JPH0588209A - Lcd shutter - Google Patents

Abstract

(57) [Summary] [Structure] The present invention provides a mixture of a low-molecular liquid crystal and a high-molecular liquid crystal,
Alternatively, a mixture of a low-molecular liquid crystal, a high-molecular liquid crystal and an optically active substance, sandwiched between substrates with at least one transparent electrode in a temperature range exhibiting a cholesteric phase,
It forms an optically opaque state by applying a low-frequency AC electric field, and it can be maintained even when the electric field is blocked.By applying a high-frequency AC electric field, an optically transparent state is formed and blocked. The liquid crystal shutter is characterized in that it can be maintained even in the opened state and has excellent printability, so that it can have a large area. [Effect] The liquid crystal shutter of the present invention is a liquid crystal element that does not require a polarizing plate and enables a large area, and exhibits the effect as a shutter by applying and blocking an electric field.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal shutter, and more particularly to a liquid crystal shutter which reversibly exhibits an optically opaque state and a transparent state when an alternating electric field is applied.

[0002]

2. Description of the Related Art The use of liquid crystal as a display device has already been realized in many fields. For example, calculators, devices for displaying audio display portions or advertisement graphics and characters on a flat surface, and recently, full-color liquid crystal televisions have come into practical use. Many of these are operated in the twisted nematic mode, and the operating principle is known (edited by Kobayashi and Okano, "Liquid Crystal").
(Baifukan, 1985).

Many uses are considered in addition to the use as the display element. As one of them, research and development of a larger area light-shielding shutter is being conducted. For example, shutters for blindfolds, large glass for vehicles, electric curtains, etc.

In the conventional method using liquid crystals, the liquid crystal is sandwiched between two substrates which have been subjected to orientation treatment by vapor deposition of an organic substance such as polyimide or lecithin or quartz or gold on a glass plate with a transparent electrode. The structure was such that the sandwiched substrate was further sandwiched by polarizing plates. Therefore, there is a limit to the size increase. That is, the liquid crystal is fluid, and it is difficult to apply or enclose it to a large-area substrate uniformly and with a constant thickness, and it is difficult to make a large polarizing plate.
In addition, since a polarizing plate is used, the main reason is that the contrast between when light is shielded and when it is transparent is reduced, and the light transmittance when transparent is reduced.

As a material system that can be driven without a polarizing plate, there is a mixed system of a low molecular cholesteric liquid crystal and a nematic liquid crystal having a negative dielectric anisotropy. In this system, the initial orientation of the liquid crystal is a transparent state called the Grangen state, and when a low-frequency AC electric field is applied to this system, dynamic scattering occurs and the liquid crystal becomes opaque and becomes opaque. Even if the electric field is cut off, the liquid crystal takes an opaque state called a focal conic state and the state is stably maintained. It is possible to apply a high-frequency AC electric field from the opaque state to the transparent state. Also, this state is maintained stable over time even if the electric field is cut off. Since each of these states can be maintained without applying an electric field, it is a well-known technique that has been actively researched from the late 1960s to the early 1970s (for example, GHHeilmeier et al, Proc. IEEE, 5).
7,34 (1969)). However, since it has a high operating voltage and a slow response speed, it has been removed from the scope of research and is currently in use. From the viewpoint of increasing the area, it is considered difficult because the liquid crystal has no self-supporting property.

In recent years, a polymer dispersed liquid crystal film has been actively studied as a material for manufacturing a large shutter (hereinafter referred to as PDLC, JWDOANE et al., Mol.C.
Ryst, Liq. Cryst., Vol 165,533 (1988), JP-A-60-2
No. 52687). This is a structure in which liquid crystal is dispersed in a polymer medium, and the liquid crystal is dispersed in particles having a wavelength of visible light or in a three-dimensional complex network. The dispersion state of the liquid crystal varies depending on the material or manufacturing method, but creates a state where the refractive index of the liquid crystal and that of the polymer medium match or do not match when an AC electric field is applied or blocked, producing an optically transparent or opaque state, respectively. It is possible to use it as a shutter. PDLC is promising as a method for manufacturing a large-sized shutter because it compensates for the self-supporting property that liquid crystal itself does not have by dispersing it in a polymer medium, and further requires no polarizing plate.

