JP2002072198A - Reflective liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflective liquid crystal display device excellent in a white display and a black display and having high contrast. SOLUTION: A prism 9 is formed on a front surface of an incident side substrate 6. An electrode 4, on which an alignment layer 2 is formed, is formed on a back surface of the incident side substrate 6. A reflective film 8, on which an electrode 5 and an alignment layer 3 are serially formed, is formed on a front surface of a reflection side substrate 7. The incident side substrate 6 and the reflection side substrate 7 are disposed opposite each other, and a liquid crystal layer 1 is sandwiched between the alignment layer 2 and the alignment layer 3. The prism 9 has a surface perpendicular to the incident side substrate 6 and a slope surface, in which a sectional configuration thereof is serrate. As to the prism 9, an absorption layer 11 is formed on the surface perpendicular to the incident side substrate 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type liquid crystal display device having a liquid crystal layer modulated between a transmission state and a state including at least a scattering action.

[0002]

2. Description of the Related Art At present, applications of a reflection type liquid crystal display device are expanding in various fields mainly for mobile devices such as mobile phones and portable game machines.

[0003] In contrast to a transmissive liquid crystal display device, a reflective liquid crystal display device does not require a backlight, so that power for a light source can be reduced, and further, space and weight of the backlight are saved. It has features such as being able to. That is, power consumption can be reduced as a whole of the liquid crystal display device. Therefore, a small battery can be used, and the liquid crystal display device is suitable for a device that needs to be reduced in weight and thickness. Also, without changing the size or weight of the equipment,
A large battery can be used, and a dramatic increase in operating time can be expected.

[0004] In view of the contrast characteristics of the display surface, the contrast of a self-luminous display device such as a CRT or a transmissive liquid crystal display device is significantly reduced outdoors in the daytime. On the other hand, the reflective liquid crystal display device obtains display light proportional to the amount of ambient light, and is particularly suitable for outdoor use.

As described above, despite having a very promising application field, the contrast ratio, the reflectance, the full color display, the high definition display, the ability to cope with moving images, and the like are insufficient. No reflective color liquid crystal display device having a practical utility has been obtained.

At present, as a reflection type liquid crystal display device, a reflection type liquid crystal display device using two or one polarizing plate is widely used. Such a reflection type liquid crystal display device has a TN (tw) that performs display by controlling the optical rotation of the liquid crystal layer by an electric field.
ECB (electrically controlled) which displays by controlling the birefringence of the liquid crystal layer by an electric field.
A birefringence mode, a mixed mode combining a TN mode and an ECB mode, and the like are mainly applied.

However, in a reflection type liquid crystal display device using a polarizing plate, there is a limit in light use efficiency and a viewing angle.
Further, the polarizing plate has a problem of an absorption profile, that is, the polarizing plate absorbs blue light and the incident light becomes yellowish. For this reason, when a polarizing plate is used in a reflective liquid crystal display device, the brightness decreases.

Therefore, a liquid crystal display device using a polymer dispersed liquid crystal or a cholesteric liquid crystal, which can be expected to have high brightness and high contrast without using a polarizing plate, has been developed. These methods utilize the characteristic that the liquid crystal layer switches optically between a transmission state and a scattering state or between a transmission state and a reflection state by controlling the voltage applied to the liquid crystal layer. is there.

As a structure of a liquid crystal display device using a polymer-dispersed liquid crystal, Japanese Patent Application Laid-Open No. 3-186816 (prior art (1)) discloses a structure in which an absorption surface is disposed on the back surface. In this liquid crystal display device, a polymer-dispersed liquid crystal is arranged on a black substrate, and when no voltage is applied, the polymer-dispersed liquid crystal becomes a scattered state and becomes turbid, thereby giving a white display.
When a voltage is applied, the polymer-dispersed liquid crystal is in a transmissive state, and the black substrate disposed on the lower side is seen to give a black display.

Also, "Full-Color Reflective LCD Usi
ng Internal-Reflection Inverted-Scattering (IRIS) M
ode "(SID 97 digest pp. 1023-1026, prior art (2)) includes a liquid crystal layer 93 between a front substrate 91 and a rear substrate 92 on which a reflective film 94 is formed, as shown in FIG. A liquid crystal display device having a structure in which a liquid crystal layer 93 is sandwiched between the liquid crystal display device and the liquid crystal layer 93 is scattered by arranging a mirror-like reflective film 94 on the back surface.

