Production method of heat-shrinkable sleeve with high and low temperature shrinkage function

Abstract

The invention relates to the technical field of high polymer material processing and application, and discloses a production method of a heat-shrinkable sleeve with a high and low temperature shrinkage function, and the heat-shrinkable sleeve comprises the following raw materials by weight: 25-35% of an ethylene vinyl acetate copolymer; 10%-20% of crosslinked polyethylene; 5%-14% of anti-impact co-polypropylene; 5%-10% of polyimide; 5%-8% of polyvinylidene fluoride; 4%-9% of a styrene-ethylene-butylene-styrene copolymer; 4%-8% of synthetic gutta-percha; 5-9% of silicone rubber; 7%-11% of an environment-friendly halogen-free flame retardant; 0.5%-1% of an antioxidant; 0.5%-1% of an anti-dripping agent; 1%-1.5% of a radiation crosslinking auxiliary agent; 1%-2% of an assistant crosslinker; 0.5%-1% of a lubricant; the preparation method comprises the following steps: pre-treating the raw materials, sequentially carrying out matrix blending, functional resin / elastomer gradient addition and auxiliary agent composite blending, and carrying out extrusion, irradiation crosslinking, expansion sizing and surface treatment to obtain the casing pipe with wide temperature range shrinkage characteristic, high flame retardant property, low smoke density and excellent weather resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer material processing and application, and particularly to a production method of heat-shrinkable tubes with high and low temperature shrinkage functions. Background Art

[0002] With the rapid development of high-tech industries such as new energy vehicles, higher requirements are put forward for the performance of heat-shrinkable tubes. Traditional heat-shrinkable tubes mostly use materials containing halogens, heavy metals and other harmful substances, which not only cause environmental pollution, but also have problems of insufficient flame retardancy and high shrinkage temperature under complex working conditions of high temperature, low temperature alternation, mechanical vibration and chemical corrosion, and it is difficult to meet the strict requirements of the new energy vehicle industry for material environmental protection, high flame retardancy and durability.

[0003] In addition, there are some defects in the production process of traditional heat-shrinkable tubes: its production process usually involves complex processes such as multi-step extrusion molding, chemical cross-linking and multiple heating expansions. The process steps are long and the requirements for equipment accuracy are high, resulting in low production efficiency; problems such as uneven wall thickness and shrinkage rate fluctuation are likely to occur. In terms of environmental protection, some processes also involve solvent cleaning or chemical treatment links, which will produce secondary pollution of waste gas and waste water, and will further increase the environmental burden.

[0004] Therefore, under the dual restrictions of materials and processes, traditional heat-shrinkable tubes can neither meet the requirements of new energy vehicles for high performance and high environmental protection, nor conform to the development trend of modern industrial green and low-carbon. Developing a production method of heat-shrinkable tubes with high and low temperature shrinkage functions, using environmentally friendly halogen-free flame retardant materials, optimizing the material formula and production process, to achieve rapid and uniform shrinkage of heat-shrinkable tubes at ultra-low temperature, improving their high flame retardancy and durability, while reducing production costs and energy consumption, has become an urgent technical problem in this field. Summary of the Invention

[0005] (I) Technical Problems to be Solved Aiming at the deficiencies of the prior art, the present invention provides a production method of heat-shrinkable tubes with high and low temperature shrinkage functions, which has the advantages of environmental protection and pollution-free, high flame retardancy, ultra-low temperature shrinkage, high energy efficiency and reliable quality, and solves the problems of environmental pollution, insufficient flame retardancy, high shrinkage temperature, complex production process, high energy consumption and poor quality stability of traditional heat-shrinkable tube materials.

