High-rigidity thin optical polyester film and method for producing the same

Abstract

This invention belongs to the field of polyester film technology and relates to a high-rigidity thin optical polyester film and its preparation method. The film includes a B layer and an A layer located on both sides of the B layer, forming an ABA superimposed structure. The raw materials for preparing the B layer include 5-10% by mass of modified copolyester, with the remainder being pure polyester. The raw materials for preparing the A layer include 3-5% by mass of UV blocking masterbatch, 5-10% by mass of opening agent masterbatch, with the remainder being pure polyester. The modified copolyester is prepared by esterification polycondensation of a glycol mixture and a diacid; the molar ratio of the glycol mixture to the diacid is (1.2-1.28):1; the glycol mixture consists of anthracene-containing glycol and ethylene glycol, with a molar ratio of (1:9) to (3:7) between the anthracene-containing glycol and the ethylene glycol. The high-rigidity thin optical polyester film prepared by this application has the characteristics of high light transmittance, low haze, and high rigidity.

Description

Technical Field

[0001] This invention belongs to the field of polyester film technology, and relates to a high-rigidity thin optical polyester film and its preparation method. Background Technology

[0002] Polyethylene terephthalate (PET) is a type of thermoplastic polyester with good abrasion resistance, high light transmittance, and electrical insulation. Through various processing methods, it can be used in different fields, such as spinning, engineering plastics, and films. Polyester film is made from polyethylene terephthalate through melt co-extrusion and biaxial stretching. Due to its excellent mechanical, thermal, electrical insulation, and optical properties, it is widely used in electronics, displays, and protective equipment. With the increasing demands for thinner and lighter products in electronics, displays, and protective equipment, the development of lightweight and thinner optical polyester film technologies and products has received significant attention in recent years.

[0003] A key characteristic of thin optical polyester films is the requirement for high light transmittance and low haze. To ensure these properties, it's typically necessary to avoid adding inorganic particles that affect transmittance and haze to the core layer of the polyester film during production. This results in the following consequences: the polyester film lacks inorganic particles that can act as nucleating agents, leading to insufficient crystallinity after biaxial stretching. This manifests as insufficient film rigidity, making it prone to warping, unevenness, and poor temperature resistance during downstream processing and reheating. These issues negatively impact product usability, especially noticeable in thin optical polyester films smaller than 30 micrometers.

[0004] To address the issue of insufficient rigidity in thin optical polyester films, current technical solutions include: 1. Increasing the crystallinity of the PET material by raising the process temperature during biaxial stretching, thereby improving product rigidity. 2. Applying functional coatings to the surface of the polyester film, utilizing the inherent high rigidity of the coating material to enhance the overall rigidity of the film.

[0005] Although engineers have conducted extensive research on improving the rigidity of thin optical polyester films, current technical solutions for addressing the insufficient rigidity of thin optical polyester films still have many shortcomings: 1. Increasing the process temperature during biaxial stretching can increase crystallinity to some extent, but the increase is limited and cannot meet the requirements for improving product rigidity. Furthermore, increasing the process temperature can easily cause unevenness on the film surface due to excessive temperature. 2. Functional coating treatments on the polyester film surface have limited effect on improving film rigidity, and the coating process is prone to problems such as poor coating appearance, decreased yield, increased costs, and reduced versatility. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention provides a high-rigidity thin optical polyester film and its preparation method. The prepared high-rigidity thin optical polyester film has the characteristics of high light transmittance, low haze, and high rigidity. This significantly reduces problems such as warping, unevenness, and poor temperature resistance in downstream processing and use of thin optical polyester films. The product can be widely used in high-end protective / release films, window films, MLCC release films, and other fields.

[0007] The technical solution adopted by the present invention to solve its technical problem is: a high-rigidity thin optical polyester film, comprising a B layer and an A layer located on both sides of the B layer, and the whole having an ABA superimposed structure;

[0008] The raw materials for preparing the B layer include: 5-10% by mass of modified copolyester, with the remainder being pure polyester.

[0009] The raw materials for preparing the A layer include: 3-5% by mass of UV blocking masterbatch, 5-10% by mass of opening agent masterbatch, and the balance being pure polyester.

[0010] The modified copolyester is prepared by esterification polycondensation reaction of a mixture of glycols and a diacid; the molar ratio of the glycol mixture to the diacid is (1.2-1.28):1;

[0011] The diol mixture consists of an anthracene-containing diol and ethylene glycol, wherein the molar ratio of the anthracene-containing diol to the ethylene glycol is (1:9)-(3:7).

[0012] As an improved technical solution of this application, the dicarboxylic acid is an aromatic diacid.

[0013] As an improved technical solution of this application, the diol containing anthracene group is one of 1,4-anthracitediol, 9-anthracitemethanol, or 2-pentyl-9,10-anthracitediol.

[0014] As an improved technical solution of this application, the UV blocking masterbatch is a UV blocking masterbatch that can block wavelengths below 350nm while allowing wavelengths above 350nm to pass through.

[0015] As an improved technical solution of this application, the opening agent masterbatch is composed of pure polyester and silica particles, the content of silica particles is 0.3%-1.5% of the weight of the opening agent masterbatch, and the silica particle size is 1.0-2.0μm.

[0016] As an improved technical solution of this application, the thickness of the polyester film is 6-50μm.

[0017] As an improved technical solution of this application, the thickness of the A layer of the polyester film is independently 1-2 μm.

[0018] Another objective of this application is to provide a method for preparing a high-rigidity thin optical polyester film, comprising the following steps:

[0019] Step 1: In extruder I, add pure polyester, UV barrier masterbatch, and opening agent masterbatch according to the specified ratio for melt extrusion; in extruder II, add pure polyester and modified copolyester according to the specified ratio for melt extrusion.

[0020] Step 2: The melt extruded from extruder I is fed into layer A of the three-layer die head with an ABA structure; the melt extruded from extruder II is fed into layer B of the three-layer die head with an ABA structure; the melts of layers A and B flow out together according to their respective thickness ratios; after casting, longitudinal stretching, transverse stretching, shaping, cooling, UV irradiation, and winding, the high-rigidity thin optical polyester film is obtained.

[0021] As an improved technical solution of this application, the wavelength of the UV irradiation is 365nm, the UV irradiation power is 160-200w, and the UV irradiation time is 2-5 seconds.

[0022] The beneficial effects are:

[0023] 1. This invention employs a modified copolyester containing anthracene groups added to the main thickness layer (B layer) of a thin optical polyester film. Utilizing the good co-solubility of the modified copolyester and pure polyester, and its uniform distribution, after biaxial stretching and cooling, the anthracene groups in the modified copolyester undergo a cyclization reaction under UV irradiation of a specific wavelength, forming a uniform and dense three-dimensional network structure in the B layer material, thereby improving the rigidity of the thin optical polyester film.

