Halogen-free flame-retardant environment-friendly heat-resistant cable and preparation method thereof

Abstract

The invention discloses a halogen-free flame-retardant environment-friendly heat-resistant cable and a preparation method thereof, belongs to the technical field of cable material processing, and is used for solving the technical problem that the mechanical strength and heat resistance of a halogen-free flame-retardant environment-friendly cable in the prior art need to be further improved. The cable comprises a plurality of cable conductors, a wrapping layer and a sheath layer which are sequentially arranged from inside to outside, and the sheath layer comprises the following components in parts by weight: 70-80 parts of low-density polyethylene, 20-30 parts of modified polysiloxane, 10-16 parts of modified polyvinyl alcohol, 15-18 parts of modified kaolin, 2-3 parts of an initiator and 3-4 parts of an auxiliary additive. Low-density polyethylene is reinforced and modified through modified kaolin, modified polyvinyl alcohol and modified polysiloxane, so that not only are the mechanical strength and flame retardance of the environment-friendly heat-resistant cable effectively improved, but also the high-temperature resistance of the cable is improved, and the service life of the cable in a high-temperature environment is prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of cable material processing, and in particular to a halogen-free, flame-retardant, environmentally friendly, heat-resistant cable and a preparation method thereof. Background Art

[0002] As people's awareness of safety and environmental protection continues to increase, especially in important departments and public places such as high-rise buildings, subways, power plants, nuclear power plants and rail transit, higher requirements are placed on the safety performance of cables. Traditional polyvinyl chloride cables will release toxic gases and a lot of smoke when burning, which not only threatens the safety of personnel, but also hinders fire rescue work. Compared with ordinary PVC cables, halogen-free flame-retardant cables will not release corrosive gases and toxic smoke when burning, and have better safety and environmental protection.

[0003] The flame retardant properties of halogen-free flame retardant cables in the prior art mainly rely on a large amount of filled metal hydroxides, such as magnesium hydroxide and aluminum hydroxide. These flame retardants can decompose at high temperatures to produce water and metal oxides, absorb a large amount of heat and inhibit the continued combustion of the material. However, the addition of a large amount of inorganic flame retardants will significantly reduce the mechanical and electrical properties of the material, thereby affecting the practicality and reliability of the cable. In addition, traditional cables have poor high temperature resistance. Cables are prone to thermal aging or thermal shrinkage when exposed to high temperature environments for a long time, resulting in a shorter service life of the cable.

[0004] In view of the technical defects in this aspect, a solution is now proposed. Summary of the invention

[0005] The object of the present invention is to provide a halogen-free flame-retardant, environmentally friendly, heat-resistant cable and a preparation method thereof, so as to solve the technical problem in the prior art that the mechanical strength and heat resistance of the halogen-free flame-retardant, environmentally friendly cable need to be further improved.

[0006] The purpose of the present invention can be achieved through the following technical scheme: a halogen-free flame-retardant, environmentally friendly and heat-resistant cable, comprising a plurality of cable conductors, a wrapping layer and a sheath layer arranged in sequence from the inside to the outside, wherein the sheath layer comprises the following components in parts by weight: 70-80 parts of low-density polyethylene, 20-30 parts of modified polysiloxane, 10-16 parts of modified polyvinyl alcohol, 15-18 parts of modified kaolin, 2-3 parts of initiator and 3-4 parts of auxiliary additives.

[0007] Furthermore, the cable conductor is composed of a core composed of several copper conductors twisted together and a polyethylene insulation layer wrapped around the outside of the core, the wrapping layer is obtained by wrapping a wrapping tape around the outside of several cable conductors, the wrapping tape is a PET polyester tape, the initiator is diisopropylbenzene peroxide, and the auxiliary additives are composed of a plasticizer, a dispersant and a lubricant in a weight ratio of 5:2:2, the plasticizer is a phthalate, the dispersant is a stearate, and the lubricant is one or more of butyl stearate, oleamide, and ethylene bisstearamide.

[0008] Further, the modified polysiloxane is processed by the following steps:

[0009] A1. Add tetramethyltetravinylcyclotetrasiloxane, octamethylcyclotetrasiloxane and modified antioxidant into xylene and stir. Raise the temperature of the reaction system to 110-120° C., add catalyst to the reaction system, keep the temperature for 2-3 hours, add end-capping agent to the reaction system, keep the temperature for 4-6 hours, and post-treat to obtain polysiloxane.

[0010] The synthetic reaction formula of polysiloxane is:

[0011]

[0012] Where:

[0013]

[0014] The synthetic reaction mechanism of polysiloxane is:

[0015] Under the action of high temperature and catalyst, tetramethyltetravinylcyclotetrasiloxane and octamethylcyclotetrasiloxane are ring-opened to form siloxane chains with silanol activity, the siloxane bonds on the modified antioxidant molecules are broken to form silanol groups, and then the siloxane chains with silanol activity are condensed to form siloxane silicon segments modified with olefin double bonds and antioxidants, (1,1,3,3-tetramethyl-1,3-disiloxanediyl) dimethanol is used as a capping agent, and under the action of high temperature and catalyst, the siloxane bonds of the capping agent molecules are broken, and hydroxyl end caps are formed at both ends of the long siloxane silicon segments to prepare polysiloxane.

