Medium-voltage fireproof cable and preparation method thereof

Abstract

The invention discloses a medium-voltage fireproof cable and a preparation method thereof, and relates to the technical field of cables. When the medium-voltage fireproof cable is prepared, the mica-based fireproof layer is coated on the surface of the conductor, the copper protection layer is coated on the surface of the mica-based fireproof layer, and the protection sleeve is coated on the surface of the copper protection layer; the protective sleeve is prepared from modified polyethylene, modified silicon dioxide, a catalyst, a plasticizer and a lubricant; the modified polyethylene is prepared by the following steps: grafting maleic anhydride grafted polyethylene with 3-amino-1-phenyl-2-pyrazoline-5-ketone, reacting with diazonium salt, and reacting with allylboronic acid; the modified silicon dioxide is obtained by polymerizing p-hydroxystyrene on the surface of silicon dioxide modified by vinyltrimethoxysilane, then reacting with 3, 4-dinitrophenol, reducing, then reacting with 2-((2-nitrobenzyl) thio) ethylamine, and then deprotecting. The medium-voltage fireproof cable prepared by the invention has good fire resistance and aging resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of cables, in particular to a medium-voltage fireproof cable and a preparation method thereof. Background Art

[0002] With the acceleration of urbanization, power cables, as the core carriers of energy transmission, need to traverse densely populated areas and densely populated buildings. These cables face multiple challenges due to long-term exposure to complex natural environments and external forces. On the one hand, environmental factors such as high temperature, humidity, and ultraviolet radiation can easily cause cable sheaths to age and become brittle. Traditional flame retardants migrate and fall off under the long-term effects of heat and oxygen, causing fire resistance to significantly degrade over time. On the other hand, frequent bending of cables during installation and use can easily cause microcracks in the sheath and copper protective layer. Furthermore, long-term ultraviolet exposure can cause molecular chain breakage in the sheath, leading to a sharp drop in anti-aging properties. This leads to insufficient mechanical strength in the sheath, resulting in stress concentration and rupture at the bends, which accelerates the spread of flames. Therefore, it is crucial to develop fire-resistant cables that combine high fire resistance with long-term resistance to UV aging. Summary of the Invention

[0003] The object of the present invention is to provide a medium voltage fireproof cable and a preparation method thereof, so as to solve the problems existing in the prior art.

[0004] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0005] A method for preparing a medium-voltage fireproof cable comprises coating a mica-based fireproof layer on the surface of a conductor, coating a copper protective layer on the surface of the mica-based fireproof layer, and coating a protective sheath on the surface of the copper protective layer.

[0006] As an optimization, the protective cover is prepared from modified polyethylene, modified silica, a catalyst, a plasticizer, and a lubricant.

[0007] As an optimization, the modified polyethylene is obtained by grafting maleic anhydride-grafted polyethylene with 3-amino-1-phenyl-2-pyrazolidine-5-one, reacting with a diazonium salt, and then reacting with allylboric acid.

[0008] As an optimization, the modified silica is obtained by polymerizing p-hydroxystyrene on the surface of vinyltrimethoxysilane-modified silica, reacting with 3,4-dinitrophenol, reducing it, reacting it with 2-((2-nitrobenzyl)thio)ethylamine, and then deprotecting it.

[0009] As an optimization, the preparation method of the protective cover is:

[0010] (1) Dissolving dicumyl peroxide in styrene, mixing it with polyethylene and maleic anhydride in a high-speed mixer, and then extruding it in a twin-screw extruder to obtain maleic anhydride-grafted polyethylene; reacting the maleic anhydride-grafted polyethylene with 3-amino-1-phenyl-2-pyrazol-5-one to obtain pretreated polyethylene;

[0011] (2) 4-chloro-2-nitroaniline, pure water, 2 mol / L hydrochloric acid, and sodium nitrite are reacted to obtain diazonium salt; after the pretreated polyethylene and diazonium salt are reacted, thiourea dioxide is added to obtain pre-modified polyethylene;

[0012] (3) Pre-modified polyethylene, allylboric acid, solvent, tetrakis(triphenylphosphine)palladium, potassium carbonate, and tetrabutylammonium bromide were mixed, heated to 85-90°C for reaction for 10-12 hours, precipitated with 0-5°C ethanol, filtered, washed, and dried to obtain modified polyethylene;

[0013] (4) reacting silica and vinyltrimethoxysilane to obtain vinyl silica; reacting vinyl silica and p-hydroxystyrene to obtain pretreated silica; reacting pretreated silica, phosphorus oxychloride, and 3,4-dinitrophenol to obtain pre-modified silica;

[0014] (5) reacting pre-modified silica, thiourea dioxide, and sodium bicarbonate to obtain amino silica; reacting amino silica, glyoxal, and 2-((2-nitrobenzyl)thio)ethylamine to obtain a modified silica precursor, and irradiating the modified silica precursor with light to obtain modified silica;

[0015] (6) Modified polyethylene, modified silica, catalyst, plasticizer and lubricant are added into a high-speed mixer in a mass ratio of 1:(0.05-0.07):(0.001-0.002):(0.01-0.02):(0.01-0.02) and mixed, and then transferred to a twin-screw extruder for extrusion to obtain a protective sleeve; the mixing temperature is 80-90°C, the screw speed of the twin-screw extruder is 150r / min, and the heating temperatures of each section of the extruder are: 180°C, 190°C, 200°C, 200°C, 200°C, 200°C, 190°C.

[0016] As an optimization, the mass ratio of polyethylene, maleic anhydride, benzoyl peroxide, and styrene in step (1) is 1:(0.2-0.3):(0.001-0.002):(0.01-0.02), the screw speed of the twin-screw extruder is 150 r / min, and the heating temperatures of each section of the extruder are 180°C, 190°C, 200°C, 200°C, 200°C, 200°C, 200°C, and 190°C; the polyethylene model is HE3490-LS; the mass ratio of the maleic anhydride-grafted polyethylene, 3-amino-1-phenyl-2-pyrazol-5-one, dimethylaminopyridine, and xylene is 1:(0.3-0.5):(0.5-0.7):(10-12).

