JP3049875B2 - Liquid crystal element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal device made of a liquid crystal material, and more particularly to a liquid crystal device having excellent light transmittance control performance.

[0002]

2. Description of the Related Art In buildings and automobiles, the inflow of solar energy from windows greatly affects the air conditioning load in a room. Therefore, it is important to provide a window with a dimming function from the viewpoint of energy saving. Is coming.

[0003] Practically desired dimming ranges include at least a transparent glass currently used as a window glass,
It is considered necessary to be able to select an optical characteristic value with the heat ray absorbing glass for the purpose of absorbing sunlight energy, and this dimming range is a variation range of transmittance of sunlight energy (hereinafter abbreviated as “ΔT”). It is preferably at least 15%.

Conventionally, an electrochromic device has been known as one of the devices having such a dimming function. The electrochromic device uses a material that changes the optical spectrum due to an electrochemical redox reaction, such as tungsten oxide and Prussian blue, to adjust the transparency and control the amount of transmitted sunlight energy by absorbing light. I have.

[0005] However, since the electrochromic element is a current-driven type, the response speed is remarkably reduced due to a large voltage drop when the area is increased. Deterioration is unavoidable, and a large-area element having practically sufficient durability has not been realized.

[0006] Therefore, as a substitute for such a current-driven electrochromic element, a voltage-driven dimming element has attracted attention. As a liquid crystal element having excellent durability and a dimming function capable of easily increasing the area, a nematic (NCAP: Nematic Curvilinear Ali) having a curvilinear array phase described in JP-A-58-501631 is disclosed.
gned Phase) liquid crystal element, and JP-A-60-502128
There is known a liquid crystal element obtained by a phase separation method described in Japanese Patent Application Laid-Open No. H10-26095. These elements operate based on the following principle.

In a liquid crystal device in which small droplets of a liquid crystal substance are dispersed in an inexpensive polymer, when no voltage is applied, the liquid crystal is arranged along the curved surface of the polymer wall so that the optical path is twisted or the polymer and the liquid crystal are twisted. Light is reflected and scattered at the interface with the droplet, and looks 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. At this time, the ordinary refractive index no of the liquid crystal and the refractive index np of the polymer must be selected so as to match. As a result, light that is perpendicularly incident on the liquid crystal element surface passes through the interface between the liquid crystal and the polymer without being reflected, so that the liquid crystal element is transparent.

[0009]

However, although the visibility of the liquid crystal element can be adjusted in the liquid crystal element, most of the light incident on the liquid crystal element when no voltage is applied is on the side opposite to the incident side (hereinafter referred to as “the light incident side”). Since the light was scattered forward, the amount of transmitted solar energy hardly decreased compared to when voltage was applied, and only a few% ΔT was obtained.

On the other hand, in order to solve the above problem, a method of adding a polychromatic dye to a liquid crystal material used in the liquid crystal element to increase light absorption when no voltage is applied is disclosed in Japanese Patent Laid-Open Publication No. Hei. No. 66162. Although the device obtained by this method has a large ΔT, it is used for outdoor applications such as buildings or automobiles that are exposed to sunlight for a long period of time because the polychromatic dye is inherently deteriorated by light and heat. I couldn't do that.

The present invention has been made to solve the conventional problems, and provides a liquid crystal element which has excellent durability, is easy to increase in area, and has a dimming performance of ΔT of 15% or more. The purpose is to do.

[0012]

That is, the present invention provides a liquid crystal device in which a medium having a liquid crystal material held in a gap is interposed between a pair of substrates having a transparent conductive film, and wherein the liquid crystal material has an average refractive index na. , The refractive index nb of the medium, the total surface area S [μm ⁻¹ ] (hereinafter abbreviated as “total surface area S”) per unit volume, and the distance t [μm] between the transparent conductive films.
(Hereinafter sometimes simply referred to as “thickness”)
A liquid crystal element satisfying the following expression.

