The present invention refers to a stretch film made of plasticized PVC, to be used with automatic packaging machines, wherein the plasticizers are of a renewable origin (raw materials from vegetable or animal source) .

Stretch plastic films are aimed to package fresh and perishable food products placed in a tray, in particular: meats, fruits and vegetables, fish products and cheeses.

This type of film, for being suitable for this purpose, must have adequate:

mechanical properties,

anti-fogging properties,

- gas transmission properties,

free from extraction of additives (plasticizers )

anti-static properties,

puncture resistance,

- transparency, gloss and capability of being colored .

Herein below, the above properties will be described in more detail.

Particular care is given to the behavior on packaging machines, since the chance of making packages automatically and with high productivity must be guaranteed.

The installation of the stretch plastic film on automatic packaging machines requires features compatible with the "mechanization". The stresses exerted by the machine and the needs of the machine itself, requires particular technical and mechanical features of the materials which are not strictly necessary to satisfy the shelf life and appeal features of the packaged food, these features being however mandatory to guarantee an efficient use with automatic packaging machines.

Fresh food products are arranged in a tray made of various materials (foamed polystyrene, cardboard and the like) , wrapping then everything with a stretch and transparent film. It is a known and widespread packaging technique, aimed in particular to foodstuff stored under refrigerated conditions, at a temperature generally included between 0°C and 8°C; the shelf life of the thereby packaged product, in particular meat products, generally ranges around 4÷7 days.

The use of these films on automatic packaging machines (such as, for example, Automac machines of the Gruppo Fabbri Vignola S.p.A.) requires specific features related to unrolling, adhesion ("cling effect"), cutting and hot sealing.

The adhesion capability on itself or on other supports gives rise to the closure of the package and it is the base of this packaging solution. Such property must however be commensurate to an adequate resistance offered to sliding, to ensure a correct unwinding and, therefore, a suitable functioning on automatic packaging machines.

Though apparently in mutual contradiction, the above adhesivity and unrolling performances, together with an easy cutting and packaging resistance, are typical of plastic films based on Poly Vinyl Chloride (PVC) and strictly related to the presence of "plasticizing" substances.

The currently used plasticizers comprise esters such as adipates, benzoates, citrates, cyclo- esanoates, ortho-phtalates , sebacates, terephtalates and trimellitates .

These substances, which are the reaction product of an alcohol with an acid, are all mainly of a fossil origin (synthesis processes of an oil derivation) and, as such, have a strong environmental impact.

A commercial example which can be cited is the film called "KOEX 814", marketed by Gruppo Fabbri Vignola S.p.A., which is currently the reference product in the market.

Various formulations are known of polymers and plastic materials with biodegradability and/or compostability features; among which, the following three documents can be cited:

IT1392800 dated 23/03/2012 "Film estensibile biodegradabile" in the name of Manuli Stretch S.p.A.;

IT1402747 dated 18/09/2013 "Poliestere biodegradabile e pellicole aderenti per 1' imballaggio con esso realizzate" in the name of Novamont S.p.A.;

- IT1392986 dated 02/032012 "Pellicola multistrato in materiale biodegradabile e processo per la produzione di tale pellicola" in the name of Sipa Industriale S.r.l.

These are materials having great industrial interest and already nowadays available and capable of replacing traditional plastic materials in several applications, with undoubted benefits of an environmental character. Their use is however currently limited by the scarce economic competitiveness and, still more, by their reduced versatility, with respect to polymers of a fossil origin, which is an obstacle to the possible creation of successful solutions.

In the specific application, the mentioned materials and, more in general, the so-called bioplastics today do not guarantee the peculiarities and the right requirements to satisfy the realization of thin, stretch films for application on automatic packaging machines (wrapping machines) ; for this application the "stickiness" of the film on moving parts is particularly critical and is such to require dedicated "set-up" interventions, which force to unacceptably impair the film performances on the packaging machine.

Machines are known to automatically form this type of packages, equipped with means which unwind a section of film from a roll and arrange it on a plane, subjecting it to a known stretching. The tray containing the product is lifted and forced against the section of plane film, which simultaneously offers a slackening, known as "pandering step", to adjust the film tension on the tray itself. At the end of the lifting, the film edges are stretched and overlapped in a suitable sequence on the bottom of the tray, which, when wound, is discharged, while in the correct step, the winding film is cut and separated from the film coming from the roll.

Known packaging machines are set to optimize the film consumption and to self-adapt some of their movements depending on features, sizes and shape of the product to be packaged.

In order to prevent sealing and package appeal from being impaired, the stretch plastic film must not be subjected to any relaxation after its stretching, keeping the wrapping toughness unchanged.

