JP2010224012A - Multi-domain vertical alignment type liquid crystal panel and liquid crystal display device having the same - Google Patents

Abstract

In a MVA mode liquid crystal display device, there is provided a liquid crystal panel in which a decrease in light transmittance accompanying a decrease in pixel aperture ratio is improved and a decrease in viewing angle is compensated.
In a liquid crystal panel having an MVA-LC sandwiched between two linearly polarizing plates (H-1) and (H-2), between the liquid crystal cell and the linearly polarizing plate (H-1), A quarter-wave plate (R-1), a retardation film A plate (A-1), and a retardation film C plate (C-1) are arranged between the liquid crystal cell and the linear polarizing plate (H-2). A retardation film C plate (C-3), a quarter wave plate (R-2), a retardation film A plate (A-2), and a retardation film C plate (C-2) To do.
[Selection] Figure 5

Description

  The present invention relates to a multi-domain vertical alignment liquid crystal panel and a liquid crystal display device including the same.

In recent years, with the expansion of the thin display market represented by liquid crystal televisions, there is an increasing demand for realizing clearer images at a lower price.
As an image display mode of a liquid crystal display (liquid crystal display device), there are various types such as a TN mode, an OCB mode, an IPS mode, and a VA mode. Among them, the VA mode is an image display mode in which productivity, response characteristics, and the like are balanced, and has been widely used in display devices in recent years.

In the VA mode, when no voltage is applied, the liquid crystal molecules are aligned perpendicular to the substrate surface constituting the liquid crystal cell, and in this state, a black display can be obtained by arranging linearly polarizing plates at right angles on both sides of the liquid crystal cell. .
When the liquid crystal molecules are uniformly vertically aligned, the viewing angle characteristics can be compensated for by a negative C plate retardation film.
On the other hand, when performing intermediate color display with a little voltage applied, the refractive index of the liquid crystal molecules changes in the viewing direction, resulting in viewing angle dependency. In order to solve this problem, in the VA mode, a technique for reducing the viewing angle dependency by making a plurality of directions in which liquid crystal molecules align in a pixel (multi-domain) is known. This is called a multi-domain VA mode (see, for example, Patent Document 1).

Japanese Patent No. 2947350 Japanese Patent Laid-Open No. 2002-40428 Japanese Patent No. 4105437

However, if the liquid crystal molecules are aligned in multiple directions (multi-domain) in the pixel, the alignment direction of the liquid crystal molecules in the boundary region is indefinite. The rate decreases. This is undesirable from an energy efficiency perspective.
In order to solve such a problem, a technique has been proposed in which a circularly polarizing plate is used to effectively use light in a region where the alignment direction of the liquid crystal molecules is indefinite (see, for example, Patent Document 2 above). In a liquid crystal panel using circularly polarized light, there is a problem that good viewing angle characteristics cannot be obtained.
In order to obtain good viewing angle characteristics, a technique using a quarter-wave plate has also been proposed, but the manufacturing process is complicated, and the effect of improving the viewing angle characteristics is still insufficient (for example, the above-mentioned patent document). 3).

  Therefore, an object of the present invention is to provide a multi-domain vertical alignment (multi-domain VA mode: MVA) type liquid crystal panel and a liquid crystal display device including the same, which have improved viewing angle characteristics.

  As a result of diligent research on the liquid crystal panel configuration in order to improve the viewing angle characteristics of the multi-domain VA mode liquid crystal panel, the present inventors have found a liquid crystal panel configuration capable of solving the above-described problems of the prior art, and It came to complete.

[1] A multi-domain including liquid crystal molecules having a negative dielectric anisotropy that is vertically aligned with respect to the surfaces of the first and second substrates when no voltage is applied between the first substrate and the second substrate. Vertical alignment type liquid crystal cells, and linearly polarizing plates (H-1) and (H-2) are arranged on both outer sides of the vertically aligned liquid crystal cells, respectively. Between the liquid crystal cell and the linear polarizing plate (H-1), from the linear polarizing plate (H-1) side, a C plate (C-1) and an A plate (A-1) which are retardation films ), A quarter-wave plate (R-1) showing a quarter-wave retardation in the plane is sequentially disposed, and between the vertical alignment type liquid crystal cell and the linearly polarizing plate (H-2). From the linear polarizing plate (H-2) side, a retardation film C plate (C-2), A plate ( -2), a quarter-wave plate (R-2) showing a quarter-wave retardation in the plane is sequentially disposed, and the C plate (C-1) and the A plate (A-1) Have the same sign, the C plate (C-2) and the A plate (A-2) have the same sign, and with respect to the transmission axis of the linear polarizing plate (H-1, H-2) The in-plane slow axis of the quarter-wave plate (R-1, R-2) is set to an angle of 45 degrees, and the in-plane slow axis of the A plate (A-1, A-2) is 90 degrees. The transmission axis of the pair of linear polarizing plates (H-1, H-2), the slow axis of the pair of quarter-wave plates (R-1, R-2), and the pair of A plates (A- 1, A-2) in-plane slow axes are orthogonal to each other, and between the vertically aligned liquid crystal cell and the quarter-wave plate (R-1, R-2), The vertical alignment type liquid crystal cell A negative C plate amortization, provides one side (C-3) / or both (C-3, C-4) multi-domain vertical alignment liquid crystal panel having a vertical alignment type liquid crystal cell.

