Functional polyester chip for polyester film and solid phase polycondensation process thereof

Abstract

This invention relates to the field of polymer material synthesis technology, specifically to functional polyester chips for polyester films and their solid-state polycondensation process; it includes steps such as preparation of reactive multifunctional comonomers, pulping and esterification, melt polycondensation, pre-crystallization, and solid-state polycondensation; the process combines diacid and diol monomers, introducing specific benzotriazole reactive multifunctional comonomers for co-polymerization reaction; its core is to covalently bond large-volume rigid UV-resistant groups to the polyester macromolecular backbone, preventing them from being extracted and lost under the high temperature and nitrogen purging of solid-state polycondensation; this invention changes the traditional physical blending modification method of small molecule additives, using a chemical bonding mechanism to solve the problem of additive volatility and precipitation leading to loss of film anti-aging function, overcoming the technical defect that functional modification and high viscosity are difficult to achieve simultaneously, and realizing the unity of excellent weather resistance, high-temperature dimensional stability, and high mechanical strength of the material.

Description

Technical Field

[0001] This invention belongs to the field of polymer material synthesis technology, specifically functional polyester chips for polyester films and their solid-state polycondensation process. Background Technology

[0002] Polyethylene terephthalate (PET) films are widely used in high-end fields such as photovoltaic backsheets, optical displays, flexible electronics, and outdoor building materials due to their excellent mechanical properties, optical transparency, and chemical stability. However, conventional PET molecular chains are prone to photo-oxidative degradation under long-term ultraviolet irradiation, leading to yellowing, embrittlement, and a significant decrease in mechanical properties. Furthermore, the intrinsic viscosity of PET chips prepared by conventional melt polycondensation is typically between 0.60 and 0.65 dL / g, which is insufficient to meet the high molecular weight requirements of high-strength barrier films. Currently, the main industrial method to improve weather resistance is to physically blend small-molecule UV absorbers or antioxidants during the extrusion and casting process of polyethylene terephthalate (PET) films. However, this method has the following technical drawbacks: small-molecule additives are prone to volatilization during high-temperature polyester extrusion, which not only pollutes the production environment but also makes the actual amount remaining uncontrollable. During long-term use of the film, small molecules are prone to migrate to the surface and precipitate, leading to increased film haze, decreased light transmittance, and ultimately loss of anti-aging function. To improve the intrinsic viscosity of polyethylene terephthalate, solid-state polycondensation is often used in industry. However, under the high temperature and high vacuum or high-purity nitrogen purging environment of solid-state polycondensation, small molecule additives that are physically blended are prone to significant extraction and loss during the solid-state polycondensation process, making it difficult to simultaneously achieve functional modification and high molecular weight of the polyester. Summary of the Invention

[0003] The purpose of this invention is to provide functional polyester chips for polyester films and their solid-state polycondensation process, aiming to solve the problems in the prior art where small molecule additives in physical blending are prone to volatilization and precipitation to the surface, leading to loss of the anti-aging function of the film, and significant extraction loss easily occurs in the solid-state polycondensation process; specifically, the technical solution of this invention is as follows: The functional polyester chips for polyester film are prepared by copolymerization reaction of dicarboxylic acid monomer, diol monomer and reactive multifunctional comonomer; wherein the dicarboxylic acid monomer is purified terephthalic acid, the diol monomer is ethylene glycol and the reactive multifunctional comonomer is 2-[2-hydroxy-4,6-bis(2-hydroxyethoxy)phenyl]-2H-benzotriazole.

[0004] Preferably, the amount of the reactive multifunctional comonomer added is 0.5 mol%-3.0 mol% of the total molar amount of purified terephthalic acid.

