MULTILAYER POLYMER FILM

DESORPTION Field of the invention

The present invention relates to multilayer polymeric films, in particular to monomaterial multilayer polymeric films suitable to recycling and also to methods for the preparation thereof.

State of prior art

In the field of plasticization, paper converting and packaging, the main used films are: polypropylene (PP), polyethylene terephthalate (or more simply, PET) and polyethylene (PE). In some specific applications, such as for example food packaging, it is required that the polymeric films, also called pellicles, have a sufficiently low water vapour transmission rate (WVTR) and oxygen transmission rate (OTR) to preserve the content thereof and then to lengthen the product shelf-life. The pellicles for wrapping and/or packaging with low water vapour transmission rate and low oxygen transmission rate known in the art are generally produced by lamination sheets, metalized films (for example aluminium on PET, PE or PP) or by use of metal oxides (for example, silicon dioxide (S1O2) o aluminium oxide (AI2O3)). However, the addition of metalized films or metalized oxides makes the production of these films much more expensive and the recovery and recycling process much more complex. Other films used in packaging and/or wrapping thanks to their excellent barrier properties and low water vapour and oxygen transmission rates are the laminated films made of polyvinylidene chloride (PVDC), which however are more expensive to be produced than the films made of polyolefins. The laminated films made of PVDC are further highly hydrophilic, namely they tend to absorb humidity and to lose the capability of barrier to gases, and even much fragile by involving the formation of micro-holes and then an additional barrier loss. In order to limit the problem, one would have recourse to an additional lamination with other support so as to coat the film itself, but this would result to be highly expensive, both in terms of time and costs.

Nowadays, the products for food use are wrapped and/or packaged in polycoupled multilayer films, by combining an outer layer of BOPET (bi-oriented polyethylene terephthalate, usually with a thickness of 12 pm), BOPP (bi-oriented polypropylene, usually with a thickness of 20 pm) or OPA (oriented polyamide, usually with a thickness of 15 pm) which provide optimum adaptability to moulding and good mechanical features to the final pack with an internal functional layer for example made of polyethylene (PE) or polypropylene (PP), apt to guarantee weldability and slipperiness features to the final package.

However, the polycoupled films do not guarantee a barrier to water vapour and/or oxygen apt to obtain the wished product shelf-life.

Should a higher barrier to oxygen be required and then a more prolonged shelf-life, as inner functional layer, co-extruded structures made of polyethylene or polypropylene with ethylene vinyl alcohol (EVOH) can be used, an ethylene copolymer capable of providing an excellent barrier to gases such as oxygen, carbon dioxide and methane.

However, to the best of knowledge of the inventors, for coupling said outer (for example, PET) and inner (for example, PE/EVOH/PE) layers typically glues and/or adhesives are used, such as for example polyurethane adhesives, with a quite expensive lamination process, both in terms of time and costs, providing the cross-linking of glue by curing or hardening of glue in hot chamber, necessary for the subsequent use of film in packaging. Even if the polycoupled films show excellent features of barrier to oxygen, since they are made of materials different from each other and since they require the use of glues and adhesives, they are not recyclable.

The multi-material films have necessarily to be disposed of by incineration or through laborious separation processes of the different layers composing them. Moreover, even assuming that the same polymer, for example polyethylene, is selected both for the outer layer and for the inner one, the presence of glues and adhesives, such as the polyurethane adhesives, would however make difficult to recover it and it would not guarantee the same performances.

Therefore, there is still the need for polymeric films having the wished chemical-physical properties, in particular low water vapour and oxygen transmission rates, mechanical resistance and transparency, which at the same time are wholly recyclable and then more sustainable than those known in the state of art. Brief description of figures

FIGURE 1 (A) shows the structure of a 5-layer multilayer film according to an embodiment of the invention and FIGURE 1 (B) shows the structure of a 7-layer multilayer film according to an embodiment of the invention. FIGURE 2 shows a co-extrusion line for a 5-layer film.

FIGURE 3 shows a standard blow extrusion system.

FIGURE 4 shows a MDO ( Machine Direction Orientation) system integrated in the extrusion system (between blow and rewinder).

FIGURE 5 shows a FIFFS (Horizontal Form Fill Seal) line for preparing pillow bags.

FIGURE 6 shows a HFFS (Horizontal Form Fill Seal) line for applying pellicles on trays.

FIGURE 7 shows a VFFS (Vertical Form Fill Seal) line for preparing pillow bags. FIGURE 8 shows the calorimetric thermogram of a film according to the invention. FIGURE 9 shows the stress-strain curves related to the machine direction (MD) and to the transversal direction (TD) of a film according to the invention.

FIGURE 10 shows the graph of puncture resistance of a film according to the invention.

FIGURE 11 shows the graph force on temperature by hot welding HOTTACK (on the left) and cold welding HEATSEAL (on the right) of a film according to the invention.

FIGURE 12 shows the anti-fog effect of a film according to the invention subjected to anti-fog (or anti-fogging) test in cold room at 5°C for 30m in (A), 3h (B), 24h (C), 48h (D). Glossary

The terms used in the context of the present invention, unless where differently designated, are commonly understood by a person skilled in the art.

In the context of the present invention, under “multilayer"’ polymeric film a polymeric film is meant comprising at least two equal or different layers made of polymeric material.

In the context of the present invention, under “asymmetric” multilayer polymeric film a polymeric film is meant having at least a high-density outer upper layer (for example, HDPE) and at least a low-density outer inferior layer (for example, LDPE).

In the context of the present invention, under “monocoupled” or “monomateriar polymeric film a polymeric film is meant wherein the layers composing it are made of the same polymeric material or a derivative thereof.

In the context of the present invention, under “polycoupled” or “polymateria polymeric film a polymeric film is meant comprising at least two layers of polymeric material different from each other.

In the context of the present invention, under “stretch ratio " the ratio is meant between thickness of the film before orientation and thickness of the film after orientation.

ABSTRACT OF THE INVENTION

The purpose of the present invention is to develop a wholly recyclable multilayer film, for example based upon the current EN 13430 standard, with good mechanical and barrier properties and which is transparent. Another purpose of the invention is to develop a method for the preparation of said multilayer monomaterial film.

The present invention then relates to a multilayer monomaterial film and to a method for the preparation thereof. The invention further relates to the use of a multilayer monomaterial film for wrapping and/or packaging products, in particular food products, and final items including it.

DETAILED DESCRIPTIO OF THE INVENTION

According to an embodiment, the multilayer film of the invention comprises at least one barrier layer, encapsulated between a first high-density layer and a second high-density layer, in case bonded to each other by polymeric adhesive layers, suitable to the orientation process described below.

