KR20170008478A

KR20170008478A - Phase difference film, preparation method thereof and liquid crystal display device comprising the same

Info

Publication number: KR20170008478A
Application number: KR1020150099710A
Authority: KR
Inventors: 강병일; 최은정; 성다은; 한창훈
Original assignee: 주식회사 엘지화학
Priority date: 2015-07-14
Filing date: 2015-07-14
Publication date: 2017-01-24
Also published as: KR101993736B1

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a retardation film having a retardation in the retardation in the plane direction and a retardation in the retardation in the thickness direction, and an excellent viewing angle compensation effect, a method for manufacturing the same, and a liquid crystal display device including the same. Accordingly, since the retardation film includes a polymer film having a specific range of physical properties (weight average molecular weight and glass transition temperature), the deviation in the retardation in the plane direction and the retardation in the thickness direction can be controlled not excessively large, It can be excellent.

Description

TECHNICAL FIELD The present invention relates to a phase difference film, a method of manufacturing the same, and a liquid crystal display device including the phase difference film,

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a retardation film having a retardation in the retardation in the plane direction and a retardation in the retardation in the thickness direction, and an excellent viewing angle compensation effect, a method for manufacturing the same, and a liquid crystal display device including the same.

2. Description of the Related Art In recent years, display technology using various methods such as a liquid crystal display (LCD), a plasma display panel (PDP) and the like has been developed and commercialized due to the development of optical technology.

Among them, the liquid crystal display technology is divided into various modes depending on the initial arrangement of the liquid crystal and the manner in which the electric field is applied. Typical examples thereof include TN (Twisted Nematic), VA (Vertical Alignment) Fringe Field Switching) mode. Each mode represents different optical properties and has different application device areas. TN mode, which has high productivity but relatively poor viewing angle, is mainly applied to a laptop computer display or a monitor which does not need a wide viewing angle technique. In VA mode, IPS mode and FFS mode, . In the VA mode, a retardation film must be applied to realize a wide viewing angle. However, the IPS mode and the FFS mode can realize a certain viewing angle without using a retardation film. In particular, in the IPS mode, since the liquid crystal having a positive dielectric anisotropy is horizontally aligned, the optical anisotropy at the oblique angle in the non-driven state is not greater than that in the other modes, so that an excellent viewing angle can be secured even by using the isotropic protective film alone. Compensation for the absorption axis of the polarizer at the inclination angle is not performed at all, so that contrast reduction and color modulation depending on the viewing angle may occur. Therefore, application of a retardation film suitable for the IPS mode is indispensable.

A retardation film is an anisotropic film that is optically not an isotropic refractive index property, and is known as the most effective method for compensating the viewing angle in a display technology such as a liquid crystal display. Currently, a structure in which a retardation film for IPS mode is composed of two or more layers of multilayer films is proposed. Typically, a method of uniaxially stretching a cyclic olefin polymer (COP) and then coating a nematic liquid crystal, which is a positive plate, to compensate the viewing angle is known. However, in the case of the above method, even if the orientation of the liquid crystal and the thickness of the coating are slightly changed due to the high birefringence of the nematic liquid crystal, the retardation of the entire compensating film is largely changed. In addition, the manufacturing cost is high due to the expensive liquid crystal unit price, and it is difficult to commercialize the liquid crystal display device.

As another method, a retardation compensation film for IPS mode has been developed in which a non-liquid crystalline retardation developing material having a negative C plate phase difference is coated on an acrylic retardation film to adjust the retardation in the plane direction and the retardation in the thickness direction. However, the acrylic film is generally vulnerable to an organic solvent such as an aromatic hydrocarbon or an organic chlorine used in a coating process, and when the phase difference developing material is coated using these solvents, adhesion failure, brittleness increase , The phase difference is lowered, and a stain occurs.

Therefore, it is required to develop a phase difference film which is easily applicable to an IPS (in-plane switching) mode liquid crystal display device and is relatively inexpensive and thus has a high competitive power.

KR 10-2014-0000431 A

SUMMARY OF THE INVENTION It is an object of the present invention to provide a phase difference film having improved durability with improved viewing angle compensation characteristics by adjusting retardation in the plane direction and retardation in the thickness direction.