[0017] As an optimization, the preparation method of the pre-modified polyethylene in step (2) is as follows: 4-chloro-2-nitroaniline, pure water, and 2 mol / L hydrochloric acid are mixed in a mass ratio of 1: (25-30): (12-15), cooled to 0-5°C, 0.15 g / mL sodium nitrite aqueous solution of 5-6 times the mass of 4-chloro-2-nitroaniline is added, stirring is continued for 40-50 minutes, and the mixture is stored in the dark at 0-5°C to obtain diazonium salt; the pre-treated polyethylene, pure water, and dispersant are mixed at 50°C for 10-20 minutes, cooled to 10-15°C, and heated at 1 mL / min. n, add diazonium salt at a rate of 1:1, add sodium lauryl sulfate after the addition is completed, react for 2-3 hours, heat to 80-85°C, add thiourea dioxide in four times, with an interval of 30 minutes between each addition, continue to react for 2-3 hours after the addition is completed, cool to 5-10°C, filter, wash, and dry to obtain pre-modified polyethylene; the mass ratio of pretreated polyethylene, pure water, dispersant, diazonium salt, sodium lauryl sulfate, and thiourea dioxide is 1:(10-12):(0.05-0.07):(55-65):(0.01-0.02):(0.5-0.7).

[0018] As an optimization, the mass ratio of the pre-modified polyethylene, allylboric acid, solvent, tetrakis(triphenylphosphine)palladium, potassium carbonate, and tetrabutylammonium bromide in step (3) is 1:(1.3-1.5):(20-30):0.01:(0.5-0.7):(0.02-0.03); the solvent is a mixture of toluene and N,N-dimethylformamide in a volume ratio of 3:1.

[0019] As an optimization, the preparation method of the pre-modified silica in step (4) is as follows: silica, vinyl trimethoxysilane, anhydrous ethanol and pure water are mixed in a mass ratio of 1: (2-3): (10-12): (10-12), hydrochloric acid is used to adjust the pH to 4, the temperature is raised to 70-80 ° C and the reaction is carried out for 7-8 hours, and the vinyl silica is obtained by filtering, washing and drying; vinyl silica, p-hydroxystyrene, N, N-dimethylformamide and azobisisobutyronitrile are mixed in a mass ratio of 1: (2-3): (20-30): (0.01-0.02), the temperature is raised to 75-85 ° C and the reaction is carried out for 5-6 hours, and the pre-treated silica is obtained by filtering, washing and drying; the pre-treated silica, tetrahydrofuran, phosphorus oxychloride and pyridine are stirred at 0-5 ° C for 2-3 hours. After the stirring is completed, the mixture is filtered and dispersed to 0.2 g / mL. Lithium chloride is added to a 3,4-dinitrophenol-tetrahydrofuran solution, the temperature is raised to 50-60°C, the reaction is carried out under nitrogen protection for 10-12 hours, and the solution is filtered, washed, and dried to obtain pre-modified silica; the mass ratio of pretreated silica, tetrahydrofuran, phosphorus oxychloride, pyridine, 3,4-dinitrophenol, and lithium chloride is 1:(20-30):(1-2):(1-2):(2-3):(0.03-0.05).

[0020] As an optimization, the preparation method of the modified silica in step (5) is as follows: pre-modified silica, thiourea dioxide, and 10 wt% sodium bicarbonate aqueous solution are mixed in a mass ratio of 1: (0.5-0.7): (20-30), heated to 70-80 ° C, reacted for 5-6 hours, filtered, washed, and dried to obtain amino silica; amino silica, glyoxal, and phosphate buffer with a pH of 7.4 are mixed in a mass ratio of 1: (2-3): (20-30 ) was stirred at room temperature for 2-3 hours, filtered and added to a 0.2 g / mL 2-((2-nitrobenzyl)thio)ethylamine-acetonitrile solution, wherein the mass of 2-((2-nitrobenzyl)thio)ethylamine is 2-3 times that of aminosilica, and the reaction was carried out in the dark under nitrogen protection for 10-12 hours, and the modified silica precursor was obtained by filtration, washing and drying. The modified silica precursor was placed in a quartz reactor and irradiated under a 365 nm ultraviolet light source with a power of 50 mW / cm 2 , irradiate at 0-5℃ for 30-40min, and then wash and dry to obtain modified silica.

[0021] As an optimization, the preparation method of the 2-((2-nitrobenzyl)thio)ethylamine is as follows: lithium hydroxide, pure water, ethanol, and cysteamine hydrochloride are mixed in a mass ratio of 1:20:50:3 to obtain a mixed solution, 2-nitrobenzyl bromide (4.6 times the mass of lithium hydroxide) and ethanol are mixed in a mass ratio of 1:20 to obtain a 2-nitrobenzyl bromide solution, and the 2-nitrobenzyl bromide solution is added dropwise to the mixed solution at a rate of 1 mL / min. After the addition is completed, the mixture is stirred at 30-35° C. for 40 minutes, extracted with dichloromethane, dried over anhydrous sodium sulfate, filtered and concentrated to obtain 2-((2-nitrobenzyl)thio)ethylamine.

[0022] The present invention also provides a medium-voltage fireproof cable prepared according to the above-mentioned method for preparing the medium-voltage fireproof cable.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] When preparing a medium-voltage fireproof cable, the present invention comprises the following steps: coating a mica-based fireproof layer on the surface of a conductor, coating a copper protective layer on the surface of the mica-based fireproof layer, and coating a protective sleeve on the surface of the copper protective layer; the protective sleeve is prepared from modified polyethylene, modified silica, a catalyst, a plasticizer, and a lubricant; the modified polyethylene is prepared by grafting 3-amino-1-phenyl-2-pyrazolidine-5-one onto polyethylene grafted with maleic anhydride, reacting the polyethylene with a diazonium salt, and then reacting the polyethylene with allylboronic acid; and the modified silica is prepared by polymerizing p-hydroxystyrene on the surface of silica modified with vinyltrimethoxysilane, reacting the polystyrene with 3,4-dinitrophenol, reducing the polystyrene, reacting the polystyrene with 2-((2-nitrobenzyl)thio)ethylamine, and then deprotecting the polystyrene.

