Heat tracing band and preparation method thereof

Abstract

The invention relates to the technical field of polymer thermoelectric composite materials, in particular to a heat tracing band, which comprises an outer insulating layer, a shielding layer, an inner insulating layer and a conductive core band, and is characterized in that the conductive core band comprises two conductive buses arranged in parallel and a PTC (Positive Temperature Coefficient) composite material coating the conductive buses; the PTC composite material comprises the following components in parts by weight: 180-220 parts of carbon black-carbon fiber composite conductive powder, 600-700 parts of linear low density polyethylene, 50-100 parts of an ethylene-octylene copolymer, 2-4 parts of an antioxidant and 1-3 parts of an ultraviolet light absorber. According to the invention, the ethylene-octene copolymer long-chain branch and the linear low-density polyethylene chain segment are entangled to form a special molecular network; at low temperature, linear low-density polyethylene ensures that the structure is stable, and an ethylene-octylene copolymer flexible chain segment absorbs impact and relieves low-temperature brittleness; at high temperature, the molecular chain of the former is anchored by the long-chain branch of the latter, the sliding of the chain segment is blocked, and a proper amount of balance toughening and heat-resisting agent is added, so that the heat deformation temperature is increased, and the material softening is delayed.

Description

Technical Field

[0001] This application relates to the field of polymer thermoelectric composite materials technology, specifically to a heat tracing cable and its preparation method. Background Technology

[0002] Heat tracing cables (electric heat tracing cables) are core application products in the field of polymer thermoelectric composite materials. They are widely applicable to industrial, civil and commercial scenarios in extremely cold regions. Their core function is to maintain (insulate) or thaw the temperature of equipment such as pipelines and storage tanks through the conversion of electrical energy to thermal energy, solving problems such as fluid freezing and equipment failure in low-temperature environments. They are key equipment to ensure the continuity of industrial production and the stability of public facilities.

[0003] However, under conditions such as prolonged high temperature and outdoor ultraviolet radiation, the polymer matrix in the heat tracing cable is prone to oxidative degradation; at the same time, the interfacial bonding force between the conductive filler and the polymer matrix will decrease accordingly. These two factors together cause the tensile strength and conductivity of the heat tracing cable to degrade too quickly, significantly shortening its service life. Summary of the Invention

[0004] To effectively improve the aging resistance of heat tracing cables and extend their service life, this application provides a heat tracing cable and its preparation method.

[0005] Firstly, this application provides a heat tracing cable, which adopts the following technical solution: A heat tracing tape includes an outer insulation layer, a shielding layer, an inner insulation layer, and a conductive core strip. The conductive core strip includes two parallel conductive busbars and a PTC composite material covering the outside of the conductive busbars. The PTC composite material comprises the following components in parts by weight: 180-220 parts of carbon black-carbon fiber composite conductive powder, 600-700 parts of linear low-density polyethylene, 50-100 parts of ethylene-octene copolymer, 2-4 parts of antioxidant, and 1-3 parts of ultraviolet absorber.

[0006] Through the above technical solution, the long branches of the ethylene-octene copolymer can entangle with the main chain or short branches of linear low-density polyethylene (LDPE), forming a molecular network of "rigid skeleton + ethylene-flexible buffer". At low temperatures, LDPE provides overall structural stability to the material, while the flexible segments of the ethylene-octene copolymer can absorb impact energy through their own movement, preventing the LDPE molecular chains from breaking directly due to "freezing", thus alleviating the low-temperature brittleness of the material. At high temperatures, the thermal motion of the LDPE molecular chains is "anchored" by the entanglement of the long branches of the ethylene-octene copolymer, increasing the sliding resistance of the chain segments. At the same time, by adding appropriate amounts of balanced toughening and heat resistance, the heat distortion temperature is increased, making it difficult for the material to undergo plastic deformation, thereby delaying softening caused by molecular chain relaxation.

[0007] Preferably, the antioxidant is a compound of hindered phenolic antioxidant and phosphite antioxidant, and the mass ratio of the two is 1:(0.8-1.2).

