Multilayer structure

Abstract

The invention relates to a multilayer structure comprising:-an adhesive layer consisting of a composition A comprising a copolyester resin having a glass transition temperature of less than 0 DEG C and a crystallinity of less than 10%,-a heat-sealable polyester polymer layer, and-a composable polyester polymer layer, wherein the adhesive layer is located between the heat sealable layer and the compostable layer. The invention further relates to a method for producing a multilayer structure according to the invention. The invention also relates to a resealable package. Finally, the invention relates to the use of the multilayer structure according to the invention.

Description

Technical Field

[0001] This invention relates to multilayer structures, methods of manufacturing them, their uses, and resealable packaging. Background Technology

[0002] Multilayer (or laminated) products are used in many fields for packaging a wide variety of products, particularly in food processing, cosmetics, and detergents. These products can be flexible or rigid, depending on requirements. Flexible packaging is particularly common. These products are typically composed of different materials (composite multilayer products). Materials can be selected from paper, metals, or thermoplastic polymers.

[0003] The characteristics and properties of multilayer articles will depend particularly on the materials used to produce the layers. Therefore, layers containing different materials are often combined to obtain multilayer articles, very often composite multilayer articles, which combine the characteristics and properties of different individual layers, and thus have specific characteristics and properties.

[0004] Multi-layered products include resealable packaging used in the food processing industry and by large retailers for packaging food, especially fresh products. These packages typically consist of a container (or receiver) and a lid (or cap film) forming the top, which are hermetically attached to each other by heat welding. After the lid has been opened for the first time and a portion of the food contained in the receiver has been consumed, the user can reposition the lid onto the receiver to essentially reseal the packaging hermetically and store the remaining product. Sequences of reopening and resealing are also possible.

[0005] The receivers of these packages typically consist of thermoformed polyethylene terephthalate (PET) sheets to present a flat bottom and a flat strip around the perimeter on which food is placed. This perimeter, usually parallel to the bottom, is typically heat-welded to a lid composed of multiple layers of film.

[0006] During the consumer's unpacking, the cap film is manually separated from the receiver at its perimeter flat strip. This operation exposes the adhesive layer originally included in the cap film.

[0007] Then, once the lids have been repositioned on the container according to their position in the packaging before opening, simple manual pressure can reseal the packaging.

[0008] In most commercially available resealable packaging, the cap film is a multi-layered structure containing an HMPSA (hot melt pressure-sensitive adhesive) layer that combines a composite layer and a heat-sealable layer.

[0009] The composite layer can be laminated with other layers to prepare a cover film, for example, laminated with a rigid layer to improve the mechanical strength of the film.

[0010] HMPSA layers typically comprise one or more tackifying resins and one or more styrene block copolymers. Applied in a molten state, it solidifies upon cooling to form an adhesive layer that provides bonding between composite and heat-sealing layers.

[0011] A heat-sealing layer allows the cap film to be sealed to the receiver via heat welding. It is typically composed of polyolefins, particularly polyethylene, due to its low-temperature heat-sealing properties. However, because the PET of the container has a much higher softening temperature, containers made of PET co-extruded with polyolefins must be used to enable the cap film to be heat-welded at low temperatures.

[0012] Therefore, the resulting packaging contains materials with very different properties (styrene block copolymers, polyolefins, polyesters), which are very difficult to separate from each other, causing problems in recycling them.

[0013] The present invention aims to solve this recycling problem.

[0014] Therefore, the present invention aims to provide a fully recyclable multilayer structure and a fully recyclable resealable packaging.

[0015] Furthermore, the present invention aims to improve the resealing quality of resealable packaging, particularly to limit the risk of packaging opening during storage or transportation. Summary of the Invention

[0016] This invention relates to a multilayer structure comprising:

[0017] - An adhesive layer comprising composition A, wherein composition A comprises a copolyester resin having a glass transition temperature of less than 0°C and a crystallinity of less than 10%.

[0018] - A heat-sealing layer based on polyester polymer, and

[0019] - Composite layers based on polyester polymers,

[0020] The adhesive layer is located between the heat-sealing layer and the composite layer.

[0021] Furthermore, the present invention relates to a method for manufacturing a multilayer structure according to the present invention, comprising:

[0022] - The step of coating the adhesive containing composition A onto the surface of the first film, then

[0023] - The step of laminating the surface of the second film onto the coated surface of the first film.

[0024] One of the films contains the heat-sealing layer or is bonded to the heat-sealing layer after the lamination step, and

[0025] One of the films contains the composite layer or is incorporated into the composite layer after the lamination step.

[0026] The present invention also relates to resealable packaging comprising a multilayer structure according to the invention.

[0027] Finally, the present invention relates to the use of the multilayer structure according to the invention for manufacturing resealable packaging.

[0028] The multilayer structure according to the invention overcomes the problem of separating layers of different materials, making it easier to recycle. In particular, styrene block copolymers are not required in the adhesive layer of the multilayer structure according to the invention. Furthermore, the multilayer structure according to the invention can be directly heat-welded to PET containers, avoiding previous co-extrusion with (different properties) polyolefins, thus enabling container recycling. Moreover, compared to conventional multilayer structures (comprising styrene block copolymer-based layers and polyolefin layers), the multilayer structure according to the invention results in improved resealability. Detailed Implementation

[0029] Invention Description

[0030] Multi-layer structure

[0031] The term "polyester polymer" is intended to refer to a polymer containing at least two ester groups, which can be a homopolymer or a copolymer.

[0032] The term “homogeneous polyester polymer” is intended to refer to a polyester polymer whose main chain contains i) ester bonds linking a single unit derived from a polyol and a single unit derived from a polycarboxylic acid, or ii) ester bonds linking a single unit derived from a hydroxylated carboxylic acid, said units being repeated multiple times.

[0033] The term "polyol" should be understood to mean a compound containing at least two hydroxyl groups (-OH). Preferably, the polyol is a diol.

[0034] The term "polycarboxylic acid" should be understood to mean a compound containing at least two carboxylic acid groups (–C(=O)-OH). Preferably, the polycarboxylic acid is a dicarboxylic acid.

[0035] According to i), the homopolymer of polyester can be obtained by polymerizing a single type of polyol monomer and a single type of polycarboxylic acid monomer (or its ester derivative, such as anhydride or (methyl)ethyl ester, preferably methyl ester).

[0036] In particular, the homopolymer of i) can be a polymer whose main chain contains ester bonds linking a single unit derived from a diol and a single unit derived from a dicarboxylic acid.

[0037] According to ii), the homopolymer can be obtained by polymerizing a compound containing at least one ester bond involved in the ring (e.g., lactone or cyclic diester such as glycolide or lactide), or it can be a polymer obtained by polymerizing a hydroxylated carboxylic acid.

[0038] The term "copolyester polymer" is intended to refer to a polyester polymer whose main chain contains i) ester bonds linking units derived from polyols and polycarboxylic acids, wherein at least one unit derived from a polyol and / or at least one unit derived from a polycarboxylic acid is different from the other units (i.e., the copolyester polymer contains 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, wherein the units are repeated multiple times.

[0039] According to i), the copolyester polymer can be obtained by polymerizing one or more types of polyol monomers and one or more types of polycarboxylic acid monomers (or their ester derivatives, such as anhydrides or (methyl)ethyl esters, preferably methyl esters), wherein at least one polyol monomer and / or at least one polycarboxylic acid monomer (or derivative) are different from each other.

[0040] In particular, the copolyester polymer according to i) can be a polymer whose main chain contains ester bonds linking one or more units derived from diols and one or more units derived from dicarboxylic acids, wherein at least one unit derived from a diol and / or at least one unit derived from a dicarboxylic acid is different from the other units.

[0041] According to ii), the copolyester polymer can be obtained by polymerizing a variety of compounds containing at least one ester bond involved in the ring (each compound is, for example, a lactone or a cyclic diester, such as glycolide or lactide) or by polymerizing a variety of hydroxylated carboxylic acids.

[0042] Adhesive layer

[0043] The adhesive layer allows for the direct or indirect bonding of the heat-sealing layer and the composite layer. Specifically, other layers can be present in the multilayer structure, particularly between the adhesive layer and the heat-sealing layer.

[0044] The adhesive layer is composed of composition A, which contains a copolyester resin with a glass transition temperature of less than 0°C and a crystallinity of less than 10%.

[0045] Copolyester resins enable composition A to possess adhesive properties, particularly pressure-sensitive adhesive properties.

