FR2736579A1 - Prodn. of composite material from plastic waste - Google Patents

Abstract

Prodn. of composite parts from a base of waste plastic material in the form of strip pieces and at least one mineral and/or organic filler consists of: putting into a mixer the plastic waste and the filler which has a mt. pt. higher than the plastic and with at least part of the ingredients having a size of 0-2mm. Heat the mixture while continuously gently stirring at a temp. equal to the plastic mt.pt. for a short rough time for the filler to stick to the plastic surface. Remove the hot mixture and subject to a mechanical action e.g. compression to agglomerate the constituents. Also claimed is the equipment consisting of a rotating drum mixer (1) with internal radial blades (4), a loading and discharge opening and heating means.

Description

Method and installation for the production of composite products and products thereof.

The present invention relates to a process for manufacturing composite products, an installation for implementing this process and the resulting composite products.

The manufacture of various articles such as coatings, articles molded from a mixture consisting essentially of scrap plastic, preferably thermoplastic, and at least one mineral and / or organic filler are well known. Indeed, the multiplication of waste of all kinds, in particular plastic waste, today requires the implementation of recovery and reprocessing processes for these plastic materials with a view to their incorporation in processes which allow the manufacture new products. However, such methods can have an implementation cost such that they economically prevent any implementation of said methods.

The processes known to date are inspired by conventional plastics processes with in particular the use of an extruder screw for the plasticization of materials.

The use of this material implies a careful washing of plastic materials under penalty of rapid abrasion of the material. In this case, the process is long and expensive.

The other methods not using an extruder screw use a quantity of fillers substantially equal to or in excess relative to the quantity of plastics, which limits the possible applications of these plastics.

Examples of processes exhibiting such drawbacks are for example described in WO-A-93.08974. In this process, it is necessary to preheat the load before mixing the load with the thermoplastic material. In addition, the charge is present in the mixture in a very large amount. It is the same for the manufacturing process described in DE-A-2,226,287 and DE-A2,311,797. FR-A-2.258.414 does not recommend, unlike the other documents mentioned above, the preheating of the load.

On the other hand, it requires the use of a quantity of fillers substantially equal to that of the quantity of plastics used, thus limiting the use of plastics.

In addition, the objective of all these known methods is to obtain, during the heating operation, a homogeneous filler / material mixture generally in the form of a paste. It is often accompanied by violent mixing of the mixture and requires the presence of a powerful and therefore expensive mixer. In addition, the mixture obtained, due to its presentation in the form of a viscoelastic paste, is difficult to handle at the outlet of the mixer because of the shape memory characteristics of the materials. Therefore, the further processing of this dough requires devices, such as extruders, whose maintenance and upkeep are problematic due to the presence of abrasive charges.

The object of the present invention is therefore to alleviate the aforementioned drawbacks by proposing a process for manufacturing composite articles which, on the one hand, allows both the use of highly abrasive fillers and plentiful plastic materials important, on the other hand only requires a single unitary brewing operation to allow obtaining a mixture which can subsequently undergo any processing operation.

Another object of the present invention is to maintain, in the mixture, the charge / plastic interface intact for as long as possible almost until the shaping operation so as to obtain a mixture which is easy to handle and which, at final stage, is particularly homogeneous.

To this end, the subject of the invention is a process for the manufacture of composite objects essentially based on scrap plastic materials coming together reduced to pieces in the form of strips, shavings or the like and of at least one mineral filler and / or organic, characterized in that the said plastic waste and the charge, the melting point of which is higher than the melting point of the said plastic materials, and in which at least part of the constituents have a particle size between 0 and 2 mm, in that the mixture subjected to continuous gentle stirring is heated to a temperature at least equal to the melting temperature of the plastics for a sufficiently short time so that the fillers can adhere to the partially molten surface of the thermoplastic materials and coating them, in that the heated mixture in the divided form of said mixer is extracted e t in that said mixture is subjected to mechanical stress, such as compression, during the shaping of said mixture to allow agglomeration of said constituents of the mixture.

The invention also relates to an installation for the implementation of this process and the resulting composite products.

The invention will be clearly understood on reading the following description of an exemplary embodiment, with reference to the single figure which represents a view in vertical section of an installation according to the invention.

Composite objects, manufactured using the process that is the subject of the invention, consist essentially of scrap plastic materials mixed with an organic and / or mineral filler.

