The present application concerns methods for decolouring coloured thermoplastic material, as well as methods for colouring thermoplastic granules or flakes. The application furthermore concerns methods for manufacturing a master batch of thermoplastic granules or flakes, as well as methods for manufacturing a colour master batch of coloured thermoplastic granules or flakes.

Thermoplastic plastic products, for example rigid plastic containers, are commonly made of polyolefin such as polyethylene (PE) and polypropylene (PP). Methods for manufacturing such products use batches of granules or pebbles of the material in question also referred to as master batches. Polyolefin itself is generally white and, when used to form a layer having a thickness common to the exemplary rigid plastic containers, somewhat transparent. To give these products a particular colour, the master batch is mixed with what is referred to as a colour master batch (CMB): A batch of which the material is well known and of which the colour is well defined. One mix may for example be 98% master batch and 2% colour master batch. The mix may be used to blow mould rigid plastic containers such as bottles. Bottles may be filled with any one of a number of consumable products such as medicine, foodstuffs, or beauty products. Bottles may be thereafter provided with a label and a cap. Once the product is consumed and/or when the bottle is effectively empty, the bottle is discarded as waste.

Production of rigid plastic containers has hit an all-time high in the last couple of years, bringing with it an equally rapidly increasing stream of waste. While there are advantages to manufacturing rigid plastic containers using a master batch of brand-new plastic (also referred to as virgin material) the industry is more and more called upon to come up with ways to also recycle used rigid plastic containers.

In the current recycling process, rigid plastic containers are shredded into numerous flakes. To be able to reuse these flakes in a master batch once again, the flakes are washed and dried. However, while washing cleans the flakes, it does not adequately decolour them. Instead, the resulting flakes are only partially and/or non-uniformly decoloured. Consequently, the resulting mix of flakes has varying colours with varying intensities and is not considered to be of the same quality as a master batch of virgin material.

Batches of flakes from recycled rigid plastic containers are often used to manufacture products for which either the colour of the master batch, and/or the colour of the final product is less important. Using recycled material for products of which the requirements are less demanding, rather than for the original products, is also known as down-cycling. Well known products which use down- cycled batches of flakes are flowerpots and outdoor benches.

Waste that is not down-cycled can have an even less eco-friendly fate: Rigid plastic containers frequently end up in waste incineration or landfills. It is a goal of the invention to provide an improved method and/or apparatus for recycling plastic products. It is a further goal of the invention to provide a method and/or apparatus that can recycle plastic waste products to such a degree that the resulting recycled material can be used in a master batch when manufacturing the original product. It is a further goal to provide a method and/or apparatus capable of efficiently colouring and/or decolouring plastics.

According to one aspect of the invention, at least some of these goals are at least partially achieved in a method for decolouring coloured thermoplastic material, comprising comminuting the thermoplastic material into coloured flakes, subjecting the coloured flakes to an extrusion process for producing coloured extruded material, and decolouring the coloured extruded material using a decolouring substance.

By subjecting the coloured flakes to an extrusion process before the decolouring step, or, alternatively phrased, by decolouring the thermoplastic material in an extruded form, the shape and/or size of the coloured thermoplastic material upon decolouring can be controlled to much greater accuracy. Hence, the shape and/or size of the coloured extruded material can be adapted to the decolouring step very well, thus allowing for almost completely and effectively uniformly decoloured extruded material.

Additionally, the applicant finds that during methods according to the invention the thermoplastic material is subjected to much less thermal stress, meaning that the quality of the thermoplastic material remains roughly the same.

Alternatively, or in addition to, the decolouring substance, pressure may be applied to the coloured extruded material.

By subjecting the coloured extruded material to a pressure, it was found that the colorant of the coloured extruded material degraded. Preferably, a pressure of at least 10 bar is applied, more preferably at least 20 bar is applied.

Preferably the coloured thermoplastic material upon which this method is performed is a thermoplastic polyolefin, such as polyethylene, PE, or polypropylene, PP. Preferably the coloured thermoplastic material upon which the method is performed comprises waste products such as disposables and/or rigid plastic containers.

In a preferred embodiment, the coloured thermoplastic material is comminuted into coloured flakes by grinding, shredding and/or cutting the coloured thermoplastic material into said coloured flakes. The resulting coloured flakes are more suitable to be extruded into an extruded material when using readily available extruders.

In a preferred embodiment, the extrusion process is a foil extrusion process and the coloured extruded material is a coloured foil preferably having a thickness of 3000 micron or less, preferably 2000 micron or less, more preferably 1000 micron or less, and even more preferably having a thickness of 500 micron or less. Alternatively, the extrusion process is a strand extrusion process for producing a coloured strand and wherein the coloured extruded material is a coloured filament, the method further comprising rolling the coloured strand for producing the coloured filament, preferably having a thickness of 3000 micron or less, preferably 2000 micron or less, more preferably 1000 micron or less, and even more preferably having a thickness of 500 micron or less.

Both foils and filaments are shapes in which the thermoplastic material can extruded, and which are of a uniform and constant thickness. This ensures that the thermoplastic material, when exposed to the decolouring substance, is decoloured almost completely and effectively uniformly.

In a preferred embodiment of the method, an additive is added to the coloured flakes during the extrusion process.

In a preferred embodiment, the extruded material is decoloured by submerging the coloured extruded material in the decolouring substance, and preferably by guiding the extruded material through the decolouring substance, preferably in a continuous process.

Decolouring the coloured thermoplastic material via a continuous process is made possible by first forming it into the coloured extruded material. The skilled person will be well aware of the trade-offs between processing in batches, or in a continuous process.

In a preferred embodiment, the method further comprising storing the decoloured extruded material, preferably by winding the decoloured extruded material onto a spool.

In a preferred embodiment, the method further comprising washing and drying the coloured flakes before subjecting them to the extrusion process for producing coloured extruded material. This removes material from the coloured flakes that is undesired, and that may deteriorate the shape and/or size of the material once extruded.

According to a further aspect of the invention, at least some of these goals are at least partially achieved in a method of manufacturing a master batch of thermoplastic granules or flakes, the method comprising decolouring coloured thermoplastic material according to any of the previously mentioned methods, and comminuting the decoloured extruded material into thermoplastic granules or flakes.

Additionally, the applicant finds that during methods according to the invention the thermoplastic material is subjected to much less thermal stress, meaning that the quality of the thermoplastic material remains roughly the same.