[0005] Preferably, it includes the following steps: Step 1: 2-(2H-benzotriazol-2-yl)benzene-1,3,5-triol and ethylene carbonate are reacted at a molar ratio of 1:2.0-1:2.5 with N,N-dimethylformamide as a solvent at 125°C and under the action of anhydrous potassium carbonate catalyst to obtain the reactive multifunctional comonomer. Purified terephthalic acid, ethylene glycol and the reactive multifunctional comonomer are added to a pulping tank and mixed evenly. A catalyst and an anti-complexation stabilizer are added, and esterification reaction is carried out at an absolute pressure of 0.15MPa-0.25MPa and a temperature of 240°C-260°C to obtain oligomers. Step 2: Under programmed gradient pressure reduction conditions, the oligomer obtained in Step 1 is heated to 275℃-285℃ at a heating rate of 10℃ / h, and then kept at this temperature for melt polycondensation reaction for 1.5-2.5 hours; after extrusion, water cooling, and pelletizing, amorphous functional polyester prepolymer chips are obtained. Step 3: The amorphous functional polyester prepolymer chips obtained in Step 2 are fed into a fluidized bed crystallizer and pre-crystallized at 160℃-170℃ for 1-2 hours to achieve a crystallinity of 35%-45%, resulting in crystalline chips. The crystalline chips are then fed into a solid-phase polycondensation reactor, where high-purity nitrogen is introduced and the solid-phase polycondensation reaction is carried out at 215℃-225℃ for 12-24 hours. After cooling to room temperature under nitrogen protection, the product is discharged to obtain functional polyester chips for polyester film.

[0006] Preferably, in step one, the total molar amount of ethylene glycol and the reactive multifunctional comonomer is denoted as total diol, and the molar ratio of the total diol to purified terephthalic acid is controlled at 1.1:1-1.3:1.

[0007] Preferably, the esterification catalyst is a titanium-based catalyst, and the anti-complexation stabilizer is a phosphite stabilizer.

[0008] Preferably, the titanium catalyst is tetrabutyl titanate, and the phosphite stabilizer is triphenyl phosphite.

[0009] Preferably, in step two, the programmed gradient depressurization condition is that the absolute pressure is gradually reduced from standard atmospheric pressure to below 100 Pa; the intrinsic viscosity of the resulting amorphous functional polyester prepolymer chips is 0.60 dL / g-0.65 dL / g.

[0010] Preferably, in step three, the dew point of the high-purity nitrogen gas is less than -40°C, and the gas-solid mass ratio when the high-purity nitrogen gas is introduced is 1.5:1-2.1:1; the intrinsic viscosity of the functional polyester chips for polyester film obtained is 0.85 dL / g-1.05 dL / g.

[0011] The beneficial effects of this invention are as follows: Functional groups are covalently bonded to the polyester backbone, solving the problems of volatilization and precipitation of small molecule additives; since the UV-resistant monomer has become part of the macromolecular skeleton, it will not be extracted in the solid-state polycondensation process purged with high-temperature and high-purity nitrogen, realizing the combination of functionalization and high viscosity; thereby improving the dimensional stability and mechanical strength of functional polyester chips at high temperatures. Detailed Implementation

[0012] The technical solutions in the embodiments of the present invention will be clearly and completely described below; the described embodiments are only 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.

