Use of a granulated PET recyclate for producing a PET regranulate and method for producing the same

Description

Field of the invention

[0001] The invention relates to the use of a granulated PET recyclate for producing a PET regranulate according to the preamble of claim 1, the use of a granulated PET recyclate for producing a container according to the preamble of claim 7 and a method for producing a PET regranulate. State of the art

[0002] The production of plastic containers, particularly plastic bottles, for example from polyethylene or polypropylene, is generally carried out using the extrusion blow molding process. A plastic tube is extruded from a tube head, introduced into a blow molding tool with a cavity, inflated via a blow mandrel using excess pressure, and thereby pressed against the inside of the cavity, where it is cured by cooling. As the inside of the cavity hardens, the outside of the blow-molded article takes on the contours of the inside of the cavity. After curing, the blow-molded article is removed from the blow molding tool. The extrusion blow molding machines used for this purpose generally have at least one extruder for feeding and melting the plastic material. The extruder outlet is connected to the tube head, from whose outlet nozzle the opening of which can preferably be adjusted is where the extruded tube exits.When the blow-molding tool closes to squeeze the plastic hose inserted between its halves, parts of the plastic hose protrude from the top and bottom, known as slugs. These are separated in a separate step and can be fed into the recycling stream. The plastic hose can be single- or multi-layered; it can be extruded as a plastic hose with visible stripes, decorative stripes, or with multiple segments, for example, of different colors, along its circumference.

[0003] The blowing station with the blowing mandrel is usually located to the side of the hose head, whereby the blow molding tool loaded with the extruded plastic hose must be moved into the blowing station, where the blowing mandrel is then usually inserted into the blow mold cavity from above.

[0004] The plastic tube is usually extruded vertically. Gravity pulls the plastic tube exiting the blowing nozzle downward. However, if the material of the plastic tube is too thin, meaning it lacks sufficient melt strength, its own weight will cause the plastic tube to shrink in length to such an extent that the subsequent blowing process is no longer possible.

[0005] For the production of PET containers on extrusion blow molding machines, extrusion blow molding can only be used if the PET molding compound has the necessary melt strength, i.e., the plastic tube has a shape and consistency when the blow mold halves close, which, during subsequent inflation and curing, results in a hollow body that meets the specified specifications. The melt strength of the PET material used for the stretch blow molding process, in which the containers are formed from a preform produced by an injection molding process, does not meet the requirements for extrusion blow molding, as its intrinsic viscosity is too low and, when used in extrusion blow molding, leads to the aforementioned impermissible lengths of the plastic tube. For extrusion blow molding, the PET material must be modified accordingly.

[0006] According to the state of the art, PET molding compounds known by abbreviations such as PET X (extrudable), PET G (glycol modified), and PET B (branched) are used for extrusion blow molding. In the USA, terms such as EPET, PETE, or EBM PET are also commonly used. These are PET materials specifically developed for extrusion blow molding. The production quantities are small and therefore the price is correspondingly high. However, some of the PET hollow bodies produced with these PET molding compounds in the EBM process cannot be fed into the PET recycling stream because they cannot be recycled like standard PET.

[0007] Standard PET types are linear PET types (no branched ones) with a low copolymer content of less than 5 wt.% and an intrinsic viscosity (IV) between 0.74 and 0.86 dl / g (according to ASTM D 4603).

[0008] Patent document EP 1 829 914 A1 describes a method for recycling a PET material.

[0009] US 2013 / 0029068 A1 proposes a PET molding compound suitable for the EBM process and intended to be non-hazardous in the PET recycling stream. The PET molding compound is made from virgin PET, i.e., so-called "virgin PET," or v-PET for short. By definition, virgin PET has not been extruded after its production from fossil or renewable raw materials.

[0010] Due to its insufficient melt strength, post-consumer PET, so-called r-PET, is unsuitable for use in an EBM machine. The reason for the insufficient melt stability of r-PET is likely that the plastic mass degrades further during extrusion due to the additional heat and shear forces, thus further reducing the molecular weight.

