JPH04371927A - Color display element and driving method thereof - Google Patents

Abstract

PURPOSE:To constitute the reflection type color liquid crystal display having a high display grade by expressing a color display and the black and white display of a high contrast with the same picture elements. CONSTITUTION:This element has the structure which is disposed with a color filter layer 10 between a 1st light control layer 9 and a 2nd light control layer 11 and is provided with a light absorption layer 12 in the direction opposite from the incident direction of natural light 13. Incident light is absorbed by the light absorption layer 12 if both of the 1st light control layer 9 and the 2nd light control layer 11 are put into a transparent state and, therefore, the black display is obtd. The light scattered by the 2nd light control layer is emitted through the color filter layer 10 to the outside of the element if the 1st light control layer 9 is put into the transparent state and the 2nd light control layer 11 into the light scattering state and, therefore, the color display is obtd. The white display is obtd. if the 1st light control layer 9 is put into the light scattering state.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color display element and a method for driving the same.

0002

[Prior Art] In order to construct a reflective liquid crystal display that cannot use a backlight, it is necessary to make it look natural by using only natural light that enters the liquid crystal element from outside the liquid crystal panel. , it is assumed that no polarizing plate is used. In order to perform such a display, a guest-host type or a scattering type display method is considered to be promising. Among these, the former reflective liquid crystal panel using a guest-host type dimmer is configured as shown in FIG. 6(a). That is, in this type of 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 reflecting layer 6 are laminated at positions opposite to the transparent electrode 3. The device has a structure in which 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. Note that the transparent electrode 5 and the light reflecting layer 6 may not only be formed separately, but may also be a metal reflecting mirror that serves as the transparent electrode 5 and the light reflecting layer 6. As a disclosed example of a liquid crystal display device having such a structure, one constructed using a black dye guest-host type liquid crystal as the light control layer 4 was announced in Eurodisplay '87 lecture number P2.4. In this structure, the incident light that has passed through the transparent substrate 1 passes 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 reflection layer 6, and the reflected light is The light travels the opposite course and is emitted from the transparent substrate 1. For example, light that has taken such a course will be emitted from the transparent substrate 1 with a red spectrum if it has passed through a red color filter, so that the reflected light will appear red when viewed from the outside. Therefore, in a display having this structure, color display is possible.

A reflective color display having a structure other than that shown in FIG. 6(a) has a transparent electrode 3 formed on the surface of a transparent substrate 1, as shown in FIG. 6(b). On the other substrate 7, a transparent electrode 5, a color filter 2 that determines the spectrum of transmitted light, and a light reflection layer 6 are laminated on the substrate 7 at positions opposite to the transparent electrode 3. The device has a structure in which 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. Note that the order of the transparent electrode 5, the light reflection layer 8, and the light reflection layer 6 may not necessarily be in the order shown in FIG. 6(b), and the functions may be integrated. A disclosed example of a liquid crystal display device having such a structure is one in which a black dye guest-host type polymer dispersed liquid crystal is used as the light control layer 4.
There is page 2 of the January 1991 issue of the magazine. In this structure, incident light that has passed through the transparent substrate 1 passes 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 reflection layer 6, and the reflected light follows the course described above. The light travels the opposite course and is emitted from the transparent substrate 1. For example, light that has taken such a course will have a red spectrum if it has passed through a red color filter.
This reflected light appears red when viewed from the outside because it is emitted further to the outside. Therefore, color display is possible even with a display having this structure.

In addition, in a reflective black and white display, a transparent electrode 3 is formed on the surface of a transparent substrate 1, as shown in FIG. A structure in which a transparent electrode 5 and a light absorption layer 8 are laminated on a substrate 7 is known. The device has a structure in which a liquid crystal is sandwiched between the transparent electrode 3 and the transparent electrode 5 to form a light control layer 4. As a disclosed example of a liquid crystal display device having such a structure, one constructed using a polymer dispersed liquid crystal as a light control layer was disclosed at the 13th International
Liquid Crystal Conference
ce lecture number APP-34P-P-Tue. In this structure, when the light control layer 4 is in a transparent state, the incident light that has passed through the transparent substrate 1 is transmitted through the transparent electrode 3, the light control layer 4, and the transparent electrode 5, and is absorbed by the light absorption layer 8. As a result, a black display is obtained. Furthermore, if the light control layer 4 is in a scattering state, the incident light that has passed through the transparent substrate 1 is transmitted 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 backscattered component and a forwardscattered component, and the backscattered component passes through the transparent electrode 3 and the transparent substrate 1 and is emitted to the outside. On the other hand, the forward scattering component is absorbed by the light absorption layer 8 by passing through the transparent electrode 5 and is not reflected. As a result, in this state, it appears white when observed from the outside and a white display is possible, and as a result of the above, a black and white display is possible depending on whether the light control layer 4 is in a transparent state or a light scattering state.

