An optical grade polyethylene naphthalate film and its preparation method

Abstract

The present invention belongs to the field of materials chemistry. Disclosed is an optical grade polyethylene naphthalate film and its preparation method. Using dimethyl 2,6-naphthalenedicarboxylate and dimethyl 2,7-naphthalenedicarboxylate as monomers, under the action of a catalyst and an antioxidant, an esterification reaction occurs with ethylene glycol, and methanol is removed; after adding an antioxidant, a polycondensation reaction occurs to remove small molecule ethylene glycol, obtaining PEN resin; the PEN resin is melted and then cast into sheets, and then after cutting, it is preheated, stretched and annealed to obtain an optical grade polyethylene naphthalate film. In the present invention, a mixture of 2,6-NDC and 2,7-NDC, which are the carboxylated and esterified products of 2,6-DMN and 2,7-DMN, is used as a monomer to directly synthesize PEN resin, effectively reducing the molecular chain regularity, significantly interfering with the crystallization behavior during the forming process, and thus improving the light transmittance of the film.

Description

Technical Field

[0001] The present invention belongs to the technical field of materials and chemical engineering, and particularly relates to an optical grade polyethylene naphthalate film and a preparation method thereof. Background Art

[0002] Optical grade polymer films are widely used in various fields such as display devices, optical detection devices, and communication electronic products due to their special optical properties such as high light transmittance and low haze, and are one of the key materials in the electronic information industry chain. Due to the high industry entry threshold and complex product processes, they are expensive. With the development of the science and technology information field and the continuous innovation of optoelectronic devices, the industry has put forward higher requirements for the light transmittance of optical grade polymer films. Compared with PET resin, the conjugated structure formed by the naphthalene ring structure and ester bond in the polyethylene naphthalate (PEN) molecular chain can absorb ultraviolet light with a wavelength of 200 - 400 nm and has poor absorbability to visible light, which makes it exhibit good optical properties and is an ideal material for optical grade polymer films.

[0003] Currently, the transesterification method is used in industry to produce PEN resin, and the reaction temperature is relatively high. The temperatures of the two steps of removing methanol by-products and ethylene glycol by-products are 265 - 300 °C, which leads to easy occurrence of side reactions, and then formation of more diglycol structures, affecting the product performance.

[0004] Industrially, 2,6-NDC and ethylene glycol are used as monomers for polycondensation reaction to produce PEN resin. Its monomer 2,6-NDC is expensive, which greatly limits the popularization of PEN resin. The industrial production route of monomer 2,6-NDC is as follows: naphthalene is alkylated with methanol to obtain monomer precursor 2,6-dimethylnaphthalene (2,6-DMN), then carboxylated to obtain 2,6-naphthalenedicarboxylic acid, and finally esterified to obtain 2,6-NDC. Among them, the methanol alkylation reaction of naphthalene is the most critical step in the whole synthesis route. In this process, a variety of isomers will be generated. The boiling points of 2,6-dimethylnaphthalene and 2,7-dimethylnaphthalene differ by only 0.3 °C, and their thermodynamic compositions are similar. The yield in 100 hours is only 14%, resulting in a relatively high cost of substrate monomers, making the price of optical grade PEN resin film high and difficult to promote and use.

[0005] The PEN resin synthesized with 2,6-NDC as the monomer has a good molecular chain structure symmetry, which makes it easy to form spherulites and a microphase separation structure due to ordered packing during the biaxial stretching process. When light passes through the film, complex optical behaviors occur when it irradiates the ordered structure, resulting in a decrease in light transmittance and seriously affecting the optical properties of the film. Summary of the Invention

[0006] To solve the problems in the prior art, the object of the present invention is to propose an optical grade polyethylene naphthalate film and its preparation method to overcome the deficiencies of the prior art. This method uses a mixture of 2,6-NDC and 2,7-NDC, which is difficult to separate, as monomers, and undergoes polycondensation reaction with ethylene glycol through transesterification to synthesize PEN resin with poor molecular chain symmetry, and then obtains a high light transmittance optical grade PEN film after biaxial stretching.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A preparation method of an optical grade polyethylene naphthalate film, comprising the following steps:

[0009] Using dimethyl 2,6-naphthalenedicarboxylate and dimethyl 2,7-naphthalenedicarboxylate as monomers, reacting with ethylene glycol under the action of a catalyst and an antioxidant to carry out an esterification reaction and remove methanol; after adding an antioxidant, a polycondensation reaction occurs to remove small molecule ethylene glycol to obtain PEN resin;

[0010] Melting the PEN resin and then casting it into sheets, and then cutting, preheating, stretching and annealing to obtain an optical grade polyethylene naphthalate film.

[0011] Further, the PEN resin is specifically prepared through the following process: by mass, mixing 20-50 parts of dimethyl 2,6-naphthalenedicarboxylate, 10-40 parts of dimethyl 2,7-naphthalenedicarboxylate, 32-34 parts of ethylene glycol, 0.001-0.1 part of a catalyst and 0.001-0.1 part of an antioxidant, carrying out a transesterification reaction to remove methanol, and then adding 0.001-0.1 part of antioxidant 1010, carrying out a polycondensation reaction to remove ethylene glycol to obtain PEN resin.

[0012] Further, the catalyst is one of zinc acetate and antimony glycolate.

[0013] Further, the antioxidant is one or both of antioxidant 1010 and triphenyl phosphite.

[0014] Further, the specific process of removing methanol by transesterification reaction is: under nitrogen protection, heating to 160-190 °C, controlling the nitrogen flow rate to be 300-600 mL / min, the rotation speed to be 200-300 r / min, and reacting for 2-4 hours.

[0015] Further, the specific process of removing ethylene glycol by polycondensation reaction is as follows: under nitrogen protection, the temperature is raised to 250 - 260 °C, the nitrogen flow rate is controlled at 300 - 600 ml / min, the rotation speed is 200 - 300 r / min, and the reaction lasts for 3 - 4 hours; then the temperature is raised to 260 - 270 °C, the nitrogen flow rate is controlled at 50 - 100 ml / min, the rotation speed is 30 - 50 r / min, the pressure is 100 - 200 Pa, and the reaction lasts for 2 - 3 hours; then the temperature is raised to 270 - 280 °C, the nitrogen is turned off, the rotation speed is 20 - 30 r / min, the pressure is 50 - 100 Pa, and the reaction lasts for 1 - 2 hours.

[0016] Further, the preheating temperature is 135 - 145 °C, and the time is 30 - 300 s.

[0017] Further, the stretching temperature is 130 - 160 °C, the transverse stretching ratio is 2 - 6 times, and the longitudinal stretching ratio is 2 - 7 times.

[0018] Further, the annealing temperature is 130 - 140 °C, the time is 30 - 600 s, and the thickness of the cast film is 30 - 500 μm.

