Anti-icing film

Abstract

The invention relates to a protective film comprising a polyurethane layer, wherein the polyurethane is a thermoplastic polyurethane having a hard phase composed of an aliphatic isocyanate and a diol having 4 to 20 carbon atoms and a soft phase composed of a polyether diol and / or a polyester diol, and has a glass transition temperature determined by dynamic-mechanical thermoanalysis at 1 Hz of at most -35°C, wherein the polyurethane layer contains an ultrahigh molecular weight silicone which is distributed homogeneously in the layer and does not migrate, and to methods and to the use of the protective film for protection of wind turbines or wind turbine parts from erosion and ice adhesion, in which the protective film is stuck onto a wind turbine part.

Description

Anti-icing film

[0001] The present invention relates to the use of a thermoplastic protective film comprising a layer of thermoplastic polyurethane containing homogeneously distributed silicone for protecting wind turbines, in particular their rotor blades, from icing and erosion.

[0002] With the increased use of renewable energies for electricity generation, wind turbines are of particular interest. On the one hand, wind is available worldwide, and on the other hand, wind turbines are a highly developed technology that requires low investment compared to alternatives such as solar and hydropower. Wind turbines are very often part of wind farms with multiple wind turbines. A wind turbine comprises a rotor with a hub and rotor blades, as well as a nacelle in which the generator and often a gearbox are located. The nacelle is usually mounted on a tower so it can rotate. In addition, monitoring and control systems, as well as grid connection technology, are located in the nacelle and in the base or outside the tower.

[0003] One problem during the operation of wind turbines is the formation of ice on the rotor blades. This reduces efficiency and can also lead to rotor imbalance. Chunks of ice falling or being thrown away by the rotational movement pose a potential hazard below the rotor blades and in the immediate vicinity of the wind turbine. As a result, the turbines must generally shut down automatically when ice forms. Many proposals have already been made to solve this problem. For example, the rotor blades should be equipped with heating and / or an ice-repellent coating should be applied to the surface. Examples of this prior art include DE 196 21 485 A1, AT 13 020 U1, US 2017 / 0043860 A1, WO 2021 / 179069 A1 and DE 10 2012 025 087 A1.

[0004] Another problem is surface erosion, particularly on the rotor blades of wind turbines. UV radiation, wind-borne particles and insects, weather conditions such as rain and hail, and temperature fluctuations place significant stress on the surfaces of the rotor blades, as well as the nacelle and tower surfaces. For aircraft, it has already been proposed to protect the surface against erosion by means of a coating, see, for example, WO 2016 / 172016 A1 and EP 2 183 331 B1.

[0005] For both cases, various materials have been discussed as coatings; typically, hydrophobic coatings based on polyurethane, silicone, or fluoropolymers are used. Textured surfaces are intended to enhance the effect. In both coatings for protection against ice adhesion and those for protection against erosion, in addition to the direct application of the coating, usually in the form of a paint, to the surface to be protected, the application of the coating to a film, or its provision as a film or film layer, and the subsequent bonding of the film to the surface has been mentioned.

[0006] A disadvantage of the known paint-based coatings is that their renewal is very costly, as the existing coating must be removed. It is also not clear from the publications whether a coating designed to protect against icing protects against erosion, and vice versa.

[0007] Therefore, the task still remains to protect parts of wind turbines from icing and erosion in a cost-effective, simple, and effective manner. Surprisingly, it has now been discovered that films with a polyurethane layer containing homogeneously distributed and essentially stationary silicone as the uppermost layer, i.e. the layer furthest away from the wind turbine part, offer both protection against icing and erosion, provided the polyurethane is a thermoplastic polyurethane that does not contain aromatic compounds. Contains isocyanate groups and has a soft phase of polyesterdiol. This film can be used as a self-adhesive protective film or as a combination of a separate adhesive, such as a spray adhesive, and film.

[0008] The stated object is therefore achieved by a protective film comprising a polyurethane layer as the uppermost layer, wherein the polyurethane is a thermoplastic polyurethane (abbreviated TPU) with a hard phase consisting of an aliphatic isocyanate and a diol having 4 to 20 carbon atoms and a soft phase consisting of a polyester diol, a glass transition temperature (abbreviated T g ) of a maximum of -35 °C, and wherein the polyurethane layer contains an ultra-high molecular weight silicone that is homogeneously distributed throughout the layer and does not migrate. The problem is further solved by a wind turbine component with an adhered protective film, as well as by the use of the protective film and a method for protecting wind turbine components from erosion and ice adhesion using the protective film.

