Optical compensation film and preparation method and application thereof

Abstract

The invention provides an optical compensation film and a preparation method and application thereof.The optical compensation film comprises modified cellulose acetate with the structure shown in the formula (I): # imgabs0 # (I), n is larger than or equal to 150 and smaller than or equal to 500, R1, R2 and R3 are independently selected from a hydrogen atom, an acetyl group and a modified group A, R1, R2 and R3 at least comprise the acetyl group and the modified group A, the modified group A is selected from C3-C22 acyl groups and amido groups, n is larger than or equal to 150 and smaller than or equal to 500, and n is larger than or equal to 50 and smaller than or equal to 500. The total substitution degree X of the acetyl and the total substitution degree Y of the modified group A meet the following conditions: 2.3 < = X + Y < = 3, and 1.5 < = X < = 2.85.

Description

Technical Field

[0001] The present disclosure relates to the technical field of functional optical film preparation, and in particular to an optical compensation film and a preparation method and application thereof. Background Art

[0002] With the development of the information age, optical display devices, as key components of modern information interaction systems, play a vital role in information dissemination and communication. Liquid crystal displays (LCDs), with their excellent display performance, low power consumption, and lightweight design, have become widely used in a variety of information display devices, including televisions, laptops, desktop computers, smartphones, and in-car navigation systems. The structure of an LCD panel is a composite structure composed of multiple layers of precisely stacked functional optical films. The functions of these optical films directly influence the performance of the display panel. Therefore, the preparation of functional optical films has become a key link in the optical display industry chain.

[0003] As a key material for optical compensation films, cellulose acetate (CA) plays a key role in improving the performance of liquid crystal displays (LCDs) across various display modes due to its excellent optical transparency, thermal stability, and mechanical properties. However, current approaches to controlling the birefringence of cellulose acetate-based compensation films rely primarily on physical blending methods, which offer limited control over optical properties and pose challenges such as uniformity and compatibility. Furthermore, the inherent birefringence of cellulose acetate materials and the difficulty in controlling the oriented birefringence caused by the inevitable molecular orientation during industrial processing pose significant technical bottlenecks in the research and preparation of cellulose acetate-based optical compensation films, limiting their further application in high-performance display devices.

[0004] Therefore, developing an optical compensation film that can achieve precise control and has excellent optical stability, mechanical properties and thermal stability has become a technical problem that needs to be urgently solved in the current optical display field. Summary of the Invention

[0005] In view of this, the main purpose of the present disclosure is to provide an optical compensation film and a preparation method and application thereof, in order to at least partially solve at least one of the above-mentioned technical problems.

[0006] To achieve the above objectives, the technical solutions disclosed herein are as follows:

[0007] In one aspect of the present disclosure, an optical compensation film and a preparation method and application thereof are provided. The optical compensation film includes modified cellulose acetate having a structure as shown in formula (I):

[0008] (I)

[0009] Wherein, 150≤n≤500, R1, R2, and R3 are independently selected from a hydrogen atom, an acetyl group, and a modifying group A, and R1, R2, and R3 contain at least an acetyl group and a modifying group A, the modifying group A is selected from a C3-C22 acyl group and an amide group, and the total substitution degree X of the acetyl group and the total substitution degree Y of the modifying group A satisfy: 2.3 ≤ X + Y ≤ 3, and 1.5 ≤ X ≤ 2.85.

[0010] In another aspect of the present disclosure, a method for preparing the optical compensation film is provided, comprising:

[0011] Dissolving a modified cellulose acetate having a structure as shown in formula (I) in an organic solvent to obtain a homogeneous solution;

[0012] volatilizing the organic solvent in the homogeneous solution to obtain an initial film;

[0013] The initial film is preheated, uniaxially stretched, and quenched to obtain an optical compensation film, wherein the stretching ratio of the stretching treatment is 1.05 to 2.0, and the stretching speed is 0.1 mm / s to 20 mm / s.

[0014] In another aspect of the present disclosure, there is provided an application of the optical compensation film in at least one of the following optical devices: a polarizer, a liquid crystal display, and an organic light emitting diode display.

[0015] According to an embodiment of the present disclosure, an optical compensation film is proposed. The molecular structure of cellulose acetate is modified by chemical modification, and the hydroxyl groups in the cellulose molecules are replaced with acyl groups or amide groups, thereby obtaining a functionalized modified cellulose acetate ester. Furthermore, by regulating the type and degree of substitution of the substitution groups, the in-plane retardation value (R e ) and out-of-plane retardation (R th ) is regulated to meet the performance requirements of the optical compensation film. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a line graph showing the optical results of the in-plane and out-of-plane retardation values of the unstretched initial films of Examples 1 to 5 of the present disclosure and Comparative Example 1 as a function of the molar feed ratio at 550 nm;

[0017] Figure 2 It is a line graph of the optical results of the in-plane and out-of-plane retardation values at 550 nm of the optical compensation films in Examples 1 to 5 of the present disclosure and Comparative Example 1 when the stretching ratio is 1.5 as a function of the molar feed ratio. DETAILED DESCRIPTION

[0018] In order to make the objectives, technical solutions and advantages of the present disclosure more clearly understood, the present disclosure is further described in detail below in conjunction with specific embodiments.

