Electrical insulation material, in particular for frost protection pads

Abstract

The invention relates to an electrically insulating composite material (40), characterized in that the material is a composite material comprising a matrix (42) made of an elastomer or a polymer, and inclusions (41) providing the material with a thermal conductivity of greater than 0.6 W / mK at room temperature, in particular greater than 1.5 W / mK at room temperature.

Description

Technical Field

[0001] The present invention relates to an electrically insulating and thermally conductive material for heat dissipation on aircraft components.

[0002] It is advantageously used for anti - frosting pads, especially for aircraft components, although other applications are also possible. Background Art

[0003] Frost formation on an aircraft, especially during flight, can change the aerodynamic characteristics of the aircraft and impair its performance.

[0004] Furthermore, if ice cubes formed or accumulated on elements of the aircraft fuselage or on engine air intakes break off, these ice cubes can hit certain parts of the aircraft and damage it.

[0005] Frost formation can cause at least partial blockage of the air intake, which can also lead to power loss and even engine shutdown.

[0006] This is why aircraft are usually equipped with anti - frosting devices, also known as defrosting devices, installed, for example, on the leading edges of wings, rudders, radomes or engine air intakes.

[0007] In addition, on propeller - driven aircraft, the leading edges of the blades or cowlings are usually equipped with anti - frosting devices.

[0008] Such anti - frosting devices have the function of defrosting or preventing frost formation.

[0009] Combined anti - frosting devices for defrosting and preventing frost formation are also known.

[0010] There are various techniques for anti - frosting devices, such as pneumatic devices with mechanical effects, hot - air circulation defrosters, etc.

[0011] The present invention more particularly relates to anti - frosting devices having anti - frosting pads, especially thermoelectric pads.

[0012] Such an anti - frosting pad is a heating pad applied to the surface of a component that needs to be protected from frost. It provides a defrosting or anti - frosting function through the Joule effect by circulating an electric current in a layer incorporating at least one heating resistor. It can operate cyclically or be controlled according to an operating mode that ensures continuous heating.

[0013] Specifically, in known structures, the layer incorporating the heating resistor is usually covered with an electrically insulating layer, such as an electrically insulating layer made of an elastomeric material. The electrically insulating layer is respectively assembled between the heating resistor and the surface to be defrosted and between the heating resistor and the external environment.

[0014] It is known to add fillers made of electrically insulating materials, such as silica, chalk or kaolin, to a rubber matrix to improve the strength and mechanical properties of the material.

[0015] However, the presence of such a layer weakens the transfer of the heat generated to the surface to be defrosted. In addition, the thermal insulation of the substrate increases the temperature inside the resistor and the substrate, including energy losses and the accelerated aging of the resistor and the insulating layer.

[0016] In addition, too high a temperature may damage the surface to be defrosted, especially when the surface to be defrosted is made of a composite material. Summary of the Invention

[0017] An object of the present invention is to propose a solution that allows better heat dissipation while ensuring good electrical insulation.

[0018] To this end, the present invention provides an electrically insulating composite material, characterized in that the material is a composite material comprising the following substances:

[0019] - a substrate made of an elastomer or a polymer, and

[0020] - inclusions,

[0021] providing the material with a thermal conductivity greater than 0.6 W / mK at room temperature, especially a thermal conductivity greater than 1.5 W / mK at room temperature.

[0022] Preferably, the electrically insulating composite material has a volume resistivity greater than 1E9 Ω·m, preferably greater than 1E10 Ω·m.

[0023] Advantageously, the inclusions are ceramics. The inclusions may be boron nitride, aluminum nitride and / or alumina.

[0024] Advantageously, the substrate is selected from polyurethane, nitrile resin, neoprene resin, silicone, fluorosilicone and / or epoxy resin. The substrate may be made of a thermoplastic polymer, especially polyetheretherketone "PEEK", polyetherketoneketone "PEKK", polyetherimide "PEI", polysulfone "PSU", polyethersulfone "PESU", polyphenylsulfone "PPSU", polyamide-imide "PAI" or polyphthalamide "PPA".

[0025] Preferably, the volume ratio of the inclusions is between 10% by volume and 70% by volume, especially between 20% by volume and 50% by volume, especially between 30% by volume and 50% by volume.

[0026] The present invention also relates to a defrosting mat, especially for at least one aircraft component, comprising at least one heating layer, especially combined with at least one heating resistor, and at least one intermediate layer made of the composite material described above.

[0027] Preferably, the anti-frost mat comprises at least one heating layer, in particular incorporating at least one heating resistor, and at least one reinforcing layer arranged between the heating layer and the external environment, characterized in that the reinforcing layer has a thermal conductivity perpendicular to the general extension plane of the reinforcement greater than 0.6 W / mK at room temperature.

[0028] According to advantageous and non-limiting characteristics, alone or in any combination:

[0029] - the reinforcing layer comprises a network of woven, non-woven and / or reticulated fibres or threads having a longitudinal thermal conductivity greater than 0.6 W / mK at room temperature;

[0030] - the fibres or threads of the reinforcing layer have a longitudinal thermal conductivity greater than 50 W / mK at room temperature;

[0031] - the fibres or threads of the reinforcing layer have a longitudinal thermal conductivity greater than 120 W / mK at room temperature;

[0032] - the reinforcing layer comprises carbon threads or carbon fibres;

[0033] - the carbon threads or carbon fibres are pitch threads or pitch fibres, in particular coal pitch or petroleum pitch;

[0034] - the reinforcing layer comprises threads or fibres having a polyacrylonitrile (PAN) type precursor;

[0035] - the reinforcing layer comprises threads or fibres selected from glass fibres, basalt fibres, silica fibres or metal wires.

