Highly transparent flame-retardant modified polyester film and preparation method thereof

Abstract

The application provides a high-transmittance flame-retardant modified polyester film and a preparation method thereof, PETG and PEN are introduced into PET for blending, an ionic liquid flame retardant is introduced into a PET flame-retardant film system for use in combination with a phosphorus-based flame retardant, a DOPO derivative 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is introduced, and nano montmorillonite is introduced as a multifunctional nano filler. The prepared polyester film has the characteristics of high light transmittance, excellent flame-retardant performance, poor precipitation of the flame retardant, good mechanical performance and high dimensional stability.

Description

Technical Field

[0001] This invention relates to the field of polymer thin film technology, specifically to a high-transmittance flame-retardant modified polyester film and its preparation method. Background Technology

[0002] Biaxially oriented polyethylene terephthalate (PET) film is widely used in electronics insulation, packaging printing, optical displays, and architectural decoration due to its excellent mechanical strength, electrical insulation properties, dimensional stability, and good transparency. However, PET is a flammable material with a limiting oxygen index (LOI) of only about 21%, making it prone to melting and dripping during combustion, posing a significant fire hazard. With increasing public awareness of safety, especially the rising fire safety requirements in electronics, transportation, and architectural decoration, higher demands are being placed on the flame-retardant properties of polyester films. How to maintain the high light transmittance of PET polyester film while simultaneously imparting good flame retardancy has become one of the most pressing technical challenges in this field.

[0003] Currently, the main technical routes for imparting flame-retardant properties to polyester films fall into two categories: additive flame-retardant modification and reactive flame-retardant modification. The preparation methods primarily include copolymerization and blending. However, existing flame-retardant polyester films still face a series of pressing technical challenges that need to be addressed.

[0004] Firstly, it is difficult to simultaneously achieve flame retardancy and high light transmittance. Studies have shown that whether a flame-retardant coating is applied to the surface of a PET polyester film or a flame retardant is added to the formulation system, the light transmittance of the PET polyester film is easily reduced. CN102634064A discloses a phosphorus-containing flame retardant, a flame-retardant polyester film, and its preparation method. This flame retardant contains an oxazoline structure, which, although possessing excellent flame retardant properties and high mechanical properties and thermal stability, suffers from poor light transmittance and low clarity. CN108467574A discloses a transparent flame-retardant PET masterbatch and its film, employing core-shell structured flame-retardant microspheres. However, the manufacturing process requires nano-processing and electrostatic spraying, making the manufacturing process complex and expensive. CN117586608A discloses a flame-retardant masterbatch for transparent PET sheets and its preparation method, using phosphate esters combined with DOPO derivative halogen-free flame retardants. The amount of phosphate ester flame retardant added is as high as 20-45 parts, and such a high addition inevitably has a significant impact on light transmittance and haze in actual film products. Traditional transparent PET films typically contain flame retardants at concentrations as high as 25%. When additive flame retardants have poor compatibility with the polyester matrix, they easily form phase separation structures within the matrix, causing the flame retardant particles to become light scattering centers and resulting in a decrease in film transmittance.

[0005] Secondly, the interfacial compatibility between flame retardants and the polyester matrix is ​​insufficient. Most additive flame retardants are small molecule compounds, lacking strong chemical bonds with the polyester matrix. They are prone to agglomeration during melt blending and pose risks of migration and precipitation during use. The migration of flame retardants not only leads to a decline in the flame retardant performance of the film over time, but the precipitated flame retardants may also contaminate contact parts. While conventional physical blending can partially disperse flame retardants, it is difficult to form a stable interfacial bond.

[0006] Third, the resin matrix is ​​singular, resulting in low functional integration. Existing flame-retardant polyester film technologies mostly use a single PET resin as the matrix, and there are no reports of systematically designing flame-retardant film systems from the perspective of multi-component polyester resin blending to achieve synergistic optimization of flame-retardant, optical, and mechanical properties. In particular, the simultaneous introduction of amorphous copolyester and intrinsically flame-retardant polyester into the PET flame-retardant film system, utilizing the crystallization inhibition effect of the amorphous component and the synergistic function of the naphthalene ring structure, is not publicly disclosed in existing technologies. Summary of the Invention

[0007] To overcome the above shortcomings, this invention proposes a high-transmittance flame-retardant modified polyester film and its preparation method. The polyester film obtained has the characteristics of high light transmittance, excellent flame retardant performance, low precipitation of flame retardant, good mechanical properties and high dimensional stability.

[0008] In the first aspect, a high-transmittance flame-retardant modified polyester film is prepared by mixing composite flame-retardant masterbatch and pure PET chips at a mass ratio of 1:2-5.

