Ultraviolet light cross-linking transparent double-walled heat-shrinkable sleeve and preparation method thereof

Abstract

The application belongs to the technical field of pipe preparation, and provides a transparent double-wall heat-shrinkable sleeve prepared by ultraviolet light cross-linking and a preparation method thereof. The transparent double-wall heat-shrinkable sleeve comprises an outer skin material and an inner rubber material; the outer skin material is prepared from a vinyl polymer, a photoinitiator, a cross-linking agent and an antioxidant; the inner rubber material is selected from polyamide hot melt adhesive; the vinyl polymer is ethylene-ethyl acrylate copolymer, ethylene-methyl methacrylate copolymer and ethylene-octene copolymer; and the transparent double-wall heat-shrinkable sleeve is prepared by ultraviolet light cross-linking technology. The application has the advantages of short production cycle, excellent product transparency, mechanical property, aging property, expansion stability and cross-linking degree, and wide application.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of pipe preparation, and provides a kind of ultraviolet light crosslinking transparent double-wall heat shrinkable sleeve and its preparation method. BACKGROUND

[0002] Double-wall heat shrinkable tube is a kind of heat shrinkable tube composed of crosslinked polyolefin material with heat shrinkage memory function as outer layer and hot melt adhesive providing bonding and sealing effect as inner layer. The hot melt adhesive melts when heated, thereby bonding the double-wall tube to the object to be protected, realizing the function of insulation and sealing, and having high insulation strength. It is used for the protection and identification of wires, cables, connectors and terminals, and has wide application in all industries, including medical, marine and military fields.

[0003] At present, the research on double-wall heat shrinkable tube mainly focuses on how to improve its sealing performance. For example, Chinese invention patent CN113978076A discloses a kind of heat shrinkable material and its preparation method, application, double-wall shrinkable sleeve, which comprises outer layer masterbatch and hot melt adhesive modified masterbatch. The outer layer masterbatch comprises polyethylene, ethylene-methyl acrylate copolymer, polyethylene octene copolymer elastomer, sensitizer, antioxidant and lubricant. The hot melt adhesive modified masterbatch comprises ethylene-vinyl acetate copolymer hot melt adhesive, polyamide hot melt adhesive, copper inhibitor, free radical absorber and antioxidant. The double-wall heat shrinkable sleeve has the characteristics of rapid shrinkage at high temperature, no cracking after high temperature baking and sealing and waterproof for multi-strand wire harness.

[0004] With the continuous development of economy, the demand for heat shrinkable double-wall sleeve is increasing, and higher performance is required, such as flame retardance and transparency. Chinese invention patent application CN108794853A discloses a preparation method of flame-retardant flexible heat shrinkable sleeve, which mixes reed powder, organically modified hydrotalcite and ethyl acetate to obtain wood and stone fibers, puts high-density polyethylene masterbatch particles into a rubber mixing machine for melting, and adds wood and stone fibers to obtain a rubber compound. The rubber compound is transferred to a banbury mixer and mixed with ethylene-vinyl acetate copolymer to obtain a flame-retardant flexible heat shrinkable sleeve with good flame-retardant performance. However, the addition of flame retardant in the formula cannot process the heat shrinkable sleeve into a transparent state, and the heat shrinkable sleeve cannot meet the requirements in high fire rating environments.

[0005] Chinese invention patent application CN108948497A discloses a kind of transparent flame-retardant double-wall heat shrinkable sleeve and its preparation method, which adds liquid flame retardant to give excellent flame retardant performance without affecting the transparency of the product. The crosslinking is carried out by cobalt-60 gamma rays or medium-energy electron accelerator. However, the electron accelerator has strong penetration, and the flowability of the hot melt adhesive after irradiation will decrease, and the sealing performance will be poor.

