KR20180136314A - Optical film, polarizing plate comprising the same and liquid crystal display apparatus comprising the same - Google Patents

Abstract

Provided are: an optical film, which is a styrene-containing (meth) acrylic-based optical film, wherein the optical film has an in-plane retardation Re of 100 to 250 nm at the wavelength of 550 nm in the formula 1, Re = (nx - ny) x d, and has an MIT value according to JIS P8115 of 100 or more; a polarizing plate comprising the same; and a liquid crystal display apparatus comprising the same. An object of the present invention is to provide the optical film, which does not show the breakage of rail end during transfer and roll winding, and is capable of double width correspondence, and which has excellent flexibility and allows a display to be seen at any cases when using polarizing sunglasses.

Description

TECHNICAL FIELD [0001] The present invention relates to an optical film, a polarizing plate including the polarizing plate, and a liquid crystal display device including the polarizing plate.

The present invention relates to an optical film, a polarizing plate including the same, and a liquid crystal display device including the same. More particularly, the present invention relates to an optical film which is free from rupture during conveying and roll winding, can cope with a wide width, is excellent in bending resistance, can display a picture on both sides when using polarizing sunglasses, To a liquid crystal display device.

A liquid crystal display device essentially includes a polarizing plate to which a protective film is adhered to a polarizer. As the protective film of the polarizer, triacetylcellulose film is usually used. However, when the thickness of the triacetyl cellulose film is reduced, sufficient mechanical strength can not be obtained, the moisture permeability is high, and the polarizer is liable to be deteriorated. In addition, triacetyl cellulose films are expensive and require low cost alternative materials.

An acrylic film can be sought as a substitute material for a triacetyl cellulose film. Among the acrylic films, PMMA (polymethylmethacrylate) film exhibits high light transmittance and excellent moldability and can be used as an optical material. Further, the acrylic film is increasingly used as an optical member such as an image display device such as a liquid crystal display device, a plasma display, and an organic EL display device. However, a film made of PMMA alone may have a low glass transition temperature, resulting in a decrease in film strength. Accordingly, attempts have been made to improve the physical properties of the film by adding other monomers to PMMA. However, depending on the type of the added monomer, the film is brittle and broken when the film is extruded, resulting in breakage in conveying and roll winding, which may lower the usability.

The background art of the present invention is disclosed in Korean Patent No. 1418755 and the like.

An object of the present invention is to provide an optical film which is free from rupture during conveying and roll winding, can cope with a wide width, is excellent in bending resistance, and can display a picture on both sides when using polarized sunglass.

Another object of the present invention is to provide a polarizing plate comprising the optical film of the present invention.

It is still another object of the present invention to provide a liquid crystal display device including the polarizing plate of the present invention.

The optical film of the present invention is a styrene-containing (meth) acrylic-based optical film, and the optical film has an in-plane retardation Re of 100 nm to 250 nm of the following formula 1 at a wavelength of 550 nm, and the MIT value according to JIS P8115 is 100 times or more Can:

<Formula 1>

Re = (nx - ny) xd

(Where nx and ny are refractive indexes in the slow axis direction and the fast axis direction of the optical film at a wavelength of 550 nm, respectively, and d is the thickness (unit: nm) of the optical film).

The polarizing plate of the present invention includes an optical film formed on the light exit surface of the polarizer and the polarizer, and the optical film may include the optical film of the present invention.

The liquid crystal display device of the present invention may include the polarizing plate of the present invention.

The present invention provides an optical film which is free from breakage during conveyance and roll winding, can cope with a wide width, is excellent in bending resistance, and can display a picture on both sides when using polarized sunglass.

The present invention provides a polarizing plate comprising the optical film of the present invention.

The present invention provides a liquid crystal display device including the polarizing plate of the present invention.

The embodiments are described below in order to facilitate a person skilled in the art to which the present invention pertains. The present invention may be embodied in many different forms and is not limited to the embodiments described herein.

