Environment-friendly halogen-free flame-retardant composite special cable

Abstract

The invention discloses an environment-friendly halogen-free flame-retardant composite special cable, and belongs to the technical field of cable preparation, the special cable sequentially comprises a conductor, an insulating layer, a glass fiber rope layer and an outer protective sleeve from inside to outside, and the insulating layer and the outer protective sleeve are prepared from a modified flame-retardant copolymer. The modified flame-retardant copolymer is prepared from the following raw materials in parts by weight: 65 to 80 parts of linear low-density polyethylene, 20 to 38 parts of ethylene-vinyl acetate copolymer, 5 to 10 parts of modified P-N-Si flame retardant 1, 3 to 6 parts of modified P-N-Si flame retardant 2, 0.5 to 1 part of initiator, 0.2 to 0.5 part of antioxidant and 25 to 35 parts of non-reactive flame retardant through melt copolymerization; a polyfunctional and rigid organic modified P-N-Si flame retardant is grafted, so that the migration of the flame retardant is reduced, the crosslinking degree is increased, and the mechanical and high-temperature-resistant properties are improved; the organic P-N-Si, the inorganic non-reactive flame retardant metal hydroxide and the nano inorganic particles have a synergistic effect, so that the cable is endowed with high flame retardance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of cable preparation, in particular to an environment-friendly halogen-free flame-retardant composite special cable. BACKGROUND

[0002] As the blood vessels of modern society, the safe and stable operation of power and communication networks highly depends on high-performance cables. The insulation layer and sheath layer of the cable, as the key protective structure, directly affect its use safety and service life. At present, polyethylene, polyvinyl chloride and other polymer binders are widely used in the preparation of insulation layer and sheath layer. These binders have good processability, insulation and corrosion resistance, but they have hidden fire hazards and may release halogen-containing toxic gases during combustion, which poses a serious threat to personnel safety and the environment. Especially under extreme conditions such as overload, short circuit or high temperature, traditional cables are more likely to cause fires and accelerate the spread of flames.

[0003] In order to balance environmental protection and flame-retardant safety, the development of halogen-free flame-retardant special cables has become a research focus. By adding environmentally friendly halogen-free flame retardants to the polymer matrix, the flame propagation can be effectively inhibited during combustion and almost no toxic smoke is generated. However, the introduction of flame retardants also faces challenges: insufficient addition has limited flame-retardant effect; excessive addition is prone to poor compatibility with the matrix, resulting in a decrease in the mechanical properties of the cable; in addition, the use of flame retardants also causes migration, resulting in the loss of flame-retardant properties. Therefore, how to achieve efficient flame retardation while ensuring mechanical properties is the core direction of current research and development of environmentally friendly composite special cables. SUMMARY

[0004] In order to overcome the above-mentioned deficiencies of the prior art, the present application provides an environment-friendly halogen-free flame-retardant composite special cable, the insulation layer and the outer protective sleeve of which are prepared from a modified flame-retardant copolymer, wherein the base material used is linear low-density polyethylene and ethylene-vinyl acetate copolymer, which is green and environment-friendly; the flame-retardant performance of the cable can be greatly improved by the synergistic effect of the grafted organic reaction-type modified P-N-Si flame retardant and the addition of inorganic non-reaction-type flame retardant, on the one hand, the grafted flame retardant can avoid migration, the P, N and Si elements in the reaction-type modified flame retardant synergistically act together, the phosphoric acid ester group decomposes into a viscous semi-solid substance to cover the surface and promotes dehydration and carbonization of the outer protective sleeve and the insulation layer of the cable, thereby insulating the penetration of oxygen and the transmission of heat; the nitrogen-containing melamine and p-phenylenediamine flame-retardant groups decompose to release nitrogen, nitrogen oxide and water vapor and other non-combustible gases to dilute the oxygen concentration and take away energy; the 1-ethenyl-1,1,3,3-tetramethyldisiloxane decomposes or activates to catalyze the crosslinking between the molecular chains of the copolymer, thereby promoting the combustion to form carbon instead of volatile combustible substances. On the other hand, the non-reaction-type flame retardant magnesium hydroxide burns to form a dense magnesium oxide protective film on the surface of the outer protective sleeve and the insulation layer to insulate the further contact of air with the outer protective sleeve and the insulation layer, and meanwhile, the magnesium hydroxide and the silicon dioxide capture free radicals to reduce the number of free radicals to inhibit the chain reaction of combustion, thereby further improving the flame-retardant performance of the cable. In addition, the conjugated benzene ring and naphthalene ring with greater rigidity contained in the grafted organic reaction-type modified P-N-Si flame retardant can improve the rigidity of the cable, and the multi-function double bond can construct a three-dimensional network structure with the polyolefin base material, thereby further improving the mechanical properties and high-temperature resistance of the cable.

