Polarizer supporting film, preparation method thereof and liquid crystal display device

Abstract

The invention discloses a polaroid supporting film, a preparation method thereof and a liquid crystal display device, and belongs to the technical field of polaroid supporting films. The preparation method comprises the following steps: providing a polyester resin raw material; feeding a polyester resin raw material into an extruder, and carrying out extrusion molding to obtain a cast sheet; and biaxially stretching the casting sheet to obtain the polaroid supporting film, and the in-plane retardation value of the polaroid supporting film under the wavelength of 550 nm is smaller than 800 nm. The problem of rainbow patterns generated by the polaroid supporting film in liquid crystal display is effectively solved or at least partially solved.

Description

Technical Field

[0001] The present application relates to the technical field of polarizer support films, and in particular to a polarizer support film and a preparation method thereof, and a liquid crystal display device. Background Art

[0002] In the information society, new display technologies such as liquid crystal display and organic light-emitting display have become an indispensable part of daily life and professional fields, and are widely used in mobile phones, televisions, computers, and high-end fields such as aerospace and military defense. The composition of liquid crystal display devices mainly includes backlight, liquid crystal unit and polarizing plate. Among them, the key component of the polarizing plate is the polarizer, which is made of iodine-dyed and stretched polyvinyl alcohol (PVA) film. This material is easily ineffective due to moisture absorption. In order to protect and support the polarizer, a polarizer support film must be attached to both sides of it.

[0003] Polyester materials have gradually become a strong candidate for polarizer support films due to their excellent thermodynamic properties, reliable processability, good visible light transmittance, excellent water barrier properties, good UV blocking properties and greater price advantages. However, polyester materials themselves have large birefringence characteristics and are prone to orientation during processing, resulting in anisotropy, which can cause rainbow patterns that affect display effects, which severely limits their application in polarizers.

[0004] The above contents are only used to assist in understanding the technical solution of the present application and do not constitute an admission that the above contents are prior art. Summary of the invention

[0005] The main purpose of the present application is to provide a polarizer support film and a preparation method thereof, and a liquid crystal display device, aiming to solve or at least partially solve the problem of rainbow patterns generated by the polarizer support film in liquid crystal displays.

[0006] To achieve the above object, the present invention provides a method for preparing a polarizer support film, comprising the following steps:

[0007] Provide polyester resin raw materials;

[0008] The polyester resin raw material is fed into an extruder and extruded to obtain a casting sheet;

[0009] The cast sheet is biaxially stretched to obtain a polarizer support film, wherein the polarizer support film has an in-plane retardation value of less than 800 nm at a wavelength of 550 nm.

[0010] In one embodiment, the longitudinal stretching ratio λ of the biaxial stretching is MD and transverse stretch ratio λ TD Satisfy between: λ MD -0.5≤λ TD ≤λMD -0.1.

[0011] In one embodiment, the ratio of the transverse strain rate to the longitudinal strain rate of the biaxial stretching is 0.5-1.

[0012] In one embodiment, before the step of obtaining the polarizer support film, the method further comprises:

[0013] The biaxially stretched film obtained after the biaxial stretching is subjected to heat treatment, wherein the heat treatment temperature is T g +50~T g +150℃, the T g is the glass transition temperature of the polyester resin raw material.

[0014] The embodiment of the present application also provides a polarizer support film, which is a polyester film, has an in-plane retardation value of less than 800 nm at a wavelength of 550 nm, and is prepared by the polarizer support film preparation method as described above.

[0015] In one embodiment, the thickness of the polarizer support film is 1-80 um.

[0016] In one embodiment, the thickness uniformity of the polarizer support film is less than 2%.

[0017] In one embodiment, the ratio of the longitudinal tensile strength to the transverse tensile strength of the polarizer support film is 0.9 to 1.1.

[0018] In one embodiment, the transverse thermal shrinkage rate and the longitudinal thermal shrinkage rate of the polarizer support film are both less than 1%.

[0019] An embodiment of the present application further provides a liquid crystal display device, which includes the polarizing plate support film as described above.

[0020] In one embodiment, the liquid crystal display device comprises: a liquid crystal unit and a polarizing plate disposed on at least one side of the liquid crystal unit;

[0021] The polarizing plate comprises: a polarizer and at least one polarizer supporting film, wherein the polarizer supporting film is arranged on a side of the polarizer away from the liquid crystal unit and / or on a side of the polarizer close to the liquid crystal unit.

