Cold-resistant self-heating cable and method for manufacturing the same

Abstract

This invention discloses a cold-resistant self-heating cable and its preparation method, belonging to the field of functional special cable technology. The cable, from the inside out, comprises parallel conductive cores, a heating core layer, an electrical insulation layer, an electromagnetic shielding layer, and a cold-resistant outer sheath layer. The heating core layer contains a core-shell phase change material, which consists of a phase change core material composed of a eutectic organic compound, a low-modulus elastic silicone rubber encapsulation layer surrounding the core material, and an outermost brittle conductive shell. This invention utilizes the temperature response stress of the phase change core material to drive the splitting (high resistance) or bonding (low resistance) of the cracked conductive network in the brittle conductive shell, thus achieving a synergistic effect of micro-mechanical switching. This results in a macroscopically rapid, precise, and high-switching-ratio self-limiting temperature function. Simultaneously, supplemented by a heat-conducting network and a secondary conductive network, it exhibits excellent cold-start performance, thermal uniformity, cycle stability, and cold resistance, making it particularly suitable for pipeline antifreeze and insulation in cold regions.

Description

Technical Field

[0001] This invention relates to the field of functional special cable technology, and in particular to a cold-resistant self-heating cable and its preparation method. Background Technology

[0002] In low-temperature winter environments, freeze protection and insulation of open-air pipelines for oil, gas, and water transportation are crucial to ensuring the safety of energy transmission and the normal operation of public facilities. Traditional solutions mainly rely on external heat tracing systems, such as constant-power electric heat tracing tape, self-regulating temperature (PTC) heat tracing tape, and heating cables that rely on external thermostats.

[0003] Constant power electric heating tape has a simple structure, but its output power is constant, and it heats continuously once powered on. It must be used in conjunction with a temperature sensor and an external controller to achieve temperature control. This system has the risks of high energy consumption, temperature control lag, and potential for localized overheating or even accidents if the temperature controller malfunctions.

[0004] Currently, self-regulating temperature (PTC) heating tapes are more widely used. Their core heating material is typically a composite of conductive filler (such as carbon black) and crystalline polymer (such as polyethylene). Their working principle is based on the positive temperature coefficient (PTC) effect of polymers: at low temperatures, the polymer crystallizes, the conductive particles are in close contact, resulting in low resistance and high heating power; as the temperature rises, the polymer lattice melts and expands, forcing the conductive particles to separate, causing a sharp increase in resistance, thus automatically limiting the heating power. However, this type of PTC material has inherent drawbacks: 1) Limited on / off ratio and response accuracy: Its resistance change depends on the thermal expansion of the polymer, and the on / off ratio (high temperature / low temperature resistance ratio) is typically only around 10. 1 -10 2 The magnitude of the current means that residual current and heat remain even when the circuit is off, resulting in a wide temperature control range and low precision.

[0005] 2) Slow response speed and thermal inertia overshoot: The melting and expansion of polymer is a relatively slow heat transfer and deformation process, which leads to a lag in temperature response and is prone to temperature overshoot.

[0006] 3) Poor long-term stability: The conductive filler tends to migrate and agglomerate in the polymer matrix, and the polymer is prone to aging under repeated thermal cycling, which leads to PTC characteristic drift or even failure, resulting in limited cycle life.

[0007] 4) The contradiction between high thermal conductivity requirements and insulation safety: In order to quickly and evenly dissipate heat from the wire core, the thermal conductivity of the material needs to be improved. However, adding thermally conductive fillers (such as ceramic powder) may interfere with the conductive network and affect the PTC characteristics; if added in excess, it may also damage the electrical insulation strength.

[0008] Therefore, there is an urgent need for a self-heating cable technology that can achieve a higher switching ratio, faster response speed, more precise temperature control, longer cycle life, and take into account both efficient thermal management and safe insulation. Summary of the Invention

[0009] This invention aims to overcome the shortcomings of existing technologies and provide a cold-resistant self-heating cable and its preparation method. The core of this cable lies in its heating core layer containing a smart core-shell phase change material. This material can undergo a cracking-closing physical state transition of the surface conductive shell near a precisely set phase change point (such as 0℃, 5℃, etc.) caused by a sudden change in the volume of the phase change core material. This results in a sudden change in the resistivity of the entire heating core layer of at least three orders of magnitude, realizing the on / off of the heating function or a sudden increase or decrease in heating power.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: (a) Overall structure of the cable: The cold-resistant self-heating cable of the present invention is a multi-layer co-extruded flat or circular structure, which consists of the following components from the center outwards: Two parallel metal conductive wire cores: usually tin-plated copper stranded wire or multi-strand copper wire, providing current carrying channels and part of the Joule heating. The parallel arrangement is conducive to generating a uniform planar thermal field.

[0011] Heating core layer: Tightly wrapping two conductive wire cores, this is the core layer for realizing the intelligent temperature control function of this invention. Its composition is described in detail below.

[0012] Electrical insulation layer: Covering the heating core layer, it is made of polymer materials that are resistant to high and low temperatures and have high insulation strength, such as cross-linked polyethylene (XLPE) and silicone rubber, to ensure safe use.

[0013] Electromagnetic shielding layer: usually a braided or wrapped layer of metal wire (tin-plated copper wire, silver-plated copper wire), used to shield the electromagnetic field generated by the cable itself, prevent interference with other equipment, and also serve as a safety ground.

[0014] Cold-resistant outer sheath: The outermost protective layer, made of low-temperature resistant, aging-resistant, and wear-resistant elastomer materials, such as cold-resistant polyvinyl chloride (PVC), thermoplastic polyurethane (TPU), chlorosulfonated polyethylene (CSPE), etc., to provide mechanical protection and environmental protection.

[0015] (II) The precise composition and functional mechanism of the heating core layer: The heating core layer is the essence of the technical solution of this invention, and its components and functions are shown in Table 1 below: Table 1. Explanation of the formula and function of the heating core layer

[0016] Detailed Explanation of the Three-Layer Structure of Core-Shell Phase Change Materials: This material consists of microscopic spheres with a diameter of 15μm-60μm, divided into three distinct layers from the inside out: 1. Phase change core material (core, trigger source): Composition: An anhydrous organic eutectic compound (eutectic principle) is prepared by compounding low-temperature dilution components and phase change main components in a mass ratio of (3-4):(6-7).

