Composite flame-retardant cable material and preparation method thereof

Abstract

The present invention discloses a composite flame-retardant cable material and a preparation method thereof, relating to the field of cable technology, and addressing the problems of flame retardants and polymers separating at high temperatures in cable materials and reducing the mechanical strength of cable materials. The preparation method comprises: obtaining a modified suspension based on an inorganic material and a silane coupling agent; melt-blending LDPE, HPCTP, and PBPP at a preset temperature to form a uniformly dispersed inner layer matrix; uniformly dispersing the modified suspension on the surface of the inner layer matrix by coating to form a barrier protective layer to obtain a composite matrix; mixing the composite matrix with DCP and TAIC, cross-linking, and extruding at a high temperature to form a composite flame-retardant material; extruding the composite flame-retardant material, cooling it to form it, and then heat-treating the extruded material to obtain a composite flame-retardant cable material. This solution addresses the problem of flame retardants and polymers separating at high temperatures while ensuring the mechanical strength of the cable material.

Description

Technical Field

[0001] The present invention relates to the technical field of cables, and in particular to a composite flame-retardant cable material and a preparation method thereof. Background Art

[0002] Cable materials are widely used in modern industry and communications, and their performance is directly related to the safety and reliability of cables. To meet flame retardancy requirements in high-temperature environments, conventional cable materials are often filled with flame retardants to enhance their flame retardancy. However, when using flame retardants to enhance the flame retardancy of cable materials, the bonding between the flame retardant and the polymer is poor, and separation can easily occur under high temperatures or other extreme conditions, shortening the service life of the cable. While filling with high levels of flame retardants can improve flame retardancy, it significantly reduces the processing properties and mechanical strength of the cable material, making it impossible to achieve a balance between flame retardancy and processing properties. Summary of the Invention

[0003] The purpose of the present invention is to provide a composite flame-retardant cable material and a preparation method thereof, so as to solve the problems that the flame retardant and polymer in the existing cable material separate at high temperature and the addition of the flame retardant significantly reduces the processing performance and mechanical strength of the cable material.

[0004] To achieve this object, the present invention adopts the following technical solutions:

[0005] In a first aspect, the present invention provides a method for preparing a composite flame-retardant cable material, the preparation method comprising:

[0006] S1: obtaining a modified suspension according to an inorganic material and a silane coupling agent, wherein the inorganic material comprises one or more of expanded graphite, montmorillonite, and magnesium hydroxide;

[0007] S2: melt-blending LDPE, HPCTP, and PBPP at a preset temperature to form a uniformly dispersed inner layer matrix;

[0008] S3: uniformly dispersing the modified suspension on the surface of the inner layer substrate by coating to form a barrier protective layer to obtain a composite substrate;

[0009] S4: mixing the composite matrix with DCP and TAIC, cross-linking and extruding at a high temperature to form a composite flame retardant material;

[0010] S5: Extruding the composite flame-retardant material and cooling it to form it, and then heat-treating the extruded material to obtain a composite flame-retardant cable material.

[0011] Preferably, the step S1: obtaining a modified suspension based on an inorganic material and a silane coupling agent, wherein the inorganic material comprises one or more of expanded graphite, montmorillonite, and magnesium hydroxide, includes:

[0012] S11: adding the inorganic material into the anhydrous ethanol solution at a mass ratio of 1:10 and stirring and dispersing the inorganic material; during the dispersion process, ultrasonic oscillation is used to assist the dispersion to obtain an inorganic suspension;

[0013] S12: Weighing a silane coupling agent according to 5% to 8% of the mass of the inorganic material and preparing an activation solution, adjusting the pH value of the activation solution, and stirring to obtain an activated coupling agent solution;

[0014] S13: slowly adding the inorganic suspension into the activated coupling agent solution and continuously stirring for 2 hours to obtain a modified suspension, wherein the suspended matter in the modified suspension is the modified inorganic substance.

[0015] Preferably, the step of melt-blending LDPE, HPCTP and PBPP at a preset temperature to form a uniformly dispersed inner layer matrix comprises:

[0016] S21: dry-mix 15% to 25% HPCTP and 5% to 10% PBPP powder to obtain a uniformly distributed flame retardant powder;

[0017] S22: adding 60% to 70% LDPE into the extruder, and controlling the LDPE pellets to melt into a viscous state according to preset conditions;

[0018] S23: adjusting the temperature in the extruder and adding the flame retardant powder into the extruder in multiple times;

[0019] S24: adjusting the speed and maintaining the temperature, performing high shear mixing on the mixture and then extruding the inner layer matrix.

[0020] Preferably, when the modified inorganic substance needs to be stored for a long time, the step S2 further includes step S14: vacuum filtering the modified suspension to separate, washing, and drying the modified inorganic substance;

[0021] The S3 includes S30: preparing an ethanol-water mixed solution to obtain the modified inorganic substance, and slowly adding the modified inorganic substance to the ethanol-water mixed solution to obtain the modified suspension.

[0022] Preferably, the modified inorganic substance accounts for 8% to 12% of the composite matrix.

[0023] Preferably, the step S4: mixing the composite matrix with DCP and TAIC, and performing high-temperature extrusion and cross-linking reaction at 170° C. to 190° C. to form a composite flame retardant material comprises:

[0024] S41: obtaining DCP and TAIC, dissolving the DCP and TAIC in a small amount of anhydrous ethanol, and stirring to form a uniform cross-linking spray solution;

[0025] S42: spraying the cross-linking spray liquid uniformly onto the composite substrate through a spraying device, while controlling the composite substrate to mix and rotate;

[0026] S43: Drying the mixed composite matrix, DCP, and TAIC, and feeding the dried mixture into a twin-screw extruder;

[0027] S44: performing segmented processing on the mixture entering the twin-screw extruder to complete crosslinking and then extrude to obtain a molten material, wherein the segmented processing sequentially includes: feeding processing, melting processing, mixing processing, and homogenizing processing;

[0028] S45: Extruding the molten material to obtain a composite flame retardant material.

