The object of the invention is a method of manufacturing polyester packaging with increased heat resistance intended for hot pouring food products and/or intended for sterilisation with an assumed heat resistance in the temperature range of 80-100°C.

At present, heat-resistant food contact packaging for pouring hot products and/or sterilisation before filling is not produced from polyesters. The films produced for the manufacture of packaging for pouring hot products and/or sterilisation are made of polypropylene or CPET, i.e. polyester with an increased crystalline phase content. The temperature resistance of standard PET packaging is around 60-70°C. At present, thermally resistant packaging is not produced from films that have been made from recyclates, especially laminate recyclates. Recycling of packaging made from laminates (e.g. PET/PE) or co-extruded films is particularly difficult as these materials combine materials with different properties and different processing capacities in the form of layers. The reprocessing of such materials is therefore difficult. The products obtained from mixing these materials have different properties from their layered counterparts and are often not suitable for reuse. For example, PET/PE laminate, when ground and melted, becomes a blend of two incompatible materials with different properties from those of the pure materials. Such a mixture is characterized e.g. by low transparency/high haze, which makes it impossible to reuse such post- production waste in the production of e.g. transparent polyester films. The problem related to recycling of film waste concerns both different processing capacities of the materials they contain and problems related to the preparation of such raw material for processing, e.g. drying. PET is a plastic that easily undergoes hydrolytic degradation under processing conditions, so it must be well dried before processing. The drying temperature of PET is much higher than the melting temperature of PE. Therefore, the preparation and drying of PET/PE raw material requires the development of technology. In case of solid films, the removal of moisture can be performed during extrusion by connecting a vacuum pump to the first zones of the cylinder. In the case of extrusion of foamed films, it will be necessary to dry the raw material at a lower temperature (to avoid sticking) and thus to equip the dryers with systems facilitating moisture removal at lower temperatures under reduced pressure. Both solid and foamed films can be used for heat-resistant packaging. Packaging made of foamed films in comparison to that made from solid films is characterised by better thermal insulation properties and, due to lower density, reduced unit weight. The melt resulting from PET/PE laminate is a good material for the manufacture of packaging film for pouring hot products or when sterilisation is required, e.g. for the dairy industry. In this application, the turbidity of the film is a desirable phenomenon as dairy products age faster when exposed to light. Efficient foaming of PET is possible through the use of chemical and physical foaming agents.

Containers known from description US 6600143 B2 are made of polypropylene for products heated in microwaves, e.g. for so-called "ready meals". The containers are made of multilayer film with an inner layer of foamed polypropylene and an outer layer of unfoamed polypropylene with talc. These containers are characterised by high deformation resistance and thermal resistance. However, polypropylene materials are characterised by low oxygen barrier properties, so in many applications an additional barrier layer is added, which however makes it difficult to recycle these packaging materials. In addition, these packaging materials do not contain recyclates in their composition.

Products made of foamed PET and methods for their production are known from the description US 2012/0232175 (A1). The method according to the invention comprises mixing the plastic material with a physical foaming agent, which is a mixture of carbon dioxide and nitrogen (in a ratio from 4/1 to 1/1), and extruding a sheet to be thermoformed. The resulting products are made from the original PET pellets and have a temperature resistance of up to approximately 70°C. These materials are therefore not suitable for pouring hot products or sterilisation. The presented production method does not use recycled materials, which makes the production highly wasteful.

Description EP 2081745 A1 relates to a method of thermally shaping a foamed polyester sheet with low crystallinity to produce a container with improved heat resistance. The method comprises the steps of heating a sheet of foamed polyester to a pre-shaping temperature in contact with one heating plate and cooling the heated sheet of foamed polyester on an unheated mould element. The moulded containers obtained in this way are characterised by their resistance to high temperatures (approx. 200°C) and are intended for packaging of ready meals heated in microwaves or ovens. The packaging is characterised by increased thermal resistance due to the transformation of amorphous PET (APET) during the packaging manufacture into partially crystalline form (CPET). The containers produced in this way obtain increased thermal resistance by increasing the content of the crystalline phase and not, as in the invention, by introducing additional layers made of materials with a chemical structure different from PET. The containers so manufactured are furthermore not made of recycled laminates.

The invention (US 2011/0221097 (A1)) relates to a method for producing polyester sheets from original PET pellets and recycled PET for forming food containers. The method according to the invention comprises adding epoxy polymer chain elongating substances to a recycled PET flake; loading the mixture into an extruder; melting the mixture with simultaneous degassing, increasing the molar mass of PET and trapping by-products; coextruding the PET into a sheet form, wherein the layer made from recycled PET is the inner layer and the outer layers are the original PET. The recycled raw material does not come from recycled laminates, the resulting film is not foamed and the containers made of this film have a maximum temperature resistance of 70°C.