[0009] In contrast to the installation of heaters, the protective film according to the invention and used in the invention can be bonded to any existing rotor blade or other parts of an existing wind turbine. The stretchability of the film allows it to be bonded even to curved surfaces and across acute angles. The polyurethane layer containing ultra-high molecular weight silicone provides the bonded part with reliable anti-icing protection. Compared to silicone-based coatings, the protective films according to the invention based on polyurethane with homogeneously distributed and anchored silicone exhibit better weathering properties. Compared to fluoropolymers, this results in more effective anti-icing protection. The protective film exhibits high cut and tear resistance, which provides effective protection against impacting particles. The protective film possesses very high rebound resilience and thus enables good erosion protection in the rain. In addition, The protective film is electrically insulating, which counteracts lightning strikes. A service life of at least 20 years is expected with good protection against erosion, weathering, ice and lightning strikes.

[0010] The use according to the invention enables the protection of all parts of a wind turbine, i.e. tower, nacelle and rotor blades, as well as of particularly stressed parts of the surface of these parts, e.g. the rotor blade tips and / or leading edges (i.e. the edges at the front in the direction of rotation of the blades).

[0011] Polyurethanes, including thermoplastic polyurethanes, are well known, as is their use in coatings. For example, the brochure "Thermoplastic Polyurethane Elastomers (TPU)" from BASF SE describes a variety of commercially available TPU types. The brochure does not specify which types are suitable as material for protective films and which properties determine their suitability. With the exception of one (L1185A12 on page 46), all of the types specifically investigated are based on aromatic isocyanate groups. According to the invention, the polyurethane is a thermoplastic polyurethane with a hard phase consisting of an aliphatic diisocyanate and a short-chain diol, as well as a soft phase consisting of polyester diol. Aromatic diisocyanates are not suitable because they yellow. This can be seen, for example, in the brochure and in KR 10 2019 0088431 A1, which deals with TPU for the production of artificial leather for automotive interiors.The short-chain diol in the hard phase typically has 4 to 12 carbon atoms, preferably 4 to 10 carbon atoms; butanediol is particularly preferred. Suitable diisocyanates include known aliphatic diisocyanates, e.g., hexamethylene diisocyanate, isophorone diisocyanate, and diisocyanatodicyclohexylmethane; diisocyanatodicyclohexylmethane is particularly preferred. Polyesterdiols are suitable for the soft phase. In a preferred embodiment, the polyesterdiols are not made from lactones, but from dicarboxylic acids and dialcohols. Many TPUs with a soft phase made of lactone have too low a Erosion resistance. Typically, TPU granules have weight-average molecular weights measured by gel permeation chromatography in the range of 80,000 g / mol to 170,000 g / mol.

[0012] It has been shown that an important parameter for assessing erosion resistance is the glass transition temperature. The measurement of the T g is conveniently carried out using a dynamic mechanical thermal analysis, abbreviated DMTA, according to DIN EN ISO 6721-4:2019-09, analogous to the loss modulus E". DMTA is the most sensitive method for determining the glass transition temperature. In the present invention, a measurement frequency of 1 Hz is used. The determination is carried out on laminates with a thickness of approximately 300 pm TPU layer with approximately 60 pm adhesive layer. The TPU should have the lowest possible glass transition temperature. According to the invention, the T g of the TPU at -35 °C and below, preferably at -40 °C and below, particularly preferably at -45 °C or -50 °C and below. The glass transition temperature here is the T gThe soft phase is meant. The hard phase also generally has a softening temperature, but it is significantly higher. The polyurethane layer also has high tensile strength and elongation at break; in particular, it does not tear in the tensile test according to DIN / EN 527, and the elongation at break, measured according to ISO 527-3, is 450 to 850%.

[0013] Suitable layer thicknesses for the TPU layer are in the range of, for example, 100 to 500 pm, preferably 280 to 320 pm. If used, thicknesses of, for example, 40 to 80 pm are well suited for the adhesive layer, with 50 to 70 pm being preferred, e.g., approximately 60 pm.

