JP3183634B2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device applied to a computer display device, a television receiver, and the like, and more particularly to a liquid crystal display device capable of color display.

[0002]

2. Description of the Related Art As a conventional liquid crystal display device, a twisted nematic (TN) mode liquid crystal display device using a nematic liquid crystal has been put to practical use. However, this liquid crystal display device has a disadvantage that the response speed is slow. Further, it has a disadvantage that the viewing angle at which an image can be properly viewed is narrow, and when viewed from an oblique direction, the brightness and contrast are reduced, and the brightness is inverted at a halftone. Therefore, it is difficult to apply the present invention to a display device that requires high-speed moving image display or good visibility even from an oblique direction.

Therefore, for example, Japanese Patent Application Laid-Open No. 7-8425.
As disclosed in No. 4, an optically compensated bend (OCB) mode liquid crystal display device having an extremely fast response speed and a relatively wide viewing angle has been proposed.

[0004] In this OCB mode liquid crystal display device, for example, as shown in FIG.
The pixel electrode 1 is provided on a pair of transparent substrates 13 and 14 constituting the pixel electrode 1.
5, an opposite electrode 16, and alignment films 17 and 18 are formed.

As shown in FIG. 1, the alignment films 17 and 18 have liquid crystal molecules 12a and 12a near the alignment films 17 and 18, respectively.
The orientation processing is performed so that a bend orientation in which b is symmetrically inclined is formed. More specifically, the surfaces of the alignment films 17 and 18 are rubbed in parallel and in the same direction so that the pretilt angle is about several degrees to 10 degrees. Note that, depending on conditions, the bend orientation may include a twist near the center of the transparent substrates 13 and 14.

The polarizing plate 1 is provided on both sides of the liquid crystal cell 11.
9.20 are provided. Transparent substrate 14 and polarizing plate 20
Between them, a phase compensation layer 21 for optically compensating the orientation of the liquid crystal 12 is provided. Specifically, as the phase compensation layer 21, the refractive index in the direction perpendicular to the film surface is smaller than the refractive index in the direction in the film surface, that is, the light transmitted through the phase compensation layer 21 has a negative refractive index. A retardation film or the like for giving a phase difference is used.

In the liquid crystal display device configured as described above,
When no voltage is applied between the pixel electrode 15 and the counter electrode 16, the liquid crystal molecules are in a spray mode in which the liquid crystal molecules are aligned in a direction substantially parallel to the transparent substrates 13 and 14. When a voltage is applied, the state shifts to bend alignment as shown in FIG. The display of an image is performed in a state where the bend alignment is maintained by applying a predetermined bias voltage.

When the bend alignment is formed as described above, the change of the liquid crystal molecules with respect to the change of the driving voltage applied between the pixel electrode 15 and the counter electrode 16 is fast, so that the response speed can be increased. Can be This increase in speed can be obtained especially in a change between halftones where the difference in luminance is small.
In addition, the symmetry of the bend orientation increases the viewing angle (for example, ±±) in a plane including the XZ axis in FIG.
About 50 °). On the other hand, the phase compensation layer 21
The viewing angle in a plane including the axis (vertical direction of the display screen) is enlarged (for example, about ± 40 °). The phase compensation layer 21 also contributes to a reduction in drive voltage.

[0009]

However, when a liquid crystal display device that performs color display using this type of OCB mode is constructed, the transmittance of the liquid crystal differs depending on the wavelength of the transmitted light. Therefore, there is a problem that the display hue tends to change.

That is, for example, as shown in FIG.
The transmittances of green and red light are different from each other.
More specifically, for example, the pixel electrode 15 and the counter electrode 16
And when a voltage of 2 V is applied between them, the transmittance of blue, green, or red light is 0.08, 0.045, or 0.4.
025. Therefore, the display is such that the entire screen takes on a blue color.

Here, the above-mentioned liquid crystal display device is manufactured as follows. That is, the alignment film 17.
8 as polyimide-based alignment film PSI- manufactured by Chisso Corporation
A2204, liquid crystal 12 as MT-5 manufactured by Chisso Corporation
540, a biaxially stretched film manufactured by Nitto Denko is used as the phase compensation layer 21, the gap between the liquid crystal cells 11 is set to about 5 μm, the pretilt angle is set to 5 to 6 °, and the upper and lower transparent substrates 13.
Reference numeral 4 is attached so that the rubbing directions of the alignment films 17 and 18 are parallel. The center wavelengths of the measured spectra of blue, green, and red light are each about 450
nm, about 540 nm, or about 630 nm.

