DE102018003711A1 - METHOD FOR PRODUCING A MULTILAYER PLASTIC TRACK, MULTILAYER PLASTIC TRACK AND PACKING TRAY - Google Patents

Abstract

The invention relates to a method for producing a multilayer plastic web having at least a first layer of foamed plastic and a second layer of a cover layer connected to the first layer. The method enables the production of the multilayer plastic web by means of coextrusion and optionally the use of Recyclat.Als starting material for the multilayer plastic sheet is polyethylene terephthalate into consideration. In addition, nitrogen can be used as blowing agent. Overall, according to the invention, a multilayer plastic web with unique material properties and a packaging shell with unique properties can be achieved.

Description

The invention relates to a method for producing a multilayer plastic sheet, a plant, a multilayer plastic sheet and a packaging tray.

In particular, the invention relates to a method for producing a multilayer plastic web comprising a first layer of foamed plastic and a covering layer connected to the foamed plastic, a system for carrying out the method, a multilayer plastic web comprising a first layer of foamed plastic and one with the foamed plastic bonded cover layer and a packaging shell made of such a multilayer plastic sheet.

Foamed plastics as well as methods of making foamed plastics are well known in the art. Furthermore, multilayer plastic webs and methods of making such in the art are also widely known.

Also, packaging, in particular food packaging, from such multilayer plastic sheets are already known in the art, including on the EP 2 081 745 B1 is referenced.

The EP 3 231 575 Al discloses a method and apparatus for producing a thermoplastic material product by extrusion, wherein a twin screw extruder is formed with two intermeshing conical screws, the two screws being rotated in the same direction during extrusion by a drive.

The invention has for its object to provide the prior art an improvement or an alternative.

According to a first aspect of the invention, the object solves a method for producing a multilayer, in particular two-layer, plastic web, comprising a layer of foamed plastic and a cover layer connected to the foamed plastic, wherein the multilayer plastic web is coextruded and emerges from a slit nozzle.

• Zunächst sei ausdrücklich darauf hingewiesen, dass im Rahmen der hier vorliegenden Patentanmeldung unbestimmte Artikel und Zahlenangaben wie „ein“, „zwei“ usw. im Regelfall als „mindestens“-Angaben zu verstehen sein sollen, also als „mindestens ein...“, „mindestens zwei ...“ usw., sofern sich nicht aus dem jeweiligen Kontext ausdrücklich ergibt oder es für den Fachmann offensichtlich oder technisch zwingend ist, dass dort nur „genau ein ...“, „genau zwei ...“ usw. gemeint sein können.

Conceptually, the following is explained:

• First of all, it should be expressly pointed out that, in the context of the present patent application, indefinite articles and numbers such as "a", "two" etc. should as a rule be understood as "at least" information, ie as "at least one ...", "At least two ..." etc., unless expressly stated in the respective context or it is obvious or technically imperative for the skilled person that there only "exactly one ...", "exactly two ..." etc. can be meant.

In the context of the present patent application, the expression "in particular" should always be understood to mean that this expression introduces an optional, preferred feature. The term is not to be understood as "and" and not as "namely".

A "plastic web" is a web of thermoplastic material having a substantially constant thickness and a substantially constant width. A plastic sheet may consist of one or more layers which are interconnected.

A "layer of foamed plastic" is understood to mean a material layer which consists of "foamed plastic". Foamed plastic is an artificially manufactured fabric with a cellular structure and low density. For foaming plastic to a foamed plastic almost all known plastics are suitable. A foamed plastic is characterized by its low density and reduced thermal conductivity. A foamed plastic is understood in particular as meaning any substance which has been chemically, physically or mechanically foamed.

By "topcoat" is meant a layer of compact non-foamed plastic bonded to a layer of foamed plastic. In particular, the top layer has no antimony oxide or only very small amounts thereof.

By "coextruded" is meant that the same or foreign plastic melts are merged before leaving the slot. In particular, a layer of foamed plastic and a cover layer of a compact plastic are combined before leaving the slit nozzle.

A "split nozzle" is a device that is adapted to allow a plastic to escape. In particular, a slit nozzle means a slot die or a ring slit nozzle. A split nozzle may have a plurality of actuators configured to adjust a nozzle gap.

The prior art has heretofore provided that multilayer plastic webs, which is a layer made of a foamed plastic are prepared such that the foamed plastic layer are first prepared independently of the cover layer, wherein they each emerge separately from each other from a slot and these layers were subsequently connected together.

In particular, the state of the art has hitherto provided that the cover layer and the layer of foamed plastic have been joined to an additionally required adhesive material.

By way of derogation, it is proposed here to co-extrude the layers, wherein both the foamed plastic layer and the cover layer are produced simultaneously and brought together before the common exit of the material layers from a gap nozzle.

Advantageously, this can be achieved by the fact that the method for producing can be designed more cost-effective and also the space required for a manufacturing device is lower.

In addition, it can be achieved with a suitable setting that a coextruded multilayer plastic web can be produced, which is characterized by a reliable bond between the layer of foamed plastic and the cover layer and the composite without additional adhesive layer reliable and full surface get along, which also costs saved and the environment can be relieved.

Advantageously, it can be additionally or alternatively achieved that the multilayer plastic web has a very good thermoformability and excellent suitability for food packaging.

A preferred embodiment can be realized in that the slit nozzle is a ring slit nozzle, wherein preferably the cover layer is connected to the layer of foamed plastic on the inside of the layer of foamed plastic and / or the outside of the layer of foamed plastic.

• Unter einer „Ringschlitzdüse“ wird eine Sonderform einer Spaltdüse verstanden, wobei die Spaltdüse insbesondere einen ringförmigen Düsenspalt aufweist. Wesentliches Merkmal einer Ringschlitzdüse ist, dass eine aus einer Ringschlitzdüse austretende Kunststoffbahn einen Kunststoffschlauch bildet. So kann eine Ringschlitzdüse eine beliebige Form des Düsenspaltes aufweisen, bei der die austretende Kunststoffbahn einen Kunststoffschlauch bildet, beispielsweise kann sie auch eine elliptische Form des Düsenspaltes aufweisen.

Conceptually, the following is explained:

• A "ring slit nozzle" is understood to mean a special form of a slit nozzle, wherein the slotted nozzle in particular has an annular nozzle gap. An essential feature of a Ringschlitzdüse is that a leaking from a Ringschlitzdüse plastic web forms a plastic tube. Thus, a Ringschlitzdüse having any shape of the nozzle gap, wherein the exiting plastic web forms a plastic tube, for example, it may also have an elliptical shape of the nozzle gap.

