Polyester film with high CTI value and preparation method thereof

Abstract

The invention relates to a polyester film with a high CTI value and a preparation method thereof, and belongs to the technical field of polyesters, the polyester film provided by the invention is a three-layer structure film composed of a surface layer, a core layer and a surface layer, raw materials participating in preparation of the surface layer and the core layer comprise high-CTI modified polyester chips, and modified silicon dioxide is added for modification during preparation. The preparation method of the modified silicon dioxide comprises the following steps: S1, polymerizing dopamine hydrochloride to coat silicon dioxide; s2, carrying out exchange reaction on allyl alcohol and 3-urea propyl trimethoxy silane to synthesize a urea-based tracking-resistant agent; s3, under the action of an initiator, synthesizing a polymeric urea-based anti-creepage tracking agent; and S4, surface modification of the polymerized carbamido anti-creepage tracking agent. The polyester film provided by the invention is high in CTI value and high in tracking resistance, the probability of surface electric leakage and insulation failure can be greatly reduced, the application scene of the polyester film in household appliance products is widened, and the market competitiveness is improved.

Description

Technical Field

[0001] This invention belongs to the field of polyester technology, specifically relating to a high CTI value polyester film and its preparation method. Background Technology

[0002] In household appliances, insulating materials are typically subjected to a combination of electrical charge, heat, and complex environmental conditions over extended periods, inevitably leading to the accumulation of contaminants such as dust, oil, and moisture on their surfaces. Under the influence of an electric field, these conductive or semi-conductive contaminants can easily form leakage current paths on the surface of the insulating material, potentially causing surface creep, short circuits, or even fires. Therefore, resistance to tracking has become a crucial indicator for evaluating the safety of insulating materials used in household appliances. The CTI value, as a key characterization parameter, reflects the material's ability to resist tracking under harsh conditions such as humidity and pollution.

[0003] Polyester film, due to its good mechanical strength, heat resistance, electrical insulation, and processing properties, is widely used in insulation layers and insulating sheets in household appliances. However, conventional polyester film still has certain shortcomings in resistance to tracking, with its CTI value generally being low. In actual use environments, when its surface is contaminated and damp, continuous leakage can easily form between electrodes, leading to surface carbonization and corrosion, gradually forming conductive marks, thus significantly reducing insulation reliability. For household appliances operating at high voltages or running continuously for extended periods, polyester film with a low CTI value cannot meet the design requirements for higher safety levels, limiting its application in complex environments and scenarios with high safety requirements. Summary of the Invention

[0004] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a polyester film with a high CTI value and a method for preparing the same, thus solving the problems mentioned in the background section.

[0005] (II) Technical Solution To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, a high CTI value polyester film is provided, wherein the polyester film is a three-layer structure consisting of a surface layer, a core layer, and another surface layer; the thickness of the surface layer accounts for 10-20% of the thickness of the polyester film; the thickness of the polyester film is 12-50 μm; the raw materials for preparing the surface layer include, by weight percentage, 70-100% high CTI modified polyester chips and 0-30% high gloss polyester chips; the raw materials for preparing the core layer include, by weight percentage, 10-50% high gloss polyester chips and 50-90% high CTI modified polyester chips.

[0006] In a preferred embodiment of the present invention, the method for preparing the high CTI modified polyester chips includes the following steps: Purified terephthalic acid, ethylene glycol, and catalyst are esterified in a reactor under a nitrogen atmosphere until the esterification rate reaches 95-96.5%. Additives and modified silica are added, and the reaction is accelerated to reduce the pressure. The product is then discharged, cast into strips, cooled, and pelletized. After dehydration, a rotary drum solid-phase thickening device is used to thicken the product until the intrinsic viscosity reaches 0.75-0.85 dL / g.

[0007] Specifically, the weight ratio of the purified terephthalic acid, the ethylene glycol, the catalyst, the additive, and the modified silica is 50-60:22-27:0.01-0.014:0.005-0.01:0.8-1.1; the catalyst is at least one of antimony-based catalysts and titanium-based catalysts; and the additive is at least one of triphenyl phosphite and triphenyl phosphate.

