Optical film, method of making and use thereof

Abstract

This invention relates to an optical film, its preparation method, and its application. The optical film comprises a polyester matrix resin and a cyclic olefin copolymer dispersed in the polyester matrix resin in particulate form, and satisfies at least the following conditions: (1) the particle size distribution coefficient is less than or equal to 0.25; (2) the particles separate from the polyester matrix resin interface to form a microporous structure, and the ratio of the pore size of the microporous structure to the particle size is 0.7~1.3; (3) the glass transition temperature of the cyclic olefin copolymer is T. g,COC The glass transition temperature of the polyester matrix resin is T. g,Polyester And T g,COC -T g,Polyester ≥40℃. The optical film of this invention has excellent reflectivity and heat resistance.

Description

Technical Field

[0001] This invention relates to the field of optical element technology, and in particular to an optical film, its preparation method, and its application. Background Technology

[0002] Currently, microporous optical films are mainly classified into two technical routes: inorganic stretching pore formation and organic stretching pore formation. Among them, the organic stretching pore formation method often uses polyolefin materials such as polytetramethylpentene (TPX) and polypropylene (PP) as incompatible resins. However, the refractive index difference between these polyolefin materials and the resin matrix is ​​small, resulting in low reflectivity. At the same time, their heat resistance is insufficient, and the microporous structure is prone to collapse under high temperature environments, which seriously affects the reflectivity retention and dimensional stability of the optical film. Summary of the Invention

[0003] Therefore, it is necessary to provide an optical film, its preparation method, and its application to address the above problems. The optical film has excellent reflectivity and heat resistance.

[0004] An optical film, the bulk of which comprises a polyester matrix resin and a cyclic olefin copolymer (COC) dispersed in the polyester matrix resin in particulate form, and satisfies at least the following conditions:

[0005] (1) The particle size distribution coefficient (PDI) of the particles is less than or equal to 0.25;

[0006] (2) The particles separate from the polyester matrix resin interface to form a microporous structure, and the ratio of the pore size of the microporous structure to the particle size is 0.7~1.3;

[0007] (3) The glass transition temperature of the cyclic olefin copolymer is T. g,COC The glass transition temperature of the polyester matrix resin is T. g,Polyester And T g,COC -T g,Polyester ≥40℃.

[0008] In one embodiment, the body of the optical film also satisfies at least one of the following conditions:

[0009] (1) The pore size range of the microporous structure is 0.5 μm to 2.0 μm;

[0010] (2) The particle size is 0.5μm~3.0μm;

[0011] (3) The particle size distribution coefficient of the particles is less than or equal to 0.2;

[0012] (4) 60℃≤T g,COC -T g,Polyester ≤120℃;

[0013] (5) The porosity of the body is 30%~50%;

[0014] (6) The mass ratio of the cyclic olefin copolymer to the polyester matrix resin is 5:95 to 25:75;

[0015] (7) The body further includes an interface regulator, and a metastable bonding layer formed by the interface regulator exists at the interface between the particles and the polyester matrix resin.

[0016] (8) The body further includes an additive selected from at least one of UV absorbers, light stabilizers, flame retardants or inorganic particles.

[0017] In one embodiment, the polyester matrix resin is selected from at least one of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polypropylene terephthalate, polyethylene terephthalate-1,4-cyclohexanediol, bio-based polyethylene furanate, or polycarbonate.

[0018] And / or, the cyclic olefin copolymer is selected from T g,COC It is a norbornene cyclic olefin copolymer with a temperature range of 130℃ to 185℃;

[0019] And / or, the mass fraction of the interface modifier in the bulk is 0.05% to 1.0%;

[0020] And / or, the interface modifier is selected from at least one of maleic anhydride-grafted polyester or glycidyl methacrylate (GMA)-grafted polyolefin.

[0021] In one embodiment, the polyester matrix resin is selected from T g,Polyester The cyclic olefin copolymer is a polyethylene terephthalate with a temperature of 70℃~80℃. g,COC The temperature ranges from 160℃ to 185℃.

[0022] Alternatively, the polyester matrix resin is selected from T g,Polyester The polybutylene terephthalate is at a temperature of 40℃ to 50℃, and the T of the cyclic olefin copolymer is... g,COC The temperature ranges from 160℃ to 185℃.

[0023] Alternatively, the polyester matrix resin is selected from T g,Polyester The cyclic olefin copolymer is a polyethylene naphthalate with a temperature range of 115℃ to 125℃. g,COC The temperature ranges from 170℃ to 185℃.

[0024] In one embodiment, the difference between the refractive index of the polyester matrix resin and the refractive index of the cyclic olefin copolymer is 0.03 to 0.08.

[0025] And / or, the polyester matrix resin is selected from naphthalene-containing modified polyethylene terephthalate with a refractive index greater than or equal to 1.56, and the cyclic olefin copolymer is selected from cyclic olefin copolymers with a refractive index less than or equal to 1.53.

[0026] In one embodiment, the optical film has a multilayer structure, including a body and a surface layer located on at least one side of the body, wherein the surface layer is selected from a pure polyester resin layer, a polyester resin layer containing inorganic particles, or a polyester resin layer with a cyclic olefin copolymer content of less than 1 wt%.

[0027] In one embodiment, the optical film satisfies at least one of the following conditions:

[0028] (1) When the optical film includes a surface layer, the thickness of the body in the optical film accounts for 70% to 90%;

[0029] (2) The thickness of the optical film is 20μm~150μm;

[0030] (3) The density of the optical film is 0.85 g / cm³. 3 ~1.00g / cm 3 .

[0031] A method for preparing an optical film as described above includes the following steps:

[0032] A masterbatch is obtained by melt-blending and extruding a cyclic olefin copolymer with a portion of a polyester matrix resin, wherein the ratio of the melt viscosity of the cyclic olefin copolymer to the melt viscosity of the polyester matrix resin is 0.5 to 2.0.

[0033] The remaining polyester matrix resin is melt-co-extruded with the masterbatch to obtain a cast sheet;

[0034] The casting is biaxially stretched at a temperature that satisfies the requirement that the loss tangent of the polyester matrix resin is greater than or equal to 0.2 and the loss tangent of the cyclic olefin copolymer is less than or equal to 0.1, to obtain a film. The film is then heat-set to obtain an optical film.

