Fire-resistant flexible inorganic mineral insulated cable and method for producing the same

Abstract

The application belongs to the technical field of wire and cable manufacturing, and particularly relates to a fire-resistant flexible inorganic mineral insulated cable and a preparation method thereof; aiming at the performance balance problem among flexibility, fire resistance and strength of the current cable; the cable comprises, from inside to outside, a conductor, a flexible base layer, a thermal response transition layer, a dynamic reinforcing layer and an outer sheath; the flexible base layer adopts modified silicone rubber as a base body, and through nano dispersion technology, ultra-fine aluminum hydroxide, zinc borate and specific sheet-like silicate are uniformly dispersed in the flexible base layer to form a three-dimensional network prestructure; the thermal response transition layer is wrapped with composite alkali-free glass fiber cloth impregnated with nano phenolic aldehyde resin and zinc borate; and the dynamic reinforcing layer is mixed with aluminum oxide fiber yarns pre-coated with ceramic precursors and high-nickel alloy filaments, so that the application in the insulated cable is realized.

Description

Technical Field

[0001] This invention belongs to the field of wire and cable manufacturing technology, specifically relating to a fire-resistant flexible inorganic mineral insulated cable and its preparation method. Background Technology

[0002] With the increasing demands for fire safety in modern buildings, fire-resistant cables are becoming an important guarantee for maintaining the operation of critical equipment in the event of a fire, and their market demand is growing. Although traditional mineral-insulated cables have excellent fire resistance, they suffer from poor flexibility, large bending radius, and difficult installation due to the use of rigid inorganic insulation materials, which seriously limits their application in complex wiring environments (CN121260580A).

[0003] Currently, flexible fire-resistant cables on the market mainly adopt the following technical approaches: First, mica tape is used as the fire-resistant layer, but the interlayer bonding of mica tape is weak, and delamination easily occurs under high temperatures in a fire, affecting the continuity of fire resistance. Second, ceramicized silicone rubber is used as the insulation layer. Although it has good flexibility, the volume shrinkage during the ceramicization process can cause the insulation layer to crack, affecting electrical performance. Third, polymer-based composite materials filled with inorganic minerals are used, but the interface bonding between the filler and the matrix is ​​not strong, and filler agglomeration and detachment easily occur at high temperatures. However, the common problem with the above existing technologies is that it is difficult to achieve a good balance between flexibility, fire resistance, and mechanical strength. Increasing the content of inorganic fillers can enhance fire resistance, but it will significantly reduce the flexibility of the material; using a flexible matrix can improve processing performance, but the fire resistance is often insufficient; adding a reinforcing layer can improve mechanical strength, but it will sacrifice overall flexibility.

[0004] In summary, developing a new type of fire-resistant cable that can simultaneously achieve flexibility, fire resistance, and mechanical strength has become a pressing technical challenge in this field. Summary of the Invention

[0005] This invention provides a fire-resistant flexible inorganic mineral insulated cable and its preparation method. Through a three-layer synergistic structure design, it effectively solves the problem of balancing flexibility, fire resistance and mechanical strength.

[0006] The specific technical solution is as follows:

[0007] A fire-resistant flexible inorganic mineral-insulated cable and its preparation method are as follows:

[0008] S1: Preparation of modified silicone rubber.

[0009] S11: Mix methyl vinyl silicone rubber raw rubber, hydrogen-containing silicone oil, phenyl hydrogen-containing silicone oil, and diethyl allyl phosphate, stir and dehydrate to obtain a dehydrated mixture.

[0010] S12: The dehydrated mixture prepared by S11 is cooled to 70°C, a platinum catalyst and an inhibitor are added, the mixture is stirred, heated to 130°C, and cooled to room temperature to obtain modified silicone rubber.

[0011] S2: Fabrication of the flexible base layer.

[0012] S21: Add KH-550 to ethanol and deionized water at pH 5 and stir to obtain silane hydrolysate; mix aluminum hydroxide and zinc borate with ethanol and stir to obtain filler slurry; add silane hydrolysate to filler slurry, shear reaction at 60-80℃, filter, wash, dry, grind, and pass through a 300-mesh sieve to obtain pretreated inorganic filler.

[0013] S22: The modified silicone rubber prepared in S12 is plasticized, then the pretreated inorganic filler prepared in S21 is added, and the mixture is mixed. Then, organic montmorillonite is added, and the mixture is continued to be mixed. The mixture is cooled to room temperature to obtain the compound.

[0014] S23: The compound rubber prepared in S22 is passed through a thin tube, and then 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane is added, dispersed, made into strips, extruded onto a continuously passing conductor, and vulcanized at high temperature to obtain a wire core covered with a flexible base layer.

[0015] S3: Preparation of thermally responsive transition layer.

[0016] S31: Add nano-phenolic resin and zinc borate to ethanol and stir to obtain an impregnation solution with a solid content of 30%.

[0017] S32: The alkali-free glass fiber cloth is passed through the impregnation solution prepared in S31, squeezed and controlled to 30% of the dry weight of the alkali-free glass fiber cloth, and then dried to obtain the pre-impregnated cloth.

[0018] S33: Wrap the prepreg fabric prepared in S32 around the wire core with the flexible base layer prepared in S23 to obtain the wire core with the middle layer covered by the thermal response transition layer.

[0019] S4: Preparation of dynamic reinforcement layer.

