Ultraviolet crosslinking halogen-free flame-retardant cable material and preparation method thereof

Abstract

The invention discloses an ultraviolet crosslinking halogen-free flame-retardant cable material and a preparation method thereof. The cable material is prepared from an ethylene-vinyl acetate copolymer, a polyolefin elastomer, a reactive modified composite flame-retardant filler, a lubricant, an anti-dripping agent, a photo-crosslinking agent and a photoinitiator through microwave pretreatment, melt blending, ultraviolet irradiation and heat-assisted post-curing. Wherein the flame-retardant filler is constructed by biomimetic coating of aluminum hydroxide with polydopamine, modification with vinyl silane and chemical anchoring of melamine cyanurate and aluminum hypophosphite, and a'core-shell 'structure with a firm interface and crosslinking activity is formed. Through cooperation of filler interface engineering, flame-retardant system optimization and process innovation, the oxygen index of the material reaches 31.8-34.5%, the flame-retardant grade reaches UL94 V-0 grade, the tensile strength is kept at 17.5-19.8 MPa, the gel content exceeds 73%, the smoke density is remarkably reduced to 115-130 Ds, the comprehensive performance is excellent, and the material is suitable for a high-end cable insulating layer or sheath layer.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of cable materials, and particularly relates to a halogen-free flame-retardant cable material crosslinked by ultraviolet light and a preparation method thereof. BACKGROUND

[0002] With the increasingly stringent global environmental regulations and the continuous improvement of fire safety requirements, the wire and cable industry is facing a strategic transformation from traditional halogen-containing flame-retardant materials to environmentally friendly halogen-free flame-retardant materials. As an environmentally friendly and smoke-suppressing halogen-free flame retardant, aluminum hydroxide (ATH) has attracted much attention. However, to achieve UL94 V-0 level flame retardation, the traditional filling amount of ATH often needs to exceed 60 parts, which inevitably leads to serious deterioration of the mechanical properties, processing flowability and environmental stress cracking resistance of the composite material.

[0003] To solve this dilemma, the industry has tried to modify ATH and combine it with ultraviolet light crosslinking technology. However, the existing technical path has a series of deep-seated contradictions that have not been overcome: Firstly, at the level of filler interface engineering, the interface bonding force of traditional silane coupling agents (such as KH-560 containing epoxy groups) modification mainly depends on physical adsorption and weak chemical action, which is easy to be damaged in high temperature and high shear processing. More importantly, such modification does not change the "chemical inertness" nature of ATH, and the surface functional groups cannot participate in the crosslinking reaction of the matrix, which seriously breaks the continuity of the matrix, hinders the formation of uniform and complete three-dimensional crosslinking network, and leads to low gel content and poor mechanical strength.

[0004] Secondly, at the level of flame-retardant system construction, the existing technology mostly uses physical mixing method to simply compound melamine cyanurate (MCA) and other gas-phase flame retardants with ATH. This physical blending system lacks firm chemical bonding and stable microstructure between components, the flame retardant is easy to migrate and precipitate, resulting in poor flame-retardant efficiency and durability, and it is difficult to achieve high efficiency in gas, solid and condensed three phases, and cannot achieve high flame-retardant grade at low filling amount.

[0005] Thirdly, at the level of matrix processing and crosslinking process, the strong scattering and absorption effect of inorganic fillers on ultraviolet light is an obstacle that ultraviolet light crosslinking technology cannot overcome. Conventional single intensity irradiation process easily leads to excessive crosslinking on the surface of the material and insufficient crosslinking in the inner layer, resulting in large internal stress and performance gradient. At the same time, the compatibility between the unactivated polymer matrix and the modified filler is still not ideal, and the traditional thermal mechanical blending is difficult to achieve uniform dispersion of the fillers at the nanoscale, and the interface defects become the short board of performance.

[0006] In addition, the material network after crosslinking often has unreacted active points and internal stress, and the prior art lacks effective post-processing means to stabilize and strengthen the crosslinked structure, which affects the long-term thermal stability and mechanical properties of the product.

[0007] To sum up, the technical field urgently needs a comprehensive technical solution that can systematically solve the above problems. The solution should be able to construct an interface layer on the surface of ATH that is firmly bonded and has ultraviolet light crosslinking activity; it should be able to introduce a multi-mechanism synergistic high-efficiency flame-retardant system through chemical bonding; and it should be able to achieve efficient dispersion of fillers, uniform construction of crosslinked networks, and stress relief through innovative pretreatment and controlled crosslinking post-processing. This is the core technical problem that the present invention aims to solve. SUMMARY

[0008] The present invention provides a kind of ultraviolet light crosslinking halogen-free flame-retardant cable material and its preparation method to solve the above technical problems.

