Patent Description:
Depending on their use, plastic products are manufactured from thermoplastics or thermosets. Thermoplastics have the feature that, when exposed to heat, they become liquid. This effect is caused by the fact that thermoplastics are formed by molecular chains which are only bonded to each other by Van der Waals bonds. The Van der Waals bonds are broken when exposed to heat, whereby the individual chains can move along each other. A thermoplastic can thus melt. A thermoplastic can thus be recycled multiple times in simple manner. In the case of thermosets the molecular chains are interconnected. This interconnectedness is referred to as a cross-link. The cross-links are covalent bonds which are many times stronger than the Van der Waals bonds. Because the molecular chains are cross-linked, a thermoset has a strong and rigid structure. When exposed to heat, the molecular chains can however not start to move relative to each other. Hereby, the thermosets retain their shape when exposed to heat. When heated, the covalent cross-links break, and the molecule chains are broken. A thermoset is thus decomposed into multiple lumps of smaller molecules. These molecules produce black, charred remnants and malodorous and combustible gases. This makes thermosets difficult to recycle. As a result, thermosets are often incinerated in an incinerator. Thermosets and thermoplastics are typically used for manufacturing toys. Such toys however have a relatively short lifespan and are difficult or impossible to recycle.

<CIT> describes process for making a molded article having a granular or speckled appearance, including color compounding a first polymeric material and at least one pigment to form a color compound of the at least one pigment with the first polymeric material; comminuting the color compound; mixing the reduced particle size color compound with a second polymeric material having a color different from or contrasting with the at least one pigment to form a mixture wherein the reduced particle size color compound is distributed in the second polymeric material; and molding the mixture to form a molded article having a granular or speckled appearance, and an article.

<CIT> describes a system for recycling reusable resin mold products recovered from discarded apparatuses is disclosed. This recycling system includes a crushing system for crushing resin mold products one kind by one kind into crushed resinous pieces and packing the same in a bag, a classification system for irradiating a light beam to the resin in the bag and classifying the bags into respective kinds of resins based on a reflected beam therefrom, a cleaning system for separately cleaning the respective kind of crushed resinous pieces taken out of the bag to remove foreign matters adhered onto the surfaces of the crushed resinous pieces therefrom, and a recovery system for recovering the cleaned crushed resinous pieces.

<CIT> describes a process for the recovery of a plastic product from ASR or ESR mixtures can include five or more process steps selected from DEXRT; XRF; size reduction; density separation; NIR sorting; Electrostatic separation; LD sorting; Wood removal; rubber removal; metal removal; and glass removal.

<CIT> describes a process in which the cellular interior is formed by the use of a comparatively large granular plastics material containing a blowing agent and a further process in which the fine powder material and granular material containing a blowing agent are charged together to the mould and after rotation at a first temperature to form the skin, mould and its contents are further heated to a second temperature at which the granular material is expanded to form the cellular interior.

Embodiments of the invention have the object of providing a method in order to obtain an improved recycling of plastic, preferably an improved recycling of plastic toys.

The invention provides for this purpose a method for recycling plastic according to any one of the appended claims.

The above and other advantageous features and objectives of the invention will become more apparent and the invention better understood with reference to the following detailed description when read in combination with the accompanying figures, in which:.

The invention will now be further described with reference to exemplary embodiments shown in the figures. The same or similar elements are designated in the figures with the same reference numeral.

<FIG> and <FIG> illustrate an embodiment of a method for recycling plastic according to the invention. <FIG> shows particularly a flowchart of the method, wherein the method comprises the following steps:.

