GB2551559A

GB2551559A - Plastic recycling

Info

Publication number: GB2551559A
Application number: GB1610929.0A
Authority: GB
Inventors: Clark Wayne
Original assignee: Preston Plastics Ltd
Current assignee: Preston Plastics Ltd
Priority date: 2016-06-22
Filing date: 2016-06-22
Publication date: 2017-12-27
Also published as: GB201610929D0

Abstract

A method for reclaiming polymeric material from mixed plastics, comprising polymeric material and adhesive backed polymerics. The method comprises: feeding polymeric material reduced to 5 to 20 mm particle size pieces; melting the polymeric material after feeding into a chamber, preferably using a helical screw; mixing the melted polymeric material with adhesive backed polymerics to form a melted composition; and extruding the melted composition through a die to produce thermoplastic pellets of 3-4 mm. The melted polymeric composition comprises between 1 and 30% adhesive backed polymerics by weight. Preferably the adhesive backed polymeric is polypropylene. In a preferred embodiment, metallic contaminants are removed with a magnet prior to recycling. In further preferred embodiment, calcium carbonate is added at 5-20 wt%. Also claimed is an apparatus for recycling mixed plastics comprising; a chamber for sintering and melting mixed plastics, a shredder for reducing the size of plastics prior to melting, an extrusion die for pelletising, a fountain blender for mixing pellet batches, a filter for removing gases after outgassing melted plastics and magnets to remove metal contaminants.

Description

DESCRIPTION

PLASTIC RECYCLING

The present disclosure relates to recycling of plastic waste products. In particular, to the recycling of plastic products containing adhesive.

Recycling of plastics is an important consideration, both environmentally and as a way of generating new plastics products. Whilst some plastics materials are relatively easy to recycle, others are more difficult.

One particularly difficult material to recycle is adhesive backed or adhesive coated plastics. Typically, such plastics are not able to be recycled due to the adhesive interfering with the process and/or potential damage to the recycling machinery due to the adhesive.

Adhesive backed plastic labelling is commonly used in large spools, making recycling difficult. Also, given how adhesive backed plastic labelling is often used for displaying branding on packaging, which is subject to change at short notice, large quantities of these adhesive backed polymeric materials are often wasted, creating a need for safe and efficient recycling, which up until now has proven to be not possible due to the adhesive interfering with the recycling process. EP2817131 describes a method of recycling adhesive coated film material. In this example, the film waste is initially coarsely chopped into pieces between 50- 150 mm in a chopping device. A liquid or powdered additive that reduces the strength of the adhesive on the film waste is added to material in the chopping device or sprayed on components of the chopping device. The waste material exits the chopping device through a perforated sheet as clumps of material, which are then fed into an agglomerator, where they are agglomerated or compacted into strands of material. However, the end product produced by the recycling method is different, producing an agglomerated end product. This is less dense and inconsistently sized, with a non-uniform crumb. Such agglomerate is also unsuited for injection moulding.

Summary

According to a first aspect of the present disclosure, there is provided a method for reclaiming polymeric material from mixed plastics, comprising polymeric material and adhesive backed polymeries, said method comprising the steps of: feeding the polymeric material into an apparatus adapted to reduce the polymeric material to pieces having a maximum dimension ranging between 5 to 20 mm particle size; feeding the polymeric material into a chamber; melting the polymeric material; mixing the melted polymeric material with adhesive backed polymeries to form a melted polymeric composition; extruding the melted polymeric composition through a die to produce thermoplastic pellets having a maximum dimension ranging between 3 to 4 mm; wherein the melted polymeric composition comprises between 1 and 30% adhesive backed polymeries by weight.

The method described above produces a uniform, consistent pellet that is suitable for subsequent use in injection moulding techniques. Such pellets tend to have a melt flow index of between 4 and 6 g/10min.

By selectively ensuring that the amount of adhesive backed polymeries lies within the range of 1% to 30%, the adhesive backed polymeries can be recycled together with normal plastics waste. Preferably the melted polymeric composition comprises one of between 5 and 30%, or 10 and 30%, or 15 and 25%, adhesive backed polymeries by weight. It has surprisingly been found that this range allows recycling of adhesive backed polymeries. Excess quantities of adhesive backed polymeries does not allow consistent extrusion. Preferably the amount of adhesive backed polymeries is 20% by weight.

