WO2013080143A1

WO2013080143A1 - Polyester based multilayered films

Info

Publication number: WO2013080143A1
Application number: PCT/IB2012/056799
Authority: WO
Inventors: Roberto Forloni
Original assignee: Cryovac, Inc.
Priority date: 2011-11-28
Filing date: 2012-11-28
Publication date: 2013-06-06
Also published as: EP2785510A1

Abstract

The present invention relates to an oriented fully polyester based multilayered film having at least one non-multiplied layer and at least one multiplied layer. The film object of the invention shows higher tear resistance properties and lower shrink tension compared to the same non-multiplied film.

Description

"POLYESTER BASED MULTILAYERED FILMS"

Field of the invention

The present invention relates to an oriented fully polyester based multilayered film having at least one non- multiplied layer and at least one multiplied layer.

The resultant multilayered film has higher tear resistance properties and lower shrink tension compared to the same non-multiplied film.

State of the art

Polyester films are commonly used as lidding films in particular for ready meals and case ready containers. Packaging system comprising a rigid heat-stable container having a thin flexible thermoplastic film sealed onto it are commonly used for food products which only require heating to be ready for consumption.

Heating can be carried out in a microwave or conventional oven but since the temperatures involved in the heating step are very high, only few materials can be used to make containers and lids.

Biaxially oriented PET is commonly used as lidding film due to its high thermal stability at standard food heating or cooking temperatures.

Heat-shrinkable and thin oriented PET films known in the art typically have low tear resistance properties and consequently may be difficult to run on tray lidding type equipment, in particular where very low film thickness is required or desired. Additionally, these known films generally have high shrink tension properties, so they may cause problems of tray distortion when the film is sealed on to the tray or wrapped around a tray and the final package is subjected to heat treatment (e.g. pasteurization, heating), thus rendering the resulting package not appealing to the final consumer.

WO2009/013284 (Cryovac) relates to a fully polyester-based heat shrinkable film with shrink in each direction of less than 5% at 100°C or higher than 5% at 150 °C, and a heat-sealable coating applied on one surface of the base film. The film preferably presents two or three layers made of a blend of polyethylene-terephthalate and a copolymer of terephthalic acid with ethylene glycol and 1 ,4-cyclohexandimethanol.

WO2007/093495 (Cryovac) relates to a coextruded biaxially oriented heat-shrinkable film having a base layer comprising a polyester having intrinsic viscosity (IV) higher than 0.75 dl/g and a first outer heat-sealable layer directly adhered to said base layer. Heat sealable layer comprises amorphous or crystallized polyester having a melting temperature lower than the melting temperature of the base layer. A blend of PET and a polyamide was used to obtain hermeticity and sealability.

The shrinkable and thin oriented films disclosed in the cited documents of prior art are conventional fully polyester films showing low tear resistance properties in particular where very low film thickness is required. A low tear resistance may give rise to "skeleton breaking" problems with consequent undesired interruptions of packaging cycle, i.e. breaking of the dragging part of the film which remains after trimming on the trays during packaging operation. Additionally, such films generally have high shrink tension that may induce problems of tray distortion, thus making the final package not particularly appealing to the final consumer.

EP592284 (Minnesota Mining and Manufacturing Company) relates to a tear resistant and stiff multilayer film comprising interdigitated layers of a ductile polymeric material, a stiff polymeric material and an optionally inserted intermediate material. Useful stiff materials are polyesters. The individual layers of stiff polyester or copolyester typically have an average nominal thickness of at least about 0.5 microns, more preferably from greater than 0.5 microns to 75 microns and, most preferably, from about 1 to 25 microns. Useful ductile materials include ethylene copolymers, polyesters (PET, PETg), polyamide, and polyurethanes. According to the specification, ductile material loading up to about 10 to 20 weight % may be used although exceeding this range may reduce the tear resistance of films made therewith. This document does not discuss shrinking properties of the final film or possible resulting tray distortion problems in packaging applications.

These films are useful in a wide variety of products, including, for example, sign faces and backings for coated abrasive articles, particularly as security control laminates for shatter-proofing glazing members against impact or explosions.

These films may be oriented and, optionally, heat set according to standard methods. The actual heat set temperature and time will vary depending on the composition of the film and its intended application but should not be selected so as to substantially degrade the tear resistant properties of the film.

A further drawback of some polyester films disclosed in the state of the art concerns the manufacturing process, in particular the drying step needed before blending hygroscopic polyester resins such as PET and PETg before the extrusion process. The temperatures to be applied for an effective drying are different for the two resins: about 150°C for PET and about 70°C for PETg. As a consequence, in order to avoid sticking of the resins and related problems of dosage and feeding, it becomes mandatory to cool down PET before mixing with PETg. This further cooling step adds up costs, procedural steps and equipment, so the use of resins in alternate layers rather than in admixture can be economically and operatively advantageous.

There is still a need in the art for a polyester film having high tear resistance and low shrink tension properties to make it suitable for packaging applications, in particular for tray lidding application in both ready meals and case ready applications; which is transparent; which can withstand both microwave cooking procedures and conventional oven temperatures and which has reduced environmental impact due to lower amount of material used and to higher recyclability of a fully polyester article. Said fully polyester oriented films showing improved tear resistance properties are characterized by good machinability and reduced "skeleton break" problems. Furthermore fully polyester low shrink tension films, when used in packaging applications, would not distort the package. Finally, the use of alternating resins not requiring a blending process brings to many economic and operative advantages.

Brief description of drawings

FIG. 1 is a cross-sectional view of a multilayer film 1 according to the present invention.

FIG. 2 is a detailed perspective view of a layer-multiplier which may be used for manufacturing the present films. FIG. 3 is a scheme of a process for making the multilayer film 1 shown in FIG. 1 , including a layer-multiplier module 21.

Description of the invention

We have now found that a fully polyester based oriented film comprising at least a multiplied layer shows higher tear resistance and lower shrink tension properties.

Therefore the object of the present invention is an oriented fully polyester based multilayered film comprising at least one non-multiplied layer and at least one multiplied layer, said multiplied layer comprising a microlayer sequence having a number n of identical repeating units, each unit comprising the microlayer sequence A/B/ and optionally C, wherein A, B and C, if present, are polyester alternating resins, wherein A and C are equal or different and both are different from B, and n is an integer of 3 or more, wherein the thickness of each microlayer within the multiplied layer of the multilayer film is lower than 0.5 μίη, preferably lower than 0.4 μίπ.

Preferably the thickness of each microlayer within the multiplied layer of the multilayer film is higher than 0.03 μίη and lower than 0.5 μίτι, preferably higher than 0.05 μίτι and lower than 0.4 μίπ

Preferably the oriented fully polyester based multilayered film of the present invention comprises two outer non- multiplied layers and an inner-multiplied layer.