[0006] Therefore, further research is needed to improve the comprehensive performance of transparent double-wall heat shrinkable sleeve. SUMMARY

[0007] The present application provides a kind of UV crosslinking transparent double-wall heat shrinkable sleeve and its preparation method to solve the problems in the prior art, by the selection and ratio optimization of vinyl polymer, the transparent double-wall heat shrinkable sleeve obtained by combining UV crosslinking technology has excellent transparency, mechanical properties, aging performance, expansion stability and crosslinking degree, and is more widely applied.

[0008] One of the technical solutions of the present application is:

[0009] A kind of UV crosslinking transparent double-wall heat shrinkable sleeve is provided, the transparent double-wall heat shrinkable sleeve includes outer skin material and inner rubber material;The outer skin material is prepared from vinyl polymer, photoinitiator, crosslinking agent and antioxidant;The vinyl polymer is ethylene-ethyl acrylate copolymer (EEA), ethylene-methyl methacrylate copolymer (EMMA) and ethylene-octene copolymer (POE).

[0010] Further, the outer skin material includes vinyl polymer 90-100 parts, photoinitiator 1-5 parts, crosslinking agent 1-5 parts and antioxidant 0.5-2 parts by weight.

[0011] Further, the vinyl polymer is ethylene-ethyl acrylate copolymer (EEA) 15-30 parts, ethylene-methyl methacrylate copolymer (EMMA) 60-80 parts and ethylene-octene copolymer (POE) 5-10 parts by weight.

[0012] Further, the photoinitiator is selected from benzophenone or its derivative.

[0013] In some embodiments of the present application, the benzophenone derivative is selected from 4-methylbenzophenone or 2,4,6-trimethylbenzophenone.

[0014] Further, the crosslinking agent is selected from triallyl cyanurate (TAC), triallyl isocyanurate (TAIC), trimethylolpropane triacrylate (TMPTA) or pentaerythritol tetraallyl ether (PETAE).

[0015] Further, the antioxidant is selected from at least one of tetrakis [beta-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] pentaerythritol ester, N,N'-1,6-hexanediyl-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionamide], didodecyl thiodipropionate, tris(2,4-di-tert-butylphenyl) phosphite, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl) benzene, 4,4-bis(alpha,alpha-dimethylbenzyl) diphenylamine and N,N-bis(1,4-dimethylpentyl)-p-phenylenediamine.

[0016] Further, the ethylene-ethyl acrylate copolymer has an ethyl acrylate content of 5-15 wt.%; the ethylene-methyl methacrylate copolymer has a methyl methacrylate content of 5-18 wt.%.

[0017] Further, the ethylene-ethyl acrylate copolymer has a melt index MI of 1.0-5.0 g / 10 min; the ethylene-methyl methacrylate copolymer has a melt index MI of 1.0-5.0 g / 10 min; and the ethylene-octene copolymer has a melt index MI of 0.5-5.0 g / 10 min.

[0018] Further, the ethylene-octene copolymer has a Mooney viscosity (ML 1+4, 121℃) of 10-40.

[0019] Further, the inner adhesive is selected from a polyamide hot melt adhesive.

[0020] Further, the polyamide hot melt adhesive has a ring and ball softening point of 105-130℃ and a viscosity of 7000-14000 MPa.S / 200℃.

[0021] The second technical solution of the present application is:

[0022] A preparation method of the transparent double-walled heat-shrinkable sleeve is provided, comprising the following steps:

[0023] (1) uniformly mixing a vinyl copolymer, a photoinitiator, a crosslinking agent and an antioxidant, and extruding and molding, and pelletizing to obtain an outer skin material;

[0024] (2) uniformly mixing the inner adhesive with talc powder, and then co-extruding and molding with the outer skin material, and drying to obtain a double-walled sleeve;

[0025] (3) crosslinking the double-walled sleeve after molding and drying by ultraviolet irradiation, expanding by heating, and setting by cooling, to obtain the transparent double-walled heat-shrinkable sleeve.

[0026] Further, in step (1), the extruding and molding temperature is 110-125℃.

