High-flame-retardant silica gel cold shrink tube

Abstract

The invention relates to the technical field of high polymer materials, and discloses a high-flame-retardant silica gel cold shrink tube which comprises the following components in parts by mass: 85-90 parts of a silica gel matrix; 5-8 parts of a phosphorus-nitrogen flame retardant; 3-5 parts of a phase change material; 1-2 parts of a toughening agent; 0.5 to 2 parts of filler; the method comprises the following steps: weighing the components according to the proportion, separately preparing, premixing and stirring, mixing and fusing, carrying out hot press molding, and naturally cooling, so as to ensure that a rubber material fully flows and complete a cross-linking reaction, thereby finally obtaining a high-flame-retardant silica gel cold shrink tube finished product with stable size and shape. By constructing a phosphorus-nitrogen synergistic flame-retardant system, introducing the phase-change filler and the flexibilizer and assisting with the fumed silica nanofiller, the flame retardance, thermal management performance, low-temperature flexibility and dimensional stability of the cold shrink tube are remarkably improved, and the problems that an existing material is embrittled, large in deformation, unstable in processing and the like are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, and particularly to a highly flame-retardant silicone cold shrinkable tube. Background Art

[0002] With the increasing demand for high-performance materials in the fields of electric power, electrical equipment, and construction, cold shrinkable tubes, as a material used for cable joints and the protection of other electrical equipment, have been widely applied. However, the existing cold shrinkable tube technology still has certain limitations in terms of flame retardancy, thermal stability, low-temperature toughness, and ultraviolet aging resistance. Especially in high-temperature environments and long-term exposure to ultraviolet light, the performance of traditional cold shrinkable tube materials is prone to degradation, resulting in dimensional changes, cracking, or aging of the cold shrinkable tubes, thereby affecting their service life and safety.

[0003] Firstly, existing cold shrinkable tubes usually use a single type of flame retardant to enhance their flame retardancy. Although such materials can meet the basic fire prevention requirements, their flame retardant effects are difficult to meet more stringent requirements under high-temperature and fire conditions. Most traditional flame retardants only carry out flame retardancy through a single gas-phase or condensed-phase effect, resulting in the easy decline of the flame retardancy of cold shrinkable tubes under long-term high-temperature exposure and being unable to effectively protect electrical equipment from fire. In addition, existing materials often lack an effective thermal management mechanism when dealing with temperature fluctuations, and problems such as dimensional instability and morphological changes caused by temperature fluctuations are still relatively prominent.

[0004] Secondly, the performance of existing cold shrinkable tubes is insufficient in low-temperature environments. Especially in cold regions or extreme environments, traditional toughening agents often cannot maintain good mechanical properties at low temperatures. Although some cold shrinkable tubes use rubber-based toughening agents to improve toughness, at extremely low temperatures, these toughening agents are prone to embrittlement, resulting in cracks or fractures in the cold shrinkable tubes and affecting their long-term use performance. Therefore, how to improve the toughness and stability of cold shrinkable tubes in low-temperature environments remains a technical problem.

[0005] Finally, the existing cold shrinkable tube materials also face challenges in ultraviolet aging. The ultraviolet resistance of traditional cold shrinkable tube materials is poor, and long-term ultraviolet irradiation easily causes cracks, aging, and even fracture on the material surface. The protection against ultraviolet light in existing technologies mainly relies on basic fillers and additives, but these methods have not effectively delayed the damage of ultraviolet light to the material, thereby limiting the service life of cold shrinkable tubes. Especially in an environment of long-term exposure to strong ultraviolet light, the aging resistance of the material has not been fully improved; therefore, the present invention proposes a highly flame-retardant silicone cold shrinkable tube to solve the deficiencies of the existing technology. Summary of the Invention

[0006] In view of the deficiencies of the prior art, the present invention provides a highly flame-retardant silicone cold-shrinkable tube. By adopting the composite technology of phosphazene flame retardants, phase change materials, toughening agents, and specific fillers, the flame retardancy, thermal stability, low-temperature toughness, and ultraviolet resistance are significantly improved, and the performance degradation problems of traditional cold-shrinkable tubes in extreme environments such as high temperature, low temperature, and ultraviolet aging are solved.

