JP2733992B2 - Liquid crystal device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION (Industrial Application Field) The present invention relates to a liquid crystal-encapsulating thin film that can be formed into a large area, and a liquid crystal device of the present invention is capable of blocking, opening, and limiting transmission of light or illumination light. It can be electrically operated for blocking, transmission, and is used as a screen for blocking the view of a building window or a show window, as well as a curtain for lighting control, and displays characters and figures for high-speed response. Thus, by electrically switching the display, it is used as a display device such as an advertising board, a guide board, a decorative display board, or the like.

(Prior art) The liquid crystal display element is a conventional TN using nematic liquid crystal.
Type and STN type are in practical use. Further, a device using a ferroelectric liquid crystal has been proposed. These require a polarizing plate and also require an alignment treatment. On the other hand, as a method of manufacturing a large, inexpensive liquid crystal device that does not require them and has good brightness and contrast, there is known a method of dispersing liquid crystal droplets in a polymer by encapsulating liquid crystal and forming the polymer into a film. Have been. Here, gelatin, gum arabic, polyvinyl alcohol and the like have been proposed as encapsulating substances (Japanese Patent Publication No. 58-501631, US Pat. No. 4,350,047).

In the technology disclosed in the above specification, the liquid crystal molecules encapsulated in polyvinyl alcohol can be used in the presence of an electric field if they have a positive dielectric anisotropy in a thin layer. There are arranged in the direction of the electric field, when the refractive index n _p of the refractive index n _o and the polymer of the liquid crystal are equal, express transparency. When an electric field is removed, the liquid crystal molecules are returned to the random sequence, the refractive index of the liquid crystal droplets is deviated from the n _o, the liquid crystal droplets scatter light at the boundary surface, since blocking the transmission of light, Ususotai is It becomes cloudy. Several techniques other than those described above for forming a thin film of a polymer in which liquid crystals encapsulated in this manner are dispersed and encapsulated are known.
No. 2128 discloses a liquid crystal dispersed in an epoxy resin, and JP-A-62-2231 discloses a liquid crystal dispersed in a special ultraviolet-curable polymer.

(Problems to be Solved by the Invention) Important characteristics required for practical use of the large-sized liquid crystal device as described above include (i) driving at a low voltage, (ii) sufficient contrast, and (iii) time-division driving. There are things you can do.

In particular, (i) and (iii) are extremely important characteristics to make the driving part of the device inexpensive. However, a liquid crystal device that does not require a polarizing plate having the properties (i) to (iii) has not been manufactured so far.

The present inventors have intensively studied a preferable combination of the structure of a liquid crystal device and the chemical structure of a liquid crystal material used in the device. As a result, the present invention can be driven at a much lower voltage than a conventional large liquid crystal device, and furthermore, a polarizing plate We succeeded in producing a liquid crystal device that can be made larger without requiring the use of.

(Means for Solving the Problems) The present invention provides a liquid crystal device described below to solve the above problems.

That is, the liquid crystal device according to the present invention has two substrates having at least one electrode layer which are transparent, and a dimming layer supported between the substrates, and the dimming layer has the following general formula (I) A) a nematic liquid crystal material containing a compound of the following general formula (II) and a transparent solid substance, that is, an ultraviolet-curable resin, wherein the liquid crystal material forms a continuous layer, and the transparent solid substance, A liquid crystal device, wherein an ultraviolet curable resin is dispersed in the liquid crystal material in a three-dimensional network.

General formula (I) (Wherein, R ¹ represents a linear alkyl group having 1 to 10 carbon atoms or a linear alkoxyl group; Represents (Hereinafter, referred to as a compound of the formula (I)).

General formula (II) (Wherein, R ² represents a linear alkyl group having 1 to 10 carbon atoms, R ³ represents a cyano group, a linear alkyl group having 1 to 10 carbon atoms or a linear alkoxyl group, Or Represents (Hereinafter, referred to as a compound of the formula (II)).