It is proposed that the formation of the layer of foamed plastic and the cover layer takes place in a ring-slit nozzle which has the features necessary for coextrusion.

Furthermore, it is optionally proposed that the plastic web emerging from the annular slot nozzle be cut laterally in the longitudinal direction of the plastic web so as to form a flat plastic web.

Advantageously, this can be achieved that instead of a plastic sheet, a plastic tube can be extruded, whereby the space required for the system for performing the method is reduced and the energy requirements for the implementation of the method can be reduced because of lower convection and radiation losses are benefited can.

Optionally, the multilayer plastic web exits the slit nozzle predominantly in the horizontal direction, in particular in the machine direction at an angle to the horizontal of less than 40 °, more preferably less than 30 °, particularly preferably less than 15 °.

• Die „Maschinenrichtung“ ist die Richtung, in der die Laufstrecke der Kunststoffbahn durch die Maschine verläuft. Insbesondere ist die Maschinenrichtung keine globale Richtung, vielmehr kann sie sich mit der Laufstrecke der Kunststoffbahn durch die Maschine ändern.

Conceptually, the following is explained:

• The "machine direction" is the direction in which the run of the plastic web passes through the machine. In particular, the machine direction is not a global direction, but may change with the travel of the plastic web through the machine.

It should be expressly understood that the foregoing values for the angles to the horizontal are not to be understood as sharp boundaries, but rather are to be exceeded or fallen below on an engineering scale, without departing from the described aspect of the invention. In simple words, the values are intended to provide an indication of the size of the angle proposed here relative to the horizontal.

Advantageously, it can thereby be achieved that the variability of the method for producing the multilayer plastic web can be increased.

Preferably, the multilayer plastic web is after the exit from the slit nozzle by Contact with an aerosol and / or a liquid cooled.

• Unter einem „Aerosol“ wird ein heterogenes Gemisch von festen und/oder flüssigen Schwebeteilchen in einem Gas verstanden.

Conceptually, the following is explained:

• By an "aerosol" is meant a heterogeneous mixture of solid and / or liquid suspended particles in a gas.

A "liquid" is understood to mean a substance in the liquid state of matter.

Thus, it is proposed here that the multilayer plastic web is cooled after exiting the slit nozzle by contact with an aerosol and / or a liquid by utilizing the enthalpy of vaporization of an aerosol and / or a liquid which is generated by the evaporation of the aerosol or the liquid arises in the immediate vicinity of the multilayer plastic sheet or in the direct contact with the multilayer plastic sheet. In this case, the aerosol and / or the liquid evaporates, since the temperature of the multilayer plastic web after leaving the slit nozzle is preferably higher than the evaporation temperature of the aerosol and / or the liquid.

In particular, it is therefore conceivable here to cool the multilayer plastic web by releasing a spray in the immediate vicinity of the multilayer plastic web.

Advantageously, this can be achieved that the multilayer plastic web can be cooled, whereby the dimensional stability of the plastic sheet can be improved. As a result, the manufacturing process can be better controlled and the homogeneity and / or the quality of the multilayer plastic web can be improved.

According to a second aspect of the invention, the object solves a method for producing a multilayer, in particular two-layer, plastic web, comprising a layer of foamed plastic and a covering layer connected to the foamed plastic, in particular a method according to the first aspect of the invention, wherein as a starting material a recycled material is used for the layer of foamed plastic, the proportion of recyclate being at least 30% by weight, preferably at least 60% by weight, particularly preferably at least 90% by weight.

• Unter einem „Ausgangsstoff“ wird hier derjenige Stoff verstanden, aus dem die Schmelze für betreffende Kunststoffschicht gebildet wird, insbesondere für die Schicht aus geschäumtem Kunststoff und/oder die Deckschicht.

Conceptually, the following is explained:

• A "starting material" is understood here as the substance from which the melt is formed for the relevant plastic layer, in particular for the layer of foamed plastic and / or the covering layer.

A "recyclate" is understood as the product of a recycling process. If necessary, a recyclate has been separated from metals or other contaminants that are not part of the plastic of the recyclate and then re-used for the production of new plastic-based products.

The use of a recyclate thus inevitably leads to a second material cycle. Examples of frequently occurring recyclates are the so-called "bottle flakes" from the recycling of PET beverage bottles, which are available in large quantities and in a suitable specification. Further recyclates result from the recycling of packaging trays, in particular of packaging trays according to the fifth aspect of the invention.

By "% by weight" is meant the percentage by weight of a component or by indicating multiple components in a mixture.

The state of the art has hitherto provided that multilayer plastic webs comprising a layer of foamed plastic and a cover layer connected to the foamed plastic, in particular also in the layer of foamed plastic, were not produced with a starting material based on recyclate.

Recyclate, however, is a readily available raw material that, through its processing, enables the material to have a further life cycle, which is particularly beneficial for conserving resources and relieving the burden on the environment.

If the multilayer plastic web is further processed into a packaging shell, as is concretely proposed according to the fifth aspect of the invention, then the top layer may only have extremely small amounts of antimony oxide, which is why the use of recycled material in the top layer can be problematic and thus only under certain Requirements are optional but not mandatory.

For this reason, in the past, no recycled material was used to produce a corresponding multilayer plastic web.

By way of derogation, it is proposed here to also use recycled material as the starting material for the layer of foamed plastic, while no recycled material is used for the covering layer.

It should be expressly understood that the above values for the proportion of recyclate should not be construed as being in a strict spirit but should be able to be exceeded or fallen below on an engineering scale without departing from the described aspect of the invention. In simple words, the values are intended to provide an indication of the size of the recycled content proposed here.

Advantageously, this can be achieved that the recyclate available in large quantities can be advantageously recycled into the material cycle and new packaging can be produced, which meet the requirements of food. This can significantly relieve the burden on the environment.

Likewise, it can advantageously be achieved by using a coextrusion method that the layer of foamed plastic and the cover layer adhere firmly to one another without the addition of an additional adhesive layer, whereby a method established in the prior art is improved, the otherwise necessary adhesive material is saved and thus also the recyclability can be improved.

Polyethylene terephthalate (PET) is preferably used as a starting material for the foamed plastic layer, in particular exclusively polyethylene terephthalate.

By PET is meant in particular a slowly crystallizing PET copolymer.

Advantageously, this can be achieved that the multilayer plastic web can use the positive material properties of PET by the use of PET for the layer of foamed plastic and can be used as starting material and the available in large quantities and suitable specifications bottle flakes of PET bottles.

In particular, by foaming the PET a weight reduction of 30% compared to comparable multilayer plastic webs made of CPET can be made possible.

