RU2785808C2 - Installation and method for operational processing of cuttings on lines for extrusion of film made of plastic material - Google Patents

Abstract

FIELD: material processing.

SUBSTANCE: invention relates to an installation for operational processing of cuttings on lines for extrusion of film made of plastic material. The installation contains a device for separation of side parts – cuttings from film made of plastic material coming out of the device to form the specified film. A device for transportation of the specified cuttings is located downstream relatively to the specified cutting device. The device includes an extruder for processing of the specified cuttings. A device for dosage and supply of granules is made for formation of film made of plastic material in the specified extruder. The specified extruder and the specified device for dosage and supply of granules are located upstream relatively to the specified device for formation of the specified film. A device for preprocessing of cuttings obtained as a result of separation of side parts of the specified film and transported to the specified device for preprocessing by means of the specified transportation device is installed on an inlet of the specified extruder. The specified device for preprocessing consists of a shredder located coaxially relatively to the specified extruder.

EFFECT: invention provides an extruder, which is suitable for direct processing of cuttings and, thus, directly participates in the manufacture of part of the final product, not only granules.

10 cl, 5 dwg

Description

The present invention relates to a plant for the on-line processing of scraps in film extrusion lines made from plastic material.

The present invention also relates to a process for the on-line processing of scraps in film extrusion lines made from plastic material.

The production of plastic film having a relatively thin thickness (commonly referred to as "film") and suitable as flexible packaging in domestic and industrial applications has been growing almost continuously for several decades, and along with the increase in the required quantity, the quality of products is constantly improving and specializing in .

Evidence of this fact is that during these years, various types of production plants have appeared on the market in order to meet the needs of end users as much as possible.

In particular, a film of the type described herein typically (but not exclusively) has a variable thickness ranging from a few microns (5-6 microns in total) up to about 500 microns, with above this limit being used to define this product group. , mainly the term "sheet", in which case the production technology is significantly different from what this context implies.

However, one of the most significant limitations of any type of plastic film machine is the processing and recovery of the so-called "off-cuts", which are the part of the film that is located (but again not exclusively) along the side edges of the film, and which, for various reasons, is directly connected to production process and (in any case) cannot be used because it does not match the characteristics of the rest of the plastic film.

The percentage of this part of the film that cannot be directly used can range from a few percent (in any case not less than 3-4%) up to a level that can even reach 35-40% of the produced film.

In some specific cases, which still make up a small proportion, said scraps cannot be reused in any way in the same process, since, for example, they consist of materials that must be separated from each other in order to be recycled. be used later (for example, in the manufacture of so-called "protective" films, or in the case of films bonded to non-plastic components such as paper or aluminium), but even if these materials can actually be reused, their use always involves a number of steps and processes that cause deterioration of the characteristics of the material itself or significant difficulties in control and that do not fit well with an industrial production line.

More specifically, two systems have been proposed in the state of the art for scrap removal and recycling that appear to be superior in terms of prevalence and efficiency to other lesser known systems:

- processing by regranulation (or "regeneration") scraps in a specific extruder (Fig. 1);

- processing by grinding the scraps in the so-called "mill" and the subsequent supply to the extruder of the production line by means of suitable systems (Fig. 2).

Both systems have their own advantages, as well as disadvantages, which will be discussed in this paper, and which have not yet been eliminated to date.

The regranulation extruder cuttings processing system consists mainly of transporting the cuttings from the extrusion line (from which the cuttings are separated by any cutting system 11, blade, or round blade, or pressure blade, or other device) through any transport system 14 to the operating extruder nineteen; usually, but not exclusively, conveying systems can be operated using the Venturi concept, or cross fans, or again (depending on the type of film produced, and in particular compatibility with its thickness and production speed) through a series of motorized rollers and rolls.

The offcuts, which can be continuously or pre-refined by well-known systems commonly referred to as "multi-blade cutters" 20, can then be introduced directly into the extruder which, by means of a screw with a defined geometric shape (which differs depending on the manufacturer of the extruder and the type of the recovered material) melts the thus obtained material and pushes it into the extrusion head 21, characterized by a series of holes (usually, but not exclusively round in shape), through which a series of so-called "spaghetti" is extruded.

At the outlet of said die, there is usually (but not exclusively) a blade of some type that cuts the spaghetti, producing small granules, the size of which can be changed in the direction of extrusion by appropriately controlling the speed and/or number of said rotating blades, and changing the diameter (or side) can be carried out using a head having holes, the size of which is suitable for this purpose.