[0007] To achieve the above objectives, the present invention is realized through the following technical solutions: A highly flame-retardant silicone cold-shrinkable tube, the cold-shrinkable tube comprises the following components in parts by mass: silicone matrix: 85-90 parts; phosphazene flame retardant: 5-8 parts; phase change material: 3-5 parts; toughening agent: 1-2 parts; filler: 0.5-2 parts.

[0008] The silicone matrix is selected as room-temperature vulcanized polydimethylsiloxane, which serves as the basic framework material of the cold-shrinkable tube and has excellent flexibility, thermal stability, and electrical insulation properties.

[0009] The polydimethylsiloxane molecular chain is flexible, with a low glass transition temperature and excellent resilience, enabling the cold-shrinkable tube to have good shrinkage performance and shape recovery ability. Its silicon-oxygen main chain structure endows the material with excellent thermal stability and weather resistance, suitable for thermal aging and cold-shrinkage applications in power insulation environments. After the vulcanization reaction forms a cross-linked structure, its dimensional stability and tear resistance are improved, providing physical support for the long-term service of the cold-shrinkable tube.

[0010] The phosphazene flame retardant adopts trimethylamino vinyl acetamide dichlorophosphate, which is blended with the silicone matrix to form a synergistic flame retardant system for enhancing the flame retardancy of the cold-shrinkable tube.

[0011] During the pyrolysis process, the phosphazene flame retardant releases phosphorus- and nitrogen-containing intermediate products, forming a dense polyphosphate carbon layer on the surface of the burning material, inhibiting the escape of combustible gases, blocking heat transfer, and playing an oxygen barrier and flame retardant role. Among them, the phosphorus component promotes the carbonization reaction, and the nitrogen component participates in diluting the atmosphere in the combustion zone, synergistically exerting the gas-phase and condensed-phase flame retardant effects, thereby increasing the limiting oxygen index of the material and delaying the heat release rate.

[0012] The phase change material is selected from magnesium oxide or aluminum oxide, which is added to the system as a functional filler for regulating the thermal management performance and improving the thermal conductivity.

[0013] Both magnesium oxide and aluminum oxide have high specific heat capacity and thermal conductivity, can absorb heat when the temperature rises, play a role in buffering the heat peak and stabilizing the system temperature. Its microscopic structure can temporarily store thermal energy during the phase change process, avoiding uneven thermal expansion of the cold-shrinkable tube caused by drastic temperature changes. This thermal buffering mechanism helps to improve the thermal response stability of the cold-shrinkable tube during load operation and extend the service life of the material.

[0014] The toughening agent is a modified polyester or a block polyurethane elastomer, which forms an interpenetrating network structure with the silicone system to improve the mechanical properties and low-temperature flexibility of the material.

[0015] The soft segments in the toughening agent endow the system with better ductility and flexibility, while the hard segments enhance its rigidity and impact resistance. After physical cross-linking or partial chemical reaction with the silicone matrix, a multiphase structure is formed, significantly improving the tensile strength and elongation at break of the cold-shrinkable tube, while reducing the risk of low-temperature embrittlement. During the cable shrinkage process, the material can maintain stable resilience and mechanical compatibility, reducing the concentration of shrinkage stress.

[0016] The filler is selected from fumed silica or carbon black, and is added to the system to improve the rheological properties and surface properties of the rubber compound.

[0017] Fumed silica has a small particle size and a large specific surface area, forming a three-dimensional network structure in the matrix, improving the viscoelasticity, thixotropy and processability of the system; at the same time, it is evenly distributed in the silicone matrix, enhancing the interfacial strength and suppressing the uneven size shrinkage of the cold-shrinkable tube. Carbon black, as a conductive filler or light-shielding filler, can improve the ultraviolet resistance and aging resistance of the material, and to a certain extent, enhance the surface strength and wear resistance.

