Flame-retardant cable

Abstract

The invention provides a flame-retardant cable, and relates to the technical field of cables, the flame-retardant cable comprises a conductor, and the exterior of the conductor is sequentially sleeved with a cooling layer, a flame-retardant layer and a protective layer; the cooling layer is a phase change layer, micro-channels which are circumferentially and uniformly distributed are formed in the outer side of the cooling layer, and the cooling layer expands to fill the micro-channels after being heated and melted and is attached to the inner surface of the flame-retardant layer; the protective layer comprises an inner protective layer and an outer protective layer, corrugated grooves containing microcapsules are formed in the inner side of the inner protective layer, and the microcapsules are broken under extrusion of the cooling layer and the flame-retardant layer; the flame-retardant layer is of a porous structure, and a liquid-phase material of the cooling layer and liquid released by the microcapsules are jointly immersed into pores of the flame-retardant layer to form a sealing layer. Through cooperation of the cooling layer, the flame-retardant layer and the microcapsules, the flame-retardant effect of the flame-retardant layer is improved, and the flame-retardant capability of the cable during short circuit and overload is improved.

Description

Technical Field

[0001] The invention relates to the technical field of cables, and in particular to a flame-retardant cable. Background Art

[0002] Flame-retardant cables refer to cables that, after being ignited under specified test conditions, have a limited flame spread and can extinguish themselves. Its core function is to inhibit the spread of fire, slow down the burning speed through special materials, and buy time for personnel evacuation and fire rescue.

[0003] A Chinese patent with application number CN201780055161.2 discloses a self-extinguishing power cable with microcapsules, comprising a conductive layer, an inner semiconductive layer, an insulating layer, an outer semiconductive layer, a first neutral conductor water-blocking layer, a concentric neutral conductor, a second neutral conductor water-blocking layer and an outer sheath layer, wherein microcapsules filled with an active agent for extinguishing flames are applied to at least one of the first neutral conductor water-blocking layer and the second neutral conductor water-blocking layer; wherein the size of the microcapsules is 5 μm to 100 μm, and the allowable rupture temperature is in the range of 90°C and 150°C; in the above invention, microcapsules are arranged in the cable to extinguish the flame of the cable and prevent the occurrence of serious fires.

[0004] Similar to the above-mentioned prior art, although microcapsules can solve the problem of cable fire caused by short circuit, when the cable is overloaded for a long time, the internal temperature of the cable will gradually increase. If the cable temperature reaches the rupture temperature of the microcapsule at this time, and the cable has not caught fire, the microcapsule will rupture prematurely. When the subsequent cable temperature reaches the fire condition, the ruptured microcapsule cannot effectively flame retard the cable.

[0005] At the same time, when laying a cable with microcapsules inside, the microcapsules located at the bends of the cable are easily broken under the action of the squeezing force, causing the cable to lose its flame retardant effect. The cable can only be flame retardant when a fire occurs inside the cable, and the heat dissipation performance is poor. When the cable is overloaded for a long time, the cable cannot be effectively cooled.

[0006] Therefore, in order to solve the above problems, the present invention proposes a flame retardant cable, which aims to improve the flame retardant ability of the cable to resist spontaneous combustion caused by short circuit or overload. Summary of the invention

[0007] The purpose of the present invention is to provide a flame retardant cable, aiming to solve the problem of spontaneous combustion of the cable due to short circuit or overload.

[0008] To achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a flame-retardant cable, comprising a conductor, characterized in that a cooling layer, a flame-retardant layer and a protective layer are sequentially sheathed on the outside of the conductor; the cooling layer is a phase change layer, and microchannels uniformly distributed on its outer side are provided, and the cooling layer expands and fills the microchannels after being melted by heat and adheres to the inner surface of the flame-retardant layer; the protective layer comprises an inner protective layer and an outer protective layer, and a corrugated groove containing microcapsules is provided on the inner side of the inner protective layer, and the microcapsules are broken under the squeezing of the cooling layer and the flame-retardant layer; the flame-retardant layer is a porous structure, and the liquid phase material of the cooling layer and the liquid released by the microcapsules are immersed in the pores of the flame-retardant layer together to form a sealing layer.

