JP2723060B2 - Liquid crystal optical 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 display device for displaying characters, figures, etc., a light control window for controlling transmission / scattering or transmission / blocking of incident light, and a liquid crystal optical element used for an optical shutter. It is.

[0002]

2. Description of the Related Art Conventionally, as a display element using a liquid crystal, a TN type or an STN type using a nematic liquid crystal has been put to practical use. In recent years, ferroelectric liquid crystals and antiferroelectric liquid crystals have been developed. However, these elements have a drawback that they require a polarizing plate and are therefore limited in brightness and contrast.

On the other hand, the method disclosed in Japanese Patent Publication No. 3-52843, in which liquid crystal is encapsulated and dispersed in a polymer resin, has the advantage that light use efficiency is high because a polarizing plate is not required. I have. This liquid crystal optical element called PDLC or NCAP utilizes the fact that the refractive index of the liquid crystal in the capsule changes depending on the presence or absence of an electric field. In other words, by setting the refractive index of the polymer resin to be equal to the refractive index of the liquid crystal when applying a voltage, an optical element that transmits light when the voltage is applied and becomes transparent and scatters light when the voltage is removed and becomes opaque can be obtained. . However, since the liquid crystal optical element utilizes a difference in refractive index between the polymer resin and the liquid crystal, there are problems such as a large temperature dependence of light transmittance and a large viewing angle dependence of light transmittance. .

On the other hand, in the method disclosed in International Application No. 92/19695 in which a trace amount of a polymer resin is dispersed in a chiral nematic liquid crystal, the liquid crystal phase forms a planar texture when no electric field is applied, and the element becomes transparent. Thus, a liquid crystal optical element which forms a focal conic texture when a voltage is applied and becomes opaque has been obtained. Generally PSCT
This liquid crystal optical element, which is called a liquid crystal optical element, utilizes a light transmission and scattering phenomenon due to a phase change of a chiral nematic liquid crystal, and does not utilize a difference in refractive index between liquid crystal and a polymer resin. Therefore, there is an advantage that the temperature dependency of the light transmittance is small and the viewing angle dependency of the light transmittance is also small. Further, by adjusting the chiral pitch, selective reflection becomes possible.

[0005]

The above-mentioned international application 92/1
No. 9695 exemplifies 4,4'-bisacryloylbiphenyl as a polymer resin precursor. However, the liquid crystal optical element of the above disclosed technology has a high driving voltage of 14 V or more, and the thin film transistor (TF
T) and the like, there is a problem that it cannot be driven. In addition, the device according to the above disclosed technique has a problem that the hysteresis is large and a gray scale display cannot be performed. further,
The contrast, which is a value obtained by dividing the light transmittance when no voltage is applied (maximum light transmittance) by the light transmittance when voltage is applied (minimum light transmittance), is as small as about 20 and a clear image cannot be displayed. There was also.

Japanese Patent Application Laid-Open No. Hei 5-224187 proposes an improvement in the characteristics of the liquid crystal optical element, in which 4,4'-diacryloyloxy 3,4 is used as a polymer resin precursor.
3 ', 5,5'-tetramethylbiphenyl is exemplified. However, this liquid crystal optical element also has a high driving voltage of about 10 V and a large hysteresis of 0.8 V.
Not enough. These two disclosed technologies are:
In each case, a compound having a biphenyl skeleton is used as a polymer precursor.

[0007]

In general, it is known that the interaction between a polymer resin and a chiral nematic liquid crystal greatly influences electro-optical characteristics such as driving voltage, hysteresis, and contrast. The interaction cannot be predicted from the chemical structure.

The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that a compound obtained by polymerizing a polymer precursor containing a (meth) acryloyl-based compound can be used as the above-mentioned phase-change type liquid crystal optical element. By using as a polymer resin dispersed in a chiral nematic liquid crystal or a cholesteric liquid crystal, a low voltage drive is possible, and a liquid crystal element having excellent hysteresis characteristics is obtained.

That is, the present invention relates to a liquid crystal optical element comprising a light control layer comprising a chiral nematic liquid crystal or a cholesteric liquid crystal and a polymer resin sandwiched between at least one transparent substrate and an electrode layer. The molecular resin is a compound obtained by polymerizing a polymer precursor containing a (meth) acryloyl-based compound represented by the general formula (I). Note that the (meth) acryloyl-based compound in the present invention refers to an acryloyl-based compound and a methacryloyl-based compound.

