Transparent double-wall heat-shrinkable tube as well as preparation process and application thereof

Abstract

The invention discloses a transparent double-wall heat-shrinkable tube and a preparation process and application thereof.The transparent double-wall heat-shrinkable tube comprises an inner wall layer and an outer wall layer, the outer wall layer is arranged on the periphery of the inner wall layer, and the outer wall layer is prepared from linear low-density polyethylene, ethylene vinyl acetate copolymer and a cross-linking agent; and the raw material of the inner wall layer is selected from polyamide hot melt adhesive. The outer wall layer of the transparent double-wall heat-shrinkable tube has the characteristics of good heat shrinkage, high transparency and low volatile organic compounds (VOC), and the inner wall layer can be effectively adhered to the polyethylene (PE) and / or polyvinyl chloride (PVC) insulating layer. The heat-shrinkable tube has the characteristics of adhesion prevention after heat shrinkage, short retraction time, rapid cooling, heat aging resistance and high-temperature and high-humidity resistance, and is especially suitable for sealing, insulation and protection of automobile wire harnesses, aviation wire harnesses and complex wire harnesses in other industrial fields with harsh requirements.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heat shrinkable tube, in particular to a transparent double-wall heat shrinkable tube and its preparation process and application. BACKGROUND

[0002] Heat shrinkable tube is widely used in electronic, electrical, automotive industry and other fields, for wrapping, insulation and protection of cable joints, terminals, etc. Single-wall heat shrinkable tube provides basic insulation and mechanical protection, while double-wall heat shrinkable tube adds a layer of hot melt adhesive to its inner wall. When heated and shrunk, the adhesive layer melts and flows, forming a more excellent sealing and moisture-proof effect.

[0003] The outer layer of existing double-wall heat shrinkable tube is mostly made of polyolefin materials, such as low-density polyethylene (LDPE), high-density polyethylene (HDPE) or ethylene-vinyl acetate copolymer (EVA). However, these materials have limitations in certain applications: 1) insufficient transparency, which is not conducive to observing the internal connection; 2) easy to stick between the tubes after shrinking, affecting the construction efficiency and appearance; 3) the shrinking speed may be slow, affecting the production efficiency; 4) the adhesion and sealing of common cable insulation materials (such as PE and PVC) are not ideal, especially the inner wall layer is usually optimized for one material, making it difficult to simultaneously consider both PE and PVC.

[0004] Therefore, there is an urgent need for a double-wall heat shrinkable tube that has high transparency, fast shrinking, fast cooling, anti-sticking properties, and an inner wall layer that can simultaneously adhere to PE and PVC sheathed wire bundles. SUMMARY

[0005] The present application aims to overcome the above-mentioned deficiencies of the prior art and provide a transparent double-wall heat shrinkable tube and its preparation process and application.

[0006] The technical problem of the present application is solved by the following technical solution.

[0007] The present application provides a transparent double-wall heat shrinkable tube, comprising: an inner wall layer and an outer wall layer, the outer periphery of the inner wall layer is provided with the outer wall layer, and the raw material of the outer wall layer comprises linear low-density polyethylene, ethylene-vinyl acetate copolymer and crosslinking agent.

[0008] The present application provides a preparation process for the above-mentioned transparent double-wall heat shrinkable tube, which comprises: forming a double-layer tube blank by co-extrusion process with the raw material of the outer wall layer and the raw material of the inner wall layer, then crosslinking by electron beam irradiation, and then heating, expanding and cooling to form the transparent double-wall heat shrinkable tube.

[0009] The present application provides an application of the above-mentioned transparent double-wall heat shrinkable tube in sealing, insulation and protection of complex wire harnesses in automotive wire harnesses, aviation wire harnesses and other industrial fields.

