JPH0720457A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To provide the flat plate type liquid crystal display element which uses a scatter type liquid crystal display mode, has a high contrast. and can be driven with a low voltage. CONSTITUTION:The liquid crystal display element, equipped with a liquid crystal cell 10 having a pair of transparent substrates which have transparent pixel electrodes on their internal surfaces and are isolated and arranged opposite each other and a liquid crystal layer which varies in light scattering performance by electric field application, is a reflection type liquid having a selective light reflecting means 30, which transmits light having an angle of incidence within a specific range including a view direction and reflects light in other incidence angle ranges to a direction other than the view direction, and thus has light transmission/reflection switching angle selectivity, on the reverse side of the liquid crystal layer, a light source unit 80 which irradiates the selective light reflecting means 30 with illumination light having at least part of the light reflected within the reflection angle range, and a light absorbing means 20 on the reverse side of this light source unit 80.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a light-scattering type liquid crystal display device, particularly a liquid crystal display using a so-called polymer dispersion type liquid crystal display device having a liquid crystal dispersion film formed of a liquid crystal and a three-dimensional fine structure made of a polymer or the like. Regarding the device.

[0002]

2. Description of the Related Art A liquid crystal display device uses a polarizing plate represented by a twisted nematic mode or a super twisted nematic mode to utilize birefringence and optical rotatory power of a liquid crystal, and a dynamic scattering mode or a liquid crystal display device. There is a system that utilizes light scattering by liquid crystals without using a polarizing plate as represented by a phase transition mode. Among them, the light-scattering method does not require a polarizing plate, and therefore has a feature that brighter display is possible without loss (absorption) of light by the polarizing plate. One of the light scattering methods is a polymer-dispersed liquid crystal display element, which has been actively developed in recent years. This has a structure in which a liquid crystal is dispersed in a droplet form by a support such as a resin or a liquid crystal dispersion film in which a resin network structure is formed in the liquid crystal is sandwiched by a substrate with electrodes. In this method, generally, when no voltage is applied, the orientation of the liquid crystal is disturbed by the support, and light is scattered due to a slight fluctuation in the refractive index. When a voltage is applied to this element, when the liquid crystal has a positive dielectric anisotropy, the liquid crystal molecules are aligned in the direction of the electric field and the fluctuation of the refractive index is reduced, so that the liquid crystal layer becomes transparent. This method has the advantage that the response speed is fast in addition to the brightness of the display. When such a light-scattering liquid crystal display device is used as a reflection type direct-view display device, in general, a black background is provided behind the device to provide a black display when the device is in a transparent state and the device is in a scattering state. In that case, the method of displaying white by back light scattering by the device is simple. However, since the backscattered light intensity of such a light-scattering type liquid crystal display element is small, sufficient whiteness cannot be obtained. For example, FIG. 1 shows an example of a conventional polymer-dispersed reflective liquid crystal display device. A liquid crystal layer 13 composed of a liquid crystal dispersion layer has a transparent substrate 11a, 1 having transparent electrodes 12a, 12b on the inner surface thereof
A liquid crystal cell 10 is formed by being sandwiched by 1b. The liquid crystal dispersion layer is composed of a liquid crystal 13a and a support 13b which is formed so as to divide the liquid crystal portion into fine regions and is made of a polymer material or the like. A light absorbing means 20 such as a black film is provided below the liquid crystal cell. When no voltage is applied to the liquid crystal cell, the orientation of the liquid crystal is disturbed by the wall surface of the support, which causes a slight fluctuation in the refractive index in the liquid crystal layer. In such a state, as shown in FIG. 4, incident light 50 from the outside receives the liquid crystal layer 1
Scattered by 3. A part 501 of the backscattering component travels in the viewing direction and enters the observer's eyes 40, resulting in white display.
When a voltage is applied to the liquid crystal layer, the liquid crystal is aligned parallel to the direction of the electric field (thickness direction of the liquid crystal layer), and the fluctuation of the refractive index is small. Therefore, as shown in FIG. 3, the incident light 50 progresses with almost no scattering. The light reaches the light absorption layer 20, is absorbed, and is displayed as black display. However, in the case of this configuration,
As shown in FIG. 2, even if the liquid crystal layer is in the light scattering state, the proportion of the forward scattering component 502 is large, and more than half of the light is absorbed by the light absorbing layer. As a result, sufficient white is not obtained, and the display has low contrast. In order to solve such a problem, measures such as increasing the thickness of the liquid crystal layer are adopted. However, such a measure has a problem that the driving voltage of the element is increased. In particular, the polymer dispersion type liquid crystal display device originally has a higher operating voltage than other scattering type devices, and this problem was very important. As another method, there is known a method in which a mirror surface is provided on the back side of the liquid crystal cell, and further an external light blocking means provided with a black surface is provided on the upper surface of the element so that the specularly reflected light of external light is not directly visible. (Japanese Patent Publication No. 45-21729). In this case, when the pixel is in the scattering state, white display is obtained by visually recognizing scattered light of light having an incident angle from a direction other than the direction of specular reflection, and when the pixel is in the transparent state, it is observed by the observer's eyes. Since no light reaches, a black display is obtained. However, this method has problems that the display device does not have a flat plate shape and the brightness of the white portion is insufficient. In view of such a problem, the present inventors have shown that the light absorption layer and the reflection characteristics only for an incident angle in a specific range, and an angle-selective light reflection plate and a scattering layer that transmit light in other incident angle ranges. Has invented a reflection type liquid crystal display element capable of obtaining a bright white background by a structure in which liquid crystal display elements of the same type are sequentially stacked (Japanese Patent Application No. 5-3.
No. 1267). However, although this device can obtain excellent display quality in a bright environment, it has a problem of insufficient brightness in a dark environment.