[0005] The present application aims to provide an environment-friendly halogen-free flame-retardant composite special cable.

[0006] The present application is implemented by the following technical solutions: An environment-friendly halogen-free flame-retardant composite special cable, which comprises, from inside to outside, a conductor, an insulation layer, a glass fiber rope layer and an outer protective sleeve, wherein the insulation layer and the outer protective sleeve are prepared from a modified flame-retardant copolymer, and the modified flame-retardant copolymer comprises, by weight fraction, the following components: linear low-density polyethylene 65-80 parts, ethylene-vinyl acetate copolymer 20-38 parts, modified P-N-Si flame retardant 1 5-10 parts, modified P-N-Si flame retardant 2 3-6 parts, initiator 0.5-1 part, antioxidant 0.2-0.5 part and non-reaction-type flame retardant 25-35 parts.

[0007] In a specific embodiment, the modified P-N-Si flame retardant 1 and the modified P-N-Si flame retardant 2 have structural formulas as shown in Formula 1 and Formula 2, respectively. Formula 1, Formula 2.

[0008] In one specific embodiment, the antioxidant is antioxidant 1010; In one specific embodiment, the initiator is one of dicumyl peroxide, di-tert-butyl peroxide, α,α'-di(tert-butylperoxy)diisopropylbenzene; In one specific embodiment, the preparation of the modified P-N-Si flame retardant 1 comprises the following steps: S1. Under nitrogen, add melamine, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and a base catalyst to a solvent, stir at 120-160 ℃ for 8-14 hours; cool, add ice saturated brine to precipitate, filter, re-precipitate and dry to obtain product A; S2. Under a nitrogen atmosphere, dissolve product A in anhydrous toluene and add dropwise to 1-vinyl-1,1,3,3-tetramethyldisiloxane, then add a base, react at 90-110 ℃ for 16-24 hours; cool, neutralize with acetic acid, distill under reduced pressure, add n-hexane and dissolve at 50-70 ℃, then cool to crystallize, filter and dry to obtain the modified P-N-Si flame retardant 1.

[0009] In one specific embodiment, in step S1, the amount of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is 1.95-2.05 times the molar amount of melamine; the amount of base catalyst is 0.3-1.5 times the molar amount of melamine, and the base catalyst is one of triethylamine, pyridine, and potassium carbonate; the solvent is one of DMF, DMSO, and NMP.

[0010] In one specific embodiment, in step S2, the amount of 1-vinyl-1,1,3,3-tetramethyldisiloxane is 2.02-2.10 times the molar amount of product A; the amount of base is 0.1-0.5 times the molar amount of product A, and the base is triethylamine.

[0011] In one specific embodiment, the preparation of the modified P-N-Si flame retardant 2 comprises the following steps: S1. Under a nitrogen atmosphere, add p-phenylenediamine and binol phosphate to anhydrous THF, add dropwise triethylamine, react at 25-50 ℃ for 4-8 hours; cool, extract, evaporate and concentrate the organic phase; wash the organic phase with dilute acid, concentrate, purify by column chromatography, and dry to obtain product B; S2. Under nitrogen atmosphere, product B is dissolved in anhydrous toluene and slowly added to 1-vinyl-1,1,3,3-tetramethyldisiloxane, then triethylamine is added, and the reaction is carried out at 90-110 ℃ for 16-24 hours; cooling, adding acetic acid for neutralization, distillation under reduced pressure, adding n-hexane and dissolving at 50-70 ℃, then cooling and crystallization, filtering and drying to obtain modified P-N-Si flame retardant 2.