Object of the present invention is solving the above prior art problems, by providing a stretch film made of plasticized PVC wherein the contribution of the plasticizers is not of a fossil origin, but of a renewable origin (raw materials from plant or animal sources) , and therefore with low environmental impact, simultaneously satisfying the requirements for its use on automatic packaging machines .

The above and other objects and advantages of the invention, as will appear from the following description, are obtained with a stretch film made of plasticized PVC as claimed in claim 1. Preferred embodiments and non-trivial variations of the present invention are the subject matter of the dependent claims.

It is intended that all enclosed claims are an integral part of the present description.

It will be immediately obvious that numerous variations and modifications (for example replacement of ingredients with others having equivalent functional groups) can be made to what is described, without departing from the scope of the invention as appears from the enclosed claims.

The present invention will be better described by some preferred embodiments thereof, provided as a non-limiting example, with reference to the enclosed drawings, in which:

- Figure 1 shows the behavior of the stress- elongation curve pointing out a mechanical behavior of the packaging material; and

- Figure 2 shows a diagram along the transverse direction of the film for the comparison of PVCp biobased TD and the reference "KOEX 818".

Unless otherwise indicated, all designated percentages for the various components or ingredients are in weight and are referred to the total weight of the composition or formulation.

The invention therefore deals with a stretch film made of plasticized PVC, to be used with automatic packaging machines having as feature an elongation at break in the transverse direction of the film equal to 330% (+ 20%) for a film thickness ranging from 11 to 19 μπΐ; such film contains plasticizers based on esters, polyesters and natural oils of a renewable origin, namely raw materials from plant or animal sources, wherein, with respect to the total film weight:

the esters are in an amount <25%;

the polyesters are in an amount <15%; the natural oils are in an amount <15%, The composition of the mixture of the plasticized PVC according to the invention provides for the presence of esters, polyesters and natural oils .

The esters used in the formulation of the invention are obtained from fatty acids of a renewable origin with alcohols or poly-alcohols, always of a renewable origin (glycerin, ethanol, hetero-cyclic compounds derived from glucose) . Moreover, they are obtained from the purification and/or transformation of natural oils of a renewable origin (from seeds of soy, palm, castor oil, flax, cotton, olive, etc.) in an amount <25%.

More in detail, such esters are:

. triglyceride of capric and caprilic acid

. acetyl tri-n-butyl citrate

. triethyl citrate

. dibutyl sebacate

. C2-C24, aliphatic, linear, mono-carboxylic acids, coming from natural fats and oils, glycerol mono-, di- and tri-esters thereof (branched fatty acids at naturally occurring levels are included)

. 1, 2-propylene glycol monolaurate

. glicerine diacetate monolaurate

. sorbitan monolaurate or monostearate or monooleateglicerine monooleate or monopalmitate or monostearate, ester with citric acid or ascorbic acid.

The polyesters used in the formulation of the invention are obtained through reaction of bi and tri-functional carboxylic acids of a renewable origin (citric acid, succinic acid, sebacic acid, azelaic acid, etc.) with glycols and poly-glycols of a renewable origin, in an amount <15%.

More in detail, such polyesters are:

. polyesters of 1, 2-propanediol and/or 1,3- and/or 1 , 4-butanediol and/or polypropyleneglycol with adipic acid, which may be end-capped with acetic acid or C12-C18 fatty acids or n-octanol and/or n- decanol

polyesters of adipic acid and 1 , 3-butanediol , 1, 2-propanediol and 2-ethyl-l-esanol .

The natural oils used in the formulation of the invention are of a renewable origin, epoxidized and/or hydrogenated (soy, palm, castor oil, flax, cotton, olive, etc.) in an amount <15%.

The formulation of the invention is completed with components such as: anti-fogging agents (typically esters of fatty acids) in an amount on the order of 1-3%; stabilizers in an amount on the order of 1-2% and lubricants in an amount on the order of 0.1-0.3%.

The above mentioned film is obtained through a preliminary mixing step of PVC resin and the various components composing the "dry Blend" mixture, where the "compounding" process occurs producing a PVC compound which must be left at rest to allow its cooling and its complete homogenization .

The following step implies the horizontal extrusion of a tubular from the above compound which, through an extruding head, forms an air- inflated bubble which, suitably contained and compressed through rollers, is collected in rolls of double-layered thin films with thickness on the order of 8 ÷ 35 μπι (the range between 20 and 35 μπι being dedicated to frozen products) .

The film thickness is given by the size of the gap on the extrusion head and the air inflation, which stretches the walls of the material forming the bubble.

