KR20110070576A - Liquid crystal display device - Google Patents

Abstract

PURPOSE: A liquid crystal display device is provided to improve viewing angel characteristics in a diagonal direction by changing polarization characteristics of the light. CONSTITUTION: A liquid crystal display element(201) includes as follows. A liquid crystal display panel includes an active layer. A first and second polarization plate polarizes the light. A first negative biaxial film(221) changes the polarization state of the light by being included between the liquid crystal display panel and a second polarization plate. A second negative biaxial film(225) changes a polarization state of the light by being included between the liquid crystal display panel and the first negative biaxial film.

Description

Liquid crystal display device

The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device having a negative biaxial film and a (+) C plate to improve viewing angle characteristics.

Recently, with the development of various portable electronic devices such as mobile phones, PDAs, notebook computers, there is an increasing demand for flat panel display devices for light and small size that can be applied thereto. Liquid crystal display devices (LCDs), plasma display panels (PDPs), field emission displays (FEDs), etc. are being actively researched as such flat panel displays. (LCD) is in the limelight.

Such liquid crystal display devices have various display modes according to the arrangement of liquid crystal molecules. However, TN mode liquid crystal display devices are mainly used due to the advantages of easy monochrome display, fast response speed, and low driving voltage. In such a TN mode liquid crystal display, liquid crystal molecules oriented horizontally with respect to the substrate are almost perpendicular to the substrate when a voltage is applied. Therefore, there is a problem that the viewing angle is narrowed upon application of voltage due to the refractive anisotropy of the liquid crystal molecules.

In order to solve this viewing angle problem, liquid crystal display devices of various modes having side viewing angle characteristics have recently been proposed, but among them, the liquid crystal display device of the lateral field mode (In Plane Switching Mode) is applied to actual production. It is produced. The IPS mode liquid crystal display device aligns liquid crystal molecules in a plane by forming at least one pair of positive electrodes arranged in parallel in a pixel to form a transverse electric field substantially parallel to the substrate.

1 is a plan view showing a conventional IPS mode liquid crystal display device.

As shown in FIG. 1, the pixels of the liquid crystal panel 1 are defined by gate lines 3 and data lines 4 arranged vertically and horizontally. The thin film transistor 10 is formed at the intersection of the gate line 3 and the data line 4 in the pixel. The thin film transistor 10 includes a gate electrode 11 to which a scan signal is applied from the gate line 3, and a semiconductor layer formed on the gate electrode 11 and activated as a scan signal is applied to form a channel layer. 12 and a source electrode 13 and a drain electrode 14 formed on the semiconductor layer 12 and to which an image signal is applied through the data line 4, to apply an image signal input from the outside to the liquid crystal layer. do.

In the pixel, a plurality of common electrodes 5 and a pixel electrode 7 are arranged substantially parallel to the data line 4. In addition, a common line 16 connected to the common electrode 5 is disposed in the middle of the pixel, and a pixel electrode line 180 connected to the pixel electrode 7 is disposed on the common line 16. It overlaps with the common line 16. An accumulation capacitance Cst is formed in the transverse electric field mode liquid crystal display device due to the overlap between the common line 16 and the pixel electrode line 180.

As described above, in the constructed IPS mode liquid crystal display device, the liquid crystal molecules are oriented substantially in parallel with the common electrode 5 and the pixel electrode 7. When the thin film transistor 10 is operated to apply a signal to the pixel electrode 7, a transverse electric field substantially parallel to the liquid crystal display panel 1 is generated between the common electrode 5 and the pixel electrode 7. Since the liquid crystal molecules rotate on the same plane along the transverse electric field, gray level inversion due to the refractive anisotropy of the liquid crystal molecules can be prevented.

On the other hand, the IPS mode liquid crystal display device as described above has the following problems.

That is, in the IPS mode liquid crystal display device, since the liquid crystal molecules rotate on the same plane along the transverse electric field, the gray scale inversion due to the refractive anisotropy of the liquid crystal molecules can be prevented, so that the viewing angle characteristics in the vertical direction and the left and right directions are improved. The viewing angle characteristic in the diagonal direction does not improve.

The present invention is to solve the above problems, by using two negative biaxial film and one (+) C plate to change the polarization characteristics of the light transmitted through the liquid crystal display element in the diagonal direction It is an object of the present invention to provide a liquid crystal display device capable of improving viewing angle characteristics.

According to an exemplary embodiment of the present invention, a liquid crystal display device includes a liquid crystal display panel including a liquid crystal layer, first and second polarizing plates positioned at upper and lower portions of the liquid crystal display panel to polarize incident light, and the liquid crystal display panel and the first liquid crystal display panel. A first negative biaxial film provided between the two polarizing plates to change the polarization state of light and having a phase retardation value Re = 30 to 70 nm in the horizontal direction and a retardation value Rth = 100 to 180 nm in the thickness direction, the liquid crystal display panel and the first negative A second negative biaxial film and a first negative second biaxial film having a phase difference value Re = 30 to 70 nm in a horizontal direction and a phase difference value Rth = 100 to 180 nm in a thickness direction provided between the biaxial films to change the polarization state of light. And a positive uniaxial film having a phase difference value Re = nm in the horizontal direction and a phase difference value Rth = -300 to -150nm in the thickness direction.

The liquid crystal display device according to the present invention comprises two negative biaxial films and one (+) C plate between the liquid crystal display panel and the polarizing plate to change the polarization characteristics of the polarized light incident on the liquid crystal display panel. The viewing angle characteristic in the diagonal direction can be improved.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

This is because the light leakage occurs in the diagonal direction of the liquid crystal display device because the viewing angle characteristic is deteriorated in the diagonal viewing angle direction of the liquid crystal display device. As shown in FIG. 2, in a general IPS mode LCD, first and second polarizers 110 and 120 are attached to upper and lower portions of the LCD panel 100 to be input to the LCD panel 100 and output. Linearly polarizes the light.