[0036] The invention also relates to an assembly comprising at least one component having an outer surface, in particular an aircraft component, characterized in that the outer surface is covered with the anti-frost mat described above. [[ID=?]] [[ID=?]]

[0037] Preferably, the contact layer of the anti-frost mat arranged between the component and the heating layer is glued or co-vulcanized to the component. <?

[0038] The invention also relates to a method for manufacturing the composite material described above, comprising at least the following steps:

[0039] - providing at least one base material for the formulation of an elastomer and / or polymer,

[0040] - adding inclusions to the base material, the inclusions having a thermal conductivity greater than 0.4 W / mK at room temperature, in particular greater than 0.6 W / mK at room temperature, in particular greater than 0.8 W / mK at room temperature, in particular greater than 1.5 W / mK at room temperature,

[0041] - vulcanizing the base material incorporating the inclusions. Description of the drawings Note: There seems to be an issue with the tags in lines 28 - 32 where the tags are not in the standard format. I've translated them as best as possible while maintaining the integrity of the text. If these are specific tags with a particular meaning in your system, you may need to correct them for a more accurate translation.

[0042] Other features and advantages of the present invention will become apparent upon reading the following description of the preferred embodiments. The description will be made with reference to the accompanying drawings, which include:

[0043] - Figure 1 Schematically shows an assembly including a component and an anti - frost pad according to an embodiment of the present invention;

[0044] - Figure 2 Schematically shows a multi - layer structure of the anti - frost pad according to an embodiment of the present invention;

[0045] - Figure 3 Schematically shows a composite material of the electrically insulating and heat - conducting layer;

[0046] - Figure 4 Shows a measuring device for determining the electrical resistance of the anti - frost pad according to the present invention; and

[0047] - Figure 5 Shows a measuring device for determining the electrical resistance and leakage current of the anti - frost pad according to the present invention. Detailed Description

[0048] In the description of the present invention to be provided hereinafter, the terms "lateral", "longitudinal", and "radial" define the direction of extension of the layer, fiber, and / or wire.

[0049] Thus, the lateral corresponds to the direction perpendicular to the extension surface of the layer. It corresponds to the thickness of the layer. In addition, the lateral is similar to the radial of the fiber or wire of the elements constituting the layer. The lateral is represented by Figure 2 the axis T in.

[0050] In addition, the longitudinal corresponds to the direction of extension of the fiber and / or wire of the elements constituting the layer. For the fiber and / or wire extending along the surface of the elements constituting the layer, the longitudinal can be defined by two components represented by Figure 2 the axis X and axis Y in.

[0051] Figure 1 Schematically shows an assembly that includes a component BA, particularly an aircraft component BA, particularly the leading edge of an aircraft wing or propeller, which is protected from frost by an anti - frost pad 1, particularly a thermoelectric pad 1.

[0052] The anti - frost pad 1 is attached to the outer surface 11 of the component BA it conforms to, for example, by gluing using an adhesive layer (not shown).

[0053] The anti - frost pad 1 includes a multi - layer structure as Figure 2 schematically shown.

[0054] From the component BA to be protected from frost towards the external environment, particularly according to Figure 2In the example shown, the multi-layer structure particularly includes a stack of multiple layers:

[0055] - The contact layer 2, which is intended to be in contact with the component BA to be protected, particularly with the leading edge, and has the function of forming an electrical barrier and a thermal barrier;

[0056] - The heating layer 3, which is intended to serve as a heat source capable of providing a defrosting and / or anti-frosting function for the component BA to be protected, particularly through the Joule effect;

[0057] - The intermediate layer 4, which is intended to provide electrical insulation and thermal conductivity functions;

[0058] - The strengthening layer 5, which is intended to provide a protective function for the anti-frost pad 1, particularly the heating layer 3, against impacts;

[0059] - The outer layer 6, which is intended to provide a function of resistance to the external environment, particularly resistance to the harsh weather and temperature conditions that an aircraft may encounter.

[0060] The stack of different layers has a relatively small thickness, typically less than 2 mm, particularly less than 1.5 mm, and advantageously less than 1 mm.

[0061] If necessary, the multi-layer structure can be covered with a paint layer 7.

[0062] In particular, the anti-frost pad 1 including the multi-layer structure can have an electrical insulation resistance of at least 10 MΩ, particularly at least 100 MΩ.

[0063] According to Figure 2 In the exemplary embodiment shown, the contact layer 2 is disposed in the multi-layer structure in such a way as to be between the outer surface 11 of the component BA to be defrosted and the heating layer 3.

[0064] The contact layer 2 is designed to be in contact with the component BA to be protected, particularly with the leading edge, and its function is to form an electrical barrier and a thermal barrier.

[0065] In particular, the contact layer 2 can be made of a material having electrical insulation and thermal insulation properties.

[0066] Therefore, the contact layer 2 allows avoiding excessive contact temperature with the component BA to be defrosted.

[0067] The material of the contact layer 2 can be an elastomer, a polymer, particularly a thermoplastic polymer or a thermosetting polymer, particularly epoxy resin.

[0068] Alternatively, the contact layer 2 can be made of insulating foam.