In such a structure, since no polarizing plate is used, the light use efficiency can be improved. In addition, even when evaluation is performed from the viewpoint of color, the wavelength dependency is small as compared with the TN mode and the ECB mode, and
Further, it is expected that good white display can be realized by being freed from problems such as the absorption profile of the polarizing plate itself. In addition, when the evaluation is performed from the viewpoint of the wavelength dependence of the modulation amount such as the scattering ratio and the reflectance, the mode in which the liquid crystal layer optically switches between the transmission state and the scattering state is the transmission mode and the reflection state. Better than the mode that switches between.

As for the liquid crystal used in the liquid crystal display device having no polarizing plate, a guest-host type liquid crystal element in which a dichroic dye is added to the liquid crystal has been developed. In a liquid crystal display device having such a liquid crystal,
Black display is realized using a dichroic dye.

The mode in which the liquid crystal layer is optically switched between a transmission state and a scattering state is such that, when used as a direct-view reflection type liquid crystal display device, the liquid crystal layer normally displays black in the transmission state,
It is configured to realize white display in a scattering state. However, as a function of the liquid crystal layer, the backscattering ratio of emitting the incident light toward the observer while scattering the incident light is not sufficient at present. Therefore, in order to realize a bright white display, it is necessary to use forward scattering of the liquid crystal layer. In order to achieve both a good black state and a bright white state when the liquid crystal layer is in a transmission state, a technique using a prism or an optical member having the same function as the prism has been developed.

JP-A-6-51306 (prior art (3)) discloses a reflective reverse PDLC liquid crystal display element comprising a liquid crystal layer containing a dichroic dye and a light refractor having prism-like protrusions. The structure to be combined is described. With such a structure, the contrast can be improved.

Further, Japanese Patent Application Laid-Open No. Hei 8-95035 (prior art (4)) discloses a reflection type liquid crystal display device in which an aperture is arranged outside. Further, by providing a front substrate having an inclined surface on the front surface of the liquid crystal modulation layer in the reflection type liquid crystal display device, or by arranging an inclined reflection surface on the back surface of the liquid crystal modulation layer, good display quality is realized. here,
The inclined front substrate and the inclined reflecting surface have the same function as the prism.

Further, Japanese Patent Application Laid-Open No. 8-160412 (prior art (5)) discloses a liquid crystal display device having an optical member having a predetermined angle and capable of utilizing the multiple interference effect. Have been. Further, the liquid crystal display device includes a light shielding layer.

[0017]

However, these structures have the following problems.

In the structure of the prior art (1), the black display is excellent when the liquid crystal layer is in the transmission state. However, at the time of white display when the liquid crystal layer is in the scattering state, only light scattered backward from the polymer dispersed liquid crystal is involved in white display, and all light scattered forward is absorbed by the black substrate. Would. For this reason, the light utilization efficiency is actually significantly reduced, and the white display becomes dark.

In the structure of the prior art (2), since the reflection film 94 has a mirror surface, the white display becomes bright, but the black display becomes a mirror surface and an image is reflected.

Further, in the structure of the prior art (3), a dichroic dye is used to realize black display. However, when a dichroic dye is added, the reliability is poor and the Since the dichroic ratio is low, there is a problem that a sufficient contrast cannot be obtained. In particular, lack of contrast significantly reduces color purity in color display using a color filter, so it is necessary to combine with a color filter having high color purity. In addition, there is a problem that the advantage of realizing high brightness by not using a polarizing plate is impaired.

In the structure of the prior art (4), black display is realized by using an aperture arranged outside the reflection type liquid crystal display device, but black display is realized by the reflection type liquid crystal display device alone. Can not do.

In the structure of the prior art (5), incident light from the vertical direction of the liquid crystal display device is assumed, and it cannot be used as it is in a direct-view reflection type liquid crystal display device.
Although a light-shielding layer is provided, the light-shielding layer is not indispensable for black display. That is, although the liquid crystal layer realizes black display in the scattering state, even if not all of the scattered light is absorbed by the light-shielding layer, that is, even if a part of the scattered light is emitted outside the liquid crystal display device, Black display is possible, and the display condition is different from that of the direct-view reflective liquid crystal display device.

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a reflection type liquid crystal display device having good white display and black display and high contrast.

[0024]

According to the present invention, there is provided a reflection type liquid crystal display device having a liquid crystal layer which changes between a transmission state and a scattering state. The following measures have been taken.

That is, the reflection type liquid crystal display device is provided on a reflection film for reflecting light from the liquid crystal layer, and on a side opposite to the reflection film with respect to the liquid crystal layer, and the liquid crystal layer is in a transmission state. In this case, a semi-absorbing semi-transmissive layer is provided which guides incident light from a direction parallel or nearly parallel to the normal to the display surface to the reflective film and absorbs the reflected light from the reflective film.

