FR2922141A1 - Recycling of polyolefin film waste previously shredded, crushed, and fragmented, useful to obtain granules to prepare formulations, comprises compressing waste fragment, extruding, compression melting, filtrating the fragmented wastes - Google Patents

Abstract

Recycling of polyolefin film waste previously shredded, crushed, and fragmented, comprises (a) compressing waste fragments by incorporating powder fillers, (b) extruding, compression melting, and filtrating the fragmented wastes in mono screw extruder, where in a step (d) the extruded and filtered material obtained from mono screw extruder is introduced in melted condition in a twin-screw extruder mixed with powder filler and is subjected to a degassing and a second filtration before granulating.

Description

METHOD OF STYLED RECYCLING OF POLYOLEFIN FILMS AND MASTER MIXTURE WITH HIGH PULVERULENT LOAD CONTENT FROM THE PROCESS

FIELD OF THE INVENTION

The invention relates to a process for recycling by compounding extrusion of polyolefin film waste.

The invention relates more particularly to a process for recycling by compounding extrusion, unsorted polyolefinic film waste, which can comprise both printed or non-printed films, thick films or thin films in the limit of the absence of contaminations such as paper labels or soil residues or other contaminants such as for example films of other chemical nature.

Such undifferentiated polyolefin film waste, for example, may be post-industrial waste, such as production falls, both during extrusion and printing of such films, as production falls resulting from the manufacture, by cutting, folding and welding of bags and sachets, or - post consumer waste, that is to say after use, indifferently unprinted or very strongly printed, having, for some of these 30 film wastes, have been prewashed to remove the paper labels on some of these end-of-life flexible packaging, or to remove some soil such as soil fragments, in the case of films used in the agricultural field.

Such waste film is now systematically collected, by selective collections, and become available for material recovery all the more demanding as the quantities collected become important. In fact, the laws in force in most developed countries require the recovery of packaging materials and waste and the recycling rates for such materials have been revised upwards by the legislator.

STATE OF THE ART

Polyolefin film production scrap, as well as polyolefin film waste for end-of-life packaging, is now recycled by state-of-the-art processes and techniques. These processes comprise the steps, optionally washing, shredding and grinding, densification of the film, extrusion compounding in extruders generally mono-screw, melt filtration to separate the impurities present, and finally granulation.

Recycled pellets, called recycled or regenerated, thus produced are then reused in the plastic processing in order to manufacture any other product, generally of lesser quality, because the degree of purity obtained for this recycled material is rarely at the virgin material level. For example, making a thick tube from film waste is actually less critical than making a film, and in particular a thin film.

For example, DE 19,860,352 discloses a stepwise method operating in a closed-loop concept for recycling clothing covers made of polyolefin films, comprising a) shredding and grinding, b) melting the crushed fragments in a first extruder, c) degassing of volatile impurities, d) filtration of particulate impurities, e) granulation of the plasticized melt, f) cooling and drying of granules thus produced, g) metering of said granules with additions of virgin polyethylene granules and additives in a second extruder, h) plasticization of this metered mixture, ie its melting and homogenization, i) filtration of residual solid impurities, j) supply of the melt in a film extruder, k ) formation in an annular die of a sheath to manufacture a film by blown bubble techniques, 1) cooling and setting, thickness and size of said blown film sheath, m) nip between two rolls of the sheath and pulling, n) winding, cutting and welding of the sheath, in order to obtain new garment covers.

By polyolefins is meant a mixture mainly of low density polyethylene, linear low density polyethylene, with minority addition of high density polyethylene and polypropylene.

The film sheath resulting from the process comprises between 5% and 30% by weight of low density polyethylene and / or virgin linear low density polyethylene.

However, such an integrated recycling process has several limitations, in particular that of not being able to optimize the feeding of the first extruder, insofar as the apparent density of the film crushes is very low, as well as that of being relatively limited in terms of degassing power, being able, in this sense, to recycle only materials that are very slightly polluted with volatile matter, that is to say without printing, and, consequently, can only lead to thick films medium and not thin.

The reason for this impossibility to extrude such recycled materials to thin thicknesses, that is to say of the order of 30 microns, is the presence of what the skilled person calls unpolluted. These unmelted material particles constituting hard points present and which fail to melt into the melt. These unmelted ones cause tear initiation points when the material is extruded into the annular die and is blown into thin film, stretched in the machine direction and in the cross direction, depending on the rate of inflation of the bubble, in order to obtain a film sheath of the desired thickness.

The formation of unmelted material results from oxidation and crosslinking caused by the thermal degradation of low molecular weight synthetic organic materials which are, inter alia, printing inks, these oxidation points being able to go as far as constituting particles. of literally carbonized material, of size substantially equal to the thickness of the film.

In a so-called open recycling loop concept, that is operating from waste for processing in another application, JP 10249859 discloses a method of recycling polyethylene pipe falls in order to to obtain, by conventional methods of extrusion of blown sheath, a film. The process consists of the addition of virgin low density polyethylene with a melt index ranging from 0.2 to 0.8 g / 10 min and a masterbatch of calcium carbonate concentrated to 80% mineral filler in 20% of water. a virgin polyolefin matrix. Such a method is quite conventional, but very specific, as regards both its composition and the incoming flux to be recycled, the addition of masterbatch being of the order of 40% in the final composition of the film. thus produced. The films obtained can only be very thick.

EP 1,401,623 discloses a method for producing a thermoplastic material containing a filler comprising the steps of charging a thermoplastic base material into a container provided with mixing and stirring means, raising the temperature of the thermoplastic material base until said material has reached a softened state, mixing a mineral filler with said softened thermoplastic material within said container, collecting said material containing said filler from said container and performing a step of densifying said material softened and loaded. The mixing and stirring means deployed in this process comprises a so-called friction and shock disintegrating means which has the effect of causing softening of the thermoplastic material, which softening takes place in a temperature range from its melting point. at a value of 25 ° C below its softening point, also called Vicat point, and therefore at a temperature below the melting temperature of the thermoplastic material. The densification step is an extrusion step, this extrusion taking place by means of a single-screw extruder. The thermoplastic material is an industrial waste to be recycled.

Such a method does not strongly charge a thermoplastic waste mineral load. In addition, such a method does not make it possible to recycle such materials, generally available in the form of films, at very high flow rates of several tons per hour, and especially to produce very homogeneous and non-infused recycled materials for thin film extrusion applications.

The document FR 2870477 describes a recycling process, by extrusion-compounding, of polyolefin film waste highly polluted by impressions, in granules, the composition of which consists of said waste and a pulverulent inorganic filler, in particular of carbonate of calcium, which can be transformed into opalescent or colored films, of medium to shallow thickness, less than 50 microns, even 30 microns, of good appearance and good mechanical properties, and having in this sense partly solved this problem previously mentioned training crippling of infertile.

This recycling process of polyolefin film waste uses a special twin-screw extruder corotative and operating under very special conditions. The incorporation rate of the pulverulent inorganic filler in the composition is 30 to 70% by weight of the composition. Film waste is introduced into the twin-screw extruder in the preferred form of film crushes, and / or possibly densified flakes, optionally combined with recycled granules obtained by simple melting, extrusion and granulation. The retained polyolefins constituting these film wastes have a melt index in the range of 0.2 g / 10 min to 7 g / 10 min. The granules obtained according to the process are used for the production of films with a thickness of between 200 microns and 30 microns, from mixtures formed of said granules and granules of virgin or recycled polyolefins in a conventional manner.

This process is certainly efficient, but does not allow, for the granulate thus produced, on the one hand to obtain mineral fillers higher than 70% by weight in the composition, and on the other hand to optimize the flow rates of production, by feeding the twin-screw extruder preferentially given to the form, fragment of film waste, rather than any other physical form.

There is therefore a need to improve the process, in particular in terms of the mineral load contents and the flow rates possible at these high levels.

OBJECT OF THE INVENTION

A first object of the invention is to recycle waste polyolefin films, of any thickness, governing by the same the fluidity indices of the polyolefins constitutive of these films, regardless of their subsequent state of transformation, in particular films strongly printed or not.

A second object of the invention is to be able to transform this waste into a quality recycled material, ie homogeneous and free, as far as possible, of unmelted, and in the physical form of a granule.

Another object of the invention is to be able to transform this recycled material, in the physical form of a granule, into films, opalescent or colored, of good appearance and good mechanical properties, medium and low thicknesses, less than 30 microns, and to be able to use these recycled materials at the highest possible rates, without having to dilute them too strongly with virgin materials and to be able to transform them by the conventional techniques of bubble extrusion, also well in monolayer than in multilayer.

Many objectives are therefore assigned to the process according to the invention to be recycled, by a step process, operating continuously, very high speed, that is to say several tons per hour, flows that can not be achieved with the processes of the state of the art, all waste polyolefin films strongly printed or not, however separated beforehand from particular pollutants such as paper labels or residues of earth or other films of different chemical nature, and this with a view to to produce a granulate very highly charged in powdery charge, that is to say in particular even more than 70% by weight, and intended for the manufacture of other quality films, in particular of good homogeneity and free from unmelted, and thin, without having to dilute too heavily highly charged granulate, from these recycled materials in virgin materials with consequent material costs high.

SUMMARY OF THE INVENTION All the objectives assigned to the subject of the invention can be achieved by creating a stepwise process operating continuously and at a very high flow rate and leading to the production of a highly charged granulate. pulverulent filler free from defects found and suffered, in particular, the particulate nonferrous.