The liquid crystal material is held in the voids, and the above formula (1) holds whether the voids are independent of each other or some or all are connected in the medium. Hereinafter, the gap is referred to as a capsule for convenience.

| Na−nb | × S × t ≧ 4.2 (1) By the way, it is known that the average refractive index na of the liquid crystal material is represented by the following equation (2).

Na = (2 × no + ne) / 3 (2) In the above equation, no represents the ordinary light refractive index of the liquid crystal material, and ne represents the extraordinary light refractive index of the liquid crystal material.

FIG. 1 is a schematic view of a liquid crystal device according to the present invention. In FIG. 1, reference numeral 1 denotes a substrate, 2 denotes a transparent conductive film, 3 denotes a liquid crystal material, and 4 denotes a medium. The total surface area S is theoretically expressed by the following equation (3) using the parameters V and D.

S = 6 × V / D (3) In the above equation, V is the ratio of the volume of the liquid crystal substance to the total volume of the liquid crystal substance and the medium (hereinafter abbreviated as “liquid crystal ratio”), and D is the average diameter of the capsule. (Hereinafter abbreviated as “capsule diameter”). Here, the capsules can be considered as independent capsules even when some of them are connected. Therefore, the D is obtained by converting the volume of each independent capsule into a sphere having the same volume as that of the capsule. It represents the average value of the diameter of a sphere in the case.

The inventor of the present invention varied the parameters of the liquid crystal element and examined the relationship with ΔT in detail. As a result, it was found that ΔT was represented by the following equation (4). That is, by suitably combining a plurality of parameters, it becomes possible to scatter more forward incident light to the incident side (hereinafter abbreviated as “rearward”). As a result, the amount of transmitted light when no voltage is applied is reduced. The light transmittance control performance was significantly enhanced.

ΔT = 3.57 × | na−nb | × S × t (4) If the total surface area S is fixed, the extraordinary light refractive index n of the liquid crystal material
e and the difference between the ordinary refractive index no, that is, the birefringence Δn (= n
By making e-no) larger, the average refractive index na becomes larger and ΔT increases.

If Δn is fixed, ΔT increases by increasing the total surface area S or increasing the thickness. To increase the value of S, the capsule diameter may be reduced or the liquid crystal ratio may be increased.

In order to make ΔT 15% or more, the above (4)
The parameters of the liquid crystal element may be combined so that the right side of the expression is 15% or more, that is, the expression (1) is satisfied.

In order to satisfy the expression (1), it is preferable that the parameters of the liquid crystal element be in the following ranges.

The diameter of the capsule greatly affects the scattering state of the liquid crystal element. When the capsule diameter is less than 0.5 μm, the transmittance on the long wavelength side in the visible light region increases, and the ability to block the field of view when no voltage is applied decreases. On the other hand, when the capsule diameter exceeds 3 μm, the total surface area S of the capsule decreases and the amount of transmitted light increases. Therefore, the capsule diameter is 0.5-3μ
m is preferably in the range. More preferably,
It is in the range of 0.8 to 2 μm.

On the other hand, when the capsule diameter is fixed, the higher the liquid crystal ratio, the larger the total surface area S of the capsule. Therefore, since the amount of backscattered light increases, the control width of the transmitted light increases. However, when the liquid crystal ratio becomes very high (at most 1), it becomes difficult to form a gap for holding the liquid crystal substance, and the degree of scattering of incident light is reduced, so that the control width of transmitted light is reduced. For these reasons, the liquid crystal ratio is preferably in the range of 0.5 to 0.9.

Further, when the distance between the substrates with the transparent conductive film becomes short, the amount of the liquid crystal substance and the amount of the capsule to be sandwiched also decrease, so that the total surface area S of the capsule decreases. Therefore, the control width of the transmitted light decreases. On the other hand, as the distance increases, the control width of the transmitted light increases. However, a proportionally higher applied voltage is required and power consumption is increased. Therefore, it is not preferable to make the distance too long. Therefore, the distance between the substrates with a transparent conductive film is preferably in the range of 10 to 40 μm.

