High-transparency halogen-free flame-retardant polymer film as well as flame-retardant master batch and preparation method thereof

Abstract

The invention discloses a high-transparency halogen-free flame-retardant polymer film as well as a flame-retardant master batch and a preparation method thereof. The polymer film is prepared from a raw material composition, and the composition comprises a thermoplastic matrix and a halogen-free synergistic flame-retardant system composed of a phosphorus-based flame retardant, a metal hydroxide and an intumescent flame retardant. The invention further discloses the flame-retardant master batch and a method for preparing the film through the steps of side feeding, vacuum exhausting, two-way stretching, beta-ray closed-loop thickness measurement and the like. The thickness of the high-transparency halogen-free flame-retardant polymer film is 5-200 [mu] m, the total halogen content is less than or equal to 900 ppm, the UL-94VTM-0 flame-retardant grade is met, the limit oxygen index LOI is greater than or equal to 30%, meanwhile, the high-transparency halogen-free flame-retardant polymer film has the tensile strength greater than or equal to 29 MPa, the high light transmittance greater than or equal to 86% and the low haze less than or equal to 5%, and the problem that the ultra-thin, transparent, halogen-free and efficient flame-retardant aspects are difficult to take into account in the prior art is solved.

Description

Technical Field

[0001] This invention relates to the field of polymer material processing, specifically to a polymer film, and more particularly to a highly transparent halogen-free flame-retardant polymer film, its flame-retardant masterbatch, and its preparation method. Background Technology

[0002] With the rapid development of industries such as electronics, new energy, and rail transportation, especially in high-end applications such as Mini-LED backlight modules, 5G flexible packaging, and power battery packs, stringent requirements have been placed on the comprehensive performance of polymer films. On the one hand, regulations such as EU RoHS 2.0 and IEC 61249-2-21 have tightened halogen limits to ≤900ppm and strictly controlled smoke density during combustion (e.g., Ds-4 ≤200), leading to the phasing out of traditional halogen-based flame retardants. On the other hand, application scenarios require films to become ultra-thin and highly transparent.

[0003] Therefore, the market urgently needs a flame-retardant film that can simultaneously meet the standards of halogen-free, ultra-thin, high transparency, and high flame retardancy. However, this is a technical challenge in the current technology. Existing halogen-free flame-retardant solutions mainly have the following technical problems: While current halogen-free flame retardant technologies (such as some flame retardant masterbatch technologies for rubber) have solved the flame retardant problem, they are often used in fields where transparency requirements are not high (such as wires and cables, rubber seals). When these existing technologies are directly applied to optical films, the mismatch between the refractive index of the flame retardant and the matrix resin, as well as the disordered arrangement of particles in the film, will lead to severe light scattering, resulting in high haze ('white fog' phenomenon) in the film. This cannot meet the stringent requirements of high light transmittance and low haze for Mini-LED backlighting, flexible display packaging, etc. Inorganic flame retardants, such as aluminum hydroxide (ATH) or magnesium hydroxide (MDH), are the most common halogen-free solutions. However, their flame retardant efficiency is low, requiring extremely high addition levels (typically ≥50wt%) to achieve V-0 flame retardancy. Such high filler loading leads to: (a) severe embrittlement of the film's mechanical properties; (b) inability to achieve ultra-thin films, with film thicknesses typically needing to be ≥80μm to barely meet the standard; and (c) severe deterioration of optical properties, with high filler content causing a sharp drop in film transmittance (≤72%) and a surge in haze (≥18%). While phosphorus-nitrogen systems, exemplified by ammonium polyphosphate (APP), exhibit high efficiency, their charring effect in ultrathin films (e.g., 25 μm) is limited due to low heat capacity and easy dripping of molten droplets. Consequently, their flame retardant rating often only reaches V-1, making VTM-0 difficult to achieve. Furthermore, conventional APP is prone to thermal decomposition during processing, releasing ammonia gas and causing bulging and yellowing of the finished product. To improve transparency, flame retardant particles need to be made in the micrometer or even nanometer size. However, even if microencapsulation is used to reduce the particle size to 5 μm, there is a natural difference in refractive index (RI) between the inorganic flame retardant and the polymer matrix (e.g., Δn≈0.04). This refractive index mismatch will produce severe light scattering (Mie scattering) at the particle interface, resulting in high film haze and low transparency, which cannot meet the requirements of optical applications. In addition, although synergists such as carbon nanotubes and graphene can significantly reduce the amount of flame retardant used, their dark color causes the film to turn black, making it unsuitable for high-transparency applications, and they are also costly. Therefore, there is an urgent need for a high-transparency halogen-free flame-retardant polymer film, its flame-retardant masterbatch, and its preparation method. Summary of the Invention

