JPH07175045A - Liquid crystal light control device and manufacturing method thereof - Google Patents

Abstract

(57) [Summary] [Object] To provide a liquid crystal light control device having high contrast, low driving voltage, small hysteresis, and stability and moldability practically sufficient. A polymer-dispersed liquid crystal light control device comprising a pair of electrode layers, at least one of which is transparent, and a light control layer in which a liquid crystal composition and a transparent liquid substance are dispersed in a transparent resin is sandwiched between the electrode layers. The liquid crystal light control device is characterized in that the light control layer is composed of three elements which are insoluble in each other, a transparent resin, a liquid crystal composition and a transparent liquid substance.

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 control device whose principle of operation is light scattering. More specifically, it relates to a polymer dispersion type liquid crystal light control device having a light control layer in which a liquid crystal composition and a transparent liquid substance are dispersed in a transparent resin.

[0002]

2. Description of the Related Art A liquid crystal light control device is known which utilizes a phenomenon in which optical characteristics such as scattering, absorption and reflection change when an electric field is applied. These are widely used for displays and optical shutters. In recent years, a polymer dispersion type liquid crystal light control device of a light scattering mode has been attracting attention as a new type of liquid crystal light control device. This element has the following excellent points. Since it is not necessary to perform orientation processing on the substrate, the device can be easily manufactured. In addition, since it is easy to control the film thickness over a wide area, it is possible to manufacture a device having a uniform large area display.
Further, since no polarizing plate is required, bright display is possible. Further, since the light scattering effect is used, it has a feature that the viewing angle is wide. Due to these excellent properties, the liquid crystal light control device is expected to be applied to the fields such as light control glass, projection type displays, and large area displays.

A conventional polymer-dispersed liquid crystal light control device is
The light control layer has a structure in which liquid crystal droplets having a particle size of about several μm are dispersed in a transparent resin, or a structure in which liquid crystals are filled and dispersed in a three-dimensional sponge-like transparent resin in a communicating state. FIG. 1 shows a sectional view of an example of a conventional polymer dispersion type liquid crystal light control device. The liquid crystal light control device includes a pair of electrode layers (1.
A light control layer (1.2) is sandwiched between 1). The light control layer (1.2) is made of a transparent resin (1.
3) has a structure in which the liquid crystal composition (1.4) is dispersed in a continuous state. Generally, the operation principle of the polymer-dispersed liquid crystal light control device is considered as follows. When no voltage is applied, the transparent resin-liquid crystal composition interface (1.
The liquid crystal composition is randomly aligned by the interaction of 5). Since the liquid crystal composition (1.4) having birefringence is randomly oriented and dispersed in the transparent resin (1.3) in the order of the wavelength of visible light, the light control layer (1. 2)
Indicates strong light scattering. When an electric field is applied to this, the liquid crystal composition (1.4) is aligned in one direction along the electric field, so that the light control layer (1.2) changes to a transparent state. When the electric field is removed from this state, the transparent resin-liquid crystal composition interface (1.
By the interaction of 5), the liquid crystal composition returns to a random orientation, and the light control layer (1.2) shows strong light scattering again. Moreover, the light scattering intensity can be adjusted by applying an electric field of an appropriate magnitude.

In a conventional polymer-dispersed liquid crystal light control device, in general, the particle size of liquid crystal droplets or the size of voids in a transparent resin network is controlled to about 1 to 2 μm in order to increase the light scattering intensity. . In fact, if the particle size is too large, the number of times of light scattering decreases, and if it is too small and smaller than the wavelength of visible light, the light scattering intensity also decreases. The drive voltage of the liquid crystal light control device depends on the film thickness of the light control layer or the weight fraction of the liquid crystal composition in the light control layer. For example, as the film thickness becomes thinner or the weight fraction of the liquid crystal composition becomes higher, the driving voltage tends to decrease and the electro-optical characteristics tend to improve. Generally, the change in light transmittance with respect to the applied voltage of these liquid crystal light control devices (applied voltage-light transmittance curve) is
A hysteresis curve is shown without following the same locus when the voltage is increased and when the voltage is decreased. When the hysteresis becomes large, it is difficult to display halftones, especially when the liquid crystal light control device is used as a display device. It is generally considered that this hysteresis characteristic depends on the state of the interface between the transparent resin and the liquid crystal composition.

