Method for producing an rpet plastic material for use in a thin-wall injection molding method and containers, such as cups, bowls, trays or multi-compartment packagings produced by the thin-wall injection molding method

Abstract

The invention relates to a method by which a starting material for injection molding having a viscosity of between 0.50 and 0.7 dl / g is produced from a recycled post-consumer PET having a viscosity of between 0.72 and 0.86 dl / g according to ASTM D4603 and a copolymer fraction of at most approximately 3%, adding a low-viscosity PET material. According to the method, the comminuted and dried PET material is melted and decontaminated to such a degree that it is suitable for applications in the food sector and the consumer goods sector.

Description

[0001] 1040 - 25227 1 22.04.2022

[0002] Process for producing an rPET plastic material for use in a thin-wall injection molding process and containers produced by the thin-wall injection molding process, such as cups, trays, tubs or ribbed packaging

[0003] Field of the invention

[0004] The present invention relates to a method for producing an rPET plastic material for use in a thin-wall injection molding process according to the preamble of claim 1 and to containers produced in the thin-wall injection molding process, such as cups, bowls, tubs or strip packaging, in particular for storing food.

[0005] State of the art

[0006] Containers for storing food, such as cups for yogurt, cream, salad dressings or containers for margarine, curd cheese and the like, are now either deep-drawn or manufactured using the thin-wall injection molding process.

[0007] Deep drawing creates a stamping grid that is difficult to recycle because it must be melted at least a second time. Many companies only partially manage internal recycling, i.e., the utilization of waste from their own production lines.

[0008] Unlike the deep-drawing process, the thin-wall injection molding process does not produce a lead frame. The thin-wall injection molding process is therefore becoming increasingly important for the production of food containers, especially because the largest quantities are processed in the food sector.

[0009] Polyolefins such as polypropylene (PP), high-density polyethylene (HDPE), and polystyrene such as high-impact polystyrene (HIPS) are currently being processed in both thermoforming and injection molding technologies. These materials are widely used, but have not yet achieved approval from the European Food Safety Authority for post-consumer recycling.

[0010] Since the EU's environmental objectives and legislation require plastic recycling, but the aforementioned materials are not approved for direct food contact, they can only be sold on the market for a limited period of time or with burdensome levies.

[0011] The standard PET types currently used for bottle production in a stretch blow molding process are predominantly linear PET types (no branched ones) with a low copolymer content of less than 5 wt.% and an intrinsic viscosity (IV) between 0.72 and 0.86 dl / g (according to ASTM D 4603). When PET is processed using the most commonly used one- or two-stage stretch blow molding process (injection stretch blow molding = ISBM), the material typically degrades to a viscosity between 0.01 and 0.09 dl / g, while the copolymer content remains essentially unchanged. Studies have shown that the copolymer content can increase slightly, as even atypical packaging with higher copolymer content sometimes enters the recycling stream and cannot be easily sorted out. In addition, reactions occur in which more diethylene glycol (DEG) is formed and more DEG is incorporated into the polymer chain.

[0012] However, unlike the stretch blow molding process most commonly used for PET bottle production, thin-wall injection molding requires viscosities between 0.5 and 0.7 dl / g. This means that the material generated in the standard PET recycling process, including the regenerated material from it, cannot be used for the injection molding process.

[0013] According to recent legislation, the European packaging industry is required to use up to 35% recycled material in newly manufactured PET articles. This legal requirement applies to both the ISBM and injection molding processes. It would be desirable, in principle, for injection-molded articles made from low-viscosity material to be collected separately so that the recovered material could be reused for the production of injection-molded articles. Unfortunately, this is currently not possible for economic reasons, as economies of scale do not allow for this separate collection and recycling stream for very small quantities.

[0014] However, in the standard PET recycling stream, the low-viscosity injection-molded articles, which are usually only present in small quantities, do not cause any problems, since the "cross esterification" taking place in the melt causes the chain lengths to equalize and very low viscosities to build up quickly in the recycling plant, particularly through condensation in an SSP process.

[0015] PET for blow molding, with a viscosity of 0.72 to 1.4 dl / g according to ASTM D4603, is far too hard and tough to be used to produce complex, thin-walled parts. If injection-molded parts are to be produced at a typical pressure of up to 3000 bar, standard PET cannot be used with a typical wall thickness (L) to flow path (D) ratio of 1:100 to 1:350 (thin-wall injection molding up to 1:500), because large portions of the mold would then be impossible to fill.

[0016] PET materials are known to be virgin with a viscosity of 0.5 to 0.7 dl / g (ASTM D4603), which is designed precisely for these applications. However, there is no separate recycling stream specifically for these polyester types. Packaging manufacturers who wish to use this material will still have to demonstrate a recycled content of 25% to 50% in the future, depending on which legal regulation or voluntary commitment is binding for the distributor by 2025 or 2030. However, a much higher recycled content of 40 to 100% is usually required for polyester applications.

[0017] For injection-molded packaging, a PET recycling material with a viscosity of 0.5 to 0.7 dl / g is required. This sounds quite simple at first, as PET can be easily broken down to the desired viscosity using water and heat.