Therefore, the invention relates to a process for recycling waste polyolefin films previously shredded, crushed, fragmented and comprising the successive steps of: a) densification of fragmented waste, with incorporation of pulverulent fillers, b) extrusion-plasticizing- filtration in a single-screw extruder, charged fragmented waste, characterized in that, in a step d), the extruded and filtered material from the single-screw extruder is introduced in the molten state into a two-part compounding extruder. screw, receives a complement of pulverulent charge and is subjected to degassing and a second filtration before granulation.

The invention also relates to the recycled product resulting from the recycling process by step operating continuously and at a very high flow rate, that is to say a granulated masterbatch whose charge rate is, when this charge is mineral, between 30.degree. and 85% by weight in a polyolefin matrix, resulting from the waste of recycled films available, having a melt index in the range from 0.1 to 10 g / 10 min, and preferably from 0.2 to 4 g / 10 min, ie fluidity indices corresponding to those used to make films of high or low thicknesses.

The invention finally relates to the use of the recycled product resulting from the process, which is a recycled granular masterbatch with a high content of pulverulent filler, used for the production of opalescent or colored films, with a thickness of between 200 microns and 30 microns, from mixtures formed of said recycled granulated masterbatch and virgin recycled polyolefin granules or polyolefins in a conventional manner, in proportions ranging from 10% to 100% by weight of said granulated masterbatch. DETAILED DESCRIPTION OF THE INVENTION

The recycling process, according to the invention, concerns waste polyolefin films pigmented or not, whether or not loaded with mineral material or other, previously stabilized or not against UV radiation, covering the field of non-printed until totally printed, that is to say polluted on the surface by printing inks and / or polluted on the surface by adhesives, said film wastes having already been previously cleaned off, by washing, of pollutants such as adhesive labels, paper or other, or inorganic soils such as soil residues in the case of films used in agriculture.

In other words, the recycling process according to the invention operates from a deposit of undifferentiated polyolefin film waste, such as post-industrial waste, production losses, post-consumer waste, ie after use, indifferently covering the field of unprinted until fully printed.

Polyolefin films are understood to mean all films made from all types of polyolefins usually converted into films by any technique, such as annular or flat die, mono or bi-oriented film, single-layer or multilayer film. Polyolefins are understood to mean both low-density radical polyethylenes (LDPE) and linear low-density polyethylenes (LLDPE), and very low density polyethylenes (VLDPE) than medium-density polyethylene (MDPE) and high-density polyethylenes (LDPE). HDPE), polypropylenes (PP), but in a small proportion, that is to say no more than 5% by weight of the mixture of film waste to be recycled, in their homo or copolymer form obtained by any polymerization process. , using or not any type of catalyst, modified or not, alone or in mixture, formulated or not.

These olefin polymers are the result of the polymerization of olefins (C2-C12) with comonomers and in which the olefin segment is present in significant amount relative to other comonomers.

In particular, homopolymers such as polyethylenes and polypropylenes, copolymers such as propylene copolymers, ethylene-alpha-olefin copolymers, ethylene-vinyl acetate copolymers, ethylene-acrylate copolymers or ethylene methacrylate, copolymers of ethylene with 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene.

The densities of the polyolefins selected are in the range 0.850 to 0.900 g / cm 3, in the case of polypropylene, in the range 0.850 to 0.928 g / cm 3, in the case of low density polyethylene, in the range 0.925 to 0.935 g / cm 3 for medium density polyethylene, and in the range 0.900 to 0.970 g / cm 3 for high density polyethylene when measured according to ASTM 1505.

It should be noted that the polyolefins retained in the field of films have a melt index in the range of 0.1 to 10 g / 10 min (ASTM D 1238 - 2.16 kg - 190 CO). Usually, the melt indexes are in the range of 0.2 and 4.0 g / 10 min for the low density polyethylene and linear low density polyethylene films which constitute the bulk of the waste collected and therefore treated. according to the process, the polypropylene films and the high density polyethylene films appearing as very minor, ie being present by weight only at proportions of less than 5% of the treated waste and can therefore be ignored because diluted in a large mass of low density polyethylene.

The thickest films are generally made from polyolefins of lower melt indexes and vice versa. It should also be noted that the polyolefins with lower melt indexes are difficult to miscible with polyolefins whose melt indexes are higher.

This film waste can also be more or less wet, depending on whether it has been stored outdoors or in bad weather. They can also have, in small quantities, degradations by prolonged exposure to ultraviolet radiation, in particular for neutral films, in agricultural applications.

According to the invention,

Preparation of the material intended for the process The preparation of the material aims at a controlled and homogeneous supply of the process, both in the physical form and in the variability of the material to be recycled. To do this, the waste film feed to be recycled is performed in such a way as to create homogeneity, before the shredding / grinding and intermediate storage of the crushed film waste to be recycled.

Waste polyolefin films in the form of bags, bundles, bundles of sheets, individualized sheets, pieces, strips, strips, flaps, folded film pieces, crumpled balls and other shapes physical, are introduced into a shredding / grinding unit. These films or sheaths have thicknesses ranging between 500 and 10 microns depending on the types of films and the applications concerned. As an illustration, an agricultural cover will have a thickness of 300 microns while a stretch film will have a thickness of 10 to 20 microns once stretched.

These film wastes may, prior to densification in whole or in part have been washed at modest temperatures in the case of films polluted or soiled on the surface, but whose pollution can be extracted by simple washing with water in the presence possible detergents. Even intensive and abrasive washing will not be able to eliminate the inks present on these films if they are strongly printed. The film fragments are generally dried, but the storage conditions may cause the residual moisture content in the bales of compressed film fragments to be quite high.

The film waste is shredded / crushed continuously to a fragment size ranging in average value from 5 to 25 mm on the side and by at least one means of shredding / grinding, generally operating dry, called shredding / grinding unit, this unit preferably implementing shredders / grinders with knives and possibly against blades. These shreds, also called film flakes, are stored in at least one intermediate storage silo equipped with a homogenization system by air circulation. This at least one intermediate silo feeds, continuously and in metered quantities, a densification unit of step a) of the process.

In a preferred mode of preparation of the material, in order to supply the process, the at least one shredder / mill is fed with film waste to be recycled by means of at least one loading belt. Each of the at least one carpet feeds a shredding / grinding unit of films, making it possible to reduce the size of the film waste before intermediate storage and then to enter the densification unit.

Operators deposit on the at least one feed belt, the waste film to be recycled, either in the form of compressed bales opened by the operator, or in the form of pieces and strips of film cut also delivered in bales or in container.

The at least one feed belt is thus loaded from at least one waste stream to be recycled. In the case where several waste streams are to be recycled, these flows can be very different and are in any case perfectly indexed.

The operator in charge of the at least one carpet ensures that the quantities disposed on this at least one carpet from the different stocks of waste to be recycled and corresponding to the identified flows, are regular.

The at least one carpet feeds a shredding / grinding unit, connected to at least one intermediate storage silo. In the case of the presence of several storage silos, these silos are then loaded in parallel with the crushed film waste thus produced.

In the case of the presence of, for example, two feed mats, each can, in some way, be dedicated to types of film scrap of different origins, particularly thick films ranging from 100 to 300 microns and films. thin films ranging from 10 to 100 microns, these films having each been manufactured from polyethylenes of grades, that is to say of melt index, ranging from 0.1 to 1 g / 10 min for films thick and in the range 1 to 3 g / 10 min for the thinnest films, that is to say particular fluidity indices. Similarly, the specific risks of contamination associated with a film type, for example for post-consumer films, as opposed to film waste resulting from defective fabrications and collected in the same manufacturing plant, can thus be distributed very regularly. on all of the at least one intermediate storage silo.

The moisture content of the film waste does not need to be controlled, while some of the film bales that have been stored outside and thus have been subjected to bad weather bring high humidity levels.

Film waste, which does not belong to the family of polyethylenes, that is to say essentially polypropylene films, is previously eliminated by the operator, but these quantities are very small, because the choice of Supplies are made in relation to types of film waste of known types, shapes and applications.

A washing line may possibly be associated with the preparation of the material. The washed film waste thus constitutes one or more flows entering the at least one feed belt.

This film waste is the shredding and grinding mixture. The respective amounts of the various films, of various thicknesses, of various melt indexes, of various densities, and of various natures, involved in the mixture of shredding and grinding film waste are determined by the characteristics that one wishes to obtain. for the product resulting from the process. These characteristics are both in particular a viscosity and a consistency of this viscosity fixed in a statistical interval as narrow as possible.

The percentage of thick film waste, that is to say greater than 100 microns, involved in the shredded / milled mixture feeding the process may vary from 0 to 50% by weight of the total introduced in step a) of process.

Step a) of densification, In a first step a) of the method according to the invention, called densification stage, the densification unit is fed continuously with waste prepared from crushed films to be recycled, by the at least one silo intermediate. In the case where several silos are present, each of these silos supplies a controlled quantity of the hopper of the densification unit in proportions that can vary from 0% to 100% for each intermediate storage silo. These proportions are expressed by weight of crushed film scrap, by means of scales, each silo supplying these quantities to the controlled weight scales. These feed ratios between silo can be changed at any time.

