High-pressure-resistant flame-retardant heat-shrinkable sleeve and preparation method thereof

Abstract

The invention discloses a high-voltage-resistant flame-retardant heat-shrinkable sleeve and a preparation method thereof, and belongs to the technical field of insulating materials, the adopted silicone rubber has excellent insulating property and high resistivity, the resistance value of the silicone rubber is kept stable in a wide temperature and frequency range, and the high-voltage-resistant flame-retardant heat-shrinkable sleeve is suitable for high-voltage-resistant flame-retardant heat-shrinkable sleeves. The strength of the material is reduced due to the fact that the silicone rubber material is in the polymer composite material, so that a reinforcing agent is needed for reinforcement, but the conventional white carbon black has hydrophilicity, and the adopted modified white carbon black has hydrophobic property, so that good dispersion of the white carbon black in the polymer material is ensured, and the service life of the material is prolonged. The characteristics of softness and high voltage resistance of the sleeve are realized by adding the silicone rubber, the strength of the silicone rubber is enhanced by adding the modified white carbon black, and the flame retardant property of the material is realized by adding the flame retardant.

Description

Technical Field

[0001] The invention relates to the technical field of insulating materials, and in particular to a high-voltage resistant flame-retardant heat shrinkable sleeve and a preparation method thereof. Background Art

[0002] In today's industrial and technological fields, the safety and reliability requirements for electrical equipment and lines are increasing day by day. With the continuous development of power systems and the widespread application of electronic equipment, various complex working environments have put forward higher challenges to insulation protection materials.

[0003] High-voltage flame-retardant heat shrink tubing has emerged as the times require, and it has become one of the key components to ensure the safe operation of electrical systems. Under high-voltage environments, electrical equipment and lines need to withstand extremely high voltages, and traditional insulating materials often have difficulty meeting the requirements of high voltage resistance and achieving good flame retardant effects. High-voltage flame-retardant heat shrink tubing, with its special material structure and performance, can effectively withstand the effects of high-voltage electric fields and prevent electrical breakdown and leakage.

[0004] At the same time, fire is one of the major safety hazards facing electrical systems. Once a fire occurs, ordinary insulating materials may burn and aggravate the spread of the fire, causing huge losses to life and property. High-voltage flame-retardant heat shrink tubing has excellent flame-retardant properties, which can prevent the spread of flames when a fire occurs, buying precious time for personnel evacuation and fire extinguishing. However, although the existing high-voltage flame-retardant heat shrink tubing has good high-voltage resistance and flame-retardant properties, its mechanical strength, wear resistance and dielectric properties are poor. Summary of the invention

[0005] The present invention provides a high-voltage flame-retardant heat shrink tubing and a preparation method thereof, which effectively solves the technical problems that traditional insulating materials are often difficult to achieve good flame-retardant effects while being resistant to high voltage, and that the existing high-voltage flame-retardant heat shrink tubing has good high-voltage resistance and flame-retardant properties but poor mechanical strength, wear resistance and dielectric properties. At the same time, a high-voltage flame-retardant heat shrink tubing with excellent insulation performance, high resistivity and stable resistance within a wide temperature and frequency range is provided.

[0006] The first object of the present invention is to provide a high-pressure flame-retardant heat shrinkable sleeve, which is made of the following raw materials in parts by weight: 20 to 50 parts of silicone rubber, 10 to 30 parts of ethylene-vinyl acetate copolymer, 5 to 20 parts of polyethylene resin, 5 to 15 parts of maleic anhydride grafting agent, 5 to 15 parts of modified white carbon black, 1 to 5 parts of titanium dioxide, 40 to 80 parts of flame retardant, 1 to 3 parts of antioxidant, 0.5 to 1 part of lubricant, and 1 to 32 parts of cross-linking agent.

[0007] As a preferred embodiment, the modified silica is specifically: adding silica to a silane coupling agent pre-hydrolyzate at a dosage ratio of 1 g: 10-20 mL, adjusting the pH value to 6.8-7.2, performing hydrophobic modification at 48° C.-52° C., standing, removing ethanol, and drying to obtain modified silica.

[0008] As a preferred embodiment, the preparation method of the silane coupling agent pre-hydrolysis liquid is specifically as follows: adding silane coupling agent KH570 to anhydrous ethanol, and then adding deionized water, the mass ratio of KH570 to deionized water is 2.8 to 3:1, and a pre-hydrolysis reaction occurs under stirring.

[0009] As a preferred implementation, the silicone rubber is methyl vinyl silicone rubber 110 - 0 and / or methyl vinyl silicone rubber 110 - 3.

[0010] As a preferred implementation, the ethylene-vinyl acetate copolymer is ethylene-vinyl acetate copolymer UL00328 and / or ethylene-vinyl acetate copolymer EVA1820; the polyethylene resin is polyethylene resin DFDA7042 and / or polyethylene resin 3364NT.

