Thermoplastics, such as for instance polyethylene terephthalate, are used for all kinds of applications, for instance as packaging for diverse types of goods such as food. After the packaged goods have been removed from the packaging, the thermoplastic usually ends up in a separate or non- separate waste flow. It is desirable for reasons of

sustainability to recycle these thermoplastics.

Various techniques are known for this purpose, although recycling polyethylene terephthalate in particular forms a great challenge with the techniques known at the moment. The current problems are clarified in, among others, the Netherlands Institute for Sustainable Packaging report of 4 October 2016, "PET trays: working towards structural

solutions " .

A first known technology is known from patent publication WO 2008/042385 A2. Polyethylene terephthalate is processed here together with a number of other substances. The resulting material reduces the proportion of material actually recycled and thereby has an adverse effect on the recycling.

A second known technology for processing

polyethylene terephthalate comprises of processing amorphous polyethylene terephthalate to a monolithic material by means of injection moulding in a mould. This technology too has a number of drawbacks. Injection moulding requires that the material remains in the mould for a longer period during both heating and cooling. Because a mould for injection moulding and the other equipment required for injection moulding are costly to purchase, the method becomes expensive because only one monolithic element can be manufactured at a time. The element created moreover differs greatly in appearance from for instance marble.

The technology in question has moreover been found particularly unsuitable for multilayer polyethylene

terephthalate, such as polyethylene terephthalate combined with ethylene vinyl alcohol (PET-EVOH) , polyethylene or a lacquer layer.

It is now an object of the invention to reduce or even obviate the above stated problems.

This object is achieved using a method for processing a thermoplastic to a monolithic element such as a tile, comprising the steps of:

- providing a container with a bottom and a peripheral wall standing upright from the bottom;

- arranging a thermoplastic in pieces, such as in flakes, in the container;

- heating the bottom and/or peripheral wall of the container during a first melting step such that at least the parts of the thermoplastic arranged in the container which lie along the bottom and/or peripheral wall melt; and

- melting the content of the container during a second melting step after the first melting step by directing at least heat radiation at the content of the container.

As a consequence of the heating the pieces will melt and fuse to each other, thereby forming a monolithic element.

In the method according to the invention the walls and bottom of the container are heated in the first melting step so that the thermoplastic close to these walls and bottom will melt. Air between the pieces of thermoplastic has the opportunity to escape during this first melting step. At the end of this step the thermoplastic close to the peripheral wall will in many cases have become somewhat discoloured and have sunk to a lower level compared to the thermoplastic at a distance from the peripheral wall.

During the second melting step heat radiation is directed at the content of the container, preferably from the open upper side of the container. Melting of the thermoplastic according to the procedure during the first melting step is preferably also continued during this second melting step in addition to the melting by heat radiation.

The first melting step preferably lasts longer than the second melting step. The first melting step preferably lasts about five times as long as the second melting step. The duration of the first melting step is hereby defined by the moment that the thermoplastic close to the peripheral wall has sunk to a lower level and, if applicable, has become

discoloured. In many cases the duration of this first melting step is in the order of 25 minutes, which means that in this case the second melting step will last about 5 minutes.

It is preferable to have the heating take place at a temperature of about 40 to 80 and preferably about 60 degrees Celsius above the melting point of the chosen thermoplastic.

The pieces are for instance flakes or granulate or other types of ground or pulverized material. They are

preferably distributed uniformly over the container.

It is possible with the method according to the invention to obtain a flat monolithic homogeneous element without air bubbles and internal stresses which does not therefore bend, and with a shiny surface.

To the extent this is not apparent from the foregoing, it must be stated that the method is preferably performed at atmospheric pressure. This makes the process less expensive to perform than for instance when carried out under vacuum, and makes automation simpler. In a first preferred embodiment of the method according to the invention the thermoplastic consists at least partially, and preferably substantially or wholly, of

polyethylene terephthalate (PET) , such as amorphous PET (a- PET), (semi-) crystalline PET (c-PET) , polyethylene

terephthalate glycol (PETG) or multilayer polyethylene

terephthalate, such as polyethylene terephthalate combined with ethylene vinyl alcohol (PET-EVOH) , polyethylene or a lacquer layer, or of a mixture of one or more of these

substances.

