KR20100069964A - Liquid crystal display device using vertical field including optical retardation film - Google Patents

Abstract

The present invention relates to a vertical field type liquid crystal display device, and more particularly, to a liquid crystal display device including an optical compensation polarizing plate including an optical compensation film.

A feature of the present invention is an optical compensation polarizer of a vertical field type liquid crystal display device, wherein the optical compensation polarizer includes a composite compensation film composed of a negative biaxial film and a reactive mesogen layer. It is.

As a result, it is possible to reduce the diagonal light leakage of the panel in a high contrast ratio, a wide viewing angle, and a black state, compared with compensating for the residual phase delay value of the liquid crystal layer using a conventional WV-TAC film.

Therefore, color inversion according to the viewing angle can be improved, thereby improving optical characteristics of the optical compensation polarizing plate, and in particular, it is possible to reduce the volume and weight of the total polarizing plate in comparison with the conventional.

Description

Liquid crystal display device using vertical field including optical retardation film

The present invention relates to a vertical field type liquid crystal display device, and more particularly, to a liquid crystal display device including an optical compensation polarizing plate including an optical compensation film.

Cathode ray tube (CRT), one of the widely used display devices, has been mainly used for monitors such as TVs, measuring devices, information terminal devices, etc., but due to the large weight and size of CRT itself, It could not respond actively to the demand for weight reduction.

In order to replace the CRT, a liquid crystal display device having advantages of small size and light weight has been actively developed. Recently, the liquid crystal display device has been developed enough to perform a role as a flat panel display device, and its demand is gradually increasing.

The image realization principle of the liquid crystal display device uses the optical anisotropy and polarization property of the liquid crystal. The liquid crystal has a thin and long molecular structure and polarization in which the direction of the molecular array changes depending on its size when placed in an electric field and an anisotropy having an orientation in the array. It has a nature. The liquid crystal display is an essential component of a liquid crystal panel composed of a pair of transparent insulating substrates, each having a liquid crystal layer interposed therebetween, and having a field generating electrode formed therebetween. Various images are displayed by artificially adjusting the arrangement direction of the molecules and using the light transmittance which is changed at this time.

At this time, a polarizing plate for visualizing the liquid crystal alignment change of the liquid crystal display device is positioned on the upper and lower portions of the liquid crystal panel. The polarizing plate transmits light having a polarization component coinciding with the transmission axis. The degree of transmission of light is determined by the arrangement characteristics of the liquid crystals.

1 is a view schematically showing a general vertical field type liquid crystal display including a compensation film.

As shown in the figure, the liquid crystal display includes a first and second substrates 1 and 3 facing each other, a liquid crystal layer 5 filled between the two substrates, and a lower portion of each of the first and second substrates 1 and 3; It consists of the first and second polarizing plates 20, 30 formed on the top.

Herein, the transmission axes of the first and second polarizers 20 and 30 are disposed perpendicular to each other, and the first and second polarizers 20 and 30 respectively have a polarization layer 21 having a polarization axis for changing the polarization characteristics of light. , And first and second TAC films (23a, 23b, 33a, 33b) formed on both sides of the polarization layers 21 and 31 to protect and support the polarization layers 21 and 31. It consists of.

On the other hand, such a vertical field type liquid crystal display device has a disadvantage in that the viewing angle characteristics such as color inversion or image distortion are poor when viewed from an oblique angle from the front side with respect to the front side.

Accordingly, the first TAC films 23a and 33a adjacent to the liquid crystal panel 10 of the first and second polarizers 20 and 30 have a negative uniaxial property, that is, a negative C-plate ( plate), and compensates for the phase change of the light inside the liquid crystal layer (5).

However, the retardation value of the first TAC films 23a, 23b, 33a, and 33b of the first and second polarizing plates 20 and 30 is very low compared to a general compensation film (not shown). It will not function enough to compensate.

Therefore, in recent years, a separate compensation film (not shown) should be further used to improve the narrow viewing angle problem.