The raw materials used, in particular plastic waste, may, due to their diverse origins, be very variable from one object to another. Generally, plastics are thermoplastic materials such as polyolefins used for example for the manufacture of tarpaulins constituting tunnels forming greenhouses in the field of agriculture. These plastics have therefore been subjected, during their use, to various treatments and sometimes even to coatings with mineral or organic filler. Such is the case of the plastic material mentioned above which is generally covered with a layer of finely pulverized chalk such as Meudon white to attenuate the light passing through the film. In addition, this plastic waste is generally in a state of variable cleanliness, since it often contains traces of soil.

Prior to the implementation of the manufacturing process which is the subject of the invention, it is therefore advisable to reduce these raw materials in the form of pieces which can have any shape. Indeed, these pieces can be constituted by strips, shavings or the like according to the shredding or reduction device selected for the breaking up of said plastic waste then drying and sieving so as to remove most of the water and soil dirtying plastics. This operation is a conventional operation implemented in all processes of this type.

It can also be associated with a washing operation for said plastic waste. Once this operation of reducing the plastic waste scrap coming from pieces, it is advisable to introduce into the mixer the plastic materials and the mineral and / or organic fillers in variable quantity and proportions. Generally, the charge is introduced before the plastic waste to prevent any adhesion of the plastic to the walls of the mixer.

The quantity of fillers introduced into the mixture depends on a certain number of parameters, in particular on the final composite object to be produced, the heating temperature, the nature and the particle size of said fillers. However, it is known that, among the fillers used introduced into said mixture, at least a portion of said fillers must consist of fillers of small particle size preferably within the range of O - 2 mm. These charges in the form of fines or of powdered or finely ground materials prevent agglomeration of the plastic waste between them during the heating operation. The finer the fillers, the less the quantity necessary to avoid agglomeration of the thermoplastic materials. Thanks to these fillers of small particle size, it is observed, during the implementation of the method, a coating of the particles of thermoplastic materials with said fillers in order to prevent any agglomeration of the thermoplastic materials between them. Such a result can only be obtained provided that the stirring carried out during the heating operation is a gentle stirring.

To carry out this double gentle heating / stirring operation, the fillers and the plastic materials are introduced into a mixer of the type for example of that shown in the single figure. This mixer has generally been preheated to a temperature between 150 and 250 ° C., preferably of the order of 200 ° C. When the mixture is introduced into this mixer, the temperature inside the mixer drops. This mixer consists of a drum 1 mounted for rotation about a substantially horizontal axis 2. This drum 1, comprising at least one opening 3 to allow the introduction and the exit of the mixture, is equipped on its interior walls with pallets 4 arranged radially projecting from said interior walls to promote mixing. This mixer submits the constituent elements of the mixture to gentle stirring due to the low speed of rotation of the drum 1 and the absence of movable elements inside the drum. Indeed, the objective is not to destroy, during the heating operation, the physical structure of the waste plastic particles but simply to ensure that the surfaces of these particles are covered with charges.

The speed of rotation of the mixer obviously depends on the size of the mixer, the composition of the mixture and the composite product to be produced. However, by way of example, in the case of a mixer having a cylindrical shape having a diameter equal to 35 cm and a cylinder height equal to 55 cm, the mixer will be rotated in a speed range between 10 and 100 rpm, preferably 30 to 60 rpm. The slow speed allowing gentle mixing of the constituent elements of the mixture prevents any premature agglomeration of said particles together, in particular when approaching the melting temperature at which these particles pass into the liquid state. This heating of the particles is carried out by means of, for example, a burner bank 5 arranged below the drum 1.

The plastics are heated to a temperature above their melting temperature for a very short time of the order of a few minutes, until all the material contained in the drum has reached a uniform temperature. The temperatures reached are generally in the range of 1500C to 250 "C.

When the plastic particles of the mixture reach a temperature such that their surface melts and therefore allows the adhesion of said fillers to the surface of the particles, the mixing operation is stopped and the mixture is quickly extracted from the mixer without it is left to cool.

This mixture is in the form of a divided material formed to schematize plastic particles generally in globular form coated with fillers. This mixture is, possibly after weighing, directly poured into a mold where it is compression molded. Indeed, it is essential, after the heating operation, to subject said components of the mixture to mechanical stress such as a compression operation. However, well known processing methods, such as rolling and compression operations, stamping, thermoforming, stamping, can also be implemented in the context of the present process. The object, once shaped, is taken out of the mold and constitutes a finished product. Obviously, during the molding operation, it is possible to incorporate elements of any kind into the mixture, in particular reinforcing elements, depending on the destination of the finished product.