[0024] 2. This invention employs a method in which inorganic particles that are beneficial for providing crystal nucleation agents are not added to the main thickness layer (B layer) of the thin optical polyester film. This avoids the decrease in film transmittance and the increase in haze caused by the reflection, refraction, and scattering of transmitted light by inorganic particles. While ensuring good rigidity, it also possesses excellent optical performance.

[0025] 3. The present invention employs adding a UV blocking masterbatch that can block wavelengths below 350nm while allowing wavelengths above 350nm to pass through to the outer layer A of a thin optical polyester film. This can prevent the already cyclic anthracene groups from de-cyclicating due to UV irradiation in the wavelength band below 350nm in natural light.

[0026] In summary, this invention significantly improves the rigidity of polyester film, enhances the convenience of downstream processing of polyester film and its resistance to deformation when heated again, and effectively reduces problems such as warping, unevenness and poor temperature resistance. Detailed Implementation

[0027] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0029] The thin optical polyester film provided by this invention includes a B layer (intermediate layer) and an A layer (surface layer) located on both sides of the B layer. By adding a modified copolyester containing anthracene groups to the B layer, the B layer material, without the addition of inorganic particles, forms a uniform and dense three-dimensional network structure in the B layer through the cyclization reaction of the anthracene groups under UV irradiation of a specific wavelength, thereby improving the rigidity of the thin optical polyester film. A UV-blocking masterbatch that can block wavelengths below 350nm while allowing light to pass through wavelengths above 350nm is added to the A layer, preventing the already cyclized anthracene groups from dissociating due to UV irradiation in the wavelength range below 350nm in natural light. The B layer and A layer are melt-co-extruded in multiple layers, cast on a film production line, and then subjected to longitudinal stretching, transverse stretching, shaping, and cooling. After being irradiated with a specific wavelength of UV light, a uniform and dense three-dimensional network structure is formed in the B layer through the cyclization reaction of the anthracene groups, and then the film is wound up. The polyester film produced by this structural design has high overall rigidity, which improves the convenience of downstream processing of the polyester film and its resistance to deformation when heated again. It also has excellent optical properties, which cannot be achieved by conventional polyester films.

[0030] In the production of thin polyester films, a certain amount of small-diameter inorganic particles are typically added to the core layer as nucleating agents to improve the rigidity of the product and enhance the crystallization effect of the core layer, which constitutes the main component of the thin film. However, the addition of inorganic particles can adversely affect the optical properties of polyester films, such as light transmittance, haze, and clarity. The three-dimensional network structure formed by the photocyclic reaction of copolyesters containing anthracene groups can replace inorganic particle nucleating agents, avoiding the decrease in film transmittance and increase in haze caused by the reflection, refraction, and scattering of transmitted light by inorganic particles. This ensures both good rigidity and excellent optical properties.

[0031] In this invention, by mass percentage, layer B consists of 5%-10% modified copolyester containing anthracene groups and 90%-95% pure polyester. Under long-wave ultraviolet light (>300 nm), the anthracene groups undergo a bimolecular [4+4] photo-cycling reaction to form dimers. These dimer rings are uniformly distributed in the pure resin, forming a dense three-dimensional network structure that is tightly interwoven with the pure polyester, acting as a skeleton and reducing the free movement of the pure polyester around the skeleton, thus improving the rigidity of layer B. However, when the content of modified copolyester containing anthracene groups is too high, it may alter the overall color tone of layer B. Furthermore, the excessive three-dimensional network structure tends to saturate in improving the rigidity of layer B and significantly increases product cost.

[0032] In this invention, the modified copolyester is copolymerized from a mixture of glycols and a diacid through esterification and polycondensation reactions. The molar ratio of the glycol mixture to the diacid is 1.2-1.28:1, more preferably 1.23-1.25:1. An excessively high molar ratio will affect the diethylene glycol content of the copolyester, negatively impacting the heat resistance of thin polyester film products using this copolyester. An excessively low molar ratio will lead to reduced esterification efficiency and esterification rate, which is detrimental to product quality and production.

[0033] In this invention, the molar ratio of the anthracene-containing diol to ethylene glycol in the diol mixture is (1:9)-(3:7), preferably (1.5:8.5)-(2.5:7.5). The anthracene-containing diol is one of 1,4-anthracene diol, 9-anthracene methanol, or 2-pentyl-9,10-anthracene diol, preferably 2-pentyl-9,10-anthracene diol. 2-pentyl-9,10-anthracene diol contains two hydroxyl groups, which allows for more effective esterification crosslinking with terephthalic acid.

[0034] In this invention, the dicarboxylic acid can be a straight-chain fatty diacid, but it is mainly an aromatic diacid, such as terephthalic acid, terephthalic acid, and terephthalic acid, with terephthalic acid and terephthalic acid being preferred, and terephthalic acid being more preferred from an economic point of view.

[0035] In this invention, by mass percentage, layer A is composed of 3-5% UV blocking masterbatch, 5-10% opening agent masterbatch and pure polyester.

[0036] Anthracene groups, through photo-cyclization, readily depolymerize under short-wave ultraviolet light (<300 nm), regenerating the original anthracene groups. To prevent the depolymerization of the three-dimensional network structure in layer B by short-wave ultraviolet light during use of high-rigidity thin optical polyester film products, a UV-blocking masterbatch capable of blocking wavelengths below 350 nm while allowing light to pass through wavelengths above 350 nm is added to the two outer layers (layer A) of layer B. This prevents the already cyclic anthracene groups from decyclizing due to UV irradiation below 350 nm in natural light. Adding 3-5% of the UV-blocking masterbatch can achieve full blocking of ultraviolet wavelengths below 350 nm in layer A. However, the UV-blocking masterbatch has a certain color, and adding too much will affect the color tone of the thin optical polyester film product.

[0037] In the typical polyester film production process, a certain amount of opening agent masterbatch needs to be added to the surface to improve the smoothness of the film and prevent scratches from forming on the roller surface. The effective components of commonly used opening agent masterbatches are mostly inorganic particles such as silicon dioxide, calcium carbonate, and barium sulfate.

[0038] In this invention, the opening agent masterbatch is composed of pure polyester and silica particles. The content of silica particles is 0.3%-1.5% of the weight of the opening agent masterbatch, preferably 0.3%. The average particle size of the silica particles is 1.0-2.0 μm, preferably 1.0-1.5 μm. The specific silica particle content and particle size can be determined according to the different light transmittance, haze, and surface roughness requirements of the polyester film.

[0039] In this invention, the pure polyester in layer A and layer B can be different polyesters or the same polyester, but all polyesters used are polymers of diacids and diols. In this invention, the thickness of the polyester film is 6-50 μm, more preferably 6-38 μm.