The compensation film (not shown) is to use a biaxial film (biaxial film), this biaxial film is the inner side of the first and second polarizing layers (21, 31) of the first and second polarizing plates (20, 30). It is common to use WV (wide view)-TAC film (not shown) in which a discotic liquid crystal layer in which discotic liquid crystal molecules are arranged in a hybrid form on a TAC film is used. to be.

However, the discotic liquid crystal molecules of WV-TAC film (not shown) have poor thermal stability due to low phase transition temperature (Tg), and WV-TAC film (not shown) when exposed to high temperature generated when driving the liquid crystal display device for a long time. The orientation direction of the discotic liquid crystal molecules of) is deformed, thereby causing light leakage by accompanied by a change in refractive index.

In particular, due to the expensive discotic liquid crystal molecules, the manufacturing cost of the compensation film (not shown) is improved, which causes the overall manufacturing cost of the liquid crystal display device to be improved.

The first TAC films 23a and 33a have a thickness of about 80 μm due to the limitation of the phase difference value, and the total thickness of the compensation film (not shown) including the WV-TAC film (not shown) is about 90 μm. Has

This causes a problem of increasing the total volume and weight of the liquid crystal display.

The present invention is to solve the above problems, the first object is to reduce the volume and weight while improving the optical properties of the optical compensation polarizing plate.

In addition, the second object is to reduce the manufacturing cost.

In order to achieve the above object, the present invention provides a liquid crystal panel comprising a first and a second substrate; Located on each of the outer surfaces of the first and second substrates, respectively, sequentially made of a reactive mesogen layer, a negative biaxial film, a polarizing layer and a tri-acetatecellulose (TAC) film And a first optical compensation polarizing plate, wherein the reactive mesogen layer provides a vertical field type liquid crystal display device having a pretilt angle of the liquid crystal molecules in a range of 10 to 85 °.

The negative biaxial film satisfies the refractive index of n _x > n _y > n _z (n _x , n _y is the refractive index in the XY direction of the plane, n _z is the refractive index in the normal direction) , The phase retardation value (R _in = (n _x -n _y ) × d) _{in the} plane ranges from 130 to 250 nm, and the phase retardation value (R _th = (n _z- n _y ) × d) in the thickness direction is − It is in the range of 60-120 nm, and said negative biaxial film has an optical axis extended in the transverse direction (TD direction, cross MD direction).

In this case, the negative biaxial film includes polyether sulfone (PES) or cycloolefin polymer (COP), and the reactive mesogen layer is the same as the polarization axis of the polarization layer. Direction-oriented films are included.

The retardation (Δnd) of the reactive mesogen layer is in the range of 90 to 120 nm, and the retardation (Δnd) at the polar angle of the reactive mesogen layer is in the range of 10 to 130 nm.

In this case, the reactive mesogen layer is a material in which a dopant is determined to determine a twist angle between the ultraviolet curable liquid crystal and the ultraviolet curable liquid crystal.

As described above, in the optical compensation polarizer of the vertical field type liquid crystal display device, the optical compensation polarizer includes a composite compensation film composed of a negative biaxial film and a reactive mesogen layer. By using the conventional WV-TAC film, it is possible to reduce the diagonal light leakage of the panel in a high contrast ratio, wide viewing angle, and black state, compared to compensating for the residual phase delay value of the liquid crystal layer. .

Therefore, color inversion according to the viewing angle can be improved, and the optical characteristics of the optical compensation polarizing plate can be improved.

In particular, there is an effect that can reduce the volume and weight of the total optical compensation polarizer compared to the conventional.

In addition, there is an effect that can reduce the process cost.

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

2A to 2B are schematic diagrams for examining the characteristics of light passing through the liquid crystal panel according to the exemplary embodiment of the present invention.

As illustrated, the liquid crystal display device includes a liquid crystal panel 10 and a backlight 20 for supplying light from a rear surface thereof, and the liquid crystal panel 10 includes a first surface facing the liquid crystal layer 6. And first and second polarizers 12 and 14 attached to the second substrates 2 and 4 and outer surfaces of the first and second substrates 2 and 4, respectively.

At this time, the inner surface of the first substrate 2 is provided with a plurality of pixels having a transparent pixel electrode and a thin film transistor for controlling the liquid crystal driving voltage delivered to each of the pixel electrodes, the second substrate 4 The inner surface is provided with a color filter and a common electrode for color implementation.

