JP2762783B2 - Color display element and driving method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color display device.

[0002]

2. Description of the Related Art In order to construct a reflection type liquid crystal display in which a backlight cannot be used, it is necessary to use only natural light incident on a liquid crystal element from the outside of a liquid crystal panel so as to make it look natural. It is assumed that no polarizing plate is used. In order to perform such display, a guest-host type or a scattering type is promising. Among them, the former reflection type liquid crystal panel using a guest-host type dimmer is configured as shown in FIG. That is, this color liquid crystal panel
A color filter 2 for determining the spectrum of transmitted light is provided on the surface of one transparent substrate 1, and a transparent electrode 3 is formed on the color filter 2. On the other substrate 7, a transparent electrode 5 and a light reflection layer 6 are laminated at a position facing the transparent electrode 3. In addition, a liquid crystal is sealed in a gap formed between the transparent electrode 3 and the transparent electrode 5 to form a light control layer 4. The transparent electrode 5
And the light reflection layer 6 are not only separately formed,
In some cases, it is a metal reflecting mirror serving as the transparent electrode 5 and the light reflecting layer 6. As a disclosure example of a liquid crystal display device having such a structure, a device formed by using a black dye guest-host type liquid crystal as the dimming layer 4 is Pro.
c. Eurodisplay '87, page 131. In this structure, the incident light transmitted through the transparent substrate 1 is transmitted through the color filter 2, the transparent electrode 3, the light control layer 4, and the transparent electrode 5, and is reflected by the light reflecting layer 6,
The reflected light travels on a course opposite to the course described above and exits from the transparent substrate 1. For example, if the light that has taken such a course has passed through a red color filter, it is emitted out of the transparent substrate 1 with a red spectrum.
Therefore, a color display is possible in a display having this structure.

In a reflection type color display having a structure other than that shown in FIG. 1A, a transparent electrode 3 is formed on the surface of a transparent substrate 1 as shown in FIG. On the other substrate 7, a transparent electrode 5, a color filter 2 for determining a spectrum of transmitted light, and a light reflection layer 6 are laminated on the substrate 7 at a position facing the transparent electrode 3. And
Liquid crystal is sealed in a gap formed between the transparent electrode 3 and the transparent electrode 5 to form a light control layer 4. Note that the order of the transparent electrode 5, the light reflecting layer 8, and the light reflecting layer 6 may not always be the order shown in FIG. 1B, and the functions may be integrated. As a disclosure example of a liquid crystal display device having such a structure, one in which a dimming layer 4 is formed by using a black dye guest-host type polymer-dispersed liquid crystal is disclosed in DISPLAYS, January 1991, p. It is described in. In this structure, the incident light transmitted through the transparent substrate 1 is transmitted through the transparent electrode 3, the light control layer 4, the transparent electrode 5, and the color filter 2 and is reflected by the light reflecting layer 6, and the reflected light is transmitted through the course. Goes out of the transparent substrate 1 through the reverse course. For example, if the light having passed such a course has passed through a red color filter, it is emitted out of the transparent substrate 1 with a red spectrum, so that the reflected light looks red when viewed from the outside. Therefore, even a display having this structure can perform color display.

[0004] Further, a reflection type black and white display has a transparent electrode 3 formed on the surface of a transparent substrate 1 as shown in FIG. A transparent electrode 5 and a light absorbing layer 8 are formed on the substrate 7 at positions. In addition, a liquid crystal is sandwiched in a gap formed between the transparent electrode 3 and the transparent electrode 5 to form a light control layer 4. As a disclosure example of a liquid crystal display device having such a structure, one configured using polymer-dispersed liquid crystal as a dimming layer,
13th International Liquid
CrystalConference Preprints, No.2
Separate volume, 21 pages, 1990. In this structure,
When the light control layer 4 is in a transparent state, the incident light transmitted through the transparent substrate 1 passes through the transparent electrode 3, the light control layer 4, and the transparent electrode 5 and is absorbed by the light absorption layer 6, and as a result, a black display is obtained. obtain. Also,
If the light control layer 4 is in the scattering state, the incident light transmitted through the transparent electrode 1 passes through the transparent electrode 3 and enters the light control layer 4. At this time, since the light control layer 4 is in a scattering state, the incident light is divided into a back scattering component and a forward scattering component, and the back scattering component is emitted to the outside by transmitting through the transparent electrode 3 and the transparent substrate 1. On the other hand, the forward scattering component is absorbed by the light absorbing layer 8 by transmitting through the transparent electrode 5 and is not reflected. As a result, in this state, it looks white when viewed from the outside, and white display is possible. As a result, black and white display is possible depending on whether the light control layer 4 is in the transparent state or the light scattering state.

[0005]

In the conventional reflection type color liquid crystal panel, the color filter layer is disposed in front of the light control layer 4 (FIG. 1A) or behind the light control layer 4 (FIG. 1A). 1 (b)). for that reason,
In the case of FIGS. 1A and 1B, the light control layer 4 changes between a black state and a transparent state. Although there is no major problem, in the case of performing white display, all light incident on the liquid crystal panel passes through the color filter, so that at least 2/3 of the light energy is lost, so that complete white display is required. Not recognized
It feels gray and cannot be completely displayed in black and white. If the light control layer 4 changes between a transparent state and a light scattering state in FIGS. 1A and 1B, color display can be performed when the light control layer 4 is in the transparent state. However, if the light control layer 4 is in a light scattering state, in the case of FIG. 1A, the incident light always passes through the color filter, so that gray display is obtained and neither white display nor black display is obtained. Further, in the case of FIG. 1B, the scattered light is emitted to the outside from the transparent substrate 1 as it is, so that white display is performed. In this case, black display cannot be performed. In FIG. 1C, monochrome display is possible, but color display cannot be performed.

An object of the present invention is to provide a color display and a high-contrast black and white display at the same pixel, which are impossible with the above-mentioned conventional reflection type display, by using a light transmission-light absorption change layer and a light scattering-transparency change layer. An object of the present invention is to provide a reflective color liquid crystal panel having a wide color reproduction range and high display quality by providing a liquid crystal element which can be realized by combining with a color filter.