[0016] A2. Under the protection of inert gas, add polysiloxane into xylene and stir, raise the temperature of the reaction system to 70-80°C, add isocyanatepropyltriethoxysilane into the reaction system, keep the temperature for 3-5h, and post-treat to obtain modified polysiloxane.

[0017] The synthetic reaction formula of modified polysiloxane is:

[0018]

[0019] The synthetic reaction mechanism of modified polysiloxane is:

[0020] Under nitrogen protection, the hydroxyl groups on the polysiloxane chain segment molecules react with the isocyanate groups on the isocyanatepropyltriethoxysilane molecules to form triethoxysilane modification on the polysiloxane chain segment, thereby preparing modified polysiloxane.

[0021] Furthermore, in step A1, the amount ratio of the tetramethyltetravinylcyclotetrasiloxane, octamethylcyclotetrasiloxane, modified antioxidant, xylene, catalyst and end-capping agent is 3-5g:8-10g:2-3g:60-70mL:6-7g:3-4g, the catalyst is 50-60wt% sulfuric acid, and the end-capping agent is (1,1,3,3-tetramethyl-1,3-disiloxanediyl) dimethanol. The post-treatment includes: after the reaction is completed, the temperature of the reaction system is lowered to room temperature, purified water is added to the reaction system, stirred for 10 minutes, allowed to stand for separation, the organic phase is washed with purified water until neutral and then dried, the organic phase is transferred to a rotary evaporator with a water bath temperature of 80-90°C, and the solvent is removed under reduced pressure to obtain polysiloxane.

[0022] Furthermore, in step A2, the usage ratio of the polysiloxane, xylene and isocyanatepropyltriethoxysilane is 7g:70mL:1g, and the post-treatment includes: after the reaction is completed, heat preservation, and evaporation under reduced pressure to remove the solvent to obtain modified polysiloxane.

[0023] Furthermore, the preparation method of the modified antioxidant is: under the protection of inert gas, antioxidant SP and 3-isocyanatepropylmethyldiethoxysilane are added to tetrahydrofuran and stirred, the temperature of the mixed system is increased to 55-65°C, the reaction is kept warm for 80-100 minutes, and post-processed to obtain the modified antioxidant.

[0024] The synthetic reaction formula of the modified antioxidant is:

[0025]

[0026] The synthetic reaction mechanism of the modified antioxidant is:

[0027] During the reaction, the phenolic hydroxyl group on the antioxidant SP molecule reacts with the isocyanate group on the 3-isocyanatepropylmethyldiethoxysilane molecule to undergo a condensation reaction, and methyldiethoxysilane is modified on the antioxidant SP molecule to prepare a modified antioxidant. The mass spectrometry analysis data of the modified antioxidant are: m / z: 623.3431 (100.0%), 624.3464 (42.2%), 625.3498 (8.7%), 624.3427 (5.1%),

[0028] 625.3399(3.3%),625.3460(2.1%),626.3433(1.4%),626.3532(1.2%).

[0029] Furthermore, the dosage ratio of the antioxidant SP and 3-isocyanatepropylmethyldiethoxysilane is 1 mol:1 mol, the dosage ratio of the antioxidant SP and tetrahydrofuran is 1 g:8 mL, and the post-treatment includes: after the reaction is completed, heat preservation, and evaporating the solvent under reduced pressure to obtain a modified antioxidant.

[0030] Furthermore, the preparation method of modified polyvinyl alcohol is as follows: polyvinyl alcohol is added to purified water and stirred, the temperature of the reaction system is increased to 85-95°C, and stirred until the system is dissolved, phosphoric acid solution is added to the reaction system, and the mixture is stirred for 2-3 hours at a temperature of 100-200°C. Urea solution is added dropwise to the reaction system, and after the addition is completed, the mixture is reacted for 3-4 hours at a temperature of 100-200°C, and the modified polyvinyl alcohol is obtained by post-treatment.

[0031] The synthetic reaction mechanism of modified polyvinyl alcohol is:

[0032] Under high temperature, phosphate ions react with hydroxyl groups in polyvinyl alcohol molecules to form phosphate ester bonds, embedding the phosphate groups into the polyvinyl alcohol molecular chains, and the amino groups in the urea molecules form hydrogen bonds with the hydroxyl groups in the phosphoric acid or polyvinyl alcohol molecules, thereby improving the stability of the reaction intermediates and products. The hydroxyl groups or phosphate ester groups in the polyvinyl alcohol molecules can form cross-linked structures with calcium ions, promoting aggregation and precipitation between polyvinyl alcohol molecules, and preparing modified polyvinyl alcohol.

[0033] Furthermore, the dosage ratio of the polyvinyl alcohol, purified water, phosphoric acid solution and urea solution is 10g:100mL:2g:5mL, the mass fraction of the phosphoric acid solution is 85-90%, and the urea solution is composed of urea and purified water in a dosage ratio of 1g:5mL. The post-treatment includes: after the reaction is completed, the temperature of the reaction system is reduced to room temperature to obtain a polyvinyl alcohol reaction liquid, the polyvinyl alcohol reaction liquid is added dropwise to a 30wt% calcium chloride solution, and the solution is aged for 2-3h at room temperature, and then filtered. The filter cake is washed with purified water for 5 times and then dried, and the filter cake is placed in a drying oven at a temperature of 60-70°C, and vacuum dried to constant weight to obtain modified polyvinyl alcohol.