The invention (EP 0182378 (B1)) relates to polyester materials used to produce packaging with improved mechanical properties and higher barrier properties against gases in relation to analogous packaging obtained from pure polyethylene terephthalate). The presented materials are made of polyethylene terephthalate) and a copolymer based on poly(ethylene isophthalate) and aliphatic hydroxy acid in the form of a blende or multilayer structure. These materials are not produced in foamed form and have a lower thermal resistance than pure PET, below 70°C, which varies depending on the polyethylene isophthalate) content. In addition, recycled raw materials are not used in the method described.

The invention (US 5250333) relates to polyester heat resistant materials for the manufacture of packaging for pouring hot products made of poly(ethylene terephthalate) modified with polyhydroxy alcohol and 2,6-naphthalenedicarboxylic acid. These materials have a temperature resistance of up to approximately 120°C due to the higher glass transition temperature of the copolyester in relation to pure PET. The packaging is not made in foamed form or from recycled materials, much less from recycled laminates.

An invention (EP 0390723 (B1)) concerning a method of 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 in 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 about 0.4 to about 1.25 g/cm3 and thermally shaping the sheet in a heated mould to produce the final product. Polyethylene added to the extruder in small quantities is in the form of original granules and is not recovered from laminate recycling. The increase in thermal resistance is achieved by the transformation of APET to CPET and not by the introduction of an additional layer.

The aim of the invention was to develop a method of manufacturing heat- resistant PET packaging made of polyester film containing recyclates (also recycled laminates) and suitable for food contact. These packages are intended to be used for pouring hot products and/or intended for sterilisation.

The packaging manufacturing method is a three-stage process and consists of a recyclate drying stage, a film extrusion stage and a thermoforming stage. Mixtures of raw materials with different contents of bottle flake and milling with different bulk densities were prepared. Mixtures of PET/PE milling/bottle flake in weight proportions 10/90, 20/80, 30/70, 40/60, 50/50, 60/40, 70/30, 80/20, 90/10 were tested respectively. In the first stage, recyclates in the form of milling or granulate or in the form of mixtures of any composition with bulk viscosity from 0.6 dl/g to 1.2 dl/g are heated in a heater in hot air flow to the temperature close to drying temperature (20°C to 80°C). Once the set temperature is reached, the material is transported through a suction line to a conveyor-bed tower, where it is dried for 1 to 10 hours under reduced pressure of 1000 to 0.01 mbar and/or in an inert gas flow (which facilitates moisture removal) of 0.1 l/h/kg to 0.5 l/h/kg of raw material. In the second stage, the material is directed to a main single or twin screw extruder and the film is extruded in a continuous process using a device equipped with one main extruder and possibly additional extruders. Any additional extruders can be fed with pre-plasticised virgin plastic. The input material is fed through dosing systems of individual extruders, plasticised and homogenised together with typical additives such as viscosity and impact modifiers, fillers, dyes, compatibilisers, chemical foaming agents in the plasticising system of the main extruder and additional extruders, in which subsequent zones of the extruder "A" are heated to a temperature in the range of 240-260°C and from 240 to 270°C on the extruder "B" in the case of solid films, and subsequent zones of the extruder "A" are heated to a temperature in the range of 240-260°C and from 230 to 260°C on the extruder "B" in the case of foamed films, increasing along the extruder and by the movement of the screws and it is pressed through the flow channels, extruder filter unit, co-extrusion block and extrusion head. In the co-extrusion block, the streams of molten plastic from the main extruder and additional extruders are combined into one with different structure depending on the applied insert, as a result of which an arrangement of B, AB or ABA layers is obtained. In the third stage, the cooled film is directed from the reel or directly from the extruder to the thermoforming machine. The film is first heated in the preheating station to a temperature of 50-60°C, and then in the basic heating station with one or two heating plates to a sheet surface temperature ranging from 70°C to 160°C, after which the film is formed in the mould cavity and the formed packs are collected, the entire forming cycle lasts from 2s to 5s.

The drying process is preferably carried out at a temperature of 20-80°C. The drying process is preferably carried out over a period of 1-10 hours.

The drying process is preferably carried out under reduced pressure of 3 to 12 mbar.

The drying process is preferably carried out in a dryer with an inert gas flow of 0,2 l/h/kg of raw material.

Nitrogen and/or carbon dioxide are advantageously used as an inert gas. Advantageously, the foamed films are extruded at an inert gas flow rate of 300-600 g/h.