[0018] If 100 to 000 ppm of water is added to the most commonly used PET recycling material during PET injection molding, the PET will degrade exactly as planned to a viscosity of 0.5 to 0.7 dl / g, but this degradation (hydrolysis) will cause the material to become whitish and cloudy and semi-crystalline. Bubbles may also form. Uncontrolled crystallization results in sink marks, cavities, and severely distorted parts, which, due to their low viscosity and high residual stress, are far too brittle for their final use as packaging.

[0019] The main PET recycling stream available on the market consists primarily of PET bottles produced from a material with a viscosity of approximately 0.72 to 0.86 dl / g using a stretch blow molding process (ISBM process). This recycling stream has a viscosity that is too high for injection molding thin-walled parts. The recycled material from the main stream available on the market primarily contains PET ISBM bottles with a copolymer content of 2 to 3%. This copolymer content varies greatly depending on whether the recycled material contains a large amount of film and thermoformed articles, PET-G, or reusable bottles. In general, the copolymer content is too unstable to produce stable, thin-walled injection-molded parts from rPET that are not subject to uncontrolled crystallization.

[0020] Due to other components in the recycling stream, such as thermoforming film, and the degradation of PET during processing, the average viscosity of the recycled product is 0.02 to 0.09 dl / g lower than the original material. However, to be suitable for food contact, it must be decontaminated using heat and vacuum (or nitrogen). This decontamination can take place in a dryer before the recycling extruder, in the recycling extruder, or after the recycling extruder in a so-called SSP process. Combinations are also common.

[0021] During decontamination, not only is the gas removed, but the polyester fabric inevitably rebuilds under these conditions and the chains become longer.

[0022] Even though some highly degraded PET is available on the market, which would be suitable in terms of viscosity, its composition and contamination are unsuitable for the production of thin-walled PET injection-molded packaging. This is because it has not been decontaminated using a vacuum and, in addition, crystallizes too quickly.

[0023] It is known that PET can be specifically degraded by adding monoethylene glycol (glycolysis). WO0001997020886A1, for example, discloses a process that recycles previously used polyester materials by means of glycolysis and subsequent purification. Recycled PET is contacted with 1.1 to 10 mol of ethylene glycol per mol of dicarboxylic acid in the polyester at a temperature in the range of 150 to 300 °C for between 10 minutes and 4 hours to depolymerize the polyester and produce a reaction mixture containing monomeric and oligomeric dihydroxy species. Excess ethylene glycol is then removed, and the reaction mixture is dissolved in a hot solvent. The hot solution is then filtered to remove unwanted impurities. The solution is then cooled, and the dihydroxy species precipitate as a solid.

[0024] It is also known that PET undergoes cross- and trans-esterification through the addition of low-molecular-weight esters or polyesters, and that its viscosity adjusts under heat as polyesters are exchanged in the chain. Thus, a polyester with monomers A and B and a second polyester with monomers B and C can be transesterified to produce a third copolyester containing monomers of types A, B, and C in its chains. This is known for PET polyesters with isophthalic acid (IPA) and diethylene glycol (DEG), but also for PET copolyesters with naphthalenedicarboxylic acid (NDC) and furandicarboxylic acid (FDCA).

[0025] Unlike polypropylene (PP) or polystyrene (PS), polyethylene terephthalate (PET) is very sensitive to injection molding and quickly forms degradation products that manifest as gases, which immediately cause problems in PET thin-wall injection molding. Tests have shown that PET materials with a viscosity between 0.2 and 0.4 dl / g (measured according to ASTM D4603) can be injected, but either break during demolding or subsequently break during free fall from a height of 0.5 to 1.5 m.

[0026] Another disadvantage of containers made of PET material is that they tend to stick together if placed on top of each other or stacked immediately after production. The stacked or stacked containers are subsequently difficult to separate.

[0027] Task

[0028] The object of the present invention is to provide thin-walled injection-moulded

[0029] To propose a PET container, particularly for food storage, that is easy to demold and so stable that it does not shatter when dropped from a height of 1.5 m. Another goal is to provide an rPET material that is particularly suitable for thin-wall injection molding and contains the highest possible proportion of rPET obtained from the collection of post-consumer PET articles, particularly bias-molded PET bottles. Another goal is to propose an rPET material that can be injection molded at 1000 to 5000 bar, ideally at pressures between approximately 1500 and 2500 bar, particularly preferably at approximately 2100 bar, with a wall thickness to flow path ratio of 1:100 to 1:400, or up to 1:500 for thin-wall injection molding. In particular, it is a goal that the proposed material crystallizes only slowly. Another goal is that the material can be processed in such a way that it is transparent, i.e.It remains essentially crystal-clear, and no crystallization of the material scatters the light to the point where the contents are no longer visible. Another goal is to prevent the containers from sticking together when placed on top of each other or stacked after production.

[0030] Definitions:

[0031] In the context of the present invention, the term "viscosity" is understood to mean the intrinsic viscosity (IV) measured according to ASTM 4603-03 standard.

[0032] For the purposes of the present invention, "pure PET" means that PET has been sorted within the scope of current technological possibilities, so that the weight proportion of non-pure plastic is less than 2%, preferably less than 1%, and particularly preferably less than 0.5%. rPET is used herein as an abbreviation for recycled post-consumer PET.

[0033] "Bottle Grade PET Post-consumer Recycling Flake" is rPET processed into flakes which comes from the collection of post-consumer PET articles, in particular PET bottles

[0034] In the context of the present invention, ISBM-PET is understood to mean PET (including PET copolymers) that is suitable for use in an ISBM process, ie has an IV between 0.72 dl / g and 0.86 dl / g (viscosity measurement according to ASTM D4603).

