PL248661B1 - Method of manufacturing polyester packaging with increased thermal resistance intended for food products poured hot and/or intended for sterilization - Google Patents

Abstract

The subject of the application is a method for manufacturing polyester packaging with increased thermal resistance for hot-filled and/or sterilizable products. The method involves heating PET recyclate in the form of regrind or granulate, or in the form of PET/PE blends in the solid state, in a flow of hot air to a temperature of 20°C to 80°C under reduced pressure and/or in an inert gas flow. After drying, the raw material is fed to a main single- or twin-screw extruder and extruded into a continuous film using a device equipped with one main extruder and optionally additional extruders. Optionally, in a co-extrusion block, the molten material streams from the main extruder and optionally additional extruders are combined into one, obtaining a multi-layer system, wherein the amount of recyclate in the multi-layer film is greater than 80%. In the second stage, the cooled foil is directed to the thermoforming machine and is first heated in the preheating station to a temperature of 50 - 60 C, and then in the main heating station with one or two heating plates to a sheet surface temperature ranging from 70 C to 160 C, after which the foil is formed in the mold cavity, the entire forming cycle lasts from 2 to 5 seconds, and the finally formed package is cut out.

Description

The subject of the invention is a method for manufacturing polyester packaging with increased thermal resistance intended for food products poured hot and/or intended for sterilization with assumed thermal resistance in the temperature range of 80-100°C.

Currently, food contact packaging with increased thermal resistance for hot-filled products and/or intended for sterilization before filling is not manufactured from polyester. Films used for packaging for hot-filled products and/or intended for sterilization are made from polypropylene or CPET, i.e., polyester with an increased crystalline phase content. The thermal resistance of standard PET packaging is approximately 60-70°C. Currently, packaging with increased thermal resistance is not manufactured from films produced using recycled materials, especially laminate recyclates. Recycling packaging made from laminates (e.g., PET/PE) or coextruded films is particularly difficult because these materials combine layers of materials with different properties and processing capabilities. Reprocessing such materials is therefore difficult. Products obtained by mixing these materials have different properties than their layered counterparts and are often not suitable for reuse. For example, after grinding and melting, a PET/PE laminate becomes a blend of two incompatible materials exhibiting properties different from those of pure materials. Such a blend is characterized by, for example, low transparency/high haze, which prevents the reuse of such post-production waste in the production of transparent polyester films. The problem with recycling laminated waste concerns both the different processing capabilities of the materials it comprises and the challenges of preparing such a raw material for processing, such as drying. PET is a material that readily undergoes hydrolytic degradation under processing conditions, so it must be thoroughly dried before processing. The drying temperature of PET is significantly higher than the melting point of PE. Therefore, the preparation and drying of PET/PE raw material requires the development of a technology. In the case of solid films, moisture removal can be achieved during extrusion by connecting a vacuum-generating pump to the first zones of the cylinder. When extruding foamed films, it will be necessary to dry the raw material at a lower temperature (to avoid sticking) and, therefore, equip the dryers with systems that facilitate moisture removal at lower temperatures under reduced pressure. Both solid and foamed films can be used to produce packaging with increased thermal resistance. Compared to solid films, packaging made from foamed films has better thermal insulation properties and, due to its lower density, a reduced unit weight. Regrind from PET/PE laminate is a good material for producing films for packaging hot-filled products or when sterilization is required, such as for the dairy industry. In this application, film turbidity is desirable because dairy products age more quickly when exposed to light. Effective PET foaming is achieved through the use of chemical and physical foaming agents.

US 6600143 B2 describes polypropylene containers intended for microwaveable products, such as "ready meals." The containers are made of a multilayer film, with the inner layer being expanded polypropylene and the outer layers being unexpanded polypropylene with talc. These containers are characterized by high deformation resistance and thermal resistance. However, polypropylene materials have a low oxygen barrier, so in many applications, an additional barrier-enhancing layer is added, which hinders material recycling. Furthermore, these containers do not contain recycled materials.

