Preparation method and application of heat shrink tube replacing stripping solution for stripping film layer magnet

Abstract

The invention relates to a preparation method and application of a heat shrink tube for replacing a deplating solution to decoat a magnet with a film layer, the magnet is sleeved with a layer of modified heat shrink tube, deplating of the magnet surface film layer by the deplating solution is reduced, and the modified heat shrink tube is good in shrinkage performance, good in coating effect and capable of being repeatedly used; the side face is sleeved with a heat shrink tube, the end face is coated with a protective film, the length of the heat shrink tube is accurately controlled, the magnet is not damaged, the cost is reduced to the maximum extent, resources are recycled, and the coating uniformity is guaranteed.

Description

Technical Field

[0001] The present invention belongs to the technical field of heat shrinkable tubes, and particularly relates to a preparation method and application of a heat shrinkable tube for replacing a plating stripping solution to strip a coating film on a magnet. Background Art

[0002] In the process of coating production, the product to be coated is fixed on an umbrella for coating. In this process, magnets are required. After repeated use and coating, the film layer on the surface of the magnets accumulates relatively thickly, and a plating stripping solution is needed to strip the film layer. Because the plating stripping solution will not only strip the film layer on the magnets, but also cause certain damage to the magnets, reducing the lifespan of the magnets. Moreover, the strong magnetism of the magnets makes it easy to adsorb, inconvenient for plating stripping, and prone to plating stripping damage to the magnets.

[0003] Vacuum coating machines belong to high-precision instruments. By sleeving a heat shrinkable tube on the magnet, the harm of the plating stripping solution to the magnet can be greatly reduced, potential safety hazards during the plating stripping process can be reduced, damage to the magnet can be reduced, and it is convenient for replacement. However, it is found during use that after the conventional heat shrinkable tube is used, it cannot completely fit and cover the magnet. Firstly, the covered area is uneven and pores will be generated. This slight non-fitting will cause the instrument precision to decrease and affect the uniformity during the coating process. Secondly, after the heat shrinkable tube is heat-shrunk and covered, it is difficult to control the length precision of the heat shrinkable tube. If it is too short after heat shrinkage, the film layer will still accumulate on the side of the magnet that is not covered, affecting the magnet lifespan and service life, thereby affecting the coating efficiency. If it is too long after heat shrinkage, the end face is also covered. During the subsequent cutting and trimming process, it cannot be completely trimmed clean, or the magnet end face will also be damaged, affecting the magnetism of the magnet, thereby affecting the coating uniformity, etc. Therefore, how to ensure the complete covering and fitting degree of the heat shrinkable tube and control the length of the heat shrinkable tube to fit the magnet side is the research focus of the present invention.

[0004] Heat shrinkable materials utilize the principle of "elastic memory" of polymer compounds, and are a kind of functional polymer materials made from rubber and plastic materials as the base material through mixing, molding, cross-linking, heating, expansion, and cooling and shaping. They are an important branch of shape memory polymers. The preparation process of heat shrinkable materials determines the product quality. Therefore, the key technologies in its preparation process have always been the research direction in this field.

[0005] Heat shrinkable tube materials belong to the unstable structure of organic molecules. When the shape of the internally aged heat shrinkable tube changes, stress is generated, which will cause fracture. Traditional steel rods or ceramic rods of heat shrinkable tubes cannot play a role in restraining the aging deformation of heat shrinkable tubes. Therefore, how to enhance the shrinkage performance of heat shrinkable tubes, etc., is the research focus of the present invention.

[0006] As the requirements for the flame retardancy of materials become increasingly strict, the filling amount of flame retardants added to polymers is also increasing. Since the surfaces of the vast majority of flame retardants are hydrophilic and oleophobic, they have poor compatibility with polymers. An excessive filling amount seriously damages the mechanical properties of the materials. Therefore, a compatibilizer needs to be added to improve the mechanical properties of the materials.