On the other hand, Japanese Patent Laid-Open No. 5-107563 discloses that
Disclosed is an emulsion-type liquid crystal light control device having a light control layer composed of a liquid crystal composition and a liquid other than the liquid crystal composition.
The light control layer of this liquid crystal light control device has a structure in which a liquid substance is dispersed as colloidal fine particles in a liquid crystal composition. FIG. 2 shows a sectional view of this emulsion type liquid crystal light control device. Similar to FIG. 1, the liquid crystal light control device has a light control layer (2.2) sandwiched between a pair of opposing electrode layers (2.1). The light control layer (2.2) has a structure in which the transparent liquid substance (2.6) is dispersed in the liquid crystal composition (2.4) in an isolated state. Since the phase separation system of the liquid crystal composition and the transparent liquid substance is driven by the same operation principle as that of the polymer dispersion type liquid crystal light control device, it is bright and has a wide viewing angle. When no voltage is applied, the liquid crystal composition is randomly aligned due to the interaction between the liquid crystal composition-transparent liquid substance interface (2.7), and the light control layer (2.2) exhibits strong light scattering. When a voltage is applied to this, the liquid crystal composition is arranged in one direction along the electric field, and the light control layer (2.2) changes to a transparent state. In this liquid crystal light control device, a sufficient light scattering effect and good contrast were obtained even if the weight ratio of the transparent liquid substance to the liquid crystal composition was reduced. Therefore, it was possible to operate at a low driving voltage by decreasing the weight fraction of the transparent liquid substance and increasing the ratio of the liquid crystal composition. In addition, depending on the type of transparent liquid substance, the effect of reducing hysteresis was also recognized.

[0006]

In the conventional polymer-dispersed liquid crystal light control device, its structure and composition are changed,
Attempts have been made to obtain desired electro-optical properties by adding a surfactant or other additives. However, in those attempts, it has not been possible to obtain an element having sufficiently high contrast, low driving voltage, and sufficiently small hysteresis of applied voltage-light transmittance curve.

In the emulsion type liquid crystal light control device disclosed in Japanese Patent Laid-Open No. 5-107563, a satisfactory device is obtained in terms of contrast, driving voltage and hysteresis. However, since the moldability of the light control layer is poor, it is difficult to control the thickness of the light control layer and it is difficult to increase the area of the device. Further, when left for a long period of time, the transparent liquid substance aggregates and fuses, resulting in a problem that electro-optical characteristics deteriorate.

The present invention provides a polymer-dispersed liquid crystal light control device which has a high contrast, a low driving voltage, and a small hysteresis, yet has sufficient stability and moldability, and which can have a large area. The purpose is to do.

[0009]

According to the present invention, after enclosing a photopolymerizable composition, a liquid crystal composition and a transparent liquid substance and optionally a polymerization initiator between a pair of electrode layers, at least one of which is transparent, A polymer dispersion characterized in that a transparent resin is formed by polymerizing the photopolymerizable composition, and a light control layer in which a liquid crystal composition and a transparent liquid substance are dispersed is sandwiched between the transparent resins thus obtained. Type liquid crystal light control device and a method for producing a polymer-dispersed liquid crystal light control device, which comprises irradiating ultraviolet rays when polymerizing the photopolymerizable composition.

The photopolymerizable composition used in the present invention is a monomer or an oligomer, which is polymerized to give a transparent resin. Specific examples of the photopolymerizable composition are not particularly limited as long as the obtained transparent resin is insoluble in the liquid crystal composition and the transparent liquid substance. For example, styrene, N-vinylpyrrolidone, methyl acrylate, methyl methacrylate, butyl acrylate, cyclohexyl acrylate, benzyl acrylate, carbitol acrylate, 2-ethylhexyl acrylate, lauryl methacrylate,
2-hydroxyethyl acrylate, phenoxyethyl acrylate, 2-hydroxyethyl methacrylate,
2-hydroxypropyl acrylate, glycidyl methacrylate, ethylene glycol diacrylate, diethylene glycol dimethacrylate, triethylene glycol diacrylate, diethylene glycol diacrylate, butylene glycol diacrylate, neopentyl glycol diacrylate, 1,4 -Butanediol diacrylate, 1,6-hexanediol diacrylate, pentaerythritol diacrylate, pentaerythritol triacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetra (3-mercaptopropio Nate), pentaerythritol (mercaptoacetate), trimethylsilyl methacrylate, 2- (trimethy! Photopolymerizable monomers such as siloxy) ethyl methacrylate, (trimethylsilylmethyl) methacrylate, 3-methacryloxypropyltrimethoxysilane, or photopolymerization of polyethylene glycol diacrylate, polyester acrylate, epoxy acrylate, urethane acrylate, etc. A polymerizable oligomer can be preferably used. These photopolymerizable compositions may be used alone or in combination of two or more kinds.