[0011] Standard PET (polyethylene terephthalate) is unsuitable for extrusion blow molding due to its low melt strength. Therefore, modified PET molding compounds have been developed that possess improved melt strength. The improved melt strength can be achieved, among other things, by extending or crosslinking the molecular chains by adding chain extender or crosslinker additives to the PET. However, such PET molding compounds cannot be added to the PET recycling stream from containers produced from a preform, as the extender and crosslinker additives are considered contaminants in the PET recycling stream.

[0012] Post-consumer PET, so-called PET recyclate (r-PET), as available on the market, has an intrinsic viscosity of a maximum of 0.88 dl / g according to ASTM D 4603 and is unsuitable for use in the extrusion blow molding process. Object of the invention

[0013] The disadvantages of the described prior art give rise to the object initiating the present invention of proposing a PET molding compound which contains at least a certain proportion of PET recyclate and is suitable for extrusion blow molding. Description of the invention

[0014] The use of a granulated PET recyclate for producing a PET regranulate is proposed, wherein the granulated PET recyclate is obtainable by comminuting post-consumer PET bottles and / or industrial waste from PET bottle production to flakes, and subsequently melting the flakes by extrusion using an extruder with simultaneous reduction of the intrinsic viscosity and increase of the reactive carboxyl and hydroxyl end groups, wherein the PET recyclate is condensed by means of a solid-state polycondensation at a temperature between 185 °C and 230 °C and without adding chain extension and / or crosslinking additives, so that the PET regranulate has an intrinsic viscosity (IV) measured according to ASTM D 4603 of at least 0.95 dl / g, preferably greater than 1.0 dl / g and particularly preferably between 1.1 dl / g and 1.7 dl / g and is suitable for the production of extrusion blow-molded containers.

[0015] According to the invention, PET recyclate is used which has between 30 mmol / kg and 60 mmol / kg carboxyl end groups and between 30 mmol / kg and 70 mmol / kg hydroxyl end groups and before the modification of the PET recyclate to PET regranulate, a water content of the PET recyclate is adjusted between 100 ppm and 5000 ppm.

[0016] The term "granulated PET recyclate" refers to the material available for processing into bottles stretch-blown from injection-molded preforms. The PET recyclate is obtained from post-consumer PET bottles and / or industrial waste from PET bottle production fed into the PET recycling stream. To this end, the post-consumer PET bottles and / or industrial waste from PET bottle production are first washed if necessary and then shredded into flakes. If necessary, the flakes are washed again. The flakes are then melted by extrusion, the melt is forced through a perforated plate to form a strand, and the strand is cooled in a water bath. Finally, the cooled strand is granulated into PET recyclate.PET regranulate means that the PET recyclate has been modified in such a way that it achieves an intrinsic viscosity that allows it to be used to produce a container using the extrusion blow molding process. The PET regranulate is made entirely from PET recyclate without the need to add chain extender and / or crosslinking additives. Accordingly, containers made from PET regranulate using the extrusion blow molding process can be fed into the PET recycling stream from PET bottles. Because the PET regranulate was made from post-consumer PET containers, the PET regranulate has been extruded at least twice, i.e. melted twice and thus exposed to shear forces and heat twice. Experience has shown that containers made from PET regranulate have a yellow tinge, which can be lightened if necessary by adding v-PET. Here, v-PET can be used in a maximum of 40 wt.-% can be added. Typically, between 10 wt.% and 30 wt.% of v-PET can be added, with the percentage referring to the total amount of PET regranulate and v-PET. The yellow tint can also be masked by adding color, preferably a blue or green color. The PET regranulate thus enables the production of transparent containers using the EBM process.

[0017] According to a further embodiment of the invention, the PET recyclate has an intrinsic viscosity measured according to ASTM D 4603 of less than 0.8 dl / g. Typically, the PET recyclate has an intrinsic viscosity measured according to ASTM D 4603 of less than 0.74 dl / g, and preferably between 0.74 dl / g and 0.73 dl / g. It has been shown that PET recyclate with such a low intrinsic viscosity is particularly suitable for modification into PET regranulate at a reasonable cost.

