Halogen-free flame-retardant reinforced PP / ABS alloy material, preparation method thereof and explosion-proof distribution box shell

Abstract

The invention relates to the technical field of high polymer materials, in particular to a halogen-free flame-retardant reinforced PP / ABS alloy material, a preparation method thereof and an explosion-proof distribution box shell, and aims at solving the problems that although efficient flame retardance can be achieved through a traditional halogen flame-retardant scheme, a large amount of toxic smoke dust and corrosive hydrogen halide gas are released in the combustion process, and the flame retardance is poor. And increasingly strict environmental protection laws and regulations are seriously violated. The invention solves the problems that the interface compatibility of matrix resin and filler is deteriorated, the mechanical property of the material is obviously deteriorated, the tensile strength and impact toughness are greatly reduced, the processing fluidity becomes poor and the forming is difficult due to the fact that the common filler such as aluminum hydroxide or magnesium hydroxide needs to reach the same flame retardant grade at an extremely high adding proportion after turning to a halogen-free flame retardant system. By optimizing the proportion of matrix resin and introducing halogen-free flame-retardant components and glass fibers for reinforcement, the flame-retardant and mechanical properties are effectively balanced, meanwhile, halogen pollution is avoided, and the halogen-free flame-retardant glass fiber reinforced plastic has excellent halogen-free flame-retardant properties, good mechanical strength and environment-friendly characteristics.

Description

Technical Field

[0001] This application relates to the field of polymer materials technology, and more specifically, to a halogen-free flame-retardant reinforced PP / ABS alloy material, its preparation method, and an explosion-proof distribution box housing. Background Technology

[0002] Explosion-proof distribution boxes, as critical safety equipment, are widely used in flammable and explosive environments such as petrochemical plants, mining operations, and charging facilities for new energy vehicles. Their casing materials must simultaneously meet multiple stringent requirements: flame retardancy must reach UL94V-0 level to suppress flame spread; antistatic capability must ensure surface resistance remains stable within a safe threshold to prevent static electricity buildup; impact resistance must be sufficient to withstand mechanical shocks to avoid structural failure; and wide-temperature-range weather resistance is required to adapt to long-term service conditions from -40℃ to 85℃. However, existing material systems have revealed systemic defects in practical applications.

[0003] While traditional halogen-based flame retardant solutions achieve high flame retardancy, the combustion process releases large amounts of toxic fumes and corrosive hydrogen halide gases, severely violating increasingly stringent environmental regulations. Switching to halogen-free flame retardant systems requires extremely high proportions of fillers such as aluminum hydroxide or magnesium hydroxide to achieve the same flame retardancy rating. This leads to deterioration of the interfacial compatibility between the matrix resin and the filler, resulting in significant degradation of the material's mechanical properties, manifested as a substantial decrease in tensile strength and impact toughness, and poor processing flowability, making molding difficult. Regarding antistatic properties, existing technologies rely on a single internally added antistatic agent, whose mechanism depends on the continuous migration of active ingredients to the material surface. While initially achieving the required surface resistance, with prolonged service life, the antistatic components are gradually depleted, causing the surface resistance to rise to dangerous levels, resulting in loss of antistatic protection and a potential for electrostatic discharge accidents. In terms of mechanical properties, unreinforced PP / ABS alloys lack sufficient impact strength and are unable to withstand external impacts. Introducing glass fiber reinforcement results in weak bonding between the fiber and matrix, making the material prone to brittle fracture at low temperatures, leading to sealing failure and reduced explosion-proof reliability. In terms of weather resistance, long-term outdoor exposure causes materials to suffer from the combined effects of ultraviolet radiation and temperature cycling, triggering an irreversible photo-oxidation reaction. This manifests as surface chalking, cracking, and a decline in mechanical properties, failing to meet the 15-20 year design life requirements of explosion-proof equipment. A deeper problem lies in the fact that existing technical solutions often optimize single performance indicators in isolation, failing to comprehensively coordinate the multi-dimensional requirements of flame retardancy, antistatic properties, mechanical strength, and weather resistance. For example, while increasing the amount of flame retardant can improve the flame retardant effect, it exacerbates the deterioration of mechanical properties; increasing the amount of antistatic agent may interfere with processing stability. This interplay of properties makes it difficult for the overall material performance to achieve the comprehensive balance required for explosion-proof applications.

[0004] To address the aforementioned issues, existing technologies urgently need improvement. Summary of the Invention

[0005] (a) Technical problems to be solved The purpose of this application is to provide a halogen-free flame-retardant reinforced PP / ABS alloy material, its preparation method, and an explosion-proof distribution box housing, which has excellent halogen-free flame-retardant properties, good mechanical strength, and environmental protection characteristics.

[0006] (II) Technical Solution This application provides a halogen-free flame-retardant reinforced PP / ABS alloy material, the technical solution of which is as follows: By mass fraction, the materials include: 62%-68% matrix resin, which is a blend of polypropylene and acrylonitrile-butadiene-styrene copolymer, with a mass ratio of polypropylene to acrylonitrile-butadiene-styrene copolymer of 1.8:1 to 2.2:1; 16%-19% halogen-free flame retardant system, which includes ammonium polyphosphate, melamine cyanurate and nano-montmorillonite; and 9%-11% glass fiber.

[0007] Furthermore, this application also proposes that the polypropylene in the matrix resin includes homopolymer polypropylene and copolymer polypropylene, wherein the mass ratio of homopolymer polypropylene to copolymer polypropylene is 6.5:3.5 to 7.5:2.5.

[0008] Furthermore, this application also proposes that the mass ratio of ammonium polyphosphate to melamine cyanurate in the halogen-free flame retardant system is 1.9:1 to 2.1:1; and the amount of nano-montmorillonite added is 4.5%-5.5% of the total mass of the halogen-free flame retardant system.

[0009] Furthermore, this application also proposes that it further includes a composite antistatic system of 3.2%-4.8%, the composite antistatic system comprising a quaternary ammonium salt type antistatic agent and a carbon black dispersion; the addition amount of the quaternary ammonium salt type antistatic agent is 2.8%-4.2%, and the mass fraction of nano carbon black in the carbon black dispersion is 9%-11%.

[0010] Furthermore, this application also proposes to include 4.2%-5.8% of a compatibilizer, which includes maleic anhydride-grafted polypropylene and maleic anhydride-grafted ethylene-octene copolymer; the amount of maleic anhydride-grafted polypropylene added is 3.8%-5.2%, and the amount of maleic anhydride-grafted ethylene-octene copolymer added is 1.2%-2.8%.

[0011] Furthermore, this application also proposes that it further includes an anti-aging system of 1.1%-1.9%, which includes ultraviolet absorbers, antioxidants and nano zinc oxide; the amount of ultraviolet absorbers added is 0.9%-1.7%, the amount of antioxidants added is 0.5%-1.1%, and the amount of nano zinc oxide added is 0.35%-0.75%.

[0012] Furthermore, this application also proposes that the glass fiber has a length of 3-6 mm and a diameter of 10-15 μm; the glass fiber is surface-treated with a silane coupling agent.

[0013] Furthermore, this application also proposes a method for preparing the above-mentioned halogen-free flame-retardant reinforced PP / ABS alloy material, comprising the following steps: Step S1: Polypropylene, acrylonitrile-butadiene-styrene copolymer, ammonium polyphosphate, melamine cyanurate, nano-montmorillonite, quaternary ammonium salt antistatic agent, maleic anhydride-grafted polypropylene, maleic anhydride-grafted ethylene-octene copolymer, ultraviolet absorber, antioxidant, and nano-zinc oxide are mixed in a high-speed mixer at 112-128℃ for 13-17 minutes, with a mixing speed of 780-1020 rpm. Step S2: Dry the uniformly mixed material until the moisture content is ≤0.11%; Step S3: Melt extrusion is performed using a twin-screw extruder. The twin-screw extruder includes a premixing section and a main extrusion section along the material travel direction. The screw length in the premixing section is 22%-28% of the total screw length, and the screw length in the main extrusion section is 72%-78% of the total screw length. The twin-screw extruder has an exhaust port in the main extrusion section, and the vacuum degree is controlled at -0.078 to -0.082 MPa through the exhaust port. The extrusion temperature is set as follows: Zone 1 178-182℃, Zone 2 188-192℃, Zone 3 198-202℃, Zone 4 208-212℃, Zone 5 218-222℃, and Die 208-212℃. The screw speed is 190-310 rpm. Step S4: After extrusion, water cooling and pelletizing are performed to prepare PP / ABS alloy granules.

[0014] Furthermore, this application also proposes that, in step S3, the exhaust port of the twin-screw extruder is located in the middle and rear part of the main extrusion section, and at least one screw conveying element is provided between the exhaust port and the die head of the twin-screw extruder; the twin-screw extruder is provided with a side feed port in the main extrusion section, through which glass fiber is added, and the side feed port is located upstream of the exhaust port.

[0015] Furthermore, this application also proposes an explosion-proof distribution box housing, the housing being made of the aforementioned halogen-free flame-retardant reinforced PP / ABS alloy material; The housing also includes a silicone rubber gasket, and the housing and the silicone rubber gasket are connected by hot-pressing composite bonding. The hot-pressing composite bonding temperature is 112-128℃, the pressure is 4.2-5.8MPa, and the time is 1.8-3.2min. Before hot pressing, the shell also undergoes plasma surface treatment at a temperature of 55-85℃ for 2.5-5.5 minutes and a power of 190-310W. The shell is manufactured using a two-color injection molding process. The mold has an integrated structure of explosion-proof stop and sealing groove. The injection temperature is set as follows: Zone 1 178-182℃, Zone 2 188-192℃, Zone 3 198-202℃, Zone 4 218-222℃. The holding pressure is 78-102MPa, the holding time is 2.8-5.2s, and the cooling time is 24-31s.

[0016] (III) Beneficial Effects Compared with the prior art, the beneficial effects of the present invention are as follows: This application provides a halogen-free flame-retardant reinforced PP / ABS alloy material, its preparation method, and an explosion-proof distribution box shell. By mass fraction, the material comprises: 62%-68% matrix resin, which is a blend of polypropylene and acrylonitrile-butadiene-styrene copolymer, with a mass ratio of polypropylene to acrylonitrile-butadiene-styrene copolymer of 1.8:1 to 2.2:1; 16%-19% halogen-free flame-retardant system, including ammonium polyphosphate, melamine cyanurate, and nano-montmorillonite; and 9%-11% glass fiber. By optimizing the matrix resin ratio, introducing halogen-free flame-retardant components, and glass fiber reinforcement, the flame retardancy and mechanical properties are effectively balanced, while avoiding halogen pollution. It exhibits excellent halogen-free flame-retardant properties, good mechanical strength, and environmentally friendly characteristics. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A schematic diagram of the preparation process for halogen-free flame-retardant reinforced PP / ABS alloy materials. Detailed Implementation

[0019] Traditional explosion-proof distribution box housing materials, such as pure ABS resin, PP resin, or PC / ABS alloy, have many shortcomings in terms of balancing halogen-free flame retardancy and environmental friendliness, insufficient mechanical properties, low explosion-proof reliability, and a single formulation system. Specifically, existing solutions mostly rely on halogenated flame retardants, which produce toxic gases during combustion; halogen-free flame retardants require large amounts, leading to a decrease in mechanical properties; insufficient mechanical properties make them prone to brittleness at low temperatures, resulting in low explosion-proof reliability; and the single formulation system makes synergistic optimization difficult.