[0019] The endpoints of the ranges and any values disclosed in this disclosure are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in this disclosure.

[0020] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The terms "comprise," "include," etc. used herein indicate the presence of the features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0021] Liquid crystal display (LCD) technology, one of the core technologies in modern information display, has been widely used in a variety of information display terminals, including televisions, computers, and mobile phones, and plays an irreplaceable role in daily life and industrial production. In the field of optical compensation films, cellulose acetate (CA), due to its excellent optical transparency, thermal stability, and mechanical properties, has become a key material for optical compensation films in optical devices. It plays a particularly key role in improving the performance of LCDs in various display modes.

[0022] In the process of realizing the present disclosure, it was found that the current regulation of the birefringence performance of cellulose acetate-based compensation films mainly relies on physical blending methods. Taking the traditional optical compensation film based on triacetyl cellulose (TAC) as an example, it mainly relies on small molecule additives to regulate its in-plane and out-of-plane retardation values and wavelength dispersion characteristics. However, this regulation method has significant limitations. Specifically, the introduction of small molecule additives may cause the optical properties of the film material to show obvious instability. In particular, its compensation effect is prone to fluctuations when the ambient temperature and humidity change, thereby adversely affecting the optical properties of the display. In addition, the compatibility problem between the small molecule additives and the triacetyl cellulose matrix may induce phase separation, resulting in reduced mechanical strength and long-term durability of the film.

[0023] Based on this, the present disclosure provides an optical compensation film, a preparation method thereof, and an application thereof. By introducing specific functional groups and utilizing chemical modification to modify the molecular structure of cellulose acetate, the regulation of optical properties, especially the controllable adjustment of its in-plane and out-of-plane retardation values, is achieved. The modified cellulose acetate film exhibits more stable optical compensation characteristics. When used as an optical compensation film, it can not only achieve precise regulation of the retardation value, but also maintain excellent mechanical properties and thermal stability while having excellent optical compensation performance to meet the needs of different display modes. In addition, the preparation method of modified cellulose acetate and the preparation process of the optical compensation film disclosed in the present disclosure have the advantages of simple operation, wide source of raw materials, and low cost, and show significant application value. The chemical modification method not only overcomes the limitations of the traditional physical blending method, but also provides a new technical path for improving the performance of optical compensation films, thereby promoting the development of display technology.

[0024] According to an embodiment of one aspect of the present disclosure, an optical compensation film and a preparation method and application thereof are provided. The optical compensation film includes modified cellulose acetate having a structure as shown in formula (I):

[0025] (I)

[0026] wherein 150 ≤ n ≤ 500, R1, R2, and R3 are independently selected from a hydrogen atom, an acetyl group, and a modifying group A, and R1, R2, and R3 include at least an acetyl group and a modifying group A, the modifying group A is selected from a C3-C22 acyl group and an amide group, and the total degree of substitution X of the acetyl group and the total degree of substitution Y of the modifying group A satisfy the following conditions: 2.3 ≤ X + Y ≤ 3, and 1.5 ≤ X ≤ 2.85.

[0027] According to the embodiments of the present disclosure, the molecular structure of cellulose acetate is modified by chemical modification, and the hydroxyl groups in the cellulose molecules are replaced with acyl groups or amide groups, thereby obtaining functionalized modified cellulose acetate ester. The modification process significantly affects the birefringence characteristics of the film by introducing substituent groups with specific optical properties and steric hindrance. Since different types of substituent groups contribute differently to birefringence, the orientation of the side groups and the free space between molecules can be adjusted by selecting appropriate substituent groups and precisely controlling their degree of substitution. This not only enables precise control of the retardation value, but also ensures the stability of the optical compensation film under different environmental conditions, avoiding the optical performance fluctuations and phase separation problems caused by small molecule additives in traditional physical blending methods.

[0028] According to an embodiment of the present disclosure, the structural formula of the modification group A is:

[0029] or ,

[0030] R4 and R5 are independently selected from any one of C1-C20 straight-chain alkanes, C4-C20 substituted or unsubstituted alicyclic hydrocarbons, and C6-C20 substituted or unsubstituted aromatic cyclic hydrocarbons. Examples of straight-chain alkanes include ethyl and propyl groups; examples of alicyclic hydrocarbons include cyclohexane and cyclopentane; examples of aromatic cyclic hydrocarbons include benzene, naphthalene, and biphenyl; and examples of substituents include halogen atoms (F, Cl, Br, I, etc.), alkyl groups, carboxyl groups, and amino groups.

[0031] According to embodiments of the present disclosure, the thickness of the optical compensation film is 40 μm to 100 μm, for example, 40 μm, 50 μm, 70 μm, 90 μm, 100 μm, etc. Optical compensation films of different thicknesses can be selected based on actual use needs. The thickness uniformity of the optical compensation film is preferably less than 5%, more preferably less than 4%, and particularly preferably less than 3%. Good uniformity can reduce variations in retardation values caused by thickness errors, which can lead to inconsistent changes in polarization states in different regions and affect display effects.