[0019] The thickness of the optical grade polyethylene naphthalate film prepared by the method as described above is 25 - 150 μm, the light transmittance is 90 - 97%, the transverse tensile strength is 165 - 249 MPa, and the tensile strength in the longitudinal direction is 197 - 295 MPa.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] Since the molecular chain structure of PEN resin synthesized from dimethyl 2,6-naphthalenedicarboxylate (2,6-NDC) and dimethyl 2,7-naphthalenedicarboxylate (2,7-DMN) as monomers is regular and it is a semi-crystalline polymer, it is prone to crystallization during the molding process. In this invention, a mixture of 2,6-NDC and 2,7-NDC, which are the products after carboxylation and esterification of 2,6-DMN and 2,7-DMN, is used as monomers to directly synthesize PEN resin, effectively reducing the regularity of the molecular chain, significantly interfering with the crystallization behavior during the molding process, and then improving the light transmittance of the film, solving the problem that the existing PEN resin with regular molecular chains has poor light transmittance of the film due to easy crystallization during the biaxial stretching process. The process conditions for polyester synthesis in this invention will also affect the color of the polyester material, and thus affect the light transmittance. In this invention, ethylene glycol is used as the raw material for polyester synthesis, and it is prone to condensation side reactions under high-temperature conditions, and it is easy to form a diglycol structure in the molecular chain. Diglycol is easily oxidized to yellow edges, resulting in the darkening of the resin color. Therefore, it is very necessary to strictly control the reaction conditions to reduce the occurrence of side reactions. Importantly, this invention directly uses a mixture of 2,6-NDC and 2,7-NDC as monomers, skillfully avoiding the high-energy-consuming and low-yield separation steps of 2,6-DMN and 2,7-DMN, significantly improving the overall production efficiency, preparing an optical-grade PEN film with high light transmittance, greatly reducing the production cost of optical-grade PEN resin, and having great economic benefits and commercial value.

[0022] Furthermore, in this invention, the methanol removal reaction is carried out under the condition of 160 - 190 °C. By reducing the reaction temperature, the formation of the diglycol structure is avoided, and side reactions can be effectively avoided in the early stage of the reaction.

[0023] Furthermore, in the diglycol removal step, this invention adopts staged heating, effectively avoiding the formation of diglycol, being beneficial to the formation of PEN resin with a lighter color, and enhancing the light transmittance of the film material. Detailed implementation manners

[0024] The following describes the present invention more comprehensively in combination with embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive.

[0025] For polymer materials, the different refractive indices of the crystalline region and the amorphous region for visible light are the main reasons for their poor light transmittance. The higher the degree of crystallization, the more obvious the scattering degree of visible light, and the lower the light transmittance. Therefore, reducing the regularity of the PEN molecular chain and interfering with its crystallization process are important methods to improve the visible light transmittance.

[0026] Since the PEN molecular chains in the present invention are regular, they are prone to crystallization during the molding process, resulting in a decrease in light transmittance. The use of a mixture of 2,6-NDC and 2,7-NDC as mixed monomers to synthesize PEN resin reduces the regularity of the molecular chain structure, hinders its crystallization behavior during the molding process, and effectively improves the light transmittance. Since the boiling points of the monomer precursors 2,6-DMN and 2,7-DMN are close and difficult to separate, it is the fundamental reason for the high price of the polymerization monomers. The present invention uses mixed monomers, which can avoid the energy consumption caused by separating the monomers and greatly reduce the cost.

[0027] A method for preparing an optical grade polyethylene naphthalate (PEN) film using a mixture of dimethyl naphthalate isomers as monomers according to the present invention comprises the following steps:

[0028] (1) The method for synthesizing PEN resin is as follows: Using two isomers of dimethyl naphthalate, 2,6-NDC (dimethyl 2,6-naphthalenedicarboxylate) and 2,7-NDC (dimethyl 2,7-naphthalenedicarboxylate), as monomers, an esterification reaction is carried out with ethylene glycol under the action of a catalyst and an antioxidant, and the by-product methanol is removed; after adding an antioxidant, a polycondensation reaction is carried out to remove the small molecule by-product ethylene glycol, obtaining a PEN resin with poor molecular chain regularity.

[0029] Specifically, by mass, take 20 - 50 parts of dimethyl 2,6-naphthalenedicarboxylate, 10 - 40 parts of dimethyl 2,7-naphthalenedicarboxylate, 32 - 34 parts of ethylene glycol, 0.001 - 0.1 part of a catalyst, and 0.001 - 0.1 part of an antioxidant in a reaction kettle. First, carry out a transesterification reaction to remove methanol. The specific operation is as follows: Replace the air in the kettle with nitrogen at room temperature, heat up from room temperature to 160 - 190 °C, control the nitrogen flow rate at 300 - 600 mL / min, set the rotation speed at 200 - 300 r / min, react under these conditions for 2 - 4 hours, and collect the by-product methanol; then add 0.001 - 0.1 part of an antioxidant to the reaction kettle, and finally carry out a polycondensation reaction to remove ethylene glycol. The specific operation is as follows: Heat up to 250 - 260 °C, control the nitrogen flow rate at 300 - 600 ml / min, set the rotation speed at 200 - 300 r / min, and the pressure in the kettle is normal pressure. React under these conditions for 3 - 4 hours, and collect the by-product ethylene glycol; heat up from 250 - 260 °C to 260 - 270 °C, control the nitrogen flow rate at 50 - 100 ml / min, reduce the rotation speed to 30 - 50 r / min, and the pressure in the kettle is 100 - 200 Pa. React under these conditions for 2 - 3 hours; heat up from 260 - 270 °C to 270 - 280 °C, turn off the nitrogen, reduce the rotation speed to 20 - 30 r / min, and the pressure in the kettle is 50 - 100 Pa. After reacting under these conditions for 1 - 2 hours, end the reaction, cool down, and obtain a PEN resin with an irregular molecular chain, that is, a poor molecular chain symmetry.

[0030] The catalyst is one of zinc acetate and antimony glycolate.

[0031] The antioxidant is one of antioxidant 1010 and triphenyl phosphite, or a mixture of both.

[0032] After methanol is removed, the added antioxidant is antioxidant 1010. Because the reaction temperature for removing by-product methanol is low and the reaction temperature for removing small molecule by-product ethylene glycol is high, the added antioxidant can only be antioxidant 1010.

[0033] (2) The preparation method of the high light transmittance optical grade PEN film is as follows: melt the PEN resin in an extruder and then cast it into a sheet with a thickness of 30 - 500 μm. After cutting it into regular shape, place it in a synchronous biaxial stretching machine for preheating, stretching and annealing to obtain the high light transmittance optical grade PEN film.

[0034] Specifically, in the synchronous biaxial stretching machine, the preheating temperature is 135 - 145 °C and the time is 30 - 300 s; the stretching temperature of the film is 130 - 160 °C, the transverse stretching ratio is 2 - 6 times, and the longitudinal stretching ratio is 2 - 7 times; the annealing temperature of the PEN film after stretching is 130 - 140 °C and the annealing time is 30 - 600 s. The prepared high light transmittance optical grade PEN film has a thickness of 25 - 150 μm, a light transmittance of 90 - 97%, a tensile strength of 165 - 249 MPa (transverse), and 197 - 295 MPa (longitudinal).

[0035] The technical solution of the present invention will be described in detail below through specific examples.

[0036] Example 1

[0037] This example provides a preparation method of an optical grade polyethylene naphthalate film using a mixture of naphthalene dicarboxylic acid dimethyl ester isomers as monomers, including the following steps:

[0038] (1) Take 150 g of dimethyl 2,6-naphthalenedicarboxylate, 150 g of dimethyl 2,7-naphthalenedicarboxylate, 155 g of ethylene glycol, 0.05 g of zinc acetate, and 0.05 g of triphenyl phosphite and put them into a 1 L stainless steel reactor. Open the nitrogen valve to replace the air in the kettle with nitrogen, heat up to 180 °C, set the nitrogen flow rate to 400 mL / min, set the rotation speed to 200 r / min, react for 3 hours, and collect methanol.

[0039] (2) Weigh another 0.05 g of antioxidant 1010 and disperse it in 50 g of ethylene glycol, and add it into the reaction kettle through the feeding port.

[0040] (3) Continue to heat up to 255 °C, control the nitrogen gas flow rate at 500 ml / min, set the rotation speed at 300 r / min, keep the pressure in the reactor at atmospheric pressure, react for 4 hours under this condition, and collect the by-product ethylene glycol; heat up to 265 °C, control the nitrogen gas flow rate at 100 ml / min, reduce the rotation speed to 50 r / min, and keep the pressure in the reactor at 150 Pa, react for 2 hours under this condition; heat up to 275 °C, turn off the nitrogen gas, reduce the rotation speed to 20 r / min, and keep the pressure in the reactor at 50 Pa, end the reaction after reacting for 1 hour; cool down to obtain PEN resin.