However, since the PDLC is a two-phase composite, complete phase separation such as the liquid crystal portion and the polymer medium portion does not occur and the voltage applied to the liquid crystal portion is lowered, and the PDLC has a high voltage due to the polymerization reaction. When a method of forming a molecular medium is used, unreacted substances remain and become impurities, which raises the operating voltage of the liquid crystal as a drawback.

On the other hand, there is a polymer liquid crystal as a liquid crystal material having a self-supporting property and capable of being formed into a film, and there are great expectations for its practical application. However, many polymer liquid crystals synthesized so far have high viscosity by themselves,
Practical application has been delayed due to slow response speed and high operating temperature range.

The present inventors have found that a mixed system of a polymer liquid crystal exhibiting a cholesteric phase and a nematic liquid crystal having a negative dielectric anisotropy is capable of switching between a Granden state and a focal conic state and has a focal conic state. It was found that the conic state has a strong scattering power and is stable over time, and that this mixed system is suitable for forming a liquid crystal layer by using printing.

[0010]

DISCLOSURE OF THE INVENTION The present invention provides a mixture of a polymer liquid crystal exhibiting a cholesteric phase and a low molecular weight nematic liquid crystal having a negative dielectric anisotropy in order to enable a large area without a polarizing plate. In a system, it is intended to provide a liquid crystal element that exhibits an effect as a shutter by applying and blocking an electric field.

[0011]

That is, the present invention provides a mixture of a low molecular weight liquid crystal and a high molecular weight liquid crystal, or a mixture of a low molecular weight liquid crystal, a high molecular weight liquid crystal and an optically active substance, in at least one of the temperature regions exhibiting a cholesteric phase. Is sandwiched between substrates with transparent electrodes and forms an optically opaque state by application of a low-frequency AC electric field, which can be maintained even when the electric field is cut off. The liquid crystal shutter is characterized in that an optically transparent state is formed by application of an electric field and can be maintained even when the state is blocked, and the printability is excellent, so that a large area can be achieved.

[0012]

The change from the transparent state (Grangen state in FIG. 1) to the opaque state (focal conic state in FIG. 2) is performed by applying a low frequency electric field, and vice versa. .. Even if the electric field is cut off after changing the state, each state is maintained stable over time. On the basis of such an operation principle, the present invention has a self-supporting property and enables a large area by using a mixed system of a high-molecular liquid crystal and a low-molecular liquid crystal.

[0013]

DETAILED DESCRIPTION OF THE INVENTION The present invention is based on the results of investigation of a liquid crystal system which has printability, can be formed into a film, and can stably maintain a transparent state and an opaque state with time. In order for the mixed system to exhibit a cholesteric phase, at least one of the high-molecular liquid crystal and the low-molecular liquid crystal exhibits a cholesteric phase, or both liquid crystals have a nematic phase,
It is necessary to add an optically active substance.

There are three possible states of the cholesteric liquid crystal: the Grangen state of FIG. 1, the focal conic state of FIG. 2 and the homeotropic state of FIG. Of these, the Grangen state and the homeotropic state are optically transparent. For use as a shutter, two kinds of switching are possible between a homeotropic state and a focal conic state, and between a grand gen state and a focal conic state. In the former case, continuous application of an electric field is required to maintain the optically transparent homeotropic state. On the other hand, in the latter case, it is necessary to apply the electric field only when changing the state, and there is an advantage that the electric field need not be applied after the state is changed. The present invention is
This is achieved by using this latter method.