[0004] The purpose of this invention is to address the deficiencies in the prior art by proposing a highly transparent halogen-free flame-retardant polymer film, its flame-retardant masterbatch, and its preparation method.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A highly transparent halogen-free flame-retardant polymer film, wherein the film has a thickness of 5 μm to 200 μm, a total halogen content of not more than 900 ppm, and meets the UL-94VTM-0 rating and a limiting oxygen index of not less than 30%; The membrane is prepared by a melt-film forming process from a raw material composition, and the raw material composition comprises, by weight of the total raw material composition: 50 wt% to 90 wt% of a matrix resin, wherein the matrix resin is selected from at least one of thermoplastic polyesters and polyolefins; The halogen-free flame retardant comprises 5 wt% to 40 wt% of a phosphorus-based flame retardant, a metal hydroxide, and an intumescent flame retardant; the phosphorus-based flame retardant is selected from at least one of microencapsulated ammonium polyphosphate and melamine polyphosphate; the metal hydroxide is selected from at least one of aluminum hydroxide and magnesium hydroxide; and the intumescent flame retardant is selected from at least one of piperazine pyrophosphate and expandable graphite. The synergist is selected from at least one of silicone resin, montmorillonite, carbon nanotubes, and graphene, at a concentration of 1 wt% to 10 wt%. 0.5 wt% to 5 wt% of a coupling agent, wherein the coupling agent is selected from silanes or titanates; 0 wt% to 5 wt% of processing aids; The weight ratio of the phosphorus-based flame retardant, the metal hydroxide, and the intumescent flame retardant is 1:0.2-2:0.1-1; and the particle size D50 of the halogen-free flame retardant is not higher than 5 μm.

[0006] Further, the matrix resin is PET with an intrinsic viscosity of 0.70 dL / g to 0.85 dL / g, or copolymer polypropylene with a melt flow rate of 5 g / 10 min to 15 g / 10 min under 230°C and 2.16 kg load, or LLDPE with a density of 0.918 g / cm³ to 0.930 g / cm³.

[0007] Furthermore, the phosphorus-based flame retardant is microencapsulated ammonium polyphosphate, the capsule material of the microencapsulated ammonium polyphosphate is melamine-formaldehyde resin, the capsule wall thickness is 50nm to 200nm, and the phosphorus content is not less than 28wt%.

[0008] Furthermore, the synergist is organomontmorillonite modified by quaternary ammonium salt intercalation, and the interlayer distance d001 of the organomontmorillonite is not less than 2.5 nm.

[0009] Furthermore, the particle size D50 of the halogen-free flame retardant is not higher than 2 μm, and when the phosphorus-based flame retardant is microencapsulated ammonium polyphosphate, the absolute value of the difference between the refractive index of its capsule wall and the refractive index of the matrix resin is not higher than 0.02.

[0010] Furthermore, the membrane is a biaxially oriented membrane, and the long axis dimension of the dispersed phase particles composed of the halogen-free flame retardant and the synergist is not higher than 100 nm, and the orientation degree along the membrane surface is not less than 80%.

[0011] Furthermore, the membrane is a multilayer composite membrane, comprising at least one flame-retardant layer formed from the raw material composition of claim 1, and at least one reinforcing layer or heat-sealing layer formed from pure thermoplastic resin; the thickness of the flame-retardant layer accounts for 20% to 60% of the total thickness of the membrane.

[0012] A flame-retardant masterbatch for preparing a highly transparent halogen-free flame-retardant polymer film, wherein the concentration of the halogen-free flame retardant in the masterbatch is 40wt% to 80wt%, and the remainder consists of a matrix resin, synergist, coupling agent, and processing aid; the masterbatch has a melt flow rate of 5g / 10min to 20g / 10min under conditions of 230℃ and 2.16kg load, and a water content of not more than 0.05wt%.

