JPH09160066A - Reflection type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device capable of executing effective white display and color display. SOLUTION: In the full color liquid crystal display device 1, a red display device 40, a green display device 30 and a blue display device 20 which are high polymer dispersion type liquid crystal display devices capable of switching between a red, green or blue colored state and a colorless transparent state in response to voltage are successively laminated on a light absorbing body 50. A white display device 10 to be a high polymer dispersion type liquid crystal display device capable of switching between a white state and a colorless transparent state in response to voltage is arranged on the outermost layer of the laminated layers.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a reflective liquid crystal display device.

[0002]

2. Description of the Related Art Conventionally, various types of liquid crystal display devices have been proposed. For example, a TFT liquid crystal in which a thin film transistor is arranged for each pixel has been put to practical use. However, the TFT liquid crystal is capable of high-definition display, but requires a precise and complicated manufacturing process, and has the disadvantage of low yield and high cost.

Therefore, a polymer-dispersed liquid crystal display device using a liquid crystal-polymer composite film in which a liquid crystal is dispersed in a polymer material, which is relatively easy to produce, has attracted attention.

For example, in USP 3,578,844,
It has been reported that a liquid crystal display device using a cholesteric liquid crystal as a liquid crystal material and having a liquid crystal-polymer composite film obtained by dispersing this liquid crystal in a polymer exhibits bistability. This is because the chiral nematic liquid crystal becomes a focal conic state in which the helical axis becomes random when a low voltage pulse is applied and transmits light, and a selective reflection state in which the helical axis is aligned by applying a high voltage pulse. Is used to perform reflective display.

In the following description, the side facing the display surface of the reflective liquid crystal display device is called the observation side.

The above two states of the cholesteric liquid crystal have a stable memory property when no voltage is applied. For this reason, a high-definition display is possible only by a simple matrix drive without using a complicated circuit using an active element such as a TFT liquid crystal.

As such a polymer dispersion type liquid crystal display device, for example, USP 5,200,845 and Japanese Patent Publication No.
No. 507505 discloses a liquid crystal display device that performs color display in a colored transparent state and a scattered state by selective reflection of a cholesteric phase, and LIQUID CRYS.
TALS, 1992, Vol. 12, No. 1,49-
In 58, liquid crystal display devices having selective reflection wavelengths corresponding to red light, green light, and blue light are laminated, and a simple matrix drive is performed for each display device to obtain red,
It is disclosed that a reflective display light of a mixed color of green and blue can be obtained.

[0008]

However, the selective reflection wavelength of the cholesteric liquid crystal has a viewing angle dependence,
There was a drawback that the display color changed when viewed from an angle. Therefore, in the above display device having a three-layer laminated structure, good white display can be performed when white display is performed by simultaneously setting the layers of the red display device, the green display device, and the blue display device to the reflective state. could not.

As described above, a liquid crystal display device capable of performing excellent white display and color display has not been obtained so far.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a liquid crystal display device capable of performing excellent white display and color display.

[0011]

In order to achieve the above object, the present invention comprises a liquid crystal-polymer composite film in which a liquid crystal is dispersed in a polymer, sandwiched between transparent conductive substrates, At least one color display device that switches between a selective reflection state that selectively reflects visible light of a specific wavelength and a light transmission state that transmits visible light in response to an applied voltage; and a liquid crystal dispersed in a polymer. The liquid crystal-polymer composite film formed by sandwiching it between transparent conductive substrates switches between a light transmission state in which visible light is transmitted and a light scattering state in which visible light is scattered in response to an applied voltage. It is characterized by being laminated with a white display device.

[0012]

1 is a sectional view of a full-color liquid crystal display device 1 according to an embodiment of the present invention. As shown in FIG.
In this display device 1, a red display device 40 that performs red display is stacked on a transparent substrate 94, and then a transparent substrate 93, a green display device 30 that performs green display, a transparent substrate 92, and a blue display that performs blue display in order. The device 20, the transparent substrate 91, the white display device 10 for displaying white, and the transparent substrate 90 are laminated, and a power supply 200 for applying a voltage to each display device is further provided.

In FIG. 1, when white light such as natural light is radiated from above toward the full-color display device 1,
One of the display devices reflects visible light of a specific wavelength, which is observed as a display of a specific color.

Reference numeral 50 indicates a light absorber provided in the lowermost layer as viewed from the viewing side, if desired. Light absorber 50
When the above is provided, it becomes possible to absorb light having a wavelength other than the selective reflection light from the color liquid crystal display device and display black.

Each of the display devices 10, 20, 30 and 40 of each color is provided with a sheet-like transparent electrode and a liquid crystal-polymer composite film sandwiched between the transparent electrodes.

The white display device 10 comprises a liquid crystal-polymer composite film 12 sandwiched between transparent electrodes 11 and 13 connected to a power source 200, respectively, and is responsive to a voltage applied between the transparent electrodes. Then, the light transmission state of transmitting visible light is switched to the light scattering state of scattering visible light, or conversely, the light scattering state is switched to the light transmission state. The white display device looks white in the light scattering state because visible light is scattered, and is colorless and transparent in the light transmitting state because visible light is transmitted.

The blue display device 20 has basically the same structure as the white display device 10, and comprises a liquid crystal-polymer composite film 22 and transparent electrodes 21 and 23. In the blue display device, in response to a voltage applied between the transparent electrodes, a selective reflection state in which blue is selectively reflected and a light transmission state in which visible light is transmitted are switched. That is, the blue display device 20 is either colored blue or is colorless and transparent.

