KR20150093386A - Optical film, liquid crystal display including the same and method for preparing the same - Google Patents

Abstract

The present invention relates to an optical film, a liquid crystal display including the same, and a method of manufacturing the same. The optical film of the present invention may have a rate of change of in-plane retardation (R ₀ ) of 30% or less and a rate of change of _Nz value of 20% or less after 500 hours at 85 ° C.

Description

TECHNICAL FIELD [0001] The present invention relates to an optical film, a liquid crystal display including the same, and a method of manufacturing the same.

The present invention relates to an optical film, a liquid crystal display including the same, and a method of manufacturing the same.

In recent years, the display field has been rapidly developed, and various flat panel display devices having excellent performance such as thinning, light weight, and low power consumption have been developed and replaced with existing CRT (cathode ray tube) .

Specific examples of such a flat panel display include a liquid crystal display (LCD), a plasma display panel (PDP), a field emission display (FED), an organic electroluminescent display Organic Electroluminescence Device).

Of these, liquid crystal displays are one of the most widely used flat panel displays. In general, a liquid crystal display has a structure in which a liquid crystal layer is sealed between a TFT (Thin Film Transistor) array substrate and a color filter substrate.

In order to drive such a liquid crystal display, a polarizing plate is required, and the polarizing plate is composed of an optical film commonly called a polarizing film and a protective film.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an optical film having a small rate of change in retardation even under a high temperature environment, and to provide a liquid crystal display device including the optical film.

It is another object of the present invention to provide a production method for easily producing the optical film.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a method of manufacturing the same.

In order to achieve the above object, the optical film according to an embodiment of the present invention may have an in-plane retardation (R ₀ ) change rate of 30% or less and a _Nz value change rate of 20% or less after 500 hours at 85 ° C.

The optical film may have a biaxial stretching ratio in the range of 1: 0.95 to 1: 1.05.

The optical film may include a polyester-based material.

The optical film may be composed of a polyethylene terephthalate type, a polyethylene naphthalate type, or a copolymer thereof.

According to an aspect of the present invention, a polarizing film may include a polarizer and the optical film disposed on at least one side of the polarizer.

A TAC system, a phase difference COP, and an acrylic film may be disposed on one side of the polarizer.

According to an aspect of the present invention, there is provided a liquid crystal display comprising a liquid crystal cell, a backlight unit, a lower polarizer disposed between the liquid crystal cell and the backlight unit, and an upper polarizer disposed on the viewer side of the liquid crystal cell, And the upper polarizer, the lower polarizer, or the upper polarizer and the lower polarizer may include the polarizing film.

The upper polarizer and the lower polarizer may include the polarizing film.

According to an aspect of the present invention, there is provided a method for manufacturing an optical film, the method comprising: melting and extruding a thermoplastic resin; providing a phase difference in the extruded thermoplastic resin; and biaxially stretching , The phase difference imparting step may include passing a thermoplastic resin extruded through the first forming rollers including a pair of rollers and generating a shearing force in the film along with the running of the first forming roll, .

The pair of rollers of the first forming roll may be different in elasticity from each other.

The pair of rollers of the first forming roll may have different rotational speeds from each other.

The pair of rollers of the first forming roll may have different elasticity and rotational speed from each other.

According to another aspect of the present invention, there is provided a method of manufacturing an optical film, the method comprising: melting and extruding a thermoplastic resin; providing a phase difference in the extruded thermoplastic resin; and biaxially stretching , The step of imparting the retardation passes the thermoplastic resin extruded between the first shaping roll and the second shaping roll including a pair of rollers, and the tensile forces of the first shaping roll and the second shaping roll are different from each other So that a phase difference can be given.

The first forming roll and the second forming roll may have different rotational speeds from each other.

The first forming roll is adjacent to the extruder, the second forming roll is adjacent to the stretching machine, and the rotational speed of the second forming roll is relatively faster than the rotational speed of the first forming roll.

The biaxial stretching step may be stretched at an MD: TD stretching ratio in the range of 1: 0.95 to 1: 1.05.

The details of other embodiments are included in the detailed description and drawings.

The embodiments of the present invention have at least the following effects.

That is, the optical film of the present invention is excellent in high-temperature stability and can improve the high-temperature reliability of the device to which it is applied.

