JP2003215572A - Semi-transparent liquid crystal display element and image display device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semi-transparent color liquid crystal display element by which the thickness of a liquid crystal layer in a pixel is equal, white display is sufficiently bright, and white and black display is performed with high contrast in constitution of recessing and projecting the shape of a reflecting surface. <P>SOLUTION: The semi-transparent color liquid crystal display element is provided with a liquid crystal cell 12 having liquid crystal sealed between a pair of substrates 13 and 19, polarization films 10a and 10b, one or more birefringence films 11a, 11b, 11c and 11d, and a reflection layer 17. On the lower substrate 19, a recessed and projected layer 18, a semi-transparent reflection layer 17, a flat layer 16 and a transparent electrode 14 are formed in this laminating order from a substrate side. Recessing and projecting structure is provided so that the twist angle of the liquid crystal layer may be not smaller than 220° and not larger than 270° and the diffuse reflectance Rdif of the recessed and projected semitransparent reflection layer consisting of the recessed and projected layer 18 and the reflection layer 17 may be not smaller than 40% and not larger than 70%. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transflective liquid crystal display element used in an image display device.

[0002]

2. Description of the Related Art With the rapid spread of information communication devices such as mobile phones and PDAs (Personal Digital Assistants), a communication infrastructure that anyone can easily access and make calls at any time and place is being established. Since these are premised on mobile applications, the development of lightweight, thin, and low power consumption display elements is required, and liquid crystal display elements are currently at the center.

The liquid crystal display element displays by changing the light transmission intensity by driving the liquid crystal molecules with an effective voltage of several volts, but since the liquid crystal is a non-luminous substance, the visibility is maintained. Requires a light source such as a backlight. Furthermore, in order to improve visibility outdoors, a semi-transmissive liquid crystal display device that has a semi-transmissive reflector under the liquid crystal panel and also uses ambient light has been devised. Can be realized. The transflective liquid crystal display element is becoming indispensable as one of the displays of portable information terminals.

A typical configuration example of a conventional transflective liquid crystal display device is shown in FIG. In FIG. 6, reference numeral 60 denotes a polarizing plate and 6
Reference numeral 1 is a birefringent film, 62 is a liquid crystal cell, 63 is a glass substrate, 64 is a transparent electrode, 65 is a liquid crystal layer, and 66 is a scattering plate. The scattering plate 66 scatters ambient light. In addition, the birefringence effect of the birefringence film 61 ensures a predetermined display brightness.

[0005]

However, in the conventional transflective liquid crystal display, since the display is performed by using the ambient light, the display may be dark depending on the ambient lighting environment. It potentially has the challenge of being. In the configuration shown in FIG. 6, in order to obtain a brighter display, it is necessary to reduce the reflectance of incident light, and the semi-transmissive reflector is bright, that is, the diffuse reflectance Rdif of the single semi-transmissive reflector is It is necessary to strengthen.

However, if such a semi-transmissive reflector having a strong diffuse reflectance is provided below the liquid crystal cell, the white display reflectance decreases due to total reflection, and the black display reflectance increases due to depolarization, resulting in a contrast ratio. Will decrease.
When the light incident on the liquid crystal layer is diffused and reflected by the semi-transmissive reflection plate and is emitted, part of the light is totally reflected at the interface between the transparent electrode and the glass, so that the intensity of the emitted light is significantly reduced. Become. Therefore, the diffuse reflectance Rp in the liquid crystal display device becomes low, and the display becomes very dark.

For example, the diffuse reflectance R of the semi-transmissive reflector alone
Assuming that the transmittance of the polarizing plate is 45% and the transmittance of the color filter is 65% when dif is 90%, the theoretical diffused reflectance Rp of the liquid crystal display element is 17.1%. On the other hand, the measured value is significantly reduced to 7.7%, which confirms that the display is very dark. Also,
Since depolarization occurs, the reflectance of black display is 2.0% and the contrast ratio is 3.9, which is poor.

In the present invention, in view of the above circumstances,
It is an object of the present invention to provide a semi-transmissive liquid crystal display device having a bright white display, a high contrast and a good image.

