Mica tape cross-linked polyethylene insulated cable

Abstract

The invention relates to the technical field of cable processing, and discloses a mica tape cross-linked polyethylene insulated cable which comprises a copper conductor, a mica tape, a cross-linked polyethylene insulating layer, a filling material, a wrapping layer and a cable sheath from inside to outside, the mica tape comprises mica paper, a reinforcing material and an adhesive, and the adhesive comprises tung maleic anhydride type mica glue and MgO / gamma-Al2O3 composite filler. The adhesive adopted by the mica tape comprises the MgO / gamma-Al2O3 composite filler and the tung maleic anhydride type mica glue, and the MgO / gamma-Al2O3 composite filler can improve the heat conductivity coefficient and the dielectric property of the tung maleic anhydride type mica glue, so that the heat conductivity and the insulativity of the mica tape are improved.

Description

Technical Field

[0001] This invention relates to the field of cable processing technology, and in particular to a mica tape cross-linked polyethylene insulated cable. Background Technology

[0002] Cross-linked polyethylene (XLPE) insulated cables are widely used in power transmission and distribution, using XLPE as the insulation material. The conductor in XLPE insulated cables is typically wrapped with mica tape to provide fire resistance. However, existing mica tape has poor thermal conductivity. Wrapped between the conductor and the XLPE insulation layer, its poor thermal conductivity increases thermal resistance, essentially adding an "insulation layer" to the conductor's heat dissipation path. This can lead to higher conductor operating temperatures compared to ordinary cables of the same specifications without mica tape, or, at the same temperature, a lower maximum allowable current carrying capacity to prevent overheating.

[0003] Chinese invention patent CN107974165B discloses a heating cable with a conductor and a mica tape wrapping layer around the conductor. A thermally conductive insulation layer is provided outside the mica tape wrapping layer, and a sheath is provided outside the thermally conductive insulation layer. While the thermally conductive insulation layer improves the cable's heat conduction, it cannot fundamentally solve the problem of the poor thermal conductivity of the mica tape. Summary of the Invention

[0004] The purpose of this invention is to provide a mica tape cross-linked polyethylene insulated cable with good thermal conductivity and insulation properties.

[0005] The above-mentioned technical objective of the present invention is achieved through the following technical solution: a mica tape cross-linked polyethylene insulated cable, comprising, from the inside out, a copper conductor, a mica tape, a cross-linked polyethylene insulation layer, a filler material, a wrapping layer and a cable sheath, wherein the mica tape comprises mica paper, a reinforcing material and an adhesive, and the adhesive comprises tung oil anhydride type mica glue and MgO / γ-Al2O3 composite filler.

[0006] In the technical solution of this application embodiment, mica tape is directly wrapped around the copper conductor. Mica is a non-flammable inorganic mineral with a high melting point and excellent insulation and heat resistance properties, making it the main insulation material in cables. The main function of the filler material is to fill the gaps inside the cable, keeping the cable structure round and stable, and also providing buffering, water blocking, heat insulation, and flame retardancy. The cross-linked polyethylene insulation layer provides insulation during normal operation. The wrapping layer maintains the stability of the internal structure of the insulated cable. The cable sheath provides mechanical protection and suppresses the spread of flames and reduces toxic fumes in a fire.

[0007] The mica tape in this invention is composed of mica paper, reinforcing materials, and an adhesive. Its thermal conductivity mainly depends on the thermal conductivity of the adhesive. The adhesive is made from tung oil anhydride-type mica glue and MgO / γ-Al2O3 composite filler. The main components of the tung oil anhydride-type mica glue are epoxy resin and tung oil anhydride, with the introduction of bismaleimide resin with excellent heat resistance and a special curing accelerator. This adhesive has strong adhesion, contains cyclic structures, double bonds, ether bonds, and acetic acid groups in its molecules, and the cured product has good toughness, excellent and stable dielectric properties, mechanical properties, and good moisture resistance. The bismaleimide resin forms an interpenetrating network structure with the epoxy and acid polymers in the system, thereby improving the heat resistance of the adhesive, with a maximum heat resistance rating of F.

[0008] MgO possesses high dielectric strength, ranging from 10 to 35 kV / mm, higher than that of mica tape (15 to 25 kV / mm), and exhibits excellent insulation properties. It also demonstrates good heat resistance, capable of withstanding prolonged exposure to temperatures up to 1000℃. Most importantly, MgO exhibits good thermal conductivity, facilitating heat dissipation. However, MgO is highly hygroscopic. When it absorbs moisture, it significantly reduces the volume resistivity of the insulating material and ionizes under high electric fields, inducing partial discharge and ultimately leading to insulation breakdown. Furthermore, MgO has poor interfacial bonding with organic polymers, such as tung oil anhydride-based mica adhesives, easily creating micro-gaps. These micro-gaps are weak points where electric fields concentrate.

