Low-smoke halogen-free ceramicized silicone rubber composite fire-resistant cable and preparation method thereof

Abstract

The application belongs to the technical field of cables, and discloses a low-smoke and halogen-free ceramicized silicone rubber composite fire-resistant cable and a preparation method thereof, and aims to solve the problem that the existing fire-resistant cable is prone to cracking when becoming porcelain at high temperature and cannot be self-repaired. The cable comprises, from inside to outside, a conductor, a low-smoke and halogen-free crosslinked polyethylene insulation layer, a modified microcrystalline glass fiber belt wrapping layer and a low-smoke and halogen-free ceramicized silicone rubber sheath layer. The core innovation lies in that the modified microcrystalline glass fiber is doped with components and is surface-modified, the softening and melting temperatures of the modified microcrystalline glass fiber are accurately matched with the porcelain formation and crack initiation interval of the sheath layer, the molten liquid can penetrate into the crack and eutectic with the ceramic filler at high temperature, and self-healing is achieved; and a chemical bonding interface is formed between the two, the overall structure is improved, the preparation process comprises conductor preparation, insulation layer extrusion and crosslinking, wrapping, sheath extrusion and vulcanization, and secondary vulcanization and shaping, the cable has high fire resistance, crack self-repairing function and low-smoke and halogen-free environmental protection characteristics, and has high practicability and economy.

Description

Technical Field

[0001] This invention relates to the field of cable technology, and in particular to a low-smoke, halogen-free ceramicized silicone rubber composite fire-resistant cable and its preparation method. Background Technology

[0002] Fire-resistant cables must maintain their integrity for a certain period during a fire to provide power to fire protection and emergency systems, which is crucial for ensuring the safety of people and property. Currently, fire-resistant cables on the market primarily achieve their fire-resistant function by using ceramization-grade silicone rubber as the sheath or insulation layer. When the cable is exposed to high-temperature flames, the ceramization-grade silicone rubber forms a hard insulating ceramic layer, thus preventing conductor short circuits and line interruptions.

[0003] However, existing ceramicized silicone rubber fire-resistant cables still face several core technical challenges. First, during flame burning, the ceramic layer often experiences localized cracking or even peeling due to factors such as the decomposition of organic components, sintering of inorganic fillers, and internal cable stress. These cracks and defects can lead to a decrease in the insulation performance of the ceramic layer, or even expose the conductor, resulting in a loss of fire-resistant integrity. Furthermore, current technologies typically only increase the content of ceramicized fillers or adjust the component ratio to improve the ceramicization effect and strength. However, this often sacrifices the cable's processing performance and flexibility, increases costs, and has limited effectiveness in suppressing ceramic layer cracks. Some existing technologies, such as Chinese patent CN215954894U, use glass fiber to reinforce the ceramicized silicone rubber structure. However, traditional glass fiber typically has a melting point of around 1100℃, far exceeding the ceramicization temperature, making it prone to detaching from the ceramic layer during the ceramicization process, thus affecting the integrity of the ceramic layer.

[0004] Therefore, how to effectively suppress the cracks generated by ceramicized silicone rubber under high temperature, improve the integrity and mechanical strength of the ceramic layer, and at the same time not significantly sacrifice the flexibility and processing performance of the cable is a technical problem that urgently needs to be solved in the field of fire-resistant cables. Summary of the Invention

[0005] The technical problem to be solved by this invention is that low-smoke halogen-free ceramicized silicone rubber fire-resistant cables in the prior art are prone to cracking and local peeling during the high-temperature ceramicization process. To address this, we propose a low-smoke halogen-free ceramicized silicone rubber composite fire-resistant cable and its preparation method.

[0006] To achieve the above objectives, this application adopts the following technical solution: a low-smoke halogen-free ceramicized silicone rubber composite fire-resistant cable, comprising, from the inside out, a conductor, a low-smoke halogen-free cross-linked polyethylene insulation layer, a modified microcrystalline glass fiber tape wrapping layer, and a low-smoke halogen-free ceramicized silicone rubber sheath layer; the modified microcrystalline glass fiber tape wrapping layer is a wrapping structure formed by microcrystalline glass fiber braided tape with component doping and surface modification, wherein the softening temperature of the modified microcrystalline glass fiber used in the microcrystalline glass fiber braided tape is between the pyrolysis termination temperature of the organic matrix and the ceramicization initiation temperature of the low-smoke halogen-free ceramicized silicone rubber sheath layer, and the melting temperature falls within the ceramicization temperature range and crack initiation temperature range of the low-smoke halogen-free ceramicized silicone rubber sheath layer.