[0069] According to a specific embodiment, the contact layer 2 can also be made of an insulating honeycomb structure. Alternatively or additionally, the contact layer 2 can also be made of a mixture of an elastomer or a polymer filled with glass beads, especially hollow glass beads.

[0070] By being configured in this way, the contact layer 2 protects the component BA on which the anti-frost pad 1 is mounted from possible overheating. In fact, due to the thermal insulation properties of the contact layer 2, the heat released by the heating layer 3 is directed towards the outer surface of the anti-frost pad 1 that may frost. According to the multi-layer structure, this outer surface of the anti-frost pad 1 is arranged to face away from the contact layer 2 and thus away from the component BA to be protected against frost.

[0071] In addition, it is desirable to avoid any current circulation between the heating layer 3 and the component BA.

[0072] In particular, the contact layer 2 can have a volume resistivity of at least 1E9 Ω·m, preferably greater than 1E10 Ω·m.

[0073] The thermal conductivity of the contact layer 2, considered perpendicular to the total extension plane of the contact layer 2, also known as the transverse thermal conductivity, is less than 0.4 W / mK at room temperature. In this specification, room temperature refers to a temperature of approximately 20 °C.

[0074] The thickness of the contact layer 2 can be less than 1.5 mm, especially less than 1 mm, and advantageously less than 0.7 mm. In addition, the thickness of the contact layer 2 can be greater than 0.2 mm, especially greater than 0.3 mm, and advantageously greater than 0.6 mm.

[0075] According to Figure 2 the exemplary embodiment shown, the heating layer 3 is arranged in the multi-layer structure in a manner intermediate between the contact layer 2 and the intermediate layer 4.

[0076] The heating layer 3 is designed to provide a heat source for the component BA to be protected that can ensure the defrosting and / or anti-frosting function through the Joule effect.

[0077] In particular, the heating layer 3 can be a resistive layer for Joule heating.

[0078] However, the heating layer 3 can be made of any heating device capable of generating a heat flux, especially, for example but not limited to, metal tracks, heating wires, conductive inks, fabrics or non-woven fabrics using fibers, etc.

[0079] For example, the heating layer 3 can be integrated with a metal track network that is designed to allow current to pass through to generate a heat flux through the Joule effect.

[0080] The metal tracks can be very close to each other to cover the surface as evenly as possible. However, as will be understood more specifically from the following description, the longitudinal heat conduction ensured by the fibers and / or wires of the reinforcement allows for a greater spacing between the metal tracks than is currently possible according to the prior art.

[0081] In particular, the metal tracks cover at least 50% of the surface of the heating layer 3, especially at least 70% of the surface of the heating layer 3.

[0082] The power electrical connection allows for connection to a power source to supply power to the metal tracks.

[0083] Generally, the heating power released by the heating layer 3 is between 1 and 5 W / cm 2 and especially between 2 and 5 W / cm 2 depending on whether the heating layer operates in a cyclic mode or a continuous mode.

[0084] The thickness of the heating layer 3 can be less than 0.3 mm, especially less than 0.25 mm, advantageously less than 0.15 mm. In addition, the thickness of the heating layer 3 can be greater than 0.015 mm, especially greater than 0.05 mm. Generally, the thickness of the heating layer 3 can be about 0.15 mm.

[0085] According to Figure 2 the exemplary embodiment shown, the intermediate layer 4 is disposed in the multi-layer structure in a manner intermediate between the heating layer 3 and the reinforcement layer 5.

[0086] The intermediate layer 4 is designed to provide both electrical insulation and heat conduction functions.

[0087] In particular, the intermediate layer 4 can be made of a selected composite material having good electrical insulation and good heat conduction.

[0088] The intermediate layer 4 helps to direct the heat flux generated by the heating layer 3 to the outer surface of the anti-frost pad 1, that is, away from the contact layer 2 and thus away from the component BA to be anti-frosted.

[0089] In particular, the intermediate layer 4 can have a volume resistivity of at least 1E9 Ω·m, preferably greater than 1E10 Ω·m.

[0090] The thermal conductivity of the intermediate layer 4, considered perpendicular to the total extension plane of the intermediate layer 4, also known as the transverse thermal conductivity, is greater than 0.4 W / mK at room temperature, especially less than 0.6 W / mK at room temperature, especially greater than 0.8 W / mK at room temperature, especially greater than 1.5 W / mK at room temperature, and this thermal conductivity is determined according to the methods described in standard ISO 8302 or ASTM C177.

[0091] The thickness of the intermediate layer 4 can be less than 1.5 mm, particularly less than 1 mm, and advantageously less than 0.7 mm. Additionally, the thickness of the intermediate layer 4 can be greater than 0.2 mm, particularly greater than 0.3 mm. Generally, the thickness of the intermediate layer 4 can be about 0.4 mm.

[0092] As Figure 3 More specifically shown in

[0093] According to Figure 2 the exemplary embodiment shown, the reinforcement layer 5 is disposed in the multi-layer structure in a manner intermediate the heating layer 3 and the outer layer 6.

[0094] The reinforcement layer 5 is designed to provide the protection antifrost mat 1, particularly the heating layer 3, against impacts such as gravel, hail, maintenance-related knocks, etc.

[0095] In particular, the reinforcement layer 5 can be made of a material that allows the heat flux generated by the heating layer 3 to circulate towards the outer surface of the antifrost mat 1, that is, away from the contact layer 2 and thus away from the component BA to be antifrosted.

