Fireproof coated pipe as well as preparation method and application thereof

Abstract

The invention discloses a fireproof coated pipe as well as a preparation method and application thereof, and relates to the field of organic composite materials. The fireproof coated pipe comprises a mother blank material and a liquid waterproof agent, wherein the mother blank material comprises a flame-retardant polymer matrix, coated graphite and a heat-conducting filler; the coated graphite is formed by expanded graphite and a coating layer on the surface, and the coating layer comprises a silicon source and a phosphorus source. The surface of the expanded graphite is coated with the silicon dioxide-phosphide composite material, so that the compatibility of the filler and a specific type of flame-retardant polymer matrix can be improved, the addition amount of the heat-conducting filler is reduced to ensure uniform dispersion, and synergistic multiplication of a flame-retardant function and optimization of a heat-conducting network are realized; meanwhile, a specific type of liquid waterproof agent is introduced and is extruded and blended with the master batch, so that the material is endowed with excellent waterproofness, meanwhile, the compatibility with other core properties is ensured, the waterproof coated pipe material with efficient heat conduction, flame retardance, waterproofness and mechanical strength is provided, and the application field is expanded.

Description

Technical Field

[0001] This invention relates to the field of organic composite materials, and more particularly to a fireproof coated pipe, its preparation method, and its application. Background Technology

[0002] With the rapid development of industries such as power, communications, and energy, the requirements for the safety protection of critical lines such as cables and optical fibers are becoming increasingly stringent. When these lines operate under complex conditions, they not only generate heat due to current loads but also pose potential risks of short circuits, overloads, or fires caused by external ignition sources. Therefore, developing a multifunctional sheathing material that can simultaneously achieve efficient heat dissipation, active fire prevention, physical protection, and environmental isolation has become an important research direction in the field of cable protection.

[0003] Currently, most common cable sheathing materials use ordinary flame-retardant polymers, such as flame-retardant polyvinyl chloride (PVC), flame-retardant polyethylene (PE), or flame-retardant polyolefins. These materials mainly achieve basic fire resistance by adding traditional flame retardants such as halogen-antimony compounds or metal hydroxides. However, these materials have significant limitations. First, their thermal conductivity is generally poor, which is not conducive to the timely dissipation of internal heat during cable operation, easily leading to heat accumulation, accelerating material aging, and creating safety hazards. Second, traditional flame-retardant systems often struggle to balance flame-retardant efficiency, environmental friendliness, and smoke suppression. For example, halogen-based flame retardants produce toxic and corrosive gases when burning.

[0004] To improve heat dissipation, current technologies employ methods to prepare thermally conductive polymers by adding high thermal conductivity fillers such as aluminum nitride, silicon carbide, and carbon fibers. However, simply combining thermal conductivity and flame retardancy presents significant challenges. On one hand, most high thermal conductivity fillers, such as metal oxides and nitrides, do not inherently possess flame retardancy. On the other hand, poor interfacial compatibility between the filler and the polymer matrix can lead to uneven dispersion, affecting not only the stability of thermal conductivity and flame retardancy but also severely compromising the material's mechanical strength and environmental resistance, such as water resistance. Summary of the Invention

[0005] This invention provides a fireproof coated pipe, its preparation method, and its application. By constructing a silica-phosphide composite coating layer on the surface of expanded graphite, the compatibility between the filler and the polymer matrix is ​​improved, giving the material high mechanical strength and waterproof performance, and effectively improving flame retardancy and thermal conductivity.

[0006] To address the aforementioned technical problems, one objective of this invention is to provide a fireproof coated pipe, comprising a preform and a liquid waterproofing agent, wherein the liquid waterproofing agent accounts for 0.5%-3% of the mass fraction of the preform; the preform comprises a flame-retardant polymer matrix, coated graphite, and thermally conductive filler in a mass ratio of (50-80):(15-30):(5-20); the flame-retardant polymer matrix comprises at least one of flame-retardant polybutylene terephthalate, flame-retardant nylon 6, and flame-retardant nylon 66; The preparation method of the coated graphite includes the following steps: dispersing expanded graphite in a solvent, adding a silicon source solution and a phosphorus source solution dropwise under heating and stirring conditions, and after the reaction is completed, separating, washing and drying to prepare coated graphite, wherein the mass ratio of expanded graphite to coated graphite is 100:(103-108). The liquid waterproofing agent includes at least one of the following: polydimethylsiloxane waterproofing agent, amino-modified silane waterproofing agent, perfluoroalkyl ethyl acrylate waterproofing agent, fluorine-modified siloxane waterproofing agent, epoxy-modified polyurethane waterproofing agent, and acrylate-modified silane waterproofing agent.

[0007] This application overcomes the limitations of traditional cable sheathing materials, which suffer from poor synergy between thermal conductivity and flame retardancy, and have limited functionality, by constructing a multifunctional integrated process of "core-shell structure design - step-by-step compounding - precision molding". First, by constructing a silica-phosphide composite coating layer on the surface of expandable graphite, not only is the compatibility between the filler and the polymer matrix improved, but the synergistic multiplication of flame retardant function and optimization of the thermal conductivity network are also achieved. Second, by compounding this functionalized graphite with high-modulus fillers in a flame-retardant polymer matrix, a highly efficient integrated network of "thermal conductivity - flame retardancy - reinforcement" is constructed. At the same time, by introducing a specific type of liquid waterproofing agent and extruding and blending it with the master preform, excellent waterproofing is imparted to the material while ensuring compatibility with other core properties.

