The subject matter of the invention is a coating composition, a method for obtaining and curing said coating composition and its use to passively protect surfaces against icing, and in particular the outer surface of aircraft, the surface of wind turbine blades and the surface of industrial structures such as bridges, scaffolding or frames.

In aviation, there are de-icing systems that are used to remove ice from a protected aircraft surface and are activated when icing occurs [3], In the case of public transport, heating of the leading edge of the wing is often used. This solution, however, is limited to turbine engines only. In smaller aircraft, Goodrich pneumatic systems are often used, which are made of rubber pockets mounted on the edges of the wings and stabilisers [1], Anti-icing systems prevent the formation of ice on protected surfaces and must be activated before an aircraft enters an area where icing may occur [3, 4], Many of these systems are used and quite common in general aviation aircraft. Some of these can also be considered as a type of icing removal systems. The most commonly used systems to prevent ice formation are: heating of surfaces or spraying antifreeze liquids (propylene glycol or ethylene glycol) onto them, i.e. the so-called TKS system.

New solutions in anti-icing systems use: a) vibrations of protected components caused by electromagnetic actuators - Raytheon. A limitation of this system is that it is difficult to install it in already existing aircraft. b) thin layers of electrically heated graphite - Lancair. It is a relatively easy solution to apply to existing aircraft but requires the use of electricity [2],

Anti-icing systems used in everyday life in the form of electric heating cables and mats are powered by electricity. Danfoss and Matec are the main manufacturers of such systems. Using devices of this type can prevent icing on pavements, roofs and gutters [5, 6],

Because of the impact that icing can have on the ability of solar and wind power plant devices to generate electricity, many of these require anti-icing systems. These systems can be divided into two categories: active solutions and passive solutions. Active solutions, for protected surfaces, are methods of removing ice once it has deposited. These include mechanical removal, thermal systems and the use of anti-icing fluids. Passive solutions involve modifying a surface before it is exposed to harsh weather conditions, so that it acquires properties that prevent ice formation, by reducing the adhesion of ice and water to the protected surfaces. Active methods are now widely used in aviation, but passive methods are more environmentally friendly as they do not consume energy and do not require the use of environmentally harmful chemical substances. Passive methods are also cheaper than active solutions, the latter usually being expensive to produce and use [17], As for passive solutions, one possible option may be the use of hydrophobic coatings. Currently, a material that can completely prevent the accumulation of ice or snow on its surface is not known, but some coatings can provide reduced adhesion of ice to their surface [18], As far as smooth surfaces are concerned, an increase in their hydrophobicity results in reduced ice adhesion [19], As mentioned above, all active systems require the use of electricity or chemical compounds, which are expensive and contribute to environmental pollution. Passive methods, on the other hand, have great application potential as far as icing prevention systems are concerned. One way to achieve this type of anti-icing protection may be to use highly hydrophobic surfaces, which is the object of the present invention.

The structure of highly/superhydrophobic coatings should be hierarchical (structures at the micro- and nanoscale) [31], High/superhydrophobic coatings can reduce or prevent ice formation by reducing ice adhesion to their surface. This results from the fact that the freezing process is delayed on surfaces of this type [31-33], and that a supercooled water droplet can bounce off the surface before it has time to freeze [33-35], Tourkine et al [33] demonstrated that this could be caused by the air trapped in the recesses of textured highly hydrophobic surfaces. The air, by forming a thermal barrier and insulating the supercooled water against the surface, delays the process of water freezing. On the other hand, Alizadeh [32] shows that delayed freezing, or a reduction in the macroscopic rate of ice nucleation, is caused both by a reduction in the contact area between water and substrate and by an increase in the activation energy for nucleation, which are characteristic of high water contact angles. Wang [34] showed that superhydrophobic coatings can be effective in retarding surface icing, but also lead to an increase in the duration of the water freezing process compared to flat surfaces tested under the same conditions. In the case of a superhydrophobic surface, the contact area between the water droplet and the substrate is small, which has the effect of reducing the adhesion of ice to the surface by minimising the contact of ice with the test surface [36-38], Superhydrophobic coatings have been demonstrated to reduce ice adhesion more than smooth hydrophobic surfaces of the same chemical composition and therefore exhibit very good anti-icing properties [18, 39, 40], Nosonovsky and Hejazi [41] showed that forming voids between the structures on a superhydrophobic surface and ice - the voids serving as stress concentrators and potentially causing microcracks - reduces the adhesion of ice to the surface. The size of the microcracks on the interfacial surface is an important parameter that regulates the adhesion of ice to a highly/superhydrophobic surface. This may provide an explanation as to why some surfaces exhibit more ice adhesion and some exhibit it less. The reason is that the latter do not provide sufficiently large voids at the interface. In high humidity conditions, water can condense as very small droplets that will get into the recesses in the superhydrophobic surface structures, thus reducing the water contact angle and changing the surface properties. If a water droplet freezes in this state, this can result in a very high adhesion of ice to the surface, i.e., the so-called anchoring effect [42], It is worth noting that ice shows very strong adhesion to hydrophilic materials, due to the polarity of ice molecules interacting with the solid surface.