[0018] Preferably, the silicone matrix is room-temperature vulcanized polydimethylsiloxane; the phosphorus-nitrogen-based flame retardant includes trimethylamine vinylamide dichlorophosphate; the phase change material is selected from magnesium oxide and aluminum oxide.

[0019] Preferably, the toughening agent is a modified polyester or a block polyurethane elastomer.

[0020] Preferably, the filler is selected from fumed silica and carbon black.

[0021] The present invention also provides a method for preparing a highly flame-retardant silicone cold-shrinkable tube, comprising the following steps: S1. Weigh the silicone matrix, phosphorus-nitrogen-based flame retardant, phase change material, toughening agent and filler in a certain proportion, and prepare each component separately; S2. Add the phosphorus-nitrogen-based flame retardant, phase change material and filler into a high-speed dispersion device for premixing, stir for a certain time to make each component evenly dispersed; S3. Add the premixed material, silicone matrix and toughening agent into a mixing device, and carry out mixing under vacuum conditions to make each component fully fused to obtain a uniform rubber compound; S4. Inject the obtained uniform rubber compound into a mold, and adopt a hot pressing molding process to ensure that the rubber compound fully flows in the mold and completes the cross-linking reaction; S5. After demolding, naturally cool the cold-shrinkable tube to make the size and shape of the cold-shrinkable tube stable during the cooling process, and obtain the finished product of the highly flame-retardant silicone cold-shrinkable tube.

[0022] Preferably, in step S1, the silicone matrix, the phosphorus-nitrogen-based flame retardant, the phase change material, the toughening agent and the filler are weighed separately in certain proportions, and an electronic balance is used for weighing. Each component should be weighed separately and placed in a clean weighing pan or plastic container, and each component is prepared separately for subsequent mixing treatment.

[0023] Preferably, in step S2, the phosphorus-nitrogen-based flame retardant, the phase change material and the filler are added to a high-speed dispersion device, the stirring speed is set to 1500 - 2500 rpm, the stirring temperature is 30°C - 40°C, and stirring is continued for 10 - 20 minutes to achieve uniform dispersion and avoid agglomeration.

[0024] Preferably, in step S3, the uniform premix obtained in step S2, the silicone matrix and the toughening agent are added together to a twin-screw mixer for mixing; mixing is carried out under vacuum conditions, the vacuum degree is absolute pressure ≤ 0.08 MPa, the mixing temperature is controlled at 35°C - 50°C, and the mixing time is 40 - 60 minutes. After mixing, a uniform rubber compound is obtained.

[0025] Preferably, in step S4, the uniform rubber compound obtained in step S3 is injected into a pre-prepared mold and cured by a hot pressing molding process; the molding temperature is set to 160°C - 175°C, the applied pressure is 15 - 18 MPa, and the pressure holding time is 7 - 10 minutes, so that the rubber compound fully flows in the mold and completes the cross-linking reaction. After the molding process, it is cooled to room temperature to obtain a formed cold shrinkable tube.

[0026] Preferably, in step S5, after the formed cold shrinkable tube is demolded from the mold, it is placed in an environment of 20°C - 30°C for natural cooling, and the cooling time is not less than 2 hours, so that the appearance size of the cold shrinkable tube is stable and there are no bubbles or defects.

[0027] The present invention provides a highly flame-retardant silicone cold shrinkable tube. It has the following beneficial effects: 1. By introducing the phosphorus-nitrogen synergistic flame retardant trimethylaminoethyl vinylamide dichlorophosphate, the present invention constructs a composite condensed-phase flame retardant system to form a carbon layer barrier on the combustion surface. It significantly improves the flame resistance and thermal stability of the material. Different from the traditional single phosphorus-based or nitrogen-based flame retardant systems, the present invention avoids the problems of thermal decomposition instability and low flame retardancy efficiency, and overcomes the long-term performance decline caused by the migration or precipitation of the flame retardant during the combustion process.