[0013] Example 1: This example provides functional polyester chips for polyester film, specifically including the following steps: S1. Preparation of reactive multifunctional comonomer: 1.00 mol of 2-(2H-benzotriazol-2-yl)benzene-1,3,5-triol, 2.20 mol of ethylene carbonate, and 1.0 wt% anhydrous potassium carbonate of the triol were added to a reactor equipped with stirring, reflux condensation, and nitrogen protection. N,N-dimethylformamide was then added as a solvent, with the solvent amount being 4 times the mass of the triol. The temperature was raised to 125°C and held for 6 hours. After the reaction was completed, the temperature was lowered to 70°C, deionized water was added to precipitate the product, and the product was filtered. The filter cake was washed with ethanol and then dried under vacuum at 60°C for 12 hours to obtain 2-[2-hydroxy-4,6-bis(2-hydroxyethoxy)phenyl]-2H-benzotriazole, denoted as UV-M. This intermediate UV-M is a reactive multifunctional comonomer. The benzotriazole group in its molecular structure can effectively absorb ultraviolet light in the final product, while the two hydroxyethoxy groups can undergo a cocondensation reaction with the diacid monomer, thereby chemically attaching to the polyester backbone and avoiding loss during later processing and use. The product yielded 281.6 g, with a yield of 85.0%. The purity, determined by high-performance liquid chromatography (HPLC), was 98.6%. The structural confirmation data are as follows: ¹H NMR (400 MHz, DMSO-d6) δ (ppm): 11.2 (s, 1H, phenolic hydroxyl group), 8.05-7.42 (m, 4H, benzotriazole ring proton), 6.78 (d, 1H, benzene ring proton), 6.45 (d, 1H, benzene ring proton), 4.85 (t, 2H, fatty alcohol hydroxyl group), 4.10-3.75 (m, 8H, -OCH2CH2O-); MS (ESI) m / z: 332.1 [M+H]+, consistent with the theoretical structure of the target product. S2. Pulping and Esterification: 100 mol purified terephthalic acid, 118.5 mol ethylene glycol, and 1.5 mol UV-M were added to a pulping vessel and stirred until homogeneous to form a slurry. In this embodiment, stirring was performed at 200 rpm for 30 min. 30 ppm tetrabutyl titanate and 150 ppm triphenyl phosphite (based on Ti) were added. Esterification was carried out at an absolute pressure of 0.20 MPa and a temperature of 250 °C until the distillate water content reached 96.0% of the theoretical value, thus obtaining the esterified oligomer. The intermediate esterified oligomer serves as a direct precursor for subsequent polycondensation reactions. Its low degree of polymerization and the proportion of terminal hydroxyl groups provide a necessary foundation for the formation of subsequent long-chain molecules. In this embodiment, the molar ratio of total diol to purified terephthalic acid is 1.20:1. The appropriate alcohol-acid ratio helps to balance the esterification rate and the formation of the byproduct diethylene glycol, resulting in a basic oligomer with excellent overall performance. S3. Melt polycondensation: The esterified oligomer is transferred to a polycondensation reactor, and the pressure is gradually reduced from standard atmospheric pressure to 50 Pa within 60 min. The heating rate is controlled at 10 °C / h, and the temperature is held at 280 °C for 2.0 h. The product is then extruded, water-cooled, and pelletized to obtain amorphous functional polyester prepolymer chips. The intrinsic viscosity of the prepolymer is measured to be 0.62 dL / g. The intermediate amorphous functional polyester prepolymer chips have low crystallinity and a specific prepolymer intrinsic viscosity, which can provide a structural morphology that facilitates nitrogen diffusion and mass transfer for subsequent solid-phase polycondensation, thereby ensuring the efficient progress of solid-phase polycondensation. In this embodiment, the polycondensation pressure was reduced to 50 Pa and then heated to 280 °C for 2.0 hours. The combination of these parameters effectively promoted end-group polycondensation and timely eliminated small molecule byproducts, resulting in a prepolymer intrinsic viscosity of 0.62 dL / g. S4. Pre-crystallization and solid-state polycondensation: The prepolymer chips are fed into a fluidized bed crystallizer and treated at 165°C for 1.5 hours, resulting in a chip crystallinity of 38%. The crystallized chips are then fed into a solid-state polycondensation reactor, where high-purity nitrogen gas with a dew point of -45°C is introduced at a gas-to-solid mass ratio of 1.8:1, and the reaction is carried out at 220°C for 16 hours. The product is then cooled and discharged to obtain functional polyester chips. In this embodiment, the pre-crystallization temperature is 165°C and the gas-to-solid mass ratio is 1.8:1. These process parameters ensure that the chips achieve a crystallinity of 38% before solid-state polycondensation.

