Drip-proof flame retardant and method for preparing the same

Abstract

This invention relates to the field of flame retardant modification technology for polymer materials, specifically to an anti-drip flame retardant and its preparation method. The anti-drip flame retardant comprises polytetrafluoroethylene (PTFE) micropowder that has undergone spheroidization treatment and has a double-modified surface structure and sulfonic acid group grafting, a toughening compensating component composed of MBS and POE, a maleic anhydride-grafted polypropylene carrier resin, and a synergistic flame retardant component consisting of a phosphorus-nitrogen intumescent flame retardant and a metal hydroxide. The sulfonic acid groups can undergo ionic cross-linking reactions with the polyol component under combustion conditions, promoting the formation of an interpenetrating structure between the PTFE fibrillary network and the intumescent char layer. This invention effectively solves the problems of decreased material toughness, processing instability, and lack of active flame retardant synergy caused by traditional anti-drip agents, achieving integrated synergy of melt flow suppression, dense char layer construction, and smoke suppression, thereby improving the fire safety level and mechanical properties of the material.

Description

Technical Field

[0001] This invention relates to the field of flame retardant modification technology of polymer materials, specifically to an anti-drip flame retardant and its preparation method. Background Technology

[0002] Polytetrafluoroethylene (PTFE) is widely used as an anti-dripping agent in the combustion process of thermoplastic polymers due to its excellent thermal stability, chemical inertness, and low surface energy. In the flame retardant modification of easily dripping polymers such as ABS, PP, PA, and PBT, PTFE is often added in the form of micron-sized powder or pre-dispersed masterbatch. By forming a fibrous network structure on the melt surface, it inhibits melt flow and dripping behavior, thereby reducing the risk of flame propagation. In recent years, to meet the demand for halogen-free, low-smoke, and low-toxicity flame retardant materials in the electronics, automotive interiors, and other fields, researchers have attempted to design composites of PTFE with other halogen-free flame retardant components. For example, PTFE is introduced into intumescent flame retardant systems to balance char strength and melt rheology regulation, or it is blended with phosphorus- or nitrogen-containing flame retardants to construct multi-effect synergistic systems. In related technologies, PTFE is usually used as a physical modifier in formulation design, mainly playing a role in rheological regulation and physical barrier. Some studies have also explored PTFE modified by surface modification or in-situ grafting. Derivatives are used to improve their dispersibility and interfacial compatibility in polymer matrices. However, in the existing technology, anti-drip agents based on polytetrafluoroethylene (PTFE) still face technical difficulties when applied to easily dripping thermoplastic polymers, such as significant deterioration of material mechanical properties, insufficient processing stability, poor component dispersion uniformity, and lack of active synergistic flame retardancy. It is difficult to simultaneously meet the comprehensive application requirements of high toughness, high processing efficiency, and high flame retardancy. Summary of the Invention

[0003] In order to overcome the shortcomings and deficiencies of the existing technology, the purpose of this invention is to provide an anti-drip flame retardant that can solve the technical problems of existing PTFE-based anti-drip agents when applied to easily dripping thermoplastic polymers, such as a significant decrease in impact toughness, poor processing stability, uneven dispersion, and lack of synergistic flame retardant ability.

[0004] The objective of this invention is achieved through the following technical solution: an anti-drip flame retardant for halogen-free flame retardant modification of thermoplastic polymers, comprising a carrier resin, a dispersant, an anti-drip functional component, a toughening compensating component, and a synergistic flame retardant component; characterized in that: the anti-drip functional component is polytetrafluoroethylene (PTFE) micropowder that has undergone spheroidization treatment and has a double-modified surface structure, with an average particle size of 0.3-1.5 μm and a sphericity of not less than 0.92; the double-modified structure comprises: an inner layer of a silane coupling agent chemically anchored to the PTFE surface through a hydrolysis-condensation reaction, and an outer layer of a polymeric dispersant coated on the inner layer through hydrogen bonding, wherein the PTFE matrix is ​​also grafted with sulfonic acid groups at a grafting rate of 3.5-5.0 wt%; the toughening compensating component is MBS and POE in a mass ratio of 3:1. The compounded elastomer system is uniformly dispersed in a carrier resin; the carrier resin is maleic anhydride-grafted polypropylene (MAH-g-PP) with an anhydride grafting rate of 1.2-1.8%, and together with the polymeric dispersant, it forms a stable dispersion microenvironment; the synergistic flame retardant component includes a phosphorus-nitrogen intumescent flame retardant and a metal hydroxide, and under combustion conditions, the sulfonic acid group can undergo an ionic crosslinking reaction with the polyol component in the phosphorus-nitrogen intumescent flame retardant, promoting the formation of an interpenetrating structure between the PTFE fibrillary network and the intumescent char layer, thereby achieving integrated synergistic effects of melt flow suppression, dense char layer construction, and flue gas suppression.

