A high-strength fireproof cable and its preparation method

Abstract

This application relates to the field of cable materials, and specifically discloses a high-strength fireproof cable and a preparation method thereof. The high-strength fireproof cable includes a conductor, an insulating layer, a flame retardant layer, and an outer sheath. The outer sheath material comprises the following raw materials: modified polyamide-imide resin, linear low-density polyethylene, amino-modified carbon fiber, styrene-maleic anhydride copolymer, and genipin. The preparation method comprises the following steps: firstly heating and mixing the modified polyamide-imide resin, amino-modified carbon fiber, and genipin, then adding the remaining raw materials for melt blending and pelletizing to obtain the outer sheath; and sequentially assembling the conductor, insulating layer, flame retardant layer, and outer sheath to obtain the high-strength fireproof cable. This application has the characteristics of improving the mechanical strength of the cable under long-term high-temperature conditions and enhancing the mechanical strength and thermal aging performance of the cable.

Description

Technical Field

[0001] The present application relates to the field of cable materials, and more specifically, it relates to a high-strength fireproof cable and a preparation method thereof. Background Art

[0002] With the acceleration of the global urbanization process and the improvement of public safety awareness, fireproof cables, as key materials to ensure the safe operation of power systems and public safety, have become increasingly important. Especially in key infrastructure such as high-rise buildings, data centers, subway tunnels, and industrial facilities, fireproof cables have become standard equipment. These places have put forward higher requirements for the fireproof performance, high-temperature resistance characteristics, and mechanical strength of cables, which has promoted the research and development and application of high-strength fireproof cables. In addition, the rapid development of the new energy field, such as new energy vehicle charging piles and smart grid transformation projects, has also put forward higher requirements for the performance of fireproof cables.

[0003] A fireproof cable generally consists of a conductor, an insulating layer, a separating layer, and an outer sheath. The conductor is formed by winding multiple strands of metal materials to ensure good electrical conductivity; the insulating layer is a key part of the fireproof cable and is made of high-temperature, non-combustible refractory materials such as mica, ceramics, and magnesium oxide. These have high heat resistance and electrical properties and can maintain the integrity of the cable in a high-temperature environment, preventing current leakage and short circuits.

[0004] The separating layer is mainly used to enhance the fire resistance of the cable and is usually made of inorganic mineral materials, which can effectively prevent the spread of fire and further protect the internal structure of the cable from damage; the outer sheath is the outermost layer of the fireproof cable and is generally made of low-smoke and non-toxic plastic materials such as polyvinyl chloride or halogen-free low-smoke flame-retardant polyolefin materials, which can improve the corrosion resistance and electrical properties of the cable and reduce the toxic gases and smoke generated during a fire.

[0005] The fireproof cable prepared by the above method has obvious deficiencies in dealing with extreme high temperatures and mechanical strength. Especially when exposed to a fire source for a long time or under the pressure of heavy objects, the cable material ages and becomes brittle at high temperatures for a long time, reducing the mechanical strength of the cable and making it difficult to ensure the structural integrity of the cable. Summary of the Invention

[0006] In order to improve the mechanical strength of the cable under long-term high-temperature conditions and enhance the mechanical strength and thermal aging performance of the cable, the present application provides a high-strength fireproof cable and a preparation method thereof.

[0007] In the first aspect, the present application provides a high-strength fireproof cable, adopting the following technical solution:

[0008] A high-strength fireproof cable includes a conductor, an insulating layer, a flame-retardant layer, and an outer sheath. The outer sheath material is prepared from the following raw materials in parts by weight:

[0009] 15 - 30 parts of modified polyamide - imide resin, 30 - 50 parts of linear low - density polyethylene, 5 - 10 parts of amino - modified carbon fiber, 10 - 20 parts of styrene - maleic anhydride copolymer, and 1 - 3 parts of genipin;

[0010] The modified polyamide - imide resin is prepared by subjecting polyamide - imide resin to ring - opening treatment in an alkaline solution and then performing composite modification with ethylenediamine and calcium lignosulfonate.

[0011] By adopting the above - mentioned technical solution, in the present application, the outer sheath is mainly composed of low - density polyethylene and modified polyamide - imide resin (PAI). The imide ring in the polyamide - imide resin has good thermal stability. After ring - opening treatment in an alkaline solution and modification with ethylenediamine, primary amine groups can be introduced. Then, under the action of genipin, it can form a cross - linked structure with amino - modified carbon fiber, and can also form a bond with the styrene - maleic anhydride copolymer, enhancing the cross - linking between copolymer molecular chains and improving its high - temperature resistance. Moreover, the polyamide - imide resin is also modified with calcium lignosulfonate. The sulfonic acid group in calcium lignosulfonate can form an ionic bond with the amino group after the ring - opening of PAI, and the hydroxyl group in calcium lignosulfonate can also form a chemical bond with the amino group. Functional groups such as hydroxyl and sulfonic acid groups are further introduced into the modified PAI molecular chain, which can further interact with the maleic anhydride chain segment in the styrene - maleic anhydride copolymer, further improving the compatibility between PAI and polyethylene. In addition, the introduction of the rigid aromatic ring structure in calcium lignosulfonate is dispersed in the PAI matrix. The benzene ring structure and sulfonic acid group in the calcium lignosulfonate molecule can enhance the intermolecular interaction at high temperatures, inhibit the thermal movement of polyethylene molecular chains, improve the high - temperature resistance, and further enhance its high - temperature stability.

[0012] In addition, the addition of carbon fiber in the present application not only has better high - temperature resistance, but also better mechanical properties. Under continuous high - temperature conditions, the carbon fiber acts as a reinforcing skeleton to bear thermal stress, preventing the outer sheath from cracking due to high temperature and ensuring the integrity of the shape and structure of the outer sheath at high temperatures; after amino - modification, it can form a cross - linked interaction with the modified polyamide - imide resin and the styrene - maleic anhydride copolymer, improving its high - temperature stability and mechanical strength.

[0013] Linear low - density polyethylene also has certain temperature resistance. Its crystallinity is relatively high. The crystalline region can play a role in stabilizing the molecular structure under high - temperature conditions, and can also adapt to a certain amount of thermal stress through slight sliding without destroying the structural integrity of the entire material, providing certain flexibility and thermal buffering performance for the outer sheath. Moreover, as a polyolefin material, it improves the corrosion resistance and electrical properties of the fire - resistant cable.

[0014] The addition of styrene-maleic anhydride copolymer, where maleic anhydride can form covalent bond connections with amino groups in PAI, and the styrene segment has a similar structure to polyethylene, can form good physical compatibility. Thus, through bridging action, the interfacial tension between the two can be reduced, and the compatibility between PAI and polyethylene can be improved. Moreover, under the action of genipin, the primary amines introduced in PAI can form chemical interactions with the amino groups introduced in amino-modified carbon fibers and calcium lignosulfonate, ultimately forming a cross-linked network structure, and finally having better high-temperature stability and mechanical properties.

