KR102315905B1 - Polyester-based film, display device comprising the same and manufacturing method for the same - Google Patents

Abstract

The embodiment relates to a polyester-based film having excellent durability, moisture permeability and visibility, a display device including the same, and a method for manufacturing the same, and the in-plane retardation (Ro, 550 nm) of the polyester-based film is 7,000 nm or more.

Description

Polyester-based film, display device including same, and manufacturing method thereof

The embodiment relates to a polyester-based film, a display device including the same, and a method for manufacturing the same.

As we enter the information society, the frequency of use of portable mobile devices such as smartphones, laptops, and tablet PCs is increasing. Because data is stored, there is a need to strengthen security.

To this end, a method for enhancing security by using a sensor capable of recognizing biometric information has been proposed, and in particular, a technique for performing system registration or authentication using a fingerprint of a finger has become common.

A method for recognizing such a fingerprint may be largely classified into a capacitive type, an optical type, an ultrasonic type, and the like. Among them, the optical fingerprint recognition method acquires a fingerprint image reflected in visible light and compares it with previously registered fingerprint information.

On the other hand, when applied to a portable mobile device adopting such an optical fingerprint recognition method, a protective film capable of accurately recognizing a fingerprint as well as protecting the display from external impact is required.

An embodiment is to provide a polyester film having excellent durability, moisture permeability and visibility, a display device including the same, and a manufacturing method thereof.

The polyester-based film according to an embodiment has an in-plane retardation (Ro, 550 nm) of 7,000 nm or more.

A protective film according to another embodiment includes the polyester-based film.

A display device according to another embodiment includes the protective film.

The polyester-based film manufacturing method according to an embodiment comprises the steps of forming a polyester-based sheet with a composition for preparing a polyester-based film; preparing a stretched film by stretching the polyester-based sheet 1.0 to 1.5 times in the MD direction and 3.0 to 5.0 times in the TD direction; and heat-setting the stretched film at a temperature of 160 to 230° C. to prepare a polyester film.

The polyester-based film according to the embodiment may secure excellent durability, moisture permeability and visibility by satisfying in-plane retardation within a specific range. Therefore, the polyester film can exhibit excellent properties when applied to a protective film for a display device.

In addition, since the polyester film according to another embodiment does not contain a sunscreen, it is possible to solve the problem of dissolution of the sunscreen that occurs after a certain time has elapsed, and it is economical because it has the effect of reducing time and cost.

Hereinafter, the invention will be described in detail through embodiments. The embodiments are not limited to the contents disclosed below and may be modified in various forms as long as the gist of the invention is not changed.

In the case where each film or layer or the like is described herein as being formed “on” or “under” each film or layer, etc., “on” and “under” each film or layer, etc. "includes both "directly" or "indirectly through" another element. In addition, the reference for the upper / lower of each component will be described with reference to the drawings. The size of each component in the drawings may be exaggerated for explanation, and does not mean the size actually applied. Also, like reference numerals refer to like elements throughout.

In the present specification, "comprising" means that other components may be further included unless otherwise specified.

In addition, it should be understood that all numbers and expressions indicating amounts of components, reaction conditions, etc. described herein are modified by the term "about" in all cases unless otherwise specified.

In the present specification, unless otherwise specified, the expression "a" or "a" is interpreted as meaning including the singular or the plural as interpreted in context.

In this specification, terms such as first, second, etc. are used to describe various components, and the components should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component from another.

In the present specification, the "~" system may mean including a compound corresponding to "~" or a derivative of "~" in the compound. "Derivative" refers to a compound in which the structure and properties of the parent are not changed, such as introduction of a functional group, oxidation, reduction, or substitution of atoms, using a specific compound as a parent.

polyester film

Embodiment is to provide a polyester-based film excellent in durability, moisture permeability and visibility.

The polyester-based film according to an embodiment for achieving this object has an in-plane retardation (Ro, 550 nm) of 7,000 nm or more.

The in-plane retardation (Ro) is a parameter defined by the product (ANxy × d) of the refractive index anisotropy (ANxy = |nx-ny|) of the biaxial orthogonal refractive index in the plane of the film and the film thickness d (nm), optical isotropy or It is a measure of anisotropy.