The effects according to the present invention are not limited by the contents exemplified above, and more various effects are included in the specification.

1 is a cross-sectional view schematically showing an optical film according to an embodiment of the present invention.
2 is a cross-sectional view schematically showing a liquid crystal display device according to an embodiment of the present invention.
3 is a cross-sectional view schematically illustrating a liquid crystal cell of a liquid crystal display according to an embodiment of the present invention.
4 is a schematic process flow diagram of a method for manufacturing an optical film according to an embodiment of the present invention.
5 is a schematic view showing a part of a process of manufacturing an optical film according to an embodiment of the present invention.
6 is a schematic view showing a part of a process for producing an optical film according to another embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Is provided to fully convey the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims.

It is to be understood that elements or layers are referred to as being "on " other elements or layers, including both intervening layers or other elements directly on or in between. Like reference numerals refer to like elements throughout the specification.

Although the first, second, etc. are used to describe various components, it goes without saying that these components are not limited by these terms. These terms are used only to distinguish one component from another. Therefore, it goes without saying that the first component mentioned below may be the second component within the technical scope of the present invention.

It should also be understood that the steps constituting the manufacturing method described herein may be sequential or sequential, or one step and the other step constituting one manufacturing method may be performed in the order described in the specification It is not construed as limited. Therefore, the order of the steps of the manufacturing method can be changed within a range that can be easily understood by a person skilled in the art, and a change apparent to a person skilled in the art accompanying thereto is included in the scope of the present invention.

Optical film

Hereinafter, the optical film according to one embodiment of the present invention will be described in more detail.

The optical film according to an embodiment of the present invention is from 85 ℃ after 500 hours in-plane retardation (R ₀₎ rate of change is 30% or less, and N _z is the rate of change be not more than 20%.

It is a matter of course that the R ₀ change rate and the N _z change rate can be calculated as absolute values in a positive or negative number in a calculation formula described below.

The in-plane retardation (R ₀ ) can be obtained by multiplying the value obtained by subtracting the refractive index of the phase axis from the refractive index of the slow axis. That is, the in-plane retardation (R ₀ ) can be expressed by the following equation (1).

R ₀ = (nx - ny) * d (Equation 1)

In the above equation, nx and ny are the refractive indexes in the slow axis direction and the fast axis direction, respectively, and d is the film thickness.

The slow axis means an axis having the greatest refractive index at a specific wavelength in the plane of the film. In contrast to this, the phase axis, which is the axis perpendicular to the ground axis and the plane, can be mentioned.

The in-plane retardation change rate can be expressed as a percentage after dividing the value obtained by subtracting the initial in-plane retardation from the in-plane retardation by the in-plane retardation. That is, it can be expressed by the following expression (2).

(Equation 2)

In the exemplary embodiment, the value obtained by subtracting the in-plane retardation at 85 DEG C from the in-plane retardation at 85 DEG C after 500 hours at 85 DEG C is divided by the in-plane retardation at 85 DEG C after 500 hours, multiplied by 100, Can be obtained.

The N _z value is a value obtained by subtracting the refractive index in the thickness direction from the refractive index in the slow axis direction divided by a value obtained by subtracting the refraction index in the fast axis direction from the refractive index in the geostationary axis direction.

_{N z = (nx - nz)} / (nx - ny) ( Equation 3)

In the above equation, nx is the refractive index in the slow axis direction, ny is the refractive index in the fast axis direction, and nz is the thickness direction refractive index.

N _z value of the rate of change can be calculated dividing the value obtained by subtracting the first value from the last N N _{z z z} N value to the first value multiplied by 100. That is, the rate of change of the _Nz value can be expressed by the following equation (4).

(Equation 4)

In an exemplary embodiment, N _z value change rate from 85 ℃ after 500 hours N _z value at 85 ℃ around 500 hours in the N _z a value obtained by subtracting the value passed in 85 ℃ 500 days ago gave the N _z value multiplied by 100 (%) Can be obtained.

In another exemplary embodiment, the optical film may have a MD: TD biaxial stretch ratio in the range of 1: 0.95 to 1: 1.05. As the biaxial stretching ratio is closer to 1: 1, the rate of change at high temperature is also similar, so that the in-plane retardation change rate can be kept below the desired level.

