JPH10239668A - Reflection type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the reflection type liquid crystal display device which has high definition, high contrast, and no parallax by equipping a liquid crystal element with an insulating substrate, a light reflecting member, a polymer dispersed liquid crystal layer whose twist angle of liquid crystal alignment is specified, and a 1/4-wavelength plate. SOLUTION: The liquid crystal element is equipped with insulating substrates 2 and 3 having at least a transparent electrode 10 formed, the light reflecting member 8 which has a light reflecting film formed on the surface of one of the insulating substrates 2 and 3 and an opposite electrode for driving display in cooperation with a transparent electrode 10, the polymer dispersed liquid crystal layer 13 which is a composite layer consisting of a liquid phase and polymer resin between the insulating substrates 2n and 3 and light reflecting member 8 and has the twist angle of liquid crystal orientation set to 40 to 50 deg. between the insulating substrates 2 and 3 and light reflecting member 8, and the 1/4-wavelength plate 5 which is formed between the light reflecting member 8 and polymer dispersed liquid crystal layer 13. Consequently, the majority of scattered light can pass through a polarization plate 7 and this device enters what is called a light display state.

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, and more particularly, to various video equipment such as a word processor, a notebook type personal computer, an electronic still camera, a portable video camera, a portable information terminal, a car information display device, and the like. The present invention relates to a reflective liquid crystal display device suitably used for an information display device, a game device, and the like.

[0002]

2. Description of the Related Art In recent years, the application of liquid crystal display devices to various types of information and video display devices such as notebook personal computers and portable television receivers has been rapidly advancing. In particular, among liquid crystal display devices, a reflective liquid crystal display device that performs display by reflecting ambient light incident from the outside does not require a backlight as a light source, has low power consumption, and can be thin and lightweight. Attention has been paid to this.

[0003] Conventionally, a reflection type liquid crystal display device has a TN (twisted nematic) type and an S type.
Liquid crystal display elements of the TN (super twisted nematic) type are used. However, these have a configuration in which the liquid crystal display element is sandwiched between a pair of polarizing plates in terms of the principle of the display type.
It is necessary to install a reflection plate outside of it. Therefore, due to the thickness of the glass substrate used for the liquid crystal display device, the angle at which the user looks at the glass substrate, that is, the angle between the normal direction of the glass substrate and the direction at which the user looks at the liquid crystal display device, depends on the angle. There is a problem that parallax occurs and the display is recognized twice.

A reflection type TN (45 ° twist type) liquid crystal display device using one polarizing plate and a 波長 wavelength plate is disclosed in Japanese Patent Application Laid-Open No. 55-48733. In this prior art, the distance between the upper and lower substrates sandwiching the liquid crystal layer is four.
By using a liquid crystal layer twisted by 5 degrees and controlling the applied electric field, the plane of polarization of the incident linearly polarized light can be divided into two states: a state parallel to the optical axis of the quarter-wave plate and a state having an angle of 45 degrees. Control and display in black and white. This liquid crystal display device has a 45 ° twist liquid crystal display device having a liquid crystal layer twisted by 45 ° between a polarizing plate and an upper and lower substrate sandwiching the liquid crystal layer from the incident light side.
It is composed of a wave plate and a reflector.

A voltage control method for a display state according to the above technique will be described below. Linearly polarized light from the polarizing plate enters the liquid crystal layer from the incident side, passes through the liquid crystal layer while rotating the plane of polarization following the twist of the orientation of the liquid crystal (twist). The light becomes a light in a vibration direction parallel to the slow axis or the fast axis and is incident on the １ ／ wavelength plate. The linearly polarized light having a polarization plane parallel to the optical axis of the quarter-wave plate passes through the quarter-wave plate while maintaining the linear polarization state, and is reflected by the reflector. The reflected light passes through the quarter-wave plate with linear polarization as in the case of the incident light, and passes through the liquid crystal layer while rotating the plane of polarization following the twist of the orientation of the liquid crystal. As a result, the reflected light has the same direction as the incident light. It becomes linearly polarized light having a plane of polarization. At this time, the outgoing light passes through the polarizing plate and becomes a bright display.

On the other hand, in a state where the twist is eliminated by applying a voltage to the liquid crystal layer, the linearly polarized light from the polarizing plate passes through the liquid crystal layer without rotating the plane of polarization and remains as linearly polarized light.
The light is incident at approximately 45 degrees with respect to the optical axis of the 波長 wavelength plate. In a quarter-wave plate, for example, the polarization state changes to clockwise circularly polarized light,
Light enters the reflector. The traveling direction of the circularly polarized light reflected by the reflection plate is reversed, for example, counterclockwise circularly polarized light. Further, when the reflected light passes through the quarter-wave plate again, it becomes linearly polarized light having a polarization plane orthogonal to the linearly polarized light incident on the quarter-wave plate at the time of incidence. In the opposite direction, it passes with linearly polarized light. At this time, as in the case of incidence, the polarization plane does not rotate, so that the light becomes linearly polarized light having the absorption direction of the polarizing plate, and dark display is achieved. In the above description, the polarization state after the incident light has passed through the liquid crystal layer and the quarter-wave plate is clockwise circularly polarized light. However, the same effect can be obtained even if this is counterclockwise. That is, in this prior art, display is realized by modulating the plane of polarization of linearly polarized light incident on the quarter-wave plate with the liquid crystal layer.

A dark display is realized when such a voltage is applied,
In addition to the arrangement that provides a bright display when no voltage is applied (hereinafter referred to as a normally white arrangement), the orientation of the optical axis of the quarter-wave plate is shifted by 45 ° to realize dark display when no voltage is applied. An arrangement for realizing a bright display when a voltage is applied (hereinafter, referred to as a normally black arrangement) is also possible. In this case 1
The conversion of the oscillation direction of the linearly polarized light by the 波長 wavelength plate is performed when no voltage is applied.

In either case of normally black or normally white, a liquid layer cell having a twist angle of 45 degrees is disposed between one polarizing plate and a と wavelength plate to obtain a conventional TN. The point that the same display as that of the liquid crystal display device of the type is enabled by one polarizing plate.