[0020] S41: Immerse alumina fiber yarn in aluminum sol, squeeze and control the adhesive to make the coating amount reach 10% of the dry weight of the fiber, and dry to obtain pretreated alumina fiber.

[0021] S42: The pretreated alumina fiber and high-nickel alloy wire prepared in S41 are mixed and woven onto the wire core with the thermal response transition layer prepared in S33 to obtain the wire core with the outer dynamic reinforcement layer.

[0022] S5: Extrusion of outer sheath. A layer of flame-retardant polyethylene sheath material is extruded over the core of the dynamic reinforcement layer prepared in S42 and cooled to room temperature to obtain the finished cable.

[0023] Furthermore, the stirring dehydration described in S11 has the following parameter settings: temperature 80~100℃, vacuum degree -0.095MPa, rotation speed 20~60rpm, and duration 1~2h.

[0024] The dehydrated mixture described in S11 is based on 100 parts of methyl vinyl silicone rubber raw rubber, containing 0.5 to 2 parts of hydrogen-containing silicone oil, 3 to 15 parts of phenyl hydrogen-containing silicone oil, and 5 to 20 parts of allyl phosphate diethyl ester.

[0025] The platinum catalyst described in S12 is added in an amount of 10 to 50 ppm of the total mass of the dehydrated mixture, based on platinum metal.

[0026] The inhibitor described in S12 has a mass of 1 to 5 times the weight of platinum in the platinum catalyst.

[0027] Furthermore, the aluminum hydroxide described in S21 has a mass ratio of 4:1 to zinc borate.

[0028] The drying process described in S21 has the following parameters: temperature 80-100℃, duration 6-12h.

[0029] The pretreated inorganic packing material described in S21 is based on 100 parts of total packing material, with 1.5 to 3.5 parts of KH-550, 200 to 400 parts of ethanol, and 10 to 20 times the mass of KH-550 of deionized water.

[0030] The mixing parameters described in S22 are: temperature 60-80℃, duration 8-10min.

[0031] The high-temperature vulcanization described in S23 has the following parameters: temperature 160-180℃, duration 5-10min.

[0032] The wire core covered with the flexible base layer described in S23 is based on 100 parts of modified silicone rubber, with 40 to 70 parts of pretreated inorganic filler, 5 to 15 parts of organic montmorillonite, and 0.5 to 2 parts of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane.

[0033] Furthermore, the zinc borate described in S31 is based on 100 parts of solid nano-phenolic resin and contains 10 to 30 parts of zinc borate.

[0034] The stirring described in S31 has the following parameters: rotation speed 300-500 rpm, duration 30-60 min.

[0035] The drying process described in S32 has the following parameters: temperature 100-130℃, duration 2-5 minutes.

[0036] Furthermore, the drying process described in S41 has the following parameter settings: temperature 80-120°C, duration 1-3 min.

[0037] The high-nickel alloy wire described in S42 has a strand ratio of 3:1 to 1:1 with the pretreated alumina fiber.

[0038] The mixed weaving described in S42 has the following parameter settings: weaving angle 30°~60°, coverage 70%~95%.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] 1. The flexible base layer of this invention uses nano-dispersion technology to form a uniformly dispersed three-dimensional network prestructure of inorganic fillers in the silicone rubber matrix, which not only ensures the flexibility of the material, but also provides uniform reaction sites for high-temperature ceramization, avoiding the volume shrinkage problem of traditional ceramized silicone rubber.

[0041] 2. This invention adopts a hybrid structure of ceramic fiber and metal wire, which can maintain good mechanical properties throughout the entire temperature range, and solves the problem that it is difficult to balance the high and low temperature performance of a single material reinforcement layer. Attached Figure Description

[0042] Figure 1 This is a process flow diagram for the preparation of a fire-resistant flexible inorganic mineral insulated cable.

[0043] Figure 2 This is the FTIR image of the modified silicone rubber prepared in S1 of Example 1.

[0044] Figure 3 This is a scanning electron microscope image of the compound prepared by S2 in Example 1. Detailed Implementation

[0045] The following embodiments further explain and illustrate the technical solutions of the present invention. It should be specifically noted that each specific embodiment is a concretization and explanation of the technical solution and should not be considered as a limitation on the scope of protection of the present invention. Those skilled in the art still have the right to modify the technical solutions of these embodiments and make equivalent substitutions for some or all of the technical features, and these modifications or substitutions do not change the essence of the corresponding technical solutions, nor do they cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions described in the present invention.

[0046] This invention proposes a fire-resistant flexible inorganic mineral-insulated cable and its preparation method, including the fine design of the microstructure, intelligent response of the middle layer, and dynamic protection of the outer layer. (See attached diagram) Figure 1 The diagram shows a method for preparing a fire-resistant flexible inorganic mineral-insulated cable, the detailed technical solution of which is as follows:

[0047] 1. Preparation of modified silicone rubber

[0048] Methyl vinyl silicone rubber raw rubber, hydrogen-containing silicone oil, phenyl hydrogen-containing silicone oil, and diethyl allyl phosphate were mixed, stirred and dehydrated to obtain a dehydrated mixture. The mixture was then cooled to 70°C, and a platinum catalyst and inhibitor were added. The mixture was stirred, heated, and cooled to room temperature to obtain modified silicone rubber.