[0035] In the context of the present invention, "chain breakers" are understood to mean chemical compounds that are suitable for degrading PET or for being incorporated into the polymer chain as a copolymer.

[0036] The term "flow path" refers to the distance between the injection point and the furthest point.

[0037] Containers include, in particular, cups, trays, and tubs. In the case of cups and tubs, the area enclosed by the edges of the container opening is generally larger than the base area. Furthermore, ribbed packaging with several adjacent trays or trays should also be considered containers.

[0038] Description

[0039] The invention relates to a process for producing an rPET plastic material for use in a thin-wall injection molding process with a ratio of wall thickness (L) to flow path (D) of 1 to 50 to 1 to 400, which process comprises the following steps: a) sorting, washing and comminuting post-consumer PET articles, ie PET bottles produced predominantly using the ISBM process, the PET material of which has an intrinsic viscosity of between 0.72 and 0.86 dl / g according to ASTM D4603, b) removing contaminants such as metal or paper before, simultaneously with or after process step a), c) subsequently drying the comminuted PET material, d) melting the comminuted and dried PET material and preferably decontamination thereof in a degassing or degassing process.Recycling extruder and subsequent granulation, with optional upstream and / or downstream solid phase condensation (SSP process), and e) production of a thin-walled injection-molded article from the PET material in an injection molding process.

[0040] According to the invention, the object is achieved in a method according to the preamble of claim 1 in that a low-viscosity virgin PET material, hereinafter referred to as "vPET", is added to the granulated material and the mixture of granules and vPET is reactively extruded and injected directly into an injection mold, wherein the process is conducted such that the intrinsic viscosity of the injection-molded article is reduced during extrusion to 0.5 to 0.7 dl / g and preferably to 0.5 to 0.65 dl / g and a thin-walled injection-molded article can be produced in an injection molding process in which the ratio of wall thickness (L) of the injection-molded article to the flow path (D) is from 1 to 50 to 1 to 400 or up to 1 to 500 in the case of thin-wall injection molding.What is new and surprising is that PET materials with a very short chain length and recycled PET from the bottle recycling stream with a long chain length can be combined in such a way that the material is ideally suited for injection molding the products. This process therefore has the advantage that rPET from a conventional PET recycling stream, in particular from bias-molded PET bottles, can also be used for the production of thin-walled injection-molded articles. Various tests have shown that by adding post-consumer recycling material with a higher viscosity of 0.6 to 1.0 dl / g, a mixing ratio can be adjusted so that the final product has a viscosity of 0.5 to 0.7 dl / g and can be demolded without problems or can withstand a drop height of 0.5 to 1.5 m during demolding.

[0041] Advantageously, the extrusion temperature and the residence time of the material in the extruder are selected so that the extruded material has an intrinsic viscosity (IV) greater than 0.5 dl / g, in particular between 0.52 and 0.68 dl / g, and preferably between 0.55 and 0.65 dl / g. Such material can be easily processed into thin-walled, strip-free articles.

[0042] Advantageously, vPET has an intrinsic viscosity between 0.2 and 0.45 dl / g, preferably between 0.25 and 0.40 dl / g, measured according to ASTM D4603. Virgin PET with the aforementioned viscosities can be ideally combined with rPET from bottle recycling.

[0043] The proportion of rPET in the mixture is advantageously between 20 and 80 wt.%, preferably between 30 and 70 wt.%, and particularly preferably between 40 and 60 wt.%. Such a high proportion of rPET also allows compliance with recent legal regulations.

[0044] To obtain stable and shatter-proof containers, the mixture is preferably extruded at temperatures between 250 and 350 °C.

[0045] It is advisable to preheat the mixture before entering the extruder. This prevents material degradation. The mixture is advantageously preheated to a temperature between 70 and 170°C, measured at the extruder inlet. This significantly reduces the shear forces acting on the mixture in the extruder.

[0046] According to a preferred process variant, the mixture is dried before extrusion so that the water content is less than 100 ppm. This allows for reproducible conditions to be created. It has been shown that the moisture content in the material is highly dependent on storage conditions. The longer a material is stored, the more it can absorb moisture. The higher the ambient humidity and the higher the ambient temperature, the faster the material absorbs moisture in granular form. The size of the granules, the packaging, and the handling and storage in the plant also play a role.

[0047] The inventors have determined that all factors influencing moisture content have a direct impact on the viscosity of the PET material. To avoid weather, storage conditions, and other influences, it is important to work with dried PET blends. The injection conditions must under no circumstances be dependent on weather, pellet size, or other factors influencing moisture content. For the implementation of the inventive process, a specific, consistently constant moisture content or a minimum moisture content below 100 ppm is desired. Drying of the PET material or the blend with rPET with hot air, nitrogen, or vacuum should preferably be carried out in such a way that the material does not build up uncontrollably in the dryer due to the removal of water, glycol, and diethylene glycol, thus making it unsuitable for thin-wall injection molding. For this purpose, the temperature and residence time must be adjusted accordingly.

[0048] Unlike the PET stretch blow molding process for bottles, very low drying conditions have proven successful, typically between 100 and 160°C, ideally with a residence time of 4 to 24 hours. When using dry air, the desired degree of dryness is to have a dew point between -80 and -10°C. Furthermore, an air flow between 0.5 and 3m³ is preferred. 3 / kg PET used in the drying process.