[0008] Specifically, the esterification reaction is carried out at a temperature of 220-250°C and a pressure of 0.2-0.3 MPa; the compression polymerization is carried out at a temperature of 278-282°C, a vacuum of 50-80 Pa, and a time of 90-120 min.

[0009] Specifically, the method for preparing the modified silica includes the following steps: Step S1: Disperse silica and Tris-HCl buffer under sonication, add dopamine hydrochloride, and stir the reaction under controlled temperature for the first time. After centrifugation, collect the precipitate, wash with deionized water and dry to obtain coated silica. Step S2: Under a nitrogen atmosphere, allyl alcohol, 3-ureapropyltrimethoxysilane and toluene are mixed by temperature-controlled stirring, tetrabutyl titanate is added, and the reaction is carried out by temperature-controlled stirring for a second time. The volatiles are distilled off, and the reaction is carried out by temperature-controlled stirring for a third time. After purification, urea-based anti-tracking agent is obtained. Step S3: Under a nitrogen atmosphere, the urea-based anti-tracking agent, azobisisobutyronitrile and N,N-dimethylformamide are stirred and reacted for the fourth time under controlled temperature. After standing, the solid phase is filtered out, washed with toluene and dried to obtain the polymeric urea-based anti-tracking agent. Step S4: Under a nitrogen atmosphere, the polymeric urea-based anti-tracking agent, coated silica, and dimethyl sulfoxide aqueous solution are stirred for the fifth time under controlled temperature. After centrifugation, the precipitate is collected, washed with deionized water, and then dried.

[0010] In step S1, the weight ratio of silica, Tris-HCl buffer solution, and dopamine hydrochloride is 2.6-3.8:192-215:4.5-5.2.

[0011] In step S1, the stirring and dispersion refers to stirring at 25°C for 20-80 minutes; the gas atmosphere for stirring and dispersion is nitrogen or air; the first temperature-controlled stirring reaction refers to reflux stirring at 25-40°C for 12-24 hours; the gas atmosphere for the first temperature-controlled stirring reaction is air.

[0012] In step S2, the weight ratio of allyl alcohol to toluene is 10-17:220-238; the molar ratio of allyl alcohol to 3-ureapropyltrimethoxysilane is 1-2:1; and the amount of tetrabutyl titanate used is 0.3-1% of the total weight of allyl alcohol and 3-ureapropyltrimethoxysilane.

[0013] Specifically, step S2, temperature-controlled stirring and mixing, refers to mixing under reflux at 30-48℃ for 5-15 minutes; the second temperature-controlled stirring reaction refers to mixing under reflux at 75-82℃ for 2.5-3 hours; and the third temperature-controlled stirring reaction refers to mixing under reflux at 75-82℃ for 2-2.5 hours.

[0014] In step S2, the distillation temperature is 85-90℃ and the time is 7-12 min; the purification refers to the process of removing low-boiling substances by vacuum distillation; the absolute pressure of vacuum distillation is 4-8 kPa, the temperature is 60-75℃, and the time is 40-60 min.

[0015] In step S3, the weight ratio of the urea-based tracking agent to the N,N-dimethylformamide is 6-6.6:135-155; and the weight ratio of the urea-based tracking agent to the azobisisobutyronitrile is 100-120:0.8.

[0016] The fourth temperature-controlled stirring reaction mentioned in step S3 refers to the reaction being refluxed and stirred at 80°C for 1-1.5 hours.

[0017] In step S4, the weight ratio of the polymeric urea-based anti-tracking agent, the coated silica, and the dimethyl sulfoxide aqueous solution is 0.4-0.9:1.5:150-170.

[0018] The fifth temperature-controlled stirring reaction in step S4 refers to the reaction being refluxed and stirred at 100-110℃ for 12-16 hours.