[0035] In one embodiment, during the process of melt-blending and extruding COC with a polyester matrix resin, the melt temperature is 260°C to 290°C and the shear rate is 100 s. -1 ~1100s -1 ;

[0036] And / or, the extrusion temperature of the masterbatch is 250℃~285℃, and the screw speed is 200rpm~400rpm;

[0037] And / or, in the process of melt co-extruding the polyester matrix resin and the masterbatch, the casting sheet comprising a body and a surface layer is formed by extrusion through a multi-layer co-extrusion die, wherein the extrusion temperature of the body is 5°C to 15°C higher than the extrusion temperature of the surface layer;

[0038] And / or, in the biaxial stretching process, the longitudinal stretching ratio is 2.5 to 6.0 times, and the transverse stretching ratio is 3.0 to 5.0 times;

[0039] And / or, the temperature of the heat setting treatment is 90℃~150℃, and the time is 3s~10s.

[0040] An application of an optical film as described above in an optical component.

[0041] In the optical film of the present invention, COC is selected as an incompatible resin. The large refractive index difference between COC and the polyester matrix resin can be used to improve the reflectivity of the optical film. Furthermore, by controlling the PDI of COC particles and the ratio of micropore diameter to COC particle size, the present invention can significantly increase the number of COC particle-air interfaces. By utilizing the high refractive index difference at this interface, high reflectivity across the entire wavelength range can be achieved, thereby effectively improving the reflectivity of the optical film.

[0042] Meanwhile, this invention utilizes the glass transition temperature difference (ΔT) between the polyester matrix resin and COC. g Strict control of the COC particles ensures they maintain a glassy rigidity in a long-term high-temperature environment, effectively supporting the pore walls and resisting the thermal shrinkage stress and molecular chain creep of the polyester matrix resin under high-temperature conditions, preventing the collapse and closure of the micropore walls. Furthermore, by controlling the PDI of the COC particles and the ratio of micropore diameter to COC particle size, this invention can also effectively avoid the deterioration of optical properties caused by particle loosening and displacement during thermal expansion or contraction of the polyester matrix resin. Therefore, it can effectively improve the heat resistance stability of the optical film, thereby enabling the optical film to maintain excellent dimensional stability and high reflectivity at high temperatures. Detailed Implementation

[0043] To facilitate understanding of the present invention, it will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to make the disclosure of the present invention more thorough and complete.

[0044] 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 specification of this invention is for the purpose of describing particular embodiments or examples only and is not intended to limit the invention. The optional scope of the term "and / or" as used herein includes any one of two or more of the related listed items, as well as any and all combinations of the related listed items, including any two related listed items, any more related listed items, or a combination of all related listed items.

[0045] In this invention, numerical ranges are involved. Unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe features or characteristics, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0046] The present invention provides an optical film, the body of which comprises a polyester matrix resin and a COC that is thermodynamically incompatible with the polyester matrix resin. The COC is an amorphous thermoplastic material copolymerized from cyclic olefins and ethylene, with a transmittance of over 90% in the visible light region (400nm~700nm) and a large difference in refractive index from the polyester matrix resin, thereby enabling the optical film to have excellent reflectivity.

[0047] Furthermore, during the stretching process, COC, which is thermodynamically incompatible with the polyester matrix resin, will be dispersed in the polyester matrix resin in the form of particles and separate from the polyester matrix resin interface, thus forming a microporous structure in the bulk. In this invention, by controlling the PDI of the particles to be less than or equal to 0.25, for example, PDI of 0.25, 0.24, 0.23, 0.22, 0.21, 0.20, 0.19, 0.18, 0.17, 0.16, 0.15, 0.14, 0.13, 0.12, 0.11, or 0.10, and simultaneously controlling the ratio of the pore size of the microporous structure to the particle size to be 0.7 to 1.3, for example, any ratio of 0.8, 0.9, 1.0, or 1.1, the number of COC particles and air interfaces can be significantly increased. Utilizing the high refractive index difference formed at this interface, high reflectivity across the entire wavelength band can be achieved, thereby effectively improving the reflectivity of the optical film. Specifically, the reflectivity of the optical film in the visible light band at 550 nm can be greater than or equal to 95.0%.

[0048] In addition, COC has a high glass transition temperature and heat distortion temperature, good dimensional stability, and a long-term heat resistance temperature of up to 150℃. Moreover, COC has a tensile strength of 65MPa~75MPa, a flexural modulus of 2500MPa~3000MPa, and an impact strength of 8kJ / m. 2 ~12kJ / m 2 It has excellent mechanical properties, which can effectively improve the heat resistance and mechanical properties of optical films, thereby improving the problem of optical films being prone to collapse at high temperatures, and giving optical films good dimensional stability and high reflectivity retention in high-temperature environments.

[0049] To further improve the thermal stability of the optical film, this invention further controls the glass transition temperature T of the cyclic olefin copolymer. g,COC Glass transition temperature T of polyester matrix resin g,Polyester The difference between them, such that they satisfy ΔT g =T g,COC -T g,Polyester ≥40℃, for example, ΔT g For temperatures of 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, and 130℃, ΔT is given here. g Within a certain range, COC particles maintain glassy rigidity in long-term high-temperature environments, effectively supporting the pore walls and resisting the thermal shrinkage stress and molecular chain creep of the polyester matrix resin under high-temperature conditions, preventing the collapse and closure of the micropore walls. Furthermore, the specific PDI of COC particles and the specific ratio of micropore diameter to COC particle size can effectively prevent the degradation of optical properties of the polyester matrix resin due to particle loosening and displacement during thermal expansion or contraction.

[0050] Therefore, this invention can effectively improve the heat resistance stability of optical films, thereby enabling them to maintain excellent dimensional stability and high reflectivity even at high temperatures. Specifically, after heat-treating the optical film at 150°C for 1 hour, the reflectivity retention rate at 550nm in the visible light band is greater than or equal to 98%.

[0051] Furthermore, since both the polyester matrix resin and COC are organic polymers without hydrophilic groups, the problem of interfacial moisture absorption is effectively alleviated, and the corrosion resistance of the optical film is also improved. Specifically, after being treated in an environment of 60°C and 90% relative humidity for 500 hours, the optical film of the present invention preferably retains a reflectance of greater than or equal to 98% in the visible light band at 550nm.

