Low smoke halogen-free medium voltage power cable based on environmentally friendly materials

Abstract

The invention discloses a low-smoke halogen-free medium-voltage power cable based on environmentally friendly materials, which is used to solve the technical problem that the mechanical properties, flame retardant properties and environmental protection of power cables in the prior art need to be further improved. The invention introduces siloxane segments and integrates them into a carboxylated polypropylene skeleton through chemical bonds. At the same time, multiple chemical bonds such as urethane bonds, urea bonds and carboxylate bonds are introduced to form a cross-linked network, which effectively improves the overall mechanical strength and high temperature resistance of the cable material. The prepared modified flame retardant forms a flame retardant protective layer on the surface of the composite polyolefin. The cable material with multiple chemical bonds and materials acting in synergy has greatly improved environmental protection, mechanical structure and flame retardant properties, and meets the dual needs of modern cable applications for high performance and environmental protection.

Description

Technical Field

[0001] The invention relates to the technical field of power cable processing, and in particular to a low-smoke, halogen-free medium-voltage power cable based on environmentally friendly materials. Background Art

[0002] Medium voltage power cables are a vital component of the power system. Their main responsibility is to transmit medium voltage electricity at the level of 6KV-35KV. These cables transmit the medium voltage electricity generated by substations or distribution stations to smaller substations, distribution boxes or large industrial users. They are the key link between high voltage transmission networks and low voltage distribution networks. In layman's terms, they are like the "highways" in the power grid, responsible for delivering electricity from transfer stations to the "entrances" of cities or factories.

[0003] Traditional medium-voltage cables usually use polymer materials such as PVC (polyvinyl chloride) as insulation and sheath. However, these materials will release a large amount of toxic gases, such as hydrogen chloride (HCl) and thick smoke when burning. Combined with moisture in the air, they will form highly corrosive hydrochloric acid, corroding equipment and damaging the environment. In addition, the temperature resistance level of PVC (polyvinyl chloride) is relatively low. As the base material of the cable, its mechanical properties are poor and it is easily softened or cracked by temperature. In addition, the halogen-containing flame retardants that are often added will decompose at high temperatures to produce harmful substances, which will affect the electrical and mechanical properties of the material and even cause failure.

[0004] Therefore, there are great challenges in terms of mechanical properties, flame retardancy and environmental protection for power cable substrates. Summary of the invention

[0005] The purpose of the present invention is to provide a low-smoke halogen-free medium-voltage power cable based on environmentally friendly materials, which is used to solve the technical problem that the mechanical properties, flame retardant properties and environmental protection of power cables in the prior art need to be further improved.

[0006] The object of the present invention can be achieved by the following technical scheme: a low-smoke halogen-free medium-voltage power cable based on environmentally friendly materials, comprising a plurality of cable conductors, a wrapping layer, a buffer shielding layer and a flame-retardant outer sheath layer arranged in sequence from the inside to the outside;

[0007] The wrapping layer is obtained by wrapping a mica insulating wrapping tape around the outside of a plurality of cable conductors;

[0008] The buffer shielding layer is obtained by bonding the flexible foam metal copper to the surface of the wrapping layer;

[0009] The flame retardant outer sheath layer is obtained by coating a composite flame retardant modified polyolefin cable material composed of high-density polyethylene resin, low-density polyethylene resin, modified polypropylene, modified reinforcing agent, modified flame retardant, modified reinforcing agent, initiator, dispersant, heat stabilizer and lubricant on the outside of the buffer shielding layer.

[0010] Furthermore, the modified reinforcing agent is obtained by processing the following steps:

[0011] S1, adding hydroxypropyl-terminated polydimethylsiloxane, toluene-2,4-diisocyanate, xylene and triethylamine into a reaction kettle and stirring, raising the temperature of the reaction kettle to 50-60° C. under nitrogen protection, keeping the temperature for reaction for 4-6 hours, and post-treating to obtain intermediate I;

[0012] The reaction equation for preparing intermediate I is:

[0013]

[0014] Where:

[0015] The synthesis principle of intermediate I is:

[0016] Triethylamine acts as a tertiary amine catalyst to increase the nucleophilicity of the hydroxyl group, making it easy to attack the carbon atom on the isocyanate. The oxygen atom on the activated hydroxyl group acts as a nucleophile to attack the carbon atom of an isocyanate group of toluene-2,4-diisocyanate, thereby generating a carbamate group. Since toluene-2,4-diisocyanate is in excess, an isocyanate-terminated siloxane intermediate I is generated.

[0017] S2. Add intermediate I, 5-hexene-1-amine, methanol solution and triethylamine into a reaction kettle and stir. Under nitrogen protection, increase the temperature of the reaction kettle to 50-60° C. and keep the temperature for 6-8 hours. Post-process to obtain a modified enhancer.

