JP2870860B2 - Liquid crystal display device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a birefringence effect type liquid crystal display device.

[Conventional technology]

Recently, the number of display pixels of a dot matrix liquid phase display element for displaying a television image or the like has become extremely large in order to increase the screen size and the resolution, and accordingly, multiplex driving with a high duty is required. Is required, but TN has been widely used
The liquid crystal display element of the type has a problem that when multiplex driving is performed at a high duty, an operation margin is reduced, so that a display contrast is reduced and a viewing angle characteristic is also deteriorated.

For this reason, use of a birefringent effect type liquid crystal display device has recently been studied in order to improve the multiplex drive characteristics. As this birefringence effect type liquid crystal display element,
There are ECB type or STN type.

However, in this birefringence effect type liquid crystal display element, since the refractive index anisotropy Δn of the liquid crystal has wavelength dependence, the phase between the ordinary ray and the extraordinary ray differs for each wavelength light, and the total visible light Since the transmittance cannot be equalized over the band, and the display is colored, there is a problem that good black-and-white display or full-color display cannot be obtained.

Therefore, it has been studied to eliminate the coloring of the display of the above-mentioned birefringent effect type liquid crystal display element. As a means, a light incident side of an ECB type or STN type display liquid crystal cell having a display electrode is used. Alternatively, a color compensating means (liquid crystal cell or phase plate) for compensating for coloring of transmitted light due to the wavelength dependence of the liquid crystal of the display liquid crystal cell is provided on the emission side, and the display is colored by the color compensating action of the color compensating means. Is thought to be eliminated.

FIGS. 4 and 5 show a conventional liquid crystal display device provided with a color compensating means. Here, an ECB type liquid crystal cell is used as a color compensating means on the light incident side (lower side) of an ECB type display liquid crystal cell. The figure shows an arrangement of liquid crystal cells for color compensation.

The structure of this liquid crystal display element will be described. In FIGS. 4 and 5, reference numerals 1, 2, and 3 denote upper, middle, and lower three transparent substrates, respectively, an upper substrate 1, an intermediate substrate 2, and an intermediate substrate. The substrate 2 and the lower substrate 3 are polymerized and bonded via frame-shaped sealing materials 4a and 4b, respectively. Nematic liquid crystals LCa and LCb are sealed between the upper substrate 1 and the intermediate substrate 2 and between the intermediate substrate 2 and the lower substrate 3, respectively. A liquid crystal cell for display (hereinafter, referred to as a display cell) A is constituted by the above, and a liquid crystal cell for color compensation (hereinafter, referred to as a color compensation cell) B is constituted by the intermediate substrate 2, the lower substrate 3, and the liquid crystal layer therebetween.

Transparent electrodes 5 and 6 for display are formed on opposite surfaces of both substrates (upper substrate and intermediate substrate) 1 and 2 of the display cell A, respectively.
The horizontal alignment processing films 7a and 8a are formed thereon. The alignment processing directions (for example, rubbing directions) of the alignment processing films 7a and 8a are directions substantially opposite to each other (substantially parallel and opposite directions), and the molecules a of the liquid crystal LCa of the display cell A are shown in FIG. As described above, the electrodes are homogeneously arranged in the direction of the vertical axis y of the substrate.

Further, on the opposing surfaces of both substrates (intermediate substrate and lower substrate) 2, 3 of the color compensation cell B, there are no display electrodes, and only horizontal alignment processing films 7b, 8b are formed. This alignment treatment film 7b, 8b
Of the liquid crystal LCb of the color compensation cell B are substantially orthogonal to each other and substantially perpendicular to the alignment processing directions of the alignment films 7a and 8a of the display cell A.
As shown in FIG. 5, the liquid crystal molecules are homogeneously aligned in a direction (horizontal axis x direction) orthogonal to the liquid crystal molecule alignment direction of the display cell A.

In FIG. 4, reference numerals 9a and 9b denote a pair of upper and lower polarizing plates disposed on both sides of the display cell A and the color compensating cell B, and the polarization axes of the polarizing plates 9a and 9b ( The directions of the transmission axis or the absorption axis) are substantially orthogonal to each other, and are approximately 45 ° with respect to the liquid crystal molecule alignment direction of the display cell A and the color compensation cell B.

This ECB type liquid crystal display element is configured so that coloring of transmitted light due to the wavelength dependence of the liquid phase LCa in the display cell A is compensated by the color compensation cell B. If the homogeneous arrangement directions of the molecules a and b are substantially orthogonal as described above, since the phase difference between the ordinary ray and the extraordinary ray for each wavelength light generated in the display cell A is canceled by the color compensation cell B, Good black-and-white display or full-color display can be obtained without coloring the display.