[0052] Optionally, the glass transition temperature T of the cyclic olefin copolymer g,COC Glass transition temperature T of polyester matrix resin g,PolyesterThe difference ΔT g The temperature can be further controlled within the range of 60℃ to 120℃, which can further improve the heat resistance of the optical film; the PDI of the particles can be further controlled within 0.2, and the ratio of the pore size of the microporous structure to the particle size can be further controlled within the range of 0.9 to 1.1, which can further improve the reflectivity and heat resistance of the optical film.

[0053] Optionally, the pore size range of the microporous structure is preferably 0.5μm to 2.0μm, and can be any value among 0.5μm, 1.0μm, 1.5μm or 2.0μm or any range between two; the particle size of the COC is preferably 0.5μm to 3.0μm, and can be any value among 0.5μm, 1.0μm, 1.5μm, 2.0μm, 2.5μm or 3.0μm or any range between two. Controlling the pore size and the particle size of the COC particles within this range can also suppress interference fringes caused by COC particle agglomeration or large-sized voids, giving the optical film better light uniformity and color purity.

[0054] Optionally, COC is preferably a norbornene cyclic olefin copolymer, T g,COC The preferred temperature is 130℃ to 185℃, for example, any one of 130℃, 140℃, 150℃, 160℃, 170℃, 180℃ or 185℃ or a range between any two.

[0055] Optionally, the polyester matrix resin is selected from at least one of PET, PBT, PEN, PTT, PETG, PEF, or PC; preferably, the polyester matrix resin is selected from T g,Polyester For PET at 70℃~80℃, the T of COC g,COC The temperature range is 160℃ to 185℃; or, the polyester matrix resin is selected from T. g,Polyester For PBT at 40℃~50℃, the T of COC g,COC The temperature range is 160℃ to 185℃; or, the polyester matrix resin is selected from T. g,Polyester The T value for PEN and COC is 115℃~125℃. g,COC The temperature is controlled between 170℃ and 185℃. This control allows the optical film to have good heat resistance.

[0056] To further improve the reflectivity of the optical film, the refractive index difference between COC and the polyester matrix resin can be controlled. Specifically, the refractive index n of the polyester matrix resin can be adjusted. Polyester The refractive index n is greater than that of COC COC It can also be the refractive index n of the polyester matrix resin. Polyester Refractive index n less than COC COCThis allows for multiple scattering by leveraging the refractive difference at the COC particle-air interface formed by the microporous structure.

[0057] Optionally, the refractive index n of the polyester matrix resin Polyester The refractive index n of COC COC The difference is 0.03 to 0.08, and more preferably 0.04 to 0.08. For example, the difference is any one of 0.03, 0.04, 0.05, 0.06, 0.07 or 0.08 or any range between two of them.

[0058] For example, the polyester matrix resin may be selected from naphthalene-containing modified polyethylene terephthalate with a refractive index greater than or equal to 1.6, and the cyclic olefin copolymer may be selected from cyclic olefin copolymers with a refractive index less than or equal to 1.53.

[0059] In order to obtain a high reflectivity and to ensure that the optical film still has good heat resistance and stability at high temperatures, the bulk porosity of the optical film is preferably 30% to 50%, and can be selected as any value of 30%, 35%, 40%, 45% or 50% or any range between two. It can be understood that the porosity is the percentage of the volume of the micropores to the total volume of the optical film.

[0060] Optionally, based on 100 parts of the total mass of the bulk material, the mass ratio of the cyclic olefin copolymer to the polyester matrix resin is preferably 5:95 to 25:75, and can be any one of 5:95, 10:90, 15:85, 20:80 or 25:75 or any range between two; furthermore, when preparing a high-reflectivity optical film, the mass ratio of the cyclic olefin copolymer to the polyester matrix resin is preferably 10:90 to 18:82; when preparing a high-flexibility optical film, the mass ratio of the cyclic olefin copolymer to the polyester matrix resin is preferably 5:95 to 10:90.

[0061] To better form micropores and improve the reflectivity of the optical film, the bulk material also contains an interface regulator. A metastable bonding layer formed by the interface regulator exists at the interface between the particles and the polyester matrix resin. The mass fraction of the interface regulator in the bulk material is preferably 0.05% to 1.0%. The interface regulator can be selected from at least one of maleic anhydride-grafted polyester or glycidyl methacrylate-grafted polyolefin.

[0062] To adapt to different application scenarios, additives can be added to the optical film as needed. These additives can be selected from at least one of UV absorbers, light stabilizers, flame retardants, or inorganic particles. For example, UV absorbers and hindered amine (HALS) light stabilizers can be added to prepare optical films with UV resistance and weather resistance; flame retardants can be added to prepare flame-retardant optical films; and modified silica (SO2) inorganic particles can be added to improve the mechanical properties of the optical film.

[0063] The optical film of the present invention can be a multilayer structure, including a body and a surface layer located on at least one side of the body. The surface layer is selected from a pure polyester resin layer, a polyester resin layer containing inorganic particles, or a polyester resin layer with a COC content of less than 1 wt%.

[0064] When the optical film includes a surface layer, the thickness of the body in the optical film accounts for 70% to 90%. Preferably, the optical film includes a body and a first surface layer and a second surface layer located on both sides of the body layer, and the thickness ratio of the first surface layer, the body and the second surface layer is preferably 5 to 15: 70 to 90: 5 to 15, for example, any ratio among 5: 90: 5, 10: 80: 10, 15: 80: 5, 10: 75: 15 or 15: 70: 15.

[0065] Optionally, the thickness of the optical film is preferably 20μm to 150μm, and can be any value among 20μm, 40μm, 60μm, 80μm, 100μm, 120μm, 140μm or 150μm or any range between two.

[0066] Because the density of COC is only 1.02 g / cm³ 3 Therefore, the density of the optical film of the present invention can reach 0.85 g / cm³. 3 ~1.00g / cm 3 It can effectively reduce the weight of optical components when applied.

[0067] In addition, the microporous structure formed by the polyester matrix resin-cyclic olefin copolymer has small reflectivity fluctuations at different incident angles and can maintain stable high reflectivity performance. Specifically, the absolute value of the reflectivity difference between the 30° incident angle and the 0° reference angle is less than 0.1%, which is better than the range of less than 0.2% of the traditional technology.