Depending on the flow rate of the extruder and the type of material to be recovered (and thus the corresponding operating temperature), the cooling of said pellets (which are obviously produced in the molten state or in any case at temperatures of the processed polymer material close to the respective Vicat softening temperature) can be carried out with the use of a fan which, by transporting the material along a more or less long path in specially made tubes 22, ensures its cooling, or with the use of a so-called "water bath" where the pellets must "fall" in order to cool in a short time.

After cooling in said bath, the pellets are in this case also conveyed by means of a fan/compressor (usually, but not exclusively) along the section previously prepared for their drying, and then decanted (as in the previous case) by means of a cyclone 23 or any other air separation system and particles (in this case granules).

One can easily identify the most significant and most obvious limitations of this method:

1 - High energy consumption as this process is absolutely comparable to "conventional" extrusion and has also been shown to reduce the overall throughput of the production line by several percent.

2 - The need for an almost constant presence of the operator near the extruder, which, in essence, is a separate production line, often located near, but in the place where the "actual" production line is located, since it is a source of dust and dirt of various types.

3 - There is a (very definite) risk of deterioration in the properties of the processed material, in particular from a physico-chemical point of view, due to the additional plasticization process to which it is subjected before being reused on the production line; in particular, very often, if not always, there is a change in the value of the melt flow index (MFI), which characterizes the viscosity of the material in the molten state, which is crucial for the characterization of the final product and its compatibility with any other possible resins used in the mixture.

4 - The need to provide a cooling circuit using water (or some other fluid suitable for this purpose) in the case of extruders for high productivity or for regranulation of raw materials, the processing of which requires particularly high temperatures.

5 - The very frequent use of the water cooling system creates another obvious problem; in the case of materials of a hygroscopic nature (such as, for example, polyamide or nylon, or materials containing inorganic fillers such as calcium carbonate CaCO ₃ ), it thus becomes necessary to also provide a subsequent drying system for the granules produced in this way, which leads to additional (and significant) energy consumption.

6 - The dimensions, sometimes quite significant, of the entire plant (cuttings conveyance + extruder + extrusion head + cutting at the die + possible water cooling + possible drying system + pellet conveying), as can be seen in FIG. 1, which requires the allocation of a room from the production area intended exclusively for this equipment.

7 - A final but no less significant drawback is the difficulty of maintaining a constant flow to the extruder, since almost all cutting transport systems use air as a driving force, which is notoriously difficult to "control" and can thus , it is easy to create a turbulence phenomenon that makes the scraps transported and thus fed to the extruder irregular; the logical consequence of this instability is the creation of large fluctuations in the flow rate of the regeneration extruder and the subsequent production of granules, also having significantly different sizes.

This fact is unfavorable for the possibility of subsequent reuse of the granules obtained in this way, since the significant variability in the particle size of the material significantly affects its apparent density and thus significantly affects the regularity of the supply of these granules in a conventional production line.

This last drawback can be overcome by installing an intermediate grinding mill of any shape or size located immediately upstream of the regeneration extruder; due to this configuration, regular feeding to said extruder is possible, since said mill grinds the cuttings, suppressing any possible irregularities in the regular flow and thus ensuring proper feeding.

The system for processing offcuts by grinding them in a suitable grinding mill, which is shown in FIG. 2 consists essentially of transporting the trims from the extrusion line (from which the trims are separated by any cutting system 11, blade or round blade or pressure blade or other device) via any transport system 14 to the mill 24; usually, but not exclusively, conveying systems can be operated using the Venturi concept, or cross fans, or again (depending on the type of film produced, and in particular compatibility with its thickness and production speed) through a series of motorized rollers and rolls.

The trimmings, which can be continuously or pre- "grinded" by means of well-known systems, commonly referred to by the term "multiblade cutters", enter directly into the so-called mill 24, which is a rotor equipped with a number of blades that rotate at a constant or variable speed around its axis; a row of fixed blades is located on a circle with respect to this rotor at a very small distance from the blades that are mounted on the rotor (usually, but not exclusively, this distance is from 0.05 to 0.5 mm), and thus cuttings, passing through this channel are subjected to scissor-type cutting.