[0006] (II) Technical Solutions To achieve the above object, the present invention provides the following technical solutions: A production method of heat-shrinkable tubes with high and low temperature shrinkage functions, comprising the following steps: Step 1. Select raw materials: Select ethylene vinyl acetate copolymer, crosslinked polyethylene, impact copolymer polypropylene, polyimide, polyvinylidene fluoride, styrene-ethylene-butene-styrene copolymer, synthetic eucommia rubber, silicone rubber, environmentally friendly halogen-free flame retardant, antioxidant, anti-dripping agent, radiation crosslinking aid, co-crosslinking agent, lubricant, light stabilizer and carbon nanotubes in the prepared formula ratio as raw materials; Step 2. Pretreatment of raw materials: Pretreat the above raw materials; Step 3. Matrix mixing: Add the pretreated ethylene vinyl acetate copolymer and crosslinked polyethylene into the carbon nanotubes, and mix in a high-speed mixer at a vacuum degree of -0.05 to -0.08 MPa and a temperature of 110 - 120 °C for 12 - 15 min; Step 4. Add high-performance resins: Control the temperature between 115 - 125 °C, adjust the rotation speed to 300 - 400 r / min, and sequentially add impact copolymer polypropylene, polyimide and polyvinylidene fluoride, and continue to mix for 8 - 12 min to make the particle size distribution D90 ≤ 50 μm; Step 5. Add elastomers: Lower the temperature to 90 - 100 °C, and then add styrene-ethylene-butene-styrene copolymer, synthetic eucommia rubber and silicone rubber, and mix for 10 - 15 min; Step 6. Add functional additives: First add 70% of the environmentally friendly halogen-free flame retardant and antioxidant, and mix for 4 - 8 min, then add anti-dripping agent, radiation crosslinking aid, co-crosslinking agent, lubricant, light stabilizer and the remaining 30% of the environmentally friendly halogen-free flame retardant at a temperature of 100 - 110 °C and a rotation speed of 400 - 500 r / min, and mix for 8 - 11 min; Step 7. Extrusion molding: Convey the uniformly mixed material into a twin-screw extruder, set the parameters for extrusion molding to obtain a preliminarily formed tubular object; Step 8. Irradiation crosslinking: Send the preliminarily formed tubular object into an electron accelerator for irradiation crosslinking treatment; Step 9. Expansion molding: According to the specifications of the required heat shrinkable tube, set the expansion ratio for expansion to form a heat shrinkable tube with a specific shrinkage ratio from the irradiated crosslinked tubular object; Step 10. Cooling and shaping: The expanded heat shrinkable tube is quickly cooled and shaped through a 10 - 20 °C cooling water bath; Step 11. Post-treatment: Spray a nano-fluorosilicone resin hydrophobic coating with a thickness of 3 - 10 nm on the surface of the heat shrinkable tube.

[0007] Preferably, the raw materials and their weight ratios in Step 1 are as follows: ethylene-vinyl acetate copolymer 25% - 35%; crosslinked polyethylene 10% - 20%; impact copolymerized polypropylene 5% - 14%; polyimide 5% - 10%; polyvinylidene fluoride 5% - 8%; styrene-ethylene-butene-styrene copolymer 4% - 9%; synthetic eucommia rubber 4% - 8%; silicone rubber 5% - 9%; environmentally friendly halogen-free flame retardant 7% - 11%; antioxidant 0.5% - 1%; anti-dripping agent 0.5% - 1%; radiation crosslinking aid 1% - 1.5%; co-crosslinking agent 1% - 2%; lubricant 0.5% - 1%; light stabilizer 0.5% - 1%; carbon nanotubes 0.2 - 1%.

[0008] Preferably, for the raw material pretreatment in Step 2: Place the ethylene-vinyl acetate copolymer and crosslinked polyethylene in a drying oven at 90 - 95°C for 5 - 6 hours according to the formula ratio.

[0009] Preferably, for the raw material pretreatment in Step 2: Put the impact copolymerized polypropylene, polyimide, and polyvinylidene fluoride in a crusher according to the formula ratio respectively to crush them into uniformly sized particles, and then sieve them through a 100 - 120 mesh sieve.

[0010] Preferably, for the raw material pretreatment in Step 2: Put the styrene-ethylene-butene-styrene copolymer and synthetic eucommia rubber in a kneader according to the formula ratio and conduct a plasticizing treatment at 90 - 105°C for 12 - 15 minutes.

[0011] Preferably, for the raw material pretreatment in Step 2: Cut the silicone rubber into 1 - 1.5 cm³ cubes and let them stand at room temperature for 24 - 36 hours.

