Halogen-free flame-retardant masterbatch, preparation method thereof and transparent flame-retardant film

Abstract

The present application relates to the technical field of polyester film flame-retardant modification, and particularly relates to a halogen-free flame-retardant master batch, a preparation method thereof and a transparent flame-retardant film. The halogen-free flame-retardant master batch comprises polyester resin, hexaphenoxycyclotriphosphazene, aluminum diethylphosphinate and hyperbranched flame retardant, wherein the hyperbranched flame retardant is an epoxy-terminated hyperbranched polyester grafted with a DOPO group. When the halogen-free flame-retardant master batch is used to prepare a flame-retardant film, the film has high transparency, flame-retardant grade, processability and mechanical strength.

Description

Technical Field

[0001] This invention relates to the field of flame retardant modification technology of polymer materials, specifically to a halogen-free flame retardant masterbatch and its preparation method, and a transparent flame retardant film. Background Technology

[0002] Polyethylene terephthalate (PET) film is widely used in electronic insulation, display base films, and new energy battery separators. However, its limiting oxygen index is only about 21%, and it produces severe dripping during combustion, making it difficult to meet fire safety requirements. Adding flame-retardant masterbatch to modify PET film for flame retardancy is a common industrial method. Flame-retardant masterbatch is an intermediate material made by pre-blending and granulating flame retardants with carrier resins. It is directly mixed with the film base material and extruded during use, facilitating dispersion and metering.

[0003] Flame retardant masterbatches are classified into halogenated and halogen-free types based on whether they contain halogens. Halogenated flame retardant masterbatches tend to produce toxic fumes when burning, thus halogen-free flame retardant masterbatches are receiving more attention. However, some existing halogen-free flame retardant masterbatches require high levels of flame retardant to achieve a VTM-0 rating, resulting in high costs and limited anti-dripping effects. Others use physical blending methods to add flame retardants, which can easily migrate and leach out, making it difficult to guarantee flame retardant durability. Still others require copolymerizing flame retardant monomers with PET monomers to obtain modified resins, which are then used to make masterbatches, resulting in complex manufacturing processes and a tendency to decrease film transparency and mechanical properties. Therefore, existing halogen-free flame retardant masterbatches cannot simultaneously enable PET films to meet the requirements for transparency, flame retardancy, processability, and mechanical properties. Summary of the Invention

[0004] This invention provides a halogen-free flame retardant masterbatch, its preparation method, and a transparent flame retardant film, to solve the problem that existing halogen-free flame retardant masterbatches cannot simultaneously enable PET films to meet the requirements of transparency, flame retardancy, processability, and mechanical properties.

[0005] In a first aspect, the present invention provides a halogen-free flame retardant masterbatch comprising polyester resin, hexaphenoxycyclotriphosphazene (HPCTP), aluminum diethylphosphite (ADP), and a hyperbranched flame retardant; wherein the hyperbranched flame retardant is an epoxy-terminated hyperbranched polyester grafted with DOPO groups (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide).

[0006] In one optional embodiment, the grafting rate of DOPO groups in the hyperbranched flame retardant is 30% to 50%.

[0007] In one optional embodiment, by weight, the polyester resin comprises 50-80 parts, the hexaphenoxycyclotriphosphazene comprises 6-20 parts, the diethylaluminum hypophosphite comprises 4-15 parts, and the hyperbranched flame retardant comprises 5-20 parts.

[0008] In one alternative embodiment, it further comprises at least one of a nano-carbonization enhancer, an antioxidant, a lubricant, and a dispersant.

[0009] In one optional embodiment, the nano-char-forming reinforcing agent is 0.5-5 parts, the antioxidant is 0.1-1 parts, the lubricant is 0.1-1 parts, and the dispersing agent is 0.1-1 parts. The amount of the nano-char-forming reinforcing agent is preferably 0.5-3 parts, more preferably 1-2 parts. In one optional embodiment, the polyester resin includes at least one of PET (polyethylene terephthalate) and PBT (polybutylene terephthalate).

[0010] In one alternative embodiment, the hyperbranched flame retardant is prepared by a method comprising the following steps: Synthesis of hyperbranched polyester: Polyols and AB2 type monomers are subjected to melt polycondensation reaction in the presence of a catalyst to obtain hyperbranched polyesters; Epoxy end-capping reaction: Hyperbranched polyester is subjected to an epoxy end-capping reaction with an epoxidizing agent to obtain epoxy-end-modified hyperbranched polyester; DOPO grafting reaction: Epoxy-terminated hyperbranched polyester and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide are mixed in an organic solvent to carry out DOPO grafting reaction to obtain hyperbranched flame retardant.