The position below this rotor is usually (but not always) occupied by a kind of "grid" 25, which can have through holes of various shapes and sizes (as a rule, from several millimeters to several centimeters), which ensures the passage of "fragments" of the film only if when they reach the minimum size that allows them to pass.

Thus, as a result of this operation, a lot of "confetti", commonly referred to by the term "flakes", is obtained, which are formed from continuous (or pre-cut) scraps, and whose apparent density is in any case significantly less than the density of the original or regenerated granules, and can also vary to a large extent depending on the size of the fragments, which, in turn, is associated, which is obvious, with the size of the through holes in the specified grid.

In any case, even in the best case, the apparent density of said flakes never exceeds a level of 0.05 to 0.10 kg/dm ³ , in contrast to the value of the apparent density of the granules, which, on the other hand, is usually about 0.55 to 0.60 kg / dm ³ .

Thus, as can be seen, the difference in density (and hence volume occupied) between the two molds is approximately one order of magnitude.

During the grinding operation of the scraps, natural heat generation or heating of the flakes occurs due to the cutting action of the blades; in any case, the mill must be of such size and design that this heating never brings the material to its softening point, i.e. so that it always remains in a solid state and thus does not change its molecular structure (and therefore does not run any risk of breaking down).

These flakes are then transported via any system 26 from the mill to the extruder 16 (or extruders) of the production line, being usually, but not exclusively, discharged via a cyclone 27 and then fed to the extruder 16 via various devices, which may be devices from simple screw conveyor 28 to more complex rotating throughput systems; in any case, these systems should have, as a common denominator, the goal of increasing the density of the flakes until it becomes (hopefully) comparable to the density of the granules, or at least not of the same order of magnitude, providing, in the same time, (partial) mixing of said components.

The most significant and most obvious limitations of this process can be easily identified:

1 - When grinding the trimmings, dust is inevitably generated, which is subsequently transported by the system 26, and which must be separated in some way from the rest of the flakes, so as not to create problems associated with subsequent extrusion on the production line; thus, there is a need for dust-removing systems, which can take a wide variety of forms (simple exhaust hoses, automatic dust removal systems, etc.), but which in any case require maintenance and periodic "emptying"; otherwise, performance may be significantly degraded in terms of dust removal results, leading to deterioration in the quality of the final film.

2 - Undoubtedly, the main problem relates to the re-feeding of said ground product into the extruder (or extruders) of the production line, mainly due to the significant difference in apparent density compared to the original granules; however, any system used must provide a sufficiently significant "hydraulic seal" at the inlet of the extruder to bring the apparent density of the flakes to levels comparable to the density of the granules, but in any case it is a system in which the main principle of operation is friction, acting on the flakes through rotating element.

3 - It thus proves to be particularly difficult to ensure that the extruder (or extruders) of the production line is fed consistently, in particular when the film to be shredded in turn consists of different materials, which can therefore exhibit their own behavior, which also significantly distinguishes them from each other; this inevitably leads to significant difficulties in ensuring the stability of the corresponding production of the final product.

4 - The entire system has significant overall dimensions, as can be seen in FIG. 2, and in addition, the inevitable generation of dust during the process often (if not always) requires the use of a separate room for this system in order to avoid contamination of the final product with said dust during the production process.

The general aim of the present invention is to overcome the shortcomings of the prior art, and in view of this aim, according to the present invention, the use of a plant and method for processing offcuts has been proposed in order to ensure the maximum regularity of supply and, at the same time, the absolute absence of the risk of deterioration material quality.

This goal is achieved by means of the method and installation, which are defined in paragraph 1 and dependent claims of the attached claims.

In particular, according to the present invention, the use of an extruder for regeneration is proposed, but not as an independent installation, but as part of a production line that ensures the manufacture of a part of the final product (or its “layer”).

In other words, since almost all manufactured films are characterized by multiple layers (at least two, very often more than three layers), therefore, production lines are equipped with a corresponding multiple extruders, which are usually (but not exclusively) used to produce a single layer (but also multiple layers); the aim of the present invention is to "replace" one of said extruders with a corresponding extruder which is suitable for the direct processing of offcuts and thus takes a direct part in the manufacture of part of the final product, and not just pellets.

Thus, the novelty that distinguishes the present invention is a complete "bypass" of the "auxiliary" stages, which are described above, namely:

1 - Production of regenerated pellets using scraps (continuous, pre-cut or even pre-crushed) in the case of the first described system.

2 - Grinding and all additional subsequent processing of flakes in the case of the second described system.