The liquid crystal composition used in the present invention may be one that is insoluble in the transparent resin and the transparent liquid substance. Although not limited to nematic liquid crystals, cholesteric liquid crystals, smectic liquid crystals, etc., nematic liquid crystals can be particularly preferably used.

For example, the general formula (1)

[Chemical 1] Liquid crystal compound wherein represented in, R ₁ is 1 to the number of carbon atoms
Represents a linear alkyl group having 10 carbon atoms or an alkenyl group having 2 to 10 carbon atoms, R ₂ represents a linear alkyl group having 1 to 10 carbon atoms or a linear alkoxy group, or —CN or fluorine; _{atom, -CF 3, -CHF 2, -OCF} 3
Or represents -OCHF _2, S _1, S ₂ may be the same or different, each represents a hydrogen atom, a fluorine atom, -CF
_3, -CHF _2, represents -OCF ₃ or -OCHF _2,
Z _{1 is, -COO -, - CH 2 CH} 2 -, - CH = CH
-, - C≡C- or a single bond, A ₁ is Formula (2)

[Chemical 2] Or a liquid crystal compound represented by the general formula (3)

[Chemical 3] [In the formula, R ₃ has the same meaning as R _{1 in the} general formula (1),
R ₄ has the same meaning as R _{2 in the} general formula (1), and S ₃ and S ₄ are
They may be the same or different and each has the same meaning as S ₁ and S _{2 in} the general formula (1), Z ₂ and Z ₃ may be the same or different, and Z ₁ and Z _{1 in the} general formula (1) respectively. A ₂ and A ₃ may be the same or different and each has the same meaning as A _{1 of the} general formula (1). ] And the like can be used.

The components of these liquid crystal compositions may be a single component or a mixture of a plurality of components. For example,
E-8, E-44 made by BDH and GR made by Chisso Corporation
A mixed liquid crystal such as −63 can be used. Also,
It may contain a dichroic dye or the like. The liquid crystal composition used is preferably one having a large refractive index anisotropy (Δn) in order to increase the contrast of the liquid crystal light control device. Further, in order to reduce the driving voltage, a material having a large dielectric anisotropy (Δε) is preferable.

The transparent liquid substance used in the present invention may be any substance that is insoluble in the transparent resin and the liquid crystal composition.
For example, water, polyhydric alcohols, derivatives of polyhydric alcohols, liquid paraffins, silicone oils, fluorine oils and the like are not particularly limited, but silicone oils and fluorine oils are particularly preferably used. it can. These transparent liquid substances may be used alone 2
You may use together 1 or more types. The transparent liquid substance used is preferably a substance having a high boiling point and a low volatility, a substance having a low explosiveness / toxicity and a low risk, and a substance which is chemically stable.

The proportion of the liquid crystal composition in the light control layer is
50% (% by weight, the same applies below) and preferably 70
% Or more. When the proportion of the liquid crystal composition that responds to the electric field is smaller than 50%, the electro-optical characteristics of the light control layer are extremely deteriorated.

On the other hand, the proportion of the transparent liquid substance in the light control layer is 0.1 to 45%, preferably 1 to 25%. If the proportion of the transparent liquid substance is less than 0.1%, the area of the interface between the liquid crystal composition and the transparent liquid substance is reduced, and the effect of the transparent liquid substance is reduced. When it is more than 45%, the ratio of the transparent resin is relatively lowered, and the stability and moldability of the light control layer are lowered.

The proportion of the photopolymerizable composition in the light control layer is 5 to 49.9%, preferably 20 to 40%.
Is.

A transparent liquid substance, a liquid crystal composition as described above,
After encapsulating the photopolymerizable composition and optionally an additive such as a polymerization initiator between a pair of electrode layers, at least one of which is transparent, a transparent resin is formed by polymerizing the photopolymerizable composition. A liquid crystal composition and a transparent liquid substance are well dispersed in the transparent resin thus obtained to form a light control layer. At this time, as a method of polymerizing the photopolymerizable composition, (1) heating and (2) irradiation with radiation such as visible light, ultraviolet light, electron beam or X-ray can be considered, but the present invention is not necessarily limited to these. However, UV irradiation is particularly preferable for practical use. At this time, the reaction can be facilitated by adding a small amount of a known radical polymerization initiator or photopolymerization initiator.

