JP2000347223A - Liquid crystal dimming body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal dimming body which can be easily formed into a large area and which has excellent controlling performance for the viewing field and transparency when voltage is applied. SOLUTION: The liquid crystal dimming body is produced by forming a transparent conductive film on each inner face of a pair of transparent substrates and holding a medium containing a liquid crystal material and a dichroic pigment which is oriented according to the orientation of the liquid crystal between the transparent conductive films. In body, the double refractive index (Δn) of the liquid crystal material is <=0.15, and the absorbance (A//) in the major axial direction of the molecule of the dichroic pigment and the absorbance (A⊥) in the minor axial direction are in the relation of 1.0>=[(A//-A⊥)/(A//+2A⊥)]>=0.75.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal light adjuster,
More specifically, the present invention relates to a liquid crystal light control device that can be used as a screen for blocking a visual field in a window or a partition of an automobile or a building, or as a curtain for controlling lighting.

[0002]

2. Description of the Related Art In recent years, the need to adjust the transmittance of glass has been increasing in many fields using glass.
In particular, in applications such as construction or automobiles, it is desired to arbitrarily adjust the transmittance of a window glass from the viewpoint of privacy protection and lighting control, and dimming glass and partitions for realizing this are attracting attention. Have been.

[0003] In order to meet this demand, excellent durability,
As a liquid crystal light modulating body having a light modulating function that can easily have a large area, for example, a nematic (NCAP: Nematic) having a curved arrangement phase disclosed in Japanese Patent Publication No. 58-501631 is disclosed.
Curvilinear Aligned Phase) LCD dimmer, Tokuyo Sho 6
A liquid crystal light adjuster obtained by a phase separation method described in Japanese Patent Application Laid-Open No. 0-502128 is known. These liquid crystal light adjusters operate based on the following principle.

That is, the liquid crystal light modulator disclosed in the above-mentioned publication in which small droplets of a liquid crystal substance are dispersed in an inexpensive polymer does not have a voltage applied thereto (hereinafter referred to as “when no voltage is applied”). By arranging the liquid crystal along the curved surface, the optical path is twisted, or light is reflected and scattered at the interface between the polymer and the liquid crystal droplet, and the liquid crystal looks milky.

On the other hand, when a voltage is applied (hereinafter referred to as “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 the ordinary refractive index (no) of the liquid crystal at this time.
And the refractive index (np) of the polymer are selected so as to match, so that the light perpendicularly incident on the liquid crystal dimmer surface passes without reflection at the interface between the liquid crystal and the polymer, so that the liquid crystal dimmer is transparent. Becomes

As described above, since the degree of scattering of the incident light is adjusted by the applied voltage, the liquid crystal light adjuster exhibits a milky white color when no voltage is applied. Therefore, when the liquid crystal light adjuster is used, for example, as a window of a building or a window of an automobile, its design may be significantly impaired.

Therefore, a technique for coloring a liquid crystal light adjuster has attracted attention. As one means for solving this problem, for example, JP-A-3-66162 discloses a method in which a dichroic dye is added to a liquid crystal material used for a liquid crystal light adjuster to absorb incident light when no voltage is applied. A method for increasing is disclosed.

As described above, Japanese Patent Application Laid-Open No. 58-5016
No. 31, JP-A-60-502128 and JP-A-3-66162 disclose a liquid crystal light adjuster, in which no light is scattered and absorbed when no voltage is applied, so that the visual field is blocked. Get dark. On the other hand, when a voltage is applied, the liquid crystal light adjuster becomes transparent, so that a transmitted image is clearly recognized and a visual field can be secured as in a normal transparent window.

[0009]

A dimmer used as a window of an automobile or a window or a partition of a building or the like has a high transparency when it is transparent, as in the case of a conventional glass plate. When a field of view is required to be ensured and is opaque, the field of view is sufficiently blocked to ensure privacy, and there is a strong demand to block lighting.

[0010] However, if the transmittance when no voltage is applied is reduced in order to enhance the visual field control performance, the transmittance when a voltage is applied also decreases. In addition, the haze ratio at the time of applying a voltage is increased, and the transparency is reduced. On the other hand, if the transmittance at the time of applying a voltage is increased, the transmittance at the time of applying no voltage is also increased, and sufficient visual field control ability cannot be obtained. For this reason, in the liquid crystal light adjuster according to the prior art, a liquid crystal light adjuster having a change in visible light transmittance (hereinafter referred to as “ΔTvis”) of 30% or more and a haze ratio of 10% or less is obtained. I didn't. Here, the haze ratio indicates a ratio of scattered light to total transmitted light.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and provides a liquid crystal light modulator which is easy to increase in area, and has excellent visual field control performance and transparency when voltage is applied. With the goal.

