Method for treating a plastic film by means of atmospheric plasma

Abstract

The invention relates to an advantageous method for treating a low-hydrophilicity plastic film, wherein the method comprises the following successive steps performed on a surface of the film while it is moving: (a) activation by exposure to a cold plasma at atmospheric pressure in a first gaseous atmosphere A1 comprising a plasma gas GP1; (b) intermediate treatment by exposure to a cold plasma at atmospheric pressure in a second gaseous atmosphere A2 comprising a plasma gas GP2 and a treatment gas GT comprising an alkane, alkene or alkyne hydrocarbon gas; and (c) deposition of a thin film by exposure to a cold plasma at atmospheric pressure in a third gaseous atmosphere A3 comprising a plasma gas GP3, at least one volatile silicon precursor, and an oxidising gas.

Description

[0001] METHOD FOR TREATING A PLASTIC FILM BY ATMOSPHERIC PLASMA

[0002] Technical field

[0003] The present invention relates to the field of plastic films, particularly those which are not very hydrophilic or hydrophobic.

[0004] In this context, the present invention provides a method of treating such films so as to give them an excellent and advantageous "anti-drip" character (also called "anti-drip" or "drip-proof" character) which, moreover, is durable and resistant to subsequent thermoforming / embossing.

[0005] The present invention also provides a plastic film obtained by said method as well as its use (i) in a horticultural building, such as cultivation greenhouses, as a wall and / or roof or (ii) in the field of cooling towers.

[0006] Prior art

[0007] Growing greenhouses with walls made of transparent plastic are relatively widespread because the use of plastic, especially compared to glass greenhouses, is very advantageous on several levels, including: lightness, ease of handling, flexibility, mechanical resistance, thermal insulation and more affordable price.

[0008] Many plastics have found their use in this horticultural context, but halogenated polymers (chloropolymers or fluoropolymers) have stood out due to their excellent properties in terms of transparency, durability, weather resistance, anti-fouling properties, etc. Examples of halogenated polymers used in this context are PVC (or polyvinyl chloride) and ETFE (or ethylene tetrafluoroethylene). In particular, ETFE is often chosen because of its long service life, good UV resistance, excellent light transparency, and good mechanical and thermal properties.

[0009] However, these polymers are highly hydrophobic, which creates some drawbacks. When a hydrophobic plastic film is used for a horticultural building, moisture condensation is much more likely to form on the inner surface of the film, usually in the form of droplets. Such condensation then results in a loss of light transmission of the film (detrimental to the growth of cultivated plants). In addition, the water droplets that form on the surface of the film are very likely, once they reach a critical size, to detach and fall onto the cultivated plants, causing adverse effects on the crop. Finally, the suspended droplets and droplets that have fallen onto the plants can also generate a "magnifying glass effect" if they focus the sunlight.This can then lead to damaging “burns” on the leaves, particularly in the case of fragile plants.

[0010] Solutions have been proposed in the prior art in order to benefit from the advantages of the halogenated plastic films mentioned above while reducing their disadvantages due to their hydrophobicity.

[0011] One of the simplest solutions is to apply a liquid to one of the sides of the plastic film (the one facing the inside of the building) using a wet chemical method, for example by spraying, followed by drying the latter, in order to obtain a hydrophilic coating. For example, the application of a mixture of a silica-type sol and a surfactant is known. However, with the coating obtained by this treatment, the hydrophilic character is not very durable and it is therefore necessary to periodically carry out a new application treatment, with a significant impact in terms of costs and time, especially if the surface to be treated is large. In addition, the applied coating also often has a negative impact on the stability and transparency to UV as well as on the mechanical properties of the plastic film.These disadvantages therefore make wet chemical treatment unattractive, particularly for horticultural buildings.

[0012] Besides this, it is also known to process plastic films by the "dry method".

[0013] For example, document EP2 5301 12A proposes to surface hydrophilize an ETFE film by a corona treatment that incorporates oxygen atoms on the surface of the film. This treatment results in an increase in the polarity of the surface making water more likely to wet said surface, thus reducing the formation of drops. However, this hydrophilization effect is also highly subject to aging and corona treatment can no longer be carried out in situ. Another example is given in document CA3120783A1 which proposes to treat an ETFE film in order to avoid condensation / drip problems in horticultural buildings. The film treated according to the teaching of this document has a hydrophilic character defined by a contact angle with water < 60° and comprises at least 1 at.% of silicon on the coated surface.The treatment is for example carried out by low pressure plasma (0.01-0.5mbar) using a silicon precursor of the organosilicon type chosen from silanes, siloxanes, silazanes.