The green display device 30 has the same structure as the white display device 10, and is composed of a liquid crystal-polymer composite film 32 and transparent electrodes 31 and 33. In the green display device, in response to a voltage applied between the transparent electrodes, a selective reflection state in which green is selectively reflected and a light transmission state in which all visible light is transmitted are switched. In other words, the green display device 30 is either colored green or is colorless and transparent.

The red display device 40 also has the same structure as the white display device 10, and the liquid crystal-polymer composite film 4 is used.
2, consisting of transparent electrodes 41 and 43. In the red display device 40, in response to the voltage applied between the transparent electrodes, the selective reflection state in which red is selectively reflected and the light transmission state in which all visible light is transmitted are switched. That is, the red display device 40 is either colored red or is colorless and transparent.

When color display is performed by the full-color liquid crystal display device 1, the white color display device 10 is set to the light transmitting state and the desired color display device is set to the selective reflection state. At this time, it is possible to display mixed colors by simultaneously setting a plurality of color display devices in a selective reflection state. When white display is performed by the full-color liquid crystal display device 1, the white display device 10 is set to a light scattering state.

The stacking order of each display device is not limited to that shown in FIG. 1 and can be set arbitrarily.
As shown in FIG. 7, arranging the white display device closest to the observation side is advantageous for increasing the reflection intensity during white display.

When three color display devices for displaying red, green, and blue are stacked, each display device should be stacked in the order of blue, green, and red when viewed from the observation side, as in this embodiment. As a result, it is possible to suppress a decrease in the intensity of reflected light.

The pair of transparent electrodes forming each of the above display devices are provided with a plurality of strip electrodes arranged in parallel with each other at a fine interval, and the strip electrodes are arranged in directions perpendicular to each other. The upper and lower transparent electrodes are made to face each other so that Display is performed by sequentially energizing these upper and lower strip electrodes and sequentially applying voltage to the liquid crystal-polymer composite film in a matrix. By such matrix driving, it is possible to display an image by the full-color display device 1 and express halftones and intermediate colors.

In order to switch the colored state and the colorless and transparent state of each display device, it is preferable to use a pulse voltage as the voltage applied between the transparent electrodes.

Examples of the liquid crystal-polymer composite film included in the white display device and the color display device of each color include, for example, irradiating a mixture of liquid crystal and a photocurable resin material with light such as ultraviolet rays to cure the resin, A liquid crystal-resin composite film obtained by phase-separating a liquid crystal and a resin can be used.

As the liquid crystal used in the liquid crystal-polymer composite film included in the white display device and the color display device of each color, for example, cholesteric liquid crystal can be used. Cholesteric liquid crystals have a layered structure in which the long axes of liquid crystal molecules are arranged in parallel, and in each layer, have a helical structure in which the long axes of adjacent molecules are slightly shifted.

As the cholesteric liquid crystal, those exhibiting a cholesteric phase at room temperature are particularly preferable.

As the cholesteric liquid crystal, a chiral nematic liquid crystal obtained by adding a chiral dopant to a nematic liquid crystal can be used. The nematic liquid crystal has rod-shaped liquid crystal molecules arranged in parallel, but does not have a layered structure. By adding chiral dopant to nematic liquid crystal,
An additive having a function of twisting molecules of a nematic liquid crystal. By adding a chiral dopant to a nematic liquid crystal, a helical structure of liquid crystal molecules having a predetermined pitch is generated, thereby generating a cholesteric phase.

The chiral nematic liquid crystal has an advantage that the pitch of the helical structure of the chiral nematic liquid crystal can be changed by changing the amount of the chiral dopant to be added, whereby the selective reflection wavelength of the liquid crystal can be controlled. is there. In general, a helical pitch defined by a distance between molecules when a liquid crystal molecule rotates 360 ° along a helical structure of a liquid crystal molecule is used as a term indicating a pitch of a helical structure of the liquid crystal molecule.

As the chiral dopant, a cholesteric liquid crystal having a cholesteric ring, a chiral nematic liquid crystal, and other organic compounds having no liquid crystallinity but having an action of twisting molecules of nematic liquid crystals, for example, organic compounds S811 and S1011 manufactured by Merck & Co., Inc. Commercially available chiral dopants represented by, for example, can be used.

The liquid crystal-polymer composite film thus obtained is
Voltage is applied between a light transmission state that transmits visible light and a selective reflection state that selectively reflects visible light of a specific wavelength, or a light scattering state that scatters visible light and a light transmission state that transmits visible light. In response, it can be switched, and each state can be maintained even when no voltage is applied.

In the case of the liquid crystal-polymer composite film using the chiral nematic liquid crystal, the arrangement state of the liquid crystal molecules is switched between the planar arrangement and the focal conic arrangement by applying two kinds of high and low pulse voltages. You can Thereby, the liquid crystal display device using the liquid crystal-polymer composite film, the light transmission state and the selective reflection state, or
It is possible to switch between a light scattering state and a light transmitting state.

Liquid crystal using chiral nematic liquid crystal
In the polymer composite film, the amount of the chiral dopant added to the nematic liquid crystal is adjusted, and the helical pitch of the chiral nematic liquid crystal is adjusted so that the selective reflection wavelength becomes, for example, red light, green light, and blue light, respectively. With the planar arrangement, red, green,
A liquid crystal-polymer composite film which is in a selective reflection state colored in blue and is in a colorless and transparent light transmission state in a focal conic arrangement is obtained. By sandwiching the liquid crystal-polymer composite film thus obtained between the transparent electrodes, a color liquid crystal display device can be obtained.