The stretching method is not particularly limited, and longitudinal and transverse axial biaxial stretching, longitudinal and transverse simultaneous biaxial stretching, and the like can be employed. As the stretching means, any appropriate stretching machine such as a roll stretching machine, a tenter stretching machine, or a pantograph or linear motor type biaxial stretching machine can be used.

The material that can be used as the optical film is not particularly limited as long as it is transparent, but may be, for example, a thermoplastic resin, but is not limited thereto. Specific examples of the thermoplastic resin may include a cycloolefin resin, a polycarbonate resin, a polyolefin resin, an aromatic vinyl resin, a polyamide resin, a polyimide resin, a polyester resin and an acrylic resin. , Or a mixture of two or more of them may be used, but the present invention is not limited thereto.

In an exemplary embodiment, the thermoplastic resin may be a polyester-based material and the polyester-based material may be selected from, for example, terephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6- Naphthalene dicarboxylic acid, 1,4-naphthalene dicarboxylic acid, 1,5-naphthalene dicarboxylic acid, diphenylcarboxylic acid, diphenoxyethane dicarboxylic acid, diphenylsulfone carboxylic acid, anthracene dicarboxylic acid Cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethyl-1,3-cyclohexane dicarboxylic acid, There may be mentioned acid anhydrides such as malonic acid, succinic acid, 3,3-diethylsuccinic acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid, trimethyladipic acid, pimelic acid, , Sebacic acid, suberic acid, dodecadicarboxylic acid and the like, and aliphatic dicarboxylic acids such as ethylene glycol, propylene glycol Cyclohexanedimethanol, 1,4-cyclohexanedimethanol, decamethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentane Diols such as diol, 1,6-hexadiol, 2,2-bis (4-hydroxyphenyl) propane and bis (4-hydroxyphenyl) sulfone. A homopolymer obtained by polycondensing one kind of each of the above materials or a copolymer obtained by polycondensing at least one kind of dicarboxylic acid and two or more kinds of diols or a copolymer obtained by polycondensing two or more kinds of dicarboxylic acids and one or more kinds of diols And a blend resin obtained by blending two or more of these homopolymers or copolymers. However, the present invention is not limited to these.

In an exemplary embodiment, an aromatic polyester may be used from the viewpoint that the polyester exhibits crystallinity, and examples thereof include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and copolymers thereof However, the present invention is not limited to these.

The polyester film is obtained by, for example, a method of melt-extruding the above-mentioned polyester resin into a film form and then cooling and solidifying it by a casting drum to form a film. In the present invention, a stretched polyester film can be suitably used from the viewpoint of imparting crystallinity to the polyester film and achieving the above properties. The stretching may be biaxial stretching. Further, in the case of using an aromatic polyester as a main component as the first protective film and / or the second protective film, such a film may contain a resin, an additive or the like other than the aromatic polyester.

The thickness of the optical film can be variously manufactured according to the applied device or device. For example, it may have a thickness in the range of 10 [mu] m to 150 [mu] m, but is not limited thereto. If a thin optical film is required recently due to thinning of the display device, it may have a thickness in the range of 10 to 40 mu m.

Polarizing film

Hereinafter, a polarizing film according to an embodiment of the present invention will be described with reference to FIG. 1 is a cross-sectional view schematically showing a polarizing film according to an embodiment of the present invention.

Referring to FIG. 1, a polarizing film 100 according to an embodiment of the present invention includes a first protective film 101 and a second protective film 103 positioned on both surfaces in a thickness direction, and a first protective film And a polarizer 102 interposed between the second protective film 103 and the second protective film 103.

In an exemplary embodiment, at least one of the first protective film 101 and the second protective film 103 may be the optical film described above. In some cases, one of the first protective film 101 and the second protective film 103 may be omitted. In this case, the protective film 101 or 103, which is not omitted, may be the optical film.