It has been found that the method is highly suitable for processing these substances, or a mixture thereof, and that it is no longer necessary here to add additives such as adhesive agents. When a multilayer PET is used, it has then been found that it is advantageous to use a substantially semi-crystalline multilayer PET.

In view of the melting point of polyethylene

terephthalate of 260 degrees Celsius, it is preferable to heat the kiln used to a temperature of between 300 and 340 degrees Celsius, preferably about 320 degrees Celsius.

In a second preferred embodiment of the method according to the invention the method further comprises the steps of:

- providing a cover;

- placing the cover on the container prior to the first melting step;

- removing the cover placed on the container after the first melting step and preferably before the second melting step.

Providing a cover which covers the top side of the container during the first melting step, and which is removed from the top side of the container during the second melting step, makes it possible to perform the two steps in the same device, such as for instance a kiln such as a kiln with a ceramic plate. In the first step the cover on the container placed in the kiln here excludes heat radiation which reaches the thermoplastic substantially only during the second melting step, and in this way acts as a kind of heat shield.

The cover is preferably re-placed after the second melting step so that the formed monolithic element can cool in controlled manner without deforming. The cover eliminates the influence of draught, while the hot air can however gradually escape via the ventilation openings which have preferably been arranged for this purpose in the cover.

In a third preferred embodiment of the method according to the invention the method comprises the step of cooling the thermoplastic after the first and second melting step.

After cooling it is easy to grasp the formed

monolithic element with the hands for further processing.

In a fourth preferred embodiment of the method according to the invention the step of cooling the

thermoplastic comprises the step of cooling the content of the container at room temperature in the container with the cover on the container.

A gradual cooling takes place by cooling the formed monolithic element in the container, this reducing the chance of crack formation and/or build-up of stress in the monolithic element .

In a fifth preferred embodiment of the method according to the invention the thermoplastic lies solely under its own weight in the container.

Because the thermoplastic lies solely under its own weight in the container during the method (the thermoplastic is therefore not pressed) , the possibility of crack formation during cooling of the formed monolithic element is reduced or even avoided. The thermoplastic arranged at a relative

distance from the bottom of the container will of course exert pressure on the thermoplastic arranged closer to the bottom. Because pressing is not used, the orientation of the container is horizontal during the melting steps.

Because the pieces are not pressed here, the colours of the material will disperse, whereby the monolithic element obtained is highly similar in appearance to marble, in

contrast to monolithic elements produced by injection

moulding.

In a sixth preferred embodiment of the method according to the invention the method further comprises the steps of:

- removing the formed monolithic element from the container after the second melting step; and

- finishing the removed monolithic element, such as by sanding, sawing into pieces, priming, laser cutting, water jet cutting and/or laser engraving.

It is possible with the finishing to make the formed monolithic element ready for further use. Sanding, sawing, priming, laser cutting, water jet cutting and laser engraving are per se known techniques which can advantageously be used. Sanding preferably entails a step wherein the upper side

(which has lain at a distance from the bottom in the

container) is made flat, running substantially parallel to the side which has lain parallel to and against the bottom of the container .

In a seventh preferred embodiment of the method according to the invention the method further comprises the step of preheating the container and/or the thermoplastic prior to the step of arranging the thermoplastic in the container . By preheating the container and/or the thermoplastic the container and/or thermoplastic respectively are already heated to some extent, whereby the duration of the melting steps can be shortened. The container, which is usually made substantially of steel, can for instance be heated by means of induction, where the thermoplastic can for instance be heated in a storage tank. When the container is preheated to just above the melting temperature of the thermoplastic and the thermoplastic to just below this melting temperature, the duration of the melting steps can then be shortened to a total of 10 minutes in the case of polyethylene terephthalate .

In an eighth preferred embodiment of the method according to the invention the thermoplastic layer comprises a residual flow layer which consists at least substantially of thermoplastic.