[0034] Further, the modified kaolin is processed by the following steps:

[0035] B1. Add kaolin to the activation solution and stir, raise the temperature of the reaction system to 70-80°C, keep warm for 2-3h, and post-treat to obtain activated kaolin;

[0036] B2. Add activated kaolin and KH-560 into anhydrous ethanol and stir. Raise the temperature of the reaction system to 60-70°C. Add a catalyst into the reaction system and keep it warm for 90-120 minutes. Add melamine into the reaction system and keep it warm for 2-3 hours. After post-treatment, obtain modified kaolin.

[0037] The synthetic reaction formula of modified kaolin is:

[0038]

[0039] Where:

[0040] To activate kaolin particles;

[0041] .

[0042] The synthetic reaction mechanism of modified kaolin is:

[0043] Sulfuric acid provides protons, and hydrogen peroxide releases strong oxidizing oxygen free radicals under acidic conditions to activate kaolin, thereby increasing the surface activity of kaolin particles and the modification concentration of KH-560 on the kaolin surface. Under alkaline conditions, the epoxy groups on the KH-560 molecules undergo ring-opening condensation with melamine, modifying the kaolin molecules with melamine to prepare modified kaolin.

[0044] Furthermore, in step B1, the amount ratio of kaolin and activation solution is 1g:7-10mL, the activation solution is composed of 40-50wt% sulfuric acid, 25-30wt% hydrogen peroxide and polyethylene glycol 1000 in the amount ratio of 60-70mL:25-35mL:5-10g, and the post-treatment includes: after the reaction is completed, the temperature of the reaction system is lowered to room temperature, filtered, the filter cake is washed with purified water until it is neutral and then dried, the filter cake is transferred to a drying oven at a temperature of 70-80°C, and vacuum dried to constant weight to obtain activated kaolin.

[0045] Furthermore, in step B2, the amount ratio of the activated kaolin, KH-560, anhydrous ethanol and melamine is 10g:3g:70mL:40mL:2g, and the post-treatment includes: after the reaction is completed, the temperature of the reaction system is lowered to room temperature, filtered, the filter cake is washed with purified water at a temperature of 70-80°C until it is neutral and then dried, the filter cake is transferred to a drying oven at a temperature of 75-85°C, and vacuum dried to constant weight to obtain modified kaolin.

[0046] The present invention also provides a method for preparing a halogen-free, flame-retardant, environmentally friendly, heat-resistant cable, comprising the following steps:

[0047] S1. Wrapping a plurality of cable conductors together using a wrapping tape to form a wrapping layer outside the plurality of cable conductors;

[0048] S2. Mix low-density polyethylene, modified polysiloxane, modified polyvinyl alcohol, modified kaolin, initiator and auxiliary additives at 135-145°C for 20-30 minutes, transfer to a twin-screw extruder, melt-extrude and coat the outer surface of the wrapping layer through the twin-screw extruder, cool and solidify to obtain an environmentally friendly heat-resistant cable.

[0049] The present invention has the following beneficial effects:

[0050] 1. The halogen-free flame-retardant, environmentally friendly, heat-resistant cable of the present invention uses modified kaolin as filler, modified polyvinyl alcohol and modified polysiloxane as reinforcing materials. The polysiloxane molecular chain itself has good flexibility, and it cooperates with low-density polyethylene to improve the mechanical strength of the material. In the high-temperature melting and mixing process with low-density polyethylene, modified polyvinyl alcohol is used as a compatibilizer to increase the compatibility between the modified polysiloxane and the low-density polyethylene. Under the action of an initiator, the low-density polyethylene is cross-linked and bonded to strengthen the low-density polyethylene, thereby improving the mechanical strength, aging and heat resistance of the polyethylene sheath layer based on the low-density polyethylene. Performance and flame retardant properties; when preparing modified polysiloxane, a large number of unsaturated double bonds are introduced into the polysiloxane chain segment and triethoxysilane capping is formed at its end, and under the action of initiator and high temperature, the unsaturated double bonds on the modified polysiloxane molecular chain undergo free radical polymerization with the low-density polyethylene or modified polyvinyl alcohol molecular chain, thereby improving the crosslinking degree of the modified polyvinyl alcohol, modified polysiloxane and low-density polyethylene molecular chains. In a high humidity environment, the siloxane bonds on the modified polysiloxane molecular chain can also be hydrolyzed to form silanol groups that bond with the active groups on the modified kaolin or modified polyvinyl alcohol molecules, thereby improving the mechanical strength of the material.

[0051] 2. The halogen-free flame-retardant, environment-friendly and heat-resistant cable of the present invention introduces an antioxidant SP modification on the molecular chain of the modified polysiloxane when preparing the modified polysiloxane. The antioxidant SP is uniformly dispersed in the low-density polyethylene material along with the modified polysiloxane, giving the material good anti-aging performance. Kaolin itself has good thermal stability, which can increase the antioxidant performance of the material. When preparing the modified kaolin, a nitrogen-containing compound based on melamine is introduced into the external modification to form a nitrogen-containing compound coating on the outside of the kaolin particles, which can prevent the penetration of heat and oxygen, further improve the thermal stability of the material, thereby reducing the oxidative degradation rate of the polyethylene material at high temperature, and cooperates with the antioxidant SP modified on the modified polysiloxane molecular chain to further improve the heat aging resistance of the material. In addition, by modifying the kaolin, the polarity of the surface of the modified kaolin particles is enhanced, so that the interaction force between the modified kaolin and the low-density polyethylene molecular chain is increased, the uniform dispersion of the modified kaolin in the low-density polyethylene is promoted, and the mechanical strength and heat aging resistance of the material are improved.