More in particular, the multilayer film of the invention comprises at least one barrier layer having a first surface and a second surface, a first adhesive layer (or tye layer) on, or bonded to, the first surface of the barrier layer and a second adhesive layer above, or bonded to, the second surface of the barrier layer, at least a high-density upper layer above, or bonded to, the first adhesive layer and at least a low-density inferior layer above, or bonded to, the second adhesive layer. Under “high-density layer” in the context of the present description an upper layer is meant comprising, or consisting of, a polymeric material having a density comprised between about 0.930 and about 0.990 g/cm ³ , preferably between about 0.930 and about 0.965 g/cm ³ . Under “low-density layeh’ in the context of the present description an inferior layer is meant comprising, or consisting of, a polymeric material having a density comprised between about 0.850 and about 0.930, preferably between about 0.900 and about 0.925 g/cm ³ .

Therefore, the present invention relates to a multilayer film comprising: - at least one barrier layer having a first surface and a second surface;

- a first adhesive layer above, or bonded to, the first surface of the barrier layer and a second adhesive layer above, or bonded to, the second surface of the barrier layer;

- at least an upper layer of high-density polymer above, or bonded to, the first adhesive layer and at least an inferior layer of low-density polymer above, or bonded to, the second adhesive layer, wherein preferably the high-density upper layer has a density comprised between 0.930 and 0.965 g/cm ³ and the low- density inferior layer has a density comprised between 0.900 and 0.925 g/cm ³ .

The high-density upper layer above, or bonded to, the first adhesive layer for example can include, or consists of, high-density polyethylene (HDPE).

High-density polyethylenes (HDPE) suitable to the object of the invention include ethylene polymers and/or ethylene copolymers and a-olefins (preferably from about 10% to about 30% by weight). In an embodiment, the high-density upper layer includes, or consists of, a HDPE (or pure HDPE) homopolymer. The high-density polyethylene generally is synthetized through polymerization by coordination with a catalytic system of Ziegler-Natta type in solution and it can be easily found on the market, for example, under the tradename HDPE HTA 108 by ExxonMobil™ or Eltex ^® A4009MFN1325 by INEOS. The low-density inferior layer above, or bonded to, the second adhesive layer for example can include, or consist of, low-density polyethylene (LDPE).

Low-density polyethylenes (LDPE) suitable to the object of the invention include ethylene polymers or ethylene copolymers and a-olefins (preferably from about 10% to about 30% by weight). In an embodiment, the low-density inferior layer includes, or consists of, low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE) such as butene linear low-density polyethylene (LLDPE C4), hexene linear low-density polyethylene (LLDPE C6), octene linear low- density polyethylene (LLDPE C8), metallocene linear low-density polyethylene (mLLDPE) or mixtures thereof such as, for example, mixture of linear low-density polyethylene with low-density polyethylene (LLDPE + LDPE) or mixture of metallocene linear low-density polyethylene with low-density polyethylene (mLLDPE + LDPE). The low-density polyethylene generally is synthetized by radical polymerization according to the methods known in the art and it can be easily found on the market, for example, under the tradename of Lupolen 2426 F by LyondellBasell or LD 158 JD by ExxonMobil™.

Therefore, the invention further relates to a multilayer film comprising:

- at least one barrier layer having a first surface and a second surface; - a first adhesive layer above, or bonded to, the first surface of the barrier layer and a second adhesive layer above, or bonded to, the second surface of the barrier layer;

- at least an upper layer of high-density polyethylene (HDPE) above, or bonded to, the first adhesive layer and at least an inferior layer of low-density polyethylene (LDPE) above, or bonded to, the second adhesive layer.

The barrier layer can include, or consist of, ethylene vinyl alcohol (EVOH) or derivatives thereof, preferably ethylene vinyl alcohol. Even if any type of EVOH is suitable to the object of the present invention, EVOH with low molar ethylene content, for example from 24% to 35%, have higher barrier properties and therefore they are preferred.

According to an embodiment, the barrier layer includes, or consists of, one or more layers of EVOH containing 32% mol ethylene.

In an embodiment, the multilayer film comprises at least one barrier layer. In other embodiments, instead, several barrier layers can be included, for example two, three or four barrier layers, so as to further reduce the oxygen transmission rate of the multilayer film.

Therefore, the invention further relates to a multilayer film comprising: - at least one barrier layer of ethylene vinyl alcohol (EVOH) having a first surface and a second surface;

- a first adhesive layer above, or bonded to, the first surface of the barrier layer and a second adhesive layer above, or bonded to, the second surface of the barrier layer;

- at least an upper layer of high-density polyethylene (HDPE) above, or bonded to, the first adhesive layer and at least an inferior layer of low-density polyethylene (LDPE) above, or bonded to, the second adhesive layer.

According to an embodiment, the multilayer film includes, or consists of, at least five or at least seven layers thereamong high-density polyethylene or derivatives thereof, ethylene vinyl alcohol or derivatives thereof, low-density polyethylene or derivatives thereof, and a suitable adhesive.

The difference between a five-layer film and a seven-layer film lies in the fact that whereas in a five-layer film there are only one upper layer and only one inferior layer, in a seven-layer film there are two upper layers (an inner one and an outer one) and two inferior layers (an inner one and an outer one).

Therefore, in the context of the present invention the words “at least an upper layer"’ can include one, two or more upper layers, in particular of high- or low- density polyethylene, equal or different therebetween (for example, an upper outer layer of HDPE and an upper inner layer of HDPE or an upper outer layer of HDPE and an upper inner layer of LLDPE+ LDPE), and “at least an inferior layer"’ can designate one, two or more inferior layers, in particular two or more inferior layers of low-density polyethylene, equal or different therebetween (for example, an inferior inner layer of LLDPE and an inferior outer layer of LLDPE).

Therefore, the present invention further relates to an asymmetric multilayer film comprising:

- at least one barrier layer of ethylene vinyl alcohol (EVOH) having a first surface and a second surface;

- a first adhesive layer bonded to the first surface of the barrier layer and a second adhesive layer bonded to the second surface of the barrier layer;

- at least an upper outer layer of high-density polyethylene above, or bonded to, the first adhesive layer and at least an inferior outer layer of low-density polyethylene above, or bonded to, the second adhesive layer. Said asymmetric multilayer film can further comprise an upper inner layer interposed between the first adhesive layer and the upper outer layer, and an inferior inner layer interposed between the second adhesive layer and the inferior outer layer, preferably wherein the upper inner layer is of high- or low-density polyethylene and the inferior inner layer is of low-density polyethylene.

The high- or low-density polyethylene is as above defined. In particular said low-density polyethylene includes, or consists of, low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), metallocene linear low-density polyethylene (m LLDPE) or a mixture thereof, wherein said mixture is preferably a mixture of linear low-density polyethylene with low-density polyethylene (LLDPE + LDPE) or a mixture of metallocene linear low-density polyethylene with low-density polyethylene (mLLDPE + LDPE).

The multilayer film according to any one of the herein described embodiments can further include additives, for example, selected among the group consisting of: anti-fog (AF or antifogging) agents, slipping agents, antiblocking (AB), processing aids, adhesion promoters, antimicrobial agents, antistatic agents, binders, dispersants, flame retardants, colorants, stabilizers, viscosity regulators, waxes, catalyzers and mixtures thereof. More preferably the additives are selected among the group consisting of: anti-fog agents, slipping agents, sliding agents, antiblocking and processing aids and mixtures thereof.