Patent application US3720639 describes a fluorinated polyol that results from the polymerisation reaction of a diglycidyl ether with a fluorinated dihydroxy hydrocarbon. The polymerisation can be carried out with a tertiary amine catalyst and with or without a polar solvent. The reaction can take place in-situ as a coating on the surface or as an adhesive between laminates or as a moulding material in a mould. The product is useful in applications requiring the hydrophobic properties of fluorine in combination with the adhesion and injection properties of epoxy resins, but the solution does not address the applications in anti-icing coatings with low ice adhesion. A further object is to provide a class of fluoropolyols that combine the desired properties of epoxy resins with those of hydrofluorocarbons. An additional object is to provide a class of 5-fluoropolyols that have hydrophobic, oleophobic and low-friction properties. Another object is to provide curable mixtures of polyglycidyl polyether and fluorinated dihydroxy hydrocarbon. Another object is to provide various methods for the preparation, use and curing of fluorinated polyols. In the description of the preferred 15 embodiments, it is stated that the above and additional objects are first achieved by reacting dihydroxy phenol with halohydrin, such as monohydrins, epi-20 halohydrins and the like. The intermediate polyglycidyl polyether thus formed is then cured with a fluorinated dihydroxy hydrocarbon to produce a fluorinated polyol product.

Document US2015344748 discloses epoxy resin compositions made using amino group- terminated fluoroalkyl ethers. Epoxy resin compositions exhibit low adhesion to surfaces, making them useful as coatings, paints, mouldings, adhesives and fibre-reinforced composites. Given the properties possessed by the materials according to the invention disclosed in said US application, the materials can be used in the various forms mentioned above for applications such as, but not limited to: aircraft and spacecraft (launch vehicles, helicopters, unmanned aerial vehicles, etc.); surfaces to prevent the adhesion of various materials such as insects, ice, dirt and dust and other deposits; ship hulls, ship surfaces, barge surfaces, offshore platforms surfaces, pipes, valves and pumps (internal and external), electrical transmission lines and cables, filters, filter elements, electronic components, printed circuit boards (PCB), devices for controlled fluid flow, medical implants, cars, trucks, motorbikes and boats surfaces, racing vehicle surfaces, infrastructural surfaces such as roads, bridges, building fagades and interiors, stairs, balustrades, fire-fighting clothing and equipment, tactical, rescue and emergency clothing, protective clothing and equipment, wind turbine blades (windmills) and wind turbine systems and exposed surfaces.

