A forming process for biaxially oriented polymer film

Abstract

The application relates to the field of high polymer material and film processing technology, in particular to a forming and processing technology of a biaxially stretched polymer film; the technology comprises the steps of inorganic particle surface modification, esterification, polycondensation, melt extrusion casting and biaxial stretching and winding; the technology combines specific monomer copolymerization to provide main chain rigidity and steric hindrance, and cooperates with multifunctional crosslinking monomers to build a slightly long branched and micro-crosslinked structure in the system; the core is to introduce an end group reaction agent and a macromolecular antioxidant to close the polar end group to inhibit degradation, and to combine the surface modified nanoparticles with the monomer containing a sulfonate group to form a polar ion aggregate in the amorphous region; the application overcomes the defects that the traditional process lacks a main chain rigidity cooperative design and an end group closing mechanism, causes a significant increase in thermal shrinkage and a decrease in dielectric performance in a high temperature and high frequency scene, improves the thermal dimensional stability of the material, and improves the dielectric breakdown strength and the surface metal layer adhesion.

Description

Technical Field

[0001] This invention relates to the field of polymer materials and film processing technology, specifically to a molding and processing technology for biaxially oriented polymer films. Background Technology

[0002] In the current field of polymer material processing, biaxially oriented polymer films are widely used substrates, and their molding and processing are crucial. In order to meet the requirements of specific industrial fields for the comprehensive performance of materials, the processing technology usually needs to go through multiple stages such as inorganic particle dispersion, esterification polycondensation, melt extrusion and biaxial stretching. These stages together determine the performance indicators of the final film, such as thermal dimensional stability, dielectric properties, surface antistatic ability and metal adhesion. Traditional polymer film preparation relies heavily on basic polyester synthesis and conventional mechanical stretching processes. It lacks systematic molecular-level modification and optimization evaluation of molecular chain structure and additive components in the molding and processing dimension, which can easily lead to the overall performance of the material failing to meet the expected standards or the defect rate exceeding the control range. In existing technologies, although some processes attempt to improve film performance through conventional physical blending or the addition of conventional inorganic fillers, these methods generally suffer from poor compatibility between the inorganic phase and the matrix and insufficient particle dispersion uniformity. Meanwhile, most existing thin film processing methods neglect the logical dependence between the rigid synergistic design of the polyester backbone, the control of end-group defect degradation, and the construction of polarity in amorphous regions. This results in the optimization of a single property often leading to a decline in other physicochemical properties, which limits its application in actual high-temperature and high-field environments. In addition, when faced with complex scenarios such as high-frequency insulation and surface metallization processing, traditional substrates, due to the lack of micro-crosslinking structures and effective end-group sealing mechanisms, are prone to a significant increase in thermal shrinkage, deterioration of dielectric loss, and failure of surface adhesion, making it difficult to adapt to the actual and varied comprehensive performance requirements. Therefore, there is an urgent need in the field for a biaxially oriented polymer film molding process that can systematically solve the above-mentioned defects. Summary of the Invention

[0003] The purpose of this invention is to provide a molding and processing technology for biaxially oriented polymer films, aiming to solve the problems in existing technologies where the lack of a synergistic mechanism between rigid main chain design, end-group closure, and polar amorphous region construction, coupled with poor compatibility between inorganic particles and the matrix, leads to a significant increase in thermal shrinkage, a decrease in dielectric properties, and failure of surface adhesion in high-temperature and high-frequency environments. Specifically, the technical solution of this invention is as follows: A molding and processing technology for a biaxially oriented polymer film includes: Step 1: The nano-inorganic particles are ultrasonically dispersed in an ethanol aqueous solution, a reactive silane coupling agent is added and reacted under reflux. After separation, purification and drying, surface-modified nanoparticles are prepared. Step 2: Mix terephthalic acid, 2,6-naphthalenedicarboxylic acid, 5-sulfoisophthalic acid monosodium salt, ethylene glycol and isosorbide, add the surface-modified nanoparticles, the amount of surface-modified nanoparticles added is 0.1%-1.0% of the total mass of the dicarboxylic acid, and perform gradient temperature esterification; Step 3: Add composite catalyst, heat stabilizer, macromolecular antioxidant containing reactive functional groups, and multifunctional crosslinked monomers accounting for 0.05%-0.3% of the total molar amount of monomers for vacuum polycondensation. The reaction temperature of the vacuum polycondensation is 260-290℃, and the vacuum degree is less than 100Pa. At the end of the polycondensation reaction, after releasing the vacuum to normal pressure by purging with nitrogen, add end-group reactant accounting for 0.2%-1.0% of the total mass of the system, discharge, cool, and pelletize. Step 4: After drying, the slices are melt-extruded at 260–290℃ and attached to a cooling drum to form the desired shape; Step 5: Perform biaxial stretching, heat setting, and cooling and winding on the unstretched casting to obtain a film with a thickness of 2-6 μm.