In the normally black mode, the polarization axes of the first polarizer 110 and the second polarizer 120 attached to the upper and lower substrates are perpendicular to each other. Therefore, the light transmitted through the first polarizing plate 110 is linearly polarized in the X-axis direction and input to the liquid crystal display device. When no signal is applied to the liquid crystal display panel 100, since the liquid crystal molecules 142 of the liquid crystal display panel 100 are arranged in the X-axis direction, light incident to the liquid crystal display panel 100 is X. The liquid crystal display panel 100 passes through the LCD in a linearly polarized state along the axial direction.

The polarization axis of the second polarizing plate 120 located on the upper portion of the liquid crystal display panel 100 is perpendicular to the polarization direction of the light passing through the liquid crystal layer, so that all of the light is absorbed by the polarizing plate of the upper substrate. ) The screen is black because no light is output to the outside.

However, when the liquid crystal display device as described above is viewed in a diagonal direction, the polarization directions of the first polarizing plate 110 and the second polarizing plate 120 are not substantially vertically disposed. That is, when viewed from the front of the liquid crystal display panel 100, the polarization axes of the first polarizing plate 110 and the second polarizing plate 120 are disposed perpendicular to each other, but when viewed in a diagonal direction, the vertical polarization is broken.

3A is a view showing the arrangement of the polarization axes of the first and second polarizing plates when the liquid crystal display device is viewed from the front, that is, in the path of light transmitted perpendicularly to the screen of the liquid crystal display device, and FIG. 3B shows the liquid crystal display device. When viewed diagonally, that is, the polarization axes of the first and second polarizers in the path of light passing through the screen of the liquid crystal display at a constant polar angle and azimuthal angle.

In this case, the dotted line in the drawing is the direction of the polarization axis (ie, the light absorption axis) in the first polarizing plate 110 and the solid line is the direction of the light absorption axis in the second polarizing plate 120.

As shown in FIG. 3A, the polarization axes of the first and second polarizing plates 110 and 120 when the liquid crystal display device is viewed from the front (that is, when light is transmitted perpendicularly to the screen of the liquid crystal display device) are mutually different. It is vertical. In contrast, as illustrated in FIG. 3B, the polarization axes of the first and second polarizing plates 110 and 120 when the liquid crystal display is viewed diagonally (when transmitted at a constant polar angle and azimuth with the screen of the liquid crystal display) It is arranged at a constant angle θ rather than vertical.

As described above, when the liquid crystal display device is viewed in a diagonal direction, since the polarization directions of the first and second polarizing plates 110 and 120 do not become vertical, the polarization directions of the first and second polarizing plates 110 are linearly polarized on the first polarizing plate 110. The transmitted light is not all absorbed by the second polarizer 120, and a part of the light is transmitted through the second polarizer 120. Therefore, even in the normally black state, when the liquid crystal display is viewed diagonally, part of the light leaks, and thus, the black state cannot be maintained.

Therefore, in order to improve the viewing angle characteristic when the liquid crystal display is viewed in a diagonal direction, the light polarized by the first polarizing plate 110 must be absorbed by the second polarizing plate 120. To this end, in the present invention, the optical axis of the light incident on the second polarizing plate 120 is changed by changing the polarization direction of the light passing through the liquid crystal display panel 100 using the compensation film (that is, the light of the second polarizing plate 120). Absorption layer).

Compensation films may be classified into uniaxial films and biaxial films. Uniaxial films are anisotropic birefringent films having only one optical axis and biaxial films are anisotropic birefringent films having two optical axes. Among such compensation films, uniaxial films may be classified into A-compensation film and C-compensation film according to the direction and size of the optical axis.

4A and 4B are diagrams illustrating a positive A-compensation film and a negative compensation film, respectively.

)과 Z축 방향의 굴절율(

)이 서로 동일하고(

=

), X축 방향의 굴절율(

)은 Y축 방향의 굴절율(

) 및 X축 방향의 굴절율(

)과 다른 것을 특징으로 한다.(

≠

=

)As shown in FIGS. 4A and 4B, the A-compensation film has a refractive index in the Y-axis direction (

) And the refractive index in the Z-axis direction (

) Are the same as each other (

=

), Refractive index in the X-axis direction (

) Is the index of refraction in the Y-axis direction (

) And the index of refraction in the X-axis direction (

) And other features.

≠

=

)

)이 Y축 방향의 굴절율(

)보다 크면 포지티브(Positive) A-보상필름이고, X축 방향의 굴절율(

)이 Y축 방향의 굴절율(

) 보다 작으면 네가티브(Negative) A-보상필름이다.As shown in Fig. 4A, the refractive index in the X-axis direction (

) Is the index of refraction in the Y-axis direction (

If larger than), it is a positive A-compensation film and the refractive index in the X-axis direction (

) Is the index of refraction in the Y-axis direction (

Less than), it is a negative A-compensation film.

Each of these positive A-compensation films and negative A-compensation films is defined by Equation 1 as follows.

〉=

〉 =

〈

=

〈

=

)과 Y축 방향의 굴절율(

)이 서로 동일하고(

=

), Z축 방향의 굴절율(

)이 X축 방향의 굴절율(

) 및 Y축 방향의 굴절율(

)과 다른 것을 특징으로 한다.(

≠

=

)5A and 5B are diagrams illustrating a positive C-compensation film and a negative C-compensation film, respectively. As shown in FIGS. 5A and 5B, the C-compensation film has a refractive index in the X-axis direction (

) And the refractive index in the Y-axis direction (

) Are the same as each other (

=

), The refractive index in the Z-axis direction (

) Is the index of refraction in the X-axis direction (

) And the refractive index in the Y-axis direction (

) And other features.

