Electromagnetic shielding heat shrink tube and preparation method thereof

Abstract

The invention discloses an electromagnetic shielding heat-shrinkable tube and a preparation method thereof.The preparation method of the electromagnetic shielding heat-shrinkable tube comprises the steps of (1) manufacturing the heat-shrinkable tube and (2) adding a conductive layer to the inner wall of the heat-shrinkable tube, specifically, the step (1) comprises the following steps of heat-shrinkable tube raw material preparation, banburying, granulation, stripping, extrusion, irradiation, recoiling and expansion shaping; the step (2) comprises the steps of conductive slurry preparation, spraying, irrigation, soaking and curing. The adhesive force of the conductive layer of the electromagnetic shielding heat-shrinkable tube prepared by the technical scheme provided by the invention is greatly improved, and the electromagnetic shielding heat-shrinkable tube is not easy to crack after being bent for multiple times; in addition, 50-68dB shielding effectiveness is achieved in the frequency band of 30 MHz to 1.5 GHz, and compared with the prior art, the shielding effectiveness is greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of heat shrinkable tubes, and in particular to an electromagnetic shielding heat shrinkable tube and a preparation method thereof. Background Art

[0002] At present, there are many deficiencies in the preparation of electromagnetic shielding heat shrink tubing in the existing technology. Some solutions achieve the shielding effect by adding conductive fillers to the heat shrink tubing base material, but the conductive fillers have poor dispersibility and low compatibility with the base material, which can easily lead to a decrease in the mechanical properties of the heat shrink tubing and uneven shielding effectiveness; other solutions use a surface coating conductive layer, but the coating process (such as spraying and brushing) has problems with uneven coating thickness and poor adhesion. During the expansion and shaping process of the heat shrink tubing, the conductive layer is prone to cracking and falling off, seriously affecting the durability of the shielding performance. In addition, in the existing preparation process, the application method of the conductive material is single, which is difficult to adapt to the production needs of heat shrink tubing of different specifications, and the shielding effectiveness is generally low (usually less than 40dB), which cannot meet the stringent requirements of electromagnetic shielding in high frequency bands (such as 30MHz~1.5GHz).

[0003] Furthermore, during the manufacturing process, conventional heat shrink tubing suffers from unstable control of molecular crosslinking, leading to fluctuations in heat shrinkage performance and significant differences in axial and longitudinal shrinkage ratios, which in turn affects the uniformity of the conductive layer and shielding effectiveness. Therefore, developing a method for preparing electromagnetic shielding heat shrink tubing with high shielding effectiveness, stable performance, and suitability for large-scale production has become a pressing technical challenge in this field. Summary of the Invention

[0004] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide an electromagnetic shielding heat shrink tube and a preparation method thereof, aiming to solve the technical problems of poor adhesion of the conductive layer and low shielding effectiveness of the electromagnetic shielding heat shrink tube in the prior art.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: A method for preparing an electromagnetic shielding heat shrink tube comprises the steps of (1) making the heat shrink tube, and (2) adding a conductive layer to the inner wall of the heat shrink tube, wherein: Step (1) includes the following steps: (1.1) Heat shrink tubing raw material preparation: Prepare powdered ethylene-vinyl acetate copolymer, magnesium hydroxide, phosphorus-based flame retardant, and masterbatch material according to the pre-set ratio; (1.2) Mixing: Take out the heat shrink tubing raw materials prepared in step (1.1) and pour them evenly into the mixer for mixing; (1.3) Granulation: The material obtained in step (1.2) is fed into the hopper of the granulator for granulation; (1.4) Drawing noodles: The material obtained in step (1.3) is fed into a drawing machine, which converts the granules into noodles and then cuts them into granules by a high-speed rotating cutter; (1.5) Extrusion: The material obtained in step (1.4) is fed into an extruder to obtain a semi-finished heat shrink tubing extrusion product; (1.6) Irradiation: irradiating the semi-finished heat shrink tubing obtained in step (1.5) using an electron beam irradiation source; (1.7) Reeling: The heat shrink tubing treated by electron beam irradiation in step (1.6) is extruded into semi-finished products and orderly pulled onto the pay-off rack for reeling; (1.8) Expansion and shaping: Select an appropriate mold, pull the heat shrink tubing semi-finished product after the roll is pulled through the wire rack, fill it with compressed gas within the set heating temperature range to expand it to a predetermined multiple, and shape it by vacuum cooling water to form a heat shrink tubing with memory function; Step (2) includes the following steps: (2.1) Prepare conductive paste: Prepare one of silver-coated aluminum paste, silver-coated copper paste, silver-coated zinc paste or copper paste as the conductive paste; (2.2) Spraying: Fix the expanded and shaped heat shrink tubing, select suitable spraying equipment and nozzles to spray the conductive slurry on the inner wall of the heat shrink tubing; (2.3) Irrigation: Seal one end of the heat shrink tube, inject the conductive paste into the heat shrink tube, and cut the sealed end after it is filled to allow the conductive paste to adhere to the inner wall of the heat shrink tube; (2.4) Soaking: After wrapping the outer insulation layer of the heat shrink tube, place it in a container filled with conductive paste and soak it. After taking it out, remove the wrapping layer and allow the conductive paste to adhere to the inner wall of the heat shrink tube; (2.5) Curing: Bake the heat shrink tubing obtained in step (2.4) to dry and solidify the conductive paste on the inner wall to obtain an electromagnetic shielding heat shrink tubing.