[0004] Preferably, the multifunctional crosslinking monomer is pyromellitic dianhydride or trimellitic anhydride; the macromolecular antioxidant containing reactive functional groups is a hindered phenol containing hydroxyl groups or a phosphite containing hydroxyl groups; and the end-group reactant is 1,3-phenylenebisoxazoline or polymeric carbodiimide.

[0005] Preferably, in step two of the molding process, the molar ratio of the total molar amount of ethylene glycol and isosorbide to the total molar amount of terephthalic acid, 2,6-naphthalenedicarboxylic acid, and sodium 5-sulfoisophthalate is 1.1:1-1.5:1; the molar amount of 2,6-naphthalenedicarboxylic acid accounts for 5%-25% of the total molar amount of the diacids, the molar amount of sodium 5-sulfoisophthalate accounts for 1%-5% of the total molar amount of the diacids, and the molar amount of terephthalic acid accounts for 70%-94% of the total molar amount of the diacids; The isosorbide accounts for 2%-10% of the total molar amount of the diols, the ethylene glycol accounts for 90%-98% of the total molar amount of the diols, and the sum of the molar percentages of terephthalic acid, 2,6-naphthalenedicarboxylic acid and 5-sulfoisophthalic acid monosodium salt is 100%, and the sum of the molar percentages of ethylene glycol and isosorbide is 100%.

[0006] Preferably, in step two, the temperature range of the gradient heating is 180-240℃; the esterification reaction ends when the system output reaches more than 90% of the theoretical output.

[0007] Preferably, in step three, the composite catalyst is a mixture of tetrabutyl titanate and antimony glycolate, wherein the mass ratio of tetrabutyl titanate to antimony glycolate is 1:1 to 1:5; the heat stabilizer is trimethyl phosphate or carboxyethylphenylphosphonic acid.

[0008] Preferably, in step four, the drying is vacuum drying at a temperature of 110-130℃ for 4-8 hours; the extruder used for melt extrusion is a twin-screw extruder; and the surface temperature of the cooling drum is 20-40℃.

[0009] Preferably, the bidirectional stretching includes longitudinal stretching and transverse stretching, wherein the longitudinal stretching temperature is 90–120℃ and the stretching ratio is 3.0–4.5 times; the transverse stretching temperature is 100–130℃ and the stretching ratio is 3.0–4.5 times; and the heat setting temperature is 200–230℃.

[0010] The beneficial effects of this invention are as follows: The copolymerization of specific dicarboxylic acids and diol monomers provides main chain rigidity and steric hindrance, and the synergistic effect of multifunctional crosslinking monomers to construct a slightly long-branched and micro-crosslinked structure in the system restricts the movement and slippage of molecular chain segments under high temperature conditions of 150°C. This structural design improves the polymer's resistance to thermal creep at high temperatures, reduces the thermal shrinkage rate of the film, and significantly improves the thermal dimensional stability of the material. Introducing end-group reactants and macromolecular antioxidants containing reactive functional groups can block the polar end groups of polyester, reduce the concentration of polar groups to inhibit high-temperature autocatalytic degradation, and fix the antioxidants in the system through chemical bonding to avoid migration and loss during thermal processing. This mechanism improves the color stability of the film, reduces dielectric loss under high field strength environment and improves dielectric breakdown strength. Modified nano-inorganic particles with surface-grafted reactive groups are combined with monomers containing sulfonate groups for esterification, which chemically bonds the inorganic phase with the polymer matrix, improving the dispersion uniformity of the particles. The above reaction forms polar ion aggregates in the amorphous region, which enhances the intrinsic surface polarity and antistatic ability of the film, and improves the adhesion of the surface metal layer and the overall optical performance of the film. Detailed Implementation

[0011] The technical solutions in the embodiments of the present invention will be clearly and completely described below; the described embodiments are some embodiments of the present invention, but not all embodiments. 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; in the following embodiments and comparative examples, the average original particle size of the nano-silica and nano-alumina is limited to 15-40 nm, and the specific surface area is 120-180 m² / g; in the ethanol aqueous solution in step one, the mass fraction of ethanol is 75%-85%.

