Anti-corrosion multilayer plastic film

Abstract

The invention relates to a multilayer plastic film (2) comprising a heat-resistant outer layer (3), a heat-sealable inner layer (4) and a barrier layer (5) against oxygen and water vapour, arranged between the outer layer and the inner layer, the outer, inner and barrier layers being made of a polypropylene monomer.

Description

Multi-layer anti-corrosion plastic film

[0001] The invention falls within the field of multilayer anti-corrosion plastic films used for example as protective packaging against moisture and oxygen.

[0002] Multilayer anti-corrosion plastic films represent a major innovation because they offer a unique combination of corrosion barrier, heat resistance, and heat-sealing properties, facilitating packaging production. These films are designed to meet the growing demands of the food, pharmaceutical, and electronics industries, where protection against oxygen, moisture, and UV radiation is crucial.

[0003] Until recently, corrosion barrier properties were achieved by adding a layer of metal, but this has now been replaced by metallizing one of the plastic layers. This metallization process has evolved significantly over the last few decades, allowing for continuous performance improvements and reduced production costs. Deposition processes, such as vacuum metallization and sputtering, are commonly used to apply an extremely thin layer of metal, usually aluminum, to plastic substrates. This metallic layer gives the film exceptional barrier properties, preventing the penetration of gases and vapors, while also improving tear and puncture resistance.

[0004] The heat resistance of the film is generally provided by a layer of PET type plastic, while the heat-sealable layer is provided by PE type plastic.

[0005] However, despite these advantages, challenges remain, particularly regarding recyclability. Recycling these films is very expensive due to the presence of different materials that need to be separated. Incineration therefore remains the most common method for recovering value from this type of waste, which generates significant amounts of CO2 and pollutants.

[0006] To reduce greenhouse gas emissions, a solution described in patent EP3888911 involves using a multi-layered metallized plastic film made from at least 80% recycled plastic by weight.

[0007] Although the plastic film described in patent EP3888911 reduces its carbon footprint compared to a non-recycled plastic film, the plastic film of patent EP3888911 is itself difficult to recycle.

[0008] The objective of the invention is therefore to solve the aforementioned problems by proposing a new multilayer plastic film that offers barrier performance equivalent to or superior to existing films, while improving its impermeability and recyclability, and thus its carbon footprint. The invention therefore meets the growing needs of modern industries while respecting environmental requirements.

[0009] To this end, the invention relates to a multilayer plastic film comprising a heat-resistant outer layer, a heat-sealable inner layer and an oxygen and water vapor barrier layer arranged between the outer layer and the inner layer, characterized in that the outer, inner and barrier layers are made of a polypropylene monomer.

[0010] The idea behind the invention is to create a multilayer plastic film composed of a single polypropylene monomer, allowing for recycling to a level 5, thus avoiding incineration, which generates significant CO2 emissions. The concept also involves obtaining a heat-resistant outer layer, a heat-sealable inner layer, and a corrosion-resistant barrier layer that meets industrial preservation standards in both crumpled and smooth surfaces. The film according to the invention therefore meets both industrial corrosion resistance criteria and environmental criteria, complying with French and international recycling standards.

[0011] The multilayer plastic film according to the invention may also have the following characteristics:

[0012] - the barrier layer is high-density metallized;

[0013] - the barrier layer is an oriented polypropylene or a biaxially oriented polypropylene;

[0014] - the outer layer and the inner layer are made of cast polypropylene;

[0015] - the outer layer has a certain first heat-sealing temperature and the inner layer has a certain second heat-sealing temperature, the temperature of the second heat-sealing temperature being lower than the first heat-sealing temperature according to a certain temperature delta;

[0016] - the temperature difference is greater than or equal to 10°C;

[0017] - the temperature difference is preferably between 30 and 40°C;

[0018] - the outer layer has a thickness between 8 and 100 µm;

[0019] - the outer layer has a nominal thickness of approximately 25 µm;

[0020] - the inner layer has a thickness between 20 and 100 µm;

[0021] - the inner layer has a nominal thickness of approximately 40 µm;

[0022] - the barrier layer has a thickness of between 8 and 25 µm;

[0023] - the barrier layer has a nominal thickness of approximately 12 µm;

[0024] - the barrier layer comprises at least one assembly made up of several polypropylene underlayers;

[0025] - the underlayers of the barrier layer are joined together by an adhesive;

[0026] - the mass of metal present in the barrier layer is less than 5% of the total mass of the film;

[0027] - the optical density of the barrier layer is between 2.0 and 5.0;

[0028] - the optical density of the barrier layer is preferably around 3.

[0029] The invention also extends to a container such as a bag, a cover, a pouch, formed of a multilayer plastic film according to the invention and in which the outer layer is oriented towards the outside of the container while the inner layer is oriented towards the inside of the container.

[0030] The present invention will be better understood and other advantages will become apparent upon reading the detailed description of the embodiment, taken by way of non-limiting example and illustrated by the accompanying drawings, in which:

[0031] - is a schematic representation of a cross-section of a film according to the invention.