In order to prevent such a change in display hue, it is conceivable to adjust the applied voltage for each color. This leads to an increase in scale and manufacturing costs.

In view of the above, it is an object of the present invention to provide a liquid crystal display device capable of adjusting the transmittance for each color without adjusting the applied voltage and capable of displaying an appropriate hue. And

[0014]

A liquid crystal display device according to the present invention has a liquid crystal sandwiched between substrates. The liquid crystal has a bend alignment, and liquid crystal molecules near the substrate surface have a predetermined pretilt angle. A liquid crystal display device having a plurality of pixels, the plurality of pixels having a plurality of color filters that transmit light of a specific color, and the predetermined pretilt in different color pixels. It is characterized by different corners.

With this configuration, the transmittance of each color can be adjusted without adjusting the applied voltage, and an appropriate hue can be displayed.

More specifically, when the same pre-tilt angle is applied between the pixel electrodes corresponding to pixels of different colors and the counter electrode,
By setting the pixels of each color to have the same transmittance, the voltage-transmittance characteristics of the pixels of each color can be made equal, and the shift of the display hue can be suppressed reliably.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a liquid crystal cell 38 constituting a liquid crystal display device has a liquid crystal 37 having a nematic liquid crystal having a positive dielectric anisotropy between transparent substrates 33 and 36 made of glass. Is enclosed. The transparent substrate 33 includes transparent pixel electrodes 31 a to 31 c corresponding to blue, green, or red pixels, and an alignment film 3.
2 are formed. On the other hand, the counter electrode 34 and the alignment film 35 are formed on the transparent substrate 36. The distance between the transparent substrate 33 and the transparent substrate 36 is maintained at a predetermined distance by interposing a spherical spacer 51 therebetween. On both sides of the liquid crystal cell 38, polarizing plates 39 and 40 are provided. On the outer side of the polarizing plate 40, blue, green, and red regions 41a to 41a
A color filter 41 having 1c is provided.

The transparent pixel electrodes 31a to 31c are each formed in a rectangular shape having a length of 100 μm and a width of 300 μm, for example, and a plurality of sets of these are arranged so that a bitmap image can be displayed. However, in FIG. 1, only one set of pixels is schematically depicted.

Each of the alignment films 32 and 35 is subjected to an alignment process in the same direction and parallel to each other, so as to give a predetermined pretilt angle to liquid crystal molecules near the surface thereof. That is, when no voltage is applied to the liquid crystal cell 38, the liquid crystal molecules form a splay alignment, and when a predetermined voltage is applied, they form a bend alignment.

More specifically, the predetermined pretilt angle is determined by the color filters 41 in the alignment films 32 and 35, respectively.
32a, 35a, 32b, 35b, 32c, corresponding to the blue, green, or red regions 41a, 41b, 41c of
It is set so as to increase in the order of 35c, that is, in the order corresponding to the blue, green, and red pixels, so that the transmittance characteristics of the liquid crystal 37, which differ according to the wavelength of the transmitted light, are compensated.

The formation of the alignment films 32 and 35 and the alignment treatment as described above are performed, for example, as follows.

(1) First, a polyamic acid type polyimide alignment film PSI-A manufactured by Chisso Corporation is formed on the entire surface of the transparent pixel electrodes 31a to 31c formed on the transparent substrate 33.
2204 is applied with a spinner and cured to form an alignment film 32
To form

(2) Negative resist OMR- manufactured by Tokyo Ohka
By applying 83, exposing using a photomask, and developing, a resist layer is formed so as to open only the region 32c corresponding to the red pixel. In this state, a vertical alignment agent made of Merck was diluted and applied, and chemically bonded to the surface. By adding the vertical alignment agent in this manner, this region 32c
Has a large pretilt angle.

(3) After removing the resist layer, a normal rubbing process is performed on the entire surface of the alignment film 32.

(4) Further, using a photomask, the wavelength is selectively changed to only the region 32a corresponding to the blue pixel.
Irradiate with UV light of 0 nm. By this ultraviolet irradiation,
Since the decomposition reaction of the alignment film occurs, the pretilt angle of the region 32a decreases.

(5) In the same manner as in the above (1) to (4),
An alignment film 35 is formed on the surface of the counter electrode 34 formed on the transparent substrate 36, and an alignment process is performed.