[0017] Low-temperature dilution component: selected from low-melting-point, low-viscosity organic compounds such as n-octanol, ethyl decanoate, and methyl hexanoate. Its function is to lower the freezing point of the mixture and adjust the phase transition temperature.

[0018] The main phase change component is selected from organic compounds with high phase change enthalpy such as decanol, lauryl alcohol, and lauric acid. Its role is to provide significant latent heat of phase change and the volume change required during solid-liquid transition.

[0019] Performance requirements (all three must be met simultaneously): The freezing point is adjustable: it can be precisely set within the range of 5℃ to 20℃ (e.g., 0℃, 5℃, 10℃). High volume change rate: The volume expansion rate during phase change (melting) needs to be greater than 5%, preferably 7%-15%, to provide sufficient mechanical driving force; High resistance switching ratio: When the solid state is heated from 20°C below the phase transition point to 20°C above the phase transition point, its own volume resistivity needs to increase by at least 1000 times; this ensures that the phase transition of the core material itself can cause a huge change in intrinsic resistance, laying the foundation for the macroscopic resistance change.

[0020] 2. Polymer encapsulation layer (elastic intermediary, stress amplifier): Composition and structure: An elastic silicone rubber layer wrapped around the phase change core material.

[0021] Key parameters: Thickness: 10%-25% of the solid diameter of the core material. This thickness range has been optimized: too thin and it is prone to breakage; too thick and rigidity increases, weakening stress transmission. Modulus: Young's modulus below 50 MPa, preferably below 10 MPa. It must possess high elasticity (elongation at break > 300%) and low modulus. Core functions: Sealing: Prevents leakage of liquid core material; Stress transmission and amplification: The tiny volume expansion of the core material is transformed into a large, outward bulging deformation. Due to its extremely low modulus and the extremely high modulus of the brittle outer shell, this deformation generates highly localized tensile stress at the interface, which is the key to triggering brittle shell cracking.

[0022] 3. Response conductive shell (brittle switch, actuator layer): Composition: A composite coating consisting of conductive fillers, brittle binders and brittle reinforcing agents.

[0023] Conductive filler: Flake-shaped nano silver powder (0.5μm-3μm in diameter) provides high conductivity.

[0024] Brittle adhesives: thermosetting phenolic resins or high cross-linking density epoxy resins, which form a hard and brittle continuous phase after curing.

[0025] Brittleness enhancer: Rigid nanoparticles with a particle size of 0.05μm-1μm (such as fumed SiO2, nano Al2O3) further improve the brittleness of the coating and prevent cracking.

[0026] Key parameters: Thickness: 0.3μm-1.5μm. Too thin and it will be discontinuous; too thick and it will be difficult to crack and expensive.

[0027] Mechanical properties: Elongation at break after curing <3%, Young's modulus >3.5 GPa. This ensures that it undergoes brittle fracture rather than plastic deformation under the stress transmitted by the encapsulation layer.

[0028] Core functions: It remains intact at low temperatures, providing the main conductive path; when the temperature exceeds the phase transition point, it undergoes brittle cracking under concentrated stress, forming an insulating crack network that causes a sharp increase in resistance.

[0029] Working principle of the heating core layer (synergistic effect of micro-switches): In low temperature environments (T < T) p T p (phase transition point) The phase change core material is solid and small in size → the polymer encapsulation layer is in a relaxed state → the brittle response conductive shell is intact (or the cracks that appeared earlier have closed under contraction force) → current can smoothly pass through the continuous silver network of the brittle shell, the secondary network constructed by the auxiliary conductive agent, and the contacting core-shell particles → the heating core layer as a whole exhibits a low resistance state (R). on High heat generation power (P) after power-on on ∝V 2 / R on ).

[0030] When the ambient temperature rises above the phase transition point (T > T), p ): The phase change core material melts into a liquid state, and its volume expands (ΔV > 5%) → the soft polymer encapsulation layer is stretched outward, undergoing large deformation → due to the increase in the modulus of the encapsulation layer (E... encap Approximately 10 MPa) is far lower than the brittle shell modulus (E shell>3.5 GPa), deformation concentrates at the interface, generating extremely high local tensile stress on the brittle shell → the brittle shell (fracture strain <3%) cannot withstand this stress, and instantaneous brittle cracking occurs, forming a large number of micron-nano-scale cracks → the continuous silver conductive path is physically severed → at this point, the current path mainly relies on: ① a liquid core material with extremely poor conductivity (resistivity has increased by more than 1000 times), ② some incompletely fractured silver layer, ③ an auxiliary conductive agent network. The overall resistance jumps sharply to a high level (R off ), and R off >>R on (usually >10) 3 (times), heating power drops sharply (P) off ∝V 2 / R off ).

[0031] When the temperature drops below the phase transition point again (T < T), p ): The process is completely reversible. Core material solidifies and shrinks → encapsulation layer elastically retracts → cracks in the brittle shell close tightly again under pressure, the conductive silver network recovers → resistance returns to a low value R. on .

[0032] Thus, by synchronously opening and closing countless micro-temperature relays (core-shell phase change materials), the macroscopic resistance and power of the entire heating core layer are transformed, and the response temperature precisely corresponds to the solidification point / melting point of the core material.

[0033] (III) Material and process details of each structural layer: Electrical insulation layer: Cold-resistant cross-linked polyethylene (XLPE) is preferred, as it possesses excellent electrical properties (dielectric strength > 20kV / mm), heat resistance (long-term operating temperature 90℃), and low-temperature resistance (embrittlement temperature < -70℃). It is produced by extrusion followed by electron irradiation or chemical cross-linking. Silicone rubber can also be used, offering better flexibility and a wider temperature range (-60℃-200℃).

[0034] Electromagnetic shielding layer: A tin-plated copper wire braided layer with a braiding angle of 45±5° is used, with a coverage of ≥85%. This structure balances shielding effectiveness (SE>30dB), flexibility, and manufacturability. For applications with higher requirements, a combination of aluminum-plastic composite tape wrapping and copper wire braiding can be used for shielding.

[0035] Cold-resistant outer sheath: Thermoplastic polyurethane (TPU) is the preferred choice due to its superior overall performance: low-temperature resistance (no cracking at -50℃), abrasion resistance, oil resistance, weather resistance, and tear resistance. Extrusion technology is mature. Alternatively, specially formulated cold-resistant PVC (embrittlement temperature -40℃) or chlorosulfonated polyethylene (CSM) can be selected based on cost considerations.