[0008] Through the above technical solution, hindered phenols are the main antioxidants, which provide active hydrogen to capture free radicals generated during the thermal aging of materials and terminate the oxidation chain reaction; phosphites are the auxiliary antioxidants, which can decompose the hydroperoxides generated by thermal oxidation into harmless alcohols or ketones, preventing the hydroperoxides from further decomposing and generating new free radicals. Moreover, the amount of free radicals captured by hindered phenols is in balance with the amount of hydroperoxides decomposed by phosphites, resulting in a higher antioxidant efficiency than that of a single antioxidant.

[0009] When phosphites are insufficient, hydroperoxides cannot be effectively decomposed, and the oxidation reaction will continue to accelerate through branching reactions, leading to a decrease in antioxidant rate. At this time, although hindered phenols can capture free radicals, they cannot block the branching growth of the oxidation chain, resulting in a decrease in overall antioxidant efficiency. When phosphites are excessive, the excess phosphites will compete with hindered phenols to capture free radicals, causing the hindered phenols to be unable to play their full role, resulting in a decrease in overall antioxidant efficiency.

[0010] Preferably, the carbon black-carbon fiber composite conductive powder comprises, by weight: 50-60 parts carbon black, 8-12 parts carbon fiber, and 32-38 parts binder.

[0011] Through the above technical solution, carbon fiber, with its advantages of "high conductivity + skeleton support", forms a highly efficient conductive backbone, which serves as a "macroscopic conductive skeleton" to construct a through-type conductive path; carbon black precisely fills the micron-level gaps between carbon fibers, forming "microscopic conductive nodes"; the binder effectively encapsulates carbon black and carbon fiber, building branch bridges. The three work together to construct a "continuous, uniform, and low-resistance" conductive network, effectively reducing the volume resistivity of the core material, thereby improving the conductivity.

[0012] Preferably, the short-cut carbon fibers in the carbon black-carbon fiber composite conductive powder are compounded with carbon black at a mass ratio of 1:(5-6.25).

[0013] Through the above technical solution, when there is an excess of carbon black, the excess carbon black is prone to secondary agglomeration. It is difficult to build a continuous macroscopic conductive skeleton by carbon fiber alone, which leads to an increase in the resistivity of the core material and a reduction in conductivity. When carbon black is insufficient, it cannot accurately fill the micron-level gaps between carbon fibers, easily forming "conductive islands," resulting in discontinuous conductive pathways and even localized non-conductive areas. The core material resistivity is too high, reducing conductivity.

[0014] Preferably, the adhesive is low-melting-point polyethylene.

[0015] Through the above technical solution, low-melting-point polyethylene can melt and coat carbon black and carbon fibers at low temperatures, avoiding damage to conductive components or agglomeration caused by high temperatures. Moreover, low-melting-point polyethylene, linear low-density polyethylene, and ethylene-octene copolymer all belong to polyolefins, with excellent compatibility. When blended, the interfacial repulsion is weak, which can effectively reduce interfacial defects and improve the bending resistance of composite materials. At the same time, low-melting-point polyethylene has good fluidity after melting, and the flexible layer formed by cooling can fix the position of conductive components and buffer stress, taking into account both conductivity stability and toughness.

[0016] Preferably, the carbon black-carbon fiber composite conductive powder further includes a conductive additive, which includes at least one of reduced graphene oxide and carbon nanotubes.

[0017] Through the above technical solutions, the addition of binder fills the gaps between carbon black and carbon fibers, separating the conductive components, reducing the direct contact points between conductive particles, and decreasing the conductivity of the material. Reduced graphene oxide, with its sheet-like structure, simultaneously contacts multiple carbon black particles or carbon fibers, forming a "surface-to-point / surface-to-line" conductive channel, reducing the detour loss of current transmission; carbon nanotubes, with their high aspect ratio, act like "wires" to bridge the dispersed carbon black particles, avoiding the formation of local conductive islands. Both can effectively reduce the volume resistivity of the composite conductive powder, thereby improving conductivity.

[0018] In addition, reduced graphene oxide sheets and carbon nanotubes can also serve as "nano-reinforcers," tightly bonding with low-melting-point polyethylene during dispersion, reducing the shedding of carbon black and carbon fibers during processing or use, while slightly improving the material's bending resistance and preventing electrical conductivity failure due to mechanical damage.

[0019] Preferably, the conductive additive is reduced graphene oxide.

