MULTIFUNCTIONAL ADHESIVE FILM FOR THE SURFACE PROTECTION OF WORKPIECES

Abstract

A multilayer thermoformable film to protect the surface of a workpiece includes an underlayer having first and second faces. The underlayer is made from an adhesive material configured to adhere to the surface of the workpiece by the first face. At least one layer of polymer material is attached to the second face of the adhesive underlayer. The layer of polymer material is resistant to erosion by solid particles and to erosion by liquid particles. It is formed from a polymer material chosen from a polyurethane, a polyether ether ketone and a polyethylene having a very high molecular weight, with a Shore D hardness of between 50 and 65 D. A method of surface protection of the workpiece includes thermoforming the film in a shape adapted to match the shape of at least a portion of the workpiece and applying the film thermoformed onto the surface of the workpiece.

Claims

1-11. (canceled)

12. A multilayer thermoformable film to protect a surface of a part, comprising: a sublayer of an adhesive material, referred to as an adhesive sublayer, comprising first and second faces, the sublayer configured to adhere to the surface of the part via the first face; at least one layer made of polymer material attached to the second face of the adhesive sublayer opposite the first face, and said at least one layer made of polymer material is resistant to erosion by solid particles and to erosion by liquid particles; and wherein said at least one layer made of polymer material is formed from a polymer material selected from a polyurethane, a polyether ether ketone and an ultra-high molecular weight polyethylene, with a Shore D hardness of between 50 and 65 D.

13. The multilayer thermoformable film as claimed in claim 12, wherein said at least one layer made of polymer material has a thickness between 50 and 500 μm.

14. The multilayer thermoformable film as claimed in claim 13, wherein said at least one layer made of polymer material has a thickness between 100 and 300 μm.

15. The multilayer thermoformable film as claimed in claim 14, wherein said at least one layer made of polymer material has a thickness equal to 200 μm.

16. The multilayer thermoformable film as claimed in claim 12, wherein said at least one layer made of polymer material is surface-functionalized.

17. The multilayer thermoformable film as claimed in claim 12, further comprising at least one functional layer made of polymer material having at least one of an anti-icing and fouling resistance function, said at least one functional layer being superposed or juxtaposed, on the adhesive sublayer, with said at least one layer made of polymer material.

18. The multilayer thermoformable film as claimed in claim 12, further comprising at least one second layer made of polymer material having a surface structuring that limits drag in air, superposed or juxtaposed, on the adhesive sublayer, with said at least one layer made of polymer material that is resistant to erosion by solid particles and to erosion by liquid particles.

19. The multilayer thermoformable film as claimed in claim 18, wherein constituent layers juxtaposed or superposed with one another are joined to one another by an adhesive, heat-sealed to on another, or co-extruded to on another.

20. The multilayer thermoformable film as claimed in claim 17, wherein constituent layers juxtaposed or superposed with one another are joined to one another by an adhesive, heat-sealed to on another, or co-extruded to on another.

21. The multilayer thermoformable film as claimed in claim 12, wherein the adhesive sublayer is formed of a pressure-sensitive adhesive material.

22. The multilayer thermoformable film as claimed in claim 21, wherein the pressure-sensitive adhesive material is chosen from acrylic, rubber and silicone materials.

23. The multilayer thermoformable film as claimed in claim 12, wherein the adhesive sublayer has a thickness between 25 and 100 μm.

24. A process for protecting a surface of a part, comprises the steps of: thermoforming the multilayer thermoformable film as claimed in claim 12 to a shape matching a shape of at least one section of the part; and applying the multilayer thermoformable film to the surface of said at least one section of the part.

25. The process of claim 24 is utilized to protect on an outer surface of an aircraft.

26. A kit for protecting a surface of a part, comprising a plurality of multilayer thermoformable films as claimed in claim 12 that are thermoformed such that each multilayer thermoformable film matches a shape of a section of the part and said plurality of multilayer thermoformable films together cover an entire surface of the part to be protected.