[0009] To achieve the above purpose, the technical solution provided by the present invention is as follows: A preparation method of ultraviolet light crosslinking halogen-free flame-retardant cable material, comprising the following steps: (1) Disperse aluminum hydroxide powder in Tris-HCl buffer solution with pH of 8.5, add dopamine hydrochloride, stir and polymerize at room temperature for 12-24 hours to coat polydopamine on the surface of aluminum hydroxide, and obtain polydopamine-coated aluminum hydroxide composite filler; (2) Disperse the composite filler prepared in step (1) in a mixed solution of ethanol and water, add 3-5% of vinyltriethoxysilane based on the mass of the composite filler, adjust the pH to 4-5 with acetic acid, and carry out hydrolysis and condensation reaction at 70-80°C for 1-2 hours; then add 8-12% of melamine cyanurate and 5-10% of aluminum hypophosphite based on the mass of the composite filler, and continue to stir at constant temperature for 2-3 hours; after the reaction is completed, filter, wash and dry to obtain a reaction-type modified composite flame-retardant filler; (3) Put 50-65 parts of ethylene-vinyl acetate copolymer and 15-25 parts of polyolefin elastomer into a microwave reactor, treat at a power of 400-600W for 1-3 minutes until the surface of the polymer shows a slight melting luster, and obtain a pretreated base resin; (4) Put all the pretreated base resin prepared in step (3), 30-40 parts of the reaction-type modified composite flame-retardant filler prepared in step (2), 1-3 parts of lubricant and 0.5-2 parts of anti-dripping agent into an internal mixer, and mix at 120-135°C for 4-6 minutes; then add 2-4 parts of 2,4,6-triallyloxy-1,3,5-triazine and 1-2 parts of 2-hydroxy-2-methyl-1-phenyl-1-propanone, and continue to mix for 3-5 minutes; (5) The material after mixing is pressed into a sheet with a thickness of 1.5-2.5 mm; the sheet is placed in a nitrogen-protected ultraviolet light irradiation box, and a zoned gradient irradiation method is adopted, wherein the irradiation intensity of the first zone is 30-40 mW / cm 2 , the irradiation intensity of the second zone is 50-70 mW / cm 2 , the irradiation time of the sheet in the first zone accounts for 30-40% of the total irradiation time, and the remaining time in the second zone, and the total cumulative irradiation dose is 10-20 J / cm 2 ; (6) The irradiated sheet is quickly transferred to a hot air circulating oven at 80-100°C for heat-assisted post-curing for 20-40 minutes to obtain the ultraviolet crosslinked halogen-free flame-retardant cable material.

[0010] Further, in step (1), the addition amount of dopamine hydrochloride is 1.5-2.5% of the mass of aluminum hydroxide. By precisely controlling the addition amount of dopamine hydrochloride, a complete, dense and not too thick polydopamine coating layer is formed on the surface of aluminum hydroxide, providing an optimal active platform for subsequent high-density silane grafting, which is the key to achieving strong interfacial bonding.

[0011] Further, in step (2), the particle size ratio of melamine cyanurate to aluminum hypophosphite is controlled in the range of (1.2-1.8):1, and the particle size D50 of aluminum hypophosphite is less than 3 μm. By controlling the particle size ratio of melamine cyanurate to aluminum hypophosphite, the particles of different functional flame retardants can achieve closer physical packing, and a dense and continuous intumescent barrier carbon layer can be formed more quickly and efficiently during combustion, thereby synergistically improving the flame-retardant and smoke-suppressing efficiency Further, in step (2), the mass ratio of aluminum hypophosphite to melamine cyanurate is 1:(1.2-2.5). By controlling the mass ratio of aluminum hypophosphite to melamine cyanurate, the optimal ratio balance of gas phase flame retardation (cooling, dilution) and condensed phase flame retardation (carbon formation, protection) is achieved, and the optimal flame-retardant synergistic effect is obtained at the lowest addition cost.

[0012] Further, in step (3), the monomer content of vinyl acetate in the ethylene-vinyl acetate copolymer is 33-40%. By limiting the monomer content of vinyl acetate in the ethylene-vinyl acetate copolymer, the excellent polarity and flexibility of EVA resin in this content range are fully utilized, which enables better interfacial compatibility with the polar modified filler, while ensuring good processing fluidity of the matrix resin itself and flexibility of the final product.

[0013] Furthermore, in step (4), the lubricant is a composite lubricating system composed of lignite wax and silicone masterbatch at a mass ratio of 1:(0.5~1). By employing the composite lubricating system of lignite wax and silicone masterbatch, the excellent internal lubricity of lignite wax and the persistent migration and external lubricity of silicone masterbatch are utilized. This ensures good processing fluidity of the material while avoiding adverse effects on the material's mechanical properties and interfacial bonding caused by excessive lubricant or precipitation.

[0014] Furthermore, in step (4), the anti-dripping agent is a coated polytetrafluoroethylene powder, the coating layer of which is a methyl methacrylate-styrene copolymer. Using polytetrafluoroethylene coated with methyl methacrylate-styrene copolymer as an anti-dripping agent effectively improves the dispersibility of PTFE in the polymer matrix, avoiding the "fisheye" problem caused by uneven dispersion. Simultaneously, by forming a fiber network structure during combustion, it significantly enhances the material's anti-dripping performance.

[0015] Furthermore, in step (6), the temperature of the heat-assisted post-curing is 85~95℃, and the time is 25~35 minutes. By precisely controlling the temperature and time of the heat-assisted post-curing, the optimal post-repair conditions are provided for the cross-linked network, which can promote further cross-linking of unreacted active sites and eliminate internal stress, while avoiding the thermo-oxidative aging of the polymer matrix caused by excessively high temperatures, and ultimately ensuring the stability and consistency of product performance.

