JP2003149685A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semitransparent liquid crystal display device which can suppress a reflection-in phenomenon by expanding a visual field angle and effectively suppressing the influence of reflection and interface reflection by the spiral structure of a semitransparent cholesteric layer. SOLUTION: The semitransparent liquid crystal display is provided with a liquid crystal display element 1 for modulating the phase of incident light for every pixel according to applied voltage. A liquid crystal display element 1 has a pair of transparent substrates 2 and 3 arranged opposing each other and a liquid crystal layer 4 inserted and held between the pair of transparent substrates 2 and 3. A first circularly light-polarization plate 7 is arranged on the observation side of the display element 1. An illumination light source 9 is arranged on the rear surface of the display element 1, and a second circularly light-polarization plate 8 is arranged between this light source 9 and the display element 1. On the inner surface of the transparent substrate 2 on the rear surface side of the display element 1, the semitransparent cholesteric layer 5 reflecting the circular light-polarization components of a single direction of light in all the wavelength band of red, green and blue by a prescribed ratio is laminated. In addition, on the surface of the observation side of this cholesteric layer 5, an overcoat layer 6 having light scattering property is laminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a semi-transmissive liquid crystal capable of displaying both a transmissive display utilizing back light and a reflective display utilizing external light. Regarding display device.

[0002]

2. Description of the Related Art In recent years, a layer having a cholesteric regularity (cholesteric layer) has been widely used as a circularly polarized light control element such as a circularly polarizing plate or a color filter used in a liquid crystal display device from the viewpoint of ease of manufacturing. Is starting to appear.

The cholesteric layer is made of liquid crystal such as cholesteric liquid crystal and chiral nematic liquid crystal, and has the characteristic that the director changes spirally in space in addition to the alignment order in the plane of the liquid crystal molecular axis. . That is, in a plane parallel to the liquid crystal molecular axis, the liquid crystal has an alignment order similar to that of a nematic phase, and when moving to another adjacent plane, this local alignment direction is slightly rotated. Therefore, such a change is sequentially and continuously generated along the normal direction of the cholesteric layer, so that a spiral structure is formed as the entire liquid crystal molecule.

In the cholesteric layer having such a spiral structure, when light is incident along the spiral axis, only a circularly polarized light component in the same direction as the twisting direction of the liquid crystal is reflected, and a circularly polarized light component opposite to this is obtained. Is transparent. At this time, since the phase of the reflected light with respect to the incident light does not change, the polarization direction before and after the incident of the reflected light does not change, and the wavelength of the reflected light is a specific wavelength according to the pitch of the twist of the liquid crystal. Limited to the area. Therefore, when natural light such as backlight light or external light (light in an arbitrary wavelength range including both right-handed and left-handed circularly polarized light components) is incident, the light in a specific wavelength range Only the circularly polarized light component is reflected, and the circularly polarized light component in the opposite direction and light in other wavelength regions are transmitted.

By the way, in recent years, a semi-transmissive liquid crystal display device capable of displaying both a transmissive display utilizing back light and a reflective display utilizing external light is becoming widespread. In the liquid crystal display device, as an optical element that reflects the external light and transmits the backlight light,
A semi-transmissive circularly polarized light reflection layer is used.

For example, in Japanese Unexamined Patent Publication No. 2000-193962, such a semi-transmissive circularly polarized light reflection layer, that is, not a 100% reflection of a specific circular polarization component of a specific wavelength range, A certain proportion (eg 50
%), A method for realizing a circularly polarized light reflective layer that transmits only (%) using a cholesteric liquid crystal is described. That is, in the transflective liquid crystal display device, by disposing the transflective circularly polarized light reflection layer (cholesteric layer) on the back side of the liquid crystal layer of the liquid crystal display element (the side of the illumination light source that illuminates the backlight light), In the case of a reflection type display using external light, a specific circularly polarized light component of a specific wavelength range of external light is reflected by this cholesteric layer, and in the case of a transmission type display using backlight light, a backlight is used. A specific circularly polarized light component in a specific wavelength range of light is transmitted.

Such a semi-transmissive circularly polarized light reflection layer (cholesteric layer) reflects a unidirectional circularly polarized light component of light in all wavelength regions of red, green and blue at a predetermined ratio. However, such a cholesteric layer can be produced by stacking three cholesteric layers that reflect light in the respective wavelength bands of red, green and blue at a predetermined ratio (Japanese Patent Laid-Open No. 2001-2001). -484
3 gazette).