[0028] 2. The present invention introduces magnesium oxide or aluminum oxide as a functional phase change filler in the formulation, which not only improves the thermal conductivity but also introduces a thermal buffering and regulating mechanism. The material can absorb and release heat when the load fluctuates, delaying local overheating. Compared with the inert filler system commonly used in existing silicone materials, which lacks temperature control ability, the present invention significantly improves the temperature rise control ability of the cold shrinkable tube under high-load operation and solves the problem of large deformation rate in high-temperature environments.

[0029] 3. The present invention uses modified polyester or block polyurethane as the toughening phase component, endowing the material with excellent flexibility and resilience. It can withstand multiple deformations without breaking and still maintain good mechanical properties at low temperatures. While existing silicone cold shrinkable tubes usually have problems such as low-temperature embrittlement and tensile fracture, the present invention effectively improves its deformation adaptability and broadens the environmental adaptability range of the product.

[0030] 4. The present invention adds fumed silica as a highly dispersed filler to construct a nanoscale framework structure, enhancing the structural compactness and thixotropy of the rubber compound, improving the flow performance and processing consistency. Compared with the traditional single addition of carbon black, it improves the surface uniformity and dimensional stability of the material, overcomes the problems of poor fluidity and warping of the forming corners during the molding process, and improves the product yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a flow chart of the preparation method of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0033] Please refer to the attached Figure 1 : Example 1: High flame retardancy performance optimization type Raw material ratio (parts by mass) Silicone matrix (room temperature vulcanized PDMS): 88 parts Trimethylaminoethylamide dichlorophosphate: 7 parts Magnesium oxide: 3.5 parts Modified polyester toughening agent: 1 part Fumed silica: 0.5 part Preparation process flow and parameters Premixing (S2): Stir the flame retardant, magnesium oxide and fumed silica at 1500 rpm for 15 minutes, and control the temperature at 35°C. Mixing (S3): Add the silica gel matrix and toughening agent, and mix in a twin-screw mixer, with a vacuum degree of ≤0.08MPa, a mixing temperature of 45°C, and a mixing time of 50 minutes. Hot pressing molding (S4): Inject the glue into the mold, molding temperature 170℃, pressure 16MPa, keep the pressure for 8 minutes Natural cooling (S5): After demoulding, place it in a 25℃ environment to cool for 2 hours Example 2: Enhanced flexibility and low temperature performance Raw material ratio (mass fraction) Silica gel matrix: 85 parts Flame retardant: 5 parts Alumina: 4.5 parts Block polyurethane elastomer: 2 parts Carbon black: 1.5 parts Preparation process and parameters Premixing (S2): Alumina, flame retardant and carbon black were premixed at a stirring speed of 2000 rpm, a temperature of 30°C, and a time of 10 minutes. Mixing (S3): Mixing the silicone matrix and toughening agent, the mixing temperature is 40°C, the vacuum degree is ≤0.06MPa, and the time is 60 minutes. Hot pressing molding (S4): Molding temperature is 165°C, pressure is 17MPa, and pressure is maintained for 9 minutes. Cooling (S5): Natural cooling time is extended to 3 hours, and the ambient temperature is controlled at 20°C Example 3: Type that takes both dimensional stability and molding fluidity into consideration Raw material ratio (mass fraction) Silicone matrix: 90 parts Flame retardant: 6 parts Magnesium oxide: 3 parts Modified polyester toughening agent: 1.5 parts Fumed silica: 2 parts Preparation process and parameters Premixing (S2): high-speed shearing in a dispersing device, speed 2500rpm, temperature 38°C, premixing for 20 minutes Mixing (S3): vacuum degree ≤ 0.08MPa, temperature maintained at 50°C, mixing time 45 minutes Hot pressing (S4): molding temperature 175°C, pressure 18MPa, holding time 10 minutes Cooling (S5): After demoulding, cool in a ventilated drying oven and cool naturally for 2 hours Comparative Example 1: Compared with Example 1, the difference is that no phosphorus-nitrogen flame retardant is added, and the rest is the same.

