JPH05100251A - Liquid crystal element - Google Patents

Abstract

PURPOSE:To obtain the liquid crystal element having excellent light resistance and weather proofness and wider visual field angle by interposing many liquid crystal-contg. particles formed by holding a liquid crystal material in porous particles consisting of a transparent material between transparent conductive films. CONSTITUTION:The liquid crystal material is injected into a beaker contg. the porous particles to immerse the porous particles therein. The liquid crystal material is impregnated into the pores of the porous particles and is confined into nearly spherical or other curved surfaces. The excess liquid crystal material is removed and only the liquid crystal-contg. particles 3 holding the liquid crystal material in the pores of the porous particles are extracted. A mixture composed of such liquid crystal-contg. particles 3 and a supporting medium 4 is applied at a required thickness on the surface of the transparent conductive film 2 of the substrate 1 previously formed with the transparent conductive film 2 by using a doctor blade and is dried; further, this laminate is laminated and put with another substrate 1 with the transparent conductive film 2 side positioned on the inner surface side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal element made of a liquid crystal material, and more particularly to a liquid crystal element which selectively scatters or transmits light in response to the presence or absence of an electric field.

[0002]

2. Description of the Related Art Conventionally, a TN system using a nematic liquid crystal as a liquid crystal element or an STN system has been put into practical use. Also, a liquid crystal device using a ferroelectric liquid crystal has been proposed. These require polarizing plates and require alignment treatment. The polarizing plate has the drawbacks of absorbing light to darken the screen and narrowing the viewing angle, and the alignment treatment limits the increase in the area of the liquid crystal element.

On the other hand, a nematic (NCAP) having a curvilinear array phase described in JP-A-58-501631 is disclosed as a liquid crystal element which does not need them and has a good contrast and a large area. : Nematic Curv
An ilinear Aligned Phase liquid crystal element (hereinafter referred to as an NCAP liquid crystal element) is known.

In the NCAP liquid crystal element described in the above-mentioned publication, in which liquid crystal droplets are dispersed in an inexpensive polymer, the liquid crystal is arranged along the curved surface of the polymer wall without applying a voltage, whereby the optical path is twisted, At the interface between the polymer and the liquid crystal droplets, light is reflected and scattered to appear milky white.

On the other hand, when a voltage is applied, the liquid crystals in the liquid crystal droplets are arranged in the direction of the electric field by an external electric field, and at this time, the ordinary refractive index no of the liquid crystal and the refractive index np of the polymer should be selected to match. As a result, light incident perpendicularly on the surface of the liquid crystal element passes through the interface between the liquid crystal and the polymer without being reflected, so that the NCAP liquid crystal element becomes transparent.

By the way, the above-mentioned liquid crystal element is disclosed in
As described in JP-A-0-252687, after mixing a liquid crystal and a latex or stirring while mixing, an emulsifier is kneaded, and this emulsion (hereinafter referred to as emulsion) is applied onto a transparent electrode substrate. After being dried, it is manufactured by a method of sandwiching it with the other transparent electrode substrate.

[0007]

However, since the stirring for forming the emulsion in the above method is performed by a mechanical means such as a colloid mill or a high speed disperser, the liquid crystal particle diameter of the emulsion after emulsification is considerably large. It is uneven. Since the liquid crystal particle size has a great influence on the performance of the NCAP liquid crystal element, it is extremely important to strictly control the particle size, but it is difficult for the above mechanical means to completely meet the demand. ..

On the other hand, in Japanese Patent Laid-Open No. 13918/1993,
In order to solve the above problems, a method of manufacturing an NCAP liquid crystal device using a special filter is disclosed.
That is, an aqueous solution of polyvinyl alcohol (hereinafter referred to as PVA) is flown to one side of the filter, and liquid crystal is injected from the opposite side of the filter through the filter at a constant pressure to form an emulsion in which liquid crystal spheres are dispersed in the aqueous PVA solution. Then, the water content of this emulsion is partially evaporated to increase the viscosity, and this is coated on a substrate and dried to form N.
A CAP liquid crystal device is manufactured.

However, in the above prior art,
Since the amount of the water dispersion medium in the PVA aqueous solution is larger than that of the liquid crystal dispersoid, it is difficult to increase the liquid crystal content in the NCAP liquid crystal element even if the water content of the emulsion is evaporated.
Therefore, there is a problem in that light cannot be sufficiently scattered without applying a voltage, and therefore high contrast cannot be obtained.

