JPH11337922A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal device which shows a high contrast ratio without being affected by light scattering through a color filter, etc. SOLUTION: A display is carried out by controlling the transmissivity of light from a back light unit 22 by switching more than two display state in pixels. When the display is carried out, the tilt angles of long axes of liquid crystal molecules to the surfaces of a pair of glass substrates 1 and 2 holding a liquid crystal layer 14 between them, become nearly equal to each other in between the display states. This device is equipped with a slit plate 23 which passes only light whose the angle of incidence for the normal of the glass substrate 2 to respective pixels is less than a specific angle among the lights from the back light unit 22. Consequently, since the luminance in a dark state decreases greatly as compared with a cell which is not equipped with the slit plate 23, the contrast ratio is improved.

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 which provides a high quality display by improving a contrast ratio.

[0002]

2. Description of the Related Art In a thin film transistor (TFT) type liquid crystal display device, which is a type of liquid crystal display device, a thin film transistor is provided for each of a large number of pixels constituting a display surface.
The switching state of the liquid crystal is controlled by the thin film transistor. In general, a row electrode is scanned row by row, a gate of a thin film transistor arranged for a pixel belonging to the row is opened, and a switching state of the pixel (intermediate) is determined by a peak value of a voltage applied to a source (or a drain) at that time. Control). Active research and development are being conducted on such a liquid crystal display device having an active matrix structure to realize a large screen which is considered difficult.

On the other hand, the ferroelectric liquid crystal display device has a so-called simple matrix configuration and provides high-quality display due to the memory property (bistability) of the ferroelectric liquid crystal itself without adding an active element such as a transistor. It is attracting attention because it can be realized. The switching of the display state in the ferroelectric liquid crystal display device is performed while the liquid crystal molecules are kept substantially parallel to the pair of substrates sandwiching the liquid crystal layer. Therefore, in a ferroelectric liquid crystal display device, a high contrast ratio (ratio between luminance in a white display state and luminance in a black display state) can be obtained not only for a viewing angle in the front direction but also for a viewing angle in an oblique direction. And exhibits extremely good viewing angle characteristics.

In practical use of a ferroelectric liquid crystal display device, it is important to realize a high image quality equal to or higher than that of an active matrix structure by a simple matrix structure.
In particular, it is important to obtain a high contrast ratio. Therefore, in order to obtain a high contrast ratio, conventionally, a liquid crystal material,
Improvements in liquid crystal alignment technology, liquid crystal driving methods, and the like are being made.

In an active matrix type liquid crystal display device, a TN (Twisted Nematic) liquid crystal is conventionally used, and a driving method of applying a voltage in a vertical direction to a substrate sandwiching a liquid crystal layer is adopted. When no voltage is applied, the liquid crystal molecules have a twisted structure as a whole, but are individually positioned substantially parallel to the substrate. When the applied voltage is increased to switch the display state, the liquid crystal molecules gradually start to rise in a voltage application direction (a direction perpendicular to the substrate).
That is, the tilt angle of the liquid crystal molecules with respect to the substrate surface changes according to the display state. As described above, the switching that involves the change in the tilt angle of the liquid crystal molecules has a viewing angle dependency that a high contrast ratio cannot be obtained depending on the viewing angle.

Therefore, even in an active matrix type liquid crystal display device, in order to reduce the viewing angle dependency,
In-plane switching liquid crystals have been introduced.
When a nematic liquid crystal is made to function as an in-plane switching liquid crystal, switching is performed while maintaining a substantially parallel posture with respect to a substrate holding a liquid crystal layer.
Extremely good viewing angle characteristics can be obtained.

[0007]

However, in a liquid crystal display device, although a high contrast ratio can be obtained with a relatively small test cell, the improvement of the viewing angle characteristics as described above is applied to a large panel which is to be put to practical use. In some cases, when the technique for the above is applied, the high contrast ratio obtained in the test cell cannot be reproduced. This is because the test cell is relatively small and good orientation is easily obtained, and the structure of the test cell differs greatly from that of the large panel.