[0019] Secondly, a method for preparing a polyester film with a high CTI value, the method comprising the following steps: Step A1: After drying the raw materials for core layer preparation, melt extrusion is performed using a single-screw extruder to obtain core layer melt; Step A2: After drying the raw materials for the surface layer, melt extrusion is performed using a twin-screw extruder to obtain the surface layer melt; Step A3: The core melt and the surface melt are conveyed to the die head, merged and extruded, cast onto the cooling roller, bidirectionally stretched, shaped, pulled, corona-treated, and wound up.

[0020] In a preferred embodiment of the present invention, the temperature of the melt extrusion in step A1 is 255-275°C and the vacuum degree is 5-10 mbar.

[0021] In a preferred embodiment of the present invention, the temperature of the melt extrusion in step A2 is 265-280°C and the vacuum degree is 5-10 mbar.

[0022] In a preferred embodiment of the present invention, the temperature of the cooling roller in step A3 is 18-25°C.

[0023] In a preferred embodiment of the present invention, the corona discharge in step A3 refers to corona discharge to a surface wetting tension of 50-56 dynes.

[0024] When silica is dispersed in polyester material, it forms a continuous inorganic insulating phase. When the surface of the polyester film begins to form a conductive path under the influence of external factors, it will play a cutting and blocking role, inhibiting the development of tracking, thereby improving the CTI value of the polyester film and enhancing its resistance to tracking.

[0025] Silica is dispersed in polyester materials through in-situ composite methods, which not only improves the uniformity of dispersion but also adjusts the crystallinity of polyester, densifies the polyester film, and further promotes resistance to tracking.

[0026] Urea-based anti-tracking agents belong to the nitrogen-containing class of substances. They can capture free radicals generated during the tracking process, interrupting the continuous degradation reaction, thereby protecting the matrix molecular chains, reducing carbon layer accumulation, and improving the CTI value. Urea-based anti-tracking agents are produced through an exchange reaction. Not only are they nitrogen-containing substances, but they are also polymerizable monomers containing methoxy groups. Under the action of an initiator, they generate polymeric urea-based anti-tracking agents. According to the laws of kinetics and thermodynamics, high molecular weight substances generally have higher decomposition activation energies and are more difficult to thermally decompose. Therefore, they can be surface modified, and functional loss is avoided when they are in situ compounded with silica. The degree of polymerization of polymeric urea-based anti-tracking agents has a significant impact on the CTI value. A higher degree of polymerization is not always better. While excessively large molecular weight further increases the decomposition activation energy, the entanglement of the molecular chains can form agglomeration nuclei, reducing dispersion stability.

[0027] Dopamine hydrochloride polymerizes to form polydopamine (PDA), whose backbone is rich in aromatic rings and catechol. The methoxy groups of the polymeric urea-based anti-tracking agent undergo condensation reactions via hydroxyl functional groups after hydrolysis, achieving surface modification. PDA belongs to a conjugated π-electron system with a highly polarized electron cloud distribution, enabling the modified polymeric urea-based anti-tracking agent to form a deeper electron potential trap, significantly increasing its sensitivity to free radicals and improving its capture ability.

[0028] (III) Beneficial Effects of the Technical Solution This invention provides a polyester film with a high CTI value and strong resistance to tracking, which can meet higher safety design requirements. It not only broadens the application scenarios in household appliances, but is also applicable to other fields without significant application limitations. Detailed Implementation

[0029] To better illustrate the objectives, technical solutions, and advantages of this invention, the invention will be further described below with reference to specific embodiments. Those skilled in the art should understand that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0030] Unless otherwise specified, all raw materials used in the following examples and comparative examples are commercially available general materials; in particular, the pH of the Tris-HCl buffer is 8.3, the grade of the Dayouguang polyester chips is FG600 (Sinopec), and the type of silica is M757694 (Maclean). To further clarify, the centrifugation temperature was 25℃, the rotation speed was 10000rpm, and the time was 10min; the thickness of the upper and lower surfaces was the same; the drying temperature in step S1 was 80℃ and the time was 24h; the drying temperature in step S3 was 60℃ and the time was 24h; the drying temperature in step S4 was 100℃ and the time was 24h; steps A1 and A2 were dried until the moisture content was below 50ppm.