Further, in the specifications of British Patent Nos. 1442360 and 1540878, light is reflected and scattered when no voltage is applied, and liquid crystals are aligned in the direction of the electric field by an external electric field when the voltage is applied. Then, a liquid crystal element which becomes transparent is disclosed, and it is described that a glass substrate having an uneven surface is used as a means for scattering light.

However, the amount of the liquid crystal whose alignment is disturbed by the glass substrate is overwhelmingly smaller than the amount of the other liquid crystals, and therefore, in the above technique, the light cannot be sufficiently scattered, and High contrast cannot be obtained.

Furthermore, Applied Physics Letter, Vol. 40, No. 1 (1982)
(Year) discloses a liquid crystal device in which a liquid crystal is impregnated into a porous body.

However, in the above technique, the porous body for forming the liquid crystal element is a filter having a mesh structure. Liquid crystal particle size, distribution and density are NCA
Since the performance of the P liquid crystal element is greatly affected, it is extremely important to strictly control them, but it is difficult for the above-mentioned technique to completely meet the demand.

The present invention has been made to solve the above-mentioned conventional problems, and is excellent in light resistance and weather resistance,
It is intended to provide a liquid crystal element having a wider viewing angle.

[0015]

That is, according to the present invention, a transparent conductive film is provided on each of inner surfaces of a pair of substrates, at least one of which is transparent, and a liquid crystal substance is held in the pores of porous particles made of a transparent material. The liquid crystal element is characterized in that a large number of liquid crystal-containing particles are interposed between the transparent conductive films.

Further, in the present invention, the gap between the liquid crystal-containing particles and the gap between the particles and the transparent conductive film may be filled with a supporting medium having a refractive index substantially matched with that of the porous particles. preferable. At this time, it is desirable that the difference between the refractive index of the porous particles and the refractive index of the support medium is 0.02 or less, in order to avoid generation of an optical interface due to scattering.

Furthermore, it is preferable that the supporting medium also has a binder function for adhering the liquid crystal-containing particles and the electrode substrate to each other.

By filling the gaps between the liquid crystal particles and the gaps between the particles and the transparent conductive film with the supporting medium having the above-mentioned properties, a liquid crystal element excellent in optical uniformity and physical durability can be obtained. be able to. As such a supporting medium, for example, a polymer material such as latex or PVA, or an inorganic material such as frit glass can be applied.

The liquid crystal substance used in the present invention is not particularly limited, but nematic liquid crystal, cholesteric liquid crystal and smectic liquid crystal are preferable.
Among them, nematic liquid crystal exhibiting positive dielectric anisotropy is particularly preferable, and for example, ordinary refractive index is no = 1.4 to 1.5.
It is possible to appropriately select a liquid crystal substance that matches the refractive index of the porous particles and does not cause distortion of the image macroscopically from the nematic liquid crystal in the range.

The diameter of the liquid crystal substance in the produced liquid crystal element depends on the pore diameter of the porous particles. Therefore, the particle size and pore size distribution are very narrow, and the pore sizes are almost the same,
In addition, the strict control is achieved by selecting porous particles that have a chemical property that retains the liquid crystal substance on the inner surface of the pores and that has a refractive index that matches the refractive index of the liquid crystal substance used. Provided is a liquid crystal device having the above described liquid crystal-containing particle size.

As such porous particles of the present invention, the particle diameters are substantially uniform, and, for example, the refractive index n = 1.49.
A porous glass powder having No. 7 or a transparent body such as shirasu balloon can be used. Further, as the pore shape of the porous particles for holding the liquid crystal substance, either a through hole or a depressed hole can be applied.

The smaller the pore size of the porous particles, the larger the applied voltage required to align the liquid crystal substance, but the liquid crystal substance is uniformly aligned in the direction of the electric field, and the light incident perpendicularly to the liquid crystal element surface is not affected. It is preferable because it passes through the liquid crystal and the polymer without being reflected at the interface to form a more transparent state, and the response time is shortened accordingly. In the present invention, the particle size of the porous particles is 0.01 to 50 μm, and the pore size is 0.01 to 10 μm.
It is preferable to use the above range. In particular, it is desirable to match the refractive indexes of the porous particles, the liquid crystal substance and the support medium in the range of 0.1 to 10 μm in pore size where scattering occurs.