[0008] In some embodiments, the expanded graphite has a mesh size of 500-1500.

[0009] The expanded graphite in this application undergoes high-temperature treatment, which expands its interlayer structure, resulting in a loose, porous network structure. This gives the expanded graphite a higher specific surface area and adsorption capacity, as well as good flexibility and compressibility. It can be used as a filler in a flame-retardant matrix to improve waterproof performance. Controlling the mesh size of the expanded graphite within the aforementioned range avoids excessively large or small particle sizes in the prepared coated graphite. Excessively large particle sizes will lead to a decrease in the waterproof performance of the coated tube after filling, while excessively small particle sizes will easily cause agglomeration, affecting its dispersibility in the flame-retardant matrix and consequently impacting the overall waterproof, flame-retardant, and thermal conductivity properties.

[0010] In some embodiments, the solvent in the method for preparing coated graphite includes at least one of water, methanol, and ethanol.

[0011] In some embodiments, the solvent in the method for preparing the coated graphite comprises ethanol and water in a volume ratio of (1-3):(1-2).

[0012] In some embodiments, in the method for preparing the coated graphite, the solid-liquid ratio of the expanded graphite and the solvent is 1:(10-25), with units of g / mL.

[0013] In some embodiments, the heating temperature in the method for preparing the coated graphite is 50-80 ℃.

[0014] In some embodiments, the stirring rate in the method for preparing the coated graphite is 300-600 rpm.

[0015] In some embodiments, the reaction time in the method for preparing the coated graphite is 3-6 h.

[0016] In some embodiments, the molar ratio of silicon source in the silicon-containing solution to phosphorus source in the phosphorus-containing solution is (1-3):1.

[0017] In some embodiments, the silicon source in the silicon source solution is at least one selected from tetraethyl orthosilicate, methyl orthosilicate, methyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, and sodium silicate.

[0018] In some embodiments, the mass fraction of silicon source in the silicon source solution is 15%-20%.

[0019] In some embodiments, the silicon-containing source solution further includes an organic solvent, wherein the organic solvent is ethanol.

[0020] In some embodiments, the phosphorus source in the phosphorus source solution is at least one of phytic acid, ammonium dihydrogen phosphate, triphenyl phosphate, ammonium polyphosphate, and aluminum phosphate.

[0021] In some embodiments, the mass fraction of the phosphorus source in the phosphorus source solution is 5%-15%.

[0022] In some embodiments, the phosphorus source solution also includes water.

[0023] In some embodiments, the particle size of the thermally conductive filler is 1-30 μm.

[0024] In some embodiments, the particle size of the thermally conductive filler is 1-20 μm.

[0025] In some embodiments, the thermally conductive filler includes at least one selected from aluminum nitride, boron nitride, aluminum oxide, silicon carbide, diamond powder, magnesium oxide, and zinc oxide.

[0026] In some embodiments, the liquid waterproofing agent has an ion content of ≤500 ppm.

[0027] In some embodiments, the preparation method of the master preform includes the following steps: adding the flame-retardant polymer matrix, coated graphite and thermally conductive filler into a twin-screw extruder, and after melt plasticizing, blending and dispersing, underwater pelletizing to prepare the master preform.

[0028] In some embodiments, in the method for preparing the master preform, the processing temperature of the twin-screw extruder is 180-260 ℃, the screw speed is 200-500 rpm, and the screw element assembly of the twin-screw extruder includes a high-shear kneading block and a toothed mixing disc to ensure efficient dispersion of the filler.

[0029] In some embodiments, the preform comprises a flame-retardant polymer matrix, coated graphite, and thermally conductive filler in a mass ratio of (60-70):(20-25):(10-15).

[0030] In some embodiments, the mass ratio of expanded graphite to coated graphite is 100:(104-106).

[0031] This application controls the mass ratio of expanded graphite to coated graphite within the above-mentioned preferred range, thereby controlling the particle size of the coated graphite to improve its compatibility with the flame-retardant polymer matrix. At the same time, it also ensures that the coated graphite has high flame-retardant and thermal conductivity properties, which can be combined with thermally conductive fillers to improve the flame-retardant and thermal conductivity of the coated tube.

[0032] In some embodiments, the molar ratio of silicon source in the silicon-containing solution to phosphorus source in the phosphorus-containing solution is (1.5-2.5):1.

[0033] This application controls the molar ratio between silicon and phosphorus sources in the coating layer of coated graphite within the above-mentioned preferred range. This ratio can effectively improve the interfacial compatibility with the polymer matrix through siloxane bonds, and promote the formation of a dense carbon layer during combustion by utilizing the phosphorus-silicon synergistic effect, thereby minimizing the impact on the intrinsic thermal conductivity path of graphite while ensuring flame retardant efficiency.

[0034] In some embodiments, both the silicon-containing source solution and the phosphorus-containing source solution include a solvent, wherein the solvent is at least one of water, methanol, and ethanol.