Preferably the repeating unit comprises the microlayer sequence A/B/C, more preferably it consists of the sequence A/B/C. Preferably A and C are equal.

The polyester based oriented film according to the present invention shows higher tear resistance properties compared with the same non-multiplied film. In addition such multilayer film comprising a multiplied layer shows shrink tension and shrink force properties unexpectedly lower than the non-multiplied films having a comparable composition, in terms of resin kind and percentage by weight, and thickness: this is really advantageous in packaging applications such as wrapping and tray lidding, particularly in both ready meals and case ready tray lidding applications, to avoid tray distortion during the packaging and post-packaging processes. Said fully polyester downgauged films, showing improved tear resistance properties, are characterized by good machinability and reduced "skeleton break" problems.

As used herein, the term "polyester" refers to both homo- and co-polyesters, wherein homo-polyester are defined as polymers obtained from the condensation of one dicarboxylic acid with one diol and co-polyesters are defined as polymers obtained from the condensation of one or more dicarboxylic acids with one or more diols

The term "multiplied" referred to a film or sheet means a film or a sheet having a comparable total composition and thickness of a conventional coextruded structure but comprising a greater number of very thin layers, i. e. till hundred or more microlayers, instead of the small number of layers of standard thickness, as the films defined for instance in WO2009095231.

As used herein the term "outer non-multiplied layer" means the layer that is not multiplied and has only one of its principal surfaces directly adhered to another layer of the film.

As used herein the term "inner layer" refers to a film layer having both its principal surfaces directly adhered to another layer of the film.

As used herein the term "inner-multiplied layer" refers to an inner layer comprising the multiplied sequence of microlayers according to the present invention.

As used herein the term "intermediate layer" refers to an inner layer having one of its surfaces adhered to one

"outer non-multiplied layer" and the other surface adhered to the "inner-multiplied layer".

As used herein the term "orientation" refers to the process of solid state orientation carried out at a temperature higher than the highest T_g (glass transition temperature) of resins making up the majority of the structure and lower than the temperature at which at least some of the resins making up the structure are not in the molten state. The orientation may be mono-axial, either longitudinal or transversal or bi-axial.

As used herein the term "longitudinal", herein abbreviated (L), refers to a direction along the length of the film, i.e. in the direction of extrusion or coating of the film.

As used herein the term "transversal", herein abbreviated (T), refers to the direction across the film, perpendicular to the longitudinal direction.

As used herein, the term "coextrusion" and "extruded sheet" refers to two or more thermoplastic polymeric materials which are brought together from a plurality of extrusion means and placed in contact with one another prior to their exit through an extrusion die to form the extruded film.

As used herein, the term "peelable" refers to a film which, after having been sealed on to a substrate, can be easily removed by peeling off.

As used herein the term "peelable seal" refers to a seal which is strong enough to guarantee the hermeticity of the package during its life-cycle but which can be easily opened by tearing apart by hand the two materials that were joined by the seal. A method of measuring the force of a peelable seal, also referred to as "peel force" is described in ASTM F-88-00. Acceptable peel force values generally range from 200 g/25 mm to 850 g/25 mm, from 300 g/25 mm to 830 g/25 mm, from 350 g/25 mm to 820 g/25 mm, from 400 g/25 mm to 800 g/25 mm. The films according to the present invention can be peelable or not peelable depending on the intended use. The fully polyester films object of the present invention can be shrinkable or not depending on the intended use in particular said film can be non-shrinkable or low shrinkable for ready meals application and shrinkable for case ready application.

Typically, for tray lidding applications, the films of the present invention have no or negligible shrink at temperatures below 140°C. The shrink (in each direction) is generally at most 15% at temperatures below 100°C, below 120°C, and even below 140°C.

Usually the shrink (in each direction) does not exceed 20% over the common heat-sealing temperature range of polyester films, namely in the range of from 140 to 200°C. The shrink (in each direction) generally does not exceed 20% (in each direction) at 180°C, at 160°C and at 150°C.

The polyester film object of the present invention can be used as lidding films in particular for ready meals and case ready containers; preferably packaging system comprises a heat-sealable container having said film sealed onto it.

Alternatively the present polyester film can be used in wrapping applications. Typically, for wrapping applications, the films of the present invention show at least 20%, at most 40% of shrink in each direction at 140°C. The shrink (in each direction) is generally comprised between 20% and 30% at 140°C in each direction.

Therefore is a further object of the present invention a package comprising a heat-sealable container and said fully polyester based multilayer film, according to the present invention, sealed onto or wrapped around to it. Said heat-sealable container is preferably a tray, preferably a rigid tray, and comprises a base or bottom portion of any desired shape, for example rectangular, squared, circular, oval, etc. The tray can be a mono-layer or a multi-layer structure, foamed, partially foamed or solid and can be made of any suitable material. Examples of suitable materials for said container are styrene-based polymers, such as polystyrene and high impact polystyrene, polypropylene, high density polyethylene, polyesters, such as polylactate, polyethyleneterephthalate and polyethylenenaphthalenate homo- and co-polymers, polyvinylchloride, acrylic polymers, polycarbonates and the like.

Furthermore another object of the present invention is the use of the film according to the present invention in a packaging system comprising a heat-stable container having said film sealed onto or wrapped around it.

A preferred embodiment is the use of the film according to the present invention as lidding film in a packaging system comprising a heat- stable container having said film sealed onto it.

The polyesters used in the present invention are clear amorphous thermoplastic polymers and crystalline thermoplastic polymers that can be sheet extruded. Preferably the polyesters used in the present invention contain ethylene units and include, based on the dicarboxylate units, at least 90 mol%, more preferably 95 mol%, of terephthalate units. The remaining monomer units are selected from other dicarboxylic acid or diols. Suitable other aromatic dicarboxylic acids are isophthalic acid, phthalic acid, 2,5-, 2,6-or 2,7-naphthalenedicarboxylic acid; cycloaliphatic dicarboxylic acids such as cyclohexane dicarboxylic acids, preferably cyclohexane-1 ,4-dicarboxylic acid; aliphatic dicarboxylic acids such as C3-C19 alkanedioic acids, preferably succinic acid, sebacic acid, adipic acid, azelaic acid, suberic acid or pimelic acid. Suitable other aliphatic diols are aliphatic diols such as ethylene glycol, triethylene glycol, propylene glycol, 1,3-butane diol, 1 ,4-butane diol, 1 ,5-pentane diol, 2,2-dimethyl-1 ,3- propane diol, neopentyl glycol and 1,6-hexane diol; cycloaliphatic diols such as 1 ,4-cyclohexanedimethanol and 1 ,4-cyclohexane diol; optionally heteroatom-containing diols having one or more rings. Preferably the polyester used in the present invention are selected from polyethylene terephthalate (PET), polylactic acid (PLA) derivatives, polyethylene terephthalate - glycol (PETg), polycaprolactone (PCL), polyesteramides (PEA), polyhydroxyalkanoates such as polyhydroxybutyrate (PHB), polyhydroxybutyrate-co-hydroxyvalerate (PHBHV), polyhydroxybutyrate-co-hydroxyhexanoate (PHBHx), polyhydroxybutyrate-co-hydroxyoctanoate (PHBHO), polyhydroxybutyrate-co-hydroxyoctadecanoate (PHBHOd); aliphatic polyesters and copolyesters such as polybutylenenesuccinate (PBS), polybutylene-succinate-adipate (PBSA); aromatic copolyesters such as polybutylene-adipate-co-terephthalate (PBAT) or mixture thereof.

