Optical polyester film and preparation method thereof

Abstract

The invention belongs to the technical field of optical film preparation, and particularly relates to an optical polyester film and a preparation method thereof. By adding a certain amount of heat stabilizer and light stabilizer, the yellowing resistance and high temperature resistance of the formed optical polyester film are effectively improved. The optical polyester film is further promoted to better adapt to extreme climate and environment, and the service life is effectively prolonged. According to the optical polyester film, on the premise that the mechanical property and optical property of a BOPET material are guaranteed, the thermal shrinkage rate of the BOPET material is effectively reduced, and the thermal stability and light stability of the BOPET material are further improved. By adopting an asynchronous two-way stretching process, the optical polyester film is subjected to two-way stretching to obtain good orientation and crystallinity, so that the mechanical property stability of the optical polyester film is guaranteed.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of optical film preparation, and particularly relates to an optical polyester film and a preparation method thereof. BACKGROUND

[0002] Biaxially oriented polyester film (BOPET) is made of polyethylene terephthalate (PET) as raw material, and is made into a thick sheet by melt extrusion method, and then is made into a film by a biaxial stretching process. It has the characteristics of high strength, good rigidity, low haze, high light transmittance, good thermal stability and recyclability. Therefore, the BOPET film can not only be applied to the ordinary packaging and printing industry as a packaging material, but also be applied to the optical and electronic display field as a high-end optical substrate. With the gradual improvement of new display technology, the application scenarios of liquid crystal display equipment are gradually expanding from the conventional home appliances 3C to vehicle-mounted display systems, outdoor large-screen displays, intelligent factory supporting fields and the like. Therefore, the liquid crystal display equipment not only works in a single "comfortable" room temperature environment, but also needs to consider its stability in extreme weather conditions. For example, after the car is parked in the outdoor parking lot for a period of time in summer, the temperature in the car is as high as 60℃ or above, which puts a great demand on the thermal stability of the vehicle-mounted display system.

[0003] The optical film product will have a certain time effect in the process of high-strength outdoor operation environment, that is, the performance of the optical film will gradually decrease with time. The general design process only designs a margin at the edge of the screen, that is, a larger film is used to cover the display layer, but this can only alleviate the inconvenience caused by the poor thermal stability of the material to a certain extent. At the same time, for strong light working conditions, the common method currently used in the industry is to shorten the replacement cycle, which also means that the optical film needs to be replaced frequently to maintain its good performance. However, this will undoubtedly increase the cost of open-air display equipment.

[0004] As a core material in the backlight module of the liquid crystal display, the BOPET film will have aging phenomena such as thermal deformation and embrittlement when it is affected by high temperature from the outside, and in a strong light environment, the product will undergo photo-oxidation after absorbing ultraviolet rays, causing self-oxidation and degradation of the polymer, breaking and cross-linking of the chemical bonds of the polymer, resulting in deterioration of the color, appearance and physical properties of the product, reduction of strength, shortening of service life (yellowing), and then affecting the display effect. Therefore, in order to cope with more complex application scenarios, higher requirements are put forward for the comprehensive performance of the BOPET film substrate. SUMMARY

[0005] The present application is to overcome the defects of the prior art, such as high thermal shrinkage rate of the optical film product, difficulty in adapting to extreme climate and environment, easy deformation, embrittlement and yellowing caused by heat or long-term outdoor exposure, poor thermal stability and short service life, and provides an optical polyester film and a preparation method thereof.

[0006] To achieve the above-mentioned purposes of the application, the application is implemented by the following technical solutions. An optical polyester film, comprising at least two layers of film base structures, the film base structure comprising a surface layer and a core layer, the raw material of the surface layer being a first modified PET composite material, the first modified PET composite material comprising a first modified PET resin and a first stabilizer; the raw material of the core layer being a second modified PET composite material, the second modified PET composite material comprising a second modified PET resin and a second stabilizer, the mass ratio of the first stabilizer and the second stabilizer being (2-5):(5-9).

[0007] Preferably, the mass ratio of the surface layer to the core layer is (1-10):(80-98).

[0008] Preferably, the stabilizer comprises a heat stabilizer and a light stabilizer.