In the present specification, "in-plane retardation (Re)" is represented by the following formula 1, "thickness direction retardation (Rth)" is represented by the following formula 2 and "biaxiality degree (NZ) have:

<Formula 1>

Re = (nx - ny) xd

(Where nx and ny are refractive indexes in the slow axis direction and the fast axis direction of the optical film at a wavelength of 550 nm, respectively, and d is the thickness (unit: nm) of the optical film).

<Formula 2>

Rth = ((nx + ny) / 2 - nz) xd

(Where nx, ny and nz are the refractive indexes in the slow axis direction, the fast axis direction and the thickness direction of the optical film at a wavelength of 550 nm, respectively, and d is the thickness (unit: nm) of the optical film).

<Formula 3>

NZ = (nx - nz) / (nx - ny)

(Where nx, ny, and nz are refractive indexes in the slow axis direction, the fast axis direction, and the thickness direction of the optical film at a wavelength of 550 nm, respectively).

As used herein, "area ratio" is the ratio of the surface area of the film after final stretching to the surface area before stretching of the unstretched film.

In the present specification, the "difference in stretching ratio" is an absolute value of the difference between the TD stretching ratio and the MD stretching ratio.

As used herein, "(meth) acrylic" means acrylic and / or methacrylic.

The optical film of the present invention is a styrene-containing (meth) acrylic-based optical film, and has an MIT value of 100 or more according to JIS P8115 and an in-plane retardation Re of 100 nm to 250 nm at a wavelength of 550 nm. In the MIT range, even if the styrene-containing (meth) acrylic-based optical film alone or the laminate of the polarizer and the optical film is rolled or transported, there may be no breakage or breakage. In the in-plane retardation range, the polarized light can be polarized by circularly polarized light or elliptically polarized light, so that the polarized light can be visually recognized by the polarized sunglass.

The present inventors have found that when an unstretched film formed by melt extrusion of a composition for an optical film containing a styrene-containing (meth) acrylic copolymer is stretched at an area ratio of 7.0 times or more and a stretching ratio difference of 0.2 to 2.0 times, And a film having an in-plane retardation of 100 nm to 250 nm at a wavelength of 550 nm could be produced. A film having an in-plane retardation of 100 nm to 250 nm at a wavelength of 550 nm and an MIT value of 100 or more can be produced within the above-mentioned area ratio range and stretching ratio difference range. Preferably, the area ratio may be from 7.0 times to 10.0 times, the difference in stretching ratio from 0.5 times to 2.0 times, and from 0.8 times to 1.5 times. Preferably, the optical film may be a biaxially oriented film.

The optical film produced therefrom can exhibit the following properties.

The thickness direction retardation Rth of the optical film may be -300 nm or more, for example, -300 nm to 0 nm or -300 nm to -100 nm. Within this range, there may be a depolarizing effect.

The optical film may have Re / Rth (Re ratio to Rth) of not less than -3, for example, from -3 to 0, for example, from -3 to -0.4. Within this range, there may be a depolarizing effect.

The optical film may have a degree of biaxiality NZ of not less than -3.0, for example, -3.0 to 0, for example, -2.0 to -0.1. Within this range, there may be a depolarizing effect.

The optical film may have nx of 1.5 to 1.7, ny of 1.5 to 1.6, and nz of 1.5 to 1.7 at a wavelength of 550 nm. Within this range, there may be a depolarizing effect.

The nx-ny of the optical film may be 0.001 to 0.01 at a wavelength of 550 nm. Within this range, there may be a depolarizing effect.

The refractive index of the optical film may be 1.50 to 1.60, specifically 1.53 to 1.55 or 1.55 to 1.57. Within the above range, a resin having stable durability and optical effect can be obtained.