27. The kit as claimed in claim 26, further comprising a tool to apply said plurality of multilayer thermoformable films to the surface of the part.

Description

[0056] The features and advantages of the invention will become more clearly apparent in light of the exemplary embodiments hereinbelow, provided simply by way of illustration and without in any way limiting the invention, with the support of FIGS. 1A to 5B, in which:

[0057] FIG. 1A schematically represents a film according to a first embodiment of the invention;

[0058] FIG. 1B schematically represents a film according to a second embodiment of the invention;

[0059] FIG. 2A schematically represents a film according to a third embodiment of the invention;

[0060] FIG. 2B schematically represents a film according to a fourth embodiment of the invention;

[0061] FIG. 3A schematically represents a film according to a fifth embodiment of the invention, applied to an aircraft leading edge;

[0062] FIG. 3B schematically represents a film according to a sixth embodiment of the invention, applied to an aircraft leading edge;

[0063] FIGS. 4A and 4B show parts covered with an adhesive film, respectively with a polyurethane-based film from the prior art (FIG. 4A) and with a PEEK-based film in accordance with the invention (FIG. 4B), at the end of a P-JET rain erosion test, each line corresponding to the number of impacts by liquid particles indicated in front of it; and

[0064] FIGS. 5A and 5B show parts covered with an adhesive film, respectively with a polyurethane-based film in accordance with the invention (FIG. 5A) and with a polyurethane-based film of lower hardness (FIG. 5B), at the end of a sand erosion test for 200 g of projected particles.

[0065] A first example of a film 10 according to the invention, in which the various constituent layers are juxtaposed (“horizontal complexing”), and of planar conformation, is shown in FIG. 1A. In this figure, as in the following figures, for reasons of clarity, the various elements are represented slightly spaced out from one another, although they are in actual fact tightly applied against one another. Similarly, the relative dimensions of the various constituent elements of the film are in no way representative of the reality.

[0066] The film 10 is applied to a part 20, which may in particular be an aircraft structural part likely to be subjected, in operation, to highly erosive conditions, such as a leading edge.

[0067] The film 10 comprises an adhesive sublayer 11, formed from a pressure-sensitive adhesive material, for instance of the acrylic or rubber or silicone family. This adhesive sublayer is continuous and it has a thickness between 25 and 100 μm. It comprises a first face 111, applied against the surface of the part 20, and an opposite second face 112, to which the various constituent functional layers of the film 10 are attached.

[0068] The film 10 comprises a layer 12 made of polymer material(s) that is resistant to erosion by solid particles and to erosion by liquid particles. This layer 12, referred to as an erosion-resistant layer, is formed of three layer portions: two end layer portions 13, 13′ formed from a first polymer material and that are resistant to erosion by solid particles, and a central layer portion 14 formed from a second polymer material and that is resistant to erosion by liquid particles.

[0069] The first polymer material and the second polymer material are in particular chosen from the following materials: TPU, PEEK and UHMW-PE.

[0070] The film also comprises two anti-icing functional layers 15, 15′, that are juxtaposed, on the adhesive sublayer 11, with the erosion-resistant layer 12, on either side of the latter. These anti-icing layers 15, 15′ are formed of polymer material.

[0071] Any solution known to a person skilled in the art may be used to form the anti-icing layers of the film according to the invention. By way of examples, these layers may comprise: [0072] a coating containing from 25 to 29% of silicon atoms, from 22 to 45% of oxygen atoms and from 26 to 49% of carbon atoms, relative to the total atomic % of the coating, this coating having a structuring, in particular in the form of a pattern of dots or lines; [0073] a coating obtained by plasma polymerization of hexamethyldisiloxane (HMDSO); or [0074] a coating containing from 15 to 75% of fluorine atoms and from 25 to 85 atomic % of other components, relative to the total atomic % of the coating, this coating having a structuring, in particular in the form of a pattern of dots or lines.