[0010] The present application has the following beneficial effects: The present application provides a kind of transparent double-wall heat shrinkable tube and its preparation process and application, the transparent double-wall heat shrinkable tube provided by the present application, including outer wall layer and the inner wall layer located the inner surface of outer wall layer, the raw material of outer wall layer includes linear low density polyethylene, ethylene vinyl acetate copolymer and crosslinking agent, the raw material of outer layer selects the LLDPE (linear low density polyethylene) of low molecular weight distribution, its transparency is higher than HDPE (high density polyethylene) can improve transparency, crystallinity is higher than LDPE (low density polyethylene) can improve retraction speed, a small amount of EVA (ethylene vinyl acetate copolymer) is added simultaneously to improve the transparency and toughness of outer layer, the transparent double-wall heat shrinkable tube prepared using the above raw materials, while taking into account the processing performance, the double-wall heat shrinkable tube can also have the characteristics of anti-adhesion after heat shrinkage, short retraction time, rapid cooling, heat aging resistance, especially suitable for demanding automotive wiring harness, aviation wiring harness and other industrial complex wiring harness sealing, insulation and protection. BRIEF DESCRIPTION OF DRAWINGS

[0011] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments, it should be understood that the following drawings only show some embodiments of the present application, therefore should not be regarded as a limitation on the scope, for those skilled in the art, without creative labor, other related drawings can also be obtained according to these drawings.

[0012] Figure 1 is the schematic diagram of the radial cross-section structure of the double-wall heat shrinkable tube of the present application; Figure 2 is the schematic diagram of the heat shrinkable tube in the shrinkage state; Figure 3 is the schematic diagram of the heat shrinkable tube wrapped around the cable joint after heating and shrinking; Figure number: transparent double-wall heat shrinkable tube-1, outer wall layer-2, inner wall layer-3, insulation layer-4, joint-5. DETAILED DESCRIPTION

[0013] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme in the embodiments of the present application will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market.

[0014] The transparent double-wall heat shrinkable tube provided by the present application and its preparation process and application will be described in detail below.

[0015] In a first aspect, the present application provides a transparent double-walled heat-shrinkable tube, see Figure 1 The transparent double-walled heat-shrinkable tube 1 is a hollow tubular structure, which comprises a transparent, heat-shrinkable outer wall layer 2 and a hot-melt inner wall layer 3. The raw material of the outer wall layer comprises linear low-density polyethylene (LLDPE), ethylene-vinyl acetate copolymer (EVA) and crosslinking agent.

[0016] The molecular main chain of linear low-density polyethylene (LLDPE) is basically linear structure, only a small amount of short and regular branches are introduced by copolymerization (the branching degree is lower than that of low-density polyethylene (LDPE)), the molecular arrangement is more compact than that of low-density polyethylene (LDPE), and the density is slightly higher. Ethylene-vinyl acetate copolymer (EVA) has good flexibility and elasticity, easy processability, compatibility and adhesion, but its temperature resistance is poor, and the long-term use temperature is usually not more than 80℃, and it is easy to soften and deform at high temperature, and cannot be used in environments requiring high temperature resistance, and the aging resistance is general.

[0017] In the present application, linear low-density polyethylene and ethylene-vinyl acetate copolymer are used as the main raw material (also referred to as base material), and a crosslinking agent is added at the same time, so that linear low-density polyethylene and ethylene-vinyl acetate copolymer can form a suitable three-dimensional network structure under the action of the crosslinking agent. The transparent double-walled heat-shrinkable tube obtained has the following characteristics and advantages: High transparency: the optimized polyolefin formula ensures excellent transparency of the outer layer, facilitating observation of the internal connection state.

[0018] Anti-blocking property: the specific linear low-density polyethylene (LLDPE) / ethylene-vinyl acetate copolymer (EVA) mixed system makes the pipe material not easy to be mutually adhered after heat shrinkage, facilitating construction and appearance maintenance.

[0019] Fast retraction: the material formula and crosslinking degree are optimized, so that the heat-shrinkable response time is relatively fast, improving the installation efficiency.