[0014] In order to increase the hydrophilicity of an ET E film intended for use in greenhouses and obtain an anti-drip effect, document EPI 829916A1 discloses the deposition of a layer by plasma treatment under vacuum or at reduced pressure in an oxygen-hydrocarbon gas mixture (e.g. ethylene).

[0015] These "hydrophilized" halogenated plastic films are also advantageous in other applications such as stadium covers or cooling towers, for example.

[0016] In the particular case of a cooling tower, it is of great interest that the material / film intended for air-water heat exchanges allows maximum spreading of the water on its surface. In an open tower, hot water from a condenser (sometimes including a few % of additives) is sprayed in microdroplets on the exchange surface, spreads out and then trickles down this surface. The trickling water thus cooled is collected and can return to the condenser for a subsequent cycle. The formation of drops by condensation on an exchange surface that is too hydrophobic would make the process significantly less efficient by drastically reducing the exchange surface.

[0017] In some of the above-mentioned applications, particularly cooling towers, it is often desired / necessary to thermoform or heat emboss the film (also sometimes referred to as "embossing") to give / print it a chosen three-dimensional shape, which increases the air-water heat exchange surface. PVC is often considered in this specific context.

[0018] However, the known "dry" processing / hydrophilization methods result in a plastic film with a coating that is not resistant to subsequent embossing treatment. Indeed, during thermoforming / embossing, the plastic film expands and the coating is damaged and even partially delaminates, which leads to a deterioration of the overall hydrophilic properties of the film. The film then no longer has a satisfactory anti-drip character over its entire surface.

[0019] Thus, it would be of particular interest to have an improved treatment method for imparting a durable anti-drip hydrophilic character to the surface of a hydrophobic plastic film, and at the same time allowing the implementation of thermoforming / embossing on said film with little or no alteration of its hydrophilic character.

[0020] Objectives of the invention

[0021] An objective of the present invention is to overcome the drawbacks of the state of the art, in particular those described above.

[0022] In particular, an objective of the present invention is to provide a treatment method for imparting a durable anti-drip character to the surface of a plastic film which is not very hydrophilic or hydrophobic.

[0023] Another objective of the present invention is to provide a treatment method for imparting a durable anti-drip character to the surface of a plastic film that is not very hydrophilic or hydrophobic, and for allowing the implementation of thermoforming / embossing on said film with little or no alteration of its hydrophilic character.

[0024] Yet another object of the present invention is to provide a treatment method for imparting a durable anti-drip character to the surface of a plastic film which is not very hydrophilic or hydrophobic, and retaining as much as possible the intrinsic properties / advantages of said film.

[0025] Finally, yet another object of the present invention is to provide a treatment method for imparting a durable anti-drip character to the surface of a low hydrophilic or hydrophobic plastic film, which significantly reduces the formation of water droplets by condensation in the case of its use as a wall / roof of a horticultural building.

[0026] Finally, yet another objective of the present invention is to provide a treatment method for imparting a durable anti-drip character to the surface of a plastic film that is not very hydrophilic or hydrophobic, which is rapid and economically advantageous (for example, less expensive and quicker to operate than the methods of the prior art).

[0027] Description of the invention

[0028] To achieve the above-mentioned objectives, the invention provides a method for treating a plastic film (i) having a first surface and a second surface and (ii) having a static contact angle with water greater than or equal to 70°, said method comprising the following successive steps carried out on said first surface of the film as it moves:

[0029] (a) activation by exposure to a cold plasma at atmospheric pressure, in a first gaseous atmosphere Al comprising a plasmagenic gas GP1 and optionally an activation gas GA,

[0030] (b) an intermediate treatment by exposure to a cold plasma at atmospheric pressure, in a second gaseous atmosphere A2 comprising a plasmagenic gas GP2 and a treatment gas GT different from the activation gas GA, said treatment gas GT comprising a hydrocarbon gas of the alkane, alkene or alkyne type; and

[0031] (c) the deposition of a thin layer by exposure to a cold plasma, in a third gaseous atmosphere A3 comprising a plasmagenic gas GP3, at least one volatile silicon precursor and an oxidizing gas.

