A fire resistant flame retardant cable jacket and method of making the same

Abstract

This invention relates to the field of polymer compound technology, specifically to a fire-resistant and flame-retardant cable outer sheath and its preparation method. The method includes mixing KH550 with lignin, then sequentially adding functional microencapsulated ammonium polyphosphate, polydimethylsiloxane-polyimide block copolymer, polyamide, and organically modified montmorillonite, continuing mixing, and then adding ethylene-vinyl acetate copolymer, linear low-density polyethylene, maleic anhydride-grafted polyolefin elastomer, lubricant EBS, antioxidant 1010, and antioxidant 168. The mixture is then mixed at room temperature to obtain a premix. This invention introduces disulfide bond dynamic covalent crosslinking units into the microcapsule shell. When microcracks occur in the microcapsule shell during extrusion, cable bending, or long-term thermal stress, the reversible exchange reaction of the dynamic covalent bonds can be triggered by Joule heating during cable operation or external heating, resulting in healing of the microcapsule shell at the cut and reducing APP exposure.

Description

Technical Field

[0001] This invention relates to the field of polymer compound technology, and in particular to a fire-resistant and flame-retardant cable outer sheath and its preparation method. Background Technology

[0002] Cables, as an important carrier of power transmission and information communication, are widely used in various sectors of the national economy, such as construction, transportation, energy, and communications. The outer sheath of a cable is the outermost protective material in the cable structure. Its main function is to protect the internal insulation layer and cable core from damage caused by external factors such as mechanical damage, chemical corrosion, humid environments, and fire. Therefore, cable outer sheath materials not only need to have good mechanical properties and weather resistance, but also need to have excellent flame retardant and fire-resistant properties under fire conditions to ensure personnel safety and line integrity.

[0003] Polyolefin polymers (such as ethylene-vinyl acetate copolymer, linear low-density polyethylene, etc.) are widely used as the base resin for cable sheaths due to their excellent electrical insulation, processability and mechanical properties. However, the limiting oxygen index (LOI) of polyolefins is only about 18%, which makes them flammable materials. Under fire conditions, they will burn rapidly and release a large amount of heat, dense smoke and molten drips. Not only will they fail to protect the internal cable core, but they will also help the fire spread.

[0004] Traditional ammonium polyphosphate (APP), as an acid source for intumescent flame retardants, contains a large number of ammonium groups in its molecular structure. Its strong hydrophilicity makes it prone to moisture absorption and agglomeration in high humidity environments, which not only reduces the flame retardant efficiency but also seriously degrades the insulation performance and mechanical uniformity of the cable sheath. Therefore, in response to the problems mentioned above, this invention proposes a fire-resistant and flame-retardant cable outer sheath and its preparation method. Summary of the Invention

[0005] The purpose of this invention is to provide a fire-resistant and flame-retardant cable outer sheath and its preparation method, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a fire-resistant and flame-retardant cable outer sheath and its preparation method, comprising the following steps:

[0007] S1. By weight, mix 0.5-2 parts of KH550 with 3-8 parts of lignin for 5-10 minutes. Then, add 20-35 parts of functional microencapsulated ammonium polyphosphate, 5-12 parts of polydimethylsiloxane-polyimide block copolymer, 4-10 parts of polyamide, and 2-5 parts of organically modified montmorillonite in sequence. Continue mixing for 10-15 minutes. Then, add 50-70 parts of ethylene-vinyl acetate copolymer, 20-40 parts of linear low-density polyethylene, 8-15 parts of maleic anhydride-grafted polyolefin elastomer, 0.5-2 parts of lubricant EBS, 0.3-0.6 parts of antioxidant 1010, and 0.3-0.6 parts of antioxidant 168. Mix at room temperature for 8-12 minutes to obtain the premix.

[0008] S2. The premixed material is fed into a twin-screw extruder for melt blending and extrusion. The extruded melt is cooled and shaped in a cooling water tank, and the surface moisture is removed by air drying with an air knife. The material is then granulated by a pelletizer to obtain cylindrical particles. The particles are dried at 80-90℃ for 4-6 hours to obtain outer sheath particles.

[0009] S3. The outer sheath particles are extruded through a cable extruder and coated onto the surface of the cable core to form a sheath layer. An electron beam irradiation device is used for irradiation crosslinking treatment with an irradiation dose of 80-150 kGy and an energy of 1.5-2.5 MeV. After the treatment, a fire-resistant and flame-retardant cable outer sheath is obtained.

[0010] The functional microencapsulated ammonium polyphosphate is prepared through the following steps:

[0011] S11. Melamine, formaldehyde aqueous solution, and cystamine crosslinking agent are mixed, and the pH is adjusted to 8.0-9.0 with sodium hydroxide solution. The mixture is reacted at 70-80℃ for 1-2 hours to obtain a resin prepolymer. Tetraethyl orthosilicate is added to the resin prepolymer, and the pH is adjusted to 4.0-5.0 with dilute hydrochloric acid. The mixture is then subjected to a hydrolysis-condensation reaction at 60-70℃ for 2-4 hours to obtain a modified prepolymer.

[0012] S12. Under stirring conditions, the modified prepolymer is added dropwise to the core material suspension, the pH is adjusted to 4.5-5.5 with dilute hydrochloric acid, and in-situ polymerization and coating are carried out at 75-85℃ for 3-5 hours. After the reaction is completed, the mixture is cooled to room temperature, filtered, washed, vacuum dried and ground to obtain encapsulated ammonium polyphosphate.