[0052] 3. The halogen-free flame-retardant, environment-friendly and heat-resistant cable of the present invention introduces a phosphoric acid group into the molecular chain of the polyvinyl alcohol when preparing the modified polyvinyl alcohol. The polarity and hydrophilicity of the phosphoric acid group help to reduce the interfacial tension between the modified polyvinyl alcohol and the low-density polyethylene, making it easier to disperse evenly in the low-density polyethylene. At the same time, the improvement in the dispersibility also helps to improve the compatibility of the components in the composite material. Moreover, the phosphoric acid group itself has certain flame retardant properties, and the phosphoric acid group, the nitrogen-containing compound loaded on the modified kaolin, the kaolin body and the polysiloxane chain segment constitute a synergistic flame retardant system to improve the flame retardant properties of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] 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.

[0054] Figure 1 It is a schematic diagram of the three-dimensional structure of the environmentally friendly heat-resistant cable of the present invention.

[0055] In the figure: 1. Cable conductor; 2. Wrapping layer; 3. Sheath layer. DETAILED DESCRIPTION

[0056] 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.

[0057] The molecular weight of the polyvinyl alcohol used in the present invention is 5000;

[0058] The low-density polyethylene used in the present invention is produced by Sinopec, with a grade of M2720A and a melt flow rate of 18.0-22.0.

[0059] Example 1

[0060] This embodiment provides a method for preparing a halogen-free, flame-retardant, environmentally friendly, heat-resistant cable, comprising the following steps:

[0061] S1. Modified antioxidant

[0062] Weigh: 40.7 g antioxidant SP, 21.7 g 3-isocyanatepropylmethyldiethoxysilane, and 325.6 mL tetrahydrofuran, add into a three-necked flask protected by nitrogen and stir, raise the temperature of the three-necked flask to 55° C., keep warm and react for 80 minutes, evaporate the solvent under reduced pressure to obtain a modified antioxidant.

[0063] S2. Preparation of modified polysiloxane

[0064] Weigh: 30 g of tetramethyltetravinylcyclotetrasiloxane, 80 g of octamethylcyclotetrasiloxane, 20 g of modified antioxidant, and 600 mL of xylene, add them into a three-necked flask and stir, raise the temperature of the three-necked flask to 110° C., add 60 g of 50 wt% into the reaction system, keep warm for 2 h, add 30 g of (1,1,3,3-tetramethyl-1,3-disiloxanediyl) dimethanol into the three-necked flask, keep warm for 4 h, lower the temperature of the three-necked flask to room temperature, add 300 mL of purified water into the reaction system, stir for 10 min, stand for separation, wash the organic phase with purified water until neutral and then drain, transfer the organic phase to a rotary evaporator with a water bath temperature of 80° C., remove the solvent under reduced pressure, and obtain polysiloxane;

[0065] Weigh: 700 g of polysiloxane and 7000 mL of xylene are added to a nitrogen-protected reactor and stirred. The temperature of the reactor is raised to 70° C. 100 g of isocyanatepropyltriethoxysilane is added to the reactor. The reaction is kept warm for 3 h. The solvent is evaporated under reduced pressure to obtain modified polysiloxane.

[0066] S3. Preparation of modified polyvinyl alcohol

[0067] Mix urea and purified water in a ratio of 1 g:5 mL to obtain a urea solution for later use;

[0068] Weigh: 100 g of polyvinyl alcohol and 1000 mL of purified water are added to a three-necked flask and stirred. The temperature of the three-necked flask is raised to 85°C and stirred until the system is dissolved. 20 g of 85 wt% phosphoric acid solution is added to the three-necked flask and stirred for 2 h. 50 mL of urea solution is added dropwise to the three-necked flask. After the addition is complete, the reaction is carried out by keeping the temperature for 3 h. The temperature of the reaction system is lowered to room temperature to obtain a polyvinyl alcohol reaction solution.

[0069] Under stirring, add the polyvinyl alcohol reaction liquid dropwise into a three-necked flask containing 30wt% calcium chloride solution. After the addition is completed, let it stand for aging for 2h at room temperature, filter it, wash the filter cake with purified water 5 times and then dry it. Put the filter cake into a drying oven at 60℃ and vacuum dry it to constant weight to obtain modified polyvinyl alcohol.