[0020] Fast cooling: the characteristic LLDPE enables the pipe material to quickly form crystals after heat shrinkage, effectively shortening the pipe material cooling and setting time.

[0021] High crosslinking degree: the crosslinked structure provides good elastic memory effect, and high crosslinking degree enables the polyolefin outer layer to shrink to realize tight fitting of the wiring harness, providing excellent sealing and strain relief effect.

[0022] In some alternative embodiments, the weight ratio of linear low density polyethylene to ethylene vinyl acetate copolymer in the raw material of the outer wall layer is 30%-90%:10%-70%, wherein different proportions of LLDPE and EVA will affect the appearance and performance of the product, and when LLDPE is more than 70%, the transparency will decrease, and when LLDPE is less than the lower limit, the shrinkage time will become longer and the product will be sticky after shrinkage; Preferably, the low density polyethylene is selected from at least one of linear low density polyethylene produced by Dow Chemical Company with the brand numbers 2032, 2045, 2036G, 2042G, 2045G, 2049G, 2064G, 2083G, GM8070G, GM8090, or linear low density polyethylene resin with a melt index of 0.5-3 g / 10 min, a melting point of 105-125℃, a Vicat softening point of 100℃-120℃, and a haze of 1%-15%, wherein the melt index determines the smoothness of the outer surface of the double-walled pipe, and the higher the melt index, the smoother the surface. Selecting LLDPE with different melting points can produce products with a temperature resistance upper limit of 105-125℃. Raw materials with low haze can improve the transparency of the product, and Vicat softening point close to melting point can speed up the heat shrinkage speed of the product; Preferably, the ethylene vinyl acetate copolymer is selected from at least one of ethylene vinyl acetate copolymer produced by Dow Chemical Company with the brand numbers 3120, 760, 770, 450, 470, 650Q, 560, 550, 3165, 3130, 3170, 3174, or ethylene vinyl acetate copolymer with a VA content of 10%-25%, a melt index of 0.5-53 g / 10 min, and a melting point of 85-100℃, wherein too low VA content will make the material performance close to LDPE, increasing the hardness of the product and reducing the transparency, and too high VA content will reduce the hardness of the product and increase the sticking rate during shrinkage. As an auxiliary material in the base material, the melting point should be selected in conjunction with the melting point of LLDPE.

[0023] In some alternative embodiments, the raw material of the inner wall layer is polyamide hot melt adhesive; Preferably, the raw material of the inner wall layer is selected from PLATAMID 1276 produced by ARKEMA Company. The PA adhesive layer of the inner wall layer can form a firm bond to the PE and / or PVC insulation layer, and is more widely applicable.

[0024] In some alternative embodiments, the raw material of the outer wall layer further comprises antioxidants, anti-adhesion agents, and silicon dioxide powder; Preferably, the total weight of the cross-linking agent, the antioxidant, the anti-sticking agent and the silica powder is not more than 10% of the total weight of the outer wall layer, more preferably, the cross-linking agent comprises at least one of TAC, TAIC, TMPTMA and TMPTA, the antioxidant comprises at least one of a steric-hindering phenol and a thioether, the anti-sticking agent comprises at least one of stearic acid amide, ethylene bis-oleic acid amide and erucic acid amide, in some specific embodiments, the cross-linking agent can be selected from Taicros TAC products of the Winhov Group, the antioxidant can be selected from Irganox 1035 and Irganox 800 of the BASF SE, the anti-sticking agent can be selected from Optislip SRV of the Cargill, Inc., and the silica powder can be selected from Aerosil R974 of the Winhov Group, and the diameter of the silica particles can be 20 μm to 140 μm. Preferably, the raw material of the outer wall layer comprises the following components in the following weight percentages: linear low-density polyethylene 30%-90%, ethylene-vinyl acetate copolymer 10%-70%, cross-linking agent 0.5%-5%, antioxidant 0.1%-2%, anti-sticking agent 0.1%-2% and silica powder 1%-10%, and the diameter of the silica particles is 20 μm to 140 μm.