[0035] To address the aforementioned technical problems, a second objective of this invention is to provide a method for preparing a fire-resistant coated pipe, comprising the following steps: (1) The preform and liquid waterproofing agent are added together to a single-screw extruder for extrusion blending to obtain a functionalized composite melt; (2) The functionalized composite melt is extruded and cooled by an extrusion device equipped with an internal pressure sizing pipe mold, a vacuum sizing sleeve and a cooling device to prepare a fireproof coated pipe.

[0036] This application pre-extrudes a flame-retardant polymer matrix, coated graphite, and thermally conductive filler to prepare a master blank. Then, the master blank is melt-extruded with a liquid waterproofing agent for a second time. This avoids the liquid waterproofing agent affecting the dispersion and interface control of the filler during the high-temperature melt extrusion process. This can give the coated tube material excellent waterproofness while ensuring compatibility with other core properties, and ensure that the coated tube has excellent mechanical strength, flame retardancy, and thermal conductivity.

[0037] In some embodiments, in step (1), the extrusion blending temperature is 150-190 °C and the screw speed is 100-300 rpm.

[0038] In some embodiments, in step (2), the extrusion molding process temperature is 160-250 ℃, the vacuum degree is -0.04 to -0.08 MPa, and the traction ratio is 1.02-1.10.

[0039] In some embodiments, in step (2), the wall thickness of the fireproof covering tube is 1-4 mm.

[0040] To address the aforementioned technical problems, a third objective of this invention is to provide an application of fire-resistant sheathing tubing in the field of cable sheathing.

[0041] Compared with the prior art, the present invention has the following beneficial effects: 1. This application utilizes a core-shell structure heterogeneous modification method to coat the surface of expanded graphite with a silica-phosphide composite material, which can improve the compatibility between the filler and the flame-retardant polymer matrix, reduce the amount of thermally conductive filler added to ensure uniform dispersion, and achieve synergistic enhancement of flame-retardant function and optimization of thermal conductivity network. At the same time, by introducing a specific type of liquid waterproofing agent and extruding and blending it with the master preform, the material is endowed with excellent waterproofness while ensuring compatibility with other core properties. This overcomes the limitations of traditional cable sheathing materials, which have difficulty in synergizing thermal conductivity and flame retardancy and have a single function, and constructs a highly efficient integrated waterproof sheathing pipe material that combines thermal conductivity, flame retardancy and reinforcement.

[0042] 2. The fireproof coated tube prepared in the embodiments of this application has excellent thermal conductivity, fire safety, waterproof protection and mechanical strength. This excellent comprehensive performance does not come from the simple superposition of single components, but is achieved by constructing a three-dimensional functional network with "core-shell structure functionalized graphite" as the core, forming a synergistic enhancement effect with thermally conductive filler, and achieving the synergistic effect through the "step extrusion" process to precisely control the distribution of each functional phase and the interface bonding. Attached Figure Description

[0043] Figure 1 This is a schematic flowchart of a method for preparing a fireproof coated pipe according to Embodiment 1 of the present invention. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0046] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0047] As used in this article: In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0048] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0049] In the description of this invention, it should be understood that the terms "upper", "lower", "left", "right", "top", "bottom", etc., indicating orientation or positional relationship are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0050] To further illustrate the present invention, the following detailed description is provided in conjunction with embodiments, but these should not be construed as limiting the scope of protection of the present invention. Table 1 below shows the sources of the raw materials used in the embodiments and comparative examples of this application. Unless otherwise specified, all raw materials used are commercially available, and the same raw materials were used in parallel experiments.

[0051] Table 1 - Sources and types of raw materials used in the embodiments and comparative examples of this application Example 1 A method for preparing a fireproof coated pipe, such as Figure 1 As shown, it includes the following steps: (1) Expanded graphite (EG, which is obtained by instantaneous expansion of natural flake graphite at a high temperature of about 1000 °C) with a mesh size of 1000 mesh was dispersed in a mixed solvent, which included ethanol and deionized water with a volume ratio of 1:1 and a solid-liquid ratio of 1:20, in g / mL. The mixture was continuously stirred mechanically at 60 °C and 500 rpm. Then, tetraethyl orthosilicate solution and phytic acid solution were added dropwise to modify the surface heterogeneous shell. The reaction time was 4 h. After the reaction was completed, the solid and liquid were separated by filtration and washed with 50% ethanol aqueous solution until the filtrate was neutral. The filtrate was dried in a vacuum drying oven at 100 °C for 2 h to obtain coated graphite. The molar ratio of tetraethyl orthosilicate to phytic acid is 1.5:1, the mass ratio of expanded graphite to coated graphite is 100:105, the tetraethyl orthosilicate solution includes 15% tetraethyl orthosilicate by mass and the remainder is ethanol, and the phytic acid solution includes 10% phytic acid by mass and the remainder is deionized water. (2) Flame-retardant polybutylene terephthalate (PBT), coated graphite, and flake aluminum nitride were mixed in a mass ratio of 65:22:13. The particle size of the flake aluminum nitride was 10 μm. The mixture was fed into a co-rotating twin-screw extruder. The extruder processing temperature was set to 250 ℃ and the screw speed was 450 rpm. After melt plasticizing, blending, and dispersion, the mixture was granulated underwater to prepare the master preform. (3) The master preform and liquid waterproofing agent are fed together into a single-screw extruder for secondary extrusion blending. The liquid waterproofing agent is an amino-modified silane, and the liquid waterproofing agent accounts for 1.5% of the mass fraction of the master preform. The processing temperature is controlled at 180 ℃ and the screw speed is 200 rpm to obtain a functionalized composite melt. (4) The functionalized composite melt is extruded and cooled by an extruder equipped with an internal pressure sizing pipe mold, a vacuum sizing sleeve and a cooling water tank. The extruder temperature is set to 240 ℃, the vacuum sizing pressure is -0.07 MPa, the cooling water tank is used for staged cooling, and the traction ratio is 1.05. A fireproof coated pipe with a wall thickness of 2.5 mm is prepared.