In addition, the multilayer plastic sheet, in addition to a high rigidity and a high temperature resistance also achieves an excellent thermal insulating effect.

It is also optionally proposed to use a plastic based on polyethylene furanate (PEF) or polylactide (PLA) as starting material for the layer of foamed plastic.

It is understood that the advantages of a method for producing a multilayer, in particular two-layer, plastic web comprising a layer of foamed plastic based on PET and a covering layer connected to the foamed plastic, as described above, directly on a method for producing a multi-layered, in particular two-layered, plastic web, comprising a layer of foamed plastic made of a plastic based on PEF or PLA and a cover layer connected to the foamed plastic.

Optionally, PET is used as a starting material for the cover layer, in particular exclusively polyethylene terephthalate.

It is proposed to use an antimony-free and slowly crystallizing PET raw material for the production of the cover layer.

In particular, it is also proposed here that a PET without Ti catalyst (without anti-Montrioxide) is used for the production of the cover layer. In this way, it can be advantageously achieved that particularly low migration values can be achieved in an oven at a temperature between 160 ° C. and 200 ° C.

It is also proposed that the raw material for forming the overcoat has an intrinsic viscosity of 0.82 and a crystallinity of more than 48% according to ASTM D1505.

• Unter der „intrinsischen Viskosität“ wird die Viskosität eines gelösten Polymers verstanden. Sie berechnet sich aus der auf die Viskosität des Lösungsmittels bezogenen Differenz aus der Viskosität des gelösten Polymers und der Viskosität des Lösungsmittels. Die intrinsische Viskosität ist demnach einheitslos.

Conceptually, the following is explained:

• By "intrinsic viscosity" is meant the viscosity of a dissolved polymer. It is calculated from the difference, based on the viscosity of the solvent, from the viscosity of the dissolved polymer and the viscosity of the solvent. The intrinsic viscosity is therefore unitless.

Advantageously, it can thereby be achieved that the multilayer plastic web has an excellent visual appearance.

Furthermore, this can be achieved by the fact that the cover layer is sealable at about 120 ° C to 180 ° C.

In addition, in combination with a first layer of PET, an extremely advantageous recyclability of the multilayer plastic web and packaging trays produced from it can be achieved, whereby the environment can be sustainably relieved.

It is also optionally proposed to use a plastic based on polyethylene (PE) or polyethylene furanoate (PEF) or polylactide (PLA) as starting material for the cover layer.

It is understood that the advantages of a method for producing a multilayer, in particular two-layer, plastic web, comprising a layer of foamed plastic and a PET-based cover layer connected to the foamed plastic, as described above, are directly related to a method for producing a multi-layered, in particular two-layer, plastic sheet, comprising a layer of foamed plastic and a cover layer made of a plastic based on PE or PEF or PLA, which is connected to the foamed plastic.

A preferred embodiment can be realized in that the method comprises the process steps of crosslinking, blowing agent addition, homogenization and molding.

• Unter einem Prozessschritt „Vernetzen“ wird verstanden, dass die Polymere gezielt vernetzt werden, wodurch sich die Kettenlänge eines vernetzten Polymers verlängert.

Conceptually, the following is explained:

• A "crosslinking" process step is understood to mean that the polymers are crosslinked in a targeted manner, which prolongs the chain length of a crosslinked polymer.

A "blowing agent additive" process step is understood to mean that a blowing agent is supplied to the melt. In particular, it is customary to add a blowing agent in an extruder to a melt.

A "homogenizing" process step is understood to mean that a melt is homogenized thermally and / or materially.

By "thermal homogenization" is meant that the temperature of a melt is homogenized. In other words, the temperature differences in a melt are degraded during thermal homogenization.

By a "material homogenization" is meant that the mixture of substances is homogenized a melt. In other words, the material differences in a melt are degraded during a material homogenization. In particular, it is intended here, inter alia, to think of a material homogenization after the addition of a nucleating agent.

A "steps" process step is understood as the formation of a geometric structure. In particular, it is intended here to the molding of a plastic tube, which is formed when leaving a plastic melt from a Ringschlitzdüse.

Here it is therefore proposed to chemically crosslink the melt, in particular the melt for the layer of foamed plastic and / or the melt for the cover layer, by the use of suitable crosslinking agents in the process step crosslinking.

After the melt has been crosslinked, it is proposed to add a blowing agent to the melt in a subsequent process step, in particular in an extruder.

It is further proposed to homogenize the melt after the addition of the blowing agent in the process step homogenizing. In particular, it is proposed to homogenize the melt in a downstream second extruder.

After homogenization, it is proposed to form the melt into a multilayer plastic sheet or a multilayer plastic hose.

Specifically, it should be remembered that the listed process steps are performed in a single plant or in several plants. It is conceivable that the material flow through several plants runs serially and / or in parallel.

Advantageously, it can thereby be achieved that a particularly high-quality multilayer plastic web can be produced by the proposed method sequence, which has the desired material properties for a packaging tray, in particular for a packaging tray according to the fifth aspect of the invention.

Optionally, the method comprises the process step dehumidify.

• Unter einem Prozessschritt „Entfeuchten“ wird verstanden, dass der Ausgangsstoff oder die Schmelze entfeuchtet und/oder entgast wird.

Conceptually, the following is explained:

• A "dehumidifying" process step is understood to mean that the starting material or the melt is dehumidified and / or degassed.

It can advantageously be achieved by this that the starting material or the melt satisfies the requirements necessary for the production of the multilayer plastic sheet.

Optionally, the process comprises the process step nucleation additive, wherein as nucleating agent in particular up to 5 wt.% Calcium carbonate is added, preferably up to 3 wt.%, Particularly preferably up to 1.5 wt.%.

• Unter einem Prozessschritt „Nukleierungszusatz“ wird der Zusatz eines Nukleierungsmittels in die Schmelze verstanden.

Conceptually, the following is explained:

• A "nucleation additive" process step is understood to be the addition of a nucleating agent into the melt.

A "nucleating agent" is understood as meaning a suitable substance which promotes nucleation, in particular, it is intended for a suitable nucleating agent of calcium carbonate.

In concrete terms, other conventional nucleating agents are also to be added to the plastic melt. In particular, it is proposed to add up to 5% by weight of calcium carbonate as nucleating agent, preferably up to 3% by weight, more preferably up to 1.5% by weight.

It is to be expressly understood that the foregoing values for the weight percent of calcium carbonate as a nucleating agent should not be construed as being "sharp" but rather should be exceeded or undershot on an engineering scale without departing from the described aspect of the invention. In simple terms, the values are intended to provide an indication of the size of the weight percent of calcium carbonate as nucleating agent proposed herein.