[0016] This invention also provides an ultraviolet-crosslinked halogen-free flame-retardant cable material, prepared by the above method. Due to the innovative manufacturing process, this cable material possesses excellent comprehensive properties such as high flame retardancy, high mechanical strength, high crosslinking degree, and low smoke density, meeting the stringent material requirements of high-end cables.

[0017] The present invention also provides a cable whose insulation layer or sheath layer is made of the above-mentioned ultraviolet cross-linked halogen-free flame-retardant cable material, which enables the cable to maintain excellent electrical insulation and mechanical properties while possessing an extremely high flame-retardant safety level and low smoke and non-toxic characteristics, making it particularly suitable for places with extremely high fire safety requirements.

[0018] Compared with the prior art, the present invention has the following beneficial effects: I. This invention employs an innovative stepwise modification process. First, it utilizes the biomimetic strong adhesion properties of polydopamine to form a robust primary coating layer on the surface of aluminum hydroxide. This coating layer is rich in active functional groups, providing an ideal platform for subsequent reactions. Then, through the hydrolytic condensation of vinyl silane, molecular bridges with vinyl groups at their ends are constructed on the polydopamine layer. This design forms a stable chemical bond structure of "ATH-polydopamine-silane," completely solving the problem of easy interface failure in traditional physical coatings. More importantly, the vinyl groups on the surface can copolymerize with the crosslinking network of the matrix resin under ultraviolet irradiation, transforming the filler from a traditional inert isolating point into an actively participating crosslinking node. This not only greatly improves the compatibility between the filler and the matrix but also makes the filler part of a three-dimensional crosslinking network, thereby repairing the damage to the matrix continuity caused by high filler content at the microscopic level and significantly improving the tensile strength, elongation at break, and gel content of the material.

[0019] II. This invention abandons simple physical blending and instead uses a chemical reaction to simultaneously anchor melamine cyanurate (MCA) and aluminum hypophosphite (AHP) onto the surface of the modified filler, forming a unique composite flame-retardant structure. During combustion, MCA rapidly decomposes, effectively diluting combustibles and lowering the system temperature by absorbing heat and generating inert gases (gas-phase flame retardancy). Simultaneously, AHP decomposes to generate phosphoric acid, strongly catalyzing the dehydration of the polymer matrix and itself into char, and together with the dehydration products of aluminum hydroxide, constructs a dense and robust expanded char layer (condensed-phase flame retardancy), isolating heat and oxygen. This multi-level synergistic mechanism of "gas-phase flame retardancy - catalytic char formation - ceramic protection" through chemical bonding avoids the migration and loss of flame-retardant components, ensuring the durability and stability of flame-retardant efficiency. Thus, even with a low filler content of 30-40 parts, the material's oxygen index can be increased to over 32%, meeting the highest UL94 V-0 flame retardant standard, while significantly reducing smoke density.

[0020] Third, this invention innovatively combines microwave pretreatment, zoned gradient ultraviolet irradiation, and heat-assisted post-curing processes, systematically solving the problems of ultraviolet light shielding effect and cross-linking internal stress in highly filled inorganic systems. Microwave pretreatment selectively activates the matrix resin molecular chains and induces micro-melting, significantly enhancing its wetting and encapsulation capabilities for modified fillers. This achieves nanoscale uniform dispersion of fillers in the matrix, laying the foundation for subsequent uniform cross-linking. The zoned gradient irradiation process employs a "weak-then-strong" energy input strategy. It first induces moderate surface cross-linking at a lower intensity to prevent the closure of internal reaction channels due to excessively rapid surface cross-linking. Then, at a higher intensity, it ensures sufficient irradiation dose to the core, achieving uniform and deep cross-linking from the material surface to the interior, effectively eliminating performance gradients. The final heat-assisted post-curing process provides an "annealing" environment for the cross-linked network, promoting further reaction of unreacted active sites while simultaneously relaxing and rearranging existing cross-linking bonds, thoroughly releasing internal stress, and ultimately obtaining cable material products with stable structure, uniform performance, and excellent long-term thermal aging life. Detailed Implementation

[0021] The specific embodiments are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. Unless otherwise specified, the raw materials and reagents used in the examples are commercially available.

[0022] Example 1 (1) Add 10.0 kg of aluminum hydroxide powder to a reactor, add 30.0 kg of ethanol and 15.0 kg of deionized water, and start mechanical stirring to disperse at 200 rpm to form a uniform slurry. In another container, add 0.2 kg of dopamine hydrochloride (accounting for 2.0% of the mass of aluminum hydroxide) to a solution composed of 2.4 kg of ethanol and 0.6 kg of deionized water, and pre-hydrolyze at room temperature for 30 minutes. Slowly add the pre-hydrolyzed solution dropwise to the aluminum hydroxide slurry. Raise the temperature to 75°C and keep stirring for 18 hours to fully coat the surface of the aluminum hydroxide with polydopamine. After the reaction is complete, perform vacuum filtration and wash with 15.0 kg of anhydrous ethanol three times, 5.0 kg each time. Finally, dry in a vacuum drying oven at 80°C for 12 hours to obtain polydopamine-coated aluminum hydroxide composite filler.