[0020] Through the above technical solutions, the edges of reduced graphene oxide sheets can form van der Waals forces with low-melting-point polyethylene molecular chains, making them easier to be coated by binders than carbon nanotubes, thereby reducing the risk of agglomeration during processing. At the same time, as a single-layer or few-layer two-dimensional carbon material, reduced graphene oxide has an ultra-large specific surface area and abundant edge sites, which can cover and contact multiple dispersed conductive particles like an "ultra-thin carbon sheet", providing a physical carrier for the "bridging" between particles. Compared with carbon nanotubes, the two-dimensional sheets of reduced graphene oxide can achieve multi-dimensional contact modes of "surface-to-point" (with carbon black) and "surface-to-line" (with carbon fibers), with a wider contact range and higher bridging efficiency, thereby improving conductivity.

[0021] Furthermore, when the material is bent or undergoes thermal expansion and contraction, the deformation of the matrix may cause the carbon black and carbon fibers to detach from their original position. Reduced graphene oxide "anchors" these conductive particles to the same two-dimensional platform through bridging, effectively limiting their displacement and thus improving the bending resistance of the composite material. Therefore, reduced graphene oxide is the preferred choice.

[0022] Preferably, the carbon black-carbon fiber composite conductive powder also includes glyceryl stearate.

[0023] By adding glyceryl stearate to the carbon black-carbon fiber composite conductive powder, glyceryl stearate can melt before low-melting-point polyethylene. Through its lipophilic groups, it breaks up the agglomerates of reduced graphene oxide, dispersing it into a thin-layer structure, avoiding "conductive blind spots," and ensuring a stable reduction in volume resistivity, thereby improving conductivity. Furthermore, without glyceryl stearate, the molten system formed by mixing carbon black-carbon fiber composite conductive powder and low-melting-point polyethylene would require high-temperature processing to maintain fluidity due to high friction between conductive particles and resin, resulting in high viscosity. However, this temperature far exceeds the thermal decomposition temperature of antioxidants, leading to their rapid decomposition. With the addition of glyceryl stearate, its lubricity reduces the viscosity of the system, allowing for processing at low temperatures. This prevents the antioxidants from decomposing at high temperatures, making the three-level conductive network of "carbon fiber-carbon black-reduced graphene oxide" more continuous and stabilizing the resistance fluctuation range of the PTC effect.

[0024] Secondly, this application provides a method for preparing a heat tracing cable, which employs the following technical solution: A method for preparing a heat tracing tape includes the following steps: S1. Mix the low-melting-point polyethylene, glyceryl stearate, reduced graphene oxide, carbon black and chopped carbon fibers in the specified amounts, and then pulverize them to obtain carbon black-carbon fiber composite conductive powder. S2. The carbon black-carbon fiber composite conductive powder, linear low-density polyethylene, ethylene-octene copolymer, antioxidant, and ultraviolet absorber in the specified amounts are mixed and then granulated to obtain heat tracing particles. S3. The PTC conductive composite material particles are melt-extruded and coated onto two parallel conductive busbars, and then cross-linked by irradiation to obtain a conductive core strip; S4. An inner insulation layer, a shielding layer, and an outer insulation layer are sequentially wrapped around the surface of the conductive core strip to obtain a heat tracing cable.

[0025] In summary, this application has the following beneficial effects: 1. In this application, the long branches of the ethylene-octene copolymer can entangle with the main chain or short branches of linear low-density polyethylene (LDPE) to form a molecular network of "rigid skeleton + ethylene-flexible buffer". At low temperatures, LDPE provides overall structural stability to the material, while the flexible segments of the ethylene-octene copolymer can absorb impact energy through their own movement, preventing the LDPE molecular chains from breaking directly due to "freezing", thereby alleviating the low-temperature brittleness of the material. At high temperatures, the thermal motion of the LDPE molecular chains is "anchored" by the entanglement of the long branches of the ethylene-octene copolymer, increasing the sliding resistance of the chain segments. At the same time, by adding appropriate amounts of toughening and heat-resistant agents, the heat distortion temperature is increased, making it difficult for the material to undergo plastic deformation, thereby delaying the softening caused by molecular chain relaxation. 2. This application adds reduced graphene oxide to carbon black-carbon fiber composite conductive powder. As a two-dimensional material, reduced graphene oxide can cover and bridge multiple conductive particles in the form of "ultra-thin carbon sheets", realizing "surface-to-point / surface-to-line" multi-dimensional contact and improving bridging efficiency. After the reduced graphene oxide is bridged, electrons can be transferred from carbon black to carbon fiber through its sheets, which is equivalent to opening up the "conductive breakpoints", making the conductive network more complete and thus improving the conductivity. 3. This application adds glyceryl stearate to carbon black-carbon fiber composite conductive powder, which melts before low-melting-point polyethylene. The lipophilic groups break up the agglomerates of reduced graphene oxide, dispersing it into a thin-layer structure, avoiding conductive blind spots, and ensuring a stable decrease in volume resistivity. At the same time, it plays a lubricating role, reducing the thermal decomposition of antioxidants, and forming a lubricating film after melting, reducing the agglomeration force of carbon black and the friction between carbon fiber and melt, making the three-level conductive network of "carbon fiber-carbon black-reduced graphene oxide" more continuous, thereby stabilizing the resistance change amplitude of the PTC effect. Detailed Implementation