Preferably the film object of the present invention comprises at least one non-multiplied layer and at least one multiplied layer comprising a microlayer sequence A/B/C wherein A and C are equal.

The film object of the present invention can also contain some enhancers of peelability such as polyamides, polystyrenes, in particular styrene-butadiene block copolymers, ionomers, ethylene/unsaturated carboxylic acid copolymers such as ethylene-acrylic acid copolymer (EAA) or ethylene/methacrylic acid copolymers, ethylene/propylene copolymers and ethylene/cyclic olefin copolymers such as ethylene/norbornene copolymers, or mixture thereof. Preferably EAA is used. A specific example of particularly preferred enhancer of peelability thermoplastic resin is Primacor 3440, sold by Dow, which is an ethylene/acrylic acid copolymer with a co- monomer content acrylic acid 9.7%. Preferably said enhancer of peelability is blended with other suitable resins within the non-multiplied layer.

The film object of the present invention can be made by alternating crystalline resins or by alternating a crystalline polyester resin and an amorphous polyester resin or by alternating amorphous polyester resins. Preferably the film object of the present invention is made by alternating a crystalline polyester resin and an amorphous polyester resin.

The crystalline polyesters used in the present invention are selected from polyethylene terephthalate (PET), polylactic acid (PLA) derivatives, polycaprolactone (PCL), polyesteramides (PEA), polyhydroxyalkanoates such as polyhydroxybutyrate (PHB), polyhydroxybutyrate-co-hydroxyvalerate (PHBHV), polyhydroxybutyrate-co- hydroxyhexanoate (PHBHx), polyhydroxybutyrate-co-hydroxyoctanoate (PHBHO), polyhydroxybutyrate-co- hydroxyoctadecanoate (PHBHOd); aliphatic polyesters and copolyesters such as polybutylenenesuccinate (PBS), polybutylene-succinate-adipate (PBSA); aromatic copolyesters such as polybutylene-adipate-co- terephthalate (PBAT) or mixture thereof; preferably crystalline polyethylene terephthalate (PET) and its copolyesters are used. Specific examples of suitable crystalline PET are Eastapak Copolyester 9921 , sold by Eastman and Ramapet N180 sold by Indorama

The amorphous polyesters used in the present invention are selected from polyethylene terephthalate (PET), polylactic acid (PLA) derivatives, polyethylene terephthalate - glycol (PETg), polycaprolactone (PCL), polyesteramides (PEA), polyhydroxyalkanoates such as polyhydroxybutyrate (PHB), polyhydroxybutyrate-co- hydroxyvalerate (PHBHV), polyhydroxybutyrate-co-hydroxyhexanoate (PHBHx), polyhydroxybutyrate-co- hydroxyoctanoate (PHBHO), polyhydroxybutyrate-co-hydroxyoctadecanoate (PHBHOd); aliphatic polyesters and copolyesters such as polybutylenenesuccinate (PBS), polybutylene-succinate-adipate (PBSA); aromatic copolyesters such as polybutylene-adipate-co-terephthalate (PBAT) or mixture thereof; preferably polyethylene terephthalate - glycol (PETg) is used. Preferred amorphous polyester resins for use in the present invention are co-polyesters of an aromatic dicarboxylic acid, preferably terephthalic acid, with an aliphatic diol and a cycloaliphatic diol, preferably ethylene glycol and 1 ,4-cyclohexanedimethanol. The preferred molar ratios of the cycloaliphatic diol to the aliphatic diol are in the range from 10:90 to 60:40, preferably in the range from 20:80 to 40:60, more preferably from 30:70 to 35:65. Specific examples of amorphous polyesters are PETG Eastar® 6763 sold by Eastman and Embrace sold by Eastman Chemical, (glass transition temperature 70.6°C, density 1.32 g/cc).

More preferably the crystalline and amorphous polymers used in the present invention are PET and PETg.

Preferably the non-multiplied layer is made of a polyester selected from PET, PETg, polycaprolactone (PCL), polyesteramides (PEA), polyhydroxyalkanoates such as polyhydroxybutyrate (PHB), polyhydroxybutyrate-co- hydroxyvalerate (PHBHV), polyhydroxybutyrate-co-hydroxyhexanoate (PHBHx), polyhydroxybutyrate-co- hydroxyoctanoate (PHBHO), polyhydroxybutyrate-co-hydroxyoctadecanoate (PHBHOd); aliphatic polyesters and copolyesters such as polybutylenenesuccinate (PBS), polybutylene-succinate-adipate (PBSA); aromatic copolyesters such as polybutylene-adipate-co-terephthalate (PBAT) or mixture thereof. More preferably the non- multiplied layer is made of a major proportion of PETg. Preferably the non-multiplied layer optionally contains an antiblock aid such as antiblock silica in polyethylene terephthalate-glycol (PETg MB).

As used herein, the term "major proportion" refers to a percentage per weight of resin higher than 50%, preferably higher than 70%, more preferably comprised between 80% and 100%.

Still more preferably the film object of the present invention comprises a non-multiplied layer made of a major proportion of PETg and a multiplied layer, with the microlayer sequence A/B/C wherein A and C are PETg and B is PET.

The film object of the present invention optionally comprises another outer non-multiplied layer which is made of a polyester selected from PET, PETg, polycaprolactone (PCL), polyesteramides (PEA), polyhydroxyalkanoates such as polyhydroxybutyrate (PHB), polyhydroxybutyrate-co-hydroxyvalerate (PHBHV), polyhydroxybutyrate-co- hydroxyhexanoate (PHBHx), polyhydroxybutyrate-co-hydroxyoctanoate (PHBHO), polyhydroxybutyrate-co- hydroxyoctadecanoate (PHBHOd); aliphatic polyesters and copolyesters such as polybutylenenesuccinate (PBS), polybutylene-succinate-adipate (PBSA); aromatic copolyesters such as polybutylene-adipate-co- terephthalate (PBAT) or mixture thereof, preferably said other outer non-multiplied layer is made of a major proportion of PET; preferably the other outer non-multiplied layer optionally contains an antiblock aid such as antiblock silica in polyethylene terephthalate-glycol (PETg MB), the two outer non-multiplied layer may be made of the same or different polyester composition.