[0032] The invention is thus based on a new and inventive approach. Indeed, the inventors have found, surprisingly, that the combination of the specific steps of the method of the invention, carried out in the order stated, makes it possible to achieve all the objectives. Thus, in particular, by using a specific activation of a low hydrophilic film, followed by a specific intermediate treatment and finally, a specific thin layer deposition, by cold plasma at atmospheric pressure, a very good and durable anti-drip character is obtained on the treated surface and this anti-drip character resists well to a subsequent hot embossing / thermoforming treatment. In addition, the intrinsic properties / advantages of the film are preserved after the treatment of the invention, in particular, its light transmission properties and its mechanical properties.

[0033] Thanks to the treatment of the invention, in the case of the use of the treated film in horticultural buildings, during the condensation of ambient / atmospheric water on the surface of the film (face facing the interior of the building), a thin continuous layer of water is formed (instead of drops), potentially flowing by gravity in the direction of the slope of the greenhouse. The water can then be collected in particular by gutters, for example.

[0034] The invention also relates to a plastic film, obtainable by the treatment method of the invention, in particular supplied in a roll. It also relates to the use of the plastic film obtained as a wall and / or roof in a horticultural building, said first surface being that facing the interior space of said building.

[0035] Other features, details and advantages of the invention will emerge from the description.

[0036] In this description and the claims, it is clearly understood that the terms "a", "an" or "the" mean "at least one" and should not be limited to "a single one", unless explicitly stated otherwise. Furthermore, when a range of values ​​is stated, the ends are included. Finally, all integral and sub-range values ​​within a numerical range / range are expressly included as if explicitly written.

[0037] In the present description and claims, the term "thin film" relates to the related field, in particular the field of plasma processing / deposition, and is fully understood by those skilled in the art.

[0038] The expression "at atmospheric pressure" according to the invention also includes a pressure close to atmospheric pressure, that is to say a pressure which deviates from atmospheric pressure by a pressure difference (positive or negative) which does not exceed a few tens or one or two hundred Pa. More precisely, the pressure in step (a) and / or (b) and / or (c) deviates from atmospheric pressure by no more than ± 100 Pa.

[0039] According to the invention, the plastic film, before undergoing the treatment process of the invention, has a static contact angle with water greater than or equal to 70°, preferably greater than or equal to 75° or even greater than or equal to 80°. The film is thus not very hydrophilic, or even hydrophobic according to the definition given to hydrophobicity. The static contact angle value with water according to the invention is usually obtained, at a temperature of 23°C and with a relative humidity level of 50%, on a drop of water deposited on the treated surface of the film, by determining the angle formed at the location where the drop meets said surface, from the tangent at the point of contact of the drop with said surface. The hydrophobicity / hydrophilicity of a film can usually be characterized by its static contact angle value (in degrees), which evaluates the high or low capacity of a liquid to wet / spread on the surface of the film.In general, it is considered that if the contact angle with water is less than 90°, the surface is hydrophilic; and, if the contact angle with water is greater than 90°, the surface is hydrophobic.

[0040] The first surface of the treated film obtained by the process according to the invention, i.e. the one having undergone the treatment, advantageously has a more hydrophilic character. In particular, said first surface shows a static contact angle with water that is reduced compared to the static contact angle with water of the starting plastic film (before the treatment according to the invention). In particular, said first surface shows a static contact angle with water less than or equal to 65°, preferably less than or equal to 60°, 50°, 40°, 30°, or even 20° or even 10°.

[0041] According to one embodiment of the invention, the plastic film is made of a halogenated polymer, in particular fluorinated or chlorinated. Preferably, the plastic film is made of a fluorinated polymer. According to an advantageous embodiment, particularly for horticultural building applications, the plastic film is made of ET E (or ethylene tetrafluoroethylene) or PTFE (or propylene tetrafluoroethylene) or PVDF (or polyvinylidene fluoride). These polymers have indeed shown good intrinsic properties for their use in greenhouses (mechanical resistance, transparency, etc.). Alternatively, the plastic film is made of a chlorinated polymer. According to an advantageous embodiment, particularly in cooling towers, the plastic film is made of PVC (or polyvinyl chloride), particularly transparent or colored (for example black and opaque).

[0042] The film according to the invention may have variable dimensions, those commonly considered in the intended application and in particular those accessible to the device used to implement the method. In particular, the method of the invention makes it possible to treat a film having a large width, for example 2 meters or more. Its thickness is also variable and can range from a few microns to a few millimeters, for example from 4 microns to 2 mm.

