ITMO20110055A1 - METHOD FOR THE RECOVERY OF MATERIALS CONSTITUTING OPTICAL DISCS. - Google Patents

Description

"METHOD FOR THE RECOVERY OF MATERIALS MAKING UP THE OPTICAL DISCS"

DESCRIPTION

The present invention relates to a method for recovering the materials constituting the optical discs, with a view to recycling.

It is known that optical discs, such as CDs (Compact Discs) and DVDs (Versatile Digital Discs) in particular, are increasingly popular for storing data in digital format.

These discs are essentially made up of a multilayer structure comprising a support in synthetic material (polycarbonate) which has an engraved face for storing data and the opposite face covered with a sheet of reflective metal material (aluminum in CDs and silver in DVDs ), on which additional paper labels can be applied.

Given their composite nature, optical discs are not biodegradable, nor can they be recycled directly with common plastic and present many problems related to disposal that can only take place through treatment in an incinerator.

For this reason, various essentially mechanical techniques for recovering optical discs have been developed, which allow the recovery of at least the polycarbonate constituting the support but considerably degrade its qualities by limiting subsequent reuse.

According to one of these techniques, for example, it is foreseen to carry out mechanical abrasion operations of the engraved face of the support and its subsequent reworking but due to the degradation of the material, it is no longer reusable for storing data.

Alternatively, a technique is known which provides for the execution of a mechanical removal process by scraping the metal layer and any labels applied on it by the polycarbonate support, which, once cleaned, can then be ground to obtain polycarbonate granules to be reused. The scraped material in the form of dust and flakes can be vacuumed, collected and heat treated to recover any metals.

These known methods are not free from drawbacks, including the fact that performing mechanical operations to remove the metallic material deposited on the support necessarily involves the loss of a portion of polycarbonate which is separated together with the metallic layer.

Furthermore, these techniques do not allow to separate and recover both the polycarbonate and any metals forming the optical disc at the same time and require the use of dedicated equipment for handling and processing the discs.

These purely mechanical techniques also cause degradation of the polycarbonate with a decrease in the optical grade and limitations in subsequent re-uses. Last but not least, the mechanical processing of these materials involves the production of powders potentially harmful to health, which must be suitably treated by using auxiliary suction and separation apparatuses for air purification.

The aim of the present invention is to eliminate the aforementioned drawbacks of the known art by devising a method for recovering the materials constituting the optical discs which allows the polycarbonate and any metal materials forming the disc to be recovered in full. Within the scope of this technical task, another object of the present invention is to obtain the recovery of the polycarbonate and any metals by means of a single treatment step and without requiring complex dedicated machinery.

Still, an object of the present invention is to not involve the formation of dust or other polluting agents in the air of the environments in which the processing is carried out.

Another object of the present invention is to be relatively easy to implement in practice, safe in use and effective in operation, as well as relatively low in cost.

This task and these purposes are all achieved by the present method for the recovery of materials constituting the optical discs comprising a polycarbonate support associated with at least one metallized layer, characterized in that it comprises the following steps:

immersion of at least one said optical disc or fragments thereof in a bath comprising an aqueous solution of an alkali or alkaline earth metal hydroxide to obtain the separation of said polycarbonate support from said metallized layer; And

separation, from the said bath, of a liquid phase and of materials in the solid phase, containing at least said poly carbonate.

Further characteristics and advantages of the present invention will become more evident from the detailed description of a preferred but not exclusive embodiment of a method for the recovery of materials constituting the optical discs, illustrated by way of example, but not of limitation, in the attached drawings. in which:

Figure 1 is a schematic representation of the steps of the method according to the invention;

Figure 2 is a graphical representation of the correlation between the molar concentration of the alkali metal hydroxide in aqueous solution and the time required for the detachment of the polycarbonate support from the metallized layer as a function of the treatment temperature;

Figure 3 is a graphical representation of the correlation between the ratio of the weights of the solid phase and of the solution and the time necessary for the detachment of the polycarbonate support from the metallized layer;

Figure 4 is a graphic representation of the exhaustion of the aqueous solution of alkali metal hydroxide expressed as a correlation between the number of cycles of use of the same solution and the time necessary for the detachment of the polycarbonate support from the metallized layer.

With particular reference to the aforementioned figures, the method for recovering materials constituting the optical discs, consisting of a polycarbonate support associated with at least one metallized layer, according to the invention, essentially comprises an immersion step 101 of at least one optical disc or fragments thereof, in a bath comprising an aqueous solution of an alkaline or alkaline earth metal hydroxide to obtain the separation of the polycarbonate from the metallized layer and a subsequent separation step 102 of the solid phase (polycarbonate and metals) and of the liquid phase. This method makes it possible to process different types of optical discs, such as CDs, DVDs and the like.