[0018] The reaction equation for preparing the modified reinforcing agent is:

[0019]

[0020] The synthetic principle of the modified enhancer is:

[0021] During the reaction, the lone pair of electrons on the nitrogen atom in the amino group on 5-vinyl-1-amine acts as a nucleophile to attack the carbon atom of the isocyanate group on the isocyanate-terminated siloxane, generating a urea bond to form a modifier with an unsaturated double bond modified end group. At this time, the end of the siloxane molecule is connected to a group with a vinyl group through a urea bond to generate a modified enhancer.

[0022] Furthermore, in step S1, the amount ratio of the hydroxypropyl-terminated polydimethylsiloxane, toluene-2,4-diisocyanate, xylene and triethylamine is 2g:1g:6mL:0.1mL, and the post-treatment includes: after the reaction is completed, the temperature of the reactor is set to 70-80°C, the organic solvent is removed by reduced pressure distillation, suction filtering, the product is washed with anhydrous ethanol 5 times, suction filtering, the product is placed in a vacuum drying oven at 80°C, and dried to constant weight to obtain intermediate I; in step S2, the amount ratio of intermediate I, 5-hexene-1-amine, methanol solution and triethylamine is 1g:0.2g:2mL:0.1mL, and the post-treatment includes: after the reaction is completed, the temperature of the reactor is set to 70-80°C, the organic solvent is removed by reduced pressure distillation, suction filtering, the product is washed with anhydrous ethanol 5 times, suction filtering, the product is placed in a vacuum drying oven at 80°C, and dried to constant weight to obtain a modified enhancer.

[0023] Further, the modified polypropylene is processed by the following steps:

[0024] A1. Add polypropylene particles and acetone into an ultrasonic cleaner for washing, raise the temperature of the cleaner to 60-80°C, stir for 2-3 hours, and post-treat to obtain pretreated polypropylene;

[0025] A2. Add pretreated polypropylene, acrylic acid solution and HMPP solution into a reaction kettle, move to an ultraviolet light box, perform ultraviolet light grafting reaction, and post-treat to obtain modified polypropylene.

[0026] The reaction equation for preparing modified polypropylene is:

[0027]

[0028] The synthesis principle of modified polypropylene is:

[0029] During the reaction, HMPP absorbs ultraviolet light energy, undergoes intramolecular or intermolecular electron transfer, forms free radicals, and captures hydrogen atoms from polypropylene chains or acrylic acid molecules. The generated polypropylene free radicals are activated and react with acrylic acid to form free radicals with acrylic acid monomers. These free radicals continue to react with more acrylic acid monomers, causing the acrylic acid chain to continue to grow, forming polyacrylic acid chain segments. Acrylic acid monomers are continuously grafted onto the main chain of polypropylene to generate carboxylated polypropylene.

[0030] Furthermore, in step A1, the amount ratio of the polypropylene particles to acetone is 1g:5mL, and the post-treatment includes: after the impurity removal is completed, the temperature of the cleaning device is lowered to room temperature, suction filtration is performed, and the polypropylene solid is placed in a vacuum dryer at 80°C and dried to constant weight to obtain pretreated polypropylene; in step A2, the amount ratio of the pretreated polypropylene, acrylic acid solution and HMPP solution is 7g:25mL:1mL, the acrylic acid solution is composed of acrylic acid and acetone mixed in a ratio of 30g:100mL, the HMPP solution is composed of HMPP and acetone solution mixed in a volume ratio of 5:100, the ultraviolet light wavelength is 249nm, and the energy is 510mJ / cm 2 , the oxygen content is 0.3%, and the post-treatment includes: after the reaction is completed, placing it in a 95% ethanol aqueous solution, ultrasonic cycle cleaning to remove unreacted monomers and oligomers, filtering, and placing the product in a vacuum drying oven at a temperature of 40°C, drying to constant weight to obtain modified polypropylene.

[0031] Further, the modified flame retardant is processed by the following steps:

[0032] B1. Add DOPO and toluene into a reactor and stir. Raise the temperature of the reactor to 100-120°C, condense and reflux, add acrylamide solution, keep the temperature for 5-6 hours, and post-treat to obtain intermediate II.

[0033] The reaction equation for preparing intermediate II is:

[0034]

[0035] The synthesis principle of intermediate II is:

[0036] The PH bond of DOPO is activated under heating conditions and adds to the carbon-carbon double bond of acrylamide to form intermediate II of the phosphoamide derivative.

[0037] B2. Add intermediate II and DMSO into a vacuum reactor and stir to dissolve. Increase the temperature of the reactor to 60-80°C, add 4-allylbenzoic acid and triethylamine, react for 4-6 hours, and post-treat to obtain a modified flame retardant.

[0038] The reaction equation for preparing the modified flame retardant is:

[0039]

[0040] The synthesis principle of modified flame retardant is:

[0041] Under the condition of triethylamine as an alkaline catalyst, the amide group in intermediate II is hydrolyzed to generate a carboxyl group, which undergoes an esterification reaction with 4-allylbenzoic acid, and the olefin functional group of 4-allylbenzoic acid is connected to intermediate II through an ester bond to generate a modified flame retardant with reactive activity.