[0034] Comparative Example 2: Compared with Example 1, the difference lies in that magnesium oxide is replaced by talcum powder (a non-phase change functional filler), and the rest are the same.

[0035] Comparative Example 3: Compared with Example 1, the difference lies in that the vacuum mixing step is cancelled and direct atmospheric pressure mixing is carried out, and the rest are the same.

[0036] Comparative Example 4: Compared with Example 2, the difference lies in that the block polyurethane elastomer toughening agent is not added, and the rest are the same.

[0037] Comparative Example 5: Compared with Example 2, the difference lies in that alumina is replaced by calcium carbonate filler, and the rest are the same.

[0038] Comparative Example 6: Compared with Example 2, the difference lies in that the hot pressing temperature is reduced to 140 °C, and the rest are the same.

[0039] Comparative Example 7: Compared with Example 3, the difference lies in that fumed silica is not added, and the rest are the same.

[0040] Comparative Example 8: Compared with Example 3, the difference lies in that the dosage of the toughening agent is reduced to 0.2 parts, and the rest are the same.

[0041] Comparative Example 9: Compared with Example 3, the difference lies in that the mixing temperature is not controlled (operating at room temperature), and the rest are the same.

[0042] Test Example 1: Description of Flame Retardant Performance Comparative Test I. Test Purpose To verify the flame retardant synergistic effect of the phosphorus-nitrogen based flame retardant and the phase change filler in the cold shrinkable tube composite material, to investigate the influence of key components and key processes on the combustion behavior of the material, and to highlight the significant advantages of the technical solution of the present invention.

[0043] 1. Test Samples 2. Example 1 Comparative Example 1 (without flame retardant) Comparative Example 2 (magnesium oxide → talcum powder) Comparative Example 3 (cancelling vacuum mixing) III. Test Items and Methods Limiting Oxygen Index (LOI) Test Standard: GB / T2406.2-2009 Instrument: Oxygen Index Meter (temperature control 23 °C, relative humidity 50%) Test specifications: 100mm×10mm×4mm Flow rate setting: Adjust the O2 / N2 flow rates to the required ratios respectively, and take the average value after 3 tests Vertical burning test (UL-94) Standard: UL94 Plastic Flammability Test Standard Specimen size: 125mm×13mm×3mm Ignition time: 10 seconds×2 rounds, observe the extinguishing time and dripping situation to determine the V level Observation of char layer formation Cool the residual char layer after burning with an open flame Use a caliper to measure the char layer thickness, and record the surface cracks and structural integrity Take a photo to record the cross-section and observe the continuity and density The experimental data is shown in the following table: Table 1: Comparative test results of the flame retardant properties of Example 1 and comparative sample Sample Number LOI Value (%) UL-94 Rating Char Layer Thickness (mm) Evaluation of Char Layer Integrity Example 1 29.6 V-0 2.1 Dense, without cracks Comparative Example 1 21.3 Unqualified 0.4 Loose, fragile, with obvious cracks Comparative Example 2 24.5 V-2 1 Porous, with obvious cracks Comparative Example 3 26.1 V-1 1.4 Partially loose, with slight cracks The summary of Test Example 1 shows that the experimental results show that Example 1 performs significantly better than all comparative examples in terms of limiting oxygen index and UL-94 rating, especially in forming a dense and continuous carbonization barrier in the char layer structure. This phenomenon verifies the dual mechanisms of "condensed-phase flame retardancy" and "gas-phase interference" exerted by the selected phosphorus-nitrogen synergistic flame retardant during the pyrolysis process. The phosphorus component promotes the carbonization reaction during heating, generating a polyphosphate network that effectively covers the material surface; while the nitrogen component releases inert gases during decomposition to dilute the combustible atmosphere and delay the spread of combustion. This synergistic effect is difficult to achieve in a single-component flame retardant system, reflecting the composite innovation idea in the design of the flame retardant system of the present invention.