[0007] This invention also provides a method for preparing a low-smoke halogen-free ceramicized silicone rubber composite fire-resistant cable, comprising the following steps: S1. Conductor preparation: oxygen-free copper wire is stranded according to a preset specification, the stranding pitch being 16-20 times the conductor diameter, and annealed after stranding to eliminate internal stress; S2. Insulation layer extrusion and cross-linking: low-smoke halogen-free cross-linked polyethylene insulation material is extruded onto the outside of the conductor using an extruder, the extrusion temperature being controlled at 160-180℃; after extrusion, it is subjected to electron beam irradiation cross-linking treatment, the cross-linking degree being controlled at 70%-80%, forming a low-smoke halogen-free cross-linked polyethylene insulation layer; S3. Modified microcrystalline glass fiber tape wrapping: microcrystalline glass fiber tape is wrapped around the outside of the low-smoke halogen-free cross-linked polyethylene insulation layer using a wrapping machine, the wrapping tension being adjusted to make the microcrystalline glass fiber tape... The glass fiber tape is tightly adhered to the outer surface of the insulation layer without looseness, wrinkles, or damage, forming a modified microcrystalline glass fiber tape wrapping layer; S4. Sheath extrusion and preliminary vulcanization: The low-smoke halogen-free ceramicized silicone rubber material is extruded onto the outside of the modified microcrystalline glass fiber tape wrapping layer using a special extruder, with the extrusion temperature controlled at 120-140℃; during the extrusion process, preliminary vulcanization is carried out simultaneously, with a vulcanization temperature of 150-160℃ and a vulcanization time of 5-10 minutes, forming a low-smoke halogen-free ceramicized silicone rubber sheath layer; S5. Secondary vulcanization and shaping: The cable after the first step is sent into a vulcanization tank for secondary vulcanization treatment, with the vulcanization temperature controlled at 170-180℃ and the vulcanization time of 15-20 minutes; after vulcanization, it is naturally cooled to room temperature to complete the shaping.

[0008] The technical effects and advantages of this invention are as follows: By adding a modified microcrystalline glass fiber tape wrapping layer between the low-smoke halogen-free cross-linked polyethylene insulation layer and the low-smoke halogen-free ceramicized silicone rubber sheath layer, under the high temperature of a fire, when the low-smoke halogen-free ceramicized silicone rubber sheath layer begins to pyrolyze and transform into ceramics, cracks easily initiate inside due to the decomposition of the organic matrix and uneven shrinkage of the inorganic fillers. The cracks lose their insulating effect, and the temperature rises rapidly. When the temperature reaches the temperature range between the termination of pyrolysis of the organic matrix and the initiation of ceramicization in the low-smoke halogen-free ceramicized silicone rubber sheath layer, the glass fibers of the modified microcrystalline glass fiber tape, after softening, can deform along with the ceramic layer and melt within the ceramicization and crack initiation range of the low-smoke halogen-free ceramicized silicone rubber sheath layer as the temperature further rises. The molten microcrystalline glass melt can rapidly penetrate the microcracks formed in the low-smoke halogen-free ceramicized silicone rubber sheath layer through capillary action, and undergo a eutectic reaction with some of the ceramic fillers in the sheath to generate a dense calcium silicate glass ceramic phase, thereby effectively sealing and self-healing the cracks, significantly improving the integrity and long-term fire resistance of the ceramicized layer. Attached Figure Description

[0009] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts:

[0010] Figure 1 This is a schematic diagram of the cable cross-section structure of the present invention; Figure 2 This is a schematic diagram of the preparation method of the present invention.