By the above-described alignment processing, for example, the regions 32a.
The pretilt angle at 35a is about 2 °, the pretilt angles at the areas 32c and 35c corresponding to the red pixels are both about 19 °, and the area 32b corresponding to the green pixel without any special processing. The pretilt angle at 35b is about 5 to 6 degrees, as in the case of the conventional liquid crystal display device.

FIG. 2 shows the transmittance-applied voltage characteristics of the liquid crystal display device configured as described above. As is apparent from the figure, almost the same results were obtained for the transmittance of light of the three primary colors of blue, green and red, irrespective of the applied voltage. Therefore, even if the same voltage is applied to the three primary colors without separately adjusting the voltage, the color balance is not particularly degraded, and an appropriate hue can be displayed. Here, the transmittance-applied voltage characteristics do not necessarily have to match in all the applied voltage ranges, but need only match in the driving range of the liquid crystal display device (for example, 1.4 V or more).

The size of each pretilt angle is not limited to the above, and the dilution concentration of the vertical alignment agent, the irradiation energy of ultraviolet rays, and the like are adjusted according to the light transmittance characteristics of each color in the liquid crystal 37. It may be set accordingly.

However, from the viewpoint of display characteristics and the like, it is preferable to set within the following range. That is, as described above, the pretilt angle corresponding to the blue pixel is minimized. However, if the pretilt angle is too small, the energy required for the transition from the splay alignment to the bend alignment becomes large, and the above transition becomes easy. Will be gone. Therefore, it is necessary to set a pretilt angle corresponding to blue within a range where the transition easily occurs. On the other hand, the pretilt angle corresponding to the red pixel is the largest, but setting the pretilt angle to a too large value is not desirable because it impairs the display due to proper bend orientation, and it is not preferable to set the pretilt angle to about 30 ° or less. It is necessary to put.

In view of the symmetry of the viewing angle, it is preferable that the pretilt angles are set to be equal in the opposing regions of the alignment films 32 and 35. You may make it easy to change.

The method of setting the pretilt angle is not limited to the above-described method. For example, different alignment film materials may be used in the respective regions 32a to 32c and 35a to 35c, or ultraviolet rays having different energy densities and polarization directions may be irradiated. May be.

Further, by providing a phase compensator on one or both sides of the liquid crystal cell 38, the viewing angle characteristics may be improved and the driving voltage may be reduced.

Further, a chiral agent is added to the liquid crystal 37,
A bend orientation including a twist may be formed.

[0035]

As described above, according to the present invention, since the pretilt angles of the liquid crystal molecules are set differently for the pixels of different colors, the pretilt angles of the respective colors can be adjusted without adjusting the applied voltage. Transmittance can be adjusted,
Therefore, the voltage-transmittance characteristics of the pixels of each color are made equal, the shift of the display hue is reliably suppressed, and the display of the appropriate hue can be performed.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view illustrating a configuration of a liquid crystal display device according to an embodiment.

FIG. 2 is a graph showing transmittance-applied voltage characteristics of the liquid crystal display device of the embodiment.

FIG. 3 is a longitudinal sectional view showing a configuration of a conventional liquid crystal display device.

FIG. 4 is a graph showing transmittance-applied voltage characteristics of a conventional liquid crystal display device.

[Explanation of symbols]

 31a to 31c Blue, green, or red transparent pixel electrode 32 Alignment film 32a to 32c Blue, green, or red region 33 Transparent substrate 34 Counter electrode 35 Alignment film 35a to 35c Blue, green, or red region 36 Transparent substrate 37 liquid crystal 38 liquid crystal cell 39 polarizing plate 40 polarizing plate 41 color filter 41a-41c blue, green, or red region

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02F 1/1337 G02F 1/139

Claims (3)

(57) [Claims] 1. A liquid crystal sandwiched between substrates, wherein the liquid crystal forms a bend alignment, and the substrate surface is subjected to an alignment treatment so that liquid crystal molecules near the substrate surface have a predetermined pretilt angle. A liquid crystal display device having pixels, the pixels having color pixels having a plurality of types of color filters that transmit light of a specific color, wherein the predetermined pretilt angles are different in mutually different color pixels. Liquid crystal display device. 2. A method according to claim 1, wherein the plurality of types of color filters are blue,
2. The liquid crystal display device according to claim 1, wherein the three color filters pass green and red, and a pretilt angle of a color pixel corresponding to the color filter increases in the order of blue, green, and red. . 3. The liquid crystal display device according to claim 1, wherein the liquid crystal display element is in a mode in which transmittance increases with an increase in voltage.