[0005] The beneficial effects of this invention are as follows: This scheme uses PTFE micropowder with spheroidized treatment and dual-modified structure and sulfonic acid group grafting as the anti-drip functional component, combined with a specific ratio of MBS and POE compound toughening system, MAH-g-PP carrier resin, and phosphorus-nitrogen intumescent flame retardant and metal hydroxide synergistic flame retardant components to construct an integrated synergistic flame retardant system; by controlling the sphericity and particle size of PTFE micropowder, its stress concentration effect in the matrix is ​​reduced, so that the material maintains high strength while avoiding embrittlement; the PTFE is enhanced by the dual coating of silane coupling agent and polymeric dispersant and the grafting of sulfonic acid groups. The interfacial compatibility with polar resins and flame-retardant systems ensures uniform dispersion of components during high-shear processing, avoiding performance fluctuations caused by agglomeration. The stable microenvironment constructed using the MAH-g-PP carrier and dispersant, combined with a delayed fibrillation mechanism, effectively reduces the risks of screw seizing and mesh clogging during processing. Furthermore, the ionic crosslinking reaction between sulfonic acid groups and polyol components in the intumescent flame retardant promotes the formation of an interpenetrating structure between the PTFE fibrillary network and the expanded char layer, thereby effectively suppressing melt flow, rapidly constructing a dense char layer, and significantly reducing smoke release. This effectively solves the problems of decreased material toughness, processing instability, and lack of active flame-retardant synergy caused by traditional anti-drip agents, improving the fire safety level, mechanical property retention rate, and continuous stability of the production process of the composite material under high-temperature and hot conditions, meeting the dual requirements of halogen-free flame retardancy and high impact resistance in high-end applications.

[0006] Another object of the present invention is to provide a method for preparing an anti-drip flame retardant as described in any of the above claims.

[0007] Another objective of this invention is achieved through the following technical solution: a method for preparing an anti-drip flame retardant, comprising the following steps: (a) preparation of spherical PTFE micro powder: PTFE emulsion is mixed with deionized water and sprayed into a spray drying tower via high-pressure atomization. Precursor particles are obtained by drying at an inlet temperature of 180°C and an outlet temperature of 90°C. Then, in a nitrogen atmosphere, the temperature is increased to 360°C at 10°C / min and held for 2 hours to obtain PTFE micro powder with a sphericity ≥0.92 and an average particle size of 0.8±0.2 μm; (b) dual surface modification: the PTFE micro powder obtained in step (a) is dispersed in an ethanol-water mixed solvent, the pH is adjusted to 4.5–5.0, KH-570 is added, and the mixture is stirred at 60°C for 2 hours. Subsequently, a PVP solution is added, and stirring continues for 1 hour. The mixture is centrifuged, washed, and vacuum dried to obtain KH-570 / PVP. (c) Radiation grafting of sulfonic acid groups: The product of step (b) is placed in a nitrogen-protected container and irradiated with γ-rays (dose 15-25 kGy) to initiate surface free radicals; sodium styrene sulfonate aqueous solution is introduced and reacted at 60℃ for 3 hours; dialyzed and freeze-dried to obtain sulfonated PTFE with a grafting rate of 3.5-5.0 wt%; (d) Masterbatch melt blending and granulation: The product of step (c), MBS, POE, MAH-g-PP, phosphorus-nitrogen intumescent flame retardant, metal hydroxide and polyether amide dispersant are mixed according to the formula and melt-blended in a twin-screw extruder. The feeding zone temperature is 160-170℃, the plasticizing zone temperature is 200-220℃, the die temperature is 210℃, the screw speed is 300-400 rpm, and a backflow barrier section is set at the vacuum port. The product is granulated underwater and dried to obtain the anti-drip flame retardant.

