IE44957B1 - A process for producing a packaging material - Google Patents

Description

This invention relates to a packaging material which is produced from waste material and, in particular, to a packaging material which is produced from waste partially expanded polystyrene sheet.

In the conventional manufacture of sheet polystyrene articles, a mixture of solid crystalline polystyrene, together with certain additives, is fed to an extruder. The additives include, for example, various dyes, if the desired end product is coloured, citric acid and sodium bicarbonate which aid in the foaming of the polystyrene. During its passage through the extruder, the mixture is converted into a viscous liquid and it is simultaneously impregnated with an organic liquid of low boiling point, such as pentane.

The polystyrene material emerges from the extruder through an annular head in the form of a tube. On emerging from the extruder, the material expands due to a reduction in pressure, With conventional extruders, the tube formed has a circumference of approximately 1,300 mm. The tube is then cut continuously along its length to give two flat sheets of foamed polystyrene, which are drawn onto rollers in conventional manner, until rolls of convenient size are formed. The foamed polystyrene sheet material so produced is approximately 2 mm in thickness ar.d 650 mm in width.

The sheet material so produced is used to form various moulded articles, especially, trays or other packaging elements, by a thermoforming process. During this process the sheet material is fed discontinuously frcm a given roll under a conventional heater. The heated material is then passed to one or more moulds where desired shapes are formed by a combined vacuum snd pressure technique. The trays or other packaging elements are then punched out of the moulded sheet. The thermoforming process has been estimated to increase the thickness of the sheet material by about 50¾ to 3 mm.

Xn some cases, such as the formation of dividers which are used for packaging fruit in boxes, the article stamped out occupies almost the whole usable width of the sheet. In such cases, only the extreme edges of the sheet and transverse strips of material between the dividers remain after the punching out operation and form what is known in the trade as the ladder form. - 3 In other cases, several articles may be stamped out simultaneously from a given width of sheet, for example, in the formation of small trays of the kind used for packaging fruit in supermarkets. Depending on the number and shape of articles stamped out, small waste pieces of polystyrene of various shapes are produced. In the case of trays one obtains both the ladder form and diamond shapes as waste, said diaipond shapes form where four trays meet. The volume of ladder form has been estimated to be about ten times that of the diamond shapes.

Normally the waste material is fed to a pulverizer and, subsequently, to an extruder, which is also a degasser, where the material increases in density due to the extraction of volatile material therefrom. The degassed material emerges from the extruder as a viscous liquid which is cooled to a solid strip, and which is then fed continuously into another pulverizer. The resulting product may be reused along with virgin crystalline polystyrene in the production of expanded sheet polystyrene.

The waste polystyrene material left after the punching operation still contains some of the volatile blowing agent used to produce the foamed polystyrene sheet. It has occured to us that if suitably shaped pieces of sheet polystyrene waste, such as diamond shapes, are further expanded in a conventional pre-expanding machine, of the kind used in the production of expanded polystyrene board, 49 5 7 they could serve as an acceptable substitute for loose fill expanded polystyrene packaging material which is currently marketed in various forms and which is purpose made from purchased raw material.

The current value of degassed polystyrene for re-cycling is approximately £300 per ton, after one has deducted the processing cost, whereas, loose fill polystyrene packaging material is currently being sold on the Irish market at prices in the order of £1,200 per ton.

In view of the much higher market value of waste polystyrene as loose fill, it would be desirable to convert as much waste sheet polystyrene as possible to this form. For example, in the case of ladder form waste it would be desirable to cut the ladder into pieces Of suitable area and shape which, following further expansion, would be suitable for use as loose packaging material.

It is an object of the present invention to produce a stable and economical loose fill packaging material from the waste from partially expdnded polystyrene sheet material.

Accordingly, the present invention provides a process for producing a packaging material which comprises feeding cut pieces of partially expanded sheet polystyrene waste, containing residual volatile blowing agent, to the bottcm of a steaming vessel, treating the polystyrene pieces with steam as they enter the vessel thus causing them to expand and distort, the polystyrene pieces rising in the vessel by virtue of a decrease in their density and the pressure exerted by further polystyrene pieces as they are fed to the bottom of the vessel, and stirring the polystyrene pieces continually as they rise in the vessel, the expanded', distorted pieces, on reaching the top of the vessel, flowing therefrom and being conveyed in a hot air stream to a cooling vessel for slow cooling.

The cooled, expanded, distorted pieces of polystyrene obtained by the aforementioned process may be used as a packaging material.

Preferably, the polystyrene pieces used in the process of the invention are triangular in shape. Further, preferably, the steaming vessel is a conventional pre-expanding machine of the kind used in the production of expanded polystyrene board.