[0008]

By the way, in the above-mentioned conventional transflective liquid crystal display device, the transflective circularly polarized light reflecting layer that reflects the external light and transmits the backlight light is made of cholesteric liquid crystal. A semi-transmissive cholesteric layer is used. Here, since the spiral axis of the liquid crystal extends along the normal direction of the cholesteric layer, the reflected light of the external light in the case of the reflective display has a regular reflection relationship in which the incident angle is equal to the reflection angle. Further, surface reflection (so-called glare phenomenon) occurs due to reflection due to the spiral structure and interface reflection in the semi-transmissive cholesteric layer. Therefore, when the transflective liquid crystal display device is viewed in a reflective display, the image is recognized only when viewed from a certain viewing direction, the viewing angle is very narrow, and the surface reflection ( There is a problem that the display image is difficult to see due to the influence of the reflection phenomenon.

By the way, as a method for solving such a problem, for example, a method of disturbing the alignment state of the surface of the cholesteric layer is known (Japanese Unexamined Patent Publication No. 2000-25).
8623 publication).

However, it is generally very difficult to control the degree of disorder of the alignment state on the surface of the cholesteric layer, and it is practically difficult to secure the quality of the displayed image.

The present invention has been made in consideration of the above points, and is of a semi-transmissive type capable of displaying both a transmissive display utilizing back light and a reflective display utilizing external light. A liquid crystal display device capable of expanding the viewing angle and effectively suppressing the influence of reflection and interface reflection due to its spiral structure in the semi-transmissive cholesteric layer to suppress the reflection phenomenon. An object of the present invention is to provide a liquid crystal display device of the type.

[0012]

SUMMARY OF THE INVENTION The present invention is a liquid crystal display element for modulating the phase of incident light for each pixel according to an applied voltage, and a pair of transparent substrates arranged to face each other, and a pair of these transparent substrates. A liquid crystal display element having a liquid crystal layer sandwiched between the transparent substrates, a first polarizing plate disposed on the observation side of the liquid crystal display element, and an illumination light source disposed on the back side of the liquid crystal display element, A second polarizing plate disposed between the illumination light source and the liquid crystal display element, and a second polarizing plate disposed between the liquid crystal layer of the liquid crystal display element and the illumination light source, and all wavelength bands of red, green and blue. A semi-transmissive cholesteric layer that reflects the unidirectional circularly polarized light component of the light at a predetermined ratio,
A liquid crystal display device, comprising: an overcoat layer having a light-scattering property, which is laminated on an observation side surface of the cholesteric layer.

In the present invention, it is preferable that the cholesteric layer is laminated on the observation side surface of the rear transparent substrate of the pair of transparent substrates.

According to the present invention, light scattering is performed on the observation-side surface of the semi-transmissive cholesteric layer that reflects the unidirectional circularly polarized light component of all wavelength bands of red, green and blue at a predetermined ratio. Since a transparent overcoat layer is laminated, in a transflective liquid crystal display device incorporating such a transflective cholesteric layer, the viewing angle is expanded and the transflective cholesteric layer is used. It is possible to effectively suppress the influence of the interfacial reflection of the and to suppress the reflection phenomenon. Moreover, since the overcoat layer is laminated on the observation side surface of the semi-transmissive cholesteric layer 5,
It is possible to effectively prevent the surface of the cholesteric layer from being scratched when the transflective cholesteric layer is assembled to the transflective liquid crystal display device.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the liquid crystal display device according to the present embodiment is a semi-transmissive type capable of displaying both a transmissive display utilizing backlight light and a reflective display utilizing external light. The liquid crystal display device includes the liquid crystal display element 1 that modulates the phase of incident light for each pixel according to an applied voltage.

The liquid crystal display element 1 has a pair of transparent substrates 2 and 3 arranged to face each other, and a liquid crystal layer 4 sandwiched between the pair of transparent substrates 2 and 3. Here, a TFT element (not shown), an ITO film (not shown) as a pixel electrode, and the like are provided on the inner surfaces of the transparent substrates 2 and 3, and a voltage is independently applied to the liquid crystal layer 4 for each pixel. Can be applied. The TFT element is provided on either side of the transparent substrates 2 and 3, but is preferably provided on the inner surface of the transparent substrate 2 on the back side,
As a result, it is possible to secure the brightness in the reflection type display using the external light. Further, on the inner surfaces of the transparent substrates 2 and 3 (for example, the inner surface of the transparent substrate 3 on the observation side), a color filter (not shown) including pixel regions of three colors of red, green and blue is provided for each pixel. It is provided.