[0032] – Laest is a schematic representation of a container according to the invention using a film according to the invention visible in the zoom. Detailed description of the invention

[0033] The invention relates to a container 1, as shown in, of the type bag, sachet, pouch or cover perfectly adapted for making packaging for products of various sizes, shapes and weights.

[0034] More particularly, the container 1 according to the invention is made of a multilayer plastic film 2 according to the invention, as represented in, giving it in particular heat-sealable, corrosion barrier and heat-resistant properties.

[0035] The film 2 according to the invention typically comprises an outer heat-resistant layer 3, an inner heat-sealable layer 4 and an oxygen and water vapor barrier layer 5 arranged between the outer layer 3 and the inner layer 4.

[0036] The film 2 forming the container 1 according to the invention is, for example, folded back on itself to be heat-sealed at the edges and form an opening through which the product can be inserted. The film 2 is advantageously folded so that the outer layer 3 faces outwards from the container 1 and the inner layer 4 faces inwards from the container 1.

[0037] More specifically, the outer layer 3, the inner layer 4 and the barrier layer 5 are made of a polypropylene monomer.

[0038] It can be envisaged that the barrier layer 5 will be metallized at high density in order to optimize the anti-corrosion effect while increasing the recyclability of film 2. Indeed, the low content of metal added by metallization and the presence of a single polypropylene monomer allows film 2 to be considered as a single material and therefore as easily recyclable and recoverable.

[0039] More specifically, barrier layer 5 can be an oriented polypropylene also called OPP or even, depending on the requirements, a biaxially oriented polypropylene also called BOPP.

[0040] For their part, the outer layer 3 and the inner layer 4 can be made of cast polypropylene, also known as CPP.

[0041] One of the advantages of the invention is to use an outer layer 3 having a certain first heat-sealing temperature and an inner layer 4 having a certain second heat-sealing temperature, lower than the first heat-sealing temperature.

[0042] This temperature difference is here called the temperature delta and is preferably greater than or equal to 10°C and even more preferably between 30 and 40°C.

[0043] It is also of particular importance that the outer layer 3 has a thickness between 8 and 100 µm, preferably with a nominal thickness of approximately 25 µm. This layer thickness allows for a sufficiently thin layer to limit the amount of polypropylene to be recycled while maintaining good heat resistance properties.

[0044] For its part, the inner layer 4 can have a thickness between 20 and 100 µm with a nominal thickness of approximately 40 µm. This layer thickness helps to ensure good heat sealing.

[0045] The barrier layer 5 can have a thickness ranging from 8 to 25 µm, and more preferably a nominal thickness of approximately 12 µm. The barrier layer 5 itself can either consist of a single layer or comprise an assembly of 5S polypropylene sublayers. The advantage of assembling 5S sublayers is that it allows for adaptation to industrial needs. In film 2 according to the invention, the 5S sublayers of the barrier layer 5 can be bonded together using an adhesive such as an ultrathin adhesive, or even heat-sealed together at low temperature.

[0046] Advantageously, the barrier layer 5 can be designed to include at least two high-density metallized 5S underlayers. The most convincing corrosion resistance results were measured with three high-density metallized 5S underlayers (see Tables 1 and 2).

[0047] Metallization may be carried out using at least one metal chosen from the following list: aluminum, zinc, copper, nickel, chromium, silver, gold, and cobalt. For use in industrial packaging, aluminum is preferred due to its low cost and good corrosion resistance.

[0048] It can also be predicted that the mass of metal present in the barrier layer 5 is less than 5% of the total mass of film 2. This percentage has been determined in order to comply with recyclability standards while maintaining sufficient corrosion resistance.

[0049] The amount of metal in the barrier layer 5 of the film 2 can be determined by spectrometry. Thus, the optical density of the barrier layer 5 according to the invention can be between 2.0 and 5.0, and preferably 3.0.

[0050] Film 2 according to the invention has also been developed to meet various French and international standards which impose performance characteristics in terms of tear resistance, corrosion and water vapor.

[0051] The film 2 according to the invention was tested for its water vapor transmission rate and oxygen transfer coefficients. The term "samples," used in the tests detailed below, refers to portions of the film according to the invention, comprising an outer layer 3 of high-sit (High SIT) CPP with a thickness of 25 µm, an inner layer 4 of low-sit (Low SIT) CPP with a thickness of 40 µm, and a barrier layer 5 of OPP comprising three high-density metallized polypropylene 5S sublayers with aluminum, for a total thickness of 12 µm. The optical density of the film 2 is 3.5. This density corresponds to an aluminum content relative to the mass of the film 2 of less than 5%.

[0052] Determination of water vapor transmission rates:

[0053] The samples are kept at 23°C throughout their storage prior to analysis. The dimensions of the cut samples are 100 cm² and the test area is 50 cm². The sample was taken from the center of film 2.

