The present invention relates to a film for packaging purposes, e.g. for food applications, medicines, and general merchandise products, and to a polymer and a polymer composition that can be used therein. More particular, the invention relates to a polymer film comprising one or more layers, and to a barrier film comprising a top layer, a base layer and a core layer interposed between the top layer and the base layer.

Films for general packaging purposes need to have some common properties like proper balance in rigidity and flexibility; sufficient mechanical strength, such as tear strength; sufficient protection of the product, e.g. punch resistance;

scratch resistance and non-sticking surface, provided by the top layer; sealing characteristics, e.g. thermal sealability, provided by the base layer.

Depending on specific applications, these films must further exhibit different combinations of properties, which might include: high barrier properties against oxygen, water and/or water vapor, aroma- and flavor molecules; printability; adhesion of labels; transparency; stretch ability; thermo-formable; steam sterilizable or retortable; thermally stability, i.e. not producing degradation products during the thermal treatment for one of the above treatments; and good organoleptic properties.

Films for such packaging purposes can be divided in 2 main groups.

The first group views on films that protect the product contained in certain extend while at the same time revealing the product. Such films have to be transparent while providing a barrier e.g. against moisture. The second group views on films where the requirements on barrier properties dominate, e.g. oxygen barrier, and where transparency is not an issue. Such latter films generally comprise a core layer that provides for such better barrier properties.

To comply with the different property requirements, packaging films generally consist of multiple layers consisting of different materials to enable the list of complementary properties. Such films are known in the art and comprise, for example, a PET top layer and a base layer of a PE containing material, such as EPDM, LDPE, LLDPE, or HDPE/PP. The films may also comprise a tie layer. Optionally, the films comprise a core layer consisting of an inorganic material or a metal, to provide the films with the required barrier properties.

In view of sustainability requirements it is preferred to make products, at least in part, from renewable raw materials. This is also valid for barrier films, and in particular those for food packaging. This is not an easy task in view of the other requirements that specialty packaging materials have to fulfill.

The main object of the present invention is to provide a film for packaging purposes, more particular a barrier film, at least partially made of renewable raw materials, meanwhile having a good balance in properties, as well as to provide a material that can be used therein.

The present invention in particular aims to provide a film for food applications, medicines, and general merchandise products, and to a polymer and a polymer composition that can be used therein. More particular, the invention relates to a barrier film comprising a top layer, a base layer and a core layer interposed between the top layer and the base layer.

This aim has been achieved with the films according to the invention, and with a semi-crystalline polyester that can be used in these films.

In a first embodiment, the invention provides a semi-crystalline polyester comprising repeat units derivable from an aromatic dicarboxylic acid and a short chain diol and 15 - 50 wt.% of residual units of a dimer fatty acid derivative.

In a second embodiment, the invention provides a polymer composition comprising the semi-crystalline polyester according to the invention, and at least one additive.

In a third embodiment, the invention provides a polymer film comprising at least a top layer or a base layer made of a semi-crystalline polyester or a polymer composition according to the invention.

In a fourth embodiment, the invention provides a barrier film comprising a top layer, a base layer, and a core layer interposed between the top layer and the base layer, wherein the top layer and/or the base layer consist of a semi- crystalline or a polymer composition according to the invention, and the core layer consists of an inorganic material or metal.

The effect of the films according to the invention and of the semi- crystalline polyester, respectively the polymer composition comprising the semi- crystalline polyester, used therein is not only that the films are partial green or renewable, i.e. at least part of the film composition is made of renewable raw materials, but also that the films combine good properties suitable for many applications including food packaging. The films have a relative low water vapor transmission rate, good mechanical strength and good puncture resistance, and is better thermo-oxidative resistant, stretchable and thermo-formable, compared to polyolefins. The films with the semi-crystalline polyester in the base layer have good organoleptic properties and are better sealable than polyesters. The films with the semi-crystalline polyester in the top layer exhibit good printability, and adhesion of labels. The polymer film made of the semi-crystalline polyester, respectively the polymer composition comprising the semi-crystalline polyester is optical transparent and is better UV absorbent (compared to LDPE). The barrier film has good oxygen barrier properties, while integrating the good properties of the base layer and/or the top layer comprising the semi-crystalline polyester. Moreover, both the top layer and the base layer in the barrier film, as well as the polymer film can be integrally made of the semi-crystalline polyester or polymer composition based thereupon, while showing a good balance in properties required for respectively the base layer and top layer. Meanwhile, this enhances the recyclability of the polymer film, respectively the barrier film.

