GB2331953A

GB2331953A - Utilisation of scrap plastics material

Info

Publication number: GB2331953A
Application number: GB9826201A
Authority: GB
Inventors: Philip Arthur Hadley
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-12-02
Filing date: 1998-12-01
Publication date: 1999-06-09
Anticipated expiration: 2018-12-01
Also published as: GB9826201D0; GB2331953B; GB9725456D0; GB2331953A8

Abstract

A method and machine for the utilisation of scrap plastics material involves the use of a granulator (15), to which scrap plastics material is delivered, to produce particles having a size of no greater than about 10mm, which is then heated in a oven to an extent sufficient to cause part at least of the surface of the granules to become molten, but insufficient to cause substantial melting of the granules. The granules are then compressed together into the form of a desired article, which may subsequently be subjected to a finishing or machining operation. The partly heated granules are compressed conveniently in a mould such as a continuous extrusion mould. The material may be processed by an injection moulding process.

Description

1 2331953 PATENTS ACT 1977 WL/A9276GB Title: Method and Machine for the

Utilisation of Scrap Plastics Material

Description of Invention

This invention relates to a method and machine for the utilisation of scrap plastics material, and is particularly but not exclusively concerned with the utilisation of scrap plastics material as is currently used in packaging, such as, for example, scrap polythene in sheet form.

The utilisation of such scrap plastics material is desirable both economically and environmentally, and new legislation is shortly to be introduced in the United Kingdom concerning the re-use of packaging waste, including scrap plastics.

Several methods are known for the utilisation of scrap plastics material, one of which is disclosed in our earlier European patent no. 0496080. The method and machine in EP 0496080 is concerned with the utilisation of scrap plastics material by enabling the material to be melted and subsequently reextruded whilst in a molten condition, and whilst the method and associated machine is very suitable for the production of extruded products made from scrap plastics material, the associated running costs are relatively high and there is a limitation as to the application of the method.

Additionally, the re-extrusion process means that, in general, different grades of plastics need to be processed separately.

It is thus an object of the present invention to provide an improved method and machine for the utilisation of scrap plastics material.

According to one aspect of the invention, there is provided a method for the utilisation of scrap plastics material comprising the steps:

2 a) procuring generally granular scrap plastics material; b) heating the material so as to melt at least part of the outer surface of the granules; and C) compressing the granules together whilst in their heated state.

Preferably the granules are compressed in a mould or die, into a form in which they may be used, if necessary prior to carrying out subsequent operational stages, such as machining, finishing, coating or the like.

It is to be appreciated that the term "granular" should be interpreted in a broad sense, in that the scrap plastics material concerned need not necessarily constitute granules per se, but that the term "granular" is intended to refer to particles which are generally Eree flowing when in an unheated state, and which would typically have a diameter of no more than approximately 10 mm.

The generally granular scrap plastics material may be produced by a variety of different methods, but conveniently, the material is obtained by first comminuting the plastics material in its "raw" form, (for example sheet form), drying the comminuted material, transferring the dried material by use of a screw or auger, to a granulator which produces plastics material of the required generally granular form.

The screw/auger may impart additional heat to the material and may also compress the material slightly so as to produce more uniforrnly sized and shaped particles. In this case, the granulator may be water cooled, and the material leaving the granulator may thus be hot, and may be removed from the granulator pneumatically, which causes a cooled "skin" to form on the outer surface of the granules.

Subsequent heating of the material may be by use of an oven, preferably having a temperature in the range 300 to 1200T, preferably 800 to 1000'C, and conveniently 900T.

If desired the granules may be heated on passage through the oven by the use of a horizontal conveying means, but conveniently a vertical oven is i 3 utilised, through which the granules are caused to fall, and in which they attain the desired temperature. Conveniently, an oven is utilised having a height of between 1 and 3m, conveniently approximately 1.5m.

The granular size, the temperature of the oven, and the height of the oven are chosen such that on exiting the oven, at least part of the granules' outer surface is in fluid condition, although in practice it may be desirable to melt all of the granules' outer surface, and flirthermore, it will be appreciated that the heated portion of the granules may in fact extend beyond the outer surface per se, perhaps to approximately 10-20% of the granules radius. The partly heated granules are then compressed, conveniently M a mould such as a continuous extrusion mould, whereby the granules stick together by virtue of their heated outer surfaces.

It will be appreciated that by altering the degree of compression imparted by the mould, the density of the resultant moulded article may be altered as desired.

Moreover, the method allows different types of scrap plastics material to be utilised as part of a single process, which is not the case with known methods which rely on re-extrusion of the scrap material.

Alternatively tile material may be processed by an injection moulding process.

It has been found by the applicant that the resultant moulded article may be subjected to a variety of flu-ther processes, which may be chosen in accordance with the requirements of the finished product.

For example, the product may be machined to remove any exterior roughness, with the discarded material subsequently being reprocessed (for example in accordance with the present invention).