[0012] In a specific embodiment, in step S1, the amount of binaphthol phosphate is 0.9-1 times the molar amount of p-phenylenediamine; the amount of triethylamine is 0.1-0.5 times the molar amount of p-phenylenediamine; the dilute acid is dilute hydrochloric acid with pH<3; In a specific embodiment, in step S2, the amount of 1-vinyl-1,1,3,3-tetramethyldisiloxane is 2.02-2.10 times the molar amount of product B; the amount of triethylamine is 0.1-0.5 times the molar amount of product B.

[0013] In a specific embodiment, the preparation of the non-reactive flame retardant comprises the following steps: A silane coupling agent is taken and diluted with ethanol; a mixture of metal hydroxide and nano inorganic particles is added to a high-speed mixer, and the diluted silane coupling agent solution is added dropwise, and stirred for 10-15 minutes; the mixed filler is transferred to a drying oven at 80-100 ℃ for drying for 2-3 hours, and then cooled, sealed and stored for use, to obtain a non-reactive flame retardant treated with a silane coupling agent.

[0014] In a specific embodiment, the metal hydroxide is one of magnesium hydroxide and aluminum hydroxide; the nano inorganic particles are silicon dioxide or diantimony trioxide; the mass ratio of the metal hydroxide to the nano inorganic particles is (8~9):(1~2); the silane coupling agent is one of KH550, KH560, KH602 and KH858, and the amount is 0.5-2wt% of the total mass of the metal hydroxide and the nano inorganic particles; the amount of ethanol is 1~5 times the volume of the silane coupling agent.

[0015] The application also discloses a preparation method of the environment-friendly halogen-free flame-retardant composite special cable. S1. Linear low-density polyethylene and ethylene-vinyl acetate copolymer are added to a high-speed mixer, and melt blended at 150-170 ℃ and a rotation speed of 300-500 rpm / min for 2-3 minutes; modified P-N-Si flame retardant 1, modified P-N-Si flame retardant 2, antioxidant and non-reactive flame retardant are fully stirred for 3-5 minutes; and finally, an initiator is added for copolymerization for 1-3 minutes, to obtain a modified flame-retardant copolymer; S2. Stirring at 170-190 DEG C for 1-2 minutes, the modified flame-retardant copolymer is coated on the periphery of the conductor, and is cooled and shaped by spraying with normal temperature water under a spraying pressure of 0.2-0.5 MPa for 10-30 s to form an insulation layer with a thickness of 1.5-2 mm; a glass fiber rope is wound behind the insulation layer, the modified flame-retardant copolymer is coated on the periphery of the glass fiber rope layer, and is cooled and shaped by spraying with normal temperature water under a spraying pressure of 0.2-0.5 MPa to form a flame-retardant outer protective jacket with a thickness of 4.5-5 mm, thereby preparing the environment-friendly halogen-free flame-retardant composite special cable.

[0016] Advantages

[0017] The application provides an environment-friendly halogen-free flame-retardant composite special cable, wherein the insulation layer and the outer protective jacket of the environment-friendly halogen-free flame-retardant composite special cable are prepared from a modified flame-retardant copolymer, and the modified flame-retardant copolymer is prepared by melt blending and copolymerization of linear low-density polyethylene, ethylene-vinyl acetate copolymer, modified P-N-Si flame-retardant 1, modified P-N-Si flame-retardant 2, initiator and antioxidant. The base material used in the application is linear low-density polyethylene and ethylene-vinyl acetate copolymer, which is green and environment-friendly. The flame-retardant performance of the cable is improved by using grafted organic reaction-type modified P-N-Si flame-retardant and adding inorganic non-reaction-type flame-retardant. On the one hand, the grafted flame-retardant can avoid migration of the flame-retardant. The P, N and Si elements in the reaction-type modified flame-retardant synergistically act together, the phosphoric acid ester group is decomposed into viscous semi-solid substances to cover on the surface and promote dehydration and carbonization of the outer protective jacket and the insulation layer, so as to isolate oxygen from permeating and heat from transferring. The nitrogen-containing melamine and p-phenylenediamine flame-retardant group are decomposed to release nitrogen, nitrogen oxide and water vapor and other non-combustible gases to dilute the oxygen concentration and take away energy. The 1-ethenyl-1,1,3,3-tetramethyldisiloxane is decomposed or activated to catalyze crosslinking between the molecular chains of the copolymer, so as to promote combustion into carbon instead of volatile combustible substances. On the other hand, the non-reaction-type flame-retardant magnesium hydroxide is used to generate a dense magnesium oxide protective film on the surface of the outer protective jacket and the insulation layer to isolate air from further contacting the outer protective jacket and the insulation layer. Meanwhile, the magnesium hydroxide and the silicon dioxide are used to capture free radicals to reduce the number of free radicals, so as to inhibit the chain reaction of combustion and further improve the flame-retardant performance of the cable. In addition, the grafted organic reaction-type modified P-N-Si flame-retardant contains rigid conjugated benzene ring and naphthalene ring, which can improve the rigidity of the cable, and has multiple functionalities of double bonds, so as to construct a three-dimensional network structure with the polyolefin base material, and further improve the mechanical properties and high-temperature resistance of the cable. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 Synthetic path for preparing modified P-N-Si flame-retardant 1 from product A and modified P-N-Si flame-retardant 2 from product B; Figure 2 Grafting mechanism of modified P-N-Si flame retardant 1 and modified P-N-Si flame retardant 2 as reaction type flame retardants; Figure 3 NMR hydrogen spectrum of modified P-N-Si flame retardant 1; Figure 4 NMR hydrogen spectrum of modified P-N-Si flame retardant 2. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0020] In the embodiments, the experimental methods used are conventional methods, and the materials, reagents, etc. used are commercially available unless otherwise specified.