[0026] The raw materials in this application include the following: Carbon black: Commercially available product with CAS number 1333-86-4 is used; Carbon fiber: Commercially available product of Shenzhen Hengtai Carbon Fiber Co., Ltd., model H-189; Ethylene-octene copolymer: The commercially available product, model 8407, from Shanghai SABACK International Trade Co., Ltd. is used. Hindered phenolic antioxidants: Commercially available products with CAS number 6683-19-8 are used; Phosphite antioxidants: Commercially available products with CAS number 31570-04-4 are used; Ultraviolet absorber: Commercially available product with CAS number 1843-05-6 is used; Low melting point polyethylene: Uses commercially available products with Taiwan plastic grade 8010; Low-density polyethylene: Commercially available products with CAS number 9002-88-4 are used; Reduced graphene oxide: Commercially available product XT-Go from Shanghai Xiangtian Nanomaterials Co., Ltd. was used; Glyceryl stearate: Uses commercially available product with CAS number 123-94-4; Tinned copper conductor: The product used is a commercially available Φ14 conductor from Qingdao Leikeshi Electric Technology Co., Ltd. Polyvinyl chloride: Uses commercially available products with CAS number 9002-86-2; Tinned copper wire braided mesh: Commercially available products manufactured by Shanghai Darou Special Cable Co., Ltd. Fluoroplastics: Commercially available product with brand name 416HPX from Dongguan Zhongsu Youpin New Materials Co., Ltd.

[0027] Example 1 A method for preparing a heat tracing tape includes the following steps: S1. Add 700g of low-melting-point polyethylene to a high-speed mixer, keep it at 90℃ and stir at 1000rpm for 15min until completely melted; add 1100g of carbon black and 200g of short-cut carbon fiber in 3 batches (5min interval between each batch), adjust the speed to 800rpm, and continue mixing for 45min to form a uniform molten composite. S2. The molten composite is fed into a twin-screw granulator, the speed is set to 350 rpm and the time is 12 min. After extrusion granulation, it is crushed to a particle size of 100 μm to obtain carbon black-carbon fiber composite conductive powder. S3. Add 2000g of carbon black-carbon fiber composite conductive powder, 6500g of linear low-density polyethylene, 750g of ethylene-octene copolymer, 30g of antioxidant, and 20g of ultraviolet absorber to a twin-screw extruder. The antioxidant includes 15g of hindered phenolic antioxidant and 15g of phosphite antioxidant. Set the extruder temperature gradient as follows: feeding section 90℃, melting section 130℃, homogenization section 135℃, and die head temperature 130℃. Control the screw speed at 240rpm. The raw materials are uniformly mixed by screw shearing to obtain a mixture. S4. After the mixture is extruded through a twin-screw extruder, it is immediately cooled in a 70°C water bath and then fed into a pelletizer to obtain PTC composite material particles with a length of 3.0 mm × a diameter of 2.0 mm. S5. The obtained PTC conductive composite material particles are melt-extruded through a single screw extruder and coated onto two parallel tin-plated copper wires to obtain a dumbbell-shaped conductive core strip. The extrusion temperature of the single screw extruder is 160℃. S6. Polyvinyl chloride, tinned copper wire braided mesh, and fluoroplastic are sequentially coated onto the conductive core strip using a single-screw extruder to obtain the heat tracing tape.

[0028] Example 2-3 Examples 2-3 are based on the preparation method of Example 1, with adjustments made to the weight proportions of each component of the PTC composite material, as shown in Table 1.

