TWI433913B - Liquid crystal material and liquid crystal display device - Google Patents

Description

Liquid crystal material and liquid crystal display device

The present invention relates to a liquid crystal material and a liquid crystal display device, and more particularly to a liquid crystal material and a liquid crystal display device which can improve the operation speed.

As a flat panel display device, a liquid crystal display device has various advantages. However, the response speed of the liquid crystal display device is slower than that of a plasma panel or the like.

In a general liquid crystal display device, the alignment of liquid crystal molecules is changed by an electric field to control display. The operating speed of the liquid crystal display device is from an OFF state in which no electric field is applied to an ON state in which an electric field is applied, and the liquid crystal molecules are effectively aligned to change the rising response speed to the end, and from the on state to the off state. The liquid crystal molecules are effectively determined by the downward response speed of the change to the end. It is known that the rising response speed can be improved by the shape of the applied voltage waveform or the like. It is known that the falling response speed is affected by the characteristics of the liquid crystal material. The improvement of the drop characteristics is not easy, and is considered to be the biggest weakness of the liquid crystal display device.

A host-guer liquid crystal display device in which a dichroic dye is added to a liquid crystal as a guest is known. The color of the display can be changed by the direction of the two-color pigment.

Japanese Laid-Open Patent Publication No. 2001-337351 discloses that the difference in light transmittance between the host and the guest liquid crystals at the time of opening and closing is small, and it is proposed to add a dichroic dye and nano particles to the nematic liquid crystal. The nanoparticle is composed of, for example, a carbon nanotube having a carbon number of 24 to 96. It is shown that at the time of opening, the nanoparticles disperse the arrangement of the two coloring pigments and increase the light absorption.

JP-A-2004-347618 proposes to add metal nanoparticles having a diameter of 1 nm to 100 nm to a liquid crystal base material, by switching the frequency of the applied electric field from a low frequency to a high frequency to turn on the photoelectric response, by switching from a high frequency to a low frequency. To turn off the photoelectric response of the liquid crystal display device. The frequency modulation range of the photoelectric response is, for example, 20 Hz to 100 kHz. The metal material of the nanoparticle is, for example, Ag, Pd, Au, Pt, Rh, Ru, Cu, Fe, Co, Ni, Sn, Pb.

[Patent Document 1] JP-A-2001-337351 (Patent Document 2) JP-A-2004-347618

Nanoparticles are used in a wide variety of fields to produce a variety of effects. Although the nanoparticles used in the above proposal are formed of carbon and metal, the nanoparticles can be formed of various materials. The phenomenon of nanoparticles has not been fully understood.

It is an object of the present invention to provide a novel liquid crystal material using nano particles and a liquid crystal display device using the liquid crystal material.

According to a first aspect of the present invention, there is provided a liquid crystal material comprising: a liquid crystal base material; and a metal oxide nanoparticle added to the liquid crystal base material.

According to another aspect of the present invention, there is provided a liquid crystal display device comprising: a liquid crystal display element including a pair of transparent substrates disposed oppositely, a transparent electrode formed on an opposite surface of the transparent substrate, covering the transparent electrode And an alignment film formed on the transparent substrate; and a liquid crystal material comprising a liquid crystal base material and a metal oxide nanoparticle added to the liquid crystal base material between the alignment films of the counter substrate; A driving circuit for supplying a driving signal to be connected to the transparent electrode.

When a metal oxide nanoparticle is added to a liquid crystal base material, it is understood that at least the liquid crystal falling response speed is improved.

Best form for implementing the invention

Hereinafter, the inventors will explain in accordance with experiments conducted.

Nanoparticles of metal oxides used in ultraviolet shielding paints and the like are commercially available. The inventors obtained S1 (S refers to a sample) prepared by CI: ITO, S2: Al ₂ O ₃ (alumina), S3: cobalt blue, S4: CeO ₂ , S5: Fe ₂ O ₃ , S6: Fe ₃ O ₄ , S7: MgO, S8: TiO ₂ (titanium dioxide), S9: Y ₂ O ₃ , and S1A made of Mitsubishi material: ITO, catalytically formed S8B: TiO ₂ as a metal oxide nanoparticle. The diameter of the nanoparticles is a particle size distribution of about 30 nm. There are nine kinds of materials for the nanoparticles, and since there are two kinds of nano particles of ITO and TiO ₂ , there are 11 types of nano particles. The nanoparticles of these metal oxides are not treated, but are directly mixed into the nematic liquid crystal, and dispersed by ultrasonic waves or the like to produce a liquid crystal material. These liquid crystal materials are used to produce a twisted nematic (TN) liquid crystal display cell.

