A polyester ultrathin special film and its preparation method

Abstract

This invention relates to the field of specialty films, specifically to an ultrathin polyester specialty film and its preparation method. The ultrathin polyester specialty film, by weight, comprises the following components: 100 parts PET matrix resin, 5-12 parts synergistic toughening agent, 0.3-1.2 parts composite antioxidant, 0.8-3.5 parts nano-nucleating agent, 0.2-0.6 parts lubricant, 0.05-0.2 parts opening agent, and 0.2-0.6 parts heat stabilizer. The synergistic toughening agent used in this invention possesses both a triazine nitrogen-based rigid structure and a DOPO phosphorus-based flexible segment. In the PET matrix, the rigid triazine ring can form strong hydrogen bonds with the ester groups of the PET molecular chain, effectively maintaining the tensile strength and thermal dimensional stability of the film; the flexible phosphorus-based segment can form a uniform elastic dispersed phase in the matrix. Combined with the nano-nucleating agent, this significantly improves the elongation at break, bending fatigue resistance, and low-temperature impact resistance of the ultrathin film.

Description

Technical Field

[0001] This invention relates to the field of special films, specifically to a polyester ultrathin special film and its preparation method. Background Technology

[0002] Polyethylene terephthalate (PET) polyester film, with its excellent mechanical strength, optical transparency, electrical insulation, temperature resistance, and processability, has become a core material in high-end fields such as electronics, new energy, flexible displays, and semiconductor packaging. As downstream industries rapidly develop towards miniaturization, thinning, and flexibility, ultra-thin PET film (thickness ≤ 6μm) has become a core technological trend. It possesses irreplaceable application value in scenarios such as ultra-thin protective substrates for flexible foldable electronics, ultra-thin insulating films for semiconductor packaging, ultra-thin encapsulation layers for new energy soft-pack batteries, substrates for 5G high-frequency flexible circuit boards, and ultra-thin separators for microelectronic components. Simultaneously, these scenarios also impose requirements on the flame-retardant safety of the film, necessitating compliance with halogen-free environmental standards to avoid safety risks under extreme conditions such as high temperatures, short circuits, and overloads.

[0003] However, in the existing technology, there are still unsolvable problems in the preparation, toughening and flame retardant modification of ultrathin PET films, which seriously limit their large-scale high-end applications. Specifically: (1) The inherent structural defects of ordinary PET resin are amplified after ultrathinning. The large number of rigid benzene ring structures in the PET molecular chain result in high molecular chain rigidity and high regularity, which easily forms coarse spherulites. It has problems such as high notch sensitivity, poor low-temperature toughness and low elongation at break. After ultrathinning, the effective load-bearing cross section of the film is greatly reduced. Even a small amount of structural defects or stress concentration will cause the film to break. Ultrathin films prepared by conventional PET resin are very prone to breakage during biaxial stretching, resulting in a very low yield. Moreover, the bending resistance and impact resistance of the finished product cannot meet the requirements of high-end scenarios. (2) The existing PET toughening modification technology cannot adapt to the preparation requirements of ultrathin films. Copolymer modification, by introducing flexible comonomers to disrupt the regularity of PET molecular chains, can improve toughness, but it will significantly reduce the crystallinity, heat resistance and modulus of PET, resulting in extremely poor thermal dimensional stability of ultrathin films and a significantly narrowed processing window; thermoplastic elastomer blending toughening technology (such as POE, EVA, TPU, etc.) has the problem of large polarity difference and poor compatibility with PET matrix, which easily leads to phase separation and additive agglomeration. In ultrathin films, a large number of crystal points and fish eyes will be formed, which not only seriously damages the flatness and optical properties of the film, but also becomes the starting point of film breakage during the stretching process. At the same time, it will cause a significant loss of tensile strength of the film, making it impossible to achieve a balance between high strength and high toughness under ultrathinness, and it has no flame retardant effect. (3) Existing PET flame retardant modification technology cannot meet the comprehensive performance requirements of ultrathin films. While halogenated flame retardants offer high flame retardancy, they pose environmental risks by releasing toxic and corrosive gases during combustion, failing to meet the environmental requirements of high-end applications. Inorganic flame retardants (such as aluminum hydroxide and magnesium hydroxide) require high addition levels to achieve flame retardancy, severely damaging the mechanical and processing properties of PET. They are also prone to agglomeration defects in ultra-thin films, leading to stretching and film breakage. Conventional phosphorus-based flame retardants have poor compatibility with the PET matrix, are prone to migration and precipitation, and significantly reduce the mechanical strength and thermal dimensional stability of the film, failing to simultaneously meet the requirements of ultra-thinness, high toughness, and high flame retardancy.

