JPH08190100A - Liquid crystal display medium and its driving method - Google Patents

Abstract

PURPOSE: To make it possible to easily control the orientation state of liquid crystal molecules after removal of an impressed voltage by forming two sheets of transparent electrode plates of materials exhibiting resistance values varying from each other. CONSTITUTION: ITO films 5 consisting essentially of indium oxide are respectively deposited as transparent electrodes on the inner surface of a pair of glass substrates 4, 4 having a thickness of about 1mm in order to impress voltage on the liquid crystal molecules. The combination of the respective resistors of the ITO electrodes 5 deposited on these two glass substrates 4, 4 consist of the material exhibiting the high resistance value on the thick high-polymer layer side and the material exhibiting the low resistance value on the thin high-polymer layer side. The volumetic resistivity value of the high polymer of such liquid crystal display medium is higher than the resistance value of the nematic liquid crystals and the dielectric constant is low and, therefore, the high polmer plays the role of a capacitor and the intensity of the electric filed is changed by a frequency. The resistance values of two transparent electrode plates are different with each other and therefore, the polarization of electric field is caused. The easy control of the so-called memory characteristic is made possible by changing the frequency of the impressed voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display medium,
In particular, the present invention relates to a liquid crystal display medium whose memory property can be controlled and a driving method thereof.

[0002]

2. Description of the Related Art Liquid crystals are located in an intermediate phase between solids and liquids, and although the substance is in the liquid state,
It exhibits optical anisotropy such as a solid crystal. Therefore, it is possible to make a liquid crystal having a thickness of several μm by utilizing the liquid state of the liquid crystal, and it is possible to change the direction of the molecular axis by a slight electric current as compared with a solid. Utilizing this property, a liquid crystal cell in which a liquid crystal is enclosed between electrode substrates to form a panel has characteristics of low voltage driving, low power consumption, passive type that does not emit light by itself, and flat type.

When the liquid crystal was first put into practical use, it was applied to the character display of a wristwatch by utilizing such characteristics of the liquid crystal, but since then, further research has progressed, and in recent years, color television and in-vehicle devices have been applied. It has been put to practical use as a display for navigation systems for automobiles and as a color panel for notebook computers.

As the field of application has expanded, it has become necessary to develop a new liquid crystal material having a performance satisfying the requirements according to the specifications of various displays. However, since it is difficult to realize all requirements with a single liquid crystal material, in reality, a mixed liquid crystal in which about 10 kinds of liquid crystal compounds are mixed is developed. Polymer dispersed liquid cryst is a composite of polymer and nematic liquid crystal.
al: Hereinafter, abbreviated as PDLC) has also been studied.

In this PDLC, nematic liquid crystals of spherical droplets are dispersed in a polymer, and the arrangement of liquid crystal molecules in the nematic liquid crystal is changed by applying a voltage, and the change in the refractive index due to the change is applied. It is a thing. In other words, in the off state when no voltage is applied, the optical axes of the liquid crystal droplets are irregularly oriented, so the refractive index of extraordinary light does not match the refractive index of the polymer, and the light is scattered to form an opaque white color. Indicates. On the other hand, in the ON state where a voltage is applied, the optical axes of the droplets are arranged in the voltage direction, and the refractive index of ordinary light substantially matches the refractive index of the polymer, so that light scattering is reduced and the liquid crystal becomes transparent.

Here, a typical structure of the PDLC is shown in FIGS. 9 and 10. FIG. 9 shows a droplet type structure, and FIG. 10 shows a reverse type structure. Further, (a) is a peeled surface of the PDLC1 cell, and (b) is a sectional view.

It can be seen from FIG. 9 that in the droplet type PDLC 1 sandwiched between a pair of glass substrates 4, the nematic liquid crystal 3 of spherical droplets is uniformly dispersed in the polymer 2.

Further, from FIG. 10, a reverse type PD
The LC1 has a nematic liquid crystal 3 in the gap between the macromolecules 2 assembled in a spherical shape.
Also has a uniform structure.

Since such a PDLC 1 does not need a polarizing plate, it can obtain a bright display, has good visual characteristics, and has flexibility, so that it can be applied to a large area of light control glass or a new display. It is attracting attention for its potential application.