[0014] Example 2: This example provides functional polyester chips for polyester film, specifically including the following steps: The preparation of S1 and UV-M is the same as in Example 1; S2. Pulping and Esterification: 100 mol purified terephthalic acid, 109.5 mol ethylene glycol, and 0.5 mol UV-M were added to a pulping vessel; the molar ratio of total diol to purified terephthalic acid was 1.10:1; 25 ppm tetrabutyl titanate and 120 ppm triphenyl phosphite (based on Ti) were added, and esterification was carried out at an absolute pressure of 0.15 MPa and a temperature of 240°C until the amount of water distilled reached 95.0% of the theoretical value, thus obtaining the esterified oligomer. In this embodiment, a lower molar ratio of total diol to purified terephthalic acid of 1.10:1, as well as a lower absolute esterification pressure of 0.15 MPa and a temperature of 240°C, were used. These parameter differences can effectively reduce the probability of side reactions in the system. Although the esterification time may be slightly prolonged, the desired esterified oligomer precursor can still be obtained stably. S3, Melt Polycondensation: Under programmed gradient depressurization, the pressure is reduced to 90 Pa, and the temperature is increased to 275°C at a rate of 10°C / hour, and held for 1.5 hours; extrusion, water cooling, and pelletizing are performed to obtain prepolymer chips with an intrinsic viscosity of 0.60 dL / g; In this embodiment, the polycondensation pressure is reduced to 90 Pa, and the temperature is increased to 275°C and held for 1.5 hours. Compared with Example 1, these parameter settings result in a slight decrease in the intrinsic viscosity of the prepolymer to 0.60 dL / g, but it still meets the basic requirements for subsequent pre-crystallization and solid-phase polycondensation; S4. Pre-crystallization and solid-state polycondensation: Pre-crystallization was performed at 160℃ for 1.0 hour, resulting in a crystallinity of 35% for the chips; solid-state polycondensation was then carried out at 215℃ for 12 hours, with a nitrogen dew point of -42℃ and a gas-to-solid mass ratio of 1.6:1, to obtain functional polyester chips. In this embodiment, the pre-crystallization temperature was 160℃ and the gas-to-solid mass ratio was 1.6:1. Combined with the above parameters, the intrinsic viscosity of the chips after solid-state polycondensation reached 0.86 dL / g. While ensuring a certain level of UV aging resistance, the reaction energy consumption was also taken into account, achieving optimization of the core results.

[0015] Example 3: This example provides functional polyester chips for polyester film, specifically including the following steps: The preparation of S1 and UV-M is the same as in Example 1; S2. Pulping and Esterification: 100 mol purified terephthalic acid, 121.0 mol ethylene glycol, and 2.0 mol UV-M were added to a pulping vessel; the molar ratio of total diol to purified terephthalic acid was 1.23:1; 35 ppm tetrabutyl titanate and 160 ppm triphenyl phosphite (based on Ti) were added, and esterification was carried out at an absolute pressure of 0.22 MPa and a temperature of 255°C until the amount of water distilled reached 96.5% of the theoretical value, thus obtaining the esterified oligomer. In this embodiment, a higher molar ratio of total diol to purified terephthalic acid of 1.23:1, as well as a higher absolute esterification pressure of 0.22 MPa and a temperature of 255°C, were used. These parameter differences were designed to accelerate the esterification reaction process, improve esterification efficiency, and thus quickly obtain the desired esterified oligomer. S3, Melt Polycondensation: Under programmed gradient depressurization, the pressure was reduced to 40 Pa, and the temperature was increased to 282°C at a rate of 10°C / hour, and held for 2.2 hours; extrusion, water cooling, and pelletizing were performed to obtain prepolymer chips with an intrinsic viscosity of 0.64 dL / g; In this embodiment, the polycondensation pressure was further reduced to 40 Pa, and the temperature was increased to 282°C and held for 2.2 hours. Compared with Example 1, the lower polycondensation pressure and the higher temperature and holding time effectively improved the removal rate of small molecule byproducts, resulting in an increase in the intrinsic viscosity of the prepolymer to 0.64 dL / g; S4. Pre-crystallization and solid-state polycondensation: Pre-crystallization was performed at 168℃ for 1.8 hours, resulting in a crystallinity of 41% for the chips; solid-state polycondensation was then carried out at 222℃ for 18 hours, with a nitrogen dew point of -48℃ and a gas-to-solid mass ratio of 2.0:1, yielding functional polyester chips. In this embodiment, the pre-crystallization temperature was 168℃ and the gas-to-solid mass ratio was 2.0:1. Combined with these high process parameters, the final crystallinity of the chips reached 41%, and the intrinsic viscosity after solid-state polycondensation was as high as 0.96 dL / g, significantly improving the mechanical properties and weather resistance of the chips, demonstrating a good optimization effect on the core results within this parameter range.