[0011] Legend: 1. Conductor; 2. Low-smoke halogen-free cross-linked polyethylene insulation layer; 3. Modified microcrystalline glass fiber tape wrapping layer; 4. Low-smoke halogen-free ceramicized silicone rubber sheath layer. Detailed Implementation

[0012] The technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. The components of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of this application, but merely represents selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application. It should be noted that similar reference numerals and letters in the following drawings indicate similar items; therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. Furthermore, in the description of this application, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0013] Example 1: As Figure 1 As shown, this invention provides a low-smoke halogen-free ceramicized silicone rubber composite fire-resistant cable, comprising, from the inside out, a conductor 1, a low-smoke halogen-free cross-linked polyethylene insulation layer 2, a modified microcrystalline glass fiber tape wrapping layer 3, and a low-smoke halogen-free ceramicized silicone rubber sheath layer 4. The conductor 1 can be made of multiple strands of oxygen-free copper wire twisted together, and its cross-sectional area can be determined according to actual application requirements. The low-smoke halogen-free cross-linked polyethylene insulation layer 2 is extruded onto the outside of the conductor 1, providing the main insulation performance.

[0014] The modified microcrystalline glass fiber tape wrapping layer 3 is one of the core features of this invention. This wrapping layer is formed from a microcrystalline glass fiber braided tape that has undergone component doping and surface modification. The wrapping method of this braided tape is overlapping wrapping, with the overlap rate controlled at 20%-30%. The wrapping tension is adjusted to ensure that the fiber tape tightly adheres to the low-smoke halogen-free cross-linked polyethylene insulation layer 2 without tensile damage. After wrapping, the tape surface is flat, forming a composite structure without interface gaps with the low-smoke halogen-free ceramicized silicone rubber sheath layer 4. This overlapping wrapping structure ensures that the glass fiber layer forms a continuous skeleton when the cable is exposed to fire, effectively supporting and reinforcing the sheath layer. The microcrystalline glass fiber braided tape is made using a plain weave process, controlling the yarn tension uniformly during weaving. The weaving density ensures the tape is continuous and without pores. The single filament diameter of the glass fiber is 10-20 μm, and the tape thickness is 0.1-0.3 mm, possessing good flexibility and wrapping adaptability to meet cable bending and processing requirements.

[0015] The modified microcrystalline glass fiber tape wrapping layer 3 is doped with the following composition: 5%–7% boron oxide, 3%–4% phosphorus pentoxide, and 2%–3% calcium oxide are added to the microcrystalline glass fiber melt spinning raw material, with the alkali metal oxide mass fraction ≤0.8%. Specifically, this embodiment uses 6% boron oxide, 3.5% phosphorus pentoxide, and 2.5% calcium oxide, with an alkali metal oxide mass fraction of 0.7%. Through this compositional doping modification, the softening temperature of the modified microcrystalline glass fiber is 580–620℃ (600℃ in this embodiment), and the melting temperature is 680–720℃ (700℃ in this embodiment).

[0016] The surface modification process of the modified microcrystalline glass fiber tape wrapping layer 3 is as follows: pretreatment with dilute hydrochloric acid, immersion in silane coupling agent hydrolysate, and curing grafting. Dilute hydrochloric acid pretreatment removes impurities from the glass fiber surface and increases surface active sites. Immersion in silane coupling agent hydrolysate is a key step. In this embodiment, a vinyl-type silane coupling agent (such as vinyltrimethoxysilane) is used. After hydrolysis, it forms active silanol groups, which, through immersion, form a monolayer or multilayer covering on the glass fiber surface. The curing grafting process allows the silane coupling agent to bond to the glass fiber surface through covalent or hydrogen bonds, while simultaneously exposing vinyl and other organic functional groups. This enhances the interfacial bonding between the glass fiber and the subsequent low-smoke halogen-free ceramicized silicone rubber sheath layer 4, preventing interfacial delamination and enabling the two to work synergistically.

[0017] A low-smoke, halogen-free ceramicized silicone rubber sheath layer 4 is wrapped around the outside of a modified microcrystalline glass fiber tape wrapping layer 3. Its components, by weight, are: 45 parts silicone rubber matrix, 35 parts inorganic ceramic filler, 12 parts halogen-free flame retardant, 1.5 parts crosslinking agent, and 2.5 parts additives. The halogen-free flame retardant is a compound of aluminum hydroxide and magnesium hydroxide; in this embodiment, the mass ratio of aluminum hydroxide to magnesium hydroxide is 2:1.