[0005]

[Problems to be Solved by the Invention] Conventional reflective color liquid crystal panels have either a color filter layer disposed in front of the light control layer 4 (FIG. 6(a)) or a color filter layer disposed behind the light control layer 4 (FIG. 6(a)). 6(b)). Therefore, in the cases of FIGS. 6(a) and 6(b), the light control layer 4
changes between a black state and a transparent state, so there is no major problem with display quality when displaying black or color, but when displaying white, all the light that enters the liquid crystal panel At least 2/2 of the light energy passes through the color filter.
3, it is not recognized as a complete white display, but instead appears as a gray display, making it impossible to display a complete black and white display. Furthermore, if the light control layer 4 changes between the transparent state and the light scattering state in FIGS. 6(a) and 6(b), it is possible to perform color display when the light control layer 4 is in the transparent state. However, if the light control layer 4 is in a light scattering state, then FIG. 6(a)
In this case, the incident light always passes through the color filter, resulting in a gray display and neither white nor black display. Further, in the case of FIG. 6(b), the scattered light is directly emitted from the transparent substrate 1 to the outside, resulting in a white display, but in this case, a black display cannot be performed. Further, in FIG. 6(c), black and white display is possible, but color display is not possible.

The present invention provides a liquid crystal element capable of expressing color display and high-contrast black and white display in the same pixel, which was impossible with the conventional reflective display, thereby achieving high display quality. The purpose is to provide a reflective color liquid crystal panel.

[0007]

[Means for Solving the Problems] The present invention provides a substrate, an electrode, a first light control layer whose light scattering state and transparent state can be controlled by an external electric field, a color filter layer, a light scattering state and a transparent state. a second light control layer whose state can be controlled by an external 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 light absorbs the light transmitted through the first light control layer, the color filter layer, and the second light control layer. This is a color display element characterized in that an absorption layer is provided behind the second light control layer when viewed from the light incident side.

The first light control layer and the second light control layer only need to be able to transition between a light scattering state and a transparent state by applying an electric field. It is possible to use the DSM method in , the scattering transparency change by ferroelectric liquid crystal, the scattering state of the focal conic structure in the cholesteric layer, etc. Note that the term "polymer-dispersed liquid crystal" as used herein 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 the form of a three-dimensional network.

[0009] The first light control layer and the second light control layer may each be held between substrates. That is, FIG. 3(a)
As shown in FIG.
The liquid crystal cells sandwiched by the liquid crystal cells 20 can also be stacked with a color filter 22 sandwiched therebetween, as shown in FIG. 3(b). However, as shown in FIG.
If at least one of the light control layers 29 is made of liquid crystal in a solid state that can stand on its own, such as polymer-dispersed liquid crystal, the number of substrates can be reduced and the light transmittance can be increased.

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

[0011] The color filter layer may display the unique color of the color filter layer alone, or may partially display the 3rd color of light.
It may be divided into primary colors or three primary colors to display a mixed color.

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

The light absorption layer may be provided between the second light control layer and the electrode, between the electrode and the substrate, or under the substrate. Further, a light absorption layer may be used as a substrate. When the light absorption layer is located above the substrate, the substrate does not need to be transparent, and may be an opaque substrate made of metal, semiconductor, plastic, or the like. Similarly, if the light absorbing layer is located above the electrode, the electrode need not be transparent.

[0014] In this method of driving a color display element, when performing a black display, both the first light control layer and the second light control layer are set to a transparent state, and when performing a color display, the first light control layer is set to a transparent state. The second light control layer is in a light scattering state, and when displaying white, the first light control layer is in a light scattering state. The second light control layer when displaying white may be in a light scattering state or in a transparent state.