[0029] Comparative Examples 1-2 Comparative Example 1 is based on the preparation method of Example 1, except that linear low-density polyethylene is replaced with polyethylene, and the other conditions remain unchanged. The specific adjustments are shown in Table 1.

[0030] Comparative Example 2 adjusts the weight proportions of each component of the PTC composite material based on the preparation method of Example 1. The specific adjustments are shown in Table 1.

[0031] The heat tracing tapes prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to the following performance tests, and the test results are shown in Table 1.

[0032] The performance testing is as follows: (1) Tensile strength The heat tracing samples provided in Examples 1-3 and Comparative Examples 1-2 of this application were tested according to the GB / T1040-2006 standard. The tensile strength of the heat tracing samples was tested. The sample size was: 170 mm in length, 10 mm in width, and 4 mm in thickness. The sample was dumbbell-shaped. The test speed was 50 mm / min.

[0033] (2) Tensile strength retention rate The test was conducted according to GB / T7141-2008 standard. The material was placed in a high-temperature aging test chamber at a temperature of 100°C. After 168 hours, samples were taken to test the tensile strength as described above, and the tensile strength retention rate was calculated.

[0034] Table 1 Performance test results of Examples 1-3 and Comparative Examples 1-2

[0035] Referring to Table 1, comparing Examples 1-3 and Comparative Examples 1-2, it can be seen that the toughness and heat resistance of Examples 1-3 are higher than those of Comparative Examples 1-2. This is because Examples 1-3 added ethylene-octene copolymer, which can significantly improve the flexibility of linear low-density polyethylene, making the material less prone to cracking under conditions such as low-temperature bending, thereby improving toughness. In contrast, Comparative Example 1 replaced linear low-density polyethylene with ordinary polyethylene, resulting in increased material rigidity and decreased toughness. Moreover, the ordinary polyethylene in Comparative Example 1 has worse heat resistance stability than linear low-density polyethylene, and its heat resistance is not as good as that of Examples 1-3. Comparative Example 2 lacks ethylene-octene copolymer, resulting in poor matrix toughness, which makes both of them prone to deformation and cracking in low-temperature bending tests, and significantly reduces both toughness and heat resistance.

[0036] In comparison, the heat tracing cable of Example 1 has the best overall performance, therefore Example 1 is preferred.

[0037] Examples 4-7 Examples 4-7 are based on the preparation method of Example 1, but the mass ratio of the antioxidant being a mixture of hindered phenolic antioxidant and phosphite antioxidant is adjusted, as shown in Table 2.

[0038] The heat tracing tapes prepared in Examples 4-7 were subjected to the following performance tests, and the test results are shown in Table 2.

[0039] Table 2. Mass ratios and performance test results of the compound formulations of hindered phenolic antioxidants and phosphite antioxidants in Examples 1 and 4-7.

[0040] Referring to Table 2, a comparison of Examples 4-7 and Example 1 shows that both insufficient and excessive amounts of phosphite antioxidants can lead to a decrease in the aging resistance of the heat tracing cable. This is because when phosphite is insufficient, hydroperoxides cannot be effectively decomposed, and the oxidation reaction will continue to accelerate through branching reactions. At this time, although hindered phenols can capture free radicals, they cannot block the branching growth of the oxidation chain, resulting in a decrease in overall aging resistance. When phosphite is excessive, the excess phosphite will compete with hindered phenols to capture free radicals, making it difficult for hindered phenols to fully exert their effects, resulting in a decrease in overall aging resistance.

[0041] Examples 8-9 Examples 8-9 are based on the preparation method of Example 1, with adjustments made to the weight proportions of carbon black-carbon fiber composite conductive powder, as shown in Table 3.

[0042] The heat tracing tapes prepared in Examples 8-9 were subjected to the following performance tests, and the test results are shown in Table 3.

[0043] The performance testing is as follows: Volume resistivity According to the GB / T1410—2006 standard, the core material sample of the heat tracing cable should first be cut into 100mm×10mm sections, cleaned and dried, and placed in an environment of 25℃ and 55%RH for 24 hours. Then, the sample is attached to the parallel plate electrode, and a 100V adapter voltage is applied using a high resistance meter. After stabilization, the volume resistivity is recorded. Finally, the result is calculated according to the formula ρv=Rv×A / L (A is the effective area of ​​the electrode, and L is the thickness of the sample). The same sample is measured 3 times and the average value is taken.