Another object of the present invention is to provide a method for producing the above retardation film.

It is still another object of the present invention to provide a liquid crystal display device including at least one of the retardation films.

In order to solve the above problems, the present invention provides a liquid crystal display comprising: a substrate having at least one optically anisotropic property; And a polymer film having a positive retardation, wherein a phase difference (R _in ) _in a plane direction with respect to light having a wavelength of 380 nm is 120 nm to 140 nm and a thickness direction retardation (R _th ) is 60 nm to 80 nm Film.

The present invention also relates to a process for preparing a polymeric film comprising coating a polymer solution on at least one surface of at least one optically anisotropic substrate to form a polymer film (step A), wherein said polymer is a substituted styrenic system Wherein the retardation film is produced by polymerizing a monomer.

[Chemical Formula 1]

In the above formula (1), R is a substituent group including a nitrogen group, an oxygen group, or a halogen group element.

In addition, the present invention provides a liquid crystal display device including at least one of the retardation films.

Since the retardation film according to the present invention includes a polymer film having a specific range of physical properties (weight average molecular weight and glass transition temperature), the deviation in the retardation in the plane direction and the retardation in the thickness direction can be controlled not excessively large, Can be excellent.

Further, the method for producing a retardation film according to the present invention is a method of producing a polymer by using a specific ratio (less than 0.01 part by weight) of a styrene monomer having a specific substituent (for example, a monomer represented by the general formula (2) The prepared polymer can have a certain range of physical properties and the polymer film produced using the polymer can have a properly controlled retardation so that the finally produced retardation film can exhibit an excellent viewing angle compensation effect .

In addition, the liquid crystal display device according to the present invention can improve the wide viewing angle by including the above retardation film.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate preferred embodiments of the invention and together with the description of the invention serve to further the understanding of the technical idea of the invention, It should not be construed as limited.
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram schematically showing x-axis, y-axis and z-axis of a substrate, a polymer film or a retardation film according to the present invention.
FIG. 2 illustrates a structure of a retardation film according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail in order to facilitate understanding of the present invention.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

The term "retardation _in plane direction (R _in )" used in the present invention is a numerical value calculated by the following equation (1), and "retardation in thickness direction (R _th )" is a numerical value calculated by the following equation

[Equation 1]

R _in = (N _x -N _y ) x d

&Quot; (2) "

_{R th = (N z -N y} ) × d

In the above equations (1) and (2), Nx, Ny and Nz denote refractive indexes in the x-axis direction, the y-axis direction and the z-axis direction, respectively, and d denotes the thickness of the film or substrate. The x-axis, the y-axis, and the z-axis may be defined as shown in Fig. 1, and the x-axis and the y-axis have a vertical relationship on the same plane and the z-axis is perpendicular to the plane.

The present invention provides a retardation film excellent in durability in which the retardation in the plane direction and the retardation in the thickness direction are adjusted to improve the viewing angle.

The retardation film according to an embodiment of the present invention includes a substrate having at least one optically anisotropic property; And a polymer film having a positive retardation, wherein a retardation in plane direction (R _in ) with respect to light having a wavelength of 380 nm is 120 nm to 140 nm and a retardation in thickness direction (R _th ) is 60 nm to 80 nm do.

The retardation film has a retardation ratio (R _th / R _in ) in the thickness direction to a retardation in the plane direction of 0.5 to 0.6.

The retardation film according to an exemplary embodiment of the present invention has the retardation characteristics described above and can be applied to a liquid crystal display device to exhibit an improved viewing angle.

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

Wherein the retardation film comprises a substrate having at least one optically anisotropic property as described above; And a polymer film having a positive retardation. Here, the polymer film having the positive retardation may be a coating layer formed on at least one surface of the substrate. That is, the retardation film according to an embodiment of the present invention may be a multi-layer structure including a first layer composed of a substrate having one or more optically anisotropic properties and a second layer composed of the polymer film as shown in Fig.

The substrate having the at least one optically anisotropic may be one having an optically coaxial negative B plate retardation. Further, the substrate may be a polymer resin film. That is, the substrate according to an embodiment of the present invention may be a polymer film produced by a polymeric resin to have the above retardation by a stretching method described later.

