JPH0743476B2 - Liquid crystal light modulator - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light modulator using liquid crystal.

[0002]

2. Description of the Related Art A device using a ferroelectric liquid crystal has been reported in view of the shortcomings of the response of a liquid crystal light modulation device (Japanese Patent Laid-Open Publication No. Sho.
56-107216 or U.S. Pat. No. 4,367,924). The most important technical problem in this device is to align the ferroelectric liquid crystal molecules in a certain preferred direction parallel or almost parallel to the substrate surface. According to the above publication, it is reported that the above arrangement can be obtained by applying a strong magnetic field or applying shear stress. However, in general, if the liquid crystal layer is as thin as several μm, it is difficult to obtain uniformly arranged elements even if a fairly strong magnetic field is applied, and even if it is obtained, it can be said that it is not practical in the production process. The same applies to the case of shear stress, which is not practical. On the other hand, a sufficient alignment cannot be obtained by a method of rubbing a SiO oblique vapor deposition film or a polymer film with a cloth or the like in a specific direction, which has been used for the alignment control of the conventional nematic liquid crystal or cholesteric liquid crystal, There is a problem with poor contrast.

A liquid crystal display element is a typical example of the light modulation element. FIG. 1 shows a ferroelectric liquid crystal display device. A transparent electrode 3, which is generally called a Nesa film (a thin film of indium oxide and tin oxide), is formed on the two glass substrates 2, and a thin film of a polymer such as polyimide is formed on the transparent electrode 3 and a fiber such as gauze or cloth. The alignment control film 4 is formed by rubbing the liquid crystal in the rubbing direction. The two glass substrates 2 are kept at an arbitrary interval by a spacer 5, and the ferroelectric liquid crystal 1 is enclosed between them. The transparent electrode 3 is connected to an external power source 7 by a lead wire.
A polarizing plate 8 is attached to the outside of the glass substrate 2. Since FIG. 1 is a transmissive type, a light source 9 is provided. Incident light I0 emitted from the light source 9 passes through the liquid crystal element and is transmitted light I0.
Next, it enters the eyes of the observer.

FIG. 2 is a diagram for explaining the movement of the ferroelectric liquid crystal molecules 10 when a voltage is applied to the liquid crystal 1 of FIG. When an electric field E is applied to the liquid crystal 1 through the electrode 3, an array structure such as a state (A) or a state (B) is taken according to the direction of the electric field. In the state of (A), the major axis direction 101 of the liquid crystal molecule 10 coincides with the polarization axis direction 81 of the one polarizing plate 8. (B)
In this state, the liquid crystal molecules 101 move by an angle θ formed with the alignment direction 12 (rubbing direction in this case) with the long axis direction 101 separated from the polarization axis direction 81. Therefore, in the state of (A), birefringence does not occur. Polarization axis 82 of the other polarizing plate 8
Is arranged so as to be substantially orthogonal to the polarization axis 81 of the first polarizing plate 8, the intensity of the transmitted light I is weak to the observer,
It looks dark. In the state of (B), since the major axis direction 101 is away from the polarization axis direction 81 by 2θ, the transmitted light I looks bright. Thus changing the direction of the electric field, ie (+),
Display by (-). Note that θ is π / 8
The contrast becomes maximum at (22.5 °).

By the way, it is well known that when the liquid crystal has dichroism, the element structure shown in FIG. 3 has a light modulation function. In this case, usually, the polarizing plate 8 is installed outside one of the glass substrates 2. FIG. 4 is FIG.
FIG. 6 is a diagram for explaining the movements of the ferroelectric liquid crystal 10 and the dichroic dye 11 when a voltage is applied to the liquid crystal 1 of FIG. In order for the liquid crystal to have both ferroelectricity and dichroism, the ferroelectric liquid crystal molecule itself exhibits dichroism and the ferroelectric liquid crystal 1 as shown in this figure.
In some cases, the dichroic dye 11 is mixed with 0, but the latter is more general.

When an electric field E is applied to the liquid crystal 1 through the electrode 3, an array structure such as a state (A) or a state (B) is taken according to the direction of the electric field. In the state of (A), the major axis direction 101 of the liquid crystal molecules 10 matches the polarization axis direction 81 of the polarizing plate 8. In the state of (B), the liquid crystal molecules 101 move by an angle θ formed with the alignment direction 12 (rubbing direction in this case) in a state where the major axis direction 101 is away from the polarization axis direction 81. Therefore, in the state of (A), the intensity of the transmitted light I is weak to the observer and the liquid crystal having absorption in the major axis direction looks dark. In the state of (B), since the major axis direction 101 is away from the polarization axis direction 81 by 2θ, the transmitted light I looks bright. In this way, the display is performed by changing the direction of the electric field, that is, (+) and (-). Note that θ is π / 4 (45 °), and the contrast becomes maximum.