[0041] (4) Take an appropriate amount of PEN resin and melt it into a sheet in an extruder with a thickness of 200 μm. After cutting, place it in a synchronous biaxial stretching machine, set the temperature at 140 °C, and the preheating time at 300 s; heat up to 140 °C, set the stretching rate at 50 mm / min, the transverse stretching ratio at 3 times, and the longitudinal stretching ratio at 4 times, and then anneal it statically at 130 °C for 300 s to obtain a PEN resin film.

[0042] Determine the light transmittance of the film according to the method shown in the national standard GB / T 2410-2008. Test the tensile strength of the film in the transverse and longitudinal directions according to the national standard GB / T 1040.1-2018. The results are shown in the following table:

[0043] Table 1 Light transmittance and tensile strength of the resin film obtained in Example 1

[0044] Category Light transmittance Tensile strength (transverse / longitudinal) Unit ％ MPa Example 1 97 215 / 266

[0045] Example 2

[0046] This example provides a method for preparing an optical grade polyethylene naphthalate film using a mixture of dimethyl naphthalate isomers as monomers, including the following steps:

[0047] (1) Take 120 g of dimethyl 2,6-naphthalate, 150 g of dimethyl 2,7-naphthalate, 186 g of ethylene glycol, 0.05 g of zinc acetate, and 0.05 g of triphenyl phosphite and put them into a 1 L stainless steel reactor. Open the nitrogen valve to replace the air in the reactor with nitrogen, heat up to 180 °C, set the nitrogen gas flow rate at 400 mL / min, set the rotation speed at 200 r / min, react for 3 hours, and collect methanol.

[0048] (2) Weigh another 0.05 g of antioxidant 1010 and disperse it in 50 g of ethylene glycol, and add it into the reaction kettle through the feeding port.

[0049] (3) Continue to heat up to 255 °C, control the nitrogen gas flow rate at 500 ml / min, set the rotation speed at 300 r / min, keep the pressure inside the autoclave at atmospheric pressure, react under these conditions for 4 hours, and collect the by-product ethylene glycol; heat up to 265 °C, control the nitrogen gas flow rate at 100 ml / min, reduce the rotation speed to 50 r / min, and keep the pressure inside the autoclave at 150 Pa, react under these conditions for 2 hours; heat up to 275 °C, turn off the nitrogen gas, reduce the rotation speed to 20 r / min, and keep the pressure inside the autoclave at 50 Pa, end the reaction after reacting for 1 hour under these conditions; cool down to obtain PEN resin.

[0050] (4) Take an appropriate amount of PEN resin and melt and cast it into a film in an extruder with a thickness of 200 μm. After cutting, place it in a synchronous biaxial stretching machine, set the temperature at 140 °C, and the preheating time at 300 s; heat up to 140 °C, set the stretching rate at 50 mm / min, the transverse stretching ratio at 3 times, and the longitudinal stretching ratio at 4 times, and then anneal it statically at 130 °C for 300 s to obtain a PEN resin film.

[0051] Measure the light transmittance and tensile strength of the film by the method shown in Example 1, and the results are shown in the following table:

[0052] Table 2 Light transmittance and tensile strength corresponding to the resin film obtained in Example 2

[0053] Category Light transmittance Tensile strength (transverse / longitudinal) Unit ％ MPa Example 2 96 157 / 236

[0054] Example 3

[0055] This example provides a method for preparing an optical grade polyethylene naphthalate film using a mixture of dimethyl naphthalate isomers as monomers, including the following steps:

[0056] (1) Take 150 g of dimethyl 2,6-naphthalate, 120 g of dimethyl 2,7-naphthalate, 186 g of ethylene glycol, 0.05 g of zinc acetate, and 0.05 g of triphenyl phosphite and put them into a 1 L stainless steel reactor. Open the nitrogen valve to replace the air inside the autoclave with nitrogen. Heat up to 180 °C, set the nitrogen gas flow rate at 400 mL / min, set the rotation speed at 200 r / min, react for 3 hours, and collect methanol.

[0057] (2) Weigh another 0.05 g of antioxidant 1010 and disperse it in 50 g of ethylene glycol, and add it into the reaction kettle through the feeding port.

[0058] (3) Continue to heat up to 255 °C, control the nitrogen gas flow rate at 500 ml / min, set the rotation speed at 300 r / min, keep the pressure inside the autoclave at atmospheric pressure, react for 4 hours under this condition, and collect the by-product ethylene glycol; heat up to 265 °C, control the nitrogen gas flow rate at 100 ml / min, reduce the rotation speed to 50 r / min, and keep the pressure inside the autoclave at 150 Pa, react for 2 hours under this condition; heat up to 275 °C, turn off the nitrogen gas, reduce the rotation speed to 20 r / min, and keep the pressure inside the autoclave at 50 Pa, end the reaction after reacting for 1 hour; cool down to obtain PEN resin.

[0059] (4) Take an appropriate amount of PEN resin and melt and cast it into a film in an extruder with a thickness of 200 μm. After cutting, place it in a synchronous biaxial stretching machine, set the temperature at 140 °C, and the preheating time at 300 s; heat up to 140 °C, set the stretching rate at 50 mm / min, the transverse stretching ratio at 3 times, and the longitudinal stretching ratio at 4 times, and then anneal it statically at 130 °C for 300 s to obtain a PEN resin film.

[0060] Measure the light transmittance and tensile strength of the film by the method shown in Example 1, and the results are shown in the following table:

[0061] Table 3 Light transmittance and tensile strength of the resin film obtained in Example 3

[0062] Category Light transmittance Tensile strength (transverse / longitudinal) Unit ％ MPa Example 3 94 209 / 254

[0063] Example 4

[0064] This example provides a method for preparing an optical grade polyethylene naphthalate (PEN) film using a mixture of dimethyl naphthalate isomers as monomers, including the following steps:

[0065] (1) Take 150 g of dimethyl 2,6-naphthalate, 150 g of dimethyl 2,7-naphthalate, 155 g of ethylene glycol, 0.05 g of zinc acetate, and 0.05 g of triphenyl phosphite and put them into a 1 L stainless steel reactor. Open the nitrogen valve to replace the air inside the autoclave with nitrogen. Heat up to 180 °C, set the nitrogen gas flow rate at 400 mL / min, set the rotation speed at 200 r / min, react for 3 hours, and collect methanol.

[0066] (2) Weigh another 0.05 g of antioxidant 1010 and disperse it in 50 g of ethylene glycol, and add it into the reaction kettle through the feeding port.

[0067] (3) Continue to heat up to 255 °C, control the nitrogen gas flow rate at 500 ml / min, set the rotation speed at 300 r / min, keep the pressure inside the autoclave at atmospheric pressure, react for 4 hours under this condition, and collect the by-product ethylene glycol; heat up to 265 °C, control the nitrogen gas flow rate at 100 ml / min, reduce the rotation speed to 50 r / min, and keep the pressure inside the autoclave at 150 Pa, react for 2 hours under this condition; heat up to 275 °C, turn off the nitrogen gas, reduce the rotation speed to 20 r / min, and keep the pressure inside the autoclave at 50 Pa, end the reaction after reacting for 1 hour; cool down to obtain PEN resin.