[0022] One or more technical solutions proposed in this application have at least the following technical effects: providing a method for preparing a polarizer support film, by providing a polyester resin raw material; then feeding the polyester resin raw material into an extruder, extruding and molding a cast sheet; then biaxially stretching the cast sheet to obtain a polarizer support film, wherein the polarizer support film has an in-plane retardation value of less than 800nm ​​at a wavelength of 550nm. Through the biaxial stretching process, a polyester film (i.e., a polarizer support film) is obtained, and its in-plane retardation value at a wavelength of 550nm is less than 800nm, so it is close to isotropy, thereby reducing the birefringence characteristics; and because rainbow stripes are generated by interference of light when passing through a material with birefringence characteristics, when the birefringence characteristics of the material are reduced, the interference effect of light is weakened, thereby effectively avoiding the generation of rainbow stripes. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic flow chart of a method for preparing a polarizer support film according to an embodiment of the present application;

[0024] Figure 2 It is a schematic diagram of the structure of a liquid crystal display device involved in an embodiment of the present application.

[0025] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0027] Hereinafter, the polarizer support film and its preparation method, and the implementation mode of the liquid crystal display device of the present application are specifically disclosed with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

[0028] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that a range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0029] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0030] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0031] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, a method may also include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0032] If there is no special explanation, the "include" and "comprising" mentioned in this application represent open-ended or closed-ended expressions. For example, "include" and "comprising" may represent that other components not listed may also be included or only listed components may be included or only listed components may be included.

[0033] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0034] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and understandable, the technical solution of the present application is further described below in conjunction with the accompanying drawings and embodiments. However, the present application is not limited to the listed embodiments, and should also include any other known changes within the scope of the rights claimed in the present application.

[0035] The term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present application. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0036] In order to better understand the technical solution of the present application, a detailed description will be given below in conjunction with the accompanying drawings and specific implementation methods.

[0037] In conventional technology, polyester materials themselves have large birefringence characteristics, and are prone to orientation during processing, resulting in anisotropy, thereby causing rainbow stripes that affect the display effect, which seriously limits its application in polarizing plates. In conventional methods for preparing polarizing plate support films, the in-plane retardation value of the support film is usually increased to a certain extent (for example, the in-plane retardation value is 5000-7000nm) by stretching, thereby suppressing the generation of rainbow stripes. However, a film with a large in-plane retardation value usually means that its thickness is large, and in a display device, a thicker support film is not conducive to achieving the demand for thinning. At the same time, since the support film is used near the liquid crystal unit side, the large in-plane retardation value will affect the polarization properties of light, causing the liquid crystal display device to leak light in the dark state, affecting the display effect. Therefore, the support film with a large in-plane retardation value can usually only be used on the side of the polarizing plate near the light source near the light source, or used on the side of the polarizing plate near the observation side, resulting in its application position in the display panel being limited.

[0038] In the embodiment of the present application, a polyester film (i.e., a polarizer support film) is obtained through a biaxial stretching process, and its in-plane retardation value at a wavelength of 550nm is less than 800nm, which is close to isotropy, thereby effectively reducing the birefringence characteristics. Since rainbow stripes are generated by interference of light when passing through a material with birefringence characteristics, when the birefringence characteristics of the material are reduced, the interference effect of light is weakened, thereby effectively avoiding the generation of rainbow stripes.

[0039] The first aspect of the present application provides a method for preparing a polarizer support film, referring to Figure 1 , including the following steps:

[0040] Step S10, providing polyester resin raw material;

[0041] In a feasible embodiment, polyester resin is used as the raw material of the support film, wherein the polyester resin can be a polyester resin obtained by condensation of dicarboxylic acid and diol.

[0042] Exemplarily, the dicarboxylic acid includes: at least one of terephthalic acid, isophthalic acid, phthalic acid, 2,5-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, 1,4-naphthalene dicarboxylic acid, 1,5-naphthalene dicarboxylic acid, diphenyl carboxylic acid, diphenoxyethane dicarboxylic acid, diphenyl sulfone carboxylic acid, anthracene dicarboxylic acid, 1,3-cyclopentane dicarboxylic acid, 1,3-cyclohexane dicarboxylic acid, 1,4-cyclohexane dicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethylmalonic acid, succinic acid, 3,3-diethylsuccinic acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyl adipic acid, trimethyl adipic acid, pimelic acid, azelaic acid, dimer acid, sebacic acid, suberic acid and dodecanedicarboxylic acid.