[0036] (iv) Key steps in the preparation method: The preparation method of this invention covers the entire chain from functional material synthesis to cable forming, and the core steps are as follows: Step 1: Precise formulation of phase change core material Calculate the eutectic ratio based on the target phase transition point, and melt-blend at 60℃-80℃ for 1-2 hours under an inert atmosphere. After cooling, a homogeneous and transparent eutectic material is obtained.

[0037] Step 2: Preparation of silicone rubber phase change microcapsules (formation of encapsulation layer) In-situ emulsification-crosslinking polymerization technology was employed. A phase change core material was used as the oil phase, hydrogen-containing silicone oil as the crosslinking agent, and platinum as the catalyst; a vinyl silicone oil emulsion and deionized water were used as the aqueous phase, and polyvinyl alcohol (PVA) as the emulsifier. After high-speed shear emulsification to form an O / W emulsion, the mixture was heated to 70℃-80℃ and reacted for 4-8 hours, causing a hydrosilylation reaction on the surface of the oil droplets to form a crosslinked elastic silicone rubber shell. After washing and drying, a free-flowing microcapsule powder was obtained.

[0038] Step 3: Construction of core-shell phase change material (coating with a brittle conductive shell) A fluidized bed coating method was employed. At a temperature below the core material's solidification point (ensuring the core material remained solid and the microcapsules were robust), a prepared brittle conductive slurry (an ethanol dispersion of silver powder / phenolic resin / SiO2) was atomized and sprayed onto the surface of the fluidized microcapsules; subsequently, a stepped temperature-curing process was performed. First stage (e.g., 80℃, 30min): Solvent evaporation, resin pregelation, and formation of a certain wet strength; The second stage (e.g., 120℃, 60min): The resin initially cures and mechanical properties are formed; at this time, the temperature has exceeded the phase change point of the core material, and the core material melts and expands, but since the outer shell has been initially cured, microcracks begin to appear under expansion stress; this step is the key to pre-cracking. The third stage (e.g., 160℃, 120min): The resin is completely cured and reaches final brittleness; the crack morphology is stable; after cooling, a fully functional core-shell phase change material is obtained, whose brittle shell has a pre-installed crack network and has the characteristics of low-temperature closure and high-temperature closure. Step 4: Heating Core Layer Forming The core-shell phase change material, thermally conductive filler (h-BN), auxiliary conductive agents (CNTs), and a liquid flexible polymer matrix (such as hydrogenated nitrile butadiene rubber HNBR compound) and vulcanizing agent are thoroughly mixed in an internal mixer or open mill. The compound is then extruded onto two parallel conductive cores using a cold-feed extruder with a figure-eight or flat die. It is subsequently subjected to continuous vulcanization and shaping in a high-temperature vulcanization pipeline (e.g., 170°C) to form the cable core. This process requires precise control of temperature and shear force to avoid damaging the fragile core-shell structure.

[0039] Step 5: Multi-layer co-extrusion cabling After vulcanization, the core wire passes through different extrusion units in sequence: The first extruder extrudes XLPE insulation layers, which are then cooled and placed in the irradiation crosslinking zone.

[0040] The copper wire shielding layer is woven using a braiding machine.

[0041] The second extruder extrudes the TPU outer sheath, which is then thoroughly cooled and shaped in a long cooling water tank.

[0042] Finally, the cable is wound up to obtain the finished cable.

[0043] (V) Description of key materials, processes and their parameters: It should be further noted that the flexible polymer matrix is ​​selected from any one of silicone rubber, hydrogenated nitrile rubber, or ethylene-acrylate elastomer. These materials can maintain good elasticity and flexibility at temperatures of -50°C or even lower.

[0044] It should be further noted that the phase change core material is composed of anhydrous organic eutectic compounds with a freezing point between 5°C and 20°C. This eutectic compound is formulated by combining low-temperature dilution components (such as n-octanol, ethyl decanoate, and methyl hexanoate) and phase change bulk components (such as decanol, lauryl alcohol, and lauric acid) using the eutectic principle. By adjusting the ratio, its freezing point (i.e., phase change point) can be precisely set at the target antifreeze warning temperature, such as 0°C or 5°C. Importantly, when the temperature of the phase change core material rises from 20°C below its phase change point to 20°C above its phase change point, its volume resistivity increases by at least 1000 times, mainly due to its phase change from a solid state (relatively good conductivity) to a liquid state (extremely poor conductivity).

[0045] It should be further noted that the polymer encapsulation layer is made of low-modulus, high-elasticity silicone rubber, with a thickness of 10%-25% of the total solid diameter of the phase change core material, and a Young's modulus of less than 50 MPa, preferably less than 10 MPa. Its main function is to seal the phase change core material and amplify and transmit the volume expansion / contraction deformation of the phase change core material.

[0046] It should be further noted that the responsive conductive shell comprises the following components by weight percentage: 65%-78% conductive filler: The conductive filler is flake-shaped nano silver powder (flake diameter 0.5-3μm, thickness <100nm). 18%-30% of brittle binder: The brittle binder is a thermosetting phenolic resin or a high crosslinking density epoxy resin; 4%-12% of brittleness reinforcing agent: The brittleness reinforcing agent is a rigid nanoparticle with a particle size of 0.05μm-1μm. The brittleness reinforcing agent is selected from fumed silica, nano alumina or nano silicon carbide. This shell is prone to cracking under the concentrated stress transmitted by the polymer encapsulation layer.

[0047] In some preferred embodiments of the present invention, the thermally conductive reinforcing filler is flake boron nitride or modified alumina, used to improve the lateral thermal conductivity of the heating core layer, so that heat can be transferred more evenly to the cable periphery.

[0048] In some preferred embodiments of the present invention, the auxiliary conductive agent is carbon nanotubes or graphene nanosheets, used to construct a secondary conductive network in a flexible polymer matrix, improve the conductivity of the matrix itself, and ensure that the heating core layer has a sufficiently low initial resistance when the conductive shell is closed.