[0006] Furthermore, in step (1.2) of the method for preparing the electromagnetic shielding heat shrink tube, the mixer hopper temperature is 40-80° C., and the stirring speed is 300-2000 rpm.

[0007] Furthermore, in step (1.3) of the method for preparing the electromagnetic shielding heat shrink tube, the granulation working temperature is 100-160° C. and the pressure is 1.5-10 MPa.

[0008] Furthermore, in step (1.4) of the method for preparing the electromagnetic shielding heat shrink tubing, the drawing working temperature is 90-180° C. and the pressure is 1.5-8 MPa.

[0009] Furthermore, in step (1.5) of the method for preparing the electromagnetic shielding heat shrink tube, a three-screw extruder is used, the extrusion temperature is 120-150° C., and the screw pressure is 2-10 MPa.

[0010] Furthermore, in step (1.6) of the method for preparing the electromagnetic shielding heat shrink tubing, the electron beam irradiation dose is 5 to 12 Mrad.

[0011] Furthermore, in step (1.8) of the method for preparing the electromagnetic shielding heat shrink tube, the heating temperature for expansion and shaping is 100-220° C., and the expansion multiple is 2-3 times.

[0012] Furthermore, in step (2.4) of the method for preparing the electromagnetic shielding heat shrink tube, the immersion time is 1 to 3 minutes.

[0013] Furthermore, in step (2.5) of the method for preparing the electromagnetic shielding heat shrink tube, the baking temperature is 40-90° C., and the baking time is 20 minutes to 3 hours.

[0014] Accordingly, the present invention provides an electromagnetic shielding heat shrink tube, comprising a heat shrink tube and a conductive layer arranged on the inner wall of the heat shrink tube. Different from the prior art, the heat shrink tube is made by the preparation method of the electromagnetic shielding heat shrink tube described above.

[0015] Beneficial effects: The present invention provides an electromagnetic shielding heat shrink tube and a preparation method thereof, which have at least the following advantages compared to the prior art: (1) Electron beam irradiation (5~12Mrad) regulates the inner wall of the heat shrink tube to form a microporous structure of Ra1.5~3.0μm. Combined with DBE solvent penetration and multiple application processes (spraying, irrigation, and soaking), the adhesion of the conductive layer is greatly improved. After 100 bending tests, the conductive layer does not fall off, solving the problem of cracking of the conductive layer in traditional processes.

[0016] (2) The vacuum cooling water shaping process stabilizes the transverse heat shrinkage rate at 50%~58%, and the difference between the axial and longitudinal heat shrinkage rates is ≤10% (the difference in traditional processes is >30%).

[0017] (3) Achieve 50~68dB shielding effectiveness in the 30MHz~1.5GHz frequency band, which is significantly improved compared to the existing technology (<40dB). Among them, the silver-coated copper paste reaches 68dB at 1.5GHz, meeting the stringent shielding requirements of 5G communications and high-frequency electronic equipment. DETAILED DESCRIPTION

[0018] To make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0019] The method for preparing the electromagnetic shielding heat shrink tube comprises the steps of (1) making the heat shrink tube and (2) adding a conductive layer to the inner wall of the heat shrink tube.

[0020] Step (1) includes the following steps: (1.1) Preparation of heat shrink tubing raw materials: Prepare powdered ethylene-vinyl acetate copolymer, magnesium hydroxide, phosphorus-based flame retardant, and masterbatch materials according to a pre-set ratio.

[0021] (1.2) Mixing: Take out the heat shrink tubing raw materials prepared in step (1.1) and pour them evenly into the blender for mixing.

[0022] (1.3) Granulation: The material obtained in step (1.2) is fed into the hopper of the granulator for granulation.

[0023] (1.4) Strip Drawing: The material obtained in step (1.3) is fed into a strip drawing machine, which converts the granules into noodles and then cuts them into granules using a high-speed rotating cutter. The core significance of this step is to further plasticize the granules and process them into granules of a specific shape, thereby optimizing the material structure density and uniformity, providing a stable material foundation for subsequent extrusion processes.