[0031] Example 1 A high CTI value polyester film, wherein the polyester film is a three-layer structure consisting of a surface layer, a core layer, and another surface layer; the thickness of the two surface layers accounts for 14% of the thickness of the polyester film; the thickness of the polyester film is 40 μm; the raw materials for preparing the surface layer include 80% high CTI modified polyester chips and 20% high gloss polyester chips by weight percentage; the raw materials for preparing the core layer include 10% high gloss polyester chips and 90% high CTI modified polyester chips by weight percentage.

[0032] The preparation method of the high CTI modified polyester chips includes the following steps: 60 parts by weight of purified terephthalic acid, 25 parts by weight of ethylene glycol, and 0.01 parts by weight of tetrabutyl titanate were esterified in a reactor under nitrogen atmosphere until the esterification rate reached 95%. Then, 0.01 parts by weight of triphenyl phosphate and 0.8 parts by weight of modified silica were added, followed by reduced-pressure polymerization. The mixture was discharged, cast into strips, cooled, and pelletized. Water was removed until the moisture content reached 50 ppm. Thickening was performed using a rotary drum solid-phase thickening device until the intrinsic viscosity reached 0.8 dL / g. The thickening temperature was 230℃, and the vacuum degree was 50 Pa. The esterification reaction temperature was 240℃, and the pressure was 0.2 MPa; the reduced-pressure polymerization temperature was 280℃, the vacuum degree was 50 Pa, and the time was 90 min.

[0033] The method for preparing the modified silica includes the following steps: Step S1: 2.6 parts by weight of silica and 200 parts by weight of Tris-HCl buffer were dispersed by stirring at 25°C under nitrogen atmosphere for 20 min under ultrasonication at 50 kHz. 4.5 parts by weight of dopamine hydrochloride were added and the mixture was refluxed under air atmosphere at 25°C for 12 h. After centrifugation, the precipitate was collected, washed with deionized water and dried to obtain coated silica.

[0034] Step S2: Under a nitrogen atmosphere, 12 parts by weight of allyl alcohol, 3-ureapropyltrimethoxysilane, and 220 parts by weight of toluene were mixed and refluxed at 35°C for 10 min. Butyl titanate was added, and the mixture was refluxed at 78°C for 2.5 h. The volatiles were removed by distillation at 85°C for 10 min, followed by reflux at 78°C for 2.5 h. Low-boiling substances were removed by vacuum distillation at an absolute pressure of 8 kPa, a temperature of 70°C, and a time of 45 min to obtain a urea-based anti-tracking agent. The molar ratio of allyl alcohol to 3-ureapropyltrimethoxysilane was 2:1. The amount of butyl titanate used was 0.5% of the total weight of allyl alcohol and 3-ureapropyltrimethoxysilane.

[0035] Step S3: Under a nitrogen atmosphere, 6.6 parts by weight of urea-based anti-tracking agent, azobisisobutyronitrile and 140 parts by weight of N,N-dimethylformamide are refluxed and stirred at 80°C for 1.2 h, allowed to stand at 25°C for 25 min, the solid phase is filtered out, washed with toluene and dried to obtain polymeric urea-based anti-tracking agent; the weight ratio of the urea-based anti-tracking agent to the azobisisobutyronitrile is 100:0.8.

[0036] Step S4: In a nitrogen atmosphere, 0.5 parts by weight of polymeric urea-based anti-tracking agent, 1.5 parts by weight of coated silica and 170 parts by weight of 99 wt% dimethyl sulfoxide aqueous solution are refluxed and stirred at 110°C for 12 h. After that, the mixture is centrifuged, the precipitate is collected, washed with deionized water and dried.