[0043] According to the method of the invention, the successive steps (a), (b) and (c) are carried out on said first surface of the moving film. In particular, the moving is carried out from a film source to a collection point of said film. The moving of the film in step (a) and / or (b) and / or (c) can advantageously be carried out by a so-called "roll-to-roll" device. The moving speed can be adapted as required. It can also be different between steps (a), (b) and (c). According to one embodiment, the moving speed of the film in step (a) and / or step (b) and / or step (c) is between 1 and 30 m / min, preferably between 3 and 20 m / min.

[0044] Step (a) according to the invention is an activation by exposure to a cold plasma at atmospheric pressure, in a first gaseous atmosphere Al. According to this step, said plasma is generated in a gaseous atmosphere Al so as to lead to an activation of the surface, that is to say a modification (in particular chemical) of the surface state of the film. By "cold plasma" according to the invention, we mean the definition commonly accepted in the field and clearly understood by those skilled in the art (and as opposed to "hot" or "thermal" plasma, which have very high temperatures, up to several thousand degrees centigrade, and used for example for cutting or welding metal parts).

[0045] According to the invention, said first gaseous atmosphere Al comprises a plasma gas GP1 and, optionally, an activation gas GA. Preferably, the first gaseous atmosphere Al comprises a plasma gas GP1 and an activation gas GA.

[0046] Also preferably, the plasma gas GP1 is selected from the group consisting of noble gases, nitrogen and their mixtures. Argon, nitrogen and their mixture are particularly preferred.

[0047] Also preferably, if present, the activating gas GA is selected from the group consisting of N2O, O2, CO2, H2, air and mixtures thereof.

[0048] Said second gaseous atmosphere Al may also comprise one or more other gases.

[0049] Preferably, said plasma of step (a) is formed by controlled discharge by dielectric barrier (DBD or "Dielectric Barrier Discharge"), a technique known as such for generating a plasma from the plasmagenic gas (in step (a): GP1). According to a particular embodiment, the activation step (a) is carried out at a temperature below 100°C, in particular by maintaining the plasma enclosure and / or the film at a temperature below 100°C.

[0050] According to another particular embodiment, the activation step (a) is carried out during a period of time between 0.05 and 1.5 seconds, preferably between 0.1 and 1 second.

[0051] Step (b) according to the invention is an intermediate treatment by exposure to a cold plasma at atmospheric pressure, in a second gaseous atmosphere A2. According to this step, said plasma is generated in a gaseous atmosphere A2 so as to lead to an activation of the surface and / or to a deposition of a thin layer.

[0052] According to the invention, said second gaseous atmosphere A2 comprises a plasma gas GP2 and a treatment gas GT, said treatment gas GT being different from the activation gas GA and comprising a hydrocarbon gas of the alkane, alkene or alkyne type.

[0053] Preferably, the plasma gas GP2 is selected from the group consisting of noble gases, nitrogen and their mixtures. Argon, nitrogen and their mixture are particularly preferred.

[0054] According to an advantageous embodiment, said hydrocarbon gas advantageously has a number of carbon atoms between 1 and 5.

[0055] Most preferably, the GT treatment gas consists essentially, or even consists, of a hydrocarbon gas of the alkane, alkene or alkyne type.

[0056] Said second gaseous atmosphere A2 may also comprise one or more other gases, such as, for example, hydrogen (H2).

[0057] Preferably, said plasma of step (b) is formed by controlled discharge by dielectric barrier (DBD or "Dielectric Barrier Discharge"), a technique known as such for generating a plasma from the plasmagenic gas (in step (b): GP2). According to a particular embodiment, the intermediate treatment step (b) is carried out at a temperature below 100°C, in particular by maintaining the plasma enclosure and / or the film at a temperature below 100°C.

[0058] According to another particular embodiment, the intermediate treatment step (b) is carried out during a period of time between 0.1 and 3 seconds, preferably between 0.2 and 2 seconds.

[0059] Step (c) according to the invention is a deposition of a thin layer by exposure to a cold plasma at atmospheric pressure, in a third gaseous atmosphere A3. According to this step, said plasma is generated in a gaseous atmosphere A3 so as to lead to a deposition of a thin layer.

[0060] According to the invention, said third gaseous atmosphere A3 comprises a plasma gas GP3, at least one volatile silicon precursor and an oxidizing gas.

[0061] Preferably, the oxidizing gas of step (c) is oxygen.

[0062] Also preferably, the plasma gas GP3 is selected from the group consisting of noble gases, nitrogen and their mixtures. Argon, nitrogen and their mixture are particularly preferred.