[0007]

According to the present invention, there is provided a substrate, an electrode, a first light control layer capable of controlling a light scattering state and a transparent state by an external electric field, and a light absorbing state and a transparent state. A second dimming layer controllable by an electric field, an electrode facing the electrode, and a substrate facing the substrate are provided in this order from the light incident side, and the first dimming layer and the second A light reflection layer that reflects light transmitted through the light control layer is provided behind the second light control layer as viewed from the light incident side, and a color filter is provided between the first light control layer and the light reflection layer. A color display element characterized by being arranged.

The first dimming layer only needs to be able to transition between a light scattering state and a transparent state by application of an electric field. For example, a DSM method using a polymer dispersed liquid crystal or a nematic liquid crystal, a DSM method using a smectic A layer, a strong It is possible to make use of the change in scattering and transparency by the dielectric liquid crystal and the scattering state of the focal conic structure in the cholesteric layer.

The second light control layer only needs to be able to transition between the light absorption state and the transparent state by application of an electric field.
Any guest-host type liquid crystal element in which a chromatic dye is mixed and dispersed in a liquid crystal can be used. For example,
A method in which a cholesteric liquid crystal and a black dichroic dye are mixed and a nematic-cholesteric phase transition is caused by applying an electric field, and a liquid crystal component in which a dichroic dye is mixed and dispersed is further dispersed in a polymer. A polymer-dispersed guest-host liquid crystal having a structure is used.

The polymer-dispersed liquid crystal in the above description means that the liquid crystal material may be dispersed in the cured product or the cured product may exist in the liquid crystal material in a three-dimensional network.

In a liquid crystal optical element wherein the transparent solid substance is present in the liquid crystal material in the form of particles or a network, glass beads or beads of various polymers are used as the transparent solid substance. Can be Polymer substances include polyethylene, polymethyl methacrylate,
Polystyrene, polyamide, there are polyvinyl chloride and copolymers thereof, preferably not dissolved in the liquid crystal material, the ordinary refractive index of the refractive index of the liquid crystal material (n _o) or the extraordinary refractive index (n _e) or Any material may be used as long as it matches or is close to one of the refractive indexes (n _LC ) when the liquid crystal material is randomly aligned.

In a liquid crystal optical element characterized in that a liquid crystal material is dispersed in a transparent solid substance, examples of the transparent solid substance include polyvinyl alcohol, polyvinyl formal, polymethyl methyl methacrylate, and polystyrene. A polymer substance is used, which separates from the liquid crystal material,
It is sufficient that the refractive index matches or is close to one of the ordinary light refractive index (n _o ) or the extraordinary light refractive index ( _ne ) of the liquid crystal material and the refractive index (n _LC ) when the liquid crystal material is randomly aligned. .

[0013] The first light control layer and the second light control layer may be individually held by a substrate. That is, as shown in FIG. 4A, a liquid crystal cell in which the dimming layer 18 is sandwiched between substrates 16 and 20 with transparent electrodes is laminated with a color filter 22 therebetween as shown in FIG. 4B. It can also be. However, as shown in FIG. 5, at least one of the first light control layer 27 and the second light control layer 29 is made of a liquid crystal having a self-supporting solid shape such as a polymer-dispersed liquid crystal, so that The number of sheets can be reduced, and the light transmittance can be increased.

The electrode of the present invention may be a material such as ITO, which has a very low light absorption in the visible light range and exhibits conductivity. Further, the shape of the electrode may be formed uniformly on the substrate, may be formed in a specific pixel shape,
The upper and lower substrates may be formed on a strip. Further, an active element such as a transistor or a diode may be added to each pixel.

The color filter layer may display the unique color of the color filter layer alone, or may partially display the color of light.
The image may be divided into primary colors or three primary colors to display a mixed color. The position may be located anywhere between the first light control layer and the second light control layer and above the light reflection layer. However, in order to simplify the manufacturing, the color filter is provided in the first light control layer. And the second
It is desirable to arrange between the light control layers or between the light reflection layer and the second light control layer.

As the substrate, a substrate such as a glass substrate or a polyethylene terephthalate (PET) film that transmits light in a visible light amount range is used.

The light reflecting layer may be made of a substance that reflects incident light. Specifically, a metal, a dielectric reflection film, or the like can be used. Desirably, a material having high reflectivity and having no wavelength dependence, such as silver, aluminum, chromium, tin, nickel, and tantalum, is used as the reflection film.

The position of the light reflecting layer may be provided between the second light control layer and the electrode, between the electrode and the substrate, or below the substrate. Further, the light reflecting layer may be used as a substrate, or the light reflecting layer and the electrode may be integrated by forming the light reflecting layer with a conductive material such as a metal. When the light reflecting layer is located on the optical path before the substrate, the substrate does not need to be transparent, and the metal may be an opaque substrate such as a semiconductor or plastic. Similarly, when the light reflection layer is located on the optical path before the electrode, the electrode does not need to be transparent.

The method of driving the color display element is such that, when performing black display, the first light control layer is made transparent and the second light control layer is made light absorbing. When performing color display, the first light control layer and the second light control layer are both made to be in a transparent state, and when performing white display, the first light control layer is in a light scattering state. I do. The second dimming layer for performing white display may be in a light absorbing state or a transparent state.

When each dimming layer is individually held by a substrate with electrodes, the above driving method can be easily realized by controlling each dimming layer independently.

In the case where a polymer-dispersed liquid crystal is used for each light control layer and two light control layers are sandwiched and controlled by a pair of electrodes, FIG.
This can be realized by elements having characteristics as shown in (a) to (d). In FIG. 3, the solid line 14 is the first line.
, And the dotted line 15 shows the light transmittance characteristic of the second light control layer.

In FIG. 3A, the first dimming layer shows a light transmitting state when no voltage is applied, and changes to a scattering state when a voltage equal to or higher than a predetermined threshold is applied. It shows a light absorbing state when no voltage is applied, and changes to a light transmitting state when a voltage equal to or higher than a predetermined threshold value lower than the threshold voltage of the first dimming layer is applied. As a result, when the applied voltage is gradually increased from 0, the display changes to black display, color display, and white display as shown in the figure.

In FIG. 3B, the first light control layer shows a light scattering state when no voltage is applied, and changes to a transparent state when a voltage equal to or higher than a predetermined threshold is applied. It shows a light transmitting state when no voltage is applied, and changes to a light absorbing state when a voltage equal to or higher than a predetermined threshold higher than the threshold voltage of the first dimming layer is applied. As a result, when the applied voltage is gradually increased from 0, the display changes to white display, color display, and black display as shown in the figure.