[0009] The raw materials for the composite flame retardant masterbatch include:

[0010] PET slices: 80-94 pieces

[0011] PETG slices: 3-12 pieces

[0012] PEN (polyethylene naphthalate) slices: 3-8 pieces

[0013] Phosphorus-containing flame retardant: 10-30 parts

[0014] Ionic liquid flame retardant: 0.5-3 parts

[0015] DOPO derivative synergistic flame retardant: 2-8 parts

[0016] Antioxidant: 0.2-0.5 parts

[0017] Dispersing lubricant: 0.5-2 parts

[0018] Modified nano-montmorillonite: 0.5-3 parts.

[0019] Preferably, the phosphorus-containing flame retardant is selected from triphenyl phosphate, polymeric phosphonate, resorcinol bis(diphenyl phosphate) or a mixture thereof.

[0020] Preferably, the ionic liquid flame retardant is selected from phosphorus-containing heterocyclic ionic liquids, nitrogen-containing heterocyclic ionic liquids or a mixture thereof.

[0021] Preferably, the DOPO derivative synergistic flame retardant is selected from DOPO-melamine condensate synergistic flame retardants, DOPO-acrylate adduct synergistic flame retardants or a mixture thereof.

[0022] Preferably, the antioxidant is Antioxidant 1010, Antioxidant 168 or a mixture thereof.

[0023] Preferably, the dispersing lubricant is polyethylene wax, calcium stearate or a mixture thereof.

[0024] In a second aspect, a method for preparing a high-light-transmittance flame-retardant modified polyester film comprises the following steps:

[0025] Step 1: Preparation of composite flame-retardant masterbatch

[0026] The materials are batched in parts by mass, mixed uniformly in a high-speed mixer, then melt-blended in a twin-screw extruder, extruded and pelletized to obtain the composite flame-retardant masterbatch.

[0027] Preferably, the raw materials of the composite flame-retardant masterbatch comprise:

[0028] PET chips: 80-94 parts

[0029] PETG chips: 3-12 parts

[0030] PEN chips: 3-8 parts

[0031] Phosphorus-containing flame retardant: 10-30 parts

[0032] Ionic liquid flame retardant: 0.5-3 parts

[0033] DOPO derivative synergistic flame retardant: 2-8 parts

[0034] Antioxidant: 0.2-0.5 parts

[0035] Dispersing lubricant: 0.5-2 parts

[0036] Modified nano-montmorillonite: 0.5-3 parts.

[0037] Step 2: Preparation of functional film

[0038] The composite flame-retardant masterbatch and pure PET chips are uniformly mixed at a mass ratio of 1:2-5, and subjected to melt extrusion, casting sheet forming, biaxial stretching and heat setting treatment to obtain the high-light-transmittance flame-retardant modified polyester film.

[0039] This invention introduces PETG and PEN to blend with PET. PETG has a similar refractive index to PET, and its amorphous structure effectively suppresses the crystallization behavior of PET during processing. The introduction of PETG allows the blended system to maintain lower crystallinity and a more uniform amorphous structure after cooling and stretching, thereby reducing light scattering caused by the difference in refractive index between crystalline and amorphous regions, further improving the light transmittance of the film. PEN contains a rigid naphthalene ring structure in its molecular chain, which has higher physical and mechanical properties and heat resistance than PET. PEN has a similar structure to PET and good compatibility. The introduction of PEN can improve the mechanical properties and heat resistance of the blended system; at the same time, the ultraviolet absorption characteristics of the naphthalene ring endow the film with excellent resistance to ultraviolet aging.

[0040] This invention introduces a combination of ionic liquid flame retardants and phosphorus-based flame retardants into a PET flame-retardant film system. Ionic liquid flame retardants are a novel type of halogen-free flame retardant; adding only 1.5% of the ionic liquid flame retardant is sufficient to achieve a UL94 VTM-0 flame retardancy rating for a 0.05mm thick PET film. When combined with phosphorus-based flame retardants such as triphenyl phosphate, a synergistic flame-retardant effect is achieved. The ionic liquid flame retardant exerts a free radical quenching effect in the gas phase, while the phosphorus-based flame retardant promotes char formation in the condensed phase. Together, they inhibit combustion from both the gas and condensed phases. This synergistic flame-retardant mechanism allows the target flame retardancy rating to be achieved with a lower total flame retardant dosage, minimizing the adverse effects of the flame retardant on the film's light transmittance.