[0004] In summary, existing polyester films cannot simultaneously achieve high mechanical properties, halogen-free flame retardancy, bending fatigue resistance, and environmental stability at ultra-thin thicknesses, and therefore cannot meet the comprehensive performance requirements of downstream high-end industries for ultra-thin polyester specialty films. Summary of the Invention

[0005] To address the problems existing in the prior art, the purpose of this invention is to provide a polyester ultrathin special film and its preparation method.

[0006] The objective of this invention is achieved through the following technical solution: A polyester ultrathin specialty film, comprising the following components by weight: 100 parts PET matrix resin, 5-12 parts synergistic toughening agent, 0.3-1.2 parts composite antioxidant, 0.8-3.5 parts nano nucleating agent, 0.2-0.6 parts lubricant, 0.05-0.2 parts opening agent, and 0.2-0.6 parts heat stabilizer.

[0007] Preferably, the PET matrix resin is polyethylene terephthalate, with a density of 1.33-1.34 g / cm³ at 25°C. 3 At 250℃ and 2.16kg, the melt index is 12-20g / 10min, the intrinsic viscosity is 0.68-0.78dL / g, and it is vacuum dried at 140℃ for 6-8h before use, with a moisture content ≤20ppm.

[0008] Preferably, the synergistic toughening agent is obtained by combining 2-amino-4,6-dimethoxy-1,3,5-triazine and allyl alcohol glycidyl ether, followed by a click chemical reaction with thiolated DOPO to a thio-olefin.

[0009] Preferably, the composite antioxidant is a mixture of a primary antioxidant and a secondary antioxidant in a mass ratio of 1:1-3; the primary antioxidant is one or a combination of two of antioxidant 1010 and antioxidant 1076, and the secondary antioxidant is one or a combination of two of antioxidant 168 and antioxidant 626.

[0010] Preferably, the nanonucleating agent is a nanofiller whose surface has been modified with silane coupling agent KH-560.

[0011] More preferably, the nanofiller includes one or more of nano-montmorillonite, nano-talc, and nano-silicon carbide, with a particle size of 10-40 nm.

[0012] Preferably, the preparation method of the nanonucleating agent includes: Add 10g of nanofiller and 2-3g of silane coupling agent KH-560 to 100mL of 70wt% ethanol solution, mix thoroughly, reflux and stir at 70-80℃ for 5-6h, cool, filter, wash and dry to obtain nanonucleating agent.

[0013] Preferably, the lubricant is one or more of calcium stearate, zinc stearate, and ethylene bis-stearamide (EBS).

[0014] Preferably, the opening agent is nano-sized silica with a particle size of 30-80 nm.

[0015] Preferably, the heat stabilizer is one or more of triphenyl phosphate, trimethyl phosphate, and triethyl phosphate.