The particle size of the liquid crystal composition in the light control layer varies depending on the combination and mixing ratio of the transparent resin, the liquid crystal composition and the transparent liquid substance, or the manufacturing method of the light control layer. The liquid crystal composition preferably has an average particle diameter of usually 100 μm or less, more preferably 1.0 to 20 μm.
The particle size may have a wide distribution. The thickness of the light control layer is usually 1 to 100 μm, preferably 2 to 20 μm. If the film thickness is less than 1 μm, the scattering intensity of the light control layer is lowered to deteriorate the contrast, and if it exceeds 100 μm, the driving voltage is increased.

In addition to the small amount of the polymerization initiator, the light control layer may also contain a small amount of various substances such as a light absorbing substance, a light stabilizer, an antioxidant, a lubricant, a surfactant, an inorganic filler, and the like. You may include the agent.

At least one of the two electrode layers for applying an electric field to the light control layer needs to be transparent. Specific examples of the electrode layer include ITO (Indium Tin O
In addition to transparent metal oxides such as xide) and tin oxide, conductive metals such as copper and aluminum can be used. Further, by providing transparent electrodes on both sides, the produced liquid crystal light control device becomes a transmissive type and can be used for an optical shutter, a projection type display and the like.

[0022]

The present invention provides a phase composed of three elements, a transparent resin, a liquid crystal composition and a transparent liquid substance obtained by heating or irradiating a mixture of a photopolymerizable composition, a liquid crystal composition and a transparent liquid substance. A polymer-dispersed liquid crystal light control device having a separate light control layer. This polymer-dispersed liquid crystal light control device maintains the conventional performance while maintaining the contrast,
The drive voltage and hysteresis characteristics are improved.
In the liquid crystal light control device of the present invention, the transparent resin, the liquid crystal composition, and the transparent liquid substance are insoluble in each other, and therefore, the transparent resin-liquid crystal composition, the liquid crystal composition-transparent liquid substance, and the transparent resin-transparent liquid substance can be used. A seed interface occurs. Since each of these three types of interfaces becomes a light scattering factor, the light scattering intensity of the light control layer when no voltage is applied is higher than that of the conventional polymer dispersion type liquid crystal light control device or emulsion type liquid crystal light control device. And the contrast is improved.

The structure of the light control layer changes depending on factors such as the composition ratio of the transparent resin, the liquid crystal composition and the transparent liquid substance, the density, the surface tension, and the dissolution parameter. In the present invention, it is considered that the liquid crystal composition and the transparent liquid substance are dispersed in a three-dimensional sponge-like transparent resin, for example.

FIG. 3 shows a sectional view of an example of the liquid crystal light control device of the present invention. Similar to FIGS. 1 and 2, the liquid crystal light control device has a light control layer (3.2) sandwiched between a pair of electrode layers (3.1) facing each other. The light control layer (3.2) has a structure in which a liquid crystal composition (3.4) and a transparent liquid substance (3.6) are dispersed in a three-dimensional sponge-like transparent resin (3.3). . Therefore, the liquid crystal composition (3.4) and the transparent liquid substance (3.6) having fluidity are stably retained in the transparent resin (3.3). As shown in the figure, when the ratio of the liquid crystal composition-transparent liquid substance interface (3.7) is larger than that of the transparent resin-liquid crystal composition interface (3.5), the liquid crystal composition-transparent liquid substance Interface (3.7)
The interaction becomes dominant, and good electro-optical characteristics are obtained.

[0025]

The present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

[0026]

Example 1 As a photopolymerizable composition, 2-ethylhexyl acrylate (EHA), trimethylolpropane triacrylate (TMPTA) and ThreeBond Co., Ltd.
Made of photo-curable resin (3052), liquid crystal composition of nematic mixed liquid crystal (GR-63) made by Chisso Corporation, and silicone oil (KF-56) made by Shin-Etsu Chemical Co., Ltd. as transparent liquid substance. Ratio is EHA / TMPTA / 30
52 / GR-63 / KF-56 = 4/4/9/75/8
Mixed so that Then, a polymerization initiator (Darocur 1173) manufactured by Merck Ltd. was added so as to be 1.0% with respect to the precursor monomer to prepare a mixed solution.
The mixed solution was interleaved with a spacer for holding the space 2
After being injected between the glass substrates with ITO electrodes, the liquid crystal light control device was prepared by irradiating ultraviolet rays to polymerize the photopolymerizable composition. This liquid crystal light control device showed strong light scattering at room temperature and was stable for a long period of time. 0-5 for the obtained liquid crystal light control device.
A voltage of 0 V was applied and the relationship between the applied voltage and the light transmittance was examined. Figure 4 shows EHA / TMPTA / 3052 / GR-6.
The applied voltage-light transmittance curve of the liquid crystal light control device of 3 / KF-56 = 4/4/9/75/8 is shown. This liquid crystal light control device had a contrast of 4.5, a threshold voltage of 5V, and a hysteresis magnitude ΔV of 1.5V.

