JPH07239465A - Light control sheet - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a light control sheet suitable for various light control applications such as blinds, skylights, window lighting materials, displays, and partitions, and particularly to a light control sheet having excellent light resistance. [Structure] A dimming layer in which a liquid crystal substance is dispersed in a polymer is provided between two substrates having conductivity and at least one of which is transparent, and transmits or scatters light depending on whether or not an electric field is applied. In the light control sheet configured to control the light control layer, the light control layer irradiates the composition mainly composed of the liquid crystal substance, the electron beam curable resin and the ultraviolet absorber with an electron beam to cure the electron beam curable resin. The light control sheet is characterized in that it is obtained by curing liquid crystal and phase-separating liquid crystal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light control sheet suitable for various light control applications such as blinds, skylights, daylighting materials for windows, displays, partitions and the like, and is excellent in light resistance.

[0002]

2. Description of the Related Art In recent years, a light control sheet made of polymer-dispersed liquid crystal utilizing the anisotropy of refractive index of liquid crystal has been proposed. This light control sheet comprises, for example, a light control layer in which fine liquid crystal droplets are dispersed in a polymer matrix or a continuous phase of liquid crystal is formed between conductive layers of two transparent films each having an electrode layer. The principle is to control the light transmittance by changing the orientation degree of the liquid crystal and adjusting the refractive index difference with the polymer matrix to form a light transmission or scattering state depending on whether or not an electric field is applied between them. . That is, when no electric field is applied, the liquid crystal is randomly oriented, so that light is diffusely reflected and the light control sheet has an opaque appearance. When an electric field is applied, the liquid crystal is oriented in a certain direction and becomes transparent. It is a thing.

A light control sheet based on this principle is of a type in which a porous film is impregnated with liquid crystal and is sandwiched between two transparent conductive polymer films (Appl. Phys.
Lett. 40 (1) 22 (1982) H, C, Graighead et al.), Using polyvinyl alcohol to micro-encapsulate the liquid crystal, and the resin layer containing this is made of two transparent conductive polymer films. Of the type provided between (Special Publication Sho-58-501631
No.), a liquid crystal is dissolved in an organic solvent liquid of epoxy resin, the solvent is evaporated, and at the same time the resin is cured and the liquid crystal is phase-separated (Japanese Patent Publication No. 61-502128). Examples thereof include a type in which an acrylate is dissolved in an organic solvent liquid, the solvent is evaporated and the resin is cured at the same time, and the liquid crystal is phase-separated (JP-A-63-43993).

However, each of the above-mentioned light control sheets has a problem that when exposed to sunlight for a long period of time, the voltage required for transparency increases, and in an extreme case, transparency does not occur even when a voltage is applied. .

Further, a type in which the resin is cured and the liquid crystal is phase-separated by irradiating with ultraviolet rays has been studied, and the method is a high-performance and large-sized light control sheet can be efficiently obtained. As with the above method, the light resistance is a problem. Therefore, in order to improve the light resistance, it is considered to add an ultraviolet absorber, but in the type that can cause the curing of the resin and the phase separation of the liquid crystal by irradiating with ultraviolet rays, the resin can be added by adding an ultraviolet absorber. Under the present circumstances, it is difficult to cure sufficiently and phase separation does not occur to obtain the intended light control sheet.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a light control sheet which can change from an opaque state to a transparent state even with a low applied voltage and is excellent in light resistance.

[0007]

According to the present invention, a dimming layer in which a liquid crystal substance is dispersed in a polymer is provided between two substrates having conductivity and at least one of which is transparent. In a light control sheet configured to control the transmission / scattering of light depending on the presence / absence of application, a light control layer has a composition mainly composed of a liquid crystal substance, an electron beam curable resin and an ultraviolet absorber, It is a light control sheet characterized by being irradiated with a ray to cure an electron beam curable resin and to cause phase separation of liquid crystal.

Further, the electron beam curable resin comprises a monofunctional monomer containing one electron beam curable functional group and a polyfunctional monomer and / or a polyfunctional oligomer containing two electron beam curable functional groups. It is a light control sheet. In addition, it is a light control sheet in which the monofunctional monomer is isobornyl acrylate or isobonyl methacrylate. Further, in the light control sheet, the ultraviolet absorber is a benzotriazole-based compound.