Ro = ｜nx-ny｜ × d

In the above formula, Ro is the in-plane retardation value, d is the thickness of the film, nx is the in-plane refractive index in the slow axis direction, and ny is the in-plane refractive index in the fast axis direction. The phase difference value is an absolute value and is positive.

The in-plane retardation (Ro, 550 nm) of the polyester-based film may be 7,000 nm to 50,000 nm. For example, the in-plane retardation (Ro, 550 nm) of the polyester film may be 7,000 nm to 30,000 nm, 7,000 nm to 20,000 nm, 8,000 nm to 30,000 nm, or 8,000 nm to 20,000 nm, but is limited thereto no.

The polyester film having the in-plane retardation value maximizes the difference in refractive index between the MD direction and the TD direction so that distortion of light cannot be recognized, thereby ensuring visibility.

In addition, the polyester-based film according to the embodiment may have an in-plane retardation deviation within 5%.

Specifically, the in-plane retardation deviation is a value calculated based on the average in-plane retardation value by measuring the in-plane retardation at intervals of 300 mm across the entire width and evaluating the deviation. The in-plane retardation deviation within 5% means -5% to +5%.

The polyester film satisfying the in-plane retardation deviation range maximizes the difference in refractive index between the MD direction and the TD direction so that distortion of light cannot be recognized, thereby ensuring visibility.

On the other hand, thickness direction retardation (Rth) refers to two birefringences ΔNxz (= | Nx-Nz |) and ΔNyz (= | Ny-Nz |) when viewed from a cross section in the film thickness direction, respectively. It is calculated as the average of the retardation obtained by multiplying the film thickness d.

Rth = ｜nx-nz｜ × d

In the above formula, Rth is the thickness direction retardation, d is the thickness of the film, nx is the refractive index in the in-plane slow axis direction, and nz is the refractive index in the thickness direction. The phase difference value is an absolute value and is positive.

The polyester-based film according to an embodiment may have a thickness direction retardation (Rth) of 7,000 nm or more, for example, 7,000 nm to 30,000 nm, for example, 11,000 to 15,000 nm or 11,500 to 13,000 nm can When a polyester film having such a thickness direction retardation is applied, it is clearer and has excellent visibility, and a protective film and a display device that maximizes the difference in refractive index between the MD and TD directions so that distortion of light cannot be recognized. can do.

The polyester-based film according to another embodiment does not include a sunscreen.

The sunscreen includes a known material that absorbs or blocks ultraviolet rays. Specifically, the UV blocker includes an organic UV absorber and an inorganic UV absorber.

In general, a polyester-based film has a problem in that a UV absorber is applied in a composition for preparing a polyester-based film to improve the durability of the polyester-based film.

The polyester-based film according to the embodiment solves the problem of dissolution of the sunscreen, has the advantage of being economical through process simplification and cost reduction, and has secured mechanical properties and optical properties above a certain level.

The polyester-based film according to an embodiment has MD-direction UV durability (TSM _UV ) of Equation 1 below 80%.

<Equation 1>

TSM _UV = (TSM2/TSM1) × 100

In Equation 1, the TSM _UV is the UV durability (%) in the MD direction, the TSM1 is the initial tensile strength in the MD direction, and the TSM2 is the MD measured after exposure to UV light for 48 hours with an output of ^{0.68 W/m 2} directional tensile strength.

The polyester-based film may have MD-direction ultraviolet durability (TSM _UV ) evaluated by Equation 1 of 82% or more, 80% to 100%, or 80% to 95%.

In addition, the polyester-based film according to another embodiment has a TD direction UV durability (TST _UV ) of Formula 2 below 80% or more.

<Equation 2>

TST _UV = (TST2/TST1) × 100

In Equation 2, the TST _UV is the UV durability (%) in the TD direction, the TST1 is the initial tensile strength in the TD direction, and the TST2 is the TD measured after exposure to UV light for 48 hours with an output of ^{0.68 W/m 2} directional tensile strength.

The polyester-based film may have a TD direction UV durability (TST _UV ) evaluated by Equation 2 of 85% or more, 88% or more, 80% to 100%, or 80% to 95%.