[0020] In response to this, this application proposes a halogen-free flame-retardant reinforced PP / ABS alloy material. This material, by mass fraction, comprises 62%-68% matrix resin, wherein the matrix resin is a blend of polypropylene and acrylonitrile-butadiene-styrene copolymer, with a mass ratio of polypropylene to acrylonitrile-butadiene-styrene copolymer of 1.8:1 to 2.2:1; 16%-19% halogen-free flame-retardant system, which includes ammonium polyphosphate, melamine cyanurate, and nano-montmorillonite; and 9%-11% glass fiber. By optimizing the matrix resin composition, the synergistic effect of the halogen-free flame-retardant system, and the glass fiber reinforcement, this application aims to address the shortcomings of existing explosion-proof distribution box shell materials in balancing halogen-free flame retardancy and environmental friendliness, insufficient mechanical properties, low explosion-proof reliability, and a single formulation system, while completely avoiding the use of halogen flame retardants.

[0021] For ease of understanding, the following explains some key terms in this embodiment: Halogen-free flame-retardant reinforced PP / ABS alloy material refers to a composite material made of polypropylene and acrylonitrile-butadiene-styrene copolymer, which are blended without halogen flame retardants and whose mechanical properties are improved by adding reinforcing materials. This material is mainly used in fields with strict requirements for flame retardancy, mechanical properties, and environmental protection, such as explosion-proof distribution box housings.

[0022] The matrix resin refers to the polymer component that constitutes the main body of the material. In this application, it is a blend of polypropylene and acrylonitrile-butadiene-styrene copolymer, which provides the material with basic mechanical and processing properties.

[0023] Polypropylene (PP) is a thermoplastic resin with good rigidity, heat resistance and processing fluidity.

[0024] Acrylonitrile-butadiene-styrene copolymer (ABS) is a thermoplastic engineering plastic with good toughness, impact resistance and surface hardness.

[0025] Halogen-free flame retardant systems refer to combinations of flame retardants that do not contain halogen elements. They inhibit the combustion of materials through physical or chemical actions, while avoiding the generation of toxic and harmful gases.

[0026] Ammonium polyphosphate (APP) is an effective intumescent halogen-free flame retardant that decomposes at high temperatures to produce polyphosphoric acid, promoting char formation on the material surface and forming a dense char layer that insulates against heat and oxygen.

[0027] Melamine cyanurate (MCA) is a nitrogen-based halogen-free flame retardant that decomposes at high temperatures to release inert gases, dilute the concentration of flammable gases, and absorb heat, thus exhibiting gas-phase flame retardant properties.

[0028] Nano-montmorillonite is a layered silicate nanomaterial with a large specific surface area and interlayer spacing. It can be used as a synergistic flame retardant to enhance the density of the char layer and improve flame retardant efficiency through intercalation or exfoliation structures.

[0029] Glass fiber is an inorganic non-metallic material with high strength and high modulus. When added to the matrix resin as a reinforcing filler, it can effectively improve the mechanical properties of the material, such as tensile strength, flexural strength and impact strength.

[0030] This application provides a halogen-free flame-retardant reinforced PP / ABS alloy material, wherein the mass fraction of the matrix resin is 62%-68%, and it is composed of a blend of polypropylene and acrylonitrile-butadiene-styrene copolymer. The mass ratio of polypropylene to acrylonitrile-butadiene-styrene copolymer can be from 1.8:1 to 2.2:1. For example, the polypropylene can be a general-purpose homopolymer polypropylene, and the acrylonitrile-butadiene-styrene copolymer can be a grade with medium impact strength. In the preparation process, the polypropylene and acrylonitrile-butadiene-styrene copolymer can be pre-mixed using a high-speed mixer, followed by melt extrusion. The content of the matrix resin can be adjusted within the range of 62%-68% to balance the overall mechanical properties and processing properties of the material.

[0031] In one implementation, the halogen-free flame retardant system comprises 16%-19% by mass and includes ammonium polyphosphate, melamine cyanurate, and nano-montmorillonite. The ammonium polyphosphate can be a product with a relatively high degree of polymerization, for example, ammonium polyphosphate with an average degree of polymerization greater than 1000. The melamine cyanurate can be a product with an average particle size of 5-10 micrometers. The nano-montmorillonite can be an organically modified product, for example, nano-montmorillonite modified with quaternary ammonium salts. These components can be combined in different proportions; for example, the mass ratio of ammonium polyphosphate to melamine cyanurate can be 1:1, and the amount of nano-montmorillonite added can be 3% of the total mass of the flame retardant system. During preparation, these flame retardant components can be added together with the matrix resin into a mixing device to ensure uniform dispersion.

[0032] Furthermore, the material contains 9%-11% glass fiber by mass. The glass fiber can be chopped glass fiber, with a length of 2 mm and a diameter of 18 μm. When adding the glass fiber to the matrix resin, it can be fed directly, for example, into a twin-screw extruder through a side feed port. The surface of the glass fiber does not require special treatment, or only simple cleaning. The amount of glass fiber added can be adjusted within the range of 9%-11% to meet different mechanical property requirements of the material.

[0033] The halogen-free flame-retardant reinforced PP / ABS alloy material provided in this embodiment achieves a synergistic effect of effective halogen-free flame retardancy and excellent mechanical properties through precise formulation of the matrix resin, compounding of the halogen-free flame-retardant system, and quantitative reinforcement of glass fiber. This material achieves the UL94 V-0 flame retardant standard without using any halogenated flame retardants, and releases no toxic or harmful gases during combustion, meeting environmental protection requirements. Simultaneously, the material possesses good rigidity, good toughness, and good processing fluidity. Its impact strength and other mechanical properties meet the stringent requirements for explosion-proof distribution box housings, effectively improving explosion-proof reliability and addressing the shortcomings of existing explosion-proof distribution box housing materials in terms of flame retardancy, environmental protection, mechanical properties, and a single formulation system.

[0034] In some of the embodiments described above in this application, polypropylene in the matrix resin is proposed to provide the rigidity and processability of the material. However, in this process, the lack of a specific type of polypropylene may result in insufficient material toughness, poor low-temperature impact resistance, and affect the reliability and long-term stability of the explosion-proof housing.

[0035] In this regard, this application further proposes that the polypropylene in the matrix resin of the above-mentioned halogen-free flame-retardant reinforced PP / ABS alloy material includes homopolymer polypropylene and copolymer polypropylene, and the mass ratio of homopolymer polypropylene to copolymer polypropylene is 6.5:3.5 to 7.5:2.5.

[0036] Specifically, the homopolymer polypropylene is a polymer material polymerized from a single propylene monomer. It has a regular molecular chain structure, high crystallinity, and typically exhibits high tensile strength, flexural modulus, and hardness. In composite materials, homopolymer polypropylene primarily provides rigidity, strength, and a good heat distortion temperature, making it a major contributor to the material's structural support. The homopolymer polypropylene can be injection molding or extrusion grade homopolymer polypropylene with a melt flow index (MFR) in the range of 5-20 g / 10min (230℃, 2.16kg) to ensure good processing performance; or high-crystallinity homopolymer polypropylene can be selected, such as homopolymer polypropylene produced using metallocene catalysts, which has higher rigidity and thermal stability, to further enhance the material's structural strength.

[0037] The copolymer polypropylene is a polypropylene copolymerized by introducing a small amount of other olefin monomers (such as ethylene, butene, etc.) during the propylene polymerization process. Due to the introduction of comonomers, the molecular chain regularity is broken, and the crystallinity is reduced, thus giving the material better toughness, impact resistance, and low-temperature performance. In composite materials, copolymer polypropylene is mainly used to improve the toughness of the material, especially its low-temperature impact resistance, compensating for the brittleness of homopolymer polypropylene at low temperatures. The copolymer polypropylene can be random copolymer polypropylene, in which ethylene or butene monomers are randomly distributed in the propylene chain, providing good flexibility; or block copolymer polypropylene, in which ethylene or butene monomers exist in block form, providing superior impact resistance, especially suitable for low-temperature environments.

[0038] The mass ratio of homopolymer polypropylene to copolymer polypropylene is between 6.5:3.5 and 7.5:2.5. This ratio range has been finely optimized to achieve the best balance between material rigidity and toughness. Within this range, homopolymer polypropylene dominates (65%-75%), ensuring sufficient rigidity and strength to meet the structural stability and load-bearing capacity requirements of the explosion-proof distribution box housing. Simultaneously, the presence of copolymer polypropylene at a proportion of 25%-35% significantly improves the material's toughness, particularly its low-temperature impact resistance, effectively preventing brittle fracture at low temperatures and thus ensuring the integrity and sealing of the explosion-proof housing.

[0039] Through the above technical solution, this application, by refining the polypropylene component in the matrix resin and compounding homopolymer polypropylene and copolymer polypropylene in a specific ratio, effectively solves the problems of insufficient material toughness and poor low-temperature impact resistance caused by a single type of polypropylene. Homopolymer polypropylene provides the necessary rigidity and strength, ensuring the structural stability of the explosion-proof enclosure; while copolymer polypropylene significantly improves the toughness of the material, especially in harsh low-temperature environments such as -40℃, effectively preventing the enclosure from cracking due to impact, thereby ensuring the reliability and long-term stability of the explosion-proof distribution box under extreme conditions.

[0040] Building upon this, the optimized polypropylene component exhibits a synergistic effect with the aforementioned PP / ABS alloy matrix, halogen-free flame-retardant system, and glass fiber reinforcement system. The more resilient polypropylene matrix demonstrates better compatibility with acrylonitrile-butadiene-styrene copolymer (ABS), improving the overall uniformity of the matrix texture. Simultaneously, the enhanced matrix toughness provides a more stable carrier for the halogen-free flame-retardant system and glass fibers, reducing the decrease in interfacial bonding caused by matrix brittleness, thus allowing the flame retardant and reinforcing fiber performance to be fully realized. This synergistic effect not only improves the material's low-temperature impact resistance but also ensures that the material meets the flame-retardant and mechanical properties required for explosion-proof applications, while possessing excellent overall performance, extending the service life of the explosion-proof distribution box housing, and reducing maintenance costs.

[0041] In some of the solutions described above in this application, a halogen-free flame retardant system is proposed to provide flame retardant performance. However, in this process, an improper ratio of ammonium polyphosphate to melamine cyanurate may lead to insufficient flame retardant synergistic effect and affect flame retardant efficiency. At the same time, an improper amount of nano-montmorillonite may cause uneven dispersion, thereby reducing the mechanical properties and processing stability of the material.