[0046] Pressure-sensitive adhesives can generally be defined as substances that impart instant tack (also known as "adhesion") to the substrate to which they are coated, enabling them to adhere instantly to another substrate under brief and slight pressure at ambient or lower temperatures (e.g., 3°C to 25°C).

[0047] The term "copolyester resin" should be understood as the reaction product obtained at the end of the synthesis of the copolyester polymer or a mixture of different reaction products obtained at the end of the synthesis of different copolyester polymers, preferably the reaction product obtained at the end of the synthesis of the copolyester polymer.

[0048] Therefore, as a reaction product, the copolyester resin comprises one or more copolyester polymers, but may also contain, for example, unreacted monomers, possible catalysts (for accelerating the synthesis of the copolyester polymer), and / or monomers formed in situ through the reaction of other monomers that can form part of the copolyester polymer backbone. Typically, the relative amounts of monomer residues constituting the copolyester polymer are the same as or very similar to the relative amounts of the monomers used to manufacture it. However, it is possible that other monomers are formed during the production of the copolyester polymer, and these formed monomers can form part of the final copolyester polymer. For example, when monoethylene glycol is used, small amounts of diethylene glycol can be formed in situ, and its residues can be integrated into the structure of the copolyester polymer, as is known to those skilled in the art.

[0049] The glass transition temperature (Tg) of copolyester resins can be measured by differential scanning calorimetry (DSC), for example according to standard ASTM E1356-08, where the modification is to use a temperature scan of 15°C / min instead of 10°C / min.

[0050] Unless otherwise stated, the standards mentioned throughout the patent application are those that were in effect at the date the patent application was filed.

[0051] Advantageously, the glass transition temperature of the copolyester resin is less than -4°C, preferably -5°C to -20°C.

[0052] The crystallinity of copolyester resins can be measured by DSC, for example, according to standard ASTM E793-06.

[0053] Preferably, the copolyester resin of composition A is amorphous (i.e., it does not have a melting point according to DSC).

[0054] The softening temperature of the copolyester resin can be between 50°C and 150°C, preferably between 70°C and 130°C, and more preferably between 80°C and 110°C. The softening temperature can be measured according to the standard ASTM E28-67.

[0055] The storage modulus G' of composition A at 25°C can be less than 1 MPa, preferably less than 0.7 MPa.

[0056] In the context of this invention, the storage modulus G' can be measured using a rheometer, particularly according to the standard ASTM D4440, for example by using a 25 mm parallel plate to vary the temperature from 140°C to -40°C at 10 rad / sec.

[0057] The weight-average molecular weight of the copolyester polymer in the copolyester resin can be from 5,000 g / mol to 150,000 g / mol, preferably from 30,000 g / mol to 100,000 g / mol, and more preferably from 60,000 g / mol to 90,000 g / mol.

[0058] In this invention, number-average or weight-average molecular weight can be measured by size exclusion chromatography, particularly using polystyrene standards, for example, using tetrahydrofuran as a solvent.

[0059] The copolyester polymer of the copolyester resin can be obtained by reacting at least one polyol with at least one polycarboxylic acid or its esterification derivative (e.g., acid anhydride or (methyl) ethyl ester, preferably methyl ester).

[0060] This reaction can be carried out by any conventional method used to obtain the copolyester, particularly by transesterification and / or esterification. In particular, catalysts can be used, especially organometallic catalysts, such as organozinc, organotitanium and / or organotin (preferably organozinc and / or organotitanium), for example zinc acetate dihydrate, butyltin tris(2-ethylhexanoate), dibutyltin diacetate, tetra(2-ethylhexyl) titanate, tetrabutyl titanate and / or dibutyltin oxide.

[0061] The molar equivalent ratio of polyol / polycarboxylic acid (or ester derivative) used during the preparation of the copolyester polymer can be from 1.1 to 2.5, preferably from 1.2 to 2, and more preferably from 1.3 to 1.8.

[0062] The polyol / polycarboxylic acid (or esterification derivative) molar equivalent ratio is defined as equal to the molar equivalent number of -OH groups of the polyol used in the preparation of the copolyester polymer divided by the molar equivalent number of -C(O)OH groups of the polycarboxylic acid (or esterification group).

[0063] The molar equivalent number of the -OH group in a polyol is equal to: f(-OH) (m 多元醇 / M 多元醇 ), where f(-OH) is the number of -OH groups in the polyol, M 多元醇 It is the mass of the introduced polyol, in g and M 多元醇This is the molar mass of the polyol, expressed in g / mol. Preferably, the polyol is a diol, therefore f(-OH) equals 2.

[0064] The molar equivalent number of the -C(O)OH group in a polycarboxylic acid is equal to: f(-C(O)OH) (m 酸 / M 酸 ), where f(-C(O)OH) is the number of –C(O)OH groups in the polycarboxylic acid, m 多元醇 It is the mass of the introduced polycarboxylic acid, in g, and M 多元醇 This is the molar mass of the polycarboxylic acid, expressed in g / mol. The molar equivalent number of the esterifying group in the esterified polycarboxylic acid derivative is calculated in a similar manner. Preferably, the polycarboxylic acid is a dicarboxylic acid (or its esterified derivative), therefore f(-C(O)OH) (or f(esterifying group)) equals 2.

[0065] Advantageously, the copolyester polymer of the copolyester resin is obtained by reacting at least one diol with at least one dicarboxylic acid or its ester derivative.

[0066] Preferably, the copolyester polymer of the copolyester resin is obtained by reacting at least one acyclic diol with at least one cyclic dicarboxylic acid or its ester derivative and at least one acyclic dicarboxylic acid or its ester derivative containing at least 4 (preferably 4 to 15, more preferably 6 to 12) carbon atoms (the at least 4 carbon atoms are carbon atoms of the carbonyl group (C=O) and carbon atoms between the carbonyl group; for example, carbon atoms of the alkoxy group of the ester are not considered).

[0067] The term "acyclic" should be understood to mean that it does not contain (aromatic or non-aromatic) rings.

[0068] The term "cyclic dicarboxylic acid" should be understood to mean a dicarboxylic acid containing at least one (aromatic or alicyclic) ring.

[0069] For example, the copolyester polymer of the copolyester resin can be obtained by reacting 52 mol% to 80 mol% (preferably 54 mol% to 76 mol%, more preferably 56 mol% to 66 mol%) of an acyclic diol with 10 mol% to 24 mol% (preferably 12 mol% to 23 mol%, more preferably 17 mol% to 22 mol%) of a cyclic dicarboxylic acid (or ester-forming derivative) containing at least 4 carbon atoms, the mol% content being calculated based on the total number of moles of the acyclic diol, cyclic dicarboxylic acid (or ester-forming derivative), and acyclic dicarboxylic acid (or ester-forming derivative) containing at least 4 carbon atoms.

[0070] Preferably, at least one acyclic diol is selected from monoethylene glycol, polyethylene glycol (preferably having a number average molecular weight of 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 known as polytetramethylene glycol, preferably having a number average molecular weight of 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 selected from monoethylene glycol, 2,2-dimethyl-1,3-propanediol and mixtures thereof, especially monoethylene glycol.

[0071] Advantageously, at least one cyclic dicarboxylic acid (or its esterified derivative) comprises an alicyclic dicarboxylic acid (or its esterified derivative), such as 1,4-cyclohexanedicarboxylic acid, and / or an aromatic dicarboxylic acid (or its esterified derivative) containing an aromatic ring, wherein the two functional groups (carboxylic acid, methyl ester, etc.) are located in a meta or ortho position relative to each other, particularly in the meta position. Preferably, at least one cyclic dicarboxylic acid comprises isophthalic acid (or its esterified derivative) and / or phthalic acid (or its esterified derivative), particularly isophthalic acid (or its esterified derivative). More preferably, at least one cyclic dicarboxylic acid is a mixture of aromatic dicarboxylic acids (or their esterified derivatives) containing isophthalic acid or its esterified derivative. In particular, at least one cyclic dicarboxylic acid is a mixture of terephthalic acid (or its esterified derivative, particularly dimethyl terephthalate) and isophthalic acid (or its esterified derivative).

[0072] Advantageously, at least one acyclic dicarboxylic acid (or its ester derivative) containing at least four (preferably four to fifteen, more preferably six to twelve) carbon atoms is linear. Preferably, the at least one linear dicarboxylic acid is selected from succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, 1,12-dodecanoic acid, its ester derivatives and mixtures thereof, more preferably from azelaic acid, sebacic acid, its ester derivatives and mixtures thereof, particularly azelaic acid or its ester derivatives.