Preferably, the adhesive backed polymeries comprises polypropylene matrix. Such polypropylene matrix are particularly difficult to recycle in a traditional extrusion method. For example, the polypropylene matrix may comprise spools of adhesive backed polymeric film.

In another embodiment, the polymeric material comprises polypropylene.

Optionally, the step of melting of the polymeric material may include the step of relatively rotating the polymeric material and the chamber to heat the polymeric material by friction. The chamber may be rotated relative to the polymeric material, or visa versa. Relative rotation provides enough friction to at least begin to melt the polymeric material.

Magnetic filtering of the polymeric material prior using a magnetic source to remove metallic contaminants from the polymeric material may be utilized. This improves the polymeric purity of the thermoplastic pellets.

In examples, the extruding step may further comprise the step of feeding the melted polymeric material into the extruder using a helical screw. The helical screw is typically integral with the extruder.

The method may further comprising the step of: filtering the melted polymeric material prior to feeding the melted polymeric material into the extruder to remove excess gas from the melted polymeric material. Providing a filter prior to the extrusion aids degassing of the melted polymeric material. This filter step aids the extrusion and allows for extrusion of melted polymeric material having a proportion of adhesive polymeries by weight.

The method may also further comprise the step of: filtering the melted polymeric composition after extruding the melted polymeric composition to remove excess gas from the melted polymeric composition. This filtering step provides further degassing.

Additionally, the method may further comprise the step of degassing the melted polymeric composition during extrusion using a filter.

In some embodiments the step of blending the melted polymeric material further comprises the step of blending the melted polymeric material with a mineral filler, such as calcium carbonate. The melted polymeric composition may comprise between 5% to 20% calcium carbonate by weight. This blending step aids recycling of adhesive backed polymeric materials.

In embodiments, the mineral filler is calcium carbonate, mica, clay, or other suitable mineral filler. The particle size of the mineral filler may be comparable to or smaller than the size of the pieces of mixed plastics material

Furthermore, by reducing the polymeric material into pieces having dimensions between 5 and 20 mm, ensures an even coating of the pieces with the calcium carbonate.

In a further embodiment, the thermoplastic pellets may be blended with previous batches of thermoplastic pellets to provide a more uniform consistency of pellets between batches. The batches of pellets may be blended by weight. The thermoplastic pellets and the existing thermoplastic pellets may be blended in a fountain blender. The existing thermoplastic pellets used to blend, may be created using the method as described above.

According to a second aspect of the present invention, there is provided a method for reclaiming polymeric material from mixed plastics, comprising polymeric material and adhesive backed polymeries, said method comprising the steps of: feeding the mixed plastics into an apparatus adapted to reduce the mixed plastics into pieces having a maximum dimension ranging between 5 to 20 mm particle size; feeding the mixed plastics into an chamber; combining the mixed plastics with a mineral filler; melting the mixed plastics; mixing the melted mixed plastics to form a melted polymeric composition; extruding the melted polymeric composition through a die to produce thermoplastic pellets having a maximum dimension ranging between 3 to 4 mm.

In embodiments, the mineral filler comprises calcium carbonate. In other embodiments the mineral filler comprises mica, clay or other suitable mineral filler. The particle size of the mineral filler may be comparable to or smaller than the size of the pieces of mixed plastics material.

In this aspect, it can be appreciated that reducing the mixed plastics into pieces having sizes in the range of 5 to 20 mm, as well as helping to ensure an even blend of the mixed plastics composition between polymeric material and adhesive backed polymeric material, also provides a greater degree of mixing of the adhesive backed polymeric material with the calcium carbonate. This helps to reduce the adhesive properties of the adhesive backed polymeries, and allows for a higher relative percentage of adhesive backed polymerise to polymeric material to be used. In examples, the adhesive backed polymeric material comprises between 1 and 30% of the mixed plastics. In other examples, the adhesive backed polymeric material comprises up to 50% of the mixed plastics, and optionally or preferably around 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40% or 45%.