[0025] First, maleic anhydride is grafted onto polyethylene via a melt grafting method. 3-amino-1-phenyl-2-pyrazolin-5-one is then grafted via a reaction between the anhydride and amino groups. 4-chloro-2-nitroaniline is then prepared as a diazonium salt, which undergoes a coupling reaction with the active hydrogen on 3-amino-1-phenyl-2-pyrazolin-5-one. This is then reduced and cyclized with a reducing agent to form a benzotriazole ring. The structure connecting the nitrogen heterocycle and the benzotriazole stabilizes the ground state structure through intramolecular hydrogen bonding, dissipates energy through excited-state proton transfer, and enhances absorption properties through N-heterocycle conjugation, giving the material excellent light aging resistance. A double bond is then introduced through a Suzuki coupling reaction between the chlorine on the 4-chloro-2-nitroaniline and allylboronic acid.

[0026] The structure of the nitrogen heterocycle and benzotriazole connected together and the schematic diagram of the ultraviolet absorption principle of the structure are as follows: the structure has two tautomers, the enol form and the keto form;

[0027]

[0028] Secondly, in the presence of an initiator, p-hydroxystyrene polymerizes on the surface of vinyltrimethoxysilane-modified silica, modifying the silica surface with phenolic hydroxyl groups. A phosphate structure with excellent flame retardant properties is then generated through an ester exchange reaction between 3,4-dinitrophenol and phosphorus oxychloride. The nitro group on the 3,4-dinitrophenol is then reduced to an amino group, and glutaraldehyde is used as a cross-linking agent to generate a Schiff base structure, which is then grafted with 2-((2-nitrobenzyl)thio)ethylamine. The o-nitrobenzyl structure on the 2-((2-nitrobenzyl)thio)ethylamine can be removed under light, thereby releasing a thiol group.

[0029] Finally, the modified polyethylene, modified silica, etc. are mixed and melt-extruded to prepare a protective cover, which is then coated on the copper protective layer. During the melt extrusion process, the double bonds on the modified polyethylene side chains and the thiol groups on the modified silica are cross-linked through a click reaction to form sulfide. In the presence of a catalyst, the double bonds will also self-polymerize to form a more complex cross-linked network, thereby enhancing the mechanical properties of the protective cover material. During the modification process, the nitrogen heterocycle, phosphate, and Schiff base structures of the polyethylene side chains have good complexing ability for metals, and can form a dense protective layer on the copper protective layer to protect the internal copper protective layer from corrosion. During the modification process, the introduction of nitrogen, phosphorus, and sulfur elements can also synergistically flame retardant, further improving the flame retardant properties of the material. DETAILED DESCRIPTION

[0030] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0031] In the following examples and comparative examples, the polyethylene model is HE3490-LS; the dispersant is polyvinyl alcohol; the plasticizer is dioctyl adipate; the lubricant is vinyl bisstearamide; the silica particle size is 200 nm; the conductor is annealed copper, purchased from Nanyuan Copper (Dongguan) Co., Ltd.; the mica-based refractory layer is a mica tape, purchased from Yangzhou Huidong Cable Materials Co., Ltd., with a thickness of 0.2 mm; the copper protective layer is an annealed soft copper tape, purchased from Shandong Xinyihua Copper Co., Ltd.

[0032] Example 1:

[0033] A method for preparing a medium-voltage fireproof cable, comprising the following steps: coating a mica-based fireproof layer on the surface of a conductor, coating a copper protective layer on the surface of the mica-based fireproof layer, and coating a protective sheath on the surface of the copper protective layer; the protective sheath is prepared by:

[0034] (1) After dissolving dicumyl peroxide in styrene, the mixture was mixed with polyethylene and maleic anhydride in a high-speed mixer, and then extruded in a twin-screw extruder to obtain maleic anhydride grafted polyethylene; the mass ratio of polyethylene, maleic anhydride, benzoyl peroxide, and styrene was 1:0.2:0.001:0.01, the screw speed of the twin-screw extruder was 150 r / min, and the heating temperatures of each section of the extruder were 180°C, 190°C, 200°C, 200°C, 200°C, 200°C, 200°C, and 190°C; maleic anhydride grafted polyethylene, 3-amino-1-phenyl-2-pyrazol-5-one, dimethylaminopyridine, and xylene were mixed in a mass ratio of 1:0.3:0.5:10, and reacted at 110°C for 8 hours to obtain pretreated polyethylene;

[0035] (2) 4-chloro-2-nitroaniline, pure water, and 2 mol / L hydrochloric acid were mixed in a mass ratio of 1:25:12, cooled to 5°C, and 0.15 g / mL sodium nitrite aqueous solution (5 times the mass of 4-chloro-2-nitroaniline) was added, and the mixture was stirred for 50 min. The mixture was stored at 5°C in the dark to obtain diazonium salt. Pretreated polyethylene, pure water, and dispersant were mixed at 50°C for 20 min, cooled to 15°C, and diazonium salt was added at a rate of 1 mL / min. After the addition was completed, sodium lauryl sulfate was added, and the mixture was reacted for 3 h. The mixture was heated to 85°C, and thiourea dioxide was added four times with an interval of 30 min each time. After the addition was completed, the mixture was reacted for 3 h. The mixture was cooled to 10°C, filtered, washed, and dried to obtain pre-modified polyethylene. The mass ratio of pretreated polyethylene, pure water, dispersant, diazonium salt, sodium lauryl sulfate, and thiourea dioxide was 1:10:0.05:55:0.01:0.5.