[0049] The aim is to achieve a viscosity of less than 0.01 dl / g in the dryer.

[0050] To produce containers from a mixture of vPET and rPET, an extrusion machine is required that can generate a pressure between 500 and 5000 bar, preferably between 1500 and 2500 bar.

[0051] Advantageously, an injection molding machine is used that can inject faster than 10 g / sec per cavity. This condition must be achievable if containers are to be produced from a mixture of vPET and rPET. Preferably, a PET bottle stream is used that contains particularly little contamination from polymers other than PET (e.g. PA blends). In the context of the present invention, particularly low is understood to mean that the proportion of PA blends, radical scavengers and other additives such as oxygen scavengers, acetaldehyde scavengers, UV absorbers, slip additives, infrared absorbers, etc. is less than 10 wt. %, preferably less than 5 wt. %, and particularly preferably less than 3 wt. %.

[0052] Advantageously, with an rPET content of preferably more than 30, 40, or 50%, a chain breaker is also added in process step e). By adding a chain breaker, the higher-viscosity material can be further degraded reactively to obtain a material with an intrinsic viscosity between 0.5 and 0.7 dl / g.

[0053] According to one process variant, either a specific amount of monoethylene glycol or a specific amount of water is used as a chain breaker. With the help of monoethylene glycol or water, the IV can be reduced by splitting the PET molecules directly during the injection molding process, allowing thin-walled articles to be produced.

[0054] Preferably, PET recycling material with a water content between 100 and 1000 ppm, and preferably between 300 and 1000 ppm, is used for extrusion. This means that the preceding drying and decontamination is preferably carried out to achieve the desired water content. Alternatively, the PET recycling material can be re-enriched with water after drying and / or decontamination (process steps c) and / or d)).

[0055] Instead of water, between 50 and 1000 ppm of monoethylene glycol can be added or dosed into the granulated material. This also leads to the desired reduction of the intrinsic viscosity during the injection process.

[0056] According to another preferred process variant, compounds are used as chain breakers, which can be incorporated into the PET polymer molecules, thus leading to a higher copolymer content. Surprisingly, by increasing the copolymer content, the intrinsic viscosity can be reduced and the crystallization rate slowed to such an extent that thin-walled, transparent, and stripe-free articles can be injected. This effect was unexpected, as it was expected that the material would become cloudy. Furthermore, it was expected that bubbles and small cracks would form in the injection-molded article, similar to the process that occurs when water is used to degrade the rPET.By adding suitable chain breakers and incorporating them into the PET polymer chains, the copolymer content can be increased during extrusion by at least 1%, preferably at least 2%, and particularly preferably by at least 3%, as desired, and the viscosity of the material can be reduced. The proposed process exploits the fact that higher copolymer contents alter the PET molecular chain in such a way that crystallization is inhibited or suppressed.

[0057] Monoethylene glycol is known as a chain breaker. However, monoethylene glycol is already a component of the PET chain. Adding monoethylene glycol breaks the chain but does not increase the copolymer content.

[0058] Diols, which can be incorporated into the chain as copolymers, are advantageously used as chain breakers. Preferred diols are diethylene glycol, propylene glycol, and / or butylene glycol, but also cyclic polyols such as 3,9-bis(l,l-dimethyl-2-hydroxyethyl)-2,4,8,10-tetraoxaspiro[5.5]undecane (spirol glycol).

[0059] Another process variant uses dicarboxylic acids as chain breakers. These are also very suitable for reducing chain lengths.

[0060] Preferred dicarboxylic acids as chain breakers are isophthalic acid, 2,5-furandicarboxylic acid and / or naphthalenedicarboxylic acid, since these can be incorporated into the polymer chain as a copolymer.

[0061] According to an advantageous process variant, diesters are used as chain breakers. Suitable diesters include dimethyl isophthalate and / or bis(hydroxyethyl)isophthalate. The diols, dicarboxylic acids, and diesters can be used individually or as mixtures.

[0062] PET copolymer chains with 2 to 20 monomers containing isophthalic acid (I PA), furandicarboxylic acid (FDCA), naphthalenedicarboxylic acid or diethylene glycol are advantageously used as chain breakers.

[0063] The proportion of isophthalic acid (IPA), furandicarboxylic acid (FDCA), naphthalenedicarboxylic acid or diethylene glycol is advantageously between 3 and 10 wt.%.

[0064] It is also conceivable to use compounds containing an alcohol group and a dicarboxylic acid or an ester group as chain breakers. Examples of such compounds are hydroxyethanoic acid (hydroxyacetic acid), hydroxypropanoic acid, and hydroxybutanoic acid.

[0065] Advantageously, the chain breaker is added in process step f) before or during melting of the granulate.

[0066] Advantageously, the post-consumer PET material used before drying and recycling process step d) has a copolymer content of a maximum of approximately 3% and preferably a copolymer content of a maximum of 2.5%.

[0067] Process step f) is preferably carried out such that the total copolymer content in the rPET is increased to 2.5 to 8%, preferably to 3.0 to 8%, and particularly preferably to 3.5 to 8%. An increased copolymer content leads to a reduction in the IV and simultaneously a slowing of the crystallization rate, which makes the injection molding of thin-walled articles possible.