[0042] Furthermore, in the step B1, the amount ratio of DOPO, toluene and acrylamide solution is 4g:15mL:5mL, the acrylamide solution is composed of acrylamide and deionized water mixed in a ratio of 2g:3mL, and the post-treatment includes: after the reaction is completed, the temperature of the reactor is lowered to room temperature, filtered, and the obtained solid is extracted with ethanol in a Soxhlet extractor for 10 hours, and dried under reduced pressure to obtain intermediate II; in step B2, the amount ratio of intermediate II, DMSO, 4-allylbenzoic acid and triethylamine is 3g:9mL:2-3g:0.3-0.4mL, and the post-treatment includes: after the reaction is completed, the reaction solution is dehydrated, dried, crystallized, the crystals are separated, and the modified flame retardant is obtained after drying.

[0043] Furthermore, the composite flame retardant modified polyolefin cable material includes the following components in parts by weight: the weight ratio of the high-density polyethylene resin, the low-density polyethylene resin, the modified polypropylene, the modified flame retardant, the modified reinforcing agent, the initiator, the dispersant, the heat stabilizer and the lubricant is 100-120:50-70:10-30:60-80:10-15:1-2:1-2:1-2:1-2, the dispersant is one or two of polyethylene wax and polypropylene wax, the heat stabilizer is one or more of zinc calcium acid, magnesium calcium acid, and aluminum calcium acid, the initiator is one or more of bis (2,4-di-tert-butylphenyl) phosphate sodium salt (NA-11) and bis (2,4-di-tert-butylphenyl) aluminum phosphate, and the lubricant is one or more of zinc stearate, magnesium stearate, and calcium stearate.

[0044] Furthermore, the preparation process of melt extrusion coating is as follows: adding the composite flame retardant modified polyolefin cable material to a twin-screw extruder, the temperatures of the eight temperature sections of the twin-screw extruder from the feed port to the discharge port are 150°C, 155°C, 160°C, 160°C, 170°C, 170°C, 185°C, and 185°C, respectively, the main engine speed of the twin-screw extruder is 90-120rpm, and the pressure is 120-160 bar. After melt extrusion, it is coated on the outside of the buffer shielding layer to obtain a cable precursor, and the cable precursor is transferred to a water vapor box, heat-insulated for 6-8 hours, cooled and discharged to obtain a cable.

[0045] The present invention has the following beneficial effects:

[0046] 1. The modified siloxane prepared by the present invention reduces interfacial slip by introducing siloxane segments and integrating them into the carboxylated polyethylene skeleton through chemical bonds. The high bond energy of the Si-O bond in the siloxane gives the material excellent high temperature resistance, so that the modified polyolefin material can still maintain good structure and performance at higher temperatures. At the same time, the introduced urethane bonds, urea bonds, carboxylate bonds and other chemical bonds form a cross-linked network, which effectively improves the glass transition temperature and heat resistance of the polyolefin material, enhances the overall temperature resistance of the material, and reduces degradation and performance attenuation at high temperatures. In terms of mechanical properties, the flexibility of the siloxane segments improves the breaking strength and elongation of the material, making the cable less prone to damage during installation, bending and stretching. In addition, the presence of these chemical bonds also inhibits the creep of polyolefins, improves dimensional stability, and ensures the stable performance of the cable during long-term use. Through the cross-linking of chemical bonds, the compatibility of siloxane with the polyolefin substrate is also improved, reducing the phase separation of the material, and further enhancing the overall mechanical strength and high temperature resistance of the cable material.

[0047] 2. At the same time, by introducing carboxyl groups, the polarity of polyolefin materials is enhanced and the compatibility with additives is improved. Carboxylated polyethylene can also improve charring ability, reduce combustion smoke and toxic gases, and improve flame retardant safety. The modified materials are easier to degrade or recycle under certain conditions, reducing environmental hazards. The synergistic effect of multiple chemical bonds and materials greatly improves the environmental protection and high temperature resistance of modified polypropylene cable materials, meeting the dual needs of modern cable applications for high performance and environmental protection.

[0048] 3. The core of the composite polyolefin cable outer sheath material prepared by the present invention is the use of a phosphorus-containing modified flame retardant. The flame retardant significantly improves the compatibility with polyolefins by introducing amide groups. More importantly, the flame retardant can cross-link with carboxylated polyolefins to form covalent bonds, which effectively avoids the migration and precipitation problems that are prone to occur in traditional flame retardants, thereby ensuring the durability of the flame retardant effect. In addition, the flame retardant also contains olefin functional groups, which decompose at high temperatures to produce free radicals. These free radicals can capture the free radicals produced by polymer combustion, thereby terminating the chain combustion reaction, slowing down the thermal decomposition of the polymer, and effectively hindering the combustion. The free radicals produced by the modified flame retardant can not only inhibit combustion, It can also initiate polymerization or cross-linking reactions, further improving the thermal stability of the material. The formed cross-linked network can be more evenly dispersed in the polyolefin material and form a protective layer on the surface of the composite polyolefin, reducing heat transfer and combustible release. The phosphoric acid released by the phosphoamide derivative during combustion also further inhibits the combustion reaction, and the cross-linked network formed by the cross-linking reaction can better resist chemical corrosion and degradation, thereby improving the chemical resistance of the material. This multiple mechanism works together to make the outer sheath layer have excellent flame retardant properties, which can effectively prevent the spread of fire and protect the normal function of the cable. At the same time, the cross-linked structure enables the material to better resist thermal decomposition and degradation, and improve mechanical strength, rigidity and durability. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0050] Figure 1 It is a schematic diagram of the overall three-dimensional structure of the present invention.