[0013] A method for preparing the highly transparent halogen-free flame-retardant polymer film includes the following steps: pre-drying the halogen-free flame retardant and coupling agent at 80°C to 120°C and a vacuum degree not exceeding -0.08MPa, and then performing surface modification; A twin-screw extruder with an aspect ratio (L / D) of not less than 40 is used to melt-blend the surface-modified material with the matrix resin via side feeding. The extrusion temperature is 180°C to 250°C, and vacuum degassing is performed to prepare flame-retardant masterbatch. The flame retardant masterbatch is diluted with pure resin at a weight ratio of 1:4 to 1:9, and then formed by single-layer casting, blow molding or co-extrusion of three or more layers. Subsequently, it is biaxially stretched and the thickness is controlled by a β-ray closed-loop thickness measurement system. Finally, it is subjected to online corona treatment to obtain a highly transparent halogen-free flame retardant polymer film.

[0014] Furthermore, the co-extrusion molding adopts a co-extrusion die head with an ABA or ABC structure, the die head temperature fluctuation is no higher than ±1℃, and the surface roughness Ra of the cooling roller is no higher than 0.05μm; and the feedback response time of the β-ray closed-loop thickness measurement system is no higher than 200ms, and the thickness tolerance is controlled within ±1.5μm.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This method achieves a balance between high light transmittance and low haze in polymer films, solving the problem of optical performance degradation caused by the addition of flame retardants. By selecting halogen-free flame retardants with a particle size D50≤2μm and strictly limiting the absolute value of the refractive index difference between the microencapsulated ammonium polyphosphate (MC-APP) capsule wall and the matrix resin to ≤0.02, Mie scattering and refraction of light at the two-phase interface are effectively suppressed. In addition, by combining a biaxial stretching process, the flat dispersed phase particles formed by the flame retardant and the intercalated modified organomontmorillonite are highly oriented along the film surface (orientation degree ≥80%), constructing a micro-ordered structure that facilitates light penetration. This is superior to existing technical solutions that do not perform refractive index matching or particle size control, thus meeting the application requirements of high-end optical display fields.

[0016] By employing a specific ratio (1:0.2-2:0.1-1) of phosphorus-based flame retardants, metal hydroxides, and intumescent flame retardants, a multi-synergistic mechanism of gas-phase free radical capture, condensed phase charring for heat insulation, and metal hydroxide endothermic cooling is utilized to overcome the defect of single halogen-free systems being difficult to flame retard in ultrathin films due to their low heat capacity. Even under extreme conditions with a film thickness of only 25μm, it can still stably pass the test, and the limiting oxygen index (LOI) reaches more than 30%, thus solving the technical problem that ultrathin films cannot simultaneously achieve halogen-free environmental protection and high flame retardancy.

[0017] Compared to traditional technologies that rely on high amounts (typically >50%) of metal hydroxides, the introduction of synergistic technology reduces the total filler content, and combined with coupling agent surface modification and biaxially oriented technology, it maintains the continuity and toughness of the polymer matrix, thus outperforming traditional high-filler solutions. Attached Figure Description

[0018] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0019] Figure 1This is a schematic diagram of the preparation method of the high-transparency halogen-free flame-retardant polymer film according to an embodiment of the present invention; Figure 2 This is a schematic cross-sectional view of the multilayer composite membrane described in an embodiment of the present invention; Figure 3 This is a schematic diagram of the twin-screw extruder side feeding and vacuum exhaust process for preparing flame-retardant masterbatch in an embodiment of the present invention. Figure 4 This is a transmittance-wavelength curve of the polymer film described in Example 7 of the present invention; Figure 5 This is a stress-strain curve of the polymer film described in Example 7 of the present invention. Detailed Implementation

[0020] The technical solutions provided by the present invention will be clearly and completely described below with reference to the embodiments. It should be noted that the described embodiments are merely some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] Unless otherwise stated, all materials and reagents used in the embodiments of this invention are commercially available.

[0022] raw materials PET: Intrinsic viscosity IV = 0.75 dL / g, optical grade polyester chips.

[0023] PP: Random copolymer polypropylene, with a melt flow rate (MFR) of 10 g / 10 min at 230 °C and 2.16 kg load.

[0024] LLDPE: Linear low-density polyethylene, density 0.920 g / cm³.