The residual units of a dimer fatty acid derivative in the semi- crystalline polyester according to the present invention, and used in the films, may be units derived from a dimer fatty acid, a dimer fatty amine and/or a dimer fatty diol.

Dimer fatty acid can be represented by the following general formula:

HOOC-R-COOH

Herein R represents the biradical structure resulting from dimerization of the aliphatic chains of two fatty acid molecules. R is a predominantly aliphatic structure that can have a number of carbon atoms varying over a wide range. Suitably R comprises 20-48, preferably 30-40 carbon atoms.

It is noted that dimer fatty acid produced by dimerization of fatty acids always comprises some amount of trimerized fatty acid as well. This trimer fatty acid is herein understood to be part of dimer fatty acid. Dimer fatty amine and dimer fatty diol are products that can be are obtained from dimer fatty acid by chemical modification.

In the same way as for dimer fatty acid, dimer fatty amine can be represented by the following formula:

H2N-R-NH2

Analogously, dimer fatty diol can be represented by the following formula:

HO-R-OH

Herein R has the same meaning as for the dimer fatty acid.

It is noted that the number of carbon atoms in the aliphatic structure in the dimer fatty amines and dimer fatty diols is typically 2 more than in the dimer fatty acid from which the dimer fatty amines respectively the dimer fatty diols have been derived. These 2 extra carbon atoms result from reduction of the carboxylic groups to amine respectively alcohol groups.

The semi-crystalline polyester used in the films according to the present invention can be represented by the following formula

[A]m-[X-R-X]n,

wherein [X-R-X]n are residual units of the dimer fatty acid derivative, wherein X is CO, NH or O, and [A]n are repeat units of other components.

The residual units derived from dimer fatty acid, dimer fatty amine and dimer fatty diol are thus presented by the formulas

[CO-R-CO], respectively [NH-R-NH] and [0-R-O].

The semi-crystalline polyester suitably is a semi-crystalline semi- aromatic polyester comprising repeat units derivable from an aromatic dicarboxylic acid and a short chain diol. The aromatic dicarboxylic acid may be chosen, for example, from terephthalic acid and 2,6- naphthalene dicarboxylic acid. The short chain diol suitably comprises 2-6 carbon atoms, and preferably is chosen from ethylene glycol, 1 ,3-propylene glycol and 1 ,4-butanediol.

Preferably, the repeat units aromatic dicarboxylic acid and short chain diol consist of polyethyleneterephthalate (PET) or polyethylenenaphthalate (PEN).

The semi-crystalline polyester according to the invention may comprise, next to the dimer fatty acid derivative, the aromatic dicarboxylic acid and short chain diol, units of other constituents. Such constituents can be monofunctional constituents, such as mono-alcohols and mono-carboxylic acids, tri-functional and higher functional alcohols and carboxylic acids, aliphatic dicarboxylic acids and cyclo- aliphatic alcohols. The amount of such constituents will generally be limited, in order to allow for a high crystallinity in the semi-crystalline polyester. Preferably, the amount is in the range of 0-10 wt.%, more preferably 0-5 wt.%, relative to the total weight of the semi-crystalline polyester.

The repeat units derivable from aromatic dicarboxylic acid and short chain diol can be represented by the following formula:

{[CO-R'-CO]-[0-R"-0]}m,

wherein

R' is the aromatic backbone of the aromatic dicarboxylic acid, and

R" is the aliphatic backbone of the short chain diol. These repeat units are preferably present in an amount of 50 - 85 wt.%, relative to the total weight of the semi-crystalline polyester.

It is noted that the units derivable from aromatic dicarboxylic acid, and the units derivable from short chain diol do not need to be present in equimolar amounts. The amounts can deviate from equimolarity for example by the presence of alcohol constituents other than the short chain diol, or by the presence of dicarboxylic acid constituents other than the aromatic dicarboxylic acid.