[0009]

In order to achieve the above object, a transflective liquid crystal display device according to the present invention has a liquid crystal layer between a first substrate and a second substrate, and the first substrate is It has an upper transparent electrode on the liquid crystal layer side and 1 on the opposite side.
The second substrate has one or a plurality of birefringent films and a polarizing film, and the second substrate has an uneven layer, a semi-transmissive reflective layer that transmits a part of light, and a flat uneven surface on the surface on the liquid crystal layer side. In a semi-transmissive liquid crystal display device, in which a flattening layer and a lower transparent electrode are sequentially formed from the second substrate side, and one or more birefringent films and a polarizing film are provided on the opposite surface,
The twist angle of the liquid crystal layer is 220 ° or more and 270 ° or less, and the uneven semi-transmissive reflective layer composed of the uneven layer and the semi-transmissive reflective layer has diffuse reflectivity, and is collected under diffuse illumination by excluding the specular reflection component. When the reflection brightness of the uneven transflective layer measured by the light integration is Bdif and the reflection brightness of the standard white plate measured by the light integration by removing the specular reflection component under diffuse illumination is Bd0, it is defined by (Equation 1). The diffused reflectance Rdif of the uneven reflection layer is 40% or more and 70% or less.

(Formula 1) Rdif = Bdif / Bd0 × 100 (%) With such a configuration, it is possible to reduce the reduction of the light reflected in the semi-transmissive reflection layer due to the total reflection. Therefore, the reflectance of black display due to depolarization is reduced. It is possible to suppress the rise of the white color and realize white display with high reflectance.

Further, since the thickness of the liquid crystal layer can be made constant, a semi-transmissive liquid crystal display device having good optical characteristics with no display unevenness, that is, a high contrast ratio and having a good image outdoors or at night. Can be provided.

Further, in the transflective liquid crystal display element according to the present invention, in the uneven layer, the film thickness difference between the convex portion and the concave portion is 0.1.
It is preferable that the distance is between μm and 1.0 μm and the distance between the adjacent convex portions is between 3 μm and 15 μm. This is because within this range, the diffuse reflectance falls within the range of 40% or more and 70% or less.

Further, in the transflective liquid crystal display element according to the present invention, it is preferable that the concavo-convex layer is made of a material which expands and contracts by light irradiation and heat, and the shape can be controlled by light irradiation and heat. Further, in the semi-transmissive liquid crystal display element according to the present invention, the semi-transmissive reflective layer is preferably formed of a metal containing aluminum or silver as a constituent element.

Next, in order to achieve the above object, the image display device according to the present invention is characterized by having the above-mentioned transflective liquid crystal display element.

With such a structure, the reduction of the light reflected by the semi-transmissive reflective layer due to the total reflection can be reduced, so that the increase of the reflectance of black display due to the depolarization can be suppressed and the white of high reflectance can be suppressed. Since it is possible to realize a display and the liquid crystal layer thickness can be made constant, there is no display unevenness, that is, an image display having good optical characteristics with a high contrast ratio and a good image even outdoors or at night. It becomes possible to provide a device.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A transflective liquid crystal display device according to embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing a transflective liquid crystal display element according to an embodiment of the present invention. In FIG. 1, 1
0a is a polarizing film (1), 10b is a polarizing film (2), 11a is a birefringent film (1), 11b is a birefringent film (2), 11c is a birefringent film (3), and 11d is The birefringent film (4) is shown respectively. Further, 12 is a liquid crystal cell, 13 is an upper transparent substrate, 14 is a transparent electrode, 15 is a liquid crystal layer, 16 is a flattening layer, 17 is a semi-transmissive reflective layer, 18 is an uneven layer, and 19 is The lower transparent substrates are shown respectively.