[0073] According to one embodiment, the copolyester polymer of the copolyester resin is obtained by performing the following reaction:

[0074] - at least one acyclic diol and

[0075] - At least one cyclic dicarboxylic acid (or its esterified derivative), comprising an alicyclic dicarboxylic acid (or its esterified derivative) and / or an aromatic dicarboxylic acid (or its esterified derivative) comprising an aromatic ring, wherein the two functional groups are in a meta position relative to each other, and

[0076] - At least one acyclic dicarboxylic acid (or its ester derivative), which contains at least 4 (preferably 4 to 15, more preferably 6 to 12) carbon atoms and is linear.

[0077] Preferably, the copolyester polymer of the copolyester resin is obtained by reacting the following substances:

[0078] - At least one acyclic diol selected from monoethylene glycol, polyethylene glycol (preferably having a number average molecular weight of 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 of less than or equal to 3,000 g / mol, more preferably between 950 g / mol and 1050 g / mol), and mixtures thereof, and

[0079] - at least one cyclic dicarboxylic acid comprising isophthalic acid (or its esterified derivative) and / or phthalic acid (or its esterified derivative), and

[0080] - At least one straight-chain dicarboxylic acid selected from succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, 1,12-dodecanoic acid, their ester derivatives and mixtures thereof.

[0081] Specifically, the copolyester polymer of the copolyester resin is obtained by performing the following reaction:

[0082] - Monoethylene glycol, and

[0083] -Terephthalic acid (or its ester derivatives, especially dimethyl terephthalate),

[0084] -Isophthalic acid (or its ester derivatives), and

[0085] - Azelaic acid (or its ester derivatives).

[0086] For example, copolyester polymers of copolyester resins are obtained by performing the following reaction:

[0087] -52-80 mol% (preferably 54-76 mol%, more preferably 56-66 mol%) of monoethylene glycol, and

[0088] -5-12 mol% (preferably 6-13 mol%, more preferably 10-12 mol%) of terephthalic acid (or its esterified derivatives),

[0089] -5-12 mol% (preferably 6-10 mol%, more preferably 7-10 mol%) of isophthalic acid (or its esterified derivatives), and

[0090] -10-24 mol% (preferably 12-23 mol%, more preferably 17-22 mol%) of azelaic acid (or its esterified derivatives),

[0091] The mol% content is calculated based on the total number of moles of acyclic diols, cyclic dicarboxylic acids (or ester derivatives) and acyclic dicarboxylic acids (or ester derivatives) containing at least 4 carbon atoms.

[0092] Advantageously, composition A comprises at least 90% by weight, preferably at least 95% by weight, and more preferably at least 99% by weight of copolyester resin relative to the total weight of composition A.

[0093] Composition A may also contain one or more additives, such as those selected from antifogging agents, lubricants / anti-blocking agents, UV stabilizers (or antioxidants), and tackifying resins, preferably selected from UV stabilizers (or antioxidants). These additives do not participate in the synthesis reaction of the copolyester polymer and can therefore be introduced before, during, or after obtaining the copolyester resin.

[0094] The total content of additives relative to the total weight of composition A can be up to 10% by weight, preferably up to 5% by weight, and more preferably 0.1% to 1% by weight.

[0095] The antifogging agent may be selected from sorbitol esters, glycerol esters, poly(oxyethylene) esters, alkylbenzene sulfonates and mixtures thereof; the esters are particularly fatty acid esters.

[0096] The content of the antifogging agent relative to the total weight of composition A may be in the range of up to 5% by weight.

[0097] Slippers / anti-blocking agents may be selected from erucamide, oleamide, docosamide, stearamide, palmitamide, ethylene bis(stearamide), ethylene bis(oleamide) and mixtures thereof.

[0098] The content of the lubricant / anti-blocking agent may be up to 5% by weight relative to the total weight of composition A.

[0099] UV stabilizers are typically introduced to prevent degradation caused by reactions with oxygen, which can occur through the action of heat or light. UV stabilizers may include antioxidants that can scavenge free radicals.

[0100] UV stabilizers (or antioxidants) can be selected from benzotriazole, benzophenone, and hindered phenols, such as octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (CAS: 2082-79-3), pentaerythritol tetra(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (CAS: 6683-19-8), and ethylene bis(oxyethylene)bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate] (CAS: 36443-68-2), hindered amines. Examples include bis(1-octyloxy-2,2,6,6-tetramethyl-4-piperidinyl) sebacate, bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate, bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate (CAS No.: 41556-26-7), methyl 1,2,2,6,6-pentamethyl-4-piperidinyl sebacate (CAS No.: 82919-37-7), and 4,4'-bis(α,α-dimethylbenzyl) diphenylamine, and mixtures thereof.

[0101] Preferably, the UV stabilizer (or antioxidant) is selected from hindered phenols, hindered amines, and mixtures thereof, more preferably from hindered phenols. Hindered phenols are typically phenols substituted with at least one bulky group (e.g., tert-butyl), preferably in the ortho position relative to the hydroxyl group.

[0102] The content of UV stabilizer (or antioxidant) relative to the total weight of composition A may be up to 5% by weight, preferably between 0.1% and 1% by weight.

[0103] Tackifying resins can be selected from esters of natural and modified rosin, especially esters of glycerol and pentaerythritol.

[0104] Composition A may also contain trace amounts (e.g., less than 0.05% by weight relative to the total weight of composition A) of solvent, which has been pre-used to facilitate the coating of composition A on one of the layers of a multilayer structure.

[0105] The solvent used to dilute the copolyester resin can be an organic solvent, such as methyl ethyl ketone, toluene, xylene, benzene, monochlorobenzene, dichloromethane, 2-nitropropane, nitrobenzene, dichlorobenzene, dioxolane, tetrahydrofuran, esters (ethyl acetate, n-butyl acetate, 2-ethoxyethyl acetate), cyclohexanone and / or dioxane, especially esters such as ethyl acetate, n-butyl acetate, 2-ethoxyethyl acetate, etc.

[0106] However, composition A, which constitutes the adhesive layer of the multilayer structure, contains only trace amounts of solvent, because if a solvent is used to facilitate the coating of composition A on one layer of the multilayer structure, the solvent will evaporate after coating.

[0107] Advantageously, composition A does not contain styrene block copolymers or saturated aliphatic polymers (e.g., polyethylene or polypropylene). This is because these compounds may hinder the recyclability of multilayer structures. Furthermore, composition A preferably does not contain crosslinking agents, such as polyisocyanates.

[0108] According to a preferred embodiment, composition A comprises (preferably consisting of) at least 95% by weight of a copolyester resin and at most 5% by weight of a UV stabilizer (or antioxidant), preferably at least 99% by weight of a copolyester resin and 0.1% to 1% by weight of a UV stabilizer (or antioxidant), the percentages being relative to the total weight of composition A.

[0109] Copolyester resins and UV stabilizers (or antioxidants) are as defined above.

[0110] The amount of composition A per unit surface area in a multilayer structure can vary over a very wide range, for example, 1 g / m². 2 Up to 30 g / m 2 2 g / m 2 Up to 20 g / m 2 Especially 4 g / m 2 Up to 16 g / m 2 .

[0111] Heat-resistant sealing layer

[0112] The heat-sealing layer is different from the adhesive layer. In particular, it is not a pressure-sensitive adhesive.

[0113] The heat-sealable layer allows for the sealing of multilayer structures to a substrate when heated, particularly to temperatures between 80°C and 180°C, preferably between 100°C and 160°C. Therefore, the heat-sealable layer advantageously has a softening temperature between 80°C and 180°C. The softening temperature can be measured according to the standard ASTM E28-67.

[0114] The energy storage modulus G' of the heat-sealed layer at 25°C can be greater than 1 MPa, or even too hard to be accurately measured.

[0115] The heat-sealing layer is based on a polyester polymer. In particular, the heat-sealing layer comprises at least 90% by weight of one or more polyester polymers, preferably at least 95% by weight, and more preferably at least 99% by weight, relative to the total weight of the layer.

[0116] Therefore, the heat-sealing layer comprises one or more polyester polymers, but may also contain, for example, unreacted monomers, possible catalysts, and / or monomers formed in situ through the reaction of other monomers that can form part of the polyester polymer backbone.