[0007] The varieties of silicon-based flame retardants mainly include polysiloxane, silicone rubber, silicon dioxide and other silicon-based flame retardants, which have the advantages of high efficiency, low toxicity, smoke suppression and promoting carbon formation. Since silicon-based flame retardants can not only endow the substrate with excellent flame retardant properties, but also improve other properties of the substrate, such as processing properties, mechanical properties, heat resistance, etc., and the recycled use effect of flame retardant materials is better and can meet the strict requirements for flame retardants, the silicon-based flame retardants and their flame retardant technologies have developed rapidly in recent years. Therefore, one of the research directions of the present invention is to select a suitable flame retardant, reduce the use of compatibilizer and maximize the various properties of the material. Summary of the Invention

[0008] To solve the above technical problems, the specific preparation process of the present invention is as follows:

[0009] (1) A preparation method of a heat shrinkable tube:

[0010] According to the basic formula of polyethylene: ethylene-vinyl acetate copolymer: crosslinking agent = 70:30:1, 0.5 - 0.8 parts of antioxidant, adding 1 - 3% of the flame retardant formula, premixing at a temperature of 50 - 55°C and a rotation speed of 650 - 1300 RPM and then adding it to an internal mixer, mixing at 155°C with a rotation speed of 40 - 80 RPM for 10 min and then discharging; pouring it into a screw extruder to obtain a tubular object, sealing it with a PE film, irradiating it with an electron beam accelerator, with a radiation dose of 90 KGy, and then expanding it to 40 mm to obtain a heat shrinkable tube;

[0011] The antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate];

[0012] The crosslinking agent is benzyl acrylate.

[0013] The flame retardant formula is obtained by mixing 8 - 10 parts of flame retardant and 2 - 4 parts of compatibilizer at 50 - 60°C under a low speed of 100 RPM for 10 - 20 min.

[0014] The flame retardant is methyl 3-trimethylsilyloxy-2-butenoate.

[0015] (2) Application of a heat shrinkable tube obtained by the above preparation method in replacing a stripping solution to strip a coating film on a magnet:

[0016] Coat the upper and lower end faces of the magnet with end face protective film, put a heat shrinkable tube on the magnet, and leave 2-3 cm more at the edge. After heating with a hot air blower, when the heat shrinkable tube is completely shrunk to cover the magnet, cut off the excess heat shrinkable tube at both ends and tear off the protective film on the end face of the magnet. When the surface of the heat shrinkable tube adsorbs a relatively thick film layer after being used for a period of time, only need to cut it open and replace it with a new heat shrinkable tube, and repeat the above steps.

[0017] The preparation process of the end face protective film is as follows: Add 30-40 parts of polytetrafluoroethylene, 8-10 parts of isophorone diisocyanate, and 2-5 parts of polyethylene glycol into 30-36 parts of a modifier with a mass fraction of 30-50% heated to 80-85 °C, stir at 200 RPM for 30 min and then react for 2 h, drop in 1-3 parts of ethyl o-methoxybenzoate and 1-3 parts of 1,4-butanediol, then cool down to 70 °C, add 2-5 parts of triethylamine as a catalyst and react for 0.5 h, and at the same time add an equal amount of water for emulsification; finally, carry out vacuum distillation to obtain the end face protective film.

[0018] The modifier is 3-pyridyltriethoxysilane.

[0019] The beneficial effects of the present invention are as follows:

[0020] 1. The present invention relates to a preparation method and application of a heat shrinkable tube for replacing a plating stripping solution to strip the film layer of a magnet. By putting a modified heat shrinkable tube on the magnet, the present invention reduces the stripping of the film layer on the surface of the magnet by the plating stripping solution. The modified heat shrinkable tube not only has good shrinkage performance and good coating effect, can be reused, but also reduces the damage of the plating stripping solution to the magnet. The heat shrinkable tube is put on the side and the end face is coated with a protective film, the length of the heat shrinkable tube is precisely controlled and the magnet is not damaged, the cost is minimized, resources are reused, and the coating uniformity is ensured.

[0021] 2. The present invention is to put a heat shrinkable tube on the surface of the magnet. After heating with a hot air blower, the tube will shrink to wrap the magnet, leaving only the end face. After trimming the excess heat shrinkable tube, the protective film on the end face can be torn off, which will not affect the damage to the magnet during this process. The surface of the heat shrinkable tube is rough, and the film layer during the coating process is more likely to adhere to the surface of the heat shrinkable tube. It is convenient to replace, can save time, and greatly reduce the cost.

