EP3833523A1

EP3833523A1 - Method for reclaiming thermoplastic materials intended for recycling

Info

Publication number: EP3833523A1
Application number: EP19755307.6A
Authority: EP
Inventors: Robert Siegl
Original assignee: Alpla Werke Alwin Lehner GmbH and Co KG
Current assignee: Alpla Werke Alwin Lehner GmbH and Co KG
Priority date: 2018-08-06
Filing date: 2019-08-06
Publication date: 2021-06-16
Also published as: CH715231A1; US20210316484A1; CN112689555A; US11794378B2; MX2021000840A; WO2020030657A1

Abstract

The invention relates to a method for reclaiming thermoplastic materials intended for recycling, such as for example polyethylene terephthalate (PET), in the form of flakes. According to the invention, in a first step, the flakes are exposed to an oxidative fluid and heat until contaminated flakes are modified such that, in a second step, they are separated from the remaining flakes as a result of this modification.

Description

Process for reprocessing

provided thermoplastics

The invention relates to a method according to the preamble of claim 1. The invention also relates to a semifinished product or plastic packaging, such as beverage bottles, which are produced with a thermoplastic, which have been processed according to this method, and a processing system for carrying out this method.

Polyethylene terephthalate (PET for short), a thermoplastic, is very often used today in the packaging of food, soft drinks and water. Such plastic packaging should to a large extent be fed into the recycling stream and thus be processed again and again. For packaging of food, soft drinks, water and the like, PET packaging, in particular PET bottles, is used which have been produced entirely from recycled PET. This 100% recycling rate is possible, but the exception, as impurities in PET generally do not allow this to be 100%.

One of the known problems with repeated recycling is the progressive yellowing, clouding and graying of the PET. With each further recycling cycle, the PET becomes yellow, cloudy and gray. The yellow tinge can be compensated for by adding blue color. With this color compensation, however, the PET becomes darker and grayer. A PET that has become yellow and / or darker with ongoing recycling stages can often no longer meet the optical requirements of high-quality packaging.

Another problem that arises with continuous recycling is the increasing number of foreign bodies in the regrind (glass splinters, foreign polymers, paper, wood, etc.), which increases with each subsequent cycle. Such foreign bodies either cloud the PET themselves or they act as crystallization nuclei, which lead to the PET crystallizing locally, the turbidity being increased by the additional crystalline structure. Another problem is the chemical contamination, which either no longer directly permits the use of the regrind for the food sector or forms unwanted reaction products during further processing, which no longer permits the use for the food sector or for consumer goods. In addition, PET bottles can contain polyamide in layers or mixed to provide a barrier against oxygen and carbon dioxide. Such PET bottles mixed with polyamides have a particularly negative effect on the yellow tinge of the regrind, since polyamide yellows much more than PET over time and at an elevated temperature. In addition, the polyamide in the regenerated PET forms small polyamide domains that scatter the light and thus additionally cloud the regenerated PET. It was therefore tried not to include PET bottles with polyamide in the recycling stream.

Furthermore, PET bottles can be laminated with labels or sleeves based on polystyrene or PET G, which cannot be completely separated, and which can lead to severe yellowing and sticking at the elevated temperatures. Also particularly critical are adhesives, paints and varnishes on the bottles, which cannot be separated from the regrind and which can lead to undesirable reaction products at elevated temperatures.

It is known to separate different thermoplastics via their physical properties, such as near infrared absorption or density. After the separation, the essentially single-variety thermoplastic is washed and contaminations, such as paper or adhesive, are removed in the process. Basically, they are not changed when washing thermoplastics. The thermoplastics are only cleaned of impurities and brought into a form that enables further processing or preparation, for example as flakes, which are usually 2 to 30 mm ^{2 in} size as regrind. It is also known to dehumidify the flakes by heating them in vacuo or in a low-oxygen environment and thereby remove volatile contaminants. In special processes, such as solid state polymerization (SSP process), it is also possible to initiate a new polycondensation by heating in a vacuum or in the absence of oxygen. It is possible lent to increase the polymer chain length to the level of the original raw material. It is also known to dry the flakes hot or cold before extrusion; but even in these known methods, attempts are made to dry as gently as possible in order to keep reactions and their consequences, such as yellowing, as low as possible.

Another known problem in the subsequent processing of recycled flakes is that the elevated temperatures repeatedly lead to yellowing, which - as explained above - limits the usability of the recycled flakes and the intermediates produced therefrom As a rule, not only recycled thermoplastics are used in the manufacture of packaging, especially bottles, but a pure mixture of recycled and newly produced thermoplastics is used. So far, for example, the use of a mixture of 30% recycled PET and 70% virgin PET has been common for PET bottles in the European Union.