[0015] When each light control layer is sandwiched between substrates with electrodes, the above driving method can be easily realized by controlling each light control layer independently.

When a polymer-dispersed liquid crystal is used in each light control layer and the two light control layers are held between a pair of electrodes for control, as shown in FIG.
This can be realized using elements having the characteristics shown in (a) to (d).

In FIG. 2(a), the first light control layer exhibits a light scattering state when no voltage is applied, changes to a transparent state when a voltage higher than a predetermined threshold is applied, and the second light control layer exhibits a light scattering state when no voltage is applied. It exhibits a transparent state when applied, and changes to a light-scattering state when a voltage equal to or higher than a predetermined threshold voltage, which is greater than the threshold voltage of the first light control layer, is applied. As a result, when the applied voltage is gradually increased from 0, the display changes to white, black, and color as shown in the figure.

In FIG. 2(b), both the first light control layer and the second light control layer exhibit a light scattering state when no voltage is applied, and exhibit a transparent state when a voltage equal to or higher than a predetermined threshold voltage is applied. If the threshold voltage of the first light control layer is set lower than the threshold voltage of the second light control layer, the display changes from white display to color display to black display as voltage is applied.

FIGS. 2(c) and 2(d) are respectively similar to FIGS. 2(a) and 2(d).
This is a configuration in which the first light control layer and the second light control layer in (b) are replaced.

For example, in an element exhibiting the characteristics shown in FIG. 2(a), the first light control layer is constructed using a liquid crystal with positive dielectric constant anisotropy, and the second light control layer is constructed using a liquid crystal with positive dielectric constant anisotropy. It is constructed using a liquid crystal that takes negative or both positive and negative values. Here, the second light control layer orients the liquid crystal so that it is in a transparent state when no voltage is applied. For this purpose, a mixed solution of a liquid crystal material whose dielectric constant anisotropy can take negative or both positive and negative values and a photocurable compound is irradiated with light and cured while applying at least one of an electric field or a magnetic field. What is necessary is just to form a second light control layer.

Further, as an element exhibiting the characteristics shown in FIG. 2(b), a liquid crystal with positive dielectric anisotropy is used, and the dielectric anisotropy Δε1 of the liquid crystal component of the first light control layer is changed to the second light control layer. The threshold voltage is lowered by increasing the dielectric anisotropy Δε2 of the liquid crystal component of the layer.

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

[0023]

[Function] In the color display element of the present invention, light incident from the outside is divided into two light control layers, either scattered or transmitted, and these two light control layers are either in a scattering state or in a transparent state. It is possible to display white, black or color depending on the combination of the following. The operation of the color display element according to the present invention will be described below.

FIG. 1 is a diagram for explaining the operation of the color display element of the present invention. The structural feature of the color display element of the present invention is that a color filter layer 10 is arranged between the first light control layer 9 and the second light control layer 11, and a light absorption layer 12 is provided on the opposite side to the natural light incident direction 13. The point is that When this structure is adopted, the first light control layer 9 and the second light control layer 11 located above and below the color filter layer 10 each exhibit a scattering state or a transparent state depending on the combination. There are 4 states. That is, ■ The first and second light control layers are both in a transparent state. ■ The first light control layer is in a transparent state, and the second light control layer is in a scattering state. ■ The first light control layer is in a transparent state.
The light control layer is in a scattering state, the second light control layer is in a transparent state ■First, second
The light control layer is in four states, all of which are scattering states. The effects of each state will be explained below.

In the state (■), the first light control layer 9 and the second light control layer 9
Since both the light control layer 11 are transparent, the incident light passes through the first light control layer 9, the color filter layer 10, and the second light control layer 11 and reaches the light absorption layer 12, so that no light reflection occurs. As a result, a black display is obtained.

In the state (2), since the first light control layer 9 is transparent, light passes through and enters the color filter layer 10. The light that has passed through the color filter layer 10 is scattered by the second light control layer 11, and most of the light passes through the color filter layer 10 and the first light control layer 9 again and is emitted out of the device again. On the other hand, among the light scattered by the second light control layer 11, the light emitted in the direction that passes through the second light control layer 11 is absorbed by the light absorption layer 12 and is not reflected. As a result, it becomes possible to display colors unique to the color filter layer 10.