[0040] In this invention, the thickness of layer A is independently 1-2 μm. If the thickness of layer A is too low, it will be difficult for layer A to completely block ultraviolet light below 350 nm. If the thickness of layer A is too high, it will affect the overall transmittance and haze of the high-rigidity thin optical polyester film.

[0041] The present invention also provides a method for preparing the high-rigidity thin optical polyester film, the method comprising the following steps:

[0042] Step 1: In extruder I, add pure polyester, UV barrier masterbatch, and opening agent masterbatch in proportion and perform melt extrusion; in extruder II, add pure polyester and modified copolyester in proportion and perform melt extrusion.

[0043] Step 2: The melt extruded from extruder I is fed into layer A of the three-layer die head with an ABA structure, and the melt extruded from extruder II is fed into layer B of the three-layer die head with an ABA structure. The melts of layers A and B flow out together according to their respective thickness ratios. After casting, longitudinal stretching, transverse stretching, shaping, cooling, UV irradiation, and winding, a high-rigidity thin optical polyester film is obtained.

[0044] Step 1: In extruder I, pure polyester, UV barrier masterbatch, and opening agent masterbatch are added in proportion and melt extruded at a temperature of 276℃-286℃; in extruder II, pure polyester and modified copolyester are added in proportion and melt extruded at a temperature of 276℃-286℃.

[0045] Step 2: The melt extruded from extruder I is fed into layer A of the three-layer die head with an ABA structure, and the melt extruded from extruder II is fed into layer B of the three-layer die head with an ABA structure. The melts of layers A and B flow out together according to their respective thickness ratios. After casting, longitudinal stretching, transverse stretching, shaping, cooling, UV irradiation, and winding, a high-rigidity thin optical polyester film is obtained.

[0046] Among them, ① the casting is stretched longitudinally, and the longitudinal stretching ratio is 3.0-4.0.

[0047] ②Stretch the longitudinal stretching sheet laterally, with a lateral stretching ratio of 3.3-4.5.

[0048] ③ The stretched film is heat-set at a temperature of 225-245℃.

[0049] ④ Cool the shaped film at a temperature of 40-120℃.

[0050] ⑤ After cooling, the film is subjected to UV irradiation with a power of 160-200W.

[0051] ⑥ The UV-irradiated film is wound up to obtain a high-rigidity thin optical polyester film.

[0052] It should be noted that the longitudinal stretching ratio, transverse stretching ratio, heat setting temperature, and UV irradiation power involved in the preparation method described in this invention can be appropriately adjusted by those skilled in the art according to different product requirements, including but not limited to the parameters and conditions proposed in this invention.

[0053] The polyester film prepared according to the above method is tested using the following specific methods:

[0054] Thickness: Tested according to GB / T33399-2016.

[0055] Optical performance: tested according to ASTM D1003 (instrument model: BYK-4725) (T: transmittance, H: haze).

[0056] Rigidity: While ensuring the flatness of the polyester film, take a long strip of polyester film measuring 15mm × 160mm along the MD direction (longitudinal: longitudinal stretching direction), place it horizontally, and clamp it with a length of 20mm. The horizontal position difference between the free end and the clamped end is used as the evaluation standard for the rigidity of the polyester film. The smaller the horizontal difference, the higher the rigidity of the polyester film.

[0057] Temperature resistance: A 1260mm wide polyester film roll was passed through a 32m long oven at 160℃ at a speed of 40m / min under a traction tension of 15N / m. The smoothness of the polyester film surface was then observed. The better the smoothness, the better the temperature resistance of the polyester film. "○" indicates excellent temperature resistance; "△" indicates average temperature resistance; "×" indicates poor temperature resistance.

[0058] Appearance: Cut a piece of polyester film, 1 meter wide and 1 meter long, and carefully observe its appearance using a high-intensity flashlight (model: RJW7102A / LT, Ocean King Lighting Technology Co., Ltd.). If there are no scratches / abrasions or only one very minor scratch / abrasion is visible but uncertain, mark it with "○"; if obvious scratches / abrasions are visible (quantity) ≤ 5, mark it with "△"; if obvious scratches / abrasions are visible across the entire surface, mark it with "×".

[0059] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0060] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0061] Example 1

[0062] Preparation of modified copolyesters:

[0063] The mixture of glycols and terephthalic acid has a molar ratio of 1.25:1, and the molar ratio of 9-anthracene methanol to ethylene glycol in the glycol mixture is 10:90. The commonly used catalyst, antimony glycolate, is added at 200 ppm. The commonly used stabilizer, triphenyl phosphate, is added at 20 ppm. After thorough mixing, the mixture is added to a polyester synthesis reactor. Esterification is carried out under nitrogen protection at a reactor temperature of 220-260℃ and an initial pressure of 0.15-0.2 MPa. The pressure is released when the esterification rate reaches 96%, completing the esterification reaction. After the esterification reaction, excess glycols are removed, and the mixture is polycondensed at 280-290℃ and 130 Pa for 3.5 hours to obtain the modified copolyester.

[0064] In extruder I, polyethylene terephthalate, UV barrier masterbatch, and opening agent masterbatch are added in proportion for melt extrusion. In extruder II, polyethylene terephthalate and modified copolyester are added in proportion for melt extrusion. The melt extruded from extruder I is fed into layer A of a three-layer ABA-structured die, and the melt extruded from extruder II is fed into layer B of the same die.

[0065] Extruder I and Extruder II extrude simultaneously and are simultaneously fed into a T-die. Inside the T-die, the melt from Extruder I is evenly distributed to both sides of the melt from Extruder II. Following an A / B / A three-layer structure, the two sets of melts are stacked and merged, flowing onto a rotating casting cooling drum with a surface temperature of 20°C to obtain a laminated casting film. The laminated casting film is preheated at 70-85°C and then rapidly stretched longitudinally (in the length direction) by 3.5 times under infrared heating conditions using two rollers rotating at different speeds. It is then gradually cooled at 30-60°C to obtain a longitudinally stretched film. The longitudinally stretched film is clamped at both sides by a clamp and fed into a transverse stretching box. After preheating at 90-115℃, the longitudinally stretched film is stretched 3.8 times in the transverse (width direction) multiple times at 110-130℃. It is then heat-treated at 240℃ for 7-15 seconds, cooled at 40℃, and irradiated with UV light at a wavelength of 365nm and a power of 160w for 2 seconds before being pulled and wound up to obtain a high-rigidity thin optical polyester film with a thickness of 38μm, of which the thickness of layer A is 2.0μm.

[0066] In this example:

[0067] The raw materials for layer A are: 3 parts by weight of UV blocking masterbatch that can block wavelengths below 350nm, 8 parts by weight of opening agent masterbatch, and 89 parts by weight of polyethylene terephthalate.

[0068] The raw materials for layer B are: 5 parts by weight of modified copolyester and 95 parts by weight of polyethylene terephthalate.