[0027]

[Comparative Example 1] EHA / TMPTA / 3052 / GR-6
A liquid crystal light control device was produced in the same manner as in Example 1 except that the weight ratio of 3 was 6/6/13/75 and silicon oil was not added. This liquid crystal light control device showed strong light scattering at room temperature and was stable for a long period of time. A voltage of 0 to 50 V was applied to the obtained liquid crystal light control device, and the relationship between the applied voltage and the light transmittance was examined. Figure 5 shows EHA / TMPTA / 3052 / G
The applied voltage-light transmittance curve of the liquid crystal light control device of R-63 = 6/6/13/75 is shown. This liquid crystal light control device had a contrast of 2.3, a threshold voltage of 7 V, and a hysteresis magnitude ΔV of 2.2 V, and was inferior in electro-optical characteristics to those of Example 1.

[0028]

Comparative Example 2 The weight ratio of KF-56 / GR-63 is 25 /.
At 75, a liquid crystal light control device was produced in the same manner as in Example 1 except that the photopolymerizable composition and the polymerization initiator were not added. This liquid crystal light control device showed strong light scattering, but the scattering intensity decreased when left for 2 days. This device was an emulsion type liquid crystal light control device, and was inferior in stability and moldability to the device of Example 1.

[0029]

The liquid crystal light control device of the present invention has high contrast, low driving voltage, small hysteresis, sufficient stability and moldability, and its practical value is great.

[Brief description of drawings]

FIG. 1 shows a cross-sectional view of an example of a conventional polymer-dispersed liquid crystal light control device.

FIG. 2 shows a sectional view of an example of an emulsion type liquid crystal light control device.

FIG. 3 is a sectional view showing an example of a liquid crystal light control device according to the present invention.

4 shows an applied voltage-light transmittance curve of the liquid crystal light control device of Example 1. FIG.

5 shows an applied voltage-light transmittance curve of the liquid crystal light control device of Comparative Example 1. FIG.

[Explanation of symbols]

 1.1, 2.1, 3.1 ... Electrode layer 1.2, 2.2, 3.2 .... Light control layer 1.3, 3.3 .... Transparent resin 1. 4, 2.4, 3.4 .... Liquid crystal composition 1.5, 3.5 .. Interface of transparent resin-liquid crystal composition 2.6, 3.6 .... Transparent liquid substance 2 .7, 3.7 .... Interface between liquid crystal composition and transparent liquid substance

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location C09K 19/38 9279-4H 19/54 Z 9279-4H G02F 1/13 101

Claims (5)

[Claims] 1. A photopolymerizable composition, a liquid crystal composition, a transparent liquid substance and, if necessary, a polymerization initiator enclosed between a pair of electrode layers, at least one of which is transparent. By forming a transparent resin by polymerizing,
A polymer-dispersed liquid crystal light control device, comprising a transparent resin thus obtained, and a light control layer in which a liquid crystal composition and a transparent liquid substance are dispersed, sandwiched therebetween. 2. The liquid crystal light control device according to claim 1, wherein the liquid crystal composition is a nematic liquid crystal or a cholesteric liquid crystal. 3. The liquid crystal light control device according to claim 1, wherein the liquid crystal composition is a smectic liquid crystal. 4. The liquid crystal light control device according to claim 1, wherein the transparent liquid substance is either silicon oil or fluorine oil. 5. A photopolymerizable composition, a liquid crystal composition and a transparent liquid substance and, if necessary, a polymerization initiator are enclosed between a pair of electrode layers, at least one of which is transparent, and then the mixture is irradiated with ultraviolet rays. A transparent resin is formed by polymerizing the photopolymerizable composition, and the transparent resin thus obtained is sandwiched with a light control layer in which a liquid crystal composition and a transparent liquid substance are dispersed. A method for manufacturing a molecular dispersion type liquid crystal light control device.