In this device, the substrate may be a rigid material such as glass, metal or the like, or a flexible material such as a plastic film. The two substrates are opposed to each other and are obtained at an appropriate interval. At least one of them must be transparent so that the dimming layer supported between the two can be seen from the outside. However, complete transparency is not essential. If the liquid crystal device is used to act on light passing from one side of the device to the other, both substrates are provided with the appropriate transparency. Appropriate transparent and opaque electrodes may be disposed on the entire or partial surface of the substrate depending on the purpose.

A liquid crystal material and a transparent solid component are interposed between the two substrates. Incidentally, it is usually desirable to interpose a spacer for maintaining a gap between the two substrates in a usual manner, similarly to a well-known liquid crystal device.

Liquid crystal materials require that a continuous layer be formed between two substrates. If the ratio of the liquid crystal material components is low, it is difficult to form a continuous layer. The ratio of the liquid crystal material to the light control layer component is preferably 70% by weight or more, and more preferably 70 to 90% by weight (hereinafter,% means% by weight).

The transparent solid component interposed in the continuous layer of the liquid crystal material may be dispersed in particles, but preferably has a three-dimensional network structure. In any case, it is indispensable to form an optical boundary surface with the liquid crystal material and express light scattering. The transparency can be appropriately determined according to the purpose of use of the device, and the solidity of the device is not limited to a solid one, as long as it can meet the purpose.
It may have flexibility, flexibility, and elasticity. In the case of particles, light scattering properties cannot be expected if the particles are too large or too small compared to the wavelength of light, but those having an appropriate size and shape can be selected according to the purpose.

As these transparent solid components, UV-curable resins are suitable. As a material giving a three-dimensional network structure, a UV-curable monomer or oligomer is preferable.

The production of these liquid crystal devices can preferably be performed as follows.

That is, the liquid crystal material as an essential component between at least one of the two substrates having an electrode layer having transparency,
UV-curable polymer-forming monomers or oligomers, and a solution comprising a polymerization initiator, a chain transfer agent, a photosensitizer, a dye crosslinking agent, and the like as optional components, and irradiate ultraviolet rays through a transparent substrate, thereby By polymerizing the monomer or oligomer, a liquid crystal material forms a continuous layer and a liquid crystal device in which a transparent solid synthetic resin component in a three-dimensional network, that is, an ultraviolet curable resin component is dispersed in the liquid crystal continuous layer. How to

In this method, the ultraviolet-curable polymer-forming monomer or oligomer, which is an essential component, may be any as long as it forms a three-dimensional network in a continuous layer of the liquid crystal material by the irradiated ultraviolet light. Preferred examples of the molecule-forming monomer include trimethylolpropane triacrylate, tricyclodecane dimethylol acrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, hexanediol diacrylate, neopentyl glycol diacrylate, and tris (acryloxyethyl) isocyanurate. And so on.

Similarly, a good example of a polymer-forming oligomer is caprolactone-modified hydroxypivalic acid ester neopentyl glycol diacrylate.

Examples of the optional component include a polymerization initiator, a chain transfer agent, a photosensitizer, a dye, a crosslinking agent, and the like, and may be appropriately selected according to the type of the monomer, the oligomer, and the like, and desired performance of a liquid crystal device. it can.

In particular, the use of a chain transfer agent is extremely effective depending on the type of monomer or oligomer, and prevents the degree of crosslinking of the resin from becoming too high, whereby the liquid crystal material is easily responsive to an electric field, and low voltage is applied. Drivability is exhibited.
Preferred examples of the chain transfer agent include butanediol dithiopropionate, pentaerythritol tetrakis (β-thiopropionate), triethylene glycol dimercaptan, and the like. The amount of the chain transfer agent varies depending on the type of the monomer or oligomer used. However, if the amount is too small, the effect is weak, and if the amount is too large, the opacity of the device is reduced and the display contrast is deteriorated. The effective amount is considered to be 0.05 to 30% based on the monomer or oligomer, but is preferably 0.1 to 20%.

In order to support a solution containing such components between two substrates, the solution may be injected between the substrates. However, the solution is applied to one of the substrates using a coater such as a spinner, Next, the other substrate may be stacked.

The uncured solution can be cured by irradiating it with a suitable dose of ultraviolet light through a transparent substrate. Depending on the type of monomer or oligomer or optional component, heat or electron beam can be used instead.