[0052] Example 2 A method for preparing a fireproof coated pipe includes the following steps: (1) 1000 mesh expanded graphite (EG) was dispersed in a mixed solvent, which included ethanol and deionized water in a volume ratio of 3:2 and a solid-liquid ratio of 1:15, in g / mL. The mixture was continuously stirred mechanically at 60 °C and 400 rpm. Then, γ-glycidyl etheroxypropyltrimethoxysilane solution and ammonium dihydrogen phosphate solution were added dropwise for surface heterogeneous shell modification. The reaction time was 5 h. After the reaction was completed, solid-liquid separation was performed by filtration and the filtrate was washed with deionized water at 60 °C until it was neutral. The filtrate was then dried in a vacuum drying oven at 100 °C for 2 h to prepare coated graphite. The molar ratio of γ-glycidoxypropyltrimethoxysilane to ammonium dihydrogen phosphate is 2:1, the mass ratio of expanded graphite to coated graphite is 100:104, the γ-glycidoxypropyltrimethoxysilane solution includes 20% γ-glycidoxypropyltrimethoxysilane by mass and the balance being ethanol, and the ammonium dihydrogen phosphate solution includes 10% ammonium dihydrogen phosphate by mass and the balance being deionized water. (2) Flame-retardant nylon 6 (PA6), coated graphite and mixed filler are mixed in a mass ratio of 70:20:10. The mixed filler includes flake aluminum nitride and aluminum oxide in a mass ratio of 1:1. The particle size of flake aluminum nitride and aluminum oxide is 15 μm. The mixture is fed into a co-rotating twin-screw extruder. The extruder processing temperature is set to 255 ℃ and the screw speed is 350 rpm. After melting, plasticizing, blending and dispersing, the mixture is granulated underwater to prepare the master preform. (3) The master blank and liquid waterproofing agent are fed into a single screw extruder for secondary extrusion and blending. The liquid waterproofing agent is polydimethylsiloxane and the liquid waterproofing agent is 0.5% of the mass fraction of the master blank. The processing temperature is controlled at 180 ℃ and the screw speed is 200 rpm to obtain a functionalized composite melt. (4) The functionalized composite melt is extruded and cooled by an extruder equipped with an internal pressure sizing pipe mold, a vacuum sizing sleeve and a cooling water tank. The extruder temperature is set to 210 ℃, the vacuum sizing pressure is -0.05 MPa, the cooling water tank is used for staged cooling, and the traction ratio is 1.08. A fireproof coated pipe with a wall thickness of 2.5 mm is prepared.

[0053] Example 3 A method for preparing a fireproof coated pipe includes the following steps: (1) 1000 mesh expanded graphite (EG) was dispersed in a mixed solvent, which included ethanol and deionized water in a volume ratio of 2:1 and a solid-liquid ratio of 1:25 (unit: g / mL). The mixture was continuously stirred mechanically at 70 °C and 600 rpm. Then, methyltrimethoxysilane solution and ammonium polyphosphate solution were added dropwise for surface heterogeneous shell modification. The reaction time was 4 h. After the reaction was completed, the mixture was centrifuged at 5000 rpm. The precipitate was washed three times with a 50% ethanol aqueous solution and dried in a vacuum drying oven at 100 °C for 2 h to obtain coated graphite. The molar ratio of methyltrimethoxysilane to ammonium polyphosphate is 2.5:1, the mass ratio of expanded graphite to coated graphite is 100:106, the methyltrimethoxysilane solution includes 15% methyltrimethoxysilane by mass and the balance being ethanol, and the ammonium polyphosphate solution includes 10% ammonium polyphosphate by mass and the balance being deionized water. (2) Flame-retardant nylon 66 (PA66), coated graphite and boron nitride were mixed in a mass ratio of 60:25:15. The particle size of the flake boron nitride was 1 μm. The mixture was fed into a co-rotating twin-screw extruder. The extruder processing temperature was set to 260 ℃ and the screw speed was 200 rpm. After melt plasticizing, blending and dispersing, the mixture was granulated underwater to prepare the master preform. (3) The master preform and liquid waterproofing agent are fed together into a single-screw extruder for secondary extrusion blending. The liquid waterproofing agent is a fluorinated siloxane, and the liquid waterproofing agent accounts for 3% of the mass fraction of the master preform. The processing temperature is controlled at 150 ℃ and the screw speed is 300 rpm to obtain a functionalized composite melt. (4) The functionalized composite melt is extruded and cooled by an extruder equipped with an internal pressure sizing pipe mold, a vacuum sizing sleeve and a cooling water tank. The extruder temperature is set to 250 ℃, the vacuum sizing pressure is -0.08 MPa, the cooling water tank is used for staged cooling, and the traction ratio is 1.10. A fireproof coated pipe with a wall thickness of 2.5 mm is prepared.

