Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Process of treating scrap or waste product containing solid...
Reexamination Certificate
1999-03-18
2001-01-09
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Process of treating scrap or waste product containing solid...
C521S048000, C528S500000, C528S501000
Reexamination Certificate
active
06172125
ABSTRACT:
The present invention relates to a process for the recycling of articles, and in particular of sheets, based on vinyl chloride polymers.
Vinyl chloride polymers, and in particular polyvinyl chloride (PVC), are widely used for the manufacture of a variety of articles. They are used, for example, for the manufacture of sheets—generally reinforced with reinforcing fibres—intended for the covering of vehicles, for the concealing of buildings on which work is being carried out, for the construction of sets for entertainments or exhibitions, or for advertizing purposes. These sheets generally have a large surface area. Furthermore, in many applications, most particularly in advertising applications or in applications involving sets for entertainments or exhibitions, which at the present time are growing considerably, their lifetime is short, typically a few weeks or months. For these reasons, large quantities of such sheets are scrapped each year. The process of recycling them consequently constitutes a major ecological and economic problem.
The same situation applies with regard to other articles based on one or more, flexible or rigid, vinyl chloride polymers, for example with regard to conveyor belts, coated fabrics and other elements for the interior furnishing of vehicles, pipes and hoses, window frames or polymer-insulated power cables.
Thorough grinding of these articles usually results in a mixture of fine particles of heterogeneous composition, which is difficult to purify and reuse. Furthermore, in the case of fibre-reinforced articles (for example, polyester-fibre-reinforced articles), the fibres often form a kind of wadding which makes it much more complicated to reuse the ground particles.
Various processes based on dissolving, using organic solvents, have already been proposed; however, they often cause safety and pollution problems. Furthermore, they do not always make it possible to recover plastics of sufficient purity to allow them to be re-utilized from an advantageous economic standpoint. Another drawback of these methods is that they generally cause the additives (e.g. plasticizers) contained in vinyl chloride polymers to be extracted, this having the effect of preventing them from being reused directly. Additionally, these known processes lead to the formation of very fine polymer particles (of the order of 1 micron), which are difficult to filtrate and to reprocess.
Consequently, the present invention aims to provide a recycling process and which allows plastics of high purity and advantageous morphology to be recovered, while substantially preventing any additives from being extracted therefrom.
More specifically, the present invention relates to a process for recycling an article based on at least one vinyl chloride polymer, in which:
(a) the article is shredded into fragments having an average dimension of 1 cm to 50 cm, should it exceed these dimensions;
(b) the fragments of the article, which are substantially dry, are brought into contact with a substantially anhydrous solvent capable of dissolving the vinyl chloride polymer, forming an azeotrope with water;
(c) the polymer dissolved in the solvent is precipitated by injecting steam in the solution thus obtained, which moreover leads to the stripping of the water-solvent azeotrope and so leaves behind a mixture essentially consisting of water and of solid polymer particles;
(d) the polymer particles are recovered.
The articles in question may be of any kind, as long as they essentially consist of one or more vinyl chloride (VC) polymers. VC polymer should be understood to mean any homopolymer or copolymer containing at least 50% by weight of VC. Polyvinyl chloride (PVC), i.e. a homopolymer, is generally used. Apart from one or more VC polymers, the articles may also contain one or more of the usual additives such as, for example, plasticizers, stabilizers, antioxidants, fire retardants, pigments, fillers, etc., including reinforcing fibres, for example glass fibres or fibres of a suitable plastic, such as a polyester.
The articles may be in any form, for example in the form of flexible pipes or hoses or rigid pipes, containers, sheets for covering soils, tarpaulins, window frames insulating sheaths of power cables, etc. They may have been manufactured by any known technique: extrusion, coating, injection moulding, etc.
The term “sheet” should be understood to mean any thin, flexible or rigid, single-layer or multilayer article, which may or may not be reinforced by reinforcing fibres embedded in the plastic. These sheets have any thickness, however this is generally less than 10 mm; their thickness is usually between 0.1 and 5 mm. The process is particularly advantageous for recycling tarpaulins, i.e. fibre-reinforced sheets, intended especially for covering vehicles, for concealing buildings on which work is being carried out, for the construction of sets for entertainments or exhibitions, or for advertising purposes. The sheets may have been manufactured by any technique, for example by calendering or by coating; the reinforced sheets are often manufactured by coating a network of fibres by means of a plastisol and heating.
The articles do not necessarily have to be in the form of objects having a well-defined shape; the process applies equally well to articles in a liquid or pasty state, especially to sludge recovered when cleaning plants used for the manufacture of articles made from vinyl plastisols. Apart from one or more vinyl chloride polymers, these articles in a liquid or pasty state may also contain one or more solvents, for example white spirit.
The possible reinforcing fibres may be of any kind—natural or synthetic; glass fibres, cellulose fibres or plastic fibres may especially be used. Often these are plastic fibres, particularly polyester fibres. Polyethylene terephthalate (PET) gives good results, especially for the reinforcement of sheets used as tarpaulins. The diameter of the fibres is usually of the order of 10 to 100 &mgr;m. They are often long fibres, the length of which may be up to several meters. However, they may also be shorter fibres—ranging from a few millimeters to a few centimeters in length—possibly forming a woven fabric, a nonwoven fabric or a felt. By way of illustration, the fibres may represent from 1 to 40% of the weight of a reinforced sheet.
The first step (a) of the process according to the invention consists, if necessary, in shredding the articles so as to reduce them to small-sized fragments which are easy to handle. The average dimension of these fragments is preferably at least 2 cm. Moreover, it is advantageously at most 30 cm. It is clear that if the article is already in the form of fragments of suitable dimensions, the shredding step is superfluous.
Shredding by means of conventional machines such as low-speed twin-shaft grinders without a grid or high-speed knife-type grinders (with a speed of greater than approximately 400 rpm) do not generally give excellent results since these machines often transform any reinforcing fibres into a kind of wadding, which cannot easily be reused and/or disrupts the operation of the shredding machine.
Consequently, within the context of the present invention, a low-speed grinder with a grid is used, which is capable of shredding reinforced fibres, such as those described above, without causing excessive heating and which, with regard to any reinforcing fibres, prevents the formation of wadding while ensuring that they are fragmented in such a way that the average length of the fibre pieces is, however, at least 5 mm.
It has proved to be advantageous to use a shredding machine comprising two rotating shafts provided with partially imbricated knives rotating above and a short distance away from a grid (the central part of which is approximately in the form of a double cylinder sector) provided with perforations of an average dimension of the order of 1 to 10 cm (for example of round shape). These so-called main shafts rotate in opposite directions, preferably at a speed not exceeding 100 rpm. Associated with each of thes
Scheffer Jacques
Vandenhende Bernard
Yernaux Jean-Marie
Cain Edward J.
Schneller Marina V.
Solvay S.A. (Societe Anonyme)
Spencer George H.
Venable
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