[0012] Preferably, for the raw material pretreatment in Step 2: Prepare a 3% - 5% ethanol solution with a silane coupling agent, add the environmentally friendly halogen-free flame retardant in the formula ratio to the solution, stir it at 400 - 500 r / min for 25 - 35 minutes, take it out and place it in a drying oven at 75 - 80°C for 6.5 - 7.5 hours. The reaction equation is as follows: R-Si(OEt)3 + Flame retardant surface functional group → R-Si-O-Flame retardant surface functional group + 3EtOH In the formula, R represents the organic functional group of the silane coupling agent, which undergoes chemical bonding with the polymer chain segment in the matrix material. R-Si(OEt)3 represents the siloxane part of the silane coupling agent, where OEt represents ethoxy group. The flame retardant surface functional group represents the polar functional group on the surface of the flame retardant. R-Si-O-Flame retardant surface functional group represents the chemical bonding structure formed after the reaction of the silane coupling agent with the flame retardant surface functional group, and 3EtOH represents the ethanol molecules released during the reaction process.

[0013] Preferably, in the raw material pretreatment in Step 2: antioxidants, anti-dripping agents, radiation cross-linking aids, co-crosslinking agents, lubricants, and light stabilizers in the formula ratio are respectively ground into fine powders, and the particle size is controlled between 100 and 200 mesh.

[0014] Preferably, in the extrusion molding conditions in Step 7: set the temperatures of each section of the extruder, the temperature of the first zone is 165 - 170 °C, the temperature of the second zone is 175 - 180 °C, the temperature of the third zone is 185 - 190 °C, the temperature of the fourth zone is 195 - 200 °C, and the die head temperature is 195 - 200 °C; the screw speed is controlled at 45 - 50 r / min; The irradiation cross-linking conditions in Step 8 are: set the irradiation dose to 50 - 80 kGy, control the transmission speed of the tubular material between 5 - 12 min / m, and enable the tubular material to fully undergo cross-linking reaction under the irradiation of the electron beam.

[0015] Preferably, in the expansion molding conditions in Step 9: set the expansion ratio to 3.5 - 4 times, and through expansion, heat the cross-linked tubular material in the expansion mold at 145 - 150 °C and a pressure of 0.5 - 1.0 MPa for 10 - 15 min.

[0016] Compared with the prior art, the present invention provides a production method of heat shrinkable tubing with high and low temperature shrinkage functions, and has the following beneficial effects: 1. By adopting an environmentally friendly halogen-free flame retardant and optimizing its proportion in the raw material formula, the present invention achieves the beneficial effect of low smoke and halogen-free flame retardancy. By using the environmentally friendly halogen-free flame retardant to increase the flame retardancy, the heat shrinkable tubing of the present invention can effectively inhibit combustion under fire conditions, reduce its smoke density, thus meeting the strict requirements of the new energy vehicle industry for the environmental protection and high flame retardancy of materials. Compared with halogen-containing flame retardants, the materials of the present invention do not release corrosive gases during the combustion process, which will reduce the smoke and toxicity in the air, thereby improving the fire safety.

[0017] 2. By optimizing the elastomer network and the irradiation cross-linking process, the present invention achieves the beneficial effects of excellent high and low temperature adaptability and mechanical properties. By introducing styrene-ethylene-butene-styrene copolymer and synthetic eucommia rubber, the heat shrinkable tubing of the present invention can maintain good mechanical properties in both low and high temperature environments, and the elongation at break increases significantly. At the same time, due to the adoption of the irradiation cross-linking process, a dense three-dimensional network structure is formed inside, thereby improving the heat resistance and dimensional stability of the tubing and further increasing its temperature cycle resistance. The above improvements enable the heat shrinkable tubing to still maintain stable performance in extreme temperature environments and meet the high standards of the new energy vehicle industry for materials.