The optically uniaxial castle in that the refractive index of the x-axis direction of the substrate (N _x1), at least two of the index of refraction (N _y1) and refractive index (N _z1) of the z-axis direction of the y-axis direction is substantially equal to, that described x Axis direction refractive index ( _Nx1 ), the y-axis refractive index ( _Ny1 ), and the z-axis refractive index ( _Nz1 ) is less than 0.005.

The negative (negative) B plates (plate) phase is the refractive index (N _x1), refractive index in the y-direction (N _y1) and the refractive index in the z-axis direction (N _z1) of the x-axis direction of the substrate N _x1> N _y1> _Nz1 , < / RTI >

Here, the x-axis, the y-axis, and the z-axis may be defined as described above.

The polymer resin may be one or more selected from the group consisting of a polyolefin resin, a cyclic polyolefin resin, and a cellulose ester resin.

Specifically, the polyolefin-based resin may be a polyethylene resin or a polypropylene resin, but is not limited thereto.

The cyclic polyolefin-based resin may be a polynorbornene resin, but is not limited thereto.

The cellulose ester resin may be a polyvinyl chloride resin, a polyacrylonitrile resin, a polysulfone resin, a polyacrylate resin, a polyvinyl alcohol resin or a TAC (triacetyl cellulose) resin, but is not limited thereto.

The substrate may be 20 [mu] m to 100 [mu] m thick. Specifically, the substrate may have a thickness of 40 탆 to 60 탆.

Also, the substrate may have a retardation in the plane direction with respect to 380 nm light of 50 nm to 150 nm, and a ratio (R _th / R _in ) in the thickness direction retardation to the retardation in the plane direction may be 0.2 to 0.6.

The polymer film having the positive retardation may be a coating layer formed on at least one surface of the substrate as described above and may be formed by coating a polymer solution on at least one surface of the substrate by a manufacturing method described below.

Specifically, the polymer film may be a positive C plate or a positive B plate phase difference.

The positive (positive) C-plate retardation is refractive index in the x-axis direction of the polymer film (N _x2), refractive index in the y-direction (N _y2) and a refractive index in the z-axis direction (N _z2) is N _x2 = N _y2 <N _z2 a can be an indication of that satisfying the condition, a positive (positive) B-plate retardation is refractive index in the x-axis direction of the polymer film (N _x2), refractive index in the y-direction (N _y2) and a refractive index in the z-axis direction (N _z2 ) May satisfy that N _y2 < N _x2 < N _z2 . At this time, the x-axis, the y-axis, and the z-axis may be defined as described above.

The polymer film may have a retardation in a plane direction with respect to light having a wavelength of 380 nm of 100 nm to 160 nm, and a ratio of retardation in thickness direction to retardation in a retardation direction (R _th / R _in ) may be 0.3 to 0.7. Further, the retardation in the thickness direction per 1 μm of the unit thickness may be 7 or more, specifically 10 or more, more specifically 10 to 20.

On the other hand, the polymer film includes a polymer containing a unit derived from a substituted styrene monomer. The polymer has a weight average molecular weight (Mw) of 100,000 g / mol to 1,000,000 g / mol and a glass transition temperature (Tg) of 130 Lt; 0 > C or more. Specifically, the polymer may have a weight average molecular weight (Mw) of 100,000 g / mol to 1,000,000 g / mol and a glass transition temperature (Tg) of 130 ° C to 200 ° C. The polymer film according to an embodiment of the present invention may exhibit the retardation as described above by including a polymer having the above physical properties (weight average molecular weight and glass transition temperature), and as a result, the retardation film including the polymer may have a viewing angle compensation The effect can be excellent.

Herein, the weight average molecular weight is measured by dissolving the polymer in tetrahydrofuran (THF) solution at a concentration of 0.25% and using Gel Permeation Chromatography (GPC), and the glass transition temperature (Tg) And was measured using a differential scanning calorimetry.

The polymer includes a unit derived from a substituted styrene-based monomer, and may be one prepared by polymerizing a substituted styrene-based monomer as described later. That is, the polymer according to an embodiment of the present invention may be a substituted styrenic polymer.

Specifically, the substituted styrenic monomer may be represented by the following general formula (1).