[0069] The masterbatch for opening agents contains 0.5% silica particles by weight and has a particle size of 2.0 μm.

[0070] Example 2

[0071] Preparation of modified copolyesters:

[0072] The mixture of glycols and terephthalic acid is in a molar ratio of 1.2:1, with 2-pentyl-9,10-anthracene glycol and ethylene glycol in a molar ratio of 1:9. Common catalysts include antimony glycolate at 200 ppm and triphenyl phosphate at 20 ppm. After thorough mixing, the mixture is added to a polyester synthesis reactor. Esterification is carried out under nitrogen protection at a reactor temperature of 220-260℃ and an initial pressure of 0.15-0.2 MPa. Pressure is released when the esterification rate reaches 96%, completing the esterification reaction. After esterification, excess glycols are removed, and the mixture is polycondensed at 280-290℃ and 130 Pa for 3.5 hours to obtain the modified copolyester.

[0073] In extruder I, polyethylene terephthalate, UV barrier masterbatch, and opening agent masterbatch are added in proportion for melt extrusion. In extruder II, polyethylene terephthalate and modified copolyester are added in proportion for melt extrusion. The melt extruded from extruder I is fed into layer A of a three-layer ABA-structured die, and the melt extruded from extruder II is fed into layer B of the same die.

[0074] Extruder I and Extruder II extrude simultaneously and are simultaneously fed into a T-die. Inside the T-die, the melt from Extruder I is evenly distributed to both sides of the melt from Extruder II. Following an A / B / A three-layer structure, the two sets of melts are stacked and merged, flowing onto a rotating casting cooling drum with a surface temperature of 20°C to obtain a laminated casting film. The laminated casting film is preheated at 70-85°C and then rapidly stretched longitudinally (in the length direction) by 3.5 times under infrared heating conditions using two rollers rotating at different speeds. It is then gradually cooled at 30-60°C to obtain a longitudinally stretched film. The longitudinally stretched film is clamped at both sides by a clamp and fed into a transverse stretching box. After preheating at 90-115℃, the longitudinally stretched film is stretched 3.8 times in the transverse (width direction) multiple times at 110-130℃. It is then heat-treated at 240℃ for 7-15 seconds, cooled at 100℃, and irradiated with UV light at a wavelength of 365nm and a power of 160w for 2 seconds before being pulled and wound up to obtain a high-rigidity thin optical polyester film with a thickness of 12μm, of which the thickness of layer A is 1.0μm.

[0075] In this example:

[0076] The raw materials for layer A are: 5 parts by weight of UV blocking masterbatch that can block wavelengths below 300nm, 10 parts by weight of opening agent masterbatch, and 85 parts by weight of polyethylene terephthalate.

[0077] The raw materials for layer B are: 5 parts by weight of modified copolyester and 95 parts by weight of polyethylene terephthalate.

[0078] The silica particles in the opening agent masterbatch contain 0.3% silica particles with a particle size of 1.5 μm.

[0079] Example 3

[0080] Preparation of modified copolyesters:

[0081] The mixture of glycols and terephthalic acid is in a molar ratio of 1.2:1, and the molar ratio of 1,4-anthracene glycol to ethylene glycol in the glycol mixture is 2:8. The commonly used catalyst, antimony glycolate, is added at 200 ppm, and the commonly used stabilizer, triphenyl phosphate, is added at 20 ppm. After thorough mixing, the mixture is added to a polyester synthesis reactor. Esterification is carried out under nitrogen protection at a reactor temperature of 220-260℃ and an initial pressure of 0.15-0.2 MPa. The pressure is released when the esterification rate reaches 96%, completing the esterification reaction. After the esterification reaction, excess glycols are removed, and the mixture is polycondensed at 280-290℃ and 130 Pa for 3.5 hours to obtain the modified copolyester.

[0082] In extruder I, polyethylene terephthalate, UV barrier masterbatch, and opening agent masterbatch are added in proportion for melt extrusion. In extruder II, polyethylene terephthalate and modified copolyester are added in proportion for melt extrusion. The melt extruded from extruder I is fed into layer A of a three-layer ABA-structured die, and the melt extruded from extruder II is fed into layer B of the same die.

[0083] Extruder I and Extruder II extrude simultaneously and are simultaneously fed into a T-die. Inside the T-die, the melt from Extruder I is evenly distributed to both sides of the melt from Extruder II. Following an A / B / A three-layer structure, the two sets of melts are stacked and merged, flowing onto a rotating casting cooling drum with a surface temperature of 20°C to obtain a laminated casting film. The laminated casting film is preheated at 70-85°C and then rapidly stretched longitudinally (in the length direction) by 3.5 times under infrared heating conditions using two rollers rotating at different speeds. It is then gradually cooled at 30-60°C to obtain a longitudinally stretched film. The longitudinally stretched film is clamped at both sides by a clamp and fed into a transverse stretching box. After preheating at 90-115℃, the longitudinally stretched film is stretched 3.8 times in the transverse (width direction) multiple times at 110-130℃. It is then heat-treated at 240℃ for 7-15 seconds, cooled at 60℃, and irradiated with UV light at a wavelength of 365nm and a power of 200W for 3 seconds before being pulled and wound up to obtain a high-rigidity thin optical polyester film with a thickness of 25μm, of which the thickness of layer A is 1.5μm.

[0084] In this example:

[0085] The raw materials for layer A are: 5 parts by weight of UV blocking masterbatch that can block wavelengths below 350nm, 5 parts by weight of opening agent masterbatch, and 90 parts by weight of polyethylene terephthalate.

[0086] The raw materials for layer B are: 8 parts by weight of modified copolyester and 92 parts by weight of polyethylene terephthalate.

[0087] The silica particles in the opening agent masterbatch contain 0.3% silica particles with a particle size of 2.0 μm.

[0088] Example 4

[0089] Preparation of modified copolyesters:

[0090] The mixture of glycols and terephthalic acid was in a molar ratio of 1.23:1, with a molar ratio of 2-pentyl-9,10-anthracene glycol to ethylene glycol of 1.5:8.5. A common catalyst, antimony glycolate, was added at 200 ppm, and a common stabilizer, triphenyl phosphate, was added at 20 ppm. After thorough mixing, the mixture was added to a polyester synthesis reactor. Esterification was carried out under nitrogen protection at a reactor temperature of 220-260℃ and an initial pressure of 0.15-0.2 MPa. The pressure was released when the esterification rate reached 96%, completing the esterification reaction. After the esterification reaction, excess glycols were removed, and the mixture was polycondensed at 280-290℃ and 130 Pa for 3.5 hours to obtain the modified copolyester.