[0042] In this regard, this application further proposes that the mass ratio of ammonium polyphosphate to melamine cyanurate in the halogen-free flame retardant system is 1.9:1 to 2.1:1; and the amount of nano-montmorillonite added is 4.5%-5.5% of the total mass of the halogen-free flame retardant system.

[0043] Specifically, in the halogen-free flame retardant system, ammonium polyphosphate, as an intumescent flame retardant, decomposes at high temperatures to produce phosphoric acid, promoting char formation in the polymer matrix and forming a dense char layer, thereby effectively isolating heat, oxygen, and flammable gases. Melamine cyanurate, as a nitrogen-based flame retardant, decomposes at high temperatures to release non-flammable gases such as ammonia, thereby diluting the concentration of flammable gases and absorbing heat, thus playing a role in gas-phase flame retardancy and cooling. This application limits the mass ratio of ammonium polyphosphate to melamine cyanurate to the range of 1.9:1 to 2.1:1, aiming to optimize the synergistic flame retardant effect of these two flame retardants in the gas and condensed phases. Those skilled in the art may also try other mass ratios in practical applications; for example, when the mass ratio of ammonium polyphosphate to melamine cyanurate is 1:1, the focus may be on balancing the flame retardant effect in the gas and condensed phases; when the mass ratio is 3:1, the char formation effect of the condensed phase may be emphasized more. However, these ratios may not achieve the optimal synergistic flame retardant efficiency desired in this application.

[0044] The nano-montmorillonite is a layered silicate nanomaterial whose unique layered structure and high specific surface area enable it to perform multiple functions in polymers. In terms of flame retardancy, nano-montmorillonite can delay the transfer of heat and flammable gases by forming a physical barrier, and promote the formation and densification of the char layer. Regarding mechanical properties, when uniformly dispersed in a polymer matrix, nano-montmorillonite can act as a nano-reinforcement, improving the strength and stiffness of the material. In terms of processing performance, an appropriate amount of nano-montmorillonite helps improve melt rheology. This application limits the addition amount of nano-montmorillonite to 4.5%-5.5% of the total mass of the halogen-free flame retardant system, aiming to achieve an optimal balance between dispersibility, flame retardant enhancement, and mechanical / processability protection. Besides the addition range specified in this application, the addition amount of nano-montmorillonite can also be other ranges. For example, when the addition amount is less than 4.5%, an effective nano-dispersed structure may not be formed, and the flame retardant and reinforcing effects are not obvious; when the addition amount is greater than 5.5%, nano-montmorillonite may agglomerate, resulting in uneven dispersion, which in turn reduces the mechanical properties and processing fluidity of the material.

[0045] By precisely controlling the mass ratio of ammonium polyphosphate to melamine cyanurate within the range of 1.9:1 to 2.1:1 using the above technical solution, the synergistic effect of gas-phase and condensed-phase flame retardancy can be maximized, ensuring that the material still achieves excellent flame retardant performance even with a relatively low total amount of flame retardant added. Simultaneously, limiting the addition of nano-montmorillonite to 4.5%-5.5% of the total mass of the halogen-free flame retardant system effectively avoids the agglomeration problem caused by excessive addition of nano-montmorillonite, ensuring its uniform dispersion in the matrix. This improves flame retardant efficiency while effectively protecting the material's mechanical properties, such as impact strength and tensile strength, and also improves the material's processing stability. This precise control of proportions and addition amounts allows the halogen-free flame retardant system to work synergistically with the matrix resin (a blend of polypropylene and acrylonitrile-butadiene-styrene copolymer) and the glass fiber reinforcement system. This avoids a decline in the overall material performance caused by uneven dispersion or improper proportions of the flame retardant components, thus ensuring that the halogen-free flame retardant reinforced PP / ABS alloy material can stably meet multiple requirements for flame retardancy, mechanical properties, and processing performance in harsh application scenarios such as explosion-proof distribution box housings.

[0046] In some of the embodiments described above in this application, halogen-free flame-retardant reinforced PP / ABS alloy materials are proposed to meet the requirements of flame retardancy and mechanical properties in explosion-proof environments. However, in the process of implementation, the material lacks an effective antistatic system, resulting in insufficient antistatic performance and short duration, requiring frequent replacement of the shell, which increases maintenance costs and safety hazards.

[0047] In this regard, this application further proposes that the halogen-free flame-retardant reinforced PP / ABS alloy material also includes a composite antistatic system of 3.2%-4.8%, the composite antistatic system including a quaternary ammonium salt type antistatic agent and a carbon black dispersion; the addition amount of the quaternary ammonium salt type antistatic agent is 2.8%-4.2%, and the mass fraction of nano carbon black in the carbon black dispersion is 9%-11%.

[0048] The composite antistatic system aims to provide comprehensive and durable antistatic performance through the synergistic effect of multiple mechanisms. The introduction of this system effectively solves the problems of short-term effectiveness and unstable performance of single antistatic agents in explosion-proof environments, ensuring that the material maintains good electrostatic dissipation capabilities during long-term use. The quaternary ammonium salt antistatic agent, as an internally added antistatic component, primarily provides a rapid, initial antistatic effect by continuously migrating from within the material to the surface, forming a temporary conductive pathway. For example, alkyl quaternary ammonium salts or polyether-modified quaternary ammonium salts can be selected, as they possess good thermal stability and migration properties, continuously replenishing the conductivity of the material surface reduced by wear or consumption. The carbon black dispersion, as an externally applied antistatic component, refers to a liquid in which nano-sized carbon black particles are uniformly dispersed in a specific solvent or carrier, such as an aqueous dispersion or an organic solvent dispersion. This is applied by spraying or other methods to form a dense, continuous conductive network on the shell surface after material molding. This conductive network provides long-lasting and stable antistatic performance, fundamentally compensating for the potential time-limited problems of internally added antistatic agents. The addition amount of the quaternary ammonium salt antistatic agent is controlled at 2.8%-4.2% to optimize its dispersibility, migration rate, and antistatic effect in the matrix resin, ensuring that it can effectively exert its initial antistatic effect without negatively impacting the processing and mechanical properties of the material. The mass fraction of nano-carbon black in the carbon black dispersion is 9%-11%. This range is designed to ensure good dispersion stability of the nano-carbon black in the dispersion and to form an effective conductive network after spraying. This avoids discontinuous conductive network due to excessively low carbon black content, or agglomeration of nano-carbon black due to excessively high content, which would affect the uniformity of the dispersion and the conductivity of the sprayed coating.

[0049] Through the above technical solution, the halogen-free flame-retardant reinforced PP / ABS alloy material of this application can achieve a composite antistatic mechanism of "internal quaternary ammonium salt + external carbon black coating", forming a dual antistatic effect of "immediate replenishment + long-term support". The internally added quaternary ammonium salt antistatic agent continuously migrates to the material surface, providing a rapid initial antistatic effect and replenishing the potentially damaged surface conductive layer; the externally coated carbon black dispersion forms a durable conductive layer on the material surface, ensuring long-term static dissipation capability. This composite system enables the surface resistance of the material to be stably maintained within the explosion-proof requirements, significantly extending the antistatic aging time, effectively solving the problems of short aging time and frequent shell replacement required by traditional single antistatic agents, thereby significantly reducing maintenance costs and eliminating the safety hazard of electrostatic discharge-induced explosions. At the same time, the precise quantitative design of this composite antistatic system ensures that while achieving excellent antistatic performance, it is highly compatible with the matrix resin, halogen-free flame-retardant system, and glass fiber reinforcement system, without negatively affecting the flame-retardant performance, mechanical properties, and processing performance of the material, avoiding the industry pain point of sacrificing other comprehensive properties to improve antistatic performance in existing technologies. Furthermore, the continuous migration and replenishment of the internally added quaternary ammonium salt can repair minor wear on the external carbon black coating during long-term use. Combined with the excellent dispersibility of nano-carbon black in the carbon black dispersion, this ensures the stability and uniformity of the antistatic effect, maintaining good antistatic performance even in the complex structures of explosion-proof distribution boxes, further enhancing safety. This external carbon black dispersion is also compatible with subsequent plasma surface treatment and hot-pressing composite processes for silicone rubber gaskets, ensuring the sealing reliability of the explosion-proof housing and its overall explosion-proof performance.

[0050] In some embodiments described above in this application, a matrix resin, a halogen-free flame retardant system, and glass fiber are proposed to improve the flame retardancy and mechanical strength of the material. However, in the process of implementation, the poor interfacial compatibility between the components leads to insufficient material toughness, which makes the material prone to brittleness at low temperatures and affects the reliability of explosion protection.

[0051] In this regard, this application further proposes a halogen-free flame-retardant reinforced PP / ABS alloy material, which further includes 4.2%-5.8% compatibilizer, wherein the compatibilizer includes maleic anhydride-grafted polypropylene and maleic anhydride-grafted ethylene-octene copolymer; the amount of maleic anhydride-grafted polypropylene added is 3.8%-5.2%, and the amount of maleic anhydride-grafted ethylene-octene copolymer added is 1.2%-2.8%.

[0052] Compatibilizers are substances used to improve the interfacial compatibility between different components in polymer blends. In multi-component polymer composites, phase separation easily occurs due to differences in polarity, surface energy, and other properties among the components, leading to weak interfacial bonding and decreased mechanical properties. Compatibilizers improve the overall performance of the material by forming bridging effects at the interfaces between different components, reducing interfacial tension, and promoting uniform dispersion among the components. For example, a compatibilizer can be a block copolymer, where different blocks are compatible with different components in the blend; or it can be a graft copolymer, where the grafted functional groups react with one component or form strong interactions, while the polymer backbone is compatible with the other component.

[0053] Maleic anhydride-grafted polypropylene is a commonly used reactive compatibilizer. Its polypropylene backbone exhibits good compatibility with the polypropylene in the matrix resin, while the grafted maleic anhydride groups possess strong polarity, enabling them to chemically react with or form hydrogen bonds with polar groups (such as the nitrile groups of acrylonitrile-butadiene-styrene copolymer) in the matrix resin, thereby establishing an effective interfacial bond between the polypropylene and the acrylonitrile-butadiene-styrene copolymer. Furthermore, the maleic anhydride groups can also interact with the hydroxyl groups on the glass fiber surface, enhancing the interfacial bonding between the glass fiber and the matrix resin. Its function is to strengthen the interfacial bonding between rigid components, improving the overall structural stability of the material.

[0054] Maleic anhydride-grafted ethylene-octene copolymer is a polymer that combines toughening and compatibility. The ethylene-octene copolymer backbone possesses good flexibility and elasticity, effectively absorbing impact energy and thus imparting excellent toughness to the material, especially at low temperatures. Simultaneously, the grafted maleic anhydride groups enable compatibility with polypropylene, acrylonitrile-butadiene-styrene copolymers, and glass fibers, ensuring uniform dispersion in the composite material and maximizing its toughening effect, avoiding poor toughening due to phase separation. Its role is to introduce flexible segments, improving the material's low-temperature toughness and resistance to brittle fracture.