[Chemical Formula 1]

More specifically, the substituted styrenic monomer may be one or more of those represented by the following general formulas (2) to (4).

(2)

(3)

[Chemical Formula 4]

The polymer film according to an embodiment of the present invention may have a weight average molecular weight and a glass transition temperature as described above by including a polymer containing the substituted styrene-based monomer-derived units described above. And can have a properly controlled retardation without a separate stretching process.

The polymer film may have a thickness of 5 탆 to 20 탆, and in particular may be 10 탆 to 20 탆 thick.

The present invention also provides a method for producing the retardation film.

The method according to one embodiment of the present invention comprises the step of coating a polymer solution on at least one surface of a substrate having at least one optically anisotropy to form a polymer film (step A) Wherein the modified styrene-based monomer is represented by the following general formula (1).

Step A is a step of coating a polymer solution on at least one surface of the substrate to form a polymer film on at least one surface of the substrate having at least one optically anisotropy to produce a retardation film.

The substrate having at least one optically anisotropic property may be a polymeric resin film having optical coaxial negative B plate phase difference as described above, and a detailed description of the substrate is as described above.

Specifically, the substrate may be a polymer resin film produced by stretching a polymer resin.

The stretching may be longitudinal (MD) stretching or transverse (TD) stretching, or may be performed in one step or in multiple steps. In this case, the longitudinal (MD) stretching may be performed using a speed difference between the rolls, and the transverse (TD) stretching may be performed using a tenter. The time of railing of the tenter is usually within 10 degrees, thereby suppressing the bowing phenomenon occurring in the lateral direction calculation and regularly controlling the angle of the optical axis.

Specifically, the stretching may be performed through a preheating step, a stretching step, and a heat treatment step, though not particularly limited, and may be performed using a manufacturing apparatus equipped with a preheating zone, a stretching zone, and a heat treatment zone.

The preheating step is a step of heating and softening the polymer resin so that the polymer resin can be stretched well in the subsequent stretching step.

The heating in the preheating step may be performed at a constant temperature in a range of (Tg-30) to Tg, where Tg is the glass transition temperature of the polymer resin. The heating time may be, for example, For 1 minute to 10 minutes. If the preheating step is carried out under the above-mentioned temperature range and heating time condition, the polymer resin can be sufficiently softened, so that the deviation of retardation upon stretching can be reduced. On the other hand, when the preheating step is heated for a long time outside the above temperature range and heating time condition, the degree of softening is large, so that a stretching at a high magnification may be required, or sufficient birefringence may be difficult to manifest.

The stretching step after the preheating step can be performed by uniaxially stretching in a temperature range of (Tg-20) to (Tg + 30), where Tg is the glass transition temperature of the polymer resin. In this case, the stretching speed and the stretching magnification can be appropriately adjusted by the thickness of the polymer resin, the required phase difference, etc. For example, the stretching speed may be generally from 10% / min to 500% / min, And may be usually from 1.1 times to 3 times. If the stretching magnification is less than 1.1 times, it may be difficult to obtain a sufficient retardation because the birefringence to be expressed is low. If the stretching magnification exceeds 3 times, a deviation of the retardation of the produced retardation film becomes large, There may arise a problem of an increase.

The heat treatment step after the stretching step may be performed at a temperature lower than the stretching temperature. For example, the temperature of the heat treatment step may be performed in a temperature range of (stretching temperature -50) to (stretching temperature-10) can do.

The polymer solution may be one in which the polymer is dissolved in a solvent.

The polymer may be one prepared by polymerizing a substituted styrenic monomer, and the polymerization may be bulk polymerization, solution polymerization, emulsion polymerization or suspension.

Specifically, it may be prepared by polymerizing the substituted styrenic monomer in the presence of a polymerization solvent and a polymerization initiator. At this time, the substituted styrenic monomer may be as described above.

The polymerization solvent is not particularly limited, but it can be deionized water or organic solvent and can be appropriately selected according to the substituted styrene monomer. Specifically, when the substituted styrenic monomer is water-soluble (hydrophilic), the polymerization solvent may be deionized water, and when the substituted styrenic monomer is water-insoluble (hydrophobic) . For example, when the substituted styrenic monomer is represented by Formula 2, the polymerization solvent is deionized water, and when the substituted styrenic monomer is represented by Formula 3 or Formula 4, . Here, the organic solvent is not particularly limited, but may be, for example, toluene.

