Method for producing uniaxially stretched multilayer film

Abstract

Method for producing monoaxially stretched multilayer film comprising the steps of: a) providing a multilayer film having two external layers comprising virgin thermoplastic material, and an internal layer comprising post-consumer recycled thermoplastic material, said film having a thickness greater than 100µm, b) heating said multilayer film to a temperature between 70 and 85°C, c) monoaxially stretching said multilayer film, while maintaining the temperature between 70 and 85°C, to a thickness of less than 100µm, d) annealing said monoaxially stretched film by maintaining the temperature of said film between 70 and 85°C for at least 20 seconds. Preferably, the internal layer, or core, comprises recycled PET, while external layers comprise virgin PET. The invention also relates to a monoaxially stretched multilayer film of thickness less than 100µm having two external layers comprising virgin PET and an internal layer comprising recycled thermoplastic material.

Description

[0001] METHOD FOR PRODUCING MONOAXIALLY STRETCHED MULTILAYER

[0002] FILM .

[0003] The present invention relates to a method for producing monoaxially stretched multilayer, which can be used for closing any type of containers used in food, pharmaceutical , medical, logistic or any other sector of industry.

[0004] Currently, the films used for closing trays in the food packaging sector are made of 100% virgin polyethylene terephthalate and polypropylene (PET-PP) which is suitable fox- sealing polypropylene trays, or are made of 100% virgin polyethylene terephthalate and polyethylene (PET-PE) which is suitable for sealing polypropylene or cardboard trays .

[0005] The problem of using 100% virgin (PET-PP) or (PET- PE) is the massive negative impact on the environment, which now represents huge challenge for the sector. Indeed, governmental organizations have started to adopt measures to force the industry to reduce the consumption of certain plastic products, such as the Directive (EU) 2019 / 904 of the European Parliament and of the Council on the reduction of the impact of certain plastics products on the environment .

[0006] The sector of food or phar*maceutical packaging has started to use PET films include recycled materials (typically 80%) , such films comprise of two external layers made from 100% virgin material, as they come into direct contact with food products, these two external layers have a thikness in the range of 20 pm each; the film further comprises an internal layer made of 80% recycled material and is 140 pm thick. This internal layer cannot come into contact with food products ,

[0007] Currently only 100% virgin materials can be used to seal polypropylene, polyester and cardboard trays . The aforementioned films comprising recycled materials cannot be used due to their high thicknesses . In fact, the films with 80% recycled material currently on the market are too thick to be used as films, sheets, strips or films for sealing food trays with heat sealers or to create flexible bags or containers .

[0008] More precisely, the films of recycled material available in the market have a typical thickness of 180 pm while the films, sheets, strips or films used to close the trays have a thickness ranging from 40 to 80 pm.

[0009] With the aim of providing films for closing trays made at least partly of recycled materials, which can be safely used in food or pharmaceutical packaging, the Applicant has now found a method for reducing the thickness of the films available in the market through monoaxial stretching process .

[0010] In particular, the Applicant has found a method for producing monoaxially stretched multilayer film comprising the subsequent steps of : a- providing a multilayer film having two external layers comprises virgin thermoplastic material, and an internal layer comprises at least partially post-consumer recycled thermoplastic material, said multilayer film has a thickness greater than 140 pm, b- progressively heating said multilayer film to a temperature comprised between 70 to 85°C, c- progressively and monoaxially stretching said multilayer film, while maintaining the temperature between 70 to 85°C, to a thickness less than 100 pm obtaining a monoaxially stretched multilayer film, d- annealing said monoaxially stretched multilayer film by maintaining the temperature of said multilayer film between 70 to 85°C for at least 20 seconds .

[0011] The monoaxial stretching of the multilayer films leads to the alignment of the polymeric chains and consequently improve their resistance to perforation through an increase in the stiffness of the films due to the phenomenon of mono-orientation,

[0012] The progressive heating followed by the progressive monoaxially stretching of the multilayer film ensures a gradual path without altering its physical and chemical characteristics .