[0054] Water vapor transmission rates are measured according to ASTM F1249. Samples are cut and placed in the cells of the permeability measuring device. The inner layer 4 of film 2 is continuously swept with dry nitrogen, while the outer layer 3 is swept with nitrogen saturated with moisture. The water vapor present in the humidified gas diffuses through film 2. The carrier gas then becomes saturated with water vapor and is directed towards an infrared sensor. Water vapor transmission rates are expressed in g / (m².day). The device used is a PERMATRAN W3 / 33 (MOCON) with an infrared detector. The carrier gas is pure dry nitrogen with a flow rate set at 10 ml / min. The set temperature and humidity are 38°C (dry gas) on the inner layer 4 side and 90% RH on the outer layer 3 side.

[0055] Three samples were submitted to the tests, named Test Specimen No. 1, Test Specimen No. 2 and Test Specimen No. 3.

[0056] Determination of oxygen transfer coefficients:

[0057] The samples are kept at 23°C throughout their storage prior to analysis. The dimensions of the cut samples are 100 cm² and the test area is 50 cm². The sample for the test tubes is taken from the center of film 2.

[0058] Oxygen transfer coefficient measurements are performed according to ASTM D3985 and ASTM F1927 standards. Samples are cut and placed in the cells of the permeability measuring apparatus. The inner surface of film 2 is continuously scanned with the carrier gas, while the outer surface is scanned with the test gas. Oxygen diffuses through film 2 and is directed to the detector.

[0059] The oxygen transfer coefficient is expressed in cm² / (m².day.1 atm). The instrument used here is an OXTRAN 2 / 21 with a coulometric detector and a 95% N / 5% H carrier gas with a flow rate set at 10 ml / min. The measurement range is from 0.005 to 200 cm² / m² / day / 1 atm. The test gas is pure oxygen with a flow rate set at 20 ml / min.

[0060] The set temperature and humidity are respectively 23°C and 50%RH on the outer layer 3 side / 50%RH on the inner layer 4 side.

[0061] Two samples were subjected to tests named Test Specimen No. 1 and Test Specimen No. 2.

[0062] These results show that film 2 according to the invention exhibits high barrier properties against moisture and gases.

[0063] Film 2 according to the invention is currently the best compromise in terms of heat resistance, sealing and corrosion barrier.

[0064] The table below compares the properties mentioned above for the most commonly used plastics currently used in packaging films. The higher the number of stars, the more suitable the plastic is for the properties indicated. Properties PEPPPETT Heat resistance (outer layer)*********Barrier obtained by metallization of the polymer film (barrier layer)***********Heat sealing (inner layer)**********

[0065] This table shows that polypropylene presents the best compromise for all the properties necessary to form a container according to the invention of the packaging type.

[0066] Indeed, the heat-sealing temperature delta between the outer layer in CPP High SIT and the inner layer in CPP low SIT is sufficient to allow the use of polypropylene alone as a plastic constituent.

Claims

multilayer plastic film (2) comprising an outer heat-resistant layer (3), an inner heat-sealable layer (4) and an oxygen and water vapor barrier layer (5) arranged between the outer layer and the inner layer, the outer, inner and barrier layers being made of a polypropylene monomer, characterized in that the barrier layer comprises at least one assembly composed of several high-density metallized polypropylene sublayers (5S). Multilayer plastic film according to claim 1, characterized in that the barrier layer is an oriented polypropylene or a biaxially oriented polypropylene. Multilayer plastic film according to any one of the preceding claims, characterized in that the outer layer and the inner layer are made of cast polypropylene. Multilayer plastic film according to any one of the preceding claims, characterized in that the outer layer has a certain first heat-sealing temperature and the inner layer has a certain second heat-sealing temperature, and in that the temperature of the second heat-sealing temperature is lower than the first heat-sealing temperature by a certain temperature delta. Multilayer plastic film according to claim 4, characterized in that the temperature delta is greater than or equal to 10°C. Multilayer plastic film according to claim 5, characterized in that the temperature delta is preferably between 30 and 40°C. multilayer plastic film according to any one of the preceding claims, characterized in that the outer layer has a thickness between 8 and 100 µm. Multilayer plastic film according to claim 7, characterized in that the outer layer has a nominal thickness of 25 µm. multilayer plastic film according to any one of the preceding claims, characterized in that the inner layer has a thickness between 20 and 100 µm. Multilayer plastic film according to claim 9, characterized in that the inner layer has a nominal thickness of 40 µm. Multilayer plastic film according to any one of the preceding claims, characterized in that the barrier layer has a thickness of between 8 and 25 µm. Multilayer plastic film according to claim 11, characterized in that the barrier layer has a nominal thickness of 12 µm. Multilayer plastic film according to claim 12, characterized in that the sublayers of the barrier layer are assembled together by an adhesive. Multilayer plastic film according to claim 1, characterized in that the mass of metal present in the barrier layer is less than 5% of the total mass of the film. Multilayer plastic film according to any one of the preceding claims, characterized in that the optical density of the barrier layer is between 2.0 and 5.

0. Multilayer plastic film according to claim 15, characterized in that the optical density of the barrier layer is 3. Container (1), such as a bag, cover, pouch, formed of a multilayer plastic film according to any one of the preceding claims, characterized in that the outer layer is oriented towards the outside of the container while the inner layer is oriented towards the inside of the container.

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