≠

=

)

) 및 Y축 방향의 굴절 율(

)이 Z축 방향의 굴절율(

) 보다 작으면 포지티브 C-보상필름이고, X축 방향의 굴절율(

) 및 Y축 방향의 굴절율(

)이 Z축 방향의 굴절율(

) 보다 크면 네가티브 C-보상필름이다. 이들 포지티브 C-보상필름과 네가티브 C-보상필름 각각을 수학식 2에 의해 정의하면 다음과 같다. As shown in FIG. 5A, the refractive index in the X-axis direction (

) And the index of refraction in the Y-axis direction (

) Is the index of refraction in the Z-axis direction (

Less than), the positive C-compensation film, and the refractive index in the X-axis direction (

) And the refractive index in the Y-axis direction (

) Is the index of refraction in the Z-axis direction (

Greater than), the negative C-compensation film. Each of these positive C-compensation films and negative C-compensation films is defined by Equation 2 as follows.

=〈

= <

=

〉

=

〉

)과, Y축 방향의 굴절율(

) 및 Z축 방향의 굴절율(

)에 의해 결정되는데, 수학식 3에 위상차와 굴절율(

,

,

)의 관계를 나타냈다.In addition, the phase difference by the compensation film is the refractive index of the X-axis direction (

) And the refractive index in the Y-axis direction (

) And the refractive index in the Z-axis direction (

) Is determined by the phase difference and refractive index (

,

,

) Relationship.

=(-)d

= (-) d

=(

-

)d

= (

-

) d

Here, Re is a retardation value in the horizontal direction, Rth is a retardation value in the thickness direction, and d is the thickness of the compensation film.

The A-compensation film and the C-compensation film mainly use cycloolefin polymer film or polycarbonate film, UV curing type horizontal or horizontal alignment liquid crystal film, polystyrene resin, polyethylene terephthalate.

,

,

가 서로 다른 값으로서, 포지티브 이축필름과 네가티브 이축필름 및 Z축 연식 이축필름으로 분류된다. 도 6에 이축필름이 X축 방향의 굴절율(

)과 Y축 방향의 굴절율(

) 및 Z축 방향의 굴절율(

)이 도시되어 있다. Biaxial film

,

,

Are classified as positive biaxial film, negative biaxial film and Z-axis soft biaxial film. 6 shows a biaxial film having a refractive index in the X-axis direction (

) And the refractive index in the Y-axis direction (

) And the refractive index in the Z-axis direction (

) Is shown.

)과 Y축 방향의 굴절율(

) 및 Z축 방향의 굴절율(

)의 크기에 따라 포지티브 이축필름, 네가티브 이축필름 및 Z축 연신 이축필름으로 분류되는데, 이들 포지티브 이축필름, 네가티브 이축필름 및 Z축 연신 이축필름은 각각 다음의 수학시 4에 의해 정의된다. T The biaxial film has a refractive index in the X-axis direction (

) And the refractive index in the Y-axis direction (

) And the refractive index in the Z-axis direction (

The positive biaxial film, the negative biaxial film, and the Z-axis biaxial film are classified according to the size of the bipolar film.

〉〉

〉〉

〉

〉

〉

〉

〉

〉

〉

〉

In addition, the biaxiality (Nz) of the biaxial film is defined as in Equation 5 below.

=/

= /

As defined in Equation 3, Re is a retardation value in the horizontal direction, Rth is a retardation value in the thickness direction, and d represents the thickness of the compensation film.

≥1이고, 포지티브 이축필름은

〈0으로 되며, Z축 연신 이축필름은 0〈

〈1이된다. By the definition of Equations 4 and 5, the negative biaxial film is

≥1, positive biaxial film

<0, Z-oriented stretched biaxial film is 0

<1.

In the present invention, by providing such a compensation film, the phase polarized light in the first polarizing plate (110 in FIG. 2) is phase-converted to make the polarization direction of the light completely perpendicular to the polarization direction of the second polarizing plate (120 in FIG. 2). All the light incident on the second polarizer 120 is absorbed.

The polarization state of the light can be analyzed by the Jones Matrix, which is called the unitary matrix, which represents the polarization transmission characteristics of the transparent medium because the Jones operation ignores the reflection of light at the interface. The matrix can be represented by Poincare shpere.

Since the Jones vector can represent only fully polarized light, the Stokes parameter defined by Equation 6 must be used to express partial polarized light.

및

는 각각 X축 및 Y축 방향으로의 전계성분을 나타낸다. 이때, 이들 네변수 사이에는

≥

+

+

의 부등식이 성립하는데, 이 부등식은 완전 편광에서만 맞는다. 즉, 완전 편광의 경우, S1, S2 및 S3를 빛의 밝기 S0로 나눈 규격화된 변수 s1, s2 및 s3 사이에는 다음의 수학식 7의 관계가 성립한다.Where <> represents the time average,

And

Denotes the electric field component in the X-axis and Y-axis directions, respectively. In this case, between these four variables

≥

+

+

The inequality of is true, which is true only in fully polarized light. That is, in the case of fully polarized light, the relationship of Equation 7 below holds between the standardized variables s1, s2, and s3 obtained by dividing S1, S2, and S3 by the brightness S0 of light.

This is the equation of Poangcare sphere with radius 1 in three-dimensional space, where (s1, s2, s3) is the point of Cartesian coordinates.