[0029] Preferably, the step S5 of extruding the composite flame retardant material, cooling and forming the material, and then heat-treating the extruded material to obtain a composite flame retardant cable material comprises:

[0030] S51: Cooling the composite flame retardant material by combining water cooling and air cooling, and screening qualified composite flame retardant materials;

[0031] S52: performing a hot air drying process on the composite flame retardant material, first adjusting the temperature step by step to increase the activation of the cross-linking reaction;

[0032] S53: Cooling the composite flame-retardant material that has undergone cross-linking reaction again to obtain the composite flame-retardant cable material.

[0033] Preferably, the preparation method further comprises: S6: uniformly dispersing the modified suspension on the surface of the composite flame-retardant cable material by coating to form a protective layer.

[0034] In a second aspect, the present invention provides a composite flame-retardant cable material, which is prepared according to the preparation method provided in the first aspect. The ratio of raw materials of the composite flame-retardant cable material includes:

[0035] Low-density polyethylene (LDPE): 60%-70%; Hexaphenoxycyclotriphosphazene (HPCTP): 15%-25%; Phenoxypolyphosphazene (PBPP): 5%-10%; Dicumyl peroxide (DCP): 1.2%-2%; Triallyl isocyanurate (TAIC): 0.3%-0.5%; Modified suspension;

[0036] The proportions of the modified suspension include:

[0037] Inorganic materials: 8% to 12%, wherein the inorganic materials include one or more of expanded graphite, montmorillonite, and magnesium hydroxide;

[0038] Ethanol: 60% to 70%;

[0039] Water: 10% to 20%;

[0040] Silane coupling agent: 5% to 8%;

[0041] Glacial acetic acid: trace amount (about 0.5%).

[0042] Preferably, the inorganic material comprises: expanded graphite, montmorillonite and magnesium hydroxide, and the mass ratio thereof is 4:3:3.

[0043] Compared with the prior art, the present invention has the following beneficial effects: a barrier protective film is formed on the surface of an inner layer matrix produced by melt blending LDPE, HPCTP and PBPP using an inorganic material to form a composite matrix; the LDPE is then cross-linked at a high temperature and extruded using DCP and TAIC; the extruded composite flame-retardant material is heat-treated to obtain a composite flame-retardant cable material; during the heat treatment, the LDPE is controlled to further cross-link, the cross-linking degree of the material is increased, the three-dimensional network structure is optimized, and the flame retardancy and mechanical properties of the cable material are improved.

[0044] Modifying the surface of the inorganic material with a silane coupling agent enhances the compatibility between the inorganic material and the matrix material, improving the interfacial bonding strength of the barrier protective layer. LDPE, HPCTP, and PBPP are melt-blended prior to cross-linking to ensure uniform dispersion of the components, avoid localized enrichment, and enhance the material's flame retardant uniformity. The inorganic material is coated on the outside of the inner matrix to form a complete barrier protective layer, effectively preventing HPCTP migration under high-temperature conditions and enhancing the material's long-term flame retardant properties. DCP and TAIC ensure a uniform cross-linking reaction and increase the composite material's cross-linking degree. Furthermore, under the cross-linking reaction conditions, the inorganic material is prevented from melting and its performance is unaffected, maintaining the integrity and interlayer structure of the inner and outer layers and avoiding interface damage or performance degradation during high-temperature extrusion. Finally, the extruded composite flame-retardant material is heat-treated to further activate the residual cross-linking reaction, forming a stable three-dimensional cross-linked structure, enhancing the material's flame retardant properties and thermal stability. The heat treatment also releases residual stress within the composite flame-retardant material, improving its dimensional stability and long-term weather resistance, and extending the cable's service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0046] The structures, proportions, sizes, etc. depicted in the drawings of this specification are only used to match the contents disclosed in the specification so as to facilitate understanding and reading by persons familiar with this technology. They are not intended to limit the conditions under which the present invention can be implemented and therefore have no substantive technical significance. Any structural modifications, changes in proportional relationships, or adjustments in size should still fall within the scope of the technical contents disclosed in the present invention without affecting the effects and objectives that can be achieved by the present invention.

[0047] Figure 1 A schematic flow chart of the method for preparing the composite flame-retardant cable material provided in Example 1; DETAILED DESCRIPTION

[0048] In order to make the purpose, features, and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0049] In the description of the present invention, it should be understood that the terms "upper," "lower," "top," "bottom," "inner," "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate the description of the present invention and simplify the description. They are not intended to indicate or imply that the devices or elements referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. It should be noted that when a component is considered to be "connected" to another component, it may be directly connected to the other component or there may be a centrally located component.

[0050] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific implementation methods.

[0051] Example 1

[0052] Please refer to Figure 1 , an embodiment of the present invention provides a method for preparing a composite flame-retardant cable material, the preparation method comprising:

[0053] S1: obtaining a modified suspension according to an inorganic material and a silane coupling agent, wherein the inorganic material comprises one or more of expanded graphite, montmorillonite, and magnesium hydroxide.

[0054] Specifically, the ethanol solution uses anhydrous ethanol, a polar solvent that helps reduce van der Waals forces on the surface of the flaky inorganic material, allowing the flakes to be fully dispersed. The silane coupling agent is a compound whose molecules contain siloxy groups (such as Si-OH) and organic functional groups, such as γ-aminopropyltriethoxysilane (KH550) and methyltriethoxysilane (MTES). Through surface modification with the silane coupling agent, the hydrophilic surface of the inorganic material is converted to hydrophobic, improving its dispersibility and interfacial bonding in the organic matrix (LDPE).