Here, the color compensation cell B is provided on the light incident side of the display cell A.
Has been described. However, even if the color compensation cell B is arranged on the light emission side (upper side) of the display cell A, the coloration of the display can be similarly eliminated.

Such an achromatic display can also be performed in an STN type liquid crystal display device in which the twist angle of the liquid crystal molecule arrangement is larger (180 ° to 270 °) than a normal TN type liquid crystal display device (90 ° twist). That is, in the case of the STN type liquid crystal display element, an STN type liquid crystal cell in which liquid crystal molecules are twisted at the same angle in the direction opposite to the twist direction of the liquid crystal molecule alignment of the display cell is used as a color compensation cell. The cells may be arranged on the light incident side or the emission side of the display cell such that the liquid crystal molecule alignment directions on the adjacent sides of both cells are substantially orthogonal to each other. In this STN-type liquid crystal display element, the polarization axis directions of a pair of polarizing plates disposed on both sides of the display cell and the color compensation cell are substantially orthogonal to each other, and one of the polarizing plates, for example, The polarization axis direction of the polarizing plate on the display cell side is in a direction of 35 ° to 50 ° with respect to the liquid crystal molecule alignment direction on the polarizing plate side of the display cell.

Further, the color compensation means disposed on the light incident side or the emission side of the display cell may use a phase plate instead of the liquid crystal cell,
Also in this case, the phase difference of the phase plate and the refractive index thereof according to the value of Δn · d (the product of the refractive index anisotropy Δn of the liquid crystal and the thickness d of the liquid crystal layer) of the display cell and the alignment state of the liquid crystal molecules. If the maximum direction is appropriately selected, the coloring of the display can be eliminated as in the case of using the liquid crystal cell for color compensation.

[Problems to be solved by the invention]

However, the conventional ECB-type or STN-type liquid crystal display element in which the color compensation means (color compensation liquid crystal cell or phase plate) is arranged on the light incident side or the emission side of the display liquid crystal cell as described above has a viewing angle disparity. Significantly, therefore, when the display is observed from a direction along the normal line of the display surface, the display is hardly colored, but when viewed from a direction inclined with respect to the normal line, the display appears to be colored. .
This is because the value of Δn · d of the color compensation cell B decreases as the viewing angle (the angle of the observation direction with respect to the normal) increases.

That is, FIG. 6 shows the viewing angle inconsistency of the voltage-transmittance characteristic of the conventional liquid crystal display element. In the conventional liquid crystal display element, when the inclination angle θ of the search direction with respect to the normal becomes about 30 °, The voltage-transmittance characteristic changes greatly, and the display looks remarkably colored.

In particular, in a large-screen liquid crystal display device, even if the observation direction with respect to the vicinity of the center of the screen is the direction of the normal, the outer peripheral side of the screen is observed from a direction inclined with respect to the normal. The closer to the outer periphery of the screen, the more noticeable the coloring of the display becomes. Therefore, the display on the outer periphery of the screen is colored in black and white display, and the display color on the outer periphery of the screen is discolored in full color display.

The present invention has been made in view of the above circumstances, and aims to eliminate the coloring of the display, and furthermore, the display can be performed even when viewed from a direction inclined with respect to the normal to the display surface. It is an object of the present invention to provide a birefringent effect type liquid crystal display element in which the viewing angle is widened without coloring.

[Means for solving the problem]

The liquid crystal display element of the present invention is a birefringent effect type display liquid crystal comprising an opposing display electrode, an alignment film subjected to alignment treatment in substantially opposite directions to each other, and a liquid crystal layer interposed between the opposing alignment films. A cell, having a birefringent layer having an optical axis in a direction substantially perpendicular to the orientation direction of the display liquid crystal cell, and a color compensation unit for compensating coloring of transmitted light due to wavelength dependence of the display liquid crystal cell; A viewing angle compensating unit having a birefringent layer having an optical axis in a thickness direction, and a display liquid crystal cell, the color compensating unit, and the viewing angle compensating unit, which are arranged with a stacked body interposed therebetween, and one of the polarization axes is the display direction. And a pair of polarizing means arranged in a direction substantially 45 ° with respect to the alignment processing direction of the liquid crystal cell for use and arranged so that their polarization axes are substantially orthogonal to each other.