In addition, the liquid crystal layer 6 interposed between the two substrates 2 and 4 is a TN mode, and in the voltage off state, the long axis direction of the molecules is kept in parallel with the two substrates 2 and 4. The alignment state twisted at an azimuth angle of 90 degrees from the first substrate 2 to the second substrate 4 is shown, and the polarization axes of the first and second polarizing plates 12 and 14 are perpendicular to each other.

The backlight 20 supplies scattered light close to natural light to the liquid crystal panel 10.

Therefore, when the voltage as shown in FIG. 2A is in an off state, the scattered light emitted from the backlight 20 is transmitted by the first polarizing plate 12 to transmit only linearly polarized light parallel to its polarization axis and absorb the rest, and the liquid crystal layer 6 While passing through), it is rotated by 90 ° along its azimuth angle, thereby passing through the second polarizing plate 14 to display white.

Next, when the voltage as shown in FIG. 2B is turned on, the long axes of the liquid crystal molecules are vertically arranged with respect to the two substrates 2 and 4 to lose optical rotatory power of 90 °. Linearly polarized light transmitted through the polarizing plate 12 is blocked by the second polarizing plate 14 to display black.

On the other hand, the liquid crystal display of the present invention is characterized in that the viewing angle characteristics are improved by the optical compensation polarizing plate including the optical compensation film, and the volume and weight of the optical compensation polarizing plate are reduced compared to the conventional ones. I'll see.

3 is a view schematically illustrating a vertical field type liquid crystal display device including an optical compensation polarizing plate and an optical compensation polarizing plate according to an exemplary embodiment of the present invention.

As illustrated, the first optical compensation polarizer 120 is positioned below the liquid crystal panel 110, and the second optical compensation polarizer 130 is positioned above the liquid crystal panel 110.

Although not shown, the liquid crystal panel 110 may include a liquid crystal layer 105 positioned between the lower first substrate 101, the upper second substrate 103, and the first and second substrates 101 and 103. Include. In the liquid crystal panel 110, a thin film transistor and a pixel electrode are formed on an inner surface of the first substrate 101, and a black matrix, a color filter layer, and a common electrode are formed on an inner surface of the second substrate 103. Formed. In addition, an overcoat layer covering the black matrix and the color filter layer may be formed on the inner surface of the second substrate 103.

In this case, the transmission axes of the first and second optical compensation polarizers 120 and 130 are disposed perpendicular to each other, and the first and second optical compensation polarizers 120 and 130 have polarization axes for changing the polarization characteristics of light, respectively. First and second polarizing layers 121 and 131, first and second TAC films tri-acetatecellulose films 123 and 133 formed on one side of the first and second polarizing layers 121 and 131, and And first and second composite compensation films 129 and 139 formed on the other side of the first and second polarizing layers 121 and 131 on which the first and second TAC films 123 and 133 are formed.

Looking at each of them in more detail, the transmission axis is formed in one direction perpendicular to each other, the first and second polarization layers 121, 131 has a characteristic that only light of a component parallel to the transmission axis is transmitted. This property is made possible by stretching polyvinyl alcohol (polyvinylalcohol: PVA) absorbing iodine, which is a polarizer, with strong tension.

The first and second TAC films 123 and 133 are formed on each side of the first and second polarizing layers 121 and 131, and are made of tri-acetatecellulose, and thus the first and second polarizing layers. While supporting and protecting (121, 131), and serves to maintain the stretched state of the first and second polarizing layers (121, 131).

The first and second composite compensation films 129 and 139 are formed on the other side of the first and second polarizing layers 121 and 131 opposite to the first and second TAC films 123 and 133. It consists of first and second negative biaxial films 125 and 135 and first and second reactive mesogen layers 127 and 137.

In this case, the first and second reactive mesogen layers 127 and 137 are positioned adjacent to the liquid crystal panel 110.

Here, the first and second polarization layers 121 and 131 are positioned between the first and second TAC films 123 and 133 and the first and second composite compensation films 129 and 139, respectively. It is protected and supported by the TAC films 123 and 133 and the first and second composite compensation films 129 and 139.