[0043] Exemplarily, the diol includes at least one of ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, decamethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-bis(4-hydroxyphenyl)propane and bis(4-hydroxyphenyl)sulfone.

[0044] Exemplarily, the polyester resin includes at least one of polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate.

[0045] Preferably, the polyester resin includes at least one of polyethylene terephthalate, polyethylene naphthalate and polybutylene naphthalate.

[0046] Step S20, feeding the polyester resin raw material into an extruder, and extruding and molding to obtain a casting sheet;

[0047] In a feasible embodiment, a polyester resin raw material is fed into an extruder and extruded to obtain a cast sheet, wherein the cast sheet comprises at least a three-layer structure of A / B / A, wherein the A layer is a polyester resin with an opening agent added thereto, and the B layer is a polyester resin. The opening agent is added to improve the peelability between the melt cast sheet and the extrusion die.

[0048] Exemplarily, the anti-blocking agent includes at least one of talc, diatom and silicon dioxide.

[0049] Exemplarily, the opening agent is selected from silicon dioxide, and its particle size is 1-10um, preferably 1.5-5um. Although increasing the particle size of the opening agent helps to increase the slippery effect, it will also increase the surface haze, and too small a particle size makes it difficult to ensure the slippery effect, so the particle size of silicon dioxide is determined to be 1-10um.

[0050] Exemplarily, the concentration of the opening agent is 500-9000ppm, preferably 800-6000ppm. If the content of the opening agent is too high, it may affect the optical and mechanical properties of the support film; but if the content of the opening agent is too low, it is difficult to solve the adhesion problem of the support film. Therefore, the concentration of the opening agent is determined to be 500-9000ppm.

[0051] Exemplarily, the polarizer support film can be subjected to various functionalization treatments during the preparation process, such as adding UV absorbers, hydrophilic treatment, and coating with functional coatings (e.g., antistatic coatings, anti-pollution coatings, anti-reflective coatings, anti-scratch coatings, and / or anti-glare coatings).

[0052] Exemplarily, the polyester resin chips are dried, extruded through a single-screw or twin-screw extruder, and quenched below the glass transition temperature of the polyester resin to obtain an amorphous casting sheet.

[0053] Exemplarily, the polyester resin is PET, and PET chips added with functional additives (for example, ultraviolet absorbers) are dried as the B layer masterbatch in the three-layer structure of the casting sheet, and are sent to a single-screw main extruder for melt extrusion; PET chips containing an opening agent are used as the A layer masterbatch in the three-layer structure, and are sent to a twin-screw auxiliary extruder for melt extrusion; the A and B layer melts are transported to a multi-layer composite die through a runner and a melt distributor; the A / B / A three-layer melt flowing out of the die is attached to a cooling roller with a roller temperature of 10 to 50°C by electrostatic attachment to prepare a casting sheet.

[0054] Step S30, biaxially stretching the cast sheet to obtain a polarizer support film, wherein the polarizer support film has an in-plane retardation value of less than 800 nm at a wavelength of 550 nm.

[0055] In one feasible embodiment, the cast sheet is biaxially stretched to obtain a biaxially stretched polyester film (i.e., a polarizer support film) having an in-plane retardation value (Re) of less than 800 nm at a wavelength of 550 nm, wherein Re = n×d, n is the birefringence in the film plane, and d is the film thickness.

[0056] Generally speaking, since the melt viscosity of polyester materials is very low, during the processing, its molecular chains are easily oriented along the stress direction, thereby generating anisotropy, that is, it is difficult to prepare a polyester film with a small in-plane retardation value. However, the embodiment of the present application successfully prepared a polyester film with an in-plane retardation value of less than 800nm ​​at a wavelength of 550nm by accurately controlling the biaxial stretching process parameters, which can be used as a polarizer support film, effectively avoiding the generation of rainbow lines.

[0057] For example, the biaxial stretching can be asynchronous biaxial stretching or synchronous biaxial stretching. Asynchronous biaxial stretching refers to a process in which the cast sheet is first stretched longitudinally (i.e., the direction of travel of the film processing machine) and then stretched transversely (i.e., perpendicular to the direction of travel of the machine) after preheating; and the preheating temperature before longitudinal stretching should be greater than the glass transition temperature T of the polyester resin. g .

