FR2796879A1 - PROCESS FOR THE RECYCLING OF MAGNETIC STRIPS BY EXTRUSION - Google Patents

Abstract

The invention concerns a method for recycling magnetic tapes (7) by extrusion which consists in directly introducing said tapes (7) by one of their two ends at the extruder screw(s) (2) inside the sheath (1) containing them, without any prior crushing step.

Description

 The invention relates to a method for enabling the recycling of magnetic tapes, in particular by extrusion.

The tapes in question are both audio and video tapes, as well as computer tapes that run on large computers.

Traditionally, these magnetic strips consist first of a support, made of polyester, or any other plastic material, on which is deposited a thin layer of binder, containing magnetic charges, whose mass ratio varies between 15 and 25% of the weight of the starting strip, and whose nature is a function of the destination of said bands. In particular, the predominant Fe203 iron oxide type bands are predominantly Cr203 chromium oxide type bands.

The binder is of organic type, especially polyurethane or chlorinated compound. This binder decomposes at high temperature, being capable of generating products of a toxic nature, such as chloroethanol.

The objective of the process according to the invention is to achieve the production of aggregates from the treatment of these strips, intended to allow the production of injection molded parts or the production of textile raw materials by extrusion I spinning . It is also intended to allow the direct production of either extruded profiles or molded parts, or son to be stretched and / or woven.

Given the large number of magnetic tapes used, the question arises of the desirability of their recycling, particularly in the field of plastics and plastics. textile industry.

Traditionally, <B> plastic recycling, regardless of the physical form in which it occurs, firstly comprises a grinding step using one or more grinders, to reduce the dimensions plastic elements thus obtained.

The fact is that this grinding step leads sometimes to degradation of the polymer due to the resulting heating, thus requiring cold operation. This specific step therefore requires a particular infrastructure and is relatively energy-consuming. In addition, it is inappropriate with elements in the form of thin sheets, precisely the form in which the magnetic tapes occur.

In fact and to date, magnetic tapes have not been the subject of in-depth studies on their recycling, because of this disadvantage, which sometimes can be prohibitive. However, it has been proposed various methods of recycling such strips, which systematically recommend a prior step of grinding or cutting strips, possibly associated with a heating step. It is then recommended the addition of binders prior to an ultimate injection step, in order to result in a product of definitive shape (see for example WO 9415767).

The major drawbacks have previously been shown to proceed with such a preliminary step of cutting or grinding.

The object of the present invention is therefore to overcome these drawbacks, namely in particular the specific step of grinding and secondly, the difficulty of covering such a step with elements in the form of thin sheets, by proposing an extrusion process, wherein the strips are directly introduced through one of their two ends, at the extrusion screw (s) within the sheath containing them.

In other words, the invention consists in eliminating, in addition to the grinding step, any feed hopper at the level of the extrusion screw, and positioning at this point the free end of a or several magnetic tapes.

Due to the phenomena of friction occurring between the end of the magnetic strip or strips considered against the walls of the barrel of the extruder, inherent in the action of the screw, it is created in a drive inducing the unwinding of the said one or more strips within the barrel, until reaching the compression zone at which the rise in temperature inherent to the compression or, inherent in a localized heating system, induces the melting of the polyester support, or moreover. general plastic material constituting said strips. Their conformation according to a determined profile is carried out in a traditional way by the shape of the die located downstream of the zone of compression and fusion.

According to one characteristic of the invention, several bands are assembled together in the form of a strand, which is then positioned at the level of the extrusion screw, in order to lead to its driving within the sheath. In addition, the strips are advantageously stored in the form of coils or flanges, resting by their axis of rotation on a support allowing them free rotation, or simply on their sidewalls. When the dimensions of the coils are relatively large, inducing an increase in weight, the axis of rotation of said coils can be motorized to facilitate their unwinding, and hence their routing within the extruder, the rotation of said coils being a function of the desired drive speed. According to another specific embodiment, the strips are previously steamed before being inserted at the level of the extrusion screw. This prior stoving phase makes it possible to reduce the level of moisture in the strips, given the sensitivity of the polyester to hydrolysis. In another embodiment of the invention, the extrusion device is replaced by a screw and sheath plasticizer, the screw also acting as an injection piston, the die being then replaced by a mold. The manner in which the invention can be realized and the advantages which result therefrom will emerge more clearly from the exemplary embodiments which follow given by way of indication and not limitation in support of the attached text. Figure 1 is a schematic representation in longitudinal section of a single-screw extruder, of the type used in the method according to the invention.

Figure 2 is a schematic view also in longitudinal section of a twin-screw extruder, also capable of being implemented by the method of the invention. According to a fundamental characteristic of the invention, the method of recycling magnetic tapes aims first and foremost to overcome the prior grinding step described in the preamble of the present description. To do this, the magnetic strips (7) stored in the form of coils or flanges (6) are either simply placed on one of their side, or mounted on an axis free to rotate, or possibly motorized. They are introduced by their free ends upstream of the feed zone (4) of an extrusion screw designated by its cylindrical sheath (1) and its extruder screw (2) itself. Advantageously, several strips are assembled together in the form of a strand, which, for the sake of optimizing the driving of the strips within said sleeve by the extrusion screw, ensures a twist on itself, in particular at the orifice (8) of the upstream portion of the feed zone (4). In the example described with reference to FIG. 2, the feeding principle remains the same. On the other hand, the extruder comprises two co-rotating or counter-rotating screws.