[0049] It should be noted that the preparation method of the aforementioned cold-resistant self-heating cable, particularly the key preparation processes of the core-shell phase change material and the heating core layer, includes the following steps: (1) Preparation of shell slurry: The conductive filler, brittle binder and brittle reinforcing agent are mixed to prepare shell slurry; (2) Preparation of silicone rubber phase change microcapsules: Vinyl silicone oil emulsion was used as the aqueous phase of silicone rubber precursor and phase change core material was used as the oil phase, and in-situ emulsification polymerization was carried out to generate the microcapsules. (3) Preparation of core-shell phase change material: By fluidized bed coating method, at a temperature below the solidification point of the phase change core material, the shell slurry obtained in (1) is coated on the surface of the silicone rubber phase change microcapsule powder obtained in (2), and then the temperature is increased in stages for curing. After cooling to room temperature, the core-shell phase change material is obtained. At this time, the core-shell phase change material obtained by heating deformation cracks, and the surface responsive conductive shell has formed a crack network conductive structure. The resistivity at temperatures above and below the phase change point can be used to detect whether the structure has been formed. (4) Heating core layer forming: The core-shell phase change material, thermally conductive filler, auxiliary conductive agent and liquid flexible polymer matrix are mixed to obtain composite slurry; the composite slurry is extruded onto the conductive wire core and vulcanized to form cable core wire; (5) Cable making: The core wire is sequentially covered with an electrical insulation layer, an electromagnetic shielding layer and a cold-resistant outer sheath layer. This process is a conventional process and will not be described in detail (the materials of each layer and the extrusion process are described in detail in the instruction manual).

[0050] Preferably, the stepped temperature curing in (3) includes the following steps: first, heat preservation at 75℃-85℃ for 20-40 minutes, then heat preservation at 115℃-125℃ for 40-70 minutes, and finally heat preservation at 155℃-170℃ for 80-150 minutes.

[0051] Preferably, the preparation process of the silicone rubber phase change microcapsules is as follows: ①Oil phase preparation: Mix 100g of phase change core material, 5g-15g of hydrogen-containing silicone oil (crosslinking agent, H content 0.1%-0.2%), and 0.1g-0.2g of platinum catalyst (isopropanol solution of chloroplatinic acid with Pt content of 500ppm); ② Aqueous phase preparation: Mix 400g of deionized water and 5g-10g of emulsifier (such as PVA1788), then add 20g-60g of vinyl silicone oil emulsion (solid content 50%, average particle size 0.5μm, as the base polymer for the encapsulation layer), and perform high-speed shear pre-emulsification. ③ Emulsification: Slowly add the oil phase to the aqueous phase under high-speed stirring (8000rpm-12000rpm) and emulsify for 20-40 minutes to form a stable oil / water (O / W) emulsion. The target droplet size is 1.1-1.3 times the required capsule size (considering polymerization shrinkage). ④ Polymerization / Crosslinking: The emulsion is transferred to a reaction vessel and stirred for 4-8 hours under nitrogen protection at 60℃-80℃. Hydrogen-containing silicone oil and vinyl silicone oil undergo hydrosilylation reaction under the action of platinum catalyst, and crosslinking and curing on the surface of oil droplets to form an elastic silicone rubber shell. ⑤ Post-processing: After the reaction is complete, cool, filter, wash with hot water and ethanol 2-3 times to remove the emulsifier, and vacuum dry at 40℃-50℃ to constant weight to obtain white free-flowing silicone rubber phase change microcapsule powder with a particle size D. 50 The range is 15μm-60μm.

[0052] (vi) Cable Applications: This invention further provides the application of the aforementioned cold-resistant self-heating cable in winter freeze protection and insulation of oil, gas, or water pipelines in cold regions. Its key technical features are as follows: 1) Precise temperature control and sudden power change: By designing a phase change core material with a specific freezing point and a brittle response conductive shell, rapid and significant changes (switching or sudden changes) in heating power are achieved near the set temperature point (such as 0℃), resulting in high temperature control accuracy and significant energy-saving effect.

[0053] 2) High reliability: The volume change of phase change materials is a physical process with a rapid and reversible response. The cracking / closing of the brittle shell is a mechanical behavior that does not depend on the chemical aging of the material, resulting in good long-term cycling stability.

[0054] 3) Excellent cold resistance: Low-temperature resistant elastomers are used as flexible polymer matrix and outer sheath to ensure that the cable does not become brittle in extremely cold environments and remains flexible.

[0055] 4) Self-sensing and self-adaptation: The cable itself integrates temperature sensing (phase change) and actuation (resistance change) functions, eliminating the need for complex external temperature control circuits and simplifying the system structure.

[0056] 5) The preparation process is feasible: the microcapsule preparation, fluidized bed coating, cable extrusion and other processes involved are all improvements and combinations of existing technologies, which are easy to achieve large-scale production.

[0057] Compared with the prior art, the beneficial effects of the present invention are: 1. The temperature sensing and switching functions of this invention do not rely on the slow thermal expansion of traditional PTC materials, but rather on the phase change core material at a set temperature point (T). p This is triggered by a rapid and drastic volume change (ΔV > 5%). The mechanical driving force is amplified through the low-modulus elastic encapsulation layer, ultimately leading to the physical fracture of the brittle conductive outer shell. This mechanical switching mechanism can switch the conductive path from the low resistance (R) of the metal-level layer... on Instantly switches to a near-insulating high resistance (R) off It achieves an ultra-high and precise resistance switching ratio, resulting in high temperature control accuracy and significant energy-saving effect.

[0058] 2. In this invention, the phase transition process (solid-liquid transition) of the core-shell phase change material is rapid, and the stress generated by the volume change is transmitted to the brittle shell and causes cracking in a near-instantaneous mechanical response process. This bypasses the slow overall thermal expansion of the polymer, which is dependent on traditional PTCs, resulting in a fast response speed, no thermal inertia overshoot, and excellent dynamic performance. This makes the cable highly responsive to changes in ambient temperature, allowing for rapid adjustment of the heating state and effectively avoiding temperature overshoot caused by thermal inertia, thus improving the stability and safety of system control.

[0059] 3. The entire temperature control function of this invention is based on a reversible physical process—phase change (solid-liquid) and brittle cracking (opening-closing). The phase change material itself is chemically stable and its volume change is reversible; the opening and closing of the brittle shell is a purely mechanical behavior, without involving material aging or degradation or the migration of conductive fillers. Each functional layer is firmly encapsulated in the polymer matrix, thus exhibiting excellent cycle stability and long-term reliability. After 1000 severe temperature cycles, the core switching performance of the cable exhibits minimal attenuation (<10%), far superior to traditional PTC materials (>40% attenuation), indicating a longer service life and lower maintenance costs.