[0036] (3) Pre-modified polyethylene, allyl boronic acid, solvent, catalyst, potassium carbonate, and tetrabutylammonium bromide were mixed, heated to 90°C for reaction for 12 hours, precipitated with ethanol at 5°C, filtered, washed, and dried to obtain modified polyethylene; the mass ratio of pre-modified polyethylene, allyl boronic acid, solvent, tetrakistriphenylphosphine palladium, potassium carbonate, and tetrabutylammonium bromide was 1:1.3:20:0.01:0.5:0.02; the solvent was a mixture of toluene and N,N-dimethylformamide in a volume ratio of 3:1;

[0037] (4) Silica, vinyltrimethoxysilane, anhydrous ethanol and pure water were mixed in a mass ratio of 1:2:10:10, and the pH was adjusted to 4 with hydrochloric acid. The mixture was heated to 80°C and reacted for 8 hours. The mixture was filtered, washed and dried to obtain vinyl silica. Vinyl silica, p-hydroxystyrene, N,N-dimethylformamide and azobisisobutyronitrile were mixed in a mass ratio of 1:2:20:0.01, and the mixture was heated to 85°C and reacted for 6 hours. The mixture was filtered, washed and dried to obtain pretreated silica. The pretreated silica, tetrahydrofuran, phosphorus oxychloride and pyridine were stirred at 5°C for 3 hours. After the stirring was completed, the mixture was filtered and dispersed to 0.2 g / mL. Lithium chloride was added to a 3,4-dinitrophenol-tetrahydrofuran solution, the temperature was raised to 60°C, and the mixture was reacted under nitrogen for 12 hours. The mixture was filtered, washed, and dried to obtain pre-modified silica. The mass ratio of pre-treated silica, tetrahydrofuran, phosphorus oxychloride, pyridine, 3,4-dinitrophenol, and lithium chloride was 1:20:1:1:2:0.03.

[0038] (5) Pre-modified silica, thiourea dioxide, and 10 wt% sodium bicarbonate aqueous solution were mixed in a mass ratio of 1:0.5:20, heated to 80 ° C, reacted for 6 hours, filtered, washed, and dried to obtain amino silica; lithium hydroxide, pure water, ethanol, and cysteamine hydrochloride were mixed in a mass ratio of 1:20:50:3 to obtain a mixed solution, 2-nitrobenzyl bromide (4.6 times the mass of lithium hydroxide) and ethanol were mixed in a mass ratio of 1:20 to obtain a 2-nitrobenzyl bromide solution, and the 2-nitrobenzyl bromide solution was added dropwise to the mixed solution at a rate of 1 mL / min. After the addition was completed, the mixture was stirred at 35 ° C for 40 minutes, extracted with dichloromethane, and dried. The mixture was dried over sodium sulfate, filtered and concentrated to obtain 2-((2-nitrobenzyl)thio)ethylamine; aminosilica, glyoxal, and phosphate buffer with a pH of 7.4 were stirred at room temperature for 3 hours in a mass ratio of 1:2:20, filtered and added to a 0.2 g / mL 2-((2-nitrobenzyl)thio)ethylamine-acetonitrile solution, wherein the mass of 2-((2-nitrobenzyl)thio)ethylamine is twice that of aminosilica, and the mixture was reacted in the dark under nitrogen protection for 12 hours. The modified silica precursor was filtered, washed, and dried to obtain the modified silica precursor, which was placed in a quartz reactor and irradiated under a 365 nm ultraviolet light source with a power of 50 mW / cm 2 , irradiating at 5°C for 40 min, washing and drying to obtain modified silica;

[0039] (6) Modified polyethylene, modified silica, benzoyl peroxide, plasticizer, and lubricant were added into a high-speed mixer at a mass ratio of 1:0.05:0.001:0.01:0.01 for mixing, and then transferred to a twin-screw extruder for extrusion to obtain a protective sleeve; the mixing temperature was 90°C, the screw speed of the twin-screw extruder was 150 r / min, and the heating temperatures of each section of the extruder were: 180°C, 190°C, 200°C, 200°C, 200°C, 200°C, 190°C.

[0040] Example 2:

[0041] A method for preparing a medium-voltage fireproof cable, comprising the following steps: coating a mica-based fireproof layer on the surface of a conductor, coating a copper protective layer on the surface of the mica-based fireproof layer, and coating a protective sheath on the surface of the copper protective layer; the protective sheath is prepared by:

[0042] (1) After dissolving dicumyl peroxide in styrene, the mixture was mixed with polyethylene and maleic anhydride in a high-speed mixer, and then extruded in a twin-screw extruder to obtain maleic anhydride grafted polyethylene; the mass ratio of polyethylene, maleic anhydride, benzoyl peroxide, and styrene was 1:0.25:0.001:0.015, the screw speed of the twin-screw extruder was 150 r / min, and the heating temperatures of each section of the extruder were 180°C, 190°C, 200°C, 200°C, 200°C, 200°C, 200°C, and 190°C; maleic anhydride grafted polyethylene, 3-amino-1-phenyl-2-pyrazol-5-one, dimethylaminopyridine, and xylene were mixed in a mass ratio of 1:0.4:0.6:11, and reacted at 105°C for 7 hours to obtain pretreated polyethylene;

[0043] (2) 4-chloro-2-nitroaniline, pure water, and 2 mol / L hydrochloric acid were mixed in a mass ratio of 1:27:13, cooled to 3°C, and a 0.15 g / mL sodium nitrite aqueous solution (5.5 times the mass of 4-chloro-2-nitroaniline) was added. The mixture was stirred for 45 min and stored at 3°C ​​in the dark to obtain diazonium salt. Pretreated polyethylene, pure water, and dispersant were mixed at 50°C for 15 min, cooled to 12°C, and diazonium salt was added at a rate of 1 mL / min. After the addition was completed, sodium lauryl sulfate was added. The mixture was reacted for 2.5 h, heated to 85°C, and thiourea dioxide was added four times with an interval of 30 min each time. After the addition was completed, the mixture was reacted for 2.5 h. The mixture was cooled to 7°C, filtered, washed, and dried to obtain pre-modified polyethylene. The mass ratio of pretreated polyethylene, pure water, dispersant, diazonium salt, sodium lauryl sulfate, and thiourea dioxide was 1:11:0.06:50:0.01:0.6.