Specifically, the UV durability is evaluated based on tensile strength, and since the polyester-based film is a stretched film, it may have different UV durability depending on the direction.

The polyester-based film according to the embodiment has both MD direction UV durability (TSM _UV ) and TD direction UV durability (TST _UV ) of 80% or more, thereby maintaining excellent durability even in repeated strong UV rays.

The polyester-based film according to an embodiment has a thickness of 30 to 150 μm. Specifically, the polyester-based film has a thickness It may be 50 to 150 μm, 60 to 150 μm, or 80 to 130 μm, but is not limited thereto.

When the thickness of the polyester film is within the above range, it is possible to maintain appropriate durability and UV transmittance.

In the polyester-based film according to another embodiment, the thickness deviation is within 2.5% based on the thickness of the film. When the thickness deviation is within 2.5% based on the thickness of the film, it means that the thickness deviation is within -2.5% to +2.5% based on the thickness of the film.

When the thickness deviation of the polyester-based film is within the above range, uniform visibility may be maintained by reducing the retardation deviation when applied to a protective film and a display device.

The polyester-based film according to another embodiment may have a light transmittance of 80% or more for light having a wavelength of 380 nm. For example, the polyester film may have a light transmittance of 80 to 99%, 80 to 95%, or 85 to 95% for light having a wavelength of 380 nm, but is not limited thereto.

The polyester film having such excellent light transmittance can secure a high fingerprint recognition rate when the polyester film is applied as a protective film to a portable device.

The polyester-based film according to an embodiment may have a moisture permeability of 17 g/m ² .day or less. For example, the moisture permeability of the polyester film is 0.1 to 17 g/m ² .day, 0.1 to 16 g/m ² .day, 0.1 to 15 g/m ² .day, 1 to 15 g/m ² . day, 1 to 12 g/m ² .day, 5 to 11 g/m ² .day, or 5 to 10 g/m ² .day, but is not limited thereto.

The polyester-based film having a water vapor transmission rate in the above range has significantly superior water vapor transmission characteristics compared to the TAC film applied as a protective film, and when the polyester-based film is applied to a protective film and furthermore a display device, it is protected from external moisture. The display device can be protected.

The polyester film according to another embodiment may have a light transmission amount of 91% or more. For example, the amount of light passing through the polyester film may be 91.3% or more, 91.5% or more, 91.8% or more, 91% to 99%, 91% to 98%, 91% to 95%, but is limited thereto no.

The light passage means the maximum amount of light transmitted at a specific angle between the polarizing film and the polyester film.

The polyester-based film includes a polyester resin.

The polyester resin may be a homopolymer resin or a copolymer resin in which dicarboxylic acid and diol are polycondensed. In addition, the polyester resin may be a blend resin in which the homopolymer resin or copolymer resin is mixed.

Examples of the dicarboxylic acid include terephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5 -naphthalenedicarboxylic acid, diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylsulfonecarboxylic acid, anthracenedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,3- Cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethylmalonic acid, succinic acid, 3,3-diethylsuccinic acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid trimethyladipic acid, pimelic acid, azelaic acid, sebacic acid, suberic acid, dodecadicarboxylic acid and the like.

In addition, examples of the diol include 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, bis(4-hydroxyphenyl)sulfone, and the like.

Preferably, the polyester resin may be an aromatic polyester resin having excellent crystallinity, for example, a polyethylene terephthalate (PET) resin may be a main component.

Various properties for the constituent components and physical properties of the above-described polyester-based film may be combined.

protective film

A protective film according to an embodiment includes a polyester-based film.

The protective film according to another embodiment may further include a primer layer, a hard coating layer, a silicone adhesive layer, and the like on one or both surfaces of the polyester film.

For example, a first primer layer and a second primer layer may be included on both surfaces of the polyester-based film, respectively.

Specifically, the first primer layer is located on one side of the polyester-based film, the first primer layer is located on the other side of the polyester-based film, and the hard surface of the first primer layer on which the polyester-based film is not located. The coating layer is positioned, and the silicone adhesive layer may be positioned on the side where the polyester-based film of the second primer layer is not positioned, but is not limited to this structure.