[0015] Optionally, the modified polyamide-imide resin is prepared by the following method:

[0016] 1), Add polyamide-imide resin to N-methylpyrrolidone and heat to 60 - 70 °C, stir to dissolve, then cool it to 30 - 40 °C, and dropwise add sodium hydroxide solution with a mass concentration of 0.1 - 0.8 mol / L. After the addition is completed, heat to 40 - 50 °C and stir and react for 2 - 3 h;

[0017] 2), Then heat to 70 - 80 °C, add ethylenediamine under stirring conditions, and react at this temperature for 1 - 2 h. After the reaction is completed, cool to room temperature and adjust the pH to neutral, then add methanol as a precipitant. After the modified polyamide-imide resin precipitates out, filter it, wash it with alcohol, and dry it to obtain ethylenediamine-modified polyamide-imide resin;

[0018] 3), Mix calcium lignosulfonate with an ethanol aqueous solution to prepare a calcium lignosulfonate suspension, then add an amino silane coupling agent, heat to 50 - 60 °C and stir and react for 20 - 40 min, and then dry it to obtain pretreated calcium lignosulfonate;

[0019] 4), Mix the ethylenediamine-modified polyamide-imide resin prepared in step 2) and the pretreated calcium lignosulfonate prepared in step 3), add an antioxidant, then melt and blend, add an initiator, react at 120 - 140 °C for 30 - 40 min, and then cool to obtain the modified polyamide-imide resin.

[0020] By adopting the above technical solution, first, the polyamide-imide resin is dissolved, and then an alkali solution is added dropwise to open the imide ring. After the ring-opening reaction returns, the temperature is raised and ethylenediamine is added, so that the carboxyl group generated after ring-opening reacts with the primary amine in ethylenediamine to form an amide bond, introducing the primary amine group into the molecular chain of the polyamide-imide resin to realize the amination modification of the polyamide-imide resin. Then, it is melt-blended with lignocellulose treated with an amino-silane coupling agent, and an initiator is added to promote the condensation of the amino group in the ethylenediamine-modified polyamide-imide resin with the sulfonic acid group in calcium lignosulfonate. After calcium lignosulfonate is first treated with an amino-silane coupling agent, the silane in the amino-silane coupling agent can hydrolyze and condense with the hydroxyl group of calcium lignosulfonate, forming a hydrogen bond with the amino group after the PAI ring-opening, introducing the silane coupling agent into the modified polyamide-imide resin. Utilizing its amino and ethoxy bifunctional groups to improve the binding between PAI and polyethylene, and enabling it to form a chemical bond between the amino-modified carbon fiber and calcium lignosulfonate-modified polyethylene after modification, forming a more complex network structure, thereby improving its temperature resistance stability. At the same time, the carbon fiber can also compensate for the loss of mechanical properties caused by the introduction of amino groups, and finally still has excellent mechanical properties at high temperatures and maintains its structural integrity.

[0021] Optionally, during the preparation of the modified polyamide-imide resin,

[0022] In step 1), the mass ratio of the polyamide-imide resin to N-methylpyrrolidone is 1:(3 - 4), and the addition amount of the sodium hydroxide solution is 5 - 8 wt% of the polyamide-imide resin;

[0023] In step 2), the addition amount of ethylenediamine is 8 - 15 wt% of the addition amount of the polyamide-imide resin;

[0024] In step 3), the ethanol aqueous solution is prepared by mixing ethanol and water according to a mass ratio of 8 - 10:1, and the mass ratio of calcium lignosulfonate to the ethanol aqueous solution is 1:(4 - 6), and the addition amount of the amino-silane coupling agent is 5 - 10 wt% of calcium lignosulfonate;

[0025] In step 4), the mass ratio of the ethylenediamine-modified polyamide-imide resin to the pretreated calcium lignosulfonate is 1:(0.2 - 0.3), and the addition amount of the antioxidant is 0.5 - 1 wt% of the ethylenediamine-modified polyamide-imide resin, and the addition amount of the initiator is 1.5 - 3 wt% of the ethylenediamine-modified polyamide-imide resin.

[0026] Optionally, 3 - 5 parts by weight of maleic anhydride grafted polyethylene are further added to the raw materials of the outer sheath.

[0027] By adopting the above technical solution, the addition of maleic anhydride grafted polyethylene can utilize the carboxyl group of maleic anhydride to form amide bonds with the amino groups in the modified polyamide-imide resin. At the same time, the grafted polyethylene segments are compatible with the polyethylene matrix, thereby improving the interfacial bonding force between the two and enhancing the mechanical properties and high-temperature stability of the cable.

[0028] Optionally, the amino-modified carbon fiber is prepared by the following method:

[0029] Carbon fiber pretreatment: Immerse the carbon fiber in concentrated nitric acid for impregnation treatment, then wash and dry to obtain activated carbon fiber;

[0030] Amination modification: Immerse the obtained activated carbon fiber in γ-aminopropyltriethoxysilane solution, add ethylenediamine after impregnation for 1 - 2 h, react at 100 - 120 °C for 40 - 60 min, then wash and dry to obtain amino-modified carbon fiber.

[0031] By adopting the above technical solution, first immerse the carbon fiber in concentrated nitric acid for impregnation treatment to activate the carbon fiber and introduce oxygen-containing functional groups such as hydroxyl and carboxyl groups on the carbon fiber surface. Then, when the activated carbon fiber is immersed in γ-aminopropyltriethoxysilane solution, the silane coupling agent hydrolyzes and condenses with the hydroxyl groups on the carbon fiber surface to achieve the modification of the silane coupling agent and introduce amino functional groups on the carbon fiber. Moreover, the introduction of ethylenediamine can introduce amino functional groups on the carbon fiber surface to achieve the amino modification of the carbon fiber, so that crosslinking with the modified polyamide-imide resin can be achieved under the action of genipin.

[0032] Optionally, when preparing the amino-modified carbon fiber, in the carbon fiber pretreatment step, the mass concentration of concentrated nitric acid is 65 - 68%, and concentrated nitric acid and water are mixed according to a volume ratio of (3 - 4):1 and then the carbon fiber is immersed. After the carbon fiber is immersed in the concentrated nitric acid solution, it is ultrasonically treated at 55 - 65 °C for 40 - 60 min;

[0033] In the amination modification step, the γ-aminopropyltriethoxysilane solution is obtained by mixing γ-aminopropyltriethoxysilane and ethanol according to a mass ratio of 1:(9 - 10). The added mass ratio of the activated carbon fiber to the γ-aminopropyltriethoxysilane solution is 1:(5 - 6), and the impregnation temperature is 25 - 30 °C. After impregnation, ethylenediamine is added. The addition amount of ethylenediamine is 8 - 15 wt% of the activated carbon fiber, and it is added after being dissolved in 4 - 6 mass times of water.

