least 95% by weight, more preferably at least 99% by weight).

[0208] The polyester polymer(s) of the receptacle may be chosen from homopolyester polymers, copolyester polymers, and mixtures thereof, preferably from homopolyester polymers.

[0209] The homopolyester polymer(s) are in particular chosen from polyester polymers whose main chain comprises ester bonds linking a single unit derived from polyol and a single unit derived from polycarboxylic acid.

[0210] Advantageously, the polyol-derived unit of the homopolyester polymer(s) is derived from an acyclic diol. For example, the polyol-derived unit may be derived from monoethylene glycol, polyethylene glycol (preferably diethylene glycol), propane-1,2-diol, propane-1,3-diol, butanediol (-1,4, -1,3 and / or -1,2), pentanediol, hexanediol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol or polytetrahydrofuran, preferably monoethylene glycol or polyethylene glycol, especially monoethylene glycol.

[0211] Advantageously, the polycarboxylic acid-derived unit of the homopolyester polymer(s) is derived from a cyclic (preferably aromatic), in particular aromatic, dicarboxylic acid. For example, the polycarboxylic acid-derived unit may be derived from phthalic acid, isophthalic acid, terephthalic acid, in particular terephthalic acid.

[0212] According to one embodiment, the homopolyester polymer is poly(ethylene terephthalate).

[0213] The copolyester polymer(s) of the receptacle are in particular chosen from polyester polymers whose main chain comprises ester bonds linking units derived from polyol(s) and polycarboxylic acid(s), at least one unit derived from polyol and / or at least one unit derived from polycarboxylic acid being different from the others.

[0214] Advantageously, the copolyester polymer(s) comprise at least one unit derived from an acyclic diol and at least one unit derived from a cyclic dicarboxylic acid (preferably aromatic).

[0215] For example, the acyclic diol-derived unit of the copolyester polymer(s) may be derived from monoethylene glycol, polyethylene glycol (preferably diethylene glycol), propane-1,2-diol, propane-1,3-diol, butanediol (-1,4, -1,3 and / or -1,2), pentanediol, hexanediol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol and / or polytetrahydrofuran, preferably monoethylene glycol and / or polyethylene glycol, especially monoethylene glycol.

[0216] For example, the cyclic dicarboxylic acid derived unit may be derived from cyclohexanedicarboxylic acid, phthalic acid, isophthalic acid and / or terephthalic acid, preferably terephthalic acid and optionally isophthalic acid.

[0217] In addition to the at least one unit derived from a cyclic dicarboxylic acid, the copolyester polymer(s) may also comprise at least one unit derived from an acyclic dicarboxylic acid, for example derived from maleic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid and / or 1,12-dodecanedioic acid, preferably azelaic acid and / or sebacic acid.

[0218] According to one embodiment, the copolyester polymer(s) comprise a unit derived from monoethylene glycol, a unit derived from terephthalic acid and a unit derived from cyclic dicarboxylic acid (different from terephthalic acid), in particular a unit derived from isophthalic acid.

[0219] The receptacle may further comprise one or more additives, for example chosen from UV stabilizers (or antioxidants), slip / anti-blocking agents, pigments, antistatic agents, and mixtures thereof.

[0220] The total content of additive(s) may be up to 10% by weight relative to the total weight of the receptacle, preferably up to 5% by weight, more preferably up to 1% by weight.

[0221] The UV stabilizer (or antioxidant) may be chosen from benzotriazoles, benzophenones, so-called hindered phenols such as octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) and ethylenebis(oxyethylene) bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate], so-called hindered amines such as bis(1-octyloxy-

[0222] 2.2.6.6-tetramethyl-4-piperidyl)sebacate, bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate, bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate, methyl

[0223] 1,2,2,6,6-pentamethyl-4-piperidyl sebacate and 4,4'-bis(a,a-dimethylbenzyl)diphenylamine, and mixtures thereof.

[0224] The glidant / anti-blocking agent may be selected from organic and / or inorganic, preferably inorganic, glidant / anti-blocking agents. For example, the glidant / anti-blocking agent may be selected from erucamide, oleamide, docosanamide, stearamide, palmitamide, ethylene bis-stearamide, ethylene bis-oleamide, silica, talc, calcium carbonate, glass beads, and mixtures thereof, preferably from silica, talc, calcium carbonate, glass beads, and mixtures thereof.