The solution described in the publication by Psarski, Maciej & Celichowski, Grzegorz & Marczak, Jacek & Gumowski, Konrad & B. Sobieraj, Grzegorz, entitled "Superhydrophobic dual-sized filler epoxy composite coatings", Surface and Coatings Technology 225, 66-74, (2013), 10.1016/j.surfcoat.2013.03.017 comprises a superhydrophobic composite epoxy resin coating containing fillers in the form of nanoparticles (AI2O3) with a diameter of 11 ±3 nm and SiCh microspheres with a diameter of 26 ± 7 pm, where after a sandblasting process the coating is subjected to hydrophobisation by surface chemical modification with a modifier from the group of alkylsiloxanes and fluoroalkylsiloxanes. As opposed to the invention described in the present application, the above coating is surface-modified, which means that it can be easily damaged by scratching and deprived of its superhydrophobic properties. The coating to be claimed here is modified in volume and thus has highly hydrophobic properties and low ice adhesion even after being scratched. Furthermore, the coating described in the above publication does not have anti-icing properties as does the composition presented in the present patent application.

Creating a passive anti-icing system that will be effective continuously for several years and not require the use of electricity or solar power is of key importance for many areas of life and industry. The problem to be solved is to reduce the adhesion of supercooled water droplets to the substrate and consequently prevent ice formation, or to reduce the adhesion of ice to the protected surfaces under various weather conditions. Another problem to be solved by the invention in the area of anti-icing systems is to produce a durable superhydrophobic/highly hydrophobic coating with low ice adhesion, which is resistant to weather conditions (water/humidity/UV) and which, as a result of it being chemically modified in volume, retains and reproduces its properties (even after being scratched).

The subject matter of the invention is a coating composition comprising: a. a modified resin composition comprising an epoxy resin, a modifier and a curing agent, in an amount of from 53 to 69 wt% based on the total weight of the composition; b. a filler in the form of SiCh microspheres with a diameter in the range of 40-70 pm in an amount of from 25 to 35 wt% based on the total weight of the composition; c. a filler in the form of AI2O3 nanoparticles with a diameter of 10-30 nm in an amount of from 6 to 12 wt% based on the total weight of the composition; wherein the epoxy resin is an epoxy resin obtained from bisphenol A or bisphenol A/F, the curing agent is an amine curing agent dedicated by the resin manufacturer, characterised in that the modifier is a perfluorinated diol or perfluorinated oxirane.

Preferably, the modifier is always present in an amount of 4 wt% in relation to the content of the resin with the respective curing agent, which together constitute 96 wt%.

Preferably, the filler in the form of AI2O3 nanoparticles has a diameter of 10 nm.

Preferably, the perfluorinated diol or perfluorinated oxirane is selected from the group comprising: 2,2,3,3-tetrafluoro-l,4-butanediol; 2-[2,2,3,3,4,4,5,5-octafluoro-6-(oxiran-2- yl)hexyl]oxirane; (2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,9-heptadecafluorononyl)oxir ane.

Preferably, the composition of the invention comprises 61 wt% of the modified epoxy composition, 9 wt% of AI2O3 nanoparticles and 30 wt% of SiCh microspheres based on the total weight of the composition.

Another subject matter of the invention is a method for obtaining and curing the coating composition of the invention, characterised in that it comprises the following steps: a. 4 wt% of the selected modifier, in relation to the total resin with curing agent in the composition, is added to the weighed amount of the curing agent and heated at a temperature of about 100°C for about 2 h; b. the selected resin is then added and everything is stirred vigorously; c. then the fillers, i.e., AI2O3 nanoparticles and SiCh microspheres, are added, this is stirred vigorously again and applied to the substrate; d. the composition applied to the substrate is left to cure at room temperature for 12-48 h; e. optionally, the cured coating of the composition is sandblasted.

Preferably, the composition is applied to the substrate with a spatula, brush, roller or by spraying, wherein the application by spraying requires the addition of about 5-15 wt% of acetone to the composition to reduce the viscosity of the composition.

Preferably, the size of corundum grains used for sandblasting is 1040 pm, the air pressure during sandblasting is about 5 mBar, the sandblasting time is 8 min, the sample to nozzle distance is 2-3 cm.

Still another subject matter of the invention is the use of the coating composition of the invention prepared by the method of the invention to passively protect surfaces against icing.

Preferably, the protected surface is selected from the outer surface of aircraft, the surface of wind turbine blades and the surface of industrial structures such as bridges, scaffolding or frames.