In this case, the primer layer may include at least one component selected from the group consisting of an acrylic resin, a polyurethane resin, a polyester resin, and an inorganic silica, but is not limited thereto. This primer layer serves to increase transmittance and strengthen adhesion with the hard coating layer.

The hard coating layer can secure excellent scratch resistance by being applied to the protective film.

The silicone adhesive layer has a release adhesive effect that secures transparency by being applied to the protective film.

The in-plane retardation (Ro, 550 nm) of the protective film according to an exemplary embodiment is 7,000 nm or more.

Specifically, the in-plane retardation (Ro, 550 nm) of the protective film may be 7,000 nm to 50,000 nm. For example, the in-plane retardation (Ro, 550 nm) of the polyester film may be 7,000 nm to 30,000 nm, 7,000 nm to 20,000 nm, 8,000 nm to 30,000 nm, or 8,000 nm to 20,000 nm, but is limited thereto no.

The protective film having the in-plane retardation value can secure visibility by maximizing the distortion of light by increasing the difference in refractive index between the MD direction and the TD direction.

In the protective film, the polyester-based film has substantially the same configuration and properties as the polyester-based film according to the above-described embodiment.

display

A display device according to an embodiment includes the protective film according to the embodiment.

Specifically, the display device includes a display panel; and the polyester-based film according to the embodiment disposed on one surface of the display panel.

Alternatively, the display device may include a display panel; and a protective film according to the embodiment disposed on one surface of the display panel.

In the display device, the polyester-based film or the protective film has substantially the same configuration and characteristics as the polyester-based film or the protective film according to the above-described embodiment.

Specifically, the polyester-based film can implement the properties required for the cover of the flexible display device by controlling the deformation dimension according to the tensile and relaxation cycles, and as a result, the polyester-based film and the protective film including the same are flexible. It is applied to the cover of the display device to maintain its original characteristics even when folded repeatedly.

Polyester-based film manufacturing method

The method for producing the above-described polyester-based film, the step of forming a polyester-based sheet (unstretched sheet); preparing a stretched film by stretching the sheet; and heat-setting the stretched film to prepare a polyester-based film.

Specifically, the method for producing a polyester-based film includes: forming a polyester-based sheet with a composition for preparing a polyester-based film; preparing a stretched film by stretching the polyester-based sheet 1.0 to 1.5 times in the MD direction and 3.0 to 5.0 times in the TD direction; and heat-setting the stretched film at a temperature of 160 to 230° C. to prepare a polyester film.

The prepared polyester-based film has substantially the same configuration and properties as the polyester-based film according to the above-described embodiment.

The manufacturing method of the polyester-based film excellent in durability, moisture permeability and visibility will be described in detail as follows.

First, a composition for preparing a polyester film is prepared, and a polyester sheet is formed from the composition. In this case, the polyester-based sheet is an unstretched sheet.

The polyester-based resin included in the composition for preparing a polyester-based film includes a dicarboxylic acid component and a diol component. A transesterification reaction is performed by mixing the dicarboxylic acid component and the diol component.

In this case, one or more catalysts selected from manganese acetate, calcium and zinc may be used as a catalyst for the transesterification reaction. The content of the catalyst used is preferably 0.02 to 0.2 parts by weight based on 100 parts by weight of the dicarboxylic acid compound.

After the transesterification reaction is completed, at least one additive selected from silica, potassium, and magnesium; stabilizers such as trimethylphosphate; and a polymerization catalyst selected from antimony trioxide and tetrabutylene titanate; and the like may be optionally added.

The polyester-based film production composition is extruded to form a polyester-based sheet.

Specifically, the composition is extruded through a T die at an extrusion temperature of 260 to 300° C. or 270 to 290° C. and then cooled.

After extruding the composition, the polyester sheet obtained by cooling is passed through a roll while conveying. In this case, the thickness of the desired film can be adjusted by controlling the speed and the discharge amount of the polyester-based sheet. For example, in this step, the thickness of the film is 30 to 150 μm, It can be adjusted to 50 to 150㎛, 60 to 150㎛ or 80 to 130㎛.

Next, a stretched film is prepared by stretching the polyester-based sheet.