One of the two outer non-multiplied layers, being the sealant, can also contain some enhancers of peelability such as polyamides, polystyrenes, in particular styrene-butadiene block copolymers, ionomers, ethylene/unsaturated carboxylic acid copolymers such as ethylene-acrylic acid copolymer (EAA) or ethylene/methacrylic acid copolymers, ethylene/propylene copolymers and ethylene/cyclic olefin copolymers such as ethylene/norbornene copolymers, or mixture thereof. Preferably EAA is used.

The multilayer film object of the present invention optionally comprises at least one further intermediate layer between the non-multiplied layer and the multiplied layer, which is made of a polyester selected from polyethylene terephthalate (PET), polylactic acid (PLA) derivatives, polyethylene terephthalate - glycol (PETg), polycaprolactone (PCL), polyesteramides (PEA), polyhydroxyalkanoates such as polyhydroxybutyrate (PHB), polyhydroxybutyrate-co-hydroxyvalerate (PHBHV), polyhydroxybutyrate-co-hydroxyhexanoate (PHBHx), polyhydroxybutyrate-co-hydroxyoctanoate (PHBHO), polyhydroxybutyrate-co-hydroxyoctadecanoate (PHBHOd); aliphatic polyesters and copolyesters such as polybutylenenesuccinate (PBS), polybutylene-succinate-adipate (PBSA); aromatic copolyesters such as polybutylene-adipate-co-terephthalate (PBAT) or mixture thereof. Preferably the intermediate layer is made of PET.

The number n of identical repeating unit, each comprising the microlayer sequence A/B and optionally C, wherein A and C, if present, are equal or different and both are different from B, is from 3 to 400, preferably from 6 to 100, more preferably from 8 to 32, even more preferably from 14 to 18.

The total number of microlayers in the multiplied layer is preferably lower than 500, more preferably lower than 300, even more preferably lower than 100, still more preferably lower than 50.

The total thickness of the multilayer film object of the present invention is preferably of from about 10 μίη to about 100 μιτι; preferably of from about 15 μίτι to about 50 μίτι.

The thickness of each microlayer within the multiplied layer of the multilayer film object of the present invention is preferably lower than 0.5 μίτι, more preferably lower than 0.4 μίπ.

The thickness of each microlayer within the multiplied layer of the multilayer film object of the present invention is preferably higher than 0.03 μίτι, more preferably higher than 0.05 μίτι.

The thickness of each microlayer within the multiplied layer of the multilayer film object of the present invention is preferably higher than 0.03 μίτι and lower than 0.5 μίτι, more preferably higher than 0.05 μίτι and lower than 0.4 μίτι.

In the film of the present invention, the total amount of each single resin A, B and C, if present, with respect to the film total weight is preferably higher than 10%, more preferably higher than 20%, even more preferably higher than 30% by weight percentage.

The film object of the present invention is preferably formed by coextrusion of the layers of polymeric material. The film object of the present invention can be generally transparent, opaque, colored, for instance by addition of colored pigment additives, or printed as desired for intended end use.

The multilayered film object of the present invention can also optionally comprise at least one surface provided with antifogging properties. Typically, the antifogging surface is the surface on the heat-sealable layer, which is the surface directly facing the product in the container.

To obtain an antifogging surface antifogging agents may be compounded directly into the polyester resins of the heat-sealable layer before extrusion of the film object of the present invention. Suitable antifogging agents are for instance non-ionic fluorinated surfactants such as alkylester fluorides, perfluoroalkyl ethylenoxides, anionic fluorinated surfactants, such as quaternary ammonium salt of perfluoroalkyl sulfonates, non-ionic surfactants such as polyhydric alcohol fatty acid esters, higher fatty acid amines, higher fatty acid amides and ethylene oxide adducts of higher fatty acid amines or amides and the like, polyoxyethylene ether of a fatty alcohol, glycerol fatty acid ester, preferably polyhydric alcohol fatty acid ester and their ethoxylated derivatives, more preferably ethoxylated sorbitan derivatives with higher fatty acids such as those marketed under the trade name of Tweens or Polysorbates, preferably with fatty acids from C14 to C24, in particular ethoxylated sorbitan monooleate marketed as Tween 80 or ethoxylated sorbitan ester Atmer 116 commercialised by Croda. The amount of anti- fogging agent added to the heat-sealable layer is generally from 0.5 to 8%, from 1 to 5%, from 1 to 3%, preferably from 0.5% to 2.5% by weight of the heat-sealable layer.

Alternatively the antifogging agent may be in the form of a coating applied onto the heat-sealable non-multiplied outer layer. Conventional techniques can be used for the application of the antifogging agent to the heat-sealable layer such as for example gravure coating, reverse kiss coating, fountain bar coating or spraying.

The application of the antifogging agent may be carried out either by in-line method involving application during the manufacture or by off-line method involving the application after the manufacture of the film. The amount of the antifogging agent is not particularly limited, but it may be added in an amount of from about 0.1 mL/m² to 8 mL/m², preferably from about 0.5 mL/m² to 7 mL/m², more preferably from about 0.5 mL/m² to 5 mL/m².

Suitable antifogging agents for this application method can be selected from non-ionic surfactants such as polyhydric alcohol fatty acid esters, higher fatty acid amines, higher fatty acid amides, polyoxyethylene ethers of higher fatty alcohols and ethylene oxide adducts of higher fatty acid amines or amides. Preferably polyhydric alcohol fatty acid esters and their polyethoxylated derivatives, polyoxyethylene ethers of higher fatty alcohols and glycerin fatty acid esters are used, ethoxylated sorbitan derivatives with higher fatty acids such as those marketed under the trade name of Tweens or Polysorbates, preferably with fatty acids from C14 to C24, are more preferred, in particular ethoxylated sorbitan monooleate marketed as Tween 80 or ethoxylated sorbitan ester Atmer 116 commercialised by Croda.

Preferably spray-coating technique is used to obtain antifogging surface of the film object of the present invention. In the film of present invention any other additive or aid commonly used in the art of multilayer plastic films may be added if desired or needed.

Orientation ratios of the film object of the present invention is of at least 3:1 in both longitudinal (L) and transversal (T) directions; orientation can be done either sequentially or simultaneously, typically on a tenterframe type stretching equipment.