[0063] According to an advantageous embodiment, in step (c), the at least one volatile silicon precursor is chosen from alkoxides of formula Si(O(CH2)nCH3)4 with n > 0, and mixtures thereof. Preferably, according to this embodiment, n takes the value 0; 1; 2; 3 or 4 and, ideally, 0 or 1. TEOS (or tetraethoxysilane; CAS 78-10-4) has given very good results (n = 1).

[0064] According to one embodiment of the invention, the thin layer deposited in step (c) comprises at least the following elements: silicon, carbon and oxygen. In particular, it consists of a composition of the SiCxOy type.

[0065] According to one embodiment, said thin layer deposited in step (c) has a thickness of less than 10 nm, preferably less than 8 nm, or even less than 5 nm.

[0066] Preferably, said plasma of step (c) is formed by dielectric barrier discharge (DBD), a technique known as such for generating a plasma from the plasmagenic gas (in step (c): GP3). According to another particular embodiment, step (c) is carried out for a period of time between 0.2 and 6 seconds, preferably between 0.4 and 4 seconds.

[0067] According to the invention, the plasma gas GP1, the plasma gas GP2 and the plasma gas GP3 can be chosen independently of each other.

[0068] Step (a) and / or step (b) and / or step (c) is / are advantageously carried out in a plasma chamber. By "plasma chamber" is meant, as commonly accepted in the field, the chamber in which the film undergoes plasma treatment and comprising one or more electrodes and gas injection means. The electrode makes it possible (thanks to its counter-electrode and a current source) to create a discharge generating, from the plasma gas GPx, the plasma. Said injection means, for example adjacent to the electrodes, make it possible to inject the gas or gases forming the atmosphere concerned (Al, A2 or A3), in particular directly in front of the electrodes and / or onto the surface of the film to be treated.

[0069] The successive steps (a), (b) and (c) according to the invention can be carried out continuously (or “in line”) or, alternatively, discontinuously.

[0070] The successive steps (a), (b) and (c) according to the invention can be carried out:

[0071] Either continuously in three successive plasma enclosures, one plasma enclosure for each stage;

[0072] Either continuously in the same plasma enclosure using a succession of electrodes and atmospheres required for each stage (Al, then A2 then A3, in the direction of movement);

[0073] Either discontinuously in two enclosures, the film being removed from the plasma enclosure between step (a) and step (b) or between step (b) and step (c), and one of the two plasma enclosures using a succession of electrodes and the two required atmospheres (Al then A2, or A2 then A3);

[0074] Either discontinuously in the same plasma chamber, the film being removed from the chamber between step (a) and step (b) and between step (b) and step Most preferably, the successive steps (a), (b) and (c) are carried out in the same plasma chamber. This is then referred to as a "multi-zone" process. This is particularly advantageous insofar as it generates a saving of time and also because the partially treated film (after step (a) or after step (b)) is not exposed to the ambient air before being completely treated.

[0075] Preferably, step (a) and / or step (b) and / or step (c) is / are carried out in a single exposure to the plasma (or, in other words, in a single pass / scroll). Most preferably, step (a) and step (b) and step (c) are each carried out in a single exposure to the plasma (or, in other words, in a single pass / scroll).

[0076] In one embodiment of the invention, said dielectric barrier controlled discharge in step (a) and / or step (b) and / or step (c) is at low frequency. In practice in this case, the electrodes are connected to a low frequency HV generator (typically a few tens or hundreds of kHz) and of variable power.

[0077] Preferably, said dielectric barrier controlled discharge in step (a) is such that the power density is between 0.10 W / cm 2 and 10 W / cm 2 , more preferably between 0.15 and 8 W / cm 2 , more particularly between 0.2 and 5 W / cm 2 , the surface unit referring to the cumulative surface area of ​​the electrodes used for said discharge.

[0078] Preferably, said dielectric barrier controlled discharge in step (b) is such that the power density is between 0.10 W / cm 2 and 10 W / cm 2, more preferably between 0.15 and 8 W / cm 2 , more particularly between 0.2 and 5 W / cm 2 , the surface unit referring to the cumulative surface area of ​​the electrodes used for said discharge.

[0079] Preferably, said dielectric barrier controlled discharge in step (c) is such that the power density is between 0.10 W / cm 2 and 10 W / cm 2 , more preferably between 0.15 and 8 W / cm 2 , more particularly between 0.2 and 5 W / cm 2 , the surface unit referring to the cumulative surface area of ​​the electrodes used for said discharge.