[0055] Said S1 comprises:

[0056] S11: adding the inorganic material to the anhydrous ethanol solution at a mass ratio of 1:10 and stirring and dispersing the inorganic material; and performing ultrasonic oscillation to assist the dispersion during the dispersion process to obtain an inorganic suspension.

[0057] The inorganic material water is added to the anhydrous ethanol solution and stirred and dispersed for 30 minutes to allow the inorganic surface to adsorb the liquid to break the surface agglomeration state; during the dispersion process, ultrasonic oscillation (frequency 20kHz, power 200W) is used to assist dispersion. By combining ultrasonic oscillation with the action of anhydrous ethanol solvent, the initial dispersion of the inorganic material is improved to the nanoscale, further improving the uniformity of the inorganic sheet and avoiding agglomeration.

[0058] S12: Weighing a silane coupling agent according to 5% to 8% of the mass of the inorganic material and preparing an activation solution, adjusting the pH value of the activation solution, and stirring to obtain an activated coupling agent solution.

[0059] Pour anhydrous ethanol into a reaction vessel equipped with a stirrer, obtain silane coupling agent based on 5% to 8% of the mass of the inorganic material and add it dropwise to the anhydrous ethanol, control the stirring speed at 200 to 300 rpm, and stir until the silane coupling agent is completely dissolved; after stirring evenly, add a small amount of deionized water and stir at room temperature for 10 to 15 minutes to fully hydrolyze the coupling agent to obtain an activated coupling agent solution.

[0060] Determination of the amount of anhydrous ethanol and deionized water:

[0061] First, obtain an amount of anhydrous ethanol based on 5 times the mass of the coupling agent and an amount of deionized water based on 2 times the mass of the coupling agent. Then, adjust the volume ratio of anhydrous ethanol to deionized water to 9:1 to 8:2. First, determine the mass of anhydrous ethanol and deionized water based on the mass of the coupling agent. Determine the amount of solvent based on the mass of the coupling agent to ensure that the amount of solvent matches the reaction requirements of the coupling agent to avoid waste or insufficient solvent. Convert the mass of anhydrous ethanol and deionized water to solvent volume and determine whether the converted anhydrous ethanol to deionized water volume ratio is within 9:1 to 8:2. If not, adjust the solvent volume to bring it within this range. Adjust the anhydrous ethanol to deionized water ratio to within this range to ensure reaction rate and hydrolysis effect.

[0062] Adjust the pH of the activation solution with glacial acetic acid and stir at 30°C-40°C for 10-20 minutes to obtain an activated coupling agent solution. Adding a small amount of deionized water and adjusting the pH to 3-5 with glacial acetic acid can inhibit premature self-condensation of the silane coupling agent and maintain the chemical activity of the silanols in the solution. Furthermore, the small amount of water balances the rate and efficiency of the silane coupling agent hydrolysis reaction within the solution, allowing the activation solution to generate uniform silanols under stable conditions. (A small amount of water can induce partial hydrolysis of the siloxy groups, forming intermediate reactive Si-OH groups.)

[0063] S13: slowly adding the inorganic suspension to the activated coupling agent solution and continuously stirring for 2 hours to obtain a modified suspension.

[0064] Slow addition can ensure that the activated coupling agent solution is evenly contacted with the inorganic material suspension, avoiding excessive local reaction of the coupling agent, thereby making the reaction more uniform. Preferably, the addition speed is controlled to 1 mL / min.

[0065] Under the temperature condition of 30-40°C, the stirring speed is set to 200 rpm and stirring is continued for 2 hours to ensure the uniformity of the reaction and help the coupling agent to be evenly distributed on the surface of the inorganic material to promote the reaction while avoiding the side reaction of the coupling agent caused by excessively high temperature.

[0066] Preferably, after stirring is completed, unreacted substances or large impurities can be removed by filtration to ensure the purity and uniformity of the modified suspension. The filtered modified suspension can be further processed as needed, such as ultrasonic dispersion or re-stirring to ensure that the particles are completely and evenly dispersed.

[0067] Preferably, the preparation of the modified suspension further comprises adding 0.1% of a dispersant, wherein the dispersant comprises polyvinylpyrrolidone (PVP).

[0068] Furthermore, the preparation of the modified suspension is carried out in a nitrogen protection environment, that is, nitrogen is added to the reaction vessel to prevent moisture or oxygen in the air from interfering with the hydrolysis reaction of the coupling agent, thereby ensuring the smooth progress of the reaction. By controlling the reaction environment, the occurrence of side reactions is avoided, thereby ensuring the stability and efficiency of the modified inorganic substance.

[0069] S2: melt-blending LDPE, HPCTP, and PBPP at a preset temperature to form a uniform inner layer matrix;

[0070] LDPE (low-density polyethylene) serves as the base material, while HPCTP (hexaphenoxycyclotriphosphazene) and PBPP (phenoxypolyphosphazene) powders are uniformly mixed as flame retardants. LDPE, HPCTP, and PBPP are thoroughly melt-blended to form a flame-retardant matrix with a uniform distribution of the components. Finally, the inner layer is formed by extrusion.

[0071] S3: uniformly dispersing the modified inorganic substance on the surface of the inner layer material through a coating process to form a barrier protective layer to obtain a composite matrix;

[0072] The modified inorganic material is dispersed in a mixed solution of ethanol and water (the volume ratio of ethanol to water is 8:2), 2% to 5% of polyvinyl alcohol (PVA) is added as a binder, and stirred to form a coating liquid.

[0073] The coating liquid is evenly applied to the surface of the inner substrate particles using electrostatic spraying or dip coating, with a controlled spray thickness of 10-20 μm. After coating, the coating is dried at 80°C for 3 hours to form a stable barrier layer. This improves the interfacial bonding and heat resistance of the flame-retardant material; the barrier layer forms a dense carbonized layer at high temperatures, inhibiting flame spread.