The liquid crystal substance 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 particularly preferable.

As a medium for holding the liquid crystal material so as to increase ΔT and not to impair the see-through performance at the same time, the refractive index nb of the medium matches the ordinary light refractive index no or the extraordinary light refractive index ne of the liquid crystal material. As long as the material is selected as described above and holds the liquid crystal substance in the voids, it can be used regardless of the type of the inorganic material and the organic material. Among them, it is preferable to use a resin that can easily adjust the refractive index and increase the area of the element. For example, JP
Latex described in JP-A-252687 is a suitable material, and it is possible to obtain a liquid crystal element excellent in adhesion to a substrate, optical uniformity, and physical durability.

In order to prepare a medium containing the liquid crystal substance, it is preferable to add a surfactant. However, it is desirable that the amount of the surfactant used is the minimum necessary for stabilizing the liquid crystal particle diameter in the emulsion.

Further, in order to prepare a medium containing the liquid crystal substance, it is preferable to add a crosslinking agent. The addition of the crosslinking agent improves the adhesion between the medium and the transparent conductive film formed on the substrate surface, and can provide a liquid crystal element having excellent moisture resistance.

The substrate with a transparent conductive film used in the present invention is preferably made of indium tin oxide (ITO).
In addition to a general glass substrate having a film and a tin oxide (SnO ₂ ) film formed on the surface, other light-transmitting members such as a plastic substrate or a flexible plastic film can be used.

[0031]

According to the present invention, the average refractive index na of the liquid crystal material, which is a parameter, and the refractive index n of the medium holding the liquid crystal material,
b, thickness t, liquid crystal ratio V, capsule diameter D,
By suitably combining them so as to satisfy the following expression (5) derived from the expression and the expression (3), a liquid crystal element having a dimming performance of ΔT of 15% or more can be obtained.

| Na−nb | × (6 × V / D) × t ≧ 4.2 (5) Such performance increases the ratio of incident light scattered backward when no voltage is applied. It became possible by doing. Unlike conventional dimming devices, light is scattered backward instead of absorbing light, in other words, light is reflected to improve dimming performance. Is excellent in durability with almost no deterioration of the material constituting it.

Further, the liquid crystal element of the present invention can sufficiently adjust the transparency.

[0034]

Hereinafter, embodiments of the present invention will be described.
The present invention is not limited to these examples.

For example, the liquid crystal device of the present invention is manufactured by the following manufacturing method.

First, an emulsion as a medium is prepared by directly mixing a liquid crystal substance and latex. Alternatively, an emulsion may be prepared by mixing a liquid crystal substance and an aqueous phase, and then the emulsion may be mixed with latex. When preparing an emulsion, a surfactant is added to stabilize the particle diameter of the liquid crystal substance. The mixing is performed using various mixers such as a blender and a colloid mill. Next, a crosslinking agent is added to the emulsion, and the mixture is stirred slowly. Thereafter, the emulsion in which the liquid crystal substance is dispersed is applied to a required thickness on the transparent conductive film surface of the substrate on which the transparent conductive film has been formed using a knife blade or other means, and dried. Furthermore, a liquid crystal element is obtained by bonding the transparent conductive film side to another substrate with the inner surface facing the transparent conductive film side.

(Example 1) In order to produce a liquid crystal device of the present invention, a surfactant IGEPAL CO-610 (manufactured by GAF) was added to nematic liquid crystal E49 (manufactured by BDH) in an amount of 0.5 w.
Neoles R-9 containing 40 wt% of latex particles so that the liquid crystal ratio becomes 0.62.
67 (manufactured by Polyvinyl Chemical), and stirred at 7000 rpm for 10 minutes using a homogenizer to obtain an emulsion. Next, while slowly mixing, the crosslinking agent CX-100 is used.
(Manufactured by Polyvinyl Chemical) in 3 wt% for R-967
%.