In the state (2), since the first light control layer 9 is in a scattering state, most of the incident light is scattered and emitted again to the outside of the element. On the other hand, since the second light control layer 11 is transparent, some of the light that penetrates the first light control layer 9 passes through the color filter layer 10 and the second light control layer 11 and reaches the light absorption layer 12. absorbed by. Therefore, since the light emitted to the outside is only the light scattered by the first light control layer 9, it is possible to obtain a white display.

In the state (■), the first light control layer 9 and the second light control layer 9
Since both the light control layer 11 is in a scattering state, the incident light is in the first
The light is scattered by the light control layer 10 and also by the second light control layer 11 . In this case, the light scattered by the first light control layer 9 is considered to be white, but the light scattered by the second light control layer 5 has a certain color because it has passed through the color filter. ing. Therefore, it is considered that the emitted light is not achromatic but has a certain degree of chroma. However, if the color arrangement of the color filter 10 is dense and it can be considered that there is no wavelength dispersion in the light reflected by the second light control layer 11, it is considered that white display is possible.

Depending on the combination of the transparent state and the scattering state of the first light control layer 9 and the second light control layer 11, four combinations are possible as described above. However, since it is possible to obtain the same white display in both the case of ■ and the case of ■, the display combination that should actually be realized is either ■−■−■ or ■−■−■. be. 1st
If drive electrodes correspond to each of the light control layer 9 and the second light control layer 11, 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 held together by a pair of electrodes and do not have independent electrodes, control may be performed as shown in FIG. 2.

FIG. 2(a) is a diagram showing the relationship between the applied voltage and the degree of light scattering in the case of ■-■-■. Here, the first light control layer uses liquid crystal with positive dielectric anisotropy and is driven in a normal mode. On the other hand, the second light control layer uses a liquid crystal whose dielectric constant anisotropy has negative or both positive and negative values, and is driven in reverse mode. As shown in the figure, if 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 exhibits a light scattering state when no voltage is applied, and the first light control layer exhibits a light scattering state when no voltage is applied. Since the second light control layer exhibits a transparent state, it is possible to display white. When a voltage is applied and the voltage exceeds the threshold voltage of the first light control layer, the first light control layer changes to a transparent state, so that black display becomes possible. When the applied voltage is further increased and exceeds the threshold voltage of the second light control layer, the second light control layer changes to a light scattering state.
Color display is possible.

FIG. 2(b) 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 normal mode. As shown in the figure, if 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 will
Both the light control layer and the second light control layer exhibit a light scattering state and can display white. When a voltage is applied and the threshold voltage of the first light control layer is exceeded, the first light control layer changes to a transparent state, so that a color display can be performed. Furthermore, when the applied voltage is increased and the threshold voltage of the second light control layer is exceeded, the second light control layer also changes to a transparent state, so that a black display can be performed.

FIG. 2(c) is a diagram showing the relationship between the applied voltage and the degree of light scattering in the case of ■-■-■. Here, the first light control layer uses a liquid crystal whose dielectric constant anisotropy takes negative or both positive and negative values, and is driven in reverse mode. On the other hand, the second light control layer has a liquid crystal whose dielectric constant anisotropy takes a positive value, and is driven in a normal mode. As shown in the figure, if 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 will be in a transparent state when no voltage is applied, and the second light control layer will be in a transparent state. Since the light control layer exhibits a light scattering state, color display is possible. When a voltage is applied and the threshold voltage of the second light control layer is exceeded,
Since the second light control layer changes to a transparent state, black display becomes 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, making it possible to display white.

FIG. 2(d) 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 reverse mode. As shown in the figure, if the threshold voltage of the first light control layer is set higher than the threshold voltage of the second light control layer, both the first light control layer and the second light control layer are It shows a transparent state and can be displayed in black. When a voltage is applied and the threshold voltage of the second light control layer is exceeded, the second light control layer changes to a scattering state, so that color display can be performed. Furthermore, when the applied voltage is increased and exceeds the threshold voltage of the first light control layer, the first light control layer also changes to a light scattering state, so that a white display can be performed.