[0009] The heat stabilizer helps to inhibit or delay the molecular degradation reaction at high temperature, and improves the high-temperature resistance of the optical polyester film material by absorbing and transferring heat energy, neutralizing free radicals, stabilizing the molecular structure, etc. The light stabilizer is an additive that can absorb and transfer ultraviolet light energy. The light stabilizer can react with the excited state electrons in the PET molecule, thereby stabilizing the molecular structure, reducing the occurrence of oxidation reaction, and then improving the ultraviolet light resistance of the optical polyester film material, avoiding yellowing.

[0010] Biaxially oriented polyester film (BOPET) has the characteristics of high strength, good rigidity, low haze, high light transmittance, good thermal stability and recyclability, and is often used as high-end optical substrate in the field of optical electronic display. However, the main raw material for preparing BOPET, i.e. polyethylene terephthalate (PET), has benzene ring and ester group structure, which is prone to hydrolysis and deorientation at high temperature, resulting in molecular chain rupture, degradation, and change in the direction of the molecular chain. In addition, PET is prone to absorb ultraviolet light and cause oxidation reaction, resulting in changes in the molecular structure and yellowing. Therefore, under the premise of ensuring the mechanical properties and optical properties of BOPET material, in order to reduce the thermal shrinkage of BOPET material and further improve its thermal stability and light stability, the application adds a certain amount of heat stabilizer and light stabilizer to effectively improve the yellowing resistance and high-temperature resistance of the formed optical polyester film. Further promote the optical polyester film to better adapt to extreme climate and environment, and effectively prolong the service life.

[0011] Preferably, the heat stabilizer is any one or a combination of rare earth, phosphite, triethyl phosphate, titanium / silicon oxide polymer.

[0012] As a further preference, the heat stabilizer is a combination of any one or both of triethyl phosphate and titanium / silicon oxide polymer.

[0013] As a further preference, the heat stabilizer is triethyl phosphate.

[0014] The rare earth, phosphite, triethyl phosphate, titanium / silicon oxide polymer heat stabilizer has high thermal stability, can resist oxidation, decomposition and degradation reactions in high temperature environment, and helps to extend the service life of the optical polyester film. At the same time, the above-mentioned heat stabilizer can effectively inhibit the degradation of the optical performance of the optical polyester film during use, such as reduction of transparency, color change, etc., thereby maintaining the excellent optical performance of the optical polyester film. In addition, the above-mentioned heat stabilizer has good antioxidant properties, can effectively inhibit the oxidation reaction of oxygen to the optical polyester film, and slow down the aging speed of the film. It can also improve the mechanical properties of the optical polyester film, such as strength, toughness and wear resistance, etc., which helps to enhance the tensile, tear resistance and wear resistance of the optical polyester film. Among them, triethyl phosphate as a heat stabilizer also helps to enhance the light transmittance of the optical polyester film. Thus, the effect of ensuring thermal stability and preventing material degradation during processing or use while considering optical performance is achieved.

[0015] As a preference, the light stabilizer is any one or a combination of two of benzotriazole, oxalic acid amide, and triazine light stabilizers.

[0016] As a further preference, the light stabilizer (two combinations are preferred according to the functional classification) is any one or a combination of two of ① ultraviolet absorber: oxalic acid amide light stabilizer UV312 (C 18 H 20 N2O3), benzotriazole light stabilizer UV327 (C 20 H 24 ClN3O) ② free radical trapping agent: hindered amine light stabilizer UV2020 (C 33 H 60 N8O), UV3346 (C 31 H 58 C l2 N8O), wherein the ultraviolet absorber has wide applicability, but its protection effect mainly acts within a certain depth and cannot effectively protect the surface of the product and thin products, the free radical trapping agent is light in color and has outstanding light stabilizing effect, and the main protection range is the surface of the product and thin products. The two are used together and complement each other to achieve excellent light stabilizing effect.

[0017] The ultraviolet absorbers such as benzotriazole (UV327), oxalic acid amide (UV312) light stabilizers can absorb ultraviolet light, convert its energy into heat energy, thereby reducing the damage of ultraviolet light to the optical polyester film material, effectively reducing the aging rate of the optical polyester film material, further prolonging the service life of the optical polyester film material. Hindered amine light stabilizers (UV2020, UV3346) can capture and neutralize free radicals to reduce the number of free radicals, thereby slowing down the material aging process. In addition, it can also transfer the energy of ultraviolet light to the lower energy level of the optical polyester film material through energy transfer, thereby reducing the direct absorption of ultraviolet light to the optical polyester film material, effectively avoiding the temperature rise and accelerated aging rate of the optical polyester film material. Further improve the weather resistance of the optical polyester film and prolong its service life.