[0024] (1.5) Extrusion: The material obtained in step (1.4) is fed into an extruder to produce a semi-finished heat shrink tubing extrusion product. The core significance of this step is to achieve efficient plasticization, uniform dispersion, and precise extrusion of the material, laying the foundation for obtaining a heat shrink tubing extrusion semi-finished product with precise dimensions and a dense structure.

[0025] (1.6) Irradiation: The semi-finished heat shrink tubing extruded product obtained in step (1.5) is irradiated using an electron beam irradiation source. The core significance of this step is to precisely control the irradiation dose to regulate the crosslinking degree and molecular structure of the heat shrink tubing substrate, so that it has both stable shape memory function and suitable mechanical properties, laying the foundation for subsequent conductive layer adhesion and overall shielding effectiveness.

[0026] (1.7) Reeling: The heat shrink tubing, which has been irradiated by the electron beam in step (1.6), is extruded into a semi-finished product and orderly pulled onto a pay-off rack for reeling. The core significance of this step is to orderly pull the heat shrink tubing obtained in step (1.6) onto the pay-off rack, converting it into a regularly reeled semi-finished product. This process avoids problems such as tangling and knotting of the tubing, ensuring that the reel of heat shrink tubing is ventilated from beginning to end without blockage or holes, laying the foundation for precise control of the subsequent expansion multiple.

[0027] (1.8) Expansion and shaping: Using a suitable mold, the semi-finished heat shrink tubing, after being rolled out, is pulled through a pay-off frame. It is then expanded to a predetermined multiple by filling it with compressed gas within a set heating temperature range. The heat shrink tubing is then shaped using vacuum and cooling water to create a memory-like heat shrink tubing. This "vacuum and cooling water shaping" process involves applying negative pressure to the tubing, pressing it against the mold. This combined with the rapid cooling of the cooling water rapidly cools the expanded heat shrink tubing, fixing its expanded shape and creating a "shape memory" feature.

[0028] Step (2) includes the following steps: (2.1) Prepare conductive paste: Prepare one of silver-coated aluminum paste, silver-coated copper paste, silver-coated zinc paste or copper paste as the conductive paste.

[0029] (2.2) Spraying: After expansion and shaping, secure the heat shrink tubing and use appropriate spray equipment and nozzles to spray the inner surface of the tubing with a conductive slurry. This step atomizes the conductive slurry into droplets of 5-20 μm in diameter, which are evenly deposited on the inner surface of the tubing, forming a continuous conductive layer 10-30 μm thick. The atomized droplets penetrate the micropores (roughness Ra 1.5-3.0 μm) of the inner surface of the irradiated and cross-linked heat shrink tubing, achieving a filling rate exceeding 90%, forming a dense conductive network.

[0030] (2.3) Irrigation: Seal one end of the heat shrink tubing and inject the conductive slurry into the tubing. Once the tubing is fully filled, cut the sealed end to allow the conductive slurry to adhere to the inner wall of the tubing. The irrigation process controls the slurry injection volume and flow time to form a uniform coating on the inner wall. The optimal irrigation pressure range is 0.1-0.5 MPa. In actual applications, the appropriate pressure should be selected based on the size of the tubing.

[0031] (2.4) Soaking: After wrapping the outer insulation layer of the heat shrink tubing, place it in a container filled with conductive paste and soak it. After removing it, remove the wrapping layer and allow the conductive paste to adhere to the inner wall of the heat shrink tubing. The core significance of this step is to balance the uniformity of the conductive paste adhesion to the inner wall, coating thickness, and production efficiency by precisely controlling the soaking time, thereby avoiding coating defects caused by too short or too long soaking time.

[0032] (2.5) Curing: Bake the heat shrink tubing obtained in step (2.4) to dry and solidify the conductive paste on the inner wall, resulting in an electromagnetic shielding heat shrink tubing. The core significance of this step is to achieve complete curing of the conductive paste, stable maintenance of the substrate properties, and a strong bond between the conductive layer and the inner wall of the heat shrink tubing.

[0033] In the above step (1.1), the raw materials of the heat shrink tube are preferably: 100 parts of powdered ethylene-vinyl acetate copolymer, 40-60 parts of magnesium hydroxide, 20~30 parts of phosphorus flame retardant, 10~20 parts of masterbatch material.