[0032] According to embodiments of the present disclosure, the optical compensation film has a light transmittance of 92% or higher, for example, 93%, 95%, 97%, 98%, 99%, etc. This high light transmittance can ensure that the optical compensation film reduces light loss during use, thereby improving display quality. The haze is below 1%, for example, 0.9%, 0.7%, 0.6%, 0.5%, 0.3%, etc. This low haze value indicates that the optical compensation film of the present disclosure has excellent optical transparency and can effectively reduce light scattering, thereby ensuring the clarity and sharpness of the displayed image.

[0033] According to the embodiments of the present disclosure, in the present disclosure, R e (λ), R th (λ) represents the in-plane retardation and the thickness direction retardation at wavelength λ, respectively. The measurement wavelength λ nm is within the visible light region, specifically, any wavelength within the range of 400-800 nm, preferably within the range of 400-750 nm, and more preferably within the range of 420-720 nm. Unless otherwise specified, R in this disclosure is e 、R thIt means the value measured at 500-600 nm (or the value calculated based on the measured value). In-plane retardation is measured using RETS-100L (manufactured by Otsuka Electronics Co., Ltd.) by introducing light with a wavelength of λ perpendicular to the film surface. By introducing light with a wavelength of λ at an inclination angle of 30 to 70 degrees relative to the normal direction of the film surface, the in-plane slow axis (determined by RETS-100L) is taken as the inclination axis, and based on the measured retardation value, the average refractive index and the thickness of the film entering, the RETS-100L is calculated according to the following equations (1) and (2) to obtain R th (λ) value. The average refractive index can be obtained using an Abbe refractometer (e.g., NAR-1T; ATAGO, Japan). The RETS-100L can calculate nx, ny, and nz from a given average refractive index and film thickness. Furthermore, Nz = (nx - nz) / (nx - ny) can be calculated from the obtained nx, ny, and nz.

[0034] According to an embodiment of the present disclosure, the slow axis refers to a direction in which the refractive index is the largest.

[0035] (1)

[0036] where R e (θ) represents the retardation value in a direction that differs from the normal direction by an angle of θ.

[0037] (2)

[0038] In formulas (1) and (2), d represents the film thickness, nx represents the refractive index in the slow axis direction in the plane, ny represents the refractive index in the direction orthogonal to nx in the plane, and nz represents the refractive index in the direction orthogonal to the nx and ny directions.

[0039] According to the embodiment of the present disclosure, the optical compensation film satisfies the following conditions within the wavelength range of 400 nm to 800 nm: 0 nm ≤ R e ≤ 120 nm, -100 nm ≤ R th ≤ 100 nm, preferably 0 nm ≤ R e ≤ 10 nm, -25 nm ≤ R th ≤25 nm. R e For example, it can be 0 nm, 2 nm, 4 nm, 5 nm, 6 nm, 8 nm, 10 nm, etc. th For example, it can be -25 nm, -20 nm, -15 nm, -10 nm, 0 nm, 10 nm, 15 nm, 20 nm, 25 nm, etc. eRepresents the in-plane retardation value of the material, reflecting the optical anisotropy within the plane; R th Represents the out-of-plane retardation value, characterizing the optical anisotropy in the thickness direction. The optical compensation film disclosed herein exhibits both in-plane and out-of-plane retardation values close to zero, significantly reducing the material's optical anisotropy over a wide wavelength range and enabling precise control of optical retardation properties. Furthermore, the slow axis deviation of the optical compensation film disclosed herein is less than ±6°, effectively reducing color deviation and brightness unevenness caused by inconsistent slow axis orientation, thereby improving the visual quality of displays.

[0040] According to another embodiment of the present disclosure, there is provided a method for preparing the optical compensation film, comprising:

[0041] dissolving modified cellulose acetate in an organic solvent to obtain a homogeneous solution;

[0042] volatilizing the organic solvent in the homogeneous solution to obtain an initial film;

[0043] The initial film is preheated, uniaxially stretched, and quenched to obtain an optical compensation film, wherein the stretching ratio of the stretching treatment is 1.05 to 2.0, and the stretching speed is 0.1 mm / s to 20 mm / s.

[0044] According to the embodiments of the present disclosure, the preparation process of the optical compensation film first obtains an initial film by solvent evaporation. Subsequently, the initial film is treated by a stretching and quenching process to change the molecular orientation of the optical compensation film. During the stretching process, the polymer molecular chains align along the stretching direction under the action of the stretching force, forming a molecular orientation structure with optical anisotropy. The molecular orientation structure directly affects the birefringence properties of the film, which in turn determines its optical retardation value (R e and R th By controlling parameters such as stretching ratio, stretching speed, and stretching temperature, the birefringence characteristics of the film can be regulated, thereby enabling it to meet the needs of different applications such as zero-retardation film and positive C film.

[0045] According to embodiments of the present disclosure, modified cellulose esters can be obtained by modifying acetylated cellulose esters with a certain degree of substitution, or by directly modifying cellulose. The source of cellulose is not particularly limited and can be derived from cotton linters, wood pulp, and the like. Furthermore, various types of modified cellulose esters can be mixed in any proportion.