[0008] Another beneficial effect of the present invention is that, through the above-mentioned multi-component synergistic design and refined structural control, the transformation from passive anti-drip to active flame retardancy and toughness maintenance has been achieved, forming a logically rigorous and functionally complementary technical closed loop, which significantly improves the overall performance and application value of flame retardants.

[0009] Preferably, the PTFE micro powder has an average particle size of 0.8±0.2 μm and a sphericity ≥0.92.

[0010] Preferably, the silane coupling agent is γ-methacryloxypropyltrimethoxysilane (KH-570), and the polymeric dispersant is polyvinylpyrrolidone (PVP), with the total thickness of the synergistic coating being 20-50 nm.

[0011] More preferably, the silane coupling agent is γ-methacryloxypropyltrimethoxysilane (KH-570), and the polymeric dispersant is polyvinylpyrrolidone (PVP), with the total thickness of the synergistic coating being 20-50 nm.

[0012] Preferably, the anhydride grafting rate of the MAH-g-PP is 1.2-1.8%, and the mass ratio of MBS to POE is 3:1.

[0013] Preferably, the phosphorus-nitrogen intumescent flame retardant comprises ammonium polyphosphate, pentaerythritol and melamine, and the sulfonic acid group undergoes an ionic crosslinking reaction with pentaerythritol at a combustion temperature ≥300°C.

[0014] More preferably, the interpenetrating network structure has a 12% higher carbon residue rate at 700°C than the control sample without grafted sulfonic acid groups, and the resulting carbon layer exhibits a dense and continuous structure without macroscopic cracks under a scanning electron microscope.

[0015] Preferably, in step (d), the vacuum port of the twin-screw extruder is provided with a backflow barrier section to prevent low-volatile substances from escaping and causing blockages or bubble defects.

[0016] More preferably, the anti-drip flame retardant obtained in step (d) has a PTFE content of 18-22 wt%, a toughening compensation component content of 10-15 wt%, and the balance being carrier resin and additives; the particle size distribution D90≤350 μm, no crystal points, and no stratification after 6 months of storage.

[0017] The anti-drip functional component described in this invention plays a key role in suppressing melt flow and constructing a dense carbon layer.

[0018] In summary, the technical solution provided in this application, through multi-component synergistic design and refined structural control, achieves a transformation from passive drip prevention to active flame retardancy and toughness maintenance, forming a logically rigorous and functionally complementary technical closed loop, which significantly improves the overall performance and application value of flame retardants. Detailed Implementation

[0019] The present application will now be described in further detail with reference to embodiments. It is to be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the scope of the application.

[0020] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments. The content mentioned in the embodiments is not intended to limit the present invention.

[0021] Unless otherwise specified, all materials, reagents, and instruments used in the embodiments of this invention are commercially available. Key raw materials include: polytetrafluoroethylene (PTFE) emulsion (60% solids content, particle size 200-300 nm); γ-methacryloyloxypropyltrimethoxysilane (KH-570, purity ≥98%); polyvinylpyrrolidone (PVP, K30 type); sodium styrene sulfonate (purity ≥95%); maleic anhydride-grafted polypropylene (MAH-g-PP, anhydride grafting rate 1.2-1.8%); methyl methacrylate-butadiene-styrene copolymer (MBS); polyolefin elastomer (POE); ammonium polyphosphate (APP, degree of polymerization >1000); pentaerythritol (PER); melamine (MEL); magnesium hydroxide (MDH); and polyether amide dispersants. The equipment includes: a high-pressure spray drying tower (inlet air temperature controllable range 100-250℃); a programmable temperature-controlled muffle furnace (maximum temperature 1000℃); a gamma-ray irradiation device (cobalt-60 source); a twin-screw extruder (length-to-diameter ratio L / D=40:1, with side feed port and vacuum devolatilization system); a laser particle size analyzer; a scanning electron microscope (SEM); a limiting oxygen index (LOI) tester; a cone calorimeter; and a universal testing machine. Characterization and testing methods are as follows: average particle size and sphericity were determined using a laser particle size analyzer combined with image analysis; grafting rate was determined using elemental analysis (sulfur content conversion) or X-ray photoelectron spectroscopy (XPS); char residue was tested according to GB / T 9345 at 700℃ under a nitrogen atmosphere; char layer morphology was observed using SEM; the limiting oxygen index (LOI) was tested according to GB / T 2406; the vertical burning rating was tested according to UL94 standard; and the notched impact strength was tested according to GB / T 1043.