[0091] In extruder I, polyethylene terephthalate, UV barrier masterbatch, and opening agent masterbatch are added in proportion for melt extrusion. In extruder II, polyethylene terephthalate and modified copolyester are added in proportion for melt extrusion. The melt extruded from extruder I is fed into layer A of a three-layer ABA-structured die, and the melt extruded from extruder II is fed into layer B of the same die.

[0092] Extruder I and Extruder II extrude simultaneously and are simultaneously fed into a T-die. Inside the T-die, the melt from Extruder I is evenly distributed to both sides of the melt from Extruder II. Following an A / B / A three-layer structure, the two sets of melts are stacked and merged, flowing onto a rotating casting cooling drum with a surface temperature of 20°C to obtain a laminated casting film. The laminated casting film is preheated at 70-85°C and then rapidly stretched longitudinally (in the length direction) by 3.5 times under infrared heating conditions using two rollers rotating at different speeds. It is then gradually cooled at 30-60°C to obtain a longitudinally stretched film. The longitudinally stretched film is clamped at both sides by a clamp and fed into a transverse stretching box. After preheating at 90-115℃, the longitudinally stretched film is stretched 3.8 times in the transverse (width direction) multiple times at 110-130℃. It is then heat-treated at 240℃ for 7-15 seconds, cooled at 60℃, and irradiated with UV light at a wavelength of 365nm and a power of 160w for 4 seconds before being pulled and wound up to obtain a high-rigidity thin optical polyester film with a thickness of 38μm, of which the thickness of the A layer is 1.5μm.

[0093] In this example:

[0094] The raw materials for layer A are: 3 parts by weight of UV blocking masterbatch that can block wavelengths below 350nm, 8 parts by weight of opening agent masterbatch, and 89 parts by weight of polyethylene terephthalate.

[0095] The raw materials for layer B are: 8 parts by weight of modified copolyester and 92 parts by weight of polyethylene terephthalate.

[0096] The silica particles in the opening agent masterbatch contain 0.3% silica particles with a particle size of 2.0 μm.

[0097] Example 5

[0098] Preparation of modified copolyesters:

[0099] The mixture of glycols and terephthalic acid is in a molar ratio of 1.25:1, with a molar ratio of 2-pentyl-9,10-anthracene glycol to ethylene glycol of 2:8. Commonly used catalysts include antimony glycolate at 200 ppm and triphenyl phosphate at 20 ppm. After thorough mixing, the mixture is added to a polyester synthesis reactor. Esterification is carried out under nitrogen protection at a reactor temperature of 220-260℃ and an initial pressure of 0.15-0.2 MPa. Pressure is released when the esterification rate reaches 96%, completing the esterification reaction. After esterification, excess glycols are removed, and the mixture is polycondensed at 280-290℃ and 130 Pa for 3.5 hours to obtain the modified copolyester.

[0100] In extruder I, polyethylene terephthalate, UV barrier masterbatch, and opening agent masterbatch are added in proportion for melt extrusion. In extruder II, polyethylene terephthalate and modified copolyester are added in proportion for melt extrusion. The melt extruded from extruder I is fed into layer A of a three-layer ABA-structured die, and the melt extruded from extruder II is fed into layer B of the same die.

[0101] Extruder I and Extruder II extrude simultaneously and are simultaneously fed into a T-die. Inside the T-die, the melt from Extruder I is evenly distributed to both sides of the melt from Extruder II. Following an A / B / A three-layer structure, the two sets of melts are stacked and merged, flowing onto a rotating casting cooling drum with a surface temperature of 20°C to obtain a laminated casting film. The laminated casting film is preheated at 70-85°C and then rapidly stretched longitudinally (in the length direction) by 3.5 times under infrared heating conditions using two rollers rotating at different speeds. It is then gradually cooled at 30-60°C to obtain a longitudinally stretched film. The longitudinally stretched film is clamped at both sides by a clamp and fed into a transverse stretching box. After preheating at 90-115℃, the longitudinally stretched film is stretched 3.8 times in the transverse (width direction) multiple times at 110-130℃. It is then heat-treated at 240℃ for 7-15 seconds, cooled at 60℃, and irradiated with UV light at a wavelength of 365nm and a power of 180w for 4 seconds before being pulled and wound up to obtain a high-rigidity thin optical polyester film with a thickness of 12μm, of which the A layer has a thickness of 1.5μm.

[0102] In this example:

[0103] The raw materials for layer A are: 4 parts by weight of UV blocking masterbatch that can block wavelengths below 350nm, 5 parts by weight of opening agent masterbatch, and 91 parts by weight of polyethylene terephthalate.

[0104] The raw materials for layer B are: 10 parts by weight of modified copolyester and 90 parts by weight of polyethylene terephthalate.

[0105] The silica particles in the opening agent masterbatch contain 0.3% silica particles with a particle size of 1.5 μm.

[0106] Example 6

[0107] Preparation of modified copolyesters:

[0108] The mixture of glycols and terephthalic acid has a molar ratio of 1.24:1, and the molar ratio of 9-anthracene methanol to ethylene glycol in the glycol mixture is 2.5:7.5. The commonly used catalyst, antimony glycolate, is added at 200 ppm, and the commonly used stabilizer, triphenyl phosphate, is added at 20 ppm. After thorough mixing, the mixture is added to a polyester synthesis reactor. Esterification is carried out under nitrogen protection at a reactor temperature of 220-260℃ and an initial pressure of 0.15-0.2 MPa. The pressure is released when the esterification rate reaches 96%, completing the esterification reaction. After the esterification reaction, excess glycols are removed, and the mixture is polycondensed at 280-290℃ and 130 Pa for 3.5 hours to obtain the modified copolyester.

[0109] In extruder I, polyethylene terephthalate, UV barrier masterbatch, and opening agent masterbatch are added in proportion for melt extrusion. In extruder II, polyethylene terephthalate and modified copolyester are added in proportion for melt extrusion. The melt extruded from extruder I is fed into layer A of a three-layer ABA-structured die, and the melt extruded from extruder II is fed into layer B of the same die.

[0110] Extruder I and Extruder II extrude simultaneously and are simultaneously fed into a T-die. Inside the T-die, the melt from Extruder I is evenly distributed to both sides of the melt from Extruder II. Following an A / B / A three-layer structure, the two sets of melts are stacked and merged, flowing onto a rotating casting cooling drum with a surface temperature of 20°C to obtain a laminated casting film. The laminated casting film is preheated at 70-85°C and then rapidly stretched longitudinally (in the length direction) by 3.5 times under infrared heating conditions using two rollers rotating at different speeds. It is then gradually cooled at 30-60°C to obtain a longitudinally stretched film. The longitudinally stretched film is clamped at both sides by a clamp and fed into a transverse stretching box. After preheating at 90-115℃, the longitudinally stretched film is stretched 3.8 times in the transverse (width direction) multiple times at 110-130℃. It is then heat-treated at 240℃ for 7-15 seconds, cooled at 80℃, and irradiated with UV light at a wavelength of 365nm and a power of 180w for 5 seconds before being pulled and wound up to obtain a high-rigidity thin optical polyester film with a thickness of 6μm, of which the A layer has a thickness of 1μm.