More preferably, this amount of repeat units derivable from aromatic dicarboxylic acid and short chain diol is in the range of 60-80 wt.%, whereas the amount of residual units of a dimer fatty acid derivative is in the range of 20-40 wt.%, relative to the total weight of the semi-crystalline polyester. This provides the best balance in properties needed for the top layer and the base layer, in case the films according to the invention comprises both a top layer and a base layer comprising the same semi-crystalline polyester.

In case the films according to the invention comprise both a top layer and a base layer comprising different semi-crystalline polyesters, the semi-crystalline polyester in the base layer preferably comprises a higher content of residual units of dimer fatty acid derivative than the semi-crystalline polyester in the top layer.

Preferably, in the semi-crystalline polyester in the base layer, the dimer fatty acid derivative is present in an amount of 30- 50 wt.%, relative to the total weight of the semi-crystalline polyester. Such a higher amount is positive for the sealing properties. Also preferably, in the semi-crystalline polyesters in the top layer, the dimer fatty acid derivative is present in an amount of 15 - 35 wt.%, relative to the total weight of the semi-crystalline polyester. Such a lower amount is positive for the scratch resistance and puncture resistance of the film.

The semi-crystalline polyester according to the present invention can be prepared by conventional processes applied for preparing polyesters.

The invention also relates to a polymer composition comprising a semi-crystalline polyester according to the present invention and at least one other component. The other component may be another polymer or an additive. The semi- crystalline polyester according to the invention may be compounded together with other polymers. The other polymer is preferably present in an amount in the range of 0- 25 wt.%, preferably 0-10 wt.% is relative tot the total weight of the polymer composition. Such composition suitably contains the usual additives comprised by films for packaging applications, for example heat stabilizers, UV stabilizers, antistatic agents, flame retardants, lubricants and mould release agents. The polymer composition suitably contains stabilizers for the stabilization of polyesters, and/or stabilizers used typically in polyolefines. The additive or additives are suitably present in a total amount in the range of 0 - 10 wt.%, preferably 0.1 - 2 wt.%. Herein the wt.% is relative tot the total weight of the polymer composition.

If the polymer composition is used for transparent films, the additives are suitably selected from materials that have very fine particles and are used in limited amount only, in order not to detract or only in very limited amount of the transparency of the semi-crystalline polyester.

The polymer composition according to the invention can be produced by conventional processes applied fort making thermoplastic polymer products, for example by melt mixing and extrusion.

The semi-crystalline polyester and the polymer composition according to the invention are suitably used in films, such as polymer films and barrier films, for packaging of food, medicines and general merchandise products.

The invention also relates to a polymer film. The film according to the invention can consist of a monolayer, or may comprise multiple layers including a top layer and a base layer as separately discernable layers. In case of a monolayer the top layer and base layer are considered to be integrated as one single layer in the monolayer.

In the film according to the invention, at least a top layer or a base layer is made of, or comprises a semi-crystalline polyester or polymer composition according to the invention, or a preferred embodiment thereof, as described here above.

The film according to the invention comprising multiple layers may comprise a tie layer between the top layer and the base layer, but not necessarily so.

In a specific embodiment, both the top layer and the base layer comprise a semi-crystalline polyester as according to the invention. Preferably, the top layer and the base layer are made of different semi-crystalline polyesters or different polymer compositions according to the invention, wherein the semi-crystalline polyester comprised by the base layer has a higher content in dimer fatty acid derivative than the semi-crystalline polyester comprised by the top layer. Such a film is preferably made as a 2-layer film by co-extrusion. Such a process results in good adhesion between the two layers without the use of a tie layer. The polymer film consisting of a monolayer or comprising both a top layer and base layer made of the semi-crystalline polyester according to the invention or a composition based thereupon, suitably is a biaxially stretched film. Such a stretched film can be produced by a process comprising a biaxially stretching step.

The invention also relates to a barrier film. This barrier film comprises a top layer, a base layer, and a core layer interposed between the top layer and the base layer, wherein the core layer consists of an inorganic material or metal. Herein either the top layer or the base layer, or both, consists of a semi-crystalline polyester or polymer composition according to the present invention, or a preferred embodiment thereof as described above.

The metal in the core layer suitably consists of aluminum. The aluminum may be, for example, a film, a, or a vapor deposition layer.

Instead of metal, an inorganic material may be used in the core layer. The inorganic material suitably consists of aluminum oxide (alumina, AI203) or a silicon oxide (SiOx).