[0034] Optionally, when preparing the amino-modified carbon fiber, after obtaining the amino-modified carbon fiber, it is further treated as follows before addition:

[0035] Nano-silica loading: The nano-silica is first impregnated and modified in a 3-carboxypropyltriethoxysilane solution, centrifuged, washed and dried to obtain carboxylated nano-silica. Then, the carboxylated nano-silica is mixed with an aqueous solution of polyvinyl alcohol and sprayed on the prepared amino-modified carbon fiber, followed by drying and curing to obtain a modified carbon fiber loaded with nano-silica;

[0036] Modification: The prepared modified carbon fiber loaded with nano-silica is immersed in a 1-butyl-3-methylimidazolium dihydrogen phosphate ionic liquid solution, and after impregnation, it is dried to obtain an amino-composite modified carbon fiber.

[0037] By adopting the above technical solution, the nano-silica is first impregnated and modified in a 3-carboxypropyltriethoxysilane solution. The silanol formed after the hydrolysis of 3-carboxypropyltriethoxysilane condenses with the hydroxyl groups of the nano-silica to achieve the silanization modification of the nano-silica, introducing carboxyl groups on the surface of the nano-silica. Then, it is sprayed and loaded on the amino-modified carbon fiber. In this way, the hydroxyl groups on the surface of the nano-silica and the amino groups on the surface of the carbon fiber form amide bonds, improving the bonding strength between the two;

[0038] Moreover, the amide bonds formed on the modified carbon fiber can form hydrogen bond interactions with the amino groups in PAI, and the hydroxyl groups on the surface of the nano-silica can form a hydrogen bond network with the amino groups on the polyamide-imide resin, improving the compatibility between the carbon fiber and the PAI and polyethylene systems. At the same time, the hydroxyl groups on the surface of the nano-silica can also act through van der Waals forces with PE, thus improving the compatibility between PAI and polyethylene;

[0039] In addition, the modified carbon fiber is subsequently only impregnated and modified with 1-butyl-3-methylimidazolium dihydrogen phosphate ionic liquid. The dihydrogen phosphate at the polar end can bind to the amino and carboxyl groups of PAI through ionic bonds or hydrogen bonds, and the butyl chain of the imidazolium cation in the non-polar segment is compatible with the alkane chain segment of PE through van der Waals forces, forming a molecular-level interfacial transition layer. Finally, the modified carbon fiber can not only have better compatibility with the system but also promote the compatibility between the polyamide-imide resin and polyethylene, having better comprehensive properties.

[0040] Optionally, during the post-treatment of the amino-modified carbon fiber and in the process of nano-silica loading, the 3-carboxypropyltriethoxysilane solution is prepared by mixing 3-carboxypropyltriethoxysilane, ethanol and water according to a mass ratio of 1:(6 - 8):(2 - 3), and the pH value of the 3-carboxypropyltriethoxysilane solution is adjusted to 4.5 - 6, the impregnation temperature is 50 - 55 °C, the impregnation time is 40 - 60 min, and the added mass ratio of nano-silica to the 3-carboxypropyltriethoxysilane solution is 1:(8 - 10);

[0041] The mass concentration of polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 5-10 wt%, and the carboxylated nano-silica and the polyvinyl alcohol aqueous solution are mixed according to a mass ratio of 1:(3-4) to prepare a spraying solution, and the spraying amount of the spraying solution is 10-20 wt% of the addition amount of the amino-modified carbon fiber;

[0042] In the modification treatment step, the 1-butyl-3-methylimidazolium dihydrogen phosphate ionic liquid solution is prepared by mixing 1-butyl-3-methylimidazolium dihydrogen phosphate with water and acetone according to a mass ratio of 1:(8-10):(6-8), and the modified carbon fiber loaded with nano-silica is immersed in the 1-butyl-3-methylimidazolium dihydrogen phosphate ionic liquid solution, the impregnation temperature is 30-40 °C, the impregnation time is 30-40 min, and the impregnation pressure is 0.6-0.8 MPa.

[0043] In a second aspect, the present application provides a method for preparing a high-strength fireproof cable, adopting the following technical solution:

[0044] A method for preparing a high-strength fireproof cable includes the following steps:

[0045] S1. First, heat the modified polyamide-imide resin, amino-modified carbon fiber and genipin to 120-130 °C, mix for 20-30 min, then add the remaining raw materials for melt blending and pelletizing, and the melting temperature is 180-210 °C to obtain an outer sheath;

[0046] S2. Assemble the conductor, insulation layer, flame retardant layer and outer sheath in sequence to obtain a high-strength fireproof cable.

[0047] In summary, the present application has the following beneficial effects:

[0048] 1. In the present application, the outer sheath is mainly composed of low-density polyethylene and modified polyamide-imide resin (PAI). The imide ring in the polyamide-imide resin has good thermal stability. After ring-opening treatment in an alkaline solution and modification with ethylenediamine, primary amine groups can be introduced. Furthermore, under the action of genipin, it can form a cross-linked structure with the amino-modified carbon fiber, and can also form a bond with the styrene-maleic anhydride copolymer, enhancing the cross-linking between copolymer molecular chains and improving its high-temperature resistance performance;

[0049] 2. In this application, the polyamide-imide resin is modified with calcium lignosulfonate. The sulfonic acid group in calcium lignosulfonate can form an ionic bond with the amino group after the ring-opening of PAI, and the hydroxyl group in calcium lignosulfonate can also form a chemical bond with the amino group. Functional groups such as hydroxyl and sulfonic acid groups are also introduced into the modified molecular chain of PAI, which can further interact with the maleic anhydride chain segment in the styrene-maleic anhydride copolymer, further improving the compatibility between PAI and polyethylene. Moreover, the introduction of the rigid aromatic ring structure in calcium lignosulfonate is dispersed in the PAI matrix. The benzene ring structure and sulfonic acid group in the calcium lignosulfonate molecule can enhance the intermolecular interaction at high temperature, inhibit the thermal movement of the polyethylene molecular chain, improve the high-temperature resistance performance, and further improve its high-temperature stability. Detailed implementation mode

[0050] The following further elaborates on this application with reference to examples. It should be specifically noted that: for those not specifying specific conditions in the following examples, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. Except for special instructions, the raw materials used in the following examples can all be obtained from ordinary commercial sources.

[0051] In the following preparation examples and examples, the polyamide-imide resin selects the polyamide-imide (PAI) resin powder Torlon 4000TF from Dongguan Tianzhihong Plastic Co., Ltd.;

[0052] The linear low-density polyethylene selects the linear low-density polyethylene with the brand M200024 from Shanghai Yuangao Plastic Technology Co., Ltd.;

[0053] The styrene-maleic anhydride copolymer selects the styrene-maleic anhydride copolymer with the brand Keleweili model 3000P from Shanghai Longdi Chemical Co., Ltd.;

[0054] The maleic anhydride grafted polyethylene selects the maleic anhydride grafted polyethylene with the brand of DuPont USA and the model 4288 from Dongguan Taotao Plastic Raw Materials Co., Ltd.

[0055] The following preparation examples are for the preparation of modified polyamide-imide resin and amino-modified carbon fiber.