Master batches used as resource in manufacturing generally take the shape of thermoplastic granules or flakes. Being able to provide almost completely and effectively uniformly decoloured granules or flakes from coloured thermoplastic material allows for recycling unused or unwanted products without substantial loss of colouring capabilities. This effectively avoids having to downcycle the material and reduces limitations in re-use of the material to products of a lower quality. In preferred embodiments comminuting the decoloured extruded material comprises grinding, shredding and/or cutting the decoloured extruded material into decoloured flakes.

Alternatively, comminuting the decoloured extruded material comprises extruding the decoloured extruded material into a decoloured strand and cutting the decoloured strand into decoloured thermoplastic granules.

In a preferred embodiment, the method of manufacturing, after decolouring the coloured thermoplastic material using a method including storing the decoloured extruded material, preferably by winding the decoloured extruded material onto a spool, further comprises

- retrieving the stored decoloured extruded material, preferably by unwinding the decoloured extruded material from the spool, before comminuting the decoloured extruded material into thermoplastic granules or flakes. Storing the thermoplastic material when in an extruded form may be more space efficient and may make handling the thermoplastic material more efficient.

According to a further aspect of the invention, at least some of these goals are at least partially achieved in a method of manufacturing a colour master batch of thermoplastic granules or flakes, the method comprising decolouring coloured thermoplastic material according to any of the previously mentioned methods, colouring the decoloured extruded material using a colouring substance, and comminuting the coloured extruded material into thermoplastic granules or flakes.

For example, the colouring substance may be comprising a quinone, wherein the quinone may be one or more selected from the group of 1,2-benzoquinone, 1,4-benzoquinone, 1,4- napthoquinone, 9,10-anthraquinone, l,2-dihydroxy-9,10-anthraquinone. It was found that comprising a colouring substance comprising a quinone provides an environmentally friendly, efficient, and effective colouring of the polymeric film.

In a preferred embodiment, the decoloured extruded material is coloured by submerging the decoloured extruded material in the colouring substance, and preferably by guiding the decoloured extruded material through the colouring substance, preferably in a continuous process.

In a preferred embodiment, comminuting the decoloured extruded material comprises grinding, shredding and/or cutting the decoloured extruded material into decoloured flakes. Alternatively, comminuting the decoloured extruded material comprises extruding the decoloured extruded material into a decoloured strand and cutting the decoloured strand into decoloured thermoplastic granules.

In a preferred embodiment, the method of manufacturing, after decolouring the coloured thermoplastic material using a method including storing the decoloured extruded material, preferably by winding the decoloured extruded material onto a spool, further comprises retrieving the stored decoloured extruded material, preferably by unwinding the decoloured extruded material from the spool, before colouring the decoloured extruded material using a colouring substance. Storing the thermoplastic material when in an extruded form may be more space efficient and may make handling the thermoplastic material more efficient.

According to a further aspect of the invention, at least some of these goals are at least partially achieved in a method for recycling thermoplastic waste products comprising using the thermoplastic waste products as thermoplastic material for manufacturing a master batch according to any of the appropriate aforementioned methods, and/or a colour master batch according to any of the appropriate aforementioned methods, and manufacturing one or more thermoplastic products using the master batch and/or colour master batch.

According to a further aspect of the invention, at least some of these goals are at least partially achieved in a method for colouring thermoplastic granule or flakes, comprising subjecting the thermoplastic granule or flakes to an extrusion process for producing extruded material, and colouring the extruded material using a colouring substance.

By subjecting the thermoplastic granule or flakes to an extrusion process before the colouring step, or, alternatively phrased, by colouring the thermoplastic material in an extruded form, the shape and/or size of the thermoplastic material upon colouring can be controlled to much greater accuracy. Hence, the shape and/or size of the extruded material can be adapted to the colouring step very well, thus allowing for almost completely and effectively uniformly coloured extruded material.

Preferably the thermoplastic granule or flakes on which this method is performed are thermoplastic polyolefin, such as polyethylene, PE, or polypropylene, PP.

In a preferred embodiment, the extrusion process is a foil extrusion process and wherein the extruded material is a foil, preferably having a thickness of 3000 micron or less, preferably 2000 micron or less, more preferably 1000 micron or less, and even more preferably having a thickness of 500 micron or less.

Alternatively, the extrusion process is a strand extrusion process for producing a strand and wherein the extruded material is a filament, the method further comprising rolling the strand for producing the filament, preferably having a thickness of 3000 micron or less, preferably 2000 micron or less, more preferably 1000 micron or less, and even more preferably having a thickness of 500 micron or less.

Both foils and filaments are shapes in which material can extruded that are of a uniform and constant thickness. This ensures that the thermoplastic material, when exposed to the colouring substance, is coloured almost completely and effectively uniformly.

In a preferred embodiment, an additive is added to the thermoplastic granules or flakes during the extrusion process.

In a preferred embodiment the extruded material is coloured by submerging the extruded material in the colouring substance, and preferably by guiding the extruded material through the colouring substance, preferably in a continuous process. Colouring the thermoplastic material via a continuous process is made possible by first forming it into the extruded material. The skilled person will be well aware of the trade-offs between processing in batches, or in a continuous process.

According to a further aspect of the invention, at least some of these goals are at least partially achieved in a method of manufacturing a colour master batch of coloured thermoplastic granules or flakes, the method comprising colouring thermoplastic granules or flakes according to any of the appropriate aforementioned methods, and comminuting the coloured extruded material into coloured thermoplastic granules or flakes.

In a preferred embodiment, comminuting the coloured extruded material comprises grinding, shredding and/or cutting the coloured thermoplastic material into decoloured flakes. Alternatively, comminuting the coloured extruded material comprises extruding the coloured extruded material into a strand and cutting the strand into thermoplastic granules.

According to a further aspect of the invention, at least some of these goals are at least partially achieved in a method for decolouring coloured thermoplastic material, comprising comminuting the thermoplastic material into coloured flakes, moulding the coloured flakes into granules, each of the granules having substantially the same shape, and decolouring the coloured granules using a decolouring substance.

By subjecting the coloured flakes to a moulding process before the decolouring step, or, alternatively phrased, by decolouring the thermoplastic material in a moulded form, the shape and/or size of the coloured thermoplastic material upon decolouring can be controlled to much greater accuracy. Hence, the shape and/or size of the coloured granules can be adapted to the decolouring step very well, thus allowing for almost completely and effectively uniformly decoloured granules.

Preferably the coloured thermoplastic material upon which this method is performed is a thermoplastic polyolefin, such as polyethylene, PE, or polypropylene, PP.

Preferably, the coloured thermoplastic material upon which the method is performed comprises waste products such as disposables and/or rigid plastic containers.

In a preferred embodiment, the coloured thermoplastic material is comminuted into coloured flakes by grinding, shredding and/or cutting the coloured thermoplastic material into said coloured flakes. The resulting coloured flakes are more suitable to be moulded into granules when using readily available moulders.