[0074] S4: mixing the composite matrix with DCP and TAIC, cross-linking and extruding at a high temperature to form a composite flame retardant material;

[0075] DCP (dicumyl peroxide) decomposes at high temperatures to produce free radicals, which promote the crosslinking of LDPE. TAIC (triallyl isocyanurate) acts as a co-crosslinking agent, synergizing with DCP to improve crosslinking efficiency.

[0076] The composite matrix, DCP (1.5%), and TAIC (0.3%) are mixed uniformly in proportion and then kneaded and cross-linked at high temperature in a twin-screw extruder. The resulting flame-retardant composite material is formed after extrusion. The high-temperature cross-linking reaction of LDPE creates a three-dimensional network structure, improving the thermal stability and mechanical properties of the material.

[0077] S5: Extruding the composite flame-retardant material and cooling it to form it, and then heat-treating the extruded material to obtain a composite flame-retardant cable material.

[0078] After the composite flame retardant material is extruded by the screw, the composite flame retardant material is cooled to a certain extent and then heat-treated to further remove moisture and volatile gases in the composite flame retardant material. At the same time, the LDPE is controlled to be further cross-linked during the heat treatment process.

[0079] During high-temperature extrusion and cross-linking in step S4, the inorganic coating layer prevents complete mixing with the LDPE, HPCTP, and PBPP, forming a stable physical barrier on the surface of the inner substrate, preventing HPCTP migration. Inorganic materials (such as expanded graphite, montmorillonite, and magnesium hydroxide) are insoluble in the polymer matrix and remain stable even at high temperatures. Therefore, they isolate the inner and outer layers, preventing HPCTP precipitation. Furthermore, the protective layer formed by the inorganic material not only provides thermal insulation but also helps reduce HPCTP migration in the outer layer, minimizing its contact with the external environment and further reducing the risk of precipitation.

[0080] DCP decomposes at high temperatures, generating free radicals that attack the LDPE molecular chains, initiating a crosslinking reaction. During the extrusion process, DCP comes into contact with LDPE, and the resulting free radicals can break the LDPE chain segments and crosslink them with surrounding molecules, forming a three-dimensional crosslinked network.

[0081] TAIC, as a crosslinking aid, further promotes the crosslinking reaction through its olefin groups reacting with free radicals. It not only enhances crosslinking uniformity but also increases the degree of crosslinking, preventing excessively rapid or slow crosslinking reactions that can lead to uneven material properties. TAIC helps LDPE molecular chains crosslink to form a more stable network structure, which not only increases the material's mechanical strength and thermal stability but also prevents HPCTP migration. The denser crosslinked LDPE structure reduces free volume, limiting the mobility of the flame retardant.

[0082] By combining the insulating and protective properties of the inorganic materials (expanded graphite, montmorillonite, and magnesium hydroxide) in the outer layer with the crosslinking reaction of the inner matrix, the crosslinking structure of LDPE, HPCTP, and PBPP is optimized while preventing HPCTP from precipitating at high temperatures. This improves the material's thermal stability, flame retardancy, and long-term weather resistance. This technical solution, through the synergistic effect of crosslinking and the inorganic barrier, effectively addresses the issues of HPCTP migration and uneven crosslinking at high temperatures, enhancing the overall performance of the cable material.

[0083] In this embodiment, an inorganic material is used to form a barrier protective film on the surface of an inner layer substrate produced by melt blending LDPE, HPCTP and PBPP to form a composite substrate. DCP and TAIC are then used to promote cross-linking of LDPE at high temperature and then extruded. The extruded composite flame-retardant material is heat-treated to obtain a composite flame-retardant cable material. During the heat treatment, the LDPE is controlled to further cross-link, the cross-linking degree of the material is increased, the three-dimensional network structure is optimized, and the flame retardancy and mechanical properties of the cable material are improved.

[0084] Modifying the surface of the inorganic material with a silane coupling agent enhances the compatibility between the inorganic material and the matrix material, improving the interfacial bonding strength of the barrier protective layer. LDPE, HPCTP, and PBPP are melt-blended prior to cross-linking to ensure uniform dispersion of the components, avoid localized enrichment, and enhance the material's flame retardant uniformity. The inorganic material is coated on the outside of the inner matrix to form a complete barrier protective layer, effectively preventing HPCTP migration under high-temperature conditions and enhancing the material's long-term flame retardant properties. DCP and TAIC ensure a uniform cross-linking reaction and increase the composite material's cross-linking degree. Furthermore, under the cross-linking reaction conditions, the inorganic material is prevented from melting and its performance is unaffected, maintaining the integrity and interlayer structure of the inner and outer layers and avoiding interface damage or performance degradation during high-temperature extrusion. Finally, the extruded composite flame-retardant material is heat-treated to further activate the residual cross-linking reaction, forming a stable three-dimensional cross-linked structure, enhancing the material's flame retardant properties and thermal stability. The heat treatment also releases residual stress within the composite flame-retardant material, improving its dimensional stability and long-term weather resistance, and extending the cable's service life.

[0085] In one embodiment, the step S2: melt-blending LDPE, HPCTP, and PBPP at a preset temperature to form a uniform inner layer matrix comprises:

[0086] S21: dry-mix 15% to 25% HPCTP and 5% to 10% PBPP powder to obtain a uniformly distributed flame retardant powder;

[0087] Pre-weigh according to the proportions of LDPE: 60%-70%, HPCTP: 15%-25%, and PBPP: 5%-10%. LDPE is added in the form of particles to ensure uniform particle diameter (about 2-5 mm). HPCTP and PBPP are added in the form of powder with a particle size controlled below 20 μm.

[0088] Preferably, 15% to 25% HPCTP and 5% to 10% PBPP powders are dry-mixed in a drum mixer for 5 minutes to obtain a flame retardant powder with uniform distribution of HPCTP and PBPP, thereby reducing the risk of agglomeration between the components and facilitating the uniformity of subsequent melt blending.