[0016] Example 4: This example provides functional polyester chips for polyester film, specifically including the following steps: The preparation of S1 and UV-M is the same as in Example 1; S2. Pulping and Esterification: 100 mol purified terephthalic acid, 127.0 mol ethylene glycol and 3.0 mol UV-M were added to a pulping vessel; the molar ratio of total diol to purified terephthalic acid was 1.30:1; 30 ppm tetrabutyl titanate and 150 ppm triphenyl phosphite (based on Ti) were added, and esterification was carried out at an absolute pressure of 0.25 MPa and a temperature of 260 °C until the amount of water distilled reached 95.5% of the theoretical value, thus obtaining the esterified oligomer. S3, Melt polycondensation: Under programmed gradient depressurization, the pressure is reduced to 70 Pa, the temperature is increased to 285 °C at 10 °C / hour, and held for 2.5 hours; extrusion, water cooling, and pelletizing are performed to obtain prepolymer chips with an intrinsic viscosity of 0.63 dL / g; S4. Pre-crystallization and solid-state polycondensation: Pre-crystallization was carried out at 170℃ for 2.0 hours, and the crystallinity of the chips was 36%; solid-state polycondensation was carried out at 225℃ for 24 hours, with a nitrogen dew point of -46℃ and a gas-solid mass ratio of 2.1:1; functional polyester chips were obtained.

[0017] Comparative Example 1: The difference between this comparative example and Example 1 is that UV-M is not added in step S2, and the other operation steps and process parameters are exactly the same as in Example 1; the obtained slices are polyethylene terephthalate slices without benzotriazole structure.

[0018] Comparative Example 2: The difference between this comparative example and Example 1 is that UV-M is not added in step S2, but instead, an equal molar amount of benzotriazole small molecule UV absorber 2-(2H-benzotriazole-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol is added before extrusion in step S3. Other operating steps and process parameters are exactly the same as in Example 1.

[0019] Comparative Example 3: The difference between this comparative example and Example 1 is that the esterification catalyst in step S2 is replaced by tetrabutyl titanate with an equal molar amount of antimony trioxide, while the other operating steps and process parameters are exactly the same as in Example 1.

[0020] Comparative Example 4: The difference between this comparative example and Example 1 is that triphenyl phosphite is not added in step S2, while the other operating steps and process parameters are exactly the same as in Example 1.

[0021] Comparative Example 5: The difference between this comparative example and Example 1 is that the pre-crystallization treatment in step S4 is omitted, and the prepolymer slices are directly fed into the solid-phase polycondensation reactor. Other operating steps and process parameters are exactly the same as in Example 1.

[0022] Comparative Example 6: The difference between this comparative example and Example 1 is that the amount of UV-M added in step S2 is increased from 1.5 mol% to 4.0 mol%, while the other operating steps and process parameters are exactly the same as in Example 1.