The helical pitch of the chiral nematic liquid crystal is adjusted by adjusting the addition amount of the chiral dopant.
When the selective reflection wavelength is adjusted to be infrared light, a liquid crystal-polymer composite film exhibiting a colorless and transparent light transmission state in a planar arrangement and a light scattering state in which white light appears by isotropic scattering in a focal conic arrangement is obtained. The liquid crystal thus obtained
A white display device can be obtained by sandwiching the polymer composite film between the transparent electrodes.

The relationship between the helical pitch p (nm) and the selective reflection wavelength λ (nm) is expressed by the following formula [I].

Λ = n × p [I] Here, n represents the average refractive index, and n ² = (n ₁ ² + n ₂ ² )
/ 2. n ₁ represents the refractive index when light is incident in the long axis direction of the liquid crystal molecule, and n ₂ represents the refractive index when light is incident in the direction perpendicular to the long axis direction of the liquid crystal molecule.

To manufacture a white display device or a color display device of each color, for example, a mixture of liquid crystal and a photo-curable resin material is sandwiched between a pair of transparent electrodes,
It is possible to adopt a method of curing the photocurable resin material in the mixture by irradiating it with light such as ultraviolet rays to phase-separate the liquid crystal and the resin. At this time, if a spacer is sandwiched between the transparent electrodes together with the mixture, the thickness of the liquid crystal-polymer composite film can be easily controlled.

As the photocurable resin material, a mixed solution of a photocurable monomer or oligomer and a photopolymerization initiator may be used. When using a mixed solution in which such a photocurable monomer or oligomer and a photopolymerization initiator are mixed, after the mixed solution is mixed with liquid crystal, the resin material is photocured by irradiating with ultraviolet rays. As the light absorber which can adopt the photopolymerization phase separation method of phase-separating the liquid crystal and the resin, for example, a black film can be used. Also, of the display device,
It is also possible to apply a black paint such as black ink to the lowermost surface as viewed from the observation side to form a light absorber.

As the chiral dopant added to the nematic liquid crystal, plural kinds of chiral dopants may be mixed and used. The use of multiple chiral dopants increases the phase transition temperature of the liquid crystal, improves the transparency of the composite film in the transparent state, and particularly speeds up the display switching between the transparent state and the selective reflection state of the color display device. It is effective to do.

As a color display device of a specific color, a first display device having a composite film using a left-handed chiral nematic liquid crystal, and a light of the same wavelength as the left-handed chiral nematic liquid crystal are selectively reflected and right-handed. A laminate of a second display device having a composite film using a chiral nematic liquid crystal having a polar property may be used. By doing so, it is possible to increase the reflectance and perform better color display. Particularly, when blue and red, which have a lower relative luminous efficiency than green, are strongly displayed, the overall color balance is improved, and thus such a multilayer structure is effective in a blue display device or a red display device.

A smectic liquid crystal may be added to the liquid crystal-polymer composite film used for the white display device. By adding the smectic liquid crystal, the transparency of the liquid crystal-polymer composite film can be improved and the contrast between the colorless transparent state and the white state can be increased.

Liquid crystal used for the display device of each color
The film thickness of the polymer composite film is not particularly limited, but the film thickness of the liquid crystal-polymer composite film used for the white display device should be made larger than the film thickness of the liquid crystal-polymer composite film used for the color display device. Is desirable.

Hereinafter, the present invention will be described in more detail with reference to specific experimental examples.

Experimental Example 1 Production of White Display Device Tolan-based Fluorine-containing Nematic Liquid Crystal MN1000XX (Chisso Corp., Δn = 0.
219, T _NI = 69.9 ° C.), 30% by weight of liquid crystal S2 (Merck) having a smectic phase at room temperature and 19.8% by weight of chiral dopant S811 (Merck) were added for selection. A chiral nematic liquid crystal having a reflection wavelength of 1100 nm (helical pitch: 685 nm) was prepared. In addition, Δn is the d-line (wavelength: 5
89 nm), and T _NI represents the temperature at which the liquid crystal phase changes from the liquid crystal phase to the isotropic phase during the temperature rising process, that is, the phase transition temperature.

Next, 3% by weight of the photopolymerization initiator DAROC
A photocurable resin material was prepared by adding UR1173 (manufactured by Ciba Geigy) to monofunctional acrylate R128H (manufactured by Nippon Kayaku).

A mixture of the chiral nematic liquid crystal and the photo-curable resin material in a weight ratio of 9: 1 is 2
A white display device was manufactured by sandwiching the transparent conductive film between the two sheets with a spacer of 20 μm interposed therebetween, and irradiating with ultraviolet rays of 15 mW / cm ² for 5 minutes at room temperature to cure the phase separation. The phase transition temperature was 41.0 ° C.

For the measurement of the phase transition temperature, a part of the liquid crystal-polymer composite film produced by the same procedure as described above was sampled and sandwiched between a slide glass and a cover glass. It was carried out by observing the process of increasing the temperature of the product at a rate of about 1 ° C./min with a polarizing microscope and measuring the temperature at which an isotropic phase began to appear. Phase transition temperature is 40
It is desirable that the temperature is not less than ° C.

When a pulse voltage of 140 V (± 5 ms) was applied between the conductive films of the white display device thus manufactured, the white display device exhibited a transparent state (transmittance: 65%, color stimulus value: 3.5). . Furthermore, in this state, 7
When a pulse voltage of 0 V (± 5 ms) was applied, the white display device exhibited a light scattering state (transmittance: 2%). The switching time between the transparent state and the light scattering state was 500 ms.