[0068] The present invention also provides a method for preparing the optical film, comprising the following steps:

[0069] COC was melt-blended and extruded with a portion of the polyester matrix resin. The melt viscosity η of COC was determined. COC Melt viscosity η of polyester matrix resin Polyester The ratio is 0.5~2.0, and masterbatch is obtained;

[0070] The remaining polyester matrix resin is melt-co-extruded with the masterbatch to obtain a cast sheet;

[0071] The cast sheet was subjected to biaxial stretching at a temperature that satisfied the loss tangent tanδ of the polyester matrix resin. Polyester Greater than or equal to 0.2, and the loss tangent of COC is tan δ COCA film is obtained when the value is less than or equal to 0.1; the film is then heat-set to obtain an optical film.

[0072] In the process of melt blending and extrusion of COC and polyester matrix resin, using polyester matrix resin and COC with a large ΔTg and using a shear field to control the melt viscosity ratio of COC and polyester matrix resin within a certain range can most effectively break COC into microspheres with uniform particle size, thereby inhibiting the aggregation or excessive elongation of the COC dispersed phase and avoiding subsequent problems such as wide micropore size distribution and decreased optical performance.

[0073] Optionally, the melting temperature of the masterbatch is preferably 260℃ to 290℃, and can be any value among 260℃, 270℃, 280℃, or 290℃, or a range between any two; the shear rate is preferably 100 s. -1 ~1100s -1 100s is an option -1 200s -1 400s -1 600s -1 800s -1 1000s -1 Or 1100s -1 any point value in the range or any range between the two.

[0074] To obtain a better microporous structure and ensure more uniform dispersion of COC in the polyester matrix resin without macroscopic phase separation, the extrusion temperature of the masterbatch is preferably 250℃~285℃, and can be any value among 250℃, 260℃, 270℃, 280℃ or 285℃ or any range between two; the screw speed is preferably 200rpm~400rpm, and can be any value among 200rpm, 250rpm, 300rpm, 350rpm or 400rpm or any range between two.

[0075] To further balance processing stability and pore-forming efficiency, an interface modifier, such as maleic anhydride-grafted polyester or GMA-grafted polyolefin, can be added at a mass fraction of 0.05 wt% to 1.0 wt% during masterbatch preparation. This interface modifier forms a "metastable bonding layer" at the interface, providing sufficient interfacial bonding energy to prevent delamination under normal temperature and low stress processing conditions; under high-stress tensile conditions at high temperatures, its bonding strength is lower than the interfacial peeling threshold, preferentially fracturing to assist in brittle pore formation.

[0076] Optionally, to adapt to different application scenarios, functional additives can be added as needed when preparing the masterbatch. For example, UV absorbers and light stabilizers can be added to prepare optical films with UV resistance and weather resistance; flame retardants can also be added to prepare flame-retardant optical films; and inorganic particles can also be added to improve the mechanical properties of the optical film.

[0077] In the process of melt co-extruding polyester matrix resin and masterbatch, the casting sheet comprising a body and a surface layer is formed by extrusion through a multi-layer co-extrusion die. Preferably, the extrusion temperature of the body is 5°C to 15°C higher than that of the surface layer. It can be selected as any value among 5°C, 7°C, 11°C, 13°C or 15°C or any range between the two. By controlling the temperature difference in this way, it is possible to obtain a complete and continuous surface layer while promoting the formation of micropores in the body.

[0078] In the biaxial stretching process of the cast sheet, a polyester matrix resin and COC with a large ΔTg are used, while the stretching temperature is controlled to meet the loss tangent value tan δ of the polyester matrix resin. Polyester Greater than or equal to 0.2, and the loss tangent of COC is tan δ COC Under conditions where the loss tangent is less than or equal to 0.1, the polyester matrix resin is in a highly elastic plateau region during the moment of stretching, exhibiting excellent ductility and deformation capacity; while the COC dispersed phase is in a deep glassy state, exhibiting an extremely brittle rigid body. The difference of more than 10 times in the loss tangent values ​​between the two induces extreme stress concentration at the interface, causing instantaneous "brittle peeling" rather than "ductile debonding" between the COC particles and the matrix interface, thereby forming a microporous structure with smooth pore walls and regular shapes, effectively preventing pore rupture and interconnection.

[0079] Optionally, the biaxial stretching process is preferably asynchronous biaxial stretching. The longitudinal stretching ratio is preferably 2.5 to 6.0 times, selectable from any one of 2.5, 3.0, 4.0, 5.0, or 6.0 times, or any range between two values; the transverse stretching ratio is preferably 3.0 to 5.0 times, selectable from any one of 3.0, 3.5, 4.0, 4.5, or 5.0 times, or any range between two values. More preferably, an asynchronous biaxial stretching process is used, with the longitudinal stretching ratio being 4.0 to 6.0 times, and the transverse stretching employing a two-step process, resulting in a cumulative transverse stretching ratio of 3.0 to 5.0 times. The asynchronous biaxial stretching process can induce the formation of micropores of different scales at different stretching stages, forming a hierarchical structure of "micron-scale primary pores + nanometer-scale secondary pores," further improving light scattering efficiency.

[0080] Optionally, the temperature of the heat setting treatment can be 90℃ to 150℃, and can be any value or a range between 90℃, 100℃, 110℃, 120℃, 130℃, 140℃ or 150℃; the heat setting treatment time is preferably 3s to 10s, and can be any value or a range between 3s, 5s, 7s, 9s or 10s.

[0081] The present invention also provides an application of the optical film described above in an optical component, wherein the optical component is selected from liquid crystal display (LCD) backlight modules, reflectors, etc.

[0082] The technical solution of the present invention will be further described below through specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention. Unless otherwise specified, specific conditions in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used without specified manufacturers are all commercially available conventional products.

[0083] Example 1

[0084] With T g,Polyester PET, with an intrinsic viscosity of 0.65 dL / g and a refractive index of 1.58, is used as the polyester matrix resin at 75℃. T... g,COC Optical films were prepared using COC (Mitsui Chemicals Topas 6017) with a refractive index of 1.53 at 170℃.

[0085] 30 wt% COC and 70 wt% polyester matrix resin were fed into a twin-screw extruder for granulation, with a melt temperature of 270℃ and a shear rate of 600 s⁻¹. -1 Control η COC / η Polyester The ratio is 1.2, the extrusion temperature of the masterbatch is 270℃, and the screw speed is 300rpm to obtain the masterbatch.