[0046] According to an embodiment of the present disclosure, the organic solvent includes any one of halogenated hydrocarbons, esters, ketones, ethers, alcohols, and hydrocarbons, specifically including N,N-dimethylformamide, chlorohydrocarbons, methyl formate, acetone, ether, and the like. Suitable organic solvents can effectively disperse the modifying groups, ensuring that the modified cellulose acetate ester is fully dissolved and evenly dispersed in the solution. The solid content of the modified cellulose acetate ester in the homogeneous solution is preferably 5-40 wt%, more preferably 10-30 wt%, and most preferably 15-30 wt%. An appropriate solid content can balance the fluidity of the solution and the uniformity of film formation, ensuring the quality of the optical compensation film. It can also reduce the amount of solvent used, shorten drying time, improve production efficiency, and reduce energy consumption and costs.

[0047] According to an embodiment of the present disclosure, the process of volatilizing the organic solvent in the homogeneous solution specifically includes: drying pre-treatment, dissolution in a dissolving kettle, and solvent volatilization film formation.

[0048] For example, in actual operation, the pre-drying treatment method can be hot air drying or vacuum oven drying to dry the modified cellulose acetate ester particles. Preferably, the water content of the modified cellulose acetate ester particles needs to be reduced to below 3%. In order to ensure that the subsequent dissolution process in the reactor is stable and not interfered with by moisture, it is more preferred to reduce the water content of the modified cellulose acetate ester particles to below 1%. Modified cellulose acetate has a certain degree of hygroscopicity, so the drying temperature is preferably above the boiling point of water. The drying temperature is selected from 110°C to 180°C, preferably 120°C to 150°C. The drying time is preferably more than 6 hours. The longer the drying time, the lower the water content of the modified cellulose acetate ester particles. During the drying process, the material should be turned over at least once an hour to ensure sufficient drying, so that the particles do not clump and the moisture content meets the requirements.

[0049] The dried modified cellulose acetate particles and organic solvent are fully dissolved in a dissolving kettle to obtain a homogeneous solution. Taking a conventional dissolving kettle as an example, the modified cellulose acetate and solvent are mixed together under the stirring of a screw. By controlling the temperature of the dissolving kettle and the speed of the stirring screw, the modified cellulose acetate is fully dissolved to obtain a homogeneous solution. The temperature of the reactor needs to be controlled between 0 and 200°C. The stirring speed will also affect the temperature inside the reactor. The stirring speed can be increased while ensuring uniform stirring and stable reactor temperature.

[0050] A solvent volatilization film-forming method is employed, using an automatic scraper to apply the solution to a homogeneous solution. The homogeneous solution is poured into the scraper's hopper, which is then moved at a constant speed to apply the homogeneous solution to a smooth glass plate, forming a semi-dried initial film. The semi-dried initial film is then dried in an oven to evaporate the solvent, resulting in a transparent initial film with a smooth surface and uniform thickness. After drying, the residual solvent in the initial film is preferably 0-2 wt%, and more preferably 0-1 wt%.

[0051] According to an embodiment of the present disclosure, the preheating device can use hot air heating to preheat the film with a uniform thermal effect, ensuring that the film temperature is uniform. The preheating temperature is Tg-50°C to Tg+50°C, and more preferably the preheating temperature is Tg-20°C to Tg+20°C. Tg is the glass transition temperature of modified cellulose acetate. Preheating near Tg can ensure that the film has good molecular orientation ability during the subsequent stretching process, while avoiding molecular chain relaxation caused by excessive temperature.

[0052] According to an embodiment of the present disclosure, the optical compensation film uses a unidirectional stretching process during the film stretching process, and specifically, a high-temperature unidirectional film stretching machine can be used. The stretching ratio of the stretching treatment can be, for example, 1.05, 1.1, 1.3, 1.5, 1.7, 2.0, etc., and the stretching ratio is preferably 1.1 to 1.6; the stretching speed can be, for example, 0.1 mm / s, 1 mm / s, 5 mm / s, 10 mm / s, 15 mm / s, 20 mm / s, etc., and the stretching speed is more preferably 1 mm / s to 5 mm / s. The stretching temperature can be 150 to 210°C. By optimizing the stretching ratio, speed and temperature, the birefringence properties of the optical compensation film can be precisely controlled. The stretching treatment can induce the directional arrangement of the molecular chains, thereby adjusting the in-plane delay (R e ) value and out-of-plane retardation (R th ) value to meet specific optical performance requirements.

[0053] According to embodiments of the present disclosure, the quenching process involves rapidly cooling the stretched film from the stretching temperature to a liquid nitrogen temperature. This process rapidly cools the stretched film to fix its molecular orientation, preventing relaxation or rearrangement of the molecular chains during subsequent cooling. This ensures that the film's birefringence remains stable during subsequent use, resulting in an optical compensation film with stable optical performance.

[0054] According to an embodiment of the present disclosure, the preparation method of modified cellulose acetate includes steps S1 to S3:

[0055] Step S1: dissolving cellulose acetate in a polar organic solvent to obtain a mixed solution.

[0056] Step S2: Under an inert gas atmosphere, a modifying agent is added to the mixed solution, and the mixed solution and the modifying agent are stirred and reacted at a reaction temperature of 20-100° C. for 2-24 hours to obtain a reaction solution.