[0070] S4. Preparation of modified kaolin

[0071] 40wt% sulfuric acid, 25wt% hydrogen peroxide and polyethylene glycol 1000 were mixed uniformly in a dosage ratio of 60mL:25mL:5g to obtain an activation solution for standby use;

[0072] Weigh: 100 g of kaolin and 700 mL of activation solution, add them into a three-necked flask and stir, raise the temperature of the three-necked flask to 70°C, keep it warm for 2 hours, lower the temperature of the three-necked flask to room temperature, filter, wash the filter cake with purified water until it is neutral and then dry it, transfer the filter cake to a drying oven at a temperature of 70°C, and vacuum dry it to constant weight to obtain activated kaolin;

[0073] Weigh: 100 g of activated kaolin, 30 g of KH-560, and 700 mL of anhydrous ethanol, add into a three-necked flask and stir, raise the temperature of the three-necked flask to 60°C, add 400 mL of 10 wt% sodium hydroxide solution into the three-necked flask, and keep warm for 90 min, add 20 g of melamine into the three-necked flask, and keep warm for 2 h, lower the temperature of the three-necked flask to room temperature, filter, wash the filter cake with purified water at a temperature of 70°C until it is neutral, and then drain, transfer the filter cake to a drying oven at a temperature of 75°C, and vacuum dry to constant weight to obtain modified kaolin.

[0074] S5. Preparation of environmentally friendly heat-resistant cables

[0075] Using a PET polyester tape to wrap five cable conductors 1 together, forming a wrapping layer 2 outside a plurality of cable conductors 1;

[0076] Diisobutyl phthalate, calcium stearate and butyl stearate are mixed uniformly in a weight ratio of 5:2:2 to obtain an auxiliary additive for later use;

[0077] Weigh by weight: 70 parts of low-density polyethylene, 20 parts of modified polysiloxane, 10 parts of modified polyvinyl alcohol, 15 parts of modified kaolin, 2 parts of diisopropylbenzene peroxide, and 3 parts of auxiliary additives, add them to a twin-roll open mill at a temperature of 135°C, mix for 20 minutes in an environment with an ambient humidity of 50%, and transfer them to a twin-screw extruder while hot. The temperatures of the six temperature sections of the twin-screw extruder from the feed end to the discharge end are 235°C, 240°C, 240°C, 245°C, 245°C, and 250°C, respectively. The main shaft speed of the twin-screw extruder is 12r / min. The materials are melt-extruded and coated on the outside of the winding layer 2 through the twin-screw extruder, and then cooled and solidified to obtain an environmentally friendly heat-resistant cable.

[0078] Example 2

[0079] This embodiment provides a method for preparing a halogen-free, flame-retardant, environmentally friendly, heat-resistant cable, comprising the following steps:

[0080] S1. Modified antioxidant

[0081] Weigh: 40.7 g antioxidant SP, 21.7 g 3-isocyanatepropylmethyldiethoxysilane, and 325.6 mL tetrahydrofuran, add into a three-necked flask protected by nitrogen and stir, raise the temperature of the three-necked flask to 60° C., keep warm and react for 90 min, evaporate the solvent under reduced pressure to obtain a modified antioxidant.

[0082] S2. Preparation of modified polysiloxane

[0083] Weigh: 40g of tetramethyltetravinylcyclotetrasiloxane, 90g of octamethylcyclotetrasiloxane, 25g of modified antioxidant, and 650mL of xylene, add them into a three-necked flask and stir, raise the temperature of the three-necked flask to 115°C, add 65g of 55wt% to the reaction system, keep warm for 2.5h, add 35g of (1,1,3,3-tetramethyl-1,3-disiloxanediyl) dimethanol to the three-necked flask, keep warm for 5h, lower the temperature of the three-necked flask to room temperature, add 300mL of purified water to the reaction system, stir for 10min, stand and separate, wash the organic phase with purified water until neutral and then drain, transfer the organic phase to a rotary evaporator with a water bath temperature of 85°C, remove the solvent under reduced pressure, and obtain polysiloxane;

[0084] Weigh: 700 g of polysiloxane and 7000 mL of xylene are added to a nitrogen-protected reactor and stirred. The temperature of the reactor is raised to 75° C. 100 g of isocyanatepropyltriethoxysilane is added to the reactor. The reaction is kept warm for 4 hours. The solvent is evaporated under reduced pressure to obtain modified polysiloxane.

[0085] S3. Preparation of modified polyvinyl alcohol

[0086] Mix urea and purified water in a ratio of 1 g:5 mL to obtain a urea solution for later use;

[0087] Weigh: 100 g of polyvinyl alcohol and 1000 mL of purified water are added to a three-necked flask and stirred. The temperature of the three-necked flask is raised to 90°C and stirred until the system is dissolved. 20 g of 88 wt% phosphoric acid solution is added to the three-necked flask and stirred for 2.5 h. 50 mL of urea solution is added dropwise to the three-necked flask. After the addition is complete, the reaction is kept warm for 3.5 h. The temperature of the reaction system is lowered to room temperature to obtain a polyvinyl alcohol reaction solution.

[0088] Under stirring, add the polyvinyl alcohol reaction liquid dropwise into a three-necked flask containing 30wt% calcium chloride solution. After the addition is completed, let it stand and age for 2.5h at room temperature, filter it, wash the filter cake with purified water 5 times and then dry it. Put the filter cake into a drying oven at 65℃ and vacuum dry it to constant weight to obtain modified polyvinyl alcohol.