[0023] (2) Disperse all the composite filler obtained in step (1) in a mixed solution consisting of 30 kg ethanol and 15 kg deionized water. Add 0.45 kg vinyltriethoxysilane (3.6% of the composite filler mass), adjust the pH to 4.5 with acetic acid, and carry out a hydrolysis-condensation reaction at 75°C for 1.5 hours. Then add 1.2 kg melamine cyanurate (particle size D50 = 3.2 μm, accounting for 9.6% of the composite filler mass) and 0.72 kg aluminum hypophosphite (particle size D50 = 2.5 μm, accounting for 5.76% of the composite filler mass), and continue to stir at 75°C for 2.5 hours (at this time, the particle size ratio of melamine cyanurate to aluminum hypophosphite is 1.28:1, and the mass ratio is 1:0.6). After the reaction is completed, perform vacuum filtration and wash with 15.0 kg anhydrous ethanol three times, 5.0 kg each time. Finally, the filler was dried in a vacuum drying oven at 80℃ for 12 hours to obtain the reactive modified composite flame retardant filler.

[0024] (3) By weight, 6.0 kg of ethylene-vinyl acetate copolymer (VA content of 36%) and 2.0 kg of polyolefin elastomer (POE) were placed in a microwave reactor and treated at 500W power for 2 minutes until the polymer surface showed a uniform micro-melting gloss, thus obtaining the pretreated matrix resin.

[0025] (4) Add all the pretreated matrix resin obtained in step (3), 3.5 kg of the reactive modified composite flame retardant filler obtained in step (2), 0.12 kg of lignite wax, 0.08 kg of silicone masterbatch (total mass of lubricant 0.2 kg, mass ratio of lignite wax to silicone masterbatch 1:0.67), and 1.0 kg of coated polytetrafluoroethylene powder (its coating layer is methyl methacrylate-styrene copolymer) to a preheated internal mixer. Mix at 130°C for 5 minutes, with the rotor speed controlled at 50 rpm, to ensure that all components are thoroughly mixed. Then add 0.36 kg of 2,4,6-trienylpropoxy-1,3,5-triazine and 0.18 kg of 2-hydroxy-2-methyl-1-phenyl-1-propanone, and continue mixing for 4 minutes. During this stage, the temperature of the internal mixer naturally drops to 125°C to ensure that the crosslinking agent and photosensitizer are evenly dispersed and do not crosslink prematurely.

[0026] (5) Transfer the uniformly mixed material to a two-roll mill and press it into a flat sheet with a thickness of 2.0 mm. Preheat the sheet in a 75°C oven for 4 minutes, and then transfer it to a nitrogen-protected ultraviolet irradiation chamber. A zoned gradient irradiation process is adopted: the irradiation intensity of the first zone is 35 mW / cm². 2 Irradiation time accounted for 35% of the total time; the irradiation intensity in the second zone was 60 mW / cm². 2 Irradiation time accounted for 65% of the total time; the total cumulative radiation dose reached 15 J / cm². 2.

[0027] (6) The irradiated sheet is quickly transferred to a hot air circulating oven at 90°C for heat-assisted curing for 30 minutes. After curing, the sheet is granulated by a pelletizer to obtain UV cross-linked halogen-free flame-retardant cable material.

[0028] Example 2 (1) Add 10.0 kg of aluminum hydroxide powder to a reactor, add 28.0 kg of ethanol and 14.0 kg of deionized water, and start mechanical stirring to disperse at 220 rpm to form a uniform slurry. In another container, add 0.15 kg of dopamine hydrochloride (1.5% of the mass of aluminum hydroxide) to a solution composed of 2.4 kg of ethanol and 0.6 kg of deionized water, and pre-hydrolyze at room temperature for 30 minutes. Slowly add the pre-hydrolyzed solution dropwise to the aluminum hydroxide slurry. Heat to 70℃ and keep stirring for 24 hours to fully coat the surface of the aluminum hydroxide with polydopamine. After the reaction is complete, perform vacuum filtration and wash with 15.0 kg of anhydrous ethanol three times, 5.0 kg each time. Finally, dry in a vacuum drying oven at 80℃ for 12 hours to obtain polydopamine-coated aluminum hydroxide composite filler.

[0029] (2) Disperse all the composite filler obtained in step (1) in a mixed solution consisting of 28 kg ethanol and 14 kg deionized water. Add 0.375 kg vinyltriethoxysilane (3.0% of the composite filler mass), adjust the pH to 4.0 with acetic acid, and carry out a hydrolysis-condensation reaction at 70°C for 2 hours. Then add 1.0 kg melamine cyanurate (particle size D50 = 3.6 μm, accounting for 8.0% of the composite filler mass) and 0.48 kg aluminum hypophosphite (particle size D50 = 3.0 μm, accounting for 4.0% of the composite filler mass), and continue to stir at 70°C for 3 hours (at this time, the particle size ratio of melamine cyanurate to aluminum hypophosphite is 1.2:1, and the mass ratio is 1:0.48). After the reaction is completed, perform vacuum filtration and wash with 15.0 kg anhydrous ethanol three times, 5.0 kg each time. Finally, the filler was dried in a vacuum drying oven at 80℃ for 12 hours to obtain the reactive modified composite flame retardant filler.

[0030] (3) By weight, 5.0 kg of ethylene-vinyl acetate copolymer (VA content of 33%) and 2.5 kg of polyolefin elastomer (POE) were placed in a microwave reactor and treated at 400W power for 3 minutes until the polymer surface showed a uniform micro-melting gloss, thus obtaining the pretreated matrix resin.