[0068] (4) Take an appropriate amount of PEN resin and melt it into a sheet in an extruder with a thickness of 200 μm. After cutting, place it in a synchronous biaxial stretching machine, set the temperature at 140 °C, and the preheating time at 300 s; heat up to 140 °C, set the stretching rate at 50 mm / min, the transverse stretching ratio at 4 times, and the longitudinal stretching ratio at 5 times, and then anneal it statically at 130 °C for 300 s to obtain a PEN resin film.

[0069] Measure the light transmittance and tensile strength of the film according to the method shown in Example 1, and the results are shown in the following table:

[0070] Table 4 Light transmittance and tensile strength of the resin film obtained in Example 4

[0071] Category Light transmittance Tensile strength (transverse / longitudinal) Unit ％ MPa Example 4 93 242 / 288

[0072] Example 5

[0073] This example provides a method for preparing an optical grade polyethylene naphthalate (PEN) film using a mixture of naphthalenedicarboxylic acid dimethyl ester isomers as monomers, including the following steps:

[0074] (1) Take 150 g of dimethyl 2,6-naphthalenedicarboxylate, 150 g of dimethyl 2,7-naphthalenedicarboxylate, 155 g of ethylene glycol, 0.05 g of zinc acetate, and 0.05 g of triphenyl phosphite and put them into a 1 L stainless steel reactor. Open the nitrogen valve to replace the air inside the autoclave with nitrogen. Heat up to 180 °C, set the nitrogen gas flow rate at 400 mL / min, set the rotation speed at 200 r / min, react for 3 hours, and collect methanol.

[0075] (2) Weigh another 0.05 g of antioxidant 1010 and disperse it in 50 g of ethylene glycol, and add it into the reaction kettle through the feeding port.

[0076] (3) Continue to heat up to 255 °C, control the nitrogen gas flow rate at 500 ml / min, set the rotation speed at 300 r / min, keep the pressure inside the autoclave at atmospheric pressure, react for 4 hours under this condition, and collect the by-product ethylene glycol; heat up to 265 °C, control the nitrogen gas flow rate at 100 ml / min, reduce the rotation speed to 50 r / min, and keep the pressure inside the autoclave at 150 Pa, react for 2 hours under this condition; heat up to 275 °C, turn off the nitrogen gas, reduce the rotation speed to 20 r / min, and keep the pressure inside the autoclave at 50 Pa, end the reaction after reacting for 1 hour; cool down to obtain PEN resin.

[0077] (4) Take an appropriate amount of PEN resin and melt it into a sheet in an extruder with a thickness of 200 μm. After cutting, place it in a synchronous biaxial stretching machine, set the temperature at 140 °C, and the preheating time at 300 s; heat up to 140 °C, set the stretching rate at 50 mm / min, the transverse stretching ratio at 5 times, and the longitudinal stretching ratio at 6 times, and then anneal it statically at 130 °C for 300 s to obtain a PEN resin film.

[0078] Measure the light transmittance and tensile strength of the film by the method shown in Example 1, and the results are shown in the following table:

[0079] Table 5 Light transmittance and tensile strength of the resin film obtained in Example 5

[0080] Category Light transmittance Tensile strength (transverse / longitudinal) Unit ％ MPa Example 5 90 249 / 295

[0081] Example 6

[0082] This example provides a method for preparing an optical grade polyethylene naphthalate (PEN) film using a mixture of naphthalenedicarboxylic acid dimethyl ester isomers as monomers, including the following steps:

[0083] (1) Put 150 g of dimethyl 2,6-naphthalenedicarboxylate, 150 g of dimethyl 2,7-naphthalenedicarboxylate, 155 g of ethylene glycol, 0.05 g of zinc acetate, and 0.05 g of triphenyl phosphite into a 1 L stainless steel reactor. Open the nitrogen valve to replace the air inside the autoclave with nitrogen. Heat up to 180 °C, set the nitrogen gas flow rate at 400 mL / min, set the rotation speed at 200 r / min, react for 3 hours, and collect methanol.

[0084] (2) Weigh another 0.05 g of antioxidant 1010 and disperse it in 50 g of ethylene glycol, and add it into the reaction kettle through the feeding port.

[0085] (3) Continue to heat up to 255 °C, control the nitrogen gas flow rate at 500 ml / min, set the rotation speed at 300 r / min, keep the pressure in the reactor at atmospheric pressure, react for 4 hours under these conditions, and collect the by-product ethylene glycol; heat up to 265 °C, control the nitrogen gas flow rate at 100 ml / min, reduce the rotation speed to 50 r / min, and keep the pressure in the reactor at 150 Pa, react for 2 hours under these conditions; heat up to 275 °C, turn off the nitrogen gas, reduce the rotation speed to 20 r / min, and keep the pressure in the reactor at 50 Pa, end the reaction after reacting for 1 hour; cool down to obtain PEN resin.

[0086] (4) Take an appropriate amount of PEN resin and melt-cast it into a film in an extruder with a thickness of 200 μm. After cutting, place it in a synchronous biaxial stretching machine, set the temperature at 140 °C, and the preheating time at 300 s; heat up to 140 °C, set the stretching rate at 50 mm / min, the transverse stretching ratio at 3 times, and the longitudinal stretching ratio at 4 times, and then anneal it statically at 130 °C for 60 s to obtain a PEN resin film.

[0087] Measure the light transmittance and tensile strength of the film according to the method shown in Example 1, and the results are shown in the following table:

[0088] Table 6 Light transmittance and tensile strength of the resin film obtained in Example 6

[0089] Category Light transmittance Tensile strength (transverse / longitudinal) Unit ％ MPa Example 6 97 187 / 238

[0090] Example 7

[0091] This example provides a method for preparing an optical grade polyethylene naphthalate (PEN) film using a mixture of dimethyl naphthalate isomers as monomers, including the following steps:

[0092] (1) Put 150 g of dimethyl 2,6-naphthalate, 150 g of dimethyl 2,7-naphthalate, 155 g of ethylene glycol, 0.05 g of zinc acetate, and 0.05 g of triphenyl phosphite into a 1 L stainless steel reactor. Open the nitrogen valve to replace the air in the reactor with nitrogen. Heat up to 180 °C, set the nitrogen gas flow rate at 400 mL / min, set the rotation speed at 200 r / min, react for 3 hours, and collect methanol.

[0093] (2) Weigh another 0.05 g of antioxidant 1010 and disperse it in 50 g of ethylene glycol, and add it into the reaction kettle through the feeding port.

[0094] (3) Continue to heat up to 255 °C, control the nitrogen gas flow rate at 500 ml / min, set the rotation speed at 300 r / min, keep the pressure inside the autoclave at atmospheric pressure, react for 4 hours under this condition, and collect the by-product ethylene glycol; heat up to 265 °C, control the nitrogen gas flow rate at 100 ml / min, reduce the rotation speed to 50 r / min, keep the pressure inside the autoclave at 150 Pa, react for 2 hours under this condition; heat up to 275 °C, turn off the nitrogen gas, reduce the rotation speed to 20 r / min, keep the pressure inside the autoclave at 50 Pa, end the reaction after reacting for 1 hour; cool down to obtain PEN resin.

[0095] (4) Take an appropriate amount of PEN resin and melt and cast it into a film in an extruder with a thickness of 200 μm. After cutting, place it in a synchronous biaxial stretching machine, set the temperature at 140 °C, and the preheating time at 300 s; heat up to 140 °C, set the stretching rate at 50 mm / min, the transverse stretching ratio at 3 times, and the longitudinal stretching ratio at 4 times, and then anneal it statically at 130 °C for 500 s to obtain a PEN resin film.