[0009]

However, according to the conventional reflection type liquid crystal display principle, if the reflector does not maintain good polarization, the clockwise circularly polarized light as described above is changed to the leftward circularly polarized light. The conversion, or the reverse conversion, and the conversion from linearly polarized light to linearly polarized light are not efficiently performed, and the contrast is reduced. Therefore, a flat mirror-reflecting member can be used as the reflecting plate for maintaining the polarization property, but this has a disadvantage that the display is difficult to see in a bright display because an external object is reflected as it is.

In order to compensate for this disadvantage and to scatter ambient light also in the viewing direction, it is necessary to use a stretched aluminum film for diffusing ambient light as the reflector. However, with this reflector, the above-described conversion from clockwise circularly polarized light to counterclockwise circularly polarized light, or vice versa, and conversion from linearly polarized light to linearly polarized light are not efficiently performed, and the contrast is reduced. There is a problem to do. That is, it is impossible to achieve both the diffusivity and the polarization maintaining property with the conventional reflector.

For example, in a liquid crystal display device described in Japanese Patent Application Laid-Open No. 55-70817, one
Since the 波長 wavelength plate and the reflection plate are provided, a shift occurs in the liquid crystal layer that passes when the light is incident and when the light is reflected.
The direction in which high-definition and high-quality display can be observed is limited. Therefore, an object of the present invention is to solve the above-described problems and to provide a reflective liquid crystal display device having high definition, high contrast, and no parallax.

[0012]

In order to achieve the above object, according to the present invention, there is provided a reflective liquid crystal display device having a polarizing plate on a light incident side of a liquid crystal element. In the liquid crystal device, at least an insulating substrate on which a transparent electrode is formed, a light reflection film formed on one surface of the insulating substrate, and a light reflection film formed with a counter electrode for driving display in cooperation with the transparent electrode A member, a composite layer composed of a liquid crystal phase and a polymer resin phase between the insulating substrate and the reflecting member, and a twist angle of liquid crystal alignment of 40 to 50 degrees between the insulating substrate and the reflecting member. And a quarter-wave plate formed between the light-reflecting member and the polymer-dispersed liquid crystal layer.

With this configuration, by using a reflective film having good polarization maintaining performance, a good black display can be realized when performing a dark display, and a scattering effect as well as reflection can be obtained when performing a bright display. By utilizing this, ambient light is directed toward the observer to realize a bright white display, a display with high contrast can be obtained, and parallax can be eliminated.

In addition, the liquid crystal polymer composite layer exhibits a scattering property strongly dependent on polarized light.
The transmission axis of the polarizing plate is arranged so as to coincide with any direction of the twisted liquid crystal alignment of the polymer dispersed liquid crystal.

The rotation of the polarization plane in the liquid crystal polymer composite layer may be a case where the scattering action is small. For this purpose, the liquid crystal state in which the rotation of the polarization plane can be prevented from exhibiting a scattering state. 4. A polymer similar to the liquid crystal may be oriented in the same manner as the liquid crystal, wherein the polymer material constituting the polymer dispersed liquid crystal layer is a material exhibiting birefringence, The liquid crystal layer does not show a scattering state when no voltage is applied, but shows a scattering state when a voltage is applied.

Further, the fact that the reflection film is close to the liquid crystal layer so that the reflected light passes through the liquid crystal layer in the same display state as at the time of incidence also provides a means for obtaining a high-definition display. Therefore,
According to a fourth aspect of the present invention, the light reflecting film forming the light reflecting surface of the light reflecting member is disposed on the polymer dispersed liquid crystal layer side of the light reflecting member.

According to a fifth aspect of the present invention, in the reflection type liquid crystal display device, the light reflecting surface is a flat mirror mirror or a diffusion mirror having smooth irregularities.

According to a sixth aspect of the present invention, in the reflection type liquid crystal display device, the quarter-wave plate is obtained by fixing liquid crystal alignment from a liquid crystal polymer or from a low molecule having a liquid crystal property. Characterized by being made of a polymer.

According to a seventh aspect of the present invention, in the reflective liquid crystal display device, the quarter-wave plate is formed on a light reflecting film of the light reflecting member, and the transparent film is formed on the quarter wave film. An electrode is formed, and the transparent electrode is defined as an electrode facing the transparent electrode formed on the insulating substrate.

According to another aspect of the present invention, in the reflection type liquid crystal display device, a color filter layer is formed on the insulating substrate or on a transparent electrode formed on the insulating substrate. And

According to a ninth aspect of the present invention, in the reflective liquid crystal display device according to the ninth aspect, the quarter-wave plate includes at least two layers. On the other hand, the second layer has a retardation of 120 to 150 nm, and the second layer is disposed so as to sandwich the first layer between the second layer and the reflecting surface, and the second layer has a retardation almost twice that of the first layer. The direction of the slow axis in the plane of the first layer and the second layer is 60 ° or more.
It is characterized by a difference of 120 °.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. Here, a description will be given of how to improve the optical quality of a reflection type liquid crystal display device using a scattering function to display a black state with a reflection plate having high polarization maintaining performance and to use a scattering function in a bright display. First, in the case of a dark display, it is necessary for a high-contrast display to make the display light component in the observer direction as small as possible. Therefore, it is important that the liquid crystal display device has a low reflectance and that the reflection film has high polarization maintaining performance. further,
Under normal observation conditions, the observer avoids the reflection of a light source from a ceiling light or the like, for example, in front of a display element.
Use it at a position that avoids specular reflection components from the light source. In this position, when the reflection film is a mirror surface or a reflection surface having small scattering (diffusion), the amount of display light directed toward the observer is small, which is preferable for black display. Thus, a good black display state is realized in combination with the black display effect realized by the reflection plate having good polarization maintaining properties.

On the other hand, in the case of bright display, if the reflection film has a high specularity and a low scattering effect, the surrounding state is easily reflected because the reflectance of the liquid crystal display element itself is high. Furthermore, in an arrangement that the observer prefers, that is, in a position that prevents reflection of the light source, the light from the light source has a large amount of specular reflection on the liquid crystal display surface, and the display light directed to the observer is small, resulting in a bright display. And good visibility cannot be obtained.