Specifically, a stretched film is prepared by stretching the polyester-based sheet (unstretched sheet) in a transverse direction (tenter direction, TD) and a longitudinal direction (longitudinal direction, LD, mechanical direction, MD).

When stretching in the MD direction is performed by 1.0 to 1.5 times, it is possible to manufacture a base film having superior UV durability and excellent UV transmittance and light transmission. Specifically, the stretching in the MD direction may be performed at 1.0 to 1.4 times, 1.0 to 1.3 times, 1.0 to 1.2 times, or 1.0 to 1.1 times, but is not limited thereto.

Stretching in the TD direction may be performed at 3.0 to 5.0 times, 3.5 to 5.0 times, and 4.0 to 4.8 times or 4.1 to 4.5 times. When the stretching is performed in such a ratio, it is possible to manufacture a polyester film having excellent utility as a base film due to excellent UV transmittance, light passage, and UV durability.

The stretching speed may be 2 times / min to 8 times / min, 2.5 times / min to 6 times / min, or 2.5 times / min to 3 times / min, but is not limited thereto.

In addition, the stretching temperature may be conducted at a temperature of 75 to 120 ℃. When the stretching temperature is low, the stretchability is excellent, but fracture of the film may occur. In addition, when the stretching temperature is too high, the film may break due to the occurrence of cloudiness during stretching of the film. Specifically, the stretching temperature in the longitudinal direction is 75 to 85 ℃, the stretching temperature in the width direction may be applied to 80 to 120 ℃, but is not limited thereto.

Next, the stretched film is heat-set to prepare a polyester film.

The heat setting process is It is a process of preparing a base film by heat-setting the stretched film at a temperature of 160 to 230 °C, specifically, at a temperature of 175 to 215 °C. If the heat setting temperature is too low, the film shrinkage may increase, and if it is too high, breakage may occur, resulting in poor manufacturability.

After the heat setting is carried out for 0.5 to 10 minutes, specifically 0.5 to 5 minutes, the temperature may be gradually lowered to prepare a polyester-based film.

Even when a film is manufactured using the same dicarboxylic acid component, diol component, and each content, the physical properties of the manufactured film may be significantly different according to specific process steps.

A polyester-based film having a desired level of in-plane retardation may be realized through the process process according to the embodiment.

The above will be described in more detail with reference to the following examples. However, the following examples are only for illustrating the present invention, and the scope of the examples is not limited thereto.

< Example >

Example One

Polyethylene terephthalate resin (manufactured by SKC) to which ethylene glycol and terephthalic acid are applied in a molar ratio of 1:1, respectively, is melt-extruded through an extruder at about 280°C, cooled on a casting roll at about 25°C to 45°C, and then undrawn poly An ester-based sheet was prepared. The unstretched polyester sheet was stretched in the longitudinal direction and the width direction at the temperature shown in Table 1 at the magnification shown in Table 1 below, and the stretched film was heat-set at the temperature shown in Table 1 below. A polyester-based film having the thickness described was prepared.

Examples 2 to 4, Comparative Examples 1 to 3

A polyester film was prepared in the same manner as in Example 1, except that the polyester film having the thickness described in Table 1 was prepared at the draw ratio, the stretching temperature, and the heat setting temperature described in Table 1 below. In addition, in Comparative Example 1, a polyester sheet was prepared by mixing a polyethylene terephthalate resin and a sunscreen together.

Comparative Example 4

A TAC film (triacetylcellulose film) was purchased and evaluated under the same conditions as in Examples below and Comparative Example 4.

< evaluation example >

evaluation example 1: Tensile strength and UV durability

Tensile strength of the prepared polyester film was measured in the MD and TD directions using a universal measuring instrument (initial tensile strength, TSM1, TST1, unit: kg/mm ² ). Specifically, the tensile strength was measured by dividing the maximum load by the original cross-sectional area of the film from the value increased by applying a load to the film according to KS B 5521.

After exposing the same film to ^{UV light of 0.68 W/m 2} output for 48 hours using QLab’s QUV model, the tensile strength was measured again with the same device as above (tensile strength after exposure, TSM2, TST2, unit: kg/ mm ² ).