[0014] The silicone ensures the necessary reduction of ice adhesion. For this purpose, an ultra-high molecular weight silicone (abbreviated to uhmw silicone) is homogeneously distributed in the polyurethane layer and essentially anchored in place. Previous proposals considered migration of the contained silicone to the film surface to be advantageous or necessary, e.g., US 2019 / 062591 A1. a silicone is used in which such migration does not occur, as it has surprisingly been shown that this is essential for the durability of the ice-repellency. For this reason, ultra-high molecular weight silicones are chosen, preferably those bonded to a - preferably mineral - carrier such as fumed silica. This preferably mineral carrier, loaded with uhmw silicone, is not mobile in the TPU layer. Starting from the carrier, the chains of the uhmw silicone extend into the TPU matrix and the uhmw silicone thus fulfils the desired function across the entire layer cross-section. This means that ice-repelling function is also achieved in the event of weathering-related erosion. The weight-average molecular weight of the uhmw silicone should be at least 150,000 g / mol. A particularly suitable silicone is polydimethylsiloxane. Suitable dosages of the uhmw silicone are from 1 to 15 wt.-% silicone based on the total weight of the polyurethane layer, preferably from 2 to 8 wt.%. This does not include any carrier that may be present. A commercially available product of this type is Genioplast® Pellet S from Wacker Chemie AG, Germany. Genioplast® Pellet S contains 30 wt.% mineral carrier. The use of Genioplast® Pellet S, among others, is mentioned in JP 2017-078131 A as an additive in TPU coatings with improved scratch resistance and haptics, as well as designability. The TPU can be based on either aromatic or aliphatic isocyanates.

[0015] The film preferably comprises an adhesive layer, i.e. the protective film is a self-adhesive film. Such an adhesive layer is formed by a weather-resistant adhesive that adheres to both the TPU layer and the typical materials of wind turbine components. An adhesive layer that does not affect the T gof the laminate. Acrylate adhesives, particularly acrylic hot melt adhesives or UV-curing acrylate adhesives, are particularly suitable, as their adhesion is not affected by weathering factors such as sun, water, and salt. Such adhesives are commercially available from, for example, 3M Corp., USA; Tesa SE, Germany; and Henkel AG & Co. KGaA, Germany. The adhesive bond strength after 24 hours on glass fiber reinforced plastic (GRP) according to the Finat test method should typically be between 1 and 10 N / 2.5 cm, with primer up to 25 N / 2.5 cm. Typically, the adhesive layer is covered by a release liner in a conventional manner until the protective film is applied to a wind turbine component. As is also known, the adhesive layer can also be applied to the release liner and only then laminated to the polyurethane layer or a carrier layer arranged underneath it.

[0016] Alternatively, the protective film can be bonded to the part of the wind turbine to be protected using a separate adhesive, preferably a spray adhesive. The protective film and adhesive are preferably provided as a kit. A suitable adhesive, for example, is 3M High Strength 90.

[0017] The protective film according to the invention can be produced in any known manner. Polyurethane and silicone are preferably either premixed or fed in parallel to an extruder. The molten material is then formed into films through a slot die and / or a calender and fixed by means of one or more chill rolls. If an adhesive layer is present, it can be produced on a release liner, as already mentioned, and laminated to the TPU layer obtained as a film. Alternatively, the adhesive layer can be obtained by applying the adhesive, or a solution, suspension, or melt thereof, directly to the TPU layer. Applying precursors of the adhesive to the TPU layer is also possible.

[0018] The protective film may have a carrier layer beneath the polyurethane layer or, in the case of self-adhesive protective films, between the adhesive layer and the polyurethane layer, but this is not necessary and therefore not preferred. Such a carrier layer, if present, consists of a thermoplastic or elastomer with a breaking elongation of the material as a film in the range of 100 to 250%, a 2% modulus in the range of 7 to 25 N / 15 mm, and a tensile strength in the range of 25 to 40 N / 15 mm (all (measured according to DIN EN ISO 527-3 / 2 / 200). The elongation at break is preferably in the range of 150 to 200%, the 2% modulus in the range of 11 to 15 N / 15 mm, and the tensile strength in the range of 15 to 18 N / 15 mm. If desired, the protective film can also have additional layers, such as decorative layers, although this is also not preferred.