[0080] Advantageously, the spacing between the active surface of the electrodes used to produce dielectric barrier controlled discharge and the moving film can be adjusted, in particular to ensure the stability and homogeneity of the plasma. For example, the distance between the film and the active surface of the electrodes can be adjusted between 1 and 2 mm.

[0081] The method of the invention may also comprise an extraction step, so as to extract / evacuate the gas(es) present in the enclosure and / or any by-products created in the plasma and not recovered on the film, for example between two steps in the case where these two steps are carried out in the same enclosure. In this case, the plasma enclosure may comprise an extraction system.

[0082] The method of the invention can, for example, advantageously use an installation as described in the Applicant's patent application WO2018078237 or WO2018091797A1.

[0083] The present invention also relates to a plastic film obtainable by the treatment method of the invention, in particular supplied in a roll. This plastic film is particularly advantageous because, in addition to the intrinsic properties of the plastic from which it is made, it has a durable hydrophilic character. In addition, it allows the implementation of thermoforming / embossing without altering or with very little alteration of its hydrophilic character.

[0084] The method of the invention can be used for many applications. For example, it can be used to manufacture plastic films that can be recycled in horticultural buildings such as greenhouses, stadium covers, or cooling towers.

[0085] The invention also relates to the use of a plastic film according to the invention as a wall and / or roof in a horticultural building, said first surface being that facing the interior space of said building.

[0086] Finally, the invention also relates to the use of a plastic film according to the invention as an exchange surface in an evaporative cooling device such as a cooling tower or a similar device.

[0087] It is understood that the present invention is in no way limited to the embodiments described above and that modifications may be made thereto without departing from the scope of the claims. It is further understood that the invention also encompasses all possible combinations of features and preferred characteristics described herein and recited in the claims. In addition, the following examples are provided for the purpose of illustration and are not intended to limit the scope of the present invention.

[0088] Examples

[0089] Example 1:

[0090] A plastic film was treated in ETRE (thickness: 0.1 mm; static contact angle with water: 104°) according to the method of the invention, using a “roll-to-roll” installation (roll width 1600 mm).

[0091] Steps (a), (b) and (c) according to the invention were carried out in a single pass (continuously) in the same plasma enclosure (“multi-zone”) comprising 7 electrodes and 3 successive exposure zones:

[0092] Zone 1, 1 electrode

[0093] Al: Argon (1 13.41 / min), hydrogen (0.0281 / min)

[0094] Zone 2, 2 electrodes l ère electrode, A2: Argon (1 13.41 / min), nitrogen (0.481 / min), ethylene (0.021 / min)

[0095] 2 ème electrode, A2: Argon (85.81 / min), nitrogen (0.481 / min), ethylene (0.021 / min),

[0096] Zone 3, 4 electrodes

[0097] A3: Argon (354.81 / min), TEOS (0.2625g / min), oxygen (0.1891 / min).

[0098] The film running speed was 7 m / min and the spacing between the film and the active surface of the electrodes was set to approximately 1 mm.

[0099] The film obtained after treatment was analyzed by X-ray induced photoelectron spectrometry or XPS, on the side of the treated surface. The atomic percentages of the elements F, O, N, C, Si were determined from flyby spectra with a Nova-Kratos™ type device with a monochromatized Al-Ka source (225 W) over an area of ​​300 mx 700 pm in normal detection (detection angle 0 = 0°). The results are presented in Table 1. They show that the surface of the film treated according to the invention (analysis thickness < 10 nm) presents the elements C, Si, N and O in significant quantities. The XPS spectrum also shows a non-negligible signal contribution due to the ETFE of the film itself (fluorine), the concentrations given therefore do not reflect the absolute composition at the surface of the film but give an indication of the chemical elements present there.

[0100] Table 1

[0101] The anti-drip character of the treated films (example according to the invention and comparative examples) was also evaluated, on the side of the treated surface. The treated film was placed as the upper wall of a test chamber, the treated surface being turned towards the inside of the chamber. An inclination of the film of 10° with respect to the horizontal was arranged. The bottom of the chamber contained water at a controlled temperature of 35°C and the chamber was placed in a refrigerator at a controlled temperature of 10°C.