[0057] Step S3: adding a precipitant to the reaction solution to form a precipitate, wherein the precipitating solvent includes any one of ethanol, methanol, and deionized water, preferably methanol or deionized water, and filtering and washing to obtain modified cellulose acetate.

[0058] According to an embodiment of the present disclosure, in step S1, the molecular weight of cellulose acetate is 30,000 to 300,000, preferably 50,000 to 200,000, to ensure that cellulose acetate has good solubility and dispersibility in polar organic solvents, thereby providing a uniform reaction system for subsequent modification reactions. The polar organic solvent includes any one of N,N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, and acetone, or a mixed solvent. The mass ratio of cellulose acetate to the polar organic solvent is 1:10 to 20, for example, 1:10, 1:13, 1:15, 1:17, 1:20, etc., so that the cellulose acetate ester can be fully dissolved in the polar organic solvent.

[0059] According to an embodiment of the present disclosure, in step S2, the inert gas may be argon or nitrogen, preferably nitrogen, to ensure the stability of the reaction system and prevent interference from oxygen or other reactive gases, thereby ensuring efficient reaction and product purity. The modifying reagent comprises any one of an isocyanate, an acyl chloride, or an acid anhydride. The molar ratio of the modifying reagent to the hydroxyl group of cellulose acetate is (1-3):1, preferably (1-2):1. When the modifying reagent is an acyl chloride, a basic compound catalyst such as an amine is added to the reaction; when the modifying reagent is an acid anhydride, a protic catalyst such as sulfuric acid is added to the reaction; when the modifying reagent is an isocyanate, no catalyst is required. By properly selecting the catalyst and reaction conditions, the efficient modification reaction can be ensured while reducing the formation of impurities and byproducts, thereby improving the performance and quality of the modified cellulose acetate.

[0060] According to an embodiment of the present disclosure, in step S2, the reaction temperature can be, for example, 20°C, 25°C, 30°C, 35°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, etc. Appropriate reaction temperature and reaction time can activate the chemical reaction between the modifying agent and cellulose acetate while avoiding side reactions or molecular chain degradation that may be caused by excessively high temperatures. The reaction time can be, for example, 2 h, 4 h, 6 h, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, 24 h, etc. to ensure that the reaction is fully carried out and that there is sufficient contact and reaction between the modifying agent and cellulose acetate, thereby achieving uniform and efficient chemical modification.

[0061] According to an embodiment of the present disclosure, in step S3, the mass ratio of the precipitation solvent to the reaction liquid ranges from 1:50 to 1:200, for example, 1:50, 1:100, 1:150, 1:200, etc., so that the modified cellulose acetate ester is fully precipitated, and the mixing of residual impurities and unreacted products is reduced, thereby improving the purity and quality of the product. Vigorous stirring is required during the precipitation process, and magnetic stirring or mechanical stirring can be selected. The speed of magnetic stirring can be selected from 500 to 1000 rpm, preferably from 700 to 1000 rpm. The speed of mechanical stirring can be selected from 200 to 500 rpm.

[0062] According to the embodiments of the present disclosure, the modified cellulose acetate ester prepared by the present disclosure is a white solid. The prepared modified cellulose acetate ester is dried at 50-120° C. for 2-72 hours. The drying method includes vacuum drying or forced air drying to ensure that the residual solvent of the modified cellulose acetate ester is effectively removed.

[0063] According to an embodiment of yet another aspect of the present disclosure, there is provided an application of the optical compensation film in at least one of the following optical devices: a polarizer, a liquid crystal display (LCD), and an organic light emitting diode display (OLED).

[0064] According to the embodiments of the present disclosure, the optical compensation film of the present disclosure can effectively compensate for optical anisotropy, reduce color deviation and brightness unevenness, thereby significantly improving the display effect and meeting the diverse optical performance requirements of different optical devices such as polarizers, LCDs and OLEDs. At the same time, its precisely controlled in-plane retardation (R e ) and out-of-plane retardation (R th ) can optimize the viewing angle characteristics of optical devices, reduce color drift and brightness attenuation when the viewing angle changes, ensure good visual effects at a large viewing angle, and provide reliable material support for current display technology.

[0065] In order to make the purpose, technical solutions and advantages of the present disclosure more clearly understood, the present disclosure is further described in detail below in conjunction with specific examples and drawings. Where specific techniques or conditions are not specified in the examples, they are all conventional methods and can be carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. It should be noted that the methods provided in the present disclosure are all conventional methods unless otherwise specified, and the reactants and reagents can be obtained from public commercial channels unless otherwise specified.

[0066] According to the embodiments of the present disclosure, the average refractive index of the optical compensation film is measured using an Abbe refractometer (trade name NAR-1T; ATAGO, Japan). The retardation value of the optical compensation film is measured using a phase difference meter (trade name RETS-100L; manufactured by Otsuka Electronics Co., Ltd.) to measure the in-plane retardation value R e and out-of-plane retardation Rth The glass transition temperature was measured using a differential scanning calorimeter (DSC Q2000, manufactured by TA Instruments, USA).