[0037] A method for preparing a polyester film with a high CTI value, the method comprising the following steps: Step A1: After drying the raw materials for the core layer, melt extrusion is performed using a single-screw extruder at a temperature of 270°C and a vacuum of 5 mbar to obtain the core layer melt. Step A2: After drying the raw material for the surface layer, melt extrusion is performed using a twin-screw extruder at a temperature of 280°C and a vacuum of 5 mbar to obtain the surface melt. Step A3: The core melt and the surface melt are conveyed to the die head, combined and extruded, cast onto a cooling roller at 25°C, biaxially stretched, shaped, pulled, corona-electrode until the surface wetting tension is 50 dynes, and then wound up.

[0038] Example 2 A high CTI value polyester film, wherein the polyester film is a three-layer structure consisting of a surface layer, a core layer, and another surface layer; the thickness of the two surface layers accounts for 20% of the thickness of the polyester film; the thickness of the polyester film is 50 μm; the raw materials for preparing the surface layer include 90% high CTI modified polyester chips and 10% high gloss polyester chips by weight percentage; the raw materials for preparing the core layer include 15% high gloss polyester chips and 85% high CTI modified polyester chips by weight percentage.

[0039] The preparation method of the high CTI modified polyester chips includes the following steps: 60 parts by weight of purified terephthalic acid, 24 parts by weight of ethylene glycol, and 0.012 parts by weight of tetrabutyl titanate were esterified in a reactor under nitrogen atmosphere until the esterification rate reached 96%. Then, 0.01 parts by weight of triphenyl phosphate and 1 part by weight of modified silica were added, followed by reduced-pressure polymerization. The mixture was discharged, cast into strips, cooled, and pelletized. Water was removed until the moisture content was 50 ppm. Thickening was performed using a rotary drum solid-phase thickening device until the intrinsic viscosity reached 0.82 dL / g. The thickening temperature was 225℃, and the vacuum degree was 50 Pa. The esterification reaction temperature was 245℃, and the pressure was 0.3 MPa; the reduced-pressure polymerization temperature was 280℃, the vacuum degree was 50 Pa, and the time was 100 min.

[0040] The method for preparing the modified silica includes the following steps: Step S1: 3.5 parts by weight of silica and 215 parts by weight of Tris-HCl buffer were dispersed by stirring at 25°C under nitrogen atmosphere for 30 min under ultrasonication at 50 kHz. 4.8 parts by weight of dopamine hydrochloride were added and the mixture was refluxed under air atmosphere at 30°C for 18 h. After centrifugation, the precipitate was collected, washed with deionized water and dried to obtain coated silica.

[0041] Step S2: Under a nitrogen atmosphere, 15 parts by weight of allyl alcohol, 3-ureapropyltrimethoxysilane, and 230 parts by weight of toluene are mixed and refluxed at 35°C for 15 min. Butyl titanate is added, and the mixture is refluxed at 80°C for 3 h. The volatiles are removed by distillation at 85°C for 12 min, followed by refluxed at 80°C for 2 h. Low-boiling substances are removed by vacuum distillation at an absolute pressure of 6 kPa, a temperature of 75°C, and a time of 50 min, yielding a urea-based anti-tracking agent. The molar ratio of allyl alcohol to 3-ureapropyltrimethoxysilane is 1.8:1. The amount of butyl titanate used is 0.6% of the total weight of allyl alcohol and 3-ureapropyltrimethoxysilane.

[0042] Step S3: Under a nitrogen atmosphere, 6 parts by weight of urea-based anti-tracking agent, azobisisobutyronitrile and 150 parts by weight of N,N-dimethylformamide are refluxed and stirred at 80°C for 1.5 h, allowed to stand at 25°C for 30 min, the solid phase is filtered out, washed with toluene and dried to obtain polymeric urea-based anti-tracking agent; the weight ratio of the urea-based anti-tracking agent to the azobisisobutyronitrile is 120:0.8.

[0043] Step S4: In a nitrogen atmosphere, 0.6 parts by weight of polymeric urea-based anti-tracking agent, 1.5 parts by weight of coated silica and 170 parts by weight of 99 wt% dimethyl sulfoxide aqueous solution are refluxed and stirred at 100°C for 16 h. After that, the mixture is centrifuged, the precipitate is collected, washed with deionized water and dried.