There are no passive anti-icing system solutions available on the market, so the use of the superhydrophobic/highly hydrophobic surfaces described in this patent application as passive anti-icing systems has great application potential. The invention in the form of a coating can be used in passive anti-icing systems, i.e., systems that do not require electricity to work. Moreover, it can counteract icing on critical components of aircraft wings or wind turbine blades. Thus, protected surfaces in aviation lead to increased passenger safety, reduced emissions of toxic products generated by the use of existing anti-icing systems (CO2, de-icing liquids based on toxic glycols) and reduced fuel consumption. Furthermore, in the wind power industry, protecting wind turbine blades with the invention (with a superhydrophobic/highly hydrophobic coating with low ice adhesion) will minimise icing on the said device parts and consequently help to reduce the number of wind turbine faults, as well as contribute to a reduction in losses in wind power generation caused by changes in the aerodynamics of the blades by accumulated ice. The advantage of the solution according to the invention in the form of an anti-icing coating obtained by the disclosed method over the solutions currently used on the market is its high effectiveness for a period of several years after application, no need for it to use electricity and solar energy to work, good anti-wear properties confirmed by erosion tests and low toxicity to the environment (<5 wt% of fluorine compounds incorporated into the chemical structure of the epoxy resin, they do not require the use of environmentally harmful chemical compounds in the form of de-icing liquids and, importantly, do not emit carbon dioxide when used). The composite is resistant to temperature changes in the range of -60°C to 100°C and does not degrade under UV radiation. Because the fluorine compounds may only be released into the environment with the destruction of the coating, the toxicity of this solution is much lower than that of the chemical systems currently in use.

As the outer layer of the prior art coating wears away, its hydrophobic and anti-icing properties are lost. To solve this problem, the present invention introduces a chemical modifier in the form of, for example, a perfluorinated diol or a perfluorinated oxirane, which is incorporated into the chemical structure of the resin (its volume is modified), thereby ensuring uniform hydrophobic properties and low ice adhesion throughout the volume of the sandblasted composite material obtained from the modified resin composition and fillers. With this solution, it can be assured that in the event of erosion, the coating will still have highly hydrophobic properties and low ice adhesion. The introduction of nanoparticles and SiCh microspheres into the epoxy resin results in an increase in surface development in the process of surface texturisation. The stochastic surface texture produced is extremely important, as sandblasting guarantees the formation of structures of different sizes at the micro- and nanoscale, which contributes to reduced wetting of the surface by water droplets of different sizes, and consequently an increased effectiveness of the coating as a result of its maintaining highly hydrophobic properties and low ice adhesion under varying climatic conditions (even below 10°C). This sets the prepared coating apart from other commercially available solutions. Also, this can contribute to the formation of stress in the ice structure when it is built up on the coating and result in its cracking, thus weakening the adhesion of ice to the coating surface and facilitating its removal. In addition, it should be added that chemical modification of the resin composition throughout the entire volume of the coating results in a long-term maintenance of the coating's highly hydrophobic properties and low ice adhesion even after erosion tests (sandblasting with corundum grains) - if the top layer of the coating is scraped off/damaged by sand, stones or other hard particles, the properties of the coating are not altered and the stochastic surface topography at the micro- and nanoscale is reproduced (owing to the fillers used, i.e. glass microspheres and ceramic nanoparticles). An additional advantage of the preparation process of the present coating is that it is made shorter than known methods, by eliminating the two steps that followed the sandblasting of the coating with corundum. The first is plasma treatment of the coating, during which the resin is etched to expose the nanoparticles and reactive -OH groups are generated, followed by a hydrophobisation step through chemical modification (application of a thin hydrophobic film), which increased the hydrophobic properties of the coating (its outer layer). This not only brings key savings in production time, but also a reduction in production costs because it is no longer necessary to purchase any relevant apparatus needed to perform the eliminated steps, and also saves space on the production floor. Furthermore, the proposed invention can be used on surfaces made of different materials, i.e., steel, ceramic, aluminium or glass. The invention is characterised by its ease of manufacture, as it does not require complex operations during production, which means that personnel can be quickly trained to be able to produce it. The novelty of the proposed solution is that there is no requirement to apply the coating several times during the winter season in the case of wind turbines and that the coating does not have to be applied to the wings of an aircraft each time before take-off. Based on the tests carried out in accelerated ageing chambers (thermal shock chamber, climatic chamber and UV chamber) and the fact that the properties of the coatings were not lost after the tests, it is estimated that the applied coating will continue to be effective for several years regardless of the number of flights made by aircraft or the revolutions of wind turbine blades in any weather conditions, while maintaining the same effectiveness. A further advantage of the proposed technology is that it can also protect the surfaces of aircraft or wind power plants that already exist on the market.