According to a third aspect of the present invention, there is provided an apparatus for recycling mixed plastics comprising polymeric material and adhesive backed polymeries, said apparatus comprising a chamber for sintering and melting pieces of mixed plastics; a shredder for reducing the size of the mixed plastics into pieces prior to loading into the chamber; and an extrusion die for pelletising the melted mixed plastics into pellets, wherein the mixed plastics comprise between 1 and 30% of adhesive backed polymeric material.

In embodiments, the apparatus may further comprise a fountain blender for mixing the pellets with previous batches of pellets.

Additionally, the apparatus may further comprise one or filters for removing gases outgassed from the melted plastics. Furthermore, one or more magnets for removing waste magnetic material from the mixed plastics may be used.

According to a fourth aspect of the present invention, there is provided a system configured to perform the method of any embodiment of the first aspect.

According to a fifth aspect of the present invention, there is provided a thermoplastic pellet made via the method of the first aspect.

The above discussion is not intended to represent every example embodiment or every implementation within the scope of the current or future Claim sets. The Figures and Detailed Description that follow also exemplify various example embodiments. Various example embodiments may be more completely understood in consideration of the following Detailed Description in connection with the accompanying Drawings.

Brief description of Drawings

Embodiments will be described, by way of example only, with reference to the drawings, in which figure 1 shows a plastic recycling system for undertaking the method of the present invention.

It should be noted that the Figures are diagrammatic and not drawn to scale. Relative dimensions and proportions of parts of these Figures have been shown exaggerated or reduced in size, for the sake of clarity and convenience in the drawings. The same reference signs are generally used to refer to corresponding or similar feature in modified and different embodiments.

Detailed description of embodiments

An example of a plastic recycling system is shown in figure 1. The plastic recycling system 100 generally comprises a series of conveyors or belts 102, 110 for feeding waste plastics material 104 into a plasticizing chamber 130. The waste plastics material typically comprises bulk waste plastics or polymeric material 120, such as polypropylene, although other plastics may be processed using the described method. Prior to feeding into the chamber 130, the plastics material 104, 120 is de-sized by being passed along a first belt 102 to a shredder 106, the material 120 is then shredded into particles 122 between 5mm and 20mm average size. In embodiments, the waste plastics material 104 may comprise a mixture of polymeric material or plastics and adhesive backed polymeric material or plastics. A number of magnets (not shown), typically two, are aligned beside the shredder to filter magnetic particles 122 from the shredded material. This ensures that the majority of the material 120 is the desired plastics material.

In addition to the shredded particles 122, a predefined percentage by weight of adhesive backed plastics 124 is also fed into the chamber 130. Typically the predefined percentage of adhesive backed plastics is between 1 and 20% of the shredded particles 122 by weight, typically 5%, 10%, 15%, or 20%. Although shown as fed into the chamber 130 separately, it can be appreciated that the plastics 124 may be mixed with the plastics material 120 of the particles 122. Such mixing may occur before or after shredding, depending upon the relative size of the adhesive backed plastics 124.

The chamber 130 is a compacting drum that rotates and heats the material within via friction. The friction is typically generated by the use of knives (not shown) that act to separate and further divide the particles 122 as the drum rotates. The heat generated acts to melt the particles 122 and the adhesive backed plastics 124. The knives further act to constantly separate and divide the melted mixture, prevent aggregation, cooling and clumping. .

Once entered into the chamber 130 the particles 122 sinter and melt to become a melted polymeric composition. Chalk, such as calcium carbonate, or an alternative mineral filler, may be added to the melted polymeric composition or may be added before the particles are melted. Adding the chalk prior to melting may aid in a reduction in the adhesive properties of the mixed plastics and reduce clumping. The total amount of added chalk may equal between 1% and 20% of the total melted composition by weight. The calcium carbonate acts as a mineral filler or additive to decrease the surface energy of the melted composition, which improves the final product. Additionally, when added to adhesive backed polymeric material prior to melting, the calcium carbonate reduces the adhesive properties of the adhesive backed polymeric material. The bulk density of the calcium carbonate may be chosen to tailor the composition for the desired end product. The calcium carbonate typically forms 5% by weight of the melted composition. Although described as calcium carbonate, any suitable mineral filler may be used. Such mineral fillers include mica and clay. Average particle sizes of mineral filler in the order of the shredded plastic material size, or lower, are typically used.

