WO2019020687A1

WO2019020687A1 - Coil of irradiated barrier film, optionally mono-oriented, for the production of collapsible tubes

Info

Publication number: WO2019020687A1
Application number: PCT/EP2018/070156
Authority: WO
Inventors: Massimo CENTONZE; Simonetta LANATI
Original assignee: Industria Termoplastica Pavese S.P.A.
Priority date: 2017-07-26
Filing date: 2018-07-25
Publication date: 2019-01-31
Also published as: IT201700085388A1; EP3658370A1

Abstract

A description is given of a coil (100) of co-extruded blown or cast barrier film (3"), intended for the production of flexible containers (200) in the form of tubes, characterised in that said co-extruded barrier film is also surface irradiated on at least one of the two opposite outer layers (10; 50) with a base of olefin (co)polymers, said film further comprising an intermediate barrier layer (30) and optionally at least two intermediate binding layers (20; 40).

Description

COIL OF IRRADIATED BARRIER FILM, OPTIONALLY MONO- ORIENTED, FOR THE PRODUCTION OF COLLAPSIBLE TUBES

DESCRIPTION

The present invention relates to a coil of multilayered barrier film (hereinafter also referred to as flat sheet), also with high thickness, intended for the subsequent production of flexible packagings in the form of tubes, where said film is a co- extruded film, blown or cast, with a base of polyolefins and irradiated, which comprises at least three layers whereof one barrier.

More particularly the present invention relates to a coil of multilayered flat sheet, mainly a polyolefins-based sheet, with barrier properties and non-heat-shrinkable, preferably treated on the surface with a corona discharge treatment, intended for the subsequent production of tubes, where said flat sheet is blown or cast co-extruded and subsequently irradiated.

Moreover, the present invention relates to a process for producing the aforesaid coil of barrier film comprising a phase of irradiation and optionally a preceding phase of machine orientation (mono-oriented) and/or annealing.

The market for flexible tubes (whether for the pharmaceutical or cosmetic sector or the food sector) is emblematic more than others of the great benefit brought by plastic materials in the packaging/containment of products.

The aluminium tube has been almost completely replaced by tubes in plastic material with various degrees of rigidity, barrier, colouring/printing, because plastic materials are able to ensure the same performances and function as metal, and to also add some further benefits including, for example, the lower environmental impact, the better aesthetic quality also during use and emptying of the same by the consumer (e.g. the plastic tube during pressing has always reversible deformations).

The first technology that appeared on the market for producing these plastic tubes used extrusion of the tube directly by a circular die. This technique has the advantage of providing a tube already ready for filling (after welding and application of the cap), yet the disadvantages of the considerable volume required in transport ("empty" tubes are transported) and above all of the dimensional restraint linked to the diameter of the die (should the size of the tube have to be changed, it would be necessary to change the extrusion head), beyond the limit, real and extremely felt, of the tendency towards deformation (ovalization) when several tubes are transported under an excessive weight of superimposition.

Thus, the solution gained ground of the tube made from a flat sheet which, cut adequately, can be bent/rolled on itself so as to be shaped into a tube and subsequently heat- welded vertically and horizontally for the closure of the tube.

This technique certainly offers a greater flexibility in the design of the dimensions of the tube which can be varied if needed without any investment in production technologies, yet requires an exceptionally seal of the weld (high welding force) also under stress and under the effect of pressure.

In all cases an essential requirement is a good overall rigidity of the tube which must not appear too soft during handling and use by the consumer. Moreover the tube must ensure a perfect barrier to steam, gases and aromas, and to the component chemical products of the cream contained, and must be aesthetically shiny and with an attractive appearance and printable.

The primary requisite of a very high barrier to gases and to aromas (as well as to humidity) once ensured only by aluminium, no longer represents a problem, because barriers at the level of that offered by the metal sheet can be obtained by appropriately choosing the resins which form the barrier layer.

Most of the solutions present on the market for flat sheet films are however laminated films, that is derived from the coupling of different films, and existing in themselves as single entities wound into a coil, which, superimposed one on the other and assembled with various technologies, allow complementary functions to be combined, that is an outer bi-oriented film can ensure rigidity, thermal resistance, shine and brilliance, an intermediate film can ensure the barrier properties, a film or an inner layer can ensure sealing of the weld, etc. The limits of this technology of production of the film (lamination) lie in the fact that the films to be assembled, being obtained by means of different technologies, have different profiles of molecular orientation which are not always combined adequately in the assembled structure and which, during the subsequent processing system for making the tube, can generate a competition of forces such as to cause distortions and ovalizations in the tube.