According to the above invention, black display or white display is performed according to the state of the liquid crystal layer. When the liquid crystal layer is in a transmission state, light from a direction parallel to or nearly parallel to the normal to the display surface is guided to the reflection film via the semi-absorbing semi-transmissive layer. Light reflected from the reflective film is transmitted through the liquid crystal layer again, guided to the semi-absorbing semi-transmissive layer, and absorbed. Thus, incident light from a direction parallel to or nearly parallel to the display surface normal does not reach the observer. Therefore, good black display can be performed.

On the other hand, when the liquid crystal layer is in a scattering state, light incident through the semi-absorbing semi-transmissive layer is back-scattered in the liquid crystal layer and a part of the light is directed to an observer. In addition, a part of the incident light is scattered forward in the liquid crystal layer and is guided to the reflection film, and is again guided to the liquid crystal layer. Here, the light is scattered again and a part thereof is directed to the observer. As described above, not only the backscattered light but also the forward scattered light contributes to the white display, so that a good white display can be obtained.

As described above, a reflection type liquid crystal display device having high white display brightness and high contrast ratio can be realized without using a polarizing plate or a dye. Also, by combining such a reflective liquid crystal display device with a color filter,
It is possible to realize a liquid crystal display device capable of multicolor display which is very easy to see.

The semi-absorbing semi-transmissive layer is a prism which is inclined at a predetermined angle with respect to the liquid crystal layer and has a surface on which the incident light is incident and a surface provided with an absorbing portion for absorbing the reflected light. Preferably, there is. In this case, with a simple configuration,
The reflected light can be reliably absorbed by the absorbing section.

If the refractive index of the prism is n ₁ , the inclination angle is α _1, and the refractive index in the atmosphere is n ₀ , 2 × α ₁ ≧ arcsin [sin (α ₁ ) / n ₁ ] + arcsin [ n ₀ / n
₁ ] is preferably satisfied. As long as this expression is satisfied,
High quality black display is guaranteed.

The reflecting film may have a reflecting surface inclined. This makes it possible to effectively use incident light having a large incident angle distribution. In this case, the refractive index in the atmosphere is n ₀ , the refractive index of the prism is n ₁ , the refractive index of a substance adjacent to the front surface of the reflective film is n _2, and the inclination angle of the prism is α _1, and when the inclination angle of the reflecting surface and _{α 2, α 1 + arcsin [} n 2 / n 1 × sin (2 × α 2 -arcsin [n 1 / n 2 × sin (ar
_{csin [sin (α 1) /} n 1] -α 1)])] ≧ arcsin [ unless satisfying n ₀ / n _1], high-quality black display is ensured.

When the prism is provided in a sawtooth shape,
It is preferable to further provide a transparent parallel layer on the prism. When a plurality of prisms are provided in a sawtooth shape, a problem that hard coating is difficult is caused. Therefore,
By providing a transparent parallel layer on these prisms, the above problem can be solved.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [Embodiment 1] An embodiment of the present invention will be described with reference to FIGS.
It is as follows.

FIG. 1 is a sectional view showing a structural example of a reflection type liquid crystal display device. As shown in FIG. 1, the reflective liquid crystal display device according to the present embodiment includes an incident-side substrate 6 provided with an alignment film 2, an electrode 4, and a prism 9, and an alignment film 3, an electrode 5, and a reflective film 8. The liquid crystal layer 1 is sandwiched by the reflection-side substrate 7.

On the incident side substrate 6, a prism 9 which is a semi-absorbing and semi-transmitting layer is formed. The surface of the incident side substrate 6 on which the prism 9 is formed is the front surface of the reflection type liquid crystal display device. The electrode 4 is formed on the surface of the incident-side substrate 6 opposite to the surface on which the prism 9 is formed, that is, on the rear side of the incident-side substrate 6, and the alignment film 2 is formed on the upper surface thereof. I have. A reflection film 8 is formed on the front surface of the reflection-side substrate 7, and an electrode 5 is formed on the upper surface thereof.
And the alignment film 3 are formed in this order. The incident side substrate 6 and the reflection side substrate 7 are arranged to face each other, and the liquid crystal layer 1 is sandwiched between the alignment films 2 and 3.

The incident side substrate 6 and the reflecting side substrate 7 are formed of a material such as a transparent glass plate or a polymer film. The electrodes 4 and 5 apply a voltage to the liquid crystal layer 1. As a means for applying a voltage to the electrode 4 and the electrode 5, an active element or the like may be used, but the present invention is not limited to this. The alignment films 2 and 3 are formed of a horizontal alignment film, and the liquid crystal layer 1 is in a horizontal alignment state when no voltage is applied. The types of the alignment film 2 and the alignment film 3 are not limited to the horizontal alignment film, and may be other types. The reflection film 8 is formed of silver. The reflection film 8 is formed on the reflection-side substrate 7 by vapor deposition to a thickness of 2000 mm, and the surface is in a flat mirror surface state.