[0013] The annealing step increases the strength of the monoaxially stretched multilayer film, particularly when the stretch ratio in this step is kept in the range of 0. 99 to 1.01.

[0014] Advantageously, the method of the present invention also comprises a step of : e - gradually cooling the monoaxially stretched multilayer film to a temperature comprised between 30 to 40°C.

[0015] The gradual cooling of the stretched multilayer film allows to maintain its physical properties .

[0016] Advantageously, the virgin thermoplastic material comprises polyethylene terephthalate (PET) , preferably the virgin thermoplastic material is PET-PP and / or PET- PE . Additionally, the at least partially post-consumer recycled thermoplastic material comprises at least partially post -consumer recycled PET, preferably, the at least partially post- consumer recycled thermoplastic material is at least partially post-consumer recycled PET-PP and / or PET -PE.

[0017] As indicated, PET-PP ox* PET- PE are widely used in the food packaging sector due to their remarkable chemical resistance and high mechanical and gas barrier properties .

[0018] In a preferred embodiment, up to 80% by weight of the monoaxially stretched multilayer film consists of the internal layer comprising at least partially post- consumer recycled thermoplastic material . Preferably, each layer of the two external layers comprising virgin thermoplastic material represents 10% by weight of the monoaxially stretched multilayer film.

[0019] This ratio between recycled / virgin thermoplastic materials satisfies the European Directive (EU) 201.9 / 904 .

[0020] Preferably, the multilayer film is stretched monoaxially at a stretching ratio comprised between 2 to 6 times preferably 4 times in terms of area ratio.

[0021] In a preferred and advantageous embodiment, the method of the present, invention is conducted through a monoaxial MDO (machine direction orientation) stretching machine comprising a plux'ality of heating rollers , a plurality of stretching rollers, a plux'ality of annealing rollers and optionally a plurality of cooling rollers

[0022] These machines are available on the market with different sizes and capacities and are usually connected to a PC equipped with a software dedicated to control the process .

[0023] Advantageously, the plurality of heating rollers have progressively increasing temperatures .

[0024] In other words, the multilayer film can be heated sequentially by the plurality of heating rollers comprising, for example, a first heating roller, a second heating roller, and a third heating roller. The third heating roller has a temperature higher than the temperature of the second heating roller, and the temperature of the second heating roller is higher than the temperature of the first heating roller.

[0025] Advantageously, the plurality of stretching rollers has progressively decreasing stretching gaps .

[0026] This means that the multilayer film is stretched monoaxially by a plurality of stretching rollers comprising a first stretching roller, a second stretching roller, a third stretching roller and a fourth stretching roller. The multilayer film is initially stretched between the first stretching roller and the second stretching roller and then is stretched between the third stretching roller and the fourth stretching roller, wherein a first stretching gap between the first stretching roller and the second stretching rollex* is greater than the second stretching gap between the third stretching roller and the fourth stretching roller.

[0027] Preferably, the thickness of the multilayer film is comprised between 140 and 240 pm, preferably 180 pm.

[0028] Preferably, the thickness of said monoaxially stretched multilayer film is comprised between 50 and 100 pm .

[0029] Another aspect of the present invention consists in a monoaxially stretched multilayer film having two external layers comprising virgin thermoplastic material, and an internal layer comprising at. least partially post-consumer recycled thermoplastic material, said monoaxially stretched multilayer film having a thickness of less than 100 pm, wherein said virgin thermoplastic material comprises polyethylene terephthalate (PET) .

[0030] Preferably, said virgin thermoplastic material is PET-PP and / or PET- PE.

[0031] Preferably, said at least partly post-consumer recycled thermoplastic material comprises post-consumer recycled PET, preferably said at least partly post- consumer recycled thermoplastic material is post- consumer recycled PET-PP and / or post-consumer recycled PET-PE.

[0032] This monoaxially stretched multilayer film complies with Directive (EU) 2019 / 904 of the European Parliament and of the Council .