[0009] A further technical solution of the present invention is that the cooling layer changes from a solid phase to a liquid phase after the temperature rises, and the microchannel provides expansion space when the cooling layer melts.

[0010] A further technical solution of the present invention is that the outer protective layer is arranged on the outer side of the inner protective layer, and a plurality of microcapsules are arranged in the groove.

[0011] A further technical solution of the present invention is that the outer surface of the conductor is covered with an insulating layer, the outer surface of the insulating layer is provided with a shielding layer, a filling layer is provided between the insulating layer and the shielding layer, and the insulating layer, the filling layer and the shielding layer are located between the conductor and the cooling layer.

[0012] A further technical solution of the present invention is that the conductor comprises a cable core composed of one or more strands of conductive material wound together, and the surface of the conductor is coated with a boron nitride nanosheet coating.

[0013] A further technical solution of the present invention is that the insulating layer includes a cross-linked polyethylene matrix, magnesium hydroxide nanoparticles and carbon nanotubes.

[0014] A further technical solution of the present invention is that the shielding layer is a grid-like structure, and the outer surface of the shielding layer is coated with an electromagnetic interference coating.

[0015] A further technical solution of the present invention is that the flame retardant layer cooperates with the cooling layer and the microcapsules to achieve double flame retardancy.

[0016] A further technical solution of the present invention is that the outer protective layer includes polyvinyl chloride and graphene, and the inner protective layer includes thermoplastic polyurethane and nano-silicon dioxide.

[0017] A further technical solution of the present invention is that the radial cross section of the groove is corrugated, and the interior of the microcapsule is filled with a liquid that is resistant to high temperatures and has electrical insulation properties.

[0018] The beneficial effects are: 1. The present invention arranges microcapsules and grooves in cooperation with the inner protective layer. When the cable is squeezed or twisted by external force, the corrugated structure can disperse the local pressure and reduce the risk of cracking of the protective layer. Moreover, the grooves provide a buffer space for the microcapsules to avoid premature rupture of the capsules due to mechanical impact. At the same time, the microcapsules can cool the flame retardant layer to achieve the effect of flame retardancy, thereby achieving the purpose of enhancing the protective ability and flame retardancy.

[0019] 2. The present invention cooperates with the cooling layer and the microcapsules to act on the flame retardant layer. The flame retardant layer adopts a porous ceramic silicone rubber matrix. When the phase change material of the cooling layer melts and expands, it penetrates into the flame retardant layer together with the silicone oil released by the microcapsules to form a dense sealing layer. This sealing layer can isolate oxygen contact and inhibit the combustion chain reaction, thereby improving the flame retardant ability of the cable when facing short circuit or overload.

[0020] 3. The present invention improves the ability of the cable to respond quickly in a short circuit and to provide continuous protection in an overload by providing a cooling layer, microcapsules and a flame retardant layer. When the cable is short-circuited, the current suddenly increases, causing the local temperature to exceed the melting point of paraffin. The cooling layer quickly undergoes a phase change and absorbs heat, forming a "temperature platform" effect to suppress temperature rise while performing directional fire extinguishing, i.e., the microcapsules at the corresponding positions rupture, releasing silicone oil for directional cooling and filling the pores to prevent the spread of flames. When the cable is continuously overloaded, the cooling layer continues to melt and absorb heat, slowing down the rate of temperature rise, and the liquid paraffin in the cooling layer and the silicone oil after the microcapsules rupture jointly impregnate the flame retardant layer to form a dynamic sealing layer to block heat transfer. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a structural diagram of embodiment 1 of the present invention.

[0022] Figure 2 It is a schematic diagram of the structure of the microchannel in a specific embodiment of the present invention.

[0023] Figure 3 It is a structural diagram of embodiment 2 of the present invention.

[0024] Figure 4 It is a schematic diagram of the structure of the groove in a specific embodiment of the present invention.

[0025] Figure 5 The present invention Figure 3 A partial enlarged view of point A in the middle.