[0021] The raw materials used in the examples and comparative examples are described as follows: Base catalyst: triethylamine (TEA), 99.5%, purchased from Shanghai Macklin Biochemical Technology Co., Ltd.; P flame-retardant functional component 1: 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 99.7%, purchased from Shanghai Macklin Biochemical Technology Co., Ltd.; P flame-retardant functional component 2: binaphthyl phosphate, 98%, purchased from Shanghai Haohong Biomedical Technology Co., Ltd.; N flame-retardant functional component 1: melamine, 99%, purchased from Shanghai Macklin Biochemical Technology Co., Ltd.; N flame-retardant functional component 2: p-phenylenediamine, 97%, purchased from Shanghai Macklin Biochemical Technology Co., Ltd.; Si flame-retardant functional component: 1-vinyl-1,1,3,3-tetramethyldisiloxane, 97%, purchased from Shanghai Macklin Biochemical Technology Co., Ltd.; Main flame-retardant filler: magnesium hydroxide, 1250 mesh, purchased from Wuhan Jiyesheng Chemical Co., Ltd.; Auxiliary flame-retardant filler: nano-silicon dioxide, product number R033053, purchased from Shanghai Yenn Chemical Technology Co., Ltd.; Linear low-density polyethylene: product number V34068, purchased from Shanghai Yuanye Biotechnology Co., Ltd.; Ethylene-vinyl acetate copolymer: product number R002145, purchased from Shanghai Yenn Chemical Technology Co., Ltd.; Antioxidant: Antioxidant 1010, 94%, purchased from Tianjin Li'anlong New Material Co., Ltd. Silane coupling agent: KH550, 99%, purchased from Shandong Yifike Trading Co., Ltd. Initiator: dicumyl peroxide, purchased from Tianjin Chemical Reagent Factory No. 1; Modified P-N-Si flame retardant 1: self-made, the preparation method is as follows: S1. Preheat melamine and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide in a 90 ℃ oven for 3 hours; under nitrogen conditions, add melamine (1 mole equivalent), 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (1.95 mole equivalents) and triethylamine (1 mole equivalent) to a DMF solution, and stir at 140 ℃ for 14 hours until the reaction is complete; cool, add ice saturated brine to precipitate the precipitate, filter, re-precipitate and dry to obtain product A; S2. Dry product A (1 mole equivalent) and 1-vinyl-1,1,3,3-tetramethyldisiloxane (2.05 mole equivalents) in a 50 ℃ vacuum drying oven for 2 hours, then dissolve product A in anhydrous toluene under a nitrogen atmosphere; slowly add the prepared solution to 1-vinyl-1,1,3,3-tetramethyldisiloxane, then add triethylamine (0.3 mole equivalent), and react at 100 ℃ for 24 hours until the reaction is complete; cool to room temperature, add a small amount of acetic acid to neutralize the basic catalyst; remove the organic phase solvent under reduced pressure, add n-hexane to the remaining material and heat to 60 ℃ to dissolve and slowly cool to precipitate crystals for purification, and finally filter and dry to obtain modified P-N-Si flame retardant 1.