[0003]

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to provide a flat panel liquid crystal display device capable of driving with high contrast and low voltage using a scattering type liquid crystal display mode. To provide.

[0004]

The present invention relates to a liquid crystal cell having a pair of transparent substrates which have transparent pixel electrodes on the inner surface and are arranged to face each other, and a liquid crystal layer which is sandwiched between the substrates and whose light scattering property is changed by application of an electric field. In a liquid crystal display device including a light transmitting element that transmits light with an incident angle in a specific range including the viewing direction to the back side of the liquid crystal layer and reflects light with a range other than the viewing angle in a direction other than the viewing direction. A selective light reflection means having a switching angle selectivity of reflection / reflection, a light source device for irradiating the selective light reflection means with illumination light having at least a part of light reflected within the reflection angle range, The present invention relates to a reflection-type liquid crystal display element having a light absorbing unit on the back side of a light source device.

The liquid crystal display device of the present invention will be described in detail with reference to a constitutional example, using a polymer dispersion type liquid crystal cell as an example. FIG. 4 shows a configuration example of the liquid crystal display element according to the present invention. The liquid crystal cell 10 is the same as the conventional example, but is on the lower side of the liquid crystal layer-in this example, the lower side of the liquid crystal cell-and transmits light of an incident angle in a specific range between the light absorbing means 20, A selective light reflecting means 30 having an angle selectivity for reflecting light in other directions in a direction other than the visual recognition direction, and a light source device 80 for irradiating the selective light reflecting means with light are provided. FIG. 5 illustrates the operation of the selective light reflecting means used in the present invention. As shown in this figure, the selective light reflecting means transmits incident light having an incident angle i smaller than ic1 (or ic2) (for example, 51 in the figure) and transmits incident light from other angles (for example, 52 in the figure). It has a reflective property. 6
1 and 62 are boundaries of incident angles when incident light is transmitted and when incident light is reflected. The light source device 80 includes the selective light reflecting means 3
The illumination light is arranged to enter the reflecting means in an angle range including a reflection angle range of 0 (i> ic1, i> ic2). In this example, the light source device 80 adjusts the irradiation angle by a lamp such as a cold cathode fluorescent lamp or a hot cathode fluorescent lamp, a reflecting plate, a light shielding portion 83, and a louver 84.