[0054] Example 4 A method for preparing a fireproof coated tube, wherein each step and the reagents, equipment and process parameters used in each step are the same as those in Example 1, except that in step (1), the mass ratio of expanded graphite to coated graphite is 100:108.

[0055] Example 5 A method for preparing a fireproof coated tube, wherein each step and the reagents, equipment and process parameters used in each step are the same as those in Example 1, except that in step (1), the mass ratio of expanded graphite to coated graphite is 100:103.

[0056] Example 6 A method for preparing a fireproof coated tube, wherein each step and the reagents, equipment and process parameters used in each step are the same as those in Example 1, except that in step (1), the molar ratio of tetraethyl orthosilicate and phytic acid is 2:1.

[0057] Example 7 A method for preparing a fireproof coated tube, wherein each step and the reagents, equipment and process parameters used in each step are the same as those in Example 1, except that in step (1), the molar ratio of tetraethyl orthosilicate and phytic acid is 1:1.

[0058] Example 8 A method for preparing a fireproof coated tube, wherein each step and the reagents, equipment and process parameters used in each step are the same as those in Example 1, except that in step (2), the particle size of the sheet aluminum nitride is 20 μm.

[0059] Example 9 A method for preparing a fireproof coated tube, wherein each step and the reagents, equipment and process parameters used in each step are the same as those in Example 1, except that in step (2), the particle size of the sheet aluminum nitride is 30 μm.

[0060] Example 10 A method for preparing a fireproof coated tube, wherein each step and the reagents, equipment and process parameters used in each step are the same as those in Example 1, except that in step (2), the mass ratio of flame-retardant polybutylene terephthalate (PBT), coated graphite and sheet aluminum nitride is 50:30:20.

[0061] Example 11 A method for preparing a fireproof coated tube, wherein each step and the reagents, equipment and process parameters used in each step are the same as those in Example 1, except that in step (2), the mass ratio of flame-retardant polybutylene terephthalate (PBT), coated graphite and sheet aluminum nitride is 80:15:5.

[0062] Example 12 A method for preparing a fireproof coated tube, wherein each step and the reagents, equipment and process parameters used in each step are the same as those in Example 1, except that in step (2), the mass ratio of flame-retardant polybutylene terephthalate (PBT), coated graphite and flake aluminum nitride is 65:20:15.

[0063] Example 13 A method for preparing a fireproof coated tube, wherein each step and the reagents, equipment and process parameters used in each step are the same as those in Example 1, except that in step (2), the mass ratio of flame-retardant polybutylene terephthalate (PBT), coated graphite and sheet aluminum nitride is 65:25:10.

[0064] Example 14 A method for preparing a fireproof coated tube, wherein each step and the reagents, equipment and process parameters used in each step are the same as those in Example 1, except that in step (1), the expanded graphite (EG) has a mesh size of 500.

[0065] Example 15 A method for preparing a fireproof coated tube, wherein each step and the reagents, equipment and process parameters used in each step are the same as those in Example 1, except that in step (1), the expanded graphite (EG) has a mesh size of 1500.

[0066] Comparative Example 1 A method for preparing a fireproof coated tube, wherein each step and the reagents, equipment and process parameters used in each step are the same as those in Example 1, except that in step (2), the coated graphite is replaced by an equal amount of expanded graphite (EG).

[0067] Comparative Example 2 A method for preparing a fireproof coated tube, wherein each step and the reagents, equipment and process parameters used in each step are the same as those in Example 1, except that in step (2), the sheet aluminum nitride is replaced by an equal amount of flame-retardant polybutylene terephthalate (PBT).

[0068] Comparative Example 3 A method for preparing a fireproof coated tube, wherein each step and the reagents, equipment and process parameters used in each step are the same as those in Example 1, except that in step (3), the amount of liquid waterproofing agent added is 0.

[0069] Comparative Example 4 A method for preparing a fireproof coated pipe includes the following steps: (1) 1000 mesh expanded graphite (EG) was dispersed in a mixed solvent, which included ethanol and deionized water in a volume ratio of 1:1 and a solid-liquid ratio of 1:20 (unit: g / mL). The mixture was continuously stirred mechanically at 60 °C and 500 rpm. Then, tetraethyl orthosilicate solution and phytic acid solution were added dropwise for surface heterogeneous shell modification. The reaction time was 4 h. After the reaction was completed, solid-liquid separation was performed by filtration. The filtrate was washed with 50% ethanol aqueous solution until it was neutral. The filtrate was dried in a vacuum drying oven at 100 °C for 2 h to obtain coated graphite. The molar ratio of tetraethyl orthosilicate to phytic acid is 1.5:1, the mass ratio of expanded graphite to coated graphite is 100:105, the tetraethyl orthosilicate solution includes 15% tetraethyl orthosilicate by mass and the remainder is ethanol, and the phytic acid solution includes 10% phytic acid by mass and the remainder is deionized water. (2) Flame-retardant polybutylene terephthalate (PBT), coated graphite, and flake aluminum nitride were mixed in a mass ratio of 65:22:13 to obtain a premix. The particle size of the flake aluminum nitride was 10 μm. The premix and liquid waterproofing agent were fed together into a co-rotating twin-screw extruder. The liquid waterproofing agent was an amino-modified silane, and the liquid waterproofing agent accounted for 1.5% of the mass fraction of the master preform. The extruder processing temperature was set to 250 ℃, and the screw speed was 450 rpm. After melt plasticizing, blending, and dispersion, the mixture was granulated underwater to prepare a functionalized composite melt. (3) The functionalized composite melt is extruded and cooled by an extruder equipped with an internal pressure sizing pipe mold, a vacuum sizing sleeve and a cooling water tank. The extruder temperature is set to 240 ℃, the vacuum sizing pressure is -0.07 MPa, the cooling water tank is used for staged cooling, and the traction ratio is 1.05. A fireproof coated pipe with a wall thickness of 2.5 mm is prepared.