[0075] In variants of the invention, illustrated in FIG. 1B, the film 10 has the same features as those described above, with the exception of the erosion-resistant layer 12, which is in this case formed of a single block of a single polymer material that gives it a good resistance both to sand erosion and to rain erosion. This polymer material is selected from the following materials: TPU, PEEK and UHMW-PE, with a Shore D hardness of between 50 and 65 D.

[0076] A third example of a film 10 according to the invention, in which the various constituent layers are juxtaposed or superposed with one another (“mixed complexing”), and of planar conformation, is shown in FIG. 2A.

[0077] The film 10 is applied to a part 20, via its adhesive sublayer 11.

[0078] It comprises a layer 12 made of polymer material(s) that is resistant to erosion by solid particles and to erosion by liquid particles. This erosion-resistant layer 12 is formed of two layer portions that are superposed on one another on the adhesive sublayer 11: a lower layer portion 13 formed of a first polymer material and that is resistant to erosion by solid particles, and an upper layer portion 14 formed of a second polymer material and that is resistant to erosion by liquid particles.

[0079] The film also comprises two anti-icing functional layers made of polymer material 15, 15′, that are juxtaposed, on the adhesive sublayer 11, with the erosion-resistant layer 12, on either side of the latter.

[0080] It additionally comprises two functional layers made of polymer material 16, 16′ that limit drag in air, which are juxtaposed with the anti-icing functional layers 15, 15′, on either side of these layers. These so-called drag reduction layers have a sawtooth surface texturing.

[0081] Another example of a film 10 according to the invention, represented in FIG. 2B, is identical to the film described above with reference to FIG. 2A, with the exception of the erosion-resistant layer 12, which is formed of a single polymer material having a high performance in terms of resistance to erosion both by liquid particles and by solid particles, chosen from materials of PU, PEEK and UHMW-PE type, with a Shore D hardness of between 50 and 65 D.

[0082] The films 10 shown in FIGS. 1A, 1B, 2A and 2B all have a surface density less than or equal to 590 g/m.sup.2. They are easy to apply and remove, and they make it possible to effectively protect the part, in a localized manner, both against attacks by liquid particles and against attacks by solid particles, including in cases of severe exposure.

[0083] Generally, the exact configuration of the film 10 is chosen to be suited to the protection requirements of the various zones of the part, so as to ensure an optimal protection thereof.

[0084] By way of example, particular configurations of films 10 suitable for the protection of a leading edge 20 of an aircraft are shown in FIG. 3A. In these figures, the various layers and layer portions are represented slightly spaced out from one another for reasons of clarity. However, such a configuration in no way limits the invention, the various layers and layer portions juxtaposed with one another being on the contrary preferentially tightly applied against one another.

[0085] In the embodiment illustrated in FIG. 3A, the film 10 comprises an erosion-resistant layer 12 formed of two layer portions 13, 13′ made of a first polymer material that are resistant to erosion by solid particles, referred to as sand erosion-resistant layer portions, which are juxtaposed on either side of a central layer portion 14 formed of a second polymer material and that is resistant to erosion by liquid particles, referred to as a rain erosion-resistant layer portion. It additionally comprises two anti-icing functional end layers 15, 15′, which are positioned on either side of the erosion-resistant layer 12.

[0086] More particularly, the film 10 is positioned on the part 20 such that the rain erosion-resistant layer portion 14 is positioned at the zone of normal incidence of the part, and the sand erosion-resistant layer portions 13, 13′ and the anti-icing layers 15, 15′ are positioned at zones of low-angle incidence, thus ensuring an optimal targeted protection of the part with respect to the stresses to which it will be exposed in flight.

[0087] In the embodiment illustrated in FIG. 3B, the film 10 is identical to the film described above with reference to FIG. 3A, with the exception of the erosion-resistant layer 12, which is formed of a single polymer material having a high performance in terms of resistance to erosion both by liquid particles and by solid particles, chosen from materials of PU, PEEK and UHMW-PE type, with a Shore D hardness of between 50 and 65 D. This layer extends over the zone of normal incidence and the contiguous zones of low-angle incidence of the aircraft part 20.