Said anti-fog can be selected for example in the group consisting of: glycerol or polyglycerol esters with fatty acids such as glyceryl stearate; polyoxymethylene esters such as polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monooleate and polyoxyethylene sorbitan trioleate; sorbitan esters such as sorbitan monolaureate and sorbitan monostearate; alcohol ethoxylates such as polyethoxylated fatty alcohols; polyhydric alcohol; propylene triol; propylene glycol and mixtures thereof. According to a preferred embodiment, the anti-fog is selected among polyoxyethylene sorbitan trioleate and polyoxyethylene sorbitan monooleate and preferably it is polyoxyethylene sorbitan monooleate.

All above-mentioned additives can be both in the solid and liquid state and preferably they are in form of dispersions based on LDPE and/or LLDPE. Generally, these dispersions based on LDPE and/or LLDPE have a content of additive (for example, anti-fog agents, slipping agents, antiblocking and processing aids) until a maximum of 10%.

As described hereinafter, the additives are added in one or more polymeric mixtures composing the different layers, during the co-extrusion process, by suitable gravimetric dosing system. Each layer of the monomaterial film, as so far described, can include one or more additives, so as to give it the wished chemical-physical and mechanical properties. Preferably, the additives are added to the low-density inferior outer and/or inner layer.

Byway of example, but in no way for limitative purposes, the present invention then relates to a five-layer monomaterial film comprising, or consisting of: HDPE / adhesive / EVOH / adhesive / LLDPE, preferably HDPE / adhesive / EVOH / adhesive / LLDPE+LDPE, still more preferably HDPE / adhesive / EVOH / adhesive / mLLDPE+LDPE+at least an AF.

Byway of example, but in no way for limitative purposes, the present invention then further relates to a seven-layer monomaterial film comprising two upper layers (an outer one and an inner one) and two inferior layers (an outer one and an inner one), that is to a film comprising, or consisting of: HDPE / HDPE / adhesive / EVOH / adhesive / LLDPE / LLDPE, preferably HDPE / HDPE / adhesive / EVOH / adhesive / LLDPE / mLLDPE+LDPE, more preferably HDPE / LLDPE+LDPE/ adhesive / EVOH/ adhesive / LLDPE+AF/ LLDPE + at least an AB+ at least an AF.

According to a particularly preferred embodiment, the multilayer film of the present invention comprises, or consists of, HDPE / LLDPE+LDPE/ adhesive / EVOH / adhesive / LLDPE+AF/ LLDPE + at least an AB + at least an AF

As it can be understood from the above-illustrated structures, it is important that the film is asymmetric, that is it has at least a high-density upper outer layer (for example, HDPE) which guarantees stiffness, transparency and above all thermal resistance and at least a low-density inferior outer layer (for example, LDPE) as welding layer. This asymmetric structure results to be particularly advantageous during the wrapping and/or packaging processes. In fact, when the film is used on the packaging lines and then welded on itself or on other supports such as trays, a temperature gradient (At) has to form between the upper outer layer of film (for example, HDPE) which comes in contact to the welding bars of the machine and the welding inferior outer layer of film (for example, LDPE) which necessarily has to melt. Should this temperature gradient given by the different welding temperatures of different density films be not present, for example in case upper outer layer and inferior outer layer are equal and then melt at the same temperature (i.e. HDPE / adhesive / EVOH / adhesive / HDPE or LDPE / adhesive / EVOH / adhesive / LDPE), one would run the risk of burning the outer portion of the package and/or of obtaining a low-sealing inner welding.

The asymmetric multilayer film of the invention, when in use, is used in the shape comprising, in order from top to bottom, the following layers:

- at least a high-density upper layer;

- a first adhesive layer;

- at least one barrier layer;

- a second adhesive layer; and - at least a low-density inferior layer.

More in particular, the five-layer monomaterial film according to any one of the herein described embodiments - when in use - includes, in order from top to bottom, the following layers: an upper layer of high-density polyethylene, a first adhesive layer, at least one barrier layer of ethylene vinyl alcohol, a second adhesive layer, and an inferior layer of low-density polyethylene (FIGURE 1 (A)). Whereas, the seven-layer monomaterial film according to any one of the herein described embodiments - when in use - includes, in order from top to bottom, the following layers: an upper outer layer of high-density polyethylene, an upper inner layer of high- or low-density polyethylene, a first adhesive layer, at least one barrier layer of ethylene vinyl alcohol, a second adhesive layer, an inferior inner layer of low-density polyethylene, and an inferior outer layer of low-density polyethylene (FIGURE 1 (B)).

The adhesive layer is selected among the adhesives generally known to the person skilled in the art. According to a preferred embodiment, the polyolefin is selected based upon the material of the upper and lower polymeric layers to be glued, so as to be able to obtain a multilayer monomaterial film which is suitable to recycling. By way of example, but not for limitative purposes, adhesives suitable to the present invention can be then selected among the group comprising, or consisting of: polyolefins grafted with maleic anhydride or derivatives thereof, other grafted plastomer and/or polyethylene maleate.

Therefore, the present invention further relates to a multilayer film according to any one of herein described embodiments wherein said adhesive layer includes, or consists of, a polyolefin grafted with maleic anhydride, preferably polyethylene grafted with maleic anhydride (PE-g-MAH), other grafted plastomer and/or polyethylene maleate, for example, LLDPE maleate.

In an embodiment, the adhesive layer includes, or consists of, polyethylene grafted with maleic anhydride. PE-g-MAH can be prepared according to any one of the methods known in the art and it is available on the market, for example, under the name COESIVE ^® L851 F.

As seen above, the polyolefin is preferably selected based upon the material of the upper and lower polymeric layers to be glued, so as to be able to obtain a multilayer monomaterial film which is suitable to recycling. Therefore, only byway of example, when the upper and lower layers are based on polyethylene PE-g- MAH and/or polyethylene maleate will be selected, and when the upper and lower layers are based on another polymer (i.e. polypropylene) polypropylene grafted with maleic anhydride (PP-g-MAH) will be selected.

Although the weight ratio between each one of the polymers is not a main feature of the invention, this can be varied to obtain multilayer film with the wished features.

The at least one barrier layer, for example, can be present in an amount between 5% w/w and 15% w/w, preferably comprised between 5% w/w and 10% w/w respect to the total film composition. The upper and inferior layers can be overall present, for example, in an amount between 60% w/w and 80% w/w respect to the total film composition.

The first and second adhesive layer can be overall present in an amount comprised between 15% w/w and 25% w/w respect to the total film composition.

The possible additives, if any, can be in an amount comprised between 1% and 7% w/w, preferably lower than 5% w/w respect to the total film composition.