In FIG. 3C, the first dimming layer shows a light scattering state when no voltage is applied, and changes to a transparent state when a voltage above a predetermined threshold is applied. On the other hand, the second dimming layer shows a light absorbing state when no voltage is applied, and changes to a light transmitting state when a voltage equal to or higher than a predetermined threshold higher than the threshold voltage of the first dimming layer is applied. As a result, when the applied voltage is gradually increased from 0, the display changes to white display, black display, and color display as shown in the figure.

In FIG. 3D, the first dimming layer shows a transparent state when no voltage is applied, and changes to a light scattering state when a voltage equal to or higher than a predetermined threshold is applied. It shows a light transmitting state when no voltage is applied, and changes to a light absorbing state when a voltage equal to or higher than a predetermined threshold value lower than the threshold voltage of the first light control layer is applied. As a result, as the applied voltage is gradually increased from 0, the color display, black display, and white display change as shown in the figure.

The characteristics of FIGS. 3B and 3D are shown in FIG.
It has characteristics opposite to those of FIGS.

As an element having the characteristics shown in FIG. 3A, the first dimming layer is formed by using a liquid crystal whose dielectric anisotropy takes a negative or both positive and negative value, and a second dimming control is performed. The layer is composed of a mixture of a liquid crystal having a positive dielectric anisotropy and a black dichroic dye. Here, the first dimming layer orients the liquid crystal so as to be in a transparent state when no voltage is applied. For this, a mixed solution of a liquid crystal material and a photocurable compound whose dielectric anisotropy can take both negative and positive values,
The second light modulating layer may be formed by irradiating and curing light while applying at least one of an electric field and a magnetic field.

As the element having the characteristics shown in FIG. 3C, a liquid crystal having a positive dielectric anisotropy is used, and the dielectric anisotropy Δε ₁ of the liquid crystal component of the first light control layer is set to the second. The threshold voltage is lowered by changing the physical constants of the liquid crystal such as increasing the dielectric anisotropy Δε ₂ of the liquid crystal component of the light control layer.

When a polymer-dispersed liquid crystal is used as the light control layer, it can be prepared by the following method. A mixed solution of a photocurable compound and a liquid crystal material is applied to the substrate on which electrodes are formed by a thin film forming method such as screen printing, offset printing, letterpress transfer, intaglio transfer, or spin coating, and cured by irradiating light. Thus, a light control layer is formed. Further, as a method of forming a color filter layer directly thereon, there are the above-mentioned printing method, dyeing method, pigment printing method, photolithography method and the like.

[0030]

According to the color display element of the present invention, the light incident from the outside is scattered or transmitted by the first light control layer, and is divided by the second light control layer. Split. White, black or color display can be performed by a combination of whether the two light control layers are in a scattering state, a transparent state, a light absorbing state, or a light transmitting state. Hereinafter, the operation of the color display element according to the present invention will be described for the case where the color filter is disposed between the first light control layer and the second light control layer.

FIG. 2 is a diagram for explaining the operation of the color display element of the present invention. The structural features of the color display element of the present invention are as follows: the first light control layer 9 is a light control layer that causes a scattering-transparency change; the second light control layer 11 is a light control layer that causes a light absorption-light transmission change; The point is that the color filter layer 10 is disposed between them, and the light reflection layer 12 is provided on the side opposite to the natural light incident direction 13. When this structure is adopted, it is roughly divided,
The first light control layer 9 and the second light control layer 11 above and below the color filter layer 10 have four states depending on a combination of a light scattering state, a light transmission state, a light absorption state, and a light transmission state, respectively. I do. That is, the first dimming layer 9 is in a transparent state, the second dimming layer 11 is in a transmitting state, the first dimming layer 9 is in a transparent state, the second dimming layer 11 is in an absorbing state, the first dimming layer 9 is in a scattering state, The second light control layer 11 is in a transmission state. The first light control layer 9 is in a scattering state, and the second light control layer 11 is in an absorption state. The operation of each state will be described below.

In the state (1), the first light control layer 9 is in a transparent state, and the second light control layer 11 is in a transmission state. The light passes through the dimming layer 11 and reaches the light reflecting layer 12. The light that reaches the light reflection layer 12 is reflected again, passes through the second light control layer 11, the color filter layer 10, and the first light control layer 9 and exits outside the liquid crystal element. As a result, in this combination, a color display can be obtained.

In the state (1), since the first light control layer 9 is transparent, light is transmitted and enters the color filter layer 10. The light transmitted through the color filter layer 10 is absorbed by the second light control layer 11, so that no light is emitted to the outside again. As a result, a black display can be obtained.

In the state (1), since the first dimming layer 9 is in a scattering state, most of the incident light is scattered and is emitted out of the element again. On the other hand, a part of the light that has passed through the first light control layer 9 passes through the color filter layer 10 and the second light control layer 11 because the second light control layer 11 is in a transmission state.
2 and is reflected by the light reflecting layer 12. The reflected light passes through the second light control layer 11 and the color filter layer 10 again to enter the first light control layer, the forward scattered light of the first light control layer 9 is emitted to the outside, and the back scattered light is again returned. The process reaches the light reflection layer 12 and repeats this process. Therefore, the light emitted to the outside is the sum of the backscattered component of the light scattered by the first light control layer 9 and the light reflected by the light reflection layer 12. At this time, if the color pitch of the color filter 10 is fine, the difference in color cannot be identified by human eyes, and it is possible to assume that the light transmitted through the light reflection layer 12 is also white. The display can be obtained.

In the state (1), the first dimming layer 9 is in a scattering state, so that most of the incident light is scattered and emitted out of the element again. On the other hand, part of the light that has penetrated the first light control layer 9 passes through the color filter layer 10 and is absorbed by the second light control layer 11 because the second light control layer 11 is in an absorbing state, and is observed from outside. Are only the light scattered by the first light control layer 9. As a result, it is considered that white display is possible in this case as well.

When the drive electrodes correspond to the first light control layer 9 and the second light control layer 11, respectively, the above combination may be realized according to the drive mode of each liquid crystal.

When the first light control layer 9 and the second light control layer 11 are sandwiched by a pair of electrodes and do not have independent electrodes, control may be performed as shown in FIG. In the description of the operation, a polymer-dispersed liquid crystal is used as one dimming layer 9,
As the second dimming layer, a polymer-dispersed liquid crystal in which a guest-host liquid crystal is dispersed is used.