[0018] 3. The present invention achieves beneficial effects of versatility and high performance by adding carbon nanotubes and surface treatment technology. Among them, by adding carbon nanotubes, the surface resistance of the heat shrinkable tube is significantly reduced, its antistatic performance is significantly improved, and at the same time, its thermal conductivity is enhanced. In addition, a nano-fluorosilicone resin hydrophobic coating with a thickness of 3 - 10 nanometers is sprayed on the surface of the heat shrinkable tube, improving its weather resistance and moisture resistance, and the contact angle reaches more than 115°. The above functional additives and surface treatment technology can not only improve the comprehensive performance of the tube, but also expand the application scope of the heat shrinkable tube in the fields of electronics, communication, automotive, aerospace, etc., meeting the market demand for high-performance and high-safety heat shrinkable tubes. Description of the Drawings

[0019] Figure 1 It is a flowchart of the method steps of the present invention. Detailed Embodiments Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a 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 those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0020] Please refer to Figure 1 , a production method of a heat shrinkable tube with high and low temperature shrinkage functions, including the following steps: Step 1. Select raw materials: Select and prepare ethylene-vinyl acetate copolymer, crosslinked polyethylene, impact copolymer polypropylene, polyimide, polyvinylidene fluoride, styrene-ethylene-butene-styrene copolymer, synthetic eucommia rubber, silicone rubber, environmentally friendly halogen-free flame retardant, antioxidant, anti-dripping agent, radiation crosslinking aid, co-crosslinking agent, lubricant, light stabilizer, and carbon nanotubes as raw materials in the formula ratio; Step 2. Pretreat the raw materials: Pretreat the above raw materials; Step 3. Matrix mixing: Add the pretreated ethylene-vinyl acetate copolymer and crosslinked polyethylene into the carbon nanotubes, and mix them in a high-speed mixer at a vacuum degree of -0.05 to -0.08 MPa and a temperature of 110 - 120 °C for 12 - 15 minutes. Control the temperature in two stages: 110 °C for the first 8 minutes → 120 °C for the next 7 minutes, to avoid local overheating and make the two main matrix materials fully blend to form a stable basic system; Step 4. Add high-performance resin: Control the temperature between 115 - 125 °C, adjust the rotation speed to 300 - 400 r / min, and sequentially add impact copolymer polypropylene, polyimide, and polyvinylidene fluoride, and continue to mix for 8 - 12 minutes to make the particle size distribution D90 ≤ 50 μm, so that these high-performance resins are evenly dispersed in the matrix, endowing the heat shrinkable tube with high strength and high temperature resistance characteristics; Step Five: Addition of elastomers: Lower the temperature to 90 - 100 °C to prevent thermal degradation of styrene - ethylene - butene - styrene copolymer, then add styrene - ethylene - butene - styrene copolymer, synthetic eucommia rubber, and silicone rubber, and mix for 10 - 15 min. This step is used to improve the flexibility, elasticity, and high and low temperature resistance of the material, ensuring that the heat - shrinkable tube can still maintain good mechanical properties in extreme temperature environments; Step Six: Addition of functional additives: Add 70% of environmentally friendly halogen - free flame retardant and antioxidant, and mix for 4 - 8 min. Add the flame retardant in batches to reduce dust. Then add anti - dripping agent, radiation cross - linking agent, co - cross - linking agent, lubricant, light stabilizer, and the remaining 30% of environmentally friendly halogen - free flame retardant and mix at a temperature of 100 - 110 °C and a rotation speed of 400 - 500 r / min for 8 - 11 min to evenly distribute all functional additives in the system, providing the heat - shrinkable tube with multiple properties such as flame retardancy, antioxidant, anti - dripping, and anti - ultraviolet; Step Seven: Extrusion molding: Convey the uniformly mixed material to a twin - screw extruder, set the parameters for extrusion molding to obtain a preliminarily formed tubular product; Step Eight: Irradiation cross - linking: Send the preliminarily formed tubular product into an electron accelerator for irradiation cross - linking treatment; Step Nine: Expansion molding: According to the specifications of the required heat - shrinkable tube, set the expansion ratio for expansion to form a heat - shrinkable tube with a specific shrinkage ratio from the irradiated cross - linked tubular product; Step Ten: Cooling and shaping: The expanded heat - shrinkable tube is rapidly cooled and shaped through a 10 - 20 °C cooling water bath. Through the rapid cooling at this temperature, the shape of the heat - shrinkable tube is quickly fixed, and at the same time, excessive internal stress caused by too fast cooling speed is avoided, ensuring the dimensional accuracy and performance stability of the heat - shrinkable tube; Step Eleven: Post - treatment: Spray a nano - fluorosilicone resin hydrophobic coating with a thickness of 3 - 10 nm on the surface of the heat - shrinkable tube, which helps to improve its weather resistance and moisture resistance. The coating with this thickness has a super - hydrophobic surface and excellent heat resistance, moisture resistance, and dust - proof ability, and can maintain stable performance in a wide range of humidity and harsh environments.