Another limit of the laminated structure is represented by the fact that these tubes, when they contain aggressive ingredients (e.g. surfactants, alcoholic components), may come up against processes of delamination. The presence of aggressive components in the products contained in these tubes is in effect a problem greatly felt in the packagings sector, in light of the fact that the times of exposure to these substances are normally very long (because the packaged products have conservation times lasting years) and that there is a considerable variability of chemical substances inserted in the product contained, which cannot be absolutely controlled by those who make the container tube. The tube moreover has to demonstrate excellent resistance to these chemical agents also at the welds since small leaks in this zone would cause a serious loss of product.

In light of this it appears important to increase the chemical resistance to aggression of the components.

Irradiated barrier films are also known which are however made to be heat-shrinkable so as to adhere to fresh food products such as meat, when said food products are packaged under vacuum. However this type of films, are made with double or triple bubble extrusion technologies that are able to give very high shrinking properties both in terms of size (% of shrinkage) and in terms of compactness of the food, once it has been vacuum packed (retraction force); said films, which also normally have low thickness, are generally characterized by a softness and flaccidity which does not render them suitable for making dispenser tubes with a certain rigidity, and a proper shape and consistency also when empty, which are required to be collapsible and sometime also squeezable, such as for example tubes dispensing cosmetic products.

The object of the present invention is that of overcoming, at least in part, the disadvantages of the prior art by providing a co-extruded film with a base of polyolefins apt to produce flexible tube containers, having an improved chemical resistance to the aggression of the components of the product contained in the flexible tube.

Another object is that of making such a film using a simple and economical process. These objects are achieved by the film in a coil according to the invention which has the features listed in the appended independent claim 1.

Advantageous embodiments of the invention are disclosed by the dependent claims. An object of the present invention relates to a coil of barrier film, more particularly non-heat-shrinkable, co-extruded, blown or cast, surface irradiated, intended for the production of flexible containers in the form of tubes (e.g. collapsible tube containers), which generally have their own shape even when empty, where said co-extruded and irradiated barrier film is a film comprising two outer layers with a base of olefin (co)polymers, at least one intermediate barrier layer and optionally at least two intermediate binding layers.

More particularly, at least the outer layer of the present film which is intended to be the inner surface of the tube, is irradiated/radiated, and preferably also treated on the surface with corona discharge treatment.

In practice the film wound into a coil of the present invention is made by adopting at least the following steps:

blown co-extrusion or cast co-extrusion, preferably blown co-extrusion, - optional machine orientation and/or annealing of the co-extruded film, and

subsequent irradiation of the co -extruded film, optionally oriented and/or annealed, to perform crosslinking between the polymer chains of the material which forms at least the outer layer of the film which is intended to be the inner surface of the future tube.

In a preferred embodiment the object of the present invention is a coil of multilayered flat polyolefin-based sheet, preferably polyolefins of high molecular weight, with barrier properties and non-heat-shrinkable, preferably treated on the surface with a corona discharge treatment, where said flat sheet is blown or cast co-extruded and also preferably treated on the surface with corona discharge treatment. It should be noted that the aforesaid flat sheet is particularly suitable for making flexible and soft tubes which dispense products in cream, paste or the like, which are required to be collapsible and at times also squeezable, as well as printable on the outside such as for example tubes dispensing cosmetic products.

The corona discharge treatment is particularly advantageous in order to promote the adhesion of the printing inks on the sheet which will then be transformed into a tube. The film and sheet that are the object of the present invention are not to be considered heat-shrinkable in that when they are subjected to the test of Unrestrained Linear Thermal Shrinkage of Plastic Film and sheeting in accordance with ASTM D 2732, they show a quite null linear swelling in both direction (longitudinal and transversal) that it is to be considered non measurable with respect to the effectively heat- shrinkable films of the prior art which in the case of primary packaging show percentage of shrinkage even in the order of 80-90%.

The term "heat-shrinkable" generally refers to a film which, when it is subjected to a source of heat, shrinks up to approximately 50% of the initial size, at least in one of the directions, adhering to the object around which it has been wound, thus compacting the packaging. After cooling, the film maintains its new shape.

The term "barrier" here is intended to identify those materials which, thanks to their chemical structure, (normally containing polar functional groups for the different electrical negativity of the atoms constituting the bond) are able to form hydrogen bridge bonding, generating in this way a sort of net which hinders the passage of molecules, even small ones, such as those of the gases (whether 0₂, N₂, CO2, and others) where the properties of impermeability to aeriform substances are measured according to measurement methods of the coulometric type, for example that provided by ASTM D3985 and ASTM F1927.