After dosing with the calcium carbonate, the melted composition is typically formed of approximately 20% by weight of adhesive at this stage, resultant from the recycled adhesive backed plastics 124 fed into the chamber 130.

The melted polymeric composition is then extruded out of the chamber 130 by an extrusion screw 140. The extrusion screw 140 is typically a helically threaded extrusion screw. In the embodiment shown, the screw comprises two sections as will be described in further detail below.

The melted polymeric composition steadily cools as it passes along the extrusion screw towards a die where pelletisation occurs. The die typically produces pellets 150 of 3 to 4 mm diameter. The die is typically a spaghetti die, although alternative dies may be utilised, depending upon the application.

In order to improve the consistency of the final pellets, a number of filters are employed that act to degas the melted polymeric composition. A first filter 160 filters the composition prior to extrusion by the extrusion screw 140. The use of such a first filter ensures a more consistent final product and removes irregularities in the melted composition that can occur with the addition of adhesive backed polymeric material. Further filters provide for further degassing and removal of irregularities. A total of four filters may be used. A number of vents or filters, typically two, allow for volatile gases to be expelled from the chamber. The volatile gases are typically out gasses from the adhesive backed plastics 124 fed into the chamber 130 during melting. The volatile gases may be captured to reduce pollution and allow for recycling of the gases as desired or available.

As noted above, the extrusion screw 140 comprises two separate sections, separated by an open section where the melted polymeric composition is forced through a second filter 162 that acts to further refine the extrudent and further degas the melted polymeric composition.

After filtering, the melted polymeric composition is further extruded by a second section of the extruder screw 140 towards the die. A third filter 164 is also used to provide further degassing and ensure a consistent final pellet. Additional filters may be employed, as desired, along the screw line, prior to the mixture being passed through the die.

Finally, the filtered melted plastics composition is passed into and through a spaghetti die. This allow pelletisation by cutting the extruded plastics spaghetti into thermoplastic pellets of the desired size.

The final pellet typically has a size range of 3-4 MM. and can be used to form a wide range of new plastics materials, such a plant pots, furniture etc. Such pellets are suitable for injection moulding techniques, which make them a versatile product. Such pellets tend to have a melt flow index of between 4 and 6 g/10min. A final step, after pelletisation using the extruder screw and the die, is blending of the thermoplastic pellets with thermoplastic pellets from earlier processes (or other processes). This again provides a homogenisation step to ensure a consistent final product. Blending may be achieved by use of a continuously rotating drum, known as a fountain blender, holding a steady volume of material, such as 10 tons of material. By feeding the thermoplastic pellets into the fountain blender, a consistent blend of pellets may be provided, removing potential minor differences or irregularities between different pellets produced by earlier processes. Finally, the blended pellets are then removed from the blender, weighed and bagged.

From reading the present disclosure, other variations and modifications will be apparent to the skilled person. Such variations and modifications may involve equivalent and other features which are already known in the art of plastics recycling and which may be used instead of, or in addition to, features already described herein.

Although the appended claims are directed to particular combinations of features, it should be understood that the scope of the disclosure of the present invention also includes any novel feature or any novel combination of features disclosed herein either explicitly or implicitly or any generalisation thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention.

Features which are described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination. The applicant hereby gives notice that new claims may be formulated to such features and/or combinations of such features during the prosecution of the present application or of any further application derived therefrom.

For the sake of completeness it is also stated that the term "comprising" does not exclude other elements or steps, the term "a" or "an" does not exclude a plurality, a single device or other unit may fulfil the functions of several means recited in the claims and reference signs in the claims shall not be construed as limiting the scope of the claims.