[0044] A method for preparing a polyester film with a high CTI value, the method comprising the following steps: Step A1: After drying the raw materials for core layer preparation, melt extrusion is performed using a single-screw extruder. The melt extrusion temperature is 275℃ and the vacuum degree is 5mbar to obtain the core layer melt. Step A2: After drying the raw material for the surface layer, melt extrusion is performed using a twin-screw extruder at a temperature of 275°C and a vacuum of 5 mbar to obtain the surface melt. Step A3: The core melt and the surface melt are conveyed to the die head, merged and extruded, cast onto a cooling roller at 20°C, biaxially stretched, shaped, pulled, corona-electrode until the surface wetting tension is 52 dynes, and then wound up.

[0045] Comparative Example 1 A high CTI value polyester film and its preparation method are carried out according to the method in Example 2, except that step S4 is changed to: in a nitrogen atmosphere, 0.6 parts by weight of polymeric urea-based anti-tracking agent and 1.5 parts by weight of coated silica are mixed evenly.

[0046] Comparative Example 2 A high CTI value polyester film and its preparation method are carried out according to the method in Example 2, except that step S4 is changed to: under a nitrogen atmosphere, 0.6 parts by weight of urea-based anti-tracking agent, 1.5 parts by weight of coated silica and 170 parts by weight of 99 wt% dimethyl sulfoxide aqueous solution are refluxed and stirred at 100°C for 16 h, then centrifuged, the precipitate is collected, washed with deionized water and dried. Step S3 is not performed.

[0047] Comparative Example 3 A high CTI value polyester film and its preparation method are carried out according to the method in Example 2, except that step S4 is changed to: under a nitrogen atmosphere, 0.6 parts by weight of polymeric urea-based anti-tracking agent, 1.5 parts by weight of silica and 170 parts by weight of 99 wt% dimethyl sulfoxide aqueous solution are refluxed and stirred at 100°C for 16 h, then centrifuged, the precipitate is collected, washed with deionized water and dried. Step S1 is not performed.

[0048] Comparative Example 4 A polyester film with a high CTI value and its preparation method are carried out according to the method in Example 2, except that the weight ratio of the urea-based anti-tracking agent and the azobisisobutyronitrile is changed to 125:0.8.

[0049] Comparative Example 5 A polyester film with a high CTI value and its preparation method are carried out according to the method in Example 2, except that the weight ratio of the urea-based anti-tracking agent and the azobisisobutyronitrile is changed to 130:0.8.

[0050] Example 3 A high CTI value polyester film, wherein the polyester film is a three-layer structure consisting of a surface layer, a core layer, and another surface layer; the thickness of the two surface layers accounts for 20% of the thickness of the polyester film; the thickness of the polyester film is 20 μm; the raw materials for preparing the surface layer include 70% high CTI modified polyester chips and 30% high gloss polyester chips by weight percentage; the raw materials for preparing the core layer include 50% high gloss polyester chips and 50% high CTI modified polyester chips by weight percentage.

[0051] The preparation method of the high CTI modified polyester chips includes the following steps: 60 parts by weight of purified terephthalic acid, 27 parts by weight of ethylene glycol, and 0.014 parts by weight of tetrabutyl titanate were esterified in a reactor under nitrogen atmosphere until the esterification rate reached 96.5%. Then, 0.01 parts by weight of triphenyl phosphate and 1.1 parts by weight of modified silica were added, followed by reduced-pressure polymerization. The mixture was discharged, cast into strips, cooled, and pelletized. Water was removed until the moisture content was 50 ppm. Thickening was then performed using a rotary drum solid-phase thickening device until the intrinsic viscosity reached 0.85 dL / g. The thickening temperature was 230℃ and the vacuum degree was 50 Pa. The esterification reaction temperature was 250℃ and the pressure was 0.3 MPa; the reduced-pressure polymerization temperature was 282℃, the vacuum degree was 80 Pa, and the time was 120 min.