This barrier can be a "high barrier" or a "low barrier", as defined, for example, by the standard UNI 10534. The term "co-extruded" here is intended to identify a film obtained from the process of extrusion of two or more materials, in the molten state, through one or more orifices arranged in a way that the extruded parts fuse and weld together in a laminar structure before cooling, without the aid of any type of glue. Co-extrusion can be performed according to the prior art with blowing in a bubble, flat head, extrusion coating or the like. The present film is preferably co-extruded using screw extruders and bubble blowing or flat head extrusion.

The term "machine direction orientation" (MDO) (uniaxial orientation) here is intended to identify a process of orientation which stretches the film mainly in a single direction.

The term "annealing" here is intended to identify a process of heating and subsequent cooling of a film for reducing and/or cancelling out the tensions which may have been generated during the previous processing phases, in particular during the co-extrusion of different layers of different thicknesses and composition.

With the terms "irradiated/radiated", "irradiation" here the intent is to identify a treatment of irradiation of at least one surface of a film with ionizing radiations, for example by means of bombarding with accelerated electrons (electron beam) having energy comprised between 0.05 and 10 Mev, where this irradiation can also penetrate the thickness (and the layers) of the film according to the depth at which it is intended to arrive with crosslinking of the polymer.

In the sector of food packaging, the ionizing rays produced by beams of accelerated electrons (electron beam) are used for different purposes such as the decontamination and sterilisation of material, or the drying of inks and paints.

The Applicant has found that the process of electronic irradiation of the film is able to determine such a crosslinking of the polymer chains as to give high chemical resistance to the film.

Simultaneously to the chemical resistance it is possible to give to the co-extruded film, blown or cast, high and/or improved mechanical features, subjecting it to a process of machine orientation and annealing before being subjected to irradiation. The phases of machine orientation and of annealing allow the film to be heated and stretched by means of mechanical action of a series of rollers which work at different temperatures and at different speeds, obtaining a perfect planarity of the film itself and a greater orientation of the molecular chains.

This orientation and annealing entail a benefit in terms of:

- greater barrier to aeriform substances and to aromas;

- greater mechanical resistance to traction in longitudinal direction;

- improved quality of the coils made (thickness and alignment of the edges particularly uniform). Further features of the invention will be made clearer by the following detailed description, referred to one of its embodiments purely by way of a non-limiting example, illustrated in the accompanying drawings, in which:

Figure 1 is a schematic view of a system of blown extrusion and stretching by annealing of the present coil;

Figure 2 is a schematic view of the appliance used for the irradiation;

Figure 3 is a schematic view of the steps of production of a tube starting from a coil in accordance with the present invention;

Figure 4 illustrates schematically the tube obtained from the steps illustrated in Fig. 3; Figure 5 illustrates schematically the layers forming a first embodiment of the film of the present invention (5-layers);

Figure 6 illustrates schematically the layers forming a first embodiment of the film of the present invention (7-layers);

The process in accordance with the present invention provides for a series of successive steps which will be described here below with reference to Figures 1-2 where the relative apparatuses are shown.

Starting from the left zone of Figure 1, the first step of the present process is represented by blown co-extrusion of a multilayered film 3 which takes place in "n" extruders where "n" corresponds to the number of layers of the co-extruded film of which Figure 1 shows only an extruder for simplicity of illustration, denoted in Fig. 1 by reference numeral 1.

The blown extruder 1 is an apparatus in itself known which is generally composed of an endless screw which conveys the molten material in an annular extrusion head 15, fed simultaneously by a series of extruders (not shown in the drawing), each one fed with a respective polymer material chosen to form the relative layer of the multilayered film 3,

Since this apparatus is in itself known, its functioning will not be detailed nor even less so that of the relative drive rollers 2 (nip rolls) which determine the flattening of the bubble to form the flat film 3.

Generally, the overall thickness of the film 3 intended for the production of collapsible tubes varies from 100 to 400 μιη, preferably from 200 to 350 μιη.

It is understood that it is possible to obtain by blowing, or by means of cast co- extrusion, a film 3 also of different thickness from what is indicated above, for example greater than 400 μιη or lower than ΙΟΟμιη and subject it to the process in accordance with the invention without thereby departing from the scope of the present invention.

In a preferred embodiment of the film of the present invention the overall thickness is at least 100 μιη.