[0022] 3. The present invention selects benzyl acrylate as a raw material for blending and combines radiation crosslinking. The obtained heat shrinkable tube not only has good shrinkage performance, will not age, deform or twist after long-term use. The introduction of benzyl acrylate improves the shrinkage characteristics of the heat shrinkable tube, ensures that it can shrink better at high temperatures, better coats the side of the magnet without leaving gaps, and maintains a stable shape during long-term use. It can better withstand external forces, reduce the phenomenon of cracking, and thus extend the service life of the heat shrinkable tube.

[0023] 4. Benzyl acrylate has the advantages of good chemical stability, excellent corrosion resistance, easy processing, and low price. The acrylic acid in benzyl acrylate can have a good combination with inorganic particles, so it can improve the properties of materials to a certain extent. During the compounding process of benzyl acrylate, the C-H structure in the macromolecular chain also generates free electrons under electron beam irradiation. Therefore, through the bridging effect between the two, chemical bonds are formed, and further reactions form a network structure between macromolecules, increasing the crosslinking degree of the material. This crosslinking enhances the durability of the material and reduces the risks of aging and deformation caused by the instability of organic molecules.

[0024] 5. The flame retardant material used in the present invention is environmentally friendly. It not only improves the flame retardant performance but also has good corrosion resistance and aging resistance, thereby enhancing its characteristic of rapid shrinkage. When the material burns, due to the presence of an organosilicon component in methyl 3-trimethylsilyloxy-2-butenoate, methyl 3-trimethylsilyloxy-2-butenoate forms a hard Si / C layer on the surface of the material, playing a dual role of isolating oxygen and flame and preventing the decomposition of the polymer. The flame retardant mechanism mainly plays a physical barrier role in the condensed phase, thereby achieving the purpose of flame retardancy.

[0025] 6. Methyl 3-trimethylsilyloxy-2-butenoate generates a glassy substance covering the surface of the substance during combustion, promoting the formation of a dense carbon layer in the material, effectively isolating the transfer of combustible substances, and strengthening the carbonization and smoke suppression effects of the material. Therefore, the flame retardant performance of the system is improved. Methyl 3-trimethylsilyloxy-2-butenoate is a highly active flame retardant substance. The oxidation substances generated during combustion can promote the dehydration and carbonization of the polymer, and the formed carbon layer can isolate the external oxygen and heat from the internal polymer during combustion, thereby playing a flame retardant role, so that good shrinkage performance can also be maintained at a relatively high temperature.

[0026] 7. Conventionally, a relatively large amount of compatibilizer needs to be added to make the flame retardant well compatible with the substrate. Methyl 3-trimethylsilyloxy-2-butenoate in the present invention has a structural advantage and can coat inorganic particles to generate a flexible interfacial layer, making the inorganic particles disperse evenly and reducing the agglomeration phenomenon. This improves the compatibility between the inorganic particles and the substrate, and the mechanical properties of the composite material system can be improved by adding a small amount of compatibilizer.

[0027] 8. In the present invention, a heat shrinkable tube is used to coat the magnet. During the process of trimming the excess heat shrinkable tube, a protective film is attached to both ends of the magnet to protect the integrity of the magnet to the greatest extent and is easy to peel off after use without damaging the magnet, ensuring the integrity and magnetism of the magnet, thereby ensuring the uniformity of the coating process.

[0028] 9. The decomposition temperature of the skeleton of the magnet end face protective film prepared after being modified with 3 - pyridyltriethoxysilane increases, and the mass loss decreases. The introduction of 3 - pyridyltriethoxysilane brings more Si - O groups. After transesterification with phenol substances, Si - O successfully connected to the benzene ring undergoes self - polymerization with free Si - O to form Si - O - Si bonds with high bond energy, showing good heat resistance, thus improving the stability of the modified skeleton. And as the silicon element gradually increases, the water contact angle on the surface of the coating film gradually increases, and the water resistance, tensile strength, and elongation at break are improved, making it easier to peel during subsequent cutting.