[0031] (4) Add all the pretreated matrix resin obtained in step (3), 3.0 kg of the reactive modified composite flame retardant filler obtained in step (2), 0.1 kg of lignite wax, 0.05 kg of silicone masterbatch (total mass of lubricant 0.15 kg, mass ratio of lignite wax to silicone masterbatch 1:0.5), and 0.5 kg of coated polytetrafluoroethylene powder (its coating layer is methyl methacrylate-styrene copolymer) to a preheated internal mixer. Mix at 120°C for 6 minutes, with the rotor speed controlled at 45 rpm, to ensure that all components are thoroughly mixed. Then add 0.24 kg of 2,4,6-trienylpropoxy-1,3,5-triazine and 0.12 kg of 2-hydroxy-2-methyl-1-phenyl-1-propanone, and continue mixing for 5 minutes. During this stage, the temperature of the internal mixer naturally drops to 120°C to ensure that the crosslinking agent and photosensitizer are evenly dispersed and do not crosslink prematurely.

[0032] (5) Transfer the uniformly mixed material to a two-roll mill and press it into a flat sheet with a thickness of 1.5 mm. Preheat the sheet in a 70℃ oven for 5 minutes, and then transfer it to a nitrogen-protected ultraviolet irradiation chamber. A zoned gradient irradiation process is adopted: the irradiation intensity of the first zone is 30 mW / cm². 2 Irradiation time accounted for 40% of the total time; the irradiation intensity in the second zone was 50 mW / cm². 2 Irradiation time accounted for 60% of the total time; the total cumulative radiation dose reached 10 J / cm². 2 .

[0033] (6) The irradiated sheet was quickly transferred to a hot air circulating oven at 80°C and heat-assisted curing was performed for 40 minutes. After curing, the sheet was granulated by a pelletizer to obtain UV cross-linked halogen-free flame-retardant cable material.

[0034] Example 3 (1) Add 10.0 kg of aluminum hydroxide powder to a reactor, add 32.0 kg of ethanol and 16.0 kg of deionized water, and start mechanical stirring to disperse at 180 rpm to form a uniform slurry. In another container, add 0.3 kg of dopamine hydrochloride (3.0% of the mass of aluminum hydroxide) to a solution composed of 2.4 kg of ethanol and 0.6 kg of deionized water, and pre-hydrolyze at room temperature for 30 minutes. Slowly add the pre-hydrolyzed solution dropwise to the aluminum hydroxide slurry. Heat to 80℃ and keep stirring for 12 hours to fully coat the surface of the aluminum hydroxide with polydopamine. After the reaction is complete, perform vacuum filtration and wash with 15.0 kg of anhydrous ethanol three times, 5.0 kg each time. Finally, dry in a vacuum drying oven at 80℃ for 12 hours to obtain polydopamine-coated aluminum hydroxide composite filler.

[0035] (2) Disperse all the composite filler obtained in step (1) in a mixed solution consisting of 32 kg ethanol and 16 kg deionized water. Add 0.625 kg vinyltriethoxysilane (5.0% of the composite filler mass), adjust the pH to 5.0 with acetic acid, and carry out a hydrolysis-condensation reaction at 80°C for 1 hour. Then add 1.44 kg melamine cyanurate (particle size D50 = 2.7 μm, accounting for 12.0% of the composite filler mass) and 1.2 kg aluminum hypophosphite (particle size D50 = 1.5 μm, accounting for 8.0% of the composite filler mass), and continue to stir at 80°C for 2 hours (at this time, the particle size ratio of melamine cyanurate to aluminum hypophosphite is 1.8:1, and the mass ratio is 1:0.83). After the reaction is completed, vacuum filter the solution and wash it three times with 15.0 kg anhydrous ethanol, 5.0 kg each time. Finally, the filler was dried in a vacuum drying oven at 80℃ for 12 hours to obtain the reactive modified composite flame retardant filler.

[0036] (3) By weight, 6.5 kg of ethylene-vinyl acetate copolymer (VA content of 40%) and 1.5 kg of polyolefin elastomer (POE) are placed in a microwave reactor and treated at 600W power for 1 minute until the polymer surface shows a uniform micro-melting gloss to obtain the pretreated matrix resin.

[0037] (4) Add all the pretreated matrix resin obtained in step (3), 4.0 kg of the reactive modified composite flame retardant filler obtained in step (2), 0.2 kg of lignite wax, 0.2 kg of silicone masterbatch (total mass of lubricant 0.4 kg, mass ratio of lignite wax to silicone masterbatch 1:1), and 2.0 kg of coated polytetrafluoroethylene powder (its coating layer is methyl methacrylate-styrene copolymer) to a preheated internal mixer. Mix at 135°C for 4 minutes, with the rotor speed controlled at 55 rpm, to ensure that all components are thoroughly mixed. Then add 0.48 kg of 2,4,6-trienylpropoxy-1,3,5-triazine and 0.24 kg of 2-hydroxy-2-methyl-1-phenyl-1-propanone, and continue mixing for 3 minutes. During this stage, the temperature of the internal mixer naturally drops to 130°C to ensure that the crosslinking agent and photosensitizer are evenly dispersed and do not crosslink prematurely.