[0012] Example 1: This example provides a molding and processing technology for biaxially oriented polymer films, specifically including the following steps: Step 1: Inorganic particle surface modification: 20 parts by weight of nano-silica were added to 100 parts by weight of ethanol aqueous solution to form a dispersion system. After ultrasonic dispersion, 1 part by weight of reactive silane coupling agent containing dihydroxyl functional groups was added. The mixture was heated and refluxed at 70°C for 4 hours. After the reaction was completed, the mixture was filtered, washed and vacuum dried to obtain modified nano-silica with surface-grafted reactive groups. Step 2, Esterification reaction: Terephthalic acid, 2,6-naphthalenedicarboxylic acid, sodium 5-sulfoisophthalate, ethylene glycol and isosorbide are mixed and prepared into a slurry, which is then added to the esterification reactor. The molar ratio of the total molar amount of the diol to the total molar amount of the diacid is 1.2:1. At the same time, modified nano-silica with surface-grafted reactive groups obtained in Step 1 is added, and its addition amount accounts for 0.5% of the total mass of the diacid. In this mixture, 2,6-naphthalenedicarboxylic acid accounts for 15% of the total molar amount of the diacids, 5-sulfoisophthalic acid monosodium salt accounts for 3% of the total molar amount of the diacids, and terephthalic acid accounts for 82% of the total molar amount of the diacids; isosorbide accounts for 6% of the total molar amount of the diols, and ethylene glycol accounts for 94% of the total molar amount of the diols; esterification is carried out under nitrogen protection with a gradient temperature increase, from 180℃ to 240℃ at a uniform rate, and the esterification ends when the amount of water discharged from the system reaches 92% of the theoretical amount of water discharged, thus obtaining the esterified oligomer. The esterified oligomer serves as the prepolymer skeleton for subsequent polycondensation reactions to improve polymerization efficiency. Step 3, Polycondensation reaction: Add a composite catalyst, a heat stabilizer, a hindered phenolic antioxidant containing hydroxyl groups and a pyromellitic dianhydride crosslinking monomer to the esterified oligomer obtained in Step 2, and carry out polycondensation by gradually increasing the temperature under vacuum conditions of 280℃ and 50Pa. The composite catalyst, comprising 0.05% of the total mass of the system, is a mixture of tetrabutyl titanate and antimony glycolate in a mass ratio of 1:3. The heat stabilizer is carboxyethylphenylphosphonic acid, comprising 0.02% of the total mass of the system. The macromolecular antioxidant containing reactive functional groups is a hindered phenolic antioxidant containing hydroxyl groups, comprising 0.1% of the total mass of the system. The multifunctional crosslinking monomer is pyromellitic dianhydride, which accounts for 0.15% of the total molar amount of the monomer. At the end of the polycondensation reaction, 1,3-phenylene bisoxazoline is added as an end-group reactant, which accounts for 0.6% of the total mass of the system. After the reaction, the material is discharged, cooled with water, and granulated to obtain modified polyester chips. The modified polyester chips are used as the base resin material for subsequent melt extrusion. Step 4, Melt Extrusion and Casting: The modified polyester chips obtained in Step 3 are vacuum dried at 120°C for 6 hours and then fed into a twin-screw extruder for melt extrusion. The extrusion temperature is controlled at 275°C. After filtration and static degassing, the melt is extruded through a die and attached to a cooling drum at 30°C for cooling to form an unstretched thick sheet. Step 5, Biaxial Stretching and Winding: The unstretched sheet obtained in Step 4 is stretched longitudinally and transversely; the longitudinal stretching temperature is 105℃ and the stretching ratio is 3.8 times; the transverse stretching temperature is 115℃ and the stretching ratio is 3.7 times; after stretching, it is heat-set at 215℃, cooled, trimmed and wound up to obtain a biaxially stretched polymer film with a thickness of 4μm.