[0044] Table 3 Performance test results for Examples 1 and 8-9

[0045] Referring to Table 3, it can be seen from the comparison between Examples 8-9 and Example 1 that Examples 8-9 can all prepare heat tracing materials with low volume resistivity and excellent conductivity.

[0046] Examples 10-13 Examples 10-13 are based on the preparation method of Example 1, in which the mass ratio of short-cut carbon fibers to carbon black in carbon black-carbon fiber composite conductive powder is adjusted, as shown in Table 4.

[0047] The heat tracing tapes prepared in Examples 10-13 were subjected to the following performance tests, and the test results are shown in Table 4.

[0048] Table 4. Performance test of short-cut carbon fiber and carbon black in carbon black-carbon fiber composite conductive powder of Examples 1 and 10-13 by mass ratio.

[0049] Referring to Table 4, a comparison of Examples 10-13 and Example 1 shows that both insufficient and excessive carbon black addition will lead to a decrease in the conductivity of the heat tracing cable. This is because when there is excessive carbon black, it is easy for the excess carbon black to undergo secondary agglomeration, making it difficult to build a continuous macroscopic conductive skeleton with carbon fibers alone, thus causing an increase in the resistivity of the core material and reducing the conductivity of the heat tracing cable. When there is insufficient carbon black, it is difficult to accurately fill the micron-level gaps between carbon fibers, easily forming "conductive islands", which leads to a decrease in the continuity of the conductive path, resulting in a higher resistivity of the core material and reducing the conductivity of the heat tracing cable.

[0050] Example 14 Example 14 is based on the preparation method of Example 1, except that low-melting-point polyethylene is replaced with polyethylene, while the other conditions remain unchanged.

[0051] The performance of the heat tracing cable prepared in Example 14 was tested as follows, and the test results are shown in Table 5.

[0052] Table 5 Performance test results for Examples 1 and 14

[0053] Referring to Table 5, a comparison of Example 1 and Example 14 shows that Example 1 has higher conductivity stability and toughness than Example 14. This is because low-melting-point polyethylene can melt and coat carbon black and carbon fibers at low temperatures, avoiding damage to conductive components or agglomeration caused by high temperatures. In addition, low-melting-point polyethylene, linear low-density polyethylene, and ethylene-octene copolymer all belong to polyolefins, which have excellent compatibility. When blended, the interfacial repulsion is weak, which can effectively reduce interfacial defects and improve the bending resistance of the composite material. At the same time, low-melting-point polyethylene has good fluidity after melting, and the flexible layer formed by cooling can fix the position of conductive components and buffer stress, thus taking into account both conductivity stability and toughness.

[0054] Examples 15-16 Example 15 is based on the preparation method of Example 1. In S1, 26g of reduced graphene oxide and low-melting-point polyethylene are heated together at 60°C and stirred at 800rpm for 30min, and then the temperature is raised to 90°C. All other conditions remain unchanged.

[0055] Example 16 is based on the preparation method of Example 15, except that the reduced graphene oxide is replaced with carbon nanotubes, while the other conditions remain unchanged.

[0056] The heat tracing tapes prepared in Examples 15-16 were subjected to the following performance tests, and the test results are shown in Table 6.

[0057] Table 6 Performance Test Tables for Examples 1 and 15-16

[0058] Referring to Table 6, a comparison of Examples 1 and 15-16 shows that Examples 15-16 exhibit higher conductivity and toughness than Example 1. This is because both reduced graphene oxide and carbon nanotubes effectively reduce the volume resistivity of the composite conductive powder, thereby improving conductivity. The reduced graphene oxide sheets and carbon nanotubes also act as "nano-reinforcements," tightly bonding with low-melting-point polyethylene during dispersion, reducing the shedding of carbon black and carbon fibers, and slightly improving the material's bending resistance, thus preventing conductivity failure due to mechanical damage.

[0059] In comparison, the heat tracing cable of Example 15 has better overall performance, therefore Example 15 is preferred.

[0060] Example 17 Example 17 is based on the preparation method of Example 15. In S1, 26g of reduced graphene oxide, glyceryl stearate and low-melting-point polyethylene are stirred together at 60°C for 800rpm for 30min and then heated to 90°C. All other conditions remain unchanged.