According to another embodiment, the asymmetric multilayer film can include 5% w/w of layer or barrier layers and 95% w/w of upper and lower layers of polyethylene. Therefore, the present invention further relates to a multilayer film, wherein at least one barrier layer is present in an amount between 5% and 15 % w/w, the first and second adhesive layer are overall present in an amount between 15% and 25% w/w, the upper and inferior layers are overall present in an amount between 60% w/w and 80% w/w and the additives, if any, are present in an amount between 1 % and 7 % w/w respect to the total film composition.

The multilayer film according to any one of the herein described embodiments has optimum barrier properties. In fact, it has water vapour transmission rates (WVTR) measured at conditions of 37.8°C and 90% RH (Relative Humidity) lower than 20 g/m ² /day, preferably lower than 15 g/m ² /day and still more preferably lower than 10 g/m ² /day. As demonstrated in the following examples, a film according to an embodiment of the invention can have a WVTR measured at 37.8°C and 90% RH equal to 8 g/m ² /day. The film according to any one of the so far described embodiments can further have an oxygen transmission rate (OTR) measured at 23°C and 65% of RH lower than 15 cc/m ² /day, preferably lower than 10 cc/m ² /day and still more preferably lower than 7 cc/m ² /day. As demonstrated in the following examples, a film according to an embodiment of the invention can have an OTR measured at 23°C and 65% RH equal to 1.1 cc/m ² / day.

The multilayer film according to any one of the herein described embodiments has even optimum mechanical properties, in particular high longitudinal module, allowing an optimum stiffness and dimensional stability, both during moulding and final use, an optimum puncture resistance, high breaking stress and low tearability.

The both five-layer and seven-layer multilayer films according to any one of the herein described embodiments are further characterized by high transparency with values of HAZE, that is opacity, lower than 30, preferably lower than 25 and still more preferably lower than 20 (FIGURE 12). The measurement is performed by using a suitable HAZE METER instrument according to ISO standard 13468 and ASTM D1003. Moreover, the multilayer film according to any one of the herein described embodiments is suitable to contact with food, that is sufficiently inert as to avoid that the transfer of its components could influence the human health, involve modifications unacceptable to the quality of food and/or cause a deterioration of the organoleptic features thereof.

Thanks to its excellent chemical-physical features, the multilayer film of the invention can have several intended uses such as wrapping and/or packaging products, in particular food products, both fresh and dry products.

Therefore, the present invention further relates to items including, or consisting of, the film according to any one of the herein described embodiments. By way of example, but not for limitative purposes, said items can be selected among the group consisting of: peelable films, heat-sealable films, food films, resealable films, protective films, used for example to cover/close trays, trays, S.U.P. pouches ( stand-up pouch, that is packs capable of keeping upright on their own base), pillow packs (that is bags with and without dorsal welding), square bottom pack, envelopes and bags comprising, or consisting of, the multilayer film according to any one of the herein described embodiments.

Moreover, the present invention further relates to the use of the film or of the item according to any one of the herein described embodiments for wrapping and/or packaging, in particular food products.

The wrapping or packaging of food products (or other similar product) is performed according to techniques known in the art, for example, on VFFS ( Vertical Form Fill Seal) packaging machines wherein the film, thanks to its mechanical and slippering features, is drawn-in along the packaging line so as to acquire the final pack shape to be then welded dorsally and at the two ends (FIGURE 7), or on FIFFS {Horizontal Form Fill Seal) packaging machines wherein the film is drawn-in in the packaging line by sliding parallelly above a belt which receives packages in form of trays whereon it is then thermo-welded and cut (FIGURE 5 and FIGURE 6).

The multilayer film according to any one of the embodiments of the invention can be prepared by means of any one of the methods known in the art such as, for example, co-extrusion.

According to an embodiment, the multilayer film is prepared with a blow co extrusion process as known in literature and generally known to the person skilled in the art. In short, the first passage is the one of melting the polymeric materials composing the different layers, and possible additives, in the extruders i.e. an extruder for each layer or polymeric material. For example, in case one wants to obtain a five-layer film of HDPE/PE-g-MAH/EVOH/PE-g-MAH/LDPE type, five extruders will be provided, one for each layer. The melting flows are made to flow in the blowing head wherein a circular die is integrated to form a tubular or blow with concentric layers. In the above example, the layers from outside towards inside the tubular will be HDPE/PE-g-MAH/EVOH/PE-g-MAH/LDPE. At the outlet of the integrated circular die, the film tubular or blow is dragged upwards by a calender and at the same time inflated by inletting compressed air, with the purpose of obtaining the wished film thickness and width. The film is hit by fresh air which cools it down by stabilizing it. In the upper portion of the blowing system the blow is flattened, that is folded on itself, to give a double multilayer film (for example, HDPE/PE-g-MAH/EVOH/PE-g-MAH/LDPE + LDPE/PE-g- MAH/EVOH/PE-g-MAH/HDPE). The double film, without the side ends, is addressed downwards, separated in two single films (for example, HDPE/PE-g- MAH/EVOH/PE-g-MAH/LDPE) and then wound on two distinct coils.

However, in order to obtain a multilayer film with high mechanical and barrier performances, the co-extrusion process has to be coupled with the MDO ( Machine Direction Orientation) process which allows to orient uniaxially the polymeric chains of the film by giving it the wished mechanical properties. The MDO technology comprises a film stretching step through a system of cylinders rotating at different speeds and heated at temperatures involving the softening of film which is then stretched in the forwarding direction by orienting the polymeric matrix chains in longitudinal direction (or in the machine direction). Preferably, the orientation temperature is comprised between 80 and 120°C below the melting temperature of the inferior layer. For example, when the inferior layer is LDPE the orientation temperature is comprised between 90 and 100°C.

The oriented film then can be cooled down on a second series rollers at temperature comprised between 10 and 30°C to start a crystallization process leading to stabilize the new shape of the polymeric chains.

Therefore, according to an embodiment of the invention, once collapsed on itself the blow of multilayer film to produce the double film, the latter is subjected to uniaxial stretching by MDO technology. As described above, MDO provides for the heating of the film polymeric matrix by suitable rollers, until the softening point of the polymers composing it. However, due to heating and stretching of the double film, during MDO, the two low-density outer inferior layers can weld irreversibly therebetween, by preventing the subsequent separation in two single films.

It is also to be noted that having available two distinct MDO systems, the problem of separating the two films would not arise since, as the films are oriented singularly, the packing between the two substrates would not happen. However, often it is not possible to equip oneself with more than one MDO system both for due to the overall dimensions and to the costs associated to the MDO systems and to the management thereof. Therefore, it would be very advantageous to develop a process to obtain multilayer film, in particular a multilayer film according to any one of the herein described embodiments, by using only one MDO mono-orientation system.

For the above reasons, another object of the present invention is to obtain a multilayer film, in particular a multilayer film according to any one of the herein described embodiments, by using only one MDO mono-orientation system.