The polarizer 102 is a film that can convert natural light or polarized light into arbitrary polarized light, and can generally be converted into specific linearly polarized light. As the polarizer 102, a hydrophilic polymer film such as a polyvinyl alcohol film, a partially porous polyvinyl alcohol film, or an ethylene-vinyl acetate copolymerization system partially saponified film may be formed by adsorbing a dichroic substance such as iodine or a dichroic dye, , A polyene-based oriented film such as a dehydrated product of phlyvinyl alcohol or a dehydrochlorinated product of polyvinyl chloride, and the like, but the present invention is not limited to these. In the exemplary embodiment, a polyvinyl alcohol-based film having a high degree of polarization and excellent in adhesion to the protective films 101 and 103 can be cited. However, the present invention is not limited thereto.

One of the first protective film 101 and the second protective film 103 may include a material different from the optical film.

In this case, an optical isotropic material having substantially no birefringence, or a birefringent material having an extremely small retardation value or an excellent in-plane uniformity in the optical axis direction can be used. Such a material is not particularly limited, but a transparent polymer having a uniform optical property can be used, and from the viewpoint of transparency, an amorphous polymer can be used. For example, a resin such as a cellulose resin, a cyclic polyolefin resin (norbornene resin), a polycarbonate resin, a polyarylate resin, an amorphous polyester resin, a polyvinyl alcohol resin, a polysulfone resin, Resin, and the like. However, the present invention is not limited thereto. In an exemplary embodiment, it may be a TAC series, a phase difference COP, an acrylic film, but is not limited thereto.

Liquid crystal display

FIG. 2 is a cross-sectional view schematically showing a liquid crystal display device according to an embodiment of the present invention, and FIG. 3 is a schematic cross-sectional view of a liquid crystal cell included in a liquid crystal display device.

Referring to FIGS. 2 and 3 together with FIG. 1, a liquid crystal display 10 includes a liquid crystal cell 200, a backlight unit 300, a lower polarizer plate (not shown) disposed between the liquid crystal cell 200 and the backlight unit 300 And an upper polarizer 110 disposed on the viewing side of the liquid crystal cell 200. [

The liquid crystal cell 200 includes a liquid crystal panel including a first substrate 210, a second substrate 230, a liquid crystal layer 220 sealed between the first substrate 210 and the second substrate 230, , And the upper polarizer 110 may be laminated on one surface (upper surface) of the first substrate 210. The upper polarizer plate 110 may be composed of the polarizing film 100 of the present invention.

The lower polarizer 120 may be laminated on the lower surface of the second substrate 230. When the two polarizers 110 and 120 are positioned above and below the liquid crystal cell 200, Orthogonal or parallel. The lower polarizer 120 may be composed of the polarizing film 100 of the present invention.

The first substrate 210 may be a color filter (CF) substrate. Although not shown in detail in FIG. 3, for example, a black matrix for preventing light leakage, a color filter for red, green, and blue, and a transparent (transparent) material such as ITO or IZO are formed on a lower surface of a substrate made of a transparent insulating material such as glass or plastic. And a common electrode which is an electric field generating electrode formed of a conductive oxide.

The second substrate 230 may be a TFT (Thin Film Transistor) substrate. Though not specifically shown in FIG. 3, for example, a thin film transistor composed of a gate electrode, a gate insulating film, a semiconductor layer, a resistive contact layer, and a source / drain electrode, and a thin film transistor formed of a transparent insulating material such as ITO Or a pixel electrode that is an electric field generating electrode formed of a transparent conductive oxide such as IZO.

The plastic substrate that can be used for the first substrate 210 and the second substrate 230 may be a plastic substrate such as PET (polyethylene terephthalate), PC (polycarbonate), PI (polyimide), PEN (polyethylene naphthalate) sulfone, PAR (polyarylate), and COC (cycloolefin copolymer). However, the present invention is not limited thereto. Also, the first substrate 210 and the second substrate 230 may be made of a flexible material.

The liquid crystal layer 220 may be a twisted nematic (TN) mode having a positive dielectric constant anisotropy, a vertically aligned (VA) mode or a horizontally aligned (IPS, FFS) mode or the like. 3, the TN mode will be described as an example.

When there is no voltage difference between the pixel electrode and the common electrode, that is, the electric field generating electrode, the electric field is not applied to the liquid crystal layer 220. As shown in Fig. 3, And is arranged parallel to the surfaces of the substrate 210 and the second substrate 230 and has a structure in which the first substrate 210 and the second substrate 230 are spirally twisted by 90 °.