FIG. 3A shows the relationship between the applied voltage and the degree of light scattering in the case of-. Here, the first dimming layer drives a liquid crystal in which the dielectric anisotropy takes both negative and positive values in a reverse mode. On the other hand, the second dimming layer uses liquid crystal having a positive dielectric anisotropy and is driven in a normal mode. As shown in the drawing, when the threshold voltage of the first light control layer is set higher than the threshold voltage of the second light control layer, the first light control layer is in a light transmitting state when no voltage is applied. Shown, second
Since the dimming layer shows a light absorbing state, black display can be performed. When a voltage is applied to exceed the threshold voltage of the second light control layer, the second light control layer changes to a transmission state, so that color display is possible. When the applied voltage is further increased and exceeds the threshold voltage of the first light control layer, the first light control layer changes to a light scattering state, so that white display is possible.

FIG. 3B is a diagram showing the relationship between the applied voltage and the degree of light scattering in the case of-. Here, the first dimming layer has a liquid crystal whose dielectric anisotropy takes a positive value, and is driven in a normal mode. On the other hand, the second dimming layer uses a liquid crystal in which the dielectric anisotropy takes both negative and positive values, and is driven in a reverse mode. As shown in the figure, when the threshold voltage of the first light control layer is set lower than the threshold voltage of the second light control layer, the first light control layer shows a scattering state when no voltage is applied. Since the second light control layer shows a transmission state, white display can be performed. When a voltage is applied to exceed the threshold voltage of the first light control layer, the first light control layer changes to a transparent state, so that color display is possible. Further increase the applied voltage,
If the threshold voltage of the second light control layer is exceeded, the second light control layer changes to a light absorbing state, so that black display is possible.

FIG. 3C shows the relationship between the applied voltage and the degree of light scattering in the case of-. Here, both the first light control layer and the second light control layer are driven in the normal mode.
As shown in the figure, when the threshold voltage of the first light control layer is set lower than the threshold voltage of the second light control layer, the first light control layer is in a light scattering state when no voltage is applied. , The second light control layer indicates a light absorbing state, and white display can be performed. When a voltage is applied to exceed the threshold voltage of the first light control layer, the first light control layer changes to a transparent state, so that black display can be performed. Further, when the applied voltage is increased to exceed the threshold voltage of the second light control layer, the second light control layer also changes to a transparent state, so that color display can be performed.

FIG. 3D is a diagram showing the relationship between the applied voltage and the degree of light scattering in the case of-. Here, both the first light control layer and the second light control layer are driven in the reverse mode. As shown in the figure, when the threshold voltage of the first light control layer is higher than the threshold voltage of the second light control layer, the first light control layer is in a transparent state when no voltage is applied, The second light control layer shows a transmission state, and color display can be performed. When a voltage is applied to exceed the threshold voltage of the second light control layer, the second light control layer changes to an absorption state, so that black display can be performed. Further, when the applied voltage is increased to exceed the threshold voltage of the first light control layer, the first light control layer also changes to a light scattering state, so that white display can be performed.

The reverse mode device is manufactured as follows. Curing by irradiating light while applying at least one of an electric field or a magnetic field so that a mixed solution of a liquid crystal material and a photocurable compound, whose dielectric anisotropy can take both negative and positive and negative values, becomes transparent. Then, a light control layer is formed. When the photocurable compound is cured while the liquid crystal molecules are oriented so as to be transparent by applying an electric or magnetic field, after the photocurable compound is cured, the liquid crystal molecules are fixed to the electric or magnetic field by anchoring at the interface. Cannot be returned to a random state even if is removed, and is fixed. This state cannot be changed in a liquid crystal having a positive dielectric anisotropy, but can be changed to a light scattering state in a liquid crystal in which the dielectric anisotropy can take a negative value.

[0043] For example, the crossover frequency f _c is 10
kHz, at frequencies below this the dielectric anisotropy Δε is Δ
It is assumed that a liquid crystal that satisfies ε> 0 and Δε <0 at a frequency higher than ε is used. When curing the photocurable compound, 1
When curing is performed while applying a voltage having a frequency lower than 0 kHz between the substrates, the direction of the liquid crystal molecules is fixed in a direction perpendicular to the substrates. Assuming that the light transmission state at this time is a transparent state, it can be changed to a light scattering state by applying a voltage higher than 10 kHz during driving.

In a normal liquid crystal molecule having an aromatic ring such as a benzene ring, the dielectric anisotropy Δε can be either positive or negative depending on the molecular shape, but the magnetization anisotropy Δχ is only a positive value. Not possible. From this, when a photocurable compound is cured while applying a magnetic field sufficiently stronger than the Freedericks transition point of the liquid crystal in a direction perpendicular to the substrate using a liquid crystal having a negative dielectric anisotropy, the liquid crystal molecules The direction is fixed in a direction perpendicular to the substrate. Assuming that the light transmission state at this time is a transparent state, when a voltage is applied during driving, the liquid crystal molecules change to a light scattering state because their directions change in a direction parallel to the substrate.

In the operation section, the color filter layer 10
Has been described assuming that the light exists between the first light control layer 9 and the second light control layer 11, but according to the principle of the present invention, the light transmitted through the first light control layer 9 is light. It may be present before the light is reflected by the reflective layer 12 and reenters the first light control layer 9. Therefore, the color filter layer 10 is provided not only between the first light control layer 9 and the second light control layer 11 but also in the second light control layer 1.
1 and the light reflection layer 12, or even if the second light control layer 12 is divided into two layers and arranged between them, the color filter layer 1 may be colored by coloring the second light control layer itself.
Needless to say, both 0 and the second light control layer 11 may be used.

[0046]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist.

Embodiment 1 An embodiment of a color display device according to the present invention will be described with reference to FIG.

The color display element in this embodiment is shown in FIG.
As shown in (a), transparent electrodes 17 and 19 made of ITO are used.
Is applied on the transparent electrode 19 by a screen printing method as a light control layer 18 using a pair of transparent substrates 16 and 20 having a surface formed thereon.
The transparent substrate 16 on which a spacer having a diameter of 20 μm is scattered is overlapped so that air bubbles do not enter, and after applying pressure, the cell gap is set to approximately 20 μm. Cured to obtain polymer dispersed liquid crystal. The polymer-dispersed liquid crystal used in the present example was a UV-curable compound composed of 10% of a polymerizable monomer, 2-ethylhexyl acrylate, and 20% of a polymerizable oligomer UN-9000PEP.
% And a mixture of 60% and 0.2% of a polymerization initiator benzophenone with E8 of a nematic liquid crystal.