[0033] Advantageously, the monoaxially stretched multilayer film is sealable, peelable and / or has UV blocking properties .

[0034] Another aspect, of the present invention consist in a p3.cks.5i ng article comprising n10110ci.xia.lly stretched, multilayer film according to the present invention.

Claims

CLAIMS1) Method for producing monoaxially stx-etched multilayer film comprising the subsequent steps of : a- providing a multilayer film having two external layers comprising virgin thermoplastic material, and an internal layer comprising at least partially post- consumer recycled thermoplastic material, said multilayer film having a thickness greater than 140 pm, b- progressively heating said multilayer film to a temperature comprised between 70 and 85 °C, c~ progressively and monoaxially stretching said multilayer' film, while maintaining the temperature between 70 and 85°C, to a thickness of less than 100 pm obtaining a monoaxially stretched multilayer film, d- annealing said monoaxially stretched multilayer film by maintaining the temperature of said multilayer film between 70 and 85 °C for at least 20 seconds .2) Method for producing monoaxially stretched multilayer film according to claim 1, further comprising a step of : e~ gradually cooling said monoaxially stretched multilayer film to a temperature comprised between 30 and 40 °C.3 . Method for producing monoaxially stretched multilayer film according to claim 1 or 2, wherein said virgin thermoplastic material comprises polyethylene terephthalate (PET) , preferably said virgin thermoplastic material is PET-PP and / or PET-PE.4) Method for producing monoaxially stretched multilayer film according to any one of the preceding claims, wherein said at least partially post -consumer recycledthermoplastic material comprises post - consumer recycled PET, preferably said at least partially post -consumer recycled thermoplastic material is post-consumer recycled PET-PP and / or PET- PE .

5. Method for producing monoaxially stretched multilayer film according to claim 4 , wherein up to 80% by weight of the monoaxially stretched multilayer film consists of the internal layer comprising at least partially post - consumer recycled thermoplastic material .

6. Method for producing monoaxially stretched multilayer film according to any one of the preceding claims , wherein said multilayer film is monoaxially stretched to a stretching ratio comprised between 2 to 6 times preferably 4 times in terms of area ratio.7) Method for producing monoaxially stretched multilayer film according to any one of the preceding claims, wherein said method is carried out through a monoaxial MDO (machine direction orientation) stretching machine comprising a plurality of heating rollers, a plurality of stretching rollers, a plurality of annealing rollers and optionally a plurality of cooling rollers .

8. Method for producing monoaxially stretched multilayer film according to claim 7 , wherein said plurality of heating rollers has progressively increasing temperatures .

9. Method for producing monoaxially stretched multilayer film according to claim 7 or 8 , wherein said plurality of thinning rollers has progressively decreasing stretching gaps .

10. Method for producing monoaxially stretchedmultilayer film according to any one of the preceding claims, wherein said thickness of said multilayer film is comprised between 140 and 240 pm, preferably 180 pm.

11. Method for producing monoaxially stretched multilayer film according to any one of the preceding claims, wherein said thickness of said monoaxially stretched multilayer film is comprised between 50 and 100 pm .12) Monoaxially stretched multilayer film having two external layers comprising virgin thermoplastic material, and an internal layer comprising at least partially post -consumer recycled thermoplastic material, said monoaxially stretched multilayer film having a thickness of less than 100 pm, wherein said virgin thermoplastic material comprises polyethylene terephthalate (PET) .13) Monoaxially stretched multilayer film according to claim 12 , wherein said virgin thermoplastic material is PET-PP and / or PET- PE .14) Monoaxially stretched multilayer film according to claim 12 or 13 , wherein said at least partly post- consumer recycled thermoplastic material is post- consumer recycled PET, preferably said at least partly post-consumer recycled thermoplastic material is post- consumer recycled PET-PP and / or PET-PE .

15. Packaging article comprising a monoaxially stretched multilayer film according to any one of the preceding laims f roui 12 to 14 .

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