The polarized light of linearly polarized light passes through the liquid crystal layer 220 and changes due to retardation due to the refractive index anisotropy of the liquid crystal. When the dielectric anisotropy (DELTA epsilon) of the liquid crystal and the chiral pitch or the thickness of the liquid crystal layer 220, i.e., the cell gap, are adjusted, the linearly polarized light direction of the light passing through the liquid crystal layer 220 is 90 °.

The backlight unit 300 may generally include a light source, a light guide plate, a reflective film, and the like. Depending on the configuration of the backlight, it can be arbitrarily divided into a direct-down system, a sidelight system, and a planar light source system.

Optical film manufacturing method

5 is a schematic diagram showing a part of a process of manufacturing an optical film according to an embodiment of the present invention, and FIG. 6 is a schematic view showing a process of manufacturing an optical film according to an embodiment of the present invention. Fig. 7 is a schematic view showing a part of a process for producing an optical film according to another embodiment of the invention.

Referring to these drawings, a method of manufacturing an optical film includes a step (S10) of melting and extruding a thermoplastic resin, a step (S20) of imparting a retardation by generating a shearing force in an extruded thermoplastic resin, and a step (S30).

In an exemplary embodiment, the drying step may be performed prior to melt extrusion to adjust the moisture content of the thermoplastic resin feedstock.

If the amount of water present in the raw material in the melt extrusion step (S10) is higher than a certain level, defective product in a bubble state such as an orange fill shape may occur. Therefore, the moisture content should be controlled to a certain level or less. The shape of the dryer is not particularly limited, and examples thereof include a dehumidifying dryer, a hot air dryer, and the like, but are not limited thereto. The drying temperature is preferably lower than the glass transition temperature of the resin raw material, and can be, for example, in the range of 20 to 200 ° C, more preferably in the range of 50 to 150 ° C, and particularly preferably in the range of 70 to 130 Lt; 0 > C. However, it goes without saying that the drying temperature can be appropriately selected depending on the kind of resin used and the glass transition temperature. If the drying temperature is too low, there is no drying effect. On the contrary, if the drying temperature is higher than necessary, the characteristics of the raw material are changed and it is not appropriate. The drying time of the raw material may be in the range of 0.5 to 5 hours, but can be easily selected in consideration of the ambient humidity and the like.

The dried raw materials can be supplied to the raw material storage (hopper) (not shown) located at the entrance of the extrusion facility 300, respectively. In some cases, it is preferable to pass the filtration apparatus while circulating air primarily in the reservoir in order to primarily remove impurities that may be contained in the raw material.

The charged raw material is filled in the first section of a screw (not shown) inside the extrusion facility. The first section serves to transfer the raw material to the extrusion equipment cylinder. The temperature setting may be in the range of 20 to 350 ° C, more preferably in the range of 150 to 250 ° C, but is not limited thereto.

Then, the second section is a section in which the melting of the raw material is started, and is preferably set to a temperature higher than the glass transition temperature of the resin raw material. For example, in the range of 150 to 350 ° C, and preferably in the range of 200 to 280 ° C, but is not limited thereto.

The third section serves to completely convert the raw material to the melt. The temperature setting can be maintained in the same range as the second section, but is not limited thereto.

The fourth section increases the density of the molten material by increasing the pressure of the molten raw material, thereby securing a stable discharge amount. In this process, the temperature condition may be maintained in the same range as the second and third intervals so as not to melt the discharged melt, but is not limited thereto.

In some cases, it passes through a gear pump section that transfers the melt to the tee die by a certain amount. When the raw material is fed directly to the tie die through the screw in the extrusion equipment (300) cylinder, the quantity of the transferred raw material is irregular and the product of excellent quality can not be obtained. Therefore, the gear pump can store irregularly charged raw materials from the extruding equipment cylinder in a certain space, and can steadily supply a certain amount of molten material to the tie die, thereby minimizing a change in the pressure distribution.

A section in which the melt is finally discharged out of the extrusion equipment 300 can be defined as a tee section. The shape of the film and the production thickness are determined according to the shape of the Ti-die. The shape of the tee die can be classified into a "T" die, a coat hanger die, a fish tail die, and the like, but is not limited thereto. The type of tie dies can be selectively used depending on the flowability of the melt.