Examples

In the following embodiments of the invention, a resin composition (resin + curing agent) was used based on commercially available epoxy resins obtained from bisphenol A or bisphenol A/F (for example, Epidian 5 from Ciech Sarzyna S.A. or Epoxydharz L from R&G Faserverbundwerkstoffe GmbH) with curing agents dedicated by manufacturers (Table 1). The amount of curing agent in relation to the resin was always added as recommended by the manufacturer.

Table 1

Example 1

Obtaining the coating composition and preparing a highly hydrophobic sandblasted coating

Modification of the resin was carried out as follows. The modified resin composition was obtained by ionic bonding of the modifier to the curing agent. To prepare 10 g of the modified resin composition, Epidian 5 resin and IDA curing agent were used, the latter modified with oxirane - (2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,9-heptadecafluorononyl)oxir ane). The modification process of IDA curing agent was carried out in sealed tubes at a temperature of about 100°C for 2 h. Following the modification, 39.0 wt% of Epidian 5 resin; 30.0 wt% of microsilica and 9.0 wt% of AI2O3 nanoparticles relative to the total composition were added (exact amounts of components are shown in Table 2). The modified resin was then subjected to cross-linking. The cross-linking process was carried out for a minimum of 12 h (preferably a minimum of 24 h) at room temperature. The cured compositions are sandblasted to produce a stochastic structure on their surface, which increases their hydrophobicity and reduces ice adhesion (the size of corundum grains used for sandblasting was 1040 pm, air pressure during sandblasting was about 5 mBar, sandblasting time was 8 min, the sample to nozzle distance was 2-3 cm). After texturisation, the samples were purified of aggregate residues in a stream of compressed air or cold water. The samples were left to dry.

Table 2

Example 2

Preparation of highly hydrophobic sandblasted coatings

Following the procedure disclosed in Example 1, coating compositions were obtained with different compositions as indicated in Table 3.

The method of preparing the composition involved the following steps:

1. The amount (as indicated in Table 3) of the curing agent recommended by the manufacturer to cure a given type of resin was weighed into the test tube.

2. 4 wt% of the selected modifier, in relation to the total resin with curing agent in the composite, was added to the test tube with the curing agent inside. Particular attention should be paid to the state of matter and fineness of the modifier when the resin is being synthesised; if the modifier used is in solid form, it should be ensured that it has been sufficiently finely ground. Large modifier crystals may require more time to react in the reaction mass.

3. The test tube was heated in a water bath at a temperature of 100°C for 2 h.

4. The contents of the test tube were transferred to a vessel and an appropriate amount of the selected resin was added. This was stirred well.

5. Appropriate amounts of fillers (AI2O3 nanoparticles and SiCh microspheres) were added according to Table 2, stirred well and applied to a metal or glass substrate. When preparing the composite, care should be taken to ensure that the components are completely mixed so that the composite is fully homogeneous before being applied to the substrate. Special attention should be paid to filler agglomerates, which should be removed by thorough mixing of the composition. If modifier crystals are present when the synthesis is completed, this may indicate that the synthesis was not long enough or that the modifier was over-weighted.

6. This was left to cure at room temperature for 12-48 h.

Composites cured for 12 to 48 hours at room temperature will maintain particularly preferred properties. The cured composites are sandblasted to produce a stochastic structure on their surface, which increases their hydrophobicity and reduces ice adhesion (the size of corundum grains used for sandblasting was 1040 pm, air pressure during sandblasting was about 5 mBar, sandblasting time was 8 min, the sample to nozzle distance was 2-3 cm).