[0044] The introduction of magnesium oxide not only acts as a thermal conductivity filler, but also exhibits a certain phase change slow-release effect under thermal exposure conditions, making the internal heat distribution of the material tend to be uniform, thereby reducing the pyrolysis rate caused by local overheating. After replacing with talc powder in Comparative Example 2, the material lacks a thermal buffering mechanism, and the char layer thickness and structure are significantly degraded, indicating that although the phase change material is not the main flame retardant component, it plays an important regulatory role in stabilizing the pyrolysis process and optimizing the char layer forming conditions. This synergistic strengthening idea combines the material design concept of integrating structure and function.

[0045] In addition, the vacuum mixing process plays a key role in the uniform dispersion of functional components. After canceling this step in Comparative Example 3, although the sample still contains key components, their distribution is uneven and the interfacial bonding is poor, resulting in rapid local combustion spread, decreased flame retardant performance, fractures and voids in the char layer, and weakened overall stability. This verifies the strategy of emphasizing both process and formulation in the present invention: only by synergistically optimizing material design and processing control can the composite flame retardant performance of each functional component be maximized.

[0046] Test Example 2: Comparative Test Instructions for Low Temperature Flexibility and Mechanical Properties I. Test Purpose Evaluate the influence of the toughening agent and phase change functional filler used in the present invention on the mechanical properties of materials under low temperature environment, and verify the key sources of flexibility, brittleness resistance and deformation recovery force.

[0047] II. Test Samples Example 2 Comparative Example 4 (without toughening agent) Comparative Example 5 (the filler is replaced with calcium carbonate) Comparative Example 6 (low molding temperature) III. Test Items and Methods Tensile Property Test Standard: GB / T528 - 2009 Instrument: Electronic Universal Material Testing Machine Test Conditions: 23°C, tensile rate 500 mm / min Indicators: Tensile Strength (MPa), Elongation at Break (%) Low Temperature Bending Test (-30°C) Standard: GB / T2941 - 2006 The sample is refrigerated for 2 hours and then bent 180°, and observe whether there are cracks Qualified Standard: No fracture or obvious whitening occurs Rebound Elasticity Evaluation (Recovery Rate) Fold the sample in half and hold for 30 seconds, then relax and measure the rebound angle Used to judge the elastic recovery ability at low temperature The experimental data are shown in the following table: Table 2: Comparative Test Results of Low Temperature Mechanical Properties of Example 2 and Comparative Example Samples Sample Number Tensile Strength (MPa) Elongation at Break (%) Bending Result at -30°C Rebound Angle (°) Example 2 6.3 267 Without cracks 158 Comparative Example 4 4.1 123 Slightly cracked 97 Comparative Example 5 5.2 158 Obvious whitening 113 Comparative Example 6 5 144 Microcracks 101 Summary of Test Example 2 Example 2 exhibits excellent comprehensive mechanical properties under low temperature conditions, especially maintaining good flexibility and continuity in the -30°C bending test. In contrast, in Comparative Example 4, due to the absence of a toughening agent, the elongation at break of the material decreases significantly and the rebound ability weakens. Combining with the previous mechanism analysis, the soft segment in the block polyurethane elastomer provides the intermolecular activity space, and the hard segment provides the structural support, enabling the entire silica gel network to still maintain the stress diffusion ability at low temperature, thus significantly delaying the occurrence of brittle fracture. This "rigid-flexible combination" phase structure adjustment is the key to achieving the low temperature deformation resistance ability.

[0048] In addition, the thermal buffering function of the phase change filler also showed an indirect effect in the test. In Comparative Example 5, after replacing alumina with inert calcium carbonate, the material rapidly lost heat at low temperatures, with severe structural shrinkage, easily triggering microcracks and whitening phenomena. On the contrary, in Example 2, the phase change material had a heat absorption and release delay effect during ambient temperature fluctuations, effectively slowing down the concentration of thermal stress and maintaining the flexible distribution of the matrix. This further confirmed its auxiliary role in low-temperature mechanical stability.