[0055] The amount of compatibilizer added is crucial to the performance of composite materials. An appropriate amount of compatibilizer can fully exert its interfacial modification effect, effectively improving the compatibility between components, thereby enhancing the material's mechanical properties, processability, and long-term stability. If the amount added is too small, it will not completely cover all interfaces, resulting in insignificant compatibility; if the amount added is too large, it may lead to decreased material rigidity, excessively high melt viscosity, affecting processing fluidity, and increasing material costs. Therefore, precisely controlling the amount of compatibilizer added is key to achieving comprehensive material performance optimization.

[0056] Through the above technical solutions, the halogen-free flame-retardant reinforced PP / ABS alloy material of this application can significantly improve the interfacial compatibility between multiple components, thereby effectively solving the problems of insufficient material toughness and low-temperature brittleness. Specifically, maleic anhydride-grafted polypropylene serves as the main compatibilizer, with its polypropylene segments compatible with the polypropylene in the matrix resin. The maleic anhydride groups form chemical bonds or hydrogen bonds with the acrylonitrile-butadiene-styrene copolymer and the glass fiber surface, achieving effective bridging between polypropylene, acrylonitrile-butadiene-styrene copolymer, and glass fiber, strengthening the interfacial bonding force between rigid components, and avoiding mechanical property loss due to phase separation. At the same time, maleic anhydride-grafted ethylene-octene copolymer serves as an auxiliary toughening compatibilizer, with its flexible ethylene-octene segments forming elastic microregions inside the material, significantly improving the material's low-temperature toughness and crack resistance, effectively solving the problem of easy brittleness in low-temperature environments. This synergistic mechanism of "rigid interface strengthening + flexible toughness enhancement" allows the material to maintain sufficient rigidity and structural strength while improving toughness, achieving an optimized balance between rigidity and toughness. Furthermore, the optimized interface structure facilitates the uniform dispersion of flame retardants and nano-montmorillonite in the matrix, further enhancing the flame retardant effect and improving the melt flowability of the material, thus increasing processing yield. Overall, this compatibilizer system is highly compatible with halogen-free flame retardant systems and antistatic systems, ensuring synergistic improvement of various material properties rather than mutual restriction, thereby significantly enhancing the explosion-proof reliability and service life of the explosion-proof distribution box housing in harsh environments.

[0057] In some of the embodiments described above in this application, halogen-free flame-retardant reinforced PP / ABS alloy materials are proposed to meet the flame-retardant, mechanical, and processing requirements of explosion-proof equipment. However, during long-term outdoor exposure, the material is easily affected by ultraviolet radiation and oxidation, leading to intensified photo-oxidation reactions, yellowing, cracking, and decreased mechanical properties, resulting in insufficient service life.

[0058] In response, this application further proposes a halogen-free flame-retardant reinforced PP / ABS alloy material, which, in addition to the aforementioned matrix resin, halogen-free flame-retardant system, and glass fiber, also includes an anti-aging system of 1.1%-1.9%. This anti-aging system aims to effectively address the aging problem of the material in outdoor environments, significantly improving the material's weather resistance and service life.

[0059] The anti-aging system comprises ultraviolet (UV) absorbers, antioxidants, and nano-zinc oxide. The UV absorber is a chemical substance that selectively absorbs UV radiation and converts it into harmless heat or fluorescence. Its function is to block UV-induced polymer chain breakage and photo-oxidation reactions at the source, protecting materials from UV degradation. Common UV absorbers include benzotriazoles, such as 2-(2H-benzotriazole-2-yl)-4,6-di-tert-pentylphenol (UV-328) or 2-(2H-benzotriazole-2-yl)-4,6-di-tert-butylphenol (UV-327); or benzophenones, such as 2-hydroxy-4-n-octyloxybenzophenone (UV-531) or 2-hydroxy-4-methoxybenzophenone (UV-9). Antioxidants are chemical substances that can inhibit or delay the oxidative degradation process of polymer materials. They typically function by capturing free radicals, decomposing peroxides, or passivating metal ions. Their aim is to suppress free radical chain reactions generated by heat and oxygen during processing and use, preventing the material from experiencing a decline in mechanical properties and embrittlement due to oxidation. Common antioxidants include hindered phenols, such as pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1010) or octadecyl-β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (antioxidant 1076); and phosphites, such as tris(2,4-di-tert-butylphenyl) phosphite (antioxidant 168). Nano zinc oxide refers to zinc oxide particles with a particle size ranging from 1 to 100 nanometers. It possesses unique physical and chemical properties and can perform multiple functions in anti-aging systems, including UV shielding, photocatalytic inhibition, thermal stabilization, and flame retardant synergy. In addition to nano zinc oxide, other nano metal oxides such as nano titanium dioxide or nano cerium oxide can also be considered, as they also have certain UV shielding and anti-aging functions.

[0060] In this application, the amount of ultraviolet absorber added is 0.9%-1.7%, the amount of antioxidant added is 0.5%-1.1%, and the amount of nano-zinc oxide added is 0.35%-0.75%. Through the above technical solution, this application achieves a significant improvement in the anti-aging performance of halogen-free flame-retardant reinforced PP / ABS alloy materials. This ternary anti-aging system absorbs ultraviolet radiation from the source through ultraviolet absorber, blocking the photodegradation chain reaction; the antioxidant effectively captures free radicals generated during material processing and use, inhibiting the thermal oxidation process; and the nano-zinc oxide enhances the durability of ultraviolet protection through physical shielding and photocatalytic inhibition, and can synergistically improve the flame-retardant performance of the material. This full-chain anti-aging mechanism of "source absorption + process blocking + physical shielding" effectively solves the problems of single protection and short time-limited effect of traditional anti-aging systems, enabling materials to effectively resist ultraviolet radiation and thermal oxidation when exposed to the outdoors for a long time, avoiding problems such as yellowing, cracking, and decline in mechanical properties.

[0061] Specifically, the introduction of this anti-aging system enables the material to maintain excellent performance stability and high mechanical property retention during long-term use in a wide temperature range of -40℃ to 85℃ outdoor environments, significantly extending the material's service life and meeting the 15-20 year design life requirements of explosion-proof equipment, thereby greatly reducing equipment maintenance costs. Furthermore, the addition of nano-zinc oxide not only enhances anti-aging performance but also forms a synergistic effect with the halogen-free flame-retardant system, catalyzing the char formation of the flame-retardant system and further strengthening the material's flame-retardant properties, ensuring that the material maintains its UL94 V-0 flame-retardant rating even after long-term use. The components of this anti-aging system and their precise addition ratios have been optimized to ensure that long-term anti-aging is achieved without compromising the material's mechanical properties, antistatic properties, and processing properties. It is highly compatible with the matrix resin, halogen-free flame-retardant system, glass fiber, and any potential composite antistatic systems and compatibilizer systems, thus guaranteeing the synergistic stability of the various functional characteristics of the halogen-free flame-retardant reinforced PP / ABS alloy material and fully meeting the stringent comprehensive requirements of explosion-proof distribution box housings. Meanwhile, the presence of antioxidants effectively inhibits the thermal oxidative degradation of materials during high-temperature processing such as twin-screw extrusion and injection molding, improving processing yield and ensuring the performance stability of materials in long-term use.

[0062] In some of the embodiments described above in this application, glass fiber is proposed to enhance the mechanical strength of the material. However, in the process of its implementation, improper size and surface treatment of the glass fiber may lead to poor compatibility with the matrix resin, affecting the toughness and low-temperature performance of the material, thereby reducing the explosion-proof reliability.

[0063] In this regard, this application further proposes that the glass fiber has a length of 3-6 mm and a diameter of 10-15 μm; the glass fiber is surface treated with a silane coupling agent.

[0064] Specifically, the length of glass fibers is one of the key parameters affecting the mechanical properties of composite materials. Appropriate fiber length ensures that the fibers effectively transfer loads within the matrix, forming a continuous reinforcing network, thereby significantly improving the tensile, flexural, and impact resistance of the material. Fibers that are too short cannot effectively transfer stress, resulting in poor reinforcement; fibers that are too long may become entangled or break during processing, affecting dispersion uniformity and material flowability. In other embodiments, the length of the glass fibers can be adjusted to meet the specific requirements of different application scenarios for material flowability or reinforcement effects. For example, for applications requiring higher flowability, chopped glass fibers with a length in the range of 1-3 mm can be selected; while for applications seeking higher strength and rigidity, long glass fibers with a length in the range of 6-10 mm can be considered.

[0065] Meanwhile, the diameter of the glass fiber affects its specific surface area, rigidity, and interfacial bonding ability with the matrix resin. A smaller diameter generally means a larger specific surface area, which is beneficial for forming a tighter interface with the matrix resin. However, an excessively small diameter may lead to insufficient fiber rigidity and easy agglomeration; a larger diameter may result in an excessively small specific surface area, reduced interfacial bonding, and a tendency to form stress concentration points in the matrix. In other embodiments, the diameter of the glass fiber can also be adjusted according to specific performance requirements. For example, to achieve better lightweight and high strength, ultrafine glass fibers with a diameter of less than 10 μm can be selected; if cost-effectiveness is the primary consideration and general reinforcement requirements are met, coarse glass fibers with a diameter of more than 15 μm can be selected.

[0066] In addition, the glass fibers are surface-treated with silane coupling agents. Silane coupling agents are organosilicon compounds with dual reactive properties; one end contains a group that can react with inorganic substances (such as hydroxyl groups on the glass fiber surface), and the other end contains a group that can react with or be compatible with organic polymers (such as the PP / ABS matrix). Surface treatment of glass fibers with silane coupling agents can establish chemical bonds or physical entanglements between the glass fibers and the matrix resin, thereby significantly improving interfacial compatibility and bond strength, reducing interfacial defects, and enhancing the mechanical properties of the composite material, particularly toughness and water resistance. In other embodiments, besides silane coupling agents, other types of coupling agents can be used for surface treatment of the glass fibers, such as titanate coupling agents or aluminate coupling agents. These interact with the glass fiber surface and the polymer matrix through different chemical mechanisms to improve interfacial properties. Furthermore, physical surface modification methods such as plasma treatment and corona treatment can also be used to change the wettability and activity of the glass fiber surface, thereby enhancing its bonding force with the matrix resin.

[0067] Through the above technical solution, the optimized glass fiber size parameters (length 3-6mm, diameter 10-15μm) combined with silane coupling agent surface treatment significantly improve the interfacial compatibility between glass fiber and PP / ABS matrix resin, effectively solving the problems of poor interfacial bonding, material toughness, and decreased low-temperature performance caused by improper size and lack of surface treatment. This optimized design enables the glass fiber to form a uniform and efficient reinforcing network in the matrix, thereby synergistically improving the material's impact strength, tensile strength, and flexural strength, while maintaining excellent toughness in low-temperature environments such as -40℃, avoiding brittleness and significantly improving the explosion-proof reliability of the explosion-proof distribution box shell. At the same time, the appropriate glass fiber size avoids fiber breakage, entanglement, or abnormal melt viscosity during processing such as twin-screw extrusion and two-color injection molding, ensuring the material's melt flowability and molding processability, and ensuring the molding accuracy of the explosion-proof shell and the consistency of performance in various parts. In addition, the surface treatment of silane coupling agents not only strengthens the interfacial bonding force, but also promotes the uniform dispersion of other functional components such as halogen-free flame retardant system and anti-aging system in the matrix, forming a synergistic effect with the composite compatibilizer system, further improving the overall structural stability and long-term performance of the material, and meeting the design life requirement of more than 15 years for explosion-proof equipment.