[0041] This invention introduces a DOPO derivative, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide. This compound contains a biphenyl ring structure and active PH bonds, enabling it to exert a PN synergistic flame-retardant effect with the main flame retardant. Specifically, the nitrogen element in the DOPO derivative molecule can synergistically enhance free radical scavenging ability in the gas phase and promote the formation of a denser char layer in the condensed phase. More importantly, the PH bonds in the DOPO derivative molecule can react with the terminal carboxyl groups on the PET molecular chain upon heating, forming chemical bonds. This anchors the flame-retardant component within the matrix at the molecular level, fundamentally preventing the migration and precipitation of the flame retardant.

[0042] This invention introduces nano-montmorillonite (MMT) as a multifunctional nanofiller. The addition of montmorillonite improves the thermal stability and flame retardancy of PET, while not significantly reducing film transmittance at low addition levels. Nano-montmorillonite, dispersed in the PET matrix as exfoliated or intercalated nanostructures, significantly enhances the polymer's mechanical properties, heat resistance, and barrier properties. During combustion, the montmorillonite nanosheets form a dense silicate carbon layer on the material surface, acting as a thermal and oxygen barrier, providing multiple flame-retardant protection with phosphorus-based and ionic liquid flame retardants. Furthermore, after organic modification, nano-montmorillonite exhibits good compatibility with the PET matrix, and its impact on film transmittance is minimal at low addition levels.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] 1. Introduce PETG and PEN into the PET flame retardant film system simultaneously. PETG has a similar refractive index to PET, and its amorphous structure effectively inhibits PET crystallization, reducing light scattering caused by the difference in refractive index between the crystalline and amorphous regions; PEN's rigid naphthalene ring structure improves mechanical properties, heat resistance, and UV shielding function, and produces a synergistic flame retardant effect with phosphorus-based flame retardants.

[0045] 2. By introducing ionic liquid flame retardants, only extremely low addition amounts (0.3-1.5%) are required to significantly improve flame retardant efficiency. The ionic liquid flame retardants, together with phosphorus-based flame retardants, exert a synergistic gas-phase-condensed-phase flame retardant effect, reducing the total amount of flame retardant added by more than 60% compared to traditional technologies. This fundamentally reduces the adverse effects of flame retardants on film transmittance.

[0046] 3. The introduced DOPO derivative contains active PH bonds that can chemically react with PET end groups to form covalent bonds, chemically anchoring the flame retardant components in the polyester molecular network, fundamentally preventing the migration and precipitation of flame retardants, and giving the film excellent long-term stability.

[0047] 4. Nano-montmorillonite is dispersed in the PET matrix at the nanoscale, forming multiple flame-retardant protections with phosphorus-based flame retardants and ionic liquid flame retardants; at the same time, it improves the mechanical properties, heat resistance and gas barrier properties of the film, and has minimal impact on light transmittance at extremely low addition levels. Detailed Implementation

[0048] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] Example 1

[0050] A high-transmittance, flame-retardant modified polyester film is prepared by the following steps:

[0051] Step 1: Preparation of composite flame retardant masterbatch

[0052] Ingredients by weight:

[0053] PET chips (intrinsic viscosity 0.68 dL / g): 88 parts

[0054] PETG chips (amorphous copolyester): 8 parts

[0055] PEN chips (intrinsic viscosity 0.68 dL / g): 4 parts

[0056] Phosphorus-containing flame retardant (triphenyl phosphate): 20 parts

[0057] Ionic liquid flame retardant (phosphorus-containing heterocyclic ionic liquid): 1.5 parts

[0058] DOPO-melamine condensate synergistic flame retardant (phosphorus content 9.5wt%): 5 parts

[0059] Antioxidant 1010 and Antioxidant 168 are mixed at a mass ratio of 1:1: 0.3 parts

[0060] Polyethylene wax: 1.0 part

[0061] Organically modified nano-montmorillonite (interlayer spacing 2.8 nm): 1.0 part

[0062] The above materials were mixed evenly in a high-speed mixer (800 r / min, 10 min), and then fed into a twin-screw extruder for melt blending and extrusion. The temperatures of each zone of the extruder were set as follows: zone 1 190℃, zone 2 230℃, zone 3 250℃, zone 4 260℃, and die head 250℃; screw speed 250 r / min; vacuum degree -0.09 MPa. The extrudate was water-cooled, pelletized, and dried at 80℃ for 4 h to obtain composite flame-retardant masterbatch.

[0063] Step 2: Preparation of functional thin films

[0064] The composite flame-retardant masterbatch and pure PET chips were uniformly mixed at a mass ratio of 1:3 and melt-extruded through a single-screw extruder (extrusion temperature 275℃). The melt was cast onto a cooling drum through a T-die (cooling drum temperature 35℃). The cast sheet was first longitudinally stretched by a longitudinal stretching machine (stretch ratio 3.5 times, stretching temperature 100℃), and then transversely stretched by a transverse stretching machine (stretch ratio 4.0 times, stretching temperature 110℃). Subsequently, it entered the heat setting zone for heat setting treatment (temperature 220℃, time 60 s). After cooling, edge trimming, and winding, a high-transmittance flame-retardant modified polyester film with a thickness of 50 μm was obtained.