[0010]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The application relating to No. 1 can be roughly classified into a property that liquid crystal molecules aligned by applying a voltage retain the alignment even after the voltage is removed, that is, a memory property and a property that does not have a memory property.

For example, Japanese Laid-Open Patent Publication No. 58-501631 relates to a PDLC1 having no memory property, but the PDLC1 having no memory property controls the alignment of liquid crystal molecules to maintain a transmissive state. To keep
It is not efficient because the voltage application must be continued.

On the other hand, the PDLC 1 having a memory property
As the publications regarding the above, Japanese Patent Publication No. 63-501512, Japanese Patent Application Laid-Open No. 1-312527, and Japanese Patent Application Laid-Open No. 3-155.
No. 525 is available. The one described in Japanese Patent Publication No. 63-501512 is a droplet type PDL.
Since it is C1, there is a problem that the memory property cannot be maintained. Further, the one described in Japanese Patent Laid-Open No. 1-312527 is neither a droplet type nor a reverse type, and has a structure in which a transparent resin is dispersed in the liquid crystal 3, and since the liquid crystal 3 is contained in a large amount, it is a resin. The effect of is small, and the memory performance can be maintained for only a few days. Furthermore, JP-A-3-
The one described in Japanese Patent No. 155525 is a droplet type using the smectic liquid crystal 3 and has a problem that the driving voltage must be large.

As described above, P having a memory property is generally used.
The DLC 1 has an efficient surface because it can maintain the alignment state even after the voltage application is removed, but there is a problem that the liquid crystal 3 needs to be heated to such an extent that phase transition occurs when the liquid crystal state is returned to the cloudy state.

Regarding the memory property of the PDLC 1 as described above, it is known that the memory property is increased or decreased by changing the kind of the polymer material. It is not known that the memory property can be controlled.

Therefore, the present invention overcomes the above-mentioned problems in the prior art and changes the frequency of the applied voltage to easily control the alignment state of the liquid crystal molecules after the applied voltage is removed. An object is to provide a display medium and a driving method thereof.

[0016]

In order to achieve the above-mentioned object, a liquid crystal display medium according to claim 1 of the present invention comprises two transparent electrode plates having electrodes and a support between the transparent electrode plates. A liquid crystal display medium comprising a composite of a polymer and a nematic liquid crystal, characterized in that the electrodes of the two transparent electrode plates are formed of materials having different resistance values.

According to a second aspect of the present invention, there is provided a method for driving a liquid crystal display medium, wherein the liquid crystal display medium according to the first aspect is driven by a low frequency voltage to increase the memory transmittance. It has a feature.

[0018]

In the liquid crystal display medium of the present invention, since the volume resistivity of the polymer is larger than that of the nematic liquid crystal and the permittivity is small, the polymer acts as a capacitor and the strength of the electric field depends on the frequency. Changes. Also, 2
Since the resistance values of the transparent electrode plates are different from each other, the electric field is biased. Therefore, even if the applied voltage is removed, an interaction to maintain the alignment occurs at the interface between the polymer and the liquid crystal, and this has the property of depending on the frequency of the electric field. The so-called memory property can be easily controlled.

Further, according to the driving method of the liquid crystal display medium of the present invention, since the liquid crystal display medium has a property of depending on the frequency of the electric field, by driving the liquid crystal display medium at a low frequency, The memory transmittance can be increased.

[0020]

The present invention will be described below with reference to the embodiments shown in the drawings.

FIG. 1 shows the structure of a liquid crystal display medium using PDLC 1 which is an embodiment of the present invention, and FIG.
As a structure of DLC1, (a) peeling surface view and (b) sectional view are shown.

The liquid crystal display medium has a thickness of about 1 mm.
On the inner surfaces of the pair of glass substrates 4 and 4, an ITO film 5 containing indium oxide as a main component is attached as a transparent electrode for applying a voltage to liquid crystal molecules, and patterned according to the purpose. . The pair of glass substrates 4 and 4 are spaced apart by several μm, that is, the so-called PDLC.
It is bonded so as to keep the cell thickness, which is the thickness of the cell. At this time, in order to obtain a constant cell thickness, fine particles having a uniform particle size such as silicon dioxide are used as the spacer 6. The spacers 6 are sealed between the glass substrates 4 and 4 in a mixed solution in which the predetermined nematic liquid crystal 3 and the polymer 2 are uniformly mixed.