In a preferred embodiment, the granules are substantially spherical, egg-shaped, or oval.

In a preferred embodiment, the method further comprising washing and drying the coloured flakes before moulding them into substantially spherical granules. This removes material from the coloured flakes that is undesired, and that may deteriorate the shape and/or size of the material once moulded. In a preferred embodiment, the granules are substantially of the same size and/or weight. Cross-sections of the granules are then fairly uniform and of somewhat constant thickness. This ensures that the thermoplastic material, when exposed to the decolouring substance, is decoloured almost completely and effectively uniformly.

Alternatively, or in addition to, the decolouring substance, pressure may be applied to the coloured extruded material.

By subjecting the coloured extruded material to a pressure, it was found that the colorant of the coloured extruded material degraded. Preferably, a pressure of at least 10 bar is applied, more preferably at least 20 bar is applied.

Alternatively, the granules are not substantially of the same size and/or weight. In this embodiment, the method further comprising providing a plurality of batches of granules, wherein the granules are divided over said batched based on their size and/or weight, decolouring each batch of the plurality of batches separately using a decolouring process adapted to the size and/or weight of the granules in said batch such that the degree to which the granules in each batch are decoloured is substantially the same. Batches of granules can then be individually decoloured, each using a decolouring step fine-tuned for the granules included in said batch. Consequently, the granules of each batch can be decoloured almost completely and effectively uniformly.

In a preferred embodiment, providing the plurality of batches of granules comprises moulding the flakes into granules and sorting the granules in the plurality of batches based on their size and/or weight. Alternatively, providing the plurality of batches of granules comprises sorting the flakes in a plurality of batches based on their size and/or weight; and, moulding each batch of flakes into a batch of granules having substantially the same size and/or weight. That is, the sorting process can be performed when the thermoplastic material has the form of flakes, or when it has the form of granules.

In a preferred embodiment, each decolouring process is adapted by varying at least one of the temperature at which said process is performed, the concentration of the decolouring substance that is used, and/or the amount of time for which the process is applied.

Adapting these parameters allows for fine-tuning the decolouring step to the shape and/or size of the granule, and/or the type of thermoplastic material upon which the method is performed. The skilled person will appreciate that this is particularly advantageous to take into account when working with the aforementioned batches.

In a preferred embodiment, the decolouring substance comprises a solvent and a decolouring agent and wherein the concentration of the decolouring substance corresponds to the concentration of the decolouring agent.

According to a further aspect of the invention, at least some of these goals are at least partially achieved in a method of manufacturing a colour master batch of thermoplastic granules or flakes, the method comprising decolouring coloured thermoplastic material according to any of the aforementioned appropriate methods, and colouring the decoloured granules using a colouring substance.

For example, the colouring substance may be comprising a quinone, wherein the quinone may be one or more selected from the group of 1,2-benzoquinone, 1,4-benzoquinone, 1,4- napthoquinone, 9,10-anthraquinone, l,2-dihydroxy-9,10-anthraquinone. It was found that comprising a colouring substance comprising a quinone provides an environmentally friendly, efficient, and effective colouring of the polymeric film.

In a preferred embodiment, in which decolouring thermoplastic material comprises providing a plurality of batches of granules and decolouring each batch separately colouring the decoloured granules comprises colouring each batch of the plurality of batches separately using a colouring process adapted to the size and/or weight of the granules in said batch such that the degree to which the granules in each batch are coloured is substantially the same.

In a preferred embodiment, each colouring process is adapted by varying at least one of the temperature at which said process is performed, and the concentration of the colouring substance that is used, and/or the amount of time for which the process is applied.

In a preferred embodiment, the colouring substance comprises a solvent and a colouring agent and wherein the concentration of the colouring substance corresponds to the concentration of the colouring agent.

Further details and advantages of the present disclosure will become apparent from the following description of a few exemplifying embodiments. Reference is made to the accompanying figures, wherein: figure 1 schematically shows a method for manufacturing a colour master batch by recycling thermoplastic waste products; figures 2-4 schematically show methods for recycling thermoplastic waste products; figures 5-7 schematically show methods for manufacturing a colour master batch; and, figure 8 schematically shows an apparatus for colouring or decolouring a foil or filament, figures 9-10 show in isometric perspective (parts of) means for colouring and/or decolouring a thermoplastic extruded material; figure 11 shows a cross-section of means for colouring and/or decolouring a thermoplastic extruded material; figure 12 shows a method, and an isometric view of an apparatus for performing said method for manufacturing and storing an uncoloured extruded material by recycling thermoplastic waste products; figure 13 shows a method, and an isometric view of an apparatus for performing said method for manufacturing a colour master batch from an uncoloured extruded material; figure 14 schematically shows a further embodiment of a method for manufacturing a colour master batch by recycling thermoplastic waste products according to the invention; figures 15 schematically shows a further embodiment of a method for decolouring the thermoplastic material of waste products according to the invention.

Referring to figure 1, a schematic representation of a method for manufacturing a colour master batch by recycling thermoplastic waste products is shown. Specifically, each of the steps and/or means comprised in the method is enumerated using numbers and each of the (intermediate) products is enumerated by letters.

Thermoplastic waste products may refer to used consumables (such as cutlery or cups) and substantially empty rigid plastic containers (such as packaging used for foodstuffs, medicine and/or beauty products). Additionally and/or alternatively, thermoplastic waste products may also refer to synthetic textile and/or products made of synthetic textile.

The application is not limited to processing thermoplastic waste products. Any thermoplastic material may be processed; for example thermoplastic polyolefin, such as polyethylene (PE), or polypropylene (PP).

Specifically, in the method shown in figure 1 :

- Thermoplastic waste products A are comminuted to produce a mix of flakes B, for example by a grinder 1. Waste products A may also be shred or cut into the aforementioned flakes. In the present application comminuting refers to any method that turns items made of thermoplastic material into numerous pieces such as granule or flakes, each being substantially smaller than the initial item. In anticipation of the later discussed extrusion process, the grinding process preferably provides in flakes that are fairly uniform in weight and/or size. This allows for extruders to process these flakes faster.

- Mix of flakes B is washed in a hot washer 2, resulting in a mix of clean, but wet flakes C. Washing may be performed using water and various cleaning solutions known by the skilled person. Said mix C is then dried in a dryer 3, resulting in a mix of clean and dry flakes D. The steps of washing and drying the flakes are not always necessary, but advantageous if mix of flakes B is diluted with waste accidently included in the original batch of thermoplastic waste products. For example by (parts of) labels originally attached to the thermoplastic waste products, and/or, in case the waste products are rigid plastic containers, remains of product once stored in said container. In further anticipation of the later discussed extrusion process, the hot washing process preferably increases the temperature of the thermoplastic and/or mix of flakes B closer to and/or up to the temperature at which said extrusion process is performed. This allows for the extruders to process these flakes faster.