[0011] As a preferred embodiment, the flame retardant is melamine cyanurate, two or three of magnesium hydroxide and aluminum hydroxide; the lubricant is a mixture of PE wax and silicone masterbatch, and the silicone content of the silicone masterbatch is ≥60%; the antioxidant is a mixture of hindered phenol 1010 and thioester DLTP; the co-crosslinking agent is trimethylolpropane (TMP), trimethylamine (TMA) or triallyl isocyanurate (TAIC).

[0012] The second object of the present invention is to provide a method for preparing the above-mentioned high-pressure resistant flame-retardant heat shrinkable tubing, comprising the following steps:

[0013] Weigh the following raw materials in parts by weight: 20-50 parts of silicone rubber, 10-30 parts of ethylene-vinyl acetate copolymer, 5-20 parts of polyethylene resin, 5-15 parts of maleic anhydride grafting agent, 5-15 parts of modified white carbon black, 1-5 parts of titanium dioxide, 40-80 parts of flame retardant, 1-3 parts of antioxidant, 0.5-1 part of lubricant, and 1-32 parts of cross-linking agent;

[0014] The silicone rubber, modified white carbon black and titanium dioxide are mixed in an open mill at 65-120° C. to obtain a silicone rubber compound;

[0015] At 140° C. to 150° C., the silicone rubber compound, ethylene-vinyl acetate copolymer, polyethylene resin, maleic anhydride grafting agent, flame retardant, antioxidant, lubricant and cross-linking agent are mixed in an internal mixer, extruded and granulated to obtain a polyolefin heat shrink tube material masterbatch;

[0016] The polyolefin heat shrinkable tube material masterbatch is extruded into a tube to obtain a tube, the tube is irradiated with an electron beam, cross-linked to obtain a cross-linked tube, preheated at 135-150° C., an expander is used to externally expand the preheated cross-linked tube to double the diameter of the tube mouth, and then quickly cooled to room temperature to obtain a high-pressure resistant flame-retardant heat shrinkable tube.

[0017] As a preferred embodiment, the dose of the electron beam irradiation is 150 kGy to 170 kGy.

[0018] As a preferred embodiment, the mixing time of the open mixer is 10 min to 20 min, and the mixing time of the internal mixer is 15 min to 20 min.

[0019] As a preferred embodiment, the polyolefin heat shrink tube material masterbatch is extruded into a tube by a twin-screw extruder, and the temperature of the twin-screw extruder is: feed section: 105°C ~ 115°C, melting section: 130°C ~ 140°C, die head: 140°C ~ 150°C, and a 200-mesh filter screen is provided at the die head to filter impurities in the melt before extrusion granulation.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention provides a high-pressure flame-retardant heat shrinkable sleeve, which is made of silicone rubber, ethylene-vinyl acetate copolymer, polyethylene resin, maleic anhydride grafting agent, modified white carbon black, titanium dioxide, flame retardant, antioxidant, lubricant and cross-linking agent. The silicone rubber used in the present invention has excellent insulation performance, high resistivity, and its resistance value remains stable in a wide temperature and frequency range. Since the silicone rubber material in the polymer composite material will cause the material strength to decrease, a reinforcing agent is required for reinforcement, but conventional white carbon black has hydrophilicity, and the modified white carbon black used has hydrophobicity, thereby ensuring the good dispersion of white carbon black in the polymer material, and the softness and high-pressure resistance of the sleeve are achieved by adding silicone rubber, the strength of the silicone rubber is reinforced by adding modified white carbon black, and the flame retardant of the material is achieved by adding the flame retardant. The titanium dioxide used in the present invention can not only give the sleeve a white appearance, but also effectively reflect and scatter ultraviolet rays, reduce the degradation effect of ultraviolet rays on polymer materials, thereby improving the weather resistance of the heat shrinkable sleeve, and indirectly improving its high temperature resistance and corrosion resistance. The particles of titanium dioxide can be filled between the molecular chains of the polymer material, increase the density of the material, and then improve the wear resistance of the heat shrinkable sleeve. When combined with other additives, titanium dioxide can enhance the effect of antioxidants, reduce the double damage of oxygen and ultraviolet rays to the material, and cooperate with lubricants to improve the processing fluidity of the material, so that each component is more evenly dispersed during the processing process, and further improve the comprehensive performance of the heat shrinkable sleeve. In the heat shrinkable sleeve, the antioxidant captures the free radicals generated by the material at high temperature, high pressure or contact with oxygen, interrupts the oxidation chain reaction, and thus improves the high temperature resistance and corrosion resistance of the heat shrinkable sleeve. The antioxidant and titanium dioxide work synergistically, titanium dioxide reflects ultraviolet rays to reduce the free radicals generated by the material due to photooxidation, and the antioxidant further removes the remaining free radicals, the two complement each other, and enhance the stability of the material. The cross-linking agent will produce some active groups during the cross-linking process, and the antioxidant can control the reaction degree of these active groups, avoid excessive cross-linking to cause the material performance to become brittle, and ensure that the heat shrinkable tube still has good flexibility and wear resistance after cross-linking. The present invention uses a lubricant to disperse the components more evenly, avoid performance defects caused by local agglomeration, and indirectly improve the high pressure resistance and high temperature resistance. The lubricant and titanium dioxide work together to help titanium dioxide better disperse in the polymer matrix and give full play to its shielding effect on ultraviolet rays. When combined with an antioxidant, the lubricant can reduce the friction heat generated by the material during the processing, reduce the oxidation reaction rate caused by high temperature, and enhance the effect of the antioxidant. In addition, the lubricant can also form a thin lubricating film on the surface of the heat shrinkable tube, improve the smoothness of its surface, reduce friction with external objects, and improve wear resistance. The cross-linking agent used in the present invention promotes the cross-linking reaction between the molecular chains of the polymer material, forming a three-dimensional network structure, thereby improving the strength, hardness, chemical corrosion resistance and high temperature resistance of the material.In heat shrink tubing, the cross-linking agent enables the polymer material to cross-link quickly when heated to form a stable structure, enhance the high-pressure resistance of the heat shrink tubing, and make it less likely to deform or damage under high-pressure environments. The cross-linking agent works in conjunction with the antioxidant to control the rate and degree of the cross-linking reaction to avoid deterioration of material properties due to excessive cross-linking. The cross-linking agent and lubricant work together to improve the processing fluidity of the material, allowing the cross-linking agent to be more evenly distributed in the material, improving the uniformity of cross-linking, and thus improving the overall performance of the heat shrink tubing. At the same time, the three-dimensional network structure after cross-linking can better fix the titanium dioxide particles and enhance the density and wear resistance of the material. DETAILED DESCRIPTION