[0009] A MgO / γ-Al2O3 composite filler was obtained by coating MgO with γ-Al2O3. While the insulating properties of γ-Al2O3 are lower than those of mica paper, its thermal conductivity is better. Combining MgO with γ-Al2O3 can simultaneously improve the thermal conductivity and dielectric properties of the mica tape. γ-Al2O3 has a loose cubic spinel structure, a large specific surface area, and high activity, making it easily dispersed in methyl methacrylate anhydride-based mica adhesive. Coating the MgO surface allows the MgO / γ-Al2O3 composite filler to be uniformly dispersed in the methyl methacrylate anhydride-based mica adhesive, which is beneficial for forming a thermally conductive network. Furthermore, the water absorption of γ-Al2O3 is much lower than that of MgO, and coating MgO with it can reduce the hygroscopicity of MgO.

[0010] The MgO / γ-Al2O3 composite filler, when incorporated into tung oil anhydride-type mica adhesive, can improve the thermal conductivity and dielectric properties of the tung oil anhydride-type mica adhesive, thereby enhancing the thermal conductivity and insulation properties of the mica tape. Under high-temperature conditions, the MgO / γ-Al2O3 composite filler can generate a stable ceramic barrier (spinel MgAl2O4), thereby improving the fire resistance and flame retardant properties of the mica tape.

[0011] A further embodiment of the present invention is that the MgO / γ-Al2O3 composite filler has a core-shell structure, comprising an MgO core and a γ-Al2O3 shell covering the MgO core.

[0012] A further provision of the present invention is that the preparation method of the MgO / γ-Al2O3 composite filler includes the following steps:

[0013] S1. Prepare solution A by mixing aluminum isopropoxide and isopropanol. After mixing magnesium hydroxide, sodium polyacrylate, and triethanolamine evenly, solution B is prepared by mixing them with isopropanol, water, and ammonium bifluoride.

[0014] S2. Under stirring conditions, solution B is added dropwise to solution A, and the reaction is heated to obtain a magnesium hydroxide-hydrated aluminum oxide mixture.

[0015] S3. Filter and dry the magnesium hydroxide-hydrated alumina mixture to obtain magnesium hydroxide-hydrated alumina powder;

[0016] S4. Calcine magnesium hydroxide-hydrated alumina powder at 400~600℃ to obtain MgO / γ-Al2O3 composite filler.

[0017] In the technical solution of this application embodiment, magnesium hydroxide, sodium polyacrylate, and triethanolamine are mixed evenly by ball milling. Sodium polyacrylate can improve the dispersibility of magnesium hydroxide. Triethanolamine combines with the surface of magnesium hydroxide through hydrogen bonds. During the heating reaction, the generated hydrated alumina is easily combined with triethanolamine, thereby coating the surface of magnesium hydroxide. After calcination, magnesium hydroxide decomposes to generate MgO, and hydrated alumina generates γ-Al2O3, thereby obtaining a core-shell structure MgO / γ-Al2O3 composite filler with an MgO core and a γ-Al2O3 shell coating the MgO core.

[0018] The present invention is further configured such that, in solution A, the mass ratio of aluminum isopropoxide to isopropanol is (3~6):10;

[0019] The mass ratio of magnesium hydroxide, sodium polyacrylate, triethanolamine, water and isopropanol in solution B is (5~10):(0.025~0.08):(0.05~0.15):(6~12):(60~100);

[0020] The molar ratio of water to aluminum isopropoxide is (2~4):1;

[0021] The mass ratio of ammonium bifluoride to aluminum isopropoxide is (2~10):100.

[0022] The present invention is further configured such that, in step S2, solution B is added to solution A over a period of 2 to 3 hours, and the heating reaction temperature is 60 to 90°C.

[0023] The present invention further specifies that the particle size of magnesium hydroxide is 200~400nm.

[0024] In the technical solution of this application embodiment, magnesium hydroxide with a particle size of 200~400nm is selected. The resulting MgO / γ-Al2O3 composite filler has a relatively moderate particle size, which makes it easy to form a conductive network in the adhesive and improves the mechanical properties of the adhesive.

[0025] The present invention is further configured such that the mass fraction of MgO / γ-Al2O3 composite filler in the adhesive is 20%~25% of the methyl methacrylate anhydride type mica adhesive.