[0026] Reference numerals: 1. Conductor; 2. Insulating layer; 21. Filling layer; 3. Shielding layer; 4. Cooling layer; 41. Microchannel; 5. Flame retardant layer; 6. Protective layer; 61. Outer protective layer; 62. Inner protective layer; 621. Groove; 622. Microcapsule. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] Embodiment 1 To improve the flame retardancy and flexibility of flame retardant cables, Figure 1 and Figure 2 As shown, in the first embodiment of the present invention, a flame retardant cable is proposed, including a conductor 1, the outside of the conductor 1 is sequentially covered with a cooling layer 4 and a flame retardant layer 5, the outside of the flame retardant layer 5 is covered with a protective layer 6, the cooling layer 4 is a phase change layer, and the outside of the cooling layer 4 is provided with a plurality of microchannels 41, the cooling layer 4 is melted after being subjected to high temperature, expands and adheres to the inner surface of the flame retardant layer 5 to form a sealing layer.

[0029] It should be noted that the provision of the microchannel 41 increases the flexibility of the cable. When the cable is locally twisted during installation or movement, the provision of the microchannel 41 can solve the problem of rupture in the torsional area of ​​the cable caused by excessive torsional stress. At the same time, the provision of the microchannel 41 leaves expansion space for the cooling layer 4. After melting, the cooling layer 4 expands in volume and fills the microchannel 41, so that the melted cooling layer 4 adheres to the inner side of the flame retardant layer 5, thereby increasing the heat transfer performance of the flame retardant layer 5.

[0030] In this embodiment, the cooling layer 4 changes from a solid phase to a liquid phase after the temperature rises, and a plurality of microchannels 41 are evenly distributed on the outer side of the cooling layer 4 in a circumferential shape.

[0031] It should be noted that the cooling layer 4 can be a phase change layer made of organic paraffin as a phase change material and expanded graphite as a supporting structure. Paraffin has a high latent heat of phase change. When the temperature rises to the range of 47°-64°, the paraffin enters the main melting stage. The heat is mainly used to destroy the van der Waals force between molecules rather than continue to increase the temperature. Therefore, the temperature remains relatively stable, forming a "temperature platform" phenomenon, which plays a role in regulating the temperature. Expanded graphite has good thermal conductivity and supporting function, which can improve the thermal conductivity and stability of the phase change layer.

[0032] In this embodiment, the outer surface of the conductor 1 is covered with an insulating layer 2, the outer sleeve of the insulating layer 2 is provided with a shielding layer 3, a filling layer 21 is provided between the insulating layer 2 and the shielding layer 3, and the insulating layer 2, the filling layer 21 and the shielding layer 3 are located between the conductor 1 and the cooling layer 4.

[0033] The conductor 1 includes a cable core composed of one or more strands of conductive material wound together, and the surface of the conductor 1 is coated with a boron nitride nanosheet coating. For example, the conductor 1 can be a silver-plated copper core, which has good electrical conductivity and thermal conductivity, and can quickly transmit current and conduct away the generated heat. The boron nitride nanosheet coating on the conductor 1 has a thickness of 3-13 μm, and the boron nitride nanosheet coating has high thermal conductivity and chemical stability. The directional arrangement structure is formed by chemical vapor deposition, which can further improve the axial thermal conductivity of the conductor 1 and accelerate the heat transfer speed.

[0034] The insulating layer 2 includes a cross-linked polyethylene matrix, magnesium hydroxide nanoparticles and carbon nanotubes. Exemplarily, the insulating layer 2 forms a three-dimensional thermal conductive network through electron beam irradiation. The mass fraction of the magnesium hydroxide nanoparticles can be 10-20%, and the mass fraction of the carbon nanotubes can be 3-5%.

[0035] It should be noted that magnesium hydroxide nanoparticles have good flame retardant properties, can decompose and absorb heat when a fire occurs, and inhibit the spread of flames. Carbon nanotubes have excellent thermal conductivity, can improve the thermal conductivity of the insulating layer 2, and promote heat dissipation. The three-dimensional thermal conductive network formed by electron beam irradiation enables heat to be quickly transferred in the insulating layer 2, thereby improving the heat dissipation capacity of the insulating layer 2. In addition, the filling layer 21 can further enhance the mechanical properties and protective properties of the insulating layer 2.