[0049] The catalyst activates the Si-H bond, causing it to undergo irreversible addition with the carbon-carbon double bond on the modifier molecule to form a stable Si-C bond, thereby permanently fixing the functional side chain to the silicone rubber backbone in a covalent manner.

[0050] 2. Fabrication of flexible base layer

[0051] KH-550 was added to ethanol and deionized water solution and stirred to obtain silane hydrolysate; aluminum hydroxide and zinc borate were mixed with ethanol and stirred to obtain filler slurry; the silane hydrolysate was added to the filler slurry, sheared, filtered, washed, dried, ground, and passed through a 300-mesh sieve to obtain pretreated inorganic filler; modified silicone rubber was plasticized, then the pretreated inorganic filler was added and mixed, then organic montmorillonite was added and mixed again, cooled to room temperature to obtain compound rubber, thinly passed through, and finally 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane was added, dispersed, made into strips, extruded onto a continuously passing conductor, and vulcanized at high temperature to obtain a wire core covered with a flexible base layer.

[0052] Silane coupling agents hydrolyze in acidic water to generate highly reactive silanols. The -Si-OH groups on the silanols undergo dehydration condensation with the -OH groups on the surface of the inorganic fillers to form stable -Si-O-Al / B- chemical bonds, thus firmly "anchoring" the coupling agent molecules to the filler surface. The organic long chains of coupling agents grafted onto the filler surface improve the interfacial compatibility between the originally hydrophilic inorganic fillers and the hydrophobic silicone rubber matrix. During subsequent mixing, the fillers can be more uniformly dispersed, reducing agglomeration and enhancing the interfacial bonding force between the fillers and rubber. The pretreated micro-nano fillers act as "islands," uniformly dispersed in the rubber "sea." Aluminum hydroxide and zinc borate decompose endothermically and generate metal oxides. Silicone rubber decomposes at high temperatures to generate silicon dioxide. These products fuse with lamellar silicates at high temperatures to form a continuous, hard, ceramicized protective layer on the residual carbon skeleton, isolating flames and oxygen.

[0053] 3. Fabrication of thermally responsive transition layer

[0054] Nano-phenolic resin and zinc borate are added to ethanol and stirred to obtain an impregnation solution; alkali-free glass fiber cloth is passed through the impregnation solution, squeezed to control adhesive, and dried to obtain a pre-impregnated cloth; the pre-impregnated cloth is wrapped around the wire core covered with a flexible base layer to obtain a wire core covered with a thermally responsive transition layer.

[0055] At room temperature (<150℃), nano-phenolic resin is uniformly loaded onto the fiberglass cloth skeleton in a partially prepolymerized solid form, ensuring that the layer will not crack during cable laying and bending, and providing basic mechanical protection. During the thermal shock stage (150~400℃), the resin decomposes rapidly when heated, releasing gas, and undergoes aromatization and cross-linking reactions, leaving a highly porous but robust foam carbon layer. This carbon layer expands in volume, effectively insulating heat transfer to the inner layer, and serves as the skeleton for subsequent reactions. Zinc borate begins to lose its water of crystallization at around 300℃, and then melts to form a viscous borate glass. This glass flows and covers the porous carbon skeleton formed by the phenolic resin, sealing pores and cracks, making the loose carbon layer dense and complete. The rapid charring of phenolic resin provides a framework for the attachment of borate, while the molten flow of borate repairs and strengthens the char layer structure. Together, they form a robust, dense, and thermally insulating "carbon-ceramic composite barrier" in situ between the flame and the inner insulating layer. Accompanied by volume expansion, this barrier effectively fills interlayer gaps that may arise from thermal deformation, buffering stress. As the temperature further increases (>400℃), the remaining organic components completely decompose, and the borate glass and char framework further bond and ceramicize at high temperatures, ultimately forming a continuous, hard protective layer with extremely high thermal stability, primarily composed of borosilicate ceramic and thermally stable carbon. This layer resists direct burning and heat radiation from the flame, ensuring that the internal "flexible base layer" continues to function under protected conditions.

[0056] 4. Preparation of dynamic reinforcement layer

[0057] Alumina fiber yarn is immersed in aluminum sol, extruded and controlled, and dried to obtain pretreated alumina fiber; the pretreated alumina fiber and high-nickel alloy wire are mixed and braided onto a core covered with a thermally responsive transition layer to obtain a core covered with an outer dynamic reinforcement layer.

[0058] At room temperature, the high-nickel alloy wire, as the continuous phase, provides excellent tensile strength, resistance to bending fatigue, and impact resistance, ensuring the cable is not damaged during installation, dragging, or vibration. Alumina fiber, as the reinforcing phase, provides auxiliary support. The network structure formed by these two components provides basic mechanical protection while ensuring the overall flexibility and bendability of the cable. When the temperature rises above 300℃, the alumina sol coating on the fiber surface begins to dehydrate and undergo a crystal transformation, eventually converting in-situ into nano-sized Al2O3 ceramic particles. These nano-ceramic particles sinter and bond with the alumina fiber body, which serves as the framework, at the interface, building a strong "ceramic bridge" at and around the fiber interlacing points. This upgrades the fiber network, originally bound by friction, into a continuous, three-dimensional interconnected ceramic skeleton. Simultaneously, selective oxidation occurs on the surface of the high-nickel alloy wire, generating an extremely thin and dense protective oxide film. This film effectively blocks oxygen from diffusing inward, allowing the internal metal core to remain intact at high temperatures. Although the absolute strength decreases due to the high temperature, the residual metal core encased in this high-strength oxide film still provides valuable toughness and tensile strength, preventing the ceramic skeleton from shattering instantly under thermal shock due to brittleness. When the temperature rises above 800℃, the oxide film on the alloy wire thickens further, and the metal core is gradually consumed, but its reinforcing effect continues. The bond between the alumina fiber and the transformed ceramic phase becomes stronger, and the ceramic skeleton completes its final sintering, forming a high-strength, high-refractory ceramic tubular armor. This protects the cable structure from burn-through and inhibits the expansion pressure caused by the high-temperature decomposition of internal materials, providing the final physical space guarantee for the innermost conductor insulation system.