In this case, all points on the equator line in the Phuang Karegu correspond to linear polarization, the polar point corresponds to the right-hand circular polarization, and the south pole corresponds to the left-hand circular polarization. And all the points in the northern hemisphere correspond to the right hand ellipse polarization, and all the points in the southern hemisphere correspond to the left hand ellipse polarization.

7A and 7B are diagrams illustrating poang curry vectors corresponding to arbitrary elliptical polarizations in the Cartesian coordinate system, respectively.

As shown in FIGS. 7A and 7B, the latitude angle of the Poangkage vector P corresponding to the elliptically polarized light having an azimuthal angle of Ψ and an ellipse angle of x is 2x and an azimuth angle of the long axis of the polarized ellipse. Is 2Ψ and the Cartesian coordinates are (cons (2Ψ) cons (2x), sin (2Ψ) cos (2x), sin (2x)). If this point is in the northern hemisphere, the direction of rotation of the electric field vector is clockwise; in the southern hemisphere, it is counterclockwise. At this time, the opposite points on the Poangaregu represent polarization states orthogonal to each other.

In addition, the Unity Jones matrix, which describes the change in polarization state when light passes through a transparent medium, can be interpreted as a rotational transformation over the Poangkaregu.

FIG. 8 is a diagram illustrating a Poangaregu showing the polarization states of the first and second polarizers when the IPS mode liquid crystal display is seen from the front as shown in FIG. 3A.

Since the opposite points in the Poangaregu represent polarization states orthogonal to each other, the point A represents the light absorption axis of the first polarizing plate 110 and the light transmission axis of the second polarizing plate 120, and the point B represents the first polarizing plate 110. ) And a light absorption axis of the second polarizing plate 120. As shown in FIG. 8, when the IPS mode liquid crystal display device is viewed from the front, the light transmission axis of the first polarizing plate 110 maintains the same linear polarization state as the light absorption axis of the second polarizing plate 120. This is because the light absorption axis of the first polarizing plate 110 and the light absorption axis of the second polarizing plate 120 are perpendicular to each other when the IPS liquid crystal display device is viewed from the front, and the light transmission axis of the first polarizing plate 110 and the second polarizing plate are vertical. This is because the light absorption axes of the 120 are parallel to each other.

As such, the light transmission axis of the first polarizing plate 110 and the light absorption axis of the second polarizing plate 120 are parallel to each other so that the light transmission axis of the first polarizing plate 110 and the light of the second polarizing plate 120 are in the Pangaregou. Since the absorption axes are located at the same point, the linearly polarized light transmitted through the first polarizing plate 110 is absorbed by the second polarizing plate 120 so that the light is not transmitted to the outside of the second polarizing plate 120. As a result, when the IPS mode liquid crystal display is viewed from the front in the normally black mode, it is possible to maintain a complete black state.

On the other hand, Figure 9 is a view showing a Poangkaregu showing the polarization state of light when the IPS mode liquid crystal display device viewed in a diagonal direction as shown in Figure 3b.

In FIG. 9, the A1 point represents the light absorption axis of the first polarizing plate 110, and the A2 point opposite thereto indicates the light transmission axis of the first polarizing plate 110 orthogonal to the light absorption axis. In addition, point B1 represents the light transmission axis of the second polarizing plate 120 and point B2 represents the light absorption contraction of the second polarizing plate 110.

As shown in FIG. 3B, when the IPS mode LCD is viewed in a diagonal direction, the polarization directions of the first polarizing plate 110 and the second polarizing plate 120 do not form a right angle with each other, but form a predetermined angle θ. The A2 point which is the light transmission axis of the first polarizing plate 110 and the B2 point which is the light absorption axis of the second polarizing plate 120 do not coincide with each other and are spaced apart by x.

The interval of x means an angle between the light transmission axis of the first polarizing plate 110 and the light absorption axis of the second polarizing plate 120, and the light transmission axis of the first polarizing plate 110 and the second polarizing plate 120. As much as the angle corresponding to the angle between the light absorption axis of the () is to pass through the second polarizing plate (120).

Therefore, in order to prevent light leakage in the diagonal direction of the IPS mode liquid crystal display device, the light transmission axis of the first polarizing plate 110 and the light absorption axis of the second polarizing plate 120 are parallel to each other by matching the A2 and B2 points. As a result, the light polarized by the first polarizer 110 must be absorbed by the second polarizer 120.

In the present invention, by changing the polarization state of the linearly polarized light in the first polarizing plate 110 using a compensation film to match the A2 point and the B2 point on the Puangkaregu generated by the light transmitted through the second polarizing plate 120 It is to prevent the light leakage phenomenon.

Hereinafter, specific examples of the present invention will be described. In this case, the polarization state of the liquid crystal display device according to the exemplary embodiment of the present invention will be described using the Poang Curregu. As described above, in the present invention, light leakage in the diagonal direction of the liquid crystal display device can be prevented by changing the polarization state of the light using the biaxial film.

10 is a view showing the structure of a liquid crystal display device according to a first embodiment of the present invention.

As shown in FIG. 10, the liquid crystal display device 201 according to the first exemplary embodiment of the present invention may include a liquid crystal display panel 200 that implements an image and a first surface attached to an upper portion of the liquid crystal display panel 200. The compensation film 221 and the second compensation film 225, the first polarizing plate 210 attached to the lower portion of the liquid crystal display panel 200, and the second polarizing plate attached to the upper portion of the second compensation film 225 ( 220).

Although not shown in detail in the drawing, the liquid crystal display panel 200 includes a liquid crystal layer formed between the first and second substrates and the two substrates. Various electrodes are formed, and the second substrate is formed with a color filter layer for real color and a black matrix for preventing light from leaking into the image non-display area and degrading image quality.