[0052] The method for preparing the modified silica includes the following steps: Step S1: 3.8 parts by weight of silica and 215 parts by weight of Tris-HCl buffer were dispersed by sonication at 60 kHz and stirring at 25 °C in air for 80 min. 5.2 parts by weight of dopamine hydrochloride were added, and the mixture was refluxed and stirred at 40 °C in air for 24 h. After centrifugation, the precipitate was collected, washed with deionized water, and dried to obtain coated silica.

[0053] Step S2: Under a nitrogen atmosphere, 17 parts by weight of allyl alcohol, 3-ureapropyltrimethoxysilane, and 238 parts by weight of toluene were mixed and refluxed at 48°C for 15 min. Butyl titanate was added, and the mixture was refluxed at 82°C for 3 h. The volatiles were removed by distillation at 90°C for 7 min, followed by refluxed at 82°C for 2.5 h. Low-boiling substances were removed by vacuum distillation at an absolute pressure of 8 kPa, a temperature of 75°C, and a time of 60 min to obtain a urea-based anti-tracking agent. The molar ratio of allyl alcohol to 3-ureapropyltrimethoxysilane was 2:1. The amount of butyl titanate used was 1% of the total weight of allyl alcohol and 3-ureapropyltrimethoxysilane.

[0054] Step S3: Under a nitrogen atmosphere, 6.6 parts by weight of urea-based anti-tracking agent, azobisisobutyronitrile and 155 parts by weight of N,N-dimethylformamide are refluxed and stirred at 80°C for 1.5 h, allowed to stand at 25°C for 25 min, the solid phase is filtered out, washed with toluene and dried to obtain polymeric urea-based anti-tracking agent; the weight ratio of the urea-based anti-tracking agent to the azobisisobutyronitrile is 110:0.8.

[0055] Step S4: In a nitrogen atmosphere, 0.9 parts by weight of polymeric urea-based anti-tracking agent, 1.5 parts by weight of coated silica and 170 parts by weight of 99 wt% dimethyl sulfoxide aqueous solution are refluxed and stirred at 110°C for 16 h. After that, the mixture is centrifuged, the precipitate is collected, washed with deionized water and dried.

[0056] A method for preparing a polyester film with a high CTI value, the method comprising the following steps: Step A1: After drying the raw materials for the core layer, melt extrusion is performed using a single-screw extruder. The melt extrusion temperature is 275℃ and the vacuum degree is 10mbar to obtain the core layer melt. Step A2: After drying the raw material for the surface layer, melt extrusion is performed using a twin-screw extruder at a temperature of 280°C and a vacuum of 10 mbar to obtain the surface melt. Step A3: The core melt and the surface melt are conveyed to the die head, merged and extruded, cast onto a cooling roller at 18°C, biaxially stretched, shaped, pulled, corona-electrode until the surface wetting tension is 56 dynes, and then wound up.

[0057] CTI value test: The CTI values ​​of the polyester films of Example 2 and the comparative example above were tested according to the standard IEC60112:2003.

[0058] Table 1. CTI Values As shown in Table 1, the CTI value of Example 2 was 640V / 150 drops. The CTI values ​​of the comparative examples decreased, with Comparative Example 2 showing the largest decrease. This was mainly due to the thermal decomposition of the urea-based anti-tracking agent, which fundamentally affected its function. Secondly, Comparative Examples 1 and 3 could not effectively enhance the response sensitivity of the polymeric urea-based anti-tracking agent to free radicals through polydopamine, resulting in a decrease in the CTI value. Comparative Examples 4 and 5 increased the degree of polymerization of the polymeric urea-based anti-tracking agent, increasing the molecular weight, and the CTI value showed a gradual decreasing trend.