[Action]

That is, the liquid crystal display element of the present invention eliminates the coloring of the display by canceling out the phase difference of each wavelength light generated in the birefringent effect type display liquid crystal cell by the color compensating means, and has an optical axis in the thickness direction. The viewing angle compensating means is provided to reduce the viewing angle inconsistency.Therefore, according to this liquid crystal display element, the coloring of the display is eliminated, and even if the display is observed from a direction inclined with respect to the normal to the display surface. The viewing angle can be widened so that the display is not colored.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS.

FIGS. 1 and 2 show the structure of the liquid crystal display element of this embodiment. Here, an ECB type color is provided as a color compensation means on the light incident side (lower side) of the ECB type display liquid crystal cell A. A liquid crystal cell B for compensation is arranged, and a liquid crystal cell C for compensating for viewing angle of homeotropic alignment is arranged between the liquid crystal cell A for display and the liquid crystal cell B for color compensation as a visual angle compensating means. .

The structure of this liquid crystal display element will be described. In FIGS. 1 and 2, reference numerals 11, 12a, 12b, and 13 denote four transparent substrates which are vertically opposed to each other. substrate
12a, intermediate lower substrate 12b and lower substrate 13, and intermediate upper substrate 12a
And the intermediate lower substrate 12b are frame-shaped sealing materials 14a, 14b, 1 respectively.
Polymerized and bonded through 4c. Nematic liquid crystals LCa and LCb are sealed between the upper substrate 11 and the intermediate upper substrate 12a and between the intermediate lower substrate 12b and the lower substrate 13, respectively. A liquid crystal cell for display (hereinafter referred to as display cell) A is constituted by the liquid crystal layer, and a liquid crystal cell for color compensation (hereinafter referred to as color compensation cell) B is constituted by the intermediate lower substrate 12b, the lower substrate 13 and the liquid crystal layer therebetween. ing. A nematic liquid crystal LCc is sealed between the upper intermediate substrate 12a and the lower intermediate substrate 12b. A liquid crystal cell for compensating viewing angles (hereinafter referred to as a viewing angle) is formed by the upper intermediate substrate 12a, the lower intermediate substrate 12b, and a liquid crystal layer therebetween. C (referred to as a compensation cell).

Both substrates (upper substrate and intermediate upper substrate) of the display cell A 11,1
Transparent electrodes 15 and 16 for display (scanning electrode and signal electrode for simple matrix type liquid crystal cell, pixel electrode and counter electrode for TFT active matrix type liquid crystal cell) are formed on the opposite surface of 2a, respectively. The horizontal alignment processing films 17a and 18a are formed thereon. This alignment treatment film 17a, 1
The alignment treatment direction (eg, rubbing direction) of 8a is almost directly opposite (substantially parallel and opposite) to each other. It is homogeneously arranged in the y direction.

Further, on the surface of the color compensation cell B opposite to the two substrates (the intermediate lower substrate and the lower substrate) 12b and 13, there are no display electrodes, and only horizontal alignment processing films 17b and 18b are formed. This alignment treatment film 1
The alignment processing directions of 7b and 18b are almost exactly opposite to each other and substantially orthogonal to the alignment processing directions of the alignment processing films 17a and 18a of the display cell A. The molecules b of the liquid crystal LCb of the color compensation cell B are As shown in FIG. 2, the liquid crystal molecules are homogeneously oriented in a direction (substrate horizontal axis x direction) orthogonal to the liquid crystal molecule alignment direction of the display cell A.

On the other hand, there is no display electrode on the opposing surface of both substrates (intermediate upper substrate and intermediate lower substrate) 12a and 12b of the viewing angle compensation cell C,
Only the vertical alignment treatment films 21 and 22 are formed, and the molecules c of the liquid crystal LCc of the viewing angle compensation cell C are, as shown in FIG. Is homeotropically oriented.

In FIG. 1, reference numerals 19a and 19b denote a pair of upper and lower polarizing plates disposed on both sides of the display cell A, the viewing angle compensation cell C, and the color compensation cell B, respectively. The directions of the polarization axes (transmission axis or absorption axis) of 19a and 19b are substantially perpendicular to each other, and are substantially 45 ° with respect to the liquid crystal molecule alignment direction of the display cell A and the color compensation cell B.