[0086] The body was formulated with 45 wt% masterbatch and 55 wt% polyester matrix resin, while the surface layer was formulated with 1 wt% SiO2 with a particle size of 2.5 μm and 99 wt% polyester matrix resin. The body and surface layer materials were fed into separate extruders and extruded and co-extruded at a temperature of 270°C for the body and 265°C for the surface layer, yielding a cast sheet with a thickness of 220 μm and a thickness ratio of 10:80:10.

[0087] The cast sheet was longitudinally stretched at 95°C with a stretch ratio of 3.5; then transversely stretched at 105°C with a stretch ratio of 4.0, while maintaining tan δ. Polyester =0.24, tan δ COC The value was 0.006, and a thin film was obtained.

[0088] The film was heat-set at 140℃ for 5 seconds to obtain the optical film.

[0089] Example 2

[0090] The only difference between Example 2 and Example 1 is that the main body is formulated with 75 wt% masterbatch and 25 wt% polyester matrix resin.

[0091] Example 3

[0092] The only difference between Example 3 and Example 1 is that the main body is formulated with 30 wt% masterbatch and 70 wt% polyester matrix resin.

[0093] Example 4

[0094] The difference between Example 4 and Example 1 is only that: the cast sheet is longitudinally stretched at 95°C with a stretching ratio of 4.0; then it is transversely stretched at 105°C with a stretching ratio of 4.5, while maintaining tan δ. Polyester =0.28, tan δ COC The value was 0.07, and a thin film was obtained.

[0095] Example 5

[0096] The difference between Example 5 and Example 1 is only that: the cast sheet is longitudinally stretched at 90°C with a stretching ratio of 3.5 times; then it is transversely stretched at 100°C with a stretching ratio of 4.0 times, while maintaining tan δ. Polyester =0.33, tan δ COC The value was 0.008, and a thin film was obtained.

[0097] Example 6

[0098] With T g,Polyester The PET matrix resin is a polyester resin with an intrinsic viscosity of 0.65 dL / g and a refractive index of 1.58 at 75℃; T... g,COC Optical films were prepared using COC (Mitsui Chemicals Topas 6015S) with a refractive index of 1.53 at 185℃.

[0099] 30 wt% COC and 70 wt% polyester matrix resin were fed into a twin-screw extruder for granulation, with a melt temperature of 275℃ and a shear rate of 500 s⁻¹. -1 Control η COC / η Polyester The masterbatch was obtained by setting the value to 1.0, the extrusion temperature of the masterbatch to 270℃, and the screw speed to 320rpm.

[0100] The body was formulated with 42 wt% masterbatch and 58 wt% polyester matrix resin, while the surface layer was formulated with 1 wt% SiO2 and 99 wt% polyester matrix resin. The body and surface layer materials were fed into separate extruders and extruded and co-extruded at 270°C for the body and 265°C for the surface layer, yielding a cast sheet with a thickness of 220 μm and a thickness ratio of 10:80:10.

[0101] The cast sheet was longitudinally stretched at 95°C with a stretch ratio of 3.5; then transversely stretched at 105°C with a stretch ratio of 4.0, while maintaining tan δ. Polyester =0.32, tan δ COC The value was 0.005, and a thin film was obtained.

[0102] The film was heat-set at 150℃ for 5s to obtain an optical film. The optical film was subjected to performance tests, and the results are as follows: (1) Heat resistance test: After heat treatment at 150℃ for 1h, the reflectivity retention rate at 550nm in the visible light band reached 100%, and the micropores did not collapse. (2) Damp heat resistance: After treatment in an environment of 60℃ and 90% relative humidity for 500h, the reflectivity retention rate at 550nm in the visible light band was 99.7%.

[0103] Example 7

[0104] The only difference between Example 7 and Example 6 is that: T g,Polyester The PET matrix resin is a polyester resin with an intrinsic viscosity of 0.65 dL / g and a refractive index of 1.58 at 75℃; T... g,COC Optical films were prepared using COC (Mitsui Chemicals Topas 8007) with a refractive index of 1.53 at 140℃.

[0105] The optical film prepared in this embodiment was subjected to heat resistance testing: after heat treatment at 130°C for 1 hour, the reflectivity at 550nm in the visible light band was maintained at 98.5%; after heat treatment at 150°C for 1 hour, the reflectivity at 550nm in the visible light band decreased to 96.2%, which is because the high temperature caused thermal degradation of the optical film material.

[0106] Example 8

[0107] The only difference between Example 8 and Example 1 is that: T g,Polyester PET, with an intrinsic viscosity of 0.65 dL / g and a refractive index of 1.58, is used as the polyester matrix resin at 80℃; T... g,COC It is a type A COC with a refractive index of 1.53 and a temperature of 170℃. g,COC Optical films were prepared using type B COC at 140℃ and a refractive index of 1.53.

[0108] 16 wt% of type A COC, 14 wt% of type B COC and 70 wt% of polyester matrix resin were fed into a twin-screw extruder for granulation to obtain masterbatch.

[0109] The optical film prepared in this embodiment was subjected to a damp heat resistance test: after being treated in an environment of 60°C and 90% relative humidity for 500 hours, the reflectivity retention rate in the visible light band at 550nm was 99.4%.

[0110] Example 9

[0111] The only difference between Example 9 and Example 6 is that: T g,Polyester The PET matrix resin is a polyester resin with an intrinsic viscosity of 0.65 dL / g and a refractive index of 1.58 at 75℃; T... g,COC Optical films were prepared using COC at 160℃ and with a refractive index of 1.52.

[0112] Example 10

[0113] With T g,Polyester A naphthalene-modified PET resin with an intrinsic viscosity of 0.65 dL / g and a refractive index of 1.60 was used as the polyester matrix resin; an optical film was prepared using Topas 6017 COC from Mitsui Chemicals.

[0114] 30 wt% COC and 70 wt% polyester matrix resin were fed into a twin-screw extruder for granulation, with a melt temperature of 260℃ and a shear rate of 600 s⁻¹. -1 Control η COC / η Polyester The ratio is 1.1, the extrusion temperature of the masterbatch is 270℃, and the screw speed is 300rpm to obtain the masterbatch.

[0115] The body was formulated with 42 wt% masterbatch and 58 wt% polyester matrix resin, while the surface layer was formulated with 1 wt% SiO2 with a particle size of 2.5 μm and 99 wt% polyester matrix resin. The body and surface layer materials were fed into separate extruders and extruded and co-extruded at 275°C for the body and 270°C for the surface layer, yielding a cast sheet with a thickness of 220 μm and a thickness ratio of 10:80:10.