[0012]

That is, according to the present invention, a transparent conductive film is provided on each of opposing surfaces of a pair of transparent substrates,
A liquid crystal light adjuster in which a liquid crystal material and a medium holding therein a dichroic dye oriented in accordance with the orientation of the liquid crystal material are interposed between the transparent conductive films, wherein the birefringence of the liquid crystal material is (Hereinafter referred to as “Δn”) is 0.15 or less, and the absorbance of the dichroic dye in the molecular long axis direction (hereinafter “A //”)
) And the absorbance in the molecular minor axis direction (hereinafter referred to as “A⊥”) satisfy the following expression (1). 1.0 ≧ [(A // − A⊥) / (A // + 2A⊥)] ≧ 0.75 (1)

In the present invention, the method of adjusting the performance of the liquid crystal light adjuster can be performed by selecting several factors constituting the liquid crystal light adjuster. That is,
The following five points are the most effective methods for increasing ΔTg. 1) Increase the order parameter (hereinafter referred to as “S”) of the dichroic dye 2) Increase the Δn of the liquid crystal material 3) Decrease the droplet (capsule diameter) (hereinafter referred to as “D”) of the liquid crystal material 4) Increase the ratio of the liquid crystal material to the medium (polymer) (liquid crystal ratio). 5) Increase the distance (thickness) (t) between the transparent conductive films.

Here, S is represented by the following equation (2), and indicates the parallelism of the dye molecule absorption axis with respect to the alignment direction of the liquid crystal molecules. Practically, it is an amount that controls the display contrast of the liquid crystal element. As S approaches 1, a brighter and clearer display becomes possible. S = [(A // − A⊥) / (A // + 2A⊥)] (2)

The above methods 3) and 5) require application of a larger voltage, so that the same applied voltage lowers the transmittance when the voltage is applied and increases the haze ratio.

In the above method 4), when the liquid crystal ratio is high, the capsules are bonded to each other, and when D is too large, a point-like defect is caused and the quality is deteriorated.

Further, in the method 2), the larger the value of Δn, the higher the haze ratio when a voltage is applied.

On the other hand, the method 1) can increase ΔTvis without a decrease in transmittance due to a decrease in transmittance at an applied voltage or a rise in haze ratio.

However, when Δn exceeds 0.15, the difference between the extraordinary refractive index (ne) of the liquid crystal and the refractive index of the polymer increases, and the haze ratio increases when a voltage is applied. Also, △
If n exceeds 0.15, a haze ratio of 10% or less cannot be secured. Further, when S is smaller than 0.75, A // also decreases with a decrease in S, which decreases the light absorption performance of the dye, and thus ΔTvis when no voltage is applied increases. As a result, ΔTvis does not exceed 29%. On the other hand, by using a dichroic dye having S of 0.75 or more and using a liquid crystal material having Δn of 0.15 or less as in the present invention, ΔTvis is 30% or more and
It is possible to secure a haze ratio of 10% or less.

Assuming that the ordinary light refractive index of the liquid crystal material is no and the extraordinary light refractive index is ne, Δn is known to be represented by the following equation (3). Δn = ne−no (3)

The liquid crystal material used in the present invention is not particularly limited, but is preferably a nematic liquid crystal, a cholesteric liquid crystal, or a smectic liquid crystal. Among them, a nematic liquid crystal is preferable, and a nematic liquid crystal having a positive dielectric anisotropy is particularly preferable.

The dichroic dyes include anthraquinone dyes and azo dyes.

The medium (polymer) holding the liquid crystal material is a material selected so that the refractive index (n) of the medium and the ordinary light refractive index (no) of the liquid crystal material are matched. What is necessary is just to hold | maintain a partition in volume, and it can be used regardless of the kind of an inorganic or organic. Among them, it is preferable to use a resin that can easily adjust the refractive index and manufacture a large-area liquid crystal light adjuster. In particular, JP-A-60-2526
Latex described in JP-A-87-87 is preferably a material, and it is possible to provide a liquid crystal light modulator excellent in adhesion to a substrate, optical uniformity, and physical durability.

Further, as the substrate with a transparent conductive film used in the present invention, a glass plate or a plastic film having an indium tin oxide (ITO) film or a tin oxide (SnO ₂ ) film formed on the surface is used. can do.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.

The liquid crystal light adjuster of the present invention is produced, for example, by the following method.

First, an emulsion is prepared by mixing a liquid crystal substance and an aqueous phase, and the emulsion is added to latex, or an emulsion is prepared by directly mixing the liquid crystal substance and latex. When forming an emulsion, it is preferable to add a surfactant in order to form stable liquid crystal particles. Mixing is performed by various mixers such as a blender and a colloid mill. Next, a crosslinking agent is added to crosslink the latex to form a medium, and then the medium is coated on a transparent substrate having a transparent conductive film formed thereon by a knife blade or other suitable means, and dried. Then, it is bonded to another transparent substrate with a transparent conductive film to obtain a liquid crystal light adjuster.

Specific examples of the present invention are shown below.