[0070] Comparative Example 5 A method for preparing a fireproof coated tube, wherein each step and the reagents, equipment and process parameters used in each step are the same as those in Example 1, except that in step (3), the liquid waterproofing agent is stearic acid.

[0071] Comparative Example 6 A method for preparing a fireproof coated tube, wherein each step and the reagents, equipment and process parameters used in each step are the same as those in Example 1, except that in step (2), flame-retardant polybutylene terephthalate (PBT) is replaced by flame-retardant acrylonitrile-butadiene-styrene copolymer (ABS) in an equal amount.

[0072] Comparative Example 7 A method for preparing a fireproof coated tube, wherein each step and the reagents, equipment and process parameters used in each step are the same as those in Example 1, except that in step (1), the mass ratio of expanded graphite to coated graphite is 100:101.

[0073] Comparative Example 8 A method for preparing a fireproof coated tube, wherein each step and the reagents, equipment and process parameters used in each step are the same as those in Example 1, except that in step (1), the mass ratio of expanded graphite to coated graphite is 100:110.

[0074] Comparative Example 9 A method for preparing a fireproof coated tube, wherein each step and the reagents, equipment and process parameters used in each step are the same as those in Example 1, except that in step (1), expanded graphite (EG) is replaced by an equal amount of graphite.

[0075] Comparative Example 10 A method for preparing a fireproof coated tube, wherein each step and the reagents, equipment and process parameters used in each step are the same as those in Example 1, except that in step (2), the coated graphite is replaced by an equal amount of sheet aluminum nitride.

[0076] Performance testing 1. Tensile property test: The fireproof coated tube samples prepared in the examples and comparative examples were cut open axially and flattened, and processed into standard dumbbell-shaped specimens (Type IB) using a CNC cutting machine. According to the People's Republic of China National Standard GB / T1040.2-2022 "Determination of tensile properties of plastics - Part 2: Test conditions for molded and extruded plastics", the tensile properties of the specimens were tested using an Instron or equivalent universal testing machine (such as model 5967, equipped with a 5 kN sensor). The test speed was 50 mm / min, and at least 5 parallel test samples were ensured for each group. The average value of the results was taken. The test results are shown in Table 2 below.

[0077] 2. Vertical Burning Test: The fireproof coated tube samples prepared in the examples and comparative examples were cut and processed into standard sheet-like specimens (125 mm × 13 mm × thickness). The vertical burning test (V method) was conducted according to the People's Republic of China National Standard GB / T 2408-2008 "Determination of Burning Performance of Plastics - Horizontal and Vertical Methods". Using a standard vertical burning tester, two 10-second flame impacts were applied to the lower end of the vertically clamped specimen using a specified acetylene flame. The flaming burning time, flameless burning time, and whether burning droplets igniting the absorbent cotton were recorded. At least five sets (five specimens per set) of parallel test samples were ensured for each group. The flame retardant rating was determined according to the standard, such as V-0, V-1, V-2, or NR. The test results are shown in Table 2 below.

[0078] 3. Thermal conductivity test: The fireproof coated tube samples prepared in the examples and comparative examples were cut and pressed into flat, smooth sheet-like specimens (recommended size: 30 mm diameter discs). According to the People's Republic of China National Standard GB / T32064-2015 "Determination of Thermal Conductivity and Thermal Resistance of Building Materials - Heat Flow Meter Method", a thermal conductivity meter (such as model TPS 2500S) was used for testing. Before testing, the specimens were placed in a specified environment to reach thermal equilibrium. At the set average temperature (25℃) and temperature difference, the heat flux density and temperature difference passing through the specimens were measured, and the thermal conductivity was calculated. At least three parallel test samples were ensured for each group, and the average value of the results was taken. The test results are shown in Table 2 below.

[0079] 4. Waterproof Protection Rating (IP Code) Test: Fireproof covered pipe samples were prepared using the examples and comparative examples. Both ends of the samples were sealed with plugs that were tightly bonded to the pipe material to form a complete protective shell. The test was conducted according to the corresponding test method for the second characteristic digit (waterproof rating) in the People's Republic of China National Standard GB 4208-2008 / IEC 60529:2001 "Degrees of Protection Provided by Enclosures (IP Code)" (such as the water spray test corresponding to IPX5 rating). Standard test equipment (such as a water spray device with a nozzle diameter of 6.3 mm) was used to spray water on the sample from all directions at a specified distance, water pressure, and time. After the test, the plugs were opened to check whether there was any water intrusion inside the shell. At least three parallel test samples were ensured for each group. The waterproof ratings from low to high were IPX0, IPX1, IPX2, IPX3, IPX4, IPX5, IPX6, IPX7, IPX8, and IPX9. The test results are shown in Table 2 below.