The liquid crystal layer 1 uses a polymer dispersed liquid crystal as a light scattering liquid crystal. For example, a liquid crystal composition 1a made of TL213 (manufactured by Merck, Δn = 0.238)
And the ultraviolet curable prepolymer 1b in a weight ratio of 80:
The mixture was adjusted to 20 and a small amount of a polymerization initiator (manufactured by Ciba-Geigy) was added thereto to prepare a prepolymer liquid crystal mixture exhibiting a nematic liquid crystal phase at room temperature. The prepolymer liquid crystal mixture is irradiated with an actinic ray such as an ultraviolet ray and photocured to obtain an ultraviolet curable liquid crystal. As described above, since heating is not required in the step of producing the ultraviolet-curable liquid crystal, the use of the ultraviolet-curable liquid crystal as the polymer-dispersed liquid crystal in the liquid crystal layer 1 can prevent adverse effects on other members. .

The polymer-dispersed liquid crystal may be prepared by dissolving a mixture of a low-molecular liquid crystal composition and an unpolymerized prepolymer and then polymerizing the unpolymerized prepolymer. The type of the polymer-dispersed liquid crystal is not particularly limited as long as it can be obtained by polymerizing the prepolymer.

As the light scattering type liquid crystal, any of a polymer dispersed type liquid crystal, a nematic-cholesteric phase transition type liquid crystal and a liquid crystal gel may be used. Further, assuming that the liquid crystal layer 1 is modulated between a transmission state and a state including at least a scattering action, any of a cholesteric liquid crystal, a polymer dispersed liquid crystal, and the like may be used as the liquid crystal layer 1. . The cholesteric liquid crystal switches in a transmission-reflection state in which the domain size of the liquid crystal molecules is controlled to impart a diffusivity. The polymer-dispersed liquid crystal has a holographic function of switching in a transmission-reflection state in which light is diffused by exposure to diffused light.

The light incident on the liquid crystal layer 1 as described above is modulated in accordance with the applied voltage according to the scattering and transmission states of the aligned liquid crystal layer 1. In the present embodiment,
When no voltage is applied, the liquid crystal layer 1 is set to be in a transmission state, and when a voltage is applied, the liquid crystal layer 1 is set to be in a scattering state.

The prism 9 is made of PEN (Polyethylene Nap).
It is formed of a transparent resin (manufactured by Teijin Ltd.) having a refractive index of 1.66 and made of htahalate. The prism 9 has a surface perpendicular to the incident side substrate 6 and an inclined surface, and has a saw-tooth shape as shown in FIG. In the prism 9, an absorption film 11, which is an absorption portion, is formed on a plane perpendicular to the incident side substrate 6, and an inclination angle 10 of the inclined surface with respect to the incident side substrate 6 is set to 30 °. I have.

By forming the prism 9 on the incident side substrate 6, incident light which is incident on the incident side substrate substantially perpendicularly is totally reflected by the prism 9 and is not emitted out of the prism 9, It is absorbed efficiently. Thereby, good black display can be achieved.

The sectional shape of the prism 9 is not limited to a sawtooth shape, and it is sufficient that the absorbing film 11 is provided on at least one of the surfaces constituting the prism 9.

Hereinafter, the display principle of the reflective liquid crystal display device according to the present embodiment will be described in detail.

The black display operation will be described with reference to FIG. However, it is assumed that the reflection type liquid crystal display device is in the atmosphere.

When the light emitted from the reflection type liquid crystal display device traces the light from the observer side and the light path reaches the absorbing film 11 without reaching the light source, a good black state is realized. can do.

The incident lights 12 and 13 are incident lights that enter the liquid crystal layer 1 in the transmission state from a direction parallel or nearly parallel to the normal to the display surface when no voltage is applied. The incident light 12 is
The light is refracted by the prism 9, enters the panel, passes through the liquid crystal layer 1 in the transmission state, is reflected by the reflection film 8, passes through the liquid crystal layer 1 in the transmission state again, and is absorbed by the absorption film 11. The incident light 13 is refracted by the prism 9 and enters the panel, passes through the liquid crystal layer 1 in the transmission state, is reflected by the reflection film 8, passes through the liquid crystal layer 1 in the transmission state again, and passes through the prism 9.
It is totally reflected at the interface between the air and the air layer and is absorbed by the absorbing film 11. That is, when the liquid crystal layer 1 is in a transmission state,
The reflection type liquid crystal display device guides incident light from a direction parallel or nearly parallel to the display surface normal to the reflective film 8 and absorbs the reflected light from the reflective film 8 by total reflection at the interface with the air layer. Alternatively, a prism 9 having an absorbing film 11 as a semi-absorbing semi-transmissive layer for directly absorbing is provided. Accordingly, incident light that is incident from a direction parallel or nearly parallel to the display surface normal does not reach the observer, and the reflective liquid crystal display device takes a good black display state.