A guest-host type in which 0.4 wt% of a black dichroic azo dye is mixed with nematic liquid crystal E8 as a liquid crystal component constituting the liquid crystal cell and the light control layer 18 prepared as described above. The liquid crystal cells using the liquid crystal are used as the liquid crystal cells 21 and 23, respectively, and the color filter 22 is disposed between the liquid crystal cells 21 and 23 as shown in FIG. Was mounted on the surface of the liquid crystal cell 23 opposite to the color filter 22. In this embodiment, the first liquid crystal cell 21,
Since each of the 23 light control layers is independently controlled through a separate power supply, it is possible to realize all four states described in the operation section. That is, the liquid crystal cells 21 and 23 are in a state in which a voltage is applied, and color display is performed. In this state, a voltage is applied to only the liquid crystal cell 21. In this state, a black display is performed. And white display, and a state where no voltage is applied to both of the liquid crystal cells 21 and 23, and white display is performed.

The color filter 22 constructed in this embodiment
Is configured by arranging red, green, and blue color filters in a strip shape, and the transparent electrodes of the liquid crystal cells 21 and 23 corresponding to the strip-shaped color filters 22 are configured in the same manner as the color filters. ing. Also,
In this embodiment, the color filter 22 is replaced with the one shown in FIG.
Although the structure sandwiched between the liquid crystal cell 21 and the liquid crystal cell 23 was used as shown in FIG. 4, even if the color filter 22 was arranged between the liquid crystal cell 23 and the light reflection layer 24 as shown in FIG. As in the case of FIG. 4B, it was possible to display all of white, black, and color.

Although the color combinations of the color filters are red, green, and blue in this embodiment, sufficient color reproducibility can be obtained even when a color filter of a combination of cyan, magenta, and yellow is used. Was. Further, in the present embodiment, the background color (the color of the non-selected portion) is set to black, but it is obvious that the background color can be set to white.

Embodiment 2 In FIG. 4B of Embodiment 1, a color display element is realized by combining the liquid crystal cells 21 and 23 produced independently. However, when the configuration shown in Embodiment 1 is adopted, The transparent electrodes and the transparent substrate above and below the filter layer 22 are not necessarily required. Therefore, in this embodiment, an example in which the present invention is realized by a configuration in which light control layers are directly provided above and below a color filter will be described with reference to FIG.

The color display element in this embodiment is shown in FIG.
As shown in (a), a transparent substrate 25 on which a transparent electrode 26 made of ITO is formed on the surface, a light reflecting layer 31 is formed on the surface, and a transparent electrode 30 made of ITO is formed on the surface of the light reflecting layer 31. A liquid mixture of an ultraviolet curable compound and a guest / host liquid crystal containing a black dichroic dye is applied as a second light modulating layer 29 on the transparent electrode 30 to a thickness of about 20 μm by a screen printing method. Irradiation cures the mixed solution to form a polymer dispersed liquid crystal. After curing, a color filter 28 is directly formed on the second light control layer 29 by a printing method, and a mixed solution of an ultraviolet curable compound and a liquid crystal is applied thereon by about 20 μm by a screen printing method. After overlapping the transparent substrate 25 with 26 so as to prevent air bubbles from entering, the mixed solution is cured by irradiating ultraviolet rays from the transparent substrate 25 side to form the first dimming layer 27, thereby forming a color display element. . In the nematic liquid crystal used in this embodiment, a liquid crystal having a positive dielectric anisotropy is used for both the first light control layer 27 and the second light control layer 29. In this embodiment, the second light control layer 29 is formed first for the sake of convenience. However, as can be seen from FIG. 5, except for the light reflection layer 31, a plane symmetrical structure around the color filter 28 is used. It goes without saying that no problem arises even if the first light control layer 27 is formed first.

In this structure, an electric field applied to the liquid crystal cell is applied between the transparent electrode 26 and the transparent electrode 30, so that a uniform electric field is applied to the first light control layer 27 and the second light control layer 29. Will be applied. Therefore, in order to perform color display, the threshold voltage of the first light control layer 27 is changed by changing the composition of the first light control layer 27 and the second light control layer 29. By lowering the threshold voltage and making the threshold voltages of the first dimming layer 27 and the second dimming layer 29 different, the light scattering characteristic shown in FIG. 3C is obtained. In the case of this example, the threshold voltage in the case of curing was changed by changing the ratio of monomer (2-ethylhexyl acrylate) / oligomer (UN-9000 PEP) / liquid crystal (E8) of the polymer precursor. It was realized by doing. In particular,
The first dimming layer 27 is formed by mixing the monomer and the oligomer at a ratio of 1: 2, and forming the ultraviolet curable resin 35 thus prepared.
[Wt%] and liquid crystal 65 [wt%] were mixed and cured at 15 degrees. The second dimming layer 29 is obtained by mixing a monomer and an oligomer at a ratio of 1: 1. The ultraviolet curable resin 30 [wt%] thus prepared is mixed with a guest-host liquid crystal (0.4 wt% azo dye in the liquid crystal). % Of a guest-host type liquid crystal) (70% by weight) and cured at 10 degrees.

When a voltage is applied to the thus-produced reflective color display element, the white display when no voltage is applied increases the voltage, and when the voltage exceeds 6 [V], the first display is performed. The first light control layer 27 starts to change from the light scattering state to the transparent state, and color display becomes possible, and complete color display is achieved at 10 [V]. When the voltage is further increased, 12 [V]
Further, since the second light control layer 29 changes from a light scattering state to a transparent state, the reflection luminance decreases, and the first light control layer and the second light control layer 29 become transparent near 24 [V]. Display.