Next, the operation of the present invention will be described. FIG. 6 is a diagram for explaining the operation when a voltage is applied to the device to bring the liquid crystal layer into a transparent state. The illumination light 52 having an incident angle of ic1 or more on the selective reflection means is reflected by the selective light reflection means and is transmitted through the liquid crystal layer 13 in the transparent state. However, this transmitted light does not reach the eyes of the observer 40. The illumination light 51 having an incident angle of ic1 or less is transmitted through the selective reflection means 30, reaches the light absorption means, and is absorbed. In this way, when the liquid crystal layer is in the transparent state, the illumination light does not reach the observer who is outside the angular range of the reflected light of the selective light reflecting means, and a black display is obtained. FIG. 7 is a diagram for explaining the action when no voltage is applied to the device or a voltage below the threshold voltage is applied to bring the liquid crystal layer into a scattering state. The illumination light 52 having an incident angle of ic1 or more on the selective reflection means is reflected by the selective light reflection means, enters the liquid crystal layer 13 in the scattering state, and is scattered. A part of the scattered light 531 has its optical path bent and reaches the eyes of the observer 40. The illumination light 51 having an incident angle of ic1 or less is transmitted through the selective reflection means 30, reaches the light absorption means, and is absorbed.
In this way, when the liquid crystal layer is in a scattering state, the reflected light from the selective light reflecting means reaches the observer,
A white display is obtained. As is clear from this description, since the light reaching the observer is forward scattered light having a high light intensity, a much brighter white background can be obtained as compared with the case of using the backscattering of the conventional example. It is essential that the incident angle of the illumination light to the selective light reflecting means includes the angle range of the incident angle at which the selective reflecting means causes reflection, but the more the incident angle component of this range is, the brighter the display is. It is preferable for it to be obtained, and it is most preferable that all the illumination light is in the angular range of the incident angle at which the selective reflection means causes reflection. FIG. 8 is a configuration example including the second light source device 90. In this case, the white background can be made brighter and the uniformity of brightness can be improved. In order to make the brightness of pixels near the light source device and pixels far from the light source device uniform, a light amount control means for reducing the incident light toward the light source device is provided in the optical path between the lamp and the liquid crystal layer. preferable. In the above description, the illumination light by the light source device provided in the element is described, but in reality, room lighting, external light such as sunlight also contributes to the display, and a brighter display may be obtained under bright external light. In addition, it can be used as a reflective display element without operating the light source device.

As described above, the selective light reflecting means used in the present invention has a characteristic of transmitting incident light from an angle range including at least the observer direction and reflecting light in other incident angle ranges. It is necessary to have. Incidentally, if it has a characteristic of reflecting an incident angle from the direction of the observer, reflected light of incident light such as external light from the reflecting direction is observed due to the property of regressiveness of light, and the contrast is Will fall. As such a selective light reflecting means, a prism group formed on a plate-like transparent substrate is particularly preferably used.
FIG. 9 shows a preferred specific example of the selective light reflecting means 30. A minute prism group is formed on the surface of a translucent plate-like substrate such as an acrylic resin or a polycarbonate resin. The operation of the selective reflection means of this example will be described with reference to the sectional view of FIG. In this example, a prism having an apex angle α of 90 ° is formed. The refractive index of the plate-like substrate in this example is 1.41. The incident light 53 having an incident angle i of 45 ° is incident on the bottom surface at an incident angle of 45 °, but the critical angle δ of total reflection is δ.
Since it is equal to c, it is totally reflected on the bottom surface, the absolute value is equal to the incident angle, and the light is emitted in a direction symmetrical with respect to the normal line N (light ray 53).
1). The light 54 having a larger incident angle is also totally reflected by the bottom surface (light ray 541). On the other hand, the lights 55 and 56 having an incident angle smaller than 45 ° are transmitted through the reflecting means 30 because the incident angle to the bottom surface is equal to or less than the critical angle δc of total reflection. FIG. 11 shows the relationship between the reflectance and the incident angle in this example. The characteristic is that the incident light from the front direction is transmitted and the oblique incident light is reflected. Generally, it is preferable that the direction of the observer is designed to be a normal direction of the display surface of the device or a direction inclined at an angle within 30 ° from the normal direction. In this example, the incident angle is 4
Since 5 ° is the transmission / reflection switching angle, the reflected light does not reach the direction of the observer. In the configuration of this example, the incident angles ic1 and ic2 at which transmission / reflection is switched can be adjusted by changing the structure of the prism. Specifically, ic can be adjusted by changing the apex angle α of the prism, the inclination angle β of the prism bottom surface, and the inclination angle γ of the prism shown in FIG. By decreasing the apex angle, the angular range of transmitted light (Δic = ic1-ic2) becomes small, and by increasing the apex angle, Δic can be increased. When ic is small, the margin of incident angle becomes wider,
Although the light intensity from the scattering portion of the device is increased and high contrast is obtained, there is a problem that the viewing angle is narrowed. On the contrary, when ic is increased, the viewing angle is widened, but the margin of the incident angle is narrowed, and when used in the reflection mode, there is a problem that the brightness is reduced. Preferred i
The range of c is 30 ° to 55 °, more preferably 35 ° to 50 °. In order to obtain such ic, the apex angle of the prism is set in the range of 30 ° to 150 ° in consideration of the refractive index range (1.4 to 1.65) of glass or plastic that can be used as the prism. Preferably, the range of 40 ° to 140 ° is more preferable. Both the tilt angle of the bottom surface and the tilt angle of the prism can make the selective transmission angle range asymmetric with respect to the normal line. Considering the preferred observation direction (within 30 ° from the normal line), the inclination angle of the bottom surface is preferably within 20 °, and the inclination angle of the prism is preferably within 30 °. Further, the shape of the prisms forming the prism group is made different in consideration of the uniformity of brightness and the viewing angle so that the prism group can transmit a plurality of types of light.
It is also possible to use a prism having a reflection switching angle.

