JP2783197B2 - 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, and the like, a dimming window for controlling transmission / scattering or transmission / blocking of incident light, and a liquid crystal optical element used for an optical shutter. Things.

[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 PSC
This liquid crystal optical element, called T, utilizes the transmission scattering phenomenon of light due to the phase change of chiral nematic liquid crystal,
It does not utilize the difference in the refractive index between the liquid crystal and the polymer resin. Therefore, the temperature dependence of the light transmittance is small, and
There is an advantage that the viewing angle dependence of the light transmittance is small.

[0005]

The above-mentioned international application 92/1
No. 9695, the polymer precursor is 4,
4'-Bisacryloylbiphenyl is exemplified.
However, the liquid crystal optical element according to the above disclosed technique has a problem that the driving voltage is as high as 14 V or more, so that it cannot be driven by a thin film transistor (TFT) or the like. 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. Furthermore, the contrast, which is the value obtained by dividing the light transmittance without voltage application (maximum light transmittance) by the light transmittance (minimum light transmittance) reduced by the voltage application, is as small as about 20, and a clear image display is achieved. There was also a problem that it could not be done.

Japanese Patent Application Laid-Open No. 5-224187 proposes an improvement in the characteristics of the above-mentioned liquid crystal optical element. As a polymer precursor, 4,4'-diacryloyloxy 3,3 ',
5,5'-tetramethylbiphenyl is exemplified.
However, this liquid crystal optical element also has a driving voltage of about 10 V
And the hysteresis is as large as 0.8 V, which is not sufficient. These two disclosed technologies both use a polymer precursor having a biphenyl skeleton.

Further, in the above two disclosed techniques, as a means for forming a polymer resin dispersed in a liquid crystal, a mixed solution comprising a liquid crystal, a polymer precursor, a polymerization initiator and others is irradiated with ultraviolet rays to polymer. The polymer is obtained by polymerizing the precursor. At this time, if the compatibility between the polymer precursor and the liquid crystal is not good, the polymer substance obtained by irradiating the mixed solution with ultraviolet light is dispersed and dispersed, so that the properties and uniformity of the liquid crystal optical element are poor. There is a problem.

An object of the present invention is to provide a liquid crystal device having excellent hysteresis characteristics and uniformity at a low driving voltage using a polymer precursor having good compatibility with liquid crystals. .

[0009]

In general, it is known that the interaction between a polymer substance and a chiral nematic liquid crystal greatly affects the 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 on high molecular substances without resorting to the biphenyl skeleton in order to solve the above-mentioned problems. As a result, the high molecular substances polymerize the compound represented by the general formula (I). A chiral nematic liquid crystal or a cholesteric liquid crystal of the above-mentioned phase change type liquid crystal optical element, or a polymer material obtained by copolymerizing a compound represented by the general formula (I) with another polymerizable compound. By using as a polymer substance dispersed in,
It has been found that a liquid crystal element having excellent hysteresis characteristics and excellent uniformity can be obtained by low-voltage driving.

[0011]

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That is, the present invention relates to a liquid crystal optical element having a light control layer comprising a chiral nematic liquid crystal or a cholesteric liquid crystal and a polymer substance sandwiched between at least one transparent substrate and an electrode layer. The molecular substance is a polymer substance obtained by polymerizing the compound represented by the general formula (I), or a polymer substance obtained by copolymerizing the compound represented by the general formula (I) and another polymerizable compound. It is characterized by the following.

Here, it is desirable that R and R 'are the same, but they may be different.

Here, it is advantageous that R ₁ is a hydrogen atom or a methyl group since the reactivity when polymerizing the compound of the formula (I) is increased. In other words, when the number of carbon atoms increases, the bulkiness increases, so that polymerization becomes difficult, and it becomes difficult to use the polymer for practical use.

If the number of carbon atoms of R ₂ is more than 10, the solubility of the compound in the liquid crystal becomes low, so that it becomes difficult to manufacture the device, which is not preferable. The hydrocarbon group of R ₂ may be linear, branched, or cyclic.

The polymer substance used in the light control layer of the liquid crystal optical element of the present invention is not limited to the polymer substance dispersed in the chiral nematic liquid crystal of the above-mentioned phase change type liquid crystal optical element. For example, the present invention can be applied to a polymer substance used for a liquid crystal optical element called PDLC or NCAP described in [Prior Art].

The polymer substance used in the light control layer of the liquid crystal optical element of the present invention may be obtained by polymerizing only one kind of the compound represented by the general formula (I) alone, or may be obtained by polymerizing the general formula (I ) Or a copolymer with one or more polymer precursors represented by other chemical formulas. As the other 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. Although the ratio of the general formula (I) in the copolymer is not particularly limited,
When the content is about 50 mol% or more, the effect of the compound of the general formula (I) can be sufficiently exhibited.