The thickness of the light modulating layer is usually adjusted in the range of 5 microns to 30 microns.

The liquid crystal device configured in this manner can perform time-division driving that was impossible with a conventional droplet dispersion type liquid crystal device, and further, compared with a conventional droplet dispersion type liquid crystal device,
The driving voltage is low, the contrast is large, and the response speed is fast. For example, in a conventional droplet dispersion type liquid crystal device, an effective value of 60 V or more, and in many cases, a driving voltage of 100 V or more is required, whereas the liquid crystal device of the present invention is approximately
A rise response time of 3 to 4 ms and a fall response time of 3 to 4 ms are realized with a drive voltage of 20V.

(Examples) Examples of the present invention will be shown below, and the present invention will be described more specifically. However, the present invention is not limited to these examples.

Example 1 Trimethylolpropane triacrylate 19.8% by weight (the same applies hereinafter) as a polymer-forming monomer, 2-hydroxy-2-methyl-1-phenylpropan-1-one 0.2% as a polymerization initiator, and a liquid crystal material described later. Liquid crystal (A) 80% mixed, average particle size 10μm as spacer
A small amount of alumina powder was added and inserted between two ITO glass plates of 20 cm × 20 cm and irradiated with ultraviolet rays to cure (polymerize) the monomer. The curing conditions were such that the liquid crystal device was passed under a metal halide lamp (80 W / cm) at a speed of 3.5 m / min and irradiated with ultraviolet rays. The energy given is 50
It corresponds to 0 mJ / cm ² . The electrode spacing of the device is 11 μm. When a cross section of the light control layer formed between the two glass plates was observed with a scanning electron microscope, a three-dimensional network of the polymer was observed.

The resulting liquid crystal device has a threshold voltage and V ₁₀
= 7.9 V, V ₉₀ = 15.8 V, contrast = 1: 20, rise response time 2.5 ms, fall response time 3.6 ms, number of time division lines N _max = 2.
It was eight.

(1) Liquid crystal (A) composition Transition temperature 70.4 ℃ (N-I point) -7 ℃ (C-N point) refractive index _{n e = 1.757 n o = 1.531} Δn = 0.226 threshold voltage (V _th) viscosity of 1.11V 20 ℃ 59.8cp (2 ) Number of time-division driving lines N _max = [(α ² +1) / (α ² -1)] ² where α = V ₉₀ / V ₁₀ (3) The light transmittance of the device when no voltage is applied is 0% When the light transmittance becomes 100% when the light transmittance does not change with the increase of the applied voltage, the applied voltage when the light transmittance becomes 90% is V ₉₀ , and when the light transmittance becomes 10%. the applied voltage and V _10.

(Effects of the Invention) Since the present invention is as described above, it is a large-area thin-film liquid crystal device, and can be driven at a low voltage of about 16 V. High response speed of 4 ms and transparent-opaque contrast of approx. 1:
It has a high threshold value of 20 and has a half-duty time-division drive. Therefore, large-sized display such as adjustment of lighting, adjustment of view, advertisement, etc. becomes extremely easy, and the production of such a liquid crystal device is made extremely easy and inexpensive.

Claims (3)

(57) [Claims] An at least one transparent electrode having an electrode layer.
A light control layer supported between the substrates and the substrate, wherein the light control layer has a general formula (Wherein, R ¹ represents a linear alkyl group having 1 to 10 carbon atoms or a linear alkoxyl group; Represents ) And the general formula (Wherein, R ² represents a linear alkyl group having 1 to 10 carbon atoms, R ³ represents a cyano group, a linear alkyl group having 1 to 10 carbon atoms or a linear alkoxyl group, Represents A) a liquid crystal material comprising a nematic liquid crystal material and a transparent solid material, the liquid crystal material forming a continuous layer, and the transparent solid material dispersed in the liquid crystal material in a three-dimensional network; A liquid crystal device, wherein the transparent solid substance is an ultraviolet curable resin. 2. The liquid crystal device according to claim 1, wherein the liquid crystal material accounts for 70% by weight or more of the components of the light control layer. 3. The liquid crystal device according to claim 1, wherein the light control layer has a thickness of 5 to 30 microns.