In a preferred embodiment of the present invention, the oriented fully polyester based multilayer film is a three- layer film wherein one outer non-multiplied layer is made of a major proportion of polyethylene terephthalate glycol modified (PETg); the inner-multiplied layer comprises a microlayer sequence having a number n of identical repeating units each comprising the microlayer sequence A/B/C, wherein A and C are PETg, B is PET and n is an integer of 3 or more, preferably 4, 8, 16 or 32 and the other outer non-multiplied layer is made of a major proportion of polyethylene terephthalate (PET).

In a further preferred embodiment of the present invention, the oriented fully polyester based multilayer film is a five-layer film wherein one outer non-multiplied layers is made of a major proportion of polyethylene terephthalate glycol modified (PETg); the other outer non-multiplied layer is made of a major proportion of polyethylene terephthalate (PET); the two intermediate layers are made of polyethylene terephthalate (PET), and the inner-multiplied layer comprises a microlayer sequence having a number n of identical repeating units each comprising the microlayer sequence A/B/C, wherein A and C are PETg, B is PET and n is an integer of 3 or more, preferably 4, 8, 16 or 32.

A still more preferred embodiment of the present invention is the oriented fully polyester based multilayer film wherein the multiplied layers comprises a microlayer sequence having a number n of identical repeating units each comprising the microlayer sequence A/B/C, made of alternating crystalline polyester and amorphous polyester. Preferably the crystalline polyester is PET and the amorphous polyester is PETg.

Referring now to FIG. 1, a preferred film 1 in accordance with the present invention comprises one outer non- multiplied layer 11 made of a major proportion of polyethylene terephthalate glycol modified (PETg); another outer non-multiplied layer 12 made of a major proportion of polyethylene terephthalate (PET); two intermediate layers 13 and 14 made of polyethylene terephthalate (PET), and the inner-multiplied layer comprising a microlayer section 15, said microlayer section having twenty-five (25) microlayers 16 (this number is for illustration purposes only).

"Microlayers" 16 are thin, generally very thin, in relation to conventional layers, such as for instance the intermediate layers 13 or 14. This relationship may be expressed mathematically, e.g., as a ratio, given that each of the microlayers 16 and conventional layers have a thickness. In accordance with the present invention, the ratio of the thickness of any of the microlayers 16 to the thickness of conventional layers is at least about 1 :2, such as at least about 1:3, 1:4, 1:5, 1:6, 1 :7, 1:8, 1 :9, 1 :10, 1 :11 , 1 :12, 1 :13, 1 :14, 1 :15, 1 :16, 1 :17, 1 :18, 1 :19, 1 :20, etc., for example ranging from 1 :2 - 1:50, 1 :3 - 1 :40, 1 :4 - 1 :35, 1 :5 - 1 :30, etc. The multilayer film object of the present invention can be "non-shrinkable", "low-shrinkable" or "shrinkable" depending on the final use.

The shrink level is obtained by acting on the temperatures and relaxation in the last zones (heat setting or annealing zones) of the tenterframe oven.

The process to obtain the multilayered film object of the present invention comprises the following steps:

a) The three alternating inner layers were coextruded through a "top" three-layer feedblock b) Said three layers were multiplied to 3 x n microlayers using a layer multiplier

c) Said 3 x n microlayers entered - as central layers - a "bottom" feedblock, where adjacent intermediate layers, sealant and skin layers were coextruded together with the alternating sequence by passing the molten flow corresponding to the desired alternating sequence into a suitable feedblock and then through a suitable coextrusion die.

d) The whole layers were then distributed to their final width using a flat coextrusion die.

e) The melt coming out from the die was quenched onto a chill roll; electrostatic pinning system was used to favor the intimate contact between melt and chill roll.

f) The so formed cast was then oriented in the longitudinal direction, through an MDO (Machine Direction Orientation) equipment, at a ratio of from 3.0:1 to 5.0:1. MDO temperatures used were from about 70°C to about 100°C (for preheating), from about 80°C to about 100°C (for stretching), from about 80°C to about 110°C (for annealing), at about 38°C (for cooling).

g) The mono-oriented materials were then oriented in the transversal direction, through a TDO (Transverse Direction orientation) equipment, at a ratio of from 3.0:1 to 5.5:1. TDO temperatures were from about 90°C to about 120°C (for preheating) and from about 90°C to about 130°C (for stretching). TDO annealing temperature varied from about 130°C to about 230°C depending on the desired final shrink properties. Biaxial orientation can be obtained by subsequent stretching steps or by using a simultaneous tenterframe such as LISIM™ line by Bruckner or a pantograph line such as a MESIM line™ by DMT/Andritz, but also conventional equipment can be used.

h) Bioriented films were then cooled, edge trimmed and wound into mill logs.

Preferably the multilayer film object of the present invention is coextruded.

Films in accordance with the present invention, e.g., as film 1 shown in FIG. 1 , may be produced using layer- multiplying technology, as well known in the art and disclosed, e.g., in U.S. Pat. Nos. 5,094,793 and 5,269,995. In particular the present films may be produced using a layer multiplier as illustrated in FIG.2.

In FIG. 2, layer-multiplier module 21 will be described in further detail. The combined two-layer polymer flow from extruders D1 and D2 (described below and shown in FIG. 3), flowing into and through feedblock 22, is represented by arrow 24. The layer-multiplier module 21 depicted in FIG. 2 is a four-channel type of multiplier, which divides the combined two-layer flow 24 from extruders D1/D2 into four branches 24a-d, via the four channels 26a-d, each of which has a respective entrance port 28a-d in communication with feedblock 22 to effect the 4-way division of flow 24. Each of the channels 26a-d leads the respective two-layer polymer flow 24a-d flowing therein to stacking/combining/expansion unit 30, which receives each of the flows 24a-d in a stacked configuration from respective channels 26a-d. Thus, as may be seen from FIG. 2, channels 26a-d convert flow 24 from a relatively wide, horizontal flow to a relatively narrow, vertical flow, with the two-layer D1/D2 flow 24b on top, followed thereunder by two-layer flow 24d, then two-layer flow 24a, and finally two-layer flow 24c on the bottom. Unit 30 receives the stacked flows 24a-d, combines them, then flattens them out again so that the resultant combined flow 24' flowing from the exit slot 31 has the same or similar flat shape as the original flow 24. As may be appreciated, however, whereas the original flow 24 had two juxtaposed layers D1/D2, the recombined flow 24' has eight (8) juxtaposed layers D1/D2/D1/D2/D1/D2/D1/D2.