[0022] Experiment 1: This experiment aims to provide a composite flame retardant with both high-efficiency anti-dripping and active flame-retardant functions, along with its optimal preparation process, and to perform physical characterization. Specifically: Step 1: Preparation of spherical PTFE micropowder. PTFE emulsion and deionized water were mixed at a mass ratio of 1:1 and sprayed into a spray drying tower through a high-pressure atomizing nozzle. The inlet temperature was controlled at 180℃ and the outlet temperature at 90℃ to obtain precursor particles. The precursor particles were placed in a nitrogen-protected, temperature-controlled muffle furnace and heated to 360℃ at a rate of 10℃ / min. Sintering was carried out at this temperature for 2 hours, and after natural cooling, spherical PTFE micropowder with an average particle size of 0.8 μm and a sphericity of 0.94 was obtained.

[0023] Step 2: Dual Surface Modification. 100 g of the PTFE micropowder obtained in Step 1 was dispersed in 500 mL of an ethanol-water mixture (volume ratio 3:1), and the pH was adjusted to 4.8 with dilute hydrochloric acid. 3 g of KH-570 was added, and the mixture was mechanically stirred at 60 °C for 2 hours. Subsequently, 2 g of PVP (dissolved in 50 mL of water) was added, and stirring continued for 1 hour. After the reaction was complete, the mixture was centrifuged, washed three times with ethanol, and vacuum dried to obtain KH-570 / PVP bilayer-coated PTFE micropowder with a coating thickness of approximately 35 nm.

[0024] Step 3: Radiation grafting of sulfonic acid groups. The product from Step 2 was placed in a sealed container filled with nitrogen and irradiated with gamma rays at an absorbed dose of 20 kGy. Immediately after removal, an aqueous solution containing 5 g of sodium styrene sulfonate was introduced, and the reaction was carried out at 60°C for 3 hours. The reaction solution was dialyzed to remove unreacted monomers, and after freeze-drying, sulfonated PTFE micropowder with a grafting rate of 4.2 wt% was obtained.

[0025] Step 4: Masterbatch melt blending and granulation. Weigh 200 g of the product from Step 3 (PTFE content basis), 75 g of MBS, 25 g of POE, 400 g of MAH-g-PP, 150 g of ammonium polyphosphate, 50 g of pentaerythritol, 50 g of melamine, 50 g of magnesium hydroxide, and 10 g of polyether amide dispersant, and premix thoroughly. Add the mixture to a twin-screw extruder, setting the feeding zone temperature to 165℃, the plasticizing zone temperature to 210℃, the die temperature to 210℃, and the screw speed to 350 rpm. Open the vacuum port and confirm that the backflow barrier section is working properly. The extruded strip is water-cooled, pelletized, and dried to obtain anti-drip flame retardant masterbatch.

[0026] Results: The prepared masterbatch had a smooth appearance without crystal points and a particle size distribution D90 of 320 μm. Testing showed that PTFE was uniformly dispersed in the matrix without macroscopic agglomeration.

[0027] Conclusion: This experiment successfully prepared an anti-drip flame retardant with spheroidization, dual modification and sulfonic acid group grafting characteristics. The components were well dispersed, the process parameters were stable, and the product met the expected design specifications.

[0028] Experiment 2: This experiment aims to verify the impact of the lower limit of PTFE micron particle size on the technical effect.

[0029] Under the same preparation conditions as in Experiment 1, only the spray drying and sintering process parameters in step 1 were adjusted to obtain PTFE micro powder with an average particle size of 0.3 μm and a sphericity of 0.93, thereby obtaining anti-drip flame retardant masterbatch.

[0030] The results show that the product still achieves the technical effects of the present invention, with no crystal points and good dispersibility in the masterbatch. Although the smaller particle size leads to an increased specific surface area, no serious agglomeration occurs under the effect of the dual-modified structure, proving the feasibility of the technical solution at the lower limit of the particle size defined in the claims.

[0031] Experiment 3: This experiment aims to verify the effect of the upper limit of PTFE micron particle size on the technical effect.

[0032] Under the same preparation conditions as in Experiment 1, only the spray drying and sintering process parameters in step 1 were adjusted to obtain PTFE micro powder with an average particle size of 1.5 μm and a sphericity of 0.92, thereby obtaining anti-drip flame retardant masterbatch.