[0011] In one optional embodiment, the polyol includes at least one of triols and tetraols; And / or, the AB2 type monomer includes at least one of dimethylolpropionic acid and dimethylolbutyric acid; And / or, the catalyst includes a sulfonic acid catalyst; And / or, the molar ratio of the polyol to the AB2 type monomer is 1:(5~15). And / or, the amount of the catalyst used is 0.3% to 0.8% of the mass of the AB2 type monomer; And / or, the temperature of the melt polycondensation reaction is 140~160℃; And / or, the melt polycondensation reaction takes 4 to 8 hours.

[0012] In one optional embodiment, the epoxidizing agent includes at least one of epichlorohydrin and epibromopropane; And / or, the molar ratio of hydroxyl groups to epoxidizing agents in the terminal hydroxyl hyperbranched polyester is 1:(3~8). And / or, the epoxy end-capping reaction is carried out under alkaline conditions; And / or, the epoxy end-capping reaction is performed at a temperature of 40~80℃; And / or, the epoxy end-capping reaction time is 2-6 hours.

[0013] In one optional embodiment, the organic solvent includes at least one of ether solvents and amide solvents; And / or, the molar ratio of the epoxy group to 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide in the terminal epoxy hyperbranched polyester is 1:(0.3~0.7). And / or, the temperature of the DOPO grafting reaction is 60~100℃; And / or, the DOPO grafting reaction time is 4~12h.

[0014] In one optional embodiment, the purity of the hexaphenoxycyclotriphosphazene is not less than 98%; the median particle size of the diethylaluminum hypophosphite is 3~10μm; and the nano-carbonization reinforcing agent includes, but is not limited to, fumed nano-silica with a specific surface area of ​​200~400m². 2 / g, with an average primary particle size of 7~40nm. This nano-char-forming enhancer improves powder flowability and prevents particle adhesion during masterbatch preparation. During film combustion, the nano-silica particles can act as char-forming sites, synergistically interacting with phosphorus-based flame retardants (HPCTP, ADP, and EHBPE-g-DOPO) to promote the formation of a dense, expanded, and high-strength char layer, significantly enhancing the flame-retardant effect of the condensed phase and reducing the heat release rate. The antioxidants include primary and secondary antioxidants, with primary antioxidants including but not limited to antioxidant 1010 and secondary antioxidants including but not limited to antioxidant 168. The lubricants include but are not limited to calcium stearate. The dispersing aids include but are not limited to pentaerythritol stearate.

[0015] Secondly, the present invention also provides a method for preparing halogen-free flame retardant masterbatch as described in the first aspect, comprising the following steps: The hyperbranched flame retardant was mixed with polyester resin, hexaphenoxycyclotriphosphazene, and diethyl aluminum hypophosphite, and then melt-extruded and granulated.

[0016] In one optional embodiment, at least one of the following is added during the mixing step: a nano-carbonization enhancer, an antioxidant, a lubricant, and a dispersant.

[0017] Thirdly, the present invention also provides a transparent flame-retardant film, comprising at least one flame-retardant layer, wherein the flame-retardant layer comprises the halogen-free flame-retardant masterbatch described in the first aspect or the halogen-free flame-retardant masterbatch prepared by the method described in the second aspect.

[0018] In one optional embodiment, the transparent flame-retardant film has an A / B / A three-layer structure, where layer A is the surface layer, layer B is the core layer, and both layers A and B contain the halogen-free flame-retardant masterbatch described in the third aspect, with the content of halogen-free flame-retardant masterbatch in layer B being higher than that in layer A.

[0019] The technical solution of this invention has the following advantages: 1. The halogen-free flame retardant masterbatch provided by this invention comprises a hyperbranched flame retardant, hexaphenoxycyclotriphosphazene, and diethylaluminum hypophosphite. Typically, increasing the amount of flame retardant added reduces film transparency, while reducing the amount makes it difficult to achieve a VTM-0 rating. Physically blended flame retardants are prone to migration, while chemical copolymerization affects mechanical properties. In this application, the three components are compounded so that the epoxy groups of the hyperbranched flame retardant can undergo ring-opening reactions with the PET end groups during processing, forming chemical bonds, thereby effectively inhibiting the migration of the flame retardant components. Its hyperbranched structure improves processability. Simultaneously, the gas-phase flame retardant (DOPO in the hyperbranched flame retardant) and the condensed-phase char formation (diethylaluminum hypophosphite) complement each other within the same system, and the phosphorus-nitrogen structure of the hexaphenoxycyclotriphosphazene further enhances the flame retardant efficiency. The synergistic effect of these three components allows the masterbatch to achieve a VTM-0 rating for polyester film with a relatively low total addition amount, while maintaining high transparency and mechanical properties.