A first circular polarization plate 7 is arranged on the observation side of the liquid crystal display element 1. When the liquid crystal layer 4 has a function as a retardation plate (λ / 4 plate), a linear polarizing plate can be used instead of the first circular polarizing plate 7. Further, on the back side of the liquid crystal display element 1, an illumination light source 9
Is arranged, and the second circularly polarizing plate 8 is arranged between the illumination light source 9 and the liquid crystal display element 1. The illumination light source 9
Is a light guide body 10 that emits the light incident from the side surface from one of the upper surface and the lower surface, a linear light source 12 that emits light toward the side surface of the light guide body 10, and a light source that is emitted from the lower surface of the light guide body 10. It has the reflection plate 11 which reflects light. A reflection plate 13 is provided on the back surface of the linear light source 12.

Here, on the inner surface (observation side surface) of the transparent substrate 2 on the back side of the liquid crystal display element 1, a unidirectional circular polarization component of light in all wavelength bands of red, green and blue is predetermined. The semi-transmissive cholesteric layer 5 that reflects light at a ratio (for example, 50%) is laminated, and the light-scattering overcoat layer 6 is further laminated on the observation side surface of the cholesteric layer 5.

Of these, the cholesteric layer 5 is a layer having cholesteric regularity, and is made of cholesteric liquid crystal, chiral nematic liquid crystal, or the like. Specifically, the cholesteric layer 5 can be manufactured by stacking three cholesteric layers that reflect light in respective wavelength ranges of red, green and blue at a predetermined ratio (Japanese Patent Laid-Open No. 2001-2001). As a material for each cholesteric layer, a polymerizable monomer molecule or a polymerizable oligomer molecule, a liquid crystal polymer, or the like can be used. Here, when a polymerizable monomer molecule is used as the material of the cholesteric layer, the method disclosed in Japanese Patent Application Laid-Open No. 2001-1
A mixture of a liquid crystal monomer and a chiral compound as described in Japanese Patent No. 00004 can be used.
When a polymerizable oligomer molecule is used, a molecule in which a polymerizable functional group is introduced at the terminal of a cyclic organopolysiloxane compound having a cholesteric phase as described in JP-A-57-165480. Can be used. On the other hand, when a liquid crystal polymer is used as the material for the cholesteric layer, a polymer in which a mesogenic group exhibiting liquid crystal is introduced into the main chain, a side chain, or both positions of the main chain and the side chain, and a cholesteryl group in the side chain Introduced polymer cholesteric liquid crystal, liquid crystalline polymer as described in JP-A-9-133810, JP-A-11-2
A liquid crystal polymer as described in Japanese Patent No. 93252 can be used.

On the other hand, the overcoat layer 6 is a layer having a light-scattering property, and contains a diffusing agent made of organic or inorganic fine particles in a translucent resin made of cellulose-based, acrylic-based or epoxy-based resin or the like. Any thing can be used. Here, it is preferable that the difference in refractive index between the translucent resin and the diffusing agent is 0.02 or more and 1.0 or less. This is because the difference in refractive index between the translucent resin and the diffusing agent is 0.
This is because when it is at least 02, a sufficient diffusion effect can be obtained while the content of the diffusing agent is kept to the necessary minimum, and the difference in refractive index between the light-transmitting resin and the diffusing agent is 1.
This is because when the content is 0 or less, the content of the diffusing agent can be sufficiently secured and uniform light diffusing characteristics can be obtained.
The particle size of the diffusing agent is preferably 5 nm or more and 10 μm or less. This is because by setting the particle size of the diffusing agent to 5 nm or more, the diffusing agent can be easily dispersed in the translucent resin, and the particle size of the diffusing agent is set to 10 μm or less. Thereby, it is possible to prevent the diffusing agent from protruding on the surface of the light-transmissive resin to cause whitening of the surface and deterioration of the visibility of the displayed image.