[0049] Comparative Example 6 demonstrated the importance of process factors. Its molding temperature was too low, resulting in insufficient cross-linking of the silicone matrix, a loose network structure, weakened intermolecular forces, and ultimately manifested as a decrease in mechanical strength and poor resilience. Consistent with the "close relationship between cross-linking density and recovery performance" mentioned in the mechanism, it shows that the precise temperature control in the present invention not only concerns processing efficiency but also directly affects the performance stability and use reliability of the finished product.

[0050] Test Example Three: Comparative Test Explanation of Dimensional Stability and Processing Performance I. Test Purpose This experiment was used to evaluate the overall performance of the present invention in terms of dimensional stability, molding processing consistency, and mixing uniformity after heat treatment. It focused on verifying the mechanism of action and actual effects of the content of fumed silica and toughening agent, as well as the mixing temperature control process.

[0051] II. Test Samples Example 3 Comparative Example 7 (without adding fumed silica) Comparative Example 8 (the dosage of toughening agent is only 0.2 parts) Comparative Example 9 (mixing at room temperature, without temperature control) III. Test Items and Methods Test for Dimensional Change Rate during Thermal Aging Standard: GB / T7762 - 2020 Sample Specification: 100mm×10mm×2mm Treatment Conditions: Thermal aging at 150°C for 72 hours Measure the length change before and after, and calculate the dimensional change rate (%). Molding Flow Integrity Score Use a mold to form a test plate, observe the filling situation at the corners and the edge integrity, and score on a 5-point scale (5 is excellent, 1 is a serious defect). Detection of Mixing Uniformity Observe the filler distribution by slicing, take pictures to evaluate particle agglomeration, streaks, and color differences. Expert Group Score (5 is completely uniform, 1 is significantly uneven). The experimental data is shown in the following table: Table 3: Test Results of Dimensional and Processing Performance of Example 3 and Comparative Example Samples The summary of Test Example 3 shows that Example 3 is significantly superior to each comparative example in terms of dimensional retention after thermal aging, verifying the skeletal stabilizing function of fumed silica in the system. With its high specific surface area and surface hydroxyl activity, this component forms multiple physical bonds in the silica gel network, enhancing the adhesion between molecular chains and inhibiting the segment migration and stress relaxation induced by heat. As a result, the material still maintains good dimensional stability even after being subjected to high temperatures. In contrast, due to the lack of support from this structure, Comparative Example 7 shows significant shrinkage after heat treatment, with the edge corrugation aggravated and the deformation being irreversible.

[0052] The control of the toughener content also has an important impact on the flow balance during the compression molding process. The appropriate amount of polyester toughener in Example 3 improves the flexibility of the system, enabling the rubber compound to have better spreading property and corner coverage in the mold cavity; while in Comparative Example 8, the insufficient amount of toughener reduces the fluidity, resulting in insufficient filling at the corners and the appearance of air pockets on the mold edge. At the same time, its rigid main chain cannot effectively disperse the local stress during the compression molding process, ultimately resulting in an incomplete structure.

[0053] The mixing temperature control affects the overall uniformity of the material. In Comparative Example 9, the mixing temperature was not controlled, resulting in a decrease in the interfacial wettability between the filler and the silica gel system, leading to obvious agglomeration, color difference, and streaks, directly affecting the surface quality and mechanical consistency of the final product. The present invention promotes the activation and uniform dispersion of the filler at a moderate temperature through temperature-controlled mixing, forming a stable network structure with the silica gel matrix, reflecting the design concept that emphasizes both the formulation and the process.

[0054] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A highly flame-retardant silicone cold-shrinkable tube, characterized in that, The cold-shrinkable tube comprises the following components in parts by mass: Silicone matrix: 85 - 90 parts; Phosphorus-nitrogen based flame retardant: 5 - 8 parts; Phase change material: 3 - 5 parts; Toughening agent: 1 - 2 parts; Filler: 0.5 - 2 parts.