Any configuration can also be envisaged in which, for example, 60% of the shredded / shredded film waste quantities to be introduced into the densification unit comes from two silos Sla and Slb and 40% comes from two silos S2a and S2b, the Sla and Slb silos have been dedicated to thin film waste and silos S2a and S2b have been dedicated to thick film waste. These quantities of waste crushed film identified are delivered to the densification unit, thus allowing to adjust the viscosity of the product to be recycled upon entry into the first stage of the recycling process. If, for example, the silos Sla and Slb are dedicated to waste of small thicknesses, thus coming from material with a higher melt flow index, they can be mixed in a chosen proportion with materials of lower melt index, because from films of greater thickness and thus manufactured from polyethylene of lower melt index, for example between 0.2 and 1.0 g / 10 min.

The mixture of crushed fragments of polyolefin film waste, that is to say the flakes resulting from the prior operation of shredding / crushing film waste, is loaded into the chamber of a mechanical shear device with rotating blades, such as for example the REGENOLUX Type RL 900/2 called WEISS densification system, supplied by Giersbach D-35701 Haiger.

Preferably, the multi-rotor and blade systems, either co-rotating or counter-rotating, are used for the purpose of increasing the densification capabilities.

Intensive mixers, such as those provided by, for example, HENSCHEL, are also suitable if modified to include means for cooling the mixture of the various film fragments and various additions.

The shredded / shredded fragment mixture of film scrap is strongly agitated, so that the film fragments collide with the blades of the rotating blades, with the inner sheath of the chamber of the mechanical shearing device and with other fragments of films present in the room. The mixture is stirred with sufficient force, so that the resulting mechanical friction causes a rise in temperature of said mixture of film fragments which can cause the softening and at most melting of said film fragments of the mixture. When the softening temperature and optionally at most the melting temperature of the polyolefins is reached, the film fragments shrink, due to the residual orientation present in any extruded film, allowing a more or less pronounced phenomenon of heat-shrinking, then agglomerate with each other during impacts with other fragments.

Advantageously, the walls of the chamber of the mechanical shearing device can be heated to reduce the time required to raise the temperature of the mixture to the level required to generate this agglomeration.

The resulting mixture demonstrates a regularity of size of agglomerated particles, which appear as very regular. As a result, the apparent density of the agglomerated particle mixture is relatively high.

After the temperature of the mixture has reached the softening point and bonding of the polyolefins constituting said mixture, or at most the melting temperature of these polyolefins, it is advantageous to cool the mixture to avoid melting completely the polyolefin particles with the risk of forming large agglomerates. The mixture is preferably cooled by the introduction of a sufficient amount of water which is vaporized. The agglomerated particles are cooled by evaporation of the quantity of water introduced, so that the temperature of the agglomerated particle mixture passes rapidly below the softening and bonding point of the polyolefins thus densified. The mixture of the agglomerated particles must be stirred during the cooling to maintain the different agglomerated particles distinct from each other in the dense mixture thus formed.

The temperature at which the polyolefin particles adhere to themselves, and therefore the moment at which the cooling phase of the mixture is to be triggered, can be determined by any conventional method which makes it possible to monitor the temperature rise at the temperature. inside the device chamber. Preferably, the softening and sticking point of the polyolefin flakes processed in the device is determined by monitoring the intensity of the current supplying the driving motor (s) of the rotary blades of the device and generating the mechanical shear.

When the softening point and stickiness of the polyolefins is reached, there is a significant increase in the friction forces experienced by the device, and corresponding increase in the intensity of the supply current of the motors of the rotating blades. When this increase is detected, the cooling, by spraying the mixture, is started. This spraying can be a fine spray of water droplets under pressure in a controlled amount. This cooling can also be achieved by means of a flow of air that can be refrigerated. Depending on the applications, and depending on both the initial size of the film flakes, and the moisture content of the initial blend, as well as the density and average size of the agglomerated particles controlling the desired bulk density, it can be It is advantageous to perform a single cycle or cycles of heating, stirring and cooling to obtain a particular agglomerated particle size distribution.

This process can, as previously explained, either operate in sequences, with automatic loading and unloading, or operate continuously according to the architectures of the devices used. For example, the device may comprise specific zones in which the temperature rise phase takes place and specific zones in which the cooling takes place, the passage of the densified product from one zone to another operating by difference in apparent density naturally resulting from the densification mechanisms, the densification being consecutive to the temperature increase resulting in concomitant shrinkage, capture of the surface charge and inside the shrink film particles, bonding of the particles to each other other.

Thus densified particles becoming heavier as they densify can, despite mechanical agitation move towards the bottom of the tank of the device and enter the area dedicated to cooling, thus setting the size and morphology of densified particles.

After completion of all cycles, the agglomerated particle mixture is discharged from the densification chamber by means of a worm system associated with a feed system of a single-screw extruder of the next step b), connected to said densification device. It may be desirable to place a buffer device between the densification unit and the single-screw extruder, ie between steps a) and b), in order to ensure the coherence of the flow rates and the permanence of the supply of the single-screw extruder.

The agglomerated particle size distribution is regular, the agglomerated particles being in substantially oblong or substantially spherical geometrical shape, with an average particle size value d50 of about 2 mm, for extremes ranging from 1 to 10 mm in their largest dimension, to be compared with particle sizes ranging from 0.2 to 40 mm in conventional film densification processes.

Therefore, it appears that the densification of the fragmented waste is carried out, in step a) by heating to preferably the softening temperature and at most the melting temperature of each polyolefin constituent waste to densify, then simultaneous retraction said fragments of film waste, the heating being done by mechanical effect and / or external thermal input, under a shearing mechanical action, followed by cooling always under mechanical action by means of a cooling fluid.

The bulk density of the unfilled densified resulting from the agglomerated polyolefin particle mixture mixture varies between 0.3 and 0.4 g / cm 3 depending on the size of the film fragments, their thickness and their nature and orientation resulting from the conditions of manufacture of the waste. of films thus treated.

In this step a) of the process, a powdery filler is added during the course of this phase of temperature rise of the mixture of crushed film waste. The filler particles adhere to the fragments of films which have become, by shrinkage and agglomeration, polyolefin particles, this adhesion being made both on the surface and inside said agglomerated particles thus formed.

This pulverulent filler is preferably a mineral filler, but can also be an organic filler. When this filler is a mineral filler, it is preferably calcium carbonate.

In this step, the feed rate introduced into the agglomerated polyolefin particles varies between 0.1% and 15% by weight relative to the total mass of the product resulting from the process.

The incorporation rate is controlled, in the process, according to the invention, by a gravimetric dosing balance of the load. The speed of rotation of the screw of the feed device is constant, this screw being under-fed by the dosing balance.

The flow of the scale is measured by a weighing hopper. The regulation of the flow of the balance is obtained by the speed of rotation of the metering screw of the hopper of storage of the load.

The feed rate of the film waste fragments feeding the densification unit is also controlled in weight flow by scales and servo screw devices.

The mixture of agglomerated partially charged particles constitutes the incoming stream of step b) of the process.

Step b) Extrusion - plastification - filtration The mixture of agglomerated particles, charged with a small percentage of charge, is introduced into a single-screw extruder. This introduction can be made by any suitable means, including, for example, a forced feeding hopper.

This single-screw extruder is equipped with a filtration unit which may for example be a micro-perforated filter called a laser filter. The micro-perforated filter of the filtration unit has a filtration fineness of 0.08 to 0.30 mm and preferably of 0.11 to 0.23 mm, that is to say hole diameters of between 110 and 230. microns and a filter surface that varies with the flow rates of the extruder. According to the contamination noted for the incoming flow of the waste of films to be recycled, a filter of greater or lesser filtration fineness will be installed, in order not to compromise neither the flow rate nor the temperature balance of the mass. fondue passing through the filter.

This single-screw extruder also has a degassing zone.

The mixture of charged agglomerated particles is naturally plasticized by raising the temperature at the melting point of the polyolefins, or even slightly above it, then is optionally partially degassed and is homogenized in this extruder whose screw profile is standard, for a length of screw, expressed in length to diameter ratio, (L / D) ranging from 25 to 45.

The temperature profile of the single screw extruder is a conventional profile, as practiced for the extrusion of polyethylenes, well known in the state of the art. The temperature in the feed zone is generally between 160 ° C. and 200 ° C., and is between 200 ° C. and 240 ° C. in the filtration zone, these temperatures not being those of the melt. The rotational speed of the screw of the single-screw extruder which conditions the flow is conventional and can be between 50 and 200 rpm.

The filler, especially when it is a mineral filler, and even more particularly when it is calcium carbonate, is sufficient to capture the volatile compounds released during the plasticization of the mixture of agglomerated particles from heavily printed film waste and from the densification step a). The presence of a minimum moisture content in the incoming stream, that is to say in the mixture of homogenized agglomerated particles, promotes the degradation of volatile organic compounds which are partially removed by this first degassing. The moisture content must not go beyond a certain limit, which corresponds, on the one hand, to the degradation and vapor leaching of the volatile organic compounds incorporated, on the one hand, and to the degassing capacities of the other, on the other hand. single-screw extruder and subsequent degassing performed beyond this step.

The product resulting from this single-screw extrusion-plasticizing step is a filled melt with a low filler content and having undergone a first filtration.

