JPH0115850B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a display system that performs display by changing the luminous efficiency of fluorescence by utilizing the effect of changing the alignment of liquid crystal molecules due to an electric field, and in particular provides a new and useful technology regarding the liquid crystal display device. Electro-optical effects of liquid crystals include dynamic scattering effect (DSM), twisted nematic field effect (TN
-FEM), guest-host effect (GH), cholesteric-nematic phase transition effect (PTM), etc. are generally well known. However, all of these electro-optic effects are effects that display by scattering or absorbing external light, and are not effects that produce a light-emitting display by themselves. Therefore, display systems that utilize the electro-optic effect consume less energy for display than display systems that emit light themselves, such as conventional lamp displays, light-emitting diode displays, electroluminescence displays, or plasma displays. Although this has the advantage of being easy to use, there remains a problem in terms of display quality, such as lack of brightness in the display. The present invention provides an effective solution to the above problem, and while taking advantage of the low power consumption that is a characteristic of so-called passive displays that do not emit light by themselves, the present invention provides a bright display of active displays that emit light by themselves. The purpose is to provide a new and useful display method that incorporates The technical idea of adding a fluorescent substance into a liquid crystal material and modulating the fluorescence using an electric field has already been developed by R.
Proposed by D. Larrabee (RCA, Rev.
Vol.34.P329.1973). However, R.D.
Larrabee says in his paper that he has been unable to find a liquid crystal material that does not absorb ultraviolet (UV) light at room temperature. That is, the effect of adding a fluorescent substance as a fluorescent species into a liquid crystal material, changing the amount of light absorption of the fluorescent species according to the alignment state of the liquid crystal, and modulating the amount of fluorescence emitted according to the amount of light absorption. Therefore, the excitation light is absorbed by the liquid crystal layer,
This is thought to be because the fluorescent species could not be effectively excited. Therefore, until now, applications to display devices have remained fruitless. The present invention has developed a liquid crystal material that forms a cholesteric phase at room temperature and can efficiently excite fluorescent species, which can be applied to display devices for electronic devices, etc., thereby achieving low power consumption light emission that could not be achieved in the past. This is the realization of a display device. DESCRIPTION OF THE PREFERRED EMBODIMENTS The liquid crystal display device of the present invention and its operating principle will be explained in detail below with reference to illustrated embodiments. FIG. 1 is a schematic structural diagram of a liquid crystal display device showing one embodiment of the present invention. Roughly speaking, a liquid crystal display device is composed of an electrode section, a liquid crystal layer containing fluorescent species, a reflective material that reflects fluorescence, and a container filled with the liquid crystal layer. A display electrode 1 made of a transparent material such as In ₂ O ₃ , SnO ₂ or TiO ₂ is attached to the inner surface of a transparent substrate 2 made of glass, quartz plate, acrylic, polyethylene, etc., and a container is formed on the transparent substrate 2. For this purpose, a sealing material 3 made of epoxy resin, silicone resin, frit glass, polymer sheet, etc. is provided as a side wall, and a back substrate 4 made of a transparent material or a reflective material is provided at a position facing the transparent substrate 2. On the inner surface of the back substrate 4, a back electrode 5 facing the display electrode 1 is made of a reflective material such as Al, Au, Cr, Ag, or In ₂ O ₃ .
It is formed from a transparent material such as SnO ₂ or TiO ₂ and attached. At least one of the back substrate 4 or the back electrode 5 is made of a reflective material. This container is filled with a liquid crystal material 6 having a cholesteric phase. The surfaces of the display electrode 1 and back electrode 5 in contact with the liquid crystal material 6 are coated with a liquid crystal molecule alignment layer 7, such as a rubbing layer of SiO, SiO ₂ , etc., an oblique evaporation layer of SiO, SiO ₂ , etc., a long-chain alkyl group or a long-chain fluorocarbon. A layer of an active surfactant having an alkyl group or a silane compound having an amino group is formed. Further, the liquid crystal material 6 contains a two-color absorbing fluorescent species 8 that emits fluorescence almost uniformly in a dissolved state or a dispersed state such as a colloidal state. The principle of display operation of the liquid crystal display device having the above structure will be explained below with reference to FIGS. 2 and 3. The liquid crystal material 6 is preferably a material having a cholesteric phase with so-called positive dielectric anisotropy, which exhibits a large dielectric constant in the major axis direction.