In order to maintain the transparent state and the opaque state more stably, the ratio between the size of the helical pitch (p) and the film thickness of the liquid crystal mixed system (d) is d / p> 10. It has been known. The problem here is the size of the helical pitch. In the following examples, the copolymer polymer liquid crystal having a cholesteryl group and a cyanobiphenyl group in the side chain in the acrylic main chain was used, but the pitch can be adjusted by changing the ratio of the cholesteryl group, It can also be adjusted by the ratio of the low-molecular liquid crystal to be mixed or the addition amount of the optically active substance.

The viscosity suitable for printing (about several tens Pas) can be adjusted by changing the mixing ratio of the high-molecular liquid crystal and the low-molecular liquid crystal. It can also be realized by increasing the degree of polymerization of the polymer liquid crystal. Comparing high-polymerization and low-polymerization polymer liquid crystals in which the number of side chain mesogenic groups exhibiting liquid crystallinity is the same throughout the system, no significant difference in liquid crystallinity appears, and viscosity is remarkable. Since there are differences, it can be said that this is an effective means. Since the operating voltage may increase as the content of the polymer liquid crystal increases, it is necessary to pay attention to the mixing ratio. However, if operated at 100 V or less, it is considered to be sufficient for applications such as household electric curtains.

[0017]

【Example】

<Example 1> In the compound shown in Chemical formula 1, X = Y =
Acrylic skeleton copolymerized cholesteric side chain type polymer liquid crystal represented by O, m: n = 1: 2, and k = 1 = 5 (these values are not limited to the values described here but indicate a cholesteric phase). The weight average molecular weight was about 15,000) and a low molecular weight nematic liquid crystal product name "ZLI-3640" (negative dielectric anisotropy) manufactured by MERCK was used in a weight ratio of 3: 7. Were mixed in the ratio. This mixed system was bar-coated on a transparent film with an electrode so as to have a thickness of about 9 μm. Then, it was sandwiched with a counter electrode film (see FIG. 4). The helical pitch was about 0.9 micron and the viscosity was 20 pascals.

Immediately after the bar coating, the mixed system is in a Grangen state and is in a transparent state. The haze value was about 40. When an alternating voltage of 60 Hz and 100 V was applied to this element, it became cloudy due to the dynamic scattering effect and exhibited a strong light scattering state. The haze value at that time was about 65. When the voltage application was cut off, it became a focal conic state, which was a mechanism different from that when a voltage was applied, but turned white turbid and showed a light scattering state. Even in this state, the haze value was almost the same as when the voltage was applied. When the haze value was measured after 30 minutes, almost no change was observed.

For the element in the focal conic state, 5
When a voltage of 100 V was applied at kHz, the state changed to Grangen in 0.8 seconds. The haze value at this time was about 40, which was almost the same as that immediately after the bar coating, and the Glangen state and the focal conic state could be reversibly controlled by applying and shutting off the voltage.

Example 2 The polymer liquid crystal of Example 1 and the low molecular weight nematic liquid crystal LIXON-EN40 manufactured by Chisso Corporation were mixed in a ratio of 3: 7. The helical pitch was approximately 0.9 microns and the viscosity was 15 pascals. After performing bar coating and sandwiching in the same manner as in Example 1, the haze value in each state was measured. In the Grangen state immediately after the bar coat, about 35, about 65 at 60 Hz and 90 V applied, and almost no change was observed even after 30 minutes had passed since the voltage was cut off. When an AC voltage of 5 kHz and 90 V was applied to the focal conic state, the state changed to the Grangen state in 0.6 seconds, and the haze value at that time was about 65.

<Embodiment 3> In the chemical formula 1, X = O, Y = N
A polymer liquid crystal (weight average molecular weight: about 30,000) represented by H, m: n = 1: 2 and K = 1: 5 and a low molecular weight nematic liquid crystal LIXON-EN40 manufactured by Chisso Corporation were mixed at a ratio of 3: 7. .. Helical pitch is approximately 0.8 microns, viscosity is 25
It was Pascal. After performing bar coating and sandwiching in the same manner as in Example 1, the haze value in each state was measured. In the Grangen state immediately after the bar court, it is about 35, 60H.
When z and 90 V were applied, there was about 70, and when the voltage was cut off for 30 minutes, almost no change was observed. When an AC voltage of 5 kHz and 90 V was applied to the focal conic state, the state changed to the Grangen state in 0.5 seconds, and the haze value at that time was about 70.