According to an embodiment of the method for recycling plastic, the step <NUM> comprises of grinding the plastic into plastic pieces <NUM>. In a preferred embodiment the plastic is plastic toys. It will be apparent to the skilled person that the grinding of the plastic can be performed by means of different types of grinding device, use can for instance be made of a horizontal or vertical hammer mill and so on. Step <NUM> is particularly performed by a grinding device wherein the plastic is ground into plastic pieces <NUM> with a desired minimum size. The minimum size of plastic pieces <NUM> corresponds to a maximum section D2 of the plastic pieces <NUM>, such that this is preferably greater than <NUM>, preferably greater than <NUM>, more preferably greater than <NUM>. An advantage hereof his based on the insight that plastic, and particularly plastic toys, often comprise components which are made from different colours. The plastic components, which are coupled or attached to each other, can be detached from each other in simple manner by the grinding. A further advantage is that because the plastic pieces comprise a determined minimum size, the step <NUM> of sorting the plastic pieces by colour can thus take place rapidly and thoroughly.

Step <NUM> of the method comprises of sorting the plastic pieces <NUM> based on type of plastic. It will be apparent to the skilled person that the sorting of the plastic pieces <NUM> based on type can be carried out by means of different techniques. The plastic pieces can thus for instance be sorted based on density in order to thus obtain the desired material type of plastic. According to a preferred embodiment of the method, the plastic pieces are sorted by means of an optical Near-Infrared, NIR, sorting device.

Step <NUM> of the method comprises of sorting the plastic pieces <NUM> based on colour of the plastic pieces. According to a preferred embodiment, the step <NUM> is performed by an optical sorting device. The colour of the plastic pieces is preferably determined by means of spectral imaging. Spectral imaging is imaging which makes use of one or more wavelength bands in the electromagnetic spectrum. A normal camera typically captures light across three wavelength bands in the visible spectrum, red, green and blue, RGB. Spectral imaging comprises a wide variety of techniques that go beyond RGB. Spectral imaging can map the infrared spectrum, the visible spectrum, the ultraviolet spectrum, x-rays or a combination of the above spectra. The spectral imaging preferably comprises multispectral and/or hyperspectral imaging. An advantage of multispectral and/or hyperspectral imaging is that image data can be collected in visible and non-visible wavelength bands simultaneously. A further advantage is that use can be made of illumination from outside the visible range, or of optical filters for capturing a specific spectral range. Multispectral imaging typically relates to the capturing of at least three wavelength bands to about ten wavelength bands. Hyperspectral imaging typically relates to the capturing of hundreds of wavelength bands. A resolution of each wavelength band, and a width thereof, can be adjusted depending on the application. The spectral imaging is preferably Near-Infrared, NIR, spectroscopy. NIR spectroscopy makes use of infrared, IR, radiation. This IR radiation is directed at the plastic piece to be examined. The plastic piece lets through a part of this radiation, absorbs a part, and can reflect this radiation. From this, a spectrum is created which shows which wavelengths were absorbed or conversely let through. The materials and/or colours in question can then be determined based on this spectrum, since each molecule will absorb this radiation in a different way. NIR spectroscopy provides the advantage that it can be used both for sorting by type of plastic of the plastic pieces and for sorting by colour of the plastic pieces. A further advantage of NIR spectroscopy is that the colour can be determined rapidly and accurately in advantageous manner.

Step <NUM> of the method comprises, after sorting of the plastic pieces, of shredding the sorted plastic piece into plastic flakes. The step <NUM> of shredding must be performed after steps <NUM> and <NUM>. The shredding can be performed by different shredding devices. The shredding device can be similar to the grinding device of step <NUM>. Alternatively, the shredding device can differ from the grinding device of step <NUM> in that the plastic pieces are shredded into plastic flakes, wherein the plastic flakes have dimensions with a maximum section D1. The maximum section D1 is preferably smaller than <NUM>, more preferably smaller than <NUM>, still more preferably smaller than <NUM>, most preferably smaller than <NUM>. In an embodiment the size of the plastic flakes can be verified <NUM> by means of a screen (shown in <FIG>). The screen can for instance be a trommel screen or a vibrating screen, wherein the screen has a passage size or screen size which corresponds to the maximum section D1 of the plastic flakes.