[0018] The inorganic ceramic filler is composed of a composite of the main ceramic-forming filler, fluxing filler, and reinforcing synergistic filler. The components, by weight, are as follows: 12 parts kaolin, 10 parts quartz powder, 7 parts zinc borate, and 6 parts mica powder. Kaolin and quartz powder serve as the main ceramic-forming filler, forming a stable ceramic framework at high temperatures. Zinc borate acts as a fluxing filler, melting at lower temperatures to facilitate the ceramicization reaction and fill some cracks. Mica powder acts as a reinforcing synergistic filler; its plate-like structure acts as a flame barrier and increases mechanical toughness during the ceramicization process. The total weight of all components is 35 parts.

[0019] Working principle explanation: Under the action of high temperature in a fire, the organic matrix in the low smoke halogen-free ceramicized silicone rubber sheath layer 4 begins to pyrolyze, releasing a small amount of smoke and leaving inorganic ceramic fillers to form the initial ceramic layer. As the temperature rises, especially in the ceramic forming temperature range of 700-800℃, the inorganic ceramic fillers will be further sintered and densified to form a ceramic layer with insulation and barrier functions. However, due to volume shrinkage and internal stress caused by the decomposition of organic matter, micro-cracks inevitably occur in the ceramic layer during its formation. Simultaneously, the modified microcrystalline glass fiber wrapping layer 3 in this invention is located inside the sheath layer 4. The organic matrix pyrolysis termination temperature of the low-smoke halogen-free ceramicized silicone rubber sheath layer 4 is approximately 500-600℃, and the ceramicization initiation temperature is approximately 650-700℃. The softening temperature of the modified microcrystalline glass fiber is set at 580-620℃, precisely between the organic matrix pyrolysis termination temperature and the ceramicization initiation temperature. This ensures that in the early stages of the ceramicization reaction, after the organic matter has fully decomposed, the glass fiber begins to soften, forming a certain degree of flexibility to better adapt to the deformation of the sheath layer. The melting temperature of the modified microcrystalline glass fiber is 700℃ (within the range of 680-720℃). Within the range of the low-smoke halogen-free ceramicized silicone rubber sheath layer 4, the local temperature often rises to the melting temperature of the modified microcrystalline glass fiber. At this time, the glass fiber melts rapidly into a low-viscosity molten glass liquid, which quickly penetrates and fills the cracks through capillary action. The molten glass liquid reacts chemically with silicate and other components in the ceramic layer at high temperature and solidifies after cooling to form a dense and hard glass phase filler, which effectively seals the cracks and prevents the flame and heat from spreading to the conductor. At the same time, the unmelted or partially molten glass fiber acts as an internal skeleton to continuously provide mechanical support for the ceramic layer, significantly improving its integrity and impact resistance at high temperatures.

[0020] Preparation Method Example 1: The present invention also provides a preparation method for a low-smoke halogen-free ceramicized silicone rubber composite fire-resistant cable, which is used to prepare the low-smoke halogen-free ceramicized silicone rubber composite fire-resistant cable as described in claim 1 above. The process includes the following steps: S1. Conductor preparation: oxygen-free copper wire with a specification of 2.5mm² is twisted into a multi-strand conductor bundle according to a preset twisting pitch (for example, 18 times the conductor diameter). After twisting, annealing treatment is performed to eliminate internal stress and ensure the flexibility and conductivity of the conductor.

[0021] S2. Insulation Extrusion and Crosslinking: Low-smoke halogen-free crosslinked polyethylene insulation material (e.g., density 0.92 g / cm³, melt index 1.5 g / 10 min) is extruded onto the outside of the conductor 1 using an extruder, with the extrusion temperature controlled at 170°C. After extrusion, the cable undergoes crosslinking treatment using an electron beam irradiation crosslinking device, with the crosslinking degree controlled at 75%, forming a low-smoke halogen-free crosslinked polyethylene insulation layer 2 with a thickness of 0.7 mm.

[0022] S3. Modified microcrystalline glass fiber tape wrapping: The modified microcrystalline glass fiber woven tape (monofilament diameter 15μm, tape thickness 0.2mm) described in Example 1 is wrapped around the outside of the low-smoke halogen-free cross-linked polyethylene insulation layer 2 using a wrapping machine. The wrapping method is overlapping wrapping, with the overlap rate controlled at 25%. The wrapping tension is adjusted to ensure that the fiber tape is tightly attached to the insulation layer without tensile damage. After wrapping, the tape surface is visually smooth, forming the modified microcrystalline glass fiber tape wrapping layer 3.