In order to avoid the welding of the two outer inferior layers of low-density polyethylene which join and weld during the orientation step, one thought to admixture the polymeric mixture composing them with suitable excipients/additives. To this purpose several additives were tested, without success or with unsatisfactory results, thereamong slipping agents (for example erucamide-based), antiblocking agents (for example, based on synthetic and/or natural silica, in particular silicon dioxide dispersed on LDPE), talcum and calcium carbonate. However, none of these demonstrated effective in allowing the separation of the two outer inferior layers of low-density polyethylene, that is of the orientated double film in two oriented single films.

After extensive experimentation, the inventors of the present invention surprisingly found that by adding an anti-fog agent to the inferior outer layer and/or to the inferior inner layer of the film it is possible separating the oriented (that is subjected to MDO) double film in two oriented multilayer films, which could be then wound in two separate coils. Anti-fogs are oily additives which are generally added to the polymeric films intended to package products with high content of humidity so that, by lowering the surface tension of film, the water included inside the package deposits on the film surface in a very thin and continuous layer, by avoiding the formation of small drops or fog which would jeopardize the product viewing and the pack appeal.

The fog appears on a film when the water vapour condenses on its surface, that is when the closed air mass cools down until temperatures below the water dew point. At this temperature, the air cannot include all water vapour anymore which then condenses by forming small water drops (fogging). The extent of the phenomenon depends upon the relative humidity and upon the temperature of the air mass and of the plastic film. The condensation process can be divided into homogeneous and heterogeneous condensation. The detected condensation type depends upon the surface wettability and then upon the surface tension. During wrapping food, fogging is a felt problem since most packaging materials are hydrophobic polyolefins and even because the fogging risk is increased by low-temperature environments such as, for example, the refrigerated compartments.

Nowadays, anti-fog agents are then known for having the function of avoiding fogging of the plastic films typically used in the field of packaging but, to the best of knowledge of the inventors, AFs were never used to ease the separation of the double film subjected to mono-orientation in two single films.

The AF additives used in mass during extrusion generally are non-ionic surfactants having a hydrophilic head and a lipophilic tail. Anti-fogs suitable to the purpose of the present invention can be selected, for example, among the group consisting of: glycerol or polyglycerol esters with fatty acids such as glyceryl stearate; polyoxymethylene esters such as polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monooleate and polyoxyethylene sorbitan trioleate; sorbitan esters such as sorbitan monolaureate and sorbitan monostearate; alcohol ethoxylates such as polyethoxylated fatty alcohols; polyhydric alcohol; propylene triol; propylene glycol and mixtures thereof. According to a preferred embodiment, the anti-fog is selected among polyoxyethylene sorbitan trioleate and polyoxyethylene sorbitan monooleate, preferably polyoxyethylene sorbitan monooleate (tradename tween 80, Montanox 80, Alkest TW 80, PS 80) characterized in having as liphophilic group the oleic acid which provides the product with such an oiliness so as to allow an easy division of film after passing through high-temperature mono-orientation system (then the irreversible collapse of the film on itself is avoided). The polyoxyethylene sorbitan monooleate has a molar mass of 1310 g/mol, density 1.06-1.09 g/mL, and viscosity 300-500 centistokes a 25°C (Development of a polymeric film with anti-fogging properties, Luis A. et al. , Revista colombiana de quimica, volumen 40, n. 1 de 2011). The selected anti-fogs are particularly advantageous since they allow the separation of the two film faces without jeopardizing the functionality of the welding layer.

According to a particularly preferred embodiment, the anti-fog is a special AF by POLYONE with abbreviation AF PE 8044 having an oiliness features which no other tested AF had. Tested AF which did not give good results, or better did not indeed give the possibility of separating the two films are instead AF 0255 by CONSTAB, AF 7380 by TOSAF, AF PE 9679 by POLYONE and AF 1092 by SCHULMANN.

As seen before, the anti-fogs (as well as the other possibly present additives) in form of masterbatch, are added during the extrusion step by suitable dosing system in the extruder corresponding to the layer or polymeric mixture which one wants to additivate (for example, in the extruder corresponding to the inferior outer and/or inner layer of low-density polyethylene). The surfactant agents, due to the chemical incompatibility with the polymeric matrix, migrate towards the film surface by forming a hydrophilic layer which avoids the irreversible melting of the two low-density layers which arrive adjacent after flattening of the extrusion blow and during the MDO process and then it eases the separation of the oriented double film in two single films.

Moreover, as described above, thanks to this additive it also possible to guarantee an anti-fogging effect, for example, in wrapping and/or packaging food products.

The present invention then further relates to a method for the preparation of an asymmetric multilayer film, according to any one of the herein described embodiments, comprising the co-extrusion of the layers of polymeric materials as so far described, the monoaxial orientation of the so-obtained (double) film and its possible separation in two monomaterial asymmetric mono-oriented single films. Optionally, the separate films can be subjected even to corona treatment.

Although the method has been described so far relating to the monomaterial film of the present invention, it is meant that this can be used for implementing a multilayer film based on any other type of polymeric material, preferably having the density gradient as herein described that is a film having a high-density upper outer layer (corresponding to the outer layer of the extrusion blow) and a low- density inferior outer layer (inner layer of the extrusion blow).

The present invention then further relates to a method for the preparation of a multilayer film having at least an upper layer and at least an inferior layer comprising the blow co-extrusion of as many polymeric materials as the layers making up the multilayer film, a polymeric material for extruder, said co-extrusion comprising the addition of at least an anti-fog agent in the extruder dedicated to said inferior layer.

The antifog used in the method of the present invention is as above defined. In particular, the antifog can be a non-ionic surfactant.

Said anti-fog agent can be selected, for example, among the group consisting of: glycerol or polyglycerol esters with fatty acids; polyoxymethylene esters; sorbitan esters; alcohol ethoxylates; polyhydric alcohol; propylene triol; propylene glycol and mixtures thereof. According to an embodiment said anti-fog is selected among the group consisting of: glycerol or polyglycerol esters with fatty acids such as for example glyceryl stearate; polyoxymethylene esters such as for example polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monooleate and polyoxyethylene sorbitan trioleate; sorbitan esters such as for example sorbitan monolaureate and sorbitan monostearate; alcohol ethoxylates such as for example polyethoxylated fatty alcohols; polyhydric alcohol; propylene triol; propylene glycol and mixtures thereof. In particular, said anti-fog can be selected among polyoxyethylene sorbitan trioleate and polyoxyethylene sorbitan monooleate, and preferably it is polyoxyethylene sorbitan monooleate. Obviously, the method can include the addition of other suitable additives as defined above. Preferably the additives are added to the inferior outer and/or inner layer of the film that is those facing inside the tubular or blow.

The layers composing the multilayer film of the present method can be ordered according to any one of the herein described embodiments. Preferably, the concentric layers are from outside towards inside the tubular or blow: an upper outer layer of high-density polyethylene, a first adhesive layer, at least one barrier layer of ethylene vinyl alcohol, a second adhesive layer, an inferior outer layer of low-density polyethylene and, optionally, even an upper inner layer of high- or low-density polyethylene interposed between the first adhesive layer and the upper outer layer, and an inferior inner layer of low-density polyethylene interposed between the second adhesive layer and the inferior outer layer.