In general, efforts are being made to increase the proportion of recycled thermoplastic. However, limitations come to light here that are due to the discoloration, i.e. due to yellowing, graying, turbidity, and the like, as well as due to chemical contamination of the recycled thermoplastic. If the proportion of recycled thermoplastic becomes too high, it is usually no longer possible to achieve the required optical and chemical properties in order to be able to produce high-quality packaging.

This is where the invention comes in. It is therefore an object of the invention to provide a method which enables the processing of thermoplastic materials, in particular polyethylene terephthalate (PET), in which the quality of the processed thermoplastics is further improved compared to the processing methods known from the prior art. In particular, the quality of the processed thermoplastic should be improved to such an extent that this thermoplastic for plastic packaging can be used in particular for food, which packaging should convey a high quality impression. This impression of quality arises, for example, from beverage bottles due to high transparency.

Recycled thermoplastics of high quality enable the proportion of recycled thermoplastic to be increased further and accordingly the proportion of newly manufactured thermoplastics to be reduced in the manufacture of semi-finished products or plastic packaging. The method according to the invention is intended to complement existing processing processes, to be as economical as possible and to take ecological history into account. Here, the invention makes use of the knowledge that different contaminations of the thermoplastic to be recycled, when exposed to elevated temperatures, specifically lead to different reactions, which release reaction products and / or can result in discoloration, yellowing or adhesive bonding. This applies, among other things, to foreign plastics, oxygen scavengers, oils, sugar, polyamides, polystyrenes, UV absorbers, especially if they react particularly quickly with oxygen under heat and discolour and, under certain circumstances, undesirable reaction products such as cyclic hydrocarbons (benzenes, Form xylenes, toluenes, phenols) or aldehydes (formaldehyde, acetaldehyde). Some of these contaminants are thermally unstable and change, i.e. discolor, split off or split off low-molecular reaction products due to the high temperatures.

The invention relates to a process for the preparation of thermoplastics intended for reuse in the form of flakes, which is characterized in that the flakes are subjected to an oxidative fluid under heat in a first step until contamination by chemical and / or change physical effects so that in a second step due to the

Change can be separated from the flakes. Chemical effects in the sense of the invention can be, for example, the formation of reaction products or the elimination of reaction products. Discoloration, yellowing, turbidity or agglomerates formed as a result of clumping represent, for example, physical effects in the sense of the invention. The heating can take place directly by convection of the heated oxidative fluid, as well as indirectly by heat conduction, friction (sound) or radiation (microwave, UV, visible light, IR radiation). The oxidative fluid can absorb and remove chemical contaminations that are already present, as well as those that only arise at elevated temperature. The

According to the invention, solid contaminations are identified on the basis of the specific changes described above (for example discoloration, clumping) which take place on these and on the contaminated flakes during the process. A first separation of solid contaminants according to the second step can be carried out by sieving technologies, which in particular screen out adhered contaminations or contaminations that have become brittle and crumbly as a result of the heat and oxidation treatment or have turned into dust.

Discolored (yellowed, greened, grayed) solid contaminations can be separated using conventional sorting systems from well-known manufacturers such as Sesotec, Tomra, Bühler or Pellenc. The separation preferably takes place while still hot, i.e. H. above 90 ° C. Here, solid contaminations are identified as such and separated.

In a preferred embodiment, the invention uses the CIELAB color model (also Lab colors, CIEL * a * b *) to identify discolorations. The color of plastics is therefore determined by the three parameters L, a and b. The parameters are represented as L, a, b or often also as L * a * b *. The L * a * b * color space (also: Lab colors, CIELAB, CIEL * a * b *) describes all perceptible colors. The most important features of the L * a * b * color model include device independence and perception-relatedness, which means that colors are defined regardless of how they are generated or reproduced, as they would be perceived by a normal observer in a standard lighting condition. The color model is standardized in EN ISO 11664-4 "Colorimetry - Part 4: CIE 1976 L * a * b * Color space". The application of the CIELAB color model is explained below. The parameter L is a measure of the darkness. The higher the L value, the lighter the flakes. Flakes with values of L <65 are very dark and rather gray, whereas flakes with values of L> 85 are light. For example, newly manufactured PET without recycled content (so-called virgin PET) can easily be produced with an L value above 85, for example L = 89. There is also gray virgin PET, with L values below 85, that contains coal dust, IR absorbers or other additives that cloud the virgin PET.