[2] The A plate (A-1, A-2) as the retardation film and the C plate (C-1, C-2) as the retardation film are both negative or positive plates. A multi-domain vertical alignment type liquid crystal panel according to claim 1 is provided.

[3] The liquid crystal panel according to claim 1 or 2 and a back surface of the liquid crystal panel that is provided on the linear polarizing plate (H-1) side and irradiates light toward the linear polarizing plate (H-1). Provided is a liquid crystal display device comprising an illumination unit.

  According to the present invention, an effect of improving viewing angle characteristics can be obtained in a multi-domain vertical alignment type liquid crystal panel and a liquid crystal display device.

The schematic block diagram of an example of a linearly-polarized-light LCD panel is shown. The schematic block diagram of an example of a circularly-polarizing LCD panel is shown. A refractive index ellipsoid schematic diagram is shown. The schematic block diagram of an example of the circularly polarized light type | mold MVA-LCD panel without optical compensation is shown. The schematic block diagram of an example of the circular polarization-type MVA-LCD panel with an optical compensation in this embodiment is shown. The schematic diagram for demonstrating the principle of the optical compensation in a Poincare sphere is shown. The contrast of the circularly polarized MVA-LCD panel without optical compensation is shown. The contrast of a circularly polarized MVA-LCD panel with optical compensation is shown. The color difference of a circularly polarized light MVA-LCD panel without optical compensation is shown. The color difference of a circularly polarized MVA-LCD panel with optical compensation is shown. The contrast of the circularly polarized MVA-LCD panel without optical compensation is shown (actual measurement). The contrast of the circularly polarized MVA-LCD panel with optical compensation is shown (actual measurement). The color difference of the circularly polarized MVA-LCD panel without optical compensation is shown (actual measurement). The color difference of the circularly polarized MVA-LCD panel with optical compensation is shown (actual measurement).

DESCRIPTION OF EMBODIMENTS Hereinafter, modes for carrying out the present invention (hereinafter referred to as the present embodiment) will be described with reference to the drawings.
In the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. Further, the positional relationship such as up, down, left, and right is based on the positional relationship shown in the drawings unless otherwise specified, and the dimensional ratio in the drawing is not limited to the illustrated ratio.
Further, in this specification, the term with “abbreviation” indicates the meaning of the term excluding the “abbreviation” within the technical common sense of those skilled in the art. Shall also be included.

FIG. 1 shows a schematic diagram of an example of a linearly polarized LCD panel including a multi-domain liquid crystal, and a description will be given of a decrease in light transmittance that occurs in such a configuration.
In an optical system of a multi-domain vertical alignment type (VA mode) liquid crystal cell (hereinafter sometimes referred to as MVA-LC), liquid crystal molecular alignment directions are various in one pixel.
For this reason, as shown in FIG. 1, in the case where the MVA-LC is disposed between the linear polarizing plates (H-1, H-2) whose transmission axes are orthogonal, the linear polarizing plates (H-1, H -2) where the transmission axis orientation and the orientation orientation of the liquid crystal are parallel or orthogonal to each other, the light transmittance is zero, and the light transmittance is reduced over the entire surface of the liquid crystal cell. The back lighting unit) is assumed to be disposed below the linear polarizing plate (H-1) (the same applies to FIGS. 2, 4, and 5).
In FIG. 1, 45 degrees and 135 degrees are numerical values indicating the transmission axis directions of the linearly polarizing plates (H-1) and (H-2) based on the coordinates in the lower part of FIG.

FIG. 2 shows a schematic diagram of an example of a circularly polarized LCD panel including a multi-domain liquid crystal.
In FIG. 2, MVA-LC is sandwiched between two quarter-wave plates (R-1, R-2), and the transmission axis of the linearly polarizing plates (H-1, H-2) is 1 The angle of the in-plane slow axis in the plane of the / 4 wavelength plate (R-1, R-2) is 45 degrees (H-1 vs. R-1, H-2 vs. R-2 is 45 degrees). In addition, when a so-called circularly polarized optical system is used, there is no influence of the alignment direction of MVA-LC, and even in multi-domain alignment, the same transmittance as in the case of mono-domain alignment can be obtained.

As described above, by using circularly polarized light, the MVA-LC panel can increase the transmittance from the front (perpendicular to the linearly polarizing plates H-1 and H-2). Even in this configuration, the problem of poor viewing angle characteristics remains when observed obliquely.
In order to improve the viewing angle characteristics, in addition to the use of circularly polarized light, it is necessary to take measures against light leakage when observed from an oblique direction and to compensate for vertically aligned liquid crystal.