[0022] Modified P-N-Si flame retardant 2: self-made, the preparation method is as follows: S1. Dry p-phenylenediamine (1 mole equivalent) and binaphthyl phosphate (0.92 mole equivalent) in a 100 ℃ vacuum drying oven for 4 hours; under a nitrogen atmosphere, add p-phenylenediamine and binaphthyl phosphate to anhydrous THF and stir to dissolve; slowly add triethylamine (0.3 mole equivalent), heat to 50 ℃ and stir for 8 hours until the reaction is complete; cool, extract, evaporate and concentrate the organic phase; wash the organic phase with dilute hydrochloric acid with pH < 3, concentrate, purify by column chromatography and dry to obtain product B; S2. The product B (1 mole equivalent) and 1-vinyl-1,1,3,3-tetramethyldisiloxane (2.05 mole equivalents) were dried in a vacuum oven at 50°C for 2 hours, and then product B was dissolved in anhydrous toluene under a nitrogen atmosphere; the prepared solution was slowly added dropwise to 1-vinyl-1,1,3,3-tetramethyldisiloxane, and then triethylamine (0.3 mole equivalent) was added, and the reaction was carried out at 100°C for 24 hours; after the reaction was completed, the reaction solution was cooled to room temperature, a small amount of acetic acid was added to neutralize the basic catalyst; the organic phase solvent was removed by distillation under reduced pressure, and then n-hexane was added to the residue and heated to 60°C to dissolve and slowly cool to precipitate crystals for purification, and finally filtration and drying were carried out to obtain the modified P-N-Si flame retardant 2.

[0023] Non-reactive flame retardant: self-made, and the preparation method is as follows: Magnesium hydroxide (80 wt%) was placed in a vacuum drying oven at 100°C for 5 hours, and nano-silicon dioxide (20 wt%) was placed in a vacuum drying oven at 125°C for 3 hours, and then the two were mixed and cooled for standby use; silane coupling agent KH550 (1%) was taken, and 5 times the volume of ethanol was added for dilution; the mixture was added to a high-speed mixer, and the diluted silane coupling agent solution was slowly added dropwise while stirring, and then stirring was continued for 15 minutes; the mixed filler was transferred to a 100°C drying oven and dried for 3 hours, and then cooled and sealed for standby use, thereby obtaining the non-reactive flame retardant after surface treatment of the silane coupling agent.

[0024] The component raw materials used in the embodiments and comparative examples of the present application are all commercially available raw materials unless otherwise specified, and the component raw materials used in each parallel experiment are all the same.

[0025] Examples and comparative examples An environmentally friendly halogen-free flame-retardant composite special cable, and the weight formula is shown in Table 1, and the preparation method is as follows: S1. Linear low-density polyethylene and ethylene-vinyl acetate copolymer were added to a high-speed mixer, and melt blending was carried out at 160°C and a rotation speed of 500 rpm / min for 3 minutes; modified P-N-Si flame retardant 1, modified P-N-Si flame retardant 2, antioxidant, and non-reactive flame retardant were added, and stirring was carried out for 4 minutes; finally, an initiator was added, and copolymerization was carried out for 3 minutes, thereby obtaining a modified flame-retardant copolymer; S2. The temperature was increased to 190°C, and stirring was carried out for 1 minute; the modified flame-retardant copolymer was wrapped around the conductor, and was cooled and shaped by spraying with normal temperature water under a spraying pressure of 0.3 MPa for 30 seconds, thereby forming an insulation layer; the thickness was 1.5-2 mm; a glass fiber rope was wound behind the insulation layer, and the modified flame-retardant copolymer was wrapped around the glass fiber rope and was cooled and shaped by spraying with normal temperature water under a spraying pressure of 0.3 MPa, thereby forming a flame-retardant outer protective sleeve; the thickness was 4.5-5 mm, thereby obtaining an environmentally friendly halogen-free flame-retardant composite special cable.

[0026] The modified flame-retardant copolymer in the environmentally friendly halogen-free flame-retardant composite special cable was extruded by an extruder to form a 20*20*0.3 cm sheet, and a vertical pressure of 1.2 MPa was applied, and the sheet was demolded by spray cooling to prepare a sheet of outer protective sleeve and insulation layer for subsequent performance testing.