[0027] In some embodiments of the present application, the preparation method of the outer skin material comprises: weighing the vinyl copolymer, the photoinitiator, the crosslinking agent and the antioxidant according to the weight fraction, and uniformly mixing them in a blender; extruding the uniformly mixed material in a double-screw extruder, water-cooling, drawing, pelletizing, and air-drying; and then putting the air-dried material into the blender again for uniform stirring, and then loading it into an aluminum-plastic light-shielding bag for standby.

[0028] Further, in step (2), the outer skin material extrusion temperature is 145-155℃, and the inner glue material extrusion temperature is 130-140℃.

[0029] In some embodiments of the present application, the inner tube material polyamide hot melt adhesive needs to be dried in an air-circulating oven at 65-75℃ for 6-8 hours before use, and after drying, it is mixed with 2% talcum powder for use.

[0030] In some embodiments of the present application, the co-extrusion molding uses two combined single-screw extruders equipped with a double-wall heat-shrinkable tube co-extrusion mold.

[0031] Further, in step (3), the ultraviolet light irradiation crosslinking uses a high-voltage electrodeless mercury lamp as the irradiation light source, the irradiation power is 10-20kW, and the irradiation time is 8-15s.

[0032] Further, in step (3), the expansion temperature is 140-170℃.

[0033] In some embodiments of the present application, the ultraviolet light irradiation uses an irradiation box equipped with a cooling device to ensure that the temperature does not exceed 70℃ during irradiation, maintaining the size stability of the double-wall heat-shrinkable sleeve.

[0034] In some embodiments of the present application, the semi-finished double-wall heat-shrinkable sleeve after ultraviolet light irradiation is heated and expanded in glycerol by an expansion machine and then cooled and shaped to obtain a transparent double-wall heat-shrinkable sleeve.

[0035] Compared with the prior art, the present application has the following beneficial effects:

[0036] (1) The present application applies ultraviolet light crosslinking technology to the production of heat-shrinkable sleeves, which greatly reduces the equipment site cost and production energy consumption compared with electron accelerator irradiation crosslinking, and due to the integration of extrusion and irradiation, the product production cycle is significantly reduced.

[0037] (2) By adjusting the selection of vinyl polymers and controlling the component ratio, the transparency of the double-wall tube outer skin is improved while the crystallinity of the material is reduced, enabling ultraviolet light crosslinking in a non-melting state, which provides feasible conditions for the application of ultraviolet light irradiation crosslinking to heat-shrinkable sleeves without internal support.

[0038] (3) The transparent double-wall tube inner glue material of the present application does not contain a photoinitiator or a crosslinking agent, and almost no reaction occurs during ultraviolet light irradiation, so it has no effect on the flowability of the hot melt adhesive. However, the flowability of the hot melt adhesive after irradiation by the existing electron accelerator irradiation crosslinking is reduced, and the sealing performance is poor. Therefore, the transparent double-wall tube using ultraviolet light irradiation crosslinking has better sealing performance. DETAILED DESCRIPTION

[0039] The following non-limiting examples can provide a more complete understanding of the application to those of ordinary skill in the art, but are not intended in any way to limit the scope of the application. The following merely illustrates the scope of the application claimed, and those skilled in the art can make various changes and modifications to the application disclosed based on the disclosed content, which should also belong to the scope of the application claimed. Unless otherwise specified, the materials or reagents provided in the examples are all ordinary commercially available products.

[0040] Example 1

[0041] (1) Take ethylene-ethyl acrylate copolymer 20 parts (the ethylene-ethyl acrylate copolymer used has an ethyl acrylate content of 13%, and a melt index MI of 3.0 g / 10 min), ethylene-methyl methacrylate copolymer 70 parts (the ethylene-methyl methacrylate copolymer used has a methyl methacrylate content of 18%, and a melt index MI of 3.0 g / 10 min), ethylene-octene copolymer 10 parts (the ethylene-octene copolymer used has a melt index MI of 3.0 g / 10 min), benzophenone 1.5 parts, triallyl isocyanurate 1.0 part, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene 0.8 part, and mix them well in a blender, then extrude and granulate in a twin-screw extruder at a temperature interval of 120°C, mix the prepared granules again in a blender, and then put them into an aluminum-plastic light-shielding bag as the outer skin material for standby;