[0096] In particular, the reinforcement layer 5 can be provided, for example, in the form of a woven, non-woven (e.g., felt) or mesh reinforcement that extends along the total extension plane of the reinforcement layer 5.

[0097] The thermal conductivity of the reinforcement layer 5, considered perpendicular to the total extension plane of the reinforcement layer 5, also known as the transverse thermal conductivity, is greater than 0.4 W / m.K at room temperature, particularly greater than 0.6 W / m.K at room temperature, particularly greater than 0.8 W / m.K at room temperature, particularly greater than 1.5 W / m.K at room temperature, and this thermal conductivity is determined according to the method described in standard ISO 8302 or ASTM C177.

[0098] More specifically, the reinforcement layer 5 can include fibers and / or threads. In such a configuration, the fibers and / or threads of the reinforcement layer can also have a longitudinal thermal conductivity greater than 0.6 W / mK at room temperature.

[0099] The longitudinal thermal conductivity refers to the thermal conductivity considered along the direction parallel to the extension direction of the fibers and / or threads. Thus, the longitudinal thermal conductivity of the fibers and / or threads corresponds to the thermal conductivity along the total extension plane of the reinforcement layer 5.

[0100] A longitudinal thermal conductivity greater than 10 W / mK at room temperature allows for the longitudinal temperature homogenization of the reinforcement layer 5, that is, homogenization within the total extension plane of the reinforcement layer 5.

[0101] Alternatively, to ensure uniformity, the longitudinal thermal conductivity can be greater than 50 W / mK, particularly along the fiber axis.

[0102] Advantageously, the radial thermal conductivity of the fibers corresponds to the transverse thermal conductivity of the anti-frost mat 1. Therefore, it must logically be equivalent to the thermal conductivities of the intermediate layer 4 and the outer layer 6, as described below.

[0103] Such thermal conductivity is particularly important when the heating layer 3 consists of a network of metal tracks with a non-uniform heating surface. In fact, in such a case, the heat flux emitted by the metal tracks of the heating layer 3 is non-uniform longitudinally.

[0104] The homogenization of the heat flux in the total extension plane of the reinforcing layer 5 allows for greater defrosting or anti-frosting efficiency, since the heat flux generated by the heating layer 3 diffuses to ensure that the defrosting and / or anti-frosting function spreads over the entire surface of the anti-frost mat 1 without non-uniformities.

[0105] It should also be noted that the reinforcing layer 5, particularly in the form of a fabric, non-woven, knitted, meshed and / or unidirectional reinforcement, their combinations and / or stacks, provides a homogenization function that allows for relaxation of the restrictions on the track spacing of the heating layer 3. Therefore, compared to what is currently possible in known solutions of the prior art, heating metal tracks that are further apart from each other can be used.

[0106] Therefore, the present invention provides the possibility of using techniques for manufacturing the heating layer 3, particularly for manufacturing heating resistors, especially by additive manufacturing.

[0107] Preferably, the reinforcing layer 5 includes a network of woven, non-woven, knitted, meshed fibers and / or threads, and / or unidirectional reinforcements, particularly carbon fibers made from an asphalt fiber precursor (particularly coal or petroleum asphalt), and / or threads having a longitudinal thermal conductivity greater than 50 W / mK at room temperature.

[0108] More preferably, the woven or meshed reinforcement of the reinforcing layer 5 includes fibers having a longitudinal thermal conductivity greater than 120 W / mK at room temperature.

[0109] The fibers and / or threads of the reinforcing layer 5 can be of different types, such as glass fibers, basalt fibers, silica fibers, metal wires, etc.

[0110] Preferably, the reinforcing layer 5, particularly in the form of a woven, non-woven or meshed reinforcement, is made of carbon fiber, which has the advantage of good thermal conductivity.

[0111] More preferably, the carbon fibers of the reinforcing layer 5 are made from coal or petroleum asphalt. This production method of carbon fibers allows for a radial thermal conductivity greater than 0.6 W / mK, particularly greater than 10 W / mK, and / or a longitudinal thermal conductivity greater than 5 MW / mK, particularly greater than 120 W / mK.

[0112] According to another embodiment, the fibers of the reinforcement layer 5 comprise carbon fibers based on a polyacrylonitrile (PAN) type precursor. Such an embodiment has a radial thermal conductivity greater than 1 W / mK and a longitudinal thermal conductivity greater than 10 W / mK.

[0113] It should also be pointed out that the reinforcement layer 5 can also participate in a protection function, that is, a protection function against electrostatic discharge (ESD), also known by the abbreviation “ESD”.

[0114] For example, in case the reinforcement layer 5 is made of carbon fabric and / or contains metal, the reinforcement layer 5 may be used for grounding to ensure the discharge of static charges.

[0115] Under this premise, the reinforcement layer 5 can at least partially contribute to lightning protection.

[0116] The thickness of the reinforcement layer 5 can be less than 1.5 mm, in particular less than 1 mm, in particular less than 0.7 mm, advantageously less than 0.3 mm. In addition, the thickness of the reinforcement layer 5 can be greater than 0.02 mm, in particular greater than 0.05 mm. Typically, the thickness of the reinforcement layer 5 can be about 0.1 mm.

[0117] according to Figure 2 In the exemplary embodiment shown, the outer layer 6 is arranged in the multilayer structure between the reinforcement layer 5 and the lacquer layer 7 .

[0118] Alternatively, the outer layer 6 is arranged in the multilayer structure in such a manner that it is arranged on the reinforcement layer 5 and is in direct contact with the external environment.