[0025] Microencapsulated APP (MC-APP): Melamine-formaldehyde resin is used as the encapsulation material, with a capsule wall thickness of 100nm and a phosphorus content of 28.5wt%. The D50 particle size is controlled at 1.2μm by air jet milling, and the absolute value of the difference between the refractive index of the capsule wall and the refractive index of the PET matrix is ​​controlled within 0.02.

[0026] Piperazine pyrophosphate (PER): Commercially available, D50 particle size 3μm.

[0027] Aluminum hydroxide (ATH): Commercially available, D50 particle size 2.5μm.

[0028] Organomontmorillonite (OMMT): modified by quaternary ammonium salt intercalation, with an interlayer distance d001=3.4nm.

[0029] Coupling agent KH-550: Silane coupling agent.

[0030] Coupling agent PP-g-MAH: Maleic anhydride grafted polypropylene.

[0031] Decabromodiphenyl ethane (DBDPE): Commercially available, used for comparative studies.

[0032] Antimony trioxide (Sb2O3): Commercially available, used for comparative analysis.

[0033] Untreated APP: D50 particle size 8μm, not microencapsulated.

[0034] Refractive index mismatch APP: D50 particle size 1.2μm, capsule wall made of silicone resin, with a refractive index difference of 0.09 between silicone resin and PET matrix.

[0035] Performance testing methods Halogen content: determined according to EN 14582 (combustion-ion chromatography).

[0036] Limiting Oxygen Index (LOI): Determined according to GB / T2406.2-2020 standard.

[0037] Vertical burning (UL-94): Tested according to GB / T2408-2021 (equivalent to UL-94) standard, with film samples using VTM rating.

[0038] Mechanical strength: The tensile strength and elongation at break of the film were determined according to ASTM D882 standard.

[0039] Optical performance: The transmittance and haze of the film were measured according to ASTM D1003 standard.

[0040] Example 1: (a) 20 wt% microencapsulated APP (MC-APP, D50=2 μm), 4 wt% melamine polyphosphate (MPP), 3 wt% organosilicon resin and 1 wt% coupling agent KH-550 ethanol solution were premixed at high speed at 80 °C and vacuum degree -0.08 MPa and dried for 3 hours to perform surface modification.

[0041] (b) Using a twin-screw extruder with an aspect ratio of L / D=40, 72wt% PET chips with an intrinsic viscosity of 0.75dL / g (dried in nitrogen at 160°C for 4h) were added from the main feed port as the matrix resin; The modified flame retardant and synergist mixture from step (a) is added to the melting section of the extruder via side feeding. The extruder temperature is set as follows: Zone 1 160℃, Zone 2 180℃, Zones 3 to 7 200–230℃, Die head 230–240℃, Screw speed 300 rpm, and vacuum exhaust is turned on (vacuum degree -0.08MPa). The melt was water-cooled, stretched, pelletized, and dried to obtain flame retardant masterbatch with an MFR (230℃ / 2.16kg) of 15g / 10min and a moisture content of ≤0.05wt%.

[0042] (c) The flame retardant masterbatch obtained in step (b) is mixed with pure PET chips at a mass ratio of 30:70 (dilution ratio of about 1:2.3, which is in line with the application of concentrated masterbatch dilution in the range of 1:4-1:9). The mixture is fed into a single screw extruder at a barrel temperature of 280°C. After being filtered through an 80 / 120 mesh double-layer screen, the mixture is cast into a 480μm sheet through a T-die at 275°C. The cast sheet is then shaped on a cooling roller (surface roughness Ra=0.04μm) at 25°C. The material was then subjected to bidirectional stretching: longitudinal stretching of 3.5 times at 85℃ / 105℃ / 90℃; followed by transverse stretching of 3.5 times at 100℃ / 110℃ / 220℃ with 2% relaxation. During the stretching process, an online thickness control system using a β-ray closed-loop thickness measurement system (feedback response time 180ms) was employed to stabilize the final thickness at 50±1.5μm. Finally, it was wound up after online corona treatment at 42kW·min / m².