The styrene-containing (meth) acrylic copolymer may be a copolymer of a monomer mixture comprising a (meth) acrylic monomer and a styrene-containing monomer. The styrene-containing monomer may be included in the copolymer to increase the glass transition temperature of the copolymer. The styrene-containing (meth) acrylic copolymer may have an effect of enhancing heat resistance by including maleic anhydride. (Meth) acrylic copolymer containing maleic anhydride at a ratio of the area ratio and the stretching ratio, the MIT value can be 100 times or more and the Re value can be 100 nm to 250 nm. In one embodiment, the styrene-containing (meth) acrylic copolymer may be a ternary copolymer of a monomer mixture comprising a (meth) acrylic monomer, a styrene-containing monomer, and a maleic anhydride. The terpolymer may include at least one of a random copolymer, a block copolymer, and an alternating copolymer, but is not limited thereto.

For example, the monomer mixture may comprise from 10 mol% to 50 mol%, for example from 20 mol% to 50 mol%, from 20 mol% to 40 mol%, from 40 mol% to 80 mol% of the styrene-containing monomer For example, from 50 mol% to 80 mol%, 50 mol% to 70 mol%, and 1 mol% to 30 mol%, 5 mol% to 30 mol% of maleic anhydride. Within the above range, there may be an effect of maintaining high heat resistance and not breaking. The styrene-containing monomer in the monomer mixture may have a larger molar number than that of the (meth) acrylic monomer and maleic anhydride, respectively, so that the MIT of the present invention can be satisfied at the time of stretching due to the difference between the area ratio and the stretching ratio.

The styrene-containing monomer may include at least one of styrene, methylstyrene, and ethylstyrene. The styrene-containing monomer may be styrene. The (meth) acrylic monomer may be at least one selected from the group consisting of methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, cyclohexyl (meth) acrylate, benzyl (meth) Acrylate, biphenyl (meth) acrylate, isobornyl (meth) acrylate, phenoxyethyl (meth) acrylate, and ethyladamantyl (meth) acrylate. Preferably, the (meth) acrylic monomer is methyl methacrylate as the alkyl (meth) acrylate monomer.

The styrene-containing (meth) acrylic copolymer can be produced by copolymerizing the above monomer mixture. The copolymerization method is not particularly limited, and bulk polymerization, suspension polymerization, emulsion polymerization, and solution polymerization can be applied. The styrene-containing (meth) acrylic copolymer may be prepared by adding a polymerization initiator, a chain transfer agent, a dispersant, a buffer, and the like to the monomer mixture.

The composition for an optical film may further contain other components in addition to the styrene-containing (meth) acrylic copolymer. For example, it may further include an antioxidant, a lubricant, an ultraviolet absorber, a defoaming agent, a stabilizer, and the like. Antioxidants, lubricants, ultraviolet absorbers, antifoaming agents and stabilizers can be of any conventional type known to those skilled in the art, but are not limited thereto.

The optical film can be produced by stretching the unstretched film formed by melt extrusion of the composition for optical film by an area ratio of 7.0 times or more, for example, 7.0 to 10.0 times, and a stretching ratio of 0.2 to 2 times.

The melt extrusion process can be performed, for example, by an extrusion die having a die lip. At this time, the resin material is heated and melted in the extrusion die, and is continuously discharged from the die lip to form a film.

The extrusion temperature of melt extrusion is preferably 130 占 폚 or higher and 300 占 폚 or lower, and more preferably 150 占 폚 or higher and 280 占 폚 or lower. If the extrusion temperature is 130 占 폚 or higher, the copolymer in the resin material is sufficiently melted and kneaded, so that the unmelted material can be sufficiently prevented from remaining on the film. If the temperature is lower than 300 占 폚, problems such as coloring of the film due to thermal decomposition and adherence of the decomposition product to the die lip can be sufficiently prevented.

In the stretching step, an unstretched film (original film) obtained in the melt extrusion step is stretched to obtain an optical film. As the stretching method, for example, inter-roll longitudinal stretching using a main speed difference or transverse stretching using a tenter device, and a sequential biaxial stretching method combining these can be applied. Further, in the tenter stretching apparatus, a simultaneous biaxial stretching apparatus in which the clip interval for gripping the film end portion is widened in the transport direction of the film may also be used. The stretching device may be a line which is consistent with the pushing-out block. Alternatively, the original film wound by the extrusion blower may be fed off-line to a stretching device and stretched.