[0096] Measure the light transmittance and tensile strength of the film by the method shown in Example 1, and the results are shown in the following table:

[0097] Table 7 Light transmittance and tensile strength of the resin film obtained in Example 7

[0098] Category Light transmittance Tensile strength (transverse / longitudinal) Unit ％ MPa Example 6 95 244 / 268

[0099] Example 8

[0100] This example provides a method for preparing an optical grade polyethylene naphthalate (PEN) film using a mixture of naphthalene dicarboxylic acid dimethyl ester isomers as monomers, including the following steps:

[0101] (1) Put 150 g of dimethyl 2,6-naphthalenedicarboxylate, 150 g of dimethyl 2,7-naphthalenedicarboxylate, 155 g of ethylene glycol, 0.05 g of zinc acetate, and 0.05 g of triphenyl phosphite into a 1 L stainless steel reactor. Open the nitrogen valve to replace the air inside the autoclave with nitrogen. Heat up to 180 °C, set the nitrogen gas flow rate at 400 mL / min, set the rotation speed at 200 r / min, react for 3 hours, and collect methanol.

[0102] (2) Weigh another 0.05 g of antioxidant 1010 and disperse it in 50 g of ethylene glycol, and add it to the reaction kettle through the feeding port.

[0103] (3) Continue to heat up to 255 °C, control the nitrogen gas flow rate at 500 ml / min, set the rotation speed at 300 r / min, keep the pressure inside the autoclave at atmospheric pressure, react under these conditions for 4 hours, and collect the by-product ethylene glycol; heat up to 265 °C, control the nitrogen gas flow rate at 100 ml / min, reduce the rotation speed to 50 r / min, and keep the pressure inside the autoclave at 150 Pa, react under these conditions for 2 hours; heat up to 275 °C, turn off the nitrogen gas, reduce the rotation speed to 20 r / min, and keep the pressure inside the autoclave at 50 Pa, end the reaction after reacting under these conditions for 1 hour; cool down to obtain PEN resin.

[0104] (4) Take an appropriate amount of PEN resin and melt and cast it into a film in an extruder with a thickness of 200 μm. After cutting, place it in a synchronous biaxial stretching machine, set the temperature at 130 °C, and the preheating time at 300 s; heat up to 140 °C, set the stretching rate at 50 mm / min, the transverse stretching ratio at 3 times, and the longitudinal stretching ratio at 4 times, and then anneal it statically at 140 °C for 200 s to obtain a PEN resin film.

[0105] Measure the light transmittance and tensile strength of the film by the method shown in Example 1, and the results are shown in the following table:

[0106] Table 8 Light transmittance and haze of the resin film obtained in Example 8

[0107] Category Light transmittance Tensile strength (transverse / longitudinal) Unit ％ MPa Example 8 92 165 / 197

[0108] Example 9

[0109] This example provides a method for preparing an optical grade polyethylene naphthalate (PEN) film using a mixture of naphthalenedicarboxylic acid dimethyl ester isomers as monomers, including the following steps:

[0110] (1) Take 150 g of dimethyl 2,6-naphthalenedicarboxylate, 150 g of dimethyl 2,7-naphthalenedicarboxylate, 155 g of ethylene glycol, 0.05 g of zinc acetate, and 0.05 g of triphenyl phosphite and put them into a 1 L stainless steel reactor. Open the nitrogen valve to replace the air inside the autoclave with nitrogen, heat up to 180 °C, set the nitrogen gas flow rate at 400 mL / min, set the rotation speed at 200 r / min, react for 3 hours, and collect methanol.

[0111] (2) Weigh another 0.05 g of antioxidant 1010 and disperse it in 50 g of ethylene glycol, and add it to the reaction kettle through the feeding port.

[0112] (3) Continue to raise the temperature to 255 °C, control the nitrogen gas flow rate at 500 ml / min, set the rotation speed at 300 r / min, keep the pressure inside the autoclave at atmospheric pressure, react under these conditions for 4 hours, and collect the by-product ethylene glycol; raise the temperature to 265 °C, control the nitrogen gas flow rate at 100 ml / min, reduce the rotation speed to 50 r / min, and keep the pressure inside the autoclave at 150 Pa, react under these conditions for 2 hours; raise the temperature to 275 °C, turn off the nitrogen gas, reduce the rotation speed to 20 r / min, and keep the pressure inside the autoclave at 50 Pa, end the reaction after reacting under these conditions for 1 hour; cool down to obtain PEN resin.

[0113] (4) Take an appropriate amount of PEN resin and melt it into a sheet in an extruder with a thickness of 200 μm. After cutting, place it in a synchronous biaxial stretching machine, set the temperature at 145 °C, and the preheating time at 300 s; raise the temperature to 140 °C, set the stretching rate at 50 mm / min, the transverse stretching ratio at 3 times, and the longitudinal stretching ratio at 4 times, and then anneal it statically at 140 °C for 200 s to obtain a PEN resin film.

[0114] Measure the light transmittance and tensile strength of the film according to the method shown in Example 1, and the results are shown in the following table:

[0115] Table 9 Light transmittance and tensile strength of the resin film obtained in Example 9

[0116] Category Light transmittance Tensile strength (transverse / longitudinal) Unit ％ MPa Example 9 96 214 / 270

[0117] Comparative Example 1

[0118] This comparative example provides a method for preparing an optically grade polyethylene naphthalate (PEN) film using a mixture of dimethyl naphthalate isomers as monomers, including the following steps:

[0119] (1) Put 305 g of dimethyl 2,6-naphthalate, 155 g of ethylene glycol, 0.05 g of zinc acetate, and 0.05 g of triphenyl phosphite into a 1 L stainless steel reactor. Open the nitrogen valve to replace the air inside the autoclave with nitrogen. Raise the temperature to 180 °C, set the nitrogen gas flow rate at 400 mL / min, set the rotation speed at 200 r / min, react for 3 hours, and collect methanol.

[0120] (2) Weigh another 0.05 g of antioxidant 1010 and disperse it in 50 g of ethylene glycol, and add it into the reaction kettle through the feeding port.

[0121] (3) Continue to heat up to 255 °C, control the nitrogen gas flow rate at 500 ml / min, set the rotation speed at 300 r / min, keep the pressure inside the autoclave at atmospheric pressure, react for 4 hours under this condition, and collect the by-product ethylene glycol; heat up to 265 °C, control the nitrogen gas flow rate at 100 ml / min, reduce the rotation speed to 50 r / min, keep the pressure inside the autoclave at 150 Pa, react for 2 hours under this condition; heat up to 275 °C, turn off the nitrogen gas, reduce the rotation speed to 20 r / min, keep the pressure inside the autoclave at 50 Pa, end the reaction after reacting for 1 hour; cool down to obtain PEN resin.

[0122] (4) Take an appropriate amount of PEN resin and melt it into a film in an extruder with a thickness of 200 μm. After cutting, place it in a synchronous biaxial stretching machine, set the temperature at 140 °C, and the preheating time at 300 s; heat up to 140 °C, set the stretching rate at 50 mm / min, the transverse stretching ratio at 3 times, and the longitudinal stretching ratio at 4 times, and then anneal it statically at 140 °C for 200 s to obtain a PEN resin film.

[0123] The light transmittance and tensile strength of the film of Comparative Example 1 were measured by the method shown in Example 1, and the results are shown in the following table:

[0124] Table 10 Light transmittance and tensile strength of the resin film obtained in Comparative Example 1

[0125] Category Light transmittance Tensile strength (transverse / longitudinal) Unit ％ MPa Comparative Example 1 81 157 / 211

[0126] Comparative Example 2

[0127] This comparative example provides a method for preparing an optical grade polyethylene naphthalate (PEN) film using a mixture of dimethyl naphthalate isomers as a monomer, including the following steps:

[0128] (1) Put 305 g of dimethyl 2,6-naphthalate, 155 g of ethylene glycol, 0.05 g of zinc acetate, and 0.05 g of triphenyl phosphite into a 1 L stainless steel reactor. Open the nitrogen valve to replace the air inside the autoclave with nitrogen. Heat up to 180 °C, set the nitrogen gas flow rate at 400 mL / min, set the rotation speed at 200 r / min, react for 3 hours, and collect methanol.