[0016] Preferably, the preparation method of the synergistic toughening agent includes: S1. Add 2-amino-4,6-dimethoxy-1,3,5-triazine, catalyst, and 1,4-dioxane to a four-necked flask equipped with a magnetic stirrer. Purge with nitrogen for protection and heat to 35-40°C while stirring until completely dissolved. Slowly add allyl alcohol glycidyl ether dropwise. After the addition is complete, heat to 60-65°C and maintain the temperature for 4-6 hours. After the reaction is complete, cool to room temperature and perform post-treatment to obtain the triazine double bond intermediate. S2. Add 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide and mercaptoacetic acid to xylene, mix well, then add p-toluenesulfonic acid, heat to 70-90℃ and react for 2-5 hours. After the reaction is complete, cool to room temperature, concentrate, precipitate, filter and dry to obtain DOPO-SH. S3. Add the triazine double bond intermediate, DOPO-SH and tetrahydrofuran to the reaction flask, continuously purge with nitrogen for 30 minutes to remove oxygen, and stir until homogeneous; add the initiator and irradiate with ultraviolet light for 15-30 minutes; after precipitation, filtration and drying, obtain the synergistic toughening agent.

[0017] Preferably, in S1, the ratio of 2-amino-4,6-dimethoxy-1,3,5-triazine, allyl alcohol glycidyl ether, and 1,4-dioxane is 10g:(14.6-16.1)g:(80-120)mL.

[0018] Preferably, in S1, the catalyst is triethylamine, and the amount added is 0.5%-1% of the mass of 2-amino-4,6-dimethoxy-1,3,5-triazine.

[0019] Preferably, in S2, the ratio of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-hydroquinone, mercaptoacetic acid, p-toluenesulfonic acid and xylene is 10g:(5.7-6.5)g:(0.4-0.8)g:(100-150)mL.

[0020] Preferably, in S3, the ratio of the triazine double bond intermediate, DOPO-SH and tetrahydrofuran is 4.5g:(5.3-5.7)g:(50-100)mL.

[0021] Preferably, in step S3, the photoinitiator is benzoin n-butyl ether or benzoin dimethyl ether, and the amount added is 1%-3% of the mass of the triazine double bond intermediate.

[0022] Secondly, this invention discloses a method for preparing an ultrathin polyester special film, comprising the following steps: Step 1: Add the dried PET matrix resin, synergistic toughening agent, composite antioxidant, nano nucleating agent, lubricant, opening agent, and heat stabilizer to a high-speed mixer according to the specified ratio, mix evenly, and obtain a uniformly dispersed premix. Step 2: Add the premixed material to a twin-screw extruder for melt extrusion. After filtration, the melt is cast onto a cooling roller through a slit die and cooled to obtain a cast sheet. Step 3: The casting sheet is subjected to longitudinal and transverse stretching processes in sequence; the stretched film is then heat-set, followed by thickness measurement, cooling, edge trimming, and winding to obtain an ultra-thin polyester special film with a thickness of 2-6 μm.

[0023] The beneficial effects of this invention are as follows: 1. The synergistic toughening agent used in this invention possesses both a rigid triazine nitrogen structure and a flexible DOPO phosphorus segment. In the PET matrix, the rigid triazine ring can form strong hydrogen bonds with the ester groups of the PET molecular chain, effectively maintaining the tensile strength and thermal dimensional stability of the film. The flexible phosphorus segment can form a uniform elastic dispersed phase in the matrix, which, combined with the heterogeneous nucleation effect of the nano-nucleating agent, significantly improves the elongation at break, bending fatigue resistance, and low-temperature impact resistance of the ultrathin film. Simultaneously, the phosphorus and nitrogen elements in the toughening agent synergistically exert a dual flame-retardant effect in both the gas-phase and condensed-phase phases, achieving halogen-free flame retardancy even at low addition levels. This solves the problem in existing technologies where flame retardancy and mechanical properties cannot be simultaneously achieved, and ultrathinness and high flame retardancy cannot be simultaneously balanced.

[0024] 2. The toughening agent of this invention, through molecular structure design, introduces a triazine heterocyclic structure that matches the polarity of PET. Its compatibility with the matrix is ​​far superior to that of traditional elastomer toughening agents and small molecule flame retardants. It can achieve nanoscale uniform dispersion without the need for additional compatibilizers, avoiding defects such as crystal points, fish eyes, and agglomeration in ultrathin films. It significantly reduces the film breakage rate during biaxial stretching, improves the yield and thickness uniformity, and can stably prepare ultrathin films. It solves the problems of complex traditional modified formulation systems, poor compatibility of multiple additives, and poor stability of ultrathin film formation.