In this embodiment, as in the case of the first embodiment, the color filter layer 28 as shown in FIG. 5B can be disposed between the second light control layer 29 and the light reflection layer 31. It is. However, when such an arrangement is performed, the first light control layer 27 and the second light control layer 29 come into direct contact with each other, and the components of the liquid crystal forming the first light control layer 27 and the second light control layer 29 are changed. If different, the liquid crystal between the two layers must not be mixed. Therefore, in the present embodiment, a polyimide film was formed by a spin coating method between the first light control layer 27 and the second light control layer 29 to prevent the liquid crystal from being mixed, thereby forming an interlayer separation film 33. Further, in this embodiment, a polyimide spin coat film is used as the interlayer separation film 33, but the purpose of the interlayer separation film 33 is to use the first light control layer 2
It is needless to say that a substance which is transparent to visible light, for example, glass, polymer, or the like, can be used because it is to prevent the liquid crystal 7 from mixing with the liquid crystal of the second light control layer 29.

Example 3 In Example 2, the nematic liquid crystal used was the first liquid crystal.
Both the light control layer 27 and the second light control layer 29 use liquid crystal having a positive dielectric anisotropy. In this embodiment, the first light control layer 27
By using a two-frequency driving liquid crystal as the liquid crystal component, the state of the first dimming layer 27 is made transparent when no voltage is applied, and changes to a light scattering state by applying a voltage.

[0058] In order to obtain such an optical change, the liquid crystal in the present embodiment of the two-frequency driving type as a liquid crystal component constituting the first dimmer layer 27 (Chisso Co., Ltd. n _o = 1.50
9, Δn = 0.154), and a mixture of a monomer (2-ethylhexyl acrylate) and an oligomer (UN-9000EP) at a ratio of 1: 1 is used as a polymer precursor. When forming by irradiating ultraviolet rays, the mixed solution is cured by irradiating ultraviolet rays while applying a low frequency (100 [Hz]) voltage of 50 [V], and the liquid crystal molecules become vertical to the substrate in an initial state. To do. At this time, the second dimming layer 29 is a mixture of the monomer and the oligomer at a ratio of 1: 2, and the ultraviolet curable resin 35 [wt%] thus prepared and the liquid crystal (the azo dye is added to E8 by 0.4%). [Wt%] mixed guest-host type liquid crystal) was mixed by 65 [wt%] and irradiated with ultraviolet rays to be cured. By configuring the first dimming layer 27 and the second dimming layer 29 by the method described above, FIG.
The light scattering characteristic shown in (a) is obtained. At this time, in the case of the liquid crystal used when forming the first dimming layer 27 in this embodiment, the crossover frequency

[0059]

(Equation 1)

Is 10 [kHz], so Δε <0 at or above this frequency. Therefore, the high frequency voltage (100
[KHz], the black display when no voltage is applied increases the voltage, and when the voltage exceeds 6 [V], the second dimming layer 29 changes from the light absorbing state to the light transmitting state. At first, it becomes transparent at 10 [V]. At this time, since the first light control layer 27 is still in a transparent state, it becomes a color. When the applied voltage is further increased, the first dimming layer 27 starts to change from the transparent state to the scattering state at 25 [V], and becomes 45 [V].
As a result, a completely scattered state was obtained, and a white display could be obtained. As a result, it was possible to perform monochrome display and color display with good contrast in the same pixel.

The device that can be used as the first dimming layer 27 in the present embodiment may be a device such as DSM that exhibits a characteristic of changing from a transparent state to a scattering state, and a two-frequency drive type liquid crystal may be used. It is not limited to the used polymer-dispersed liquid crystal.

Embodiment 4 In Embodiment 3, FIG. 3B shows that the first dimming layer becomes transparent when no voltage is applied by using a two-frequency driving liquid crystal for the first dimming layer 27. FIG. 3B shows that the second dimming layer is in a light transmitting state when no voltage is applied by using a two-frequency driving liquid crystal for the second dimming layer in this embodiment. Achieve the indicated properties.

In order to obtain such an optical change, in this embodiment, a liquid crystal (E8) having a positive dielectric anisotropy is used as a liquid crystal component constituting the first dimming layer 27, and a polymer precursor is used. Is a ratio of monomer (2-ethylhexyl acrylate) to oligomer (UN-9000 PEP) of 1: 2
, And 35 [wt%] of the thus prepared ultraviolet curable resin and 65 [wt%] of liquid crystal were mixed and cured by irradiation with ultraviolet rays.
The second dimmer layer 29 at this time, the two-frequency driving liquid crystal (Chisso Co., Ltd. n _o = 1.509, Δn = 0.1
54) guest mixed with 0.4 [wt%] of azo dye
A liquid crystal of a host type is used, a mixture of a monomer and an oligomer in a ratio of 1: 1 is used as a polymer precursor, and the second light modulating layer 29 is formed by irradiating ultraviolet rays with a low frequency (50 V). The mixed solution was cured by irradiating ultraviolet rays while applying a voltage so that the liquid crystal molecules were perpendicular to the substrate in the initial state. By configuring the first dimming layer 27 and the second dimming layer 29 by the method described above, the light scattering characteristic shown in FIG. 3B is obtained. At this time, in the case of the liquid crystal used for forming the second dimming layer 29 in this embodiment, the crossover frequency

[0064]

(Equation 2)

Is 10 [kHz], so that Δε <0 at or above this frequency. Therefore, the high frequency voltage (100
[KHz], the white display when no voltage is applied increases the voltage, and when the voltage exceeds 6 [V], the second dimming layer 29 changes from the light absorbing state to the light transmitting state. Start to be transparent at 10 [V]. At this time, since the first light control layer 27 is still in a transparent state, it becomes a color. When the applied voltage is further increased, the first dimming layer 27 starts to change from the transparent state to the scattering state at 25 [V], and becomes 45 [V].
As a result, a completely scattered state was obtained, and a black display could be obtained. As a result, also in the present embodiment, it was possible to perform monochrome display and color display with good contrast in the same pixel.

Embodiment 5 In Embodiments 3 and 4, the first light modulating layer 27 is transparent when no voltage is applied, and becomes a light scattering state when a voltage is applied. Although a two-frequency drive liquid crystal was used as a liquid crystal component constituting a liquid crystal layer,
In this example, the base skeleton had an aromatic ring, Δε was a negative value, and the initial orientation was given by a magnetic field, whereby the film was transparent when no voltage was applied, and a light scattering state was created when a voltage was applied.