[0067] Example 1:

[0068] This embodiment provides an optical compensation film, and the specific preparation steps are as follows:

[0069] Under a nitrogen atmosphere, cellulose diacetate (3% hydroxyl group by mass) was dissolved in N,N-dimethylformamide at a mass ratio of 1:10 with stirring. p-Toluene isocyanate was added dropwise at 80°C. The reaction was allowed to proceed under nitrogen for 4 hours to obtain a reaction solution containing modified cellulose acetate. The molar ratio of hydroxyl groups of cellulose diacetate to p-Toluene isocyanate was 1:1.

[0070] After the reaction is completed, methanol is added dropwise to the reaction solution and stirred vigorously to obtain a heterogeneous liquid containing a white flocculent solid. The heterogeneous liquid is subjected to solid-liquid separation to obtain a white solid product.

[0071] The obtained white solid product was dissolved in dichloromethane and slowly added to methanol again for solid-liquid separation. This process was repeated until the impurities in the white solid were completely washed away. The product was then dried in an oven at 60°C to obtain the modified cellulose acetate ester (1). The structural formula of the modified cellulose acetate ester (1) is as follows:

[0072] (1).

[0073] The obtained modified cellulose acetate (1) was dissolved in N,N-dimethylformamide at a solid content of 10 wt%, and the solvent was evaporated to form a film, thereby obtaining an unstretched initial film 1.

[0074] The unstretched initial film 1 is subjected to a stretching process, and the specific stretching parameters and process are as follows:

[0075] The unstretched initial film 1 was stretched using a homemade unidirectional film stretching device (reference patents CN103063689A, CN203275319U). The stretching process parameters were as follows: preheating time was 5 min, stretching temperature was 10 ± 0.5 °C above the glass transition temperature, stretching rate was 1 mm / s, stretching method was unrestricted unidirectional stretching, and the initial film 1 was stretched within a stretch ratio range of 1.2 to 1.6 to obtain a stretched optical compensation film 1.

[0076] Example 2

[0077] This embodiment provides an optical compensation film. The specific preparation steps are the same as those in Example 1, except that the molar feed ratio of the hydroxyl group of cellulose diacetate to p-toluene isocyanate is 1:1.1, and an unstretched initial film 2 is prepared.

[0078] The unstretched initial film 2 is subjected to a stretching treatment to obtain a stretched optical compensation film 2 .

[0079] Example 3

[0080] This embodiment provides an optical compensation film. The specific preparation steps are the same as those in Example 1, except that the molar feed ratio of the hydroxyl group of cellulose diacetate to p-toluene isocyanate is 1:1.25, and an unstretched initial film 3 is prepared.

[0081] The unstretched initial film 3 is stretched to obtain a stretched optical compensation film 3 .

[0082] Example 4

[0083] This embodiment provides an optical compensation film. The specific preparation steps are the same as those in Example 1, except that the molar feed ratio of the hydroxyl group of cellulose diacetate to p-toluene isocyanate is 1:1.5, and an unstretched initial film 4 is prepared.

[0084] The unstretched initial film 4 is subjected to a stretching treatment to obtain a stretched optical compensation film 4 .

[0085] Example 5

[0086] This embodiment provides an optical compensation film. The specific preparation steps are the same as those in Example 1, except that the molar feed ratio of the hydroxyl group of cellulose diacetate to p-toluene isocyanate is 1:1.75, and an unstretched initial film 5 is prepared.

[0087] The unstretched initial film 5 is subjected to a stretching treatment to obtain a stretched optical compensation film 5 .

[0088] Example 6

[0089] This embodiment provides an optical compensation film. The specific preparation steps are the same as those in Example 1, except that the reactant is changed to n-butyl isocyanate, and the molar feed ratio of the hydroxyl group of cellulose diacetate to n-butyl isocyanate is 1:1.75. The reaction time is 6 hours to obtain modified cellulose acetate (2). The structural formula of the modified cellulose acetate (2) is as follows:

[0090] (2)

[0091] The obtained modified cellulose acetate (2) was dissolved in N,N-dimethylformamide at a solid content of 10 wt%, and the solvent was evaporated to form a film to prepare an unstretched initial film 6. The unstretched initial film 6 was stretched to obtain a stretched optical compensation film 6.

[0092] Example 7

[0093] This embodiment provides an optical compensation film. The specific preparation steps are the same as those in Example 1, except that the reactant is changed to p-butylbenzene chloride, and the molar feed ratio of the hydroxyl group of cellulose diacetate to p-butylbenzene chloride is 1:1.75. Pyridine is added in an amount equal to the molar amount of p-butylbenzene chloride. The reaction temperature is 20°C and the reaction time is 2 hours to obtain modified cellulose acetate ester (3). The structural formula of the modified cellulose acetate ester (3) is as follows:

[0094] (3)

[0095] The obtained modified cellulose acetate (3) was dissolved in N,N-dimethylformamide at a solid content of 10 wt%, and the solvent was evaporated to form a film to prepare an unstretched initial film 7. The unstretched initial film 7 was stretched to obtain a stretched optical compensation film 7.