[0025] 3. The toughening agent of this invention is a halogen-free phosphorus-nitrogen synergistic flame retardant system, which releases no toxic or corrosive gases during combustion, exhibiting excellent safety. The phosphorus-nitrogen synergistic effect forms a dense, expanded carbonized layer in the condensed phase during combustion, blocking oxygen and heat transfer, while simultaneously capturing combustion free radicals in the gas phase to inhibit chain reactions. Furthermore, the triazine structure of the toughening agent enhances the thermo-oxidative stability of the film, forming a synergistic effect with the composite antioxidants and heat stabilizers in the formulation, effectively inhibiting the degradation of PET molecular chains during high-temperature processing and long-term use, thus improving the long-term stability and weather resistance of the film.

[0026] 4. The formulation system of this invention is relatively simple, requiring no additional compatibilizers or dispersants. The processing technology adopts the industry-standard biaxially oriented polyester film production line, requiring no additional modifications to existing equipment. The process parameter window is wide and highly controllable, possessing excellent prospects for industrial application. Detailed Implementation

[0027] The technical solution of the present invention is illustrated below through specific examples. It should be understood that the one or more method steps mentioned in the present invention do not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps; it should also be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention. Furthermore, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or defining the scope of the present invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the present invention.

[0028] To better understand the above technical solutions, exemplary embodiments of the present invention are described in more detail below. While exemplary embodiments of the present invention are shown, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the invention to those skilled in the art.

[0029] The present invention will be further described below with reference to the following embodiments. Example 1

[0030] A polyester ultrathin specialty film, comprising the following components by weight: 100 parts PET matrix resin, 8 parts synergistic toughening agent, 0.7 parts composite antioxidant, 2.0 parts nano nucleating agent, 0.4 parts lubricant, 0.12 parts opening agent, and 0.4 parts heat stabilizer.

[0031] The PET matrix resin is polyethylene terephthalate, with a density of 1.335 g / cm³ at 25°C. 3 At 250℃ and 2.16kg, the melt index is 18g / 10min, the intrinsic viscosity is 0.72dL / g, and it is vacuum dried at 140℃ for 7h before use, with a moisture content ≤18ppm.

[0032] Among them, the composite antioxidant is antioxidant 1010 and antioxidant 168 compounded in a mass ratio of 1:2; the nano nucleating agent is KH-560 modified nano montmorillonite (particle size 20nm); the lubricant is ethylene bis-stearamide (EBS); the opening agent is nano silica (particle size 50nm); and the heat stabilizer is triphenyl phosphate (TPP).

[0033] The preparation methods of nanonucleating agents include: The nano-montmorillonite with a particle size of 20 nm, modified with silane coupling agent KH-560, was prepared by adding 10 g of nano-montmorillonite and 2.5 g of KH-560 to 100 mL of 70 wt% ethanol aqueous solution, dispersing thoroughly, refluxing and stirring at 75 °C for 5.5 h, cooling to room temperature, filtering, washing the filter cake three times with anhydrous ethanol, and vacuum drying at 80 °C for 12 h.