[0089] S4. Preparation of modified kaolin

[0090] 45wt% sulfuric acid, 28wt% hydrogen peroxide and polyethylene glycol 1000 were mixed uniformly in a dosage ratio of 65mL:30mL:7g to obtain an activation solution for standby use;

[0091] Weigh: 100 g of kaolin and 850 mL of activation solution are added to a three-necked flask and stirred. The temperature of the three-necked flask is raised to 75°C and kept warm for 2.5 hours. The temperature of the three-necked flask is lowered to room temperature and filtered. The filter cake is washed with purified water until it is neutral and then dried. The filter cake is transferred to a drying oven at a temperature of 75°C and vacuum dried to constant weight to obtain activated kaolin.

[0092] Weigh: 100 g of activated kaolin, 30 g of KH-560, and 700 mL of anhydrous ethanol, add into a three-necked flask and stir, raise the temperature of the three-necked flask to 65°C, add 400 mL of 10 wt% sodium hydroxide solution into the three-necked flask, and keep warm for 105 min, add 20 g of melamine into the three-necked flask, and keep warm for 2.5 h, lower the temperature of the three-necked flask to room temperature, filter, wash the filter cake with purified water at a temperature of 75°C until it is neutral, and then dry it, transfer the filter cake to a drying oven at a temperature of 80°C, and vacuum dry it to constant weight to obtain modified kaolin.

[0093] S5. Preparation of environmentally friendly heat-resistant cables

[0094] Using a PET polyester tape to wrap five cable conductors 1 together, forming a wrapping layer 2 outside a plurality of cable conductors 1;

[0095] Dimethyl phthalate, zinc stearate and oleamide are uniformly mixed in a weight ratio of 5:2:2 to obtain an auxiliary additive for standby use;

[0096] Weigh by weight: 75 parts of low-density polyethylene, 25 parts of modified polysiloxane, 13 parts of modified polyvinyl alcohol, 16 parts of modified kaolin, 2.5 parts of diisopropylbenzene peroxide, and 3.5 parts of auxiliary additives, add them to a twin-roll open mill at a temperature of 140°C, mix for 25 minutes in an environment with an ambient humidity of 55%, transfer them to a twin-screw extruder while hot, the temperatures of the six temperature sections of the twin-screw extruder from the feed end to the discharge end are 235°C, 240°C, 240°C, 245°C, 245°C, and 250°C, respectively, the main shaft speed of the twin-screw extruder is 12r / min, and the materials are melt-extruded and coated on the outside of the winding layer 2 by the twin-screw extruder, and then cooled and solidified to obtain an environmentally friendly heat-resistant cable.

[0097] Example 3

[0098] This embodiment provides a method for preparing a halogen-free, flame-retardant, environmentally friendly, heat-resistant cable, comprising the following steps:

[0099] S1. Modified antioxidant

[0100] Weigh: 40.7 g of antioxidant SP, 21.7 g of 3-isocyanatepropylmethyldiethoxysilane, and 325.6 mL of tetrahydrofuran, add into a three-necked flask protected by nitrogen and stir, raise the temperature of the three-necked flask to 65° C., keep the reaction for 100 min, evaporate the solvent under reduced pressure to obtain a modified antioxidant.

[0101] S2. Preparation of modified polysiloxane

[0102] Weigh: 50 g of tetramethyltetravinylcyclotetrasiloxane, 100 g of octamethylcyclotetrasiloxane, 30 g of modified antioxidant, and 700 mL of xylene, add to a three-necked flask and stir, raise the temperature of the three-necked flask to 120° C., add 70 g of 60 wt% to the reaction system, keep warm for 3 h, add 40 g of (1,1,3,3-tetramethyl-1,3-disiloxanediyl) dimethanol to the three-necked flask, keep warm for 6 h, lower the temperature of the three-necked flask to room temperature, add 300 mL of purified water to the reaction system, stir for 10 min, stand and separate, wash the organic phase with purified water until neutral and then drain, transfer the organic phase to a rotary evaporator with a water bath temperature of 90° C., remove the solvent under reduced pressure, and obtain polysiloxane;

[0103] Weigh: 700 g of polysiloxane and 7000 mL of xylene are added to a nitrogen-protected reactor and stirred. The temperature of the reactor is raised to 80° C. 100 g of isocyanatepropyltriethoxysilane is added to the reactor. The reaction is kept warm for 5 hours, and the solvent is evaporated under reduced pressure to obtain modified polysiloxane.

[0104] S3. Preparation of modified polyvinyl alcohol

[0105] Mix urea and purified water in a ratio of 1 g:5 mL to obtain a urea solution for later use;

[0106] Weigh: 100 g of polyvinyl alcohol and 1000 mL of purified water are added to a three-necked flask and stirred. The temperature of the three-necked flask is raised to 95°C and stirred until the system is dissolved. 20 g of 90 wt% phosphoric acid solution is added to the three-necked flask and stirred for 3 h. 50 mL of urea solution is added dropwise to the three-necked flask. After the addition is complete, the reaction is carried out by keeping the temperature for 4 h. The temperature of the reaction system is lowered to room temperature to obtain a polyvinyl alcohol reaction solution.

[0107] Under stirring, add the polyvinyl alcohol reaction liquid dropwise into a three-necked flask containing 30wt% calcium chloride solution. After the addition is completed, let it stand for aging for 3 hours at room temperature, filter it, wash the filter cake with purified water 5 times and then dry it. Put the filter cake into a drying oven at 70°C and vacuum dry it to constant weight to obtain modified polyvinyl alcohol.