[0058] Exemplarily, the preheating temperature is preferably 70-110° C., preferably 80-100° C. Within this temperature range, the casting sheet can be fully heated, the molecular chains are activated, and the film can be stretched evenly, and the structure is more uniform.

[0059] In one possible embodiment, the longitudinal stretching ratio λ of the biaxial stretching MD and transverse stretch ratio λ TD Satisfy between: λ MD -0.5≤λ TD ≤λ MD -0.1. For example, the longitudinal stretch ratio λ of biaxial stretching MD and transverse stretch ratio λ TD Satisfy between: λ TD =λ MD -0.1, λ TD =λ MD -0.15, λ TD =λ MD -0.2, λ TD =λ MD -0.25, λ TD =λ MD -0.3, λ TD =λ MD -0.35, λ TD =λ MD -0.4, λ TD =λ MD -0.45, λ TD =λ MD -0.5 etc.

[0060] The longitudinal stretching is in the form of roller pulling, that is, the fast roller and the pressure roller clamp the film and pull the film at a linear speed (V1), and the slow roller and the pressure roller clamp the film and pull the film at a linear speed (V2), V1>V2, so as to achieve the stretching deformation of the film, and the longitudinal stretching ratio λ MD =V1 / V2.

[0061] The transverse stretching is done by clamping the film on both sides and then stretching it along the guide rail while increasing its width. TD It is defined as the ratio of the width L2 of the guide rail after stretching to the width L1 of the film entering the guide rail before stretching, that is, λ TD =L2 / L1.

[0062] For example, when the transverse stretching temperature and transverse stretching speed are the same as the longitudinal stretching temperature and speed, it is necessary to control λ TD <λ MD .

[0063] For example, the longitudinal stretch ratio λ MD 2 to 7, for example, 2, 2.2, 2.4, 2.5, 2.6, 2.8, 3, 3.2, 3.4, 3.5, 3.6, 3.8, 4, 4.2, 4.4, 4.5, 4.6, 4.8, 5, 5.2, 5.4, 5.5, 5.6, 5.8, 6, 6.2, 6.4, 6.5, 6.6, 6.8, 7, etc. If the stretching ratio is too small, the amorphous structure in the casting cannot be stretched uniformly. If the stretching ratio is too large, the material will undergo stretching induced crystallization, and the highly oriented crystals will require a very large pulling force in the second stretching, which is easy to cause film breakage.

[0064] In one feasible embodiment, the ratio of the transverse strain rate to the longitudinal strain rate of biaxial stretching is 0.5-1; for example, the ratio of the transverse strain rate to the longitudinal strain rate of biaxial stretching is 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, etc.

[0065] The longitudinal strain rate refers to the ratio of strain per unit time during longitudinal stretching, specifically (λ MD -1) / t MD , where t MD is the time for the required strain to occur during the longitudinal stretching process. Assuming that the length of the film clamped by the fast roller and the slow roller during the stretching process is L0, then t MD is defined as 2*L0 / (V1+V2). Then the deformation rate ε MD =(λ MD -1)×(V1+V2) / (2×L0).

[0066] The transverse strain rate is defined as (λ TD -1) / t TD , t TD is the time taken for the film to be stretched from width L1 to width L2. Assuming that the film is clamped on both sides and moves along the guide rail at a speed of V3, and the longitudinal distance of the film deformation section on the guide rail is L4, then t TD =L4 / V3, then the transverse strain rate ε TD =(λ TD -1)×V3 / L4.

[0067] Exemplarily, V3 ≥ V2, because only when V3 is slightly larger than V2 can the film maintain a certain tension in the actual production process to facilitate uniform lateral stretching.

[0068] In one feasible implementation, before step S30, the step of obtaining the polarizer support film, the method further includes:

[0069] Step S31, heat treating the biaxially stretched film obtained after biaxial stretching, wherein the heat treatment temperature is T g +50~T g +150℃, T g It is the glass transition temperature of polyester resin raw material.

[0070] In a feasible embodiment, after the biaxially stretched film is obtained by biaxially stretching, the biaxially stretched film is subjected to a heat treatment for not less than 30 seconds, wherein the heat treatment temperature is T g +50~T g +150℃, T g It is the glass transition temperature of polyester resin raw material. Through heat treatment, the film can be properly shrunk to eliminate the internal stress in the film.