[0020] 2. This invention introduces nano-fumed silica as a nano-carbonization reinforcing agent. It is not simply used as an inert filler, but rather its high specific surface area (200~400m²) is utilized. 2 The nano-size effect, combined with the phosphorus-silicon synergistic char-forming effect of HPCTP, ADP, and DOPO polyphosphorus components during combustion, generates a phosphorus-silicon synergistic char-forming effect. Nano-SiO2 particles are uniformly dispersed in the char layer, forming physical cross-linking points and skeletal support, significantly improving the density, thermal stability, and barrier properties of the char layer. The char residue rate is increased by more than 6 percentage points compared to the binary system without the addition of nano-char-forming enhancers. This effect exceeds the expectations of simple processing aids and constitutes an important characteristic of flame-retardant synergistic technology.

[0021] 3. The transparent flame-retardant film provided by this invention employs a three-layer A / B / A structure, with both the surface layer and the core layer containing HPCTP (approximately 1.59~1.61), and the HPCTP concentration in the core layer being higher than that in the surface layer. Utilizing the similarity in refractive index between HPCTP and PET (approximately 1.57~1.58), a refractive index gradient is formed through the concentration difference, reducing interlayer interface reflection and maintaining high film transparency while ensuring flame-retardant performance. Detailed Implementation

[0022] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0023] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0024] Example 1 This embodiment provides a method for preparing halogen-free flame retardant masterbatch and transparent flame retardant film, the specific steps of which are as follows: 1. Preparation of hyperbranched flame retardant (EHBPE-g-DOPO): 1.1 Synthesis of hydroxyl-terminated hyperbranched polyester (HBPE-OH): A second-generation (G2) hydroxyl-terminated hyperbranched polyester was synthesized via melt polycondensation using trimethylolpropane (TMP) as the core and 2,2-dimethylolpropionic acid (bis-MPA) as the AB2 monomer. The specific steps are as follows: In a reactor equipped with a mechanical stirrer, nitrogen inlet, thermometer, and condenser, 13.4 g (0.1 mol) of trimethylolpropane, 120.6 g (0.9 mol) of 2,2-dimethylolpropionic acid, and 0.67 g of p-toluenesulfonic acid (p-TSA) (catalyst, accounting for 0.5 wt% of the total monomer mass) were added. Nitrogen gas was introduced for protection, and the temperature was raised to 140 °C and reacted at atmospheric pressure for 1 h. Subsequently, the vacuum was gradually reduced to 30-50 kPa over 1 h, and the reaction continued for another 1 h to remove the generated water. The temperature was raised to 160 °C, and the vacuum was further reduced to <10 kPa. The reaction was stopped when the acid value of the system dropped below 15 mg KOH / g. The product was dissolved in tetrahydrofuran after cooling, precipitated with diethyl ether, and dried under vacuum to give a pale yellow solid HBPE-OH. The number-average molecular weight of the obtained product was approximately 2100 g / mol, and the hydroxyl value was approximately 480 mg KOH / g.

[0025] 1.2 Epoxy End-Capping Reaction (Anhydrous Solid Alkali Method): The HBPE-OH obtained in step 1.1 was dissolved in epichlorohydrin and added to a three-necked flask equipped with a mechanical stirrer, a nitrogen inlet, and a thermometer. Powdered sodium hydroxide and tetrabutylammonium bromide (TBAB) were added, wherein the molar ratio of sodium hydroxide to the hydroxyl groups in HBPE-OH was 1.2:1, and the amount of TBAB was 3% of the mass of HBPE-OH. The reaction was carried out under nitrogen protection at 25°C with stirring for 2 hours. The temperature was slowly increased to 45°C, and the reaction was continued for 4 hours. After the reaction was completed, sodium chloride and excess sodium hydroxide were removed by filtration, and the filter cake was washed with a small amount of dry tetrahydrofuran. The filtrates were combined, and unreacted epichlorohydrin was recovered by vacuum distillation below 35°C. The residue was dissolved in tetrahydrofuran, filtered again, and the filtrate was added dropwise to cold diethyl ether to precipitate the product. The precipitate was dried under vacuum to obtain terminal epoxy hyperbranched polyester (EHBPE). The presence of epoxy groups in the product was confirmed by titration using the hydrochloric acid-acetone method, indicating that the terminal hydroxyl groups had been converted to epoxy groups.