[0025] In some alternative embodiments, the thickness of the outer wall layer is 0.8-0.9 mm, the outer diameter is 4.2-4.6 mm, the thickness of the inner wall layer is 0.8-0.9 mm, and the inner diameter is 0.9-1.0 mm.

[0026] In some alternative embodiments, the temperature resistance of the transparent double-walled heat-shrinkable tube ranges from -40°C to 125°C.

[0027] In some alternative embodiments, the thickness of the outer wall layer is 0.8-0.9 mm, the outer diameter is 4.2-4.6 mm, the thickness of the inner wall layer is 0.8-0.9 mm, and the inner diameter is 0.9-1.0 mm.

[0028] In some alternative embodiments, the process comprises the following steps: granulating the raw material of the outer wall layer to obtain granules, and mixing the granules with the raw material of the inner wall layer to form a double-layer tube blank with the inner wall coated with a glue layer by double-walled tube co-extrusion; after cross-linking by electron beam irradiation, heating the double-layer tube blank to 150-170°C, and then introducing high-pressure gas to radially expand the tube blank by gas pressure; and keeping the expanded state and rapidly cooling the tube blank to shape the tube blank in the expanded state to obtain the transparent double-walled heat-shrinkable tube with heat-shrinkable performance. Preferably, the irradiation dose is 130-150 kGy, and the weight ratio of the raw material of the outer wall layer to the raw material of the inner wall layer is 1:1.

[0029] It is worth mentioning that the double-layer tube blank needs to be gradually heated to soften after irradiation treatment, and then high-pressure gas is quickly introduced to expand the inside of the tube blank by using the gas pressure, and the tube material is shaped in the expanded state by rapid cooling in the expanded state, so that the transparent double-wall heat-shrinkable tube with heat-shrinking performance is prepared.

[0030] In a third aspect, the application provides an application of the above-mentioned transparent double-wall heat-shrinkable tube in sealing, insulation and protection of complex wire harnesses in automobile wire harnesses, aviation wire harnesses and other industrial fields.

[0031] In some optional embodiments, the transparent double-wall heat-shrinkable tube is used for bonding wire harnesses made of polyethylene (PE) and / or polyvinyl chloride (PVC). The above-mentioned transparent double-wall heat-shrinkable tube provided by the application can be used for bonding wire harnesses made of polyethylene (PE) or polyvinyl chloride (PVC). Alternatively, it can be used for simultaneously bonding wire harnesses made of polyethylene (PE) and / or polyvinyl chloride (PVC).

[0032] The transparent double-wall heat-shrinkable tube provided by the application, its preparation process and application will be described in detail below in combination with embodiments, but they should not be understood as limitations on the protection scope of the application.

[0033] The transparent double-wall heat-shrinkable tube provided by the application has a structure as shown in the structural schematic diagram Figure 1 The transparent double-wall heat-shrinkable tube is a hollow tubular structure, which includes a transparent and heat-shrinkable polyolefin outer wall layer 2 and a hot-melt inner wall layer 3. The inner wall layer 3 is uniformly coated on the inner surface of the outer layer 2 by a co-extrusion process, which is the form when it leaves the factory, and the inner diameter is larger to facilitate the sleeving of the cable to be protected.

[0034] Figure 2 The heat-shrinkable tube 1 is shown in the state after shrinking, which is the form before expansion.

[0035] Figure 3 The heat-shrinkable tube 1 is shown in the state after being completely shrunk after being heated (for example, using a hot air gun). The heat makes the outer layer 2 return to its original diameter, and at the same time, the inner wall layer 3 melts into a good sealing viscous fluid, fills the gap and bonds on the cable insulation layer 4 and the joint 5, forming a structure integrated with sealing, insulation and protection.