[0034] Furthermore, in step (1.2) of the method for preparing electromagnetic shielding heat shrink tubing, the mixer hopper temperature is 40-80°C, and the stirring speed is 300-2000 rpm. Powdered ethylene-vinyl acetate copolymer (EVA) gradually softens within the 40-80°C temperature range, and the surface activity of inorganic fillers such as magnesium hydroxide and phosphorus-based flame retardants is enhanced with increasing temperature. The pigment particles in the masterbatch must be evenly dispersed in the resin matrix. A temperature of 40-80°C reduces the resin viscosity, making it easier for the pigment particles to break up aggregates under the shear force of stirring, thereby avoiding color shading or localized pigment accumulation and ensuring a consistent appearance of the heat shrink tubing. A speed range of 300-2000 rpm provides varying shear strengths. A low speed (300-800 rpm) is suitable for the initial feeding stage to avoid powder splashing caused by high-speed stirring and to ensure initial spreading and mixing of the components. High speed (1000~2000 rpm) is used for later homogenization. The strong shear force breaks the hydrogen bonds of inorganic fillers such as magnesium hydroxide, making them evenly dispersed in the EVA matrix as nano- or micron-sized particles, reducing mechanical defects caused by filler agglomeration (such as rupture of heat shrink tubes).

[0035] Furthermore, in step (1.3) of the method for preparing electromagnetic shielding heat shrink tubing, the granulation operating temperature is 100-160°C and the pressure is 1.5-10 MPa. The temperature range of 100-160°C ensures complete melting of the EVA and allows the surfaces of inorganic fillers such as magnesium hydroxide and phosphorus-based flame retardants to be fully infiltrated by the molten resin. The pressure of 1.5-10 MPa forces the molten material to be fully compacted within the granulator screw, eliminating voids within the granules and preventing breakage of the granules due to stress release during the drawing process.

[0036] Furthermore, in step (1.4) of the method for preparing electromagnetic shielding heat shrink tubing, the drawing process operates at a temperature of 90-180°C and a pressure of 1.5-8 MPa. The low-temperature range (90-120°C) is suitable for initially softening the pelletized material to prevent premature melting of the EVA and resulting adhesion to the equipment. The medium-high temperature range (130-180°C) allows the EVA to fully melt and activates the surface activity of the phosphorus-based flame retardant, forming a stronger interface with the EVA matrix. The pressure of 1.5-8 MPa ensures that the molten material is fully compacted within the drawing machine, eliminating micropores within the pellets.

[0037] Furthermore, in step (1.5) of the method for preparing electromagnetic shielding heat shrink tubing, a three-screw extruder is used, with an extrusion temperature of 120-150°C and a screw pressure of 2-10 MPa. The "triangular" screw arrangement of the three-screw extruder generates multiple shear fields and meshing zones. For systems containing inorganic fillers such as magnesium hydroxide and phosphorus-based flame retardants, the strong meshing action of the three screws can completely break up filler agglomerates, achieving a nanoscale uniform dispersion of the fillers within the EVA matrix and reducing stress concentration caused by uneven filler distribution. The temperature range of 120-150°C is optimized for the melting characteristics of EVA, ensuring complete melting while preventing thermal oxidative degradation of the EVA due to high temperatures. The screw pressure of 2-10 MPa ensures that the molten material is fully compacted within the die, eliminating bubbles and microvoids.

[0038] Furthermore, in step (1.6) of the method for preparing the electromagnetic shielding heat shrink tubing, the electron beam irradiation dose is 5 to 12 Mrad. A suitable irradiation dose ensures sufficient melt strength in the heat shrink tubing substrate, preventing uneven wall thickness or cracking during expansion. Electron beam irradiation bombards EVA molecular chains with high-energy electrons, initiating free radical reactions and forming crosslinks. A dose of 5 to 12 Mrad can control the crosslinking degree of the EVA within a range of 60% to 75%.

[0039] Furthermore, in step (1.8) of the method for preparing the electromagnetic shielding heat shrink tube, the heating temperature for expansion and shaping is 100-220° C., and the expansion multiple is 2-3 times.

[0040] In order to improve production efficiency, the above step (2.1) can be implemented simultaneously with step (1), rather than waiting until step (1) is fully completed before implementing step (2.1).

[0041] There are many options for the conductive paste in step (2.1).

[0042] When the conductive paste is silver-coated aluminum paste, its components include, by weight: 100 parts of silver paste, 1-700 parts of aluminum paste, and 1-200 parts of DBE solvent.

[0043] When the conductive paste is a silver-coated copper paste, its components, by weight, include: 100 parts of silver paste, 1-600 parts of copper paste, and 1-200 parts of DBE solvent.

[0044] When the conductive paste is silver-coated zinc paste, its components include, by weight: 1-100 parts of silver paste, 1-500 parts of zinc paste, and 1-200 parts of DBE solvent.

[0045] When the conductive paste is copper paste, its components include, by weight: 100 parts of copper paste, 1-50 parts of polyester resin, and 1-20 parts of DBE solvent.