[0027] Table 1 Environmentally friendly halogen-free flame-retardant composite special cable (weight parts)

[0028] The sheets of outer protective sleeve and insulation layer in the composite special cables prepared in the examples and comparative examples were subjected to the following performance tests, and the results are shown in Figure 3 , 4 and Table 2.

[0029] 1. Nuclear magnetic resonance hydrogen spectrum: The synthesized modified P-N-Si flame retardant 1 and modified P-N-Si flame retardant 2 samples were dissolved in deuterated DMSO to prepare a solution with a concentration of 1.0 wt%, and the nuclear magnetic spectrum of the sample was determined by a nuclear magnetic resonance hydrogen spectrometer, with a test condition of 400 MHz, and the results are shown in Figure 3 and Figure 4 . Figure 3 The integral of twice the modified P-N-Si flame retardant 1 is consistent with the number of hydrogens, Figure 3 the integral number is consistent with the modified P-N-Si flame retardant 2, and the position of H corresponds to its chemical environment, indicating that the modified P-N-Si flame retardant 1 and the modified P-N-Si flame retardant 2 are successfully synthesized.

[0030] 2. Tensile strength and elongation at break: According to GB / T 2951.11-2008 “General test methods for cable and optical cable insulation and sheath materials”, the sheet was cut into a 20*20*0.05 cm size, and a universal testing machine was used to detect the tensile strength and breaking tensile properties of the outer protective sleeve and insulation layer.

[0031] 3. Limiting oxygen index (LOI): According to GB / T2406-2008 standard, the sheet with a length size of 10 cm*0.65 cm*0.3 cm was cut and tested on an oxygen index tester.

[0032] 4. High temperature resistance: The sheet was heated from 25 ℃ to 800 ℃ at a rate of 10 ℃ / min by a thermal gravimetric analyzer, and the percentage of residual weight to original weight was calculated to evaluate the high temperature resistance.

[0033] 5. Vertical combustion test: according to GB / T 8332-2008 "Foamed plastic combustion performance test method Horizontal burning method" test method, the sheet is cut into a sample of 10 cm*1.3 cm*0.3 cm for experiment. The bottom end of the sample strip is placed 1 cm above the center of the flame, the flame is removed immediately after the sample strip is ignited for 10 s, and the afterflame extinguishing time t1 is recorded; repeat the operation, record the second extinguishing time t2, test 5 times for each sample; according to the ratio of t1 and t2, judge the UL-94 grade, V-0: single sample strip (t1 / t2)≤10 s, all sample strips t1+t2≤50 s, indicating that the sample is not burnt out, and the molten droplets do not ignite the cotton; V-1: single sample strip (t1 / t2)≤30 s, all sample strips t1+t2≤250 s, indicating that the sample is not burnt out, and the molten droplets do not ignite the cotton; V-2: single sample strip (t1 / t2)≤30 s, all samples t1+t2≤250 s, indicating that the sample is not burnt out, and the molten droplets ignite the cotton.

[0034] Table 2 Performance test results of the sheet of the outer protective sleeve and the insulating layer in the composite special cable

[0035] From Table 2, Examples 1-6 and Comparative Example 4, it can be seen that the grafting of the rigid modified P-N-Si flame retardant 1, modified P-N-Si flame retardant 2 in polyethylene and ethylene vinyl acetate copolymer greatly improves the mechanical properties of the cable outer protective jacket and insulation layer, and improves the wear resistance of the cable outer protective jacket and insulation layer. In addition, the addition of non-reactive flame retardant and grafting of reactive modified flame retardant together endows the material with excellent flame retardant performance. On the one hand, the synergistic effect of P, N and Si elements in the reactive modified flame retardant, the use of phosphate groups to burn and decompose viscous semi-solid substances to cover the surface and promote the dehydration and carbonization of the cable outer protective jacket and insulation layer, to isolate the penetration of oxygen and heat transfer; the use of nitrogen-containing melamine and p-phenylenediamine flame retardant groups to release nitrogen, nitrogen oxides and water vapor and other non-combustible gases to dilute the oxygen concentration and take away energy through decomposition; the use of 1-ethenyl-1,1,3,3-tetramethyldisiloxane to decompose or activate and then catalyze the crosslinking between the molecular chains of the copolymer to promote the combustion to form carbon rather than volatile combustible substances. On the other hand, the use of non-reactive flame retardant magnesium hydroxide to generate a dense magnesium oxide protective film on the surface of the outer protective jacket and insulation layer to isolate air and further contact of the outer protective jacket and insulation layer, while using the free radical capturing properties of magnesium hydroxide and silicon dioxide to reduce the number of free radicals to inhibit the chain reaction of combustion, further improving the flame retardant performance of the cable, with a limiting oxygen index of 36 or more and a vertical burning rating of V-0. In Comparative Examples 1-2 and Comparative Example 4, only one type of reactive flame retardant is grafted or only non-reactive flame retardant is added, and due to the reduced content of flame retardant groups, the flame retardant performance is poor. In Comparative Example 3, two types of reactive flame retardants are grafted, and even without the addition of non-reactive flame retardant, the flame retardant performance is relatively low.