[0038] (5) Transfer the uniformly mixed material to a two-roll mill and press it into a flat sheet with a thickness of 2.5 mm. Preheat the sheet in an 80℃ oven for 3 minutes, and then transfer it to a nitrogen-protected ultraviolet irradiation chamber. A zoned gradient irradiation process is adopted: the irradiation intensity of the first zone is 40 mW / cm². 2 Irradiation time accounts for 30% of the total time; the irradiation intensity in the second zone is 70 mW / cm². 2 Irradiation time accounted for 70% of the total time; the total cumulative radiation dose reached 20 J / cm². 2 .

[0039] (6) The irradiated sheet is quickly transferred to a hot air circulating oven at 100°C and heat-assisted curing is performed for 20 minutes. After curing, the sheet is granulated by a pelletizer to obtain UV cross-linked halogen-free flame-retardant cable material.

[0040] Comparative Example 1 Comparative Example 1 (Traditional Physical Mixture Modification) Preparation process: (1) 10.0 kg of aluminum hydroxide powder was preheated to 100°C in a high-speed mixer, and 0.45 kg of vinyltriethoxysilane was sprayed while stirring. The stirring was continued for 15 minutes. Then, 1.2 kg of melamine cyanurate (particle size D50 = 3.2 μm) and 0.72 kg of aluminum hypophosphite (particle size D50 = 2.5 μm) were added and physically mixed for 30 minutes. The mixture was dried in a vacuum drying oven at 80°C for 12 hours to obtain modified aluminum hydroxide.

[0041] (2) Add 6.0 kg of ethylene-vinyl acetate copolymer (VA content 36%), 2.0 kg of polyolefin elastomer (POE), 3.5 kg of the above-mentioned modified aluminum hydroxide, 0.12 kg of lignite wax, 0.08 kg of silicone masterbatch, and 1.0 kg of coated polytetrafluoroethylene powder to a preheated internal mixer. Mix at 130°C for 5 minutes with the rotor speed controlled at 50 rpm. Then add 0.36 kg of 2,4,6-trienylpropoxy-1,3,5-triazine and 0.18 kg of 2-hydroxy-2-methyl-1-phenyl-1-propanone, and continue mixing for 4 minutes.

[0042] (3) Press the uniformly mixed material into sheets with a thickness of 2.0 mm. Preheat the sheets in a 75°C oven for 4 minutes, then transfer them to a nitrogen-protected ultraviolet irradiation chamber. Use single-intensity irradiation: irradiation intensity 50 mW / cm². 2 Total cumulative radiation dose: 15 J / cm 2 After irradiation, the material was granulated to obtain the control cable material.

[0043] Comparative Example 2 (No microwave pretreatment or heat-assisted post-curing) Preparation process: (1)~(2) are the same as steps (1)~(2) in Example 1. (3) 6.0 kg of ethylene-vinyl acetate copolymer (VA content of 36%) and 2.0 kg of polyolefin elastomer (POE) were directly fed into the internal mixer without microwave pretreatment.

[0044] (4) Same as step (4) in Example 1 (5) Same as step (5) in Example 1 (6) The heat-assisted curing step is omitted, and the material is directly granulated after UV cross-linking to obtain the comparative cable material.

[0045] Comparative Example 3 (Non-reactive silane modification) Preparation process: (1) Add 10.0 kg of aluminum hydroxide powder to a reactor, along with 30.0 kg of ethanol and 15.0 kg of deionized water. Start mechanical stirring to form a homogeneous slurry. In a separate container, mix 0.45 kg of aminosilane (KH-550) with 2.4 kg of ethanol and 0.6 kg of deionized water for 30 minutes for pre-hydrolysis. Add the pre-hydrolyzed silane solution to the aluminum hydroxide slurry and adjust the pH to 4.5 with acetic acid. Heat to 75°C and maintain stirring for 1.5 hours. Then add 1.2 kg of melamine cyanurate (particle size D50 = 3.2 μm) and 0.72 kg of aluminum hypophosphite (particle size D50 = 2.5 μm), and continue stirring at 75°C for another 2.5 hours. Subsequent treatment is the same as in Example 1.

[0046] (2) to (6) are the same as steps (3) to (6) in Example 1. Comparative Example 4 (outside the preferred mass ratio range) Preparation process: (1) Same as step (1) in Example 1; (2) Disperse all the composite filler obtained in step (1) in a mixed solution consisting of 30 kg ethanol and 15 kg deionized water; add 0.45 kg vinyltriethoxysilane (accounting for 3.6% of the composite filler mass), adjust the pH to 4.5 with acetic acid, and carry out a hydrolysis-condensation reaction at 75°C for 1.5 hours. Then add 1.0 kg melamine cyanurate (particle size D50 = 3.2 μm, accounting for 8.0% of the composite filler mass) and 1.0 kg aluminum hypophosphite (particle size D50 = 2.5 μm, accounting for 8.0% of the composite filler mass), and continue to stir the reaction at 75°C for 2.5 hours (at this time, the mass ratio of aluminum hypophosphite to melamine cyanurate is 1:1, which is lower than the lower limit of the preferred range of claim 4); after the reaction is completed, the subsequent treatment is the same as in Example 1.