[0023] Performance Testing and Datasheets The intrinsic viscosity was measured at 25°C using a mixed solvent of phenol and 1,1,2,2-tetrachloroethane in a mass ratio of 60:40. The glass transition temperature and melting point were determined using differential scanning calorimetry (DSC). The crystallinity of the slices was calculated using DSC. The transmittance and yellow index of the film were determined according to GB / T2410 standard. The elongation at break was determined according to GB / T1040 standard. The slices were melt-extruded and biaxially stretched to form 50 μm films, which underwent 1000 hours of UV aging testing in a UV fluorescence accelerated aging chamber. The lamp was UVB-313, the chamber temperature was 60°C, and the irradiance was 0.71 W / m². The extraction loss rate was calculated as the percentage of the theoretically added UV-absorbing component in the extract after 24 hours of Soxhlet extraction in chloroform. Sample data are as follows: Table 1 Performance test data for each embodiment and comparative example As can be seen from the comparison of the test results of Example 1 and Comparative Example 1 in Table 1, omitting UV-M will lead to a significant decrease in the UV aging resistance of the film, as shown by the light transmittance decreasing from 91.0% to 78.4% after 1000 hours, ΔYI increasing from 1.4 to 8.7, and the elongation at break retention decreasing from 93% to 61%. The mechanism of action is that, in Example 1, the benzotriazole structure is chemically bonded to the polyester backbone, which can absorb high-energy light under ultraviolet irradiation and inhibit photo-oxidative chain breakage through intramolecular energy dissipation; in Comparative Example 1, the molecular chain does not contain this absorption structure, and the ester bonds and end groups in the polyester backbone are more prone to photo-oxidation reactions, leading to the accumulation of carbonyl groups and chromophores, thus aggravating yellowing, reducing light transmittance, and reducing mechanical retention; at the same time, the glass transition temperature of Example 1 is higher than that of Comparative Example 1, indicating that the rigid aromatic heterocyclic structure also restricts chain segment movement; As can be seen from the comparison of the test results of Example 1 and Comparative Example 2 in Table 1, after the reactive comonomer was replaced with a physically blended small molecule UV absorber, the intrinsic viscosity after solid-phase polycondensation decreased from 0.92 dL / g to 0.84 dL / g, the extraction loss rate reached 64.5%, and the weather resistance also decreased significantly. Its mechanism of action is that the small molecule absorbent does not enter the polyester backbone and will volatilize, migrate and be carried out by nitrogen during the melt polycondensation and solid-phase polycondensation stages, resulting in a decrease in the actual amount retained; the residual small molecules will also occupy the free volume and interfere with the contact of the end groups in the solid phase, leading to a decrease in the chain growth efficiency of solid-phase polycondensation; in Example 1, UV-M is covalently bonded to the polyester chain and is not easily lost under extraction and high-temperature nitrogen purging conditions, so the intrinsic viscosity and weather resistance are maintained at a high level. As can be seen from the comparison of the test results of Example 1 and Comparative Example 3 in Table 1, after replacing the titanium-based esterification catalyst with antimony trioxide, the intrinsic viscosity of the prepolymer decreased from 0.62 dL / g to 0.56 dL / g, and the intrinsic viscosity after solid-phase polycondensation decreased from 0.92 dL / g to 0.79 dL / g, and the crystallinity also decreased. Its mechanism of action is that the nitrogen-containing heterocycle of benzotriazole is prone to coordination with some metal centers, changing the effective concentration of catalytic active sites; titanium-based catalysts are more suitable for the esterification and polycondensation reactions of this system and can maintain a high reaction rate under UV-M conditions; when antimony trioxide is used, the coordination effect is more obvious, the molecular weight of oligomers is lower, the end group distribution is not conducive to the subsequent solid-phase chain growth, so the improvement of intrinsic viscosity is limited, and a small amount of sticky particles appear. As can be seen from the comparison of the test results of Example 1 and Comparative Example 4 in Table 1, after omitting triphenyl phosphite, the intrinsic viscosity after solid-phase polycondensation decreased from 0.92 dL / g to 0.82 dL / g, ΔYI increased from 1.4 to 4.2, and the elongation at break retention decreased from 93% to 81%. Its mechanism of action is that phosphites can inhibit thermal oxidative degradation during high-temperature processing and reduce the adverse effects of nitrogen-containing comonomers on the catalytic center. Without this stabilizer, the system is more likely to form peroxides and colored byproducts, resulting in molecular chain breakage and color deepening. Therefore, the intrinsic viscosity, transmittance and mechanical retention after aging all decrease. As can be seen from the comparison of the test results of Example 1 and Comparative Example 5 in Table 1, after omitting the pre-crystallization treatment, the intrinsic viscosity after solid-phase polycondensation decreased from 0.92 dL / g to 0.71 dL / g, the crystallinity was only 11%, and obvious agglomeration occurred. Its mechanism of action is that when the prepolymer chips are in an amorphous state and approach the solid-state polycondensation temperature, the chain segments have strong mobility, the particle surface is easy to soften and they stick together, resulting in a decrease in effective specific surface area and obstruction of nitrogen mass transfer; after the particles agglomerate, the end-group polycondensation byproducts are difficult to remove in time, and the solid-state chain growth efficiency is significantly reduced; Example 1 controls the crystallinity at 38% so that the chips maintain the particle shape at 220°C, thereby ensuring the stable solid-state polycondensation. As can be seen from the comparison of the test results of Example 1 and Comparative Example 6 in Table 1, after increasing the UV-M addition amount to 4.0 mol%, the intrinsic viscosity after solid-phase polycondensation decreased to 0.74 dL / g, the crystallinity decreased to 18%, and severe agglomeration occurred. Its mechanism of action lies in the fact that UV-M contains large-volume rigid aromatic heterocycles and flexible ether chains. Appropriate introduction can increase the glass transition temperature and moderately inhibit the crystallization rate. When the amount added is too high, the regularity of the polyester chain is excessively destroyed, and the chips are difficult to form enough crystalline regions to maintain morphological stability at the solid-state polycondensation temperature. The particles are more likely to soften and agglomerate during the solid-state polycondensation stage, resulting in deterioration of mass transfer and end-group contact conditions, and difficulty in improving intrinsic viscosity. This result shows that controlling the molar addition of UV-M within the range of 0.5% to 3.0% as specified in this invention is more conducive to balancing the weather resistance of the material and the continuous feasibility of the solid-state polycondensation process.