The reverse mode device is manufactured as follows. A mixed solution of a liquid crystal material whose dielectric constant anisotropy can take negative or both positive and negative values and a photocurable compound is cured by irradiating it with light while applying at least one of an electric field or a magnetic field that makes it transparent. to form a light control layer. When a photocurable compound is cured with the liquid crystal molecules oriented in a transparent state by applying an electric or magnetic field, after the photocurable compound is cured, the liquid crystal molecules will be affected by the electric or magnetic field due to the anchoring at the interface. Even if you remove it, it cannot return to a random state and becomes fixed. This state cannot be changed in a liquid crystal whose dielectric constant anisotropy is positive, but it can be changed to a light scattering state in a liquid crystal whose dielectric constant anisotropy can take a negative value.

For example, if the crossover frequency fc is 1
Assume that a liquid crystal is used in which the dielectric constant anisotropy Δε becomes Δε>0 at frequencies below 0 kHz, and Δε<0 at frequencies above this. When curing a photocurable compound,
When curing is performed while applying a voltage with a frequency lower than 10 kHz between the substrates, the direction of the liquid crystal molecules is fixed in a direction perpendicular to the substrates. Assuming that the light transmitting state at this time is a transparent state, it can be changed to a light scattering state by applying a voltage with a frequency higher than 10 kHz during driving.

Furthermore, in ordinary liquid crystal molecules having an aromatic ring such as a benzene ring, the dielectric anisotropy Δε can take either a positive or negative value depending on the molecular shape, but the value of the magnetization anisotropy Δχ can only be a positive value. It's impossible. From this, it can be seen that if a photocurable compound is cured using a liquid crystal with negative dielectric anisotropy and a magnetic field sufficiently stronger than the Frederick's transition point of the liquid crystal is applied in a direction perpendicular to the substrate, the liquid crystal molecules The direction is fixed perpendicular to the substrate. Assuming that the light transmitting state at this time is a transparent state, when a voltage is applied during driving, the liquid crystal molecules change direction in a direction parallel to the substrate, and thus change to a light scattering state.

[0038]

[Examples] The present invention will be explained in detail below using Examples, but the present invention is not limited to the following Examples unless the gist of the invention is exceeded. Example 1 One example of a color display element according to the present invention will be described with reference to FIG.

The color display element in this example is shown in FIG.
As shown in (a), transparent electrodes 17 and 19 made of ITO
A mixed solution of an ultraviolet curable compound and liquid crystal is applied as a light control layer 18 onto the transparent electrode 19 by screen printing, and a spacer with a diameter of 20 μm is formed on the transparent electrode 19. Transparent substrate 1 sprayed with
6 were piled up without air bubbles, and the cell gap was set to approximately 20 μm by applying pressure.
By irradiating this liquid crystal cell with ultraviolet rays, the ultraviolet curable compound is cured to form a polymer dispersed liquid crystal. In the polymer dispersed liquid crystal used in this example, the ultraviolet curable compound was 10% of 2-ethylhexyl acrylate as a polymerizable monomer and UN-9000PEP as a polymerizable oligomer.
20% and nematic liquid crystal E8 60% and 0.2%
A mixed solution of the polymerization initiator benzophenone was used.

[0040] The liquid crystal cell produced as described above was
The color filter 22 is arranged between the liquid crystal cells 21 and 23 as shown in FIG. It was manufactured by attaching it to the opposite side of No. 22. In this embodiment, the first liquid crystal cell 21,
Since the 23 dimming degrees are independently controlled through separate power supplies, it is possible to realize all the four states described in the operation section. That is, when voltage is applied to both the liquid crystal cells 21 and 23, the state becomes black display, and when voltage is applied only to the liquid crystal cell 21, the state becomes color display, when voltage is applied only to the liquid crystal cell 23. When this happens, the state becomes the state ``■'', resulting in a white display.If no voltage is applied to both the liquid crystal cells 21 and 23, the state becomes the state ``■'', resulting in a white display.