[0119] The outer layer 6 is designed to provide protection against the external environment, in particular against adverse weather, temperature conditions and fluid jets that the aircraft may encounter.

[0120] In particular, the outer layer 6 may be made of an elastomer or a polymer resistant to the external environment, in particular to the adverse weather and temperature conditions that the aircraft may encounter.

[0121] In particular, the outer layer 6 resists erosion under the conditions defined by the standard sand and dust RTCA-DO-160.

[0122] Furthermore, the outer layer 6 contributes to shock protection.

[0123] Furthermore, the outer layer 6 may also be a composition comprising a filler enabling it to dissipate electrostatic charges.

[0124] Furthermore, the outer layer 6 is thermally conductive and does not necessarily have electrical insulating properties.

[0125] The thickness of the outer layer 6 can be less than 1.5 mm, particularly less than 1 mm, and advantageously less than 0.5 mm. Additionally, the thickness of the outer layer 6 can be greater than 0.1 mm, particularly greater than 0.2 mm. Generally, the thickness of the outer layer 6 can be about 0.2 mm.

[0126] According to Figure 2 the exemplary embodiment shown, the paint layer 7 can be applied to the multi-layer structure to cover the multi-layer structure.

[0127] In particular, the paint layer 7 is designed to have properties resistant to the external environment and / or resistant to erosion, particularly under the conditions of the standard sand and dust RTCA-DO-160.

[0128] Furthermore, the paint layer 7 can also be a composition including fillers, which enables it to dissipate static charges.

[0129] Moreover, applying the paint layer 7 on the multi-layer structure may require pre-applying an adhesion primer on the multi-layer structure, particularly on the reinforcing layer 5, or performing an adhesion treatment by a dry method (such as by plasma).

[0130] So configured and according to the present invention, the total thickness of the anti-frost pad 1 is less than 1.9 mm, particularly less than 1.5 mm, and particularly less than 1 mm.

[0131] As previously mentioned, the intermediate layer 4 can be made of a composite material 40 including a matrix 42 and inclusions 41.

[0132] The matrix 42 is made of an electrically insulating elastomer. This elastomer is selected to have good tolerance within the typical operating temperature range of the anti-frost pad 1.

[0133] The maximum operating temperature of the anti-frost pad 1 is the temperature that the heating layer 3 can reach during the heat flux required to generate the defrosting cycle.

[0134] Since the intermediate layer 4 is in direct contact with the heating layer 3, one surface of the intermediate layer 4 in contact with the heating layer 3 must withstand the maximum operating temperature.

[0135] Since the heating layer 3 is covered by the intermediate layer 4, there is also a heat flux accumulation effect at the interface between the heating layer 3 and the intermediate layer 4. The maximum temperature is generally between 100 °C and 110 °C.

[0136] Preferably, the matrix 42 is made of a thermosetting polymer, particularly an elastomeric material or an epoxy resin.

[0137] However, the matrix 42 can also be made of other types of polymers, such as thermoplastic polymers.

[0138] To obtain good resistance within the operating temperature range between the lowest and the highest temperatures and to ensure suitable mechanical properties, it is particularly advantageous for the matrix 42 to be made of a polymer selected from polyurethane, nitrile resin, neoprene resin, silicone, fluorosilicone and / or epoxy resin.

[0139] In particular, the matrix 42 can be made of a thermoplastic polymer, such as polyetheretherketone, also denoted by the acronym PEEK, polyetherketoneketone, also denoted by the acronym PEKK, polyetherimide, also denoted by the acronym PEI, polysulfone, also denoted by the acronym PSU, polyethersulfone, also denoted by the acronym PESU, polyphenylsulfone, also denoted by the acronym PPSU, polyamide-imide, also denoted by the acronym PAI, or polyphthalamide, also denoted by the acronym PPA.

[0140] The advantage of these materials is in particular their ability to withstand the contact temperature with the heating layer 3, to continuously generate a heat flux of approximately 100 °C, which is particularly advantageous for ensuring the defrosting and / or anti-frosting function.

[0141] Advantageously, the material of the matrix 42 is suitable for being shaped by a vulcanization method after incorporating the inclusions 41. This method allows fixing the position of the inclusions 41.

[0142] Another advantage of this vulcanization shaping is that it can be co-vulcanized with other materials of adjacent layers, such as the heating layer 3 which requires close contact.

[0143] In an embodiment where the heating layer 3 is made of metal tracks or heating wires, the metal tracks or heating wires are advantageously coated with a primer capable of ensuring connection with the matrix 42.

[0144] Furthermore, the different layers of the multi-layer structure of the anti-frost pad 1 can entirely have different connection modes, such as adhesion, co-vulcanization or more generally co-firing.

[0145] The matrix 42 includes inclusions 41. In particular, the inclusions 41 are made of a material having a high volume resistivity, in particular greater than 1E9 Ω·m, preferably greater than 1E10 Ω·m.

[0146] The inclusions 41 having such a resistivity allows obtaining a material: whose total resistivity corresponds to the electrical insulation requirements of the intermediate layer 4 in direct contact with the heating layer 3.

[0147] Furthermore, the inclusions 41 have a thermal conductivity greater than 1.5 W / mK at room temperature, in particular above 20 W / mK.

[0148] The inclusions 41 having such a thermal conductivity allows increasing the thermal conductivity of the intermediate layer 4. Thus, this configuration allows better transfer of the heat flux generated by the heating layer 3 towards the surface to be defrosted.