However, when the reflection of the bright display is not close to a mirror surface and the scattering effect is strong, the surrounding reflection becomes unclear due to the scattering effect, and the display contents can be easily recognized. White display is realized. In addition, in the arrangement for preventing the reflection of the light source, the ratio of the display light amount toward the observer increases, and the display becomes brighter for the observer, as compared with the case where the specularity of the reflective film is strong. Is obtained. In order to realize a bright display and a good black display as described above, it is effective to control not only the reflectivity but also the scattering properties of the liquid crystal.

Therefore, a detailed description will be given with reference to the configuration of a typical liquid crystal layer of the present invention. For example, a liquid crystal layer using a so-called polymer dispersed liquid crystal mode in which a liquid crystal polymer composite film shows a scattering state when no voltage is applied and shows a transparent state when a voltage is applied will be described. The polymer dispersed liquid crystal mode is subjected to an alignment treatment such as rubbing or the like, and a liquid crystal layer in which the alignment of the liquid crystal is twisted by 40 to 50 degrees is formed on two substrates. The liquid crystal polymer composite film can be switched between a transparent state and a scattering state by switching a voltage. For example, a so-called NCAP (Nemate) in which fine liquid crystal droplets are dispersed in a polymer in a capsule shape.
c Curvilinear Aligned Pha
se) (US Pat. No. 4,435,047). Further, PN (Polymer Network) LC in which a polymer network structure is formed in a continuous liquid crystal layer is also suitable (Japanese Display 1989,
690-693).

In such a scattering control type liquid crystal display mode, when the liquid crystal layer is twisted, the light traveling through the polymer liquid crystal composite layer propagates while rotating the plane of polarization, and further the scattering of the composite film occurs. It also has an effect. Figure 1 shows this situation.
(A) schematically shows this. That is, the liquid crystal molecules rotate the plane of polarization as in a normal TN type liquid crystal element, and a scattering effect occurs due to a difference in the refractive index from the polymer.

In the above-described example, the liquid crystal of the polymer-dispersed liquid crystal layer subjected to the alignment treatment is twist-aligned when no voltage is applied, and the light transmitted therethrough is scattered while rotating the polarized light in accordance with the liquid crystal molecular alignment. , １ ／ wavelength plate. At this time, if the main axis direction of the quarter-wave plate is arranged (normally white arrangement) so as to be directed to the plane of polarization of linearly polarized light incident on the quarter-wave plate, the prior art is disclosed in 4
A bright display in which a scattering effect is added to the bright display similar to that of JP-A-8733 is realized.

On the other hand, when a voltage is applied, the liquid crystal is oriented perpendicular to the translucent electrode and the reflective electrode, and light incident from the outside and emitted again is polarized in the transmission direction of the incident side polarizing plate. The light reaches the quarter-wave plate with the surface kept, and passes twice back and forth. For this reason, a phase difference of substantially 波長 wavelength is generated, the polarization plane is rotated by 90 degrees, and at the time of emission, the entering light is absorbed by the polarizing plate, and the display state becomes a dark display. At this time, if a reflective film having good specularity and good polarization holding performance is used, a good black state is exhibited. Further, since there is almost no scattering action by the liquid crystal polymer composite film, even if there is incident light that is not absorbed by the polarizing plate, it does not reach the observer. FIG. 1B shows the state of light transmitted through the liquid crystal portion.
Is schematically shown in FIG. There is no difference in the refractive index between the liquid crystal and the polymer, and almost no scattering effect occurs. Hereinafter, the mode in which the light scattered by the twisted liquid crystal polymer composite layer performs a bright display by the quarter-wave plate without rotating the polarization plane will be referred to as a twist scattering mode.

Next, a description will be given of a liquid crystal layer using a polymer dispersed liquid crystal layer which shows a transparent state when no voltage is applied and shows a scattering state when a voltage is applied. This display mode is hereinafter referred to as a twist transparent mode to distinguish it from the twist scattering mode. The liquid crystal and polymer of the oriented polymer-dispersed liquid crystal layer which have been subjected to the orientation treatment of the polymer-dispersed liquid crystal are twist-aligned when no voltage is applied, and light transmitted through the liquid crystal is hardly scattered and polarized. Is transmitted while rotating according to the twisted orientation. At this time, the state of the transmitted light is schematically shown in FIG. 1/4 with the composite membrane
By combining a quarter-wave plate in which the principal axis direction of the wave plate is arranged in a direction different from the polarization plane of linearly polarized light incident on the quarter-wave plate by 45 ° (normally black arrangement), The display state is controlled. That is, when no voltage is applied, a phase difference of half a reciprocating wavelength occurs as in the case of applying the voltage in the twist scattering mode described above. Due to the effect of this wave plate, the linearly polarized light orthogonal to the time of incidence becomes liquid crystal. Since the light passes through the polymer composite layer and is absorbed by the polarizer at the time of emission, a dark display is obtained. That is, the liquid crystal rotates the plane of polarization as in a normal TN-type liquid crystal element. At this time, since there is no difference in refractive index from the polymer, no scattering effect occurs.

When a voltage is applied, a scattering effect occurs and no rotation of the polarization plane occurs. If the quarter-wave plate is installed as described above, linearly polarized light polarized in the principal axis direction of the quarter-wave plate will be incident, and the presence of the quarter-wave plate will cause a change in its polarization state. The display is bright without any occurrence. This bright display is also a bright bright display in which a scattering effect is added to a state with a high transmittance as in the case of the bright display in the twist scattering mode. At this time, the state of the transmitted light is schematically shown in FIG. That is, since the liquid crystal rises with respect to the substrate, the plane of polarization of light passing through the liquid crystal layer does not rotate, and a scattering effect is caused by a difference in refractive index between the liquid crystal and the polymer.

A liquid crystal polymer composite film suitable for such a twist transparent mode shows a liquid crystal phase in a low molecular state,
A polymer-dispersed liquid crystal composite film made by mixing an organic material that retains its optical anisotropy even when polymerized into a polymer, and a liquid crystal material that does not polymerize, and polymerized by phase separation Is available. The reflection type liquid crystal display device using the above liquid crystal phase will be described more specifically with reference to embodiments, but it is needless to say that the present invention is not limited thereto.