[0051] In the figure: 1. Cable conductor; 2. Wrapping layer; 3. Buffer shielding layer; 4. Flame retardant outer sheath layer. DETAILED DESCRIPTION

[0052] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0053] The high-density polyethylene resin and low-density polyethylene resin used in the present invention are based on Shandong Xinwei Chemical Technology Co., Ltd. The high-density polyethylene resin has a CAS number of 25213-02-9 and the low-density polyethylene resin has a molecular weight of CAS number of 9002-88-4;

[0054] The polyethylene wax and polypropylene wax used in the present invention are from Shanghai Xinnuo Chemical Co., Ltd., and the CAS number is 9002-88-4.

[0055] Example 1

[0056] See also Figure 1 This embodiment provides a method for preparing a low-smoke, halogen-free medium-voltage power cable based on environmentally friendly materials, comprising the following steps:

[0057] S1. Preparation of modified reinforcing agent

[0058] Weigh: 200 g of hydroxypropyl-terminated polydimethylsiloxane, 100 g of toluene-2,4-diisocyanate, 600 mL of xylene and 10 mL of triethylamine, add into a reactor and stir, under nitrogen protection, raise the temperature of the reactor to 50° C., keep warm and react for 4 hours, after the reaction is completed, set the temperature of the reactor to 70° C., remove the organic solvent by vacuum distillation, filter, wash the product with anhydrous ethanol 5 times, filter, place the product in a vacuum drying oven at 80° C., dry to constant weight, and obtain intermediate I;

[0059] Weigh: 400 g of intermediate I, 80 g of 5-hexene-1-amine, 800 mL of methanol solution and 40 mL of triethylamine, add into the reactor and stir. Under nitrogen protection, the temperature of the reactor is raised to 50°C and kept warm for 6 hours. After the reaction is completed, the temperature of the reactor is set to 70°C, and the organic solvent is removed by vacuum distillation. The product is filtered and washed with anhydrous ethanol 5 times. The product is filtered and placed in a vacuum drying oven at 80°C and dried to constant weight to obtain a modified enhancer.

[0060] S2. Preparation of modified polypropylene

[0061] Weigh: 300 g of polypropylene particles and 1500 mL of acetone are added to an ultrasonic cleaner for washing, the temperature of the cleaner is raised to 60°C, stirred for 2 hours, and after the impurity removal is completed, the temperature of the cleaner is lowered to room temperature, filtered, and the polyethylene solid is placed in a vacuum dryer at 80°C and dried to constant weight to obtain pretreated polyethylene;

[0062] Weigh: 700 g of pretreated polypropylene, 2500 mL of acrylic acid solution and 100 mL of HMPP solution into a reactor, move to a UV light box, and perform UV grafting reaction. The acrylic acid solution is composed of acrylic acid and acetone mixed in a dosage ratio of 30 g:100 mL, and the HMPP solution is composed of HMPP and acetone solution mixed in a volume ratio of 5:100. The wavelength of the UV light is 249 nm, and the energy is 510 mJ / cm 2 , the oxygen content is 0.3%. After the reaction is completed, it is placed in a 95% ethanol aqueous solution and ultrasonically cleaned to remove unreacted monomers and oligomers. The product is filtered and placed in a vacuum drying oven at 40°C and dried to constant weight to obtain modified polypropylene.

[0063] S3. Preparation of modified flame retardant

[0064] Weigh: 400 g of DOPO and 1500 mL of toluene are added to a reactor and stirred. The temperature of the reactor is raised to 110°C, condensed and refluxed, 500 mL of acrylamide solution is added, and the reaction is kept warm for 5 hours. After the reaction is completed, the temperature of the reactor is lowered to room temperature, filtered, and the obtained solid is extracted with ethanol in a Soxhlet extractor for 10 hours, and dried under reduced pressure to obtain intermediate II;

[0065] Weigh: 300 g of intermediate II and 900 mL of DMSO are added into a vacuum reactor, stirred and dissolved, the temperature of the reactor is increased to 60°C, 200 g of 4-allylbenzoic acid and 30 mL of triethylamine are added, and the reaction is carried out for 4 hours. After the reaction is completed, the reaction solution is dehydrated, dried, crystallized, the crystals are separated, and the modified flame retardant is obtained after drying.