In the above description, the prisms are arranged one-dimensionally, but it is also possible to use prisms arranged two-dimensionally as shown in FIG. 14 to 17 show
6 is a schematic view showing an example of a sectional structure of a selective reflection means having a similar effect (reflection characteristics with angle selectivity).
The prism cross section is not limited to the shape of an isosceles triangle as in the above example, and the effect is exhibited as long as it is an aggregate of structures having a surface inclined with respect to the display surface of the element. In these cases, it is desirable that the angle α formed by the two inclined surfaces is within the above preferable range. Further, it may have a structure in which a plurality of types of structures are mixed as shown in FIG. Each of the five structural examples shown here has a surface parallel to the display surface of the device or having a different tilt angle. Therefore, the above-mentioned ic becomes unclear, but on the contrary, there is also an advantage that this feeling reduces discomfort in the visual sense. 19 and 20 show a configuration example in which the prism is tilted, a prism bottom surface is tilted, and the optical path 6 of the light beam at the critical angle it of total reflection.
1 and 62 are shown. In these examples, the angle range of the transmitted light can be made asymmetric with respect to the normal direction, and thus it is particularly suitable for applications where the element is observed from an oblique direction. FIG. 21 shows another configuration example of the selective light reflecting means according to the present invention. In this example, another layer 32 is provided on the prism structure 31 of the selective light reflection means. 32 and 33 are formed for the purpose of protecting the prism structure and controlling the refraction angle. In order to provide the above-mentioned incident angle selectivity, 32 needs to be formed of a material having a refractive index smaller than that of the prism structure 31. As described above, the selective light reflecting means according to the present invention may be formed at any place on the plate-shaped transparent substrate.

Materials for forming the selective light reflecting means include inorganic materials such as glass, polystyrene, polyester,
Most transparent materials such as polycarbonates, polyolefins, polyarylates, polysulfones, polyether sulfones, polyacrylates, epoxy resins, polysilicones, polyvinyl alcohols, and resins such as acetyl cellulose can be used. The refractive index of the material used is generally in the range of 1.4 to 1.6. The pitch of the prism structure (see Fig. 8) is
The range of 0.05 mm to 1 mm is preferable, and the range of 0.1 mm to 0.5 mm is more preferable. If the pitch is too short, it becomes difficult to form the prism structure itself and the cost becomes high. Further, if it is too large, the prism structure is visually recognized by an observer, which is not preferable in view of display quality. As the light absorbing means arranged on the back side of the selective reflecting means,
Any material that absorbs light, such as colored glass, metal, or plastic, can be used. Generally, those colored in black are preferably used, and in this case, the device displays black and white. When it has a color, it is colored / white. The light absorbing means is preferably provided separately from the selective reflecting means. It is also possible to form the light absorbing means on the lower surface of the prism by a method such as coating, but in this case, the light is made of a material whose refractive index is sufficiently smaller than that of the prism so that total reflection at the bottom surface of the prism occurs. It is necessary to configure the absorption layer.