[0018] As preferred, the mass ratio of the heat stabilizer to the light stabilizer is 1:3~6:1.

[0019] As preferred, the first modified PET resin and the second modified PET resin are each independently selected from PET resin master particle grafted acrylate derivative.

[0020] As preferred, the mass ratio of the acrylate derivative to the modified resin is 2.5~5%.

[0021] As preferred, the crystallinity of the first modified PET resin and the second modified PET resin is 30~35%.

[0022] As preferred, the master particle substrate of the PET resin is any one or a combination of more than one of FG610, FG611, FG612, FG620. As preferred, the preparation of the first modified PET composite material includes the following components by weight fraction: 800~1000 parts of the first modified PET resin, 15~30 parts of the first coupling agent, 1~2 parts of the first inorganic filler, 5~30 parts of the first heat stabilizer, 5~15 parts of the first light stabilizer.

[0023] As preferred, the preparation of the second modified PET composite material includes the following components by weight fraction: 750~900 parts of the second modified PET resin, 5~20 parts of the second coupling agent, 0.1~1 parts of the second inorganic filler, 5~30 parts of the second heat stabilizer, 5~15 parts of the second light stabilizer.

[0024] As preferred, the first coupling agent or the second coupling agent is each independently selected from any one or a combination of more than one of titanate, aluminate, and oxysilane coupling agent.

[0025] Titanate, aluminate, and oxysilane coupling agents can form chemical bonds between the surface layer and the core layer, thereby enhancing the adhesion between the surface layer and the core layer, and improving the overall performance of the optical polyester film. At the same time, the above coupling agents can effectively inhibit the thermal decomposition and oxidation reaction of the optical polyester film at high temperature, and improve the heat resistance of the film. The addition of coupling agents helps to reduce impurities and defects in the optical polyester film, and improves optical transparency and uniformity, and improves its optical performance. Coupling agents can also improve the mechanical properties of the optical polyester film, such as tensile strength, scratch resistance, and wear resistance. In addition, the addition of coupling agents can further improve the chemical stability of the optical polyester film.

[0026] As preferred, the first inorganic filler or the second inorganic filler is each independently selected from a combination of any one or more of silicon oxide, glass fiber, barium sulfate, calcium carbonate, and kaolin.

[0027] Silicon oxide, glass fiber, barium sulfate, calcium carbonate, and kaolin inorganic fillers can increase the hardness, strength, and stiffness of the composite material, thereby improving the tensile strength and wear resistance of the optical polyester film, and enhancing its mechanical properties. The above inorganic fillers have high density and shielding properties, which can effectively block the penetration of light, gas, and moisture, and effectively improve the barrier properties of the optical polyester film. At the same time, the above inorganic fillers effectively improve the thermal stability and heat resistance of the composite material, making it perform better in extreme environments such as high temperature. In addition, the above inorganic fillers can also change the flowability and melt viscosity of the composite material, which helps to improve the processing performance of the optical polyester film and further prolong its service life.

[0028] A method for preparing an optical polyester film as claimed in any one of claims 1-9, comprising the following steps: (S.1) Melt extrusion: The additives are mixed and modified with PET resin according to the formulation amount, and then granulated to obtain a modified PET composite material. Then the modified PET composite material is mixed and melted and extruded to obtain a modified PET melt; (S.2) Casting: The modified PET melt obtained in step (S.1) is laminated into A / B or A / B / A structure through two or more layer dies to obtain a cast polyester sheet, and then cooled and solidified to obtain a PET film; (S.3) Longitudinal stretching: The PET film obtained in step (S.2) is placed on a longitudinal stretching machine under heating conditions for stretching and cooling to obtain a longitudinally stretched film. The longitudinal stretching heating temperature is 110-160°C, and the longitudinal stretching ratio is 2.0-5.3 times; (S.4) Transverse stretching: the longitudinal stretched film obtained in step (S.3) is stretched in a transverse direction under heating, and then is subjected to heat setting treatment and cooling to obtain a transversely stretched film; the transverse stretching temperature is 115-180℃, the transverse stretching ratio is 2.5-6.0 times; the heat setting treatment temperature is 150-260℃; finally, the transversely stretched film after stretching and setting is drawn and wound to obtain the optical polyester film.