1A and 1B are plan views and cross-sectional views schematically showing the structure of a liquid crystal display cell. On the opposite surfaces of the pair of transparent substrates 11A and 11B, a transparent segment electrode SEG and transparent common electrodes COM1 and COM2 are formed by indium-tin-oxide (ITO), and an alignment film is coated on the transparent substrate covering the transparent electrode. 13A, 13B, rubbing in the orthogonal direction. A pair of polarizers P1, P2 are provided on the outer surface of the transparent substrates 11A, 11B. The sheet 15 was sheeted between the two transparent substrates to adjust the cell gap to 4 μm. In the interstitial space, nematic liquid crystals each having a dielectric anisotropy Δ ε > 0 added with 0.1% by weight of the above 11 kinds of metal oxide nanoparticles were filled. Further, as a comparison, a comparative sample C0 (according to a conventional technique) without adding nanoparticles was also produced.

A drive circuit DRI is connected between the segment electrode SEG and the common electrodes COM1 and COM2. A voltage waveform was applied to each electrode of the samples to measure the response speed.

FIG. 1C shows a voltage waveform applied to the segment electrode SEG, the common electrodes COM1 and COM2, and a liquid crystal which is applied to the opposite portion of the liquid crystal layer, the segment electrode SEG and the common electrode COM2 of the counter electrode SEG and the common electrode COM1. The voltage waveform of the layer. SEG-COM1 (SEG-COM2) shows the voltage applied between the segment electrode SEG and the common electrode COM1 (COM2). The liquid crystal cell is driven at 1/2 operation and frame rate of 1 kHz.

The rise time Rise Time from 10% to 90% by voltage application, the Decay Time from 90% to 10% due to the applied voltage release, the rise time from the moment when the voltage is turned on to 90% T0 Rise Time , the falling time T0 Decay Time from the moment when the voltage is turned off to 10%.

Fig. 2 is a table 1 showing the measurement results. If the comparison sample C0 is regarded as a reference, the rise response speed (Rise Time, T0 Rise Time) may be worse. All samples S1 to S9 of the nanoparticles with added metal oxide improved the Decay Time (T0 Decay Time). In particular, the speed of the decrease in the response speed of S7 (MgO) and S9 (Y ₂ O ₃ ) is remarkable.

In the sample subjected to the measurement of Table 1, the amount of the nanoparticles added was 0.1% by weight, but next, when the amount of the metal oxide nanoparticles was changed to 0.02% by weight and 1.0% by weight, Y ₂ O _{3 was} investigated. The change in response speed caused by nanoparticle.

3A and 3B are a table 2 and a graph showing the measurement results of the addition amounts of 0.02% by weight and 1.0% by weight, which are obtained by combining the measured values when the amount is 0.1% by weight. When the amount of addition is reduced to 0.02% by weight, the effect of improving the response speed is slightly weak. Even if the amount added is increased to 1.0% by weight, the effect is not seen very much. When considering the comparative sample C0, the Decay Time (T0 Decay Time) is added by adding nanoparticles of metal oxides in the range of 0% by weight to 0.02% by weight and 0.02% by weight to 0.1% by weight. Shows a noticeable improvement. In the range of 0.1% by weight to 1.0% by weight, as shown in Fig. 3B, the characteristics are stable. Even if the amount of addition of the nanoparticle of the metal oxide is increased by 0.1% by weight or more, the change in response characteristics is small. Further, when the amount of the nanoparticles mixed in the liquid crystal is 0.02% by weight, about half of the particles are aggregated. If the total amount can be uniformly dispersed, even if the amount of addition is half, the same effect can be expected.

According to these results, when 0.02% by weight to 1.0% by weight of the metal oxide nanoparticles are added to the liquid crystal base material, it is expected to improve the drop response characteristics of the liquid crystal material. However, since it is not necessary to add an excessive amount of the metal oxide nanoparticle, it is preferable to add 0.02% by weight to 0.5% by weight of the metal oxide nanoparticle to the liquid crystal base material. The amount of the metal oxide nanoparticles to be added is preferably 0.1% by weight or less.