[0026] 1.3 DOPO grafting reaction: The EHBPE obtained in step 1.2 was dissolved in anhydrous tetrahydrofuran and added to a three-necked flask equipped with a mechanical stirrer, a nitrogen inlet, and a reflux condenser. 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was added, with the molar amount of DOPO being half the total molar amount of the hydroxyl groups in HBPE-OH used in step 1.1, i.e., grafting at 50% of the total hydroxyl group amount. A catalyst amount of triphenylphosphine was added, and the mixture was stirred to dissolve. Nitrogen gas was introduced for protection, and the mixture was heated to 70°C and reacted for 8 hours. The reaction endpoint was determined by the disappearance of the pH characteristic peak of DOPO, monitored using NMR phosphorus spectroscopy. After the reaction was complete, the reaction solution was concentrated, slowly added dropwise to cold diethyl ether to precipitate, filtered, washed with diethyl ether, and dried under vacuum to obtain the hyperbranched flame retardant EHBPE-g-DOPO. The product was characterized by NMR phosphorus spectroscopy, and characteristic peaks of PC bonds were observed. No pH characteristic peak of free DOPO was detected, indicating that DOPO had been grafted onto the polymer backbone via PC bonds, with no free DOPO residue. Combined epoxy titration and phosphorus content elemental analysis confirmed that the DOPO grafting rate (approximately 48%) was close to the theoretical feed ratio.

[0027] 2. Preparation of halogen-free flame retardant masterbatch HPCTP-ADP-EHBPE-g-DOPO: 2.1. By weight, weigh 70 parts of PET chips (intrinsic viscosity 0.68 dL / g), 12 parts of hexaphenoxycyclotriphosphazene (HPCTP, purity ≥98%), 6 parts of aluminum diethylphosphite (ADP, D50≈5μm), 10 parts of the hyperbranched flame retardant EHBPE-g-DOPO prepared in step 1, and fumed silica nanoparticles (specific surface area 300m²). 2 / g) 1.2 parts, antioxidant 1010 0.1 parts, antioxidant 168 0.2 parts, calcium stearate 0.2 parts, pentaerythritol stearate 0.3 parts.

[0028] 2.2 PET chips were vacuum dried at 150℃ for 5 hours until the moisture content was ≤50ppm, HPCTP was dried at 80℃ for 2 hours, ADP was dried at 130℃ for 3 hours, and fumed silica nanoparticles were dried at 110℃ for 2 hours. The above components were added to a high-speed mixer according to the specified ratio and mixed at 600rpm for 8 minutes. Melt-blending extrusion was performed using a co-rotating twin-screw extruder (L / D ratio L / D=44). The extruder temperatures were set as follows: feed section 235℃, compression section 255℃, metering section 265℃, die head 270℃, and screw speed 280rpm. The extruded strips were water-cooled and then granulated. The granules were dried at 100℃ for 3 hours to obtain halogen-free flame-retardant masterbatch M1.

[0029] 3. Preparation of transparent flame-retardant PET film 3.1 Raw material preparation: Prepare the raw materials for layer A and layer B according to the following proportions.

[0030] Layer A raw materials (surface layer accounting for 30%): 92.5 parts by weight of PET chips (intrinsic viscosity 0.68 dL / g) and 7.5 parts by weight of halogen-free flame retardant masterbatch M1.

[0031] B-layer raw materials (70% of the core layer): 85 parts by weight of PET chips (intrinsic viscosity 0.68 dL / g) and 115 parts by weight of halogen-free flame retardant masterbatch M1.

[0032] After mixing the raw materials of each layer evenly, vacuum dry them at 150℃ for 5 hours until the moisture content is ≤100ppm.

[0033] 3.2 Three-layer co-extrusion cast sheet: Three single-screw extruders are used to plasticize the A-layer and B-layer raw materials respectively. The materials are then converged and cast onto the quench roll through a three-layer co-extrusion die (A / B / A structure) to form a cast sheet. Extruder temperature settings: A-layer extruder feed section temperature 235℃, compression section temperature 255℃, metering section temperature 265℃, die head temperature 270℃; B-layer extruder feed section temperature 240℃, compression section temperature 260℃, metering section temperature 270℃, die head temperature 275℃, quench roll temperature 20℃. The cast sheet thickness is controlled at 500μm, with the A-layer accounting for 18% of the total thickness and the B-layer accounting for 64%.

[0034] 3.3 Biaxial Tensile Testing: The cast sheet was subjected to simultaneous biaxial tensile testing on a biaxial tensile testing machine. The preheating temperature was 105℃, the preheating time was 60s, the longitudinal tensile ratio was 3.5, the transverse tensile ratio was 3.5, the tensile speed was 20mm / s, and the film thickness after stretching was 25μm. Then, it was cooled to room temperature and wound up to obtain transparent flame-retardant PET film sample F1.

