Thick polyester film and method for producing the same

Abstract

The application discloses a thick polyester film and a preparation method thereof, and relates to the technical field of polyester films. The preparation process is as follows: S1. 120-142 parts of a dicarboxylic acid composition, 160-188 parts of a dihydric alcohol composition, 2-6 parts of polyoxymethylene glycol, 5-8 parts of polytrimethylhexamethylene terephthalate, 1-3 parts of an antioxidant, 1.2-2 parts of a modified additive, 1-2 parts of a catalyst and 0.5-1.1 parts of a stabilizer are premixed and dried; S2. the raw materials are sent into an extruder to be melted and extruded, so that a polyester film is obtained; S3. a pair of compression rollers are arranged in parallel, the polyester film is sequentially subjected to longitudinal stretching and transverse stretching, and the thickness of the polyester film is stretched to 300-350 mu m; S4. the excess part on the front and rear sides of the polyester film after stretching is cut, and the surface of the polyester film is subjected to high-voltage corona treatment; and S5. the treated polyester film material is wound and formed. The thick polyester film prepared by the application has strong mechanical properties, high light transmittance and low haze.

Description

Technical Field

[0001] This application relates to the field of polyester film technology, and in particular to a thick polyester film and a method for preparing the same. Background Technology

[0002] Polyester film, due to its excellent mechanical properties, good dimensional stability, high transparency, and chemical resistance, is widely used in various industries, especially as protective films, reflective films, and diffusion films in medium and large flat panel displays where high optical performance is required. These types of films require polyester films to have high transparency, low haze, good smoothness, and a certain thickness, typically between 38-300 μm, while thick polyester films are usually between 120-3000 μm thick.

[0003] However, during the production of thick polyester films of about 300μm, the heat cannot be dissipated in time due to the excessive thickness of the cast sheet, resulting in a high crystallinity of the sheet formed by the melt. Consequently, the polyester film obtained after biaxial stretching has excessive haze and insufficient gloss. Summary of the Invention

[0004] In order to improve the light transmittance and reduce the haze value of thick polyester films, this application provides a thick polyester film and a method for preparing the same.

[0005] This application provides a thick polyester film, which adopts the following technical solution:

[0006] A thick polyester film and its preparation method are disclosed. The raw materials mainly include the following components: 120-142 parts of dicarboxylic acid composition, 160-188 parts of diol composition, 2-6 parts of polydecyl diamine, 5-8 parts of poly(trimethylhexamethylene terephthalamide), 1-3 parts of antioxidant, 1.2-2 parts of modifying additive, 1-2 parts of catalyst, and 0.5-1.1 parts of stabilizer; wherein the modifying additive is modified nano-silica.

[0007] By employing the above technical solution, a polyester film is prepared by copolymerizing a dicarboxylic acid composition and a diol composition. This reduces the regularity of the molecular chain. Simultaneously, the addition of polydecanoyldiamine and poly(trimethylhexamethylene terephthalamide) to the polyester molecule segments further reduces the regularity of the polyester molecular chain structure while increasing the spacing between the polyester molecules, thereby improving the transparency and brightness of the polyester film. Polydecanoyldiamine has high ductility, high tensile strength, and excellent impact and low-temperature performance, effectively improving the mechanical properties of the polyester film. Poly(trimethylhexamethylene terephthalamide) has high visible light transmittance, effectively suppressing the crystallinity of the polyester film, effectively increasing its light transmittance, and reducing its haze value.

[0008] Preferably, the dicarboxylic acid composition mainly comprises isophthalic acid, phthalic acid, and cyclohexanedicarboxylic acid, with a weight ratio of 1:(1-1.5):(0.6-1.2).

[0009] Preferably, the diol composition mainly comprises ethylene glycol, neopentyl glycol, and cyclohexanediol, with a weight ratio of 1:(0.5-0.9):(0.6-1.2).