[0022] In order to enable those skilled in the art to better understand the technical solution of the present invention and implement it, the present invention is further described below in conjunction with specific examples, but the examples are not intended to limit the present invention. The following test methods and detection methods, unless otherwise specified, are conventional methods; the reagents and raw materials, unless otherwise specified, are commercially available.

[0023] The background technology of the present invention mentions that although the existing high-voltage flame-retardant heat shrink tubing has good high-voltage resistance and flame-retardant properties, its mechanical strength, wear resistance and dielectric properties are poor. Based on the above technical problems, the present invention provides a high-voltage flame-retardant heat shrink tubing and a preparation method thereof.

[0024] The technical solution of the present invention is analyzed and explained in detail below.

[0025] The invention firstly provides a high-pressure flame-retardant heat shrinkable sleeve, which is made of the following raw materials in parts by weight: 20-50 parts of silicone rubber, 10-30 parts of ethylene-ethyl acetate copolymer, 5-20 parts of polyethylene resin, 5-15 parts of maleic anhydride grafting agent, 5-15 parts of modified white carbon black, 1-5 parts of titanium dioxide, 40-80 parts of flame retardant, 1-3 parts of antioxidant, 0.5-1 part of lubricant and 1-32 parts of cross-linking aid.

[0026] In the above technical scheme, the raw materials have a mutual synergistic effect. The modified silica has hydrophobic properties, which ensures the good dispersion of silica in the polymer material. The softness and high pressure resistance of the sleeve are achieved by adding silicone rubber, the strength of silicone rubber is reinforced by adding modified silica, and the flame retardant of the material is achieved by adding flame retardants. Titanium dioxide particles can be filled between the molecular chains of polymer materials, increase the density of the material, and thus improve the wear resistance of the heat shrinkable sleeve. When combined with other additives, titanium dioxide can enhance the effect of antioxidants, reduce the dual damage of oxygen and ultraviolet rays to the material, and cooperate with lubricants to improve the processing fluidity of the material, so that the components are more evenly dispersed during the processing process, and further improve the comprehensive performance of the heat shrinkable sleeve. Antioxidants and titanium dioxide work synergistically. Titanium dioxide reflects ultraviolet rays to reduce the free radicals generated by photooxidation of the material, while antioxidants further remove the remaining free radicals. The two complement each other and enhance the stability of the material. The cross-linking agent will produce some active groups during the cross-linking process. The antioxidant can control the reaction degree of these active groups, avoid excessive cross-linking that causes the material performance to become brittle, and ensure that the heat shrink tubing still has good flexibility and wear resistance after cross-linking. When combined with the antioxidant, the lubricant can reduce the friction heat generated by the material during the processing process, reduce the oxidation reaction rate caused by high temperature, and enhance the effect of the antioxidant. In addition, the lubricant can also form a thin lubricating film on the surface of the heat shrink tubing, improve its surface smoothness, reduce friction with external objects, and improve wear resistance. The cross-linking agent and the antioxidant work together to control the rate and degree of the cross-linking reaction and avoid the deterioration of material performance due to excessive cross-linking. The synergistic effect of the cross-linking agent and the lubricant improves the processing fluidity of the material, enables the cross-linking agent to be more evenly distributed in the material, improves the uniformity of cross-linking, and thus improves the overall performance of the heat shrink tubing. At the same time, the three-dimensional network structure after cross-linking can better fix the titanium dioxide particles and enhance the density and wear resistance of the material.