[0096] Example 8

[0097] This embodiment provides an optical compensation film. The specific preparation steps are the same as those in Example 1, except that the reactant is changed to n-hexyl isocyanate, and the molar feed ratio of the hydroxyl group of cellulose diacetate to n-hexyl isocyanate is 1:1.75. The reaction time is 6 hours to obtain modified cellulose acetate (4). The structural formula of the modified cellulose acetate (4) is as follows:

[0098] (4)

[0099] The obtained modified cellulose acetate (4) was dissolved in N,N-dimethylformamide at a solid content of 10 wt%, and the solvent was evaporated to form a film, thereby preparing an unstretched initial film 8.

[0100] The unstretched initial film 8 is stretched to obtain a stretched optical compensation film 8 .

[0101] Comparative Example 1

[0102] This embodiment provides an optical compensation film, which differs from Example 1 in that unmodified cellulose acetate is dissolved in N,N-dimethylformamide at a solid content of 10 wt %, and the solvent is evaporated to form a film, thereby obtaining an unstretched and unmodified initial film 9.

[0103] The unstretched initial film 9 is subjected to a stretching treatment to obtain a stretched optical compensation film 9 .

[0104] The basic performance parameters of film thickness and glass transition temperature of the initial films in Examples 1 to 8 and Comparative Example 1 were tested. The experimental conditions and specific test results are recorded in Table 1.

[0105] Table 1

[0106]

[0107] Comparing the test results in Table 1, the modified initial film obtained in the embodiment of the present disclosure has a lower glass transition temperature than that of the comparative example, and the glass transition temperature decreases with the increase of the reaction degree, which is beneficial to the subsequent processing of the optical compensation film.

[0108] The optical properties of the initial films in Examples 1-8 and Comparative Example 1 were tested, and the in-plane retardation value R of the films at a specific wavelength was measured using a phase difference meter. e and out-of-plane retardation R th ,The test results are summarized in Table 2.

[0109] Table 2

[0110]

[0111] Figure 1 1 is a line graph showing the optical results of the in-plane and out-of-plane retardation values of the unstretched initial films at 550 nm as a function of the molar feed ratio in Examples 1 to 5 of the present disclosure and Comparative Example 1.

[0112] observe Figure 1 And comparing the test results in Table 2, we can see that:

[0113] The refractive index of the modified cellulose acetate film is significantly higher than that of the unmodified film, and the refractive index is closely related to the reaction conditions. While maintaining the reaction temperature and time constant, increasing the feed ratio can enhance the reaction rate, thereby increasing the refractive index. This indicates that by adjusting reaction conditions such as feed ratio, reaction temperature, and reaction time, film materials with varying refractive indices can be obtained to meet the desired requirements for optical compensation films.

[0114] Furthermore, by comparing the examples and comparative examples, it can be seen that the transmittance and haze of the modified cellulose acetate initial film meet the basic requirements of optical films, that is, the transparency is above 90% and the haze is below 3%, and it can be used as an optical film in display devices. e Mainly regulated by stretching, the in-plane retardation value of the unstretched optical film is small, basically close to 0 nm; the out-of-plane retardation value Rth It is mainly regulated by adding additives. By comparing all the examples with the comparative examples, it can be seen that the optical film prepared by modified cellulose acetate is R th The R th .

[0115] The thickness of the optical compensation films after stretching at different stretching ratios in Examples 1 to 8 and Comparative Example 1 was measured using a micrometer. The stretching process parameters and test results are summarized in Table 3.

[0116] Table 3

[0117]

[0118] The optical performance of the stretched optical compensation films in Examples 1 to 8 and Comparative Example 1 was tested, and the in-plane retardation value R of the optical compensation films at a specific wavelength was measured using a phase difference meter. e and out-of-plane retardation R th ,The results are summarized in Table 4.

[0119] The draw ratio (DR) is defined as follows in this disclosure:

[0120] , where L is the length of the stretched spline.

[0121] Table 4

[0122]

[0123] Figure 2 It is a line graph of the optical results of the in-plane and out-of-plane retardation values at 550 nm of the optical compensation films in Examples 1 to 5 of the present disclosure and Comparative Example 1 when the stretching ratio is 1.5 as a function of the molar feed ratio.

[0124] observe Figure 2 And comparing the test results in Table 4, we can see that:

[0125] The R of the optical compensation film obtained by using unmodified cellulose acetate in Comparative Example 1 is e 、R th As the stretching ratio increases, it gradually increases, and the change range is large. In contrast, in Examples 1 to 8 of the present disclosure, the optical compensation film obtained by using the modified cellulose acetate ester has R e 、R th As the stretching ratio increases, the change is smaller, showing more stable optical properties.

[0126] Through the comparative analysis of Examples 1 to 8, it can be found that under the same stretching ratio, as the feed ratio increases, the R eFirst decrease and then increase, R th As the feed ratio increases, regulation from positive to negative values is achieved.

[0127] Further comparing the test results of Comparative Example 1 and Example 2, the optical film of Example 2 has a stretch ratio of 1.6. e With R th Compared to Comparative Example 1, the retardation is significantly reduced, meeting the requirements of 0 nm ≤ Re ≤ 10 nm and -25 nm ≤ Rth ≤ 25 nm. The film thickness is 36 μm, meeting the requirements for optical films. If a lower retardation value is required, the initial film can be made thinner or the stretch ratio can be adjusted appropriately.