In some embodiments, washing and drying is performed centrifugally, which the applicant finds is an energy and water efficient manner to wash and dry thermoplastic flakes.

- Mix of dried flakes D, preferably together with an additive E, is subjected to an extruding process by extruder 4 for producing an extruded material F, preferably a foil or filament having a thickness of 3000 micron or less, preferably 2000 micron or less, more preferably 1000 micron or less, and even more preferably having a thickness of 500 micron or less. Mix of dried flakes D may also be supplemented with virgin thermoplastic material.

The applicant finds that to manufacture and handle during further processing a foil is more convenient. At the same time, the applicant finds that a filament, generally smaller in width than the foil, are easier to decolour.

The thermoplastic material, now having the shape of extruded material F, comprises the colouring substances which were present in each of the waste products A. One class of colouring substances that may be included in thermoplastic material are quinones. In practise, these batches of waste products comprise products of wildly varying colours and consequently extruded material F is of a poorly defined colour and/or may comprise any mixture of any number of colouring substances.

One approach conceivable to avoid downcycling is to sort waste products by colour. Would a batch of waste products of a particular colour be grinded and decoloured using readily known method, the resulting mix of partially decoloured plastic flakes may be incompletely and non- uniformly decoloured, but since the remaining colouring substances provide the same or at least a very similar colour, such a mix of partially coloured plastic flakes could be used when producing a new thermoplastic product of said colour.

However, the skilled person will appreciate that to sort thermoplastic waste products and/or flakes by colour is an already challenging task and even if it could be done efficiently, would likely results in so many individual streams of waste (one for each colour) that whether enough waste of each colour would be present to viably continue recycling it, would become an entirely new problem in itself.

- Extruded material F may be decoloured using a decolouring substance, for producing a decoloured extruded material G. For example by being submerged in said decolouring substance. In some embodiments, a segment of extruded material F is wound on a spool and then submerged. In other embodiments, extruded material F is being guided through said decolouring substance in a continuous process. Such a process may be implemented by means 5 for decolouring an extruded material, examples of which are discussed in relation to figures 8-11. The presently disclosed decolouring method decolours extruded material F almost completely and effectively uniformly. What colours the flakes included in mixes of flakes B, C, or D, and products included in the batch of waste products A originally had therefore has little to no effect on the product resulting from this decolouring method. Consequently, the waste products do not have to be sorted by colour to arrive at a recycled master batch that can be used to manufacture a thermoplastic product of said colour.

The thermoplastic of which the waste products are made is preferably a polyolefin, as for example polyethylene (PE) or polypropylene (PP). The colouring substance(s) that are to be removed from the waste products may be dispersive colouring substances such as an anthraquinone and/or colouring substances of 800 nmol or smaller, such as 780 nmol, and preferably 500 nmol or smaller.

For example, the colouring substance may be comprising a quinone, wherein the quinone may be one or more selected from the group of 1,2-benzoquinone, 1,4-benzoquinone, 1,4- napthoquinone, 9, 10- anthraquinone, l,2-dihydroxy-9,10-anthraquinone.

Means 5 may hold the aforementioned decolouring substance, as well as, to improve the decolouring process, a swelling agent. The decolouring substance may be a decolouring substance and/or natrium hydroxide. The skilled person will be aware of further decolouring substances and/or swelling agents that may be employed to effectively decolour extruded material F.

Optionally, after exiting means 5 for decolouring an extruded material, decoloured extruded material G may be dried by a dryer, like a hot air drier (not shown in figure 1).

- Decoloured extruded material G may be stored in storage 6, for example by being wound onto a spool by winding unit 61. Storage 6 may hold a plurality of spools of decoloured extruded material G. The decoloured extruded material G are alternatively referred to as uncoloured extruded material H. Uncoloured extruded material H may be retrieved from storage 6, for example by being unwound from their spool by unwinding unit 62.

In the embodiment shown in figure 1, storage unit 6 is arranged in between means 5 for decolouring extruded material and means 7 for colouring extruded material. However, storage unit 6 may be arranged in the process of figure 1 in between any two steps for which extruded material is the intermediate product. Storage unit 6 may for example be implemented in between extrusion process 4 and means 5 for decolouring and may be configured to store coloured extruded material F. Storage unit 6 may specifically be implemented in between any two steps of the process for which the intermediate product is a strand, foil, or filament.

- Uncoloured extruded material H, at this point, is a thermoplastic which comprises no colouring substances, or which at least comprises so little of previously contained colouring substances that the presence of such trace substances may be neglected. Extruded material H may be coloured using a colouring substance I, for example by being submerged in said colouring substance I, and preferably by being guided through said colouring substance in a continuous process. Such a process may for example be implemented by means 7 for colouring an extruded material, in the same, or at least a very similar way that means 5 for decolouring an extruded material may be implemented.

In some embodiments, uncoloured extruded material H that is stored in storage unit 6 may be an uncoloured foil. In those embodiments, the uncoloured foil may be retrieved from storage unit 6, for example by being unwound from their spool by unwinding unit 62, and then cut into filaments before being coloured by means 7 for colouring an extruded material as discussed earlier. This increases the surface of uncoloured extracted material H, thus improving the rate at which it can absorb colouring substances.

That is, means 7 may be the same, or at least very similar, to means 5, except for the fact that means 7 for colouring an extruded material may not use a general decolouring substance but instead may use colouring substance I. That is, while extruded material F of any colour, or at least most colours, may be decoloured with the same decolouring substance, the skilled person will appreciate that to manufacture a colour master batch it is essential to choose a specific, and well-defined colouring substance I.

Means 7 may hold the aforementioned colouring substance, as well as, to improve the decolouring process, a swelling agent. The colouring substance(s) may be dispersive colouring substances, such as an anthraquinone and/or colouring substances of 800 nmol or smaller, such as 780 nmol, and preferably 500 nmol or smaller. The skilled person will be aware of further colouring substances and/or swelling agents that may be employed to effectively colour extruded material F.

Optionally, after exiting means 7 for colouring an extruded material, coloured extruded material J may be dried by a dryer, like a hot air drier (not shown in figure 1).