[0046] Furthermore, in step (2.4) of the method for preparing the electromagnetic shielding heat shrink tubing, the immersion time is 1 to 3 minutes. This immersion time allows the solvent (DBE, polyester resin, etc.) in the conductive paste (such as silver-coated aluminum paste, copper paste, etc.) to fully penetrate the micropores on the inner surface of the heat shrink tubing (roughness Ra 1.5 to 3.0 μm after radiation cross-linking).

[0047] Furthermore, in step (2.5) of the method for preparing the electromagnetic shielding heat shrink tube, the baking temperature is 40-90° C., and the baking time is 20 minutes to 3 hours.

[0048] The present invention provides an electromagnetic shielding heat shrink tubing, comprising a heat shrink tubing and a conductive layer disposed on the inner wall of the heat shrink tubing. Unlike the prior art, the invention is manufactured using the aforementioned method for preparing electromagnetic shielding heat shrink tubing. Conductive slurries (such as silver-coated aluminum slurries and copper slurries) contain ingredients such as DBE solvent and polyester resin. Temperatures between 40°C and 90°C allow the solvent to gradually evaporate while avoiding boiling. At temperatures below 40°C, the solvent evaporates too slowly, leaving the slurry with residual viscosity, resulting in insufficient adhesion of the conductive layer. At temperatures above 90°C, the rapid evaporation of the solvent may generate bubbles (e.g., the sudden change in the evaporation rate of DBE at high temperatures), causing pits on the surface of the conductive layer and reducing shielding effectiveness.

[0049] For ease of understanding, the following examples are given to further illustrate.

[0050] Silver-clad aluminum paste conductive layer embodiment Example 1 Heat shrink tubing raw materials (parts by weight): 100 parts of EVA, 40 parts of magnesium hydroxide, 20 parts of phosphorus flame retardant, and 10 parts of masterbatch.

[0051] Process parameters: Internal mixing: 60℃, 500 rpm; Granulation: 120℃, 3MPa; Drawing: 110℃, 2MPa; Extrusion: three-screw extruder, 130℃, 5MPa; Irradiation: 8 Mrad; Expansion setting: 150℃, expansion 3 times; Conductive paste: 100 parts silver paste + 100 parts aluminum paste + 50 parts DBE solvent; Soak: 1 minute; Curing: Bake at 60℃ for 2 hours.

[0052] Electromagnetic shielding heat shrink tubing performance: 30MHz shielding effectiveness 55dB, 1.5GHz shielding effectiveness 58dB, no cracking after heat shrinkage, horizontal heat shrinkage rate 50%.

[0053] Example 2 Heat shrink tubing raw materials (parts by weight): 100 parts of EVA, 50 parts of magnesium hydroxide, 25 parts of phosphorus flame retardant, and 15 parts of masterbatch.

[0054] Process parameters: Internal mixing: 70℃, 1000 rpm; Granulation: 140℃, 5MPa; Drawing: 140℃, 4MPa; Extrusion: three-screw extruder, 140℃, 6MPa; Irradiation: 10 Mrad; Expansion setting: 180℃, expansion 2 times; Conductive paste: 100 parts silver paste + 300 parts aluminum paste + 100 parts DBE solvent; Soak: 2 minutes; Curing: Bake at 70℃ for 1.5 hours.

[0055] Electromagnetic shielding heat shrink tubing performance: 30MHz shielding effectiveness 62dB, 1.5GHz shielding effectiveness 65dB, no cracking after heat shrinkage, horizontal heat shrinkage rate 52%.

[0056] Example 3 Heat shrink tubing raw materials (parts by weight): 100 parts of EVA, 60 parts of magnesium hydroxide, 30 parts of phosphorus flame retardant, and 20 parts of masterbatch.

[0057] Process parameters: Mixing: 80℃, 2000 rpm; Granulation: 160℃, 10MPa; Drawing: 180℃, 8MPa; Extrusion: three-screw extruder, 150℃, 10MPa; Irradiation: 12 Mrad; Expansion setting: 220℃, expansion 2.5 times; Conductive paste: 100 parts silver paste + 500 parts aluminum paste + 150 parts DBE solvent; Soak: 3 minutes; Curing: Bake at 80℃ for 1 hour.

[0058] Electromagnetic shielding heat shrink tubing performance: 30MHz shielding effectiveness 58dB, 1.5GHz shielding effectiveness 60dB, no cracking after heat shrinkage, horizontal heat shrinkage rate 58%.

[0059] Silver-clad copper paste conductive layer embodiment Example 4 Heat shrink tubing raw materials (parts by weight): 100 parts of EVA, 45 parts of magnesium hydroxide, 22 parts of phosphorus flame retardant, and 12 parts of masterbatch.

[0060] Process parameters: Mixing: 40℃, 300 rpm; Granulation: 100℃, 1.5MPa; Drawing: 90℃, 1.5MPa; Extrusion: three-screw extruder, 120℃, 2MPa; Irradiation: 5 Mrad; Expansion setting: 100℃, expansion 2 times; Conductive paste: 100 parts silver paste + 100 parts copper paste + 30 parts DBE solvent; Soak: 1 minute; Curing: Bake at 40℃ for 3 hours.