[0013] Example 2: This example provides a biaxially oriented polymer film, the preparation steps of which are basically the same as those in Example 1, except that: In step one, nano-inorganic particles are selected as nano-alumina. 20 parts by weight of nano-alumina are added to 100 parts by weight of ethanol aqueous solution to form a dispersion system. After ultrasonic dispersion, 1 part by weight of reactive silane coupling agent containing dihydroxyl functional group is added. The mixture is heated and refluxed at 60°C for 6 hours to obtain modified nano-alumina with surface grafted reactive groups. In step two, the molar ratio of the total molar amount of diol to the total molar amount of diacid is 1.2:1; the amount of modified nano-alumina with surface-grafted reactive groups accounts for 0.5% of the total mass of diacid; the molar amount of 2,6-naphthalenedicarboxylic acid accounts for 5% of the total molar amount of diacid, the molar amount of 5-sulfoisophthalic acid monosodium salt accounts for 1% of the total molar amount of diacid, the molar amount of terephthalic acid accounts for 94% of the total molar amount of diacid; the molar amount of isosorbide accounts for 2% of the total molar amount of diol, and the molar amount of ethylene glycol accounts for 98% of the total molar amount of diol; In step three, the composite catalyst accounts for 0.05% of the total mass of the system, with a mass ratio of tetrabutyl titanate to antimony glycolate of 1:1; trimethyl phosphate is selected as the heat stabilizer, accounting for 0.02% of the total mass of the system; pentaerythritol diphosphite derivative, a hydroxyl-containing phosphite antioxidant, is selected as the macromolecular antioxidant containing reactive functional groups, accounting for 0.1% of the total mass of the system; trimellitic anhydride is selected as the multifunctional crosslinking monomer, accounting for 0.05% of the total molar amount of the monomer; polycondensation is carried out under vacuum conditions of 265℃ and 80Pa, and at the end of the polycondensation reaction, a polymeric carbodiimide compound is selected as the end-group reactant, accounting for 0.2% of the total mass of the system; In step four, the modified polyester chips are vacuum dried at 110℃ for 8 hours, the extrusion temperature is controlled at 260℃, and the surface temperature of the cooling drum is 20℃. In step five, the longitudinal stretching temperature is 90℃ and the stretching ratio is 3.0 times; the transverse stretching temperature is 100℃ and the stretching ratio is 3.0 times; the heat setting temperature is 200℃, and a biaxially oriented polymer film with a thickness of 6μm is obtained.

[0014] Example 3: This example provides a biaxially oriented polymer film, the preparation steps of which are basically the same as those in Example 1, except that: In step one, 20 parts by weight of nano-silica were added to 100 parts by weight of ethanol aqueous solution to form a dispersion system. After ultrasonic dispersion, 1 part by weight of reactive silane coupling agent containing dihydroxyl functional groups was added. The mixture was heated and refluxed at 80°C for 2 hours to obtain modified nano-silica with surface-grafted reactive groups. In step two, the molar ratio of the total molar amount of diol to the total molar amount of diacid is 1.2:1; the amount of modified nano-silica with surface-grafted reactive groups accounts for 0.5% of the total mass of diacid; the molar amount of 2,6-naphthalenedicarboxylic acid accounts for 25% of the total molar amount of diacid, the molar amount of 5-sulfoisophthalic acid monosodium salt accounts for 5% of the total molar amount of diacid, the molar amount of terephthalic acid accounts for 70% of the total molar amount of diacid; the molar amount of isosorbide accounts for 10% of the total molar amount of diol, and the molar amount of ethylene glycol accounts for 90% of the total molar amount of diol; In step three, the composite catalyst accounts for 0.05% of the total mass of the system, with a mass ratio of tetrabutyl titanate to antimony glycolate of 1:5; the heat stabilizer is carboxyethylphenylphosphonic acid, accounting for 0.02% of the total mass of the system; the macromolecular antioxidant containing reactive functional groups is a hindered phenolic antioxidant containing hydroxyl groups, accounting for 0.1% of the total mass of the system; the multifunctional crosslinking monomer is pyromellitic dianhydride, accounting for 0.30% of the total molar amount of the monomer; polycondensation is carried out under vacuum conditions of 285℃ and 40Pa, and at the end of the polycondensation reaction, the end-group reactant is 1,3-phenylenebisoxazoline, accounting for 1.0% of the total mass of the system. In step four, the modified polyester chips are vacuum dried at 130°C for 4 hours, the extrusion temperature is controlled at 290°C, and the surface temperature of the cooling drum is 40°C. In step five, the longitudinal stretching temperature is 120℃ and the stretching ratio is 4.5 times; the transverse stretching temperature is 130℃ and the stretching ratio is 4.5 times; the heat setting temperature is 230℃, and a biaxially oriented polymer film with a thickness of 2μm is obtained.