[0036] The preparation process of the above-mentioned transparent double-wall heat-shrinkable tube includes the following steps: Step one: preparation of outer wall layer granules includes: linear low-density polyethylene, ethylene-vinyl acetate polymer, crosslinking agent, antioxidant, anti-adhesive agent, and silica are poured into a high-speed mixer according to the formula in Table 1 and stirred for 10 minutes, and then underwater cutting granulation is performed by a three-screw extruder, and the outer wall layer granules are obtained.

[0037] Step 2: The inner wall layer uses a commercially available polyamide hot melt adhesive, characterized by a suitable melt index (suitable for co-extrusion) and good adhesion strength to both PE and PVC. For example, ARKEMA PLATAMID® 1276 can be used.

[0038] Step 3: Add the outer wall layer granules and the inner wall layer granules to two co-extrusion extruders respectively, and pass them through a double-wall tube co-extrusion die to form a double-layer tube blank with an inner wall coated with an adhesive layer.

[0039] The double-layer tube blank is cross-linked by an electron beam irradiation device with an irradiation dose of 150 kGy.

[0040] The cross-linked pipe is heated to above its melting temperature (usually 10-30°C higher than the melting point), and then radially expanded to an inner diameter of 6 mm using internal air pressure.

[0041] Rapid cooling (usually water cooling) while maintaining the expanded state allows the pipe to retain its expanded shape, thus achieving thermal shrinkage properties.

[0042] Table 1 below provides the composition of the outer wall layer raw materials in Examples 1-8 and Comparative Examples 1-4.

[0043] Table 1. Raw materials for the outer wall layer

[0044] Continued from Table 1: Outer Wall Layer Raw Materials

[0045] Continued from Table 1: Outer Wall Layer Raw Materials

[0046] Experimental results The transparent double-wall heat shrink tube products prepared in Examples 1-8 and Comparative Examples 1-4 were tested. Since the expansion only facilitates subsequent cutting and does not change the performance of the product, the products were tested immediately after irradiation. The test results are shown in Tables 2-4.

[0047] Table 2. Properties of the transparent outer wall layer (after irradiation crosslinking)

[0048] Table 2 (Continued) Properties of the transparent outer wall layer (after irradiation crosslinking)

[0049] Table 3. Properties of the inner wall hot melt adhesive layer (after irradiation crosslinking)

[0050] Table 3 (Continued) shows the properties of the inner wall hot melt adhesive layer (after irradiation crosslinking).

[0051] Table 4 Performance of transparent double-wall heat-shrinkable tube (after irradiation crosslinking)

[0052] Table 4 Performance of transparent double-wall heat-shrinkable tube (after irradiation crosslinking)

[0053] As can be seen from the above, Examples 1-4 in Table 1 are prepared by LLDPE (Doelex 2036G, melting point 125℃, Vicat softening point 119℃) and EVA760 in different proportions, and Examples 5-8 are prepared by LLDPE (Doelex 2083G, melting point 124℃, Vicat softening point 108℃) and EVA760 in different proportions.

[0054] As can be seen from Tables 2-3, the higher the proportion of LLDPE in the formula, the greater the tensile strength of the outer wall layer, and the corresponding elongation at break will decrease; and the proportion of LLDPE and EVA in the outer wall layer base material has little effect on the hot melt adhesive layer after irradiation, and the viscosity and softening point of the hot melt adhesive are basically the same in the eight examples, and the hot melt adhesive will not be tested in the subsequent comparative examples.