The product may also be subjected to a process known as "hot sweeping" whereby the rough exterior is passed through a very hot die, to the extent that the surface becomes molten, and subsequently forced through a 4 sizing die where any high spots are removed and pushed into adjacent low spots.

The product may also be laminated, for example by extruding a material over the rough surface, to present a regular and consistent finish, and secondary lamination is also envisaged whereby the product may be coated with a still further material, for example for aesthetic purposes.

VAfilst the applicants envisage that the granules may be heated solely by a vertical oven, it has been found that a superior product may be obtained if the scrap material is first heated by the discharge screw/auger extending to the granulator, and transferred to the granulator in a hot (semi-molten) condition, and granulated whilst in the hot condition.

The granules may then be removed pneumatically from the granulator, this forming a cooled "skin" on the outside thereof, and the semi-molten material may then be stored for example in a hopper, for up to 20 minutes, during which time the applicants have found that the temperature of the material remains relatively constant.

Thus, on subsequent re-heating in the vertical oven, the outside becomes molten, enabling the material to stick together upon compression, with the heated interior of the granules enabling a greater degree of compression, and a greater degree of homogeneity in the moulded product to be obtained.

According to this invention there is provided a machine for the utilisation of scrap plastics material comprising a) a heating means; b) delivery means for delivering generally granular scrap material to the heating means, wherein the material is heated to melt at least part of the outer surface of the granular materials, but no so as to melt the whole of the granules; and C) means to compress the heated granules to cause the granules to stick together by virtue of their melted outer surfaces.

Preferably the heating means is operative to heat the granules to a depth of no greater than 2(YYo of the radius of the granules, preferably less than 10% of the said radius.

Preferably the machine comprises granulating means to granulate scrap plastics material for delivery by the delivery means to the heating means, and preferably also comprises feeding means, conveniently in the form of a screw or auger, to deliver scrap plastics material to the granulating means.

Preferably the machine comprises a shredding means to shred scrap plastics material prior to delivery thereof to the feeding means.

Preferably the machine comprises cooling means to cool the granules prior to delivery to the heating means, conveniently by the provision of a storage means such as a hopper, to which the granules are delivered by the delivery means, and within which the granules may be retained, prior to passage through the heating means.

Preferably the heating means is provided by an oven, preferably having an interior temperature lying within the range 300 - 1200'C, preferably in the range 800 - 1 OOO'C.

Preferably the oven is a vertical oven, through which granules fall, during which they are heated to melt at least part of the outer surface thereof.

Preferably the machine comprises means to perform a mechanical operation on the heated granules, to compress the granules together into the form of an article for subsequent use.

A preferred manner of carrying out the invention will now be described by way of example only, by reference to the accompanying drawing.

Scrap plastics material of the type suitable for use with the present invention (for example scrap polythene in sheet form, although it will be appreciated that many different types and conditions of plastics material may be used) is conveyed to a shredder 10 of generally conventional form, which 6 shredder size reduces the plastics material to enable it to be easily transported, and which also enables different types of plastics material to be blended.

The shredded material is then transferred to a large holding hopper/blender 11, conveniently by a conveyor belt or the like, in which blender relatively heavy particles of material (for example, foreign bodies such as stones) may be pneumatically separated from the remainder, and in which the material may be preheated, and thus dried, prior to further processing. In effect, the hopper/blender provides a climate controlled environment to assist further processing of the scrap plastics material.

The shredded and partly "filtered" material is then transferred to an agglomerater 12 in which the blended materials are further size reduced, and in which frictional heat is applied to the materials to further dry them. The mixed material may be retained in the agglomerater until a desired temperature/humidity is attained, at which point the material may be passed to a second agglomerater 13 in which the incoming material is mixed with residual, retained, material. During the input of the mixed plastics material from the first agglomerater 12 it is envisaged that other materials may be introduced, conveniently on a metered basis, that may be desirable to enhance the finished product, such as colouring agents or the like.

The agglomerated plastics material is then passed, via a heated auger/screw 14 to a water cooled granulator 15. The auger/screw has a depth of flight such that it does not present a restriction to any item within the mixed materials, and the heat imparted to the auger/screw, conveniently by electrical elements located adjacent thereto, ensures that materials which require extra heat to attain the desired condition are catered for. Desirably, the screw has a slight compression, which enables a plastic "chip" to be produced rather than "crumb", in the sense that particles of more uniform size and shape may be produced.

i 5 I 7 The granulator 15 produces plastics materials of the required generally granular form, and it will be appreciated that the term "granular" is intended to refer to particles which are generally free-flowing when in an unheated state, and which typically have a diameter of no more than approximately 10mm. It will however be appreciated that by virtue of the heated auger/screw which transfers material to the granulator, that the material leaving the granulator, is hot, and liable to stick together. The hot, tacky, material is then removed from the granulator using a pneumatic conveying system 16, to a small holding hopper 17. The pneumatic removal enables the surface of the granules to be cooled in air to a sufficient extent to enable an outer generally solid skin to form, which allows the resultant particles to be generally free flowing, whilst retaining heat towards the interior thereof, and therefore remaining generally deformable in the core.