[0116] The cast sheet was longitudinally stretched at 100°C with a stretch ratio of 3.5; then transversely stretched at 110°C with a stretch ratio of 4.0, while maintaining tan δ. Polyester =0.42, tan δ COC The value was 0.004, and a thin film was obtained.

[0117] The thin film was heat-set at 140℃ for 5 seconds to obtain the optical film. The prepared optical film was subjected to a damp heat resistance test: after being treated in an environment of 60℃ and 90% relative humidity for 500 hours, the reflectivity retention rate at 550nm in the visible light band was 99.6%.

[0118] Example 11

[0119] With T g,Polyester PBT with a refractive index of 1.54 and a temperature of 45℃ was used as the polyester matrix resin; the optical film was prepared using COC of Mitsui Chemicals Topas 6017.

[0120] 30 wt% COC and 70 wt% polyester matrix resin were fed into a twin-screw extruder for granulation, with a melt temperature of 265℃ and a shear rate of 500 s⁻¹. -1 Control η COC / η Polyester The masterbatch was obtained by setting the value to 1.0, the extrusion temperature of the masterbatch to 270℃, and the screw speed to 300rpm.

[0121] The body was formulated with 42 wt% masterbatch and 58 wt% polyester matrix resin, while the surface layer was formulated with 1 wt% SiO2 with a particle size of 2.5 μm and 99 wt% polyester matrix resin. The body and surface layer materials were fed into separate extruders and extruded and co-extruded at 250°C for the body and 245°C for the surface layer, yielding a cast sheet with a thickness of 220 μm and a thickness ratio of 10:80:10.

[0122] The cast sheet was longitudinally stretched at 75°C with a stretch ratio of 3.5; then transversely stretched at 90°C with a stretch ratio of 4.0, while maintaining tan δ. Polyester =0.23, tan δ COC The value was 0.008, and a thin film was obtained.

[0123] The film was heat-set at 140℃ for 5 seconds to obtain a chemically resistant optical film.

[0124] Example 12

[0125] With T g,Polyester The optical film was prepared using PEN as the polyester matrix resin with a temperature of 120℃ and a refractive index of 1.64, and COC of Mitsui Chemicals Topas 6015S.

[0126] 35 wt% COC and 65 wt% polyester matrix resin were fed into a twin-screw extruder for granulation, with a melt temperature of 290℃ and a shear rate of 200 s. -1 Control η COC / ηPolyester The ratio is 0.9, the extrusion temperature of the masterbatch is 285℃, and the screw speed is 320rpm to obtain the masterbatch.

[0127] The body was formulated with 50 wt% masterbatch and 50 wt% polyester matrix resin, while the surface layer was formulated with 1 wt% SiO2 with a particle size of 2.5 μm and 99 wt% polyester matrix resin. The body and surface layer materials were fed into separate extruders and extruded and co-extruded at 285°C for the body and 280°C for the surface layer, respectively, to obtain a cast sheet with a thickness of 220 μm and a thickness ratio of 10:80:10.

[0128] The cast sheet was longitudinally stretched at 135°C with a stretch ratio of 3.5; then transversely stretched at 150°C with a stretch ratio of 4.0, while maintaining tan δ. Polyester =0.22, tan δ COC The value was 0.008, and a thin film was obtained.

[0129] The thin film was heat-set at 120℃ for 5 seconds to obtain the optical film. The obtained optical film was subjected to heat resistance testing: after heat treatment at 180℃ for 1 hour, the reflectivity retention rate at 550nm in the visible light band reached 99.8%.

[0130] Example 13

[0131] With T g,Polyester PETG with a refractive index of 1.57 and a temperature of 80℃ was used as the polyester matrix resin; the optical film was prepared using COC of Mitsui Chemicals Topas 6017.

[0132] 25 wt% COC and 75 wt% polyester matrix resin were fed into a twin-screw extruder for granulation, with a melt temperature of 250℃ and a shear rate of 300 s. -1 Control η COC / η Polyester The ratio is 1.1, the extrusion temperature of the masterbatch is 255℃, and the screw speed is 300rpm to obtain the masterbatch.

[0133] The body was formulated with 45 wt% masterbatch and 55 wt% polyester matrix resin, while the surface layer was formulated with 1 wt% SiO2 with a particle size of 2.5 μm and 99 wt% polyester matrix resin. The body and surface layer materials were fed into separate extruders and extruded and co-extruded at 255°C for the body and 250°C for the surface layer, yielding a cast sheet with a thickness of 220 μm and a thickness ratio of 10:80:10.

[0134] The cast sheet was longitudinally stretched at 85°C with a stretching ratio of 3.0; then transversely stretched at 95°C with a stretching ratio of 3.5, while maintaining tan δ. Polyester =0.32, tan δ COC The value was 0.003, and a thin film was obtained.

[0135] The film was heat-set at 130℃ for 5 seconds to obtain an optical film. The obtained optical film was subjected to mechanical property testing: the elongation at break was greater than 100%, and it can be deep-drawn.

[0136] Example 14

[0137] With T g,Polyester The polyester matrix resin was PEF with a temperature of 85℃ and a refractive index of 1.56; the optical film was prepared using COC of Mitsui Chemicals Topas 6017.

[0138] 30 wt% COC and 70 wt% polyester matrix resin were fed into a twin-screw extruder for granulation, with a melt temperature of 280℃ and a shear rate of 500 s⁻¹. -1 Control η COC / η Polyester The ratio is 0.9, the extrusion temperature of the masterbatch is 260℃, and the screw speed is 300rpm to obtain the masterbatch.

[0139] The body was formulated with 58 wt% masterbatch and 42 wt% polyester matrix resin, while the surface layer was formulated with 1 wt% SiO2 with a particle size of 2.5 μm and 99 wt% polyester matrix resin. The body and surface layer materials were fed into separate extruders and extruded and co-extruded at 260°C for the body and 255°C for the surface layer, yielding a cast sheet with a thickness of 220 μm and a thickness ratio of 10:80:10.

[0140] The cast sheet was longitudinally stretched at 88°C with a stretching ratio of 3.5 times; then transversely stretched at 98°C with a stretching ratio of 4.0 times, while maintaining tan δ. Polyester =0.25, tan δ COC The value was 0.006, and a thin film was obtained.

[0141] The film was heat-set at 135℃ for 5 seconds to obtain the optical film.