[0042] (2) Dry the inner rubber material polyamide hot melt adhesive in a 70°C air-circulating oven for 6 hours, and mix it with 2% talcum powder after drying to prepare the inner rubber material;

[0043] (4) Put the outer skin material and the treated polyamide hot melt adhesive into two combined single-screw extruders equipped with a non-adjustable double-wall heat-shrinkable tube co-extrusion die to extrude and form a double-wall tube, with an outer skin extrusion temperature of 150°C and an inner glue extrusion temperature of 130°C;

[0044] (5) After the extruded and formed double-wall tube is cooled and shaped in a water tank and air-dried, it is put into a ultraviolet light irradiation box for ultraviolet light irradiation crosslinking, the ultraviolet light irradiation equipment uses a high-voltage non-polar mercury lamp as the irradiation light source, the irradiation power is 20 kW, and the irradiation time is 10 s (the irradiation box is equipped with a cooling device to ensure that the temperature in the box does not exceed 70°C to maintain the size stability of the sleeve), and a semi-finished double-wall sleeve is obtained;

[0045] (6) The semi-finished double-wall sleeve after ultraviolet light irradiation is expanded and cooled in glycerol by an expander to obtain a transparent double-wall heat-shrinkable sleeve, with an expansion temperature of 150°C.

[0046] Example 2

[0047] (1) Take ethylene-ethyl acrylate copolymer (the ethylene-ethyl acrylate copolymer used has an ethyl acrylate content of 15%, and a melt index MI of 4.0 g / 10 min) 30 parts, ethylene-methyl methacrylate copolymer 60 parts (the ethylene-methyl methacrylate copolymer used has a methyl methacrylate content of 15%, and a melt index MI of 3.5 g / 10 min), ethylene-octene copolymer 8 parts (the ethylene-octene copolymer used has a melt index MI of 1.0 g / 10 min), 4-methyl benzophenone 1.5 parts, trimethylolpropane triacrylate 1.0 part, and tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid] pentaerythritol ester 0.8 part, mix them well in a blender, and then extrude and granulate in a twin-screw extruder at a temperature interval of 110°C. After mixing the granules again in a blender, place them in an aluminum-plastic light-shielding bag as the sheath material, and reserve them for use;

[0048] (2) Dry the inner adhesive polyamide hot melt adhesive in an air-circulating hot oven at 65°C for 8 hours. After drying, mix it with 2% talcum powder and reserve it for use;

[0049] (4) Put the sheath material and the treated polyamide hot melt adhesive into two combined single-screw extruders equipped with a non-adjustable double-wall heat-shrinkable tube co-extrusion die to extrude and form a double-wall tube. The sheath extrusion temperature is 145°C, and the inner adhesive extrusion temperature is 130°C;

[0050] (5) After the extruded double-wall tube is cooled and shaped in a water tank and air-dried, it is placed in a UV irradiation box for UV irradiation crosslinking. The UV irradiation equipment uses a high-voltage non-polar mercury lamp as the irradiation light source, with an irradiation power of 15 kW and an irradiation time of 8 s. The irradiation box is equipped with a cooling device to ensure that the temperature in the box does not exceed 70°C, so as to maintain the stability of the sleeve size. The semi-finished double-wall sleeve is obtained;

[0051] (6) The semi-finished double-wall sleeve after UV irradiation is expanded and cooled in glycerol by an expander to obtain a transparent double-wall heat-shrinkable sleeve. The expansion temperature is 130°C.