The color stimulus value was measured using a spectrocolorimeter CM-1000 manufactured by Minolta. The color stimulus values of the following display devices were also measured using the same device. The color stimulus value in the colorless and transparent state is preferably 4.5 or less. In the white state, 10.0
As described above, 15.0 or more in the red state and 20.
It is desirable to have a color stimulus value of 0 or more and 8.0 or more in the blue state.

The transmittance was measured by irradiating a white display device with a stabilized He-Ne laser and detecting the intensity of the transmitted light or scattered light with a photodiode.

Further, the switching time is measured by the digital oscilloscope (when the high transmittance pulse is applied to the display device in the planar arrangement state and the arrangement of the liquid crystal molecules is changed for a moment until the original transmittance is restored. COR55
21; manufactured by Kikusui Co., Ltd.).

The method of measuring the transmittance, the phase transition temperature, and the switching time is the same for each display device described below.

FIG. 2 shows the spectral reflection characteristics of the above white display device. As is apparent from FIG. 2, the spectral reflection characteristic of the white display device is flat without a specific peak value. The spectral reflection characteristics are measured by a spectrophotometer CM-1.
000 (manufactured by Minolta). The spectral reflection characteristics of each display device described below were also measured in the same manner.

Fabrication of blue display device Tolan-based nematic liquid crystal MN1000XX showing a nematic phase at room temperature (manufactured by Chisso Corporation, Δn = 0.
219, T _NI = 69.9 ° C.), chiral dopants S811 and S1011 (both manufactured by Merck)
17.9% by weight of a mixture of 1: 1 by weight was added to prepare a chiral nematic liquid crystal having a selective reflection wavelength of 490 nm (helical pitch: 303 nm).

Next, 3% by weight of the photopolymerization initiator DAROC
A photocurable resin material was prepared by adding UR1173 (manufactured by Ciba Geigy) to monofunctional acrylate R128H (manufactured by Nippon Kayaku).

A mixture of the chiral nematic liquid crystal and the photo-curable resin material in a weight ratio of 7: 1 is 2
After sandwiching it between the transparent conductive films of 10 μm with a spacer of 10 μm interposed between them, ultraviolet rays of 15 mW / cm ² were irradiated for 5 minutes at room temperature to cure, thereby causing phase separation to produce a blue display device. The phase transition temperature was 45.9 ° C.

When a pulse voltage of 130 V (± 5 ms) was applied between the conductive films of the blue display device thus manufactured, blue selective reflection was exhibited. Furthermore, when a pulse voltage of 70 V (± 5 ms) was applied in this state, the blue display device showed a transparent state (color stimulus value: 3.5). The switching time between the blue selective reflection state and the transparent state is 2
It was 00 ms.

FIG. 3 shows the spectral reflection characteristics when the blue display device is brought into the blue selective reflection state.

Preparation of green display device Tolan-based nematic liquid crystal MN1000XX showing a nematic phase at room temperature (manufactured by Chisso Corporation, Δn = 0.
219, T _NI = 69.9 ° C.), chiral dopants S811 and S1011 (both manufactured by Merck)
15.1 wt% of a mixture of 1: 1 by weight was added to prepare a chiral nematic liquid crystal having a selective reflection wavelength of 570 nm (helical pitch: 351 nm).

Next, 3% by weight of the photopolymerization initiator DAROC
A photocurable resin material was prepared by adding UR1173 (manufactured by Ciba Geigy) to monofunctional acrylate R128H (manufactured by Nippon Kayaku).

A mixture of the chiral nematic liquid crystal and the photocurable resin material in a weight ratio of 7: 1 is used as 2
After sandwiching it between the transparent conductive films of 10 sheets through a spacer of 10 μm, it was irradiated with ultraviolet rays of 15 mW / cm ² for 5 minutes at room temperature to be cured, thereby causing phase separation to produce a green display device. The phase transition temperature was 48.6 ° C.

When a pulse voltage of 120 V (± 5 ms) was applied between the conductive films of the green display device thus manufactured, green selective reflection was exhibited. Furthermore, when a pulse voltage of 60 V (± 5 ms) was applied in this state, the green display device showed a transparent state (color stimulus value: 3.8). The switching time between the green selective reflection state and the transparent state is 4
It was 00 ms.

FIG. 4 shows the spectral reflection characteristics when the green display device is brought into the green selective reflection state.

Preparation of red display device Tolan-based nematic liquid crystal MN1000XX showing nematic phase at room temperature (manufactured by Chisso Corp., Δn = 0.
219, T _NI = 69.9 ° C.), chiral dopants S811 and S1011 (both manufactured by Merck)
13.0% by weight of a mixture of 1: 1 by weight was added to prepare a chiral nematic liquid crystal having a selective reflection wavelength of 650 nm (helical pitch: 400 nm).

Next, 3% by weight of the photopolymerization initiator DAROC
A photocurable resin material was prepared by adding UR1173 (manufactured by Ciba Geigy) to monofunctional acrylate R128H (manufactured by Nippon Kayaku).

A mixture of the chiral nematic liquid crystal and the photo-curable resin material in a weight ratio of 7: 1 is 2
After sandwiching the 10 μm spacers between the transparent conductive films, it was irradiated with ultraviolet rays of 15 mW / cm ² for 5 minutes at room temperature to be cured, thereby phase-separating to produce a red display device. The phase transition temperature was 51.6 ° C.