For example, in a ferroelectric liquid crystal display device, when a panel is enlarged, a color filter for color display is arranged, and a transparent electrode (for example, an ITO electrode) is used.
In order to minimize the slack of the voltage applied to the liquid crystal due to the increase in the wiring resistance, metal wirings are often provided in parallel with the transparent electrodes, and such color filters and metal wirings cause light scattering. Therefore, a large panel may cause a loss in contrast ratio that was not evident in the test cells without them.

[0009] The present invention has been made in view of the above circumstances, and has as its object to provide a liquid crystal display device having a high contrast ratio.

[0010]

In order to solve the above-mentioned problems, the liquid crystal display device of the present invention controls the transmittance of light from a light source by switching between two or more display states in a pixel. In the liquid crystal display device, in which the inclination angles of the major axes of the liquid crystal molecules with respect to the surfaces of the pair of substrates sandwiching the liquid crystal layer are substantially equal between the display states, of the light from the light source, It is characterized in that it is provided with incident light restricting means for passing only light whose incident angle with respect to the normal is equal to or smaller than a predetermined angle.

In the above configuration, the tilt angle of the long axis of the liquid crystal molecules with respect to the substrate surface is substantially equal between the display states, so that the optical characteristics of the liquid crystal do not change even when the viewing angle for viewing the display surface changes (that is, the viewing angle is wide). ). In such a liquid crystal display device having a wide viewing angle, by providing the incident light restricting means, light having an incident angle equal to or less than a predetermined angle passes,
Light whose incident angle exceeds a predetermined angle is blocked. As a result, the brightness in the dark state is greatly reduced, and as a result, the contrast ratio in front of the display surface is significantly improved. This is particularly noticeable in a large liquid crystal display device.

As described above, in a large liquid crystal display device,
The metal wiring provided along with the color filter and the transparent electrode causes light scattering. Light having a high incident angle causing light scattering is limited by the incident light limiting means. Therefore, the occurrence of light scattering is suppressed, and the contrast ratio is increased.

In Japanese Patent Application Laid-Open Nos. 61-284731 and 4-9818, only light having a certain range of incident angle out of light from a light source is made incident on a liquid crystal panel, and after passing through the liquid crystal panel (light modulation). It is disclosed that the display quality is improved by diffusing the light (later). These technologies are used in liquid crystal display devices with poor viewing angle characteristics.
After light modulation is performed with light having a small incident angle to increase the contrast ratio, the light is diffused to improve the contrast ratio in directions other than the front direction.

In Japanese Patent Application Laid-Open No. 1-25123,
It is disclosed that in a super-twisted nematic liquid crystal, a contrast ratio is improved by limiting incident light from a light source within a range of ± 20 °. In this technology, in a cell having a super-twisted nematic liquid crystal in which grayscale inversion easily occurs, the display quality is improved by limiting incident light as described above and not using light having a viewing angle that causes grayscale inversion. It is planned.

However, such a liquid crystal display device has a problem that the contrast ratio also decreases as the size of the liquid crystal display device increases. Further, since the liquid crystal display device of the first aspect includes a liquid crystal (for example, an in-plane switching liquid crystal) having a wide viewing angle and not causing grayscale inversion due to the viewing angle as described above, the liquid crystal display device receives the light for expanding the viewing angle. There is no need to limit light at large angles. On the other hand, the inventor of the present application has limited the light incident on each pixel to light having a relatively small incident angle in such a liquid crystal display device having a wide viewing angle (particularly, a large liquid crystal display device). It has been found that the contrast ratio in front of the display surface is improved as shown in FIG.

In the liquid crystal display device according to the first aspect, it is preferable that the liquid crystal layer is mainly formed of a ferroelectric liquid crystal. Like an in-plane switching liquid crystal applied to an active matrix type liquid crystal display device, a ferroelectric liquid crystal is a liquid crystal in which the tilt angle of the major axis of liquid crystal molecules with respect to the substrate surface is almost equal between display states. Therefore, also in the liquid crystal display device using the ferroelectric liquid crystal, the contrast ratio in front of the display surface can be improved as in the liquid crystal display device of the first aspect.

In the liquid crystal display device according to the first or second aspect, the incident light restricting means may include a contrast ratio (a white display state) in a direction perpendicular to the substrate (front of the display surface). (Ratio of luminance to luminance in black display state) is 70
It is preferable to limit the incident light as described above. A contrast ratio of about 70 is sufficient for practical use.