<Embodiment 4> In the chemical formula 1, Y = O, m = 0,
A nematic side chain type polymer liquid crystal having an acrylic skeleton represented by l = 5 (weight average molecular weight was about 35,000)
And Chisso's low-molecular nematic liquid crystal LIXON E
N-40 (negative in dielectric anisotropy) was mixed in a weight ratio of 4: 6. Furthermore, M is added to this mixture as an optically active substance.
5 ERCK Chiral Dopant ZLI-4572
% Added. The spiral pitch was about 1 micron and the viscosity was 18 pascals. After this mixed system was bar-coated and held in the same manner as in Example 1, the haze value in each state was measured.

4 in the Grangen state immediately after the bar court
At about 0, 60 Hz and 100 V, about 60 was applied, and almost no change was observed even after 30 minutes had passed since the voltage was cut off. When an AC voltage of 5 V and 100 V was applied to the focal conic state, the state changed to the Grangen state in 0.8 seconds, and the haze value at that time was about 40.

[0024]

The liquid crystal shutter of the present invention is a liquid crystal element capable of enlarging the area without the need for a polarizing plate, and is a liquid crystal element that exhibits the effect as a shutter by applying and blocking an electric field. According to the present invention, it is possible to manufacture a liquid crystal shutter having a large area and a light weight because it is stable over time and further, this mixed liquid crystal system is suitable for forming a liquid crystal layer by using printing.

[0025]

[Brief description of drawings]

FIG. 1 is a schematic view showing a Grangen state in which the cholesteric phase can be an optically transparent state in which the helical axis is perpendicular to the substrate in the present invention.

FIG. 2 is a schematic view showing a focal conic state which can be taken by a cholesteric phase, is stable over time, and is optically light-shielding in the present invention.

FIG. 3 is a schematic diagram showing an optically transparent homeotropic state that can be obtained when a sufficiently high voltage is applied to the cholesteric liquid crystal.

FIG. 4 is a schematic diagram showing a configuration of a liquid crystal shutter of the present invention.

[Explanation of symbols]

 10 ... film 12 ... transparent electrode 14 ... liquid crystal layer 16 ... power supply 18 ... switch 20 ... incident light 22 ... transmitted light 24 ... reflected light

Claims (4)

[Claims] 1. A mixture of a low molecular weight liquid crystal and a high molecular weight liquid crystal or a mixture of a low molecular weight liquid crystal, a high molecular weight liquid crystal and an optically active substance, which is sandwiched between substrates with electrodes, at least one of which is transparent in a temperature range exhibiting a cholesteric phase. It is possible to form an optically opaque focal conic orientation state by applying a low frequency AC electric field, and maintain the orientation state in a state in which the AC electric field is blocked, and in the focal conic orientation state, a high frequency A liquid crystal shutter characterized by exhibiting an optically transparent state when an AC electric field is applied and maintaining the transparent state even when the AC electric field is blocked. 2. A polymer liquid crystal has the following structural formula: (Wherein m and n are numbers of 0 or more, X and Y represent substitution by O or NH atoms, and k and l represent positive integers). LCD shutter described. 3. The liquid crystal shutter according to claim 1, wherein the low-molecular liquid crystal has a negative dielectric anisotropy. 4. A mixture of a low-molecular liquid crystal and a high-molecular liquid crystal or a mixture of a low-molecular liquid crystal, a high-molecular liquid crystal and an optically active substance is sandwiched between substrates with electrodes, at least one of which is transparent in a temperature range exhibiting a cholesteric phase. The liquid crystal shutter according to claim 1, wherein a printing method can be applied to the formation of the liquid crystal layer.