[0010] By adopting the above technical solution, using a mixture of isophthalic acid, phthalic acid, and cyclohexanedicarboxylic acid as a dicarboxylic acid composition, and a mixture of ethylene glycol, neopentyl glycol, and cyclohexanediol as a diol composition, and using it for copolymerization to prepare polyester film, the regularity of polyester molecular chains can be effectively reduced, thereby improving the transparency and brightness of the polyester film.

[0011] Preferably, the antioxidant comprises 2,6-di-tert-butyl-4-methylphenol and phosphite in a weight ratio of 1:(2-4).

[0012] By adopting the above technical solution, using 2,6-di-tert-butyl-4-methylphenol and phosphite composite as antioxidants, the oxidation of various components in polyester film can be effectively inhibited, thereby effectively improving the mechanical properties, light transmittance and other properties of polyester film.

[0013] Preferably, the raw materials for the modified nano-silica mainly include: 2-3 parts nano-silica, 24-30 parts anhydrous ethanol, 10-15 parts silane coupling agent, and 20-30 parts deionized water.

[0014] By adopting the above technical solution, silica is modified with silane coupling agent. Some hydroxyl groups on the surface of silica are replaced by alkoxy groups of silane coupling agent, which weakens the hydrogen bonding between silica particles. The two particles are connected by Si-O-Si bonds, which effectively inhibits the agglomeration of silica, thereby better exerting the mechanical and optical properties of nano silica and improving the light transmittance and mechanical properties of polyester release film.

[0015] This application provides a method for preparing a thick polyester film, which adopts the following technical solution:

[0016] A method for preparing a thick polyester film, characterized by comprising the following steps:

[0017] S1. Premixing and drying: 120-142 parts of dicarboxylic acid composition, 160-188 parts of diol composition, 2-6 parts of polydecyl diamine, 5-8 parts of poly(trimethylhexamethylene terephthalamide), 1-3 parts of antioxidant, 1.2-2 parts of modifying additive, 1-2 parts of catalyst, and 0.5-1.1 parts of stabilizer are premixed and dried;

[0018] S2. Melt extrusion: The dried raw material is fed into an extruder to melt and extrude, resulting in a polyester film.

[0019] S3. Flat stretching: Place the pressure rollers in parallel and stretch the polyester film longitudinally and laterally in sequence to stretch the thickness of the polyester film to 300-350μm.

[0020] S4. Corona treatment: The excess parts on the front and back sides of the stretched polyester film are cut off, and the surface of the polyester film is subjected to high voltage corona treatment.

[0021] S5. Winding and Slitting: The corona-treated polyester film material is wound into shape, and the cutting device then cuts the winding drum of the polyester film evenly and at equal intervals and collects it.

[0022] By adopting the above technical solution and using the flat stretching process to prepare polyester film, the uniformity of stretching of thick polyester film can be effectively improved by placing the pressure rollers in parallel and increasing the holding force, thereby improving the mechanical properties and significantly increasing tensile strength and elongation at break.

[0023] Preferably, the longitudinal stretching includes the following steps:

[0024] The polyester film is preheated at 70-90℃, then heated in an infrared heating zone at 130-160℃, and longitudinally stretched at a linear velocity of 0.8-1.5m / s, followed by longitudinal relaxation at a linear velocity of 0.2-0.3m / s.

[0025] Preferably, the longitudinally stretched polyester film is preheated at 90-120°C, then heated in an infrared heating zone at 130-160°C, longitudinally stretched at a linear velocity of 1.0-1.8 m / s, then laterally relaxed at a linear velocity of 0.2-0.3 m / s, and then shaped.

[0026] Preferably, the method for preparing the modified nano-silica includes the following steps:

[0027] S1. Add 2-3 parts of nano-silica to 24-30 parts of anhydrous ethanol and mix, stirring until evenly dispersed to obtain a dispersion of nano-silica; add 10-15 parts of silane coupling agent to 20-30 parts of deionized water and stir for 1-2 hours to obtain an aqueous solution of silane coupling agent.