[0052] Example 3

[0053] (1) Take ethylene-ethyl acrylate copolymer 10 parts (the ethylene-ethyl acrylate copolymer used has an ethyl acrylate content of 8%, and a melt index MI of 2.0 g / 10 min), ethylene-methyl methacrylate copolymer 80 parts (the ethylene-methyl methacrylate copolymer used has a methyl methacrylate content of 12%, and a melt index MI of 5.0 g / 10 min), ethylene-octene copolymer 5 parts (the ethylene-octene copolymer used has a melt index MI of 5.0 g / 10 min), 2,4,6-trimethyl benzophenone 1.5 parts, polytriallyl cyanurate 1.0 part, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tri-butyl-4-hydroxybenzyl) benzene 0.8 part, and mix them well in a blender, then extrude and granulate in a twin-screw extruder at a temperature range of 120°C, mix the prepared granules well in a blender again, and then put them into an aluminum-plastic light-shielding bag as the outer skin material for standby;

[0054] (2) Dry the inner rubber material polyamide hot melt adhesive in an air-circulating hot oven at 70°C for 6 hours, and mix it well with 2% talcum powder after drying for standby;

[0055] (4) Put the outer skin material and the treated polyamide hot melt adhesive into two combined single-screw extruders equipped with a non-adjustable double-wall heat-shrinkable tube co-extrusion die to extrude and form a double-wall tube, with an outer skin extrusion temperature of 155°C and an inner glue extrusion temperature of 140°C;

[0056] (5) The extruded double-wall tube is cooled and shaped in a water tank and then dried by air cooling, and then enters a ultraviolet light irradiation box for ultraviolet light irradiation crosslinking, the ultraviolet light irradiation equipment uses a high-voltage non-polar mercury lamp as the irradiation light source, the irradiation power is 10 kW, and the irradiation time is 15 s (the irradiation box is equipped with a cooling device to ensure that the temperature in the box does not exceed 70°C to maintain the size stability of the sleeve), and a semi-finished double-wall sleeve is obtained;

[0057] (6) The semi-finished double-wall sleeve after ultraviolet light irradiation is heated and expanded in glycerol by an expander and then cooled and shaped to obtain a transparent double-wall heat-shrinkable sleeve, with an expansion temperature of 170°C.

[0058] Test Example 1

[0059] The transparent double-wall heat-shrinkable sleeve prepared by Examples 1-3 of the present application is tested for relevant performance, and the test method and test results are shown in Table 1:

[0060] Table 1 Test method and results of relevant performance of transparent double-wall heat-shrinkable sleeve

[0061]

[0062]

[0063] From the test results in Table 1, it can be seen that the present application can realize ultraviolet crosslinking in a non-melted state, and the mechanical properties and crosslinking degree (gel content) of the prepared transparent double-walled heat-shrinkable sleeve fully meet the requirements of UL224; in addition, the viscosity of the polyamide hot melt adhesive used for the inner tube before and after the formation of the double-walled heat-shrinkable sleeve (the viscosity of the raw material is 11900 MPa·S / 200℃) changes, and the use of ultraviolet irradiation crosslinking has little effect on the flowability of the hot melt adhesive, and the process stability is higher, and the slight decrease in viscosity in the test results is mainly due to a small amount of degradation of the hot melt adhesive during the extrusion heating process, which can be ignored.

[0064] Comparative Example 1

[0065] The difference from Example 1 is that the ethylene-methyl methacrylate copolymer is replaced by an equal amount of ethylene-vinyl acetate copolymer (the ethylene-vinyl acetate copolymer used has a vinyl acetate content of 15% and a melt index MI of 5.0 g / 10 min);

[0066] The other components and the preparation method are the same as in Example 1.

[0067] Comparative Example 2

[0068] The difference from Example 1 is that the ethylene-ethyl acrylate copolymer is replaced by an equal amount of low-density polyethylene (the low-density polyethylene used has a melt index MI of 5.0 g / 10 min and a light transmittance > 85%);

[0069] The other components and the preparation method are the same as in Example 1.

[0070] Comparative Example 3

[0071] The difference from Example 1 is that the ethylene-based polymer includes ethylene-ethyl acrylate copolymer 22.5 parts and ethylene-methyl methacrylate copolymer 77.5 parts;

[0072] The other components and the preparation method are the same as in Example 1.