[0059] 5. Preparation of outer protective sleeve

[0060] A layer of flame-retardant polyethylene (PE) sheath is extruded over the core of the dynamic reinforcement layer and cooled to room temperature to obtain the finished cable.

[0061] Example 1

[0062] A method for preparing a fire-resistant flexible inorganic mineral-insulated cable is as follows:

[0063] Table 1 Main Raw Materials

[0064]

[0065] S1: Preparation of modified silicone rubber.

[0066] S11: Mix 100g of methyl vinyl silicone rubber raw material, 1.3g of hydrogen-containing silicone oil, 9g of phenyl hydrogen-containing silicone oil, and 12.5g of diethyl allyl phosphate, stir and dehydrate to obtain a dehydrated mixture. The stirring and dehydration parameters are set as follows: temperature 90℃, vacuum degree -0.095MPa, rotation speed 40rpm, and time 1.5h.

[0067] S12: The dehydrated mixture prepared in S11 is cooled to 70°C, a platinum catalyst (Castel catalyst) and an inhibitor (ethynylcyclohexanol) are added, stirred, heated to 130°C, and cooled to room temperature to obtain modified silicone rubber. The amount of platinum catalyst added, based on platinum metal, is 30 ppm of the total mass of the dehydrated mixture, and the mass of the inhibitor is three times the weight of platinum in the platinum catalyst.

[0068] S2: Fabrication of the flexible base layer.

[0069] S21: KH-550 was added to an ethanol and deionized water solution at pH 5 and stirred to obtain a silane hydrolysate. Aluminum hydroxide and zinc borate were mixed with ethanol and stirred to obtain a filler slurry. The silane hydrolysate was added to the filler slurry, and a shear reaction was performed at 70°C. The mixture was then filtered, washed, dried, ground, and passed through a 300-mesh sieve to obtain the pretreated inorganic filler. The drying parameters were set as follows: temperature 90°C, duration 9 hours. The pretreated inorganic filler was based on 100g of total filler (80g aluminum hydroxide and 20g zinc borate), with 2.5g of KH-550, 300g of ethanol, and 15 times the mass of deionized water (KH-550).

[0070] S22: Take 100g of the modified silicone rubber prepared in S12 and masticate it. Then add 55g of the pretreated inorganic filler prepared in S21 and mix. Then add 10g of organic montmorillonite and continue mixing. Cool to room temperature to obtain the compound. The mixing parameters are set as follows: temperature 70℃, time 9min.

[0071] S23: The compound rubber prepared in S22 is passed through a thin tube, then 1.3g of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane is added, dispersed, and formed into strips. These strips are then extruded onto a continuously passing conductor and vulcanized at high temperature to obtain a wire core coated with a flexible base layer. The high-temperature vulcanization parameters are set as follows: temperature 170℃, duration 8min.

[0072] S3: Preparation of thermally responsive transition layer.

[0073] S31: Add 100g of nano-phenolic resin and 20g of zinc borate to ethanol and stir to obtain an impregnation solution with a solid content of 30%. The stirring parameters are set as follows: speed 400 rpm, duration 45 min.

[0074] S32: The alkali-free glass fiber cloth is passed through the impregnation solution prepared in S31, and the adhesive is squeezed and controlled to 30% of the dry weight of the alkali-free glass fiber cloth. It is then dried to obtain the pre-impregnated cloth. The drying parameters are set as follows: temperature 115℃, time 3.5min.

[0075] S33: Wrap the prepreg fabric prepared in S32 around the wire core with the flexible base layer prepared in S23 to obtain the wire core with the middle layer covered by the thermal response transition layer.

[0076] S4: Preparation of dynamic reinforcement layer.

[0077] S41: Immerse alumina fiber yarn in alumina sol, extrude and control the adhesive to achieve a coating amount of 10% of the fiber's dry weight, and dry to obtain pretreated alumina fiber. The drying parameters are set as follows: temperature 100℃, time 2 minutes.

[0078] S42: The pretreated alumina fibers prepared in S41 and high-nickel alloy wires (nickel to chromium mass ratio of 4:1) are mixed and braided onto the core of the wire prepared in S33 with a thermally responsive transition layer to obtain a core with an outer dynamic reinforcement layer. The ratio of high-nickel alloy wire to pretreated alumina fibers is 2:1; the mixing parameters are set as follows: braiding angle 45°, coverage 90%.

[0079] S5: Extrusion of outer sheath. A layer of flame-retardant PE sheath material is extruded over the core of the dynamic reinforcement layer prepared in S42, and cooled to room temperature to obtain the finished cable.