[0034] The preparation methods of synergistic toughening agents include: S1. Preparation of the triazine double bond intermediate: 10 g of 2-amino-4,6-dimethoxy-1,3,5-triazine, 0.08 g of triethylamine, and 100 mL of 1,4-dioxane were added to a four-necked flask. Under nitrogen protection, the mixture was heated to 38 °C and stirred until completely dissolved. 15.2 g of allyl alcohol glycidyl ether was slowly added dropwise over 1.5 h, with the temperature controlled at ≤45 °C. After the addition was complete, the temperature was raised to 62 °C and the reaction was maintained for 5 h. After cooling, the mixture was separated into liquid and liquid phases. The organic phase was distilled under reduced pressure at 48 °C to remove the solvent, yielding a pale yellow transparent triazine double bond intermediate with a yield of 94.2%. S2. Synthesis of thiolated DOPO (DOPO-SH): 10 g DOPO-HQ and 6.1 g mercaptoacetic acid were added to 120 mL xylene, mixed well, and then 0.6 g p-toluenesulfonic acid was added. The mixture was reacted at 80 °C for 3.5 h. After cooling and concentration, the reaction solution was added to 3.5 times its volume of n-hexane to precipitate the precipitate. After filtration and washing, the precipitate was dried under vacuum at 45 °C for 12 h to obtain DOPO-SH, with a yield of 92.7%. S3. UV-induced thiol-ene grafting reaction: Add 4.5g of triazine double bond intermediate, 5.5g of DOPO-SH and 80mL of tetrahydrofuran to the reaction flask, purge with nitrogen for 30min to remove oxygen, and stir until homogeneous; add benzoin dimethyl ether as a photoinitiator with a triazine double bond intermediate content of 2wt%, and apply a 365nm UV lamp (15mW / cm²). 2 The reaction was irradiated for 22 min; 3.5 times the volume of anhydrous methanol was added to the reaction solution to precipitate the precipitate, which was then filtered, washed, and vacuum dried at 50°C for 12 h to obtain a synergistic toughening agent with a yield of 93.5%.

[0035] The method for preparing the above-mentioned polyester ultrathin special film includes: Step 1, Premixing: Add each raw material to a high-speed mixer according to the ratio, and stir at 1300 rpm for 15 minutes at room temperature to obtain a uniform premix. Step 2, melt extrusion casting: The premixed material is added to a twin-screw extruder. The temperatures of the twin-screw extruder from the feed section to the die are 245℃, 255℃, 265℃, 270℃, 268℃, and 265℃ respectively, with the die temperature at 265℃ and the screw speed at 380 rpm. After the melt is filtered through a 5μm high-precision filter, it is cast onto a 25℃ cooling roller and shaped to obtain a casting with a thickness of 80±2μm. Step 3: The cast sheet undergoes biaxial stretching treatment: longitudinal stretching: the cast sheet is preheated to 95℃ and stretched 3.5 times at 90℃; transverse stretching: after longitudinal stretching, the film is preheated to 115℃ and stretched 3.6 times at 110℃. Step 4, Heat setting and winding: The biaxially stretched film is fed into a segmented heat setting oven for segmented heat setting. The first segment is set at 215℃ for 15 seconds, and the second segment is set at 185℃ for 10 seconds. After setting, the film is cooled, trimmed, and wound up to obtain an ultra-thin polyester film. The average thickness of the film was measured to be 3.98 μm. Example 2

[0036] A polyester ultrathin specialty film, comprising the following components by weight: 100 parts PET matrix resin, 4 parts synergistic toughening agent, 0.3 parts composite antioxidant, 0.8 parts nano nucleating agent, 0.2 parts lubricant, 0.05 parts opening agent, and 0.2 parts heat stabilizer.

[0037] The PET matrix resin is polyethylene terephthalate, with a density of 1.335 g / cm3 at 25℃, a melt index of 18 g / 10 min at 250℃ and 2.16 kg, an intrinsic viscosity of 0.72 dL / g, and is vacuum dried at 140℃ for 7 h before use, with a moisture content ≤18 ppm.

[0038] Among them, the composite antioxidant is antioxidant 1076 and antioxidant 626 compounded in a mass ratio of 1:1; the nano nucleating agent is KH-560 modified nano montmorillonite (particle size 20nm); the lubricant is ethylene bis-stearamide (EBS); the opening agent is nano silica (particle size 50nm); and the heat stabilizer is triphenyl phosphate (TPP).

[0039] The preparation method of the nanonucleating agent is the same as that in Example 1.

[0040] The preparation method of the synergistic toughening agent is the same as that in Example 1.