The orientation in a thin film is therefore bidirectional and is determined by the stretch due to the film winder (machine direction) and by the side stretch determined by the inflation, to define the bubble diameter (transversal direction) .

The particular combination of the mixture of the plasticxzers and the specific mixing conditions used in the plasticizing step, guarantee the homogeneity of the melt materials . Similarly, to the compound formulation, the bidirectional orientation imparted during the extrusion step cooperates to define the features and the final performances of the resulting plastic film in terms of chemical, physical, mechanical, thermal and optical characteristics.

The additives incorporated and characterizing the above compound are those that allow conferring to the film the above desired properties, and in particular :

mechanical properties,

anti-fogging properties,

gas transmission properties,

low migration of additives- anti-static properties ,

resistance to perforation,

transparency, gloss and capability of being colored.

The mechanical properties are the physical properties satisfying the mechanical performances of the packaging material, including the friction and resistance properties.

The anti-fogging properties refer to a particularly appreciated feature, which allows avoiding the micro-condensation of humidity, which fogs up the packages of fresh and refrigerated products, typically meat and vegetable products.

The gas transmission refers to the phenomenon of the permeation of gas and vapors through a packaging material, and it is extraordinarily important for the quality of the packaged food product, allowing breathing and natural metabolism of fresh products.

The low migration of additives is the property that defines the low release of additives from the plastic film to the wrapped product, thus guaranteeing food safety.

The anti-static property, , due to a reduction of the surface resistance, ensures that the film is not statically charged during its production and use .

Puncture resistance is the property for which the package is capable of resisting to the penetration of objects having a sharpened shape, with which it should accidentally get in contact.

Transparency, gloss and capability of being colored are properties which refer to the package appeal .

Three examples for making the invention will now be provided. Such Examples do not limit the scope of the invention, as detailed by the enclosed claims .

EXAMPLE 1

A first formulation has been prepared, with the following composition:

PVC resin 67.4% monomeric plasticizer based on capric and caprilic acid triglyceride 6.7% polymeric plasticizer based on polyesters of 1, 2-propandiol and/or 1,3- and/or 1, 4-butandiol and/or polypropyleneglycol with adipic acid

6.1% acetyl tri-n-butyl citrate 4.7% epoxidized soybean oil 4.0% - tri-ethyl citrate 3.4%

di-butyl sebacate 3.4% mixtures of esters of fatty acids 2.7% - fatty acid salts of Ca/Zn in epoxidized soybean oil 1.4% - stearic acid 0.2%.

EXAMPLE 2

A second formulation has been prepared, having the following composition:

PVC resin 67.4% - monomeric plasticizer based on capric and caprilic acid triglyceride 6.7% polymeric plasticizer based on polyesters of 1, 2-propandiol and/or 1,3- and/or 1, 4-butandiol and/or polypropylenglycole with adipic acid

4.7% acetyl tri-n-butyl citrate 4.7% epoxidized soybean oil 4.0% tri-ethyl citrate 3.4% di-butyl sebacate 3.4% mixtures of esters of fatty acids 2.7% fatty acid salts of Ca/Zn in epoxidized soybean oil 1.4% stearic acid 0.2%.

EXAMPLE 3

A third formulation has been prepared, having the following composition:

PVC resin 67.4% polymeric plasticizer based on polyesters of 1, 2-propandiol and/or 1,3- and/or 1, -butandiol and/or polypropylenglycole with adipic acid

10.1% acetyl tri-n-butyl citrate 10.1% epoxidized soybean oil 4.0% di-butyl sebacate 4.0% mixtures of esters of fatty acids 2.7% fatty acid salts of Ca/Zn in epoxidized soybean oil 1.3% stearic acid 0.1%.

The resulting films with plasticization from renewable sources according to Examples 1, 2 and 3 have been verified in laboratory and compared with the current reference film in the market, the above mentioned "KOEX 814" formulated with plasticizers of a fossil origin.

Table 1 includes the optical properties ("haze" and "gloss") , the gas transmission properties (0 ₂ , C0 ₂ and WV-water vapor) and the mechanical properties (elongation at break and tensile strength at break) of the three formulations in Examples 1, 2 and 3, and of "KOEX 814", such properties having been obtained according to the cited ASTM standards.

From the comparison between the features of the formulations of the invention and those of the "KOEX 814", it follows that the invention guarantees the peculiarities, the performances and the reliability of PVC films with plasticization from fossil source.

In a preferred structure, the present invention provides for an amount in weight of mixture of plasticizers from a renewable source between 10% and 40% and, preferably, between 20% and 30%.