[0068] In some of the solutions mentioned above in this application, the composition of halogen-free flame-retardant reinforced PP / ABS alloy materials is proposed to solve the problems of flame retardancy, antistatic properties, mechanical properties and weather resistance. However, in the preparation process, uneven mixing may lead to uneven distribution of flame retardant, affecting flame retardant efficiency. Residual moisture can easily cause processing defects and material degradation. Accumulation of extruded volatiles can cause bubbles or fluctuations in mechanical properties, thereby reducing the stability and reliability of the final product.

[0069] In this regard, such as Figure 1 As shown, this application proposes a method for preparing a halogen-free flame-retardant reinforced PP / ABS alloy material, which includes the following steps: First, in step S1, polypropylene, acrylonitrile-butadiene-styrene copolymer, ammonium polyphosphate, melamine cyanurate, nano-montmorillonite, quaternary ammonium salt antistatic agent, maleic anhydride-grafted polypropylene, maleic anhydride-grafted ethylene-octene copolymer, ultraviolet absorber, antioxidant, and nano-zinc oxide are mixed in a high-speed mixer at 112-128°C for 13-17 minutes at a mixing speed of 780-1020 rpm. This step aims to achieve preliminary uniform mixing of the various components of the halogen-free flame-retardant reinforced PP / ABS alloy material. Operating in a high-speed mixer ensures that the matrix components such as polypropylene and acrylonitrile-butadiene-styrene copolymer, along with the halogen-free flame-retardant system components such as ammonium polyphosphate, melamine cyanurate, and nano-montmorillonite, as well as various functional additives such as quaternary ammonium salt antistatic agent, maleic anhydride-grafted polypropylene, maleic anhydride-grafted ethylene-octene copolymer, ultraviolet absorber, antioxidant, and nano-zinc oxide, achieve a fully and uniformly dispersed state before entering the subsequent melt extrusion stage. The mixing temperature is controlled between 112-128℃. This temperature range typically softens the surface of resin components such as polypropylene, increasing their wettability to powder additives and facilitating the penetration and dispersion of powder particles. It also prevents excessively high temperatures from causing premature decomposition or inactivation of some heat-sensitive additives (such as antioxidants and UV absorbers). In practice, this temperature can be adjusted according to the softening point of the specific resin and the thermal stability of the additives. For example, a lower temperature of 100-110℃ can be used to further protect the heat-sensitive components; or, while ensuring the stability of the additives, the temperature can be appropriately increased to accelerate the mixing process. The mixing time is set at 13-17 minutes to provide sufficient mixing time to ensure all components are fully contacted and achieve a macroscopically uniform distribution, avoiding localized concentration differences. In practical applications, the mixing time can also be adjusted according to the efficiency of the mixer and the mixing difficulty of the materials. For example, for easily dispersed material systems, the mixing time can be shortened to 10-12 minutes; for systems containing a high proportion of nanofillers, it can be extended to 18-20 minutes to ensure effective dispersion. The mixing speed is 780-1020 rpm. The strong shear force generated by the high-speed rotation helps to break up the agglomeration of powder additives and promotes the microscopic uniform dispersion of different components, especially for nano-sized fillers such as nano-montmorillonite and nano-zinc oxide, as well as components with large viscosity differences. In addition to high-speed mixers, other mixing equipment with high shear capacity can also be used. For example, mixers with special blade designs can be selected, or a segmented mixing strategy can be adopted, mixing at low speed first and then at high speed to optimize the mixing effect.

[0070] Next, in step S2, the uniformly mixed material is dried to a moisture content ≤0.11%. This step aims to effectively remove adsorbed moisture from the material to prevent moisture from vaporizing and forming bubbles during subsequent high-temperature melt extrusion, which could affect the appearance and mechanical properties of the final product. Simultaneously, reducing the moisture content also prevents moisture from reacting with certain hydrophilic components (such as ammonium polyphosphate and nano-montmorillonite) or causing hydrolytic degradation of polymer matrices such as polypropylene and acrylonitrile-butadiene-styrene copolymers, thus ensuring the structural integrity and performance stability of the material. Drying the material to a moisture content ≤0.11% is a strict control target, ensuring that the material has extremely low moisture content when entering the extrusion stage. Methods to achieve this drying effect include, but are not limited to: using a hot air circulating oven at 80-100°C for a long time (e.g., 4-6 hours); or using a vacuum drying oven at a lower temperature (e.g., 60-70°C) to efficiently remove moisture while protecting heat-sensitive components; or using a dehumidifying dryer to achieve the target moisture content by controlling the dew point of the circulating drying air.

[0071] Subsequently, in step S3, a twin-screw extruder is used for melt extrusion. The twin-screw extruder includes a premixing section and a main extrusion section along the material travel direction. The screw length in the premixing section is 22%-28% of the total screw length, and the screw length in the main extrusion section is 72%-78% of the total screw length. The twin-screw extruder has an exhaust port in the main extrusion section, and the vacuum degree is controlled at -0.078 to -0.082 MPa through the exhaust port. The extrusion temperature is set as follows: Zone 1 178-182℃, Zone 2 188-192℃, Zone 3 198-202℃, Zone 4 208-212℃, Zone 5 218-222℃, and Die 208-212℃; the screw speed is 190-310 rpm. This step is crucial for achieving material melting, plasticizing, uniform mixing, and devolatilization. Due to its excellent mixing and conveying capabilities, the twin-screw extruder is particularly suitable for processing multi-component composite materials. A twin-screw extruder consists of a premixing section and a main extrusion section along the material travel direction. The screw length in the premixing section is 22%-28% of the total screw length, while the screw length in the main extrusion section is 72%-78% of the total screw length. This segmented design allows for preliminary melting and conveying of the material before it enters the main mixing zone, providing a more stable feed to the main extrusion section and ensuring that the main extrusion section has sufficient length for thorough mixing, venting, and plasticizing. Besides this length allocation, the ratio of the premixing section to the main extrusion section can be adjusted according to the melting characteristics and mixing requirements of the material. For example, for materials that are more difficult to melt or require stronger shear, the proportion of the main extrusion section can be appropriately increased; or more conveying elements can be installed in the premixing section, and more kneading blocks and shearing elements can be installed in the main extrusion section. The twin-screw extruder has a vent in the main extrusion section, and the vacuum degree is controlled at -0.078 to -0.082 MPa through the vent. The function of the vent is to efficiently remove volatile substances from the melt, such as trace amounts of moisture not completely removed in step S2, low molecular weight substances produced by polymer degradation, and volatile additives. Precisely controlled vacuum ensures that these volatiles are effectively extracted, preventing them from forming bubbles or voids in the final product. The location of the vent can be adjusted according to the volatility characteristics of the material and the specific design of the extruder. For example, it can be located in the middle or rear of the main extrusion section to ensure that volatilization occurs after the material has fully melted. The vacuum level can also be fine-tuned according to the volatile content of the material and product requirements. For example, for materials with a high volatile content, the vacuum level can be appropriately increased. The extrusion temperature is set as follows: Zone 1: 178-182℃; Zone 2: 188-192℃; Zone 3: 198-202℃; Zone 4: 208-212℃; Zone 5: 218-222℃; Die: 208-212℃. This gradient heating setting allows the material to melt and plasticize gradually and gently from the feed inlet to the die, avoiding polymer degradation or additive failure caused by local overheating. At the same time, it ensures that the melt has suitable viscosity and fluidity at the die, which is convenient for extrusion molding.A die temperature slightly lower than the highest zone temperature helps stabilize melt flow and reduce melt fracture. Besides the above temperature settings, the temperatures in each zone can be finely adjusted based on the specific ratio of polypropylene to acrylonitrile-butadiene-styrene copolymer, the type of additives, and the extruder model. For example, the highest temperature zone can be set in zone four, and then gradually reduced to the die temperature. The screw speed is 190-310 rpm. Screw speed directly affects the shear force and residence time of the material in the barrel. Selecting an appropriate speed within this range provides sufficient shear force to promote uniform mixing and dispersion of the components, while avoiding excessive shear heat from excessive speed leading to material degradation, and also considering production efficiency. In actual production, the screw speed can be adjusted according to output requirements and mixing effect. For example, while ensuring mixing quality, the speed can be appropriately increased to improve capacity; or, when higher mixing requirements are needed, the speed can be appropriately decreased to extend the residence time.

[0072] Finally, in step S4, the extruded material is water-cooled and pelletized to prepare PP / ABS alloy granules. This step aims to rapidly cool and solidify the extruded melt and cut it into uniform granules for subsequent storage, transportation, and further molding processes. Rapid water cooling can quickly remove heat from the melt, allowing the polymer to crystallize or solidify rapidly, helping to maintain the material's microstructure and preventing component segregation that may occur during slow cooling (such as filler sedimentation due to density differences). Water cooling is a highly efficient cooling method that ensures the melt reaches its solidification temperature in a short time. In addition to water cooling, other cooling media can be used, such as air cooling or mist cooling, but water cooling generally has higher cooling efficiency. Pelletizing involves cutting the cooled strip or sheet material into uniformly sized granules. Common pelletizing methods include strip pelletizing, underwater pelletizing, or die-face hot cutting. Choosing a suitable pelletizing method yields PP / ABS alloy granules with regular shapes and uniform sizes, thereby ensuring the stability of subsequent molding processes.

[0073] The above preparation method effectively solves the problems of uneven mixing, residual moisture, and accumulation of extruded volatiles in the preparation of halogen-free flame-retardant reinforced PP / ABS alloy materials, thereby significantly improving the stability and reliability of the final product. Specifically, the high-speed mixing in step S1 ensures that the matrix resins such as polypropylene, acrylonitrile-butadiene-styrene copolymer, and halogen-free flame-retardant system components such as ammonium polyphosphate, melamine cyanurate, and nano-montmorillonite, as well as various functional additives such as composite antistatic systems, compatibilizers, and anti-aging systems, achieve a highly uniform dispersion state before entering the extrusion stage. This avoids problems such as decreased flame-retardant efficiency and fluctuations in antistatic performance caused by uneven component distribution, allowing each functional component to fully exert its synergistic effect. The deep drying in step S2 strictly controls the material moisture content to ≤0.11%, and combined with the exhaust port of the main extrusion section of the twin-screw extruder and its precisely controlled vacuum degree in step S3, a highly efficient dual dehumidification and volatilization mechanism is formed. This completely eliminates the risk of moisture vaporization and bubble formation during high-temperature extrusion, avoiding processing defects such as porosity and silver streaks in the product. It also effectively prevents the hydrolytic degradation of the polymer matrix and hydrophilic additives, thus ensuring the structural integrity and mechanical property stability of the material. Furthermore, the segmented screw design of the twin-screw extruder in step S3 (reasonable length distribution between the premixing section and the main extrusion section), gradient temperature control, and optimized screw speed ensure that the material is fully plasticized and uniformly mixed during melt extrusion, further promoting the micro-dispersion of each component. The efficient devolatilization effect of the vent also effectively removes low-molecular-weight volatiles generated during melting, avoiding bubbles or melt viscosity fluctuations caused by volatile accumulation, thereby ensuring the consistency of the mechanical properties of the final PP / ABS alloy particles. Finally, the water-cooled pelletizing in step S4 achieves rapid solidification of the melt, effectively preventing component segregation that may occur during cooling, locking in a uniform microstructure of the material, and providing high-quality, stable PP / ABS alloy particles for subsequent molding processes. In summary, by precisely controlling and optimizing the process parameters of the entire process, including mixing, drying, melt extrusion, and pelletizing, this preparation method can maximize the synergistic effect of each component in the halogen-free flame-retardant reinforced PP / ABS alloy material formulation, significantly improving the stability, consistency, and reliability of the material's comprehensive properties such as flame retardancy, antistatic properties, mechanical properties, and weather resistance. This provides a solid technical guarantee for applications with stringent material performance requirements, such as explosion-proof distribution box housings.