Step <NUM> of the method comprises of processing plastic flakes into a recycled good by means of rotational moulding, wherein a micronized plastic is added during the rotational moulding. In a first processing step the flakes are placed in a mould of a rotational moulding device. Depending on the object of the recycled good, a desired quantity of micronized plastic is added. By rotating the rotational moulding device the plastic flakes will mix with the micronized plastic. The mould is rotated in an oven or, in an alternative embodiment, can also comprise heating elements itself. When the mould is heated, the micronized plastic will melt and form the bond between the plastic flakes. The mould rotates along two mutually perpendicular axes, whereby the melted material is pressed against the mould wall and takes on the shape of the mould. A recycled good is thus obtained. Research has shown that in some cases the use of plastic flakes results in recycled goods with poor structural properties. Because the molecules cannot move relative to each other, bonds can no longer be created during recycling of the plastic. Owing to the rotational moulding, the wall thickness of the recycled good can be determined and the melted micronized plastic will surround the plastic flakes during the rotational moulding, whereby an improved structural integrity of the recycled good is obtained.

<FIG> shows a similar flowchart of a method shown in <FIG> according to the invention. The method is similar to the method shown in <FIG> shows particularly that the steps of grinding <NUM>, sorting by type <NUM> and sorting by colour <NUM> are successive. It will however be apparent that the steps <NUM> and <NUM>, as shown in <FIG>, are interchangeable in an alternative embodiment. <FIG> further shows that step <NUM> and step <NUM> can be preceded by the step <NUM> of washing the plastic. Plastic, and particularly plastic toys, can be contaminated by attached contaminants such as sand, dust, oil and so on. The further steps of the method can hereby be impeded or hampered. The structural integrity of the recycled good can further also deteriorate. By performing the step of washing before the steps of sorting false positives in the sorting are avoided and the structural integrity of the recycled good is improved.

In an alternative embodiment the size of the plastic flakes can be verified <NUM> by means of a screen after the step <NUM> of the shredding into plastic flakes. When the size of a plastic flake or a plurality of plastic flakes does not meet requirements, they can once again undergo the step <NUM> of shredding so as to ultimately comply with the predetermined size, as described with reference to <FIG>.

<FIG> illustrate an embodiment of a part of the method for recycling plastic according to the invention. The figures particularly show that the sorting of the plastic pieces in step <NUM> and <NUM> comprises of subdividing the plastic pieces into groups according to a type <NUM>, <NUM>, <NUM>, and so on and/or a colour <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. Each group has plastic pieces which are substantially of the same type of plastic and/or colour as each other.

<FIG> illustrates particularly that the step <NUM> of sorting of the plastic pieces based on type of plastic comprises of subdividing the plastic pieces into groups according to a type <NUM>, <NUM>, <NUM>. The groups comprise plastic pieces of substantially the same type. Plastic can typically be subdivided into three types: thermoplastics, thermosets and elastomers. The group <NUM> in the method corresponds for instance to the type thermosets, the group <NUM> to the type thermoplastics and the group <NUM> to the type elastomers. It will be apparent to the skilled person that, after sorting, the groups are separated from each other. The sorting of plastic according to type is described in the step <NUM> of <FIG>. In an alternative embodiment the sorting by type of plastic can take place by means of float-sink density separation. Float-sink density separation is based on a difference in density between the different types of plastic and a density of a liquid in a separation container. Depending on the density of the plastics, they will float or sink in the liquid. The floating and the sunk plastics can then be removed from the separation container in succession. The plastics can thus be mutually separated from each other. The liquids used in the separation container can be selected depending on the types of plastic.

<FIG> illustrates that the step <NUM> of sorting of the plastic pieces based on colour comprises of subdividing the plastic pieces into groups according to a colour <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. The groups comprise plastic pieces of substantially the same colour. The group <NUM> for instance corresponds to the colour red, the group <NUM> corresponds to the colour green and the group <NUM> for instance corresponds to the colour blue. It will be apparent to the skilled person that the plastic pieces can also be sorted according to many other colours, for instance purple, orange, yellow and so on, and that the number of groups illustrated in <FIG> is not limitative to the sorting. It will be apparent to the skilled person that the groups are separated from each other after the sorting.