As the liquid crystal display system which can be used in the present invention, any liquid crystal display system can be used as long as the light scattering property is changed by application of a voltage, and the conventionally known dynamic scattering system, phase transition system, polymer A method using a nematic liquid crystal such as a dispersion method, a method using a thermoelectro-optical effect of a smectic liquid crystal, a method using light scattering of a ferroelectric liquid crystal, or the like can be used. These display methods generally have a problem that the operating voltage rises when trying to obtain a high contrast by increasing the light scattering property. For example, increasing the liquid crystal layer thickness, decreasing the cholesteric pitch in the phase transition method, and miniaturizing the liquid crystal droplets in the polymer dispersion method all have the effect of increasing the scattering property, but both increase the driving voltage. There is an adverse effect. When the present invention is applied to these methods, when the same liquid crystal cell as the conventional one is used, the contrast is improved by improving the scattering property, and when the contrast is the same as the conventional one, the driving voltage is lowered. You can Among these methods, in a so-called polymer dispersion type liquid crystal display element in which a liquid crystal layer is composed of a liquid crystal region and a support configured to divide the liquid crystal region into fine parts, low voltage driving and light scattering property are used. Since it is particularly difficult to satisfy both requirements, the above advantages are particularly remarkable when the present invention is applied. The internal structure of the polymer dispersion layer that can be used in the present invention is not particularly limited, and a drop in which liquid crystal typified by a dispersion film produced by an emulsion method or the like is dispersed in the support as substantially spherical droplets. The support structure such as a polymer divides the liquid crystal part into fine areas in some way, such as a ret structure or a network structure in which the support forms a network structure that is easily formed by the photopolymerization method and the liquid crystals in the network communicate with each other. Any structure can be used. The term "fine" as used herein is generally 0.2 μm.
To 10 μm. The thickness of the liquid crystal dispersion layer may be the same as that of a conventionally known polymer dispersion type liquid crystal display device, and is generally in the range of 3 μm to 30 μm. Also,
The ratio of the liquid crystal to the support may be the same as that in a conventionally known polymer-dispersed display device, and the liquid crystal is 40% to 90% of the whole film.
The range of% is common.

[0011]

The present invention will be described in more detail with reference to the following examples. Example 1 Prepolymer KAYARAD HX62 manufactured by Nippon Kayaku Co., Ltd.
Photopolymerization initiator Darocur1173 manufactured by Merck Ltd.
Was added in an amount of 3% by weight to prepare a photocurable resin composition.
A glass substrate having a transparent conductive film was overlaid with a 7 μm spacer interposed therebetween to produce a liquid crystal cell having a cell gap of 6 μm. A liquid crystal composition BL036 manufactured by Merck & Co., Inc. and a photocurable resin composition were mixed so that the ratio of the liquid crystal composition was 70% by weight, heated to a temperature at which the liquid became uniform, and injected into a liquid crystal cell. A liquid crystal cell 1 having a polymer-dispersed liquid crystal layer by subjecting this to light irradiation with a high-pressure mercury lamp to polymerize the prepolymer to phase-separate the liquid crystal and the polymer.
Was produced. Directly below the liquid crystal cell 1, a selective reflection plate of a polycarbonate product (refractive index 1.58) having prisms having an apex angle of 90 ° and a pitch of 0.3 mm in a structure as shown in FIG. 8 was arranged in parallel. The selective transmitted light range of the present reflector was within a range of ± 36 ° symmetrical with respect to the normal to the display surface, and it functioned as a reflector for incident light having a larger incident angle. Further, immediately below the selective reflection plate, a light absorbing means made of a black film having a roughened surface was provided. A light source device composed of a 4 W hot cathode tube, a reflection plate, a light shielding plate, and a colored louver is arranged on the upper end of the selective reflection plate,
A liquid crystal display device A was produced so that the incident angle of the illumination light on the reflection plate was 45 ° or less. As a reference sample, a reflective liquid crystal display element R1 having the configuration of FIG.
Was produced. When these liquid crystal display elements were observed from the front under a fluorescent lamp in the room, all of the elements exhibited good black display when a voltage of 20 V was applied, but the scattered light intensity when no voltage was applied was clearly in the present invention. A was excellent. Further, in A, a white background brighter than R1 was obtained even when the illumination light was turned off.

Examples 2 to 9 Liquid crystal display elements were produced in the same manner as in Example 1, except that selective reflection plates having different prism structures as shown in Table 1 were used. The preferable apex angle range varies depending on the material used, but it was possible to perform high-contrast display by selecting the apex angle within the range of 30 ° to 150 °.

[Table 1]

[0013]

According to the reflective liquid crystal display element of the present invention, at least part of the illumination light is reflected within the reflection angle range of the scattering liquid crystal layer and the light reflecting means having angle selectivity and the selective light reflecting means. Since it has a light source device that operates, forward scattering with high scattered light intensity can be used, and extremely bright white display can be performed. Further, by utilizing the angle selectivity of the selective light reflecting means, the non-scattering pixels are displayed in black, and clear and high-contrast black and white display like a printed matter is possible. Further, since strong light scattering can be obtained without increasing the light scattering property of the liquid crystal layer, the driving voltage for obtaining the same contrast is low.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a cross-sectional structure of an example of a conventional polymer-dispersed liquid crystal display element.

FIG. 2 is a diagram showing a light path of a liquid crystal cell of FIG. 1 in a voltage non-application state.