Next, the PDL used in this embodiment
The structure of C1 will be described. In FIG. 2, the PDLC 1 enclosed between the pair of glass substrates 4 and 4 has a polymer layer 2 formed mainly of spherical polymers 2.
Are separated so that one of the two glass substrates 4 and 4 is thickened, and both polymer layers 2 are connected to each other by a column-shaped polymer in some places. The liquid crystal rich layer 3 mainly composed of the nematic liquid crystal 3 is sandwiched between the two.
Furthermore, the IT attached to the two glass substrates 4 and 4
Regarding the combination of the resistances of the O electrode 5, the thick polymer layer 2 side is made of a material showing a high resistance value, and the thin polymer layer 2 side is made of a material showing a low resistance value.

As described above, the structure of the PDLC 1 of this embodiment is different from that of the conventional PDLC 1 shown in FIG. 9 and FIG. 10 in that the PDLC 1 has a reverse type structure. The structure is characterized by having a liquid crystal rich layer 3, and is characterized by having a non-uniform structure in which a large number of polymer layers 2 are present on the upper side of the substrate and a large number of liquid crystal layers 3 are present on the lower side of the substrate. Such a structure results from the fact that the polymerization reaction of the polymer 2 proceeds from the direction of irradiation with ultraviolet rays, as shown in FIG. That is, when the ultraviolet rays are irradiated from above, the polymerization reaction proceeds from above, and accordingly, the liquid crystal 3 is phase-separated, is expelled to the outside of the polymer 2, and moves downward.

Therefore, the position of the liquid crystal rich layer 3 can be controlled by the irradiation direction of ultraviolet rays. For example, when ultraviolet rays are irradiated from both directions, as shown in FIG. The liquid crystal rich layer 3 is present.

Next, a method for producing the PDLC1 cell constituting the liquid crystal display medium of this embodiment will be described by showing concrete materials and numerical values.

First, a nematic liquid crystal E7 is used as the liquid crystal 3.
And 2-hydroxyethyl methacrylate (hereinafter abbreviated as HEMA) as a monomer in a weight ratio of 1: 1 and 3 g of Irgacure 184 as a polymerization initiator is mixed therein.
Add wt% to make a uniform solution. 10μ in this homogeneous solution
Two glass substrates 4 to which ITO electrodes 5 showing different resistance values are attached after mixing spacers 6 for liquid crystal of m diameter,
4 is coated on one side, and the other glass substrate with an electrode 4 is attached thereto to form a PDLC cell. At this time, the resistance values of the electrodes attached to the glass substrates 4 and 4 are, for example, 200 (Ω / □) and 50 (Ω / □).
□), 500 (Ω / □) and 200 (Ω / □), 600
The combination is such that (Ω / □) and 200 (Ω / □). The main wavelength of the PDLC cell is 365.
UV light having a wavelength of 60 mW / cm ² is irradiated from the high resistance side of the ITO electrode 5 for 10 minutes, and the opaque white PDLC 1 is obtained by phase separation of the polymer 2 generated by the polymerization reaction of the monomer and the nematic liquid crystal 3. . Therefore, ITO
The thick polymer layer 2 is formed on the side of the electrode 5 having a high resistance value, and the thin polymer layer 2 is formed on the side of the electrode 5 having a low resistance value.

The above-mentioned mixing of the solution and other processing are all performed at room temperature.

The liquid crystal display medium thus produced was observed with an electron microscope, and the electro-optical characteristics (on-memory characteristics) were measured by driving the liquid crystal display medium while changing the voltage and frequency. This result is shown in FIG.
Through FIG.

The frequency and voltage drive control at this time is changed using a high-speed power amplifier, a function generator, and a digital multimeter to ensure high accuracy, and the transmittance is changed to light with a wavelength of 632.8 nm. Measured.