The b-value is a measure of the yellow-blue discoloration of the flakes. Yellowed flakes, for example, have a b-value greater than 5 (b> 5,) which, for example, can reach values of b> 20 with strongly yellowed PET. A negative b-value describes the degree of blue coloring of the flakes. Virgin PET, for example, has b values between -3 and 0. The blue tint is generated via additives, for example cobalt compounds. For example, Virgin PET is set to a bluish tint, since it inevitably becomes more yellow during processing and the b-value thus increases. The a value is a measure of the red-green discoloration of the flakes. In addition to the yellowing of the regrind, there is usually also a green discoloration of the regrind, which is compensated with red color, and which also makes the regrind darker in the color compensation if the additive color mixture is intended to suppress the green tint.

With every recycling process that goes through a thermoplastic, the L-value drops, whereas the b-value increases. The a-value tends to decrease to a comparatively small extent. Not only do the flakes become more yellow even during the recycling runs, but the yellow tinge is particularly enhanced by impurities which contaminate the flakes during a recycling cycle.

The advantageous embodiment variants of the invention listed below lead, alone or in combination with one another, to further improvements of the method according to the invention.

In a further embodiment, the method according to the invention is carried out after carrying out already generally known methods for processing flakes. Such processes are washing the flakes, for example in alkalis or cold sorting to separate contaminants such as metals and other plastics. The contamination according to the invention is preferably separated from the other flakes before the extrusion and granulation. The method according to the invention enables the polymer chain length to be increased to the level of the original raw material. It is optionally possible to carry out an SSP process in accordance with the process according to the invention in order to further increase the polymer chain lengths.

The discoloration of solid contaminations can be determined by means of one or more optical sensors and the discoloration can be assessed on the basis of the CIELAB color model explained above.

Experiments have shown that good qualities of reprocessed flakes are obtained if flakes with a Color b value greater than 0, preferably greater than 4 are separated, i.e. are excreted from the amount of flakes intended for reprocessing. The result of this selection is that flakes are obtained for reuse, which at most have a low degree of yellowing.

Prepared flakes that are well suited for the production of transparent or crystal-clear packaging are obtained when flakes with a clear red cast, i.e. are separated with a Color a value less than minus 4 and / or if flakes with a clear green tint, i.e. a Color a value less than 4 can be separated. Furthermore, the flakes should have a Color L value that is greater than 50 and thus flakes with a Color L value of less than 50 are separated according to the invention.

According to the invention, an air-gas mixture with an oxygen content of at least 5% can be used as the fluid. With the method according to the invention in particular solid contaminations such as mixtures of thermoplastics with a radical scavenger as well as adhesives, PVC and polystyrene can be separated. To ensure the rapid yellowing of this contamination, an air-gas mixture with an oxygen content of at least 5% is used as the fluid and the flakes are heated in the range from 160 ° C to 240 ° C and preferably in the range from 175 ° C to 205 °, the particularly preferred temperature range being 185 ° C to 195 ° C. The aim is to keep the temperature of the fluid essentially constant during the process, a fluctuation of + / 15 ° C. being acceptable in order to regulate the temperature in the reaction space. The application of hot fluid to the flakes can take between 5 minutes and 10 hours.

According to the invention, the process conditions are thus selected such that the contaminations are forced to react and / or outgas during the implementation of the method and can be separated from the reaction space together with the oxidative fluid.

In the process, dehumidified or dried flakes with a temperature of 90 ° C. to 200 ° C. are preferably supplied. Therefore, in order to prevent Neukontamination in particular with steam, the fluid, in one embodiment of the invention in which feed a relative humidity in the order of 10- ^6% and 10% to ^-2. The supplied fluid is usually air and preferably has a dew point of -10 ° C to -100 ° C when it is supplied. This allows the flakes to be dried to a water content of less than 50 ppm while the fluid is flowing through them.

Contaminated flakes and agglomerates, in particular, which are glued or crumbled during reactive processing, are separated or separated in one embodiment of the invention by sieving technologies, such as mechanical sorting methods. The reason for the disturbance of the flowability of the flakes is usually the high temperatures.

Stirrers and other aids to support the flowability can be used so that the flakes do not stick locally or clump too much.

In order to increase the crystallinity of the material and to obtain granules which are easy to pour, the temperature profile during the process can be selected such that the thermoplastic crystallizes to more than 30% and preferably more than 40%.