[0013] S13. Disperse the encapsulated ammonium polyphosphate in anhydrous ethanol, add KH570, sonicate for 15-30 min, adjust the pH to 4.0-5.5 with glacial acetic acid, stir and react at 60-80℃ under nitrogen protection for 4-8 h. After the reaction is complete, filter, wash the precipitate 2-3 times with anhydrous ethanol, and vacuum dry at 60-80℃ for 6-12 h to obtain functional microencapsulated ammonium polyphosphate.

[0014] As a preferred embodiment of the present invention, the core material suspension in step S12 is prepared through the following steps:

[0015] S121. Disperse ammonium polyphosphate in deionized water and stir at 60-80℃ for 30-35 min to form a suspension. Add zinc nitrate to the suspension, adjust the pH to 5-7 with dilute ammonia, and stir the reaction at 70-90℃ for 4-8 h.

[0016] S122. After the reaction is complete, filter the solution, wash the precipitate 2-3 times with deionized water, dry it under vacuum at 100-110℃ for 12-24 hours, grind and sieve to obtain modified ammonium polyphosphate.

[0017] S123. Disperse modified ammonium polyphosphate in deionized water, add sodium dodecylbenzenesulfonate as an emulsifier, and stir and emulsify at 60-70℃ for 30-35 minutes to obtain a core material suspension.

[0018] As a preferred embodiment of the present invention, the mass ratio of melamine, formaldehyde aqueous solution and cystamine crosslinking agent in S11 is 1:(1.5-3.5):(0.05-0.15), and the mass ratio of resin prepolymer to tetraethyl orthosilicate is 1:(0.1-0.3).

[0019] As a preferred embodiment of the present invention, the mass ratio of the modified prepolymer to the core material suspension in S12 is 1:(4-8).

[0020] As a preferred embodiment of the present invention, the mass ratio of encapsulated ammonium polyphosphate, anhydrous ethanol, and KH570 in S13 is 1:(3-6):(0.05-0.15).

[0021] As a preferred embodiment of the present invention, the temperature settings of each zone of the twin-screw extruder in S2 are as follows: feeding zone 140-160℃, melting zone 160-180℃, mixing zone 170-190℃, homogenizing zone 180-200℃, and die head temperature 185-195℃; the screw speed is 200-300 r / min.

[0022] As a preferred embodiment of the present invention, the mass fraction of sodium hydroxide solution in S11 is 2-4%, the mass fraction of dilute hydrochloric acid in S11 and S12 is 10-15%, and the mass fraction of glacial acetic acid in S13 is 4-6%.

[0023] As a preferred embodiment of the present invention, in S121, the mass ratio of ammonium polyphosphate to deionized water is 1:(5-10), the mass ratio of zinc nitrate to suspension is 1:(15-30), and the mass fraction of dilute ammonia is 5-10%.

[0024] As a preferred embodiment of the present invention, the mass ratio of modified ammonium polyphosphate, deionized water, and sodium dodecylbenzenesulfonate in S123 is 1:(3-6):(0.005-0.02).

[0025] As a preferred technical solution of the present invention, a fire-resistant and flame-retardant cable outer sheath is prepared according to the preparation method described above.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] 1. This invention introduces disulfide bond dynamic covalent crosslinking units into the microcapsule shell. When microcracks are generated in the microcapsule shell during extrusion processing, cable bending, or long-term thermal stress, the reversible exchange reaction of dynamic covalent bonds can be triggered by Joule heating during cable operation or external heating. The microcapsule shell at the cut heals, reducing APP exposure. This damage-self-healing ability significantly delays the leakage and moisture absorption failure of internal APP, enabling the sheath material to maintain stable flame retardant performance during long-term service.

[0028] 2. This invention pre-modifies the APP core material through ion exchange using transition metal ions, partially replacing ammonium ions in the APP. The introduction of metal ions alters the thermal decomposition kinetics of the APP, delaying the release window of polyphosphoric acid and enabling synchronous release with the main thermal decomposition stage of the polyolefin matrix. When the cable sheath is heated, the matrix begins to decompose, and the acid source begins to release a large amount of polyphosphoric acid, which immediately catalyzes the formation of a dense carbon layer, avoiding the inefficiency of premature failure or delayed decomposition of the acid source. At the same time, the metal ions themselves can catalyze cross-linking carbonization reactions at high temperatures, further enhancing the continuity and thermal stability of the carbon layer. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the preparation process of the fire-resistant and flame-retardant cable outer sheath in this invention;

[0030] Figure 2 This is a schematic diagram of the preparation process of functional microencapsulated ammonium polyphosphate in this invention;

[0031] Figure 3 This is a schematic diagram of the preparation process of the core material suspension in this invention. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Please see Figures 1-3 This invention provides a technical solution for a fire-resistant and flame-retardant cable outer sheath and its preparation method:

[0034] Preparation steps of polydimethylsiloxane-polyimide block copolymer:

[0035] Step 1: Dehydrate and deoxygenate the three-necked flask. Under nitrogen protection, add 2g of 4,4'-diaminodiphenyl ether, 5g of α,ω-diaminopropyl-terminated polydimethylsiloxane, and 450g of anhydrous N,N-dimethylacetamide to the dry three-necked flask and stir until completely dissolved. Add 30g of hexafluorodianhydride under ice bath conditions and stir for 2 hours. Continue stirring at room temperature for 20 hours to obtain a polyamic acid block copolymer solution.