The polymer precursor having a polymerizable group copolymerizable with the compound represented by the general formula (I) of the present invention includes:
2-ethylhexyl acrylate, butylethyl acrylate, butoxyethyl acrylate, 2-cyanoethyl acrylate, benzyl acrylate, cyclohexyl acrylate, 2-hydroxypropyl acrylate, 2-ethoxyethyl acrylate, N, N-diethylaminoethyl acrylate, N, N-dimethylamino Ethyl acrylate, dicyclopentanyl acrylate, dicyclopentenyl acrylate, glycidyl acrylate, tetrahydrofurfuryl acrylate, isoamyl acrylate, isobonyl acrylate, isodecyl acrylate, lauryl acrylate, morpholine acrylate, phenoxyethyl acrylate, phenoxydiethylene glycol acrylate, isoamyl acrylate , Tetra Le Oro furfuryl acrylate, 2,2,2-trifluoroethyl acrylate,
Monofunctional acrylate compounds such as 2,2,3,3,3-pentafluoropropyl acrylate, 2- (perfluorobutyl) ethyl acrylate, 2- (perfluorodecyl) ethyl acrylate, 2-ethylhexyl methacrylate, 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) ) Monofunctional methacrylate compounds such as ethyl methacrylate, 2- (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, trimethylolpropanetri Acrylate, pentaerythritol tetraacrylate, pentaerythritol triacrylate, ditrimethylolpropane tetraacrylate, dipentaerythritol hexaacrylate, dipentaerythritol monohydroxypentaacrylate, urethane acrylate oligomer, 4,
4'-diacryloyloxystilbene, 4,4'-diacryloyloxydiethylstilbene, 4,4'-diacryloyloxydipropylstilbene, 4,4'-
Diacryloyloxydibutylstilbene, 2,2
3,3,4,4-hexafluoro-1,5-pentanediol diacrylate, 2,2,3,3,4,4,5,5
Polyfunctional acrylate compounds such as -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 methacrylates oligomer, 4,4'-dimethacryloyl oxy stilbene,
4,4'-dimethacryloyloxydiethylstilbene, 4,4'-dimethacryloyloxydipropylstilbene, 4,4'-dimethacryloyloxydibutylstilbene, 2,2,3,3,4,4-hexafluoro1, 5-pentanediol dimethacrylate, 2,2
Examples include, but are not limited to, polyfunctional methacrylate compounds such as 3,3,4,4,5,5-octafluoro-1,6-hexanediol dimethacrylate, styrene, aminostyrene, and vinyl acetate.

It is desirable that the polymer substance is 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 in the photopolymerization method 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
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.

As the material of the substrate used in the present invention, glass, plastic, metal and the like can be used. 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 preferably 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 used in a normal 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 then irradiating 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.

The liquid crystal optical element of the present invention can be used as a display material for displaying building materials such as windows and partitions, characters and figures.

[0035]

BEST MODE FOR CARRYING OUT THE INVENTION 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, contrast and hysteresis described in the embodiments of the present invention are defined as follows.

Driving voltage: The light transmittance when no voltage is applied is 10
0% (initial transmittance), the applied voltage at which the light transmittance of the device becomes 10% when the light transmittance reduced by the voltage application is set to 0% (minimum transmittance).

Contrast: In an optical system having an F value of 15, contrast is a value obtained by dividing the light transmittance when no voltage is applied (initial transmittance) by the light transmittance (minimum transmittance) that has been reduced by applying a voltage.

Hysteresis: When the light transmittance when no voltage is applied is 100% (initial transmittance), and the light transmittance that has been reduced by the voltage application is 0% (minimum transmittance), the applied voltage increases from 0V. When the light transmittance of the device is 5
The voltage at which the light transmittance becomes 0% is defined as V (50). After the voltage is further applied to reduce the light transmittance to 0%, the voltage at which the light transmittance becomes 50% when the applied voltage is reduced is defined as V (50: reverse)
Then, the hysteresis is expressed by the following equation.

Hysteresis = V (50) −V (50: reverse) (Example 1) Fluorine-based nematic liquid crystal RDP-4095
7 (Rodick) 95 wt%, Chiral agent S811
A mixed solution of 2.7 wt% (manufactured by Merck), 2.25 wt% of a polymerizable compound represented by the following formula, and 0.05 wt% of benzoin methyl ether was prepared. The liquid mixture was uniformly mixed, and the liquid crystal and the polymerizable compound represented by the following formula exhibited good compatibility at room temperature. Mix the mixture 2
It was injected into a liquid crystal cell having a gap of 10 μm and comprising two transparent alignment-treated transparent glass substrates with an electrode layer.
The liquid crystal cell was kept at 20 ° C. and irradiated with ultraviolet rays (wavelength 365 nm) of 0.1 mW / cm ² for 150 minutes to cure the polymerizable compound.