[0036] The shielding layer 3 has a grid structure, and the outer surface of the shielding layer 3 is coated with an electromagnetic interference coating. The material of the shielding layer 3 can be metal. The grid structure can effectively shield external electromagnetic interference and protect the signal transmission inside the cable from interference. The electromagnetic interference coating can further enhance the shielding effect of the shielding layer 3 and improve the anti-interference ability of the cable.

[0037] The flame retardant layer 5 is arranged in a porous structure, and can cooperate with the cooling layer 4 and the microcapsule 622 to achieve double flame retardancy. Exemplarily, the flame retardant layer 5 can be a porous ceramic layer made of a ceramic silicone rubber matrix composite zinc borate or melamine polyphosphate, and the porosity of the porous ceramic layer is ≥60%. The ceramic silicone rubber matrix has good flexibility and flame retardant properties. When a fire occurs, it can be quickly ceramicized to form a hard ceramic protective layer to prevent the spread of flames. Zinc borate and melamine polyphosphate have a synergistic flame retardant effect, which can improve the flame retardant effect of the flame retardant layer 5. The high porosity of the porous ceramic layer makes it have good thermal insulation properties, which can further reduce the temperature inside the cable and improve the flame retardant properties of the cable.

[0038] In this embodiment, the conductor 1 is set as a silver-plated copper core coated with a boron nitride nanosheet coating, a shielding layer 3 is set outside the insulating layer 2, and a cooling layer 4, a flame retardant layer 5 and a protective layer 6 are sequentially arranged outside the shielding layer 3, and the cooling layer 4 is a phase change layer made of organic paraffin as a phase change material and expanded graphite as a supporting structure, and a plurality of microchannels 41 are provided on the outside of the cooling layer 4. The above arrangement improves the thermal management ability and heat dissipation ability of the cable, reduces the possibility of cable combustion, strengthens the cable's anti-electromagnetic interference ability, improves the cable's flexibility, and prevents the cooling layer 4 from excessively expanding and damaging the flame retardant layer 5.

[0039] Embodiment 2 In actual use, the cable may be short-circuited or overloaded, causing the internal temperature of the cable to rise, resulting in the problem of cable self-ignition. When the cable is short-circuited, the resistance between conductors 1 approaches zero, and the current instantly reaches 10-1000 times the normal value. According to Joule's law, the square increase of the current causes the heat to rise exponentially, thus causing the cable to self-ignite; when the cable is overloaded, the heat generated by the resistance of conductor 1 cannot be dissipated in time, the temperature continues to rise, and the insulation layer 2 begins to decompose. If it reaches the ignition point, it can directly self-ignite.

[0040] To solve the above technical problems, Figures 3 to 5 As shown, in another embodiment of the present invention, a plurality of microcapsules 622 are provided on the inner side of the protective layer 6 of the flame retardant cable, and the microchannels 41 and the microcapsules 622 can assist the flame retardant layer 5 in improving the flame retardant effect of the cable when the cable is caught by short circuit and overload, that is, the liquid phase material of the cooling layer 4 and the liquid released by the microcapsules 622 are immersed in the pores of the flame retardant layer 5 together to form a sealing layer, thereby improving the flame retardant effect.

[0041] The protective layer 6 also includes an inner protective layer 62 sleeved on the flame retardant layer 5, the outer side of the inner protective layer 62 is sleeved with the outer protective layer 61, the inner side of the inner protective layer 62 is provided with a plurality of grooves 621 matching the microcapsules 622, and the plurality of microcapsules 622 are respectively located in the corresponding grooves 621. The inner protective layer 62 with the grooves 621 and the microcapsules 622 can buffer when the cable is impacted, thereby protecting the cable.

[0042] The outer protective layer 61 includes polyvinyl chloride and graphene, and the inner protective layer 62 includes thermoplastic polyurethane and nano-silicon dioxide.

[0043] It should be noted that polyvinyl chloride has good mechanical properties and chemical corrosion resistance, and graphene has excellent electrical and thermal conductivity, which can improve the strength and heat dissipation performance of the outer protective layer 61. Thermoplastic polyurethane has good flexibility and wear resistance, and nano-silicon dioxide can improve the hardness and aging resistance of the inner protective layer 62. The outer protective layer 61 and the inner protective layer 62 cooperate to achieve mechanical protection and flame retardancy.