FIG. 2 is an optical configuration diagram of the transflective liquid crystal display element according to the embodiment of the present invention. In FIG. 2A, 20 is the reference line, 21 is the alignment direction of the liquid crystal molecules on the upper substrate, 22 is the alignment direction of the liquid crystal molecules on the lower substrate, and 23 is the birefringence near the liquid crystal cell. The slow axis direction of the film (1), 24 is the slow axis direction of the birefringent film (2) on the polarizing film side, and 25 is the absorption axis direction of the polarizing film (1). In FIG. 2 (b), 26 is a birefringent film (3) on the side close to the liquid crystal cell.
27, the slow axis direction of the polarizing film, the slow axis direction of the birefringent film (4) on the polarizing film side, and the absorption axis direction of the polarizing film (2). Further, φ _LC0 is the angle between the alignment direction 22 of the liquid crystal molecules on the lower substrate 19 and the reference line 20, and φ _LC is the angle between the alignment direction 21 of the liquid crystal molecules on the upper transparent substrate 13 and the reference line 20. Φ _F1 is the slow axis direction 23 of the birefringent film (1) 11a and the reference line 20.
Φ _F2 is the angle between the slow axis direction 24 of the birefringent film (2) 11b and the reference line 20, and φ _F3 is the slow axis direction 26 of the birefringent film (3) 11c. Line 2
The angle formed by 0 and φ _F4 is the birefringent film (4) 11d.
Is the angle between the slow axis direction 27 of the polarizing film 10a and the reference line 20, φ _p1 is the angle between the absorption axis direction 25 of the polarizing film 10a and the reference line 20, and φ _p2 is the absorption axis direction 2 of the polarizing film 10b.
The angle between 8 and the reference line 20 is shown,
The liquid crystal twist direction is positive. Note that Ω _LC
Indicates the twist angle of the liquid crystal.

The detailed structure of the semi-transmissive liquid crystal display device according to this embodiment will be described below by following the manufacturing procedure. The numbers shown in the description mean the numbers shown in the configuration diagrams of FIGS. 1 and 2.

First, glass substrates are used as the upper transparent substrate 13 and the lower transparent substrate 19, and on the upper transparent substrate 13,
Indium / tin / oxide (IT
O) forms a pixel electrode. Further, light and heat-stretchable resin are applied to the entire surface of the lower transparent substrate 19 by spin coating so as to have a film thickness of 2.0 μm, and ultraviolet rays are applied to
After irradiation with 0 to 100 mJ / cm ² , 1 in a clean oven
By heat treatment at 50 ° C. for 1 hour, expansion and contraction are caused to form an uneven layer 18 having an average distance between convex portions of 10 μm and an average height difference of 0.4 μm between the highest and lowest portions of the irregularities.

Next, the surface is covered with a stainless mask having a predetermined shape, and aluminum having a film thickness of 40 nm is formed by vapor deposition to form the semi-transmissive reflective layer 17.
The diffuse reflectance Rdif of the uneven semi-transmissive reflective layer formed by the uneven layer 18 and the semi-transmissive reflective layer 17 formed here is 50%.
become.

Further, the planarizing layer 1 is formed on the entire surface of the substrate.
6, a heat-effective acrylic resin film was applied by spin coating to a film thickness of 3.0 μm, and then cured in a clean oven at 230 ° C. for 1 hour to give an average film thickness of 2.8 μm and an average surface roughness of 0. The flattening layer 16 having a thickness of 08 μm is formed. Then, a pixel electrode made of indium, tin, and oxide (ITO) is formed as the transparent electrode 14 on the flattening layer 16.

After forming an alignment film on the transparent electrodes 14 formed on the upper transparent substrate 13 and the lower transparent substrate 19, alignment treatment is performed by rubbing. Then, a thermosetting sealing resin mixed with 1.0% by weight of glass fiber is screen-printed on the peripheral portion on the upper transparent substrate 14,
On the lower transparent substrate 19, resin beads with a predetermined diameter of 200
Disperse at a rate of pcs / mm ² . Then, the upper transparent substrate 1
4 and the lower transparent substrate 19 are attached to each other, and the sealing resin is cured by heat treatment at 150 ° C. for 2 hours. And
A mixed liquid crystal in which a predetermined amount of a chiral agent is mixed into an ester nematic liquid crystal having Δn = 0.14 is vacuum-injected, and after sealing with an ultraviolet curable resin, it is cured by irradiation with ultraviolet rays.