[0055] As can be seen from Table 4, the transparent double-wall tube prepared by different types of LLDPE and different proportions of resin processing can meet the requirements of heat shrinkage sealing and sealing after aging. In the application test, the heat shrinkage time and cooling time of the product with LLDPE 2036 base material are better than those with LLDPE 2083G base material; in addition, as the proportion of LLDPE increases, the shrinkage time, cooling time and adhesion rate of the heat shrinkable tube all decrease significantly. Since the Vicat softening point of LLDPE is higher, it means that the molecular weight distribution of LLDPE 2036G is narrower than that of LLDPE 2083G, and the crystallization speed is faster, so it is not easy to occur molecular entanglement after shrinkage. Therefore, the product with LLDPE 2036G base material is obviously better than the product with LLDPE 2083G base material in the above three application performance aspects.

[0056] According to the test results of Examples 1-8, considering the processing performance, Example 3 is selected as the best formula. The following Example 3 is used as the preferred transparent double-wall heat-shrinkable tube product, which is compared with the transparent double-wall heat-shrinkable tube prepared by Comparative Examples 1-4, and the comparison results are shown in Tables 5 and 6 as follows: Table 5 Performance comparison results of transparent double-wall heat-shrinkable tube of Example 3 and Comparative Examples 1-3

[0057] Table 6 Effect of crosslinking agent on irradiation dose

[0058] As can be seen in Table 5 above: in Comparative Example 1, the outer wall layer substrate only uses HDPE, due to the higher crystallinity of HDPE, the light transmittance decreases, the stress distribution in the outer wall layer material is uneven, so the outer layer tensile strength is improved, but the thermal shock test cracks, and the product haze is high, which does not meet the application performance requirements.

[0059] In Comparative Example 2, the outer wall layer substrate only uses LDPE, due to the low crystallinity and high molecular weight branching of LDPE, the product performance and application performance are close to Example 3, but due to the existence of branched structure, molecular entanglement occurs between the products after thermal shrinkage, resulting in a high sticking rate.

[0060] In Comparative Example 3, the outer wall layer substrate only uses EVA, due to the low molecular crystallinity of EVA containing carboxyl functional groups, the transparency is high, but after the thermal aging experiment, the carboxyl group is thermally decomposed, producing small molecule acetic acid gas, resulting in bubbles in the adhesive layer, and the sealing fails, and due to the hydrogen bonding of the carboxyl group, the sticking rate of the product after thermal shrinkage is 100%.

[0061] As can be seen from Table 6: in Comparative Example 4, no crosslinking agent TAIC is added, at the same thermal modulus, there is no obvious difference in product performance, but the irradiation dose is significantly improved, resulting in partial splitting of the outer wall layer of Comparative Example 4 at high irradiation dose, so the tensile strength and elongation at break of the product decrease, and at the same irradiation dose, the outer layer of Comparative Example 4 has a significantly lower thermal modulus, indicating that the crosslinking degree of the material is insufficient, thus it is concluded that the TAIC crosslinking agent can promote the crosslinking of the outer wall layer raw material, reduce the irradiation dose, and the production and processing cost is lower.

[0062] As can be seen above, the transparent double-walled heat shrinkable tube prepared by using the scientifically proportioned LLDPE and EVA with narrow molecular weight distribution as the outer wall layer substrate and suitable additives has the characteristics of anti-sticking after thermal shrinkage, short shrinkage time, rapid cooling and heat aging resistance, and has obvious improvement in application performance compared with the existing transparent double-walled heat shrinkable tube.

[0063] The above is only a preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A transparent double-walled heat-shrinkable tube, characterized in that, It comprises: an inner wall layer and an outer wall layer, wherein the outer wall layer is disposed around the periphery of the inner wall layer, and the raw materials of the outer wall layer include linear low-density polyethylene, ethylene vinyl acetate copolymer and crosslinking agent.