[0089] S22: adding 60% to 70% LDPE into the extruder, and controlling the LDPE pellets to melt into a viscous state according to preset conditions;

[0090] The twin-screw extruder is set to a low-temperature zone of 90°C to 100°C according to a preset temperature. LDPE pellets are first added to the barrel and plasticized in the low-temperature zone. The screw speed is set to 60 rpm for 2 minutes, gradually melting the LDPE into a viscous state. This initial low-temperature treatment ensures uniform melting of the LDPE pellets, forming a viscous matrix that prepares for the subsequent addition of the flame retardant while preventing premature thermal decomposition of the flame retardant or degradation of the matrix caused by excessive temperatures.

[0091] S23: adjusting the temperature in the extruder, and adding the flame retardant powder into the extruder in multiple times to obtain a mixture;

[0092] After LDPE is completely melted (about 100°C), the premixed HPCTP and PBPP powders are quantitatively added into the extruder multiple times.

[0093] Preferably, HPCTP and PBPP powders are added to the extruder in three batches: 40% of the total amount is added in the first batch, 40% in the second batch, and the remaining 20% ​​in the third batch. Each batch of additions is controlled to last 2 minutes, with the screw speed maintained at 50-60 rpm and the barrel temperature simultaneously increased to 130°C.

[0094] By adding the flame retardant in stages, excessive instantaneous contact between the flame retardant and LDPE can be avoided, the risk of uneven dispersion can be reduced, and the flame retardant can be gradually dispersed into the molten matrix, ultimately forming a uniform inner layer matrix material.

[0095] S24: adjusting the speed and maintaining the temperature to perform high shear mixing on the mixture, and completing high shear mixing and extrusion to obtain an inner layer matrix;

[0096] The screw speed was increased to 80 rpm while the barrel temperature was maintained at 130°C. The mixture in the extruder was subjected to high shear mixing for 5 minutes. At the same time, a dispersion disc structure was added to the extruder to further refine the flame retardant particles through high shear force and evenly distribute them in the matrix.

[0097] High-shear dispersion evenly embeds the HPCTP and PBPP powders into the LDPE matrix, forming a tight molecular mosaic structure that ensures uniformity within the inner matrix and prevents localized aggregation that can affect performance. The combined effects of high-shear dispersion and the dispersion disc enhance the microscopic distribution of the flame retardant and improve the stability of the material.

[0098] After the mixing is completed, the volatile impurities and possible moisture are discharged through the exhaust holes of the twin-screw extruder. The extrusion temperature is maintained at 130°C, the screw speed is adjusted to 40 rpm, and the initial discharge is completed under low speed conditions. The initially extruded material is in granular form and is collected after cooling for later use.

[0099] The initially discharged granular material is sieved (sieve hole diameter 1mm) to remove large particles or unmixed parts; the sieved granules are placed in a vacuum drying oven and dried at 80°C for 4 hours to ensure complete dehydration; the dried granules are sealed and stored in a dry environment (relative humidity <10%).

[0100] In one embodiment, the step S3: uniformly dispersing the modified inorganic substance on the surface of the inner layer material by coating to form a barrier protective layer to obtain a composite matrix, includes:

[0101] S31: using an electrostatic spraying method or a dipping method, the modified suspension is evenly covered on the surface of the inner layer substrate to form the barrier protection layer, thereby obtaining a composite substrate.

[0102] When using an electrostatic sprayer, calibrate the airflow before spraying to ensure uniform spraying (spray pressure 2-4 MPa). Lay the inner layer substrate flat on a rotating coating platform, adjust the platform speed, and maintain a spray distance of approximately 15 cm. Repeat the spraying process multiple times, spraying 50-80 μL per application, ensuring the coating thickness is within the 10-20 μm range. After coating, allow the material to rest for 15 minutes to allow initial surface adhesion.

[0103] When using the immersion method to evenly coat the modified inorganic material on the surface of the inner layer material to form a barrier protective layer, immerse the inner layer substrate in the modified suspension for 2 to 5 minutes to ensure uniform wetting of the inner layer material surface. During the immersion process, ensure that the inner layer substrate is completely immersed in the suspension and that the modified inorganic material is evenly covered on its surface.

[0104] When the composite matrix needs to be stored for a long time, step S3 further includes:

[0105] S32: Place the coated composite substrate in a hot air circulation drying oven, control the temperature at 50-60°C, and dry it for 30-60 minutes; turn the material every 10 minutes during the drying process to prevent adhesion between particles or uneven coating.

[0106] S33: The coated granular material is sieved through a 2 mm sieve to remove any agglomerates that may have formed.

[0107] The screened materials are packed into dry sealed bags and stored in an environment with a humidity below 10% and a temperature below 25°C.

[0108] In one embodiment, when the modified suspension needs to be stored for a long time, S2 further includes S14: vacuum filtering, separating, washing, and drying the modified suspension to obtain the modified inorganic substance;

[0109] The S3 further includes S30: preparing an ethanol-water mixed solution to obtain the modified inorganic substance, and slowly adding the modified inorganic substance to the ethanol-water mixed solution to obtain the modified suspension.

[0110] Specifically, after the reaction is completed, the modified inorganic substance is separated by vacuum filtration, and the filter cake is obtained and washed with anhydrous ethanol 3 to 4 times to remove unreacted coupling agent and by-products; finally, it is rinsed once with pure water to ensure that there are no impurities remaining on the surface of the inorganic substance, thereby achieving the preparation of high-purity modified inorganic substances and avoiding impurities affecting the interface bonding performance.

[0111] The washed modified inorganic material was placed in a vacuum drying oven at 80°C and 50 kPa for 8 hours. During the drying process, the modified inorganic material was gently stirred every 2 hours to prevent agglomeration. The dried modified inorganic material was then sieved through a fine sieve (pore size 150 μm) to remove large particles or agglomerates.