[0044] (3) Pre-modified polyethylene, allyl boronic acid, solvent, catalyst, potassium carbonate, and tetrabutylammonium bromide were mixed, heated to 86°C for 11 hours, precipitated with ethanol at 3°C, filtered, washed, and dried to obtain modified polyethylene; the mass ratio of pre-modified polyethylene, allyl boronic acid, solvent, tetrakis(triphenylphosphine)palladium, potassium carbonate, and tetrabutylammonium bromide was 1:1.4:25:0.01:0.6:0.02; the solvent was a mixture of toluene and N,N-dimethylformamide in a volume ratio of 3:1;

[0045] (4) Silica, vinyltrimethoxysilane, anhydrous ethanol and pure water were mixed in a mass ratio of 1:2.5:11:11, and the pH was adjusted to 4 with hydrochloric acid. The mixture was heated to 75°C and reacted for 7.5 hours. The mixture was filtered, washed and dried to obtain vinyl silica. Vinyl silica, p-hydroxystyrene, N,N-dimethylformamide and azobisisobutyronitrile were mixed in a mass ratio of 1:2.5:25:0.01, and the mixture was heated to 80°C and reacted for 5.5 hours. The mixture was filtered, washed and dried to obtain pretreated silica. The pretreated silica, tetrahydrofuran, phosphorus oxychloride and pyridine were stirred at 3°C ​​for 2.5 hours. After the stirring was completed, the mixture was filtered and dispersed to 0.2 g / mL. Lithium chloride was added to a 3,4-dinitrophenol-tetrahydrofuran solution, the temperature was raised to 55°C, and the mixture was reacted for 11 hours under nitrogen protection. The mixture was filtered, washed, and dried to obtain pre-modified silica. The mass ratio of pre-treated silica, tetrahydrofuran, phosphorus oxychloride, pyridine, 3,4-dinitrophenol, and lithium chloride was 1:25:1.5:1.7:2.5:0.04.

[0046] (5) Pre-modified silica, thiourea dioxide, and 10 wt% sodium bicarbonate aqueous solution were mixed in a mass ratio of 1:0.6:25, heated to 75 ° C, reacted for 5.5 hours, filtered, washed, and dried to obtain amino silica; lithium hydroxide, pure water, ethanol, and cysteamine hydrochloride were mixed in a mass ratio of 1:20:50:3 to obtain a mixed solution, 2-nitrobenzyl bromide (4.6 times the mass of lithium hydroxide) and ethanol were mixed in a mass ratio of 1:20 to obtain a 2-nitrobenzyl bromide solution, and the 2-nitrobenzyl bromide solution was added dropwise to the mixed solution at a rate of 1 mL / min. After the addition was completed, the mixture was stirred at 32 ° C for 40 minutes, extracted with dichloromethane, and anhydrous sulfuric acid. The mixture was dried over sodium sulfate, filtered and concentrated to obtain 2-((2-nitrobenzyl)thio)ethylamine; aminosilica, glyoxal, and phosphate buffer with a pH of 7.4 were stirred at room temperature for 2.5 hours in a mass ratio of 1:2.5:25, filtered and added to a 0.2 g / mL 2-((2-nitrobenzyl)thio)ethylamine-acetonitrile solution, wherein the mass of 2-((2-nitrobenzyl)thio)ethylamine is 2.5 times that of aminosilica, and the mixture was reacted in the dark under nitrogen protection for 11 hours, filtered, washed, and dried to obtain a modified silica precursor, which was placed in a quartz reactor and irradiated under a 365 nm ultraviolet light source with a power of 50 mW / cm2 , irradiated at 3°C ​​for 35 min, and then washed and dried to obtain modified silica;

[0047] (6) Modified polyethylene, modified silica, benzoyl peroxide, plasticizer, and lubricant were added into a high-speed mixer at a mass ratio of 1:0.06:0.001:0.01:0.01 for mixing, and then transferred to a twin-screw extruder for extrusion to obtain a protective sleeve; the mixing temperature was 85°C, the screw speed of the twin-screw extruder was 150 r / min, and the heating temperatures of each section of the extruder were: 180°C, 190°C, 200°C, 200°C, 200°C, 200°C, 190°C.

[0048] Example 3:

[0049] A method for preparing a medium-voltage fireproof cable, comprising the following steps: coating a mica-based fireproof layer on the surface of a conductor, coating a copper protective layer on the surface of the mica-based fireproof layer, and coating a protective sheath on the surface of the copper protective layer; the protective sheath is prepared by:

[0050] (1) After dissolving dicumyl peroxide in styrene, the mixture was mixed with polyethylene and maleic anhydride in a high-speed mixer, and then extruded in a twin-screw extruder to obtain maleic anhydride grafted polyethylene; the mass ratio of polyethylene, maleic anhydride, benzoyl peroxide, and styrene was 1:0.3:0.002:0.02, the screw speed of the twin-screw extruder was 150 r / min, and the heating temperatures of each section of the extruder were 180°C, 190°C, 200°C, 200°C, 200°C, 200°C, 200°C, and 190°C; maleic anhydride grafted polyethylene, 3-amino-1-phenyl-2-pyrazol-5-one, dimethylaminopyridine, and xylene were mixed in a mass ratio of 1:0.5:0.7:12, and reacted at 100°C for 6 hours to obtain pretreated polyethylene;

[0051] (2) 4-chloro-2-nitroaniline, pure water, and 2 mol / L hydrochloric acid were mixed in a mass ratio of 1:30:15, cooled to 0°C, and 0.15 g / mL sodium nitrite aqueous solution (6 times the mass of 4-chloro-2-nitroaniline) was added, and the mixture was stirred for 40 min. The mixture was stored at 0°C in the dark to obtain diazonium salt. Pretreated polyethylene, pure water, and dispersant were mixed at 50°C for 10 min, cooled to 10°C, and diazonium salt was added at a rate of 1 mL / min. After the addition was completed, sodium lauryl sulfate was added, and the mixture was reacted for 2 h. The mixture was heated to 80°C, and thiourea dioxide was added four times with an interval of 30 min each time. After the addition was completed, the mixture was reacted for 2 h. The mixture was cooled to 5°C, filtered, washed, and dried to obtain pre-modified polyethylene. The mass ratio of pretreated polyethylene, pure water, dispersant, diazonium salt, sodium lauryl sulfate, and thiourea dioxide was 1:12:0.07:65:0.02:0.7.