It can thereby be achieved that the cell or foam formation is supported within the production of the layer of foamed plastic by the nucleating agent.

A preferred embodiment can be realized in that the process step of crosslinking for a melt for producing the layer of foamed plastic has a mean residence time of 0.5 to 30 minutes and a melt temperature between 240 ° C and 310 ° C, preferably a mean residence time of 1 to 5 min and a melt temperature between 275 ° C and 300 ° C, more preferably an average residence time of 2 to 3 minutes and a melt temperature between 280 ° C and 290 ° C.

• Unter einer „mittleren Verweilzeit“ wird die mittlere Zeit verstanden, die ein Kunststoff in einem Extruder verbleibt. Sie lässt sich mathematisch aus dem zeitgemittelten Quotienten des freien Volumens in einem Extruder zu dem Volumenstrom des Extruders bestimmen. Das freie Volumen eines Extruders kann auch als das Kanalvolumen des Extruders bezeichnet werden.

Conceptually, the following is explained:

• An "average residence time" is understood to mean the average time that a plastic remains in an extruder. It can be determined mathematically from the time-averaged quotient of the free volume in an extruder to the volume flow of the extruder. The free volume of an extruder may also be referred to as the extruder's channel volume.

A "melt temperature" is understood to mean the temperature of a plastic melt.

It can advantageously be achieved hereby that a time-efficient and energy-efficient crosslinking of the polymer can be achieved by the temperature and the residence time in the process step crosslinking.

For foaming to produce the layer of foamed plastic, in a blowing agent addition process step, a blowing agent preferably has a nitrogen content of at least 50% by volume, preferably 75% by volume, particularly preferably 97% by volume.

Conceptually, the following is explained:

By "frothing" is meant that a blowing agent is added to a molten plastic, a so-called "melt". The blowing agent is fed to the melt in an extruder. In reducing the pressure acting on the melt, in practice in any case when the melt exits the die, or when changing the temperature of the melt, the gas or propellant emanating from the blowing agent itself gains in volume, causing the gas particles shifted melt thus foamed plastic gains in volume and the density is reduced accordingly. After solidification of the plastic results in a foamed plastic with an average cell size of the plastic bubbles that enclose the gas.

A "propellant" is understood to mean a gas and / or a substance in another state of matter which is suitable for foaming a plastic melt.

A "nitrogen content" is understood to mean the proportion of nitrogen relative to the total volume, in particular the proportion of the substance nitrogen, which is based on the volume of the propellant.

"Vol .-%" refers to the percentage volume of a component or the corresponding number of components in a mixture.

Here it is proposed to introduce a blowing agent into the melt for foaming. In particular, it is envisaged that the blowing agent is introduced into the melt in an extruder, from which the layer of foamed plastic is produced.

So propellant, the known blowing agents can be introduced into the melt. Suitable blowing agents are, for example, physical blowing agents, preferably suitable gases, in particular nitrogen, carbon dioxide, methane, ethane, propane, butane, cyclo-pentane or hexane. In addition, slightly volatile liquids and chemical blowing agents can be used.

It is to be expressly understood that the above values for the nitrogen content of the propellant should not be understood to be a strict limit but should rather be exceeded or undershot on an engineering scale without departing from the described aspect of the invention. In simple words, the values are intended to provide an indication of the size of the nitrogen content of the propellant proposed herein.

Advantageously, it can thereby be achieved that the layer of foamed plastic has a particularly fine-pored cell structure at the desired density of the foamed plastic.

An optional embodiment can be realized in that the homogenizing process step has a thermal and / or material homogenization and in particular takes place in an extruder, in particular in a second extruder downstream of the first extruder.

An "extruder" is understood to mean a plasticizing machine which is used in numerous fields, inter alia, in the plastics processing industry. In particular, an extruder is understood to mean a plasticizing machine which conveys, melts and homogenizes plastics in order to subsequently direct the plastic melt to a shaping nozzle for forming a continuous product. The products are, for example, profiles, tubes, foils, blow moldings, plates, filaments, nonwovens, tapes, semi-finished products, hoses, cables, granules, compound or semifinished foam products. An extruder is understood to mean, in particular, single-screw extruders and multi-screw extruders, in which a single-screw extruder has an extruder screw and a multi-screw extruder several extruder screws.

A "first extruder" is understood to mean that extruder which for the first time melts the plastic in the plant for carrying out the process. In particular, in the system according to the third aspect of the invention. A "downstream second extruder" is understood to mean an extruder which is downstream of the first extruder in relation to the designated material flow in the system.

Specifically, it is proposed that thermal homogenization takes place in the homogenizing step, the melt being thermally homogenized in such a way that after the homogenizing step, the remaining temperature differences occurring in the melt are less than 1 ° C. In this way, it can be advantageously achieved that the cell structure of the layer of foamed plastic can be improved, wherein an improvement can also consist in a homogenization of the cell structure.

It can advantageously be achieved by this means that the method described leads to a layer of foamed plastic with particularly preferred material properties. In particular, it is intended here to the fine-pored homogeneous cell structure of the foamed plastic.

A preferred embodiment can be realized in that the homogenizing process step for a melt for producing the foamed plastic layer has a mean residence time of 0.5 to 30 minutes and a melt temperature between 240 ° C and 280 ° C, preferably a mean residence time of 1 to 10 min and a melt temperature between 250 ° C and 270 ° C, more preferably a mean residence time of 2 to 5 min and a melt temperature between 255 ° C and 265 ° C.

It is proposed to cool the melt after the process step blowing agent additive in addition to the homogenization.

In this way, it can be advantageously achieved that the stability of the cells in the melt, which have a gaseous phase, are improved and a particularly fine foam can be achieved.

Optionally, the melt used for producing the layer of foamed plastic according to the process step homogenizing a centrifuge average molecular weight M _z in a range from 250,000 to 500,000 g / mol, particularly preferably a centrifuge-average molecular weight M _z in a range from 300,000 to 400,000 g / mol , more preferably, a centrifuge-average molecular weight M _z in a range of 300,000 to 350,000 g / mol.

• Unter dem „zentrifugenmittleren Molekulargewicht M_z“ wird ein spezifisches Molekulargewicht verstanden, welches zentrifugengemittelt ist und beispielsweise durch Messung des Sedimentationsgleichgewichts ermittelt werden kann.

Conceptually, the following is explained:

• The "centrifuge-average molecular weight M _z " is understood to mean a specific molecular weight which is centrifuge-averaged and can be determined, for example, by measuring the sedimentation equilibrium.