[0073] Comparative Example 4

[0074] The difference from Example 1 is that the ethylene-based polymer includes ethylene-ethyl acrylate copolymer 15 parts, ethylene-methyl methacrylate copolymer 65 parts, and ethylene-octene copolymer 20 parts;

[0075] The other components and the preparation method are the same as in Example 1.

[0076] Comparative Example 5

[0077] The difference from Example 1 is that the ethylene-methyl methacrylate copolymer is replaced by an equal amount of ethylene-ethyl acrylate copolymer, i.e., the ethylene-ethyl acrylate copolymer in the outer skin formula is increased to 90 parts;

[0078] Other components and preparation methods are the same as Example 1.

[0079] Comparative Example 6

[0080] The difference from Example 1 is that the ethylene-ethyl acrylate copolymer is replaced by ethylene-methyl methacrylate copolymer in equal amount, that is, the ethylene-methyl methacrylate copolymer in the sheath formula is increased to 90 parts.

[0081] Other components and preparation methods are the same as Example 1.

[0082] The transparent double-walled heat-shrinkable sleeve prepared in Comparative Examples 1-6 of the present application is tested for relevant performance according to the performance test method of Example 1-3, and the test results are shown in Table 2:

[0083] Table 2 Test results of transparent double-walled heat-shrinkable sleeve

[0084]

[0085] From the results of Table 1 and Table 2, it can be seen that:

[0086] Comparative Example 1, Comparative Example 2 and Example 1 can be compared to see that different types of ethylene-based polymers have a significant effect on the degree of ultraviolet crosslinking of the outer tube material; ethylene-methyl methacrylate copolymer has lower crystallinity and higher transparency than ethylene-vinyl acetate copolymer, and ethylene-ethyl acrylate copolymer has lower crystallinity than low-density polyethylene, so under the same irradiation conditions, the crosslinking effect is better, the crosslinking degree is high, the mechanical properties and aging performance of the finished product are better, and the expansion stability also meets the production requirements.

[0087] Comparative Example 3 and Example 1 can be compared to see that ethylene-octene copolymer has a significant effect on the shrinkage performance of the finished heat-shrinkable sleeve, and ethylene-octene copolymer has weaker polarity, which can reduce the adhesion of the sleeve caused by the polar side groups of ethylene-methyl methacrylate copolymer and ethylene-ethyl acrylate copolymer.

[0088] Comparative Example 3, Comparative Example 4 and Example 1 can be compared to see that too high or too low content of ethylene-octene copolymer in the sheath material will affect the crosslinking degree of the outer tube under ultraviolet light; too low content of ethylene-octene copolymer will make the structure of the outer tube material more regular, increase the crystallinity and increase the crosslinking difficulty, thus reducing the crosslinking degree; too high content of ethylene-octene copolymer will reduce the transparency of the outer tube material, increase the difficulty of ultraviolet light penetration, and reduce the crosslinking degree. In addition, low crosslinking degree will also lead to a decrease in expansion stability, which cannot meet the production requirements.

[0089] Comparative Example 5, Comparative Example 6 and Example 1, it can be seen that the single ethylene-methyl methacrylate copolymer or ethylene-ethyl acrylate copolymer cannot meet the crosslinking degree requirement of the heat-shrinkable sleeve by blending with a small amount of ethylene-octene copolymer. The single ethylene-methyl methacrylate copolymer or ethylene-ethyl acrylate copolymer has a higher crystallinity than the ethylene-methyl methacrylate / ethylene-ethyl acrylate blend, so the crosslinking degree under the same ultraviolet irradiation condition will be reduced, in addition, the ethylene-ethyl acrylate copolymer has a lower transparency than the ethylene-methyl methacrylate copolymer and ethylene-octene copolymer, which further increases the crosslinking difficulty, and the crosslinking degree is too low, not only the irradiated semi-finished product cannot expand, but also the crosslinking type material will be degraded into a non-crosslinking type material during the aging process, thereby melting during the aging process.

[0090] Finally, it should be noted that the above content is only used to illustrate the technical solutions of the present application, and is not a limitation on the protection scope of the present application. Simple modifications or equivalent replacements of the technical solutions of the present application made by those skilled in the art do not deviate from the essence and scope of the technical solutions of the present application.