[0027] In order to achieve the hydrophobic modification of silica, the modified silica is specifically as follows: silica is added to a silane coupling agent pre-hydrolyzate according to a dosage ratio of 1 g: 10-20 mL, the pH value is adjusted to 6.8-7.2, the hydrophobic modification is performed at 48° C.-52° C., the mixture is allowed to stand, ethanol is removed, and the mixture is dried to obtain the modified silica.

[0028] Preparation of silane coupling agent pre-hydrolysis liquid: adding silane coupling agent KH570 to anhydrous ethanol, and then adding deionized water to the silane coupling agent KH570 according to a mass ratio of silane coupling agent KH570 to deionized water of 2.8 to 3:1, and performing a pre-hydrolysis reaction under stirring to obtain the obtained product.

[0029] Add white carbon black to the pre-hydrolyzed solution of silane coupling agent, adjust the pH value to 6.8-7.2, perform hydrophobic modification at 48-52°C, let stand for 24 hours, remove ethanol, and dry in a vacuum drying oven at 70°C to obtain modified white carbon black.

[0030] It should be noted that the silicone rubber used in the present invention is methyl vinyl silicone rubber 110-0 and / or methyl vinyl silicone rubber 110-3. The ethylene-vinyl acetate copolymer is ethylene-vinyl acetate copolymer UL00328 and / or ethylene-vinyl acetate copolymer EVA1820; the polyethylene resin is polyethylene resin DFDA7042 and / or polyethylene resin 3364NT. The flame retardant is melamine cyanurate (MCA), two or three of magnesium hydroxide and aluminum hydroxide; the lubricant is a mixture of PE wax and silicone masterbatch, and the silicone content of the silicone masterbatch is ≥60%; the antioxidant is a mixture of hindered phenol 1010 and thioester DLTP; the auxiliary cross-linking agent is trimethylolpropane (TMP), trimethylamine (TMA) or triallyl isocyanurate (TAIC).

[0031] The present invention also provides a method for preparing the high-pressure resistant flame-retardant heat shrinkable tubing, comprising the following steps:

[0032] Weigh the following raw materials in parts by weight: 20-50 parts of silicone rubber, 10-30 parts of ethylene-vinyl acetate copolymer, 5-20 parts of polyethylene resin, 5-15 parts of maleic anhydride grafting agent, 5-15 parts of modified white carbon black, 1-5 parts of titanium dioxide, 40-80 parts of flame retardant, 1-3 parts of antioxidant, 0.5-1 part of lubricant, and 1-32 parts of cross-linking agent;

[0033] Silicone rubber, modified white carbon black and titanium dioxide are mixed in an open mill at 65-120°C to obtain a silicone rubber compound. If the temperature is lower than 65°C, the raw materials cannot be melted and cannot be fully mixed; if the temperature is higher than 120°C, the raw materials will have the risk of oxidation and aging, thus affecting the performance of the heat shrink tubing.

[0034] At 140°C to 150°C, the silicone rubber compound, ethylene-vinyl acetate copolymer, polyethylene resin, maleic anhydride grafting agent, flame retardant, antioxidant, lubricant and cross-linking agent are mixed by an internal mixer, extruded and granulated to obtain a polyolefin heat shrink tube material masterbatch. For the above mixing temperature, if the temperature is lower than 140°C, the raw materials cannot be fully melted, resulting in uneven mixing; if the temperature is higher than 150°C, the raw materials will age and decompose, thereby adversely affecting the performance of the material.

[0035] The polyolefin heat shrinkable tube material masterbatch is extruded into a tubular shape to obtain a tube, and the tube is irradiated with an electron beam, cross-linked, and the double bonds of the polymer material are broken and re-bonded, and the chain structure is changed into a mesh structure to obtain a cross-linked tube, which is preheated at 135-150°C, and an expander is used to expand the preheated cross-linked tube by external force, and the diameter of the tube mouth is doubled, and then quickly cooled to room temperature to obtain a high-pressure flame-retardant heat shrinkable tube. The electron beam irradiation process is convenient for irradiating tubular materials, is efficient, environmentally friendly, has no excess chemical cross-linking agent residue, and does not affect the material properties. The electron beam is a high-energy electron flow that can stimulate double bond breakage and recombination. For the above-mentioned preheating temperature, the temperature is lower than 135°C, and the heat shrinkable tube is prone to cracking. If the temperature is higher than 150°C, the material softens, thereby affecting the molding effect.

[0036] It should be noted that the dose of the electron beam irradiation is 150 kGy to 170 kGy.