By "weight average molecular weight M _w " is meant a specific molecular weight which is weight average. The molecular weight of the polymer is weighted by the relative mass fraction that this polymer has.

Here, it is concretely proposed, inter alia, to increase the centrifuge-average molecular weight M _{z of} the polymer by crosslinking.

With reference to PET, inter alia, an increase in the ratio of centrifuge-average molecular weight M _z and weight-average molecular weight M _w by more than 10%, preferably by more than 200%, and more preferably by more than 350%, is suggested by the crosslinking.

It should be expressly understood that the above values for the centrifuge average molecular weight M _{z of} the melt for producing the layer of foamed plastic after the homogenization step should not be understood as being sharp limits, but rather should be exceeded or fallen below on an engineering scale, without departing from the described aspect of the invention. In simple terms, the values are intended to provide an indication of the size of the centrifuge-average molecular weight M _{z of} the melt proposed here for producing the layer of foamed plastic after the homogenizing step.

Advantageously, this can be achieved that the material properties of the melt are improved, the improvement is largely responsible for the fact that a high-quality layer of foamed plastic with a fine-pored homogeneous cell structure and a low density can be produced, especially with a plastic based on PET ,

The process step dehumidifying preferably comprises, in particular, degassing and / or drying of the starting material.

• Unter „Entgasen“ wird die Reduktion oder Entfernung von Gasen und/oder anderen flüchtigen Substanzen aus einem Stoff verstanden. Das betreffende Verfahren wird insbesondere mit einer Entgasungseinrichtung umgesetzt. Dabei sei insbesondere an eine Entgasungseinrichtung gedacht, bei welcher der entsprechende zu entgasende Stoff durch ein Vakuum geleitet wird, insbesondere wird ein Unterdruck auf die Schmelze aufgebracht.

Conceptually, the following is explained:

• "Degassing" is understood to mean the reduction or removal of gases and / or other volatile substances from a substance. The process in question is implemented in particular with a degassing device. In this case, in particular, a degassing device is intended, in which the corresponding substance to be degassed is passed through a vacuum, in particular a negative pressure is applied to the melt.

By "drying" is meant a special form of degassing in which substantially moisture is removed from the fabric, in particular removed from the melt.

Among other things, it is proposed to dry the starting material in the process step dehumidifying to a residual moisture content of less than 50 ppm.

It should be expressly pointed out that the above value for the residual moisture should not be understood as a sharp limit, but should rather be exceeded or fallen below on an engineering scale, without leaving the described aspect of the invention. In simple words, the value should provide an indication of the size of the residual moisture of the starting material proposed here.

Advantageously, this can be achieved in that the stability and the robustness of the manufacturing process can be increased because the contamination of the melt by liquid or other volatile substances can be reduced.

Optionally, the melt for producing the foamed plastic layer has an intrinsic viscosity of from 0.6 to 1.0, preferably from 0.7 to 0.79, more preferably from 0.73 to 0.76.

It is to be expressly understood that the above values for the intrinsic viscosity of the melt for producing the foamed plastic layer should not be understood as being sharp limits, but rather should be exceeded or fallen below on an engineering scale, without the described aspect of the invention to leave. In simple terms, the values are intended to provide an indication of the size of the intrinsic melt viscosity proposed herein for producing the foamed plastic layer.

It can thereby be advantageously achieved that plastics with a low intrinsic viscosity can also be used to produce the layer of foamed plastic.

It should be expressly understood that the subject matter of the second aspect may be advantageously combined with the subject matter of the foregoing aspect of the invention, cumulatively either singly or in any combination.

According to a third aspect of the invention, the object solves a system with at least one extruder for plasticizing a thermoplastic material and a slotted nozzle for releasing the thermoplastic material for carrying out a method according to the first and / or the second aspect of the invention.

It is understood that the advantages of a method for producing a multilayer, in particular two-layer, plastic web, comprising a layer of foamed plastic and a covering layer connected to the foamed plastic, according to the first and / or the second aspect of the invention, as described above , extend directly to a system having at least one extruder and a gap nozzle for performing a method according to the first and / or the second aspect of the invention.

It is to be expressly understood that the subject matter of the third aspect may be advantageously combined with the subject matter of the foregoing aspects of the invention, cumulatively either alone or in any combination.

According to a fourth aspect of the invention, the object is achieved by a multilayer plastic web, in particular a two-layer plastic web comprising a layer of foamed plastic and a cover layer connected to the foamed plastic, wherein the plastic web is provided with a method according to the first and / or second aspect of the invention or with a plant according to the third aspect of the invention has been produced.

The state of the art has not heretofore provided that a multilayer plastic web having a layer of foamed plastic and a cover layer was produced in the process of coextrusion.

Furthermore, the state of the art has hitherto not provided for a recycled material to be used as a starting material in the production of a multilayer plastic web with a layer of foamed plastic and a cover layer.

By way of derogation, it is proposed here to produce a multilayered plastic web with a layer of foamed plastic and a cover layer by the process of coextrusion and / or with the addition of a recycled material as a starting material.

It is understood that the advantages of a method for producing a multilayer, in particular two-layer, plastic web, comprising a layer of foamed plastic and a covering layer connected to the foamed plastic, according to the first and / or the second aspect of the invention, as described above , directly on a multilayer plastic web, in particular two-layer plastic web, comprising a layer of foamed plastic and a covering layer connected to the foamed plastic, wherein the plastic web with a method according to the first and / or second aspect of the invention or with a system according to the third aspect of the invention has been produced.

The layer of foamed plastic preferably consists of a plastic based on PET or polyethylene furanate (PEF) or polylactide (PLA).

The state of the art provided that corresponding multilayer plastic webs were not produced with a foam layer based on PET, since PET was considered to be too expensive as starting material.

With a manufacturing method according to the first and / or the second aspect of the invention, however, a foam layer made of PET can be produced in prototype experiments, a reduction of the density of the foamed plastic layer of PET of 30% over the CPET known in the art could be achieved ,

Advantageously, this can be achieved by the lower density of the product produced and the necessary material use of the starting material can be reduced, whereby the production costs can be reduced.

In addition, a method according to the second aspect of the invention allows the use of a PET recyclate as a starting material for the production of the multilayer plastic sheet, whereby also a reduction of the manufacturing costs and a relief of the environment can be achieved.

Furthermore, the use of a PET-based starting material for the production of the multilayer plastic web also allows the use of high-quality material properties of PET for the multilayer plastic web, whereby a high rigidity of the layer of foamed plastic and thus the entire multilayer plastic web can be achieved.