[0043] Example 2: 80 wt% random copolymer PP, 12 wt% piperazine pyrophosphate, 5 wt% melamine cyanurate (MCA), 2 wt% organomontmorillonite (OMMT, d001=2.8nm) and 1 wt% PP-g-MAH coupling agent were dried at 90℃ and then premixed at high speed. Flame retardant masterbatch is obtained by melt blending in a twin-screw extruder at 190-220℃, followed by side feeding and vacuum degassing granulation. The masterbatch was then fed into a single-screw blown film mill. The barrel temperature was set at 175℃, 195℃, 210℃, and 215℃, and the die temperature at 220℃. The screw speed was 38 rpm, the blow-up ratio was 2.8, and the traction ratio was 3.5. The film bubble thickness was controlled to 25±1 μm using a rotary infrared closed-loop system, and then wound up after online corona treatment at 38 kW·min / m².

[0044] Example 3: 72.2 wt% LLDPE (density 0.920 g / cm³), 22 wt% aluminum hydroxide (ATH), 5 wt% silane-modified POE, and 0.8 wt% antioxidant 1010 were premixed at high speed and then granulated by twin-screw extruder at 180-200-200℃. The granules are fed into the blown film unit (barrel 175-185-195℃, die 200℃), with a blow-up ratio of 2.5 and a traction ratio of 3.0. The thickness is measured online at 40±2μm, and the film is then wound up after corona treatment at 40kW·min / m².

[0045] Example 4: A three-layer co-extrusion casting process was adopted. Layer A (flame retardant layer) used PET flame retardant masterbatch prepared in Example 1, and layer B (heat-sealing layer) used pure PE granules. The PET flame retardant layer was 20 μm thick, the PE heat-sealing layer was 30 μm thick, and the total thickness was 50 μm. The flame retardant layer thickness ratio was 20 μm / 50 μm = 40%. An ABC structure co-extrusion die was used, with a die temperature of 270℃ (fluctuation controlled within ±1℃), a cooling roller temperature of 25℃ (Ra≤0.05μm), β-ray closed-loop thickness control of 50±2μm, and corona discharge of 42kW·min / m².

[0046] Example 5: The film was produced using a three-stage co-extrusion blown film process. The outer layer (layer A) consisted of PP flame-retardant granules (formulation from Example 2), 30 μm; the middle layer (layer B) consisted of EVOH barrier resin, 15 μm; and the inner layer (layer C) consisted of a PP heat-sealing layer, 30 μm, for a total thickness of 75 μm. The flame-retardant layer thickness accounted for 30 μm / 75 μm = 40%. The die temperature was 220°C, the blow-up ratio was 3.0, and the online thickness measurement was 75 ± 3 μm.

[0047] Example 6 50wt% PET, 20wt% PP, 25wt% aluminum hydroxide, 3wt% expanded graphite, and 2wt% epoxy silane are granulated by a twin-screw extruder at 220-240-235℃, then fed into a casting machine with a 250℃ die, a 30℃ cooling roller, β-ray thickness control of 100±3μm, corona treatment of 45kW·min / m², and finally wound up.

[0048] Example 7: like Figure 4-5 As shown, the preparation method is the same as in Example 1, with the following optimization of raw material parameters: The MC-APP (D50=2μm) in Example 1 was replaced with MC-APP that was further ground by steam jet mill (-20℃ nitrogen circulation) to make its D50=1.2μm.

[0049] Ensure that the absolute value of the difference between the refractive index of the MC-APP capsule wall (melamine-formaldehyde resin) and the refractive index of the PET matrix is ​​≤0.02; The silicone resin in Example 1 was replaced with a novel organoclay (OMMT) intercalated with quaternary ammonium salts, with d001=3.4nm; After biaxial stretching, the resulting 25 μm film, measured by 2D-SAXS, showed that the long axis dimension of the dispersed phase particles (MC-APP and OMMT) was ≤100 nm and the orientation degree along the film surface was ≥80%.

[0050] Comparative Example 1: A 25 μm film was prepared by blending 80 wt% PET, 15 wt% decabromodiphenyl ethane, and 5 wt% antimony trioxide, followed by the same drying-casting-biaxial stretching process as in Example 1. The halogen content of this film far exceeded 900 ppm.

[0051] Comparative Example 2: A 50 μm film was prepared using 55 wt% random PP as the matrix, with the addition of 40 wt% aluminum hydroxide and 5 wt% PP-g-MAH, under the blow molding conditions of Example 2. The amount of flame retardant added (40 wt%) was comparable to that in the embodiment of this invention, but a synergistic system was not used.