<Embodiment 1> An embodiment of the twist scattering mode described with reference to FIG. 1 will be described below. FIG.
FIG. 1 is a cross-sectional view of a reflective liquid crystal display device (hereinafter abbreviated as a liquid crystal display device) according to a first embodiment of the present invention. The liquid crystal display device 1 includes a pair of transparent glass substrates 2 and 3, on which a metal reflection film 7 made of a metal material such as aluminum, nickel, chromium or silver is formed, and is a light reflection member. The reflector 8 is formed. The metal reflection film 7
A quarter-wave plate 5 is formed thereon, and an alignment film 9 is further formed.

The glass substrate 3 facing the glass substrate 2
A transparent electrode 10 made of, for example, ITO (indium tin oxide) is formed on the surface of the substrate, and an electric field is applied to the liquid crystal layer by the metal reflection film 7 and the transparent electrode 10. Further, a polarizing plate 4 is disposed on the display surface side of the glass substrate 3. An alignment film 11 is formed by covering the glass substrate 3 on which the transparent electrode 10 is formed, and the peripheral portions of the glass substrates 2 and 3 facing each other are sealed with a sealing material 12 described later. 4 between the alignment films 9 and 11
Rubbing treatment is performed so as to be twisted five degrees.

The reflective electrode 7 is formed by depositing a high-reflectance, low-resistance metal member such as Al or Ag by a sputtering method or a vapor deposition method. Therefore, it is necessary to control the film forming temperature, the film forming rate, and the like, and to form a mirror-finished surface. Further, the film thickness needs to be set in a range where the reflectivity is sufficient and the resistance is low, and it is preferable that the film thickness is about 0.2 to 2 μm.

The liquid crystal layer 13 has, for example, a dielectric anisotropy Δε
PN is a polymer-dispersed liquid crystal material having a positive
A liquid crystal material such as M-106 (manufactured by Dainippon Ink and Chemicals, Inc.) is sealed. Adjust the chiral agent according to the setting of the twist angle, adjust the liquid crystal layer so that it twists 45 degrees between the upper and lower substrates, seal it after vacuum injection, irradiate ultraviolet rays, phase separate polymer and liquid crystal, The molecules are twisted by 45 degrees. The member forming the substrate 2 is a translucent substrate 3
The material may be the same as that described above, but is not necessarily required to be translucent.

The polymer-dispersed liquid crystal layer 13 has a solid portion in which the liquid crystal 14 is composed of a polymer (hereinafter, referred to as a polymer matrix).
15 may be used as long as they are dispersed and held in the liquid crystal 15, for example, liquid crystals that form independent liquid bubbles and are encapsulated in microcapsules (NCAP) and liquids in which these liquid bubbles communicate (PNLC) Used. Further, the polymer matrix may be crosslinked in a gel state, or the polymer matrix in which a large number of fine holes are opened may be filled with liquid crystal. The polymer matrix 15 desirably has no birefringence because the twist scattering mode is adopted. For example, an epoxy resin or an acrylic resin is suitable. The liquid crystal 14 and the polymer matrix 15
Are omitted in the figure.

The liquid crystal 14 has a cyanobiphenyl-based liquid crystal,
A liquid crystal having a positive dielectric anisotropy, such as phenylcyclohexane, which is generally used for a TN type or STN type is used. The content ratio of the liquid crystal and the polymer in the polymer dispersed liquid crystal layer 13 is preferably set in a range of about 50 to 98% by weight of the liquid crystal.

When the content ratio of the liquid crystal is low, the difference between the refractive index of the polymer and the refractive index of the liquid crystal with respect to ordinary light is preferably 0.04 or less, in order to increase the transparency when voltage is applied. Desirably, it is within 0.02. When the content ratio of the liquid crystal is sufficiently high, it is not necessary to pay particular attention to such a point. In order to prevent the observer's face and surroundings from being reflected on the display surface and to reduce the operating voltage, it is better that the liquid crystal has a high light scattering property, and therefore the liquid crystal has a birefringence of 0.1. It is desirable that it is 1 or more, more preferably 0.15 or more.

As a method of manufacturing the polymer dispersed liquid crystal layer 13, a raw material of a polymer matrix and a liquid crystal are mixed in advance,
Either a method of causing phase separation by thermal polymerization (for example, JP-A-63-501512) or a method of causing phase separation by polymerization with ultraviolet rays (for example, JP-A-1-198725) May be used.

As a method for obtaining the polymer-dispersed liquid crystal layer 13 having a certain thickness, a method of preparing a mixed solution of a polymer matrix raw material and liquid crystal, casting the solution on an electrode substrate, and curing the solution, As in the case of the conventional TN type liquid crystal display device,
A method in which the periphery of the electrode substrate is sealed with an adhesive, a mixed solution of a polymer matrix material and liquid crystal is injected from an injection port, and the mixture is cured by heat or ultraviolet light can be used. On this occasion,
Needless to say, it is necessary to appropriately control the size of the scattering unit of the liquid crystal droplet or the network polymer in order to secure the above-mentioned scattering property.

For the quarter-wave plate 5, for example, a UV-curable liquid crystal can be used. Since the wavelength at which the visibility is highest is 530 to 550 nm, the retardation of the １ ／ wavelength plate 5 is 133 to 13 in the present embodiment.
The thickness is preferably set to 8 nm, but is appropriately adjusted in accordance with the wavelength dispersion of the refractive index anisotropy inherent to the material used. In the present embodiment, the polarization axis of the polarizing plate 4 and the 波長 wavelength plate 5
Are arranged such that their respective polarization axes and optical axes are at 45 degrees to each other.