[0225] The pigment may be selected from organic and inorganic pigments, and mixtures thereof. For example, the pigment may be selected from manganese ferrite, titanium dioxide, carbon black, iron oxide, aluminum, talc, and mixtures thereof, in particular titanium dioxide, carbon black, and mixtures thereof.

[0226] The antistatic agent may be selected from alkali metal sulfonates, polyether-modified polydiorganosiloxanes, polyalkylphenylsiloxanes, tertiary amines, glycerol monostearate, mixtures of glycerol monostearate and tertiary amines, and mixtures thereof.

[0227] Use of multi-layer structure

[0228] The present invention also relates to the use of the multilayer structure according to the invention for the manufacture of a resealable package.

[0229] Advantageously, the multi-layer structure is used as a lid for the resealable packaging.

[0230] Preferably, the resealable package is as described above, including preferred embodiments and features.

[0231] Within the scope of the invention, the ranges of values ​​are understood to include the limits. For example, the range “between 0% and 25%” includes in particular the values ​​0% and 25%.

[0232] All the embodiments described above can be combined with each other. In particular, the different features of the above-mentioned layers of the multi-layer structure, and in particular the preferred features, can be combined with each other.

[0233] The following examples are given purely for illustrative purposes of the invention and should not be interpreted as limiting its scope.

[0234] Examples

[0235] Example 1: Compositions for the adhesive layer

[0236] Comparative composition A1 based on styrenic block copolymer

[0237] Comparative composition A1 is marketed by BOSTIK under the reference M650.F and comprises a mixture of tackifying resin and styrene-isoprene-styrene (SIS) copolymer.

[0238] Composition A2 of copolyester resin according to the invention

[0239] A copolyester resin is prepared according to the procedure indicated below.

[0240] In a 2-liter reactor under an inert atmosphere (nitrogen), equipped with a distillation column (to remove methanol and water), 554 g of monoethylene glycol (8.9 mol), 416 g of dimethyl terephthalate (2.1 mol), 0.19 g of tetra-n-butyl titanate (Tyzor® TnBT, by Dorf Ketal) and 3.6 g of pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (Irganox® 1010, by BASF) are introduced. The whole is heated from room temperature to about 180°C. When the temperature reaches about 180°C, it is increased to about 205°C.

[0241] After approximately 1.5 hours, the temperature reaches about 205°C. It is then reduced to room temperature to introduce 173 g of monoethylene glycol (2.8 mol). After 15 minutes of stirring, 242 g of isophthalic acid (1.5 mol) and 679 g of azelaic acid (3.6 mol) are added. The temperature is then increased to about 190°C, then to about 240°C. The temperature is left at about 240°C for 0.5 hours.

[0242] The resulting reaction mixture is then heated to about 255°C under vacuum (less than 0.27 kPa) until the intrinsic viscosity is between 0.80 and 0.90 dL / g (ASTM D5225-14).

[0243] The resulting copolyester resin is amorphous, has a Tg of about -11 °C (ASTM E1356-08 with the modification that a sweep temperature of 15 °C per minute instead of 10 °C per minute is used), a softening temperature of about 99 °C (ASTM E28-67) and a weight average molecular weight of about 75 kg / mol.

[0244] This resin is then diluted in ethyl acetate, so as to obtain a composition A2 comprising 20% ​​by weight of resin relative to the total weight of composition A2 (the remaining 80% being ethyl acetate).

[0245] Preparation of multilayer structures

[0246] The multilayer structure 1 is a multilayer film consisting of a 15 μm thick polyethylene layer and a 30 μm thick polyethylene layer, bonded together by an adhesive layer obtained from the composition A1. The multilayer structure 1 is obtained by sheath blown coextrusion, the coextrusion head having a temperature of approximately 190°C.

[0247] Multilayer structure 2 is a multilayer film consisting of an 8 μm thick PET-based film and another 30 μm thick PET-based film, bonded together by an adhesive layer obtained from a composition A2.

[0248] The 8 µm thick PET film is breakable and is a biaxially oriented film comprising a heat-sealable outer layer of an ethylene terephthalate copolyester coextruded with multiple layers of PET, the outer PET layer having undergone corona treatment.

[0249] The 30 µm thick PET film consists of a bi-oriented homopolymer PET film coextruded on one side with a copolyester.