[0052] Comparative Example 3: A 40μm monolayer film was blow-molded using 65wt% LLDPE, 30wt% ATH and 5wt% PE-g-MAH.

[0053] Comparative Example 4: The preparation method is basically the same as in Example 6, except that the MC-APP with D50=1.2μm is replaced with untreated APP with D50=8μm (unmicroencapsulated).

[0054] Comparative Example 5: The preparation method is basically the same as in Example 6, except that the capsule wall of MC-APP is replaced with silicone resin with a refractive index of 1.48. The absolute value of the difference between this refractive index and that of the PET matrix (approximately 1.57) is 0.09, which is much greater than 0.02.

[0055] To verify the performance of the flame-retardant films in each embodiment and comparative example, the performance of the flame-retardant adhesives prepared in each embodiment and comparative example was tested.

[0056] The testing methods include: Limiting Oxygen Index (LOI): According to GB / T2406.2-2020, the volume fraction of oxygen required to sustain combustion of a sample for 3 minutes or burn off 50 mm is determined, and the result is expressed as a percentage.

[0057] Vertical burning (UL-94): According to GB / T2408-2021 (equivalent to UL-94), record the afterflame time t1 after the first flame application and the afterflame + afterglow time t2 after the second flame application, and observe whether molten drips fall and ignite the degreased cotton. Rating determination: V-0 / V-1 / V-2 / NR.

[0058] Halogen content: determined according to EN 14582 (combustion-ion chromatography).

[0059] Mechanical strength: The mechanical strength (tensile strength and elongation at break) of the film was determined according to ASTM D882.

[0060] Optical properties: The transmittance of the film was measured according to ASTM D1003.

[0061] Performance test results The films prepared in the above embodiments and comparative examples were subjected to performance tests, and the results are summarized in Table 1.

[0062] Table 1: Test Results of Articles Prepared in Each Example and Comparative Example .

[0063] As can be seen from the above, the total halogen content of Examples 1-7 is far below 900 ppm, which meets the halogen-free standard. Although Comparative Example 1 meets the flame retardancy standard, its bromine content is as high as 123,500 ppm, which is a halogenated flame retardant and does not meet the high-end application positioning of this invention. Example 2 (PP-based) and Example 3 (LLDPE-based) both achieved a V-0 flame retardancy rating. However, Comparative Example 2 (40% ATH) and Comparative Example 3 (30% ATH), with similar or higher inorganic filler additions, only achieved a V-0 flame retardancy rating (Comparative Example 2) or failed to meet the standard (Comparative Example 3), and their mechanical properties (28 MPa / 40%) and optical properties (72%) were significantly inferior to those of the embodiments of this invention (e.g., Example 2: 52 MPa / 109%; 88%). This demonstrates the superiority of the synergistic flame retardant system of this invention. Comparing Example 7 (D50=1.2μm, Δn≤0.02) with Comparative Example 4 (D50=8μm) and Comparative Example 5 (Δn=0.09), it can be seen that flame retardant components alone are insufficient to achieve high transparency. Although the components of Comparative Examples 4 and 5 are similar to those of the present invention, due to the lack of micro-particle size control and refractive index matching, their haze is as high as 15.0% and 8.0% respectively, showing obvious turbidity or interference patterns. Only by satisfying the specific combination of particle size + refractive index matching + orientation degree in the present invention can the excellent optical effect of 2.1% haze be obtained. This invention achieves simultaneous breakthroughs in four key indicators of thin films: halogen-free, highly efficient flame retardancy, high transparency, and high strength and toughness, by combining a synergistic flame retardant system, microstructure control, and preparation process, thus overcoming the deficiencies in the prior art.