The structural and functional characteristics of the present invention and its advantages over the prior art will become clearer and clearer from the following description with reference to the accompanying figures, which illustrate a possible non-restrictive embodiment of the present invention.

Illustrations include:

- in Fig. 1 schematically illustrates a plant for processing scraps by regranulation (or "regeneration") in a particular extruder, said plant being made according to the prior art;

- in Fig. 2 schematically illustrates a plant for processing offcuts by grinding the offcuts in a so-called "mill" and then feeding them to an extruder of a production line by means of suitable systems, said plant being manufactured according to the state of the art;

- in Fig. 3 schematically illustrates a scrap processing plant according to the present invention;

- in Fig. 4 illustrates a pulverizer located directly and coaxially with respect to the extruder according to the present invention;

- in Fig. 5 illustrates a grinding mill mounted orthogonally to the direction of melt flow in an extruder and in the feed system of said extruder according to the present invention.

As shown in FIG. 3:

- conditional number 10 denotes a film (of any type) before the removal of scraps;

- reference number 11 denotes a device for removing scraps (which, as you know, can have a variety of options for implementation);

- conditional number 12 denotes a film without scraps;

- conditional number 13 denotes a device for winding or in any case for "collecting" the manufactured film;

- reference number 14 denotes a device for transporting cuttings (which, as you know, can have a variety of options for implementation);

- conditional number 15 indicates a device for "pre-treatment" (cutting or grinding) of scraps;

- conditional number 16 denotes an extruder for processing these scraps;

- conditional number 17 denotes a device for dosing and supplying granules to the specified extruder;

- reference number 18 denotes a device for forming a film (manufactured according to a known embodiment).

According to the present invention, the installation for the on-line processing of scraps on the lines of extrusion of plastic material 10 contains:

- a device 11 for separating side parts, so-called trimmings, from a film 10 of plastic material coming out of the device 18 for forming said film 10;

- a device 14 for transporting said cuttings, located downstream of said cutting device 11;

- extruder 16 for processing said scraps;

- a device 17 for dosing and supplying granules for forming a plastic film in said extruder 16, wherein said extruder 16 and said device 17 for dosing and supplying granules are located upstream of said device 18 for forming said film 10.

Said pretreatment device 15 is provided in conjunction with said extruder 16.

According to an embodiment, at the inlet of said extruder 16, a device 15 is installed for pre-treatment of scraps obtained by removing the side parts of said film 10 and transported to said device 15 for pre-treatment by means of said transport device 14.

According to the present invention, said pre-treatment device 15 is a device for pre-chopping and/or pre-grinding said trimmings.

Said pre-treatment device 15 is located in line with devices 16, 17, 18 for manufacturing said plastic material 10.

As illustrated in FIG. 3, said device 15 for pre-cutting or pre-grinding continuous trims is installed before the inlet to the extruder 16.

The presence of said device 15 actually makes it possible to ensure a corresponding consistency of feed to the extruder, which is obviously significantly affected by the significant difference in density that exists between the original granules (the feed of which must in any case be independently ensured and trims.

More specifically, for production lines where there is a significant amount of trimmings, this pre-chipping or pre-grinding device 15 is of great importance because the percentage ratio between the amounts of trimmings incoming and the amount of pellets dispensed in the extruder can be high.

Typically (but not exclusively), for production lines using what is called "injection" technology, the actual percentage of offcuts can reach quite significant levels; in this case, in order to ensure an appropriate supply to the extruder (or extruders) for processing scraps, it is preferred to pre-chop or pre-grind said continuous scraps in such a way as to significantly increase their density in relation to the density of the granules.

This pre-chipping or pre-grinding device 15 can take a wide variety of forms, which can be an actual grinding mill, or a so-called compactor, or again a grinder, the latter device being preferably, but not exclusively, provided for coaxial arrangement with said extruder, such in a manner that not only cuts the scraps, but also transports (or "pushes") them into the extruder 16.

The pre-chipping or pre-grinding device 15 can be connected directly or indirectly to the extruder 16. In the case of an indirect connection, the two devices are separate, while in the case of a direct connection, the two devices form a single element.

In particular, this latter solution is particularly suitable for this purpose, since it provides a seal as a whole, while at the same time guaranteeing a constant effective supply.