[0036] Step 2: Heat the polyamic acid block copolymer solution. The heating program is set as follows: 80℃ for 2 hours; 150℃ for 1 hour; 200℃ for 1 hour; 300℃ for 1 hour. High-temperature ring-closure imidization is performed. After cooling, polydimethylsiloxane-polyimide block copolymer is obtained.

[0037] Example 1:

[0038] A method for preparing a fire-resistant and flame-retardant cable outer sheath includes the following steps:

[0039] I. Core Material Suspension:

[0040] S121. Disperse 100g of ammonium polyphosphate (degree of polymerization n≥1000) in 500g of deionized water, stir at 60℃ for 30min to form a suspension, add 5g of zinc nitrate to every 75g of suspension, adjust the pH to 5.0 with 5% (w / w) dilute ammonia water, and stir at 70℃ for 4h.

[0041] S122. After the reaction is complete, filter the solution, wash the precipitate twice with deionized water, dry it under vacuum at 100℃ for 12 hours, grind it through a 200-mesh sieve, and obtain modified ammonium polyphosphate.

[0042] S123. Disperse 100g of modified ammonium polyphosphate in 300g of deionized water, add 0.5g of sodium dodecylbenzenesulfonate, and stir and emulsify at 60℃ for 30min to obtain a core material suspension.

[0043] II. Preparation of functional microencapsulated ammonium polyphosphate:

[0044] S11. Mix 100g of melamine, 150g of 37% formaldehyde aqueous solution, and 5g of cystamine crosslinking agent. Adjust the pH to 8.0 with 2% sodium hydroxide solution and react at 70℃ for 1h to obtain a resin prepolymer. Add 10g of tetraethyl orthosilicate to every 100g of resin prepolymer, adjust the pH to 4.0 with 10% dilute hydrochloric acid, and hydrolyze and condense at 60℃ for 2h to obtain a modified prepolymer.

[0045] S12. Under stirring conditions, 100g of modified prepolymer was added dropwise to 400g of core material suspension. The pH was adjusted to 4.5 with 10% hydrochloric acid by mass. The reaction was carried out at 75℃ for 3h. After the reaction was completed, the mixture was cooled to room temperature, filtered, washed 3 times with deionized water, vacuum dried at 100℃ for 12h, and ground through a 300-mesh sieve to obtain encapsulated ammonium polyphosphate.

[0046] S13. Disperse 100g of encapsulated ammonium polyphosphate in 300g of anhydrous ethanol, add 5g of KH570, sonicate for 15min, adjust the pH to 4.0 with 4% glacial acetic acid, stir and react for 4h at 60℃ under nitrogen protection, filter after reaction, wash the precipitate twice with anhydrous ethanol, and vacuum dry at 60℃ for 6h to obtain functional microencapsulated ammonium polyphosphate.

[0047] III. Preparation of fire-resistant and flame-retardant cable outer sheath material:

[0048] S1. Mix 5g KH550 and 30g lignin in a high-speed mixer for 5 minutes. Then, add 200g functional microencapsulated ammonium polyphosphate, 50g polydimethylsiloxane-polyimide block copolymer, 40g polyamide (relative viscosity 2.4), and 20g organic modified montmorillonite in sequence. Continue mixing for 10 minutes. Finally, add 500g ethylene-vinyl acetate copolymer (VA content 26%), 200g linear low-density polyethylene, 80g maleic anhydride grafted polyolefin elastomer, 5g lubricant EBS, 3g antioxidant 1010, and 3g antioxidant 168. Mix at room temperature for 8 minutes to obtain the premix.

[0049] S2. The premixed material is fed into a co-rotating twin-screw extruder for melt blending and extrusion. The temperatures of each zone are set as follows: feeding zone 140℃, melting zone 160℃, mixing zone 170℃, homogenizing zone 180℃, and die head 185℃; screw speed 200r / min; vacuum degree at the vacuum exhaust port -0.08MPa. The extruded melt is cooled and shaped in a cooling water tank (first stage water temperature 40℃, second stage 25℃), and the surface moisture is removed by air knife drying. The pellets are granulated by a pelletizer to obtain cylindrical particles with a diameter of 2-3mm and a length of 3-4mm. The particles are dried in an 80℃ forced-air drying oven for 4 hours to obtain outer sheath particles.

[0050] S3. The outer sheath particles are extruded onto the surface of the cable core using a single-screw cable extruder to form a sheath layer. The extruder temperature settings are as follows: barrel zone I 140℃, zone II 160℃, zone III 175℃, zone IV 185℃, flange 185℃, and die head and mold 190℃; screw speed 25r / min; traction line speed 30m / min; the mold adopts a tube extrusion type with a draw ratio of 2.8. After extruding the sheath, it is subjected to irradiation crosslinking treatment using an electron beam irradiation device with an irradiation dose of 80kGy and an energy of 1.5MeV. After the treatment, a fire-resistant and flame-retardant cable outer sheath is obtained.