[0080] Table 2 - Performance test results of fireproof coated pipes in the embodiments and comparative examples of this application As shown in Table 2, Examples 1-3 of this application achieved a synergistic multiplication of flame-retardant function and optimization of the thermal conductivity network through surface heterogeneous shell modification of expandable graphite and synergistic compounding of thermally conductive fillers. Simultaneously, the introduction of a specific type of liquid waterproofing agent and its extrusion blending with the master preform imparted excellent waterproofing properties to the material while ensuring compatibility with other core properties, successfully producing a high thermal conductivity fireproof coated pipe with excellent comprehensive performance. Example 1, as the optimal solution, had all component ratios and process parameters within the preferred range, achieving the best balance between tensile strength of 92 MPa, thermal conductivity of 2.1 W / (m·K), flame retardant rating of V-0, and waterproof rating of IPX7, demonstrating the highly efficient synergistic effect among the components.

[0081] Compared to Example 1, the waterproof coating tube of Comparative Example 1 uses expanded graphite without coating modification. Since the expanded graphite surface is not coated with a silicon dioxide-phosphide composite layer, its interfacial compatibility with flame-retardant polybutylene terephthalate is reduced, resulting in uneven dispersion and affecting the overall mechanical, thermal conductivity, and flame-retardant effect of the coating tube. Furthermore, the waterproofness of the material is also reduced. This demonstrates that surface heterogeneous shell modification of expanded graphite is the basis for constructing a stable multifunctional network.

[0082] Compared to Example 1, Comparative Example 2 did not add thermally conductive filler aluminum nitride, and the thermal conductivity of the waterproof coating tube dropped sharply to 0.8 W / (m·K). Meanwhile, in Comparative Example 10, aluminum nitride was used instead of graphite coating, which led to a decrease in the thermal conductivity, tensile strength, and flame retardancy of the waterproof coating tube. Therefore, the necessity of constructing a thermally conductive network by means of multiple fillers such as graphite coating and aluminum nitride in this application is highlighted.

[0083] Compared to Example 1, Comparative Example 3 did not add any liquid waterproofing agent, and the waterproof rating of the waterproof-coated pipe was only IPX2. Meanwhile, Comparative Example 5 used stearic acid as a waterproofing agent, resulting in a lower waterproof rating for the waterproof-coated pipe. This is mainly because acidic substances may corrode high-modulus fillers, and small-molecule acids may weaken the intermolecular forces of polymers and accelerate the hydrolytic degradation of matrices such as PBT / PA. This demonstrates that acidic waterproofing agents are difficult to meet high waterproofing requirements, illustrating the crucial role of the type of liquid waterproofing agent in the long-term reliability of the coated pipe in humid environments.

[0084] Compared to Example 1, the liquid waterproofing agent in Comparative Example 4, along with the flame-retardant polymer matrix, coated graphite, and aluminum nitride, was produced using a one-step extrusion process, resulting in a comprehensive decline in all properties, especially a significant reduction in tensile strength and poor mechanical properties. This demonstrates the importance of a stepwise extrusion strategy for achieving effective dispersion and interface control of the various functional components.

[0085] Compared to Example 1, the flame-retardant polymer matrix of Comparative Example 6, made of flame-retardant acrylonitrile-butadiene-styrene copolymer (ABS), showed a significant decrease in tensile strength (64 MPa), flame retardancy rating (V-1), and waterproof rating (IPX6). This is mainly because the heat resistance, thermal stability, and mechanical strength at high temperatures of ABS are generally lower than those of flame-retardant polyesters (such as PBT) and flame-retardant nylons (PA6 / PA66 series). At higher processing temperatures, ABS is more prone to thermal degradation or viscosity instability, affecting the strong bonding and uniform dispersion of its interface with functionalized graphite and thermally conductive fillers. This weakens the construction effect of the integrated "thermal conductive-flame retardant-reinforcement" network, resulting in lower overall performance.

[0086] Compared to Example 1, the mass ratio of expanded graphite to coated graphite in Comparative Examples 7-8 did not meet the requirement of 100:(10³-10⁸). In Comparative Example 7, the coating layer in the coated graphite was too thin, resulting in an incomplete or uneven silica-phosphide composite layer on its surface. This failed to effectively improve the interfacial compatibility with the polymer matrix and could not provide sufficient phosphorus-silicon synergistic flame retardant effect. Therefore, its flame retardant rating, thermal conductivity, and waterproof rating were all poor, and its performance was close to that of uncoated expanded graphite. In Comparative Example 8, the coating layer in the coated graphite was too thick. On the one hand, it might excessively cover or even block the porous structure of the expanded graphite, weakening its ability to expand and char during combustion. On the other hand, the excessively thick inorganic coating layer itself had poor thermal conductivity and might become a defect point due to stress concentration or poor bonding with the matrix, resulting in a significant decrease in thermal conductivity, limited improvement in mechanical properties, and an imbalance in overall performance. The study verified the key role of controlling the weight gain ratio of the coating layer within the range of 100:(103-108) in balancing interface modification, flame retardant synergy and thermal conductivity maintenance.