[0015] Example 4: This example provides a biaxially oriented polymer film, the preparation steps of which are basically the same as those in Example 1, except that: In step one, the nano-inorganic particles used are nano-silica; In step two, the molar amount of 2,6-naphthalenedicarboxylic acid accounts for 10% of the total molar amount of diacids, the molar amount of 5-sulfoisophthalic acid monosodium salt accounts for 4% of the total molar amount of diacids, and the molar amount of terephthalic acid accounts for 86% of the total molar amount of diacids; the molar amount of isosorbide accounts for 8% of the total molar amount of diols, and the molar amount of ethylene glycol accounts for 92% of the total molar amount of diols; In step three, the composite catalyst accounts for 0.05% of the total mass of the system, with a mass ratio of tetrabutyl titanate to antimony glycolate of 1:2; trimethyl phosphate is selected as the heat stabilizer, accounting for 0.02% of the total mass of the system; a hydroxyl-containing hindered phenolic antioxidant is selected as the macromolecular antioxidant containing reactive functional groups, accounting for 0.1% of the total mass of the system; trimellitic anhydride is selected as the multifunctional crosslinking monomer, accounting for 0.10% of the total molar amount of the monomer; polycondensation is carried out under vacuum conditions of 275℃ and 60Pa, and at the end of the polycondensation reaction, 1,3-phenylenebisoxazoline is selected as the end-group reactant, accounting for 0.4% of the total mass of the system; In step five, the longitudinal stretching temperature is 100℃ and the stretching ratio is 3.5 times; the transverse stretching temperature is 110℃ and the stretching ratio is 3.6 times; the heat setting temperature is 210℃, and a biaxially oriented polymer film with a thickness of 5μm is obtained.

[0016] Comparative Example 1: The difference between this comparative example and Example 1 is that 2,6-naphthalenedicarboxylic acid and isosorbide are not added in step two, while the other operating steps and process parameters are exactly the same as in Example 1.

[0017] Comparative Example 2: The difference between this comparative example and Example 1 is that 1,3-phenylenebisoxazoline is not added in step three, while the other operating steps and process parameters are exactly the same as in Example 1.

[0018] Comparative Example 3: The difference between this comparative example and Example 1 is that pyromellitic dianhydride is not added in step three, while the other operating steps and process parameters are exactly the same as in Example 1.

[0019] Comparative Example 4: The difference between this comparative example and Example 1 is that 5-sulfoisophthalic acid monosodium salt is not added in step two, while the other operating steps and process parameters are exactly the same as in Example 1.

[0020] Comparative Example 5: The difference between this comparative example and Example 1 is that: no inorganic particle surface modification is performed in step one, and nano-silica without surface grafting reactive groups is added in step two. Other operation steps and process parameters are exactly the same as in Example 1.

[0021] Comparative Example 6: The difference between this comparative example and Example 1 is that no macromolecular antioxidant containing reactive functional groups is added in step three, while the other operating steps and process parameters are exactly the same as in Example 1.

[0022] Performance Testing and Datasheets Thin film properties were tested according to conventional thin film testing methods; glass transition temperature was determined by differential scanning calorimetry, terminal carboxyl group content was determined by chemical titration, thermal shrinkage rate at 150℃ for 30 min was calculated by dimensional changes before and after heat treatment, dielectric loss and breakdown strength were determined by electrical performance testing methods, and surface resistivity, metal layer adhesion, haze and yellowing index were determined by conventional thin film testing methods. Table 1. Performance test results of the thin films in the examples and comparative examples.