In particular, the liquid crystal display panel 200 of the present invention is an IPS mode liquid crystal display panel. Accordingly, the common electrode and the pixel electrode are disposed parallel to each other on the first substrate to apply an electric field parallel to the surface of the substrate to the liquid crystal layer. In addition, the FFS mode may be used as the liquid crystal display panel of the present invention.

The first polarizer 210 includes a first polarizer 214, a first support 212, and a second support 216. The first polarizer 214 is a film that can convert natural light into any polarized light.

In this case, when the first polarizer 214 divides incident light into two orthogonal polarization components, one polarization component of two polarization components passes and the other polarization component absorbs, reflects or scatters. Having can be used.

Although there is no restriction | limiting in particular as an optical film used for the said 1st polarizing material 214, For example, The polymer film which has polyvinyl alcohol (PVA) type resin containing an iodine or a dichroic dye as a main component, The 0 type polarizer which orientated the liquid crystalline composition containing a dichroic substance and a liquid crystalline compound in the fixed direction, and the E type polarizer which orientated the lytropic liquid crystal in the fixed direction can be used.

The first support 212 is for protecting the first polarizer 214, and is mainly made of a general protection film without phase retardation. Any of these protective films can be used, but mainly uses triacetylcellulose (TAC).

The second support 216 may be formed of a general protective film without phase delay to protect the first polarizer 214, for example, 0-RT (modified TAC in which Rth approaches 0 nm). It may be made of 0-TAC) or COP (Cyclo-olefin-Polymer). For reference, the expression that there is no phase delay means that Re is 0. The TAC is a protective film where Re is 0 and Rth is not 0. The 0-RT is a protective film where Re is 0 and Rth is close to 0. Corresponds to

In addition, the second polarizer 220 includes a second polarizer 227 and a third support 229. Like the first polarizer 214, the second polarizer 227 is made of polyvinyl alcohol-based resin, and the third support 229 uses triacetyl cellulose as a transparent protective film.

,

,

)은

>

>

의 관계를 갖는다.The first compensation film 221 is a negative biaxial compesation film, and the retardation value Re in the horizontal direction of the first compensation film 221 is Re = 30 to 70 nm and the retardation value in the thickness direction ( Rth) is Rth = 100-180 nm. The biaxiality Nz of the biaxial film of the first compensation film 221 is 2.5 <Nz <3.3 by Equation 5. In general, when the biaxiality (Nz) of the biaxial film is Nz> 1, the biaxial film is a negative biaxial film, and the refractive index in the X, Y and Z axis directions (

,

,

)silver

>

>

Has a relationship.

In addition, the second compensation film 225 is a biaxial compensation film, and has the same characteristics as the first compensation film 221.

Accordingly, the first and second compensation films 221 and 225 are negative biaxial films in which the biaxiality Nz of the biaxial film is Nz> 1.

The first and second compensation films 221 and 225 may be UV curable liquid crystal films using nematic liquid crystals, polycarbonates, polyethylene terephthalates, polystyrenes, and uniaxially stretched TACs. stretched TAC), uniaxially stretched PNB (polynorbonene), biaxially stretched PC (polycarbonate), biaxially stretched COP, biaxial LC film, etc. It may have a flat wavelength dispersion characteristic and a reverse wavelength dispersion characteristic.

The C plate 223 is positioned between the first and second compensation films 221 and 225, and the C plate 223 is a positive film. The positive C plate 223 is mainly formed of a UV curable vertically oriented liquid crystal film, a biaxially stretched polymer film, and the like. In this case, the positive C plate 223 has a thickness retardation value Rth = Rth = -300 to -150 nm (Re = 0).

)의 방향은 0°로 배치되고 제2 보상필름(225)의 X축 방향의 굴절율(

)의 방향은 90°의 각도로 배치되며, 액정표시패널(200)의 러빙방향도 90°로 이루어진다.The absorption axis of the first polarizing plate 210 is disposed at an angle of 90 ° and the absorption axis of the second polarizing plate 220 is disposed at an angle of 0 °. In addition, the refractive index of the first compensation film 221 in the X-axis direction (

) Direction is 0 ° and the refractive index of the second compensation film 225 in the X-axis direction (

) Is disposed at an angle of 90 degrees, and the rubbing direction of the liquid crystal display panel 200 is also 90 degrees.

The liquid crystal molecules of the liquid crystal layer of the liquid crystal display panel 200 are disposed along the rubbing direction of the alignment layer in the off state of the liquid crystal display panel 200. Therefore, the optical axis of liquid crystal molecules is also made 90 degrees.

The polarization state of the liquid crystal display according to the first exemplary embodiment of the present invention configured as described above will be described with reference to FIGS. 11 and 12. 11 is a diagram illustrating polarization states in respective configurations of the liquid crystal display of FIG. 10, and FIG. 12 is a diagram illustrating poangaregu representing the polarization states of the liquid crystal display of FIG. 10.

방향은 제1 편광판(210)의 광흡수축 및 액정표시패널(200)의 러빙방향과 수직으로 이루어진다.(즉,

방향이 0°를 형성한다.)As shown in FIG. 11, the first compensation film 221 made of a negative biaxial film is disposed between the liquid crystal display panel 200 and the C plate 223, wherein the first compensation film 221

The direction is perpendicular to the light absorption axis of the first polarizing plate 210 and the rubbing direction of the liquid crystal display panel 200.

Direction forms 0 °.)