The surface of the overcoat layer 6 has a haze value in the normal direction of 3 or more and 85 or less, and a haze value in the normal direction and a haze value in the direction of ± 60 ° from the normal direction. Is preferably 0.1 to 7.
This is because the haze value in the normal direction of the overcoat layer 6 is 3
If it is less than 85, there is no light diffusing property, and if it is more than 85, the light diffusing property is too strong and it becomes cloudy, and the haze value in the normal direction and the haze value in the direction of ± 60 ° from the normal direction. This is because if the difference between and exceeds 7, the uniform brightness of the display image cannot be obtained and the display quality is degraded. The surface roughness Ra of the overcoat layer 6 is preferably 2 μm or less (more preferably 0.3 μm or less).

As the translucent resin in the overcoat layer 6, various resin compositions can be used, and in particular, triacetyl cellulose (refractive index 1.5
0), cellulose acetate propionate (refractive index 1.47), cellulose acetate butyrate (refractive index 1.47 to 1.50), cellulose (refractive index 1.5).
4), and cellulose-based resins such as cellulose tributyrate (refractive index 1.48) are preferable. In addition, as the diffusing agent, it is preferable to use an organic substance such as plastic beads, and it is particularly preferable that the diffusing agent has high transparency and has a difference in refractive index from the light-transmitting resin as described above. Such plastic beads include melamine beads (refractive index 1.57), acrylic beads (refractive index 1.4).
9), acrylic-styrene beads (refractive index 1.54),
Polycarbonate beads, polyethylene beads, vinyl chloride beads, etc. are used. Further, as the diffusing agent, an inorganic material such as cerium oxide (refractive index 1.63) may be used.

Next, the operation of the transflective liquid crystal display device shown in FIG. 1 will be described with reference to FIGS. 2 (a) and 2 (b). Figure 2 (a)
(b) is a schematic diagram for explaining the operation of the semi-transmissive liquid crystal display device shown in FIG. 1, and shows a path of light together with main constituent elements. In the following description, the first
The circularly polarizing plate 7 and the second circularly polarizing plate 8 are circularly polarizing plates that transmit the right-handed circularly polarized light component, and the semi-transmissive cholesteric layer 5 reflects the right-handed circularly polarized light component at a predetermined ratio. An example will be described in which the case has a reflection characteristic.

First, referring to FIG. 2A, a case of performing transmissive display utilizing backlight light in the transflective liquid crystal display device shown in FIG. 1 will be described.

As shown in FIG. 2A, the backlight light (natural light) emitted from the illumination light source 9 is emitted from the second circular polarization plate 8
In the second circularly polarizing plate 8, only the circularly polarized light component (right-handed circularly polarized light component) that matches the reflection characteristic of the semi-transmissive cholesteric layer 5 passes therethrough, and the circularly polarized light component that is the opposite of this circularly polarized light component. (Left-handed circularly polarized light component) is absorbed. The right circularly polarized light (white light) that has passed through the second circularly polarizing plate 8 is transmitted through the semi-transmissive cholesteric layer 5 by a predetermined ratio (for example, 50%), and the transmitted right circularly polarized light (white light) is After being scattered by the overcoat layer 6, it reaches the liquid crystal layer 3 and remains at the right circularly polarized light or is converted to left circularly polarized light depending on the modulation state of the pixel, and reaches the first circularly polarizing plate 7. Specifically, for example,
When no voltage is applied to the pixel ("OF" in Fig. 2 (a))
In the case of "F"), the light is left-handed circularly polarized light, and when a voltage is applied to the pixel (in the case of "ON" in Fig. 2 (a)), it is converted into left-handed circularly polarized light. When the polarized light reaches the first circular polarization plate 7 as it is, it is converted into linearly polarized light by the first circular polarization plate 7 and emitted to the observation side to display a bright state.
On the other hand, when the circularly polarized light is converted to the left circularly polarized light and reaches the first circularly polarizing plate 7, the circularly polarized light that is the reverse of the circularly polarized light that can be passed by the first circularly polarizing plate 7 is given here. It is cut off and the dark state is displayed.

The remaining (for example, 50%) right circularly polarized light reflected by the semi-transmissive cholesteric layer 5 passes through the second circularly polarizing plate 8 in the opposite direction and is returned to the illumination light source 9. And
The right circularly polarized light returned in this manner is reflected by the illumination light source 9 (reflector 11 (see FIG. 1)) and is used again as backlight light.

Next, referring to FIG. 2 (b), description will be given of a case where the transflective liquid crystal display device shown in FIG.