Further, more preferably, 5 having good visibility is provided.
In order to satisfy the ４ wavelength condition not only for the light in the vicinity of 50 nm but also for light in a wider wavelength range, before generating a phase difference of 130 nm, a shift in the polarization state for each wavelength due to the wavelength is compensated. A layer may be provided. At this time, the amount of birefringence of the compensation layer is optimally set to a 波長 wavelength condition, and the azimuth of the optical axis between the １ ／ wavelength plate and the compensation 波長 wavelength layer is 60 ° to 120 °. It has been found that this compensation can be optimally performed when set between degrees. With a wider band than usual configured in this way. A retardation film that satisfies the 波長 wavelength condition may be used instead of the ５ wavelength plate 5. In this case, the direction corresponding to the optical axis of the 波長 wavelength plate is the direction in which linearly polarized light is converted to circularly polarized light. Needless to say, it is good.

The reflecting film 7 is preferably formed on the polymer dispersed liquid crystal layer 13 side of the substrate 2 in order to eliminate the parallax effect. In this case, the quarter-wave plate 5 is also provided as shown in FIG. Is disposed on the polymer dispersed liquid crystal layer 13 side of the substrate 2. On the opposite side of the glass substrate 3 from the liquid crystal layer 13, for example, a polarizing plate 4 having a single transmittance of 48% is arranged.

In the above structure, the polymer dispersed liquid crystal layer 13
The liquid crystal 14 is twisted at 45 degrees when no voltage is applied, and while the light transmitted through the liquid crystal 14 is scattered, it retains the polarization characteristics of the scattered light. , And the display state of the present apparatus is a so-called bright display. In this bright display, since the polymer-dispersed liquid crystal layer 13 is in a white scattering state, so-called reflection from the surroundings may occur even if the surface of the reflective electrode 7 joined to the polymer-dispersed liquid crystal layer 13 is a mirror surface. The visibility is small and the visibility is hardly reduced. As a result of intensive studies, the present inventors have found that scattered light almost retains polarization as shown in FIG. FIG.
In the arrangement shown in (a), the liquid crystal cell is rotated in a plane,
This is the result of measuring the intensity of the scattered light at each rotation angle, and receiving and measuring the scattered light with a crossed Nicol polarizing plate as shown in FIG. 5B. FIG. 4 shown here is
FIG. 7 is a diagram illustrating the polarization dependence of scattered light of a liquid crystal cell manufactured by the above procedure in a parallel liquid crystal orientation for simplicity.

As shown in FIG. 4, only the polarization component of the incident light in the liquid crystal alignment direction is scattered, and the scattered light is also scattered while maintaining the polarization. Is absorbed by. In addition, in the arrangement of the crossed Nicols polarizers, when the liquid crystal is different in orientation from each of the polarizers by, for example, 45 degrees, the polarization is aligned in the orientation direction of the liquid crystal due to the scattering action of the liquid crystal, and the polarization component is further 45 degrees. Since the light is received by different light receiving polarizers, the intensity is the highest among the crossed Nicols, and is about １ ／ of the peak intensity of the unpolarized light. This property is that the liquid crystal alignment is 4
It was confirmed that the same was true even when twisted five times. Therefore, there is almost no loss in the amount of light other than absorption by the polarizing plate at the time of incidence, and when the intensity of scattered light of the liquid crystal display device according to the present embodiment is measured in the arrangement of FIG. It was confirmed that only a change in the 生 じ occurred.

On the other hand, when a voltage is applied, the liquid crystal 14
Since it is oriented perpendicular to 0, no birefringence effect occurs for vertically incident light. Therefore, the change in the polarization state is caused only by the quarter-wave plate 5. Light incident from the outside is reflected by the reflective electrode 7, passes through the 板 wavelength plate 5 and the polarizing plate 4, and returns to the outside again. 1/4 wavelength plate 6
, Twice, so that a phase change of substantially 波長 wavelength is generated. Therefore, the plane of polarization rotates 90 degrees,
The light is absorbed by the polarizing plate 7 at the time of emission, and the display state of the device is a so-called dark display. In this case, a scattering effect does not occur by applying a voltage, and a black display without scattering can be achieved.

As shown in FIG. 7, the metal reflective film 7 and the transparent electrode 10 are connected to the scanning circuit 16 and the data circuit 1 respectively.
7 is connected. Scanning circuit 16 and data circuit 17
The voltage generation circuit 1 scans the metal reflection film 7 and the transparent electrode 10 based on display data corresponding to display contents under the control of a control circuit 18 such as a microprocessor.
The display is realized by applying the display voltage or the non-display voltage from No. 9.

FIG. 8A is a diagram showing an optical configuration of the polarizing plate 4, the polymer-dispersed liquid crystal layer 13, and the quarter-wave plate 5. As shown in FIG.
An angle θ1 formed by the axis direction L2 of the slow axis of the quarter-wave plate in the clockwise direction with respect to the axis direction L1 of the absorption axis or transmission axis of the polarizing plate 4 is set to, for example, 45 degrees. On the other hand, of the orientation directions of the liquid crystal molecules of the polymer-dispersed liquid crystal layer 13 shown in FIG.
Is set to, for example, 0 degree.

Next, the manufacturing procedure of this embodiment will be described. A polyimide resin film is formed on each glass substrate 3,
Bake at 200 ° C. for 1 hour. For example, SE150 (manufactured by Nissan Chemical Industries, Ltd.) for aligning liquid crystal parallel to the substrate was used. Thereby, the alignment films 9 and 11 are formed. Thereafter, a rubbing treatment for aligning the polymer dispersed liquid crystal molecules 13 is performed.

On the other hand, the reflection electrode 7 is previously provided on the glass substrate 2.
Of aluminum was formed, and then the quarter-wave plate 5 was formed. As this method, a method was used in which a polyimide resin film (not indicated) similar to that of the substrate 3 was formed on the reflection electrode 7 on the glass substrate 2, baked, and then rubbed. The rubbing direction is 1 / L2
A base treatment for forming a slow axis of the four-wavelength plate 5;
After this treatment, a quarter-wave plate 5 was formed through the steps of applying a UV-curable liquid crystal, heating, aligning, and curing by UV exposure polymerization. A polyimide resin film is further formed on the 硬化 wavelength plate 5 polymerized and cured, and baked to form an alignment film 9. Further, the alignment film 11 formed on the substrate 3 by the rubbing treatment and the alignment film 9 were manufactured to determine the alignment of the polymer dispersed liquid crystal layer 13. At this time, the rubbing direction was determined so that a twist angle of 45 degrees was realized between the substrates 2 and 3. The sealant 12 for sealing between the glass substrates 2 and 3 is formed by screen printing or dispenser application of an epoxy-based adhesive sealant mixed with a spacer having a diameter of 11 μm, for example.

