NL2032033B1

NL2032033B1 - Method for decolouring and colouring thermoplastic

Info

Publication number: NL2032033B1
Application number: NL2032033A
Authority: NL
Inventors: Vos Hendré
Original assignee: Orange Dynamics B V
Priority date: 2022-05-31
Filing date: 2022-05-31
Publication date: 2023-12-12

Abstract

The present application concerns a method for decolouring coloured thermoplastic material. The method comprises comminuting the thermoplastic material into coloured ﬂakes, moulding the coloured ﬂakes into granules, each of the granules having substantially the same shape, decolouring the coloured granules using a decolouring substance.

Description

METHOD FOR DECOLOURING AND COLOURING THERMOPLASTIC

The present application concerns method for decolouring coloured thermoplastic material, as well as a method for manufacturing a colour master batch from thermoplastic granules or flakes.

The application further concerns a method for recycling thermoplastic waste products.

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 tlakes.

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 tlakes 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, 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 tlakes 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, 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 one 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.

In a preferred embodiment, in which decolouring thermoplastic material comprises providing a plarality 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.

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 and decolouring the thermoplastic waste according to any of the appropriate aforementioned methods and/or manufacturing a colour master batch from the thermoplastic waste according to any of the appropriate aforementioned methods, and manufacturing one or more thermoplastic products using the decoloured granules and/or colour master batch.

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 schematically shows a method for decolouring the thermoplastic material of waste products.

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). 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.

- 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 5 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 E. However, the application is not limited to this shape in particular; itis also possible for the granules to be egg-shaped, oval, or other shapes, as long as most granules have substantially the same shape.

Granules E 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 E, when they are not of substantially of the same size and/or weight, are sorted into a plurality of batches Fy, Fo, …F, based on their size and/or weight by a sorting system 5. Specifically, each batch of the plurality of batches Fy, F>, ...F. 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 E 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 Fy may include mostly granules smaller than the mesh size of the first sieve. A second batch F: 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 E, now divided over batches Fi, Fa, ...F,, are decoloured using a decolouring substance. Specifically, each batch of the plurality of batches Fy, Fa, ….F, may be decoloured separately from the other batches using decolouring means 6. Said means 6 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 Gi, Ga, ...Gn are decoloured, may be substantially the same for all batches Gi, Gz, ...Ga.

The presently disclosed decolouring method decolours coloured granules E 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 6 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 natriom hydroxide. The skilled person will be aware of further decolouring substances and/or swelling agents that may be employed to effectively decolour batches Fy, I, … Fu - The decoloured granules, divided over batches Gi, Go, ...G, may be coloured a specific colour using a corresponding colouring substance I. Specifically, each batch of the plurality of batches Gi, Ga, …G, may be coloured separately from the other batches using colouring means 7.

Said means 7 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 Gi.

Ga, Ga are coloured may be substantially the same. After having been coloured, the coloured granules from each of the batches Gi, Go, … Gn: may be combined into a colour master batch H.

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 ata 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 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 anthraguinone 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

Gi, Go, ... Gu

Finally, the skilled person will appreciate that colouring the decoloured granules of batches

Gi. Go, ...Gn is not essential to achieving the abovementioned advantages. That is, a method not comprising said step — for example the method shown in figure 2 — 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 1 and 2, 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.

Claims

CONCLUSIONS

Claims 1. A method for decolorizing colored thermoplastic material, comprising: crushing the thermoplastic material into colored flakes; forming the colored flakes into granules, each of the granules having substantially the same shape; decolorizing the colored granules using a decolorizing substance.

2. Method according to claim 1, wherein the colored thermoplastic material is a thermoplastic polyolefin, such as polyethylene, PE, or polypropylene, PP.

3. Method according to claim 1 or 2, wherein the colored thermoplastic material comprises waste products, such as disposable products and/or hard plastic containers.

4. Method according to claim 1, 2 or 3, wherein the colored thermoplastic material is crushed into colored flakes by grinding, shredding and/or cutting the colored thermoplastic material into colored flakes.

A method according to any one of claims 1-4, wherein the granules are substantially spherical, egg-shaped, or oval.

A method according to any one of the preceding claims, further comprising washing and drying the colored flakes before forming them into substantially spherical granules.

A method according to any one of claims 1-5, wherein the granules have substantially the same size and/or the same weight.

A method according to any one of claims 1-5, wherein the granules are not substantially the same size and/or the same weight, further comprising: providing a plurality of batches of granules, wherein the granules are distributed among the batches based on their size and/or weight; the separate decolorization of each batch from the plurality of batches using a decolorization process adapted to the size and/or weight of the granules in this batch, such that the extent to which the granules in each batch are decolorized is essentially the same.

The method of claim 8, wherein providing the plurality of batches of granules includes: forming the flakes into granules; and sorting the grains into the plurality of lots based on their size and/or weight.

The method of claim 8, wherein providing the plurality of batches of granules includes: sorting the flakes into a plurality of batches based on their size and/or weight; separately forming each batch of flakes into a batch of granules of substantially the same size and/or the same weight.

A method according to any one of claims 8-10, wherein each decolorization process is adapted by varying at least one of: the temperature at which the process is carried out; the concentration of decolorizing substance used; and/or the amount of time for which the process is applied.

A method according to claim 11, wherein the decolorizing substance comprises a solvent and a decolorizing agent, and wherein the concentration of the decolorizing substance corresponds to the concentration of the decolorizing agent.

A method for manufacturing a color master batch of thermoplastic granules or flakes, the method comprising: decolorizing colored thermoplastic material according to any of claims 1-12; coloring the decolorized grains using a coloring substance.

A method according to claim 13, comprising decolorizing thermoplastic material according to any one of claims 8-12, wherein coloring the decolorized granules comprises: separately coloring each batch from the plurality of batches using a coloring process adapted to the size and/or weight of the granules in this batch, such that the extent to which the granules are colored in each batch is substantially the same.

A method according to claim 14, wherein each coloring process is adjusted by varying at least one of: the temperature at which the process is performed; the concentration of coloring substance used; and/or the amount of time for which the process is applied.

A method according to claim 15, wherein the coloring substance comprises a solvent and a dye, and wherein the concentration of the coloring substance corresponds to the concentration of the dye.

17. Method for recycling thermoplastic waste products, comprising: using the thermoplastic waste products as thermoplastic material and decolorizing the thermoplastic waste according to any one of claims 1-12 and/or manufacturing a color master batch from the thermoplastic waste according to any of claims 13-16; manufacturing one or more thermoplastic products using the decolorized granules and/or color master batch.