[0061] Electromagnetic shielding heat shrink tubing performance: 30MHz shielding effectiveness 52dB, 1.5GHz shielding effectiveness 57dB, no cracking after heat shrinkage, horizontal heat shrinkage rate 54%.

[0062] Example 5 Heat shrink tubing raw materials (parts by weight): 100 parts of EVA, 55 parts of magnesium hydroxide, 28 parts of phosphorus flame retardant, and 18 parts of masterbatch.

[0063] Process parameters: Internal mixing: 50℃, 800 rpm; Granulation: 130℃, 4MPa; Drawing: 130℃, 3MPa; Extrusion: three-screw extruder, 135℃, 7MPa; Irradiation: 9 Mrad; Expansion setting: 200℃, expansion 2.5 times; Conductive paste: 100 parts silver paste + 300 parts copper paste + 80 parts DBE solvent; Soak: 2 minutes; Curing: Bake at 90℃ for 20 minutes.

[0064] Electromagnetic shielding heat shrink tubing performance: 30MHz shielding effectiveness 65dB, 1.5GHz shielding effectiveness 68dB, no cracking after heat shrinkage, horizontal heat shrinkage rate 51%.

[0065] Example 6 Heat shrink tubing raw materials (parts by weight): 100 parts of EVA, 52 parts of magnesium hydroxide, 26 parts of phosphorus flame retardant, and 16 parts of masterbatch.

[0066] Process parameters: Internal mixing: 75℃, 1500 rpm; Granulation: 150℃, 8MPa; Drawing: 160℃, 6MPa; Extrusion: three-screw extruder, 145℃, 9MPa; Irradiation: 11 Mrad; Expansion setting: 210℃, expansion 2 times; Conductive paste: 100 parts silver paste + 600 parts copper paste + 120 parts DBE solvent; Soak: 2.5 minutes; Curing: Bake at 50℃ for 2.5 hours.

[0067] Electromagnetic shielding heat shrink tubing performance: 30MHz shielding effectiveness 59dB, 1.5GHz shielding effectiveness 63dB, no cracking after heat shrinkage, horizontal heat shrinkage rate 52%.

[0068] Silver-coated zinc paste conductive layer embodiment Example 7 Heat shrink tubing raw materials (parts by weight): 100 parts of EVA, 48 parts of magnesium hydroxide, 23 parts of phosphorus flame retardant, and 14 parts of masterbatch.

[0069] Process parameters: Mixing: 55℃, 600 rpm; Granulation: 110℃, 2MPa; Drawing: 100℃, 2MPa; Extrusion: three-screw extruder, 125℃, 3MPa; Irradiation: 6 Mrad; Expansion setting: 120℃, expansion 2.5 times; Conductive paste: 50 parts silver paste + 100 parts zinc paste + 20 parts DBE solvent; Soak: 1.5 minutes; Curing: Bake at 55℃ for 2.8 hours.

[0070] Electromagnetic shielding heat shrink tubing performance: 30MHz shielding effectiveness 50dB, 1.5GHz shielding effectiveness 52dB, no cracking after heat shrinkage, horizontal heat shrinkage rate 55%.

[0071] Example 8 Heat shrink tubing raw materials (parts by weight): 100 parts of EVA, 53 parts of magnesium hydroxide, 27 parts of phosphorus flame retardant, and 17 parts of masterbatch.

[0072] Process parameters: Internal mixing: 65℃, 1200 rpm; Granulation: 145℃, 6MPa; Drawing: 150℃, 5MPa; Extrusion: three-screw extruder, 138°C, 8MPa; Irradiation: 10 Mrad; Expansion setting: 190℃, expansion 3 times; Conductive paste: 100 parts silver paste + 300 parts zinc paste + 80 parts DBE solvent; Soak: 2 minutes; Curing: Bake at 75℃ for 1.5 hours.

[0073] Electromagnetic shielding heat shrink tubing performance: 30MHz shielding effectiveness 56dB, 1.5GHz shielding effectiveness 59dB, no cracking after heat shrinkage, horizontal heat shrinkage rate 56%.

[0074] Example 9 Heat shrink tubing raw materials (parts by weight): 100 parts of EVA, 58 parts of magnesium hydroxide, 29 parts of phosphorus flame retardant, and 19 parts of masterbatch.