[0044] The radial cross-section of the groove 621 is corrugated, and the interior of the microcapsule 622 is filled with a high-temperature resistant and electrically insulating liquid. Exemplarily, a plurality of microcapsules 622 are evenly distributed inside the groove 621. The high-temperature resistant and electrically insulating liquid filled in the microcapsule 622 may be silicone oil. The microcapsule 622 may release silicone oil when ruptured, thereby filling the cracks in the inner protective layer 62 and isolating oxygen, thereby achieving the purpose of flame retardancy and enhancing protective capabilities.

[0045] It should be noted that the radial cross-section of the groove 621 is designed to be corrugated. Together with the inner protective layer 62, when the cable is squeezed or twisted by external force, the corrugated structure can disperse local pressure and reduce the risk of cracking of the protective layer. In addition, the groove 621 provides a buffer space for the microcapsule 622 to prevent the microcapsule 622 from rupturing prematurely due to mechanical impact.

[0046] In this embodiment, an inner protective layer 62 is provided inside the outer protective layer 61, a groove 621 is provided inside the inner protective layer 62, and microcapsules 622 filled with silicone oil are provided inside the groove 621. Not only can the cable be protected by the inner protective layer 62 and the microcapsules 622, but also the inner protective layer 62 can be repaired when cracks are generated due to aging. When cracks occur at the aging position of the inner protective layer 62, the microcapsules 622 at the corresponding positions will be torn at the same time, and the microcapsules 622 release silicone oil to fill the cracks through capillary action, thereby restoring the protection integrity and extending the service life of the cable. The microcapsules 622 achieve the purpose of enhancing the protection capability and flame retardancy.

[0047] It should be noted that the flame retardant layer 5 is made of a porous ceramic silicone rubber matrix (porosity ≥ 60%). When the phase change material (such as paraffin) of the cooling layer 4 melts and expands, it penetrates into the pores together with the silicone oil released by the microcapsules 622 to form a dense sealing layer. This sealing layer can isolate oxygen from contact and inhibit the combustion chain reaction.

[0048] At the same time, zinc borate and melamine polyphosphate are added to the flame retardant layer 5 to form a synergistic flame retardant effect with silicone oil. Zinc borate decomposes at high temperature to generate glassy borates to cover the surface of the material; melamine polyphosphate releases inert gas to dilute oxygen; silicone oil penetration enhances sealing, and the three synergistically improve the limiting oxygen index, thereby improving the flame retardant effect.

[0049] And through the above arrangement, when facing the situation of cable short circuit, the local temperature inside the cable rises sharply, the cooling layer 4 is in a solid-liquid mixed state, the solid therein passes through the flame retardant layer 5, squeezes the microcapsules 622 in the corresponding area, and the silicone oil inside flows out to cool the flame retardant layer 5.

[0050] When facing the situation of cable overload, the internal temperature of the cable continues to rise. After the temperature reaches the melting point of paraffin, the paraffin in the cooling layer 4 absorbs heat and melts. Because the volume of paraffin will expand significantly when it melts (the expansion rate is about 10%-20%), the melted liquid of the cooling layer 4 will penetrate into the flame retardant layer 5 after expansion, so that the flame retardant layer 5 forms a sealed state and isolates the external air. At the same time, the cooling layer 4 will squeeze the flame retardant layer 5, and then squeeze the microcapsule 622. After the microcapsule 622 is squeezed, the silicone oil inside will soak the flame retardant layer 5, and while cooling the flame retardant layer 5, it will further form a sealed state of the flame retardant layer 5, isolate the external air, and improve the flame retardant effect.

[0051] When the cable faces an external fire, the magnesium hydroxide nanoparticles in the insulating layer 2 decompose and absorb heat when a fire occurs, thereby suppressing the spread of the flame; the ceramic silicone rubber in the flame retardant layer 5 can be quickly ceramicized when a fire occurs, forming a hard ceramic protective layer to prevent the spread of the flame; the porous ceramic layer has good thermal insulation properties, which can further reduce the temperature of the cable.