The incident light 14 is incident light from a direction near parallel to the display surface and from a side far from the observer. Incident light 14
Is refracted by the prism 9 and enters the panel, passes through the transmissive liquid crystal layer 1, is reflected by the reflective film 8, passes through the transmissive liquid crystal layer 1 again, is refracted by the prism 9 and transmits again. Then, the light is emitted in a direction parallel to the display surface and farther from the observer. As described above, when the observer observes the panel from a direction close to the display surface and far from the observer, the reflective liquid crystal display device is in a reflective state.

That is, in order for the reflection type liquid crystal display device to realize good black display, it is sufficient to consider incident light from a direction parallel to or nearly parallel to the display surface normal. Under a condition of observing from a near side and from a side far from the observer, the reflective liquid crystal display device is in a reflective state and cannot achieve a good black display.

Considering that at least the observer of the panel observes the panel from the front direction, as shown in FIG. 3, the region where the reflective liquid crystal display device takes a black display state is expressed by the following formula (1) 2 × _{α 1 ≧ arcsin [sin (α} 1) / n 1] + arcsin [n 0 / n 1] ... satisfy the conditions is required of (1). By satisfying the expression (1), the boundary 30 between the observation direction in which the reflection type liquid crystal display device takes a black display state and the observation direction in which the reflection type liquid crystal display device takes a reflection state is located in a region farther from the viewer side than the normal to the display surface. Becomes

Here, n ₀ is the refractive index in the atmosphere, n ₁ is the refractive index of the prism 9, and α ₁ is the angle of the inclination angle 10 of the prism 9.

When incident light incident from a direction nearly parallel to the normal of the display surface passes through the liquid crystal layer 1, is reflected by the reflection film 8, and is reflected at the interface between the prism 9 and the atmosphere.
When the reflection angle becomes the critical angle, the above equation (1) holds the equal sign. For example, assuming that the refractive index n _{1 of} the prism 9 is 1.66 and the angle α ₁ of the inclination angle 10 of the prism 9 is α ₁ = 30 °, incident light incident from a direction 10 ° farther from the normal of the display surface to the observer side, When the light passes through the liquid crystal layer 1, is reflected by the reflection film 8, and is reflected at the interface between the prism 9 and the atmosphere, the reflection angle becomes a critical angle.

The operation of white display will be described below.

When a voltage is applied, the incident light incident on the liquid crystal layer 1 in the scattering state is divided into straight transmitted light, forward scattered light and back scattered light. The incident light is scattered backward in the liquid crystal layer 1, and part of the light is directed toward the observer as straight transmitted light. In addition, a part of the incident light is scattered forward, reflected by the reflection film 8, returned to the liquid crystal layer 1 and scattered again, and a part thereof is directed toward the observer. Thus, not only backscattered light,
A part of the forward scattered light can also be used, so that the brightness is high and a good white display is possible.

As described above, the structure of the reflection type liquid crystal display device in which the light scattering type liquid crystal is arranged is provided on the front surface of the liquid crystal layer 1 by the absorption film 1.
By adopting a structure in which the prism 9 having 1 is disposed, the reflective liquid crystal display device has a good black display state using the transmission state of the light scattering liquid crystal and a good black display state using the scattering state of the light scattering liquid crystal. The white display state can be compatible. Such a structure is effective not only for the liquid crystal display device using the light scattering type liquid crystal but also for all display devices that switch between the transmission state and the scattering state. Further, since it is not necessary to use a polarizing plate, the wavelength dependency can be reduced. Also, the incident light does not take on a yellow tint, and the brightness and contrast are high. Thus, the chromaticity characteristics are significantly improved.

Next, the reflectance and contrast of the reflective liquid crystal display device according to the present embodiment are compared with those of the reflective liquid crystal display device shown in FIG. The former reflective liquid crystal display device is referred to as sample A, and the latter reflective liquid crystal display device as sample B, and the reflectance and contrast thereof are measured by a measuring device. However, the sample B is a reflection type liquid crystal display device described in JP-A-3-186816 (prior art (1)).