[0023] As can be seen from the comparison of the test results of Example 1 and Comparative Example 1 in Table 1, after omitting the co-polymerization of 2,6-naphthalenedicarboxylic acid and isosorbide, both the glass transition temperature and thermal dimensional stability decreased. 2,6-naphthalenedicarboxylic acid provides main chain rigidity, and isosorbide provides steric hindrance. Together, they restrict the chain segment movement at high temperatures. After omitting this feature, the rigidity of the polyester main chain decreases, and the molecular chains in the amorphous region are more prone to relaxation and slippage, resulting in a decrease in Tg from 123°C to 81°C, an increase in the heat shrinkage rate at 150°C for 30 min from 0.8% to 4.9%, and a decrease in breakdown strength. As can be seen from the comparison of the test results of Example 1 and Comparative Example 2 in Table 1, the content of terminal carboxyl groups, dielectric loss and breakdown strength all deteriorated significantly after omitting the end-group reactant. 1,3-Phenylidene bisoxazoline can react with the terminal carboxyl groups of polyester, reduce the concentration of terminal carboxyl groups, and play a chain-extending role in the molecular chain. After omitting this feature, there are unreacted free terminal carboxyl groups in the system, which are more likely to initiate autocatalytic degradation under high temperature conditions of 150°C. At the same time, the increase in polar end groups will increase the dielectric loss. Therefore, the content of terminal carboxyl groups increased from 7 mol / t to 24 mol / t, tanδ increased from 0.0021 to 0.0049, and the breakdown strength decreased from 328 kV / mm to 248 kV / mm. As can be seen from the comparison of the test results of Example 1 and Comparative Example 3 in Table 1, the heat shrinkage rate and breakdown strength both decreased after omitting the multifunctional crosslinking monomer. Pyromellitic dianhydride can form a slightly long-branched and micro-crosslinked structure in polyester under low addition conditions, which restricts the molecular chain and improves the melt strength and thermal creep resistance at high temperature. After omitting this feature, the polyester chain segments are more likely to slip when heated, and the film with a thickness of 2-6 μm is more likely to undergo irreversible dimensional shrinkage. Therefore, the heat shrinkage rate at 150°C for 30 min increased from 0.8% to 3.8%, and the breakdown strength decreased from 328 kV / mm to 274 kV / mm. As can be seen from the comparison of the test results of Example 1 and Comparative Example 4 in Table 1, omitting the monosodium 5-sulfoisophthalate significantly reduced both surface resistivity and metal layer adhesion. After the monosodium 5-sulfoisophthalate copolymerizes into the polyester chain, it can form a polar ion aggregate structure in the amorphous region, thereby improving the intrinsic surface polarity of the material and enhancing its electrostatic conductivity. Omitting this feature results in insufficient surface polarity of the film, increased tendency for electrostatic accumulation, and a decrease in surface resistivity. Rise to The adhesion of the metal layer decreased from 5.4 N / 25 mm to 2.6 N / 25 mm; As can be seen from the comparison of the test results of Example 1 and Comparative Example 5 in Table 1, the use of unmodified nano-silica resulted in adverse changes in haze, breakdown strength, and dielectric loss. The nano-inorganic particles with surface-grafted reactive groups can chemically combine with the polyester chains during the polyester polycondensation process, reducing the tendency of particle aggregation and improving dispersion uniformity. The unmodified nanoparticles have poor compatibility with the polyester matrix and are prone to local aggregation. The corresponding areas will cause light scattering and are also prone to forming weak electrical properties. Therefore, the haze increased from 0.8% to 3.6%, the breakdown strength decreased from 328kV / mm to 246kV / mm, and tanδ increased from 0.0021 to 0.0031. As can be seen from the comparison of the test results of Example 1 and Comparative Example 6 in Table 1, after omitting the macromolecular antioxidant containing reactive functional groups, the yellowing index increased and the breakdown strength decreased accordingly. The macromolecular antioxidant containing reactive functional groups can be fixed in the polyester system through reactive groups, reducing migration and loss during high-temperature processing and inhibiting thermal oxidative degradation. After omitting this feature, the polyester is more prone to thermal oxidation reaction during polycondensation, extrusion and stretching heat treatment, resulting in a decrease in film color stability, an increase in the yellowing index from 1.6 to 3.5, an increase in internal defects in the material, and a decrease in breakdown strength from 328 kV / mm to 310 kV / mm.