On the upper transparent substrate 13 of the liquid crystal cell 12 thus manufactured, a polycarbonate film having a predetermined retardation value is used as the birefringent film (1) 11a and the birefringent film (2) 11b. , Two pieces are attached so that the slow axes each have a predetermined angle. Furthermore, as the polarizing film 10a on it,
A neutral gray polarizing film (SQ-1852AP manufactured by Sumitomo Chemical Co., Ltd.) subjected to anti-glare (AG) treatment is attached so that the direction of the absorption axis forms a predetermined angle. The birefringent films 11c and 11d and the polarizing film 10b are attached to the lower transparent substrate 19 in this order in the same manner as above.

By doing so, it is possible to secure a sufficient difference in retardation of the liquid crystal for white display and black display, and it is possible to compensate for the coloring due to the birefringence effect of the liquid crystal. It is possible to realize a normally black mode semi-transmissive liquid crystal display device that can obtain an achromatic black display with a low reflectance evenly within a pixel and an achromatic white display with a high reflectance.

Regarding the twist angle of the liquid crystal, in the case of simple matrix driving, the duty ratio, which is the number of selectable electrodes, is affected. The larger the twist angle, the smaller the duty ratio can be, and the number of selected lines can be increased. The number of pixels can be increased. In the present embodiment, the duty ratio is 1/20 by setting the twist angle of the liquid crystal within the range of 220 ° or more and 270 ° or less.
It has been confirmed that a good display can be obtained even when driven at 0 or less. It has also been confirmed that the phenomenon of double images does not occur.

Specifically, Δn_LC・ D_LC= 900n
m, R_film(1) = 520 nm, R _film(2) = 700
nm, R_film(3) = 140 nm, R_film(4) = 27
0 nm, φ_LC0= -35 °, φ_LC= 35 °, Ω_LC= 25
0 °, φ_F1= 154 °, φ_F2= 93 °, φ_F3= 100
°, φ_F4= 165 °, φ_p1= 119 °, φ_p2= 0 °, R
The result of measuring the optical characteristics when dif = 50% is shown.
You The measurement was made by Otsuka Electronics LCD-7.
000 is used and the duty ratio is positive at 1/160.
It is the result measured as surface characteristics.

According to this, the contrast is 13.0 both in the reflective display and in the transmissive display, and the white display reflectance in Y value conversion is 68.5% and the transmittance is 3.5%, which are excellent characteristics. I was able to get Further, it can be confirmed that the display changes to achromatic color from black display to white display, and it can be also confirmed that the variation in the reflectance within the pixel is within 0.2% in the vertical direction. From these results, it can be confirmed that an achromatic black and white display can be performed during both reflective display and transmissive display, and a semi-transmissive liquid crystal display device having a high contrast ratio can be realized.

The retardation value Δn _LC · d _{LC of} the liquid crystal layer and the retardation value R _film (i) of the birefringent film used here are retardation values for light having a wavelength λ = 550 nm.

Here, as a comparative experiment, a semi-transmissive liquid crystal display element was produced for various samples having different diffuse reflectances Rdif of the uneven transflective layers 17 and 18 in the above reflective liquid crystal display element, and the front characteristics Was measured.

First, Rdif is 38%, or Rdif
Concavo-convex semi-transmissive reflective layers 17 and 1 having characteristics of f of 40%
For No. 8, the white reflectance of the semi-transmissive liquid crystal display device was compared. As a result, when Rdif is 40%, the white reflectance is 1
While it was 0.0%, when Rdif was 38%, the white reflectance was 7.9%. Therefore, it can be seen that white display with good brightness cannot be obtained when the diffuse reflectance of the uneven transflective layer is less than 40%.

Further, Rdif is 70% or Rdif
Concavo-convex semi-transmissive reflective layers 17 and 18 having f of 74%
The black reflectance and the contrast of the semi-transmissive liquid crystal display element were compared. When Rdif is 70%, the black reflectance is 3.5% and the contrast is 8.8.
When dif was 74%, the black reflectance was 5.0% and the contrast was 4.8. Therefore, when the diffuse reflectance of the concave-convex reflective layer is in the range of more than 70%, the contrast is deteriorated because the reflectance of black display is high, and a good image cannot be obtained. .