As countermeasures against this, it is possible to cope with light leakage when observed from an oblique direction, that is, to compensate for the deviation between the transmission axis and the absorption axis of the two polarizing plates when viewed from an oblique direction, and to adjust the vertical alignment type liquid crystal. In order to perform compensation, it is necessary to use a retardation film.
In FIG. 3, the schematic schematic of the three-dimensional refractive index ellipsoid for demonstrating the characteristic of retardation film is shown.
In the three-dimensional refractive index ellipsoid, the refractive indexes in the X-axis, Y-axis, and Z-axis directions are Nx, Ny, and Nz, respectively.
The thickness of the retardation film is t (not shown).
Here, Nx and Ny are refractive indexes in the in-plane direction of the retardation film, and there is a relationship of Nx ≧ Ny, where Nx is called a slow axis and Ny is called a fast axis.
Nz is the refractive index in the thickness direction of the retardation film.
The retardation Re in the in-plane direction is (Nx−Ny) × t, the retardation Rth in the thickness direction is | (Nx + Ny) / 2−Nz) | × t, and the NZ coefficient is (Nx−Nz) / (Nx− Ny), respectively.
Assuming these, examples of the retardation film include the following films.

Examples of the uniaxial retardation film include a positive A plate (also referred to as “positive A plate”), a negative A plate (also referred to as “negative A plate”), and a positive C plate (“positive C plate”). And negative C plate (also referred to as “negative C plate”).
The positive A plate satisfies the relationship Nx> Ny≈Nz, and the optical axis is in the Nx direction.
The negative A plate satisfies the relationship Nz≈Nx> Ny, and the optical axis is in the Ny direction.
The positive C plate satisfies the relationship Nz> Nx≈Ny, and the optical axis is in the Nz direction.
The negative C plate satisfies the relationship Nx≈Ny> Nz, and the optical axis is in the Nz direction.
Examples of the biaxial retardation film include those satisfying the relationship of Nx>Ny> Nz, those satisfying the relationship of Nz>Nx> Ny, and those satisfying the relationship of Nx>Nz> Ny.

  In addition, the said 1/4 wavelength plate means a thing with a retardation whose magnitude | size is 1/4 of a wavelength especially among A plates. Specifically, when the irradiation light is visible light, it means that it has a retardation (Re) value of 137.5 nm with respect to a wavelength of 550 nm representative of visible light, and converts linearly polarized light into circularly polarized light. It has effective characteristics when

Next, in the circularly polarized MVA-LCD panel, an example in which optical compensation is not performed and an example in which optical compensation is performed will be described with reference to FIGS. 4 and 5, and characteristics will be compared.
First, FIG. 4 shows a schematic configuration diagram of an example of a circularly polarized MVA-LCD panel without optical compensation.
In FIG. 4, a multi-domain vertical alignment type liquid crystal cell (MVA-LC cell) is sandwiched between two quarter-wave plates (R-1, R-2) in the vertical direction in FIG. Therefore, it has a structure sandwiched between linearly polarizing plates (H-1, H-2).
These linear polarizing plates (H-1, H-2) and quarter wave plates (R-1, R-2) are 135 degrees, 45 degrees, and 0 degrees, respectively, in the coordinates shown in FIG. , Has an optical axis of 90 degrees.
Two quarter-wave plates (R-1, R-2) are in-plane retardation of 137.5 nm and are positive A plates.
The MVA-LC preferably has a thickness of 2 μm to 10 μm from the viewpoint of birefringence characteristics of liquid crystal and light ON / OFF control using the same, and has a thickness of 3 μm to 6 μm. The retardation in the thickness direction is about 400 nm in consideration of the influence of the tilt angle when the thickness of the liquid crystal is 4 μm and the birefringence is 0.1.
Further, a negative C plate (negative C plate (C-3)) is provided between the MCA-LC cell and the quarter wavelength plate (R-2).
The negative C plate (C-3) compensates for the retardation in the thickness direction of the MVA-LC cell and the quarter wave plates (R-1) and (R-2).

Next, FIG. 5 shows a schematic configuration diagram of an example of a circularly polarized MVA-LCD panel with optical compensation.
The circularly polarized MVA-LCD panel of FIG. 5 is vertically aligned with a pair of predetermined substrates (first substrate, second substrate) with respect to the surfaces of the first and second substrates when no voltage is applied. And a multi-domain vertical alignment type liquid crystal cell (MVA-LC) including liquid crystal molecules having negative dielectric anisotropy.
A linearly polarizing plate (H-1) and a linearly polarizing plate (H-2) are disposed on both outer sides of the vertical alignment liquid crystal cell, respectively. Between this linear polarizing plate (H-1) side, C plate (C-1), A plate (A-1), 1/4 wavelength plate showing retardation of 1/4 wavelength in the plane (R-1) are sequentially arranged.
Between the vertical alignment type liquid crystal cell (MVA-LC) and the linear polarizing plate (H-2), the C plate (C-2) and the A plate (A-2) from the linear polarizing plate (H-2) side. ), A quarter-wave plate (R-2) showing a quarter-wave retardation in the plane is sequentially arranged.
The C plate (C-1) and the A plate (A-1) have the same sign, and the C plate (C-2) and the A plate (A-2) have the same sign.
The in-plane slow axis of the quarter-wave plate (R-1, R-2) is set to an angle of 45 degrees with respect to the transmission axis of the linear polarizing plate (H-1, H-2). The in-plane slow axis of the plates (A-1, A-2) is set to an angle of 90 degrees.
Transmission axis of a pair of linear polarizing plates (H-1, H-2), slow axis of a pair of quarter wave plates (R-1, R-2), a pair of A plates (A-1, A- The in-plane slow axes of 2) are orthogonal to each other.
A negative C plate (C-3) for compensating the vertical alignment type liquid crystal cell is provided between the vertical alignment type liquid crystal cell and the quarter wavelength plate (R-2).
The negative C plate may be provided as a C plate (C-4) between the liquid crystal cell and the quarter wavelength plate (R-1).