The stretching temperature is preferably not less than Tg + 2 (占 폚) and not more than Tg + 20 (占 폚), more preferably not less than Tg + 5 (占 폚) and not more than Tg + 15 (占 폚), when the glass transition temperature of the original film is Tg ) Or less. If the stretching temperature is Tg + 2 (占 폚) or more, problems such as breakage of the film during stretching and increase in haze of the film can be sufficiently prevented. In addition, when Tg + 20 (占 폚) or less, the polymer main chain tends to be oriented, and a better polymer main chain orientation degree tends to be obtained. For example, the stretching temperature may be 100 占 폚 to 200 占 폚, preferably 130 占 폚 to 160 占 폚.

The stretching magnification is set to be 7.0 times or more in area ratio. In the above area ratio range, the in-plane retardation may be 100 nm to 250 nm at a wavelength of 550 nm or more for 100 times or more of the MIT when the unstretched film formed from the composition for optical films containing a styrene-containing (meth) acrylic copolymer is stretched.

The unstretched film can be stretched by biaxial stretching. The MD stretching ratio may be 2 to 3 times, and the TD stretching ratio may be 3 to 4 times. In the above range, an optical film satisfying MIT and in-plane retardation without film breakage may be produced. In one embodiment, the TD stretching ratio may be larger than the MD stretching ratio, and the MD stretching may be followed by the TD stretching to allow sequential biaxial stretching.

By stretching the original film formed by the melt film formation method, the polymer main chain can be oriented and the bending resistance of the film can be improved. On the other hand, if the film is not made of a polymer material having a small birefringence, the retardation value of the film increases, The quality of the liquid crystal display device deteriorates when the liquid crystal display device is assembled. In this embodiment, an optical film having excellent optical properties and bending resistance can be obtained by using the above-described resin material and adjusting the draw ratio within the above range.

The optical film may have a glass transition temperature of 100 占 폚 or higher, for example, 100 占 폚 or higher and 150 占 폚 or lower. Within the above range, the durability of the optical film may be stable.

The thickness of the optical film may be 10 탆 to 100 탆, for example, 20 탆 to 60 탆. Within the above range, there may be an effect of optically effective and stable conveyance.

The optical film may have a haze of 2% or less, for example, 0% to 1%. In the above range, it can be used in an optical display device.

The optical film may be used alone, or may be surface-treated with an optical film or formed by further forming a functional layer. For example, the functional layer may be a hard coating layer, a translucent layer, an antireflection layer, an antiglare layer or the like, but is not limited thereto.

The polarizing plate of the present invention may include the optical film of the present invention.

The polarizing plate of the present invention may include the optical film of the present invention on the light exit surface of the polarizer and the polarizer. Therefore, the polarized light emitted from the polarizer passes through the optical film and is elliptically polarized or circularly polarized, so that the screen can be viewed even with polarized sunglasses. The optical film may be arranged so that the absorption axis of the polarizer and the MD of the optical film on the polarizer light exit surface are 40 DEG to 50 DEG, preferably 45 DEG. Within this range, there may be a depolarizing effect.

The polarizer can polarize the incident light from the liquid crystal panel and emit it as an optical film. The polarizer may comprise conventional polarizers known to those skilled in the art. Specifically, the polarizer may include a polyvinyl alcohol polarizer produced by uniaxially stretching a polyvinyl alcohol film or a polyene polarizer produced by dehydrating a polyvinyl alcohol film. The polarizer may have a thickness of 5 占 퐉 to 40 占 퐉. In the above range, it can be used in a liquid crystal display device.