As described later, the inventor of the present application has set a predetermined angle of 50 ° in a liquid crystal display device having a specific configuration (according to the liquid crystal display device of claim 1 or 2). It was confirmed that a contrast ratio of 70 could be obtained by setting. Since the predetermined angle at which the contrast ratio of 70 can be ensured depends on the configuration of the liquid crystal display device (for example, the width and pitch of the metal wiring),
It cannot be uniquely identified. However, if the predetermined angle is set to 50 °, light having a relatively small incident angle of 50 ° or less is incident on the pixel. Therefore, even if the configuration of the liquid crystal display device is slightly different from that of the above-described liquid crystal display device, the influence thereof is reduced. It is considered that a contrast ratio close to 70 can be obtained without receiving much.

According to a fifth aspect of the present invention, in the liquid crystal display device having the above-mentioned specific configuration,
It was confirmed that a higher contrast ratio was obtained by setting the predetermined angle to 10 °.

The liquid crystal display device according to claim 1 or 2 is provided with a light blocking member (for example, a black matrix) that blocks light from the light source in the region between the pixels, as described in claim 6. It is preferable that this light shielding member also serves as the incident light limiting means. As described above, by using the light shielding member generally provided in the color liquid crystal display device or the like as the incident light limiting means, it is possible to suppress an increase in the number of components.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

The liquid crystal display device according to the present embodiment is shown in FIG.
(Hereinafter, referred to as a liquid crystal cell) 21. The liquid crystal cell 21 includes two glass substrates 1 and 2 facing each other. If it is a translucent substrate,
Instead of the glass substrates 1 and 2, a resin substrate such as polymethyl methacrylate may be used. Also, the glass substrate 1
A deflection plate (not shown), whose deflection axes are orthogonal to each other, is attached to the outer surface of each of the two.

On the surface of the glass substrate 1 facing the glass substrate 2, transparent electrodes 3 using, for example, ITO (indium tin oxide) as an electrode material are arranged in parallel stripes. On the glass substrate 1, metal wires 4 are arranged in stripes together with the electrodes 3. The metal wiring 4 is made of a metal having lower resistance than the electrode 3 and is formed so as to be covered by the electrode 3. With the metal wiring 4, the wiring resistance of the electrode 3 can be reduced. Further, on the electrodes 3...
A transparent insulating layer 5 made of O ₂ (silicon oxide), SiN (silicon nitride) or the like is laminated.

On the other hand, the glass substrate 1 in the glass substrate 2
Are provided with a color filter layer 8 having a color filter 6 and a black matrix 7. The color filter layer 8 has a structure in which red, green, and blue color filters 6 and black matrices 7 are arranged alternately in parallel. Further, the color filter layer 8 may have an overcoat film (flattening film) that covers the color filter 6 and the black matrix 7 as necessary.

On the color filter layer 8, for example, ITO
Are arranged in stripes parallel to each other so as to be orthogonal to the electrodes 3. Further, on the color filter layer 8, metal wirings 10 are provided in a stripe shape in the same manner as the metal wirings 4 described above. This metal wiring 10 also has a function of reducing the wiring resistance of the electrode 9. Further, on the electrodes 9...
A transparent insulating film 11 made of O ₂ , SiN or the like is laminated.

Further, on the insulating films 5 and 11 are formed alignment films 12 and 13 which have been subjected to a uniaxial alignment process such as a rubbing process. As the alignment films 12 and 13,
A film made of an organic polymer such as polyimide, nylon, or polyvinyl alcohol, a SiO ₂ oblique deposition film, or the like is used. When an organic polymer film is used for the alignment films 12 and 13, an alignment process is generally performed so that liquid crystal molecules are aligned substantially parallel to the glass substrates 1 and 2.

The glass substrates 1 and 2 are kept at a predetermined interval by a spacer (not shown), and a sealing agent (not shown)
As a result, they are bonded to each other at the peripheral portions of the glass substrates 1 and 2. The space formed between the glass substrates 1 and 2 is filled with a liquid crystal material, so that a liquid crystal layer 14 is formed. As the above liquid crystal material,
A liquid crystal material such as a ferroelectric liquid crystal is used such that the inclination angle of the long axis of the liquid crystal molecules with respect to the surfaces of the glass substrates 1 and 2 becomes substantially equal between different display states. Ferroelectric liquid crystals can display high-capacity and high-definition images because they have excellent characteristics such as high-speed response and memory properties.