As described above, the multi-domain vertical alignment type liquid crystal panel shown in FIG. 5 in the present embodiment has the A plate (A-1, A-2) in addition to the negative C plate (C-3) for liquid crystal compensation. ) And C plates (C-1, C-2) are arranged between the linearly polarizing plates (H-1, H-2) and the quarter wave plates (R-1, R-2). It has the characteristics.
With such a configuration, the visual field characteristics can be improved, and light leakage when observed from an oblique direction can be reduced.

In the multi-domain vertical alignment type liquid crystal panel of the present embodiment, the arrangement order of each A plate and C plate is from a linear polarizing plate to a C plate, an A plate, and a quarter wavelength plate. In the case where the A plate is disposed adjacent to the linear polarizing plate, polarization conversion does not occur and a desired effect cannot be obtained.
Further, the A plate is arranged such that its optical axis coincides with the absorption axis of the linearly polarizing plate provided at the position sandwiching the C plate.
The retardation value shown in FIG. 5 is an example for explaining the configuration and effect of the multi-domain vertical alignment type liquid crystal panel of the present embodiment, and is not limited to this example.

In addition, regarding the positive and negative of each of the A plate and C plate, which are retardation films constituting the multi-domain vertical alignment type liquid crystal panel of the present embodiment, (A-1 and C-1), (A-2 and C-2) should just be the same code | symbol, respectively.
Therefore, (A-1, C-1)-(A-2, C-2) are (positive, positive)-(positive, positive), (positive, positive)-(negative, negative), (negative) , Negative)-(positive, positive) and (negative, negative)-(negative, negative).
The combination of these retardation films can improve the visual field characteristics.

  The C plate (C-3) must be a negative plate because it compensates the liquid crystal itself, and a positive plate cannot be used.

Next, the principle of the optical compensation will be described using a Poincare sphere display.
The display by the Poincare sphere is described, for example, in “Physical Optics” published by Morikita Publishing Co., Ltd., Chapter 5, p102 to p163, edited by the Applied Physics Optics Roundtable.
FIG. 6 is a schematic diagram for explaining the principle of optical compensation in the Poincare sphere, and shows the Poincare sphere observed from the azimuth 0 degree direction.
In the following description, the multi-domain vertical alignment type liquid crystal panel having the configuration shown in FIG. 5 is used for explanation, and C plate (C-1, C-2), A plate (A-1, A-2). ) Shall be all negative plates.

In FIG. 6, S1, S2, and S3 are axes indicating Stokes parameters, respectively.
After the light emitted from the predetermined light source passes through the linearly polarizing plate (H-1) shown in FIG. 5, the polarization state is at 10 on the Poincare sphere. This point 10 corresponds to the transmission axis of the linearly polarizing plate (H-1).
In order to improve the visual field characteristics, it is necessary to convert the polarization state to the position of reference numeral 11 which is the absorption axis of the linearly polarizing plate (H-2) when observed from an oblique direction.
Reference numeral 10, which is the polarization state of the transmission axis of the linear polarizing plate (H-1), is converted by the optimized negative C plate (C-1) (reference numeral 14) and converted by the negative A plate (A-1). According to (reference numeral 18), the polarization state 12 is obtained.
The polarization state 12 corresponds to the intermediate position of the axial angle between the transmission axis of the linearly polarizing plate (H-1) and the absorption axis of the linearly polarizing plate (H-1), and is at all azimuth angles and polar angles. Corresponding position is an effective position for the subsequent design of circular polarization. The polarization state is equivalent to that seen from the front rather than from the diagonal.
Here, the arrangement order of the negative A plate (A-1) and the negative C plate (C-1) is important, and if these are arranged in reverse, the conversion to the polarization state of reference numeral 12 becomes impossible.

After that, the polarization state 12 is set to the ¼ wavelength plate (R-1), the liquid crystal cell (MVA-LC), the negative C plate (C-3), the linear polarizing plate (H) on the linear polarizing plate (H-1) side. -2) passes through the ¼ wavelength plate (R-2) on the side, but in the black state, these conversions (R-1, liquid crystal cell, C-3, R-2) are always 16, 17 By moving up and down only on the meridian of the Poincare sphere and optimizing the negative C plate (C-3), it comes to 12 positions from any angle.
Thereafter, the state of polarization 11 is obtained by the conversion by the negative A plate (A-2) (reference numeral 19) and the conversion by the negative C plate (C-2) (reference numeral 15), and the absorption axis of the linearly polarizing plate (H-2). As a result, light is absorbed and light leakage does not occur.
When light is desired to pass, voltage is applied to the liquid crystal cell and the retardation is changed, so that the maximum light is allowed to pass if the polarization state immediately before the linearly polarizing plate (H-2) is 13 circularly polarized. And high contrast can be obtained.