[0029] Therefore, the present application has the following beneficial effects: (1) The present application effectively improves the yellowing resistance and high temperature resistance of the formed optical polyester film by adding a certain amount of heat stabilizer and light stabilizer, further promotes the optical polyester film to better adapt to extreme climate and environment, and effectively prolongs the service life; (2) The optical polyester film of the present application effectively reduces the thermal shrinkage of BOPET material under the premise of ensuring the mechanical properties and optical properties of BOPET material, further improves the thermal stability and light stability of BOPET material; (3) The present application adopts an asynchronous bidirectional stretching process, and the optical polyester film is stretched in two directions to obtain good orientation and crystallinity, thereby ensuring the stability of the mechanical properties of the optical polyester film. DETAILED DESCRIPTION

[0030] The present application will be further described below in conjunction with specific embodiments. Those skilled in the art will be able to implement the present application based on these descriptions. In addition, the embodiments of the present application involved in the following description are generally only a part of the embodiments of the present application, not all the embodiments. Therefore, based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor shall fall within the scope of protection of the present application.

[0031] Example 1 An optical polyester film is provided in this embodiment.

[0032] An optical polyester film includes a three-layer film substrate structure, and the film substrate includes two surface layers and one core layer. The total extrusion mass ratio of the surface layer to the core layer is 10:90, and both the surface layer and the core layer are prepared from modified PET composite material. Among them, the surface layer is prepared from modified PET composite material I, and the core layer is prepared from modified PET composite material II. The stabilizer includes a heat stabilizer and a light stabilizer.

[0033] The modified PET composite material I for preparing the surface layer includes the following components by weight fraction: 900 parts of PET resin, 20 parts of coupling agent, 2 parts of inorganic filler, 20 parts of heat stabilizer, and 10 parts of light stabilizer.

[0034] The modified PET composite material II for preparing the core layer comprises the following components by weight: 800 parts of PET resin, 10 parts of coupling agent, 0.5 parts of inorganic filler, 20 parts of thermal stabilizer, and 10 parts of light stabilizer.

[0035] The PET resin is a master batch substrate (FG610 of SINOPEC Yizheng Chemical Fibre Co., Ltd.) grafted with methyl methacrylate, the grafting rate is 65%, and the crystallinity measured by DSC is 82%. The coupling agent is commercially available KH550. The thermal stabilizer is commercially available triethyl phosphate. The light stabilizer is commercially available light stabilizer UV312 and UV2020, with a weight ratio of 6:4. The inorganic filler in the modified PET composite material I for preparing the surface layer is commercially available glass fiber with a mesh size of more than 4000. The inorganic filler in the modified PET composite material II for preparing the core layer is commercially available silicon dioxide powder with a mesh size of more than 6000.

[0036] The embodiment also provides a preparation method of the optical polyester film.