Generally, in an optical disc, a connection means, for example a layer of resin, is interposed between a polycarbonate support of the optical disc and a face of a metallized layer, comprising or consisting of at least one layer of metallic material, for example a layer of silver or aluminum, a paper layer possibly being coupled to the other face of the metallized layer. In the aqueous solution, the polycarbonate support and the metal material layer separate, for example, by dissolution of the connecting medium in alkali metal or alkaline earth hydroxide solution, but the polycarbonate support retains its integrity.

In the case of CDs, the metal material used can be aluminum and the method according to the invention is mainly aimed at the separation and recovery of the polycarbonate; in fact, the aluminum reacts with the alkali or alkaline earth metal hydroxide and forms aluminum hydroxide which can be removed from the liquid phase according to known methods.

In DVDs, on the other hand, the metal material used is usually silver and the method according to the invention allows simultaneous separation and recovery of both the polycarbonate and the silver. In this case, the silver layer which is very thin, generally between 0.1 and 1000 microns, detaches from the polycarbonate support, disintegrates and forms "specks", which are separated and recovered, for example, by a subsequent phase of separation 102.

Any further solid phase materials, for example paper and various impurities, dissolve in the aqueous solution of alkali or alkaline earth metal hydroxide, remain dispersed in the solution and are eliminated by the subsequent separation step 102, for example by screening.

The alkali or alkaline earth metal hydroxide employed can be selected from the group comprising sodium or potassium or lithium or calcium hydroxide and preferably consists of sodium hydroxide.

Furthermore, the molar concentration of the alkali or alkaline earth metal hydroxide in the aqueous solution is comprised between 0.5 mol / 1 and 10 mol / 1 and preferably equal to 5 mol / 1. The concentration value must be chosen considering that as it increases, a reduction in process times is obtained, against an increase in the costs of carrying out the same.

Furthermore, in the immersion step 101, the bath is preferably maintained at a temperature higher than the ambient one and lower than 120 ° C, for example of the order of 60-70 ° C. This heating contributes to the reduction of the duration of the treatment.

The bath, in the immersion step 101, is preferably kept under agitation at a speed of between 100 rpm and 500 rpm, for example 300 rpm, to facilitate contact between the solution and the optical discs.

The immersion step 101 can be carried out in a conventional thermostated tank equipped with an internal mixing apparatus.

Furthermore, in order to obtain an adequate distribution of the optical discs or fragments thereof in the bath, it is provided to introduce an amount such that the ratio between the weight of the same and that of the solution is between 1/1 and 1/8, and preferably of the order of 1/4.

The duration of the immersion phase 101 is generally between 30 min and 24 hours, in relation to the parameters mentioned above.

In a preferred embodiment, a preliminary step 103 is provided for grinding the one or more optical discs to obtain a plurality of composite fragments, i.e. each comprising a portion of the polycarbonate support and the corresponding portion of the coating layer or layers, to be fed towards the next immersion phase 101.

The grinding step 103 is aimed at obtaining fragments having, for example, an average diameter of between 2mm and 20mm, and preferably of the order of 5mm. In fact, it has been found that a reduction in the size of these fragments corresponds to a contraction in the duration of the subsequent immersion phase 101.

The grinding step 103 can be carried out by using a conventional automatic shredder.

The duration of the immersion phase 101 depends on the molar concentration of the alkali or alkaline earth metal hydroxide solution, on the temperature and stirring speed of the bath and on the ratio between the weight of the optical discs, or relative composite fragments, and that of the solution: for example, considering submitting at least one optical disc to the grinding step 103 to obtain composite fragments with an average diameter of 5 mm and using a bath containing an alkaline solution of sodium hydroxide (caustic soda) with a molar concentration equal to 5 mol / 1, kept at 60-70 ° C and stirred at a speed of 300 rpm, and to introduce into the bath itself a quantity of fragments weighing four times less than that of the solution, the duration of the immersion phase 101 is 'order of 45 min-1 hour. When the immersion step 101 is preceded by the grinding step 103, the subsequent separation can be carried out by means of a screening step 102 comprises at least two filtration stages in series with decreasing particle size, of which the first is for the recovery of the polycarbonate fragments and the second for the collection of the remaining solid phase materials. If the optical discs treated are of the CD type, it is in fact sufficient to perform a two-stage screening of which the first through the use of a sieve with a weft of about 2mm for the interception of the polycarbonate and the second having weft of dimensions lower to retain the remaining portion of the solid phase.