[0041]

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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 shown in Table 1.

Example 2 Fluorine-based liquid crystal RDP-203
12 (Rodick) 95.5wt%, Chiral agent S
A mixed liquid of 2.2 wt% of 811 (manufactured by Merck), 2.25 wt% of a compound represented by the following formula, and 0.05 wt% of 2,2-diethoxyacetophenone was prepared. The liquid mixture was uniformly mixed, and the liquid crystal and the polymerizable compound represented by the following formula exhibited good compatibility at room temperature. The mixture was injected into a liquid crystal cell having a gap of 10 μm and comprising two transparent glass substrates with electrode layers that had been subjected to a homogeneous alignment treatment.

[0044]

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The light control portion of the manufactured liquid crystal optical element was uniform, and the light transmittance of the light control portion changed without unevenness according to the applied voltage. UV irradiation conditions and electro-optical characteristics evaluation conditions were the same as those in Example 1.

(Example 3) Chlorine-based nematic liquid crystal TL2
15 (manufactured by Merck) 95% by weight, chiral agent S811
2.8 wt% (manufactured by Merck), 2.15 wt% of a compound represented by the following formula, and benzoin methyl ether 0.0
A mixed solution of 5 wt% was prepared. The liquid mixture was uniformly mixed, and the liquid crystal and the polymerizable compound represented by the following formula exhibited good compatibility at room temperature. The mixture was injected into a liquid crystal cell having a gap of 10 μm and comprising two transparent glass substrates with electrode layers that had been subjected to a homogeneous alignment treatment.

[0047]

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The light control portion of the manufactured liquid crystal optical element was uniform, and the light transmittance of the light control portion changed without unevenness according to the applied voltage. UV irradiation conditions and electro-optical characteristics evaluation conditions were the same as those in Example 1.

Example 4 Fluorine-based nematic liquid crystal RD
95 wt% of P-40957 (manufactured by Roddick), 2.8 wt% of chiral agent S811 (manufactured by Merck), 1.3 wt% of compound represented by the following formula (a) and compound 0 represented by the following formula (b) A mixture of 0.85 wt% and 0.05 wt% benzoin methyl ether was prepared. The liquid mixture was uniformly mixed, and the liquid crystal and the polymerizable compound represented by the following formula exhibited good compatibility at room temperature. The mixture was injected into a liquid crystal cell having a gap of 10 μm and comprising two transparent glass substrates with electrode layers that had been subjected to a homogeneous alignment treatment. Equation (a)

[0050]

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Equation (b)

[0052]

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The light control portion of the manufactured liquid crystal optical element was uniform, and the light transmittance changed without unevenness according to the applied voltage.
UV irradiation conditions and electro-optical characteristics evaluation conditions were the same as those in Example 1.

(Comparative Example 1) 4,4 'as a polymerizable compound
-Bisacryloyloxybiphenyl (the following formula, 2.2
(5 wt%), except that the same conditions as in Example 1 were used.

[0055]

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(Comparative Example 2) As a polymerizable compound,
4'-bisacryloyloxybiphenyl (the following formula,
Except for using 2.25 wt%), the same conditions as in Example 2 were used.

[0057]

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[0058]

[Table 1]

[0059]

The liquid crystal optical element of the present invention has good uniformity. Further, since the contrast is improved as compared with the conventional liquid crystal optical element, clear image display is possible. Further, since the driving voltage is reduced, TFT driving is possible. Further, since the hysteresis is reduced, gradation display is possible.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating a structure of a liquid crystal optical element according to a first embodiment of the present invention.

[Explanation of symbols]

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

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C09K 19/54 CA (STN) REGISTRY (STN)

Claims (2)

(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 substance 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 polymer substance obtained by polymerizing the compound represented by the general formula (I), or a polymer substance obtained by copolymerizing the compound represented by the general formula (I) and another polymerizable compound. Characteristic liquid crystal optical element. Embedded image R ₁ : a hydrogen atom or a methyl group R ₂ : a C 1-10 hydrocarbon group or a C 1-10 hydrocarbon group containing an ether bond. ) (2) 7. the polymer substance is 0.5% by weight or more;
2. The composition according to claim 1, wherein the content is 0% by weight or less.
The liquid crystal optical element according to the above.