[0129] (2) Weigh another 0.05 g of antioxidant 1010 and disperse it in 50 g of ethylene glycol, and add it to the reaction kettle through the feeding port.

[0130] (3) Continue to heat up to 255 °C, control the nitrogen gas flow rate at 500 ml / min, set the rotation speed at 300 r / min, keep the pressure in the autoclave at atmospheric pressure, react under these conditions for 4 hours, and collect the by-product ethylene glycol; heat up to 265 °C, control the nitrogen gas flow rate at 100 ml / min, reduce the rotation speed to 50 r / min, keep the pressure in the autoclave at 150 Pa, react under these conditions for 2 hours; heat up to 275 °C, turn off the nitrogen gas, reduce the rotation speed to 20 r / min, keep the pressure in the autoclave at 50 Pa, end the reaction after reacting under these conditions for 1 hour; cool down to obtain PEN resin.

[0131] (4) Take an appropriate amount of PEN resin and melt and cast it into a film in an extruder with a thickness of 200 μm. After cutting, place it in a synchronous biaxial stretching machine, set the temperature at 140 °C, and the preheating time at 300 s; heat up to 140 °C, set the stretching rate at 50 mm / min, the transverse stretching ratio at 3 times, and the longitudinal stretching ratio at 4 times, and then anneal it statically at 140 °C for 200 s. It was found that the film was broken during the stretching process and could not form a film.

[0132] Comparative Example 3

[0133] This comparative example provides a method for preparing an optical grade polyethylene naphthalate (PEN) film using a mixture of dimethyl naphthalate isomers as monomers, including the following steps:

[0134] (1) Put 150 g of dimethyl 2,6-naphthalate, 150 g of dimethyl 2,7-naphthalate, 155 g of ethylene glycol, 0.05 g of zinc acetate, and 0.05 g of triphenyl phosphite into a 1 L stainless steel reactor. Open the nitrogen valve to replace the air in the autoclave with nitrogen. Heat up to 180 °C, set the nitrogen gas flow rate at 400 mL / min, set the rotation speed at 200 r / min, react for 3 hours, and collect methanol.

[0135] (2) There is no operation of adding antioxidant 1010 as a supplement.

[0136] (3) Continue to heat up to 255 °C, control the nitrogen gas flow rate at 500 ml / min, set the rotation speed at 300 r / min, keep the pressure in the autoclave at atmospheric pressure, react under these conditions for 4 hours, and collect the by-product ethylene glycol; heat up to 265 °C, control the nitrogen gas flow rate at 100 ml / min, reduce the rotation speed to 50 r / min, keep the pressure in the autoclave at 150 Pa, react under these conditions for 2 hours; heat up to 275 °C, turn off the nitrogen gas, reduce the rotation speed to 20 r / min, keep the pressure in the autoclave at 50 Pa, end the reaction after reacting under these conditions for 1 hour; cool down to obtain PEN resin.

[0137] (4) Take an appropriate amount of PEN resin and melt-cast it into a film in an extruder with a thickness of 200 μm. After cutting, place it in a synchronous biaxial stretching machine, set the temperature to 145 °C, and the preheating time to 300 s; raise the temperature to 140 °C, set the stretching rate to 50 mm / min, the transverse stretching ratio to 3 times, and the longitudinal stretching ratio to 4 times. Then, anneal it statically at 140 °C for 200 s to obtain a PEN resin film.

[0138] Measure the light transmittance and tensile strength of the film of Comparative Example 3 by the method shown in Example 1, and the results are shown in the following table:

[0139] Table 11 Light transmittance and tensile strength of the resin film obtained in Comparative Example 3

[0140]

[0141]

[0142] Comparative Example 4

[0143] This comparative example provides a method for preparing an optical grade polyethylene naphthalate (PEN) film using a mixture of dimethyl naphthalate isomers as monomers, including the following steps:

[0144] (1) Put 305 g of dimethyl 2,6-naphthalate, 155 g of ethylene glycol, 0.05 g of zinc acetate, and 0.05 g of triphenyl phosphite into a 1 L stainless steel reactor. Open the nitrogen valve to replace the air in the kettle with nitrogen. Raise the temperature to 180 °C, set the nitrogen flow rate to 400 mL / min, set the rotation speed to 200 r / min, react for 3 hours, and collect methanol.

[0145] (2) Weigh 0.05 g of antioxidant 1010 and disperse it in 50 g of ethylene glycol, and add it into the reaction kettle through the feeding port.

[0146] (3) Continue to raise the temperature to 255 °C, control the nitrogen flow rate to 500 ml / min, set the rotation speed to 300 r / min, and the pressure in the kettle is normal pressure. React under this condition for 4 hours, and collect the by-product ethylene glycol; raise the temperature to 265 °C, control the nitrogen flow rate to 100 ml / min, reduce the rotation speed to 50 r / min, and the pressure in the kettle is 150 Pa. React under this condition for 2 hours; raise the temperature to 275 °C, close the nitrogen, reduce the rotation speed to 20 r / min, and the pressure in the kettle is 50 Pa. React for 1 hour under this condition and then end; cool down to obtain PEN resin.

[0147] (4) Take an appropriate amount of PEN resin and melt-cast it into a film in an extruder with a thickness of 200 μm. After cutting, place it in a synchronous biaxial stretching machine. Set the temperature to 140 °C and the preheating time to 300 s. Set the stretching temperature to 125 °C, the stretching rate to 50 mm / min, the transverse stretching ratio to 3 times, and the longitudinal stretching ratio to 4 times. Then, anneal it statically at 140 °C for 200 s. Take out the film and find that its surface size is uneven and necking appears, making it unusable.

[0148] Comparative Example 5

[0149] This comparative example provides a method for preparing an optical grade polyethylene naphthalate (PEN) film using a mixture of dimethyl naphthalate isomers as monomers, including the following steps:

[0150] (1) Put 305 g of dimethyl 2,6-naphthalate, 155 g of ethylene glycol, 0.05 g of zinc acetate, and 0.05 g of triphenyl phosphite into a 1 L stainless steel reactor. Open the nitrogen valve to displace the air in the kettle with nitrogen. Heat up to 180 °C, set the nitrogen flow rate to 400 mL / min, set the rotation speed to 200 r / min, react for 3 hours, and collect methanol.

[0151] (2) Weigh another 0.05 g of antioxidant 1010 and disperse it in 50 g of ethylene glycol, then add it into the reaction kettle through the feeding port.

[0152] (3) Continue to heat up to 255 °C, control the nitrogen flow rate to 500 ml / min, set the rotation speed to 300 r / min, and keep the pressure in the kettle at atmospheric pressure. React under these conditions for 4 hours and collect the by-product ethylene glycol. Heat up to 265 °C, control the nitrogen flow rate to 100 ml / min, reduce the rotation speed to 50 r / min, and keep the pressure in the kettle at 150 Pa. React under these conditions for 2 hours. Heat up to 275 °C, close the nitrogen, reduce the rotation speed to 20 r / min, and keep the pressure in the kettle at 50 Pa. React for 1 hour under these conditions and then end the reaction. Cool down to obtain PEN resin.

[0153] (4) Take an appropriate amount of PEN resin and melt-cast it into a film in an extruder with a thickness of 200 μm. After cutting, place it in a synchronous biaxial stretching machine. Set the temperature to 140 °C and the preheating time to 300 s. Heat up to 140 °C, set the stretching rate to 50 mm / min, the transverse stretching ratio to 3 times, and the longitudinal stretching ratio to 4 times. Then, anneal it statically at 140 °C for 800 s to obtain a PEN resin film.