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

Post-consumer waste bottles and other PET packaging, post-production waste from extrusion, thermoforming, preforming, bottles and other PET and PET/PE packaging are preferably used as recyclate PET and PET/PE.

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

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

Carbon dioxide or nitrogen are advantageously used as inert gases.

Advantageously, the cutting of the packaging takes place in the forming station or in a separate station behind the forming station.

The films obtained are characterised by a density in the range from 0.5 g/cm3 to 1.35 g/cm3 and a thickness in the range from 0.3 mm to 2 mm. The polyester film obtained according to the method is multilayer. Advantageously, thermoplastic nonfoamed layers are used as the outer layers or the outer layer, as they facilitate welding with the top film and/or enable printing. The outer layers are applied by coextrusion.

Packaging according to the invention is characterised by increased heat resistance compared to APET packaging. The main idea of this invention is to obtain packaging with similar food contact properties with a recyclate content of up to 90%. The cutting station is located in the forming station or in a separate station behind the forming station. The material remaining after the cutting of packaging in the form of openwork is wound on a winder in order to be reused in other processes. The packaging obtained is usually in the shape of bowls, cups, etc.

Example 1 .

The raw material in the form of a mixture of PET bottle flake and post-production waste from PET/PE thermoforming process (40%/60% by weight) with an average essential viscosity of 0.69 dl/g was directed to a preheater, where it was heated in hot air flow to the temperature of 40°C. While the raw material was being heated in one preheater, another preheater was filled to achieve process continuity. The machine in use is equipped with three preheaters. After being heated to the required temperature, the raw material was directed through a suction line to a dryer with a conveyor-bed, where it was kept at a temperature of 40°C, under a pressure of approx. 10 mbar for 7 hours at a nitrogen flow rate of 0.2 l/h/kg of raw material, which facilitates the removal of water and volatile impurities. The mixed raw material was then dosed continuously into the main twin-screw extruder (B). Additionally, an additive such as the white dye SUKANO Tcc S598 was dosed into the main extruder in the amount of 1% by weight with respect to the weight of the base raw material. The recyclates together with the additive were plasticised and homogenised in the plasticising system of the main extruder. The temperatures of the individual zones of the main extruder were in the range from 240 to 270°C. At the same time, the original copolyester pellets after pre-drying at 100°C for 5h were dosed into an additional single-screw extruder (A) and plastified and homogenized in the temperature range from 240 to 260°C. In the co-extrusion block, the melt streams from individual extruders were combined into one and an AB layer system was obtained, where the weight of layer A was 10% of the total film weight. During the process the film was siliconised on one side. The obtained film was two-layered and had a density of 1.33 g/cm3 and thickness of 1.0 mm. The film was transferred directly to the preheating cabinet of the thermoformer, where it was heated to 50°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 moved, it was heated and plasticised to a sheet surface temperature of 120-130°C. The plasticised film was then transferred to the forming station, where part of the sheet underwent the thermoforming process. The plasticised film goes to the mould, where with the use of compressed air and mechanical work of punches the initial shape of the packaging took place, cups with the upper diameter of 95 mm and volume of 0.2 I. After the moulding stage, the resulting packs were transported to a stacking station. The forming cycle lasted 2.6 s.

Example 2.

The raw material in the form of a mixture of PET bottle flake and post-production waste from PET/PE thermoforming process (50%/50% by weight) with an average essential viscosity of 0.71 dl/g was directed to a preheater, where it was heated in hot air flow to 60°C. While the raw material was being heated in one preheater, another preheater was filled to achieve process continuity. The machine in use is equipped with three preheaters. After being heated to the preset temperature, the raw material was directed through a suction line to a dryer with a conveyor-bed, where it was kept at a temperature of 60°C, under a pressure of about 10 mbar for 4 hours at a nitrogen flow rate of 0.2 l/h/kg of raw material, which facilitates the removal of water and volatile impurities. The mixed raw material was then dosed continuously into the main twin-screw extruder (B). Additionally, an additive such as the white dye SUKANO Tcc S598 in the amount of 1 .5 wt.% in relation to the weight of the base raw material was dosed into the main extruder. Recyclates with the additive were plasticised and homogenised in the plasticising system of the main extruder. The temperatures of the individual zones of the main extruder were in the range from 240 to 270°C. At the same time the original copolyester pellets after predrying at 100°C for 5h were dosed into an additional single-screw extruder (A) and plastified and homogenized in the temperature range from 240 to 260°C. In the coextrusion block, the melt streams from the individual extruders were combined into one and an ABA layer system was obtained, where the weight of the A layers represented 20% of the total film weight. During the process the film was siliconised on one side. The obtained film was three-layered and had a density of 1.31 g/cm3 and thickness of 1 .0 mm. The film was transferred directly to the preheating cabinet 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 moved, it was heated and plasticised to a sheet surface temperature of 130-140°C. The plasticised film was then transferred to the forming station, where part of the sheet underwent the thermoforming process. The plasticised film goes to the mould, where with the use of compressed air and mechanical work of punches the initial shape of the packaging took place, cups with the upper diameter of 95 mm and volume of 0.2 I. After the moulding stage, the resulting packs were transported to a stacking station. The forming cycle lasted 2.6 s.