- Coloured extruded material J may be extruded by extruder 8 in a strand K. Directly after coming from extruder 8, Strand K may be too hot to be processed further. Therefore extruder 8 may be succeeded by cooler 9 which may be implemented by a bath of water at room temperature, or at least at a temperature lower than strand K directly after coming from extruder 8. Strand K may alternatively be cooled by just letting it rest at room temperature for a sufficient amount of time, in which case water cooler 9 is not necessary. Either approach will result in a solid, coloured strand L.

In some embodiments, cooling may also be achieved in by and/or during the abovementioned submerging of extruded material in a decolouring or colouring substance. In such embodiments, means 5 or means 7 and cooler 9 may be embodiment by one and the same device.

The applicant does find that the thermoplastic material shouldn’t be cooled to much as leftover heat in the material when leaving the extruder is advantageous when decolouring or colouring the thermoplastic material in further steps. The skilled person will appreciate that the step of extruding coloured extruded material J into a strand K can additionally be used to mix the coloured extruded material J with further functional additives such as UV-blockers or flame retarders.

- Coloured strand L may be comminuted into colour master batch M. Strand L may for example be cut into granules using cutter 10. This approach to processing extruded material J to manufacture a colour master batch is advantageous as it results in the earlier mentioned granules which can be cut to have a commonly used and consistent size.

Steps 8 and 9 as shown in figure 1 are optional. Accordingly, coloured extruded material J may be comminuted into colour master batch M, without being extruded and/or cooled first. If extruded material J is shaped as a foil, or shaped as one or more filaments, that may be cut, and/or shredded into colour master batch M without changing its shape first.

While not shown in figure 1, the method for manufacturing a colour master batch by recycling thermoplastic waste products may be succeeded by any number of processing steps using the colour master batch made from recycled thermoplastic waste products.

Referring to figures 2-4, schematic representations of methods for decolouring thermoplastic material are shown.

Specifically, in the method shown in figure 2:

- Thermoplastic waste products A are comminuted to produce a mix of flakes B, for example by a grinder 1.

- Mix of flakes B, preferably together with an additive E, is subjected to an extruding process by extruder 4 for producing an extruded material F, preferably a foil or filament having a thickness of 3000 micron or less, preferably 2000 micron or less, more preferably 1000 micron or less, and even more preferably having a thickness of 500 micron or less.

The skilled person will appreciate that if extruder 4 is a foil extruder that, optionally, extruded material F may be cut into a plurality of ribbons before being subjected to the further steps of the decolouring method. Additionally, extruded material F may be provided with a plurality of micro-holes to speed up the decolouring process.

- Extruded material F may be decoloured using a decolouring substance, for example by being submerged in said decolouring substance, and preferably by being guided through said decolouring substance in a continuous process. Such a process may for example be implemented by means 5 for decolouring an extruded material.

The skilled person will appreciate that the way in which extruded material F is decoloured in the method shown in figure 1 (e.g. first cleaning and drying flakes, before extruding extruded material F and/or directly decolouring extruded material F) and the way in which extruded material is coloured in the methods shown in figures 2, 3, and 4 (e.g. first cooling and/or flattening the extruded material) can be used interchangeably. In the embodiment shown in figure 3, extruder 4 is implemented by a foil extruder 40 which is be configured to extrude mix B, and optionally additive E, into a foil Fl preferably having a thickness of 3000 micron or less, preferably 2000 micron or less, more preferably 1000 micron or less, and even more preferably having a thickness of 500 micron or less. Optionally, foil extruder 40 is succeeded by roll 41. This may, for example, be the case when foil extruder is not capable to, or at least not configured to produce a foil having any of the preferred aforementioned thicknesses. Roll 41 may be configured to flatten foil Fl to produce a thinner foil F2. Alternatively, roll 41 may be included if extruded foil Fl has a thickness that is not uniform, or at least not uniform enough. The skilled person will appreciate that no foil has an exactly uniform thickness but will acknowledge that variations in thickness which are sufficiently small may be neglected.

In the embodiment shown in figure 4, extruder 4 is implemented by a strand extruder 42 which is configured to extrude mix B, and optionally additive E, into a strand F3. Directly after coming from strand extruder 42, strand F3 may be too hot to be processed further. Therefore extruder 8 may be succeeded by a cooler 43, which may be implemented in the same way, or in an at least very similar way, as cooler 9. Cooler 43 may be succeeded by roll 41 configured to flatten strand F4 to produce a filament F5 preferably having a thickness of 3000 micron or less, preferably 2000 micron or less, more preferably 1000 micron or less, and even more preferably having a thickness of 500 micron or less.

The skilled person will appreciate that depending on the exact thermoplastic material used, the temperature of said material directly after coming from strand extruder 42, and the type of roll 41 that is used, the heat remaining from the extrusion process may means that strand F3 can actually be flattened by roll 41 more effectively. In this case it may be advantageous to omit cooler 43 and flatten strand F3 almost directly after exiting strand extruder 42.

While not shown in figures 2-4, these methods for decolouring thermoplastic material may be succeeded by any number of processing steps using the decoloured extruded material.

The decoloured extruded material G may for example be used to manufacture a thermoplastic master batch. In this case, any of the methods shown in the figures 2-4 may be succeeded by a step of comminuting the decoloured extruded material G into granules or flakes.

The decoloured extruded material G may for example be used to manufacture a colour master batch. In this case, any of the methods shown in the figures 2-4 may be succeeded by a step of colouring the decoloured extruded material G and thereafter comminuting it into granules or flakes.

Referring to figure 5, a schematic representation of a method for colouring thermoplastic granules or flakes is shown.

Specifically, in the method shown in figure 5 :

- A master batch Bl comprising thermoplastic granules or flakes, preferably together with an additive E, is subjected to an extruding process by extruder 4 for producing an extruded material H, preferably a foil or filament having a thickness of 3000 micron or less, preferably 2000 micron or less, more preferably 1000 micron or less, and even more preferably having a thickness of 500 micron or less. The thermoplastic granules or flakes from master batch Bl comprise no colouring substances, or at least comprise so little colouring substances that the presence of such trace substances may be neglected.

- Extruded material H may be coloured using a colouring substance I, for example by being submerged in said colouring substance I, and preferably by being guided through said colouring substance in a continuous process. Such a process may for example be implemented by means 7 for colouring an extruded material as discussed earlier.

The skilled person will appreciate that if extruder 4 is a foil extruder that, optionally, extruded material H may be cut into a plurality of ribbons before being subjected to the further steps of the colouring method. Additionally, extruded material H may be provided with a plurality of micro-holes to speed up the colouring process.

- Optionally, the coloured extruded material J may be comminuted into colour master batch M. Extruded material J may for example be cut into flakes using cutter 10. Alternatively extruded material J may be ground and/or shredded. This approach to comminuting extruded material J is advantageous as it does not require an additional extrusion step, therefore having less of an impact on the overall integrity of the thermoplastic.