[0010]

Embedded image

Incidentally, Japanese Patent Application Laid-Open No. 58-109481,
JP-A-61-73792 discloses a liquid crystal compound having a dioxane compound similar to the compound of the present invention and a liquid crystal display device using the same. These compounds are used as a liquid crystal chiral compound or a liquid crystal composition. It is completely different from the (meth) acryloyl-based compound having a dioxane group or a dioxolane group in the present invention, which is a polymer precursor, in terms of molecular structure, usage, and the like.

The polymer resin used for the light control layer of the liquid crystal optical element of the present invention is not limited to being used only as the polymer resin dispersed in the chiral nematic liquid crystal of the phase change type liquid crystal optical element. For example, the present invention can be applied to a polymer resin used for a liquid crystal optical element called PDLC or NCAP mentioned in the above-mentioned conventional technique.

The polymer resin used for the light control layer of the liquid crystal optical element of the present invention may be one obtained by polymerizing only one type of the (meth) acryloyl-based compound represented by the general formula (I). And two or more types of (meth) in the general formula (I)
It may be a copolymer of an acryloyl-based compound or a copolymer with one or more polymer precursors represented by other chemical formulas. As the other polymerizable polymer precursor, any polymer precursor having a usual polymerizable group such as an acryloyl group and a vinyl group can be used. The polymerizable group is
There may be more than one in one molecule of the polymer precursor.

The (meta) represented by the general formula (I) of the present invention
Examples of the polymer precursor having a polymerizable group copolymerizable with an acryloyl-based compound include 2-ethylhexyl acrylate, butyl ethyl acrylate, butoxyethyl acrylate, 2-cyanoethyl acrylate, benzyl acrylate, cyclohexyl acrylate, 2-hydroxypropyl acrylate, -Ethoxyethyl acrylate, N, N-diethylaminoethyl acrylate,
N, N-dimethylaminoethyl acrylate, dicyclopentenyl acrylate, dicyclopentenyl acrylate, glycidyl acrylate, tetrahydrofurfuryl acrylate, isoamyl acrylate, isobonyl acrylate, isodecyl acrylate, lauryl acrylate, morpholine acrylate, phenoxyethyl acrylate, phenoxy Diethylene glycol acrylate, isoamyl acrylate, tetrafluorofurfuryl acrylate, 2,2,2-trifluoroethyl acrylate, 2,2,3,3,3-pentafluoropropyl acrylate, 2- (perfluorobutyl) ethyl acrylate, 2 Monofunctional acrylate compounds such as-(perfluorodecyl) ethyl acrylate, 2-ethylhexylmethac Rate, butylethyl methacrylate, butoxyethyl methacrylate, 2-cyanoethyl methacrylate, benzyl methacrylate, cyclohexyl methacrylate, 2-hydroxypropyl methacrylate, 2-ethoxyethyl acrylate, N, N-diethylaminoethyl methacrylate, N, N-dimethylaminoethyl methacrylate, Dicyclopentanyl methacrylate, dicyclopentenyl methacrylate, glycidyl methacrylate, tetrahydrofurfuryl methacrylate, isobonyl methacrylate, isodecyl methacrylate, lauryl methacrylate, morpholine methacrylate, phenoxyethyl methacrylate, phenoxydiethylene glycol methacrylate, 2,2,2
Trifluoroethyl methacrylate, 2,2,3
3,3-pentafluoropropyl methacrylate, 2-
(Perfluorobutyl) ethyl methacrylate, 2-
(Perfluorohexyl) ethyl methacrylate, 2-
Monofunctional methacrylate compounds such as (perfluorodecyl) ethyl methacrylate, diethylene glycol diacrylate, 1,4-butanediol diacrylate,
1,3-butylene glycol diacrylate, dicyclopentanyl diacrylate glycerol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, tetraethylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate Pentaerythritol triacrylate, ditrimethylolpropane tetraacrylate, dipentaerythritol hexaacrylate, dipentaerythritol monohydroxypentaacrylate, urethane acrylate oligomer, 4,4'-diacryloyloxystilbene, 4,4'-diacryloyloxydiethylstilbene 4,4'-diacryloyloxydipropylstilbene, 4,4'- Acryloyloxy dibutyl stilbene, 4,4-diaryl methacryloyloxy fluoro stilbene, 4,4'-diaryl methacryloyloxy dichloro stilbene, 2,2,3,3,4,4-hexafluoro-1,
5-pentanediol diacrylate, 2,2,3
Polyfunctional acrylate compounds such as 3,4,4,5,5-octafluoro-1,6-hexanediol diacrylate, diethylene glycol dimethacrylate, 1,4-
Butanediol dimethacrylate, 1,3-butylene glycol dimethacrylate, dicyclopentanyl dimethacrylate glycerol dimethacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol dimethacrylate, tetraethylene glycol dimethacrylate, trimethylolpropane trimethacrylate Pentaerythritol tetramethacrylate, pentaerythritol trimethacrylate, ditrimethylolpropane tetramethacrylate, dipentaerythritol hexamethacrylate, dipentaerythritol monohydroxypentamethacrylate, urethane methacrylate oligomer, 4,4'-dimethacryloyloxystilbene, 4,4'- Dimethacryloyloxydiethylstilbene, 4,4'-dimethacryloyloxydipropylstilbene, 4,4'-dimethacryloyloxydibutylstilbene, 4,4-dimethacryloyloxyfluorostilbene, 4,4'-dimethacryloyloxydichlorostilbene, 2,2,3,3 Polyfunctional methacrylate compounds such as 2,4,4-hexafluoro-1,5-pentanediol dimethacrylate, 2,2,3,3,4,4,5,5-octafluoro-1,6-hexanediol dimethacrylate, Styrene, aminostyrene,
Examples include, but are not limited to, vinyl acetate.