Next, the contrast of the circularly polarized MVA-LCD panel with optical compensation having the configuration shown in FIG. 5 was compared with the contrast of the circularly polarized MVA-LCD panel without optical compensation having the configuration shown in FIG.
Here, the in-plane retardation (Re) of the two negative A plates (A-1, A-2) is 137.5 nm, and the optimum value of the C plate (C-3) for liquid crystal compensation is 264.5 nm. The thickness of the multi-domain vertical alignment type liquid crystal cell was 4 μm, and the 1/4 wavelength plate was a positive 1 / 4λ. Moreover, the retardation (Rth) of the thickness direction of two negative C plates (C-1, C-2) was 40.8 nm, the computer simulation was implemented, and the contrast was calculated.
FIG. 7 shows the calculation result of the contrast of the circularly polarized MVA-LCD panel without optical compensation, and FIG. 8 shows the calculation result of the contrast of the circularly polarized MVA-LCD panel with optical compensation.
From the contrast calculation results, the contrast of the circularly polarized MVA-LCD panel with optical compensation achieved a contrast of 50 or more within a polar angle of 80 degrees, and a wide viewing angle of 5 times or more compared to the case without optical compensation. It turns out that it has achieved.

Next, the color difference of the circularly polarized MVA-LCD panel with optical compensation having the configuration shown in FIG. 5 was compared with the color difference of the circularly polarized MVA-LCD panel without optical compensation having the configuration shown in FIG.
FIG. 9 shows the calculation result of the color difference of the circularly polarized MVA-LCD panel without optical compensation, and FIG. 10 shows the calculation result of the color difference of the circularly polarized MVA-LCD panel with optical compensation.
In the vicinity of a black polar angle of 60 degrees (Polar angle 60 °), there is a slight value in FIG. 9, and FIG. 10 is 0 and no color difference occurs. This indicates that the black color is accurate when viewed obliquely.
From these results, it was found that in the circularly polarized MVA-LCD panel with optical compensation, the color change does not increase, but rather the color change in the dark state can be reduced.

[Multi-domain liquid crystal cell (MVA-LC)]
As the multi-domain liquid crystal cell, one produced by a conventionally known method can be used.
For example, an oblique electric field method by patterning an electrode, a rib method for forming a projection on the electrode on the substrate surface, a method of applying a pretilt in a plurality of directions, and the like.

[Phase difference film: C plate (C-1), (C-2)]
A conventionally well-known thing can be used for retardation film C plate (C-1, C-2).
TAC (triacetyl cellulose) is usually used for a protective film for a linearly polarizing plate, and it is an effective method to divert it to an optical system.
The retardation (Rth) in the thickness direction is preferably 20 nm to 100 nm, and particularly preferably 30 nm to 50 nm, from the viewpoint of improving visual field characteristics.

[¼ wavelength plates (R-1), (R-2)]
The quarter-wave plates (R-1) and (R-2) are not particularly limited as long as the in-plane retardation is around 137.5 nm.
Since it is preferable that the retardation has the same wavelength dispersion, it is preferable to use the same ¼ wavelength plates (R-1) and (R-2). It can also be used.
When the same material is used, it is preferable to use a negative quarter wave plate in consideration of retardation (Rth) in the thickness direction of the liquid crystal cell in design.

[Negative C plates (C-3) and (C-4) for compensating liquid crystal]
The retardation in the thickness direction of the negative C plate that compensates for the liquid crystal is preferably 100 nm to 500 nm, and more preferably 150 nm to 400 nm, from the viewpoint of improving the visual field characteristics.
The negative C plate for compensating the liquid crystal may be disposed only on one side of the multi-domain vertical alignment liquid crystal cell (MVA-LC) as shown in the example of FIG. (C-3)), C plates (C-3) and (C-4: not shown) may be arranged on both sides of the MVA-LC. In this case, the total value of the retardation (Rth) in the thickness direction of the C plates (C-3) and (C-4) when two plates are arranged is the C plate when arranged only on one side of the MVA-LC It is assumed that the thickness direction retardation (Rth) of (C-3) is equal, and in particular, the thickness direction retardation of C plates (C-3) and (C-4) is equal to obtain a good balance. It is preferable from the viewpoint.

[Phase difference film: A plate (A-1), (A-2)]
A conventionally well-known thing can be used for retardation film A plate (A-1, A-2).
These in-plane retardations are preferably from 50 nm to 300 nm, particularly preferably from 100 nm to 150 nm, from the viewpoint of improving visual field characteristics.