[0071] Preferably, the heat treatment temperature is T g +80~T g +120℃.

[0072] For example, the film needs to be retracted by 0.1 to 15% in both the transverse and longitudinal directions; preferably, the retraction amount is 1 to 8%. If the retraction amount is too small, it is difficult to completely relax the stress; if the retraction amount is too large, the film will wrinkle when it is rolled up and cannot be stably rolled up.

[0073] Exemplarily, the shrinking process and the heat treatment process are carried out simultaneously, that is, the film shrinking rate is adjusted so that the film is in a state of uniform shrinkage throughout the high-temperature heat treatment process.

[0074] In this embodiment, a polyester film (i.e., a polarizer support film) is obtained through a biaxial stretching process, and its in-plane retardation value at a wavelength of 550 nm is less than 800 nm, which is close to isotropy, thereby effectively reducing the birefringence characteristics. Since rainbow stripes are generated by interference of light when passing through a material with birefringence characteristics, when the birefringence characteristics of the material are reduced, the interference effect of light is weakened, thereby effectively avoiding the generation of rainbow stripes.

[0075] Furthermore, an embodiment of the present application also provides a polarizer support film, which is a polyester film, has an in-plane retardation value of less than 800 nm at a wavelength of 550 nm, and is prepared by the above method.

[0076] When the in-plane retardation value exceeds twice the minimum visible light band (i.e. 1000nm), interference rainbow patterns caused by birefringence will be generated, affecting the display effect; therefore, the embodiment of the present application reduces the birefringence characteristics of the material by preparing a polarizer support film with an in-plane retardation value less than 800nm, thereby effectively avoiding the generation of rainbow patterns.

[0077] Exemplarily, the in-plane retardation value of the polarizer support film at a wavelength of 550 nm is 2 to 800 nm, for example, 2 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, etc. As the in-plane retardation value is smaller, the influence of the film thickness fluctuation on the in-plane retardation value increases, and thus the film with too small in-plane retardation value has higher requirements for the uniformity of the film structure and thickness, which increases the process difficulty.

[0078] In a feasible implementation, the thickness of the polarizer support film is 1 to 80 um. For example, 1 um, 10 um, 20 um, 30 um, 40 um, 50 um, 60 um, 70 um, 80 um, etc. If the thickness of the polarizer support film is too large, the thickness of the entire polarizing plate will be greatly increased, so that the thickness of the entire display device will increase, and the flexibility of the film will also be greatly reduced. Therefore, the thickness of the polarizer support film is determined to be 1 to 80 um.

[0079] For example, the thickness of the polarizer support film is 1 to 50 um.

[0080] In one feasible embodiment, the thickness uniformity of the polarizer support film is less than 2%. The in-plane retardation value is determined by the molecular chain orientation and thickness. Therefore, in order to reduce the uneven distribution of the retardation value in the film caused by thickness fluctuation, the thickness uniformity of the polarizer support film needs to be less than 2%.

[0081] Thickness uniformity D = (d max -d min ) / d×100%, where D is a measure of thickness uniformity, dmax and d min are the maximum and minimum values ​​of thickness respectively, and d is the average thickness.

[0082] In one feasible embodiment, the ratio of the longitudinal tensile strength to the transverse tensile strength of the polarizer support film is 0.9 to 1.1. For example, the ratio of the longitudinal tensile strength to the transverse tensile strength is 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, 1.1, etc. Within this range, it is shown that the film has a similar structure in different directions, and therefore, isotropy can be achieved, thereby achieving a smaller in-plane retardation value.

[0083] In one feasible embodiment, the transverse thermal shrinkage rate and the longitudinal thermal shrinkage rate of the polarizer support film are both less than 1%.

[0084] In order to prevent the polarizer support film from shrinking during subsequent application with the polarizer, causing uneven bonding or internal stress, the transverse and longitudinal thermal shrinkage rates of the polarizer support film in a high temperature environment (for example, 120-200° C.) are both less than 1%.

[0085] In a feasible embodiment, the transmittance of the polarizer support film at a visible light wavelength of 400-700nm is not less than 85% to achieve a better display effect. The transmittance of the polarizer support film at an ultraviolet wavelength below 390nm is less than 15%, preferably less than 10%; preferably less than 5%.