[0112] An ethanol-water mixed solution is prepared, wherein the volume ratio of ethanol to water is 9:1 to 8:2; 5% to 10% by weight of the inorganic material of the modified inorganic material is obtained, and the modified inorganic material is slowly added to the ethanol-water mixed solution to obtain a coating medium;

[0113] Before adding the modified inorganic material to the ethanol-water mixed solution, the modified inorganic material was placed in a vacuum drying oven with the temperature set to 80° C. and the drying time set to 2 hours to completely remove residual moisture and solvent.

[0114] The modified inorganic compound was slowly added to the ethanol-water mixed solution while stirring and ultrasonically treating for 10 minutes (frequency 25 kHz, power 300 W) to form a uniform suspension.

[0115] Preferably, an appropriate amount of binder (such as polyvinyl alcohol, PVA) is added to the suspension at a ratio of 2% to 5%, and stirring is continued for 15 minutes to ensure that the viscosity of the solution is stable (viscosity range: 800 to 1200 mPa·s). The addition of the binder also enhances the adhesion between the suspension and the inner layer substrate, and can form a uniform barrier protective layer on the surface of the inner layer substrate.

[0116] Furthermore, before S31, the process further includes: slicing the inner substrate, wiping and cleaning the inner substrate with ethanol to remove surface impurities and oil, and then slightly roughening the inner substrate surface with sandpaper to form a microscopic rough structure to improve the adhesion of the coating layer. After roughening, the inner substrate surface is cleaned of residual dust using a high-pressure airflow and then wiped with ethanol to ensure a clean surface.

[0117] In one embodiment, the step S4 of mixing the composite matrix with DCP and TAIC, and performing high-temperature extrusion and cross-linking reaction at 170° C. to 190° C. to form a composite flame retardant material comprises:

[0118] S41: Obtain DCP (crosslinking agent dicumyl peroxide) and TAIC (triallyl isocyanurate), dissolve DCP and TAIC in a small amount of anhydrous ethanol, and stir to form a uniform crosslinking spray solution;

[0119] Furthermore, 1.2% to 2% of DCP and 0.3% to 0.5% of TAIC were dissolved in a small amount of anhydrous ethanol and stirred to form a uniform cross-linking spray solution.

[0120] Furthermore, DCP and TAIC were dissolved in a small amount of anhydrous ethanol at a mass ratio of 3:1 to 5:1, and the amount of DCP and TAIC was obtained based on 2% to 3% of the composite matrix.

[0121] DCP and TAIC were dissolved in a small amount of anhydrous ethanol at 30°C and stirred for 10 minutes to form a uniform cross-linking spray solution.

[0122] S42: spraying the cross-linking spray liquid uniformly onto the composite substrate through a spraying device, while controlling the composite substrate to mix and rotate;

[0123] In a low-speed mixing device, evenly spray the crosslinking spray solution onto the surface of the composite matrix particles using a spray device. Mix the solution with a drum while spraying to ensure that the crosslinker is evenly attached to the composite matrix particles. Continue mixing for 3-5 minutes to ensure that the DCP and TAIC are fully in contact with the composite matrix.

[0124] S43: Drying the mixed composite matrix, DCP, and TAIC, and adding the dried mixed material to a twin-screw extruder;

[0125] Place the mixed material in a vacuum drying oven, set the temperature to 80°C ~ 90°C, maintain the vacuum degree at 50 ~ 70kPa, and control the drying time to 2 ~ 3 hours to ensure that the moisture content of the material drops below 0.1%.

[0126] S44: performing segmented processing on the mixture entering the twin-screw extruder to complete crosslinking and then extrude to obtain a molten material, wherein the segmented processing sequentially includes: feeding processing, melting processing, mixing processing, and discharging processing;

[0127] The barrel is divided into sections:

[0128] The feeding zone is used for feeding processing. The temperature is set at 150°C to partially soften the mixture and enhance its fluidity, ensuring that the mixture can smoothly enter the extruder;

[0129] The melting zone is used for melting treatment. The temperature is set at 170 degrees and the screw speed is set at 60 rpm, so that LDPE, HPCTP, PBPP, DCP, and TAIC are completely melted, plasticized, and mixed together to provide conditions for subsequent cross-linking.

[0130] The mixing zone is used for mixing. The temperature is set at 180°C to 190°C, and the screw speed is increased to 60-80 rpm. Under the conditions of screw shear force and high temperature, DCP is activated to decompose, generate free radicals, and complete the initial cross-linking reaction.

[0131] The discharge area is used for discharge processing. The die temperature is controlled at 180°C, and the material after the cross-linking reaction is extruded through the die.

[0132] S45: Cooling the extruded molten material and placing it in a hot air circulation for fixing, and obtaining the composite flame retardant material after the fixing is completed.

[0133] The extruded material is rapidly cooled by passing through a water cooling tank (temperature 25°C) and collected into a sheet-like or granular composite material. After cooling, the sheet-like or granular composite material is placed in a hot air circulation oven (80°C, 2 hours) for post-curing treatment to further stabilize the cross-linked structure. After curing, a composite flame retardant material is obtained.

[0134] In one embodiment, the step S5 of extruding the composite flame-retardant material and cooling it to form it, and then heat-treating the extruded material to obtain a composite flame-retardant cable material includes:

[0135] S51: Cooling the composite flame retardant material by combining water cooling and air cooling, and screening qualified composite flame retardant materials;

[0136] Set the temperature of the water bath cooling system to 15°C ~ 25°C, send the composite flame retardant material just extruded from the die mouth into the water bath cooling system for the first cooling. After staying for 1 to 2 minutes, continue to send the composite flame retardant material to the air cooling channel for the second cooling. Control the air flow rate to 5 to 10 m / s, and the duration is 30 to 60 seconds.