In an embodiment in accordance with the present invention, the multilayered structure of the present extruded film 3 is with five layers composed as follows (Fig. 5):

- outer layer 10 with a base of olefin (co)polymers, (detailed here below), e.g. PE;

- intermediate layer 20; binder (detailed here below);

- intermediate layer 30: barrier layer (detailed here below);

- intermediate layer 40; binding layer (detailed here below);

- outer layer 50 with a base of olefin (co)polymers, (detailed here below), e.g. PE, where the two outer layers 10 and 50, which are opposite one to the other, define the outer face and the inner one of the co-extruded bubble.

As olefin (co)polymers suitable for forming the outer layers 10 and 50 here are understood to be both olefin homopolymers (olefin polymers) and copolymers among olefin and other types of comonomers.

In particular, as olefin polymers suitable for forming the outer layer 10 which is to be the outer layer of the tube, mention can be made, for example, of: polyethylenes such as LD-PE (low-density polyethylene), MD-PE (medium-density polyethylene), HD-PE (high-density polyethylene), LLD-PE (linear low-density polyethylene) mLLD-PE (metallocene linear low-density polyethylene), in all of the various commercially available densities or mixtures thereof.

Said outer layer 10 can also be made in PP (polypropylene), PP-PE copolymers and optional terpolymers, elastomers and plastomers copolymers propylene-ethylene and the like, or said outer layer 10 can be made with the materials mentioned above, but in a mixture with other polymers, such as for example EVA (ethylene-vinylacetate copolymer), ethylene-acrylic esters copolymers such as for example EMA (ethylene- methylacrylate copolymer), EBA (ethylene-butylacrylate copolymer), EEHA (ethylene-2-ethylhexylacrylate copolymer), EEA (ethylene-ethylacrylate copolymer), ethylene-acrylic acid copolymers, such as EAA (ethylene-acrylic acid copolymer) EMAA (ethylene-methacrylic acid copolymer), and relative ionomers where the polar comonomer content (VA, MA, BA, EHA, EA, AA, MAA) is such as to promote the adhesion of inks given the intrinsically polar nature and to promote the overlap welding which takes place in a longitudinal direction in the tube; said polar polymers can also be used pure.

This outer layer 10 is that normally intended to be subsequently printed on the surface, at least in some parts thereof, so that it could undergo corona discharge treatment, in a special apparatus 500 (Fig. 1).

Said corona discharge treatment apparatus 500, which very often is placed immediately downstream of the extrusion system 1 and upstream of the winding section 4 (Fig. 1) can be placed downstream of the stretching and/or annealing section 300 (Fig. 1) so as to subject the film to corona discharge treatment before being irradiated.

Or said corona discharge treatment apparatus can be placed in the irradiation system (before or after the phase of irradiation) and in all cases has the purpose of increasing the wettability of the surface which is treated and promoting adhesion of the ink and, in some cases, promoting the subsequent coupling of the outer layer 10 by means of lamination to other films normally thinner which have various functions (protection of the outer surface 10 from scratches and abrasions arising from handling, thermal resistance, increase in shine or conferring of a different surface appearance: more opaque, "silky", soft touch). The binding layers 20 and 40 have the purpose of binding one to the other the layers 10 and 30, or the layers 50 and 30, respectively, which, being normally poorly compatible one with the other, given the different polymeric nature, risk separating easily during the operations of preparation, filling and use of the future tube.

Normally the binding layers 20 and 40 are constituted by any polymer of the layer 10 or 50 provided it is grafted, or copolymerised, with maleic anhydride.

The barrier layer 30 can be constituted by EVOH (ethylene vinyl alcohol), PVOH (polyvinyl alcohol), PA (polyamide, in all its forms of PA6 homopolymer, of copolyamide, terpolyamide, and the like, and aromatic polyamides) and also any other polymer capable of providing a barrier to gases and aromas, such as polyvinylidene chloride, Barex (polyacrylonitrile methyl acrylate), polyketones, or any polyolefin added with nanofillers capable of improving the barrier to gases of the base polyolefin in which they are dispersed.