The skilled person will appreciate that the way in which coloured extruded material J is comminuted in the method shown in figure 1 (e.g. first processing extruded material J into strand L and cutting said strand into granules) and the way in which coloured extruded material J is comminuted in the methods shown in figures 5, 6, and 7 (e.g.. directly grinding, cutting and/or shredding the coloured extruded material into flakes) can be used interchangeably.

Referring to figures 6-7, schematic representations of methods for manufacturing a colour master batch are shown.

In the embodiment shown in figure 6, extruder 4 is implemented by a foil extruder 40 which is be configured to extrude master batch Bl, and optionally additive E, into a foil Hl preferably having a thickness of 3000 micron or less, preferably 2000 micron or less, more preferably 1000 micron or less, and even more preferably having a thickness of 500 micron or less. Optionally, foil extruder 40 is succeeded by a roll 41. This may, for example, be the case when foil extruder is not capable to, or at least not configured to produce a foil having any of the preferred aforementioned thicknesses. Roll 41 may be configured to flatten foil Hl to produce a thinner foil H2. Alternatively, roll 41 may be included if extruded foil Hl has a thickness that is not uniform, or at least not uniform enough, as discussed earlier.

In the embodiment shown in figure 7, extruder 4 is implemented by a strand extruder 42 which is configured to extrude master batch Bl, and optionally additive E, into a strand H3. Directly after coming from strand extruder 42, strand H3 may be too hot to be processed further. Therefore extruder 8 may be succeeded by a cooler 43, which may be implemented in the same way, or in an at least very similar way, as cooler 9. Cooler 43 may be succeeded by roll 41 configured to flatten strand H4 to produce a filament H5 preferably having a thickness of 3000 micron or less, preferably 2000 micron or less, more preferably 1000 micron or less, and even more preferably having a thickness of 500 micron or less.

The skilled person will appreciate that depending on the exact thermoplastic material used, the temperature of said material directly after coming from strand extruder 42, and the type of roll 41 that is used, the heat remaining from the extrusion process may means that strand H3 can actually be flattened by roll 41 more effectively. In this case it may be advantageous to omit cooler 43 and flatten strand H3 almost directly after exiting strand extruder 42.

Referring to figure 8, a conceptual drawing of means 5/7 for colouring and/or decolouring a thermoplastic extruded material is shown. Said means may comprise a basin 101 filled with decolouring substance and a plurality of rolls and/or pullies 103, arranged and configured to have the extruded material tensioned between them, and to guide the extruded material through the basin of decolouring substance. Extruded materials that may be coloured and/or decoloured are extruded materials F and H, any of the foils Fl, F2, Hl, H2, and any of the filaments F5 or H5.

Extruded material may arrive (Pl) at the shown means for (de)colouring from a preceding processing step such as an extruder, a cooler, or a roll. Alternatively, the extruded material may be retrieved from storage 6, for example by being unwound from a spool by unwinding unit 62. With at least one pully from the plurality of pullies 103 being submerged, the extruded material is submerged (P2) in the decolouring substance while being guided through the plurality of pullies. To be (de)coloured, extruded material is submerged at least one and preferably twice or more. Once (de)coloured, extruded material may leave (P3) the shown means and continue to any one of a number of processing steps such as an extruder or cutter. Alternatively, the now (de)coloured extruded material may be stored in storage 6, for example by being wound onto a spool by winding unit 61.

Referring to figures 9 and 10, isometric views of (parts of) embodiments of means 5/7 for colouring and/or decolouring a thermoplastic extruded material is shown. Similar to the embodiment shown in figure 8, these embodiments comprise basin 101 filled with (de)colouring substance 102, and rolls 103. The embodiments are further shown to comprise lead/lag pullies 106, motor 105 arranged to drive at least one of lead/lag rolls 106, back plate 104 to which each of the pullies from the plurality of pullies 103 may be rotatably attached, and motor 107 arranged to drive at least one of the pullies from the plurality of pullies 103. In the embodiments shown, the plurality of pullies 103 includes an adjustable pully 103’ which may be adjusted to tension extruded material F/H when said material is being fed through basin 101. A cross-section of the embodiment shown in figures 9- 10 is shown in figure 11, in which additionally extruded material F/H is included. From figure 11 the skilled person will be able to derive how extruded material F/H may be fed through (de)colouring substance 102.

In exemplary embodiments, extruded material may be fed through means 5/7 at a speed of at least 0.07 meter per second and at most 0.04 meter per second. The extruded material may pass through means 5/7 in at least 10 seconds, and at most 55 seconds.

In a preferred embodiment, means 5/7 is provided with a vibration unit (not shown) configured to produce vibrations, for example ultrasonic vibrations. Said vibration unit may be arranged such that the produced vibrations propagate to basin 101 and/or to the decolouring substance and/or decolouring substance in basin 101. These vibrations cause continuous movement, specifically turbulence, in the (de)colouring substance, which causes more of the (de)colouring substance to come into contact with the extruded material that is being fed through basin 101.

In a preferred embodiment, the basin of decolouring substance is continuously emptied to remove at least partially saturated decolouring substance therefrom, and continuously filled back up with unsaturated decolouring substance (or, a decolouring substance less saturated than what is removed). In said embodiment, the rate with which saturated decolouring substance is removed and the rate with which unsaturated or less saturated decolouring substance is added are preferably equal.

In some embodiments, means 5/7 for colouring and/or decolouring a thermoplastic extruded material is provided with a plurality of basins. In such embodiments, the extruded material may be fed through each of the plurality of basins in turn, becoming more (de)coloured in the process.

Embodiments of the method for manufacturing a colour master batch by recycling thermoplastic waste products are disclosed in figure 1 and the corresponding parts of the description. Each of these embodiments should be understood as disclosing a first sub-method (method for manufacturing and storing an uncoloured extruded material by recycling thermoplastic waste products), and a second sub-method (method for manufacturing a colour master batch from an uncoloured extruded material), in isolation (i.e. as stand-alone methods) as well.

Referring to figure 12, a method, and an apparatus for performing said method for manufacturing and storing an uncoloured extruded material by recycling thermoplastic waste products is shown. Specifically, a method is shown in which:

- Thermoplastic waste products A are comminuted to produce mix of flakes B by grinder 1,

- Mix of flakes B is washed in a hot washer 2, resulting in a mix of clean, but wet flakes C,

- Said mix C is then dried by dryer 3’, resulting in a mix of clean and dry flakes D,

- Mix of dried flakes D, together with an additive E, is subjected to an extruding process by extruder 4 for producing an extruded material F, - Extruded material F is decoloured by means 5 for decolouring an extruded material (and using a decolouring substance) and dried by dryer 3”, for producing a decoloured extruded material G,

- Decoloured extruded material G is stored by being wound onto a spool by winding unit 61.