[0052] (3) Pre-modified polyethylene, allyl boronic acid, solvent, catalyst, potassium carbonate, and tetrabutylammonium bromide were mixed, heated to 85°C for reaction for 10 hours, precipitated with ethanol at 0°C, filtered, washed, and dried to obtain modified polyethylene; the mass ratio of pre-modified polyethylene, allyl boronic acid, solvent, tetrakistriphenylphosphine palladium, potassium carbonate, and tetrabutylammonium bromide was 1:1.5:30:0.01:0.7:0.03; the solvent was a mixture of toluene and N,N-dimethylformamide in a volume ratio of 3:1;

[0053] (4) Silica, vinyltrimethoxysilane, anhydrous ethanol and pure water were mixed in a mass ratio of 1:3:12:12, and the pH was adjusted to 4 with hydrochloric acid. The mixture was heated to 70°C for 7 hours, and the mixture was filtered, washed and dried to obtain vinyl silica. Vinyl silica, p-hydroxystyrene, N,N-dimethylformamide and azobisisobutyronitrile were mixed in a mass ratio of 1:3:30:0.02, and the mixture was heated to 75°C for 5 hours, and the mixture was filtered, washed and dried to obtain pretreated silica. The pretreated silica, tetrahydrofuran, phosphorus oxychloride and pyridine were stirred at 0°C for 2 hours. After the stirring was completed, the mixture was filtered and dispersed to 0.2 g / mL. Lithium chloride was added to a 3,4-dinitrophenol-tetrahydrofuran solution, the temperature was raised to 50°C, and the mixture was reacted under nitrogen for 10 hours. The mixture was filtered, washed, and dried to obtain pre-modified silica. The mass ratio of pre-treated silica, tetrahydrofuran, phosphorus oxychloride, pyridine, 3,4-dinitrophenol, and lithium chloride was 1:30:2:2:3:0.05.

[0054] (5) Pre-modified silica, thiourea dioxide, and 10 wt% sodium bicarbonate aqueous solution were mixed in a mass ratio of 1:0.7:30, heated to 70 ° C, reacted for 5 h, filtered, washed, and dried to obtain amino silica; lithium hydroxide, pure water, ethanol, and cysteamine hydrochloride were mixed in a mass ratio of 1:20:50:3 to obtain a mixed solution, 2-nitrobenzyl bromide (4.6 times the mass of lithium hydroxide) and ethanol were mixed in a mass ratio of 1:20 to obtain a 2-nitrobenzyl bromide solution, and the 2-nitrobenzyl bromide solution was added dropwise to the mixed solution at a rate of 1 mL / min. After the addition was completed, the mixture was stirred at 30 ° C for 40 min, extracted with dichloromethane, and dried. The mixture was dried over sodium sulfate, filtered and concentrated to obtain 2-((2-nitrobenzyl)thio)ethylamine; aminosilica, glyoxal, and phosphate buffer with a pH of 7.4 were stirred at room temperature for 2 h in a mass ratio of 1:3:30, filtered and added to a 0.2 g / mL 2-((2-nitrobenzyl)thio)ethylamine-acetonitrile solution, wherein the mass of 2-((2-nitrobenzyl)thio)ethylamine is 3 times that of aminosilica, and the mixture was reacted in the dark under nitrogen protection for 10 h, filtered, washed, and dried to obtain a modified silica precursor, which was placed in a quartz reactor and irradiated under a 365 nm ultraviolet light source with a power of 50 mW / cm 2, irradiating at 0°C for 30 min, washing and drying to obtain modified silica;

[0055] (6) Modified polyethylene, modified silica, benzoyl peroxide, plasticizer, and lubricant were added into a high-speed mixer at a mass ratio of 1:0.07:0.002:0.02:0.02 for mixing, and then transferred to a twin-screw extruder for extrusion to obtain a protective sleeve; the mixing temperature was 80°C, the screw speed of the twin-screw extruder was 150 r / min, and the heating temperatures of each section of the extruder were: 180°C, 190°C, 200°C, 200°C, 200°C, 200°C, 190°C.

[0056] Comparative Example 1:

[0057] The preparation method of the medium-voltage fireproof cable of Comparative Example 1 differs from that of Example 2 in that polyethylene is not modified, specifically, steps (1) to (3) are not included, and step (6) is modified as follows: polyethylene, modified silicon dioxide, benzoyl peroxide, plasticizer, and lubricant are added into a high-speed mixer in a mass ratio of 1:0.06:0.001:0.01:0.01 for mixing, and then transferred to a twin-screw extruder for extrusion to obtain a protective sheath; the mixing temperature is 85°C, the screw speed of the twin-screw extruder is 150 r / min, and the heating temperatures of the various sections of the extruder are: 180°C, 190°C, 200°C, 200°C, 200°C, 200°C, 190°C. The remaining steps are the same as those of Example 2.

[0058] Comparative Example 2:

[0059] The preparation method of the medium-voltage fireproof cable of Comparative Example 2 differs from that of Example 2 in that the silicon dioxide is not modified, specifically, steps (4) to (5) are not included, and step (6) is modified as follows: modified polyethylene, silicon dioxide, benzoyl peroxide, plasticizer, and lubricant are added into a high-speed mixer in a mass ratio of 1:0.06:0.001:0.01:0.01 for mixing, and then transferred to a twin-screw extruder for extrusion to obtain a protective sleeve; the mixing temperature is 85°C, the screw speed of the twin-screw extruder is 150 r / min, and the heating temperatures of the various sections of the extruder are: 180°C, 190°C, 200°C, 200°C, 200°C, 200°C, 190°C. The remaining steps are the same as those of Example 2.

[0060] Comparative Example 3:

[0061] The preparation method of the medium-voltage fireproof cable of Comparative Example 3 differs from that of Example 2 in that the pre-modified silica is not subjected to the next step of modification, specifically, step (5) is not included, and step (6) is modified as follows: modified polyethylene, pre-modified silica, benzoyl peroxide, plasticizer, and lubricant are added into a high-speed mixer in a mass ratio of 1:0.06:0.001:0.01:0.01 for mixing, and then transferred to a twin-screw extruder for extrusion to obtain a protective sleeve; the mixing temperature is 85°C, the screw speed of the twin-screw extruder is 150 r / min, and the heating temperatures of the various sections of the extruder are: 180°C, 190°C, 200°C, 200°C, 200°C, 200°C, 200°C, and 190°C. The remaining steps are the same as those of Example 2.

[0062] Test Example 1:

[0063] Fire performance test:

[0064] Test method: Fire resistance test was conducted on the fire-resistant cables prepared in the examples and comparative examples according to the standard GB / T 19216.11-2003, with the flame temperature at 950°C.