At the same time, the crystallization drives out contaminations that are poorly or not at all soluble in the crystallized PET. Another advantageous aspect of the method according to the invention is that contaminations with a molecular mass less than 350 Da (Dalton) that have already migrated into the flakes due to forced reactions as a result of the exposure to the hot fluid and the presence of oxygen from the Migrate flakes into the fluid and can be easily separated from it.

The method according to the invention differs from previously known methods in that “contaminating” reactions are deliberately triggered in order to produce contaminations (yellowing, graying, benzene formation, phenol formation) in order then to separate them in a targeted manner. Another advantageous aspect of the method according to the invention is that gaseous reaction products and other gases which arise during the implementation of the process or migrate from the flakes can be separated from the process together with the oxidative fluid and thus removed from the process and slipped off Contamination also reaction products and the other gases can be removed from the flakes.

The method according to the invention is preferably carried out with pre-sorted flakes. This means that, for example, only flakes of one type of plastic are treated in the process. If the flakes to be processed are made of polyethylene terephthalate (PET), apart from the solid contaminations and other impurities, no other thermoplastics are processed together with the flakes made of polyethylene terephthalate (PET).

The process according to the invention is particularly suitable for the processing of flakes from polyethylene terephthalate (PET) and can also be used with great success for other thermoplastics, such as in particular for polyactides (PLA), polyethylene furanoate (PEF), polypropylene (PPF), high density polyethylene (HDPE) or polypropylene (PP) can be used. The advantage of the method according to the invention is that solid contaminations are removed and other contaminants have already reacted due to the degradation reactions forced due to the high temperatures. As a result of the forced reaction and separation at high temperatures according to the invention, those prepared according to the invention arise during further processing

Thermoplastics hardly any or only very few new contaminations. This is remarkable because every further processing always means a thermal load for the thermoplastics.

The use of the method according to the invention is particularly advantageous in the preparation of PET for bottles, preforms, tubes or other containers. This is because containers made from PET often undergo two transformations under the influence of high temperatures and are therefore exposed to multiple thermal loads during further processing.

Investigations by the applicant have shown that containers which are made from PET, which is based on PET flakes, are compatible with the inventive

Processes are treated, in the area of the CIELAB values, in particular in the area of the CIELAB b value, can be improved by about +5 to +10 points. This means that PET flakes to be processed with a b-value in the range from 0 to 15 after processing with the method according to the invention have a b-value from -5 to 5. The invention also relates to a semifinished product or plastic packaging, in particular beverage bottles, which contain a thermoplastic, in particular polyethylene terephthalate (PET), which has been processed using the method according to the invention.

In a preferred embodiment, a semifinished product or a plastic packaging with polyethylene terephthalate (PET) has a first proportion of at most 40% virgin polyethylene terephthalate (PET), preferably of at most 30% PET and particularly preferably at most 25% PET and a second proportion of at least 60% Polyethylene terephthalate (PET), preferably of at least 70% PET and particularly preferably at least 75% PET, which has been processed using the method according to the invention. Flakes treated with the process according to the invention and thus the semi-finished products and plastic packaging produced therefrom preferably contain less than 0.3 ppm benzene, toluene or xylene. In addition, the method according to the invention enables the production of flakes and thus of semi-finished products and plastic packaging which contain less than 0.03 ppm phenols, such as in particular bispehnol A or

Bispehnol S contains. These products are therefore suitable for use in the food sector for packaging food and beverages.

The method according to the invention can be carried out primarily in processing plants for processing thermoplastic intended for reuse, in particular polyethylene terephthalate (PET) in the form of flakes, the device for carrying out the method according to the invention being preceded by a washing device for washing the flakes from thermoplastics and another Process for the formation of a thermoplastic granulate can be connected downstream. In addition, a device for carrying out a solid state polymerization process (SSP process) can be connected downstream.

The optional features mentioned can be implemented in any combination, provided that they are not mutually exclusive. Particularly where preferred ranges are given, further preferred ranges result from combinations of the minima and maxima mentioned in the ranges.

Claims

EXPECTATIONS

1. Process for the preparation of thermoplastics in the form of flakes intended for reuse,

characterized,

that in a first step an oxidative fluid is applied to the flakes under heat until contamination by chemical and / or physical effects changes so that in a second step these are separated from the other flakes due to this change.

2. The method according to claim 1,

characterized,

that the contamination is still hot, i.e. be separated above 90 ° C.

3. The method according to claim 1 or 2;

characterized,

that the contaminations during the implementation of the process are forced to react and / or outgas by appropriate selection of the process conditions and are separated from the reaction space together with the oxidative fluid.