In addition, the first and second optical compensation polarizers 120 and 130 may be attached to one side of the first and second reactive mesogen layers 127 and 137 of the first and second composite compensation films 129 and 139. The adhesive layer (not shown) may include a pressure sensitive adhesive for attaching the first and second optical compensation polarizers 120 and 130 to the first and second substrates 101 and 103. : PSA).

Further, a surface treatment layer (not shown) is further included on one side of the second TAC film 133 of the second optical compensation polarizing plate 130, and the surface treatment layer (not shown) is silica beads (not shown). It may be an anti-glare layer, or a hard coating layer for preventing damage to the surface of the polarizing plate 130, a sticking prevention layer for preventing adhesion to the adjacent layer.

In this case, a lower protective layer (not shown) may be included below the adhesive layers (not shown) of the first and second optical compensation polarizing plates 120 and 130, which are detachable in the attaching process of the polarizing plates 120 and 130. It exposes the adhesive layer (not shown), and serves to protect the adhesive layer (not shown) from being contaminated in the process of transportation and transport.

In this case, the first and second TAC films 123 and 133 may have a phase difference. In this case, the first and second TAC films 123 and 133 may have optical characteristics of a negative C-plate as in the prior art.

As such, the first and second optical compensation polarizers 120 and 130 of the present invention may simultaneously function as a protective film for protecting the first and second polarization layers 121 and 131 and a function of the optical compensation film. By including the optical films 129 and 139, the thickness is reduced.

That is, in the present invention, the conventional polarizing plates 20 and 30 of FIG. 1 have a thickness of 80 μm on both sides of the polarizing layers 21 and 31 of FIG. 21 to protect the polarizing layers 21 and 31 of FIG. 21. By having the 1st and 2nd TAC films (23a, 23b, 33a, 33b of FIG. 21) which have, TAC films (23a, 23b, 33a, 33b of FIG. 21) in one polarizing plate (20, 30 of FIG. This thickness is at least 160 µm.

Accordingly, the present invention includes the TAC films 123 and 133 only on one side of the polarizing layers 121 and 131, and the optical optical films 129 and 139 capable of performing optical compensation functions on the other side of the polarizing layers 121 and 131. ), The thickness of the TAC films 123 and 133 in the one polarizing plate (120, 130) is only about 80㎛, the overall thickness of the polarizing plate (120, 130) is reduced by at least 80㎛ or more compared to the conventional You can see the effect.

In particular, the present invention, although the total thickness of the polarizing plate (120, 130) is reduced compared to the conventional, the optical compensation polarizing plate (120, 130) of the present invention has a high contrast ratio and wider than the conventional compensation film (not shown) The field of view and light leakage in the black display state can be reduced. Let's take a closer look at this.

Negative biaxial films 125 and 135 have refractive indices of n _x , n _y , n _z according to the spatial coordinate system, and the relation thereof has a relationship of n _x > n _y > n _z .

The refractive indices n _x , n _y are the refractive indices in the XY direction of the plane of the negative biaxial films 125 and 135, and n _z is the refractive index in the normal direction of the negative biaxial films 125 and 135. .

Thus, the negative biaxial films 125 and 135 have a function of refracting incident light according to the refractive index.

The negative biaxial films 125 and 135 defined as described above may be represented by a plane phase retardation value R _in and a retardation value R _{th in the} thickness direction represented by Equations 1 and 2 below.

R _in = (n _x -n _y ) × d ....

(Where d is the thickness of a negative biaxial film)

R _th = (n _{z -} n _y ) × d ....

(Where d is the thickness of a negative biaxial film)

Here, R _{in, which} is a phase retardation value of the negative biaxial films 125 and 135 calculated by Equation 1, has a value between 50 and 300 nm, and is calculated by Equation 2 The thickness direction retardation value R _th of the negative biaxial films 125 and 135 exists between -20 and -200 nm.

Accordingly, the negative biaxial films 125 and 135 satisfy the refractive index condition of n _x > n _y > n _z , and thus the negative biaxial films 125 and 135. It is preferable that the phase retardation value on the surface has a value of 130 to 250 nm, and the thickness retardation value of the thickness direction is preferably -60 to -120 nm.