<FIG> illustrates a preferred embodiment of the method according to the invention. <FIG> particularly illustrates that the groups of plastic pieces, which were sorted according to type <NUM>, <NUM>, <NUM> or colour <NUM>, <NUM>, <NUM>, can go through the further subsequent steps as groups. The method can thus for instance first sort the plastic pieces by type of plastic <NUM>, <NUM>, <NUM>, and then further sort the type <NUM>, which for instance corresponds with thermosets, by a colour <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. As shown in <FIG>, the plastic first goes through the step <NUM> of grinding of the plastic into plastic pieces <NUM>. The plastic pieces are then preferably sorted by type of plastic into groups <NUM>, <NUM>, <NUM> which comprise substantially the same type of plastic. In a preferred embodiment the group <NUM> which corresponds with plastic parts of the thermosets type is then sorted by colour in the step <NUM>. The plastic pieces are thus sorted into groups comprising plastic pieces with substantially the same colour. The group <NUM> can for instance be sorted according to three colours: red <NUM>, blue <NUM>, green <NUM>. Each group will then be shredded in step <NUM> into plastic flakes and be processed in step <NUM> into a recycled good. It will be apparent that the alternative embodiments illustrated in <FIG> can also be applied in the method of <FIG>.

<FIG> and <FIG> show plastic pieces <NUM>, <NUM>, <NUM> or plastic pieces <NUM>, <NUM>, <NUM>. The plastic pieces are obtained after the step <NUM> of grinding. The step <NUM> is particularly performed by a grinding device, wherein the plastic is ground into plastic pieces <NUM> with a desired minimum size. The minimum size of plastic pieces <NUM> corresponds to a maximum section D2 of the plastic pieces <NUM>, such that this section can be inscribed in a circle with a diameter which is preferably greater than <NUM>, preferably greater than <NUM>, more preferably greater than <NUM>. It will be apparent that the plastic parts have different shapes.

<FIG> is similar to <FIG> and shows that, after the step <NUM> of shredding, the plastic flakes <NUM>, <NUM>, <NUM>, similar to the plastic pieces, have a maximum size corresponding with a maximum section D1 of the plastic flakes, such that this section is preferably smaller than <NUM>, more preferably smaller than <NUM>, still more preferably smaller than <NUM>, most preferably smaller than <NUM>. The step <NUM> of verifying, which is illustrated in <FIG>, can be performed in both cases.

<FIG> shows a recycling system <NUM> for recycling plastic, preferably recycling plastic toys, comprising a grinding device <NUM> which is configured to grind the plastic into plastic pieces, a first sorting device <NUM> configured to sort the plastic pieces based on type of plastic, a further sorting device <NUM> configured to sort the plastic pieces based on colour, a shredding device <NUM> configured to shred the sorted plastic pieces, after sorting of the plastic pieces, into plastic flakes, and a processing device <NUM> configured to process the plastic flakes into a recycled good by means of rotational moulding, wherein a micronized plastic is added during the rotational moulding.

Claim 1:
Method for recycling plastic, preferably recycling plastic toys, wherein the method comprises the steps of:
- grinding (<NUM>) the plastic into plastic pieces (<NUM>);
- washing the plastic pieces after grinding the plastic into plastic pieces;
- sorting (<NUM>) the plastic pieces based on type of plastic;
- sorting (<NUM>) the plastic pieces based on colour;
- after sorting of the plastic pieces, shredding (<NUM>) the sorted plastic pieces into plastic flakes (<NUM>);
- processing (<NUM>) the plastic flakes (<NUM>) into a recycled good by means of rotational moulding, wherein, during the rotational moulding, a micronized plastic is added.