Erosion Resistance Tests

[0088] Parts covered with films in accordance with the present invention were subjected to tests aiming to evaluate their resistance to erosion by liquid particles (rain erosion) and to erosion by solid particles (sand erosion).

A) Experiment 1

[0089] Films according to the invention comprising an acrylic adhesive sublayer and an erosion-resistant layer are deposited on an SAE 1008 steel plate or on a painted plate (aluminum 2024 substrate, plated, anodized and painted with an epoxy primer layer, having a thickness between 15 and 25 μm, and finished by a polyurethane layer, having a thickness between 50 and 130 μm), then subjected to the high-pressure cleaner test, according to the protocol described below.

[0090] The erosion-resistant layers of the various adhesive films tested are formed as follows: high-hardness thermoplastic polyurethane (TPU) (55 to 60 Shore D) (Film F1), PEEK (65 Shore D) (Film F2), UHMW-PE (50 Shore D) (Film F3).

[0091] By way of comparative example, also subjected to the test is a plate covered with an adhesive film comprising a layer of thermoplastic polyurethane proposed by the prior art, with a Shore D hardness of 35, lower than that recommended by the present invention (Film F0).

[0092] A.1) Resistance to rain erosion

[0093] The duration of the test is 60 s. The objective is to evaluate the resistance of the selected adhesive films to a pressurized water jet in order to simulate a high-velocity “rain” environment. The apparatus that makes it possible to spray the water is a Karcher-type cleaner with a water spray nozzle. There is therefore an impact of a continuous jet and not of drops of water. This test therefore simulates, in a close way, the erosion phenomenon encountered by a leading edge of a helicopter blade or of an airplane wing in a rain environment.

[0094] The operating conditions are the following.

[0095] Pressure: 150 bar

[0096] Nozzle/part distance: 4.7 cm

[0097] Angle of impact on the part: 90 degrees

[0098] Water flow rate: 9 L/min

[0099] For the steel plates, the nozzle/substrate distance is constant. It is the time required for the perforation of the adhesive film that is measured. The test is stopped after 60 s of exposure if the film is not perforated.

[0100] For the painted plates, the test time is constant (10 s). It is the nozzle/part distance required for the perforation that is measured.

[0101] The results obtained are indicated in table 1 below.

TABLE-US-00001 TABLE 1 Results of the rain erosion test with the high-pressure cleaner, where: Nd = not degraded; ✓ = Film not perforated, not damaged after 10 s; X = Film perforated after a test time less than or equal to 10 s Parameter measured Time before 1.sup.st degradation Nozzle/part distance Substrate Steel plate Painted plate Nozzle/part distance (cm) 4 4 6 10 20 30 40 50 Film F0 <1 s x x x x x x ✓ Film F1 Nd x x ✓ ✓ ✓ ✓ ✓ Film F2 Nd ✓ ✓ ✓ ✓ ✓ ✓ ✓ Film F3 Nd ✓ ✓ ✓ ✓ ✓ ✓ ✓

[0102] These results demonstrate that the films in accordance with the invention all have a much better behavior, in terms of resistance to rain erosion, than the film F0 proposed by the prior art.

[0103] A.2) Resistance to Sand Erosion

[0104] The objective is to evaluate the resistance of the films to a pressurized jet of sand in order to simulate a high-velocity “air+sand” environment. The apparatus that makes it possible to spray this jet of sand is an industrial sand blaster.

[0105] For this test, the part used is an SAE 1008 steel plate. One such painted plate, without film, is also subjected to the test (Control).

[0106] The operating conditions are the following:

[0107] Pressure: 1.4 bar

[0108] Nozzle/part distance: 4.7 cm

[0109] Angle of impact: 90 degrees

[0110] Sand: aluminum oxide (diameter 200 μm)

[0111] Flow rate: (10 ±3) g/s

[0112] The results obtained are indicated in table 2 below.