Thermoplastics recycling often creates (for instance due to poor separation or contamination) a very cheap residual flow with impurities, such as a mixture of thermoplastics or a mixture consisting substantially of thermoplastics but mixed with materials other than thermoplastics. There are at the moment insufficient applications for this residual flow. It is possible with the invention to construct a part of the formed element from residual flow. The resulting element will be considered monolithic because it will then still consist substantially of one thermoplastic.

This preferably takes place by introducing the residual flow, preferably in the form of flakes, as further layer on top of the already melted (first) thermoplastic layer. The thermoplastic layer has a higher purity and forms the visual side of the monolithic element, while the residual flow layer forms the side of the monolithic element which is hidden from view. The introduction of the residual flow layer preferably takes place here between the first and the second melting step. The residual flow layer melts here on the thermoplastic layer, whereby one monolithic element is created .

In a ninth preferred embodiment of the method according to the invention the method further comprises the step of painting the outer surface of the thermoplastic layer with impurities.

Painting the outer surface of the thermoplastic layer (optionally providing it with a texture) following production of the element (such as a tile) makes it possible to conceal that the element is at least partially constructed from residual flow. Painting moreover makes it possible to have the thermoplastic layer consist wholly of residual flow.

The invention also relates to a container for use in the method according to any of the foregoing claims,

comprising :

- a bottom;

- a peripheral wall standing upright from the bottom; and

- a cover preferably releasable from the container.

Such a container can be used in the method to arrange the thermoplastic therein. The cover ensures here that in the first melting step the heat radiation is substantially excluded and that melting substantially takes place via conduction along the bottom and peripheral wall, while after removal of the cover in the second melting step the

thermoplastic also melts under the influence of heat

radiation. This can be a loose cover, but for instance also a cover which is mounted on the container for pivoting between an open and closed position along for instance a hinge.

In an embodiment the container is constructed from a tray with a depth similar to the height of the monolithic element to be formed, with a peripheral wall which is arranged on the tray and extends in line with the walls and which serves as guide for the flakes, on which peripheral wall the cover is arranged.

In a first preferred embodiment of the container according to the invention the container and preferably the cover of the container are provided with one or more

ventilation openings.

Providing ventilation openings in the container makes it possible to allow escape of air and heat which accumulate in the container during the melting steps. The ventilation openings are preferably small here such that in the first step any heat radiation possibly present in the device used and directed at the thermoplastic present in the container is substantially excluded.

At the moment when the cover is removed prior to the second melting step, there is then no longer any need for the presence of specific ventilation openings in the container since the opening in the container, which was covered by the cover during the first melting step, can in that case function as ventilation opening.

In a second preferred embodiment of the container according to the invention the container is smooth on the side directed toward the thermoplastic.

By making the container smooth on the inside it is easier to remove from the container the monolithic element formed after the first and second melting steps. This

smoothing can take place for instance by polishing or by providing the container on the inner side with a releasing coating layer along the peripheral wall or bottom. A releasing coating layer has the advantage here compared to polishing that it is not necessary to disassemble the container.

In a third preferred embodiment of the container according to the invention the container is constructed from flat plate parts releasable from each other and fixing means for fixing the plate parts to each other.

Constructing the container from plate parts and fixing means (such as bolts, screws and nuts such as wing nuts) has the advantage that it is easier to take the

container apart so that the monolithic element formed in the method is simple to remove for further use. It is moreover advantageous to embody the walls and bottom of the container as plate part, because plate parts are easier to clean, for instance by means of polishing, after use in the method.

In addition to the plate parts and fixing means, there is also the option of for instance arranging a locking ring between a nut and a plate part.

The invention also relates to a combination for use in the method according to the invention comprising:

- at least one kiln;

- transport means, such as a conveyor belt, extending through the at least one kiln; and

- a container according to the invention arranged on the transport means.

It is preferred to automate the method according to the invention as far as possible since this will increase the production speed and purity of the end product and reduce the chance of errors. The containers are preferably arranged for this purpose on transport means, such as a conveyor belt, which transport means transport the containers in and out of the kiln via a preferably separate kiln entrance and exit. The first and second melting steps are preferably performed here in a separate first and second kiln, whereby the method can be performed more quickly. If the container is preheated, a preheating kiln is then further arranged for this purpose which precedes the first kiln. The thermoplastic layer is preferably fed into the container via an automatic dispensing station .