In the illustrated embodiment, layer-multiplier module 21 has a first stage 32 and a second stage 34, which is essentially identical to first stage 32. As just described, at the end of the first stage 32, the flow 24' has eight juxtaposed polymer layers flowing in a relatively flat configuration out of exit slot 31. In second stage 34, this process is repeated, with flat flow 24' being divided into four branches and vertically stacked via the four illustrated channels 36a-d, then received, combined, and flattened out again by stacking/combining/expansion unit 38. In this manner, the resultant recombined flow 24" flowing from the exit slot 40 has the same or similar flat shape as the incoming flow 24'. However, whereas the incoming flow 24' had eight (8) juxtaposed layers D1/D2/D1/D2/D1/D2/D1/D2, the exiting flow 24" has thirty two (32) layers alternating between D1 and D2, i.e., 16 layers of polymer from extruder D1 interdigitated with 16 layers of polymer from extruder D2.

The 32-layer recombined polymer flow 24" that emerges from exit slot 40 of layer-multiplier module 21 is merged with the others layers from feedblocks (not shown) in a combining unit of a coextrusion die, to become the microlayer section 15 in the resultant multilayer film according to the present invention.

In FIG. 3 schematically illustrates a suitable extrusion system 46 for producing films according to the present invention as film 1 represented in FIG. 1. Extrusion system 46 may include a coextrusion die 48, a first extruder "A" to produce outer layers 11 and 12, a second extruder "B" to produce the intermediate layers 13 and 14, and fourth and fifth extruders "D1" and "D2" to produce microlayers 16. Coextrusion die 48 may include feedblocks 41 a, b to receive molten polymer from extruder A, feedblocks 42a, b to receive molten polymer from extruder B, and feedblock 22, along with layer-multiplier module 21 , to receive molten polymer from extruders D1 and D2.

In the illustrated embodiment, the output from extruder A is split, e.g., evenly, and travels through conduits 58a, b to simultaneously supply polymer to both feedblock 41a and 41b, such that the composition of the outer layers 11 , 12 is the same. Similarly, the output from the extruder B is split, e.g., evenly, via conduits 60a, b to form the intermediate layers 13, 14. The output from extruders D1 and D2 are directed via respective conduits 64, 66 into feedblock 22, in which they are combined to form a two-layer polymeric flow, i.e., in the form of two juxtaposed layers of molten polymer, which is then fed into the layer-multiplier module 21 as described above.

The feedblocks 41, 42 and layer-multiplier module 21 convert the molten polymer received from the associated extruders A, B, D1 and D2 into polymer layers, which are then gathered and combined by combining unit 70 to form the final multilayer film 1 , which emerges from unit 70 via die slot 72.

The invention further provides a package comprising a container and a film object of the present invention, said film being preferably a lid film. The surface of the container in contact with the product, i.e. the surface involved in the sealing, can comprise a polyester resin. The container can be made of a cardboard coated with polyester or can be integrally made of polyester resin obtaining a fully polyester made package which facilitates recycling operations.

In tray lidding applications, the package is produced by techniques known in the art, i.e. once the product to be packaged has been introduced into the container, the film object of the present invention is sealed onto the container by means of temperature and/or pressure using conventional techniques and equipment. The film is placed onto the container such that the outer heat-sealable layer of said film is in contact with the surface of the container, said outer heat sealable layer preferably comprising PETg. Sealing is carried out using conventional techniques at a temperature of from about 140°C to about 200°C, preferably from about 150°C to about 190°C at a pressure of from about 2 bar to about 10 bar, preferably, from about 4 bar to about 8 bar, for a time generally of from about 0.3 s to 2 s, preferably of from about 0.5 s to 1.0 s. The heat-sealable film object of the present invention is easily sealed to the container without distortion of said container to give a taut hermetically sealed lid. The portion of the film extending beyond the perimeter of the tray can be cut or used to peel off the film when needed.

Although in the present context the film object of the present invention will be described in more details in its preferred application for packaging of food products, all features are intended to be suitable for their application in packaging any products.

For the purpose of the present description and of the claims which follow, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term "about". Also, all ranges include any combination of the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein. Examples and comparative examples were evaluated by the methods described below.

% SHRINK: i.e. the percent dimensional change in a 10 cm x I0 cm specimen of film when subjected to a selected heat, has been measured following ASTM Standard Test Method D 2732, immersing the specimen for 5 seconds in a heated oil bath.

SHRINK TENSION: i.e. the force per original unit width developed by a film in the longitudinal (LD) or transversal (TD) direction at a specified temperature in its attempt to shrink while under restraint, has been measured by the following internal test method: a 25.4 mm wide strip of film is cut from the sample in the longitudinal or transverse direction. The force measurement is made by a load cell on which a clamping jaw is connected. Opposed to this jaw, a second one on which the specimen is fixed, can be adjusted in position by an external hand knob to pretension the specimen. The two jaws keep the specimen in the center of a channel into which an impeller blows heated air. In the air channels three thermocouples are fixed to measure the temperature. The temperature of the specimen, as measured by the thermocouples, is increased at a rate of about 2°C/second up to about 180°C and the force is measured continuously. The maximum value of the measured force is then divided by the specimen original width to obtain the shrink force and further divided by the thickness of the film sample to give the shrink tension. Typically the shrink tension is expressed in kg/cm².

TEAR PROPAGATION (ASTM -D1938): This test method covers the determination of the force necessary to propagate a tear in plastic films and thin sheeting. The specimens are cut both in the machine direction and in transverse direction and shall consist of strips 75 mm long by 25,4 mm wide and shall have a clean longitudinal slit 50 mm long. The two tongues of the specimens are secured to the two jaws of the testing machine (dynamometer), one of the two jaws being fixed and the other being allowed moving in the opposite direction. The load necessary to propagate the tear through the entire unslit 25 mm portion is then recorded and the average value of tear strength curve is calculated in g. Total thickness of the specimens, measured before starting the test, must also be reported.

The thickness of the non-multiplied layers are measured using the electronic microscope; the thickness of each microlayer of the multiplied sequence A/B/C is calculated by dividing the theoretical thickness, based on the flow exiting the extruder before entering the multiplier, by the number n of the multiplied sequence. For instance in table 1 below, the theoretical thickness for resin A, at the exit of the extruder, is 3.5 μίη, the number of the multiplied sequence n is 16, and so the thickness of each microlayer A in this structure is 3.5 / 16, that is 0.22 μίτι.

As used herein the term "layer ratio" refers to the ratio of a specific layer thickness compared to the total thickness of the film expressed as percentage.

The resins that have been used in the examples are the following:

Polyethylene Terephthalate/Glycol - PETg: EASTAR PETG 6763, Eastman Chemical, density (g/L): 1.27; MFI (g/10min): 2.8 (200°C, 5Kg); Brookfield viscosity (mPa-sec): 0.75; Tg (°C): 81.

Polyethylene Terephthalate - PET: EASTAPAK 9921 , Eastman Chemical, density (g/L): 1.4; Tm (°C): 255. AntiBlock Silica in Polyethylene Terephthalate/Glycol - PETg MB (Masterbatch): EASTAR 6763 C0235, Eastman Chemical, density (g/L): 1.29; ASH (10%): 10.