[0149] By increasing the heat flux transfer, the necessary energy savings can be achieved to ensure the defrosting and / or anti-frosting function of the component BA to be protected.

[0150] In addition, the good thermal conductivity of the intermediate layer 4 allows reducing the cumulative effect of the heat flux at the heating layer 3. Therefore, the temperature to which the intermediate layer 4 is exposed below it can be reduced near the contact area between the intermediate layer 4 and the heating layer 3. Reducing the temperature of the above contact area prevents the material deterioration of the matrix 42 to a certain extent.

[0151] Therefore, on the premise that the surface temperature of the component BA to be protected is maintained within a reasonable range, the improved thermal conductivity allows extending the service life of the heating layer 3 and / or using other materials with poorer high-temperature resistance to produce the matrix 42.

[0152] Advantageously, the material of the inclusion 41 is a ceramic with good thermal conductivity and electrical insulation.

[0153] Preferably, the inclusion 41 is made of boron nitride, aluminum nitride, alumina or a mixture of these fillers.

[0154] Other ceramics with different resistivity and thermal conductivity parameters can be used.

[0155] According to a specific embodiment, the volume ratio of the inclusion 41 in the matrix 42 is generally 10 vol% to 70 vol%, especially 20 vol% to 50 vol%, and particularly 30 vol% to 50%.

[0156] Such a volume ratio allows maintaining the mechanical properties of the matrix 42 for the forming and use of the intermediate layer 4, while allowing the use of the thermal properties of the inclusion 41 to improve the overall thermal conductivity of the material.

[0157] Now, an example of the manufacturing method of the composite material capable of forming the intermediate layer 4 will be described.

[0158] The first step includes providing a base material for the formulation of the matrix polymer 42. This base material is usually provided in the form of a plate, a flap or granules and does not include any solvent. For example, the starting material can be rubber.

[0159] In the second step, the base material is mixed, for example, in a closed mixer with several propellers or a cylindrical mixer also called an open mixer.

[0160] The components of the base material are heated by the shear effect during the mixing process.

[0161] In the second step, the base material is transformed into a homogeneous viscous material.

[0162] In the third step, particles for forming the inclusions 41 are added. Such particles are provided in powder form and may agglomerate during production or storage.

[0163] In the third step, which consists of a mixing step, particles are added. The third step allows any agglomerates to be dispersed and the particles to be evenly distributed in the viscous material for forming the matrix 42, in particular a matrix 42 made of a polymer.

[0164] After the inclusions 41 are distributed in the matrix 42, in the fourth step, an intermediate layer 4 is formed, the thickness of which can be between 0.2 mm and 0.7 mm, typically about 0.4 mm.

[0165] The formation of the intermediate layer 4 can be carried out by calendering, extrusion, in particular by extruding a film in a flat die.

[0166] Subsequently, in the fifth step, the matrix 42 is shaped using a dedicated tool and then vulcanized to hold the inclusions 41 in place and fix the geometry of the intermediate layer 4.

[0167] In some embodiments, an intermediate layer 4 that is in direct contact with the heating layer 3 can be formed. In this case, co-vulcanization is carried out between the polymer matrix 42 and the heating layer 3. This co-vulcanization allows ensuring good mechanical and thermal contact between the intermediate layer 4 and the heating layer 3.

[0168] To test the intermediate layer 4, and more generally the structure of the anti-frost mat 1, a test device 400 as Figure 4 shown is used.

[0169] Advantageously, the anti-frost mat 1 including the contact layer 2, the heating layer 3, the intermediate layer 4, the reinforcement layer 5 and the outer layer 6 is tested.

[0170] The test device 400 includes a conductive reservoir 401, typically a metal reservoir, filled with a certain amount of water 402.

[0171] A laminate structure including at least the contact layer 2, in particular the electrically insulating intermediate layer 4 made of a composite material 40, and the heating layer 3 is immersed in a certain amount of water 402.

[0172] Alternatively, the anti-frost mat 1 including the contact layer 2, the heating layer 3, the intermediate layer 4, the reinforcement layer 5 and the outer layer 6 is immersed in a certain amount of water 402.

[0173] As a result, two electrodes 411, 412 are connected to the heating layer 3 via a power line and an electrical connection 413 is established with a resistance measuring device 410 (such as an ohmmeter). The resistance measuring device 410 is electrically connected to the reservoir 401.

[0174] Then, a voltage is applied between the liquid reservoir 401 and the electrodes 411, 412 connected to the heating layer 3, in particular a voltage of 500 VDC.

[0175] Preferably, the voltage applied during the test is twice the operating voltage of the defrosting and / or anti-frosting device for the component BA to be defrosted, and the operating voltage can be 220 V to 230 V.

[0176] Alternatively, the operating voltage of the defrosting and / or anti-frosting device for the component BA to be defrosted can be provided at 110 V.

[0177] As a result, the first test step includes measuring the insulation resistance, which is measured by the resistance measuring device 410.

[0178] If the following conditions are met, the result of the first test step is considered valid:

[0179] - The laminated structure including the heating layer 3 is intact, that is, no damage caused by electric arcs can be seen between the surface of the heating layer 3 and the surface of the contact layer 2 and / or between the surface of the heating layer 3 and the surface of the outer layer 6; and

[0180] - The insulation resistance measured by the resistance measuring device 410 is greater than 10 MΩ, in particular greater than 100

[0181] MΩ.