[0065] Example 2

[0066] A high-transmittance, flame-retardant modified polyester film is prepared by the following steps:

[0067] Step 1: Preparation of composite flame retardant masterbatch

[0068] Ingredients by weight:

[0069] PET chips (intrinsic viscosity 0.70 dL / g): 85 parts

[0070] PETG chips (amorphous copolyester): 10 parts

[0071] PEN chips (intrinsic viscosity 0.72 dL / g): 5 parts

[0072] Phosphorus-containing flame retardant (polymeric phosphonate, phosphorus content 15wt%, refractive index approximately 1.56): 25 parts

[0073] Ionic liquid flame retardant (nitrogen-containing heterocyclic ionic liquid): 2.0 parts

[0074] DOPO-acrylate adduct synergistic flame retardant (phosphorus content 8.5wt%): 6 parts

[0075] Antioxidant 1010 and Antioxidant 168 are mixed at a mass ratio of 1:1: 0.4 parts

[0076] Calcium stearate: 1.5 parts

[0077] Organically modified nano-montmorillonite (interlayer spacing 3.0 nm): 1.5 parts

[0078] The above materials were mixed evenly in a high-speed mixer (900 r / min, 12 min), and then fed into a twin-screw extruder for melt blending and extrusion. The temperatures of each zone of the extruder were set as follows: zone 1 195℃, zone 2 235℃, zone 3 255℃, zone 4 265℃, and die head 255℃; screw speed 280 r / min; vacuum degree -0.092 MPa. The extrudate was water-cooled, pelletized, and dried at 80℃ for 4 h to obtain composite flame-retardant masterbatch.

[0079] Step 2: Preparation of functional thin films

[0080] The composite flame-retardant masterbatch and pure PET chips were uniformly mixed at a mass ratio of 1:4 and melt-extruded through a single-screw extruder (extrusion temperature 280℃). The melt was cast onto a cooling drum through a T-die (cooling drum temperature 38℃). The cast sheet was first longitudinally stretched by a longitudinal stretching machine (stretch ratio 3.8 times, stretching temperature 105℃), and then transversely stretched by a transverse stretching machine (stretch ratio 4.3 times, stretching temperature 115℃). Subsequently, it entered the heat setting zone for heat setting treatment (temperature 225℃, time 80 s). After cooling, edge trimming, and winding, a high-transmittance flame-retardant modified polyester film with a thickness of 75 μm was obtained.

[0081] Example 3

[0082] A high-transmittance, flame-retardant modified polyester film is prepared by the following steps:

[0083] Step 1: Preparation of composite flame retardant masterbatch

[0084] Ingredients by weight:

[0085] PET chips (intrinsic viscosity 0.66 dL / g): 92 parts

[0086] PETG chips (amorphous copolyester): 5 parts

[0087] PEN chips (intrinsic viscosity 0.65 dL / g): 3 parts

[0088] Phosphorus-containing flame retardant (resorcinol bis(diphenyl phosphate), phosphorus content 12.5wt%, refractive index approximately 1.57): 15 parts

[0089] Ionic liquid flame retardant (phosphorus-containing heterocyclic ionic liquid): 1.0 part

[0090] DOPO-melamine condensate synergistic flame retardant (phosphorus content 10.0wt%): 3.5 parts

[0091] Antioxidant 1010 and Antioxidant 168 are mixed at a mass ratio of 1:1: 0.25 parts

[0092] Polyethylene wax: 0.8 parts

[0093] Organically modified nano-montmorillonite (interlayer spacing 2.6 nm): 0.8 parts

[0094] The above materials were mixed evenly in a high-speed mixer (750 r / min, 10 min), and then fed into a twin-screw extruder for melt blending and extrusion. The temperatures of each zone of the extruder were set as follows: zone 1 185℃, zone 2 225℃, zone 3 245℃, zone 4 255℃, and die head 248℃; screw speed 230 r / min; vacuum degree -0.085 MPa. The extrudate was water-cooled, pelletized, and dried at 80℃ for 4 h to obtain composite flame-retardant masterbatch.