[0026] In the technical solution of this application embodiment, adding an appropriate mass fraction of MgO / γ-Al2O3 composite filler is necessary to simultaneously improve the thermal conductivity and dielectric properties of the mica tape. If the amount added is too low, a thermally conductive network cannot be formed, resulting in low thermal conductivity. If the amount added is too high, the MgO / γ-Al2O3 composite filler will agglomerate, reducing the dielectric properties of the adhesive.

[0027] The present invention is further configured such that the preparation method of the adhesive includes the following steps: dispersing the coupling agent in anhydrous ethanol to obtain a coupling agent dispersion;

[0028] The MgO / γ-Al2O3 composite filler was mixed with a coupling agent dispersion, heated to 70°C, ultrasonically vibrated and stirred, and reacted for 2-3 hours. After drying and grinding, the coupling agent-modified MgO / γ-Al2O3 composite filler was obtained.

[0029] The adhesive was obtained by uniformly mixing tung oil anhydride-type mica gum with coupling agent-modified MgO / γ-Al2O3 composite filler.

[0030] In the technical solution of this application embodiment, by adding a coupling agent, the compatibility of MgO / γ-Al2O3 composite filler can be improved, thereby improving the thermal conductivity of the adhesive.

[0031] The present invention is further configured such that the coupling agent includes at least one of DB550 and DB560.

[0032] The present invention is further configured such that the mass fraction of the coupling agent in the adhesive is 2% to 3% of the methyl methacrylate anhydride type mica adhesive.

[0033] The present invention is further configured such that the reinforcing material is alkali-free glass cloth.

[0034] The beneficial effects of this invention are:

[0035] 1. In this invention, mica tape is directly wrapped around the copper conductor. Mica is a non-flammable inorganic mineral with a high melting point and excellent insulation and heat resistance properties, making it a major insulating material in cables. The adhesive used in this invention for the mica tape includes MgO / γ-Al2O3 composite filler and tung oil anhydride-type mica adhesive. The MgO / γ-Al2O3 composite filler can improve the thermal conductivity and dielectric properties of the tung oil anhydride-type mica adhesive, thereby improving the thermal conductivity and insulation properties of the mica tape. Under high temperature conditions, the MgO / γ-Al2O3 composite filler can generate a stable ceramic barrier (spinel MgAl2O4), thereby improving the fire resistance and flame retardant properties of the mica tape.

[0036] 2. Magnesium hydroxide, sodium polyacrylate, and triethanolamine are mixed evenly using a ball milling method. Sodium polyacrylate can improve the dispersibility of magnesium hydroxide. Triethanolamine binds to the surface of magnesium hydroxide through hydrogen bonds. During the heating reaction, the generated hydrated alumina is easily bound to triethanolamine, thus coating the surface of magnesium hydroxide. After calcination, magnesium hydroxide decomposes to generate MgO, and hydrated alumina generates γ-Al2O3, thereby obtaining a core-shell structure MgO / γ-Al2O3 composite filler with an MgO core and a γ-Al2O3 shell coating the MgO core.

[0037] 3. By adding coupling agents, the compatibility of MgO / γ-Al2O3 composite fillers can be improved, thereby increasing the thermal conductivity of the adhesive. Attached Figure Description

[0038] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0039] Figure 1 This is a schematic diagram of the structure of an embodiment of this application. Detailed Implementation

[0040] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion. I. Specific Implementation Methods

[0043] Example 1:

[0044] A type of mica tape cross-linked polyethylene insulated cable, such as Figure 1 As shown, from the inside out, the cable includes a copper conductor 1, a mica tape 2, a cross-linked polyethylene insulation layer 3, a filler material 4, a wrapping layer 5, and a cable sheath 6. The filler material 4 is made of alkali-free glass fiber, the wrapping layer 5 is made of glass fiber tape, and the cable sheath 6 is made of halogen-free, low-smoke, flame-retardant, and low-toxicity polyolefin sheath material.

[0045] The preparation method of mica tape includes the following steps:

[0046] (1) Disperse 60g of aluminum isopropoxide with a purity ≥99.999% in 100g of isopropanol to prepare solution A. Mix 5g of magnesium hydroxide with a particle size range of 200~400nm, sodium polyacrylate and triethanolamine by ball milling to obtain a mixed slurry. Mix the mixed slurry with 100g of isopropanol, 6.2g of water and 6g of ammonium bifluoride to prepare solution B.

[0047] (2) Heat solution A to 60°C and keep it warm. Add solution B dropwise to solution A for 3 hours. Stir the reaction to obtain a magnesium hydroxide-hydrated aluminum oxide mixture.

[0048] (3) Filter and dry the magnesium hydroxide-hydrated alumina mixture to obtain magnesium hydroxide-hydrated alumina powder.