Thus, among other things, it is proposed to use PET cost-effectively as the starting material for the foam layer of the multilayer plastic web.

Advantageously, a multilayer plastic web with unique material properties can be achieved in this way, in particular with a high rigidity, a high temperature resistance and an excellent insulating effect, while at the same time the production costs for a multilayer plastic web can be reduced.

It is also optionally proposed to produce the layer of foamed plastic by a process according to the first and / or second aspect of the invention such that the layer of foamed plastic is produced from a plastic based on polyethylene furanoate (PEF) or polylactide (PLA).

It is understood that the advantages of a multilayer, in particular two-layer, plastic web, comprising a layer of foamed plastic based on PET and one connected to the foamed plastic Covering layer, as described above, directly on a multilayer, especially two-layer, plastic sheet, comprising a layer of foamed plastic based on PEF or PLA and a cover layer connected to the foamed plastic extend.

Optionally, the top layer consists of a plastic based on PET or polyethylene (PE) or polyethylene furanoate (PEF) or polylactide (PLA).

Advantageously, this can achieve, inter alia, that the cover layer is sealable at comparatively low temperatures of 120 ° C to 180 ° C and has a low migration effect in the oven even at high temperatures.

A preferred embodiment can be achieved in that the density of the layer of foamed plastic is 80 to 1250 g / l, preferably 100 to 720 g / l, particularly preferably 200 to 650 g / l.

It is to be expressly understood that the above values for the density of the foamed plastic layer should not be understood to be sharp limits, but rather are to be exceeded or undershot on an engineering scale without departing from the described aspect of the invention. In simple words, the values are intended to provide an indication of the size of the density of the foamed plastic layer.

It can advantageously be achieved by this means that the density of the layer of foamed plastic is comparatively low, as a result of which the density of the multilayer plastic web can be significantly reduced. The latter leads to the achievement of the advantages already outlined above based on a low density of the multilayer plastic web.

The layer of foamed plastic preferably has a thickness of 0.3 to 8 mm, preferably 0.5 to 4 mm, particularly preferably 0.8 to 2 mm.

It is to be expressly understood that the above values for the thickness of the foamed plastic layer should not be understood to be sharp limits, but rather are to be exceeded or undershot on an engineering scale without departing from the described aspect of the invention. In simple words, the values are intended to provide an indication of the size of the thickness of the foamed plastic layer.

Advantageously, this can be achieved that the thickness of the multilayer plastic sheet is optimally adapted to the needs of a packaging tray according to the fifth aspect of the invention.

Optionally, the cover layer has a thickness of 2 to 100 μm, preferably 5 to 30 μm, particularly preferably 10 to 20 μm.

It should be expressly understood that the above values for the thickness of the top layer should not be understood as being sharp boundaries, but rather should be exceeded or fallen below on an engineering scale, without departing from the described aspect of the invention. In simple words, the values are intended to provide an indication of the size of the thickness of the topcoat.

It can advantageously be achieved in this way that the density of the multilayer plastic web is only slightly influenced by the density of the compact cover layer, although the cover layer is so thick that it can guarantee a sufficient barrier function.

A preferred embodiment can be realized in that the layer of foamed plastic cells having a mean cell diameter of 50 to 600 microns, preferably 100 to 400 .mu.m, more preferably 150 to 250 microns.

• Unter einem „mittlerer Zellendurchmesser“ wird der über die Anzahl der Zellen gemittelte Durchmesser einer durchschnittlichen Zelle verstanden.

Conceptually, the following is explained:

• A "mean cell diameter" is understood as the average cell diameter averaged over the number of cells.

It should be expressly understood that the above values for the mean cell diameter of the foamed plastic layer should not be understood to be sharp limits, but rather are to be exceeded or undershot on an engineering scale without departing from the described aspect of the invention. In simple words, the values are intended to provide an indication of the size of the average cell diameter of the foamed plastic layer.

Advantageously, it can be achieved thereby that a layer of foamed plastic with a fine-pored cell structure and a low density can be used for the multilayer plastic web.

A preferred embodiment can be realized in that the layer of foamed plastic has up to 5 wt.% Calcium carbonate, preferably up to 3 wt.%, Particularly preferably up to 1.5 wt.%.

It should be expressly understood that the foregoing values for the weight percent of calcium carbonate should not be construed as being in any way limited, but rather should be exceeded or disregarded on an engineering scale without departing from the described aspect of the invention. In simple words, the values are intended to provide an indication of the size of the weight percent of calcium carbonate proposed herein.

The layer of foamed plastic preferably has a centrifuge-average molecular weight M _z in a range from 250,000 to 500,000 g / mol, particularly preferably a centrifuge-average molecular weight M _z in a range from 300,000 to 400,000 g / mol, particularly preferably a centrifuge-average molecular weight M _z in a range of 300,000 to 350,000 g / mol.

It is to be expressly understood that the above values for the centrifuge average molecular weight M _{z of} the foamed plastic layer should not be understood as being sharp, but rather should be exceeded or undershot on an engineering scale without departing from the described aspect of the invention , In simple words, the values are intended to provide an indication of the size of the centrifuge-average molecular weight M _{z of} the foamed plastic layer proposed herein.

In this case, referring to PET, inter alia, an increase in the ratio of centrifuge-average molecular weight M _z and weight-average molecular weight M _w by more than 10% is proposed for the layer of foamed plastic, preferably by more than 200% and particularly preferably by more than 350%. The absolute value of the ratio of centrifuge-average molecular weight M _z and weight-average molecular weight M _w of PET to more than 25 increases.

Advantageously, this can be achieved that excellent material properties of the layer of foamed plastic can be used, the improvement is significantly responsible for the fact that the multilayer plastic web has a high-quality layer of foamed plastic with a fine-pored homogeneous cell structure and a low density, in particular with a Plastic based on PET.

Optionally, the layer of foamed plastic comprises pigments and / or dye.

• Unter einem „Pigment“ wird eine farbgebende und unlösliche Substanz verstanden. Im Gegensatz zu einem „Farbstoff“, der ebenfalls farbgebend ist, ist ein Pigment nicht wasserlöslich.

Conceptually, the following is explained:

• By a "pigment" is meant a coloring and insoluble substance. Unlike a "dye", which is also a colorant, a pigment is not water soluble.

It is therefore proposed here to add pigments and / or dye to the starting material for the layer of foamed plastic, so that the finished layer of foamed plastic has pigments and / or dye.

Advantageously, this can be achieved by the fact that the layer of foamed plastic has a desired coloring.

Preferably, the cover layer is transparent.