Coatings were applied to steel, aluminium and glass using various methods: brush, roller and spray (with the addition of 10 wt% acetone). Regardless of the application method, no changes were observed in the measured values of ice adhesion and water contact angle.

Coatings with thicknesses in the range 60 pm - 120 pm were produced. The thickness of the coating does not affect its hydrophobic properties or ice adhesion.

The methodology for measuring the water contact angle (WCA) and the adhesion of ice to the substrate is described in Examples 4 and 5, respectively.

Example 3

Preparation of highly hydrophobic non-sandblasted coatings

Table 4 below shows, for comparison, the measurement results of the water contact angle (WCA) and the adhesion of ice to the substrate obtained for non-sandblasted coatings, which have lower roughness than textured coatings, which, for the aviation industry, may be advantageous (relevant) due to the possible effect of roughness on changing the aerodynamics of the wings (undesirable effect). For wind turbines, this is not so important. The coatings were made as in Example 2 with the optional sandblasting step omitted.

Table 4

Table 5 below shows, for comparison, the measurement results of the water contact angle (WCA) and the adhesion of ice to the substrate obtained for sandblasted coatings using AI2O3 nanoparticles with a diameter of 30 nm. The coatings were made as in Example 2.

Table 5

Example 4

Measurement of the water contact angle (WCA)

To measure the water contact angle (WCA) on the tested surfaces, the most commonly used method was used, i.e., the so-called sessile drop method. The measurement was performed using OCA 35 goniometer from DataPhysics and involved taking a photo of a water droplet deposited on the tested surface and determining and measuring the water contact angle, i.e., the angle between the tangent to the droplet and the tangent to the substrate at the point of contact between the three phases (liquid, solid, gas). The user specified the line of contact between the droplet and the substrate, and the software of the instrument adjusted the envelope around the droplet and measured the WCA. A major advantage is the simplicity of this method and the fact that a small amount of liquid (5 micro litres) and a small surface area (a few square centimetres) are required for measurement. Measurements were taken at 5 different points on the surface of the test sample, which made it possible to assess its homogeneity. The results of the water contact angle (WCA) measurements for the compositions tested are included in Tables 3 and 4 above, where the mean result is indicated along with the deviation. Example 5

Measurement of the ice adhesion to the substrate

The measurement was performed on an instrument specially designed for this purpose and involved placing the test sample on a table of the instrument (between the cooling system and special clamps). An ice cube made in a special 2x2 cm silicone mould with a basket inside to hang it was hung on the extension shaft of the force gauge. The cube was always formed from an equal volume of water filling the mould to the brim, together with a basket with a hook dipped in it. The ice cube was then lowered to the surface of the test sample and pressed against it. The cooling system was switched on so that the ice cube placed on the surface would have the opportunity to freeze to the surface of the sample. During the measurement, the surface temperature of the sample was measured. The time of the ice cube freezing to the sample was 10 minutes in each case. The temperature on the sample dropped to -10°C. The programme for measuring ice adhesion to the substrate was then run and the measurement started. The actuator, using motors, moved vertically upwards with the cube attached to it, pulling it away from the surface of the sample. The measured force required to vertically detach the ice cube from the surface of the test sample was converted by the software into ice adhesion. The test for a given surface type was performed at least 5 times. Each time, the samples had the same thickness. The mean value together with the deviation was the result included in this document. The measurement was performed in a closed chamber of the instrument to limit temperature fluctuations. Once the measurement was complete, the ice cube was removed and left to melt. Each time a new ice cube was used for measurement, taken immediately before measurement from the mould placed in the freezer. After the measurement, the cooling was switched off. The table on which the samples were placed was dried. Thus prepared, the instrument was ready for the next measurement. The results of measuring the adhesion of ice to the substrate for the tested compositions are included in Tables 3 and 4 above.

The results for ice adhesion obtained for the tested compositions are satisfactory for the aviation industry, as they do not exceed the value of 30 kPa. Lower ice adhesion values (better parameters) were obtained for coatings modified with a compound from the group of oxiranes.