[0066] S4. Preparation of polyolefin cables modified with composite flame retardants

[0067] Wrapping the mica insulation wrapping tape around the outside of the four cable conductors 1 to form a wrapping layer 2;

[0068] The flexible foamed metal copper is bonded to the surface of the wrapping layer 2 to obtain a buffer shielding layer 3;

[0069] Weigh by weight: 100 parts of high-density polyethylene resin, 50 parts of low-density polyethylene resin, 10 parts of modified polypropylene, 60 parts of modified flame retardant, 10 parts of modified reinforcing agent, 1 part of double 2,4-di-tert-butylphenyl aluminum phosphate, 1 part of polyethylene wax, 1 part of zinc calcium acid and 1 part of zinc stearate, and add them into a twin-screw extruder. The temperatures of the eight temperature sections of the twin-screw extruder from the feed port to the discharge port are 150°C, 155°C, 160°C, 160°C, 170°C, 170°C, 185°C, and 185°C, respectively. The main engine speed of the twin-screw extruder is 90 rpm, and the pressure is 120 bar. After melt extrusion, it is coated on the outside of the buffer shielding layer 3 to obtain a cable precursor. The cable precursor is transferred to a water vapor box, heat-insulated for 6 hours, cooled and discharged to obtain a cable.

[0070] Example 2

[0071] See also Figure 1 This embodiment provides a method for preparing a low-smoke, halogen-free medium-voltage power cable based on environmentally friendly materials, comprising the following steps:

[0072] S1. Preparation of modified reinforcing agent

[0073] Weigh: 200 g of hydroxypropyl-terminated polydimethylsiloxane, 100 g of toluene-2,4-diisocyanate, 600 mL of xylene and 10 mL of triethylamine, add into a reactor and stir, under nitrogen protection, raise the temperature of the reactor to 55° C., keep warm for 5 hours, after the reaction is completed, set the temperature of the reactor to 75° C., remove the organic solvent by vacuum distillation, filter, wash the product with anhydrous ethanol 5 times, filter, place the product in a vacuum drying oven at 80° C., dry to constant weight, and obtain intermediate I;

[0074] Weigh: 400 g of intermediate I, 80 g of 5-hexene-1-amine, 800 mL of methanol solution and 40 mL of triethylamine, add into the reactor and stir. Under nitrogen protection, the temperature of the reactor is raised to 55°C and kept warm for 7 hours. After the reaction is completed, the temperature of the reactor is set to 75°C, and the organic solvent is removed by vacuum distillation. The product is filtered and washed with anhydrous ethanol 5 times. The product is filtered and placed in a vacuum drying oven at 80°C and dried to constant weight to obtain a modified enhancer.

[0075] S2. Preparation of modified polypropylene

[0076] Weigh: 300 g of polypropylene particles and 1500 mL of acetone are added to an ultrasonic cleaner for washing, the temperature of the cleaner is raised to 70°C, stirred for 2.5 hours, and after the impurity removal is completed, the temperature of the cleaner is lowered to room temperature, filtered, and the polyethylene solid is placed in a vacuum dryer at 80°C and dried to constant weight to obtain pretreated polyethylene;

[0077] Weigh: 700 g of pretreated polyethylene, 2500 mL of acrylic acid solution and 100 mL of HMPP solution into a reactor, move to a UV light box, and perform UV grafting reaction. The acrylic acid solution is composed of acrylic acid and acetone mixed in a dosage ratio of 30 g:100 mL, and the HMPP solution is composed of HMPP and acetone solution mixed in a volume ratio of 5:100. The UV wavelength is 249 nm and the energy is 510 mJ / cm 2 , the oxygen content is 0.3%. After the reaction is completed, it is placed in a 95% ethanol aqueous solution and ultrasonically cleaned to remove unreacted monomers and oligomers. The product is filtered and placed in a vacuum drying oven at 40°C and dried to constant weight to obtain modified polypropylene.

[0078] S3. Preparation of modified flame retardant

[0079] Weigh: 400 g of DOPO and 1500 mL of toluene are added to a reactor and stirred. The temperature of the reactor is raised to 110°C, condensed and refluxed, 500 mL of acrylamide solution is added, and the reaction is kept warm for 5.5 hours. After the reaction is completed, the temperature of the reactor is lowered to room temperature, filtered, and the obtained solid is extracted with ethanol in a Soxhlet extractor for 10 hours, and dried under reduced pressure to obtain intermediate II;

[0080] Weigh: 300 g of intermediate II and 900 mL of DMSO are added into a vacuum reactor, stirred and dissolved, the temperature of the reactor is increased to 70°C, 250 g of 4-allylbenzoic acid and 40 mL of triethylamine are added, and the reaction is carried out for 5 hours. After the reaction is completed, the reaction solution is dehydrated, dried, crystallized, the crystals are separated, and the modified flame retardant is obtained after drying.