[0111] In this example:

[0112] The raw materials for layer A are: 5 parts by weight of UV blocking masterbatch that can block wavelengths below 350nm, 5 parts by weight of opening agent masterbatch, and 90 parts by weight of polyethylene terephthalate.

[0113] The raw materials for layer B are: 10 parts by weight of modified copolyester and 90 parts by weight of polyethylene terephthalate.

[0114] The silica particles in the masterbatch of the opening agent contain 0.3% silica particles with a particle size of 1.0 μm.

[0115] Example 7

[0116] Preparation of modified copolyesters:

[0117] The mixture of glycols and terephthalic acid has a molar ratio of 1.26:1, and the molar ratio of 1,3-anthracene glycol to ethylene glycol in the glycol mixture is 3:7. The commonly used catalyst, antimony glycolate, is added at 200 ppm, and the commonly used stabilizer, triphenyl phosphate, is added at 20 ppm. After thorough mixing, the mixture is added to a polyester synthesis reactor. Esterification is carried out under nitrogen protection at a reactor temperature of 220-260℃ and an initial pressure of 0.15-0.2 MPa. The pressure is released when the esterification rate reaches 96%, completing the esterification reaction. After the esterification reaction, excess glycols are removed, and the mixture is polycondensed at 280-290℃ and 130 Pa for 3.5 hours to obtain the modified copolyester.

[0118] In extruder I, polyethylene terephthalate, UV barrier masterbatch, and opening agent masterbatch are added in proportion for melt extrusion. In extruder II, polyethylene terephthalate and modified copolyester are added in proportion for melt extrusion. The melt extruded from extruder I is fed into layer A of a three-layer ABA-structured die, and the melt extruded from extruder II is fed into layer B of the same die.

[0119] Extruder I and Extruder II extrude simultaneously and are simultaneously fed into a T-die. Inside the T-die, the melt from Extruder I is evenly distributed to both sides of the melt from Extruder II. Following an A / B / A three-layer structure, the two sets of melts are stacked and merged, flowing onto a rotating casting cooling drum with a surface temperature of 20°C to obtain a laminated casting film. The laminated casting film is preheated at 70-85°C and then rapidly stretched longitudinally (in the length direction) by 3.5 times under infrared heating conditions using two rollers rotating at different speeds. It is then gradually cooled at 30-60°C to obtain a longitudinally stretched film. The longitudinally stretched film is clamped at both sides by a clamp and fed into a transverse stretching box. After preheating at 90-115℃, the longitudinally stretched film is stretched 3.8 times in the transverse (width direction) multiple times at 110-130℃. It is then heat-treated at 240℃ for 7-15 seconds, cooled at 120℃, and irradiated with UV light at a wavelength of 365nm and a power of 160w for 2 seconds before being pulled and wound up to obtain a high-rigidity thin optical polyester film with a thickness of 6μm, of which the thickness of layer A is 1.0μm.

[0120] In this example:

[0121] The raw materials for layer A are: 3 parts by weight of UV blocking masterbatch that can block wavelengths below 350nm, 5 parts by weight of opening agent masterbatch, and 92 parts by weight of polyethylene terephthalate.

[0122] The raw materials for layer B are: 5 parts by weight of modified copolyester and 95 parts by weight of polyethylene terephthalate.

[0123] The silica particles in the masterbatch of the opening agent contain 0.3% silica particles with a particle size of 1.0 μm.

[0124] Example 8

[0125] Preparation of modified copolyesters:

[0126] The mixture of glycols and terephthalic acid is in a molar ratio of 1.28:1, with 2-pentyl-9,10-anthracene glycol and ethylene glycol in a molar ratio of 2:8. Commonly used catalysts include antimony glycolate at 200 ppm and triphenyl phosphate at 20 ppm. After thorough mixing, the mixture is added to a polyester synthesis reactor. Esterification is carried out under nitrogen protection at a reactor temperature of 220-260℃ and an initial pressure of 0.15-0.2 MPa. Pressure is released when the esterification rate reaches 96%, completing the esterification reaction. After esterification, excess glycols are removed, and the mixture is polycondensed at 280-290℃ and 130 Pa for 3.5 hours to obtain the modified copolyester.

[0127] In extruder I, polyethylene terephthalate, UV barrier masterbatch, and opening agent masterbatch are added in proportion for melt extrusion. In extruder II, polyethylene terephthalate and modified copolyester are added in proportion for melt extrusion. The melt extruded from extruder I is fed into layer A of a three-layer ABA-structured die, and the melt extruded from extruder II is fed into layer B of the same die.

[0128] Extruder I and Extruder II extrude simultaneously and are simultaneously fed into a T-die. Inside the T-die, the melt from Extruder I is evenly distributed to both sides of the melt from Extruder II. Following an A / B / A three-layer structure, the two sets of melts are stacked and merged, flowing onto a rotating casting cooling drum with a surface temperature of 20°C to obtain a laminated casting film. The laminated casting film is preheated at 70-85°C and then rapidly stretched longitudinally (in the length direction) by 3.5 times under infrared heating conditions using two rollers rotating at different speeds. It is then gradually cooled at 30-60°C to obtain a longitudinally stretched film. The longitudinally stretched film is clamped at both sides by a clamp and fed into a transverse stretching box. After preheating at 90-115℃, the longitudinally stretched film is stretched 3.8 times in the transverse (width direction) multiple times at 110-130℃. It is then heat-treated at 240℃ for 7-15 seconds, cooled at 120℃, and irradiated with UV light at a wavelength of 365nm and a power of 200W for 3 seconds before being pulled and wound up to obtain a high-rigidity thin optical polyester film with a thickness of 25μm, of which the thickness of layer A is 1.5μm.

[0129] In this example:

[0130] The raw materials for layer A are: 4 parts by weight of UV blocking masterbatch that can block wavelengths below 350nm, 8 parts by weight of opening agent masterbatch, and 88 parts by weight of polyethylene terephthalate.

[0131] The raw materials for layer B are: 8 parts by weight of modified copolyester and 92 parts by weight of polyethylene terephthalate.

[0132] The silica particles in the opening agent masterbatch contain 1.0% silica particles with a particle size of 2.0 μm.