The polymer resin is desirably contained in an amount of 0.5% by weight or more and 8.0% by weight or less. If the amount is too small, a so-called memory phenomenon in which the focal conic texture is maintained develops. If the amount is too large, the driving voltage increases and the transmittance when no voltage is applied decreases.

Examples of the method for polymerizing the polymer precursor include a photopolymerization method and a heat polymerization method, and the photopolymerization method is preferred.

As a light source used for the photopolymerization of the polymer precursor, an electron beam or ultraviolet light can be used. When performing photopolymerization by ultraviolet rays, it is desirable to add a photopolymerization initiator to promote the reaction. As the photopolymerization initiator, 2,2-diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenyl-1-one, 1- (4-
Isopropylphenyl-)-2-hydroxy-2-methylpropan-1-one, 1- (4-dodecylphenyl)
-2-hydroxy-2-methylpropan-1-one, 2
-Methyl-1- [4- (methylthio) phenyl] -2-
Acetophenones such as morpholinopropane-1, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin such as benzyldimethyl ketal, benzophenone, benzoylbenzoic acid, 4-phenylbenzophenone, 3,3-dimethyl-4-methoxybenzophenone Benzophenones, such as
Usual photopolymerization initiators such as thioxanthone, diazonium salt, sulfonium, iodonium, selenium salt and the like such as thioxanthone, 2-chlorothioxanthone and 2-methylthioxanthone can be used. The initiator may be a solid or a liquid, but it is desirable that the initiator be dissolved or compatible with the liquid crystal in view of the uniformity of the device. The initiator concentration is preferably 30% by weight or less of the polymer resin precursor. If necessary, a photoinitiating auxiliary such as methyldiethanolamine and 4-dimethylaminobenzoic acid may be added.

As a liquid crystal material used in the liquid crystal optical element of the present invention, a chiral nematic liquid crystal obtained by mixing a chiral agent in a nematic liquid crystal is used in addition to a nematic liquid crystal. Conventional cholesteric liquid crystals can also be used.

As the nematic liquid crystal, any liquid crystal such as cyano-based, fluorine-based and chlorine-based can be used, but a liquid crystal having a high charge retention and a high Δn is desirable, and a chlorine-based liquid crystal is particularly effective. . The chiral agent is not particularly limited, but is preferably compatible with the liquid crystal.

The mixing ratio between the nematic liquid crystal and the chiral agent is as follows:
It is determined by the desired chiral pitch. The chiral pitch of the chiral nematic liquid crystal is desirably 1.0 μm or more and 5.0 μm or less from the relationship between the driving voltage of the element and the contrast when used as a light transmission type. In addition, when used as a selective reflection type, 0.25 μm or more and 1.0
μm or less is desirable.

The material of the substrate used in the present invention can be glass, plastic, metal or the like. Coloring can be achieved by using a substrate having a color filter, or by dispersing a pigment or a dye in the substrate.