The above points will be described below with reference to FIGS. 3 to 5.

First, the diffuse reflectance Rdi of the concave-convex reflective layer alone.
f and diffuse reflectance R during white display of the transflective liquid crystal display element
The relationship between p and depolarization was investigated. The results are shown in Fig. 3.
In addition, in order to measure the diffuse reflection component of the light reflected in the uneven semi-transmissive reflective layer, a spectrocolorimeter CM508d manufactured by Minolta Co., Ltd. was used as a measuring device, and the depolarizing property was measured by a circle on the liquid crystal cell. The measurement was performed on a sample in which a polarizing plate was placed and a pseudo black display was realized.

As can be seen from FIG. 3, the white display diffuse reflectance Rp of the semi-transmissive liquid crystal display element tends to increase in the range where the diffuse reflectance Rdif of the concave-convex semi-transmissive reflective layer alone is 60% or less, and is about 60. Takes the maximum value around%.
On the other hand, it shows a decreasing tendency in the range of the diffuse reflectance Rdif of 60% or more.

The reason for this will be described below with reference to FIG. Unlike the case of the specular reflector, the light that has passed through the liquid crystal layer and reached the surface of the diffuse reflector is reflected in many directions in the observation direction other than the specular reflection direction. That is, the high diffuse reflectance Rdif means that when the incident light is reflected by the surface of the diffuse reflector, the opening angle of the emitted light becomes large.

In FIG. 5, the reflection angle of the reflection plate 17 is θ ₁ , the emission angle from the polarizing film 10 is θ ₂ , and the liquid crystal layer 15 is shown.
The refractive index n _LC is n _LC = 1.5, and the refractive index n _air is n
Assuming _air = 1.0, Snell's law gives
When the relational expression of (Equation 2) exists and 0 ° ≦ θ ₁ ≦ 42 ° (hereinafter, referred to as “range A”), the incident light is reflected from the uneven semi-transmissive reflective layer 17 and from the liquid crystal layer 15. It comes out.

[0037]

[Number 2] _{n LC · SINθ 1 = n air} · SINθ 2 _{However, 42 <θ 1 ≦ 90 °} ( hereinafter, "the range B" hereinafter.), The reflected light from the concave-convex semi-transmissive reflective layer 17,
It becomes impossible to emit light from the polarizing film 10 due to the total reflection.
That is, in the case of Rdif ≦ 60%, the reflected light component of the range A component largely contributes to the Rdif of the uneven reflection layer 17.
Rp increases with increasing. Also, Rdif> 60%
In the case of, since not only the component of the range A but also the component of the range B is included, R accompanying the increase of the reflectance Rdif
It can be seen that a decrease in p occurs.

As can be seen from FIG. 4, the pseudo black reflectance Rb tends to increase as the diffuse reflectance Rdif of the uneven semi-transmissive reflective layer increases. Therefore, when the diffuse reflectance is Rdif ≧ 70%, the reflectance increases due to depolarization during black display, and the contrast decreases.

From the above points, it can be explained that the diffuse reflectance of the concave-convex semi-transmissive reflective layer is preferably 40% ≦ Rdif ≦ 70%. The thickness difference between the concave and convex portions of the uneven layer is 0.1 μm.
Is 1.0 μm, and the distance between adjacent convex portions is 3 μm
It has been confirmed that the diffuse reflectance of the uneven transflective layer having a thickness of 12 μm is within the above range, and the flatness of the surface of the flattening layer 16 can be also reduced to 0.1 μm or less. .

In the above-mentioned embodiment, aluminum is used as the reflective layer,
The present invention is not particularly limited to this, and the same effect can be obtained by using, for example, a metal layer containing silver as a constituent element.

Further, in the above-mentioned embodiment, the retardation values of the birefringent film are 520 nm and 70.
Two pieces of 0 nm are used, but the retardation value and the optical axis angle are not particularly limited to the above, and similar effects can be obtained even in the case of the other birefringent film structure. You can The optical axis angle of the polarizing film is not particularly limited to this, and similar effects can be obtained in other configurations.