[Back lighting unit]
The backlight unit may be any unit provided in a known liquid crystal display device and functioning as a light source. Examples thereof include a cold cathode tube (CCFL) and an LED.
In the present embodiment, the backlight unit is provided on the linear polarizing plate (H-1) side in FIG.

  The liquid crystal display device of this embodiment described above can sufficiently reduce light leakage from an oblique direction even in black display while ensuring sufficient optical compensation. Accordingly, the viewing angle characteristics (particularly during black display) are greatly improved as compared with the conventional liquid crystal display device.

Examples of the present invention and comparative examples will be specifically described below.
First, materials and evaluation / measurement methods applied to Examples and Comparative Examples will be described.

[Production of multi-domain liquid crystal cell]
First, two glass substrates were prepared, and an orientation process was performed on each one side of these glass substrates.
As the glass substrate, a soda glass substrate manufactured by EHC Corporation was used. This glass substrate has an ITO film deposited on the entire surface of one side, and is called an ITO solid substrate.

A vertical alignment film (manufactured by JALS-204 JSR) was spin-coated on one side of the two glass substrates.
Spin coating was performed at 3000 rpm for 25 seconds.
Then, the baking process was performed at 180 degreeC for 1 hour.
Subsequently, ultraviolet (UV) irradiation was performed at a tilt angle of 45 degrees from a direction parallel to the stripe pattern through a predetermined optical mask having a stripe width of 150 μm.
As a result, as will be described later, a pretilt angle can be created when liquid crystal is injected.
Next, the stripe optical mask was moved 150 μm in the direction perpendicular to the stripe, and UV irradiation was performed at an inclination angle of 45 degrees from the opposite direction.
In the above, when the wavelength of the irradiated ultraviolet light was 254 nm and the light irradiation amount was 1.0 J / cm ² , a pretilt angle of 0.2 degrees could be formed.
Two types of pretilts were formed in parallel with the stripes and with the tilt directions reversed.

Next, the two glass substrates are bonded to each other with the surfaces subjected to the alignment treatment facing each other, and using a predetermined spacer, a gap for injecting liquid crystal described later is provided. It was.
The gap between the substrates was 4 μm.
Next, negative nematic liquid crystal (MLC-2038 manufactured by Merck & Co., Inc.) was injected into this to produce a liquid crystal cell.
Through the above-described steps, four regions having different pretilt orientations were formed in the liquid crystal layer.

A voltage of 5 V was applied to the liquid crystal cell produced as described above, and the liquid crystal cell was observed with a polarizing microscope.
Cross pattern domains could be observed corresponding to the applied voltage, confirming the formation of 4 domains.

Furthermore, when a circularly polarizing plate was set on both sides and observed, the cross pattern disappeared and the maximum light transmittance was about 36%.
For comparison, instead of a circularly polarizing plate, a linearly polarizing plate was set on both sides and observed, and the maximum light transmittance was 25%. When both were compared, the direction when the circularly polarizing plate was set increased by 10% or more.
As the linear polarizing plate, “HLC2-2418” manufactured by Sanlitz Co., Ltd. was used, and a positive quarter wave plate manufactured by Nitto Denko was overlapped with the optical axis shifted by 45 degrees with respect to the linear polarizing plate. A polarizing plate was used.

Next, using the liquid crystal cell manufactured as described above, a liquid crystal display panel having the configuration shown in FIG. 5 is manufactured as an example, and a liquid crystal display panel having the configuration shown in FIG. 4 is manufactured as a comparative example, and these are used. The viewing angle was measured. The optical axis direction and retardation Re are as shown in FIG.
Linear polarizing plate (H-1, H-2, C-1, C-2): (HLC2-2418, Sanritz Corp. with TAC)
Negative C plate (C-3): C plate for liquid crystal compensation (biaxially stretched from JSR Arton film)
Negative A plate (A-1, A-2): manufactured by Asahi Kasei Chemicals Corporation (manufactured by the method described later)
1/4 wavelength plate (R-1, R-2): Positive 1/4 wavelength plate (Nitto Denko)

[Manufacturing Method of Negative A Plate (A-1), (A-2)]
<1> Styrene-maleic anhydride copolymer A styrene-maleic anhydride copolymer was synthesized by continuous solution polymerization using a stainless steel polymerization apparatus.
First, 91.7 parts by mass of styrene and 8.3 parts by mass of maleic anhydride (100 parts by mass in total) were prepared so as not to mix. Next, 5 parts by mass of methyl alcohol and 0.03 part by mass of 1,1-tert-butylperoxy-3,3,5-trimethylcyclohexane as a polymerization initiator were mixed with styrene to obtain a first preparation liquid. This first preparation liquid was continuously supplied at a rate of 0.95 kg / hour to a jacketed complete mixing polymerization machine having an internal volume of 4 L.
On the other hand, maleic anhydride heated to 70 ° C. as the second preparation liquid was supplied to the complete mixing polymerization machine at a rate of 0.10 kg / hour and polymerized at 111 ° C. When the polymerization conversion reached 54%, the polymerization solution was continuously taken out from the polymerization machine. The taken out polymerization liquid was first preheated to 230 ° C., then kept at 230 ° C., and supplied to a devolatilizer whose pressure was reduced to 20 torr. Next, after maintaining the polymerization liquid in the devolatilizer for 0.3 hours with an average residence time, the polymerization liquid was continuously discharged from the lower gear pump of the devolatilizer. The discharged polymer solution was continuously transferred to an extruder in a molten state, and extruded with an extruder to obtain pellets of a styrene-maleic anhydride copolymer (P-1).
The obtained styrene-maleic anhydride copolymer (P-1) pellets are colorless and transparent. As a result of composition analysis by neutralization titration of this polymer, the copolymerization ratio of styrene is 85% by mass, maleic anhydride. The unit copolymerization ratio was 15% by mass. The melt flow rate value measured at 230 ° C. under a load of 2.16 kg measured according to ASTM-D1238 was 2.0 g / 10 min.