[0021] Specifically, the weight ratio of raw materials and their functions in Step One are as shown in Table 1 below: Table 1

[0022] Specifically, in Step Two, pretreatment of raw materials: Place ethylene - vinyl acetate copolymer and cross - linked polyethylene in a drying oven at 90 - 95 °C for 5 - 6 h to remove the possible moisture in the raw materials, avoiding the generation of bubbles due to water vaporization during subsequent processing, which may affect the quality and performance of the heat - shrinkable tube.

[0023] Specifically, for the raw material pretreatment in step two: the impact copolymer polypropylene, polyimide, and polyvinylidene fluoride in the formula ratio are respectively put into a crusher and crushed into particles with uniform particle size, and then sieved through a 100 - 120 mesh sieve to ensure that the raw material particles are of the same size, which is conducive to subsequent uniform mixing.

[0024] Specifically, for the raw material pretreatment in step two: the styrene - ethylene - butene - styrene copolymer and synthetic eucommia rubber in the formula ratio are put into a mixer and subjected to plasticizing treatment at 90 - 105 °C for 12 - 15 min. The purpose is to reduce their viscosity, enhance plasticity and dispersibility, so that they can better blend with other raw materials in the subsequent mixing process.

[0025] Specifically, for the raw material pretreatment in step two: the silicone rubber in the formula ratio is cut into cubes of 1 - 1.5 cm³ and left standing at room temperature for 24 - 36 h to fully soften it and improve the uniformity when mixing with other raw materials.

[0026] Specifically, for the raw material pretreatment in step two: an ethanol solution of 3% - 5% is prepared using a silane coupling agent, and the environmentally friendly halogen - free flame retardant in the formula ratio is added to the solution, and stirred at 400 - 500 r / min for 25 - 35 min, then taken out and dried in an oven at 75 - 80 °C for 6.5 - 7.5 h. The reaction equation is: R - Si(OEt)3 + surface functional groups of flame retardant → R - Si - O - surface functional groups of flame retardant + 3EtOH In the formula, R represents the organic functional group of the silane coupling agent, such as amino group and epoxy group, and these functional groups can form chemical bonds with the polymer segments in the matrix material. R - Si(OEt)3 represents the siloxane part of the silane coupling agent, where OEt represents ethoxy group (-OCH2CH3), the surface functional groups of the flame retardant represent the polar functional groups on the surface of the flame retardant, such as hydroxyl group (-OH), and R - Si - O - surface functional groups of the flame retardant represent the chemical bonding structure formed after the reaction of the silane coupling agent with the surface functional groups of the flame retardant. 3EtOH represents the ethanol molecules released during the reaction. The flame retardant treated with the silane coupling agent is more uniformly dispersed in the matrix material, reducing the agglomeration phenomenon of the flame retardant. The enhanced compatibility enables the flame retardant to play a more effective flame - retardant role under fire conditions and improves the fire - proof performance of the material.

[0027] Specifically, for the raw material pretreatment in step two: the antioxidant (1010), anti - dripping agent, radiation cross - linking aid, co - cross - linking agent, lubricant, and light stabilizer in the formula ratio are respectively ground into fine powders, and the particle size is controlled between 100 - 200 meshes to ensure that each additive can be uniformly dispersed during the mixing process and fully play its role.

