JP4290795B2 - Manufacturing method of polymer dispersion type liquid crystal display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a polymer-dispersed liquid crystal display device among methods for manufacturing a liquid crystal display device.
[0002]
[Prior art]
Since liquid crystal display devices have many excellent features such as thinness and low power consumption, they are widely used as display panels for devices for various purposes.
As a display method of the liquid crystal display device, one or two polarizing plates represented by a TN (twisted nematic) mode or STN (super twisted nematic) mode are used as a general liquid crystal display method. Some systems use birefringence or optical rotation using liquid crystals. The light utilization efficiency of the TN mode or STN mode is theoretically 50% or less because of the light absorption loss by the polarizing plate, and the display becomes dark.
[0003]
On the other hand, there is a method using light scattering by liquid crystal without using a polarizing plate as typified by a phase transition mode and a polymer dispersion mode. Since these light scattering methods do not require a polarizing plate, there is no light absorption loss by the polarizing plate, and light can be used effectively, so that bright display is possible.
In recent years, polymer dispersion type liquid crystal panels are attracting attention among light scattering modes because they can reduce voltage and hysteresis.
[0004]
A polymer-dispersed liquid crystal panel is a nematic liquid crystal in which a polymer layer is disposed between a pair of electrode substrates on which at least one of the electrodes is provided with a transparent electrode, and the polymer layer has positive dielectric anisotropy. Is used in the form of small droplets or a fine continuous phase (hereinafter referred to as a polymer-dispersed liquid crystal layer). Generally, no polarizing plate or alignment film is required. Has a feature that it can be made 80% or more.
[0005]
A method for producing a conventional polymer-dispersed liquid crystal will be described below.
The polymer-dispersed liquid crystal layer mixes and disperses UV-polymerizable polymer resin and TN liquid crystal with an appropriate blend, encloses them at an interval of several μm between electrode substrates, and irradiates ultraviolet rays. The blended TN liquid crystal is uniformly dispersed in the polymer network, and has a property that combines the functions of the polymer and the TN liquid crystal. This is a light scattering mode type display element that scatters incident light by utilizing a difference in refractive index between a polymer network and a TN liquid crystal. Not only does the deflecting plate used in the conventional TN-LCD unnecessary, but also an alignment film is not required, so that a bright display is possible due to very little light loss.
[0006]
In the polymer dispersion type liquid crystal panel, the display is milky white due to the light scattering action when no voltage is applied (OFF state), and the light scattering action is eliminated and the display is transparent when the voltage is applied (ON state). .
[0007]
[Problems to be solved by the invention]
In the conventional method for producing a polymer dispersed liquid crystal described above, UV curing is performed using a UV lamp 21 on a planar polymer dispersed liquid crystal panel 22C as shown in FIG. FIG. 7 shows the voltage transmittance characteristics of the polymer dispersed liquid crystal panel 22C produced by this method when it is flat. FIG. 7 shows that when the voltage is ON (Vsat1) and the transmittance is 85%, and when the voltage is OFF (0V) and the transmittance is 5%, the contrast ratio is about 17: 1 when the static drive is performed. It can be seen that high display quality can be obtained. Therefore, in FIG. 5, the observer 24 can clearly see the display characters 23C of the polymer dispersed liquid crystal panel 22C. On the other hand, as shown in FIG. 4, the voltage-transmittance characteristics when a polymer film (for example, polycarbonate or polyethersulfone) is used for the transparent electrode substrate as a curved display panel are shown in FIG. FIG. 6 shows that the transmittance is 85% when the voltage is ON (Vsat2), the transmittance is 60% when the voltage is OFF (0V), and the contrast ratio is about 1.4: 1 when static driving is performed. This indicates that there is a problem that the performance decreases. That is, it is difficult for the observer 24 in FIG. 4 to visually recognize the display characters 23B on the liquid crystal panel 22C.
[0008]
In short, when curved display is performed with a polymer-dispersed liquid crystal panel produced by a conventional manufacturing method, the orientation of liquid crystal molecules occurs in the direction of the curved display panel, and the scattering characteristics when the voltage is OFF are significantly reduced (transmittance increased). Curved surface display was impossible.
[0009]
[Means for Solving the Problems]
In the method for producing a polymer dispersed liquid crystal according to the present invention, the panel is held on a curved surface in the step of curing by ultraviolet irradiation. By this method, the orientation of the curved panel was prevented, the scattering characteristics when the voltage was turned off were remarkably improved, and a display quality with extremely high contrast was obtained with a curved display.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
Example 1
FIG. 1 is a view showing a UV irradiation process of the polymer dispersion type liquid crystal display device of the first embodiment, and FIG. 9 is a cross-sectional structure diagram of the polymer dispersion type crystal display device of the first embodiment. As shown in FIG. 9, the liquid crystal panel 22A includes a pair of transparent substrates 11A and 11B having patterned transparent electrodes 12A and 12B, and light modulation sandwiched between the transparent substrates 11A and 11B. It is composed of the layer 13. The liquid crystal panel 10 was prepared so that the cell gap was 10 μm. A reflector 50 is disposed behind the liquid crystal panel 22A (lower side in FIG. 9).