Step c) homogenization - degassing, Optionally, in a third step c) of the variant process in the context of the process according to the invention, the so-called homogenization step - degassing, the molten polymer mass resulting from step b ) enters a second single-screw extruder positioned between the single-screw plasticizing extruder of step b) and the twin-screw compounding extruder of the next step d). The temperature of the melt present in the single-screw extruder homogenization-degassing is homogeneous. This melt comprising polymer and filler is subjected to a powerful degassing by means of a vacuum pump, then is homogenized again in order to supply, always continuously, without breaking the flow and without changing the temperature, the next step d) the process according to the invention. Degassing takes place under a vacuum of about 100 millibars.

This second extruder of diameter substantially identical to the diameter of the first extruder to manage flow rates and screw length of between 15 and 30 times its diameter, the material entering the extruder is already at good temperature. The temperature profile is identical to that deployed in the first extruder, that is to say as practiced for the extrusion of polyethylenes.

Compounding step d), according to the invention, finally comprises a step d) said compounding step during which a complementary powdery charge preferably of the same nature as that introduced in step a) or of nature different, is incorporated into the melt of recycled polyolefins, having undergone a first filtration, from step b) or c) when it is present.

The filtered extruded material from the single-screw extruder of step b) or c) is melt-fed into a twin-screw compounding extruder, receives the additional charge and is degassed and removed. at a second filtration followed by granulation.

The equipment used in the context of the invention for step d) is a co-rotating twin-screw extruder-compounder, the two screws being of identical diameter and rotating in the same direction. This main co-rotating twin-screw extruder-compounder is specific in that it also allows the sequential incorporation of fillers in powder form.

For this purpose, this main corotative bi-screw extruder-compounder comprises at least two inlet orifices each fed by a gaveuse lateral extruder, at least two degassing zones, and is equipped with a filtration zone, and a pumping means feeding a granulation unit with overhead cutting.

This main co-rotating twin-screw extruder-compounder may, for example, have a screw diameter D of 96 mm and an active length of 40 to 50 times the screw diameter (40 × D at 50 × D). It comprises a first inlet port fed by a first co-rotating side extruder which is also a co-rotating twin-screw extruder, for example with a screw diameter D of 60 mm, but having an active length of only 6 × D. The angle that the axes of the extruder-compounder and the at least two side-fed extruders make is at most 90 ° when observed in the direction of travel of the material. This first inlet orifice is positioned on the side of the main twin-screw extrudeuser in such a way that it opens on the material in the perfectly molten, homogeneous, weakly charged state, inside the extruder -compoundeuse twin-screw main.

This main co-rotating twin-screw extruder-compounder, also comprises a second inlet port fed by a second twin-screw side extruder, positioned parallel to the first lateral extruder. This second inlet orifice is positioned in such a way that it opens on polyolefinic material already more heavily laden. This fully fused material will have been homogenized again with respect to this charge addition in this first zone of the main twin-screw extruder-compounder. The distance between these two inlet ports is of the order of 4 to 8 times the diameter of the screw. Each zone of the sheath of the main twin-screw extruder-compounder, adjacent to one or the other of the inlet ports, is equipped with an opening and a de-aeration system - degassing in order to extract the air present in the charge being incorporated in the form of a powder system, which would interfere with obtaining a melt loaded homogeneous charge and free of air inclusion, if it does not was not properly deaerated.

Thus, these at least two extruders for feeding the pulverulent charge positioned laterally are associated at their point of entry with degassing orifices making it possible to reduce the air introduced during the feeding of the pulverulent material.

Therefore, these at least two side extrusion machines ensure the incorporation of the pulverulent filler and allow to obtain high levels of incorporation, without excessive addition of fluidifier, and without the presence of air that can not be extracted later even by the powerful degassing unit located downstream of the main twin-screw extruder.

The filler introduced according to the invention may be a mineral filler or an organic filler, such as, for example, those used in polymers to render them degradable.

When the feed introduced is of mineral origin, it is chosen from the group consisting of calcium carbonate, kaolin, clays, silicas, titanium oxide, talc, alumina, calcium sulphate, barium sulfate, but calcium carbonate is preferably chosen for reasons of high availability and cost.

More specifically, when the calcium carbonate is used in the context of the invention, it is chosen from the group consisting of ground carbonates having a specific surface area of between 1 and 12 m 2 / g and preferably between 4 and 10 moles. m2 / g.

The pulverulent inorganic filler used has a particle size cut-off of at most 10 microns, and preferably at most equal to 5 microns and a median diameter of 50% of between 1 and 5 microns and preferably between 1.5 and 2 microns. .

This inorganic filler can be surface-treated with stearic acid, or esters or salts of stearic acid.

The total incorporation rate of the powdery filler in the formulation is of the order of 30% to 85% by weight and preferably 60% to 80% relative to the total mass of the granule, that is to say of the masterbatch, that is to say the product resulting from the process.

The ratio of incorporation of the pulverulent filler between the two side-fed extruders is 60% to 80% for the first wrapper and 40% to 20% for the second wrapper.

For example, in the case of a total mineral filler of 85% by weight, with a prior incorporation of 15% during the densification step a), the percentages of the two gaveuses are respectively 40% for the first and 30% for the second. In the case of a total mineral load of 55%, the percentages of the gaveuses are respectively 30% and 20% in the extreme case or a 5% addition was made during the densification step. Such a device thus offers a great flexibility of settings.

The rates of these incorporations are controlled, in the method according to the invention, by gravimetric dosing scales of the pulverulent charge. The rotational speeds of the screws of the twin screw extruders are constant and they are underfed in powdery load by the dosing scales.

The flow rate of each balance is measured by a weighing hopper. The flow control of each scale is obtained by the speed of rotation of the dosing screw of the hopper.

In order to facilitate the very high-grade feed without sacrificing the extrusion rate, the twin-screw compounding extruder may also have a third feed port and a third side feed extruder. The percentages of introduction of the pulverulent charge into each of the orifices are adapted accordingly.

The pulverulent filler may also be provided in the form of a concentrate diluted in a polymer matrix in the form of charged granules. However, the introduction in pulverulent form is preferentially chosen for reasons of cost control and process control.

The composition of the recycled granulate thus obtained, that is to say the recycled masterbatch, comprises from 30 to 85% by weight of filler and from 70% to 15% by weight of polyolefin film waste. This composition preferably comprises from 50% to 85% by weight of filler and from 50% to 15% by weight of polyolefin waste.

Additives of known types such as antioxidants, lubricants, calcium or zinc stearate, dispersants, photon degradation agents, in amounts of 0.1 to 10% by weight, dyes, white titanium oxide, carbon black may be introduced into the composition.

The incorporation into the composition according to the invention of these various additives is made by their introduction into the twin-screw extruder by means of a hopper. All the additives are thus melted and homogenized with the polyolefin materials being recycled and melt in the first zone of the two screws of the compounding extruder. As previously explained, the complementary powdery filler is introduced via the at least two co-rotating, co-rotating, twin-screw extruders into the molten and homogenized polyolefin matrix, containing all the additives and dyes from a zone positioned at approximately 10 x D of the inlet hopper of the main co-rotating twin-screw compounding extruder.

The additives can also be introduced by means of a lateral extruder which makes it possible to incorporate any additives in the form of a dispersion in a melt, pasty, liquid medium. These additives are then added, either in the form of a dispersion in a generally polyolefin fusible matrix compatible with the polyolefin material to be recycled, and they are then added in the form of specific concentrated masterbatches, either in pasty or liquid form.

The perfect homogenization of the material thus formulated, ie the final composition, is achieved by this co-rotating twin-screw compounding extruder with a screw profile offering homogeneous and low shear throughout the screw profile. . The extruder-compounder operates under temperature profile conditions such that there is no risk of local overheating. The homogenization and dispersion of the initial charge and the additional charge as well as any pigments and other additives in the melt are obtained by a series of mixing heads and shearing discs which are judiciously mounted on each of the two screws of the twin-screw compounder extruder. The shear rates of the melt in the thread channel of the two co-rotating screws are particularly low, of the order of 200 s-1 at most, and in the shear discs the shearing of the material is controlled and rates are below 2000 s-1.

With, for example, a screw rotation speed of 350 rpm at 450 rpm for a flow rate of 2500 kg / h, the residence time of the melt in the co-rotating twin screw extruder is well below one minute. This combination of low shear rates, low residence times and perfectly controlled temperatures avoids a degradation of the material and allows a very good homogenization, this constituting as many factors of reduction of infertility creation.

There are no longer any heterogeneities due to the possible differences in fluidity indices of the incoming polyolefins, nor differences or variations in the melt flow indices, nor the risk of viscosity modification that could result from the crosslinking initiation process. .

The advantage of the at least two feeding extruders, allowing the additional incorporation of the charges, in particular powdery mineral, also lies in the fact that the rotational speed of the twin-screw compounding extruder can be thus optimized and this in spite of very high production rates of several tons per hour. In fact, to obtain such high pulverulent incorporation rates, it would have been necessary to rotate the two screws of the co-rotating main extruder much faster, and thus to take the risk of heating the material much more rapidly. Thus formulated, with the consequences of formation of crosslinking points and carbonization points that are known, leading to the creation of = unacceptable melts to the process of extrusion bubble bubble thin films.

This ability to strongly homogenize the polyolefin composition thus formulated is also interesting insofar as it avoids having to select waste that can be either neutral or non-printed, or fully printed, or having to select them according to their initial thicknesses, associated with different fluidity indices corresponding to the polyolefins constituting recycled film waste.