[0023] S4. Sheath Extrusion and Preliminary Vulcanization: The low-smoke halogen-free ceramicized silicone rubber material described in Example 1 is extruded onto the outside of the modified microcrystalline glass fiber tape wrapping layer 3 using a dedicated extruder. The extrusion temperature is controlled at 130°C. Preliminary vulcanization is carried out simultaneously during the extrusion process in a crawler-type vulcanizing furnace at a vulcanization temperature of 155°C for 8 minutes, forming a low-smoke halogen-free ceramicized silicone rubber sheath layer 4 with a thickness of 1.0 mm.

[0024] S5. Secondary Vulcanization and Shaping: The cable processed in step S4 is sent to a vulcanization tank for secondary vulcanization. The vulcanization temperature is controlled at 175℃, and the vulcanization time is 18 minutes. After vulcanization, the cable is allowed to cool naturally at room temperature to complete the shaping process and obtain the final product.

[0025] Example 2: The main difference between this example and Example 1 is the composition doping scheme of the modified microcrystalline glass fiber tape wrapping layer 3.

[0026] The modified microcrystalline glass fiber with wrapping layer 3 has the following composition doping scheme: 7%-9% boron oxide, 4%-5% phosphorus pentoxide, and 3%-4% calcium oxide are added to the microcrystalline glass fiber melt spinning raw material, with the alkali metal oxide mass fraction ≤0.9%. Specifically, this embodiment uses 8% boron oxide, 4.5% phosphorus pentoxide, and 3.5% calcium oxide, with an alkali metal oxide mass fraction of 0.8%. Through this compositional doping modification, the softening temperature of the modified microcrystalline glass fiber is 620-650℃ (635℃ in this embodiment), and the melting temperature is 720-760℃ (740℃ in this embodiment). The remaining structure and preparation process are the same as in Example 1. This formulation relatively increases the softening point and melting point of the glass fiber, making it suitable for specific ceramicized silicone rubber systems where the organic matrix pyrolysis termination temperature and ceramic formation initiation temperature are slightly higher, or where a melt repair function is desired only after the ceramic layer has formed.

[0027] Example 3: The main difference between this example and Example 1 lies in the composition doping scheme of the modified microcrystalline glass fiber tape cladding layer 3. The composition doping scheme of the modified microcrystalline glass fiber tape cladding layer 3 is as follows: 9%-10% boron oxide, 4%-5% phosphorus pentoxide, and 3%-4% calcium oxide are added to the microcrystalline glass fiber melt spinning raw material, with the mass fraction of alkali metal oxides ≤1.0%. Specifically, this example uses 9.5% boron oxide, 4.5% phosphorus pentoxide, and 3.5% calcium oxide, with a mass fraction of alkali metal oxides of 0.95%. Through this compositional modification, the softening temperature of the modified microcrystalline glass fiber is 650-680℃ (665℃ in this example), and the melting temperature is 760-790℃ (775℃ in this example). The remaining structure and preparation process are the same as in Example 1. This formulation further increases the softening point and melting point of the glass fiber, making it suitable for extreme high-temperature refractory scenarios where the glass fiber only begins to melt and repair at higher temperatures.

[0028] Example 4: The main difference between this example and Example 1 lies in the type of silane coupling agent and the composition of the low-smoke halogen-free ceramicized silicone rubber sheath layer 4. In the surface modification process of the modified microcrystalline glass fiber tape wrapping layer 3, the silane coupling agent used is a trimethoxysilane-based silane coupling agent (such as γ-methacryloyloxypropyltrimethoxysilane). The composition of the low-smoke halogen-free ceramicized silicone rubber sheath layer 4 is as follows (by weight): 40 parts silicone rubber matrix, 40 parts inorganic ceramic filler, 15 parts halogen-free flame retardant, 1 part crosslinking agent, and 3 parts additives. The mass ratio of aluminum hydroxide to magnesium hydroxide in the halogen-free flame retardant is 3:2. The composition of the inorganic ceramic filler is as follows: 15 parts kaolin, 12 parts quartz powder, 8 parts zinc borate, and 5 parts mica powder. The remaining structure and preparation process are the same as in Example 1.

[0029] This embodiment increases the proportion of inorganic ceramic fillers by adjusting the formulation of the silicone rubber sheath, aiming to achieve a stronger ceramization effect. Simultaneously, the trimethoxysilane coupling agent exhibits better hydrolytic stability and compatibility with silicone rubber, further enhancing interfacial bonding.