[0037] It should be emphasized that the mixing time of the open mixer is 10 min to 20 min, and the mixing time of the internal mixer is 15 min to 20 min.

[0038] In order to obtain a heat shrinkable tube with higher purity and better performance, the polyolefin heat shrinkable tube material masterbatch is extruded into a tube by a twin-screw extruder. The temperature of the twin-screw extruder is: feeding section: 105°C ~ 115°C, melting section: 130°C ~ 140°C, die head: 140°C ~ 150°C. A 200-mesh filter screen is provided at the die head to filter impurities in the melt before extrusion granulation.

[0039] The technical effects of the present invention are described below through embodiments and comparative examples.

[0040] Example 1

[0041] A high-pressure flame-retardant heat shrink tubing is made of the following raw materials in parts by weight: 40 parts of silicone rubber, 25 parts of ethylene-vinyl acetate copolymer, 15 parts of polyethylene resin, 10 parts of maleic anhydride grafting agent, 8 parts of modified white carbon black, 2 parts of titanium dioxide, 50 parts of flame retardant, 1 part of antioxidant, 0.8 parts of lubricant and 1.2 parts of cross-linking aid.

[0042] Among them, the silicone rubber is methyl vinyl silicone rubber 110-0 and methyl vinyl silicone rubber 110-3 in a mass ratio of 1:1; the ethylene-ethyl acetate copolymer is ethylene-ethyl acetate copolymer UL00328 and ethylene-ethyl acetate copolymer EVA1820 in a mass ratio of 4:1; the polyethylene resin is DFDA7042 linear low-density polyethylene; the flame retardant is a compound of MCA and magnesium hydroxide in a mass ratio of 1:1, and the co-crosslinking agent is TAIC.

[0043] The method for preparing the high-pressure flame-retardant heat shrink tubing comprises the following steps:

[0044] Weigh the above raw materials in parts by weight;

[0045] The silicone rubber, modified silica and titanium dioxide were mixed in an open mixer at 65° C. for 20 min to obtain a silicone rubber compound.

[0046] The silicone rubber compound, ethylene-vinyl acetate copolymer, polyethylene resin, maleic anhydride grafting agent, flame retardant, antioxidant, lubricant and cross-linking agent are mixed in an internal mixer at 140° C. for 15 minutes, extruded and granulated to obtain a polyolefin heat shrink tube material masterbatch;

[0047] The polyolefin heat shrink tube material masterbatch is extruded into a tube by a twin-screw extruder, the temperature of the twin-screw extruder is as follows: feed section: 110°C, melting section: 135°C, die head: 145°C, a 200-mesh filter screen is provided at the die head for filtering impurities in the melt before extrusion granulation to obtain a tube, the tube is irradiated with an electron beam at a dosage of 150 kGy, cross-linked to obtain a cross-linked tube, preheated at 135°C, an expander is used to externally expand the preheated cross-linked tube, the diameter of the tube mouth is doubled, and then the tube is rapidly cooled to room temperature to obtain a high-pressure flame-retardant heat shrink tubing.

[0048] Example 2

[0049] A high-pressure flame-retardant heat shrink tubing is made of the following raw materials in parts by weight: 30 parts of silicone rubber, 30 parts of ethylene-ethyl acetate copolymer, 20 parts of polyethylene resin, 10 parts of maleic anhydride grafting agent, 8 parts of modified white carbon black, 2 parts of titanium dioxide, 50 parts of flame retardant, 1 part of antioxidant, 0.8 parts of lubricant and 1.2 parts of cross-linking aid.

[0050] Among them, the silicone rubber is methyl vinyl silicone rubber 110-0 and methyl vinyl silicone rubber 110-3 in a mass ratio of 1:1; the ethylene-ethyl acetate copolymer is ethylene-ethyl acetate copolymer UL00328 and ethylene-ethyl acetate copolymer EVA1820 in a mass ratio of 4:1; the polyethylene resin is polyethylene resin 3364NT; the flame retardant is a compound of MCA and magnesium hydroxide in a mass ratio of 1:1, and the auxiliary cross-linking agent is TAIC.

[0051] The method for preparing the high-pressure flame-retardant heat shrink tubing comprises the following steps:

[0052] Weigh the above raw materials in parts by weight;

[0053] The silicone rubber, modified silica and titanium dioxide were mixed in an open mixer at 120° C. for 10 min to obtain a silicone rubber compound.