[0018] According to a further embodiment of the invention, the PET recyclate from which the PET regranulate is produced has carboxyl end groups between 32 mmol / kg and 40 mmol / kg, and hydroxyl end groups between 50 mmol / kg and 60 mmol / kg. It has been shown that the extrusion and melting of the PET flakes is particularly important for the production of the PET recyclate. The repeated exposure of the PET flakes, which are made from post-consumer PET bottles and / or industrial waste from PET bottle production and which have already been subjected to heat and shear forces during extrusion in an upstream manufacturing process, and the associated reduction in the intrinsic viscosity or molecular weight, generates a high number of reactive end groups.By removing water through vacuum and heating, or by heating and purging at atmospheric pressure with nitrogen, the carboxyl end groups combine with the hydroxyl end groups. PET recyclate with carboxyl end groups between 32 mmol / kg and 40 mmol / kg and hydroxyl end groups between 50 mmol / kg and 60 mmol / kg in particular tends to combine rapidly, resulting in chain elongation and an increase in intrinsic viscosity. This is likely also the reason why experts have not yet considered the use of PET recyclate in the EBM process.

[0019] According to a further embodiment of the invention, the modification is carried out by condensation. Instead of condensation, the terms polymerization or esterification are also used. This process can be carried out, for example, in a solid-state polycondensation (SSP) reactor. Instead of an SSP reactor, a dryer can also be used for condensation. The SSP process can take place either separately in a recycling plant or in the plant where the EBM production process is carried out. It has been shown that PET recyclate is more reactive than v-PET and is therefore easier to condense than v-PET. This is a major advantage because it reduces production times.

[0020] According to a further embodiment of the invention, the PET regranulate is formed as spherical granules. The spherical granule shape, which the PET recyclate already possesses, can ensure that the condensation of the PET recyclate occurs evenly. This ensures a homogeneous distribution of the intrinsic viscosity throughout the PET regranulate. Typically, the intrinsic viscosity range of the PET regranulate in the form in which the customer receives it for processing is in the range of 0.03 dl / g. Since PET recyclate and PET regranulate are bulk materials, abrasion or shedding is largely prevented by the spherical shape. In contrast, when pouring cylindrical PET recyclate, edges usually shear off. These fragments condense more quickly.The range of intrinsic viscosity within a granule can also be wider with a cylindrical shape, since within this geometric configuration, flat surfaces and curved surfaces collide, which exhibit different condensation behaviors. This can consequently lead to a wider range of intrinsic viscosity for customers, who also encounter abrasion and fragments in the delivery, with a cylindrical regranulate than with the spherical version.

[0021] According to a further embodiment of the invention, the PET regranulate is modified by solid-state polycondensation at a temperature between 185°C and 230°C, preferably between 195°C and 220°C, and particularly preferably between 200°C and 210°C. Under the aforementioned conditions, the PET recyclate can be condensed quickly and cost-effectively into the PET regranulate.

[0022] According to a further aspect of the invention, the use of a granulated PET recyclate for producing a container, in particular a bottle, is proposed according to the preamble of claim 7. The PET recyclate used has between 30 mmol / kg and 60 mmol / kg carboxyl end groups and between 30 mmol / kg and 70 mmol / kg hydroxyl end groups. Before the PET recyclate is modified to form PET regranulate, the water content of the PET recyclate is adjusted to between 100 ppm and 5000 ppm. Extrusion-blown containers made from the PET regranulate according to the invention can be labeled with the number 01 of the "SPI resin identification codes system" and thus fed into the normal PET recycling stream.

[0023] According to a further embodiment of the invention, the PET regranulate is food-safe. This allows extrusion-blown containers for food storage to be produced from the PET regranulate.