The substrate is set so that the electrode layer is on the light control layer side.

As the electrode layer, a material such as ITO can be used. However, if the substrate used has conductivity, the substrate can also be used as an electrode. The electrode layer is provided in a state of being in close contact with the light control layer.

These substrates with electrode layers may not be treated so that the liquid crystal is oriented, but are desirably treated. At this time, the two substrates may be in a homogeneous orientation, or one may be in a homogeneous orientation,
A so-called hybrid in which the other is homeotropic alignment may be used. This alignment treatment includes TN
Ordinary alignment films such as polyimide used for liquid crystal, STN liquid crystal and the like can be used. It is desirable to perform a rubbing process.

For setting the distance between the substrates, a rod-shaped or spherical spacer made of glass or a polymer resin or the like, which is used for an ordinary liquid crystal device, can be used, and the distance is desirably about 3 μm to 30 μm.

The liquid crystal optical element of the present invention can be manufactured by sandwiching a mixture of a chiral nematic liquid crystal and a monomer between substrates having a fixed gap and irradiating the mixture with light. At this time, the mixture may be injected under reduced pressure or normal pressure. If necessary, heating may be performed.

The liquid crystal optical element of the present invention is applicable not only to a light transmission type in which a light control layer is sandwiched between two transparent substrates having an electrode layer but also to a light reflection type in which one substrate is opaque. it can. For example, an element structure in which a light modulating layer is sandwiched between a transparent substrate having an electrode layer and a light reflecting plate having an electrode layer, and an element structure in which a light modulating layer is sandwiched between a transparent substrate having an electrode layer and a light absorbing plate having an electrode layer. is there.

The light reflecting plate may be made of an inorganic material or an organic material as long as it is made of a material that reflects light. Further, the reflection intensity or the reflection wavelength can be arbitrarily changed according to the target device characteristics. The structure may be such that the light reflecting material forms the entire light reflecting plate, or the light reflecting material may be coated on a substrate made of another material such as glass.
When a light reflecting material is coated, the light reflecting material does not need to be on the light control layer side. The substrate on which the light reflecting material is coated is not necessarily required to be transparent when the light reflecting material is not located on the light control layer side.

The light absorbing plate may be an inorganic material or an organic material as long as it is made of a material that absorbs light. The absorption intensity or absorption wavelength can be arbitrarily changed depending on the target device characteristics. The structure may be such that the light absorbing material forms the entire light absorbing plate, or the light absorbing material may be coated on a substrate made of another material such as glass. When coated with a light absorbing material, the light absorbing material need not be on the light modulating layer side. Further, the substrate on which the light absorbing material is coated is not necessarily required to be transparent when the light absorbing material is not located on the light control layer side. When the light reflecting material or the light absorbing material has conductivity, these can also be used as electrodes.

Applications of the liquid crystal optical element of the present invention include a building material such as a window and a partition, and a display device for displaying characters and figures.

[0031]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist.

The driving voltage and the response time described in the embodiment of the present invention are defined as follows.

Driving voltage: When the light transmittance when no voltage is applied (maximum light transmittance) is 100%, and when the light transmittance saturated by applying a voltage (minimum light transmittance) is 0%, the light transmittance of the element is determined. Is 10%.

Response time: The ON response time is assuming that the light transmittance when no voltage is applied (maximum light transmittance) is 100% and the light transmittance saturated by applying a voltage (minimum light transmittance) is 0%. After the voltage is applied, the light transmittance of the device is 100% to 10%.
Time to time to decrease to%. The off response time is from 0% to 90% after the applied voltage is removed.
It is time to increase to%.

Charge holding ratio: A pulse voltage of 5 V and 60 μs is applied to the device. Assuming that the voltage held by the element after 16.7 ms is V, the charge holding ratio is expressed by the following equation.

Charge retention = (V / 5) × 100 (%) Contrast: In an optical system with an F value of 15, the maximum light transmittance when no voltage is applied is divided by the minimum light transmittance saturated by applying a voltage. Value.