The polymers which form the outer layer 50, which is intended to be the inner side of the tube 200 (Fig. 4), can be for example polyethylenes such as LD-PE (low-density polyethylene), MD-PE (medium-density polyethylene), HD-PE (high-density polyethylene), LLD-PE (linear low-density polyethylene) mLLD-PE (metallocene linear low-density polyethylene), VLD-PE (very low-density polyethylene), elastomers and plastomers, propylene-ethylene copolymers and the like, possibly grafted or copolymerized with maleic anhydride (MA), or mixtures thereof to ensure good welding capacity. However in some cases it can contain polymers different from simple polyethylene, such as for example EVA (ethylene-vinylacetate copolymer), ethylene-acrylic esters copolymers such as for example EMA (ethylene-methylacrylate copolymer), EBA (ethylene-butylacrylate copolymer), EEHA (ethylene-2- ethylhexylacrylate copolymer), EEA (ethylene-ethylacrylate copolymer), ethylene- acrylic acid copolymers such as EAA (ethylene-acrylic acid copolymer), EMAA (ethylene-methacrylic acid copolymer), which are normally used also to improve the seal of welding or even ionomers, these polymers can also be mixed with polyethylenes.

In another embodiment the extruded film 3 is a multilayered film with seven layers comprising also one or more intermediate functional layers, with various technological functions in order to increase some properties such as mechanical strength and rigidity of the structure, defined as follows (Fig. 6): - outer layer 10 with a base of polyolefins

- intermediate functional layer 10A

- intermediate Binding layer 20

- intermediate barrier layer 30, e.g. EVOH

- intermediate Binding layer 40

- intermediate functional layer 50 A

- outer layer 50 with a base of polyolefins, intended to be the inner surface of the tube.

These functional layers 10A and 50A can for example be constituted by LD-PE, HD- PE (to confer rigidity), or MD-PE or also LLD or also other polymers present in the other layers but their function is that of incorporating components which it is preferable not to place in the outer layers.

There is a series of essential functions in the final application yet which often require non-advantageous polymers in the outer layers. For example the layer 10A and/or 50A can be advantageously filled with white master with a base of titanium dioxide, useful for conferring a white colouring to the tube but which, if added in the outer layer 10 or 50, would jeopardise the surface shine. The same may occur again with polymers such as HD-PE, useful for achieving the necessary rigidity of the tube (necessary to the extent that the thicknesses of the film are reduced according to a tendency towards lightening of the packaging which involves also this type of containers), yet which confer typically opacity to the surface of the tube.

These layers are found to be very advantageous also for use, alone or in a mixture, of PCR (post-consumed recycled material) polymers, typically post-consumed HD-PE, which allow the use of recycled materials not directly in contact with the product contained and not even with the outer surface, but below a functional barrier (represented in fact by the layers 10 and 50 respectively) as required by legislation in force, in the case of materials intended for contact with foodstuffs (cf. Regulation (EU)/ 10/2011 and subsequent amendments).

It is understood that, even if not explicitly described, co-extruded films 3 can be provided with a structure with nine layers or more, without thereby departing from the scope of the present invention. Moreover, even if not explicitly described, films 3 can also be provided which provide in their structure more than one barrier layer (using different polymers included in the list given above for the barrier layer 30, possibly positioned in different layers) and/or a number of functional layers greater than two, without thereby departing from the scope of the present invention.

In each of the layers 10, 20, 30, 40, 50 of the extruded film 3 in accordance with the present invention, including the functional layers 10A, 50A, it is possible to provide for the addition of one or more functionalising additives including, typically, coloured masters (white, but also other colours), antiblock (e.g. silica), slip, antistatic, anti- condensation, antimicrobial, anti-UV, antioxidant, process aids, nanofiller additives, and others known in the art. These additives are not explicitly included in the formulas mentioned but can be added in one or more of the layers of the co-extruded item.

Once the multilayered extruded film 3 has been obtained, it is subjected to a phase of irradiation, downstream of the blown extruder 1.

In this phase of irradiation at least the outer layer 50, intended to be the inner layer of a tube 200 (Fig. 4) directly in contact with the content, will undergo irradiation as will be explained in detail here below, even if it is possible to irradiate simultaneously also one or more of the other layers forming the film 3, operating appropriately on the power of irradiation so as to confer a further improved mechanical resistance and to the diffusion of gas and vapours (increase in barrier properties).

Irradiation can take place in line with the production of the film 3 or off line at a later time. In the latter case the film 3 exiting from the rollers 2 of the blown extruder 1 is wound in coils in a winding section 4 in order to be stored and treated off line.

During the irradiation, the co-extruded film 3 is sent into a special irradiation station which, as mentioned, can be downstream of the blown extruder 1 or in a separate line where the film 3 is subjected to ionizing rays (Fig. 2) for example by means of bombardment with high-energy electrons, in particular accelerated electrons with energy from 0.05 to 10 Mev. More particularly the co-extruded film 3 is subjected to the abovementioned irradiation treatment by passing into a special chamber in which the irradiating apparatus is placed.