• Unter einer „transparenten“ Schicht wird eine durchsichtige Schicht verstanden.

Conceptually, the following is explained:

• By a "transparent" layer is meant a transparent layer.

Advantageously, this can be achieved that the transparent cover layer makes it possible to look at the layer of foamed plastic, whereby the multi-layer plastic sheet can be given a pleasant and high-quality appearance.

It is to be expressly understood that the subject matter of the fourth aspect may be advantageously combined with the subject matter of the foregoing aspects of the invention, cumulatively, either singly or in any combination.

According to a fifth aspect of the invention, the object solves a packaging shell comprising a multilayer plastic sheet according to the fourth aspect of the invention.

Specifically, packaging trays in the form of a bowl for warming ready meals, a drinking cup or a bowl for serving heated or cooled food are proposed here, among other things.

The orientation of the multilayer plastic web is preferably such that the cover layer forms the surface with which, in the predetermined manner of use, the good to be packaged is brought into contact.

As a result of this orientation, the cover layer not only forms a sealing layer in the edge region of a packaging tray to be produced, on which a sealing film can be sealed for closing the food introduced into the packaging tray, but also forms the contact layer for the foodstuff to be packaged and separates it from the product, if appropriate Incorporation of recycled material made of foamed plastic layer.

It is understood that the advantages of a multilayer plastic sheet according to the fourth aspect of the invention, as described above, extend directly to a packaging tray made of a multilayer plastic sheet according to the fourth aspect of the invention.

Further advantages of a packaging tray produced from a multilayer plastic web according to the fourth aspect of the invention are that the packaging tray can be used in a temperature range between -20 ° C. and 200 ° C. and has an excellent thermal insulation effect through the layer of foamed plastic. Thus, chilled or heated food or drinks in such a packaging tray remain cool or warm for a particularly long time. In addition, the thermal insulation effect of the packaging shell to the fact that you can touch and hold the shell even with very hot or particularly cold food or drink with your bare hands, and without the risk of burning or undercooling. Another effect of the excellent thermal insulation of the packaging tray is that it helps to maintain the cold chain of packaged goods.

The combination of the thermal application area and the outstanding thermal insulation effect of the packaging shell of a multilayer plastic sheet according to the fourth aspect of the invention means that the contents of such a packaging tray are heated together with the packaging tray in microwave ovens and other ovens simply and again with bare fingers can be taken out without running the risk of getting burned.

The layer of foamed plastic has a soft but not slippery surface. This advantageously allows the packaging tray to have a pleasant feel, with the packaging tray resting securely in the hand due to its non-slippery surface. The achievable metallic appearance of the packaging shell leads advantageously to a positive salient external appearance, which can highlight the presentation of the packaged good advantageous.

The excellent barrier protection layer of the packaging shell made of a multilayer plastic sheet according to the fourth aspect of the invention and the ideal sealing advantageously guarantee a durable packaging of the packaged goods, whereby the quality of the packaged goods can be preserved for a particularly long time. Furthermore, the special surface structure of the packaging tray advantageously allows it to be sealed faster, easier and at a lower cost.

The comparatively low density of a packaging tray of a multilayer plastic web according to the fourth aspect of the invention advantageously allows a lower weight of the packaging tray, which allows a very good CO ₂ balance of the packaging tray.

Furthermore, the comparatively low density of the foamed plastic advantageously allows a small volume of disposed packaging trays, since they can be excellently compressed.

In a particularly advantageous embodiment of the packaging shell, this consists exclusively of a plastic based on PET, whereby excellent recycling properties can be achieved.

Optionally, it is specifically intended here that the packaging shell is produced by deep drawing and singulation of sections from the multilayer plastic web according to the fourth aspect of the invention.

Preferably, a packaging tray has a peripheral sealing edge.

It is to be expressly understood that the subject matter of the fifth aspect may be advantageously combined with the subject matter of the foregoing aspects of the invention, cumulatively either alone or in any combination.

• 1 schematisch einen Verfahrensablauf.

The invention will be explained in more detail with reference to an embodiment with reference to the drawing. There shows

• 1 schematically a procedure.

The procedure 1 in 1 For producing a multilayer, in particular two-layer, plastic web, comprising a layer of foamed plastic and a cover layer connected to the foamed plastic, consists essentially of the process steps dehumidifying 2 , Networking 3 , Propellant additive 4 , Nucleating additive 5 , Homogenizing 6 and shapes 7 , which are mainly run in this order.

The process step dehumidify 2 Degas and / or dries the starting material for the melt, so that a residual moisture of less than 50ppm is achieved. If the starting material already has a lower residual moisture, the Dehumidification step considered optional. It is also conceivable to omit the process step dehumidifying in all cases, whereby, however, the quality of the end product can be reduced.

Dehumidify the process step 2 closes the process step crosslinking 3 on. The process step network 3 can be done in a so-called "chain extender".

During the process step network 3 the melt temperature is between 270 ° C and 300 ° C. The average residence time of the melt in the process step crosslinking 3 is 120 s to 600 s.

Referring to PET, here is the networking of the polymer in the process step 3 an increase in the ratio of centrifuge average molecular weight M _z and weight average molecular weight M _{w achieved} by over 300% for the layer of foamed plastic. The absolute value of the ratio of centrifuge-average molecular weight M _z and weight-average molecular weight M _w for a plastic based on PET increases to more than 25.

The process step networking 3 follows the process step propellant additive 4 , wherein in the process step propellant additive 4 the melt is supplied to a blowing agent.

Optionally follows the process step propellant additive 4 the process step nucleation additive 5 , wherein the process step nucleation additive 5 optionally also parallel to and / or before the process step blowing agent additive 4 can be performed, and wherein in the process step nucleation additive 5 a nucleating agent is fed to the melt.

The nucleating agent supports the structure of the cell structure in the layer of foamed plastic, wherein the cell density and the amount of cells are significantly influenced by the nucleating agent.

In addition, the addition of a nucleating agent has a positive influence on the gloss of the surface of the multilayer plastic sheet and the density and thickness of the multilayer, especially two-layer, plastic sheet, comprising a layer of foamed plastic and a cover layer connected to the foamed plastic.

Subsequently, the process step homogenizing 6 performed, wherein the melt is homogenized thermally and / or material, wherein the melt is thermally homogenized such that after the homogenizing process step, the remaining temperature differences occurring in the melt are smaller than 1 ° C. In this way, it can be advantageously achieved that the cell structure of the layer of foamed plastic can be improved, wherein an improvement can also consist in a homogenization of the cell structure.