FIG. 5 shows a case where the combination of the resistance values of the ITO electrode 5 is a resistance showing 200 (Ω / □) on the thick side of the polymer layer 2 and a resistance showing 50 (Ω / □) on the thin side. FIG. 6 shows the results of the voltage / light transmission characteristics. In FIG. 6, the thick side of the polymer layer 2 has a resistance of 500 (Ω / □), and the thin side has a resistance of 20.
FIG. 7 shows the results of the voltage / light transmission characteristics when the resistance is 0 (Ω / □). In FIG. 7, the thick side of the polymer layer 2 is 600 (Ω
It is the result of the voltage / light transmission characteristics when the resistance indicating (//) and the resistance on the thin side is 200 (Ω / □).

In each figure, the vertical axis shows the transmittance (%) and the horizontal axis shows the voltage (V). Also,
"●" indicates that the frequency is 50 Hz and voltage is applied,
"○" indicates a case where a voltage was applied with a frequency of 1 KHz, the solid line represents the ON characteristic showing the transmittance in the state where the voltage was applied, and the broken line represents the memory characteristic showing the transmittance after removing the applied voltage. ing.

From these figures, in any combination of resistances, the on-characteristics show a transmittance of about 1% when the voltage is 0 (V) for both the frequencies of 50 Hz and 1 KHz. After that, the transmittance increased with an increase in the voltage, and when a voltage of 100 (V) was supplied, the transmittance showed 80%, which was almost the same tendency.

On the other hand, the memory characteristic has a transmittance of about 1% when the voltage is 0 (V) when the frequency is 50 Hz, and the transmittance increases as the voltage increases to 100%.
When the voltage is (V), the transmittance is about 60%, and it can be seen that the liquid crystal display medium of this example has a memory property under this condition. On the other hand, when the frequency is 1 KHz, the transmittance is slightly increased even if the voltage is increased, and the transmittance is several% at the voltage of 100 (V),
Under this condition, it can be seen that the liquid crystal display medium of this example has no memory property.

Next, in order to examine the relationship between the frequency of the applied voltage and the memory transmittance which is the transmittance after removal of the applied voltage,
A voltage of 100 (V) was applied while changing the frequency, and the transmittance after removing the applied voltage was measured. IT in Figure 8
As a combination of the resistances of the O electrodes 5, the thick side of the polymer layer 2 is a resistance showing a resistance value of 500 (Ω / □), and the thin side is 2
The results of frequency / light transmittance characteristics when a resistance having a resistance value of 00 (Ω / □) is shown.

From this figure, the frequency of the applied voltage is 50 Hz.
When it was driven at 100 Hz and 100 Hz, the memory transmittance was about 60%, but the frequency of the applied voltage was 200 H.
When it was driven at a frequency higher than z and increased to 500 Hz and 1000 Hz, the memory transmittance was extremely low, ie, several percent, and the liquid crystal display medium had no memory property.

Therefore, when the liquid crystal display medium of this embodiment is driven at a frequency of the applied voltage of 100 Hz or less, the memory transmittance becomes large and it has a memory property, but the frequency of the applied voltage is 200 Hz or more. It can be seen that, when driven by, the memory transmittance is small and has no memory property, and this memory property depends on the frequency of the applied voltage. Therefore, in order to increase the memory transmissivity, the frequency of the applied voltage may be drive-controlled at a low frequency.

On the other hand, in order to compare with the present embodiment, the combination of the resistance values of the ITO electrode 5 is the case where the thick side and the thin side of the polymer layer 2 have the same resistance value, and the case of the present embodiment. Contrary to the example, an experiment was conducted to determine whether or not there is a frequency dependency of the memory property even when the polymer layer 2 has a low resistance value on the thick side and a high resistance value on the thin side. However, in any case, the tendency of frequency dependence was not recognized.

As described above, the memory property of the liquid crystal display medium of this embodiment depends on the frequency of the applied voltage because of the influence of the bias of the electric field and between the molecules at the interface between the liquid crystal 3 and the polymer layer 2. It is thought to be due to the interaction of. That is,
The volume resistivity of the polymer layer 2 is 10 ¹⁴ (Ω · cm) or more for a general methacrylate polymer 2, and the dielectric constant is 2
5 to 10 and ¹⁰ 10 to 10 in nematic liquid crystal E7.
¹² (Ω · cm), dielectric constant of 10 or more, polymer layer 2
Has a larger volume resistivity than the liquid crystal layer 3, the polymer layer 2 serves as a capacitor. Further, since the polymer layer 2 has a volume specific resistance larger than that of the liquid crystal layer 3 and has a small dielectric constant, the impedance changes depending on the frequency, and an electric field difference occurs at the interface between the polymer layer 2 and the liquid crystal layer 3. Further, due to the difference in the thickness of the polymer layer 2, a large electric field is generated on the thick polymer layer 2 side, and a small electric field is generated on the thin polymer layer 2 side, so that there is a bias in the electric field between the two.