[0086] In this embodiment, the in-plane retardation value of the prepared polyester film (i.e., the polarizer support film) at a wavelength of 550 nm is less than 800 nm, which is close to isotropy, thereby effectively reducing the birefringence characteristics. Since rainbow stripes are generated by interference of light when passing through a material with birefringence characteristics, when the birefringence characteristics of the material are reduced, the interference effect of light is weakened, thereby effectively avoiding the generation of rainbow stripes.

[0087] Furthermore, an embodiment of the present application also provides a liquid crystal display device, which includes the polarizer support film prepared by the above method, or the above polarizer support film.

[0088] In one feasible embodiment, a liquid crystal display device includes: a liquid crystal unit and a polarizing plate disposed on at least one side of the liquid crystal unit;

[0089] The polarizing plate includes: a polarizer and at least one polarizer supporting film, wherein the polarizer supporting film is arranged on a side of the polarizer away from the liquid crystal unit and / or on a side of the polarizer close to the liquid crystal unit.

[0090] In conventional technology, if the polyester polarizer support film is set on the side of the polarizer away from the liquid crystal unit, it is easy to cause rainbow lines. If the polyester polarizer support film is set on the side of the polarizer close to the liquid crystal unit, it is necessary to avoid using a support film with a large in-plane retardation value; this is because a support film with a large in-plane retardation value will affect the polarization properties of light, causing light leakage in the liquid crystal display device in the dark state, affecting the display effect. Therefore, the application location of polyester films with large in-plane retardation values ​​is greatly limited.

[0091] The polyester polarizer support film prepared in the embodiment of the present application has a low in-plane retardation value, so even if it is set on the side of the polarizer away from the liquid crystal unit, it can effectively avoid the generation of rainbow lines. At the same time, the polyester polarizer support film prepared in the embodiment of the present application can also be set on the side of the polarizer close to the liquid crystal unit. Since the in-plane retardation value of the support film is low, it does not affect the polarization properties of light, thereby ensuring a better display effect.

[0092] Exemplarily, the liquid crystal display device includes: a liquid crystal unit and a first polarizing plate and a second polarizing plate arranged on both sides of the liquid crystal unit; the first polarizing plate includes: a first polarizer and a first polarizer supporting film arranged on a side of the first polarizer away from the liquid crystal unit; the second polarizing plate includes: a second polarizer and a second polarizer supporting film arranged on a side of the second polarizer away from the liquid crystal unit.

[0093] Exemplarily, the liquid crystal display device includes: a liquid crystal unit and a first polarizing plate and a second polarizing plate arranged on both sides of the liquid crystal unit; the first polarizing plate includes: a first polarizer and a first polarizer supporting film arranged on a side of the first polarizer close to the liquid crystal unit; the second polarizing plate includes: a second polarizer and a second polarizer supporting film arranged on a side of the second polarizer close to the liquid crystal unit.

[0094] Exemplarily, the liquid crystal display device includes: a liquid crystal unit and a first polarizing plate and a second polarizing plate arranged on both sides of the liquid crystal unit; the first polarizing plate includes: a first polarizer, a first polarizer supporting film arranged on a side of the first polarizer away from the liquid crystal unit, and a second polarizer supporting film arranged on a side of the first polarizer close to the liquid crystal unit; the second polarizing plate includes: a second polarizer, a third polarizer supporting film arranged on a side of the second polarizer away from the liquid crystal unit, and a fourth polarizer supporting film arranged on a side of the second polarizer close to the liquid crystal unit.

[0095] It should be understood that, in addition to the polyester polarizer support film with low in-plane retardation prepared in the embodiment of the present application, the liquid crystal display device may also use polarizer support films made of other materials, and the embodiment of the present application does not limit this.

[0096] Exemplarily, the liquid crystal display device includes: a backlight source, a liquid crystal unit, and polarizing plates arranged on both sides of the liquid crystal display unit.

[0097] The backlight source may be at least one of a cold cathode fluorescent lamp, a hot cathode fluorescent lamp, and an LED light source.

[0098] The polarizing plates on both sides of the liquid crystal unit are composed of a polarizing plate and a polarizing plate support film arranged on both sides of the polarizing plate.

[0099] Exemplarily, the liquid crystal display device may further include: a light guide plate, a reflective plate, a diffusion plate, a color filter and / or an incremental plate.