[0060] 4. This invention creatively separates the conductive and thermal conduction paths. The conductive path is primarily supported by a brittle conductive shell and an auxiliary conductive network, and is controlled by a mechanical switch. The thermal conduction path is constructed using independently added sheet-like thermally conductive filler (such as h-BN), specifically designed to rapidly and uniformly conduct the Joule heat generated by the conductor along the radial direction to the outer sheath and the pipe to be heated. This unique thermal-electrical-mechanical decoupling design achieves a perfect balance between efficient thermal management and safe insulation. After adding the thermally conductive filler, the radial temperature difference of the cable decreases from ≥25℃ to ≤5℃, effectively preventing localized overheating of the conductor, protecting the insulation layer, and significantly improving long-term operational safety. Furthermore, the heat distribution is uniform, expanding the effective heating area and improving heat tracing efficiency. The addition or removal of the thermally conductive filler has almost no impact on the switching ratio, enabling independent optimization of thermal management and electrical control functions, solving the problem of mutual constraints between the two in traditional PTC materials.

[0061] 5. This invention constructs a three-dimensional secondary conductive network within a flexible polymer matrix by adding a small amount of auxiliary conductive agents such as carbon nanotubes and graphene. Without this network, at low temperatures, relying solely on core-shell particle contact results in high initial resistance, slow startup, or even failure. This invention ensures that even with poor contact among individual core-shell particles in the low-temperature switch-closed state, the overall initial resistance (R0) remains sufficiently low. on This ensures that heating can start quickly and reliably in extremely cold environments, adapting to extreme conditions.

[0062] 6. This invention, through a unique core-shell phase change material design and multi-layered synergistic structure, integrates temperature sensing (phase change), signal conversion (volume change → mechanical stress), and actuation (resistance change) functions into a complete self-feedback system within the cable itself. It eliminates the need for complex external temperature control circuits and sensors, simplifying system design, reducing installation and maintenance costs, and improving system robustness. Furthermore, the involved microencapsulation, fluidized bed coating, and cable co-extrusion processes are innovative combinations and optimizations of existing mature technologies. In particular, the stepped temperature curing process pre-installs a crack network during curing, ensuring the reliability and consistency of the final product's performance and possessing the potential for large-scale production. Detailed Implementation

[0063] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0064] I. Examples of Preparation and Comparative Preparation of Phase Change Core Materials and Core-Shell Phase Change Materials All preparations were carried out under nitrogen protection to avoid the effects of oxidation and moisture. Performance testing methods are as follows: Phase transition temperature (T) pPhase transition enthalpy (ΔH): Differential scanning calorimeter (DSC), heating / cooling rate 5℃ / min.

[0065] Volume change rate (ΔV): Measured by a density meter for solids (T) p -20℃) and liquid (T p The density was calculated at +20℃.

[0066] Resistance switching ratio (core material): Measured using a high-resistivity meter to measure the volume resistivity (ρ) of the solid and liquid states. s , ρ l On / off ratio = ρ l / ρ s .

[0067] Core-shell material resistance switching ratio: The core-shell material is pressed into a circular sheet with a diameter of 10 mm and a thickness of 1 mm, and conductive silver paste is applied to both ends. It is then placed on a temperature control platform, and the resistance switching ratio T is measured. p -20℃ and T p Resistance at +20℃ (R) low R high On / off ratio = R high / R low .

[0068] Preparation Example 1 (PE-1). Core-shell phase change material with a phase transition point of 0℃: Phase change core material preparation: Ethyl decanoate (low-temperature diluent) and lauryl alcohol (phase change host) were melt-mixed at 70°C for 1.5 hours in a eutectic ratio of 4:6 by mass, and after cooling, a transparent liquid was obtained. Actual measured T p =0.2℃, ΔH=145J / g, ΔV=11.2%, ρ s =5.8×10 4 Ω·cm, ρ l =7.9×10 8 Ω·cm, resistance switching ratio ≈ 1.36 × 10 4 .

[0069] Preparation of silicone rubber microcapsules: Following the optimized formulation and process specified in the instructions, 100g of the above core material was used as the oil phase and mixed with 10g of hydrogen-containing silicone oil and 0.15g of platinum catalyst. The aqueous phase consisted of 450g of deionized water, 6g of PVA1788, and 40g of vinyl silicone oil emulsion. After high-speed shear emulsification (10000rpm, 30min), the mixture was reacted at 75℃ for 6 hours. After washing and drying, a white powder with a particle size D50 = 35μm was obtained.

[0070] Coating a brittle conductive shell: Prepare a slurry (75wt% flake-shaped nano-silver powder, 21wt% phenolic resin, and 4wt% ethanol dispersion of fumed SiO2). Incubate at 5°C (below T). pUnder fluidized bed conditions, the slurry was sprayed onto the surface of the microcapsules. Step curing: 80℃ / 30min→120℃ / 60min→160℃ / 120min. After cooling, the core-shell material PCM-1 was obtained.

[0071] Performance: 10,000x high-resolution optical microscopy revealed crack closure at room temperature; upon heating to 20°C, a uniform network of cracks appeared on the surface. Resistance switching ratio (R0) high / R low ) ≈ 2.1 × 10 3 .

[0072] Preparation Example 2 (PE-2). Core-shell phase change material with a phase transition point of 5℃: Phase change core material preparation: Octanol and decanol are compounded in a mass ratio of 3:7. Actual measured T p =5.1℃, ΔH=158J / g, ΔV=9.8%, ρ s =3.2×10 4 Ω·cm, ρ l =5.6×10 8 Ω·cm, resistance switching ratio ≈ 1.75 × 10 4 .

[0073] Microencapsulation and coating: Same process as PE-1, but with a different core material. The resulting core-shell material, PCM-2, has a particle size D50 of 40 μm. Performance: Resistance switching ratio ≈ 1.8 × 10⁻⁶ 3 .

[0074] Compared to Preparation Example 1 (CPE-1), the core material volume change rate is insufficient. Phase change core material formulation: using lauric acid (T) alone p ≈44℃ (not the target temperature; this is for comparative formulation adjustments). Adjustment was made by adding trace amounts of solvent to achieve this temperature. p ≈5.0℃, but ΔV is only 2.1%, ΔH = 120 J / g, ρ s =1.0×10 5 Ω·cm, ρ l =3.0×10 7 Ω·cm, resistance switching ratio ≈ 3.0 × 10 2 .

[0075] Microcapsule and coating: The process is the same as for PE-1, yielding material CPCM-1. Performance: Due to insufficient core material expansion driving force, the brittle shell exhibits sparse cracks. The resistance switching ratio is only 12.