[0036] From the examples, it can be seen that the organic reactive modified P-N-Si flame retardant containing rigid conjugated benzene rings and naphthalene rings can improve the rigidity of the cable, and has multiple functionality double bonds to construct a three-dimensional network structure with the polyolefin base material, so that the cable prepared by the present application has good high temperature resistance, and after sufficient combustion at 800°C, it still maintains a residual amount of 30% or more, which can be applied in high temperature working environment.

[0037] The preferred embodiments of the present application disclosed above are only used to help explain the present application. The preferred embodiments do not describe all the details and limit the present application to the specific embodiments described. Obviously, many modifications and changes can be made according to the content of the present application. The present application selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present application, so that those skilled in the art can well understand and utilize the present application. The present application is limited only by the claims and their entire scope and equivalents.

Claims

1. An environmentally friendly halogen-free flame-retardant composite special cable, characterized in that, The special cable sequentially comprises a conductor, an insulation layer, a glass fiber rope layer and an outer protective sleeve from inside to outside, the insulation layer and the outer protective sleeve are prepared from a modified flame-retardant copolymer, the modified flame-retardant copolymer comprises the following components in parts by weight: linear low-density polyethylene 65-80 parts, ethylene-vinyl acetate copolymer 20-38 parts, modified P-N-Si flame retardant 1 5-10 parts, modified P-N-Si flame retardant 2 3-6 parts, initiator 0.5-1 part, antioxidant 0.2-0.5 part and non-reactive flame retardant 25-35 parts.

2. An environmentally friendly halogen-free flame-retardant composite special cable according to claim 1, characterized in that, The structural formulae of the modified P-N-Si flame retardant 1 and the modified P-N-Si flame retardant 2 are shown in formula 1 and formula 2 respectively. Formula 1, Formula 2.

3. An environment-friendly halogen-free flame-retardant composite special cable according to claim 1, characterized in that, The preparation of the modified P-N-Si flame retardant 1 comprises the following steps: S1. Under the condition of nitrogen, melamine, 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and an alkali catalyst are added to a solvent, and stirred at 120-160 ℃ for 8-14 hours; after cooling, ice saturated brine is added to precipitate a precipitate, which is filtered, re-precipitated and dried to obtain product A; S2. Under the condition of nitrogen, product A is dissolved in anhydrous toluene and slowly added to 1-vinyl-1, 1, 3, 3-tetramethyldisiloxane, and then an alkali is added, and reacted at 90-110 ℃ for 16-24 hours; after cooling, acetic acid is added for neutralization, and then distilled under reduced pressure, and then n-hexane is added and dissolved at 50-70 ℃, and then cooled and crystallized, filtered and dried to obtain the modified P-N-Si flame retardant 1.

4. An environment-friendly halogen-free flame-retardant composite special cable according to claim 3, characterized in that, In step S1, the amount of 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is 1.95-2.05 times the molar amount of melamine; the alkali catalyst is one of triethylamine, pyridine and potassium carbonate, and the amount is 0.3-1.5 times the molar amount of melamine; the solvent is one of DMF, DMSO and NMP; in step S2, the amount of 1-vinyl-1, 1, 3, 3-tetramethyldisiloxane is 2.02-2.10 times the molar amount of product A; and the alkali is triethylamine, and the amount is 0.1-0.5 times the molar amount of product A.