Referring to figure 13, a method, and an apparatus for performing said method for manufacturing a colour master batch from an uncoloured extruded material is shown. Specifically, a method is shown in which:

- Uncoloured extruded material H is retrieved from storage by being unwound from their spool by unwinding unit 62.

- The apparatus shown performs the optional step of laminating uncoloured extruded material H with additional layers using laminater 108.

- The apparatus shown further performs the optional step of cutting extruded material H, which was stored as a foil, into a plurality of filaments before being coloured by means 7, using cutter 109.

- Uncoloured extruded material H is coloured by means 7 for colouring an extruded material (and using a colouring substance I) and dried by dryer 3” ’, for producing coloured extruded material J,

- Coloured extruded material J is comminuted into colour master batch M by grinder 10, and, when exiting grind 10, may be received by a container 110 or any other suitable storage medium.

In this method, as for all other methods for manufacturing a colour master batch according to the invention, it is possible to provide multiple means for colouring an extruded material - said means having different colouring substances. Preferably, means are provided for the primary colours; red, yellow, and blue. Other combinations are also possible, depending on the exact colour kitchen that is desired. Said multiple means may be arranged such that uncoloured extruded material may be coloured by one, or by multiple means - e.g. the means may operate both in series or in parallel.

In a preferred embodiment, uncoloured extruded material H forms the polymeric backbone layer in a method for colouring a polymeric film. In this embodiment the aforementioned additional layers are polymeric layers.

According to a further aspect of the invention, a method for colouring a polymeric film is provided, comprising the steps of providing a polymeric film comprising a polymeric backbone layer and one or more polymeric layers arranged on the polymeric backbone layer, each of the one or more polymeric layers having a respective glass transition temperature, wherein the one or more polymeric layers that are arranged on a same side of the polymeric backbone layer are arranged in an order of decreasing glass transition temperature starting from said same side, the glass transition temperature of each of said one or more polymeric layers being lower than that of the polymeric backbone layer, and colouring the one or more polymeric layers in an order of their glass transition temperature starting with the polymeric layer(s) having the highest glass transition temperature.

According to a further aspect of the invention, also provided is a coloured polymeric film, comprising a polymeric backbone layer and one or more polymeric layers arranged on the polymeric backbone layer, each of the one or more polymeric layers having a respective glass transition temperature, wherein the one or more polymeric layers that are arranged on a same side of the polymeric backbone layer are arranged in an order of decreasing glass transition temperature starting from said same side, the glass transition temperature of each of said one or more polymeric layers being lower than that of the polymeric backbone layer, and a colourant, wherein the colourant is at least embedded in the one or more polymeric layers.

For the present disclosure, any step that includes combining two or more products (e.g. when mixing mix of flakes D with additive E before extruder 4 as shown in figure 4; e.g. when adding a colouring substance I to means 7 for colouring thermoplastic extruded material), may be at least partially implemented by providing a dosing feeder, configured to provide an appropriate amount of at least one of the aforementioned two or more products that have to be combined.

Using, for example, the method shown in figure 1, or the method shown in the combination of figures 12 and 13, old plastic bottles (and any other disposed rigid plastic packaging) may be recycled into a colour master batch or thermoplastic master batch respectively. These batches recycled batches may each be used to blow mould new bottles which satisfy the same quality requirements as the old plastic bottles did, thus allowing for complete bottle to bottle recycling.

Referring to figure 14, a schematic representation of a method for manufacturing a colour master batch by recycling thermoplastic waste products is shown. Specifically, each of the steps and/or means comprised in the method is enumerated using numbers and each of the (intermediate) products is enumerated by letters.

Thermoplastic waste products may refer to used consumables (such as cutlery or cups) and substantially empty rigid plastic containers (such as packaging used for foodstuffs, medicine and/or beauty products). The application is not limited to processing thermoplastic waste products. Any thermoplastic material may be processed; for example thermoplastic polyolefin, such as polyethylene, PE, or polypropylene, PP.

Specifically, in the method shown in figure 14:

- Thermoplastic waste products A are comminuted to produce a mix of flakes B, for example by a grinder 1. Waste products A may also be shred or cut into the aforementioned flakes. In the present application comminuting refers to any method that turns items made of thermoplastic material into numerous pieces such as granule or flakes, each being substantially smaller than the initial item.

- Mix of flakes B is washed in a hot washer 2, resulting in a mix of clean, but wet flakes C. Washing may be performed using water and various cleaning solutions known by the skilled person. Said mix C is then dried in a dryer 3, resulting in a mix of clean and dry flakes D. The steps of washing and drying the flakes are not always necessary, but advantageous if mix of flakes B is diluted with waste accidently included in the original batch of thermoplastic waste products. For example by (parts of) labels originally attached to the thermoplastic waste products, and/or, in case the waste products are rigid plastic containers, remains of product once stored in said container.

- The flakes from mix D, or at least a substantial amount thereof, are moulded into coloured, substantially spherical granules N. However, the application is not limited to this shape in particular; it is also possible for the granules to be egg-shaped, oval, or other shapes, as long as most granules have substantially the same shape.

Granules N may have a cross-section of approximately 3000 micrometre or smaller, preferably 2000 micrometre or smaller, more preferably 1000 micrometre or smaller, and even more preferably 500 micrometre or smaller.

Moulding of flakes from mix D may for example be implemented in the following two-step process. First, these flakes may be pushed through a pellet die (e.g. a circular or cylindrical grate with openings of a particular size) by one or more rollers arranged inside of said pellet die, and cut to pieces once pushed through said pallet die, to form somewhat elongated pellets. Secondly, these pellets may be polished in one or more rotating drums until they are substantially spherical granules. The skilled person will appreciate that other implementations are also possible.

Controlling the shape and/or size of the thermoplastic material by moulding it, is particularly advantageous as it can be performed at room temperature, and thus high temperatures, that can be degrade the thermoplastic material, are not necessary.

- Substantially spherical granules N, when they are not of substantially of the same size and/or weight, are sorted into a plurality of batches Oi, O2, ...On based on their size and/or weight by a sorting system 5. Specifically, each batch of the plurality of batches Oi, O2, ...O _n may comprise granules according to a corresponding range of sizes and/or weights and preferably these ranges do not overlap.

Sorting granules can be implemented using known sorting systems. The skilled person will appreciate that the following example should not be construed as limiting to the application.