<2> Styrene-methacrylic acid copolymer A styrene-methacrylic acid copolymer was synthesized by continuous solution polymerization using a polymerization apparatus in which all of the apparatus was made of stainless steel. First, 75.2% by mass of styrene, 4.8% by mass of methacrylic acid, and 20% by mass of ethylbenzene were prepared, and 1,1-tert-butylperoxy-3,3,5-trimethylcyclohexane was used as a polymerization initiator there. Was added to obtain a preparation liquid (monomer solution). This prepared solution was continuously supplied at a rate of 1 L / hour to a complete mixing polymerization machine equipped with a stirrer with an internal volume of 2 L and polymerized at 136 ° C. A polymerization solution containing 49% solids was continuously taken out. The taken out polymerization solution was first preheated to 230 ° C., then kept at 230 ° C., and supplied to a devolatilizer whose pressure was reduced to 20 Torr. Next, after maintaining the polymerization liquid in the devolatilizer for 0.3 hours with an average residence time, the polymerization liquid was continuously discharged from the lower gear pump of the devolatilizer. The discharged polymerization solution was continuously transferred to an extruder in a molten state, and extruded with an extruder to obtain pellets of a styrene-methacrylic acid copolymer (P-2).
The obtained pellets of styrene-methacrylic acid copolymer (P-2) were colorless and transparent. As a result of composition analysis by neutralization titration of this polymer, the copolymerization ratio of styrene was 92% by mass, and the copolymer of methacrylic acid. The polymerization rate was 8.1% by mass. The melt flow rate value measured at 230 ° C. under a load of 3.8 kg measured in accordance with ASTM-D1238 was 5.1 g / 10 minutes.

<3> Styrene-acrylonitrile copolymer A styrene-methacrylic acid copolymer was synthesized by continuous solution polymerization. A mixed liquid (monomer solution) consisting of 72% by mass of styrene, 13% by mass of acrylonitrile, and 15% by mass of ethylbenzene is continuously supplied to a complete mixing polymerization apparatus with a stirrer having an internal volume of 3 L, at 150 ° C. and a residence time of 2 hours. Was polymerized. The obtained polymerization solution was continuously transferred to an extruder in a molten state, and extruded with the extruder, and at the same time, the unreacted monomer and solvent were recovered, and the styrene-acrylonitrile copolymer (P-3) pellets. Got.
The obtained pellets of styrene-acrylonitrile copolymer (P-3) were colorless and transparent. As a result of composition analysis by neutralization titration of this polymer, the copolymerization ratio of styrene was 80% by mass, and the copolymerization ratio of acrylonitrile. Was 20% by mass. The melt flow rate value at 220 ° C. and 10 kg load measured in accordance with ASTM-D1238 was 13 g / 10 min.

<4> Methyl methacrylate-methyl acrylate copolymer To a mixture comprising 89.2 parts by mass of methyl methacrylate, 5.8 parts by mass of methyl acrylate, and 5 parts by mass of xylene, 0.0294 parts by mass of oxy-3,3,5-trimethylcyclohexane and 0.115 parts by mass of n-octyl mercaptan were added and mixed uniformly to obtain a preparation solution (monomer solution).
This mixed solution was continuously supplied to a sealed pressure resistant reactor having an internal volume of 10 L, and polymerized under stirring at an average temperature of 130 ° C. and an average residence time of 2 hours. Thereafter, the polymerization solution is continuously sent to a storage tank connected to the reactor, and the volatile matter is removed under a certain condition. Then, extrusion molding was performed using an extruder to obtain pellets of methyl methacrylate-methyl acrylate copolymer (P-4).
As a result of compositional analysis by neutralization titration of the obtained methyl methacrylate-methyl acrylate copolymer (P-4), the copolymerization ratio of methyl acrylate was 6.0% by mass, and the copolymerization ratio of methyl methacrylate was The melt flow rate value measured at 92.0 mass%, according to ASTM-D1238 at 230 ° C. and 3.8 kg load was 1.0 g / 10 min.