[0068] Advantageously, decontamination of the post-consumer incoming goods is carried out by degassing the volatile contaminants at an elevated temperature between 70° and 330°C, preferably between 180 and 220°C before the recycling extruder, ie process step d), and / or in the recycling extruder and / or after the recycling extruder, by means of a vacuum of less than 0.2 bar absolute, or

[0069] Nitrogen purging occurs between 0.1sec and 20 hours, preferably during 4 to 10 hours.

[0070] After extrusion in the recycling extruder, the granules can optionally be degassed in an SSP reactor at a temperature of 180 to 220°C for 1 to 15 hours, preferably 4 to 10 hours, under vacuum. This simultaneously undergoes polymerization (polycondensation).

[0071] Decontamination using heat and vacuum can be performed in the extruder and the downstream SSP reactor. Of course, nitrogen can also be used instead of vacuum to remove contaminants. Heat and vacuum or a protective gas atmosphere (e.g., nitrogen) can generally be used during material preparation before the recycling extruder.

[0072] Preferably, the material is decontaminated by a subsequent treatment in the SSP reactor, but the viscosity is not increased so high that it can be turned into a PET that is well suited for the stretch blow molding process, but rather leaves the SSP with a viscosity of < 0.72 dl / g.

[0073] Preferably, the material is decontaminated before the actual injection molding process step f) to such an extent that it is suitable for applications in the food and / or consumer goods sector.

[0074] It is advantageous to produce a masterbatch from the chain breaker, which is then metered directly into the injection molding machine's inlet. This has the advantage that the chain breaker content can be easily controlled and ensures thorough mixing in the extruder.

[0075] Preferably, the shredded PET recycling material is dried after the washing process at temperatures between 60 and 180°C for 1 to 8 hours.

[0076] Advantageously, the intrinsic viscosity of the material used is reduced by 0.05 to 0.3 dl / g, preferably 0.1 to 0.25 dl / g, through the reactive extrusion in process step f).

[0077] Advantageously, the crystallization fraction of the treated rPET injection-molded part is reduced by at least 10% compared to the untreated material without increased copolymer content.

[0078] According to a preferred process variant, the temperature during extrusion and the amount of Chain Breaker are selected so that the extruded material has an IV greater than 0.5 dl / g and in particular between 0.5 and 0.7 dl / g.

[0079] Advantageously, between 0.05 wt.% and 2.8 wt.%, preferably between 0.1 wt.% and 1.0 wt.% and particularly preferably between 0.1 wt.% and 0.6 wt.%, of chain breaker are added to the PET of process step f).

[0080] The residence time of the polyester material in the injection molding unit or recycling extruder is advantageously between 20 and 400 seconds, preferably between 30 and 300 seconds, and particularly preferably between 40 and 200 seconds. With the aforementioned residence times, the IV of the polyester material can be reduced by 0.05 to 0.3 dl / g in the presence of a chain breaker during extrusion.

[0081] According to a further embodiment of the invention, the extruded melt is filtered before granulation. According to a further embodiment of the invention, the extruded melt is pressed through a perforated filter with a hole size between 30 pm and 300 pm, and preferably between approximately 50 pm and 100 pm. This ensures that the melt has sufficient purity, and turbidity and impurities can be prevented in the final injection-molded product.

[0082] According to a further embodiment of the invention, the rPET material is degassed and decontaminated during extrusion in process step d)

[0083] According to another variant, the melt is divided into thin layers or strands in the extruder. This increases the surface area of ​​the material and allows for very rapid decontamination.

[0084] According to one embodiment of the invention, the extrusion takes place in a vacuum or in a protective gas atmosphere, in particular under nitrogen.

[0085] In a further embodiment of the process, it is an alternative form of injection molding or a mixed form of injection molding in the sense of compression molding or continuous compression molding,

[0086] A further embodiment of the process involves an alternative form of injection molding or a mixed form of injection molding in the sense of spray foaming.

[0087] The present invention also relates to a container produced by injection molding, in which the base area of ​​the container is smaller than the area enclosed by the edges of the opening of the container, optionally with one or more chambers, in particular for the storage of foodstuffs, preferably with an acetaldehyde and formaldehyde value of less than 50 ppm and a wall thickness between 0.1 and 0.5 mm, preferably with a wall thickness between 0.2 and 0.4 mm, and particularly preferably with a wall thickness between 0.24 and 0.34 mm and a pouring area that is larger than the base area.

[0088] According to the invention, the container is made from a blend of virgin PET with at least 5 wt.% rPET, obtainable from the reprocessing of PET bottles, mostly produced using the ISBM process, whose PET material has an intrinsic viscosity between 0.72 and 0.86 dl / g according to ASTM D4603, whereby the blend produced from the virgin PET and the rPET has a viscosity between 0.5 and 0.7 dl / g. These can be designed as cups, trays, tubs, or as ribbed packaging, the base area of ​​which is smaller than the area enclosed by the edges of the container opening.

[0089] Preferably, the virgin PET material has an intrinsic viscosity between 0.2 and 0.45 dl / g, preferably between 0.25 and 0.40 dl / g. Preferably, rPET is used, which has an intrinsic viscosity between 0.6 and 1.0 dl / g.