In order to obtain such an optical change, in this embodiment, a liquid crystal having a negative Δε (n _o = 1.509, Δn = 0.15) is used as a liquid crystal component constituting the first dimming layer 27.
4, Δε = −3.1), and a mixture of a monomer (2-ethylhexyl acrylate) and an oligomer (UN-9000 PEP) at a ratio of 1: 1 is used as a polymer precursor. 35 [wt%], liquid crystal 6
When a solution mixed at a ratio of 5 wt% is irradiated with ultraviolet rays and formed, the Frederix transition point of the liquid crystal is a sufficiently large value. The mixed solution is cured so that the liquid crystal molecules are perpendicular to the substrate in the initial state.
The light control layer 27 is formed. Also, the second light control layer 2 at this time
Reference numeral 9 denotes a mixture of a monomer and an oligomer at a ratio of 1: 2, and a UV-curable resin 35 [wt%] produced in this manner and a liquid crystal (0.4 wt% of an azo dye mixed with E8).
65 [wt%] was mixed and cured by irradiating ultraviolet rays. By forming the first dimming layer 27 and the second dimming layer 29 by the method described above, the light scattering characteristic shown in FIG. 3A is obtained. At this time, in the case of the liquid crystal used for forming the second dimming layer 29 in the present embodiment, the black display when no voltage is applied is increased, and the voltage is increased when the voltage exceeds 6 [V]. 2
The light control layer 29 starts to change from the light absorbing state to the light transmitting state,
It becomes transparent at 10 [V]. At this time, since the first light control layer 27 is still in a transparent state, color display is performed. When the applied voltage was further increased, the first dimming layer 27 began to change from a transparent state to a scattering state at 30 [V], and became completely scattered at 52 [V], making it possible to obtain a white display. As a result, it was possible to perform monochrome display and color display with good contrast in the same pixel.

Embodiment 6 In the case of the fifth embodiment, the fourth embodiment is different from the third embodiment.
By setting the first dimming layer to a normal type and the second dimming layer to a reverse type as described above, the characteristics shown in FIG. 3B can be realized.

In this embodiment, in order to make the first dimming layer 27 a PDLC exhibiting a normal response, a liquid crystal (E8) having a positive dielectric anisotropy is used as a liquid crystal component, and the polymer precursor is , Monomer (2-ethylhexyl acrylate) and oligomer (UN-9000PEP) in a ratio of 1: 2
, And 35 [wt%] of the thus prepared ultraviolet curable resin and 65 [wt%] of liquid crystal were mixed and cured by irradiation with ultraviolet rays.
On the other hand, as the second dimming layer 29, the liquid crystal (n _o =
1.509, Δn = 0.154, Δε = −3.1) and 0.4 wt% of an azo dye] are mixed, and a guest-host type liquid crystal is used. When the polymer mixture is formed by irradiating ultraviolet rays to a solution obtained by mixing 35 [wt%] of the polymer precursor and 65 [wt%] of the liquid crystal, the Freedericks transition point of the liquid crystal is used. 10 which is a sufficiently large value
By irradiating ultraviolet rays while applying a magnetic field of [kG], the mixed solution is cured to make the liquid crystal molecules perpendicular to the substrate in the initial state, thereby forming the second dimming layer 29 having a reverse response.

By forming the first dimming layer 27 having the normal response and the second dimming layer 29 having the reverse response as described above, the light scattering characteristic shown in FIG. 3B is obtained. . At this time, the white display when no voltage is applied increases the voltage, and when the voltage exceeds 6 [V], the first dimming layer 27 starts to change from the scattering state to the transparent state.
[V] becomes transparent. At this time, since the second light control layer 29 is still in the transmission state, color display is performed. When the applied voltage was further increased, the second dimming layer 29 started to change from a transparent state to a scattering state at 30 [V], and became completely scattered at 52 [V], making it possible to obtain a white display. As a result, it was possible to perform monochrome display and color display with good contrast in the same pixel.

In the above-described embodiments 2 to 6, the case where the color filter exists between the first light control layer 27 and the second light control layer 29 has been described. Similarly to the above, the color filter layer 28 as shown in FIG. 5B can be arranged between the second light control layer 29 and the light reflection layer 31. In this case, since the color filter layer 28 can be directly formed on the light reflection layer 31, in this case, the light reflection layer 31 made of metal or the like is formed on the substrate 32, and A color filter layer 28 is applied by a printing method, an electrodeposition method, or the like.
A transparent electrode 30 made of
A manufacturing method for forming a second light control layer on the transparent electrode 30 was employed. However, when such an arrangement is performed, the first
Since the light control layer 27 and the second light control layer 29 are in direct contact with each other, if the components of the liquid crystal forming the first light control layer 27 and the second light control layer 29 are different, the liquid crystal between the two layers will be We have to keep them from mixing. Therefore, in this embodiment, a polyimide film is formed by a spin coating method to form an interlayer separation film 33 for the purpose of preventing the liquid crystal from being mixed between the first light control layer 27 and the second light control layer 29. Further, in this embodiment, a polyimide spin coat film is used as the interlayer separation film 33, but the purpose of the interlayer separation film 33 is to use the first light control layer 2
It is needless to say that a substance transparent to visible light, for example, glass or a polymer can also be used, since the purpose is to prevent the mixture of the liquid crystal 7 and the liquid crystal of the second light control layer 29.

Seventh Embodiment In the first to fourth embodiments, the description has been made by applying a voltage to the liquid crystal element by static or time division. However, it is obvious that the liquid crystal element according to the present invention is driven by the active element. It is possible. FIG. 6 is a cross-sectional view of a liquid crystal device according to the present invention configured by adding an active device for each pixel. In the case of the present embodiment, the light reflecting layer 31 in FIG. 5 is made of silver (or a metal such as aluminum or chromium) to be integrated with the transparent electrode 30.