When a pulse voltage of 110 V (± 5 ms) was applied between the conductive films of the red display device thus manufactured, red selective reflection was exhibited. Furthermore, when a pulse voltage of 50 V (± 5 ms) was applied in this state, the red display device showed a transparent state (color stimulus value: 4.2). The switching time between the red selective reflection state and the transparent state is 5
It was 00 ms.

FIG. 5 shows the spectral reflection characteristics when the red display device is in the red selective reflection state.

Preparation of full color display device The above red display device was laminated on a black film as a light absorber, and then the above green display device was laminated in order.
By laminating the blue display device and the white display device, a full-color display device having the laminated constitution shown in FIG. 1 was produced. In addition, as shown in FIG. 1, a transparent substrate was arranged between the light absorber and the red display device, between the display devices, and on the observation surface side of the green display device.

As is clear from FIGS. 3 to 5, in the spectral reflectance characteristics of each display device, the transmittance on the shorter wavelength side than the selective reflection wavelength of the display device is larger than the selective reflection wavelength of the display device. The transmittance on the long wavelength side is higher. Therefore, in this experimental example, a decrease in the amount of reflected light is prevented by stacking display devices of respective colors in the order of blue, green, and red when viewed from the observation side.

In this experimental example, blue, green,
Two types of chiral dopants are mixed and used when manufacturing each red display device. As a result, the phase transition temperature is higher than that when a single chiral dopant is used, the transparency when the polymer dispersed liquid crystal is in the transparent state is improved, and the transparent state and the selective reflection state display of each color display device are improved. The effect that switching between and becomes faster is obtained.

Table 1 shows the types of pulse voltage applied to each display device and the state of each display device when white display is performed. Further, in Table 2, the kind of pulse voltage applied to each display device in the case of performing color display and the state of each display device are summarized by taking the case of performing green display as an example.

[0073]

[Table 1]

[0074]

[Table 2]

FIG. 6 shows the spectral reflection characteristics when white display is performed by the full color display device, that is, when the white display device is in the light scattering state and each of the red, green and blue display devices is in the selective reflection state. .

As shown in FIG. 6, the spectral reflection characteristics are flat without a specific peak value, and a favorable white color appears even when viewed obliquely. It is considered that this is because, as described with reference to FIG. 2, the white display device itself has a flat spectral reflection characteristic having no specific peak value.

Further, as is clear from the comparison between FIG. 6 and FIG. 2, the full-color display device of this experimental example has a high reflectance and can perform black-and-white display with high contrast. Specifically, when the contrast is measured, when the white display device is arranged on the light absorber, the contrast is 3:
Although it was about 1, when performing white display as shown in Table 1 in the full-color display device of this experimental example,
It became 6: 1.

When the white display device is provided closer to the observation surface side than the color display device as in the present embodiment, if the white display device is in the light scattering state, the light entering from the observation surface side becomes scattered light and the color Light enters the display device at various angles. Therefore, it is considered that light is reflected from the color display device at various angles, and flat spectral reflection characteristics can be obtained as the entire display device. In addition, more reflected light is returned from the color display device to the white display device, and it is considered that a high reflectance is obtained.

The black arrows in FIG. 1 schematically show how the light incident on the full-color display device is reflected or scattered.

<Experimental Example 2> A full-color liquid crystal display device 2 in which a red display device, a green display device and a blue display device are sequentially laminated on a light absorber in the same manner as in Experimental Example 1 except that the white display device is not provided. Was produced. FIG. 7 shows a sectional view of the liquid crystal display device thus manufactured. Note that, in FIG. 7, for simplification, the same members as those shown in FIG. 1 are denoted by the same reference numerals.

FIG. 8 shows the spectral reflection characteristics of the full-color display device 2 when all the red, green, and blue display devices are in the selective reflection state. As shown in FIG. 8, the spectral spectrum has a mountain shape, and even if the spectrum is set to be white in the direction perpendicular to the observation surface, when the full-color display device is viewed obliquely, it does not look white,
Good black and white display becomes difficult. It is considered that this is because the spectrum shifts to the short wavelength side according to the following formula [II].

Λ = λ ₀ cos θ ′ = λ ₀ √ (1-sin ² θ / n ² ) [II] In the above formula [II], λ is the wavelength of reflected light from the observed display device, and λ ₀ is the selective reflection wavelength of each display device, θ'is the liquid crystal-polymer composite film when light is incident toward the reference point in the direction of the straight line connecting the reference points on the viewing surface of the display device. The angle formed by the direction of the light traveling inside and the helical axis, θ is the angle of the straight line connecting the observation point and the reference point on the observation surface with respect to the vertical direction of the observation surface, and n is the average refractive index n ² = (n ₁ ² + n ₂ ² ) / 2.

<Experimental Example 3> Fabrication of green display device Tolan-based nematic liquid crystal MN1008XX (manufactured by Chisso Corp., Δn = 0.218, T) showing a nematic phase at room temperature.
_NI = 73.9 ° C) for chiral dopant S81
1 and S1011 (both manufactured by Merck Ltd.) were mixed at a weight ratio of 1: 1 and 13.2% by weight was added to give a selective reflection wavelength of 570 nm (helical pitch: 35).
3 nm) chiral nematic liquid crystal was prepared.

Next, 3% by weight of the photopolymerization initiator DAROC was used.
A photocurable resin material was prepared by adding UR1173 (manufactured by Ciba Geigy) to monofunctional acrylate R128H (manufactured by Nippon Kayaku).