[0102] After 5 days under these conditions, the film was observed and evaluated for the condensation formed and the level of coverage of its surface by drops. A score from 1 to 10 was given, according to the following scale:

[0103] Score 1: 100% of the surface covered with drops

[0104] Score 2: > 80% of the surface covered with drops Score 3: > 70% of the surface covered with drops Score 4: >50% of the surface covered with drops Score 5: > 40% of the surface covered with drops Score 6: > 30% of the surface covered with drops Score 7: > 20% of the surface covered with drops Score 8: > 10% of the surface covered with drops

[0105] Score of 9: 0% of the surface covered with visible drops and drips Score of 10: 0% of the surface covered with drops and no visible drips.

[0106] Example 1 according to the invention obtained a score of 9, i.e. it did not have any drops on its surface, demonstrating excellent results obtained with the process according to the invention. Example 2:

[0107] A black PVC plastic film (thickness: 100 microns; static contact angle with water: 97°) was treated according to the method of the invention, using a “roll-to-roll” installation (roll width 1600 mm).

[0108] Steps (a), (b) and (c) according to the invention were carried out in a single pass (continuously) in the same plasma enclosure (“multi-zone”) comprising 7 electrodes and 3 successive exposure zones:

[0109] Zone 1, 1 electrode

[0110] Al: Argon (1 13.41 / min), hydrogen (0.0281 / min)

[0111] Zone 2, 2 electrodes l ère electrode, A2: Argon (1 13.41 / min), nitrogen (0.481 / min), ethylene (0.021 / min)

[0112] 2 ème electrode, A2: Argon (85.81 / min), nitrogen (0.481 / min), ethylene (0.021 / min),

[0113] Zone 3, 4 electrodes

[0114] A3: Argon (354.81 / min), TEOS (0.2625g / min), oxygen (0.1891 / min).

[0115] The film running speed was 7 m / min and the spacing between the film and the active surface of the electrodes was set to approximately 1 mm.

[0116] The hydrophilic and anti-drip character of the film thus treated was evaluated.

[0117] The static water contact angle was determined at 23°C and 50% relative humidity. Using a syringe, a small drop of water was placed on the treated surface of the film. A side image was captured using a camera to clearly show the profile of the drop. The angle formed at the point where the drop meets the surface was determined, from the tangent at the point of contact of the drop with the surface. The film shows, on the side of the treated surface, a static water contact angle of 50°.

[0118] Wettability was assessed visually by observing, on a 10X20cm film sample completely dipped in a tank of water, the surface covered by a water film compared to the total surface of the film when it was removed from the tank in a vertical position. The film shows, on the side of the treated surface, very good wettability. A water film covers a significant part of the surface.

[0119] A 10x20 cm treated film sample also subsequently underwent a thermoforming process at 120°C, in a known manner, in order to imprint, in its center, a circular shape of 6 cm in diameter and a thickness of approximately 6 millimeters. The wettability was evaluated in the same way after this process: the sample exhibits unaltered wettability after thermoforming.

[0120] Example 3:

[0121] A treatment of a plastic film made of PET, BOPP (or "biaxially oriented polypropylene"; static contact angle with water: 105°) and ET E was carried out using a "roll-to-roll" installation (roll width 1600 mm).

[0122] Steps (a), (b) and / or (c) were carried out in a single pass (continuously) in the same plasma chamber (“multi-zone”) comprising 7 electrodes and 3 successive exposure zones.

[0123] Zone 1, 1 electrode o Al: Argon (1 13.41 / min), hydrogen (0.0281 / min)

[0124] Zone 2, 2 electrodes o 1st electrode, A2: Argon (1 13.41 / min), nitrogen (0.481 / min), ethylene (0.021 / min) o 2nd electrode, A2: Argon (85.81 / min), nitrogen (0.481 / min), ethylene (0.021 / min),

[0125] Zone 3, 4 electrodes o A3: Argon (354.81 / min), TEOS (0.2625g / min), oxygen (0.1891 / min).

[0126] The film running speed was 7 m / min and the spacing between the film and the active surface of the electrodes was set to approximately 1 mm.

[0127] In the case of the examples of the invention, all zones were activated during the passage (step (a) and (b) and (c), while in the case of the comparative examples, one or two zone(s) were deactivated.

[0128] The anti-drip character of the treated films (example according to the invention and comparative examples) was evaluated, on the side of the treated surface, as explained in example 1. After 24h and 240h, the film was observed and evaluated as to the condensation formed and the level of coverage of its surface by drops, on the basis of the scale presented above (score from 1 to 10).