[0100] In order to enable the details and operations of the above embodiments of the present application to be clearly understood by those skilled in the art, and to significantly demonstrate the improved performance of the embodiments of the present application, the above technical solutions are illustrated by means of multiple embodiments below.

[0101] Example 1

[0102] (1) Provide PET polyester chips;

[0103] (2) drying the PET polyester chips and feeding them into an extruder for extrusion molding to obtain cast sheets;

[0104] (3) Biaxially stretching the cast sheet to obtain a polarizer support film with a thickness of 40 μm, wherein the longitudinal stretching ratio is 3.3, the longitudinal strain rate is 0.358, the transverse stretching ratio is 3, and the transverse strain rate is 0.333.

[0105] Example 2

[0106] (1) Provide PET polyester chips;

[0107] (2) drying the PET polyester chips and feeding them into an extruder for extrusion molding to obtain cast sheets;

[0108] (3) Biaxially stretching the cast sheet to obtain a polarizer support film with a thickness of 38 μm, wherein the longitudinal stretching ratio is 3.3, the longitudinal strain rate is 0.358, the transverse stretching ratio is 3.2, and the transverse strain rate is 0.333.

[0109] Example 3

[0110] (1) Provide PET polyester chips;

[0111] (2) drying the PET polyester chips and feeding them into an extruder for extrusion molding to obtain cast sheets;

[0112] (3) Biaxially stretching the cast sheet to obtain a polarizer support film with a thickness of 41 μm, wherein the longitudinal stretching ratio is 3.3, the longitudinal strain rate is 0.358, the transverse stretching ratio is 2.8, and the transverse strain rate is 0.333.

[0113] Example 4

[0114] (1) Provide PET polyester chips;

[0115] (2) drying the PET polyester chips and feeding them into an extruder for extrusion molding to obtain cast sheets;

[0116] (3) Biaxially stretching the cast sheet to obtain a polarizer support film with a thickness of 40 μm, wherein the longitudinal stretching ratio is 3.3, the longitudinal strain rate is 0.358, the transverse stretching ratio is 2.8, and the transverse strain rate is 0.356.

[0117] Example 5

[0118] (1) Provide PET polyester chips;

[0119] (2) drying the PET polyester chips and feeding them into an extruder for extrusion molding to obtain cast sheets;

[0120] (3) Biaxially stretching the cast sheet to obtain a polarizer support film with a thickness of 40 μm, wherein the longitudinal stretching ratio is 3.3, the longitudinal strain rate is 0.358, the transverse stretching ratio is 3, and the transverse strain rate is 0.18.

[0121] Example 6

[0122] (1) Provide PET polyester chips;

[0123] (2) drying the PET polyester chips and feeding them into an extruder for extrusion molding to obtain cast sheets;

[0124] (3) Biaxially stretching the cast sheet to obtain a polarizer support film with a thickness of 39 μm, wherein the longitudinal stretching ratio is 3.3, the longitudinal strain rate is 0.358, the transverse stretching ratio is 3.1, and the transverse strain rate is 0.182.

[0125] Comparative Example 1

[0126] (1) Provide PET polyester chips;

[0127] (2) drying the PET polyester chips and feeding them into an extruder for extrusion molding to obtain cast sheets;

[0128] (3) Biaxially stretching the cast sheet to obtain a polarizer support film with a thickness of 40 μm, wherein the longitudinal stretching ratio is 3.3, the longitudinal strain rate is 0.358, the transverse stretching ratio is 3.5, and the transverse strain rate is 0.333.

[0129] Comparative Example 2

[0130] (1) Provide PET polyester chips;

[0131] (2) drying the PET polyester chips and feeding them into an extruder for extrusion molding to obtain cast sheets;

[0132] (3) Biaxially stretching the cast sheet to obtain a polarizer support film with a thickness of 40 μm, wherein the longitudinal stretching ratio is 3.3, the longitudinal strain rate is 0.358, the transverse stretching ratio is 3, and the transverse strain rate is 0.161.

[0133] Comparative Example 3

[0134] (1) Provide PET polyester chips;

[0135] (2) drying the PET polyester chips and feeding them into an extruder for extrusion molding to obtain cast sheets;

[0136] (3) Biaxially stretching the cast sheet to obtain a polarizer support film with a thickness of 41 μm, wherein the longitudinal stretching ratio is 3.3, the longitudinal strain rate is 0.358, the transverse stretching ratio is 3.4, and the transverse strain rate is 0.411.