[0035] Example 2 This embodiment provides a method for preparing halogen-free flame-retardant masterbatch and transparent flame-retardant film. The difference from Embodiment 1 is that in step 2, when preparing the halogen-free flame-retardant masterbatch, 70 parts by weight of PET chips, 8 parts of HPCTP, 10 parts of ADP, 10 parts of the hyperbranched flame retardant prepared in step 1 of Embodiment 1, 1.2 parts of fumed silica, 0.1 parts of antioxidant 1010, 0.2 parts of antioxidant 168, 0.2 parts of calcium stearate, and 0.3 parts of pentaerythritol stearate are weighed to obtain halogen-free flame-retardant masterbatch M2. In step 3, when preparing the transparent flame-retardant PET film, halogen-free flame-retardant masterbatch M2 is used instead of M1, while maintaining the total flame retardant content of the final film consistent with F1, resulting in transparent flame-retardant PET film sample F2. Other conditions are the same as in Embodiment 1.

[0036] Example 3 This embodiment provides a method for preparing halogen-free flame-retardant masterbatch and transparent flame-retardant film. The difference from Example 1 is that in step 2, when preparing the halogen-free flame-retardant masterbatch, 70 parts by weight of PET chips, 14 parts of HPCTP, 4 parts of aluminum diethyl phosphite, 10 parts of the hyperbranched flame retardant prepared in step 1 of Example 1, 1.2 parts of fumed silica, 0.1 parts of antioxidant 1010, 0.2 parts of antioxidant 168, 0.2 parts of calcium stearate, and 0.3 parts of pentaerythritol stearate are weighed to obtain halogen-free flame-retardant masterbatch M3. In step 3, when preparing the transparent flame-retardant PET film, halogen-free flame-retardant masterbatch M3 is used instead of M1, while maintaining the same total flame retardant content as F1 in the final film, resulting in transparent flame-retardant PET film sample F3. Other conditions are the same as in Example 1.

[0037] Example 4 This embodiment provides a method for preparing halogen-free flame-retardant masterbatch and transparent flame-retardant film. The difference from Example 1 is that in step 1, when preparing the hyperbranched flame retardant, the DOPO feeding amount in step 1.3 is adjusted to 23.1 g (0.107 mol). Other conditions are the same as in step 1 of Example 1, resulting in a hyperbranched flame retardant with a DOPO grafting rate of 34.2%. In steps 2 and 3, this hyperbranched flame retardant is used to replace the hyperbranched flame retardant prepared in step 1 of Example 1, yielding halogen-free flame-retardant masterbatch M4 and transparent flame-retardant PET film sample F4. Other conditions are the same as in Example 1.

[0038] Example 5 This embodiment provides a method for preparing a uniform structure flame-retardant PET film, the specific steps of which are as follows: 1. Preparation of halogen-free flame retardant masterbatch: Halogen-free flame retardant masterbatch M1 was prepared using the same method as step 2 of Example 1.

[0039] 2. Preparation of transparent flame-retardant PET film: Halogen-free flame-retardant masterbatch M1 was mixed with PET chips in a certain proportion to ensure that the total flame retardant content of the final film was consistent with that of F1 in Example 1. The film was prepared using a single-layer extrusion biaxial stretching process. The temperatures of the single-screw extruder were 235°C in the feed section, 255°C in the compression section, 265°C in the metering section, 270°C in the die head, 275°C in the quench roll, and 20°C in the quenching roll. The cast sheets were simultaneously biaxially stretched on a biaxial tensile testing machine with a preheating temperature of 95°C and a preheating time of 60s. The longitudinal stretch ratio was 3.5, the transverse stretch ratio was 3.8, and the stretching speed was 300% / min. The film thickness after stretching was 25μm. The stretched film was heat-set at 210°C for 15s, cooled to room temperature, and then wound up to obtain a uniform transparent flame-retardant PET film sample F5.

[0040] Comparative Example 1 This comparative example provides a method for preparing a single HPCTP flame-retardant PET film, the specific steps of which are as follows: 1. Preparation of halogen-free flame retardant masterbatch: By weight, weigh 70 parts PET chips, 28 parts hexaphenoxycyclotriphosphazene, 1.2 parts fumed silica nanoparticles, 0.1 parts antioxidant 1010, 0.2 parts antioxidant 168, 0.2 parts calcium stearate, and 0.3 parts pentaerythritol stearate. Using the same preparation process as step 2 of Example 1, halogen-free flame retardant masterbatch C1 is obtained.

[0041] 2. Preparation of transparent flame-retardant PET film: Prepare layer A and layer B raw materials according to the following ratios. Layer A raw materials: 92.5 parts by weight of PET chips, 7.5 parts by weight of halogen-free flame-retardant masterbatch C1. Layer B raw materials: 85 parts by weight of PET chips, 15 parts by weight of halogen-free flame-retardant masterbatch C1. Using the same preparation process as step 3 of Example 1, obtain transparent flame-retardant PET film sample C1, controlling the hexaphenoxycyclotriphosphazene content in the final film to be the same as the total flame retardant content of F1 in Example 1.