[0051] Example 2:

[0052] A method for preparing a fire-resistant and flame-retardant cable outer sheath includes the following steps:

[0053] I. Core Material Suspension:

[0054] S121. Disperse 100g of ammonium polyphosphate (degree of polymerization n≥1000) in 800g of deionized water, stir at 70℃ for 33min to form a suspension, add 5g of zinc nitrate to every 100g of suspension, adjust the pH to 6.0 with 7.5% (w / w) dilute ammonia water, and stir at 80℃ for 6h.

[0055] S122. After the reaction is complete, filter the solution, wash the precipitate twice with deionized water, dry it under vacuum at 105℃ for 18 hours, grind it through a 200-mesh sieve, and obtain modified ammonium polyphosphate.

[0056] S123. Disperse 100g of modified ammonium polyphosphate in 400g of deionized water, add 1.3g of sodium dodecylbenzenesulfonate, and stir and emulsify at 65℃ for 33min to obtain a core material suspension.

[0057] II. Preparation of functional microencapsulated ammonium polyphosphate:

[0058] S11. Mix 100g of melamine, 220g of 37% formaldehyde aqueous solution, and 10g of cystamine crosslinking agent. Adjust the pH to 8.5 with 3% sodium hydroxide solution and react at 75℃ for 1.5h to obtain a resin prepolymer. Add 20g of tetraethyl orthosilicate to every 100g of resin prepolymer, adjust the pH to 4.5 with 12.5% ​​dilute hydrochloric acid, and hydrolyze and condense at 65℃ for 3h to obtain a modified prepolymer.

[0059] S12. Under stirring conditions, 100g of modified prepolymer was added dropwise to 600g of core material suspension. The pH was adjusted to 5 with 12.5% ​​dilute hydrochloric acid. The reaction was carried out at 80℃ for 4h. After the reaction was completed, the mixture was cooled to room temperature, filtered, washed 3 times with deionized water, vacuum dried at 100℃ for 12h, and ground through a 300-mesh sieve to obtain encapsulated ammonium polyphosphate.

[0060] S13. Disperse 100g of encapsulated ammonium polyphosphate in 450g of anhydrous ethanol, add 10g of KH570, sonicate for 22min, adjust the pH to 5.0 with 5% glacial acetic acid, stir and react for 6h at 70℃ under nitrogen protection, filter after reaction, wash the precipitate twice with anhydrous ethanol, and vacuum dry at 70℃ for 9h to obtain functional microencapsulated ammonium polyphosphate.

[0061] III. Preparation of fire-resistant and flame-retardant cable outer sheath material:

[0062] S1. Mix 15g KH550 and 50g lignin in a high-speed mixer for 8 minutes. Then, add 280g functional microencapsulated ammonium polyphosphate, 80g polydimethylsiloxane-polyimide block copolymer, 70g polyamide (relative viscosity 2.4), and 40g organic modified montmorillonite in sequence. Continue mixing for 13 minutes. Finally, add 600g ethylene-vinyl acetate copolymer (VA content 26%), 300g linear low-density polyethylene, 110g maleic anhydride grafted polyolefin elastomer, 15g lubricant EBS, 4g antioxidant 1010, and 4g antioxidant 168. Mix at room temperature for 10 minutes to obtain the premix.

[0063] S2. The premixed material is fed into a co-rotating twin-screw extruder for melt blending and extrusion. The temperatures of each zone are set as follows: feeding section 150℃, melting section 170℃, mixing section 180℃, homogenizing section 190℃, and die head 190℃; screw speed 250r / min; vacuum degree at the vacuum exhaust port -0.08MPa. The extruded melt is cooled and shaped in a cooling water tank (first section water temperature 40℃, second section 25℃), and the surface moisture is removed by air knife drying. The pellets are granulated by a pelletizer to obtain cylindrical particles with a diameter of 2-3mm and a length of 3-4mm. The particles are dried in an 85℃ forced-air drying oven for 5 hours to obtain outer sheath particles.

[0064] S3. The outer sheath particles are extruded onto the surface of the cable core through a single-screw cable extruder to form a sheath layer. The extruder temperature settings are as follows: barrel zone I 140℃, zone II 160℃, zone III 175℃, zone IV 185℃, flange 185℃, and die head and mold 190℃; screw speed 25r / min; traction line speed 30m / min; the mold adopts a tube extrusion type with a draw ratio of 2.8. After extruding the sheath, it is subjected to irradiation crosslinking treatment using an electron beam irradiation device with an irradiation dose of 120kGy and an energy of 2MeV. After the treatment, a fire-resistant and flame-retardant cable outer sheath is obtained.

[0065] Example 3:

[0066] A method for preparing a fire-resistant and flame-retardant cable outer sheath includes the following steps:

[0067] I. Core Material Suspension:

[0068] S121. Disperse 100g of ammonium polyphosphate (degree of polymerization n≥1000) in 1000g of deionized water, stir at 80℃ for 35min to form a suspension, add 5g of zinc nitrate to every 150g of suspension, adjust the pH to 7.0 with 10% by mass dilute ammonia, and stir at 90℃ for 8h.

[0069] S122. After the reaction is complete, filter the solution, wash the precipitate three times with deionized water, dry it under vacuum at 110℃ for 24 hours, grind it through a 200-mesh sieve, and obtain modified ammonium polyphosphate.