[0049] (4) Calcine magnesium hydroxide-hydrated alumina powder at 400℃ to obtain MgO / γ-Al2O3 composite filler.

[0050] (5) Disperse 3g of coupling agent in anhydrous ethanol to obtain a coupling agent dispersion, mix 20g of MgO / γ-Al2O3 composite filler with the coupling agent dispersion, heat to 70°C, ultrasonically vibrate and stir, react for 3h, dry at 90°C for 10h, grind to obtain coupling agent modified MgO / γ-Al2O3 composite filler.

[0051] The tung oil anhydride type mica adhesive was mixed with coupling agent modified MgO / γ-Al2O3 composite filler and stirred at high speed of 800 r / min for 2 h to obtain the adhesive.

[0052] (6) After bonding mica paper and alkali-free glass cloth with adhesive, they are hot-pressed and cured at 160°C to obtain mica tape.

[0053] Example 2:

[0054] A type of mica-taped cross-linked polyethylene insulated cable, such as Figure 1As shown, from the inside out, the cable includes a copper conductor 1, a mica tape 2, a cross-linked polyethylene insulation layer 3, a filler material 4, a wrapping layer 5, and a cable sheath 6. The filler material 4 is made of alkali-free glass fiber, the wrapping layer 5 is made of glass fiber tape, and the cable sheath 6 is made of halogen-free, low-smoke, flame-retardant, and low-toxicity polyolefin sheath material.

[0055] The preparation method of mica tape includes the following steps:

[0056] (1) Disperse 30g of aluminum isopropoxide with a purity ≥99.999% in 100g of isopropanol to prepare solution A. Mix 10g of magnesium hydroxide with a particle size range of 200~400 nm, sodium polyacrylate and triethanolamine by ball milling to obtain a mixed slurry. Mix the mixed slurry with 60g of isopropanol, 12.4g of water and 0.6g of ammonium bifluoride to prepare solution B.

[0057] (2) Heat solution A to 90°C and keep it warm. Add solution B dropwise to solution A for 2 hours. Stir the reaction to obtain a magnesium hydroxide-hydrated aluminum oxide mixture.

[0058] (3) Filter and dry the magnesium hydroxide-hydrated alumina mixture to obtain magnesium hydroxide-hydrated alumina powder.

[0059] (4) Calcine magnesium hydroxide-hydrated alumina powder at 600℃ to obtain MgO / γ-Al2O3 composite filler.

[0060] (5) Disperse 2g of coupling agent in anhydrous ethanol to obtain a coupling agent dispersion, mix 25g of MgO / γ-Al2O3 composite filler with the coupling agent dispersion, heat to 70°C, ultrasonically vibrate and stir, react for 2h, dry at 90°C for 10h, grind to obtain coupling agent modified MgO / γ-Al2O3 composite filler;

[0061] The tung oil anhydride type mica adhesive was mixed with coupling agent modified MgO / γ-Al2O3 composite filler and stirred at high speed of 800 r / min for 2 h to obtain the adhesive.

[0062] (6) After bonding mica paper and alkali-free glass cloth with adhesive, they are hot-pressed and cured at 160°C to obtain mica tape.

[0063] Comparative Example 1:

[0064] The difference between Comparative Example 1 and Example 1 is that the adhesive used 20g of nano-γ-Al2O3 as a filler.

[0065] Comparative Example 2:

[0066] The difference between Comparative Example 2 and Example 1 is that no coupling agent was added during the preparation of the adhesive.

[0067] Comparative Example 3:

[0068] The difference between Comparative Example 3 and Example 1 is that no filler was added to the adhesive.

[0069] II. Detection Methods

[0070] 1. Thermal conductivity test method: The adhesive is cured to form a 15mm×15mm×10mm sample. The thermal conductivity of the sample is tested according to GB 3399 Test Method for Thermal Conductivity of Plastics. The thermal conductivity is measured by the heat-protected plate method.

[0071] 2. Dielectric constant testing method: The adhesive is cured to form a sample with a radius of 50 mm and a thickness of 1 mm. The relative permittivity is determined according to GB / T 1409-1988 Test method for relative permittivity and dielectric loss factor of solid insulating materials at power frequency.

[0072] 3. Volume resistivity test method: The volume resistivity is determined according to GB1410-89 Test method for volume resistivity and surface resistivity of solid insulating materials.

[0073] III. Experimental Data

[0074] The thermal conductivity and electrical conductivity of the adhesives prepared in Examples 1-2 and Comparative Examples 1-3 were tested, and the test results are shown in Table 1 below.