The part cooled granules may be retained in the small holding hopper 17 for up to about 20 minutes, it having been found by the applicants that sufficient heat is retained by the granules during this time to enable the subsequent steps to be carried out satisfactorily.

At required intervals, the part-cooled granular material is transferred volurnetrically to the top of a vertical oven 18, through which the granules then fall, the oven 18 conveniently having a temperature of around 900T, and a height of around 1.5 metres. During their passage through the vertical oven 18, the previously cooled outer surfaces of each granule melt, to enable subsequent compression, as described below.

On exiting the oven 18, the molten skinned granules are collected in a transfer die, within which the granules adhere together prior to cooling. The newly formed material is then water cooled as it leaves the transfer die so as to rigidify the outer surface of the material.

At this stage, the material may have a generally rough surface, such that further processing may be required in order to obtain an acceptable product.

8 It will be appreciated that the "rough" product may be further processed in a variety of ways depending on the requirements of the finished product.

For example, the rigidified form may be passed through a heated former to size the product by removing any high spots, and transferring that material to any low spots, or the rigidified form may be passed through a heated die wherein an additional layer of fluid plastics material is applied to the surface to finish or further size the product.

As a further alternative, a reinforcing layer may be applied prior to or with the additional plastics layer, and these additional fluid plastics and reinforcing layer steps may of course be repeated as desired.

Additionally, the applicants have found that material formed using the above method may be subjected to a variety of machining processes whereby a particular shape may be given to a required product. For example, the material may be cut, for example by using a band-saw, or turned on a lathe.

The features disclosed in the foregomg description, or the following claims, or the accompanying drawings, expressed m their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention m diverse forms thereof i 9

Claims

A method of utilising scrap plastics material comprising the steps:a) procuring generally granular scrap plastics material; b) heating the material so as to melt at least part of the outer surface of the granules; and c) compressing the granules together whilst in their heated state.
2 A method according to Claim 1 wherein the granules are compressed in a mould or die into an article of manufacture.
3 A method according to one of Claim 1 and 2 wherein the granules have a diameter of no more than approximately 1Omm.
4 A method according to any one of the preceding claims involving the step of comminuting raw plastics material prior to heating thereof.
A method according to any one of the preceding claims involving the step of drying the comminuted material.
6 A method according to any one of the preceding claims wherein the material is heated in an oven having a temperature lying within the range 300 to 12001C.
7 A method according to Claim 6 wherein the oven is vertical, through which granules fall.
8 A method according to any one of the precedmg claims wherein the granules are heated so as to cause the granules to melt to a depth of no greater than 201/o of the radius of the granules, preferably less than 10% of the radius.
9 A method according to any one of the precedmg claims wherein the heated granules are compressed together in a mould or die.
A method according to any one of Claim 1 to 8 wherein the heated granules are processed in an injection moulding machine.
11 A machine for the utilisation of scrap plastics material comprising:a) heating means; b) delivery means for delivering generally granular scrap plastics material to the heating means, wherein the material is heated to melt at least part of the outer surface of the granular materials; and c) means to compress the heated granules to cause the granules to stick together by virtue of their melted outer surfaces.
12 A machine according to Claim 11 wherein the heating means is operative to heat the granules to a depth of no greater than 20% of the radius of the granules, preferably less than 10% of the radius.
13 A machine according to any one of Claims I I and 12 comprising granulating means to granulate scrap plastics material for delivery by the delivery means to the heating means.
14 A machine according to Claim 12 comprising feeding means to deliver scrap plastics material to the granulating means.
i i 1 11 A machine according to Claim 14 wherein the feeding means is provided by a screw or auger.
16 A machine according to any one of Claims 14 and 15 comprising shredding means to shred scrap plastics material prior to delivery thereof to the feeding means.
17 A machine according to any one of Claim 11 to 16 comprising cooling means to cool the granules prior to delivery to the heating means.
18 A machine according to Claim 17 wherein the cooling means is M the form of a hopper to which the granules are delivered from the delivery means.
19 A machine according to any of Claims 11 to 18 wherein the heating means is provided by an oven, having a temperature in the range 300 to 120TC.
A machine according to Claim 19 wherein the oven is operative within the range 800 to 10OTC.
21 A machine according to any one of Claims 19 and 20 wherein the oven is vertical, through which granules fall.
22 A machine according to any one of Claims 19 and 20 wherein the oven is a horizontal oven, through which the granules are conveyed.
23 A machine according to any of Claims 11 to 22 wherein the compression means is operative to compress the granules into a part at least finished article.

12
24 A method of utilisation of scrap plastics material, when carried substantially as hereinbefore described.
A machine for utilisation of scrap plastics material, constructed and arranged substantially as hereinbefore described.
26 Any novel feature, or novel combination of features, hereinbefore described.

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