[0061] The performance of the heat tracing tape prepared in Example 17 was tested as follows, and the test results are shown in Table 7.

[0062] The performance testing is as follows: PTC Strength Test The test first involves cutting a core material sample of the heat tracing cable into 100mm × 10mm sections and measuring and recording the volume resistivity (R1) at room temperature (23℃). Then, the sample is placed in a constant temperature oil bath / oven and heated from room temperature to 150℃ or until the resistivity stabilizes at a rate of 5℃ / min. The resistivity is recorded every 10℃ increase. Finally, the maximum resistivity (R2) near the Curie point is taken, and the ratio of R2 to R1 is calculated. This ratio is the PTC intensity, which is used to quantify the sensitivity and stability of the heat tracing cable's high-temperature resistance.

[0063] Table 7 Performance Test Tables for Examples 15 and 17

[0064] Referring to Table 7, comparing Examples 15 and 17, it can be seen that the conductivity and PTC strength of Example 17 are higher than those of Example 15. This is because glyceryl stearate is added to the carbon black-carbon fiber composite conductive powder. Glyceryl stearate can melt before low-melting-point polyethylene, and break the agglomeration of reduced graphene oxide through its lipophilic groups, dispersing it into a thin-layer structure, avoiding "conductive blind zones", ensuring a stable reduction in volume resistivity, and thus improving conductivity. In addition, glyceryl stearate can also act as a flow aid in the molten system formed by mixing carbon black-carbon fiber composite conductive powder and low-melting-point polyethylene to improve its processing performance, thereby making the three-level conductive network of "carbon fiber-carbon black-reduced graphene oxide" more continuous and stabilizing the resistance change amplitude of the PTC effect.

[0065] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A tracing tape, characterized in that, It includes an outer insulation layer, a shielding layer, an inner insulation layer, and a conductive core strip. The conductive core strip includes two parallel conductive busbars and a PTC composite material covering the outside of the conductive busbars. The PTC composite material includes the following components in parts by weight: 180-220 parts of carbon black-carbon fiber composite conductive powder, 600-700 parts of linear low-density polyethylene, 50-100 parts of ethylene-octene copolymer, 2-4 parts of antioxidant, and 1-3 parts of ultraviolet absorber.

2. The heat tracing cable according to claim 1, characterized in that: The antioxidant is a compound of hindered phenolic antioxidant and phosphite antioxidant, and the mass ratio of the two is 1:(0.8-1.2).

3. The heat tracing cable according to claim 1, characterized in that: The carbon black-carbon fiber composite conductive powder comprises, by weight: 50-60 parts carbon black, 8-12 parts carbon fiber, and 32-38 parts binder.

4. The heat tracing cable according to claim 3, characterized in that: The short-cut carbon fibers in the carbon black-carbon fiber composite conductive powder are compounded with carbon black at a mass ratio of 1:(5-6.25).

5. The heat tracing cable according to claim 3, characterized in that: The adhesive is low-melting-point polyethylene.

6. The heat tracing cable according to claim 5, characterized in that: The carbon black-carbon fiber composite conductive powder also includes conductive additives, which include at least one of reduced graphene oxide and carbon nanotubes.

7. The heat tracing cable according to claim 6, characterized in that: The conductive additive is reduced graphene oxide.

8. The heat tracing cable according to claim 7, characterized in that: The carbon black-carbon fiber composite conductive powder also includes glyceryl stearate.

9. The method for preparing the tracing tape according to any one of claims 1-8, characterized in that, Includes the following steps: S1. Mix the low-melting-point polyethylene, glyceryl stearate, reduced graphene oxide, carbon black and chopped carbon fibers in the specified amounts, and then pulverize them to obtain carbon black-carbon fiber composite conductive powder. S2. The carbon black-carbon fiber composite conductive powder, linear low-density polyethylene, ethylene-octene copolymer, antioxidant, and ultraviolet absorber in the specified amounts are mixed and then granulated to obtain PTC composite material. S3. The PTC conductive composite material particles are melt-extruded and coated onto two parallel conductive busbars, and then cross-linked by irradiation to obtain a conductive core strip; S4. An inner insulation layer, a shielding layer, and an outer insulation layer are sequentially wrapped around the surface of the conductive core strip to obtain a heat tracing cable.

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