[0133] Example 9

[0134] Preparation of modified copolyesters:

[0135] The mixture of glycols and terephthalic acid is in a molar ratio of 1.28:1, with 2-pentyl-9,10-anthracene glycol and ethylene glycol in a molar ratio of 1:9. Commonly used catalysts include antimony glycolate at 200 ppm and triphenyl phosphate at 20 ppm. After thorough mixing, the mixture is added to a polyester synthesis reactor. Esterification is carried out under nitrogen protection at a reactor temperature of 220-260℃ and an initial pressure of 0.15-0.2 MPa. The pressure is released when the esterification rate reaches 96%, completing the esterification reaction. After esterification, excess glycols are removed, and the mixture is polycondensed at 280-290℃ and 130 Pa for 3.5 hours to obtain the modified copolyester.

[0136] In extruder I, polyethylene terephthalate, UV barrier masterbatch, and opening agent masterbatch are added in proportion for melt extrusion. In extruder II, polyethylene terephthalate and modified copolyester are added in proportion for melt extrusion. The melt extruded from extruder I is fed into layer A of a three-layer ABA-structured die, and the melt extruded from extruder II is fed into layer B of the same die.

[0137] Extruder I and Extruder II extrude simultaneously and are simultaneously fed into a T-die. Inside the T-die, the melt from Extruder I is evenly distributed to both sides of the melt from Extruder II. Following an A / B / A three-layer structure, the two sets of melts are stacked and merged, flowing onto a rotating casting cooling drum with a surface temperature of 20°C to obtain a laminated casting film. The laminated casting film is preheated at 70-85°C and then rapidly stretched longitudinally (in the length direction) by 3.5 times under infrared heating conditions using two rollers rotating at different speeds. It is then gradually cooled at 30-60°C to obtain a longitudinally stretched film. The longitudinally stretched film is clamped at both sides by a clamp and fed into a transverse stretching box. After preheating at 90-115℃, the longitudinally stretched film is stretched 3.8 times in the transverse (width direction) multiple times at 110-130℃. It is then heat-treated at 240℃ for 7-15 seconds, cooled at 40℃, and irradiated with UV light at a wavelength of 365nm and a power of 160w for 2 seconds before being pulled and wound up to obtain a high-rigidity thin optical polyester film with a thickness of 50μm, of which the thickness of layer A is 2.0μm.

[0138] In this example:

[0139] The raw materials for layer A are: 5 parts by weight of UV blocking masterbatch that can block wavelengths below 350nm, 10 parts by weight of opening agent masterbatch, and 85 parts by weight of polyethylene terephthalate.

[0140] The raw materials for layer B are: 10 parts by weight of modified copolyester and 90 parts by weight of polyethylene terephthalate.

[0141] The silica particles in the opening agent masterbatch contain 1.0% silica particles with a particle size of 2.0 μm.

[0142] Comparative Example 1

[0143] No modified copolyester is added.

[0144] In extruder I, polyethylene terephthalate, UV barrier masterbatch, and opening agent masterbatch are added in proportion for melt extrusion. In extruder II, polyethylene terephthalate is added in proportion, and the melt extruded from extruder II is fed into layer B of the three-layer die with an ABA structure.

[0145] Extruder I and Extruder II extrude simultaneously and are simultaneously fed into a T-die. Inside the T-die, the melt from Extruder I is evenly distributed to both sides of the melt from Extruder II. Following an A / B / A three-layer structure, the two sets of melts are stacked and merged, flowing onto a rotating casting cooling drum with a surface temperature of 20°C to obtain a laminated casting film. The laminated casting film is preheated at 70-85°C and then rapidly stretched longitudinally (in the length direction) by 3.5 times under infrared heating conditions using two rollers rotating at different speeds. It is then gradually cooled at 30-60°C to obtain a longitudinally stretched film. The longitudinally stretched film is clamped at both sides by a clamp and fed into a transverse stretching box. After preheating at 90-115℃, the longitudinally stretched film is stretched 3.8 times in the transverse (width direction) multiple times at 110-130℃. It is then heat-treated at 240℃ for 7-15 seconds, cooled at 60℃, and irradiated with UV light at a wavelength of 365nm and a power of 160w for 4 seconds before being pulled and wound up to obtain a high-rigidity thin optical polyester film with a thickness of 38μm, of which the thickness of the A layer is 1.5μm.

[0146] In this example:

[0147] The raw materials for layer A are: 3 parts by weight of UV blocking masterbatch that can block wavelengths below 350nm, 8 parts by weight of opening agent masterbatch, and 89 parts by weight of polyethylene terephthalate.

[0148] The raw material for layer B is 100 parts by weight of polyethylene terephthalate.

[0149] The silica particles in the opening agent masterbatch contain 0.3% silica particles with a particle size of 2.0 μm.

[0150] Comparative Example 2

[0151] Preparation of modified copolyesters:

[0152] The mixture of glycols and terephthalic acid is in a molar ratio of 1.3:1, and the molar ratio of 1,4-anthracene glycol to ethylene glycol in the glycol mixture is 4:6. The commonly used catalyst, antimony glycolate, is added at 200 ppm, and the commonly used stabilizer, triphenyl phosphate, is added at 20 ppm. After thorough mixing, the mixture is added to a polyester synthesis reactor. Esterification is carried out under nitrogen protection at a reactor temperature of 220-260℃ and an initial pressure of 0.15-0.2 MPa. The pressure is released when the esterification rate reaches 96%, completing the esterification reaction. After the esterification reaction, excess glycols are removed, and the mixture is polycondensed at 280-290℃ and 130 Pa for 3.5 hours to obtain the modified copolyester.

[0153] In extruder I, polyethylene terephthalate, UV barrier masterbatch, and opening agent masterbatch are added in proportion for melt extrusion. In extruder II, polyethylene terephthalate and modified copolyester are added in proportion for melt extrusion. The melt extruded from extruder I is fed into layer A of a three-layer ABA-structured die, and the melt extruded from extruder II is fed into layer B of the same die.

[0154] Extruder I and Extruder II extrude simultaneously and are simultaneously fed into a T-die. Inside the T-die, the melt from Extruder I is evenly distributed to both sides of the melt from Extruder II. Following an A / B / A three-layer structure, the two sets of melts are stacked and merged, flowing onto a rotating casting cooling drum with a surface temperature of 20°C to obtain a laminated casting film. The laminated casting film is preheated at 70-85°C and then rapidly stretched longitudinally (in the length direction) by 3.5 times under infrared heating conditions using two rollers rotating at different speeds. It is then gradually cooled at 30-60°C to obtain a longitudinally stretched film. The longitudinally stretched film is clamped at both sides by a clamp and fed into a transverse stretching box. After preheating at 90-115℃, the longitudinally stretched film is stretched 3.8 times in the transverse (width direction) multiple times at 110-130℃. It is then heat-treated at 240℃ for 7-15 seconds, cooled at 140℃, and irradiated with UV light at a wavelength of 365nm and a power of 250w for 8 seconds before being pulled and wound up to obtain a high-rigidity thin optical polyester film with a thickness of 50μm, of which the A layer has a thickness of 4.0μm.