These negative biaxial films 125 and 135 include polyether sulfones (PES) or cycloolefin polymers (COP), and PES and COPs are reliable at high temperature and high humidity. It is excellent in this and has the characteristics which can be produced by a melting method.

In this case, the negative biaxial films 125 and 135 may be stretched in the transverse direction (TD direction, cross MD direction) to form an optical axis in this direction.

As a result, the negative biaxial films 125 and 135 may be formed of the polarizing layers 121 and 131 having the absorption axis in the longitudinal direction (MD direction and machine direction) during the manufacturing process of the polarizing plates 120 and 130. When laminating both films in a roll-to-roll state in the longitudinal direction, the optical axis and polarization layers 121 and 131 of the negative biaxial films 125 and 135 are laminated. The absorption axis of) becomes orthogonal.

Therefore, the rolls, which are continuous processes, are formed on the polarizing plates 120 and 130 on which the negative biaxial films 125 and 135 and the polarizing layers 121 and 131 formed through separate rolls are formed. The integrated optical compensation polarizers 120 and 130 may be manufactured by laminating by a roll-to roll lamination process.

The first and second reactive mesogen layers 127 and 137 may determine the alignment direction of the liquid crystal molecules in contact with the alignment layer (not shown) according to the surface conditions of the alignment layer (not shown) on which the coating is performed. And the second reactive mesogen layers 127 and 137 are oriented in the same direction as the polarization axes of the polarizing layers 121 and 131.

That is, the retardation (Δnd) of the first and second reactive mesogenic layers 127 and 137 corresponds to the product of the thickness d of the liquid crystal layer and the refractive index anisotropy (Δn) of the liquid crystal molecules forming the liquid crystal layer. It can be expressed as a value.

Here, the first and second reactive mesogenic layers 127 and 137 of the present invention are oriented in the same direction as the polarization axis of the polarizing layers 121 and 131, thereby reducing the first and second reactive mesogenic layers 127 and 137. More preferably, the pretilt angle of the liquid crystal molecules is designed to be in the range of 10 to 85 degrees so as to have a range of 0 to 90 degrees.

Accordingly, the first and second reactive mesogenic layers 127 and 137 may determine phase difference values of the first and second reactive mesogenic layers 127 and 137 according to the thickness of the liquid crystal layer in which the liquid crystal molecules actually move.

The retardation values of the first and second reactive mesogen layers 127 and 137 of the present invention have a value within 70 to 150 nm, preferably 90 to 120 nm.

In addition, the first and second reactive mesogen layers 127 and 137 have a specific phase difference value at a polar angle (−50 to 50 °) in a 45 ° viewing angle direction with respect to the liquid crystal alignment direction. It has a value of 5 ~ 200nm, preferably to a value of 10 ~ 130nm.

The first and second reactive mesogenic layers 127 and 137 may be aligned in a predetermined direction on a negative biaxial film 125 and 135 extending in the transverse direction (TD direction). After forming a coating), after coating a dopant congested material that determines the twist angle of the ultraviolet (UV) cured liquid crystal and the ultraviolet cured liquid crystal used as the reactive mesogen material on the alignment film (not shown), It forms by hardening.

The liquid crystal molecules of the first and second reactive mesogenic layers 127 and 137 have high thermal stability due to the high phase transition temperature Tg.

Therefore, the optically compensated polarizing plates 120 and 130 of the present invention have a discotic liquid crystal molecule of WV-TAC film (not shown) which is inferior in thermal stability due to the conventional low phase transition temperature (Tg). The orientation direction of the molecules is deformed, and thus the problem of generating light leakage can be prevented by being accompanied by a change in refractive index.

In particular, the first and second reactive mesogen layers (127, 137) are cheaper than the discotic liquid crystal molecules of the conventional WV-TAC film (not shown), thus manufacturing costs compared to the compensation film (not shown) In this case, the overall manufacturing cost of the liquid crystal display device can be reduced.

4A to 4B illustrate contrast ratios and viewing angle characteristics of a liquid crystal display device having a compensation film including a conventional WV-TAC film and a liquid crystal display device having a composite compensation film according to the present invention. It is a graph.