[0029] 10. Compared with other organosilicons, this modification liquid does not introduce too many ethyl groups. 3 - pyridyltriethoxysilane has high thermal stability, which improves the thermal stability of the modified product more. Reducing the small - molecule groups at both ends of the chain segment can also improve the stability of the modified end face protective film.

[0030] 11. Using 3 - pyridyltriethoxysilane to modify the end face protective film replaces the polar hydroxyl groups in the structure. The polarity of the modified end face protective film decreases, improving the material compatibility and the adhesion between the protective film and the heat - shrinkable tube. Therefore, during the cutting and peeling process, the heat - shrinkable tube and the protective film that excessively wrap the magnet end face can be peeled off conveniently and quickly without residue. Specific Embodiments

[0031] The present invention will be further described in detail below with reference to the embodiments. All the magnets used below are neodymium - iron - boron magnets.

[0032] Example 1

[0033] According to the basic formula of polyethylene: ethylene - vinyl acetate copolymer: benzyl acrylate = 70:30:1, 0.6 parts of pentaerythritol tetra[β - (3,5 - di - tert - butyl - 4 - hydroxyphenyl)propionate], adding a 2% flame - retardant formula, which is obtained by mixing 9 parts of methyl 3 - trimethylsiloxy - 2 - butenoate and 3 parts of maleic anhydride - grafted copolymer at 55°C under low speed of 100 RPM for 15 min. After premixing at a temperature of 52°C and a speed of 980 RPM, it is added to a mixer and kneaded at 155°C at a speed of 60 RPM for 10 min and then discharged; it is poured into a screw extruder to obtain a tubular object, sealed with a PE film, irradiated with an electron beam accelerator with a radiation dose of 90 KGy, and then expanded to 40 mm to obtain a heat - shrinkable tube;

[0034] Example 2

[0035] According to the basic formula of polyethylene: ethylene-vinyl acetate copolymer: benzyl acrylate = 70:30:1, 0.5 parts of pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] are added, and a 3% flame retardant formula is added. The flame retardant formula is obtained by mixing 10 parts of methyl 3-trimethylsiloxy-2-butenoate and 2 parts of maleic anhydride graft copolymer at a low speed of 100 RPM for 10 minutes at 60 °C. After premixing at a temperature of 55 °C and a rotation speed of 650 RPM, it is added to an internal mixer and kneaded at 155 °C at a rotation speed of 80 RPM for 10 minutes and then discharged; it is poured into a screw extruder to obtain a tubular object, sealed with a PE film, irradiated with an electron beam accelerator, the radiation dose is 90 KGy, and then it is expanded to 40 mm to obtain a heat shrinkable tube;

[0036] Example 3

[0037] According to the basic formula of polyethylene: ethylene-vinyl acetate copolymer: benzyl acrylate = 70:30:1, 0.8 parts of pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] are added, and a 1% flame retardant formula is added. The flame retardant formula is obtained by mixing 8 parts of methyl 3-trimethylsiloxy-2-butenoate and 4 parts of maleic anhydride graft copolymer at a low speed of 100 RPM for 20 minutes at 50 °C. After premixing at a temperature of 50 °C and a rotation speed of 1300 RPM, it is added to an internal mixer and kneaded at 155 °C at a rotation speed of 40 RPM for 10 minutes and then discharged; it is poured into a screw extruder to obtain a tubular object, sealed with a PE film, irradiated with an electron beam accelerator, the radiation dose is 90 KGy, and then it is expanded to 40 mm to obtain a heat shrinkable tube;

[0038] Comparative Example 1

[0039] The difference between this comparative example and Example 1 is that benzyl acrylate is not added, and the rest is the same as in Example 1.

[0040] Comparative Example 2

[0041] The difference between this comparative example and Example 1 is that the benzyl acrylate is triallyl isocyanurate, and the rest is the same as in Example 1.