[0108] S4. Preparation of modified kaolin

[0109] 50wt% sulfuric acid, 30wt% hydrogen peroxide and polyethylene glycol 1000 were mixed uniformly in a dosage ratio of 70mL:35mL:10g to obtain an activation solution for standby use;

[0110] Weigh: 100 g of kaolin and 1000 mL of activation solution, add them into a three-necked flask and stir, raise the temperature of the three-necked flask to 80°C, keep it warm for 3 hours, lower the temperature of the three-necked flask to room temperature, filter, wash the filter cake with purified water until it is neutral and then dry it, transfer the filter cake to a drying oven at 80°C, and vacuum dry it to constant weight to obtain activated kaolin;

[0111] Weigh: 100 g of activated kaolin, 30 g of KH-560, and 700 mL of anhydrous ethanol, add into a three-necked flask and stir, raise the temperature of the three-necked flask to 70°C, add 400 mL of 10 wt% sodium hydroxide solution into the three-necked flask, and keep warm for 120 min, add 20 g of melamine into the three-necked flask, and keep warm for 3 h, lower the temperature of the three-necked flask to room temperature, filter, wash the filter cake with purified water at a temperature of 80°C until it is neutral, and then drain, transfer the filter cake to a drying oven at a temperature of 85°C, and vacuum dry to constant weight to obtain modified kaolin.

[0112] S5. Preparation of environmentally friendly heat-resistant cables

[0113] Using a PET polyester tape to wrap five cable conductors 1 together, forming a wrapping layer 2 outside a plurality of cable conductors 1;

[0114] Dibutyl phthalate, magnesium stearate and ethylene bisstearamide are uniformly mixed in a weight ratio of 5:2:2 to obtain an auxiliary additive for later use;

[0115] Weigh by weight: 80 parts of low-density polyethylene, 30 parts of modified polysiloxane, 16 parts of modified polyvinyl alcohol, 18 parts of modified kaolin, 3 parts of diisopropylbenzene peroxide and 4 parts of auxiliary additives, add them to a twin-roll open mill at a temperature of 145°C, mix for 30 minutes in an environment with an ambient humidity of 60%, transfer them to a twin-screw extruder while hot, the temperatures of the 6 temperature sections from the feed end to the discharge end of the twin-screw extruder are 235°C, 240°C, 240°C, 245°C, 245°C and 250°C respectively, the main shaft speed of the twin-screw extruder is 12r / min, and the materials are melt-extruded and coated on the outside of the winding layer 2 by the twin-screw extruder, and then cooled and solidified to obtain an environmentally friendly heat-resistant cable.

[0116] Comparative Example 1

[0117] The difference between this comparative example and Example 3 is that the modified polysiloxane in step S5 is replaced by the polysiloxane in step S2.

[0118] Comparative Example 2

[0119] The difference between this comparative example and Example 3 is that the modified polyvinyl alcohol in step S5 is replaced by polyvinyl alcohol in step S3.

[0120] Comparative Example 3

[0121] The difference between this comparative example and Example 3 is that the modified kaolin in step S5 is replaced by activated kaolin in step S4.

[0122] Performance Test:

[0123] With reference to standard XF 306.1-2007 "Classification and requirements for flame retardant and fire resistant cables, plastic insulated flame retardant and fire resistant cables Part 1: Flame retardant cables", the tensile strength, elongation at break, thermal shrinkage, heat aging resistance and flame retardancy grade of the environmentally friendly heat-resistant cables prepared in Examples 1-3 and Comparative Examples 1-3 were measured. The specific test results are shown in Table 1 below.

[0124] Table 1-Performance test data of the sample

[0125]

[0126] Data Analysis:

[0127] A comparative analysis of the data in Table 1 above shows that the tensile strength of the environmentally friendly heat-resistant cable prepared by the present invention reaches 16.8 MPa, the elongation at break reaches 215.5%, the thermal shrinkage rate is reduced to 0.75%, and the flame retardant level reaches IA level. Moreover, after heat aging treatment, the tensile strength of the environmentally friendly heat-resistant cable reaches 16.1 MPa, the retention rate reaches 95.8%, the elongation at break reaches 208.0%, and the retention rate reaches 96.5%. All performance test data are better than those of the comparative example. The present invention uses modified kaolin as a filler and modified polyvinyl alcohol and modified polysiloxane as reinforcing materials to enhance and modify low-density polyethylene, which not only effectively improves the mechanical strength and flame retardant properties of the environmentally friendly heat-resistant cable, but also improves its high temperature resistance, thereby extending the service life of the cable in a high temperature environment.

[0128] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to only specific implementation methods. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order 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. A halogen-free, flame-retardant, environmentally friendly, heat-resistant cable, comprising a plurality of cable conductors (1), a wrapping layer (2), and a sheath layer (3) arranged in sequence from the inside to the outside, characterized in that: The sheath layer (3) comprises the following components in parts by weight: 70-80 parts of low-density polyethylene, 20-30 parts of modified polysiloxane, 10-16 parts of modified polyvinyl alcohol, 15-18 parts of modified kaolin, 2-3 parts of initiator, and 3-4 parts of auxiliary additives.