[0137] The newly extruded composite flame retardant material is quickly cooled and initially formed through water cooling and air cooling to ensure that the extruded composite flame retardant material maintains a stable shape while avoiding internal stress accumulation or appearance defects caused by excessive cooling, providing high-quality semi-finished products for subsequent heat treatment.

[0138] During the cooling process, monitor whether the composite flame retardant material has cracks, bubbles, etc., pick out unqualified products, and screen out qualified composite flame retardant materials for the next step.

[0139] S52: performing a hot air drying process on the composite flame retardant material, first adjusting the temperature step by step to increase the activation of the cross-linking reaction;

[0140] S53: Cooling the composite flame-retardant material that has undergone cross-linking reaction again to obtain the composite flame-retardant cable material.

[0141] The cooled composite flame retardant material is placed in a hot air circulation drying system. In the first stage, the temperature is raised from 50°C to 150°C, and the heating rate is controlled at 5°C / min. The material is heated gradually to avoid stress concentration in the material due to excessive temperature difference. In the second stage, the temperature is controlled at 195°C~205°C, and the composite flame retardant material is kept at a constant temperature for 8~10 minutes to stimulate the cross-linking reaction, activate the residual cross-linking reaction, and increase the degree of cross-linking. In the third stage, the material is cooled gradually at a cooling rate of 10°C / min to prevent cracks in the material due to sudden cooling. After cooling, the composite flame retardant cable material is obtained.

[0142] Through heat treatment, the incompletely decomposed DCP is further activated to generate more free radicals, complete the residual cross-linking reaction, and increase the cross-linking degree of the material to 90% to 95%, forming a stable three-dimensional network structure; stress is released during the heating and cooling process to avoid cracks in the composite flame-retardant cable material and other phenomena that affect the quality of the cable material.

[0143] In one embodiment, cooling the composite flame retardant material by a combination of water cooling and air cooling and screening qualified composite flame retardant materials further comprises: uniformly dispersing the modified suspension on the surface of the composite flame retardant material by coating to form a protective layer.

[0144] In the composite flame retardant material extruded through step S4, the inorganic material will be partially mixed in the interior of the mixture of LDPE, HPCTP and PBPP, and the HPCTP will be located on the surface of the material. In order to meet higher usage requirements or when the cable material will be in a high-temperature environment, after the composite flame retardant material is extruded, the modified suspension obtained in steps S11 to S13 is coated on the surface of the composite flame retardant material by immersion or electrostatic spraying to form a protective layer, which is used to prevent the HPCTP from precipitating when the composite flame retardant material is in a high-temperature state during heat treatment or in subsequent processes, affecting the quality of the composite flame retardant cable material and its service life.

[0145] Example 2

[0146] Based on the preparation method of the composite flame-retardant cable material described in Example 1 above, the raw material ratio of the composite flame-retardant cable material is:

[0147] Low-density polyethylene (LDPE): 60%-70%; Hexaphenoxycyclotriphosphazene (HPCTP): 15%-25%; Phenoxypolyphosphazene (PBPP): 5%-10%; Dicumyl peroxide (DCP): 1.2%-2%; Triallyl isocyanurate (TAIC): 0.3%-0.5%; Modified suspension;

[0148] The proportions of the modified suspension include:

[0149] Inorganic materials: 8% to 12%, wherein the inorganic materials include one or more of expanded graphite, montmorillonite, and magnesium hydroxide;

[0150] Ethanol: 60% to 70%;

[0151] Water: 10% to 20%;

[0152] Silane coupling agent: 5% to 8%;

[0153] Glacial acetic acid: trace amount (about 0.5%).

[0154] The inner layer matrix is ​​formed by melt-blending 60% to 70% LDPE, 15% to 25% HPCTP, and 5% to 10% PBPP using the method described in step S2, wherein LDPE is the main raw material, and HPCTP and PBPP are flame retardants.

[0155] The inorganic material is modified with a silane coupling agent to generate a modified suspension, which is then coated multiple times to form a barrier protective layer outside the inner layer matrix to obtain a composite matrix. The barrier protective layer can prevent the HPCTP in the inner layer matrix from precipitating during subsequent high-temperature cross-linking reactions and subsequent cable material use, thereby affecting the quality of the cable material or shortening its service life.

[0156] The cross-linking agents (DCP and TAIC) promote the cross-linking structure of LDPE through step S4, thereby improving the thermal stability and mechanical strength of the cable material and ensuring the performance of the cable under high temperature and external environment.

[0157] When preparing the modified suspension, a chemical bonding layer is formed between the coupling agent and the inorganic surface to enhance the stability and adhesion of the barrier protective layer. The modified suspension ensures the high performance of the final cable material through precise component ratio and process control, including excellent flame retardancy, thermal stability, mechanical properties and excellent processability.

[0158] In one embodiment, the modified suspension is prepared using three inorganic materials: expanded graphite, montmorillonite, and magnesium hydroxide, and the mass ratio of expanded graphite, montmorillonite, and magnesium hydroxide is 4:3:3.

[0159] Furthermore, the preparation of the modified suspension further includes adding 0.1% of a dispersant and stirring uniformly, wherein the dispersant includes polyvinylpyrrolidone (PVP).

[0160] In one embodiment, the raw material ratio of the composite flame retardant cable material is:

[0161] Low-density polyethylene (LDPE): 60%; Hexaphenoxycyclotriphosphazene (HPCTP): 20%; Phenoxypolyphosphazene (PBPP): 10%; Dicumyl peroxide (DCP): 1.5%; Triallyl isocyanurate (TAIC): 0.3%; Modified suspension;

[0162] The modified suspension comprises the following proportions: expanded graphite: 8%; ethanol: 65%; water: 10%; silane coupling agent: 6%; and glacial acetic acid: a trace amount (about 0.5%).