The amount of the polymerization solvent to be used is not particularly limited. For example, the substituted styrene-based monomer and the polymerization solvent may be used in an amount that represents a weight ratio of 2: 8 to 7: 3.

Examples of the polymerization initiator include, but are not limited to, cumene hydroperoxide, diisopropylbenzene hydroperoxide, di-t-butylperoxide, lauryl peroxide, benzoyl peroxide, t-butyl peroxyisopropyl carbonate, organic peroxides such as t-amyl peroxy-2-ethylhexanoate; Azo compounds such as 2,2'-azobis (isobutyronitrile), 1,1'-azobis (cyclohexanecarbonitrile), 2,2'-azobis (2,4-dimenyl valeronitrile) , Azo compounds such as 2'-azobisisobutylate, and the like. These polymerization initiators may be used alone or in combination of two or more.

The amount of the polymerization initiator used may be less than 0.01 part by weight based on 100 parts by weight of the substituted styrenic monomer. If the amount of the polymerization initiator used is more than 0.01 part by weight, the weight average molecular weight of the polymer produced can not be in the range as described above, so that it is difficult to control the phase difference of the polymer film containing the polymer As a result, the viewing angle compensating effect of the finally produced retardation film may be deteriorated.

The polymerization for preparing the polymer may be carried out in a temperature range of 60 ° C to 90 ° C.

The solvent contained in the polymer solution is not particularly limited, but examples thereof include deionized water, toluene, methyl isobutyl ketone, cyclopentanone, methylene chloride, 1,2-dichloroethane, methyl amyl ketone, methyl ethyl ketone and methyl isoamyl Ketones, and the like. The solvent may be appropriately selected depending on the polymer. For example, when the polymer is prepared by polymerizing a substituted styrenic monomer represented by the general formula (2), deionized water may be used. In the case of the polymer prepared by polymerizing the substituted styrenic monomer represented by the general formula (4), toluene and the like may be used in addition to deionized water.

The liquid crystal display according to an exemplary embodiment of the present invention may be implemented in an in-plane switching (IPS) mode, a vertically aligned (VA) mode, an optically compensated birefringence (OCB) mode, a twisted nematic .

Specifically, the liquid crystal display device may be an IPS (In-Plane Switching) mode liquid crystal display device.

The IPS (In-Plane Switching) mode liquid crystal display may be a device including a liquid crystal cell and a first polarizer and a second polarizer provided on both surfaces of the liquid crystal cell, and the retardation film according to the present invention may be referred to as a first polarizer Between the first polarizer and the liquid crystal cell, between the second polarizer and the liquid crystal cell, or between the first polarizer and the liquid crystal cell, and between the second polarizer and the liquid crystal cell.

The first polarizing plate and the second polarizing plate may include a protective film on one or both sides. The protective film may be a triacetate cellulose (TAC) film, a poly (arylene sulfide) film formed by ring opening metathesis polymerization (ROMP) A norbornene-based film, a ring opening metathesis polymerization followed by hydrogenation (HROMP) polymer film obtained by hydrogenating a ring-opening polymerized cyclic olefin polymer, a polyester film, or a polynorbornene-based film produced by addition polymerization .

In addition, the IPS mode liquid crystal display device may be an apparatus including a monolithic polarizer having the protective film of the retardation film according to the present invention on one side or both sides of the polarizing film.

As the polarizing film, a film made of polyvinyl alcohol (PVA) containing iodine or a dichroic dye can be used. The integrated polarizing plate can be manufactured by laminating the retardation film and the polarizing film. At this time, the laminate can be carried out using an adhesive. For example, the adhesive may be coated on the surface of the polarizing film by using a roll coater, a gravure coater, a bar coater, a capillary coater or the like, The retardation film and the polarizing film can be laminated by heating or pressing at room temperature with a pile roll.

The adhesive may be, for example, a one-component or two-component PBA adhesive, a polyurethane adhesive, an epoxy adhesive, a styrene-butadiene rubber (SBR) adhesive or a hot melt adhesive. When a polyurethane-based adhesive is used, it may be a polyurethane-based adhesive prepared by using an aliphatic isocyanate-based compound which is not yellowed by light.