[0028] S2. Add the dispersion of nano-silica to the aqueous solution of silane coupling agent and stir evenly, and reflux at 60-80℃ for 2-4 hours; after the reaction is completed, wash, filter, dry and grind the product to obtain modified nano-silica powder.

[0029] By adopting the above technical solution, silica is modified with silane coupling agent. Some hydroxyl groups on the surface of silica are replaced by alkoxy groups of silane coupling agent, which weakens the hydrogen bonding between silica particles. The two particles are connected by Si-O-Si bonds, which effectively inhibits the agglomeration of silica, thereby better exerting the mechanical and optical properties of nano silica and improving the light transmittance and mechanical properties of polyester release film.

[0030] In summary, this application includes at least one of the following beneficial technical effects:

[0031] 1. By adopting the above technical solution, a polyester film is prepared by copolymerizing a dicarboxylic acid composition and a diol composition, which reduces the regularity of the molecular chain. At the same time, the addition of polydecanoyldiamine and polyterephthalamide to the polyester molecule segments further reduces the regularity of the polyester molecular chain structure and increases the spacing between the polyester molecules, thereby improving the transparency and brightness of the polyester film.

[0032] 2. Polydecyl dimethyl terephthalamide has high ductility, high tensile strength, and excellent impact and low-temperature properties, which can effectively improve the mechanical properties of polyester film; poly(trimethylhexamethylene terephthalamide) has high transmittance of visible light, which can effectively inhibit the crystallization rate of polyester film, effectively improve the transmittance of polyester film, and reduce the haze value of polyester film.

[0033] 3. By adopting the above technical solution, silica is modified with silane coupling agent. Some hydroxyl groups on the surface of silica are replaced by alkoxy groups of silane coupling agent, which weakens the hydrogen bonding between silica particles. The two particles are connected by Si-O-Si bonds, which effectively inhibits the agglomeration of silica, thereby better exerting the mechanical and optical properties of nano silica and improving the light transmittance and mechanical properties of polyester release film. Detailed Implementation

[0034] The present application will be further described in detail below with reference to the embodiments.

[0035] Preparation Example

[0036] Preparation Example 1

[0037] S1. Add 2g of nano-silica to 24g of anhydrous ethanol and mix. Stir at 200rpm for 30min to obtain a dispersion of nano-silica. Add 10g of silane coupling agent to 20g of deionized water and stir at 300rpm for 1h to obtain an aqueous solution of silane coupling agent.

[0038] S2. The dispersion of nano-silica was added to an aqueous solution of silane coupling agent and magnetically stirred at 600 rpm for 30 min, followed by reflux reaction at 60 °C for 2 h. After the reaction was completed, the product was washed with anhydrous ethanol and filtered. After washing until the filtrate was clear, the product was dried at 80 °C for 2 h. The dried filter cake was then ground to obtain modified nano-silica powder. The silane coupling agent used in this preparation example was KH-550.

[0039] Preparation Example 2

[0040] S1. Add 2.5g of nano-silica to 27g of anhydrous ethanol and mix. Stir at 250rpm for 40min to obtain a dispersion of nano-silica. Add 12.5g of silane coupling agent to 25g of deionized water and stir at 350rpm for 1.5h to obtain an aqueous solution of silane coupling agent.

[0041] S2. The dispersion of nano-silica was added to an aqueous solution of silane coupling agent and magnetically stirred at 700 rpm for 35 min, followed by reflux reaction at 70 °C for 3 h. After the reaction was completed, the product was washed with anhydrous ethanol and filtered. After washing until the filtrate was clear, the product was dried at 90 °C for 1.5 h. The dried filter cake was then ground to obtain modified nano-silica powder. The silane coupling agent used in this preparation example was KH-550.

[0042] Preparation Example 3

[0043] S1. Add 3g of nano-silica to 30g of anhydrous ethanol and mix. Stir at 300rpm for 50min to obtain a dispersion of nano-silica. Add 15g of silane coupling agent to 30g of deionized water and stir at 400rpm for 2h to obtain an aqueous solution of silane coupling agent.

[0044] S2. The dispersion of nano-silica was added to an aqueous solution of silane coupling agent and magnetically stirred at 800 rpm for 40 min, followed by reflux reaction at 80 °C for 4 h. After the reaction was completed, the product was washed with anhydrous ethanol and filtered. After washing until the filtrate was clear, the product was dried at 100 °C for 1 h. The dried filter cake was then ground to obtain modified nano-silica powder. The silane coupling agent used in this preparation example was KH-550.

[0045] Example

[0046] Example 1

[0047] S1. Premixing and drying: 120g of dicarboxylic acid composition, 160g of diol composition, 2g of polydecyl diamine, 5g of poly(trimethylhexamethylene terephthalamide), 1g of antioxidant, 1.2g of the modified additive obtained in Preparation Example 1, 1g of catalyst, and 0.5g of stabilizer were fed into a mixing tank and premixed for 40min at a speed of 8r / min, and then dried at a temperature of 120℃ for 1.5h.

[0048] The dicarboxylic acid composition used in this embodiment includes isophthalic acid, phthalic acid, and cyclohexanedicarboxylic acid in a weight ratio of 1:1:0.6; the diol composition includes ethylene glycol, neopentyl glycol, and cyclohexanediol in a weight ratio of 1:0.5:0.6; the antioxidant includes 2,6-di-tert-butyl-4-methylphenol and phosphite in a weight ratio of 1:2; the catalyst used is [missing information]; the stabilizer used is [missing information].

[0049] S2. Melt extrusion: The dried raw material is fed into the extruder to melt and then extruded into a polyester film at a die temperature of 280°C and an extrusion line speed of 0.5 m / s.

[0050] S3. Flat stretching: The polyester film is preheated at 70°C, then heated in an infrared heating zone at 130°C, and stretched longitudinally at a linear speed of 0.8 m / s, followed by longitudinal relaxation at a linear speed of 0.2 m / s; the longitudinally stretched polyester film is preheated at 90°C, then heated in an infrared heating zone at 130°C, and stretched longitudinally at a linear speed of 1.0 m / s, followed by transverse relaxation at a linear speed of 0.2 m / s, and set at 220°C for 10 s to obtain a thick polyester film with a thickness of 300 μm;

[0051] S4. Corona treatment: The excess parts on the front and back sides of the stretched polyester film are cut off, and the surface of the polyester film is subjected to high voltage corona treatment.

[0052] S5. Winding and Slitting: The corona-treated polyester film material is wound into shape, and the cutting device then cuts the winding drum of the polyester film evenly and at equal intervals and collects it.

[0053] Example 2

[0054] S1. Premixing and drying: 131g of dicarboxylic acid composition, 174g of diol composition, 2g of polydecyl diamine, 5g of poly(trimethylhexamethylene terephthalamide), 2g of antioxidant, 1.6g of the modified additive obtained in Preparation Example 1, 1.5g of catalyst, and 0.8g of stabilizer were fed into a mixing tank and premixed for 45min at a speed of 10r / min, and then dried at a temperature of 130℃ for 2.0h.

[0055] The dicarboxylic acid composition used in this embodiment includes isophthalic acid, phthalic acid, and cyclohexanedicarboxylic acid in a weight ratio of 1:1:0.6; the active ingredient used includes ethylene glycol, neopentyl glycol, and cyclohexanediol in a weight ratio of 1:0.5:0.6; the antioxidant used includes 2,6-di-tert-butyl-4-methylphenol and phosphite in a weight ratio of 1:2; the catalyst used is [missing information]; the stabilizer used is [missing information].

[0056] S2. Melt extrusion: The dried raw material is fed into the extruder to melt and then extruded into a polyester film at a die temperature of 300°C and an extrusion line speed of 0.6 m / s.

[0057] S3. Flat stretching: The polyester film is preheated at 80°C, then heated in an infrared heating zone at 145°C, and stretched longitudinally at a linear speed of 1.15 m / s, followed by longitudinal relaxation at a linear speed of 0.25 m / s; the longitudinally stretched polyester film is preheated at 105°C, then heated in an infrared heating zone at 145°C, and stretched longitudinally at a linear speed of 1.4 m / s, followed by transverse relaxation at a linear speed of 0.25 m / s, and set at 230°C for 12 s to obtain a thick polyester film with a thickness of 325 μm;

[0058] S4. Corona treatment: The excess parts on the front and back sides of the stretched polyester film are cut off, and the surface of the polyester film is subjected to high voltage corona treatment.

[0059] S5. Winding and Slitting: The corona-treated polyester film material is wound into shape, and the cutting device then cuts the winding drum of the polyester film evenly and at equal intervals and collects it.

[0060] Example 3

[0061] S1. Premixing and drying: 142g of dicarboxylic acid composition, 188g of diol composition, 2g of polydecyl diamine, 5g of poly(trimethylhexamethylene terephthalamide), 3g of antioxidant, 2g of the modified additive obtained in Preparation Example 1, 2g of catalyst, and 1.1g of stabilizer were fed into a mixing tank and premixed for 50min at a speed of 12r / min, and then dried at a temperature of 140℃ for 1.0h.

[0062] The dicarboxylic acid composition used in this embodiment includes isophthalic acid, phthalic acid, and cyclohexanedicarboxylic acid in a weight ratio of 1:1:0.6; the diol composition includes ethylene glycol, neopentyl glycol, and cyclohexanediol in a weight ratio of 1:0.5:0.6; the antioxidant includes 2,6-di-tert-butyl-4-methylphenol and phosphite in a weight ratio of 1:2; the catalyst used is [missing information]; the stabilizer used is [missing information].

[0063] S2. Melt extrusion: The dried raw material is fed into the extruder to melt and then extruded into a polyester film at a die temperature of 280°C and an extrusion line speed of 0.7 m / s.

[0064] S3. Flat stretching: The polyester film is preheated at 90°C, then heated in an infrared heating zone at 160°C, and stretched longitudinally at a linear speed of 1.5 m / s, followed by longitudinal relaxation at a linear speed of 0.3 m / s; the longitudinally stretched polyester film is preheated at 120°C, then heated in an infrared heating zone at 160°C, and stretched longitudinally at a linear speed of 1.8 m / s, followed by transverse relaxation at a linear speed of 0.3 m / s, and set at 240°C for 14 s to obtain a thick polyester film with a thickness of 350 μm;

[0065] S4. Corona treatment: The excess parts on the front and back sides of the stretched polyester film are cut off, and the surface of the polyester film is subjected to high voltage corona treatment.

[0066] S5. Winding and Slitting: The corona-treated polyester film material is wound into shape, and the cutting device then cuts the winding drum of the polyester film evenly and at equal intervals and collects it.

[0067] Example 4

[0068] The difference between Example 4 and Example 1 is that the mass of polydecanoyldecanoic acid diamine used in S1 in Example 4 is 4g.

[0069] Example 5

[0070] The difference between Example 5 and Example 1 is that the mass of polydecanoyldecanoic acid diamine used in S1 in Example 5 is 6g.

[0071] Example 6

[0072] The difference between Example 6 and Example 1 is that the mass of poly(trimethylhexamethylene terephthalamide) used in S1 in Example 6 is 6.5g.

[0073] Example 7

[0074] The difference between Example 7 and Example 1 is that the mass of poly(trimethylhexamethylene terephthalamide) used in S1 in Example 7 is 8g.

[0075] Example 8

[0076] The difference between Example 8 and Example 1 is that the dicarboxylic acid composition used in S1 in Example 8 includes isophthalic acid, phthalic acid, and cyclohexanedicarboxylic acid in a weight ratio of 1:1.25:0.9.