TABLE-US-00002 TABLE 2 Results of the sand erosion test Time before 1.sup.st degradations Observations Control 5 to 10 s — Film F0 >3 h Browning Film F1 1 to 2 h Cracking Film F2 3 to 6 min Cracking Film F3 1 to 2 h Cracking

[0113] These results show that the films in accordance with the invention F1 (high-hardness TPU) and F3 (UHMW-PE) offer a behavior in terms of resistance to sand erosion that is comparable to the solution from the prior art F0. They also show the great resistance of the film F2 (PEEK) with respect to bare aircraft paint.

[0114] Overall, in terms of combined protection against rain erosion and sand erosion, the films in accordance with the present invention prove much more effective than the low-hardness polyurethane-based films from the prior art.

[0115] B) Experiment 2

[0116] For this experiment, the adhesive films were tested on a part of simplified configuration representative of an airplane structural part comprising, on a pre-pickled 2024 aluminum plate, an epoxy primer layer (having a thickness between 15 and 25 μm) and a polyurethane top coat (having a thickness between 50 and 100 μm).

[0117] The films tested comprise an acrylic adhesive sublayer having a thickness of 50 μm, and an erosion-resistant layer having a thickness between 100 and 250 μm, of the following composition: high-hardness thermoplastic polyurethane (aliphatic polyurethane having a thickness of 200 μm) with a Shore D hardness of 40 to 50 (limits excluded) (Film F4, comparative example); high-hardness thermoplastic polyurethane (aliphatic polyurethane having a thickness of 250 μm) with a Shore D hardness of 50 to 60 (Film F5); high-hardness thermoplastic polyurethane (aliphatic polyurethane having a thickness of 250 μm) with a Shore D hardness of 50 to 60 (with adhesion promoter, Film F5′); semicrystalline PEEK (having a thickness of 100 μm) with a Shore D hardness of 65 (Film F6); semicrystalline PEEK (having a thickness of 100 μm) with a Shore D hardness of 65 (with adhesion promoter, Film F6′).

[0118] By way of comparative example, the film F0 described above in Experiment 1, proposed by the prior art, was also tested.

[0119] B.1) Resistance to Rain Erosion

[0120] The test protocol is in accordance with that described in document WO 2009/074514 (technique commonly known under the name P-JET). The operating parameters applied and the results obtained are indicated in table 3 below.

TABLE-US-00003 TABLE 3 Results of the rain erosion test Pressure Speed Number of Film (bar) (m/s) impacts Result F0 275 200 20 to 1000 Perforation at 100 impacts F6 350 230 20 to 1000 No visible damage F6′ 350 230 20 to 1000 No visible damage F5 350 230 20 to 1000 No visible damage F5 350 230 1000 to 8000  Perforation at around 7000 F5′ 350 230 20 to 1000 No visible damage F5′ 350 230 2200 to 3000  Perforation at around 2800 F4 275 200 20 to 1000 No visible damage F4 350 230 20 to 1000 No visible damage F4 350 230 1000 to 8000  Perforation at around 5000

[0121] It emerges from these results that the adhesive films in accordance with the invention F5 and F6 both have a rain erosion resistance capacity that is greatly improved with respect to the film F0 from the prior art, including in the presence of an adhesion promoter. They additionally have a better performance than the film F4, of lower hardness.

[0122] B.2) Resistance to rain erosion after aging

[0123] The parts coated with the various films tested were subjected to accelerated UV aging in a conventional aging chamber known under the name QUV, reproducing the damage caused by the UV portion of sunlight, the rain and the dew. The parts were subjected therein to alternating cycles of UV light and humidity (by condensation of water) at controlled high temperatures, according to the following parameters: total time 1000 h (125 cycles of 4 h condensation/4 h UVB).

[0124] The test protocol is in accordance with that described in example B.1/ above. The operating parameters applied and the results obtained are indicated in table 4 below.