The thickness of the mixture of the liquid crystal-containing particles and the supporting medium, that is, the thickness between the inner surfaces of the opposing substrates of the liquid crystal element is somewhat different depending on the particle size of the porous particles, but is about 10
The range of ˜50 μm is preferred. In addition, it is preferable to increase the volume ratio of the liquid crystal-containing particles in the above mixture in order to manufacture a liquid crystal element that is strictly controlled. Therefore, it is desirable that the particle diameter of the porous particles be as small as possible.

[0024]

In the present invention, since the liquid crystal substance is held in the pores of the porous particles, it is possible to obtain liquid crystal particles having a desired and uniform diameter. In addition, since the porous particles are an inorganic material having excellent light resistance and moisture resistance such as porous glass powder, the liquid crystal element of the present invention using the same cannot be adversely affected by incident light, and It also has excellent stability in humid environments. Therefore, continuous use over a long period of time is possible.

Further, the liquid crystal device of the present invention made of the above-mentioned porous particles can be driven at a lower voltage,
In addition, since the transmittance-voltage curve becomes steep, it is effective for dot matrix driving.

Furthermore, the liquid crystal device of the present invention made of the above-mentioned porous particles can obtain a wider viewing angle under the application of an electric field.

[0027]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic view of a liquid crystal element manufactured according to the present invention, and FIG. 2 is a conceptual view showing how the pores of porous particles are impregnated with a liquid crystal substance.

In FIG. 2, first, the classified porous particles (5) having a uniform pore size are placed in a beaker (7) (FIG. 2a). Subsequently, the liquid crystal substance (6) is injected into the beaker (7) containing the porous particles (5) to immerse the porous particles (5) (FIG. 2b). At that time, a method of stirring or vacuum defoaming is used if necessary. Thereby, the liquid crystal substance (6) is impregnated into the pores of the porous particles (5) and is confined to a substantially spherical or other curved surface.

Excess liquid crystal substance (6) is removed, and only liquid crystal-containing particles (3) having the liquid crystal substance (6) held in the pores of the porous particles are extracted (FIG. 2c). Furthermore, a supporting medium (4) having a refractive index substantially matched with the refractive index of the porous particles (5) is added to the liquid crystal-containing particles (3) (FIG. 2).
d), stirring is performed so that the liquid crystal-containing particles (3) and the supporting medium (4) are sufficiently mixed and dispersed (FIG. 2e).

Then, the transparent conductive film (2) of the substrate (1) on which the transparent conductive film (2) was previously formed by using a mixture of the liquid crystal-containing particles (3) and the supporting medium (4) with a doctor blade. On the other surface (1) with the transparent conductive film (2) side as the inner surface side.
The liquid crystal element shown in FIG. 1 is obtained by sandwiching and sandwiching.

Example 1 A liquid crystal element was produced using a porous glass powder (made by Ise Chemical Co., Ltd.) having a pore size of 1.0 μm and a particle size of 10 μm and a refractive index n = 1.497.

First, the refractive index of the porous glass powder is no =
1.497 nematic liquid crystal cyanobiphenyl E201
It was immersed in (made by BDH), stirred for 1 hour with a magnetic stirrer, and then left for 24 hours. Then, the supernatant liquid crystal substance was removed, and only the liquid crystal-containing particles in which the liquid crystal substance was held in the pores of the porous glass powder were extracted.

The obtained liquid crystal-containing particles contain, as a supporting medium, 30% by weight of latex particles having a refractive index np = 1.484 substantially matched with the refractive index of the above-mentioned porous glass powder. 212 (manufactured by Asahi Denka Kogyo) was added to the porous glass powder in a weight ratio of 1/1, and the mixture was stirred for 15 minutes.

The mixture of the liquid crystal-containing particles and the supporting medium was mixed with indium tin oxide (I) using a doctor blade.
A (TO) film was coated on the ITO film surface of a 175 μm-thick polyethylene terephthalate (PET) film previously coated and dried. The thickness after coating and drying was about 20 μm. After the mixture was dried, the other PET film was attached so that the ITO film side was in contact with the dried mixture to obtain a liquid crystal element.

The produced mixture between the ITO films of the liquid crystal element was in a state close to the closest packing in which about two layers of liquid crystal-containing particles were formed in the thickness direction. The supporting medium also filled the gaps between the liquid crystal-containing particles and between the particles and the ITO film.

A voltage was applied between the opposing ITO films of the produced liquid crystal element, and the parallel transmittance at that time was measured using a haze meter (manufactured by Suga Test Instruments Co., Ltd.). The relationship between the parallel transmittance and the applied voltage is shown by the curve shown in FIG.