It should be recalled that the polyolefins retained in the field of films have melt indexes in the wide range of 0.1 g / 10 min to 10 g / 10 min under standard conditions (ASTM D 1238-2.16 standard). kg - 190 ° C) and more generally still in the range despite everything wide from 0.2 g / 10 min to 3 g / 10 min for the low density and linear low density polyethylene films in particular, the fluidity indices the lower lying being measured on the thicker films. As previously mentioned, the polyolefins with lower melt indexes are generally difficult to miscible with polyolefins whose melt indexes are higher.

One of the fundamental characteristics of the recycling process according to the invention is that there is a degassing-deaeration zone preceding each pulverulent charge incorporation zone. This zone is located at the level of the mixing chamber constituted by the two screws of the co-rotating twin-screw extruder-compounder and the sheath. This chamber is never completely filled by the melted composition, and this, over a length between 2 times and 6 times the diameter of the screw thus allowing an excellent degassing-deaeration.

The use of special screws with low shear mixers as well as disc shear heads which ensure the perfect dispersion of the powder load in the molten polymer is absolutely necessary. The melted composition is subjected to shear rates of at most 2000sec-1. This melted composition is subjected to the lowest temperature depending on the type of waste between 180 ° C and at most 250 ° C in average value when measured at the extrusion head.

However, this temperature of the melt is chosen so as to be as low as possible. The fact that several homogenizations took place first during the preparation of the material and then after the steps a), b) and possibly c) for the melt reduces the need to adapt the temperature of the material in the mixture. compounding extruder according to the type of polyolefin film waste to be recycled and according to their original melt index. This results in easier control of the process.

As has been previously stated, the compounding extrusion according to the invention is made in a bi-screw, co-rotating extruder-compounder equipped with a powerful degassing system provided with at least one degassing zone connected to a pump particularly powerful vacuum downstream of the introduction ports of pulverulent fillers and other possible additives. The gases resulting from the decomposition of the inks, the presence of water vapor or introduced during the addition of the powdery filler, or resulting from a possible degradation of the modified polyolefin matrix by additives which could have, in a Previous phase of manufacture, to be added to it, such as for example a wax or a surface adhesive, can therefore expand naturally over a length of 25 to 30 times the diameter of the screw. The gas outlet is possible by the chimneys provided along the cylinder but especially by the particularly powerful degassing zone. The degassing is done under a residual pressure of not more than 100 millibars. The position of the degassing point along the extruder is between 25 and 30 times the diameter, from the feeding zone of the bi-screw compounding extruder.

As previously mentioned, such a twin-screw compounding extruder makes it possible to operate at relatively low shear rates. In addition, the residence time, also called the residence time of the melt in the extruder-compounder bi-screw is much less than one minute. The disadvantages of a mono-screw that would function to add high-content pulverulent fillers are thus avoided. The threads of the two screws are not completely filled by the material, except in the zone normally dedicated, situated just before the first zone of introduction of the powdery charge, over a length of 2 to 3 times the diameter of the screw, then over a length of 3 to 4 times the diameter of the screw before the degassing zone and finally in the pumping zone over 5 to 6 times the diameter of the screw.

The gases resulting from the decomposition of the inks and the water vapor possibly present can therefore expand naturally over a length of 25 to 30 times the diameter of the screw. The exit of the gases is carried out thanks to the presence of natural degassing chimneys, provided in the vicinity of the zone of introduction of the mineral charge, as well as by the usual degassing zone, particularly powerful.

In order to reduce the pressure of the molten and highly highly charged polyolefin polymer in pulverulent charge at the outlet of the twin-screw extruder-compounder at a maximum of 30 bar and between 20 and 30 bar, a melt pumping device can possibly be added. This device can be gear, worm gear large diameter. It allows to pump stabilized high flows and is positioned before the filter changer and the cutting system at the head. Such a pumping device ensures the pressurization of the molten polyolefin mass perfectly degassed, without causing the generation of unmelted consecutive thermal degradation and crosslinking that could also occur at this level. Indeed, in conventional systems, it is necessary to increase much more pressure to compensate for the pressure losses of filtration and granulation systems. This generates risks of self heating of the recycled material. This rise in pressure takes place on the area of the two co-rotating screws called compression which is spread out over a length of about 6 times the diameter, for a screw making 40 to 50 times the diameter in terms of length of screw .

The melt filtration system with filter change, automatic type, for example, scraping is coupled to a melt bypass system for starting the compounding extrusion line.

Granulation is under water and is well known in the state of the art. The granules, that is to say the marketable product resulting from the recycling process, are sent after drying, in a silo storage and homogenization before shipment.

The main feed of the co-rotating, low-filler, pulverized, pulverized, polyolefin compounding extruder, which has undergone first filtration, is carried out without flow interruption, continuously, the melt remaining at the same temperature than leaving the previous zone.

The antioxidant type additives introduced into the composition according to the invention are of phenolic type (primary antioxidant), such as for example those marketed under the trade name IRGANOX®, of CIBA SPECIALTY CHEMICALS or of phosphite or phosphonite types (secondary antioxidant), all these antioxidants being used alone or as a mixture.

The antioxidant is specifically formulated quantitatively. The quantities introduced are between 1000 ppm to 5000 ppm (by weight) and preferably from 1000 ppm to 2000 ppm (by weight) of the final total formulation.

In a particular formulation according to the invention, photonic degradation promotion additives may be introduced. These additives are, for example, iron sulphates, cobalt sulphates, and any other additive acting as a photon degradation initiator. They are introduced in order to manufacture recycled masterbatches that will have the capacity, once transformed into film, to fragment easily under the effect of light, moisture, temperature and under the mechanical action of loss of mechanical strength, in particular elongation at break, within a controlled period of time. The degradation promotion additives are added at 0.1% to 10% by weight of the total composition. Biodegradation additives can also be introduced.

In a particular formulation according to the invention, impact modifying additives may also be introduced into the formulation at a rate of not more than 10% by weight. These impact modifiers are selected from the group of elastomers consisting of ethylene-propylene rubbers (EPR), modified ethylene-propylene-diene rubbers (EPDM), styrene-butadiene-styrene (SBS), styrene-ethylene-butadiene-styrene (SEBS). ), styrene-butadiene rubbers (SBR), optionally partially or completely cross-linked, styrene-isoprene-styrene (SIS), or belongs to the group of polypropylenes (homopolymers) with amorphous and semicrystalline blocks and propylene / ethylene copolymers or alpha-olefin with amorphous and semicrystalline blocks.

Slippery additives providing slip properties can also be added to the composition. These additives are fatty acid amides such as oleamides or steramides, or erucamides. The slip additives are added in amounts ranging from 100 ppm to 500 ppm by weight of the composition.

The implementation of the recycling process, according to the invention, is done from the reception of polyolefin film waste bins to be recycled, in a completely continuous and automatic way, thus greatly reducing operating costs.

However, to further reinforce the homogeneity and regularity of the product, a specific sorting and feeding of the waste to be recycled is set up preferentially. The feedstock and all the other additives are also automatically introduced during the different process steps and at different points of the single-screw extruders and the twin-screw compounding extruder, thus making it possible to obtain a masterbatch at very low temperatures. high filler content, perfectly homogeneous, doubly filtered and non-infrequent, the matrix being a polyolefin matrix of low melt flow rate, in contrast to masterbatches of the prior art, derived from polyolefin matrices with fluidity very high and therefore with good mechanical strength, impact resistance and tear resistance, despite the origin of recycled waste.

The granules obtained according to the process, that is to say the recyclate, a masterbatch with a high content of preferably mineral filler, having recycled polyolefins from waste polyolefin films from any source and from any state, can be used for production of films having a thickness of between 30 microns and 50 microns with, for example, a mixture of 50% of recycled high filler mass masterbatch produced according to the invention and of 50% of normal recycled material, it is necessary to according to the state of the art, or for the production of films with a thickness of less than 30 microns with, for example, a mixture of 50% of the recycled masterbatch according to the invention and 5% of virgin linear low density polyethylene and of 45% of normal recycled material, ie obtained by recycling processes belonging to the state of the art.

Those skilled in the art can appreciate the advantage of not having to select waste films feeding a recycling process, by thickness or provenance, in order to produce as many different types of recycled as there are types of film waste to be recycled, but on the contrary, to offer the market preferentially a single recycled product using the method according to the invention, said product being of high quality, recycling being the most economical because concerning all the waste film collected and operating at very high rates of several tons per hour.

EXAMPLES

Example 1: The preparation of the material aims to provide a controlled and homogeneous supply of the process, both in the physical form and in the variability of the material to be recycled. To do this, the waste film feed to be recycled is performed so as to create homogeneity, before shredding / grinding and intermediate storage. In this first industrial trial, the method according to the invention was fed with film waste to be recycled by means of two loading conveyor belts operating in parallel. Each of these mats fed a film crusher, reducing the size of the film waste before intermediate storage and their entry into the densification unit.

Two operators were responsible for depositing on both of the two feed mats the waste film to be recycled, either in the form of compressed bales opened by the operator, or in the form of parts and cut strips of film also delivered in bales.