[0009]

The electrically conductive substrate that constitutes the present invention includes a metal plate, a metal film, a glass plate having an electrode layer, and a transparent film. Examples of the transparent film include:
Examples include polyester, polycarbonate, polyimide, polyether sulfone, polymethylmethacrylate and the like. In the case of these glass plates or transparent films, those to which conductivity is imparted by fixing a metal oxide such as In ₂ O ₃ : SnO _{2 on} the surface by a deposition method or a sputtering method are targeted. Here, at least one of the conductive substrates needs to be transparent, and in general, a structure in which both are transparent is used.

The thickness of the substrate is not particularly limited, but when a film-shaped substrate is used for continuous processing by winding, a thickness of 20 to 2000 μm is preferable. Here, if the thickness of the film is less than 20 μm, the uniformity of the thickness of the sheet after lamination cannot be obtained, and if it exceeds 2000 μm, the workability is remarkably reduced.

The electron beam curable resin used in the present invention is not particularly limited as long as it is a compound which is polymerized and crosslinked to be polymerized by irradiation with an electron beam, but it is generally an acryloyl group or a methacryloyl group. Is composed of a monomer or oligomer containing one or more electron beam-curable functional groups.

As the monofunctional monomer containing one electron beam-curable functional group, methyl acrylate, ethyl acrylate, butyl acrylate, N-vinylpyrrolidone, acrylonitrile and its derivatives, amide group-containing monomers such as acrylamide, (Meth) acrylate of fatty acid such as lauryl (meth) acrylate, benzyl acrylate, 2-ethylhexyl acrylate, 2
-Hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, tetrahydrofurfuryl acrylate, phenoxyethyl acrylate,
Nonylphenoxyethyl acrylate, ε-caprolactone adduct acrylate, butoxyethyl (meth) acrylate, 2-hydroxyl-3-phenoxypropyl acrylate, cyclohexyl (meth) acrylate, N, N-dimethylamino (meth) acrylate,
N, N-dimethylaminoethyl (meth) acrylate,
Examples thereof include 3-phenoxypropyl acrylate, 2-methoxyethyl (meth) acrylate, glycidyl (meth) acrylate, (meth) acryloylmorpholine and isobornyl (meth) acrylate.

The following are examples of polyfunctional monomers and oligomers having two or more electron beam-curable functional groups.
Examples of the bifunctional monomer include bisphenol-AEO modified diacrylate, isocyanuric acid EO modified diacrylate, tripropylene glycol diacrylate, pentaerythritol diacrylate monostearate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, 1,4 butanediol diacrylate. Examples thereof include acrylate and 1,6 hexanediol diacrylate.

As the trifunctional or higher functional monomer, trimethylolpropane triacrylate, trimethylolpropane triethoxyacrylate, modified glycerin triacrylate, pentaerythritol triacrylate,
Modified trimethylolpropane triacrylate, pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, tris (2-hydroxyethyl) isocyanurate (meth) acrylate, dipentaerythritol caprolactam modified acrylate (Nippon Kayaku "Product name: DPCA-20, 40, 60, 1"
20) ”and the like are exemplified.

As the bifunctional or higher oligomer, polyester acrylate (trade name: manufactured by Toagosei Kagaku Co., Ltd.)
M-6200, M-6500, M-8030, M806
0 ”), polyurethane acrylate (trade name: Ebecryl-EB220, manufactured by Daicel UCB Co., Ltd.)
Ebecryl-EB230 "), epoxy acrylate (trade name: Ebec manufactured by Daicel UCB Co., Ltd.)
ryl-EB600 ") and the like.

Here, among the above-mentioned monomers and oligomers, the monofunctional monomer has a high dissolving power for the liquid crystal substance and the ultraviolet absorber, and the polyfunctional monomer and / or the polyfunctional oligomer has a high electron beam curability, so that they are mixed. It is preferable to use it. The mixing ratio of the monofunctional monomer and the polyfunctional monomer and / or the polyfunctional oligomer varies depending on the type of each of them and the types of the liquid crystal substance and the ultraviolet absorber described below. Monomer and / or polyfunctional oligomer 90-1
0-2 wt%, preferably 80-2 to 20-80 wt%
A range of 0% by weight is suitable.