US 2012/0232175 (A1) describes products made from foamed PET and methods for their production. The method according to the invention involves mixing the material with a physical foaming agent, which is a mixture of carbon dioxide and nitrogen (in a ratio of 4/1 to 1/1), and extruding a sheet intended for thermoforming. The resulting products are obtained from virgin PET granulate and are characterized by thermal resistance up to approximately 70°C. These materials are therefore not suitable for hot-poured products or those intended for sterilization. The presented production method does not use recycled materials, which results in high-waste production.

EP 2081745 (A1) describes a method for thermoforming a low-crystalline expanded polyester film to produce a container with improved thermal resistance. The method comprises the steps of heating a sheet of expanded polyester to a preforming temperature in contact with a heating plate and cooling the heated sheet of expanded polyester on an unheated mold element. The containers thus formed are characterized by high temperature resistance (approx. 200°C) and are intended for packaging ready-to-eat meals heated in microwaves or ovens. These containers are characterized by increased thermal resistance due to the transformation of amorphous PET (APET) during packaging production into a partially crystalline form (CPET). Containers produced in this way achieve increased thermal resistance by increasing the crystalline phase content, and not, as in the invention, by introducing additional layers composed of materials with a chemical structure different from PET. Furthermore, the containers produced in this way are not made from recycled laminates.

The invention US 2011/0221097 (A1) relates to a method for producing polyester sheets from virgin PET pellets and recycled PET intended for forming food containers. The method according to the invention comprises adding epoxy polymer chain extenders to a recycled PET flake; loading the mixture into an extruder; melting the mixture while simultaneously degassing, increasing the molar mass of the PET, and capturing by-products; and co-extruding the PET into a sheet, where the layer made from recycled PET constitutes the inner layer, while the outer layers are virgin PET. The recycled raw material does not originate from recycled laminates, the resulting film is not foamed, and containers made from this film are characterized by thermal resistance up to a maximum of 70°C.

The invention EP 0182378 (B1) concerns polyester materials used to produce packaging with improved mechanical properties and a higher gas barrier compared to packaging made from pure poly(ethylene terephthalate). The presented materials are made from poly(ethylene terephthalate) and a copolymer based on poly(ethylene isophthalate) and an aliphatic hydroxy acid in the form of a blend or multilayer structure. These materials are not produced in foamed form and are characterized by lower thermal resistance than pure PET, below 70°C, which varies depending on the poly(ethylene isophthalate) content. Furthermore, the described method does not use recycled raw materials.

The invention, US 5250333, concerns polyester materials with increased thermal resistance for the production of packaging intended for hot-poured products, made from poly(ethylene terephthalate) modified with a polyhydric alcohol and 2,6-naphthalenedicarboxylic acid. These materials are characterized by thermal resistance up to approximately 120°C due to the higher glass transition temperature of the copolyester compared to pure PET. The packaging is not foamed and is made from recycled materials, especially recycled laminates.

The invention EP 0390723 (B1) relates to a method for producing foamed materials, which comprises: supplying a thermoplastic resin to an extruder and is characterized in that the thermoplastic resin comprises from about 94 to about 99% by weight of polyethylene terephthalate and from about 1 to about 6% by weight of polyolefin; mixing an inert gas into the molten thermoplastic resin in the extruder; extruding the resin through a die to produce a foamed amorphous sheet having a density in the range of from about 0.4 to about 1 g/ ^cm3 and thermoforming the sheet in a heated mold to produce the final product. The polyethylene added to the extruder in small quantities is in the form of the original granulate and is not recovered from recycled laminates. The increased thermal resistance is achieved by transforming APET into CPET, not by introducing an additional layer.

The aim of the invention was to develop a method for manufacturing PET packaging with increased thermal resistance, made from polyester film containing recycled materials (including laminate recyclates), suitable for contact with food. These packaging are intended for hot-filled products and/or for sterilization.