[0042] Comparative Example 2 This comparative example provides a method for preparing a single ADP flame-retardant PET film, the specific steps of which are as follows: 1. Preparation of halogen-free flame retardant masterbatch: By weight, weigh 70 parts PET chips, 28 parts diethylaluminum hypophosphite, 1.2 parts fumed silica nanoparticles, 0.1 parts antioxidant 1010, 0.2 parts antioxidant 168, 0.2 parts calcium stearate, and 0.3 parts pentaerythritol stearate. Using the same preparation process as step 2 of Example 1, halogen-free flame retardant masterbatch C2 is obtained.

[0043] 2. Preparation of transparent flame-retardant PET film: Prepare layer A and layer B raw materials according to the following ratios. Layer A raw materials: 92.5 parts by weight of PET chips, 7.5 parts by weight of halogen-free flame-retardant masterbatch C2. Layer B raw materials: 85 parts by weight of PET chips, 15 parts by weight of halogen-free flame-retardant masterbatch C2. Using the same preparation process as step 3 of Example 1, obtain transparent flame-retardant PET film sample C2, controlling the diethylaluminum hypophosphite content in the final film to be the same as the total flame retardant content of F1 in Example 1.

[0044] Comparative Example 3 This comparative example provides a method for preparing a binary composite flame-retardant PET film of HPCTP and ADP, and the specific steps are as follows: 1. Preparation of halogen-free flame retardant masterbatch: Weigh out 70 parts by weight of PET chips, 18 parts by weight of hexaphenoxycyclotriphosphazene, 9 parts by weight of diethylaluminum hypophosphite, 1.2 parts by weight of fumed silica nanoparticles, 0.1 parts by weight of antioxidant 1010, 0.2 parts by weight of antioxidant 168, 0.2 parts by weight of calcium stearate, and 0.3 parts by weight of pentaerythritol stearate. Using the same preparation process as step 2 of Example 1, halogen-free flame retardant masterbatch C3 is obtained.

[0045] 2. Preparation of transparent flame-retardant PET film: Prepare layer A and layer B raw materials according to the following ratios. Layer A raw materials: 92.5 parts by weight of PET chips, 7.5 parts by weight of halogen-free flame-retardant masterbatch C3. Layer B raw materials: 85 parts by weight of PET chips, 15 parts by weight of halogen-free flame-retardant masterbatch C3. Using the same preparation process as in step 3 of Example 1, obtain transparent flame-retardant PET film sample C3.

[0046] Comparative Example 4 This comparative example provides a method for preparing a flame-retardant PET film by directly adding DOPO to replace EHBPE-g-DOPO. The specific steps are as follows: 1. Preparation of halogen-free flame retardant masterbatch: By weight, weigh 70 parts PET chips, 12 parts hexaphenoxycyclotriphosphazene, 6 parts diethylaluminum hypophosphite, 10 parts 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (replacing the hyperbranched flame retardant in Example 1 by mass after phosphorus content conversion), 1.2 parts fumed silica nanoparticles, 0.1 parts antioxidant 1010, 0.2 parts antioxidant 168, 0.2 parts calcium stearate, and 0.3 parts pentaerythritol stearate. Using the same preparation process as step 2 of Example 1, halogen-free flame retardant masterbatch C4 is obtained.

[0047] 2. Preparation of transparent flame-retardant PET film: Prepare layer A and layer B raw materials according to the following ratios. Layer A raw materials: 92.5 parts by weight of PET chips, 7.5 parts by weight of halogen-free flame-retardant masterbatch C4. Layer B raw materials: 85 parts by weight of PET chips, 15 parts by weight of halogen-free flame-retardant masterbatch C4. Using the same preparation process as in step 3 of Example 1, obtain transparent flame-retardant PET film sample C4.

[0048] Test case 1. Flame retardant properties The limiting oxygen index (LOI) was tested according to GB / T 2406.2 standard, and the vertical flammability rating was tested according to UL94 standard (VTM rating was used for the thin film). The results are as follows:

[0049] The results show that samples F1-F5 using the ternary synergistic technology of this invention all achieved VTM-0 level and no dripping, with an LOI of over 34.5%, significantly better than the single HPCTP system (C1), the single ADP system (C2), the HPCTP+ADP binary system (C3), and the direct addition of DOPO (C4). Moreover, there is a significant synergistic effect between HPCTP and ADP: the LOI of F1-F5 is increased by approximately 4.5-5.3 percentage points compared to C1, and by approximately 1.7-3.0 percentage points compared to C3, fully demonstrating the synergistic effect of EHBPE-g-DOPO as the third component on the HPCTP-ADP system. The direct addition of DOPO (C4) is significantly less effective than EHBPE-g-DOPO, demonstrating the technological contribution of chemical grafting and reactive anchoring structures.