' The various forms of loose fill polystyrene are designed to produce an interlocking effect to inhibit settling of, or movement of the packaged articles through the loose filling. To aid the interlocking effect of the loose fill, one normally ovlr fills the container with loose fill and thereafter subjects it to compression. In our opinion, the optimum shape for such a loose fill packaging material, produced according to the present invention, would be a triangle, which has the sharpest possible corners. Also, the greater the distortion during steam treatment, the greater the apparent volume and interlocking ability of the resulting material. - 6 449S? The invention will be understood from the following description of an embodiment thereof given by way of example only with reference to the accompanying drawing which illustrates the change in shape of a triangular-shaped piece of poly'5 styrene waste v/hich is subjected to the process of the invention.

Triangular shaped pieces of partially expanded polystyrene (1) which are obtained by cutting ladder form waste, produced as waste in the manufacture of dividers for fruit boxes, are fed to the bottom of a cylindrical steam vessel of a conventional expanding machine, by means of a screw conveyor.

The ladder form waste is cut into triangular shaped pieces by means of a suitably Shaped frame work of electrically heated wires v/hich cut through the expanded polystyrene by melting it. A suitable cutting die may also be used for the cutting operation. As the pieces are fed into the vessel they are subjected to a jet of saturated steam at 100-110°C v/hich causes the pieces of polystyrene to expand and distort. The expanded, distorted pieces of polystyrene rise in the steaming vessel due to a decrease in density and on account of the pressure exerted by further polystyrene material as it is fed to the bottom of the steaming vessel. The polystyrene pieces are continually stirred as they rise by means of a conventional stirring element which rotates at approximately 50 r.p.m. When the hot, expanded pieces of polystyrene reach the top of the vessel, they flow from it onto a 'hot air' conveyor device which conveys them to a silo for cooling.

The pieces of polystyrene must be cooled slowly to allow air to permeate into and thus stabilize the gas bubbles. When cool, the pieces of polystyrene (2) are removed from the silo and are then ready to use as a loose fill packaging material.

The present process departs from conventional practice at the point where the waste material leaves the punching machine. Instead of pulverising and densifying the I sheet polystyrene, it is cut into pieces of suitable area and shape and expanded a third time using a conventional expanding machine such as is used during the production of expanded polystyrene sheets and mouldings. Accordingly, essentially three expanding steps are involved in producing loose fill polystyrene packaging material according to the present process. The initial extrusion step in the formation of sheet polystyrene, with gas injection, causes a reduction in density from 1.2 g/ml to 0.08 g/ml.

The thermoforming step reduces the density of the polystyrene material from 0.08 g/ml to 0.05 g/ml. Finally, steam foaming in the expanding machine causes a further reduction in density of 0.05 g/ml to approximately 0.02 g/ml.

The diamond shaped pieces obtained as waste during the stamping out of polystyrene trays may also be used in the present process. Further, the ladder form waste may be cut into pieces other than triangular shaped pieces which may then be treated according to the process of the present invention to produce loose fill polystyrene packaging material. Any residual waste material resulting from the punching out operation may be recycled in the normal way.

The present process allows for a very economical production of a packaging material which may be used in the packaging of a wide variety of articles.

The polystyrene loose fill packaging material produced according to the present process has good cusnioning and interlocking properties on account of the distorted shape of the individual pieces thereof. It has ail of the advantages of loose fill polystyrene packaging material currently in use; however, it may be produced at a fraction of the cost involved in the production of these packaging materials.

The packaging material of the present process has a low .1.0 density and weight and hence its use can result in an overall reduction in shipping costs. The interlocking ability of the individual pieces of the material results in a very stable packaging material. The present packaging material is especially suited for packaging articles, which have a variety of shapes and sizes, in the same container. Finally the present packaging material may be reused indefinitely as it is extremely stable.

Claims (4)

1. CLAIMS!1. A process for producing a packaging material which comprises feeding cut pieces of partially expanded sheet polystyrene waste, containing residual volatile 5 blowing agent, to the bottom of a steaming vessel, treating the polystyrene pieces with steam as the enter the vessel thus causing them to expand and distort, the polystyrene pieces rising in the vessel by virtue of a decrease in their density.and the pressure exerted by further poly10 styrene pieces as they are fed to the bottom of the vessel, and stirring the polystyrene pieces continuously as they * i rise in the vessel, the expanded distorted pieces, on reaching the top of the vessel, flowing therefrom and being conveyed in'a hot air stream to a cooling vessel for 15 slow cooling.

2. A process as claimed in claim 1 wherein the out pieces of waste are triangular in shape, or are further cut to a triangular shape, prior to feeding to the steaming vessel. 2Q

3. A process as claimed in claim 1, substantially as described with reference to the accompanying drawing.

4. A packaging material made by the process claimed in any preceding claim.