For example, we recover a transparent tarpaulin treated anti-Uv and used to constitute a tunnel used in agriculture. This tarpaulin was covered during its use with a layer of Meudon white.

This tarpaulin has traces of soil and a thickness of 250 μm. The mixing drum is preheated to 200 "C. 5% of fillers, again made up of Meudon white having a particle size between 0 and 50 μm, are introduced into the mixture, formed of plastic sheeting reduced to pieces. mixer of a rotational movement of a speed equal to 1 turn / s for 4 minutes. It should be noted that it is also possible to subject said drum 1 during this rotation to oscillating movements from before behind which promote mixing. To do this, this drum 1 can be equipped with an axis of oscillation 6 perpendicular to the axis of rotation 2 of said drum 1 and with oscillation means (not shown). 4 minutes of rotation, oscillation and heating, it is found that the temperature inside the mixer is close to 1700C and that there is a beginning of agglomeration between said particles. The rotation of the mixer is immediately stopped, we then introduce this mixture in a mold which is closed by means of a press so as to undergo a compression operation on said mixture. This compression operation makes it possible to obtain a perfectly homogeneous product.

Obviously, the quantity of fillers introduced and the nature of the fillers depends on the final product. Thus, in the case where it is desired to manufacture hollow bodies with thin walls, 10 to 15% by weight of very fine carbonate are mixed, constituting the fillers of said mixture with 100% by weight of general purpose plastics. On the contrary, in the case where it is desired to manufacture thin slabs of 2 cm, the quantity of filler becomes substantially equivalent to that of general purpose plastic materials. In the case, on the contrary, of manufacture of slabs thick of 50 μm, the load is in excess compared to plastics. The percentage by weight of fillers relative to the percentage by weight of plastics can therefore be included in a range from 0 to 95 t. As an example, mineral fillers such as clay, sand, corundum or organic fillers such as sawdust can be used.

The molded objects can be used in particular as coverings (slabs, etc.).

Claims (9)

1. Process for the production of composite objects essentially based on scrap plastic material which is reduced to pieces in the form of strips, shavings or the like and of at least one mineral and / or organic filler, characterized in that one introduces in a mixer, said plastic waste and the charge, the melting temperature of which is higher than the melting temperature of said plastic materials and of which at least a portion of the constituents has a particle size between 0 and 2 mm, in that one heats the mixture subjected to continuous gentle stirring at a temperature at least equal to the melting temperature of the plastics for a sufficiently short time so that the fillers can adhere to the partially molten surface of the thermoplastics and coat them, so that extracts the heated mixture in divided form from said mixer and in that said mixture is subjected to mechanical stress, such as compression, during the shaping of said mixture to allow agglomeration of said constituents of the mixture. 2. The manufacturing method according to claim 1, characterized in that the mixer is preheated to a temperature in the range of 150 to 250 "C. 3. Manufacturing method according to one of claims 1 and 2, characterized in that the mixer is rotated at a speed in the range of 10 to 100 revolutions / min, preferably 30 to 60 revolutions / min. 4. Manufacturing process according to one of claims 1 to 3, characterized in that the heated mixture extracted from the mixer is poured into a mold where the object is compression molded. 5. Manufacturing method according to claim 4, characterized in that incorporating reinforcing elements in said mold. 6. Installation for the implementation of a method according to claims 1 to 5, characterized in that it comprises a mixer (1) of the rotary drum type equipped on its internal faces with pallets (4) radial and comprising at least an opening (3) to allow the introduction and the exit of the constituent elements of the mixture and the heating means (5) of the content of said mixer (1). 7. Installation according to claim 6, characterized in that it further comprises means for oscillating said mixer to allow the oscillation of the mixer (1) about an axis (6) perpendicular to the axis of rotation ( 2) of said mixer (1). 8. Installation according to one of claims 6 and 7, characterized in that the heating means (5) consist of a burner bank arranged under said mixer (1). 9. Composite products based essentially on plastic waste and at least one mineral and / or organic filler, characterized in that they are obtained by the implementation of the process according to claims 1 to 5.