Claims

1. A UV cross-linked transparent double-wall heat shrink tubing, characterized in that, The transparent double-wall heat shrink tubing includes an outer sheath and an inner rubber material; the outer sheath is prepared from a vinyl polymer, a photoinitiator, a crosslinking agent, and an antioxidant; the vinyl polymer, by weight, is 10-30 parts of ethylene-ethyl acrylate copolymer, 60-80 parts of ethylene-methyl methacrylate copolymer, and 5-10 parts of ethylene-octene copolymer. The preparation of the ultraviolet cross-linked transparent double-wall heat shrink tubing includes the following steps: (1) Mix the vinyl copolymer, photoinitiator, crosslinking agent and antioxidant evenly, and then extrude and granulate to obtain the outer skin material; (2) The inner rubber material is dried and mixed with talc powder, and then co-extruded with the outer material and dried to obtain a double-walled tube; (3) The double-walled tube is cross-linked by ultraviolet light irradiation, heated for expansion, and cooled for stabilization to obtain the transparent double-walled heat shrink tubing.

2. The transparent double-wall heat shrink tubing according to claim 1, characterized in that, The outer skin material, by weight, comprises 90-100 parts of vinyl polymer, 1-5 parts of photoinitiator, 1-5 parts of crosslinking agent, and 0.5-2 parts of antioxidant.

3. The transparent double-wall heat shrink tubing according to claim 1, characterized in that, The photoinitiator is selected from benzophenone or its derivatives; The crosslinking agent is selected from triallyl polycyanate, triallyl isocyanurate, trimethylolpropane triacrylate or pentaerythritol tetraallyl ether; The antioxidant is selected from at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], N,N'-1,6-hexylene-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionamide], dodecanol thiodipropionate, tris(2,4-di-tert-butylphenyl) phosphite, 1,3,5-trimethyl-2,4,6tris(3,5-di-tri-butyl-4-hydroxybenzyl)benzene, 4,4-bis(α,α-dimethylbenzyl)diphenylamine, and N,N-bis(1,4-dimethylpentyl)p-phenylenediamine.

4. The transparent double-wall heat shrink tubing according to claim 1, characterized in that, The ethylene-ethyl acrylate copolymer has an ethyl acrylate content of 5-15 wt.% and a melt index (MI) of 1.0-5.0 g / 10 min; the ethylene-methyl methacrylate copolymer has a methyl methacrylate content of 5-18 wt.% and a melt index (MI) of 1.0-5.0 g / 10 min; and the ethylene-octene copolymer has a melt index (MI) of 0.5-5.0 g / 10 min.

5. The transparent double-wall heat shrink tubing according to claim 1, characterized in that, The inner adhesive is selected from polyamide hot melt adhesive.

6. The method for preparing a transparent double-walled heat-shrink tubing according to any one of claims 1-5, characterized in that, Includes the following steps: (1) Mix the vinyl copolymer, photoinitiator, crosslinking agent and antioxidant evenly, and then extrude and granulate to obtain the outer skin material; (2) The inner rubber material is dried and mixed with talc powder, and then co-extruded with the outer material and dried to obtain a double-walled tube; (3) The double-walled tube is cross-linked by ultraviolet light irradiation, heated for expansion, and cooled for stabilization to obtain the transparent double-walled heat shrink tubing.

7. The preparation method according to claim 6, characterized in that, In step (1), the extrusion molding temperature is 110-125℃; in step (2), during the co-extrusion molding process, the extrusion temperature of the outer material is 145-155℃ and the extrusion temperature of the inner material is 130-140℃.

8. The preparation method according to claim 6, characterized in that, In step (3), the ultraviolet radiation crosslinking uses a high-pressure electrodeless mercury lamp as the irradiation source, with an irradiation power of 10-20kW and an irradiation time of 8-15s.

9. The preparation method according to claim 6, characterized in that, In step (3), the expansion temperature is 130-170℃.

Images