[0074] In some of the solutions described above in this application, the exhaust and feeding configuration of the twin-screw extruder is proposed to optimize the melt extrusion process. However, in this process, improper exhaust port position may lead to incomplete discharge of volatiles, and residual moisture or bubbles may affect the material's density and flame retardant properties. At the same time, improper timing of glass fiber addition may cause premature degradation or uneven dispersion of the fiber in the high-temperature melt, reducing the material's mechanical strength and impact resistance.

[0075] In this regard, this application further proposes that in the above-mentioned preparation method, in step S3, the exhaust port of the twin-screw extruder is located in the middle and rear part of the main extrusion section, and at least one screw conveying element is provided between the exhaust port and the die of the twin-screw extruder; the twin-screw extruder is provided with a side feed port in the main extrusion section, and the glass fiber is added through the side feed port, which is located upstream of the exhaust port.

[0076] Specifically, the exhaust port of the twin-screw extruder is located in the middle to rear of the main extrusion section to ensure effective devolatilization after the material has fully melted and undergone initial mixing. The main extrusion section is the key area where the material transitions from a solid to a molten state and undergoes mixing. Positioning it in the middle to rear allows sufficient time for the material to fully melt before entering the exhaust zone, enabling the moisture and low-molecular-weight volatiles contained within to fully vaporize and diffuse to the melt surface, creating conditions for subsequent effective discharge. This arrangement avoids incomplete devolatilization due to premature exhaust, and also avoids excessive residence time of volatiles in the melt due to delayed exhaust, making complete discharge difficult. At least one screw conveying element is installed between the exhaust port and the twin-screw extruder die to maintain stable melt delivery and pressure during the exhaust process. The screw conveying element can be one or more threaded elements, kneading blocks, or combinations thereof. Its main functions include: first, preventing backflow of the melt under vacuum venting, ensuring smooth venting without affecting the normal material movement; second, further homogenizing the devolatilized melt to eliminate melt density or compositional inhomogeneity that may result from venting; and third, maintaining the extrusion pressure before the die to avoid sudden pressure drops caused by venting, thereby ensuring the uniformity and particle regularity of the extruded material. Twin-screw extruders have side feed ports in the main extrusion section, which is an effective way to introduce components into the extruder barrel. Unlike the main feed port (usually located at the extruder inlet), the side feed port allows additional components to be added to the melt during extrusion when the material is partially or completely melted. This method allows for flexible control of the timing of addition based on the characteristics of different components, optimizing their dispersion in the melt or preventing degradation at high temperatures. The side feed port typically forces the material into the extruder barrel through a separate feeding device (such as a single-screw or twin-screw feeder). Glass fibers are added through a side feed port to optimize their dispersion in the polymer melt and reduce damage at high temperatures. As a reinforcing material, the length and integrity of glass fibers are crucial to the final material's mechanical properties. If glass fibers are added at the extruder inlet along with all components, they will be exposed to high temperatures and shear forces for extended periods throughout the extrusion process, making them prone to brittle fracture and decomposition of the surface coupling agent, thus reducing their reinforcing effect. Adding them through a side feed port after the melt has formed significantly shortens the residence time of glass fibers in the high-temperature, high-shear environment, effectively protecting their length and surface activity. Positioning the side feed port upstream of the vent is a clever design optimized for glass fiber characteristics and the extrusion process. Glass fibers, especially those that are not fully dried, may absorb trace amounts of moisture. If added downstream of the vent, this moisture will be reintroduced into the devolatilized melt, affecting venting efficiency. Positioning it upstream of the vent means that the glass fibers are added only after most of the melt has undergone devolatilization.This ensures that volatiles in the melt are fully discharged, and that the melt still has sufficient shearing and transport capacity to evenly disperse the glass fibers after they are added. It also prevents the glass fibers from degrading prematurely in the high-temperature melt, thereby synergistically improving the density and mechanical properties of the material.

[0077] Through the above technical solution, this application achieves synergistic optimization of venting efficiency and glass fiber dispersion effect in the melt extrusion process of preparing halogen-free flame-retardant reinforced PP / ABS alloy materials. By placing the vent of the twin-screw extruder in the middle and rear of the main extrusion section, efficient devolatilization is ensured after the material is fully melted. This effectively removes moisture and low-molecular-weight volatiles from the melt, thus avoiding bubbles and pores caused by residual volatiles, significantly improving the material's density, and providing a good substrate for the subsequent formation of a dense char layer by the flame retardant, thereby enhancing the stability of the material's flame-retardant performance. Simultaneously, at least one screw conveying element is provided between the vent and the die, effectively preventing backflow of the melt under vacuum and further homogenizing the devolatilized melt, ensuring the stability of the extrusion process and the uniformity of product quality. Furthermore, by providing a side feed port in the main extrusion section and adding glass fibers through this side feed port, located upstream of the vent, the glass fibers are introduced only after most of the melt has undergone devolatilization. This incorporation method significantly shortens the residence time of glass fibers in high-temperature, high-shear environments, effectively preventing glass fiber brittleness and the decomposition of surface coupling agents. This maximizes the preservation of glass fiber length and reinforcement effect, ensuring the formation of a uniform and complete reinforcing network within the PP / ABS alloy matrix. This not only solves the problem of premature glass fiber degradation leading to decreased mechanical properties but also prevents trace amounts of moisture carried by the glass fibers from interfering with venting performance. Ultimately, this optimized extrusion process enables the prepared halogen-free flame-retardant reinforced PP / ABS alloy material to maintain excellent flame-retardant properties while significantly improving its impact strength, tensile strength, and flexural modulus, providing a more reliable material guarantee for explosion-proof distribution box housings.

[0078] Example 1

[0079] Formula ratio: Components specific ingredients quality score Key parameters Matrix resin Homopolymer polypropylene 32.0% - Copolymer polypropylene 14.0% Homopolymer PP:Copolymer PP = 7:3 (Total PP content: 46.0%) ABS copolymer 21% PP:ABS = 2:1 Halogen-free flame retardant system Ammonium polyphosphate (APP) 10.2% - Melamine cyanurate (MCA) 5.1% APP:MCA = 2:1 (total flame retardant system percentage: 16.8%) Nano-montmorillonite 0.84% 5% of the total mass of the flame retardant system Fiberglass Short-cut glass fiber 10.5% 4 mm in length, 12 μm in diameter, treated with silane coupling agent Composite antistatic system Quaternary ammonium salt antistatic agents 3.0% - carbon black dispersion 0.7% Nano carbon black mass fraction 10% compatibilizer Maleic anhydride-grafted polypropylene (PP-g-MAH) 4.5% - Maleic anhydride-grafted ethylene-octene copolymer (POE-g-MAH) 1.3% - Anti-aging system Ultraviolet absorber (UV531) 0.9% - Antioxidant (1010) 0.5% - Nano zinc oxide 0.46% The overall anti-aging system accounted for 1.86%. Preparation process Step S1, Mixing: Add the matrix resin (homogeneous PP, copolymer PP, ABS), halogen-free flame retardant system (APP, MCA, nano montmorillonite), composite antistatic system (quaternary ammonium salt antistatic agent, carbon black dispersion), compatibilizer (PP-g-MAH, POE-g-MAH), and anti-aging system (UV531, antioxidant 1010, nano zinc oxide) to a high-speed mixer, set the mixing temperature to 120℃, the mixing speed to 900rpm, and the mixing time to 15min to obtain the mixture.

[0080] Step S2, Drying: Place the well-mixed material into a vacuum drying oven and dry until the moisture content is ≤0.10% at a drying temperature of 85℃ for 4 hours.

[0081] Step S3, Melt Extrusion: Melt extrusion is carried out using a twin-screw extruder with a total screw length of 600mm, a premix section length of 150mm (accounting for 25%), and a main extrusion section length of 450mm (accounting for 75%).

[0082] Vent setting: In the middle and rear part of the main extrusion section (180mm away from the die head), two threaded conveying elements are set between the vent and the die head; Side feeding: A side feeding port is set in the main extrusion section (located 100mm upstream of the exhaust port), and glass fiber is added through the side feeding port; Vacuum level: controlled at -0.08MPa via the exhaust port; Extrusion temperature: Zone 1 180℃, Zone 2 190℃, Zone 3 200℃, Zone 4 210℃, Zone 5 220℃, Die head 210℃; Screw speed: 250 rpm.

[0083] Step S4, Pelletizing: The extruded melt is cooled in a water cooling tank (water temperature 25℃) and then pelletized by a pelletizer to obtain PP / ABS alloy pellets with a particle size of 3mm±0.2mm.

[0084] Example 2

[0085] The difference from Example 1 is as follows: Formula ratio: Remove the composite antistatic system (3.7%), adjust the proportion of matrix resin to 70.7% (homopolymer PP 34.0% + copolymer PP 14.6% + ABS 22.1%), and keep the proportion of other components unchanged; Process: No antistatic agent mixing step, otherwise consistent with Example 1.

[0086] Example 3

[0087] The difference from Example 1 is as follows: Formulation ratio: The compatibilizer system (5.8%) was removed, and the proportion of the matrix resin was adjusted to 72.8% (homopolymer PP 35.0% + copolymer PP 15.0% + ABS 22.8%), while the proportions of the remaining components remained unchanged; Process: No compatibilizer mixing step, the rest is the same as in Example 1.

[0088] Example 4

[0089] The difference from Example 1 is as follows: Formulation ratio: The halogen-free flame retardant system is replaced with a single MCA (16.14%), APP and nano montmorillonite are removed, and the proportions of the remaining components remain unchanged; Process: Only MCA is added during mixing; the rest is the same as in Example 1.

[0090] Example 5

[0091] The difference from Example 1 is as follows: Formulation ratio: Glass fiber (10.5%) was not treated with silane coupling agent surface treatment, and the remaining components and proportions were the same as in Example 1; Process: Glass fiber is added directly through the side feed port, and the rest is the same as in Example 1.