2. The halogen-free, flame-retardant, environmentally friendly, heat-resistant cable according to claim 1, characterized in that: The cable conductor (1) comprises a core composed of a plurality of mutually twisted copper conductors and a polyethylene insulation layer coated on the outside of the core, and the wrapping layer (2) is obtained by wrapping a wrapping tape around the outside of the plurality of cable conductors (1), the wrapping tape is a PET polyester tape, and the initiator is diisopropylbenzene peroxide.

3. The halogen-free, flame-retardant, environmentally friendly, heat-resistant cable according to claim 1, characterized in that: The modified polysiloxane is processed by the following steps: A1. Add tetramethyltetravinylcyclotetrasiloxane, octamethylcyclotetrasiloxane and modified antioxidant into xylene and stir. Raise the temperature of the reaction system to 110-120° C., add catalyst to the reaction system, keep the temperature for 2-3 hours, add end-capping agent to the reaction system, keep the temperature for 4-6 hours, and post-treat to obtain polysiloxane. A2. Under the protection of inert gas, add polysiloxane into xylene and stir, raise the temperature of the reaction system to 70-80°C, add isocyanatepropyltriethoxysilane into the reaction system, keep the temperature for 3-5h, and post-treat to obtain modified polysiloxane.

4. The halogen-free, flame-retardant, environmentally friendly, heat-resistant cable according to claim 3, characterized in that: In step A1, the amount ratio of tetramethyltetravinylcyclotetrasiloxane, octamethylcyclotetrasiloxane, modified antioxidant, xylene, catalyst and end-capping agent is 3-5g:8-10g:2-3g:60-70mL:6-7g:3-4g, the catalyst is 50-60wt% sulfuric acid, and the end-capping agent is (1,1,3,3-tetramethyl-1,3-disiloxanediyl) dimethanol; in step A2, the amount ratio of polysiloxane, xylene and isocyanatepropyltriethoxysilane is 7g:70mL:1g.

5. The halogen-free, flame-retardant, environmentally friendly, heat-resistant cable according to claim 3, characterized in that: The preparation method of the modified antioxidant is as follows: under the protection of inert gas, antioxidant SP and 3-isocyanate propyl methyl diethoxy silane are added into tetrahydrofuran and stirred, the temperature of the mixed system is increased to 55-65° C., the reaction is kept warm for 80-100 minutes, and post-processed to obtain the modified antioxidant, wherein the dosage ratio of the antioxidant SP and 3-isocyanate propyl methyl diethoxy silane is 1 mol:1 mol.

6. The halogen-free, flame-retardant, environmentally friendly, heat-resistant cable according to claim 1, characterized in that: The preparation method of modified polyvinyl alcohol is as follows: polyvinyl alcohol is added to purified water and stirred, the temperature of the reaction system is increased to 85-95°C, and stirred until the system is dissolved, phosphoric acid solution is added to the reaction system, and the mixture is stirred for 2-3 hours at a temperature maintained at room temperature, and urea solution is added dropwise to the reaction system. After the addition is completed, the mixture is reacted for 3-4 hours at a temperature maintained at room temperature, and post-processed to obtain modified polyvinyl alcohol.

7. The halogen-free, flame-retardant, environmentally friendly, heat-resistant cable according to claim 6, characterized in that: The dosage ratio of the polyvinyl alcohol, purified water, phosphoric acid solution and urea solution is 10g:100mL:2g:5mL, the mass fraction of the phosphoric acid solution is 85-90%, and the urea solution is composed of urea and purified water in a dosage ratio of 1g:5mL.

8. The halogen-free, flame-retardant, environmentally friendly, heat-resistant cable according to claim 1, characterized in that: Modified kaolin is processed by the following steps: B1. Add kaolin to the activation solution and stir, raise the temperature of the reaction system to 70-80°C, keep warm for 2-3h, and post-treat to obtain activated kaolin; B2. Add activated kaolin and KH-560 into anhydrous ethanol and stir. Raise the temperature of the reaction system to 60-70°C. Add a catalyst into the reaction system and keep it warm for 90-120 minutes. Add melamine into the reaction system and keep it warm for 2-3 hours. After post-treatment, obtain modified kaolin.

9. The halogen-free, flame-retardant, environmentally friendly, heat-resistant cable according to claim 8, characterized in that: In step B1, the amount ratio of kaolin and activation solution is 1g:7-10mL, and the activation solution is composed of 40-50wt% sulfuric acid, 25-30wt% hydrogen peroxide and polyethylene glycol 1000 in a ratio of 60-70mL:25-35mL:5-10g; in step B2, the amount ratio of activated kaolin, KH-560, anhydrous ethanol and melamine is 10g:3g:70mL:40mL:2g.

10. A method for preparing a halogen-free, flame-retardant, environmentally friendly, heat-resistant cable according to any one of claims 1 to 9, characterized in that: The following steps are involved: S1. Using a wrapping tape to wrap a plurality of cable conductors (1) together to form a wrapping layer (2) outside the plurality of cable conductors (1); S2. Low-density polyethylene, modified polysiloxane, modified polyvinyl alcohol, modified kaolin, initiator and auxiliary additives are mixed at 135-145°C for 20-30 minutes and transferred to a twin-screw extruder. The mixture is melt-extruded and coated on the outside of the wrapping layer (2) through the twin-screw extruder, and then cooled and solidified to obtain an environmentally friendly heat-resistant cable.

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