[0142] Example 15

[0143] With T g,Polyester The polyester matrix resin is PC with a temperature of 110℃ and a refractive index of 1.58; the optical film is prepared using COC of Mitsui Chemicals Topas 6017.

[0144] 35 wt% COC and 65 wt% polyester matrix resin were fed into a twin-screw extruder for granulation, with a melt temperature of 290℃ and a shear rate of 600 s⁻¹. -1 Control η COC / η Polyester The ratio is 0.9, the extrusion temperature of the masterbatch is 280℃, and the screw speed is 350rpm to obtain the masterbatch.

[0145] The body was formulated with 50 wt% masterbatch and 50 wt% polyester matrix resin, while the surface layer was formulated with 1 wt% SiO2 with a particle size of 2.5 μm and 99 wt% polyester matrix resin. The body and surface layer materials were fed into separate extruders and extruded and co-extruded at 280°C for the body and 275°C for the surface layer, yielding a cast sheet with a thickness of 220 μm and a thickness ratio of 10:80:10.

[0146] The cast sheet was longitudinally stretched at 110°C with a stretch ratio of 3.2; then transversely stretched at 120°C with a stretch ratio of 3.8, while maintaining tan δ. Polyester =0.28, tan δ COC The value was 0.006, and a thin film was obtained. The thin film was heat-set at 140℃ for 5 seconds to obtain an optical film.

[0147] Example 16

[0148] The only difference between Example 16 and Example 1 is that the main body B is formulated with 44.6 wt% masterbatch, 54.6 wt% polyester matrix resin, 0.5 wt% UV absorber (brand name: BASF TINUVIN 320, Germany) and 0.3 wt% HALS light stabilizer (brand name: BASF TINUVIN 770, Germany).

[0149] The optical film prepared in this embodiment was subjected to aging tests: QUV accelerated aging (UVA-340, 0.76W / m²) for 1000h, the reflectivity after aging was 96.2%, the retention rate was 99.2%, and the yellowing index ΔYI < 2.0.

[0150] Example 17

[0151] The only difference between Example 17 and Example 1 is that the main body B is formulated with 40.9 wt% masterbatch, 50 wt% polyester matrix resin, and 9.1 wt% phosphorus flame retardant (brand: BASF TINUVIN BDP).

[0152] The optical film prepared in this embodiment was tested for flame retardancy and passed the UL94 V-0 test (0.15mm thickness).

[0153] Example 18

[0154] The only difference between Example 18 and Example 1 is that the body material was formulated with 45 wt% masterbatch and 55 wt% polyester matrix resin, while the surface layer was formulated with 100 wt% polyester matrix resin. The body material and surface layer material were fed into different extruders, and extrusion and co-extrusion were performed at an extrusion temperature of 270°C for the body and 265°C for the surface layer, resulting in a cast sheet with a thickness of 220 μm and a thickness ratio of 5:90:5.

[0155] The optical film prepared in this embodiment was subjected to surface performance testing, and the test results are as follows: surface haze is less than 1.0%, and abrasion resistance (RCA test) is greater than 500 times without scratches.

[0156] Example 19

[0157] The only difference between Example 19 and Example 1 is that 22 wt% of COC, 74 wt% of polyester matrix, and 4 wt% of surface-treated SiO2 with a particle size of 20 nm are fed into a twin-screw extruder for granulation to obtain masterbatch.

[0158] The optical film prepared in this embodiment was subjected to mechanical property testing, and the test results are as follows: the tensile strength was increased by 15% compared with Example 1, and the elongation at break was increased by 10% compared with Example 1.

[0159] Example 20

[0160] The difference between Example 20 and Example 1 is only that: the cast sheet is longitudinally stretched at 95°C with a stretching ratio of 5.0 times; then it is transversely stretched once at 100°C with a stretching ratio of 4.0 times; and then transversely stretched a second time at 100°C with a stretching ratio of 4.0 times, while maintaining tan δ. Polyester =0.28, tan δ COC The value was 0.007, and a thin film was obtained.

[0161] Comparative Example 1

[0162] The only difference between Comparative Example 1 and Example 1 is that CaCO3 with a particle size of 0.8 μm was used instead of COC. 33 wt% CaCO3 and 67 wt% polyester matrix resin were fed into a twin-screw extruder for granulation to obtain masterbatch.

[0163] The optical film prepared in this comparative example was subjected to a damp heat resistance test: after being treated in an environment of 60℃ and 90% relative humidity for 500h, the reflectivity retention rate in the visible light band at 550nm was 88%.

[0164] Comparative Example 2

[0165] The only difference between Comparative Example 2 and Example 1 is that: T g TPX (Mitsui Chemicals DX820) with a refractive index of 1.46 and a temperature of 40℃ was used to replace COC. 27 wt% TPX and 73 wt% polyester matrix resin were fed into a twin-screw extruder for granulation to obtain masterbatch.

[0166] The optical film prepared in this comparative example was subjected to heat resistance test: after heat treatment at 120℃ for 1 hour, the reflectivity retention rate at 550nm in the visible light band was 92.0%, and the thermal shrinkage rate was greater than 3.0%.

[0167] Comparative Example 3

[0168] The only difference between Comparative Example 3 and Example 1 is that COC is replaced with T. g,COC The COC-compatible resin is suitable for temperatures up to 140℃ and is compatible with the polyester matrix resin. 22 wt% COC, 44 wt% polyester matrix resin, and 44 wt% TiO2 are fed into a twin-screw extruder for granulation to obtain masterbatch.

[0169] The optical film prepared in this comparative example was subjected to a damp heat resistance test: after being treated in an environment of 60℃ and 90% relative humidity for 500h, the reflectivity retention rate in the visible light band at 550nm was 91.5%.

[0170] Comparative Example 4

[0171] The only difference between Comparative Example 4 and Example 1 is that T... g,COC Replace COC at 170℃ with T g,COC The COC is at 60℃, and it undergoes thermal deformation during processing.

[0172] Comparative Example 5

[0173] The only difference between Comparative Example 5 and Example 1 is that COC is not added; only polyester matrix resin and TiO2 are used for granulation. 66 wt% of polyester matrix resin and 34 wt% of TiO2 are fed into a twin-screw extruder for granulation to obtain masterbatch.