The packaging production process is a three-stage process consisting of recyclate drying, film extrusion, and thermoforming. Mixtures of raw materials with varying bottle flake and regrind contents and varying bulk densities were prepared. PET/PE regrind/PET bottle flake blends were tested in weight proportions of 10/90, 20/80, 30/70, 40/60, 50/50, 60/40, 70/30, 80/20, and 90/10, respectively. In the first stage, recyclates in the form of regrind or granulate, or blends with a PET to PET/PE ratio of 1:9-9:1 and an intrinsic viscosity of 0.6 dl/g to 1.2 dl/g, are heated in a heater in a hot air flow to a temperature close to the drying temperature (20°C to 80°C). Once the desired temperature is reached, the material is transported through a suction line to a tower with a conveyor floor, where it is held for 1 to 10 hours under reduced pressure of 3 to 12 mbar and/or in an inert gas flow that facilitates moisture removal (2.78-10-8 ^m3 /s/kg - 55.56-10-8 ^m3 /s/kg). In the second stage, the material is fed to a main single- or twin-screw extruder and extruded into film in a continuous process using a device equipped with one main extruder and optional additional extruders. Optional additional extruders can be fed with pre-plasticized virgin material. Previously prepared mixtures are fed through the dosing systems of individual extruders, plasticized and homogenized together with viscosity and impact modifiers, fillers, dyes, compatibilizers, chemical foaming agents in the plasticizing system of the main extruder and additional extruders, in which subsequent zones of extruder "A" are heated to a temperature in the range of 240-260° C and from 240 to 270° C on extruder "B" in the case of solid films, and subsequent zones of extruder "A" are heated to a temperature in the range of 240-260° C and from 230 to 260° C on extruder "B" in the case of foamed films, growing along the extruder and through the movement of the screws it is forced through the flow channels, the extruder filter unit, the co-extrusion block and the extrusion head. In the coextrusion block, the molten plastic streams from the main extruder and the secondary extruders are combined into a single stream, creating a multilayer system with varying structures depending on the insert used. This results in a B, AB, or ABA layer system, with up to 90% recyclate in the multilayer film. In the third stage, the cooled film is directed from a roll or directly from the extruder to the thermoforming machine. The film is first heated in a preheating station to a temperature of 50-60°C, and then in the main heating station, using one or two heating plates, to a sheet surface temperature ranging from 70°C to 160°C. Afterwards, the film is formed in the mold cavity, and the formed packages are collected. The entire forming cycle takes 2 to 5 seconds.

The drying process is preferably carried out in a dryer with an inert gas flow of 5.56-10-8 ^m3 //s/kg of raw material.

Nitrogen and/or carbon dioxide are preferably used as the inert gas.

Preferably, the foamed films are extruded with an inert gas flow of 8.33-10 ^-5 kg/s 16.67-10 ^-5 kg/s.

Cooling of the polyester film is preferably carried out on a cooling roller.

Preferably, used PET bottles and packaging, waste from the extrusion and thermoforming processes, PET and PET/PE bottle preforms and packaging are used as PET and PET/PE recyclates.

Preferably, physical and/or chemical foaming agents are used as foaming agents.

Liquids with low boiling points or volatile hydrocarbons or inert gases are preferably used as physical foaming agents.

Carbon dioxide or nitrogen are preferably used as inert gases in the foaming step.

Preferably, the packaging is cut out in the forming station or in a separate station behind the forming station.

The resulting films have a density ranging from 0.05 g/ ^cm3 to 1.35 g/ ^cm3 and a thickness ranging from 0.3 mm to 2 mm. The polyester film obtained by this method is multilayer. It is preferable to use unfoamed thermoplastic layers as the outer layers or the outer layer, as they facilitate welding with the upper film and/or enable printing. The outer layers are applied by coextrusion.

The packaging according to the invention is characterized by increased thermal resistance compared to APET packaging. The main goal of this invention is to obtain packaging with similar properties for food contact with up to 90% recycled content. The cutting station is located within the forming station or in a separate station after the forming station. The material remaining after cutting the packaging in the form of an openwork is wound on a winder for reuse in other processes. The resulting packaging is most often shaped like bowls, cups, etc.

Example 1

The raw material in the form of a mixture of PET bottle flakes and post-production waste from the thermoforming process of PET/PE packaging (40%/60% by weight) with an average intrinsic viscosity of 0.69 dl/g was directed to the heater, where it was heated to a temperature in a flow of hot air.