In the irradiating apparatus of Fig. 2, the film 3 is made therefore to pass inside a vacuum chamber 60 in such a way as to wind the outer layer 50, intended to be the inner layer of the tube 200, towards the emitter of the electron beam 61 which is then focused towards the material to be treated, so as to make said beam 61 penetrate at least in the outer layer 50, generating radicals and creating a series of chain reactions of the radical type which lead to the formation of new bonds (e.g. crosslinking).

Among the effects of crosslinking of polymer materials, such as increase in thermal resistance, improvement in the mechanical properties, the improvement in the resistance to chemical agents appears of particular interest in the case of film for making tubes for cosmetic products and for personal care as well as for food packaging.

The electron beam 61 is generated through the thermionic effect by filaments of tungsten 62 heated to very high temperatures (above 2000°C) and accelerated by a high-voltage electrical field in a vacuum chamber.

The electron beams 61 with high dosages (starting from 10 kGy) are therefore used here to modify the molecular structure in that it was found by the Applicant that the crosslinking that can be obtained with these electron beams entails a substantial modification of the molecular structure, with respect to the film not subjected to this irradiation, so that the film itself, after irradiation as described above, has at least two distinctive features:

a) the fluidity of the polymer, understood as melt flow index measured according to ASTM D1238, passes from values of some units, e.g. 1 or 2 (expressed in g/lOmin), to such low fraction values, so as not to be measurable with conventional methods and instruments (the molten polymer subjected to irradiation does not exit the nozzle of the special instrumentation);

b) the Raman spectrum of the surface which has undergone irradiation (and therefore crosslinking) has signals which can be ascribed to the effect of crosslinking, which are not observed in the spectrum of the corresponding non-irradiated surface, demonstrating that the irradiated polymer has undergone a substantial structural modification.

The interesting consequence of this modification of molecular structure on the properties of the film is the obtaining of improved mechanical performances, improved diffusion performances (lower permeability to aeriform substances), fewer transfers through the reduction in the number of oligomers present as well as an increase in thermal and chemical resistance. Once the co-extruded and irradiated film 3" has been obtained (Fig. 2), it is wound into a coil 100 (Fig. 3) ready to be used as is for the making of the tube 200 (Fig. 4) as will be described here below in detail; or said coil 100 of irradiated film 3" can be sent to a phase of further processing such as printing on the surface and/or lamination of other functional films on the surface of the outer layer 10, of the film 3, for example to protect the print, and then sent to a section for the making of the tube 200 (Fig. 4). It is specified that the coil 100 of Figure 3 is already represented in the printed version for greater diagram clarity.

As already mentioned, without departing from the scope of the present invention, the co-extruded film 3, directly exiting from the extruder 1, as in the more typical case (or unwound from a coil produced in the winding section 4), can also be subjected to a treatment of stretching and/or of annealing before being irradiated.

In this case the co-extruded film 3 is sent into a special treatment section 300 (Fig. 1) constituted by an MDO (machine direction orientation) section and/or by an annealing section as will be described here below in detail.

The passage into the stretching and/or annealing section 300 can be performed on line at the extrusion phase by operating on the extruded film 3 exiting from the blown extruder 1, or it can take place at a later time off line by operating on the film 3 unwound from a coil prepared in the winding section 4.

In the stretching and/or annealing section 300 the following steps are performed in succession, as illustrated in Fig. 1:

Preheating: the film 3 is brought to the temperature of softening by making it pass through the first heating rollers 5;

and subsequently Stretching: the successive stretching rollers 6, divided by a narrow crack, elongate and stretch the film 3 up to ten times thanks to their rotation at a speed higher than that of the heating rollers 5;

and/or

- Annealing: the film 3 is toughened by annealing rollers 7 and subjected to voltage; the heat blocks the physical features achieved by the film in the previous steps;

and subsequently

Cooling: the film 3 is brought to ambient temperature by passing through a series of cold rollers 8, and then exiting from the section 300.

The film exiting the treatment section 300, which is a stretched and/or annealed film 3', will then be sent to the phase of irradiation (if the irradiation is to be performed in line) or of winding in a coil in the winding station 11 (if the irradiation is to be performed off line) .

The rollers 5, 6, 7, 8 of the various phases which take place in the treatment section 300 are independent and rotate at different speeds in that designed to perform different operations.