[0042] Comparative Example 3

[0043] The difference between this comparative example and Example 1 is that radiation treatment is not carried out in this comparative example. Specifically: according to the basic formula of polyethylene: ethylene-vinyl acetate copolymer: benzyl acrylate = 70:30:1, 0.6 parts of pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], adding a 2% flame retardant formulation, the flame retardant formulation is obtained by mixing 9 parts of methyl 3-trimethylsiloxy-2-butenoate and 3 parts of maleic anhydride graft copolymer at 55 °C under low speed of 100 RPM for 15 minutes. After premixing at a temperature of 52 °C and a speed of 980 RPM, it is added to an internal mixer and kneaded at 155 °C at a speed of 60 RPM for 10 minutes and then discharged; it is poured into a screw extruder to obtain a tubular object, and then it is expanded to 40 mm to obtain a heat shrinkable tube; the rest is the same as Example 1.

[0044] Comparative Example 4

[0045] The difference between this comparative example and Example 1 is the different addition amount of benzyl acrylate; specifically: according to the basic formula of polyethylene: ethylene-vinyl acetate copolymer: benzyl acrylate = 70:30:5, 0.6 parts of pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], adding a 2% flame retardant formulation, the flame retardant formulation is obtained by mixing 9 parts of methyl 3-trimethylsiloxy-2-butenoate and 3 parts of maleic anhydride graft copolymer at 55 °C under low speed of 100 RPM for 15 minutes. After premixing at a temperature of 52 °C and a speed of 980 RPM, it is added to an internal mixer and kneaded at 155 °C at a speed of 60 RPM for 10 minutes and then discharged; it is poured into a screw extruder to obtain a tubular object, sealed with a PE film, irradiated with an electron beam accelerator, the radiation dose is 90 KGy, and then it is expanded to 40 mm to obtain a heat shrinkable tube; the rest is the same as Example 1.

[0046] Comparative Example 5

[0047] The difference between this comparative example and Example 1 is the different addition amount of benzyl acrylate; specifically: according to the basic formula of polyethylene: ethylene-vinyl acetate copolymer: benzyl acrylate = 70:30:0.5, 0.6 parts of pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], adding a 2% flame retardant formulation, the flame retardant formulation is obtained by mixing 9 parts of methyl 3-trimethylsiloxy-2-butenoate and 3 parts of maleic anhydride graft copolymer at 55 °C under low speed of 100 RPM for 15 minutes. After premixing at a temperature of 52 °C and a speed of 980 RPM, it is added to an internal mixer and kneaded at 155 °C at a speed of 60 RPM for 10 minutes and then discharged; it is poured into a screw extruder to obtain a tubular object, sealed with a PE film, irradiated with an electron beam accelerator, the radiation dose is 90 KGy, and then it is expanded to 40 mm to obtain a heat shrinkable tube; the rest is the same as Example 1.

[0048] Comparative Example 6

[0049] The difference between this comparative example and Example 1 is that methyl 3-trimethylsilyloxy-2-butenoate is phenyl methacrylate; the rest is the same as Example 1.

[0050] Comparative Example 7

[0051] The differences between this comparative example and Example 1 are the addition amount of methyl 3-trimethylsilyloxy-2-butenoate and the ratio of the compatibilizer, specifically: according to the basic formula of polyethylene: ethylene-vinyl acetate copolymer: benzyl acrylate = 70:30:1, 0.6 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], adding a 2% flame retardant formulation, the flame retardant formulation is obtained by mixing 9 parts of methyl 3-trimethylsilyloxy-2-butenoate and 6 parts of maleic anhydride graft copolymer at 55°C under low speed of 100 RPM for 15 minutes, pre-mixing at a temperature of 52°C and a speed of 980 RPM and then adding it to an internal mixer, mixing at 155°C with a speed of 60 RPM for 10 minutes and then discharging; pouring it into a screw extruder to obtain a tubular object, sealing it with a PE film, irradiating it with an electron beam accelerator, with a radiation dose of 90 KGy, and then expanding it to 40 mm to obtain a heat shrinkable tube; the rest is the same as Example 1.

[0052] Comparative Example 8

[0053] The differences between this comparative example and Example 1 are the addition amount of methyl 3-trimethylsilyloxy-2-butenoate and the ratio of the compatibilizer, specifically: according to the basic formula of polyethylene: ethylene-vinyl acetate copolymer: benzyl acrylate = 70:30:1, 0.6 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], adding a 2% flame retardant formulation, the flame retardant formulation is obtained by mixing 12 parts of methyl 3-trimethylsilyloxy-2-butenoate and 3 parts of maleic anhydride graft copolymer at 55°C under low speed of 100 RPM for 15 minutes, pre-mixing at a temperature of 52°C and a speed of 980 RPM and then adding it to an internal mixer, mixing at 155°C with a speed of 60 RPM for 10 minutes and then discharging; pouring it into a screw extruder to obtain a tubular object, sealing it with a PE film, irradiating it with an electron beam accelerator, with a radiation dose of 90 KGy, and then expanding it to 40 mm to obtain a heat shrinkable tube; the rest is the same as Example 1.