[0054] The silicone rubber compound, ethylene-vinyl acetate copolymer, polyethylene resin, maleic anhydride grafting agent, flame retardant, antioxidant, lubricant and cross-linking agent are mixed in an internal mixer at 150° C. for 20 minutes, extruded and granulated to obtain a polyolefin heat shrink tube material masterbatch;

[0055] The polyolefin heat shrinkable tube material masterbatch is extruded into a tube by a twin-screw extruder, and the temperatures of the twin-screw extruder are as follows: feed section: 110° C., melting section: 135° C., and die head: 145° C. A 200-mesh filter screen is provided at the die head for filtering impurities in the melt before extrusion granulation to obtain a tube, and the tube is irradiated with an electron beam at a dosage of 170 kGy, cross-linked to obtain a cross-linked tube, preheated at 150° C., and an expander is used to externally expand the preheated cross-linked tube to double the diameter of the tube mouth, and then rapidly cooled to room temperature to obtain a high-pressure resistant flame-retardant heat shrinkable tube.

[0056] Example 3

[0057] A high-pressure flame-retardant heat shrink tubing is made of the following raw materials in parts by weight: 25 parts of silicone rubber, 35 parts of ethylene-ethyl acetate copolymer, 20 parts of polyethylene resin, 10 parts of maleic anhydride grafting agent, 8 parts of modified white carbon black, 2 parts of titanium dioxide, 50 parts of flame retardant, 1 part of antioxidant, 0.8 parts of lubricant and 1.2 parts of cross-linking aid.

[0058] Among them, the silicone rubber is methyl vinyl silicone rubber 110-0 and methyl vinyl silicone rubber 110-3 in a mass ratio of 1:1; the ethylene-ethyl acetate copolymer is ethylene-ethyl acetate copolymer UL00328 and ethylene-ethyl acetate copolymer EVA1820 in a mass ratio of 4:1; the polyethylene resin is polyethylene resin 3364NT; the flame retardant is a compound of MCA and magnesium hydroxide in a mass ratio of 1:1, and the auxiliary cross-linking agent is TAIC.

[0059] The method for preparing the high-pressure flame-retardant heat shrink tubing comprises the following steps:

[0060] Weigh the above raw materials in parts by weight;

[0061] The silicone rubber, modified silica and titanium dioxide were mixed in an open mixer at 80° C. for 16 min to obtain a silicone rubber compound.

[0062] The silicone rubber compound, ethylene-vinyl acetate copolymer, polyethylene resin, maleic anhydride grafting agent, flame retardant, antioxidant, lubricant and cross-linking agent are mixed in an internal mixer at 148° C. for 18 minutes, extruded and granulated to obtain a polyolefin heat shrink tube material masterbatch;

[0063] The polyolefin heat shrink tube material masterbatch is extruded into a tube by a twin-screw extruder, and the temperatures of the twin-screw extruder are as follows: feed section: 110° C., melting section: 135° C., and die head: 145° C. A 200-mesh filter screen is provided at the die head for filtering impurities in the melt before extrusion granulation to obtain a tube, and the tube is irradiated with an electron beam at a dosage of 160 kGy, cross-linked to obtain a cross-linked tube, preheated at 140° C., and an expander is used to externally expand the preheated cross-linked tube to double the diameter of the tube mouth, and then rapidly cooled to room temperature to obtain a high-pressure resistant flame-retardant heat shrink tubing.

[0064] In order to further illustrate the technical effect of the present invention, the present invention also sets a comparative example, which is as follows:

[0065] Comparative Example 1

[0066] Compared with Example 1, the difference is that no modified white carbon black is added.

[0067] A high-pressure flame-retardant heat shrink tubing is made of the following raw materials in parts by weight: 40 parts of silicone rubber, 25 parts of ethylene-ethyl acetate copolymer, 15 parts of polyethylene resin, 10 parts of maleic anhydride grafting agent, 2 parts of titanium dioxide, 58 parts of flame retardant, 1 part of antioxidant, 0.8 parts of lubricant and 1.2 parts of cross-linking aid.

[0068] Among them, the silicone rubber is methyl vinyl silicone rubber 110-0 and methyl vinyl silicone rubber 110-3 in a mass ratio of 1:1; the ethylene-ethyl acetate copolymer is ethylene-ethyl acetate copolymer UL00328 and ethylene-ethyl acetate copolymer EVA1820 in a mass ratio of 4:1; the polyethylene resin is DFDA7042 linear low-density polyethylene; the flame retardant is a compound of MCA and magnesium hydroxide in a mass ratio of 1:1, and the co-crosslinking agent is TAIC.

[0069] The method for preparing the high-pressure flame-retardant heat shrink tubing comprises the following steps:

[0070] Weigh the above raw materials in parts by weight;

[0071] The silicone rubber and titanium dioxide were mixed in an open mixer at 65° C. for 20 min to obtain a silicone rubber compound.