Example 3.

The raw material in the form of a mixture of PET bottle flake and post-production waste from PET/PE thermoforming process (60%/40% by weight) with an average essential viscosity of 0.72 dl/g was directed to a preheater, where it was heated in hot air flow to 80°C. While the raw material was being heated in one preheater, another preheater was filled to achieve process continuity. The machine in use is equipped with three preheaters. After being heated to a preset temperature, the raw material was fed via a suction line to a dryer with a conveyor-bed, where it was kept at a temperature of 80°C, under a pressure of about 10 mbar for 2h at a nitrogen flow rate of 0.2 l/h/kg of raw material, which facilitates the removal of water and volatile impurities. The mixed raw material was then dosed continuously into the main twin-screw extruder (B). Additionally, additives such as the white dye SUKANO Tcc S598 in the amount of 1.5 wt% and 0.6 wt% of the chemical foaming agent BAPET900 were dosed to the main extruder with respect to the weight of the base raw material. Recyclates with additives were plasticised and homogenised in the plasticising system of the main extruder. Carbon dioxide was fed to the extruder at a flow rate of 500 g/h. The temperatures of the individual zones of the main extruder were in the range 230 to 260°C. At the same time, an additional single-screw extruder (A) was dosed with original copolyester granulate after pre-drying at 100°C for 5h and plasticised and homogenised in the temperature range from 240 to 260°C. In the co- extrusion block, the melt streams from the individual extruders were combined into one and an ABA layer system was obtained, where the weight of the A layers represented 20% of the total film weight. During the process the film was siliconised on one side. The obtained film was three-layered and had a density of 0.91 g/cm3 and thickness of 1.4 mm. The film was transferred directly to the preheating cabinet 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 moved, it was heated and plasticised to a sheet surface temperature of 130-140°C. The plasticised film was then transferred to the forming station, where part of the sheet underwent the thermoforming process. The plasticised film goes to the mould, where with the use of compressed air and mechanical work of punches the initial shape of the packaging took place, cups with the upper diameter of 95 mm and volume of 0.2 I. After the moulding stage, the resulting packs were transported to a stacking station. The forming cycle lasted 2.7 s.

Example 4.

The raw material in the form of a mixture of PET bottle flake and post-production waste from PET/PE thermoforming process (60%/40% by weight) with an average essential viscosity of 0.72 dl/g was directed to a preheater, where it was heated in hot air flow to 80°C. While the raw material was being heated in one preheater, another preheater was filled to achieve process continuity. The machine in use is equipped with three preheaters. After being heated to a preset temperature, the raw material was fed via a suction line to a dryer with a conveyor-bed, where it was kept at a temperature of 80°C, under a pressure of about 10 mbar for 2h at a nitrogen flow rate of 0.2 l/h/kg of raw material, which facilitates the removal of water and volatile impurities. The mixed raw material was then dosed continuously into the main twin-screw extruder (B). Additionally, additives such as the white dye SUKANO Tcc S598 in the amount of 1.5 wt% and 0.6 wt% of the chemical foaming agent BAPET900 were dosed to the main extruder with respect to the weight of the base raw material. Recyclates with 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 500 g/h. The temperatures of the individual zones of the main extruder were in the range 230 to 260°C. At the same time, an additional single-screw extruder (A) was dosed with an original granulate after pre-drying at 100°C for 5h and plasticised and homogenised in the temperature range from 240 to 26O°C. In the co-extrusion block, the melt streams from the individual extruders were combined into one and an ABA layer system was obtained, where the weight of the A layers represented 20% of the total film weight. During the process the film was siliconised on one side. The obtained film was three-layered and had a density of 0.93 g/cm3 and thickness of 1 .6 mm. The film was transferred directly to the preheating cabinet 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 moved, it was heated and plasticised to a sheet surface temperature of 130-140°C. The plasticised film was then transferred to the forming station, where part of the sheet underwent the thermoforming process. The plasticised film goes to the mould, where with the use of compressed air and mechanical work of punches the initial shape of the packaging took place, cups with the upper diameter of 95 mm and volume of 0.4 I. After the moulding stage, the resulting packs were transported to a stacking station. The forming cycle lasted 2.9 s.