Ethylene/Acrylic Acid Copolymer - EAA: PRIMACOR 3440, DOW, density (g/L): 0,938 MFI (g/10min): 10 (190°C, 2.16 Kg); Comonomer content (%): 9.7; Vicat Temperature (°C): 76.

Example 1

A melt stream of a total 48 microlayers, repeating 16 times the sequence A/B/C where A and C are PETg and B is PET, was obtained by first co-extruding the resins through a three layer coextrusion feedblock apparatus and then feeding the multiplying devices. The outer non-multiplied layers and the intermediate layer, which polyester composition is reported below, are coextruded with the alternating sequence (A/B/C)i6 by passing the molten flow corresponding to the sequence (A/B/C)i6 into a feedblock and then through a coextrusion die. The whole layers were then distributed to their final width using a flat coextrusion die. The resultant melt coming out from the die was quenched into a chill roll. The resultant cast was then oriented through MDO equipment at a ratio of 3.0:1 , at temperatures of 79°C, for pre-heating, 94°C for annealing, and 38°C for cooling. The transversal orientation was then given through a TDO equipment, at a ratio of 4.5:1 at temperatures of about 90 - 110°C for pre-heating and 100 - 120°C for stretching and at 130-210°C for annealing.

In particular the structures of the Examples 1 , 2 and 3 were pre-heated at 102°C, stretched at 110°C and annealed at 190°C while the structures of the Examples 4 to 9 and 12 were pre-heated at 93°C, stretched at 110°C and annealed at 190°C. The structures of the Examples 10 and 11 were pre-heated at 102°C, stretched at 110°C and annealed at 148°C. The composition of the layer, the thickness and the layer ratio are reported in the following table 1.

Table 1

*Thickness based on the flow from the extruder before entering multiplier

Example 2

The procedure of Example 1 was repeated by decreasing the total thickness of the film maintaining the same layer ratios of example 1. The composition of the layer, the thickness and the layer ratio are reported in the following table 2. Table 2

Total film thickness

Example 3 (Comparative)

The comparative film 3 was prepared by following the same procedure as in examples 1 and 2 but excluding the multiplier so that the film contains a single core unit of blended resins instead of a sequence of 16 repeating unit A/B/C as in the examples 1 and 2. The compositions of the layers have been prepared by blending the resins and extruding them.

The core unit of the comparative film has the same percentage composition in PET and PETg (34% and 22%) of the corresponding multiplied films of examples 1 and 2 according to the present invention.

The composition of the layer, the thickness and the layer ratio are reported in the following table 3.

Table 3

Total film thickness = 33 μίη

The physical properties of representative films object of the present invention were evaluated as previously described.

The values of free shrink at different temperatures, shrink tension and tear propagation are reported in tables 4a, 4b and 4c respectively. Table 4a

Table 4b

Table 4c

The values of free shrink in oil (table 4a), shrink tension (table 4b) and tear propagation (table 4c) of the films prepared as described in examples 1 and 2 are compared with the values of shrink tension and tear propagation of the film prepared as described in in example 3.

Even showing the same value of free shrink in oil, it can be noticed that the shrink tension of the films according to the present invention are lower and tear propagation is higher than the shrink tension and the tear propagation measured for the comparative film. It is also surprising that even for the film described in example 2, which has a thickness of 25 μίη, these values are quite different from the comparative film.

The comparison clearly shows that the shrink tension of the film according to the present invention is remarkably lower than that of the comparative film and that the tear propagation of the film according to the present invention is significantly higher than that of the comparative film.

It is worth underlining that the difference in shrink tension and tear propagation with respect to comparative film is significant also for the film having a thickness of 25 μίη. Therefore downgauging is possible, i.e. to reduce the amount of the involved material still maintaining and, in this case, even improving the properties of the film. The following examples show the peelable structure of the films according to the present invention.

The procedure of example 1 was repeated by changing the layers' compositions and the total thickness of the films object of the present application as shown in the following examples 4, 5, 6, 7, 8, 9:

Example 4

The procedure of Example 1 was repeated and the composition of the layer, the thickness and the layer ratio are reported in the following table 5.

Table 5

Total film thickness

Example 5

The procedure of Example 1 was repeated and the composition of the layer, the thickness and the layer ratio reported in the following table 6.

Table 6

Total film thickness

B PET 16 4.6* 0.29

C PETG 11 3.1* 0.19 intermediate layer PET 11 3.3

Outer non-multiplied 98% PET+2% PETg MB 25

7.2

layer

Example 6

The procedure of Example 1 was repeated and the composition of the layer, the thickness and the layer ratio are reported in the following table 7.

Table 7

Total film thickness

Example 7

The procedure of Example 1 was repeated and the composition of the layer, the thickness and the layer ratio are reported in the following table 8.

Table 8

Total film thickness

Example 8

The procedure of Example 1 was repeated and the composition of the layer, the thickness and the layer ratio are reported in the following table 9.

Table 9

Total film thickness

Example 9

The procedure of Example 1 was repeated and the composition of the layer, the thickness and the layer ratio are reported in the following table 10.

Table 10

Total film thickness

Example 10

The procedure of Example 1 was repeated and the composition of the layer, the thickness and the layer ratio are reported in the following table 11. Table 11

Total film thickness = 25 μίη

Example 11

The procedure of Example 1 was repeated and the composition of the layers, the thickness and the layer ratio are reported in the following table 12. Total film thickness = 33 μίτι

Example 12 (Comparative)

The comparative film 12 was prepared by following the same procedure as in example 1 but excluding the multiplier so that the film contains a single core unit of blended resins instead of a sequence of 16 repeating unit A/B/C as in the previous examples. The compositions of the layers have been prepared by blending the resins and extruding them.

The core unit of the comparative film has the same percentage composition in PET and PETg (34% and 22%) of the corresponding multiplied films of examples 4 to 9 according to the present invention. The composition of the layer, the thickness and the layer ratio are reported in the following Table 13.

Table 13

Total film thickness = 33 μίη

The values of free shrink in oil, shrink tension and tear propagation of the peelable structures of the Examples 4, 5, 6, 7, 8 and 9 according to the present invention, of the peelable comparative structure of Example 12, and of the non-peelable structures of Examples 10 and 11 according to the present invention, are shown respectively in tables 13a, 13b and 13c.