[0047] (3) to (6) are the same as steps (3) to (6) in Example 1. The performance of Examples 1-3 and Comparative Examples 1-4 was compared and tested using the following methods: 1. Oxygen Index Test (GB / T 2406.2-2009) The sample is vertically fixed in a transparent combustion chamber, and a controlled oxygen-nitrogen mixture is introduced. The top of the sample is ignited with an igniter, and the minimum percentage of oxygen concentration that can just support the continuous combustion of the sample is determined by testing at different oxygen concentrations.

[0048] 2. UL94 flame retardancy rating test (UL 94-2013) The vertical burning method is employed. The sample is suspended vertically, and the lower end of the sample is ignited twice for 10 seconds each time with a Bunsen burner flame (usually a 20mm blue flame) at a specific height. The V-0, V-1, or V-2 rating is determined based on the flaming burning time after each extinguishing, the flameless burning time, and whether burning drips are produced and ignite the cotton below.

[0049] 3. Tensile strength and elongation at break test (GB / T 1040.2-2006) Using a universal testing machine, a standard dumbbell-shaped specimen is stretched at a specified constant speed (usually 50 mm / min or 500 mm / min) until it breaks. The maximum tensile force and the elongation at break are recorded, and the tensile strength (maximum tensile force / original cross-sectional area) and the elongation at break (elongation / original gauge length × 100%) are calculated respectively.

[0050] 4. Heat distortion temperature test (GB / T 1634.2-2019) The specimen is placed in a dedicated heat distortion apparatus, and a specified constant bending load (usually 1.82 MPa or 0.45 MPa) is applied. The temperature is increased uniformly at a rate of 120 °C / h, and the temperature at which the specimen's bending deformation reaches the specified standard deflection (e.g., 0.21 mm or 0.34 mm) is measured. This temperature is the heat distortion temperature.

[0051] 5. Gel content test (GB / T 18474-2001) Weigh an appropriate amount of sample (usually wrapped in a mesh bag) and reflux it in a boiling inert solvent (such as xylene or decahydronaphthalene) for a specified time (usually 12-24 hours). This process will dissolve the uncrosslinked linear molecules, leaving the insoluble crosslinked network. After removing the insoluble material and drying it to constant weight, calculate the gel content percentage (dry weight of insoluble material / weight of original sample × 100%).

[0052] 6. Smoke density test (GB / T 8323.2-2008) A smoke density chamber is used. The sample is placed in a test chamber of a specific size and subjected to combustion or thermal decomposition under a specified thermal radiation intensity (with or without flame). Simultaneously, a beam of parallel light passes through the smoke, and the attenuation of the light intensity through the smoke layer is measured. The specific optical density (Ds) is calculated; a higher Ds value indicates a stronger smoke-generating property of the material.

[0053] The test results are shown in the table below: Test item Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Oxygen index (%) 34.5 31.8 33.2 27.8 31.2 30.5 31.0 UL94 rating (1.6 mm) V-0 V-0 V-0 V-2 V-1 V-1 V-1 Tensile strength (MPa) 19.8 17.5 18.6 13.2 16.5 15.8 17.8 Elongation at break (%) 480 420 450 320 380 350 410 Heat distortion temperature (°C) 128 120 125 102 118 115 121 Gel content (%) 81.5 73.2 78.8 55.3 70.2 65.8 76.5 Smoke density (Ds) 115 130 122 195 145 155 138 Analyzing the table data, we can see that: Comparative Example 1 (traditional physical mixing modification) simulated the closest existing technology path, and its comprehensive performance degradation—especially the flame retardancy rating reaching only V-2, and the severely insufficient tensile strength (13.2 MPa) and gel content (55.3%)—provides the most fundamental evidence for the inventiveness of this invention. In stark contrast, all examples consistently achieved the highest UL94 V-0 flame retardancy rating, maintained a tensile strength above 17.5 MPa, and had a gel content exceeding 73%. This difference is directly attributed to the core filler interface engineering design of this invention: the robust active interface layer constructed through "polydopamine biomimetic modification" and "vinylsilane grafting" transforms the filler from disrupting matrix continuity to participating in crosslinking, which is the cornerstone of achieving high performance.

[0054] The performance of Comparative Example 3 (non-reactive silane modification), especially its gel content (65.8%), was significantly lower than that of all other examples, indicating that simply improving the compatibility between the filler and the matrix is ​​far from sufficient; only by enabling the filler to deeply participate in the UV crosslinking network through vinyl functional groups can the structural integrity and mechanical properties of the material be improved.

[0055] The performance shortcomings of Comparative Example 2 (without microwave pretreatment and heat-assisted post-curing) demonstrate the synergistic value of optimizing the process chain. Its V-1 flame retardant rating and relatively low mechanical properties indicate that the uneven filler dispersion caused by the lack of microwave pretreatment, and the instability of the crosslinking network and internal stress caused by the lack of heat post-curing, both significantly reduce the performance of the final product. This proves that the value of this invention lies in its systematic "chemical modification-physical process" synergistic system.

[0056] The data from Comparative Example 4 (exceeding the preferred mass ratio) demonstrates the rigor of the claims. When the mass ratio deviates from the preferred range, although the basic performance is acceptable, key indicators such as flame retardancy rating (V-1) and smoke density (138 Ds) fail to reach the levels of the examples. This indicates that the specific mass ratio is crucial for achieving the optimal synergistic effect and cannot be easily determined by those skilled in the art through conventional experiments.