Preferably, such mixture of plasticizers from renewable source comprises:

a mixture of esters from a renewable source in an amount in weight <25%, and preferably included between 10% and 20%;

polyesters from a renewable source in an amount in weight <15%, and preferably between 2% and 12%; natural oils from a renewable source in an amount in weight <15%, and preferably included between 3% and 8%.

Still preferred (and such as to strictly include Example 3) , such mixture of plasticizers from a renewable source comprises a mixture of:

esters from a renewable source in an amount in weight <25%, and preferably included between 10% and 15%;

polyesters from a renewable source in an amount in weight <15%, and preferably included between 9% and 11%;

natural oils from a renewable source in an amount in weight <15%, and preferably included between 3% and 6%. The comparison with the "KOEX 814" has been made also according to the functional evaluation and reliability tests on Automac machines, comprising the traditional machines and the so- called "Elixa family".

Both automatic packaging machine families have similar mechanisms and operating analogies; however, the Elixa machines produces an important stretch of the film, even around 100%, in both D (machine direction) and TD (transversal direction) directions .

Differently, traditional machines cause a lower stretch, generally not greater than 50%.

For both machines, the transverse direction (TD) is the most stressed one, and as shown in Figure 1 which reproduces the stress and strain curve, the composition described in Example 3, proposed in a thickness of 13 μτα (with a reduction over 7% compared to the reference thickness) , faithfully reproduces of the performances of the reference material, called "KOEX 814".

The behavior of the stress and strain curve of Figure 1 points out a mechanical behavior of the packaging material suitable to satisfy quite high functional performances during packaging, such as to be particularly suitable also for automatic machines aimed for industrial production lines, capable of wrapping up to 90 trays per minute (Automac 75 and Automac 95 of the Applicant) .

The functional and performance evaluation of the film is performed under conditions deemed conservative following a consolidated procedure on Elixa 35 and A55+ machines in a climatic chamber at the temperatures, of 5°C, 20°C and 30°C, with the intention of reproducing the performances and reliability results of the market reference "KOEX 814".

Depending on history and acquired experience, it can be stated that the "highest risk" situations on which the performances of the plastic film are evaluated on an automatic packaging machine deal with :

the steps of film unwinding and stretching;

the steps of pandering and partially closing the cling film around the product (foodstuff placed in the container) ;

the steps of completely closing the cling film around the product, of film cutting and of expelling the packaged product.

Such situations have been evaluated for a range of representative trays for fresh foodstuff, specifically the packages mentioned in the enclosed TABLE 2, with the purpose of validating the invention, ascertaining its reliability and efficiency during packaging. This evaluation has been made evaluating the percentage of film tears during package production . The test results are reported in TABLE 3, wherein it is clearly shown how the formulations according to the invention perform in a substantially equivalent manner to KOEX 814.

Example 3 and its related mixture show mechanical properties satisfying the operating conditions on Automac packaging machines with reduced thicknesses (13 μπι) with respect to the reference one (KOEX 814, 14 μπι) .

Together with the 13-μπι thickness, which replicates the 14-μπι thickness, the 17-μπι thickness exactly replicates the "KOEX818" reference with a thickness of 18 μιτι, as pointed out by the diagram in Figure 2.

The chance of the novel formulation in Example 3 of reducing the thickness, keeping the mechanical properties, and therefore the performances in a wrapping machine, unchanged, is well suited with the current environmental issues in the field of sustainability and reduction of the environmental impact of plastic materials.

Always regarding environmental issues in support of the actual use of raw materials from renewable sources, analyses have been performed about the contents of carbon-14 in the film. The analyses with carbon-14 are used to univocally measure in a reproducible way the exact percentage of carbon derived from renewable sources (or biomass) : in particular, such analyses, described in the ASTM D6866 method, distinguish between modern carbon, derived from biomass, and carbon derived from fossil fuels. The biomass contains a certain amount of carbon-14 which makes it easily distinguishable from other materials, such as fossil fuels, which do not contain carbon-14. Since the amount of carbon-14 present in the biomass is known, the percentage of carbon derived from renewable resources can be easily computed on the total carbon in the sample.

From an analysis with carbon-14 for the samples disclosed in Examples 1-3, it resulted that the percentage of carbon from renewable source on the total carbon falls within the 20%-40% range, so that the "OK BIOBASED" Certification, released by the Certification Body Vingotte, now TUV AUSTRIA, has been obtained.

In particular, from an analysis with carbon- 14, the following percentages of carbon from renewable sources on the total carbon resulted:

• 36% for the film in Example 1,

• 30% for the film in Example 2,

• 32% for the film in Example 3.

MD -machine direction TD - transversal direction TABLE 1

TABLE 2

TABLE 3