[0050] 2. Optical performance According to GB / T 2410 standard, the transmittance and haze of the film were tested using a haze meter and a spectrophotometer (550 nm wavelength, 25 μm film thickness).

[0051]

[0052] The results show that the transmittance of the gradient refractive index three-layer structure films F1-F5 of this invention remains above 88.1%, and the haze is ≤3.5%, significantly better than the comparative examples. In particular, the F3 sample (high HPCTP ratio) achieves a transmittance of 90.2%, close to that of pure PET film, fully demonstrating the excellent transparency retention capability of HPCTP. Compared with the uniform structure F5, the gradient refractive index design achieves higher transmittance and lower haze at the same flame retardant content, proving the technical contribution of gradient refractive index matching to transparency retention. Phosphazene flame retardants have good dispersibility in PET and can maintain high transparency. Their flame retardant mechanism involves condensed phase carbonization and gas-phase free radical capture, thus making them suitable for transparent films. C1-C4 are three-layer structures, and the influence of structural differences has been eliminated. Their poor optical performance is mainly attributed to flame retardant dispersibility and compatibility issues.

[0053] 3. Flame retardancy and durability (anti-migration properties) After aging each sample at 70℃ and 90% relative humidity for 500 h, the LOI value was tested again, and the LOI retention rate was calculated.

[0054]

[0055] The LOI retention rate of F1 and F3 samples using EHBPE-g-DOPO exceeded 96% after aging, significantly higher than that of the physically blended systems C1 and C3 (approximately 91%). This demonstrates that the chemical bonding between the epoxy groups and the PET end groups effectively anchors the flame-retardant components, significantly improving flame-retardant durability.

[0056] 4. Processing fluidity Ubbelohde viscometer was used to test the intrinsic viscosity ([η]) of each flame-retardant masterbatch after extrusion granulation in a constant temperature water bath at (25±0.1)℃, according to GB / T 14190 standard, using a mixed solvent of phenol / tetrachloroethane (mass ratio 60:40), to evaluate the effect of flame retardant addition on the degradation degree of PET molecular chains. A higher intrinsic viscosity value indicates better retention of PET molecular weight and lower thermal and mechanochemical degradation during processing.

[0057]

[0058] After extrusion thermal processing, the intrinsic viscosity of pure PET chips decreased from 0.68 dL / g to 0.61 dL / g, indicating significant thermal degradation. The intrinsic viscosity of the binary control masterbatch without EHBPE-g-DOPO was only 0.58 dL / g, lower than that of pure PET undergoing the same thermal process, suggesting that the presence of a large amount of flame retardant particles exacerbated the shear degradation of the PET molecular chains. The intrinsic viscosity of masterbatches M1-M3 with added EHBPE-g-DOPO remained at 0.67-0.70 dL / g, comparable to or even slightly higher than the original value of pure PET chips (0.68 dL / g). This is attributed to the ring-opening reaction between the epoxy groups retained in the EHBPE-g-DOPO molecule and the terminal carboxyl / hydroxyl groups of PET during melt extrusion, forming chain extension and end-capping effects. This effectively compensated for the molecular chain breakage during processing, inhibited thermal degradation, and maintained the molecular weight of PET.

[0059] Higher intrinsic viscosity means better integrity of PET molecular chains, which is beneficial to the stability of subsequent biaxial stretching film formation process and the mechanical properties of the final film. EHBPE-g-DOPO has three functions: reactive compatibilization, chemical anchoring and processing stability, effectively overcoming the common problem of severe PET degradation in the preparation of traditional flame retardant masterbatches, and also has good processability.

[0060] 5. Mechanical properties The tensile strength and elongation at break (longitudinal) of the film were tested according to GB / T 1040.3 standard.

[0061]

[0062] Both F1 and F3 maintained good mechanical properties, with tensile strengths reaching 188-192 MPa and elongation at break of 132%-138%, significantly better than the comparative examples. EHBPE-g-DOPO improved the interfacial bonding between the flame retardant and the matrix through chemical anchoring and compatibilization, effectively inhibiting the degradation of mechanical properties. F3 with a high HPCTP content exhibited the best mechanical properties, demonstrating the advantage of good compatibility between HPCTP and PET.

[0063] 6. Cone calorimetry test A cone calorimeter was used at a thermal radiation flux of 50 kW / m². 2 Thin film samples were tested under the specified conditions.