Obviously, the operating conditions of said rollers and of said phases of stretching and/or annealing depend on the type of film to be treated and the relative multilayered structure of the co-extruded film 3. It is to be noted however that the aforesaid operation of stretching which takes place in the treatment section 300 must not be confused with the light physiological stretching which the film 3 undergoes during the formation of the bubble of film during the extrusion in the extruder 1, thanks to the fact that in the treatment section 300 the stretching conditions can be set to obtain a certain degree of stretch.

The Applicant has found that the abovementioned stretching and annealing treatment is particularly advantageous, especially in the case of co-extruded film 3 with high thickness, e.g. greater than 250 μιη, in that this treatment confers improved planarity to the film 3 and an alignment of the edges of a quality which is difficult to obtain with simple blown extrusion. It is therefore understood that the treatment of stretching and/or annealing in the station 300 is optional, even if it is preferred in that advantageous in terms of final properties of the film. In a particularly preferred embodiment, the co-extruded film 3 is subjected both to stretching and to annealing before being irradiated.

Finally it has unexpectedly been found that the step of annealing is particularly advantageous for extruded films with high thickness (such as those that are the object of the present invention) in that, in addition to conferring features of improved transparency and shine, greater elastic modulus and improved mechanical properties in general, allow the thickness to be uniformed enormously to the extent of leading to the production of coils with alignment of the edges of quality unachievable with a traditional extrusion without annealing station, with consequent reduction in the waste through scrap arising from the subsequent phase of printing.

This is valid also in the case of very low stretching levels, for example stretching ratios around 1: 1.1, or also without stretching, through the sole effect of heating and cooling.

In fact, without wishing to be tied to any theory, it can be presumed that during annealing the residual tensions which have been created during the production of the blown film, and during the possible stretching in the drive rollers 2, are reduced drastically and almost completely via annealing, thanks to the fact that the film is heated slowly and uniformly at a precise level of temperature specific for the material, followed by a period of maintaining at temperature, which depends on the material and on its thickness, in order to heat carefully and in depth the part, and subsequently returning slowly and uniformly the material to ambient temperature. The stretched and annealed film 3' is then sent to the irradiation section described above in relation to Fig. 2, repeating the same operations described above in relation to the coextruded film 3, so as to obtain an irradiated film 3".

Therefore, the tube 200 illustrated in Fig. 4 can be made from a coil 100 of co- extruded and irradiated film 3", optionally machine oriented and/or annealed previously. In practice the irradiated film 3" (flat sheet) is cut adequately and folded/wound on itself so as to be shaped into a tube and subsequently heat-welded vertically and horizontally for the closure of the tube.

The application of the rigid part (shoulder and cap) allows the closure at one end and therefore the filling of the tube 200 and finally the successive horizontal welding allows the closure from the other end.

It is understood that what is described above in relation to the film in a coil can be applied as is to a barrier film in the form of a sheet or flat sheet, intended for the production of flexible containers in the form of tubes, where said barrier film is co- extruded, subsequently cut to size, and comprises two opposite outer layers with a base of olefin (co)polymers, an intermediate barrier layer and optionally at least two intermediate binding layers wherein at least one of the two opposite outer layers of said film cut to size is irradiated at least on the surface.

The present invention is not limited to the particular embodiments described previously and illustrated in the accompanying drawings, but numerous detail changes may be made thereto, within the reach of the person skilled in the art, without thereby departing from the scope of the same invention, as defined in the appended claims.

Claims

1. Coil (100) of non-heat- shrinkable co-extruded blown or cast barrier film (3"), intended for the production of flexible containers (200) in the form of collapsible tubes, characterised in that said co-extruded blown or cast barrier film is also surface irradiated on at least one of the two opposite outer layers (10; 50) with a base of olefin (co)polymers, said film further comprising an intermediate barrier layer (30) and optionally at least two intermediate binding layers (20; 40).

2. Coil according to claim 1, wherein the overall thickness of the film (3) varies from 100 to 400 μιη, preferably from 200 to 350 μιη.

3. Coil according to claim 1 or 2, wherein said extruded film (3) has five layers composed as follows:

- outer layer (10) with a base of olefin (co)polymers, e.g. PE;

- intermediate Binding layer (20);

- intermediate barrier layer (30);

- intermediate Binding layer (40);

- outer layer (50) with a base of olefin (co)polymers, e.g. PE.

4. Coil according to claim 1 or 2, wherein said extruded blown or cast film (3) is a multilayered film with seven layers comprising also one or more intermediate functional layers, defined as follows:

- outer layer (10) with a base of olefin (co)polymers, e.g. PE;

- intermediate functional layer (10A)

- intermediate Binding layer (20)

- intermediate barrier layer (30), e.g. EVOH

- intermediate Binding layer (40)

- intermediate functional layer (5 OA)

- outer layer (50) with a base of olefin (co)polymers, e.g. PE.