[0081] S4. Preparation of polyolefin cables modified with composite flame retardants

[0082] Wrapping the mica insulation wrapping tape around the outside of the four cable conductors 1 to form a wrapping layer 2;

[0083] The flexible foamed metal copper is bonded to the surface of the wrapping layer 2 to obtain a buffer shielding layer 3;

[0084] Weigh by weight: 110 parts of high-density polyethylene resin, 60 parts of low-density polyethylene resin, 20 parts of modified polypropylene, 70 parts of modified flame retardant, 13 parts of modified reinforcing agent, 1.5 parts of bis-2,4-di-tert-butylphenyl aluminum phosphate, 1.5 parts of polyethylene wax, 1.5 parts of zinc calcium acid and 1.5 parts of zinc stearate, and add them into a twin-screw extruder. The temperatures of the eight temperature sections of the twin-screw extruder from the feed port to the discharge port are 150°C, 155°C, 160°C, 160°C, 170°C, 170°C, 185°C, and 185°C, respectively. The main engine speed of the twin-screw extruder is 100 rpm, and the pressure is 140 bar. After melt extrusion, it is coated on the outside of the buffer shielding layer 3 to obtain a cable precursor. The cable precursor is transferred to a water vapor box, heat-insulated for 7 hours, cooled and discharged to obtain a cable.

[0085] Example 3

[0086] See also Figure 1 This embodiment provides a method for preparing a low-smoke, halogen-free medium-voltage power cable based on environmentally friendly materials, comprising the following steps:

[0087] S1. Preparation of modified reinforcing agent

[0088] Weigh: 200 g of hydroxypropyl-terminated polydimethylsiloxane, 100 g of toluene-2,4-diisocyanate, 600 mL of xylene and 10 mL of triethylamine, add into a reactor and stir, under nitrogen protection, raise the temperature of the reactor to 60° C., keep warm for 6 hours, after the reaction is completed, set the temperature of the reactor to 80° C., remove the organic solvent by vacuum distillation, filter, wash the product with anhydrous ethanol 5 times, filter, place the product in a vacuum drying oven at 80° C., dry to constant weight, and obtain intermediate I;

[0089] Weigh: 400 g of intermediate I, 80 g of 5-hexene-1-amine, 800 mL of methanol solution and 40 mL of triethylamine, add them into a reactor and stir. Under nitrogen protection, the temperature of the reactor is raised to 60°C and kept warm for 8 hours. After the reaction is completed, the temperature of the reactor is set to 80°C, and the organic solvent is removed by vacuum distillation. The product is filtered and washed 5 times with anhydrous ethanol. The product is filtered and placed in a vacuum drying oven at 80°C and dried to constant weight to obtain a modified enhancer.

[0090] S2. Preparation of modified polypropylene

[0091] Weigh: 300 g of polypropylene particles and 1500 mL of acetone are added to an ultrasonic cleaner for washing, the temperature of the cleaner is raised to 80°C, stirred for 3 hours, and after the impurity removal is completed, the temperature of the cleaner is lowered to room temperature, filtered, and the polyethylene solid is placed in a vacuum dryer at 80°C and dried to constant weight to obtain pretreated polyethylene;

[0092] Weigh: 700 g of pretreated polyethylene, 2500 mL of acrylic acid solution and 100 mL of HMPP solution into a reactor, move to a UV light box, and perform UV grafting reaction. The acrylic acid solution is composed of acrylic acid and acetone mixed in a dosage ratio of 30 g:100 mL, and the HMPP solution is composed of HMPP and acetone solution mixed in a volume ratio of 5:100. The UV wavelength is 249 nm and the energy is 510 mJ / cm 2 , oxygen content is 0.3%. After the reaction is completed, it is placed in a 95% ethanol aqueous solution, ultrasonic cycle cleaning is performed to remove unreacted monomers and oligomers, and the product is filtered and placed in a vacuum drying oven at a temperature of 40°C and dried to constant weight to obtain modified polypropylene;

[0093] S3. Preparation of modified flame retardant

[0094] Weigh: 400 g of DOPO and 1500 mL of toluene are added to a reactor and stirred. The temperature of the reactor is raised to 120°C, condensed and refluxed, 500 mL of acrylamide solution is added, and the reaction is kept warm for 6 hours. After the reaction is completed, the temperature of the reactor is lowered to room temperature, filtered, and the obtained solid is extracted with ethanol in a Soxhlet extractor for 10 hours, and dried under reduced pressure to obtain intermediate II;

[0095] Weigh: 300 g of intermediate II and 900 mL of DMSO are added into a vacuum reactor, stirred and dissolved, the temperature of the reactor is increased to 80°C, 300 g of 4-allylbenzoic acid and 50 mL of triethylamine are added, and the reaction is carried out for 6 hours. After the reaction is completed, the reaction solution is dehydrated, dried, crystallized, the crystals are separated, and the modified flame retardant is obtained after drying.