TABLE-US-00004 TABLE 4 Results of the test of rain erosion after aging Pressure Speed Number of Film (bar) (m/s) impacts Result F0 275 200  20 to 1000 Perforation at 20 impacts F6′ 350 230  20 to 1000 No visible damage F6′ 350 230  6000 to 20000 Slight roughness at 8000 F5 350 230 1000 to 8000 Perforation at around 7200 F4 350 230 1000 to 6000 Perforation at around 2000

[0125] It emerges from these results that the adhesive films in accordance with the invention still have, after accelerated aging, a rain erosion resistance capacity that is greatly improved with respect to the film F0 from the prior art. The film in accordance with the invention F5 additionally has a better performance than the film F4, of lower hardness.

[0126] B.3) Resistance to Sand Erosion

[0127] The test protocol is that of the Standard ASTM G76, relating to the tests of erosion by solid particles.

[0128] Schematically, solid particles (spherical silica particles having a diameter of 200 μm) are projected by an air flow onto the substrate at a velocity of 55 m/s, at a pressure of 0.280 bar, with a particle rate of 2 g/min and an impact angle that may vary between 20 degrees and 90 degrees. The degree of erosion is determined from the linear portion of the graph of weight loss of the substrate as a function of the time.

[0129] The test is carried out at 20°, for 100 g of projected solid particles.

[0130] The results obtained are indicated in table 5 below.

TABLE-US-00005 TABLE 5 Results of the sand erosion test Film F0 F4 F5 F6 Degree of erosion 0.0389 0.1028 0.0974 0.0597 (mg/g)

[0131] These results show that the films in accordance with the invention F5 and F6 have a resistance to sand erosion that is slightly worse than that of the film F0 from the prior art, but very high all the same, and better than that of the film F4 having a

[0132] Shore D hardness lower than that recommended by the present invention. Similar results are obtained after aging.

[0133] The same test was carried out for 200 g of projected particles, for the films F5 and F4. The results obtained are shown respectively in FIGS. 5A and 5B. It is observed therein that the film F5 has withstood sand erosion much better than the film F4, having a Shore D hardness lower than 50.

[0134] Overall, for the combined protection against rain erosion and sand erosion, the films in accordance with the invention perform significantly better than the film from the prior art F0 and the film F4.

[0135] C) Experiment 3

[0136] For this experiment, the adhesive films were tested on a part of simplified configuration representative of a helicopter structural part comprising, on a pre-pickled 2024 aluminum plate, in succession, an epoxy top coat having a thickness between 15 and 25 μm and a polyurethane top coat having a thickness between 50 and 100 μm, and also, when specified, a layer of adhesion promoter having a thickness of 26 μm.

[0137] The films tested comprise an acrylic adhesive sublayer having a thickness of 50 μm, and an erosion-resistant layer having a thickness between 100 and 250 μm, of the following composition: high-hardness thermoplastic polyurethane (aliphatic polyurethane having a thickness of 200 μm) with a Shore D hardness of 40 to 50 (limits excluded) (Film F4, comparative example); high-hardness thermoplastic polyurethane (aliphatic polyurethane having a thickness of 200 μm) with a Shore D hardness of 40 to 50 (limits excluded) with adhesion promoter (Film F4′, comparative example); high-hardness thermoplastic polyurethane (aliphatic polyurethane having a thickness of 250 μm) with a Shore D hardness of 50 to 60 (Film F5); high-hardness thermoplastic polyurethane (aliphatic polyurethane having a thickness of 250 μm) with a Shore D hardness of 50 to 60 (with adhesion promoter, Film F5′); semicrystalline PEEK (having a thickness of 100 μm) with a Shore D hardness of 65 (Film F6); semicrystalline PEEK (having a thickness of 100 μm) with a Shore D hardness of 65 (with adhesion promoter, Film F6′); UHMW-PE with a Shore D hardness of 50 (ultra-high molecular weight semicrystalline thermoplastic polymer from the polyolefin family, having a thickness of 250 μm) (Film F7); UHMW-PE with a Shore D hardness of 50 (with adhesion promoter, Film F7′).