The section is arbitrarily divided for the purpose of explanation, and the section does not have to be separately defined in the facility, and the processes may be continuously performed.

5, step S20 of imparting a phase difference according to an embodiment of the present invention is performed by pressing a first molding roll 310 including a pair of rollers 311 and 312, And in this process, a shearing force is generated in the film according to the running of the pair of rollers 311 and 312, so that a phase difference can be imparted to the inside of the film.

The elasticity of the first roller 311 and the second roller 312 can be made different from each other in order to apply the shearing force. FSR rolls, SFR rolls + FSR rolls, SFR rolls + FSR rolls, metal rolls + FSR rolls, SFR rolls + SFR rolls, metal rolls + Rubber roll, or the like may be used, but is not limited thereto. The FSR roll is a roll in which a water layer and a steel layer are sequentially formed on the surface of a metal roll, and the SFR roll is a roll in which a rubber layer and a steel layer are sequentially formed on the surface of the metal roll.

Also, as another method for applying the shearing force, the rotational speeds of the first roller 311 and the second roller 312 may be different. The ratio of the rotational speed of the first roller 311 to the rotational speed of the second roller 312 may range from 0.9 to 1.1, and preferably from 0.95 to 1.05.

It goes without saying that the elasticity and the rotation speed of the first roller 311 and the second roller 312 may be different from each other in some cases.

The surface temperature of the first roller 311 and the second roller 312 may be lower than the melt extrusion temperature. And preferably lower than the glass transition temperature of the thermoplastic resin. In this case, it is possible to reduce the roughness of the surface while increasing the viscosity of the film surface, thereby strengthening the internal phase difference, but is not limited thereto.

The surface temperature of the first roller 311 and the second roller 312 may be in the range of 20 to 200 ° C, preferably in the range of 50 to 170 ° C, in a range lower than the temperature of the film after co-extrusion, Particularly preferably in the range of 80 to 130 DEG C, but the temperature range is illustrative and an appropriate temperature can be selectively used depending on the material to be charged and the like.

In an exemplary embodiment, the first roller 311 and the second roller 312 may have different surface temperatures from each other. The temperature difference may be in the range of 2 to 50 占 폚, preferably in the range of 5 to 20 占 폚, and may be optionally applied depending on the process.

Referring to FIG. 6, step S20 of imparting a phase difference according to another embodiment of the present invention is performed in such a manner that the extruded resin 320 includes a first molding roll 310 and a second molding roll 310, Rolls 330 and is produced in the form of a film. In this process, the tension of the first forming roll 310 and the second forming roll 330 are made different from each other, so that a phase difference can be imparted to the film.

The first shaping roll 310 and the second shaping roll 330 have different rotational speeds and can adjust the retardation value by adjusting the tension between the first shaping roll 310 and the second shaping roll 330 .

The first shaping roll 310 is adjacent to the extruder and the second shaping roll 330 is adjacent to the stretcher and the rotational speed of the second shaping roll 330 is greater than the rotational speed of the first shaping roll 310. In an exemplary embodiment, May be relatively faster than the rotational speed of the rotor.

In contrast, when the rotational speed of the first forming roll 310 is faster than the rotational speed of the second forming roll 330, the film is sagged between the first forming roll 310 and the second forming roll 330, Which may not be desirable.

The biaxial stretching step (S30) may employ a general wet stretching method and / or dry stretching method in the art.

Examples of the dry stretching method include inter-roll stretching method, heating roll stretching method, compression stretching method, tenter stretching method, and the like, and the wet stretching method Non-limiting examples include a tenter stretching method and a roll-to-roll stretching method.

In the case of the above wet stretching method, stretching can be performed in an alcohol, water, or boric acid aqueous solution. For example, a solvent such as methyl alcohol or propyl alcohol may be used, but not limited thereto.

Further, the stretching step S20 may be a longitudinal / transverse biaxial stretching method, a longitudinal / horizontal simultaneous biaxial stretching method, or the like.