As shown in FIG. 4, sample B has a liquid crystal layer 1, an alignment film 2, an electrode 4, an incident side substrate 6, an alignment film 3, an electrode 5, and a reflection side substrate 7, as in the case of sample A shown in FIG. Have. The sample B includes a reflective film 8 and a prism 9
However, an absorption layer 40 is formed on the surface of the reflection-side substrate 7 opposite to the surface on which the electrodes 5 are formed, that is, on the back side of the reflection-side substrate 6.

FIG. 5 shows a measuring apparatus used for measuring the reflectance. The light is emitted from all the directions of the hemisphere 50 at the same luminance, and is received by the light receiver 51 installed in a direction inclined by 8 ° from the normal to the measurement surface. At this time, the specular reflection component is removed by the light shielding plate 52. In addition,
The reflectance of the perfect diffuse reflector is 100%.

Table 1 shows the measurement results of the reflectance and the contrast. According to this, the prism 9 and the reflection film 8
By providing the structure of Sample A, the reflectance and the contrast are improved.

[0060]

[Table 1]

The shape of the prism 9 is not saw-toothed, but may be a structure in which the inclined surface of the prism 60 is inclined with a constant inclination with respect to the incident side substrate 6 as shown in FIG. That is, the thickness of the prism 60 is
An absorbing film 61 is provided at an end of the prism 60 where the thickness is different, which is different between one end and the other end of the prism 60. Even in a reflection type liquid crystal display device having such a structure,
With respect to the reflectance and the contrast, the same results as those of the reflection type liquid crystal display device having the structure shown in FIG. 1 are obtained. By providing the prism 60 and the reflection film 8, the reflectance and the contrast are improved.

Further, as shown in FIG. 7, a transparent parallel plate 70 may be arranged on the front surface of the reflection type liquid crystal display device. Thereby, even in the prism 9 having a sawtooth shape, the hard coat processing can be easily performed. Further, even when a touch panel is added to the reflective liquid crystal display device, the prism 9 can be protected against external pressure from the touch panel or the like. Therefore, even when a touch panel or the like is added to the reflective liquid crystal display device, a liquid crystal display device integrated with an input device can be provided without deteriorating display quality.

Further, by providing a color filter in such a reflection type liquid crystal display device, it is possible to obtain a reflection type liquid crystal display device capable of multicolor display which is easy to see.

[Second Embodiment] A second embodiment of the present invention will be described below with reference to FIG. Note that components having the same functions as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

FIG. 8 is a sectional view of a main part of a reflection type liquid crystal display device according to an embodiment of the present invention. As shown in FIG. 8, a reflective liquid crystal display device according to the present embodiment has a prism 9 having a liquid crystal layer 1, an alignment film 2, an electrode 4, an incident side substrate 6, and an absorption film 11, as in the first embodiment. , An alignment film 3, an electrode 5, and a reflection-side substrate 7. On the reflection side substrate 7, not the reflection film 8 but an inclined reflection plate 80 is arranged.

The cross section of the inclined reflection plate 80 has a saw-tooth shape, and the inclination angle 81 is set to 10 °. A reflection film 82 made of silver is formed on the inclined surface of the inclined reflection plate 80, and an absorption film 83 is formed on the vertical surface. The inclined reflector 80 has its upper surface (front side) covered with a transparent resin film 84 made of polyamide CRA-100 having a refractive index of 1.672. Thereby, the surface of the layer on which the inclined reflection plate 80 is formed is flattened, and the electrode 5 can be formed thereon.

As described above, the provision of the saw-toothed inclined reflecting plate 80 makes it possible to further enhance the reflection function and provide off-axis properties. This makes it possible to effectively use incident light having a large incident angle distribution. The region where the reflective liquid crystal display device takes a black display state is represented by the following equation (2): α ₁ + arcsin [n ₂ / n ₁ × sin (2 × α ₂ -arcsin [n ₁ / n ₂ × sin (arcsin [sin (α ₁ ) / n ₁ ] -α ₁ )])] ≧ arcsin [n ₀ / n ₁ ] (2) By satisfying the above expression (2), the boundary 30 between the observation direction in which the reflection type liquid crystal display device takes a black display state and the observation direction in which the reflection type liquid crystal display device takes a reflection state is located in a region farther from the viewer side than the display surface normal line. It will be.

Where n ₀ is the refractive index in the atmosphere, n ₁ is the refractive index of the prism 9, n ₂ is the refractive index of the transparent resin film 84, α
₁ is the angle of the inclination angle 10 of the prism 9, and α ₂ is the angle of the inclination angle 81 of the inclined reflection plate 80.