In the liquid crystal device according to the embodiment shown in FIG. 6A, first, a TFT 40 serving as a switching device is formed on a glass substrate 41, and a pixel electrode 39 is formed so as to cover the TFT 40. At this time, in the transmissive display, the TFT 40 and the pixel electrode 39 are completely separated and used. However, since the liquid crystal element according to the present invention is of a reflective type, the pixel electrode 39 can be arranged so as to cover the TFT 40. As a result, the operation area per pixel area is different from that of the transmission type by about 40 [%], and is 80 [%] or more, so that an extremely large opening area can be provided as compared with the transmission type. As described above, the pixel electrode 39 and the TFT 40
A UV curable resin 35 [wt%] in which a monomer and an oligomer are mixed at a ratio of 1: 2 on a glass substrate 41 on which a liquid crystal (E8 is mixed with 0.4 wt% of an azo dye is used). Guest-host type liquid crystal)
[Wt%], mixed and cured by irradiating ultraviolet rays, and a color filter 37 is formed on the second light control layer 38.
Was formed. Then, a liquid crystal having a negative Δε (n _o = 1.5) is further formed on the color filter 37 as the first light control layer 36.
09, Δn = 0.154, Δε = -3.1), and a mixture of a monomer (2-ethylhexyl acrylate) and an oligomer (UN-9000PEP) at a ratio of 1: 1 is used as a polymer precursor. This polymer precursor is
A solution obtained by mixing 5 [wt%] and liquid crystal at a ratio of 65 [wt%] is adhered on the color filter 37 by the screen printing method similarly to the second dimming layer 38, and the glass substrate 34 with the counter electrode 35 is interposed therebetween. Then, the mixture is cured by applying ultraviolet rays while applying a magnetic field (10 [kG]) sufficiently larger than the Freedericks transition point of the liquid crystal, so that the liquid crystal molecules are in the initial state. The first dimming layer 36 is formed by making the liquid crystal element perpendicular to the substrate to obtain a liquid crystal element. The component configuration of the first light control layer and the second light control layer used in this embodiment is the same as that of the fourth embodiment.
Therefore, the operating voltage and the display mode are the same as those of the fourth embodiment.

In this embodiment, an active matrix type liquid crystal element is formed by adding an active element to the liquid crystal element having the element structure of the fourth embodiment. It goes without saying that active matrix driving can be performed by adding an active element.

In the description of the present embodiment, the color filter 37 is arranged between the first light control layer 36 and the second light control layer 38. Similarly, as shown in FIG. 6B, it is needless to say that the color filter 37 can be disposed between the second light control layer 38 and the pixel electrode 39 serving also as a light reflection layer.

In the above embodiment, it goes without saying that the color of the color filter 37 may be the same for the entire liquid crystal panel, the color may be changed for each pixel, or it may be partially changed.

In the above examples, 2-ethylhexyl acrylate was used as the polymerizable monomer, UN-9000 PEP of urethane acrylate oligomer was used as the polymerizable oligomer, and benzophenone was used as the ultraviolet curing initiator. Other than the above, methyl acrylate, 2-ethylhexyl methacrylate, cyclohexyl acrylate,
It is possible to use an acrylic monomer such as butadiol monoacrylate, an epoxy acrylate oligomer as a polymerizable oligomer, and an acetophenone-based, benzoin-based, benzophenone-based, or thioxanthone-based material as an ultraviolet curing initiator. However, it is possible to use other systems.

[0078]

According to the reflection type color element of the present invention, color display and high-contrast black and white display can be expressed in the same pixel regardless of static driving, multiplex driving and active matrix driving. It is possible to configure a reflective color liquid crystal display with high display quality.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a conventional technique.

FIG. 2 is a basic configuration diagram of a reflective color display device according to the present invention.

FIG. 3 is a diagram for explaining the operation of the present invention.

FIG. 4 is a sectional view of an embodiment of the present invention.

FIG. 5 is a cross-sectional view showing another embodiment of the present invention.

FIG. 6 is a sectional view showing another embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 transparent substrate 2 color filter 3 transparent electrode 4 light control layer 5 transparent electrode 6 light reflection layer 7 substrate 8 light absorption layer 9 first light control layer 10 color filter layer 11 second light control layer 12 light reflection layer 13 natural light incident direction 14 Light Scattering Characteristics of First Light Control Layer 15 Light Scattering Characteristics of Second Light Control Layer 16 Transparent Substrate 17 Transparent Electrode 18 Light Controlling Layer 19 Transparent Electrode 20 Transparent Substrate 21 Liquid Crystal Cell 22 Color Filter 23 Liquid Crystal Cell 24 Light Reflection Layer 25 Transparent substrate 26 Transparent electrode 27 First dimming layer 28 Color filter layer 29 Second dimming layer 30 Transparent electrode 31 Light reflecting layer 32 Substrate 33 Interlayer separation film 34 Glass substrate 35 Counter electrode 36 First dimming layer 37 Color Filter 38 Second dimming layer 39 Pixel electrode 40 TFT 41 Glass electrode

Claims (7)

(57) [Claims] A first light modulating layer capable of controlling a light scattering state and a transparent state by an external electric field; and a second light controlling layer capable of controlling a light absorbing state and a transparent state by an external electric field. A light control layer, an electrode facing the electrode, and a substrate facing the substrate are provided in this order from the light incident side, and light transmitted through the first light control layer and the second light control layer is provided. A color, wherein a light reflecting layer for reflection is provided behind the second light control layer as viewed from the light incident side, and a color filter is disposed between the first light control layer and the light reflection layer. Display element. 2. The liquid crystal display device according to claim 1, wherein a dichroic dye is dispersed in the liquid crystal in the second light control layer.
The color display element as described in the above. 3. The device according to claim 1, wherein at least one of the first light control layer and the second light control layer comprises a layer in which a liquid crystal material is dispersed in a photocurable compound. Color display element. 4. At least one of the first light control layer and the second light control layer shows a light transmitting state when no voltage is applied, and the first light control layer or the second light control layer shows a light transmission state when a voltage higher than a predetermined threshold voltage is applied. 2. The color display device according to claim 1, wherein the first light control layer has a light scattering state, and the second light control layer has a light absorption state. 5. The light modulating layer comprises a layer in which a liquid crystal material whose dielectric anisotropy can take at least a negative value is dispersed in a photocurable compound. 4. The color display element according to claim 3, wherein the interface of the color display maintains a predetermined alignment state. 6. A method for driving a color display element according to claim 1, wherein when performing black display, the first light control layer is set to a transparent state, and the second light control layer is set to a light absorbing state. When performing color display, the first light control layer and the second light control layer are both in a transparent state, and when performing white display, the first light control layer is in a light scattering state. A method for driving a color display element. 7. A mixture of a liquid crystal material having a negative dielectric anisotropy and a photocurable compound having a negative value of dielectric anisotropy is irradiated with light while applying at least one of an electric field and a magnetic field to cure the mixture. 6. The method according to claim 5, wherein an optical layer is formed.