[0054] Test 1:

[0055] The mechanical properties of the heat shrinkable tubes of Examples 1-3 and Comparative Examples 1-8 were tested according to GB / T 1040-2006, with a tensile speed of 20 mm / min and a specimen thickness of 1 mm.

[0056] Shrinkage performance: Record the circumference of the heat shrinkable tube before heating after the heat shrinkable tube is put on the magnet sleeve, and the circumference of the heat shrinkable tube after heating and covering. Record the changes of the heat shrinkable tube before and after heat shrinkage covering in Examples 1-3 and Comparative Examples 1-8 to obtain the shrinkage rate.

[0057] Shrinkage rate = (original circumference - circumference after heating) / original circumference × 100%

[0058] The results are shown in Table 1.

[0059] Table 1 Performance of Heat Shrinkable Tube

[0060] Group Shrinkage rate (%) Tensile strength (MPa) Example 1 30.6 14.3 Example 2 29.3 14.2 Example 3 29.3 14.0 Comparative Example 1 16.0 8.2 Comparative Example 2 20.0 8.6 Comparative Example 3 17.3 8.9 Comparative Example 4 22.6 12.8 Comparative Example 5 26.6 10.1 Comparative Example 6 17.3 9.2 Comparative Example 7 22.6 13.5 Comparative Example 8 21.3 11.2

[0061] The following implementation methods continue the subsequent steps on the basis of Example 1.

[0062] Example 4

[0063] The preparation process of the end face protective film is as follows: Add 35 parts of polytetrafluoroethylene, 9 parts of isophorone diisocyanate, and 3 parts of polyethylene glycol to 33 parts of a modified solution of 3-pyridyltriethoxysilane with a mass fraction of 40% heated to 82 °C. Stir at 200 RPM for 30 min and then react for 2 h. Drop in 2 parts of ethyl o-methoxybenzoate and 2 parts of 1,4-butanediol. Then cool down to 70 °C, add 4 parts of triethylamine as a catalyst and react for 0.5 h, and at the same time add an equal amount of water for emulsification; finally, carry out vacuum distillation to obtain the end face protective film.

[0064] Coat the end face protective film on the upper and lower end faces of the magnet. Put the heat shrinkable tube on the magnet, with an extra 2.5 cm at the edge. After heating with a hot air blower, after the heat shrinkable tube completely shrinks and covers the magnet, cut off the excess heat shrinkable tube at both ends and tear off the protective film on the end face of the magnet;

[0065] Example 5

[0066] The preparation process of the end face protective film is as follows: Add 30 parts of polytetrafluoroethylene, 10 parts of isophorone diisocyanate, and 2 parts of polyethylene glycol to 36 parts of a modified solution of 3-pyridyltriethoxysilane with a mass fraction of 30% heated to 80 °C. Stir at 200 RPM for 30 min and then react for 2 h. Drop in 3 parts of ethyl o-methoxybenzoate and 1 part of 1,4-butanediol. Then cool down to 70 °C, add 5 parts of triethylamine as a catalyst and react for 0.5 h, and at the same time add an equal amount of water for emulsification; finally, carry out vacuum distillation to obtain the end face protective film.