[0096] S4. Preparation of polyolefin cables modified with composite flame retardants

[0097] Wrapping the mica insulation wrapping tape around the outside of the four cable conductors 1 to form a wrapping layer 2;

[0098] The flexible foamed metal copper is bonded to the surface of the wrapping layer 2 to obtain a buffer shielding layer 3;

[0099] Weigh by weight: 120 parts of high-density polyethylene resin, 70 parts of low-density polyethylene resin, 30 parts of modified polypropylene, 80 parts of modified flame retardant, 15 parts of modified reinforcing agent, 2 parts of double 2,4-di-tert-butylphenyl aluminum phosphate, 2 parts of polyethylene wax, 2 parts of zinc calcium acid and 2 parts of zinc stearate, and add them into a twin-screw extruder. The temperatures of the eight temperature sections of the twin-screw extruder from the feed port to the discharge port are 150°C, 155°C, 160°C, 160°C, 170°C, 170°C, 185°C, and 185°C, respectively. The main engine speed of the twin-screw extruder is 120rpm, and the pressure is 160 bar. After melt extrusion, it is coated on the outside of the buffer shielding layer 3 to obtain a cable precursor. The cable precursor is transferred to a water vapor box, heat-insulated for 8 hours, cooled and discharged to obtain a cable.

[0100] Comparative Example 1

[0101] The difference between this comparative example and Example 3 is that step S1 is omitted and no modifying enhancer is added in step S4.

[0102] Comparative Example 2

[0103] The difference between this comparative example and Example 3 is that the pretreated polyethylene in step S2 replaces the modified polypropylene in step S4.

[0104] Comparative Example 3

[0105] The difference between this comparative example and Example 3 is that step S3 is eliminated and no modified flame retardant is added in step S4.

[0106] The performance of the low-smoke halogen-free power cables prepared in Examples 1-3 and Comparative Examples 1-3 was tested, wherein the breaking strength of the material at room temperature and 200°C was measured according to the standard GB / T 2951.13-2008 "General Test Methods for Insulation and Sheath Materials of Electric and Optical Cables Part 13: Tensile Test Methods at High and Low Temperatures"; the oxygen index of the sample was measured to prove its flame retardant and low smoke performance according to the standard GB / T19666-2019 "General Rules for Flame Retardant and Fire Resistant Wires, Cables or Optical Cables". The specific test results are shown in Table 1:

[0107] Table 1-Performance test data of samples

[0108]

[0109] Data Analysis:

[0110] It can be seen from the relevant data in Table 1 that, compared with the comparative example, the present invention introduces siloxane segments and integrates them into the carboxylated polyethylene skeleton through chemical bonds. At the same time, the introduced urethane bonds, urea bonds, carboxylate bonds and other chemical bonds form a cross-linked network, which effectively improves the overall mechanical strength and high temperature resistance of the cable material. The prepared modified flame retardant forms a flame retardant protective layer on the surface of the composite polyolefin. The cable material with multiple chemical bonds and materials in synergy has greatly improved environmental protection, mechanical structure and flame retardant properties, meeting the dual needs of modern cable applications for high performance and environmental protection.

[0111] Compared with Examples 1-3, the breaking strength of Comparative Example 1 at room temperature and at 200°C is reduced. By introducing siloxane chain segments and integrating them into the polyethylene skeleton through chemical bonds, the introduced various chemical bonds such as carbamate bonds, urea bonds and carboxylate bonds form a cross-linked network, which effectively improves the glass transition temperature and heat resistance of the polyolefin material, and enhances the overall high temperature resistance of the material. The flexibility of the siloxane chain segments improves the breaking strength of the material, and the compatibility with the polyolefin substrate is also improved, which reduces the phase separation of the material, and further enhances the overall mechanical strength of the cable material at high temperatures.

[0112] Compared with Examples 1-3, the smoke concentration in Comparative Example 2 is reduced. The polarity of the modified polyethylene material is enhanced by introducing carboxyl groups, thereby improving the compatibility with additives. Carboxylated polyethylene can also improve the charring ability, reduce combustion smoke and toxic gases, and improve flame retardant safety.

[0113] Compared with Examples 1-3, the oxygen index of Comparative Example 3 is significantly reduced, indicating that the flame retardant significantly improves the compatibility with polyolefins by introducing amide groups. The flame retardant also contains olefin functional groups, which decompose at high temperatures to produce free radicals. These free radicals can capture the free radicals produced by the combustion of the polymer, thereby terminating the chain combustion reaction. This multiple mechanism works together to make the outer sheath layer have excellent flame retardant properties, which can effectively prevent the spread of fire and protect the normal function of the cable. At the same time, the cross-linked structure enables the material to better resist thermal decomposition and degradation, and improve mechanical strength, rigidity and durability.