[0030] Comparative Example 1: The main difference between this comparative example and Example 1 is the absence of the modified microcrystalline glass fiber tape wrapping layer 3. Its structure, from the inside out, includes a conductor 1, a low-smoke halogen-free cross-linked polyethylene insulation layer 2, and a low-smoke halogen-free ceramicized silicone rubber sheath layer 4. The material formulation, thickness, and preparation process of the low-smoke halogen-free cross-linked polyethylene insulation layer 2 and the low-smoke halogen-free ceramicized silicone rubber sheath layer 4 are exactly the same as in Example 1.

[0031] Comparative Example 2: The main difference between this comparative example and Example 1 is that the modified microcrystalline glass fiber was not doped with any components, that is, ordinary glass fiber woven tape was used for wrapping.

[0032] The softening point of this ordinary glass fiber is approximately 800-840℃, and the melting point is approximately 1000-1100℃. Other structural features, material formulations, and preparation processes are the same as in Example 1.

[0033] Comparative Example 3: The main difference between this comparative example and Example 1 is that the microcrystalline glass fibers in the modified microcrystalline glass fiber tape wrapping layer were not surface modified. Its structure, material formulation, and preparation process are the same as those in Example 1, except that the glass fibers were not pretreated with dilute hydrochloric acid, soaked in silane coupling agent, and cured for grafting.

[0034] Experimental Data and Analysis: To verify the beneficial effects of the present invention, fire-resistant cables prepared in Examples 1 and 4, as well as Comparative Examples 1, 2, and 3, were subjected to fire resistance performance tests. The cable samples were suspended vertically, a rated voltage of 600V was applied, and a current was applied to bring the conductor 1 to its maximum permissible operating temperature. The cables were then subjected to flame burning with a gas torch. The time it took for the cable to experience a short circuit or open circuit was recorded, which was the fire resistance life. The test environment temperature was 23±2℃, and the relative humidity was 50±5%.

[0035] Sample number Structural features 60-minute fire resistance test results Visual observation under flame conditions Remark Example 1 Contains modified microcrystalline glass fiber cladding (softening temperature 600℃, melting temperature 700℃). No short circuit / open circuit occurred. The ceramic layer is relatively intact, with slight surface cracks and no large-area peeling. excellent Example 4 Contains modified microcrystalline glass fiber cladding (softening temperature 635℃, melting temperature 740℃). No short circuit / open circuit occurred. The ceramic layer is relatively intact, the surface is relatively flat, and there is no large-area peeling. excellent Comparative Example 1 No wrapping A short circuit occurred after 28 minutes. Localized cracking and peeling of the ceramic layer, resulting in partial exposure of the conductor. Poor Comparative Example 2 Contains ordinary glass fiber cladding (softening temperature 820℃, melting temperature 1050℃). A short circuit occurred after 45 minutes. The ceramic layer is partially cracked, the glass fiber has not melted significantly, and it provides some support. generally Comparative Example 3 Contains unmodified microcrystalline glass fiber wrapping layer A short circuit occurred after 35 minutes. The ceramic layer is cracked, the bond between the glass fiber and the ceramic layer is poor, and there is partial delamination. Poor

[0036] Results Analysis: Excellent Performance of Examples 1 and 4: Examples 1 and 4 did not experience short circuits or open circuits during the 60-minute fire resistance test, demonstrating excellent fire resistance. After flame burning, their ceramic layers maintained good integrity, with only slight surface cracking and no large-area peeling. This verifies that the modified microcrystalline glass fiber wrapping layer in this invention can effectively resist thermal shock and thermal decomposition under flame conditions, promptly seal cracks through a melt repair mechanism, and provide mechanical support, thereby significantly extending the fire resistance life of the cable.

[0037] Compared with Comparative Example 1 (without wrapping): Comparative Example 1 experienced a short circuit after 28 minutes, with its ceramic layer locally cracking and peeling off at high temperature, exposing the conductor. This result strongly demonstrates the key role of the modified microcrystalline glass fiber wrapping introduced in this invention in improving the circuit integrity of fire-resistant cables.