[0033] The results show that the product can still form an effective anti-drip network. Although the impact strength fluctuates slightly compared to Experiment 1, it still meets the high impact resistance requirements, proving that the technical solution has good feasibility and stability at the upper limit of the particle size defined in the claims.

[0034] Experiment 4: This experiment aims to verify the impact of the lower limit of sulfonic acid group grafting rate on the technical effect.

[0035] With all other preparation conditions the same as in Experiment 1, only the γ-ray irradiation dose in step 3 was adjusted to 15 kGy, and the reaction conditions were controlled to make the grafting rate 3.5 wt%, thus obtaining the anti-drip flame retardant masterbatch.

[0036] The results showed that the product still exhibited improved char layer density in combustion tests, and the char residue was significantly improved compared to the ungrafted sample, proving that the ionic crosslinking mechanism still works under the lower limit of grafting rate, and the technical solution is feasible.

[0037] Experiment 5: This experiment aims to verify the impact of the upper limit of sulfonic acid group grafting rate on the technical effect.

[0038] With all other preparation conditions the same as in Experiment 1, only the γ-ray irradiation dose in step 3 was adjusted to 25 kGy, and the reaction conditions were controlled to make the grafting rate 5.0 wt%, thus obtaining the anti-drip flame retardant masterbatch.

[0039] The results show that the product has a more significant smoke suppression effect and a higher char residue, and the processing fluidity is not significantly negatively affected, proving the superiority and feasibility of the technical solution under the upper limit of grafting rate.

[0040] Experiment 6: This experiment aims to verify the effect of the lower limit of MAH-g-PP anhydride grafting rate on the technical effect.

[0041] Under the same preparation conditions as in Experiment 1, only MAH-g-PP with an anhydride grafting rate of 1.2% was selected as the carrier resin to prepare the anti-drip flame retardant masterbatch.

[0042] The results showed that the masterbatch did not exhibit stratification after 6 months of storage, and the interfacial bonding force with the matrix resin was sufficient to support high impact resistance, proving that the carrier resin could still play a role in stabilizing the dispersion microenvironment under the lower limit of grafting rate.

[0043] Experiment 7: This experiment aims to verify the effect of the upper limit of MAH-g-PP anhydride grafting rate on the technical effect.

[0044] Under the same preparation conditions as in Experiment 1, only MAH-g-PP with an anhydride grafting rate of 1.8% was selected as the carrier resin to prepare the anti-drip flame retardant masterbatch.

[0045] The results show that the compatibility of the components of the masterbatch is further improved and the impact strength remains excellent, proving the stability of the technical solution under the upper limit of grafting rate.

[0046] Experiment 8: This experiment aims to verify the impact of the lower limit of the thickness of the double-modified coating on the technical effect.

[0047] Under the same preparation conditions as in Experiment 1, only the amount of KH-570 and PVP in step 2 was adjusted to control the total thickness of the synergistic coating to 20 nm, thus obtaining the anti-drip flame retardant masterbatch.

[0048] The results show that the product performed well in the storage stability test, with no obvious stratification, proving that under the lower limit of coating thickness, the dual-modified structure can still effectively play the role of interfacial compatibility and anti-agglomeration, and the technical solution has good feasibility.

[0049] Experiment 9: This experiment aims to verify the impact of the upper limit of the thickness of the double-modified coating on the technical effect.

[0050] Under the same preparation conditions as in Experiment 1, only the amount of KH-570 and PVP in step 2 was adjusted to control the total thickness of the synergistic coating to 50 nm, thus obtaining the anti-drip flame retardant masterbatch.

[0051] The results show that while maintaining excellent dispersibility, the product did not hinder PTFE fibrillation due to excessive coating thickness, and the anti-drip effect remained significant, demonstrating the stability of the technical solution under the upper limit of coating thickness.

[0052] Experiment 10: This experiment aims to verify the impact of the upper temperature limit of the plasticizing zone of a twin-screw extruder on the technical performance.

[0053] With all other preparation conditions the same as in Experiment 1, only the temperature of the plasticizing zone of the twin-screw extruder in step 4 was adjusted to 220°C to obtain anti-drip flame retardant masterbatch.

[0054] The results show that at the upper limit of the temperature, the material is fully plasticized and no premature fibrillation or thermal degradation of PTFE occurs, and the masterbatch does not turn yellow, proving the adaptability and feasibility of the method of the present invention at the upper limit of the process temperature.