[0155] In this example:

[0156] The raw materials for layer A are: 10 parts by weight of UV blocking masterbatch that can block wavelengths below 300nm, 12 parts by weight of opening agent masterbatch, and 78 parts by weight of polyethylene terephthalate.

[0157] The raw materials for layer B are: 12 parts by weight of modified copolyester and 88 parts by weight of polyethylene terephthalate.

[0158] The silica particles in the opening agent masterbatch contain 0.3% silica particles with a particle size of 3.5 μm.

[0159] Comparative Example 3

[0160] Preparation of modified copolyesters:

[0161] The diol mixture and terephthalic acid were mixed in a molar ratio of 1:1. The molar ratio of 2-pentyl-9,10-anthracene diol to ethylene glycol in the diol mixture was 0.5:9.5. The commonly used catalyst, antimony glycolate, was added at 200 ppm, and the commonly used stabilizer, triphenyl phosphate, was added at 20 ppm. After the mixture was homogeneous, it was added to a polyester synthesis reactor. The esterification reaction was carried out under nitrogen protection at a reactor temperature of 220-260℃ and an initial pressure of 0.15-0.2 MPa. When the esterification rate reached 96%, the pressure was released to complete the esterification reaction. After the esterification reaction was completed, the excess diol mixture was removed, and the mixture was polycondensed at 280-290℃ and 130 Pa for 3.5 hours to obtain the modified copolyester.

[0162] In extruder I, polyethylene terephthalate, UV barrier masterbatch, and opening agent masterbatch are added in proportion for melt extrusion. In extruder II, polyethylene terephthalate and modified copolyester are added in proportion for melt extrusion. The melt extruded from extruder I is fed into layer A of a three-layer ABA-structured die, and the melt extruded from extruder II is fed into layer B of the same die.

[0163] Extruder I and Extruder II extrude simultaneously and are simultaneously fed into a T-die. Inside the T-die, the melt from Extruder I is evenly distributed to both sides of the melt from Extruder II. Following an A / B / A three-layer structure, the two sets of melts are stacked and merged, flowing onto a rotating casting cooling drum with a surface temperature of 20°C to obtain a laminated casting film. The laminated casting film is preheated at 70-85°C and then rapidly stretched longitudinally (in the length direction) by 3.5 times under infrared heating conditions using two rollers rotating at different speeds. It is then gradually cooled at 30-60°C to obtain a longitudinally stretched film. The longitudinally stretched film is clamped at both sides by a clamp and fed into a transverse stretching box. After preheating at 90-115℃, the longitudinally stretched film is stretched 3.8 times in the transverse (width direction) multiple times at 110-130℃. It is then heat-treated at 240℃ for 7-15 seconds, cooled at 35℃, and irradiated with UV light at a wavelength of 365nm and a power of 150W for 1 second before being pulled and wound up to obtain a high-rigidity thin optical polyester film with a thickness of 6μm, of which the thickness of layer A is 0.6μm.

[0164] In this example:

[0165] The raw materials for layer A are: 0 parts by weight of UV blocking masterbatch, 3 parts by weight of opening agent masterbatch, and 97 parts by weight of polyethylene terephthalate.

[0166] The raw materials for layer B are: 3 parts by weight of modified copolyester and 97 parts by weight of polyethylene terephthalate.

[0167] The silica particles in the opening agent masterbatch contain 0.3% silica particles with a particle size of 0.8 μm.

[0168] The specific implementation results are shown in Table 1 below.

[0169] Table 1 Test Results

[0170]

[0171] As can be seen from Table 1 above, Examples 1-9 and Comparative Examples 1-3, the present invention adds modified copolyester to layer B and UV blocking masterbatch and opening agent masterbatch to layer A, which can effectively improve the overall rigidity of thin optical polyester film while having good optical properties, and significantly improve the temperature resistance of polyester film when heated during reprocessing.

[0172] Under the same equipment and process flow, the rigidity of the present invention is significantly better than that of ordinary thin-film optical polyester films.

Claims

1. A high-rigidity thin optical polyester film, characterized in that, It includes layer B and layers A located on both sides of layer B, forming an overall ABA superposition structure; The raw materials for preparing the B layer include: 5-10% by mass of modified copolyester, with the remainder being pure polyester. The raw materials for preparing the A layer include: 3-5% by mass of UV blocking masterbatch, 5-10% by mass of opening agent masterbatch, and the balance being pure polyester. The modified copolyester is prepared by esterification polycondensation reaction of a mixture of glycols and a diacid; the molar ratio of the glycol mixture to the diacid is (1.2-1.28):

1. The diol mixture consists of an anthracene-containing diol and ethylene glycol, wherein the molar ratio of the anthracene-containing diol to the ethylene glycol is (1:9) to (3:7).

2. The high-rigidity thin optical polyester film according to claim 1, characterized in that, The dicarboxylic acid is an aromatic dicarboxylic acid.

3. The high-rigidity thin optical polyester film according to claim 1, characterized in that, The diol containing anthracene groups is one of 1,4-anthratrine diol or 2-pentyl-9,10-anthratrine diol.

4. The high-rigidity thin optical polyester film according to claim 1, characterized in that, The UV blocking masterbatch is a UV blocking masterbatch that can block wavelengths below 350nm while allowing wavelengths above 350nm to pass through.

5. The high-rigidity thin optical polyester film according to claim 1, characterized in that, The opening agent masterbatch is composed of pure polyester and silica particles, with the silica particle content being 0.3%-1.5% of the weight of the opening agent masterbatch, and the silica particle size being 1.0-2.0 μm.

6. The high-rigidity thin optical polyester film according to claim 1, characterized in that, The thickness of the polyester film is 6-50 μm.

7. The high-rigidity thin optical polyester film according to claim 1, characterized in that, The thickness of the A layer of the polyester film is 1-2 μm.

8. A method for preparing a high-rigidity thin optical polyester film according to any one of claims 1-7, characterized in that, Includes the following steps: Step 1: In extruder I, add pure polyester, UV barrier masterbatch, and opening agent masterbatch according to the specified ratio for melt extrusion; in extruder II, add pure polyester and modified copolyester according to the specified ratio for melt extrusion. Step 2: The melt extruded from extruder I is fed into layer A of the three-layer die head with an ABA structure; the melt extruded from extruder II is fed into layer B of the three-layer die head with an ABA structure; the melts of layers A and B flow out together according to their respective thickness ratios; after casting, longitudinal stretching, transverse stretching, shaping, cooling, UV irradiation, and winding, the high-rigidity thin optical polyester film is obtained.

9. The method for preparing a high-rigidity thin optical polyester film according to claim 8, characterized in that, The wavelength of the UV irradiation is 365nm, the UV irradiation power is 160-200w, and the UV irradiation time is 2-5 seconds.

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