[0250] Composition A2 was coated onto a 30 μm thick PET film using a Meyer bar and a speed-controlled hand applicator to achieve the target coating weight (2, 6, 11 or 15 g / m 2 ), leading to a bilayer structure. The coated film (bilayer structure) was then dried at 80°C for approximately 10 minutes, leading to the evaporation of the ethyl acetate contained in composition A2. Finally, a trilayer structure was obtained by laminating an 8 μm thick PET film on the adhesive layer side of the bilayer structure. The trilayer structure was then placed under pressure for 24 hours before being tested in a climate-controlled room at 23°C and 50% relative humidity. Properties of multilayer structures

[0251] The properties of the multilayer structures 1 and 2 prepared in Example 2 are evaluated by the tests described below and the results are shown in Table 1. Measurement of the first peel opening force (multilayer structure 1):

[0252] Rectangular E1 specimens of 25 cm length and 3 cm width were cut from the multilayer structure to be evaluated.

[0253] On the other hand, rectangular E2 specimens of 25 cm length and 3 cm width were cut from a flexible PET / polyethylene film of approximately 60 μm thickness.

[0254] The E1 specimen was then placed between two E2 specimens so that the 15 pm and 30 pm polyethylene layers were in contact with the polyethylene face of the E2 specimens.

[0255] The specimens were then partially sealed, using two heating jaws at 130°C, applied under a pressure of 0.4 MPa for 1 second, so as to obtain a rectangular sealed area (15 cm long and 1 cm wide). Said sealed area is arranged lengthwise and in contact with one of the short sides of the rectangular specimens E1 and E2 thus joined, in order to leave on the other short side of said specimens a strip of approximately 2 cm in length (free and unsealed).

[0256] The free and unsealed strip of E1 + E2 and the free and unsealed strip of E2 (in contact with the 15 pm polyethylene layer of the multilayer structure 1) are fixed on two attachment devices (called jaws) connected, respectively, to a fixed part and a mobile part of a dynamometer which are located on a vertical axis.

[0257] While a drive mechanism communicates to the moving part a uniform speed of 300 mm / minute leading to the peeling of the two sealed specimens E1 and E2, the ends gradually move along a vertical axis forming an angle of 180°. A force sensor connected to said moving part measures the force supported by the specimen thus held. The measurement is carried out in a climatic room maintained at a temperature of 23°C.

[0258] The force required to "break" the contour of the sealed area and initiate separation of the two specimens is called the peak of 1 ère opening, and the force to complete the separation of the two specimens is called the propagation of 1 ère opening.

[0259] Measurement of first peel opening force (multi-layer structure 2):

[0260] Rectangular specimens E'1 of 25 cm length and 3 cm width were cut from the multilayer structure to be evaluated. On the other hand, rectangular specimens E'2 of 25 cm length and 5 cm width were cut from a rigid amorphous PET sheet of approximately 250 μm thickness.

[0261] The two test pieces E'1 and E'2 were then placed opposite each other, so that the 8 pm thick PET layer of E'1 was in contact with E'2.

[0262] The specimens were then partially sealed, by means of two heating jaws at 140°C, applied under a pressure of 0.4 MPa for 1 second, so as to obtain a rectangular sealed area (15 cm in length and 1 cm in width). Said sealed area is arranged lengthwise and in contact with one of the short sides of the rectangular specimens E'1 and E'2 thus joined, in order to leave on the other short side of said specimens a strip of multilayer structure of approximately 2 cm in length coming from E'1 (free and not sealed) on the end of the rigid sheet of E'2 located opposite.

[0263] The free, unsealed strip of E'1 is attached to a clamping device (called a grip) connected to a moving part of a dynamometer. The specimen E'2 is held to a carriage mounted on ball bearings using a steel plate fixed using a clamp. The carriage is connected to the crosshead of the testing machine by a system of cables and pulleys.

[0264] While a drive mechanism communicates to the moving part a uniform speed of 300 mm / minute leading to the peeling of the two sealed test pieces E'1 and E'2, the end of E'1 gradually moves along a vertical axis forming an angle of 90° with the carriage. A force sensor connected to said moving part measures the force supported by the test piece thus held. The measurement is carried out in a climatic room maintained at a temperature of 23°C.

[0265] The force required to "break" the contour of the sealed area and initiate separation of the two specimens is called the peak of 1 ère opening, and the force to complete the separation of the two specimens is called the propagation of 1 ère opening.