5. An environment-friendly halogen-free flame-retardant composite special cable according to claim 1, characterized in that, The preparation of the modified P-N-Si flame retardant 2 comprises the following steps: S1. Under the condition of nitrogen, p-phenylenediamine and binaphthyl phosphate are added to anhydrous THF, and then triethylamine is added dropwise, and reacted at 25-50 ℃ for 4-8 hours; after cooling, the organic phase is extracted, evaporated and concentrated; the organic phase is washed with dilute acid, concentrated, purified by column chromatography and dried to obtain product B; S2. Under the condition of nitrogen, product B is dissolved in anhydrous toluene and slowly added to 1-vinyl-1, 1, 3, 3-tetramethyldisiloxane, and then triethylamine is added, and reacted at 90-110 ℃ for 16-24 hours; after cooling, acetic acid is added for neutralization, and then distilled under reduced pressure, and then n-hexane is added and dissolved at 50-70 ℃, and then cooled and crystallized, filtered and dried to obtain the modified P-N-Si flame retardant 2.

6. An environment-friendly halogen-free flame-retardant composite special cable according to claim 5, characterized in that, The amount of the binaphthol phosphate in the step S1 is 0.9-1 times of the molar amount of p-phenylenediamine; the amount of the triethylamine is 0.1-0.5 times of the molar amount of p-phenylenediamine; the dilute acid is dilute hydrochloric acid with pH<3; in the step S2, the amount of 1-vinyl-1,1,3,3-tetramethyldisiloxane is 2.02-2.10 times of the molar amount of the product B; the amount of the triethylamine is 0.1-0.5 times of the molar amount of the product B.

7. An environment-friendly halogen-free flame-retardant composite special cable according to claim 1, characterized in that, The preparation of the non-reactive flame retardant comprises the following steps: The silane coupling agent is diluted with ethanol; the mixture of the metal hydroxide and the nano inorganic particles is added into a high-speed mixer, and the diluted silane coupling agent solution is added dropwise, and stirred for 10-15 minutes; the mixed filler is transferred into a drying box at 80-100 ℃ and dried for 2-3 hours, and then cooled and sealed for storage, to obtain the non-reactive flame retardant treated by the silane coupling agent.

8. An environment-friendly halogen-free flame-retardant composite special cable according to claim 7, characterized in that, The metal hydroxide is one of magnesium hydroxide and aluminum hydroxide; the nano inorganic particle is silicon dioxide or diantimony trioxide; the mass ratio of the metal hydroxide to the nano inorganic particle is 8:2-9:1; the silane coupling agent is one of KH550, KH560, KH602 and KH858, and the amount is 0.5-2wt% of the total mass of the metal hydroxide and the nano inorganic particle; the amount of the ethanol is 1-5 times of the volume of the silane coupling agent.

9. An environment-friendly halogen-free flame-retardant composite special cable according to claim 1, characterized in that, The antioxidant is antioxidant 1010; the initiator is one of dicumyl peroxide, di-tert-butyl peroxide and α,α'-di(tert-butylperoxy)diisopropylbenzene.

10. The preparation method of the environmentally friendly halogen-free flame-retardant composite special cable according to any one of claims 1-9, characterized in that, The method comprises the following steps: S1. Linear low-density polyethylene and ethylene-vinyl acetate copolymer are added into a high-speed mixer, and melt-blended at 150-170 ℃ and a rotation speed of 300-500 rpm / min for 2-3 minutes; modified P-N-Si flame retardant 1, modified P-N-Si flame retardant 2, antioxidant, non-reactive flame retardant are added and stirred for 3-5 minutes; finally, initiator is added and copolymerized for 1-3 minutes, to obtain a modified flame-retardant copolymer; S2. The temperature is increased to 170-190 ℃, and the modified flame-retardant copolymer is stirred for 1-2 minutes; the modified flame-retardant copolymer is coated around the conductor, and is cooled and shaped by spraying with normal-temperature water under a spraying pressure of 0.2-0.5 MPa for 10-30 seconds to form an insulation layer with a thickness of 1.5-2 mm; a glass fiber rope is wound behind the insulation layer, and the modified flame-retardant copolymer is coated around the glass fiber rope layer and is cooled and shaped by spraying with normal-temperature water under a spraying pressure of 0.2-0.5 MPa to form a flame-retardant outer protective jacket with a thickness of 4.5-5 mm, to prepare an environmentally-friendly halogen-free flame-retardant composite special cable.

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