[0011]
As the transparent substrates 11A and 11B, in Example 1, a transparent polycarbonate film having a thickness of 200 μm was used as the polymer film. In addition, as the transparent polymer film, polyethersulfone, polysulfone, or the like may be used.
In the first embodiment, the transparent electrodes 12A and 12B are obtained by patterning a transparent conductive film made of an In2O3-SnO2 film (hereinafter referred to as an ITO film) formed by a sputtering method or a vacuum evaporation method by photolithography. In addition, SnO2 film | membrane may be used for transparent electrode 12A, 12B other than an ITO film | membrane.
[0012]
In Example 1, a polymer dispersed liquid crystal layer was used as the light modulation layer 13. The polymer-dispersed liquid crystal layer is a mixed solution in which a polymer resin such as an acrylate monomer that crosslinks and polymerizes by ultraviolet rays (UV), a nematic liquid crystal having positive dielectric anisotropy, and an ultraviolet curing initiator are uniformly mixed and dissolved Is injected into an empty liquid crystal panel 22A, and only the polymer resin is cured by UV irradiation, and nematic liquid crystal having positive dielectric anisotropy is phase-separated and manufactured. During the UV irradiation, the liquid crystal panel 22A was held in a curved surface state as shown in FIG. At this time, when the proportion of the polymer resin and the nematic liquid crystal is high, the polymer resin has a large proportion, so that independent particulate liquid crystal droplets are formed. On the other hand, when the ratio of the polymer resin is small, the polymer resin forms a network structure, and the liquid crystal exists as a continuous phase in the network structure of the polymer resin. . The liquid crystal droplets and the polymer network pore size are desirably as uniform as possible and have an average particle size in the range of 0.5 μm to 3.5 μm. When the average particle size is outside this range, the light scattering state deteriorates and the contrast cannot be increased. Preferably, the average particle size is in the range of 0.8 μm to 1.8 μm. The ratio of the blend amount of the polymer resin and the nematic liquid crystal is 8: 2 to 1: 9. In addition, the liquid crystal continuous phase structure of the polymer network is more likely to realize lower voltage and lower hysteresis than the independent liquid crystal droplet structure. Therefore, the range of 4: 6 to 1: 9 is desirable.
[0013]
Here, the voltage-transmittance characteristics of the curved surface display of the polymer-dispersed liquid crystal display panel manufactured in Example 1 are shown in FIG. When static driving is performed from FIG. 7, the transmittance when the voltage is ON (Vsat3) is 85%, the transmittance when the voltage is OFF (0V) is 5%, and the contrast ratio is about 17: 1. Display quality with very high visibility was obtained. In the first embodiment, since the polymer dispersion type liquid crystal panel is used as the reflection type, the reflection plate 50 is disposed. However, the same effect can be obtained even when the reflection plate 50 is not used as the transmission type.
[0014]
【The invention's effect】
As described above, according to the present invention, when polymer-dispersed liquid crystal is cured with ultraviolet rays, a high-contrast display quality can be obtained in curved display of polymer-dispersed liquid crystal by holding the panel in a curved surface. .
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of UV irradiation according to a first embodiment of the present invention.
FIG. 2 is an explanatory diagram of a display state of the curved display panel according to the first embodiment of the invention.
FIG. 3 is an explanatory diagram of conventional UV irradiation.
FIG. 4 is an explanatory diagram of a display state of a conventional curved display panel.
FIG. 5 is an explanatory diagram of a display state of a conventional flat display panel.
FIG. 6 shows voltage-transmittance characteristics of a conventional curved display panel.
FIG. 7 shows voltage-transmittance characteristics of the curved display panel of Example 1 of the present invention.
FIG. 8 shows voltage-transmittance characteristics of a conventional flat display panel.
FIG. 9 is a cross-sectional view of a polymer dispersion type liquid crystal display device of Example 1 of the present invention.
[Explanation of symbols]
11A, 11B ... Transparent substrate 12A, 12B ... Transparent electrode 13 ...・ ・ Light modulation layer 50 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Reflector 21 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ UV lamps 22A, 22B, 22C・ ・ ・ ・ ・ ・ ・ ・ Liquid crystal panels 23A, 23B, 23C ・ ・ ・ ・ ・ ・ ・ ・ Display character 24 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Observers Vsat1, Vsat2, Vsat3 ..ON voltage

Claims (1)

Forming a transparent electrode on a flat substrate made of a polymer film;
Forming a counter electrode on a flat counter substrate made of a polymer film;
An ultraviolet curable polymer resin and nematic liquid crystal having positive dielectric anisotropy are formed in a gap formed by facing the substrate and the counter substrate so that the transparent electrode and the counter electrode face each other. Filling the mixed solution blended at a ratio of 9 to produce a flat display panel;
By irradiating ultraviolet rays in a state where the flat display panel is held in a curved shape, the polymer resin is formed into a network structure, and a step of forming a polymer-dispersed liquid crystal layer is provided.
A method for producing a polymer-dispersed liquid crystal display device capable of curved display, wherein the average pore diameter of the network is in the range of 0.5 μm to 3.5 μm .

Images