Although the diameter of the nanoparticle to be used is about 30 nm, the diameter of the nanoparticle of the metal oxide which can be used is about 1 nm to 100 nm. Particularly preferred is 10 nm to 50 nm.

Further, a gate pulse (5 V, 40 μsec) was applied between the counter electrodes, and the voltage holding ratio of the retention time (16.6 msec) was measured. As a comparative sample, a sample C1 containing a metal (Au) nanoparticle having a bulk property as a good conductor was prepared in addition to C0 to which metal oxide nanoparticles were not added, and was measured.

Fig. 4 is a table 3 showing the voltage holding ratios of samples S1 (ITO), S8 (TiO ₂ ), S8B (TiO ₂ ), C0 (nanoparticles), and C1 (Au). It was found that C0, S8, and S8B have a retention ratio of 99% or more. The sample C1 of the nanoparticle to which the good conductor Au was added was lowered to 4.24%. The sample S1 of the nanoparticles coated with the conductor ITO was higher than the sample C1 but dropped to 15.03%. From the viewpoint of voltage holding ratio, it is judged that it is not preferable to use a nanoparticle having a bulk as a conductor material. That is, when the voltage holding characteristics are also considered, it is preferable to add nano particles of an insulating metal oxide.

The above description is based on the limited examples, but the invention is not limited thereto. For example, considering the cobalt blue of a mixture of alumina and cobalt oxide, an improved response speed than alumina can be obtained, which suggests a better improvement than the addition of cobalt oxide-containing nanoparticles. Further, a particularly excellent improvement is observed in Y ₂ O ₃ , and it is expected that similar response speed improvement is obtained when a transition metal oxide exhibiting similar properties is used. Although the case of the TN liquid crystal is described, since the super twisted nematic (STN), host (GH), and cholesterol (Ch*) liquid crystal display devices have the same operational principle, the same effect can be expected. In addition to simple matrix electrodes, the use of segment electrodes and active matrix electrodes can also be expected to improve. In addition, various modifications, substitutions, combinations, and the like are of course understood by those skilled in the art.

11. . . Transparent substrate

12. . . Transparent electrode

13. . . Orientation film

15. . . Sheet

17. . . Liquid crystal

P. . . Polarizer

DRI. . . Drive circuit

COM. . . Common electrode

SEG. . . Segment electrode

1A, 1B, and 1C are plan views, cross-sectional views, and graphs showing waveforms of applied voltages, schematically showing the structure of the liquid crystal display cell used in the experiment.

Fig. 2 is a table 1 showing the measurement results of the response speed of the liquid crystal to which the metal oxide nanoparticles are added.

3A and 3B are a table and a graph showing the measurement results of the response speed when the addition amount of the Y ₂ O ₃ nanoparticles is changed.

Fig. 4 is a table showing voltage holding ratios of samples S1 (ITO), S8 (TiO ₂ ), S8B (TiO ₂ ), C0 (nano particles), and C1 (Au).

Claims (5)

A liquid crystal material comprising: a liquid crystal base material; and nano particles of an insulating metal oxide added to the liquid crystal base material, wherein the insulating metal oxide comprises indium-tin-oxide (ITO) or aluminum oxide ( Al ₂ O ₃ ), cobalt oxide, cerium oxide (CeO ₂ ), iron oxide (Fe ₂ O ₃ , Fe ₃ O ₄ ), magnesium oxide (MgO), titanium oxide (TiO ₂ ), Y ₂ O ₃ By. The liquid crystal material according to claim 1, wherein the nano particles are added in an amount of from 0.02% by weight to 0.5% by weight. The liquid crystal material according to claim 2, wherein the amount of the nano particles added is 0.1% by weight or less. A liquid crystal display device comprising: a liquid crystal display element including a pair of transparent substrates disposed oppositely, a transparent electrode formed on a surface opposite to the transparent substrate, covering the transparent electrode and formed on the opposite side of the transparent substrate An alignment film on the surface, a liquid crystal material according to any one of claims 1 to 3, which is sandwiched between the alignment films of the opposite substrate; and a driving circuit for supplying a driving signal to be connected to the transparent film electrode. The liquid crystal display device of claim 4, wherein the liquid crystal display device operates in a display mode of any one of a twisted nematic, a super twisted nematic, a host guest, and a cholesterol (Ch*).