[0077] Example 9

[0078] The difference between Example 9 and Example 1 is that the dicarboxylic acid composition used in S1 in Example 9 includes isophthalic acid, phthalic acid, and cyclohexanedicarboxylic acid in a weight ratio of 1:1.5:1.2.

[0079] Example 10

[0080] The difference between Example 10 and Example 1 is that the diol composition used in S1 in Example 10 includes ethylene glycol, neopentyl glycol, and cyclohexanediol in a weight ratio of 1:0.7:0.9.

[0081] Example 11

[0082] The difference between Example 11 and Example 1 is that the diol composition used in S1 in Example 11 includes ethylene glycol, neopentyl glycol, and cyclohexanediol in a weight ratio of 1:0.9:1.2.

[0083] Example 12

[0084] The difference between Example 12 and Example 1 is that the antioxidant used in S1 in Example 12 includes 2,6-di-tert-butyl-4-methylphenol and phosphite in a weight ratio of 1:3.

[0085] Example 13

[0086] The difference between Example 13 and Example 1 is that the antioxidant used in S1 of Example 13 includes 2,6-di-tert-butyl-4-methylphenol and phosphite in a weight ratio of 1:4.

[0087] Example 14

[0088] The difference between Example 14 and Example 1 is that the modified additive used in S1 of Example 14 is derived from Preparation Example 2.

[0089] Example 15

[0090] The difference between Example 15 and Example 1 is that the modified additive used in S1 of Example 15 is derived from Preparation Example 3.

[0091] Comparative Example

[0092] Comparative Example 1

[0093] The difference between Comparative Example 1 and Example 1 is that the mass of polydecanoyldecanoyldiamine used in S1 in Comparative Example 1 is 1g.

[0094] Comparative Example 2

[0095] The difference between Comparative Example 2 and Example 1 is that the mass of polydecanoyldecanoyldiamine used in Comparative Example 2 in S1 is 8g.

[0096] Comparative Example 3

[0097] The difference between Comparative Example 3 and Example 1 is that the mass of poly(trimethylhexamethylene terephthalamide) used in S1 in Comparative Example 3 is 3g.

[0098] Comparative Example 4

[0099] The difference between Comparative Example 4 and Example 1 is that the mass of poly(trimethylhexamethylene terephthalamide) used in S1 in Comparative Example 4 is 10g.

[0100] Comparative Example 5

[0101] The difference between Comparative Example 5 and Example 1 is that the dicarboxylic acid composition used in S1 of Comparative Example 5 includes isophthalic acid, phthalic acid, and cyclohexanedicarboxylic acid in a weight ratio of 1:0.75:0.3.

[0102] Comparative Example 6

[0103] The difference between Comparative Example 6 and Example 1 is that the dicarboxylic acid composition used in S1 of Comparative Example 6 includes isophthalic acid, phthalic acid, and cyclohexanedicarboxylic acid in a weight ratio of 1:1.75:1.5.

[0104] Comparative Example 7

[0105] The difference between Comparative Example 7 and Example 1 is that the diol composition used in S1 of Comparative Example 7 includes ethylene glycol, neopentyl glycol, and cyclohexanediol in a weight ratio of 1:0.3:0.3.

[0106] Comparative Example 8

[0107] The difference between Comparative Example 8 and Example 1 is that the diol composition used in S1 of Comparative Example 8 includes ethylene glycol, neopentyl glycol, and cyclohexanediol in a weight ratio of 1:1.1:1.5.

[0108] Comparative Example 9

[0109] The difference between Comparative Example 9 and Example 1 is that the antioxidant used in Comparative Example 9 in S1 includes 2,6-di-tert-butyl-4-methylphenol and phosphite in a weight ratio of 1:1.

[0110] Comparative Example 10

[0111] The difference between Comparative Example 10 and Example 1 is that the antioxidant used in S1 of Comparative Example 10 includes 2,6-di-tert-butyl-4-methylphenol and phosphite in a weight ratio of 1:5.