[0024] According to a further embodiment of the invention, the container can be processed into PET recyclate after use. Because the container extrusion-blown from the PET regranulate can be fed into the normal PET recycling stream, this container can be processed again into PET recyclate, which can be condensed into PET regranulate.

[0025] According to a further embodiment of the invention, a process for producing a PET regranulate is proposed which is suitable for producing extrusion blow-molded containers and is obtainable by condensing a granulated PET recyclate obtained by crushing post-consumer PET bottles and / or industrial waste from PET bottle production into flakes, and then melting the flakes by extruding them using an extruder with simultaneous reduction of the intrinsic viscosity and increase of the reactive carboxyl and hydroxyl end groups, wherein PET recyclate is used,which has between 30 mmol / kg and 60 mmol / kg carboxyl end groups and between 30 mmol / kg and 70 mmol / kg hydroxyl end groups, and before the modification of the PET recyclate to PET regranulate, a water content of the PET recyclate is adjusted between 100 ppm and 5000 ppm, and the PET recyclate is condensed by means of solid-state polycondensation at a temperature between 185 °C and 230 °C and without the addition of chain extender and / or crosslinking additives, so that the PET regranulate has an intrinsic viscosity measured according to ASTM D 4603 of more than 0.95 dl / g, preferably greater than 1.0 dl / g, and particularly preferably a viscosity between 1.1 dl / g and 1.7 dl / g.

[0026] Further steps of the process include pressing the melt through a perforated plate to form a melt strand, subsequent cooling of the melt strand, and granulation of the cooled melt strand to form PET recyclate.

[0027] In principle, v-PET can be added to the PET recyclate before the PET recyclate is condensed into PET regranulate. This can be done directly at the plant where the PET recyclate is processed. The modification is preferably achieved by increasing the average molecular weight. This is preferably achieved by subjecting the PET recyclate / v-PET mixture to solid-state polycondensation. Solid-state polycondensation is also known as "solid-state polycondensation" (SSP). It takes place in a suitable solid-state reactor, preferably equipped with a stirrer. In this reactor, the granulated PET recyclate is gently mixed and simultaneously heated. This expels water and volatile components from the added PET recyclate, leading to condensation reactions and thus an increase in the average molecular weight. The internal temperature of the reactor is preferably between 200 and 220°C.To extract the vapor, the reactor is preferably operated at a negative pressure of less than 50 mbar, and particularly preferably less than 10 mbar. The residence time of the PET recyclate in the reactor is preferably 6 to 40 hours, particularly preferably 10 to 35 hours, and most preferably 15 to 30 hours, depending on the intrinsic viscosity to be achieved.

[0028] Advantageously, the modification of the PET recyclate to the PET regranulate takes place in a solid-state polycondensation reactor at an elevated temperature between 195 °C and 220 °C and particularly preferably between 200 °C and 210 °C.

[0029] According to a further embodiment of the invention, the PET recyclate is exposed to the elevated temperature for 6 to 40 hours, preferably for 10 to 35 hours, and particularly preferably for 15 to 30 hours. Under these conditions, water and other volatile substances are removed from the PET recyclate, and rapid chain extension occurs. This chain extension is expressed in an increased intrinsic viscosity. The thermal treatment of the PET recyclate is continued until the desired intrinsic viscosity of the PET regranulate, which is higher than that of the starting material, is achieved. Particularly preferably, the intrinsic viscosity of the PET regranulate, measured according to ASTM D 4603, is between 1.0 dl / g and 1.7 dl / g.

[0030] According to a further embodiment of the invention, the PET recyclate is exposed to a negative pressure of less than 50 mbar and preferably less than 10 mbar in the solid phase condensation reactor.

[0031] In the event that the reactivity of the PET recyclate is insufficient, reactive additives, such as ethylene glycol and / or terephthalic acid and / or isophthalic acid and / or their esters (e.g., dimethyl terephthalate), can be added. Molecules that act as chain extenders, for example, or those capable of branching two molecules together, can be added. However, because additives are expensive and their use jeopardizes the recyclability of the plastic, their use is prudently avoided.