Color filter 22 configured in this embodiment
is constructed by arranging red, green, and blue color filters in a rectangular shape, and the transparent electrodes of the liquid crystal cells 21 and 23 corresponding to the rectangular color filter 22 are constructed in the same way as the color filters. ing. A voltage is applied to this color display element to perform a color display, and the color tone and brightness of the display are measured using a color luminance system BM-5A manufactured by TOPCON.The color filter 2
Figure 4(a) shows the CIE xy chromaticity gamut when the color arrangement of 2 is red, green, and blue and the color of the non-selected part is black, and L* in the CIE L* a* b* color system.
A diagram plotted in the a* coordinate system is shown in Figure 4(b). It can be seen from FIG. 4(a) that color display is possible according to the present invention, and from FIG. 4(b) it is understood that black and white display with good contrast is possible.

[0042] In this example, the color combination of the color filters was red, green, and blue, but sufficient color reproducibility could be obtained even when a color filter with a combination of cyan, magenta, and yellow was used. Ta. Further, in this embodiment, the background color (the color of the non-selected portion) is black, but it goes without saying that the background color may also be white. Example 2 In Example 1, the liquid crystal cells 21 and 2 produced individually
Although a color display element was realized by combining 3. However, when adopting the configuration shown in Example 1, the transparent electrodes and transparent substrates above and below the color 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 provided directly above and below a color filter will be shown with reference to FIG.

The color display element in this example is shown in FIG.
As shown in the figure, a pair of transparent substrates 25 and 31 with transparent electrodes 26 and 30 made of ITO formed on their surfaces are used, and a second light control layer 29 is formed on the transparent electrodes 30 using an ultraviolet curable compound and liquid crystal. The mixed solution is printed by screen printing for about 2
The mixed solution is applied to a thickness of 0 μm and cured by irradiation with ultraviolet rays to form a polymer dispersed liquid crystal. After curing, the color filter 28 is directly formed on the second light control layer 29 by a printing method, and then a mixed solution of an ultraviolet curable compound and liquid crystal is applied to a thickness of about 20 μm by a screen printing method, and a transparent electrode is formed. After stacking the transparent substrates 25 with 26 in such a way that no air bubbles enter, the mixed solution is cured by irradiating ultraviolet rays from the side of the transparent substrates 25 to form the first light control layer 1, and the transparent electrodes 30 of the transparent substrates 31 are formed. A light absorption layer 32 is formed on the opposite surface to form a color display element. The nematic liquid crystal used in this embodiment is a liquid crystal having positive dielectric constant anisotropy for both the first light control layer 27 and the second light control layer 29. Further, in this embodiment, for convenience's sake, the second light control layer 29 is formed first, but as can be seen from FIG.
The first light control layer 27 has a plane-symmetrical structure with respect to 8.
It goes without saying that no problem will arise if the is formed first.

When this structure is adopted, the 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. Therefore, in order to perform color display, the threshold voltage is lowered by changing the composition of the first light control layer 27 and the second light control layer 29, and the threshold voltage is lowered by changing the composition of the first light control layer 27 and the second light control layer 29.
7 and the second light control layer 29, the light scattering characteristic shown in FIG. 2(b) is obtained. In the case of this example, the polymer precursor monomer (2-ethylhexyl acrylate)/oligomer (U
This was achieved by changing the threshold voltage upon curing by changing the ratio of N-9000PEP)/liquid crystal (E8). Specifically, the first light control layer 27 is made by mixing monomers and oligomers in a ratio of 1:2,
Ultraviolet curing resin 35 [wt%] produced in this way
and liquid crystal 65 [wt%] were mixed and cured at 15 degrees. In addition, the second light control layer 29 has monomers and oligomers in a one-to-one ratio.
30 [wt%] of the ultraviolet curing resin prepared in this way and 70 [wt%] of the liquid crystal were mixed at a ratio of 10 [wt%].
This was achieved by curing at high temperatures.

When a voltage is applied to the reflective color display element manufactured in this way, it shows a white display when no voltage is applied, but when the voltage is increased and exceeds 6 [V], the display becomes white. The first light control layer 27 changes from a light scattering state to a transparent state, and a color display is possible at first, and a color display becomes completely possible at 10 [V]. Furthermore, as the voltage is increased, the second light control layer 29 changes from a light scattering state to a transparent state from 12 [V], so the reflected brightness begins to decrease, and at around 24 [V], the first light control layer 29 changes from a light scattering state to a transparent state. Since the second light control layer 29 is also transparent, a black display is obtained.