[0112] Comparative Example 11

[0113] The difference between Comparative Example 11 and Example 1 is that the additive used in S1 of Comparative Example 11 is modified nano-silica.

[0114] Performance testing

[0115] 1. The transmittance and haze of the thick polyester films obtained in Examples 1-15 and Comparative Examples 1-11 were tested using GB / T 2410-2008 "Determination of transmittance and haze of transparent plastics". The results are shown in Table 1.

[0116] 2. The mechanical properties of the thick polyester films obtained in Examples 1-15 and Comparative Examples 1-11 were tested using GB / T 1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets".

[0117] The specific test results are as follows:

[0118] Table 1 Performance Test Results

[0119]

[0120]

[0121] As can be seen from the test results in Table 1, the thick polyester film and the polyester film prepared by the method provided in this application have high light transmittance and low haze, and the tensile strength of the film can reach MPa and the elongation at break can reach %, indicating that the thick polyester film provided in this application has high mechanical properties.

[0122] As can be seen from the test results of Examples 1-3, the process parameters for preparing thick polyester films provided in this application are all beneficial to improving the mechanical strength and light transmittance of thick polyester films and reducing the haze of polyester films.

[0123] As can be seen from the test results of Examples 1, 4, 5 and Comparative Examples 1, 2, when the mass of polydecyl diamine provided in this application for preparing thick polyester films increases, the light transmittance and haze value of the obtained thick polyester films change little, and the tensile strength and elongation at break of the films gradually increase. However, when the mass of polydecyl diamine exceeds 6g, the tensile strength and elongation at break basically no longer change, but the light transmittance of the polyester film decreases and the haze value increases.

[0124] As can be seen from the test results of Examples 1, 6, 7 and Comparative Examples 3, 4, when the mass of poly(trimethylhexamethylene terephthalamide) provided in this application for preparing thick polyester films increases, the light transmittance of the obtained thick polyester films gradually increases, the haze value decreases, and the tensile strength and elongation at break both increase; however, when the mass of trimethylhexamethylene terephthalamide exceeds 8g, the tensile strength and elongation at break of the polyester film basically no longer change, but the light transmittance of the polyester film decreases and the haze value increases.

[0125] The test results from Examples 1, 8, 9 and Comparative Examples 5, 6 show that when the weight ratio of isophthalic acid, phthalic acid and cyclohexanedicarboxylic acid in the dicarboxylic acid composition for preparing thick polyester films provided in this application varies within the range of 1:(1-1.5):(0.6-1.2), the mechanical properties and light transmittance of the polyester film can be improved, and the haze value of the polyester film can be reduced. However, when the ratio is lower or higher than this range, the mechanical properties of the film decrease, the light transmittance decreases, and the haze value increases.

[0126] The test results from Examples 1, 10, 11 and Comparative Examples 7, 8 show that when the weight ratio of the diol composition (ethylene glycol, neopentyl glycol, cyclohexanediol) provided in this application for preparing thick polyester films varies within the range of 1:(0.5-0.9):(0.6-1.2), the mechanical properties and light transmittance of the polyester film can be improved, and the haze value of the polyester film can be reduced. However, when the ratio is lower or higher than this range, the mechanical properties of the film decrease, the light transmittance decreases, and the haze value increases.

[0127] The test results of Examples 1, 12, 13 and Comparative Examples 9, 10 show that when the weight ratio of the antioxidant 2,6-di-tert-butyl-4-methylphenol and phosphite in the preparation of thick polyester films provided in this application varies within the range of 1:(2-4), the mechanical properties and light transmittance of the polyester film can be improved, and the haze value of the polyester film can be reduced. However, when the ratio is lower or higher than this range, the mechanical properties of the film decrease, the light transmittance decreases, and the haze value increases.

[0128] As can be seen from the test results of Examples 1, 14, 15 and Comparative Example 11, the preparation process of the modified additive for preparing thick polyester films provided in this application is beneficial to improving the mechanical strength and light transmittance of thick polyester films and reducing the haze of polyester films. Moreover, the changes in parameters within the range have little effect on the light transmittance, haze and mechanical strength of polyester films. However, when modified nano-silica is used as an additive, the mechanical properties of the obtained polyester film decrease, the light transmittance decreases and the haze value increases.