[0067] Coat the end face protective film on the upper and lower end faces of the magnet. Put the heat shrinkable tube on the magnet, with an extra 3 cm at the edge. After heating with a hot air blower, after the heat shrinkable tube completely shrinks and covers the magnet, cut off the excess heat shrinkable tube at both ends and tear off the protective film on the end face of the magnet;

[0068] Example 6

[0069] The preparation process of the end face protective film is as follows: Add 40 parts of polytetrafluoroethylene, 8 parts of isophorone diisocyanate, and 5 parts of polyethylene glycol into 30 parts of a modified solution of 3-pyridyltriethoxysilane with a mass fraction of 50% heated to 85°C. Stir at 200 RPM for 30 min and then react for 2 h. Drop in 1 part of ethyl o-methoxybenzoate and 3 parts of 1,4-butanediol. Then cool down to 70°C, add 2 parts of triethylamine as a catalyst and react for 0.5 h, and at the same time add an equal amount of water for emulsification; finally, perform vacuum distillation to obtain the end face protective film.

[0070] Coat the upper and lower end faces of the magnet with the end face protective film, put a heat shrinkable tube on the magnet, and leave 2 cm more at the edge. After heating with a hot air blower, when the heat shrinkable tube completely shrinks and wraps the magnet, cut off the excess heat shrinkable tube at both ends, and tear off the protective film on the end face of the magnet;

[0071] Comparative Example 9

[0072] In this comparative example, the end face protective film is not used for the magnet. Specifically: Put a heat shrinkable tube on the magnet, and leave 2.5 cm more at the edge. After heating with a hot air blower, when the heat shrinkable tube completely shrinks and wraps the magnet, cut off the excess heat shrinkable tube at both ends, and the rest is the same as in Example 4.

[0073] Comparative Example 10

[0074] In this comparative example, the end face protective film is not modified:

[0075] The preparation process of the end face protective film is as follows: Add 35 parts of polytetrafluoroethylene, 9 parts of isophorone diisocyanate, and 3 parts of polyethylene glycol into 33 parts of tetrafluoroethylene liquid with a mass fraction of 40% heated to 82°C. Stir at 200 RPM for 30 min and then react for 2 h. Drop in 2 parts of ethyl o-methoxybenzoate and 2 parts of 1,4-butanediol. Then cool down to 70°C, add 4 parts of triethylamine as a catalyst and react for 0.5 h, and at the same time add an equal amount of water for emulsification; finally, perform vacuum distillation to obtain the end face protective film.

[0076] Coat the upper and lower end faces of the magnet with the end face protective film, put a heat shrinkable tube on the magnet, and leave 2.5 cm more at the edge. After heating with a hot air blower, when the heat shrinkable tube completely shrinks and wraps the magnet, cut off the excess heat shrinkable tube at both ends, and tear off the protective film on the end face of the magnet, and the rest is the same as in Example 4.

[0077] Comparative Example 11

[0078] In this comparative example, the end face protective film used is a peelable protective film with the model TYU6200, and the rest is the same as in Example 4.

[0079] Comparative Example 12

[0080] In this comparative example, the addition amount of 3-pyridyltriethoxysilane is different. The specific preparation process of the end face protective film is as follows: 35 parts of polytetrafluoroethylene, 9 parts of isophorone diisocyanate, and 3 parts of polyethylene glycol are added to 45 parts of a modified solution of 3-pyridyltriethoxysilane with a mass fraction of 40% heated to 82°C. After stirring at 200 RPM for 30 min, the reaction is carried out for 2 h. 2 parts of ethyl o-methoxybenzoate and 2 parts of 1,4-butanediol are added dropwise. Then the temperature is lowered to 70°C, and 4 parts of triethylamine is added as a catalyst and the reaction is carried out for 0.5 h. At the same time, an equal amount of water is added for emulsification; finally, vacuum distillation is carried out to obtain the end face protective film; the rest is the same as in Example 4.

[0081] Comparative Example 13

[0082] In this comparative example, the addition amount of 3-pyridyltriethoxysilane is different. The specific preparation process of the end face protective film is as follows: 35 parts of polytetrafluoroethylene, 9 parts of isophorone diisocyanate, and 3 parts of polyethylene glycol are added to 20 parts of a modified solution of 3-pyridyltriethoxysilane with a mass fraction of 40% heated to 82°C. After stirring at 200 RPM for 30 min, the reaction is carried out for 2 h. 2 parts of ethyl o-methoxybenzoate and 2 parts of 1,4-butanediol are added dropwise. Then the temperature is lowered to 70°C, and 4 parts of triethylamine is added as a catalyst and the reaction is carried out for 0.5 h. At the same time, an equal amount of water is added for emulsification; finally, vacuum distillation is carried out to obtain the end face protective film; the rest is the same as in Example 4.