[0117] Preferably, the heat-sealing layer is based on an amorphous polyester polymer.

[0118] Advantageously, the polyester polymer for the heat-sealing layer is selected from copolyester polymers.

[0119] The copolyester polymer for the heat-sealing layer is particularly selected from polyester polymers whose main chain contains ester bonds linking units derived from polyols and polycarboxylic acids, wherein at least one unit derived from a polyol and / or at least one unit derived from a polycarboxylic acid is different from each other.

[0120] It should be understood that "units derived from polyols / polycarboxylic acids" refers to the portion of the polyol / polycarboxylic acid retained in the final structure of the polyester polymer. For example, a polyester polymer composed of units derived from monoethylene glycol and units derived from succinic acid contains the following structure:

[0121]

[0122] Therefore, units derived from polycarboxylic acids can be introduced into the polymer chain by reacting the polycarboxylic acid or its ester derivatives (e.g., acid anhydrides or (methyl)ethyl esters, preferably methyl esters).

[0123] Advantageously, the copolyester polymer comprises at least one unit derived from a cyclic or acyclic (preferably acyclic) diol and at least one unit derived from a cyclic (preferably aromatic) dicarboxylic acid. Preferably, the copolyester polymer comprises at least one unit derived from a diol and at least two units derived from cyclic (preferably aromatic) dicarboxylic acids.

[0124] For example, the cyclic or acyclic diols derived from copolyester polymers can be derived from monoethylene glycol, polyethylene glycol (preferably diethylene glycol), propane-1,2-diol, propane-1,3-diol, butane (-1,4-, -1,3- and / or -1,2-)diol, pentane glycol, hexane glycol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, polytetrahydrofuran and / or cyclohexanediol, preferably monoethylene glycol, polyethylene glycol and / or cyclohexanediol, especially monoethylene glycol and / or diethylene glycol.

[0125] For example, the unit derived from a cyclic dicarboxylic acid can be derived from cyclohexanedicarboxylic acid, phthalic acid, isophthalic acid and / or terephthalic acid, preferably terephthalic acid and optionally isophthalic acid.

[0126] In addition to at least one unit derived from a cyclic dicarboxylic acid, the copolyester polymer may also contain at least one unit derived from an acyclic dicarboxylic acid, such as maleic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid and / or 1,12-dodecanoic acid, preferably azelaic acid and / or sebacic acid.

[0127] According to one embodiment, the copolyester polymer comprises units derived from monoethylene glycol and / or diethylene glycol, units derived from terephthalic acid, and units derived from cyclic dicarboxylic acids (other than terephthalic acid), particularly units derived from isophthalic acid.

[0128] The heat-resistant sealing layer may also contain one or more additives, such as those selected from UV stabilizers (or antioxidants), lubricants / anti-blocking agents, anti-fogging agents, antistatic agents, processing aids, matting agents, and mixtures thereof, particularly those selected from UV stabilizers (or antioxidants), lubricants / anti-blocking agents, anti-fogging agents, and mixtures thereof.

[0129] The total content of additives may be up to 10% by weight, preferably up to 5% by weight, and more preferably up to 1% by weight, relative to the total weight of the heat-sealing layer.

[0130] UV stabilizers (or antioxidants) may be selected from benzotriazole, benzophenone, hindered phenols such as octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythritol tetra(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) and ethylene bis(oxyethylene)bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate], hindered amines such as bis(1-octoxy-2,2,6,6-tetramethyl-4-piperidinyl) sebacate, bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate, bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate, methyl 1,2,2,6,6-pentamethyl-4-piperidinyl sebacate and 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, and mixtures thereof.

[0131] The lubricant / anti-blocking agent may be selected from organic and / or inorganic lubricants / anti-blocking agents, with inorganic lubricants / anti-blocking agents being preferred. For example, the lubricant / anti-blocking agent may be selected from erucamide, oleamide, docosamide, stearamide, palmitamide, ethylene bis(stearamide), ethylene bis(oleamide), silica, talc, calcium carbonate, glass beads, and mixtures thereof, with silica, talc, calcium carbonate, glass beads, and mixtures thereof being preferred.

[0132] The antifogging agent may be selected from sorbitol esters, glycerol esters, poly(oxyethylene) esters, alkylbenzene sulfonates and mixtures thereof; the esters are particularly fatty acid esters.

[0133] The antistatic agent may be selected from alkali metal sulfonates, polyether-modified polydiorganosiloxanes, polyalkylphenylsiloxanes, tertiary amines, glyceryl monostearate, mixtures of glyceryl monostearate and tertiary amines, and mixtures thereof.

[0134] The heat-sealed layer is advantageously destructible.

[0135] The heat-sealed layer can be pre-cut in its entirety or part of its thickness, for example, using a laser or flexible mold.

[0136] The heat-sealing layer can be biaxially oriented.

[0137] The biaxial orientation of one (or more) polyester polymer-based layers can be achieved by simultaneously stretching the layer in the machine direction (also known as the axial direction) while heating (e.g., by infrared radiation, at temperatures greater than 100°C) and simultaneously stretching the layer in a direction perpendicular to the machine direction (also known as the transverse direction) while heating (e.g., between 100°C and 135°C). The layer can then be heated to 220°C and relaxed transversely at 220–170°C. The stretch factor can be between 2.0 and 4.0 (particularly about 3.0) in the machine direction and between 3.0 and 4.0 (particularly about 3.4) in the transverse direction.

[0138] The term “approximately X” is intended to mean the value of X plus or minus 10%.

[0139] The heat-resistant sealing layer may have undergone surface treatments, such as (preferably) embossing, plasma treatment, such as corona treatment, atmospheric pressure plasma treatment, flame plasma treatment, chemical plasma treatment, and especially corona treatment.

[0140] The thickness of the heat-sealing layer can be between 0.1 μm and 20 μm, preferably between 0.5 μm and 15 μm.

[0141] Composite layer

[0142] The composite layer is different from the adhesive layer. In particular, it is not a pressure-sensitive adhesive.

[0143] The term "composite layer" is well known to those skilled in the art and specifically refers to a layer that can be composited (or laminated) with other layers, such as with rigid layers, to improve the mechanical strength of multilayer structures.

[0144] The composite layer can have a storage modulus G' greater than 1 MPa at 25°C, or it may be too hard to measure G' accurately.

[0145] The composite layer is based on a polyester polymer. In particular, the composite layer comprises at least 90% by weight, preferably at least 95% by weight, and more preferably at least 99% by weight of one or more polyester polymers relative to the total weight of the layer.

[0146] Therefore, the composite layer may contain one or more polyester polymers, but may also contain, for example, unreacted monomers, possible catalysts and / or monomers formed in situ by the reaction of other monomers that can form part of the polyester polymer backbone.

[0147] The polyester polymer for the composite layer can be selected from homopolymers, copolymers and mixtures thereof, preferably homopolymers.

[0148] The homopolymer is specifically selected from polyester polymers whose main chain contains ester bonds that link single units derived from polyols and single units derived from polycarboxylic acids.

[0149] Advantageously, the units of the polyols derived from homopolymers are derived from acyclic diols. For example, the units derived from the polyols can be derived from monoethylene glycol, polyethylene glycol (preferably diethylene glycol), propane-1,2-diol, propane-1,3-diol, butane (-1,4-, -1,3- and / or -1,2-)diol, pentane glycol, 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.

[0150] Advantageously, the units of the polycarboxylic acids derived from homopolymers are derived from cyclic (especially aromatic) dicarboxylic acids. For example, the units derived from polycarboxylic acids can be derived from phthalic acid, isophthalic acid, terephthalic acid, and especially terephthalic acid.

[0151] According to one embodiment, the homopolymer is polyethylene terephthalate (PET).

[0152] The copolyester polymer for the composite layer is particularly selected from polyester polymers whose main chain contains ester bonds connecting units derived from polyols and polycarboxylic acids, wherein at least one unit derived from a polyol and / or at least one unit derived from a polycarboxylic acid is different from the other units.

[0153] Advantageously, the copolyester polymer comprises at least one unit derived from an acyclic diol and at least one unit derived from a cyclic (preferably aromatic) dicarboxylic acid.

[0154] For example, the units of acyclic diols derived from copolyester polymers can be derived from monoethylene glycol, polyethylene glycol (preferably diethylene glycol), propane-1,2-diol, propane-1,3-diol, butane (-1,4-, -1,3- and / or -1,2-)diol, pentane glycol, hexane glycol, 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.