In this case, as shown in FIG. 4, the illustrated shredder typically comprises an extrusion screw 28 which is directly and coaxially connected to a so-called shredder 29 which can be driven by the same motor 30 or by two different motors.

Thus, the inlet 31 is designed to feed the trim (possibly already pre-cut by the multi-blade cutting system), transport via any transport device 14, and there is also an inlet 32 for the supply of pellets, which can be carried out by gravity (i.e. e. with the direct use of a storage hopper corresponding to the specified inlet 32) or by means of a dosing auger.

Finally, the granules can also be introduced directly, again by means of a storage hopper from the scraps inlet 31, in such a way that a certain pre-mixing of the two said components is also ensured.

In any case, the common feature of the aforementioned pre-cutting or pre-grinding devices 15 is to provide a significant increase in the apparent density of the trims, so that they can be fed directly into the extruder 16 without the risk of creating "bridges" in the feeding process and, therefore , make it possible to obtain a suitable hydraulic seal at the inlet of the extruder 16 without the need for certain or complicated forced systems, and as a result completely eliminate the problems associated with the transport and handling of dust, which is inevitably generated at this stage.

According to a further embodiment, an actual grinding mill of the type described above can be installed on the feed inlet of the extruder 16.

Said grinding mill 24 comprises a rotor equipped with a row of rotating blades which produce a cutting effect on the trimmings due to the presence of a second row of fixed blades attached directly to the structure of the extruder 16.

An example of such a grinding mill is illustrated in FIG. 5, which also illustrates, in addition to the mill 24 and the corresponding mesh 25, an optional fan 33 located below the extruder 16 and in particular below the extruder 16 and in correspondence with the feed inlet from the mill 24 to the extruder 16. The fan 33 is suitable for suction of the ground offcuts and prevent the creation of a "bridge" that prevents proper feeding. When said fan 33 is present, it has a certain function of preventing the ground material from remaining too long in accordance with the grid 25. This could actually lead to overheating of the material to form a molten layer that could block the passage holes in said grid 25.

On the other hand, the presence of the fan 33, which by its action ensures suction at the indicated position, prevents overheating of the ground material and has no contraindications, since there is no melt in the feed area to the extruder 16, but only granules in the solid state can be present, which, obviously, complement the crushed material coming from the mill 24.

In FIG. 5, in particular, is represented with an arrow the direction of movement of the molten mass with the corresponding point of exit from the extruder, which can be connected to a filter change system, to a die, or to any other necessary device that is not represented in this figure.

The object of the present invention also relates to a method for the on-line processing of scraps on film extrusion lines made from plastic material 10.

Said method according to the present invention comprises the following steps:

- separation by means of a cutting device 11 of the side parts, so-called trimmings, from the film 10 made of plastic material coming out of the device 18 to form said film 10;

- transportation of said scraps coming out of said cutting device 11;

- processing these scraps inside the extruder 16;

- dosage and supply of granules for the formation of a film made of plastic material, in the specified extruder 16, and the specified extruder 16 and the device 17 for dosage and supply of granules located upstream relative to the specified device 18 for the formation of the specified film 10,

The pre-treatment step of the trims resulting from the separation of the side parts of said film 10 is provided in conjunction with the manufacture of the film in the extruder 16.

In particular, the pre-treatment step consists of pre-cutting and/or pre-grinding said trimmings.

As described above, the pre-treatment step is in line with the manufacturing steps of said film made from the plastic material 10.

The plant that is the object of the present invention is extremely compact and also completely eliminates the limitations and disadvantages of the two previously analyzed plants as follows.

a) With regard to regeneration, the energy consumption is practically zero, since the energy used to reprocess the offcuts is spent directly on the manufacture of a part of the final product, and not an "intermediate" product (i.e. pellets), which is then re-extrusioned; the only additional energy consumption compared to a conventional extruder is due to the trim transport system and the pre-shredder, but in both cases the indicated energy consumption values are significantly lower than the corresponding values present in the two prior art plants described above and illustrated in FIG. 1 and 2.

b) With regard to regeneration, no additional operator is required, since the extruder 16 is an integral part of the production line, which is already served by one or more dedicated operators.

c) With regard to regeneration, there is no risk of deterioration in the quality of a material that undergoes only a single processing and thus does not undergo a significant change in its physico-chemical characteristics, which provides a complete analogy from this point of view in relation to the grinding mill processing system.