A mixture of the chiral nematic liquid crystal and the photocurable resin material in a weight ratio of 7: 1 was added to 2
A 10 μm spacer was sandwiched between the transparent conductive films, and then ultraviolet rays of 15 mW / cm ² were irradiated for 5 minutes at room temperature to cure, thereby phase-separating and producing a green display device. The phase transition temperature was 52.4 ° C.

When a pulse voltage of 120 V (± 5 ms) was applied between the conductive films of the green display device thus manufactured, the green display device showed green selective reflection. Furthermore, in this state, 60 V pulse voltage (± 5 ms)
, The green display device showed a transparent state (color stimulus value: 3.6). The switching time between the green selective reflection state and the transparent state was 400 ms.

As described above, it is possible to manufacture a liquid crystal display device having the same excellent performance as that shown in Experimental Example 1 by using a liquid crystal other than the fluorine-containing tolan-based liquid crystal.

<Experimental Example 4> Preparation of green display device Cyanobiphenyl nematic liquid crystal E31LV (manufactured by Merck & Co., Δn = 0.22) showing a nematic phase at room temperature.
7, T _NI = 61.5 ° C.), a mixture of chiral dopants S811 and S1011 (both manufactured by Merck Ltd.) in a weight ratio of 1: 1 was added at 14.3% by weight to select. A chiral nematic liquid crystal having a reflection wavelength of 570 nm (helical pitch: 355 nm) was prepared.

Next, 3% by weight of the photopolymerization initiator DAROC was used.
A photocurable resin material was prepared by adding UR1173 (manufactured by Ciba Geigy) to monofunctional acrylate R128H (manufactured by Nippon Kayaku).

A mixture of the chiral nematic liquid crystal and the photocurable resin material in a weight ratio of 7: 1 was used to prepare 2
A 10 μm spacer was sandwiched between the transparent conductive films, and then ultraviolet rays of 15 mW / cm ² were irradiated for 5 minutes at room temperature to cure, thereby phase-separating and producing a green display device. The phase transition temperature was 29.2 ° C.

When a pulse voltage of 100 V (± 5 ms) was applied between the conductive films of the green display device thus produced, green selective reflection was exhibited. Furthermore, when a pulse voltage of 60 V (± 5 ms) was applied in this state, the green display device showed a transparent state (color stimulus value: 6.0). The switching time between the green selective reflection state and the transparent state is 2
It was 00 ms.

<Experimental Example 5> Fabrication of blue display device Tolan-based nematic liquid crystal MN1000XX showing nematic phase at room temperature (manufactured by Chisso Corporation, Δn = 0.
219, T _NI = 69.9 ° C.), 38.6% by weight of a chiral dopant S811 (manufactured by Merck & Co., Inc.) was added, and the selective reflection wavelength was 460 nm (helical pitch was 29.
0 nm) chiral nematic liquid crystal was prepared.

Next, 3% by weight of the photopolymerization initiator DAROC was used.
A photocurable resin material was prepared by adding UR1173 (manufactured by Ciba Geigy) to monofunctional acrylate R128H (manufactured by Nippon Kayaku).

A mixture of the chiral nematic liquid crystal and the photocurable resin material in a weight ratio of 7: 1 was sandwiched between two transparent conductive films via a spacer of 10 μm, and then 15 mW / cm. ^By irradiating with ultraviolet rays of ² for 5 minutes at room temperature to cure, the phases were separated to produce a blue display device.

The phase transition temperature of the device thus produced was 24.0 ° C. Therefore, various characteristics were measured at 20 ° C. When a pulse voltage of 130 V (± 5 ms) was applied between the conductive films of the blue display device, green selective reflection was exhibited. Furthermore, when a pulse voltage of 70 V (± 5 ms) was applied in this state, the blue display device showed a transparent state (color stimulus value: 3.5). The switching time between the blue selective reflection state and the transparent state was 200 ms.

<Experimental Example 6> Production of green display device Tolane-based fluorine-containing nematic liquid crystal MN1000XX exhibiting a nematic phase at room temperature (manufactured by Chisso Corporation, Δn = 0.
219, T _NI = 69.9 ° C.), a chiral dopant S811 (manufactured by Merck) was added in an amount of 31.0 wt%, and the selective reflection wavelength was 570 nm (helical pitch was 35).
A 5 nm) chiral nematic liquid crystal was prepared.

Next, 3% by weight of the photopolymerization initiator DAROC was used.
A photocurable resin material was prepared by adding UR1173 (manufactured by Ciba Geigy) to monofunctional acrylate R128H (manufactured by Nippon Kayaku).

A mixture of the chiral nematic liquid crystal and the photocurable resin material in a weight ratio of 7: 1 was used as 2
A 10 μm spacer was sandwiched between the transparent conductive films, and then ultraviolet rays of 15 mW / cm ² were irradiated for 5 minutes at room temperature to cure, thereby phase-separating and producing a green display device. The phase transition temperature was 30.2 ° C.

When a pulse voltage of 100 V (± 5 ms) was applied between the conductive films of this green display device, green selective reflection was exhibited. Furthermore, in this state, 60V
When the pulse voltage (± 5 ms) was applied, the green display device showed a transparent state (color stimulus value: 4.3). The switching time between the selective reflection state of green and the transparent state is 5
It was 00 ms.

<Experimental Example 7> Fabrication of blue display device Tolan-based nematic liquid crystal MN1000XX showing nematic phase at room temperature (manufactured by Chisso Corporation, Δn = 0.
219, T _NI = 69.9 ° C.), a mixture of chiral dopants S811 and CN (both manufactured by Merck Co., Ltd.) in a weight ratio of 1: 1 was added in an amount of 29.0% by weight to select. Reflection wavelength is 460 nm (helical pitch is 2
A 90 nm chiral nematic liquid crystal was prepared.