[0075] Process parameters: Internal mixing: 78℃, 1800 rpm; Granulation: 155℃, 9MPa; Drawing: 170℃, 7MPa; Extrusion: three-screw extruder, 148°C, 9.5MPa; Irradiation: 11.5 Mrad; Expansion setting: 215℃, expansion 2 times; Conductive paste: 100 parts silver paste + 500 parts zinc paste + 150 parts DBE solvent; Soak: 3 minutes; Curing: Bake at 60℃ for 2 hours.

[0076] Electromagnetic shielding heat shrink tubing performance: 30MHz shielding effectiveness 53dB, 1.5GHz shielding effectiveness 55dB, no cracking after heat shrinkage, horizontal heat shrinkage rate 54%.

[0077] Copper paste conductive layer embodiment Example 10 Heat shrink tubing raw materials (parts by weight): 100 parts of EVA, 42 parts of magnesium hydroxide, 21 parts of phosphorus flame retardant, and 11 parts of masterbatch.

[0078] Process parameters: Mixing: 45℃, 400 rpm; Granulation: 105℃, 1.8MPa; Drawing: 95℃, 1.8MPa; Extrusion: three-screw extruder, 122℃, 2.5MPa; Irradiation: 5.5 Mrad; Expansion setting: 110℃, expansion 2.2 times; Conductive paste: 100 parts copper paste + 10 parts polyester resin + 5 parts DBE solvent; Soak: 1 minute; Curing: Bake at 50℃ for 3 hours.

[0079] Electromagnetic shielding heat shrink tubing performance: 30MHz shielding effectiveness 55dB, 1.5GHz shielding effectiveness 62dB, no cracking after heat shrinkage, horizontal heat shrinkage rate 52%.

[0080] Example 11 Heat shrink tubing raw materials (parts by weight): 100 parts of EVA, 54 parts of magnesium hydroxide, 24 parts of phosphorus flame retardant, and 13 parts of masterbatch.

[0081] Process parameters: Internal mixing: 68℃, 900 rpm; Granulation: 135℃, 5MPa; Drawing: 145℃, 4.5MPa; Extrusion: three-screw extruder, 132°C, 6.5MPa; Irradiation: 7 Mrad; Expansion setting: 170℃, expansion 2.5 times; Conductive paste: 100 parts copper paste + 30 parts polyester resin + 10 parts DBE solvent; Soaking: 1.8 minutes; Curing: Bake at 80℃ for 1 hour.

[0082] Electromagnetic shielding heat shrink tubing performance: 30MHz shielding effectiveness 58dB, 1.5GHz shielding effectiveness 59dB, no cracking after heat shrinkage, horizontal heat shrinkage rate 55%.

[0083] Example 12 Heat shrink tubing raw materials (parts by weight): 100 parts of EVA, 56 parts of magnesium hydroxide, 29 parts of phosphorus flame retardant, and 15 parts of masterbatch.

[0084] Process parameters: Mixing: 72℃, 1300 rpm; Granulation: 150℃, 7MPa; Drawing: 150℃, 6MPa; Extrusion: three-screw extruder, 140℃, 7.5MPa; Irradiation: 9.5 Mrad; Expansion setting: 195℃, expansion 2 times; Conductive paste: 100 parts copper paste + 50 parts polyester resin + 20 parts DBE solvent; Soaking: 2.2 minutes; Curing: Bake at 90℃ for 40 minutes.

[0085] Electromagnetic shielding heat shrink tubing performance: 30MHz shielding effectiveness 59dB, 1.5GHz shielding effectiveness 60dB, no cracking after heat shrinkage, horizontal heat shrinkage rate 51%.

[0086] The feasibility of the preparation process of electromagnetic shielding heat shrink tubing is verified through 12 groups of embodiments (3 groups of embodiments for each of 4 types of conductive pastes).

[0087] An irradiation dose of 5-12 Mrad and an expansion factor of 2-3 form a critical coupling. For example, in Example 5, 9 Mrad irradiation combined with a 5-fold expansion achieved a crosslinking degree of 70%, no cracking in the conductive layer after heat shrinkage, a lateral heat shrinkage of 51%, and a shielding effectiveness degradation of ≤3dB. However, a lower irradiation dose (such as 5 Mrad in Example 4) combined with a 2-fold expansion resulted in a heat shrinkage of 54% but a shielding effectiveness of only 52dB, demonstrating the enhanced stability of the conductive layer due to a high crosslinking degree.

[0088] By forming an inner wall roughness of Ra1.5~3.0μm through radiation cross-linking and combining with DBE solvent penetration (such as immersion for 2 minutes in Example 2), the adhesion reaches level 0, solving the coating shedding problem in the prior art (the adhesion of the traditional process is only level 3~4).

[0089] The expansion and shaping process uses vacuum cooling water to shape the tube, so that the difference between the horizontal and vertical heat shrinkage rates is ≤10%. However, in traditional heat shrink tubing, this difference often reaches more than 30%, resulting in uneven distribution of the conductive layer.