[0024] The above are merely preferred 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. Functional polyester chips for polyester film, characterized in that: It is prepared by co-condensation reaction of dicarboxylic acid monomer, diol monomer and reactive multifunctional comonomer; wherein the dicarboxylic acid monomer is purified terephthalic acid, the diol monomer is ethylene glycol and the reactive multifunctional comonomer is 2-[2-hydroxy-4,6-bis(2-hydroxyethoxy)phenyl]-2H-benzotriazole.

2. The functional polyester chip for polyester film according to claim 1, characterized in that: The amount of the reactive multifunctional comonomer added is 0.5 mol%-3.0 mol% of the total molar amount of purified terephthalic acid.

3. A solid-state polycondensation process for functional polyester chips for polyester films as described in claim 1 or 2, characterized in that, Includes the following steps: Step 1: 2-(2H-benzotriazol-2-yl)benzene-1,3,5-triol and ethylene carbonate are reacted at a molar ratio of 1:2.0-1:2.5 with N,N-dimethylformamide as a solvent at 125°C and under the action of anhydrous potassium carbonate catalyst to obtain the reactive multifunctional comonomer. Purified terephthalic acid, ethylene glycol and the reactive multifunctional comonomer are added to a pulping tank and mixed evenly. A catalyst and an anti-complexation stabilizer are added, and esterification reaction is carried out at an absolute pressure of 0.15MPa-0.25MPa and a temperature of 240°C-260°C to obtain oligomers. Step 2: Under programmed gradient depressurization, the oligomer obtained in Step 1 is heated to 275℃-285℃ at a rate of 10℃ / h, and then kept at this temperature for melt polycondensation reaction for 1.5 hours to 2.5 hours. Amorphous functional polyester prepolymer chips were obtained by extrusion, water cooling, and pelletizing. Step 3: The amorphous functional polyester prepolymer chips obtained in Step 2 are fed into a fluidized bed crystallizer and pre-crystallized at 160℃-170℃ for 1-2 hours to achieve a crystallinity of 35%-45%, resulting in crystalline chips. The crystalline chips are then fed into a solid-phase polycondensation reactor, where high-purity nitrogen is introduced and the solid-phase polycondensation reaction is carried out at 215℃-225℃ for 12-24 hours. After cooling to room temperature under nitrogen protection, the product is discharged to obtain functional polyester chips for polyester film.

4. The solid-state polycondensation process for functional polyester chips for polyester film according to claim 3, characterized in that: In step one, the total molar amount of ethylene glycol and the reactive multifunctional comonomer is denoted as total diol, and the molar ratio of total diol to purified terephthalic acid is controlled at 1.1:1-1.3:

1.

5. The solid-state polycondensation process for functional polyester chips for polyester film according to claim 3, characterized in that: In step one, the esterification catalyst is a titanium-based catalyst, and the anti-complexation stabilizer is a phosphite stabilizer.

6. The solid-state polycondensation process for functional polyester chips for polyester film according to claim 5, characterized in that: The titanium-based catalyst is tetrabutyl titanate, and the phosphite stabilizer is triphenyl phosphite.

7. The solid-state polycondensation process for functional polyester chips for polyester film according to claim 3, characterized in that: In step two, the programmed gradient depressurization condition is that the absolute pressure is gradually reduced from standard atmospheric pressure to below 100 Pa; the intrinsic viscosity of the resulting amorphous functional polyester prepolymer chips is 0.60 dL / g-0.65 dL / g.

8. The solid-state polycondensation process for functional polyester chips for polyester film according to claim 3, characterized in that: In step three, the dew point of the high-purity nitrogen gas is less than -40°C, and the gas-solid mass ratio when the high-purity nitrogen gas is introduced is 1.5:1-2.1:1; the intrinsic viscosity of the functional polyester chips used for polyester film is 0.85 dL / g-1.05 dL / g.

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