2. The highly flame-retardant silicone cold-shrinkable tube according to claim 1, wherein The silicone matrix is room temperature vulcanized polydimethylsiloxane; the phosphorus-nitrogen based flame retardant includes trimethylamine vinylamide dichlorophosphate; the phase change material is selected from magnesium oxide and aluminum oxide.

3. A highly flame-retardant silicone cold-shrinkable tube according to claim 1, characterized in that, The toughening agent is modified polyester or block polyurethane elastomer.

4. A highly flame-retardant silicone cold-shrinkable tube according to claim 1, characterized in that, The filler is selected from fumed silica and carbon black.

5. A preparation method of a highly flame-retardant silicone cold-shrinkable tube, which is applied to a highly flame-retardant silicone cold-shrinkable tube as described in any one of claims 1-4, characterized in that, It includes the following steps: S1. Weigh the silicone matrix, phosphorus-nitrogen based flame retardant, phase change material, toughening agent and filler in certain proportions, and prepare each component separately; S2. Add the phosphorus-nitrogen based flame retardant, phase change material and filler into a high-speed dispersion device for premixing, stir for a certain time to make each component evenly dispersed; S3. Add the premix, silicone matrix and toughening agent into a mixing device together, and carry out mixing under vacuum conditions to make each component fully fused to obtain a uniform rubber compound; S4. Inject the obtained uniform rubber compound into a mold, and adopt a hot pressing molding process to ensure that the rubber compound fully flows in the mold and completes the cross-linking reaction; S5. After demolding, naturally cool the cold-shrinkable tube to make the size and shape of the cold-shrinkable tube stable during the cooling process, and obtain the finished high-flame-retardant silicone cold-shrinkable tube.

6. The preparation method of a highly flame-retardant silicone cold-shrinkable tube according to claim 5, characterized in that, In step S1, the silicone matrix, phosphorus-nitrogen based flame retardant, phase change material, toughening agent and filler are weighed in certain proportions respectively, weighed using an electronic balance, and each component should be weighed separately and placed in a clean weighing pan or plastic container respectively, and then each component is prepared for subsequent mixing treatment.

7. The preparation method of a highly flame-retardant silicone cold-shrinkable tube according to claim 5, characterized in that, In step S2, add the phosphorus-nitrogen based flame retardant, phase change material and filler into a high-speed dispersion device, set the stirring speed to 1500 - 2500 rpm, the stirring temperature to 30℃ - 40℃, and continuously stir for 10 - 20 minutes to make it evenly dispersed and avoid agglomeration.

8. The preparation method of a highly flame-retardant silicone cold-shrinkable tube according to claim 5, characterized in that, In step S3, add the uniform premix obtained in step S2, silicone matrix and toughening agent into a twin-screw mixer for mixing; carry out mixing under vacuum conditions, the vacuum degree is absolute pressure ≤ 0.08 MPa, control the mixing temperature at 35℃ - 50℃, and the mixing time is 40 - 60 minutes. After mixing, obtain a uniform rubber compound.

9. The preparation method of a highly flame-retardant silicone cold-shrinkable tube according to claim 5, characterized in that, In step S4, inject the uniform rubber compound obtained in step S3 into a pre-prepared mold, and cure it using a hot pressing molding process; set the molding temperature to 160℃ - 175℃, apply a pressure of 15 - 18 MPa, and the pressure holding time is 7 - 10 minutes to make the rubber compound fully flow in the mold and complete the cross-linking reaction. After the molding process, cool it to room temperature to obtain the molded cold-shrinkable tube.

10. The preparation method of a highly flame-retardant silicone cold-shrinkable tube according to claim 5, characterized in that, In step S5, after demolding the molded cold-shrinkable tube from the mold, place it in an environment of 20℃ - 30℃ for natural cooling, and the cooling time is not less than 2 hours to make the appearance size of the cold-shrinkable tube stable and without bubbles or defects.

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