The ferroelectric liquid crystal molecules (F
In the vicinity of the alignment films 12 and 13, the alignment molecules 1
The liquid crystal layer is inclined at a certain angle (pretilt angle) with respect to the glass substrates 1 and 2 by the interaction with the glass substrates 1 and 2, and is substantially parallel to the glass substrates 1 and 2 in the central portion and the periphery of the liquid crystal layer 14. The FLC molecule receives a force proportional to the vector product of the electric field generated from the potential difference between the electrodes 3 and 9 and the spontaneous polarization, and moves on the orbit of the conical surface.
1, the cell gap is narrow (about 1.0 to 1.5 μm).
m) Settles into a bistable state by setting. The tilt angles of the FLC molecules in the bistable state with respect to the glass substrates 1 and 2 are almost the same. Thereby, the optical characteristics of the liquid crystal layer 14 in the dark display state and the bright display state become almost the same regardless of the viewing angle, so that a wide viewing angle can be obtained.

A pixel region (not shown) is formed by a region where the electrodes 3 and 9 face each other. In this pixel region, when a voltage is applied to the electrodes 3 and 9, as described above, the alignment state of the liquid crystal molecules is switched according to the electric field generated between the electrodes 3 and 9, so that the display state ( The display is performed by changing the light transmittance (light transmittance) between light (white) and dark (black) (and even halftone).

As described above, the liquid crystal cell 21 is constituted by the above layers (films). The present liquid crystal display further includes a backlight unit 22 and a slit plate 2.
3 is provided.

Backlight unit 22 as light source
Is a surface light source that emits uniform light from the back of the transmissive liquid crystal display device. Backlight unit 22
The edge light type is often used, but another type may be used. The edge light type backlight unit 22 includes a fluorescent lamp, a light guide, and a reflector.

Slit plate 23 as incident light limiting means
Is a light-shielding plate whose surface is painted black, has a plurality of slits 23a corresponding to the respective pixel regions, and blocks light from the backlight unit 22 at portions other than the slits 23a. . The slits 23a have the same shape as the pixel area, and the angle of incidence of the light emitted from the light emitting surface 22a of the backlight unit 22 with respect to the surface normal of the glass substrates 1 and 2 to the pixel area is predetermined. Only light having an angle or less is transmitted to the pixel area. For this reason, the slit 23a has a size determined by the relationship between the arrangement position between the light emitting surface 22a and the pixel region and the above-described predetermined angle. Alternatively, the slit 23
When a has a predetermined size, the arrangement position of the slit plate 23 may be adjusted such that the slit 23a is located at a position satisfying the above-described predetermined angle condition between the light emitting surface 22a and the pixel region.

The effect of the slit plate 23 in the liquid crystal display device configured as described above will be described.

First, the contrast ratio between the test cell without the slit plate 23 and the present liquid crystal display device configured as a 17-inch direct-view large-size panel will be compared.

The test cell has a structure in which an ITO transparent electrode is provided on each of a pair of glass substrates, and an insulating film and an alignment film are sequentially provided thereon. The size of the portion where the ITO transparent electrodes overlap on both glass substrates is about 1 cm x
1 cm. On the other hand, the direct-view large-sized panel is configured as described above, and includes a color filter, a black matrix, and the like that are not included in the test cell.

The thickness (cell gap) of the liquid crystal layer (liquid crystal layer 14) of the test cell and the direct-view large-sized panel is about 1.3 μm.
m, and the ferroelectric liquid crystal material contained in the liquid crystal layer is a liquid crystal material developed by the present applicant. This liquid crystal material has a so-called τ-V _min characteristic that a characteristic curve of response speed versus applied voltage has a minimum value, and exhibits negative dielectric anisotropy. The basic physical properties of this liquid crystal material are shown below. Note that τ _min represents the minimum pulse width, and V _min represents the voltage at which τ _min is obtained. Phase transition series (phase transition temperature ^{℃) SmC * - (68.5)} -SmA- (90.7) -N * - (98.4) -Iso spontaneous polarization (25 ℃) 10nC / cm ² memory angle 2θ _m (25 ℃) 15. 6 ° τ _min (25 ° C) 9μs V _min (25 ° C) 31V

The above ferroelectric liquid crystal material includes:
It may be used SCE8 available from Merck may be used other liquid crystal material having a characteristic (τ-V _min characteristic) as described above.

The above test cell and the direct-view large-sized panel both have a three-slot (110) DRAMA driving method.
(JCJones and CVBrown, Proc. Of.Euro Display ''
96, P151-154.) Is applied to provide a data signal and a scanning signal as shown in FIG. This (110) is the first
The peak values of the data voltages of the slot, the second slot, and the third slot are (-1) × _Vd or 1 × _Vd , 1 ×, respectively.
Indicates that a V _d or _{(-1) × V d, 0} × V d. Accordingly, the data signal, first, second and third slots, respectively voltage V _d, and the rewriting signal a pulse signal which is -V _d, 0, first in the rewrite signal, the second slot It is composed of a non-rewrite signal of which voltage has been exchanged (reverse polarity), and the effective voltage value of the data signal is 5V. The scanning signal is composed of a pulse signal in which the first slot is 0 and the second to fifth slots are V _s (20 V), and two thirds of the selection period, that is, two slots are extended beyond the selection period. ing.

As a result of synthesizing the data signal and the scanning signal, two types of synthesized signals shown in FIG. 2 are given to the pixel. Specifically, when the rewriting signal and the scanning signal are combined, a combined signal on the left side in FIG. 2 is obtained, and when the non-rewriting signal and the scanning signal are combined, a combined signal on the right side is obtained.

The results of measuring the front-side contrast ratio of the test cell and the direct-view large-sized panel driven as described above are shown below.

In the case of the test cell, when the luminance of the light emitting surface 22a of the backlight unit 22 is 6432 cd / m ² , the luminance in the dark state is 8.457 cd / m ² and the luminance in the bright state is 875.3 cd / m 2. ^Since it is ² , the contrast ratio is 104. On the other hand, in the case of the direct-view large panel, when the luminance of the light emitting surface 22a is 6640 cd / m ² , the luminance in the dark state is 1.103 cd / m ² and the luminance in the bright state is 51.9.
Since it is ² cd / m ² , the contrast ratio is 47.

As described above, the contrast ratio of the large direct-view panel was much lower than the contrast ratio of the test cell. As described above, the absolute value of the luminance of the test cell differs greatly from that of the direct-view large-sized panel because the direct-view large-sized panel includes members that cause light scattering, such as the color filter 6 and the black matrix 7. It is based on the fact that the light transmission of the state is considerably smaller than in a test cell without these.

Next, as shown in FIG. 3, a slit plate 23 is arranged between the liquid crystal cell 21 and the backlight unit 22, and the slit plate 23 controls light incident on the liquid crystal cell 21 from the backlight unit 22. In a limited manner, the contrast ratio of the test cell and the direct-view large-sized panel was evaluated in the same manner as described above.

The slit plate 23 used in this evaluation
Unlike the fixed type shown in FIG. 1, is provided movably between the liquid crystal cell 21 and the backlight unit 22. By moving, the contrast ratio measurement area (hereinafter simply referred to as the measurement area A), that is, the maximum incident angle θ of light that enters the specific pixel region from the backlight unit 22 is adjusted. The maximum incident angle θ is, as described above,
And is set to about 45 °.

The results of measuring the contrast ratio in the front direction of the test cell and the large-size direct-view panel configured as described above are shown below.

In the case of the test cell, when the luminance of the light emitting surface 22a of the backlight unit 22 is 6432 cd / m ² , the luminance in the dark state is 8.293 cd / m ² and the luminance in the bright state is 879.0 cd / m 2. ^Since it is ² , the contrast ratio is 106. On the other hand, in the case of a large direct-view panel, when the luminance of the backlight source 21 is 6640 cd / m ² , the luminance in the dark state is 0.6128 cd / m ² and the luminance in the bright state is 48.45 cd / m ² . Therefore, the contrast ratio is 79.

As described above, the contrast ratio of the large direct view type panel having the slit plate 23 is much larger than the contrast ratio of the large direct view type panel not having the slit plate 23, and the contrast of the test cell is large. It is very close to the ratio. On the other hand, since the test cell originally has a high contrast ratio, the contrast ratio is not significantly improved by the slit plate 23.

Based on the above evaluation results, it can be seen that the contrast ratio is increased by limiting the light incident on the measurement area A from the backlight unit 22 to light having an incident angle equal to or less than the maximum incident angle θ. However,
If the maximum incident angle θ is too small, light enters only in a very narrow range, and the viewing angle of the liquid crystal display device becomes small.

Now, the results of measuring the contrast ratio of a large direct-view type panel with the arrangement position of the slit plate 23 different from the above case are shown. In this case, the slit 23a
FIG. 4 shows the relationship between the maximum incident angle θ to the pixel, the bright state luminance, and the dark state luminance obtained from the size of the pixel and the position of the slit 23a, and shows the relation between the maximum incident angle θ and the contrast ratio. It is shown in FIG.

FIG. 4 shows that limiting the incidence of light to the measurement area A to light having a maximum angle of incidence θ or less improves the luminance characteristics particularly in the dark state (decreases the luminance). Also, from FIG. 5, the maximum incident angle θ is about 50 °.
It can be seen that a contrast ratio 70 exceeding 47, which is the contrast ratio of a direct-view large-sized panel without the slit plate 23, can be obtained when is set to. This contrast ratio is a value sufficient for practical use. In particular, when the maximum incident angle θ is set to about 40 °, the contrast ratio reaches almost 80, and it can be seen that a contrast ratio of about 80% or more of the test cell can be obtained.

Based on the above evaluation results, the contrast ratio can be improved by restricting the incidence of light on the measurement area A to light having a maximum incident angle θ or less. Specifically, if the maximum incident angle θ is set to about 50 ° as described above, the contrast ratio can be increased as compared with the case where the incident light is not limited. In particular, when the maximum incident angle θ is 10
When set to °, as shown in FIG. 5, a contrast ratio of about 100 can be obtained in a large direct-view panel as well as in a test cell.

Therefore, if the incident light is restricted, the contrast ratio can be improved accordingly. However, if the incident light is restricted too much, the viewing angle characteristics of the liquid crystal display device may be impaired. That is, since the viewing angle depends on the incident angle,
The incident angle should be set according to the required viewing angle according to the purpose of use. For example, in the case of a television, a relatively wide viewing angle is required in order to be viewed by a plurality of viewers, while in the case of a notebook personal computer, it is assumed that the screen is viewed directly from the front. Comparatively low A narrow viewing angle is acceptable.

Further, since the incident angle depends on the structure of the panel, it is conceivable that if the structure of the panel (for example, the width or pitch of the metal wiring) is different, it changes accordingly. Therefore, if the structure is different from the direct-view large-sized panel used for the above measurement, it is expected that the maximum incident angle θ at which a contrast ratio of 70 is obtained will be slightly different from 50 °. This is because at relatively small angles of incidence of 50 ° or less,
The difference in the effect of light scattering due to metal wiring with a different structure
Although not considered to be very large, it is desirable to set the maximum incident angle θ to an angle at which a practical contrast ratio of 70 can be obtained in any of the liquid crystal display devices.

Next, a modified example of this embodiment will be described.

In the liquid crystal display device according to this modification, the maximum incident angle θ (the broken line of the glass substrate 2 shown by a broken line in the drawing) is controlled without controlling the thickness of the black matrix 7 without using the slit plate 23. Angle to the normal).
Specifically, the glass substrate 2 on which the black matrix 7 is formed is disposed on the backlight unit 22 side.
Since the black matrix 7 is a light absorbing layer, it has a function of restricting incident light to the pixel region. Therefore, as the thickness of the black matrix 7 increases, the incidence of light on the pixel region is further restricted. For example, as shown in FIG. 6, in a structure where the thickness of the glass substrate 2 is 1 mm and the size of the pixel region is 360 μm × 360 μm, the black matrix 7 is formed on the glass substrate 2 with a thickness of 360 μm. In this case, light having an incident angle of 45 ° or more is blocked by the black matrix 7. Accordingly, light incident on the pixel region in the liquid crystal layer 14 is limited to light having an incident angle smaller than 45 °.