[0028] Specifically, the extrusion molding conditions in Step 7 are as follows: set the temperatures of each section of the extruder, with the temperature of Zone 1 being 165 - 170 °C, Zone 2 being 175 - 180 °C, Zone 3 being 185 - 190 °C, Zone 4 being 195 - 200 °C, and the die head temperature being 195 - 200 °C; control the screw speed at 45 - 50 r / min. During the extrusion process, precisely adjust the temperature, pressure, and screw speed parameters of the extruder to uniformly plasticize and extrude the material under the push of the screw, forming a continuous, high-precision, and smooth-surface tubular object. Specifically, the irradiation cross-linking conditions in Step 8 are as follows: set the irradiation dose to 50 - 80 kGy, control the transmission speed of the tubular object between 5 - 12 min / m, so that the tubular object undergoes sufficient cross-linking reaction under the irradiation of the electron beam. Under the action of high-energy electron beams, the radiation cross-linking agent (TAIC) and co-cross-linking agent (TAIC) in the material promote the formation of a three-dimensional network structure among the components, improving the heat resistance, mechanical strength, and dimensional stability of the heat shrinkable tube.

[0029] Specifically, the expansion molding conditions in Step 9 are as follows: set the expansion ratio to 3.5 - 4 times. Through expansion, heat the cross-linked tubular object in the expansion mold at 145 - 150 °C and a pressure of 0.5 - 1.0 MPa for 10 - 15 min.

[0030] Examples 1 - 4 are obtained according to the formula of the present invention. Then, based on the characteristics of the heat shrinkable tube of the present invention, the raw materials in the formula are deleted and replaced to obtain Comparative Examples 1 - 4. The raw material formula table is as follows: Table 2

[0031] Make heat shrinkable tubes from the examples and comparative examples in Table 2 and conduct a performance comparison to obtain Table 3 below: Table 3

[0032] The following information is obtained from Tables 2 - 3: (1) Analyze from the aspect of optimizing the flame retardant system (Example 1 and Comparative Example 1): In Example 1, the halogen-free environmental protection flame retardant (9%) has a low smoke density (SDR = 35) and a flame retardant grade of V - 0. While in Comparative Example 1, the halogen-containing flame retardant (decabromodiphenyl ether) has a high smoke density (SDR = 85), the flame retardant grade drops to V - 2, and the release of corrosive gases increases. Therefore, the halogen-free flame retardant can significantly reduce smoke and toxicity through the gas-phase flame retardancy and carbon layer formation mechanism.

[0033] (2) Analysis from the aspect of the elastomer network effect (Example 1 and Comparative Example 2): In Example 1, SEBS + POC (a total of 12%) provides low-temperature toughness (-50°C shrinkage), and the elongation at break is 350%. In Comparative Example 2, the elastomer is removed, the lower limit of low-temperature shrinkage drops to -30°C, and the elongation at break is only 200%. The flexibility of its finished product is lost. Therefore, the synergy of SEBS / POC can enhance the chain segment movement ability and ensure the mechanical properties at extreme temperatures; (3) Analysis from the aspect of the influence of cross-linking methods (Example 1 and Comparative Example 3): In Example 1, radiation cross-linking (TAIC additive) is used, and the heat resistance reaches 180°C, and the tensile strength is 25 MPa. In Comparative Example 3, peroxide chemical cross-linking (DCP) is used, the cross-linking is uneven, the heat resistance is only 140°C, and the strength drops to 20 MPa. Therefore, the three-dimensional network of radiation cross-linking in the present invention is denser, and the dimensional stability and heat resistance are superior to traditional chemical cross-linking; (4) Analysis from the aspect of material substitution verification (Example 1 and Comparative Example 4): In Example 1, the SEBS / POC elastomer has a smooth start of low-temperature shrinkage (-50°C), while in Comparative Example 4, it is replaced by ordinary EPDM, and the start of low-temperature shrinkage is difficult (-25°C), and the chemical corrosion resistance decreases (partial swelling after electrolyte immersion). Therefore, the dynamic vulcanization characteristics of SEBS / POC are superior to ordinary EPDM, making the finished product of it have stronger resistance to extreme environments; (5) Analysis from the aspect of functional modification verification (Example 4): Since 1% carbon nanotubes (CNT) are added in Example 4, the surface resistance is reduced to 10 5 Ω, the antistatic performance is improved, and at the same time the thermal conductivity is enhanced. Therefore, nano-fillers can specifically optimize functionality and expand the application range. (6) (7)