[0064] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A highly transparent halogen-free flame-retardant polymer film, characterized in that, The membrane has a thickness of 5 μm to 200 μm, a total halogen content of no more than 900 ppm, meets the UL-94 VTM-0 rating, a limiting oxygen index of no less than 30%, a light transmittance of no less than 86%, and a haze of no more than 5%. The membrane is prepared by a melt-forming and biaxial stretching process from a raw material composition, wherein the raw material composition comprises, by weight of the total raw material composition: 50 wt% to 90 wt% of a matrix resin, wherein the matrix resin is selected from at least one of thermoplastic polyesters and polyolefins; 5 wt% to 40 wt% of halogen-free flame retardant, wherein the halogen-free flame retardant comprises phosphorus-based flame retardants, metal hydroxides and intumescent flame retardants; 1 wt% to 10 wt% of a synergist, wherein the synergist is selected from organomontmorillonite modified by quaternary ammonium salt intercalation; 0.5 wt% to 5 wt% of coupling agent; and 0 wt% to 5 wt% of processing aid; The phosphorus-based flame retardant is microencapsulated ammonium polyphosphate, the capsule material is melamine-formaldehyde resin, and the capsule wall thickness is 50nm to 200nm. The particle size D50 of the halogen-free flame retardant is not higher than 2 μm, and the absolute value of the difference between the refractive index of the capsule wall of the microencapsulated ammonium polyphosphate and the refractive index of the matrix resin is not higher than 0.

02. The membrane is a biaxially oriented membrane. The dispersed phase particles composed of the halogen-free flame retardant and the synergist are distributed in a flat shape in the membrane, with a major axis dimension not exceeding 100 nm and an orientation degree of not less than 80% along the membrane surface direction.

2. The highly transparent halogen-free flame-retardant polymer film according to claim 1, characterized in that, The matrix resin is PET with an intrinsic viscosity of 0.70 dL / g to 0.85 dL / g, or copolymer polypropylene with a melt flow rate of 5 g / 10 min to 15 g / 10 min under 230°C and 2.16 kg load, or a density of 0.918 g / cm³. 3 Up to 0.930 g / cm 3 LLDPE.

3. The highly transparent halogen-free flame-retardant polymer film according to claim 1, characterized in that, The interlayer distance d001 of the organomontmorillonite is not less than 2.5 nm.

4. The highly transparent halogen-free flame-retardant polymer film according to claim 1, characterized in that, The metal hydroxide is selected from at least one of aluminum hydroxide and magnesium hydroxide; the intumescent flame retardant is selected from at least one of piperazine pyrophosphate and expandable graphite.

5. The membrane according to claim 1, characterized in that, The membrane is a multilayer composite membrane, comprising at least one flame-retardant layer formed from the raw material composition of claim 1, and at least one reinforcing layer or heat-sealing layer formed from pure thermoplastic resin; the thickness of the flame-retardant layer accounts for 20% to 60% of the total thickness of the membrane.

6. A flame-retardant masterbatch for preparing the highly transparent halogen-free flame-retardant polymer film of claim 1, characterized in that, The concentration of halogen-free flame retardant in the masterbatch is 40wt% to 80wt%, with the remainder being matrix resin, synergist, coupling agent and processing aid; The masterbatch has a melt flow rate of 5 g / 10 min to 20 g / 10 min under conditions of 230 °C and 2.16 kg load, and a water content of no more than 0.05 wt%.

7. A method for preparing the highly transparent halogen-free flame-retardant polymer film of claim 1, characterized in that, Includes the following steps: The halogen-free flame retardant and the coupling agent were pre-dried and surface modified under conditions of 80°C to 120°C and a vacuum degree not exceeding -0.08MPa. A twin-screw extruder with an aspect ratio (L / D) of not less than 40 is used to melt-blend the surface-modified material with the matrix resin via side feeding. The extrusion temperature is 180°C to 250°C, and vacuum degassing is performed to prepare flame-retardant masterbatch. The flame retardant masterbatch is diluted with pure resin at a weight ratio of 1:4 to 1:9, and then formed by single-layer casting, blow molding or co-extrusion of three or more layers. Subsequently, it is biaxially stretched and the thickness is controlled by a β-ray closed-loop thickness measurement system. Finally, an online corona treatment was performed to obtain a highly transparent halogen-free flame-retardant polymer film.

8. The method according to claim 7, characterized in that, The co-extrusion molding adopts a co-extrusion die head with an ABA or ABC structure, the die head temperature fluctuation is not higher than ±1℃, the surface roughness Ra of the cooling roller is not higher than 0.05μm; and the feedback response time of the β-ray closed-loop thickness measurement system is not higher than 200ms, and the thickness tolerance is controlled within ±1.5μm.

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