FIG. 3 is a diagram showing a light path of a voltage applied state of the liquid crystal cell of FIG.

FIG. 4 is a diagram schematically showing a cross-sectional structure of an example of the liquid crystal display element of the present invention.

FIG. 5 is a view schematically explaining the operation of the selective light reflecting means of the present invention.

FIG. 6 is a diagram showing a light path of a liquid crystal display element of the present invention in a voltage applied state.

FIG. 7 is a diagram showing a light-scattering state of the liquid crystal layer when no voltage is applied to the liquid crystal display element of the present invention or when a voltage equal to or lower than a threshold voltage is applied.

FIG. 8 is a diagram schematically showing a cross-sectional structure of an example of the liquid crystal display element of the present invention including two light source devices.

FIG. 9 is a diagram showing a preferred specific example of the selective light reflecting means of the present invention.

10 is a sectional view of the selective light reflecting means of FIG. 9 showing the operation thereof.

FIG. 11 is a diagram showing a relationship between a reflection angle and an incident angle of the selective light reflecting means of FIG.

FIG. 12 is a diagram showing the relationship among the apex angle α of the prisms, the inclination angle β of the bottom surface, and the inclination angle γ of the prisms of the prism group constituting the light reflecting means of the present invention.

FIG. 13 is a perspective view of an example in which the selective light reflecting means of the present invention is composed of prisms arranged two-dimensionally.

FIG. 14 is a diagram showing an example of a cross-sectional structure of a prism which constitutes the selective light reflecting means of the present invention.

FIG. 15 is a diagram showing another example of the cross-sectional structure of the prism that constitutes the selective light reflecting means of the present invention.

FIG. 16 is a diagram showing another example of the cross-sectional structure of a prism which constitutes the selective light reflecting means of the present invention.

FIG. 17 is a diagram showing another example of the cross-sectional structure of a prism which constitutes the selective light reflecting means of the present invention.

FIG. 18 is a cross-sectional view of an example of the selective light reflecting means of the present invention that is configured by a plurality of types of prisms having different shapes.

FIG. 19 is a cross-sectional view of one example in which the prisms of the prism group forming the selective light reflecting means of the present invention are inclined.

FIG. 20 is a cross-sectional view of an example in which the bottom surface of the prism of the prism group that constitutes the selective light reflecting means of the present invention is inclined.

FIG. 21 is a cross-sectional view of an example of the light reflecting means of the present invention in which another layer is provided on the prism structure.

[Explanation of symbols]

10 liquid crystal cell 11a translucent substrate 11b translucent substrate 12a transparent electrode 12b transparent electrode 13 liquid crystal layer 13a liquid crystal 13b support 20 light absorbing layer 30 selective light reflecting means 40 observer's eye 50 incident light 51 incident light 52 incident Light 53 Incident light 54 Incident light 55 Incident light 56 Incident light 61 Light transmission / reflection switching angle 62 Light transmission / reflection switching angle 80 Light source device 83 Light shielding part 84 Louver 501 Part of backscattering component 502 Forward scattering component Part of 531 Reflected light 541 Reflected light ic1 Light transmission / reflection switching angle ic2 Light transmission / reflection switching angle p Pitch α Prism top angle β Prism bottom tilt angle γ Prism tilt angle α ₁ Prism top Angle α ₂ Prism apex α ₃ Prism apex angle δ Critical angle for total internal reflection

Claims (4)

[Claims] 1. A pair of transparent substrates, each having a transparent pixel electrode on the inner surface thereof and arranged to face each other at a distance, and a liquid crystal cell having a liquid crystal layer sandwiched between the substrates and having a light scattering property changed by application of an electric field. In the provided liquid crystal display element, on the back side of the liquid crystal layer,
Selective light reflection means having light-transmission / reflection switching angle selectivity that transmits light with an incident angle in a specific range including the visual recognition direction and reflects light with an incident angle range other than that in a direction other than the visual recognition direction. And a light source device for irradiating the selective light reflecting means with illumination light having at least a part of light reflected within the reflection angle range, and a light absorbing means on the back side of the light source device. Reflective liquid crystal display device. 2. The liquid crystal display element according to claim 1, wherein the selective light reflecting means is a prism group formed on a plate-shaped transparent substrate. 3. The liquid crystal display element according to claim 2, wherein the prisms forming the prism group are made up of a plurality of types of light transmission / reflection switching angles. 4. The light transmission / reflection switching angle of the selective light reflecting means is in the range of 30 ° to 55 °.
Alternatively, the liquid crystal display element according to the item 3.