[0024] The above are merely specific embodiments of the present invention and are not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments for application in other fields. However, any conventional modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the technical solution of the present invention shall still fall within the protection scope of the technical solution of the present invention.

Claims

1. A molding and processing technology for a biaxially oriented polymer film, characterized in that, include: Step 1: The nano-inorganic particles are ultrasonically dispersed in an ethanol aqueous solution, a reactive silane coupling agent is added and reacted under reflux. After separation, purification and drying, surface-modified nanoparticles are prepared. Step 2: Mix terephthalic acid, 2,6-naphthalenedicarboxylic acid, 5-sulfoisophthalic acid monosodium salt, ethylene glycol and isosorbide, add the surface-modified nanoparticles, the amount of surface-modified nanoparticles added is 0.1%-1.0% of the total mass of the dicarboxylic acid, and perform gradient temperature esterification; Step 3: Add composite catalyst, heat stabilizer, macromolecular antioxidant containing reactive functional groups, and multifunctional crosslinked monomers accounting for 0.05%-0.3% of the total molar amount of monomers for vacuum polycondensation. The reaction temperature of the vacuum polycondensation is 260-290℃, and the vacuum degree is less than 100Pa. At the end of the polycondensation reaction, after releasing the vacuum to normal pressure by purging with nitrogen, add end-group reactant accounting for 0.2%-1.0% of the total mass of the system, discharge, cool, and pelletize. Step 4: After drying, the slices are melt-extruded at 260–290℃ and attached to a cooling drum to form the desired shape; Step 5: Perform biaxial stretching, heat setting, and cooling and winding on the unstretched casting to obtain a film with a thickness of 2-6 μm.

2. The molding process according to claim 1, characterized in that: The multifunctional crosslinking monomer is pyromellitic dianhydride or trimellitic anhydride; the macromolecular antioxidant containing reactive functional groups is a hindered phenol containing hydroxyl groups or a phosphite containing hydroxyl groups; the end-group reactant is 1,3-phenylenebisoxazoline or polymeric carbodiimide.

3. The molding process according to claim 1, characterized in that: In step two, the molar ratio of the total molar amount of ethylene glycol and isosorbide to the total molar amount of terephthalic acid, 2,6-naphthalenedicarboxylic acid, and monosodium 5-sulfoisophthalate is 1.1:1-1.5:1; the molar amount of 2,6-naphthalenedicarboxylic acid accounts for 5%-25% of the total molar amount of the diacids, the molar amount of monosodium 5-sulfoisophthalate accounts for 1%-5% of the total molar amount of the diacids, and the molar amount of terephthalic acid accounts for 70%-94% of the total molar amount of the diacids; the molar amount of isosorbide accounts for 2%-10% of the total molar amount of the diols, and the molar amount of ethylene glycol accounts for 90%-98% of the total molar amount of the diols; and the sum of the molar percentages of terephthalic acid, 2,6-naphthalenedicarboxylic acid, and monosodium 5-sulfoisophthalate is 100%, and the sum of the molar percentages of ethylene glycol and isosorbide is 100%.

4. The molding process according to claim 1, characterized in that: In step two, the temperature range of the gradient heating is 180-240℃; the esterification reaction ends when the system output reaches more than 90% of the theoretical output.

5. The molding process according to claim 1, characterized in that: In step three, the composite catalyst is a mixture of tetrabutyl titanate and antimony glycolate, wherein the mass ratio of tetrabutyl titanate to antimony glycolate is 1:1 to 1:5; the heat stabilizer is trimethyl phosphate or carboxyethylphenylphosphonic acid.

6. The molding process according to claim 1, characterized in that: In step four, the drying is vacuum drying at a temperature of 110-130℃ for 4-8 hours; the extruder used for melt extrusion is a twin-screw extruder; and the surface temperature of the cooling drum is 20-40℃.

7. The molding process according to claim 1, characterized in that: The bidirectional stretching includes longitudinal stretching and transverse stretching, wherein the longitudinal stretching temperature is 90–120℃ and the stretching ratio is 3.0–4.5 times; the transverse stretching temperature is 100–130℃ and the stretching ratio is 3.0–4.5 times; and the heat setting temperature is 200–230℃.

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