In the liquid crystal display device of this embodiment, similarly to the conventional liquid crystal display device shown in FIGS. 4 and 5, coloring of transmitted light due to the wavelength dependence of the display cell A is compensated by the color compensation cell B. In this liquid crystal display element, the display cell A
The viewing angle compensating cell C located between the liquid crystal LCc and the color compensating cell B has the molecules c of the liquid crystal LCc homeotropically aligned, and therefore has an optical refractive index difference with respect to the light transmitted vertically to the substrate surface. Since there is no anisotropy, the color compensation action of the color compensation cell B is not affected by the viewing angle compensation cell C. Therefore, if the homogeneous alignment directions of the liquid crystal molecules a and b in the display cell A and the color compensation cell B are substantially orthogonal as described above, each wavelength light generated by the wavelength dependence of the liquid crystal LCa of the display cell A Since the phase difference between the ordinary ray and the extraordinary ray is canceled out by the color compensation cell B, it is possible to obtain good black-and-white display or full-color display without coloring the display.

In the liquid crystal display element of this embodiment, the viewing angle compensation cell C in which the molecules c of the liquid crystal LCc are homeotropically aligned is provided between the display cell A and the color compensation cell B. Therefore, according to this liquid crystal display element, the viewing angle can be widened so that the display is not colored even when viewed from a direction inclined with respect to the normal to the display surface. . This is because the value of Δn · d of the color compensation cell B, which is a horizontal alignment cell, decreases as the viewing angle (the angle of the observation direction with respect to the normal) increases, but the viewing angle compensation, which is a vertical alignment cell, increases. This is because the value of Δn · d of the cell C increases as the viewing angle increases, and thus the viewing angle incompatibility due to the total Δn · d of the color compensation cell B and the viewing angle compensation cell C is reduced. You.

FIG. 3 shows the viewing angle dependence of the voltage-transmittance characteristics of the liquid crystal display element of the above embodiment.
Even if the inclination angle θ of the search direction with respect to the normal is close to 30 °, the change in the voltage-transmittance characteristic is small, and therefore, the coloring of the display can be suppressed over a wide viewing angle.

In the above embodiment, the color compensation cell B is arranged on the light incident side of the display cell A. However, the color compensation cell B may be arranged on the light emission side (upper side) of the display cell A. .

Further, in the above embodiment, the liquid crystal cell was used as the color compensating means for compensating the coloring of the transmitted light in the display cell. However, this color compensating means may be a phase plate, and the viewing angle compensating means may be arranged in the thickness direction. As long as the liquid crystal cell has an optical axis, the liquid crystal cell is not limited to a liquid crystal cell in which liquid crystal molecules are homeotropically aligned.

〔The invention's effect〕

The liquid crystal display element of the present invention eliminates the color difference of the display by canceling the phase difference between the ordinary ray and the extraordinary ray for each wavelength light generated in the birefringence effect type display liquid crystal cell by the color compensation means, and has a thickness. Since the viewing angle incompatibility is reduced by providing a viewing angle compensating means having an optical axis in the direction, according to this liquid crystal display device, the display is not colored, and the display is inclined with respect to the normal line of the display surface. The viewing angle can be widened so that the display is not colored even when viewed from the direction.

[Brief description of the drawings]

FIGS. 1 to 3 show an embodiment in which the present invention is applied to an ECB type liquid crystal display device. FIGS. 1 and 2 are sectional views of the liquid crystal display device and liquid crystal molecules of each liquid crystal cell. FIG. 3 is a perspective view showing an arrangement state, and FIG. 3 is a view showing a viewing angle dependency of a voltage-transmittance characteristic of a liquid crystal display element. 4 and 5 are cross-sectional views of a conventional ECB type liquid crystal display device and perspective views of the liquid crystal molecule alignment state of each liquid crystal cell. FIG. 6 shows the voltage-transmittance characteristics of the conventional ECB type liquid crystal display device. It is a figure which shows visual angle incompatibility. A: display liquid crystal cell, B: color compensation liquid crystal cell (color compensation means), C: viewing angle compensation liquid crystal cell (viewing angle compensation means).

Claims (1)

(57) [Claims] A birefringent effect type display liquid crystal cell comprising: an opposite display electrode; an alignment film that is aligned in substantially opposite directions to each other; and a liquid crystal layer interposed between the opposite alignment films. A color compensator having a birefringent layer having an optical axis in a direction substantially perpendicular to the orientation direction of the display liquid crystal cell, and a color compensator for compensating for coloring of transmitted light due to wavelength dependence of the display liquid crystal cell; A viewing angle compensating means having a birefringent layer having an optical axis, and a display liquid crystal cell, and a laminate of the color compensating means and the viewing angle compensating means interposed therebetween, and one of the polarization axes is the display liquid crystal cell. A liquid crystal display device comprising: a pair of polarizing means arranged in a direction substantially 45 ° with respect to the alignment processing direction, and arranged so that their polarization axes are substantially orthogonal to each other.