[0087] Compared to Example 1, the coated graphite in Comparative Example 9 used ordinary graphite instead of expanded graphite, resulting in a significant drop in its flame retardant rating to V-2, as well as a marked decline in thermal conductivity and tensile strength. The fundamental reason is that ordinary graphite lacks the loose, porous, worm-like structure unique to expanded graphite. This dense structure prevents it from effectively supporting a uniform silica-phosphide composite coating layer. Secondly, and more importantly, it cannot undergo the "expansion effect" of expanding tens to hundreds of times in volume when exposed to fire, thus losing the core gas-phase flame retardant and oxygen-barrier insulation mechanism of expanded graphite in forming a dense, heat-insulating expanded char layer at the combustion front. Therefore, despite the addition of the same phosphorus-silicon components, its flame retardant efficiency is far lower than that of coated graphite with expanded graphite as the core.

[0088] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. In particular, it should be noted that any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention for those skilled in the art.

Claims

1. A fireproof coated pipe, characterized in that, The invention comprises a preform and a liquid waterproofing agent, wherein the liquid waterproofing agent accounts for 0.5%-3% of the mass fraction of the preform; the preform comprises a flame-retardant polymer matrix, coated graphite, and thermally conductive filler in a mass ratio of (50-80):(15-30):(5-20); the flame-retardant polymer matrix comprises at least one of flame-retardant polybutylene terephthalate, flame-retardant nylon 6, and flame-retardant nylon 66. The preparation method of the coated graphite includes the following steps: dispersing expanded graphite in a solvent, adding a silicon source solution and a phosphorus source solution dropwise under heating and stirring conditions, and after the reaction is completed, separating, washing and drying to prepare coated graphite, wherein the mass ratio of expanded graphite to coated graphite is 100:(103-108). The liquid waterproofing agent includes at least one of the following: polydimethylsiloxane waterproofing agent, amino-modified silane waterproofing agent, perfluoroalkyl ethyl acrylate waterproofing agent, fluorine-modified siloxane waterproofing agent, epoxy-modified polyurethane waterproofing agent, and acrylate-modified silane waterproofing agent.

2. The fireproof coated pipe as described in claim 1, characterized in that, The expanded graphite has a mesh size of 500-1500.

3. The fireproof coated pipe as described in claim 1, characterized in that, The molar ratio of silicon source in the silicon-containing solution to phosphorus source in the phosphorus-containing solution is (1-3):1; And / or, the silicon source in the silicon source solution is at least one of tetraethyl orthosilicate, methyl orthosilicate, methyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, and sodium silicate; And / or, the phosphorus source in the phosphorus source solution is at least one of phytic acid, ammonium dihydrogen phosphate, triphenyl phosphate, ammonium polyphosphate, and aluminum phosphate.

4. The fireproof coated pipe as described in claim 1, characterized in that, The particle size of the thermally conductive filler is 1-30 μm; And / or, the thermally conductive filler includes at least one of aluminum nitride, boron nitride, aluminum oxide, silicon carbide, diamond powder, magnesium oxide, and zinc oxide.

5. The fireproof coated pipe as described in claim 1, characterized in that, The liquid waterproofing agent has an ion content of ≤500ppm.

6. The fireproof coated pipe as described in claim 1, characterized in that, The method for preparing the master preform includes the following steps: adding the flame-retardant polymer matrix, coated graphite and thermally conductive filler into a twin-screw extruder, and after melt plasticizing, blending and dispersing, underwater pelletizing to prepare the master preform.

7. The fireproof coated pipe as described in claim 1, characterized in that, The preform comprises a flame-retardant polymer matrix, coated graphite, and thermally conductive filler in a mass ratio of (60-70):(20-25):(10-15); And / or, the mass ratio of the expanded graphite to the coated graphite is 100:(104-106). And / or, the molar ratio of silicon source in the silicon-containing solution to phosphorus source in the phosphorus-containing solution is (1.5-2.5):

1.

8. A method for preparing a fireproof coated pipe as described in any one of claims 1-7, characterized in that, Includes the following steps: (1) The preform and liquid waterproofing agent are added together to a single-screw extruder for extrusion blending to obtain a functionalized composite melt; (2) The functionalized composite melt is extruded and cooled by an extrusion device equipped with an internal pressure sizing pipe mold, a vacuum sizing sleeve and a cooling device to prepare a fireproof coated pipe.

9. The method for preparing the fireproof coated pipe as described in claim 8, characterized in that, In step (1), the extrusion blending temperature is 150-190 ℃ and the screw speed is 100-300 rpm; And / or, in step (2), the extrusion molding processing temperature is 160-250 ℃, the vacuum degree is -0.04~-0.08 MPa, and the traction ratio is 1.02-1.10; And / or, in step (2), the wall thickness of the fireproof covering tube is 1-4 mm.

10. The application of a fireproof sheathing tube as described in any one of claims 1-7 in the field of cable sheathing.

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