[0034] Summary: The embodiments of the present invention enable the finished product of the casing to have excellent properties such as high and low temperature adaptability (-50~180°C), low-smoke and halogen-free flame retardancy (V-0), and long life (temperature cycle resistance > 1000 times) through the core technologies of environmental protection flame retardants, elastomer networks, and radiation cross-linking. Due to the halogen-containing flame retardants in the raw materials, the lack of elastomers, chemical cross-linking or material substitution in the comparative examples, the performance of the finished product of the casing decreases. Therefore, the comparative examples verify the irreplaceability of the formula design of the present invention. (8) (9)

[0035] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirits of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A production method of heat shrinkable tube with high and low temperature shrinkage function, characterized in that, It includes the following steps: Step 1, Select raw materials: Select ethylene-vinyl acetate copolymer, crosslinked polyethylene, impact copolymerized polypropylene, polyimide, polyvinylidene fluoride, styrene-ethylene-butene-styrene copolymer, synthetic eucommia rubber, silicone rubber, environmentally friendly halogen-free flame retardant, antioxidant, anti-dripping agent, radiation crosslinking aid, co-crosslinking agent, lubricant, light stabilizer and carbon nanotubes in the prepared formula ratio as raw materials; Step 2, Pretreatment of raw materials: Pretreat the above raw materials; Step 3, Matrix mixing: Add the pretreated ethylene-vinyl acetate copolymer and crosslinked polyethylene into the carbon nanotubes, and mix them in a high-speed mixer at a vacuum degree of -0.05 to -0.08 MPa and a temperature of 110 - 120 °C for 12 - 15 min; Step 4, Add high-performance resin: Control the temperature between 115 - 125 °C, adjust the rotation speed to 300 - 400 r / min, and sequentially add impact copolymerized polypropylene, polyimide and polyvinylidene fluoride, and continue to mix for 8 - 12 min to make its particle size distribution D90 ≤ 50 μm; Step 5, Add elastomer: Lower the temperature to 90 - 100 °C, then add styrene-ethylene-butene-styrene copolymer, synthetic eucommia rubber and silicone rubber, and mix for 10 - 15 min; Step 6, Add functional additives: First add 70% of the environmentally friendly halogen-free flame retardant and antioxidant, and mix for 4 - 8 min, then add anti-dripping agent, radiation crosslinking aid, co-crosslinking agent, lubricant, light stabilizer and the remaining 30% of the environmentally friendly halogen-free flame retardant at a temperature of 100 - 110 °C and a rotation speed of 400 - 500 r / min and mix for 8 - 11 min; Step 7, Extrusion molding: Convey the uniformly mixed material into a twin-screw extruder, set the parameters for extrusion molding to obtain a preliminarily formed tubular object; Step 8, Irradiation crosslinking: Send the preliminarily formed tubular object into an electron accelerator for irradiation crosslinking treatment; Step 9, Expansion molding: According to the specifications of the required heat-shrinkable tube, set the expansion ratio for expansion to form a heat-shrinkable tube with a specific shrinkage ratio from the irradiated crosslinked tubular object; Step 10, Cooling and shaping: The expanded heat-shrinkable tube is quickly cooled and shaped through a 10 - 20 °C cooling water bath; Step 11, Post-treatment: Spray a nano-fluorosilicone resin hydrophobic coating with a thickness of 3 - 10 nm on the surface of the heat-shrinkable tube.

2. A production method of a heat-shrinkable sleeve having high and low temperature shrinkage functions according to claim 1, characterized in that, The raw materials and their weight ratios in the said Step 1 are: ethylene-vinyl acetate copolymer 25% - 35%; crosslinked polyethylene 10% - 20%; impact copolymerized polypropylene 5% - 14%; polyimide 5% - 10%; polyvinylidene fluoride 5% - 8%; styrene-ethylene-butene-styrene copolymer 4% - 9%; synthetic eucommia rubber 4% - 8%; silicone rubber 5% - 9%; environmentally friendly halogen-free flame retardant 7% - 11%; antioxidant 0.5% - 1%; anti-dripping agent 0.5% - 1%; radiation crosslinking aid 1% - 1.5%; co-crosslinking agent 1% - 2%; lubricant 0.5% - 1%; light stabilizer 0.5% - 1%; carbon nanotubes 0.2 - 1%.