Next, 3% by weight of the photopolymerization initiator DAROC was used.
A photocurable resin material was prepared by adding UR1173 (manufactured by Ciba Geigy) to monofunctional acrylate R128H (manufactured by Nippon Kayaku).

A mixture of the chiral nematic liquid crystal and the photo-curable resin material in a weight ratio of 7: 1 was added to 2
After sandwiching it between the transparent conductive films of 10 sheets through a spacer of 10 μm, it was irradiated with ultraviolet rays of 15 mW / cm ² for 5 minutes at room temperature to be cured, and thereby phase separated to produce a blue display device. The phase transition temperature was 48.0 ° C.

When a pulse voltage of 150 V (± 5 ms) was applied between the conductive films of the blue display device thus manufactured, blue selective reflection was exhibited. Furthermore, when a pulse voltage of 80 V (± 5 ms) was applied in this state, the blue display device exhibited a transparent state (color stimulus value: 4.5). The switching time between the blue selective reflection state and the transparent state is 1
It was 0 ms.

<Experimental Example 8> In this Experimental Example, one in which a blue display device using a levorotatory chiral nematic liquid crystal and a blue display device using a dextrorotatory chiral nematic liquid crystal are superposed is one. An example of a blue display device is shown.

Preparation of blue display device Tolan-based nematic liquid crystal MN1000XX showing nematic phase at room temperature (manufactured by Chisso Co., Δn = 0.
219, T _NI = 69.9 ° C.), chiral dopants R811 (Merck, dextrorotatory) and R1011.
(Merck, dextrorotatory) was mixed at a weight ratio of 1: 1 and 17.9 wt% was added to give a selective reflection wavelength of 4
A 90 nm (helical pitch was 303 nm) chiral nematic liquid crystal was prepared.

Next, 3% by weight of the photopolymerization initiator DAROC was used.
A photocurable resin material was prepared by adding UR1173 (manufactured by Ciba Geigy) to monofunctional acrylate R128H (manufactured by Nippon Kayaku).

A mixture of the chiral nematic liquid crystal and the photocurable resin material in a weight ratio of 7: 1 was used to prepare 2
After sandwiching it between the transparent conductive films of 10 μm with a spacer of 10 μm interposed between them, ultraviolet rays of 15 mW / cm ² were irradiated for 5 minutes at room temperature to cure, thereby causing phase separation to produce a blue display device. The phase transition temperature was 45.9 ° C.

When a pulse voltage of 130 V (± 5 ms) was applied between the conductive films of the blue display device thus manufactured, blue selective reflection was exhibited. Furthermore, when a pulse voltage of 70 V (± 5 ms) was applied in this state, the blue display device showed a transparent state (color stimulus value: 3.5). The switching time between the blue selective reflection state and the transparent state is 2
It was 00 ms.

The blue display device thus obtained was laminated on the blue display device manufactured in Experimental Example 1, and the spectral reflectance thereof was measured. The chiral dopants S811 and S1011 used for manufacturing the blue display device of Experimental Example 1 are both levorotatory. FIG. 9 shows the results. As is clear from the comparison between FIG. 9 and FIG. 3 described in Experimental Example 1, it is understood that the reflectance in the selective reflection wavelength region is improved as compared with the case of a single layer.

In the cholesteric liquid crystal, it is considered that the light incident parallel to the helical axis in the planar arrangement is divided into two circularly polarized lights, that is, right-handed light and left-handed light, one of which is used for selective reflection. . For this reason, the other rotatory light was supposed to be transmitted. However, by providing both layers of the dextrorotatory layer and the levorotatory layer, the rotatory light transmitted through one layer is also transmitted by the other layer. It is considered that the light will be reflected, resulting in an increase in reflectance.

As described above, the reflectance is increased by overlapping the first display device using the left-handed chiral nematic liquid crystal and the second display device using the right-handed chiral nematic liquid crystal. Therefore, the above configuration is applied to a color display device, particularly a blue display device for blue display and a red display device for red display, in a display device in which a plurality of color display devices are stacked as described in Experimental Example 1. It is effective to do.

<Experimental Example 9> In this experimental example, a red display device using a levorotatory chiral nematic liquid crystal and a red display device using a dextrorotatory chiral nematic liquid crystal are superposed on each other to give one red. An example of a display device is shown.

Manufacture of Red Display Device Tolan-based Fluorine-containing Nematic Liquid Crystal MN1000XX (Neissine, Chisso Co., Δn = 0.
219, T _NI = 69.9 ° C.), chiral dopants R811 (Merck, dextrorotatory) and R1011.
(Merck, dextrorotatory) was mixed at a weight ratio of 1: 1 and 13.0% by weight of a chiral dopant was added to give a selective reflection wavelength of 650 nm (helical pitch: 40).
0 nm) chiral nematic liquid crystal was prepared.

Next, 3% by weight of the photopolymerization initiator DAROC was used.
A photocurable resin material was prepared by adding UR1173 (manufactured by Ciba Geigy) to monofunctional acrylate R128H (manufactured by Nippon Kayaku).

A mixture of the chiral nematic liquid crystal and the photo-curable resin material in a weight ratio of 7: 1 was added to 2
After sandwiching the 10 μm spacers between the transparent conductive films, it was irradiated with ultraviolet rays of 15 mW / cm ² for 5 minutes at room temperature to be cured, thereby phase-separating to produce a red display device. The phase transition temperature was 51.6 ° C.