In addition, the sheath (1) can be temperature-controlled to promote the solid / liquid transformation phase at the compression zone (3) between the screw and said sheath.

According to the invention, the extruder is extended by a die (5) of varying shape, size and geometry, depending on the type of products that it is desired to obtain after extrusion.

This die can be cylindrical and in this case, is advantageously followed by a cooling device and granulation, to allow the realization of a raw material used directly in plastics or in the textile industry.

Moreover, and when it is desired to modify the composition of the material constituting the initial magnetic tapes, it is possible to proceed to the addition of additional materials during extrusion, in particular by the addition of virgin polyester or other material.

In another embodiment of the invention (not shown), the extrusion screw is replaced by a screw and sheath plasticizing system. In this configuration, the compression zone between the screw and the sheath causes the strips to be sufficiently plasticized and maneuverable so that they can be compressed by the extrusion screw, which then acts as an injection piston at a mold of suitable form, according to the principle of a screw-in injection molding machine, whether this is horizontal or vertical orientation.

However, given that in such an embodiment, it is necessary to implement only a predetermined quantity of plastic material, it follows a discontinuity of the process then leading to a magnetic strip supply system sequenced , enslaved or not to the process for driving said bands.

It is possible to provide in this embodiment, a device for cutting the strips at the feed zone, so as to allow, as a function of the number of strands and the geometrical characteristics of sheath and screw to determine in a relatively precise manner the amount of plastic material to be covered, and hence the duration of operation of the strip unwinding system. FIG. 2 shows a twin-screw extrusion system. The elements identical to those of Figure 1 bear the same references. In this embodiment, the conveying and plasticizing zones (9) of the kneading zones (10) are advantageously alternated, so as to impart a greater homogeneity to the plastic material that is to result therefrom.

Whatever the method of plasticization covered, namely extruder or screw and sheath plasticizing system, it may be advantageous to implement a degassing well at the sheath, and particularly at the compression zone, to allow the evacuation of water vapor, retained by the polyester strip, as well as the various products, including toxic, contained in the binder.

In this case, the extrusion and compression screw is provided with a zero pressure zone so as not to induce at the level of the degassing well the evacuation of the softened material at this level.

In another embodiment of the invention, a multi-orifice spinning head is positioned at the end of the extruder, so as to simultaneously obtain threads, with or without drawing, which are fed to a winder. Such a spinning head is in itself well known, so there is no need to describe it here in more detail.

The products obtained underwent analyzes, particularly in terms of mechanical strength. To do this, plates and test pieces of different geometries were made by injection molding. A very significant increase in flexural stiffness is observed, particularly with respect to the virgin polyester, since this increase can even reach a level of 100%. There is also an increase in thermal conductivity (35 to 70%) compared to the control.

In fact, these optimized mechanical properties, combined in addition with the thermal conduction properties as well as with the dielectric characteristics inherent to the base material, make it possible to apply these recycled materials in sectors such as the automobile, household appliances, industry (heat exchangers) and the building. In addition, the polyester-based material may advantageously be mixed with polycarbonate, so as to render the final material obtained more resistant to impact.

It is therefore conceivable the whole point of the method according to the invention, which ensures a recycling of abundant materials, whose only destiny to date was destruction, with corollary, given the materials covered for their constitution, a risk of pollution.

Claims (3)

A method for recycling magnetic tapes by extrusion, characterized in that said strips (7) are directly introduced through one of their two ends at the level of the screw (s). extrusion within the sheath containing them, and therefore in the absence of any prior grinding step. 2. A method for recycling magnetic tapes according to claim 1, characterized in that the entramement of the magnetic strips (7) within the extruder is consecutive to the friction phenomena occurring between the end of the magnetic strip or strips considered against the walls of the barrel of the extruder. 3. Method for recycling magnetic tapes according to one of claims 1 and 2, characterized in that the compression zone (3) of the extruder is capable of being heated, in order to to promote the transformation and the change of state of the plastic support of the magnetic strips (7). <B> 4. </ B> Method for recycling magnetic tapes according to one of claims 1 to 3, characterized in that the conformation of the plastic material at the extruder outlet according to a determined profile is achieved by the shape of the die (5) located downstream of the compression and melting zone. Process for the recycling of magnetic tapes according to one of Claims 1 to 3, characterized in that the conformation of the plastic material at the extruder outlet in the form of wires is carried out by means of spinning head positioned at the extruder outlet. <B> 6. </ B> The method for recycling magnetic tapes according to one of claims 1 to 5, characterized in that the end of several magnetic tapes is assembled (7). ) between them in the form of a strand, which is then positioned at the extrusion screw, in order to result in driving the strand thus formed within the sheath. Method for recycling magnetic tapes according to one of Claims 1 to 6, characterized in that the magnetic tapes (7) are stored in the form of coils or flanges (6), resting on their side or by their axis of rotation on a support allowing them free rotation. Method for the recycling of magnetic tapes according to one of Claims 1 to 6, characterized in that the magnetic tapes (7) are stored in the form of coils or flanges (6), resting by their axis of rotation on a motorized support ensuring their rotation according to the desired drive speed. 9. A method for recycling magnetic tapes according to one of claims 1 to 8, characterized in that prior to their introduction at the extruder, the magnetic tapes (7) are baked, to reduce their moisture content. <B> 10. </ B> The method for recycling magnetic tapes according to one of claims 1 to 6, characterized in that the extrusion die is replaced by a plasticizing device. screw and sheath, the screw further acting as an injection piston.