[0019] In a preferred embodiment, a primer is applied to the surface of the wind turbine component before applying the film. Common primer systems are suitable; for GRP, for example, 3M Primer W9910 or Coroplast SP 100 UV.

[0020] To apply the protective film to a wind turbine component, the surface to be protected is usually cleaned first. In one embodiment, a primer is applied to the cleaned surface to optimize adhesion.

[0021] The protective film is then cut to size, unless pre-cut pieces are provided. In particular to protect parts of the rotor blades that are subject to particular stress, the protective film used according to the invention can be provided in the form of cut pieces which are already precisely adapted in one or more cut pieces to the areas of the wind turbine part to be protected. Cut pieces can be rolled up and delivered with a marking of the intended position on the wind turbine part. If several cut pieces are required for one part, e.g. a rotor blade, provision as a packaging unit is preferred. Instructions which provide information on the order in which the cut pieces are to be applied and the intended position can be enclosed. The protective film used according to the invention can also be obtained by cutting to the desired shape, e.g. with scissors or a knife.

[0022] In the next step, a release liner is removed from the adhesive layer (if necessary), or the adhesive is applied, and the protective film is firmly bonded to the wind turbine component by pressing it down. Thanks to the mechanical properties of the carrier film, the protective film can also be bonded over edges and onto curved surfaces.

[0023] If the protective film needs to be replaced, it can often be simply removed, if necessary after heating to temperatures of 50 to 100 °C, for example. The resulting surface can be directly covered with a new protective film as described above, if necessary after reapplying primer.

[0024] The invention will be illustrated by the following examples, but is not limited to the specifically described embodiments. Unless otherwise stated or the context requires otherwise, percentages are by weight, and in case of doubt, by the total weight of the mixture.

[0025] The invention also relates to all combinations of preferred embodiments, provided they are not mutually exclusive. The terms "about" or "approx." in conjunction with a numerical value mean that values ​​that are at least 10% higher or lower, or 5% higher or lower, and in any case 1% higher or lower, are included.

[0026] Examples A variety of different film materials and additives were tested. Layers of TPU from two leading manufacturers and modified PVC were tested as the top layer of the protective film. Silicone additives from various producers and fluoropolymers were tested as additives. Films with a thickness of 250 to 350 μm were produced for testing. Tests have shown that, depending on the additive, a dry blend of the ingredients is sufficient. It is sufficient if an extruder screw with a mixing section or a twin-screw extruder is available for extruding the films. This procedure was preferred because any additional thermal stress on the TPUs should be avoided. Alternatively, the films can be produced using an additive masterbatch or by dosing the additive via a side feeder on the extruder. The films were coated with a transfer adhesive or an adhesive system for the Taber test and to determine ice adhesion. Self-adhesive films were used to test erosion resistance (particles / rain).

[0027] The materials used are listed in Table 1, and the formulations of the tested films are given in Table 2. The amounts in Table 2 are given in wt. %, based on the total weight of the mixture used to produce the layer. The glass transition temperatures in Table 1 were determined according to DIN EN ISO 6721-7 on 2 mm thick strips with a width of 10 mm and a length of 44 mm, which were clamped at a distance of 30 mm to also record the melting temperature. The glass transition temperatures measured using variants of DIN EN ISO 6721-4 and DIN EN ISO 6721-7 do not differ within the limits of measurement accuracy. The thicker samples may have resulted in an overestimation of the glass transition temperature.

[0028] Table 1 : Materials

[0029] Table 2: Films (layers)

[0030] Example 1 Optics: The protective film should be homogeneous and translucent / transparent with a defect-free surface. The visual assessment yielded the results shown in Table 3.

[0031] Table 3: Optics

[0032] The films based on the mixtures / compounds containing fluoropolymers / additives showed after processing on the extruder or rolling mill The film has a yellowish color. Such films or additives are unsuitable and were therefore not tested in further tests.

[0033] Example 2 Erosion resistance: The erosion resistance was measured using the Taber test in accordance with DIN ISO 9352, H18, 1000 g, 2000 cycles, target: less than 0.2 g weight loss, ie better than / equal to the commercial film.