[0038] Compared with Comparative Example 2 (ordinary glass fiber): Although Comparative Example 2 also used a glass fiber cladding layer, the softening and melting points of its glass fibers were much higher than the ceramicization temperature and crack initiation temperature of the ceramicized silicone rubber sheath. As a result, in the early and middle stages of burning, the glass fibers failed to melt and fill the cracks in time, and their role was mainly physical support, failing to actively repair the cracks. Therefore, although its fire resistance life was better than Comparative Example 1, it was still far inferior to Examples 1 and 4. This demonstrates the importance of modifying the glass fibers through component doping to precisely match the thermal response.

[0039] Compared to Comparative Example 3 (unmodified glass fiber): Comparative Example 3 also exhibited poor fire resistance, experiencing a short circuit after 35 minutes. This is primarily due to the poor interfacial bonding between the unmodified glass fiber and the ceramicized silicone rubber sheath. At high temperatures, interfacial delamination easily occurs between the two, and stress concentration makes cracks more likely to propagate at the interface, weakening the supporting and repairing role of the glass fiber. This confirms the necessity of surface modification for ensuring the synergistic effect of the modified microcrystalline glass fiber wrapping layer and the sheath layer to achieve optimal performance.

[0040] In summary, this invention, through the ingenious design of the composition, thermal response characteristics, and surface treatment of the modified microcrystalline glass fiber wrapping layer, enables it to achieve precise synergy with the ceramicized silicone rubber sheath layer during the operation of the fire-resistant cable. It automatically melts and repairs cracks at high temperatures and provides reliable mechanical support, thereby significantly improving the fire resistance integrity and safety of the low-smoke halogen-free ceramicized silicone rubber composite fire-resistant cable.

[0041] The above are merely embodiments of this application and are not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A low-smoke, halogen-free ceramicized silicone rubber composite fire-resistant cable, characterized in that, From the inside out, it includes a conductor, a low-smoke halogen-free cross-linked polyethylene insulation layer, a modified microcrystalline glass fiber tape wrapping layer, and a low-smoke halogen-free ceramicized silicone rubber sheath layer. The modified microcrystalline glass fiber tape wrapping layer is a wrapping structure formed by microcrystalline glass fiber braided tape that has been doped and surface modified. The softening temperature of the modified microcrystalline glass fiber used in the microcrystalline glass fiber braided tape is between the pyrolysis termination temperature of the organic matrix of the low-smoke halogen-free ceramicized silicone rubber sheath layer and the ceramic initiation temperature. The melting temperature falls within the ceramic initiation temperature range and crack initiation temperature range of the low-smoke halogen-free ceramicized silicone rubber sheath layer.

2. The low-smoke, halogen-free ceramicized silicone rubber composite fire-resistant cable according to claim 1, characterized in that, The low-smoke halogen-free ceramicized silicone rubber sheath layer is composed of the following components by weight: 40-50 parts silicone rubber matrix, 30-40 parts inorganic ceramic filler, 10-15 parts halogen-free flame retardant, 1-2 parts crosslinking agent, and 1-3 parts additives; wherein the halogen-free flame retardant is a compound of aluminum hydroxide and magnesium hydroxide.

3. The low-smoke, halogen-free ceramicized silicone rubber composite fire-resistant cable according to claim 2, characterized in that, The inorganic ceramic filler is composed of a ceramic-forming main filler, a fluxing filler, and a reinforcing synergistic filler. The contents of each component by weight are as follows: 10-15 parts kaolin, 8-12 parts quartz powder, 5-8 parts zinc borate, and 3-5 parts mica powder. Among them, kaolin and quartz powder are the ceramic-forming main fillers, zinc borate is the fluxing filler, and mica powder is the reinforcing synergistic filler. The sum of the weight parts of each component is 30-40 parts.

4. The low-smoke, halogen-free ceramicized silicone rubber composite fire-resistant cable according to claim 1, characterized in that, The modified microcrystalline glass fiber with a wrapping layer has the following composition doping scheme: 5%-7% boron oxide, 3%-4% phosphorus pentoxide, and 2%-3% calcium oxide are added to the microcrystalline glass fiber melt spinning raw material, and the mass fraction of alkali metal oxides is ≤0.8%; the softening temperature of the modified microcrystalline glass fiber is 580-620℃, and the melting temperature is 680-720℃.