40°C. While the raw material was being heated in one heater, another heater was being filled to ensure process continuity. The device used was equipped with three heaters. After heating to the set temperature, the raw material was directed through a suction line to a conveyor-bottom dryer, where it was maintained at 40°C and under a pressure of approximately 10 mbar for 7 hours under a nitrogen flow of ^{5.56-10-8 m3} /s/kg of raw material, which facilitates the removal of water and volatile impurities. The raw material mixture was then continuously fed to the main twin-screw extruder (B). Additionally, SUKANO Tcc S598 white dye, containing 60% titanium dioxide and 40% PET, was added to the main extruder at a rate of 1% by weight based on the weight of the base raw material. The recyclates, along with the additive, were plasticized and homogenized in the plasticizing system of the main extruder. Temperatures in the individual zones of the main extruder ranged from 240 to 270°C. Simultaneously, the primary copolyester granulate, pre-dried at 100°C for 5 hours, was fed to an additional single-screw extruder (A), plasticized, and homogenized at temperatures ranging from 240 to 260°C. In the coextrusion block, the molten material streams from the individual extruders were combined into a single stream, resulting in an AB layer configuration, where the weight of layer A accounted for 10% of the total film weight. During the process, the film was siliconized on one side. The resulting film was two-layered, with a density of 1.33 g/ ^cm3 and a thickness of 1.0 mm. The film was transferred directly to the thermoforming machine's preheating chamber, where it was heated to 50°C. From the preheating station, the film was transported via chain conveyor between the heated heating plates of the main heating station. As the film progressed, it heated and plasticized to a sheet surface temperature of 120-130°C. The plasticized film was then transferred to the forming station, where a portion of the sheet was thermoformed. The plasticized film was then transferred to the mold, where compressed air and the mechanical action of the punches were used to pre-shape the package into cups with a top diameter of 95 mm and a capacity of 0.2 L. After the forming stage, the resulting packages were transported to the stacking station. The forming cycle lasted 2.6 seconds.

Example 2

A raw material in the form of a mixture of PET bottle flake and PET/PE thermoforming waste (50%/50% by weight) with an average intrinsic viscosity of 0.7 dl/g was directed to a preheater, where it was heated to 60°C in a hot air flow. While the raw material was being heated in one preheater, another preheater was being filled to ensure process continuity. The device used is equipped with three preheaters. After heating to the desired temperature, the raw material was directed through a suction line to a conveyor-bottom dryer, where it was maintained at 60°C and under a pressure of approximately 10 mbar for 4 hours under a nitrogen flow of ^{5.56-10-8 m3} /s/kg of raw material, which facilitates the removal of water and volatile impurities. The mixed raw material was then continuously fed to the main twin-screw extruder (B). Additionally, SUKANO Toc S598 white dye was added to the main extruder at a rate of 1.5% by weight of the base material. The recyclates, along with the additive, were plasticized and homogenized in the plasticizing system of the main extruder. Temperatures in the individual zones of the main extruder ranged from 240 to 270°C. Simultaneously, the primary copolyester granulate, after pre-drying at 100°C for 5 hours, was fed to an additional single-screw extruder (A), where it was plasticized and homogenized at temperatures ranging from 240 to 260°C. In the coextrusion block, the molten plastic streams from the individual extruders were combined into a single stream, resulting in an ABA layer system, where the A layers accounted for 20% of the total film weight. During the process, the film was siliconized on one side. The resulting three-layer film had a density of 1.31 g/ ^cm3 and a thickness of 1.0 mm. The film was transferred directly to the thermoforming machine's preheating chamber, where it was heated to 60°C. From the preheating station, the film was transported via chain conveyor between the heated heating plates of the main heating station. As the film progressed, it heated and plasticized to a sheet surface temperature of 130-140°C. The plasticized film was then transferred to the forming station, where a portion of the sheet was thermoformed. The plasticized film was then transferred to a mold, where compressed air and mechanical punches were used to pre-shape the package into cups with a top diameter of 95 mm and a capacity of 0.2 L. After the forming stage, the resulting packages were transported to the stacking station. The forming cycle lasted 2.6 seconds.