If, on the other hand, one wishes to treat (even or only) optical discs of the DVD type, it is advisable for the separation step 102 to include three stages of screening in series with decreasing particle size, of which the first for the recovery of polycarbonate fragments, the the second for the collection of further solid-phase materials, for example paper and various impurities, and the third for the recovery of the "specks" of metallic material.

This screening step 102 can be carried out for example by using three sieves in series having wefts of decreasing dimensions, for example, respectively, of 2mm, Imm and 75pm.

The resulting liquid phase of the separation step 102 can be recovered, for example, in a tank positioned below the sieves and possibly re-introduced into the bath used for the immersion step 101. It has in fact been verified that the alkali metal hydroxide solution or alkaline earth can be reused up to 8 cycles but preferably up to 5 cycles.

In fact, a loss of effectiveness of the solution of the immersion step 101 is noted which is mainly caused by the increase in the density of the aqueous solution of alkali metal or alkaline earth.

The density of the alkaline sodium hydroxide solution increases with each cycle due to the paper and various impurities which dissolve in solution or remain dispersed in the liquid phase at each subsequent immersion phase 101 and which are not retained by the subsequent screening phase 102.

Conveniently, when the solution is re-introduced into the bath used for the immersion phase 101, a new aqueous solution of alkali metal or alkaline earth hydroxide is added, for example, in a quantity equal to 10-20% of the volume of the phase liquid recovered following the separation step 102.

Subsequently, a washing and drying step 104 of the separated solid materials can be carried out.

Washing involves spraying the separated solid materials, for example in sieves, with running water which is then disposed of.

Drying, on the other hand, consists in conveying a flow of hot air over the washed solid materials, for example in correspondence with the first and third sieves, if provided.

If the method is also aimed at the recovery of metal material, it is envisaged to perform a heat treatment of the metal recovered by separation, for example in the third sieve during the screening phase 102, to obtain the melting and compacting of the metal material into ingots. or similar .

A treatment of the exhausted liquid phase coming from the previous processing, containing aluminum, is also provided for the purpose of recovering the metal itself. The treatment consists in acidifying the liquid phase with inorganic acids, such as hydrochloric acid or sulfuric acid or nitric acid, so as to allow the precipitation of aluminum as hydroxide and its subsequent recovery through filtration.

In practice it has been found that the described invention achieves the intended aims and in particular it is emphasized that the method according to the invention allows the complete recovery of the polycarbonate and any metallic material by means of a single chemical treatment, without requiring the use of dedicated equipment and without the risk of compromising the environment in which the treatment is performed.

The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the inventive concept.

Furthermore, all the details can be replaced by other technically equivalent elements.

In practice, the materials used, as well as the contingent shapes and dimensions, may be any according to requirements without thereby abandoning the scope of the protection of the following claims.

Claims (10)

CLAIMS 1) Method for the recovery of materials constituting the optical discs comprising a polycarbonate support associated with at least one metallized layer, characterized in that it comprises the following steps: immersion of at least one said optical disc or fragments thereof in a bath comprising an aqueous solution of an alkaline or alkaline earth metal hydroxide to obtain the separation of said polycarbonate support from said metallized layer; And separation from said bath of a liquid phase and of materials in a solid phase, containing at least said polycarbonate. 2) Method according to the preceding claim, characterized in that said metallized layer consists of at least one layer of metallic material, preferably a layer of silver or aluminum. 3) Method according to claim 1 or 2, characterized in that said alkali or alkaline earth metal hydroxide is selected from the group comprising sodium or potassium or lithium or calcium hydroxide. 4) Method according to one or more of the preceding claims, characterized in that the molar concentration of said alkali or alkaline earth metal hydroxide in said solution is comprised between 0.5 mol / 1 and 10 mol / 1. 5) Method according to one or more of the preceding claims, characterized by the fact that, in said immersion step, said aqueous solution is maintained at a temperature comprised between the ambient one and 120 ° C. 6) Method according to one or more of the preceding claims, characterized in that, in said immersion step, said aqueous solution is kept under agitation at a speed between 100 rpm and 500 rpm. 7) Method according to one or more of the preceding claims, characterized in that the ratio between the weight of said at least one optical disc and that of said aqueous solution is between 1/1 and 1/8. 8) Method according to one or more of the preceding claims, characterized in that it comprises, before the immersion step, at least one step of grinding said at least one optical disc to obtain a plurality of composite fragments each comprising a portion of said polycarbonate support and a portion of said at least one metallized layer, said at least one optical disc being introduced into said aqueous solution in the form of said composite fragments. 9) Method according to one or more of the preceding claims, characterized in that said separation step takes place by screening. 10) Method according to one or more of the preceding claims, characterized in that it comprises recovering said liquid phase from the separation phase and re-introducing it into said bath.