[0155] For example, the unit derived from a cyclic dicarboxylic acid can be derived from cyclohexanedicarboxylic acid, phthalic acid, isophthalic acid and / or terephthalic acid, preferably terephthalic acid and optionally isophthalic acid.

[0156] In addition to at least one unit derived from a cyclic dicarboxylic acid, the copolyester polymer may also contain at least one unit derived from an acyclic dicarboxylic acid, such as maleic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid and / or 1,12-dodecanoic acid, preferably azelaic acid and / or sebacic acid.

[0157] According to one embodiment, the copolyester polymer comprises units derived from monoethylene glycol, units derived from terephthalic acid, and units derived from cyclic dicarboxylic acids (other than terephthalic acid), particularly units derived from isophthalic acid.

[0158] The composite layer may also contain one or more additives, such as those selected from UV stabilizers (or antioxidants), lubricants / antiblocking agents, antistatic agents, processing aids, matting agents and mixtures thereof, particularly those selected from UV stabilizers (or antioxidants), lubricants / antiblocking agents and mixtures thereof.

[0159] The total content of additives relative to the total weight of the composite layer can be up to 10% by weight, preferably up to 5% by weight, and more preferably up to 1% by weight.

[0160] UV stabilizers (or antioxidants) may be selected from benzotriazole, benzophenone, hindered phenols such as octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythritol tetra(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) and ethylene bis(oxyethylene)bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate], hindered amines such as bis(1-octoxy-2,2,6,6-tetramethyl-4-piperidinyl) sebacate, bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate, bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate, methyl 1,2,2,6,6-pentamethyl-4-piperidinyl sebacate and 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, and mixtures thereof.

[0161] The lubricant / anti-blocking agent may be selected from organic and / or inorganic lubricants / anti-blocking agents, with inorganic lubricants / anti-blocking agents being preferred. For example, the lubricant / anti-blocking agent may be selected from erucamide, oleamide, docosamide, stearamide, palmitamide, ethylene bis(stearamide), ethylene bis(oleamide), silica, talc, calcium carbonate, glass beads, and mixtures thereof, with silica, talc, calcium carbonate, glass beads, and mixtures thereof being preferred.

[0162] The antistatic agent may be selected from alkali metal sulfonates, polyether-modified polydiorganosiloxanes, polyalkylphenylsiloxanes, tertiary amines, glyceryl monostearate, mixtures of glyceryl monostearate and tertiary amines, and mixtures thereof.

[0163] The composite layer is advantageously biaxially oriented.

[0164] The composite layer can be surface treated, such as (preferably hot) embossing, plasma treatment such as corona treatment, atmospheric pressure plasma treatment, flame plasma treatment, chemical plasma treatment, especially corona treatment.

[0165] The thickness of the composite layer can be between 5 μm and 100 μm, preferably between 10 μm and 50 μm.

[0166] Other layers

[0167] The multilayer structure according to the invention may also include one or more additional layers (in addition to the adhesive layer, heat-sealing layer and composite layer described above).

[0168] For example, the multilayer structure according to the present invention may include:

[0169] - One or more additional layers on the heat-sealing layer (preferably between the adhesive layer and the heat-sealing layer), and / or

[0170] - One or more additional layers on the composite layer (between the adhesive layer and the composite layer, and / or on a surface not facing the adhesive layer, preferably between the adhesive layer and the composite layer).

[0171] In this document, the term "heat-sealed membrane" should be understood to mean an assembly formed of a heat-sealed layer and additional layers thereon, and the term "composite membrane" should be understood to mean an assembly formed of a composite layer and additional layers thereon.

[0172] Advantageously, the heat-sealable layer has a free surface (not covered by another layer); therefore, it is the outer layer. When the multilayer structure is used as a lid for a resealable package, the lid is heat-sealed to the receiver via the heat-sealable layer.

[0173] Preferably, the multilayer structure includes one or more additional layers between the adhesive layer and the heat-sealing layer. Therefore, the heat-sealing layer preferably has a free surface (not covered by another layer). It is not excluded that one or more additional layers are also heat-sealing layers, the same as or different from the heat-sealing layer described above.

[0174] According to one embodiment, the multilayer structure includes one or more additional layers between the adhesive layer and the heat-sealing layer, and one or more additional layers on the composite layer, preferably between the adhesive layer and the composite layer. Advantageously, the heat-sealing layer has a free surface.

[0175] Each additional layer is advantageously based on a polyester polymer. In particular, each additional layer comprises at least 90%, preferably at least 95%, and more preferably at least 99% by weight of one or more polyester polymers relative to the total weight of the layers.

[0176] Therefore, each additional layer contains one or more polyester polymers, but may also contain, for example, unreacted monomers, possible catalysts, and / or monomers formed in situ through the reaction of other monomers that can form part of the polyester polymer backbone.

[0177] The polyester polymer for each additional layer can be selected from homopolymers, copolymers, and mixtures thereof. Advantageously, the polyester polymer for each additional layer of the heat-sealable film is selected from homopolymers, particularly polyethylene terephthalate (PET), and each additional layer is located between the adhesive layer and the heat-sealable layer. Advantageously, the polyester polymer for each additional layer of the composite film is selected from copolymers, and each additional layer is located between the adhesive layer and the composite layer.

[0178] The homopolymer is specifically selected from polyester polymers whose main chain contains ester bonds that link single units derived from polyols and single units derived from polycarboxylic acids.

[0179] Advantageously, the units of the polyols derived from homopolymers are derived from acyclic diols. For example, the units derived from the polyols can be derived from monoethylene glycol, polyethylene glycol (preferably diethylene glycol), propane-1,2-diol, propane-1,3-diol, butane (-1,4-, -1,3- and / or -1,2-)diol, pentane glycol, 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.

[0180] Advantageously, the units of the polycarboxylic acids derived from homopolymers are derived from cyclic (especially aromatic) dicarboxylic acids. For example, the units derived from polycarboxylic acids can be derived from phthalic acid, isophthalic acid, terephthalic acid, and especially terephthalic acid.

[0181] According to one embodiment, the homopolymer is polyethylene terephthalate (PET).

[0182] Each additional layer of copolyester polymer is specifically selected from polyester polymers whose main chain contains ester bonds linking units derived from polyols and polycarboxylic acids, wherein at least one unit derived from a polyol and / or at least one unit derived from a polycarboxylic acid is different from each other.

[0183] Advantageously, the copolyester polymer comprises at least one unit derived from an acyclic diol and at least one unit derived from a cyclic (preferably aromatic) dicarboxylic acid.

[0184] For example, the units of acyclic diols derived from copolyester polymers can be derived from monoethylene glycol, polyethylene glycol (preferably diethylene glycol), propane-1,2-diol, propane-1,3-diol, butane (-1,4-, -1,3- and / or -1,2-)diol, pentane glycol, hexane glycol, 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.

[0185] For example, the unit derived from a cyclic dicarboxylic acid can be derived from cyclohexanedicarboxylic acid, phthalic acid, isophthalic acid and / or terephthalic acid, preferably terephthalic acid and optionally isophthalic acid.

[0186] In addition to at least one unit derived from a cyclic dicarboxylic acid, the copolyester polymer may also contain at least one unit derived from an acyclic dicarboxylic acid, such as units derived from maleic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid and / or 1,12-dodecanoic acid.

[0187] Each additional layer may also contain one or more additives, such as those selected from UV stabilizers (or antioxidants), lubricants / antiblocking agents, antistatic agents, processing aids, matting agents, and mixtures thereof, particularly those selected from UV stabilizers (or antioxidants), lubricants / antiblocking agents, and mixtures thereof.

[0188] The total amount of additives may be up to 10% by weight, preferably up to 5% by weight, and more preferably up to 1% by weight, relative to the total weight of each additional layer.

[0189] UV stabilizers (or antioxidants) may be selected from benzotriazole, benzophenone, hindered phenols such as octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythritol tetra(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) and ethylene bis(oxyethylene)bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate], hindered amines such as bis(1-octoxy-2,2,6,6-tetramethyl-4-piperidinyl) sebacate, bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate, bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate, methyl 1,2,2,6,6-pentamethyl-4-piperidinyl sebacate and 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, and mixtures thereof.