When the reflecting plate 8 thus formed is combined with the glass substrate 3 on which the transparent electrode 10 and the alignment film 11 are formed, a spacer having a diameter of 10 μm is dispersed between the glass substrates 2 and 3. The thickness of the liquid crystal layer is regulated. With the glass substrates 2 and 3 facing each other,
After bonding in step 2, the sealant is cured to assemble the cell, and the liquid crystal polymer precursor mixture constituting the liquid crystal layer 13 is sealed by a vacuum injection method. After the encapsulation, ultraviolet light was irradiated from the transparent substrate 3 side using a high-pressure mercury lamp to produce an oriented polymer-dispersed liquid crystal.

FIG. 9 is a graph showing the voltage / reflectance characteristics of the liquid crystal display device 1 of the present embodiment. In the present embodiment, when a voltage is applied, the reflectance in the normal direction with respect to light incident from a direction inclined by an angle of 30 degrees with respect to the normal direction of the liquid crystal display device 1 is about 45% at the maximum, and the maximum contrast ratio Was 7. As a reference member for determining the reflectance at this time, magnesium oxide M
A standard white plate of gO was used.

FIGS. 10 and 11 are views for explaining the operation of the liquid crystal display device 1 according to the present embodiment. For convenience of explanation, the liquid crystal display device 1 is shown in an exploded manner. In the light-shielding operation shown in FIG. 10, when the incident light 28 passes through the polarizing plate 4, it becomes a linearly polarized light 29 parallel to the axial direction L1 of the polarizing plate 4. The light passes through the liquid crystal layer 13 and enters the quarter-wave plate 5 as it is as linearly polarized light, and becomes, for example, clockwise circularly polarized light 30. The circularly polarized light 30 is reflected by the reflection plate 7 and becomes a counterclockwise circularly polarized light 31. When the circularly polarized light 31 passes through the quarter-wave plate 5 and passes through the liquid crystal polymer composite layer 13, it becomes linearly polarized light 32 having a polarization plane in a direction orthogonal to the direction of the linearly polarized light 29 at the time of incidence. The linearly polarized light 32 is shielded by the polarizing plate 4. That is, the reflected light from the reflection plate 8 is shielded. In this case, since the oriented polymer dispersed liquid layer does not scatter, a good black display without a scattering effect is achieved. As another example, when the light passes through the quarter-wave plate and becomes clockwise circularly polarized light, when the circularly polarized light is reflected by the reflector 8, it becomes counterclockwise circularly polarized light.

On the other hand, in the light transmitting operation shown in FIG. 11, when the incident light 28 passes through the polarizing plate 4, it becomes linearly polarized light 29 parallel to the axial direction L1. The polarization plane is rotated in accordance with the direction of the alignment treatment performed on 11, and becomes, for example, rotated linearly polarized light 29 having a 45 polarization plane counterclockwise. The linearly polarized light 29 passing through the liquid crystal layer 13 is 1
Even when the light passes through the 波長 wavelength plate, the original polarization state is maintained, the light is reflected by the reflection plate 8, and the same linear polarization state is maintained when the light again passes through the 波長 wavelength plate. Further, when the light passes through the liquid crystal layer 13, the light is rotated in the direction opposite to that of the incident light, becomes linearly polarized light having the transmission azimuth of the polarizing plate, passes through the polarizing plate 4, and is emitted. In this case, when passing through the aligned polymer-dispersed liquid crystal, the polarized light that matches the alignment direction is scattered and transmitted while rotating the polarization plane in accordance with the twist of the alignment of the liquid crystal, so that bright scattered light is emitted from the polarizing plate. A good white state can be obtained even when the light is emitted and a mirror is used for the reflection film. In this way, in addition to the conventional reflection and transmittance modulation by the polarizing plate, the liquid crystal, and the quarter-wave plate, a method of effectively changing the scattering effect so as to increase the modulation width has been realized.

In the present invention, it is necessary to form the quarter-wave plate 5 between the polymer-dispersed liquid crystal layer 13 and the reflection film 8. Is formed. In the present embodiment, a UV-curable liquid crystal is used. However, the quarter-wave plate in the present invention is not limited to this. For example, a stretched filled polyvinyl alcohol (PVA) made of polycarbonate or polymethyl methacrylate (PMMA) is used. )) Can also be used. In this case, it is needless to say that a film is disposed on the surface of the substrate 2 which is not in contact with the liquid crystal, and the substrate 2 needs to have a light-transmitting property. It is necessary to reduce the parallax to about 0.7 mm.

In the reflection type liquid crystal display device 1 of the present embodiment,
Since the surface of the reflection plate 8 on which the metal reflection film 7 is formed is disposed on the polymer dispersed liquid crystal layer 13 side, parallax when observing the liquid crystal display device 1 is eliminated, and a good display screen is obtained. Further, when the liquid crystal display device 1 is configured to be driven in an active matrix, the liquid crystal display device 1 may be used as a pixel electrode connected to a thin film transistor used as a switching element or a non-linear element having an MIM (metal-insulating film-metal) structure. It has been confirmed that good display quality can be achieved as described above.

When the reflective film 7 is used as an electrode, the polymer dispersed liquid crystal layer 13 and the quarter-wave plate 5 are interposed between the reflective electrode 7 and the transparent electrode 11 as in this embodiment, and the driving voltage is increased. And an afterimage due to charge adsorption is caused. In order to prevent this, the polymer dispersed liquid crystal layer 13 and the １ ／ wavelength plate 5
It is also effective to form a transparent electrode (not shown) between them and use this and the transparent electrode 7 for driving.