[0174] The optical film prepared in this comparative example was subjected to a damp heat resistance test: after being treated in an environment of 60℃ and 90% relative humidity for 500h, the reflectivity retention rate in the visible light band at 550nm was 85.0%.

[0175] Comparative Example 6

[0176] The only difference between Comparative Example 6 and Example 1 is that the twin-screw extrusion granulation step was omitted. Instead, 22 wt% COC, 74 wt% polyester matrix resin and 4 wt% surface-treated SiO2 with a particle size of 20 nm were directly mixed with the polyester matrix resin and fed into an extruder for casting, followed by biaxial stretching.

[0177] The test results of the optical films prepared in the above embodiments and comparative examples are shown in Table 1.

[0178] Table 1

[0179]

[0180] The performance test results of the optical films prepared in the above embodiments and comparative examples are shown in Table 2.

[0181] Table 2

[0182]

[0183] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0184] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. An optical film, characterized in that, The bulk of the optical film comprises a polyester matrix resin and a cyclic olefin copolymer dispersed in the polyester matrix resin in particulate form, and satisfies at least the following conditions: (1) The particle size distribution coefficient of the particles is less than or equal to 0.25; (2) The particles separate from the polyester matrix resin interface to form a microporous structure, and the ratio of the pore size of the microporous structure to the particle size is 0.7~1.3; (3) The glass transition temperature of the cyclic olefin copolymer is T. g,COC The glass transition temperature of the polyester matrix resin is T. g,Polyester And T g,COC -T g,Polyester ≥40℃.

2. The optical film according to claim 1, characterized in that, The body of the optical film also satisfies at least one of the following conditions: (1) The pore size range of the microporous structure is 0.5 μm to 2.0 μm; (2) The particle size is 0.5μm~3.0μm; (3) The particle size distribution coefficient of the particles is less than or equal to 0.2; (4)60℃≤T g,COC -T g,Polyester ≤120℃; (5) The porosity of the body is 30%~50%; (6) The mass ratio of the cyclic olefin copolymer to the polyester matrix resin is 5:95 to 25:75; (7) The body further includes an interface regulator, and a metastable bonding layer formed by the interface regulator exists at the interface between the particles and the polyester matrix resin. (8) The body further includes an additive selected from at least one of UV absorbers, light stabilizers, flame retardants or inorganic particles.

3. The optical film according to claim 2, characterized in that, The polyester matrix resin is selected from at least one of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polypropylene terephthalate, polyethylene terephthalate-1,4-cyclohexanediol, bio-based polyethylene furanate, or polycarbonate. And / or, the cyclic olefin copolymer is selected from T g,COC It is a norbornene cyclic olefin copolymer with a temperature range of 130℃ to 185℃; And / or, the mass fraction of the interface modifier in the bulk is 0.05% to 1.0%; And / or, the interface modifier is selected from at least one of maleic anhydride-grafted polyester or glycidyl methacrylate-grafted polyolefin.

4. The optical film according to claim 3, characterized in that, The polyester matrix resin is selected from T g,Polyester The cyclic olefin copolymer is a polyethylene terephthalate with a temperature of 70℃~80℃. g,COC The temperature ranges from 160℃ to 185℃. Alternatively, the polyester matrix resin is selected from T g,Polyester The polybutylene terephthalate is at a temperature of 40℃ to 50℃, and the T of the cyclic olefin copolymer is... g,COC The temperature ranges from 160℃ to 185℃. Alternatively, the polyester matrix resin is selected from T g,Polyester The cyclic olefin copolymer is a polyethylene naphthalate with a temperature range of 115℃ to 125℃. g,COC The temperature ranges from 170℃ to 185℃.

5. The optical film according to claim 1, characterized in that, The difference between the refractive index of the polyester matrix resin and the refractive index of the cyclic olefin copolymer is 0.03~0.08; And / or, the polyester matrix resin is selected from naphthalene-containing modified polyethylene terephthalate with a refractive index greater than or equal to 1.56, and the cyclic olefin copolymer is selected from cyclic olefin copolymers with a refractive index less than or equal to 1.

53.

6. The optical film according to any one of claims 1 to 5, characterized in that, The optical film has a multilayer structure, including a body and a surface layer located on at least one side of the body. The surface layer is selected from a pure polyester resin layer, a polyester resin layer containing inorganic particles, or a polyester resin layer with a cyclic olefin copolymer content of less than 1 wt%.

7. The optical film according to claim 6, characterized in that, The optical film satisfies at least one of the following conditions: (1) When the optical film includes a surface layer, the thickness of the body in the optical film accounts for 70% to 90%; (2) The thickness of the optical film is 20μm~150μm; (3) The density of the optical film is 0.85 g / cm³. 3 ~1.00g / cm 3 .

8. A method for preparing an optical film as described in any one of claims 1 to 7, characterized in that, Includes the following steps: A masterbatch is obtained by melt-blending and extruding a cyclic olefin copolymer with a portion of a polyester matrix resin, wherein the ratio of the melt viscosity of the cyclic olefin copolymer to the melt viscosity of the polyester matrix resin is 0.5 to 2.

0. The remaining polyester matrix resin is melt-co-extruded with the masterbatch to obtain a cast sheet; The casting is biaxially stretched at a temperature that satisfies the requirement that the loss tangent of the polyester matrix resin is greater than or equal to 0.2 and the loss tangent of the cyclic olefin copolymer is less than or equal to 0.1, to obtain a film. The film is then heat-set to obtain an optical film.

9. The method for preparing the optical film according to claim 8, characterized in that, In the process of melt blending and extruding the cyclic olefin copolymer with the polyester matrix resin, the melt temperature is 260℃~290℃ and the shear rate is 100s. -1 ~1100s -1 ; And / or, the extrusion temperature of the masterbatch is 250℃~285℃, and the screw speed is 200rpm~400rpm; And / or, in the process of melt co-extruding the polyester matrix resin and the masterbatch, the casting sheet comprising a body and a surface layer is formed by extrusion through a multi-layer co-extrusion die, wherein the extrusion temperature of the body is 5°C to 15°C higher than the extrusion temperature of the surface layer; And / or, in the biaxial stretching process, the longitudinal stretching ratio is 2.5 to 6.0 times, and the transverse stretching ratio is 3.0 to 5.0 times; And / or, the temperature of the heat setting treatment is 90℃~150℃, and the time is 3s~10s.

10. The use of an optical film as described in any one of claims 1 to 7 in an optical assembly.

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