The results of color display by the color display element according to this example were measured in the same manner as in Example 1, and as a result, similar display quality could be obtained. Example 3 In Example 2, the nematic liquid crystal used was the first
Both the light control layer 27 and the second light control layer 29 use liquid crystal with positive dielectric anisotropy. In this embodiment, the second light control layer 29
By using a two-frequency drive liquid crystal for the liquid crystal component of the second light control layer 29, the light scattering state of the second light control layer 29 is made transparent in a state where no voltage is applied.
By applying a voltage, it changes to a light scattering state.

In order to obtain such an optical change, in this embodiment, a dual-frequency drive type liquid crystal (manufactured by Chisso Corporation, n0 = 1.50) is used as the liquid crystal component constituting the second light control layer 29.
9, Δn=0.154), a 1:1 mixture of monomer (2-ethylhexyl acrylate) and oligomer (UN-9000PEP) was used as the polymer precursor, and the second light control layer 29 was formed. When forming by irradiating ultraviolet rays, the mixed solution is cured by applying ultraviolet rays while applying a low frequency (100 Hz) voltage of 50 [V], so that the liquid crystal molecules are initially perpendicular to the substrate. Make it. In addition, the first light control layer 27 at this time was made by mixing a monomer and an oligomer at a ratio of 1:2, and 65 [wt%] of the ultraviolet curing resin prepared in this way and a liquid crystal (E8).
[wt%] were mixed and cured by irradiating with ultraviolet rays. By the method described above, the first light control layer 27 and the second light control layer
By configuring the light control layer 29, the light scattering characteristics shown in FIG. 2(a) are obtained. At this time, in the case of the liquid crystal used when forming the second light control layer 29 in this example, the crossover frequency (the frequency at which the dielectric constant in the long axis direction and the dielectric constant in the short axis direction of the liquid crystal molecules become equal) is Since the frequency is 10 [kHz], Δε<0 at frequencies above this frequency. Therefore, when driven by a high frequency voltage (100 [kHz]), the first light control layer 27 changes from a white display when no voltage is applied to a transparent state from a scattering state when the voltage increases and exceeds 6 [V]. It begins to change and becomes transparent at 10 [V]. At this time, the second light control layer 29 is still in a transparent state, so the display is black. When the applied voltage is further increased to 25 [V], the second light control layer 29 begins to change from a transparent state to a scattering state 45
At [V], it became completely scattered and it became possible to obtain a color display. As a result of the above, it was possible to perform black and white display and color display with good contrast within the same pixel.

In the case of this embodiment, the second light control layer 2
Devices that can be used as 9 may be devices such as a DSM that exhibits the characteristic of changing from a transparent state to a scattering state, and are not limited to polymer dispersed liquid crystals using dual-frequency driven liquid crystals. . Example 4 In Example 3, the liquid crystal component constituting the polymer-dispersed liquid crystal layer was used in order to make the second light control layer 29 transparent when no voltage was applied and to be in a light scattering state when a voltage was applied. In this example, a liquid crystal with an aromatic ring in its basic skeleton and a negative Δε was used, and by providing the initial orientation with a magnetic field, it is transparent when no voltage is applied, and the liquid crystal is transparent when no voltage is applied. A light scattering state was created in the applied state.

In order to obtain such an optical change, in this embodiment, a liquid crystal with a negative Δε (n0 = 1.509, Δn = 0.15) is used as the liquid crystal component constituting the second light control layer 29.
4, Δε = -3.1), a 1:1 mixture of monomer (2-ethylhexyl acrylate) and oligomer (UN-9000PEP) was used as the polymer precursor, and this polymer precursor was 35 [wt%], liquid crystal 6
When a solution mixed at a ratio of 5 [wt%] is irradiated with ultraviolet rays and formed, it is irradiated with ultraviolet rays while applying a magnetic field of 10 [kG], since the value is sufficiently larger than the Frederick's transition point of liquid crystal. The mixed solution is hardened to make the liquid crystal molecules perpendicular to the substrate in the initial state, thereby forming the second light control layer 29. In addition, the first light control layer 27 at this time is made by mixing monomers and oligomers in a ratio of 1:2,
Ultraviolet curing resin 35 [wt%] produced in this way
and liquid crystal (E8) at 65 [wt%] were mixed and cured by irradiation with ultraviolet rays. By configuring the first light control layer 27 and the second light control layer 29 using the method described above, the light scattering characteristics shown in FIG. 2(a) are obtained. At this time, in the case of the liquid crystal used when forming the second light control layer 29 in this embodiment, the white display when no voltage was applied, but when the voltage was increased and the voltage exceeded 6 [V], the first Light control layer 2
7 begins to change from a scattering state to a transparent state and becomes transparent at 10 [V]. At this time, the second light control layer 29 is still in a transparent state, so the display is black. If the applied voltage is further increased, 30 [
At 52[V], the second light control layer 29 began to change from a transparent state to a scattering state, and at 52[V] it became completely scattered, making it possible to obtain a color display. As a result of the above, it was possible to perform black and white display and color display with good contrast within the same pixel.