Claims

1. A method for reclaiming polymeric material from mixed plastics, comprising polymeric material and adhesive backed polymeries, said method comprising the steps of: feeding the polymeric material into an apparatus adapted to reduce the polymeric material to pieces having a maximum dimension ranging between 5 to 20 mm particle size; feeding the polymeric material into an chamber; melting the polymeric material; mixing the melted polymeric material with adhesive backed polymeries to form a melted polymeric composition; extruding the melted polymeric composition through a die to produce thermoplastic pellets having a maximum dimension ranging between 3 to 4 mm; wherein the melted polymeric composition comprises between 1 and 30% adhesive backed polymeries by weight.

2. The method of claim 1, wherein the adhesive backed polymeries comprises polypropylene matrix.

3. The method of claim 2, wherein the polypropylene matrix comprises spools of adhesive backed polymeric film.

4. The method of any preceding claim, wherein the polymeric material comprises polypropylene.

5. The method of any preceding claim wherein the step of melting of the polymeric material comprises the step of relatively rotating the polymeric material and the chamber to heat the polymeric material by friction.

6. The method of claim 5, wherein the chamber is rotated relative to the polymeric material.

7. The method of any preceding claim, further comprising the step of: magnetic filtering the polymeric material prior using a magnetic source to remove metallic contaminants from the polymeric material.

8. The method of any preceding claim, wherein the extruding step further comprises the step of: feeding the melted polymeric material into the extruder using a helical screw.

9. The method of claim 5, wherein the helical screw is integral with the extruder.

10. The method of any preceding claim, further comprising the step of: filtering the melted polymeric material prior to feeding the melted polymeric material into the extruder to remove excess gas from the melted polymeric material.

11. The method of any preceding claim, further comprising the step of: filtering the melted polymeric composition after extruding the melted polymeric composition to remove excess gas from the melted polymeric composition.

12. The method of any preceding claim, further comprising the step of degassing the melted polymeric composition during extrusion using a filter.

13. The method of any preceding claim, wherein the step of mixing the melted polymeric material further comprises the step of adding calcium carbonate to the melted polymeric material.

14. The method of claim 13, wherein the melted polymeric composition comprises between 5% to 20% calcium carbonate by weight.

15. The method of any preceding claim, wherein the thermoplastic pellets are blended with existing thermoplastic pellets to provide a more uniform consistency of pellets between batches.

16. The method of claim 15, wherein batches of pellets are blended by weight.

17. The method of claim 15 or claim 16, wherein the thermoplastic pellets and the existing thermoplastic pellets are blended in a fountain blender.

18. The method of any one of claims 15 to 17, wherein the existing thermoplastic pellets were created using the method of any preceding claim.

19. The method of any preceding claim, wherein the melted polymeric composition comprises one of between 5 and 30%, or 10 and 30%, or 15 and 25%, or 20% adhesive backed polymeries by weight.

20. A method for reclaiming polymeric material from mixed plastics, comprising polymeric material and adhesive backed polymeries, said method comprising the steps of: feeding the mixed plastics into an apparatus adapted to reduce the mixed plastics into pieces having a maximum dimension ranging between 5 to 20 mm particle size; feeding the mixed plastics into an chamber; combining the mixed plastics with calcium carbonate; melting the mixed plastics; mixing the melted mixed plastics to form a melted polymeric composition; extruding the melted polymeric composition through a die to produce thermoplastic pellets having a maximum dimension ranging between 3 to 4 mm.

21. A method according to claim 20, wherein the melted polymeric composition comprises between 1 and 30% adhesive backed polymeries by weight.

22. An apparatus for recycling mixed plastics comprising polymeric material and adhesive backed polymeries, said apparatus comprising a chamber for sintering and melting pieces of mixed plastics; a shredder for reducing the size of the mixed plastics into pieces prior to loading into the chamber; and an extrusion die for pelletising the melted mixed plastics into pellets, wherein the mixed plastics comprise between 1 and 30% of adhesive backed polymeric material.

23. An apparatus according to claim 22, further comprising a fountain blender for mixing the pellets with previous batches of pellets.

24. An apparatus according to claim 22 or claim 23, further comprising one or filters for removing gases outgassed from the melted mixed plastics.

25. An apparatus according to any one of claims 22 to 24, one or more magnets for removing waste magnetic material from the mixed plastics.

26. A system of undertaking the method of any one of claims 1 to 21.

27. A thermoplastic pellet made via the method of any one of claims 1 to 21.