It should be noted that incident light that is incident from a direction nearly parallel to the display surface normal passes through the liquid crystal layer 1,
When the light is reflected at 0 and reflected at the interface between the prism 9 and the air layer, the above equation (2) satisfies the equal sign when the reflection angle becomes a critical angle. For example, the refractive index n ₁ of the prism 9 is 1.6.
6, the angle α ₁ of the inclination angle 10 of the prism 9 = 15 °, the refractive index n ₂ of the transparent resin film 84 adjacent to the front side of the inclined reflection plate 80 = 1.672, and the angle of the inclination angle 81 of the inclined reflection plate 80 Assuming that α ₂ = 10 °, it is 10 ° from the normal of the display surface to the observer side.
The incident light incident from a distant direction passes through the liquid crystal layer 1 and the transparent resin film 84, is reflected by the reflection film 82, and is reflected by the prism 9.
When the light is reflected at the interface between the air and the air layer, the reflection angle becomes a critical angle.

Further, the reflectance and contrast of the reflection type liquid crystal display device according to the present embodiment shown in FIG.
Are compared with the reflectance and contrast of the reflective liquid crystal display device shown in FIG. The former reflective liquid crystal display device is referred to as Sample C, and the latter reflective liquid crystal display device as Sample B, and the reflectance and contrast thereof are measured.

Table 2 shows the measurement results of the reflectance and the contrast. According to this, by providing the prism 9 and the inclined reflection plate 80 to form the structure of the sample C, the reflectance and the contrast are improved.

[0072]

[Table 2]

[0073]

As described above, the reflection type liquid crystal display device of the present invention, in the reflection type liquid crystal display device provided with the liquid crystal layer which changes between the transmission state and the scattering state, emits light from the liquid crystal layer. A reflective film for reflecting, provided on the opposite side of the reflective film with respect to the liquid crystal layer, and when the liquid crystal layer is in a transmitting state, reflects incident light from a direction parallel or nearly parallel to a normal to the display surface. And a semi-absorbing semi-transmissive layer that absorbs the reflected light from the reflective film.

In the above-mentioned reflection type liquid crystal display device, black display or white display is performed according to the state of the liquid crystal layer. When the liquid crystal layer is in a transmission state, light from a direction parallel to or nearly parallel to the normal to the display surface is guided to the reflection film via the semi-absorbing semi-transmissive layer. Light reflected from the reflective film is transmitted through the liquid crystal layer again, guided to the semi-absorbing semi-transmissive layer, and absorbed. Thus, incident light from a direction parallel to or nearly parallel to the display surface normal does not reach the observer. Therefore,
Good black display can be performed.

On the other hand, when the liquid crystal layer is in the scattering state, the light incident through the semi-absorbing semi-transmissive layer is back-scattered in the liquid crystal layer and a part of the light is directed to the observer. In addition, a part of the incident light is scattered forward in the liquid crystal layer and is guided to the reflection film, and is again guided to the liquid crystal layer. Here, the light is scattered again and a part thereof is directed to the observer. As described above, not only the backscattered light but also the forward scattered light contributes to the white display, so that a good white display can be obtained.

As a result, it is possible to realize a reflection type liquid crystal display device having high white display brightness and high contrast ratio without using a polarizing plate or a dye. In addition, by combining such a reflective liquid crystal display device with a color filter, it is possible to realize a liquid crystal display device capable of displaying multicolor images which is very easy to see.

In the reflection type liquid crystal display device of the present invention, the semi-absorbing semi-transmissive layer is inclined at a predetermined angle with respect to the liquid crystal layer, and a surface on which the incident light is incident, and an absorbing portion absorbing the reflected light. And a prism having a surface provided with. Thus, there is an effect that the reflected light can be surely absorbed by the absorber with a simple configuration.

In the reflection type liquid crystal display device of the present invention, if the refractive index of the prism is n ₁ , the inclination angle is α _1, and the refractive index in the atmosphere is n ₀ , 2 × α ₁ ≧ arcsin [sin _{(α 1) / n 1]} + arcsin [n 0 / n
₁ ]. As long as this expression is satisfied, there is an effect that high-quality black display is guaranteed.

In the reflection type liquid crystal display device of the present invention, the reflection film has a structure in which the reflection surface is inclined. Thereby, there is an effect that the incident light having a large distribution of the incident angle can be effectively used. In this case, the refractive index in the atmosphere is n ₀ , the refractive index of the prism is n ₁ ,
Assuming that the refractive index of the substance adjacent to the front surface of the reflection film is n ₂ , the inclination angle of the prism is α _1, and the inclination angle of the reflection surface is α ₂ , α ₁ + arcsin [n ₂ / n ₁ × sin (2 × α ₂ -arcsin [n ₁ / n ₂ × sin (ar
csin [sin (α ₁ ) / n ₁ ] −α ₁ )])] As long as ≧ arcsin [n ₀ / n ₁ ] is satisfied, high quality black display is guaranteed.