[0076] Comparative preparation example 2 (CPE-2). No brittle reinforcement, excessively tough shell: Phase change core material formulation: Same as PE-1 (T) p≈0℃). Coating paste: Contains only silver powder (80wt%) and phenolic resin (20wt%), with no fumed SiO2.

[0077] Coating and curing: The process is the same as PE-1, yielding material CPCM-2. Performance: Observation showed that the shell only underwent plastic bulging after heating, without brittle cracks. The resistance switching ratio is only 5.

[0078] Compared to preparation example 3 (CPE-3), the encapsulation layer modulus is too high. Phase change core material preparation: Same as PE-1. Microcapsule preparation: High-modulus methyl vinyl silicone rubber (modulus > 50 MPa) is used instead of low-modulus vinyl silicone oil emulsion, while other processes remain unchanged.

[0079] Coating: Same as PE-1, resulting in material CPCM-3. Performance: The high-modulus encapsulation layer cannot effectively amplify deformation and is insufficient for stress on brittle shells. Resistance switching ratio: 85.

[0080] Table 2. Performance Analysis of Core-Shell Phase Change Materials

[0081] Table 2 shows that PCM-1 with SiO2 enhances brittleness, and the high ΔV provides a strong driving force; the low-modulus encapsulation layer effectively transfers and amplifies stress; the brittle shell effectively cracks under stress. The pressure switch ratio is lower than that of composite materials due to the presence of contact resistance.

[0082] The PCM-2 has comparable performance to the PCM-1 and is suitable for different set temperatures. The core material of CPCM-1 has insufficient ΔV, low expansion stress, and only microcracks in the brittle shell, resulting in incomplete disconnection of the conductive path. CPCM-2 has high shell plasticity, and it only expands without cracking after heating. The silver conductive network remains connected, with almost no change in resistance. The CPCM-3 encapsulation layer has high rigidity and small deformation, resulting in insufficient stress transmission to the brittle shell and inadequate cracking. Analysis conclusion: Core-shell phase change materials achieve a high resistance switching ratio (>10). 3 Three conditions must be met simultaneously: 1) The core material has a high volume change rate (>5%) and a high intrinsic resistance switching ratio; 2) The encapsulation layer is a low-modulus, high-elastic material to amplify stress; 3) The conductive shell is a brittle composite layer with high modulus and low fracture strain. All three conditions must work together and none can be omitted.

[0083] II. Preparation of Cold-Resistant Self-Heating Cables: Cable Structure: The cold-resistant self-heating cable is a multi-layer co-extruded flat or circular structure, consisting of the following components from the center outwards: Two parallel conductive metal cores: typically tin-plated copper stranded wire or multi-strand copper wire, providing a current-carrying path and some Joule heating. Their parallel arrangement helps generate a uniform planar thermal field.

[0084] Heating core layer: Tightly wrapping two conductive wire cores, this is the core layer for realizing the intelligent temperature control function of this invention. Its composition is described in detail below.

[0085] Electrical insulation layer: Cold-resistant cross-linked polyethylene (XLPE) is preferred, as it possesses excellent electrical properties (dielectric strength > 20kV / mm), heat resistance (long-term operating temperature 90℃), and low-temperature resistance (embrittlement temperature < -70℃). It is produced by extrusion followed by electron irradiation or chemical cross-linking. Silicone rubber can also be used, offering better flexibility and a wider temperature range (-60℃-200℃).

[0086] Electromagnetic shielding layer: A tin-plated copper wire braided layer with a braiding angle of 45±5° is used, with a coverage of ≥85%. This structure balances shielding effectiveness (SE>30dB), flexibility, and manufacturability. For applications with higher requirements, a combination of aluminum-plastic composite tape wrapping and copper wire braiding can be used for shielding.

[0087] Cold-resistant outer sheath: Thermoplastic polyurethane (TPU) is the preferred choice due to its superior overall performance: low-temperature resistance (no cracking at -50℃), abrasion resistance, oil resistance, weather resistance, and tear resistance. Extrusion technology is mature. Alternatively, specially formulated cold-resistant PVC (embrittlement temperature -40℃) or chlorosulfonated polyethylene (CSM) can be selected based on cost considerations.

[0088] Basic formulation of the heating core layer: 100 kg of flexible polymer matrix (using hydrogenated nitrile butadiene rubber HNBR), 5 kg of core-shell phase change material (variable), 5 kg of sheet-like h-BN, 1.5 kg of multi-walled carbon nanotubes (MWCNTs), and appropriate amount of vulcanization system. The cable sample is 1 meter long, with a conductor measuring 2 × 1.5 mm. 2 Tinned copper stranded wire.

[0089] Test method: Resistance-temperature curve (RT): The cable is placed in a temperature control box, and the resistance of the heating core layer between the two conductors is measured as a function of temperature.

[0090] Switch ratio (cable): Take T p Resistance at -20℃ (R) on ) and T p Resistance at +20℃ (R) off ), calculate R off / R on .

[0091] Start-up performance: Apply the rated voltage (e.g., 220V) at -20℃ and record the stable operating temperature and the time it takes to reach it.

[0092] Cyclic stability: at T p After 1000 temperature cycles within a ±20℃ range, the on / off ratio was remeasured.

[0093] Low-temperature bending: Bend the cable 180° around a circular shaft with a diameter 10 times the outer diameter of the cable at -50°C and check for cracks in the sheath and insulation.

[0094] The cable products of Examples 1-3 and Comparative Examples 1-6 were tested under the following conditions: sample length 1m, conductor 2×1.5mm. 2 Rated voltage 220V; test performance is shown in Table 3 below: Table 3. Performance Analysis of Cold-Resistant Self-Heating Cables

[0095] Example 1. Using PCM-1 (T p (≈0℃): Heating core layer: PCM-1 addition amount is 50kg (approximately 33% of the rubber compound weight). Its RT curve shows a sharp change in resistance in the range of -5℃ to 5℃. on (-20℃) = 15.8Ω / m, R off (20℃) = 3.2 × 10 4 Ω / m, on / off ratio ≈ 2.0 × 10 3 Start-up performance (-20℃, 220V): The cable surface temperature rises to 5℃ within 120 seconds and enters a constant temperature fluctuation state (0-2℃). Cyclic stability: The switching ratio retention rate is 92% after 1000 cycles. Low-temperature bending: Passed, no cracks.

[0096] Example 2. Using PCM-2 (T p (≈5℃): Heating core layer: PCM-2 addition amount is 55kg (accounting for about 35% of the weight of the rubber compound).