[0080] Example 2

[0081] The composition and preparation process are the same as in Example 1, except that:

[0082] In the preparation process S11, based on 100g of methyl vinyl silicone rubber raw rubber, there is 0.5g of hydrogen-containing silicone oil, 3g of phenyl hydrogen-containing silicone oil, and 5g of allyl phosphate diethyl ester, with other components being the same.

[0083] The stirring and dehydration parameters in step S11 of the preparation process are set as follows: temperature 80℃, rotation speed 20rpm, duration 2h, and other steps are the same.

[0084] In the S12 preparation process, the amount of platinum catalyst added, based on platinum metal, is 10 ppm of the total mass of the dehydrated mixture, and the mass of the inhibitor is 1 times the weight of platinum in the platinum catalyst, with other components being the same.

[0085] In step S21 of the preparation process, a shear reaction is carried out at 60℃; the drying parameters are set as follows: temperature 80℃, duration 6h, and other steps are the same.

[0086] In the preparation process S21, the inorganic filler was pretreated based on 100g of total filler (80g of aluminum hydroxide and 20g of zinc borate), with 1.5g of KH-550, 200g of ethanol, and 10 times the mass of deionized water of KH-550, and other components were the same.

[0087] In the S22 step of the preparation process, the mixing parameters are set as follows: temperature 60℃, time 8min, and other steps are the same.

[0088] The core of the wire coated with the flexible base layer in the S23 preparation process is based on 100g of modified silicone rubber, 40g of pretreated inorganic filler, 5g of organic montmorillonite, and 0.5g of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, with other components being the same.

[0089] The high-temperature vulcanization parameters in the S23 preparation process are set as follows: temperature 160℃, duration 5min, and other steps are the same.

[0090] In preparation process S31, 100g of solid nano-phenolic resin and 10g of zinc borate were used as the basis, and other components were the same.

[0091] The stirring parameters in step S31 of the preparation process are set as follows: rotation speed 300 rpm, duration 30 min, and other steps are the same.

[0092] The drying parameters in step S32 of the preparation process are set as follows: temperature 100℃, duration 2min, and other steps are the same.

[0093] In step S41 of the preparation process, the drying parameters are set as follows: temperature 80℃, duration 1 min, and other steps are the same.

[0094] In the S42 preparation process, the ratio of high-nickel alloy wire (nickel to chromium mass ratio of 4:1) to the number of strands of pretreated alumina fiber is 3:1, and other components are the same.

[0095] In the S42 step of the preparation process, the mixed knitting parameters are set as follows: knitting angle 30°, coverage 70%, and other steps are the same.

[0096] Example 3

[0097] The composition and preparation process are the same as in Example 1, except that:

[0098] In the preparation process S11, based on 100g of methyl vinyl silicone rubber raw rubber, there are 2g of hydrogen-containing silicone oil, 15g of phenyl hydrogen-containing silicone oil, and 20g of allyl phosphate diethyl ester, with other components being the same.

[0099] The stirring and dehydration parameters in step S11 of the preparation process are set as follows: temperature 100℃, rotation speed 60rpm, duration 1h, and other steps are the same.

[0100] In the S12 preparation process, the amount of platinum catalyst added, based on platinum metal, is 50 ppm of the total mass of the dehydrated mixture, and the mass of the inhibitor is 5 times the weight of platinum in the platinum catalyst, with other components being the same.

[0101] In step S21 of the preparation process, a shear reaction is carried out at 80℃; the drying parameters are set as follows: temperature 100℃, duration 12h, and other steps are the same.

[0102] In the preparation process S21, the inorganic filler was pretreated based on 100g of total filler (80g of aluminum hydroxide and 20g of zinc borate), with 3.5g of KH-550, 400g of ethanol, and 20 times the mass of deionized water of KH-550, and other components were the same.

[0103] In the S22 step of the preparation process, the mixing parameters are set as follows: temperature 80℃, time 10min, and other steps are the same.

[0104] The core of the wire coated with the flexible base layer in the S23 preparation process is based on 100g of modified silicone rubber, 70g of pretreated inorganic filler, 15g of organic montmorillonite, and 2g of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, with other components being the same.

[0105] The high-temperature vulcanization parameters in the S23 preparation process are set as follows: temperature 180℃, duration 10min, and other steps are the same.

[0106] In preparation process S31, 100g of solid nano-phenolic resin was used as the base, along with 30g of zinc borate, and the other components were the same.

[0107] The stirring parameters in step S31 of the preparation process are set as follows: rotation speed 500 rpm, duration 60 min, and other steps are the same.

[0108] The drying parameters in step S32 of the preparation process are set as follows: temperature 130℃, duration 5min, and other steps are the same.

[0109] The drying parameters in step S41 of the preparation process are set as follows: temperature 120℃, duration 3min, and other steps are the same.

[0110] In the S42 preparation process, the ratio of high-nickel alloy wire (nickel to chromium mass ratio of 4:1) to the number of strands of pretreated alumina fiber is 1:1, and other components are the same.

[0111] In the S42 step of the preparation process, the mixed knitting parameters are set as follows: knitting angle 60°, coverage 95%, and other steps are the same.

[0112] Example 4

[0113] The composition and preparation process are the same as in Example 1, except that:

[0114] In the preparation process S11, based on 100g of methyl vinyl silicone rubber raw rubber, there is 1g of hydrogen-containing silicone oil, 5g of phenyl hydrogen-containing silicone oil, 7g of allyl phosphate diethyl ester, and other components are the same.