[0138] By way of comparative example, the film F0′ as described above in Experiment 1 and with adhesion promoter, proposed by the prior art, was also tested.

[0139] 0.1) Resistance to Rain Erosion

[0140] The test protocol is in accordance with that described with reference to Experiment 2. The operating parameters applied and the results obtained are indicated in table 6 below.

TABLE-US-00006 TABLE 6 Results of the rain erosion test Pressure Speed Number of Film (bar) (m/s) impacts Result F0′ 275 200 20 to 1000 Perforation at 20 impacts F6′ 350 230 6000 to 20000  Plastic deformation from 6000 - no visible damage F4 350 230 20 to 7000 Delamination at 7000 F4′ 350 230 1000 to 20000  Plastic deformation from 4000 - perforation at 15 000 F7 350 230 20 to 8000 Plastic deformation from 20 - no perforation F7′ 350 230 20 to 8000 Plastic deformation from 20 - no perforation F5′ 350 230 20 to 1000 No visible damage F5′ 350 230 5200 to 6000  Plastic deformation from 5400

[0141] FIGS. 4A and 4B show the parts obtained at the end of the test, respectively for the film from the prior art F0′ and for the film in accordance with the invention F6′. On each of these parts, each line corresponds to the number of impacts by the liquid particles indicated in front of it. It is clearly apparent on these figures that the part covered with the film F0′ (with adhesion promoter) is greatly damaged at the end of the test, for all the numbers of impacts tested, whereas the part covered with the film F6′ (with adhesion promoter) in accordance with the present invention is only very slightly damaged, for much higher numbers of impacts.

[0142] It emerges from these results that the adhesive films F7, and F5′, F6′ and F7′ in accordance with the invention all have a much better resistance to rain erosion than the film F0′ from the prior art.

[0143] C.2) Resistance to Sand Erosion

[0144] The test protocol is in accordance with that described with reference to Experiment 2.

[0145] The test is carried out at 20°, for 100 g of projected solid particles.

[0146] The results obtained are indicated in table 7 below.

TABLE-US-00007 TABLE 7 Results of the sand erosion test Film F0′ F6′ F4 F4′ F7 F7′ Degree of erosion 0.0282 0.0417 0.099 0.10525 0.1023 0.09815 (mg/g)

[0147] These results show that the films in accordance with the invention F6′, F7 and F7′ have a resistance to sand erosion that is slightly worse than that of the film F0′ (with adhesion promoter) from the prior art, but very high all the same.

[0148] Overall, for the combined protection against rain erosion and sand erosion, here too it is observed that the films in accordance with the invention perform significantly better than the film proposed by the prior art, and than the films F4 and F4′, the Shore D hardness of which is lower than 50.

[0149] Cohesion Test

[0150] A cohesion test was carried out by application of the film F6 according to the invention, or the film F0 from the prior art, to parts covered with a paint primer.

[0151] The parts were subjected to an aging test at 75° C. for 20 h, then 180-degree peeling at 100 mm/min.

[0152] The results are shown in table 8 below.

TABLE-US-00008 TABLE 8 Results of the cohesion test Tensile force Film tested measured Observation Film F0 15 N/cm Non-compliant measurement due to elongation - 100% delamination of the adhesive Film F6 20.7 N/cm 100% peeling of the adhesive

[0153] It is observed that the film F0 according to the invention has a delamination of the adhesive (cohesive failure) for a force of 15 N/cm, whereas the film F6 in accordance with the invention does not delaminate at 20 N/cm. Only a peeling of the film from its adhesive (adhesive failure) is observed.

[0154] The adhesive strength of the PEEK with a Shore D hardness of 65 chosen in accordance with the present invention, measured according to the standard ISO 8510-2, additionally corresponds to a mean load per width of 11.61 (N/cm), versus only 8.19 N/cm for the TPU from the prior art, with a Shore D hardness of 35.