[0065] Anti-aging performance test:

[0066] Test Method: Fire testing was performed according to the fire performance test method in accordance with the standard GB / T 16422.2-2014 after aging for 720 hours. Results are shown in Table 1.

[0067] Table 1

[0068] Continuous power supply time (min) Continuous power supply time after aging (min) Example 1 194 Example 1 190 Example 2 197 Example 2 194 Example 3 197 Example 3 195 Comparative Example 1 174 Comparative Example 1 131 Comparative Example 2 153 Comparative Example 2 143 Comparative Example 3 181 Comparative Example 3 175

[0069] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 3 in Table 1, it can be found that the coating prepared by the present invention has good fire resistance and anti-aging properties.

[0070] The fireproof and aging resistance of Examples 1 to 3 are superior to those of Comparative Examples 1 to 3, indicating that, in the presence of an initiator, p-hydroxystyrene polymerizes on the surface of silica modified with vinyltrimethoxysilane, modifying the silica surface with phenolic hydroxyl groups. A phosphate structure with excellent flame retardancy is then generated through an ester exchange reaction between 3,4-dinitrophenol and phosphorus oxychloride. The introduction of nitrogen, phosphorus, and sulfur during the modification process can also synergistically enhance flame retardancy, further improving the flame retardancy of the material.

[0071] Maleic anhydride is grafted onto polyethylene by the melt grafting method, and 3-amino-1-phenyl-2-pyrazolidine-5-one is grafted by the reaction of acid anhydride and amino group. 4-chloro-2-nitroaniline is prepared into a diazonium salt, which undergoes a coupling reaction with the active hydrogen on 3-amino-1-phenyl-2-pyrazolidine-5-one. Then, a reducing agent is used for reduction and cyclization to form a benzotriazole ring. The structure connected by the nitrogen heterocycle and the benzotriazole stabilizes the ground state structure through intramolecular hydrogen bonds, dissipates energy through excited state proton transfer, and enhances the absorption performance through N-heterocycle conjugation, giving the material good anti-light aging properties.

[0072] Test Example 2:

[0073] Corrosion resistance test:

[0074] Test method: After polishing, cleaning, and drying the surface of a 120mm x 50mm x 0.5mm copper plate, a protective cover was applied to the plate. The plate was then immersed in a 5wt% sodium chloride solution at 25°C, leaving two-thirds of its length submerged for 600 hours. The plate's appearance was then observed. The results are shown in Table 2.

[0075] Table 2

[0076] Appearance Appearance Example 1 No change Comparative Example 1 foaming Example 2 No change Comparative Example 2 Slightly bubbling Example 3 No change Comparative Example 3 Slightly bubbling

[0077] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 3 in Table 2, it can be found that the coating prepared by the present invention has good corrosion resistance.

[0078] The corrosion resistance of Examples 1 to 3 is better than that of Comparative Examples 1 to 3, indicating that during the modification process, the nitrogen heterocycle, phosphate, and Schiff base structures of the polyethylene side chain have good complexing ability with metals, and can form a dense protective layer on the copper protective layer to protect the internal copper protective layer from corrosion.

[0079] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be encompassed therein. Any reference in a claim should not be construed as limiting the claim to which it relates.

Claims

1. A method for preparing a medium voltage fireproof cable, characterized in that: A mica-based refractory layer is coated on the surface of the conductor, a copper protective layer is coated on the surface of the mica-based refractory layer, and a protective sleeve is coated on the surface of the copper protective layer; The protective cover is prepared from modified polyethylene, modified silicon dioxide, a catalyst, a plasticizer, and a lubricant; The modified polyethylene is obtained by grafting maleic anhydride-grafted polyethylene with 3-amino-1-phenyl-2-pyrazolidine-5-one, reacting with a diazonium salt, and then reacting with allylboronic acid; The modified silica is obtained by polymerizing p-hydroxystyrene on the surface of silica modified with vinyltrimethoxysilane, reacting with 3,4-dinitrophenol, reducing the polymer, reacting with 2-((2-nitrobenzyl)thio)ethylamine, and then deprotecting the polymer.

2. The method for preparing a medium voltage fireproof cable according to claim 1, characterized in that: The preparation method of the protective cover is as follows: (1) Dissolving dicumyl peroxide in styrene, mixing it with polyethylene and maleic anhydride in a high-speed mixer, and then extruding it in a twin-screw extruder to obtain maleic anhydride-grafted polyethylene; reacting the maleic anhydride-grafted polyethylene with 3-amino-1-phenyl-2-pyrazol-5-one to obtain pretreated polyethylene; (2) 4-chloro-2-nitroaniline, pure water, 2 mol / L hydrochloric acid, and sodium nitrite are reacted to obtain diazonium salt; after the pretreated polyethylene and diazonium salt are reacted, thiourea dioxide is added to obtain pre-modified polyethylene; (3) Pre-modified polyethylene, allylboric acid, solvent, tetrakis(triphenylphosphine)palladium, potassium carbonate, and tetrabutylammonium bromide were mixed, heated to 85-90°C for reaction for 10-12 hours, precipitated with 0-5°C ethanol, filtered, washed, and dried to obtain modified polyethylene; (4) reacting silica and vinyltrimethoxysilane to obtain vinyl silica; reacting vinyl silica and p-hydroxystyrene to obtain pretreated silica; reacting pretreated silica, phosphorus oxychloride, and 3,4-dinitrophenol to obtain pre-modified silica; (5) reacting pre-modified silica, thiourea dioxide, and sodium bicarbonate to obtain amino silica; reacting amino silica, glyoxal, and 2-((2-nitrobenzyl)thio)ethylamine to obtain a modified silica precursor, and irradiating the modified silica precursor with light to obtain modified silica; (6) Modified polyethylene, modified silica, catalyst, plasticizer and lubricant are added into a high-speed mixer in a mass ratio of 1:(0.05-0.07):(0.001-0.002):(0.01-0.02):(0.01-0.02) and mixed, and then transferred to a twin-screw extruder for extrusion to obtain a protective sleeve; the mixing temperature is 80-90°C, the screw speed of the twin-screw extruder is 150r / min, and the heating temperatures of each section of the extruder are: 180°C, 190°C, 200°C, 200°C, 200°C, 200°C, 190°C.