Using a doctor blade, this mixture is
An indium tin oxide (ITO) film was applied on the ITO film surface of a polyethylene terephthalate (PET) film formed in advance and dried. Thickness after drying is about 30μm
Met. After the mixture is dried, another PET film with the ITO film is placed so that the ITO film side is in contact with the dried mixture.
A liquid crystal device was obtained by laminating with a film.

Table 1 shows the parameters of the liquid crystal element thus obtained. Using these parameters, | na-
The result of calculating nb | × S × t was 4.3.

[0040]

[Table 1]

Example 2 A liquid crystal device having a combination of parameters different from that of Example 1 was manufactured.

A surfactant IGEPAL CO-610 was added to a nematic liquid crystal ZLI-1840 (manufactured by Merck Japan).
0.5 wt% (manufactured by GAF) and Neorez R-967 (manufactured by Polyvinyl Chemical) containing 40 wt% of latex particles so that the liquid crystal ratio becomes 0.62.
At 18,000 rpm using a homogenizer.
After stirring for an minute, an emulsion was obtained. Next, while slowly mixing, the crosslinking agent CX-100 (manufactured by polyvinyl chemical) was added to R-
967 was added at a ratio of 3 wt%.

Using a doctor blade, this mixture is
The ITO film was applied on the ITO film surface of the PET film on which the ITO film had been formed in advance, and dried. The thickness after drying was about 20 μm. After the mixture was dried, another ITO film-attached PET film was laminated with the ITO film so that the ITO film side was in contact with the dried mixture to obtain a liquid crystal element.

Table 1 shows the parameters of the liquid crystal element obtained in this embodiment, as in the case of the first embodiment. The calculation of | na−nb | × S × t using these parameters resulted in 4.4.

(Example 3) A liquid crystal device having a combination of parameters different from those in Examples 1 and 2 was manufactured.

The surfactant IGEPAL CO-610 (GAF) was added to the nematic liquid crystal E49 (BDH) for 1w.
Neoles R-9 containing 40 wt% of latex particles so that the liquid crystal ratio becomes 0.75.
67 (manufactured by Polyvinyl Chemical), and stirred at 12,000 rpm for 10 minutes using a homogenizer to obtain an emulsion. Next, while slowly mixing, the crosslinking agent CX-100 is used.
(Manufactured by Polyvinyl Chemical) in 3 wt% for R-967
%. Using a doctor blade, this mixture was used to prepare a PET film on which an ITO film had been formed in advance.
It was applied on the TO film surface and dried. The thickness after drying is about 2
It was 0 μm. After the mixture was dried, another ITO film-attached PET film was laminated with the ITO film so that the ITO film side was in contact with the dried mixture to obtain a liquid crystal element.

Table 1 shows the parameters of the liquid crystal device obtained in this example. Using these parameters, | na-
The result of calculating nb | × S × t was 4.5.

Example 4 A liquid crystal device having a combination of parameters different from those of Examples 1, 2 and 3 was manufactured.

The nematic liquid crystal ZLI-1840 (manufactured by Merck Japan) was treated with a surfactant IGEPAL CO-610.
0.5 wt% (manufactured by GAF) and Neorez R-967 (manufactured by Polyvinyl Chemical) containing 40 wt% of latex particles so that the liquid crystal ratio becomes 0.62.
At 14,000 rpm using a homogenizer.
After stirring for an minute, an emulsion was obtained. Next, while slowly mixing, the crosslinking agent CX-100 (manufactured by polyvinyl chemical) was added to R-
967 was added at a ratio of 3 wt%. The mixture was applied on a PET film previously coated with an ITO film using a doctor blade and dried. The thickness after drying was about 40 μm. After the mixture is dried, another IT sheet is placed so that the ITO film side is in contact with the dried mixture.
A liquid crystal device was obtained by laminating with a PET film with an O film.