[0056] Preparation Example 1

[0057] A preparation method of a modified polyamide-imide resin, comprising the following steps:

[0058] 1). Add the polyamide-imide resin to N-methylpyrrolidone and heat it to 65 °C, stir to dissolve, then cool it to 35 °C, dropwise add a sodium hydroxide solution with a mass concentration of 0.5 mol / L. After the dropping is completed, heat it to 45 °C and stir and react for 2.5 h;

[0059] Among them, the added mass ratio of polyamide-imide resin to N-methylpyrrolidone is 1:3.5, and the addition amount of sodium hydroxide solution is 6 wt% of the polyamide-imide resin;

[0060] 2), Then heat up to 75 °C, add ethylenediamine under stirring conditions. The addition amount of ethylenediamine is 10 wt% of the addition amount of polyamide-imide resin, and react at this temperature for 1.5 h. After the reaction is completed, cool to room temperature and adjust the pH to neutral. Then add methanol as a precipitant to precipitate the modified polyamide-imide resin, filter it, wash it with alcohol and then dry it to obtain ethylenediamine-modified polyamide-imide resin;

[0061] 3), Mix calcium lignosulfonate with an ethanol aqueous solution (prepared by mixing ethanol and water according to a mass ratio of 9:1) to obtain a calcium lignosulfonate suspension. Then add the amino-silane coupling agent KH-550, heat up to 55 °C and stir and react for 30 min, and then dry it to obtain pretreated calcium lignosulfonate. The added mass ratio of calcium lignosulfonate to the ethanol aqueous solution is 1:5, and the addition amount of the amino-silane coupling agent is 8 wt% of calcium lignosulfonate;

[0062] 4), Mix the ethylenediamine-modified polyamide-imide resin prepared in step 2) and the pretreated calcium lignosulfonate prepared in step 3) according to a mass ratio of 1:0.2, add antioxidant 1010, and the addition amount of the antioxidant is 0.8 wt% of the ethylenediamine-modified polyamide-imide resin. Then carry out melt blending, add the initiator diisopropylbenzene peroxide, and the addition amount of the initiator is 2 wt% of the ethylenediamine-modified polyamide-imide resin. React at 130 °C for 35 min, then carry out melt blending treatment at 230 °C for 25 min, and cool to obtain the modified polyamide-imide resin.

[0063] Preparation Example 2

[0064] A preparation method of a modified polyamide-imide resin, comprising the following steps:

[0065] 1), Add polyamide-imide resin to N-methylpyrrolidone and heat up to 60 °C, stir and dissolve it. Then cool it to 30 °C, dropwise add a sodium hydroxide solution with a mass concentration of 0.1 mol / L. After the dropping is completed, heat up to 40 °C and stir and react for 3 h;

[0066] Among them, the added mass ratio of polyamide-imide resin to N-methylpyrrolidone is 1:3, and the addition amount of sodium hydroxide solution is 5 wt% of the polyamide-imide resin;

[0067] 2), Then heat up to 70 °C, add ethylenediamine under stirring conditions. The addition amount of ethylenediamine is 8 wt% of the addition amount of polyamide-imide resin, and react for 2 h at this temperature. After the reaction is completed, cool to room temperature and adjust the pH to neutral. Then add methanol as a precipitant to precipitate the modified polyamide-imide resin, filter it, wash it with alcohol and dry it to obtain ethylenediamine-modified polyamide-imide resin;

[0068] 3), Mix calcium lignosulfonate with an ethanol aqueous solution (prepared by mixing ethanol and water according to a mass ratio of 8:1) to obtain a calcium lignosulfonate suspension. Then add an amino silane coupling agent KH-550, heat up to 50 °C and stir and react for 40 min, and then dry it to obtain pretreated calcium lignosulfonate. The added mass ratio of calcium lignosulfonate to the ethanol aqueous solution is 1:4, and the addition amount of the amino silane coupling agent is 5 wt% of calcium lignosulfonate;

[0069] 4), Mix the ethylenediamine-modified polyamide-imide resin prepared in step 2) and the pretreated calcium lignosulfonate prepared in step 3) according to a mass ratio of 1:0.2, add antioxidant 1010, and the addition amount of the antioxidant is 0.5 wt% of the ethylenediamine-modified polyamide-imide resin. Then melt and blend, add initiator dicumyl peroxide, and the addition amount of the initiator is 1.5 wt% of the ethylenediamine-modified polyamide-imide resin. React at 120 °C for 40 min, then perform melt blending treatment at 220 °C for 20 min, and cool to obtain the modified polyamide-imide resin.

[0070] Preparation Example 3

[0071] A preparation method of a modified polyamide-imide resin, comprising the following steps:

[0072] 1), Add polyamide-imide resin to N-methylpyrrolidone and heat up to 70 °C, stir and dissolve it. Then cool it to 40 °C, dropwise add a sodium hydroxide solution with a mass concentration of 0.8 mol / L. After the dropping is completed, heat up to 50 °C and stir and react for 2 h;

[0073] Among them, the added mass ratio of polyamide-imide resin to N-methylpyrrolidone is 1:4, and the addition amount of the sodium hydroxide solution is 8 wt% of the polyamide-imide resin;

[0074] 2), Then heat up to 80 °C, add ethylenediamine under stirring conditions. The addition amount of ethylenediamine is 15 wt% of the addition amount of polyamide-imide resin, and react for 1 h at this temperature. After the reaction is completed, cool to room temperature and adjust the pH to neutral. Then add methanol as a precipitant to precipitate the modified polyamide-imide resin, filter it, wash it with alcohol and dry it to obtain ethylenediamine-modified polyamide-imide resin;

[0075] 3), Mix calcium lignosulfonate with an ethanol aqueous solution (prepared by mixing ethanol and water in a mass ratio of 10:1) to obtain a calcium lignosulfonate suspension, then add the amino-silane coupling agent KH-550, heat up to 60 °C and stir for reaction for 20 min, and then dry to obtain pretreated calcium lignosulfonate. The added mass ratio of calcium lignosulfonate to the ethanol aqueous solution is 1:6, and the addition amount of the amino-silane coupling agent is 10 wt% of calcium lignosulfonate;

[0076] 4), Mix the ethylenediamine-modified polyamide-imide resin prepared in step 2) and the pretreated calcium lignosulfonate prepared in step 3) according to a mass ratio of 1:0.3, add antioxidant 1010, and the addition amount of the antioxidant is 1 wt% of the ethylenediamine-modified polyamide-imide resin. Then, perform melt blending, add the initiator dicumyl peroxide, and the addition amount of the initiator is 3 wt% of the ethylenediamine-modified polyamide-imide resin. React at 140 °C for 30 min, then perform melt blending treatment at 240 °C for 20 min, and cool to obtain the modified polyamide-imide resin.

[0077] Preparation Example 4

[0078] A preparation method of a modified polyamide-imide resin is carried out according to the method in Preparation Example 1, the difference is that step 3) treatment is not carried out, and the pretreated calcium lignosulfonate in step 4) is replaced with calcium lignosulfonate in equal amount.

[0079] Comparative Preparation Example 1

[0080] A preparation method of a modified polyamide-imide resin is carried out according to the method in Preparation Example 1, the difference is that step 3) and step 4) treatments are not carried out, and the ethylenediamine-modified polyamide-imide resin prepared in step 2) is directly used as the modified polyamide-imide resin.