The first feed belt was loaded from four very different and perfectly indexed waste streams to be recycled:

A first stream of film waste, labeled Flux la, was constituted by coils of stretch film, coils previously cut into segments of several centimeters in thickness and of dimensions equal to the width of the coils. The mechanical characteristics of this film waste 15 microns thick, slightly adhesive, transparent, were not in accordance with the specifications of the end user and the material 30 therefore had to be recycled. The polyethylene constituting this stretchable film was a linear polyethylene octene base of grade, ie of melt index 1.0 g / 10 min according to ASTM D 1238 - 2.16 kg -190 C ° and density 0.920. g / cm3 according to ASTM 1505.

A second stream of film waste, labeled Flb flux, consisted of film coils printed about 80 s from their surface, films previously colored white in the mass by addition of titanium oxide, from a manufacturer of food packaging films, these reels corresponding to the start of the print line. The film was a 50 micron thick coextruded film, one of which was a very low density linear polyethylene, 0.916 g / cm 3, and another layer, a linear density lower density polyethylene, 0.922 g / cm 3, both of the polyethylenes being grade 1.0 g / 10 min.

A third stream of film waste, labeled Flc flow, consisted of post-consumer waste collected from a distributor, and consists essentially of shrink wrapping film of small thicknesses, of the order of 50 microns, partially printed. Such films are generally made from 0.7 g / 10 min grade free radical polyethylene and a density of 0.922 g / cm 3.

A fourth stream of film waste to be recycled, denoted Fld flux, consisted of cutouts of bags of bags known as e out of case made from polyethylene of medium density, grade 0.5 g / 10 min and density 0.935. g / cm3. The film was also colored white in the mass by adding titanium dioxide.

The operator in charge of the first carpet had ensured that the quantities disposed on the carpet from the different stocks of waste and corresponding to the flows identified Fla to Flc were regular. The belt fed a grinder / shredder, connected to two intermediate storage silos Sla and Slb loaded in parallel with the crushed film thus produced.

The second feed belt was loaded from two very different waste streams and also perfectly indexed:

A first stream of film waste, denoted flux F2a, consisted of shrink film covers from building material warehouses. The film was 150 microns thick, and was made from a 0.30 g / 10 min low density radical polyethylene and a density of 0.920 g / cm 3.

Finally, a second stream of film waste, labeled flow F2b, consisted of post-consumer waste collected by an agricultural cooperative, these films having been previously washed and being supplied in agglomerated bales. It consisted of thick agricultural tarpaulins, of the order of 200 microns made from linear butene polyethylene grade 0.2 g / 10 min and density 0.920 g / cm3. These films were colored black in the mass by addition of carbon black. The two parallel storage silos operating in parallel, S2a and S2b were fed continuously by the mill associated with the second feed belt.

Thus, the two feed belts were in a sense dedicated to different types of films of different origins, in particular to thick films and thinner films, these films having each been made from polyethylenes of grades within a range of 0.1 to 1 g / 10 min for thick films and in the range 1 to 3 g / 10 min for the thinnest films, ie particular melt indexes. Similarly, the specific risks of contamination associated with a type of film, for example for post-consumer films, as opposed to films from defective fabrications and collected in the same manufacturing plant, could thus be distributed very regularly over all intermediate storage silos.

The moisture content of film wastes was not controlled, as some of the film bales were stored outdoors and thus were subjected to the weather. Film waste not belonging to the family of polyethylenes, that is to say essentially polypropylene films, had previously been eliminated by the operator, but these quantities were very small, because the choice supplies were made in relation to types of film waste of known types, shapes and applications.

The quantities introduced by the operators on the carpets during the experiment were respectively 500 kg / hour for each of the two feed mats. This quantity measurement was carried out simply in view of the film bales received which were consumed in the reference time interval.

In the first step a) of the process according to the invention, referred to as the densification step, the densification unit was fed continuously with waste prepared from crushed films for recycling, by the intermediate silos Sla and Slb and the intermediate silos S2a, respectively. and S2b, each of these silos supplying in controlled quantity the hopper of the densification unit in proportions of respectively 60% for the intermediate storage silo Sla and 40% for the intermediate silo Slb. In the same way, the two intermediate storage silos S2a and S2b fed the loading belt of the densification unit in proportions of 30% for the intermediate silo S2a and 70% for the silo S2b. These proportions, expressed as weight of crushed film waste, were determined by means of the scales, the silos Sla and Slb, as well as S2a and S2b, supplying these quantities to the controlled weight balances. These feeding proportions between Sla and Slb on the one hand and between S2a and S2b on the other hand could be modified at any time.

Another configuration was also deployed in which 60% of the quantities to be introduced into the densification unit came from the Sla and Slb silos and 40% came from the silos S2a and S2b, the silos Sla and Slb having been dedicated to the thin film waste. and the silos S2a and S2b having been dedicated to thick film waste. Its quantities of identified crushed film waste have been delivered to the carpet providing the densification unit, thus making it possible to adjust the viscosity of the product to be recycled as soon as entering the first stage of the recycling process.

The flakes of film waste, crushed / dry shredded to dimensions ranging from 10 mm to 25 mm, from the Sla and Slb silos dedicated to waste of small thicknesses, thus coming from material with a higher melt index, have mixed with flakes of film wastes from lower melt index materials, because from films of higher thicknesses and thus made from polyethylene of lower melt index, between 0.2 and 1.0 g / 10 min.

The densification unit has also continuously received a quantity of pulverulent inorganic filler of the calcium carbonate type, by means of a screw weight metering device associated with a continuous weight measuring device. The amount of calcium carbonate introduced during this industrial test was 15% by weight relative to the weight of the composition, that is to say the sum of the amounts of crushed film waste entering the densification unit increased by the amount of inorganic filler introduced, so that the hourly throughput of the densification unit operating continuously, but nevertheless in a sequenced manner with respect to the densification process, was 1.15 tons / hour. Calcium carbonate was added at the time of rise and temperature. This 15% by weight relative to the weight of the composition, that is to say the sum of the amounts of crushed film waste entering the densification unit plus the amount of mineral filler introduced, corresponds to 13% by weight. total product from the process.

The densification unit consisted of a densification equipment WEISS REGENOLUX type RL 900/2, equipped with three rotary blades with double knives, positioned in a triangle, with partial interference of the trajectories, in a cylindrical heated tank of 700 liters capacity was used. The rotating blades were set in motion at 3000 rpm by three electric motors of 110 kW.

The mixture had reached a temperature of approximately 120 ° C at the time of its sudden cooling by spraying. The mixture was continuously stirred during heating and cooling. All the water spray had evaporated. The agglomerated particle mixture was discharged from the device chamber and sent to the feed zone of the single-screw extruder of step b).

The mineral filler used was of calcium carbonate type, OMYAFILM 707 0G reference. The BET specific surface area (nitrogen method) of the load was from 5 m / g to 6 m / g. This carbonate had been surface treated with calcium stearate. The 98% cut was 7 microns for a median cut of 50% of 1.7 microns.

In the second step b) of the process according to the invention, called the plasticization-filtration step, a single-screw extruder with a diameter of 120 mm L / D 30, with a conventional screw profile, according to the state of the art. was continuously supplied with agglomerated material filled with calcium carbonate at the outlet of the densification unit, a worm type physical connection having been made between the output of the densification unit and the feed zone of the extruder to ensure flow continuity. The densified and superficially charged and partly calcium carbonate crushed film waste is partially melted during friction on the walls of the feed zone of the single-screw extruder and then mounted to a fusion temperature in contact with the sheath and the heated screw and then plasticized. The temperature profile of the single-screw extruder was in the feed zone of 180 ° C and 230 ° C in the filtration zone. The rotational speed of the single-screw was 65 to 80 rpm. A slight degassing occurs at the downstream part of this single-screw extruder. Filtration of the laser filter type, that is to say with a micro-perforated mechanical filter with a filtration fineness of 0.20 mm and a surface of 648 cm 2, made it possible to separate the partially melt-filled polyethylene. calcium carbonate, the largest impurities that could be present such as wood particles, paper particles, large non-core resulting from crosslinking reaction or carbonization. In addition, a first homogenization of the mineral filler inside the polyolefin matrix, as well as a homogenization of the various components of the matrix is performed during this plasticization filtration, but it is far from sufficient.

In the third step c) of the process according to the invention, the so-called homogenization-degassing step, the mass of molten polymer resulting from step b) fed a second single-screw extruder, with a screw diameter of 120 mm, of length L / D of 15 D, having a profile similar to the first extruder, directly connected in cascade to the single-screw plasticizing extruder. The rotational speed of the second single screw was 100 rpm. The temperature of the melt in the homogenizer-degassing single-screw extruder was homogeneous and was measured at 210 ° C before the filtration zone. This melt comprising polymer and mineral filler was subjected to a powerful degassing by means of a vacuum pump to 100 millibars, then was homogenized again to feed, always continuously, and without breaking the flow, and without temperature change, the next step d) of the method according to the invention.

In step d) of the so-called compounding step process, the molten polymer partially filled with calcium carbonate and already partially homogenized was introduced into a twin-screw extruder, equipped with two lateral feeding extruders, for the purpose of introducing the additional powdery inorganic filler, in this case calcium carbonate, to high levels in the matrix consisting of recycled polyethylene already partially loaded mineral filler, while ensuring a perfect homogeneity of the compound thus produced. The amount of partially filled molten polymer with a mineral filler in the preceding step feeding the twin-screw compounding extruder was, in the described industrial test, 1.15 tonnes / hour.