[0095] Step 2: Preparation of functional thin films

[0096] The composite flame-retardant masterbatch and pure PET chips were uniformly mixed at a mass ratio of 1:2.5 and melt-extruded through a single-screw extruder (extrusion temperature 270℃). The melt was cast onto a cooling drum through a T-die (cooling drum temperature 30℃). The cast sheet was first longitudinally stretched by a longitudinal stretching machine (stretch ratio 3.2 times, stretching temperature 95℃), and then transversely stretched by a transverse stretching machine (stretch ratio 3.5 times, stretching temperature 105℃). Subsequently, it entered the heat setting zone for heat setting treatment (temperature 210℃, time 50 s). After cooling, edge trimming, and winding, a high-transmittance flame-retardant modified polyester film with a thickness of 38 μm was obtained.

[0097] Comparative Example 1

[0098] The difference from Example 1 is that triphenyl phosphate, a phosphorus-containing main flame retardant, was not added.

[0099] Step 1: Preparation of composite flame retardant masterbatch

[0100] Ingredients by weight:

[0101] Blended resins (88 parts PET chips, 8 parts PETG chips, 4 parts PEN chips): 100 parts

[0102] Ionic liquid flame retardant (phosphorus-containing heterocyclic ionic liquid): 3 parts

[0103] DOPO-melamine condensate synergistic flame retardant (phosphorus content 9.5wt%): 8 parts

[0104] Antioxidant 1010 and Antioxidant 168 are mixed at a mass ratio of 1:1: 0.3 parts

[0105] Polyethylene wax: 1.0 part

[0106] Organically modified nano-montmorillonite: 1.0 part

[0107] The above materials were mixed evenly in a high-speed mixer (800 r / min, 10 min), and then fed into a twin-screw extruder for melt blending and extrusion. The temperatures of each zone of the extruder were set as follows: zone 1 190℃, zone 2 230℃, zone 3 250℃, zone 4 260℃, and die head 250℃; screw speed 250 r / min; vacuum degree -0.09 MPa. The extrudate was water-cooled, pelletized, and dried at 80℃ for 4 h to obtain composite flame-retardant masterbatch.

[0108] Step 2: Same as Step 2 in Example 1.

[0109] Comparative Example 2

[0110] The difference from Example 1 is that no DOPO derivative synergistic flame retardant was added.

[0111] Step 1: Preparation of composite flame retardant masterbatch

[0112] Ingredients by weight:

[0113] Blended resins (88 parts PET chips, 8 parts PETG chips, 4 parts PEN chips): 100 parts

[0114] Phosphorus-containing flame retardant (triphenyl phosphate): 24 parts

[0115] Ionic liquid flame retardant (phosphorus-containing heterocyclic ionic liquid): 2.0 parts

[0116] Antioxidant 1010 and Antioxidant 168 are mixed at a mass ratio of 1:1: 0.3 parts

[0117] Polyethylene wax: 1.0 part

[0118] Organically modified nano-montmorillonite: 1.0 part

[0119] The above materials were mixed evenly in a high-speed mixer (800 r / min, 10 min), and then fed into a twin-screw extruder for melt blending and extrusion. The temperatures of each zone of the extruder were set as follows: zone 1 190℃, zone 2 230℃, zone 3 250℃, zone 4 260℃, and die head 250℃; screw speed 250 r / min; vacuum degree -0.09 MPa. The extrudate was water-cooled, pelletized, and dried at 80℃ for 4 h to obtain composite flame-retardant masterbatch.

[0120] Step 2: Same as Step 2 in Example 1.

[0121] Comparative Example 3

[0122] The difference from Example 1 is that no ionic liquid flame retardant was added.

[0123] Step 1: Preparation of composite flame retardant masterbatch

[0124] Ingredients by weight:

[0125] Blended resins (88 parts PET chips, 8 parts PETG chips, 4 parts PEN chips): 100 parts

[0126] Phosphorus-containing flame retardant (triphenyl phosphate): 22 parts

[0127] DOPO-melamine condensate synergistic flame retardant: 6 parts

[0128] Antioxidant 1010 and Antioxidant 168 are mixed at a mass ratio of 1:1: 0.3 parts

[0129] Polyethylene wax: 1.0 part

[0130] Organically modified nano-montmorillonite: 1.0 part

[0131] After the above materials are mixed evenly, they are melt-blended and extruded through a twin-screw extruder. The extrusion process is the same as in Example 1 to obtain composite flame retardant masterbatch.

[0132] Step 2: Same as Step 2 in Example 1.

[0133] Comparative Example 4

[0134] The difference from Example 1 is that no nano-montmorillonite was added.