[0052] The present invention improves the ability to cope with spontaneous combustion caused by the increase in internal temperature of the cable by setting the cooling layer 4, the flame retardant layer 5 and the microcapsules 622. When the cable is short-circuited, the temperature of the cable rises rapidly locally. When the cooling layer 4 faces a drastic change in temperature, it is in a solid-liquid mixed state. The solid matter of the cooling layer 4 squeezes the microcapsules 622 in the corresponding area through the flame retardant layer 5, thereby cooling the flame retardant layer 5. When the cable is overloaded and the temperature does not reach the ignition condition, the temperature inside the cable continues to rise, the cooling layer 4 continues to melt and expand, and the melted liquid of the cooling layer 4 adheres to the flame retardant layer 5, improving the heat dissipation performance of the flame retardant layer 5; when the cable is continuously overloaded and heated to the point of ignition, the melted liquid of the cooling layer 4 penetrates into the flame retardant layer 5, making the flame retardant layer 5 form a sealed state and isolating the external air. At the same time, the cooling layer 4 squeezes the flame retardant layer 5 due to expansion, and then squeezes the microcapsules 622. After the microcapsules 622 are squeezed and broken, the silicone oil inside soaks the flame retardant layer 5, cooling the flame retardant layer 5 while further making the flame retardant layer 5 form a sealed state, isolating the external air, and improving the flame retardant effect. The flame retardant layer 5 cooperates with the cooling layer 4 and the microcapsules 622 to achieve double flame retardancy. In this state, the cooling layer 4 is in a state, how to cooperate with 6 to achieve the flame retardant effect. Thereby improving the flame retardant effect, solving the problem of spontaneous combustion of the cable due to internal heating when short circuit or overload occurs.

[0053] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A flame-retardant cable, comprising a conductor, characterized in that: The conductor is covered with a cooling layer, a flame retardant layer and a protective layer in sequence on its exterior; The cooling layer is a phase change layer, and microchannels evenly distributed around the circumference are arranged on the outer side thereof. After the cooling layer is heated and melted, it expands, fills the microchannels, and adheres to the inner surface of the flame retardant layer; The protective layer comprises an inner protective layer and an outer protective layer, wherein the inner side of the inner protective layer is provided with corrugated grooves containing microcapsules, and the microcapsules are broken under the pressure of the cooling layer and the flame retardant layer; The flame retardant layer is a porous structure, and the liquid phase material of the cooling layer and the liquid released by the microcapsules are immersed in the pores of the flame retardant layer to form a sealing layer.

2. The flame-retardant cable according to claim 1, characterized in that: The cooling layer changes from a solid phase to a liquid phase after the temperature rises, and the microchannel provides expansion space when the cooling layer melts.

3. The flame-retardant cable according to claim 1, characterized in that: The outer protective layer is arranged on the outer side of the inner protective layer, and a plurality of microcapsules are arranged in the groove.

4. The flame-retardant cable according to claim 1, characterized in that: The outer surface of the conductor is covered with an insulating layer, the outer sleeve of the insulating layer is provided with a shielding layer, a filling layer is provided between the insulating layer and the shielding layer, and the insulating layer, the filling layer and the shielding layer are located between the conductor and the cooling layer.

5. The flame-retardant cable according to claim 1, characterized in that: The conductor comprises a cable core formed by winding one or more strands of conductive material, and the surface of the conductor is coated with a boron nitride nanosheet coating.

6. The flame-retardant cable according to claim 4, characterized in that: The insulating layer comprises a cross-linked polyethylene matrix, magnesium hydroxide nanoparticles and carbon nanotubes.

7. The flame-retardant cable according to claim 4, characterized in that: The shielding layer is a grid structure, and the outer surface of the shielding layer is coated with an electromagnetic interference coating.

8. The flame-retardant cable according to claim 1, characterized in that: The flame retardant layer cooperates with the cooling layer and the microcapsules to achieve double flame retardancy.

9. The flame-retardant cable according to claim 3, characterized in that: The outer protective layer comprises polyvinyl chloride and graphene, and the inner protective layer comprises thermoplastic polyurethane and nano silicon dioxide.

10. The flame-retardant cable according to claim 3, characterized in that: The radial cross section of the groove is corrugated, and the interior of the microcapsule is filled with a liquid that is resistant to high temperatures and has electrical insulation properties.

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