[0137] At a central wavelength of 550 nm, the in-plane retardation values ​​Re of the polarizer support films prepared in Examples 1-6 and Comparative Examples 1-3 were measured by a phase difference meter. The results are shown in Table 1 below.

[0138] Reference Figure 2 A liquid crystal display device 10 is provided, with an LED light-emitting panel as a backlight source 11, and polarizing plate support films 13 prepared in Examples 1-6 and Comparative Examples 1-3 are respectively attached to both sides of a polarizing plate 12 formed of polyvinyl alcohol and iodine to prepare a polarizing plate; the liquid crystal display device 10 is configured in the form of a combination of the backlight source 11, the polarizing plate, the liquid crystal unit 14 and the polarizing plate.

[0139] When the liquid crystal display device is lit, the liquid crystal display device equipped with different polarizer support films is observed on the observation side and the display effect is evaluated. The results are shown in Table 1 below, where "√√" means that the display brightness is uniform at all angles and no rainbow patterns appear; "√" means that the display brightness is uniform and there are no rainbow patterns when observed from the front, and there are weaker rainbow patterns when observed from an angle; "×" means that there are rainbow patterns when observed from the front.

[0140] Table 1:

[0141]

[0142] Referring to the results in Table 1, it can be seen that the embodiment of the present application uses a biaxial stretching process and controls the process parameters to produce a polarizer support film with an in-plane retardation value of less than 800 nm at a wavelength of 550 nm. The film is close to isotropic, thereby reducing the birefringence characteristics and effectively avoiding the generation of rainbow lines.

[0143] The above are only preferred embodiments of the present application, and do not limit the scope of the present application. For those skilled in the art, the present application may have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of patent protection of the present application.

Claims

1. A method for preparing a polarizing plate support film, characterized in that: The method comprises the following steps: Provide polyester resin raw materials; The polyester resin raw material is fed into an extruder and extruded to obtain a casting sheet; The cast sheet is biaxially stretched to obtain a polarizer support film, wherein the polarizer support film has an in-plane retardation value of less than 800 nm at a wavelength of 550 nm.

2. The method for preparing a polarizing plate support film according to claim 1, wherein: The longitudinal stretching ratio λ of the biaxial stretching MD and transverse stretch ratio λ TD Satisfy between: λ MD -0.5≤λ TD ≤λ MD -0.

1.

3. The method for preparing a polarizing plate support film according to claim 1, wherein: The ratio of the transverse strain rate to the longitudinal strain rate in the biaxial stretching is 0.5-1.

4. The method for preparing a polarizing plate support film according to claim 1, wherein: Before the step of obtaining the polarizer support film, the method further comprises: The biaxially stretched film obtained after the biaxial stretching is subjected to heat treatment, wherein the heat treatment temperature is T g +50~T g +150℃, the T g is the glass transition temperature of the polyester resin raw material.

5. A polarizing plate support film, characterized in that: The polarizer support film is a polyester film, the in-plane retardation value of which at a wavelength of 550 nm is less than 800 nm, and is prepared by the method according to any one of claims 1 to 4.

6. The polarizer support film according to claim 5, characterized in that: The thickness of the polarizer support film is 1 to 80 um.

7. The polarizer support film according to claim 5, characterized in that: The thickness uniformity of the polarizer support film is less than 2%.

8. The polarizer support film according to claim 5, characterized in that: The ratio of the longitudinal tensile strength to the transverse tensile strength of the polarizer support film is 0.9 to 1.1; And / or, the transverse thermal shrinkage rate and the longitudinal thermal shrinkage rate of the polarizer support film are both less than 1%.

9. A liquid crystal display device, characterized in that: The liquid crystal display device comprises a polarizer support film made by the method according to any one of claims 1 to 4, or a polarizer support film according to any one of claims 5 to 8.

10. The liquid crystal display device according to claim 9, wherein: The liquid crystal display device comprises: a liquid crystal unit and a polarizing plate disposed on at least one side of the liquid crystal unit; The polarizing plate comprises: a polarizer and at least one polarizer supporting film, wherein the polarizer supporting film is arranged on a side of the polarizer away from the liquid crystal unit and / or on a side of the polarizer close to the liquid crystal unit.

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