WO2018149753A1

WO2018149753A1 - Extensible plastic material film and plant for its production

Info

Publication number: WO2018149753A1
Application number: PCT/EP2018/053331
Authority: WO
Inventors: Enrico SCOTUZZI; Alessandro SCOTUZZI
Original assignee: Bia S.R.L.
Priority date: 2017-02-15
Filing date: 2018-02-09
Publication date: 2018-08-23
Also published as: IT201700016728A1; EP3582947A1

Abstract

An extensible plastic material film for packaging obtained by a process comprising the following steps: - imposing a movement in the longitudinal direction to a tape (20) of stretchable plastic material film, and - applying a stretching force to the extensible plastic material film in a transversal direction with respect to the longitudinal direction of movement of the tape (20). The invention comprises also a plant (10) suitable for realizing the process described for the production of the extensible plastic material film.

Description

"EXTENSIBLE PLASTIC MATERIAL FILM AND PLANT FOR ITS PRODUCTION"

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DESCRIPTION

The present invention refers to an extensible plastic material film and to a plant for its production.

As is it known, in the packaging sector heat-shrink plastic films or, alternatively, plastic stretch films are used for wrapping the products.

In the processes in which heat shrink plastic film is used, the film is simply deposited on the products without causing appreciable stretching or straining of the film itself.

Thereafter, heat is applied, thus obtaining a consolidation of the packaging by heat-shrinking. Although this process allows to modulate the stress applied to the product, it has significant costs due to both energy consumption and to the amount of material consumed, as the film is used in significant thicknesses, of the order of 35-60 urn, therefore with a considerable consumption of material .

In the packaging processes in which stretchable plastic film is used (e.g. low density linear polyethylene), it is envisaged to considerably stretch the film during its application to the items to be packaged, so that its elastic return consolidates the products and maintains a stable packaging. The properties of these films allow them to sensibly lengthen longitudinally (up to 200- 300%), so that relatively small amounts of film make it possible to wrap relatively large surfaces.

In general, extensible films have elastic memory in the sense that, depending on the stretching force applied thereto, it is possible to identify three different conditions.

The first condition occurs when the extensible film is stretched by applying to it a stretching force not particularly intense .

In this case, the extensible film extends in a longitudinal direction by a certain amount, while maintaining a certain elastic memory such that, when the stretching force ceases, the film returns more or less to the original length, for example by shortening of an amount that is 95% of the previous lengthening.

Such extensible films can then be used for packaging in which the elastic memory property of the film may be useful.

The second condition occurs when the lengthening of the film exceeds a certain percentage and in this case the film loses the property of elastic memory and becomes a pre-stretched extensible film, having negligible shortening properties once the stretching force is not applied anymore.

Then the film becomes wider and thinner, narrowing transversely in proportion to the applied stretch.

This pre-stretched extensible film is particularly suitable for packing fragile and deformable goods, thanks to the combination of high rigidity, resistance to perforation and thin thickness and allows a stable packaging and a considerable saving of material. The third condition finally occurs when the stretch material is stretched to yielding and then to breakage.

Among the technologies for the production of stretch films, first of all it is mentioned the so-called blown technology in which raw material is used in the form of an elastomeric resin with a high degree of elasticity, but with a good mechanical resistance, but with high production costs

The technology currently considered most effective is the so- called cast extrusion, wherein different layers of polymers are extruded through a flat-head die and laid upon cooled rollers.

In general, finally, the extensible plastic material films used, although longitudinally elongated as seen above, are never widened transversely.

An object of the present invention is to improve the performance of the extensible films, by making an extensible film, particularly for packaging, which is provided with a certain degree of transverse enlargement or widening.

Another purpose is to achieve this result in a practical and economic way.

These aims are obtained by virtue of an extensible plastic material film for packaging obtained by a process comprising the following steps:

- imposing a movement in the longitudinal direction to a tape of stretchable plastic material film, and

applying a stretching force to the extensible plastic material film in a transversal direction with respect to the longitudinal direction of movement of the tape.