The low-density polyethylene is as above defined and, preferably includes, or consists of, low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), metallocene linear low-density polyethylene (mLLDPE) or a mixture thereof, said mixture being preferably a mixture of linear low-density polyethylene with low-density polyethylene (LLDPE + LDPE) or a mixture of metallocene linear low-density polyethylene with low-density polyethylene (mLLDPE + LDPE).

The method according to any one of the so far described embodiments can further include the flattening of extrusion blow or tubular to produce a double multilayer film as described above.

The method according to any one of the so far described embodiments can further include the uniaxial orientation of the double multilayer film, preferably in longitudinal direction or of the machine, more preferably with a stretch ratio between 1 : 1 and 1:10, preferably between 1 : 1 and 1 :6 and more preferably equal to 1:4.

By way of example, starting from a blow thickness of 125 pm to allow a final thickness 25 pm a stretch ratio of 1 :5 will have to be used, whereas starting from an initial thickness in blow of 150 pm to obtain the same 25 pm a stretch ratio equal to 1 :6 will have to be used.

The oriented multilayer film has a thickness comprised between 20 pm and 80 pm, preferably between 20 pm and 60 pm, still more preferably equal to 25 pm. According to an embodiment, the thickness of the barrier layer is about 6%, the overall thickness of the upper and inferior layers of polyethylene is about 74% and the overall thickness of the adhesive layers is about 20% of the final thickness of the oriented multilayer film. The method according to any one of the so far described embodiments optionally can include the separation of the oriented double multilayer film in two single films and, optionally, the corona treatment and/or the moulding of the latter.

The so-obtained oriented multilayer film has the advantage of not having to be coupled with other materials (such as in case of polycoupled films) and then it is wholly recyclable for example, based upon the current EN 13430 standard. The so-obtained oriented multilayer film can be further transformed by thermoforming, coupling or moulding; this also thanks to the surface corona treatment, on the high-density layer, which can be implemented directly in line after the stretching process according to any one of the methods known in the art. This is another important advantage of the invention method since, as seen above, by extruding the layers in the herein proposed order, a blow of double film is obtained the inner faces thereof are of low-density polyethylene. By extruding the layers in opposite order, that is with layer of high-density polyethylene inside and layer of low- density polyethylene outside, it would have been simpler to separate the double film after orientation, but it would not have been possible to apply additives to the least one low-density layer (the additives, in particular, the anti-fogs are applied inside the blow so that is includes all fumes and oils which are released during the extrusion step), nor to perform the surface corona treatment in line, since it would not be possible to treat the low-density welding and functional side of the film (which in this shape would be outside the blow). Therefore, in order to make the film mouldable, the corona treatment should be performed out of line by involving an additional passage and additional costs. To this regard, it has to be noted that, generally, the plastic films have inert and not porous chemical surfaces with low surface tensions which make them not receptive to anchoring substrates such as, for example, printing inks, adhesives and coatings. Among the different plastic films, polyethylene and polypropylene are those with lowest surface energy and they are often subjected to corona treatment. In short, as it is known to the person skilled in the art, the corona treatment systems used to increase the features of wettability and adhesion of films, apply on the surface to be treated an electric discharge, with a determined power, for a defined period of time. The surface energy, measured in dyne/cm, has to be preferably 10 dyne/cm higher than the surface tension of the liquid which one wants to apply. Thanks to such modification, the surface tension of the film is decreased, that is the contact angle between a water drop (or of liquid, generally) and the film, is decreased. Therefore, the present invention relates to a polyethylene-based asymmetric multilayer film and to a method for the preparation of an asymmetric multilayer film, preferably based on polyethylene, the main features thereof are as defined in the enclosed independent claims. Other accessory or preferred technical features are set forth in the depending claims.

In particular, the present invention relates to:

An asymmetric multilayer film comprising:

- at least one barrier layer of ethylene vinyl alcohol (EVOH) having a first surface and a second surface;

- a first adhesive layer bonded to the first surface of the barrier layer and a second adhesive layer bonded to the second surface of the barrier layer;