In addition, the second polarizing plate 210 is disposed above the liquid crystal display panel 200, where the light absorption axis of the second polarizing plate 210 is perpendicular to the rubbing direction of the liquid crystal display panel 200 (that is, The light absorption axis of the second polarizing plate 210 is formed at an angle of 0 °.)

방향은 액정표시패널(200)의 러빙 방향과는 평행을 이루고 상기 제2 평관판(210)의 광흡수축과 수직을 이룬다.(즉,

방향이 90°를 형성한다)Similarly, the second compensation film 225 made of a negative biaxial film is disposed between the positive C plate 223 and the second polarizing plate 220, wherein the second compensation film 225

The direction is parallel to the rubbing direction of the liquid crystal display panel 200 and perpendicular to the light absorption axis of the second flat plate 210.

Direction forms 90 °)

As shown in FIG. 12, when unpolarized light is incident on the first polarizing plate 210 from the backlight of the liquid crystal display panel 200, the light is linearly polarized. Most of the linearly polarized light is the first polarizing plate 210. The polarization state of the light absorbed by the absorption axis (A1 point) and transmitted through the first polarizing plate 210 is positioned at the A2 point. That is, the transmission axis of the first polarizing plate 210 is located at the point A2.

In this case, the absorption axis of the second polarizing plate 220 is located at the point E and is spaced apart from the transmission axis of the first polarizing plate 210 by a predetermined distance.

When the linearly polarized light is transmitted through the liquid crystal display panel 200, since the alignment layer is rubbed at an angle of 90 °, the polarization state of the liquid crystal display panel 200 becomes a point A2. When the linearly polarized light passes through the first compensation film 221 made of the negative biaxial film, the polarization state is rotated clockwise about the CA2 axis, and the polarization state is moved from the A2 point to the B point.

At this time, the point B is located on the quadrant of the Poang Cure district to maintain the elliptical polarization state.

When the elliptically polarized light is transmitted through the positive C plate 223, the polarization state is increased in the vertical direction about the CB axis so that the polarization state is moved from the B point to the C point.

When the elliptically polarized light is transmitted through the second compensation film 225 made of the negative biaxial film, the light is rotated clockwise around the CB axis so that the polarization state moves from the C point to the D point. The point D is located on the quadrant of the Phuang Kare District to maintain an elliptical polarization state.

As a result, the light transmitted through the second compensation film 225 is changed into linearly polarized light having the same polarization axis as the absorption axis of the second polarizing plate 220, and the polarized light is changed from the second polarizing plate 220. All of them are absorbed so that light does not pass through the second polarizing plate 260.

In other words, the linearly polarized light in the first polarizing plate 210 is changed by the first compensation film 221 whose polarization state (corresponding to point A2) is the negative biaxial film, and then + C plate 223 and the first light. The polarization state of the second compensation film 225 coincides with the point D so that the optical axis of the light incident on the second polarizing plate 220 coincides with the absorption axis of the second polarizing plate 220.

Thus, all the light polarized by the first polarizing plate 210 is absorbed by the second polarizing plate 220 to prevent light leakage in the diagonal direction.

FIG. 13 is a view showing a result of simulating luminance viewing angle characteristics in this normally black mode in the diagonal viewing direction of the liquid crystal display according to the first exemplary embodiment of the present invention.

Here, the first polarizing plate and the second polarizing plate are arranged such that the light transmission axes are perpendicular to each other, and the optical axis of the liquid crystal layer is in a state parallel to the light transmission axis of the first polarizing plate. At this time, FIG. 13 is a contrast ratio of the liquid crystal display including the optical compensation film according to the first embodiment of the present invention at an inclination angle in the range of 0 to 80 ° with respect to all the east angles (or azimuths) when white light is used. This is the result of simulating the characteristic.

The center of the circle is the case where the angle of inclination is 0, and the angle of inclination increases as the radius of the circle increases, and the numerical values along the circumference indicate the east angle.

Looking at the contrast ratio characteristics of the liquid crystal display device according to the first embodiment of the present invention, the light leakage is remarkable at 45 °, 135 °, 225 ° and 315 ° corresponding to the diagonal direction of the liquid crystal display panel in the normally black mode It can be seen that reduced. In the liquid crystal display of the present invention including the first and second compensation films 221 and 225 and the negative C plate 223 which are negative biaxial films, the maximum transmittance Tmax in the diagonal viewing angle direction is Tmax = 0.000215.

At this time, the maximum transmittance (Tmax) in the diagonal viewing angle direction in the liquid crystal display device without any optical compensation film is Tmax = 0.001920.

Accordingly, it can be seen that the transmittance in the diagonal viewing angle direction in the liquid crystal display device according to the first embodiment of the present invention is significantly reduced compared to the conventional liquid crystal display device.

14 is a diagram showing the structure of a liquid crystal display device according to a second embodiment of the present invention.

The liquid crystal display device according to the second embodiment of the present invention differs in that the liquid crystal display device and the negative C plate according to the first embodiment of the present invention are added, and the other structures are the same. Therefore, the same configuration and function as the first embodiment will be briefly described.

As shown in FIG. 14, the liquid crystal display device 301 according to the second exemplary embodiment of the present invention may include a liquid crystal display panel 300 that implements an image and a first surface attached to an upper portion of the liquid crystal display panel 300. The compensation film 321 and the second compensation film 325, the first polarizing plate 310 attached to the lower portion of the liquid crystal display panel 300, and the second polarizing plate attached to the upper portion of the second compensation film 325 ( 320).

The first polarizer 310 is composed of a first polarizer 314, a first support 312 and a negative C plate 318. The first polarizer 314 is a film capable of converting natural light into any polarized light.