d) With regard to regeneration, since there is no need to cool the pellets produced (because, thanks to the present invention, there is no need to make pellets from scraps), an independent cooling system and possible subsequent drying are not required.

e) With regard to regeneration, there is no problem with the overall dimensions of the installation, since it is "contained" by the production line, which does not have a significant change in overall dimensions in plan views or top views.

f) With regard to regeneration, there is no risk of feed irregularity, since the consistency of the entire extrusion production line increases, the consistency of the number of scraps increases, and in any case, even in the event of undesirable or unavoidable changes, it is possible to compensate for the decrease in flow rate by dosing granules (through device 17, illustrated in Fig. 3). In addition, the presence of the device 15 for pre-grinding or pre-cutting completely solves this problem.

g) With regard to the processing of flakes, there is no generation of dust, since, due to the configuration of the installation, it is not necessary to transport chopped or ground trimmings, which are loaded directly into the extruder 16.

h) With regard to the processing of flakes, there is no need to create any hydraulic seal at the inlet of the extruder 16, since the trimmings are practically "pushed" into it by said chopping or grinding device 15.

i) With regard to flake processing, feed constancy arises in particular as a result of the fact that since there is no transport of chopped or ground trimmings from the chopping or grinding device to the extruder, there is no possibility of creating any type of "accumulation" or stagnation , and thus, nevertheless, the constancy of the flow rate is guaranteed.

j) With regard to flake processing, the increase in overall dimensions is practically zero, since, as already mentioned above, the extruder 16, which processes the trimmings, is an integral part of the production line, and therefore the introduction of any type of installation or device is not required. , besides the primary conveyor for cuttings, which is in any case a really minor complication in relation to the rest of the devices in the extrusion line, regardless of their type.

Thus, the objectives of the present invention mentioned in the preamble of the description are achieved.

The scope of legal protection of the present invention is defined by the attached claims.

Claims (15)

1. Installation for the rapid processing of scraps on the lines of extrusion of a film made of plastic material (10), containing: - a device (11) for separating the side parts, so-called trimmings, from the film (10) made of plastic material coming out of the device (18) for forming said film (10); - a device (14) for transporting said cuttings, located downstream of said cutting device (11); - an extruder (16) for processing said scraps; - a device (17) for dosing and supplying granules for forming a film made of plastic material in said extruder (16), wherein said extruder (16) and said device (17) for dosing and supplying granules are located upstream of said device (18) to form said film (10), characterized in that the device (15) for pre-treatment of trims resulting from the separation of the side parts of the specified film (10) and transported to the specified device (15) for pre-treatment by means of the specified transport device (14), is installed at the inlet of the specified extruder (16 ), and the specified device (15) for pre-treatment consists of a grinder located coaxially with respect to the specified extruder (16). 2. Plant according to claim 1, characterized in that said pre-treatment device (15) is a device for pre-chopping and/or pre-grinding said trimmings. 3. Installation according to any one of the preceding claims, characterized in that said pre-treatment device (15) is located in line with devices (16, 17, 18) for producing said film made of plastic material (10). 4. Plant according to any one of the preceding claims, characterized in that said pretreatment device (15) consists of a grinding mill or compactor. 5. Installation according to any one of paragraphs. 1-4, characterized in that said pretreatment device (15) consists of a grinder directly connected to said extruder (16). 6. Installation according to claim. 1, characterized in that the extrusion screw (28) of the extruder (16) is connected directly or coaxially with the specified grinder (29), and the specified grinder (29) and the specified extrusion screw (28) are controlled by the same motor or two different motors, and at the same time the specified extruder (16) is equipped with at least one inlet (31, 32) for supplying granules and/or trimmings. 7. Installation according to any one of paragraphs. 1-4, characterized in that said device (15) for pre-treatment consists of a grinding mill (24) located at the feed inlet of the extruder (16). 8. Plant according to claim 7, characterized in that said grinding mill (24) comprises a rotor carrying a row of rotating blades which produce a cutting effect on the trimmings due to the presence of a second row of fixed blades attached directly to the structure of the extruder (16). 9. Installation according to claim 7 or 8, characterized in that the fan (33), which is installed under the feed outlet of the mill (24) into said extruder (16), is suitable for suction of the ground scraps in order to provide an appropriate supply for the formation of said film made of plastic material (10). 10. Installation according to any one of the preceding claims, characterized in that the additional trim pre-cutting device is installed upstream of said trim pre-treatment device (15).

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