3. The production method of a heat-shrinkable sleeve with high and low temperature shrinkage functions according to claim 1, characterized in that, In the raw material pretreatment in Step 2: Place ethylene-vinyl acetate copolymer and crosslinked polyethylene in a drying oven at 90-95°C for 5-6 hours according to the formulation ratio.

4. A production method of a heat shrinkable tube with high and low temperature shrinkage functions according to claim 1, characterized in that, In the raw material pretreatment in Step 2: Put impact copolymer polypropylene, polyimide, and polyvinylidene fluoride in a crusher according to the formulation ratio to crush them into uniformly sized particles, and then screen them through a 100-120 mesh sieve.

5. A production method of a heat shrinkable tube with high and low temperature shrinkage functions according to claim 1, characterized in that, In the raw material pretreatment in Step 2: Put styrene-ethylene-butene-styrene copolymer and synthetic eucommia rubber in a mixer according to the formulation ratio and conduct plasticizing treatment at 90-105°C for 12-15 minutes.

6. A production method of a heat-shrinkable sleeve having high and low temperature shrinkage functions according to claim 1, characterized in that: In the raw material pretreatment in Step 2: Cut silicone rubber into 1-1.5 cm³ cubes and let them stand at room temperature for 24-36 hours.

7. A production method of a heat-shrinkable sleeve having high and low temperature shrinkage functions according to claim 1, characterized in that: In the raw material pretreatment in Step 2: Prepare a 3%-5% ethanol solution with a silane coupling agent, add the environmentally friendly halogen-free flame retardant in the formulation ratio to the solution, stir at 400-500 r / min for 25-35 minutes, take it out and place it in a drying oven at 75-80°C for 6.5-7.5 hours. The reaction equation is: R-Si(OEt)3 + Flame retardant surface functional group → R-Si-O-Flame retardant surface functional group + 3EtOH In the formula, R represents the organic functional group of the silane coupling agent, which undergoes chemical bonding with the polymer chain segment in the matrix material. R-Si(OEt)3 represents the siloxane part of the silane coupling agent, where OEt represents ethoxy group. The flame retardant surface functional group represents the polar functional group on the surface of the flame retardant. R-Si-O-Flame retardant surface functional group represents the chemical bonding structure formed after the reaction of the silane coupling agent with the flame retardant surface functional group. 3EtOH represents the ethanol molecules released during the reaction process.

8. A production method of a heat shrinkable tube with high and low temperature shrinkage functions according to claim 1, characterized in that: In the raw material pretreatment in Step 2: Grind antioxidant, anti-dripping agent, radiation crosslinking aid, co-crosslinking agent, lubricant, and light stabilizer into fine powders according to the formulation ratio, and control the particle size to be between 100-200 meshes.

9. A production method of a heat shrinkable tube having high and low temperature shrinkage functions according to claim 1, characterized in that: In the extrusion molding conditions in Step 7: Set the temperatures of each section of the extruder. The temperature of Zone 1 is 165-170°C, the temperature of Zone 2 is 175-180°C, the temperature of Zone 3 is 185-190°C, the temperature of Zone 4 is 195-200°C, and the die temperature is 195-200°C; control the screw speed at 45-50 r / min; In the irradiation crosslinking conditions in Step 8: Set the irradiation dose to 50-80 kGy, control the transmission speed of the tubular material between 5-12 min / m, and enable the tubular material to fully undergo crosslinking reaction under the irradiation of the electron beam.

10. A method for producing a heat shrinkable sleeve having high and low temperature shrinkage functions according to claim 1, characterized in that: In the expansion molding conditions in Step 9: Set the expansion ratio to 3.5-4 times. Through expansion, heat the crosslinked tubular material in an expansion mold at 145-150°C and a pressure of 0.5-1.0 MPa for 10-15 minutes.

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