The measured values were applied to the following Equations 1 and 2 _{to evaluate UV durability in the MD direction (TSM UV,} unit: %) and UV durability in the TD direction (TST _{UV ,} unit: %).

<Equation 1>

TSM _UV = (TSM2/TSM1) × 100

<Equation 2>

TST _UV = (TST2/TST1) × 100

The results are shown in Table 2 below.

MD tensile strength
(kg/mm ² ) TD tensile strength
(kg/mm ² ) UV durability
(%) Former (TSM1) After (TSM2) Before (TST1) After (TST2) MD (TSM _UV ) TD (TST _UV ) Example 1 9.2 7.8 28.5 26.5 84.8 93 Example 2 9.1 7.8 29.6 26.8 85.7 90.5 Example 3 9.1 7.9 29.1 27 86.8 92.8 Example 4 8.8 7.8 30 26.7 88.6 89 Comparative Example 1 9 8.1 25.8 24.2 90 93.8 Comparative Example 2 9.2 8.6 28.8 18.7 93.5 64.9 Comparative Example 3 17.9 10.5 24.6 17.1 58.7 69.5 Comparative Example 4 17 12.1 15.3 11.4 71.2 74.5

evaluation example 2: thickness, in-plane phase difference , thickness direction phase difference

In-plane retardation (Ro) is a parameter defined as the product (ANxy X d) of the refractive index anisotropy (ANxy = |nx-ny|) of the biaxial orthogonal in the plane of the film and the film thickness d (nm) (ANxy X d). ，It is a measure of optical isotropy or anisotropy.

Specifically, the refractive index (nx, ny) of the orthogonal biaxial and the refractive index (nz) in the thickness direction are measured using an Otsuka refractometer (RETS, measuring wavelength 550 nm), and the thickness d (nm) of the film is an electric micrometer (Millitron 1245D, Fine Leup Co., Ltd.) was used to measure, and the unit was converted to nm. The difference between the measured biaxial refractive indices is obtained as an absolute value (|nx-ny|), and the in-plane retardation (Ro) is obtained by multiplying the film thickness d (nm) by (nxy×d), and the results are shown in Table 3 below. showed

Thickness direction retardation (Rth) refers to two birefringences ΔNxz (= | Nx-Nz |) and ΔNyz (= | Ny-Nz |) when viewed from a cross-section in the film thickness direction, respectively. It is calculated as the average of the phase differences obtained by multiplying by d.

thickness
(μm) thickness difference
(μm) Thickness deviation* Ro
(nm) Ro
Deviation** Rth
(nm) Example 1 125 1.6 Pass 11500 Pass 12500 Example 2 81 1.5 Pass 8370 Pass 11700 Example 3 80 1.6 Pass 8490 Pass 12100 Example 4 80 1.2 Pass 8660 Pass 11500 Comparative Example 1 60 0.6 Pass 6050 Pass 8520 Comparative Example 2 80 2.9 Fail 6900 Fail 11400 Comparative Example 3 75 2.5 Fail 3600 Fail 10940 Comparative Example 4 60 1.4 Pass 1.4 Pass 59

* Thickness deviation was evaluated as Pass when the thickness difference value was the same or smaller than the value corresponding to 2.5% of the measured thickness, and Fail when larger.

** Ro deviation was evaluated as a pass when the in-plane retardation was measured at 300 mm intervals across the entire width and the deviation was evaluated within 5% of the average in-plane retardation value as a pass, and a deviation of more than 5% was evaluated as Fail.

evaluation example 3: UV transmittance

UV transmittance was measured by applying Shimatsu's UV2600 instrument, and the measurement wavelength was 380 nm. The results are shown in Table 4 below.

evaluation example 4: moisture permeability measurement

Mocon's PERMATRAN_W model was applied to measure moisture permeability. The results are shown in Table 4 below.

evaluation example 5: light volume measurement

TES' 1334 A model was applied to measure the amount of light flow. The results are shown in Table 4 below.

evaluation example 6: Impact strength measurement

A mobile device with a protective film attached to the prepared polyester film was dropped from 80 cm. Depending on the degree of damage applied to the liquid crystal, it was evaluated as ◎ if there was no problem 10 times out of 10 times, and 7 times out of 10 times. If there were no problems from 9 to 9 times, it was evaluated as ○, if there were no problems 1 to 6 times out of 10, it was evaluated as △, and if there were any problems out of 10 times, it was evaluated as X. The results are shown in Table 4 below.