In the reflection type liquid crystal display device of the present invention, when the prism is provided in a saw-tooth shape, a transparent parallel layer is further provided on the prism. When a plurality of prisms are provided in a sawtooth shape, a problem that hard coating is difficult is caused. Therefore, by providing a transparent parallel layer further on these prisms, there is an effect that the above problem can be solved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a structure of a reflective liquid crystal display device according to Embodiment 1 of the present invention.

FIG. 2 is an explanatory diagram showing an optical path of incident light.

FIG. 3 is an explanatory diagram showing an area in a black display state.

FIG. 4 is a view showing Embodiments 1 and 2 of the present invention;
It is sectional drawing which shows the structure of the principal part of the reflection type liquid crystal display device of the sample used for the measurement of a reflectance and a contrast.

FIG. 5 is a configuration diagram of a measuring device used for measuring the reflectance of the reflective liquid crystal display device in the first and second embodiments of the present invention.

FIG. 6 is a sectional view showing the structure of another reflection type liquid crystal display device according to the first embodiment of the present invention.

FIG. 7 is a sectional view showing a structure of still another reflection type liquid crystal display device according to Embodiment 1 of the present invention.

FIG. 8 is a cross-sectional view illustrating a structure of a reflective liquid crystal display device according to a second embodiment of the present invention.

FIG. 9 is a cross-sectional view illustrating a structure of a main part of a conventional reflective liquid crystal display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid crystal layer 2 Alignment film 3 Alignment film 4 Electrode 5 Electrode 6 Incident side substrate (substrate) 7 Reflection side substrate (substrate) 8 Reflection film 9 Prism (semi-absorption semi-transmission layer) 10 Inclination angle 11 Absorption film (absorption part) 12 Incident light 13 Incident light 14 Incident light 30 Boundary 60 Prism (semi-absorbing semi-transmissive layer) 61 Absorbing film (absorbing portion) 70 Transparent parallel plate 80 Inclined reflecting plate (reflecting film) 81 Inclined angle 82 Reflecting film 83 Absorbing film (absorbing portion) )

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G09F 9/00 313 G09F 9/00 313 (72) Inventor Masahiko Tomikawa 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka No. Sharp Corporation F term (reference) 2H042 BA04 BA11 BA14 BA20 DA04 DC02 2H091 FA02Y FA08X FA08Z FA14Z FA15Z FA21Z FA34Z FA41Z HA07 HA09 LA17 5G435 AA02 BB12 BB16 DD11 FF03 FF14 GG03 HH02

Claims (6)

[Claims] 1. A reflection type liquid crystal display device comprising a liquid crystal layer that changes state between a transmission state and a scattering state, comprising: a reflection film for reflecting light from the liquid crystal layer; Provided on the opposite side of the reflection film, when the liquid crystal layer is in a transmission state, guides incident light from a direction parallel or nearly parallel to the normal to the display surface to the reflection film, and absorbs reflected light from the reflection film. A reflective liquid crystal display device comprising a semi-absorbing semi-transmissive layer. 2. The semi-absorbing semi-transmissive layer is inclined at a predetermined angle with respect to the liquid crystal layer, and has a surface on which the incident light is incident, and a surface provided with an absorbing portion for absorbing the reflected light. The reflective liquid crystal display device according to claim 1, wherein the reflective liquid crystal display device is a prism. 3. Assuming that the refractive index of the prism is n ₁ , the inclination angle is α _1, and the refractive index in the atmosphere is n ₀ , 2 × α ₁ ≧ arcsin [sin (α ₁ ) / n ₁ ] + arcsin [n ₀ / n
Reflection type liquid crystal display device according to claim 2, characterized by satisfying _one. 4. The reflection type liquid crystal display device according to claim 2, wherein the reflection surface of the reflection film is inclined. 5. The refractive index in the atmosphere is n ₀ , the refractive index of the prism is n ₁ , the refractive index of a substance adjacent to the front side of the reflection film is n _2, and the inclination angle of the prism is α. ₁
And then, when the inclination angle of the reflecting surface and _{α 2, α 1 + arcsin [} n 2 / n 1 × sin (2 × α 2 -arcsin [n 1 / n 2 × sin (ar
_{csin [sin (α 1) /} n 1] -α 1)])] ≧ arcsin [ reflection type liquid crystal display device according to claim 4, characterized by satisfying the n ₀ / n _1]. 6. When the prism is provided in a saw-tooth shape,
6. The reflection type liquid crystal display device according to claim 2, further comprising a transparent parallel layer provided on the prism.