In this case, when the first polarizer 314 divides the incident light into two orthogonal polarization components, one polarization component of the two polarization components passes and the other polarization component absorbs, reflects, or scatters. Having can be used.

The first support 312 is for protecting the first polarizer 314, and is mainly made of a general protection film without phase retardation. Any of these protective films can be used, but mainly uses triacetylcellulose (TAC).

The negative C plate 318 may be made of a general protective film without phase delay in order to protect the first polarizer 214, and may be replaced with triacetyl cellulose (TAC). For reference, the expression that there is no phase delay means that Re is zero. The retardation value Re in the horizontal direction of the negative C plate 318 is Re = 0, and the retardation value Rth in the thickness direction is Rth = 20 to 150 nm.

In addition, the second polarizer 320 includes a second polarizer 327 and a second support 329. Like the first polarizer 314, the second polarizer 327 is made of polyvinyl alcohol-based resin, and the second support 329 uses triacetyl cellulose (TAC) as a transparent protective film.

,

,

)은

>

>

의 관계를 갖는다.The first compensation film 321 is a negative biaxial compesation film, and the retardation value Re in the horizontal direction of the first compensation film 321 is Re = 30 to 70 nm and the retardation value in the thickness direction ( Rth) is Rth = 100-180 nm. The biaxiality Nz of the biaxial film of the first compensation film 321 is 2.5 <Nz <3.3 by Equation 5. In general, when the biaxiality (Nz) of the biaxial film is Nz> 1, the biaxial film is a negative biaxial film, and the refractive index in the X, Y and Z axis directions (

,

,

)silver

>

>

Has a relationship.

In addition, the second compensation film 325 is a biaxial compensation film, and has the same characteristics as the first compensation film 321.

Accordingly, the first and second compensation films 321 and 325 are negative biaxial films in which the biaxiality Nz of the biaxial film is Nz> 1.

A positive C plate 323 is positioned between the first and second compensation films 321 and 325, and the C plate 323 is a positive film. The positive C plate 323 is mainly formed of a UV curable vertically oriented liquid crystal film, a biaxially stretched polymer film, and the like. In this case, the positive C plate 323 has a phase difference value Rth in the thickness direction of Rth = −300˜. -150 nm (Re = 0).

)의 방향은 0°로 배치되고 제2 보상필름(325)의 X축 방향의 굴절율(

)의 방향은 90°의 각도로 배치되며, 액정표시패널(300)의 러빙방향도 90°로 이루어진다.The absorption axis of the first polarizing plate 310 is disposed at an angle of 90 ° and the absorption axis of the second polarizing plate 320 is disposed at an angle of 0 °. In addition, the refractive index of the first compensation film 321 in the X-axis direction (

) Direction is 0 ° and the refractive index of the second compensation film 325 in the X-axis direction (

) Is disposed at an angle of 90 degrees, and the rubbing direction of the liquid crystal display panel 300 is also 90 degrees.

The liquid crystal molecules of the liquid crystal layer of the liquid crystal display panel 300 are disposed along the rubbing direction of the alignment layer in the off state of the liquid crystal display panel 300. Therefore, the optical axis of liquid crystal molecules is also made 90 degrees.

FIG. 15 is a view showing polarization states in respective configurations in the liquid crystal display of FIG. 14.

방향은 제1 편광판(310)의 광흡수축 및 액정표시패널(300)의 러빙방향과 수직으로 이루어진다.(즉,

방향이 0°를 형성한다.)As shown in FIG. 14 and FIG. 15, the first compensation film 321 made of the negative biaxial film is disposed between the liquid crystal display panel 300 and the positive C plate 323, wherein the first compensation film ( 321)

The direction is perpendicular to the light absorption axis of the first polarizing plate 310 and the rubbing direction of the liquid crystal display panel 300.

Direction forms 0 °.)

In addition, the second polarizing plate 320 is disposed above the liquid crystal display panel 300, wherein the light absorption axis of the second polarizing plate 320 is perpendicular to the rubbing direction of the liquid crystal display panel 300 (that is, The light absorption axis of the second polarizing plate 320 is formed at an angle of 0 °.)

방향은 액정표시패널(300)의 러빙 방향과는 평행을 이루고 상기 제2 평관판(320)의 광흡수축과 수직을 이룬다.(즉,

방향이 90°를 형성한다)Similarly, the second compensation film 325 made of a negative biaxial film is disposed between the positive C plate 323 and the second polarizing plate 320, wherein the second compensation film 325

The direction is parallel to the rubbing direction of the liquid crystal display panel 300 and perpendicular to the light absorption axis of the second flat plate 320.

Direction forms 90 °)

In the liquid crystal display according to the second exemplary embodiment of the present invention, as shown in FIG. 12, the linearly polarized light in the first polarizing plate 310 has a positive C plate 318 having a polarization state (corresponding to the point A2). And after the change is made by the first compensation film 321 which is the negative biaxial film, the polarization state is coincided with the point D by the positive C plate 323 and the second compensation film 325. The optical axis of the light incident to 320 is coincident with the absorption axis of the second polarizing plate 320.

Therefore, all the light polarized by the first polarizing plate 310 is absorbed by the second polarizing plate 320 to prevent light leakage in the diagonal direction.

FIG. 16 is a view showing a result of simulating luminance viewing angle characteristics in this normally black mode in the diagonal viewing direction of the liquid crystal display according to the second exemplary embodiment of the present invention.

Looking at the contrast ratio characteristics of the liquid crystal display device according to the second embodiment of the present invention, the light leakage is remarkable at 45 °, 135 °, 225 ° and 315 ° corresponding to the diagonal direction of the liquid crystal display panel in the normally black mode It can be seen that reduced. In the liquid crystal display of the present invention including the negative C plate 318, the first and second compensation films 321 and 325 which are negative biaxial films, and the positive C plate 323, the maximum in the diagonal viewing angle direction. The transmittance Tmax is Tmax = 0.00032.