[0070] S123. Disperse 100g of modified ammonium polyphosphate in 600g of deionized water, add 2g of sodium dodecylbenzenesulfonate, and stir and emulsify at 70℃ for 35min to obtain a core material suspension.

[0071] II. Preparation of functional microencapsulated ammonium polyphosphate:

[0072] S11. Mix 100g of melamine, 350g of 37% formaldehyde aqueous solution, and 15g of cystamine crosslinking agent. Adjust the pH to 9.0 with 4% sodium hydroxide solution and react at 80℃ for 2 hours to obtain a resin prepolymer. Add 30g of tetraethyl orthosilicate to every 100g of resin prepolymer, adjust the pH to 5.0 with 15% dilute hydrochloric acid, and hydrolyze and condense at 70℃ for 4 hours to obtain a modified prepolymer.

[0073] S12. Under stirring conditions, 100g of modified prepolymer was added dropwise to 800g of core material suspension. The pH was adjusted to 5.5 with 15% hydrochloric acid by mass. The reaction was carried out at 85℃ for 5h. After the reaction was completed, the mixture was cooled to room temperature, filtered, washed 3 times with deionized water, vacuum dried at 100℃ for 12h, and ground through a 300-mesh sieve to obtain encapsulated ammonium polyphosphate.

[0074] S13. Disperse 100g of encapsulated ammonium polyphosphate in 600g of anhydrous ethanol, add 15g of KH570, sonicate for 30min, adjust the pH to 5.5 with 6% glacial acetic acid, stir and react for 8h at 80℃ under nitrogen protection, filter after reaction, wash the precipitate three times with anhydrous ethanol, and vacuum dry at 80℃ for 12h to obtain functional microencapsulated ammonium polyphosphate.

[0075] III. Preparation of fire-resistant and flame-retardant cable outer sheath material:

[0076] S1. Mix 20g KH550 and 80g lignin in a high-speed mixer for 10min. Then, add 350g functional microencapsulated ammonium polyphosphate, 120g polydimethylsiloxane-polyimide block copolymer, 100g polyamide (relative viscosity 2.4), and 50g organic modified montmorillonite in sequence. Continue mixing for 15min. Finally, add 700g ethylene-vinyl acetate copolymer (VA content 26%), 400g linear low-density polyethylene, 150g maleic anhydride grafted polyolefin elastomer, 20g lubricant EBS, 6g antioxidant 1010, and 6g antioxidant 168. Mix at room temperature for 12min to obtain the premix.

[0077] S2. The premixed material is fed into a co-rotating twin-screw extruder for melt blending and extrusion. The temperatures of each zone are set as follows: feeding section 160℃, melting section 180℃, mixing section 190℃, homogenization section 200℃, and die head 195℃; screw speed 300r / min; vacuum degree at the vacuum exhaust port -0.08MPa. The extruded melt is cooled and shaped in a cooling water tank (first section water temperature 40℃, second section 25℃), and the surface moisture is removed by air knife drying. The pellets are granulated by a pelletizer to obtain cylindrical particles with a diameter of 2-3mm and a length of 3-4mm. The particles are dried in a 90℃ forced-air drying oven for 6 hours to obtain outer sheath particles.

[0078] S3. The outer sheath granules are extruded onto the surface of the cable core using a single-screw cable extruder to form a sheath layer. The extruder temperature settings are as follows: barrel zone I 140℃, zone II 160℃, zone III 175℃, zone IV 185℃, flange 185℃, and die head and mold 190℃; screw speed 25r / min; traction line speed 30m / min; the mold adopts a tube extrusion type with a draw ratio of 2.8. After extruding the sheath, it is subjected to irradiation crosslinking treatment using an electron beam irradiation device with an irradiation dose of 150kGy and an energy of 2.5MeV. After the treatment, a fire-resistant and flame-retardant cable outer sheath is obtained.

[0079] Comparative Example 1:

[0080] Comparative Example 1 differs from Example 1 in that the functional microencapsulated ammonium polyphosphate is replaced with an equal mass of ammonium polyphosphate, while the remaining steps are exactly the same as in Example 1.

[0081] Comparative Example 2:

[0082] Comparative Example 2 differs from Example 1 in that the functional microencapsulated polyphosphate ammonium is replaced with an equal mass of encapsulated polyphosphate ammonium, while the remaining steps are exactly the same as in Example 1.

[0083] Comparative Example 3:

[0084] Comparative Example 3 differs from Example 1 in that the core material suspension is replaced with an equal mass of ammonium polyphosphate suspension, while the remaining steps are exactly the same as in Example 1.

[0085] Comparative Example 4:

[0086] Compared to Example 1, Comparative Example 4 omits the addition of functional microencapsulated ammonium polyphosphate, while the remaining steps are exactly the same as in Example 1.

[0087] The fire-resistant and flame-retardant cable outer sheath samples prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to uniform performance tests. All tests were conducted under standard environmental conditions (temperature 23±2℃, relative humidity 50±5%). The samples were placed in this environment for at least 24 hours before testing. 500g of sheath material granules prepared in each example and comparative example were taken and hot-pressed into sheets with thicknesses of 1.0mm and 2.0mm using a flat vulcanizing machine at 180℃ and 10MPa pressure for mechanical and flame-retardant performance testing. Cables (length ≥1.5m) after direct extrusion of the sheath in step S3 of each example and comparative example were used for fire resistance and radiation crosslinking degree testing.