A conventional optical film may be further formed on the other surface of the polarizer. For example, the optical film may be selected from the group consisting of a polyester including polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, acrylic, cyclic olefin polymer (COP), triacetyl cellulose ), Polyvinyl acetate, polyvinyl chloride (PVC), polynorbornene, polycarbonate (PC), polyamide, polyacetal, polyphenylene ether, polyphenylene sulfide, polysulfone, poly But are not limited to, one or more of ethersulfone, polyarylate, and polyimide.

The liquid crystal display device of the present invention can include the polarizing plate of the present invention as a viewing side polarizing plate. The viewer-side polarizing plate means a polarizing plate which is opposed to the backlight unit with respect to the liquid crystal panel and adhered to the liquid crystal panel.

Hereinafter, the configuration and operation of the present invention will be described in more detail with reference to preferred embodiments of the present invention. However, the following examples are provided to aid understanding of the present invention, and the scope of the present invention is not limited to the following examples.

Example  One

A styrene-containing (meth) acrylic ternary copolymer was prepared by polymerizing a monomer mixture comprising 50 mol% of styrene, 30 mol% of methyl methacrylate, and 20 mol% of maleic anhydride. The composition for an optical film containing the styrene-containing (meth) acrylic ternary copolymer thus prepared was melt-extruded to prepare an unstretched film.

The unstretched film was stretched at 130 캜 to 160 캜 at the MD stretching ratio shown in the following Table 1 and then stretched at the TD stretching ratio shown in Table 1 below to obtain a biaxially stretched optical film (Thickness: 40 mu m).

Example  2 to Example  3

An optical film was produced in the same manner as in Example 1, except that the MD stretching ratio, the TD stretching ratio, the area ratio, and the difference in stretching ratio were changed as shown in Table 1 below.

Comparative Example  1 to Comparative Example 7

An optical film was produced in the same manner as in Example 1, except that the MD stretching ratio, the TD stretching ratio, the area ratio, and the difference in stretching ratio were changed as shown in Table 1 below.

The physical properties of the optical films thus prepared were evaluated in the following Table 1.

(1) MIT according to JIS P8115: The number of times of the refraction test in the MIT is measured using a refractive index tester in a BE-201 MIT manufactured by TESTER SANGYO CORPORATION. Also, the BE-201 MIT refractivity tester manufactured by TASCHA SANGO CORPORATION is also referred to as the theft tester in MIT. The measurement conditions are weight 200 g, bending point R 0.38, bending speed 175 r / min, bending angle 135 degrees left and right, and width of the film sample 15 mm. An average value of the number of times of bending when the optical film is repeatedly bent in the carrying direction and an average value of the number of times of bending when the bending is repeated in the width direction is set as the number of times of the bending test in the MIT.

(2) Phase difference: The optical films were measured for retardation Re, Rth and NZ at a wavelength of 550 nm using Axoscan (AxoMetric).

(3) Visibility of the screen by polarizing sunglass: 42% transmittance of the optical film The specimen was manufactured by attaching the polarizing axis of the polarizer and the MD of the optical film at 45 ° to the light exit surface on the upper side of the polarizer. The prepared specimen was fixed to the viewer side polarizing plate of the liquid crystal panel. The screen was observed with polarized sunglasses. When the polarized light was viewed as a polarized sunglass and the screen was visually recognized, when the screen was not visually recognized, and when the screen was not fully visually evaluated.

MD
Stretching cost TD
Stretching cost Area ratio Difference in stretching cost MIT
(time) Re
(nm) NZ Rth
(nm) Polarized light
Whether sunglass screen is visible Example 1 2.0 3.5 7.0 1.5 175 202 -0.2 -134 O Example 2 2.5 3.5 8.8 1.0 211 145 -0.3 -119 O Example 3 2.7 3.5 9.5 0.8 214 103 -2.0 -256 O Comparative Example
One 2.7 2.8 7.6 0.1 136 57 -1.5 -116 △ Comparative Example
2 3.0 3.0 9.0 0.0 185 42 -1.7 -93 △ Comparative Example
3 3.5 3.5 12.2 0.0 545 38 -2.1 -100 △ Comparative Example 4 0.5 2.0 1.0 1.5 23 210 0 -115 O Comparative Example 5 1.5 3.0 4.5 1.5 96 207 -0.1 -126 O Comparative Example
6 0 0 0.0 0.0 One 3 1.8 -4 X Comparative Example 7 2.5 2.3 5.8 0.2 103 56 -1.4 -105 △