[0097] Example 3. Optimized Formulation (High Thermal Conductivity): Based on Example 1, the h-BN was increased to 8 kg, and the MWCNTs were reduced to 1.0 kg. The test on / off ratio was approximately 1.8 × 10⁻⁶. 3 (Slightly decreased due to the weakening of the auxiliary network); however, under 220V power supply, the radial temperature difference of the cable (the surface of the core and the surface of the outer sheath) decreased from 12°C in Example 1 to 5°C, and the thermal uniformity was significantly improved, verifying the effect of the thermally conductive filler.

[0098] Comparative Example 1. Using CPCM-1 (core material ΔV insufficient): Heating core layer: CPCM-1 addition amount 50kg, otherwise the same as in Example 1. The test RT curve showed a gradual change. on =18.2Ω / m, Roff =245Ω / m, on / off ratio only ≈13.5. Start-up performance: After power-on, continuous heating occurs, and the surface temperature exceeds 30℃ with no self-limiting temperature trend, indicating temperature control failure. This may be due to weak micro-switch action and insufficient macro-resistance change, preventing a rapid power drop.

[0099] Comparative Example 2. Using CPCM-2 (overly tough shell): Heating core layer: CPCM-2 addition amount 50kg, otherwise the same as in Example 1. Start-up performance is similar to Comparative Example 1, but the self-limiting temperature function is extremely weak. This may be because the conductive shell does not break, the circuit always exists, and the resistance change mainly originates from the resistance change of the core material itself, resulting in an extremely low on / off ratio.

[0100] Comparative Example 3. Using CPCM-3 (high encapsulation layer modulus): Heating core layer: CPCM-3 addition amount 50kg, otherwise the same as in Example 1. on =16.8Ω / m, R off =1.6×10 3 Ω / m, on / off ratio ≈95. Start-up performance: It has some self-limiting temperature capability, but the shutdown is incomplete, and there is still considerable power at 20℃, posing a risk of overheating. This may be due to insufficient stress transfer and insufficient resistance change amplitude.

[0101] Comparative Example 4. Without auxiliary conductive agent: Heating core layer: The formula is the same as in Example 1, but MWCNTs are removed. Poor start-up performance; at -20°C, due to high initial resistance, the initial heating power is low (P=U). 2 The device ( / R) takes up to 300 seconds to heat up to 0°C, exhibiting poor cold-start performance. This is likely due to the lack of a secondary conductive network, relying on perfect contact between the core-shell particles at low temperatures, resulting in low reliability.

[0102] Comparative Example 5. No thermally conductive reinforcing filler: Heating core layer: The formula is the same as in Example 1, but h-BN is removed. The switching ratio is comparable to that in Example 1, but thermal management fails: after power-on, the core overheats locally (the measured local hot spot temperature reaches 85°C), while the outer sheath temperature is only 15°C, resulting in a huge radial temperature difference. Long-term operation carries the risk of thermal aging of the insulation layer. The reason for this may be that heat cannot be quickly dissipated laterally, verifying the crucial role of thermally conductive filler in uniform heat dissipation and avoiding hot spots.

[0103] Comparative Example 6. Traditional PTC cable: Commercially available conductive polymer PTC material (carbon black / polyethylene) is used as the heating element. The RT curve changes smoothly, with an on / off ratio of approximately 10. 2Order of magnitude; Start-up performance: slow self-limiting temperature response, with thermal inertia overshoot; poor cycle stability: the on / off ratio decays to 60% of its initial value after 1000 cycles. This indicates that traditional PTCs, based on polymer thermal expansion leading to filler network separation, have slow response, low on / off ratio, and stability greatly affected by material aging.

[0104] Based on Table 3, the summary is as follows: Example 1 uses PCM-1 core-shell phase change material, which has a complete switching mechanism and a clear response. on Low starting power; R off High, with thorough temperature control.

[0105] Example 2 uses PCM-2 core-shell phase change material, which is suitable for 5℃ insulation scenarios and has balanced performance.

[0106] Example 3 uses PCM-3 core-shell phase change material, which enhances lateral thermal conductivity, resulting in more uniform heat distribution, improved safety, and a slightly reduced on / off ratio affected by the filler.

[0107] Comparative Example 1 uses CPCM-1 core-shell phase change material. The low ΔV causes the micro-switch to malfunction, the resistance rise is small, and the temperature cannot be effectively limited, resulting in functional failure.

[0108] Comparative Example 2 uses CPCM-2 core-shell phase change material. The shell is too tough, causing it to completely lose its switching function. The resistance remains almost unchanged, making it a dangerous non-self-controlled heating element.

[0109] Comparative Example 3 uses CPCM-3 core-shell phase change material. The overly rigid encapsulation layer leads to weak switching action, insufficient resistance at high temperatures, still has a large power, poor temperature control accuracy, and poor stability.

[0110] Comparative Example 4 used PCM-1 core-shell phase change material without conductive additives, resulting in startup failure: R at low temperature on If the voltage is too high (>100Ω / m), the initial power is too low, and the temperature rise is extremely slow, proving that the auxiliary conductive network is crucial to ensuring the initial conductivity.

[0111] Comparative Example 5 used PCM-1 core-shell phase change material without thermally conductive filler, resulting in thermal safety failure: the switching function was normal, but heat could not be dissipated in time, causing localized overheating (>100℃) of the polymer matrix at the core, posing a risk of aging and breakdown. This proves that thermally conductive filler is essential for heat uniformity and long-term safety.

[0112] Comparative Example 6 uses traditional carbon black / PTC materials, which have low on / off ratio, slow response, high thermal inertia, and poor cycle stability. This contrasts sharply with the comprehensive advantages of the present invention (mechanical switch) in terms of performance, accuracy, and reliability.

[0113] Final conclusion: This invention, through a precise triple structure design of high ΔV core material, low modulus encapsulation layer, and brittle conductive shell, successfully achieves a macroscopic resistance exceeding 10 ohms near a set phase transition point. 3 The on / off ratio of the material is 10 times higher than that of PTC materials based on traditional mechanisms (Comparative Example 6) and the comparative samples with design flaws (Comparative Examples 1-3).

[0114] Comparative Examples 4-5 demonstrate that although auxiliary conductive agents and thermally conductive enhanced fillers do not directly participate in the switching action, they are key components for ensuring low-temperature start-up reliability and operational thermal safety, and neither can be omitted.