[0088] I. Mechanical property testing:

[0089] 1. Tensile strength and elongation at break:

[0090] Referring to GB / T2951.11-2008, dumbbell-shaped specimens (type 5, narrow section width 6mm, gauge length 25mm) were cut from a 1.0mm thick hot-pressed sheet. Using a universal testing machine with the clamp spacing set to 50mm, the specimen was stretched at a constant tensile speed of 500mm / min until it broke. The maximum tensile force (N) and the gauge length elongation (mm) at break were recorded.

[0091] Calculate tensile strength (MPa) = maximum tensile force / initial cross-sectional area.

[0092] Calculate the elongation at break (%) = (gauge length elongation at break / initial gauge length) × 100%.

[0093] 2. Mechanical property retention rate after hot air aging:

[0094] Referring to GB / T3512-2014, the cut dumbbell-shaped specimens were placed in a forced-ventilation aging oven and aged at (100±2)℃ for 168 hours. After being removed, they were placed under standard environmental conditions for 24 hours. The tensile strength and elongation at break of the aged specimens were then tested according to the tensile strength and elongation at break procedures.

[0095] Calculate the change rate of tensile strength (%) = (strength after aging - strength before aging) / strength before aging × 100%.

[0096] Calculate the change rate of elongation at break (%) = (elongation after aging - elongation before aging) / elongation before aging × 100%.

[0097] II. Self-repair function verification:

[0098] Cut strips of 50mm × 10mm × 2.0mm from a 2.0mm thick hot-pressed sheet. Make a cut about half the thickness in the middle of the sample with a blade (simulating a microcrack). Place the sample with the cut in an 80℃ oven and heat for 4 hours (simulating cable overload or external heat source). After cooling, visually observe whether the cut has closed and healed. Perform tensile tests on the healed sample according to the tensile strength and elongation at break test methods. Compare with the undamaged sample to observe whether the fracture occurs at the original cut. If the fracture occurs in other locations, the healing is effective; if the fracture still occurs at the original cut, the self-repair effect is poor. The specific test results are shown in Table 1.

[0099] Table 1: Mechanical Performance Test Table for the Outer Sheath of Fire-Resistant and Flame-Retardant Cables

[0100]

[0101] As can be seen from the data in Table 1, the tensile strength of the fire-resistant and flame-retardant cable outer sheaths prepared in Examples 1-3 all reached above 14.0 MPa under normal conditions, and the elongation at break all exceeded 188%, with Example 2 being the best. In contrast, the mechanical properties of Comparative Examples 1-4 decreased significantly: Comparative Example 1 (unmodified APP) had a tensile strength of only 11.2 MPa and an elongation at break of 145%; Comparative Example 2 (no surface grafting) had 12.5 MPa / 162%; Comparative Example 3 (core material without ion exchange) had 10.8 MPa / 132%; and Comparative Example 4 (no flame retardant) had only 8.5 MPa / 105%. This trend indicates that the present invention effectively improves the interfacial compatibility between the flame retardant and the polymer matrix through steps such as ion exchange modification, dynamic covalent shell layer, and surface KH570 grafting, forming a chemical bond network, thereby enabling stress to be transmitted uniformly and avoiding stress concentration and mechanical property deterioration caused by the agglomeration of traditional flame retardants.

[0102] After hot air aging, the tensile strength change rate of the embodiments was controlled between -12.0% and -9.8%, and the elongation at break change rate was controlled between -14.0% and -11.5%, which was significantly better than that of the comparative examples (the absolute values ​​of the change rates were all greater than 18%). This is due to the three-dimensional network structure formed by irradiation crosslinking and the protective effect of the microcapsule shell on the internal APP, which slowed down the damage to the molecular chains caused by thermo-oxidative aging. It is particularly noteworthy that in the self-healing function test, the cuts of all the samples of the embodiments were effectively healed after heating at 80°C for 4 hours, and the tensile fracture occurred in the non-cut area, proving that the dynamic disulfide bonds underwent a reversible exchange reaction under thermal stimulation, repairing the microcracks. In contrast, the comparative examples, due to the lack of dynamic covalent bond units, always had the cuts as weak points, and the fractures all started from the original cuts. This self-healing capability is one of the core innovations of this invention. It enables the sheath material to automatically repair micro-damage caused by bending, extrusion, etc. during long-term service, significantly extending the safe service life of the cable, especially suitable for difficult-to-maintain places such as subways and nuclear power plants.

[0103] III. Flame retardant performance test:

[0104] 1. Limiting Oxygen Index:

[0105] Referring to GB / T2406.2-2009, cut a strip of sample with dimensions of 150mm×6.5mm×3.0mm from a 2.0mm thick hot-pressed sheet. Vertically install the sample in the glass combustion chamber of the oxygen index analyzer, set the initial oxygen concentration (e.g., 25%), adjust the nitrogen and oxygen flow rates to a constant total flow rate (approximately 10L / min), ignite the upper part of the sample with an igniter for approximately 10 seconds, remove the flame and observe the combustion behavior, and record the oxygen concentration when the sample maintains combustion for more than 3 minutes or extinguishes. Use the "top and bottom method" to test each sample individually to determine the critical oxygen concentration (accurate to 0.5%).