[0090] The shielding effectiveness of the 12 sets of embodiments basically reached ≥50dB, which is significantly improved compared with the existing technology (<40dB).

[0091] The above description is merely a preferred embodiment of the present invention and does not limit the present invention in any form. It is understood that those skilled in the art can make equivalent substitutions or changes based on the technical solution and inventive concept of the present invention, and all such changes or substitutions shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing an electromagnetic shielding heat shrink tube, comprising step (1) making a heat shrink tube, and step (2) adding a conductive layer to the inner wall of the heat shrink tube, characterized in that: Step (1) includes the following steps: (1.1) Heat shrink tubing raw material preparation: Prepare powdered ethylene-vinyl acetate copolymer, magnesium hydroxide, phosphorus-based flame retardant, and masterbatch material according to the pre-set ratio; (1.2) Mixing: Take out the heat shrink tubing raw materials prepared in step (1.1) and pour them evenly into the mixer for mixing; (1.3) Granulation: The material obtained in step (1.2) is fed into the hopper of the granulator for granulation; (1.4) Drawing noodles: The material obtained in step (1.3) is fed into a drawing machine, which converts the granules into noodles and then cuts them into granules by a high-speed rotating cutter; (1.5) Extrusion: The material obtained in step (1.4) is fed into an extruder to obtain a semi-finished heat shrink tubing extrusion product; (1.6) Irradiation: irradiating the semi-finished heat shrink tubing obtained in step (1.5) using an electron beam irradiation source; (1.7) Reeling: The heat shrink tubing treated by electron beam irradiation in step (1.6) is extruded into semi-finished products and orderly pulled onto the pay-off rack for reeling; (1.8) Expansion and shaping: Select an appropriate mold, pull the heat shrink tubing semi-finished product after the roll is pulled through the wire rack, fill it with compressed gas within the set heating temperature range to expand it to a predetermined multiple, and shape it by vacuum cooling water to form a heat shrink tubing with memory function; Step (2) includes the following steps: (2.1) Prepare conductive paste: Prepare one of silver-coated aluminum paste, silver-coated copper paste, silver-coated zinc paste or copper paste as the conductive paste; (2.2) Spraying: Fix the expanded and shaped heat shrink tubing, select suitable spraying equipment and nozzles to spray the conductive slurry on the inner wall of the heat shrink tubing; (2.3) Irrigation: Seal one end of the heat shrink tube, inject the conductive paste into the heat shrink tube, and cut the sealed end after it is filled to allow the conductive paste to adhere to the inner wall of the heat shrink tube; (2.4) Soaking: After wrapping the outer insulation layer of the heat shrink tube, place it in a container filled with conductive paste and soak it. After taking it out, remove the wrapping layer and allow the conductive paste to adhere to the inner wall of the heat shrink tube; (2.5) Curing: Bake the heat shrink tubing obtained in step (2.4) to dry and solidify the conductive paste on the inner wall to obtain an electromagnetic shielding heat shrink tubing.

2. The method for preparing the electromagnetic shielding heat shrink tubing according to claim 1, wherein: In step (1.2), the mixer hopper temperature is 40-80°C, and the stirring speed is 300-2000 rpm.

3. The method for preparing the electromagnetic shielding heat shrink tubing according to claim 1, wherein: In step (1.3), the granulation operating temperature is 100~160℃ and the pressure is 1.5~10MPa.

4. The method for preparing the electromagnetic shielding heat shrink tubing according to claim 1, wherein: In step (1.4), the drawing temperature is 90~180℃ and the pressure is 1.5~8MPa.

5. The method for preparing the electromagnetic shielding heat shrink tubing according to claim 1, wherein: In step (1.5), a three-screw extruder is used, the extrusion temperature is 120~150℃, and the screw pressure is 2~10MPa.

6. The method for preparing the electromagnetic shielding heat shrink tubing according to claim 1, wherein: In step (1.6), the electron beam irradiation dose is 5-12 Mrad.

7. The method for preparing the electromagnetic shielding heat shrink tubing according to claim 1, wherein: In step (1.8), the heating temperature for expansion and shaping is 100~220℃, and the expansion multiple is 2~3 times.

8. The method for preparing the electromagnetic shielding heat shrink tube according to claim 1, wherein: In step (2.4), the soaking time is 1 to 3 minutes.

9. The method for preparing the electromagnetic shielding heat shrink tube according to claim 1, wherein: In step (2.5), the baking temperature is 40-90°C, and the baking time is 20 minutes to 3 hours.

10. An electromagnetic shielding heat shrink tube, comprising a heat shrink tube and a conductive layer arranged on the inner wall of the heat shrink tube, characterized in that: The electromagnetic shielding heat shrink tube is made by the preparation method of any one of claims 1 to 9.