[0041] The preparation method of the above-mentioned polyester ultrathin special film is the same as that in Example 1. Example 3

[0042] A polyester ultrathin specialty film, comprising the following components by weight: 100 parts PET matrix resin, 12 parts synergistic toughening agent, 1.2 parts composite antioxidant, 3.5 parts nano nucleating agent, 0.6 parts lubricant, 0.2 parts opening agent, and 0.6 parts heat stabilizer.

[0043] The PET matrix resin is polyethylene terephthalate, with a density of 1.335 g / cm3 at 25℃, a melt index of 18 g / 10 min at 250℃ and 2.16 kg, an intrinsic viscosity of 0.72 dL / g, and is vacuum dried at 140℃ for 7 h before use, with a moisture content ≤18 ppm.

[0044] Among them, the composite antioxidant is antioxidant 1010 and antioxidant 168 compounded in a mass ratio of 1:1; the nano nucleating agent is KH-560 modified nano montmorillonite (particle size 20nm); the lubricant is ethylene bis-stearamide (EBS); the opening agent is nano silica (particle size 50nm); and the heat stabilizer is triphenyl phosphate (TPP).

[0045] The preparation method of the nanonucleating agent is the same as that in Example 1.

[0046] The preparation method of the synergistic toughening agent is the same as that in Example 1.

[0047] The preparation method of the above-mentioned polyester ultrathin special film is the same as that in Example 1.

[0048] Comparative Example 1 The difference from Example 1 is that no toughening agent is added, and the remaining components are completely identical to those in Example 1.

[0049] A polyester film, comprising the following components by weight: 100 parts PET matrix resin, 8 parts synergistic toughening agent, 0.7 parts composite antioxidant, 2.0 parts nano nucleating agent, 0.4 parts lubricant, 0.12 parts opening agent, and 0.4 parts heat stabilizer.

[0050] The preparation method of the polyester film is completely consistent with that of Example 1. The raw material pretreatment, premixing treatment, melt extrusion casting, biaxial stretching treatment, heat setting and winding are completed in sequence. All process parameters, equipment and operation steps are unchanged. Finally, the polyester ultrathin film of this comparative example is obtained, with a measured average thickness of 3.99 μm.

[0051] Comparative Example 2 The difference from Example 1 is that only the S1 product triazine double bond intermediate from the preparation process of the synergistic toughening agent in Example 1 is added, and the amount added is the same as that of the synergistic toughening agent in Example 1.

[0052] A polyester film, comprising the following components by weight: 100 parts PET matrix resin, 8 parts triazine double bond intermediate, 0.7 parts composite antioxidant, 2.0 parts nano nucleating agent, 0.4 parts lubricant, 0.12 parts opening agent, and 0.4 parts heat stabilizer.

[0053] The preparation method of the polyester film is completely consistent with that of Example 1. The raw material pretreatment, premixing treatment, melt extrusion casting, biaxial stretching treatment, heat setting and winding are completed in sequence. All process parameters, equipment and operation steps are unchanged. Finally, the polyester ultrathin film of this comparative example is obtained, with a measured average thickness of 4.00 μm.

[0054] Comparative Example 3 The difference from Example 1 is that only the S2 product thiolated DOPO (DOPO-SH) from the preparation process of the synergistic toughening agent in Example 1 is added, and the amount added is the same as that of the synergistic toughening agent in Example 1.

[0055] A polyester film, comprising the following components by weight: 100 parts PET matrix resin, 8 parts DOPO-SH, 0.7 parts composite antioxidant, 2.0 parts nano nucleating agent, 0.4 parts lubricant, 0.12 parts opening agent, and 0.4 parts heat stabilizer.