[0037] The preparation method of the optical polyester film comprises the following steps: (S.1) melt extrusion: The additives in the modified PET composite material I for preparing the surface layer and the PET resin raw material are vacuum dried before feeding, and then fed into a double-screw extruder for mixing and modification, and then re-pelletized to obtain the modified PET composite material I. The additives in the modified PET composite material II for preparing the core layer and the PET resin raw material are vacuum dried before feeding, and then fed into a double-screw extruder for mixing and modification, and then re-pelletized to obtain the modified PET composite material II. Two double-screw extruders are used. As another embodiment, a single-screw extruder can be used. The modified PET composite material I for preparing the upper and lower surface layers is fed into the auxiliary extruder, and the modified PET composite material II for preparing the middle core layer is fed into the main extruder, and then the modified PET composite material I and the modified PET composite material II are mixed and melted at 275°C and then extruded to obtain a modified PET melt; (S.2) sheet casting: The modified PET melt obtained in step (S.1) is laminated into an A / B / A structure through a three-layer die to obtain a cast polyester sheet, and then cooled and solidified at 20°C through a chill roller to obtain a PET film; (S.3) longitudinal stretching: The PET film obtained in step (S.2) is heated through a roller and an infrared lamp, stretched longitudinally once or twice by using the speed difference of the roller, and cooled by a chill roller group at a temperature of ≤25°C to obtain a longitudinally stretched film. The heating temperature for longitudinal stretching is 125°C, and the longitudinal stretching ratio is 3.7 times. (S.4) Transverse stretching: The longitudinally stretched film obtained in step (S.3) is clamped in a chain clip structure and fed into a transverse stretching machine to perform transverse stretching under heating. The transverse stretching preheating temperature is 135°C, the stretching zone heating temperature is 160°C, and the transverse stretching ratio is 4.5 times. Then the stretched film is relaxed in the transverse direction while being heat set, and the heat setting treatment temperature is (210) °C. The transverse stretched film is obtained by cooling with a (70) °C chill roller group. Finally, the transversely stretched film after stretching and setting is drawn and wound to obtain an optical polyester film.

[0038] Example 2 The difference between this example and Example 1 is that: In this example, an optical polyester film is provided, wherein the light stabilizer is replaced by commercially available light stabilizer UV327 instead of light stabilizer UV312. The others are the same as in Example 1.

[0039] Example 3 The difference between this example and Example 1 is that: In this example, an optical polyester film is provided, wherein the light stabilizer is replaced by commercially available light stabilizer UV3346 instead of light stabilizer UV2020. The others are the same as in Example 1.

[0040] Example 4 The difference between this example and Example 3 is that: In this example, an optical polyester film is provided, wherein the light stabilizer is replaced by commercially available light stabilizer UV327 instead of light stabilizer UV312. The others are the same as in Example 3.

[0041] Example 5 The difference between this example and Example 1 is that: In this example, an optical polyester film is provided, wherein the modified PET composite material I for preparing the surface layer comprises the following components by weight fraction: 800 parts of PET resin, 15 parts of coupling agent, 1 part of inorganic filler, 5 parts of thermal stabilizer, and 5 parts of light stabilizer.

[0042] The modified PET composite material II for preparing the core layer comprises the following components by weight fraction: 750 parts of PET resin, 5 parts of coupling agent, 0.1 parts of inorganic filler, 5 parts of thermal stabilizer, and 5 parts of light stabilizer.

[0043] The optical polyester film of the embodiment is prepared by the method of the embodiment 1, wherein the longitudinal stretching heating temperature in the step (S.3) is 110℃, and the longitudinal stretching ratio is 2.0 times. The transverse stretching preheating temperature in the step (S.4) is 115℃, the stretching zone heating temperature is 140℃, the transverse stretching ratio is 2.5 times, and the heat setting treatment temperature is 150℃. The other conditions are the same as those in the embodiment 1.

[0044] Embodiment 6 The difference between the embodiment and the embodiment 1 is that: The optical polyester film of the embodiment is prepared by the method of the embodiment 1, wherein the modified PET composite material I for preparing the surface layer comprises the following components in parts by weight: 1000 parts of PET resin, 30 parts of coupling agent, 2 parts of inorganic filler, 30 parts of heat stabilizer, and 15 parts of light stabilizer.

[0045] The modified PET composite material II for preparing the core layer comprises the following components in parts by weight: 900 parts of PET resin, 20 parts of coupling agent, 1 part of inorganic filler, 30 parts of heat stabilizer, and 15 parts of light stabilizer.

[0046] The optical polyester film of the embodiment is prepared by the method of the embodiment 1, wherein the longitudinal stretching heating temperature in the step (S.3) is 160℃, and the longitudinal stretching ratio is 5.3 times. The transverse stretching preheating temperature in the step (S.4) is 165℃, the stretching zone heating temperature is 180℃, the transverse stretching ratio is 6 times, and the heat setting treatment temperature is 260℃. The other conditions are the same as those in the embodiment 1.

[0047] Embodiment 7 The difference between the embodiment and the embodiment 1 is that: The optical polyester film of the embodiment is prepared by the method of the embodiment 1, wherein the amount of the heat stabilizer in the surface layer is 8 parts, and the amount of the light stabilizer is 4 parts (UV312:UV2020=3:1); the amount of the heat stabilizer in the core layer is 20 parts, and the amount of the light stabilizer is 10 parts (UV312:UV2020=8:2). The other conditions are the same as those in the embodiment 1.