The viscosity of the adhesive is not particularly limited, but may be a low viscosity type of 5,000 cps or less, excellent storage stability, and a light transmittance of 400 to 800 nm at 90% or more.

In addition, a pressure sensitive adhesive capable of exhibiting sufficient adhesive force may be used in place of the adhesive, and it is preferable that the pressure sensitive adhesive is cured sufficiently by heat or ultraviolet rays after the bonding, so that the mechanical strength is improved to an adhesive level.

Examples of the adhesive that can be used include a natural rubber, a synthetic rubber or an elastomer excellent in optical transparency, a vinyl chloride / vinyl acetate copolymer, a polyvinyl alkyl ether, a polyacrylate or a modified polyolefin-based pressure sensitive adhesive and a hardening agent such as isocyanate Adhesive or the like.

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

Example 1

Deionized water and sodium styrenesulfonate (Formula 2) were added to the polymerization reactor at a weight ratio of 8: 2, and 0.0001 weight parts of potassium persulfate (relative to 100 weight parts of sodium styrenesulfonate) was added. Lt; / RTI > After completion of the polymerization reaction, acetone and methanol were added to precipitate the slurry, recovered, and dried to prepare a sodium styrene sulfonate polymer.

The prepared sodium styrenesulfonate polymer was dissolved in deionized water to prepare a polymer solution. The polymer solution was coated on one surface of a uniaxially stretched cyclic polyolefin resin (COP, thickness: 40 mu m, ZEON) having a negative B plate phase difference to a thickness of 10 mu m to form a polymer film to prepare a retardation film.

Example 2

A retardation film was prepared in the same manner as in Example 1 except that potassium persulfate was added in 0.00005 parts by weight at the time of preparing the polymer.

Example 3

A retardation film was prepared in the same manner as in Example 1 except that 0.00001 parts by weight of potassium persulfate was added at the time of preparing the polymer.

Example 4

To the polymerization reactor, toluene and 4-nitrostyrene (Formula 3) were added in a weight ratio of 3: 7, 0.0001 weight parts of benzoyl peroxide (relative to 100 weight parts of 4-nitrostyrene) was added, . After completion of the polymerization reaction, acetone and methanol were added to precipitate the slurry, recovered, and dried to prepare a 4-nitrostyrene polymer.

The prepared 4-nitrostyrene polymer was dissolved in deionized water to prepare a polymer solution. The polymer solution was coated with a uniaxially stretched cyclic polyolefin resin (COP, thickness: 40 mu m, ZEON) having a negative B plate phase difference to a thickness of 10 mu m on one surface to form a polymer film to prepare a retardation film.

Example 5

A retardation film was prepared in the same manner as in Example 4 except that 4-fluorostyrene (Formula 4) was used instead of 4-nitrostyrene.

Comparative Example 1

A retardation film was prepared in the same manner as in Example 4 except that styrene was used instead of 4-nitrostyrene.

Comparative Example 2

A retardation film was prepared in the same manner as in Example 4, except that 0.01 part by weight of benzoyl peroxide was used.

Comparative Example 3

A retardation film was prepared in the same manner as in Example 5 except that 0.01 part by weight of benzoyl peroxide was used.

Comparative Example 4

A retardation film was prepared in the same manner as in Example 4 except that 3-nitrostyrene was used instead of 4-nitrostyrene.

Experimental Example

In order to comparatively analyze the characteristics of the retardation films prepared in Examples 1 to 5 and Comparative Examples 1 to 4, the following experiments were carried out, and the results are shown in Tables 1 and 2.

1) Measurement of weight average molecular weight

The weight average molecular weights of the polymers prepared in Examples 1 to 5 and Comparative Examples 1 to 4 were measured for comparative analysis. The weight average molecular weight was determined by dissolving each polymer in a tetrahydrofuran (THF) solution at a concentration of 0.25% and using Gel Permeation Chromatography (GPC).

2) Glass transition temperature

The glass transition temperature was measured in order to compare and analyze the physical properties of the polymers prepared in Examples 1 to 5 and Comparative Examples 1 to 4. The glass transition temperature (Tg) was measured using Differential Scanning Calorimetry.