[0266] Second and subsequent opening force measurement

[0267] The two parts of the previous test piece were, after the first peeling, repositioned opposite each other and brought into contact manually. They were then subjected to pressure exerted by means of a roller of mass 2 kg with which a back and forth movement is carried out in a direction parallel to the length of the test piece. The peeling test described above was then repeated and the average force (propagation force) measured corresponds to the second opening force.

[0268] The third, fourth, and fifth opening forces were measured similarly, after the second, third, and fourth peels, respectively.

[0269] Table 1

[0270] The multilayer structures 2 according to the invention have a peak of 1 ère opening of at least 5 N / 10 mm; they therefore prevent the packaging from opening without user intervention.

[0271] At a similar weight, the multilayer structure 2 according to the invention (15 g / m 2 ) presents reopening forces (2 ème -5 ème opening) significantly higher than those of the reference multilayer structure 1.

[0272] The higher the re-opening force of the multi-layer structure, the better the resealability of the packaging containing it; this helps to limit the risk of the packaging opening during storage or transport.

[0273] Thus, in addition to the fact that the multi-layer structure according to the invention is recyclable, it also makes it possible to improve the quality of resealing of the packaging.

[0274] As a result, a package comprising the multilayer structure according to the invention can undergo several opening / closing cycles while maintaining good closing quality.

Claims

Claims 1. Multi-layer structure comprising: - an adhesive layer consisting of a composition A comprising a copolyester resin having a glass transition temperature of less than 0°C and a degree of crystallinity of less than 10%, - a heat-sealable layer based on polyester polymer, and - a complexable layer based on polyester polymer, in which the adhesive layer is located between the heat-sealable layer and the complexable layer.

2. Multilayer structure according to claim 1, in which the copolyester resin of composition A is amorphous.

3. Multilayer structure according to claim 1 or 2, in which the copolyester polymer(s) of the copolyester resin is (are) obtained by reaction of at least one acyclic diol with at least one cyclic dicarboxylic acid or one of its ester-forming derivatives, and at least one acyclic dicarboxylic acid comprising at least 4 carbon atoms or one of its ester-forming derivatives.

4. A multilayer structure according to claim 3, wherein the at least one cyclic dicarboxylic acid or ester-forming derivative thereof comprises a cycloaliphatic dicarboxylic acid or ester-forming derivative thereof and / or an aromatic dicarboxylic acid or ester-forming derivative thereof comprising an aromatic ring, the two functional groups of which are in a meta or ortho position relative to each other.

5. Multilayer structure according to any one of claims 1 to 4, in which composition A comprises at least 90% by weight of copolyester resin relative to the total weight of composition A.

6. Multilayer structure according to any one of claims 1 to 5, in which the heat-sealable layer is breakable.

7. A multilayer structure according to any one of claims 1 to 6, wherein the multilayer structure does not comprise a styrenic block copolymer, a copolymer of ethylene and vinyl acetate, a copolymer of ethylene and (meth)acrylate ester(s), a copolymer of ethylene and (meth)acrylic acid and / or a polyolefin polymer.

8. A multilayer structure according to any one of claims 1 to 7, wherein the amount of composition A per unit area in the multilayer structure is between 1 g / m 2 and 30 g / m 2, the thickness of the heat-sealable layer is between 0.1 pm and 20 pm and the thickness of the complexable layer is between 5 pm and 100 pm.

9. Multilayer structure according to any one of claims 1 to 8, comprising: an adhesive layer consisting of a composition A comprising a copolyester resin having a glass transition temperature of less than 0°C, a degree of crystallinity of less than 10% and being amorphous, a heat-sealable and breakable layer based on copolyester polymer, a complexable layer based on polyester polymer, and optionally one or more additional layers based on polyester polymer.

10. Multilayer structure according to any one of claims 1 to 9, in which the heat-sealable layer has a free face.

11. A method of manufacturing the multilayer structure according to any one of claims 1 to 10, comprising: a step of coating an adhesive comprising composition A on a surface of a first film, then a step of laminating a surface of a second film on the coated surface of the first film, wherein one of the films comprises the heat-sealable layer or is bonded to the heat-sealable layer after the laminating step, and wherein one of the films comprises the complexable layer or is bonded to the complexable layer after the laminating step.

12. A resealable package comprising the multi-layer structure according to any one of claims 1 to 10.

13. Use of the multilayer structure according to any one of claims 1 to 10 for the manufacture of a resealable package.

Images