[0182] The measured insulation resistance value can be adjusted according to the performance specifications of the intended application.

[0183] In addition, in order to confirm the reliability of the material, several repeated tests can be carried out continuously.

[0184] Subsequently, the second test step includes verifying the dielectric resistivity and the leakage current.

[0185] Figure 5 The test device 400 for the second test step is shown. The elements common to Figure 4 the test device are denoted by the same reference numerals and will not be described again.

[0186] The test device 400 includes a leakage current measuring device 420, for example in the form of an ammeter, which is electrically connected to the electrodes 411 and 412 connected to the intermediate layer 4.

[0187] In addition, the test device 400 includes a voltage source 430 which is electrically connected to the leakage current measuring device 420 and the liquid reservoir 401. For example, the voltage source 430 provides a voltage of at least 1500 V with an alternating current having a frequency between 50 Hz and 60 Hz.

[0188] In the second test step, a voltage is applied. To this end, the voltage is gradually increased between 0 V and twice the operating voltage of the defrosting and / or anti-frosting device, increasing by 1000 V over 20 seconds. The resulting voltage is then maintained for one minute.

[0189] The result of the second test step is considered valid if the following conditions are met:

[0190] - The laminate structure including the heating layer 3 and the intermediate layer 4 is intact, i.e., no damage caused by arcing is visible between the components of the test device 400 and / or between the heating layer 3 and the intermediate layer 4;

[0191] - The laminate structure including the heating layer 3 is intact, i.e., no damage caused by arcing is visible between the surface of the heating layer 3 and the contact layer 2 and / or between the surface of the heating layer 3 and the outer layer 6; and

[0192] - The leakage current measured by the leakage current measuring device 420 is less than 200 mA, in particular less than 50 mA,

[0193] in particular less than 30 mA.

[0194] The value of the leakage current measured by the leakage current measuring device 420 can be adjusted according to the performance specifications of the intended application.

[0195] The intermediate layer 4 can be integrated into any laminate structure of functional layers that require electrical insulation and thermal conduction.

[0196] In Figure 1 the case of the thermoelectric anti-frosting pad 1, the intermediate layer 4 provided on the heating layer 3 improves the defrosting performance and allows the heating temperature of the heating layer 3 to be reduced.

[0197] Reducing the temperature of the heating layer 3 is beneficial for integrating the anti-frosting pad 1 on temperature-sensitive components, especially composite components.

[0198] Furthermore, the matrix 41 is advantageously made of an elastomer, thereby allowing the intermediate layer 4 and the anti-frosting pad 1 to adapt to complex component shapes, especially three-dimensional components, in particular non-unfolding three-dimensional components.

[0199] The uncured elastomer is shaped, and then the intermediate layer 4 is fixed by vulcanization. However, the elasticity of the intermediate layer 4 can be maintained after vulcanization.

[0200] Other applications besides the thermoelectric anti-frosting pad 1 are of course also possible for the materials just described, such as heat sinks.

[0201] According to the present invention, different techniques can be used to assemble the different layers of the anti-frosting pad 1.

[0202] In a possible implementation, the contact layer 2 that forms the thermoelectric barrier can be directly formed on the heating layer 3, particularly by projection.

[0203] Alternatively or additionally, the contact layer 2 includes an elastomeric sheet that is manually superimposed or automatically covered. The material of the contact layer 2 can be an elastomer, a polymer, particularly a thermoplastic polymer or a thermosetting polymer, particularly an epoxy resin.

[0204] Similarly, the intermediate layer 4 provides electrical insulation and heat conduction functions, and has a higher thermal conductivity than the contact layer 2 to direct the dissipation of the heat flux to the external environment.

[0205] Then, the reinforcement layer 5 can be assembled to the intermediate layer 4 and the outer layer 6, for example, by gluing.

[0206] The outer layer 6 can be directly formed on the reinforcement layer 5, particularly by projection.

[0207] In another possible implementation, the layers of the multi-layer structure are superimposed on each other by manual or automatic covering, and then assembled together by various assembly methods.

[0208] For various bonding operations, the surfaces to be bonded can be prepared by any bonding treatment method, particularly by dry method or plasma.

[0209] In a separate or combined manner, the method for manufacturing the anti-frost pad 1 can at least include the following steps:

[0210] - The contact layer 2, the intermediate layer 4, and / or the outer layer 6 are calendered from an elastomer mixture and are advantageously used in raw material form in all steps of the manufacturing method;

[0211] - The heating layer 3 is preferably a heating resistor obtained by chemically cutting a metal strip, and the heating resistance value of the anti-frost pad 1 is controlled in this step;

[0212] - The heating layer 3 is covered with at least one primer to allow bonding with the elastomer in the vulcanization step, and the heating layer 3 can be made of several pieces;

[0213] - Use a manufacturing tool whose geometry corresponds to the shape of the component BA to be anti-frosted, and the manufacturing tool is optionally covered with a non-stick coating;

[0214] - The reinforcement layer 5 is a fabric reinforcement layer, and the fabric reinforcement layer is adhered by adding chemicals, mainly of the aqueous solution type or chemicals containing solvents, by dry method, by powder deposition, by plasma, etc.;

[0215] - The outer layer 6 is deposited on the manufacturing tool, particularly by manual or automatic deposition;

[0216] - Deposit the reinforcement layer 5 on the outer layer 6, in particular optionally pre - form a fan shape to be able to fit the manufacturing tool;

[0217] - Deposit the intermediate layer 4 on the reinforcement layer 5;

[0218] - Deposit the heating layer 3 on the intermediate layer 4;

[0219] - The electrical connection is achieved, for example, by welding;

[0220] - Deposit the contact layer 2 on the heating layer 3;

[0221] - Then form a vacuum chamber on the multi - layer structure thus formed;

[0222] - Then vulcanize the overall structure in an autoclave furnace under vacuum;

[0223] - At the end of vulcanization, perform a demolding step and perform various finishing operations, such as in particular a trimming operation;

[0224] - A paint layer 7 can be added to the outer layer 6;

[0225] - The anti - frost pad 1 thus formed can then be assembled, for example, by a cold - bonding method to the component BA to be protected.