[0050]

[Effects of the Invention] According to the reflective color element according to the present invention, it is possible to construct a reflective color liquid crystal display with high display quality by expressing color display and high contrast black and white display in the same pixel. be.

[Brief explanation of drawings]

FIG. 1 is a basic configuration diagram of a reflective color display element according to the present invention.

FIG. 2 is a diagram for explaining the operation of the present invention.

FIG. 3 is a cross-sectional view of an embodiment of the invention.

FIG. 4 is a diagram showing the effects of the present invention.

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

FIG. 6 is a sectional view showing a conventional technique.

[Explanation of symbols]

1...Transparent substrate 2...Color filter 3...Transparent electrode 4...Dimmer layer 5...Transparent electrode 6...Light reflective layer 7...Substrate 8...Light absorption layer 9...First light control layer 10...Color filter layer 11...Second light control layer 12...Light absorption layer 13...Natural light incident direction 14...Light scattering characteristics of the first light control layer 15...Light scattering characteristics of second light control layer 16...Transparent substrate 17...Transparent electrode 18... Light control layer 19...Transparent electrode 20...Transparent substrate 21...First liquid crystal cell 22...Color filter 23...Second liquid crystal cell 24...Light absorption layer 25...Transparent substrate 26...Transparent electrode 27...First light control layer 28...Color filter layer 29...Second light control layer 30...Transparent electrode 31...Transparent substrate 32...Light absorption layer

Claims (6)

[Claims] 1. A substrate, an electrode, a first light control layer whose light scattering state and transparent state can be controlled by an external electric field, a color filter layer, and whose light scattering state and transparent state can be controlled by an external electric field. A second light control layer, an electrode facing the electrode, and a substrate facing the substrate are provided in this order from the light incident side, the first light control layer, the color filter layer, and the second light control layer. A color display element characterized in that a light absorption layer that absorbs the light transmitted through the color display element is provided behind the second light control layer when viewed from the light incident side. 2. The color display according to claim 1, wherein at least one of the first light control layer and the second light control layer is composed of a layer in which a liquid crystal material is dispersed in a photocurable compound. element. 3. The method for driving a color display element according to claim 1, wherein when performing black display, both the first light control layer and the second light control layer are in a transparent state, and when performing color display, the first light control layer and the second light control layer are both in a transparent state. Driving a color display element, characterized in that the first light control layer is in a transparent state, the second light control layer is in a light scattering state, and when displaying white, the first light control layer is in a light scattering state. Method. 4. At least one of the first light control layer and the second light control layer exhibits a light transmitting state when no voltage is applied, and exhibits a light scattering state when a voltage higher than a predetermined threshold voltage is applied. 2. The color display element according to claim 1, wherein the color display element has a light control layer having the following properties. 5. The light control layer is composed of a layer in which a liquid crystal material whose dielectric constant anisotropy can take at least a negative value is dispersed in a photocurable compound, and the photocurable compound of the liquid crystal material and 5. The color display element according to claim 4, wherein the interface maintains a predetermined orientation state. 6. A mixed solution of a liquid crystal material whose dielectric constant anisotropy can take a negative value and a photocurable compound is irradiated with light while applying at least one of an electric field or a magnetic field to cure the solution and dim. 6. The method of manufacturing a color display element according to claim 5, further comprising forming a layer.