[0190] The lubricant / anti-blocking agent may be selected from organic and / or inorganic lubricants / anti-blocking agents, with inorganic lubricants / anti-blocking agents being preferred. For example, the lubricant / anti-blocking agent may be selected from erucamide, oleamide, docosamide, stearamide, palmitamide, ethylene bis(stearamide), ethylene bis(oleamide), silica, talc, calcium carbonate, glass beads, and mixtures thereof, with silica, talc, calcium carbonate, glass beads, and mixtures thereof being preferred.

[0191] The antistatic agent may be selected from alkali metal sulfonates, polyether-modified polydiorganosiloxanes, polyalkylphenylsiloxanes, tertiary amines, glyceryl monostearate, mixtures of glyceryl monostearate and tertiary amines, and mixtures thereof.

[0192] Each additional layer can be biaxially oriented.

[0193] Each additional layer may undergo surface treatment, such as (preferably hot) embossing, plasma treatment such as corona treatment, atmospheric pressure plasma treatment, flame plasma treatment, chemical plasma treatment, and especially corona treatment.

[0194] The thickness of each additional layer can be between 0.1 μm and 100 μm, preferably between 0.5 μm and 40 μm.

[0195] The thickness of the heat-sealable film can be from 2 μm to 100 μm, preferably from 3 μm to 50 μm, and more preferably from 4 μm to 12 μm.

[0196] The thickness of the composite membrane can be from 5 μm to 100 μm, preferably from 10 μm to 50 μm.

[0197] Heat-sealing films are advantageously destructible.

[0198] Heat-sealing films can be pre-cut in all or part of their thickness, for example, using lasers or flexible molds.

[0199] The heat-sealing film can be biaxially oriented.

[0200] Composite films can be biaxially oriented.

[0201] Other features

[0202] Advantageously, each layer of the multilayer structure according to the invention is based on a polyester polymer. In particular, each layer of the multilayer structure comprises at least 90% by weight of one or more polyester polymers relative to the total weight of the layers, preferably at least 95% by weight, more preferably at least 99% by weight. The polyester polymers for each type of layer (adhesive layer, heat-sealing layer, composite layer, and other layers) are as described above.

[0203] Therefore, each layer contains one or more polyester polymers, but may also contain, for example, unreacted monomers, possible catalysts, and / or monomers formed in situ through the reaction of other monomers that can form part of the polyester polymer backbone.

[0204] Furthermore, one or more layers of the multilayer structure according to the present invention may be entirely or partially covered with ink.

[0205] Advantageously, the multilayer structure does not contain styrene block copolymers, copolymers of ethylene and vinyl acetate, copolymers of ethylene and (meth)acrylates, copolymers of ethylene and (meth)acrylic acid, and / or polyolefin polymers (i.e. obtained by polymerization of one or more olefin monomers, such as polyethylene, polypropylene, ethylene-propylene copolymers), and in particular, does not contain any of these compounds.

[0206] Advantageously, the multilayer structure does not contain styrene block copolymers and / or polyolefin polymers, and in particular, does not contain any of these compounds.

[0207] According to one embodiment, the amount of composition A per unit surface area in the multilayer structure according to the present invention is 1 g / m². 2 Up to 30 g / m 2 The thickness of the heat-sealing layer can be from 0.1 μm to 20 μm, and the thickness of the composite layer can be from 5 μm to 100 μm.

[0208] The total thickness of the multilayer structure according to the present invention can be between 5 μm and 200 μm, preferably between 10 μm and 100 μm, and more preferably between 14 μm and 62 μm.

[0209] According to one embodiment, the multilayer structure according to the present invention comprises:

[0210] - An adhesive layer comprising composition A, wherein composition A comprises a copolyester resin with a glass transition temperature of less than 0°C and a crystallinity of less than 10% and is amorphous; the copolyester polymer of the copolyester resin is preferably obtained by reacting the following reaction:

[0211] At least one acyclic diol and

[0212] At least one cyclic dicarboxylic acid (or its esterified derivative), comprising an alicyclic dicarboxylic acid (or its esterified derivative) and / or an aromatic dicarboxylic acid (or its esterified derivative) comprising an aromatic ring, wherein two functional groups are in a meta position relative to each other, and

[0213] At least one acyclic dicarboxylic acid (or its ester derivative), comprising at least four (preferably four to fifteen, more preferably six to twelve) carbon atoms and being linearly chained.

[0214] - A heat-sealable and destructible layer based on a copolyester polymer, preferably amorphous.

[0215] -Based on polyester, preferably homopolymer composite layers, and

[0216] -Optionally, one or more additional layers based on polyester polymers.

[0217] The layers of this implementation scheme are as described above, including preferred features and implementation schemes.

[0218] The amount of composition A per unit surface area in the structure is greater than or equal to 6 g / m². 2 The multilayer structure of the present invention advantageously has a second opening force by peeling of greater than or equal to 0.8 N / 10 mm, preferably greater than or equal to 1.0 N / 10 mm, and more preferably greater than or equal to 1.3 N / 10 mm, particularly when it is pre-heat-sealed onto an amorphous PET sheet. The second opening force can be measured, for example, according to Example 3.

[0219] The amount of composition A per unit surface area in the structure is greater than or equal to 6 g / m². 2 The multilayer structure of the present invention advantageously has a fifth opening force by peeling greater than or equal to 0.6 N / 10 mm, preferably greater than or equal to 0.90 N / 10 mm, particularly when it is pre-heat-sealed onto an amorphous PET sheet. The fifth opening force can be measured, for example, according to Example 3.

[0220] The multi-layer structure according to the invention can be used as a lid for a package containing a receiver. In this case, it should be understood that the multi-layer structure does not include a container.

[0221] Method for manufacturing multilayer structures

[0222] The present invention also relates to a method for manufacturing a multilayer structure according to the present invention, comprising:

[0223] - The step of coating the adhesive containing composition A onto the surface of the first film, then

[0224] - The step of laminating the surface of the second film onto the coated surface of the first film.

[0225] One of the films contains the heat-sealing layer or is bonded to the heat-sealing layer after the lamination step, and

[0226] One of the films contains the composite layer or is incorporated into the composite layer after the lamination step.

[0227] The multilayer structure, composition A, heat-sealing layer, and composite layer are as described above, including preferred features and embodiments. In particular, the heat-sealing layer preferably has a free surface.

[0228] The first and second membranes can each be single-layered or multi-layered.

[0229] The coating step can be performed on all or part of the surface of the first film, preferably continuously or substantially continuously.

[0230] To facilitate the application of composition A, the adhesive may additionally contain organic solvents such as butanone, toluene, xylene, benzene, monochlorobenzene, dichloromethane, 2-nitropropane, nitrobenzene, dichlorobenzene, dioxolane, tetrahydrofuran, esters (ethyl acetate, n-butyl acetate, 2-ethoxyethyl acetate), cyclohexanone and / or dioxane, especially esters such as ethyl acetate, n-butyl acetate, 2-ethoxyethyl acetate, etc.

[0231] When the adhesive contains solvent, its content may be from 10% to 95% by weight, preferably from 50% to 90% by weight, relative to the total weight of the adhesive.

[0232] When the adhesive contains a solvent, the method for manufacturing the multilayer structure according to the invention advantageously includes a step of drying the adhesive after the coating step and before the lamination step. The drying step can be carried out at a temperature between 25°C and 100°C, preferably between 35°C and 95°C, and more preferably between 45°C and 90°C, for a duration sufficient to allow the solvent to evaporate.

[0233] When one or more additional layers (as described above) are present in a multilayer structure, they can be obtained by co-extrusion, coating and / or lamination with one or more layers of the multilayer structure.

[0234] Resealable packaging

[0235] The present invention also relates to resealable packaging comprising a multilayer structure according to the invention.

[0236] In particular, the resealable packaging comprises a polyester polymer-based receiver and a lid consisting of a multi-layered structure according to the invention.

[0237] Advantageously, the cover is heat-sealed to the periphery of the receiver.

[0238] Advantageously, relative to the total weight of the acceptor, the acceptor comprises at least 90% by weight of polyester polymer, preferably at least 95% by weight, more preferably at least 99% by weight. Thus, the acceptor comprises one or more polyester polymers, but may also comprise, for example, unreacted monomers, possible catalysts, and / or monomers formed in situ through the reaction of other monomers that can form part of the polyester polymer backbone.