[0163] According to the above ratio and in accordance with the preparation scheme provided in Example 1, a composite flame-retardant cable material was prepared.

[0164] In one embodiment, the raw material ratio of the composite flame retardant cable material is:

[0165] Low-density polyethylene (LDPE): 65%; Hexaphenoxycyclotriphosphazene (HPCTP): 15%; Phenoxypolyphosphazene (PBPP): 10%; Dicumyl peroxide (DCP): 1.3%; Triallyl isocyanurate (TAIC): 0.4%; Modified suspension;

[0166] The modified suspension comprises the following proportions: magnesium hydroxide: 8%, ethanol: 65%, water: 15%, silane coupling agent: 5%, and glacial acetic acid: a trace amount (about 0.5%).

[0167] According to the above ratio and in accordance with the preparation scheme provided in Example 1, a composite flame-retardant cable material was prepared.

[0168] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some of the technical features thereof can be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a composite flame-retardant cable material, characterized in that: The preparation method comprises: S1: obtaining a modified suspension according to an inorganic material and a silane coupling agent, wherein the inorganic material comprises one or more of expanded graphite, montmorillonite, and magnesium hydroxide; S2: melt-blending LDPE, HPCTP, and PBPP at a preset temperature to form a uniformly dispersed inner layer matrix; S3: uniformly dispersing the modified suspension on the surface of the inner layer substrate by coating to form a barrier protective layer to obtain a composite substrate; S4: mixing the composite matrix with DCP and TAIC, cross-linking and extruding at a high temperature to form a composite flame retardant material; S5: Extruding the composite flame retardant material and cooling it to form it, and then heat-treating the extruded material to obtain a composite flame retardant cable material; The composite matrix is ​​mixed with DCP and TAIC, and subjected to high-temperature extrusion and cross-linking reaction at 170° C. to 190° C. to form a composite flame retardant material, comprising: S41: obtaining DCP and TAIC, dissolving the DCP and TAIC in a small amount of anhydrous ethanol, and stirring to form a uniform cross-linking spray solution; S42: spraying the cross-linking spray liquid uniformly onto the composite substrate through a spraying device, while controlling the composite substrate to mix and rotate; S43: Drying the mixed composite matrix, DCP, and TAIC, and feeding the dried mixture into a twin-screw extruder; S44: performing segmented processing on the mixture entering the twin-screw extruder to complete crosslinking and then extrude to obtain a molten material, wherein the segmented processing sequentially includes: feeding processing, melting processing, mixing processing, and homogenizing processing; S45: Extruding the molten material to obtain a composite flame retardant material; The method of extruding the composite flame retardant material and then cooling it to form it, and then heat-treating the extruded material to obtain the composite flame retardant cable material, comprises: S51: Cooling the composite flame retardant material by combining water cooling and air cooling, and screening qualified composite flame retardant materials; S52: performing a hot air drying process on the composite flame retardant material, first adjusting the temperature step by step to increase the activation of the cross-linking reaction; S53: Cooling the composite flame-retardant material subjected to the cross-linking reaction again to obtain the composite flame-retardant cable material; The composite flame retardant material is cooled by combining water cooling and air cooling, and after the qualified composite flame retardant material is screened, the method further comprises: uniformly dispersing the modified suspension on the surface of the composite flame retardant material by coating to form a protective layer.

2. The method for preparing a composite flame-retardant cable material according to claim 1, characterized in that: The modified suspension is obtained based on the inorganic material and the silane coupling agent, wherein the inorganic material includes one or more of expanded graphite, montmorillonite, and magnesium hydroxide, including: S11: adding the inorganic material into the anhydrous ethanol solution at a mass ratio of 1:10 and stirring and dispersing the inorganic material; during the dispersion process, ultrasonic oscillation is used to assist the dispersion to obtain an inorganic suspension; S12: Weighing a silane coupling agent according to 5% to 8% of the mass of the inorganic material and preparing an activation solution, adjusting the pH value of the activation solution, and stirring to obtain an activated coupling agent solution; S13: slowly adding the inorganic suspension into the activated coupling agent solution and continuously stirring for 2 hours to obtain a modified suspension, wherein the suspended matter in the modified suspension is the modified inorganic substance.

3. The method for preparing a composite flame-retardant cable material according to claim 2, characterized in that: The method comprises: melt-blending LDPE, HPCTP and PBPP at a preset temperature to form a uniformly dispersed inner layer matrix, comprising: S21: dry-mix 15% to 25% HPCTP and 5% to 10% PBPP powder to obtain a uniformly distributed flame retardant powder; S22: adding 60% to 70% LDPE into the extruder, and controlling the LDPE pellets to melt into a viscous state according to preset conditions; S23: adjusting the temperature in the extruder and adding the flame retardant powder into the extruder in multiple times; S24: adjusting the speed and maintaining the temperature, performing high shear mixing on the mixture and then extruding the inner layer matrix.

4. The method for preparing a composite flame-retardant cable material according to claim 3, characterized in that: When the modified inorganic substance needs to be stored for a long time, the S2 further includes S14: vacuum filtering, separating, washing, and drying the modified suspension to obtain the modified inorganic substance; The S3 includes S30: preparing an ethanol-water mixed solution to obtain the modified inorganic substance, and slowly adding the modified inorganic substance to the ethanol-water mixed solution to obtain the modified suspension.

5. The method for preparing a composite flame-retardant cable material according to claim 4, characterized in that: The modified inorganic matter accounts for 8% to 12% of the composite matrix.

6. The method for preparing a composite flame-retardant cable material according to claim 2, characterized in that: The inorganic material comprises expanded graphite, montmorillonite and magnesium hydroxide in a mass ratio of 4:3:

3.

7. A composite flame-retardant cable material, characterized in that: The composite flame-retardant cable material is made according to the preparation method according to claim 1.

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