Referring to the graph, it can be seen that the contrast ratio of the liquid crystal display device having the composite compensation film of the present invention of FIG. 4B is higher than that of the liquid crystal display device having the compensation film including the WV-TAC film of FIG. 4A. have.

In particular, it can be seen that the liquid crystal display device with the composite compensation film of the present invention has a high contrast ratio and secures a wide viewing angle in all directions, compared with the conventional WV-TAC film.

In addition, the result of measuring the contrast characteristic of a black state is shown to FIGS. 5A-5B.

Here, FIG. 5A is a result of measuring in a black display state when the residual phase delay value of the liquid crystal layer is compensated using a conventional WV-TAC film, and FIG. 5B is a composite compensation film according to an embodiment of the present invention. This is the result of measurement in the black display state when the residual phase delay value of the liquid crystal layer is compensated.

As shown in the figure, the luminance is reduced in the black display state, and the diagonal light leakage of the panel can be seen to be markedly reduced compared to when using the conventional WV-TAC film.

As described above, the optically compensated polarizing plate includes a composite compensation film composed of a negative biaxial film and a reactive mesogen layer, thereby using a conventional WV-TAC film. Compared to compensating for the residual phase delay value of, it is possible to reduce the diagonal light leakage of the panel in a high contrast ratio, a wide viewing angle, and a black state.

Therefore, color inversion according to the viewing angle can be improved, thereby improving optical characteristics of the optical compensation polarizing plate, and in particular, it is possible to reduce the volume and weight of the total polarizing plate in comparison with the conventional.

However, the present invention can reduce the total volume and weight occupied by the compensation film in the liquid crystal display as compared to the case of using a conventional TAC film.

The present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention.

1 is a view schematically showing a general vertical field type liquid crystal display having a compensation film.

2a to 2b are schematic views for examining the characteristics of the light passing through the liquid crystal panel according to an embodiment of the present invention.

3 is a schematic view of a vertical field type liquid crystal display device including a polarizing plate and an optical compensation film according to a first embodiment of the present invention.

4A to 4B illustrate contrast ratios and viewing angle characteristics of a liquid crystal display device having a compensation film including a conventional WV-TAC film and a liquid crystal display device having a composite compensation film according to the present invention. graph.

5A to 5B show the results of measuring contrast characteristics in a dark state.

Claims (8)

A liquid crystal panel comprising first and second substrates; Located on each outer surface of the first and second substrates, respectively, sequentially made of a reactive mesogen layer, a negative biaxial film, a polarizing layer and a tri-acetatecellulose (TAC) film First and second optical compensation polarizers And a reactive mesogen layer comprising a liquid crystal molecule having a pretilt angle of 10 to 85 °. The method of claim 1, The negative biaxial film satisfies the refractive index condition of nx>ny> nz (n _x , n _y is the refractive index in the XY direction of the plane, n _z is the refractive index in the normal direction), The phase delay value (R _in = (n _x -n _y ) × d) is in the range of 130 to 250 nm, and the phase delay value (R _th = (n _z- n _y ) × d) in the thickness direction is -60 to- Vertical field type liquid crystal display device in the range of 120nm. The method of claim 2, The negative biaxial film is a vertical field type liquid crystal display device having an optical axis stretched in the transverse direction (TD direction, cross MD direction). The method of claim 2, The negative biaxial film includes a polyether sulfone (PES) or a cycloolefin polymer (COP). The method of claim 1, And the reactive mesogen layer comprises an alignment layer oriented in the same direction as the polarization axis of the polarization layer. The method of claim 5, Retardation (Δnd) of the reactive mesogen layer is a vertical field type liquid crystal display device in the range of 90 to 120nm. The method of claim 5, And a retardation (Δnd) at a polar angle of the reactive mesogen layer is in a range of 10 to 130 nm. The method of claim 5, The reactive mesogen layer is a vertical field type liquid crystal display device, wherein a dopant is mixed with a dopant for determining a twist angle between the ultraviolet curable liquid crystal and the ultraviolet curable liquid crystal.

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