This and other aspects of the invention are further elucidated with reference to the accompanying drawings.

Figures 1A and IB show a container according to the invention, respectively in assembled state and with exploded parts .

Figure 2 shows the container according to figures 1A and IB filled with thermoplastic.

Figure 3 is a flow diagram of the method according to the invention.

Figure 4 shows a combination according to the invention .

Figure 5 shows another container according to the invention.

Shown in figures 1A and IB is a container 1 according to the invention constructed from a base plate 2, a bottom plate 3 and upper plate 4. Constructed between bottom plate 3 and upper plate 4 is a peripheral wall constructed from flat plate parts 5, which plate parts are polished on the side facing toward each other. Base plate 2 and upper plate 4 are fixed to each other by means of screws 6 with wing nuts 7. Plate parts 5 are fixed to each other with bolts 8 arranged on all edges and are clamped by base plate 2 and upper plate 4. A cover 9 which covers the top side of container 1 can be placed on container 1. Ventilation openings 10 and a handle 11 with opening 12 are arranged in cover 9 so that cover 9 can lie on the container in alignment with one of the screws 6 with wing nuts 7. Filled with thermoplastic, container 1 is in this way used in the first melting step.

The container is shown in figure 2 as it is used in the second melting step. In this case cover 9 has been

removed. It can now be seen that thermoplastic flakes 100 have been arranged uniformly distributed in the container. At the end of the first melting step the parts 100a close to plate parts 5 will have become discoloured and will have sunk to a slightly lower level relative to the remainder 100b of the visible surface of flakes 100.

In a method 200 according to the invention a

container 1 is provided (step 201), container 1 is filled with thermoplastic flakes (step 202), cover 9 is placed over container 1 as shown in figure 1A (step 203), wall parts 5 and base plate 2 and bottom plate 3 are heated so that area 100a melts (step 204), cover 9 is removed (step 205), the whole content of container 1 is melted by heating wall parts 5 and heat radiation is directed at thermoplastic 100 through upper plate 4 (step 206), the monolithic element formed in the steps is cooled (step 207) .

Figure 4 shows a combination 300 according to the invention on which the method according to the invention is performed. Combination 300 comprises a conveyor belt 301 which extends through a preheating kiln 302, a first kiln 303 and a second kiln 304. A first dispensing station 305 and second dispensing station 306 are arranged above conveyor belt 301. First dispensing station 305 is connected to the exit of a preheating kiln 307 and second dispensing station 306 to a preheating kiln 308. When performing the method according to the invention a container is arranged without cover 400A on conveyor belt 301, heated in preheating kiln 302 to above the melting temperature of the thermoplastic to be processed, subsequently carried under first dispensing station 305 (as container 400B) where it is filled with thermoplastic coming from source 309 and preheated in kiln 307. Cover 405 is subsequently placed on container 400C and the first melting step is performed in first kiln 303 wherein the volume of the content of the container decreases, after which the cover is removed (container 400D) . Container 400E is subsequently placed under second dispensing station 306, where it is filled with thermoplastic coming from source 310 and preheated in kiln 308, preferably a residual flow which consists

substantially of thermoplastic. The second melting step is then performed in second kiln 304 without the cover on the container, wherein the volume of the content of the container decreases further. The container then comes out of kiln 304 and cover 405 is placed on the container (as container 400G) . The cover and the formed monolithic element 450 are

subsequently removed from container 400G. Monolithic element 450 is then suitable for further processing, while container 400G can be reused for infeed as container 400A.

Figure 5 shows container 400 as in step 400F of figure 4. Container 400 comprises a tray 401 with a bottom 402 and a wall 403, with a peripheral wall 404 placed on tray 401 and extending in line with wall 403. The space between cover

405 and upper edge 406 of tray 401 is filled with

thermoplastic during the method, but because the volume of the thermoplastic decreases in the melting steps, the formed monolithic element will usually not protrude above upper edge

406 after the second melting step. The formed monolithic element 460 is constructed from a thermoplastic layer 461 and a residual flow layer 462.