[0239] Preferably, the receiver comprises at least one amorphous polyester polymer; more preferably, the receiver is composed of an amorphous polyester polymer (in particular, the amorphous polyester polymer accounts for at least 90% by weight, preferably at least 95% by weight, and more preferably at least 99% by weight, relative to the total weight of the receiver).

[0240] The polyester polymer of the receiver can be selected from homopolymers, copolymers and mixtures thereof, preferably homopolymers.

[0241] The homopolymer is specifically selected from polyester polymers whose main chain contains ester bonds that link single units derived from polyols and single units derived from polycarboxylic acids.

[0242] Advantageously, the units of the polyols derived from homopolymers are derived from acyclic diols. For example, the units derived from the polyols can be derived from monoethylene glycol, polyethylene glycol (preferably diethylene glycol), propane-1,2-diol, propane-1,3-diol, butane (-1,4-, -1,3- and / or -1,2-)diol, pentane glycol, 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.

[0243] Advantageously, the units of the polycarboxylic acids derived from homopolymers are derived from cyclic (preferably aromatic), particularly aromatic dicarboxylic acids. For example, the units derived from polycarboxylic acids can be derived from phthalic acid, isophthalic acid, terephthalic acid, and especially terephthalic acid.

[0244] According to one embodiment, the homopolymer is polyethylene terephthalate (PET).

[0245] The copolyester polymer of the acceptor is specifically selected from polyester polymers whose main chain contains ester bonds connecting units derived from polyols and polycarboxylic acids, wherein at least one unit derived from a polyol and / or at least one unit derived from a polycarboxylic acid is different from the other units.

[0246] Advantageously, the copolyester polymer comprises at least one unit derived from an acyclic diol and at least one unit derived from a cyclic (preferably aromatic) dicarboxylic acid.

[0247] For example, the units of acyclic diols derived from copolyester polymers can be derived from monoethylene glycol, polyethylene glycol (preferably diethylene glycol), propane-1,2-diol, propane-1,3-diol, butane (-1,4-, -1,3- and / or -1,2-)diol, pentane glycol, hexane glycol, 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.

[0248] For example, the unit derived from a cyclic dicarboxylic acid can be derived from cyclohexanedicarboxylic acid, phthalic acid, isophthalic acid and / or terephthalic acid, preferably terephthalic acid and optionally isophthalic acid.

[0249] In addition to at least one unit derived from a cyclic dicarboxylic acid, the copolyester polymer may also contain at least one unit derived from an acyclic dicarboxylic acid, such as maleic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid and / or 1,12-dodecanoic acid, preferably azelaic acid and / or sebacic acid.

[0250] According to one embodiment, the copolyester polymer comprises units derived from monoethylene glycol, units derived from terephthalic acid, and units derived from cyclic dicarboxylic acids (other than terephthalic acid), particularly units derived from isophthalic acid.

[0251] The receiver may also contain one or more additives, such as those selected from UV stabilizers (or antioxidants), lubricants / anti-blocking agents, pigments, antistatic agents, and mixtures thereof.

[0252] The total content of additives relative to the total weight of the receiver can be up to 10% by weight, preferably up to 5% by weight, and more preferably up to 1% by weight.

[0253] UV stabilizers (or antioxidants) may be selected from benzotriazole, benzophenone, hindered phenols such as octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythritol tetra(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) and ethylene bis(oxyethylene)bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate], hindered amines such as bis(1-octoxy-2,2,6,6-tetramethyl-4-piperidinyl) sebacate, bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate, bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate, methyl 1,2,2,6,6-pentamethyl-4-piperidinyl sebacate and 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, and mixtures thereof.

[0254] The lubricant / anti-blocking agent may be selected from organic and / or inorganic lubricants / anti-blocking agents, with inorganic lubricants / anti-blocking agents being preferred. For example, the lubricant / anti-blocking agent may be selected from erucamide, oleamide, docosamide, stearamide, palmitamide, ethylene bis(stearamide), ethylene bis(oleamide), silica, talc, calcium carbonate, glass beads, and mixtures thereof, with silica, talc, calcium carbonate, glass beads, and mixtures thereof being preferred.

[0255] Pigments can be selected from organic pigments, inorganic pigments, and mixtures thereof. For example, pigments can be selected from manganese ferrite, titanium dioxide, carbon black, iron oxide, aluminum, talc, and mixtures thereof, especially titanium dioxide, carbon black, and mixtures thereof.

[0256] The antistatic agent may be selected from alkali metal sulfonates, polyether-modified polydiorganosiloxanes, polyalkylphenylsiloxanes, tertiary amines, glyceryl monostearate, mixtures of glyceryl monostearate and tertiary amines, and mixtures thereof.

[0257] Applications of multi-layer structures

[0258] The present invention also relates to the use of the multilayer structure according to the invention in the manufacture of resealable packaging.

[0259] Advantageously, the multi-layered structure can be used as a lid for resealable packaging.

[0260] Preferably, the resealable packaging, as described above, includes preferred features and embodiments.

[0261] In the context of this invention, the range of values ​​should be understood to include extreme values. For example, the range "between 0% and 25% (0% to 25%)" specifically includes the values ​​0% and 25%.

[0262] All of the above embodiments can be combined with each other. In particular, the various features, especially the preferred features, of the layers of the multi-layer structure can be combined with each other.

[0263] The following examples are given purely by way of illustration and should not be construed as limiting the scope thereof.

[0264] Example

[0265] Example 1: Composition for Adhesive Layer

[0266] Comparative composition A1 based on styrene block copolymer

[0267] Comparative composition A1 is sold by Bostik under the designation M650.F and comprises a mixture of a tackifying resin and a styrene-isoprene-styrene (SIS) copolymer.

[0268] The copolyester resin composition A2 according to the present invention

[0269] The copolyester resin is prepared according to the procedure shown below.

[0270] Under an inert atmosphere (molecular nitrogen), 554 g of monoethylene glycol (8.9 mol), 416 g of dimethyl terephthalate (2.1 mol), 0.19 g of tetrabutyl titanate (Tyzor® TnBT, from Dorf Ketal), and 3.6 g of pentaerythritol tetra(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (Irganox® 1010, from BASF) were added to a 2-liter reactor containing a distillation column (for removing methanol and water). The combined mixture was heated from ambient temperature to approximately 180°C. When the temperature reached approximately 180°C, it was raised to approximately 205°C.

[0271] After approximately 1.5 hours, the temperature reached approximately 205°C. It was then cooled to ambient temperature to introduce 173 g of monoethylene glycol (2.8 mol). After stirring for 15 minutes, 242 g of isophthalic acid (1.5 mol) and 679 g of azelaic acid (3.6 mol) were added. The temperature was then raised to approximately 190°C, and then further raised to approximately 240°C. The temperature was maintained at approximately 240°C for 0.5 hours.

[0272] The resulting reaction mixture was then heated to approximately 255°C under vacuum (less than 0.27 kPa) until the intrinsic viscosity was 0.80–0.90 dL / g (ASTM D5225-14).

[0273] The resulting copolyester resin is amorphous, with a Tg of approximately -11°C (ASTM E1356-08, where the modification is to use a temperature scan of 15°C / min instead of 10°C / min), a softening temperature of approximately 99°C (ASTM E28-67), and a weight-average molecular weight of approximately 75 kg / mol.

[0274] The resin was then diluted in ethyl acetate to obtain composition A2 containing 20% ​​by weight of the resin relative to the total weight of composition A2 (the remaining 80% being ethyl acetate).

[0275] Example 2: Preparation of multilayer structures

[0276] Multilayer structure 1 is a multilayer film composed of a 15 μm thick polyethylene layer and a 30 μm thick polyethylene layer, bonded together by an adhesive layer obtained from composition A1. Multilayer structure 1 is obtained by film blow molding co-extrusion, with the co-extrusion head having a temperature of approximately 190°C.

[0277] The multilayer structure 2 is a multilayer film consisting of an 8 μm thick PET-based film and an additional 30 μm thick PET-based film, which are bonded together by an adhesive layer obtained from composition A2.

[0278] The 8 μm thick PET film is destructible and biaxially oriented, comprising a heat-sealable outer layer of polyethylene terephthalate copolyester co-extruded with multiple PET layers, the outer PET layers having undergone corona treatment.

[0279] The 30 μm thick PET film consists of a biaxially oriented homopolymer PET film co-extruded with a copolyester on one side.