- at least an upper outer layer of high-density polyethylene above, or bonded to, the first adhesive layer and at least an inferior outer layer of low-density polyethylene above, or bonded to, the second adhesive layer; the asymmetric multilayer film according to any one of the herein described embodiments further comprising an upper inner layer interposed between the first adhesive layer and the upper outer layer, and an inferior inner layer interposed between the second adhesive layer and the inferior outer layer; the asymmetric multilayer film according to any one of the herein described embodiments, wherein the upper inner layer is of high- or low-density polyethylene and the inferior inner layer is of low-density polyethylene; the asymmetric multilayer film according to any one of the herein described embodiments, wherein said low-density polyethylene includes, or consists of, low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), metallocene linear low-density polyethylene (m LLDPE) or a mixture thereof; the asymmetric multilayer film, wherein said mixture is preferably a mixture of linear low-density polyethylene with low-density polyethylene (LLDPE + LDPE) or a mixture of metallocene linear low-density polyethylene with low-density polyethylene (mLLDPE + LDPE); the asymmetric multilayer film according to any one of the herein described embodiments, comprising one or more additives selected among the group consisting of: anti-fog agents (AF), slipping agents, antiblocking (AB), processing aids, adhesion promoters, antimicrobial agents, antistatic agents, binders, dispersants, flame retardants, colorants, stabilizers, viscosity regulators, waxes, catalyzers and mixtures thereof, preferably among: anti-fog agents, slipping agents, sliding agent, antiblocking and processing aids; the asymmetric multilayer film according to any one of the herein described embodiments, wherein said anti-fog is selected among the group consisting of: glycerol or polyglycerol esters with fatty acids such as glyceryl stearate; polyoxymethylene esters such as polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monooleate and polyoxyethylene sorbitan trioleate; sorbitan esters such as sorbitan monolaureate and sorbitan monostearate; alcohol ethoxylates such as polyethoxylated fatty alcohols; polyhydric alcohol; propylene triol; propylene glycol and mixtures thereof, preferably among polyoxyethylene sorbitan trioleate and polyoxyethylene sorbitan monooleate, and more preferably it is polyoxyethylene sorbitan monooleate; the asymmetric multilayer film according to any one of the herein described embodiments, wherein said one or more additives are added to the inferior outer and/or inner layer; the multilayer film according to any one of the herein described embodiments, wherein the film is a five-layer film and includes, in order, the following layers: HDPE / adhesive / EVOH/ adhesive / LLDPE or HDPE / adhesive / EVOH / adhesive / LLDPE+LDPE or HDPE / adhesive / EVOH / adhesive / mLLDPE+LDPE+at least an anti-fog agent; the asymmetric multilayer film according to any one of the herein described embodiments, wherein the film is a seven-layer film and includes, in order, the following layers: HDPE / HDPE / adhesive / EVOH / adhesive / LLDPE / LLDPE or HDPE / HDPE / adhesive / EVOH / adhesive / LLDPE / mLLDPE+LDPE or HDPE / LLDPE+LDPE/ adhesive / EVOH/ adhesive / LLDPE + at least an anti fog agent / LLDPE + at least an antiblocking agent + at least an anti-fog agent; the multilayer film according to any one of the herein described embodiments, wherein the film includes, in order, the following layers: HDPE / LLDPE+LDPE/ adhesive / EVOH / adhesive / LLDPE + at least an anti-fog agent / LLDPE + at least an anti-fog agent + at least an antiblocking agent; the asymmetric multilayer film according to any one of the herein described embodiments, wherein said first and second adhesive layer includes, or consists of, a polyolefin grafted with maleic anhydride, preferably polyethylene grafted with maleic anhydride (PE-g-MAH) and/or polyethylene maleate, more preferably LLDPE maleate; the multilayer film according to any one of the herein described embodiments, wherein the at least one barrier layer is present in an amount between 5% w/w and 15% w/w, the first and second adhesive layer are overall present in an amount between 15% and 25% w/w, the upper and inferior layers are overall present in an amount between 60% w/w and 80% w/w and the additives, if any, are present in an amount between 1 % and 7% w/w respect to the total film composition; the multilayer film according to any one of the herein described embodiments, having a water vapour transmission rate measured at 37.8°C and 90% of relative humidity lower than 20 g/m ² /day, preferably lower than 15 g/m ² /day, more preferably lower than 10 g/m ² /day and still more preferably equal to 8 g/m ² /day; The multilayer film according to any one of the herein described embodiments, having an oxygen transmission rate measured at 23°C and 65% of relative humidity lower than 15 cc/m ² /day, preferably lower than 10 cc/m ² /day, more preferably lower than 7 cc/m ² /day and still more preferably equal to 1 .1 cc/m ² /day. As above anticipated, the present invention further relates to an item selected among peelable films, heat-sealable films, food films, resealable films, protective films, used for example to cover/close trays, trays, stand-up pouch packs, pillow packs, square bottom packs, envelopes and bags, comprising, or consisting of, the asymmetric multilayer film according to any one of the herein described embodiments and to the use of the film or of the item according to any one of the herein described embodiments, for wrapping and/or packaging. Moreover, the present invention further relates to a method for the preparation of a multilayer film having at least an upper layer and at least an inferior layer comprising the blow co-extrusion of as many polymeric materials as the layers making up the multilayer film, a polymeric material for extruder, said co-extrusion comprising the addition of at least an anti-fog agent in the extruder dedicated to said inferior layer; the method according to any one of the herein described embodiments, wherein said anti-fog is a non-ionic surfactant; the method according to any one of the herein described embodiments, wherein said anti-fog agent is selected among the group consisting of: glycerol or polyglycerol esters with fatty acids; polyoxymethylene esters; sorbitan esters; alcohol ethoxylates; polyhydric alcohol; propylene triol; propylene glycol and mixtures thereof; the method according to any one of the herein described embodiments wherein said anti-fog agent is selected among the group consisting of: glyceryl stearate; polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monooleate and polyoxyethylene sorbitan trioleate; sorbitan monolaureate and sorbitan monostearate; polyethoxylated fatty alcohols; polyhydric alcohol; propylene triol; propylene glycol and mixtures thereof, preferably among polyoxyethylene sorbitan trioleatee and polyoxyethylene sorbitan monooleate, and more preferably it is polyoxyethylene sorbitan monooleate; the method according to any one of the herein described embodiments, wherein said layers composing the multilayer film are from outside towards inside: an upper outer layer of high-density polyethylene, a first adhesive layer, at least one barrier layer of ethylene vinyl alcohol, a second adhesive layer, an inferior outer layer of low-density polyethylene and, optionally, even an upper inner layer of high- or low-density polyethylene interposed between the first adhesive layer and the upper outer layer, and an inferior inner layer of low-density polyethylene interposed between the second adhesive layer and the inferior outer layer; the method according to any one of the herein described embodiments, wherein said low-density polyethylene includes, or consists of, low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), metallocene linear low-density polyethylene (mLLDPE) or a mixture thereof, said mixture being preferably a mixture of linear low-density polyethylene with low-density polyethylene (LLDPE + LDPE) or a mixture of metallocene linear low-density polyethylene with low- density polyethylene (mLLDPE + LDPE). the method according to any one of the herein described embodiments, further comprising the blow flattening to produce a double multilayer film; the method according to any one of the herein described embodiments, further comprising the uniaxial orientation in machine direction of the double multilayer film preferably wherein the uniaxial orientation takes place with a stretch ratio between 1:1 and 1:10, more preferably between 1:1 e 1:6 and still more preferably equal to 1:4; the method according to any one of the herein described embodiments, further comprising the separation of the oriented double multilayer film in two single films and, optionally, the corona treatment and/or the moulding of the latter; and to the method according to any one of the herein described embodiments, wherein the oriented multilayer film has a thickness comprised between 20 pm and 80 pm, preferably between 20 pm and 60 pm, still more preferably equal to 25 pm.

The present invention further relates to a multilayer film obtained or obtainable by means of the method of any one of the herein described embodiments, preferably having a water vapour transmission rate - measured at 37.8°C and 90% of relative humidity - lower than 20 g/m ² /day, preferably lower than 15 g/m ² /day, more preferably lower than 10 g/m ² /day and still more preferably equal to 8 g/m ² /day.

The present invention further relates to a multilayer film obtained or obtainable by means of the method of any one of the herein described embodiments, preferably having an oxygen transmission rate measured at 23°C and 65% of relative humidity lower than 15 cc/m ² /day, preferably lower than 10 cc/m ² /day, more preferably lower than 7 cc/m ² /day and still more preferably equal to 1.1 cc/m ² /day. Therefore, it was shown that by laminating in several layers the same polymeric material, for example polyethylene, having different densities it is possible obtaining a multilayer monomaterial film capable of providing the package mechanical features similar to those of the polycoupled films, for example with PET or BOPP, known in the art, with higher properties of barrier to oxygen and water vapour, by guaranteeing at the same time a lower environmental impact thanks to the decrease in thicknesses and to the greater ease in recycling the monomaterial structure.

Other advantages of the multilayer film of the present invention will result evident to the person skilled in the art based upon the preceding description and the herebelow reported examples.

EXAMPLES

The herebelow reported examples are only by way of example and they are not to be meant to limit the scope of the present invention. Variations and modification of any one of the herein described embodiments, which result to be obvious to a person skilled in the art, are comprised within the scope of the enclosed claims. The person skilled in the art will also understand that the herein described five-or seven-layer films are only possible embodiments of the multilayer film of the invention and that the number of layers, their thickness and their percentage respect to the total weight of the film can be adjusted based upon the intended use of the film in order to provide it the wished chemical- physical features.