[0007]

DISCLOSURE OF THE INVENTION The present invention provides a method for controlling the alignment of ferroelectric liquid crystal molecules, which is highly practical in the production process, and as a result, a liquid crystal light modulation element having excellent responsiveness and good contrast is obtained. The purpose is to

[0008]

According to the present invention, in the liquid crystal light modulating element as described above, the temperature at which the liquid crystal layer has ferroelectricity and dichroism and becomes a smectic A phase and a cholesteric phase. It is characterized by having a region and using a rubbed polyimide film as an array control means attached to the substrate.

[0009]

When the temperature is set in the temperature range of the cholesteric phase, the rubbing method and the oblique vapor deposition method currently put to practical use are effective for controlling the alignment of liquid crystal molecules. Further, when the temperature is slowly changed to the temperature range where the uniform alignment is achieved and the ferroelectricity is exhibited, the liquid crystal has a temperature range in which the liquid crystal is in the smectic A phase. Therefore, the smectic A phase does not have to be applied when the temperature drops. It is possible to obtain a uniform layer structure in the phase state, and further, the arrangement control means is a rubbed polyimide film, and the phase changes in multiple stages of cholesteric phase → smectic A phase → smectic C ^* phase. Also in comparison with the case where PVA is used as the array control means, a uniform array is maintained as it is. If this characteristic is utilized, the array control method currently used in the production line can be directly applied to the ferroelectric liquid crystal.

Further, since the liquid crystal has dichroism and has the element structure shown in FIG. 3, the modulation characteristic becomes uniform over the entire element.
In the element having the configuration shown in FIG. 1, since the principle of light modulation is to reduce the birefringence, the contrast is wide even if the cell thickness (thickness of the liquid crystal layer) in the element is different by about 0.5 μm. If it is used as a display element, the display quality deteriorates due to remarkable color unevenness. However, in the configuration of the present invention, the change in transmitted light intensity is based on the change in light absorption due to the change in alignment of the liquid crystal. Therefore, although the difference in cell thickness may cause a slight change in contrast, the hue does not change, and an element with high display quality is provided. In addition, it does not require precise control of the cell thickness (for example, fluctuation of 0.1 μm or less), and thus is highly practical in the production process.

[0011]

[Example 1]

A polyimide-iso-indoloquinazolinedione film for controlling the alignment of liquid crystals was provided on a glass substrate provided with an indium oxide transparent electrode, and rubbed in a certain direction using gauze. A glass fiber having a diameter of 8 μm was assembled as a spacer so that the two glass substrates were parallel to each other, and the periphery was sealed except for an inlet for enclosing the liquid crystal with a sealing material to form a liquid crystal cell. Into this cell, p-octyloxybenzoic acid 4'-2 methylbutoxyphenyl ester represented by the following chemical formula was vacuum-encapsulated.

[0012]

This compound undergoes transitions as described below, and has a temperature region which becomes a ferroelectric liquid crystal phase and a temperature region which becomes a smectic A phase and a cholesteric phase.

[0014]

Here, Cr: crystalline phase, S _A : smectic A phase, S _C ^* : smectic C ^* phase (ferroelectric liquid crystal phase), Ch: cholesteric phase, I: isotropic liquid phase. By vacuum encapsulation, the temperature was raised to a temperature at which it became an isotropic liquid phase, and after encapsulation, the temperature was lowered to the temperature range at which it became a ferroelectric liquid crystal phase. Observation of the alignment state of liquid crystals and experiments on light modulation performance were conducted. .

Reference Example A liquid crystal cell prepared in the same manner as in the example was added to a ferroelectric liquid crystal compound, p-decyloxybenzylidene p'-amino-2.
-Methylbutyl cinnamate

[0017]

[0018] was vacuum-sealed, and the temperature was lowered to a temperature range where a ferroelectric liquid crystal phase was formed, and the same experiment as in the example was conducted. The above compound undergoes a phase transition as described below and does not have a temperature range where it becomes a cholesteric phase.