A material exhibiting a nematic phase represented by the following formula is added with an optically active substance to form a cholesteric phase. Here R
are normal alkyl groups C ₃ H ₇ −, C ₅ H ₁₁ , C ₇ H ₁₅
A mixture of compounds having - groups is used.
The absorption spectrum when R is C ₃ H ₇ - is shown in FIG. That is, Figure 4 is

Wavelength (horizontal axis, unit: nm) when the concentration of [formula] is 1 mg/100 ml, the layer thickness is 1 cm, and cyclohexane is used as the solvent.
It is a graph showing the relationship between and absorbance (vertical axis). As is clear from Figure 4

The strong light absorption of [Formula] is on the shorter wavelength side than about 250 nm, and there is almost no absorption of near-UV light, so it has favorable characteristics as a solvent for fluorescent species. The same applies when R is other. still,
It is a liquid crystal material that has been frequently used in the past. (hereinafter referred to as MBBA) is shown in FIG. 5 for reference. The concentration, layer thickness, and solvent are the same as in FIG. 4. MBBA absorbs at wavelengths shorter than 350 nm and cannot effectively excite fluorescence. Although the liquid crystal material 6 can be implemented in a nematic phase, a cholesteric phase is more suitable for display purposes. Fluorescent species 8 are general aromatic compounds such as anthracene, tetracene, pyrene, floretscein, 9.10-dimethylanthracene, 9.10-dienylanthracene, perylene, fluorene, paraquatafenyl, rubrenterphenyl,
2.5-diphenylfuran, 2.5-diphenyloxazole, 2-phenyl, 5-(4-biphenylyl)-1.3.4oxadiazole, 1.4-bis[2-(5-phenyloxazolyl)]benzene, Samaron Prilliant Yellow-H6GL, Prilliant Phosphine, Primulin O, 1.8-Diphenyl-1.3.5.7-Octatetracene, Acridine Yellow, Thioflavin S, Pyronin GS,
1.12 benzperylene and the like are used, but are not limited thereto. The absorption spectrum of a fluorescent species is generally anisotropic, and the absorption edge in the long axis direction of the molecule is often shifted toward the longer wavelength side between the long axis direction and the short axis direction. This is shown in FIG.
In FIG. 6, l ₁ is the absorption spectrum of the fluorescent species in the long axis direction, and l ₂ is the absorption spectrum in the short axis direction. In addition, l ₃ indicates the absorption spectrum in the long axis direction of the liquid crystal. The horizontal axis represents wavelength, and the vertical axis represents absorbance. The display device shown in FIG. ₁ is irradiated with incident excitation light having a wavelength λ ₁ at which the absorbance at l 1 in FIG. 6 exhibits a substantially maximum value. When the electric field vibration direction of the incident excitation light 9 is in the long axis direction of the fluorescent species 8 as shown in FIG. 2, the excitation light 9 is absorbed according to the absorption spectrum _l1 of FIG.
Fluorescent species 8 emits fluorescence 10. On the other hand, as shown in FIG. 3, in the case of the short axis direction of the fluorescent species 8, the excitation light 9 is not absorbed according to the absorption spectrum _l2 of FIG. 6, and the fluorescent species 8 does not emit fluorescence. By utilizing these two types of optical states, the display system of the present invention is completed. That is, the display electrode 1 and the back electrode 5 are connected to an AC power source 12 via the switch 11, respectively, and a voltage is applied to the liquid crystal composition in the container via the display electrode 1 and the back electrode 5 to generate the two types of optical signals. Control the state. When a voltage is applied, the liquid crystal alignment state changes to the third state.
The state shown in the figure is reached, and when the voltage application is removed, the second
The orientation state shown in the figure is restored. Because the fluorescence spectrum and absorption spectrum exhibit so-called specular characteristics,
A desired fluorescent color can be obtained by selecting a fluorescent species having an absorption spectrum corresponding to the fluorescent color. Figure 7 shows the fluorescence spectrum and absorption spectrum of anthracene. The horizontal axis shows wavelength, and the vertical axis shows absorption coefficient and fluorescence intensity. In the figure, the solid line is the absorption spectrum, and the broken line is the fluorescence spectrum. In Figures 2 and 3, a liquid crystal with positive dielectric anisotropy is used, and the initial orientation is in the horizontal direction, that is, in the case of a cholesteric phase, the helical axis is approximately parallel to the normal to the electrode surface, which is the Grangian orientation. However, the present invention can also be practiced by using a liquid crystal having negative dielectric anisotropy and using vertical alignment (homeotropic alignment) as the initial alignment. In particular, in the case of a liquid crystal having a cholesteric phase, a focal conic alignment in which the helical axis is approximately perpendicular to the normal to the electrode surface is also possible. FIG. 8 is a schematic structural diagram of a display device showing another embodiment of the present invention. The display device shown in FIG. 1 has a sandwich electrode structure, whereas the display device shown in FIG. 8 has an interdigital electrode structure. The same reference numerals correspond to those in FIG. 1, respectively. The transparent substrate 2, the sealing material 3, and the back substrate 4 constitute a liquid crystal filling container, and the liquid crystal material 6 and fluorescent species 8 described above are filled in the container. A pair of electrodes 13 is attached to the inner surface of the back substrate 4. The electrode 13 is connected to an AC power source 12 via a switch 11. For liquid crystal molecular orientation, vertical alignment is adopted as the initial alignment when liquid crystal with positive dielectric anisotropy is used, and horizontal alignment is adopted when liquid crystal with negative dielectric anisotropy is used. Furthermore, if a liquid crystal whose dielectric anisotropy changes depending on the frequency is used instead of the switch 11, the alignment state can be switched by changing the frequency. This is naturally applicable to the sandwich electrode structure as well. The above explanation is about the case where the orientation state of the fluorescent species 8 is changed using the electric field effect due to the dielectric anisotropy of the liquid crystal. can also be implemented. In this case, it is necessary to drive at a frequency f such that f<σ _11/ 〓 ₁₁ 〓 ₀ . Here, σ ₁₁ is the conductivity in the long axis direction of the liquid crystal molecules, and ε ₁₁ is the dielectric constant in the same direction. Moreover, ε ₀ is a dielectric constant. The liquid crystal material 6 explained in the above embodiment is

Although the formula [Formula] has been explained, the following liquid crystal materials having a cyclohexane ring, a benzene ring, and a benzene ring can also be used in the present invention. That is,

【formula】

【formula】

【formula】

【formula】

【formula】

【formula】

[Formula] etc., where R and R' are alkyl groups having 3 to 9 carbon atoms.
Note that the alkyl group is not limited to the normal type, but may be an optically active type having a side chain. The specific substance names and liquid crystal temperature ranges are shown in the table below. In the following table, T _NC
is the crystal transition temperature of the nematic phase, and T _NI is the liquid transition temperature of the nematic phase.

[Table] The substances listed in the above table are themselves in a nematic phase, but when used in the present invention, they are used as a cholestic phase by adding an optically active substance (for example, cholesteryl nonanoate, etc.), which is a common practice. Furthermore, it is clear that these liquid crystals can be used not as individual liquid crystals, but as a mixture of several types, and that liquid crystals of other compounds whose absorption edges are on the short wavelength side, such as

【formula】

【formula】

【formula】

【formula】

etc. may be combined. However, it is desirable that the mixing amount of these is 3/10 or less of the total amount of cyclohexane liquid crystal. The reason for this is that if 3/10 or more of cyclohexane is added, the characteristics of cyclohexane liquid crystal will be lost. Next, the present invention will be explained in terms of characteristics. FIG. 9 is a contrast characteristic diagram when a display device having the structure shown in FIG. When the fluorescence intensity is set to 1, the fluorescence intensity gradually decreases to about half or less as the voltage is applied, indicating contrast characteristics as a whole. The crystal used is

【formula】

【formula】

It is a eutectic mixed liquid crystal with the formula [formula], and its nematic liquid crystal temperature range is from -3°C to 51°C, which is a room temperature liquid crystal. The fluorescent species was Samaron Brilliant Yellow H6GL, and 0.02wt% was added to the liquid crystal. Liquid crystal layer thickness is 10 μm, temperature is 25
It is ℃. A high-pressure mercury lamp was used as the excitation light. In addition, the response characteristics are a rise time of 50ms when driven at 5V,
The fall time was 60 msec. As explained in detail above, the present invention has completed a passive display device that emits light and can be driven with low power consumption, which could not be expected with the conventional technology.
Applicable to all display parts such as meters and thermometers. Furthermore, since the liquid crystal is composed of a cholesteric phase, the fluorescent display state is good, and the switching control between coloring and decoloring is performed reliably. The above description mainly describes embodiments applied to the structure of a reflective display device. However, in addition to the above, the present invention is also applicable to a transmissive display device using transparent electrodes and transparent substrates for both electrode parts. It is natural that it can be applied as well. In this case, it is also effective to combine it with an excitation light source.

[Brief explanation of drawings]

FIG. 1 is a schematic structural diagram of a display device showing one embodiment of the present invention. 2 and 3 are explanatory diagrams showing the principle of display operation of the display device shown in FIG. 1. FIG.
FIG. 4 is a graph showing the spectrum of one example of the liquid crystal material used for implementing the present invention. Figure 5 shows conventionally used liquid crystal materials (MBBA)
It is a graph showing the absorption spectrum of. FIG. 6 is a graph showing absorption spectra of fluorescent species used in the implementation of the present invention. FIG. 7 is a graph showing the fluorescence spectrum and absorption spectrum of anthracene. FIG. 8 is a schematic structural diagram of a display device showing another embodiment of the present invention. FIG. 9 is a contrast characteristic diagram of the display device shown in FIG. 8. DESCRIPTION OF SYMBOLS 1... Display electrode, 2... Transparent substrate, 3... Seal material, 4... Back substrate, 5... Back electrode, 6...
...Liquid crystal material, 7...Liquid crystal molecule alignment layer, 8...Fluorescent species, 9...Incoming excitation light, 10...Fluorescence, 11...
Switch, 12... AC power supply, 13... Electrode.

Claims (1)

[Scope of Claims] 1. A liquid crystal layer in which molecules are oriented in a storage container, an electrode that applies voltage to the liquid crystal layer to convert and control the molecular orientation, and a power source connected to the electrode via a switch means. , a fluorescent species dispersed in the liquid crystal layer, wherein the liquid crystal layer is made of a compound transparent to near-ultraviolet light that contains one cyclohexane ring and one benzene ring. The fluorescent species is made of a compound that has a light absorption function for near-ultraviolet light and emits fluorescence in the visible light range, and the liquid crystal layer responds to a voltage applied from the electrodes via the switch means. A fluorescent liquid crystal display device characterized in that display is performed by modulating the amount of fluorescence generated based on the molecular orientation transformation of the fluorescent species according to the molecular orientation transformation.