Example 1 Chlorine Nematic Liquid Crystal TL2
15 (manufactured by Merck) 95.0 wt%, chiral agent S81
1 (manufactured by Merck) 3.0 wt% (chiral pitch of chiral nematic liquid crystal is 3.3 μm), 2- (paraacryloyloxyphenyl) -5-acryloyloxy-
A mixed solution of 1.95 wt% of 1,3-dioxane and 0.05 wt% of benzoin methyl ether was injected into a liquid crystal cell having a gap of 10 μm and comprising two transparent glass substrates with electrode layers which were subjected to homogeneous alignment treatment. The liquid crystal cell was kept at 20 ° C. and irradiated with 0.1 mW / cm ² of ultraviolet light (wavelength 36
(5 nm) for 180 minutes to cure the acryloyl compound.

The electro-optical characteristics of the manufactured liquid crystal optical element are as follows.
Using a helium-neon laser as a light source and a photodiode as a detector, a 100 Hz rectangular wave was applied to measure. The F value of the optical system is 15. The characteristics at 25 ° C. are as follows.

Drive voltage 6.7 V Light transmittance (when no voltage is applied) 84% Light transmittance (when 8 V is applied) 1.0% Contrast 84 Hysteresis 0.24 V Response time (ON; 8 V applied) 24 ms (OFF) 18 ms Charge retention 93% (Example 2) Cyano-based liquid crystal RDP-71120-1 (R
96.0 wt%, chiral agent S811)
2.0 wt% (chiral pitch of chiral nematic liquid crystal 4.5 μm), 1,4-bis ((5-
A transparent liquid-crystal substrate with an electrode layer that has been subjected to a homogeneous alignment treatment with a mixture of 1.95 wt% of acryloyloxy-1,3-dioxane) -2-yl) benzene and 0.05 wt% of 2.2-diethoxyacetophenone. Was injected into a liquid crystal cell having a gap of 10 μm. UV irradiation conditions and electro-optical characteristics evaluation conditions were the same as those in Example 1.

Drive voltage 6.9 V Light transmittance (when no voltage is applied) 80% Light transmittance (when 9 V is applied) 1.1% Contrast 73 Hysteresis 0.20 V Response time (ON; 9 V) 27 ms (OFF) 17 ms ( Comparative Example 1) The procedure was performed under the same conditions as in Example 1 except that 4.4'-bisacryloylbiphenyl (1.95 wt%) was used as a polymer resin precursor.

Drive voltage 13.1 V Light transmittance (when no voltage is applied) 82% Light transmittance (when 15 V is applied) 2.6% Contrast 32 Hysteresis 3.2 V Response time (fall; 15 V applied) 15 ms (rise) 19 ms Charge retention 92% (Comparative Example 2) The same operation as in Example 2 was performed except that 4.4'-bisacryloylbiphenyl (1.95 wt%) was used as a polymer resin precursor.

Drive voltage 12.4 V Light transmittance (when no voltage is applied) 81% Light transmittance (when 15 V is applied) 2.0% Contrast 41 Hysteresis 3.0 V Response time (fall; 15 V applied) 19 ms (rise) 22ms

According to the liquid crystal optical element of the present invention, the contrast of the liquid crystal optical element using the phase change is improved, and a clear image can be displayed. In addition, the driving voltage decreases and TF
T drive becomes possible. In addition, since the hysteresis is reduced, gray scale display can be performed.

[Brief description of the drawings]

FIG. 1 is a graph showing the light transmittance of a liquid crystal optical element according to Example 1 of the present invention.

FIG. 2 shows a structure of a liquid crystal optical element according to Embodiment 1 of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Electrode layer 3 Alignment film 4 Polymer resin 5 Chiral nematic liquid crystal

Claims (4)

(57) [Claims] 1. An electrode having at least one of two transparent electrodes
A liquid crystal optical element that sandwiches a dimming layer composed of a chiral nematic liquid crystal or a cholesteric liquid crystal and a polymer resin between two substrates, becomes a planar texture when no electric field is applied, and becomes a focal conic texture when an electric field is applied. Is a compound obtained by polymerizing a compound containing a (meth) acryloyl-based compound having a dioxane group or a dioxolane group. 2. The method according to claim 1, wherein the polymer resin is a compound obtained by polymerizing a polymer precursor containing a (meth) acryloyl compound represented by the general formula (I). Liquid crystal optical element. Embedded image (3) 7. the polymer resin is 0.5% by weight or more;
2. The composition according to claim 1, wherein the content is 0% by weight or less.
Or the liquid crystal optical element according to 2. (4) At least one with the electrode layer is transparent
At least one of the two substrates has a homogeneous alignment treatment.
4. The method according to claim 1, wherein
The liquid crystal optical element according to any one of the above.