[0115] In summary, the cable of this invention achieves rapid self-starting, precise self-limiting temperature (fluctuation range <5℃), excellent cycle stability and low-temperature flexibility, fully meeting the application requirements of pipeline antifreeze and insulation in cold regions, and its overall performance is significantly better than that of existing technologies.

[0116] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A cold-resistant self-heating cable, characterized in that, From the inside out, it includes two parallel metal conductive cores, a heating core layer, an electrical insulation layer, an electromagnetic shielding layer, and a cold-resistant outer sheath layer. The heating core layer comprises the following components by weight percentage: 40%-65% flexible polymer matrix: The flexible polymer matrix is ​​a low-temperature resistant elastomer; 30%-55% core-shell phase change material: The core-shell phase change material comprises, from the inside out, a phase change core, a polymer encapsulation layer, and a responsive conductive shell; the phase change core is composed of anhydrous organic eutectic material with a freezing point between 5°C and 20°C; the polymer encapsulation layer is made of silicone rubber; the responsive conductive shell is a brittle conductive layer composed of conductive filler, brittle binder, and brittle reinforcing agent, and the elongation at break after curing is less than 3%, and the Young's modulus is greater than 3.5 GPa; 3%-8% thermally conductive reinforcing filler: The thermally conductive reinforcing filler is lamellar boron nitride or modified alumina; 0.5%-2% auxiliary conductive agent: The auxiliary conductive agent is carbon nanotubes or graphene nanosheets.

2. The cold-resistant self-heating cable according to claim 1, characterized in that, The flexible polymer matrix is ​​selected from any one of silicone rubber, hydrogenated nitrile rubber, or ethylene-acrylate elastomer.

3. The cold-resistant self-heating cable according to claim 1, characterized in that, The phase change core material exhibits a volume resistivity increase of at least 1000 times when the temperature rises from 20°C below its phase change point to 20°C above its phase change point.

4. The cold-resistant self-heating cable according to claim 1, characterized in that... The anhydrous organic eutectic compound is composed of a low-temperature diluent and a phase change host component in a mass ratio of (3-4):(6-7). The low-temperature diluent is selected from one or more of n-octanol, ethyl decanoate, and methyl hexanoate. The phase change host component is selected from one or more of decanol, lauryl alcohol, and lauric acid.

5. The cold-resistant self-heating cable according to claim 1, characterized in that, The thickness of the polymer encapsulation layer is 10%-25% of the total solid diameter of the phase change core material, and its Young's modulus is less than 50 MPa. The thickness of the responsive conductive shell is 0.3μm-1.5μm, and the elongation at break after curing is less than 3%, and the Young's modulus is greater than 3.5GPa.

6. The cold-resistant self-heating cable according to claim 1, characterized in that, The responsive conductive shell comprises the following components by weight percentage: 65%-78% conductive filler: The conductive filler is flake-shaped nano silver powder; 18%-30% of brittle binder: The brittle binder is a thermosetting phenolic resin or a high crosslinking density epoxy resin; 4%-12% of brittleness reinforcing agent: The brittleness reinforcing agent is a rigid nanoparticle with a particle size of 0.05μm-1μm, and the brittleness reinforcing agent is selected from fumed silica, nano alumina or nano silicon carbide.

7. A method for preparing a cold-resistant self-heating cable as described in any one of claims 1-6, characterized in that, Includes the following steps: (1) Preparation of shell slurry: The conductive filler, brittle binder and brittle reinforcing agent are mixed to prepare shell slurry; (2) Preparation of silicone rubber phase change microcapsules: Vinyl silicone oil emulsion was used as the aqueous phase of silicone rubber precursor and phase change core material was used as the oil phase, and in-situ emulsification polymerization was carried out to generate the microcapsules. (3) Preparation of core-shell phase change material: By fluidized bed coating method, at a temperature below the solidification point of the phase change core material, the shell slurry obtained in (1) is coated on the surface of the silicone rubber phase change microcapsule powder obtained in (2), and then the temperature is increased in stages for curing. After cooling to room temperature, the core-shell phase change material is obtained. At this time, the core-shell phase change material obtained by heating deformation cracks, and the surface responsive conductive shell has formed a crack network conductive structure. The resistivity at temperatures above and below the phase change point can be used to detect whether the structure has been formed. (4) Heating core layer forming: The core-shell phase change material, thermally conductive filler, auxiliary conductive agent and liquid flexible polymer matrix are mixed to obtain composite slurry; the composite slurry is extruded onto the conductive wire core and vulcanized to form cable core wire; (5) Cable making: The core wire is sequentially covered with an electrical insulation layer, an electromagnetic shielding layer and a cold-resistant outer sheath layer.

8. The method for preparing a cold-resistant self-heating cable according to claim 7, characterized in that, The stepwise temperature curing in (3) includes the following steps: first, keep warm at 75℃-85℃ for 20-40 minutes, then keep warm at 115-125℃ for 40-70 minutes, and finally keep warm at 155℃-170℃ for 80-150 minutes.

9. The method for preparing a cold-resistant self-heating cable according to claim 7, characterized in that, In (2), the preparation process of the silicone rubber phase change microcapsules is as follows: A1. Oil phase preparation: Mix 100g of phase change core material, 5g-15g of hydrogen-containing silicone oil, and 0.1g-0.2g of platinum catalyst; A2. Aqueous phase preparation: Mix 400g of deionized water and 5g-10g of emulsifier, then add 20g-60g of vinyl silicone oil emulsion and pre-emulsify by high-speed shearing; A3. Emulsification: Slowly add the oil phase to the aqueous phase under high-speed stirring and emulsify for 20-40 minutes to form a stable oil / water emulsion. The target droplet size is 1.1-1.3 times the desired capsule size. A4. Polymerization / Crosslinking: The emulsion is transferred to a reaction vessel and stirred for 4-8 hours under nitrogen protection at 60℃-80℃. Hydrogen-containing silicone oil and vinyl silicone oil undergo hydrosilylation reaction under the action of platinum catalyst, and crosslinking and curing are performed on the surface of oil droplets to form an elastic silicone rubber shell. A5. Post-processing: After the reaction is complete, cool, filter, wash 2-3 times with hot water and ethanol to remove the emulsifier, and vacuum dry at 40℃-50℃ to constant weight to obtain white, free-flowing silicone rubber phase change microcapsule powder with a particle size D. 50 The range is 15μm-60μm.

10. The application of the cold-resistant self-heating cable as described in any one of claims 1-6 in winter antifreeze and heat preservation of oil, gas or water pipelines in cold regions.

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