<Embodiment 2> Next, as a polymer-dispersed liquid crystal, p-type nematic liquid crystal was added to E44 (manufactured by Merck),
An embodiment using RDN-94207 (manufactured by Roddick) as an n-type nematic liquid crystal and using a UV-curable liquid crystal as a polymer matrix material mixed therewith will be described. This UV-curable liquid crystal exhibits a liquid crystal phase at room temperature, is oriented in the same manner as a normal liquid crystal material, and is polymerized and cured by irradiating ultraviolet rays while maintaining the arrangement of liquid crystal molecules.
Even after curing, it retains the same birefringence as the liquid crystal phase. This liquid crystal is hereinafter referred to as an oriented polymer-dispersed liquid crystal to distinguish it from the first embodiment.

As an alignment film, in the case of a p-type nematic liquid crystal, SE150 (manufactured by Nissan Chemical Industries, Ltd.) is used to align the liquid crystal in parallel with the substrate. In the n-type nematic liquid crystal, JALS204 is used to align the liquid crystal vertically to the substrate. (Manufactured by Nippon Synthetic Rubber Co., Ltd.).

The weight ratio of the liquid crystal to the UV cure liquid crystal is 8
Mixed at 5:15. A cell having a cell thickness of 10 μm was vacuum-injected, irradiated with ultraviolet rays having an intensity of 15 mW / cm 2 for 500 seconds, and subjected to phase separation to produce an oriented polymer-dispersed liquid crystal. Table 1 shows the results of the visual observation in the state where no voltage was applied. For comparison, a polymer material that does not generate ordinary birefringence is also described.

[0061]

[Table 1]

As described above, for example, when a p-type liquid crystal is used, even if the liquid crystal is oriented in parallel to the substrate sandwiching the polymer composite layer, the ordinary polymer resin is not a polymer. While a scattering effect is observed due to a mismatch in the refractive index of the liquid crystal, no scattering is observed in the UV-curable liquid crystal, and when a voltage is applied, the liquid crystal is oriented in the direction of the electric field, so that scattering occurs.

FIG. 2 illustrates this effect in the case of a p-type liquid crystal. When no voltage is applied, the liquid crystal droplet and U
Since it is optically equivalent to a liquid crystalline polymer matrix made of V-curable liquid crystal, light propagates as if the entire composite layer is composed of a single phase of the liquid crystal layer. On the other hand, when voltage is applied, a scattering effect occurs.

For this reason, the principle of the present invention that the scattering effect is used for bright display and the scattering is suppressed in dark display is based on the “normally black” in the composite system of UV-curable liquid crystal and p-type liquid crystal. Arrangement ”, that is, when the liquid crystal is oriented in a direction parallel to the substrate and the transmitted light of the composite layer causes the rotation of the 45 ° twisted polarization plane, the polarization state is changed by ４ wavelength to obtain a black display. The example is shown in FIG. The angle θ1 (not shown) formed by the axis direction L2 of the slow axis of the quarter-wave plate in the clockwise direction with respect to the axis direction L1 of the absorption axis or transmission axis of the polarizing plate 4 is:
For example, it is set to 0 degrees. On the other hand, the oriented polymer dispersed liquid crystal layer 1
3, the angle θ2 (not shown) formed by the alignment L3 on the side in contact with the substrate 3 in a counterclockwise direction with respect to the axial direction L1 is set to, for example, 0 degree. .

The liquid crystal 14 of the oriented polymer dispersed liquid crystal layer 13 of the UV curable liquid crystal and the n-type liquid crystal does not rotate the polarization plane of the incident light due to the homeotropically oriented oriented polymer dispersed liquid crystal when no voltage is applied. And L2 are in the direction shown in FIG. Also in this dark display, since the polymer-dispersed liquid crystal layer 13 is in a transparent state, a good dark display can be obtained.

On the other hand, when the voltage is applied, if the liquid crystal 14 is of the p-type, the liquid crystal 14 is oriented perpendicular to the electrodes 10 and 7.
No birefringence effect occurs for normally incident light. for that reason,
The change in the polarization state is caused only by the quarter-wave plate 5. Light incident from the outside is reflected by the reflection electrode 7,
Although the light passes through the quarter-wave plate 5 and the polarizing plate 4 and exits again, it passes through the quarter-wave plate 2 twice before being incident on the apparatus and exiting again. A phase change of substantially 1/2 wavelength is generated. Therefore, the polarization plane is rotated by 90 degrees and is absorbed by the polarizing plate 7 at the time of emission, so that the display state of the present device is a so-called dark display. Further, the n-type liquid crystal when a voltage is applied is oriented in a parallel azimuth with respect to the substrate, so that scattering occurs due to a difference in refractive index from the oriented polymer matrix. At this time, by adding a chiral agent to the liquid crystal in advance, the polarization direction of the light incident on the ４ wavelength plate 5 can be directed to the L2 direction. No longer occurs and the display is clear.

Further, it has been confirmed that a similar effect can be obtained by using an opaque substrate such as a silicon substrate instead of the glass substrate 2 in the present embodiment. When such a silicon substrate is used as the glass substrate 2 in the above-described embodiment, circuit elements such as the above-described scanning circuit 16, data circuit 17, control circuit 18, and voltage generation circuit 19 are integrated on the silicon substrate. It has the advantage of being able to be formed. In addition, similar circuit integration, other methods,
For example, a polysilicon layer formed on a quartz glass substrate can be used, or a low-temperature process polysilicon layer formed on a glass substrate can be realized. Further, by forming a color filter layer on one of the substrates, multi-color or full-color display can be performed.

<Comparative Example> For comparison, a configuration example as shown in FIG. 12 will be described. In this example, a liquid crystal layer, a 波長 wavelength plate,
Although the scattering reflective film is sandwiched, voltage control of the scattering characteristics as described in detail in the embodiment is impossible. Therefore, the scattering characteristics of the bright display and the dark display cannot be changed, and if the scattering effect of the scattering reflective film is enhanced in accordance with the bright state,
The dark state becomes lighter, and if the scattering effect is reduced in accordance with the dark state, the light state becomes darker.