3) Phase difference measurement

The retardation of each of the retardation films prepared in Examples 1 to 5 and Comparative Examples 1 to 4 was measured.

The phase difference was obtained by measuring the light with a wavelength of 380 nm by using an Axoscan apparatus (Muller Matrix) capable of measuring 16 Muller matrices and obtaining 16 Muller matrices according to the manufacturer's manual.

division Example Comparative Example One 2 3 4 5 One 2 3 4 Weight average molecular weight (kg / mol) 300 500 1,000 100 100 150 14 18 98 Glass transition temperature
(° C) 200 200 200 190 160 100 190 190 178

division A cyclic polyolefin-based resin film Polymer film Phase difference film R _in (nm) R _th (nm) R _in (nm) R _th (nm) R _th (nm) / 1 탆 R _in (nm) R _th (nm) R _th / R _in Example 1 100 -40 22 101 10.1 122 61 0.5 Example 2 20 100 10.0 120 60 0.5 Example 3 25 108 10.8 125 68 0.54 Example 4 32 111 11.1 132 71 0.54 Example 5 37 118 11.8 137 78 0.57 Comparative Example 1 8 10 1.0 108 -30 -0.28 Comparative Example 2 17 65 6.5 117 25 0.21 Comparative Example 3 21 56 5.6 121 16 0.13 Comparative Example 4 20 76 3.8 120 36 0.3

As shown in Table 1, it was confirmed that the polymers of Examples 1 to 5 according to one embodiment of the present invention exhibited higher overall weight average molecular weight and glass transition temperature than the polymers of Comparative Examples 1 to 4.

Specifically, the styrene polymer of Comparative Example 1, which was prepared using a conventional styrene monomer instead of the substituted styrene monomer according to an embodiment of the present invention, was prepared in the same manner as in Examples 4 and 5, Exhibited significantly lower glass transition temperatures of about 52% and 62%, respectively, than the polymer of Example 5. In addition, although the substituted styrenic monomer according to one embodiment of the present invention was used, the polymers of Comparative Example 2 and Comparative Example 3 prepared using the maximum amount of the polymerization initiator in the preparation of the polymer were each prepared using the same monomer The glass transition temperature was comparable to that of the polymers of Example 4 and Example 5, but the weight average molecular weight decreased rapidly to 14% and 18%, respectively. In addition, the polymer of Comparative Example 4 prepared using 3-nitrostyrene had a weight average molecular weight of 2% and a glass transition temperature of 94% as compared with the polymer of Example 4 prepared using 4-nitrostyrene, %, And did not show the desired weight average molecular weight.

As shown in Table 2, the retardation films prepared using the polymers of Examples 1 to 5 according to one embodiment of the present invention have a ratio (R _th / R _in ) of thickness direction retardation to retardation in the plane direction, Shows that the retardation film according to an embodiment of the present invention can be effectively used as a retardation film for compensating the viewing angle of a liquid crystal display device.

In contrast, a retardation film prepared using the polymer of Comparative Example 1 having a significantly lowered glass transition temperature than the polymers of Examples 1 to 5, a polymer of Comparative Example 2 and Comparative Example 3 having a significantly lower weight average molecular weight the phase difference film and the purpose of the retardation film produced by using the polymer of Comparative did not show a weight average molecular weight in the range of example 4 prepared by significantly out of phase condition (0.5≤R _th / R _in ≤0.6) presented in this invention And thus it was confirmed that it could be unsuitable for use as a phase difference film for compensating the viewing angle of a liquid crystal display device.

As a result, it was confirmed that the retardation of the polymer film can be an important factor for controlling the retardation of the finally prepared retardation film, and the retardation of the polymer film is determined by the physical properties of the polymer used Molecular weight and glass transition temperature).

1: retardation film
101: a substrate having at least one optical anisotropy
102: polymer film

Claims

A substrate having one or more optical anisotropies; And
A polymer film having a positive retardation,
Wherein a retardation _in plane direction (R _in ) with respect to light having a wavelength of 380 nm is 120 nm to 140 nm and a retardation in thickness direction (R _th ) is 60 nm to 80 nm.