<5> Production of Film The above copolymer (P-1) was mixed to 50 parts by mass, and (P-4) was mixed to 50 parts by mass.
Moreover, 50 mass parts of copolymers (P-2) and (P-4) were mixed so as to have a composition of 50 mass parts.
Furthermore, 50 parts by mass of copolymer (P-3) and 50 parts by mass of (P-4) were mixed.
Adjust the resin temperature in the cylinder of the T-die mounting extruder (KZW15TW-25MG-NH type, width 150 mm T-die mounting, lip thickness 0.5 mm) manufactured by Technobel, and adjust the T-die temperature to 235 ° C and 240 ° C, respectively. Unstretched films were obtained by extruding each of the above three types of mixtures.
Then, the obtained three types of unstretched films were cut out so that the width was 50 mm, and uniaxially stretched at 130 ° C. using a tensile tester (between chucks: 50 mm, chuck moving speed: 500 mm / min), Three types of negative A plates were obtained.

(Viewing angle measurement)
The viewing angle measurement was performed using a gonio stage equipped with a luminance meter (Topcon, BM-7).
Contrast (calculated from luminance) and color difference were measured using the above measuring machine.
As a result, when the liquid crystal display panel after optical compensation shown in FIG. 5 is used, a contrast of 50 or more is achieved in almost all directions (FIG. 12), and before the optical compensation shown in FIG. Compared to the case of the liquid crystal display panel having the structure (FIG. 11), the result was twice or more, and it was found that the contrast was greatly improved.
Further, in the color difference measurement, when the liquid crystal display panel after optical compensation shown in FIG. 5 is used (FIG. 14) and the liquid crystal display panel before optical post-shown shown in FIG. 4 are compared (FIG. 13). It was found that the same polar angle (Polar Angle) showed almost the same color difference.
In addition, when what was produced with the said 3 types of mixture was used as a negative A plate, it turned out that all show the same property.
From the above results, the configuration of the liquid crystal panel after optical compensation (FIG. 5) provides a significant improvement in contrast as compared with the liquid crystal panel before optical compensation (FIG. 4), and the color change. It was also found that good quality was obtained in practical use.

  Since the liquid crystal panel and the liquid crystal display device of the present invention have a high effect of improving light leakage in an oblique direction particularly during black display, they are industrially used as a liquid crystal panel and a liquid crystal display device in the thin display market represented by a liquid crystal television. there is a possibility.

DESCRIPTION OF SYMBOLS 10 Transmission axis of linear polarizing plate (H-1) Absorption axis of linear polarizing plate (H-2) 12 Polarization state before and after liquid crystal cell 13 Circular polarization state 14 Conversion of negative C plate (C-1) 15 Negative C plate (C-2) Conversion 16 Liquid Crystal Cell 1/4 Wave Plate (R-1) Negative C Plate (C-3) Conversion 17 1/4 Wave Plate (R-2) Negative C Plate (C-3) Conversion 18 Conversion of negative A plate (A-1) 19 Conversion of negative A plate (A-2)

Claims (3)

Between the first substrate and the second substrate,
A multi-domain vertically aligned liquid crystal cell including liquid crystal molecules having negative dielectric anisotropy that is vertically aligned with respect to the surfaces of the first and second substrates when no voltage is applied;
A linearly polarizing plate (H-1) and a linearly polarizing plate (H-2) are disposed on both outer sides of the vertical alignment liquid crystal cell,
Between the vertical alignment type liquid crystal cell and the linearly polarizing plate (H-1), from the linearly polarizing plate (H-1) side, a C plate (C-1) and an A plate (which are retardation films) A-1), 1/4 wavelength plates (R-1) showing retardation of 1/4 wavelength in the plane are sequentially arranged,
Between the vertical alignment type liquid crystal cell and the linear polarizing plate (H-2), from the linear polarizing plate (H-2) side, a C plate (C-2) and an A plate (retarding films) A-2), a quarter-wave plate (R-2) showing a quarter-wave retardation in the plane is sequentially arranged,
The C plate (C-1) and the A plate (A-1) have the same sign,
The C plate (C-2) and the A plate (A-2) have the same sign,
With respect to the transmission axis of the linear polarizing plate (H-1, H-2),
The in-plane slow axis of the quarter-wave plate (R-1, R-2) is an angle of 45 degrees, and the in-plane slow axis of the A plate (A-1, A-2) is 90 degrees. Angle and
Transmission axis of a pair of linear polarizing plates (H-1, H-2), slow axis of a pair of quarter wave plates (R-1, R-2), a pair of A plates (A-1, A- The in-plane slow axes in 2) are orthogonal to each other,
Between the vertical alignment type liquid crystal cell and the quarter wavelength plate (R-1, R-2), a negative C plate for compensating the vertical alignment type liquid crystal cell is provided. A multi-domain vertical alignment type liquid crystal panel having one side (C-3) / or both sides (C-3, C-4).   The A plate (A-1, A-2) as the retardation film and the C plate (C-1, C-2) as the retardation film are both negative or positive plates. 2. A multi-domain vertical alignment liquid crystal panel according to 1.   The liquid crystal panel according to claim 1 or 2, and a backlight unit provided on the liquid crystal panel on the linear polarizing plate (H-1) side and irradiating light toward the linear polarizing plate (H-1). And a liquid crystal display device.