5. Coil according to any one of the preceding claims, wherein the outer layer 10 is made with olefin polymers such as for example: polyethylenes such as LD-PE (low- density polyethylene), MD-PE (medium-density polyethylene), HD-PE (high-density polyethylene), LLD-PE (linear low-density polyethylene) mLLD-PE (metallocene linear low-density polyethylene), in all of the various commercially available densities or mixtures thereof; or PP (polypropylene), PP-PE copolymers and possible terpolymers, elastomers and plastomers propylene-ethylene copolymers and the like;

the aforesaid polymers can be mixed with other polar polymers capable of promoting the adhesion of inks given the intrinsically polar nature and of promoting the overlap welding which occurs lengthwise in the tube, such as for example EVA (ethylene - vinylacetate copolymer), ethylene- acrylic esters copolymers such as for example EMA (ethylene-methylacrylate copolymer), EBA (ethylene -butylacrylate copolymer), EEHA (ethylene-2-ethylhexylacrylate copolymer), EEA (ethylene-ethylacrylate copolymer), ethylene-acrylic acid copolymers, such as EAA (ethylene-acrylic acid copolymer) EMAA (ethylene-methacrylic acid copolymer), and relative ionomers where the polar comonomer content (VA, MA, BA, EHA, EA, AA, MAA) is such as to promote the aforesaid adhesion of inks and overlap welding; said polar polymers can also be used pure.

6. Coil according to any one of the preceding claims, wherein the outer layer 50 is made with polyolefin polymers such as for example polyethylenes such as LD-PE (low-density polyethylene), MD-PE (medium-density polyethylene), HD-PE (high-density polyethylene), LLD-PE (linear low-density polyethylene) mLLD-PE (metallocene linear low-density polyethylene), VLD-PE (very low-density polyethylene), elastomers and plastomers, propylene-ethylene copolymers and the like, possibly grafted or copolymerized with maleic anhydride (MA), or mixtures thereof to ensure good welding capacity;

or said outer layer 50 is made using polymers different from simple polyethylene, such as for example EVA (ethylene- vinylacetate copolymer), ethylene-acrylic esters copolymers such as for example EMA (ethylene-methylacrylate copolymer), EBA (ethylene-butylacrylate copolymer), EEHA (ethylene-2-ethylhexylacrylate copolymer), EEA (ethylene-ethylacrylate copolymer), ethylene-acrylic acid copolymers such as EAA (ethylene-acrylic acid copolymer), EMAA (ethylene-methacrylic acid copolymer), which are normally used also to improve the seal of welding or even ionomers; said polymers can also be used when mixed with polyethylenes.

7. Coil according to any one of the preceding claims, wherein the barrier layer 30 can consist of EVOH (ethylene vinyl alcohol), PVOH (polyvinyl alcohol), PA (polyamide, in all its forms of PA6 homopolymer, of copolyamide, terpolyamide, and the like, and aromatic polyamides) and also of any other polymer capable of providing gas and aromas barrier, such as polyvinylidene chloride, Barex (polyacrylonitrile methyl acrylate), polyketones, or any polyolefin added with nanofillers capable of improving the gas barrier of the base polyolefin in which they are dispersed.

8. Coil according to any one of the preceding claims, wherein there are one or more intermediate functional layers (10A, 50A) made using polymers such as LD-PE, HD-PE (for giving rigidity), or MD-PE or also LLD, also as PCR materials, optionally added with additives generally not used in the outer layers (10, 50) such as white master with a base of titanium dioxide or colours.

9. Process to prepare the coil (100) of film (3") according to any one of the preceding claims, said process comprising the following steps:

- blown or cast co-extrusion of a film (3);

- surface irradiation treatment of at least one of the outer layers (10; 50) of said co- extruded film (3) to obtain an irradiated film (3").

10. Process to prepare the coil (100) of film (3") according to claim 9, wherein before the step of irradiation, said co-extruded film (3) is subjected to a stretching and/or annealing treatment.

11. Barrier film (3") in the form of a sheet or flat sheet, intended for the production of flexible containers (200) in the form of tubes, said barrier film comprising two opposite outer layers (10; 50) with a base of olefin (co)polymers, an intermediate barrier layer (30) and optionally at least two intermediate binding layers (20; 40), said layers being blown co-extruded, said barrier film being characterised in that it has at least one of the two opposite outer layers (10; 50) irradiated at least on the surface.