The additional inorganic filler was introduced into the partially filled molten polymer by means of two side feeding extruders, in an amount such that the twin-screw compounding extruder ultimately produces 3.65 tonnes / hour.

It will be appreciated by those skilled in the art that they are very high flows that can not be obtained in single-screw extruder configurations, at the mineral loading levels considered, and in the levels of homogeneity and regularity of properties required for low film thickness applications to extrude economically.

At the end of this compounding step, the highly loaded material in inorganic filler, at a measured rate of 73% by total weight of the product resulting from the process, was filtered by a mechanical filter equipped with a continuous scraper device in order to to ensure and efficiency and total availability of said filtering device. The material was then extruded, according to the well-known state of the art, into a die equipped with an overhead cutting unit, operating under water to allow cooling and thus produce highly charged compound pellets. These granules were dried, then stored in silo, homogenized again, then finally shipped to a user after the usual quality controls on density, melt index, mineral filler content, but also on the content. This information is valuable for the safe manufacture of thin films, as well as on the stretchability under defined temperature and shear conditions.

The granule with a high mineral filler content as obtained from the process, ie the recycled masterbatch has a melt index of 0.8 g / 10 minutes, with extremes ranging from 0.6 to 1, 0 g / 10 min, depending on the care taken in loading the process feed mats, into film waste, and thus to the regularity of composition of the incoming flows. The 73% calcium carbonate content recycled masterbatch had a density of 1.717 g / cm3. The relative humidity of the recycled masterbatch was less than 0.04%.

This masterbatch was used to make garbage bags with a KIEFEL monolayer extruder of 80 mm screw diameter, equipped with two extrusion heads with a diameter of 120 mm, the extrusion being carried out in line with a machine double track bag ROLL-0-MATIC.

Bags 700 mm wide and 950 mm long were produced, for thicknesses ranging between 75 microns and 20 microns. The thinnest film thicknesses were obtained with a composition comprising 50% by weight of the total composition of the masterbatch resulting from the process according to the invention, combined with 40% by weight of regenerated material originating from the recycling of film production waste. of free radical low density polyethylene having a melt index of 1.0 and a density of 0.920 g / cm 3 produced according to the state of the art and 10% by weight of linear polyethylene of grade 0.7 g / 10 min and density 0.923 g / cm3. The stretchability of the material employing the masterbatch according to the invention was sufficient to allow the production of thin films of 20 microns and the bubble breaking frequency observed during the extrusion sufficiently low to be compatible with industrial conditions. , and this in the extrusion conditions put in place, rate of inflation, temperature, flow, and equipment available.

Thus, the process according to the invention operates at very high flow rates, continuously, with only silos for intermediate storage silos receiving scraps of crushed films. All recycling steps are fully integrated. The process according to the invention thus makes it possible to produce granules, that is to say a highly loaded mineral-filled master batch compound, in this test, from calcium carbonate, from waste films to be recycled, without interruption of intermediate flow, and at very high flow rates of the order of 3.5 tons / hour, and therefore with several advantages including in particular a substantial energy saving, since it is not necessary to cool then recasting the recycled material between the different stages as in the state of the art. Double filtration helps to achieve a high quality for such a recycled material. Moreover, the procedures and means implemented make it possible to develop a particularly homogeneous fluidity index product, which is a great advantage for the end user who must extrude such a product to make relatively thin films from of these materials, ie post-industrial and post-consumer waste to be recycled.

Example 2: The incoming stream of waste to be recycled in the recycling facility consisted of two batches: The first batch (Lot 1) consisted of five tonnes of low-density polyethylene film from film-making scrap for the purpose of recycling. packaging of frozen products, very strongly printed on 80% of their surface. The films were in the form of reels. No washing was necessary because these films came from manufacturing scrap. These films, with a total thickness of 60 microns, had been produced by a two-layer coextrusion process, the inner layer of 20 microns being made of very low density linear polyethylene with a flow index of 1.0 g / 10 min. , and 0.925 g / cm3 density, to provide improved sealing properties, the outer layer of 40 microns having been made of butene linear polyethylene mixture of melt index 1.0 g / 10 min, and density 0.921 g / cm3, and free radical radical of 0.7 g / 10 min and density 0.923 g / cm3, in proportions of 70 / 30. The film had previously been formulated with titanium dioxide, in order to provide opacity and a white background.

In addition, the second batch (lot 2) consisted of ten tons of films recovered from a large distributor and comprising a mixture of pallet shrink covers, 120 microns thick, free of their adhesive paper labels, flow index around 0.5 g / 10 min and a density of 0.923 g / cm3, canned packaging films and other 50 micron thick transport packagings, with an estimated melt index of around 0.7 g / 10 min, for a density around 0, 923g / cm3 and palletizing stretchable films with a thickness of 15 micron melt index 0.7 g / 10 min and density 0.918 g / cm3.

The proportions of these different post-consumer film wastes, of different composition and thickness, were approximately 1/3, 1/3, 1/3. This post-consumer film waste was totally mixed and available as compressed film bales. However, the bales made of these film wastes were stored outside and consequently had a high humidity.

The shredding / grinding unit upstream of the recycling process according to the invention was fed in such a way that the printed film pieces cut from the different reels (batch 1) and the unprinted film pieces (batch 2). ) be introduced in proportions of 1/3, 2/3, and this, on a regular basis, until the 15 tons available are used up.

The flakes of films thus obtained, milled to the dimensions of 2.5 cm approximately square, were homogenized in a silo and then densified in step a) of the process according to the invention.

To do this, a densification equipment WEISS REGENOLUX type RL 900/2, equipped with three rotary blades with double knives, positioned in a triangle, with partial interference of the trajectories, in a cylindrical heated tank of 700 liters of capacity, was used. The rotating blades were set in motion at 3000 rpm by three electric motors of 110 kW.

A calcium carbonate type inorganic filler was added at the time of the temperature rise at a rate of 15% by weight of the total of the products introduced into the densification unit, that is to say 13% by total weight of the product. from the process.

As in Example 1, the densification unit operated in a cycle, but continuously. The densified film mixture with the addition of calcium carbonate had reached a temperature of about 120 ° C at the time of its sudden cooling by spraying. The mixture was continuously stirred during heating and cooling. All the water spray had evaporated. The agglomerated particle mixture was discharged from the device chamber and sent to the feed zone of the single-screw extruder of step b) of the process according to the invention.

The mineral filler used was of calcium carbonate type, OMYAFILM 707 0G reference. The BET specific surface area (nitrogen method) of the load was from 5 m / g to 6 m / g. This carbonate had been surface treated with calcium stearate. The 98% cut was 7 microns for a median cut of 50% of 1.7 microns.

The densified product lightly loaded with calcium carbonate, homogenized, was extruded, degassed, filtered in a conventional single-screw extruder, according to step b) called the plasticizing step. The single-screw extruder had a diameter of 120 mm. and screw length of 20 times its diameter The mineral filler content of this intermediate granule was measured at 15%. The melt thus weakly loaded with mineral filler was filtered on a perforated laser filter with a filtration fineness of 0.20 mm and a surface of 648 cm 2. The temperature of the melt was 220 ° C. The melt thus slightly loaded with mineral filler, degassed and filtered a first time was continuously introduced into the feed zone of the co-rotary twin-screw compounding extruder of 120 mm diameter and a screw length of 48 mm. its diameter corresponding to step d) of the process according to the invention.

The complementary pulverulent filler, in this case the same calcium carbonate introduced in step a), was introduced by means of the two side feed extruders in the main twin-screw extruder. Calcium carbonate was measured via the two gravimetric scales. The speeds of twin-screw extruders were set at 70% of their maximum speed. The extruded product had a final calcium carbonate content of 70%. This additional calcium carbonate filler was introduced into the polyolefin mass melted at 60% of the mass to be introduced, by the first feeding extruder and 40%, by the second feeding extruder.

The co-rotating speed of the screws of the twin-screw main compounding extruder was maintained at 380 rpm for a final flow rate of 3,350 tons / hour.

Antioxidant stabilization was accomplished by incorporating 1000 ppm IRGANOX @ 1010.

The granule with a high mineral filler content as obtained from the process, ie the recycled masterbatch has a melt index of 0.7 g / 10 minutes, with extremes ranging from 0.4 to 1, 0 g / 10 min, according to: The care taken in loading the process feed mats, in film waste, and thus in the regularity of composition of the incoming flows. This difference for the extremes of melt index is shown to be greater than in the previous example. The recycled masterbatch, 70% calcium carbonate content, had a density of 1. 710 g / cm 3. The relative humidity of the recycled masterbatch was less than 0.04%.

This masterbatch was then used to make garbage bags with a KIEFEL monolayer extruder of 80 mm screw diameter, equipped with two extrusion heads with a diameter of 120 mm, the extrusion being carried out in line with a double track bag machine ROLL-0-MATIC. Bags 700 mm wide and 950 mm long were produced, for thicknesses ranging between 75 microns and 30 microns.

The thickest films have been made with strong mixtures using significant proportions, of the order of 50 by weight of masterbatch according to the invention, associated with low density polyethylene granules regenerated according to the state of the art and available from the film processor. The stretchability of the material employing the masterbatch according to the invention was sufficient to allow the manufacture of thin films and the bubble breaking frequency observed during the extrusion sufficiently low to be compatible with industrial conditions.