[0055] Experiment 11: This experiment is a performance and effect verification experiment, aiming to comprehensively evaluate the physicochemical properties, flame retardant properties and mechanical properties of the anti-drip flame retardant of the present invention, and compare them with the comparative examples.

[0056] Test sample preparation: Experimental group: Masterbatch prepared in Experiment 1 (optimal), Experiment 2 (lower limit of particle size), Experiment 3 (upper limit of particle size), Experiment 4 (lower limit of grafting rate), Experiment 5 (upper limit of grafting rate), Experiment 8 (lower limit of coating thickness), and Experiment 9 (upper limit of coating thickness) were taken respectively.

[0057] Comparative example group: Comparative Example 1: PTFE flame retardant without sulfonic acid group grafting (other details are the same as in Experiment 1, skip step 3).

[0058] Comparative Example 2: Flame retardant prepared from conventional PTFE micropowder (5 μm particle size, irregular shape) without spheroidization treatment.

[0059] Comparative Example 3: Flame retardant without MBS / POE toughening compensation components (other aspects are the same as in Experiment 1).

[0060] Comparative Example 4: Commercially available ordinary PTFE anti-drip masterbatch.

[0061] Test method: The above masterbatch was added to ABS resin at a dosage of 4 phr, and injection molded into standard specimens for the following tests: limiting oxygen index (LOI), UL94 vertical flammability rating, 750°C glow wire ignition temperature (GWFI), 700°C char residue, cone calorific total smoke release (TSR), and cantilever beam notched impact strength.

[0062] Table 1. Performance test results of anti-drip flame retardant

[0063] The specific test results are shown in Table 1. As can be seen from the data in Table 1, the anti-drip flame retardants prepared in Experiments 1-9 all exhibited excellent flame retardant and mechanical balance properties in the ABS matrix. In particular, Experiment 1 achieved a LOI of 33.5%, passed the UL94 V-0 rating test, and showed no dripping during the 750℃ glow wire test. Simultaneously, its notched impact strength reached 22.5 kJ / m², far superior to Comparative Examples 2 and 3.

[0064] Furthermore, comparing the data from Comparative Example 2 and Comparative Example 3 reveals that the use of spherical PTFE micropowder prevented the significant decrease in impact strength observed in Comparative Example 2 (from 22.5 to 12.5 kJ / m²), while the presence of the MBS / POE compound toughening system completely overcame the brittleness problem in Comparative Example 3 (from 22.5 to 9.5 kJ / m²). In summary, this invention, through the synergistic design of sphericalization, dual modification, sulfonic acid grafting, and toughening compensation, successfully solved the technical problems of embrittlement, poor dispersion, and insufficient flame retardant synergy in traditional PTFE anti-dripping agents, achieving unexpected technical results.

[0065] Experimental results show that the anti-drip flame retardant prepared in this invention exhibits good flame retardant enhancement and toughness retention effects in ABS resin models, significantly improves the limiting oxygen index without dripping, and maintains a high notched impact strength. Therefore, it can be used to prepare thermoplastic polymer flame retardant materials for electronic appliances, automotive interiors, etc., to prevent and / or treat fire risks.

[0066] The above experiment is a preferred implementation of the present invention. In addition, the present invention can be implemented in other ways. Any obvious substitutions without departing from the concept of the present invention are within the protection scope of the present invention.

Claims

1. An anti-drip flame retardant for halogen-free flame retardant modification of thermoplastic polymers, comprising a carrier resin, a dispersant, an anti-drip functional component, a toughening compensating component, and a synergistic flame retardant component; characterized in that: The anti-drip functional component is polytetrafluoroethylene (PTFE) micropowder that has undergone spheroidization treatment and has a dual-modified surface structure, with an average particle size of 0.3-1.5 μm and a sphericity of not less than 0.