[0034] Table 4: Weight losses

[0035] The results for cf.7, cf.10 and cf.11 in Table 4 show that PVC is not suitable as a material for the top layer of a protective film, as its erosion resistance is too low.

[0036] Example 3 Particle erosion: To determine the resistance to erosion by impacting particles, a particle jet, approx. 6 bar, 400 pm electrocorundum, 10 min., more than 1,000 g per cm 2 directed at the foil. Target: greater than 150 pm unweary foil [ie better / equal to benchmark]. The foil, fixed on a steel sheet, is shot at with electro-corundum from a nozzle with 2" 0 at an angle of approximately 45°. After After 10 minutes, a piece of film is removed from the center where the particle beam hit and from the edge where the beam did not hit, and a cross-sectional image is taken at 12.5x magnification. Based on this image, the visually detectable non-degraded film thickness is measured. Table 5 lists the results.

[0037] Table 5: Particle erosion

[0038] The targeted modification of the composition of TPU variants II and III led to a significant improvement in resistance to particle erosion. PVC only partially achieved the required resistance. The incorporation of the additive to achieve ice-repellent properties did not impair the resistance to particle erosion. The TPU with polyetherdiol from cf. 16 performed significantly worse than the TPU with polyesterdiol.

[0039] Example 4 Droplet erosion: In a first test according to ASTM G73-10 with a rotating disk, 1 mm beam, 155 m / s, airfoil, 500 pulses / s, target: greater than 20 h without breakdown [ie better than / equal to benchmark]. The results are listed in Table 6.

[0040] Table 6: Droplet erosion

[0041] The results demonstrate that PVC-based films do not achieve the desired performance profile of > 20 hours in terms of droplet erosion resistance. In this test, all TPUs demonstrated acceptable performance, with TPU III being particularly advantageous. No significant effect on droplet erosion is expected from the addition of the additives.

[0042] Example 5 Drop erosion: In a second test according to ASTM G73-10 with swirling arms, 160 m / s peak speed, approx. 30 mm / h rain, approx. 1 - 2 mm drop size measured, target: greater than 20 h without breakdown [ie better / equal to benchmark], Table 7 lists the results.

[0043] Table 7: Droplet erosion

[0044] The target of > 20 h resistance without puncture was not achieved by TPU I in this test. The T gof TPU I is approximately -25 °C, ie it is above the limit of -35 °C. The usable TPU II, III, IV, on the other hand, have T g in the range of -40 to -45 °C.

[0045] Example 6 Ice adhesion: To assess ice adhesion, the adhesion capacity [N / mm 2 ] of an ice block with a diameter of 16 mm adhered at -15°C, Target: less than 0.5 N / mm 2 [i.e., better than / equal to benchmark] The films applied to a round aluminum support (D = 16 mm) were exposed to a liquid reservoir (ice spout) filled with a defined volume of deionized water (250 μl) and thus tempered on the sample cooling stage. The water was frozen. The temperature regime used was "-15°C" for cooling the sample and measuring apparatus. - The test setup was cooled to -8 °C in the LINKAM-LTS 350 cooling table at 2 K / min and then tempered for 5 min. - cooled to -40 °C at 1 K / min, the temperature was maintained for 10 min. - The temperature was heated to -15°C at 1 K / min and this temperature was maintained for the duration of the test. A steadily increasing feed force was applied to the frozen ice puck using a shear ram, and the shear force required to detach the ice puck from the film was determined using a load cell. Simultaneously, the advance of the ice puck was recorded using an inductive displacement sensor. The measured values ​​were recorded both analogously and digitally for further analysis. With the area between the ice puck and the film known, the required shear stress o was then calculated from the determined shear force. A measured value for ice adhesion was averaged from at least five measurements. The force values ​​were only used for the analysis if the ice puck had been cleanly torn off at the ice-film interface. The results are presented in Table 8.

[0046] Table 8: Ice adhesion

[0047] The results demonstrate that the addition of a silicone additive drastically reduces ice adhesion. Although even better results were achieved with silicone films and other mixtures, such films (layers) are unsuitable as protective films due to their lack of erosion resistance, and their service life would be far too short.