The method according to claim 1,
Wherein the retardation film has a ratio (R _th / R _in ) of thickness direction retardation to a retardation in the plane direction of 0.5 to 0.6.

The method according to claim 1,
Wherein the substrate has an optically unifocal negative B plate phase difference.

The method according to claim 1,
Wherein the base material is a polymeric resin film.

The method of claim 4,
Wherein the polymer resin is at least one selected from the group consisting of a polyolefin resin, a cyclic olefin resin, and a cellulose ester resin.

The method according to claim 1,
Wherein the base material has a thickness of 20 탆 to 100 탆.

The method according to claim 1,
Wherein the substrate has a retardation _in plane direction (R _in ) with respect to light having a wavelength of 380 nm of 50 nm to 150 nm.

The method according to claim 1,
Wherein the base material has a ratio (R _th / R _in ) of thickness direction retardation to a retardation in the plane direction of 0.2 to 0.6.

The method according to claim 1,
Wherein the polymer film is a coating layer formed on at least one side of the substrate.

The method according to claim 1,
Wherein the polymer film has a positive C plate or a positive B plate phase difference.

The method according to claim 1,
Wherein the polymer film has a retardation (Rin) in plane direction with respect to light having a wavelength of 380 nm of 100 nm to 160 nm.

The method according to claim 1,
Wherein the polymer film has a ratio (R _th / R _in ) _in thickness direction retardation to a retardation in the plane direction of 0.3 to 0.7.

The method according to claim 1,
Wherein the polymer film has a thickness direction retardation of 7 or more per unit thickness of 1 mu m with respect to light having a wavelength of 380 nm.

The method according to claim 1,
Wherein said polymer film comprises a polymer comprising substituted styrene-based monomer units,
Wherein the polymer has a weight average molecular weight (Mw) of 100,000 g / mol to 1,000,000 g / mol and a glass transition temperature (Tg) of 130 ° C or more.

15. The method of claim 14,
Wherein the substituted styrene-based monomer is represented by the following formula (1):
[Chemical Formula 1]

15. The method of claim 14,
Wherein the substituted styrene-based monomer is at least one of the following structural formulas (2) to (4):
(2)

(3)

[Chemical Formula 4]

The method according to claim 1,
Wherein the polymer film is 5 占 퐉 to 20 占 퐉 thick.

Coating a polymer solution on at least one surface of a substrate having at least one optically anisotropic to form a polymer film,
The method for producing a retardation film according to claim 1, wherein the polymer is prepared by polymerizing a substituted styrenic monomer represented by the following formula 1:
[Chemical Formula 1]

19. The method of claim 18,
Wherein the substituted styrene-based monomer is at least one of the following structural formulas (2) to (4):
(2)

(3)

[Chemical Formula 4]

19. The method of claim 18,
The polymer is prepared by polymerizing the substituted styrenic monomer in the presence of a polymerization initiator,
Wherein the polymerization initiator is used in an amount of less than 0.01 part by weight based on 100 parts by weight of the substituted styrene monomer.

19. The method of claim 18,
Wherein the substrate has an optically coaxial negative B plate phase difference.

19. The method of claim 18,
Wherein the base material is a polymeric resin film produced by stretching a polymeric resin.

23. The method of claim 22,
Wherein the polymer resin is at least one selected from the group consisting of a polyolefin resin, a cyclic polyolefin resin, and a cellulose ester resin.

19. The method of claim 18,
Wherein the polymer has a weight average molecular weight (Mw) of 100,000 g / mol to 1,000,000 g / mol and a glass transition temperature (Tg) of 130 ° C or more.

19. The method of claim 18,
Wherein the polymer film has a positive C plate or a positive B plate phase difference.

A liquid crystal display comprising at least one of the retardation films according to claim 1.

27. The method of claim 26,
Wherein the liquid crystal display device is an IPS (In-Plane Switching) mode, a VA (Vertically Aligned) mode, an OCB (Optically Compensated Birefringence) mode, a TN (Twisted Nematic) mode or an FFS (Fringe Field Switching) mode.

27. The method of claim 26,
Wherein the liquid crystal display device is an IPS (In-Plane Switching) mode.