Example 1 A dichroic dye G-241 was applied to a liquid crystal ZLI-4171 (manufactured by Merck, Δn = 0.097).
1% by weight (manufactured by Japan Photochromic Research Laboratories, S = 0.80)
And surfactant IGEPAL CO-610 (manufactured by GAF)
And 0.5% by weight of Neolez containing 40% by weight of latex particles so that the liquid crystal ratio becomes 0.6.
The mixture was added to R-967 (manufactured by Zeneca) and stirred at 7000 rpm for 10 minutes using a homogenizer to obtain an emulsion. The average capsule diameter of the emulsion was 4 μm. Next, the crosslinking agent CX-100 (manufactured by Zeneca) was added at a ratio of 3% by weight with respect to R-967 while slowly mixing. The mixture was applied on a polyethylene terephthalate (PET) film previously coated with an indium tin oxide (ITO) film using a doctor blade and dried. After drying, another sheet of PET film with an ITO film was laminated to obtain a liquid crystal light modulator. The thickness was 25 μm.

A voltage of sine wave / 100 V / 50 Hz was applied to the liquid crystal light modulator thus obtained, and its performance was measured. As a result, ΔTvis was 30% and the haze ratio was 8%. Accordingly, a liquid crystal light modulator having sufficient visual field control performance and sufficient transparency when voltage is applied was obtained.

Comparative Example 1 A dichroic dye G-289 was added to a liquid crystal ZLI-4171 (manufactured by Merck, Δn = 0.097).
1% by weight (manufactured by Japan Photochromic Laboratories, S = 0.73)
And surfactant IGEPAL CO-610 (manufactured by GAF)
And 0.5% by weight of Neolez containing 40% by weight of latex particles so that the liquid crystal ratio becomes 0.6.
The mixture was added to R-967 (manufactured by Zeneca) and stirred at 7000 rpm for 10 minutes using a homogenizer to obtain an emulsion. The average capsule diameter of the emulsion was 4 μm. Next, the crosslinking agent CX-100 (manufactured by Zeneca) was added at a ratio of 3% by weight with respect to R-967 while slowly mixing. The mixture was applied on a polyethylene terephthalate (PET) film previously coated with an indium tin oxide (ITO) film using a doctor blade and dried. After drying, another sheet of PET film with an ITO film was laminated to obtain a liquid crystal light modulator. The thickness was 25 μm.

As a result of measuring the performance of the thus-obtained liquid crystal light adjuster, ΔTvis was 25%, and the haze ratio was 8%.
Met. Since S <0.75, sufficient transparency was obtained when voltage was applied, but the visual field control performance was insufficient.

Comparative Example 2 A dichroic dye G-241 was added to a liquid crystal ZLI-3219 (manufactured by Merck, Δn = 0.205).
1% by weight (manufactured by Japan Photochromic Research Laboratories, S = 0.80)
And surfactant IGEPAL CO-610 (manufactured by GAF)
And 0.5% by weight of Neolez containing 40% by weight of latex particles so that the liquid crystal ratio becomes 0.6.
The mixture was added to R-967 (manufactured by Zeneca) and stirred at 7000 rpm for 10 minutes using a homogenizer to obtain an emulsion. The average capsule diameter of the emulsion was 4 μm. Next, the crosslinking agent CX-100 (manufactured by Zeneca) was added at a ratio of 3% by weight with respect to R-967 while slowly mixing. The mixture was applied on a polyethylene terephthalate (PET) film previously coated with an indium tin oxide (ITO) film using a doctor blade and dried. After drying, another sheet of PET film with an ITO film was laminated to obtain a liquid crystal light modulator. The thickness was 20 μm.

As a result of measuring the performance of the thus-obtained liquid crystal light adjuster, ΔTvis was 30%, and the haze ratio was 16%.
%Met. Since Δn> 0.15, sufficient visual field control performance was obtained, but sufficient transparency was not obtained when voltage was applied.

[0035]

As described above in detail, in the liquid crystal light adjuster of the present invention, the Δn of the liquid crystal material is 0.15 or less, and the absorbance (A / A / /) And the absorbance (A⊥) in the molecular minor axis direction are 1.0 [(A // − A −) /
(A // + 2A⊥)] ≧ 0.75, a liquid crystal light adjuster configured to satisfy the relational expression of ΔTvis of 30% or more and a haze ratio of 10% or less. As a result, it is possible to easily and inexpensively obtain a large-area liquid crystal light modulator excellent in view control performance and transparency when voltage is applied.

The liquid crystal light modulator of the present invention can be used, for example, in an automobile window,
When used as a window in a building, a screen for blocking a view in a partition, a curtain for lighting control, or the like, a liquid crystal light control glass having a laminated glass function can be used.

Claims (1)

[Claims] 1. A medium comprising a transparent conductive film disposed on opposing surfaces of a pair of transparent substrates and holding therein a liquid crystal material and a dichroic dye oriented in accordance with the orientation of the liquid crystal material. A liquid crystal light modulator interposed between transparent conductive films, wherein the liquid crystal material has a birefringence (Δn) of 0.15 or less;
A liquid crystal light modulator characterized in that the absorbance of the dichroic dye in the molecular major axis direction (A //) and the absorbance in the molecular minor axis direction (A⊥) have the following relationship: 1.0 ≧ [(A // − A⊥) / (A // + 2A⊥)] ≧ 0.
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