Table 13a

Table 13b

Shrink Tension

(Kg/cm²)

thickness

(micron) LD TD

Example 12

(Comparative) 33 30 45 Example 4 33 14 26

Example 5 29 14 24

Example 6 25 14 26

Example 7 21 14 22

Example 8 17 14 26

Example 9 14 14 31

Table 13c

Tear Propagation (gf)

thickness

(micron) LD TD

Example 12

(Comparative) 33 11 9

Example 4 33 22 37

Example 5 29 20 30

Example 6 25 22 31

Example 7 21 13 19

Example 8 17 15 14

Example 9 14 14 13

It can be seen that the films of the present invention, while keeping almost the same or comparable values of free shrink, show remarkably lower shrink tension than that of the comparative film and that the tear propagation of the film according to the present invention is significantly higher than that of the comparative film.

Since the shrink tension is inversely proportional to the thickness of the film one could expect a higher shrink tension for the films of the present invention that are thinner compared to the comparative examples. The lower values of shrink tension are clearly due to the lower force exhibited by the films of the present invention.

Data clearly demonstrate that the tear propagation of thin peelable structures of examples 5 to 9, is significantly higher than that of the comparative film (Table 13c).

The properties shown in tables 4a, 4b, 4c, 13a, 13b and 13c clearly demonstrate the surprising characterizing features of the films according to the present invention. Said films, showing improved shrink tension (tables 4b and 13b) and tear propagation properties (tables 4c and 13c), allow for better machinability due to less frequent skeleton break. The films according to the present application also present lower environmental impact due to the lower thickness obtainable and to the fully polyester composition.

Claims

1) An oriented fully polyester based multilayered film comprising at least one non-multiplied layer and at least one multiplied layer, said multiplied layer comprising a microlayer sequence having a number n of identical repeating units, each unit comprising the microlayer sequence A/B/ and, optionally, /C, wherein A, B and C, if present, are polyester alternating resins, wherein A and C are equal or different and both are different from B, and n is an integer of 3 or more, wherein the thickness of each microlayer within the multiplied layer of the multilayer film object of the present invention is lower than 0.5 μίη, preferably lower than 0.4 μίπ.

2) The film according to claim 1 comprising two outer non-multiplied layers and one inner multiplied layer. 3) The film according to claims 1 or 2 in which each repeating unit comprises the sequence A/B/C, wherein A and C are equal.

4) The film according to claims 1 to 3 wherein the thickness of each microlayer within the multiplied layer is higher than 0.03 μίη and lower than 0.5 μίτι, more preferably higher than 0.05 μίτι and lower than 0.4 μίπ.

5) The film according to claims 1 to 4 wherein the total amount of each single resin A, B and C, if present, with respect to the film total weight is higher than 10%, preferably higher than 20%, more preferably higher than

30% by weight .

6) The film according to claims 1 to 5, wherein said polyesters are selected from polyethylene terephthalate (PET), polylactic acid (PLA) derivatives, polyethylene terephthalate - glycol (PETg), polycaprolactone (PCL), polyesteramides (PEA), polyhydroxyalkanoates such as polyhydroxybutyrate (PHB), polyhdroxybutyrate-co- hydroxyvalerate (PHBHV), polyhydroxybutyrate-co-hydroxyhexanoate (PHBHx), polyhydroxybutyrate-co- hydroxyoctanoate (PHBHO), polyhydroxybutyrate-co-hydroxyoctadecanoate (PHBHOd); aliphatic polyesters and copolyesters such as polybutylenenesuccinate (PBS), polybutylene-succinate-adipate (PBSA); aromatic copolyesters such as polybutylene-adipate-co-terephthalate (PBAT) or mixture thereof.

7) The film according to claims 1 to 6, wherein A and C are PET and B is PETg.

8) The film according to claims 1 to 7, wherein the said at least one outer non-multiplied layer is made of polyesters selected from polyethylene terephthalate (PET), polylactic acid (PLA) derivatives, polyethylene terephthalate - glycol (PETg), polycaprolactone (PCL), polyesteramides (PEA), polyhydroxyalkanoates such as polyhydroxybutyrate (PHB), polyhydroxybutyrate-co-hydroxyvalerate (PHBHV), polyhydroxybutyrate-co- hydroxyhexanoate (PHBHx), polyhydroxybutyrate-co-hydroxyoctanoate (PHBHO), polyhydroxybutyrate-co- hydroxyoctadecanoate (PHBHOd); aliphatic polyesters and copolyesters such as polybutylenenesuccinate (PBS), polybutylene-succinate-adipate (PBSA); aromatic copolyesters such as polybutylene-adipate-co- terephthalate (PBAT) or mixture thereof; preferably said outer non-multiplied layer is made of a major proportion of PETg.

9) The film according to claims 1 to 8, also comprising at least one intermediate layer made of polyesters selected from polyethylene terephthalate (PET), polylactic acid (PLA) derivatives, polyethylene terephthalate - glycol (PETg), polycaprolactone (PCL), polyesteramides (PEA), polyhydroxyalkanoates such as polyhydroxybutyrate (PHB), polyhydroxybutyrate-co-hydroxyvalerate (PHBHV), polyhydroxybutyrate-co- hydroxyhexanoate (PHBHx), polyhydroxybutyrate-co-hydroxyoctanoate (PHBHO), polyhydroxybutyrate-co- hydroxyoctadecanoate (PHBHOd); aliphatic polyesters and copolyesters such as polybutylenenesuccinate (PBS), polybutylene-succinate-adipate (PBSA); aromatic copolyesters such as polybutylene-adipate-co- terephthalate (PBAT) or mixture thereof; preferably said intermediate layer is made of PET.

10) The film according to claims 1 to 9 wherein said microlayer sequence A/B and, optionally, IC is made of alternating crystalline polyester resins or by alternating a crystalline polyester resin and an amorphous polyester resin or by alternating amorphous polyester resins, preferably is made of alternating crystalline polyester and amorphous polyester resins.

11) The film according to claims 1 to 10 having a total thickness of from about 10 μίη to about 100 μίη; preferably of from about 15 μίτι to about 50 μίτι.

12) The film according to claims 1 to 11 , wherein n is a value from 3 to 400, preferably from 6 to 100, more preferably from 8 to 32, even more preferably from 14 to 18.

13) The film according to claims 1 to 12 wherein said oriented fully polyester based multilayer film is a five- layer film wherein one outer non-multiplied layer is made of a major proportion of polyethylene terephthalate glycol modified (PETg); the other outer non-multiplied layer is made of a major proportion of polyethylene terephthalate (PET); the two intermediate layers are made of polyethylene terephthalate (PET), and the inner multiplied layer comprises a microlayer sequence having a number n of identical repeating units each comprising the microlayer sequence A/B/C, wherein A and C are PETg, B is PET and n is an integer of 3 or more; preferably n is 4, 8, 16 or 32.

14) Use of the film according to claims 1 to 13 as lidding or wrapping film in a packaging system comprising a heat-stable container.

15) A package comprising a heat-stable container and a film according to claims 1 to 13 sealed onto or wrapped around it.