[0129] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A thick polyester film, characterized in that: The raw materials mainly include the following components: 120-142 parts of dicarboxylic acid composition, 160-188 parts of diol composition, 2-6 parts of polydecanoic acid decanediamine, 5-8 parts of poly(trimethylhexamethylene terephthalamide), 1-3 parts of antioxidant, 1.2-2 parts of modifying additive, 1-2 parts of catalyst, and 0.5-1.1 parts of stabilizer; the modifying additive is modified nano-silica; the dicarboxylic acid composition mainly includes isophthalic acid, phthalic acid, and cyclohexanedicarboxylic acid, with a weight ratio of 1:(1-1) 0.5): (0.6-1.2); The diol composition mainly includes ethylene glycol, neopentyl glycol, and cyclohexanediol, with a weight ratio of 1:(0.5-0.9):(0.6-1.2); The antioxidant includes 2,6-di-tert-butyl-4-methylphenol and phosphite, with a weight ratio of 1:(2-4); The raw materials for the modified nano silica mainly include: 2-3 parts nano silica, 24-30 parts anhydrous ethanol, 10-15 parts silane coupling agent, and 20-30 parts deionized water.

2. A method for preparing a thick polyester film according to claim 1, characterized in that: Includes the following steps: S1. Premixing and drying: 120-142 parts of dicarboxylic acid composition, 160-188 parts of diol composition, 2-6 parts of polydecanoic acid decanediamine, 5-8 parts of polyterephthaloyltrimethylhexamethylenediamine, 1-3 parts of antioxidant, 1.2-2 parts of modifying additive, 1-2 parts of catalyst, and 0.5-1.1 parts of stabilizer are premixed and dried; S2. Melt extrusion: The dried raw material is fed into an extruder to melt and extrude, resulting in a polyester film. S3. Flat stretching: Place the pressure rollers in parallel and stretch the polyester film longitudinally and laterally in sequence to stretch the thickness of the polyester film to 300-350μm. S4. Corona treatment: The excess parts on the front and back sides of the stretched polyester film are cut off, and the surface of the polyester film is subjected to high voltage corona treatment. S5. Winding and Slitting: The corona-treated polyester film material is wound into shape, and the cutting device then cuts the winding drum of the polyester film evenly and at equal intervals and collects it.

3. The method for preparing a thick polyester film according to claim 2, characterized in that: The longitudinal stretching includes the following steps: The polyester film is preheated at 70-90℃, then heated in an infrared heating zone at 130-160℃, and longitudinally stretched at a linear velocity of 0.8-1.5m / s, followed by longitudinal relaxation at a linear velocity of 0.2-0.3m / s.

4. The method for preparing a thick polyester film according to claim 2, characterized in that: The lateral stretching includes the following steps: The longitudinally stretched polyester film is preheated at 90-120℃, then heated in an infrared heating zone at 130-160℃, and transversely stretched at a linear velocity of 1.0-1.8 m / s. It is then transversely relaxed at a linear velocity of 0.2-0.3 m / s and shaped.

5. The method for preparing a thick polyester film according to claim 2, characterized in that: The method for preparing the modified nano-silica includes the following steps: S1. Add 2-3 parts of nano-silica to 24-30 parts of anhydrous ethanol and mix, stirring until evenly dispersed to obtain a dispersion of nano-silica; add 10-15 parts of silane coupling agent to 20-30 parts of deionized water and stir for 1-2 hours to obtain an aqueous solution of silane coupling agent. S2. Add the dispersion of nano-silica to the aqueous solution of silane coupling agent and stir evenly, and reflux at 60-80℃ for 2-4 hours; after the reaction is completed, wash, filter, dry and grind the product to obtain modified nano-silica powder.

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