2. The transparent double-walled heat-shrinkable tube according to claim 1, characterized in that, The weight ratio of linear low-density polyethylene to ethylene vinyl acetate copolymer in the raw material of the outer wall layer is 30%-90%: 10%-70%; Preferably, the low-density polyethylene is selected from linear low-density polyethylene of grades 2032, 2045, 2036G, 2042G, 2045G, 2049G, 2064G, 2083G, GM8070G, and GM8090 produced by Dow Chemical Company, or at least one of linear low-density polyethylene resins with a melt index of 0.5-3 g / 10 min, a melting point of 105-125°C, a Vicat softening point of 100°C-120°C, and a haze of 1%-15%. Preferably, the ethylene vinyl acetate copolymer is selected from ethylene vinyl acetate copolymers produced by Dow Chemical Company with grades 3120, 760, 770, 450, 470, 650Q, 560, 550, 3165, 3130, 3170, and 3174, or at least one of ethylene vinyl acetate copolymers with a VA content of 10%-25%, a melt index of 0.5-53 g / 10 min, and a melting point of 85-100°C.

3. The transparent double-walled heat-shrinkable tube according to claim 1, characterized in that, The raw material for the inner wall layer is selected from polyamide hot melt adhesive; Preferably, the raw material for the inner wall layer is PLATAMIDI 1276, manufactured by ARKEMA.

4. The transparent double-walled heat-shrinkable tube according to claim 1, characterized in that, The raw materials of the outer wall layer also include antioxidants, anti-sticking agents and silica powder; Preferably, the total weight of the crosslinking agent, antioxidant, anti-sticking agent, and silica powder does not exceed 10% of the total weight of the outer wall layer. More preferably, the crosslinking agent includes at least one of TAC, TAIC, TMPTMA, and TMPTA; the antioxidant includes at least one of sterically hindered phenols and thioethers; the anti-sticking agent includes at least one of stearamide, ethylene bisoleamide, and erucamide; and the diameter of the silica particles is 20 μm to 140 μm. Preferably, the raw material of the outer wall layer comprises the following components in weight percentage: 30%-90% linear low-density polyethylene, 10%-70% ethylene vinyl acetate copolymer, 0.5%-5% crosslinking agent, 0.1%-2% antioxidant, 0.1%-2% anti-sticking agent, and 1%-10% silica powder.

5. The transparent double-walled heat-shrinkable tube according to claim 1, characterized in that, The outer wall layer has a thickness of 0.8-0.9 mm and an outer diameter of 4.2-4.6 mm, while the inner wall layer has a thickness of 0.8-0.9 mm and an inner diameter of 0.9-1.0 mm.

6. The transparent double-walled heat-shrinkable tube according to any one of claims 1-5, characterized in that, The transparent double-wall heat shrink tube has a temperature range of -40℃ to 125℃.

7. A manufacturing process for a transparent double-walled heat-shrinkable tube according to any one of claims 1-6, characterized in that, It includes: forming a double-layer tube blank by co-extrusion of the raw materials for the outer wall layer and the raw materials for the inner wall layer, then cross-linking them by electron beam radiation, and then heating, expanding and cooling to obtain the transparent double-wall heat shrink tube.

8. The preparation process according to claim 7, characterized in that, The process includes the following steps: granulating the raw material for the outer wall layer and co-extruding it with the raw material for the inner wall layer to form a double-walled tube blank with an adhesive coating on the inner wall; cross-linking the double-walled tube blank by electron beam irradiation, heating it to 150-170°C, and then introducing high-pressure gas to radially expand the tube blank using gas pressure; rapidly cooling it while maintaining the expansion state to fix the tube in the expanded state, thus obtaining a transparent double-walled heat-shrinkable tube with heat-shrinkable properties. Preferably, the irradiation dose is 130-150 kGy, and the weight ratio of the raw material of the outer wall layer to the raw material of the inner wall layer is 1:

1.

9. The application of the transparent double-wall heat shrink tubing according to any one of claims 1-6 in the sealing, insulation and protection of complex wire harnesses in automotive wiring harnesses, aviation wiring harnesses and other industrial fields.

10. The application according to claim 9, characterized in that, The transparent double-wall heat shrink tubing is used to bond wire harnesses made of polyethylene (PE) and / or polyvinyl chloride (PVC).

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