[0042]

As described above, according to the semi-transmissive liquid crystal display device of the present invention, the thickness of the liquid crystal layer can be made uniform within the pixel and display unevenness can be suppressed. That is, it is possible to obtain an effective effect that a white display having a sufficiently high reflectance can be obtained, and a black display having a sufficiently low reflectance and a good image having high contrast and high visibility can be realized.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a transflective liquid crystal display element according to an embodiment of the present invention.

FIG. 2 is an optical configuration diagram of a transflective liquid crystal display element according to an embodiment of the present invention.

FIG. 3 is a characteristic diagram of diffuse reflectance Rp of a semi-transmissive liquid crystal display device during white display, with respect to diffuse reflectance Rdif of the uneven transflective layer alone according to the present invention.

FIG. 4 is a depolarization characteristic diagram with respect to the diffuse reflectance Rdif of the uneven semi-transmissive reflective layer of the present invention.

FIG. 5 is an explanatory diagram showing the principle of decreasing the diffuse reflectance Rp of the transflective liquid crystal display element of the present invention.

FIG. 6 is a cross-sectional view showing a configuration example of a conventional transflective liquid crystal display element.

[Explanation of symbols]

10a Polarizing film (1) 10b Polarizing film (2) 11a Birefringent film (1) 11b Birefringent film (2) 11c Birefringent film (3) 11d Birefringent film (4) 12 Liquid crystal cell 13 Upper transparent substrate 14 Transparent electrode 15 Liquid crystal layer 16 Flattening layer 17 Reflective layer 18 uneven layer 19 Lower substrate

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroshi Mizuno             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Tetsu Ogawa             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F-term (reference) 2H042 BA03 BA12 BA20 DA02 DA04                       DA12 DA17 DE04                 2H049 BA02 BA06 BA42 BB03 BB44                       BB63 BC22                 2H089 HA07 HA15 HA30 RA10 SA07                       SA17 TA14 TA15 TA17                 2H091 FA08X FA08Z FA11X FA11Z                       FA15Y FB08 FC22 FC23                       FD06 GA01 GA02 GA07 KA10

Claims (5)

[Claims] 1. A liquid crystal layer is provided between a first substrate and a second substrate, and the first substrate has an upper transparent electrode on the surface on the liquid crystal layer side and one or more transparent electrodes on the opposite surface. The second substrate has a plurality of birefringent films and a polarizing film, and the second substrate has a concavo-convex layer, a semi-transmissive reflective layer that transmits a part of light, and a concavo-convex surface on the surface on the liquid crystal layer side. A semi-transmissive liquid crystal display device, in which a flattening layer and a lower transparent electrode are sequentially formed from the second substrate side, and one or more birefringent films and a polarizing film are provided on the opposite surface, wherein the liquid crystal The twist angle of the layer is 220 ° or more and 270 ° or less, and the uneven transflective layer formed of the uneven layer and the semi-transmissive reflective layer has diffuse reflectivity, and excludes the specular component under diffuse illumination. The reflection brightness of the uneven transflective layer measured by light collection integration dif, the diffuse reflectance Rdif of the uneven reflective layer defined by (Equation 1) is 40, where Bd0 is the reflection brightness of the standard white plate measured by condensing integration excluding the specular reflection component under diffuse illumination. % Or more 70
% Or less, a transflective liquid crystal display device. ## EQU1 ## Rdif = Bdif / Bd0 × 100 (%) 2. In the uneven layer, the film thickness difference between the convex portion and the concave portion is 0.1 μm or more and 1.0 μm or less, and the distance between the adjacent convex portions is 3 μm or more and 15 μm or less.
The transflective liquid crystal display element described. 3. The transflective liquid crystal display element according to claim 1, wherein the uneven layer is made of a material that expands and contracts by light irradiation and heat, and the shape can be controlled by light irradiation and heat. 4. The transflective liquid crystal display element according to claim 1, wherein the transflective layer is formed of a metal containing aluminum or silver as a constituent element. 5. An image display device comprising the semi-transmissive liquid crystal display element according to claim 1. Description: