JP2710222B2 - 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 liquid crystal optical element which is in a transparent state or a selective reflection state when no voltage is applied, and which is in a scattering state when a voltage is applied. It is used for a display device for displaying an image, an optical shutter, and the like.

[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 the use efficiency of light is high because a polarizing plate is not required. ing. This PDLC or NCA
The liquid crystal optical element called P 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. That is, by setting the refractive index of the encapsulant to be equal to the refractive index of the liquid crystal under voltage application, an optical element that transmits light and becomes transparent under voltage application and scatters light when voltage is removed to obtain an opaque optical element is 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 without applying a voltage, and the element is transparent. Thus, a liquid crystal optical element which forms a focal conic texture under voltage application and becomes opaque is obtained. Generally PSCT
This liquid crystal optical element, which is called a liquid crystal optical element, utilizes a transmission and scattering phenomenon of light due to a phase change of a chiral nematic liquid crystal, and does not utilize a refractive index difference between a liquid crystal and a polymer resin.
For this reason, there is an advantage that the viewing angle dependence of the light transmittance is small and the temperature dependency of the light transmittance is 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 technique has a problem that it is a light transmission type and has a high driving voltage of 14 V or more, and 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.

JP-A-5-224187 proposes an improvement in the characteristics of the above-mentioned liquid crystal optical element, and uses 4,4'-diacryloyloxy 3,4 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 resin 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 and hysteresis. Cannot be predicted from the chemical structure.

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that the general formula (I)

[0009]

Embedded image

(Wherein, R ¹ represents —H or —CH ₃ , R ² represents —O— or a direct bond, and R ³ , R ⁴ ,
R ^5, R ⁶ are each independently, -H, -OH, halogen atom, an optionally substituted amino group, an optionally substituted alkyl group, an optionally substituted alkoxy group, an optionally substituted aryl group are shown, X is -CR ⁷ R ⁸ - (R ⁷
And R ⁸ are each independently -H, -OH, a halogen atom,
An optionally substituted amino group, an optionally substituted alkyl group, an optionally substituted alkoxy group, an aryl group which may be substituted), - O -, - NH -, - NR 9 -
(R ⁹ represents an alkyl group which may be substituted, an aryl group which may be substituted), a compound obtained by photopolymerizing a polymer resin precursor containing a (meth) acryloyl compound,
It has been found that by using the above-mentioned phase change type liquid crystal optical element as a polymer resin dispersed in a chiral nematic liquid crystal, a liquid crystal optical element which can be driven at a low voltage and has excellent hysteresis characteristics can be obtained. Reached.

That is, the present invention relates to a liquid crystal optical element in which a dimming layer composed of a liquid crystal and a polymer resin is sandwiched between two transparent substrates having at least one electrode layer. (I)

[0012]

Embedded image

(Wherein R 1 represents —H or —CH 3, R 2 represents —O— or a direct bond, and R 3, R 4,
R5 and R6 are each independently -H, -OH, a halogen atom , an amino group, an alkyl group, an alkoxyl group,
Indicates Le group, X is -CR7 R8 - (R7 and R8 are each independently -H, -OH, a halogen atom, an amino group, Al
A kill group, an alkoxyl group, or an aryl group ), -O
-, -NH-, -NR9- (R9 is an alkyl group, aryl
A liquid crystal optical element which is a compound photopolymerized polymeric resin precursor comprising shown by indicating the Le group) (meth) acryloyl compound.

The (meth) acryloyl compound in the present invention includes acrylate compounds and methacrylate compounds,
An acryloyloxy compound and a methacryloyloxy compound are shown.

The polymer resin used for the light control layer of the liquid crystal optical element of the present invention may be a homopolymer obtained by photopolymerizing a polymer resin precursor containing a (meth) acryloyl compound alone, or may be another polymer. It may be a copolymer with one or more polymer resin precursors.

As the other photopolymerizable polymer resin precursor, any polymer resin precursor having an ordinary photopolymerizable group such as an acryloyl group or a vinyl group can be used.
Further, a plurality of photopolymerizable groups may be present in one molecule of the polymer resin precursor.

The polymer resin precursor having a photopolymerizable group copolymerizable with the (meth) acryloyl compound of the present invention includes 2-ethylhexyl acrylate, butylethyl acrylate, butoxyethyl acrylate, 2-cyanoethyl acrylate, benzyl acrylate, and the like. Cyclohexyl acrylate, 2-hydroxypropyl acrylate, 2-ethoxyethyl acrylate, N, N-diethylaminoethyl acrylate, N, N-dimethylaminoethyl acrylate, dicyclopentanyl acrylate, dicyclopentenyl acrylate, glycidyl acrylate, tetrahydrofurfuryl acrylate , Isobonyl acrylate, isodecyl acrylate, lauryl acrylate, morpholine acrylate, phenoxyethyl acrylate Phenoxydiethylene glycol acrylate, 2,2,2-trifluoroethyl acrylate, 2,2,3,3,3-pentafluoropropyl acrylate, 2,2,3,3-tetrafluoropropyl acrylate, 2,2,3 Monofunctional acrylate compounds such as 4,4,4-hexafluorobutyl 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, icyclopentenyl methacrylate, glycidyl methacrylate, tetrahydrofurfuryl methacrylate, isobonyl methacrylate, isodecyl methacrylate, lauryl methacrylate, morpholine methacrylate, phenoxyethyl methacrylate, phenoxydiethylene glycol methacrylate, Monofunctional methacrylate compounds such as 2,2,2-trifluoroethyl methacrylate, 2,2,3,3-tetrafluoropropyl methacrylate, 2,2,3,4,4,4-hexafluorobutyl methacrylate, diethylene glycol diacrylate , 1,4-butanediol diacrylate, 1,3-butylene glycol diacrylate, Lopentanyl 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, 4,4'-diacryloyloxystilbene, 4,
4'-diacryloyloxydimethylstilbene, 4,
4'-diacryloyloxydiethylstilbene, 4,
4'-diacryloyloxydipropylstilbene,
4,4'-diacryloyloxydibutylstilbene,
4,4'-diacryloyloxydipentylstilbene, 4,4'-diacryloyloxydihexylstilbene, 4,4'-diacryloyloxydifluorostilbene, 2,2,3,3,4,4-hexafluoropentanediol, Polyfunctional acrylate compounds such as 1,5-diacrylate urethane acrylate oligomer, diethylene glycol dimethacrylate, 1,4-butanediol dimethacrylate, 1,3-butylene glycol dimethacrylate, dicyclopentanyl dimethacrylate glycerol dimethacrylate, 6-hexanediol methacrylate, neopentyl glycol dimethacrylate, tetraethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, pentaerythritol te La methacrylate, pentaerythritol trimethacrylate, ditrimethylolpropane tetramethacrylate, dipentaerythritol hexamethacrylate, dipentaerythritol monohydroxy penta methacrylate, 2,2,3,3,4,4
Examples include, but are not limited to, polyfunctional methacrylate compounds such as hexafluoropentanediol, 1,5-methacrylate, and urethane methacrylate oligomer, styrene, aminostyrene, and vinyl acetate.

The polymer resin is preferably contained in the chiral nematic liquid crystal in an amount of 0.5% by weight or more and 8.0% by weight or less. When the content is 0.5% by weight or less, the scattering intensity is reduced, so that the contrast is reduced. When the content is too large, the transmittance when no voltage is applied is reduced, and the driving voltage is extremely increased.

As the light beam used for photopolymerization of the polymer resin precursor, an electron beam can be used in addition to visible light and ultraviolet light. When performing photopolymerization using visible light or ultraviolet light, it is desirable to add a photopolymerization initiator to promote the reaction. Examples of the photopolymerization initiator include 2,2-diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenyl-1-one, 1- (4-isopropylphenyl-), and 2-hydroxy-2-methyl. Propan-1-one, 1- (4-dodecylphenyl) -2-hydroxy-
2-methylpropan-1-one, 2-methyl-1- [4
Acetophenones such as-(methylthio) phenyl] -2-morpholinopropane-1, benzoin such as benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, and benzyl dimethyl ketal; benzophenone; benzoyl benzoic acid; 4-phenylbenzophenone; Benzophenones such as 3,3-dimethyl-4-methoxybenzophenone, thioxanthone,
Conventional photopolymerization initiators such as thioxanthone, diazonium salt, sulfonium salt, iodonium salt, selenium salt and the like such as 2-chlorothioxanson and 2-methylthioxanson 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 can be added.

As the liquid crystal 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, and a normal cholesteric liquid crystal having similar characteristics to this is also used. Can 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, a high Δn, and a high Δε is desirable, and a chlorine-based liquid crystal is particularly effective. It is. In addition, chiral agent,
There is no particular limitation, but it is desirable that the material be 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 performed using a substrate having a color filter.

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, but 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 processed so that the liquid crystal is oriented, but are preferably processed. 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. These alignment treatments include:
Ordinary alignment films such as polyimide used for TN 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 used for a normal liquid crystal device can be used, and the distance is desirably 3 μm or more and 30 μm or less.

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 can be applied 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 structure in which one substrate is opaque. 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.

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: The light transmittance when no voltage is applied is 1
When the light transmittance saturated by application of a voltage is set to 0% (saturated transmittance), the light transmittance of the element is 1%.
0% applied voltage.

Response time: The ON response time is as follows: when the light transmittance when no voltage is applied is 100% (initial transmittance), and when the light transmittance saturated by voltage application is 0% (saturated transmittance),
This is the time after the voltage application until the light transmittance of the device decreases from 100% to 10%. Similarly, the off response time is such that the light transmittance of the device after removal of the applied voltage is 0% to 90%.
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 (%) (Example 1) 95.6 wt% of chlorinated nematic liquid crystal TL215 (manufactured by Merck), 2.4 wt% of chiral agent S811 (manufactured by Merck) A chiral nematic liquid crystal has a chiral pitch of 3.8 μm), a mixture of a polymer resin precursor 2.7-diacryloyloxyfluorene 1.9 wt% and a polymerization initiator benzoin methyl ether 0.10 wt% is subjected to two homogeneous alignment treatments. It was injected into a liquid crystal cell having a gap of 9 μm made of a transparent glass substrate provided 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 polymer resin precursor.

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 was 15. The characteristics at 25 ° C. are as follows.

Driving voltage 7.6 V Light transmittance (when no voltage is applied) 80% Light transmittance (when 8 V is applied) 1.5% Contrast 80 Hysteresis 0.21 V Response time (ON; 8 V applied) 15 ms (OFF) 12 ms Charge retention 93% (Example 2) Chlorine-based liquid crystal TL215 (manufactured by Merck) 9
5.6 wt%, chiral agent S811 (manufactured by Merck)
A mixture of 5 wt% (chiral pitch of the chiral nematic liquid crystal is 3.6 μm), 1.8 wt% of the polymer resin precursor 2.7-diacryloyl fluorene and 0.10 wt% of 2,2-diethoxyacetophenone was used for two sheets. It was injected into a liquid crystal cell having a gap of 9 μm and comprising a transparent glass substrate with an electrode layer that had been subjected to a homogeneous alignment treatment.

The irradiation conditions of ultraviolet rays and the evaluation conditions of the electro-optical characteristics were the same as those in Example 1.

Driving voltage 7.6V Light transmittance (when no voltage is applied) 84% Light transmittance (when 7V is applied) 1.2% Contrast 70 Hysteresis 0.13V Response time (ON; 8V) 18ms (OFF) 11ms Charge Retention 90% (Comparative Example 1) Example 1 was repeated except that 4,4′-bisacryloylbiphenyl (1.9 wt%) was used instead of 2.7-diaacryloyloxyfluorene as the polymer resin precursor. Performed under the same conditions.

Drive voltage 14.2 V Light transmittance (when no voltage is applied) 80% Light transmittance (when 20 V is applied) 1.5% Contrast 32 Hysteresis 4.5 V Response time (fall; 20 V applied) 12 ms (rise) 17 ms Charge retention 92% (Comparative Example 2) Example was conducted except that 4,4'-diacryloyloxybiphenyl (1.9 wt%) was used instead of 2.7-diacryloylfluorene as a polymer resin precursor. Performed under the same conditions as in Example 1.

Driving voltage 14.5 V Light transmittance (when no voltage is applied) 81% Light transmittance (when 17 V is applied) 3.0% Contrast 27 Hysteresis 3.7 V Response time (ON; 17 V) 10 ms (OFF) 12 ms Charge Retention 91% (Example 3) The same as Example 1 except that 2.7-diacryloyloxydibenzofuran (1.9% by weight) was used instead of 2.7-diaacryloyloxyfluorene as the polymer resin precursor. Performed under the same conditions.

Drive voltage 7.7 V Light transmittance (when no voltage is applied) 84% Light transmittance (when 7 V is applied) 1.5% Contrast 56 Hysteresis 0.20 V Response time (ON; 8 V) 25 ms (OFF) 15 ms Charge Retention 92% (Example 4) Same as Example 2 except that 2.7-dimethacryloylfluorene (1.9 wt%) was used instead of 2.7-diaacryloylfluorene as the polymer resin precursor. Performed under conditions.

Drive voltage 7.6 V Light transmittance (when no voltage is applied) 80% Light transmittance (when 7 V is applied) 1.0% Contrast 80 Hysteresis 0.21 Response time (ON; 8 V) 15 ms (OFF) 13 ms Charge Retention 91% (Example 5) An element was manufactured under the same conditions as in Example 1 except that the weight% of the liquid crystal was 70 wt% and the weight% of the chiral agent was 28 wt%. The fabricated device selectively reflected visible light when no voltage was applied. When a voltage of 50 V and 100 Hz is applied, a focal conic state (scattering state) is obtained.
I remembered it. Then, when a pulse voltage of 100 V was applied, the state returned to the selective reflection state of visible light. The charge retention was 90%.

[0045]

According to the liquid crystal optical element of the present invention, the driving voltage of the liquid crystal optical element using the phase change is reduced, and the TFT can be driven. 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 (1)

(57) [Claims] 1. An electrode having at least one of two transparent electrodes
In a liquid crystal optical element in which a dimming layer composed of a chiral nematic liquid crystal and a polymer resin is sandwiched between two substrates and becomes a planar texture when no electric field is applied, and a focal conics texture when an electric field is applied, the polymer resin is generally used. Formula (I) Wherein R1 represents -H or -CH3;
2 represents -O- or a direct bond, and R3, R4, R5,
R6 is each independently -H, -OH, a halogen atom ,
X represents -CR7 R8-(R7 and R8 each independently represent -H, -OH, a halogen atom , an amino group, an alkyl group, an amino group, an alkyl group, an alkoxyl group and an aryl group ;
Group, alkoxyl group, aryl group ), -O-,-
A liquid crystal optical element comprising a compound obtained by photopolymerizing a polymer resin precursor containing a (meth) acryloyl compound represented by NH- or -NR9- (R9 represents an alkyl group or an aryl group ).