Further, among the above monofunctional monomers, isobornyl acrylate and isobonyl methacrylate are
Especially excellent in dissolving power for liquid crystal substances and UV absorbers,
Moreover, it is particularly preferable because it has excellent curability.

Examples of the liquid crystal substance used in the present invention include Schiff chlorine type, azo type, azooxy type, benzoic acid ester type, cyanobiphenyl type, cyanoterphenyl type, cyclohexylcarboxylic acid type, phenylcyclohexane type, biphenylcyclohexane. System, pyrimidine system,
Dioxane-based, cyclohexylcyclohexane ester-based, cyclohexylethane-based, cyclohexane-based, tolan-based, alkenyl-based, 2,3-difluorophenylene-based nematic or smectic-based liquid crystal, and the like,
You may use it in mixture of 2 or more types as needed.

The electron beam curable resin component and the liquid crystal substance are mixed in a weight ratio of 65:35 to 10:90, preferably 60:40 to 20:80. By the way, if the blending ratio of the liquid crystal substance in the paint formulation is 35% or less, the phase separation of the liquid crystal substance tends to be insufficient, and if it is 90% or more, the solubility of the liquid crystal in the resin component is deteriorated, resulting in high quality. It is difficult to obtain a light control sheet.

The ultraviolet absorber used in the present invention must be selected so that it absorbs ultraviolet light effectively and is finely dispersed in the light control layer to such an extent that it does not hinder dissolution or transparency. Examples thereof include benzophenone compounds, benzotriazole compounds, organic nickel compounds, oxalic acid anilide compounds, hindered amine compounds and the like. Specific examples thereof include the following compounds.

Benzophenone compounds such as 2-hydroxy-4-methoxybenzophenone and 2-hydroxy-4-octoxybenzophenone, 2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2-
(2'-Hydroxy-3'-tert-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2-
(2′-hydroxy-3 ′, 5′-di-tert-aminophenyl) benzotriazole, 2- [2-hydroxy-
3,5-bis (α, α-dimethylbenzyl) phenyl]
-2H benzotriazole, 2- (2'-hydroxy-
3 ', 5'-di-tert-butylphenyl) benzotriazole, 2- (2'-hydroxy-3', 5'-di-te
rt-Butylphenyl) -5-chlorobenzotriazole and other benzotriazole compounds, nickel dibutyldithiocarbamate and other organic nickel compounds, 2-ethoxy-2'-ethyl oxalic acid bisanilide, 2-ethoxy-5- oxalic acid anilide compounds such as tert-butyl-2′-ethyl oxalic acid bisanilide, 2,2,6,6-tetramethyl-4-piperidinol, tetrakis (2,2,6,6-
Tetramethyl-4-piperidyl) 1,2,3,4-butane tetracarboxylate, (mixed 2,2,6
6-tetramethyl-4-piperidyl / tridecyl) 1,
2,3,4-butane tetracarboxylate, (mixed 1,2,2,6,6-pentamethyl-4-piperidyl / tridecyl) 1,2,3,4-butane tetracarboxylate, bis (1 , 2,2,6,6-Pentamethyl-4-piperidyl) 1,8-octane dicarboxylate and other hindered amine compounds, and dodecanedioic acid bis [2- (2-hydroxybenzoyl) hydrazide] and other hydrazide compounds Compound, 2,4-di-tert
-Butylphenyl-3 ', 5'-di-tert-butyl-
4'-hydroxybenzoate, 1,6-hexanediol-bis [3- (3,5-di-tert-butyl-4-hydroxyphenyl)] propionate, 3,5-di-te
Hindered phenolic compounds such as rt-butyl-4-hydroxybenzylphosphonate diethyl ester.

Of the above UV absorbers, benzotriazole compounds are particularly preferable because they have excellent compatibility with the electron beam curable resin and the liquid crystal, hardly inhibit phase separation, and have an excellent effect of improving light resistance.