[0072] The silicone rubber compound, ethylene-vinyl acetate copolymer, polyethylene resin, maleic anhydride grafting agent, flame retardant, antioxidant, lubricant and cross-linking agent are mixed in an internal mixer at 140° C. for 15 minutes, extruded and granulated to obtain a polyolefin heat shrink tube material masterbatch;

[0073] The polyolefin heat shrink tube material masterbatch is extruded into a tube by a twin-screw extruder, the temperature of the twin-screw extruder is as follows: feed section: 110°C, melting section: 135°C, die head: 145°C, a 200-mesh filter screen is provided at the die head for filtering impurities in the melt before extrusion granulation to obtain a tube, the tube is irradiated with an electron beam at a dosage of 150 kGy, cross-linked to obtain a cross-linked tube, preheated at 135°C, an expander is used to externally expand the preheated cross-linked tube, the diameter of the tube mouth is doubled, and then the tube is rapidly cooled to room temperature to obtain a high-pressure flame-retardant heat shrink tubing.

[0074] Comparative Example 2

[0075] Compared with Example 1, the difference is that silicone rubber and modified silica are not added.

[0076] A high-pressure flame-retardant heat shrinkable tubing is prepared from the following raw materials in parts by weight: 60 parts of ethylene-ethyl acetate copolymer, 30 parts of polyethylene resin, 10 parts of maleic anhydride grafting agent, 2 parts of titanium dioxide, 100 parts of flame retardant, 1 part of antioxidant, 0.8 parts of lubricant and 1.2 parts of cross-linking aid.

[0077] Among them, the ethylene-ethyl acetate copolymer is ethylene-ethyl acetate copolymer UL00328 and ethylene-ethyl acetate copolymer EVA1820 in a mass ratio of 4:1; the polyethylene resin is DFDA7042 linear low-density polyethylene; the flame retardant is a compound of MCA and magnesium hydroxide in a mass ratio of 1:1, and the auxiliary cross-linking agent is TAIC.

[0078] The method for preparing the high-pressure flame-retardant heat shrink tubing comprises the following steps:

[0079] Weigh the above raw materials in parts by weight;

[0080] The silicone rubber, modified silica and titanium dioxide were mixed in an open mixer at 65° C. for 20 min to obtain a silicone rubber compound.

[0081] The silicone rubber compound, ethylene-vinyl acetate copolymer, polyethylene resin, maleic anhydride grafting agent, flame retardant, antioxidant, lubricant and cross-linking agent are mixed in an internal mixer at 140° C. for 15 minutes, extruded and granulated to obtain a polyolefin heat shrink tube material masterbatch;

[0082] The polyolefin heat shrink tube material masterbatch is extruded into a tube by a twin-screw extruder, the temperature of the twin-screw extruder is as follows: feed section: 110°C, melting section: 135°C, die head: 145°C, a 200-mesh filter screen is provided at the die head for filtering impurities in the melt before extrusion granulation to obtain a tube, the tube is irradiated with an electron beam at a dosage of 150 kGy, cross-linked to obtain a cross-linked tube, preheated at 135°C, an expander is used to externally expand the preheated cross-linked tube, the diameter of the tube mouth is doubled, and then the tube is rapidly cooled to room temperature to obtain a high-pressure flame-retardant heat shrink tubing.

[0083] The properties of the sleeves prepared in the above Examples 1 to 3 and Comparative Examples 1 to 2 were tested, and the results are shown in Table 1 below.

[0084] Table 1 Performance test table of the sleeves of the embodiments of the present invention and the comparative examples

[0085]

[0086]

[0087] “-” means it cannot be measured.

[0088] As shown in Table 1, the high-pressure flame-retardant heat shrink tubing prepared by the present invention has excellent properties, with a tensile strength of up to 14.6 MPa, an elongation at break of up to 406%, and a volume resistivity of up to 1.46×10 15Ω·m, the dielectric strength can reach 32.5KV / mm, and the A-type Shore hardness can reach 94 degrees. The high-pressure flame-retardant heat shrink tubing prepared by the present invention has excellent mechanical strength, dielectric properties and wear resistance. Comparative Example 1 is to remove the modified silica in Example 1, while Comparative Example 2 is to remove the silicone rubber and the modified silica at the same time. It can be seen from the data in Table 1 that the tensile strength of the heat shrink tubing prepared in Comparative Example 1 without adding modified silica cannot be measured, and the subsequent indicators are all worse than the various properties of the high-pressure heat shrink tubing of Example 1, and the performance of Comparative Example 2 is also weaker than that of Example 1. The reasons are as follows: since modified silica has hydrophobic properties, it ensures good dispersion of silica in high molecular polymer materials. By adding modified silica to reinforce the strength of silicone rubber, the physical strength of the heat shrinkable tube is improved, and then the softness and high pressure resistance of the tube are achieved by adding silicone rubber. In Comparative Example 1 and Comparative Example 2, the modified silica and modified silica and silicone rubber are removed respectively, which will inevitably lead to insufficient tensile strength and elongation at break of the heat shrinkable tube, thereby affecting the overall performance of the heat shrinkable tube. Volume resistivity is a key parameter for measuring the insulation performance of a material. The higher the volume resistivity, the better the insulation performance of the material. Good insulation performance means that the material can effectively prevent the passage of current, and it is difficult for the internal charge to form a directional movement. Under the action of the electric field, the dielectric state of the material itself can also be better maintained. Both modified silica and silicone rubber have better dielectric properties. Since modified silica has hydrophobic properties, it has good dispersibility in high molecular polymer materials, which reduces the dielectric constant of the material as a whole, so the volume resistivity and dielectric strength of the heat shrinkable tube are better. Silicone rubber has excellent dielectric properties, high resistivity, and exhibits stable electrical properties in application scenarios.