The stretching ratio MD: TD of the biaxial stretching step S30 may be varied depending on a desired thickness range and the like, and is not particularly limited. For example, stretching can be performed in the range of 1: 0.95 to 1: 1.05.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, You will understand. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

Manufacturing example  One

An optical film having a thickness of 40 占 퐉 and an initial in-plane retardation of 77 nm was produced by a melt extrusion process, a process of imparting a retardation, and biaxial stretching at a stretching ratio (MD: TD) of 1: 0.95 using polyethylene terephthalate.

Manufacturing example  2

An optical film was produced in the same manner as in Production Example 1 except that the stretching ratio (MD: TD) was 1: 1 and the initial in-plane retardation was 71 nm.

Manufacturing example  3

An optical film was produced in the same manner as in Production Example 1 except that the stretching ratio (MD: TD) was 1: 1.05 and the initial in-plane retardation was 27.

Manufacturing example  4

An optical film was prepared in the same manner as in Production Example 1, except that the initial in-plane retardation was 306 nm.

Manufacturing example  5

An optical film was prepared in the same manner as in Production Example 2, except that the initial in-plane retardation was 595 nm.

Manufacturing example  6

An optical film was prepared in the same manner as in Production Example 3 except that the initial in-plane retardation was 631 nm.

Comparative Example  One

An optical film was produced in the same manner as in Production Example 1 except that the stretching ratio (MD: TD) was 1: 1.05 and the initial in-plane retardation was 133 nm.

Comparative Example  2

An optical film was produced in the same manner as in Production Example 1 except that the stretching ratio (MD: TD) was 1: 1.1 and the initial in-plane retardation was 30 nm.

Comparative Example  3

An optical film was produced in the same manner as in Production Example 1, except that the stretching ratio (MD: TD) was 1: 0.8 and the initial in-plane retardation was 286 nm.

Comparative Example  4

An optical film was produced in the same manner as in Production Example 1 except that the stretching ratio (MD: TD) was 1: 1.2 and the initial in-plane retardation was 93 nm.

Comparative Example  5

An optical film was produced in the same manner as in Production Example 1 except that the stretching ratio (MD: TD) was 1: 0.9 and the initial in-plane retardation was 807 nm.

Comparative Example  6

An optical film was produced in the same manner as in Production Example 1 except that the stretching ratio (MD: TD) was 1: 1.1 and the initial in-plane retardation was 365 nm.

Comparative Example  7

An optical film was produced in the same manner as in Production Example 1 except that the stretching ratio (MD: TD) was 1: 0.8 and the initial in-plane retardation was 779 nm.

Comparative Example  8

An optical film was produced in the same manner as in Production Example 1 except that the stretching ratio (MD: TD) was 1: 1.2 and the initial in-plane retardation was 474 nm.

Comparative Example  5

An optical film was produced in the same manner as in Production Example 1 except that the stretching ratio (MD: TD) was 0: 6 (TD uniaxial stretching) and the initial in-plane retardation was 10,146 nm.

Experimental Example  One

The optical films prepared in Production Examples 1 to 6 and Comparative Examples 1 to 9 were measured for initial in-plane retardation and N _z value using Axoscan, and after 500 hours at 85 캜, their optical properties were measured again. The results are shown in Table 1.

Dimensional Shrinkage (MD / TD) [%] The initial R ₀ [nm] 85 ° C, R ₀ [nm] after 500 h, R ₀ Rate of change [%] Initial N _z 85 ° C, after 500h N _z N _z Change rate [%] Production Example 1 0.95 / 0.86 77 89 16 48.0 40.8 15 Production Example 2 0.91 / 0.88 71 82 15 51.7 44.8 13 Production Example 3 0.87 / 0.93 27 25 7 133.5 148.2 11 Production Example 4 0.95 / 0.90 306 315 3 12.4 11.9 4 Production Example 5 0.93 / 0.91 595 585 2 6.5 6.6 2 Production Example 6 0.90 / 0.96 631 670 6 6.2 5.9 5 Comparative Example 1 1.12 / 0.85 133 202 52 27.7 18.2 34 Comparative Example 2 0.92 / 1.10 30 48 60 121.4 74.4 39 Comparative Example 3 1.17 / 0.83 286 489 71 13.0 7.9 39 Comparative Example 4 0.85 / 1.20 93 148 59 38.5 24.7 36 Comparative Example 5 1.22 / 0.86 807 1,164 44 4.9 3.6 27 Comparative Example 6 0.98 / 1.19 365 523 43 10.4 7.4 29 Comparative Example 7 1.26 / 0.93 779 1,196 54 5.1 3.5 31 Comparative Example 8 0.94 / 1.24 474 776 64 8.1 5.1 37 Comparative Example 9 0.71 / 4.78 10,146 14,494 43 1.6 1.2 25