[0135] Step 1: Preparation of composite flame retardant masterbatch

[0136] Ingredients by weight:

[0137] Blended resins (88 parts PET chips, 8 parts PETG chips, 4 parts PEN chips): 100 parts

[0138] Phosphorus-containing flame retardant (triphenyl phosphate): 20 parts

[0139] Ionic liquid flame retardant: 1.5 parts

[0140] DOPO-melamine condensate synergistic flame retardant: 5 parts

[0141] Antioxidant 1010 and Antioxidant 168 are mixed at a mass ratio of 1:1: 0.3 parts

[0142] Polyethylene wax: 1.0 part

[0143] After the above materials are mixed evenly, they are melt-blended and extruded through a twin-screw extruder. The extrusion process is the same as in Example 1 to obtain composite flame retardant masterbatch.

[0144] Step 2: Same as Step 2 in Example 1.

[0145] Comparative Example 5

[0146] The difference from Example 1 is that the amount of phosphorus-containing flame retardant added is too low (6 parts).

[0147] Step 1: Preparation of composite flame retardant masterbatch

[0148] Ingredients by weight:

[0149] Blended resins (88 parts PET chips, 8 parts PETG chips, 4 parts PEN chips): 100 parts

[0150] Phosphorus-containing flame retardant (triphenyl phosphate): 6 parts

[0151] Ionic liquid flame retardant: 1.5 parts

[0152] DOPO-melamine condensate synergistic flame retardant: 3 parts

[0153] Antioxidant 1010 and Antioxidant 168 are mixed at a mass ratio of 1:1: 0.3 parts

[0154] Polyethylene wax: 1.0 part

[0155] Organically modified nano-montmorillonite: 1.0 part

[0156] After the above materials are mixed evenly, they are melt-blended and extruded through a twin-screw extruder. The extrusion process is the same as in Example 1 to obtain composite flame retardant masterbatch.

[0157] Step 2: Same as Step 2 in Example 1.

[0158] Comparative Example 6

[0159] The difference from Example 1 is that the mass ratio of the composite flame retardant masterbatch to pure PET chips is 1:1 (the proportion of masterbatch is too high).

[0160] Step 1: Same as Step 1 in Example 1.

[0161] Step 2: Preparation of functional thin films

[0162] The composite flame-retardant masterbatch and pure PET chips were uniformly mixed at a mass ratio of 1:1 and melt-extruded through a single-screw extruder (extrusion temperature 275℃). The melt was cast onto a cooling drum through a T-die (cooling drum temperature 35℃). The cast sheet was first longitudinally stretched by a longitudinal stretching machine (stretch ratio 3.5 times, stretching temperature 100℃), and then transversely stretched by a transverse stretching machine (stretch ratio 4.0 times, stretching temperature 110℃). Subsequently, it entered the heat setting zone for heat setting treatment (temperature 220℃, time 60 s). After cooling, edge trimming, and winding, a flame-retardant modified polyester film with a thickness of 50 μm was obtained.

[0163] The remaining steps are the same as in Example 1.

[0164] Comparative Example 7

[0165] The difference from Example 1 is that the mass ratio of the composite flame retardant masterbatch to pure PET chips is 1:8 (the masterbatch ratio is too low).

[0166] Step 1: Same as Step 1 in Example 1.

[0167] Step 2: Preparation of functional thin films

[0168] The composite flame-retardant masterbatch and pure PET chips were uniformly mixed at a mass ratio of 1:8 and melt-extruded through a single-screw extruder (extrusion temperature 275℃). The melt was cast onto a cooling drum through a T-die (cooling drum temperature 35℃). The cast sheet was first longitudinally stretched by a longitudinal stretching machine (stretch ratio 3.5 times, stretching temperature 100℃), and then transversely stretched by a transverse stretching machine (stretch ratio 4.0 times, stretching temperature 110℃). Subsequently, it entered the heat setting zone for heat setting treatment (temperature 220℃, time 60 s). After cooling, edge trimming, and winding, a flame-retardant modified polyester film with a thickness of 50 μm was obtained.

[0169] The remaining steps are the same as in Example 1.

[0170] Comparative Example 8

[0171] The difference from Example 1 is that no antioxidants were added.

[0172] Step 1: Preparation of composite flame retardant masterbatch

[0173] Ingredients by weight:

[0174] Blended resins (88 parts PET chips, 8 parts PETG chips, 4 parts PEN chips): 100 parts

[0175] Phosphorus-containing flame retardant (triphenyl phosphate): 20 parts

[0176] Ionic liquid flame retardant: 1.5 parts

[0177] DOPO-melamine condensate synergistic flame retardant: 5 parts

[0178] Polyethylene wax: 1.0 part

[0179] Organically modified nano-montmorillonite: 1.0 part

[0180] After the above materials are mixed evenly, they are melt-blended and extruded through a twin-screw extruder. The extrusion process is the same as in Example 1 to obtain composite flame retardant masterbatch.

[0181] Step 2: Same as Step 2 in Example 1.