3. The method for preparing a medium voltage fireproof cable according to claim 1, characterized in that: In step (1), the mass ratio of polyethylene, maleic anhydride, benzoyl peroxide, and styrene is 1:(0.2-0.3):(0.001-0.002):(0.01-0.02), the screw speed of the twin-screw extruder is 150 r / min, and the heating temperatures of each section of the extruder are 180°C, 190°C, 200°C, 200°C, 200°C, 200°C, 200°C, and 190°C; the polyethylene model is HE3490-LS; the mass ratio of the maleic anhydride-grafted polyethylene, 3-amino-1-phenyl-2-pyrazol-5-one, dimethylaminopyridine, and xylene is 1:(0.3-0.5):(0.5-0.7):(10-12).

4. The method for preparing a medium voltage fireproof cable according to claim 1, characterized in that: The preparation method of the pre-modified polyethylene in step (2) is as follows: 4-chloro-2-nitroaniline, pure water, and 2 mol / L hydrochloric acid are mixed in a mass ratio of 1: (25-30): (12-15), cooled to 0-5°C, 0.15 g / mL sodium nitrite aqueous solution of 5-6 times the mass of 4-chloro-2-nitroaniline is added, stirring is continued for 40-50 min, and the mixture is stored in the dark at 0-5°C to obtain a diazonium salt; pre-treated polyethylene, pure water, and a dispersant are mixed at 50°C for 10-20 min, cooled to 10-15°C, and the diazonium salt is added at a drop rate of 1 mL / min. After the addition is completed, sodium lauryl sulfate is added, the mixture is reacted for 2-3 h, the temperature is raised to 80-85°C, thiourea dioxide is added four times, and the interval between each addition is 30 min. After the addition is completed, the mixture is reacted for 2-3 h, cooled to 5-10°C, filtered, washed, and dried to obtain a pre-modified polyethylene; The mass ratio of pretreated polyethylene, pure water, dispersant, diazonium salt, sodium lauryl sulfate and thiourea dioxide is 1:(10-12):(0.05-0.07):(55-65):(0.01-0.02):(0.5-0.7).

5. The method for preparing a medium voltage fireproof cable according to claim 1, characterized in that: In step (3), the mass ratio of the pre-modified polyethylene, allylboric acid, solvent, tetrakis(triphenylphosphine)palladium, potassium carbonate, and tetrabutylammonium bromide is 1:(1.3-1.5):(20-30):0.01:(0.5-0.7):(0.02-0.03); the solvent is a mixture of toluene and N,N-dimethylformamide in a volume ratio of 3:

1.

6. The method for preparing a medium voltage fireproof cable according to claim 1, characterized in that: The preparation method of the pre-modified silica in step (4) is as follows: silica, vinyl trimethoxysilane, anhydrous ethanol, and pure water are mixed in a mass ratio of 1: (2-3): (10-12): (10-12), hydrochloric acid is used to adjust the pH to 4, the temperature is raised to 70-80 ° C and the reaction is carried out for 7-8 hours, and the vinyl silica is obtained by filtering, washing, and drying; vinyl silica, p-hydroxystyrene, N, N-dimethylformamide, and azobisisobutyronitrile are mixed in a mass ratio of 1: (2-3): (20-30): (0.01-0.02), the temperature is raised to 75-85 ° C and the reaction is carried out for 5-6 hours, and the pre-treated silica is obtained by filtering, washing, and drying; the pre-treated silica, tetrahydrofuran, phosphorus oxychloride, and pyridine are stirred at 0-5 ° C for 2-3 hours. After the stirring is completed, the mixture is filtered and dispersed to 0.2 g / mL. Lithium chloride is added to a 3,4-dinitrophenol-tetrahydrofuran solution, the temperature is raised to 50-60°C, the reaction is carried out under nitrogen protection for 10-12 hours, and the solution is filtered, washed, and dried to obtain pre-modified silica; the mass ratio of pretreated silica, tetrahydrofuran, phosphorus oxychloride, pyridine, 3,4-dinitrophenol, and lithium chloride is 1:(20-30):(1-2):(1-2):(2-3):(0.03-0.05).

7. The method for preparing a medium voltage fireproof cable according to claim 1, characterized in that: The preparation method of the modified silica in step (5) is as follows: pre-modified silica, thiourea dioxide, and 10 wt% sodium bicarbonate aqueous solution are mixed in a mass ratio of 1: (0.5-0.7): (20-30), heated to 70-80 ° C, reacted for 5-6 hours, filtered, washed, and dried to obtain amino silica; amino silica, glyoxal, and phosphate buffer solution with a pH of 7.4 are mixed in a mass ratio of 1: (2-3): (20-30) at room temperature. The mixture was stirred at room temperature for 2-3 hours, filtered and added to a 0.2 g / mL 2-((2-nitrobenzyl)thio)ethylamine-acetonitrile solution, wherein the mass of 2-((2-nitrobenzyl)thio)ethylamine was 2-3 times that of aminosilica, and the reaction was carried out in the dark under nitrogen protection for 10-12 hours. The modified silica precursor was obtained by filtration, washing and drying. The modified silica precursor was placed in a quartz reactor and irradiated under a 365 nm ultraviolet light source with a power of 50 mW / cm 2 , irradiate at 0-5℃ for 30-40min, and then wash and dry to obtain modified silica.

8. The method for preparing a medium voltage fireproof cable according to claim 7, characterized in that: The preparation method of 2-((2-nitrobenzyl)thio)ethylamine comprises: mixing lithium hydroxide, pure water, ethanol, and cysteamine hydrochloride in a mass ratio of 1:20:50:3 to obtain a mixed solution; mixing 2-nitrobenzyl bromide (4.6 times the mass of lithium hydroxide) and ethanol in a mass ratio of 1:20 to obtain a 2-nitrobenzyl bromide solution; and adding the 2-nitrobenzyl bromide solution dropwise to the mixed solution at a rate of 1 mL / min. After the addition is completed, stirring at 30-35° C. for 40 minutes, extracting with dichloromethane, drying with anhydrous sodium sulfate, filtering, and concentrating to obtain 2-((2-nitrobenzyl)thio)ethylamine.

9. A medium voltage fireproof cable prepared according to the method for preparing a medium voltage fireproof cable according to any one of claims 1 to 8.

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