Homogenize on the process step 6 follows the process step forms 7 in which the multilayer plastic sheet is discharged from the slot nozzle, whereby the multilayer plastic sheet is formed.

LIST OF REFERENCE NUMBERS

1

process flow

2

dehumidify

3

network

4

The addition of propellant

5

Nukleierungszusatz

6

Homogenize

7

to form

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 2081745 B1 [0004]
• EP 3231575 [0005]

Claims (29)

A method for producing a multilayer, in particular two-layer, plastic web, comprising a layer of foamed plastic and a cover layer connected to the foamed plastic, characterized in that the multilayer plastic web is coextruded and exits from a slit nozzle. Method according to Claim 1 , characterized in that the gap nozzle is a Ringschlitzdüse, wherein preferably the cover layer is connected to the layer of foamed plastic on the inside of the layer of foamed plastic and / or the outside of the layer of foamed plastic. Method according to one of Claims 1 or 2 , characterized in that the multilayer plastic web emerges predominantly in the horizontal direction from the slit nozzle, in particular in the machine direction at an angle to the horizontal of less than 40 °, more preferably less than 30 °, particularly preferably less than 15 °. Method according to one of the preceding claims, characterized in that the multilayer plastic web is cooled after exiting the slit nozzle by contact with an aerosol and / or a liquid. A process for producing a multilayer, in particular two-layer, plastic web, comprising a layer of foamed plastic and a cover layer connected to the foamed plastic, in particular method according to one of the preceding claims, characterized in that a recycled material is used as a starting material for the layer of foamed plastic is, wherein the proportion of the recyclate is at least 30 wt.%, Preferably at least 60 wt.%, Particularly preferably at least 90 wt.%. Method according to one of the preceding claims, characterized in that as a starting material for the layer of foamed plastic polyethylene terephthalate (PET) is used, in particular exclusively polyethylene terephthalate. Method according to one of the preceding claims, characterized in that PET is used as a starting material for the cover layer, in particular exclusively polyethylene terephthalate. Method according to one of the preceding claims, characterized in that the method comprises the process steps crosslinking, blowing agent addition, homogenization and molding. Method according to one of the preceding claims, characterized in that the method comprises the process step dehumidifying. Method according to one of the preceding claims, characterized in that the method comprises the process step nucleating addition, wherein as nucleating agent in particular up to 5 wt.% Calcium carbonate is added, preferably up to 3 wt.%, Particularly preferably up to 1.5 wt.% , Method according to one of the preceding claims, characterized in that a process step crosslinking for a melt for producing the layer of foamed plastic has a mean residence time of 0.5 to 30 min and a melt temperature between 240 ° C and 310 ° C, preferably a middle Residence time of 1 to 5 min and a melt temperature between 275 ° C and 300 ° C, more preferably a mean residence time of 2 to 3 minutes and a melt temperature between 280 ° C and 290 ° C. Method according to one of the preceding claims, characterized in that for foaming to produce the layer of foamed plastic in a process step blowing agent additive, a blowing agent has a nitrogen content of at least 50 vol.%, Preferably 75 vol.%, Particularly preferably 97 vol.%. Method according to one of Claims 8 to 12 , characterized in that the homogenizing process step has a thermal and / or material homogenization and in particular takes place in an extruder, in particular in a second extruder downstream of the first extruder. Method according to one of Claims 8 to 13 , characterized in that the homogenizing process step for a melt for producing the foamed plastic layer has an average residence time of 0.5 to 30 minutes and a melt temperature between 240 ° C and 280 ° C, preferably a mean residence time of 1 to 10 minutes and a melt temperature between 250 ° C and 270 ° C, more preferably a mean residence time of 2 to 5 minutes, and a melt temperature between 255 ° C and 265 ° C. Method according to one of the preceding claims, characterized in that the melt used for producing the layer of foamed plastic after the homogenization step has a centrifuge average molecular weight M _z in a range of 250,000 to 500,000 g / mol, particularly preferably a centrifuge average molecular weight M _z in a range of 300,000 to 400,000 g / mol, more preferably a centrifuge average molecular weight M _z in a range of 300,000 to 350,000 g / mol. Method according to one of Claims 9 to 15 , characterized in that the dehydrating process step comprises degassing and / or drying the starting material. Plant with an extruder for plasticizing a thermoplastic material and a gap nozzle for releasing the thermoplastic material for carrying out a method according to one of the preceding claims. Multilayer plastic web, in particular a two-layer plastic web, comprising a layer of foamed plastic and a cover layer connected to the foamed plastic, wherein the plastic web is formed by a method according to one of the Claims 1 to 16 or with an attachment Claim 17 has been produced. Plastic track after Claim 18 , characterized in that the layer of foamed plastic consists of a plastic based on PET or Polyethylenfuranoat (PEF) or polylactide (PLA). Plastic track after one of the Claims 18 or 19 , characterized in that the cover layer consists of a plastic based on PET or polyethylene (PE) or Polyethylenfuranoate (PEF) or polylactide (PLA). Plastic track after one of the Claims 18 to 20 , characterized in that the density of the layer of foamed plastic is 80 to 1250 g / l, preferably 100 to 720 g / l, more preferably 200 to 650 g / l. Plastic track after one of the Claims 18 to 21 , characterized in that the layer of foamed plastic has a thickness of 0.3 to 8 mm, preferably 0.5 to 4 mm, more preferably 0.8 to 2 mm. Plastic track after one of the Claims 18 to 22 , characterized in that the cover layer has a thickness of 2 to 100 microns, preferably 5 to 30 microns, more preferably 10 to 20 microns. Plastic track after one of the Claims 18 to 23 , characterized in that the layer of foamed plastic cells having an average cell diameter of 50 to 600 microns, preferably 100 to 400 .mu.m, more preferably 150 to 250 microns. Plastic track after one of the Claims 18 to 24 , characterized in that the layer of foamed plastic up to 5 wt.% Calcium carbonate, preferably up to 3 wt.%, Particularly preferably up to 1.5 wt.%. Plastic track after one of the Claims 18 to 25 characterized in that the foamed plastic layer has a centrifuge mean molecular weight M _z in a range from 250,000 to 500,000 g / mol, more preferably a centrifuge average molecular weight M _z in a range from 300,000 to 400,000 g / mol, most preferably a centrifuge average molecular weight M _z in a range of 300,000 to 350,000 g / mol. Plastic track after one of the Claims 18 to 26 , characterized in that the layer of foamed plastic pigments and / or dye. Plastic track after one of the Claims 18 to 27 , characterized in that the cover layer is transparent. Packaging tray, comprising a multilayer plastic web according to one of Claims 18 to 28 ,

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