[0090] The container is advantageously designed as a cup, tray, tub, or as a ribbed container. According to an advantageous embodiment, ribs or ribs are provided or formed on the sides of the container to prevent containers placed on top of one another or stacked from sticking together. This has the advantage that no large-area contact area is possible between the containers, for example, in the case of stacked containers, thus preventing sticking together.

[0091] To prevent the freshly manufactured containers from sticking together, the container can alternatively have an average surface roughness between 0.2 and 0.4 pm, and preferably between 0.25 and 0.35 pm, ideally approximately 0.3 pm, as measured according to DIN EN ISO 4287-2010. This can also prevent the surfaces from sticking together.

[0092] Another way to prevent sticking is to add an anti-blocking agent to the mixture. Anti-blocking agents can be natural or synthetic silica, talc, calcium carbonate, glass microspheres, PMMA microspheres, or cross-linked silicone microspheres.

[0093] Another way to prevent sticking would be to use labels applied during the injection molding process. It is important that the labels used meet recycling requirements.

[0094] Advantageously, the container has a gate point recessed into a depression in the bottom surface of the container, so that the remaining bottom surface forms a flat base. This has the advantage that the container can rest flat.

[0095] Advantageously, the opening of the container can be closed by means of a closure cap that can be snapped into the opening edge.

[0096] According to another embodiment, the opening can be closed with a sealing film that is compatible with the recycling requirements.

[0097] Example containers are shown in the figures. It shows:

[0098] Figure 1 shows a rectangular container 11a in the shape of a bowl with a base 13, four side walls 15, and a flat peripheral edge 17. Webs 19 are formed on the side walls, minimizing the contact area between stacked containers 11a. The container 11a has an opening 21 whose area is larger than the base area.

[0099] Figure 2 shows a low container 11b with several chambers 23.

[0100] Figure 3 shows another possible embodiment of a container 11c with eight regularly arranged chambers 23. The bottom area of ​​each chamber is smaller than the chamber openings.

[0101] Figure 4 shows a yogurt cup lld, which is covered by a removable film

[0102] Description of the procedure:

[0103] For the process, post-consumer PET material is used which has a viscosity between approximately 0.7 and approximately 0.86 dl / g. Preferably, a PET bottle stream is used which contains particularly little contamination from polymers other than PET (e.g. PA blends). In the context of the present invention, particularly little is understood to mean that the proportion of PA blends, radical scavengers and other additives such as oxygen scavengers, acetaldehyde scavengers, UV absorbers, slip additives, infrared absorbers, etc. is less than 10 wt. %, preferably less than 5 wt. %, and particularly preferably less than 3 wt. %.

[0104] In a first process step, post-consumer PET bottles are sorted by type, washed, cut, and contaminants such as metal, paper, etc. are removed. During sorting, the collected PET material is first sorted by color, and then, preferably, foreign plastics are removed.

[0105] In a second process step, the cut PET flakes are dried.

[0106] In a third process step, the rPET is decontaminated and granulated in a degassing or recycling extruder.

[0107] In a fourth process step, a specific amount of a low-viscosity virgin PET (vPET) is added to the granules, and then the resulting mixture of granules and vPET is extruded and preferably injected directly into an injection mold. Under these conditions, the average molecular weight of the rPET and thus the intrinsic viscosity decreases significantly during extrusion in the injection unit. The addition of the chain breaker is primarily intended for the injection molding unit, but can be added concurrently or, in rare cases, alternatively in the recycling extruder. By adding the chain breaker not only in the extruder of the injection molding machine, but also in the extruder of the recycling machine, the recycled material can be specifically broken down during the extrusion process and enriched with copolymers.

[0108] Examples of implementation:

[0109] Example 1:

[0110] 50% of the cup weight is made from virgin PET with a viscosity of 0.40 dl / g with 50% regrind from post-consumer PET bottles with an average IV of 0.72 dl / g and an average copolymer content and with 1% isphthalic acid and 1.3% diethylene glycol are mixed with 0.5% diethylene glycol in the recycling extruder and extruded at an average temperature of 290°C. Surprisingly, the viscosity after the recycling extruder reduced much more than usual to a value of just 0.58 dl / g. A subsequent SSP (6h at 220°C, in order to achieve food contact compliance, only reduced the granulate to 0.72 dl / g). The mixture of both materials resulted in a viscosity of the cup material of 0.55 dl / g, which made this cup injection moldable with a flow path of 120mm and a wall thickness of 1mm.

[0111] Example 2:

[0112] To 30% of the cup weight of virgin PET with a viscosity of 0.40 dl / g, 70% regranulate is added. The regranulate comes from post-consumer bottle regrind, which is converted in an SSP reactor in a standard recycling process into granules for the stretch blow molding process with a viscosity of 0.76 dl / g. The dried granules and the regranulate are dried together (180°C, 6 h, dried air, 2 m 2 The mixture was fed into an injection molding machine at a temperature of 100°C (air / kg PET dew point -35°C) and mixed with 0.1% diethylene glycol. In the melt, the diethylene glycol degraded the PET to a viscosity of 0.61 dl / g, and surprisingly, a preform with a wall thickness of just 1 mm and a flow path of 120 mm could be molded.