[0089] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A high-pressure flame-retardant heat shrink tubing, characterized in that: The invention is prepared from the following raw materials in parts by weight: 20 to 50 parts of silicone rubber, 10 to 30 parts of ethylene-vinyl acetate copolymer, 5 to 20 parts of polyethylene resin, 5 to 15 parts of maleic anhydride grafting agent, 5 to 15 parts of modified white carbon black, 1 to 5 parts of titanium dioxide, 40 to 80 parts of flame retardant, 1 to 3 parts of antioxidant, 0.5 to 1 part of lubricant and 1 to 32 parts of cross-linking aid.

2. The high-pressure flame-retardant heat shrink tubing according to claim 1, characterized in that: The modified silica is specifically prepared by adding silica to a silane coupling agent pre-hydrolyzate at a dosage ratio of 1 g:10-20 mL, adjusting the pH value to 6.8-7.2, performing hydrophobic modification at 48° C.-52° C., standing, removing ethanol, and drying to obtain the modified silica.

3. The high-pressure flame-retardant heat shrink tubing according to claim 2, characterized in that: The preparation method of the silane coupling agent pre-hydrolysis liquid is specifically as follows: adding the silane coupling agent to anhydrous ethanol, and then adding water, wherein the mass ratio of KH570 to water is 2.8 to 3:1, and causing a pre-hydrolysis reaction in a stirring state to obtain the pre-hydrolysis liquid.

4. The high-pressure flame-retardant heat shrink tubing according to claim 1, characterized in that: The silicone rubber is methyl vinyl silicone rubber 110 - 0 and / or methyl vinyl silicone rubber 110 - 3.

5. The high-pressure flame-retardant heat shrink tubing according to claim 1, characterized in that: The ethylene-vinyl acetate copolymer is ethylene-vinyl acetate copolymer UL00328 and / or ethylene-vinyl acetate copolymer EVA1820; the polyethylene resin is polyethylene resin DFDA7042 and / or polyethylene resin 3364NT.

6. The high-pressure flame-retardant heat shrink tubing according to claim 1, characterized in that: The flame retardant is two or three of melamine cyanurate, magnesium hydroxide and aluminum hydroxide; the lubricant is a mixture of PE wax and silicone masterbatch, and the silicone content of the silicone masterbatch is ≥60%; the antioxidant is a mixture of hindered phenol 1010 and thioester DLTP; the auxiliary cross-linking agent is trimethylolpropane, trimethylamine or triallyl isocyanurate.

7. A method for preparing the high-pressure flame-retardant heat shrink tubing according to any one of claims 1 to 6, characterized in that: The following steps are involved: Weigh the following raw materials in parts by weight: 20-50 parts of silicone rubber, 10-30 parts of ethylene-vinyl acetate copolymer, 5-20 parts of polyethylene resin, 5-15 parts of maleic anhydride grafting agent, 5-15 parts of modified white carbon black, 1-5 parts of titanium dioxide, 40-80 parts of flame retardant, 1-3 parts of antioxidant, 0.5-1 part of lubricant, and 1-32 parts of cross-linking agent; The silicone rubber, modified white carbon black and titanium dioxide are mixed in an open mill at 65-120° C. to obtain a silicone rubber compound; At 140° C. to 150° C., the silicone rubber compound, ethylene-vinyl acetate copolymer, polyethylene resin, maleic anhydride grafting agent, flame retardant, antioxidant, lubricant and cross-linking agent are mixed in an internal mixer, extruded and granulated to obtain a polyolefin heat shrink tube material masterbatch; The polyolefin heat shrinkable tube material masterbatch is extruded into a tube to obtain a tube, the tube is irradiated with an electron beam, cross-linked to obtain a cross-linked tube, preheated at 135-150° C., and expanded to obtain a high-pressure resistant flame-retardant heat shrinkable sleeve.

8. The preparation method according to claim 7, characterized in that: The dosage of the electron beam irradiation is 150 kGy to 170 kGy.

9. The preparation method according to claim 7, characterized in that: The mixing time of the open mixer is 10 to 20 minutes, and the mixing time of the internal mixer is 15 to 20 minutes.

10. The preparation method according to claim 7, characterized in that: The polyolefin heat shrink tube material masterbatch is extruded into a tube by a twin-screw extruder, and the temperature of the twin-screw extruder is: feeding section: 105°C to 115°C, melting section: 130°C to 140°C, and die head: 140°C to 150°C.

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