The films with the lowest thicknesses, that is to say of the order of 30 microns, were obtained by adding a proportion of 10% virgin linear polyethylene in the composition described above. However, the thicknesses of 20 microns could not be obtained, suggesting less homogeneity and therefore more limited stretchability when compared to the results obtained in the context of Example 1.

Claims (33)

1. Process for recycling polyolefin film waste previously shredded, crushed, fragmented and comprising the following steps: a) densification of fragmented waste, with incorporation of pulverulent fillers, b) extrusion plasticization filtration in single-screw extruder, charged fragmented waste, characterized in that, in a step d) the extruded and filtered material from the single-screw extruder, is introduced in the molten state into a twin-screw compounding extruder, receives therein a further charge powder and is subjected to degassing and a second filtration before granulation. 2. Recycling process according to claim 1, characterized in that the polyolefin film wastes are pigmented or not, whether or not loaded with mineral or other materials, stabilized or not against radiation W and cover the field of non-printed until to totally printed. 3. Recycling process according to at least one of claims 1 and 2, characterized in that the polyolefinic film waste contain at most 5 by weight of polypropylene. 4. Recycling process according to at least one of claims 1 to 3, characterized in that the polyolefinic film waste is selected to form a mixture of film wastes with regular composition, prior to their shredding / grinding / fragmentation, on the base of the thicknesses of said films, this composition comprising from 0 to 50% of film waste between 100 and 300 microns. 5. recycling process according to at least one of claims 1 to 4, characterized in that the polyolefinic film waste is shredded, crushed, broken by means of a shredding / grinding means, to a particle size between 5 and 25 mm on the side. 6. Recycling process according to at least one of claims 1 to 5, characterized in that the polyolefinic film waste is washed in whole or in part prior to densification. 7 recycling process according to at least one of claims 1 to 6, characterized in that the shredding / grinding means, operates dry and preferably implements shredders / grinders with knives and possibly against blades. 8. Recycling process according to at least one of claims 1 to 7, characterized in that the densification of the fragmented waste is carried out in step a) by heating to preferably the softening temperature and at most the melting temperature of each polyolefin constituting the waste to be densified, then simultaneous shrinkage of said fragments of film waste, the heating being done by mechanical effect and / or external thermal input, under mechanic action shearing, followed by cooling under mechanical action . 9. Recycling process according to at least one of claims 1 to 8, characterized in that the pulverulent charge is added during the course of the temperature rise phase of the crushed film waste mixture during densification. 10. Recycling process according to claim 9, characterized in that the pulverulent filler is incorporated in a proportion of 0.1 to 15% by weight relative to the total mass of the product from the process. 11. Recycling process according to at least one of claims 1 to 10, characterized in that the hot mixture of densified and charged waste is introduced into the extrusion plasticization filtration step which is carried out in a single-screw extruder. , of screw length between 25 and 45 times its diameter, the temperature profiles and the rotational speed of screws, being those practiced for the extrusion of polyethylenes. 12. Recycling process according to at least one of claims 1 to 11, characterized in that the extrusion-lamination-filtration step comprises degassing. 13. Recycling process according to at least one of claims 1 to 12, characterized in that the extrusion plasticization filtration step is carried out by means of a filter unit micro-perforated filter said laser filter. 14. Recycling process according to claim 13, characterized in that the micro-perforated filter of the filtration unit has a filtration fineness of 0.08 to 0.30 mm and preferably 0.11 to 0.23 mm. 15. recycling process according to at least one of claims 1 to 14, characterized in that is introduced between steps b) and d), a step c) of homogenization - degassing of the molten polymer mass, from step b), by means of a second single-screw extruder. 16. Recycling process according to at least one of claims 1 to 15, characterized in that the extruded material filtered from step b) or step c) when it is practiced, is introduced in the state melted, during step d), in the twin-screw compounding extruder, preferably co-rotating, provided with at least one degassing means, a filtering means, a pumping means, a granulation means with cutting at the head. 17. Recycling process according to claim 16 characterized in that the filtering means is of filter change type. 18. Recycling process according to at least one of claims 1 to 17 characterized in that the complement of pulverulent charge is introduced by means of at least two feed extruderspositioned laterally on the twin-screw extruder of step d ). 19. recycling process according to at least one of claims 1 to 18 characterized in that the complement of powdery charge is introduced so that the accumulation of charges introduced in step a) and in step d ) represents between 30 and 85% by weight of the total of the product resulting from the process. 20. Recycling process according to claim 19, characterized in that the two feeding extruders are preferably co-rotating and operate in a gavage ratio between the first and the second ranging from 60 to 80% for the first and from 40 to 20%. % for the second expressed by weight of introduced powdery filler. 21. Recycling process according to claim 18 characterized in that the at least two extruders feeding the pulverulent charge positioned laterally are associated at their point of entry to degassing orifices to reduce the air introduced at the moment. gavage of the pulverulent material. 22. Recycling process according to at least one of claims 16 to 21, characterized in that, each degassing zone preceding each pulverulent charge incorporation zone at the mixing chamber constituted by the two screws and the sheath. of the twin-screw compounding extruder, this mixing chamber is not completely filled by the melted compound and this, over a length of between 2 and 6 times the diameter of the screw. 23. Recycling process according to at least one of claims 1 to 22, characterized in that the twin-screw compounding extruder is equipped with at least one lateral extruder for incorporating all other additives in the form of a dispersion in a medium in the molten, pasty, liquid state. 24. recycling process according to at least one of claims 1 to 23, characterized in that the filtered extruded material from step b) or successive steps b) and c) is subjected in step d) to shear rates of not more than 200 s-1 in the net channel and not more than 2000 s-1 between the mixing discs and that the shear is even, uniform throughout the mix to ensure that matter receives the same mechanical work. 25. Recycling process according to at least one of claims 1 to 24, ..characterized in that the filtered extruded material is subjected in step d) to a residence time of less than one minute. 26. Recycling process according to at least one of claims 1 to 25, characterized in that the filtered extruded material is subjected in step d) to a pressure of 20 to 30 bar. 27. The recycling method according to at least one of claims 1 to 26, characterized in that the filtered extruded material is subjected to the lowest temperature depending on the type of waste and at most 250 ° C. 28. Recycling process according to at least one of claims 1 to 27, characterized in that the degassing is under a residual pressure of at most 100 millibars. 29. Recycling process according to at least one of claims 1 to 28, characterized in that the pulverulent filler is of mineral or organic origin. 30. Recycling process according to claim 29, characterized in that the mineral filler is chosen from the group consisting of calcium carbonate, kaolin, clays, silicas, titanium oxide, talc, alumina. , calcium sulphates, barium sulphate. 31. Recycling process according to claim 30, characterized in that the mineral filler is preferably calcium carbonate. 32. Recycling process according to any one of claims 30 or 31, characterized in that the mineral filler has a specific surface area of between 5 and 6.m2 / g. 33. Recycling process according to any one of claims 30 to 32, characterized in that the inorganic filler is surface-treated with stearates, stearic acid, or esters or salts of stearic acid. 34 recycling process according to any one of claims 30 to 33, characterized in that the pulverulent inorganic filler implemented has a particle size of at most equal to 10 microns, and preferably at most equal to 5 microns and a diameter median d 50% between 1 and 5 microns and preferably between 1.5 and 2 microns. Recycling process according to claim 29, characterized in that the organic filler belongs to the group of fillers used in the polymers to render them degradable. Recycling process according to at least one of Claims 1 to 35, characterized in that at least one modifier is added to the material from the single-screw extruder to be extruded in step d). impact. Recycling process according to claim 36, characterized in that the impact modifier is introduced into the composition in step d) at a rate of at most 10% by weight. Recycling process according to at least one of claims 1 to 37, characterized in that the material from the single-screw extruder to be extruded in step d) is added with an antioxidant stabilizing agent. Recycling process according to Claim 38, characterized in that the antioxidant stabilizing agents are of phenolic type, (primary antioxidant), or of phosphite or phosphonite type (secondary antioxidant), used alone or as a mixture.40 Recycling process according to claim 38, characterized in that the antioxidant agents are added at doses of 1000 to 5000 ppm in the final composition. 41 recycling process according to at least one of claims 1 to 40, characterized in that is added to the material from the single-screw extruder to extrude in step d) a calcium stearate type lubricant or zinc in amounts of 0.2 to 0.5% of the total composition. 42 recycling process according to at least one of claims 1 to 41, characterized in that adding to the material from the single-screw extruder to be extruded in step d) photon degradation agents for the purpose of 43 recycling process according to claim 42, characterized in that the photon degradation agents in order to accelerate the degradation of the formulation according to the requirements of use are sulphates iron, cobalt. Recycling process according to Claim 42 or 43, characterized in that the photon degradation agents are incorporated at levels of 0.1 to 10% by weight of the formulation. 45 Recycling method according to at least one of Claims 1 at 44, characterized in that dyes in the form of pigments are added to the material from the single-screw extruder to be extruded in step d). 46 Use of the granules obtained according to the process according to claims 1 to 45, for the production of formulations intended to be transformed by the techniques of plastics processing. 47 Use of the granules obtained according to the process according to claims 1 to 45, for the production preferably of films between 200 microns and 20 microns, from mixtures formed of said granules and virgin or recycled polyolefin granules. .DA1: 20090417