Referring to Table 1, Preparation Examples 1 to 6. The optical film of the R ₀ rate of change was measured in both the 30% or less, Comparative Examples 1 to 9 of the optical film was determined to be R ₀ rate of change is greater than both 30%. Further, in the optical films of Production Examples 1 to 6, MD: TD stretching ratios were within the range of 1: 0.95 to 1: 1.05, and in Comparative Examples 1 to 9 which were out of the above range, it was found that there was a critical difference in high temperature reliability .

Therefore, it can be seen that when the optical film of the present invention is used in the viewing direction of the display device, the side contrast ratio can be improved and the visibility can be improved.

It will be appreciated that the embodiments described above are all exemplary and that different embodiments may be applied in combination.

10: liquid crystal display device 100: optical film
101: first protective film 102: polarizer
103: second protective film 110: upper polarizer plate
120: lower polarizer plate 200: liquid crystal cell
300: backlight unit 210: first substrate
220: liquid crystal layer 230: second substrate
300: Extrusion equipment
311: first forming roll 312: second forming roll
320: Resin

Claims (16)

Wherein an in-plane retardation (R ₀ ) change rate is 30% or less after 500 hours at 85 ° C, and a _Nz value change rate is 20% or less. The method according to claim 1,
1. An optical film having a biaxial stretching ratio in the range of from 0.95 to 1: 1.05. The method according to claim 1,
An optical film comprising a polyester-based material. The method according to claim 1,
A polyethylene terephthalate type, a polyethylene naphthalate type, or a copolymer comprising the same. Polarizer, and
A polarizing film comprising the optical film according to any one of claims 1 to 4, which is located on at least one side of the polarizer. 6. The method of claim 5,
And a TAC system, a phase difference COP, and an acrylic film are placed on one surface of the polarizer. Liquid crystal cell,
Backlight unit,
A lower polarizer plate disposed between the liquid crystal cell and the backlight unit, and
And an upper polarizer disposed on the viewing side of the liquid crystal cell,
Wherein the upper polarizer, the lower polarizer, or the upper polarizer and the lower polarizer comprise the polarizing films of claims 5 or 6. 8. The method of claim 7,
Wherein the upper polarizer and the lower polarizer comprise the polarizing film. Melting and extruding the thermoplastic resin;
Imparting a phase difference to the inside of the extruded thermoplastic resin; And
And biaxially stretching,
Wherein the step of imparting the retardation comprises passing an extruded thermoplastic resin through a first forming roll including a pair of rollers and producing an optical film which generates a shearing force inside the film as the first forming roll travels, Way. 10. The method of claim 9,
Wherein a pair of rollers of the first forming roll are different in elasticity from each other. 10. The method of claim 9,
Wherein the pair of rollers of the first forming roll are different in rotational speed from each other. 10. The method of claim 9,
Wherein a pair of rollers of the first forming roll are different in elasticity and rotational speed from each other. Melting and extruding the thermoplastic resin;
Imparting a phase difference to the inside of the extruded thermoplastic resin; And
And biaxially stretching,
The step of imparting the phase difference may be performed by passing a thermoplastic resin extruded between a first forming roll and a second forming roll including a pair of rollers, respectively, and tensioning the first forming roll and the second forming roll A method for producing an optical film which imparts a retardation. 14. The method of claim 13,
Wherein the first shaping roll and the second shaping roll have different rotational speeds from each other. 15. The method of claim 14,
Wherein the first forming roll is adjacent to the extruder, the second forming roll is adjacent to the stretching machine,
Wherein the rotational speed of the second forming roll is relatively higher than the rotational speed of the first forming roll. The method according to claim 9 or 13,
Wherein the biaxial stretching step is stretched at an MD: TD stretching ratio in the range of 1: 0.95 to 1: 1.05.

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