At this time, the maximum transmittance (Tmax) in the diagonal viewing angle direction in the liquid crystal display device without any optical compensation film is Tmax = 0.001920.

Accordingly, it can be seen that the transmittance in the diagonal viewing angle direction in the liquid crystal display device according to the second embodiment of the present invention is significantly reduced compared to the conventional liquid crystal display device.

As described above, the liquid crystal display according to the exemplary embodiment of the present invention includes two negative biaxial films and one positive C plate between the liquid crystal display panel and the polarizing plate to polarize the polarized light incident on the liquid crystal display panel. By changing the characteristic, the viewing angle characteristic in the diagonal direction can be improved.

Although the present invention has been described with reference to the embodiments illustrated in the drawings, this is merely exemplary, and it will be understood by those skilled in the art that various modifications and equivalent other embodiments are possible. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

1 is a view showing the structure of a general IPS mode liquid crystal display device.

Figure 2 is a simplified perspective exploded view showing the structure of a conventional liquid crystal display device.

Fig. 3A is a diagram showing an absorption axis of a vertical polarizer when the liquid crystal display device is viewed from the front.

3B is a view showing absorption axes of vertical polarizers when the liquid crystal display device is viewed in a diagonal direction.

4A and 4B are graphs showing the refractive index relationship in the X, Y, and Z axis directions of an A plate.

5A and 5B are graphs showing the refractive index relationship in the X, Y, and X axis directions of a C plate.

6 is a view showing a refractive index relationship in the X, Y, Z-axis direction of the biaxial compensation film.

7A and 7B are diagrams illustrating elliptical polarizations of light and corresponding Poang Curry vectors, respectively.

Fig. 8 is a diagram showing the polarization state of light in the Puangkaregu when the liquid crystal display is seen from the front.

Fig. 9 is a diagram showing the polarization state of light in the Puangkaregu when the liquid crystal display element is viewed from a diagonal direction.

10 is a view showing the structure of a liquid crystal display device according to a first embodiment of the present invention;

11 is a view showing an optical axis of the liquid crystal display device according to the first embodiment of the present invention.

FIG. 12 is a view showing a Poang Karregu indicating a polarization state of light in the liquid crystal display according to the first embodiment of the present invention; FIG.

FIG. 13 is a view showing luminance viewing angle characteristics when the liquid crystal display device according to the first embodiment of the present invention is viewed from a diagonal direction. FIG.

14 is a view showing the structure of a liquid crystal display device according to a second embodiment of the present invention.

15 is a view showing an optical axis of a liquid crystal display device according to a second embodiment of the present invention.

16 is a view showing luminance viewing angle characteristics when the liquid crystal display device according to the second exemplary embodiment of the present invention is viewed in a diagonal direction.

Claims (10)

A liquid crystal display panel including a liquid crystal layer; First and second polarizing plates positioned on upper and lower portions of the liquid crystal display panel to polarize incident light; A first negative biaxial film provided between the liquid crystal display panel and the second polarizing plate to change the polarization state of light, and having a phase difference value Re = 30 to 70 nm in a horizontal direction and a phase difference value Rth = 100 to 180 nm in a thickness direction; A second negative biaxial film provided between the liquid crystal display panel and the first negative biaxial film to change a polarization state of light, and having a phase retardation value Re = 30 to 70 nm in a horizontal direction and a retardation value Rth = 100 to 180 nm in a thickness direction; And And a positive uniaxial film provided between the first and second negative biaxial films and having a phase retardation value Re = nm in a horizontal direction and a retardation value Rth = -300 to -150 nm in a thickness direction. The method according to claim 1, The refractive index of the first negative biaxial film in the X-axis direction (

) Is disposed at 90 °, and the refractive index (X) of the second negative biaxial film

) Is in the direction of 0 ° liquid crystal display device. The method according to claim 1, The absorption axis of the first polarizing plate is disposed at an angle of 90 ° and the absorption axis of the second polarizing plate is disposed at an angle of 0 ° so that the absorption axes of the first and second polarizing plates are perpendicular to each other. The method according to claim 1, And a rubbing direction of the liquid crystal layer of the liquid crystal display panel is 90 degrees. The method according to claim 1, The first polarizer comprises a first polarizer and first and second supports attached to upper and lower portions of the first polarizer. 6. The method of claim 5, The first support attached to the upper portion of the first polarizer is a liquid crystal display device, characterized in that made of triacetyl cellulose with no phase delay. 6. The method of claim 5, The first support is a liquid crystal display device comprising a negative C plate having a phase retardation value Re in a horizontal direction of 0 and a thickness retardation value Rth in a thickness direction of 20 to 150 nm. The method according to claim 1, And the first negative biaxial film is parallel with the light absorption axis of the first polarizing plate, and the second negative biaxial film is parallel with the light absorption axis of the second polarizing plate. The method according to claim 1, The first and second negative biaxial films may include UV curable liquid crystal films, polycarbonates, polyethylene terephthalates, polystyrenes, uniaxially stretched TACs, and uniaxially stretched PNBs. Polynorbonene), biaxially stretched PC (Polycarbonate), biaxially stretched COP, a biaxial LC film (Biaxial LC film) is a liquid crystal display device comprising a material selected from the group consisting of. The method according to claim 1, The liquid crystal display panel may be an IPS (In Pkane Switching) mode liquid crystal display panel or a FFS (Fringe Field Switching) mode liquid crystal display panel.

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