[0081] Preparation Example 5

[0082] A preparation method of amino-modified carbon fiber includes the following steps:

[0083] Step 1, Carbon fiber pretreatment: Mix concentrated nitric acid with a mass concentration of 68% and water according to a volume ratio of 3:1 to obtain a concentrated nitric acid solution, then immerse the carbon fiber in the concentrated nitric acid solution and perform ultrasonic treatment at 60 °C for 50 min, the ultrasonic power is 500 w, and then wash with water, wash with alkali, and wash with water again and then dry to obtain activated carbon fiber;

[0084] Step 2. Amination modification: Mix γ-aminopropyltriethoxysilane and ethanol in a mass ratio of 1:9 to obtain a γ-aminopropyltriethoxysilane solution. Then immerse the prepared activated carbon fiber into the γ-aminopropyltriethoxysilane solution. The added mass ratio of the activated carbon fiber to the γ-aminopropyltriethoxysilane solution is 1:5, and the impregnation temperature is 25°C. After impregnation for 2 h, add an ethylenediamine solution (prepared by dissolving ethylenediamine in 5 times the mass of water), react at 110°C for 50 min, then wash with water and dry to obtain amino-modified carbon fiber. The addition amount of ethylenediamine is 10 wt% of the activated carbon fiber;

[0085] Step 3. Nanometer silicon dioxide loading: First, immerse nanometer silicon dioxide in a 3-carboxypropyltriethoxysilane solution (prepared by mixing 3-carboxypropyltriethoxysilane, ethanol, and water in a mass ratio of 1:7:2 and adjusting its pH value to 5 with acetic acid) for impregnation modification. The impregnation temperature is 50°C, the impregnation time is 50 min, and the added mass ratio of the nanometer silicon dioxide to the 3-carboxypropyltriethoxysilane solution is 1:9. After centrifugal washing and drying, carboxylated nanometer silicon dioxide is obtained;

[0086] Then mix the carboxylated nanometer silicon dioxide and an aqueous solution of polyvinyl alcohol with a mass concentration of 8 wt% in a mass ratio of 1:3 to obtain a spraying solution. Spray the spraying solution on the prepared amino-modified carbon fiber. The spraying amount of the spraying solution is 15 wt% of the added amount of the amino-modified carbon fiber, the spraying distance is 22 cm, the spraying pressure is 0.4 MPa, and it is sprayed three times with an interval of 5 min between each spraying. After spraying, first dry at 60°C, and then dry and cure under vacuum at 80°C to obtain modified carbon fiber loaded with nanometer silicon dioxide;

[0087] Step 4. Modification: Immerse the prepared modified carbon fiber loaded with nanometer silicon dioxide into an ionic liquid solution of 1-butyl-3-methylimidazolium dihydrogen phosphate (prepared by mixing 1-butyl-3-methylimidazolium dihydrogen phosphate, water, and acetone in a mass ratio of 1:9:7), and dry after impregnation to obtain amino-composite modified carbon fiber. The impregnation temperature is 35°C, the impregnation time is 35 min, and the impregnation pressure is 0.7 MPa.

[0088] Preparation Example 6

[0089] A preparation method of amino-modified carbon fiber, comprising the following steps:

[0090] Step 1. Carbon fiber pretreatment: Mix concentrated nitric acid with a mass concentration of 65% and water in a volume ratio of 3:1 to obtain a concentrated nitric acid solution. Then immerse the carbon fiber in the concentrated nitric acid solution and perform ultrasonic treatment at 55°C for 60 min with an ultrasonic power of 500 w. Then wash with water, wash with alkali, and wash with water again and then dry to obtain activated carbon fiber;

[0091] Step 2. Amination modification: Mix γ-aminopropyltriethoxysilane and ethanol in a mass ratio of 1:9 to obtain a γ-aminopropyltriethoxysilane solution. Then immerse the prepared activated carbon fiber into the γ-aminopropyltriethoxysilane solution. The added mass ratio of the activated carbon fiber to the γ-aminopropyltriethoxysilane solution is 1:5, and the impregnation temperature is 25°C. After impregnation for 2 h, add an ethylenediamine solution (prepared by dissolving ethylenediamine in 4 times the mass of water), react at 100°C for 60 min, then wash with water and dry to obtain amino-modified carbon fiber. The addition amount of ethylenediamine is 8 wt% of the activated carbon fiber;

[0092] Step 3. Nanometer silicon dioxide loading: First, immerse nanometer silicon dioxide in a 3-carboxypropyltriethoxysilane solution (prepared by mixing 3-carboxypropyltriethoxysilane, ethanol, and water in a mass ratio of 1:6:2 and adjusting its pH value to 4.5 with acetic acid) for impregnation modification. The impregnation temperature is 50°C, the impregnation time is 60 min, and the added mass ratio of nanometer silicon dioxide to the 3-carboxypropyltriethoxysilane solution is 1:8. After centrifugal washing and drying, carboxylated nanometer silicon dioxide is obtained;

[0093] Then mix the carboxylated nanometer silicon dioxide and an aqueous solution of polyvinyl alcohol with a mass concentration of 5 wt% in a mass ratio of 1:3 to obtain a spraying solution. Spray the spraying solution on the prepared amino-modified carbon fiber. The spraying amount of the spraying solution is 10 wt% of the added amount of the amino-modified carbon fiber, the spraying distance is 20 cm, the spraying pressure is 0.4 MPa, and it is sprayed in three times with an interval of 5 min between each spraying. After spraying, first dry at 60°C, and then dry and cure in vacuum at 80°C to obtain modified carbon fiber loaded with nanometer silicon dioxide;

[0094] Step 4. Modification: Immerse the prepared modified carbon fiber loaded with nanometer silicon dioxide into a 1-butyl-3-methylimidazolium dihydrogen phosphate ionic liquid solution (prepared by mixing 1-butyl-3-methylimidazolium dihydrogen phosphate, water, and acetone in a mass ratio of 1:8:6), and dry after impregnation to obtain amino-composite modified carbon fiber. The impregnation temperature is 30°C, the impregnation time is 40 min, and the impregnation pressure is 0.6 MPa.