[0106] 2. Vertical flammability rating:

[0107] Referring to UL94 (IEC60695-11-10), cut a strip of specimen with dimensions of 125mm×13mm×3.0mm from a 2.0mm thick hot-pressed sheet. Hold the specimen vertically in the combustion test chamber with the lower end about 300mm from the horizontal cotton layer. Apply a flame to the lower end of the specimen for 10s using a calibrated Bunsen burner (flame height 20mm), then remove the flame and record the first flaming burning time (t1). After the flame self-extinguishes, immediately apply the flame again for 10s and record the second flaming burning time (t2) and the flameless burning time (t3). Observe and record whether there are any molten drips that ignite the cotton layer below. Determine the V-0, V-1, or V-2 rating based on the burning time and dripping situation.

[0108] IV. Fire resistance performance test:

[0109] Reference standard: GB / T19216.21-2003 (IEC60331-21). The cable after extrusion sheathing in each embodiment and comparative example shall be no less than 1.2m in length, with the sheath stripped from both ends to expose approximately 50mm of conductor. The cable sample shall be fixed on the fire resistance test bench in an "S" shape, with the bending radius conforming to the cable diameter requirements. Connect the conductors at both ends of the cable to the power supply and indicator light circuits, apply the rated voltage (e.g., 450 / 750V) and load current (1.5 times the nominal current carrying capacity of the cable), place the tubular burner under the cable, and control the flame temperature to 950℃ using a thermocouple. Ignite the burner and continuously supply fire, observing whether the indicator light remains constantly lit (indicating circuit continuity). Record the duration of circuit interruption, and simultaneously observe the changes in the sheath layer under the flame (whether it melts and drips, whether a carbon layer forms, and whether there are penetrating cracks). The specific test results are shown in Table 2.

[0110] Table 2: Test Table of Fire Resistance and Flame Retardant Performance of Outer Sheath of Fire-Resistant and Flame Retardant Cables

[0111]

[0112] As can be seen from the data in Table 2, the limiting oxygen index of Examples 1-3 all reached over 33.0%, with Example 2 reaching as high as 34.0%. The vertical burning rating of all examples was V-0, and the fire resistance performance of all examples exceeded 90 minutes. Moreover, the char layer formed by the sheath under a 950℃ flame was dense and complete, without penetrating cracks. In contrast, the flame retardant performance of Comparative Examples 1-4 was significantly insufficient: Comparative Example 1 (unmodified APP) had an LOI of only 27.5%, a V-2 rating (with dripping), and a fire resistance time of only 42 minutes; Comparative Example 2 (no surface grafting) had an LOI of 29.0%, a V-1 rating, a fire resistance of 58 minutes, and the char layer had cracks; Comparative Example 3 (core material without ion exchange) had an LOI of 26.5%, a V-2 rating, a fire resistance of 35 minutes, and severe dripping; Comparative Example 4 (no flame retardant) had an LOI of only 19.5%, no vertical burning rating, and the sheath melted and short-circuited after only 12 minutes of fire resistance.

[0113] The above data reveals the mechanism by which the flame retardant performance of this invention is improved. First, through ion exchange modification, the thermal decomposition window of APP is shifted to a later stage, allowing for synchronous release with the main decomposition stage of the EVA / LLDPE matrix, thus avoiding the low char formation efficiency caused by premature acid release in traditional APP. Second, the silicon element introduced into the shell layer forms a Si-O-Si ceramic network at high temperature, filling the pores of the expanded char layer and significantly improving the density and thermo-oxidative stability of the char layer. Third, the KH570 grafted on the surface enables the microcapsules to form chemical bonds with the matrix, ensuring the flame retardant... During combustion, no agglomeration or premature detachment occurred. The reason why Example 2 had the best performance was that its degree of ion exchange and the content of silicon in the shell were perfectly balanced, which ensured the matching of acid release timing and avoided the catalytic effect of excessive metal ions on polymer degradation. Comparative Example 3 had the worst flame retardant effect because it did not undergo ion exchange, APP decomposed too early, the acid source and the matrix were not synchronized. Although Comparative Example 2 completed microencapsulation, it did not have surface grafting, and the slightly poor dispersibility caused cracks in the char layer. Comparative Example 1 had low flame retardant efficiency and serious dripping due to the hydrophilic agglomeration of APP.

[0114] The above are merely specific embodiments of the present invention, but the technical features of the present invention are not limited thereto. Any simple changes, equivalent substitutions, or modifications made based on the present invention to solve essentially the same technical problems and achieve essentially the same technical effects are all covered within the protection scope of the present invention.