Further, as another comparative example, a comparison is made with a configuration example in which the reflection film has a mirror surface and a scattering film is added to the entire surface of the liquid crystal display element. In this case, the polarization characteristics of the liquid crystal are ideal, but because backscattering by the scattering plate immediately returns a part of the incident light to the observer side, the black state is brightened, and in the case of dot matrix display, Since the display contents of the adjacent pixels are scattered, the display definition is deteriorated. Also,
If the scattering effect is designed to be weak in order to prevent these, the bright state will be dark similarly, and only a bright / dark display will be performed based on the reflectance of the liquid crystal portion.

[0070]

As described above, according to the present invention, the incident light reaches the reflecting member via the polarizing plate, the oriented polymer dispersed liquid crystal layer and the quarter-wave plate, and is reflected by the reflecting member. 1 /
Light is emitted through a four-wavelength plate, a liquid crystal layer, and a polarizing plate. That is, the light reflection film is formed inside the liquid crystal display element, and the reflection surface of the light reflection member is flat, has no multiple reflection, and is a reflection surface that realizes a good black display maintaining polarization. it can.

Even if one of the electrodes is a reflective electrode,
By the cloudy state of the polymer-dispersed liquid crystal in the bright display, there is no so-called reflection of the surroundings, there is no parallax,
In addition, since the light is scattered in the observation direction, it has an effect of having sufficient brightness.

Further, since a backlight is not required, a high-definition, high-definition, reflection-type liquid crystal display device having low power consumption and excellent visibility compared to a liquid crystal display device having a backlight can be realized. .

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a scattering transmission control operation of a liquid crystal polymer composite film in a twist scattering mode of the present invention.

FIG. 2 is a diagram illustrating a scattering transmission control operation of a liquid crystal polymer composite film in a twist transparent mode of the present invention.

FIG. 3 is a liquid crystal display device 1 according to the first embodiment of the present invention.
FIG.

FIG. 4 is a diagram showing an example of a measurement result of a transmission scattering characteristic of the liquid crystal polymer composite film according to the first embodiment.

FIG. 5 is an optical layout diagram for measurement and evaluation shown in FIG.

FIG. 6 is a layout diagram of a method for measuring the reflection characteristics of the liquid crystal polymer composite film according to the first embodiment.

FIG. 7 is a configuration diagram of a circuit system for driving the liquid crystal display device 1.

FIG. 8 is an optical configuration diagram of a liquid crystal alignment of a liquid crystal polymer composite film, a transmission axis of a polarizing plate, and a 波長 wavelength plate according to the first embodiment.

FIG. 9 is a characteristic diagram of a voltage-reflectance characteristic of the liquid crystal display device 1.

FIG. 10 is an explanatory diagram of a display at the time of a light shielding operation of the liquid crystal display device 1.

FIG. 11 is an explanatory diagram of a display during a light transmitting operation of the liquid crystal display device 1;

FIG. 12 is a cross-sectional view of a liquid crystal display device of Configuration Example 1 of a comparative example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 liquid crystal display device 2, 3 glass substrate 4 polarizing plate 5 波長 wavelength plate 7 metal reflective electrode 8 reflective member 9, 11 alignment film 10 transparent electrode 13 liquid crystal polymer composite layer 14 liquid crystal composition 15 polymer matrix

Claims (9)

[Claims] In a reflection type liquid crystal display device having a polarizing plate on a light incident side of a liquid crystal element, the liquid crystal element has at least an insulating substrate on which a transparent electrode is formed, and light formed on one surface of the insulating substrate. A light reflection member formed with a reflection film and a counter electrode that performs display driving in cooperation with the transparent electrode, and a composite layer including a liquid crystal phase and a polymer resin phase between the insulating substrate and the reflection member; and A polymer dispersed liquid crystal layer in which a twist angle of liquid crystal alignment is set to be 40 to 50 degrees between the insulating substrate and the reflecting member; and a liquid crystal layer formed between the light reflecting member and the polymer dispersed liquid crystal layer. And a quarter-wave plate. 2. The reflective liquid crystal display according to claim 1, wherein the transmission axis of the polarizing plate is arranged so as to coincide with one of the twisted liquid crystal orientations of the polymer dispersed liquid crystal. apparatus. 3. The polymer material constituting the polymer-dispersed liquid crystal layer is a material exhibiting birefringence, and the polymer-dispersed liquid crystal layer does not show a scattering state when no voltage is applied, but is turned on when a voltage is applied. 2. The reflective liquid crystal display device according to claim 1, wherein the reflective liquid crystal display device exhibits a scattering state. 4. The light reflecting member according to claim 1, wherein a light reflecting film forming a light reflecting surface of the light reflecting member is disposed on the polymer dispersed liquid crystal layer side of the light reflecting member. 3. The reflection type liquid crystal display device according to item 1. 5. The reflection type liquid crystal display device according to claim 1, wherein the light reflection surface is a flat mirror surface mirror or a diffusion mirror having smooth irregularities. 6. The liquid crystal display device according to claim 1, wherein the quarter-wave plate is made of a liquid crystalline polymer or a polymer obtained by fixing liquid crystal alignment from a low molecular compound having liquid crystallinity. Reflective liquid crystal display device. 7. The quarter wavelength plate is formed on a light reflection film of the light reflection member, and a transparent electrode is formed on the quarter wavelength film, and the transparent electrode is formed on the insulating substrate. 2. The reflection type liquid crystal display device according to claim 1, wherein the reflection type liquid crystal display device is defined as an electrode facing the transparent electrode formed on the substrate. 8. The reflection type liquid crystal display device according to claim 1, wherein a color filter layer is formed on the insulating substrate or on a transparent electrode formed on the insulating substrate. 9. The １ ／ wavelength plate comprises at least two layers, and among the plurality of layers, a first layer has a retardation of 120 to 150 nm with respect to a ray perpendicularly incident on the layers,
The second layer is disposed so as to sandwich the first layer between the second layer and the reflective surface, and the second layer has a retardation almost twice that of the first layer, and the surface of the first layer and the second layer The direction of the slow axis inside is 60 °
2. The reflection type liquid crystal display device according to claim 1, wherein the reflection type liquid crystal display device is different from the reflection type liquid crystal display device by 120 degrees.