[0115] The stirring and dehydration parameters in step S11 of the preparation process are set as follows: temperature 95℃, rotation speed 45rpm, duration 1.8h, and other steps are the same.

[0116] In the S12 preparation process, the amount of platinum catalyst added, based on platinum metal, is 45 ppm of the total mass of the dehydrated mixture, and the mass of the inhibitor is 4 times the weight of platinum in the platinum catalyst, with other components being the same.

[0117] In step S21 of the preparation process, a shear reaction was carried out at 75°C; the drying parameters were set as follows: temperature 83°C, duration 7 hours, and other steps were the same.

[0118] In the preparation process S21, the inorganic filler was pretreated based on 100g of total filler (80g of aluminum hydroxide and 20g of zinc borate), with 2g of KH-550, 250g of ethanol, and 18 times the mass of deionized water of KH-550. Other components were the same.

[0119] In the S22 step of the preparation process, the mixing parameters are set as follows: temperature 77℃, time 9.5min, and other steps are the same.

[0120] The core of the wire coated with the flexible base layer in the S23 preparation process is based on 100g of modified silicone rubber, 60g of pretreated inorganic filler, 12g of organic montmorillonite, and 0.7g of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, with other components being the same.

[0121] The high-temperature vulcanization parameters in the S23 preparation process are set as follows: temperature 175℃, duration 9min, and other steps are the same.

[0122] In preparation process S31, 100g of solid nano-phenolic resin was used as the base, along with 12g of zinc borate, and the other components were the same.

[0123] The stirring parameters in step S31 of the preparation process are set as follows: rotation speed 300-500 rpm, duration 30-60 min, and other steps are the same.

[0124] The drying parameters in step S32 of the preparation process are set as follows: temperature 100-130℃, duration 2-5 min, and other steps are the same.

[0125] The drying parameters in step S41 of the preparation process are set as follows: temperature 90℃, duration 1.5min, and other steps are the same.

[0126] In the S42 preparation process, the ratio of high-nickel alloy wire (nickel to chromium mass ratio of 4:1) to pretreated alumina fiber strands is 2.5:1, and other components are the same.

[0127] In the S42 step of the preparation process, the mixed knitting parameters are set as follows: knitting angle 40°, coverage 88%, and other steps are the same.

[0128] Comparative Example 1

[0129] The composition and preparation process are the same as in Example 1, except that:

[0130] In step S1 of the preparation process, the modified silicone rubber is removed, and in step S2, unmodified methyl vinyl silicone rubber of the same thickness is used, while the other steps are the same.

[0131] Comparative Example 2

[0132] The composition and preparation process are the same as in Example 1, except that:

[0133] In step S3 of the fabrication process, the thermally responsive transition layer is removed, while the other steps remain the same.

[0134] Comparative Example 3

[0135] The composition and preparation process are the same as in Example 1, except that:

[0136] The dynamic reinforcement layer is removed in step S4 of the fabrication process; the other steps remain the same.

[0137] Samples of the modified silicone rubber prepared in Example 1 were taken and tested using a Fourier transform infrared spectroscopy (FTIR) instrument. The sample was laid flat on the surface of an ATR crystal, and the ATR indenter was tightened to ensure close contact between the sample and the crystal. The sample was then tested at a depth of 4000–500 cm⁻¹. -1 The area was scanned 64 times. Figure 2 As shown, near 2160 cm⁻¹, the Si-H bond disappears, indicating that the combination with the C=C double bond is transformed into a Si-C bond. At 1250 cm⁻¹... -1 Near the 1100–1000 cm⁻¹, a new absorption peak appears, which is the stretching vibration of the phosphoryl group (P=O), indicating that phosphate ester groups have been introduced into the modified silicone rubber. -1 Nearby, strong and broad peaks are retained, indicating the presence of the polysiloxane backbone, proving that the modification process did not damage the polymer skeleton.

[0138] Samples of the compound prepared in Example 1 were taken and vulcanized (170°C, 8 min). The samples were then immersed in liquid nitrogen for cryogenic treatment (10 min), rapidly broken after treatment, and sputter-coated with gold. Field emission scanning electron microscopy (FESEM) was used to test the samples (accelerating voltage 10 kV, working distance 9 mm). Figure 3 As shown, the pretreated aluminum hydroxide, zinc borate, and montmorillonite particles are uniformly distributed in the matrix, with no obvious large agglomerates, indicating that the filler has been uniformly dispersed in the matrix.

[0139] Based on Examples 1-4 and Comparative Examples 1-3, samples of the final prepared cables were taken and subjected to repeated bending life tests: the cable samples were fixed on a reciprocating bending tester with a reciprocating bending angle of ±90° and a speed of 30 times / min. The test was conducted under the applied rated voltage and current until conductor breakage occurred, or visible cracks or damage appeared in the insulation or sheath layer, or the insulation resistance dropped below 1MΩ.