Claims

1. A method for preparing a fire-resistant and flame-retardant cable outer sheath, characterized in that, Includes the following steps: S1. By weight, mix 0.5-2 parts of KH550 with 3-8 parts of lignin for 5-10 minutes. Then, add 20-35 parts of functional microencapsulated ammonium polyphosphate, 5-12 parts of polydimethylsiloxane-polyimide block copolymer, 4-10 parts of polyamide, and 2-5 parts of organic modified montmorillonite in sequence, and continue mixing for 10-15 minutes. Then, add 50-70 parts of ethylene-vinyl acetate copolymer, 20-40 parts of linear low-density polyethylene, 8-15 parts of maleic anhydride grafted polyolefin elastomer, 0.5-2 parts of lubricant EBS, 0.3-0.6 parts of antioxidant 1010, and 0.3-0.6 parts of antioxidant 168. Mix at room temperature for 8-12 minutes to obtain the premix. S2. The premixed material is fed into a twin-screw extruder for melt blending and extrusion. The extruded melt is cooled and shaped in a cooling water tank, and the surface moisture is removed by air drying with an air knife. The material is then granulated by a pelletizer to obtain cylindrical particles. The particles are dried at 80-90℃ for 4-6 hours to obtain outer sheath particles. S3. The outer sheath particles are extruded through a cable extruder and coated onto the surface of the cable core to form a sheath layer. An electron beam irradiation device is used for irradiation crosslinking treatment with an irradiation dose of 80-150 kGy and an energy of 1.5-2.5 MeV. After the treatment, a fire-resistant and flame-retardant cable outer sheath is obtained. The functional microencapsulated ammonium polyphosphate is prepared through the following steps: S11. Melamine, formaldehyde aqueous solution, and cystamine crosslinking agent are mixed, and the pH is adjusted to 8.0-9.0 with sodium hydroxide solution. The mixture is reacted at 70-80℃ for 1-2 hours to obtain a resin prepolymer. Tetraethyl orthosilicate is added to the resin prepolymer, and the pH is adjusted to 4.0-5.0 with dilute hydrochloric acid. The mixture is then subjected to a hydrolysis-condensation reaction at 60-70℃ for 2-4 hours to obtain a modified prepolymer. S12. Under stirring conditions, the modified prepolymer is added dropwise to the core material suspension, the pH is adjusted to 4.5-5.5 with dilute hydrochloric acid, and in-situ polymerization and coating are carried out at 75-85℃ for 3-5 hours. After the reaction is completed, the mixture is cooled to room temperature, filtered, washed, vacuum dried and ground to obtain encapsulated ammonium polyphosphate. S13. Disperse the encapsulated ammonium polyphosphate in anhydrous ethanol, add KH570, sonicate for 15-30 min, adjust the pH to 4.0-5.5 with glacial acetic acid, stir and react at 60-80℃ under nitrogen protection for 4-8 h. After the reaction is complete, filter, wash the precipitate 2-3 times with anhydrous ethanol, and vacuum dry at 60-80℃ for 6-12 h to obtain functional microencapsulated ammonium polyphosphate.

2. The method for preparing a fire-resistant and flame-retardant cable outer sheath according to claim 1, characterized in that: The core material suspension in step S12 is prepared through the following steps: S121. Disperse ammonium polyphosphate in deionized water and stir at 60-80℃ for 30-35 min to form a suspension. Add zinc nitrate to the suspension, adjust the pH to 5-7 with dilute ammonia, and stir the reaction at 70-90℃ for 4-8 h. S122. After the reaction is complete, filter the solution, wash the precipitate 2-3 times with deionized water, dry it under vacuum at 100-110℃ for 12-24h, grind and sieve to obtain modified ammonium polyphosphate. S123. Disperse modified ammonium polyphosphate in deionized water, add sodium dodecylbenzenesulfonate as an emulsifier, and stir and emulsify at 60-70℃ for 30-35 minutes to obtain a core material suspension.

3. The method for preparing a fire-resistant and flame-retardant cable outer sheath according to claim 1, characterized in that: The mass ratio of melamine, formaldehyde aqueous solution and cystamine crosslinking agent in S11 is 1:(1.5-3.5):(0.05-0.15), and the mass ratio of resin prepolymer to tetraethyl orthosilicate is 1:(0.1-0.3).

4. The method for preparing a fire-resistant and flame-retardant cable outer sheath according to claim 1, characterized in that: The mass ratio of the modified prepolymer to the core material suspension in S12 is 1:(4-8).

5. The method for preparing a fire-resistant and flame-retardant cable outer sheath according to claim 1, characterized in that: The mass ratio of encapsulated ammonium polyphosphate, anhydrous ethanol, and KH570 in S13 is 1:(3-6):(0.05-0.15).

6. The method for preparing a fire-resistant and flame-retardant cable outer sheath according to claim 1, characterized in that: The temperature settings for each zone of the twin-screw extruder in S2 are as follows: feeding zone 140-160℃, melting zone 160-180℃, mixing zone 170-190℃, homogenizing zone 180-200℃, and die head temperature 185-195℃; the screw speed of the twin-screw extruder is 200-300 r / min.

7. The method for preparing a fire-resistant and flame-retardant cable outer sheath according to claim 1, characterized in that: The sodium hydroxide solution in S11 has a mass fraction of 2-4%, the dilute hydrochloric acid in S11 and S12 has a mass fraction of 10-15%, and the glacial acetic acid in S13 has a mass fraction of 4-6%.

8. The method for preparing a fire-resistant and flame-retardant cable outer sheath according to claim 2, characterized in that: In S121, the mass ratio of ammonium polyphosphate to deionized water is 1:(5-10), the mass ratio of zinc nitrate to suspension is 1:(15-30), and the mass fraction of dilute ammonia is 5-10%.

9. The method for preparing a fire-resistant and flame-retardant cable outer sheath according to claim 2, characterized in that: The mass ratio of modified ammonium polyphosphate, deionized water, and sodium dodecylbenzenesulfonate in S123 is 1:(3-6):(0.005-0.02).

10. A fire-resistant and flame-retardant cable outer sheath, characterized in that, Prepared by the method according to any one of claims 1-9.

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