[0154] Use the method shown in Example 1 to measure the light transmittance and tensile strength of the film in Comparative Example 5. The results are shown in the following table:

[0155] Table 12 Light transmittance and tensile strength of the resin film obtained in Comparative Example 5

[0156] Category Light transmittance Tensile strength (transverse / longitudinal) Unit ％ MPa Comparative Example 5 65 201 / 236

[0157] According to the above Examples 1-9 and Comparative Examples 1-5, it can be seen that using 2,6-NDC and 2,7-NDC as mixed monomers effectively enhances the light transmittance and mechanical properties of the PEN film. The ratio of the two, as well as the temperature, ratio, and annealing time during the biaxial stretching process, all affect the light transmittance and mechanical properties of the film.

[0158] Example 10

[0159] This example provides a method for preparing an optical grade polyethylene naphthalate film using a mixture of dimethyl naphthalate isomers as monomers, including the following steps:

[0160] (1) Take 20 g of dimethyl 2,6-naphthalate, 10 g of dimethyl 2,7-naphthalate, 32 g of ethylene glycol, 0.001 g of zinc acetate, and 0.001 g of triphenyl phosphite and put them into a 1 L stainless steel reactor. Open the nitrogen valve to replace the air in the kettle with nitrogen. Heat up to 160 °C, set the nitrogen flow rate to 300 mL / min, set the rotation speed to 200 r / min, react for 4 hours, and collect methanol.

[0161] (2) Weigh 0.001 g of antioxidant 1010 and disperse it in 50 g of ethylene glycol, and add it into the reaction kettle through the feeding port.

[0162] (3) Continue to heat up to 250 °C, control the nitrogen flow rate to 300 ml / min, set the rotation speed to 200 r / min, and the pressure in the kettle is normal pressure. React under this condition for 4 hours, and collect the by-product ethylene glycol; heat up to 270 °C, control the nitrogen flow rate to 50 ml / min, reduce the rotation speed to 30 r / min, and the pressure in the kettle is 200 Pa. React under this condition for 2 hours; heat up to 270 °C, close the nitrogen, reduce the rotation speed to 20 r / min, and the pressure in the kettle is 100 Pa. End the reaction after reacting for 1 hour under this condition; cool down to obtain PEN resin.

[0163] (4) Take an appropriate amount of PEN resin and melt-cast it into a sheet in an extruder with a thickness of 30 μm. After cutting, place it in a synchronous biaxial stretching machine, set the temperature to 130 °C, and the preheating time to 30 s; at 130 °C, set the stretching rate to 50 mm / min, the transverse stretching ratio to 2 times, and the longitudinal stretching ratio to 7 times, and then anneal it statically at 130 °C for 30 s to obtain a PEN resin film.

[0164] Example 11

[0165] This example provides a method for preparing an optical grade polyethylene naphthalate film using a mixture of dimethyl naphthalate isomers as monomers, including the following steps:

[0166] (1) Charge 30 g of dimethyl 2,6-naphthalenedicarboxylate, 20 g of dimethyl 2,7-naphthalenedicarboxylate, 33 g of ethylene glycol, 0.005 g of zinc acetate, and 0.003 g of triphenyl phosphite into a 1-L stainless steel reactor. Open the nitrogen valve to displace the air in the kettle with nitrogen. Heat up to 190 °C, set the nitrogen flow rate to 500 mL / min, set the rotation speed to 300 r / min, react for 2 hours, and collect methanol.

[0167] (2) Weigh another 0.005 g of antioxidant 1010 and disperse it in 50 g of ethylene glycol, then add it into the reaction kettle through the feeding port.

[0168] (3) Continue to heat up to 260 °C, control the nitrogen flow rate to 400 ml / min, set the rotation speed to 250 r / min, and keep the pressure in the kettle at atmospheric pressure. React under these conditions for 3 hours and collect the by-product ethylene glycol. Heat up to 263 °C, control the nitrogen flow rate to 60 ml / min, reduce the rotation speed to 40 r / min, and keep the pressure in the kettle at 100 Pa. React under these conditions for 3 hours. Heat up to 280 °C, close the nitrogen, reduce the rotation speed to 30 r / min, and keep the pressure in the kettle at 60 Pa. React for 2 hours under these conditions and then end the reaction. Cool down to obtain PEN resin.

[0169] (4) Take an appropriate amount of PEN resin and melt it into a sheet in an extruder with a thickness of 500 μm. After cutting, place it in a synchronous biaxial stretching machine, set the temperature to 140 °C, and the preheating time to 100 s. Heat up to 145 °C, set the stretching rate to 50 mm / min, the transverse stretching ratio to 6 times, and the longitudinal stretching ratio to 2 times. Then anneal it statically at 140 °C for 600 s to obtain a PEN resin film.

[0170] Example 12

[0171] This example provides a method for preparing an optical-grade polyethylene naphthalate film using a mixture of dimethyl naphthalenedicarboxylate isomers as monomers, including the following steps:

[0172] (1) Charge 40 g of dimethyl 2,6-naphthalenedicarboxylate, 30 g of dimethyl 2,7-naphthalenedicarboxylate, 34 g of ethylene glycol, 0.01 g of zinc acetate, and 0.08 g of triphenyl phosphite into a 1-L stainless steel reactor. Open the nitrogen valve to displace the air in the kettle with nitrogen. Heat up to 170 °C, set the nitrogen flow rate to 600 mL / min, set the rotation speed to 250 r / min, react for 3 hours, and collect methanol.

[0173] (2) Weigh another 0.01 g of antioxidant 1010 and disperse it in 50 g of ethylene glycol, then add it into the reaction kettle through the feeding port.

[0174] (3) Continue to heat up to 255 °C, control the nitrogen gas flow rate at 600 ml / min, set the rotation speed at 240 r / min, keep the pressure inside the autoclave at atmospheric pressure, react for 3.5 hours under this condition, and collect the by-product ethylene glycol; heat up to 260 °C, control the nitrogen gas flow rate at 70 ml / min, reduce the rotation speed to 35 r / min, keep the pressure inside the autoclave at 120 Pa, react for 3 hours under this condition; heat up to 272 °C, close the nitrogen gas, reduce the rotation speed to 30 r / min, keep the pressure inside the autoclave at 80 Pa, end the reaction after reacting for 1.5 hours under this condition; cool down to obtain PEN resin.

[0175] (4) Take an appropriate amount of PEN resin and melt and cast it into a film in an extruder with a thickness of 100 μm. After cutting, place it in a synchronous biaxial stretching machine, set the temperature at 135 °C, and the preheating time at 200 s; heat up to 150 °C, set the stretching rate at 50 mm / min, the transverse stretching ratio at 3 times, and the longitudinal stretching ratio at 4 times, and then anneal it statically at 135 °C for 100 s to obtain a PEN resin film.

[0176] Example 13

[0177] This example provides a method for preparing an optical grade polyethylene naphthalate film using a mixture of naphthalenedicarboxylic acid dimethyl ester isomers as monomers, including the following steps:

[0178] (1) Take 50 g of dimethyl 2,6-naphthalenedicarboxylate, 40 g of dimethyl 2,7-naphthalenedicarboxylate, 32 g of ethylene glycol, 0.05 g of antimony glycolate, and 0.1 g of antioxidant 1010 and put them into a 1 L stainless steel reactor. Open the nitrogen valve to replace the air inside the autoclave with nitrogen. Heat up to 180 °C, set the nitrogen gas flow rate at 400 mL / min, set the rotation speed at 230 r / min, react for 3 hours, and collect methanol.