Table 1 shows the parameters of the liquid crystal device obtained in this example. Using these parameters, | na-nb |
As a result of calculating × S × t, it was 4.4.

(Comparative Example 1) For comparison with the liquid crystal device of the present invention, a liquid crystal device described in JP-A-60-252687 was used.
A liquid crystal element constituted by a suitable combination of parameters was manufactured.

The surfactant IGEPAL CO-610 was added to the nematic liquid crystal ZLI-1840 (manufactured by Merck Japan).
0.5 wt% (manufactured by GAF) and Neorez R-967 (manufactured by Polyvinyl Chemical) containing 40 wt% of latex particles so that the liquid crystal ratio becomes 0.62.
And stirred at 7000 rpm for 10 minutes using a homogenizer to obtain an emulsion. Next, while slowly mixing, the crosslinking agent CX-100 (manufactured by polyvinyl chemical) was added to R-9.
It was added at a ratio of 3 wt% to 67. The mixture was applied on a PET film previously coated with an ITO film using a doctor blade and dried. The thickness after drying was about 20 μm. After the mixture was dried, it was laminated with another PET film with an ITO film to obtain a liquid crystal element.

Table 1 shows the parameters of the liquid crystal element thus obtained. Using these parameters, | na-
As a result of calculating nb | × S × t, it was 1.5.

(Examples 1 to 4 and Comparative Example 1)
4 and the liquid crystal device obtained in Comparative Example 1
According to R 3106, sunlight transmittance is measured in a state where no voltage is applied (closed state) and in a state where a voltage is applied between opposed ITO films of the liquid crystal element (open state), and further calculated from the measured values. Gave ΔT. Table 2 shows the results. Note that ΔT is the transmittance change width of sunlight energy as described above, and more specifically, represents the difference between the sunlight transmittance in the open state and the sunlight transmittance in the closed state.

[0055]

[Table 2]

From Table 2, the product of the parameters | na−nb | of the liquid crystal element and S and t is 4.2 or more, the capsule diameter is in the range of 0.5 to 3 μm, or the liquid crystal ratio is 0. Range of 5 to 0.9, or thickness of 10 to 40 μm
In each embodiment of the present invention in the range of
It can be seen that a liquid crystal element having a dimming performance of not less than% can be obtained.

Further, the liquid crystal device of this example could sufficiently adjust the transparency.

[0058]

According to the liquid crystal device of the present invention, the light transmittance control performance is improved by the preferable combination of the parameters constituting the liquid crystal device as compared with the liquid crystal device obtained by the conventional method. Are better.

[Brief description of the drawings]

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Transparent conductive film 3 Liquid crystal substance 4 Medium

Continuation of front page (56) References JP-A-3-213823 (JP, A) JP-A-60-252687 (JP, A) JP-A-4-296720 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) G02F 1/1334

Claims (4)

(57) [Claims] 1. A liquid crystal device, comprising: a transparent conductive film disposed on inner surfaces of a pair of transparent substrates, wherein a medium holding a liquid crystal material in a gap is interposed between the transparent conductive films. The average refractive index (na) of the liquid crystal material, the refractive index (nb) of the medium, the total surface area of the voids per unit volume (S) [μm ^-1 ], and the distance t [ μ
m] has the following relationship: | Na−nb | × S × t ≧ 4.2 2. The liquid crystal device according to claim 1, wherein an average diameter of a sphere having a volume equal to the volume of the void is in a range of 0.5 to 3.0 μm. 3. The liquid crystal device according to claim 1, wherein a ratio of a volume of the liquid crystal material to a total volume of the liquid crystal material and the medium is in a range of 0.5 to 0.9. 4. The distance between the transparent conductive films is 10 to 40 μm.
The liquid crystal device according to claim 1, wherein