Between the top layer and the core layer, and/or between the base layer and the core layer, an adhesion layer, i.e. a layer of an adhesive material, may be present, but not necessarily so. Because of the nature of the semi-crystalline polyester, an adhesion layer is not necessary to achieve good adhesion with the core layer.

Preferably, the top layer and the base layer are made of different semi-crystalline polyesters or different polymer compositions according to the invention, wherein the base layer has a higher content in dimer fatty acid derivative. Such a film is preferably made as a 2-layer by co-extrusion. Such a process results in good adhesion between the two layers without the use of a tie layer.

The films according to the invention may have a thickness varying over a wide range, for example in the range of 10-250 μηη.

The monolayer polymer film preferably has a thickness in the range of 10-150 μηη, more preferably 20-100 μηη.

The multilayer polymer film and the barrier film preferably have a thickness in the range of 25 - 250 μηη, more preferably 50-200 μηη.

The individual layers in these films suitably have a thickness in the following ranges: top layer: 10-125 μηη, preferably 20-50 μηη; the base layer: 10-125 μηη, preferably 20-50 μηη; and the core layer 2 - 250 μηη , preferably 5 - 100 μηη, more preferably 10-50 μηη.

The invention also relates to a process for making the barrier film. In one embodiment, the process comprises steps wherein

an inorganic material or a metal is vapor deposited onto a polymer film made of a first semi-crystalline polyester or a composition based thereupon,

a layer of a second semi-crystalline polyester, or a composition based thereupon, is extruded or laminated onto the vapor deposited layer.

The polymer film made of the first semi-crystalline polyester or composition based thereupon may be produced separately, or the production thereof may be integrated in the process for making the barrier film, for example by means of an additional extrusion step.

In another embodiment, the process for making the barrier film comprises one or more processing steps wherein

a first layer of a first semi-crystalline polyester, or a composition based thereupon, is extruded or laminated onto one side of a metal foil;

a second layer of a second semi-crystalline polyester, or a composition based thereupon, is extruded or laminated onto the other side of the metal foil.

The first and second layer my be applied by successive extrusion steps, or by simultaneous or co-extrusion steps.

Optionally, the metal layer or metal foil is provided with a layer of an adhesive material, prior to extrusion or lamination of a layer of semi-crystalline polyester onto it, or during co-extrusion.

In these embodiments, for the first semi-crystalline polyester and/or the second first semi-crystalline polyester, a semi-crystalline polyester according to the present invention is used.

The invention also relates to the use of the polymer film and the barrier film according to the invention, or any modification or preferred embodiment thereof, for packaging of food, medicines, and general merchandise products.

The invention also relates to a packaging assembly comprising a packed item in a packaging material, wherein the packaging material comprises a polymer film or a barrier film according the present invention. Suitably, the packed item in the said packaging assembly is a food product, a medicament, or a general merchandise product.

The invention is further illustrated with the following examples.

Barrier performance of two materials was determined: a PET copolymer comprising 15 wt.% dimer diol, and PBT copolymer comprising 35 wt.% dimer fatty diol. Films of these two materials were prepared with thickness 43 micrometer [PET + 15% diol] and 120 micormeter [PBT + 35% diol].

Oxygen barrier performance of these films was determined according to ASTM D3985 at 23°C and 0% RH (relative humidity). Water permeability was measured according to ISO 15106-3 at 23°C and 0 / 50 % RH. Carbondioxide permeability was measured by a method derived from ASTM D 1434-82 at 25°C and a carbondioxide partial pressure difference of 10 bars. All measured permeabilities are normalized with respect to film thickness and given in intrinsic permeability units.

Experimental values are shown in the next table. The properties are compared with properties for PET and LDPE.

Flexibility and puncture resistance for some of these materials were tested manually and rated against each other. The results are included in the next table (- = bad; + = good; ++ = very good). Table 1. Permeability values and mechanical properties

^* Values taken from "Permeability and other film properties, Plastic Design Library, ISBN 1 -884207-14-6. ^** Estimate based on data on oriented PET film, needs to verified The results show that the oxygen permeability data are much better than that of LDPE, while the water permeability is as low as PET. Meanwhile the flexibility and puncture resistance of the films is much better than of PET films.