[0032] Advantageously, the average molecular mass and / or the intrinsic viscosity of the PET recyclate used is increased by at least 20%, preferably by at least 25%, through the modification to PET regranulate.

[0033] For the production of containers with a volume between 100 ml and 300 ml, the PET recyclate is advantageously modified such that the intrinsic viscosity of the PET regranulate, measured according to ASTM D 4603, is between 0.95 dl / g and 1.3, and preferably between 1.0 dl / g and 1.2 dl / g. For the production of containers with a volume between 250 ml and 1000 ml, the PET recyclate is modified such that the intrinsic viscosity of the PET regranulate, measured according to ASTM D 4603, is between 1.1 dl / g and 1.5 dl / g, and preferably between 1.2 dl / g and 1.4 dl / g.

[0034] For the production of containers with a volume between 750 ml and 5000 ml, the r-PET is preferably modified such that the intrinsic viscosity of the PET regranulate measured according to ASTM D 4603 is between 1.2 dl / g and 1.6 dl / g and preferably between 1.3 dl / g and 1.6 dl / g.

[0035] Preferably, the PET recyclate is melted and granulated prior to modification, with the water content of the PET recyclate being adjusted between 100 ppm and 5000 ppm, and preferably between 300 ppm and 3000 ppm. By adjusting a specific water content during the granulation process, the degradation reactions of the PET can be specifically influenced, as the rate of degradation reactions increases rapidly with higher water content. Accordingly, the reactivity of the PET recyclate and its tendency toward chain formation reactions in a subsequent SSP process can be significantly influenced.

[0036] It is clear to a person skilled in the art that features of devices can, where appropriate, also be features of methods and vice versa.

[0037] The invention is described in the appended set of claims.

Claims

1. Use of a granulated PET recyclate for the production of a PET regranulate which is suitable for the production of extrusion blow-moulded containers, in particular of PET plastic bottles, wherein the granulated PET recyclate is produced by shredding post-consumer PET bottles and / or industrial waste from PET bottle production to form flakes, subsequent melting of the flakes by extrusion by means of an extruder with simultaneous reduction of the intrinsic viscosity and increase in the reactive carboxyl and hydroxyl end groups, pressing of the melt through an apertured plate to form a melt rod, cooling of the melt rod and granulation of the cooled melt rod to form PET recyclate, wherein the PET recyclate is condensed by means of a solid state polycondensation at a temperature between 185°C and 230°C and without the addition of chain extender additives and / or crosslinking additives, so that the PET regranulate has an intrinsic viscosity, measured in accordance with ASTM D 4603, of more than 1.0 dl / g and particularly preferably between 1.1 dl / g and 1.7 dl / g, characterized in that PET recyclate is used which contains between 30 mmol / kg and 60 mmol / kg of carboxyl end groups and between 30 mmol / kg and 70 mmol / kg of hydroxyl end groups, and prior to the modification of the PET recyclate into the PET regranulate, a water content of the PET recyclate is adjusted to between 100 ppm and 5000 ppm.

2. Use as claimed in claim 1, characterized in that the granulated PET recyclate has an intrinsic viscosity, measured in accordance with ASTM D 4603, of less than 0.8 dl / g.

3. Use as claimed in claim 1 or claim 2, characterized in that the PET recyclate contains between 32 mmol / kg and 40 mmol / kg of carboxyl end groups and between 50 mmol / kg and 60 mmol / kg of hydroxyl end groups.

4. Use as claimed in one of the preceding claims, characterized in that the PET regranulate is in the form of spherical granules.

5. Use as claimed in claim 4, characterized in that the condensation is carried out by a solid state polycondensation at a temperature between 195°C and 220°C and particularly preferably between 200°C and 210°C.