[0280] Composition A2 was applied to a 30 μm thick PET film at a controlled rate using a Mayer rod and a manual coater to obtain the target coating weight (2 g / m²). 2 6 g / m 2 11 g / m 2 Or 15 g / m 2 This process yields a bilayer structure. The coated film (bilayer structure) is then dried at 80°C for approximately 10 minutes, causing the ethyl acetate contained in composition A2 to evaporate. Finally, a trilayer structure is obtained by laminating an 8 μm thick PET film onto the adhesive layer side of the bilayer structure. The trilayer structure is then placed in a press for 24 h and tested in an air-conditioned room at 23°C and 50% relative humidity.

[0281] Example 3: Properties of Multilayer Structures

[0282] The performance of the multilayer structures 1 and 2 prepared in Example 2 was evaluated by the following tests, and the results are shown in Table 1.

[0283] The force used for the first opening (multi-layer structure 1) was measured by peeling:

[0284] A rectangular test sample E1 with a length of 25 cm and a width of 3 cm was cut from the multi-layer structure to be evaluated.

[0285] In addition, a rectangular test sample E2 with a length of 25 cm and a width of 3 cm was cut from a flexible PET / polyethylene film with a thickness of approximately 60 μm.

[0286] Then, sample E1 was placed between two samples E2, so that the 15 μm and 30 μm polyethylene layers were in contact with the polyethylene surface of the test sample E2.

[0287] The test sample was then partially sealed using two heated clamps at 130°C, with a pressure of 0.4 MPa applied for 1 second to obtain a rectangular sealed area (15 cm long and 1 cm wide). The sealed area was positioned along its length and contacted one small side of the rectangular test samples E1 and E2 connected therefrom, so as to leave a strip of approximately 2 cm in length (free and unsealed) on the other small side of the test samples.

[0288] The free and unsealed strips of E1+E2 and the free and unsealed strip of E2 (in contact with the 15μm polyethylene layer of the multilayer structure 1) are attached to two fastening devices (referred to as jaws), which are respectively connected to the fixed part and the movable part of the tensile testing machine located on the vertical axis.

[0289] When the drive mechanism applies a uniform rate of 300 mm / min to the movable part, it causes the two sealed test samples E1 and E2 to peel off, with their ends gradually moving along the vertical axis to form a 180° angle. A force sensor connected to the movable part measures the force exerted on the test samples thus held in place. The measurements are performed in a climate-controlled chamber maintained at 23°C.

[0290] The force required to “break” the contour of the seal and trigger the separation of the two test samples is called the initial opening peak, and the force that achieves the separation of the two test samples is called the initial opening propagation.

[0291] The force applied to the first opening (multi-layer structure 2) was measured by peeling:

[0292] A rectangular test sample E'1 with a length of 25 cm and a width of 3 cm was cut from the multi-layer structure to be evaluated.

[0293] In addition, rectangular test specimens E'2 with a length of 25 cm and a width of 5 cm were cut from a rigid sheet of amorphous PET with a thickness of approximately 250 μm.

[0294] Then, the two test samples E'1 and E'2 were placed facing each other, so that the 8 μm thick PET layer of E'1 was in contact with E'2.

[0295] The test sample was then partially sealed using two heated clamps at 140°C, with a pressure of 0.4 MPa applied for 1 second to obtain a rectangular sealed area (15 cm long and 1 cm wide). The sealed area was positioned along its length and contacted one small side of the rectangular test samples E'1 and E'2 connected thereto, so as to leave a multi-layered structural strip approximately 2 cm long on the other small side of the test samples, originating from E'1 (free and unsealed) and positioned opposite each other at the end of the rigid sheet of E'2.

[0296] The free and unsealed strip of E'1 is attached to a fastening device (called a jaw), which is connected to a movable part of the tensile testing machine. The test specimen E'2 is held on a bracket mounted on ball bearings by means of a steel plate secured by a fastening clamp. The bracket is connected to the crosshead of the testing machine via a system of cables and pulleys.

[0297] When the drive mechanism applies a uniform rate of 300 mm / min to the movable part, the two sealed test specimens E'1 and E'2 peel off, with the end of E'1 gradually moving along the vertical axis to form a 90° angle with the bracket. A force sensor connected to the movable part measures the force exerted on the test specimen thus held in place. The measurements are performed in a climate-controlled chamber maintained at 23°C.

[0298] The force required to “break” the contour of the seal and trigger the separation of the two test samples is called the initial opening peak, and the force that achieves the separation of the two test samples is called the initial opening propagation.

[0299] The force required to open the second and subsequent times was measured by peeling:

[0300] After the first peeling, the two parts of the aforementioned test sample were repositioned facing each other and manually brought into contact. They were then subjected to pressure applied by a 2 kg roller, which was used to reciprocate along a direction parallel to the length of the test sample.

[0301] Then the peel test described above is repeated, and the measured average force (propagation force) corresponds to the force of the second opening.

[0302] The forces required for the third, fourth, and fifth openings were measured in a similar manner after the second, third, and fourth peelings, respectively.

[0303] Table 1

[0304]

[0305] The peak value of the first opening of the multilayer structure 2 according to the invention is at least 5 N / 10 mm; therefore, they make it possible to prevent the packaging from opening without user intervention.

[0306] For a similar weight per unit area, the multilayer structure 2 according to the invention (15 g / m²) 2 It has significantly greater reopening forces (from the second to the fifth opening) than those of the reference multilayer structure 1.

[0307] The higher the reopening force of a multi-layered structure, the better the resealing quality of its packaging; this limits the risk of the packaging opening during storage or transportation.

[0308] Therefore, in addition to the fact that the multi-layer structure according to the invention is recyclable, it also makes it possible to improve the resealing quality of the packaging.

[0309] Therefore, a package containing a multi-layer structure according to the invention can undergo multiple opening / sealing cycles while maintaining good sealing quality.

Claims

1. A multi-layered structure comprising: - An adhesive layer comprising composition A, wherein composition A comprises a copolyester resin having a glass transition temperature of less than 0°C and a crystallinity of less than 10%. - A heat-sealing layer based on polyester polymer, and - Composite layers based on polyester polymers, The adhesive layer is located between the heat-sealing layer and the composite layer.

2. The multilayer structure according to claim 1, wherein the copolyester resin of composition A is amorphous.

3. The multilayer structure according to claim 1 or 2, wherein the copolyester polymer of the copolyester resin is obtained by reacting at least one acyclic diol with at least one cyclic dicarboxylic acid or its ester derivative, and at least one acyclic dicarboxylic acid or its ester derivative containing at least 4 carbon atoms.

4. The multilayer structure according to claim 3, wherein the at least one cyclic dicarboxylic acid or its ester derivative comprises an alicyclic dicarboxylic acid or its ester derivative and / or an aromatic dicarboxylic acid or its ester derivative containing an aromatic ring, wherein the two functional groups are located in a meta or ortho position relative to each other.

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

6. The multilayer structure according to any one of claims 1 to 5, wherein the heat-sealing layer is destructible.

7. The multilayer structure according to any one of claims 1 to 6, wherein the multilayer structure does not contain styrene block copolymers, copolymers of ethylene and vinyl acetate, copolymers of ethylene and (meth)acrylates, copolymers of ethylene and (meth)acrylic acid, and / or polyolefin polymers.

8. The multilayer structure according to any one of claims 1 to 7, wherein the amount of composition A per unit surface area in the multilayer structure is 1 g / m². 2 Up to 30 g / m 2 The thickness of the heat-sealing layer is from 0.1 μm to 20 μm and the thickness of the composite layer is from 5 μm to 100 μm.

9. The multilayer structure according to any one of claims 1 to 8, comprising: - An adhesive layer composed of composition A, wherein composition A comprises a copolyester resin with a glass transition temperature of less than 0°C, a crystallinity of less than 10%, and is an amorphous resin. - A heat-sealable and destructible layer based on copolyester polymers. - Composite layers based on polyester polymers, and -Optionally, one or more additional layers based on polyester polymers.

10. The multilayer structure according to any one of claims 1 to 9, wherein the heat-sealing layer has a free surface.

11. A method for manufacturing a multilayer structure according to any one of claims 1 to 10, comprising: - The step of coating the adhesive containing composition A onto the surface of the first film, then - The step of laminating the surface of the second film onto the coated surface of the first film. One of the films contains the heat-sealing layer or is bonded to the heat-sealing layer after the lamination step, and One of the films contains the composite layer or is incorporated into the composite layer after the lamination step.

12. A resealable package comprising a multilayer 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 manufacturing resealable packaging.

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