92. The dual-modified structure includes: an inner layer of a silane coupling agent chemically anchored to the PTFE surface through a hydrolysis-condensation reaction, and an outer layer of a polymeric dispersant coated on the inner layer through hydrogen bonding. The matrix is ​​also grafted with sulfonic acid groups at a grafting rate of 3.5–5.0 wt%. The toughening compensation component is an elastomer system formed by compounding MBS and POE at a mass ratio of 3:1 and uniformly dispersed in the carrier resin. The carrier resin is maleic anhydride-grafted polypropylene (MAH-g-PP) with an anhydride grafting rate of 1.2–1.8%, which together with the polymeric dispersant constitutes a stable dispersion microenvironment. The synergistic flame retardant component includes a phosphorus-nitrogen intumescent flame retardant and a metal hydroxide. Under combustion conditions, the sulfonic acid groups can undergo ionic crosslinking reactions with the polyol components in the phosphorus-nitrogen intumescent flame retardant, promoting the formation of an interpenetrating network structure between the PTFE fibrillary network and the expanded carbon layer, thereby achieving integrated synergistic effects of melt flow suppression, dense carbon layer construction, and flue gas suppression.

2. The anti-drip flame retardant according to claim 1, characterized in that: The PTFE micro powder has an average particle size of 0.8±0.2μm and a sphericity ≥0.

92.

3. The anti-drip flame retardant according to claim 1, characterized in that: The silane coupling agent is γ-methacryloxypropyltrimethoxysilane (KH-570), and the polymeric dispersant is polyvinylpyrrolidone (PVP). The total thickness formed by the synergistic coating of the two is 20-50 nm.

4. The anti-drip flame retardant according to claim 1, characterized in that: The anhydride grafting rate of the MAH-g-PP is 1.2-1.8%.

5. The anti-drip flame retardant according to claim 1, characterized in that: The phosphorus-nitrogen intumescent flame retardant comprises ammonium polyphosphate, pentaerythritol and melamine, and the sulfonic acid group undergoes an ionic crosslinking reaction with pentaerythritol at a combustion temperature ≥300°C.

6. The anti-drip flame retardant according to claim 1, characterized in that: The interpenetrating network structure showed a 12% higher carbon residue rate at 700% compared to the control sample without grafted sulfonic acid groups, and the resulting carbon layer exhibited a dense and continuous structure without macroscopic cracks under scanning electron microscopy.

7. A method for preparing the anti-drip flame retardant as described in any one of claims 1 to 6, characterized in that, Includes the following steps: (a) Preparation of spherical PTFE micro powder: PTFE emulsion was mixed with deionized water and sprayed into a spray drying tower through high pressure atomization. The precursor particles were dried at an inlet temperature of 180℃ and an outlet temperature of 90℃. The temperature was then increased to 360℃ at 10℃ / min and held for 2 hours in a nitrogen atmosphere to obtain PTFE micro powder with a sphericity ≥0.92 and an average particle size of 0.8±0.2μm. (b) Surface dual modification: The PTFE micro powder obtained in step (a) was dispersed in an ethanol-water mixed solvent, the pH was adjusted to 4.5–5.0, KH-570 was added, and the mixture was stirred at 60°C for 2 hours; then PVP solution was added, and stirring was continued for 1 hour. Centrifugation, washing, and vacuum drying yielded KH-570 / PVP double-layer coated PTFE. (c) Radiation grafting of sulfonic acid groups: The product of step (b) is placed in a nitrogen-protected container and irradiated with γ rays at a dose of 15-25 (kGy) to initiate surface free radicals; An aqueous solution of sodium styrene sulfonate was introduced and reacted at 60°C for 3 hours; dialysis and freeze-drying were performed to obtain sulfonated PTFE with a grafting rate of 3.5-5.0 wt%. (d) Masterbatch melt blending and granulation: The product of step (c), MBS, POE, MAH-g-PP, phosphorus-nitrogen intumescent flame retardant, metal hydroxide and polyether amide dispersant are mixed according to the formula and melt blended in a twin-screw extruder. The feeding zone temperature is 160-170℃, the plasticizing zone temperature is 200-220℃, the die temperature is 210℃, the screw speed is 300-400rpm, and a backflow barrier section is set at the vacuum port. The product is granulated underwater and dried to obtain the anti-drip flame retardant.

8. The preparation method according to claim 7, characterized in that: In step (d), the vacuum port of the twin-screw extruder is equipped with a backflow barrier section to prevent low-volatile substances from escaping and causing blockages or bubble defects.

9. The preparation method according to claim 7, characterized in that: The anti-drip flame retardant obtained in step (d) contains 18-22 wt% PTFE, 10-15 wt% toughening compensation component, and the remainder is carrier resin and additives; the particle size distribution D90≤350μm, no crystal points, and no stratification after 6 months of storage.

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