Therefore, even with such a black matrix 7, a contrast ratio of 70 or more (about 80) can be obtained.

Further, another modification of the present embodiment will be described.

The liquid crystal display device according to the present modification has a film 31 (available from Sumitomo Chemical Co., Ltd.) as shown in FIG. 7 for limiting incident light. The film 31 as the incident light restricting means has a large number of very fine prism-shaped light refracting elements (hereinafter, referred to as prism-shaped elements) 31a formed side by side in the Y direction. The film 31 configured in this manner allows light incident from the X direction perpendicular to the flat surface thereof to be refracted by the prism element 31a, and is perpendicular to the triangular groove formed by the prism element 31a. The exit angle from the film 31 of light that enters at an angle that spreads in two directions (Y direction) is limited to be smaller than the incident angle.

By arranging such a film 31 between the liquid crystal cell 21 and the backlight unit 22 as shown in FIG. 8, the angle of incidence on the liquid crystal cell 21 (the angle of emission from the film 31) is restricted. Is done. Further, two films 31 may be used by bonding together flat surfaces such that the triangular groove directions are substantially orthogonal to each other. In such a structure, it is possible to limit the incidence of light having a large incident angle or to reduce the amount of transmitted light to such an extent that there is no practical problem. Thus, the film 31
Therefore, the black matrix 7 may be provided on the glass substrate 1 side.

The above-mentioned film 31 is also used by the above-mentioned film 31.
Of course, a contrast ratio of 0 or more can be obtained.

In the film 31, the pitch of the prism elements 31a is preferably shorter than the length of one side of the pixel region (for example, 0.3 mm).

Subsequently, still another modification of the present embodiment will be described.

In the liquid crystal display device according to this modification, as shown in FIG. 9, a light refraction control element 41 such as a microlens array is arranged for each pixel P in order to limit incident light. Light refraction control element 41 as incident light limiting means
Are the upper and lower surfaces (pixel side) according to the shape of the pixel P.
Are square, and the four sides are trapezoidal.

With such an element, as shown in FIG. 10, it is possible to limit the incidence of light having a large incident angle, or to reduce the amount of transmission to a level that does not pose a practical problem. As described above, since the light incidence is restricted by the light refraction control element 41, the black matrix 7 is
It may be provided on the side. Further, it is needless to say that the contrast ratio of 70 or more can be obtained by the light refraction control element 41.

[0065]

As described above, in the liquid crystal display device according to the first aspect of the present invention, the tilt angle of the long axis of the liquid crystal molecules with respect to the surfaces of the pair of substrates sandwiching the liquid crystal layer is two or more in the pixel. A liquid crystal display device which is substantially equal between states, comprising incident light limiting means for passing only light having an incident angle with respect to a normal line of a substrate to each pixel which is equal to or less than a predetermined angle among light from a light source. Configuration.

In such a liquid crystal display device having a wide viewing angle, by providing the incident light restricting means, only light having an incident angle equal to or less than a predetermined angle passes, while light having an incident angle exceeding the predetermined angle is blocked. As a result, the brightness in the dark state is greatly reduced, and as a result, the contrast ratio is greatly improved. This is particularly noticeable in a large liquid crystal display device. Therefore, there is an effect that a liquid crystal display device with good display quality can be provided.

A liquid crystal display device according to a second aspect of the present invention comprises:
In the liquid crystal display device according to the first aspect, since the liquid crystal layer is mainly formed of ferroelectric liquid crystal, the same applies to a liquid crystal display device using a ferroelectric liquid crystal. In addition, the contrast ratio in front of the liquid crystal panel can be improved. Therefore, there is an effect that the display quality of the ferroelectric liquid crystal display device, in particular, a large ferroelectric liquid crystal display device can be improved.

A liquid crystal display device according to a third aspect of the present invention comprises:
3. The liquid crystal display device according to claim 1, wherein the incident light restricting means restricts incident light so that a contrast ratio in a direction perpendicular to the substrate is 70 or more.
It can be used sufficiently for practical use. Therefore, there is an effect that a highly practical liquid crystal display device can be provided.