6. Use as claimed in one of the preceding claims, characterized in that the PET regranulate is food-safe.

7. Use of a granulated PET recyclate for the production of a container, in particular a PET plastic bottle, which is produced from a PET regranulate as claimed in one of the preceding claims in an extrusion blow moulding process, wherein granulated PET recyclate is produced by shredding post-consumer PET bottles and / or industrial waste from PET bottle production to form flakes, and subsequent melting of the flakes by extrusion by means of an extruder with simultaneous reduction of the intrinsic viscosity and increase in the reactive carboxyl and hydroxyl end groups, pressing of the melt through an apertured plate to form a melt rod, cooling of the melt rod and granulation of the cooled melt rod to form PET recyclate, wherein the PET recyclate is condensed by means of a solid state polycondensation at a temperature between 185°C and 230°C and without the addition of chain extender additives and / or crosslinking additives, so that the PET regranulate has an intrinsic viscosity, measured in accordance with ASTM D 4603, of more than 1.0 dl / g and particularly preferably between 1.1 dl / g and 1.7 dl / g, further characterized in that PET recyclate is used which contains between 30 mmol / kg and 60 mmol / kg of carboxyl end groups and between 30 mmol / kg and 70 mmol / kg of hydroxyl end groups, and prior to the modification of the PET recyclate into the PET regranulate, a water content of the PET recyclate is adjusted to between 100 ppm and 5000 ppm.

8. Use as claimed in claim 7, characterized in that for the production of containers with a volume between 250 mL and 1000 mL, the PET regranulate used has an intrinsic viscosity, measured in accordance with ASTM D 4603, between 1.2 dl / g and 1.4 dl / g, and for the production of containers with a volume between 750 mL and 5000 mL, the PET regranulate has an intrinsic viscosity, measured in accordance with ASTM D 4603, between 1.2 dl / g and 1.6 dl / g and preferably between 1.3 dl / g and 1.6 dl / g.

9. Use as claimed in claim 8, characterized in that the container can be processed into PET recyclate after use.

10. A method for the production of a PET regranulate which is suitable for the production of extrusion blow-moulded containers and is produced by condensation of a granulated PET recyclate which is produced by shredding post-consumer PET bottles and / or industrial waste from PET bottle production to form flakes, subsequent melting of the flakes by extrusion by means of an extruder with simultaneous reduction of the intrinsic viscosity and increase in the reactive carboxyl and hydroxyl end groups, pressing of the melt through an apertured plate to form a melt rod, cooling of the melt rod and granulation of the cooled melt rod to form PET recyclate, wherein prior to the modification of the PET recyclate into the PET regranulate, a water content of the PET recyclate is adjusted to between 100 ppm and 5000 ppm and the PET recyclate is condensed by means of a solid state polycondensation at a temperature between 185°C and 230°C and without the addition of chain extender additives and / or crosslinking additives, so that the PET regranulate has an intrinsic viscosity, measured in accordance with ASTM D 4603, of more than 1.0 dl / g and particularly preferably a viscosity between 1.1 dl / g and 1.7 dl / g.

11. The method as claimed in claim 10, characterized by washing the flakes.

12. The method as claimed in one of claims 10 or 11, characterized in that the PET recyclate has an intrinsic viscosity of less than 0.8 dl / g.

13. The method as claimed in one of claims 10 to 12, characterized in that the PET recyclate is modified in a solid state polycondensation reactor at an increased temperature between 185°C and 230°C, preferably between 195°C and 220°C, and particularly preferably between 200°C and 210°C.

14. The method as claimed in claim 13, characterized in that the PET recyclate is exposed to the increased temperature for 6h to 40h, preferably for 10h to 35h, and particularly preferably for 15h to 30h.

15. The method as claimed in claim 13 or claim 14, characterized in that in the solid state polycondensation reactor, the PET recyclate is exposed to a partial vacuum of less than 50 mbar, preferably less than 10 mbar.

16. The method as claimed in one of claims 10 to 15, characterized in that prior to the modification to form the PET regranulate, a water content of the PET recyclate is adjusted to between 300 ppm and 3000 ppm.