UV transmittance
(%, 380nm) moisture permeability
(g/m ² .day) light volume
(%) impact strength Example 1 87.8 8.2 92.8 ◎ Example 2 88.9 8.6 92.3 ○ Example 3 89.3 9.1 92.6 ○ Example 4 90.1 9.2 91.9 ○ Comparative Example 1 1.8 17.8 89 △ Comparative Example 2 89.1 9.1 90.2 ○ Comparative Example 3 88.6 9.1 90.8 △ Comparative Example 4 6.7 660↑ 90 △

Referring to the results of Table 2, the polyester-based films of Examples 1 to 4 showed excellent results in both the MD direction and the TD direction in terms of UV durability, which was superior to the TAC film of Comparative Example 4. . This is a particularly excellent result compared to Comparative Example 3, which is a biaxially stretched polyester film. is a characteristic

In addition, referring to the results of Table 3, it was confirmed that the polyester-based films of Examples 1 to 4 can uniformly maintain visibility by reducing thickness deviation and retardation deviation. The visibility may be evaluated by a fingerprint recognition rate, and when the polyester-based film is applied as a protective film, it is a necessary characteristic for fingerprint recognition in a portable device.

Furthermore, referring to the results of Table 4, Examples 1 to 4 showed uniformly excellent results in terms of UV transmittance, moisture permeability, light passage and impact strength.

Specifically, the polyester-based film according to the embodiment shows a fairly excellent result in terms of moisture permeability, which is a property necessary to protect liquid crystal and improve water resistance when applied as a protective film, and in Comparative Example 1, the moisture permeability is lowered, , Comparative Example 4 was confirmed to be very vulnerable to moisture. This means that the polyester-based film according to the embodiment also serves to supplement the TAC film, which is vulnerable to moisture.

Claims (13)

As a polyester film having an in-plane retardation (Ro, 550 nm) of 7,000 nm or more, and a thickness direction retardation (Rth) of 11,500 to 13,000 nm,
_{The MD direction ultraviolet durability (TSM UV} ) of the following formula 1 of the film is 80% or more, and the TD direction ultraviolet durability (TST _UV ) of the following formula 2 is 80% or more, a polyester film.
<Equation 1>
TSM _UV = (TSM2/TSM1) × 100
In Equation 1, the TSM _UV is the UV durability (%) in the MD direction, the TSM1 is the initial tensile strength in the MD direction, and the TSM2 is the MD measured after exposure to UV light for 48 hours with an output of ^{0.68 W/m 2} directional tensile strength,
<Equation 2>
TST _UV = (TST2/TST1) × 100
In Equation 2, the TST _UV is the UV durability (%) in the TD direction, the TST1 is the initial tensile strength in the TD direction, and the TST2 is the TD measured after exposure to UV light for 48 hours with an output of ^{0.68 W/m 2} directional tensile strength.
According to claim 1,
A polyester film, wherein the film does not contain a sunscreen.
delete delete According to claim 1,
The thickness of the film is 30 to 150㎛, a polyester film.
According to claim 1,
The thickness deviation of the film is within 2.5% based on the thickness of the film, polyester-based film.
According to claim 1,
The in-plane retardation deviation of the film is within 5%, the polyester film.
According to claim 1,
The moisture permeability of the film is 17 g/m ² .day or less, a polyester-based film.
delete A protective film comprising the polyester film according to claim 1 .
A display device comprising the protective film according to claim 10 .
forming a polyester-based sheet with a composition for preparing a polyester-based film;
preparing a stretched film by stretching the polyester-based sheet 1.0 to 1.5 times in the MD direction and 3.0 to 5.0 times in the TD direction; and
Containing; heat-setting the stretched film at a temperature of 160 to 230 ℃ to prepare a polyester film;
The method for producing a polyester-based film according to claim 1.
13. The method of claim 12,
The stretching temperature in the stretching step is 75 to 120 ℃, polyester-based film manufacturing method.