[0113] The invention provides a process by which previously used polyester materials, including either production waste polyester materials and / or used polyester materials, can be conveniently and efficiently recovered and purified. The collected PET material, which has an intrinsic viscosity between 0.72 and 0.86 dl / g according to ASTM D4603, is first color-sorted, preferably re-sorted, cut into small pieces (ground), washed, dried, extruded, and preferably simultaneously decontaminated, granulated, and optionally built up and decontaminated again. Then, it is extruded into a thin-walled article with the addition of a low-viscosity virgin PET material with an intrinsic viscosity between 0.2 and 0.45 dl / g. It is important that the intrinsic viscosity of the injection-molded article is reduced to 0.5 to 0.7 dl / g and preferably to 0.5 to 0.65 dl / g during the extrusion process.

[0114] The invention relates to a process in which a starting material for injection molding with a viscosity between 0.50 and 0.7 dl / g is produced from a recycled post-consumer PET with a viscosity between 0.72 and 0.86 dl / g according to ASTM D4603 and a maximum copolymer content of approximately 3 wt.%. During the process, the shredded and dried PET material is melted and decontaminated to such an extent that it is suitable for applications in the food and consumer goods sectors. A specific amount of a virgin PET product is added to the rPET material in the melt of the recycling extruder and / or preferably the melt of the injection unit in order to reduce the viscosity and optionally enrich the PET with copolymers.

Claims

Patent claims 1. A process for producing an rPET plastic material for use in a thin-wall injection molding process with a wall thickness (L) to flow path (D) ratio of 1:50 to 1:400 or up to 1:500 in thin-wall injection molding, in which process a) post-consumer PET articles, mostly PET bottles produced using the ISBM process, whose PET material has an intrinsic viscosity between 0.72 and 0.86 dl / g according to ASTM D4603, are sorted, washed, and crushed, b) contaminants such as metal or paper are removed before, simultaneously with, or after process step a), c) the crushed PET material is subsequently dried, d) the crushed and dried PET material is then melted and preferably in a degassing or...a recycling extruder is decontaminated and subsequently granulated, and e) a thin-walled injection-molded article is produced from the PET material in an injection molding process, characterized in that f) in process step e) a low-viscosity virgin PET, hereinafter referred to as "vPET", is added to the granulated material and the resulting mixture of granules and vPET is extruded and injected directly into an injection mold, wherein the process is carried out in such a way that the intrinsic viscosity of the injection-molded article is reduced to 0.5 to 0.7 dl / g and preferably to 0.5 to 0.65 dl / g during extrusion and a thin-walled injection-molded article can be produced in an injection molding process in which the ratio of wall thickness (L) of the injection-molded article to flow path (D) is from 1 to 50 to 1 to 400.

2. Method according to claim 1, characterized in that the temperature during extrusion and the residence time of the material in the extruder are selected such that the extruded material has an intrinsic viscosity (IV) greater than 0.5 dl / g, in particular between 0.52 and 0.68 dl / g and preferably between 0.55 and 0.65 dl / g.

3. Method according to claim 1 or 2, characterized in that the vPET used has an intrinsic viscosity between 0.2 and 0.45 dl / g, preferably between 0.25 and 0.40 dl / g.

4. Method according to claim 1 or 2, characterized in that the proportion of rPET in the mixture is between 20 and 80 wt.%, preferably between 30 and 70 wt.% and particularly preferably between 40 and 60 wt.%. A method according to any one of claims 1 to 4, characterized in that the mixture is extruded at temperatures between 250 and 350 °C. A method according to any one of claims 1 to 5, characterized in that the mixture is preheated before entering the extruder. A method according to claim 6, characterized in that the mixture is preheated to a temperature between 70 and 170 °C, measured at the extruder inlet. A method according to any one of claims 1 to 7, characterized in that the mixture is dried before extrusion so that the water content is less than 100 ppm. A method according to any one of claims 1 to 8, characterized in that the extrusion takes place at a pressure between 500 and 5000 bar, preferably at a pressure between 1500 and 2500 bar, and particularly preferably at a pressure between 2000 and 2200 bar.A method according to any one of claims 1 to 9, characterized in that an injection molding machine is used which can inject per cavity faster than 10 g / sec. A method according to any one of claims 1 to 10, characterized in that a PET bottle stream is used in which the proportion of PA blends, radical scavengers, and other additives such as oxygen scavengers, acetaldehyde scavengers, UV absorbers, slip additives, infrared absorbers, etc., is less than 10 wt.%, preferably less than 5 wt.%, and particularly preferably less than 3 wt.%. A method according to any one of claims 1 to 13, characterized in that a solid-state condensation (SSP process) is performed upstream and / or downstream of process step d). A method according to any one of claims 1 to 12, characterized in that a chain breaker is additionally added in process step e) when the rPET content is preferably more than 50%.A process according to claim 13, characterized in that either a specific amount of monoethylene glycol or a specific amount of water is used as the chain breaker. A process according to claim 13, characterized in that diols, dicarboxylic acids, diesters, or PET copolymer chains with 2 to 20 monomers containing isophthalic acid (11PA), furandicarboxylic acid (FDCA), naphthalenedicarboxylic acid, or diethylene glycol are used as the chain breaker. A process according to claim 14, characterized in that compounds comprising an alcohol group and a dicarboxylic acid or an ester group, such as hydroxyethanoic acid, hydroxypropanoic acid, hydroxybutanoic acid, etc., are used as the chain breaker. A process according to any one of claims 11 to 16, characterized in that the addition of the chain breaker in process step f) takes place before or during the melting.