[0114] Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and describes these embodiments in detail to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. Low smoke halogen-free medium voltage power cable based on environmentally friendly materials, characterized by: It comprises a plurality of cable conductors (1), a wrapping layer (2), a buffer shielding layer (3) and a flame-retardant outer sheath layer (4) which are arranged in sequence from the inside to the outside; The wrapping layer (2) is obtained by wrapping a mica insulating wrapping tape around the outside of a plurality of cable conductors (1); The buffer shielding layer (3) is obtained by bonding flexible foamed metal copper to the surface of the wrapping layer (2); The flame retardant outer sheath layer (4) is obtained by coating a composite flame retardant modified polyolefin cable material composed of high-density polyethylene resin, low-density polyethylene resin, modified polypropylene, modified reinforcing agent, modified flame retardant, initiator, dispersant, heat stabilizer and lubricant on the outside of the buffer shielding layer (3).

2. The low-smoke halogen-free medium-voltage power cable based on environmentally friendly materials according to claim 1 is characterized in that: The modified reinforcing agent is obtained by processing the following steps: S1, adding hydroxypropyl-terminated polydimethylsiloxane, toluene-2,4-diisocyanate, xylene and triethylamine into a reaction kettle and stirring, raising the temperature of the reaction kettle to 50-60° C. under nitrogen protection, keeping the temperature for reaction for 4-6 hours, and post-treating to obtain intermediate I; S2. Add intermediate I, 5-hexene-1-amine, methanol solution and triethylamine into a reaction kettle and stir. Under nitrogen protection, increase the temperature of the reaction kettle to 50-60° C. and keep the temperature for 6-8 hours. Post-process to obtain a modified enhancer.

3. The low-smoke halogen-free medium-voltage power cable based on environmentally friendly materials according to claim 2 is characterized in that: In step S1, the amount ratio of the hydroxypropyl-terminated polydimethylsiloxane, toluene-2,4-diisocyanate, xylene and triethylamine is 2g:1g:6mL:0.1mL; in step S2, the amount ratio of the intermediate I, 5-hexene-1-amine, methanol solution and triethylamine is 1g:0.2g:2mL:0.1mL.

4. The low-smoke halogen-free medium-voltage power cable based on environmentally friendly materials according to claim 1, characterized in that: The modified polypropylene is obtained by processing the following steps: A1. Add polypropylene particles and acetone into an ultrasonic cleaner for washing, raise the temperature of the cleaner to 60-80°C, stir for 2-3 hours, and post-treat to obtain pretreated polyethylene; A2. Add pretreated polypropylene, acrylic acid solution and HMPP solution into a reaction kettle, move to an ultraviolet light box, perform ultraviolet light grafting reaction, and post-treat to obtain modified polypropylene.

5. The low-smoke halogen-free medium-voltage power cable based on environmentally friendly materials according to claim 4, characterized in that: In the step A1, the amount ratio of the polypropylene particles to acetone is 1 g:5 mL; in the step A2, the amount ratio of the pretreated polypropylene, the acrylic acid solution and the HMPP solution is 7 g:25 mL:1 mL, the acrylic acid solution is composed of acrylic acid and acetone mixed in a ratio of 30 g:100 mL, the HMPP solution is composed of HMPP and acetone solution mixed in a volume ratio of 5:100, the ultraviolet light wavelength is 249 nm, and the energy is 510 mJ / cm 2 , the oxygen content is 0.3%.

6. The low-smoke halogen-free medium-voltage power cable based on environmentally friendly materials according to claim 1, characterized in that: The modified flame retardant is obtained by processing the following steps: B1. Add DOPO and toluene into a reactor and stir. Raise the temperature of the reactor to 100-120°C, condense and reflux, add acrylamide solution, keep the temperature for 5-6 hours, and post-treat to obtain intermediate II. B2. Add intermediate II and DMSO into a vacuum reactor and stir to dissolve. Increase the temperature of the reactor to 60-80°C, add 4-allylbenzoic acid and triethylamine, react for 4-6 hours, and post-treat to obtain a modified flame retardant.

7. The low-smoke halogen-free medium-voltage power cable based on environmentally friendly materials according to claim 6, characterized in that: In the step B1, the amount ratio of DOPO, toluene and acrylamide solution is 4g:15mL:5mL, and the acrylamide solution is composed of acrylamide and deionized water mixed in a ratio of 2g:3mL; in the step B2, the amount ratio of intermediate II, DMSO, 4-allylbenzoic acid and triethylamine is 3g:9mL:2-3g:0.3-0.4mL.

8. The low-smoke halogen-free medium-voltage power cable based on environmentally friendly materials according to claim 1, characterized in that: The weight ratio of the high-density polyethylene resin, the low-density polyethylene resin, the modified polypropylene, the modified flame retardant, the modified reinforcing agent, the initiator, the dispersant, the heat stabilizer and the lubricant is 100-120:50-70:10-30:60-80:10-15:1-2:1-2:1-2:1-2; the dispersant is one or two of polyethylene wax and polypropylene wax; the heat stabilizer is one or more of zinc calcium acid, magnesium calcium acid and aluminum calcium acid; the initiator is one or more of bis(2,4-di-tert-butylphenyl) phosphate sodium salt (NA-11) and bis(2,4-di-tert-butylphenyl) aluminum phosphate; and the lubricant is one or more of zinc stearate, magnesium stearate and calcium stearate.

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