[0226] The anti - frost pad 1 produced in this way can be added by gluing the contact layer 2 to the outer surface 11 of the component BA to be protected.

[0227] Other assembly techniques than gluing are also possible, such as co - curing or co - vulcanization, especially when the component BA to be protected is made of a composite material.

[0228] Before depositing the adhesive on the component BA to be anti - frosted and / or on the contact layer 2, a bonding primer can be added so that at least one of the surfaces of the component BA and the contact layer 2 that will be set on top of each other can undergo a surface pretreatment, such as sanding, primer deposition or any other dry or plasma bonding treatment.

[0229] In the foregoing description, for the purpose of example, the component BA to be protected is the leading edge of an aircraft wing.

[0230] The anti - frost pad 1 according to the present invention can be attached to any other aircraft component that requires anti - frosting, such as an engine air intake, a turbine fairing, an aircraft or helicopter propeller blade, a propeller engine cone, a protective radome, etc.

[0231] It should be noted that the multi - layer structure proposed for the anti - frost pad 1 is particularly soft and comfortable. It can adapt to different three - dimensional shapes that can be considered suitable for the component BA.

[0232] In the case of the defrosting operating mode, the heating layer 3 is advantageously supplied in a circulating manner to allow the detachment of the frost that has formed on the outer surface of the anti-frost mat 1.

[0233] For example, in the case of the defrosting operating mode, the heating layer 3 is powered for a defined time at regular intervals.

[0234] Typically, in the case of the defrosting operating mode, the electrical power applied to the heating layer 3 is between 1 W / cm 2 and 3 W / cm 2 and, in particular, between 2 W / cm 2 and 3 W / cm 2 .

[0235] In the case of the anti-frosting operating mode, the heating layer 3 is continuously powered in order to continuously prevent the formation of any frost on the component BA to be protected against frost.

[0236] Typically, in the case of the anti-frosting operating mode, the electrical power applied to the heating layer 3 can reach 5 W / cm 2 .

[0237] In the detailed description of the invention given above, the terms used should not be considered as restricting the invention to the embodiments set forth in the description just presented, but should be interpreted as including all equivalents, the prediction of which is within the capabilities of a person skilled in the art by applying their common general knowledge to the embodiments of the teaching just disclosed to them.

Claims

1. An electrically insulating composite material (40), characterized in that, The material is a composite material comprising the following substances, - a matrix (42) made of an elastomer or a polymer, and - inclusions (41), providing the material with a thermal conductivity greater than 0.6 W / mK at room temperature, in particular greater than 1.5 W / mK at room temperature.

2. The electrically insulating composite material (40) according to claim 1, wherein, The material has a volume resistivity greater than 1 E9 Ω·m, preferably greater than 1 E10 Ω·m.

3. The electrical insulation composite material (40) according to claim 1 or 2, wherein, The inclusions (41) are ceramics.

4. The electrically insulating composite material (40) according to any one of the preceding claims, wherein, The inclusions (41) are made of boron nitride, aluminum nitride and / or aluminum oxide.

5. The electrically insulating composite material (40) according to any one of the preceding claims, wherein, The matrix (42) is selected from polyurethane, nitrile resin, neoprene resin, silicone, fluorosilicone and / or epoxy resin.

6. The electrically insulating composite material (40) according to any one of the preceding claims, wherein, The matrix (42) is made of a thermoplastic polymer, in particular polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyetherimide (PEI), polysulfone (PSU), polyethersulfone (PESU), polyphenylsulfone (PPSU), polyamideimide (PAI) or polyphthalamide (PPA).

7. The electrically insulating composite material (40) according to any one of the preceding claims, wherein, The volume ratio of the inclusions (41) is between 10 vol% and 70 vol%, in particular between 20 vol% and 50 vol%, in particular between 30 vol% and 50 vol%.

8. An anti-frost mat (1), in particular for at least one aircraft component (BA), comprising at least one heating layer (3), in particular incorporating at least one heating resistor, and at least one intermediate layer (4) made of the composite material (40) according to any one of the preceding claims.

9. A component, comprising at least one part (BA), in particular an aircraft part (BA), having an outer surface (11), characterized in that, The outer surface (11) is covered by the anti-frost mat (1) according to claim 8.

10. A method for manufacturing the composite material (40) according to any one of claims 1 to 6, comprising at least the following steps: - providing at least one base material for the formulation of the elastomer and / or polymer, - adding inclusions (41) to the base material, the inclusions having a thermal conductivity greater than 0.4 W / mK at room temperature, in particular greater than 0.6 W / mK at room temperature, in particular greater than 0.8 W / mK at room temperature, in particular greater than 1.5 W / mK at room temperature, - vulcanizing the base material incorporating the inclusions (41).

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