18. Method according to one of claims 13 to 17, characterized in that chain breaker compounds are used which can be incorporated into the PET polymer molecules and thus lead to a higher copolymer content.

19. Method according to claim 18, characterized in that the copolymer content is increased by at least 1%, preferably by at least 2% and particularly preferably by at least 3% compared to the PET starting material.

20. Method according to one of claims 1 to 19, characterized in that the post-consumer PET starting material used has a copolymer content of a maximum of approximately 3% and preferably a copolymer content of a maximum of 2.5% before drying and recycling process step d).

21. Method according to one of claims 1 to 20, characterized in that the process step f) is carried out such that the copolymer content in the rPET is increased to a total of 2.5 to 8%, preferably to 3.0 to 8% and particularly preferably to 3.5% to 8%.

22. Method according to one of claims 1 to 21, characterized in that decontamination of the post-consumer input material is carried out by degassing the volatile contaminants at an elevated temperature between 70° and 330°C, preferably between 180° and 220°C, before the recycling extruder, i.e., process step d), and / or in the recycling extruder and / or after the recycling extruder, by means of a vacuum of less than 0.2 bar absolute, or nitrogen purging for between 0.1 sec and 20 hours, preferably for 4 to 10 hours.

23. Method according to one of claims 1 to 22, characterized in that the material is decontaminated before the actual injection molding process step f) to such an extent that it is suitable for applications in the food and / or consumer goods sector.

24. Method according to one of claims 1 to 23, characterized in that a masterbatch is produced with material from process step d) and a chain breaker and this masterbatch is metered directly into the feed of the injection molding machine.

25. Method according to one of claims 1 to 24, characterized in that in process step c) the comminuted PET material is dried at temperatures between 60 and 180°C and preferably for 1 to 8 hours.

26. Method according to one of claims 1 to 25, characterized in that the crystallization fraction of the treated rPET injection molded part is reduced by at least 10% compared to the untreated material without increased copolymer content. TI. Method according to one of claims 1 to 26, characterized in that the extruded melt is filtered before granulation. A method according to any one of claims 1 to 11, characterized in that the extruded melt is pressed through a perforated filter with a hole size between 30 pm and 300 pm, and preferably between approximately 50 pm and 100 pm. A method according to any one of claims 1 to 28, characterized in that the material is degassed during extrusion in process step d). A method according to any one of claims 1 to 29, characterized in that the melt is divided into thin layers or strands in the extruder. A method according to any one of claims 1 to 30, characterized in that the extrusion in process step f) takes place in a vacuum or in a protective gas atmosphere, in particular under nitrogen. A method according to any one of claims 1 to 31, characterized in that the residence time of the polyester material in the injection molding unit or recycling extruder is between 20 and 400 see, preferably between 30 and 300 see.and particularly preferably between 40 and 200 see. Method according to one of claims 1 to 32, characterized in that the method is an alternative form of injection molding or a hybrid form of injection molding in the sense of compression molding or injection foaming. Containers produced by injection molding, such as cups, trays, tubs or tray packaging, in particular for the storage of food, with an acetaldehyde and formaldehyde value of less than 50 ppm and a wall thickness between 0.1 and 0.5 mm, preferably with a wall thickness between 0.2 and 0.4 mm, and particularly preferably with a wall thickness between 0.24 and 0.34 mm and a pouring surface that is larger than the base surface, characterized in that the container is made from a mixture of virgin PET and at least 5 wt.-% rPET obtainable from the reprocessing of PET bottles produced largely using the ISBM process, the PET material of which has an intrinsic viscosity between 0.72 and 0.86 dl / g according to ASTM D4603, wherein the mixture produced from the virgin PET and the rPET has a viscosity between 0.5 and 0.7 dl / g. Container according to claim 3343, characterized in that the virgin PET has an intrinsic viscosity between 0.2 and 0.45 dl / g, preferably between 0.25 and 0.40 dl / g. Container according to claim 34 or 35, characterized in that the rPET used has an intrinsic viscosity between 0.6 and 1.0 dl / g. Containers according to claims 34 to 36, characterized in that the container is designed as a cup, tray, tub, or as a ribbed container. Containers according to any one of claims 34 to 37, characterized in that ribs or flanges are provided on the side surfaces to prevent stacked or placed containers from sticking together. Containers according to any one of claims 34 to 38, characterized in that the container has an average surface roughness between 0.2 and 0.4 pm, and preferably between 0.25 and 0.35 pm, ideally approximately 0.3 pm, as measured according to DIN EN ISO 4287-2010. Containers according to any one of claims 34 to 39, characterized in that antiblocking agents are added to the mixture.Container according to claim 40, characterized in that natural or synthetic silica, talc, calcium carbonate, glass microspheres, PMMA microspheres, or cross-linked silicone microspheres are used as the antiblocking agent. Container according to any one of claims 34 to 41, characterized in that the base area of ​​the container is smaller than the area enclosed by the edges of the opening of the container. Container according to any one of claims 34 to 42, characterized in that the container has an injection point which is recessed in a depression in the area of ​​the base area of ​​the container such that the remaining base area forms a flat surface. Container according to any one of claims 34 to 43, characterized in that the opening can be closed by means of a cap that snaps into the edge of the opening.Container according to one of claims 34 to 44, characterized in that the opening can be closed by means of a sealing film.

Images