4. The method according to claim 1, 2 or 3,

characterized,

that the flakes are washed before the flakes are exposed to an oxidative fluid.

5. The method according to any one of the preceding claims,

characterized,.

that the contamination is separated from the remaining flakes before extrusion and granulation.

6. The method according to any one of the preceding claims,

characterized,

that solid contaminations such as contaminated flakes or agglomerates are identified based on their changes and then separated.

7. The method according to any one of the preceding claims,

characterized,

that the discoloration of the flakes is determined on the basis of the CIELAB color model using one or more optical sensors and contaminated flakes are identified in the process.

8. The method according to claim 6 or 7,

characterized,

that flakes with a color b value greater than 0, preferably greater than 4, are separated.

9. The method according to any one of the preceding claims 6 to 8

characterized,

that flakes with a Color a value less than minus 4 are separated.

10. The method according to any one of the preceding claims 6 to 9,

characterized,

that flakes with a Color L value of less than 50 are separated.

11. The method according to any one of the preceding claims;

characterized,

that agglomerates or flakes, which are glued or crumbled as a result of exposure to an oxidative fluid, are separated by sieving technologies.

12. The method according to any one of the preceding claims;

characterized,

that the fluid is an air-gas mixture with an oxygen content of at least 5%.

13. The method according to any one of the preceding claims;

characterized,

that the flakes are subjected to temperatures in the range from 160 ° C. to 240 ° C., the particularly preferred temperature range being from 185 ° C. to 195 ° C.

14. The method according to any one of the preceding claims;

characterized,

that the fluid has a relative humidity of the order of 10 ^-6 % and 10 ^-2 % when fed to the process.

15. The method according to any one of the preceding claims;

characterized,

that the fluid has a dew point of -10 ° C to -100 ° C when it is fed into the process and the flakes are dried to a water content of below 50 ppm during the flow.

16. V experience according to one of the preceding claims;

characterized,

that the temperature profile during the process is selected so that the thermoplastic crystallizes to more than 30% and that low molecular weight contaminations of less than 350 Da are driven out by the crystallization.

17. The method according to any one of the preceding claims;

characterized,

that the flakes are stirred in a stirrer to prevent them from clumping as much as possible.

18. The method according to any one of the preceding claims;

characterized,

that agglomerations and clumped flakes are separated by mechanical sorting processes.

19. The method according to any one of the preceding claims;

characterized,

that gaseous reaction products and gases which arise during the implementation of the process or migrate from the flakes are slid out of the reaction space together with the oxidative fluid.

20. The method according to any one of the preceding claims;

characterized, that solid contaminants such as PET mixtures with radical scavengers and adhesives, PVC and / or polystyrene are separated.

21. The method according to any one of the preceding claims,

characterized,

that the flakes are washed and pre-sorted before they are sent to reactive processing.

22. The method according to any one of the preceding claims,

characterized,

that the thermoplastic intended for reprocessing is polyethylene terephthalate (PET), polyactide (PLA), polyethylene furanoate (PEF), polypropylene furanate (PPF), high density polyethylene (HDPE) or polypropylene (PP).

23. Semi-finished or plastic packaging, in particular in the form of a beverage bottle consisting predominantly of a thermoplastic, in particular polyethylene terephthalate (PET), which has been processed according to one of the preceding claims.

24. Semi-finished product or plastic packaging, in particular in the form of a beverage bottle containing polyethylene terephthalate (PET), characterized in that the semi-finished product or plastic packaging contains a first proportion of at most 40% virgin polyethylene terephthalate (PET) and a second proportion of at least 60% polyethylene terephthalate (PET) which has been processed by the method according to any one of claims 1 to 22.

25. Semi-finished or plastic packaging according to one of claims 23 or 24, characterized in that the thermoplastic, in particular the polyethylene terephthalate (PET) contains less than 0.3 ppm benzene, toluene or xylene.

26. Semi-finished or plastic packaging according to one of claims 23, 24 or 25, characterized in that the thermoplastic, in particular the polyethylene terephthalate (PET) contains less than 0.03 ppm phenols, such as in particular bispehnol A or bispehnol S.

27. Processing plant for carrying out a method for processing thermoplastic intended for reuse, in particular polyethylene terephthalate (PET) in the form of flakes,

characterized,

that the plant comprises a washing device for washing the flakes from thermoplastics, a device for forming granules and a device for carrying out the method according to one of claims 1 to 22.