[0140] Based on Examples 1-4 and Comparative Examples 1-3, samples were taken from the flexible base layer for limiting oxygen index testing: 30 sample strips (100mm×8mm×3mm) were prepared and placed at 25℃ and 50% relative humidity for 120h. The sample strips were vertically fixed in the center of a transparent glass combustion tube, and the initial oxygen concentration was set to 45%. The oxygen and nitrogen sources were turned on, and the mixed gas was allowed to flow stably in the combustion tube for 30s. The sample strips were ignited from the top with an igniter. It was observed and recorded whether the sample strip continued to burn for more than 50mm. If it did, the oxygen concentration was reduced and the next new sample was tested. If it did not, the oxygen concentration was increased and the next new sample was tested. The above steps were repeated, and data from 15 effective extinguishing points were collected. The last 10 data points were used for calculation, referring to standard GB / T 2406.2-2009 "Determination of Combustion Behavior by Oxygen Index Method for Plastics - Part 2: Room Temperature Test".

[0141] Based on Examples 1-4 and Comparative Examples 1-3, samples of the flexible base layer were taken and subjected to tensile strength tests: the samples were prepared into dumbbell-shaped specimens, the specimens were clamped on a universal testing machine, and the specimens were stretched at a constant speed (500 mm / min) until they broke, the maximum pressure was obtained, and the tensile strength was calculated.

[0142] Based on Examples 1-4 and Comparative Examples 1-2, samples of the final prepared cables were taken for fire resistance time testing: The sample (1200mm long) was placed on the test frame and fixed at both ends. A static load plate (25mm wide) was installed above the fire-affected area in the middle of the sample, and a weight (cable outer diameter × 5N / mm) was applied. The vibration device was started (frequency 1Hz, amplitude ±5mm), the test circuit was connected (voltage 1kV), the blowtorch was started, and the flame center was aligned with the center of the fire-affected area of ​​the sample. The time was recorded until one of the following indicators appeared, indicating failure: current interruption in the test circuit, short circuit between the conductor and the load plate or ground, or downward displacement of the static load plate exceeding 50% of the initial outer diameter of the cable.

[0143] The specific test results are shown in Table 2. Figure 2 , Figure 3 As shown:

[0144] Table 2 Comparison of core performance of Examples 1-4 and Comparative Examples 1-2

[0145]

[0146] The comparison results above show that Example 1 has the best overall performance. The modified silicone rubber provides elasticity and heat resistance, the thermal response transition layer acts as a buffer and stress transfer layer during bending, and the outer dynamic reinforcement layer protects the internal structure. This indicates that Example 1 successfully solves the contradiction between flexibility, fire resistance, and strength, which is difficult to balance in traditional cables. The overall performance of Examples 2 to 4 is slightly lower than that of Example 1, but still maintains a high level. This shows that excellent performance balance is still achieved under a wide range of parameter variations. Comparative Example 1, because it uses unmodified methyl vinyl silicone rubber, has significantly poor fire resistance. In Comparative Example 2, the removal of the thermal response transition layer significantly reduced the fire resistance time, and faster structural collapse was observed during the combustion test, indicating that the dynamic reinforcement layer was exposed to high temperatures too early, leading to the failure of the overall fire-resistant structure. Comparative Example 3, lacking a dynamic reinforcement layer, had weak resistance to external bending stress, resulting in large core deformation during bending and easy fatigue fracture of the conductor. However, because Comparative Example 3 contained sufficient amounts of hydrogen-containing silicone oil, phenyl hydrogen-containing silicone oil, allyl phosphate diethyl ester, and zinc borate, these two layers together constituted a core protection system with strong intrinsic flame retardancy, good char formation, and excellent heat insulation effect, thus resulting in a longer fire resistance time compared to Example 2.

[0147] In summary, it is clear from the above embodiments and comparative examples that the fire-resistant flexible inorganic mineral insulated cable provided by the present invention is significantly superior to traditional solutions in terms of tensile strength, bending life, limiting oxygen index, and fire resistance time. This is attributed to the construction of a flexible base layer, a thermally responsive transition layer, and a dynamic reinforcement layer, thereby solving the performance balance problem between flexibility, fire resistance, and mechanical strength of the insulated cable.

Claims

1. A process for the production of a fire-resistant flexible inorganic mineral insulated electrical cable, characterized in that, Includes the following steps: S1: Preparation of modified silicone rubber; S11: Mix methyl vinyl silicone rubber raw material, hydrogen-containing silicone oil, phenyl hydrogen-containing silicone oil, and diethyl allyl phosphate, stir and dehydrate to obtain a dehydrated mixture; S12: The dehydrated mixture prepared by S11 is cooled to 70°C, a platinum catalyst and an inhibitor are added, the mixture is stirred, heated to 130°C, and cooled to room temperature to obtain modified silicone rubber. S2: Fabrication of the flexible base layer; S21: Add KH-550 to an aqueous solution of ethanol and deionized water at pH 5, stir, and obtain a silane hydrolysate; mix aluminum hydroxide and zinc borate with ethanol, stir, and obtain a filler slurry; The silane hydrolysate was added to the filler slurry, and the mixture was sheared at 60-80℃. The mixture was then filtered, washed, dried, ground, and passed through a 300-mesh sieve to obtain the pretreated inorganic filler. S22: The modified silicone rubber prepared in S12 is plasticized, then the pretreated inorganic filler prepared in S21 is added, and the mixture is mixed. Then, organic montmorillonite is added, and the mixture is continued to be mixed. The mixture is cooled to room temperature to obtain the compound. S23: The compound rubber prepared in S22 is passed through a thin tube, and then 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane is added, dispersed, made into strips, extruded onto a continuously passing conductor, and vulcanized at high temperature to obtain a wire core covered with a flexible base layer. S3: Fabrication of thermally responsive transition layer; S31: Add nano-phenolic resin and zinc borate to ethanol and stir to obtain an impregnation solution with a solid content of 30%. S32: The alkali-free glass fiber cloth is passed through the impregnation solution prepared in S31, squeezed and controlled to 30% of the dry weight of the alkali-free glass fiber cloth, and dried to obtain the pre-impregnated cloth. S33: Wrap the prepreg fabric prepared in S32 around the wire core with the flexible base layer prepared in S23 to obtain the wire core with the middle layer of thermal response transition layer. S4: Fabrication of the dynamic reinforcement layer; S41: Immerse the alumina fiber yarn in aluminum sol, squeeze and control the adhesive to make the coating amount reach 10% of the dry weight of the fiber, and dry to obtain pretreated alumina fiber. S42: The pretreated alumina fiber and high-nickel alloy wire prepared in S41 are mixed and woven onto the wire core with the thermal response transition layer prepared in S33 to obtain the wire core with the outer dynamic reinforcement layer. S5: Extrusion of outer sheath. A layer of flame-retardant polyethylene sheath material is extruded over the core of the dynamic reinforcement layer prepared in S42 and cooled to room temperature to obtain the finished cable.