[0048] Embodiment 8 The difference between the embodiment and the embodiment 1 is that: The optical polyester film of the embodiment is prepared by the method of the embodiment 1, wherein the amount of the heat stabilizer in the surface layer is 15 parts, and the amount of the light stabilizer is 10 parts (UV312:UV2020=6:4); the amount of the heat stabilizer in the core layer is 27 parts, and the amount of the light stabilizer is 18 parts (UV312:UV2020=12:6). The other conditions are the same as those in the embodiment 1.

[0049] Embodiment 9 The difference between this embodiment and embodiment 1 is that: In this embodiment, an optical polyester film is provided, wherein in the surface layer: the amount of heat stabilizer is 5 parts, and the amount of light stabilizer is 15 parts (UV312: UV2020 = 10:5); in the core layer: the amount of heat stabilizer is 10 parts, and the amount of light stabilizer is 30 parts (UV312: UV2020 = 20:10). The others are the same as in embodiment 1.

[0050] Embodiment 10 The difference between this embodiment and embodiment 1 is that: In this embodiment, an optical polyester film is provided, wherein in the surface layer: the amount of heat stabilizer is 24 parts, and the amount of light stabilizer is 4 parts (UV312: UV2020 = 3:1); in the core layer: the amount of heat stabilizer is 30 parts, and the amount of light stabilizer is 5 parts (UV312: UV2020 = 4:1). The others are the same as in embodiment 1. Comparative Example 1 The difference between this comparative example and embodiment 1 is that: In this comparative example, an optical polyester film is provided, wherein neither the modified PET composite material I for preparing the surface layer nor the modified PET composite material II for preparing the core layer is added with light stabilizer UV312. The others are the same as in embodiment 1.

[0051] Comparative Example 2 The difference between this comparative example and embodiment 1 is that: In this comparative example, an optical polyester film is provided, wherein neither the modified PET composite material I for preparing the surface layer nor the modified PET composite material II for preparing the core layer is added with light stabilizer UV2020. The others are the same as in embodiment 1.

[0052] Comparative Example 3 The difference between this comparative example and embodiment 1 is that: In this comparative example, an optical polyester film is provided, wherein neither the modified PET composite material I for preparing the surface layer nor the modified PET composite material II for preparing the core layer is added with any light stabilizer. The others are the same as in embodiment 1.

[0053] Comparative Example 4 The difference between this comparative example and embodiment 1 is that: In this comparative example, an optical polyester film is provided, wherein neither the modified PET composite material I for preparing the surface layer nor the modified PET composite material II for preparing the core layer is added with heat stabilizer and light stabilizer (i.e. neither any stabilizer is added). The others are the same as in embodiment 1.

[0054] Comparative Example 5 The difference between this comparative example and embodiment 1 is that: In the present comparative example, an optical polyester film is provided, wherein no thermal stabilizer is added in the modified PET composite I for preparing the surface layer and the modified PET composite II for preparing the core layer. The others are the same as in Example 1.

[0055] Comparative Example 6 The present comparative example is different from Example 1 in that: In the present comparative example, an optical polyester film is provided, wherein in the surface layer: the amount of thermal stabilizer is 5 parts, and the amount of light stabilizer is 5 parts (UV312: UV2020 = 3:2); in the core layer: the amount of thermal stabilizer is 50 parts, and the amount of light stabilizer is 50 parts (UV312: UV2020 = 30:20). The others are the same as in Example 1.

[0056]

Performance Test

[0057] Test method for light transmittance and haze of optical polyester film: The optical polyester film needs to meet the basic requirements of light transmittance and haze. The light transmittance and haze are detected according to the detection standard of GB / T 2410-2008. At the same time, there is a requirement for the detection environment, which needs to reach the standard of Class I in GB / T 2910-2018, i.e. the environmental temperature T = 23℃, and the relative humidity (RH) = 50%.

[0058] Test method for heat resistance of optical polyester film: According to the GB / T 11026-2106 series standard "Long-term heat resistance of electrical insulating materials", the heat resistance is tested. The test is carried out under electrical and mechanical conditions respectively.