[0092] Example 6

[0093] The difference from Example 1 is as follows: Formula ratio: The anti-aging system is replaced with a single UV531 (1.86%), antioxidants and nano zinc oxide are removed, and the proportions of the remaining components remain unchanged; Process: Only UV531 is added during mixing; the rest is the same as in Example 1.

[0094] Example 7

[0095] The difference from Example 1 is as follows: Formula ratio: The component proportions are the same as in Example 1; Process: The extrusion temperature is adjusted to 190℃ for zone 1, zone 2, zone 3, zone 4, zone 5, and die head (without gradient), while the other process parameters remain unchanged.

[0096] Example 8

[0097] The difference from Example 1 is as follows: Formula ratio: The component proportions are the same as in Example 1; Process: The plasma surface treatment step is removed, and hot pressing is performed directly, while the other process parameters remain unchanged.

[0098] Example Flame retardant rating Surface resistivity (Ω) Low-temperature impact resistance (kJ / m²) Coating adhesion (MPa) Resistance fluctuation during 1000 insertion / removal cycles Weathering life (years) Main defects 1 UL94 V-0 <![CDATA[8.5×10 7 ]]> 58 16.3 ±1.2% ≥15 / 2 UL94 V-0 <![CDATA[2.3×10¹ 0 ]]> 57 16.0 ±8.5% ≥15 No antistatic system, surface resistivity exceeds standard 3 UL94 V-0 <![CDATA[8.3×10 7 ]]> 32 15.8 ±1.3% ≥15 No compatibilizer, poor low-temperature toughness 4 UL94 V-2 <![CDATA[8.7×10 7 ]]> 56 15.7 ±1.5% ≥15 Single flame retardant, flame retardant rating not up to standard 5 UL94 V-0 <![CDATA[8.9×10 7 ]]> 41 15.6 ±1.4% ≥15 Untreated fiberglass, poor interfacial bonding 6 UL94 V-0 <![CDATA[9.1×10 7 ]]> 55 15.5 ±1.6% 8 Single anti-aging agent has insufficient weather resistance. 7 UL94 V-1 <![CDATA[1.1×10 8 ]]> 45 15.3 ±2.1% 10 No temperature gradient during extrusion, resulting in low density. 8 UL94 V-0 <![CDATA[8.6×10 7 ]]> 54 8.9 ±1.8% ≥15 No plasma treatment, low bonding strength of the sealing gasket In summary, Example 1 combines UL94V-0 flame retardancy with 10 8 It exhibits the best performance in terms of stable surface resistivity below Ω, low-temperature impact strength of 58kJ / m², and weather resistance of over 15 years; Example 2, lacking a composite antistatic system, shows a surface resistivity of 2.3×10¹. 0Ω, insertion and extraction resistance fluctuation reached ±8.5%; Example 3 lacked compatibilizer, low-temperature impact strength plummeted to 32kJ / m², and toughness decreased significantly; Example 4 used a single MCA flame retardant system, only reaching UL94V-2 level, and flame retardant performance did not meet the standard; Example 5 did not treat glass fiber with silane coupling agent, impact strength dropped to 41kJ / m², and interface bonding effect deteriorated; Example 6 used a single UV531 as anti-aging agent, weather resistance life was only 8 years, which could not meet the requirements of long-term use; Example 7 had no extrusion temperature gradient, flame retardant level dropped to UL94V-1 level, impact strength was 45kJ / m², and material density was insufficient; Example 8 did not perform plasma surface treatment, coating adhesion dropped to 8.9MPa, and sealing gasket bonding effect was significantly weakened.

[0099] Example 9

[0100] In some of the solutions mentioned above in this application, halogen-free flame-retardant reinforced PP / ABS alloy materials are proposed for manufacturing explosion-proof distribution box housings. However, in this process, insufficient sealing performance of the housing, low interfacial bonding strength, and improper processing technology may lead to a decrease in explosion-proof reliability and service life. Specifically, the sealing gaskets are not firmly bonded, insufficient surface treatment affects the bonding effect, and molding process defects cause structural weaknesses.

[0101] To address this, this application proposes an explosion-proof distribution box housing, wherein the housing is made of the aforementioned halogen-free flame-retardant reinforced PP / ABS alloy material; the housing further includes a silicone rubber sealing gasket, and the housing and the silicone rubber sealing gasket are joined by hot-press bonding, wherein the hot-press bonding temperature is 112-128℃, the pressure is 4.2-5.8MPa, and the time is 1.8-3.2min; prior to hot-press bonding, the housing undergoes plasma surface treatment, wherein the plasma surface treatment temperature is... The temperature range is 55-85℃, the time is 2.5-5.5min, and the power is 190-310W. The shell is manufactured using a two-color injection molding process, and the mold has an integrated structure of explosion-proof stop and sealing groove. The injection temperature is set as follows: Zone 1 178-182℃, Zone 2 188-192℃, Zone 3 198-202℃, Zone 4 218-222℃, the holding pressure is 78-102MPa, the holding time is 2.8-5.2s, and the cooling time is 24-31s.

[0102] Specifically, the housing is made of the aforementioned halogen-free flame-retardant reinforced PP / ABS alloy material. This material itself possesses excellent flame-retardant, antistatic, mechanical, and weather-resistant properties, providing a solid foundation for the explosion-proof distribution box housing. The silicone rubber gasket is an elastomer material with excellent resistance to high and low temperatures, aging, chemical corrosion, and good elasticity, commonly used to provide reliable sealing. It can be implemented using pre-formed O-rings, shaped gaskets, or by direct injection molding of liquid silicone rubber onto the housing. The housing and the silicone rubber gasket are joined by thermocompression bonding, a method that uses heating and pressure to create physical or chemical bonds between the two materials, aiming to achieve a strong bond between the housing and the silicone rubber gasket. Besides thermocompression bonding, similar connections can be achieved using hot-melt welding, ultrasonic welding, or adhesive bonding, but thermocompression bonding has advantages in controlling the interfacial bonding strength and uniformity. Precise control of the temperature, pressure, and time parameters of the thermocompression bonding is crucial to ensuring the quality of the composite connection. Temperature needs to reach above the material's softening point to promote the movement and diffusion of molecular chain segments, but it cannot be too high to avoid material degradation; pressure ensures tight contact at the interface, eliminates air bubbles, and promotes intermolecular forces; time ensures sufficient molecular diffusion and bonding formation.

[0103] Before hot-pressing lamination, the shell undergoes plasma surface treatment, a technique that uses plasma to modify the material surface, increasing its surface energy and activity, thereby improving adhesion. Common plasma treatment methods include atmospheric pressure plasma treatment and vacuum plasma treatment, using oxygen, argon, or nitrogen plasma. Through mechanisms such as etching, cross-linking, or introducing polar groups, the wettability and adhesion of the material surface are effectively improved. The temperature, time, and power parameters of the plasma surface treatment directly affect the surface modification effect. Temperature control avoids thermal damage to the material; time ensures the uniformity and depth of treatment; power determines the energy density of the plasma and the concentration of active particles, thus affecting the efficiency and extent of surface modification. The shell is manufactured using a two-color injection molding process, an advanced molding technology that uses two different colors or materials with different properties to form a single integrated product through two injections on the same injection molding machine. This process enables one-time molding of complex structures, improves production efficiency, and ensures a tight bond between different materials. In addition to two-color injection, multi-color injection or co-injection molding can also achieve similar functions. The mold features an integrated structure of explosion-proof stop and sealing groove. The explosion-proof stop is a structure used to limit the propagation of explosion flames and cool explosion products, while the sealing groove is used to accommodate the sealing gasket, ensuring the shell's tightness. Integrating both into the mold means that these critical functional structures are formed in one step during molding, eliminating the need for subsequent processing or assembly, thus improving structural precision and reliability. This integrated structure can adopt various geometries; for example, the explosion-proof stop can be designed as a labyrinth or stepped type, and the sealing groove can be designed as an O-ring groove or a rectangular groove to accommodate different sealing requirements and explosion-proof ratings. The zoned setting of the injection temperature aims to precisely control the temperature distribution of the molten plastic in the screw and mold runner, ensuring sufficient plasticization and good fluidity while avoiding localized overheating and degradation. The temperature gradient from Zone 1 to Zone 4 typically increases gradually to accommodate the transition of the plastic from solid particles to a molten state and to provide a suitable melt temperature for the final injection. Holding pressure and holding time are used to apply continuous pressure to the melt within the mold cavity after injection to compensate for material cooling shrinkage, ensuring dimensional accuracy and surface quality of the product and preventing defects such as shrinkage cavities and depressions. Cooling time ensures that the product is fully cured before demolding, achieving sufficient rigidity and preventing deformation. Optimizing these parameters is crucial for controlling the product's internal stress, dimensional stability, and mechanical properties.

[0104] Through the above technical solutions, the explosion-proof distribution box housing proposed in this application, based on halogen-free flame-retardant reinforced PP / ABS alloy material, significantly improves the overall sealing performance and interface bonding strength of the housing by introducing a silicone rubber sealing gasket and employing hot-pressing composite connection. The introduction of plasma surface treatment effectively activates the housing surface, greatly improving the adhesion between the housing and the silicone rubber sealing gasket, ensuring the long-lasting reliability of the seal, thereby effectively preventing the penetration of external media and enhancing the safety of the explosion-proof equipment. Furthermore, the use of a two-color injection molding process, combined with the integrated structural design of the explosion-proof stop and sealing groove in the mold, not only achieves one-time precision molding of complex functional structures, reducing defects that may be introduced in subsequent processing and assembly, but also effectively controls the molding quality of the product by optimizing process parameters such as injection temperature, holding pressure, holding time, and cooling time, reducing internal stress, ensuring the dimensional stability and mechanical properties of the housing, and further enhancing the explosion-proof reliability and service life of the explosion-proof distribution box housing. Overall, this solution comprehensively addresses the challenges of sealing, interface bonding, and processing quality of explosion-proof distribution box housings through synergistic optimization of materials, structure, surface treatment, and molding processes, ensuring long-term stable operation of the product in harsh environments.

[0105] The following example will provide a more detailed explanation of the above technical solution: A manufacturer of explosion-proof equipment needed to develop a new type of explosion-proof distribution box housing material to meet increasingly stringent environmental regulations and higher safety performance requirements. This material not only needed to meet the UL94 V-0 halogen-free flame retardant standard, but also needed to possess excellent impact resistance, long-term antistatic properties, and weather resistance for long-term use in harsh outdoor environments.