[0059] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0060] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

Claims

1. A polyester film with a high CTI value, characterized in that: The polyester film is a three-layer structure film consisting of a surface layer, a core layer, and another surface layer. The raw materials for preparing the surface layer include 70-100% high-CTI modified polyester chips and 0-30% high-brightness polyester chips by weight percentage. The raw materials for preparing the core layer include 10-50% high-brightness polyester chips and 50-90% high-CTI modified polyester chips by weight percentage.

2. The polyester film with a high CTI value according to claim 1, characterized in that: The thickness of the polyester film is 12-50 μm.

3. A high CTI value polyester film according to claim 1, characterized in that: The preparation method of the high CTI modified polyester chips includes the following steps: Purified terephthalic acid, ethylene glycol, and catalyst are esterified in a reactor. Additives and modified silica are added, and the reaction is accelerated to reduce pressure. The product is then discharged, cast into strips, cooled, pelletized, and dehydrated. Finally, a rotary drum-type solid-phase thickening device is used for thickening.

4. A high CTI value polyester film according to claim 3, characterized in that: The weight ratio of the purified terephthalic acid, the ethylene glycol, the catalyst, the additive, and the modified silica is 50-60:22-27:0.01-0.014:0.005-0.01:0.8-1.

1.

5. A high CTI value polyester film according to claim 3, characterized in that: The method for preparing the modified silica includes the following steps: Step S1: Disperse silica and Tris-HCl buffer under sonication, add dopamine hydrochloride, and stir the reaction under controlled temperature for the first time. After centrifugation, collect the precipitate, wash with deionized water and dry to obtain coated silica. Step S2: Under a nitrogen atmosphere, allyl alcohol, 3-ureapropyltrimethoxysilane and toluene are mixed by temperature-controlled stirring, tetrabutyl titanate is added, and the reaction is carried out by temperature-controlled stirring for a second time. Distillation is performed, and the reaction is carried out by temperature-controlled stirring for a third time. After purification, urea-based anti-tracking agent is obtained. Step S3: Under a nitrogen atmosphere, the urea-based anti-tracking agent, azobisisobutyronitrile and N,N-dimethylformamide are stirred and reacted for the fourth time under controlled temperature. After standing, the solid phase is filtered out, washed with toluene and dried to obtain the polymeric urea-based anti-tracking agent. Step S4: Under a nitrogen atmosphere, the polymeric urea-based anti-tracking agent, coated silica, and dimethyl sulfoxide aqueous solution are stirred for the fifth time under controlled temperature. After centrifugation, the precipitate is collected, washed with deionized water, and then dried.

6. A high CTI value polyester film according to claim 5, characterized in that: The weight ratio of silica, Tris-HCl buffer solution and dopamine hydrochloride in step S1 is 2.6-3.8:192-215:4.5-5.

2.

7. A high CTI value polyester film according to claim 5, characterized in that: In step S2, the weight ratio of allyl alcohol to toluene is 10-17:220-238; the molar ratio of allyl alcohol to 3-ureapropyltrimethoxysilane is 1-2:

1.

8. A high CTI value polyester film according to claim 5, characterized in that: In step S3, the weight ratio of the urea-based tracking agent to the N,N-dimethylformamide is 6-6.6:135-155; the weight ratio of the urea-based tracking agent to the azobisisobutyronitrile is 100-120:0.

8.

9. A high CTI value polyester film according to claim 5, characterized in that: The weight ratio of the polymeric urea-based anti-tracking agent, the coated silica, and the dimethyl sulfoxide aqueous solution in step S4 is 0.4-0.9:1.5:150-170.

10. A method for preparing a high CTI value polyester film according to any one of claims 1-9, characterized in that: The preparation method includes the following steps: Step A1: After drying the raw materials for core layer preparation, melt extrusion is performed using a single-screw extruder to obtain core layer melt; Step A2: After drying the raw materials for the surface layer, melt extrusion is performed using a twin-screw extruder to obtain the surface layer melt; Step A3: The core melt and the surface melt are conveyed to the die head, merged and extruded, cast onto the cooling roller, bidirectionally stretched, shaped, pulled, corona-treated, and wound up.

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