(Example 2) A liquid crystal device was prepared by using a porous glass powder having a pore size of 1.0 μm and a particle size of 10 μm.

The porous glass powder was dipped in nematic liquid crystal cyanobiphenyl E201, and stirred with a magnetic stirrer for 1 hour.
After stirring for an hour, it was left in a vacuum chamber at 0.1 Torr or less for 1 hour. Then, the porous glass powder immersed in the liquid crystal substance was taken out from the vacuum chamber, and a liquid crystal element was manufactured by the same method as in Example 1.

(Comparative Example 1) A method described in JP-A-60-252687, that is, a latex and a liquid crystal substance are mixed by stirring to form an emulsion, and an ITO film is previously formed as a transparent conductive film. PET film I
The emulsion is applied and dried using a doctor plate on the surface of the TO film, and sandwiched with another PET film with an ITO film to obtain an NCAP liquid crystal element having an average particle size of about 1.0 μm contained in the emulsion. It was made. The thickness of the device was about 20 μm.

The opposing I of the produced NCAP liquid crystal element
A voltage was applied between the TO films, and the parallel transmittance at that time was measured using the haze meter described above. The relationship between the parallel transmittance and the applied voltage is shown in FIG.
It shows in (b).

As is clear from FIG. 3, the saturation voltage Vsat
Is almost equal in the curves (a) and (b), the threshold voltage Vth is higher in the curve (a). That is, the liquid crystal device according to the present invention in which the porous glass powder is used as a matrix exhibits a good steepness γ = Vsat / Vth as compared with the conventional NCAP liquid crystal device, and is suitable for a display with higher density.

Next, the transmittances of the liquid crystal device obtained by using the porous glass powder of the present invention and the NCAP liquid crystal device of the comparative example were measured. This measurement was carried out by using a liquid crystal evaluation device (manufactured by Otsuka Electronics Co., Ltd.) with reference to the direction perpendicular to the liquid crystal element surface, and the relationship between the incident angle on the liquid crystal element surface and the transmittance. The results are shown in FIG. 4, respectively.

As is clear from FIG. 4, the liquid crystal element (solid line) of the present invention using porous glass powder as a matrix has N
It can be seen that it has a wider viewing angle when an electric field is applied, as compared with the conventional liquid crystal element using CAP (broken line).

Although two transparent substrates have been described above, it is not always necessary that both substrates are transparent.

[0046]

According to the present invention, since the liquid crystal substance is held in the pores of the porous particles, it is possible to obtain liquid crystal-containing particles having a uniform diameter. In addition, since the porous particles are an inorganic material having excellent light resistance and moisture resistance, the liquid crystal element of the present invention using the porous particles as liquid crystal particles cannot be adversely affected by incident light, and has a high humidity environment. It also has excellent stability underneath. Therefore, continuous use over a long period of time is possible.

Further, as is clear from the examples, it is possible to operate at a lower voltage than the liquid crystal element obtained by the conventional method, a steep relationship between applied voltage and transmittance can be obtained, and a wider viewing angle can be obtained. Is obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a liquid crystal element manufactured according to the present invention.

2 (a), (b), (c), (d) and (e) are views conceptually showing a procedure of impregnating a liquid crystal substance into porous particles according to the present invention.

FIG. 3 is a graph showing the relationship between the applied voltage and the parallel transmittance of the liquid crystal element of the present invention and the conventional liquid crystal element.

FIG. 4 is a graph comparing viewing angles of a liquid crystal device of the present invention and a conventional liquid crystal device.

[Explanation of symbols]

 (1) Substrate (2) Transparent conductive film (3) Liquid crystal containing particles (4) Support medium (5) Porous particles (6) Liquid crystal substance (7) Beaker

Claims (4)

[Claims] 1. A plurality of liquid crystal-containing particles in which a transparent conductive film is disposed on the inner side surfaces of a pair of substrates, at least one of which is transparent, and a liquid crystal substance is held in the pores of the porous particles. A liquid crystal element characterized by being interposed between 2. A gap between the large number of liquid crystal-containing particles and a gap between the particles and the transparent conductive film are filled with a supporting medium having a refractive index substantially equal to that of the porous particles. Liquid crystal particles according to. 3. The liquid crystal device according to claim 1, wherein the porous particles are made of porous glass powder. 4. The liquid crystal device according to claim 1, wherein the porous particles are shirasu balloons.