[0106] To this end, the manufacturer adopted a halogen-free flame-retardant reinforced PP / ABS alloy material. The preparation process begins with the precise formulation of the base resin. The base resin comprises 65% by mass, with the mass ratio of polypropylene to acrylonitrile-butadiene-styrene copolymer set at 2:1. This formulation aims to fully utilize the good processability and cost advantages of polypropylene, while combining the excellent toughness and impact strength of the acrylonitrile-butadiene-styrene copolymer to provide a solid foundation of mechanical properties for the final material. To further optimize the performance of the base resin, the polypropylene component is further subdivided into homopolymer polypropylene and copolymer polypropylene at a mass ratio of 7:3. Homopolymer polypropylene contributes to the material's rigidity and strength, while copolymer polypropylene effectively improves the material's low-temperature toughness and impact resistance, avoiding the brittleness that pure polypropylene may experience at low temperatures, thereby enhancing the reliability of the explosion-proof enclosure under extreme temperature conditions.

[0107] In terms of flame retardant performance, this material incorporates a halogen-free flame retardant system with a mass fraction of 18%. This system consists of ammonium polyphosphate, melamine cyanurate, and nano-montmorillonite. The mass ratio of ammonium polyphosphate to melamine cyanurate is 2:1, and the amount of nano-montmorillonite added is 5% of the total mass of the halogen-free flame retardant system. When the material is heated, ammonium polyphosphate decomposes to produce phosphoric acid, promoting the formation of a dense carbonized layer on the material surface, effectively isolating oxygen and heat transfer. Simultaneously, melamine cyanurate releases non-flammable gases at high temperatures, diluting the concentration of flammable gases, and synergistically works with ammonium polyphosphate to enhance the strength and integrity of the carbonized layer. Nano-montmorillonite, as a synergistic flame retardant, further improves the density of the carbonized layer and enhances the flame retardant efficiency. This synergistic flame retardant mechanism allows the material to achieve a V-0 flame retardant rating with a relatively low amount of flame retardant added, avoiding the problem of significant degradation of material mechanical properties caused by the large addition of traditional halogen-free flame retardants, thus achieving a balance between environmental protection and performance.

[0108] To meet the high mechanical performance requirements of explosion-proof enclosures (e.g., impact strength of not less than 50 kJ / m²), 10% glass fiber by mass was added to the material. This glass fiber is 4 mm long and 12 μm in diameter, and undergoes surface treatment with a silane coupling agent. The silane coupling agent treatment significantly improves the interfacial bonding between the glass fiber and the matrix resin, effectively solving the problem of reduced material toughness due to poor compatibility between glass fiber and the matrix in existing technologies. By enhancing the interfacial bonding, the reinforcing effect of the glass fiber is fully utilized, significantly improving the tensile strength, flexural strength, and impact strength of the material, while maintaining good toughness. Especially in low-temperature environments, it effectively avoids brittle fracture, thereby improving the overall reliability of the explosion-proof enclosure.

[0109] Furthermore, to address the short antistatic duration issue in existing technologies, this material also includes a 4% (by mass) composite antistatic system composed of a quaternary ammonium salt antistatic agent and a carbon black dispersion. The quaternary ammonium salt antistatic agent provides the initial antistatic effect, while the 10% (by mass) nano-carbon black in the carbon black dispersion forms a durable conductive network within the material. This composite system overcomes the short-lasting effect of a single antistatic agent, ensuring that the surface resistivity of the explosion-proof enclosure remains consistently below 10 ohms during long-term use. 8 Below Ω, it effectively prevents the potential explosion risk caused by static electricity accumulation.

[0110] To further optimize the compatibility between components and improve the overall mechanical properties of the material, a compatibilizer with a mass fraction of 5% was added, including maleic anhydride-grafted polypropylene and maleic anhydride-grafted ethylene-octene copolymer. Specifically, the amount of maleic anhydride-grafted polypropylene added was 4.5%, and the amount of maleic anhydride-grafted ethylene-octene copolymer added was 1.5%. These compatibilizers significantly improved the interfacial compatibility between different components by forming chemical bonds or physical entanglements with polypropylene, acrylonitrile-butadiene-styrene copolymer, and glass fiber, further enhancing the impact strength and toughness of the material and solving common compatibility problems in multi-component blend systems.

[0111] To meet the 15-20 year design life requirement of explosion-proof equipment, this material also incorporates a 1.5% (by mass) anti-aging system, including UV absorbers, antioxidants, and nano-zinc oxide. The UV absorber is added at 1.3%, the antioxidant at 0.8%, and the nano-zinc oxide at 0.5%. This system works synergistically: the UV absorber effectively absorbs harmful UV rays, the antioxidant inhibits the oxidative degradation reaction of the material, and the nano-zinc oxide provides broad-spectrum UV protection and free radical scavenging capabilities. This multi-component anti-aging system significantly extends the material's outdoor service life, solving the problems of poor weather resistance and short service life in existing technologies.

[0112] Through the precise proportioning and synergistic effect of the above components, this halogen-free flame-retardant reinforced PP / ABS alloy material achieves excellent mechanical properties (high impact strength), long-lasting antistatic properties, and outstanding weather resistance while meeting the V-0 halogen-free flame-retardant requirements. Compared with existing technologies that rely solely on halogenated flame retardants, this material avoids the generation of toxic gases, making it more environmentally friendly. Compared with solutions that only add glass fiber but have poor compatibility, this material, treated with compatibilizers and coupling agents, ensures the full utilization of glass fiber reinforcement while maintaining the material's toughness, especially in low-temperature environments. Compared with single antistatic agent solutions, the composite antistatic system provides a more durable antistatic effect. Compared with traditional anti-aging agent solutions, the multi-component anti-aging system significantly improves the material's long-term weather resistance. This synergistic optimization of multifunctional components overcomes the problem of mutual constraints among various properties in existing technologies, achieving an overall improvement in the material's comprehensive performance and providing a high-performance, high-reliability, and long-life solution for explosion-proof distribution box housings.

[0113] The above description is merely an embodiment of this application and is not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A halogen-free flame-retardant reinforced PP / ABS alloy material, characterized in that, The material comprises, by mass fraction: The matrix resin comprises 62%-68%, wherein the matrix resin is a blend of polypropylene and acrylonitrile-butadiene-styrene copolymer, and the mass ratio of polypropylene to acrylonitrile-butadiene-styrene copolymer is 1.8:1 to 2.2:1; The halogen-free flame retardant system comprises 16%-19%, and the halogen-free flame retardant system includes ammonium polyphosphate, melamine cyanurate, and nano-montmorillonite. Glass fiber 9%-11%.

2. The halogen-free flame-retardant reinforced PP / ABS alloy material according to claim 1, characterized in that, The polypropylene in the matrix resin includes homopolymer polypropylene and copolymer polypropylene, and the mass ratio of the homopolymer polypropylene to the copolymer polypropylene is from 6.5:3.5 to 7.5:2.

5.

3. The halogen-free flame-retardant reinforced PP / ABS alloy material according to claim 1, characterized in that, The mass ratio of ammonium polyphosphate to melamine cyanurate in the halogen-free flame retardant system is 1.9:1 to 2.1:1; the amount of nano-montmorillonite added is 4.5%-5.5% of the total mass of the halogen-free flame retardant system.

4. The halogen-free flame-retardant reinforced PP / ABS alloy material according to claim 1, characterized in that, It also includes a composite antistatic system of 3.2%-4.8%, wherein the composite antistatic system comprises a quaternary ammonium salt type antistatic agent and a carbon black dispersion; the addition amount of the quaternary ammonium salt type antistatic agent is 2.8%-4.2%, and the mass fraction of nano carbon black in the carbon black dispersion is 9%-11%.

5. The halogen-free flame-retardant reinforced PP / ABS alloy material according to claim 1, characterized in that, It also includes 4.2%-5.8% compatibilizer, which includes maleic anhydride-grafted polypropylene and maleic anhydride-grafted ethylene-octene copolymer; the amount of maleic anhydride-grafted polypropylene added is 3.8%-5.2%, and the amount of maleic anhydride-grafted ethylene-octene copolymer added is 1.2%-2.8%.

6. The halogen-free flame-retardant reinforced PP / ABS alloy material according to claim 1, characterized in that, It also includes an anti-aging system of 1.1%-1.9%, which includes ultraviolet absorbers, antioxidants and nano zinc oxide; the amount of ultraviolet absorbers added is 0.9%-1.7%, the amount of antioxidants added is 0.5%-1.1%, and the amount of nano zinc oxide added is 0.35%-0.75%.

7. The halogen-free flame-retardant reinforced PP / ABS alloy material according to claim 1, characterized in that, The glass fiber has a length of 3-6 mm and a diameter of 10-15 μm; the glass fiber is surface treated with a silane coupling agent.

8. A method for preparing a halogen-free flame-retardant reinforced PP / ABS alloy material as described in any one of claims 1 to 7, characterized in that, Includes the following steps: Step S1: Polypropylene, acrylonitrile-butadiene-styrene copolymer, ammonium polyphosphate, melamine cyanurate, nano-montmorillonite, quaternary ammonium salt antistatic agent, maleic anhydride-grafted polypropylene, maleic anhydride-grafted ethylene-octene copolymer, ultraviolet absorber, antioxidant, and nano-zinc oxide are mixed in a high-speed mixer at 112-128℃ for 13-17 minutes, with a mixing speed of 780-1020 rpm. Step S2: Dry the uniformly mixed material until the moisture content is ≤0.11%; Step S3: Melt extrusion is performed using a twin-screw extruder. The twin-screw extruder includes a premixing section and a main extrusion section along the material travel direction. The screw length in the premixing section is 22%-28% of the total screw length, and the screw length in the main extrusion section is 72%-78% of the total screw length. The twin-screw extruder has an exhaust port in the main extrusion section, and the vacuum degree is controlled at -0.078 to -0.082 MPa through the exhaust port. The extrusion temperature is set as follows: Zone 1 178-182℃, Zone 2 188-192℃, Zone 3 198-202℃, Zone 4 208-212℃, Zone 5 218-222℃, and Die 208-212℃. The screw speed is 190-310 rpm. Step S4: After extrusion, water cooling and pelletizing are performed to prepare PP / ABS alloy granules.

9. The preparation method according to claim 8, characterized in that, In step S3, the exhaust port of the twin-screw extruder is located in the middle and rear part of the main extrusion section, and at least one screw conveying element is provided between the exhaust port and the die of the twin-screw extruder; the twin-screw extruder is provided with a side feed port in the main extrusion section, and the glass fiber is added through the side feed port, which is located upstream of the exhaust port.

10. An explosion-proof distribution box housing, characterized in that, The housing is made of any one of the halogen-free flame-retardant reinforced PP / ABS alloy materials according to any one of claims 1 to 7; The housing also includes a silicone rubber gasket, and the housing and the silicone rubber gasket are connected by hot pressing. The hot pressing temperature is 112-128℃, the pressure is 4.2-5.8MPa, and the time is 1.8-3.2min. Before hot pressing, the shell is subjected to plasma surface treatment at a temperature of 55-85°C for 2.5-5.5 minutes and a power of 190-310W. The shell is manufactured using a two-color injection molding process. The mold has an integrated structure of explosion-proof stop and sealing groove. The injection temperature is set as follows: Zone 1 178-182℃, Zone 2 188-192℃, Zone 3 198-202℃, Zone 4 218-222℃, holding pressure is 78-102MPa, holding time is 2.8-5.2s, and cooling time is 24-31s.

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