Example 6

Wind tunnel test simulating icing conditions

Qualitative visualisation tests of the icing on a wing segment were performed, with sandblasted coatings EP5_OXI_9n_30p (1) and EP5_DIOL_9n_30p (2) (coating names are as shown in Table 3) applied to the wing section. In addition, an unmodified and nonsandblasted reference coating made of Epidian 5 epoxy resin was tested. Between the coatings there are black stripes without coatings. The results of the test are summarised in Table 6. The tests were conducted in a low-speed wind tunnel having a measurement space diameter D=l.l[m]. The tunnel is intended to test the aerodynamic characteristics of objects, including under icing conditions. The tests involved a qualitative comparison of ice deposition on areas with modified and sandblasted coatings and with a reference coating made of unmodified epoxy resin Epidian 5 and not subjected to sandblasting.

The wind tunnel is equipped with a cooling system for the air stream and a water mist injection system. The air can be cooled to sub-zero temperatures, down to -10°[C] under favourable external conditions. This makes it possible to create conditions similar to those resulting in icing during an aircraft flight. The very occurrence of the icing phenomenon is usually associated with flying in cloud or precipitation. It is the result of direct deposition of ice, snow or hail crystals, or the result of droplets freezing after they come into contact with aircraft parts. The latter mechanism is the prevailing one during the icing of aircraft. It is used in the simulation of icing formation in the wind tunnel used for testing. Water mist is injected into the measurement space of the tunnel, where the air stream at reduced temperature is flowing. The mist moving along with the air stream encounters a cooled object being flown around, which results in the formation of icing on the tested object. The object itself cools to a temperature close to the temperature of the flowing air stream. Before taking the final measurements, a scan of the water mist injected into the measurement space of the tunnel was performed using Kamika droplet analyser. The distribution of droplets injected by the injectors is similar to the distribution of droplets in clouds.

Qualitative tests of the effectiveness of the tested coatings were performed for one fixed angle of attack a=0 with 4 values of air stream velocity: v=18[m/s]; v=22[m/s]; v=25.5[m/s]; v=28.5[m/s], Prior to the measurements, the air stream was cooled to a temperature of about -5°[C], When the required sub-zero temperature was reached, water mist was injected. The process of ice deposition on the tested object was recorded with a camera. After injection, the image of the icing on the wing segment was recorded. Then water mist was injected again. The recorded video and photographic material was used to qualitatively assess the effectiveness of the tested coatings. During the tests, four water mist injections were made for each case. At the time of the injections, the temperature of the flowing air was not higher than -2°[C], At the time of the tests, the atmospheric pressure was 998.5 [hPa], During water mist injections, the air stream temperature oscillated between -4.3°[C] and -2.2°[C], Table 6 shows photographs illustrating the coatings after a wind tunnel test simulating icing conditions after 4 water injections for the highest and lowest air stream velocities v=28.5[m/s] and v=18 [m/s]. Qualitative results were obtained, where it can be seen that the reference coating of unmodified and non-sandblasted Epidian 5 epoxy resin clearly shows ice formation in the leading edge area of the wing segment marked with the letter 'A'. It can be speculated that more icing (more water mist injections) could lead to a more visible deformation of the leading edge, which could change the aerodynamics of the wings and the load carrying capacity of the aircraft. The observed ice is of a glassy nature. Glassy ice occurs at temperatures above -5°[C], Other coatings have different ice deposition than the reference coating. It can be clearly seen that it does not deform the leading edge 'A' but causes the further part of the wing profile to thicken. The leading edge on the sandblasted coating EP5_DIOL_9n_30p appears to be covered with the least ice. However, the sandblasted EP5_OXI_9n_30p coating also has a low degree of icing on the leading edge of the wing (being the most icing-prone wing element of greatest importance to its loadbearing capacity). Observations show that there is less droplet capture at the leading edges on the stripes having both modified and sandblasted coatings applied. More icing can be seen on the reference sample. The lowest icing was obtained for modified and sandblasted coatings at the lowest air stream velocities (18 m/s). References:

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