[0019]

Here, S _H ^* : Smectic H ^* phase is shown. When the two liquid crystal elements produced as described above were observed with a polarization microscope, the following differences were observed between them. In the case of Example: A uniform streak associated with the spiral structure is observed. It is a uniform monodomain in the microscope field. In the case of reference example: Many rice grain-like domains are seen. The streaks associated with the spiral structure are uniformly aligned within each domain, but the directions vary among the domains. The element is then placed between orthogonal polarizers,
A change in the amount of light transmitted by applying an AC rectangular wave of V, 50 HZ was measured. As a result, in the embodiment, the light amount change of the contrast of 10: 1 was obtained, whereas in the reference example, only the light amount change of 4: 1 was obtained. In addition, it was observed that the change in the amount of transmitted light when the polarity of the electric field changed was completed in about Ims in all the elements, and it was confirmed that the response was faster than in the conventional liquid crystal element. It was

As is clear from the above, in the case of the ferroelectric liquid crystal used in the embodiment having the temperature range of the cholesteric phase, the method conventionally used for controlling the alignment of the nematic liquid crystal can be directly applied, and the ferroelectric liquid crystal can be applied. It is possible to realize a state in which the organic liquid crystals are uniformly arranged. This applies not only to the liquid crystal compounds used in the examples, but also to all ferroelectric liquid crystals having a temperature range of a smectic A phase and a cholesteric phase. The same applies to mixed liquid crystals of the above compounds.

In the examples, even if the dichroic dye is mixed in the liquid crystal, the same effect as described above is observed as long as the mixture has a temperature range where it becomes a cholesteric phase.
As described in the [Summary of Invention] section, in FIG.
When the major axis direction 101 and the polarization axis direction 81 coincide with each other, the absorption axis of the dichroic dye 11 also coincides with the major axis direction 101 of the liquid crystal, that is, the polarization axis direction 81 by the so-called guest-host effect, and as a result, the light peculiar to the dye Is absorbed and the emitted light is colored (the light intensity becomes weak as a whole). On the other hand, at a position where the major axis direction 101 and the polarization axis direction 81 are separated from each other by 2θ, the absorption by the dye is small and the incident light is transmitted without being attenuated. An element having a uniform array as in the embodiment can obtain an ideal contrast. Therefore, the contrast is given as a function of the absorbance and concentration of the dichroic dye, the molecular tilt angle θ, the order parameter of the dye (representing the degree of alignment of the dye in the long axis direction of the liquid crystal), and the liquid crystal cell thickness.

In the element in which a large number of domains are seen as in the reference example, the absorption axis of the dye with respect to the polarization axis 81 varies from domain to domain, and as a result, the change in the light amount is significantly inferior to that in the example.

[0024]

According to the present invention, it is possible to obtain a liquid crystal light modulation element having good response and good contrast.

[Brief description of drawings]

FIG. 1 is a side sectional view showing an outline of a light modulation element using liquid crystal.

2A and 2B are schematic diagrams for explaining the movement of liquid crystal molecules when a voltage is applied to the device of FIG.

FIG. 3 is a side sectional view showing an outline of a light modulation element using a dichroic liquid crystal.

4A and 4B are schematic diagrams for explaining the movement of liquid crystal molecules when a voltage is applied to the device of FIG.

[Explanation of symbols]

2 ... Substrate, 3 ... Transparent electrode, 4 ... Array control film, 5 ... Spacer, 7 ... Power supply, 8 ... Polarizing plate, 9 ... Light source, 10 ... Ferroelectric liquid crystal

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Teruo Kitamura, 1-1 1-1 Sachimachi, Hitachi City, Ibaraki Prefecture Hitachi Ltd. Hitachi Research Laboratory (72) Inventor, Akio Mukai 3-chome, Hitachi City, Ibaraki Prefecture No. 1 No. 1 Hitachi Ltd., Hitachi Research Laboratory (56) References JP-A-56-107216 (JP, A) JP-A-57-84435 (JP, A)

Claims (1)

[Claims] 1. A liquid crystal layer, a plurality of substrates arranged so as to sandwich the liquid crystal layer, at least one of which is transparent and at least one polarizer is attached, and a voltage applied to the liquid crystal layer. A voltage applying means attached to the substrate so that voltage can be applied; an arrangement control means attached to the substrate so as to arrange the liquid crystal molecules adjacent to each other in a certain preferred orientation parallel or substantially parallel to the substrate; In a liquid crystal light modulation element comprising a sealing member formed between the substrates so as to surround a layer periphery, the alignment control means is a rubbed polyimide film, and the liquid crystal has ferroelectricity, A liquid crystal light modulation element having dichroism and further having a temperature range of a smectic A phase and a cholesteric phase.