Example 3

A raw material in the form of a mixture of PET bottle flake and PET/PE thermoforming waste (60%/40% by weight) with an average intrinsic viscosity of 0.72 dl/g was directed to a preheater, where it was heated to 80°C in a hot air flow. While the raw material was being heated in one preheater, another preheater was being filled to ensure process continuity. The device used was equipped with three preheaters. After heating to the desired temperature, the raw material was directed through a suction line to a conveyor-bottom dryer, where it was maintained at 80°C and under a pressure of approximately 10 mbar for 2 hours under a nitrogen flow of 27.78 × 10-8 ^m3 /s/kg of raw material, which facilitates the removal of water and volatile impurities. The mixed raw material was then continuously fed to the main twin-screw extruder (B). Additionally, additives such as SUKANO Tcc S598 white dye at 1.5% by weight and 0.6% by weight of the chemical blowing agent BAPET900 (an endothermic chemical blowing agent consisting of a polymer carrier and an active compound that generates carbon dioxide upon exposure to elevated temperatures) were fed to the main extruder. The recyclates, along with the additives, were plasticized and homogenized in the plasticizing system of the main extruder. Carbon dioxide was fed to the extruder at a flow rate of 13.89-10-5 kg/s. The temperatures of the individual zones of the main extruder ranged from 230 to 260°C. Simultaneously, the primary copolyester granulate was fed to an additional single-screw extruder (A) after pre-drying at 100°C for 5 hours, plasticized, and homogenized at temperatures ranging from 240 to 260°C. In the co-extrusion block, the molten polymer streams from the individual extruders were combined into a single stream, resulting in an ABA layer configuration, where the A layer mass accounted for 20% of the total film mass. During the process, the film was siliconized on one side. The resulting three-layer film had a density of 0.91 g/ ^cm3 and a thickness of 1.4 mm. The film was transferred directly to the preheating chamber of the thermoforming machine, where it was heated to 60°C. From the preheating station, the film was transported by chain conveyor between the heated heating plates of the main heating station. As the film progressed, it heated and plasticized to a sheet surface temperature of 130-140°C. The plasticized film was then transferred to the forming station, where a portion of the sheet was thermoformed. The plasticized film was then transferred to a mold, where compressed air and mechanical punches were used to pre-shape the package into cups with a top diameter of 95 mm and a capacity of 0.2 L. After the forming stage, the resulting packages were transported to the stacking station. The forming cycle lasted 2.7 seconds.

Example 4

A raw material in the form of a mixture of PET bottle flake and post-industrial waste from the PET/PE thermoforming process (60%/40% by weight) with an average intrinsic viscosity of 0.72 dl/g was directed to a preheater, where it was heated to 80°C in a flow of hot air. While the raw material was being heated in one preheater, another preheater was being filled to ensure process continuity. The device used is equipped with three preheaters. After heating to the desired temperature, the raw material was directed through a suction line to a conveyor-bottom dryer, where it was maintained at 80°C and under a pressure of approximately 10 mbar for 2 hours under a nitrogen flow of 55.56-10-8 ^m3 /s/kg of raw material, which facilitates the removal of water and volatile impurities. The mixed raw material was then continuously fed to the main twin-screw extruder (B). Additionally, additives such as SUKANO Tcc S598 white dye at 1.5% by weight and 0.6% by weight of the chemical foaming agent BAPET900, based on the weight of the base material, were fed to the main extruder. The recyclates and additives were plasticized and homogenized in the plasticizing system of the main extruder. Carbon dioxide was fed to the extruder at a flow rate of 13.89 × 10-5 kg/s. Temperatures in the individual zones of the main extruder ranged from 230 to 260°C. Simultaneously, the primary copolyester granulate, after pre-drying at 100°C for 5 h, was fed to the additional single-screw extruder (A), where it was plasticized and homogenized within a temperature range of 240 to 260°C. In the co-extrusion block, the streams of molten plastic from the individual extruders were combined into one stream and a layer system was obtained.