The compounding amount of the above-mentioned ultraviolet absorber is 0. 0 with respect to 100 parts by weight in total of the electron beam curable resin component and the liquid crystal substance.
The range of 05 to 20 parts by weight is preferable, and the range of 0.1 to 10 parts by weight is more preferable. Here, if the amount is less than 0.05 parts by weight, it is difficult to obtain the desired light resistance, and if the amount is more than 20 parts by weight, it is difficult to dissolve or disperse sufficiently, and the curability by electron beam is lowered to cause phase separation. It may be difficult to get up.

In the coating liquid for the light control layer, an organic or inorganic spacer may be added, if necessary, as long as the effect of the present invention is not impaired.
Add wetting agent, defoaming agent, surfactant, antioxidant, etc.,
It is also possible to further enhance the effect of the invention. The coating material may be mixed by stirring with a usual stirring method such as a high speed mixer, but it is preferable to use a roll mill so as not to generate bubbles.

A roll coater, a curtain coater, a die coater, a gravure coater, an offset gravure coater, or the like, which does not easily generate bubbles, is preferably used as a means for coating the substrate. It is necessary that the coating liquid be heated and applied in a transparent liquid state as necessary so that resin solids and liquid crystal do not precipitate before the electron beam irradiation. The thickness of the coating layer is about 3 to 50 μm, preferably 5 to 30 μm. Incidentally, if the thickness is 3 μm or less, the opacity tends to be insufficient, and if it exceeds 50 μm, it is uneconomical and the voltage required for transparency tends to be high.

In the present invention, by irradiating the coating layer with an electron beam, the electron beam curable resin is polymerized and crosslinked, and in the process, the liquid crystal is phase-separated and the liquid crystal is dispersed in the polymer matrix. A layer is formed. The term “dispersion” as used herein means that when liquid crystals are present in the polymer matrix in the form of minute liquid droplets and are isolated, when liquid crystal droplets are present in the polymer matrix in the form of aggregates, they are in the polymer matrix. 2 means that the liquid crystal phase exists as a three-dimensional mesh-like continuous body.

The light control sheet according to the present invention has a structure in which a light control layer in which a liquid crystal substance is dispersed in a polymer is present between two conductive substrates. The method is not particularly limited, and for example,
(1) After coating the above-mentioned dimming layer forming coating liquid on the conductive layer of the transparent conductive film, and pasting the conductive surface of another transparent conductive film on this coating layer, the transparent conductive film Method of irradiating electron beam from above, (2) coating the above dimming layer forming coating solution on the conductive layer of the transparent conductive film, irradiating with an electron beam to form a dimming layer, and then this A method of pasting the conductive surface of another transparent conductive film on the light layer, (3) Coating the above-mentioned light control layer forming coating solution on the conductive layer of the transparent conductive film, and irradiating with an electron beam to adjust. Examples include a method of sticking together the light control layer surfaces of two films having a light layer formed thereon.

The electron beam irradiation has a higher productivity than the ultraviolet irradiation and does not require a photoreaction initiator which tends to cause deterioration of light resistance, odor and coloration, and a uniform crosslinked structure is easily obtained. There is an advantage. Further, even if an ultraviolet absorber is blended, unlike curing by irradiation with ultraviolet rays, curing inhibition is unlikely to occur.

The total amount of electron beam irradiated is 5 to 10
00 kGy, preferably about 10 to 500 kGy is desirable. If it is less than 5 kGy, the resin component may not be sufficiently cured and phase separation may be incomplete.
If y is exceeded, the liquid crystal is easily damaged, which is not preferable. Further, examples of the irradiation method include a curtain beam type, a broad beam type, and a scanning type. 100 kV to 500 kV is suitable as the acceleration voltage during irradiation. It should be noted that the irradiation may be performed in multiple times.

Examples of the present invention will be described below, but the present invention is not limited to these examples.