[0128] In addition, by comparing Examples 1 to 5, it can be seen that under the same stretching conditions and the same stretching ratio, changing the reaction conditions (feed ratio, reaction time, reaction temperature) can affect the R e , R th By comparing Example 5 and Comparative Example 1, it can be seen that after changing the reaction conditions, the retardation value of the optical compensation film obtained by using modified cellulose acetate changes from positive to negative, and the property of negative C film can be changed to positive C film.

[0129] Therefore, the optical compensation film prepared by using modified cellulose acetate provided by the present disclosure has significantly lower in-plane and out-of-plane retardation values than the unmodified cellulose acetate optical compensation film. The retardation value can be achieved by regulating the reaction conditions and stretching parameters, and an optical compensation film that meets the application requirements can be prepared. In Example 5, R th Going to a negative value also offers the possibility of preparing positive C optical compensation films.

[0130] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present disclosure. It should be understood that the above are only specific embodiments of the present disclosure and are not intended to limit the present disclosure. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present disclosure should be included in the scope of protection of the present disclosure.

Claims

1. An optical compensation film, characterized in that: The optical compensation film includes modified cellulose acetate having a structure as shown in formula (I): （I） Where, 150 ≤ n ≤ 500, R1, R2, and R3 are independently selected from hydrogen atoms, acetyl groups, and modified groups A, and R1, R2, and R3 at least contain acetyl groups and modified groups A. The modified group A is selected from C3~C22 acyl group and amide group, The total substitution degree X of the acetyl group and the total substitution degree Y of the modifying group A satisfy: 2.3 ≤ X + Y ≤ 3, and 1.5 ≤ X ≤ 2.

85.

2. The optical compensation film according to claim 1, wherein The structural formula of the modified group A is: or , Wherein, R4 and R5 are independently selected from any one of C1-C20 straight-chain alkanes, C4-C20 substituted or unsubstituted aliphatic cyclic hydrocarbons, and C6-C20 substituted or unsubstituted aromatic cyclic hydrocarbons.

3. The optical compensation film according to claim 1, wherein The optical compensation film has a thickness of 40 μm to 100 μm, a light transmittance of 92% or more, and a haze of 1% or less. The optical compensation film satisfies the following conditions within the wavelength range of 400 nm to 800 nm: 0 nm ≤ R e ≤ 120 nm, -100 nm≤ R th ≤ 100 nm, preferably 0 nm ≤ R e ≤ 10 nm, -25 nm ≤ R th ≤ 25 nm.

4. A method for preparing an optical compensation film according to any one of claims 1 to 3, characterized in that: The preparation method comprises: Dissolving a modified cellulose acetate having a structure as shown in formula (I) in an organic solvent to obtain a homogeneous solution; volatilizing the organic solvent in the homogeneous solution to obtain an initial thin film; The initial film is preheated, uniaxially stretched, and quenched to obtain the optical compensation film, wherein the stretching ratio of the stretching treatment is 1.05 to 2.0, and the stretching speed is 0.1 mm / s to 20 mm / s.

5. The preparation method according to claim 4, characterized in that The organic solvent includes any one of halogenated hydrocarbons, esters, ketones, ethers, alcohols and hydrocarbons; The solid content of the modified cellulose acetate in the homogeneous solution is 5-40 wt %.

6. The preparation method according to claim 4, characterized in that The preparation method of the modified cellulose acetate comprises: dissolving cellulose acetate in a polar organic solvent to obtain a mixed solution; Under an inert gas environment, adding a modifying reagent to the mixed solution, stirring and reacting at a reaction temperature of 20-100° C. for 2-24 hours to obtain a reaction solution, wherein the modifying reagent comprises any one of isocyanate, acyl chloride, and acid anhydride, and the molar ratio of the modifying reagent to cellulose acetate is 1:(1-3); A precipitant is added to the reaction solution to form a precipitate, which is filtered and washed to obtain the modified cellulose acetate.

7. The preparation method according to claim 6, characterized in that The adding of a modifying agent to the mixed solution further comprises: When the modifying agent is an acyl chloride, a basic compound catalyst is added to carry out the reaction; When the modifying agent is an acid anhydride, a protonic catalyst is added to carry out the reaction.

8. The preparation method according to claim 6, characterized in that The molecular weight of the cellulose acetate is 30,000 to 300,000. The polar organic solvent includes any one of N,N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, acetone, or a mixed solvent. The mass ratio of the cellulose acetate to the polar organic solvent is 1:10-20. The precipitation solvent includes any one of ethanol, methanol, and deionized water. The mass ratio of the precipitation solvent to the reaction solution ranges from 1:50 to 1:

200.

9. The preparation method according to claim 4, characterized in that The preheating temperature is Tg-50°C to Tg+50°C, wherein Tg is the glass transition temperature of the modified cellulose acetate.

10. Use of the optical compensation film according to any one of claims 1 to 3 in at least one of the following optical devices: Polarizer; Liquid crystal display; Organic light-emitting diode display.

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