[0095] Preparation Example 7

[0096] A preparation method of amino-modified carbon fiber, comprising the following steps:

[0097] Step 1. Carbon fiber pretreatment: Mix concentrated nitric acid with a mass concentration of 65 - 68% and water in a volume ratio of 4:1 to obtain a concentrated nitric acid solution. Then immerse the carbon fiber in the concentrated nitric acid solution and perform ultrasonic treatment at 65°C for 40 min with an ultrasonic power of 500 w. Then wash with water, wash with alkali, and wash with water again and then dry to obtain activated carbon fiber;

[0098] Step 2. Amination modification: Mix γ-aminopropyltriethoxysilane and ethanol in a mass ratio of 1:10 to obtain a γ-aminopropyltriethoxysilane solution. Then immerse the prepared activated carbon fiber into the γ-aminopropyltriethoxysilane solution. The added mass ratio of the activated carbon fiber to the γ-aminopropyltriethoxysilane solution is 1:6, and the impregnation temperature is 30 °C. After impregnation for 1 h, add an ethylenediamine solution (prepared by dissolving ethylenediamine in 6 mass times of water), react at 120 °C for 40 min, then wash with water and dry to obtain amino-modified carbon fiber. The addition amount of ethylenediamine is 15 wt% of the activated carbon fiber;

[0099] Step 3. Nanometer silica loading: First immerse nanometer silica in a 3-carboxypropyltriethoxysilane solution (prepared by mixing 3-carboxypropyltriethoxysilane, ethanol and water in a mass ratio of 1:8:3 and adjusting its pH value to 6 with acetic acid) for impregnation modification. The impregnation temperature is 55 °C, the impregnation time is 40 min, and the added mass ratio of the nanometer silica to the 3-carboxypropyltriethoxysilane solution is 1:10. After centrifugal washing and drying, carboxylated nanometer silica is obtained;

[0100] Then mix the carboxylated nanometer silica and an aqueous solution of polyvinyl alcohol with a mass concentration of 10 wt% in a mass ratio of 1:4 to obtain a spraying solution. Spray the spraying solution on the prepared amino-modified carbon fiber. The spraying amount of the spraying solution is 20 wt% of the added amount of the amino-modified carbon fiber, the spraying distance is 25 cm, the spraying pressure is 0.4 MPa, and it is sprayed three times with an interval of 5 min between each spraying. After spraying, first dry at 60 °C, and then dry and cure under vacuum at 80 °C to obtain modified carbon fiber loaded with nanometer silica;

[0101] Step 4. Modification: Immerse the prepared modified carbon fiber loaded with nanometer silica into an ionic liquid solution of 1-butyl-3-methylimidazolium dihydrogen phosphate (prepared by mixing 1-butyl-3-methylimidazolium dihydrogen phosphate, water and acetone in a mass ratio of 1:10:8), and dry after impregnation to obtain amino-composite modified carbon fiber. The impregnation temperature is 40 °C, the impregnation time is 30 min, and the impregnation pressure is 0.8 MPa.

[0102] Preparation Example 8

[0103] A preparation method of amino-modified carbon fiber is carried out according to the method in Preparation Example 5, the difference is that the post-treatment steps of nanometer silica loading in Step 3 and modification in Step 4 are not carried out, and the amino-modified carbon fiber obtained after amination modification in Step 2 is directly added.

[0104] Preparation Example 9

[0105] A preparation method of amino-modified carbon fiber is carried out according to the method in Preparation Example 5, except that in Step 3, the loading of nano-silica is not carried out. After the amination modification in Step 2, the obtained amino-modified carbon fiber is not subjected to the nano-silica loading treatment in Step 3, and directly undergoes Step 4 to obtain the amino composite-modified carbon fiber for application.

[0106] Preparation Example 10

[0107] A preparation method of amino-modified carbon fiber is carried out according to the method in Preparation Example 5, except that in Step 4, the modification treatment is not carried out, and the modified carbon fiber loaded with nano-silica obtained in Step 3 is directly applied.

[0108] Example 1

[0109] A preparation method of a high-strength fireproof cable includes the following steps:

[0110] S1. First, heat 20 kg of the modified polyamide-imide resin prepared in Preparation Example 1, 8 kg of the amino-modified carbon fiber prepared in Preparation Example 5, and 2 kg of genipin to 125 °C. After mixing for 25 min, add 40 kg of linear low-density polyethylene, 15 kg of styrene-maleic anhydride copolymer, 0.2 kg of antioxidant 1010, and 0.2 kg of ultraviolet absorber UV-327, and carry out melt blending and granulation through a twin-screw extruder. The melting temperature is 200 °C, and the screw speed is 100 r / min to obtain the outer sheath;

[0111] S2. Using a copper core as the conductor, using ceramic silicone rubber as the insulating layer, extrude the ceramic silicone rubber (selecting the model KT-TC8710 of Shanghai Kete New Materials Co., Ltd.) as the insulating layer on the copper conductor. Then, extrude a flame retardant composed of nano-magnesium hydroxide and aluminum hydroxide with a mass ratio of 3:1 on the insulating layer to form a flame retardant layer. Finally, coat the outer sheath material obtained in Step S1 on the outside of the flame retardant layer by extrusion to form a fireproof cable.

[0112] Example 2

[0113] A preparation method of a high-strength fireproof cable includes the following steps:

[0114] S1. First, heat 15 kg of the modified polyamide-imide resin prepared in Preparation Example 2, 5 kg of the amino-modified carbon fiber prepared in Preparation Example 6, and 1 kg of genipin to 120 °C. After mixing for 30 min, add 30 kg of linear low-density polyethylene, 10 kg of styrene-maleic anhydride copolymer, 0.1 kg of antioxidant 1010, and 0.1 kg of ultraviolet absorber UV-327, and carry out melt blending and granulation through a twin-screw extruder. The melting temperature is 180 °C, and the screw speed is 100 r / min to obtain the outer sheath;

[0115] S2. Using a copper core as the conductor, ceramic silicone rubber as the insulating layer, and ceramic silicone rubber (model KT-TC8710 from Shanghai Kete New Materials Co., Ltd.) as the insulating layer, extrude it onto the copper conductor. Then, use magnesium hydroxide nanometer and aluminum hydroxide with a mass ratio of 3:1 as the flame retardant and extrude it onto the insulating layer to form a flame retardant layer. Finally, use the outer sheath material prepared in step S1 to wrap around the flame retardant layer by extrusion to form a fireproof cable.

[0116] Example 3

[0117] A method for preparing a high-strength fireproof cable, comprising the following steps:

[0118] S1. First, heat 30 kg of the modified polyamide-imide resin prepared in Preparation Example 3, 10 kg of the amino-modified carbon fiber prepared in Preparation Example 7, and 3 kg of genipin to 130 °C. After mixing for 20 min, add 50 kg of linear low-density polyethylene, 20 kg of styrene-maleic anhydride copolymer, 0.3 kg of antioxidant 1010, and 0.3 kg of ultraviolet absorber UV-327, and carry out melt blending and granulation through a twin-screw extruder. The melting temperature is 210 °C, and the screw speed is 100 r / min to obtain the outer sheath.

[0119] S2. Using a copper core as the conductor, ceramic silicone rubber as the insulating layer, and ceramic silicone rubber (model KT-TC8710 from Shanghai Kete New Materials Co., Ltd.) as the insulating layer, extrude it onto the copper conductor. Then, use magnesium hydroxide nanometer and aluminum hydroxide with a mass ratio of 3:1 as the flame retardant and extrude it onto the insulating layer to form a flame retardant layer. Finally, use the outer sheath material prepared in step S1 to wrap around the flame retardant layer by extrusion to form a fireproof cable.

[0120] Example 4

[0121] A method for preparing a high-strength fireproof cable is carried out according to the method in Example 1, except that the modified polyamide-imide resin in step S1 is the modified polyamide-imide resin prepared in Preparation Example 4.