ABA, where the weight of the A layers constituted 20% of the total film weight. During the process, the film was siliconized on one side. The resulting three-layer film had a density of 0.93 g/ ^cm3 and a thickness of 1.6 mm. The film was transferred directly to the thermoforming machine's preheating chamber, where it was heated to 60°C. From the preheating station, the film was transported via chain conveyor between the heated heating plates of the main heating station. As the film progressed, it heated and plasticized to a sheet surface temperature of 130-140°C. The plasticized film was then transferred to the forming station, where a portion of the sheet was thermoformed. The plasticized film is then transferred to a mold, where compressed air and mechanical punches are used to pre-shape the package into a cup with a top diameter of 95 mm and a capacity of 0.4 L. After the molding stage, the resulting packages were transported to a stacking station. The molding cycle lasted 2.9 seconds.

Claims (10)

1. A method for producing polyester packaging with increased thermal resistance for hot-poured products and/or intended for sterilization, characterized in that poly(ethylene terephthalate) recyclate in the form of regrind or granulate or in the form of blends of poly(ethylene terephthalate) with a blend of poly(ethylene terephthalate) and polyethylene of the composition PET to PET/PE 1:9 - 9:1 with an intrinsic viscosity of 0.6 dl/g to 1.2 dl/g in the solid state is heated in a flow of hot air to a temperature of 20°C to 80°C for 1 to 10 hours, under reduced pressure of 3 to 12 mbar and/or in an inert gas flow of 2.78-10-8 ^m3 /s/kg - 55.56-10-8 ^m3 //s/kg of raw material, the raw material after drying is directed to the main extruder of a single- or twin-screw extrusion and extrudes the film in a continuous process using a device equipped with one main extruder and optionally additional extruders, wherein optional additional extruders may be fed with pre-plasticized primary material and previously prepared mixtures are fed through the dosing systems of individual extruders, plasticized and homogenized together with viscosity and impact modifiers, fillers, dyes, compatibilizers, foaming agents in the plasticizing system of the main extruder and additional extruders, the subsequent zones of which are heated to a temperature in the range of 235-285°C increasing along the extruder and through the movement of the screws are forced through flow channels, the filtering unit of the extruders, the co-extrusion block and the extrusion head, wherein in the co-extrusion block the streams of molten material coming from the main extruder and additional extruders are combined into one stream, obtaining a system multi-layer, wherein the amount of recyclate in the multi-layer film is up to 90%, and in addition, to obtain foamed films, extrusion is carried out with an inert gas flow of 2.78-10 ^-5 kg/s - 27.78-10 ^-5 kg/s, then in the second stage the cooled film is directed from the roll or directly from the extruder to the thermoforming machine and is first heated in the preheating station to a temperature of 5060°C, and then in the main heating station with one or two heating plates to a sheet surface temperature in the range of 70°C to 140°C, after which the film is formed in the mold cavity and the finally formed packaging is cut out. 2. The method according to claim 1, characterized in that the drying process is carried out in a dryer with an inert gas flow of ^{5.56-10-8 m3} /s/kg of raw material. 3. The method according to claim 1, characterized in that nitrogen and/or carbon dioxide are used as the inert gas. 4. The method according to claim 1, characterized in that the foamed films are extruded with an inert gas flow of ^8.33-10-5 kg/s - ^16.67-10-5 kg/s. 5. The method according to claim 1, characterized in that the cooling of the polyester film is carried out on a cooling roller, 6. The method according to claim 1, characterized in that used PE bottles and packaging as well as post-production waste from the extrusion process, thermoforming, preforms, bottles and PET and PET/PE packaging are used as PET and PET/PE recyclates. 7. The method according to claim 1, characterized in that physical and/or chemical foaming agents are used as foaming agents. 8. The method according to claim 1, characterized in that liquids with low boiling points or volatile hydrocarbons or inert gases are used as physical foaming agents. 9. The method according to claim 8, characterized in that carbon dioxide or nitrogen are used as inert gases. 10. The method according to claim 1, characterized in that the cutting of packages takes place in the forming station or in a separate station downstream of the forming station.