[0059] Test method for shrinkage resistance of optical polyester film: the test equipment is purchased from the market--- The shrinkage resistance of the optical polyester film is detected according to the detection standard of GB / T 12027-2004. From the middle and both sides of the sample, each about 120 mm x 120 mm, the sample is taken, and the distance between the two samples is greater than 50 mm. Mark the initial length L0 and T0 in the middle of the sample, then place the sample in a 150℃ oven for 30 min, and then measure the length L and T between the marks again. The obtained L0-L / L0 and T0-T / T are the heat shrinkage rates in two directions.

[0060] Optical polyester film stability detection method: equipment The transmittance spectrum of the test piece at wavelengths of 390 and 420 nm was measured by using a UV-Visible spectrometer of Shimadzu (model UV-2600). The accelerated aging experiment was performed by using a Q-LAB UV tester (model QUV / se) according to a 325 nm lamp and a full irradiation light mode with an irradiation energy of 0.89 W / m 2 / nm. The samples with different irradiation times were subjected to color determination according to the CIE 15:2004 standard by using a Minolta colorimeter (model CM-3500d) to measure the YI value. The test results are shown in Table 1.

[0061] Table 1 Sample No. Tm (°C) Long-term heat resistance index (°C electrical / mechanical) Color difference before and after accelerated aging (YI initial / YI after aging) Thermal shrinkage in MD Thermal shrinkage in TD Transmittance Haze Example 1 256.8 135 / 135 1.644 / 2.160 0.6% 0.2% 92% 3.2% Example 2 261.2 140 / 135 1.753 / 2.833 0.6% 0.1% 91% 3.1% Example 3 258.5 135 / 135 1.410 / 2.705 0.7% 0.2% 91% 3.2% Example 4 259.4 140 / 145 1.659 / 2.991 0.5% 0.2% 90% 3.3% Example 5 260.2 125 / 130 1.118 / 3.280 0.6% 0.1% 90% 3.3% Example 6 264.0 145 / 145 2.215 / 3.797 0.7% 0.2% 90% 3.2% Example 7 254.4 135 / 130 1.525 / 2.458 0.7% 0.2% 92% 3.1% Example 8 260.7 145 / 140 1.882 / 2.916 0.5% 0.1% 91% 3.3% Example 9 255.3 130 / 130 1.708 / 3.154 0.6% 0.2% 91% 3.2% Example 10 263.6 145 / 145 1.389 / 3.802 0.4% 0.1% 92% 2.9% Comparative Example 1 259.7 130 / 135 1.542 / 4.582 0.6% 0.2% 89% 4.1% Comparative Example 2 258.1 130 / 135 1.614 / 5.877 0.7% 0.1% 88% 4.2% Comparative Example 3 257.6 130 / 130 1.025 / 7.881 0.7% 0.1% 86% 5.3% Comparative Example 4 245.0 105 / 105 1.057 / 7.604 1.6% 1.5% 85% 5.5% Comparative Example 5 245.5 105 / 105 1.894 / 2.530 1.6% 1.5% 88% 4.4% Comparative Example 6 255.4 140 / 145 3.476 / 4.010 0.7% 0.4% 85% 5.6% From the data analysis in Table 1, it can be known from the test results of Example 1 and Comparative Example 5 that the addition of the thermal stabilizer can obviously improve the heat resistance of the optical polyester film and reduce the thermal shrinkage rate of the optical polyester film. From the comparison of the test results of Comparative Example 3 and Comparative Examples 1 and 2, the addition of any kind of light stabilizer can obviously improve the yellowing resistance of the optical polyester film. From the comparison of the test results of Comparative Examples 1 and 2 and Example 1, the combined use of two different kinds of light stabilizers can make the material have better light resistance than the use of a single light stabilizer. From the comparison between Examples 1, 2, 3, 4 and Examples 5 and 6, different light stabilizer amount ratios and types can provide different degrees of yellowing resistance, and the additive amount will affect the initial hue of the film material.

[0062] In summary, the optical polyester film of the present application has good high-temperature resistance and anti-shrinkage performance, and the two-way shrinkage rates can meet the needs of various display devices. At the same time, the yellowing resistance is effectively improved, so that the optical polyester film of the present application can better face extreme climate and environment, and the overall service life is obviously prolonged.