2. The method for preparing a fire-resistant flexible inorganic mineral-insulated cable according to claim 1, characterized in that: The stirring dehydration described in S11 has the following parameters: temperature 80~100℃, vacuum degree -0.095MPa, rotation speed 20~60rpm, and duration 1~2h; The dehydrated mixture described in S11 is based on 100 parts of methyl vinyl silicone rubber raw rubber, containing 0.5 to 2 parts of hydrogen-containing silicone oil, 3 to 15 parts of phenyl hydrogen-containing silicone oil, and 5 to 20 parts of allyl phosphate diethyl ester. The platinum catalyst described in S12 is added in an amount of 10 to 50 ppm of the total mass of the dehydrated mixture, based on platinum metal. The inhibitor described in S12 has a mass of 1 to 5 times the weight of platinum in the platinum catalyst.

3. The method for preparing a fire-resistant flexible inorganic mineral-insulated cable according to claim 1, characterized in that: The drying process described in S21 has the following parameters: temperature 80-100℃, duration 6-12h. The pretreated inorganic packing material described in S21 is based on 100 parts of total packing material, with KH-550 being 1.5 to 3.5 parts, ethanol being 200 to 400 parts, and deionized water being 10 to 20 times the mass of KH-550. The mixing parameters described in S22 are: temperature 60-80℃, duration 8-10min.

4. The method for preparing a fire-resistant flexible inorganic mineral-insulated cable according to claim 1, characterized in that: The high-temperature vulcanization described in S23 has the following parameter settings: temperature 160-180℃, duration 5-10min; The wire core covered with the flexible base layer described in S23 is based on 100 parts of modified silicone rubber, with 40 to 70 parts of pretreated inorganic filler, 5 to 15 parts of organic montmorillonite, and 0.5 to 2 parts of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane.

5. The method for preparing a fire-resistant flexible inorganic mineral-insulated cable according to claim 1, characterized in that: The zinc borate described in S31 is based on 100 parts of solid nano-phenolic resin and 10 to 30 parts of zinc borate. The stirring described in S31 has the following parameters: rotation speed 300-500 rpm, duration 30-60 min; The drying process described in S32 has the following parameters: temperature 100-130℃, duration 2-5 minutes.

6. The method for preparing a fire-resistant flexible inorganic mineral-insulated cable according to claim 1, characterized in that: The drying process described in S41 has the following parameter settings: temperature 80-120℃, duration 1-3min; The high-nickel alloy wire described in S42 has a strand ratio of 3:1 to 1:1 with the pretreated alumina fiber. The mixed weaving described in S42 has the following parameter settings: weaving angle 30°~60°, coverage 70%~95%.

7. An insulated electrical cable of the fire resistant flexible inorganic mineral type, prepared according to the process of any one of claims 1 to 6, comprising, from the inside to the outside, in succession: The conductor, base layer, transition layer, reinforcement layer, and outer sheath are characterized by: The base layer is made of modified silicone rubber composite material and covers the outer periphery of the conductor; the modified silicone rubber composite material includes a silicone rubber matrix, inorganic filler and sheet-reinforcing filler; the transition layer is a composite alkali-free glass fiber cloth impregnated with nano phenolic resin and zinc borate, wrapped around the outer periphery of the base layer; the reinforcing layer is made of alumina fiber yarn pre-coated with aluminum sol and high-nickel alloy filaments, woven around the outer periphery of the transition layer.

8. A fire-resistant flexible inorganic mineral-insulated cable according to claim 7, characterized in that: The silicone rubber matrix is ​​methyl vinyl silicone rubber; the inorganic filler is aluminum hydroxide and zinc borate in a mass ratio of 4:1; the lamellar reinforcing filler is organic montmorillonite.

9. A fire-resistant flexible inorganic mineral-insulated cable according to claim 7, characterized in that: The high-nickel alloy wire is a nickel-chromium alloy wire with a nickel to chromium mass ratio of 4:

1.

10. A fire-resistant flexible inorganic mineral-insulated cable according to claim 7, characterized in that: The fire-resistant flexible inorganic mineral insulated cable has a tensile strength ≥14MPa and a fire resistance time ≥85min.

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