A liquid crystal display device according to a fourth aspect of the present invention comprises:
In the liquid crystal display device according to claim 1 or 2, since the predetermined angle is set to 50 °, a contrast ratio close to 70 can be obtained. Therefore, there is an effect that a liquid crystal display device with good display quality can be provided.

A liquid crystal display device according to a fifth aspect of the present invention comprises:
In the liquid crystal display device according to claim 1 or 2, since the predetermined angle is set to 10 °, a higher contrast ratio can be obtained. Therefore, there is an effect that a liquid crystal display device having extremely good display quality can be provided.

A liquid crystal display device according to a sixth aspect of the present invention comprises:
3. The liquid crystal display device according to claim 1, further comprising a light blocking member for blocking light from the light source in a region between the pixels, and the light blocking member also serving as the incident light limiting means, thereby increasing the number of components. Can be suppressed. Therefore, while suppressing the increase in product cost and structural complexity,
There is an effect that a liquid crystal display device with good display quality can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a structure of a main part of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a waveform diagram showing waveforms of a data signal, a scanning signal, and a composite signal used in evaluating a contrast ratio between the liquid crystal display device applied to a direct-view large-sized panel and a test cell.

FIG. 3 is a perspective view showing a configuration including a test cell used for evaluating a contrast ratio and a slit plate of a direct-view large-sized panel.

FIG. 4 is a graph showing a characteristic of a maximum incident angle versus luminance when a slit plate is used.

FIG. 5 is a graph showing a characteristic of a maximum incidence angle versus a contrast ratio when a slit plate is used.

FIG. 6 is a cross-sectional view showing a configuration of a main part of a modification of the embodiment of the present invention.

FIG. 7 is a perspective view showing a film for limiting incident light, which is used in another modification of the embodiment of the present invention.

FIG. 8 is a cross-sectional view illustrating a configuration of a liquid crystal display device in which the film is incorporated.

FIG. 9 is a perspective view showing a light refraction control element for limiting incident light, which is used in still another modification of the embodiment of the present invention.

FIG. 10 is a cross-sectional view illustrating a configuration of a liquid crystal display device in which the light refraction control element is incorporated.

[Explanation of symbols]

 1.2 Glass substrate 7 Black matrix (light shielding member) 14 Liquid crystal layer 21 Liquid crystal display element 22 Back light unit (light source) 23 Slit plate (incident light limiting means) 31 Film (incident light limiting means) 41 Light refraction control element (incident) Light limiting means)

 ──────────────────────────────────────────────────の Continuation of the front page (71) Applicant 390040604 United Kingdom THE SECRETARY OF STATE FOR DEFENSE IN HER BRITANNIC MAJES TY'S GOVERNMENT OF THE THE UNTERED KINGDOM OF GREEN REGISTER MONEY REGISTER MAN Borrow Ivey Road (No address) Defence Evaluation and Research Agency (72) Inventor Akira Tagawa 22-22 Nagaikecho, Abeno-ku, Osaka, Osaka

Claims (6)

[Claims] The present invention controls the transmittance of light from a light source by switching two or more display states in a pixel, and adjusts the inclination angle of the long axis of liquid crystal molecules with respect to the surfaces of a pair of substrates sandwiching a liquid crystal layer. In a liquid crystal display device which is substantially equal between display states, out of light from the light source, incident light limiting means for passing only light whose incident angle with respect to the normal of the substrate to each pixel is equal to or less than a predetermined angle is provided. A liquid crystal display device comprising: 2. The liquid crystal display device according to claim 1, wherein said liquid crystal layer is mainly formed of ferroelectric liquid crystal. 3. The liquid crystal display device according to claim 1, wherein the incident light restricting means restricts the incident light so that a contrast ratio in a direction perpendicular to the substrate becomes 70 or more. 4. The liquid crystal display device according to claim 1, wherein the predetermined angle is set to 50 °. 5. The liquid crystal display device according to claim 1, wherein the predetermined angle is set to 10 °. 6. The light-emitting device according to claim 1, further comprising a light-shielding member that shields light from the light source in a region between the pixels, wherein the light-shielding member also functions as the incident light limiting means. Liquid crystal display.