[0064]

[0065] The peak heat release rate (PHRR) of F1 and F3 was reduced by 64.5% and 67.4% respectively compared to pure PET, and the total heat release rate (THR) was reduced by 57.5% and 61.3% respectively. The char residue was increased to 24.5% and 26.8% respectively, significantly higher than the comparative ratio, and the char layer was dense and expanded. This is attributed to the nano-fumed silica in the formulation acting as a char-forming enhancer, producing a synergistic char-forming effect with the HPCTP / ADP / DOPO multi-phosphorus components. The nanoparticles play a role in physical cross-linking and skeletal support in the char layer, significantly improving the thermal stability and barrier properties of the char layer. F3, with a high HPCTP ratio, exhibited the best flame retardant performance, indicating that HPCTP has outstanding advantages in PN synergistic flame retardancy and gas-phase-condensed phase dual-phase interaction. After heating, HPCTP forms a phosphorus-containing carbonized film on the material surface. This film can isolate the heat source and oxygen, delaying the thermal decomposition process of the substrate. The multi-layered synergistic flame-retardant network formed by EHBPE-g-DOPO, HPCTP, and ADP exhibits significant effects in delaying ignition, inhibiting heat release, and promoting char formation. Comparing F1 (three-layer) and F5 (homogeneous), both containing equal amounts of flame retardant, F1 showed a lower PHRR and higher char residue, indicating that the three-layer gradient refractive index structure also has certain advantages in flame-retardant performance, possibly related to the higher concentration of flame retardant in the core layer, which more effectively contributes to char formation in the condensed phase. C4 (directly added DOPO) showed significantly lower PHRR and char residue than F1, further confirming the promoting effect of the chemical grafting structure on char formation.

[0066] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A halogen-free flame retardant masterbatch, characterized in that, It comprises polyester resin, hexaphenoxycyclotriphosphazene, diethyl aluminum hypophosphite, and hyperbranched flame retardant; wherein the hyperbranched flame retardant is an epoxy-terminated hyperbranched polyester modified with DOPO groups.

2. The halogen-free flame retardant masterbatch according to claim 1, characterized in that, The grafting rate of DOPO groups in the hyperbranched flame retardant is 30%~50%.

3. The halogen-free flame retardant masterbatch according to claim 1 or 2, characterized in that, By weight, the polyester resin is 50-80 parts, the hexaphenoxycyclotriphosphazene is 6-20 parts, the diethylaluminum hypophosphite is 4-15 parts, and the hyperbranched flame retardant is 5-20 parts.

4. The halogen-free flame retardant masterbatch according to claim 1 or 2, characterized in that, It also contains at least one of the following: nano-carbonization enhancer, antioxidant, lubricant, and dispersant.

5. The halogen-free flame retardant masterbatch according to claim 4, characterized in that, By weight, the nano-carbon-forming reinforcing agent is 0.5-5 parts, the antioxidant is 0.1-1 parts, the lubricant is 0.1-1 parts, and the dispersing agent is 0.1-1 parts.

6. The halogen-free flame retardant masterbatch according to claim 1 or 2, characterized in that, The polyester resin is PET.

7. The halogen-free flame retardant masterbatch according to claim 1 or 2, characterized in that, The hyperbranched flame retardant is prepared by a method comprising the following steps: Synthesis of hyperbranched polyester: Polyols and AB2 type monomers are subjected to melt polycondensation reaction in the presence of a catalyst to obtain hyperbranched polyesters; Epoxy end-capping reaction: Hyperbranched polyester is subjected to an epoxy end-capping reaction with an epoxidizing agent to obtain epoxy-end-modified hyperbranched polyester; DOPO grafting reaction: Epoxy-terminated hyperbranched polyester and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide are mixed in an organic solvent to carry out DOPO grafting reaction to obtain hyperbranched flame retardant.

8. A method for preparing halogen-free flame retardant masterbatch as described in any one of claims 1 to 7, characterized in that, Includes the following steps: The hyperbranched flame retardant was mixed with polyester resin, hexaphenoxycyclotriphosphazene, and diethyl aluminum hypophosphite, and then melt-extruded and granulated.

9. The preparation method according to claim 8, characterized in that, The mixing step also includes at least one of the following: a nano-carbonization enhancer, an antioxidant, a lubricant, and a dispersant.

10. A transparent flame-retardant film, characterized in that, It includes at least one flame-retardant layer, the flame-retardant layer comprising the halogen-free flame-retardant masterbatch as described in any one of claims 1 to 7 or the halogen-free flame-retardant masterbatch prepared by the method of preparing the halogen-free flame-retardant masterbatch as described in claim 8 or 9.

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