Among the advantages of the present invention it can be mentioned the fact that the film obtained by means of the aforementioned method, starting with the same initial plastic material, has a larger surface and a smaller thickness and is therefore able to perform its packaging function with clearly lower costs with respect to a traditional stretch film.

According to an embodiment of the present invention, the step of applying the stretching force in a transversal direction to the extensible plastic material film is performed in order to widen the extensible plastic material film in such a way as to leave a residual elastic memory.

An advantage of this embodiment is given by the fact that the degree of residual transverse elastic memory of the extensible film can be adjusted according to requirements.

According to a further embodiment of the present invention, the step of applying the stretching force in a transversal direction to the extensible plastic film is performed until a pre-stretch condition of the extensible film is reached.

According to a further embodiment of the present invention, the step of applying the stretching force in a transversal direction is performed concurrently with a step of applying a stretching force in a longitudinal direction by rotating a couple of rollers downstream of the first couple of rollers at a speed that is greater than the speed of rotation of the first couple of rollers.

An advantage of this embodiment is the fact that it is possible to adjust both the enlargement and the lengthening of the extensible film during a single passage of the same through the plant .

The invention has also as an object a plant for producing pre- stretch on an extensible plastic material film for packaging, wherein said plant comprises at least a first couple of pinched rollers suitable for receiving a tape of stretchable plastic material film and provided with elements suitable to create transversal stretching forces on the extensible plastic material film.

According to another embodiment of the present invention, the plant comprises a plurality of couples of pinched rollers, wherein the pinched rollers of each couple of pinched rollers placed downstream of the first couple of pinched rollers with respect to the direction of the movement have a greater width with respect to the width of the pinched rollers of the couple of pinched rollers placed immediately upstream.

Among the advantages of the plant of the present invention it can be mentioned the fact that, depending on the sizing of the rollers and on the number of pairs of pinched rollers arranged downstream in the plant, it is possible to adjust the stretching action on the film, for example until widening of the film up to the pre-stretch obtainment point, thus obtaining a stable enlargement, or to a lesser extent, for example by not using the rollers further downstream of the plant, so as to obtain a film with a residual transverse elastic memory.

Further features of the invention can be deduced from the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will become apparent by reading of the following description provided by way of non-limiting example, with the help of the drawings illustrated in the attached figures, in which:

figure 1 shows a lateral view of a plant for producing a pre-stretched extensible plastic material film for packaging, according to an embodiment of the invention; and

- figure 2 shows a frontal view of the plant of figure 1.

In figure 1 it is represented, in a lateral view, a plant for producing a pre-stretched extensible plastic material film for packaging according to an embodiment of the invention, globally indicated with the numerical reference 10.

Plant 10 comprises a support 30 suitable for receiving a main coil 25 from which an extensible plastic material film tape 20 can be unrolled.

According to a preferred embodiment of the invention, a type of plastic material particularly suitable for these purposes is described in the Italian patent application MI2013A001119, the description of which is intended herein incorporated by reference.

Briefly, it is here recalled that such plastic film for packaging is obtained by cast coextrusion in three layers.

It is provided with an inner layer which consists of propylene having an elastomeric base, containing ethylene, and metallocene polyethylene, a central layer and an outer layer are composed of metallocene polyethylene with different melt indexes, lower than that of the metallocene polyethylene of the central layer.

This does not exclude, however, that other types of extensible film are also suitable for the purposes of the present invention. Downstream of the support 30 which receives the main coil 25, at least one pair of pinched rollers 31, 32 is present, i.e. a pair of rollers placed in close contact with each other, leaving sufficient space for the passage of the extensible film tape 20.

In the exemplary embodiment of Figure 1, there are three successive pairs of pinched rollers, that is a first pair of rollers 31,32, a second pair of rollers 33,34, located downstream of the pair of rollers 31,32 and a third pair of rollers 35,36, located downstream of the second pair of rollers 33,34.

Each pair of rollers 31-36 has a grooved surface, for example provided with one or more grooves 40, fixed or movable and sliding, disposed like a helix around the cylindrical surface of the respective roller.

The grooves may be of the male or female type and affect the entire surface of the respective roller or a good part of it.

Alternatively, the surface of the rollers may be made of natural or synthetic rubber having a suitable coefficient of friction.