[0056] The preparation method of the polyester film is completely consistent with that of Example 1. The raw material pretreatment, premixing treatment, melt extrusion casting, biaxial stretching treatment, heat setting and winding are completed in sequence. All process parameters, equipment and operation steps are unchanged. Finally, the polyester ultrathin film of this comparative example is obtained, with a measured average thickness of 4.02 μm. Comparative Example 4 The difference from Example 1 is that the triazine double bond intermediate of Example 1 is physically compounded with DOPO-SH at a mass ratio of 4.5:5.5, and the total amount added is consistent with the synergistic toughening agent of Example 1. A polyester film, comprising the following components by weight: 100 parts PET matrix resin, 3.6 parts triazine double bond intermediate, 4.4 parts DOPO-SH, 0.7 parts composite antioxidant, 2.0 parts nano nucleating agent, 0.4 parts lubricant, 0.12 parts opening agent, and 0.4 parts heat stabilizer.

[0057] The preparation method of the polyester film is completely consistent with that of Example 1. The raw material pretreatment, premixing treatment, melt extrusion casting, biaxial stretching treatment, heat setting and winding are completed in sequence. All process parameters, equipment and operation steps are unchanged. Finally, the polyester ultrathin film of this comparative example is obtained, with a measured average thickness of 3.99 μm.

[0058] Performance testing (1) Thickness test: According to GB / T6672-2001, a high-precision thickness gauge was used to test 10 points and the average value was taken.

[0059] (2) Mechanical property test: According to GB / T1040.3-2006, the tensile speed of the universal tensile testing machine is 500 mm / min. The longitudinal (MD) tensile strength and elongation at break are tested. The average value of 5 samples in each group is taken.

[0060] (3) Flame retardant performance test: Limiting oxygen index (LOI) is tested according to GB / T2406.2-2009.

[0061] (4) Bending fatigue resistance: According to GB / T457-2008, MIT bending fatigue tester, load 500g, bending radius 0.38mm, bending angle 135°, record the number of bends when the sample breaks, and take the average value of 5 samples in each group.

[0062] (5) Environmental stability test: Humid heat aging: Aging in a constant temperature and humidity chamber at 85℃ / 85%RH for 168 hours, and testing the tensile strength retention rate (performance after aging / performance before aging × 100%). Thermo-oxidative aging: Aging in a 150℃ forced-air drying oven for 72 hours, tensile strength retention rate was tested, and the yellowing index change value ΔYI was tested according to GB / T2409-2008.

[0063] The test results are shown in Table 1: Table 1 Performance characteristics of different special films As can be seen from Table 1 above, Example 1 of the present invention achieves both high strength and high toughness at an ultrathin thickness of 4μm. Due to its extremely thin thickness and large specific surface area, conventional flame-retardant systems struggle to achieve high flame-retardant ratings with ultrathin films. However, Example 1 of the present invention achieves an LOI of 31.3%, far superior to the LOI of 22.5% of the blank comparative example 1. Example 1's MIT (Mean Intensity Tolerance) reaches 16,700 bending cycles, far superior to all comparative examples. After 168 hours of damp heat aging, Example 1 retains 93.7% of its tensile strength; after 72 hours of thermo-oxidative aging, it retains 95.1% of its tensile strength, with a ΔYI of only 2.1, far superior to all comparative examples.

[0064] In summary, it can be seen that the ultrathin special film prepared in Example 1 of the present invention solves the problems in the prior art where flame retardancy and mechanical properties cannot be achieved simultaneously, and ultrathinness and high flame retardancy cannot be achieved at the same time.

[0065] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. The illustrative expressions of the above terms in this specification should not be construed as necessarily referring to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0066] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A polyester ultrathin special film, characterized in that, Calculated by weight, it includes the following components: 100 parts PET matrix resin, 5-12 parts synergistic toughening agent, 0.3-1.2 parts composite antioxidant, 0.8-3.5 parts nano nucleating agent, 0.2-0.6 parts lubricant, 0.05-0.2 parts opening agent, 0.2-0.6 parts heat stabilizer; The synergistic toughening agent is obtained by combining 2-amino-4,6-dimethoxy-1,3,5-triazine and allyl alcohol glycidyl ether, followed by a click chemical reaction with thiolated DOPO.