Example 1 : Preparation of a multilayer monomaterial film made of polyethylene The preparation process is a conventional blow extrusion process, that is based upon the main following passages: preparation of the polymeric material, each one in its gravimetric dosing system placed above the mouth of the extrusion screw, suitably set with temperatures suitable to process the polymer. Once started the extruder, the screw will start to pump forward the melt material until making it to enter the extrusion head therefrom, through the die placed at the end on top of the head itself, a molten mass will exit which will be dragged upwards by a calender, inflated and suitably cooled down until forming a stable blow which allows a correct management of the thickness of the blow itself (the blow thickness depends upon the amount of material outgoing from the head and upon the stretching rate by the calender upwards). Once the blow is collapsed on itself, the film goes down from the calender again downwards through a series of accompanying cylinders until reaching the inlet of the MDO system; herein the already above-described stretching process takes place. By way of example, by blow extrusion 15% of high-density polyethylene (FIDPE, tradename Eltex® A4009MFN1325 by INEOS, density 0.960), 60% of linear low- density polyethylene (mLLDPE, tradename, PF6220KJ INEOS, density 0.918), 20% of linear polyethylene grafted with maleic anhydride (tradename ADMER™ NF911 E) and 10% of ethylene vinyl alcohol (32% molar ethyl) can be co-extruded to provide a molten mass which is stabilized by inflation, sucking and cooling down, dragged in vertical direction by a calender and collapsed on itself. At this point, the double film is subjected to orientation process (MDO) separated in two single films, which are then wound on two different coils. Analysis of a multilayer monomaterial film according to the invention

The analysed multilayer monomaterial film was obtained with the above- described conventional methods and it has the composition shown in the herebelow table: Where adhesive layer means polyethylene polyethylene grafted with maleic anhydride (PE-g-MAH). Anti-fog agent (AF) and antiblocking agent (AB) are as above defined.

The obtained oriented film has a thickness of 25 ± 7% and a grammage of 24 ± 4%. For additional analysis of its properties, it was also subjected to: - Structural characterization by differential scanning calorimetry;

- Mechanical analysis: stress-strain and puncture resistance;

- Evaluation of the welding properties (hottack and heatseal); and

- Evaluation of the properties of barrier to water vapour and oxygen.

Differential scanning calorimetry (DSC) The thermal analysis was performed with a scanning differential calorimeter METTLER TOLEDO DSC-822, by performing scanning at a heating rate of 10°C/min in nitrogen (N2) atmosphere. In particular, the samples were subjected to a thermal cycle shown in FIGURE 8 consisted of a first heating from 30°C to 200°C until melting, to evaluate the temperature of first melting (T _m ) and relative enthalpy (AH _m ), followed by a cooling down from 200°C to 30°C, allowing to determine the crystallization temperature and a subsequent heating scanning (or second heating from 30°C to 200°C) to evaluate the temperature of second melting of the sample crystalized from the melt. From the calorimetric analysis it is possible to go back to the main materials composing the film. In fact, with reference to the first melting, it can be observed:

- A peak at 115°C due to the presence of low-density polyethylene LDPE and/or LLDPE consisting the welding inferior layer and the adhesive layers;

- A peak at 134°C due to the presence of high-density polyethylene (HDPE), existing on the upper outer layer of the film, which provides it the thermal resistance and the machinability necessary to be used in the applications in which commonly PET - PE/EVOH (where PET provides the thermal resistance and machinability) are used coupled; and

- A peak at 182°C typical of EVOH with a 32% ethylene mole content. The following Tables show the enthalpies and the melting/crystallization temperatures:

Mechanical properties: effort-deformation curves and puncture resistance The analysis of the tensile properties was performed at room temperature by performing mechanical tests by means of a ZWICK dynamometric apparatus and following the method suggested by A.S.T.M. standard D882. The following Table shows the main mechanical properties recorded during the tests, that is elastic module (E), yield stress (OY), deformation (£b) and breaking stress (Ob): The machine direction orientation (MDO) is evident from the anisotropy of material between MD (machine direction) and TD (transversal direction). The young module (E) is 2550 Mpa in MD against 1350 Mpa in TD. In MD the film has no yielding, whereas in TD the yielding (OY) is of 25 MPa. In machine direction the deformation at failure £b (%) reaches 10%, with breaking stress Ob of well 144 MPa. In transversal direction the deformation at failure reaches 380%, with breaking stress of only 20 Mpa (FIGURE 10).

The puncture tests were performed by following the ASTM standard 1306 by means of zwick dynamometer, by using a 3.2 mm diameter bit. The recorded puncture resistance has a value of about 10 N ± 10% (FIGURE 11). Hot ( hottack ) and cold (heat seal ) weldability

The hot weldability tests of the film were performed by following the ASTM standard F1921 on tests having width of 15 mm by means of J&B Hot Tack 4000 at the following conditions: range of temperatures comprised between 90°C and 150°C (step of 10°C), pressure equal to 1.5 bar and welding time of 0.5 s. As shown in FIGURE 11 (on the left), the maximum force peak was reached at the temperature of 120°C, with an average value of 3.5 N/15 mm.

The cold weldability tests of the film were performed by following the ASTM standard F2029 on tests having width of 15 mm at the following conditions: range of temperatures comprised between 80°C and 180°C (step di 10 °C), pressure 2.8 bar, welding time 1 s. As shown in FIGURE 11 (on the right), the force plateau is reached at the temperature of 100°C, with a value comprised between 12-15 N/15 mm.

Barrier to water vapour and oxygen The permeability to water vapour was performed with Mocon Permatran-W 3/33 permeabilimeter, by following the standard F1249 and by exposing to permeating gas an area of 50 cm ² at a temperature (T) of 37.8°C and relative humidity (RH) equal to 90%. Under these conditions the WVTR (water vapour transmission rate) is 8 g/m ² day.

The permeability to oxygen was performed with Mocon Oxtran 2/21 permeabilimeter, by following the standard F1927 and exposing to the gas an area of 50 cm ² . The tests were performed at the temperature of 23°C with same relative humidity on both faces of the film (0. 65 and 90%). For the three surveyed relative humidities the following barriers were recorded:

- 0.8 cc/m ² day at 23°C and RH = 0%

- 1.1 cc/m ² day at 23°C and RH = 65%

- 14 cc/m ² day at 23°C and RH = 90%

The considerable barrier properties are a direct consequence of the orientation process which allows to increase the crystalline fraction of the polymeric film, which is the one required to the decrease the gas permeation rate through the film itself.

Antifoci test

The antifog tests were performed by preparing five water recipients sealed with the film, so as to expose towards water the film side containing the antifog additive. The whole was placed in cold room at 5°C so as to be able to take photos and record the antifog behaviour over the time. As it is evident from FIGURE 12, the antifog activation takes place quickly: after 30 minutes one single water layer has already formed, by avoiding the fogging of the polymeric film.