[0182] Comparative Example 9

[0183] The difference from Example 1 is that the heat setting temperature is lower (175°C).

[0184] Step 1: Same as Step 1 in Example 1.

[0185] Step 2: Preparation of functional thin films

[0186] The composite flame-retardant masterbatch and pure PET chips were uniformly mixed at a mass ratio of 1:3 and melt-extruded through a single-screw extruder (extrusion temperature 275℃). The melt was cast onto a cooling drum through a T-die (cooling drum temperature 35℃). The cast sheet was first longitudinally stretched by a longitudinal stretching machine (stretch ratio 3.5 times, stretching temperature 100℃), and then transversely stretched by a transverse stretching machine (stretch ratio 4.0 times, stretching temperature 110℃). Subsequently, it entered the heat setting zone for heat setting treatment (temperature 175℃, time 60 s). After cooling, edge trimming, and winding, a flame-retardant modified polyester film with a thickness of 50 μm was obtained.

[0187] The remaining steps are the same as in Example 1.

[0188] Performance testing

[0189] Transmittance and haze: Refer to GB / T 2410-2008 and measure using a transmittance / haze meter.

[0190] Flame retardant performance: Vertical burning test (VTM-0 / V-0 rating) was conducted in accordance with UL94 standard.

[0191] Limiting Oxygen Index (LOI): Determined according to GB / T 2406.2-2009.

[0192] Tensile strength and elongation at break: determined using a universal testing machine in accordance with GB / T 1040.3-2006.

[0193] Heat shrinkage rate: Refer to GB / T 13519-2016, measure the longitudinal and transverse shrinkage rates after heating at 150℃ for 30 min.

[0194] Flame retardant migration and precipitation test: The film sample was aged in hot air at 80℃ for 168 h. The change in phosphorus content on the film surface before and after aging was determined by X-ray fluorescence spectroscopy (XRF), and the flame retardant precipitation rate (the increase rate of surface phosphorus content) was calculated.

[0195] The results are shown in Table 1, a comparison table of performance of the embodiments and comparative examples.

[0196]

[0197] Examples 1-3 exhibited light transmittance of 86.5-88.0% and haze of only 1.3-1.8%. While maintaining excellent high light transmittance, the limiting oxygen index was increased to 30-34%, all reaching UL94 VTM-0 or V-0 ratings, achieving a synergistic balance between high light transmittance and flame retardant performance. Tensile strength remained at 168-178 MPa, and elongation at break was 108-118%, demonstrating good mechanical properties. Low thermal shrinkage and excellent dimensional stability were observed. The flame retardant exudation rate was only 0.3-0.5%, indicating that the chemical bonding of the DOPO derivative effectively inhibited the migration of the flame retardant.

[0198] Comparative Example 1 did not add triphenyl phosphate, the primary phosphorus-containing flame retardant, relying solely on ionic liquid flame retardants and DOPO derivatives as synergistic flame retardants. Although the light transmittance remained good at 87.0% and the haze was low at 1.6%, the LOI was only 26%, and the UL94 rating was only VTM-2, failing to reach the VTM-0 rating. This indicates that the char formation effect of the phosphorus-containing primary flame retardant in the condensed phase is crucial. While the ionic liquid flame retardant effectively exerts free radical quenching in the gas phase, it lacks the function of phosphorus-containing flame retardants in promoting the formation of a dense, expanded char layer in the condensed phase, resulting in insufficient flame retardant efficiency.

[0199] Comparative Example 2, without the addition of DOPO derivative synergistic flame retardants, relied solely on phosphorus-containing flame retardants and ionic liquid flame retardants. Its LOI was only 27%, and its UL94 rating was only VTM-2, failing to reach VTM-0. DOPO derivatives not only form covalent bonds with PET end groups through their active PH bonds, chemically anchoring the flame-retardant components to the matrix, but also exert a PN synergistic effect through nitrogen and phosphorus elements in their molecular structure, simultaneously enhancing the flame-retardant effect in both the gas and condensed phases. This fully demonstrates the crucial role of the DOPO derivative's chemical anchoring mechanism in inhibiting flame retardant migration.

[0200] Comparative Example 3, without the addition of ionic liquid flame retardants, had an LOI of only 28% and a UL94 rating of only VTM-2, indicating insufficient flame retardant performance. This demonstrates that the introduction of ionic liquid flame retardants is crucial for improving the flame retardant rating.

[0201] In Comparative Example 4, without the addition of nano-montmorillonite, the tensile strength decreased to 162 MPa, while in Example 1 it was 175 MPa, confirming the reinforcing effect of nano-montmorillonite.