[0048] Example 7 Contact angle: The contact angles of water and a mixture of water and 2-n-butoxyethanol in a ratio of 9:1 were determined using a DAS 100 droplet contour analysis system from Krüss, with ADVANCE 1.14 software, a DS4210 dosing system, and an ST3210 sample table. The advancing (FSW) and receding (RZW) contact angles were determined. Angles were measured at five different locations on the film. The mean values ​​are shown in Table 9.

[0049] Table 9: Contact angle

[0050] It is clearly evident from the films (Exp. 1, Comp. 13, and Comp. 14) that small receding angles of less than 30° in water + 2-n-butoxyethanol do not show a direct correlation with the observed reduced ice adhesion of the films. It appears that the contact angle of films does not represent a clear criterion for describing ice-repellent properties.

[0051] The present invention provides protection of the surface of wind turbine components against icing and erosion by means of the protective film comprising a polyurethane layer containing homogeneously distributed and firmly anchored silicone, wherein the protective film is bonded to the surface of the wind turbine components.

Claims

Patent claims 1 . A protective film comprising a polyurethane layer, wherein the polyurethane is a thermoplastic polyurethane with a hard phase consisting of an aliphatic isocyanate and a diol having 4 to 20 carbon atoms and a soft phase consisting of a polyester diol and has a glass transition temperature determined by dynamic mechanical thermal analysis at 1 Hz of a maximum of -35 °C, characterized in that the polyurethane layer contains an ultra-high molecular weight silicone which is homogeneously distributed in the layer and does not migrate.

2. Protective film according to claim 1, characterized in that the silicone has a weight-average molecular weight of at least 150,000 g / mol.

3. Protective film according to claim 1 or 2, characterized in that the silicone is bonded to a mineral carrier, preferably to pyrogenic silica, and / or the silicone is polydimethylsiloxane.

4. Protective film according to one of claims 1 to 3, characterized in that it contains from 1 to 15 wt.% of silicone based on the total weight of the polyurethane layer, preferably from 2 to 8 wt.%.

5. Protective film according to one of claims 1 to 4, characterized in that the thermoplastic polyurethane has a glass transition temperature of -40 °C or below, preferably of -45 °C or below, particularly preferably -50 °C or below.

6. Protective film according to one of claims 1 to 5, characterized in that the soft phase of the thermoplastic polyurethane consists of polyetherdiol and / or polyesterdiol with a weight-average molecular weight of at least 80,000 g / mol to 170,000 g / mol.

7. Protective film according to one of claims 1 to 6, characterized in that the protective film has an erosion resistance, determined by 10 minutes of bombardment of the film fixed on a steel sheet at an angle of approximately 45° from a nozzle with 2“ 0 electrocorundum, taking a sample in the middle where the particle beam hit and at the edge where the beam did not hit, creating a cross-sectional image with 12.5x magnification and measuring the visually recognizable, non-worn film thickness, of at least 150 pm of unbreakable film.

8. The protective film according to any one of claims 1 to 7, characterized in that the protective film has an erosion resistance, determined according to ASTM G73-10, swirling arms, 160 m / sec. peak velocity, 30 mm / h rainfall, 1 mm droplet size, of > 20 h without penetration.

9. Protective film according to one of claims 1 to 8, characterized in that an ice adhesion, determined via the adhesion of an ice puck frozen at -15 °C, is in the range of 300 to 850 kPa, preferably in the range of 300 to 500 kPa.

10. Protective film according to claims 1 to 9, characterized in that the film comprises an adhesive layer, and preferably a release liner, in particular made of siliconized paper.

11. A wind turbine component, characterized in that a protective film according to one of claims 1 to 10 is glued to its surface.

12. Wind turbine part according to claim 11, characterized in that the wind turbine part is a rotor blade or a part of a rotor blade.

13. A method for protecting the surface of wind turbine components from icing and erosion, wherein a protective film according to one of claims 1 to 10 is adhered to the surface of the wind turbine component to be protected.

14. A method according to claim 13, characterized in that the protective film comprises an adhesive layer and is adhered to the adhesive layer.

15. The method according to claim 13 or 14, characterized in that a primer is applied to the surface of the part of the wind turbine prior to adhering the protective film.

16. Use of a protective film according to any one of claims 1 to 10 for protecting wind turbines from erosion and ice adhesion, characterized in that the protective film is adhered to a part of the wind turbine to be protected, in particular a rotor blade or part thereof.

Images