[0122] Example 5

[0123] A method for preparing a high-strength fireproof cable is carried out according to the method in Example 1, except that 3 kg of maleic anhydride grafted polyethylene is added while adding the styrene-maleic anhydride copolymer in step S1.

[0124] Example 6

[0125] A preparation method of a high-strength fireproof cable is carried out according to the method in Example 1, except that in step S1, while adding styrene-maleic anhydride copolymer, 5 kg of maleic anhydride grafted polyethylene is also added.

[0126] Examples 7 - 9

[0127] A preparation method of a high-strength fireproof cable is carried out according to the method in Example 1, except that the amino-modified carbon fibers in step S1 are respectively selected from the amino-modified carbon fibers prepared in Preparation Examples 8 - 10.

[0128] Comparative Example 1

[0129] A preparation method of a high-strength fireproof cable is carried out according to the method in Example 1, except that the modified polyamide-imide resin in step S1 is selected from the modified polyamide-imide resin prepared in Comparative Preparation Example 1.

[0130] Comparative Example 2

[0131] A preparation method of a high-strength fireproof cable is carried out according to the method in Example 1, except that in step S1, the modified polyamide-imide resin is replaced with polyamide-imide resin in equal amount.

[0132] Comparative Example 3

[0133] A preparation method of a high-strength fireproof cable is carried out according to the method in Example 1, except that in step S1, the modified polyamide-imide resin is not added.

[0134] Comparative Example 4

[0135] A preparation method of a high-strength fireproof cable is carried out according to the method in Example 1, except that in step S1, the amino-modified carbon fibers are not added.

[0136] Comparative Example 5

[0137] A preparation method of a high-strength fireproof cable is carried out according to the method in Example 1, except that in step S1, the amino-modified carbon fibers are replaced with carbon fibers in equal amount.

[0138] Comparative Example 6

[0139] A preparation method of a high-strength fireproof cable is carried out according to the method in Example 1, except that in step S1, the styrene-maleic anhydride copolymer is not added.

[0140] Comparative Example 7

[0141] A preparation method of a high-strength fireproof cable is carried out according to the method in Example 1, except that in step S1, genipin is not added.

[0142] Performance detection

[0143] The tensile strength and elongation at break of the cables prepared in the examples and comparative examples of this application were measured with reference to ISO 527-2 (2012), and the results are shown in Table 1 below. In addition, after heat aging (150 °C, 7 d) with reference to IEC 60216, the elongation at break and tensile strength properties were measured to characterize its heat aging performance, and the test results are shown in Table 2 below.

[0144]

[0145]

[0146] Combining the test results in Table 1 and Table 2 above, the cables prepared in the examples of this application not only have excellent mechanical properties, but also maintain high mechanical properties after long-term heat treatment, have good heat aging performance, and have high mechanical strength under long-term high-temperature conditions, ensuring the structural integrity of the cables. Combining the test results of Example 1 and Example 4 again, when preparing the modified polyamide-imide resin, when calcium lignosulfonate is directly added without silane modification during modification, its performance is lower than that in Example 1. Combining the test results of Example 5 and Example 6, it can be seen that when maleic anhydride-grafted polyethylene is added to the outer sheath system, it can improve the compatibility between PAI and polyethylene, and is also conducive to the formation of a complex network cross-linked structure, ultimately significantly improving its mechanical properties and heat aging performance.

[0147] Combining the test results of Example 1 and Example 7 again, when preparing the amino-modified carbon fiber in Example 7, it was only modified with a silane coupling agent and not treated with loaded nano-silica and ionic liquid. It can be seen that while its mechanical properties are significantly reduced, its heat aging performance is also significantly reduced. Combining the test results in Example 8, when directly treated with ionic liquid without loaded nano-silica in Example 8, its mechanical properties and heat aging performance are improved compared to Example 7, but weaker than Example 1. Combining the test results of Example 9, when the amino-modified carbon fiber in Example 9 was treated with nano-silica without ionic liquid, its effect was still weaker than Example 1. When it is loaded with nano-silica and uses its roughness to anchor the modified carbon fiber with macromolecular resin structures such as PAI, its mechanical properties and heat aging performance can be significantly improved. The modification of ionic liquid uses its chemical bonding effect to improve the compatibility between PAI and polyethylene, which helps to improve its mechanical properties and aging resistance.

[0148] Referring to the test results of Example 1 and Comparative Example 1, when modifying the polyamide-imide resin in Comparative Example 1, when it was only modified with ethylenediamine and not modified with calcium lignosulfonate, it can be seen that while its mechanical properties decreased, its thermal aging properties also decreased significantly. The introduction of the benzene ring group and sulfonic acid group modified by calcium lignosulfonate, by introducing its rigid group, not only helps to improve its thermal aging properties, but also can improve its mechanical properties. Combining with the test results of Comparative Example 2, when the polyamide-imide resin was not modified, its mechanical properties and thermal aging properties decreased significantly, and its compatibility with polyethylene was poor, resulting in poor performance; combining with the test results of Comparative Example 3, when the modified polyamide-imide resin was not added to the outer sheath, its mechanical properties decreased significantly and its thermal aging properties were also weak. Combining with the test results of Comparative Example 4, when the amino-modified carbon fiber was not added, its mechanical properties decreased significantly and its thermal aging properties were also weak. The addition of the modified polyamide-imide resin and amino-modified carbon fiber in Example 1 of the present application can not only improve the initial mechanical properties of the cable, but also has good thermal aging properties, maintaining a high structural integrity under high temperature conditions. Combining with the test results of Comparative Example 5, when the carbon fiber in Comparative Example 5 was not added after amino modification, although it itself helps to improve the mechanical properties, due to its poor compatibility with the system, its mechanical properties and thermal aging properties are weak. Referring to the test results of Comparative Example 6 and Comparative Example 7 again, the addition of styrene-maleic anhydride copolymer helps to improve the system compatibility and thus improve the mechanical properties of the cable. In Comparative Example 7, genipin helps to form a cross-linked structure between the modified PAI and the amino-modified carbon fiber, restricting the displacement of polyethylene at high temperature and improving its thermal aging properties.

[0149] In addition, for the fireproof and flame-retardant performance of the cable prepared in the examples, the fireproof performance was detected according to the requirements of GB / T 2406.2-2009. The initial oxygen index test result was 35-38%, showing good fireproof and flame-retardant performance.

[0150] This specific embodiment is only an interpretation of the present application and does not limit the present application. Those skilled in the art can make modifications to this embodiment without creative contributions according to their needs after reading this specification, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A high-strength fire-resistant cable, comprising a conductor, an insulating layer, a flame-retardant layer and an outer sheath, characterized in that: The outer sheath material is made from the following raw materials in parts by weight: 15-30 parts of modified polyamide-imide resin, 30-50 parts of linear low-density polyethylene, 5-10 parts of amino-modified carbon fiber, 10-20 parts of styrene-maleic anhydride copolymer and 1-3 parts of genipin; The modified polyamide-imide resin is prepared by subjecting the polyamide-imide resin to ring-opening treatment in alkali solution and then compositely modified with ethylenediamine and calcium lignin sulfonate.