[0057] The technical advantages of this invention are ultimately reflected in the inherent unity and synergistic improvement of various performance indicators. High gel content is the physical basis for all of this; the high gel content of 81.5% in Example 1 directly translates into its optimal tensile strength (19.8 MPa), elongation at break (480%), and heat distortion temperature (128°C). Simultaneously, the chemically anchored "gas-solid-condensation" three-phase synergistic flame-retardant system, while imparting a high oxygen index (all >31%) and V-0 rating to the material, promotes the formation of a dense char layer during combustion, effectively suppressing smoke generation, thus achieving a balance between high flame retardancy and low smoke density. The lowest smoke density (115 Ds) in Example 1 is clear evidence of this synergistic effect.

[0058] In summary, the performance comparison of the system not only demonstrates the advantages of the present invention over existing technologies, but also reveals, through layer-by-layer analysis, how the innovative points interact to jointly contribute to the breakthrough in comprehensive performance of the material at low filler content. The excellent performance of Examples 1-3 verifies the rationality of the scope of the claims; while the significant differences compared to the comparative examples irrefutably prove the non-obviousness of the present invention and its significant technical progress.

[0059] It should be understood that the above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. It should not be considered that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A process for the preparation of a UV light crosslinked halogen free flame retardant cable compound, characterized in that, Comprising the following steps: (1) dispersing aluminum hydroxide powder in Tris-HCl buffer solution with pH of 8.5, adding dopamine hydrochloride, stirring for polymerization at room temperature for 12-24 hours to make polydopamine coated on the surface of aluminum hydroxide, obtaining polydopamine coated aluminum hydroxide composite filler; (2) dispersing the composite filler prepared in step (1) in a mixed solution of ethanol and water, adding 3-5% of vinyltriethoxysilane based on the mass of the composite filler, adjusting pH to 4-5 with acetic acid, and carrying out hydrolysis and condensation reaction at 70-80℃ for 1-2 hours; then adding 8-12% of melamine cyanurate and 5-10% of aluminum hypophosphite based on the mass of the composite filler, and continuing to carry out constant temperature stirring reaction for 2-3 hours; after the reaction is completed, filtering, washing and drying to obtain a reaction type modified composite flame retardant filler; (3) placing 50-65 parts of ethylene-vinyl acetate copolymer and 15-25 parts of polyolefin elastomer in a microwave reactor, treating at a power of 400-600W for 1-3 minutes to obtain a pretreated base resin; (4) putting all the pretreated base resin prepared in step (3), 30-40 parts of the reaction type modified composite flame retardant filler prepared in step (2), 1-3 parts of a lubricant, and 0.5-2 parts of an anti-dripping agent into an internal mixer, and mixing at 120-135℃ for 4-6 minutes; then adding 2-4 parts of 2,4,6-triallyloxy-1,3,5-triazine and 1-2 parts of 2-hydroxy-2-methyl-1-phenyl-1-propanone, and continuing to mix for 3-5 minutes; (5) The material after mixing is pressed into a sheet with a thickness of 1.5-2.5 mm; the sheet is placed in a nitrogen-protected ultraviolet light irradiation box, and a zoned gradient irradiation method is adopted, wherein the irradiation intensity of the first zone is 30-40 mW / cm 2 , the irradiation intensity of the second zone is 50-70 mW / cm 2 , the irradiation time of the sheet in the first zone accounts for 30-40% of the total irradiation time, and the remaining time is in the second zone, and the total cumulative irradiation dose is 10-20 J / cm 2 ; (6) quickly transferring the irradiated sheet to a hot air circulating oven at 80-100℃ for heat-assisted post-curing for 20-40 minutes to obtain the ultraviolet crosslinked halogen-free flame-retardant cable material.

2. The method of claim 1, wherein: In step (1), the amount of dopamine hydrochloride added is 1.5-2.5% of the mass of aluminum hydroxide.

3. The method of claim 1, wherein: In step (2), the particle size ratio of melamine cyanurate to aluminum hypophosphite is controlled in the range of (1.2-1.8):1, and the particle size D50 of the aluminum hypophosphite is less than 3μm.

4. The method of claim 3, wherein: In step (2), the mass ratio of aluminum hypophosphite to melamine cyanurate is 1:(1.2-2.5).

5. The method of claim 1, wherein: In step (3), the monomer content of vinyl acetate in the ethylene-vinyl acetate copolymer is 33-40%.

6. The method of claim 1, wherein: In step (4), the lubricant is a composite lubricating system composed of lignite wax and silicone master batch in a mass ratio of 1:(0.5-1).

7. The method of claim 1, wherein: In step (4), the anti-dripping agent is a coated polytetrafluoroethylene powder, and the coating layer is a methyl methacrylate-styrene copolymer.

8. The method of claim 1, wherein: In step (6), the temperature of heat-assisted post-curing is 85-95℃, and the time is 25-35 minutes.

9. An ultraviolet light crosslinked halogen-free flame retardant cable compound characterized by: Prepared by the method of any one of claims 1 to 8.

10. A cable, the insulation layer or sheath layer of which is made of the ultraviolet crosslinked halogen-free flame-retardant cable material of claim 9.