[0129] The results are given in Table 2. Table 2

[0130] These results show that all of steps (a) and (b) and (c) according to the invention are necessary in order to obtain high scores after 24 hours and maintain this value stable, or practically stable, over time. Example 4:

[0131] A treatment of a plastic film made of PET, BOPP and ETFE according to the invention was carried out using a “roll-to-roll” installation (roll width 1600 mm).

[0132] Steps (a), (b) and (c) were carried out in two passes (non-continuous treatment) in the same plasma chamber (“multi-zone”) comprising 7 electrodes and 2 successive exposure zones: the first step (a) and (b) according to the invention were carried out during the first pass and step (c) during the second pass.

[0133] - First pass: o Zone 1, 3 electrodes; Al: Argon, hydrogen o Zone 2, 4 electrodes; A2: Argon, nitrogen, ethylene

[0134] - Second pass, 7 electrodes; A3: Argon, TEOS, oxygen.

[0135] The film running speed was 7 m / min and the spacing between the film and the active surface of the electrodes was set to approximately 1 mm.

[0136] The anti-drip character of the films treated according to the invention was evaluated, on the side of the treated surface, as explained in example 1. After 24h and 240h, the film was observed and evaluated as to the condensation formed and the level of coverage of its surface by drops, on the basis of the scale presented above (score from 1 to 10).

[0137] The results are given in Table 3.

[0138] Table 3

[0139] These results show that a two-pass treatment (discontinuously) also gives a good improvement in the anti-drip character of the films. In comparison with examples 1 and 3, the process of the invention carried out in a single pass, therefore continuously (or in line), nevertheless gives better results.

Claims

CLAIMS 1. Method for treating a plastic film (i) having a first surface and a second surface and (ii) having a static contact angle with water greater than or equal to 70°, said method comprising the following successive steps carried out on said first surface of the film as it moves: (a) activation by exposure to a cold plasma at atmospheric pressure, in a first gaseous atmosphere Al comprising a plasmagenic gas GP1, (b) an intermediate treatment by exposure to a cold plasma at atmospheric pressure, in a second gaseous atmosphere A2 comprising a plasmagenic gas GP2 and a treatment gas GT different from the activation gas GA, said treatment gas GT comprising a hydrocarbon gas of the alkane, alkene or alkyne type; and (c) the deposition of a thin layer by exposure to a cold plasma, in a third gaseous atmosphere A3 comprising a plasmagenic gas GP3, at least one volatile silicon precursor and an oxidizing gas.

2. Treatment method according to the preceding claim, characterized in that the plastic film is made of a halogenated polymer.

3. Treatment method according to one of the preceding claims, characterized in that steps (a), (b) and (c) are carried out continuously.

4. Treatment method according to one of the preceding claims, characterized in that step (a) and / or step (b) and / or step (c) is / are carried out in a single exposure to the plasma.

5. Treatment method according to one of the preceding claims, characterized in that steps (a), (b) and (c) are carried out in the same plasma enclosure.

6. Treatment method according to one of the preceding claims, characterized in that the at least one volatile silicon precursor is chosen from alkoxides of formula Si(O(CH2)nCH3)4 with n > 0, and mixtures thereof.

7. Treatment method according to the preceding claim, characterized in that n takes the value 0; 1; 2; 3 or 4.

8. Treatment method according to one of the preceding claims, characterized in that the first gaseous atmosphere Al comprises a plasma gas GP1 and an activation gas GA.

9. Treatment method according to one of the preceding claims, characterized in that the plasma gas GP1 and the plasma gas GP2 and the plasma gas GP3 are chosen independently from the group consisting of noble gases, nitrogen and their mixtures.

10. Treatment method according to one of the preceding claims, characterized in that the activation gas GA is chosen from a group consisting of N2O, O2, CO2, H2, air and their mixtures. 1 1. Treatment method according to one of the preceding claims, characterized in that said hydrocarbon gas has a number of carbon atoms between 1 and 5.

12. Method according to any one of the preceding claims, characterized in that said thin layer has a thickness of less than 10 nm, preferably less than 5 nm.

13. Plastic film, obtainable by the treatment process according to any one of claims 1 to 12, in particular supplied in rolls.

14. Use of a plastic film according to claim 13 as a wall and / or roof in a horticultural building, said first surface being that facing the interior space of said building.

15. Use of a plastic film according to claim 13 as an exchange surface in an evaporative cooling device such as a cooling tower.

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