2. A high-strength fireproof cable according to claim 1, characterized in that: The modified polyamide-imide resin is prepared by the following method: 1) Add polyamide-imide resin to N-methylpyrrolidone and heat it to 60-70°C, stir and dissolve, then cool it to 30-40°C, drop a sodium hydroxide solution with a mass concentration of 0.1-0.8 mol / L, heat it to 40-50°C after the addition is complete, and stir and react for 2-3 hours; 2) Then, the temperature is raised to 70-80°C, ethylenediamine is added under stirring, and the reaction is carried out at this temperature for 1-2 hours. After the reaction is completed, the mixture is cooled to room temperature and the pH is adjusted to neutral. Then, methanol is added as a precipitant to precipitate the modified polyamide-imide resin, and then filtered, washed with alcohol, and dried to obtain ethylenediamine-modified polyamide-imide resin; 3) Mix calcium lignin sulfonate with ethanol aqueous solution to obtain calcium lignin sulfonate suspension, then add aminosilane coupling agent, heat to 50-60°C, stir and react for 20-40 minutes, and then dry to obtain pretreated calcium lignin sulfonate; 4) Mix the ethylenediamine modified polyamide-imide resin prepared in step 2) and the pretreated calcium lignin sulfonate prepared in step 3), add an antioxidant, then melt blend, add an initiator, react at 120-140° C. for 30-40 minutes, and cool to obtain a modified polyamide-imide resin.

3. A high-strength fireproof cable according to claim 2, characterized in that: During the preparation of modified polyamide-imide resin, In step 1), the mass ratio of polyamide-imide resin to N-methylpyrrolidone is 1:(3-4), and the amount of sodium hydroxide solution added is 5-8wt% of the polyamide-imide resin; In step 2), the amount of ethylenediamine added is 8-15wt% of the amount of polyamide-imide resin added; In step 3), the ethanol aqueous solution is prepared by mixing ethanol and water in a mass ratio of 8-10:1, and the added mass ratio of calcium lignin sulfonate to the ethanol aqueous solution is 1:(4-6), and the added amount of aminosilane coupling agent is 5-10wt% of the calcium lignin sulfonate; In step 4), the mass ratio of ethylenediamine modified polyamide-imide resin to pretreated calcium lignin sulfonate is 1:(0.2-0.3), and the amount of antioxidant added is 0.5-1wt% of the ethylenediamine modified polyamide-imide resin, and the amount of initiator added is 1.5-3wt% of the ethylenediamine modified polyamide-imide resin.

4. A high-strength fireproof cable according to claim 1, characterized in that: 3-5 parts by weight of maleic anhydride grafted polyethylene are also added to the raw materials of the outer sheath.

5. A high-strength fireproof cable according to claim 1, characterized in that: The amino-modified carbon fiber is prepared by the following method: Carbon fiber pretreatment: The carbon fiber is immersed in concentrated nitric acid for ultrasonic treatment, then washed and dried to obtain activated carbon fiber; Amination modification: The activated carbon fiber prepared is immersed in a γ-aminopropyltriethoxysilane solution, and after immersion for 1-2 hours, ethylenediamine is added, and the mixture is reacted at 100-120°C for 40-60 minutes, and then washed and dried to obtain amino-modified carbon fiber.

6. A high-strength fireproof cable according to claim 5, characterized in that: When preparing amino-modified carbon fiber, in the carbon fiber pretreatment step, the mass concentration of concentrated nitric acid is 65-68%, and the concentrated nitric acid and water are mixed in a volume ratio of (3-4):1 and then immersed in the carbon fiber, and the carbon fiber is immersed in the concentrated nitric acid solution and then ultrasonically treated at 55-65° C. for 40-60 minutes; In the amination modification step, the γ-aminopropyltriethoxysilane solution is obtained by mixing γ-aminopropyltriethoxysilane and ethanol in a mass ratio of 1: (9-10), the added mass ratio of activated carbon fiber to the γ-aminopropyltriethoxysilane solution is 1: (5-6), and the impregnation temperature is 25-30°C. After the impregnation is completed, ethylenediamine is added, and the amount of ethylenediamine added is 8-15wt% of the activated carbon fiber, and the ethylenediamine is dissolved in 4-6 times the mass of water before being added.

7. A high-strength fireproof cable according to claim 5, characterized in that: When the amino-modified carbon fiber is prepared, the amino-modified carbon fiber is further treated and then added: Nano-silica loading: Nano-silica is firstly treated by immersing in a 3-carboxypropyltriethoxysilane solution for modification, centrifugally washed and dried to obtain carboxylated nano-silica, and then the carboxylated nano-silica is mixed with a polyvinyl alcohol aqueous solution and sprayed on the obtained amino-modified carbon fiber, dried and cured to obtain modified carbon fiber loaded with nano-silica; Modification: The prepared modified carbon fiber loaded with nano-silica is immersed in a 1-butyl-3-methylimidazole dihydrogen phosphate ionic liquid solution, and then dried to obtain amino composite modified carbon fiber.

8. A high-strength fireproof cable according to claim 7, characterized in that: During the post-treatment of amino-modified carbon fiber, during the nano-silica loading process, the 3-carboxypropyl triethoxysilane solution is prepared by mixing 3-carboxypropyl triethoxysilane with ethanol and water in a mass ratio of 1: (6-8): (2-3), and the pH value of the 3-carboxypropyl triethoxysilane solution is adjusted to 4.5-6, the immersion temperature is 50-55° C., the immersion time is 40-60 min, and the addition mass ratio of nano-silica to 3-carboxypropyl triethoxysilane solution is 1: (8-10); The mass concentration of polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 5-10wt%, and the carboxylated nano-silica and the polyvinyl alcohol aqueous solution are mixed in a mass ratio of 1: (3-4) to prepare a spraying liquid, and the spraying amount of the spraying liquid is 10-20wt% of the amount of amino-modified carbon fiber added; In the modification step, a 1-butyl-3-methylimidazole dihydrogen phosphate ionic liquid solution is prepared by mixing 1-butyl-3-methylimidazole dihydrogen phosphate with water and acetone in a mass ratio of 1: (8-10): (6-8), and the modified carbon fiber loaded with nano-silica is immersed in the 1-butyl-3-methylimidazole dihydrogen phosphate ionic liquid solution, the immersion temperature is 30-40° C., the immersion time is 30-40 min, and the immersion pressure is 0.6-0.8 MPa.

9. A method for preparing a high-strength fire-resistant cable according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1. Firstly, the modified polyamide-imide resin, amino-modified carbon fiber and genipin are heated to 120-130° C., mixed for 20-30 minutes, and then the remaining raw materials are added for melt blending and granulation. The melting temperature is 180-210° C. to obtain an outer sheath; S2. Assemble the conductor, insulation layer, flame retardant layer and outer sheath in sequence to produce a high-strength fireproof cable.

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