As shown in Table 1, the acrylic optical film of the present invention is a styrene (meth) acryl-based optical film containing maleic anhydride, which has high heat resistance and has an MIT of 100 times or more and is excellent in bending resistance and has Re of 100 nm to 250 nm There was a polarization canceling effect.

On the other hand, Comparative Examples 1 to 3, which exceed the stretching ratio difference of the present invention and Comparative Example 4, Comparative Example 5 and Comparative Example 7, which deviate from the area ratio, are not included in the in-plane retardation range of the present invention, There was no. In particular, when the area ratio was increased from 4.5 times to 7.0 times by about 56% within the range of the draw ratio difference of the present invention, the MIT value increased to about 82%.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (12)

Styrene-containing (meth) acrylic-based optical film,
Wherein the optical film has an in-plane retardation Re of the following formula 1 at a wavelength of 550 nm of 100 nm to 250 nm,
Wherein the optical film has an MIT value according to JIS P8115 of not less than 100,
<Formula 1>
Re = (nx - ny) xd
(Where nx and ny are refractive indexes in the slow axis direction and the fast axis direction of the optical film at a wavelength of 550 nm, respectively, and d is the thickness (unit: nm) of the optical film).
The optical film according to claim 1, wherein the optical film is formed from a resin composition for an optical film comprising a styrene-containing (meth) acrylic copolymer.
The optical film according to claim 2, wherein the styrene-containing (meth) acrylic copolymer is a ternary copolymer of (meth) acrylic monomers, styrene-containing monomers and maleic anhydride.
The styrene-containing (meth) acrylic copolymer according to claim 3, wherein the styrene-containing (meth) acrylic copolymer is a copolymer of 10 mol% to 50 mol% of a (meth) acrylic monomer, 40 mol% to 80 mol% % Of ternary copolymer, optical film.
The styrene-containing (meth) acrylic copolymer according to claim 3, wherein the styrene-containing (meth) acrylic copolymer is a copolymer of styrene and maleic anhydride in an amount of 10 to 50 mol%, 1 to 30 mol% Chain, optical film.
The optical film according to claim 1, wherein the optical film has a thickness direction retardation Rth of not less than -300 nm,
<Formula 2>
Rth = ((nx + ny) / 2 - nz) xd
(Where nx, ny and nz are the refractive indexes in the slow axis direction, the fast axis direction and the thickness direction of the optical film at a wavelength of 550 nm, respectively, and d is the thickness (unit: nm) of the optical film).
The optical film according to claim 1, wherein the optical film has a biaxiality degree NZ of -3 or more represented by the following formula 3:
<Formula 3>
NZ = (nx - nz) / (nx - ny)
(Where nx, ny, and nz are refractive indexes in the slow axis direction, the fast axis direction, and the thickness direction of the optical film at a wavelength of 550 nm, respectively).
The optical film according to claim 1, wherein the optical film has a glass transition temperature of 100 ° C or higher.
The optical film according to claim 1, wherein the optical film is an optical film produced by extruding a resin composition for an optical film comprising a styrene-containing (meth) acrylic copolymer and then biaxially stretching at an area ratio of 7.0 times or more and a stretching ratio of 0.2 to 2 times .
A polarizer and an optical film formed on a light exit surface of the polarizer,
Wherein the optical film comprises the optical film of any one of claims 1 to 9.
The polarizer according to claim 10, further comprising an optical film on a light incident surface of the polarizer.
A liquid crystal display device comprising the polarizing plate of claim 10.