[0063] The above only describes the preferred embodiments and principles of the present application in detail. For ordinary skilled persons in the art, the specific embodiments can be changed according to the idea provided by the present application, and these changes should be regarded as the protection scope of the present application.

Claims

1. An optical polyester film, characterized by, At least two layers of film substrate structure, the film substrate includes a surface layer and a core layer, the raw material of the surface layer is a first modified PET composite material, the first modified PET composite material includes a first modified PET resin and a first stabilizer; the raw material of the core layer is a second modified PET composite material, the second modified PET composite material includes a second modified PET resin and a second stabilizer, the mass ratio of the first stabilizer and the second stabilizer is (2-5):(5-9).

2. An optical polyester film according to claim 1, wherein The first stabilizer and the second stabilizer both include a thermal stabilizer and a light stabilizer, preferably, the thermal stabilizer is any one or a combination of more of rare earth, phosphite, triethyl phosphate, titanium / silicon oxide polymer; preferably, the light stabilizer is any one or a combination of two of benzotriazole, oxalic acid amide, triazine light stabilizer.

3. An optical polyester film according to claim 2, wherein The mass ratio of the thermal stabilizer and the light stabilizer is 1:3-6:

1.

4. The optical polyester film according to any one of claims 1 to 3, characterized by The first modified PET resin and the second modified PET resin are each independently selected from PET resin master particle grafted acrylate derivative; Preferably, the mass ratio of the acrylate derivative in the modified resin is 2.5-5%; Preferably, the crystallinity of the first modified PET resin and the second modified PET resin is 30-35%.

5. An optical polyester film according to claim 4, wherein The PET resin master particle is selected from any one or a combination of more of FG610, FG611, FG612, FG620.

6. The optical polyester film according to any one of claims 1 to 5, characterized by The first modified PET composite material includes the following components by weight fraction: 800-1000 parts of first modified PET resin, 15-30 parts of first coupling agent, 1-2 parts of first inorganic filler, 5-30 parts of first thermal stabilizer, 5-15 parts of first light stabilizer.

7. The optical polyester film according to any one of claims 1 to 5, characterized by The second modified PET composite material includes the following components by weight fraction: 750-900 parts of second modified PET resin, 5-20 parts of second coupling agent, 0.1-1 parts of second inorganic filler, 5-30 parts of second thermal stabilizer, 5-15 parts of second light stabilizer.

8. The optical polyester film according to claim 1, wherein The mass ratio of the surface layer and the core layer is (1-10):(80-98).

9. An optical polyester film according to claim 6 or 7, wherein The first coupling agent or the second coupling agent is each independently selected from any one or a combination of more of titanate, aluminate, oxy-silane coupling agent; and / or the first inorganic filler or the second inorganic filler is each independently selected from any one or a combination of more of silicon oxide, glass fiber, barium sulfate, calcium carbonate, kaolin.

10. A method of producing the optical polyester film according to any one of claims 1 to 9, characterized by, The following steps are included: (S.1) melt extrusion: the additives and the PET resin are mixed and modified according to the formula amount, re-pelletized to obtain a modified PET composite material, then the modified PET composite material is mixed, melted and extruded to obtain a modified PET melt; (S.2) sheet casting: the modified PET melt obtained in step (S.1) is laminated into A / B or A / B / A structure through two or more layer dies to obtain a cast polyester sheet, and then cooled and solidified to obtain a PET film; (S.3) longitudinal stretching: the PET film obtained in step (S.2) is stretched under heating condition on a longitudinal stretching machine and cooled to obtain a longitudinal stretched film; the longitudinal stretching heating temperature is 110-160°C, and the longitudinal stretching ratio is 2.0-5.3 times; (S.4) transverse stretching: the longitudinal stretched film obtained in step (S.3) is stretched under heating condition on a transverse stretching machine, then is subjected to heat setting treatment and cooling to obtain a transverse stretched film; the transverse stretching temperature is 115-180°C, and the transverse stretching ratio is 2.5-6.0 times; the heat setting treatment temperature is 150-260°C; finally, the transverse stretched film after stretching and setting is drawn and wound to obtain an optical polyester film.