[0202] Comparative Example 5 contained 6 parts of phosphorus-containing flame retardant, which was too low in total amount, with an LOI of only 24%, and could not meet the UL94 flame retardant rating.

[0203] In Comparative Example 6, the proportion of masterbatch added was too high, resulting in a decrease in light transmittance to 82.0%, an increase in haze to 4.5%, and a significant decline in mechanical properties.

[0204] The proportion of masterbatch added in Comparative Example 7 was too low, with an LOI of only 23%, which could not meet the flame retardant rating requirements.

[0205] Comparative Example 8, without the addition of antioxidants, showed that the polyester underwent thermal oxidative degradation during processing, resulting in a decrease in light transmittance to 84.0% and an increase in haze to 3.5%, confirming the crucial role of antioxidants in maintaining the optical properties of the thin film.

[0206] Comparative Example 9, with a heat setting temperature of 175℃, is too low, resulting in a significantly increased heat shrinkage rate (MD 5.5%, TD 2.5%) and poor dimensional stability.

[0207] In summary, this invention achieves a synergistic balance of high light transmittance, flame retardancy, mechanical properties, UV resistance, and dimensional stability through the synergistic effects of multiple innovative methods, including blending of PETG / PEN / PET multi-component resins, synergistic compounding of ionic liquid flame retardants and phosphorus-based flame retardants, chemical bonding and anchoring of DOPO derivatives, and multifunctional reinforcement with nano-montmorillonite. This invention has significant technical advantages.

[0208] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A high-transmittance, flame-retardant modified polyester film, characterized in that, It is prepared by mixing composite flame retardant masterbatch and pure PET chips at a mass ratio of 1:2-5.

2. The high-transmittance flame-retardant modified polyester film according to claim 1, characterized in that, The raw materials for the composite flame retardant masterbatch include: PET slices: 80-94 pieces PETG slices: 3-12 pieces PEN (polyethylene naphthalate) slices: 3-8 pieces Phosphorus-containing flame retardant: 10-30 parts Ionic liquid flame retardant: 0.5-3 parts DOPO derivative synergistic flame retardant: 2-8 parts Antioxidant: 0.2-0.5 parts Dispersing lubricant: 0.5-2 parts Modified nano-montmorillonite: 0.5-3 parts.

3. The high-transmittance flame-retardant modified polyester film according to claim 2, characterized in that, The phosphorus-containing flame retardant is selected from triphenyl phosphate, polymeric phosphonate, resorcinol bis(diphenyl phosphate) or mixtures thereof.

4. The high-transmittance flame-retardant modified polyester film according to claim 2, characterized in that, The ionic liquid flame retardant is selected from phosphorus-containing heterocyclic ionic liquids, nitrogen-containing heterocyclic ionic liquids, or mixtures thereof.

5. The high-transmittance flame-retardant modified polyester film according to claim 2, characterized in that, The DOPO derivative synergistic flame retardant is selected from DOPO-melamine condensate synergistic flame retardant, DOPO-acrylate adduct synergistic flame retardant, or mixtures thereof.

6. The high-transmittance flame-retardant modified polyester film according to claim 2, characterized in that, The antioxidant is antioxidant 1010, antioxidant 168, or a mixture thereof.

7. The high-transmittance flame-retardant modified polyester film according to claim 2, characterized in that, The dispersing lubricant is polyethylene wax, calcium stearate, or a mixture thereof.

8. A method for preparing a high-transmittance flame-retardant modified polyester film, characterized in that, Includes the following steps: first step: Preparation of composite flame retardant masterbatch The materials are batched according to mass proportions, mixed evenly in a high-speed mixer, and then melt-blended, extruded and pelletized in a twin-screw extruder to obtain composite flame retardant masterbatch. Step 2: Preparation of functional thin films The composite flame-retardant masterbatch is uniformly mixed with pure PET chips, and then melt-extruded, cast, biaxially stretched, and heat-set to obtain a high-transmittance flame-retardant modified polyester film.

9. The method for preparing the high-transmittance flame-retardant modified polyester film according to claim 8, characterized in that, The raw materials for the composite flame retardant masterbatch include: PET slices: 80-94 pieces PETG slices: 3-12 pieces PEN slices: 3-8 pieces Phosphorus-containing flame retardant: 10-30 parts Ionic liquid flame retardant: 0.5-3 parts DOPO derivative synergistic flame retardant: 2-8 parts Antioxidant: 0.2-0.5 parts Dispersing lubricant: 0.5-2 parts Modified nano-montmorillonite: 0.5-3 parts.

10. The method for preparing the high-transmittance flame-retardant modified polyester film according to claim 8, characterized in that, The mass ratio of composite flame retardant masterbatch to pure PET chips is 1:2-5.

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