In general, therefore, the rollers 31-36 are provided with elements adapted to create transverse stretching forces on the extensible film.

As can be seen in Figure 2, each pair of rollers has a width greater than the pair of rollers placed immediately upstream thereof.

In the example of figure 2, the pair of rollers 33,34 has a width greater than the width of the rollers belonging to the previous pair of rollers 31,32, just as the pair of rollers 35,36 has a width greater than the width of the rollers belonging to the previous pair of rollers 33,34.

Moreover, each pair of rollers can be arranged in such a way that the lateral ends of each cylinder belonging to a certain pair of rollers project laterally with respect to the lateral ends of the rollers belonging to the pair of rollers preceding them.

In the operation of the system 10, the tape 20 of the extensible plastic film, is made to advance in the longitudinal direction, unwinding it from coil 25 and making it pass through the first pair of pinched rollers 31,32, whose action by means of a movable spiral generates a stretching force in a transversal direction with respect to the film.

In particular, this stretching force in a direction transverse to the film is generated during the advancement of the tape 20 and is schematically represented with the arrows F in figure 2.

According to a first variant of the invention, the step of applying the stretching force in the transverse direction is carried out until the extensible film is enlarged to such an extent as to leave it with a residual transverse elastic memory. Alternatively, it is possible to extend the step of applying the stretching force in a transverse direction until a pre- stretching condition of the extensible film is achieved.

Moreover, concurrently with the step of applying the stretching force in the transversal direction, a step of applying a longitudinal stretching force can be carried out by rotating a pair of rollers located downstream of the first pair of rollers 31, 32 at a rotation speed that is higher than that of the first pair of rollers 31,32.

In this way it is possible to adjust both the enlargement and the lengthening of the extensible film during a single passage of the same through the plant. Obviously to the invention as herein described, possible modifications or improvements determined by contingent or particular motivations may be applied, without thereby departing from the scope of the invention.

Claims

1. An extensible plastic material film for packaging obtained by a process comprising the following steps:

- imposing a movement in the longitudinal direction to a tape (20) of stretchable plastic material film, and

applying a stretching force to the extensible plastic material film in a transversal direction with respect to the longitudinal direction of movement of the tape (20) .

2. A film according to claim 1, wherein the step of applying the stretching force in a transversal direction to the extensible plastic material film is performed in order to widen the extensible plastic material film in such a way as to leave a residual elastic memory.

3. A film according to claim 2, wherein the step of applying the stretching force in a transversal direction to the extensible plastic film is performed until a pre-stretch condition of the extensible film is reached.

4. A film according to claim 1, wherein the step of applying the stretching force in a transversal direction is performed by adhering the film to a surface of at least a first couple of rollers (31,32) provided with elements suitable to create transversal stretching forces on the extensible film.

5. A film according to claim 4, wherein the step of applying the stretching force in a transversal direction is performed concurrently with a step of applying a stretching force in a longitudinal direction by rotating a couple of rollers downstream of the first couple of rollers (31,32) at a speed that is greater than the speed of rotation of the first couple of rollers (31,32) .

6. A plant (10) for producing an extensible plastic material film for packaging, wherein said plant (10) comprises at least a first couple of pinched rollers suitable for receiving a tape of stretchable plastic material film and provided with elements suitable to create transversal stretching forces on the extensible plastic material film.

7. A plant (10) according to claim 6, comprising a plurality of couples of pinched rollers (31-36) , wherein the pinched rollers (33-36) of each couple of pinched rollers placed downstream of the first couple of pinched rollers (31,32) with respect to the direction of the movement have a greater width with respect to the width of the pinched rollers of the couple of pinched rollers placed immediately upstream.

8. A plant (10) according to claims 6 or 7, wherein the elements suitable to create transversal stretching forces on the extensible film comprise fixed and/or mobile grooves (40) that develop along a helix along an external surface of the pinched rollers (31-36) .

9. A plant (10) according to claims 6 or 7, wherein the elements suitable to create transversal stretching forces on the extensible film comprise a layer of natural or synthetic rubber placed on an external surface of the pinched rollers (31-36) .