5. The low-smoke, halogen-free ceramicized silicone rubber composite fire-resistant cable according to claim 1, characterized in that, The modified microcrystalline glass fiber with a wrapping layer has the following composition doping scheme: 7%-9% boron oxide, 4%-5% phosphorus pentoxide, and 3%-4% calcium oxide are added to the microcrystalline glass fiber melt spinning raw material, and the mass fraction of alkali metal oxides is ≤0.9%; the softening temperature of the modified microcrystalline glass fiber is 620-650℃, and the melting temperature is 720-760℃.

6. The low-smoke, halogen-free ceramicized silicone rubber composite fire-resistant cable according to claim 1, characterized in that, The modified microcrystalline glass fiber with a wrapping layer has the following composition doping scheme: 9%-10% boron oxide, 4%-5% phosphorus pentoxide, and 3%-4% calcium oxide are added to the microcrystalline glass fiber melt spinning raw material, and the mass fraction of alkali metal oxides is ≤1.0%; the softening temperature of the modified microcrystalline glass fiber is 650-680℃, and the melting temperature is 760-790℃.

7. The low-smoke, halogen-free ceramicized silicone rubber composite fire-resistant cable according to claim 1, characterized in that, The surface modification process of the modified microcrystalline glass fiber tape wrapping layer is as follows: pretreatment with dilute hydrochloric acid, immersion in silane coupling agent hydrolysate, and curing grafting; the silane coupling agent is either vinyl-type or trimethoxysilyl-type.

8. The low-smoke, halogen-free ceramicized silicone rubber composite fire-resistant cable according to claim 1, characterized in that, The modified microcrystalline glass fiber tape with a wrapping layer is made using a plain weave process. During the weaving process, the yarn tension is controlled to be uniform, and the weaving density ensures that the tape is continuous and without pores. The single filament diameter of the tape is 10-20μm, and the tape thickness is 0.1-0.3mm, which gives it good flexibility and wrapping adaptability.

9. The low-smoke, halogen-free ceramicized silicone rubber composite fire-resistant cable according to claim 1, characterized in that, The wrapping process of the modified microcrystalline glass fiber tape wrapping layer meets the following requirements: the wrapping method is overlapping wrapping, the wrapping overlap rate is controlled at 20%-30%, the wrapping tension is adjusted to ensure that the fiber tape is tightly attached to the low smoke halogen-free cross-linked polyethylene insulation layer without tensile damage, the surface of the tape is flat after wrapping, and a composite structure without interface gaps is formed with the low smoke halogen-free ceramicized silicone rubber sheath layer.

10. A method for preparing a low-smoke, halogen-free ceramicized silicone rubber composite fire-resistant cable according to any one of claims 1-9, characterized in that, Includes the following steps: S1. Conductor Preparation: Oxygen-free copper wire is stranded according to a preset specification, with a stranding pitch of 16-20 times the conductor diameter. After stranding, it is annealed to eliminate internal stress. S2. Insulation Layer Extrusion and Crosslinking: Low-smoke halogen-free crosslinked polyethylene insulation material is extruded onto the outside of the conductor using an extruder. The extrusion temperature is controlled at 160-180℃. After extrusion, it undergoes electron beam irradiation crosslinking treatment, with the crosslinking degree controlled at 70%-80%, forming a low-smoke halogen-free crosslinked polyethylene insulation layer. S3. Modified Microcrystalline Glass Fiber Tape Wrapping: Microcrystalline glass fiber tape is wrapped around the outside of the low-smoke halogen-free crosslinked polyethylene insulation layer using a wrapping machine. The wrapping tension is adjusted to ensure that the microcrystalline glass fiber tape is tightly adhered to the outer surface of the insulation layer without loosening, wrinkling, or damage, forming a modified microcrystalline glass fiber tape wrapping layer. S4. Sheath Extrusion and Preliminary Vulcanization: The low-smoke halogen-free ceramicized silicone rubber material is extruded onto the outside of the modified microcrystalline glass fiber tape wrapping layer using a dedicated extruder. The extrusion temperature is controlled at 120-140℃. Preliminary vulcanization is carried out simultaneously during the extrusion process, with a vulcanization temperature of 150-160℃ and a vulcanization time of 5-10 minutes, forming a low-smoke halogen-free ceramicized silicone rubber sheath layer. S5. Secondary Vulcanization and Shaping: The cable after the first step is sent into a vulcanization tank for secondary vulcanization treatment. The vulcanization temperature is controlled at 170-180℃ and the vulcanization time is 15-20 minutes. After vulcanization, it is naturally cooled to room temperature to complete the shaping.

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