Example 1 On the surface of a transparent polyester film having a thickness of 75 μm, I
A transparent conductive film having a transparent conductive layer made of n ₂ O ₃ : SnO ₂ (manufactured by Teijin: trade name “T-COATA-7
5 ") is coated with a coating solution having the following composition so as to have a thickness of 15 μm, and an electro-curtain type electron beam irradiation apparatus (Energy Science Co., Ltd.) is used to apply 150 kGy (50 kGy × 3 times) at 165 kV on the coated layer surface. ) Electron beam was applied to cure the resin and the liquid crystal was phase-separated to form a light control layer. Another T-on this dimming layer
The conductive layer surfaces of COAT A-75 were stuck together, and drawn between two roll nips to be in close contact with each other to obtain a light control sheet.

The obtained light control sheet exhibited a milky white color in a good scattering state when no voltage was applied, and the light transmittance at 600 nm in this case was 6%. Subsequently, the electro-optical characteristics (voltage-transmittance characteristics) were measured, and it was transparent at 20 V (AC voltage), and the light control sheet had good quality.

[Paint composition for light control layer] 1) Electron beam curable resin Isobornyl acrylate 20 parts by weight Pentaerythritol triacrylate 15 parts by weight 2) Liquid crystal nematic liquid crystal (BL-002; manufactured by Merck) 65 parts by weight 3 ) Ultraviolet absorber Benzotriazole compound (Sumisorb 350; Sumitomo Chemical Co., Ltd.) 2 parts by weight

Example 2 A light control sheet was obtained in the same manner as in Example 1 except that the mixing ratio of the ultraviolet absorber in the light control layer coating material was 0.5 part by weight.

Example 3 A light control sheet was obtained in the same manner as in Example 1 except that a benzophenone compound (Sumisorb 110; manufactured by Sumitomo Chemical Co., Ltd.) was used as the ultraviolet absorber in the light control layer coating material.

Example 4 A light control sheet was obtained in the same manner as in Example 1 except that an organic nickel compound (Antigen NBC; manufactured by Sumitomo Chemical Co., Ltd.) was used as the ultraviolet absorber in the light control layer coating material. .

Comparative Example 1 A light control sheet was obtained in the same manner as in Example 1 except that the mixing ratio of the ultraviolet absorber in the light control layer coating material was changed to 0 part by weight.

Example 5 A light control sheet was obtained in the same manner as in Example 1 except that the following coating composition for light control layer was used. [Coating composition for light control layer] 1) Electron beam curable resin Phenoxyethyl acrylate 20 parts by weight Pentaerythritol triacrylate 15 parts by weight 2) Liquid crystal nematic liquid crystal (BL-002; manufactured by Merck) 65 parts by weight 3) Ultraviolet absorption Agent benzotriazole-based compound (Sumisorb 350; manufactured by Sumitomo Chemical Co., Ltd.) 1 part by weight Incidentally, when 2 parts of the above ultraviolet absorber was blended, it was not sufficiently dissolved.

Comparative Example 2 A light control sheet was obtained in the same manner as in Example 5, except that the ultraviolet absorber was not added.

The light control sheets obtained in the above Examples and Comparative Examples were attached to a window glass on the interior side facing south, exposed to sunlight, and the results of measuring the voltage required for transparency are shown in Table 1. Shown in.

[0041]

[Table 1]

[0042]

The light control sheet of the present invention can change from an opaque state to a transparent state even at a low applied voltage of 100 V or less,
Moreover, it is also extremely excellent in light resistance, such as blinds, skylights,
Suitable for various light control applications such as windows and displays.

Claims (4)

[Claims] 1. A light control layer in which a liquid crystal substance is dispersed in a polymer is provided between two substrates having conductivity and at least one of which is transparent, and transmits light depending on whether or not an electric field is applied. -In the light control sheet configured to control scattering, the light control layer irradiates the composition mainly composed of the liquid crystal substance, the electron beam curable resin and the ultraviolet absorber with the electron beam to cure the electron beam. A light control sheet, characterized in that a liquid crystalline resin is phase-separated while being cured. 2. An electron beam curable resin is a monofunctional monomer containing one electron beam curable functional group and a polyfunctional monomer and / or polyfunctional oligomer containing two electron beam curable functional groups. The light control sheet according to claim 1. 3. The light control sheet according to claim 2, wherein the monofunctional monomer is isobornyl acrylate or isobonyl methacrylate. 4. The light control sheet according to claim 1, wherein the ultraviolet absorber is a benzotriazole compound.