2. The polyester ultrathin special film according to claim 1, characterized in that, The PET matrix resin is polyethylene terephthalate, with a density of 1.33-1.34 g / cm³ at 25°C. 3 At 250℃ and 2.16kg, the melt index is 12-20g / 10min and the intrinsic viscosity is 0.68-0.78dL / g.

3. The polyester ultrathin special film according to claim 1, characterized in that, The composite antioxidant is a mixture of a primary antioxidant and a secondary antioxidant in a mass ratio of 1:1-3; the primary antioxidant is one or a combination of two of antioxidant 1010 and antioxidant 1076, and the secondary antioxidant is one or a combination of two of antioxidant 168 and antioxidant 626.

4. The polyester ultrathin special film according to claim 1, characterized in that, The nanonucleating agent is a nanofiller whose surface has been modified with silane coupling agent KH-560; the nanofiller includes one or more of nano montmorillonite, nano talc, and nano silicon carbide, with a particle size of 10-40 nm.

5. The polyester ultrathin special film according to claim 1, characterized in that, The lubricant is one or more of calcium stearate, zinc stearate, and ethylene bis-stearamide (EBS).

6. The polyester ultrathin special film according to claim 1, characterized in that, The opening agent is nano-sized silica with a particle size of 30-80 nm.

7. The polyester ultrathin special film according to claim 1, characterized in that, The heat stabilizer is one or more of triphenyl phosphate, trimethyl phosphate, and triethyl phosphate.

8. The polyester ultrathin special film according to claim 1, characterized in that, The preparation method of the synergistic toughening agent includes: S1. Add 2-amino-4,6-dimethoxy-1,3,5-triazine, catalyst, and 1,4-dioxane to a four-necked flask equipped with a magnetic stirrer. Purge with nitrogen for protection and heat to 35-40°C while stirring until completely dissolved. Slowly add allyl alcohol glycidyl ether dropwise. After the addition is complete, heat to 60-65°C and maintain the temperature for 4-6 hours. After the reaction is complete, cool to room temperature and perform post-treatment to obtain the triazine double bond intermediate. S2. Add 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide and mercaptoacetic acid to xylene, mix well, then add p-toluenesulfonic acid, heat to 70-90℃ and react for 2-5 hours. After the reaction is complete, cool to room temperature, concentrate, precipitate, filter and dry to obtain DOPO-SH. S3. Add the triazine double bond intermediate, DOPO-SH and tetrahydrofuran to the reaction flask, continuously purge with nitrogen for 30 minutes to remove oxygen, and stir until homogeneous; add the initiator and irradiate with ultraviolet light for 15-30 minutes; after precipitation, filtration and drying, obtain the synergistic toughening agent.

9. The polyester ultrathin special film according to claim 1, characterized in that, In S1, the ratio of 2-amino-4,6-dimethoxy-1,3,5-triazine, allyl alcohol glycidyl ether, and 1,4-dioxane is 10 g:(14.6-16.1) g:(80-120) mL; in S2, the ratio of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-hydroquinone, mercaptoacetic acid, p-toluenesulfonic acid, and xylene is 10 g:(5.7-6.5) g:(0.4-0.8) g:(100-150) mL; in S3, the ratio of triazine double bond intermediate, DOPO-SH, and tetrahydrofuran is 4.5 g:(5.3-5.7) g:(50-100) mL.

10. A method for preparing the polyester ultrathin special film according to claim 1, characterized in that, Includes the following steps: Step 1: Add the dried PET matrix resin, synergistic toughening agent, composite antioxidant, nano nucleating agent, lubricant, opening agent, and heat stabilizer to a high-speed mixer according to the specified ratio, mix evenly, and obtain a uniformly dispersed premix. Step 2: Add the premixed material to a twin-screw extruder for melt extrusion. After filtration, the melt is cast onto a cooling roller through a slit die and cooled to obtain a cast sheet. Step 3: The casting sheet is subjected to longitudinal and transverse stretching processes in sequence; the stretched film is then heat-set, followed by thickness measurement, cooling, edge trimming, and winding to obtain an ultra-thin polyester special film with a thickness of 2-6 μm.

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