[0075] Table 1. Test results of thermal conductivity and electrical conductivity in each embodiment and comparative example.

[0076]

[0077] As can be seen from the table above, the thermal conductivity of Examples 1 and 2 is much higher than that of Comparative Example 3, and the dielectric constant and volume resistivity are also higher than those of Comparative Example 3. This indicates that adding MgO / γ-Al2O3 composite filler to the tung oil anhydride type mica adhesive can simultaneously improve the thermal conductivity and insulation properties of the adhesive.

[0078] In Comparative Example 1, γ-Al2O3 was directly used as a filler, which reduced the thermal conductivity and significantly decreased the dielectric constant and volume resistivity. Because γ-Al2O3 has high electrical conductivity, it reduces the insulating properties of the adhesive.

[0079] In Comparative Example 3, no coupling agent was added, resulting in poor compatibility between the filler and the tung oil anhydride-type mica adhesive, which could not form a thermally conductive network, thus reducing the thermal conductivity of the adhesive.

[0080] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A mica-taped cross-linked polyethylene insulated cable, characterized in that, From the inside out, it includes a copper conductor, mica tape, cross-linked polyethylene insulation layer, filler material, wrapping layer and cable sheath. The mica tape includes mica paper, reinforcing material and adhesive. The adhesive includes tung oil anhydride type mica glue and MgO / γ-Al2O3 composite filler.

2. The mica tape cross-linked polyethylene insulated cable according to claim 1, characterized in that, The MgO / γ-Al2O3 composite filler has a core-shell structure, comprising an MgO core and a γ-Al2O3 shell covering the MgO core.

3. The mica tape cross-linked polyethylene insulated cable according to claim 1, characterized in that, The preparation method of the MgO / γ-Al2O3 composite filler includes the following steps: S1. Prepare solution A by mixing aluminum isopropoxide and isopropanol. After mixing magnesium hydroxide, sodium polyacrylate, and triethanolamine evenly, solution B is prepared by mixing them with isopropanol, water, and ammonium bifluoride. S2. Under stirring conditions, solution B is added dropwise to solution A, and the mixture is heated to react, resulting in a magnesium hydroxide-hydrated aluminum oxide mixture. S3. Filter and dry the magnesium hydroxide-hydrated alumina mixture to obtain magnesium hydroxide-hydrated alumina powder; S4. The magnesium hydroxide-hydrated alumina powder is calcined at 400~600℃ to obtain MgO / γ-Al2O3 composite filler.

4. The mica tape cross-linked polyethylene insulated cable according to claim 3, characterized in that, In solution A, the mass ratio of aluminum isopropoxide to isopropanol is (3~6):10; The mass ratio of magnesium hydroxide, sodium polyacrylate, triethanolamine, water and isopropanol in solution B is (5~10):(0.025~0.08):(0.05~0.15):(6~12):(60~100); The molar ratio of water to aluminum isopropoxide is (2~4):1; The mass ratio of ammonium bifluoride to aluminum isopropoxide is (2~10):

100.

5. The mica tape cross-linked polyethylene insulated cable according to claim 3, characterized in that, In step S2, solution B is added dropwise to solution A over a period of 2-3 hours, and the heating reaction temperature is 60-90°C.

6. The mica tape cross-linked polyethylene insulated cable according to claim 3, characterized in that, The mass fraction of MgO / γ-Al2O3 composite filler in the adhesive is 20%~25% of that in tungmaic anhydride type mica adhesive.

7. The mica tape cross-linked polyethylene insulated cable according to claim 3, characterized in that, The particle size of the magnesium hydroxide is 200~400nm.

8. The mica tape cross-linked polyethylene insulated cable according to claim 1, characterized in that, The preparation method of the adhesive includes the following steps: dispersing the coupling agent in anhydrous ethanol to obtain a coupling agent dispersion; The MgO / γ-Al2O3 composite filler was mixed with the coupling agent dispersion, heated to 70°C, ultrasonically vibrated and stirred, and reacted for 2-3 hours. After drying and grinding, the coupling agent modified MgO / γ-Al2O3 composite filler was obtained. The tung oil anhydride type mica adhesive was mixed evenly with the coupling agent-modified MgO / γ-Al2O3 composite filler to obtain an adhesive.

9. The mica tape cross-linked polyethylene insulated cable according to claim 8, characterized in that, The coupling agent includes at least one of DB550 and DB560, and the mass fraction of the coupling agent in the adhesive is 2% to 3% of the tung oil anhydride type mica adhesive.

10. The mica tape cross-linked polyethylene insulated cable according to claim 1, characterized in that, The reinforcing material is alkali-free glass cloth.

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