When a pulse voltage of 110 V (± 5 ms) was applied between the conductive films of the red display device thus manufactured, red selective reflection was exhibited. Furthermore, when a pulse voltage of 50 V (± 5 ms) was applied in this state, the red display device showed a transparent state (color stimulus value: 4.2). The switching time between the selective reflection state of red and the transparent state was 500 ms.

The red display device thus obtained was superposed on the red display device produced in Experimental Example 1,
The spectral reflectance was measured. The results are shown in FIG. As is clear from the comparison between FIG. 10 and FIG. 5 described in Experimental Example 1, it is understood that the reflectance in the selective reflection wavelength region is improved as compared with the case of a single layer.

[0118]

As described above, according to the reflective liquid crystal display device of the present invention, it is possible to switch between a selective reflection state in which visible light of a specific wavelength is selectively reflected and a light transmission state in which visible light is transmitted. Since a color liquid crystal display device and a white display device capable of switching between a light scattering state that scatters visible light and a light transmission state that transmits visible light are stacked, good white display and color display can be performed. it can.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a full-color display device that is an embodiment of the present invention.

FIG. 2 is a diagram showing spectral reflection characteristics when a white display device is in a light scattering state.

FIG. 3 is a diagram showing spectral reflection characteristics when a blue display device is in a selective reflection state.

FIG. 4 is a diagram showing spectral reflection characteristics when a green display device is in a selective reflection state.

FIG. 5 is a diagram showing spectral reflection characteristics when a red display device is in a selective reflection state.

FIG. 6 is a diagram showing spectral reflection characteristics when white display is performed in the full-color display device of FIG.

FIG. 7 is a cross-sectional view of a full-color display device in which blue, green, and red display devices are stacked.

FIG. 8 is a diagram showing spectral reflection characteristics when all the display devices in the full-color display device of FIG. 7 are in a selective reflection state.

FIG. 9 is a diagram showing spectral reflection characteristics of a blue display device formed by stacking two display devices containing chiral dopants having different optical rotatory powers.

FIG. 10 is a diagram showing spectral reflectance characteristics of a red display device formed by stacking two display devices containing chiral dopants having different optical rotatory powers.

[Explanation of symbols]

 1 Full Color Display Device 10 White Display Device 20 Red Display Device 30 Green Display Device 40 Blue Display Device 200 Power Supply

Claims (14)

[Claims] 1. A liquid crystal-polymer composite film in which a liquid crystal is dispersed in a polymer is sandwiched between transparent conductive substrates, and visible light of a specific wavelength is selected in response to an applied voltage. At least one color display device that switches between a selective reflection state in which light is selectively reflected and a light transmission state in which visible light is transmitted, and a liquid crystal-polymer composite film in which liquid crystal is dispersed in a polymer, Reflection characterized by being sandwiched between and stacked with a white display device that switches between a light transmission state of transmitting visible light and a light scattering state of scattering visible light in response to an applied voltage. Type liquid crystal display device. 2. The reflective liquid crystal display device according to claim 1, wherein the white display device is laminated on the viewing side of the color display device. 3. A blue display device in which the color display device is switched between a selective reflection state in which blue is selectively reflected in response to an applied voltage and a light transmission state in which visible light is transmitted, and an applied voltage. A green display device that switches between a selective reflection state in which green is selectively reflected in response to a light and a light transmission state in which visible light is transmitted, and a selective reflection state in which red is selectively reflected in response to an applied voltage. The reflective liquid crystal display device according to claim 1, wherein the reflective liquid crystal display device is formed by laminating a red display device that switches between a light transmission state that transmits visible light and a red display device. 4. The reflective liquid crystal display device according to claim 3, wherein the color display device is a stack of display devices in the order of blue, green, and red when viewed from the observation side. 5. The reflection type liquid crystal display device according to claim 1, further comprising a light absorber as the lowermost layer when viewed from the viewing side. 6. The reflective liquid crystal display device according to claim 1, wherein the liquid crystal-polymer composite film of the white display device and the color display device is formed by phase-separating a cholesteric liquid crystal and a polymer. 7. The reflective liquid crystal display device according to claim 6, wherein the cholesteric liquid crystal is a chiral nematic liquid crystal obtained by adding a chiral dopant to a nematic liquid crystal. 8. The reflective liquid crystal display device according to claim 7, wherein the nematic liquid crystal contains a tolan-based liquid crystal as a main component. 9. The chiral dopant is at least 2
The reflective liquid crystal display device according to claim 7, which is formed by mixing different types of chiral dopants. 10. The first display device, wherein the color display device has a liquid crystal-polymer composite film using a levorotatory chiral nematic liquid crystal, and selectively reflects light having the same wavelength as the levorotatory chiral nematic liquid crystal. The reflective liquid crystal display device according to claim 7, which is a laminate of a second display device having a liquid crystal-polymer composite film using a right-handed chiral nematic liquid crystal. 11. The reflective liquid crystal display device according to claim 1, wherein the polymer contained in the liquid crystal-polymer composite film of the white display device and the color display device is a photocurable photocurable resin. 12. The reflective liquid crystal display device according to claim 1, further comprising voltage applying means for applying a voltage to each display device. 13. The reflection type liquid crystal display device according to claim 12, wherein the voltage applying means is a pulse power source. 14. The reflective liquid crystal display device according to claim 1, wherein the liquid crystal-polymer composite film included in the white display device has a larger film thickness than the liquid crystal-polymer composite film included in the color display device.