[0179] (2) Weigh another 0.07 g of antioxidant 1010 and disperse it in 50 g of ethylene glycol, and add it to the reaction kettle through the feeding port.

[0180] (3) Continue to heat up to 252 °C, control the nitrogen gas flow rate at 450 ml / min, set the rotation speed at 270 r / min, keep the pressure inside the autoclave at atmospheric pressure, react for 3 hours under this condition, and collect the by-product ethylene glycol; heat up to 268 °C, control the nitrogen gas flow rate at 100 ml / min, reduce the rotation speed to 45 r / min, keep the pressure inside the autoclave at 160 Pa, react for 2.5 hours under this condition; heat up to 276 °C, close the nitrogen gas, reduce the rotation speed to 20 r / min, keep the pressure inside the autoclave at 70 Pa, end the reaction after reacting for 1.5 hours under this condition; cool down to obtain PEN resin.

[0181] (4) Take an appropriate amount of PEN resin and melt-cast it into a film in an extruder with a thickness of 300 μm. After cutting, place it in a synchronous biaxial stretching machine, set the temperature to 140 °C, and the preheating time to 150 s; raise the temperature to 160 °C, set the stretching rate to 50 mm / min, the transverse stretching ratio to 4 times, and the longitudinal stretching ratio to 3 times. Then, anneal it statically at 130 °C for 300 s to obtain a PEN resin film.

[0182] Example 14

[0183] This example provides a method for preparing an optical grade polyethylene naphthalate film using a mixture of dimethyl naphthalate isomers as monomers, including the following steps:

[0184] (1) Take 35 g of dimethyl 2,6-naphthalate, 15 g of dimethyl 2,7-naphthalate, 33 g of ethylene glycol, 0.1 g of zinc acetate, 0.02 g of triphenyl phosphite, and 0.02 g of antioxidant 1010 and put them into a 1 L stainless steel reactor. Open the nitrogen valve, replace the air in the kettle with nitrogen, raise the temperature to 165 °C, set the nitrogen flow rate to 450 mL / min, set the rotation speed to 270 r / min, react for 2 hours, and collect methanol.

[0185] (2) Weigh another 0.1 g of antioxidant 1010 and disperse it in 50 g of ethylene glycol, and add it to the reaction kettle through the feeding port.

[0186] (3) Continue to raise the temperature to 257 °C, control the nitrogen flow rate to 550 ml / min, set the rotation speed to 220 r / min, and the pressure in the kettle is normal pressure. React under this condition for 4 hours and collect the by-product ethylene glycol; raise the temperature to 265 °C, control the nitrogen flow rate to 80 ml / min, reduce the rotation speed to 50 r / min, and the pressure in the kettle is 170 Pa. React under this condition for 2 hours; raise the temperature to 278 °C, close the nitrogen, reduce the rotation speed to 25 r / min, and the pressure in the kettle is 90 Pa. React for 1.5 hours under this condition and then end; cool down to obtain PEN resin.

[0187] (4) Take an appropriate amount of PEN resin and melt-cast it into a film in an extruder with a thickness of 400 μm. After cutting, place it in a synchronous biaxial stretching machine, set the temperature to 140 °C, and the preheating time to 250 s; raise the temperature to 155 °C, set the stretching rate to 50 mm / min, the transverse stretching ratio to 5 times, and the longitudinal stretching ratio to 5 times. Then, anneal it statically at 140 °C for 450 s to obtain a PEN resin film.

[0188] The present invention discloses an optical grade polyethylene naphthalate (PEN) film using a mixture of dimethyl naphthalate isomers as monomers and a preparation method thereof. The method uses the mixed monomers as substrates, which can greatly reduce the economic cost caused by separating 2,6-dimethylnaphthalene and 2,7-dimethylnaphthalene. At the same time, the film products obtained from this resin have a high light transmittance and a high tensile strength, making it have broad industrial application prospects and commercial value.

[0189] The above description is only for the best embodiments of the present invention, but it should not be construed as a limitation of the claims. The present invention is not limited to the above embodiments, and its specific structure is allowed to vary. Any changes made within the protection scope of the independent claims of the present invention are within the protection scope of the present invention.

[0190] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

Claims

1. A preparation method of an optical grade polyethylene naphthalate film, characterized in that, it includes the following steps: Using dimethyl 2,6-naphthalenedicarboxylate and dimethyl 2,7-naphthalenedicarboxylate as monomers, under the action of a catalyst and an antioxidant, an esterification reaction occurs with ethylene glycol, and methanol is removed; after adding the antioxidant, a polycondensation reaction occurs to remove small molecule ethylene glycol to obtain PEN resin; The PEN resin is melted and then cast into sheets, and then after cutting, it is preheated, stretched and annealed to obtain an optical grade polyethylene naphthalate film.

2. The preparation method of the optical grade polyethylene naphthalate film according to claim 1, characterized in that, The PEN resin is specifically prepared through the following process: by mass, 20-50 parts of dimethyl 2,6-naphthalenedicarboxylate, 10-40 parts of dimethyl 2,7-naphthalenedicarboxylate, 32-34 parts of ethylene glycol, 0.001-0.1 part of a catalyst and 0.001-0.1 part of an antioxidant are mixed, then an ester exchange reaction is carried out to remove methanol, and then 0.001-0.1 part of antioxidant 1010 is added, and a polycondensation reaction is carried out to remove ethylene glycol to obtain PEN resin.

3. The preparation method of the optical grade polyethylene naphthalate film according to claim 1 or 2, characterized in that, The catalyst is one of zinc acetate and antimony glycolate.

4. The preparation method of the optical grade polyethylene naphthalate film according to claim 1 or 2, characterized in that, The antioxidant is one or both of antioxidant 1010 and triphenyl phosphite.

5. The preparation method of the optical grade polyethylene naphthalate film according to claim 2, characterized in that, The specific process of removing methanol by the ester exchange reaction is: under nitrogen protection, the temperature is raised to 160-190 °C, the nitrogen flow rate is controlled at 300-600 mL / min, the rotation speed is 200-300 r / min, and the reaction is carried out for 2-4 hours.

6. The preparation method of the optical grade polyethylene naphthalate film according to claim 2, characterized in that, The specific process of removing ethylene glycol by the polycondensation reaction is: under nitrogen protection, the temperature is raised to 250-260 °C, the nitrogen flow rate is controlled at 300-600 ml / min, the rotation speed is 200-300 r / min, and the reaction is carried out for 3-4 hours; then the temperature is raised to 260-270 °C, the nitrogen flow rate is controlled at 50-100 ml / min, the rotation speed is 30-50 r / min, the pressure is 100-200 Pa, and the reaction is carried out for 2-3 hours; then the temperature is raised to 270-280 °C, the nitrogen is turned off, the rotation speed is 20-30 r / min, the pressure is 50-100 Pa, and the reaction is carried out for 1-2 hours.

7. The preparation method of the optical grade polyethylene naphthalate film according to claim 1, characterized in that, The preheating temperature is 135-145 °C and the time is 30-300 s.

8. The preparation method of the optical grade polyethylene naphthalate film according to claim 1, characterized in that, The stretching temperature is 130-160 °C, the transverse stretching ratio is 2-6 times, and the longitudinal stretching ratio is 2-7 times.

9. The preparation method of the optical grade polyethylene naphthalate film according to claim 1, characterized in that, the annealing temperature is 130 - 140 °C, the time is 30 - 600 s, and the thickness of the cast sheet is 30 - 500 μm.

10. An optical grade polyethylene naphthalate film prepared by the method according to any one of claims 1 - 9, the thickness of the film is 25 - 150 μm, the light transmittance is 90 - 97%, the transverse tensile strength is 165 - 249 MPa, and the tensile strength is 197 - 295 MPa longitudinally.

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