As shown in FIG. 2B, external light (natural light)
Becomes a right-handed circularly polarized light through the first circularly polarizing plate 7, and is either left-handed circularly polarized light or converted to left-handed circularly polarized light in the liquid crystal layer 3 depending on the modulation state of the pixel, and is thus a semi-transmissive cholesteric layer. Reach 5. Specifically, for example, when the voltage is not applied to the pixel (“OFF” in FIG. 2B), the right circularly polarized light remains, and when the voltage is applied to the pixel (see FIG. In the case of "ON")), the light is converted to left circularly polarized light. Here, when reaching the semi-transmissive cholesteric layer 5 with the right-handed circularly polarized light, the semi-transmissive cholesteric layer 5
At a predetermined ratio (for example, 50%), is scattered by the overcoat layer 6, and then passes through the liquid crystal layer 3 again,
It is converted into linearly polarized light by the first circularly polarizing plate 7 and emitted to the observation side to display in a bright state. On the other hand, when it reaches the semi-transmissive cholesteric layer 5 after being converted into left circularly polarized light,
Although it passes through the semi-transmissive cholesteric layer 5 and reaches the second circularly polarizing plate 8, it is a circularly polarized light having a reverse rotation to the circularly polarized light that can be passed by the second circularly polarizing plate 8, and is blocked here. The dark state is displayed.

As described above, according to the present embodiment, red,
An overcoat layer 6 having a light scattering property is laminated on the observation side surface of a semi-transmissive cholesteric layer 5 which reflects a unidirectional circularly polarized light component of light in all wavelength bands of green and blue at a predetermined ratio. Therefore, in such a semi-transmissive liquid crystal display device in which the semi-transmissive cholesteric layer 5 is incorporated, the viewing angle is increased, and reflection and reflection due to the spiral structure of the semi-transmissive cholesteric layer 5 are caused. It is possible to effectively suppress the influence of interface reflection and suppress the reflection phenomenon. Further, since the overcoat layer 6 is laminated on the surface of the semi-transmissive cholesteric layer 5 on the observation side, the surface of the cholesteric layer 5 when the semi-transmissive cholesteric layer 5 is assembled to the semi-transmissive liquid crystal display device. It is possible to effectively prevent scratches on the skin.

In the above-described embodiment, the semi-transmissive cholesteric layer 5 is laminated on the inner surface (observation-side surface) of the transparent substrate 2 on the back side. Can be placed at any position between the liquid crystal layer 4 of the liquid crystal display element 1 and the illumination light source 9.

[0032]

As described above, according to the present invention, it is possible to increase the viewing angle and effectively suppress the influence of interface reflection in the semi-transmissive cholesteric layer to suppress the reflection phenomenon. it can.

[Brief description of drawings]

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

FIG. 2 is a schematic diagram for explaining the operation of the liquid crystal display device shown in FIG.

[Explanation of symbols]

1 Liquid crystal display element 2,3 transparent substrate 4 Liquid crystal layer 5 Cholesteric layer 6 Overcoat layer 7,8 circular polarizer 9 Illumination light source 10 Light guide 11,13 Reflector 12 line light source

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H048 BA04 BA64 BB03 BB10 BB37                       BB42                 2H088 GA03 HA03 JA04 JA14 MA02                       MA05 MA06 MA16 MA18                 2H091 FA10 FB02 FC29 FC30 FD07                       FD13 FD23 HA11 LA03 LA11                       LA12 LA13 LA15 LA18

Claims (2)

[Claims] 1. A liquid crystal display element for modulating the phase of incident light for each pixel according to an applied voltage, and a pair of transparent substrates arranged to face each other, and sandwiched between the pair of transparent substrates. A liquid crystal display element having a liquid crystal layer, a first polarizing plate arranged on the observation side of the liquid crystal display element, an illumination light source arranged on the back side of the liquid crystal display element, the illumination light source and the liquid crystal display element A second polarizing plate disposed between the liquid crystal layer of the liquid crystal display element and the illumination light source, and unidirectional circularly polarized light of all wavelength bands of red, green and blue. A liquid crystal display device comprising: a semi-transmissive cholesteric layer that reflects components at a predetermined ratio; and a light-scattering overcoat layer that is laminated on the observation-side surface of the cholesteric layer. 2. The liquid crystal display device according to claim 1, wherein the cholesteric layer is laminated on an observation side surface of a rear transparent substrate of the pair of transparent substrates.