Regarding the resistance value of the ITO electrode 5, the thicker side of the polymer layer 2 has a higher resistance value, and the thin polymer layer 2 has a higher resistance value.
Since the side has a low resistance value, the above-mentioned electric field difference is generated more strongly when a voltage is applied, and it is considered that this electric field difference remains even after the application.

On the other hand, considering that a voltage is applied by an AC sine wave, in the case of a low frequency of about several tens Hz,
Since the time during which the voltage is 0 (V) from the voltage applied state is long, the electric field difference at the interface between the polymer layer 2 and the liquid crystal layer 3 is likely to remain, and the alignment of the liquid crystal molecules existing near this interface is The action of the polymer 2 to be retained works sufficiently and has a memory property. On the other hand, at a high frequency of several hundreds of Hz or more, the time when the voltage is around 0 (V) becomes very short, and the liquid crystal molecules cannot fully correspond to this cycle, and therefore the action of the polymer 2 on the liquid crystal molecules is caused. It seems that it does not work well and the memory performance is reduced.

As described above, according to this embodiment, the memory property of the PDLC 1 depends on the frequency of the voltage.
By changing the frequency of the applied voltage, the alignment state of the liquid crystal molecules after removing the applied voltage can be easily controlled.

The present invention is not limited to the above embodiment, but can be modified as necessary.

For example, the liquid crystal display medium is PDLC.
1 was applied to one of the glass substrates 4 and 4, and the other glass substrate 4 was attached to the glass substrate 4, and this was prepared from the injection port or the like which was previously provided.
1 may be injected by a vacuum injection method or the like, and the injection port may be sealed with a sealing material.

[0045]

As described above, according to the liquid crystal display medium and the method of driving the same of the present invention, the memory property of the composite of the polymer and the nematic liquid crystal depends on the frequency of the voltage. By changing it, the alignment state of the liquid crystal molecules after removal of the applied voltage can be easily controlled.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of the essential parts of a liquid crystal display medium according to an embodiment of the present invention.

2A and 2B are sectional views of a PDLC used in an embodiment of the present invention.

FIG. 3 is an explanatory diagram regarding a structure in which a PDLC solution is irradiated with ultraviolet light from one direction.

FIG. 4 is an explanatory diagram regarding the structure when the PDLC solution is irradiated with ultraviolet rays from both directions.

FIG. 5: The resistance of the ITO electrode is 200 (Ω / □) and 50
Voltage / light transmission characteristics when combined to show resistance value (Ω / □)

FIG. 6 The resistance of the ITO electrode is 500 (Ω / □) and 200.
Voltage / light transmission characteristics when combined to show resistance value (Ω / □)

FIG. 7: The resistance of the ITO electrode is 600 (Ω / □) and 200
Voltage / light transmission characteristics when combined to show resistance value (Ω / □)

FIG. 8: The resistance of the ITO electrode is 500 (Ω / □) and 200
Frequency / light transmission characteristics when combined to show resistance value of (Ω / □)

9A and 9B are (a) a peeling surface view and (b) a cross-sectional view of a conventional droplet type PDLC.

FIG. 10A is a peeling side view of a conventional reverse type PDLC, and FIG.

[Explanation of symbols]

 1 PDLC (polymer dispersed liquid crystal) 2 polymer, polymer layer 3 liquid crystal, liquid crystal layer 4 glass substrate 5 ITO electrode 6 spacer

Claims (2)

[Claims] 1. A liquid crystal display medium comprising two transparent electrode plates having electrodes and a composite of a polymer and a nematic liquid crystal supported between the transparent electrode plates, said two transparent electrode plates. 2. The liquid crystal display medium, wherein the electrodes are formed of materials having different resistance values. 2. A method for driving a liquid crystal display medium, wherein the memory transmittance is increased by driving the liquid crystal display medium according to claim 1 with a low frequency voltage.