[0083] Experiment 2: Measuring the influence of the presence or absence of the end face protective film on the magnetic permeability

[0084] Referring to "JB / T 13536-2018", the magnetic permeability is tested. After the heat shrinkable tubes are sleeved in Examples 4-6 and Comparative Examples 9-13, the real and imaginary parts at different frequencies of the untreated neodymium iron boron magnets are tested by a Hewlett-Packard HP 4291B impedance analyzer. The test data of different samples at 13.56 MHz are summarized in Table 2.

[0085] Table 2 Magnetic permeability

[0086]

[0087]

[0088] Experiment 3: Tensile strength of the end face protective film

[0089] The tensile strength test is carried out according to the standard GB / T 528-2009 "Determination of Tensile Stress-Strain Properties of Vulcanized Rubber and Thermoplastic Rubber". The end face protective coating is brushed on the surface of the aluminum alloy substrate. After the coating is completely cured into a film, it is peeled off by hand, and a dumbbell-shaped specimen is cut out using a special tool. The tensile strength of the specimen is measured using a universal electronic testing machine. The results are shown in Table 3 below.

[0090] Table 3 Tensile strength

[0091] Group Tensile strength (MPa) Example 4 38.46 Example 5 38.27 Example 6 38.16 Comparative Example 10 28.41 Comparative Example 11 20.79 Comparative Example 12 36.75 Comparative Example 13 33.56

Claims

1. A method for preparing a heat shrinkable tube, characterized in that: According to the basic formula of polyethylene: ethylene-vinyl acetate copolymer: crosslinking agent = 70:30:1, 0.5-0.8 parts of antioxidant, 1-3% of flame retardant formula are added, the mixture is pre-mixed at a temperature of 50-55°C and a speed of 650-1300RPM, and then added to an internal mixer, and mixed at a speed of 40-80RPM at 155°C for 10 minutes before discharging; the mixture is poured into a screw extruder to obtain a tubular object, which is sealed with a PE film, irradiated with an electron beam accelerator with a radiation dose of 90KGy, and then expanded to 40mm to obtain a heat shrink tube; The antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; The crosslinking agent is benzyl acrylate.

2. The method for preparing a heat shrinkable tube according to claim 1, characterized in that: The flame retardant formula is obtained by mixing 8-10 parts of flame retardant and 2-4 parts of compatibilizer at 50-60° C. at a low speed of 100 RPM for 10-20 minutes.

3. The method for preparing a heat shrinkable tube according to claim 2, characterized in that: The flame retardant is 3-trimethylsilyloxy-2-butenoic acid methyl ester.

4. An application of a heat shrinkable tube prepared by the preparation method of any one of claims 1 to 3 in replacing a deplating liquid to deplate a film layer of a magnet, characterized in that: Apply end surface protective film to the upper and lower end surfaces of the magnet, put a heat shrink tube on the magnet, and leave 2-3cm more than the edge. After heating with a hot air blower, wait for the heat shrink tube to completely shrink and cover the magnet, cut off the excess heat shrink tube at both ends, and tear off the protective film on the end surfaces of the magnet.

5. Application of a heat shrink tube as claimed in claim 4 in replacing a deplating liquid to deplate a film layer magnet, characterized in that: The preparation process of the end face protection film is as follows: 30-40 parts of polytetrafluoroethylene, 8-10 parts of isophorone diisocyanate, and 2-5 parts of polyethylene glycol are added to 30-36 parts of a modifier having a mass fraction of 30-50% and heated to 80-85° C., After stirring at 200RPM for 30min, react for 2h, drop 1-3 parts of ethyl o-methoxybenzoate and 1-3 parts of 1,4-butanediol, then cool to 70°C, add 2-5 parts of triethylamine as a catalyst and react for 0.5h, and add an equal amount of water for emulsification; finally, distill under reduced pressure to obtain an end face protective film.

6. Application of a heat shrink tube as claimed in claim 5 in replacing a deplating liquid to deplate a film layer of a magnet, characterized in that: The modifier is 3-pyridyltriethoxysilane.

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