Substantially spherical granules N can for example be sorted by size by using a plurality of sieves, each consecutive sieve having a larger mesh size than the sieve preceding it. A first batch Oi may include mostly granules smaller than the mesh size of the first sieve. A second batch O2 may include mostly granules larger than the mesh size of the first sieve, and smaller than the mesh size of the second sieve, etc. Sieves may have mesh sizes of around 50 micrometre or larger, and around 250 micrometre or larger.

Alternatively, the sorting step may be the performed on the flakes rather than the pellets. In this case, each batch of flakes may be separately transformed into a batch of granules, respectively.

The skilled person will appreciate that no sorting process is perfect and that granules of which the size and/or weight is close to, but not in a range of sizes and/or weights of a particular batch may still end up in said batch, and as long as the sizes and/or weights of a substantial percentage of granules in a batch does fall within the corresponding range, said range can be still said to describe the granules in said batch.

The skilled person will appreciate that it is also possible to provide a plurality of batches over which granules are divided based on their size and/or weight in different ways. Embodiments are conceivable in which the flakes from mix of flakes D are sorted into a plurality of batches of flakes based on their size and/or weight, and in which the flakes from each batch of flakes, or at least a substantial amount thereof, are moulded into a batch of granules having substantially the same size and/or weight separately from the other batches.

- Coloured granules N, now divided over batches Oi, O2, ...On, are decoloured using a decolouring substance. Specifically, each batch of the plurality of batches Oi, O2, ...O _n may be decoloured separately from the other batches using decolouring means 12. Said means 12 may subject each batch to a decolouring process adapted to the size and/or weight of the granules in said batch. Thereby the degree to which the granules in each batch from a plurality of batches of decoloured granules Pi, P2, .. .P _n are decoloured, may be substantially the same for all batches Pi, P2, ...Pn.

The presently disclosed decolouring method decolours coloured granules N almost completely and effectively uniformly. What colours the flakes included in mixes of flakes B, C, or D, and products included in the batch of waste products A originally had therefore has little to no effect on the product resulting from this decolouring method. Consequently, the waste products do not have to be sorted by colour to arrive at a recycled master batch that can be used to manufacture a thermoplastic product of said colour.

The thermoplastic of which the waste products are made is preferably a polyolefin, as for example polyethylene (PE) or polypropylene (PP). The colouring substance(s) that are to be removed from the waste products may be dispersive colouring substances such as an anthraquinone and/or colouring substances of 800 nmol or smaller, such as 780 nmol, and preferably 500 nmol or smaller.

Means 12 may hold the aforementioned decolouring substance, as well as, to improve the decolouring process, a swelling agent. The decolouring substance may be a decolouring substance and/or natrium hydroxide. The skilled person will be aware of further decolouring substances and/or swelling agents that may be employed to effectively decolour batches Oi, O2, ■ ■ ■ O _n . - The decoloured granules, divided over batches Pi, P2, ...P _n may be coloured a specific colour using a corresponding colouring substance I. Specifically, each batch of the plurality of batches Pi, P2, ...P _n may be coloured separately from the other batches using colouring means 13. Said means 13 may subject each batch to a colouring process adapted to the size and/or weight of the decoloured granules in said batch. Thereby, the degree to which each of the granules of batches Pi, P2, ...P _n are coloured may be substantially the same. After having been coloured, the coloured granules from each of the batches Pi, P2, .. .P _n may be combined into a colour master batch Q.

The skilled person will appreciate that the (de)colouring process may be adapted to the size and/or weight of the granules by varying the temperature at which said process is performed, the amount of time for which the process is applied, or the concentration of the (de)colouring substances used.

Batches comprising relatively large granules may be subjected to the (de)colouring process at a higher temperature and/or for a longer period of time. Equivocally, batches comprising relatively small granules may be subjected to the (de)colouring process at a lower temperature and/or for a shorter period of time.

Subjecting the plastic to as few high temperature processes as possible is generally considered advantageous as such high temperature processes may reduce the lifetime of the thermoplastic. Providing a plurality of batches over which the granules are divided based on their size and/or weight as discussed in the above, allows for at least part of the whole batch of thermoplastic waste A to be subjected to a lower temperature (de)colouring process, or to be subjected to a high temperature process for a shorter amount of time.

The mentioned decolouring substance and colouring substance(s) I generally comprise a solvent, and a decolouring or colouring agent, respectively. Whenever the application mentions that a (de)colouring substance has a particular concentration, this may be understood as the (de)colouring agent being present with said concentration in the solvent. Batches comprising relatively large granules may be subjected to a (de)colouring substance having a higher concentration and batches comprising relatively small granules may be subjected to a (de)colouring substance having a lower concentration. Compared to subjecting granules to any (de)colouring substance having a ‘regular’ concentration, it may be considered advantageous to subject larger granules to a (de)colouring substance having a higher concentration because said larger granules then to not have to be subjected to the high temperature process for longer, and it may be considered advantageous to subject smaller granules to a (de)colouring substance having a lower concentration because the process then consumes less (de)colouring substance, and (de)colouring agents in particular which makes the cheaper, more efficient and/or more eco-friendly.

Means 13 may hold the aforementioned colouring substance, as well as, to improve the decolouring process, a swelling agent. The colouring substance(s) may be dispersive colouring substances, such as an anthraquinone and/or colouring substances of 800 nmol or smaller, such as 780 nmol, and preferably 500 nmol or smaller. The skilled person will be aware of further colouring substances and/or swelling agents that may be employed to effectively colour decoloured granules P1, P ₂ , ... Pn.

Finally, the skilled person will appreciate that colouring the decoloured granules of batches Pi, P ₂ , ...P _n is not essential to achieving the abovementioned advantages. That is, a method not comprising said step - for example the method shown in figure 15 - would indeed not be a method for manufacturing a colour master batch but rather a method for decolouring thermoplastic waste products. The granules which by such a method may be equally (with respect to each other) and uniformly (individually) decoloured are suitable to be included in a thermoplastic master batch and/or to be used for blow moulding a product having a quality that is the same as, or at least similar to that of the initially used thermoplastic (waste) products.

Using the methods shown in figures 14 and 15, old plastic bottles (and any other disposed rigid plastic packaging) may be recycled into a colour master batch or thermoplastic master batch respectively. These batches recycled batches may each be used to blow mould new bottles which satisfy the same quality requirements as the old plastic bottles did, thus allowing for complete bottle to bottle recycling.

It is to be understood that this disclosure is not limited to particular aspects or examples described, and, as such, may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting and that the scope of the present disclosure it determined by the appended claims.